**Meet the editor**

Dr. Boualem Djezzar, PhD, received the Diplôme des Etudes Supérieures (DES) in solid-state physics from the Uty of Constantine, Algeria; the Diplôme des Etudes Approfondies (DEA) in microelectronics from Uty of Grenoble, France; the MSc degree in thin film from Uty of Algiers, Algeria; and the PhD degree in microelectronics from Uty of Boumerdès, Algeria. He is currently affiliated

with CDTA research center. He is the team leader of the semiconductor component reliability group. His current research interests include CMOS technology reliability, especially electrical characterization and modeling of radiation and NBTI effects. He is the author and coauthor of more than 70 papers published in refereed journals and refereed conference proceedings on characterization, modeling, and simulation of MOS device reliability.

Contents

**Preface VII**

Slavica Brkić

Tatsuo Shiina

Samy Abd-elhakim Elsayed

**Aqueous Systems 83**

**Damages (Radicals) 135**

and Olga O. Babich

Chapter 1 **Application of Radiation Technologies for Quality**

Chapter 3 **Hydrogen Gas Detection by Mini-Raman Lidar 41**

**Improvement of LEDs Based upon AlGaAs 1**

Chapter 2 **Applicability of Quantum Dots in Biomedical Science 21**

Chapter 4 **Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga 61**

Chapter 5 **Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of**

Chapter 7 **Interaction with Matter of Ionizing Radiation and Radiation**

Chapter 8 **Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems 153** Romain Coulon and Jonathan Dumazert

Igor E. Makarov and Alexander V. Ponomarev

Chapter 6 **Ionizing Radiation-Induced Polymerization 113** Mohamed Mohamady Ghobashy

Betül Çalişkan and Ali Cengiz Çalişkan

Alexandr V. Gradoboev, Anastasiia V. Simonova, Ksenia N. Orlova

## Contents

### **Preface XI**


Preface

requiring resistant and protective coating.

Contrary to the common belief, ionizing radiations have beneficial applications in different fields, including environmental, medical, industrial, agricultural, and semiconductor fields. This fact has been achieved thanks to the fundamental understanding of the elementary inter‐ actions of radiations with matter. Indeed, several studies and developments have been carried out on radiations since their discovery, generating many research axes and establishing vari‐ ous technologies desired by different industries. This book addresses some aspects of ionizing radiation effects as well as their applications. Through its chapters, the book covers various applications of radiation/matter interactions, hardening process for semiconductor devices, bi‐ omedical imaging by radiation luminescent quantum dots (QDs), hydrogen gas detection by Raman lidar sensor for explosion risk assessment, water and wastewater purification by radia‐ tion treatment for environment, doping by the neutron transmutation doping (NTD) for semi‐ conductor industry, and polymerization by irradiation, which is useful for industries

The chapters in this book have been written by professors and researchers from academia lab‐ oratories and government research centers across the world. This book will be a helpful manu‐ script for teachers, researchers, postdoctoral research fellows, and senior graduate students from universities and research/development institutions interested in the field of ionizing ra‐ diation effects and applications and give focus points for future investigations. The present book consists of eight (8) chapters in a variety of field applications. The general purpose of this book is to provide a comprehensive analysis of ionizing radiations and their applications.

**Chapter 1** proposes a hardening method for light-emitting diode (LED) devices using radia‐ tion technologies. LED devices, based upon AlGaAs heterostructures, have been submitted to fast neutrons and gamma rays of 60Co source. The initial irradiation by fast neutron particles allows activation of the preexisting defects by decreasing their thermal resistance during the next step tests, especially annealing. As a consequence, the radiation resistance and reliability of LED devices can be enhanced using the combined radiation technologies. **Chapter 2** reex‐ amines the knowledge related to the fluorescent nanocrystal quantum dots (QDs). It investi‐ gates their proprieties in terms of size and band gap energy, brightness and photostability, surface coating and water solubility, as well as fluorescence intensity and lifetime. To make them useful for biomedical applications, QDs need to be conjugated to biological molecules without influencing their function. The chapter also describes their functionalization as medi‐ cal diagnostic tools in order to probe and image the biomolecules and cells. The near-infrared radiation luminescent QDs are promising for biomedical imaging. **Chapter 3** deals with hy‐ drogen gas detection and concentration monitoring using Raman lidars to prevent explosion accidents of hydrogen gas. Contrary to actual hydrogen sensors, the lidar sensors are contact‐ less types, based on Raman-scattered light, and do not alter the concentration measurement. Two lidars are described; the first is named DPSS laser-based compact Raman lidar and the second is LED-based mini-Raman lidar. They are developed for quantitative measurement of hydrogen gas. The current minimal detection limit of hydrogen gas concentration is 1% at the observation range of 0–50m with the accumulation time of 30 seconds and 0–20m with 3.5 min

## Preface

Contrary to the common belief, ionizing radiations have beneficial applications in different fields, including environmental, medical, industrial, agricultural, and semiconductor fields. This fact has been achieved thanks to the fundamental understanding of the elementary inter‐ actions of radiations with matter. Indeed, several studies and developments have been carried out on radiations since their discovery, generating many research axes and establishing vari‐ ous technologies desired by different industries. This book addresses some aspects of ionizing radiation effects as well as their applications. Through its chapters, the book covers various applications of radiation/matter interactions, hardening process for semiconductor devices, bi‐ omedical imaging by radiation luminescent quantum dots (QDs), hydrogen gas detection by Raman lidar sensor for explosion risk assessment, water and wastewater purification by radia‐ tion treatment for environment, doping by the neutron transmutation doping (NTD) for semi‐ conductor industry, and polymerization by irradiation, which is useful for industries requiring resistant and protective coating.

The chapters in this book have been written by professors and researchers from academia lab‐ oratories and government research centers across the world. This book will be a helpful manu‐ script for teachers, researchers, postdoctoral research fellows, and senior graduate students from universities and research/development institutions interested in the field of ionizing ra‐ diation effects and applications and give focus points for future investigations. The present book consists of eight (8) chapters in a variety of field applications. The general purpose of this book is to provide a comprehensive analysis of ionizing radiations and their applications.

**Chapter 1** proposes a hardening method for light-emitting diode (LED) devices using radia‐ tion technologies. LED devices, based upon AlGaAs heterostructures, have been submitted to fast neutrons and gamma rays of 60Co source. The initial irradiation by fast neutron particles allows activation of the preexisting defects by decreasing their thermal resistance during the next step tests, especially annealing. As a consequence, the radiation resistance and reliability of LED devices can be enhanced using the combined radiation technologies. **Chapter 2** reex‐ amines the knowledge related to the fluorescent nanocrystal quantum dots (QDs). It investi‐ gates their proprieties in terms of size and band gap energy, brightness and photostability, surface coating and water solubility, as well as fluorescence intensity and lifetime. To make them useful for biomedical applications, QDs need to be conjugated to biological molecules without influencing their function. The chapter also describes their functionalization as medi‐ cal diagnostic tools in order to probe and image the biomolecules and cells. The near-infrared radiation luminescent QDs are promising for biomedical imaging. **Chapter 3** deals with hy‐ drogen gas detection and concentration monitoring using Raman lidars to prevent explosion accidents of hydrogen gas. Contrary to actual hydrogen sensors, the lidar sensors are contact‐ less types, based on Raman-scattered light, and do not alter the concentration measurement. Two lidars are described; the first is named DPSS laser-based compact Raman lidar and the second is LED-based mini-Raman lidar. They are developed for quantitative measurement of hydrogen gas. The current minimal detection limit of hydrogen gas concentration is 1% at the observation range of 0–50m with the accumulation time of 30 seconds and 0–20m with 3.5 min

for DPSS laser-based compact Raman lidar and LED-based mini-Raman lidar, respectively. Raman lidar sensor could be one of the potential solutions for remote sensing device for leaked hydrogen gas, especially when the hydrogen will become an energy resource of daily life. **Chapter 4** provides a basic theoretical knowledge and experiment results on nuclear transmutation. The author presents the semiconductor materials doping by neutron transmu‐ tation doping (NTD). Particularly, the conversion of n-type germanium doped with arsenic into p-type germanium by fast reactor neutron irradiation. The insulator-metal transition is analyzed based on the dependence of the DC conductivity on the temperature of the conduc‐ tion activation energies for different irradiation doses.

In **Chapter 5**, radiation treatment of aqueous systems contaminated with organic compounds and corresponding technologies are addressed. This process is a promising method for water and wastewater purification. The following aspects are given in this chapter: major contami‐ nants of water and wastewater and their sources, interrelation between well-established pri‐ mary radiation-chemical processes, and the main ways of organic contaminant conversions as well as equipment and sources of ionizing radiation used for aqueous system purification. **Chapter 6** reports on ionizing radiation-induced polymerization, giving its advantages such as the purity of the obtained polymer, while in conventional methods, it needs complicated puri‐ fication steps. It discusses radiolysis of matter by different ionizing radiation sources like UV irradiation, X-rays, electron beam, and gamma-rays. Since different polymers respond differ‐ ently to radiation, the quantification of their responses in terms of cross-linking and chain scis‐ sion is given. Details on radiolysis of water as sources of radicals, which are responsible for polymerization reactions, are also given. In addition, the electron paramagnetic resonance (EPR) method, used for the investigation of the radiation damage centers induced by irradia‐ tion in the material structure, is presented in **Chapter 7**. In fact, the interaction of ionized radi‐ ation with a material induces some changes in its structure. These changes are called the radical or the radiation damage centers. The latter are seen as free radicals in the form of breaking bonds in the structure and as anion or cation radicals in the form of electron ex‐ change. The EPR spectroscopy method is used to investigate such impairments or paramag‐ netic centers occurring in structures of organic or inorganic materials. Data processing techniques related to radiation monitoring system are described in **Chapter 8**. Different radia‐ tion count rate data processing algorithms are presented. Methods based on frequentist infer‐ ences are more appropriate for real-time processing, enabling fast decision-making compared to Bayesian inferences, which are more adapted to postprocessing analyses. Moreover, nonlin‐ ear smoother provides an accurate estimation with minimized associated variance. The filter‐ ing technique is used to compensate measurement and moving source detection.

Finally, the editor gratefully wants to thank all the contributors of this book. Their insightful contribution helped in the successful completion of the manuscript. I am grateful to the Inte‐ chOpen publisher for putting me in charge to edit this book. Finally, I would like to thank my wife and kids, Fatima and Youcef, for their support during the preparation of the book.

#### **Dr. Boualem Djezzar, PhD**

**Chapter 1**

**Provisional chapter**

**Application of Radiation Technologies for Quality**

The investigation results of the radiation resistance and reliability of light-emitting diodes (LEDs) based upon AlGaAs are presented. The radiation model and the reliability model are described for LEDs. Preliminary irradiation by gamma-quanta and fast neutrons makes it possible to improve the radiation resistance and reliability of the LEDs during further operation. Based on the developed models, radiation technologies are proposed, and the use of which allows increasing the service properties of the LEDs. The suggested

Nowadays infrared wavelength range light-emitting diodes (IR-LEDs) are broadly used in various microelectronic devices that operate in space conditions and at nuclear power plants. Therefore, one already needs to know both their reliability and radiation resistance at the developmental stage. Moreover, operation conditions of LEDs require knowledge of their durability and reliability with complex and combined influence of radiation resistance and long-term operation [1]. In this case, we interpret that complex influence as the simultaneous impact of two or more radiation factors. Accordingly, the combined influence is the impact of two or more radiation factors spread out over a period of time. This is due to the fact that complex and/or combined influence of various types of ionizing radiation is always observed in field operating condition of semiconductor devices. Investigations in this field allow us to develop a radiation model of semiconductor device that describes the changes in its criterial

technologies can be used for other types of semiconductor devices.

**Keywords:** light-emitting diodes, AlGaAs, gamma-quanta, neutrons, reliability

**Application of Radiation Technologies for Quality** 

DOI: 10.5772/intechopen.72286

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

and reproduction in any medium, provided the original work is properly cited.

**Improvement of LEDs Based upon AlGaAs**

**Improvement of LEDs Based upon AlGaAs**

Alexandr V. Gradoboev, Anastasiia V. Simonova,

Alexandr V. Gradoboev, Anastasiia V. Simonova,

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Ksenia N. Orlova and Olga O. Babich

Ksenia N. Orlova and Olga O. Babich

http://dx.doi.org/10.5772/intechopen.72286

**Abstract**

**1. Introduction**

Team Leader of Semiconductor Device Reliability Microelectronics and Nanotechnologies Division Centre de Développement de Technologies Avancées (CDTA) Algiers, Algeria

**Provisional chapter**

## **Application of Radiation Technologies for Quality Improvement of LEDs Based upon AlGaAs Improvement of LEDs Based upon AlGaAs**

**Application of Radiation Technologies for Quality** 

DOI: 10.5772/intechopen.72286

Alexandr V. Gradoboev, Anastasiia V. Simonova, Ksenia N. Orlova and Olga O. Babich Ksenia N. Orlova and Olga O. Babich Additional information is available at the end of the chapter

Alexandr V. Gradoboev, Anastasiia V. Simonova,

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72286

#### **Abstract**

for DPSS laser-based compact Raman lidar and LED-based mini-Raman lidar, respectively. Raman lidar sensor could be one of the potential solutions for remote sensing device for leaked hydrogen gas, especially when the hydrogen will become an energy resource of daily life. **Chapter 4** provides a basic theoretical knowledge and experiment results on nuclear transmutation. The author presents the semiconductor materials doping by neutron transmu‐ tation doping (NTD). Particularly, the conversion of n-type germanium doped with arsenic into p-type germanium by fast reactor neutron irradiation. The insulator-metal transition is analyzed based on the dependence of the DC conductivity on the temperature of the conduc‐

In **Chapter 5**, radiation treatment of aqueous systems contaminated with organic compounds and corresponding technologies are addressed. This process is a promising method for water and wastewater purification. The following aspects are given in this chapter: major contami‐ nants of water and wastewater and their sources, interrelation between well-established pri‐ mary radiation-chemical processes, and the main ways of organic contaminant conversions as well as equipment and sources of ionizing radiation used for aqueous system purification. **Chapter 6** reports on ionizing radiation-induced polymerization, giving its advantages such as the purity of the obtained polymer, while in conventional methods, it needs complicated puri‐ fication steps. It discusses radiolysis of matter by different ionizing radiation sources like UV irradiation, X-rays, electron beam, and gamma-rays. Since different polymers respond differ‐ ently to radiation, the quantification of their responses in terms of cross-linking and chain scis‐ sion is given. Details on radiolysis of water as sources of radicals, which are responsible for polymerization reactions, are also given. In addition, the electron paramagnetic resonance (EPR) method, used for the investigation of the radiation damage centers induced by irradia‐ tion in the material structure, is presented in **Chapter 7**. In fact, the interaction of ionized radi‐ ation with a material induces some changes in its structure. These changes are called the radical or the radiation damage centers. The latter are seen as free radicals in the form of breaking bonds in the structure and as anion or cation radicals in the form of electron ex‐ change. The EPR spectroscopy method is used to investigate such impairments or paramag‐ netic centers occurring in structures of organic or inorganic materials. Data processing techniques related to radiation monitoring system are described in **Chapter 8**. Different radia‐ tion count rate data processing algorithms are presented. Methods based on frequentist infer‐ ences are more appropriate for real-time processing, enabling fast decision-making compared to Bayesian inferences, which are more adapted to postprocessing analyses. Moreover, nonlin‐ ear smoother provides an accurate estimation with minimized associated variance. The filter‐

ing technique is used to compensate measurement and moving source detection.

Finally, the editor gratefully wants to thank all the contributors of this book. Their insightful contribution helped in the successful completion of the manuscript. I am grateful to the Inte‐ chOpen publisher for putting me in charge to edit this book. Finally, I would like to thank my wife and kids, Fatima and Youcef, for their support during the preparation of the book.

**Dr. Boualem Djezzar, PhD**

Algiers, Algeria

Team Leader of Semiconductor Device Reliability Microelectronics and Nanotechnologies Division

Centre de Développement de Technologies Avancées (CDTA)

tion activation energies for different irradiation doses.

VIII Preface

The investigation results of the radiation resistance and reliability of light-emitting diodes (LEDs) based upon AlGaAs are presented. The radiation model and the reliability model are described for LEDs. Preliminary irradiation by gamma-quanta and fast neutrons makes it possible to improve the radiation resistance and reliability of the LEDs during further operation. Based on the developed models, radiation technologies are proposed, and the use of which allows increasing the service properties of the LEDs. The suggested technologies can be used for other types of semiconductor devices.

**Keywords:** light-emitting diodes, AlGaAs, gamma-quanta, neutrons, reliability

## **1. Introduction**

Nowadays infrared wavelength range light-emitting diodes (IR-LEDs) are broadly used in various microelectronic devices that operate in space conditions and at nuclear power plants. Therefore, one already needs to know both their reliability and radiation resistance at the developmental stage. Moreover, operation conditions of LEDs require knowledge of their durability and reliability with complex and combined influence of radiation resistance and long-term operation [1]. In this case, we interpret that complex influence as the simultaneous impact of two or more radiation factors. Accordingly, the combined influence is the impact of two or more radiation factors spread out over a period of time. This is due to the fact that complex and/or combined influence of various types of ionizing radiation is always observed in field operating condition of semiconductor devices. Investigations in this field allow us to develop a radiation model of semiconductor device that describes the changes in its criterial

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

parameters depending on the level and conditions of radiation effect and allows predicting its mode of behavior under the influence. In this case, the criterial parameter of a semiconductor device means such parameter, the change in which limits its working life.

The purpose of this work is to develop the radiation technologies focused on improving the reliability of the LEDs based upon AlGaAs heterostructures. The irradiation by fast neutrons

Application of Radiation Technologies for Quality Improvement of LEDs Based upon AlGaAs

The objects of this investigation were industrial LEDs manufactured on the basis of dual AlGaAs heterostructures with about 2 μm active layer grown on the monocrystalline n*<sup>+</sup>*

Double heterostructures significantly exceed single heterostructures and bulk materials in terms of their operation parameters. In particular, the n- and p-layers are made from wide bandgap materials except the absorption. Therefore, the wide-gap window effect is observed [15]. In addition, the used n- and p-layers can be heavily doped. Moreover, the injected electrons and holes are in a very narrow active layer, where n · p is extremely high. It increases the rate of radiative recombination [16]. In addition, LEDs based upon double AlGaAs heterostructures have a higher resistance to ionizing radiation [17, 18]. The above advantages are the main

**Figure 1** represents the structure of the double AlGaAs heterostructure of the LED. In the left part of **Figure 1**, the layers of semiconductor materials are shown (the doping impurity is indicated in parentheses). Furthermore, the thickness of the layers is given in the central part of **Figure 1**. Moreover, the distribution profile of the concentration of the main charge carriers

LEDs were manufactured using standard sandwich technology that involves metallic layer deposition and shaping processes for ohmic contact creation, photolithographic and chemical etching processes for die formation, and dicing for wafer division into individual chips. LEDs had packages and lenses made of an optical compound that was used to form the required angular pattern for output lumen. We emphasize that the preliminary investigation shows us that optical compound irradiation by fast neutrons, and gamma-quanta do not lead to changing its optical properties in given wavelength range. Consequently, we suggest that the changing of the observable light characteristics of the LEDs is due to the changing of characteristics in their active layer only.

voltage *U*op was not over *U*ор = 2.0 V. The maximum emissive wavelength was within the range of 0.82–0.90 μm. Emissive power at the given operating current was criterial parameter of the

For every LED emissive power at operating current 50 mA under normal conditions was taken using a measurement complex with spherical photometric integrator. The error did not exceed 5% of emissive power measurement of LEDs. The spread of the emissive power of the initial LEDs for each batch did not exceed ±10%. Moreover, the spread of the operating voltage was ±3%.


3

. The investigated LEDs

http://dx.doi.org/10.5772/intechopen.72286

op1 = 50 mА, and supply


and gamma-quanta 60Co is used as a basis of these radiation technologies.

wafer by means of liquid epitaxy. The crystal size was 450 × 450 μm<sup>2</sup>

and the Al content in the layers are shown on the right part of **Figure 1**.

In continuous power mode, the LED forward operating current was *I*

**2. Materials and methods**

have wide application. Ohmic contact to n+

reasons for choosing the object of research.

LEDs that determined their efficiency.

for AlGaAs layer on the (Au-Zn) basis.

In the same way, the reliability model of semiconductor devices is strictly necessary, which allows to predict the change in criterial parameters during operation.

We should note that it is urgent to add the factors of long-term operation to radiation factors in field operating conditions of the semiconductor devices. Therefore, it is necessary to develop an exploitable model of semiconductor devices [2], which allows describing the change in reliability indexes during long-term operation under conditions of complex and combined influence of various types of ionizing radiation.

At present time, there is an insignificant amount of work on combined influence of ionizing irradiation of semiconductor devices [1, 3–5]. However, works on the combined and complex influence of long-term operation factors and ionizing irradiation are almost completely absent.

Of all the variety of types of ionizing radiation, the research of the influence of irradiation by fast neutrons and gamma-quanta on the changes in the characteristics of various types of semiconductor devices is of primary concern.

Why are these two types of ionizing radiation of special interest? We note that the main effect of neutrons in semiconductor materials is to produce displacement damage. This later can cause shifts in the spectral response, the threshold current, the quantum yield, and the slope efficiency of the LEDs. At that time, ionization mechanism of defect formation dominates for gamma-quanta [6–9]. All other types of ionizing radiation can be represented by means of certain combination of interaction mechanisms of ionizing radiation in terms of their effect on materials. Therefore, the research results of irradiation by fast neutrons and gamma-quanta of various semiconductor device types can be used as a basis for analyzing the influence of other ionizing radiation types and, accordingly, can be used as a basis for developing radiation model of the semiconductor devices.

At the present time, there are no effective and sufficiently reliable methods for calculating the resistance of semiconductor devices to the influence of ionizing irradiation. Therefore, various different simulated equipments are used to determine their resistance to ionizing irradiation [10, 11].

In addition, accelerated tests are generally used to determine reliability indexes of semiconductor devices. They force the aging processes and reduce the length of time required for obtaining the reliability information [12–14]. Generally, the accelerating factors arise from temperature and exaggeration of conditions.

Analysis of the available literature data allows us to conclude that all currently available methods of semiconductor devices' reliability assessment are time-consuming, requiring significant financial expenditures and special equipments. Therefore, obtaining information about reliability and radiation resistance is difficult at the developmental stage of devices.

On the other hand, it is known that ionizing irradiation allows changing directly the parameters of various types of semiconductor devices [1].

The purpose of this work is to develop the radiation technologies focused on improving the reliability of the LEDs based upon AlGaAs heterostructures. The irradiation by fast neutrons and gamma-quanta 60Co is used as a basis of these radiation technologies.

## **2. Materials and methods**

parameters depending on the level and conditions of radiation effect and allows predicting its mode of behavior under the influence. In this case, the criterial parameter of a semiconductor

In the same way, the reliability model of semiconductor devices is strictly necessary, which

We should note that it is urgent to add the factors of long-term operation to radiation factors in field operating conditions of the semiconductor devices. Therefore, it is necessary to develop an exploitable model of semiconductor devices [2], which allows describing the change in reliability indexes during long-term operation under conditions of complex and combined

At present time, there is an insignificant amount of work on combined influence of ionizing irradiation of semiconductor devices [1, 3–5]. However, works on the combined and complex influence of long-term operation factors and ionizing irradiation are almost completely absent. Of all the variety of types of ionizing radiation, the research of the influence of irradiation by fast neutrons and gamma-quanta on the changes in the characteristics of various types of

Why are these two types of ionizing radiation of special interest? We note that the main effect of neutrons in semiconductor materials is to produce displacement damage. This later can cause shifts in the spectral response, the threshold current, the quantum yield, and the slope efficiency of the LEDs. At that time, ionization mechanism of defect formation dominates for gamma-quanta [6–9]. All other types of ionizing radiation can be represented by means of certain combination of interaction mechanisms of ionizing radiation in terms of their effect on materials. Therefore, the research results of irradiation by fast neutrons and gamma-quanta of various semiconductor device types can be used as a basis for analyzing the influence of other ionizing radiation types and, accordingly, can be used as a basis for developing radia-

At the present time, there are no effective and sufficiently reliable methods for calculating the resistance of semiconductor devices to the influence of ionizing irradiation. Therefore, various different simulated equipments are used to determine their resistance to ionizing irradiation

In addition, accelerated tests are generally used to determine reliability indexes of semiconductor devices. They force the aging processes and reduce the length of time required for obtaining the reliability information [12–14]. Generally, the accelerating factors arise from temperature

Analysis of the available literature data allows us to conclude that all currently available methods of semiconductor devices' reliability assessment are time-consuming, requiring significant financial expenditures and special equipments. Therefore, obtaining information about reliability and

On the other hand, it is known that ionizing irradiation allows changing directly the parameters

radiation resistance is difficult at the developmental stage of devices.

device means such parameter, the change in which limits its working life.

allows to predict the change in criterial parameters during operation.

influence of various types of ionizing radiation.

2 Ionizing Radiation Effects and Applications

semiconductor devices is of primary concern.

tion model of the semiconductor devices.

and exaggeration of conditions.

of various types of semiconductor devices [1].

[10, 11].

The objects of this investigation were industrial LEDs manufactured on the basis of dual AlGaAs heterostructures with about 2 μm active layer grown on the monocrystalline n*<sup>+</sup>* -GaAs wafer by means of liquid epitaxy. The crystal size was 450 × 450 μm<sup>2</sup> . The investigated LEDs have wide application. Ohmic contact to n+ -GaAs has been made on the (Au-Ge-Ni) basis and for AlGaAs layer on the (Au-Zn) basis.

Double heterostructures significantly exceed single heterostructures and bulk materials in terms of their operation parameters. In particular, the n- and p-layers are made from wide bandgap materials except the absorption. Therefore, the wide-gap window effect is observed [15]. In addition, the used n- and p-layers can be heavily doped. Moreover, the injected electrons and holes are in a very narrow active layer, where n · p is extremely high. It increases the rate of radiative recombination [16]. In addition, LEDs based upon double AlGaAs heterostructures have a higher resistance to ionizing radiation [17, 18]. The above advantages are the main reasons for choosing the object of research.

**Figure 1** represents the structure of the double AlGaAs heterostructure of the LED. In the left part of **Figure 1**, the layers of semiconductor materials are shown (the doping impurity is indicated in parentheses). Furthermore, the thickness of the layers is given in the central part of **Figure 1**. Moreover, the distribution profile of the concentration of the main charge carriers and the Al content in the layers are shown on the right part of **Figure 1**.

LEDs were manufactured using standard sandwich technology that involves metallic layer deposition and shaping processes for ohmic contact creation, photolithographic and chemical etching processes for die formation, and dicing for wafer division into individual chips. LEDs had packages and lenses made of an optical compound that was used to form the required angular pattern for output lumen. We emphasize that the preliminary investigation shows us that optical compound irradiation by fast neutrons, and gamma-quanta do not lead to changing its optical properties in given wavelength range. Consequently, we suggest that the changing of the observable light characteristics of the LEDs is due to the changing of characteristics in their active layer only.

In continuous power mode, the LED forward operating current was *I* op1 = 50 mА, and supply voltage *U*op was not over *U*ор = 2.0 V. The maximum emissive wavelength was within the range of 0.82–0.90 μm. Emissive power at the given operating current was criterial parameter of the LEDs that determined their efficiency.

For every LED emissive power at operating current 50 mA under normal conditions was taken using a measurement complex with spherical photometric integrator. The error did not exceed 5% of emissive power measurement of LEDs. The spread of the emissive power of the initial LEDs for each batch did not exceed ±10%. Moreover, the spread of the operating voltage was ±3%.

each stage of the experiments was distinguished by the temperature of the LED active layer

Therefore, we used both temperature and operating current as acceleration factors during step-by-step tests. Furthermore, limit step of the tests did not go beyond catastrophic failure (CF) development [21, 22]. The step-by-step tests were stopped when at least 80% of the LEDs

The following batches of the LEDs were composed for the research. The quantity of the LEDs

• LED-1 and LED-2 were for resistance research of irradiation by gamma-quanta and fast

• LED-4 and LED-5 were for research of influence of preliminary irradiation by gamma-

• LED-6 and LED-7 were for research of influence of preliminary irradiation by fast neutrons

Rationale selection of preliminary irradiation level by gamma-quanta and fast neutrons, and

Consider the results of a study of the resistance of batch LED-1 to ionizing irradiation. **Figure 2** shows the relative change of emissive power measured at the operating current depending on the absorbed dose of gamma-quanta [23]. Here and further, emissive power *P* measured after

Whereas **Figure 3** depicts the relative change of emissive power of the batch LED-2 measured at the operating current depending on fluence of fast neutrons [24]. The fluences *F*n1 and *F*n2 in

We note that the spread of emissive power of LEDs in the batch rises to ±15% of average value in the batch when dose of irradiation by gamma-quanta and fluence of fast neutrons increase.

These research results suggest the following radiation model of the LEDs. It describes the changes of emissive power of the LEDs under irradiation by gamma-quanta and fast neutrons:

Accordingly, the spread of operating voltage of the LEDs rises to ±5%.

of LEDs. The absorbed doses of *D<sup>γ</sup>*<sup>1</sup>

, and consumed electric power on *i* step *U*stepi. Therefore, temperature of the LED

Application of Radiation Technologies for Quality Improvement of LEDs Based upon AlGaAs

, LEDs thermal

5

and *D<sup>γ</sup>*<sup>2</sup>

in

stepi × *U*stepi. (1)

http://dx.doi.org/10.5772/intechopen.72286

*T*stepi, which depends on ambient temperature (i.e., baseplate temperature) *T*<sup>0</sup>

active layer on each stage of the tests is determined by the following equation:

*T*stepi = *T*<sup>0</sup> + *RT* + *I*

were out of service in each batch of the research LEDs.

resistance *R*<sup>T</sup>

in each batch was 20 items:

• LED-3 was for research of reliability.

with further annealing on reliability.

**3.1. Radiation resistance of the LEDs**

exposure is normalized to its initial value *P*<sup>0</sup>

**Figure 2** are explained below in the text.

**Figure 3** are explained below in the text.

quanta with further annealing on reliability.

annealing parameters will be considered below.

**3. Radiation resistance and reliability of the LEDs**

neutrons.

**Figure 1.** Structure of the double AlGaAs heterostructure.

The named characteristic of LEDs was obtained at the very beginning and after every stage of the investigation. The results were processed by means of mathematical statistics methods. Every batch of LEDs under investigation was characterized by average values of measured parameters.

Irradiation by gamma-quanta was performed with isotopic continuous source of 60Co. The exposure level was characterized by the absorbed dose Dγ [Gy]. The dose rate was about 1 Gy/s, and the average gamma-quanta energy was 1.25 MeV.

Irradiation by fast neutrons was carried out on the pulse simulator installation "Bars-4," which has got a reactor core of the metallic uranium and molybdenum alloy (10% by weight) with a pulse duration of 60 μs. The average neutron energy is 1.4 MeV [19, 20]. The exposure level was characterized by neutron fluence *F*n [n/cm2 ].

Irradiation by gamma-quanta and fast neutrons was realized in passive power mode, i.e., without the adding external electric field. Moreover, electrical lead of the LEDs was not allowing the flow of electricity.

Long-term operation was modeled using step-by-step tests. Standard certified equipment was used for experiments, and baseplate temperature was 65°С; the increment step of current was Δ*I* = +50 mА. Operating current of the first stage was *I* op1 = 50 mА. Duration of each stage was *t =* 24 h. Every stage of testing was characterized by operating current *I* stepi. Moreover, each stage of the experiments was distinguished by the temperature of the LED active layer *T*stepi, which depends on ambient temperature (i.e., baseplate temperature) *T*<sup>0</sup> , LEDs thermal resistance *R*<sup>T</sup> , and consumed electric power on *i* step *U*stepi. Therefore, temperature of the LED active layer on each stage of the tests is determined by the following equation:

$$T\_{\text{stap}} = \; T\_0 + R\_T + I\_{\text{stap}} \times \mathcal{U}\_{\text{stap}}.\tag{1}$$

Therefore, we used both temperature and operating current as acceleration factors during step-by-step tests. Furthermore, limit step of the tests did not go beyond catastrophic failure (CF) development [21, 22]. The step-by-step tests were stopped when at least 80% of the LEDs were out of service in each batch of the research LEDs.

The following batches of the LEDs were composed for the research. The quantity of the LEDs in each batch was 20 items:


Rationale selection of preliminary irradiation level by gamma-quanta and fast neutrons, and annealing parameters will be considered below.

## **3. Radiation resistance and reliability of the LEDs**

### **3.1. Radiation resistance of the LEDs**

The named characteristic of LEDs was obtained at the very beginning and after every stage of the investigation. The results were processed by means of mathematical statistics methods. Every batch of LEDs under investigation was characterized by average values of measured parameters. Irradiation by gamma-quanta was performed with isotopic continuous source of 60Co. The exposure level was characterized by the absorbed dose Dγ [Gy]. The dose rate was about 1 Gy/s,

Irradiation by fast neutrons was carried out on the pulse simulator installation "Bars-4," which has got a reactor core of the metallic uranium and molybdenum alloy (10% by weight) with a pulse duration of 60 μs. The average neutron energy is 1.4 MeV [19, 20]. The exposure

Irradiation by gamma-quanta and fast neutrons was realized in passive power mode, i.e., without the adding external electric field. Moreover, electrical lead of the LEDs was not allowing the flow

Long-term operation was modeled using step-by-step tests. Standard certified equipment was used for experiments, and baseplate temperature was 65°С; the increment step of current

was *t =* 24 h. Every stage of testing was characterized by operating current *I*

].

op1 = 50 mА. Duration of each stage

stepi. Moreover,

and the average gamma-quanta energy was 1.25 MeV.

**Figure 1.** Structure of the double AlGaAs heterostructure.

4 Ionizing Radiation Effects and Applications

level was characterized by neutron fluence *F*n [n/cm2

was Δ*I* = +50 mА. Operating current of the first stage was *I*

of electricity.

Consider the results of a study of the resistance of batch LED-1 to ionizing irradiation. **Figure 2** shows the relative change of emissive power measured at the operating current depending on the absorbed dose of gamma-quanta [23]. Here and further, emissive power *P* measured after exposure is normalized to its initial value *P*<sup>0</sup> of LEDs. The absorbed doses of *D<sup>γ</sup>*<sup>1</sup> and *D<sup>γ</sup>*<sup>2</sup> in **Figure 2** are explained below in the text.

Whereas **Figure 3** depicts the relative change of emissive power of the batch LED-2 measured at the operating current depending on fluence of fast neutrons [24]. The fluences *F*n1 and *F*n2 in **Figure 3** are explained below in the text.

We note that the spread of emissive power of LEDs in the batch rises to ±15% of average value in the batch when dose of irradiation by gamma-quanta and fluence of fast neutrons increase. Accordingly, the spread of operating voltage of the LEDs rises to ±5%.

These research results suggest the following radiation model of the LEDs. It describes the changes of emissive power of the LEDs under irradiation by gamma-quanta and fast neutrons:

We note that the low electron injection mode is characterized by weak dependence of emissive

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It should be particularly emphasized that in the third stage, the CF is observed and caused by

Additionally, the type of the ionizing radiation determines the relative contribution of the first stage of the emissive power decrease of the LEDs, which is due to the influence of the type of ionizing radiation on the efficiency of the reconstruction of the initial defect structure. We compared the experimental results presented in **Figures 2** and **3**. Therefore, under irradiation by gamma-quanta, the contribution of the first stage of the emissive power decrease of LEDs is about 40% of the initial emissive power, while for fast neutrons, it is

This radiation model of the LEDs completely corresponds to previously discussed model of LEDs based on other materials [27–29]. Therefore, the radiation model of decrease of emissive power of the LEDs can be extended to practically all LEDs made of various semiconductor materials.

Each of the named distinctive stages of the emissive power fall of the LEDs under irradiation can be described by the corresponding empirical relationships with their own damage constants. They are usually used to describe the processes of changing the criterial parameters of devices under various influences [30, 31]. The established relationships are capable of predict-

Next, consider the changes of emissive power during operation and more specifically during step-by-step tests. **Figure 4** presents relative change of emissive power of the batch LED-3

Decrease of emissive power during step-by-step tests can be characterized by three distinctive stages, which we observed previously while investigating the radiation resistance of the LEDs (part 3.1, **Figures 2** and **3**). One might assume that the first stage of step-by-step tests decrease in LED emissive power (field 1, **Figure 4**) is possible due to rearrangement of original defect structure exposed to long-term operation factors. Accordingly, emissive power gets reduced on the second stage as the result of inducing new structural defects under influence of longterm operation factors (field 2, **Figure 4**). On the third stage of emissive power fall during longterm operation (field 3, **Figure 4**), we can observe a transition into the mode of low electron injection with further origination of CF. We note that degradation of ohmic contacts' "metal

The identity of determined stages of the emissive power decrease of the LEDs under influence of ionizing radiation and long-term operation factors allows for the conclusion that the long-term operation factors correspond to the radiation factors according to their physical nature. In this case, one may talk of one whole model of the emissive power degradation of the LEDs due to the influence of ionizing radiation and long-term operation factors. At the same time, it should be specially noted that proper correlations between the established stages are observed for each of these factors. In actual fact, the contribution of

semiconductor" is a preliminary to CF during step-by-step tests [22, 26].

accelerated degradation of ohmic contacts' "metal semiconductor" [22, 26].

power of the LEDs on operating current value [25].

ing the radiation resistance of the LEDs.

**3.2. Reliability of the LEDs**

during step-by-step tests.

about 85%.

**Figure 2.** Relative decrease of the emissive power of the LEDs depending on gamma-quanta irradiation dose: 1, 2, and 3, stages of the emissive power decrease; *D*γ1 = 5 ∙ 104 Gy; *D*γ2 = 2 ∙ 106 Gy.


**Figure 3.** Relative decrease of the emissive power of the LEDs depending on fast neutron fluence: 1, 2, and 3, stages of the emissive power decrease; *F*n1 = 1012 n/cm2 ; *F*n2 = 1013 n/cm2 .

We note that the low electron injection mode is characterized by weak dependence of emissive power of the LEDs on operating current value [25].

It should be particularly emphasized that in the third stage, the CF is observed and caused by accelerated degradation of ohmic contacts' "metal semiconductor" [22, 26].

Additionally, the type of the ionizing radiation determines the relative contribution of the first stage of the emissive power decrease of the LEDs, which is due to the influence of the type of ionizing radiation on the efficiency of the reconstruction of the initial defect structure. We compared the experimental results presented in **Figures 2** and **3**. Therefore, under irradiation by gamma-quanta, the contribution of the first stage of the emissive power decrease of LEDs is about 40% of the initial emissive power, while for fast neutrons, it is about 85%.

This radiation model of the LEDs completely corresponds to previously discussed model of LEDs based on other materials [27–29]. Therefore, the radiation model of decrease of emissive power of the LEDs can be extended to practically all LEDs made of various semiconductor materials.

Each of the named distinctive stages of the emissive power fall of the LEDs under irradiation can be described by the corresponding empirical relationships with their own damage constants. They are usually used to describe the processes of changing the criterial parameters of devices under various influences [30, 31]. The established relationships are capable of predicting the radiation resistance of the LEDs.

#### **3.2. Reliability of the LEDs**

**Figure 3.** Relative decrease of the emissive power of the LEDs depending on fast neutron fluence: 1, 2, and 3, stages of

• In the first stage, the fall of emissive power of the LEDs is attributed to the radiation-stimulated reconstruction of the initial defect structure of the LED crystal (field 1 in **Figures 2** and

**Figure 2.** Relative decrease of the emissive power of the LEDs depending on gamma-quanta irradiation dose: 1, 2, and 3,

Gy.

• In the second stage, the fall of emissive power of the LEDs during irradiation is attributed

• In the third stage, the LED transits into the field of low electron injection into the active

**3**) as evidenced by saturation of this stage as the level of exposure increases.

solely to the introduction of radiation defects (field 2 in **Figures 2** and **3**).

layer of the LED (field 3 in **Figures 2** and **3**).

stages of the emissive power decrease; *D*γ1 = 5 ∙ 104 Gy; *D*γ2 = 2 ∙ 106

6 Ionizing Radiation Effects and Applications

.

; *F*n2 = 1013 n/cm2

the emissive power decrease; *F*n1 = 1012 n/cm2

Next, consider the changes of emissive power during operation and more specifically during step-by-step tests. **Figure 4** presents relative change of emissive power of the batch LED-3 during step-by-step tests.

Decrease of emissive power during step-by-step tests can be characterized by three distinctive stages, which we observed previously while investigating the radiation resistance of the LEDs (part 3.1, **Figures 2** and **3**). One might assume that the first stage of step-by-step tests decrease in LED emissive power (field 1, **Figure 4**) is possible due to rearrangement of original defect structure exposed to long-term operation factors. Accordingly, emissive power gets reduced on the second stage as the result of inducing new structural defects under influence of longterm operation factors (field 2, **Figure 4**). On the third stage of emissive power fall during longterm operation (field 3, **Figure 4**), we can observe a transition into the mode of low electron injection with further origination of CF. We note that degradation of ohmic contacts' "metal semiconductor" is a preliminary to CF during step-by-step tests [22, 26].

The identity of determined stages of the emissive power decrease of the LEDs under influence of ionizing radiation and long-term operation factors allows for the conclusion that the long-term operation factors correspond to the radiation factors according to their physical nature. In this case, one may talk of one whole model of the emissive power degradation of the LEDs due to the influence of ionizing radiation and long-term operation factors. At the same time, it should be specially noted that proper correlations between the established stages are observed for each of these factors. In actual fact, the contribution of

**4. Radiation technologies for improving reliability of the LEDs**

radiation-induced defects over change of emissive power during step-by-step tests.

measurement results were used as initial values for further research of reliability.

**Research stage Level of emissive power, % from initial value**

After preliminary irradiation by gamma-quanta — 95 8 After annealing — 102 97 Initial values before step-by-step tests 100 100 100

Before CF development 39 82 67 65 56 107 136 85 Step of the CF appearance (*I*stepi, mA) 475 550 500 500 450 400 400 450

**Table 1.** The emissive power changes of the LEDs on the different stages of radiation technology implementation.

the second stage of the emissive power fall of the LEDs (see **Figure 2**).

subgroups LED-4a and LED-4b when the step of the tests rises.

Consider the influence of preliminary irradiation by gamma-quanta with further annealing of

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Doses Dγ1 for batch LED-4 and Dγ2 for batch LED-5 were used for preliminary irradiation by gamma-quanta. The irradiation dose *D*γ1 corresponds to the first stage of decreasing the radiation power of the LEDs irradiated by gamma-quanta. Moreover, the dose *D*γ2 corresponds to

After preliminary irradiation by gamma-quanta, the annealing was carried out. Moreover, the annealing mode corresponds to the first stage of the step-by-step tests described above. **Table 1** represents the change of the emissive power after preliminary irradiation with further annealing and during step-by-step tests. Furthermore, almost complete recovery of the emissive power of the LEDs was observed to their initial values after preliminary irradiation with annealing. The

The use of selected preliminary irradiation doses makes it possible to obtain information about the correlation between the processes of decreasing the emissive power of the LEDs caused by the combined influence of ionizing radiation and long-term operation factors.

In the results of step-by-step tests, the LED-4 batch is very neatly divided into two distinctive

Next, we consider obtained results in more details. **Figure 5** depicts the change of the emissive power of the LEDs from subgroup LED-4a during step-by-step tests. Furthermore, the subgroup LED-4a is divided into two subgroups LED-4a1 (20% from the batch LED-4) and LED-4a2 (35% from the batch LED-4). Moreover, **Figure 5** illustrates for comparison the change of the emissive power of the LEDs without preliminary irradiation (LED-3 batch) during operation.

**LED-3 LED-4 LED-5**

**a1 a2 b1 b2**

**LED-4a LED-4b a b c**

**4.1. Preliminary irradiation by gamma-quanta**

**Figure 4.** Relative change of the emissive power of the LEDs depending on step number of the tests: 1, 2, and 3, stages of the emissive power decrease.

each determined stages to the overall decrease of the emissive power depends on type of influencing factors. In addition, each stage is characterized by its own value of the damage constants for each type of influencing factors.

The above-presented results have proved the identity of degradation processes in LEDs under the influence of ionizing radiation and factors of long operating time. Therefore, it has been established that under the influence of ionizing radiation on the LED and long-term operation factors, the similar stages of the radiation power decrease are observed. In this case, the first stage in both cases is characterized by saturation, which made it possible to associate its appearance with rearrangement of the initial structure of the defects. Furthermore, at the first stage, the emissive power decrease is due to identical defects and is independent of their appearance history. Similar reasoning is applicable to other determined stages. We note that the relative contribution of the stages to the overall emissive power decrease of the LEDs is defined by the type of influence.

The above-described radiation and reliability models of LEDs can be used as a basis for the development of the exploitable model of LEDs. It is a complex of relationships that describe the change in the emissive power of LEDs (criterial parameter) under the complex and combined influence of various types of ionizing radiation and long-term operation factors. The practical application of the exploitable model of LEDs will make it possible to predict the behavior of LEDs under different operating conditions. The proposed model is universal, because it describes the change in the emissive power of LEDs under the influence of damaging factors of different nature.

The physical nature of the exploitable model of the LEDs allows using it as a base for the development of exploitable models of other types of semiconductor devices.

These research results make it possible to recommend the radiation technology for improving the operational parameters of the LEDs [32, 33].

## **4. Radiation technologies for improving reliability of the LEDs**

#### **4.1. Preliminary irradiation by gamma-quanta**

each determined stages to the overall decrease of the emissive power depends on type of influencing factors. In addition, each stage is characterized by its own value of the damage

**Figure 4.** Relative change of the emissive power of the LEDs depending on step number of the tests: 1, 2, and 3, stages

The above-presented results have proved the identity of degradation processes in LEDs under the influence of ionizing radiation and factors of long operating time. Therefore, it has been established that under the influence of ionizing radiation on the LED and long-term operation factors, the similar stages of the radiation power decrease are observed. In this case, the first stage in both cases is characterized by saturation, which made it possible to associate its appearance with rearrangement of the initial structure of the defects. Furthermore, at the first stage, the emissive power decrease is due to identical defects and is independent of their appearance history. Similar reasoning is applicable to other determined stages. We note that the relative contribution of the stages to the overall emissive power decrease of the LEDs is defined by the

The above-described radiation and reliability models of LEDs can be used as a basis for the development of the exploitable model of LEDs. It is a complex of relationships that describe the change in the emissive power of LEDs (criterial parameter) under the complex and combined influence of various types of ionizing radiation and long-term operation factors. The practical application of the exploitable model of LEDs will make it possible to predict the behavior of LEDs under different operating conditions. The proposed model is universal, because it describes the change in the emissive power of LEDs under the influence of damag-

The physical nature of the exploitable model of the LEDs allows using it as a base for the

These research results make it possible to recommend the radiation technology for improving

development of exploitable models of other types of semiconductor devices.

constants for each type of influencing factors.

type of influence.

of the emissive power decrease.

8 Ionizing Radiation Effects and Applications

ing factors of different nature.

the operational parameters of the LEDs [32, 33].

Consider the influence of preliminary irradiation by gamma-quanta with further annealing of radiation-induced defects over change of emissive power during step-by-step tests.

Doses Dγ1 for batch LED-4 and Dγ2 for batch LED-5 were used for preliminary irradiation by gamma-quanta. The irradiation dose *D*γ1 corresponds to the first stage of decreasing the radiation power of the LEDs irradiated by gamma-quanta. Moreover, the dose *D*γ2 corresponds to the second stage of the emissive power fall of the LEDs (see **Figure 2**).

After preliminary irradiation by gamma-quanta, the annealing was carried out. Moreover, the annealing mode corresponds to the first stage of the step-by-step tests described above. **Table 1** represents the change of the emissive power after preliminary irradiation with further annealing and during step-by-step tests. Furthermore, almost complete recovery of the emissive power of the LEDs was observed to their initial values after preliminary irradiation with annealing. The measurement results were used as initial values for further research of reliability.

The use of selected preliminary irradiation doses makes it possible to obtain information about the correlation between the processes of decreasing the emissive power of the LEDs caused by the combined influence of ionizing radiation and long-term operation factors.

In the results of step-by-step tests, the LED-4 batch is very neatly divided into two distinctive subgroups LED-4a and LED-4b when the step of the tests rises.

Next, we consider obtained results in more details. **Figure 5** depicts the change of the emissive power of the LEDs from subgroup LED-4a during step-by-step tests. Furthermore, the subgroup LED-4a is divided into two subgroups LED-4a1 (20% from the batch LED-4) and LED-4a2 (35% from the batch LED-4). Moreover, **Figure 5** illustrates for comparison the change of the emissive power of the LEDs without preliminary irradiation (LED-3 batch) during operation.


**Table 1.** The emissive power changes of the LEDs on the different stages of radiation technology implementation.

**Figure 5.** Relative change of emissive power of subgroup LED-4a during step-by-step tests: 1 and 2, revealed stages of the emissive power fall; LED-4а1 and LED-4а2, marked subgroups; LED-3, batch LED-3.

It is apparent that all of the presented dependences have the same form. However, the dependences differ according to the contribution of the first stage in total decrease of the emissive power of the LEDs during step-by-step tests. Therefore, **Figure 5** shows that preliminary irradiation by gamma-quanta makes it possible to decrease the contribution of the first stage (up to its complete elimination for the subgroup LED-4a1) to a total decrease of the emissive power during step-by-step tests.

Each of the marked subgroups can be characterized by the eigenvalues of the efficiency coefficient η for the LEDs after preliminary irradiation and further annealing. In this case, the efficiency coefficient means the ratio of the emission power of the LEDs to the power consumption. Here and elsewhere, the efficiency coefficient is average value for the batches and the marked subgroups. Furthermore, the change of efficiency coefficient can be described by the following equation when passing from one subgroup to other subgroups:

$$
\eta\_{\text{LED-3}} < \eta\_{\text{LED-4a2}} < \eta\_{\text{LED-4a1}} \tag{2}
$$

Consequently, we obtain the following equation taking into account Eq. (3):

their specific difference for the marked subgroups of the LEDs.

marked subgroups; LED-3, batch LED-3.

possible to increase the reliability of the LEDs.

ηLED−4b2 < ηLED−4b1 < ηLED−<sup>3</sup> < ηLED−4a2 < ηLED−4a1 (4)

**Figure 6.** Relative change of the emissive power during step-by-step tests for subgroup LED-4b: LED-4b1; LED-4b2,

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Certainly, the additional research is necessary to identify the parameters that determined

In addition, the preliminary irradiation by gamma-quanta with the dose corresponding to radiation-stimulated rearrangement of the initial defect structure makes it possible to increase the resistance of ohmic contacts to the influence of long-term operation factors. Furthermore, it allows decreasing the probability of the CF development and increasing the reliability of LEDs.

Therefore, the possibility of practical application is shown to except almost completely the contribution of the first stage of decreasing the emissive power of the LEDs during step-by-step tests. It is realized by preliminary irradiation by gamma-quanta with a dose Dγ1 and further annealing. This technology allows improving significantly the operational characteristics of the LEDs. The use of different levels of preliminary irradiation by gamma-quanta within the first stage (see **Figure 2**) allows controlling these processes. Furthermore, it makes possible to control the contribution of the first stage of emissive power decrease of the LEDs during operation. Moreover, the used doses of preliminary irradiation by gamma-quanta, annealing temperature, and annealing duration are not optimal. Consequently, when the proposed radiation

technology is optimized, the obtained results can exceed the values presented here.

Therefore, the preliminary irradiation by gamma-quanta with dose corresponding to the first stage of emissive power decrease of the LEDs (see **Figure 2**) with further annealing makes it

Moreover, the dependence between emissive power fall and efficiency is absent in an explicit form for LED-3 batch.

**Figure 6** represents the established dependence of the emissive power fall during step-bystep test for subgroup LED-4b. It is divided into two subgroups LED-4b1 (35% from the batch LED-4) and LED-4b2 (10% from the batch LED-4).

It can be seen that the subgroup LED-4b is divided into two subgroups, in which the change of the emissive power is determined by the corresponding value of the efficiency by the following equation:

$$
\eta\_{\text{LED-402}} < \eta\_{\text{LED-401}} \tag{3}
$$

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**Figure 6.** Relative change of the emissive power during step-by-step tests for subgroup LED-4b: LED-4b1; LED-4b2, marked subgroups; LED-3, batch LED-3.

Consequently, we obtain the following equation taking into account Eq. (3):

**Figure 5.** Relative change of emissive power of subgroup LED-4a during step-by-step tests: 1 and 2, revealed stages of

It is apparent that all of the presented dependences have the same form. However, the dependences differ according to the contribution of the first stage in total decrease of the emissive power of the LEDs during step-by-step tests. Therefore, **Figure 5** shows that preliminary irradiation by gamma-quanta makes it possible to decrease the contribution of the first stage (up to its complete elimination for the subgroup LED-4a1) to a total decrease of the emissive power

Each of the marked subgroups can be characterized by the eigenvalues of the efficiency coefficient η for the LEDs after preliminary irradiation and further annealing. In this case, the efficiency coefficient means the ratio of the emission power of the LEDs to the power consumption. Here and elsewhere, the efficiency coefficient is average value for the batches and the marked subgroups. Furthermore, the change of efficiency coefficient can be described by

ηLED−<sup>3</sup> < ηLED−4a2 < ηLED−4a1 (2)

Moreover, the dependence between emissive power fall and efficiency is absent in an explicit

**Figure 6** represents the established dependence of the emissive power fall during step-bystep test for subgroup LED-4b. It is divided into two subgroups LED-4b1 (35% from the batch

It can be seen that the subgroup LED-4b is divided into two subgroups, in which the change of the emissive power is determined by the corresponding value of the efficiency by the following

ηLED−4b2 < ηLED−4b1 (3)

the following equation when passing from one subgroup to other subgroups:

the emissive power fall; LED-4а1 and LED-4а2, marked subgroups; LED-3, batch LED-3.

during step-by-step tests.

10 Ionizing Radiation Effects and Applications

form for LED-3 batch.

equation:

LED-4) and LED-4b2 (10% from the batch LED-4).

$$
\eta\_{\text{LED-402}} < \eta\_{\text{LED-401}} < \eta\_{\text{LED-3}} < \eta\_{\text{LED-4a2}} < \eta\_{\text{LED-4a1}} \tag{4}
$$

Certainly, the additional research is necessary to identify the parameters that determined their specific difference for the marked subgroups of the LEDs.

In addition, the preliminary irradiation by gamma-quanta with the dose corresponding to radiation-stimulated rearrangement of the initial defect structure makes it possible to increase the resistance of ohmic contacts to the influence of long-term operation factors. Furthermore, it allows decreasing the probability of the CF development and increasing the reliability of LEDs.

Therefore, the possibility of practical application is shown to except almost completely the contribution of the first stage of decreasing the emissive power of the LEDs during step-by-step tests. It is realized by preliminary irradiation by gamma-quanta with a dose Dγ1 and further annealing. This technology allows improving significantly the operational characteristics of the LEDs. The use of different levels of preliminary irradiation by gamma-quanta within the first stage (see **Figure 2**) allows controlling these processes. Furthermore, it makes possible to control the contribution of the first stage of emissive power decrease of the LEDs during operation.

Moreover, the used doses of preliminary irradiation by gamma-quanta, annealing temperature, and annealing duration are not optimal. Consequently, when the proposed radiation technology is optimized, the obtained results can exceed the values presented here.

Therefore, the preliminary irradiation by gamma-quanta with dose corresponding to the first stage of emissive power decrease of the LEDs (see **Figure 2**) with further annealing makes it possible to increase the reliability of the LEDs.

Now, turn to consider the results of step-by-step tests for batch LED-5. The LEDs of this batch were preliminary irradiated by gamma-quanta with the second dose corresponded to the second stage of the emissive power fall under irradiation by gamma-quanta (**Figure 2** and **Table 1**). We emphasize that the emissive power decrease during step-by-step tests for batch LED-5 fundamentally differs from the above-observed emissive power fall for batch LED-4. The emissive power of LEDs from the batch LED-5 (similar to batch LED-4) almost completely returns to the initial value of the emissive power after the annealing, in spite of the fact that emissive power of the LEDs decreased significantly after preliminary irradiation by gammaquanta. This is shown in **Table 1**.

**Figure 7** depicts the change of the emissive power during step-by-step tests for the batch LED-5. The batch is divided into three equal in percentage ratio subgroups (LED-5a, LED-5b, LED-5c in **Figure 7**). It should be specially noted that the observed changes of emissive power from the LED-8 batch practically do not lead to a LED failure as a result of its decrease. Moreover, the reliability of the LEDs is limited only by the development of CFs.

Two strongly marked peaks of the emissive power increase during step-by-step tests are characterized in all marked subgroups. Furthermore, some of the detected peaks clearly have a compound shape.

Each of the marked subgroups can be characterized by the eigenvalues of the efficiency coefficient for the LEDs after preliminary irradiation and further annealing. Furthermore, the change of efficiency coefficient can be described by the following equation when passing from one subgroup to other subgroups:

$$
\eta\_{\text{LED-gt}} < \eta\_{\text{LED-gt}} < \eta\_{\text{LED-gt}} \tag{5}
$$

Comparing the results of the step-by-step tests for batches LED-5 and LED-3, it allows concluding that the observable annealing is probably attributed to annealing radiation defects in particular (possibly stimulated by an external electric field). The defects' precipitation is typical for the second stage of the emissive power fall of the LEDs during step-by-step tests.

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The effective annealing temperatures can be estimated to the maximum of the emissive power rise using Eq. (1) for marked subgroups of batch LED-5. Therefore, the annealing of two distinctive types of defects is observed for each of marked subgroups of LED-5 batch. Moreover, the effective annealing temperature is in the range of 348–352 K for the first defect. Furthermore, the effective annealing temperature is in the range of 362–370 K for the second defect. Certainly, the effective temperatures have rough estimate that obtain in such a way. At present time, we cannot connect annealing defects with concrete types. This is subject for

Analysis of the results presented in **Table 1** allows concluding that the preliminary irradiation by gamma-quanta with dose Dγ2 leads to earlier appearance of CF. It is due to accelerated

Preliminary irradiation by gamma-quanta in the field of radiation defects' introduction leads to accelerated degradation of ohmic contacts and increasing the probability of CF develop-

The obtained results allow us to recommend the preliminary irradiation by gamma-quanta in

Consider the influence of preliminary irradiation by fast neutrons with further annealing the radiation-induced defects over change of the emissive power of the LEDs during operation.

The change in the emissive power of the LEDs after preliminary irradiation and further annealing is presented in **Table 2**. Here, the values of the emissive power of the LEDs measured before the CF development are shown. A partial or complete recovery of the emissive power of the LEDs to the initial values is observed after annealing. These obtained results

For batch LED-6, the preliminary irradiation by fast neutrons was chosen in the field of the first stage of the emissive power fall (**Figure 3**). **Figure 8** represents the change of the emissive power for batch LED-6 during step-by-step tests. Moreover, **Figure 8** illustrates the emissive power change for LED-3 batch in contrast. Furthermore, the batch LED-6 is divided into two distinctive subgroups LED-6a (55% from the batch LED-6) and LED-6b (45% from the batch

The following equation of the efficiency can be composed for marked subgroups of the LED-9

ηLED−6b < ηLED−<sup>3</sup> < ηLED−6a (6)

the manufacturing technology of the LEDs to improve their operational parameters.

ment. Consequently, it leads to decrease the ultimate reliability of the LEDs.

further research.

LED-6).

batch:

degradation of ohmic contacts.

**4.2. Preliminary irradiation by fast neutrons**

were used as initial values for further research of the reliability.

**Figure 7.** Relative change of the emissive power during step-by-step tests for batch LED-5: 1 and 2, recovery of the emissive power; LED-5a, LED-5b, and LED-5c, marked subgroups; LED-3, batch LED-3.

Comparing the results of the step-by-step tests for batches LED-5 and LED-3, it allows concluding that the observable annealing is probably attributed to annealing radiation defects in particular (possibly stimulated by an external electric field). The defects' precipitation is typical for the second stage of the emissive power fall of the LEDs during step-by-step tests.

The effective annealing temperatures can be estimated to the maximum of the emissive power rise using Eq. (1) for marked subgroups of batch LED-5. Therefore, the annealing of two distinctive types of defects is observed for each of marked subgroups of LED-5 batch. Moreover, the effective annealing temperature is in the range of 348–352 K for the first defect. Furthermore, the effective annealing temperature is in the range of 362–370 K for the second defect. Certainly, the effective temperatures have rough estimate that obtain in such a way. At present time, we cannot connect annealing defects with concrete types. This is subject for further research.

Analysis of the results presented in **Table 1** allows concluding that the preliminary irradiation by gamma-quanta with dose Dγ2 leads to earlier appearance of CF. It is due to accelerated degradation of ohmic contacts.

Preliminary irradiation by gamma-quanta in the field of radiation defects' introduction leads to accelerated degradation of ohmic contacts and increasing the probability of CF development. Consequently, it leads to decrease the ultimate reliability of the LEDs.

The obtained results allow us to recommend the preliminary irradiation by gamma-quanta in the manufacturing technology of the LEDs to improve their operational parameters.

## **4.2. Preliminary irradiation by fast neutrons**

**Figure 7.** Relative change of the emissive power during step-by-step tests for batch LED-5: 1 and 2, recovery of the

Now, turn to consider the results of step-by-step tests for batch LED-5. The LEDs of this batch were preliminary irradiated by gamma-quanta with the second dose corresponded to the second stage of the emissive power fall under irradiation by gamma-quanta (**Figure 2** and **Table 1**). We emphasize that the emissive power decrease during step-by-step tests for batch LED-5 fundamentally differs from the above-observed emissive power fall for batch LED-4. The emissive power of LEDs from the batch LED-5 (similar to batch LED-4) almost completely returns to the initial value of the emissive power after the annealing, in spite of the fact that emissive power of the LEDs decreased significantly after preliminary irradiation by gamma-

**Figure 7** depicts the change of the emissive power during step-by-step tests for the batch LED-5. The batch is divided into three equal in percentage ratio subgroups (LED-5a, LED-5b, LED-5c in **Figure 7**). It should be specially noted that the observed changes of emissive power from the LED-8 batch practically do not lead to a LED failure as a result of its decrease.

Two strongly marked peaks of the emissive power increase during step-by-step tests are characterized in all marked subgroups. Furthermore, some of the detected peaks clearly have a

Each of the marked subgroups can be characterized by the eigenvalues of the efficiency coefficient for the LEDs after preliminary irradiation and further annealing. Furthermore, the change of efficiency coefficient can be described by the following equation when passing from

ηLED−5c < ηLED−5b < ηLED−5a (5)

Moreover, the reliability of the LEDs is limited only by the development of CFs.

quanta. This is shown in **Table 1**.

12 Ionizing Radiation Effects and Applications

one subgroup to other subgroups:

compound shape.

emissive power; LED-5a, LED-5b, and LED-5c, marked subgroups; LED-3, batch LED-3.

Consider the influence of preliminary irradiation by fast neutrons with further annealing the radiation-induced defects over change of the emissive power of the LEDs during operation.

The change in the emissive power of the LEDs after preliminary irradiation and further annealing is presented in **Table 2**. Here, the values of the emissive power of the LEDs measured before the CF development are shown. A partial or complete recovery of the emissive power of the LEDs to the initial values is observed after annealing. These obtained results were used as initial values for further research of the reliability.

For batch LED-6, the preliminary irradiation by fast neutrons was chosen in the field of the first stage of the emissive power fall (**Figure 3**). **Figure 8** represents the change of the emissive power for batch LED-6 during step-by-step tests. Moreover, **Figure 8** illustrates the emissive power change for LED-3 batch in contrast. Furthermore, the batch LED-6 is divided into two distinctive subgroups LED-6a (55% from the batch LED-6) and LED-6b (45% from the batch LED-6).

The following equation of the efficiency can be composed for marked subgroups of the LED-9 batch:

$$
\eta\_{\text{LED-e0}} < \eta\_{\text{LED-3}} < \eta\_{\text{LED-ea}} \tag{6}
$$


effective temperatures have rough estimate that obtain in such a way. At present time, we cannot connect annealing defects with concrete types. This is subject for further research. Moreover, the

Application of Radiation Technologies for Quality Improvement of LEDs Based upon AlGaAs

http://dx.doi.org/10.5772/intechopen.72286

15

Next, **Figure 9** shows the emissive power change of the batch LED-7 during step-by-step tests. This batch is divided into two subgroups LED-7a (70% from the batch LED-7) and LED-7b

For the marked subgroups of the LEDs from the batch LED-7, the following equation can be

ηLED−7b < ηLED−7a (7)

There are two stages of the emissive power recovery with its further fall for subgroup LED-7a. This is due to annealing the corresponding defects. Moreover, the rate of the emissive power recovery exceeds significantly the previously observed values for batch LED-6. Therefore, the recovery of the emissive power for batch LED-7 during operation can be considered due to annealing of two types of defects. Additionally, the first of them can be attributed to the field of radiation-stimulated reconstruction of the initial defect structure under influence of the operation factors. The subgroup LED-7b is characterized by the fact that the first stage of the emissive power recovery is absent. The observed changes of emissive power are described by the measurement error. Therefore, the recovery of the emissive power for subgroup LED-7b

during operation can be considered due to the annealing of the second defect only.

rise using Eq. (1) for marked subgroups of batch LED-7:

• Subgroup LED-7a, ТА1 = (360 ± 2) K; ТА2 = (388 ± 2) K.

• Subgroup LED-7b, ТВ2 = (378 ± 2) K.

The effective annealing temperatures can be estimated to the maximum of the emissive power

**Figure 9.** Relative change of the emissive power of the batch LED-7 during step-by-step tests: 1, 2, and 3, the emissive

power recovery with further fall; LED-7a and LED-7b, marked subgroups; LED-3, the batch LED-3.

reliability increases for the batch LED-6 in comparison with batch LED-3.

(30% from the batch LED-7).

written as

**Table 2.** The emissive power changes of the LEDs on the different stages of radiation technology implementation.

Additionally, there are three distinctive peaks of the emissive power recovery for marked subgroups of the batch LED-6. The subgroups differ only in value of the emissive power recovery. The quantities of the peaks show the annealing of three types of defects. Therefore, the observable recovery of emissive power of the LEDs during operation is due to annealing of three types of the defects created by radiation-stimulated reconstruction of the initial defect structure that is stimulated by operation factors.

The effective annealing temperatures can be estimated to the maximum of the emissive power rise using Eq. (1) for marked subgroups of batch LED-6. Therefore, the annealing of three distinctive types of defects is observed for each of marked subgroups of batch LED-6. Moreover, the effective annealing temperature is in the range of 341–345 K for the first defect. Furthermore, the effective annealing temperature is in the range of 355–359 K for the second defect. Additionally, the effective annealing temperature is in the range of 369–376 K for the third defect. Certainly, the

**Figure 8.** Relative change of the emissive power of the batch LED-6 during step-by-step tests: 1, 2, and 3, the emissive power recovery with further fall; LED-6a and LED-6b, marked subgroups; LED-3, the batch LED-3.

effective temperatures have rough estimate that obtain in such a way. At present time, we cannot connect annealing defects with concrete types. This is subject for further research. Moreover, the reliability increases for the batch LED-6 in comparison with batch LED-3.

Next, **Figure 9** shows the emissive power change of the batch LED-7 during step-by-step tests. This batch is divided into two subgroups LED-7a (70% from the batch LED-7) and LED-7b (30% from the batch LED-7).

For the marked subgroups of the LEDs from the batch LED-7, the following equation can be written as

$$
\eta\_{\text{LED-}\forall b} < \eta\_{\text{LED-}\forall a} \tag{7}
$$

There are two stages of the emissive power recovery with its further fall for subgroup LED-7a. This is due to annealing the corresponding defects. Moreover, the rate of the emissive power recovery exceeds significantly the previously observed values for batch LED-6. Therefore, the recovery of the emissive power for batch LED-7 during operation can be considered due to annealing of two types of defects. Additionally, the first of them can be attributed to the field of radiation-stimulated reconstruction of the initial defect structure under influence of the operation factors. The subgroup LED-7b is characterized by the fact that the first stage of the emissive power recovery is absent. The observed changes of emissive power are described by the measurement error. Therefore, the recovery of the emissive power for subgroup LED-7b during operation can be considered due to the annealing of the second defect only.

The effective annealing temperatures can be estimated to the maximum of the emissive power rise using Eq. (1) for marked subgroups of batch LED-7:


**Figure 8.** Relative change of the emissive power of the batch LED-6 during step-by-step tests: 1, 2, and 3, the emissive

Additionally, there are three distinctive peaks of the emissive power recovery for marked subgroups of the batch LED-6. The subgroups differ only in value of the emissive power recovery. The quantities of the peaks show the annealing of three types of defects. Therefore, the observable recovery of emissive power of the LEDs during operation is due to annealing of three types of the defects created by radiation-stimulated reconstruction of the initial defect

stepi, mA) 475 500 425

**Research stage Level of emissive power, % from initial value**

Before CF development 39 88 73 353 284

**Table 2.** The emissive power changes of the LEDs on the different stages of radiation technology implementation.

After preliminary irradiation by fast neutrons — 95 14 After annealing 95 111 32 Initial values before step-by-step tests 100 100 100

**LED-3 LED-6 LED-7**

**a b a b**

The effective annealing temperatures can be estimated to the maximum of the emissive power rise using Eq. (1) for marked subgroups of batch LED-6. Therefore, the annealing of three distinctive types of defects is observed for each of marked subgroups of batch LED-6. Moreover, the effective annealing temperature is in the range of 341–345 K for the first defect. Furthermore, the effective annealing temperature is in the range of 355–359 K for the second defect. Additionally, the effective annealing temperature is in the range of 369–376 K for the third defect. Certainly, the

structure that is stimulated by operation factors.

Step of the CF appearance (*I*

14 Ionizing Radiation Effects and Applications

power recovery with further fall; LED-6a and LED-6b, marked subgroups; LED-3, the batch LED-3.

**Figure 9.** Relative change of the emissive power of the batch LED-7 during step-by-step tests: 1, 2, and 3, the emissive power recovery with further fall; LED-7a and LED-7b, marked subgroups; LED-3, the batch LED-3.

Consequently, the division of the initial LEDs into distinctive subgroups has been established while investigating the influence of preliminary irradiation by fast neutrons with further annealing on the operational characteristics of the LEDs. Each subgroup has its own characteristic dependence of the emissive power decrease of the LEDs during operation.

**Acknowledgements**

**Author details**

**References**

Alexandr V. Gradoboev1

[grant number 03.G25.31.0224 from 03.03.2017].

\*Address all correspondence to: gradoboev1@mail.ru

2 Kemerovo State University, Kemerovo, Russia

DOI: 10.1109/TIA.2003.821655

1979;**42**(20):1353

This work was supported by the Ministry of Education and Science of the Russian Federation

[1] Gradoboev AV, Surzhikov AP. The Radiation Resistance Microwave Devices Based on

[2] Gradoboev AV, Simonova AV. Operational model of the electronic products. In: Semipalatinsk Test Site. Radiation Legacy and Development Prospects; September 21-23, 2016; Kurchatov, VKO, Republic of Kazakhstan. Pavlodar: Publishing House; 2016. p. 131-132

[3] Martin DI, Ighigeanu DI, Mateescu EN, Craciun GD, Calinescu II, Iovu HM, et al. Combined microwave and accelerated electron beam irradiation facilities for applied physics and chemistry. IEEE Transactions on Industry Applications. 2004;**40**(1):41-52.

[4] Busatto G, De Luca V, Iannuzzo F, Sanseverino A, Velardi F. Single-event effects in power MOSFETs during heavy ion irradiations performed after gamma-ray degradation. IEEE Transactions on Nuclear Science. 2013;**60**(5):3793-3801. DOI: 10.1109/TNS.2013.2278038

[5] Liu C, Li X, Yang J, Ma G, Sun Z. Radiation defects and annealing study on PNP bipolar junction transistors irradiated by 3-MeV protons. IEEE Transactions on Nuclear Science.

[6] Chaffin RJ. Microwave Semiconductor Devices: Fundamentals and Radiation Effects.

[7] Lang DV, Petroff PM, Logan RA, Johnston Jr WD. Recombination-enhanced interactions between point defects and dislocation climb in semiconductors. Physical Review Letters.

[8] Kulakov VM, Ladygin EA. Effects of Ionizing Radiation on the Devices of Electronic

Gallium Arsenide. Tomsk: Tomsk Polytechnic University; 2005. 277 p

, Ksenia N. Orlova<sup>1</sup>

Application of Radiation Technologies for Quality Improvement of LEDs Based upon AlGaAs

and Olga O. Babich2

http://dx.doi.org/10.5772/intechopen.72286

17

\*, Anastasiia V. Simonova1

1 National Research Tomsk Polytechnic University, Tomsk, Russia

2015;**62**(6):3381-3386. DOI: 10.1109/TNS.2015.2498201

Equipment. Sovetskoe Radio: Moscow, Russia; 1980. 244 p

New York: John Wiley and Sons, Inc.; 1973. 387 p

Furthermore, each subgroup can be characterized by eigenvalues of the efficiency coefficient η for the initial LEDs (after preliminary irradiation with further annealing).

Therefore, preliminary irradiation by fast neutrons makes it possible to activate the initial defect structure by decreasing its thermal resistance during further step-by-step tests.

The obtained results allow us to recommend the present radiation technology for manufacturing the LEDs. This technology is based on preliminary irradiation by fast neutrons and further annealing for improving the operational parameters of the LEDs.

## **5. Conclusion**

The following list sums up the main investigation results of experimental studies described above:


## **Acknowledgements**

Consequently, the division of the initial LEDs into distinctive subgroups has been established while investigating the influence of preliminary irradiation by fast neutrons with further annealing on the operational characteristics of the LEDs. Each subgroup has its own charac-

Furthermore, each subgroup can be characterized by eigenvalues of the efficiency coefficient

Therefore, preliminary irradiation by fast neutrons makes it possible to activate the initial

The obtained results allow us to recommend the present radiation technology for manufacturing the LEDs. This technology is based on preliminary irradiation by fast neutrons and

The following list sums up the main investigation results of experimental studies described

**1.** The research results of the emissive power change of the LEDs based upon AlGaAs heterostructures under irradiation by gamma-quanta 60Co and fast neutrons. Based on the analysis of the present results, the radiation model of the LEDs has been developed. The

**2.** The investigation of the emissive power change of the LEDs based upon AlGaAs heterostructures during operation based on the step-by-step tests has been presented. Based on the analysis of the research, the reliability model of the LEDs has been developed. The

**3.** Combination of radiation model and reliability model allows to develop an exploitable model of the LEDs. This model makes possible the prediction of the change in emissive power of the LEDs under complex and combined influence of various types of the ionizing

**4.** Radiation technology for manufacturing LEDs based upon AlGaAs heterostructures with increased radiation resistance and reliability has been presented. It bases on preliminary

**5.** Radiation technology for manufacturing LEDs based upon AlGaAs heterostructures with increased radiation resistance and reliability has been developed. It depends on prelimi-

**6.** Decision of the optimum conditions of irradiation and annealing allows to improve significantly the radiation resistance and reliability of the LEDs based upon AlGaAs heterostruc-

**7.** Suggested complex of the radiation technologies can be recommended for other types of

established laws can be used to predict the radiation resistance of the LEDs.

established laws can be used to predict the reliability of the LEDs.

irradiation and the factors of long-term operation.

irradiation by gamma-quanta 60Со and further annealing.

nary irradiation by fast neutrons and further annealing.

tures, i.e., significantly improve their operation parameters.

semiconductor devices.

defect structure by decreasing its thermal resistance during further step-by-step tests.

teristic dependence of the emissive power decrease of the LEDs during operation.

η for the initial LEDs (after preliminary irradiation with further annealing).

further annealing for improving the operational parameters of the LEDs.

**5. Conclusion**

16 Ionizing Radiation Effects and Applications

above:

This work was supported by the Ministry of Education and Science of the Russian Federation [grant number 03.G25.31.0224 from 03.03.2017].

## **Author details**

Alexandr V. Gradoboev1 \*, Anastasiia V. Simonova1 , Ksenia N. Orlova<sup>1</sup> and Olga O. Babich2

\*Address all correspondence to: gradoboev1@mail.ru

1 National Research Tomsk Polytechnic University, Tomsk, Russia

2 Kemerovo State University, Kemerovo, Russia

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**Chapter 2**

**Provisional chapter**

**Applicability of Quantum Dots in Biomedical Science**

Quantum dots (QDs) are novel class of inorganic fluorophore with superior photophysical properties. Superior optical properties are a promising alternative to organic dyes for fluorescence biomedical applications. These nanoparticles have size-tunable emission, strong light absorbance, and very high levels of brightness and photostability. Highly luminescent QDs are prepared by coating the core with another material, resulting in core-shell quantum dots that are more stable in various chemical environments. These core-shell QDs are hydrophobic and only organic soluble as prepared. Hydrophobic QDs are insoluble in aqueous solution and cannot be directly employed in biomedical applications. They are necessarily made water soluble by surface modifying them with various bifunctional surface ligands or caps to promote aqueous solubility and enhancing biocompatibility. To make them useful for biomedical applications, QDs need to be conjugated to biological molecules without disturbing the biological function of these molecules. Most of the current studies were designed to ask questions concerning the physicochemical properties of novel QD products, not QD toxicity *per se*. The potential toxicity of the QDs is a cause for concern because they are made of heavy metals. The limitation of heavy metal–containing QDs stimulates extensive research interests in exploring alternative strategies for the design of fluorescent nanocrystals with high

**Applicability of Quantum Dots in Biomedical Science**

DOI: 10.5772/intechopen.71428

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

Quantum dots (QDs) are semiconductor nanoparticles that are restricted in three dimensions, typically with a diameter of 2–8 nm [1]. These particles are defined as particles with physical dimensions smaller than the exciton Bohr radius [2]. QDs are a bridge between

**Keywords:** quantum dot, band gap, core/shell/ligand structure, hydrophobic QD,

biocompatibility, hydrophilic QD, functionalization, toxicity

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71428

Slavica Brkić

**Abstract**

biocompatibility.

**1. Introduction**

Slavica Brkić

[33] Gradoboev AV. Study of the "memory effect" in 3-cm band Gunn diodes under irradiation by fast neutrons. In: Microwave & Telecommunication Technology (CriMiCo), 2014 24th International Crimean Conference; September 7-13, 2014; Sevastopol, Ukraine. IEEE; 2014. pp. 870-871

**Provisional chapter**

## **Applicability of Quantum Dots in Biomedical Science**

**Applicability of Quantum Dots in Biomedical Science**

DOI: 10.5772/intechopen.71428

#### Slavica Brkić Slavica Brkić Additional information is available at the end of the chapter

[32] Gradoboev AV, Rubanov PV, Ashcheulov AV. Russian Federation Patent for an Invention no.2303314. IPC: Н01 L21/18. Method for manufacturing semiconductor devices. Federal Institute of Industrial Property. Declared April 17, 2006. Published July 20, 2007; Bulletin

[33] Gradoboev AV. Study of the "memory effect" in 3-cm band Gunn diodes under irradiation by fast neutrons. In: Microwave & Telecommunication Technology (CriMiCo), 2014 24th International Crimean Conference; September 7-13, 2014; Sevastopol, Ukraine.

no. 20. 6 p

20 Ionizing Radiation Effects and Applications

IEEE; 2014. pp. 870-871

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71428

#### **Abstract**

Quantum dots (QDs) are novel class of inorganic fluorophore with superior photophysical properties. Superior optical properties are a promising alternative to organic dyes for fluorescence biomedical applications. These nanoparticles have size-tunable emission, strong light absorbance, and very high levels of brightness and photostability. Highly luminescent QDs are prepared by coating the core with another material, resulting in core-shell quantum dots that are more stable in various chemical environments. These core-shell QDs are hydrophobic and only organic soluble as prepared. Hydrophobic QDs are insoluble in aqueous solution and cannot be directly employed in biomedical applications. They are necessarily made water soluble by surface modifying them with various bifunctional surface ligands or caps to promote aqueous solubility and enhancing biocompatibility. To make them useful for biomedical applications, QDs need to be conjugated to biological molecules without disturbing the biological function of these molecules. Most of the current studies were designed to ask questions concerning the physicochemical properties of novel QD products, not QD toxicity *per se*. The potential toxicity of the QDs is a cause for concern because they are made of heavy metals. The limitation of heavy metal–containing QDs stimulates extensive research interests in exploring alternative strategies for the design of fluorescent nanocrystals with high biocompatibility.

**Keywords:** quantum dot, band gap, core/shell/ligand structure, hydrophobic QD, biocompatibility, hydrophilic QD, functionalization, toxicity

## **1. Introduction**

Quantum dots (QDs) are semiconductor nanoparticles that are restricted in three dimensions, typically with a diameter of 2–8 nm [1]. These particles are defined as particles with physical dimensions smaller than the exciton Bohr radius [2]. QDs are a bridge between

bulk materials and atomic or molecular structures and characterized by compositiondependent band gap energy. These particles are light-emitting nanocrystals with novel optical and electrical properties. Properties of QDs have attracted great interest in biology and medicine in the recent years [3]. Compared with organic dyes and fluorescent proteins, semiconductor QDs offer several unique advantages. However, the major concerns about potential toxicity of QDs have cast doubts on their practical use in biology and medicine [3].

#### **2. The band gap energy**

The small size of QDs lead to what is known as "quantum confinement" [4]. The quantum confinement effects occur when size of nanoparticle smaller than exciton Bohr radius. An exciton Bohr radius is the distance in an electron-hole pair in a bulk semiconductor. QDs are defined as particles with physical dimensions smaller than the exciton Bohr radius. The quantum confinement means that the energy levels that the electrons inhabit become discrete, with a finite separation between them. However, there are some energy levels that the electrons cannot occupy, which are collectively known as band gap [5]. Most electrons occupy energy levels below this band gap in the area known as the valence band, indeed most energy levels in the valence band are occupied. If, however, an external stimulus is applied, an electron may move from the valence band to the conduction band, i.e., those energy levels above the band gap. When the QD is hit by incident light, it absorbs a photon with a higher energy than that of the band gap of the composing semiconductor. When the electron returns to a lower energy level, a narrow, symmetric energy band emission occurs [6]. The wavelength of photon emissions depends not only on the material from which the dot is made but also its size; the smaller the size of the QDs, the larger the band gap energy and QDs emit blue light, larger QDs having smaller band gaps emit the larger wavelength. Recombination occurs when an electron from a higher energy level relaxes to a lower energy level and recombines with an electron hole. This process is accompanied by the emission of radiation, which can be measured to give the band gap size of a semiconductor. The energy of the emitted photon in a recombination process of a QD can be modeled as the sum of the band gap energy, the confinement energies of the excited electron and the electron hole, and the bound energy of the exciton [1]:

$$E = E\_{bandgap} + E\_{conthement} + E\_{exciton} \tag{1}$$

where *m<sup>e</sup>*

stant, *ε<sup>r</sup>*

. Energy of exciton:

**Figure 1.** Size-dependent band gap energy [2].

is the effective mass of the electron, *m<sup>h</sup>*

*<sup>E</sup>exciton* <sup>=</sup> <sup>−</sup>\_\_1

band gap energy as can be seen in **Figure 1**.

**3. Biomedical application of quantum dots**

reduced mass of the exciton system, and *d* is diameter of the confinement [7]. The bound exciton energy can be modeled by using the Coulomb interaction between the electron and the positively charged hole. The negative energy is proportional to Rydberg's energy (*Ry* = 13.6 eV) and inversely proportional to the square of the size-dependent dielectric con-

> *εr* 2 *μ*\_\_\_ *me Ry*

Using these models and spectroscopic measurements of the emitted photon energy *E*, it is possible to measure the band gap of QDs. Decreasing the size of a QD results in a higher degree of confinement, which produces an exciton of higher energy, thereby increasing the

Nanotechnology has been heralded as a new field that has the potential to revolutionize medicine, as well as many other seemingly unrelated subjects, such as electronics, textiles, and energy productions. In 1998, the potential of these nanoparticles for applications involving biological labeling was first reported. The first successful application of QDs to medical diagnostics has been demonstrated by immunofluorescent labeling of fixed cells and tissues and immunostaining of membrane proteins on living cells [8]. The fact that several QDs can be excited by the same wavelength of light opens up several multiplexing potentials, including high-throughput screening of biological samples [9]. Size-tunable

is the effective mass of the hole, *μ* is the

Applicability of Quantum Dots in Biomedical Science http://dx.doi.org/10.5772/intechopen.71428 23

. (3)

The confinement energy can be modeled as a simple particle in an one-dimensional box problem and the energy levels of the exciton can be represented as the solutions to the equation at the ground level (*n* = 1) with the mass replaced by the reduced mass. The magnitude of this confinement energy:

$$E\_{confluent} = \frac{\hbar^2 \pi^2}{2 \, d^2} \left(\frac{1}{\overline{m}\_\epsilon} + \frac{1}{\overline{m}\_h}\right) = \frac{\hbar^2 \pi^2}{2\mu \, d^2} \tag{2}$$

**Figure 1.** Size-dependent band gap energy [2].

bulk materials and atomic or molecular structures and characterized by compositiondependent band gap energy. These particles are light-emitting nanocrystals with novel optical and electrical properties. Properties of QDs have attracted great interest in biology and medicine in the recent years [3]. Compared with organic dyes and fluorescent proteins, semiconductor QDs offer several unique advantages. However, the major concerns about potential toxicity of QDs have cast doubts on their practical use in biology and

The small size of QDs lead to what is known as "quantum confinement" [4]. The quantum confinement effects occur when size of nanoparticle smaller than exciton Bohr radius. An exciton Bohr radius is the distance in an electron-hole pair in a bulk semiconductor. QDs are defined as particles with physical dimensions smaller than the exciton Bohr radius. The quantum confinement means that the energy levels that the electrons inhabit become discrete, with a finite separation between them. However, there are some energy levels that the electrons cannot occupy, which are collectively known as band gap [5]. Most electrons occupy energy levels below this band gap in the area known as the valence band, indeed most energy levels in the valence band are occupied. If, however, an external stimulus is applied, an electron may move from the valence band to the conduction band, i.e., those energy levels above the band gap. When the QD is hit by incident light, it absorbs a photon with a higher energy than that of the band gap of the composing semiconductor. When the electron returns to a lower energy level, a narrow, symmetric energy band emission occurs [6]. The wavelength of photon emissions depends not only on the material from which the dot is made but also its size; the smaller the size of the QDs, the larger the band gap energy and QDs emit blue light, larger QDs having smaller band gaps emit the larger wavelength. Recombination occurs when an electron from a higher energy level relaxes to a lower energy level and recombines with an electron hole. This process is accompanied by the emission of radiation, which can be measured to give the band gap size of a semiconductor. The energy of the emitted photon in a recombination process of a QD can be modeled as the sum of the band gap energy, the confinement energies of the excited electron and the electron hole, and the bound energy of

*E* = *Ebandgap* + *Econfinement* + *Eexciton* (1)

The confinement energy can be modeled as a simple particle in an one-dimensional box problem and the energy levels of the exciton can be represented as the solutions to the equation at the ground level (*n* = 1) with the mass replaced by the reduced mass. The magnitude of this

> 2 *d*<sup>2</sup> ( \_\_\_1 *me* + \_\_\_1

*<sup>m</sup>h*) <sup>=</sup> <sup>ℏ</sup><sup>2</sup> *<sup>π</sup>*<sup>2</sup> \_\_\_\_

<sup>2</sup>*<sup>μ</sup> <sup>d</sup>*2, (2)

medicine [3].

the exciton [1]:

confinement energy:

*<sup>E</sup>confinement* <sup>=</sup> <sup>ℏ</sup><sup>2</sup> *<sup>π</sup>*<sup>2</sup> \_\_\_\_

**2. The band gap energy**

22 Ionizing Radiation Effects and Applications

where *m<sup>e</sup>* is the effective mass of the electron, *m<sup>h</sup>* is the effective mass of the hole, *μ* is the reduced mass of the exciton system, and *d* is diameter of the confinement [7]. The bound exciton energy can be modeled by using the Coulomb interaction between the electron and the positively charged hole. The negative energy is proportional to Rydberg's energy (*Ry* = 13.6 eV) and inversely proportional to the square of the size-dependent dielectric constant, *ε<sup>r</sup>* . Energy of exciton:

$$E\_{\rm exciton} = -\frac{1}{\varepsilon\_r^2} \frac{\mu}{m\_e} R\_g. \tag{3}$$

Using these models and spectroscopic measurements of the emitted photon energy *E*, it is possible to measure the band gap of QDs. Decreasing the size of a QD results in a higher degree of confinement, which produces an exciton of higher energy, thereby increasing the band gap energy as can be seen in **Figure 1**.

## **3. Biomedical application of quantum dots**

Nanotechnology has been heralded as a new field that has the potential to revolutionize medicine, as well as many other seemingly unrelated subjects, such as electronics, textiles, and energy productions. In 1998, the potential of these nanoparticles for applications involving biological labeling was first reported. The first successful application of QDs to medical diagnostics has been demonstrated by immunofluorescent labeling of fixed cells and tissues and immunostaining of membrane proteins on living cells [8]. The fact that several QDs can be excited by the same wavelength of light opens up several multiplexing potentials, including high-throughput screening of biological samples [9]. Size-tunable absorption and emission property of QDs is an extremely valuable property for biological imaging as they can be tuned all the way from the UV to the near-infrared of the spectrum. For biological and medical applications, it is of importance to study the photophysical properties of QDs.

#### **3.1. Photophysical properties of quantum dots**

In the biomedical sciences, fluorescence is used as a powerful tool for labeling, imaging, tracking, detection, and therapy. The fluorescent labeling of biological molecules using organic fluorophore and QDs. QDs are new class of fluorophores that offer several advantages over traditional fluorophores. These particles have broad absorption and narrow emission spectra, high quantum yield, long life-time, high brightness, and stable against photobleaching. A great advantage of QDs compared to the classical fluorophore which emits light in the infrared and near-infrared regions, as the absorption of tissues is minimal in this region. The most popular types of QDs include CdSe, CdTe, and ZnSe. The most commonly studied and used QD is cadmium selenide. The broad absorption spectra of the QDs allows single wavelength excitation of emission from different-sized QDs. Multicolor optical coding for biological assays has been achieved by using different sizes of quantum dots with precisely controlled ratios [10]. In order to apply QDs in biomedical imaging, recent studies have focused on developing near-infrared luminescent QDs which exhibit an emission wavelength ranging from 700 to 900 nm [3]. The use of the near-infrared (NIR) photons is promising for biomedical imaging in living tissue due to longer attenuation distances and a better tissue staining without interfering with autofluorescence, since most of the tissue chromophores weakly absorb light in the infrared range of wavelengths. Hemoglobin and water have lower absorption coefficient and scattering effects in the NIR region (650– 900 nm). The QDs emission can be set to a NIR area by adjusting QD size or by incorporating rare-earth activators. The unique robust optical properties of QDs and their surface properties that allow biocompatibility and heteroconjugation make QDs highly promising fluorescent labels for biological applications with significant superiority over classic organic fluorophores [10].

**Stokes shift**

(**Figure 4**) [14].

One of the most common features of QDs is the photoluminescence redshift relative to absorption, also called Stokes shift. It was named after Irish physicist George G. Stokes. Stokes shift is the difference between QD's peak excitation and the peak emission wavelengths (**Figure 3**) [5]. The energy associated with emission is typically lower than the excitation light. The redshift of emission peaks, with respect to absorption spectra, is size dependent. Stokes shift is commonly observed in semiconductor QDs, and is one of the most important quantities that determine the optical properties of QDs. The large separation between the excitation and emission spectra of the QDs improves the detection sensitivity, as the entire emission spectra of QDs can be detected. The Stokes shift of semiconductor QDs can be as large as 300–400 nm, depending on the wavelength of the excitation light. As the radius of quantum dot increases, the redshift decreases and disappears beyond a certain radius. Each QD has a unique emission maximum; changing the dot size leads to the emission maximum shift. In addition, QDs have very broad absorption spectra, and can be excited over the entire visual wavelength range as well as far into ultraviolet [13]. Because of their exceptionally large Stokes shifts of up to 400 nm, QDs can be used for the multicolor detection with a single wavelength excitation source

Increasing size

Increasing wavelenght

Increasing fluorescence life time

CdSe Quantum Dods

Applicability of Quantum Dots in Biomedical Science http://dx.doi.org/10.5772/intechopen.71428 25

Excited state

Ground state

UV

Band Valence

Bandgap

Conduction Band

Absorbance

**Figure 2.** Band gap energy and size dependent wavelength of CdSe quantum dot [12].

#### *3.1.1. Size-dependent optical properties*

Quantum dots exhibit size-dependent discrete energy levels. The energy gap increases with decrease in the size of the nanocrystal, thus yielding a size-dependent rainbow of colors. The wavelength of the emission photon depends not on the material from which the dot is made but on its size. The ability to control the size of QD enables the manufacturer to determine the wavelength of emission, which in turn determines the color of light the human eye perceives. The smaller the dot is closer to the blue end of the spectrum, and the larger the dot is closer to the red (**Figure 2**) [9]. Light wavelengths from ultraviolet to infrared region (400–4000 nm) can be achieved with variation of the size and composition of nanoparticles [11]. The optical properties of QDs will change with proximity of quantum dots to each other.

**Figure 2.** Band gap energy and size dependent wavelength of CdSe quantum dot [12].

#### **Stokes shift**

absorption and emission property of QDs is an extremely valuable property for biological imaging as they can be tuned all the way from the UV to the near-infrared of the spectrum. For biological and medical applications, it is of importance to study the photophysical

In the biomedical sciences, fluorescence is used as a powerful tool for labeling, imaging, tracking, detection, and therapy. The fluorescent labeling of biological molecules using organic fluorophore and QDs. QDs are new class of fluorophores that offer several advantages over traditional fluorophores. These particles have broad absorption and narrow emission spectra, high quantum yield, long life-time, high brightness, and stable against photobleaching. A great advantage of QDs compared to the classical fluorophore which emits light in the infrared and near-infrared regions, as the absorption of tissues is minimal in this region. The most popular types of QDs include CdSe, CdTe, and ZnSe. The most commonly studied and used QD is cadmium selenide. The broad absorption spectra of the QDs allows single wavelength excitation of emission from different-sized QDs. Multicolor optical coding for biological assays has been achieved by using different sizes of quantum dots with precisely controlled ratios [10]. In order to apply QDs in biomedical imaging, recent studies have focused on developing near-infrared luminescent QDs which exhibit an emission wavelength ranging from 700 to 900 nm [3]. The use of the near-infrared (NIR) photons is promising for biomedical imaging in living tissue due to longer attenuation distances and a better tissue staining without interfering with autofluorescence, since most of the tissue chromophores weakly absorb light in the infrared range of wavelengths. Hemoglobin and water have lower absorption coefficient and scattering effects in the NIR region (650– 900 nm). The QDs emission can be set to a NIR area by adjusting QD size or by incorporating rare-earth activators. The unique robust optical properties of QDs and their surface properties that allow biocompatibility and heteroconjugation make QDs highly promising fluorescent labels for biological applications with significant superiority over classic organic

Quantum dots exhibit size-dependent discrete energy levels. The energy gap increases with decrease in the size of the nanocrystal, thus yielding a size-dependent rainbow of colors. The wavelength of the emission photon depends not on the material from which the dot is made but on its size. The ability to control the size of QD enables the manufacturer to determine the wavelength of emission, which in turn determines the color of light the human eye perceives. The smaller the dot is closer to the blue end of the spectrum, and the larger the dot is closer to the red (**Figure 2**) [9]. Light wavelengths from ultraviolet to infrared region (400–4000 nm) can be achieved with variation of the size and composition of nanoparticles [11]. The optical properties of QDs will change with proximity of quantum

properties of QDs.

24 Ionizing Radiation Effects and Applications

fluorophores [10].

dots to each other.

*3.1.1. Size-dependent optical properties*

**3.1. Photophysical properties of quantum dots**

One of the most common features of QDs is the photoluminescence redshift relative to absorption, also called Stokes shift. It was named after Irish physicist George G. Stokes. Stokes shift is the difference between QD's peak excitation and the peak emission wavelengths (**Figure 3**) [5]. The energy associated with emission is typically lower than the excitation light. The redshift of emission peaks, with respect to absorption spectra, is size dependent. Stokes shift is commonly observed in semiconductor QDs, and is one of the most important quantities that determine the optical properties of QDs. The large separation between the excitation and emission spectra of the QDs improves the detection sensitivity, as the entire emission spectra of QDs can be detected. The Stokes shift of semiconductor QDs can be as large as 300–400 nm, depending on the wavelength of the excitation light. As the radius of quantum dot increases, the redshift decreases and disappears beyond a certain radius. Each QD has a unique emission maximum; changing the dot size leads to the emission maximum shift. In addition, QDs have very broad absorption spectra, and can be excited over the entire visual wavelength range as well as far into ultraviolet [13]. Because of their exceptionally large Stokes shifts of up to 400 nm, QDs can be used for the multicolor detection with a single wavelength excitation source (**Figure 4**) [14].

**Figure 3.** Broad absorption and narrow emission spectrum [15].

#### **Fluorescence intensity and lifetime**

The fluorescence of QDs is generated when the excited electron emits photon and returns to the ground-state. The lifetime is a delay between the moment of absorbtion a photon from the light sorce and moment of emitted light (**Figure 5**). The lifetime of larger dots have more closely spaced energy levels in which the electron-hole pair can be trapped. Therefore, electron-hole pairs in larger dots live longer [10]. Long lifetime provides difference of QD fluorescence signal from background fluorescence. For example, see [17]. The life time of QDs and fluorophores is shown in **Figure 6**.

**Brightness and photostability**

**Figure 5.** Fluorescence lifetime [2].

Minimizing overlap between total excitation and emission bands enhances the clarity and brightness of the fluorescing QD by avoiding re-absorption of emitted light into nearby quantum dots—characteristics that display manufacturers and end-users find highly desirable. Broad absorption spectra make it possible to excite all QDs simultaneously with a single light source and minimize sample autofluorescence by choosing an appropriate excitation wavelength. QDs

larger than that of organic dyes. QDs are able to absorb 10–50 times more photons than organic

, about 10–50 times

Applicability of Quantum Dots in Biomedical Science http://dx.doi.org/10.5772/intechopen.71428 27

have very large molar excitation coefficient in the order of 0.5–5 × 10 <sup>6</sup> M <sup>−</sup><sup>1</sup>

**Figure 6.** Fluorescence lifetime quantum dots and organic fluorophore [19].

In order to extend the lifetime of the QDs, rare earths can be incorporated into the QDs which create local quantum states.

**Figure 4.** Color of light depends on size quantum dot.

**Figure 5.** Fluorescence lifetime [2].

**Fluorescence intensity and lifetime**

26 Ionizing Radiation Effects and Applications

**Figure 3.** Broad absorption and narrow emission spectrum [15].

shown in **Figure 6**.

create local quantum states.

**Figure 4.** Color of light depends on size quantum dot.

The fluorescence of QDs is generated when the excited electron emits photon and returns to the ground-state. The lifetime is a delay between the moment of absorbtion a photon from the light sorce and moment of emitted light (**Figure 5**). The lifetime of larger dots have more closely spaced energy levels in which the electron-hole pair can be trapped. Therefore, electron-hole pairs in larger dots live longer [10]. Long lifetime provides difference of QD fluorescence signal from background fluorescence. For example, see [17]. The life time of QDs and fluorophores is

In order to extend the lifetime of the QDs, rare earths can be incorporated into the QDs which

#### **Brightness and photostability**

Minimizing overlap between total excitation and emission bands enhances the clarity and brightness of the fluorescing QD by avoiding re-absorption of emitted light into nearby quantum dots—characteristics that display manufacturers and end-users find highly desirable. Broad absorption spectra make it possible to excite all QDs simultaneously with a single light source and minimize sample autofluorescence by choosing an appropriate excitation wavelength. QDs have very large molar excitation coefficient in the order of 0.5–5 × 10 <sup>6</sup> M <sup>−</sup><sup>1</sup> , about 10–50 times larger than that of organic dyes. QDs are able to absorb 10–50 times more photons than organic

**Figure 6.** Fluorescence lifetime quantum dots and organic fluorophore [19].

dyes at the same excitation photon flux, leading to a significant improvement in the probe brightness. Owing to their inorganic nature, QDs have minimal interaction with the surrounding environment which contributes to their photostability. Inorganic QDs are more photostable under ultraviolet excitation than organic molecules, and their fluorescence is more saturated [18].

#### **Quantum yield**

Quantum yield is a measure of the "brightness" of a fluorophore and is defined as the ratio of the number of photons emitted to the number of photons absorbed. Some organic dyes have quantum yields approaching 100%, but conjugates (from biological affinity molecules) made from these generally have a significantly lower quantum yield. QDs are relatively efficient with regards to conversion of the excitation light into emission, where the quantum yield is generally over 50%. QDs retain their high quantum yield even after conjugation to biological affinity molecules [14]. The fluorescence quantum yield gives the efficiency of the fluorescence process.

#### **Photobleaching**

Photobleaching (fading) is the photochemical alteration of a dye or a fluorophore molecule, such that it is permanently unable to fluoresce. This is caused by cleaving of covalent bonds or non-specific reactions between the fluorophore and surrounding molecules. QDs are several thousand times more stable against photobleaching than organic dye molecules, and are thus ideal probes for fluorescent spectroscopy and bioimaging applications [20].

outmost surface of these nanoparticles is passivated with an organic ligand.<sup>1</sup>

try, called core-shell QDs, are the core, shell, and ligand (**Figure 8**).

logical studies [26].

**4.1. Surface coatings and water-solubility**

**Figure 7.** Band gap energy core/shell/ligand structure [12].

and phase transfer method [29].

*4.1.1. The ligand exchange method*

a covalent bond with the central atom.

TOPO/TOP: Typically trioctylphosphine oxide/trioctylphosphine.

1

2

water soluble by surface modifying them with various caps to ensure aqueous solubility and enhancing biocompatibility. The three important features of QDs used in the display indus-

When these three features of QDs are tuned to how we need them, we develop exciting new applications. In order to utilize in a biological environment, they need to be made hydrophilic. Thus, they are necessarily made water soluble by surface modifying them with various bifunctional surface ligands or caps to promote aqueous solubility and enhancing biocompatibility [25]. QDs must be conjugated with molecules which have the capabilities of recognizing the target. These surface modifications can also help prevent aggregation, reduce the nonspecific binding, and are critical in achieving specific target imaging in bio-

The key to develop QDs as a tool in biological systems is to achieve water solubility, biocompatibility, and photostability [27]. QDs, single or core/shell structures, do not exhibit aqueous solubility. After synthesis, hydrophobic QD must be covered with an organic layer or incorporated within the organic shell to make them water-soluble and biocompatible [28]. Some of the techniques used to achieve solubilization include ligand exchange, surface silanization,

Native cap exchange is a strategy in which the native hydrophobic layer (TOPO/TOP)2

replaced with a bifunctional moiety that can bind QDs from one side while exposing hydrophilic

As organic ligands, molecules and ions, containing O, S, N, and P, are bonded so that their electronic pair can produce

QDs are made

29

Applicability of Quantum Dots in Biomedical Science http://dx.doi.org/10.5772/intechopen.71428

cap is

## **4. Core/shell structure quantum dot**

Quantum dots are used as bare core or as core/shell structures. Although these "core" QDs determine the optical properties of the conjugate, they are by themselves unsuitable for biological probes owing to their poor stability and quantum yield [21]. In fact, the quantum yield of QD cores has been reported to be very sensitive to the presence of particular ions in solution [22]. A bare nanocrystal core is highly reactive and toxic, resulting in a very unstable structure that is prone to photochemical degradation. The core is highly reactive due to their large surface area/volume ratio, resulting in a very unstable structure which is particularly prone to photochemical degradation. Capping the core with a semiconductor material of a higher band gap not only increases the stability and quantum yield, but also passivates the toxicity of the core by shielding reactive ions from being exposed to photo-oxidative environments, e.g., exposure to UV and air (**Figure 7**). Traditionally, the typical QDs consist of a II–IV, IV–VI, or III–V semiconductor core (CdTe, CdSe, Pb, Se, GaAs, GaN, InP, and InAs), which is surrounded by a covering of wide band gap semiconductor shell as zinc sulfide ZnS or cadmium sulfide CdS is generally used (approx. 1.5 nm thick) [23]. Capping core nanocrystals with ZnS has shown to increase stability and performance, producing QDs with improved photophysical and chemical properties at room temperature. However, ZnS capping alone is not sufficient to stabilize the core, particularly in biological solutions [24]. Quantum dots do not exhibit aqueous solubility as they are generally synthesized in organic solution. The

**Figure 7.** Band gap energy core/shell/ligand structure [12].

dyes at the same excitation photon flux, leading to a significant improvement in the probe brightness. Owing to their inorganic nature, QDs have minimal interaction with the surrounding environment which contributes to their photostability. Inorganic QDs are more photostable under ultraviolet excitation than organic molecules, and their fluorescence is more saturated [18].

Quantum yield is a measure of the "brightness" of a fluorophore and is defined as the ratio of the number of photons emitted to the number of photons absorbed. Some organic dyes have quantum yields approaching 100%, but conjugates (from biological affinity molecules) made from these generally have a significantly lower quantum yield. QDs are relatively efficient with regards to conversion of the excitation light into emission, where the quantum yield is generally over 50%. QDs retain their high quantum yield even after conjugation to biological affinity molecules [14]. The fluorescence quantum yield gives the efficiency of the fluorescence process.

Photobleaching (fading) is the photochemical alteration of a dye or a fluorophore molecule, such that it is permanently unable to fluoresce. This is caused by cleaving of covalent bonds or non-specific reactions between the fluorophore and surrounding molecules. QDs are several thousand times more stable against photobleaching than organic dye molecules, and are thus

Quantum dots are used as bare core or as core/shell structures. Although these "core" QDs determine the optical properties of the conjugate, they are by themselves unsuitable for biological probes owing to their poor stability and quantum yield [21]. In fact, the quantum yield of QD cores has been reported to be very sensitive to the presence of particular ions in solution [22]. A bare nanocrystal core is highly reactive and toxic, resulting in a very unstable structure that is prone to photochemical degradation. The core is highly reactive due to their large surface area/volume ratio, resulting in a very unstable structure which is particularly prone to photochemical degradation. Capping the core with a semiconductor material of a higher band gap not only increases the stability and quantum yield, but also passivates the toxicity of the core by shielding reactive ions from being exposed to photo-oxidative environments, e.g., exposure to UV and air (**Figure 7**). Traditionally, the typical QDs consist of a II–IV, IV–VI, or III–V semiconductor core (CdTe, CdSe, Pb, Se, GaAs, GaN, InP, and InAs), which is surrounded by a covering of wide band gap semiconductor shell as zinc sulfide ZnS or cadmium sulfide CdS is generally used (approx. 1.5 nm thick) [23]. Capping core nanocrystals with ZnS has shown to increase stability and performance, producing QDs with improved photophysical and chemical properties at room temperature. However, ZnS capping alone is not sufficient to stabilize the core, particularly in biological solutions [24]. Quantum dots do not exhibit aqueous solubility as they are generally synthesized in organic solution. The

ideal probes for fluorescent spectroscopy and bioimaging applications [20].

**4. Core/shell structure quantum dot**

**Quantum yield**

28 Ionizing Radiation Effects and Applications

**Photobleaching**

outmost surface of these nanoparticles is passivated with an organic ligand.<sup>1</sup> QDs are made water soluble by surface modifying them with various caps to ensure aqueous solubility and enhancing biocompatibility. The three important features of QDs used in the display industry, called core-shell QDs, are the core, shell, and ligand (**Figure 8**).

When these three features of QDs are tuned to how we need them, we develop exciting new applications. In order to utilize in a biological environment, they need to be made hydrophilic. Thus, they are necessarily made water soluble by surface modifying them with various bifunctional surface ligands or caps to promote aqueous solubility and enhancing biocompatibility [25]. QDs must be conjugated with molecules which have the capabilities of recognizing the target. These surface modifications can also help prevent aggregation, reduce the nonspecific binding, and are critical in achieving specific target imaging in biological studies [26].

#### **4.1. Surface coatings and water-solubility**

The key to develop QDs as a tool in biological systems is to achieve water solubility, biocompatibility, and photostability [27]. QDs, single or core/shell structures, do not exhibit aqueous solubility. After synthesis, hydrophobic QD must be covered with an organic layer or incorporated within the organic shell to make them water-soluble and biocompatible [28]. Some of the techniques used to achieve solubilization include ligand exchange, surface silanization, and phase transfer method [29].

#### *4.1.1. The ligand exchange method*

Native cap exchange is a strategy in which the native hydrophobic layer (TOPO/TOP)2 cap is replaced with a bifunctional moiety that can bind QDs from one side while exposing hydrophilic

<sup>1</sup> As organic ligands, molecules and ions, containing O, S, N, and P, are bonded so that their electronic pair can produce a covalent bond with the central atom.

<sup>2</sup> TOPO/TOP: Typically trioctylphosphine oxide/trioctylphosphine.

**Figure 8.** Core/shell/ligand structure of hydrophobic quantum dot [12].

groups on the surface to achieve optimal dispersion [30]. The ligand exchange method includes the exchange of the hydrophobic surfactant molecules with bifunctional molecules, which are hydrophilic on one side and hydrophobic on the other, to bind to the ZnS shell on the QD [23] (**Figure 9**). These biocompatible polymers usually have functional anchor groups, such as thiol, amine, and carboxyl, which can passivate QDs more strongly than the original ligand [31]. Most often thiols (−SH) as functional groups are used to bind to the ZnS and carboxyl (−COOH) groups are used as hydrophilic ends. The resulting QDs are soluble in both aqueous and polar solvents [29]. Biomolecules, such as proteins, peptides, and DNA, were also conjugated to the free carboxyl groups by crosslinking to the reactive amine. This process did not affect the optical characters of the QDs compared with the original QDs.

may reduce emission and limits their use biological applications [35]. The aqueous coating can then be tagged with various biomolecules of interest. Biomolecules, such as proteins, peptides, and antibodies, were conjugated to the free functional groups by crosslinking to the reactive amine. This process did not affect the optical characters of the QDs compared with

Applicability of Quantum Dots in Biomedical Science http://dx.doi.org/10.5772/intechopen.71428 31

Once solubilization has been achieved, QDs can be functionalized by conjugation to a number of biological molecules. QDs are adapted to the desired biological application by conjugation to biological molecules without disturbing the function of these molecules. QDs must be conjugated with molecules which have the capabilities of recognizing the target [36]. Biomolecules include antibodies, peptides, avidin, biotin, oligonucleotides, albumin, or by coating with streptavidin (**Figure 10**) [6]. Owing to large surface area-to-volume ratio, several biomolecules of varying types can be attached to a single QD. Each of these biomolecules provides a desired function which affords multi-functionality [37]. Various surface modification techniques were developed to ensure the specific bioconjugation: covalent linkage, electrostatic attraction, adsorption, and mercapto (−SH) exchange. The choice depends on the features of the biomolecule of interest

the original hydrophobic surfactant layer.

**5. Functionalization of quantum dots**

**Figure 9.** Modification from hydrophobic to hydrophilic quantum dots [12].

#### *4.1.2. Surface silanization*

Surface silanization involves the growth of a silica shell around the nanocrystal. As silica shells are highly cross-linked, they are very stable [32]. Silica coating enhances the mechanical stability of colloidal QDs and protects them against oxidation and agglomeration. The adventure of silica encapsulation is QDs chemical stability over a much broader pH range compared to carboxy-terminated ligands [29]. The chemistry of glass surfaces can be readily extended to silanized QDs, providing more flexibility for bioconjugation (**Figure 9**).

#### *4.1.3. Polymer coating (phase transfer)*

Polymer coating (phase transfer) method uses amphiphilic polymers to coat the surface [33, 34]. The hydrophobic alkyl chains of the polymer interdigitate with the alkyl groups on the QDs surface, while the hydrophilic groups orientate outwards to attain water solubility. However, coating with a polymer may increase the overall diameter of the QDs, and this

**Figure 9.** Modification from hydrophobic to hydrophilic quantum dots [12].

may reduce emission and limits their use biological applications [35]. The aqueous coating can then be tagged with various biomolecules of interest. Biomolecules, such as proteins, peptides, and antibodies, were conjugated to the free functional groups by crosslinking to the reactive amine. This process did not affect the optical characters of the QDs compared with the original hydrophobic surfactant layer.

## **5. Functionalization of quantum dots**

groups on the surface to achieve optimal dispersion [30]. The ligand exchange method includes the exchange of the hydrophobic surfactant molecules with bifunctional molecules, which are hydrophilic on one side and hydrophobic on the other, to bind to the ZnS shell on the QD [23] (**Figure 9**). These biocompatible polymers usually have functional anchor groups, such as thiol, amine, and carboxyl, which can passivate QDs more strongly than the original ligand [31]. Most often thiols (−SH) as functional groups are used to bind to the ZnS and carboxyl (−COOH) groups are used as hydrophilic ends. The resulting QDs are soluble in both aqueous and polar solvents [29]. Biomolecules, such as proteins, peptides, and DNA, were also conjugated to the free carboxyl groups by crosslinking to the reactive amine. This process did not affect the optical

Surface silanization involves the growth of a silica shell around the nanocrystal. As silica shells are highly cross-linked, they are very stable [32]. Silica coating enhances the mechanical stability of colloidal QDs and protects them against oxidation and agglomeration. The adventure of silica encapsulation is QDs chemical stability over a much broader pH range compared to carboxy-terminated ligands [29]. The chemistry of glass surfaces can be readily extended to

Polymer coating (phase transfer) method uses amphiphilic polymers to coat the surface [33, 34]. The hydrophobic alkyl chains of the polymer interdigitate with the alkyl groups on the QDs surface, while the hydrophilic groups orientate outwards to attain water solubility. However, coating with a polymer may increase the overall diameter of the QDs, and this

characters of the QDs compared with the original QDs.

**Figure 8.** Core/shell/ligand structure of hydrophobic quantum dot [12].

silanized QDs, providing more flexibility for bioconjugation (**Figure 9**).

*4.1.2. Surface silanization*

30 Ionizing Radiation Effects and Applications

*4.1.3. Polymer coating (phase transfer)*

Once solubilization has been achieved, QDs can be functionalized by conjugation to a number of biological molecules. QDs are adapted to the desired biological application by conjugation to biological molecules without disturbing the function of these molecules. QDs must be conjugated with molecules which have the capabilities of recognizing the target [36]. Biomolecules include antibodies, peptides, avidin, biotin, oligonucleotides, albumin, or by coating with streptavidin (**Figure 10**) [6]. Owing to large surface area-to-volume ratio, several biomolecules of varying types can be attached to a single QD. Each of these biomolecules provides a desired function which affords multi-functionality [37]. Various surface modification techniques were developed to ensure the specific bioconjugation: covalent linkage, electrostatic attraction, adsorption, and mercapto (−SH) exchange. The choice depends on the features of the biomolecule of interest

**5.3. Non-specific adsorption**

**5.4. Mercapto exchange**

with living tissue.

**6. Toxicity of quantum dots**

Simple small molecules such as oligonucleotides and various serum albumins were found to readily adsorb to the surface of water-soluble QDs [6]. This adsorption is nonspecific and

Applicability of Quantum Dots in Biomedical Science http://dx.doi.org/10.5772/intechopen.71428 33

Thiol-containing biomolecules can be conjugated to QDs via mercapto exchange. Thiols (SH) bond of mercapto group bind to the surface of the most often used semiconductor materials (CdSe, CdS, CdTe, and ZnS), and therefore QDs can be conjugated to biological molecules bearing mercapto (SH) groups in this way [43]. ZnS-thiol bond is not very strong. The conju-

Surface of QDs are decorated with different biomolecules: proteins, peptides, nucleic acids, ligands, or other biomolecules to achieve bioconjugation that mediate specific interactions

Most of the current studies were designed to ask questions concerning the physicochemical properties of novel QD products such as fluorescence, detectability, stability, and cell labeling efficacy, and not QD toxicity *per se*. Several studies reveal that the toxicity of QDs depends on many factors which can be summarized as inherent physicochemical properties and environmental conditions. Understanding the potential toxicity of QDs requires a fundamental grasp of QD physicochemical properties. Each QD type will need to be characterized individually to its potential toxicity. Each individual type of QD possesses its own unique physicochemical properties, which in turn determines its potential toxicity or lack thereof. QD sizes, charges, concentrations, outer coating materials and functional groups, oxidation, and mechanical stability all have been implicated as contributing factors to toxicity [44]. Most QDs consist of heavy metal which may be potentially toxic. Possibly the most important aspect of QD toxicity is their stability, both *in vivo* and during synthesis and storage. QDs with an outer ZnS shell, referred to as core-shell QDs, are generally more chemically stable. Degradation of the QD coating may also result in reaction of the QD in undesirable/unanticipated ways *in vivo*. Further, some QD coating materials have themselves been found to be cytotoxic. Cytotoxicity of QDs has been observed in a large number of *in vitro* studies [45], affecting cell growth and viability [22]. Several studies suggest QD cytotoxicity to be due to photolysis or oxidation. Under oxidative and photolytic conditions, QD core-shell coatings have been found to be labile, degrading, and thus exposing potentially toxic "capping" material or intact core metalloid complexes or resulting in dissolution of the core complex to QD core metal components, e.g., Cd and Se [46]. The toxicity is associated with the cadmium, lead, or arsenic containing QDs. For *in vivo* studies, the main concern is the robustness of the surface coating.

depends on ionic strength, pH, temperature, and surface charge of the molecule [5].

gated biomolecules may break off and the QDs may precipitate out of solution [6].

**Figure 10.** Functionalization of hydrophilic quantum dots [16].

[38]. Surface modifications can also help prevent aggregation, reduce the nonspecific binding, and are critical to achieving specific target imaging in biomedical studies [3]. QDs retain excellent stability of optical properties upon conjugation to biomolecules, and can be simultaneously excited by a single light source.

#### **5.1. Covalent linkage**

The first bioconjugation method offers a most stable covalent linkage of QDs to biomolecules and is the most commonly used approach for making biofunctionalized QDs for *in vivo* applications. Most water solubilization methods result in QDs covered with carboxylic acid, amino or thiol groups. Under these situations, it is easy to link QDs to biological molecules which also have these functional groups [39]. Using these methods, there have been numerous reports of conjugating QDs with various biological molecules, including proteins, antibodies, peptides, oligonucleotides, and albumin [5].

#### **5.2. Electrostatic interaction**

In the second procedure, an electrostatic interaction between QDs and charged adapter molecules or proteins with incorporated charged domains was employed [40, 41]. In this case, the protein of interest can be fused to a positively charged domain that will in turn bind electrostatically to the negatively charged surface of the QDs [6]. In the electrostatic interaction approach, the binding energies are highly dependent on both the chemical environment and the ambient temperature and QDs size can strongly affect the interaction efficiency. Electrostatic interactions generally are not sufficiently specific, however, given the complexity of biological milieu [5]. Therefore, conjugates made by this way are not suitable for *in vivo* or *ex vivo* cell labeling due to the possible interference with positively charged proteins [42].

#### **5.3. Non-specific adsorption**

Simple small molecules such as oligonucleotides and various serum albumins were found to readily adsorb to the surface of water-soluble QDs [6]. This adsorption is nonspecific and depends on ionic strength, pH, temperature, and surface charge of the molecule [5].

#### **5.4. Mercapto exchange**

[38]. Surface modifications can also help prevent aggregation, reduce the nonspecific binding, and are critical to achieving specific target imaging in biomedical studies [3]. QDs retain excellent stability of optical properties upon conjugation to biomolecules, and can be simultaneously

The first bioconjugation method offers a most stable covalent linkage of QDs to biomolecules and is the most commonly used approach for making biofunctionalized QDs for *in vivo* applications. Most water solubilization methods result in QDs covered with carboxylic acid, amino or thiol groups. Under these situations, it is easy to link QDs to biological molecules which also have these functional groups [39]. Using these methods, there have been numerous reports of conjugating QDs with various biological molecules, including proteins, antibodies,

In the second procedure, an electrostatic interaction between QDs and charged adapter molecules or proteins with incorporated charged domains was employed [40, 41]. In this case, the protein of interest can be fused to a positively charged domain that will in turn bind electrostatically to the negatively charged surface of the QDs [6]. In the electrostatic interaction approach, the binding energies are highly dependent on both the chemical environment and the ambient temperature and QDs size can strongly affect the interaction efficiency. Electrostatic interactions generally are not sufficiently specific, however, given the complexity of biological milieu [5]. Therefore, conjugates made by this way are not suitable for *in vivo* or *ex vivo* cell labeling due to the possible interference with positively charged

excited by a single light source.

32 Ionizing Radiation Effects and Applications

**5.2. Electrostatic interaction**

proteins [42].

peptides, oligonucleotides, and albumin [5].

**Figure 10.** Functionalization of hydrophilic quantum dots [16].

**5.1. Covalent linkage**

Thiol-containing biomolecules can be conjugated to QDs via mercapto exchange. Thiols (SH) bond of mercapto group bind to the surface of the most often used semiconductor materials (CdSe, CdS, CdTe, and ZnS), and therefore QDs can be conjugated to biological molecules bearing mercapto (SH) groups in this way [43]. ZnS-thiol bond is not very strong. The conjugated biomolecules may break off and the QDs may precipitate out of solution [6].

Surface of QDs are decorated with different biomolecules: proteins, peptides, nucleic acids, ligands, or other biomolecules to achieve bioconjugation that mediate specific interactions with living tissue.

## **6. Toxicity of quantum dots**

Most of the current studies were designed to ask questions concerning the physicochemical properties of novel QD products such as fluorescence, detectability, stability, and cell labeling efficacy, and not QD toxicity *per se*. Several studies reveal that the toxicity of QDs depends on many factors which can be summarized as inherent physicochemical properties and environmental conditions. Understanding the potential toxicity of QDs requires a fundamental grasp of QD physicochemical properties. Each QD type will need to be characterized individually to its potential toxicity. Each individual type of QD possesses its own unique physicochemical properties, which in turn determines its potential toxicity or lack thereof. QD sizes, charges, concentrations, outer coating materials and functional groups, oxidation, and mechanical stability all have been implicated as contributing factors to toxicity [44]. Most QDs consist of heavy metal which may be potentially toxic. Possibly the most important aspect of QD toxicity is their stability, both *in vivo* and during synthesis and storage. QDs with an outer ZnS shell, referred to as core-shell QDs, are generally more chemically stable. Degradation of the QD coating may also result in reaction of the QD in undesirable/unanticipated ways *in vivo*. Further, some QD coating materials have themselves been found to be cytotoxic. Cytotoxicity of QDs has been observed in a large number of *in vitro* studies [45], affecting cell growth and viability [22]. Several studies suggest QD cytotoxicity to be due to photolysis or oxidation. Under oxidative and photolytic conditions, QD core-shell coatings have been found to be labile, degrading, and thus exposing potentially toxic "capping" material or intact core metalloid complexes or resulting in dissolution of the core complex to QD core metal components, e.g., Cd and Se [46]. The toxicity is associated with the cadmium, lead, or arsenic containing QDs. For *in vivo* studies, the main concern is the robustness of the surface coating. An unstable surface coating could expose the core of the QD to UV damage or air oxidation. The toxic heavy metal ions can be easily leaked out into biological systems, if the surfaces are not properly covered by the shells or protected by ligands [44]. The stability of QDs and their resistance to metabolic degradation in live cells would allow long-term imaging studies, and several studies have indicated lack of cytotoxicity for period up to 4 months [47]. Although such QDs should not be acutely toxic as long as their polymer coating is stable enough to restrain the release of cadmium, both short- and long-term safety of QDs will need to be established in toxicological studies in clinically relevant animal models. Studies in cell lines have shown that QDs do not affect cell growth under normal media conditions and shortterm administration of QDs into animals seems not to affect the metabolism and behavior of the animals [48]. Xiao and coworkers showed that the cytotoxicity of CdSe quantum was proportional to QDs concentration in the tested range. There was a negligible cytotoxicity at concentration of 20 nM, which is twice of the applied concentration of fluorescent cell imaging test. On the other side, no size-dependent cytotoxicity was observed. For time-dependence, cytotoxicity increased along with prolongation of incubation period, and tended to be stable after 12 h of incubation. Therefore, cytotoxicity can be neglected in a typical fluorescent cell imaging procedure (10 nM/L, 12 h), and the labeling effect to microtubule can be guaranteed satisfactorily [49]. There are also concerns about toxicity related to the molecules used for surface functionalization of the QDs [6]. However, toxicity concerns are still valid for longer periods and *in vivo* applications. Given the highly intrinsic toxicity of cadmium, the biological applications of Cd-QDs have been limited. The limitation of heavy metal containing QDs stimulates extensive research interests in exploring alternative strategies for the design of fluorescent nanocrystals with high biocompatibility. In this case, the practical strategy is to develop highly fluorescent nanoparticles based on nontoxic elements [3].

and environment-friendly nature, Si QDs are used as fluorescent probes for bioimaging. Si QDs are produced in nonpolar solvents with hydrophobic ligands on their surface in other to protect the Si core. Therefore, it is a common problem that silicon QDs show poor solubility and unstable photoluminescence in aqueous solutions. Thus, fabricating good water-disperse Si QDs with stable optical characters is vital to their applications in bioimaging studies. In the demand of using biocompatible and nontoxic QDs as nanoprobes, rare-earth (RE) elements

Applicability of Quantum Dots in Biomedical Science http://dx.doi.org/10.5772/intechopen.71428 35

The ability to study molecular and cellular events by using fluorescent probes has broadly impacted many areas in biomedical research. QDs offer several adventures over traditional fluorophores. Traditional fluorophores have certain properties that limit their biomedical applications: narrow absorption and broad emission spectra, low luminescence and quantum yield, rapid photobleaching, and low brightness signal. A limitation of traditional small-molecule fluorescent dyes is in the labeling of other small molecules, drugs, transporters, and small-molecule probes to cell-surface receptors. Conjugates of dyes to these small molecules often lack sensitivity or specificity in the detection of the desired targets. Conjugates of small molecules to QDs produce conjugates with much greater light output per binding event, owing to the increased absorbance and emission of the QD [14]. The fact that several QDs can be excited by the same wavelength of light opens up several multiplexing potentials, including high-throughput screening of biological samples [9]. Size-tunable absorption and emission property of QDs is an extremely valuable property for biological imaging as they can be tuned all the way from the UV to the near-infrared of the spectrum. QDs exhibit better photophysical properties than conventional fluorophores under appropriate conditions. A limitation of traditional small-molecule fluorescent dyes is in the labeling of other small molecules, drugs, transporters, and small-molecule probes to cell-surface receptors. Conjugates of dyes to these small molecules often lack sensitivity or specificity in the detection of the desired targets. Conjugates of small molecules to QDs produce conjugates with much greater light output binding event, owing to the increased absorbance and emission of the QD. Furthermore, there is the possibility of improved avidity compared of a dye conjugate, owing to the combined effect of many molecules of the binding ligand on the surface of the quantum dot [14]. Biocompatible QDs represent a powerful tool for the direct readout of information down to single molecule level [28]. For example, by conjugating an antibody to the QD, targeting to specific cells or tissues can be affected *in vivo* or in fluorescent antibody immunoassays. QDs have shown great potential to provide spatial, temporal, and structural information for biological systems: *in vivo* cell labeling, *in vitro* cell labeling, detection of tumor marker, *in situ* tissue diagnostic, noninvasive tumor imaging, tracking of local cancer grown and its distant dissemination, detection and therapy of various disease, identifying of various types of biomarkers, more effective and early diagnosis of cancer,

are used to fabricate a new type of QDs, such as Gd-doped ZnO QDs [44].

**7. Adventures of quantum dots compared to conventional** 

**fluorophores**

imaging of live tissue, etc.

#### **6.1. Nontoxic quantum dots**

The last few years of research are focused on QDs that do not contain Cd. QDs made up of III–V semiconductors such as InP. Groups III–V QDs may provide a more stable alternative to groups II–VI (CdSe, Cd, Te, etc.) [50]. QDs due to the presence of a covalent, rather than an ionic bond, and have been reported to have lower cytotoxicity. However these QDs are difficult to prepare on a competitive time scale, and tend to have much lower quantum efficiencies, meaning uptake has been slow [51]. The most highlighted candidates for Cd-free QDs are the InP-based QDs. InP QDs a very attractive candidate for replacing cadmium-based QDs for biological studies. However, till date, there are very little studies reporting the use of InP QDs in bioimaging applications, as they are difficult to prepare because of the sensitivity of precursors and surfactants toward the reaction environment in obtaining good quality InP QDs [52]. Therefore, progresses in the synthesis of InP-based QDs occurred much slowly compared to that of CdSe QDs [53]. InP/ZnS QDs combining the brightness, photostability, and biocompatibility characteristics will serve as a new generation of targeted optical probes for several biomedical applications, including early detection of cancer, replacing the cadmium-based [54]. Silicon nanoparticle is another type of QDs which possess unique properties when their sizes are reduces to below 10 nm. Similar to their predecessors, silicon QDs also have many advantages over traditional fluorescent organic dye. Moreover, owing to silicon's nontoxic and environment-friendly nature, Si QDs are used as fluorescent probes for bioimaging. Si QDs are produced in nonpolar solvents with hydrophobic ligands on their surface in other to protect the Si core. Therefore, it is a common problem that silicon QDs show poor solubility and unstable photoluminescence in aqueous solutions. Thus, fabricating good water-disperse Si QDs with stable optical characters is vital to their applications in bioimaging studies. In the demand of using biocompatible and nontoxic QDs as nanoprobes, rare-earth (RE) elements are used to fabricate a new type of QDs, such as Gd-doped ZnO QDs [44].

## **7. Adventures of quantum dots compared to conventional fluorophores**

An unstable surface coating could expose the core of the QD to UV damage or air oxidation. The toxic heavy metal ions can be easily leaked out into biological systems, if the surfaces are not properly covered by the shells or protected by ligands [44]. The stability of QDs and their resistance to metabolic degradation in live cells would allow long-term imaging studies, and several studies have indicated lack of cytotoxicity for period up to 4 months [47]. Although such QDs should not be acutely toxic as long as their polymer coating is stable enough to restrain the release of cadmium, both short- and long-term safety of QDs will need to be established in toxicological studies in clinically relevant animal models. Studies in cell lines have shown that QDs do not affect cell growth under normal media conditions and shortterm administration of QDs into animals seems not to affect the metabolism and behavior of the animals [48]. Xiao and coworkers showed that the cytotoxicity of CdSe quantum was proportional to QDs concentration in the tested range. There was a negligible cytotoxicity at concentration of 20 nM, which is twice of the applied concentration of fluorescent cell imaging test. On the other side, no size-dependent cytotoxicity was observed. For time-dependence, cytotoxicity increased along with prolongation of incubation period, and tended to be stable after 12 h of incubation. Therefore, cytotoxicity can be neglected in a typical fluorescent cell imaging procedure (10 nM/L, 12 h), and the labeling effect to microtubule can be guaranteed satisfactorily [49]. There are also concerns about toxicity related to the molecules used for surface functionalization of the QDs [6]. However, toxicity concerns are still valid for longer periods and *in vivo* applications. Given the highly intrinsic toxicity of cadmium, the biological applications of Cd-QDs have been limited. The limitation of heavy metal containing QDs stimulates extensive research interests in exploring alternative strategies for the design of fluorescent nanocrystals with high biocompatibility. In this case, the practical strategy is to

develop highly fluorescent nanoparticles based on nontoxic elements [3].

The last few years of research are focused on QDs that do not contain Cd. QDs made up of III–V semiconductors such as InP. Groups III–V QDs may provide a more stable alternative to groups II–VI (CdSe, Cd, Te, etc.) [50]. QDs due to the presence of a covalent, rather than an ionic bond, and have been reported to have lower cytotoxicity. However these QDs are difficult to prepare on a competitive time scale, and tend to have much lower quantum efficiencies, meaning uptake has been slow [51]. The most highlighted candidates for Cd-free QDs are the InP-based QDs. InP QDs a very attractive candidate for replacing cadmium-based QDs for biological studies. However, till date, there are very little studies reporting the use of InP QDs in bioimaging applications, as they are difficult to prepare because of the sensitivity of precursors and surfactants toward the reaction environment in obtaining good quality InP QDs [52]. Therefore, progresses in the synthesis of InP-based QDs occurred much slowly compared to that of CdSe QDs [53]. InP/ZnS QDs combining the brightness, photostability, and biocompatibility characteristics will serve as a new generation of targeted optical probes for several biomedical applications, including early detection of cancer, replacing the cadmium-based [54]. Silicon nanoparticle is another type of QDs which possess unique properties when their sizes are reduces to below 10 nm. Similar to their predecessors, silicon QDs also have many advantages over traditional fluorescent organic dye. Moreover, owing to silicon's nontoxic

**6.1. Nontoxic quantum dots**

34 Ionizing Radiation Effects and Applications

The ability to study molecular and cellular events by using fluorescent probes has broadly impacted many areas in biomedical research. QDs offer several adventures over traditional fluorophores. Traditional fluorophores have certain properties that limit their biomedical applications: narrow absorption and broad emission spectra, low luminescence and quantum yield, rapid photobleaching, and low brightness signal. A limitation of traditional small-molecule fluorescent dyes is in the labeling of other small molecules, drugs, transporters, and small-molecule probes to cell-surface receptors. Conjugates of dyes to these small molecules often lack sensitivity or specificity in the detection of the desired targets. Conjugates of small molecules to QDs produce conjugates with much greater light output per binding event, owing to the increased absorbance and emission of the QD [14]. The fact that several QDs can be excited by the same wavelength of light opens up several multiplexing potentials, including high-throughput screening of biological samples [9]. Size-tunable absorption and emission property of QDs is an extremely valuable property for biological imaging as they can be tuned all the way from the UV to the near-infrared of the spectrum. QDs exhibit better photophysical properties than conventional fluorophores under appropriate conditions. A limitation of traditional small-molecule fluorescent dyes is in the labeling of other small molecules, drugs, transporters, and small-molecule probes to cell-surface receptors. Conjugates of dyes to these small molecules often lack sensitivity or specificity in the detection of the desired targets. Conjugates of small molecules to QDs produce conjugates with much greater light output binding event, owing to the increased absorbance and emission of the QD. Furthermore, there is the possibility of improved avidity compared of a dye conjugate, owing to the combined effect of many molecules of the binding ligand on the surface of the quantum dot [14]. Biocompatible QDs represent a powerful tool for the direct readout of information down to single molecule level [28]. For example, by conjugating an antibody to the QD, targeting to specific cells or tissues can be affected *in vivo* or in fluorescent antibody immunoassays. QDs have shown great potential to provide spatial, temporal, and structural information for biological systems: *in vivo* cell labeling, *in vitro* cell labeling, detection of tumor marker, *in situ* tissue diagnostic, noninvasive tumor imaging, tracking of local cancer grown and its distant dissemination, detection and therapy of various disease, identifying of various types of biomarkers, more effective and early diagnosis of cancer, imaging of live tissue, etc.

## **8. Conclusion**

Quantum dots have emerged as a new promising class of fluorescent probes for biomolecular and cellular imaging. In comparison with organic dyes and fluorescent proteins, QDs have unique optical and electronic properties. QDs do not exhibit aqueous solubility as they are generally synthesized in organic solution and are surface-stabilized with hydrophobic organic ligands. To make them useful for biomedical applications, QDs need to be conjugated to biological molecules without disturbing the biological function of these molecules. Various surface modification techniques were developed to ensure the specific bioconjugation. This is usually achieved by decorating QDs with proteins, peptides, nucleic acids, streptavidin, or other biomolecules that mediate specific interactions with living systems. Biocompatible quantum dots represent a powerful tool for the direct readout of information down to single molecule level. The limiting factor of application QDs *in vivo* is their toxicity. Although QD technology is still not in much use due to their hydrophobicity, toxicity, and many issues need to be solved in order to apply them safely in biomedical applications.

[7] Dey S, Jain YS. On the wave mechanics of a particle in two different impenetrable spheri-

Applicability of Quantum Dots in Biomedical Science http://dx.doi.org/10.5772/intechopen.71428 37

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## **Author details**

Slavica Brkić

Address all correspondence to: slavica.brkic@sve-mo.ba

Faculty of Science and Education, University of Mostar, Mostar, Bosnia and Herzegovina

## **References**


[7] Dey S, Jain YS. On the wave mechanics of a particle in two different impenetrable spherical cavities. arXiv:1002.4308v1, 2010

**8. Conclusion**

36 Ionizing Radiation Effects and Applications

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Slavica Brkić

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**Author details**

Address all correspondence to: slavica.brkic@sve-mo.ba

Quantum dots have emerged as a new promising class of fluorescent probes for biomolecular and cellular imaging. In comparison with organic dyes and fluorescent proteins, QDs have unique optical and electronic properties. QDs do not exhibit aqueous solubility as they are generally synthesized in organic solution and are surface-stabilized with hydrophobic organic ligands. To make them useful for biomedical applications, QDs need to be conjugated to biological molecules without disturbing the biological function of these molecules. Various surface modification techniques were developed to ensure the specific bioconjugation. This is usually achieved by decorating QDs with proteins, peptides, nucleic acids, streptavidin, or other biomolecules that mediate specific interactions with living systems. Biocompatible quantum dots represent a powerful tool for the direct readout of information down to single molecule level. The limiting factor of application QDs *in vivo* is their toxicity. Although QD technology is still not in much use due to their hydrophobicity, toxicity, and many issues need to be solved in order to apply them safely in biomedical

Faculty of Science and Education, University of Mostar, Mostar, Bosnia and Herzegovina

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38 Ionizing Radiation Effects and Applications

pp. 16-17


**Chapter 3**

**Provisional chapter**

**Hydrogen Gas Detection by Mini-Raman Lidar**

**Hydrogen Gas Detection by Mini-Raman Lidar**

DOI: 10.5772/intechopen.74630

Now, Hydrogen gas is of particular interest as new energy source and dangerous material in nuclear facility. Fuel cell is started to use in home power generation system in 2008 and fuel cell vehicle (FCV) is commercialized from 2014 in Japan. On contrary, the Great East Japan Earthquake revealed the fear of hydrogen explosion on Fukushima Nuclear Power plant in 2011. Contact type hydrogen sensors induce changes on the gas flow, and the actual concentration cannot be known. It is hard to get the gas concentration distribution in hydrogen leakage area. We focused on optical remote sensing for the hydrogen detection. Raman scattering detection was accomplished for the hydrogen gas with a compact Diode Pumped Solid State (DPSS) laser-based Raman lidar. The quantitative measurement was conducted on the hydrogen gas concentration of 1 - 100% and the detectable distance of <50 m. Next, a LED-based mini Raman lidar was developed with the same optical design as the former one in viewpoints of its robust operation and usability in the nuclear facility. The high-speed photon counter was developed to follow the high repetition frequency of LED pulse of >500 kHz, and the quantitative measurements of hydrogen concentration were conducted on lab-experiment and at outdoor.

Nowadays, there is a strong demand for remote sensing in near range. Needless to say, the fear of terrorism, the human daily lives whether at urban or at countryside have the threat of nonsafety. The urban polluted air, smoke on chemical factory, dust from construction site pose a threat to human social activities. Certain dangerous gas detections in volcanic zone, construction site, and water inspection, air quality check in factory, hall, park, and so on, are desired for safe life. Certain gas/dust monitoring in construction site, and air quality estimation in daily

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

**Keywords:** hydrogen, lidar, Raman, scattering, LED

http://dx.doi.org/10.5772/intechopen.74630

Tatsuo Shiina

**Abstract**

**1. Introduction**

Tatsuo Shiina

#### **Hydrogen Gas Detection by Mini-Raman Lidar Hydrogen Gas Detection by Mini-Raman Lidar**

DOI: 10.5772/intechopen.74630

#### Tatsuo Shiina Tatsuo Shiina

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74630

#### **Abstract**

Now, Hydrogen gas is of particular interest as new energy source and dangerous material in nuclear facility. Fuel cell is started to use in home power generation system in 2008 and fuel cell vehicle (FCV) is commercialized from 2014 in Japan. On contrary, the Great East Japan Earthquake revealed the fear of hydrogen explosion on Fukushima Nuclear Power plant in 2011. Contact type hydrogen sensors induce changes on the gas flow, and the actual concentration cannot be known. It is hard to get the gas concentration distribution in hydrogen leakage area. We focused on optical remote sensing for the hydrogen detection. Raman scattering detection was accomplished for the hydrogen gas with a compact Diode Pumped Solid State (DPSS) laser-based Raman lidar. The quantitative measurement was conducted on the hydrogen gas concentration of 1 - 100% and the detectable distance of <50 m. Next, a LED-based mini Raman lidar was developed with the same optical design as the former one in viewpoints of its robust operation and usability in the nuclear facility. The high-speed photon counter was developed to follow the high repetition frequency of LED pulse of >500 kHz, and the quantitative measurements of hydrogen concentration were conducted on lab-experiment and at outdoor.

**Keywords:** hydrogen, lidar, Raman, scattering, LED

## **1. Introduction**

Nowadays, there is a strong demand for remote sensing in near range. Needless to say, the fear of terrorism, the human daily lives whether at urban or at countryside have the threat of nonsafety. The urban polluted air, smoke on chemical factory, dust from construction site pose a threat to human social activities. Certain dangerous gas detections in volcanic zone, construction site, and water inspection, air quality check in factory, hall, park, and so on, are desired for safe life. Certain gas/dust monitoring in construction site, and air quality estimation in daily

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

life circumference are included in such demands for the improvement of working condition in factory and facility.

is explained. Some results of quantitative measurements are shown with actual observation

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 43

Utilization of hydrogen energy is undergoing, which is led mainly by the Agency for Natural Resources and Energy in the Ministry of Economy, Trade and Industry, Japan to promote the

Fuel cell generates electricity by chemical reaction between hydrogen and oxygen. It causes only water vapor and its power generation efficiency exceeds 30%. Hydrogen gas is stored in a high-pressure tank at 35 MPa in hydrogen station and FCV. 96 hydrogen stations were built in 2016 in Japan, and it will increase 160 stations in 2020. FCV were installed 2000 cars in 2016, and bus and forklift truck types were installed into on-site, too. The agency aims to expand it up to 40,000 cars in 2020. Now, FCV seems to conceal itself under electric vehicle (EV). FCV, however, can drive for a long travel distance of 700–850 km at one-time insufflations of hydrogen of 3 min [11]. For that reason, EV is good for small automobile for short distance, while

Home-use fuel cell system is established its technologies in complex with cogeneration. Hydrogen is generated from urban gas or LP gas, and chemically reacts with oxygen, then generates the electricity. Exhaust heat on electricity generation is utilized to the other purpose (for example hot water supply). 200,000 systems have been already installed up to 2016.

Hydrogen gas on the nuclear reactor is generated by the different process against the above. In general, the nuclear fuel rod boils water with its high temperature in nuclear reaction. At the Great East Japan Earthquake, it is considered that the tragic event was caused by the following process. The nuclear reactor was stopped automatically, while the fuel cell rod continued heating. Because the cooling system was fallen down, the water level was lowered and the rod was naked. Although the nuclear fuel rod was covered with zirconium, it reacted with water on the high temperature. As a result, zirconium took oxygen away from the water, the

Under the controlled condition to generate the electricity or the unforeseen circumstances,

Hydrogen is flammable gas. It explodes at the concentration of >4% under the oxygen circumference [12]. The Fire Defense Agency defined that the gas sensor must have the minimal detection of the one fourth of the explosion limit of the target gas. It is essential to detect such flammable gas before the risk of its explosion. Methane, Carbon oxide, and so on have

hydrogen gas monitoring is essential and should prevent the accident.

**2. Hydrogen generation – controlled and unprepared**

spread of fuel cell car (FCV) and home-use fuel cell system.

FCV has a merit for large-size automobile for long distance.

Reducing the price of the system is undergoing.

**3. Optical sensing for hydrogen gas**

hydrogen gas was generated.

data.

In the viewpoint of safety management, the working condition focus on the dust and leaked gas detections under construction site at outdoor. The mass media concerns to the atmospheric suspended materials represented as SPM (Suspended Particle Material), PM10/PM2.5, yellow sand, pollens, and also industrial dusts as dioxin, photochemical smog, and asbestos. The dust flow information, including the nuclear material, is strongly desired after the Great East Japan Earthquake. On indoor application, chemical gas flow in a factory, dust density measurement and dangerous gas monitoring such as CO, CO2 , CH4 , and H2 S in a tunnel construction site in mountain and under the sea are essential for such safety managements.

At the atmospheric monitoring indoor and outdoor, the "contact" sensors are utilized. These sensors are compact, cheap, and easy-to-use, while they need a lot to cover the whole area. A lot of sensors should be scattered in a certain area to get the target distribution and behavior. Low concentration gas and shooting out gas is difficult to perform the quantitative measurement [1, 2].

The word "LIDAR (Light Detection And Ranging)" is sometimes written as LiDAR for hard target detection and lidar for soft target detection. The former is utilized as a range finder to detect the distance up to the target. The latter is for monitoring the target condition and behavior at a certain distance. It is an ideal technique to monitor the suspended materials such as aerosol, dust, gas, and atmosphere remotely and safely [3–5]. Unlike a transmissometer which consists of an separated pair of transmitter and receiver, lidar can fix at a point and scan the observing direction. Then it can cover a certain area remotely. Lidar can obtain the distribution and change of the target in monitoring site by scanning the observation direction. Its observation range is enough long of a few to a hundred kilometers. In contrary, recently it applied for near range monitoring within a few hundred meters. Its application is industrial use.

Lidar technique utilizes various kinds of scattering. Mie scattering, Rayleigh scattering, Raman scattering, and so on. Mie scattering is generated by larger materials such as aerosols and dusts, while the Rayleigh scattering is caused by smaller materials such as molecules configuring the atmosphere. Raman scattering is brought about every material but it shifts wavelength of scattering light from the incident light one. It is convenient for target gas detection.

In this study, we developed the compact Raman lidar for hydrogen gas detection. To prevent the explosion accident of hydrogen gas, the sensor should detect the target gas of the low concentration of 1/4 of the explosion limit. In the case of hydrogen gas, its concentration is 1% [6–8]. The optical intensity of the lidar transmitter is designed to be safe for human eye and skin. This study has been started to apply for leaked gas detection in a hydrogen gas station [9, 10]. After that it has expanded to adapt to the nuclear facility. This lidar should be compact and easy-to-use. It is also applied to monitor the air qualities of working environment including hydrogen gas, atmospheric nitrogen gas and water vapor.

This report states the developments of the Diode Pumped Solid State (DPSS) laser-based compact Raman lidar and the LED-based mini-Raman lidar. At first Raman scattering and lidar principle are briefly mentioned, and after that, the development of concrete Raman lidars is explained. Some results of quantitative measurements are shown with actual observation data.

## **2. Hydrogen generation – controlled and unprepared**

life circumference are included in such demands for the improvement of working condition

In the viewpoint of safety management, the working condition focus on the dust and leaked gas detections under construction site at outdoor. The mass media concerns to the atmospheric suspended materials represented as SPM (Suspended Particle Material), PM10/PM2.5, yellow sand, pollens, and also industrial dusts as dioxin, photochemical smog, and asbestos. The dust flow information, including the nuclear material, is strongly desired after the Great East Japan Earthquake. On indoor application, chemical gas flow in a factory, dust density

struction site in mountain and under the sea are essential for such safety managements.

At the atmospheric monitoring indoor and outdoor, the "contact" sensors are utilized. These sensors are compact, cheap, and easy-to-use, while they need a lot to cover the whole area. A lot of sensors should be scattered in a certain area to get the target distribution and behavior. Low concentration gas and shooting out gas is difficult to perform the quantitative measurement [1, 2].

The word "LIDAR (Light Detection And Ranging)" is sometimes written as LiDAR for hard target detection and lidar for soft target detection. The former is utilized as a range finder to detect the distance up to the target. The latter is for monitoring the target condition and behavior at a certain distance. It is an ideal technique to monitor the suspended materials such as aerosol, dust, gas, and atmosphere remotely and safely [3–5]. Unlike a transmissometer which consists of an separated pair of transmitter and receiver, lidar can fix at a point and scan the observing direction. Then it can cover a certain area remotely. Lidar can obtain the distribution and change of the target in monitoring site by scanning the observation direction. Its observation range is enough long of a few to a hundred kilometers. In contrary, recently it applied for near range monitoring within a few hundred meters. Its application is

Lidar technique utilizes various kinds of scattering. Mie scattering, Rayleigh scattering, Raman scattering, and so on. Mie scattering is generated by larger materials such as aerosols and dusts, while the Rayleigh scattering is caused by smaller materials such as molecules configuring the atmosphere. Raman scattering is brought about every material but it shifts wavelength of scattering light from the incident light one. It is convenient for target gas detection. In this study, we developed the compact Raman lidar for hydrogen gas detection. To prevent the explosion accident of hydrogen gas, the sensor should detect the target gas of the low concentration of 1/4 of the explosion limit. In the case of hydrogen gas, its concentration is 1% [6–8]. The optical intensity of the lidar transmitter is designed to be safe for human eye and skin. This study has been started to apply for leaked gas detection in a hydrogen gas station [9, 10]. After that it has expanded to adapt to the nuclear facility. This lidar should be compact and easy-to-use. It is also applied to monitor the air qualities of working environment includ-

This report states the developments of the Diode Pumped Solid State (DPSS) laser-based compact Raman lidar and the LED-based mini-Raman lidar. At first Raman scattering and lidar principle are briefly mentioned, and after that, the development of concrete Raman lidars

, CH4

, and H2

S in a tunnel con-

measurement and dangerous gas monitoring such as CO, CO2

ing hydrogen gas, atmospheric nitrogen gas and water vapor.

in factory and facility.

42 Ionizing Radiation Effects and Applications

industrial use.

Utilization of hydrogen energy is undergoing, which is led mainly by the Agency for Natural Resources and Energy in the Ministry of Economy, Trade and Industry, Japan to promote the spread of fuel cell car (FCV) and home-use fuel cell system.

Fuel cell generates electricity by chemical reaction between hydrogen and oxygen. It causes only water vapor and its power generation efficiency exceeds 30%. Hydrogen gas is stored in a high-pressure tank at 35 MPa in hydrogen station and FCV. 96 hydrogen stations were built in 2016 in Japan, and it will increase 160 stations in 2020. FCV were installed 2000 cars in 2016, and bus and forklift truck types were installed into on-site, too. The agency aims to expand it up to 40,000 cars in 2020. Now, FCV seems to conceal itself under electric vehicle (EV). FCV, however, can drive for a long travel distance of 700–850 km at one-time insufflations of hydrogen of 3 min [11]. For that reason, EV is good for small automobile for short distance, while FCV has a merit for large-size automobile for long distance.

Home-use fuel cell system is established its technologies in complex with cogeneration. Hydrogen is generated from urban gas or LP gas, and chemically reacts with oxygen, then generates the electricity. Exhaust heat on electricity generation is utilized to the other purpose (for example hot water supply). 200,000 systems have been already installed up to 2016. Reducing the price of the system is undergoing.

Hydrogen gas on the nuclear reactor is generated by the different process against the above. In general, the nuclear fuel rod boils water with its high temperature in nuclear reaction. At the Great East Japan Earthquake, it is considered that the tragic event was caused by the following process. The nuclear reactor was stopped automatically, while the fuel cell rod continued heating. Because the cooling system was fallen down, the water level was lowered and the rod was naked. Although the nuclear fuel rod was covered with zirconium, it reacted with water on the high temperature. As a result, zirconium took oxygen away from the water, the hydrogen gas was generated.

Under the controlled condition to generate the electricity or the unforeseen circumstances, hydrogen gas monitoring is essential and should prevent the accident.

## **3. Optical sensing for hydrogen gas**

Hydrogen is flammable gas. It explodes at the concentration of >4% under the oxygen circumference [12]. The Fire Defense Agency defined that the gas sensor must have the minimal detection of the one fourth of the explosion limit of the target gas. It is essential to detect such flammable gas before the risk of its explosion. Methane, Carbon oxide, and so on have absorption lines in the near infrared spectrum, and the differential absorption technique can be adapted for these gas detections. The hydrogen gas, however, has its absorption line in < l10 nm and does not have any clear absorption lines in ultra violet, visible – near infrared spectra [13]. The hydrogen gas detection is only conducted by contact chemical sensors such as combustible material, catalyst materials (Pt or Pd), and semiconductor type (SnO2 ) [1, 2]. These sensors are high-sensitive to detect its concentration of a few tens ppm, while it is hard to get the gas distribution in whole of monitoring site. Furthermore, the contact sensor disturbs the gas flow, and its sensing direction influences to the measurement value. Its response time is slow, too.

> To estimate the quantitative concentration of hydrogen gas, Raman scattering intensities of atmospheric nitrogen is utilized. When the concentration of hydrogen gas is negligible amount than that of atmospheric nitrogen, the ratio between the Raman scattering intensities of hydrogen gas and atmospheric nitrogen can indicate the concentration of the hydrogen gas quantitatively. The ratio is calibrated by the relative Raman scattering cross sections of hydrogen and nitrogen, which is about 3:1 [5]. **Table 1** shows the concrete Raman shifts and

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 45

**Target Raman shift (cm−1) Wavelength (nm)**

Nitrogen 2331 380 Water vapor 3652 400 Oxygen 1556 369 Hydrogen 4160 408

**Table 1.** Raman shift and its wavelength against 349 nm light source.

The principle of lidar is illustrated in **Figure 2**. The pulsed laser beam was collimated and fired into the atmosphere with almost parallel to the receiver's optical axis. The optical receiver is adjusted its field of view (FOV) to detect the lidar echo from the target with an adequate signal-to-noise ratio. The receiver's FOV decides the detecting range and the blind area, which the transmitting beam cannot enter within a receiver's FOV, especially in near range. It also affects the detecting intensity of the background light. As a traditional lidar has individual optics (biaxial optics) for a laser transmitter and a receiver, the system has a blind area. The blind area also causes in the case of coaxial optics that the beam is transmitted within a receiver's area. As FOV is wider, or the beam divergence is wider, the blind area will be shortened, while the background light enters a

lot into the receiver. As a result, the signal-to-noise ratio of the lidar echo will be worse.

hard to detect an analogue signal, photon counting method is selectable.

The lidar echo is detected by high sensitive detectors such as photomultiplier and Avalanche Photo Diode (APD), and stored in PC via digitizer. When the lidar echo becomes weak and

The compact lidar is suitable to the near range observation of less than a few hundred meters, while the traditional large lidar is good at the long-range observation from a few kilometers to a hundred kilometers. The compact lidar, however, is not a down-size one of the large lidar. **Table 2** shows the spatial and time scales in atmospheric phenomena. The large phenomena such as HP/LP have a large spatial and time scales, while the small phenomena like tornado takes small spatial and time scales. That is, the small phenomenon becomes small structure and quick motion. To detect and visualize such small phenomena, the compact lidar should follow to its quick motion with high resolution. Furthermore, near range detection is often a sensing in human living space. In that meaning, the transmitting optical power should be

their shifted wavelengths against the 349 nm laser light source.

**4. Compact Raman lidar**

Hydrogen gas has strong Raman effect, which depends on material. Raman scattering shifts the wavelength of the scattering light from that of the incident light. In general, the intensity of Raman scattering is 3 digits smaller than that of the Mie scattering [14, 15]. When electrons in atmospheric molecules (or certain gas, atom, and so on) are resonant with photons, most photons are elastically scattered (it is Rayleigh scattering), such that the scattered photons have the same optical frequency and wavelength as the incident light (photons). A small fraction of such photons is scattered with a frequency different from the original frequency of the incident photons. The frequency shift is usually lower than and partially higher than the original; Stokes scattering as longer wavelength and anti-Stokes scattering as shorter wavelength. The interaction of light with a material in a linear region allows absorption and emission of a photon precisely matching the difference in energy levels of the interacting electron. The energy absorption of the molecules causes Stokes scattering, while the energy loss of the molecules generates the anti-Stokes scattering. Stokes scattering shifts the wavelength of the incident light to the longer side. Anti-Stokes scattering shifts that to the shorter side as shown in **Figure 1**. Intensity of Anti-Stokes scattering is smaller than that of Stokes scattering. In general, this trend is remarkably strong when the Raman shift becomes large. In this study, Stokes scattering of hydrogen gas is selected for the lidar detection target under these backgrounds.

**Figure 1.** Raman scattering.


**Table 1.** Raman shift and its wavelength against 349 nm light source.

To estimate the quantitative concentration of hydrogen gas, Raman scattering intensities of atmospheric nitrogen is utilized. When the concentration of hydrogen gas is negligible amount than that of atmospheric nitrogen, the ratio between the Raman scattering intensities of hydrogen gas and atmospheric nitrogen can indicate the concentration of the hydrogen gas quantitatively. The ratio is calibrated by the relative Raman scattering cross sections of hydrogen and nitrogen, which is about 3:1 [5]. **Table 1** shows the concrete Raman shifts and their shifted wavelengths against the 349 nm laser light source.

## **4. Compact Raman lidar**

absorption lines in the near infrared spectrum, and the differential absorption technique can be adapted for these gas detections. The hydrogen gas, however, has its absorption line in < l10 nm and does not have any clear absorption lines in ultra violet, visible – near infrared spectra [13]. The hydrogen gas detection is only conducted by contact chemical sensors such

These sensors are high-sensitive to detect its concentration of a few tens ppm, while it is hard to get the gas distribution in whole of monitoring site. Furthermore, the contact sensor disturbs the gas flow, and its sensing direction influences to the measurement value. Its response

Hydrogen gas has strong Raman effect, which depends on material. Raman scattering shifts the wavelength of the scattering light from that of the incident light. In general, the intensity of Raman scattering is 3 digits smaller than that of the Mie scattering [14, 15]. When electrons in atmospheric molecules (or certain gas, atom, and so on) are resonant with photons, most photons are elastically scattered (it is Rayleigh scattering), such that the scattered photons have the same optical frequency and wavelength as the incident light (photons). A small fraction of such photons is scattered with a frequency different from the original frequency of the incident photons. The frequency shift is usually lower than and partially higher than the original; Stokes scattering as longer wavelength and anti-Stokes scattering as shorter wavelength. The interaction of light with a material in a linear region allows absorption and emission of a photon precisely matching the difference in energy levels of the interacting electron. The energy absorption of the molecules causes Stokes scattering, while the energy loss of the molecules generates the anti-Stokes scattering. Stokes scattering shifts the wavelength of the incident light to the longer side. Anti-Stokes scattering shifts that to the shorter side as shown in **Figure 1**. Intensity of Anti-Stokes scattering is smaller than that of Stokes scattering. In general, this trend is remarkably strong when the Raman shift becomes large. In this study, Stokes scattering of hydrogen gas is selected for the lidar

) [1, 2].

as combustible material, catalyst materials (Pt or Pd), and semiconductor type (SnO2

time is slow, too.

44 Ionizing Radiation Effects and Applications

detection target under these backgrounds.

**Figure 1.** Raman scattering.

The principle of lidar is illustrated in **Figure 2**. The pulsed laser beam was collimated and fired into the atmosphere with almost parallel to the receiver's optical axis. The optical receiver is adjusted its field of view (FOV) to detect the lidar echo from the target with an adequate signal-to-noise ratio. The receiver's FOV decides the detecting range and the blind area, which the transmitting beam cannot enter within a receiver's FOV, especially in near range. It also affects the detecting intensity of the background light. As a traditional lidar has individual optics (biaxial optics) for a laser transmitter and a receiver, the system has a blind area. The blind area also causes in the case of coaxial optics that the beam is transmitted within a receiver's area. As FOV is wider, or the beam divergence is wider, the blind area will be shortened, while the background light enters a lot into the receiver. As a result, the signal-to-noise ratio of the lidar echo will be worse.

The lidar echo is detected by high sensitive detectors such as photomultiplier and Avalanche Photo Diode (APD), and stored in PC via digitizer. When the lidar echo becomes weak and hard to detect an analogue signal, photon counting method is selectable.

The compact lidar is suitable to the near range observation of less than a few hundred meters, while the traditional large lidar is good at the long-range observation from a few kilometers to a hundred kilometers. The compact lidar, however, is not a down-size one of the large lidar. **Table 2** shows the spatial and time scales in atmospheric phenomena. The large phenomena such as HP/LP have a large spatial and time scales, while the small phenomena like tornado takes small spatial and time scales. That is, the small phenomenon becomes small structure and quick motion. To detect and visualize such small phenomena, the compact lidar should follow to its quick motion with high resolution. Furthermore, near range detection is often a sensing in human living space. In that meaning, the transmitting optical power should be

**Figure 2.** Lidar principle.

lower for eye-safety. It causes the limit of transmitting power and the selection of optical wavelength.

The Raman scattering intensity is estimated by Eq. (1).

$$\mathbf{P}\_{\mathrm{R}} = \frac{\lambda\_{\mathrm{o}}}{\lambda\_{\mathrm{R}}} \mathbf{P}\_{\mathrm{o}} \,\chi\mathrm{p}\sigma\_{\mathrm{g}} \,\mathrm{L}\,\eta\_{\mathrm{D}} \tag{1}$$

measurement is calculated by the intensity ratio of nitrogen echo and hydrogen echo. The lidar echo is inversely proportional to the distance to the power of square. But the above intensity

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 47

The concept of the hydrogen remote sensing is to install the "remote sensor" into the area monitoring in a hydrogen station. The sensor is put on a small car and monitors the inside area of the station on the street. In that meaning, the remote sensor should be compact. The

**Figure 3.** Optics of compact Raman lidar. (a) Compact Raman lidar—optical setup. (b) Outlook of compact Raman lidar.

ratio cancels the intensity decrease [6].

eye-safety should be considered, too.

where P0 , PR are wavelength λ<sup>0</sup> , λR of laser light source and Raman scattering intensity, respectively. χ is molar function of the target, ρ is number density of the molecules, σR is Raman scattering cross-section, L is pulse length and ηD is receiver's optical efficiency. The quantitative


**Table 2.** Spatial and time scales of atmosphere.

measurement is calculated by the intensity ratio of nitrogen echo and hydrogen echo. The lidar echo is inversely proportional to the distance to the power of square. But the above intensity ratio cancels the intensity decrease [6].

The concept of the hydrogen remote sensing is to install the "remote sensor" into the area monitoring in a hydrogen station. The sensor is put on a small car and monitors the inside area of the station on the street. In that meaning, the remote sensor should be compact. The eye-safety should be considered, too.

lower for eye-safety. It causes the limit of transmitting power and the selection of optical

P0 χρσ<sup>R</sup> L η<sup>D</sup> (1)

, λR of laser light source and Raman scattering intensity, respec-

λR

**Phenomena Spatial scale Time scale** HP/LP 1000 km 10 h Typhoon 100 km 3 h Convection 50 km 2 h Thunder clouds 10 km 1 h Cumulus 2 km 10 min Down burst 600 m 7 min Tornado 200 m 5 min Boundary layer 60 m 10 s

tively. χ is molar function of the target, ρ is number density of the molecules, σR is Raman scattering cross-section, L is pulse length and ηD is receiver's optical efficiency. The quantitative

The Raman scattering intensity is estimated by Eq. (1).

PR <sup>=</sup> <sup>λ</sup>\_\_0

, PR are wavelength λ<sup>0</sup>

**Table 2.** Spatial and time scales of atmosphere.

wavelength.

**Figure 2.** Lidar principle.

46 Ionizing Radiation Effects and Applications

where P0

**Figure 3.** Optics of compact Raman lidar. (a) Compact Raman lidar—optical setup. (b) Outlook of compact Raman lidar.

In this study, we have developed the "in-line" type compact Raman lidar [16–21]. The in-line type optics has no blind area in principle. The in-line lidar has common optics for a transmitter and a receiver. An optical divider, here dichroic mirror, to separate the receiving echo and transmitting beam is installed. We designed and developed the compact Raman lidar to detect leaked hydrogen gas as minimum setup. It means that the system should be compact, light-weight and low electric power consumption. Our goal is the detection of the hydrogen gas concentration of 1% within the observation range of 0–50 m. The lidar optics is illustrated in **Figure 3**. The DPSS laser is utilized for lidar transmitting beam. Its power is 120 μJ and the wavelength is 349 nm. The receiver's aperture is 50 mmϕ. The transmitting beam is expanded to 10 mmϕ to be safe for human eye even in front of the system. The wavelength of the incident beam is decided to obtain the strong Raman signal. Shorter wavelength causes the larger Raman signal than the longer wavelength. The receiver's FOV was 2 mrad. The Raman shifted echoes passes through the first dichroic mirror (1), which is a divider, and echoes never returns to the light source. The Raman echoes are divided by the second dichroic mirror (2) depending on the wavelength for each Raman detection. The detectors are PMTs; one is for hydrogen gas (408 nm) and the other is for atmospheric nitrogen gas (380 nm). The interference filters of the wavelength widths of 3 nm are fixed on their PMTs. The nitrogen signal is used to estimate the quantitative concentration of hydrogen gas. The system size is 58 × 36 × 23 cm. It can put on the small desk.

A quantitative measurement of the Raman scattering echo intensity from hydrogen gas was conducted. The hydrogen gas was filled in a gas cell of the size of 10 cm cube, of which window is quartz. The cell was positioned at a distance of 7–8 m from the lidar system and put with a small tilt against the optical axis to reduce the reflection and fluorescent lights to return the lidar. Although the reflection and fluorescence lights appear on the hydrogen and nitrogen echoes, they can be subtracted out. Furthermore, the Raman echo from hydrogen gas fluctuates in actual gas leaks, and it can be separated from the reflection and fluorescence lights from a hard target, which are constant in time. The observation distance of 8 m is defined as the safe distance for the explosion protection of hydrogen gas. The lidar echo was measured by an

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 49

**Figure 5.** Estimation of hydrogen gas concentration. (a) High concentration of about 10–100% and (b) low concentration

of 0–15%.

oscilloscope with a photomultiplier tube (PMT) operating in analogue mode.

**Figure 4** shows the detected Raman echo of atmospheric nitrogen. Its signal was obtained from 1.5 to 50 m. The nearest echo in 0–1.5 m in **Figure 4(a)** was spoiled because of the misalignment and the aberration of the lenses. **Figure 4(b)** shows the range-corrected nitrogen Raman echo, which is corrected by the square of the distance and the overlap function between the transmitter and the receiver. The corrected echo intensity becomes flat and the fluctuation is minimum at any point within the observation range. The constant intensity indicates stable concentration of atmospheric nitrogen. This nitrogen echo is utilized to estimate the concentration of hydrogen gas in the observation range by taking the ratio between them.

**Figure 4.** Lidar echo of atmospheric nitrogen gas. (a) A-scope signal. (b) Range-corrected data.

A quantitative measurement of the Raman scattering echo intensity from hydrogen gas was conducted. The hydrogen gas was filled in a gas cell of the size of 10 cm cube, of which window is quartz. The cell was positioned at a distance of 7–8 m from the lidar system and put with a small tilt against the optical axis to reduce the reflection and fluorescent lights to return the lidar. Although the reflection and fluorescence lights appear on the hydrogen and nitrogen echoes, they can be subtracted out. Furthermore, the Raman echo from hydrogen gas fluctuates in actual gas leaks, and it can be separated from the reflection and fluorescence lights from a hard target, which are constant in time. The observation distance of 8 m is defined as the safe distance for the explosion protection of hydrogen gas. The lidar echo was measured by an oscilloscope with a photomultiplier tube (PMT) operating in analogue mode.

In this study, we have developed the "in-line" type compact Raman lidar [16–21]. The in-line type optics has no blind area in principle. The in-line lidar has common optics for a transmitter and a receiver. An optical divider, here dichroic mirror, to separate the receiving echo and transmitting beam is installed. We designed and developed the compact Raman lidar to detect leaked hydrogen gas as minimum setup. It means that the system should be compact, light-weight and low electric power consumption. Our goal is the detection of the hydrogen gas concentration of 1% within the observation range of 0–50 m. The lidar optics is illustrated in **Figure 3**. The DPSS laser is utilized for lidar transmitting beam. Its power is 120 μJ and the wavelength is 349 nm. The receiver's aperture is 50 mmϕ. The transmitting beam is expanded to 10 mmϕ to be safe for human eye even in front of the system. The wavelength of the incident beam is decided to obtain the strong Raman signal. Shorter wavelength causes the larger Raman signal than the longer wavelength. The receiver's FOV was 2 mrad. The Raman shifted echoes passes through the first dichroic mirror (1), which is a divider, and echoes never returns to the light source. The Raman echoes are divided by the second dichroic mirror (2) depending on the wavelength for each Raman detection. The detectors are PMTs; one is for hydrogen gas (408 nm) and the other is for atmospheric nitrogen gas (380 nm). The interference filters of the wavelength widths of 3 nm are fixed on their PMTs. The nitrogen signal is used to estimate the quantitative concentration of hydrogen gas. The system size is 58 × 36 ×

**Figure 4** shows the detected Raman echo of atmospheric nitrogen. Its signal was obtained from 1.5 to 50 m. The nearest echo in 0–1.5 m in **Figure 4(a)** was spoiled because of the misalignment and the aberration of the lenses. **Figure 4(b)** shows the range-corrected nitrogen Raman echo, which is corrected by the square of the distance and the overlap function between the transmitter and the receiver. The corrected echo intensity becomes flat and the fluctuation is minimum at any point within the observation range. The constant intensity indicates stable concentration of atmospheric nitrogen. This nitrogen echo is utilized to estimate the concen-

tration of hydrogen gas in the observation range by taking the ratio between them.

**Figure 4.** Lidar echo of atmospheric nitrogen gas. (a) A-scope signal. (b) Range-corrected data.

23 cm. It can put on the small desk.

48 Ionizing Radiation Effects and Applications

**Figure 5.** Estimation of hydrogen gas concentration. (a) High concentration of about 10–100% and (b) low concentration of 0–15%.

The echo intensity was obtained by the developed Raman lidar system. The concentration of hydrogen gas was controlled by adjusting the gas pressure in the cell. The results are shown in **Figure 5**, for (a) high concentration of about 10–100% and (b) enlarge graph of low concentration of 0–15%. These results were calibrated by subtracting the reference signal of the empty gas cell. The summation was about 30,000 shots. It is equal to a measurement time of about 30 s. The echo intensity ratio is linearly proportional to the hydrogen gas concentration. The result indicates the successful estimation down to the low concentration of 1%. The estimation error becomes less than ±1%. The fluctuation in the echo intensity was mainly due to the background light, unstable power of the laser beam and thermal noise of the detector. The actual leaked gas fluctuates more drastically.

laser power was gradually decreased up to the Raman detection limit, which is estimated 1 W (=10 nJ/10 ns) by the numerical analysis. The reflection light by the glass plate was utilized to decrease the laser intensity efficiently and stably. The experimental result is shown in **Figure 7**. It shows that the Raman scattering echo was successfully detected by the estimated optical

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 51

Considering the above results, we developed the LED-based mini-Raman lidar. The lidar optics is biaxial type and the gas detection method is as same as the laser based compact Raman lidar as shown in **Figure 3**. The LED lamp module of the optical power of 1 W was used as the lidar light source. The wavelength of LED light is 365 nm, and the wavelengths of Raman scattering echoes become 400 nm for atmospheric nitrogen, 420 nm for water vapor and 430 nm for hydrogen gas with the same Raman shift shown in **Table 1**. The LED mini-Raman lidar optics is shown with photo in **Figure 8**. The optical setup is the same as the DPSSlaser based compact Raman lidar. The LED-based Raman lidar added the water vapor port by changing the optical interference filter with a filter wheel. All of the wavelength widths of the

Although LED beam is hard to collimate, it never focuses after the transmission. It gives advantage in the closed space in the viewpoint of human safety concern. In this study, the transmitting beam was enlarged to 50 mmϕ. Its divergence was about 10 mrad. The LED pulsed power was <1 W (=10 nJ/10 ns), while the pulse repetition frequency was 500 kHz. The receiving telescope was Cassegrain type of the aperture of 127 mmϕ. The receiver's FOV was 3 mrad. The transmitting power is so weak, and the echo detection is photon counting with

The system is so compact and handy that one can use it in any observation direction. The system power consumption is about 2 W and can operate with a small PC battery in 8–10 h. The observation range is aimed up to 20–30 m for hydrogen Raman signal. This observation range design comes from the facility space of a nuclear reactor to detect the hydrogen gas leakage.

interference filters were 10 nm. It is the same width the used LED spectrum.

power of the transmitting beam.

photomultipliers.

The specifications are summarized in **Table 3**.

**Figure 7.** Raman scattering echo detection with lowered incident power.

## **5. LED-based mini-Raman lidar**

The developed DPSS-based compact Raman lidar is designed to be eye-safe, while it is hard to install it into a certain monitoring site. The laser beam is possible to focus on a point, and it is not acceptable especially in dangerous gas environment because of its ignition. It is also hard to use it at outdoor with no AC power supply. In such demands, we started to develop the LED-based mini-Raman lidar with low optical power.

At first, we had the experiment to obtain the minimum power to detect the Raman echo of hydrogen gas as shown in **Figure 6**. The laser beam is entered into the quartz-windows cell filled with hydrogen gas. The hydrogen gas concentration was 100%. The Raman scattering echo was detected at the vertical direction. It is because the Raman intensity becomes maximum at the perpendicular direction against the optical axis of the transmitting beam. The

**Figure 6.** Verification of Raman scattering echo measurement with the minimum light intensity.

laser power was gradually decreased up to the Raman detection limit, which is estimated 1 W (=10 nJ/10 ns) by the numerical analysis. The reflection light by the glass plate was utilized to decrease the laser intensity efficiently and stably. The experimental result is shown in **Figure 7**. It shows that the Raman scattering echo was successfully detected by the estimated optical power of the transmitting beam.

The echo intensity was obtained by the developed Raman lidar system. The concentration of hydrogen gas was controlled by adjusting the gas pressure in the cell. The results are shown in **Figure 5**, for (a) high concentration of about 10–100% and (b) enlarge graph of low concentration of 0–15%. These results were calibrated by subtracting the reference signal of the empty gas cell. The summation was about 30,000 shots. It is equal to a measurement time of about 30 s. The echo intensity ratio is linearly proportional to the hydrogen gas concentration. The result indicates the successful estimation down to the low concentration of 1%. The estimation error becomes less than ±1%. The fluctuation in the echo intensity was mainly due to the background light, unstable power of the laser beam and thermal noise of the detector.

The developed DPSS-based compact Raman lidar is designed to be eye-safe, while it is hard to install it into a certain monitoring site. The laser beam is possible to focus on a point, and it is not acceptable especially in dangerous gas environment because of its ignition. It is also hard to use it at outdoor with no AC power supply. In such demands, we started to develop

At first, we had the experiment to obtain the minimum power to detect the Raman echo of hydrogen gas as shown in **Figure 6**. The laser beam is entered into the quartz-windows cell filled with hydrogen gas. The hydrogen gas concentration was 100%. The Raman scattering echo was detected at the vertical direction. It is because the Raman intensity becomes maximum at the perpendicular direction against the optical axis of the transmitting beam. The

The actual leaked gas fluctuates more drastically.

the LED-based mini-Raman lidar with low optical power.

**Figure 6.** Verification of Raman scattering echo measurement with the minimum light intensity.

**5. LED-based mini-Raman lidar**

50 Ionizing Radiation Effects and Applications

Considering the above results, we developed the LED-based mini-Raman lidar. The lidar optics is biaxial type and the gas detection method is as same as the laser based compact Raman lidar as shown in **Figure 3**. The LED lamp module of the optical power of 1 W was used as the lidar light source. The wavelength of LED light is 365 nm, and the wavelengths of Raman scattering echoes become 400 nm for atmospheric nitrogen, 420 nm for water vapor and 430 nm for hydrogen gas with the same Raman shift shown in **Table 1**. The LED mini-Raman lidar optics is shown with photo in **Figure 8**. The optical setup is the same as the DPSSlaser based compact Raman lidar. The LED-based Raman lidar added the water vapor port by changing the optical interference filter with a filter wheel. All of the wavelength widths of the interference filters were 10 nm. It is the same width the used LED spectrum.

Although LED beam is hard to collimate, it never focuses after the transmission. It gives advantage in the closed space in the viewpoint of human safety concern. In this study, the transmitting beam was enlarged to 50 mmϕ. Its divergence was about 10 mrad. The LED pulsed power was <1 W (=10 nJ/10 ns), while the pulse repetition frequency was 500 kHz. The receiving telescope was Cassegrain type of the aperture of 127 mmϕ. The receiver's FOV was 3 mrad. The transmitting power is so weak, and the echo detection is photon counting with photomultipliers.

The system is so compact and handy that one can use it in any observation direction. The system power consumption is about 2 W and can operate with a small PC battery in 8–10 h. The observation range is aimed up to 20–30 m for hydrogen Raman signal. This observation range design comes from the facility space of a nuclear reactor to detect the hydrogen gas leakage. The specifications are summarized in **Table 3**.

**Figure 7.** Raman scattering echo detection with lowered incident power.

obtained up to 70 m (**Figure 9(a)**). After that the fluorescence echo of the tree was also detected at 80 m. The atmospheric nitrogen is stable and its echo waveform becomes smooth. On the other hand, the water vapor echo had fluctuation because of low counts (**Figure 9(b)**). It was drastically changed by depending on the humidity. In the figure, the humidity was 25% on Feb. 7 in fine day, while it was 90% on Feb. 9 in rain day. The observation range of the water vapor was 70 m, which is equal to that of the nitrogen echo. The fluorescence echoes of trees

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 53

The quantitative measurement of hydrogen gas was conducted with a large gas chamber as shown in **Figure 10**. The hydrogen gas chamber has an aperture of 200 mm and a length of 500 mm. Pyrex glass of 10 mm thickness was used for light path windows to restrict the fluorescent light. It was set 5 m ahead from the LED mini-Raman lidar. The transmitting beam was adjusted its optical path against the receiver's field of view to cross both of optical paths

The hydrogen gas concentration was adjusted by vacuuming the air inside the chamber of 0.5 Pa and inserting the 100% hydrogen. This procedure repeated twice, and the hydrogen gas concentration of 75% was prepared. We also confirmed the air and hydrogen gases were well mixed in the chamber. After the first measurement, hydrogen gas concentration set to half, that is, 37.5% by vacuuming the inside gas of 0.5 Pa and inserting the air. Repeating these procedures, hydrogen gas concentration was adjusted as 18.8%, 9.4%,

Experimental results are shown in **Figure 11**. The accumulation time was 3.5 min. The hydrogen Raman echo was appeared on the fluorescent light from the Pyrex glass. **Figure 11** shows enlargement of the peak change of the echo signals. Depending on the hydrogen gas concentration, the peak counts were changed. The echo counts of hydrogen gas Raman signal were subtracted from the reference echo (0% hydrogen gas). The results were summarized in **Figure 12**. In **Figure 12(a)**, hydrogen Raman echo counts at each detected distance were

were detected, too.

**Table 3.** Specifications of LED mini-Raman lidar.

at the chamber.

4.7%, and 2.4%.

**Figure 8.** LED mini-Raman lidar. (a) Optical structure. (b) Lidar setup.

The high-speed photon counter was developed, too. It can follow the pulse repetition frequency of >500 kHz. Its time resolution is 1 ns. It is equivalent to the spatial (distance) resolution of 0.15 m. It has 2 channels, and their simultaneous measurements are possible with a single input or output trigger signal.

**Figure 9** shows the observed Raman echo of the atmospheric nitrogen gas and the water vapor. The observation direction is nearly horizontal. The experiment was conducted in night time. Trees were captured at 80 m ahead. Accumulation was 3.5 min. Nitrogen echo was


**Table 3.** Specifications of LED mini-Raman lidar.

The high-speed photon counter was developed, too. It can follow the pulse repetition frequency of >500 kHz. Its time resolution is 1 ns. It is equivalent to the spatial (distance) resolution of 0.15 m. It has 2 channels, and their simultaneous measurements are possible with a

**Figure 9** shows the observed Raman echo of the atmospheric nitrogen gas and the water vapor. The observation direction is nearly horizontal. The experiment was conducted in night time. Trees were captured at 80 m ahead. Accumulation was 3.5 min. Nitrogen echo was

single input or output trigger signal.

52 Ionizing Radiation Effects and Applications

**Figure 8.** LED mini-Raman lidar. (a) Optical structure. (b) Lidar setup.

obtained up to 70 m (**Figure 9(a)**). After that the fluorescence echo of the tree was also detected at 80 m. The atmospheric nitrogen is stable and its echo waveform becomes smooth. On the other hand, the water vapor echo had fluctuation because of low counts (**Figure 9(b)**). It was drastically changed by depending on the humidity. In the figure, the humidity was 25% on Feb. 7 in fine day, while it was 90% on Feb. 9 in rain day. The observation range of the water vapor was 70 m, which is equal to that of the nitrogen echo. The fluorescence echoes of trees were detected, too.

The quantitative measurement of hydrogen gas was conducted with a large gas chamber as shown in **Figure 10**. The hydrogen gas chamber has an aperture of 200 mm and a length of 500 mm. Pyrex glass of 10 mm thickness was used for light path windows to restrict the fluorescent light. It was set 5 m ahead from the LED mini-Raman lidar. The transmitting beam was adjusted its optical path against the receiver's field of view to cross both of optical paths at the chamber.

The hydrogen gas concentration was adjusted by vacuuming the air inside the chamber of 0.5 Pa and inserting the 100% hydrogen. This procedure repeated twice, and the hydrogen gas concentration of 75% was prepared. We also confirmed the air and hydrogen gases were well mixed in the chamber. After the first measurement, hydrogen gas concentration set to half, that is, 37.5% by vacuuming the inside gas of 0.5 Pa and inserting the air. Repeating these procedures, hydrogen gas concentration was adjusted as 18.8%, 9.4%, 4.7%, and 2.4%.

Experimental results are shown in **Figure 11**. The accumulation time was 3.5 min. The hydrogen Raman echo was appeared on the fluorescent light from the Pyrex glass. **Figure 11** shows enlargement of the peak change of the echo signals. Depending on the hydrogen gas concentration, the peak counts were changed. The echo counts of hydrogen gas Raman signal were subtracted from the reference echo (0% hydrogen gas). The results were summarized in **Figure 12**. In **Figure 12(a)**, hydrogen Raman echo counts at each detected distance were

**Figure 10.** Hydrogen gas quantitative measurement. (a) Quantitative measurement of hydrogen gas. (b) System setup

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 55

**Figure 11.** Peak signal changes depending on hydrogen gas concentration.

and arrangement.

**Figure 9.** Atmospheric measurement by LED mini-Raman lidar. (a) Nitrogen Raman echo (b) Water Vapor echo.

graphed. The Raman echo counts at 5.25 and 5.4 m had the higher slant, while the firster (initial distance arising echo) and the later parts (main part of fluorescent light) of the peak signals showed lower slant. It means that the Raman scattering appears firster than the fluorescent light. The lidar counts at each distance in **Figure 12(a)** was summed as shown in **Figure 12(b)**. The errors were large, which came from the inexact concentration control of the hydrogen gas and the fluctuation of the fluorescent light, while the linear change was obtained down to the lowest concentration of a few percent. The Raman echo counts were remained at the 0% hydrogen gas concentration. We regarded hydrogen concentration after the procedure of vacuuming the content gas of 0.5 Pa and inserting the air two times as equal to 0%. It caused the remained echo counts at 0% concentration. And the fluctuation of the fluorescent light peak echo will cause it, too.

**Figure 10.** Hydrogen gas quantitative measurement. (a) Quantitative measurement of hydrogen gas. (b) System setup and arrangement.

**Figure 11.** Peak signal changes depending on hydrogen gas concentration.

graphed. The Raman echo counts at 5.25 and 5.4 m had the higher slant, while the firster (initial distance arising echo) and the later parts (main part of fluorescent light) of the peak signals showed lower slant. It means that the Raman scattering appears firster than the fluorescent light. The lidar counts at each distance in **Figure 12(a)** was summed as shown in **Figure 12(b)**. The errors were large, which came from the inexact concentration control of the hydrogen gas and the fluctuation of the fluorescent light, while the linear change was obtained down to the lowest concentration of a few percent. The Raman echo counts were remained at the 0% hydrogen gas concentration. We regarded hydrogen concentration after the procedure of vacuuming the content gas of 0.5 Pa and inserting the air two times as equal to 0%. It caused the remained echo counts at 0% concentration. And the fluctuation of the

**Figure 9.** Atmospheric measurement by LED mini-Raman lidar. (a) Nitrogen Raman echo (b) Water Vapor echo.

fluorescent light peak echo will cause it, too.

54 Ionizing Radiation Effects and Applications

**Figure 12.** Change of hydrogen Raman echo counts depending on hydrogen gas concentration. (a) Echo changes at each detected distance. (b) Count sum at each concentration.

The hydrogen leakage experiment was conducted at outdoor in night time as shown in **Figure 13**. The hydrogen leakage nozzle shown in **Figure 13(b)** was fixed at 2.5 m ahead from the mini-lidar. The optical alignment between the transmitter and the receiver was adjusted to overlap fully. The leaked hydrogen gas was 50 l/min. The result is summarized in **Figure 14**. The accumulation time was 3.5 min. It is the result of 3 average times. The obvious difference between the hydrogen gas leakage and leakage stop conditions was obtained. The detected counts on the leakage stop condition were caused by the fluorescent light from the materials near the hydrogen nozzle. As compared with the lab experiment in **Figure 12**, the hydrogen Raman counts was low. The leakage gas volume, especially gas flow width against the optical axis was shorter than the hydrogen gas chamber or the optical pulse length. As a result, the

**Figure 14.** Measurement result of hydrogen leakage gas outside.

**Figure 13.** Hydrogen leakage measurement experiment outside. (a) LED mini-Raman lidar setup. (b) Hydrogen nozzle.

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 57

**Figure 13.** Hydrogen leakage measurement experiment outside. (a) LED mini-Raman lidar setup. (b) Hydrogen nozzle.

**Figure 14.** Measurement result of hydrogen leakage gas outside.

**Figure 12.** Change of hydrogen Raman echo counts depending on hydrogen gas concentration. (a) Echo changes at each

detected distance. (b) Count sum at each concentration.

56 Ionizing Radiation Effects and Applications

The hydrogen leakage experiment was conducted at outdoor in night time as shown in **Figure 13**. The hydrogen leakage nozzle shown in **Figure 13(b)** was fixed at 2.5 m ahead from the mini-lidar. The optical alignment between the transmitter and the receiver was adjusted to overlap fully. The leaked hydrogen gas was 50 l/min. The result is summarized in **Figure 14**. The accumulation time was 3.5 min. It is the result of 3 average times. The obvious difference between the hydrogen gas leakage and leakage stop conditions was obtained. The detected counts on the leakage stop condition were caused by the fluorescent light from the materials near the hydrogen nozzle. As compared with the lab experiment in **Figure 12**, the hydrogen Raman counts was low. The leakage gas volume, especially gas flow width against the optical axis was shorter than the hydrogen gas chamber or the optical pulse length. As a result, the counts rate outdoor was smaller than the lab-experiment. After that, the authors repeated the quantitative measurement with more large chamber at the outdoor field. The same result in the lab-experiment was obtained.

The Raman signal is weak. It is 1/1000 of the Mie scattering signals. Our current experiments were limited in nighttime. When the DPSS laser-based lidar is fixed in a sunshade area, it will act with enough accuracy. At indoor, the artificial light was no effect for Raman signal detecting by excluding for its direct insertion to the detector even if in the case of the LED-based

Hydrogen Gas Detection by Mini-Raman Lidar http://dx.doi.org/10.5772/intechopen.74630 59

The hydrogen has a potential to become major energy resource. It will be popular in daily life near future. On contrary, its dangerousness is important to recognize once more. Remote sensing device for leaked hydrogen gas is essential. Compact and mini-Raman lidars will be

This study was granted by Chubu Electric Power Co., Inc. from 2013 to 2016. Shikoku research institution Inc. was cooperated on the outdoor experiment, too. The author really appreciates

Graduate School of Engineering, Chiba University, Yayoi-cho, Inage-ku, Chiba-shi, Japan

[1] Gu H, Wang Z, Hu Y. Hydrogen gas sensors based on semiconductor oxide nanostruc-

[2] Zeng XQ, Latimer ML, Xiao ZL, Panuganti S, Welp U, Kwok WK, Xu T. Hydrogen gas sensing with networks of ultrasmall palladium nanowires formed on filtration mem-

[3] Measures RM. Laser Remote Sensing: Fundamentals and Applications. New York: John

[5] Weitkamp C, editor. Lidar: Range-Resolved Optical Remote Sensing of the Atmosphere.

[6] Ninomiya H, Yaeshima S, Ichikawa K, Fukuchi T. Raman lidar system for hydrogen gas

[4] Fujii T, Fukuchi T, editors. Laser Remote Sensing. Taylor & Francis; 2005

lidar.

one of the solutions.

to these companies.

**Author details**

Address all correspondence to: shiina@faculty.chiba-u.jp

tures. Sensors. 2012;**12**:5517-5550

Wiley & Sons; 1984

Springer; 2005

branes. Nano Letters. 2011;**11**:262-268

detection. Optical Engineering. 2007;**46**:094301

Tatsuo Shiina

**References**

**Acknowledgements**

## **6. Discussions**

In the lab-experiment, that is, the hydrogen cell/chamber used experiments at indoor, the linear change of the lidar counts was obtained depending on the hydrogen concentration up to 1%. The accuracy is enough to evaluate the concentration quantitatively. The DPSS laser-based lidar can perform it within a few seconds by adequate setup. The LED-based lidar needs more time to evaluate the concentration. The evaluation error is remained on the current setup. At outdoor experiment, the obvious hydrogen Raman echo by the LED Raman lidar was detected at the gas leakage situation, while it is not easy to verify the concrete concentration. It is not only the system task, but also the gas flow fluctuation. As the leakage area was narrower than the pulsed beam length, the counts rate became lower. The accumulation time, beam size, and transmitting power intensity should be balanced to satisfy the demands.

The hydrogen gas detection is not only to estimate the precise concentration, but also on the easy-to-use and easy-to-install at on-site. The LED-based mini-Raman lidar is designed under this consideration. Its gas detection optics is as same as the laser-based Raman lidar, while the LED module is installed into the system. The observation range becomes short, while the system becomes so small, light-weight, low power consumption, and safe. The power consumption is enough small to operate with a small buttery. The LED-based mini-Raman lidar needs the accumulation time, and it is adequate to install it to the regular observation fixed on a certain position and monitor the stored gas on a ceiling. When Ultra Violet/Near Ultra Violet Laser Diode (UV/NUV-LD) is possible to utilize, the beam collimation will be improved and it can increase signal-to-noise ratio with the same optical pulse power. It will shorten the accumulation time, and become one of the solutions to detect the leakage hydrogen gas in the emergency case under no electrical power.

## **7. Conclusions**

We developed the compact and the mini-Raman lidars for quantitative measurement of hydrogen gas. The current minimal detection limit of hydrogen gas concentration is 1% at the observation range of 0–50 m with DPSS-based compact lidar and 0–20 m with LED-based mini-lidar. The accumulation time is 30 s for the DPSS laser-based compact Raman lidar and 3.5 min for the LED-based mini-Raman lidar.

Now, the DPSS laser-based compact Raman lidar was improved to detect the ionization effect by nuclear materials. On contrary, the LED-based mini-Raman lidar expanded the target to the environmental measurement. The Raman scattering signal is a proof of a target gas existence. Each gas has its own Raman shift, and the optical sensing method of Raman lidar becomes one of solutions in the actual atmosphere, which contains complex materials.

The Raman signal is weak. It is 1/1000 of the Mie scattering signals. Our current experiments were limited in nighttime. When the DPSS laser-based lidar is fixed in a sunshade area, it will act with enough accuracy. At indoor, the artificial light was no effect for Raman signal detecting by excluding for its direct insertion to the detector even if in the case of the LED-based lidar.

The hydrogen has a potential to become major energy resource. It will be popular in daily life near future. On contrary, its dangerousness is important to recognize once more. Remote sensing device for leaked hydrogen gas is essential. Compact and mini-Raman lidars will be one of the solutions.

## **Acknowledgements**

counts rate outdoor was smaller than the lab-experiment. After that, the authors repeated the quantitative measurement with more large chamber at the outdoor field. The same result in

In the lab-experiment, that is, the hydrogen cell/chamber used experiments at indoor, the linear change of the lidar counts was obtained depending on the hydrogen concentration up to 1%. The accuracy is enough to evaluate the concentration quantitatively. The DPSS laser-based lidar can perform it within a few seconds by adequate setup. The LED-based lidar needs more time to evaluate the concentration. The evaluation error is remained on the current setup. At outdoor experiment, the obvious hydrogen Raman echo by the LED Raman lidar was detected at the gas leakage situation, while it is not easy to verify the concrete concentration. It is not only the system task, but also the gas flow fluctuation. As the leakage area was narrower than the pulsed beam length, the counts rate became lower. The accumulation time, beam size, and transmitting power intensity should be balanced to satisfy the demands. The hydrogen gas detection is not only to estimate the precise concentration, but also on the easy-to-use and easy-to-install at on-site. The LED-based mini-Raman lidar is designed under this consideration. Its gas detection optics is as same as the laser-based Raman lidar, while the LED module is installed into the system. The observation range becomes short, while the system becomes so small, light-weight, low power consumption, and safe. The power consumption is enough small to operate with a small buttery. The LED-based mini-Raman lidar needs the accumulation time, and it is adequate to install it to the regular observation fixed on a certain position and monitor the stored gas on a ceiling. When Ultra Violet/Near Ultra Violet Laser Diode (UV/NUV-LD) is possible to utilize, the beam collimation will be improved and it can increase signal-to-noise ratio with the same optical pulse power. It will shorten the accumulation time, and become one of the solutions to detect the leakage hydrogen gas in the

We developed the compact and the mini-Raman lidars for quantitative measurement of hydrogen gas. The current minimal detection limit of hydrogen gas concentration is 1% at the observation range of 0–50 m with DPSS-based compact lidar and 0–20 m with LED-based mini-lidar. The accumulation time is 30 s for the DPSS laser-based compact Raman lidar and

Now, the DPSS laser-based compact Raman lidar was improved to detect the ionization effect by nuclear materials. On contrary, the LED-based mini-Raman lidar expanded the target to the environmental measurement. The Raman scattering signal is a proof of a target gas existence. Each gas has its own Raman shift, and the optical sensing method of Raman lidar

becomes one of solutions in the actual atmosphere, which contains complex materials.

the lab-experiment was obtained.

58 Ionizing Radiation Effects and Applications

emergency case under no electrical power.

3.5 min for the LED-based mini-Raman lidar.

**7. Conclusions**

**6. Discussions**

This study was granted by Chubu Electric Power Co., Inc. from 2013 to 2016. Shikoku research institution Inc. was cooperated on the outdoor experiment, too. The author really appreciates to these companies.

## **Author details**

Tatsuo Shiina

Address all correspondence to: shiina@faculty.chiba-u.jp

Graduate School of Engineering, Chiba University, Yayoi-cho, Inage-ku, Chiba-shi, Japan

## **References**


[7] Ninomiya H, Asahi I, Sugimoto S, Shimamoto Y. Development of remote sensing technology for hydrogen gas concentration measurement using Raman scattering effect. IEEJ Transactions on Electronics, Information and Systems. 2009;**129**:1181-1185

**Chapter 4**

Provisional chapter

. The Bohr's

**Investigating the Nature of Insulator-Metal Transition**

DOI: 10.5772/intechopen.72241

n-type germanium samples irradiated with fast reactor neutrons with a fluency range

into p-type Ge. The dc conductivity is measured in wide temperature range from 1.5 up to

radius of localization (aH) is obtained and found to be equal to 43 Å. Mott variable range hopping and Shklovskii-Efros percolation models are applicable in the present data.

Keywords: germanium, irradiation disordered, insulator-metal transition, Mott variable

Sun light consists of electromagnetic (EM) waves, which provide light and heat. Sunlight electromagnetic waves consist of infrared (IR), visible, and ultraviolet (UV) frequencies; as the color goes more into blue, the wavelength decreases and the frequency increases and vice versa, as the color goes into red color, the wave length increases and frequency decreases. Generally, the EM radiations are divided into two categories depending on wavelength ionizing and non-ionizing. This division depends on the radiation energy or frequency; high frequency radiation (>3 1015 Hz) is ionizing radiation and low frequency radiation (<3 1015 Hz) is nonionizing radiation [1]. When a substance absorbs the EM radiation with a frequency lower than 3 1015 Hz, excitation occurs, and the radiation excites the motion of molecules, or excites an electron from occupied orbital into an empty higher energy orbital. But if the absorbed EM radiation has frequency greater than

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

> © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

300 K. Insulator metal transition occurs at irradiation fluency 5 <sup>10</sup><sup>18</sup> cm<sup>2</sup>

range hopping, percolation theory of conduction, Anderson transition

. As a result of irradiation, n-Ge samples are converted

Investigating the Nature of Insulator-Metal Transition

**in Neutron-Transmutation-Doped Ge:Ga**

in Neutron-Transmutation-Doped Ge:Ga

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Samy Abd-elhakim Elsayed

Samy Abd-elhakim Elsayed

Abstract

1. Introduction

http://dx.doi.org/10.5772/intechopen.72241

from 2 <sup>10</sup><sup>16</sup> up to 1 1020 cm<sup>2</sup>

1.1. Ionizing and non-ionizing radiations


#### **Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga** Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

DOI: 10.5772/intechopen.72241

Samy Abd-elhakim Elsayed Samy Abd-elhakim Elsayed

[7] Ninomiya H, Asahi I, Sugimoto S, Shimamoto Y. Development of remote sensing technology for hydrogen gas concentration measurement using Raman scattering effect.

[8] Thomas CE. Fuel cell and battery electric vehicles compared. Hydrogen Energy. 2009;

[9] Asahi, Sugimoto S, Ninomiya H, Fukuchi T, Shiina T. Remote sensing of hydrogen gas concentration distribution by Raman lidar. Proceedings of SPIE. 2012;**8526**:85260X

IEEJ Transactions on Electronics, Information and Systems. 2009;**129**:1181-1185

[10] Shiina T. Optical design for near range lidar. Proceedings of SPIE. 2010;**7860**:78600B

[11] Suppes G. Plug-in hybrid with fuel cell battery charger. Hydrogen Energy. 2005;**30**:113-121 [12] Basquin S, Smith K, editors. Hydrogen Gas Safety Self-Study. Los Alamos National

[13] Backx C, Wight GR, Van der Wiel MJ. Oscillator strengths (10-70eV) for absorption,

[14] Leonard DA. Observation of Raman scattering from the atmosphere using a pulsed

[15] Melfi SH. Remote measurement of the atmosphere using Raman scattering. Applied

[16] Shiina T, Minami E, Ito M, Okamura Y. Optical circulator for in-line type compact lidar.

[17] Shiina T, Yoshida K, Ito M, Okamura Y. In-line type micro pulse lidar with annular

[18] Shiina T, Yoshida K, Ito M, Okamura Y. In-line type micro pulse lidar with annular

[19] Grishin M, editor. Advances in Solid-State Lasers: Development and Applications,

[20] Shiina T, Oguchi K, Fukuchi T. Polarization-independent optical circulator for high

[21] Fukuchi T, Shiina T, editors. Industrial Applications of Laser Remote Sensing. Bentham

accuracy Faraday depolarization lidar. Applied Optics. 2012;**51**:898-904

, obtained by an electron-ion coincidence

, HD and D2

method. Journal of Physics B: Atomic and Molecular Physics. 1976;**9**:315-333

**34**:6005-6020

60 Ionizing Radiation Effects and Applications

Laboratory. 2000

ionization and dissociation in H2

Applied Optics. 2002;**41**:3900-3905

Optics. 1972;**11**:1605-1610

Chapter 8. INTECH; 2010

Science Publishers Ltd; 2012

nitrogen ultraviolet laser. Nature. 1967;**216**:142-143

beam—Experiment. Applied Optics. 2005;**44**:7407-7413

beam—Theoretical approach. Applied Optics. 2005;**44**:7467-7473

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72241

#### Abstract

n-type germanium samples irradiated with fast reactor neutrons with a fluency range from 2 <sup>10</sup><sup>16</sup> up to 1 1020 cm<sup>2</sup> . As a result of irradiation, n-Ge samples are converted into p-type Ge. The dc conductivity is measured in wide temperature range from 1.5 up to 300 K. Insulator metal transition occurs at irradiation fluency 5 <sup>10</sup><sup>18</sup> cm<sup>2</sup> . The Bohr's radius of localization (aH) is obtained and found to be equal to 43 Å. Mott variable range hopping and Shklovskii-Efros percolation models are applicable in the present data.

Keywords: germanium, irradiation disordered, insulator-metal transition, Mott variable range hopping, percolation theory of conduction, Anderson transition

## 1. Introduction

#### 1.1. Ionizing and non-ionizing radiations

Sun light consists of electromagnetic (EM) waves, which provide light and heat. Sunlight electromagnetic waves consist of infrared (IR), visible, and ultraviolet (UV) frequencies; as the color goes more into blue, the wavelength decreases and the frequency increases and vice versa, as the color goes into red color, the wave length increases and frequency decreases. Generally, the EM radiations are divided into two categories depending on wavelength ionizing and non-ionizing. This division depends on the radiation energy or frequency; high frequency radiation (>3 1015 Hz) is ionizing radiation and low frequency radiation (<3 1015 Hz) is nonionizing radiation [1]. When a substance absorbs the EM radiation with a frequency lower than 3 1015 Hz, excitation occurs, and the radiation excites the motion of molecules, or excites an electron from occupied orbital into an empty higher energy orbital. But if the absorbed EM radiation has frequency greater than

<sup>3</sup> � 1015 Hz, ionization occurs, that is, removing an electron from an atom or molecule. The atom consists of nucleus and extranuclear structure. The extranuclear structure consists of electrons revolving around the nucleus in certain energy levels; each level contains a restricted number of electrons when an electron jumps from high energy level down to lower energy level; an EM radiation with energy equal to the difference between the two energy levels emits from the atom. When an electron jumps from high energy level to the low energy level, a high frequency ffi3 � 1017 Hz emits from the atom, this is X-ray radiation. The X-ray radiation is an ionizing radiation. The nucleus consists of protons which have positive charge equal to the electron charge and mass 1.67 � <sup>10</sup>�<sup>27</sup> Kg. The number of protons in the nucleus equals the number of electrons outside the nucleus and the number of protons or electrons of an atom is denoted by Z (the atomic number) and neutrons which have no electric charge, but have magnetic moment. The number of neutrons is denoted by N. The total number of protons plus neutrons in a nucleus is denoted by A = Z + N (the mass number) [2]. When the nucleus is stable, no irradiation emits from it, but some heavy nuclei excited "not stable" and need to emit some energy to reduce their energies and become more stable [3]. The nucleus emits very high EM radiations, which are gamma rays. Gamma rays have frequency 3 � 1020 Hz, and are ionizing radiations. The unstable nuclei may also emit <sup>β</sup> particles, protons or neutrons, and/or α-particles, which is the nucleus of He++ atom; sometimes, the nucleus emits high energy electromagnetic radiation gamma waves (γ). The stable nucleus is characterized by the mass number A, and the atomic number of protons' number (Z) which equals the number of neutrons (N). In large nuclei N ffi 1.7 Z, repulsion between protons causes instability in the nucleus. This instability decreases if the number of neutrons excesses the number of protons. Instable nucleus, such as U238, emits radiation. This is called natural radioactivity. Nuclear radioactivity involves three kinds of radiations: α, β, and γ radiations. Each of these radiations has distinct properties. Examples of artificial radioactivity are: when α particle collide with aluminum a proton is rejected leaving a stable silicon isotope Al<sup>27</sup> <sup>13</sup> <sup>þ</sup> He<sup>4</sup> <sup>2</sup> ! Si<sup>30</sup> <sup>14</sup> <sup>þ</sup> <sup>H</sup><sup>1</sup> <sup>1</sup> or a neutron rejected leaving an isotope of phosphorus Al<sup>27</sup> <sup>13</sup> <sup>þ</sup> He<sup>4</sup> <sup>2</sup> ! <sup>P</sup><sup>30</sup> <sup>15</sup> <sup>þ</sup> <sup>n</sup><sup>1</sup> <sup>0</sup> and this phosphorus element is instable and disintegrates into silicon by emission of positron P<sup>30</sup> <sup>15</sup> ! <sup>S</sup><sup>30</sup> <sup>14</sup> þ eþ. This type of nuclear reaction has technological application [4], opens the way of peaceful using of nuclear power, in doping semiconductor by nuclear irradiation. Semiconductor industry is playing a very important role for mankind's everyday life and economic growth. The most famous radioactive semiconductor materials' doping is the neutron transmutation doping (NTD). This new technology is used in doping semiconductor materials such as germanium and silicon; the advantages of this new method are (i) homogenous distribution of doping atoms in the host material, (ii) controlling the concentration of doping atoms by controlling the irradiation dose, and (iii) controlling the compensation K in the host material. This new technology opens the way into tailoring materials with definite conductivity at definite temperature for a certain technology application. For example:

$${}^{74}Ge(n, \gamma)^{75}Ge\frac{\beta}{82 \text{min}}\stackrel{\beta}{\uparrow}As + \nu$$

$${}^{76}Ge(n, \gamma)^{77}Ge\frac{\beta}{11.3 hr}\stackrel{\beta}{\uparrow}Ts + \nu$$

$${}^{77}As \frac{\beta}{38.3 hr}\stackrel{\gamma}{\uparrow}Se + \nu$$

$${}^{70}Ge(n, \gamma)^{71}Ge\frac{\beta}{11.4 day}\stackrel{\varepsilon}{\uparrow}Ta + \nu\tag{1}$$

But (NTD) has disadvantages like: (i) irradiation cost, (ii) reduction in minority carrier life time,

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

liquid helium temperature to at most 10<sup>22</sup> (Ω.cm)<sup>1</sup> for the best insulators or nonmetals at the same temperature [6]. These vast differences in electrical conductivity separates the metallic and non-metallic states of matter, this variation amounts to a factor at least 1031, which is probably widest variation for any physical property. Therefore, from electrical conduction

i. Metallic conduction (good electrical conductors with electrical conductivity that reaches

ii. Insulators (Poor electrical conduction with electrical conductivity that reaches to 1022(Ω.cm)<sup>1</sup>

iii. Semiconductors, this type of materials distinguishes from metals and insulators by their negative coefficient of resistance (their resistance decreases with increasing temperature,

iv. Super-conductors, in this class of materials, the resistance vanishes at low temperatures, the temperature at which resistance vanishes depends on the material's type, composi-

This chapter focused on the transition between metallic and insulator phases of conduction. Mott is first one who recognized the problem of metal-insulator transition [7]. He noticed that, although the band theory successfully explained the electronic structure of solids, it explains why some materials have metallic conductivity, other semiconductors, or insulators. But, the band theory gives incorrect ground states of some transition metal oxides such as CoO, MnO, and NiO. In the case of CoO, for example, CoO has NaCl-like structure with a unit cell containing one Co atom and one O atom. The outer shell of the Co atom has an electron configuration of 3d4s, and the O atom 2S2P, that means, the number of electrons per unit cell is 9 + 6 = 15, an odd number. Band theory predicted that crystals with unit cell containing an odd number of electrons should have metallic conductivity behavior. But experimentally it is proved that CoO is actually an insulator with a large gap. These transition metal oxides are called Mott insulators [8] and were first inadequate of band theory. Mott said there is something wrong in band theory. What is that? Mott discussed the band theory in that although it had succeeded in explaining the cause of some materials having metallic conductivity, other semiconductors, and insulators, the band theory neglected the correlation between electrons. These transition metal oxides contain strongly correlated electrons, so the band theory fails in such systems with strongly correlated electrons. Mott started from the model suggested by

characteristics, it is well-known that solid materials are divided into four categories:

(Ω.cm)<sup>1</sup> for pure metal such as copper at

http://dx.doi.org/10.5772/intechopen.72241

63

n-germanium irradiated reactor neutrons and/or γ converted into p-type germanium [5].

2. Effect of ionizing radiation on the electrical properties of

and (iii) radioactive safeguards considerations.

The electrical conductivity of solids ranges from 109

(Ω.cm)<sup>1</sup> at liquid helium temperature)

semiconductors

to 109

at liquid helium temperature)

while in metals it increases)

tion, structure, and preparation method.

But (NTD) has disadvantages like: (i) irradiation cost, (ii) reduction in minority carrier life time, and (iii) radioactive safeguards considerations.

n-germanium irradiated reactor neutrons and/or γ converted into p-type germanium [5].

## 2. Effect of ionizing radiation on the electrical properties of semiconductors

<sup>3</sup> � 1015 Hz, ionization occurs, that is, removing an electron from an atom or molecule. The atom consists of nucleus and extranuclear structure. The extranuclear structure consists of electrons revolving around the nucleus in certain energy levels; each level contains a restricted number of electrons when an electron jumps from high energy level down to lower energy level; an EM radiation with energy equal to the difference between the two energy levels emits from the atom. When an electron jumps from high energy level to the low energy level, a high frequency ffi3 � 1017 Hz emits from the atom, this is X-ray radiation. The X-ray radiation is an ionizing radiation. The nucleus consists of protons which have positive charge equal to the electron charge and mass 1.67 � <sup>10</sup>�<sup>27</sup> Kg. The number of protons in the nucleus equals the number of electrons outside the nucleus and the number of protons or electrons of an atom is denoted by Z (the atomic number) and neutrons which have no electric charge, but have magnetic moment. The number of neutrons is denoted by N. The total number of protons plus neutrons in a nucleus is denoted by A = Z + N (the mass number) [2]. When the nucleus is stable, no irradiation emits from it, but some heavy nuclei excited "not stable" and need to emit some energy to reduce their energies and become more stable [3]. The nucleus emits very high EM radiations, which are gamma rays. Gamma rays have frequency 3 � 1020 Hz, and are ionizing radiations. The unstable nuclei may also emit <sup>β</sup> particles, protons or neutrons, and/or α-particles, which is the nucleus of He++ atom; sometimes, the nucleus emits high energy electromagnetic radiation gamma waves (γ). The stable nucleus is characterized by the mass number A, and the atomic number of protons' number (Z) which equals the number of neutrons (N). In large nuclei N ffi 1.7 Z, repulsion between protons causes instability in the nucleus. This instability decreases if the number of neutrons excesses the number of protons. Instable nucleus, such as U238, emits radiation. This is called natural radioactivity. Nuclear radioactivity involves three kinds of radiations: α, β, and γ radiations. Each of these radiations has distinct properties. Examples of artificial radioactivity are: when α particle collide with aluminum

<sup>13</sup> <sup>þ</sup> He<sup>4</sup>

<sup>15</sup> ! <sup>S</sup><sup>30</sup>

<sup>2</sup> ! Si<sup>30</sup>

<sup>14</sup> <sup>þ</sup> <sup>H</sup><sup>1</sup>

<sup>0</sup> and this phosphorus element is instable

<sup>71</sup>Ga <sup>þ</sup> <sup>ν</sup> (1)

<sup>14</sup> þ eþ. This type of nuclear reaction

<sup>1</sup> or a neutron rejected

a proton is rejected leaving a stable silicon isotope Al<sup>27</sup>

and disintegrates into silicon by emission of positron P<sup>30</sup>

<sup>13</sup> <sup>þ</sup> He<sup>4</sup>

<sup>2</sup> ! <sup>P</sup><sup>30</sup>

has technological application [4], opens the way of peaceful using of nuclear power, in doping semiconductor by nuclear irradiation. Semiconductor industry is playing a very important role for mankind's everyday life and economic growth. The most famous radioactive semiconductor materials' doping is the neutron transmutation doping (NTD). This new technology is used in doping semiconductor materials such as germanium and silicon; the advantages of this new method are (i) homogenous distribution of doping atoms in the host material, (ii) controlling the concentration of doping atoms by controlling the irradiation dose, and (iii) controlling the compensation K in the host material. This new technology opens the way into tailoring materials with definite conductivity at definite temperature for a certain technology application. For example:

<sup>74</sup> Ge nð Þ ; <sup>γ</sup> <sup>75</sup>Ge!

<sup>76</sup>Ge nð Þ ; <sup>γ</sup> <sup>77</sup>Ge!

<sup>77</sup>As! β 38:3hr

<sup>70</sup>Ge nð Þ ; <sup>γ</sup> <sup>71</sup>Ge!

β 82min

β 11:3hr

ε 11:4day

<sup>77</sup>Se <sup>þ</sup> <sup>ν</sup>

<sup>75</sup>As <sup>þ</sup> <sup>ν</sup>

<sup>77</sup>As <sup>þ</sup> <sup>ν</sup>

<sup>15</sup> <sup>þ</sup> <sup>n</sup><sup>1</sup>

leaving an isotope of phosphorus Al<sup>27</sup>

62 Ionizing Radiation Effects and Applications

The electrical conductivity of solids ranges from 109 (Ω.cm)<sup>1</sup> for pure metal such as copper at liquid helium temperature to at most 10<sup>22</sup> (Ω.cm)<sup>1</sup> for the best insulators or nonmetals at the same temperature [6]. These vast differences in electrical conductivity separates the metallic and non-metallic states of matter, this variation amounts to a factor at least 1031, which is probably widest variation for any physical property. Therefore, from electrical conduction characteristics, it is well-known that solid materials are divided into four categories:


This chapter focused on the transition between metallic and insulator phases of conduction. Mott is first one who recognized the problem of metal-insulator transition [7]. He noticed that, although the band theory successfully explained the electronic structure of solids, it explains why some materials have metallic conductivity, other semiconductors, or insulators. But, the band theory gives incorrect ground states of some transition metal oxides such as CoO, MnO, and NiO. In the case of CoO, for example, CoO has NaCl-like structure with a unit cell containing one Co atom and one O atom. The outer shell of the Co atom has an electron configuration of 3d4s, and the O atom 2S2P, that means, the number of electrons per unit cell is 9 + 6 = 15, an odd number. Band theory predicted that crystals with unit cell containing an odd number of electrons should have metallic conductivity behavior. But experimentally it is proved that CoO is actually an insulator with a large gap. These transition metal oxides are called Mott insulators [8] and were first inadequate of band theory. Mott said there is something wrong in band theory. What is that? Mott discussed the band theory in that although it had succeeded in explaining the cause of some materials having metallic conductivity, other semiconductors, and insulators, the band theory neglected the correlation between electrons. These transition metal oxides contain strongly correlated electrons, so the band theory fails in such systems with strongly correlated electrons. Mott started from the model suggested by Bloch which is called "collective electron model." In this model, the electrons in the outermost shell of the atoms concerned are not supposed to be bound to their individual atoms, but are assumed to be free to move through the lattice under the effect of the atomic cores and the average field of the other electrons. This field is periodic with the period of the lattice. Mott criticized this model that the electrons tend to keep away from one another because of the Coulomb's repulsive force. In metals, each electron carries with it a surrounding sphere, into which other electrons are unlikely to come. In insulators, one of the electrons in outermost shell of an electron will not be able to move to the next atom unless an electron from the next atom gets out to create a free place to it. Mott declares that the collective electron model cannot explain the optical absorption in insulators [8].

For many years Mott insulators were neglected by most authors of solid state physics text books. By the discovery of high TC superconductors in cuprates and the rediscovery of colossal magnetoresistance in manganite's the situation changed. These materials have proved to be doped-Mott insulators. So, the physics of Mott insulators and doped Mott insulators become important in contemporary research in condensed matter physics. The main problem for Mott insulators is to find the correlation energy of the electrons. It is Hubbard energy U for double occupancy of the same orbital on the same atomic site by two electrons. Mott starts to solve the problem of strongly correlated electrons. He supposed that for an array of electrons centers with cubic structure, there are two possibilities. The first is that the crystal is metal and the second is an antiferromagnetic insulator. But an antiferromagnetic lattice can split the conduction band into full and empty bands, these are called Hubbard bands, the insulating behavior does not depend on antiferromagnetic order, and continues above Neel temperature [9].

Hubbard system which consists of four atoms and four electrons, in wide temperature range from 10 K up to 10<sup>5</sup> K. And, he found that in the specific heat Cv dependence on temperature, as seen in Figure 1, there are three maxima, two of them related to Néel transition and sudden change in magnitude of magnetic moment and the third maxima proved as Mott transition [7].

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

http://dx.doi.org/10.5772/intechopen.72241

65

Mott started to explain the metal insulator transition on the basis of Hubbard band model [16]. Mott outlines the properties of a crystalline array of one-electron centers, each described by a wavefunction φ(r) behaving as exp.(�r/aH) for large r, at distance a from each other, sufficiently large for the tight binding approximation to be useful. If the number of electron per atom deviates from integral value, the model should always predict metallic behavior, but with one or any integral number of electrons per atom this is not so, and the system is insulating [7]. The most convenient description is in terms of Hubbard intra-atomic energy U

ϕðr12j

<sup>U</sup> <sup>¼</sup> <sup>5</sup>e<sup>2</sup> 8kaH

If P is the ionization potential of each atom and E is the electron affinity, by assuming that the

� � �

<sup>2</sup> <sup>ϕ</sup>ðr2<sup>j</sup> 2 d3 x1d<sup>3</sup> x2

(2)

� � �

3.2. Mott metal insulator transition

U ¼

Figure 1. Cv dependence on temperature at different values of Hubbard energy.

functions φ are not changed by addition of an extra electron

ðð e<sup>2</sup> kr<sup>12</sup>

�

which is defined by

For hydrogen-like atom

## 3. Mott metal-insulator transition (MIT)

#### 3.1. Transition metals and their alloys

Transition metals are the metals with incomplete d state in atomic structures like Co, Fe, Ni, Cd, etc. In magnetic transition metal compounds, the conduction electrons lie wholly in a dband, with some extent of hybridization with 4s electrons. This means that the d- band is separated from conduction band and contains an integer number of electrons per atom. And a band containing an integer number of electrons must exceed a certain width if it is to be metallic. Based on Gutzweller [10], approximation of variational calculation method of the ground state wave-function for model Hamiltonian with single-binding band and with only intra-atomic Coulomb interaction between the electrons, considering the case in which one electron per atom and, they found that the Gutzweller variational state is always metallic [11]. The experimental results of Craig et al. [12] on the electrical resistivity of Ni near its Curie temperature lead Fisher et al. [13] to criticize the theoretical treatment of resistive anomaly theory suggested by de Gennes and Frieddel [14] because, in their treatment they supposed long-range fluctuations of the magnetization near the critical point and this lead to incorrect result, but the short-range order fluctuations which make the dominant contribution to the temperature dependence of resistivity. Monecke et al. [15] investigated the specific heat of the Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga http://dx.doi.org/10.5772/intechopen.72241 65

Figure 1. Cv dependence on temperature at different values of Hubbard energy.

Hubbard system which consists of four atoms and four electrons, in wide temperature range from 10 K up to 10<sup>5</sup> K. And, he found that in the specific heat Cv dependence on temperature, as seen in Figure 1, there are three maxima, two of them related to Néel transition and sudden change in magnitude of magnetic moment and the third maxima proved as Mott transition [7].

#### 3.2. Mott metal insulator transition

Bloch which is called "collective electron model." In this model, the electrons in the outermost shell of the atoms concerned are not supposed to be bound to their individual atoms, but are assumed to be free to move through the lattice under the effect of the atomic cores and the average field of the other electrons. This field is periodic with the period of the lattice. Mott criticized this model that the electrons tend to keep away from one another because of the Coulomb's repulsive force. In metals, each electron carries with it a surrounding sphere, into which other electrons are unlikely to come. In insulators, one of the electrons in outermost shell of an electron will not be able to move to the next atom unless an electron from the next atom gets out to create a free place to it. Mott declares that the collective electron model cannot

For many years Mott insulators were neglected by most authors of solid state physics text books. By the discovery of high TC superconductors in cuprates and the rediscovery of colossal magnetoresistance in manganite's the situation changed. These materials have proved to be doped-Mott insulators. So, the physics of Mott insulators and doped Mott insulators become important in contemporary research in condensed matter physics. The main problem for Mott insulators is to find the correlation energy of the electrons. It is Hubbard energy U for double occupancy of the same orbital on the same atomic site by two electrons. Mott starts to solve the problem of strongly correlated electrons. He supposed that for an array of electrons centers with cubic structure, there are two possibilities. The first is that the crystal is metal and the second is an antiferromagnetic insulator. But an antiferromagnetic lattice can split the conduction band into full and empty bands, these are called Hubbard bands, the insulating behavior does not depend on antiferromagnetic order, and continues above Neel temperature [9].

Transition metals are the metals with incomplete d state in atomic structures like Co, Fe, Ni, Cd, etc. In magnetic transition metal compounds, the conduction electrons lie wholly in a dband, with some extent of hybridization with 4s electrons. This means that the d- band is separated from conduction band and contains an integer number of electrons per atom. And a band containing an integer number of electrons must exceed a certain width if it is to be metallic. Based on Gutzweller [10], approximation of variational calculation method of the ground state wave-function for model Hamiltonian with single-binding band and with only intra-atomic Coulomb interaction between the electrons, considering the case in which one electron per atom and, they found that the Gutzweller variational state is always metallic [11]. The experimental results of Craig et al. [12] on the electrical resistivity of Ni near its Curie temperature lead Fisher et al. [13] to criticize the theoretical treatment of resistive anomaly theory suggested by de Gennes and Frieddel [14] because, in their treatment they supposed long-range fluctuations of the magnetization near the critical point and this lead to incorrect result, but the short-range order fluctuations which make the dominant contribution to the temperature dependence of resistivity. Monecke et al. [15] investigated the specific heat of the

explain the optical absorption in insulators [8].

64 Ionizing Radiation Effects and Applications

3. Mott metal-insulator transition (MIT)

3.1. Transition metals and their alloys

Mott started to explain the metal insulator transition on the basis of Hubbard band model [16]. Mott outlines the properties of a crystalline array of one-electron centers, each described by a wavefunction φ(r) behaving as exp.(�r/aH) for large r, at distance a from each other, sufficiently large for the tight binding approximation to be useful. If the number of electron per atom deviates from integral value, the model should always predict metallic behavior, but with one or any integral number of electrons per atom this is not so, and the system is insulating [7]. The most convenient description is in terms of Hubbard intra-atomic energy U which is defined by

$$
\Delta U = \iint \left(\frac{e^2}{kr\_{12}} \left| \phi(r\_{12})^2 \right| \phi(r\_2)^2 d^3 \mathbf{x}\_1 d^3 \mathbf{x}\_2 \tag{2}
$$

For hydrogen-like atom

$$U = \frac{5e^2}{8ka\_H}$$

If P is the ionization potential of each atom and E is the electron affinity, by assuming that the functions φ are not changed by addition of an extra electron

$$\mathbf{U} = \mathbf{P} \mathbf{-E} \tag{3}$$

are no longer arranged antiferromagnetically, but resonate quantum mechanically between their two positions. The band is no longer split into two Hubbard bands Figure 3; instead there is a large enhancement by 1/2ζ of the effective mass. The simplest form of metal-insulator transition is the form of semi-metal, a material for which the conduction and valence band

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Figure 3. Two Hubbard bands overlapped in metal case, and not overlapped in insulator non-metal.

In the antiferromagnetic insulator, the magnitude of the Hubbard gap is not greatly affected when the temperature goes through the Neel point TN. The Hubbard gap is then, essentially, the energy required to take an electron from an atom and put it on a distant atom where another electron is already present. The energy U needed to achieve this does not depend on coexistence of the antiferromagnetic long-range order. At zero temperature, an insulator can be described in terms of the full and empty bands determined by long-range antiferromagnetic order. In simple cubic lattice of one electron centers, if U/B > 0.27, a sharp metal-insulator transition occurs above Néel temperature. But it has been found that above Néel temperature, for a rigid lattice, the transition between an antiferromagnetic insulator and a metal as U/B varies is not sharp; Mott thought that this is a result of considering the long-range forces in Hubbard model [16]. As the temperature increases [17], the electrons are excited into the conduction band, their coupling with moments lowers the Néel temperature. Thus, the disordering of the spins with consequent increase of entropy is accelerated. Ramirez et al. [18] showed that a first-order transition to degenerate gas in the conduction band, together with

At the transition, the value of B <sup>≥</sup>U can be evaluated for hydrogen like wavefunction, <sup>U</sup> <sup>¼</sup> <sup>e</sup><sup>2</sup>

ð Þþ <sup>1</sup> <sup>þ</sup> <sup>α</sup><sup>R</sup> <sup>1</sup>

<sup>α</sup> <sup>¼</sup> ð Þ <sup>2</sup>mW<sup>0</sup>

and α is defined as the distance at which the single-well wavefunction exp.(�αR) falls off.

6 ð Þ <sup>α</sup><sup>R</sup> <sup>2</sup>

1=2

<sup>e</sup><sup>2</sup><sup>α</sup>

ℏ

<sup>I</sup> <sup>¼</sup> Ioe�α<sup>R</sup> Io <sup>¼</sup> <sup>3</sup> 2

8kaH

(4)

overlap, to a non-metal, where there is no overlap.

disordering of the moments, is possible.

since both U and B are known

I is the overlap energy integral

Since the value of B near the transition is given by

The properties of such system are the following:


B ≥ U

A metal-insulator transition then occurs, sometimes known as "Mott transition."

The Mott transition is similar to the band crossing transition, being from antiferromagnetic insulator to antiferromagnetic metal. As the overlap increases, the number n of free carriers increases, the moment on the atoms and Neel temperature will tend to zero and disappear when n = 1/2z. Figure 2 shows magnetic moment and Néel temperature at the transition between antiferromagnetism and normal metal against B/U [7], here we have two situations; first, the antiferromagnetism is absent, and after the magnetic moment have disappeared the electron gas becomes highly correlated, this means that small proportion ζ of the sites are doubly occupied at any moment, or unoccupied and the spins of the electrons on other sites

Figure 2. Magnetic moment and Nèel temperature at transition antiferromagnetism and normal metal as function of B/U.

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Figure 3. Two Hubbard bands overlapped in metal case, and not overlapped in insulator non-metal.

are no longer arranged antiferromagnetically, but resonate quantum mechanically between their two positions. The band is no longer split into two Hubbard bands Figure 3; instead there is a large enhancement by 1/2ζ of the effective mass. The simplest form of metal-insulator transition is the form of semi-metal, a material for which the conduction and valence band overlap, to a non-metal, where there is no overlap.

In the antiferromagnetic insulator, the magnitude of the Hubbard gap is not greatly affected when the temperature goes through the Neel point TN. The Hubbard gap is then, essentially, the energy required to take an electron from an atom and put it on a distant atom where another electron is already present. The energy U needed to achieve this does not depend on coexistence of the antiferromagnetic long-range order. At zero temperature, an insulator can be described in terms of the full and empty bands determined by long-range antiferromagnetic order. In simple cubic lattice of one electron centers, if U/B > 0.27, a sharp metal-insulator transition occurs above Néel temperature. But it has been found that above Néel temperature, for a rigid lattice, the transition between an antiferromagnetic insulator and a metal as U/B varies is not sharp; Mott thought that this is a result of considering the long-range forces in Hubbard model [16]. As the temperature increases [17], the electrons are excited into the conduction band, their coupling with moments lowers the Néel temperature. Thus, the disordering of the spins with consequent increase of entropy is accelerated. Ramirez et al. [18] showed that a first-order transition to degenerate gas in the conduction band, together with disordering of the moments, is possible.

At the transition, the value of B <sup>≥</sup>U can be evaluated for hydrogen like wavefunction, <sup>U</sup> <sup>¼</sup> <sup>e</sup><sup>2</sup> 8kaH since both U and B are known

$$\begin{aligned} I &= I\_o e^{-aR} \\ I\_o &= \left\{ \frac{3}{2} (1 + aR) + \frac{1}{6} (aR)^2 \right\} e^2 a \end{aligned} \tag{4}$$

I is the overlap energy integral

U ¼ P–E (3)

/U = �B/(2zU), where B is the band width B = 2zI. The Néel temper-

i. when the distance a between the centers is large, the overlap energy integral I is small, the system is expected to be antiferromagnetic, with energy below that of the ferromagnetic

ii. An extra electron placed on one of the atoms is able to move with a k vector just as in normal band. It proposed to have an energy in the "upper Hubbard band." It well polarizes the spins on surrounding atoms antiparallel to itself, or parallel if the atomic orbitals are degenerate, forming a "spin polaron." Its bandwidth is probably not very

iii. A hole formed by taking an electron away from one atom has similar properties, being able to move with wavevector k and having a range of energies not very different from B.

iv. The two bands will overlap when a is small enough, and consequently B great enough, to

B ≥ U

The Mott transition is similar to the band crossing transition, being from antiferromagnetic insulator to antiferromagnetic metal. As the overlap increases, the number n of free carriers increases, the moment on the atoms and Neel temperature will tend to zero and disappear when n = 1/2z. Figure 2 shows magnetic moment and Néel temperature at the transition between antiferromagnetism and normal metal against B/U [7], here we have two situations; first, the antiferromagnetism is absent, and after the magnetic moment have disappeared the electron gas becomes highly correlated, this means that small proportion ζ of the sites are doubly occupied at any moment, or unoccupied and the spins of the electrons on other sites

Figure 2. Magnetic moment and Nèel temperature at transition antiferromagnetism and normal metal as function of B/U.

A metal-insulator transition then occurs, sometimes known as "Mott transition."

The properties of such system are the following:

ature TN will be such that kTN is of this order.

different from B calculated without correction.

state equal to �2zI<sup>2</sup>

66 Ionizing Radiation Effects and Applications

ensure that

$$\alpha = \frac{\left(2mW\_0\right)^{1/2}}{\hbar}$$

and α is defined as the distance at which the single-well wavefunction exp.(�αR) falls off. Since the value of B near the transition is given by

$$B = 2\Im z \left(\frac{c^2 \alpha}{k}\right) e^{-\alpha R} \tag{5}$$

3.4. Mott versus Anderson explanation of metal-insulator transition

possible. By calculation, the value of n at which the transition occurs to be

n 1

doped semiconductors is of the form

tial energy follows formula v(r) = (e<sup>2</sup>

as E ! Ec, if we write a/<sup>ξ</sup> = const. (Ec � E)<sup>s</sup>

certainly.

energy EF below EC is shown.

Mott treated the metal-insulator transition problem by considering the electron gas as screening the positive charge on the donors, so the potential energy seen by electrons in heavily

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

V rð Þ¼ <sup>e</sup><sup>2</sup> kre

where k is the dielectric constant of the semiconductors, and q is the screening constant depending on the electron density n. Mott also proposed that for an electron which its poten-

would have metallic properties. But as the density of electron gas drops, bound states become

where aH is the Bohr radius of donors. It is predicted that a discontinuous transition would occur from a state at which all electrons were bound to donors to one in which they were free, this is Mott transition. Mott [7] predicted that at the transition, the indirect band gap should disappear. This proved in germanium and silicon. In these semiconductor materials, in case of electrons and holes production by irradiation, electrons and holes combine at low temperature to form excitons, which are for indirect band gap have comparatively long-life time. Excitons attract each other and droplets of an electron-hole gas formed. The electronhole gas droplets have two forms; one is the excitonic insulator, or an electron-hole metallic gas. Mott and Kavah [17] argued that if Vo/B is less than critical value, the states are localized up to mobility edge. As shown in Figures 4 and 5, the localization length ξ tends to infinity

Figure 5. Density of states with potential energy of Figure 4 showing the mobility edge Ec. The position of the Fermi

�qr (10)

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69

/kr) exp.(�qr) and if q is large enough the electron gas

<sup>3</sup>aH ¼ 0:25 (11)

, neither the constant nor the index is known with

but because of the rapid variation of e�α<sup>R</sup> and αR depend on z; αR = 5.8 [28], and if z the coordination number = 6

$$m^{1/3}a\_H \cong 0.2\tag{6}$$

This equation is used for the discussion of metal insulator transition in doped semiconductors.

#### 3.3. Anderson insulator metal transition

Anderson [19] showed that at a certain randomness, the electron wavefunction becomes localized. According to the Anderson model, as shown in Figure 4, there exists a critical value VO/B above which the diffusion is impossible at zero temperature. Anderson introduced a random potential into each well within limits �<sup>1</sup> <sup>2</sup> Vo. This leads to finite mean free path l such that a/l = 0.7(VO/B)<sup>2</sup> . If VO/B ffi 1, the value of l approaches unity. Mott and Kavah [17] showed that it cannot be smaller, and the wavefunction has the form

$$\Psi\_{\rm ext} = \sum\_{n} \mathbb{C}\_{n} \exp\left(i\varphi\_{n}\right)\psi\_{n} \tag{7}$$

where Cn are coefficients, φ<sup>n</sup> are random phases, as the VO/B increases greater than unity the phases still random, the scatter of the coefficients Cn will increase, and the wave function becomes localized having the form

$$\Psi = \text{Rraft}\left[\psi\_{ext}\right] \left\{ e^{\frac{-(r+\tau\_0)}{\zeta}} \right\} \tag{8}$$

where ro is some point in space, and ζ is the localization length. The critical value of Vo/B depends on the co-ordination number z. Mott and Kavah [17] supposed that Vo/B greater than unity, the range of energies in the band increased to (vo <sup>2</sup> + B2 ) 0.5, so they write in the mid-gab

$$\mathbf{N}(\mathbf{E}) = 1/\left\{ \mathbf{a}^3 \left( \mathbf{v}\_o^2 + \mathbf{B}^2 \right)^{0.5} \right\} \tag{9}$$

Figure 4. The potential energy of an electron in the Anderson model: (a) without a random potential, and (b) with a random potential VO. B is the band-width in case (a). The density of states N(E) is shown.

#### 3.4. Mott versus Anderson explanation of metal-insulator transition

B ¼ 23z

n<sup>1</sup>=<sup>3</sup>

<sup>Ψ</sup>ext <sup>¼</sup> <sup>X</sup> n

Ψ ¼ Rral ψext

N Eð Þ¼ <sup>1</sup><sup>=</sup> a3 vo

coordination number = 6

68 Ionizing Radiation Effects and Applications

that a/l = 0.7(VO/B)<sup>2</sup>

3.3. Anderson insulator metal transition

becomes localized having the form

random potential into each well within limits �<sup>1</sup>

that it cannot be smaller, and the wavefunction has the form

unity, the range of energies in the band increased to (vo

e<sup>2</sup>α k � � e

but because of the rapid variation of e�α<sup>R</sup> and αR depend on z; αR = 5.8 [28], and if z the

This equation is used for the discussion of metal insulator transition in doped semiconductors.

Anderson [19] showed that at a certain randomness, the electron wavefunction becomes localized. According to the Anderson model, as shown in Figure 4, there exists a critical value VO/B above which the diffusion is impossible at zero temperature. Anderson introduced a

Cnexp iφ<sup>n</sup>

where Cn are coefficients, φ<sup>n</sup> are random phases, as the VO/B increases greater than unity the phases still random, the scatter of the coefficients Cn will increase, and the wave function

� � e

where ro is some point in space, and ζ is the localization length. The critical value of Vo/B depends on the co-ordination number z. Mott and Kavah [17] supposed that Vo/B greater than

Figure 4. The potential energy of an electron in the Anderson model: (a) without a random potential, and (b) with a

random potential VO. B is the band-width in case (a). The density of states N(E) is shown.

�ð Þ rþro ζ n o

<sup>2</sup> <sup>þ</sup> B2 � �<sup>0</sup>:<sup>5</sup> n o

<sup>2</sup> + B2 )

. If VO/B ffi 1, the value of l approaches unity. Mott and Kavah [17] showed

�α<sup>R</sup> (5)

aH ffi 0:2 (6)

<sup>2</sup> Vo. This leads to finite mean free path l such

� �ψ<sup>n</sup> (7)

0.5, so they write in the mid-gab

(8)

(9)

Mott treated the metal-insulator transition problem by considering the electron gas as screening the positive charge on the donors, so the potential energy seen by electrons in heavily doped semiconductors is of the form

$$V(r) = \frac{e^2}{kr}e^{-qr} \tag{10}$$

where k is the dielectric constant of the semiconductors, and q is the screening constant depending on the electron density n. Mott also proposed that for an electron which its potential energy follows formula v(r) = (e<sup>2</sup> /kr) exp.(�qr) and if q is large enough the electron gas would have metallic properties. But as the density of electron gas drops, bound states become possible. By calculation, the value of n at which the transition occurs to be

$$m^{\ddagger}a\_H = 0.25\tag{11}$$

where aH is the Bohr radius of donors. It is predicted that a discontinuous transition would occur from a state at which all electrons were bound to donors to one in which they were free, this is Mott transition. Mott [7] predicted that at the transition, the indirect band gap should disappear. This proved in germanium and silicon. In these semiconductor materials, in case of electrons and holes production by irradiation, electrons and holes combine at low temperature to form excitons, which are for indirect band gap have comparatively long-life time. Excitons attract each other and droplets of an electron-hole gas formed. The electronhole gas droplets have two forms; one is the excitonic insulator, or an electron-hole metallic gas. Mott and Kavah [17] argued that if Vo/B is less than critical value, the states are localized up to mobility edge. As shown in Figures 4 and 5, the localization length ξ tends to infinity as E ! Ec, if we write a/<sup>ξ</sup> = const. (Ec � E)<sup>s</sup> , neither the constant nor the index is known with certainly.

Figure 5. Density of states with potential energy of Figure 4 showing the mobility edge Ec. The position of the Fermi energy EF below EC is shown.

#### 3.5. Conductivity of a metal in Anderson model

The conductivity of a metal is due to a gas non-interacting electron in the field of Anderson random potential. The conductivity of a metal is usually written in the form <sup>σ</sup> <sup>¼</sup> ne<sup>2</sup>τ=m, where n is the number of electrons per unit volume, m is the effective mass, and τ is the time of relaxation. If l is the mean free path, SF is the Fermi surface area 4πkF, and n ¼ ð Þ 8π=3 k 3 <sup>F</sup>=8π3, σ takes the form <sup>σ</sup> <sup>¼</sup> SFe<sup>2</sup>ι=12π<sup>3</sup>ℏ, Mott and Kavah [17] examined the last formula mean free path l = a, at z = 6 n = 1/a<sup>3</sup> , hence KFa=KFl = (3π<sup>2</sup> ) 1/3ffi 3.1, the conductivity is thus:

$$
\sigma \cong \frac{1}{3} \left( \frac{e^2}{\hbar a} \right) \tag{12}
$$

<sup>σ</sup>min <sup>¼</sup> <sup>0</sup>:03e<sup>2</sup> ℏLi

Figure 6. The behavior of conductivity at zero temperature of a degenerate electron gas as a function of charge carrier concentration n, so the EF moves through the mobility edge EC, (a) if σmin does not exist and (b) if it does. The broken line

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

where Li is the inelastic diffusion length, and the transition is a first-order transition. Meanwhile, Anderson transition metal insulator occurs because the existence of disorder, as the disorder increasing the wave function becomes nonlocalized (metallic state) and the transition is continuously occurring, and becomes sharp only under the effect of external magnetic field,

Samples of germanium doped with Arsenic irradiated with fast neutrons with energies of

original samples become disordered p-type [20–23]. In order to reduce the transmutation doping effect, all samples were placed in 1-mm-thick cadmium containers. During irradiation in the reactor, the ratio between thermal neutrons fluency and the fluency of fast neutrons was about 10. So, it was possible to obtain samples of germanium "doped" with acceptor-like radiation defects {Ge (RD)}. To ensure that the electrical properties were controlled by the transmutation doping, a complete annealing at 450�C for 24 h was performed. For electrical resistivity measurements, a special double wall glassy cryostat is designed [24]. This cryostat is attached with vacuum pump its evacuation rate is faster than the evaporation rate of He4 gas, thus the pressure inside the cryostat is decreased and hence the temperature. The conventional four probe method is used for electrical resistivity measurements. Ni electrode is participated in the desired position on the samples using electrochemical deposition technique (cold method). Thin Cu wires are fixed above the Ni electrodes using In. The samples were in parallelepiped shape with length about 8–12 mm, thickness about 1–2 mm, width about 2–3 mm, and the electrode apart about 3–4 mm resistivity of Ge (RD) was measured in the temperature range from 1.7 up to 300 K. The temperature was determined with a semiconductor thermistor in the interval 77.4–4.2 K, from saturated vapor pressure of He4 in the interval 4.2–1.5 K. The voltage across samples always less than 1 V and the current across the sample

. As a result of irradiation, all the

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71

and there is no minimum metallic conductivity.

<sup>E</sup> <sup>≥</sup> 0.1 MeV in the range of 2 � 1016 <sup>≤</sup><sup>Φ</sup> <sup>≤</sup> <sup>1</sup> � 1020 cm�<sup>2</sup>

4. Experimental part

shows the possible effects of interactions.

This last equation assumes a spherical Fermi surface; if a = 2 Å, the numerical value is 3000 (Ω.cm)�<sup>1</sup> . But Mott and Kavah expected the smallest conductivity in the range 2–5000 (Ω.cm)�<sup>1</sup> .

As the ratio Vo/B increases the conductivity decreases because


$$\mathcal{g} = \frac{B}{\left\{ 1.75 \left( B^2 - V\_o^2 \right)^{\frac{1}{2}} \right\}^2}$$

In this case a minimum metallic conductivity expected, and given by

$$
\sigma\_{\rm min} = \frac{e^2}{3\hbar a} g\_c^2 \approx 0.03 \frac{e^2}{\hbar a\_\prime},
\begin{array}{c}
\text{ ${}\_\text{g}$ } \\
\text{ ${}\_\text{gc}$ } \cong 1/3
\end{array} \tag{13}
$$

gc is the critical value at Anderson localization

iii. As the ratio Vo/B increases, another phenomenon appears which is called incipient localization, this phenomenon decreases the conductivity, σ ! 0 as T tends continuously to zero, as Vo/B increases to the critical value.

The Anderson transition is a phenomenon in which some systems for example, doped semiconductors, the zero temperature Fermi energy move from point above the mobility edge to a point below it. Generally, σ goes continuously to zero, as shown in Figure 6a, but if the transition is induced by magnetic field H, very sharp transition occurs as shown in Figure 6b. The conductivity at zero-field mobility edge Ec (0) is given by

$$\begin{aligned} \sigma(E\_C(0)) &= 0.03 \frac{e^2}{\hbar L}, L = L\_H = \left(\frac{c\hbar}{eH}\right)^{\frac{1}{2}} L > a\\ L &= a, \dots, \dots, \dots, \dots, \dots, \dots, \dots, L\_H < a \end{aligned} \tag{14}$$

As a conclusion of this section, in Mott model, the metal insulator transition occurs because the correlated electron gas cause increasing in the distance between the atomic centers in the lattice. There is a minimum metallic conductivity given by

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga http://dx.doi.org/10.5772/intechopen.72241 71

Figure 6. The behavior of conductivity at zero temperature of a degenerate electron gas as a function of charge carrier concentration n, so the EF moves through the mobility edge EC, (a) if σmin does not exist and (b) if it does. The broken line shows the possible effects of interactions.

$$
\sigma\_{\text{min}} = \frac{0.03e^2}{\hbar L\_i}
$$

where Li is the inelastic diffusion length, and the transition is a first-order transition. Meanwhile, Anderson transition metal insulator occurs because the existence of disorder, as the disorder increasing the wave function becomes nonlocalized (metallic state) and the transition is continuously occurring, and becomes sharp only under the effect of external magnetic field, and there is no minimum metallic conductivity.

#### 4. Experimental part

3.5. Conductivity of a metal in Anderson model

path l = a, at z = 6 n = 1/a<sup>3</sup>

70 Ionizing Radiation Effects and Applications

the form <sup>σ</sup> <sup>¼</sup> <sup>1</sup>

3 e2 ℏa � � g2,

3000 (Ω.cm)�<sup>1</sup>

ii. Where,

The conductivity of a metal is due to a gas non-interacting electron in the field of Anderson random potential. The conductivity of a metal is usually written in the form <sup>σ</sup> <sup>¼</sup> ne<sup>2</sup>τ=m, where n is the number of electrons per unit volume, m is the effective mass, and τ is the time of

takes the form <sup>σ</sup> <sup>¼</sup> SFe<sup>2</sup>ι=12π<sup>3</sup>ℏ, Mott and Kavah [17] examined the last formula mean free

This last equation assumes a spherical Fermi surface; if a = 2 Å, the numerical value is

i. As the density of states at EF decreases, the conductivity decreases, and may be written in

<sup>1</sup>:<sup>75</sup> <sup>B</sup><sup>2</sup> � <sup>V</sup><sup>2</sup>

<sup>c</sup> <sup>≈</sup> <sup>0</sup>:<sup>03</sup> <sup>e</sup><sup>2</sup>

iii. As the ratio Vo/B increases, another phenomenon appears which is called incipient localization, this phenomenon decreases the conductivity, σ ! 0 as T tends continuously to

in Figure 6b. The conductivity at zero-field mobility edge Ec (0) is given by

L ¼ a……………………………LH < a

As a conclusion of this section, in Mott model, the metal insulator transition occurs because the correlated electron gas cause increasing in the distance between the atomic centers in the

<sup>σ</sup>ð Þ¼ ECð Þ<sup>0</sup> <sup>0</sup>:<sup>03</sup> <sup>e</sup><sup>2</sup>

lattice. There is a minimum metallic conductivity given by

The Anderson transition is a phenomenon in which some systems for example, doped semiconductors, the zero temperature Fermi energy move from point above the mobility edge to a point below it. Generally, σ goes continuously to zero, as shown in Figure 6a, but if the transition is induced by magnetic field H, very sharp transition occurs as shown

<sup>ℏ</sup><sup>L</sup> , L <sup>¼</sup> LH <sup>¼</sup> <sup>c</sup><sup>ℏ</sup>

eH � �<sup>1</sup> 2 L > a

n o

)

e2 ℏa � �

. But Mott and Kavah expected the smallest conductivity in the range 2–5000 (Ω.cm)�<sup>1</sup>

o � �<sup>1</sup>

2

1/3ffi 3.1, the conductivity is thus:

<sup>ℏ</sup>a, , gc ffi <sup>1</sup>=<sup>3</sup> (13)

3 <sup>F</sup>=8π3, σ

(12)

.

(14)

relaxation. If l is the mean free path, SF is the Fermi surface area 4πkF, and n ¼ ð Þ 8π=3 k

σ ffi 1 3

<sup>g</sup> <sup>¼</sup> <sup>B</sup>

In this case a minimum metallic conductivity expected, and given by

<sup>σ</sup>min <sup>¼</sup> <sup>e</sup><sup>2</sup> 3ℏa g2

gc is the critical value at Anderson localization

zero, as Vo/B increases to the critical value.

, hence KFa=KFl = (3π<sup>2</sup>

As the ratio Vo/B increases the conductivity decreases because

Samples of germanium doped with Arsenic irradiated with fast neutrons with energies of <sup>E</sup> <sup>≥</sup> 0.1 MeV in the range of 2 � 1016 <sup>≤</sup><sup>Φ</sup> <sup>≤</sup> <sup>1</sup> � 1020 cm�<sup>2</sup> . As a result of irradiation, all the original samples become disordered p-type [20–23]. In order to reduce the transmutation doping effect, all samples were placed in 1-mm-thick cadmium containers. During irradiation in the reactor, the ratio between thermal neutrons fluency and the fluency of fast neutrons was about 10. So, it was possible to obtain samples of germanium "doped" with acceptor-like radiation defects {Ge (RD)}. To ensure that the electrical properties were controlled by the transmutation doping, a complete annealing at 450�C for 24 h was performed. For electrical resistivity measurements, a special double wall glassy cryostat is designed [24]. This cryostat is attached with vacuum pump its evacuation rate is faster than the evaporation rate of He4 gas, thus the pressure inside the cryostat is decreased and hence the temperature. The conventional four probe method is used for electrical resistivity measurements. Ni electrode is participated in the desired position on the samples using electrochemical deposition technique (cold method). Thin Cu wires are fixed above the Ni electrodes using In. The samples were in parallelepiped shape with length about 8–12 mm, thickness about 1–2 mm, width about 2–3 mm, and the electrode apart about 3–4 mm resistivity of Ge (RD) was measured in the temperature range from 1.7 up to 300 K. The temperature was determined with a semiconductor thermistor in the interval 77.4–4.2 K, from saturated vapor pressure of He4 in the interval 4.2–1.5 K. The voltage across samples always less than 1 V and the current across the sample decreases from μA to nA order as the temperature lowered. The electrical properties of Ge (RD) are determined solely by acceptor-like radiation defects [25, 26]. The least square fitting method, using a computer program Excel 2010, is used to analysis the data extracted and to calculate the uncertainty in the obtained results.

will be a contribution from carriers with energies near EF which can hop between localized states. This contribution is described by r<sup>2</sup> exp. (-W)/KT, where r<sup>1</sup> ≤ r<sup>2</sup> and W is the hopping energy of the order of half the width of the band of the states. The extracted results from

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

http://dx.doi.org/10.5772/intechopen.72241

F is the neutron flux, P300, P77 are the number of charge carriers at 300 K and 77 K respectively where E1, E2, E3, are the activation energies of different conductivity mechanisms. And m300,

Figure 8 shows the dependence of resistivity on square root of temperature. This figure is

TES <sup>¼</sup> <sup>β</sup>e<sup>2</sup> ka

where β is a constant, e is the electronic charge, k is the dielectric constant, and a is the

Figure 9 shows the dependence of resistivity on T�0.25. From this figure [30], Mott variable

Φ, cm�<sup>2</sup> p300 logp300 p77 E1, meV E2, meV E3, meV Logμ<sup>300</sup> Logμ<sup>77</sup> 0 1.6E + 15 15.20 1.5E + 15 21.2 ———— ———— 3.59 4.32 1E + 15 1.5E + 15 15.18 3.3E + 14 28.9 ———— ———— 3.42 4.24 5E + 15 2.5E + 15 15.4 9E + 14 22.6 ———— 2.27 3.45 4.24 2E + 16 5E + 15 15.7 2.23E + 15 17.8 0.73 0.79 3.39 4.17 5E + 16 1.15E + 16 16.06 6.56E + 15 11.5 1.93 0.84 3.4 3.87 8E + 16 3.7E + 16 16.57 1.18E + 16 10.7 1.57 0.92 3.45 3.64 1.6E + 17 7.4E + 16 16.87 2.2E + 16 9.2 0 0.9 3.45 3.53 5E + 18 1.4E + 17 17.14 4.05E + 16 6.4 ———— 0.63 3.48 3.23 1E + 20 4.18E + 17 17.62 1.6E + 17 3.7 0 0.03 2.99 2.69

Table 1. The concentration of holes at 300 K and at 77 K, the conductivity activation energies of the three stages of conductivity, E1 which is the band to band transition activation energy, E2 which is activation energy of inter band transition activation energy, E3 which is the hopping conduction activation energy, the mobility μ of holes at 300 K and

range hopping is applied to obtain Mott characteristic temperature from the equation

TES T <sup>05</sup>

(16)

73

r ¼ roe

m77, are the mobility of charge carriers at 300 K and, 77 K respectively.

The obtained results reveal that E1 > E2 > E3, and ro<r1<r<sup>2</sup> for all samples.

required to apply Shklovskii's percolation theory of conduction where [29]

From this equation, TES is obtained for each irradiation dose

Figure 7 are summarized in Table 1.

localization radius.

77 K, respectively.

## 5. Experimental results

Figure 7 shows the resistivity dependence on temperature of germanium samples irradiated with different doses of neutron irradiation. From this figure, the conductivity activation energy of conductivity (σ = r�<sup>1</sup> ) is obtained, from the empirical equation argued by Fritzche [27]

$$\rho = \rho\_o \exp.-\left(\mathbf{E}\_\mathrm{C} - \mathbf{E}\_\mathrm{F}\right) / \mathbf{K} \mathbf{T} + \rho\_1 \exp.-\left(\mathbf{E}\_\mathrm{A} - \mathbf{E}\_\mathrm{F} + \mathbf{W}\_1\right) / \mathbf{K} \mathbf{T} + \rho\_2 \exp.\left(\mathbf{W}\right) / \mathbf{K} \mathbf{T} \tag{15}$$

where the term (r<sup>o</sup> exp.-(EC-EF)/KT) represents transport by carriers excited beyond the mobility edge into non-localized (extended) states at EC or EV. And r is the resistivity, r<sup>o</sup> is the preexponential factor. A plot of lnr versus 1/T will yield a straight line if EC-EF is a linear function of T over the temperature range measured. As the temperature decreases, transport carriers excited into localized states at the band edges and the resistivity is given by r<sup>1</sup> exp.-(EA-EF + W1)/KT, where W1 is the activation energy for carriers hopping, W1 should decrease with decreasing temperature [28] On the account of variable-range nature of the hopping transport. However, as the temperature dependence is through the carrier activation term, approximately linear dependence of ln r versus 1/T is again expected. As the temperature lowered more, there

Figure 7. ln σ = f (1/T).

will be a contribution from carriers with energies near EF which can hop between localized states. This contribution is described by r<sup>2</sup> exp. (-W)/KT, where r<sup>1</sup> ≤ r<sup>2</sup> and W is the hopping energy of the order of half the width of the band of the states. The extracted results from Figure 7 are summarized in Table 1.

F is the neutron flux, P300, P77 are the number of charge carriers at 300 K and 77 K respectively where E1, E2, E3, are the activation energies of different conductivity mechanisms. And m300, m77, are the mobility of charge carriers at 300 K and, 77 K respectively.

The obtained results reveal that E1 > E2 > E3, and ro<r1<r<sup>2</sup> for all samples.

Figure 8 shows the dependence of resistivity on square root of temperature. This figure is required to apply Shklovskii's percolation theory of conduction where [29]

$$
\rho = \rho\_o \varepsilon^{\left(\frac{r\_{FS}}{T}\right)^{08}} \tag{16}
$$

From this equation, TES is obtained for each irradiation dose

decreases from μA to nA order as the temperature lowered. The electrical properties of Ge (RD) are determined solely by acceptor-like radiation defects [25, 26]. The least square fitting method, using a computer program Excel 2010, is used to analysis the data extracted and to

Figure 7 shows the resistivity dependence on temperature of germanium samples irradiated with different doses of neutron irradiation. From this figure, the conductivity activation energy

where the term (r<sup>o</sup> exp.-(EC-EF)/KT) represents transport by carriers excited beyond the mobility edge into non-localized (extended) states at EC or EV. And r is the resistivity, r<sup>o</sup> is the preexponential factor. A plot of lnr versus 1/T will yield a straight line if EC-EF is a linear function of T over the temperature range measured. As the temperature decreases, transport carriers excited into localized states at the band edges and the resistivity is given by r<sup>1</sup> exp.-(EA-EF + W1)/KT, where W1 is the activation energy for carriers hopping, W1 should decrease with decreasing temperature [28] On the account of variable-range nature of the hopping transport. However, as the temperature dependence is through the carrier activation term, approximately linear dependence of ln r versus 1/T is again expected. As the temperature lowered more, there

) is obtained, from the empirical equation argued by Fritzche [27]

r ¼ r<sup>o</sup> exp: � ð Þ EC � EF =KT þ r<sup>1</sup> exp: � ð Þ EA � EF þ W1 =KT þ r2exp:ð Þ W =KT (15)

calculate the uncertainty in the obtained results.

5. Experimental results

72 Ionizing Radiation Effects and Applications

of conductivity (σ = r�<sup>1</sup>

Figure 7. ln σ = f (1/T).

$$T\_{ES} = \frac{\beta \sigma^2}{ka}$$

where β is a constant, e is the electronic charge, k is the dielectric constant, and a is the localization radius.

Figure 9 shows the dependence of resistivity on T�0.25. From this figure [30], Mott variable range hopping is applied to obtain Mott characteristic temperature from the equation


Table 1. The concentration of holes at 300 K and at 77 K, the conductivity activation energies of the three stages of conductivity, E1 which is the band to band transition activation energy, E2 which is activation energy of inter band transition activation energy, E3 which is the hopping conduction activation energy, the mobility μ of holes at 300 K and 77 K, respectively.

$$
\rho = \rho\_o \varepsilon^{\left(\frac{r\_M}{T}\right)^{0.25}} \tag{17}
$$

Table 2 indicates that TM is much higher than TES, this table also clears the coexistence of Mott variable range hopping mechanisms of conduction, and Shklovskii and Efros percolation mechanism of conduction, the coexistence of both models explained the low temperature conduction mechanisms reported [31, 32] in different compositions. But it is not clear up to now, are these two mechanisms of conduction simultaneously exist or consecutively one mechanism dominates in a certain temperature range and then, the other one. Figure 10 shows the dependence of σ<sup>o</sup> on the irradiation dose ϕ, the experimentally obtained data are fitted

Table 2. Mott characteristic temperature and Efros-Shklovskii characteristic temperature at each irradiation dose.

Φ, cm�<sup>2</sup> TM, K TES, K 1.2 � <sup>10</sup><sup>17</sup> 148,454 151.50 <sup>8</sup> � <sup>10</sup><sup>16</sup> 201,906 194.94 <sup>5</sup> � <sup>10</sup><sup>16</sup> 262,951 320.4 <sup>2</sup> � <sup>10</sup><sup>16</sup> 69,232 113.89

ln <sup>ϕ</sup> <sup>¼</sup> ln <sup>σ</sup><sup>o</sup>

Figure 10. Fitting of Eq. (17) for the dependence of pre-exponential factor σ<sup>o</sup> on the irradiation flux (φ).

<sup>a</sup> <sup>þ</sup> <sup>b</sup>ln <sup>σ</sup><sup>o</sup> <sup>þ</sup> <sup>c</sup> ffiffiffiffiffiffiffiffiffiffi

where a, b, and c are coefficients to fit present experimental data, a = 777.8, b = 18, and c = 238.4. Figure 10 shows that the pre-exponential factor r decreases with increase the irradiation fluency until reaching to minimum value and start to increasing this behavior could be explained as follows, as the irradiation dose increases the charge carrier increases, which causes a diminution of the resistivity until the concentration of charge carrier reaches its critical

ln σ<sup>o</sup>

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

p (18)

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75

with Eq. (17)

where TM <sup>¼</sup> <sup>β</sup><sup>o</sup> N Eð Þ<sup>F</sup> <sup>a</sup>3, where <sup>β</sup><sup>o</sup> is a constant, N(EF) is the density of states at Fermi level, and a is Bohr radius of localization.

The obtained values of TM and TES from Figures 8 and 9 are given in Table 2.

Figure 8. ln σ = f (1/T0.5).

Figure 9. ln (σ) = f(1/T0.25).


r ¼ roe

The obtained values of TM and TES from Figures 8 and 9 are given in Table 2.

where TM <sup>¼</sup> <sup>β</sup><sup>o</sup>

Figure 8. ln σ = f (1/T0.5).

Figure 9. ln (σ) = f(1/T0.25).

Bohr radius of localization.

74 Ionizing Radiation Effects and Applications

TM T <sup>0</sup>:<sup>25</sup>

N Eð Þ<sup>F</sup> <sup>a</sup>3, where <sup>β</sup><sup>o</sup> is a constant, N(EF) is the density of states at Fermi level, and a is

(17)

Table 2. Mott characteristic temperature and Efros-Shklovskii characteristic temperature at each irradiation dose.

Table 2 indicates that TM is much higher than TES, this table also clears the coexistence of Mott variable range hopping mechanisms of conduction, and Shklovskii and Efros percolation mechanism of conduction, the coexistence of both models explained the low temperature conduction mechanisms reported [31, 32] in different compositions. But it is not clear up to now, are these two mechanisms of conduction simultaneously exist or consecutively one mechanism dominates in a certain temperature range and then, the other one. Figure 10 shows the dependence of σ<sup>o</sup> on the irradiation dose ϕ, the experimentally obtained data are fitted with Eq. (17)

$$\ln \text{ln } \phi = \frac{\ln \sigma\_o}{a + b \ln \sigma\_o + c \sqrt{\ln \sigma\_o}} \tag{18}$$

where a, b, and c are coefficients to fit present experimental data, a = 777.8, b = 18, and c = 238.4. Figure 10 shows that the pre-exponential factor r decreases with increase the irradiation fluency until reaching to minimum value and start to increasing this behavior could be explained as follows, as the irradiation dose increases the charge carrier increases, which causes a diminution of the resistivity until the concentration of charge carrier reaches its critical

Figure 10. Fitting of Eq. (17) for the dependence of pre-exponential factor σ<sup>o</sup> on the irradiation flux (φ).

Figure 11. Fitting of Eq. (3) for dependence of conductivity on temperature of sample irradiated 5 � <sup>10</sup><sup>18</sup> cm�<sup>2</sup> .

value at which sample behaves as metallic like conductivity. In metallic conductors, the charge carrier augmentation enhances the possibility of collision between the charge carriers and with the doping centers, this increases the resistivity.

Figure 11 shows the fitting of conductivity dependence on temperature of sample irradiated with dose of 5 � 1018 cm�<sup>2</sup> to equation [33]

$$
\sigma = \sigma(0) + aT^{0.5} + bT \tag{19}
$$

1.6 � 1017 cm�<sup>2</sup>

distance is

per cm�<sup>3</sup>

; σ<sup>o</sup> = 0.024 and σ<sup>o</sup> = 0.032 (Ω-cm)�<sup>1</sup>

Figure 12. Fitting of dependence of conductivity on temperature of sample irradiated 1 � <sup>10</sup><sup>20</sup> cm�<sup>2</sup>

work samples irradiated with neutron flux 1 � 1020 and 5 � 1018 cm�<sup>2</sup>

conductivity satisfied in materials just began its metallic conductivity behavior.

r<sup>3</sup> ¼ r03e

Bohr radius of localization at insulator metal transition which is 40 Å.

the minimum metallic conductivity <sup>σ</sup>min <sup>¼</sup> <sup>0</sup>:026e<sup>2</sup>

metallic conductivity to be of the range 2–5000 (Ω.cm)�<sup>1</sup>

metallic conductivity equals to 0.024 and 0.032 (Ω-cm)�<sup>1</sup>

the metallic side of conductivity is dependent on irradiation dose. Figure 10 shows the dependence of pre-exponential factor on neutron irradiation dose, it is clear that as the neutron irradiation dose increases, the value of the pre-exponential factor decreases. It reaches its minimum value at neutron irradiation dose 1.6 � 1017 cm�<sup>2</sup> and starts to increase. Mott predicted that

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

smallest conductivities to be expected, unless the density of states broadened by disorder. In this

smaller than the minimum value of metallic conductivity predicted by Mott. This may be due to the high disorder in germanium caused by neutron irradiation, or the Mott minimum metallic

Figure 13 shows the dependence of ln(r3) on average impurity center distance as predicted by Mott variable range hopping model, the relation between r<sup>3</sup> on the average impurity center

> α NAa

where r is the resistivity, α is a constant, NA is the concentration of acceptor impurity centers

radius of localization is calculated and found equal to 43 Å, which is very close to the value of

, and a is the Bohr localization radius. From the line slope of Figure 13, the Bohr

, from these values, one can say that σ<sup>o</sup> in

.

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77

<sup>ℏ</sup><sup>a</sup> . In case of a = 2 Å, he predicted minimum

, α ¼ 1:74 (20)

, and he considered that this is the

, respectively, these values are much

, having minimum

where σ(0) is the residual conductivity at 0 K, the second and third term are related to weak localization effect. The fitting parameters as obtained from this equation are σ(0) = 0, a = �0.37, and b = 0.12.

Figure 12 shows the fitting of conductivity dependence on temperature of sample irradiated with irradiation dose 1 � <sup>10</sup><sup>20</sup> cm�<sup>2</sup> using Eq. (19). The fitting parameters as obtained from this equation are σ(0) =0, a = 0.65, and b = 0.065.

Since we have insulator metal transition, this means that the sample starts as an insulator, but because of irradiation the same samples becomes a metallic-like conductor after certain irradiation dose. This means that the conduction in a material may behave like semiconductor (insulator) or metallic characteristic of conduction. The same equation, Eq. (19), did not fit the conductivity temperature dependence of sample irradiated with dose 1.6 � 1017 cm�<sup>2</sup> . This means that this sample is in the insulator side of conductivity. However, the sample irradiated with dose 5 � 1018 is in the metallic conductivity side. For sample with irradiation dose 5 � 1018 cm�<sup>2</sup> , the fitting parameter value is �0.037, the negative value of parameter a is reported in [34]. The negative value of a in some samples appears only at the beginning of metallic conductivity. From experimental data analysis of Figure 7, the extrapolation intercept with ordinate axes gives the resistivity, <sup>σ</sup><sup>o</sup> value. For sample irradiated with dose 1 � <sup>10</sup><sup>20</sup> and

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga http://dx.doi.org/10.5772/intechopen.72241 77

Figure 12. Fitting of dependence of conductivity on temperature of sample irradiated 1 � <sup>10</sup><sup>20</sup> cm�<sup>2</sup> .

value at which sample behaves as metallic like conductivity. In metallic conductors, the charge carrier augmentation enhances the possibility of collision between the charge carriers and with

Figure 11. Fitting of Eq. (3) for dependence of conductivity on temperature of sample irradiated 5 � <sup>10</sup><sup>18</sup> cm�<sup>2</sup>

Figure 11 shows the fitting of conductivity dependence on temperature of sample irradiated

where σ(0) is the residual conductivity at 0 K, the second and third term are related to weak localization effect. The fitting parameters as obtained from this equation are σ(0) = 0, a = �0.37,

Figure 12 shows the fitting of conductivity dependence on temperature of sample irradiated with irradiation dose 1 � <sup>10</sup><sup>20</sup> cm�<sup>2</sup> using Eq. (19). The fitting parameters as obtained from this

Since we have insulator metal transition, this means that the sample starts as an insulator, but because of irradiation the same samples becomes a metallic-like conductor after certain irradiation dose. This means that the conduction in a material may behave like semiconductor (insulator) or metallic characteristic of conduction. The same equation, Eq. (19), did not fit the conductivity temperature dependence of sample irradiated with dose 1.6 � 1017 cm�<sup>2</sup>

This means that this sample is in the insulator side of conductivity. However, the sample irradiated with dose 5 � 1018 is in the metallic conductivity side. For sample with irradiation

reported in [34]. The negative value of a in some samples appears only at the beginning of metallic conductivity. From experimental data analysis of Figure 7, the extrapolation intercept with ordinate axes gives the resistivity, <sup>σ</sup><sup>o</sup> value. For sample irradiated with dose 1 � <sup>10</sup><sup>20</sup> and

, the fitting parameter value is �0.037, the negative value of parameter a is

<sup>σ</sup> <sup>¼</sup> <sup>σ</sup>ð Þþ <sup>0</sup> aT<sup>0</sup>:<sup>5</sup> <sup>þ</sup> bT (19)

.

.

the doping centers, this increases the resistivity.

with dose of 5 � 1018 cm�<sup>2</sup> to equation [33]

76 Ionizing Radiation Effects and Applications

equation are σ(0) =0, a = 0.65, and b = 0.065.

and b = 0.12.

dose 5 � 1018 cm�<sup>2</sup>

1.6 � 1017 cm�<sup>2</sup> ; σ<sup>o</sup> = 0.024 and σ<sup>o</sup> = 0.032 (Ω-cm)�<sup>1</sup> , from these values, one can say that σ<sup>o</sup> in the metallic side of conductivity is dependent on irradiation dose. Figure 10 shows the dependence of pre-exponential factor on neutron irradiation dose, it is clear that as the neutron irradiation dose increases, the value of the pre-exponential factor decreases. It reaches its minimum value at neutron irradiation dose 1.6 � 1017 cm�<sup>2</sup> and starts to increase. Mott predicted that the minimum metallic conductivity <sup>σ</sup>min <sup>¼</sup> <sup>0</sup>:026e<sup>2</sup> <sup>ℏ</sup><sup>a</sup> . In case of a = 2 Å, he predicted minimum metallic conductivity to be of the range 2–5000 (Ω.cm)�<sup>1</sup> , and he considered that this is the smallest conductivities to be expected, unless the density of states broadened by disorder. In this work samples irradiated with neutron flux 1 � 1020 and 5 � 1018 cm�<sup>2</sup> , having minimum metallic conductivity equals to 0.024 and 0.032 (Ω-cm)�<sup>1</sup> , respectively, these values are much smaller than the minimum value of metallic conductivity predicted by Mott. This may be due to the high disorder in germanium caused by neutron irradiation, or the Mott minimum metallic conductivity satisfied in materials just began its metallic conductivity behavior.

Figure 13 shows the dependence of ln(r3) on average impurity center distance as predicted by Mott variable range hopping model, the relation between r<sup>3</sup> on the average impurity center distance is

$$
\rho\_3 = \rho\_{03} \varepsilon^{\frac{a}{\sum\_{\lambda} a}}, \ \alpha = 1.74 \tag{20}
$$

where r is the resistivity, α is a constant, NA is the concentration of acceptor impurity centers per cm�<sup>3</sup> , and a is the Bohr localization radius. From the line slope of Figure 13, the Bohr radius of localization is calculated and found equal to 43 Å, which is very close to the value of Bohr radius of localization at insulator metal transition which is 40 Å.

References

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1621k38s

377:253

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York and London: Plenum Press; 1979

[1] Hecht E. Optics. San Francisco, Boston, New York: Adison Wesley; 2002

[2] Das A, Ferbal T. Nuclear and Particle Physics. Toh Tuck Link, Singapore: World Scientific

Investigating the Nature of Insulator-Metal Transition in Neutron-Transmutation-Doped Ge:Ga

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79

[3] Haas EW, Martin JA. Nuclear transmutation doping from the view point of radioactivity formation. In: Messe JM, editor. Neutron Transmutation Doping in Semiconductors. New

[4] Heller EE. Isotopically Controlled Semiconductors. 2004. http://escholarship.org/uc/item/

[5] Zabrodskii AG, Alekseenko MV. Fermi level scan spectroscopy of gap states in Ge and Si–Ge alloysbased on the kinetics of neutron transmutation doping. Physica B. 2006;376-

[6] Edwards PP, Johnston RL, Rao CNR, Tunstall DP, Hensel F. The metal-insulator transition: A perspective. Philosophical Transactions of the Royal Society of London A. 1998;356 [7] Mott NF. Metal Insulator Transition. 2nd ed. London: Taylor & Francis; 1990, and refer-

[8] Duan F, Guojin J. Introduction to Condensed Matter Physics. Vol. VI. Toh Tuck Link,

[9] Mott NF. The electrical conductivity of transition metals. Proceedings of the Royal Society

[10] Gutzwiller MC. Effect of correlation on the ferromagnetism of transition metals. Physics

[11] Brinkman WF, Rice TM. Application of gutzwiller's variational method to the metal-

[12] Craig PP, Goldburg WJ, Kitchens TA, Budnick JI. Transport properties at critical points: The resistivity of s. Physical Review Letters. 1967;19:23, and references therein

[13] Fisher ME, Langer JS. Resistive anomalies at magnetic critical points. Physics Review.

[14] deGennes PE, Friedel J. Anomalies de résistivité dans certains métaux magníques. Journal

[15] Heing KH, Monecke J. Conductivity of the four-point Hubbard Model. Physica Status

[16] Hubbard J. Theory the connexion with many-body perturbation electron correlations in narrow energy bands. VI. Proceedings of the Royal Society of London A. 1967;296:100

Singapore: World Scientific Publishing Company; 2005

insulator transition. Physical Review B. 1970;2:10

of Physics and Chemistry of Solids. 1958;4

Figure 13. The dependence of ln r3on average impurity center distance (NA) 1/3.

### 6. Conclusions

The overall obtained results reveal that the n-type germanium is converted into p-type germanium by a fast reactor neutron irradiation. From analysis of the dependence, the electrical conductivity on temperature, the activation energies of conduction at different conductivity mechanism that; E1 > E2 > E3 and the pre-exponential factors r<sup>2</sup> >r<sup>1</sup> >r<sup>0</sup> were observed for each irradiation dose. But these values decrease with increasing irradiation dose. The metallic-like behavior starts at irradiation dose 5 <sup>10</sup><sup>18</sup> cm<sup>2</sup> . There are sweeping between Mott variable range hopping model and Efros-Shklovskii percolation model. Each model dominates in certain range of temperature. From analysis of Mott, variable range hopping the Bohr radius of localization at Insulator metal transition is obtained to be equal to 43 Å, and the obtained minimum metallic conductivity value is 0.024 (Ω-cm)<sup>1</sup> , which is much lower than the value predicted by Mott theory of insulator-metal transition.

### Author details

Samy Abd-elhakim Elsayed

Address all correspondence to: samy.abdelhameed@science.bsu.edu.eg

New Materials and Renewable Energy Laboratory, Physics Department, Faculty of Science, Beni-Suef University, Beni-Suef, Egypt

## References

6. Conclusions

78 Ionizing Radiation Effects and Applications

Author details

Samy Abd-elhakim Elsayed

Beni-Suef University, Beni-Suef, Egypt

behavior starts at irradiation dose 5 <sup>10</sup><sup>18</sup> cm<sup>2</sup>

minimum metallic conductivity value is 0.024 (Ω-cm)<sup>1</sup>

Figure 13. The dependence of ln r3on average impurity center distance (NA)

Address all correspondence to: samy.abdelhameed@science.bsu.edu.eg

predicted by Mott theory of insulator-metal transition.

The overall obtained results reveal that the n-type germanium is converted into p-type germanium by a fast reactor neutron irradiation. From analysis of the dependence, the electrical conductivity on temperature, the activation energies of conduction at different conductivity mechanism that; E1 > E2 > E3 and the pre-exponential factors r<sup>2</sup> >r<sup>1</sup> >r<sup>0</sup> were observed for each irradiation dose. But these values decrease with increasing irradiation dose. The metallic-like

1/3.

range hopping model and Efros-Shklovskii percolation model. Each model dominates in certain range of temperature. From analysis of Mott, variable range hopping the Bohr radius of localization at Insulator metal transition is obtained to be equal to 43 Å, and the obtained

New Materials and Renewable Energy Laboratory, Physics Department, Faculty of Science,

. There are sweeping between Mott variable

, which is much lower than the value


[17] Mott NF, Kaveh M. Metal Insulator transitions in non-crystalline systems. Advances in Physics. 1985;34:3

[33] Kawade K, Suzuki A, Tanka K. Electronic structure and electrical conductivity of amorphous Si–Ti alloys manifesting the metal-insulator transition. Journal of the Physical

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[34] Hussey NE, Tanaka K, Takagi H. Universality of the Mott–Ioffe–Regel limit in metals.

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[33] Kawade K, Suzuki A, Tanka K. Electronic structure and electrical conductivity of amorphous Si–Ti alloys manifesting the metal-insulator transition. Journal of the Physical Society of Japan. 2000;69(3):777

[17] Mott NF, Kaveh M. Metal Insulator transitions in non-crystalline systems. Advances in

[18] Ramirez R, Fallicov LM, Kimball J. Metal-insulator transitions: A simple theoretical

[19] Anderson PW. Absence of diffusion in certain random lattices. Physics Review. 1958;109:

[20] Crawford JH Jr, Cleland JW. Nature of bombardment damage and energy levels in semi-

[21] Crawford JH Jr, Lark-Horovitz K. Fast neutron bombardment effects in germanium.

[22] Cleland JW, Crawford JH, Pigg JC. Transmutation-produced germanium semiconductors.

[23] James HM, Lark-Horovitz K. Localized electronic states in bombarded semiconductors.

[24] Fritzche H, Lark Horovitz K. The electrical properties of germanium semiconductors at

[25] Dobrego VP, Ermolaev OP, Tkachev VD. Investigation of shallow radiation defect levels produced in Ge by fast neutron irradiation. Physica Status Solidi. 1977;44:435

[26] Konopleva RF, Novikov SR. Measuring the relative fast-neutron flux distribution in the VVR-M reactor with semiconductor detecting elements. Atomnaya Energiya. 1961;11:545.

[27] Fritzche H. Resistivity and hall coefficient of antimony doped germanium at low temper-

[28] Mott NF, Davis EA. Electronic Processes in Non-Crystalline Materials. Oxford: Clarendon

[29] Shklovskii BI, Efros AL. Electronic Properties of doped Semiconductors. Berlin, Heidel-

[30] Elhakim SA, Morsy MA. Simultaneous γ(Co60)-quanta irradiation and isothermal annealing-induced insulator–metal transition in a-As4Se4Te2 chalcogenide composition.

[31] El-Sayed A. Fractal explanation of Meyer-Neldel rule. Journal of Non-Crystalline Solids.

[32] El-hakim SA. Observation compensation effect and crossover between Percolation and variable-range-hopping regimes for dc conductivity in germanium irradiated with large fluencies fast neutrons. Journal of Optoelectronics and Advanced Materials. 2014;16(11–12):

Physics. 1985;34:3

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[34] Hussey NE, Tanaka K, Takagi H. Universality of the Mott–Ioffe–Regel limit in metals. Philosophical Magazine. 2004;84(24):2847

**Chapter 5**

Provisional chapter

**Radiation-Induced Degradation of Organic Compounds**

DOI: 10.5772/intechopen.72074

Environmental application of radiation technologies is an important part of radiation processing. Radiation treatment of aqueous systems contaminated with organic compounds is a promising method of water and wastewater purification and corresponding technologies are being developed. In this chapter, the following aspects of radiation treatment process are considered: sources of contamination and major contaminants of water and wastewater; primary processes in aqueous systems initiated by ionizing radiation; principal ways of contaminant conversion as consequences of primary processes (complete mineralization of organic compounds, partial decomposition of organic molecules resulted in detoxification, decolorization, disinfection of polluted water, and improvement in biological degradation of contaminant, polymerization of monomers' contaminants, oxidation-reduction processes, and coagulation of colloids); sources of ionizing radiation; and main equipment applied in radiation technologies of

Keywords: radiation chemistry, radiation technology, wastewater, electron

Changes in a matter resulted from reformation of chemical bonds structure under the action of ionizing radiation gave rise to implementation of various radiation technologies. At present, an overwhelming majority of the latter represent modification of materials, that is, polymers curing, grafting, production of thermo-shrinkable plastics, improvement of semiconductor circuits, and so on [1, 2]. At the same time, there exists an important area of radiation technologies application, namely environment conservation, where those technologies are not widespread as yet, or just are at the stage of development. One of the problems in environment

> © The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**and Radiation Technologies for Purification of**

Radiation-Induced Degradation of Organic

Compounds and Radiation Technologies

Igor E. Makarov and Alexander V. Ponomarev

Igor E. Makarov and Alexander V. Ponomarev

for Purification of Aqueous Systems

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72074

aqueous system purification.

accelerators, organic compounds

**Aqueous Systems**

Abstract

1. Introduction

#### **Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous Systems** Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous Systems

DOI: 10.5772/intechopen.72074

Igor E. Makarov and Alexander V. Ponomarev Igor E. Makarov and Alexander V. Ponomarev

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72074

#### Abstract

Environmental application of radiation technologies is an important part of radiation processing. Radiation treatment of aqueous systems contaminated with organic compounds is a promising method of water and wastewater purification and corresponding technologies are being developed. In this chapter, the following aspects of radiation treatment process are considered: sources of contamination and major contaminants of water and wastewater; primary processes in aqueous systems initiated by ionizing radiation; principal ways of contaminant conversion as consequences of primary processes (complete mineralization of organic compounds, partial decomposition of organic molecules resulted in detoxification, decolorization, disinfection of polluted water, and improvement in biological degradation of contaminant, polymerization of monomers' contaminants, oxidation-reduction processes, and coagulation of colloids); sources of ionizing radiation; and main equipment applied in radiation technologies of aqueous system purification.

Keywords: radiation chemistry, radiation technology, wastewater, electron accelerators, organic compounds

## 1. Introduction

Changes in a matter resulted from reformation of chemical bonds structure under the action of ionizing radiation gave rise to implementation of various radiation technologies. At present, an overwhelming majority of the latter represent modification of materials, that is, polymers curing, grafting, production of thermo-shrinkable plastics, improvement of semiconductor circuits, and so on [1, 2]. At the same time, there exists an important area of radiation technologies application, namely environment conservation, where those technologies are not widespread as yet, or just are at the stage of development. One of the problems in environment

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

conservation is purification of flue gases and wastewater, and radiation technologies possess a high potential in the direction providing for higher purification degree, unachievable in some cases by conventional purification technologies.

mass of carbon per mass of solution), the latter being numerically almost the same, as far as a mass of 1 dm<sup>3</sup> of diluted aqueous solution is close to 1 kg. COD is a mass of oxygen necessary for complete oxidation of organic compounds, present in unit volume of the solution, into carbon dioxide (and other inorganic compounds), while the BOD is a mass of oxygen, consumed in the process of biological oxidation of organic compounds, present in unit volume of the solution. Since biological oxidation is a long-term process, instead of BOD the notation BOD5 is often used, which means BOD measured after 5 days of biological oxidation. Like TOC, both COD and BOD are expressed in the same units and do not relate to the kind of organic compounds polluting water or wastewater, but rather reflect the total organic matter

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

http://dx.doi.org/10.5772/intechopen.72074

85

The main types of aqueous systems to be purified are considered to be water (from different

Water, consumed in the course of human activity, besides municipal water, that is, water of potable quality offered by water companies, has two natural sources: (1) groundwater, that is, water, seeped through from the surface and present in porous rocks below the surface, shallow wells, or deep aquifers, and (2) surface water, that is, water from a source that is exposed to the

Contamination of water may occur due to following reasons: municipal water—from pipelines, fittings, biofouling; groundwater—due to failing of septic systems, leaking sewer lines, and from land discharge by passage through soils and fissures or interaction with surface water; surface water—by treated wastewater, discharge of raw sewage, municipal wastewater, storm-water runoff, runoff from urban and agricultural areas, also animals and humans are

The level of water contamination usually is not high to use it for many purposes. Thus, most pristine rivers will have a 5-day carbonaceous BOD below 1 mg/L. Moderately polluted rivers may have a BOD value in the range of 2–8 mg/L. Rivers may be considered severely polluted

Groundwater from depth and confined aquifers is usually microbially safe and chemically stable in the absence of direct contamination; however, shallow or unconfined aquifers can be subject to contamination from discharges or seepages associated with agricultural practices (e.g., pathogens, nitrates, and pesticides), on-site sanitation and sewerage (pathogens and

Both groundwater and surface water have natural impurities including inorganic salts and, particularly—surface water, NOM (natural organic matter), represented mainly by humic and fulvic acids, cellulose, lignin) which have to be removed, or reduced in concentration, when using the water for drinking purposes [9, 10]. Quality specifications for drinking water are subject of policies, regulations, and standards on both national and international levels [11–14]. Guidelines are being established that determine the limit concentration of chemical compounds

content and its part that can be degraded in biological processes [6].

environment like rivers, canals, lakes, and open wells [7].

both indirect and direct contributors to the contamination.

when BOD values exceed 8 mg/L [8].

nitrates), and industrial wastes.

sources) and wastewater.

2.1. Water

Traditionally, radiation treatment (by gamma/X-rays or accelerated electrons beams) for the purification of water and wastewater is attributed to the so-called Advanced Oxidation Processes (AOPs) and corresponding technologies—to Advanced Oxidation Technologies (AOTs) (see, e.g., books [3, 4]). The reason is that initially new processes, appeared in addition to routine purification processes, such as biological treatment, coagulation, sedimentation, and filtration, have been based on the oxidation of organic impurities by strong oxidizing agent hydroxyl radicals, produced firstly in chemical reactions with participation of hydrogen peroxide, then with the use of physical methods, and irradiation of aqueous systems produces hydroxyl radicals as one of the main intermediates. However, the attribution of radiation treatment to AOPs seems to be not quite correct, since ionizing radiation initiates in irradiated media not only oxidizing processes but also reducing ones. Though the formation of reducing particles under radiolysis, as well as under photolysis, sonolysis, electrolysis, and so on, has been mentioned earlier repeatedly [3–5], the role of reductive processes in the purification of water and wastewater was not considered as specific and important one, partly due to comparatively low importance of the processes in the decomposition of organic compounds.

A significant advantage of radiation-induced processes over other AOPs consists in sufficient knowledge of mechanism of the processes including available qualitative and quantitative data on primary events of energy absorption, intermediates formation ways and properties, and reactions of organic compounds conversions. Nowadays, new research and review articles on radiation treatment are being published which demonstrate high interest to the problem of environmental application of radiation technologies.

The aim of this chapter is to show interrelation between well-established primary radiationchemical processes and the main ways of organic contaminants conversions, as well as to present the current state of radiation equipment being used at present or proposed to be used in radiation technologies of water and wastewater purification.

## 2. Types of aqueous systems to be purified

The application of radiation technologies to the purification of aqueous systems to a certain extent is determined by a subject of radiation treatment, that is, composition of the system. There are several types of aqueous systems to be purified commercially which differ considerably in qualitative and quantitative composition. The latter is usually expressed either chemically as a concentration of components (in units of moles or mass of the component per volume or mass of solution) or in units characteristic of water/wastewater purification technologies, that is, COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand), and TOC (Total Organic Carbon).

TOC is determined as the total mass of carbon atoms in dissolved organic compounds per unit solution volume and expressed usually in mg/L (mg/dm<sup>3</sup> ) or in ppm (parts per million, i.e., mass of carbon per mass of solution), the latter being numerically almost the same, as far as a mass of 1 dm<sup>3</sup> of diluted aqueous solution is close to 1 kg. COD is a mass of oxygen necessary for complete oxidation of organic compounds, present in unit volume of the solution, into carbon dioxide (and other inorganic compounds), while the BOD is a mass of oxygen, consumed in the process of biological oxidation of organic compounds, present in unit volume of the solution. Since biological oxidation is a long-term process, instead of BOD the notation BOD5 is often used, which means BOD measured after 5 days of biological oxidation. Like TOC, both COD and BOD are expressed in the same units and do not relate to the kind of organic compounds polluting water or wastewater, but rather reflect the total organic matter content and its part that can be degraded in biological processes [6].

The main types of aqueous systems to be purified are considered to be water (from different sources) and wastewater.

#### 2.1. Water

conservation is purification of flue gases and wastewater, and radiation technologies possess a high potential in the direction providing for higher purification degree, unachievable in some

Traditionally, radiation treatment (by gamma/X-rays or accelerated electrons beams) for the purification of water and wastewater is attributed to the so-called Advanced Oxidation Processes (AOPs) and corresponding technologies—to Advanced Oxidation Technologies (AOTs) (see, e.g., books [3, 4]). The reason is that initially new processes, appeared in addition to routine purification processes, such as biological treatment, coagulation, sedimentation, and filtration, have been based on the oxidation of organic impurities by strong oxidizing agent hydroxyl radicals, produced firstly in chemical reactions with participation of hydrogen peroxide, then with the use of physical methods, and irradiation of aqueous systems produces hydroxyl radicals as one of the main intermediates. However, the attribution of radiation treatment to AOPs seems to be not quite correct, since ionizing radiation initiates in irradiated media not only oxidizing processes but also reducing ones. Though the formation of reducing particles under radiolysis, as well as under photolysis, sonolysis, electrolysis, and so on, has been mentioned earlier repeatedly [3–5], the role of reductive processes in the purification of water and wastewater was not considered as specific and important one, partly due to comparatively low importance of the processes in the decomposition of organic compounds.

A significant advantage of radiation-induced processes over other AOPs consists in sufficient knowledge of mechanism of the processes including available qualitative and quantitative data on primary events of energy absorption, intermediates formation ways and properties, and reactions of organic compounds conversions. Nowadays, new research and review articles on radiation treatment are being published which demonstrate high interest to the problem of

The aim of this chapter is to show interrelation between well-established primary radiationchemical processes and the main ways of organic contaminants conversions, as well as to present the current state of radiation equipment being used at present or proposed to be used

The application of radiation technologies to the purification of aqueous systems to a certain extent is determined by a subject of radiation treatment, that is, composition of the system. There are several types of aqueous systems to be purified commercially which differ considerably in qualitative and quantitative composition. The latter is usually expressed either chemically as a concentration of components (in units of moles or mass of the component per volume or mass of solution) or in units characteristic of water/wastewater purification technologies, that is, COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand), and TOC (Total

TOC is determined as the total mass of carbon atoms in dissolved organic compounds per unit

) or in ppm (parts per million, i.e.,

cases by conventional purification technologies.

84 Ionizing Radiation Effects and Applications

environmental application of radiation technologies.

2. Types of aqueous systems to be purified

solution volume and expressed usually in mg/L (mg/dm<sup>3</sup>

Organic Carbon).

in radiation technologies of water and wastewater purification.

Water, consumed in the course of human activity, besides municipal water, that is, water of potable quality offered by water companies, has two natural sources: (1) groundwater, that is, water, seeped through from the surface and present in porous rocks below the surface, shallow wells, or deep aquifers, and (2) surface water, that is, water from a source that is exposed to the environment like rivers, canals, lakes, and open wells [7].

Contamination of water may occur due to following reasons: municipal water—from pipelines, fittings, biofouling; groundwater—due to failing of septic systems, leaking sewer lines, and from land discharge by passage through soils and fissures or interaction with surface water; surface water—by treated wastewater, discharge of raw sewage, municipal wastewater, storm-water runoff, runoff from urban and agricultural areas, also animals and humans are both indirect and direct contributors to the contamination.

The level of water contamination usually is not high to use it for many purposes. Thus, most pristine rivers will have a 5-day carbonaceous BOD below 1 mg/L. Moderately polluted rivers may have a BOD value in the range of 2–8 mg/L. Rivers may be considered severely polluted when BOD values exceed 8 mg/L [8].

Groundwater from depth and confined aquifers is usually microbially safe and chemically stable in the absence of direct contamination; however, shallow or unconfined aquifers can be subject to contamination from discharges or seepages associated with agricultural practices (e.g., pathogens, nitrates, and pesticides), on-site sanitation and sewerage (pathogens and nitrates), and industrial wastes.

Both groundwater and surface water have natural impurities including inorganic salts and, particularly—surface water, NOM (natural organic matter), represented mainly by humic and fulvic acids, cellulose, lignin) which have to be removed, or reduced in concentration, when using the water for drinking purposes [9, 10]. Quality specifications for drinking water are subject of policies, regulations, and standards on both national and international levels [11–14]. Guidelines are being established that determine the limit concentration of chemical compounds contaminating potable water. Now, there are more than 100 compounds for which guideline values have been established (see Table 1, data compiled from [11]).

level appropriate for discharge into environment. Usually, wastewater is divided into two main categories: industrial and municipal or domestic, in accordance with its specific composition. However, amenably to more strict definition adduced in [13]: "Wastewater is liquid waste discharged from homes and other residential premises, commercial and industrial premises and similar sources, to individual disposal systems or to municipal sewer pipes. It contains mainly human excreta and used water. Wastewater collected in municipal sewerage systems is called municipal wastewater or municipal sewage." A similar definition is contained in [17]: "Municipal wastewater originates from domestic, industrial, commercial and institutional sources within a given human settlement or community. Urban wastewater includes both municipal wastewater and urban runoff." It means that industrial wastewater may be regarded as a part of municipal one. Nevertheless, while considering wastewater composition, more useful is to break down wastewater by sources. Table 3 lists the data on

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

From the data of Table 3, it follows that the basic constituent of municipal and domestic wastewater is organic matter, including nutrients, which is substantially biodegradable. Special purification is required to remove pathogenic microorganisms and emerging pollutants. On the contrary, the composition of industrial wastewater differs markedly for different industries (see Table 4), the level of organic contamination is high, and organic matter is often

Impacted rivers and

Table 2. Examples of high detectable concentrations (per liter) of enteric pathogens and fecal indicators in different types

emerging pollutants (e.g., pharmaceuticals, drugs, and endocrine disruptors)

Human excreta (pathogenic microorganisms), nutrients, and organic matter. May also contain

Very wide range of contaminants, such as pathogenic microorganisms, nutrients and organic matter,

Wilderness rivers and

http://dx.doi.org/10.5772/intechopen.72074

87

Groundwater

streams

streams

Campylobacter 20–500 90–2500 0–1100 0–10 Salmonella — 3–1000 1–4 — E. coli (generic) 10,000–1,000,000 30,000–1,000,000 6000–30,000 0–1000 Viruses 1–10 30–60 0–3 0–2 Cryptosporidium 4–290 2–480 2–240 0–1 Giardia 2–30 1–470 1–2 0–1

contamination of wastewater from different sources [17].

Lakes and reservoirs

Typical components

Table 3. Typical components of wastewater from different sources.

heavy metals, and emerging pollutants

Contaminants depend on the kind of industry

almost non-biodegradable.

Pathogen or indicator

of source waters.

Sources of wastewater

Domestic wastewater

Municipal wastewater

Industrial wastewater

group

Guideline values for the chemicals listed in Table 1 are in the range of 10<sup>1</sup> –10<sup>4</sup> mg/L [15], and real contamination of water exceeds these values only in extraordinary cases when special purification is needed.

Much more significant problem of water purification is microbial contamination [11, 15]. Table 2 shows the ranges of microbial contamination of surface and groundwater.

Exact guideline values for microbial contamination are not established, in [15] being just noted that "E. coli or thermotolerant coliform bacteria must not be detectable in any 100 ml sample." However, report [16] quotes data that for tolerable drinking water densities of Enteric virus, Giardia, and Cryptosporidium are equal to 2.2 <sup>10</sup><sup>7</sup> , 6.8 <sup>10</sup><sup>6</sup> , and 1.7 <sup>10</sup><sup>6</sup> per liter, correspondingly. It means that to make water from natural sources drinkable, the concentration of microorganisms should be reduced by more than six orders of magnitude.

So, using water from natural sources for industrial purposes does not require its purification, but using it as potable water requires disinfection and in special cases removal of hazardous contaminants.

#### 2.2. Wastewater


Contamination level of wastewater is much higher than that of water and the goal of wastewater purification, except for the problems of reuse [13], is to reduce contamination down to

Table 1. Contaminants in water for which guideline values have been established (naturally occurring chemicals: As, Ba, B, Cr, F, Mn, Mo, Se, U).

level appropriate for discharge into environment. Usually, wastewater is divided into two main categories: industrial and municipal or domestic, in accordance with its specific composition. However, amenably to more strict definition adduced in [13]: "Wastewater is liquid waste discharged from homes and other residential premises, commercial and industrial premises and similar sources, to individual disposal systems or to municipal sewer pipes. It contains mainly human excreta and used water. Wastewater collected in municipal sewerage systems is called municipal wastewater or municipal sewage." A similar definition is contained in [17]: "Municipal wastewater originates from domestic, industrial, commercial and institutional sources within a given human settlement or community. Urban wastewater includes both municipal wastewater and urban runoff." It means that industrial wastewater may be regarded as a part of municipal one. Nevertheless, while considering wastewater composition, more useful is to break down wastewater by sources. Table 3 lists the data on contamination of wastewater from different sources [17].

contaminating potable water. Now, there are more than 100 compounds for which guideline

and real contamination of water exceeds these values only in extraordinary cases when special

Much more significant problem of water purification is microbial contamination [11, 15].

Exact guideline values for microbial contamination are not established, in [15] being just noted that "E. coli or thermotolerant coliform bacteria must not be detectable in any 100 ml sample." However, report [16] quotes data that for tolerable drinking water densities of Enteric virus,

correspondingly. It means that to make water from natural sources drinkable, the concentra-

So, using water from natural sources for industrial purposes does not require its purification, but using it as potable water requires disinfection and in special cases removal of hazardous

Contamination level of wastewater is much higher than that of water and the goal of wastewater purification, except for the problems of reuse [13], is to reduce contamination down to

, 6.8 <sup>10</sup><sup>6</sup>

–10<sup>4</sup> mg/L [15],

, and 1.7 <sup>10</sup><sup>6</sup> per liter,

Chemicals used in water treatment or materials in

Bromate; Bromodichloromethane; Bromoform; Chloral hydrate; Chlorate; Chlorite; Chloroform; Cyanogen chloride; Dibromoacetonitrile; Dibromochloromethane; Dichloroacetate; Dichloroacetonitrile; Formaldehyde; Monochloroacetate; Trichloroacetate; 2,4,6-Trichlorophenol; Trihalomethanes

Chlorpyrifos; DDT (and metabolites); Pyriproxyfen Organic contaminants from treatment chemicals:

Organic contaminants from pipes and fittings:

contact with drinking water

Monochloramine; Chlorine Disinfection byproducts:

Acrylamide; Epichlorohydrin

Benzopyrene; Vinyl chloride

Disinfectants:

Pesticides:

Table 1. Contaminants in water for which guideline values have been established (naturally occurring chemicals: As, Ba,

values have been established (see Table 1, data compiled from [11]).

Giardia, and Cryptosporidium are equal to 2.2 <sup>10</sup><sup>7</sup>

purification is needed.

86 Ionizing Radiation Effects and Applications

contaminants.

2.2. Wastewater

Chemicals from industrial sources, human dwellings

Benzene; Carbontetrachloride; Di(2-ethylhexyl)phthalate; 1,2-Dichlorobenzene; 1,4-Dichlorobenzene; 1,2-Dichloroethane; 1,1-Dichloroethene; 1,2-Dichloroethene;

Dichloromethane; 1,4-Dioxane; Edetic acid; Ethylbenzene; Hexachlorobutadiene; Nitrilotriacetic acid; Pentachlorophenol; Styrene; Tetrachloroethene; Toluene; Trichloroethene; Xylenes

B, Cr, F, Mn, Mo, Se, U).

Inorganic

Organic

Guideline values for the chemicals listed in Table 1 are in the range of 10<sup>1</sup>

Table 2 shows the ranges of microbial contamination of surface and groundwater.

tion of microorganisms should be reduced by more than six orders of magnitude.

Chemicals from agricultural

Alachlor; Aldicarb; Aldrin and dieldrin; Atrazine; Carbofuran; Chlordane; Chlorotoluron; Cyanazine; 1,2-Dibromo-3-chloropropane; 1,2-Dibromoethane; 1,2-Dichloropropane; 1,3-Dichloropropene; Dichlorprop; Dimethoate; Endrin; Fenoprop; Isoproturon; Lindane; MCPA; Mecoprop; Methoxychlor; Metolachlor; Molinate; Pendimethalin; Simazine; Terbuthylazine;

activities

Cd, Hg, Cyanide Nitrate/nitrite Sb, Cu, Pb, Ni

Trifluralin

From the data of Table 3, it follows that the basic constituent of municipal and domestic wastewater is organic matter, including nutrients, which is substantially biodegradable. Special purification is required to remove pathogenic microorganisms and emerging pollutants. On the contrary, the composition of industrial wastewater differs markedly for different industries (see Table 4), the level of organic contamination is high, and organic matter is often almost non-biodegradable.


Table 2. Examples of high detectable concentrations (per liter) of enteric pathogens and fecal indicators in different types of source waters.


Table 3. Typical components of wastewater from different sources.


3. Principal ways of radiation-induced chemical processes promoting

H, and hydroxyl radicals •

Impurities in water and wastewater are present, as a rule, at relatively very low concentration, except for some kinds of wastewater with very high content of organic compounds. Electron fraction of inorganic and organic substances in ground and surface water, as well as in industrial and municipal/domestic wastewater, usually does not exceed 1%. Since the absorption of ionizing radiation, both electromagnetic one and accelerated electrons in the range of energies 0.5–10 MeV, by a particular component of a mixture, is proportional to the electron fraction of the component, and almost all the radiations are absorbed by water resulting in primary processes of water radiolysis, the products of which (mainly—hydrated electrons

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

dispersed in water. As a whole, the process of water purification with the use of ionizing

In this section, the main processes induced by ionizing radiation, which can be applied to water purification technologies, are discussed together with a brief discussion on the formation and properties of the products of water radiolysis. Most principal reactions of reactive products of water radiolysis with a solute, concerning wastewater treatment by ionizing radiation,

OH) do react with substances dissolved or

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89

aqueous system purification

aq, hydrogen atoms •

radiation is presented in Figure 1.

have been overviewed recently [5].

Figure 1. Main processes of radiation purification of aqueous systems.

e 

Table 4. Wastewater characteristics in some industries (compiled from data of [17]).

The content of organic matter in wastewater from different sources varies, reaching on average up to several grams per liter. Thus, quoted in [18] the mean values for wastewater in France and USA are, respectively, the following: COD—300–1000 and 250–1000, BOD—100–400 and 110–400, suspended solids—150–500 and 100–350, total potash and nitrogen—30100 and 20–85, and total phosphorus—1–25 and 4–15. More than twofold difference between COD and BOD shows that organic matter cannot be removed by biological treatment and additional treatment of wastewater is required.

## 3. Principal ways of radiation-induced chemical processes promoting aqueous system purification

Impurities in water and wastewater are present, as a rule, at relatively very low concentration, except for some kinds of wastewater with very high content of organic compounds. Electron fraction of inorganic and organic substances in ground and surface water, as well as in industrial and municipal/domestic wastewater, usually does not exceed 1%. Since the absorption of ionizing radiation, both electromagnetic one and accelerated electrons in the range of energies 0.5–10 MeV, by a particular component of a mixture, is proportional to the electron fraction of the component, and almost all the radiations are absorbed by water resulting in primary processes of water radiolysis, the products of which (mainly—hydrated electrons e aq, hydrogen atoms • H, and hydroxyl radicals • OH) do react with substances dissolved or dispersed in water. As a whole, the process of water purification with the use of ionizing radiation is presented in Figure 1.

In this section, the main processes induced by ionizing radiation, which can be applied to water purification technologies, are discussed together with a brief discussion on the formation and properties of the products of water radiolysis. Most principal reactions of reactive products of water radiolysis with a solute, concerning wastewater treatment by ionizing radiation, have been overviewed recently [5].

Figure 1. Main processes of radiation purification of aqueous systems.

The content of organic matter in wastewater from different sources varies, reaching on average up to several grams per liter. Thus, quoted in [18] the mean values for wastewater in France and USA are, respectively, the following: COD—300–1000 and 250–1000, BOD—100–400 and 110–400, suspended solids—150–500 and 100–350, total potash and nitrogen—30100 and 20–85, and total phosphorus—1–25 and 4–15. More than twofold difference between COD and BOD shows that organic matter cannot be removed by biological treatment and additional treatment of

11–46 High levels of BOD and SS concentrations; high particulates, some

wastewater is required.

Industry type

Alcohol refining

Beer and malt

Dairy products

Fish processing

Meat and poultry

Organic chemicals

Petroleum refineries

Plastic and resins

Pulp and paper

Starch production

Sugar refining

Vegetable oils

Vegetables and fruits

Wine and vinegar

Wastewater generation, m3

88 Ionizing Radiation Effects and Applications

/ton

Typical content of effluent COD, g/L

2–7

1.5–5.2

~2.5

2–7

0.8–5

0.4–1.6

1–15

0.5–1.2

2–10

0.7–3.0

16–32 High level of BOD and COD 5–22

pH variable due to acid and alkaline cleaning agents; high temperature

plastics, feed-stock materials, byproducts, product material in soluble or particulate form, washing and cleaning agents, solvents, and added-value

phenols and chlorinated hydrocarbons—about 500 different chlorinated organic compounds identified; colored compounds and absorbable organic halogens (AOX); pollutants characterized by BOD, COD,

5–9 BOD, COD, SS, nitrogen, phosphorus—variable by individual processes;

8–18 High levels of BOD and SS concentrations; strong organics, antibiotics, growth hormones, pesticides, and insecticides

8–18 High levels of BOD and SS concentrations; strong organics, antibiotics, growth hormones, pesticides, and insecticides

0–400 Pesticides, pharmaceuticals, paints and dyes, petro-chemicals, detergents,

0.3–1.2 Production of fossil fuels—contamination from oil and gas wells and

85–240 Chlorinated lignosulfonic acids, chlorinated resin acids, chlorinated

suspended solids (SS), toxicity, and color

0.3–1.2 0.8–5

4–18 High levels of BOD and SS concentrations; 1–6

high particulates, some dissolved organics, surfactants;

high particulates, some dissolved organics, surfactants;

Coffee No data High levels of BOD and SS concentrations; 3–15

3–10 Dissolved sugars, proteins, fats, and additive residues; BOD, COD, SS, nitrogen, and phosphorus

products such as plasticizers

fracking; hot cooling water

10–1.5–42 High levels of BOD and SS concentrations;

1–5 High levels of BOD and SS concentrations;

7–35 High levels of BOD and SS concentrations;

Table 4. Wastewater characteristics in some industries (compiled from data of [17]).

dissolved organics, surfactants

#### 3.1. Initial stages of ionizing radiation action on aqueous systems

As it has been mentioned earlier, reactive products of water radiolysis are the initiators of almost all the processes of dissolved or dispersed substance conversion in such aqueous systems as water and wastewater. The mechanism of primary processes in radiolysis of water including ionization and excitation of molecules by ionizing radiation, formation, and subsequent reactions of the products of radiolysis is well established both qualitatively and quantitatively [19–21]. Briefly, it can be described as the following:

3.1.3. "Initial" yields

e �

aq •

3.1.4. Influence of oxygen

After diffusive expansion of "spurs," when the distribution of formed particles becomes nearly uniform, further reactions proceed in the bulk of solution according to the so-called homogeneous kinetics, the concentrations of water radiolysis products being determined by their "initial" radiation-chemical yield—G-value, that is, number of moles of a product formed per

G, μmol/J 0.28 0.06 0.28 <0.01 0.04 0.07 0.33 0.05

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

•OH ! •O� <sup>þ</sup> <sup>H</sup><sup>þ</sup> <sup>p</sup>K<sup>A</sup> <sup>¼</sup> <sup>11</sup>:<sup>9</sup>

•<sup>H</sup> ! <sup>e</sup>�aq <sup>þ</sup> <sup>H</sup><sup>þ</sup> <sup>p</sup>K<sup>A</sup> <sup>¼</sup> <sup>4</sup>:<sup>4</sup>

Mutual reactions of water radiolysis products go on in the bulk of solution as homogeneous

Properties of reactive free-radical products from water and their reactivity to some specific

Chemical properties of reactive radicals determining their reactions with a solute may be

Hydrated electron as a reducing particle is characterized by the following fast reactions of one-

� <sup>k</sup> <sup>¼</sup> <sup>1</sup>:<sup>9</sup> � 1010 L mol�<sup>1</sup> <sup>s</sup>�<sup>1</sup>

OH O H2 H2O2 H3O+ OH�

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91

• <sup>k</sup> ¼ �<sup>2</sup> � 1010 L mol�<sup>1</sup> <sup>s</sup>�<sup>1</sup>

� þ H<sup>þ</sup> pK<sup>A</sup> ¼ 4:7

� þ H<sup>þ</sup> pK<sup>A</sup> ¼ 11:6

1 joule of absorbed energy of ionizing radiation (see Table 5).

Product Reactive No reactive

H •

Table 5. G-values of water radiolysis products at the end of "spur" processes.

<sup>e</sup>�aq <sup>þ</sup> O2 ! •O2

•<sup>H</sup> <sup>þ</sup> O2 ! HO2

HO2

the acid-base equilibriums being established:

3.1.5. Reactions in the bulk of solution

3.1.6. Chemical properties of reactive radicals

presented as the following:

In the presence of dissolved oxygen, the following fast reactions take place:

• ! •O2

H2O2 ! HO2

ones (see Table 6), competing thereby with their reactions with a solute.

functional groups in organic compounds are listed in Tables 7 and 8.

electron transfer from its hydrated state to a molecule/ion in

#### 3.1.1. Energy absorption

Ionizing radiation, such as electromagnetic one (gamma or X-rays) and accelerated electrons in the range of energies 0.5–10 MeV, is absorbed in the liquid medium by portions of near 30 eV in small volumes (referred to as "spurs") separated by about 100 nm. Because of high local concentration of reacting species formed in "spurs," their reactions with each other are weakly influenced by a solute.

#### 3.1.2. Primary processes

Primary processes of ionizing radiation interaction with water molecules include

Excitation and ionization of water molecules, decay of singlet excited states, and primary particles formation (≤10�<sup>14</sup> s).

$$\mathrm{H\_2O} \longrightarrow \mathrm{H\_2O^\*}$$

$$\mathrm{H\_2O} \longrightarrow \mathrm{e^-} + \mathrm{H\_2O^+}$$

$$\mathrm{H\_2O^\*} \longrightarrow \mathrm{"{H}+ \text{"OH}}$$

$$\mathrm{H\_2O^\*} \longrightarrow \mathrm{H\_2} + \mathrm{O}$$

Formation of hydrated electrons e� aq, relaxation of ionized molecules of water (≤10�<sup>12</sup> s)

$$\begin{aligned} \text{e}^- &\longrightarrow \text{e}^- \xrightarrow{} \text{e}^- \xrightarrow{} \text{e}^- \text{aq} \\\\ \text{H}\_2\text{O}^+ + \text{H}\_2\text{O} &\longrightarrow \text{H}\_3\text{O}^+ + \text{"OH} \end{aligned}$$

Main reactions of formed particles in "spurs" (≤10�<sup>7</sup> s)

<sup>e</sup>�aq <sup>þ</sup> H3O<sup>þ</sup> ! •<sup>H</sup> <sup>þ</sup> H2O •<sup>H</sup> <sup>þ</sup> •<sup>H</sup> ! H2 •<sup>H</sup> <sup>þ</sup> •OH ! H2O •OH <sup>þ</sup> •OH ! H2O2 <sup>e</sup>�aq <sup>þ</sup> •OH ! OH�


Table 5. G-values of water radiolysis products at the end of "spur" processes.

#### 3.1.3. "Initial" yields

3.1. Initial stages of ionizing radiation action on aqueous systems

tatively [19–21]. Briefly, it can be described as the following:

3.1.1. Energy absorption

90 Ionizing Radiation Effects and Applications

influenced by a solute.

3.1.2. Primary processes

particles formation (≤10�<sup>14</sup> s).

Formation of hydrated electrons e�

Main reactions of formed particles in "spurs" (≤10�<sup>7</sup> s)

As it has been mentioned earlier, reactive products of water radiolysis are the initiators of almost all the processes of dissolved or dispersed substance conversion in such aqueous systems as water and wastewater. The mechanism of primary processes in radiolysis of water including ionization and excitation of molecules by ionizing radiation, formation, and subsequent reactions of the products of radiolysis is well established both qualitatively and quanti-

Ionizing radiation, such as electromagnetic one (gamma or X-rays) and accelerated electrons in the range of energies 0.5–10 MeV, is absorbed in the liquid medium by portions of near 30 eV in small volumes (referred to as "spurs") separated by about 100 nm. Because of high local concentration of reacting species formed in "spurs," their reactions with each other are weakly

Excitation and ionization of water molecules, decay of singlet excited states, and primary

H2O ! H2O<sup>∗</sup>

H2O ! <sup>e</sup>� <sup>þ</sup> H2O<sup>þ</sup> H2O<sup>∗</sup> ! •<sup>H</sup> <sup>þ</sup> •OH

H2O<sup>∗</sup> ! H2 <sup>þ</sup> <sup>O</sup>

<sup>e</sup>� ! <sup>e</sup>�therm ! <sup>e</sup>�aq

H2O<sup>þ</sup> <sup>þ</sup> H2O ! H3O<sup>þ</sup> <sup>þ</sup> •OH

<sup>e</sup>�aq <sup>þ</sup> H3O<sup>þ</sup> ! •<sup>H</sup> <sup>þ</sup> H2O

•<sup>H</sup> <sup>þ</sup> •<sup>H</sup> ! H2

•<sup>H</sup> <sup>þ</sup> •OH ! H2O

•OH <sup>þ</sup> •OH ! H2O2

<sup>e</sup>�aq <sup>þ</sup> •OH ! OH�

aq, relaxation of ionized molecules of water (≤10�<sup>12</sup> s)

Primary processes of ionizing radiation interaction with water molecules include

After diffusive expansion of "spurs," when the distribution of formed particles becomes nearly uniform, further reactions proceed in the bulk of solution according to the so-called homogeneous kinetics, the concentrations of water radiolysis products being determined by their "initial" radiation-chemical yield—G-value, that is, number of moles of a product formed per 1 joule of absorbed energy of ionizing radiation (see Table 5).

#### 3.1.4. Influence of oxygen

In the presence of dissolved oxygen, the following fast reactions take place:

$$\text{e}^-\text{aq} + \text{O}\_2 \xrightarrow{- \text{ }\text{ }\text{ }\text{O}\_2\text{-} \qquad k = 1.9 \times 10^{10} \text{ L mol}^{-1} \text{ s}^{-1}$$

$$\text{ }\text{"H} + \text{O}\_2 \xrightarrow{- \text{ }\text{ }\text{ }\text{HO}\_2\text{-} \qquad k = \sim 2 \times 10^{10} \text{ L mol}^{-1} \text{ s}^{-1}$$

the acid-base equilibriums being established:

$$\begin{aligned} \bullet \text{OH} &\longlongleftrightarrow \text{"O}^- + \text{H}^+ & \text{p} \text{K}\_\text{A} &= 11.9 \\ \text{HO}\_2^- &\longlongleftrightarrow \text{"O}\_2^- + \text{H}^+ & \text{p} \text{K}\_\text{A} &= 4.7 \\ \end{aligned}$$

$$\begin{aligned} \text{H}\_2\text{O}\_2 &\longlongleftrightarrow \text{HO}\_2^- + \text{H}^+ & \text{p} \text{K}\_\text{A} &= 11.6 \\ \end{aligned}$$

$$\begin{aligned} \text{(}^\bullet \text{H} &\longlongleftrightarrow \text{"}\_\text{aq} + \text{H}^+ \text{)} & \qquad \text{p} \text{K}\_\text{A} &= 4.4 \end{aligned}$$

#### 3.1.5. Reactions in the bulk of solution

Mutual reactions of water radiolysis products go on in the bulk of solution as homogeneous ones (see Table 6), competing thereby with their reactions with a solute.

Properties of reactive free-radical products from water and their reactivity to some specific functional groups in organic compounds are listed in Tables 7 and 8.

#### 3.1.6. Chemical properties of reactive radicals

Chemical properties of reactive radicals determining their reactions with a solute may be presented as the following:

Hydrated electron as a reducing particle is characterized by the following fast reactions of oneelectron transfer from its hydrated state to a molecule/ion in


• Organic compounds with

low –, and very low – –).

metal cations, etc.);

bons, aromatic compounds.

organic compounds.

following types:

• Addition reactions to a double bond (•

• benzene ring in aromatic compounds;

Functional group e

(including aromatic) hydrocarbons.

• heteroatomic double or triple bonds (carbonyl, nitro, nitrile);

Hydrogen atom reacts with the solute in the following types of reactions:

• some strong oxidizing inorganic anions, like CrO4

• Reactions of H-atom abstraction from saturated carbon (•

cations in acid solutions, for example, H• + Fe2+ (+H+

• Reduction reactions (one-electron transfer H• + Mn+/� ! <sup>H</sup><sup>+</sup> + M(n�1)+/�) with

• thiol, disulfide, halide, nitro functional groups in both saturated and unsaturated

� aq •

Saturated carbon >CH2 �� + ++ Amine �NH2 �� �� ++ Unsaturated carbon in: Alkenes >C=C< �� ++ ++ Nitro �NO2 ++ + � �

Nitrile �C�N + �� + Chloro �Cl + � �� Carbonyl >C=O ++ �� + Bromo �Br ++ + �� Carboxylic acids �C(OH) = O + �� + Iodo �I ++ ++ + Ester �C(OR) = O + �� + Thiol �SH ++ + ++ Amide �C(NH2)=O + �� + Disulfide �S�S� ++ + ++

Table 8. Reactivity of radicals from water to some specific functional groups in organic compounds (high ++, medium +,

H •

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

Aromatics >C=C< �� ++ ++ Hydroxy >CHOH �� + ++ Azines >C=N– ++ + ++ Ether –O– �� + ++

OH Functional group e

� aq •

http://dx.doi.org/10.5772/intechopen.72074

H • OH 93

• majority of metal cations (however, low reactivity to Cd2+, Zn2+, some rare-earth

• disulfide, iodo, bromo, nitro functional groups, and benzene ring in organic compounds.

Reactions of the last type are formally the oxidizing ones. Also, H-atom can oxidize metal

Hydroxyl radical is a strong oxidizer and reacts with the solute in oxidizing reactions of the

• all transition metal cations in lower oxidation state, majority of inorganic anions;

• Direct oxidation reactions (one-electron transfer), including those ones with

• benzene ring in aromatic compounds and some functional groups;

H + > C=C< ! >CH–•

) ! H2 + Fe3+.

<sup>2</sup>�, Cr2O7

<sup>2</sup>�, MnO4

H + > CH– ! H2 + > •

�;

C<) in unsaturated hydrocar-

C–) in any

Table 6. Homogeneous reactions in the bulk of solution.


Table 7. Properties of radicals from water.

	- all the metal cations, except for cations of alkaline and alkali-earth metals;
	- majority of oxygen-containing and other complex anions, like NO2 �, NO3 �, CrO4 2�, Cr2O7 <sup>2</sup>�, MnO4 �, Fe(CN)6 <sup>3</sup>�, and so on (low reactivity to SO4 <sup>2</sup>�, ClO4 �, CO3 <sup>2</sup>�, and some others).

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous… http://dx.doi.org/10.5772/intechopen.72074 93


Table 8. Reactivity of radicals from water to some specific functional groups in organic compounds (high ++, medium +, low –, and very low – –).

• Organic compounds with

• Inorganic compounds with

Table 7. Properties of radicals from water.

some others).

<sup>2</sup>�, MnO4

Reaction k, L mol�<sup>1</sup> s

92 Ionizing Radiation Effects and Applications

e �

e �

e �

e � aq + HO2

e � aq + •

e � aq + e �

e � aq + •

e � aq + •

e � aq + HO2

e � aq + • O2

•

•

• OH + HO2

•

• OH + •

• OH + •

• OH + HO2

• OH + • O2

OH + H2 ! •

OH + H2O2 ! HO2

OH + OH� ! •

� ! • O2

O� ! HO2

Optical absorption band:

Partial molar volume, m<sup>3</sup>

Diffusion coefficient D, m2

Standard redox potential E <sup>0</sup>

εmax, m2

aq + H2O ! •

aq + H3O+ ! •

aq + H2O2 ! •

� ! •

• ! HO2

� ! 2 HO2

Hydrated electrons Hydrogen atoms

H + OH� 19 •

H+H2O 2.3 � <sup>10</sup><sup>10</sup> •

OH + OH� 1.1 � <sup>10</sup><sup>10</sup> •

<sup>O</sup>� + OH� 3.5 � <sup>10</sup><sup>9</sup> •

OH ! OH� 3.0 � <sup>10</sup><sup>10</sup> Oxide radical ions

� 1.5 � <sup>10</sup><sup>10</sup> •

� 1.3 � <sup>10</sup><sup>10</sup> •

• + H2O 2.7 � <sup>10</sup><sup>7</sup> •

<sup>O</sup>� + H2O 1.3 � <sup>10</sup><sup>10</sup> HO2

� ~2 � <sup>10</sup><sup>10</sup> 2 HO2

e �

H+H2O 4.2 � <sup>10</sup><sup>7</sup> •

OH ! H2O2 <sup>7</sup> � <sup>10</sup><sup>9</sup> (2 <sup>k</sup>) (•

• ! O2 + H2O 6 � <sup>10</sup><sup>9</sup> HO2

� ! O2 + OH� <sup>8</sup> � <sup>10</sup><sup>9</sup> <sup>2</sup> •

Table 6. Homogeneous reactions in the bulk of solution.

<sup>H</sup> ! H2 + OH� 2.5 � <sup>10</sup><sup>10</sup> •

aq ! H2 + 2 OH� <sup>5</sup> � <sup>10</sup><sup>9</sup> (2 <sup>k</sup>) •

<sup>O</sup>� ! 2 OH� 2.2 � <sup>10</sup><sup>10</sup> •

Hydroxyl radicals •

�, Fe(CN)6

Cr2O7

• all the metal cations, except for cations of alkaline and alkali-earth metals;

<sup>3</sup>�, and so on (low reactivity to SO4

/mol <sup>7</sup>�10�<sup>6</sup> <sup>4</sup>�10�<sup>6</sup> <sup>6</sup>�10�<sup>6</sup> <sup>8</sup>�10�<sup>6</sup>

/s <sup>5</sup>�10�<sup>9</sup> <sup>7</sup>�10�<sup>9</sup> <sup>2</sup>�10�<sup>9</sup> <sup>1</sup>�10�<sup>9</sup>

, V �2.87 �2.3 1.9 1.7

�, NO3

�, CO3

<sup>2</sup>�, ClO4

�<sup>1</sup> Reaction k, L mol�<sup>1</sup> s

OH + H2 10

OH + H2O 9 � <sup>10</sup><sup>7</sup>

<sup>H</sup> ! H2 1.2 � <sup>10</sup><sup>10</sup> (2 <sup>k</sup>)

OH ! H2O 7 � <sup>10</sup><sup>9</sup>

aq + H2O 2.2 � <sup>10</sup><sup>7</sup>

OH + OH� 1.8 � <sup>10</sup><sup>6</sup>

� + H2O ~5 � <sup>10</sup><sup>8</sup>

� + OH� <sup>4</sup> � <sup>10</sup><sup>8</sup>

� 3.6 � <sup>10</sup><sup>9</sup>

� ! 2 OH� + O2 <sup>6</sup> � <sup>10</sup><sup>8</sup>

OH + H2O+O2 ~1

OH + OH� + O2) ~1

� + O2 8.9 � <sup>10</sup><sup>7</sup>

OH •

• ! H2O2 + O2 7.6 � <sup>10</sup><sup>5</sup>

� + OH� + O2 0.3

H + OH� <sup>8</sup> � <sup>10</sup><sup>7</sup>

OH) ~1 � <sup>10</sup><sup>10</sup>

H+H2O ! •

H+H2O2 ! •

H + OH� ! e

H + •

H + •

H + HO2

<sup>O</sup>� + H2O ! •

<sup>O</sup>� + H2 ! •

O� + HO2

O� + • O2

O2

• + • O2 � ! HO2

O2 �! HO2

� + H2O 7.5 � <sup>10</sup><sup>9</sup> Perhydroxyl/superoxide radical anions

aq •

Charge �10 0 �1

λmax, nm 720 <188 235 240

/mol 1850 <160 60 ~30 W1/2, eV 0.85 — ~1.5 1.5–2

<sup>O</sup>� + H2O2 ! •

O� + O2 ! O3

• + H2O2 ! •

� + H2O2 ! •

�

• ! H2O2 (2 •

O2

H •

� ! • O2

�, CrO4

2�,

�1

<sup>2</sup>�, and

O�

• majority of oxygen-containing and other complex anions, like NO2


Hydrogen atom reacts with the solute in the following types of reactions:

	- majority of metal cations (however, low reactivity to Cd2+, Zn2+, some rare-earth metal cations, etc.);
	- some strong oxidizing inorganic anions, like CrO4 <sup>2</sup>�, Cr2O7 <sup>2</sup>�, MnO4 �;
	- disulfide, iodo, bromo, nitro functional groups, and benzene ring in organic compounds.

Reactions of the last type are formally the oxidizing ones. Also, H-atom can oxidize metal cations in acid solutions, for example, H• + Fe2+ (+H+ ) ! H2 + Fe3+.

Hydroxyl radical is a strong oxidizer and reacts with the solute in oxidizing reactions of the following types:

	- all transition metal cations in lower oxidation state, majority of inorganic anions;
	- benzene ring in aromatic compounds and some functional groups;

• Addition reactions to a double bond (• OH + > C=C< ! >C(OH)–• C<) in unsaturated hydrocarbons, aromatic compounds;

important because of two main reasons: oxygen converts reducing radicals (e

ent compounds, the elimination of one carbon atom demands three to six radicals •

or wastewater), rather than model solutions prepared with purified water.

process of radiation treatment of that kind promising for implementation.

treatment in combined purification processes.

3.3. Conversion of organic molecules and elimination of functional groups

conversion of one molecule of initial compound occurs under the action of just one to two radicals. Maximal yields of mineralization, like quoted earlier, are reached at sufficient concentration of dissolved oxygen that requires some time aerating the solution during irradiation [27]. Also, it has been noted repeatedly (see, e.g., [24, 28–31]) that the presence of inorganic anions, such as Cl,

, reduces the yield of mineralization, mainly due to scavenging the •

decrease in Gminer takes place when subjects of radiation treatment are real aqueous systems (water

In spite of low values of Gminer, experimental data obtained (see, e.g., a review [32]) indicate that absorbed doses of several kilograys are sufficient to remove some hazardous pollutants, like pharmaceutical and personal care products, from contaminated water where the concentration of the pollutants is usually of the order of tens to hundreds μmol/L. It makes the

Transformations in molecules of organic substance occurring under the action of active products of water radiolysis often play an important role in the purification of water and wastewater, even if TOC at that time changes slightly or does not change at all. It is of importance when the goal of "purification" is not to just remove organic compounds but to eliminate some unwanted properties of wastewater, like color, odor, toxicity, infection, or to increase the efficiency of further

The process of polluted water/wastewater disinfection consists in the suppression of vital activity of microorganisms. Breaks occurred in the helix of DNA under direct or indirect (via

the formation of carboxyl group. However, in the absence of dissolved oxygen complete decomposition of organic compounds also takes place while the yield of the process is much lower.

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

The degree of organic compounds mineralization in aqueous solutions upon the action of ionizing radiation can be easily controlled by TOC measurements. As TOC is a mass of all carbon atoms in organic matter, the yield of decarbonization (or mineralization) Gminer, expressed in moles of eliminated carbon atoms per 1 kGy of absorbed dose D, is Gminer = (1/12)dTOC/dD. It makes it possible to compare radiation-chemical yield of carbon elimination with that of initial organic compound degradation Gdegr, as well as with the yields of radical products from water GR, being initiators of degradation process. In the absence of radiation-induced chain processes, always the following inequation is right G<sup>R</sup> > Gdegr > Gminer. Numerous experimental data concerning various organic compounds destruction under irradiation confirm this relationship. Thus, from the data of recent researches it follows that the values of Gdegr and Gminer for irradiation of some organic compounds solutions equals, respectively, for 2-naphthalenesulfonate [22]: 0.14 and 0.08, for monuron [23]: 0.15 and 0.08, for amphetamine [24]: 0.33 and 0.06, for phenol [25]: 0.25 and 0.05, for ibuprofen [26]: 0.25 and 0.05 μmol/J. Low yields of mineralization (0.05–0.08 μmol/J) compared to the yield of OH radicals (0.28 μmol/J) show that in different mechanisms ofradiation-induced conversions of differ-

) and attaches itself to carbon-centered radicals, providing thereby

oxidizing ones (•

HCO3

, HSO4

3.3.1. Disinfection

O2

, HO2 • aq, •

http://dx.doi.org/10.5772/intechopen.72074

OH, while the

OH radicals. A

H) into

95

• Reactions of H-atom abstraction from saturated carbon (• OH + > CH– ! H2O+> • C–) in any organic compounds.

Kinds of the reactions of e� aq, • H, and • OH, listed in subdivision 3.1.6, determine the ways of conversions of compounds present in an aqueous system which are considered subsequently in this section.

#### 3.2. Complete mineralization of organic compounds

In principle, every organic compound in aqueous solution can be transformed into stable inorganic substances, such as CO2 and H2O, and, if other elements are present, also into ammonium, nitrogen and sulfur oxides, halogenides, and so on, under sufficient absorbed dose of ionizing radiation, the process being called "mineralization." Because of very high energy demand, this process is hardly applicable in practice to significantly reduce the amount of organic matter in a wastewater. However, it may be successfully used to remove hazardous pollutants from wastewater when their concentrations are relatively low.

Radiation-induced process of any organic compound destruction includes C–C bonds rupture reactions (it is necessary in the case of cyclic/aromatic compounds) and consecutive reactions of terminal carbon atom oxidation into carboxyl group followed by decarboxylation, that is, elimination of the atom in the form of CO2. A simplified scheme of the process looks like this:

(a) Rapture of C–C bond (opening the ring).

$$\underbrace{\text{C}\_{\text{n}}}\_{\text{C}\_{\text{n}}} \text{-CH} \xrightarrow[\text{H}^{\text{2}} \text{ (H}^{\text{2}}\text{O})]{} \text{-C}^{\text{2}} \text{ } \text{C}^{\text{2}} \text{ } \text{-C} \xrightarrow{} \text{C}\_{\text{n}} - \text{C}\_{\text{n}}$$

(b) Oxidation (by O2 attachment) and decarboxylation.

$$\text{c}\_{\text{n}}-\overset{\text{l}}{\underset{\text{l}}{\text{c}}} \xrightarrow{\text{o}\_{2}} \text{c}\_{\text{n}}-\overset{\text{l}}{\underset{\text{l}}{\text{co}}} \text{co}^{\text{}} \xrightarrow[\text{н}\_{2}\text{O}^{\bullet}]{\text{co}} \text{c}\_{\text{n}}-\overset{\text{l}}{\underset{\text{l}}{\text{c}}} \text{c}-\overset{\text{l}}{\text{c}}-\text{o} \xrightarrow{\text{l}} \text{c}\_{\text{n}}-\overset{\text{l}}{\underset{\text{l}}{\text{c}}} \text{c}+\text{co}\_{2}; \text{ co}\_{2}^{\text{}} + \text{"OH} \xrightarrow{\text{s}} \text{OH} + \text{Co}\_{2}$$

$$\text{c}\_{\text{n-T}}\overset{\big|\text{}}{\underset{\big|}{\rightleftharpoons}}\text{c}\_{\text{n-T}}\overset{\big|\text{}}{\underset{\big|}{\text{cov}}}\text{c}\_{\text{n-T}}\overset{\big|\text{}}{\underset{\big|}{\rightleftharpoons}}\text{c}\_{\text{n-T}}\overset{\big|\text{}}{\underset{\big|}{\rightleftharpoons}}\text{c}\_{\text{n-T}}\overset{\big|\text{}}{\underset{\big|}{\rightleftharpoons}}\text{c}\_{\text{n-T}}\overset{\big|}{\underset{\big|}{\rightleftharpoons}}\text{c}\_{\text{n-T}}\overset{\big|}{\text{c}} + \text{CO}\_2\text{; }\text{CO}\_2\text{; }\text{-OH}\overset{\bigleftarrow}{\longrightarrow}\text{OH}^\cdot + \text{CO}\_2^\cdot$$

$$\text{C}\_{\text{n-2}} \rightarrow \text{C}\_{\text{n-3}} + \text{CO}\_2 \text{ etc.}$$

In reality, the mechanism of mineralization is much more complicated, especially for aromatic and heteroatomic compounds, but anyway it is a multistage one, and the more composite is organic compound, the more energy it takes to mineralize it completely. Since the process of mineralization proceeds essentially via oxidation reactions, the presence of dissolved oxygen is important because of two main reasons: oxygen converts reducing radicals (e aq, • H) into oxidizing ones (• O2 , HO2 • ) and attaches itself to carbon-centered radicals, providing thereby the formation of carboxyl group. However, in the absence of dissolved oxygen complete decomposition of organic compounds also takes place while the yield of the process is much lower.

The degree of organic compounds mineralization in aqueous solutions upon the action of ionizing radiation can be easily controlled by TOC measurements. As TOC is a mass of all carbon atoms in organic matter, the yield of decarbonization (or mineralization) Gminer, expressed in moles of eliminated carbon atoms per 1 kGy of absorbed dose D, is Gminer = (1/12)dTOC/dD. It makes it possible to compare radiation-chemical yield of carbon elimination with that of initial organic compound degradation Gdegr, as well as with the yields of radical products from water GR, being initiators of degradation process. In the absence of radiation-induced chain processes, always the following inequation is right G<sup>R</sup> > Gdegr > Gminer. Numerous experimental data concerning various organic compounds destruction under irradiation confirm this relationship. Thus, from the data of recent researches it follows that the values of Gdegr and Gminer for irradiation of some organic compounds solutions equals, respectively, for 2-naphthalenesulfonate [22]: 0.14 and 0.08, for monuron [23]: 0.15 and 0.08, for amphetamine [24]: 0.33 and 0.06, for phenol [25]: 0.25 and 0.05, for ibuprofen [26]: 0.25 and 0.05 μmol/J. Low yields of mineralization (0.05–0.08 μmol/J) compared to the yield of OH radicals (0.28 μmol/J) show that in different mechanisms ofradiation-induced conversions of different compounds, the elimination of one carbon atom demands three to six radicals • OH, while the conversion of one molecule of initial compound occurs under the action of just one to two radicals. Maximal yields of mineralization, like quoted earlier, are reached at sufficient concentration of dissolved oxygen that requires some time aerating the solution during irradiation [27]. Also, it has been noted repeatedly (see, e.g., [24, 28–31]) that the presence of inorganic anions, such as Cl, HCO3 , HSO4 , reduces the yield of mineralization, mainly due to scavenging the • OH radicals. A decrease in Gminer takes place when subjects of radiation treatment are real aqueous systems (water or wastewater), rather than model solutions prepared with purified water.

In spite of low values of Gminer, experimental data obtained (see, e.g., a review [32]) indicate that absorbed doses of several kilograys are sufficient to remove some hazardous pollutants, like pharmaceutical and personal care products, from contaminated water where the concentration of the pollutants is usually of the order of tens to hundreds μmol/L. It makes the process of radiation treatment of that kind promising for implementation.

#### 3.3. Conversion of organic molecules and elimination of functional groups

Transformations in molecules of organic substance occurring under the action of active products of water radiolysis often play an important role in the purification of water and wastewater, even if TOC at that time changes slightly or does not change at all. It is of importance when the goal of "purification" is not to just remove organic compounds but to eliminate some unwanted properties of wastewater, like color, odor, toxicity, infection, or to increase the efficiency of further treatment in combined purification processes.

#### 3.3.1. Disinfection

• Addition reactions to a double bond (•

hydrocarbons, aromatic compounds;

any organic compounds.

94 Ionizing Radiation Effects and Applications

Kinds of the reactions of e�

in this section.

• Reactions of H-atom abstraction from saturated carbon (•

H, and •

conversions of compounds present in an aqueous system which are considered subsequently

In principle, every organic compound in aqueous solution can be transformed into stable inorganic substances, such as CO2 and H2O, and, if other elements are present, also into ammonium, nitrogen and sulfur oxides, halogenides, and so on, under sufficient absorbed dose of ionizing radiation, the process being called "mineralization." Because of very high energy demand, this process is hardly applicable in practice to significantly reduce the amount of organic matter in a wastewater. However, it may be successfully used to remove hazardous pollutants from waste-

Radiation-induced process of any organic compound destruction includes C–C bonds rupture reactions (it is necessary in the case of cyclic/aromatic compounds) and consecutive reactions of terminal carbon atom oxidation into carboxyl group followed by decarboxylation, that is, elimination of the atom in the form of CO2. A simplified scheme of the process looks like this:

Cn�<sup>2</sup> ! Cn�<sup>3</sup> þ CO2, etc:

In reality, the mechanism of mineralization is much more complicated, especially for aromatic and heteroatomic compounds, but anyway it is a multistage one, and the more composite is organic compound, the more energy it takes to mineralize it completely. Since the process of mineralization proceeds essentially via oxidation reactions, the presence of dissolved oxygen is

aq, •

3.2. Complete mineralization of organic compounds

water when their concentrations are relatively low.

(b) Oxidation (by O2 attachment) and decarboxylation.

(a) Rapture of C–C bond (opening the ring).

OH + > C=C< ! >C(OH)–•

C<) in unsaturated

C–) in

OH + > CH– ! H2O+> •

OH, listed in subdivision 3.1.6, determine the ways of

The process of polluted water/wastewater disinfection consists in the suppression of vital activity of microorganisms. Breaks occurred in the helix of DNA under direct or indirect (via radicals from water) action of radiation, destroying the ability of the cell to reproduce itself and resulting in microbe inactivation. As interaction of ionizing particle or active radical with any DNA molecule is an accidental event, the dependence of a number of living cells N per unit volume on absorbed dose D during irradiation is exponential:

of ionizing radiation on clofibric acid solutions the total toxicity of the solutions at the beginning of irradiation sharply increases with increasing the dose and then decreases together with a decrease in the total content of organic matter [35]. Possible occurrence of two opposite radiolytic processes: detoxification of initial compound and formation of new toxic compounds, requires, when using radiation detoxification, taking into account real composition

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

Many kinds of wastewater, especially that of textile and dyeing industry, are colored due to contamination with organic dyes. Composite molecules of dyes include chromophore group, that is, system of conjugated double bonds, responsible for the ability of the molecule to absorb electromagnetic radiation in the visible region of spectrum, that is, light. It is enough to destroy just chromophore group, not a whole molecule, to make the molecule incapable of light absorp-

easily attached to a double bond (see subdivision 3.1.6) destroying the conjugated bonds system

<sup>e</sup>�aq <sup>þ</sup> <sup>&</sup>gt; <sup>C</sup> <sup>¼</sup> <sup>C</sup> <sup>&</sup>lt; <sup>þ</sup>H<sup>þ</sup> ð Þ ! <sup>&</sup>gt; CH–•<sup>C</sup> <sup>&</sup>lt;

•<sup>H</sup> <sup>þ</sup> <sup>&</sup>gt; <sup>C</sup> <sup>¼</sup> <sup>C</sup> <sup>&</sup>lt; ! <sup>&</sup>gt; CH–•<sup>C</sup> <sup>&</sup>lt;

•OH <sup>þ</sup> <sup>&</sup>gt; <sup>C</sup> <sup>¼</sup> <sup>C</sup> <sup>&</sup>lt; ! <sup>&</sup>gt; C OH ð Þ–•<sup>C</sup> <sup>&</sup>lt;

The yield of decolorization, if only those reactions occurred, should be as high as 0.6 μmol/J corresponding to the total yield of all initial radicals from water. However, the occurrence of reduction-oxidation reactions of the latter resulted in the formation of two kinds of dye radicals:

hydrogen transfer between two kinds of dye radicals, partial reparation of dye molecules. As a result, decolorization yields for aqueous solutions of soluble organic dyes, as a rule, are equal to 0.1–0.3 μmol/J, depending on the structure of dye (for disperse dyes, which are water-insoluble and form aqueous dispersions, the yield is lower because of impediments to radical penetration into dye particulates) [37, 38]. The yield of decolorization decreases with increasing absorbed dose, since the rate constants of radicals' reactions with original dye molecules and with the products of dye degradation are of the same order; so while the concentration of the latter increases during irradiation, the fraction of radicals being spent in reactions with those products also increases, reducing thereby the fraction of radicals required for "decolorization" of the original dye molecules. In real wastewater, which contains, besides dye, rather high amounts of organic matter, decolorization yield is decreased due to competition of other organics for reactive radicals from water. Nevertheless, recently published results on radiation treatment of real wastewater from dyeing and textile industry [39] show that doses of several kilograys provide for suffi-

Biological treatment of wastewater with activated sludge is still the basic commercially applied method applied for the removal of great amount of organic matter from wastewater. However,

H, another in reaction of •

H and •

http://dx.doi.org/10.5772/intechopen.72074

OH, makes it possible, by electron and/or

OH, are

97

tion and, thereby, to decolorize the dye. Hydrated electrons, as well as radicals •

of water/wastewater to be treated in every particular case.

3.3.3. Decolorization

one in reaction of e�

aq and •

cient decolorization of the wastewater.

3.3.4. Improvement of biological treatment

$$N = N\_0 \cdot \mathbf{e}^{-\lambda D}; \ \ln\left(N\_0/N\right) = \lambda D\_r$$

where N<sup>0</sup> is the initial number of living cells and λ—inactivation constant depending on the kind of microorganism and irradiation conditions. In practice, to assess the efficiency of radiation disinfection, instead of λ, the value D<sup>10</sup> is used which means the dose demanded to reduce the initial concentration of living cells by a factor of 10 and relates to λ as: D<sup>10</sup> = ln10/λ ffi 2.3/λ.

Database [33] contains more than 1000 values of D<sup>10</sup> measured to date. Typical values of D<sup>10</sup> for different types of microorganisms are in the range of 0.4–1.3 kGy. That is why radiation sterilization of medical equipment, cosmetics, and so on is widely used, becoming a developed branch of industry. The application of radiation treatment for the sterilization of water and wastewater is undoubtedly effective, rather easily realized and has no objections, but one: high costs of ionizing radiation sources, which restrain its implementation at present.

#### 3.3.2. Detoxification

Toxicity of many organic compounds is attributable to any specific functional groups, for example, halogenide-, nitrate-, sulfide groups, and some other, attached to hydrocarbon moiety, elimination of which decreases the toxicity sharply. Among the most widespread toxic pollutions, there are chlorine derivatives, the major constituent of "red list substances" [17]. Also, nitro groups attached to aliphatic or aromatic compounds increase the toxicity of the compound. One of the most effective radiation-induced processes of such functional groups detachment is the so-called dissociative electron attachment with the participation of hydrated electron or hydrogen atom:

$$\text{R-Cl} + \text{e}^- \xrightarrow{} \text{R}^\bullet + \text{Cl}^- \text{, or } \text{R-Cl} + \text{ }^\bullet \text{H} \xrightarrow{} \text{R}^\bullet + \text{Cl}^- + \text{H}^+$$

A clear example of such process is consecutive dechlorination of pentachlorobiphenyl [34] which occurs under reductive conditions, that is, in the absence of dissolved oxygen and other scavengers of e� aq and • H. The yield of the process is close to summarized yield of e� aq and • H, that is, rather high. A similar process takes place in organic sulfides and nitro compounds:

$$\text{R-SH} + \text{e}^- \xrightarrow[\text{aq}^-]{} \text{R}^+ + \text{SH}^+, \text{or} \\ \text{R-SH} + \text{ }^\bullet \text{H} \xrightarrow{\longrightarrow \text{R}^\bullet} \text{R}^+ + \text{SH}^+ + \text{H}^+$$

$$\text{R-NO}\_2 + \text{e}^- \xrightarrow[\text{aq}^-]{} \text{R}^+ + \text{NO}\_2^-, \text{or} \\ \text{R-NO}\_2 + \text{}^\bullet \text{H} \xrightarrow[\text{s}]{} \text{R}^+ + \text{NO}\_2^- + \text{H}^+$$

The yield of the latter is lower because of the longer life time of intermediate radical anions R–NO2 •– which partially disproportionate. Lower yield is also characteristic of dechlorination by • OH radicals which, nevertheless, does occur [35].

It is necessary to keep in mind, however, that besides elimination of toxic groups, conversion of composite organic compounds upon irradiation may be realized in the formation of some products, toxicity of which is higher than that of initial compound [36]. Thus, under the action of ionizing radiation on clofibric acid solutions the total toxicity of the solutions at the beginning of irradiation sharply increases with increasing the dose and then decreases together with a decrease in the total content of organic matter [35]. Possible occurrence of two opposite radiolytic processes: detoxification of initial compound and formation of new toxic compounds, requires, when using radiation detoxification, taking into account real composition of water/wastewater to be treated in every particular case.

#### 3.3.3. Decolorization

radicals from water) action of radiation, destroying the ability of the cell to reproduce itself and resulting in microbe inactivation. As interaction of ionizing particle or active radical with any DNA molecule is an accidental event, the dependence of a number of living cells N per unit

<sup>N</sup> <sup>¼</sup> <sup>N</sup><sup>0</sup> � <sup>e</sup>–λD; ln ð Þ¼ <sup>N</sup>0=<sup>N</sup> <sup>λ</sup>D,

where N<sup>0</sup> is the initial number of living cells and λ—inactivation constant depending on the kind of microorganism and irradiation conditions. In practice, to assess the efficiency of radiation disinfection, instead of λ, the value D<sup>10</sup> is used which means the dose demanded to reduce the initial concentration of living cells by a factor of 10 and relates to λ as: D<sup>10</sup> = ln10/λ ffi 2.3/λ.

Database [33] contains more than 1000 values of D<sup>10</sup> measured to date. Typical values of D<sup>10</sup> for different types of microorganisms are in the range of 0.4–1.3 kGy. That is why radiation sterilization of medical equipment, cosmetics, and so on is widely used, becoming a developed branch of industry. The application of radiation treatment for the sterilization of water and wastewater is undoubtedly effective, rather easily realized and has no objections, but one: high

Toxicity of many organic compounds is attributable to any specific functional groups, for example, halogenide-, nitrate-, sulfide groups, and some other, attached to hydrocarbon moiety, elimination of which decreases the toxicity sharply. Among the most widespread toxic pollutions, there are chlorine derivatives, the major constituent of "red list substances" [17]. Also, nitro groups attached to aliphatic or aromatic compounds increase the toxicity of the compound. One of the most effective radiation-induced processes of such functional groups detachment is the so-called disso-

ciative electron attachment with the participation of hydrated electron or hydrogen atom:

<sup>R</sup>–Cl <sup>þ</sup> <sup>e</sup>�aq!R• <sup>þ</sup> Cl�, or R–Cl <sup>þ</sup> •<sup>H</sup>!R• <sup>þ</sup> Cl� <sup>þ</sup> <sup>H</sup><sup>þ</sup>

A clear example of such process is consecutive dechlorination of pentachlorobiphenyl [34] which occurs under reductive conditions, that is, in the absence of dissolved oxygen and other

H, that is, rather high. A similar process takes place in organic sulfides and nitro compounds:

The yield of the latter is lower because of the longer life time of intermediate radical anions

It is necessary to keep in mind, however, that besides elimination of toxic groups, conversion of composite organic compounds upon irradiation may be realized in the formation of some products, toxicity of which is higher than that of initial compound [36]. Thus, under the action

•– which partially disproportionate. Lower yield is also characteristic of dechlorination

H. The yield of the process is close to summarized yield of e�

, or R–SH <sup>þ</sup> •<sup>H</sup>!R• <sup>þ</sup> SH– <sup>þ</sup> <sup>H</sup><sup>þ</sup>

�, or R–NO2 <sup>þ</sup> •<sup>H</sup>!R• <sup>þ</sup> NO2

aq and

� þ H<sup>þ</sup>

costs of ionizing radiation sources, which restrain its implementation at present.

volume on absorbed dose D during irradiation is exponential:

3.3.2. Detoxification

96 Ionizing Radiation Effects and Applications

scavengers of e�

•

R–NO2

by •

aq and •

<sup>R</sup>–SH <sup>þ</sup> <sup>e</sup>�aq!R• <sup>þ</sup> SH–

OH radicals which, nevertheless, does occur [35].

<sup>R</sup>–NO2 <sup>þ</sup> <sup>e</sup>�aq!R• <sup>þ</sup> NO2

Many kinds of wastewater, especially that of textile and dyeing industry, are colored due to contamination with organic dyes. Composite molecules of dyes include chromophore group, that is, system of conjugated double bonds, responsible for the ability of the molecule to absorb electromagnetic radiation in the visible region of spectrum, that is, light. It is enough to destroy just chromophore group, not a whole molecule, to make the molecule incapable of light absorption and, thereby, to decolorize the dye. Hydrated electrons, as well as radicals • H and • OH, are easily attached to a double bond (see subdivision 3.1.6) destroying the conjugated bonds system

$$\text{CH}\_{\text{aq}} + > \text{C}=\text{C}<(+\text{H}^{+}) \xrightarrow{\quad} > \text{CH-}\text{"C}<\text{C}<\text{CH-}"$$

$$\text{\textasciicircum}\text{"OH} + > \text{C}=\text{C}<\xrightarrow{\quad} > \text{CH-}\text{"C}<\text{C}<\text{CH-}"$$

$$\text{\textasciicircum}\text{"OH} + > \text{C}=\text{C}<\xrightarrow{\quad} > \text{C}(\text{OH}) - \text{"C}<\text{C}<\text{CH-}"$$

The yield of decolorization, if only those reactions occurred, should be as high as 0.6 μmol/J corresponding to the total yield of all initial radicals from water. However, the occurrence of reduction-oxidation reactions of the latter resulted in the formation of two kinds of dye radicals: one in reaction of e� aq and • H, another in reaction of • OH, makes it possible, by electron and/or hydrogen transfer between two kinds of dye radicals, partial reparation of dye molecules. As a result, decolorization yields for aqueous solutions of soluble organic dyes, as a rule, are equal to 0.1–0.3 μmol/J, depending on the structure of dye (for disperse dyes, which are water-insoluble and form aqueous dispersions, the yield is lower because of impediments to radical penetration into dye particulates) [37, 38]. The yield of decolorization decreases with increasing absorbed dose, since the rate constants of radicals' reactions with original dye molecules and with the products of dye degradation are of the same order; so while the concentration of the latter increases during irradiation, the fraction of radicals being spent in reactions with those products also increases, reducing thereby the fraction of radicals required for "decolorization" of the original dye molecules.

In real wastewater, which contains, besides dye, rather high amounts of organic matter, decolorization yield is decreased due to competition of other organics for reactive radicals from water. Nevertheless, recently published results on radiation treatment of real wastewater from dyeing and textile industry [39] show that doses of several kilograys provide for sufficient decolorization of the wastewater.

#### 3.3.4. Improvement of biological treatment

Biological treatment of wastewater with activated sludge is still the basic commercially applied method applied for the removal of great amount of organic matter from wastewater. However, many organic compounds which wastewater often contains are not biodegradable, that is, are not "eatable" by microorganisms of sludge. Moreover, some compounds are toxic for those microorganisms, "killing" them and, thereby, reducing the activity of sludge in biodegradation process.

•M'

refractory organic pollutant as polyvinyl alcohol [46].

compounds removal.

•OH <sup>þ</sup> NO2

phase and filtration or sorption:

e�aq •

Radicals •

e�aq •

Since •

presence of •

3.5. Oxidation-reduction processes in inorganic compound solutions

� ! OH� þ NO2

Mn <sup>þ</sup> •M'

Mn or• ð Þ! <sup>R</sup> products;

the polymerization rate during irradiation being proportional to the square root of dose rate and average polymer chain length—inversely proportional to the square root of dose rate.

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

The conversion of soluble or slightly soluble molecules of monomers/oligomers into insoluble polymer upon irradiation makes it possible to apply the process of radiation polymerization to the removal of monomer impurities which are often present in wastewater of chemical and textile industries. However, because of a decrease in polymer length with increasing the dose rate using electron-beam irradiation of high intensity reduces the effectiveness of the process. Nevertheless, combined radiation-induced processes of decomposition and polymerization were shown to be quite effective in the purification of aqueous systems from such typical

The application of radiation treatment to change mineral composition of water or wastewater is rarely considered to be an efficient one. Nevertheless, several radiation induces reductiveoxidative reaction of inorganic compounds may be used in the processes of inorganic toxic

oxidation state and majority of inorganic anions (see subdivision 3.1.6.3". It may be applied to convert, for example, toxic nitrite anions present in water/wastewater into less toxic nitrate anions:

Hydrated electrons and hydrogen atoms as strong reducing agents reduce majority of metal cations and oxygen-containing anions (see subdivisions 3.1.6.1 and 3.1.6.2). That process was tested in the conversion of highly toxic Cr(VI) ions into much less toxic Cr(III) ions [47] in reactions:

as well as in the removal of heavy metals, like cadmium [48] and lead [49] from aqueous system by reducing metal cations to metal atoms with subsequent sedimentation of solid

radiation-flotation process based on radiation-induced reductive-oxidative reaction of Hg has

Aqueous dispersions are very sensitive to the action of ionizing radiation, which may either increase stability of such systems or initiate coagulation even at rather low-absorbed doses.

been implemented to remove mercury from wastewater of hydrolysis works [50].

3.6. Processes of micelles recharging in aqueous dispersions

ð Þþ H Cr VI ð Þ! Cr VðÞþH<sup>þ</sup> ð Þ; 2Cr Vð Þ! Cr VI ð Þþ Cr IVð Þ; 2 Cr IVð Þ! Cr Vð Þþ Cr III ð Þ

ð Þþ H Cd II ð Þ! Cd IðÞ þH<sup>þ</sup> ð Þ; 2Cd IðÞ! Cd II ð Þþ Cd 0ð Þ; nCd 0ð Þ! Cdn↓

OH radicals oxidize reduced cations backward, the process becomes efficient in the

OH radicals scavengers, like formates, sulfides, sulfites, and so on. Combined

•; 2NO2

OH possessing high oxidation potential oxidizes all transition metal cations in lower

• ð Þ! <sup>þ</sup>H2O NO3

� þ NO2

� þ2H<sup>þ</sup> ð Þ

http://dx.doi.org/10.5772/intechopen.72074

99

Radiation-induced elimination of functional groups, as well as other kinds of molecule fragmentation, makes non-biodegradable organic compounds biodegradable and increases biodegradability of poorly biodegradable compounds. Also, the decomposition of toxic for microorganism compounds under irradiation improves biological treatment. Recently published results [40, 41] demonstrated that upon irradiation an increase in biodegradability of organic matter was observed without a significant decrease in the Total Organic Carbon. However, it should be mentioned that radiation treatment may have insignificant effect on biodegradability of wastewater with high amount of biodegradable organic matters as it has been observed on real textile and dyeing wastewater [42]. In that case, radiation treatment was much more effective when applied after biological treatment.

#### 3.3.5. Improvement of settling and sorption

A combination of organic radicals formed in organic compound reaction with any active radicals from water results in the formation of more complex molecules. Due to further increase in molecules' size, the formation of solid phase becomes possible, especially, it is characteristic of natural organic matter. The formation and aggregation of small particulates of organic matter facilitates subsequent processes of sedimentation, filtration, and sorption. Thus, it has been found [43] that electron-beam treatment of river water contaminated, mainly, with NOM, significantly decreases the color index and the amount of suspended solids and improves water quality. A dose of several kilograys was found to be sufficient for decreasing the color index to a maximum permissible value even in the most unfavorable seasons (spring and autumn). Moreover, irradiation accelerated the sedimentation of suspended solids by a factor of 50–100, as compared with non-irradiated water. The precipitate formed upon irradiation captures impurities present in water; this process along with the radiolytic decomposition of impurities resulted in water purification.

#### 3.4. Radiation polymerization

Polymerization of monomers', or oligomers', molecules in aqueous solutions under the action of ionizing radiation is initiated by primary products of water radiolysis, both radicals and ions [44, 45]. Accordingly, the process of polymerization may correspond to either a free-radical or an ionic (cationic or anionic) mechanism. Since primary anion-radicals and cation-radicals, as well as carbanions and carbocations, are very unstable in aqueous media, free-radical mechanism of polymerization usually prevails. It includes stages of

chain initiation (reaction of primary radical with a monomer molecule M).

$$\mathbf{^\bullet R} + \mathbf{M} \to \mathbf{^\bullet M};$$

chain propagation (increase in chain length):

$$\text{\textbullet \text{\textbullet\text{\textbullet}} + \text{M} \rightarrow \text{\textbullet M\textbullet} \text{\textbullet M\textbullet m} + \text{M} \rightarrow \text{\textbullet M\textbullet m} + \text{\textbullet}}$$

chain termination (radicals disappearance by combination or disproportionation).

•M' Mn <sup>þ</sup> •M' Mn or• ð Þ! <sup>R</sup> products;

the polymerization rate during irradiation being proportional to the square root of dose rate and average polymer chain length—inversely proportional to the square root of dose rate.

The conversion of soluble or slightly soluble molecules of monomers/oligomers into insoluble polymer upon irradiation makes it possible to apply the process of radiation polymerization to the removal of monomer impurities which are often present in wastewater of chemical and textile industries. However, because of a decrease in polymer length with increasing the dose rate using electron-beam irradiation of high intensity reduces the effectiveness of the process. Nevertheless, combined radiation-induced processes of decomposition and polymerization were shown to be quite effective in the purification of aqueous systems from such typical refractory organic pollutant as polyvinyl alcohol [46].

#### 3.5. Oxidation-reduction processes in inorganic compound solutions

many organic compounds which wastewater often contains are not biodegradable, that is, are not "eatable" by microorganisms of sludge. Moreover, some compounds are toxic for those microorganisms, "killing" them and, thereby, reducing the activity of sludge in biodegradation process. Radiation-induced elimination of functional groups, as well as other kinds of molecule fragmentation, makes non-biodegradable organic compounds biodegradable and increases biodegradability of poorly biodegradable compounds. Also, the decomposition of toxic for microorganism compounds under irradiation improves biological treatment. Recently published results [40, 41] demonstrated that upon irradiation an increase in biodegradability of organic matter was observed without a significant decrease in the Total Organic Carbon. However, it should be mentioned that radiation treatment may have insignificant effect on biodegradability of wastewater with high amount of biodegradable organic matters as it has been observed on real textile and dyeing wastewater [42]. In that case, radiation treatment

A combination of organic radicals formed in organic compound reaction with any active radicals from water results in the formation of more complex molecules. Due to further increase in molecules' size, the formation of solid phase becomes possible, especially, it is characteristic of natural organic matter. The formation and aggregation of small particulates of organic matter facilitates subsequent processes of sedimentation, filtration, and sorption. Thus, it has been found [43] that electron-beam treatment of river water contaminated, mainly, with NOM, significantly decreases the color index and the amount of suspended solids and improves water quality. A dose of several kilograys was found to be sufficient for decreasing the color index to a maximum permissible value even in the most unfavorable seasons (spring and autumn). Moreover, irradiation accelerated the sedimentation of suspended solids by a factor of 50–100, as compared with non-irradiated water. The precipitate formed upon irradiation captures impurities present in water; this process along

Polymerization of monomers', or oligomers', molecules in aqueous solutions under the action of ionizing radiation is initiated by primary products of water radiolysis, both radicals and ions [44, 45]. Accordingly, the process of polymerization may correspond to either a free-radical or an ionic (cationic or anionic) mechanism. Since primary anion-radicals and cation-radicals, as well as carbanions and carbocations, are very unstable in aqueous media, free-radical mecha-

•<sup>R</sup> <sup>þ</sup> <sup>M</sup> ! •M'

M;… •M'

chain termination (radicals disappearance by combination or disproportionation).

;

Mn <sup>þ</sup> <sup>M</sup> ! •M'

Mnþ<sup>1</sup>

was much more effective when applied after biological treatment.

with the radiolytic decomposition of impurities resulted in water purification.

chain initiation (reaction of primary radical with a monomer molecule M).

nism of polymerization usually prevails. It includes stages of

•M' <sup>þ</sup> <sup>M</sup> ! •M'

chain propagation (increase in chain length):

3.3.5. Improvement of settling and sorption

98 Ionizing Radiation Effects and Applications

3.4. Radiation polymerization

The application of radiation treatment to change mineral composition of water or wastewater is rarely considered to be an efficient one. Nevertheless, several radiation induces reductiveoxidative reaction of inorganic compounds may be used in the processes of inorganic toxic compounds removal.

Radicals • OH possessing high oxidation potential oxidizes all transition metal cations in lower oxidation state and majority of inorganic anions (see subdivision 3.1.6.3". It may be applied to convert, for example, toxic nitrite anions present in water/wastewater into less toxic nitrate anions:

$$\text{\textbullet }\text{\textbullet NO} + \text{NO}\_2\text{\textbullet }\rightarrow \text{OH}^- + \text{NO}\_2^- ; 2\text{NO}\_2^- \text{\textbullet } (+\text{H}\_2\text{O}) \rightarrow \text{NO}\_3^- + \text{NO}\_2^- \text{\textbullet } (+2\text{H}^+) \text{}$$

Hydrated electrons and hydrogen atoms as strong reducing agents reduce majority of metal cations and oxygen-containing anions (see subdivisions 3.1.6.1 and 3.1.6.2). That process was tested in the conversion of highly toxic Cr(VI) ions into much less toxic Cr(III) ions [47] in reactions:

$$\text{e}^-\text{aq}^-(\text{H}) + \text{Cr}(\text{VI}) \rightarrow \text{Cr}(\text{V}) \,(+\text{H}^+) ; 2\text{Cr}(\text{V}) \rightarrow \text{Cr}(\text{VI}) + \text{Cr}(\text{IV}) ; 2\text{Cr}(\text{IV}) \rightarrow \text{Cr}(\text{V}) + \text{Cr}(\text{III}) ;$$

as well as in the removal of heavy metals, like cadmium [48] and lead [49] from aqueous system by reducing metal cations to metal atoms with subsequent sedimentation of solid phase and filtration or sorption:

$$\text{Fe}^{\cdot}\text{\text{aq} (}^{\bullet}\text{H)} + \text{Cd}(\text{II}) \rightarrow \text{Cd}(\text{I}) \,(+\text{H}^{+}); 2\text{Cd}(\text{I}) \rightarrow \text{Cd}(\text{II}) + \text{Cd}(\text{0}); \text{nCd}(\text{0}) \rightarrow \text{Cd}\_{\text{n}}\downarrow$$

Since • OH radicals oxidize reduced cations backward, the process becomes efficient in the presence of • OH radicals scavengers, like formates, sulfides, sulfites, and so on. Combined radiation-flotation process based on radiation-induced reductive-oxidative reaction of Hg has been implemented to remove mercury from wastewater of hydrolysis works [50].

#### 3.6. Processes of micelles recharging in aqueous dispersions

Aqueous dispersions are very sensitive to the action of ionizing radiation, which may either increase stability of such systems or initiate coagulation even at rather low-absorbed doses.

One of the main reasons for coagulation is recharging the micelles by interaction with shortlived products of water radiolysis. Thus, negatively charged micelles preferably interact with positively charged or uncharged intermediates, participating, for example, in reactions of protonation by H+ ions or electron transfer to • OH and HO2 • radical:

sources of such radiation may be divided into two principal groups: radioactive isotopes (radionuclides) and accelerating techniques. With the help of the latter, both ion beams and electromagnetic radiation (X-rays) may be generated. All the ionizing radiation sources intended for commercial application must meet the following major requirements: be safe for environment, provide for sufficient depth of irradiation, and absorbed dose. Now, three kinds of sources are applied in radiation processing including radiation treatment of aqueous sys-

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Radiation sources based on only two γ-emitting isotopes were used in radiation technologies.

Radioisotope Cs-137 is produced by separation from other fission products formed in nuclear reactors. It decays with a half-life of 30.17 years, emitting beta-rays with energy of 0.51 MeV and gamma-rays with energy of 0.667 MeV; the product of Cs-137 decay is stable isotope of barium (Ba-137). In radiation sources isotope Cs-137 is used in the form of cesium chloride salt

Radioisotope Co-60 is produced in nuclear reactors by bombardment of stable isotope Co-59 with neutrons. It decays with a half-life of 5.27 years, emitting beta-rays with energy of 0.32 MeV and gamma-rays with energies of 1.173 and 1.332 MeV (mean gamma-rays energy of 1.25 MeV); the product of Co-60 decay is a stable isotope of nickel (Ni-60). In radiation

where I is the intensity of gamma radiation (I0—initial intensity), l—passed length (l1/2—length of half-attenuation), and μ—linear coefficient of attenuation which depends on radiation quanta energy and on medium density. In aqueous systems, values of l1/2 for cesium and cobalt gamma-radiations equal, respectively, 8 and 11 cm [19], differing due to difference in the

Because of high penetration of gamma-rays gamma-emitting sources must be shielded from environment with a sufficient thick wall of dense material which is usually lead (in compact sources) or concrete (normally near 2 m in thickness, in industrial irradiation facilities). Major components of an industrial facility include irradiation room, shielded storage room (dry or wet) for the radiation source rack, source hoist mechanism, radiation shield surrounding the irradiation room, control console (room), feed system for a product to be irradiated, shielding

When being used in the radiation treatment of aqueous systems, gamma sources, although,

• Radiation from the source is emitted spherically in all directions, so a part of it is wasted,

maze, control and safety interlock system, and supporting service equipment [52].

meet the requirement of irradiation depth, possess significant disadvantages:

reducing thereby power efficiency of the source.

; lgð Þ¼ I0=I μl; l<sup>1</sup>=<sup>2</sup> ¼ lg2=μ ffi 0:7=μ

tems: radioisotope sources, X-ray generators, and electron accelerators.

sources, radioisotope Co-60 is used in the form of metal slugs or pellets.

<sup>I</sup> <sup>¼</sup> <sup>I</sup><sup>0</sup> � <sup>e</sup>�μ<sup>l</sup>

While penetrating a medium, gamma radiation is attenuated exponentially:

There are radioisotopes of cesium (Cs-137) and cobalt (Co-60).

4.1. Isotope sources

encapsulated in a metal shell.

energy of radiation.

$$\begin{array}{c} \text{Mic}^{\text{n-}} + \text{H}^{+} \rightarrow \text{MicH}^{(\text{n-}1)-} \\\\ \text{Mic}^{\text{n-}} + \text{"OH} \rightarrow \text{Mic}^{(\text{n-}1)-} + \text{OH}^{-} \\\\ \text{Mic}^{\text{n-}} + \text{HO}\_{2}^{\bullet} \rightarrow \text{Mic}^{(\text{n-}1)-} + \text{HO}\_{2}^{-} \end{array}$$

Appearing misbalance in charges of nucleus and outer shell of micelle can promote consecutive combination with other micelles:

$$\text{Im }\mathbf{Mic}\_{\mathbf{m}}{}^{\mathfrak{n}-} + \mathbf{Mic}^{(\mathfrak{n}-1)-} \to \mathbf{Mic}\_{\mathfrak{m}+1}{}^{(\mathfrak{m}+\mathfrak{n}-1)-}$$

and, finally, the formation of large aggregates settling down from the solution. A similar situation takes place with positively charged micelles, in which positive outer-shell charge is reduced by interaction with hydrated electrons and/or hydrogen atoms:

$$\text{Mic}^{\text{n}+} + \text{e}^{-} \text{ aq } (^{\bullet}\text{H}) \rightarrow \text{MicH}^{(\text{n}-1)+} \text{ (+H}^{+}) \text{ }$$

There exists, however, another source of influence on charged micelles, which is only characteristic of electron-beam irradiation unlike irradiation with gamma or X-rays. The most distinguishing feature of irradiation by electrons under condition of their complete absorption in irradiated medium consists in the accumulation of uncompensated charge due to incident electrons. These electrons after dissipation of their energy in the processes of ionization (thereby, equal quantities of oppositely charged particles arise) and excitation are finally thermalized and localized in aqueous medium giving rise to the formation of e� aq, which carry excess negative charge. Fraction of e� aq formed by deceleration of incident electrons is low relative to e� aq formed by ionization (for 0.7 MeV electrons it is about 0.05%), and their role in radiation-induced oxidationreduction processes is negligible. However, while e� aq themselves have very short lifetime because of high reactivity, additional charge can be eliminated only by diffusion of anions to vial walls and discharging into environment, which courses relatively slow. Therefore, stationary concentration of uncompensated negative charge during irradiation may be sufficiently high to have an influence on coagulation process by stabilizing negative micelles. It was observed recently [51] in experiments concerning coagulation of humic acids and lignin in aqueous dispersions.

## 4. Ionizing radiation sources for radiation technologies of aqueous system treatment

Ionizing radiation includes electromagnetic radiation of wavelength shorter than 10�<sup>7</sup> m and accelerated ions with kinetic energy higher than lowest ionization energy of molecules, that is, near 10 eV (neutron radiation is often referred to as ionizing one, but neutrons themselves do not interact with electron shells of molecules, ionization by neutrons being indirect). All the sources of such radiation may be divided into two principal groups: radioactive isotopes (radionuclides) and accelerating techniques. With the help of the latter, both ion beams and electromagnetic radiation (X-rays) may be generated. All the ionizing radiation sources intended for commercial application must meet the following major requirements: be safe for environment, provide for sufficient depth of irradiation, and absorbed dose. Now, three kinds of sources are applied in radiation processing including radiation treatment of aqueous systems: radioisotope sources, X-ray generators, and electron accelerators.

#### 4.1. Isotope sources

One of the main reasons for coagulation is recharging the micelles by interaction with shortlived products of water radiolysis. Thus, negatively charged micelles preferably interact with positively charged or uncharged intermediates, participating, for example, in reactions of

Mic<sup>n</sup>– <sup>þ</sup> <sup>H</sup><sup>þ</sup> ! MicHð Þ <sup>n</sup>�<sup>1</sup> –

Mic<sup>n</sup>� <sup>þ</sup> •OH ! Micð Þ� <sup>n</sup>�<sup>1</sup> <sup>þ</sup> OH�

Appearing misbalance in charges of nucleus and outer shell of micelle can promote consecu-

and, finally, the formation of large aggregates settling down from the solution. A similar situation takes place with positively charged micelles, in which positive outer-shell charge is

There exists, however, another source of influence on charged micelles, which is only characteristic of electron-beam irradiation unlike irradiation with gamma or X-rays. The most distinguishing feature of irradiation by electrons under condition of their complete absorption in irradiated medium consists in the accumulation of uncompensated charge due to incident electrons. These electrons after dissipation of their energy in the processes of ionization (thereby, equal quantities of oppositely charged particles arise) and excitation are finally thermalized and localized in

aq formed by deceleration of incident electrons is low relative to e�

ionization (for 0.7 MeV electrons it is about 0.05%), and their role in radiation-induced oxidation-

because of high reactivity, additional charge can be eliminated only by diffusion of anions to vial walls and discharging into environment, which courses relatively slow. Therefore, stationary concentration of uncompensated negative charge during irradiation may be sufficiently high to have an influence on coagulation process by stabilizing negative micelles. It was observed recently [51] in experiments concerning coagulation of humic acids and lignin in aqueous dispersions.

Ionizing radiation includes electromagnetic radiation of wavelength shorter than 10�<sup>7</sup> m and accelerated ions with kinetic energy higher than lowest ionization energy of molecules, that is, near 10 eV (neutron radiation is often referred to as ionizing one, but neutrons themselves do not interact with electron shells of molecules, ionization by neutrons being indirect). All the

4. Ionizing radiation sources for radiation technologies of aqueous

m Micm<sup>n</sup>– <sup>þ</sup> Micð Þ� <sup>n</sup>�<sup>1</sup> ! Micmþ<sup>1</sup>

Micn� <sup>þ</sup> HO2

reduced by interaction with hydrated electrons and/or hydrogen atoms:

Mic<sup>n</sup><sup>þ</sup> <sup>þ</sup> <sup>e</sup>�aq •

aqueous medium giving rise to the formation of e�

reduction processes is negligible. However, while e�

Fraction of e�

system treatment

OH and HO2

• ! Micð Þ� <sup>n</sup>�<sup>1</sup> <sup>þ</sup> HO2

ð Þ! <sup>H</sup> MicHð Þþ <sup>n</sup>�<sup>1</sup> <sup>þ</sup>H<sup>þ</sup> ð Þ

• radical:

�

ð Þ mþn�1 –

aq, which carry excess negative charge.

aq themselves have very short lifetime

aq formed by

protonation by H+ ions or electron transfer to •

100 Ionizing Radiation Effects and Applications

tive combination with other micelles:

Radiation sources based on only two γ-emitting isotopes were used in radiation technologies. There are radioisotopes of cesium (Cs-137) and cobalt (Co-60).

Radioisotope Cs-137 is produced by separation from other fission products formed in nuclear reactors. It decays with a half-life of 30.17 years, emitting beta-rays with energy of 0.51 MeV and gamma-rays with energy of 0.667 MeV; the product of Cs-137 decay is stable isotope of barium (Ba-137). In radiation sources isotope Cs-137 is used in the form of cesium chloride salt encapsulated in a metal shell.

Radioisotope Co-60 is produced in nuclear reactors by bombardment of stable isotope Co-59 with neutrons. It decays with a half-life of 5.27 years, emitting beta-rays with energy of 0.32 MeV and gamma-rays with energies of 1.173 and 1.332 MeV (mean gamma-rays energy of 1.25 MeV); the product of Co-60 decay is a stable isotope of nickel (Ni-60). In radiation sources, radioisotope Co-60 is used in the form of metal slugs or pellets.

While penetrating a medium, gamma radiation is attenuated exponentially:

$$I = I\_0 \cdot \mathbf{e}^{-\mu l}; \lg(I\_0/I) = \mu l; l\_{1/2} = \lg 2/\mu \cong 0.7/\mu$$

where I is the intensity of gamma radiation (I0—initial intensity), l—passed length (l1/2—length of half-attenuation), and μ—linear coefficient of attenuation which depends on radiation quanta energy and on medium density. In aqueous systems, values of l1/2 for cesium and cobalt gamma-radiations equal, respectively, 8 and 11 cm [19], differing due to difference in the energy of radiation.

Because of high penetration of gamma-rays gamma-emitting sources must be shielded from environment with a sufficient thick wall of dense material which is usually lead (in compact sources) or concrete (normally near 2 m in thickness, in industrial irradiation facilities). Major components of an industrial facility include irradiation room, shielded storage room (dry or wet) for the radiation source rack, source hoist mechanism, radiation shield surrounding the irradiation room, control console (room), feed system for a product to be irradiated, shielding maze, control and safety interlock system, and supporting service equipment [52].

When being used in the radiation treatment of aqueous systems, gamma sources, although, meet the requirement of irradiation depth, possess significant disadvantages:

• Radiation from the source is emitted spherically in all directions, so a part of it is wasted, reducing thereby power efficiency of the source.

• Radiation from the source is emitted continuously with constant intensity, so it is not easy to switch off and on irradiation promptly and to change the dose rate.

Also, both efficiency of electron beam conversion into X-ray beam and photon energy of X-rays are increased with increasing the energy of accelerated electrons. However, electron accelerators with energy higher than 7.5 MeV are forbidden to application in industry because of the

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While being a prosperous competitor to radioisotope sources in many kinds of radiation processing (recent comparisons have shown that the capital costs and electric power costs for accelerators with electron energies of 5.0–7.0 MeV can be lower than the capital costs and source replenishment costs for cobalt-60 source loadings greater than 2.0 MCi [55]), X-ray generators, nevertheless, are not suitable for aqueous systems treatment. The reason is that in spite of capability to irradiate rather a thick layer of condensed media, the energy efficiency of X-ray generators is very low. At present, they are not proposed to be used in the field of

Among all accelerators of charged particles, only accelerators of electrons are suitable to application in radiation processing (excluding ion accelerators used in ion implantation industries). Chemical consequences of accelerated electrons action on many substances, including aqueous media, are almost the same as those of gamma and X-rays. The difference is in the depth of penetration. While the intensity of electromagnetic radiation (both gamma and X-rays) in a medium is attenuated exponentially with path length, accelerated electrons have limited penetration depth which depends on their energy. In Table 10, the penetration of

Principal characteristics of electron accelerators, important for industrial application, are energy of accelerated electrons E<sup>e</sup> (or "accelerator energy") and beam power We, which is defined as E<sup>e</sup> multiplied by electron beam current Ie: W<sup>e</sup> = E<sup>e</sup>Ie. While E<sup>e</sup> determines the range of electrons in irradiated medium, that is, the depth of electron beam penetration, W<sup>e</sup> determines the productivity of irradiation process. Market cost of accelerators is near proportional to their energy and to the square root of power. It is accepted in radiation processing to divide electron accelerators according to accelerator energy into three groups: 1—low-energy units (E<sup>e</sup> < 0.5 MeV), 2—mid-energy units (0.5 MeV < E<sup>e</sup> < 5.0 MeV), and 3—high-energy units (5.0 < E<sup>e</sup> < 10 MeV), maximum energy of 10 MeV being set for industrial accelerators to avoid

Two types of accelerator design have found industrial acceptance in the high-energy area (5.0–10 MeV): microwave linear accelerators (linacs) and the radiofrequency accelerator Rhodotron®. Now industrial linacs are produced by companies: Getinge Linac (formerly Linac Technologies), Budker Institute of Nuclear Physics, L-3 Communications Pulse

Cs-137 Co-60 0.5 MeV 1 MeV 2 MeV 5 MeV 10 MeV 8 11 0.2 0.4 0.8 2.3 4.7

Table 10. Depth of half attenuation for gamma radiation and penetration depth for accelerated electrons in cm (the data

gamma radiation is compared with that of accelerated electrons of different energies.

danger of activating the matter under irradiation.

environment conservation.

4.3. Electron accelerators

problems of induced radioactivity.

from [19]).

Gamma radiation Accelerated electrons

• Gamma sources have relatively low power; thus, the source of such high activity as 1 MCi (3.7 1016 Bq) has a power just near 10 kW. It makes gamma sources inapplicable for the treatment of aqueous systems at high flow rates.

Nowadays, Co-60 gamma sources are applied, as a rule, to reveal the mechanisms of processes in systems to be irradiated, to disinfect sewage sludge, and to develop technologies of some processes. Cs-137 gamma sources are presently not used for solving environmental problems including radiation treatment of water/wastewater.

#### 4.2. X-ray sources

Both γ-rays and X-rays are electromagnetic radiation and differ by the principle of formation. While γ-rays are emitted in the process of energy transition from excited to ground state of a nucleus, X-rays are emitted by accelerated electrons when they pass near to atomic nuclei and are deflected by their electric fields, the effect being called bremsstrahlung. Contrary to γ-rays with defined energy, X-rays produced in this manner have a continuous spectrum of photon energies extending from about 30 keV up to a maximum energy equal to the kinetic energy of the incident electron. For example, with a 5-MeV electron, the most probable photon energy is about 300 keV, the average photon energy is near 1.0 MeV, while the maximum photon energy is 5.0 MeV. The X-ray intensity increases with the electron energy and beam current and with the atomic number of the target material [53].

Two kinds of X-ray sources are produced and used commercially: X-ray tubes (or Roentgen tubes) and X-ray generators, based on electron accelerators. The former have relatively low photons energy and low power. Because of this X-ray tubes are almost not applied in radiation processing, being widely applied in medicine, material and structure analysis, and for industrial inspection.

X-ray generators are powerful analog of gamma sources. A comparison of those two kinds of electromagnetic radiation sources has been made in [54]. A distinguishing characteristic of X-ray generators is ameliorating the parameters of generated electromagnetic radiation with increasing the energy of incident electrons. Thus, while at relatively low electron energies X-rays are emitted in all directions, with electron energies higher than 2.0 MeV the X-ray emission in the direction of the incident electron beam becomes prevailing. Further increase in electrons energy results in decreasing the angular dispersion of the X-ray beam: divergence measured at half of the maximum intensity (HMI) is reduced two times when increasing electrons energy from 5 to 10 MeV (see Table 9).


Table 9. Parameters of generated electromagnetic radiation depending on electron beam energy (the data from [55]).

Also, both efficiency of electron beam conversion into X-ray beam and photon energy of X-rays are increased with increasing the energy of accelerated electrons. However, electron accelerators with energy higher than 7.5 MeV are forbidden to application in industry because of the danger of activating the matter under irradiation.

While being a prosperous competitor to radioisotope sources in many kinds of radiation processing (recent comparisons have shown that the capital costs and electric power costs for accelerators with electron energies of 5.0–7.0 MeV can be lower than the capital costs and source replenishment costs for cobalt-60 source loadings greater than 2.0 MCi [55]), X-ray generators, nevertheless, are not suitable for aqueous systems treatment. The reason is that in spite of capability to irradiate rather a thick layer of condensed media, the energy efficiency of X-ray generators is very low. At present, they are not proposed to be used in the field of environment conservation.

#### 4.3. Electron accelerators

• Radiation from the source is emitted continuously with constant intensity, so it is not easy

• Gamma sources have relatively low power; thus, the source of such high activity as 1 MCi (3.7 1016 Bq) has a power just near 10 kW. It makes gamma sources inapplicable for the

Nowadays, Co-60 gamma sources are applied, as a rule, to reveal the mechanisms of processes in systems to be irradiated, to disinfect sewage sludge, and to develop technologies of some processes. Cs-137 gamma sources are presently not used for solving environmental problems

Both γ-rays and X-rays are electromagnetic radiation and differ by the principle of formation. While γ-rays are emitted in the process of energy transition from excited to ground state of a nucleus, X-rays are emitted by accelerated electrons when they pass near to atomic nuclei and are deflected by their electric fields, the effect being called bremsstrahlung. Contrary to γ-rays with defined energy, X-rays produced in this manner have a continuous spectrum of photon energies extending from about 30 keV up to a maximum energy equal to the kinetic energy of the incident electron. For example, with a 5-MeV electron, the most probable photon energy is about 300 keV, the average photon energy is near 1.0 MeV, while the maximum photon energy is 5.0 MeV. The X-ray intensity increases with the electron energy and beam current and with

Two kinds of X-ray sources are produced and used commercially: X-ray tubes (or Roentgen tubes) and X-ray generators, based on electron accelerators. The former have relatively low photons energy and low power. Because of this X-ray tubes are almost not applied in radiation processing, being widely applied in medicine, material and structure analysis, and for indus-

X-ray generators are powerful analog of gamma sources. A comparison of those two kinds of electromagnetic radiation sources has been made in [54]. A distinguishing characteristic of X-ray generators is ameliorating the parameters of generated electromagnetic radiation with increasing the energy of incident electrons. Thus, while at relatively low electron energies X-rays are emitted in all directions, with electron energies higher than 2.0 MeV the X-ray emission in the direction of the incident electron beam becomes prevailing. Further increase in electrons energy results in decreasing the angular dispersion of the X-ray beam: divergence measured at half of the maximum intensity (HMI) is reduced two times when increasing

Electron energy (MeV) Mean photon energy (MeV) Emission efficiency (%) Divergence at HMI (degrees)

Table 9. Parameters of generated electromagnetic radiation depending on electron beam energy (the data from [55]).

5.0 1.19 8.2 20 7.5 1.38 13.3 15 10 1.56 16.2 10

to switch off and on irradiation promptly and to change the dose rate.

treatment of aqueous systems at high flow rates.

including radiation treatment of water/wastewater.

the atomic number of the target material [53].

electrons energy from 5 to 10 MeV (see Table 9).

4.2. X-ray sources

102 Ionizing Radiation Effects and Applications

trial inspection.

Among all accelerators of charged particles, only accelerators of electrons are suitable to application in radiation processing (excluding ion accelerators used in ion implantation industries). Chemical consequences of accelerated electrons action on many substances, including aqueous media, are almost the same as those of gamma and X-rays. The difference is in the depth of penetration. While the intensity of electromagnetic radiation (both gamma and X-rays) in a medium is attenuated exponentially with path length, accelerated electrons have limited penetration depth which depends on their energy. In Table 10, the penetration of gamma radiation is compared with that of accelerated electrons of different energies.

Principal characteristics of electron accelerators, important for industrial application, are energy of accelerated electrons E<sup>e</sup> (or "accelerator energy") and beam power We, which is defined as E<sup>e</sup> multiplied by electron beam current Ie: W<sup>e</sup> = E<sup>e</sup>Ie. While E<sup>e</sup> determines the range of electrons in irradiated medium, that is, the depth of electron beam penetration, W<sup>e</sup> determines the productivity of irradiation process. Market cost of accelerators is near proportional to their energy and to the square root of power. It is accepted in radiation processing to divide electron accelerators according to accelerator energy into three groups: 1—low-energy units (E<sup>e</sup> < 0.5 MeV), 2—mid-energy units (0.5 MeV < E<sup>e</sup> < 5.0 MeV), and 3—high-energy units (5.0 < E<sup>e</sup> < 10 MeV), maximum energy of 10 MeV being set for industrial accelerators to avoid problems of induced radioactivity.

Two types of accelerator design have found industrial acceptance in the high-energy area (5.0–10 MeV): microwave linear accelerators (linacs) and the radiofrequency accelerator Rhodotron®. Now industrial linacs are produced by companies: Getinge Linac (formerly Linac Technologies), Budker Institute of Nuclear Physics, L-3 Communications Pulse


Table 10. Depth of half attenuation for gamma radiation and penetration depth for accelerated electrons in cm (the data from [19]).

Sciences (formerly Titan Scan), Mevex, and EB-Tech Co Ltd. (in cooperation with the Budker Institute of Nuclear Physics); Rhodotron®—by Ion Beam Applications SA (formerly Radiation Dynamics Inc) [56].

main part, and other equipment necessary for normal functioning of radiation treatment

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Radiation reactor is an installation where flow of water is irradiated. There exist three different methods to irradiate water flow. Conditionally, they may be called "natural flow method,"

In this method, water/wastewater either flows over a surface and is irradiated from above by a vertical electron beam (Figure 2a), or falls as a wide waterfall and is irradiated by a horizontal

Water/wastewater treatment in this method may be carried out at high doses and dose rates. However, the velocity of natural flow is limited by about 1 m/s. Since the thickness of water layer is limited by accelerated electrons energy, the throughput of irradiation facility may be increased only by an increase in flow width, which results in increasing irradiation area and

The advantage of the method consists in a possibility of equipping the surface under flow with holes to input ozone or other necessary additions and/or to mix liquid under irradiation by gas bubbling. Reactors of that type were used in many pilot plans on radiation treatment of water,

In this method, polluted water is sprayed under pressure into a chamber to be irradiated from

wastewater, and sludge, in USA, Brazil, European countries, Korea, Japan, and China.

Figure 2. Natural flow reactor with vertical (a) and horizontal (b) direction of electron-beam irradiation.

"spray method," and "wide jet method," the reactors being called correspondingly.

demand of additional accelerator (or additional accelerating tube).

facility.

5.1. Reactor types: systems of water feed

5.1.1. Natural flow reactor

electron beam (Figure 2b).

5.1.2. Spray reactor

above by a vertical electron beam (Figure 3).

While being rather widely used in other fields of radiation processing, industrial high-energy accelerators are not used in the radiation treatment of water and wastewater, mainly due to high cost (including the cost of accelerator itself and the necessity of strong biological shielding because of high-intensity level of induced X-ray radiation) and relatively low-energy efficiency of linacs (ratio of beam power to power consumption is about 30%).

Low-energy accelerators produced by companies: Energy Sciences Incorporated, Broadbeam Equipment, NHV Corporation, and Advanced Electron Beams, are used, mainly, for curing or crosslinking of inks, coatings, and adhesives that are based on liquid-reactive materials which do not contain solvents. Because of very thin layer of water which electrons generated by those accelerators can penetrate, they are not applicable in radiation treatment of aqueous systems but one case; irradiation of sprayed wastewater (see Section 5.1).

Mid-energy electron accelerators are the most suitable for aqueous systems treatment. Those accelerators produce scanned beams that range in energy from 400 to 5 MeV. The units that are suitable for industrial use are all characterized by the ability to produce high beam currents, many tens of milliamps, which provide high dose rates that are needed for the treatment of aqueous systems at high flow rates.

Five electrical design systems have been used to attain mid-energy and high beam current: 1—the Cockcroft-Walton and its enhancements by Nissin-High Voltage, 2—the Insulated Core Transformer, 3—the Dynamitron, 4—a magnetic-coupled dc system, and 5—high-current pulsed beams. The Dynamitron can attain very high beam currents (60 mA) at up to 5.0 MeV (300 kW). The ICT and ELV mid-energy accelerator designs are limited in electron energy to 2.5 MeV. Medium- and low-voltage direct current accelerators may have several accelerating tubes connected to one power supply by using cable connections or gas-insulated transmission lines, flexible cable connections being limited to 800 keV and gas transmission systems up to 2 MeV. The companies that have experience in providing industry with mid-energy, highcurrent electron accelerators are Ion Beam Applications SA (formerly Radiation Dynamics Inc), NHV Corporation, Budker Institute of Nuclear Physics, Efremov Scientific Research Institute of Electrophysical Apparatus (NIIEFA), Vivirad SA (formerly Vivirad-High Voltage Corporation), and Wasik Associates [56].

As mentioned earlier, the cost of accelerators of similar energy is near proportional to the square root of power. It means that the cost per unit power decreases with increasing the power of accelerator. The data cited in [57] show that typical prices of mid-energy accelerators with power of 20–400 kW increase from 0.5 to 2.5 \$million, while the cost per 1 kW decreases from \$25,000 to \$5000.

## 5. Under-beam and other support equipment

Besides an accelerator, support equipment plays an important role in realizing radiation technology of water/wastewater treatment. The equipment includes radiation reactor, as a main part, and other equipment necessary for normal functioning of radiation treatment facility.

## 5.1. Reactor types: systems of water feed

Radiation reactor is an installation where flow of water is irradiated. There exist three different methods to irradiate water flow. Conditionally, they may be called "natural flow method," "spray method," and "wide jet method," the reactors being called correspondingly.

### 5.1.1. Natural flow reactor

Sciences (formerly Titan Scan), Mevex, and EB-Tech Co Ltd. (in cooperation with the Budker Institute of Nuclear Physics); Rhodotron®—by Ion Beam Applications SA (formerly Radia-

While being rather widely used in other fields of radiation processing, industrial high-energy accelerators are not used in the radiation treatment of water and wastewater, mainly due to high cost (including the cost of accelerator itself and the necessity of strong biological shielding because of high-intensity level of induced X-ray radiation) and relatively low-energy efficiency

Low-energy accelerators produced by companies: Energy Sciences Incorporated, Broadbeam Equipment, NHV Corporation, and Advanced Electron Beams, are used, mainly, for curing or crosslinking of inks, coatings, and adhesives that are based on liquid-reactive materials which do not contain solvents. Because of very thin layer of water which electrons generated by those accelerators can penetrate, they are not applicable in radiation treatment of aqueous systems

Mid-energy electron accelerators are the most suitable for aqueous systems treatment. Those accelerators produce scanned beams that range in energy from 400 to 5 MeV. The units that are suitable for industrial use are all characterized by the ability to produce high beam currents, many tens of milliamps, which provide high dose rates that are needed for the treatment of

Five electrical design systems have been used to attain mid-energy and high beam current: 1—the Cockcroft-Walton and its enhancements by Nissin-High Voltage, 2—the Insulated Core Transformer, 3—the Dynamitron, 4—a magnetic-coupled dc system, and 5—high-current pulsed beams. The Dynamitron can attain very high beam currents (60 mA) at up to 5.0 MeV (300 kW). The ICT and ELV mid-energy accelerator designs are limited in electron energy to 2.5 MeV. Medium- and low-voltage direct current accelerators may have several accelerating tubes connected to one power supply by using cable connections or gas-insulated transmission lines, flexible cable connections being limited to 800 keV and gas transmission systems up to 2 MeV. The companies that have experience in providing industry with mid-energy, highcurrent electron accelerators are Ion Beam Applications SA (formerly Radiation Dynamics Inc), NHV Corporation, Budker Institute of Nuclear Physics, Efremov Scientific Research Institute of Electrophysical Apparatus (NIIEFA), Vivirad SA (formerly Vivirad-High Voltage

As mentioned earlier, the cost of accelerators of similar energy is near proportional to the square root of power. It means that the cost per unit power decreases with increasing the power of accelerator. The data cited in [57] show that typical prices of mid-energy accelerators with power of 20–400 kW

Besides an accelerator, support equipment plays an important role in realizing radiation technology of water/wastewater treatment. The equipment includes radiation reactor, as a

increase from 0.5 to 2.5 \$million, while the cost per 1 kW decreases from \$25,000 to \$5000.

of linacs (ratio of beam power to power consumption is about 30%).

but one case; irradiation of sprayed wastewater (see Section 5.1).

tion Dynamics Inc) [56].

104 Ionizing Radiation Effects and Applications

aqueous systems at high flow rates.

Corporation), and Wasik Associates [56].

5. Under-beam and other support equipment

In this method, water/wastewater either flows over a surface and is irradiated from above by a vertical electron beam (Figure 2a), or falls as a wide waterfall and is irradiated by a horizontal electron beam (Figure 2b).

Water/wastewater treatment in this method may be carried out at high doses and dose rates. However, the velocity of natural flow is limited by about 1 m/s. Since the thickness of water layer is limited by accelerated electrons energy, the throughput of irradiation facility may be increased only by an increase in flow width, which results in increasing irradiation area and demand of additional accelerator (or additional accelerating tube).

The advantage of the method consists in a possibility of equipping the surface under flow with holes to input ozone or other necessary additions and/or to mix liquid under irradiation by gas bubbling. Reactors of that type were used in many pilot plans on radiation treatment of water, wastewater, and sludge, in USA, Brazil, European countries, Korea, Japan, and China.

#### 5.1.2. Spray reactor

In this method, polluted water is sprayed under pressure into a chamber to be irradiated from above by a vertical electron beam (Figure 3).

Figure 2. Natural flow reactor with vertical (a) and horizontal (b) direction of electron-beam irradiation.

While flow velocity is up to 3 m/s, the throughput of such irradiation facility is low. Also, the water before being input into reactor should be thoroughly purified from suspended particulates to prevent injector clogging and damaging.

5.2. Other equipment

capacity;

6. Conclusion

Author details

Moscow, Russia

Igor E. Makarov\* and Alexander V. Ponomarev

\*Address all correspondence to: makarov@ipc.rssi.ru

• Tubing for inlet and outlet water;

In addition to an accelerator and a reactor, other equipment is necessary to provide functioning

Radiation-Induced Degradation of Organic Compounds and Radiation Technologies for Purification of Aqueous…

http://dx.doi.org/10.5772/intechopen.72074

107

• Water pumps, some of which in the case of wide jet reactor should be of high pressure and

• Air fans (blowers) for cooling electron beam window of accelerator, discharge of ozone

Besides, the necessary part of the facility is biological shielding. Powerful accelerators must be situated in special irradiation room surrounded by walls made of dense concrete of 1.5–2.0 m thickness or more. The cost of the wall building amounts up to half of the accelerator cost. Thus, the capital cost of an industrial plant for wastewater treatment of middle productivity is near 4.0 \$million, excluding costs of land, R&D, and approval from authorities [59]. The demand of such high investments is one of the main obstacles in developing and

Radiation treatment of aqueous systems may be effectively used, without additional purification methods, for disinfection, detoxification, and decolorization of contaminated water at low concentration of organic matter. Purification of wastewater with high concentration of organic matter requires the application of combined radiation method, including biological treatment and/or filtration, sorption, and so on. Radiation technologies of aqueous systems treatment at present are being extensively developed. Electron accelerators are preferable radiation sources, especially at high flow rates. One of prerequisites for expansion of the technologies should be

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,

reducing the market prices for radiation equipment, namely electron accelerators.

The cost of reactor and listed equipment may amount to one-third of accelerator cost.

the facility on radiation treatment of water/wastewater. It includes

containing air from irradiation room, ventilation;

• Chemical laboratory equipment to analyze inlet and outlet water;

implementing radiation technologies of aqueous systems purification.

• Remote control to operate an accelerator;

• Measurement instrumentation, and so on. [58].

An advantage of the method consists in the formation of large specific surface of sprayed liquid providing for efficient penetration of surrounding gas into liquid phase. If the gas is an air or oxygen, ozone being formed under irradiation and absorbed in solution takes part in radiation-chemical reactions which improve purification process; to create reductive conditions during irradiation, the chamber may be filled with inert gas.

### 5.1.3. Wide jet reactor

In this method, wastewater is fed under pressure to irradiation area in the form of wide jet and is irradiated from above by a vertical electron beam (Figure 4).

Since flow velocity in this method may be made several meters per second, this kind of reactors is the most promising to irradiate wastewater using powerful accelerators at high flow rates. It was employed in full-scale facility in Korea on radiation treatment of dyeing company wastewater with throughput of 10,000 m3 a day [58].

Figure 3. Spray reactor.

Figure 4. Wide jet reactor with one jet (a) and two opposite jets (b).

#### 5.2. Other equipment

While flow velocity is up to 3 m/s, the throughput of such irradiation facility is low. Also, the water before being input into reactor should be thoroughly purified from suspended particu-

An advantage of the method consists in the formation of large specific surface of sprayed liquid providing for efficient penetration of surrounding gas into liquid phase. If the gas is an air or oxygen, ozone being formed under irradiation and absorbed in solution takes part in radiation-chemical reactions which improve purification process; to create reductive condi-

In this method, wastewater is fed under pressure to irradiation area in the form of wide jet and

Since flow velocity in this method may be made several meters per second, this kind of reactors is the most promising to irradiate wastewater using powerful accelerators at high flow rates. It was employed in full-scale facility in Korea on radiation treatment of dyeing

lates to prevent injector clogging and damaging.

5.1.3. Wide jet reactor

106 Ionizing Radiation Effects and Applications

Figure 3. Spray reactor.

tions during irradiation, the chamber may be filled with inert gas.

is irradiated from above by a vertical electron beam (Figure 4).

company wastewater with throughput of 10,000 m3 a day [58].

Figure 4. Wide jet reactor with one jet (a) and two opposite jets (b).

In addition to an accelerator and a reactor, other equipment is necessary to provide functioning the facility on radiation treatment of water/wastewater. It includes


The cost of reactor and listed equipment may amount to one-third of accelerator cost.

Besides, the necessary part of the facility is biological shielding. Powerful accelerators must be situated in special irradiation room surrounded by walls made of dense concrete of 1.5–2.0 m thickness or more. The cost of the wall building amounts up to half of the accelerator cost. Thus, the capital cost of an industrial plant for wastewater treatment of middle productivity is near 4.0 \$million, excluding costs of land, R&D, and approval from authorities [59]. The demand of such high investments is one of the main obstacles in developing and implementing radiation technologies of aqueous systems purification.

## 6. Conclusion

Radiation treatment of aqueous systems may be effectively used, without additional purification methods, for disinfection, detoxification, and decolorization of contaminated water at low concentration of organic matter. Purification of wastewater with high concentration of organic matter requires the application of combined radiation method, including biological treatment and/or filtration, sorption, and so on. Radiation technologies of aqueous systems treatment at present are being extensively developed. Electron accelerators are preferable radiation sources, especially at high flow rates. One of prerequisites for expansion of the technologies should be reducing the market prices for radiation equipment, namely electron accelerators.

## Author details

Igor E. Makarov\* and Alexander V. Ponomarev

\*Address all correspondence to: makarov@ipc.rssi.ru

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia

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[54] Cleland MR, Pageau GM. Comparisons of X-ray and gamma-ray sources for industrial irradiation processes. Nuclear Instruments and Methods in Physics Research B. 1987; 24–25(2):967-972. DOI: 10.1016/S0168-583X(87)80290-2

**Chapter 6**

Provisional chapter

**Ionizing Radiation-Induced Polymerization**

Ionizing radiation can induce some kinds of reactions, other than polymerization, such as dimerization, oligomerization, curing, and grafting. These reactions occur through a regular radical chain causing growth of polymer by three steps, namely, initiation, propagation, and termination. To understand ionizing radiation-induced polymerization, the water radiolysis must be taken into consideration. This chapter explores the mechanism of water molecules radiolysis paying especial attention to the basic regularities of solvent radicals' interaction with the polymer molecules for forming the crosslinked polymer. Water radiolysis is the main engine of the polymerization processes, especially the "freeradical polymerization." The mechanisms of the free-radical polymerization and crosslinking will be discussed in detail later. Since different polymers respond differently to radiation, it is useful to quantify the response, namely in terms of crosslinking and chain scission. A parameter called the G-value is frequently used for this purpose. It represents the chemical yield of crosslinks, scissions and double bonds, etc. For the crosslinked polymer, the crosslinking density increases with increasing the radiation dose, this is reflected by the swelling degree of the polymer while being immersed in a compatible solvent. If crosslinking predominates, the crosslinking density increases and the extent of swelling decreases. If chain scission predominates, the opposite occurs. A further

DOI: 10.5772/intechopen.73234

detailed discussion of these aspects is presented throughout this chapter. Keywords: gamma irradiation, polymerization, water radiolysis, radical

Since the last quarter of the twentieth century, a growing interest in polymerization induced by ionizing radiation has been observed. Throughout this period, researchers have exposed polymeric materials to ionizing radiation and reported the occurring of crosslinking and other

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

> © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Ionizing Radiation-Induced Polymerization

Mohamed Mohamady Ghobashy

Mohamed Mohamady Ghobashy

http://dx.doi.org/10.5772/intechopen.73234

Abstract

1. Introduction

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter


#### **Ionizing Radiation-Induced Polymerization** Ionizing Radiation-Induced Polymerization

DOI: 10.5772/intechopen.73234

#### Mohamed Mohamady Ghobashy Mohamed Mohamady Ghobashy

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.73234

#### Abstract

[54] Cleland MR, Pageau GM. Comparisons of X-ray and gamma-ray sources for industrial irradiation processes. Nuclear Instruments and Methods in Physics Research B. 1987;

[55] Cleland MR, Stichelbaut F. Radiation processing with high-energy X-rays. In: 2009 International Nuclear Atlantic Conference—INAC; 27 September to 2 October 2009; Rio de Janeiro. ISBN: 978-85-99141-03-8. Available from: http://www.iaea.org/inis/collection/

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[59] Han B, Kim JK, Kim Y, Choi JS, Jeong KY. Operation of industrial-scale electron beam wastewater treatment plant. Radiation Physics and Chemistry. 2012;81(9):1475-1478.

[57] Radiation Processing: Environmental Application. Vienna: IAEA; 2007. p. 71

Processing. (IAEA TechDoc-1386). Vienna: IAEA; 2004. pp. 138-152

24–25(2):967-972. DOI: 10.1016/S0168-583X(87)80290-2

112 Ionizing Radiation Effects and Applications

NCLCollectionStore/\_Public/41/097/41097063.pdf

DOI: 10.1016/j.radphyschem.2012.01.030

Ionizing radiation can induce some kinds of reactions, other than polymerization, such as dimerization, oligomerization, curing, and grafting. These reactions occur through a regular radical chain causing growth of polymer by three steps, namely, initiation, propagation, and termination. To understand ionizing radiation-induced polymerization, the water radiolysis must be taken into consideration. This chapter explores the mechanism of water molecules radiolysis paying especial attention to the basic regularities of solvent radicals' interaction with the polymer molecules for forming the crosslinked polymer. Water radiolysis is the main engine of the polymerization processes, especially the "freeradical polymerization." The mechanisms of the free-radical polymerization and crosslinking will be discussed in detail later. Since different polymers respond differently to radiation, it is useful to quantify the response, namely in terms of crosslinking and chain scission. A parameter called the G-value is frequently used for this purpose. It represents the chemical yield of crosslinks, scissions and double bonds, etc. For the crosslinked polymer, the crosslinking density increases with increasing the radiation dose, this is reflected by the swelling degree of the polymer while being immersed in a compatible solvent. If crosslinking predominates, the crosslinking density increases and the extent of swelling decreases. If chain scission predominates, the opposite occurs. A further detailed discussion of these aspects is presented throughout this chapter.

Keywords: gamma irradiation, polymerization, water radiolysis, radical

## 1. Introduction

Since the last quarter of the twentieth century, a growing interest in polymerization induced by ionizing radiation has been observed. Throughout this period, researchers have exposed polymeric materials to ionizing radiation and reported the occurring of crosslinking and other

useful effects, e.g., miscibility of blend polymer [1–3] as well as many different applications in the polymer radiation chemistry field [4, 5]. Ionizing radiation is a promising technology for preparation of cost-effective, efficient, safe, and high-quality polymers. The radiation techniques applied for polymerization processes could be carried out using many different types of radiation sources. Ionizing radiations (gamma rays, X-rays, accelerated electrons, and ions beam) initiate polymerization reactions by the formation of very reactive intermediates (energetic radicals). Energetic radicals resulting from ionizing radiation hit molecules causing electrons ejection from a particular orbit, then the atom becomes ionized [6]. As soon as their orbits begin to be ready to overlapping forming new bonds, these electrons may be much more detached by other molecules [7, 8]. This phenomenon occurs when the transferred energy is higher than that of particular orbital electrons. When the energy is not high enough for ionization, electrons are gaining energy and transfer to an upper energy level, resulting in excitation. The ionizing potential for most molecules ranges from 7 to 15 eV [9], while the energies of ionizing irradiators (gamma rays, X-rays, accelerated electrons, and ions beam) range from 1 to 100 MeV [10], so ionization is the predominating process. Energetic radicals with ionized electron excite another molecule upon calling energy transfer. The ionized species associated with the energetic radicals created by irradiation would induce various reactions. This power in a polymerization reaction is an eco-friendly process. Polymers are covalently crosslinked by ionizing radiation at room temperature. The degree of crosslinking is radiation dose-dependent besides other parameters, e.g., temperature and ambiance [11].

molecules attached to polymer backbone "closely associated with the chain end," this is the socalled "living polymerization." Consequently, radiolytic solvents could act as catalysts which govern the kind of polymerization mechanism to be either cationic or anionic when solvents

Step-growth radical polymerization induced by gamma irradiation occurs in three main stages. The first stage of the reaction is "initiated" by ionizing radiation, in which a radical (molecule with an active center) is formed, typically by radiolysis of an aqueous solvent (mainly water) or by braking C–H bond in polymer chains. The second stage is "propagation" which begins by attracting an active center that is formed in one monomer molecule with another monomer molecule. The final stage is "termination," in which the number of radical creation is terminated or the monomer molecules are consumed and mostly all monomers form polymer chains. Furthermore, the degree of polymerization depends on the monomer

Radiolysis of water is the ionization of water molecules by the absorption of ionizing radiation energy. The ionizing radiation absorbed by the water molecules is the pulse radiolysis technique [14]. The pulse radiolysis of water in high energy electromagnetic wave (ionizing radiation) gives variety of reactive species such as excited molecules, ions, and radicals [15]. It should be observed that radicals are formed by a wide variety of water radiolysis reactions, these species are chemical transformation and physical generation. The physical stage of the primary interaction of ionizing radiation with water molecules result in excitation and ioniza-

This chapter focuses attention on the radiolysis of water as a source of radicals which are responsible for polymerization reactions. ESR spectroscopy is the best detection method for

Photopolymerization induced by UV irradiation is presented as a green technology characterized by low cost electrical power input and low energy requirements. Low temperature, low noise operation, and no volatile gases are generated. Photopolymerization is performed by water photolysis, practically the excited water molecule was generated (H2O)\* through the UV radiation (λ < 240 nm) absorption process (Eq. (3)). The water molecules in the excited state are mainly located on the water surface that exposed to UV, and with the course of time, energy will transfer

photolysis reaction of UV in water molecules is homolytic bond scission (Eq. (4)). The excited

H2O ! H2O<sup>∗</sup> ð Þ Excitation (1)

Ionizing Radiation-Induced Polymerization http://dx.doi.org/10.5772/intechopen.73234 115

H2O<sup>∗</sup> ! <sup>H</sup>• <sup>þ</sup> •OH Ionization ð Þ (2)

H and •

OH). The predominant

act as Lewis acid or Lewis base, respectively.

concentration and manipulation of the radiation dose.

tion as expressed by Eqs. (1) and (2):

2.1. Radical polymerization

studying radical intermediates in radiolysis [16].

2. Photo-initiated induced by UV irradiation

to bulk molecules of water to produce (reactive species) radicals (•

Radiation crosslinking is a result of the combination of two molecules with active radicals at different three routes (head-to-head, head-to-tail, and tail-to-tail). In an amorphous region, the radical's combination is predominated rather than in crystalline region [12]. Sometimes increase of crystallinity reveals polymer crosslinking. On the other hand, the increase of amorphousity reveals polymer degradation (chain scission) [13]. Whatever, crosslinking or degradation, depends on the polymer nature. Therefore, predomination of radiation crosslinking can be achieved by removing oxidation gas (O2) and replacing it by an inert gas (N2). The percentage of dissolved oxygen could control the degree of polymerization and/or degradation of polymer chains. These processes compete through the breaking or formations of covalent bonds. The formations of new covalent bonds predominate in the case of vinyl monomer or synthetic polymer.

Water radiolysis produces neutral radicals H• and • OH with hydrated electrons ehy and molecular products H2 and H2O2. This means that the radiolysis of water gives several radiation-chemical reactions that have been studied in aqueous solutions, e.g., radiolytic reduction reaction (RRR), radiolytic oxidation reaction (ROR), and radiolytic polymerization reaction (RPR). This chapter discusses three kinds of RPR, namely; radical, cationic, and anionic polymerization.

In order to approach polymerization induced by ionizing radiation in high yield, the selected solvent should be ready for radiation radiolysis and of a high order of dissolving for the desired monomers. However, when switching to poor solvents, this might lead directly to rather broad distributions of polymer molecular weight. Non-polar solvents are ion-pairing or clustering that could interact, by radiolysis, with polymer backbone living a part of solvent molecules attached to polymer backbone "closely associated with the chain end," this is the socalled "living polymerization." Consequently, radiolytic solvents could act as catalysts which govern the kind of polymerization mechanism to be either cationic or anionic when solvents act as Lewis acid or Lewis base, respectively.

Step-growth radical polymerization induced by gamma irradiation occurs in three main stages. The first stage of the reaction is "initiated" by ionizing radiation, in which a radical (molecule with an active center) is formed, typically by radiolysis of an aqueous solvent (mainly water) or by braking C–H bond in polymer chains. The second stage is "propagation" which begins by attracting an active center that is formed in one monomer molecule with another monomer molecule. The final stage is "termination," in which the number of radical creation is terminated or the monomer molecules are consumed and mostly all monomers form polymer chains. Furthermore, the degree of polymerization depends on the monomer concentration and manipulation of the radiation dose.

Radiolysis of water is the ionization of water molecules by the absorption of ionizing radiation energy. The ionizing radiation absorbed by the water molecules is the pulse radiolysis technique [14]. The pulse radiolysis of water in high energy electromagnetic wave (ionizing radiation) gives variety of reactive species such as excited molecules, ions, and radicals [15]. It should be observed that radicals are formed by a wide variety of water radiolysis reactions, these species are chemical transformation and physical generation. The physical stage of the primary interaction of ionizing radiation with water molecules result in excitation and ionization as expressed by Eqs. (1) and (2):

$$\text{H}\_2\text{O} \xrightarrow{\text{---} \longrightarrow \qquad} \text{H}\_2\text{O}^\* \text{ (Exidation)} \tag{1}$$

$$\text{CH}\_2\text{O}^\* \xrightarrow{\text{---}} \text{H}^\* + \text{"OH (Ionization)}\tag{2}$$

This chapter focuses attention on the radiolysis of water as a source of radicals which are responsible for polymerization reactions. ESR spectroscopy is the best detection method for studying radical intermediates in radiolysis [16].

## 2. Photo-initiated induced by UV irradiation

#### 2.1. Radical polymerization

useful effects, e.g., miscibility of blend polymer [1–3] as well as many different applications in the polymer radiation chemistry field [4, 5]. Ionizing radiation is a promising technology for preparation of cost-effective, efficient, safe, and high-quality polymers. The radiation techniques applied for polymerization processes could be carried out using many different types of radiation sources. Ionizing radiations (gamma rays, X-rays, accelerated electrons, and ions beam) initiate polymerization reactions by the formation of very reactive intermediates (energetic radicals). Energetic radicals resulting from ionizing radiation hit molecules causing electrons ejection from a particular orbit, then the atom becomes ionized [6]. As soon as their orbits begin to be ready to overlapping forming new bonds, these electrons may be much more detached by other molecules [7, 8]. This phenomenon occurs when the transferred energy is higher than that of particular orbital electrons. When the energy is not high enough for ionization, electrons are gaining energy and transfer to an upper energy level, resulting in excitation. The ionizing potential for most molecules ranges from 7 to 15 eV [9], while the energies of ionizing irradiators (gamma rays, X-rays, accelerated electrons, and ions beam) range from 1 to 100 MeV [10], so ionization is the predominating process. Energetic radicals with ionized electron excite another molecule upon calling energy transfer. The ionized species associated with the energetic radicals created by irradiation would induce various reactions. This power in a polymerization reaction is an eco-friendly process. Polymers are covalently crosslinked by ionizing radiation at room temperature. The degree of crosslinking is radiation

dose-dependent besides other parameters, e.g., temperature and ambiance [11].

Water radiolysis produces neutral radicals H• and •

polymer.

anionic polymerization.

114 Ionizing Radiation Effects and Applications

Radiation crosslinking is a result of the combination of two molecules with active radicals at different three routes (head-to-head, head-to-tail, and tail-to-tail). In an amorphous region, the radical's combination is predominated rather than in crystalline region [12]. Sometimes increase of crystallinity reveals polymer crosslinking. On the other hand, the increase of amorphousity reveals polymer degradation (chain scission) [13]. Whatever, crosslinking or degradation, depends on the polymer nature. Therefore, predomination of radiation crosslinking can be achieved by removing oxidation gas (O2) and replacing it by an inert gas (N2). The percentage of dissolved oxygen could control the degree of polymerization and/or degradation of polymer chains. These processes compete through the breaking or formations of covalent bonds. The formations of new covalent bonds predominate in the case of vinyl monomer or synthetic

molecular products H2 and H2O2. This means that the radiolysis of water gives several radiation-chemical reactions that have been studied in aqueous solutions, e.g., radiolytic reduction reaction (RRR), radiolytic oxidation reaction (ROR), and radiolytic polymerization reaction (RPR). This chapter discusses three kinds of RPR, namely; radical, cationic, and

In order to approach polymerization induced by ionizing radiation in high yield, the selected solvent should be ready for radiation radiolysis and of a high order of dissolving for the desired monomers. However, when switching to poor solvents, this might lead directly to rather broad distributions of polymer molecular weight. Non-polar solvents are ion-pairing or clustering that could interact, by radiolysis, with polymer backbone living a part of solvent

OH with hydrated electrons ehy and

Photopolymerization induced by UV irradiation is presented as a green technology characterized by low cost electrical power input and low energy requirements. Low temperature, low noise operation, and no volatile gases are generated. Photopolymerization is performed by water photolysis, practically the excited water molecule was generated (H2O)\* through the UV radiation (λ < 240 nm) absorption process (Eq. (3)). The water molecules in the excited state are mainly located on the water surface that exposed to UV, and with the course of time, energy will transfer to bulk molecules of water to produce (reactive species) radicals (• H and • OH). The predominant photolysis reaction of UV in water molecules is homolytic bond scission (Eq. (4)). The excited water molecules (H2O)\* can undergo further photolysis producing reduction/oxidation agents (H+ and �OH) by intra-molecular electron transfer (as summarized in Eq. (5)). The following equations are the most common water photolysis impact of UV absorption:

$$\text{H}\_2\text{O} \xrightarrow{\text{C}} \longrightarrow \text{H}\_2\text{O}^\* \tag{3}$$

center." When a water molecule absorbed photon in UV range in the absence of oxygen, it

photoinitiator should exhibit an energetic wavelength, and undergo a rapid water photolysis to

monomer molecule to start monomers combination and build 3D polymer network [19]. In this process, the polymers chains are crosslinked by forming covalent bonds cross chains [20].

The radical polymerization process is outlined in Figures 1 and 2, water excitation by absorbing UV leads to formation of free radicals as a first stage. In this typical step, the energetic radicals transfer to monomer molecules that undergo unimolecular bond formation upon irradiation. The polymerization process is complete with integration of monomer molecules. Figure 2 shows water ionization by the UV rays that are capable to generate an active center (energetic radicals). These radicals pass energy to a monomer molecule that keeps the polymerization reaction going on. A "reactive" photoinitiator reacts with a monomer molecule to start a polymer chain formation, and the polymerization process begins with transferring the energetic radicals to monomer molecules. The crosslinked density is high in the deeper level rather than the surface level depending on oxygen concentration. While in free oxygen system, the crosslinked density is expected to be higher in the surface level rather than in the deeper

Besides photo-initiated radical polymerization that has been outlined, there are other two photo-polymerization processes; cationic and anionic polymerizations will be discussed in this section. Additives sensitive to UV radiation were required to promote cationic and anionic polymerization. In Figures 3 and 4, the common ultraviolet (UV) initiation agents are present

H) species with a high quantum yield [18]. The

Ionizing Radiation-Induced Polymerization http://dx.doi.org/10.5772/intechopen.73234 117

H). Subsequent polymerization goes on when reacting with a

OH and •

level due to further yield of radicals on the side exposed to UV radiation.

OH and •

becomes excited and forms (•

2.2. Cationic polymerization

Figure 1. Imagination of the setup of radical polymerization.

generate the initiating (•

$$\text{H}\_2\text{O}^\* \xrightarrow{\text{-}} \text{H}^\* + \text{\text{\textdegree}}\text{OH} \tag{4}$$

$$\text{H}\_2\text{O}^\* \xrightarrow{\text{-}} \text{H}^+ + \text{-}\text{OH} \tag{5}$$

In dissolving oxygen, the energy transfer processes to oxygen molecules forms dioxygen radical anion (superoxide radical) is possible according to Eq. (6). In case of complete energy transfer, relatively long-lived water molecules are produced in excited state, as the so-called the triplet state.

$$\text{H}\_2\text{O}^\* + \text{O}\_2 \xrightarrow{\text{-}} \text{H}\_2\text{O}^{+\text{-}} + \text{\text{-}\text{-}}\text{O}\_2\tag{6}$$

All the above reactions may be recombined with each other's in unlimited hypothesis, as expressed in Eqs. (7) and (8). This recombination gives excited (H2O)\* water molecules

$$\text{H}^{\bullet} + \text{O}\_{2} \xrightarrow{\text{---}} \text{HO}^{\bullet}{}\_{2} \tag{7}$$

$$\begin{aligned} \text{HO}\_2 + \text{^\*OH} &\longrightarrow \underbrace{\begin{bmatrix} \text{^\*OH} + \text{H}^+ \\ \text{O} \end{bmatrix}}\_{\text{H} \bullet \text{^\*} \end{aligned} \tag{8}$$

The hydroxyl radical (• OH) has a limited mobility and mainly abstract hydrogen atoms (H) for forming H2O. On the other hand, the number of reduction/oxidation agents (H<sup>+</sup> and �OH) increases as the addition of oxygen to the water solutions increases. Obviously, at low concentration of dissolved oxygen, the crosslinked polymer is obtained. Therefore, under condition of sufficient dissolved oxygen, photo-oxidative degradation process may predominate. This is beneficial for water treatment and elimination of organic compounds pollutants; but sometimes, a part of the dissolved organic pollutants was found to precipitate, probably as a result of functional groups condensation (acetic acid, oxalic acid, n-butanoic acid, and malonic acid) which were the most abundant degradation products detected. The photo-oxidative degradation process C–C yields a macroradical C• C• by bond session. This macroradical molecule may be recombined in the absence of oxygen (polymerization). In the presence of oxygen, the peroxy radicals C–O–O• may be formed (photo-oxidative degradation) [17]. Particularly, the photons that cause degradation are found in all electromagnetic radiations and can be enhanced at elevated temperatures. So, in polymerization reaction, the concentration of oxygen should be controlled in order to improve the polymerization induced by UV irradiation.

The role of the polymerization reaction initiation induced by UV irradiation "photoinitiator" is delayed with converting the photon energy into a chemical energy in the form of a "reactive center." When a water molecule absorbed photon in UV range in the absence of oxygen, it becomes excited and forms (• OH and • H) species with a high quantum yield [18]. The photoinitiator should exhibit an energetic wavelength, and undergo a rapid water photolysis to generate the initiating (• OH and • H). Subsequent polymerization goes on when reacting with a monomer molecule to start monomers combination and build 3D polymer network [19]. In this process, the polymers chains are crosslinked by forming covalent bonds cross chains [20].

The radical polymerization process is outlined in Figures 1 and 2, water excitation by absorbing UV leads to formation of free radicals as a first stage. In this typical step, the energetic radicals transfer to monomer molecules that undergo unimolecular bond formation upon irradiation. The polymerization process is complete with integration of monomer molecules. Figure 2 shows water ionization by the UV rays that are capable to generate an active center (energetic radicals). These radicals pass energy to a monomer molecule that keeps the polymerization reaction going on. A "reactive" photoinitiator reacts with a monomer molecule to start a polymer chain formation, and the polymerization process begins with transferring the energetic radicals to monomer molecules. The crosslinked density is high in the deeper level rather than the surface level depending on oxygen concentration. While in free oxygen system, the crosslinked density is expected to be higher in the surface level rather than in the deeper level due to further yield of radicals on the side exposed to UV radiation.

#### 2.2. Cationic polymerization

water molecules (H2O)\* can undergo further photolysis producing reduction/oxidation agents (H+ and �OH) by intra-molecular electron transfer (as summarized in Eq. (5)). The following

In dissolving oxygen, the energy transfer processes to oxygen molecules forms dioxygen radical anion (superoxide radical) is possible according to Eq. (6). In case of complete energy transfer, relatively long-lived water molecules are produced in excited state, as the so-called

All the above reactions may be recombined with each other's in unlimited hypothesis, as

<sup>H</sup>• <sup>þ</sup> O2!HO•

forming H2O. On the other hand, the number of reduction/oxidation agents (H<sup>+</sup> and �OH) increases as the addition of oxygen to the water solutions increases. Obviously, at low concentration of dissolved oxygen, the crosslinked polymer is obtained. Therefore, under condition of sufficient dissolved oxygen, photo-oxidative degradation process may predominate. This is beneficial for water treatment and elimination of organic compounds pollutants; but sometimes, a part of the dissolved organic pollutants was found to precipitate, probably as a result of functional groups condensation (acetic acid, oxalic acid, n-butanoic acid, and malonic acid) which were the most abundant degradation products detected. The photo-oxidative degradation process C–C yields a macroradical C• C• by bond session. This macroradical molecule may be recombined in the absence of oxygen (polymerization). In the presence of oxygen, the peroxy radicals C–O–O• may be formed (photo-oxidative degradation) [17]. Particularly, the photons that cause degradation are found in all electromagnetic radiations and can be enhanced at elevated temperatures. So, in polymerization reaction, the concentration of oxygen should be controlled in order to improve the polymerization induced by UV irradiation. The role of the polymerization reaction initiation induced by UV irradiation "photoinitiator" is delayed with converting the photon energy into a chemical energy in the form of a "reactive

expressed in Eqs. (7) and (8). This recombination gives excited (H2O)\* water molecules

H2O! H2O<sup>∗</sup> (3)

!H• <sup>þ</sup> •OH (4)

!H<sup>þ</sup> <sup>þ</sup> �OH (5)

<sup>2</sup> (7)

ð8Þ

H2O<sup>∗</sup> <sup>þ</sup> O2!H2O<sup>þ</sup>• <sup>þ</sup> •�O2 (6)

OH) has a limited mobility and mainly abstract hydrogen atoms (H) for

equations are the most common water photolysis impact of UV absorption:

H2O<sup>∗</sup>

H2O<sup>∗</sup>

the triplet state.

116 Ionizing Radiation Effects and Applications

The hydroxyl radical (•

Besides photo-initiated radical polymerization that has been outlined, there are other two photo-polymerization processes; cationic and anionic polymerizations will be discussed in this section. Additives sensitive to UV radiation were required to promote cationic and anionic polymerization. In Figures 3 and 4, the common ultraviolet (UV) initiation agents are present

Figure 1. Imagination of the setup of radical polymerization.

Figure 2. Proposed radical photo-polymerization induced by UV radiation.

Figure 3. DPI diphenyliodonium hexafluorophosphate.

in two forms of onium salt: diphenyliodonium DPI (Ph2I + ) and triphenylsulfonium DPS (Ph3S+ ) used as cationic photoinitiator under UV radiation [21–25]. Those are able to generate both protonic acids (carbonium ions) and free radicals (Figure 5).

This polymerization process is also called free-radical promoted cationic polymerization. This process undergoes more rapid polymerization, for example, in the curing process of epoxy resins, the ring opens and initiates both radical and cationic polymerization mechanism. Onium salt is sometimes called the curing agent, especially, for epoxy resin curing. Figure 4 shows the generation of a Bronsted acid (Lewis acid) when DPI and DPS exposed to UV

Ionizing Radiation-Induced Polymerization http://dx.doi.org/10.5772/intechopen.73234 119

Figure 5. A proposed mechanism of radical cationic photopolymerization induced by UV radiation of epoxy resin.

As depicted in Figure 5, an aryl iodine radical cation and aryl radical are formed by the photolysis of DPI salt (1). Both of these are highly reactive species which separate protons

radiation [26–28].

Figure 4. DPS triphenylsulfonium hexafluorophosphate.

Figure 4. DPS triphenylsulfonium hexafluorophosphate.

in two forms of onium salt: diphenyliodonium DPI (Ph2I

Figure 3. DPI diphenyliodonium hexafluorophosphate.

118 Ionizing Radiation Effects and Applications

Figure 2. Proposed radical photo-polymerization induced by UV radiation.

both protonic acids (carbonium ions) and free radicals (Figure 5).

(Ph3S+

+

) used as cationic photoinitiator under UV radiation [21–25]. Those are able to generate

This polymerization process is also called free-radical promoted cationic polymerization. This process undergoes more rapid polymerization, for example, in the curing process of epoxy resins, the ring opens and initiates both radical and cationic polymerization mechanism. Onium salt is sometimes called the curing agent, especially, for epoxy resin curing. Figure 4

) and triphenylsulfonium DPS

Figure 5. A proposed mechanism of radical cationic photopolymerization induced by UV radiation of epoxy resin.

shows the generation of a Bronsted acid (Lewis acid) when DPI and DPS exposed to UV radiation [26–28].

As depicted in Figure 5, an aryl iodine radical cation and aryl radical are formed by the photolysis of DPI salt (1). Both of these are highly reactive species which separate protons

from the monomer (2) generating bronsted acid (HPF6) and formatting diaryl iodine (3). The polymerization reaction rapidly involves by protonation of the epoxide oxygen with the very powerful acid (4). It is obvious that the cationic polymerization of epoxies is highly quantitative and very rapid, with low activation energy [29]. For clarity, the concurrent radical and cationic reactions in hybrid systems have dramatically changed the rate of photopolymerization [30].

Figure 5 shows a proposed mechanism of radical cationic photo-polymerization induced by UV radiation of epoxy resin.

#### 2.3. Anionic polymerization

Free cationic and radical photopolymerizations have been extensively applied in this context, whereas photo-induced anionic polymerization was limited in scope and application [31]. Kahveci et al. used a combination of cationic photo-polymerization and anionic opening ring polymerization mechanisms to confirm the amphiphilic graft copolymers of poly(ethylene oxide)-g-poly (isobutyl vinyl ether) (PEO-g-PIBVE) [32]. First, poly(ethylene oxide-co-ethoxyl vinyl glycidyl ether) was synthesized by anionic ring-opening co-polymerization of corresponding monomers using radiation for reaction initiation. Random anionic ring-opening co-polymerization of a mixture of the gaseous EO (b.p. 11C) and the respective co-monomer in an appropriate solvent can be initiated by an alkali-metal alkoxide [33]. The vinyl ether moieties were then cationic photo polymerized using diphenyliodonium iodide photoinitiator. It is clear that photoinitiator was only used for cationic polymerization, while anionic polymerization takes place spontaneously by ring opening in mild conditions. Further investigation is needed to cover unexplored areas in the field of photo-induced polymerization [34]. Radicals promote cationic photo-polymerization, since it has been demonstrated to be a very effective method for the preparation of well-defined high molecular weight epoxy resin [35].

OH, H3O<sup>+</sup> and •

formation homogenous distribution.

4. X-ray

reduction reactions.

OH, etc.) [37]. Particularly, the chemical reactions (radiolysis) occur when the

reactive species of ions and radicals are distributed nonhomogeneously in "clusters" of excitations/ionization (i.e., spurs), and homogeneously after the reactive species have diffused and thermalized [38]. Spurs were used to describe the high energy electron passed through liquids. It is well-known that the ionizing and exciting species are, in fact, nonhomogeneous and occur in clusters called "spurs." The electron is similar to a "stone" hit in the surface of the water pool, by the time the resulting "splashes" induced by "the stone hit" will expand and eventually overlap with their neighbors to result in a homogenous distribution (Figure 6). However, this simple picture is not true in some cases; the irradiation of nonaqueous systems does not

Figure 6. Inhomogeneous distribution of ionizing events (ehy) and its diffusion with time (~10<sup>7</sup>

Risse and Fricke [39, 40] had studied the radiolysis of water by X-rays in a closed vessel. Bubbles of hydrogen and carbon dioxide gas resulting from irradiation are found [41]. X-ray photons are highly powerful causing radiolysis of water to create an ion pair (H2O)<sup>+</sup> (ehy). The amount of ionization species produced is affected by the amount of energetic photons absorbed. Figure 7 shows that the positive and negative water molecules are unstable. These can break apart into smaller molecules. Free radicals can be formed by this breakup. Several

zation takes place by (•OH and •H and ehy) [42]. Also, the radiolysis products may recombine individually, forming gases such as H2 and H2O2 [43], and hence the bubbles are formed due to an evolving mixture of H2 and O2 gases. H2 present in the solution, or the "ehy," may cause

, and ehy) beside polymeri-

) and reactions reach the

Ionizing Radiation-Induced Polymerization http://dx.doi.org/10.5772/intechopen.73234 121

yield as a clear picture concerning spurs as the case in the water.

chemical reactions might occur (oxidation reduction) by (OH, H<sup>+</sup>

## 3. Electron beam

In order to complete the image of radiation-induced polymerization, another radiolysis system should be taken into consideration is electron beam. Electrons are generated in a linear beam form causing a powerful and fast water radiolysis that produce hydrated electrons (ehy). Most solvents are of a continuum for some polarity properties. The hydrated electron (ehy) is very reductive chemical species, once the solvated electron hits water molecules, water becomes ionized [36]. This depends on the time consumed for interaction and the average distance between the solvated electron (ehy) and the water ions.

The emitting powerful electron (more than 1 MeV electron) from electron accelerator hits water molecule and then scatters. The energy of electron is lost as a result of bordering a pathway for secondary electrons. Secondary electrons keep their own powerful energy, causing water ionization and forming copious quantities of variety of reactive species (e.g., H2 H2O<sup>+</sup> , H2O2,

Figure 6. Inhomogeneous distribution of ionizing events (ehy) and its diffusion with time (~10<sup>7</sup> ) and reactions reach the formation homogenous distribution.

OH, H3O<sup>+</sup> and • OH, etc.) [37]. Particularly, the chemical reactions (radiolysis) occur when the reactive species of ions and radicals are distributed nonhomogeneously in "clusters" of excitations/ionization (i.e., spurs), and homogeneously after the reactive species have diffused and thermalized [38]. Spurs were used to describe the high energy electron passed through liquids. It is well-known that the ionizing and exciting species are, in fact, nonhomogeneous and occur in clusters called "spurs." The electron is similar to a "stone" hit in the surface of the water pool, by the time the resulting "splashes" induced by "the stone hit" will expand and eventually overlap with their neighbors to result in a homogenous distribution (Figure 6). However, this simple picture is not true in some cases; the irradiation of nonaqueous systems does not yield as a clear picture concerning spurs as the case in the water.

## 4. X-ray

from the monomer (2) generating bronsted acid (HPF6)

polymerization [30].

UV radiation of epoxy resin.

120 Ionizing Radiation Effects and Applications

2.3. Anionic polymerization

molecular weight epoxy resin [35].

between the solvated electron (ehy) and the water ions.

3. Electron beam

polymerization reaction rapidly involves by protonation of the epoxide oxygen with the very powerful acid (4). It is obvious that the cationic polymerization of epoxies is highly quantitative and very rapid, with low activation energy [29]. For clarity, the concurrent radical and cationic reactions in hybrid systems have dramatically changed the rate of photo-

Figure 5 shows a proposed mechanism of radical cationic photo-polymerization induced by

Free cationic and radical photopolymerizations have been extensively applied in this context, whereas photo-induced anionic polymerization was limited in scope and application [31]. Kahveci et al. used a combination of cationic photo-polymerization and anionic opening ring polymerization mechanisms to confirm the amphiphilic graft copolymers of poly(ethylene oxide)-g-poly (isobutyl vinyl ether) (PEO-g-PIBVE) [32]. First, poly(ethylene oxide-co-ethoxyl vinyl glycidyl ether) was synthesized by anionic ring-opening co-polymerization of corresponding monomers using radiation for reaction initiation. Random anionic ring-opening co-polymerization of a mixture of the gaseous EO (b.p. 11C) and the respective co-monomer in an appropriate solvent can be initiated by an alkali-metal alkoxide [33]. The vinyl ether moieties were then cationic photo polymerized using diphenyliodonium iodide photoinitiator. It is clear that photoinitiator was only used for cationic polymerization, while anionic polymerization takes place spontaneously by ring opening in mild conditions. Further investigation is needed to cover unexplored areas in the field of photo-induced polymerization [34]. Radicals promote cationic photo-polymerization, since it has been demonstrated to be a very effective method for the preparation of well-defined high

In order to complete the image of radiation-induced polymerization, another radiolysis system should be taken into consideration is electron beam. Electrons are generated in a linear beam form causing a powerful and fast water radiolysis that produce hydrated electrons (ehy). Most solvents are of a continuum for some polarity properties. The hydrated electron (ehy) is very reductive chemical species, once the solvated electron hits water molecules, water becomes ionized [36]. This depends on the time consumed for interaction and the average distance

The emitting powerful electron (more than 1 MeV electron) from electron accelerator hits water molecule and then scatters. The energy of electron is lost as a result of bordering a pathway for secondary electrons. Secondary electrons keep their own powerful energy, causing water ionization and forming copious quantities of variety of reactive species (e.g., H2 H2O<sup>+</sup>

and formatting diaryl iodine (3). The

, H2O2,

Risse and Fricke [39, 40] had studied the radiolysis of water by X-rays in a closed vessel. Bubbles of hydrogen and carbon dioxide gas resulting from irradiation are found [41]. X-ray photons are highly powerful causing radiolysis of water to create an ion pair (H2O)<sup>+</sup> (ehy). The amount of ionization species produced is affected by the amount of energetic photons absorbed. Figure 7 shows that the positive and negative water molecules are unstable. These can break apart into smaller molecules. Free radicals can be formed by this breakup. Several chemical reactions might occur (oxidation reduction) by (OH, H<sup>+</sup> , and ehy) beside polymerization takes place by (•OH and •H and ehy) [42]. Also, the radiolysis products may recombine individually, forming gases such as H2 and H2O2 [43], and hence the bubbles are formed due to an evolving mixture of H2 and O2 gases. H2 present in the solution, or the "ehy," may cause reduction reactions.

Figure 7. In radiolysis, bulk water is ionized to form an (H2O+ )aq/(e)aq pair. The (H2O+ )aq quickly converts to (• OH) and + H to become (H2)aq. And, the hydrated electron (ehy) hits another water molecule to become (H2O)aq, which converts to (OH) and • H to become (H2)aq.

## 5. Gamma radiation

Radioisotopes, e.g., (Co-60 h1/2 = 5.3 years, Cs-137 h1/2 = 30 years, and Ir-192 h1/2 = 74 days) are considered as the sources of gamma rays. The radiation chemistry of polymers dissolved in water is the chemistry of reactions with • OH, • H, and ehy. The effect of ionizing radiation on water was first studied in 1913 by Duane and Scheuer [44] and the results were confirmed by Lanning and Lind after 25 years at 1938 [45]. Several chemical reactions occur in irradiated systems both indirect and direct reactions which take place homogeneously. The latter reactions are studied in details for the case of water radiolysis by γ-irradiation. The ultra-pure water irradiated by γ rays produces 11 reactive species resulted from 20 reactions, while in acidic water it produces 7 reactive species resulted from 10 reactions [46].

A background of water radiolysis is expected to fluctuate a detection of the majority of

Ionization of H2O occurs as: H+ � H3O<sup>+</sup> and OH�. The question here is how this really happened in ultra-pure water solution that contains water molecules? The oxygen molecule with two lone pair of electrons and two hydrogen atoms react with another water molecule under the impact of high power electromagnetic wave (ionizing radiation). The H<sup>+</sup> atom

. The production of hydrated electron (ehy) was detected surrounded with opposite charge

radiation, the water molecule returns to the initial state. The equations of radical production

The polymerization reactions depend on several parameters: (1) chemical structure of the polymer (e.g., monomer containing aromatic rings has a much greater resistance to radiation crosslinking rather than the aliphatic monomer), (2) pH and temperature of the polymerization system, (3) kind and composition of the appropriate solvent, and (4) exposure time. The control of all of these parameters facilitates the modification of polymers by radiation

of water molecules. This (ehy) hits one water molecule to produce two radicals (•

, HO�, H<sup>+</sup> ions, and ehy). A track of initial

Ionizing Radiation-Induced Polymerization http://dx.doi.org/10.5772/intechopen.73234 123

). After finishing the exposure to ionizing

H3O<sup>þ</sup> <sup>þ</sup> ehy ! 2H• <sup>þ</sup> •OH (9)

H2O<sup>þ</sup> <sup>þ</sup> ehy ! <sup>H</sup>• <sup>þ</sup> •OH (10)

<sup>H</sup><sup>þ</sup> <sup>þ</sup> ehy <sup>þ</sup> H2O ! 2H• <sup>þ</sup> •OH (11)

) is to great extent, similar to

H and •

OH)

primary products of water ions formation (H3O<sup>+</sup>

Figure 8. The close system of water radiolysis induced by gamma rays.

leaves the surrounded water molecules as (H2O<sup>+</sup>

by water ionization by (ehy) are as follows:

interacts with H2O to form H3O+ and �OH. This structure (H3O+

species formation is shown in Figure 8.

H+

In ultra-pure irradiated water, there are no impurities that can scavenge radicals and prevent the tracks of radiolysis to expand. The increase of radical concentrations leads to a homogeneous radical-radical combination (H2, H2O2, and O2). The excess radicals also react with the products of (H2, H2O2, and O2) in homogeneous reactions. All of these phenomena must be considered in polymerization reaction induced by gamma irradiation. Two cases have been established in the polymerization induced by ionizing radiation, namely, crosslinking and degradation. In the polymerization system that starts with crosslinkable monomer or polymer, the system will consume radicals (• H and • OH) in polymerization reaction and limits build-up of (H2, H2O2, and O2). While in the system that tends to degradable polymer such as natural polymer, the yield of radicals' duplicates and the breaks of C–C bonds increase and tend to enhance the polymer degradation by formation of a net of oxidative spices such as H2O2, O2, and O3.

It is interesting to investigate the proposed mechanism of the polymerization reaction induced by gamma irradiation in an aqueous system. This section, presents the steps of common three polymerization mechanisms (radical, cationic, and anionic). It should be observed that polymerization reaction randomly forms covalent bonds cross the monomer and short chains in space.

Figure 8. The close system of water radiolysis induced by gamma rays.

5. Gamma radiation

H to become (H2)aq.

122 Ionizing Radiation Effects and Applications

+

(OH) and •

consume radicals (•

water is the chemistry of reactions with •

Figure 7. In radiolysis, bulk water is ionized to form an (H2O+

H and •

Radioisotopes, e.g., (Co-60 h1/2 = 5.3 years, Cs-137 h1/2 = 30 years, and Ir-192 h1/2 = 74 days) are considered as the sources of gamma rays. The radiation chemistry of polymers dissolved in

H to become (H2)aq. And, the hydrated electron (ehy) hits another water molecule to become (H2O)aq, which converts to

)aq/(e)aq pair. The (H2O+

water was first studied in 1913 by Duane and Scheuer [44] and the results were confirmed by Lanning and Lind after 25 years at 1938 [45]. Several chemical reactions occur in irradiated systems both indirect and direct reactions which take place homogeneously. The latter reactions are studied in details for the case of water radiolysis by γ-irradiation. The ultra-pure water irradiated by γ rays produces 11 reactive species resulted from 20 reactions, while in

In ultra-pure irradiated water, there are no impurities that can scavenge radicals and prevent the tracks of radiolysis to expand. The increase of radical concentrations leads to a homogeneous radical-radical combination (H2, H2O2, and O2). The excess radicals also react with the products of (H2, H2O2, and O2) in homogeneous reactions. All of these phenomena must be considered in polymerization reaction induced by gamma irradiation. Two cases have been established in the polymerization induced by ionizing radiation, namely, crosslinking and degradation. In the polymerization system that starts with crosslinkable monomer or polymer, the system will

and O2). While in the system that tends to degradable polymer such as natural polymer, the yield of radicals' duplicates and the breaks of C–C bonds increase and tend to enhance the polymer

It is interesting to investigate the proposed mechanism of the polymerization reaction induced by gamma irradiation in an aqueous system. This section, presents the steps of common three polymerization mechanisms (radical, cationic, and anionic). It should be observed that polymerization reaction randomly forms covalent bonds cross the monomer and short chains in space.

degradation by formation of a net of oxidative spices such as H2O2, O2, and O3.

OH) in polymerization reaction and limits build-up of (H2, H2O2,

H, and ehy. The effect of ionizing radiation on

)aq quickly converts to (•

OH) and

OH, •

acidic water it produces 7 reactive species resulted from 10 reactions [46].

A background of water radiolysis is expected to fluctuate a detection of the majority of primary products of water ions formation (H3O<sup>+</sup> , HO�, H<sup>+</sup> ions, and ehy). A track of initial species formation is shown in Figure 8.

Ionization of H2O occurs as: H+ � H3O<sup>+</sup> and OH�. The question here is how this really happened in ultra-pure water solution that contains water molecules? The oxygen molecule with two lone pair of electrons and two hydrogen atoms react with another water molecule under the impact of high power electromagnetic wave (ionizing radiation). The H<sup>+</sup> atom interacts with H2O to form H3O+ and �OH. This structure (H3O+ ) is to great extent, similar to H+ . The production of hydrated electron (ehy) was detected surrounded with opposite charge of water molecules. This (ehy) hits one water molecule to produce two radicals (• H and • OH) leaves the surrounded water molecules as (H2O<sup>+</sup> ). After finishing the exposure to ionizing radiation, the water molecule returns to the initial state. The equations of radical production by water ionization by (ehy) are as follows:

$$\mathrm{H\_3O^+} + e\_{\mathrm{hy}} \xrightarrow{\cdot \longrightarrow \cdot} 2\mathrm{H^+} + \mathrm{^\*OH} \tag{9}$$

$$\text{H}\_2\text{O}^+ + e\_{ly} \xrightarrow{\text{H}^+} \text{H}^+ + ^\bullet \text{OH} \tag{10}$$

$$\text{H}^+ + e\_{\text{hy}} + \text{H}\_2\text{O} \xrightarrow{\text{---}} 2\text{H}^+ + \text{"OH} \tag{11}$$

The polymerization reactions depend on several parameters: (1) chemical structure of the polymer (e.g., monomer containing aromatic rings has a much greater resistance to radiation crosslinking rather than the aliphatic monomer), (2) pH and temperature of the polymerization system, (3) kind and composition of the appropriate solvent, and (4) exposure time. The control of all of these parameters facilitates the modification of polymers by radiation techniques. Polymerization reactions are generally classified as follows: (1) predominantly undergoing crosslinking that gives hydrogel when the polymer has hydrophilic character, (2) grafted film, (3) dimerization, and (4) oligomerization.

formed by •

corresponding (HOO•

the hydrogel formation is of high yields in oxygen-free systems.

OH radicals abstraction of hydrogen. While in non-equivalent H atoms positions

Ionizing Radiation-Induced Polymerization http://dx.doi.org/10.5772/intechopen.73234 125

) peroxyl radicals leading to strand breakage [55]. It is well-known that

Figure 10. Proposed macroradicals formation induced by ionizing irradiation of water-soluble PVA in aqueous solution.

in polymer backbone, hydroxyl radical abstract hydrogen atoms from various attitudes (randomly) lead to the formation of different kinds of macroradicals of different polymer structure. As seen in Figure 9, macroradicals may undergo intra-molecular crosslinking giving PEO hydrogel network with randomly covalent bonds beside H bonds. The inter-molecular crosslinking is the most important reaction by "recombination" of macroradicals localized on two different chains, at this condition, the yield of crosslinked hydrogel will increase [52] (Figure 9b). Furthermore, inter-molecular "disproportionation" involves either linked radical or scission in the same chain. This process does not lead to hydrogel formation [53] (Figure 9a). There is a competition between inter- and intra-molecular crosslinking fully recognized in using ionizing radiation. Energetic photon could increase the yield of inter-molecular crosslinks (Gx), defined as the number of crosslinks formed in the system upon absorption of 1 J of ionizing radiation energy [54]. So the formation of hydrogel network depends on the energy of interchain bonds formation. The radicals combine by various ways that can be estimated in a number of routes. Figure 10 presents various proposed routes of crosslinked formation of PVA. As illustrated in the figure, the hydrogen bond formation between chains increases the chance of polymerization mechanism to undergo intra-molecular "recombination" crosslinking rather than inter-molecular "disproportionation." However, in the case of oxygen gas, "disproportionation" reactions will be predominantly leading to the formation of carbonyl groups. In the presence of oxygen, the PVA radicals are converted into the

#### 5.1. Radical polymerization induced by gamma irradiation

Radical initiation is an easy and a suitable method for the synthesis of hydrogels. When vinyl monomers are exposed to ionizing radiation in aqueous media (e.g., water), the radiolysis of water leads to formation of radicals that are responsible for initiating the polymerization reactions. In the propagation steps, the rapid recombination of two monomers takes place [47–49]. Figure 9 shows the proposed mechanism of ionizing radiation-induced hydrogel formation. An example for this is hydrophilic crosslinked hydrogel. When the irradiated polymer and/or monomer is dissolved in aqueous solution, reactive radicals on C• atom are formed [50]. The main reactive species generated in water by irradiation are hydroxyl radicals • OH, hydrated electrons (ehy), and hydrogen radicals • H. The hydrated electron (ehy) reacts with water molecules to produce • OH and • H radicals (Figure 1). The direct action of ehy is very weak [51]. However, two • H radicals combine fast to form H2 gas. Figure 9 demonstrates the proposed mechanism of PEO (poly ethylene oxide) radical polymerization. The main reactive species (• OH radical) are responsible for the polymerization process. In general, the number of radicals generated in water is higher than that in polymer and/or monomer itself. Therefore, the description in Figure 9 below will only refer to the indirect mechanism. Hydroxyl (• OH)/abstract hydrogen atoms from C–H in polymer molecules leads to form macroradical (C• ). Thus, macroradical (polymer radicals) causes 3D crosslinked polymer. The rate constant of the polymerization reactions is proportional to the number of radical's production. Details are shown in Figure 9 for only polyethylene oxide, all the hydrogen atoms are equivalent in the polymer molecule, so that the only one type of macroradicals C• can be

Figure 9. Proposed macroradicals formation induced by ionizing irradiation of water-soluble PEO in aqueous solution.

formed by • OH radicals abstraction of hydrogen. While in non-equivalent H atoms positions in polymer backbone, hydroxyl radical abstract hydrogen atoms from various attitudes (randomly) lead to the formation of different kinds of macroradicals of different polymer structure.

techniques. Polymerization reactions are generally classified as follows: (1) predominantly undergoing crosslinking that gives hydrogel when the polymer has hydrophilic character, (2)

Radical initiation is an easy and a suitable method for the synthesis of hydrogels. When vinyl monomers are exposed to ionizing radiation in aqueous media (e.g., water), the radiolysis of water leads to formation of radicals that are responsible for initiating the polymerization reactions. In the propagation steps, the rapid recombination of two monomers takes place [47–49]. Figure 9 shows the proposed mechanism of ionizing radiation-induced hydrogel formation. An example for this is hydrophilic crosslinked hydrogel. When the irradiated polymer and/or monomer is dissolved in aqueous solution, reactive radicals on C• atom are formed [50]. The main reactive species generated in water by irradiation are hydroxyl radicals

the proposed mechanism of PEO (poly ethylene oxide) radical polymerization. The main

number of radicals generated in water is higher than that in polymer and/or monomer itself. Therefore, the description in Figure 9 below will only refer to the indirect mechanism.

rate constant of the polymerization reactions is proportional to the number of radical's production. Details are shown in Figure 9 for only polyethylene oxide, all the hydrogen atoms are equivalent in the polymer molecule, so that the only one type of macroradicals C• can be

Figure 9. Proposed macroradicals formation induced by ionizing irradiation of water-soluble PEO in aqueous solution.

OH and •

H. The hydrated electron (ehy) reacts

H radicals (Figure 1). The direct action of ehy is

H radicals combine fast to form H2 gas. Figure 9 demonstrates

OH radical) are responsible for the polymerization process. In general, the

OH)/abstract hydrogen atoms from C–H in polymer molecules leads to form

). Thus, macroradical (polymer radicals) causes 3D crosslinked polymer. The

grafted film, (3) dimerization, and (4) oligomerization.

•

5.1. Radical polymerization induced by gamma irradiation

OH, hydrated electrons (ehy), and hydrogen radicals •

with water molecules to produce •

very weak [51]. However, two •

124 Ionizing Radiation Effects and Applications

reactive species (•

Hydroxyl (•

macroradical (C•

As seen in Figure 9, macroradicals may undergo intra-molecular crosslinking giving PEO hydrogel network with randomly covalent bonds beside H bonds. The inter-molecular crosslinking is the most important reaction by "recombination" of macroradicals localized on two different chains, at this condition, the yield of crosslinked hydrogel will increase [52] (Figure 9b). Furthermore, inter-molecular "disproportionation" involves either linked radical or scission in the same chain. This process does not lead to hydrogel formation [53] (Figure 9a). There is a competition between inter- and intra-molecular crosslinking fully recognized in using ionizing radiation. Energetic photon could increase the yield of inter-molecular crosslinks (Gx), defined as the number of crosslinks formed in the system upon absorption of 1 J of ionizing radiation energy [54]. So the formation of hydrogel network depends on the energy of interchain bonds formation. The radicals combine by various ways that can be estimated in a number of routes. Figure 10 presents various proposed routes of crosslinked formation of PVA. As illustrated in the figure, the hydrogen bond formation between chains increases the chance of polymerization mechanism to undergo intra-molecular "recombination" crosslinking rather than inter-molecular "disproportionation." However, in the case of oxygen gas, "disproportionation" reactions will be predominantly leading to the formation of carbonyl groups. In the presence of oxygen, the PVA radicals are converted into the corresponding (HOO• ) peroxyl radicals leading to strand breakage [55]. It is well-known that the hydrogel formation is of high yields in oxygen-free systems.

Figure 10. Proposed macroradicals formation induced by ionizing irradiation of water-soluble PVA in aqueous solution.

#### 5.2. Ionic polymerization: anionic and cationic polymerization

Cationic and anionic polymerization induced by ionizing radiation are more complicated than radical polymerization mechanism, where cationic and anionic polymerization require some conditions and additives that act as Lewis acid and base, respectively. Gamma irradiation is very useful to obtain these additives by solvent radiolysis. Before formulating the main steps of the ionic polymerization mechanisms in radiation initiation, this section will consider the main concepts forcing an ionizing radiation-induced ionic polymerization. First, the nature of chemical structure of monomers, e.g., for cationic mechanism is vinyl ethers, isobutylene, βpinene, and cyclopentadiene, and for anionic mechanism is vinylidene cyanide and nitroethylene. Second, it is necessary to use the radiation tool for formation and stabilization of C<sup>+</sup> (Carbonium) in cationic and C¯ (Carbanion) in anionic mechanisms. Third, choosing appropriate halogenated solvents for cationic polymerization, e.g., methylene chloride, ethyl chloride, tetrafluoromethane, difluorodichloromethane, perchloro ethylene, etc. These solvents generally undergo radiolysis to yield Lewis acid (electron acceptor) from a Lewis base (polymer) and to form "adduct." Solvent for anionic polymerization, e.g., triethylamine, dimethyl formamide, tetrahydrofuran, isopropylamine, ethylpropyl ketone, acetone, pyridine, etc. These solvents that generally undergo radiolysis to yield Lewis base (electron donating) are suitable for anionic mechanism.

cationic polymerization reaction. Figure 11 shows the essential step of the formation of Lewis acid by solvent radiolysis. For that tetrachloroethylene, a chlorinated hydrocarbon solvent, could be used as effective reaction media to promote the cationic polymerization of

The gamma radiolysis (γ-rays) of tetrachloroethylene liberates: (i) chloride ions (Cl), (ii)

proposed mechanism, illustrated in Figure 12, of radiation-induced cationic polymerization of linear polystyrene in tetrachloroethylene gave rather good reproducibility and shows a good agreement with the results of Ueno et al. [63]. Also, in the polymerization of styrene in methylene chloride, Tsuda [64] has suggested that hydrogen chloride produced by the irradiation of chlorinated hydrocarbons causing initiation of cationic polymerization of styrene. It is

Figure 12. The proposed mechanism of styrene radical polymerization induced by gamma irradiation.

) that act as Lewis acid species [59], and/or (iii) combined cation radical

Ionizing Radiation-Induced Polymerization http://dx.doi.org/10.5772/intechopen.73234 127

) [60–62], which can induce PS linear chain recombination (crosslinking). The

styrene [58].

species (C+•

carbonium species (C<sup>+</sup>

Some compounds such as solid additives, catalyze the radiation-induced cationic polymerization, e.g., calcium, zinc, silica gel, and magnesium oxides [56, 57]. Even the monomer can be polymerized by combining the two mechanisms (radical/anionic or radical/cationic), then by changing the conditions (temperature and solvent).

#### 5.2.1. Cationic polymerization

The rate of polymerization by cationic mechanism depends on the stability of carbonium ions in the macromolecules. This can be achieved if the center of the charged ion is strongly solvated by opposite charge and the distance between solvated ions is far. For the carbonium ion to be sufficiently stable and have enough lifetimes, it is preferred to choose a monomer that has a sufficient nucleophilic character. Examples of active monomers that can undergo cationic polymerization by gamma radiation are styrene monomer. In this monomer, the combination of a carbonium with an electron donating (Lewis acid) leads to

Figure 11. The essential step is the formation of Lewis acid by solvent radiolysis.

cationic polymerization reaction. Figure 11 shows the essential step of the formation of Lewis acid by solvent radiolysis. For that tetrachloroethylene, a chlorinated hydrocarbon solvent, could be used as effective reaction media to promote the cationic polymerization of styrene [58].

5.2. Ionic polymerization: anionic and cationic polymerization

(Carbonium) in cationic and C¯

126 Ionizing Radiation Effects and Applications

for anionic mechanism.

5.2.1. Cationic polymerization

changing the conditions (temperature and solvent).

Figure 11. The essential step is the formation of Lewis acid by solvent radiolysis.

Cationic and anionic polymerization induced by ionizing radiation are more complicated than radical polymerization mechanism, where cationic and anionic polymerization require some conditions and additives that act as Lewis acid and base, respectively. Gamma irradiation is very useful to obtain these additives by solvent radiolysis. Before formulating the main steps of the ionic polymerization mechanisms in radiation initiation, this section will consider the main concepts forcing an ionizing radiation-induced ionic polymerization. First, the nature of chemical structure of monomers, e.g., for cationic mechanism is vinyl ethers, isobutylene, βpinene, and cyclopentadiene, and for anionic mechanism is vinylidene cyanide and nitroethylene. Second, it is necessary to use the radiation tool for formation and stabilization of C<sup>+</sup>

ate halogenated solvents for cationic polymerization, e.g., methylene chloride, ethyl chloride, tetrafluoromethane, difluorodichloromethane, perchloro ethylene, etc. These solvents generally undergo radiolysis to yield Lewis acid (electron acceptor) from a Lewis base (polymer) and to form "adduct." Solvent for anionic polymerization, e.g., triethylamine, dimethyl formamide, tetrahydrofuran, isopropylamine, ethylpropyl ketone, acetone, pyridine, etc. These solvents that generally undergo radiolysis to yield Lewis base (electron donating) are suitable

Some compounds such as solid additives, catalyze the radiation-induced cationic polymerization, e.g., calcium, zinc, silica gel, and magnesium oxides [56, 57]. Even the monomer can be polymerized by combining the two mechanisms (radical/anionic or radical/cationic), then by

The rate of polymerization by cationic mechanism depends on the stability of carbonium ions in the macromolecules. This can be achieved if the center of the charged ion is strongly solvated by opposite charge and the distance between solvated ions is far. For the carbonium ion to be sufficiently stable and have enough lifetimes, it is preferred to choose a monomer that has a sufficient nucleophilic character. Examples of active monomers that can undergo cationic polymerization by gamma radiation are styrene monomer. In this monomer, the combination of a carbonium with an electron donating (Lewis acid) leads to

(Carbanion) in anionic mechanisms. Third, choosing appropri-

The gamma radiolysis (γ-rays) of tetrachloroethylene liberates: (i) chloride ions (Cl), (ii) carbonium species (C<sup>+</sup> ) that act as Lewis acid species [59], and/or (iii) combined cation radical species (C+• ) [60–62], which can induce PS linear chain recombination (crosslinking). The proposed mechanism, illustrated in Figure 12, of radiation-induced cationic polymerization of linear polystyrene in tetrachloroethylene gave rather good reproducibility and shows a good agreement with the results of Ueno et al. [63]. Also, in the polymerization of styrene in methylene chloride, Tsuda [64] has suggested that hydrogen chloride produced by the irradiation of chlorinated hydrocarbons causing initiation of cationic polymerization of styrene. It is

Figure 12. The proposed mechanism of styrene radical polymerization induced by gamma irradiation.

well-known that in chlorinated solvent, the polymerization of styrene proceeds well by cationic polymerization. This proposed mechanism is in a good agreement with studies carried out by Sigwalt and Moreau [65]. As shown in Figure 12, the initiation starts by the formation of Cl due to solvent radiolysis which is released as HCl giving a carbon cation on styrene unites. Propagation step is formed by head-to-tail addition in carbocation polymerization. β-Hydrogen atoms of the propagating carbonium cation are quite acidic, owing to the delocalization of the positive charge [66] belonging to the phenyl ring. The transfer of positive charge in the phenyl ring gives a chance of addition on the phenyl ring causing the formation of 3D crosslinked polymer. Still cationic polymerization may be one of the most challenging areas of future research [67]. The final structure as seen in an ideal shape (head-to-tail), sometimes, the propagating chain may rearrange randomly.

8. Image gently advocates on the safety of radiation uses

Ionizing Radiation-Induced Polymerization http://dx.doi.org/10.5772/intechopen.73234 129

Address all correspondence to: mohamed\_ghobashy@yahoo.com;

Technology (NCRRT), Atomic Energy Authority, Nasr City, Cairo, Egypt

Radiation Research of Polymer Department, National Center for Radiation Research and

[1] Ghobashy MM, Khozemey E. Sulfonated gamma-irradiated blend poly(styrene/ethylenevinyl acetate) membrane and their electrical properties. Advances in Polymer Technology.

[2] Ghobashy MM. Effect of sulfonated groups on the proton and methanol transport behavior of irradiated PS/PEVA membrane. International Journal of Plastics Technology. 2017;

[3] Ghobashy MM, Abdel Reheem AM, Mazied NA. Ion etching induced surface patterns of blend polymer (poly ethylene glycol–poly methyl methacrylate) irradiated with gamma

[4] Ghobashy MM. In-situ core-shell polymerization of magnetic polymer nanocomposite (PAAc/Fe3O4) particles via gamma radiation. Nanocomposites. 2017;3(1):42-46. DOI:

Author details

References

Mohamed Mohamady Ghobashy

mohamed.ghobashy@eaea.org.eg

2016. DOI: 10.1002/adv.21781

10.1080/20550324.2017.1316600

21(1):130-143. DOI: 10.1007/s12588-017-9176-5

rays. International Polymer Processing. 2017;32(2):174-182

## 6. Advantages of ionizing radiation-induced polymerization

The advantages are:


## 7. Concluding remarks

This chapter presents a very brief introduction of the interactions between high energy photons with water molecules, and the subsequent physico-chemical stage of water radiolysis based on previous literatures. Some proposed mechanisms in radiation polymerization were also outlined in this chapter. The main reactive species ((ehy) hydrated electron, • OH radicals, and H• radicals) generated from water radiolysis are presented. The ionized species of water molecules involving them are ultrafast, occurring on femtosecond. The reason to focus on water radiolysis is the reactivity of radicals and hydrated electron, which are the initiators of polymerization reactions. Irradiation can be very useful in the processing of polymer blends, which often undergo physical phase separation of components due to incompatibility of materials. In a number of blend systems, irradiation has been used to induce crosslinking of one or more of the components and/or formation of crosslinking between the different phases, resulting in improvement of physical properties.

## 8. Image gently advocates on the safety of radiation uses

## Author details

well-known that in chlorinated solvent, the polymerization of styrene proceeds well by cationic polymerization. This proposed mechanism is in a good agreement with studies carried out by Sigwalt and Moreau [65]. As shown in Figure 12, the initiation starts by the formation of Cl due to solvent radiolysis which is released as HCl giving a carbon cation on styrene unites. Propagation step is formed by head-to-tail addition in carbocation polymerization. β-Hydrogen atoms of the propagating carbonium cation are quite acidic, owing to the delocalization of the positive charge [66] belonging to the phenyl ring. The transfer of positive charge in the phenyl ring gives a chance of addition on the phenyl ring causing the formation of 3D crosslinked polymer. Still cationic polymerization may be one of the most challenging areas of future research [67]. The final structure as seen in an ideal shape (head-to-tail), sometimes,

1. Easy process of polymerizing a wide range of monomers which are resistant to polymer-

2. Very safe, in case of polymerization involving hazardous compounds (e.g., Organo chlo-

4. Increased purity of polymer obtained without by product; while in conventional methods,

This chapter presents a very brief introduction of the interactions between high energy photons with water molecules, and the subsequent physico-chemical stage of water radiolysis based on previous literatures. Some proposed mechanisms in radiation polymerization were

and H• radicals) generated from water radiolysis are presented. The ionized species of water molecules involving them are ultrafast, occurring on femtosecond. The reason to focus on water radiolysis is the reactivity of radicals and hydrated electron, which are the initiators of polymerization reactions. Irradiation can be very useful in the processing of polymer blends, which often undergo physical phase separation of components due to incompatibility of materials. In a number of blend systems, irradiation has been used to induce crosslinking of one or more of the components and/or formation of crosslinking between the different phases,

OH radicals,

also outlined in this chapter. The main reactive species ((ehy) hydrated electron, •

the propagating chain may rearrange randomly.

ization reaction by conventional methods [68].

rine) that can be decomposed by radiation [69, 70].

it needs complicated purification steps [73, 74].

resulting in improvement of physical properties.

The advantages are:

128 Ionizing Radiation Effects and Applications

7. Concluding remarks

6. Advantages of ionizing radiation-induced polymerization

3. Polymerization reaction in the solid state could be carried out [71, 72].

Mohamed Mohamady Ghobashy

Address all correspondence to: mohamed\_ghobashy@yahoo.com; mohamed.ghobashy@eaea.org.eg

Radiation Research of Polymer Department, National Center for Radiation Research and Technology (NCRRT), Atomic Energy Authority, Nasr City, Cairo, Egypt

## References


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[28] Felder L, Kirchmayr R, Bellus D. U.S. Patent No. 4,088,554. Washington, DC: U.S. Patent

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**Chapter 7**

**Provisional chapter**

**Interaction with Matter of Ionizing Radiation and**

**Interaction with Matter of Ionizing Radiation and** 

DOI: 10.5772/intechopen.74691

Interaction of matter with "ionizing radiation," that is, high-energy electromagnetic radiation (X- or gamma rays) or α- or β-particles, can promote chemical change which commonly involves free radicals. Free radicals formed by high-energy radiation in solids

**Keywords:** ionizing radiation, radical, radiation chemistry, radiation damage center,

The interaction of ionized radiation with matter brings some changes in matter. These changes are called the radical or the radiation damage centers. Among the methods of radical formation in matter structure, ionizing radiation plays an important role. In addition to ionizing radiation, the chemical reactions and the thermal effects can also lead to radical formation.

In irradiative processes, the energy required to form radicals is generated either by **electromagnetic radiation (ultraviolet (UV) or visible light, X-rays, etc.)** or by **particle radiation**

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Radiation Damages (Radicals)**

**Radiation Damages (Radicals)**

Betül Çalişkan and Ali Cengiz Çalişkan

Betül Çalişkan and Ali Cengiz Çalişkan

http://dx.doi.org/10.5772/intechopen.74691

**Abstract**

**1. Introduction**

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

can then be identified by analysis of their EPR spectra.

There are three different applications for radical formation:

**c.** redox processes (oxidation-reduction reactions) [1, 2].

**a.** irradiation (photolysis and radiolysis),

**b.** thermolysis (thermal homolysis),

electron paramagnetic resonance (EPR)


#### **Interaction with Matter of Ionizing Radiation and Radiation Damages (Radicals) Interaction with Matter of Ionizing Radiation and Radiation Damages (Radicals)**

DOI: 10.5772/intechopen.74691

Betül Çalişkan and Ali Cengiz Çalişkan Betül Çalişkan and Ali Cengiz Çalişkan

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74691

**Abstract**

[69] Mincher BJ, Wells RP, Reilly HJ. Public Acceptability of the Use of Gamma Rays from Spent Nuclear Fuel as a Hazardous Waste Treatment Process. Idaho Falls, ID, United

[70] Chmielewski AG, Haji-Saeid M, Ahmed S. Progress in radiation processing of polymers. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with

[71] Okamura S, Hayashi K, Kitanishi Y. Radiation-induced solid-state polymerization of ring compounds. Journal of Polymer Science Part A: Polymer Chemistry. 1962;58(166):925-953

[72] Baysal B, Adler G, Ballantine D, Colombo P. Solid state polymerization of acrylamide initiated by gamma radiation. Journal of Polymer Science Part A: Polymer Chemistry.

[73] Cheng J, Deming TJ. Synthesis of polypeptides by ring-opening polymerization of αamino acid N-carboxyanhydrides. In: Peptide-Based Materials. Berlin Heidelberg:

[74] Erdmenger T, Guerrero-Sanchez C, Vitz J, Hoogenboom R, Schubert US. Recent developments in the utilization of green solvents in polymer chemistry. Chemical Society

States: EG and G Idaho, Inc.; 1992

1960;44(143):117-127

134 Ionizing Radiation Effects and Applications

Springer; 2011. pp. 1-26

Reviews. 2010;39(8):3317-3333

Materials and Atoms. 2005;236:1, 44-54

Interaction of matter with "ionizing radiation," that is, high-energy electromagnetic radiation (X- or gamma rays) or α- or β-particles, can promote chemical change which commonly involves free radicals. Free radicals formed by high-energy radiation in solids can then be identified by analysis of their EPR spectra.

**Keywords:** ionizing radiation, radical, radiation chemistry, radiation damage center, electron paramagnetic resonance (EPR)

**1. Introduction**

The interaction of ionized radiation with matter brings some changes in matter. These changes are called the radical or the radiation damage centers. Among the methods of radical formation in matter structure, ionizing radiation plays an important role. In addition to ionizing radiation, the chemical reactions and the thermal effects can also lead to radical formation. There are three different applications for radical formation:


In irradiative processes, the energy required to form radicals is generated either by **electromagnetic radiation (ultraviolet (UV) or visible light, X-rays, etc.)** or by **particle radiation**

(high-energy electrons; α, β, γ particles; neutrons; protons; etc.). Processes involving light absorption are called photochemistry [1]. Deterioration of the structure of the material by light effect is called photolysis. Deterioration of the structure of the material exposed to ionizing radiation is called radiolysis.

Charged particles are a **directly ionizing radiation** group. These particles include **energetic electrons (negatrons)**, **positrons**, **protons**, **alpha particles**, **charged mesons**, **muons**, and **heavy ions** (**ionizing atoms**). This type of ionizing radiation interacts primarily with matter via the Coulomb force. Particles push or attract electrons from atoms and molecules due to

Interaction with Matter of Ionizing Radiation and Radiation Damages (Radicals)

http://dx.doi.org/10.5772/intechopen.74691

137

Uncharged particles form an **indirectly ionizing radiation** group. Best examples for indirectly ionizing radiation type are **photons above 10 keV** (**X-rays** and **gamma rays**) and **all** 

Interaction of X-ray and gamma ray photons with matter causes ionization. This process is

**a. Low-energy photons** give all their energy to an electron, which causes the electrons to break apart from atoms or molecules. This type of interaction is called **photoelectric inter-**

**b. Intermediate-energy photons** interact with electrons as a result of the **Compton event**.

**c. Photons with more than 1.02 MeV of energy** are affected by pair production. (At around 1.02 MeV, the Compton effect continues, but the pair production is more effective.) As a result, the photon disappears and an electron-positron pair forms (due to momentum and energy conservation, this event occurs near a nucleus). The total kinetic energy of the electron-positron couple is equal to the photon energy, which is lower than the sum of and the rest-mass energies of the electron and the positron (1.02 MeV). These electrons and positrons act as **directly ionizing radiation**. As the positron continues its path, it loses its kinetic energy. As a result, they encounter an electron and destroy each other (the pair disappears). As a result of the pair production, two gamma photons come to the foreground. The two photons, which usually have an energy of 0.511 MeV, spread out to form an angle

A photon can enter into interaction with any of these events. However, more than 1022 MeV of energetic photons are required for double formation. The determination of the type of interaction depends on the energy of the photon and the material the photon interacts with. **Interaction of the material with the neutron** causes inelastic collisions. These are listed as neutron capture (or activation) and fission. Both interactions are nuclear interactions. A nucleus that collides inelastically with the neutron is excited at a higher energy level. This

In the neutron capture, the interacting nucleus absorbs the neutron. After all, the energy from

**action**. The photon then disappears from the medium.

Photons and electrons are scattered in different directions.

their charge.

**neutrons**.

mainly in three different ways:

of 180° with each other.

**a.** as a gamma ray, **b.** as a beta particle,

energy is thrown from the nucleus in three ways:

**c.** as both a gamma ray and a beta particle.

the nucleus goes away in four ways:

The electron paramagnetic resonance (EPR) method is used for the investigation of the radiation damage centers, which occur in the structure of the material. The breakage in the structure of the material allows the material to become paramagnetic. The paramagnetic centers are determined by EPR spectroscopy.

Much work has been done on the interaction of organic and inorganic materials with ionizing radiation. Most of these studies are on EPR [3, 4]. Generally, EPR works with gamma rays, which have the highest energy radiation [5–7].

The aim of the chapter is to recognize the types of radiation, to group the charged or uncharged particles in the ionized radiation group, and to focus on the EPR method, which will examine their effect on matter. High-energy energetic gamma and X-rays cause permanent damage to the material. They constitute defects in chemical structure. These disorders are often referred to as paramagnetic centers or radiation damage centers. Radiation damage centers are seen as free radicals in the form of breaking bonds in the structure and as anion or cation radicals in the form of electron exchange. The EPR method is used to investigate such impairments or paramagnetic centers occurring in structures of organic or inorganic materials. In this chapter, the effects of ionizing radiation on the substance will be analyzed using the EPR method.

## **2. Interaction with matter of ionizing radiation and radiation damages (radicals)**

#### **2.1. Ionizing radiation**

Ionizing or high-energy radiation devices can be examined in three groups [8–10]:


Reactive radicals can be formed by the effect of ionizing radiation [13]. Radiation breaks bonds between atoms in molecules. The deterioration of the bonds occurs in two ways. If the bonds are broken **homolytically (paramagnetic)**, **free radicals** will form. If the bonds are broken **heterolytically (diamagnetic)**, **ionic fragments** are formed [14].

Certain types of low-energy radiation, such as ultraviolet light, may also cause ionization. Such radiation is not from the ionizing radiation group. The lowest energy limit for ionizing radiation is around 10 keV.

Charged particles are a **directly ionizing radiation** group. These particles include **energetic electrons (negatrons)**, **positrons**, **protons**, **alpha particles**, **charged mesons**, **muons**, and **heavy ions** (**ionizing atoms**). This type of ionizing radiation interacts primarily with matter via the Coulomb force. Particles push or attract electrons from atoms and molecules due to their charge.

Uncharged particles form an **indirectly ionizing radiation** group. Best examples for indirectly ionizing radiation type are **photons above 10 keV** (**X-rays** and **gamma rays**) and **all neutrons**.

Interaction of X-ray and gamma ray photons with matter causes ionization. This process is mainly in three different ways:


A photon can enter into interaction with any of these events. However, more than 1022 MeV of energetic photons are required for double formation. The determination of the type of interaction depends on the energy of the photon and the material the photon interacts with.

**Interaction of the material with the neutron** causes inelastic collisions. These are listed as neutron capture (or activation) and fission. Both interactions are nuclear interactions. A nucleus that collides inelastically with the neutron is excited at a higher energy level. This energy is thrown from the nucleus in three ways:

**a.** as a gamma ray,

(high-energy electrons; α, β, γ particles; neutrons; protons; etc.). Processes involving light absorption are called photochemistry [1]. Deterioration of the structure of the material by light effect is called photolysis. Deterioration of the structure of the material exposed to ion-

The electron paramagnetic resonance (EPR) method is used for the investigation of the radiation damage centers, which occur in the structure of the material. The breakage in the structure of the material allows the material to become paramagnetic. The paramagnetic centers

Much work has been done on the interaction of organic and inorganic materials with ionizing radiation. Most of these studies are on EPR [3, 4]. Generally, EPR works with gamma rays,

The aim of the chapter is to recognize the types of radiation, to group the charged or uncharged particles in the ionized radiation group, and to focus on the EPR method, which will examine their effect on matter. High-energy energetic gamma and X-rays cause permanent damage to the material. They constitute defects in chemical structure. These disorders are often referred to as paramagnetic centers or radiation damage centers. Radiation damage centers are seen as free radicals in the form of breaking bonds in the structure and as anion or cation radicals in the form of electron exchange. The EPR method is used to investigate such impairments or paramagnetic centers occurring in structures of organic or inorganic materials. In this chapter, the effects of ionizing radiation on the substance will be analyzed using the EPR method.

**2. Interaction with matter of ionizing radiation and radiation** 

Ionizing or high-energy radiation devices can be examined in three groups [8–10]:

source is easily controlled [11, 12], it is more preferred.

broken **heterolytically (diamagnetic)**, **ionic fragments** are formed [14].

**a.** charged particle accelerators (X-ray generators, medium-energy electron accelerators, and

**c.** nuclear reactor (mixed radiation of gamma quantum and neutrons). Since the <sup>60</sup>Co beam

Reactive radicals can be formed by the effect of ionizing radiation [13]. Radiation breaks bonds between atoms in molecules. The deterioration of the bonds occurs in two ways. If the bonds are broken **homolytically (paramagnetic)**, **free radicals** will form. If the bonds are

Certain types of low-energy radiation, such as ultraviolet light, may also cause ionization. Such radiation is not from the ionizing radiation group. The lowest energy limit for ionizing

**b.** radioisotope sources (<sup>60</sup>Co beam source, <sup>137</sup>Cs beam source, and spent fuel elements),

izing radiation is called radiolysis.

136 Ionizing Radiation Effects and Applications

are determined by EPR spectroscopy.

**damages (radicals)**

**2.1. Ionizing radiation**

Van der Graaff accelerator),

radiation is around 10 keV.

which have the highest energy radiation [5–7].


In the neutron capture, the interacting nucleus absorbs the neutron. After all, the energy from the nucleus goes away in four ways:


Secondary particles cause ionization. If a heavy nucleus absorbs the neutron, then **the fission event** occurs. This may result in two lighter nuclei with radioactive character.

rays can break the bonds between atoms. The minimum energy required depends on the strength of the bond. The bond strength is usually about 10 eV. This value corresponds approximately to the wavelengths in the ultraviolet region. Therefore, UV region is the lowest-energy

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139

X- or gamma ray radiation occurs at very high values. When many solids in amorphous or crystalline form are exposed to X- or gamma rays, a large number of bonds can be broken. Thus, the free radical spectrum can be seen. Such high-energy radiation often produces **high free radical concentrations**. The electron spin (paramagnetic) resonance spectra of the radicals resulting from the high-energy irradiation have high signal-to-noise ratios as a function. However, it is difficult to say that there is a precise mechanism as a free radical production

In all irradiation experiments, it is usually necessary to use the capture mechanism to collect a large concentration of radicals. Examination of the dynamic concentration of radicals in the solution by X-ray or UV irradiation should normally be possible. The concentration at any time is determined by a balance between the rate of formation and the recombination rate. X- or gamma ray irradiation provides sufficient kinetic energy to move away from the site of molecular fragment or broken bonds at a certain speed. Thus, molecular fragments and broken bonds are trapped in the solid to prevent recombination at a sufficient distance. As a result, radicals can occur only in a viscous or a rigid solid phase and can be trapped. In ultraviolet irradiation, fragments or radicals obtained have a high rate of recombination since they do not have excess kinetic energy after bond breaking. Therefore, trapping is less likely to occur. The results obtained by ultraviolet irradiation method will be discussed first. X- or gamma ray irradiation method will be examined in terms of "organic" and "inorganic" compounds. It should be assumed that the radiation of interest completely releases the chemical bond and leaves two molecules of an electron containing an unpaired electron. Apart from bond breakage, the bond excitation state deals with the "triplet state" which is guided in the same direction, instead of breaking into a higher-energy level by reversing one of the bond electrons.

Ingram et al. [16] obtained the first electron paramagnetic resonance spectra of active radicals formed by ultraviolet irradiation and trapped at low temperatures. In the experiments, the compounds to be photolyzed are dissolved in various hydrocarbons and frozen to form solid glasses at liquid nitrogen temperatures. The viscosity of the resulting glass is an important parameter. After formation, there must be a structure with little rigidity that will not prevent the radicals from moving away from where they are. On the other hand, it must have a solid structure at the level that will prevent the deterioration of radical structure. Glass can be used at room temperature for such a trapping operation. Such experiments, which lead to the formation of stable radicals in plastic films, have been performed

The glass-trapping technique at low temperature was used in the studies by Lewis and Lipkin [18], which study reactive molecules, and Norman and Porter [19], who detect free radicals trapped by UV absorption spectroscopy. However, it has been shown that the glass required

region required for free radical formation.

*2.2.1. Ultraviolet irradiation*

by Bijl and Rose-Innes [17].

method, because there are many different types of damage.

The radiation weighting factor (wR) is a number that represents the value of **the relative biological effectiveness (RBE)** of the radiation. **The w<sup>R</sup> values** are related to **linear energy transfer (LET)** and are given in **Table 1**.

The relative biological activity (RBE) of a radiation type is defined as the inverse ratio of radiation absorption doses that produce biological effects at the same amount. The stochastic biological effect is a biological effect that is caused by ionizing radiation. The higher the dose, the greater the effect. However, this increase does not follow a certain proportion with the absorbed dose. It is a totally independent biological effect. An important example of the stochastic biological effect is cancer.

The tissue weighting factor (wT) represents the total loss in tissue or organs due to the stochastic effect caused by irradiation of the whole body. Irritation damages tissues or organs. A uniform equivalent dose applied over the entire body should be equal to the number of doses administered separately for all tissues and organs of the body [15].

#### **2.2. Interaction with matter of ionizing radiation and radiation damages (radicals)**

The separation of chemical bonds with radiation is one of the most common and direct methods that can be used to produce molecular fragments and free radicals. Ultraviolet, X- or, gamma


1 All values relate to the radiation incident on the body or, for internal sources, emitted from the source. 2 Excluding Auger electrons emitted from nuclei bound to DNA.

**Table 1.** Radiation weighting factors wR 1 . rays can break the bonds between atoms. The minimum energy required depends on the strength of the bond. The bond strength is usually about 10 eV. This value corresponds approximately to the wavelengths in the ultraviolet region. Therefore, UV region is the lowest-energy region required for free radical formation.

X- or gamma ray radiation occurs at very high values. When many solids in amorphous or crystalline form are exposed to X- or gamma rays, a large number of bonds can be broken. Thus, the free radical spectrum can be seen. Such high-energy radiation often produces **high free radical concentrations**. The electron spin (paramagnetic) resonance spectra of the radicals resulting from the high-energy irradiation have high signal-to-noise ratios as a function. However, it is difficult to say that there is a precise mechanism as a free radical production method, because there are many different types of damage.

In all irradiation experiments, it is usually necessary to use the capture mechanism to collect a large concentration of radicals. Examination of the dynamic concentration of radicals in the solution by X-ray or UV irradiation should normally be possible. The concentration at any time is determined by a balance between the rate of formation and the recombination rate. X- or gamma ray irradiation provides sufficient kinetic energy to move away from the site of molecular fragment or broken bonds at a certain speed. Thus, molecular fragments and broken bonds are trapped in the solid to prevent recombination at a sufficient distance. As a result, radicals can occur only in a viscous or a rigid solid phase and can be trapped. In ultraviolet irradiation, fragments or radicals obtained have a high rate of recombination since they do not have excess kinetic energy after bond breaking. Therefore, trapping is less likely to occur.

The results obtained by ultraviolet irradiation method will be discussed first. X- or gamma ray irradiation method will be examined in terms of "organic" and "inorganic" compounds. It should be assumed that the radiation of interest completely releases the chemical bond and leaves two molecules of an electron containing an unpaired electron. Apart from bond breakage, the bond excitation state deals with the "triplet state" which is guided in the same direction, instead of breaking into a higher-energy level by reversing one of the bond electrons.

#### *2.2.1. Ultraviolet irradiation*

**a.** as a gamma ray,

138 Ionizing Radiation Effects and Applications

**c.** as a beta particle,

**fer (LET)** and are given in **Table 1**.

stochastic biological effect is cancer.

**d.** by publishing both the gamma ray/X-ray and the beta particle.

administered separately for all tissues and organs of the body [15].

**event** occurs. This may result in two lighter nuclei with radioactive character.

Secondary particles cause ionization. If a heavy nucleus absorbs the neutron, then **the fission** 

The radiation weighting factor (wR) is a number that represents the value of **the relative biological effectiveness (RBE)** of the radiation. **The w<sup>R</sup> values** are related to **linear energy trans-**

The relative biological activity (RBE) of a radiation type is defined as the inverse ratio of radiation absorption doses that produce biological effects at the same amount. The stochastic biological effect is a biological effect that is caused by ionizing radiation. The higher the dose, the greater the effect. However, this increase does not follow a certain proportion with the absorbed dose. It is a totally independent biological effect. An important example of the

The tissue weighting factor (wT) represents the total loss in tissue or organs due to the stochastic effect caused by irradiation of the whole body. Irritation damages tissues or organs. A uniform equivalent dose applied over the entire body should be equal to the number of doses

The separation of chemical bonds with radiation is one of the most common and direct methods that can be used to produce molecular fragments and free radicals. Ultraviolet, X- or, gamma

**Type and energy range w<sup>R</sup>** Photons, all energies 1 Electrons and muons, all energies<sup>2</sup> 1 Neutrons, energy <10 keV 5 10–100 keV 10 >100 keV–2 MeV 20 >2–20 MeV 10 >20 MeV 5 Protons, other than recoil protons, energy >2 MeV 5 Alpha particles, fission fragments, heavy nuclei 20

All values relate to the radiation incident on the body or, for internal sources, emitted from the source.

Excluding Auger electrons emitted from nuclei bound to DNA.

1 .

**Table 1.** Radiation weighting factors wR

**2.2. Interaction with matter of ionizing radiation and radiation damages (radicals)**

**b.** as an X-ray,

1

2

Ingram et al. [16] obtained the first electron paramagnetic resonance spectra of active radicals formed by ultraviolet irradiation and trapped at low temperatures. In the experiments, the compounds to be photolyzed are dissolved in various hydrocarbons and frozen to form solid glasses at liquid nitrogen temperatures. The viscosity of the resulting glass is an important parameter. After formation, there must be a structure with little rigidity that will not prevent the radicals from moving away from where they are. On the other hand, it must have a solid structure at the level that will prevent the deterioration of radical structure. Glass can be used at room temperature for such a trapping operation. Such experiments, which lead to the formation of stable radicals in plastic films, have been performed by Bijl and Rose-Innes [17].

The glass-trapping technique at low temperature was used in the studies by Lewis and Lipkin [18], which study reactive molecules, and Norman and Porter [19], who detect free radicals trapped by UV absorption spectroscopy. However, it has been shown that the glass required for UV is also suitable for electron resonance studies, since the small defects that will scatter the UV wavelengths badly have no effect on the microwave radiation.

assumed to originate from a (*H*<sup>3</sup> *<sup>C</sup>* <sup>−</sup> *<sup>C</sup> <sup>H</sup>*3)

*2.2.2.2. Inorganic compounds*

**Figure 1.** The EPR spectrum of the gamma-irradiated DNA at 77 K.

+

withdrawal of the *OH* group in the structure giving the seven-line splitting.

obtained from UV-irradiated isopropyl alcohol [20]. This may be due to the partial electron

However, as in the case of UV-irradiated spectra and in stable aromatic ions, the theories of hyperfine interaction and hyperconjugation reveal these spectra in detail. Line widths are the same as those obtained from frozen UV-irradiated glasses. Thus, it can be argued that motional narrowing in these systems is due to dipolar interaction in the nearest proton.

Gordy et al. [26, 27] studied various amino, carboxylic, and hydroxy acids that have been X-irradiated. In some studies, large symmetric doublets are presumably due to the dipole-dipole interaction between the unpaired electron localized on an oxygen or a sulfur atom and a single proton near it. They also investigated the effect of temperature on the carboxylic acid spectra. The irradiated acetic acid is a good example of this. The hydrogen bond keeps the molecules very hard at 77 K. Thus, it has been assumed that the doublet occurs from the dipole-dipole interaction between an electron and a hydroxyl proton localized on hydroxyl oxygen [27].

Gordy et al. [26] obtained spectra obtained from X-radiation of various biological materials such as proteins and bone tissue. Comparing these spectra with those obtained from simpler acids, one can get an idea of the deterioration mechanisms in natural products. Uebersfeld et al. [28–30] studied sugar, cellulose, and similar materials exposed to gamma rays in detail. In their later work, they obtained an anisotropic EPR spectrum from a single crystal of glycine [31]. A similar situation has been observed in the study of single crystals of the X-irradiated alanine by Van Roggen et al. [32]. Whiffen et al. [25, 33] have also done much research on the analysis of EPR spectra from gamma-irradiated polymers with interesting "**oxygen effects.**". DNA is an organic compound. The EPR spectrum of the radical formed in gamma-irradiated DNA is shown in **Figure 1** [34]. As another organic compound, potassium hydroquinone monosulfonate (PHM) may be mentioned. In potassium hydroquinone monosulfonate single crystal, EPR spectrum of the radical structure resulting from gamma irradiation is shown in **Figure 2** [35].

Irradiation of **inorganic materials**, usually in a single crystal form, produces centers of damage trapped within the crystal lattice. This can form free atoms, molecules, or radicals in the crystal

radical group and was found to be larger than that

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141

Interaction with Matter of Ionizing Radiation and Radiation Damages (Radicals)

#### *2.2.1.1. Secondary radicals*

In such experiments, it has been observed that secondary radicals occur frequently when radicals are produced by photolysis by reacting with solvent molecules [20]. Hydroxyl radicals are derived from **hydrogen peroxide**. These radicals are very reactive. When a small amount of hydrogen peroxide is added to the hydrocarbon glass, secondary radicals are usually obtained by proton removal from the hydrocarbons. **OH radicals** were obtained by removal of an α-hydrogen from the isopropanol molecule via UV irradiation.

Hydrogen atom reactions and high irradiation are predictors of **secondary reaction products** for solid hydrocarbons [16]. EPR is also an ideal metric for the analysis of these complex radicals. For example, the H atoms in the frozen aqueous solutions of **H2 SO4** , **H3 PO4 ,** or **HClO4** present at liquid nitrogen temperatures (77 K) are quite stable. This provides excellent environments for future work [21].

#### *2.2.2. X and gamma ray irradiation*

### *2.2.2.1. Organic compounds*

**Radiation of an organic material** can lead to breakage of bonds between atoms. The minimum energy required for such a situation can be determined by the bond strength [21, 22]. Schneider et al. [23] observed the first electron spin (paramagnetic) resonance spectrum of radicals obtained from the organic polymethylmethacrylate compound by X-irradiation. They produced a very large electron spin (paramagnetic) resonance spectrum giving a complex hyperfine structure splitting. With the detailed analysis of the EPR spectrum, it is understood that the actually occurring state is the result of two separate interaction mechanisms in the *<sup>R</sup>* <sup>−</sup> *<sup>C</sup> <sup>H</sup>*<sup>2</sup> <sup>−</sup> *<sup>C</sup>*̇ (*<sup>C</sup> <sup>H</sup>*3)(*COOC <sup>H</sup>*3) radical [24, 25].

Gordy et al. [26, 27] have begun to investigate the radicals of biological substances exposed to X-radiation. As a clear result of the radiation damage, they found that the hyperfine splits originate from simple radical forms. The organic materials that gave these spectra were the various irradiated amino acids. Their EPR spectra were obtained after irradiation with 50 kV X-rays at room temperature. The triplet was obtained from glycine, *<sup>C</sup> <sup>H</sup>*<sup>2</sup> (*N H*<sup>2</sup> )*COOH*. The hyperfine interaction ion is due to a *C*̇ *H*2 radical having two protons. X-rays or other high-energy radiation can break down the molecules and create a variety of radicals. There are many ways to create radicals. One of them is to remove an electron, which is the primary action of irradiation, and to form an ionized molecule with small stable groups such as *<sup>N</sup> <sup>H</sup>*<sup>3</sup> *<sup>C</sup> <sup>O</sup>*<sup>2</sup> and (*<sup>C</sup> <sup>H</sup>*<sup>2</sup> ) + fragments of glycine [26].

It has been observed that the EPR spectrum of the irradiated alanine, *<sup>C</sup> <sup>H</sup>*<sup>3</sup> .*CH*(*<sup>N</sup> <sup>H</sup>*2).*COOH*, has five symmetrical lines. This suggests that the unpaired electron interacts with four equivalent protons and that the spin density is in a (*H*<sup>2</sup> *<sup>C</sup>* <sup>−</sup> *<sup>C</sup> <sup>H</sup>*<sup>2</sup> ) + group due to hyperconjugation [26].

It has been observed that the EPR spectrum obtained from the irradiated valine, *<sup>C</sup> <sup>H</sup>*<sup>3</sup> .*CH*(*C H*3). *CH*(*<sup>N</sup> <sup>H</sup>*2).*COOH*, is composed of five and seven overlapping lines. The seven-line splitting was assumed to originate from a (*H*<sup>3</sup> *<sup>C</sup>* <sup>−</sup> *<sup>C</sup> <sup>H</sup>*3) + radical group and was found to be larger than that obtained from UV-irradiated isopropyl alcohol [20]. This may be due to the partial electron withdrawal of the *OH* group in the structure giving the seven-line splitting.

However, as in the case of UV-irradiated spectra and in stable aromatic ions, the theories of hyperfine interaction and hyperconjugation reveal these spectra in detail. Line widths are the same as those obtained from frozen UV-irradiated glasses. Thus, it can be argued that motional narrowing in these systems is due to dipolar interaction in the nearest proton.

Gordy et al. [26, 27] studied various amino, carboxylic, and hydroxy acids that have been X-irradiated. In some studies, large symmetric doublets are presumably due to the dipole-dipole interaction between the unpaired electron localized on an oxygen or a sulfur atom and a single proton near it. They also investigated the effect of temperature on the carboxylic acid spectra. The irradiated acetic acid is a good example of this. The hydrogen bond keeps the molecules very hard at 77 K. Thus, it has been assumed that the doublet occurs from the dipole-dipole interaction between an electron and a hydroxyl proton localized on hydroxyl oxygen [27].

Gordy et al. [26] obtained spectra obtained from X-radiation of various biological materials such as proteins and bone tissue. Comparing these spectra with those obtained from simpler acids, one can get an idea of the deterioration mechanisms in natural products. Uebersfeld et al. [28–30] studied sugar, cellulose, and similar materials exposed to gamma rays in detail. In their later work, they obtained an anisotropic EPR spectrum from a single crystal of glycine [31]. A similar situation has been observed in the study of single crystals of the X-irradiated alanine by Van Roggen et al. [32]. Whiffen et al. [25, 33] have also done much research on the analysis of EPR spectra from gamma-irradiated polymers with interesting "**oxygen effects.**".

DNA is an organic compound. The EPR spectrum of the radical formed in gamma-irradiated DNA is shown in **Figure 1** [34]. As another organic compound, potassium hydroquinone monosulfonate (PHM) may be mentioned. In potassium hydroquinone monosulfonate single crystal, EPR spectrum of the radical structure resulting from gamma irradiation is shown in **Figure 2** [35].

#### *2.2.2.2. Inorganic compounds*

for UV is also suitable for electron resonance studies, since the small defects that will scatter

In such experiments, it has been observed that secondary radicals occur frequently when radicals are produced by photolysis by reacting with solvent molecules [20]. Hydroxyl radicals are derived from **hydrogen peroxide**. These radicals are very reactive. When a small amount of hydrogen peroxide is added to the hydrocarbon glass, secondary radicals are usually obtained by proton removal from the hydrocarbons. **OH radicals** were obtained by removal

Hydrogen atom reactions and high irradiation are predictors of **secondary reaction products** for solid hydrocarbons [16]. EPR is also an ideal metric for the analysis of these complex radi-

present at liquid nitrogen temperatures (77 K) are quite stable. This provides excellent envi-

**Radiation of an organic material** can lead to breakage of bonds between atoms. The minimum energy required for such a situation can be determined by the bond strength [21, 22]. Schneider et al. [23] observed the first electron spin (paramagnetic) resonance spectrum of radicals obtained from the organic polymethylmethacrylate compound by X-irradiation. They produced a very large electron spin (paramagnetic) resonance spectrum giving a complex hyperfine structure splitting. With the detailed analysis of the EPR spectrum, it is understood that the actually occurring state is the result of two separate interaction mechanisms in

Gordy et al. [26, 27] have begun to investigate the radicals of biological substances exposed to X-radiation. As a clear result of the radiation damage, they found that the hyperfine splits originate from simple radical forms. The organic materials that gave these spectra were the various irradiated amino acids. Their EPR spectra were obtained after irradiation with 50 kV X-rays at

break down the molecules and create a variety of radicals. There are many ways to create radicals. One of them is to remove an electron, which is the primary action of irradiation, and to form

five symmetrical lines. This suggests that the unpaired electron interacts with four equivalent

*CH*(*<sup>N</sup> <sup>H</sup>*2).*COOH*, is composed of five and seven overlapping lines. The seven-line splitting was

It has been observed that the EPR spectrum obtained from the irradiated valine, *<sup>C</sup> <sup>H</sup>*<sup>3</sup>

) + (*N H*<sup>2</sup>

 and (*<sup>C</sup> <sup>H</sup>*<sup>2</sup> ) +

group due to hyperconjugation [26].

radical having two protons. X-rays or other high-energy radiation can

)*COOH*. The hyperfine interac-

fragments of glycine [26].

.*CH*(*<sup>N</sup> <sup>H</sup>*2).*COOH*, has

.*CH*(*C H*3).

**SO4** , **H3 PO4**

**,** or **HClO4**

the UV wavelengths badly have no effect on the microwave radiation.

of an α-hydrogen from the isopropanol molecule via UV irradiation.

cals. For example, the H atoms in the frozen aqueous solutions of **H2**

(*<sup>C</sup> <sup>H</sup>*3)(*COOC <sup>H</sup>*3) radical [24, 25].

room temperature. The triplet was obtained from glycine, *<sup>C</sup> <sup>H</sup>*<sup>2</sup>

an ionized molecule with small stable groups such as *<sup>N</sup> <sup>H</sup>*<sup>3</sup> *<sup>C</sup> <sup>O</sup>*<sup>2</sup>

It has been observed that the EPR spectrum of the irradiated alanine, *<sup>C</sup> <sup>H</sup>*<sup>3</sup>

*H*2

protons and that the spin density is in a (*H*<sup>2</sup> *<sup>C</sup>* <sup>−</sup> *<sup>C</sup> <sup>H</sup>*<sup>2</sup>

*2.2.1.1. Secondary radicals*

140 Ionizing Radiation Effects and Applications

ronments for future work [21].

*2.2.2. X and gamma ray irradiation*

*2.2.2.1. Organic compounds*

the *<sup>R</sup>* <sup>−</sup> *<sup>C</sup> <sup>H</sup>*<sup>2</sup> <sup>−</sup> *<sup>C</sup>*̇

tion ion is due to a *C*̇

Irradiation of **inorganic materials**, usually in a single crystal form, produces centers of damage trapped within the crystal lattice. This can form free atoms, molecules, or radicals in the crystal

**Figure 1.** The EPR spectrum of the gamma-irradiated DNA at 77 K.

**Figure 2.** EPR spectrum of gamma-irradiated PHM single crystal at 125 K.

as well as breakage of chemical bonds [21]. The paramagnetic entities produced by the irradiation in these alkali halide crystals can hardly be termed "**free radicals**" in the normal sense of the word. They are better classified as "**damage centers**" or "**defects**" since they are associated with the structure of the crystal itself, rather than a broken bond in a particular molecule.

*F***-center**. The unpaired electron also moves on neighboring ions. Previous results of F-centers have also been confirmed by Feher's double resonance experiments [41]. Thanks to this technique, all the hyperfine splitting of the *F-*center in **KCI** can be solved and the coupling constants can be measured in detail. Resolved hyperfine structure has been examined by Lord [42], who studied the *F-*centers formed in **LiF** and **NaF**. Many authors have studied the molec-

**Figure 3.** EPR spectra of gamma-irradiated calcite at 77 K recorded at room temperature: (a) X-band spectrum; (b) Q-band spectrum; (c) the simulation of the X-band spectrum; and (d) the simulation of the Q -band spectrum.

given in **Figure 4**. EPR spectra of F-centers formed according to the main orientations of the

The opposite of **an** *F***-center** is **a** *V***-center**. **A positive ion deficiency (a cation vacancy) in the lattice** and **a deletion of electrons (trapped hole center**) **in one of the neighboring ions** form **a** *V***-center**. Thus, **this hole**, which is scattered over orbital neighbor ions, is **trapped in** 

case, the spins of the two electron holes are doubled and the paramagnetism ceases to exist.

on *V-*centers [52]. V-centers were obtained by X-irradiation of **KCl** at 90 K. A g-value was found between 2.0023 and 2.024 and was observed to be anisotropic. Anisotropic situation has occurred due to the fact that the hyperfine splitting originating from the two chlorine

crystal along the [100], [111], and [110] directions are

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**-center** with only one missing electron or hole between

**-center**. Kanzig made initial measurements

**-center** is obtained. In this

ular orbital interaction theory of the unpaired electron of the *F-*center [39, 43–50].

**vacancy**. When two such *V***-centers** are generated side by side, **a** *V***<sup>2</sup>**

EPR spectra of the X-irradiated LiBaF<sup>3</sup>

**-center** can be defined as **a** *V***<sup>2</sup>**

both vacancies. There is an unpaired spin like **a** *V***<sup>1</sup>**

crystal were clearly observed [51].

LiBaF<sup>3</sup>

**A** *V***<sup>3</sup>**

*2.2.2.2.2. V-centers*

The EPR study of irradiated inorganic compounds was made before organic samples. Hutchison [36] is the first person to work on this subject. He studied the EPR spectra of lithium fluoride crystals irradiated with neutrons for several hours. This work was followed by X-irradiation studies by researchers such as Schneider and Britain [37], Tinkham and Kip [38], and Kip et al. [39]. In these alkali halide crystals, it is more accurate to denote radiationgenerated paramagnetic objects as "**damage centers**" or "**defects**" rather than "**free radicals.**"

Calcite is an inorganic material. The EPR spectrum of the radical structure of gamma-irradiated calcite is shown in **Figure 3** [40].

The damage centers generated by high-energy irradiation in inorganic single crystals can be examined in three categories:


#### *2.2.2.2.1. F-centers*

**Negative ion deficiency (a halogen vacancy, an anion vacancy) in the lattice** and **trapping of an unpaired electron (trapped electron) in the Coulomb field** of the vacancy create **an**  Interaction with Matter of Ionizing Radiation and Radiation Damages (Radicals) http://dx.doi.org/10.5772/intechopen.74691 143

**Figure 3.** EPR spectra of gamma-irradiated calcite at 77 K recorded at room temperature: (a) X-band spectrum; (b) Q-band spectrum; (c) the simulation of the X-band spectrum; and (d) the simulation of the Q -band spectrum.

*F***-center**. The unpaired electron also moves on neighboring ions. Previous results of F-centers have also been confirmed by Feher's double resonance experiments [41]. Thanks to this technique, all the hyperfine splitting of the *F-*center in **KCI** can be solved and the coupling constants can be measured in detail. Resolved hyperfine structure has been examined by Lord [42], who studied the *F-*centers formed in **LiF** and **NaF**. Many authors have studied the molecular orbital interaction theory of the unpaired electron of the *F-*center [39, 43–50].

EPR spectra of the X-irradiated LiBaF<sup>3</sup> crystal along the [100], [111], and [110] directions are given in **Figure 4**. EPR spectra of F-centers formed according to the main orientations of the LiBaF<sup>3</sup> crystal were clearly observed [51].

#### *2.2.2.2.2. V-centers*

as well as breakage of chemical bonds [21]. The paramagnetic entities produced by the irradiation in these alkali halide crystals can hardly be termed "**free radicals**" in the normal sense of the word. They are better classified as "**damage centers**" or "**defects**" since they are associated with the structure of the crystal itself, rather than a broken bond in a particular molecule.

The EPR study of irradiated inorganic compounds was made before organic samples. Hutchison [36] is the first person to work on this subject. He studied the EPR spectra of lithium fluoride crystals irradiated with neutrons for several hours. This work was followed by X-irradiation studies by researchers such as Schneider and Britain [37], Tinkham and Kip [38], and Kip et al. [39]. In these alkali halide crystals, it is more accurate to denote radiationgenerated paramagnetic objects as "**damage centers**" or "**defects**" rather than "**free radicals.**" Calcite is an inorganic material. The EPR spectrum of the radical structure of gamma-irradi-

The damage centers generated by high-energy irradiation in inorganic single crystals can be

**Negative ion deficiency (a halogen vacancy, an anion vacancy) in the lattice** and **trapping of an unpaired electron (trapped electron) in the Coulomb field** of the vacancy create **an** 

ated calcite is shown in **Figure 3** [40].

**Figure 2.** EPR spectrum of gamma-irradiated PHM single crystal at 125 K.

examined in three categories:

142 Ionizing Radiation Effects and Applications

**c.** *U-*centers (Interstitial atoms).

**a.** *F-*centers, **b.** *V-*centers,

*2.2.2.2.1. F-centers*

The opposite of **an** *F***-center** is **a** *V***-center**. **A positive ion deficiency (a cation vacancy) in the lattice** and **a deletion of electrons (trapped hole center**) **in one of the neighboring ions** form **a** *V***-center**. Thus, **this hole**, which is scattered over orbital neighbor ions, is **trapped in vacancy**. When two such *V***-centers** are generated side by side, **a** *V***<sup>2</sup> -center** is obtained. In this case, the spins of the two electron holes are doubled and the paramagnetism ceases to exist. **A** *V***<sup>3</sup> -center** can be defined as **a** *V***<sup>2</sup> -center** with only one missing electron or hole between both vacancies. There is an unpaired spin like **a** *V***<sup>1</sup> -center**. Kanzig made initial measurements on *V-*centers [52]. V-centers were obtained by X-irradiation of **KCl** at 90 K. A g-value was found between 2.0023 and 2.024 and was observed to be anisotropic. Anisotropic situation has occurred due to the fact that the hyperfine splitting originating from the two chlorine

**Figure 4.** EPR spectra of the F-centers in the LiBaF3 crystal.

nuclei (*Cl*<sup>2</sup> − ion) shows an angle-dependent change. For this reason, the vacancies are defined as *V*<sup>3</sup> -centers rather than *V*<sup>1</sup> -centers, because *V*<sup>3</sup> -centers must have a central cubic symmetry [53]. The results are consistent with the measurements made on X- and gamma-irradiated and **thallium-activated KCl** [54]. The observed g-value can also be calculated very well by molecular orbital theory [55].

spectrum of this defect and obtained a strong central line with very weak satellites. While the central line [58] forms single interstitial carbon atoms, the satellites defined by mag-

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et al. [59] found that the trapping centers were produced at the same time as the interstitial atoms during their work on **neutron-irradiated magnesium oxide**. In the vacancies created by neutron irradiation, electrons are trapped and a well-resolved hyperfine structure splitting is obtained from neighboring Mg nuclei [41]. Delbecq et al. [54] observed *U-***centers** in **irradiated mixed crystals of KCl-KH** and **KCl-KD**. In this study, it is seen that the unpaired electron interacts with the negative ion vacancy and has a doublet of 500 G for **hydrogen**


molecules. Wertz

netic centers also bring about double interstitial aggregates forming C<sup>2</sup>

**Figure 5.** EPR spectra of ZnO **(a)** in the dark and **(b)** after illumination with 325-nm light.

and a triplet of 78 G for **deuterium**.

**Figure 6.** The EPR spectrum of *H i* 0 (*U2*

EPR spectra of defects occurring in ZnO with ultraviolet effect are given in **Figure 5**. These defects are the oxygen-vacancy and Zn-vacancy centers [56].

### *2.2.2.2.3. Interstitial atoms and U-centers*

Generally, **interstitial atoms (***U***-centers)** are obtained when an atom of high-energy radiation, such as neutrons, is sent to an intermediate position from a normal lattice site. For this reason, adding a single atom to the normal ionic bond of the lattice leaves a vacant site. The centers of damage expressed as *F***-center** and *V***-center** occur in the case of **pure single crystals**. However, if there is **hydride** or **deuteride in the lattice**, it is possible to create *U***-centers** defined as **negative ion vacancies containing a hydrogen or a deuterium negative ion**. Thus, the unpaired electron is localized on hydrogen and brings a large doublet hyperfine splitting. The best example of a defect generated by interstitial atoms is **neutronirradiated diamond**. Griffiths et al. [57] studied the electron spin (paramagnetic) resonance Interaction with Matter of Ionizing Radiation and Radiation Damages (Radicals) http://dx.doi.org/10.5772/intechopen.74691 145

**Figure 5.** EPR spectra of ZnO **(a)** in the dark and **(b)** after illumination with 325-nm light.

nuclei (*Cl*<sup>2</sup> −


144 Ionizing Radiation Effects and Applications

**Figure 4.** EPR spectra of the F-centers in the LiBaF3 crystal.

molecular orbital theory [55].

*2.2.2.2.3. Interstitial atoms and U-centers*

as *V*<sup>3</sup>

ion) shows an angle-dependent change. For this reason, the vacancies are defined

[53]. The results are consistent with the measurements made on X- and gamma-irradiated and **thallium-activated KCl** [54]. The observed g-value can also be calculated very well by

EPR spectra of defects occurring in ZnO with ultraviolet effect are given in **Figure 5**. These

Generally, **interstitial atoms (***U***-centers)** are obtained when an atom of high-energy radiation, such as neutrons, is sent to an intermediate position from a normal lattice site. For this reason, adding a single atom to the normal ionic bond of the lattice leaves a vacant site. The centers of damage expressed as *F***-center** and *V***-center** occur in the case of **pure single crystals**. However, if there is **hydride** or **deuteride in the lattice**, it is possible to create *U***-centers** defined as **negative ion vacancies containing a hydrogen or a deuterium negative ion**. Thus, the unpaired electron is localized on hydrogen and brings a large doublet hyperfine splitting. The best example of a defect generated by interstitial atoms is **neutronirradiated diamond**. Griffiths et al. [57] studied the electron spin (paramagnetic) resonance



defects are the oxygen-vacancy and Zn-vacancy centers [56].

spectrum of this defect and obtained a strong central line with very weak satellites. While the central line [58] forms single interstitial carbon atoms, the satellites defined by magnetic centers also bring about double interstitial aggregates forming C<sup>2</sup> molecules. Wertz et al. [59] found that the trapping centers were produced at the same time as the interstitial atoms during their work on **neutron-irradiated magnesium oxide**. In the vacancies created by neutron irradiation, electrons are trapped and a well-resolved hyperfine structure splitting is obtained from neighboring Mg nuclei [41]. Delbecq et al. [54] observed *U-***centers** in **irradiated mixed crystals of KCl-KH** and **KCl-KD**. In this study, it is seen that the unpaired electron interacts with the negative ion vacancy and has a doublet of 500 G for **hydrogen** and a triplet of 78 G for **deuterium**.

**Figure 6.** The EPR spectrum of *H i* 0 (*U2* -center) and *D i* 0-centers into (*LiH*) +.

At low temperatures below 70 K, interstitial atoms are produced by ultraviolet or X-ray irradiation. These atoms form in hydrogenated or hydroxyl-doped crystals. In the KCl, the *Hi* 0 -center (*U2* -center) and *Di* 0 -center are observed due to the ultraviolet effect [60]. In KCl, the (*LiH*)<sup>+</sup> -center is transformed to produce *Hi* 0 -center (*U2* -center) and *Di* 0 -center. The EPR spectrum of the resulting *Hi* 0 -center (*U2* -center) and *Di* 0 -center is shown in **Figure 6**.

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W.A. Benjamin, Inc., 1966. pp. 190-193

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[2] Symons M. Chemical and Biochemical Aspects of Electron-Spin Resonance Spectroscopy.

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147

[3] Caliskan B. EPR study of gamma irradiated cholestanone single crystal. Acta Physica

[4] Caliskan B, Caliskan AC, Yerli R. Electron paramagnetic resonance study of radiation damage in isonipecotic acid single crystal. Journal of Molecular Structure. 2014;**1075**:12-16.

[5] Caliskan B, Caliskan AC. EPR study of radiation damage in gamma irradiated 3-nitroacetophenone single crystal. Radiation Effects and Defects in Solids. 2017;**172**(5-6):398-

[6] Caliskan B, Caliskan AC, Er E. Electron paramagnetic resonance study of radiationinduced paramagnetic centers in succinic anhydride single crystal. Journal of Molecular

[7] Caliskan B, Caliskan AC. EPR study of free radical in gamma-irradiated bis(cyclopentadienyl)zirconium dichloride single crystal. Radiation Effects and Defects in Solids.

[9] Dole M, editor. Radiation Chemistry of Macromolecules. Vol. 1. New York: Academic

[10] Johnsen RH. Ionizing radiation, instrumentations and methods. In: Lamola AA, Ware WR, editors. Creation and Detection of the Excited State. New York: Marcel Dekker; 1971.

[11] Ranby B, Rabek JF. ESR Spectroscopy in Polymer Research. Springer-Verlag, Berlin; 1977.

[14] Bersohn M, Baird JC. An Introduction to Electron Paramagnetic Resonance. New York:

[15] Cherry RN Jr. Introduction, Chapter 48-Radiation: Ionizing. In: Cherry RN Jr, Chapter editor. Part VI - General Hazards. Online Edition: Encyclopaedia of Occupational health

[12] Roylance DK. An investigation of polymer fracture [doctorate thesis]. 1968. p. 173

[13] Perkins MJ. Radical Chemistry. New York: Ellis Horwood Limited; 1994. pp. 29-30

## **3. Conclusion**

In addition to chemical reaction and thermolysis methods, a material is subjected to a series of changes by irradiation. Photolysis or radiolysis processes are used as irradiation methods. However, radiolysis is more effective. Radiolysis is a process performed using ionizing radiation. Ionized radiation is separated into charged and uncharged particles. In this group, X-rays and gamma rays are used more effectively than neutrons. Interactions of such high-energy noncharged particle radiation or indirectly ionizing radiation with matter are effective in breaking chemical bonds or ionizing the structure. Breaking of the structure and its ionic conversion are expressed as free radicals and ionic radicals, respectively.

When organic and inorganic substances are exposed to ionizing radiation, the bond structures deteriorate. In organic and inorganic materials, UV, X-, or gamma rays can give rise to ionic radicals or free radicals. The radiation damage centers in inorganic materials can be seen as *F*-center, *V*-center, and *U*-center. In inorganic pure single crystals, *F*- and *V*-centers are named as radiation damage centers, negative ion deficiency, and positive ion deficiency, respectively. As the radical lifetimes can be very short, the detection of the radical becomes difficult. To overcome such a difficulty, EPR analysis is often performed at low temperature. The life of the radical in the sample, which is kept at low temperature, is extended.

In EPR studies, irradiation of organic or inorganic material is the first step. The type of radiation used must be highly energized. Using gamma rays leads to more accurate results. The second step is to perform EPR analysis at low temperature (77 K). Thus, the single electron formed by breaking the bonds is provided to be trapped at the point where it exists. At low temperature, the removal of the radical from the environment and the damping of the radical are prevented. This provides the appropriate time for the analysis of the radical.

## **Author details**

Betül Çalişkan<sup>1</sup> \* and Ali Cengiz Çalişkan<sup>2</sup>


## **References**

0

At low temperatures below 70 K, interstitial atoms are produced by ultraviolet or X-ray irradiation. These atoms form in hydrogenated or hydroxyl-doped crystals. In the KCl, the *Hi*


In addition to chemical reaction and thermolysis methods, a material is subjected to a series of changes by irradiation. Photolysis or radiolysis processes are used as irradiation methods. However, radiolysis is more effective. Radiolysis is a process performed using ionizing radiation. Ionized radiation is separated into charged and uncharged particles. In this group, X-rays and gamma rays are used more effectively than neutrons. Interactions of such high-energy noncharged particle radiation or indirectly ionizing radiation with matter are effective in breaking chemical bonds or ionizing the structure. Breaking of the structure and its ionic conversion are expressed as free radicals and ionic

When organic and inorganic substances are exposed to ionizing radiation, the bond structures deteriorate. In organic and inorganic materials, UV, X-, or gamma rays can give rise to ionic radicals or free radicals. The radiation damage centers in inorganic materials can be seen as *F*-center, *V*-center, and *U*-center. In inorganic pure single crystals, *F*- and *V*-centers are named as radiation damage centers, negative ion deficiency, and positive ion deficiency, respectively. As the radical lifetimes can be very short, the detection of the radical becomes difficult. To overcome such a difficulty, EPR analysis is often performed at low temperature.

In EPR studies, irradiation of organic or inorganic material is the first step. The type of radiation used must be highly energized. Using gamma rays leads to more accurate results. The second step is to perform EPR analysis at low temperature (77 K). Thus, the single electron formed by breaking the bonds is provided to be trapped at the point where it exists. At low temperature, the removal of the radical from the environment and the damping of the radical

1 Department of Physics, Faculty of Arts and Science, Pamukkale University, Denizli, Turkey

The life of the radical in the sample, which is kept at low temperature, is extended.

are prevented. This provides the appropriate time for the analysis of the radical.

2 Department of Chemistry, Faculty of Science, Gazi University, Ankara, Turkey

\* and Ali Cengiz Çalişkan<sup>2</sup>

\*Address all correspondence to: bcaliska@gmail.com

0

0



0





of the resulting *Hi*

**3. Conclusion**

radicals, respectively.

**Author details**

Betül Çalişkan<sup>1</sup>

(*LiH*)<sup>+</sup>


146 Ionizing Radiation Effects and Applications

0

0




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[17] Bijl D, Rose-Innes AC. Preparation of solid solutions of free radicals at room tempera-

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**Chapter 8**

Provisional chapter

**Recent Developments in Count Rate Processing**

DOI: 10.5772/intechopen.71233

**Associated with Radiation Monitoring Systems**

Recent Developments in Count Rate Processing

Associated with Radiation Monitoring Systems

This chapter presents some recent data processing developments associated with radiation monitoring systems. Radiation monitors have to continuously provide count rate estimations with accuracy and precision. A filtering technique based on a Centered Significance Test coupled with a Brown's double exponential filter has been developed and used in compensation measurement and moving sources detection schemes.

Keywords: data processing, nuclear counting, radiation monitor, signal processing,

During the last decades, ionizing ray detectors have grown in performance, thanks to digital electronics developments (ADC and FPGA), allowing for an advanced processing of nuclear impulse signals. It is also noteworthy that this field has favored the development of real-time

The architecture of a typical nuclear measurement system is presented in Figure 1. It can be

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Romain Coulon and Jonathan Dumazert

Romain Coulon and Jonathan Dumazert

http://dx.doi.org/10.5772/intechopen.71233

filtering, frequentist inference

processing algorithms dealing with count rate data.

Abstract

1. Introduction

divided in four parts: • Voltage supply, • Detector part,

• Front-end electronics,

• User interface.

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Provisional chapter

## **Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems** Recent Developments in Count Rate Processing

DOI: 10.5772/intechopen.71233

Associated with Radiation Monitoring Systems

Romain Coulon and Jonathan Dumazert

Additional information is available at the end of the chapter Romain Coulon and Jonathan Dumazert

http://dx.doi.org/10.5772/intechopen.71233 Additional information is available at the end of the chapter

Abstract

This chapter presents some recent data processing developments associated with radiation monitoring systems. Radiation monitors have to continuously provide count rate estimations with accuracy and precision. A filtering technique based on a Centered Significance Test coupled with a Brown's double exponential filter has been developed and used in compensation measurement and moving sources detection schemes.

Keywords: data processing, nuclear counting, radiation monitor, signal processing, filtering, frequentist inference

1. Introduction

During the last decades, ionizing ray detectors have grown in performance, thanks to digital electronics developments (ADC and FPGA), allowing for an advanced processing of nuclear impulse signals. It is also noteworthy that this field has favored the development of real-time processing algorithms dealing with count rate data.

The architecture of a typical nuclear measurement system is presented in Figure 1. It can be divided in four parts:


© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

quantitative difference between the digital pulse processing coded in VHDL or Verilog for the FPGA (very fast), and the count rate processing which can be coded in C/C++ into a microcontroller or/and the PC interface (7–8 orders of magnitude slower). In compact systems, the count rate processing is usually incorporated into the firmware while, in larger systems, the count

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

This chapter will not address pulse processing techniques, for which details can be found in [1–3], but presents some recently developed techniques to process count rate signal using frequentist inference. Bayesian inference can also be implemented to process count rate as for instance for gamma spectrum unfolding or photon-limited imaging filtering [4, 5]. These are very efficient to accurately processed nuclear counting data, but become unsuited of online applications. After describing the theoretical model of the counting process, a smoothing technique will be presented as a fundamental building block, ensuring an online and adaptive filtering of the signal. The issue of composite measurements will then be addressed with a method allowing improving metrological reliability for particle discrimination (compensation technique). Finally,

the use of detectors in a network to address moving source detection will be developed.

the concerned isotope. Major disintegration processes read: β�, β<sup>+</sup>

A <sup>Z</sup><sup>X</sup>! <sup>T</sup>1=<sup>2</sup> <sup>A</sup>

> A <sup>Z</sup><sup>X</sup>! <sup>T</sup>1=<sup>2</sup> <sup>A</sup>

A <sup>Z</sup><sup>X</sup> <sup>þ</sup> <sup>0</sup> �1 e �! <sup>T</sup>1=<sup>2</sup> <sup>A</sup>

A <sup>Z</sup><sup>X</sup>! <sup>T</sup>1=<sup>2</sup> <sup>A</sup><sup>1</sup> <sup>Z</sup>1Y<sup>1</sup>

reaches its fundamental level by gamma-ray emission:

phenomenon). The probability distribution p(τ<sup>d</sup> = t

According to the detector type, β�, β<sup>+</sup>

A <sup>Z</sup><sup>X</sup>! <sup>T</sup>1=<sup>2</sup> <sup>A</sup>�<sup>4</sup>

> A <sup>Z</sup>Y<sup>∗</sup> ! <sup>A</sup>

respectively, the observation instant and the decay constant of the nucleus, is given by:

Nuclear disintegration can occur following different processes depending on the A/Z ratio of

fission decay, presented in the following nuclear equations, where X is the mother nucleus

�<sup>1</sup>β�<sup>1</sup>

<sup>1</sup>βþ þ <sup>0</sup>

<sup>Z</sup>�<sup>1</sup>Y<sup>∗</sup> <sup>þ</sup> <sup>0</sup>

<sup>Z</sup>�<sup>2</sup>Y<sup>∗</sup> <sup>þ</sup> <sup>4</sup>

<sup>Z</sup><sup>Y</sup> <sup>þ</sup> <sup>0</sup>

0

<sup>∗</sup> <sup>þ</sup> <sup>A</sup><sup>1</sup> <sup>Z</sup>1Y<sup>2</sup>

Subsequently, the daughter nucleus is, most of the time, released in an exited state and usually

time τ<sup>d</sup> for an unstable nucleus to decay is undetermined, and takes its value in an exponential distribution whatever the time lap between its creation and the observation is (memoryless

� þ <sup>0</sup>

<sup>∗</sup> <sup>þ</sup> <sup>k</sup><sup>1</sup>

<sup>Z</sup>þ<sup>1</sup>Y<sup>∗</sup> <sup>þ</sup> <sup>0</sup>

<sup>Z</sup>�<sup>1</sup>Y<sup>∗</sup> <sup>þ</sup> <sup>0</sup>

, ε, α, and spontaneous

<sup>0</sup>υ<sup>e</sup> (1)

http://dx.doi.org/10.5772/intechopen.71233

155

<sup>0</sup>υ<sup>e</sup> (2)

<sup>0</sup>υ<sup>e</sup> (2a)

<sup>0</sup>n (4)

<sup>0</sup> and λ are,

<sup>2</sup>α (3)

<sup>0</sup>γ (5)

, α, n, or γ particles are detected and counted. The required

) of the decay instant, where t

rate processing is remotely implemented in the PC.

2. Nuclear counting model

and Y the daughter nucleus

Figure 1. Schematic architecture of a nuclear measurement apparatus.

The detector part contains the physical sensor (noble gas, scintillation material, and semiconductor) in which radiation interacts with matter. A conversion unit (preamplifier or photo-converter) converts the induced charges or photons in amplified voltage pulses. In the case of gas or semiconductor-based sensors, a high voltage is required to polarize the medium, and a low voltage is needed to supply active components of the preamplifier. In the case of scintillators, a high voltage supplies the photomultiplier.

Front-end electronics is composed of an analog filter, an analog-to-digital converter (ADC), and a digital filter. An analog shaping filter can be used to adapt the signal before digital conversion (dynamic range and respect to Shannon rules), and/or to maximize signal-to-noise ratio (SNR). The ADC digitalizes the signal with a given frequency and resolution.<sup>1</sup> This digital signal is processed into a fast electronic component, typically a microcontroller, or a fieldprogrammable gate array (FPGA). The embedded firmware has to comply with the very high-frequency of the ADC output with a processing period in the range of 1–10 ns. The algorithms implemented in the firmware perform the pulse processing, which mainly consists in triggering, first digital filtering for SNR maximization, stabilizing the baseline, estimating the dead time, and counting a number of pulse events N over a period of time Δτ. This general description is not exhaustive and a variety of architectures is conceivable, depending on the mix between analog and digital processing. Though modern trends tend to favor digital filtering, analog filtering can still be retained to comply with cost reduction or embedded strategies. For instance, the front-end associated with a scintillator can directly digitalize the output voltage of a photomultiplier using a 500 MS/s ADC and process the pulses using a FPGA (notably when pulse shape discrimination is needed). On the other hand, the initial signal can be filtered using analog components (trapezoidal filtering), before digitalization with a 10 MS/s ADC and count processing with a microcontroller.

An interface is built on a computer connected with the front-end electronic card. The software reads, at each given time interval Δt, a new count value Ni according to a defined communication protocol. This second processing can be divided in two parts: filtering of the count rate signal and displaying. The period Δt has to be chosen in compliance with continuous measurement requirement, typically close to retinal persistence of 0.1 s. We can highlight here, the

<sup>1</sup> Current ADCs are available with tradeoffs between resolution and sampling frequency such as: 16 bit / 100MS/s and 8 bit / 1 GS/s. CAEN Electronic instrumentation, 724 Digitizer Family, CEAN data sheet, 2015.

quantitative difference between the digital pulse processing coded in VHDL or Verilog for the FPGA (very fast), and the count rate processing which can be coded in C/C++ into a microcontroller or/and the PC interface (7–8 orders of magnitude slower). In compact systems, the count rate processing is usually incorporated into the firmware while, in larger systems, the count rate processing is remotely implemented in the PC.

This chapter will not address pulse processing techniques, for which details can be found in [1–3], but presents some recently developed techniques to process count rate signal using frequentist inference. Bayesian inference can also be implemented to process count rate as for instance for gamma spectrum unfolding or photon-limited imaging filtering [4, 5]. These are very efficient to accurately processed nuclear counting data, but become unsuited of online applications. After describing the theoretical model of the counting process, a smoothing technique will be presented as a fundamental building block, ensuring an online and adaptive filtering of the signal. The issue of composite measurements will then be addressed with a method allowing improving metrological reliability for particle discrimination (compensation technique). Finally, the use of detectors in a network to address moving source detection will be developed.

## 2. Nuclear counting model

The detector part contains the physical sensor (noble gas, scintillation material, and semiconductor) in which radiation interacts with matter. A conversion unit (preamplifier or photo-converter) converts the induced charges or photons in amplified voltage pulses. In the case of gas or semiconductor-based sensors, a high voltage is required to polarize the medium, and a low voltage is needed to supply active components of the preamplifier. In the case of scintillators, a

Front-end electronics is composed of an analog filter, an analog-to-digital converter (ADC), and a digital filter. An analog shaping filter can be used to adapt the signal before digital conversion (dynamic range and respect to Shannon rules), and/or to maximize signal-to-noise ratio (SNR). The ADC digitalizes the signal with a given frequency and resolution.<sup>1</sup> This digital signal is processed into a fast electronic component, typically a microcontroller, or a fieldprogrammable gate array (FPGA). The embedded firmware has to comply with the very high-frequency of the ADC output with a processing period in the range of 1–10 ns. The algorithms implemented in the firmware perform the pulse processing, which mainly consists in triggering, first digital filtering for SNR maximization, stabilizing the baseline, estimating the dead time, and counting a number of pulse events N over a period of time Δτ. This general description is not exhaustive and a variety of architectures is conceivable, depending on the mix between analog and digital processing. Though modern trends tend to favor digital filtering, analog filtering can still be retained to comply with cost reduction or embedded strategies. For instance, the front-end associated with a scintillator can directly digitalize the output voltage of a photomultiplier using a 500 MS/s ADC and process the pulses using a FPGA (notably when pulse shape discrimination is needed). On the other hand, the initial signal can be filtered using analog components (trapezoidal filtering), before digitalization

An interface is built on a computer connected with the front-end electronic card. The software reads, at each given time interval Δt, a new count value Ni according to a defined communication protocol. This second processing can be divided in two parts: filtering of the count rate signal and displaying. The period Δt has to be chosen in compliance with continuous measurement requirement, typically close to retinal persistence of 0.1 s. We can highlight here, the

Current ADCs are available with tradeoffs between resolution and sampling frequency such as: 16 bit / 100MS/s and 8 bit

high voltage supplies the photomultiplier.

154 Ionizing Radiation Effects and Applications

1

Figure 1. Schematic architecture of a nuclear measurement apparatus.

with a 10 MS/s ADC and count processing with a microcontroller.

/ 1 GS/s. CAEN Electronic instrumentation, 724 Digitizer Family, CEAN data sheet, 2015.

Nuclear disintegration can occur following different processes depending on the A/Z ratio of the concerned isotope. Major disintegration processes read: β�, β<sup>+</sup> , ε, α, and spontaneous fission decay, presented in the following nuclear equations, where X is the mother nucleus and Y the daughter nucleus

$$\mathbf{x}\_{Z}^{A}\mathbf{X}\xrightarrow{T\_{1/2}}\mathbf{z}\_{Z+1}^{A}\mathbf{Y}^{\*}+\prescript{0}{}{\mathbf{0}}\_{-1}\mathbf{\beta}^{-1}-\prescript{0}{}{\mathbf{0}}\_{\mathbf{\mathcal{E}}}\tag{1}$$

$$\mathbf{x}\_{Z}^{A}\mathbf{X}\xrightarrow{T\_{1/2}}\mathbf{z}\_{Z-1}^{A}\mathbf{Y}^{\*}+\mathbf{l}\_{1}^{0}\boldsymbol{\beta}+\ +\ \_{0}^{0}\boldsymbol{\nu}\_{\varepsilon}\tag{2}$$

$$\mathbf{e}\_Z^A \mathbf{X} + \mathbf{e}\_{-1}^0 \mathbf{e}^- \xrightarrow{T\_{1/2}} \mathbf{e}\_{Z-1}^A \mathbf{Y}^\* + \mathbf{e}\_0^0 \mathbf{v}\_e \tag{2a}$$

$$\mathbf{x}^A \mathbf{X} \xrightarrow{T\_{1/2}} \mathbf{\stackrel{A-4}{\mathbf{Z}-2}} \mathbf{Y}^\* + \mathbf{\stackrel{4}{\mathbf{2}}} \mathbf{\alpha} \tag{3}$$

$$\mathbf{Y}\_{\mathbf{Z}}^{A}\mathbf{X}\xrightarrow{T\_{1/2}}\mathbf{A}\_{\mathbf{Z}1}^{A1}\mathbf{Y}\_{1}\mathbf{\*}+\mathbf{A}\_{\mathbf{Z}1}^{A1}\mathbf{Y}\_{2}\mathbf{\*}+\mathbf{k}\_{0}^{1}\mathbf{n}\tag{4}$$

Subsequently, the daughter nucleus is, most of the time, released in an exited state and usually reaches its fundamental level by gamma-ray emission:

$$
\Lambda\_Z^A Y^\* \to \, \_Z^A Y + \, \_0^0 \mathcal{Y} \tag{5}
$$

According to the detector type, β�, β<sup>+</sup> , α, n, or γ particles are detected and counted. The required time τ<sup>d</sup> for an unstable nucleus to decay is undetermined, and takes its value in an exponential distribution whatever the time lap between its creation and the observation is (memoryless phenomenon). The probability distribution p(τ<sup>d</sup> = t 0 ) of the decay instant, where t <sup>0</sup> and λ are, respectively, the observation instant and the decay constant of the nucleus, is given by:

$$p(\pi\_d = t') = \lambda \exp\left(-\lambda t'\right) \tag{6}$$

pNt ð Þ¼ ðÞ¼ <sup>n</sup> <sup>P</sup> <sup>ρ</sup><sup>t</sup> � � <sup>¼</sup> <sup>ρ</sup><sup>t</sup> � �<sup>n</sup>

values in a Poisson distribution such as:

3. Count rate smoothing

associated variance <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>i</sup>

historical depth m + 1.

temporal precision σ bti

rate estimate <sup>ρ</sup>b<sup>i</sup>

detriment of σ bti

The relative stochastic uncertainty <sup>σ</sup> <sup>ρ</sup>b<sup>i</sup>

� � <sup>¼</sup> ð Þ <sup>m</sup>þ<sup>1</sup> <sup>Δ</sup><sup>t</sup> <sup>2</sup> ffiffi 3

<sup>ρ</sup>b<sup>i</sup> <sup>¼</sup> Ni Δt

this expectation are discussed in the next section.

memory according to the assumption that p(ρ<sup>i</sup>

likelihood of a homogenous Poisson process is the average [6]:

� � can be estimated as:

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>i</sup>

At each time ti, sampled such as t<sup>0</sup> =0& ∀ i ≥ 1, ti = ti � <sup>1</sup> + Δt, the raw estimation of the count rate ρ(ti) = ρ<sup>i</sup> is provided by measuring Ni, which is a time-dependent random variable taking its

Ni � P ρ<sup>i</sup>

A challenge in radiation monitoring is to provide count rate estimation ρ<sup>i</sup> at each time ti maximizing both precision σ(ρi) !0 and accuracy σ(ti)!0. Algorithmic techniques to meet

The aim of smoothing algorithms is to improve the estimation of ρi, originally defined as:

If we consider, in a first approach, a constant count rate ρ, the estimator which maximizes the

ð Þ m þ 1 Δt

where m + 1 is the temporal depth of the filter and ϑ is a kernel function in which each ϑj, 1 <sup>≤</sup> <sup>j</sup> <sup>≤</sup> <sup>i</sup> equal to one. According to the property of equality between variance and expectation, the

ð Þ m þ 1 Δt

In practice, counting processes are not homogenous (ρ is not constant). In this case, it is important to provide an estimate of the time bti effectively corresponding to the current count

<sup>p</sup> . We therefore see that <sup>σ</sup> <sup>b</sup>ρ<sup>i</sup>

address this issue is to actualize the temporal depth mi after every count rate estimation. The

<sup>ρ</sup>b<sup>i</sup> <sup>¼</sup> <sup>1</sup>

� � <sup>¼</sup> <sup>1</sup>

weighted, the estimate <sup>ρ</sup>b<sup>i</sup> from Eq. (12) is associated to a time estimate <sup>b</sup>ti <sup>¼</sup> ti � <sup>m</sup>þ<sup>1</sup>

. This improvement can be achieved by using past values Ni � 1, Ni � 2,… recorded in a

X i

j¼i�m

X i

j¼i�m

. Because the sampling times ti over the temporal depth m + 1 are identically

� �, leading to a degradation of accuracy when <sup>ρ</sup> is varying. One way to

� �=bρ<sup>i</sup> is inversely proportional to the square root of the

<sup>n</sup>! <sup>e</sup>

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

�ρ<sup>t</sup> (10)

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157

Δt � � (11)


Nj (12)

Nj (13)

� � can only be minimized to the

<sup>2</sup> Δt with a

The observation of an unstable nucleus over a time t forms a Bernoulli trial in which two results can be observed: the nucleus has decayed or the nucleus has not decayed. A probability of p and 1 � p can be, respectively, associated with each branch of the trial for every instant as illustrated in Figure 2.

The probability pX! <sup>Y</sup>(t) to observe a disintegration of the mother nucleus X ! Y before time t (t <sup>0</sup> = 0 being the start of the observation) is obtained as:

$$p\_{X \to Y}(t) = \int\_0^t p(\tau\_d = t')dt' = 1 - e^{-\lambda t} \tag{7}$$

In a radioactive source containing a population of NX unstable nuclei, the decay of an individual nucleus does not impact the decay of the others. The Bernoulli trial is therefore repeated NX times (Figure 3) during the observation time t, and the number of observed decays n is described by a Binomial law such as:

$$p(N\_{X \to Y}(t) = n) = \frac{N\_X!}{(N\_X - n)! n!} p\_{X \to Y}(t)^n (1 - p\_{X \to Y}(t))^{N\_X - n} \tag{8}$$

In practice, NX is very large and pX! <sup>Y</sup>(t) is usually very small (1/λ ≫ t). In these conditions, the Binomial law converges toward a Poisson law P such as:

$$p(\mathbf{N}\_{\mathbf{X}\rightarrow\mathbf{Y}}(t)=n) = \mathcal{P}\left(\mathbf{N}\_{\mathbf{X}}\mathbf{1}t\right) = \frac{\left(\mathbf{N}\_{\mathbf{X}}\lambda\mathbf{1}\right)^{n}}{n!}e^{-\mathbf{N}\_{\mathbf{X}}\lambda t} \tag{9}$$

Expectation and variance of the number of decays are equal to NXλt. The number of counts N measured before observation time t is obtained by weighting Eq. (9) with the detection efficiency ε and the probability η of the detected particle to be emitted during decay. The expected count rate ρ = εηNXλ thus becomes the parameter of the distribution of measured count values before t:

Figure 2. Illustration of the Bernoulli trail applied to an individual nucleus disintegration.

Figure 3. Illustration of Bernoulli trials applied to a population of unstable nuclei.

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems http://dx.doi.org/10.5772/intechopen.71233 157

$$p(\mathbf{N}(t) = n) = \mathcal{P}\left(\rho t\right) = \frac{\left(\rho t\right)^{n}}{n!} e^{-\rho t} \tag{10}$$

At each time ti, sampled such as t<sup>0</sup> =0& ∀ i ≥ 1, ti = ti � <sup>1</sup> + Δt, the raw estimation of the count rate ρ(ti) = ρ<sup>i</sup> is provided by measuring Ni, which is a time-dependent random variable taking its values in a Poisson distribution such as:

$$N\_i \sim \mathcal{P}\left(\rho\_i \Delta t\right) \tag{11}$$

A challenge in radiation monitoring is to provide count rate estimation ρ<sup>i</sup> at each time ti maximizing both precision σ(ρi) !0 and accuracy σ(ti)!0. Algorithmic techniques to meet this expectation are discussed in the next section.

#### 3. Count rate smoothing

p τ<sup>d</sup> ¼ t

<sup>0</sup> = 0 being the start of the observation) is obtained as:

pX!<sup>Y</sup>ðÞ¼ <sup>t</sup>

p N<sup>ð</sup> <sup>X</sup>!<sup>Y</sup>ðÞ¼ <sup>t</sup> <sup>n</sup>Þ ¼ NX!

Figure 2. Illustration of the Bernoulli trail applied to an individual nucleus disintegration.

Figure 3. Illustration of Bernoulli trials applied to a population of unstable nuclei.

Binomial law converges toward a Poisson law P such as:

ðt 0

ð Þ NX � n !n!

p N<sup>ð</sup> <sup>X</sup>!<sup>Y</sup>ðÞ¼ <sup>t</sup> <sup>n</sup>Þ ¼ <sup>P</sup>ð Þ¼ NXλ<sup>t</sup> ð Þ NXλ<sup>t</sup> <sup>n</sup>

illustrated in Figure 2.

156 Ionizing Radiation Effects and Applications

described by a Binomial law such as:

(t

before t:

<sup>0</sup> ð Þ¼ λ exp �λt

The observation of an unstable nucleus over a time t forms a Bernoulli trial in which two results can be observed: the nucleus has decayed or the nucleus has not decayed. A probability of p and 1 � p can be, respectively, associated with each branch of the trial for every instant as

The probability pX! <sup>Y</sup>(t) to observe a disintegration of the mother nucleus X ! Y before time t

p τ<sup>d</sup> ¼ t

In a radioactive source containing a population of NX unstable nuclei, the decay of an individual nucleus does not impact the decay of the others. The Bernoulli trial is therefore repeated NX times (Figure 3) during the observation time t, and the number of observed decays n is

In practice, NX is very large and pX! <sup>Y</sup>(t) is usually very small (1/λ ≫ t). In these conditions, the

Expectation and variance of the number of decays are equal to NXλt. The number of counts N measured before observation time t is obtained by weighting Eq. (9) with the detection efficiency ε and the probability η of the detected particle to be emitted during decay. The expected count rate ρ = εηNXλ thus becomes the parameter of the distribution of measured count values

<sup>0</sup> ð Þdt<sup>0</sup> ¼ 1 � e

<sup>0</sup> ð Þ (6)

�λ<sup>t</sup> (7)

�NXλ<sup>t</sup> (9)

pX!<sup>Y</sup>ð Þ<sup>t</sup> <sup>n</sup> <sup>1</sup> � pX!<sup>Y</sup>ð Þ<sup>t</sup> � �NX�<sup>n</sup> (8)

<sup>n</sup>! <sup>e</sup>

The aim of smoothing algorithms is to improve the estimation of ρi, originally defined as: <sup>ρ</sup>b<sup>i</sup> <sup>¼</sup> Ni Δt . This improvement can be achieved by using past values Ni � 1, Ni � 2,… recorded in a memory according to the assumption that p(ρ<sup>i</sup> |Ni, Ni � 1, Ni� 2,…) is more precise than p(ρi|Ni). If we consider, in a first approach, a constant count rate ρ, the estimator which maximizes the likelihood of a homogenous Poisson process is the average [6]:

$$\widehat{\rho}\_{i} = \frac{1}{(m+1)\Delta t} \sum\_{j=i-m}^{i} N\_{j} \tag{12}$$

where m + 1 is the temporal depth of the filter and ϑ is a kernel function in which each ϑj, 1 <sup>≤</sup> <sup>j</sup> <sup>≤</sup> <sup>i</sup> equal to one. According to the property of equality between variance and expectation, the associated variance <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>i</sup> � � can be estimated as:

$$\sigma^2(\hat{\rho}\_i) = \frac{1}{(m+1)\Delta t} \sum\_{j=i-m}^i N\_j \tag{13}$$

The relative stochastic uncertainty <sup>σ</sup> <sup>ρ</sup>b<sup>i</sup> � �=bρ<sup>i</sup> is inversely proportional to the square root of the historical depth m + 1.

In practice, counting processes are not homogenous (ρ is not constant). In this case, it is important to provide an estimate of the time bti effectively corresponding to the current count rate estimate <sup>ρ</sup>b<sup>i</sup> . Because the sampling times ti over the temporal depth m + 1 are identically weighted, the estimate <sup>ρ</sup>b<sup>i</sup> from Eq. (12) is associated to a time estimate <sup>b</sup>ti <sup>¼</sup> ti � <sup>m</sup>þ<sup>1</sup> <sup>2</sup> Δt with a temporal precision σ bti � � <sup>¼</sup> ð Þ <sup>m</sup>þ<sup>1</sup> <sup>Δ</sup><sup>t</sup> <sup>2</sup> ffiffi 3 <sup>p</sup> . We therefore see that <sup>σ</sup> <sup>b</sup>ρ<sup>i</sup> � � can only be minimized to the detriment of σ bti � �, leading to a degradation of accuracy when <sup>ρ</sup> is varying. One way to address this issue is to actualize the temporal depth mi after every count rate estimation. The optimal value for mi is a function of the temporal behavior of the rate ρ at the time ti: <sup>d</sup><sup>ρ</sup> dt � � � t¼ti ¼ 0

$$\text{or } \frac{d\rho}{dt}\Big|\_{t=t\_i} > 0.$$

First approaches consist in the implementation of preset count filter providing a fixed variance <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>i</sup> � �, or finite impulse response (FIR) filters in which a kernel function ϑ is used to assign more weight to recent than older count values such as Eq. (12) become:

$$\widehat{\rho}\_{i} = \frac{\sum\_{j=i-m}^{t} \mathfrak{S}\_{i-j} \mathsf{N}\_{j}}{(m+1)\Delta t \sum\_{j=1}^{m} \mathfrak{S}\_{j}} \tag{14}$$

Δρbk

The expectation <sup>E</sup> <sup>Δ</sup>ρb<sup>k</sup>

<sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup> i � � <sup>¼</sup>

We will note <sup>D</sup> <sup>E</sup> <sup>Δ</sup>ρb<sup>k</sup>

Under H0, <sup>E</sup> <sup>Δ</sup>ρb<sup>k</sup>

level 1 � <sup>α</sup><sup>k</sup>

first and second order moments.

i

ing formula, where Q<sup>1</sup>�α<sup>k</sup>

i :

<sup>i</sup> � <sup>D</sup> <sup>¼</sup> <sup>1</sup>

i � � <sup>¼</sup> <sup>E</sup> <sup>ρ</sup>bmi

we will make use of assumption <sup>Δ</sup>θ<sup>b</sup> <sup>¼</sup> <sup>ρ</sup>bmi

expectation and variance, we obtain:

ð Þ mi þ 1 Δt

summed to obtain a cumulative standard deviation for <sup>Δ</sup>ρb<sup>k</sup>

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>bmi

in compliance with a given risk of false detection α<sup>k</sup>

i

i � �; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

i � � � <sup>E</sup> <sup>ρ</sup>b<sup>k</sup>

<sup>i</sup> ð Þ mi <sup>þ</sup> <sup>1</sup> <sup>Δ</sup><sup>t</sup> � � ð Þ ð Þ mi <sup>þ</sup> <sup>1</sup> <sup>Δ</sup><sup>t</sup> <sup>2</sup> <sup>þ</sup>

i

<sup>P</sup> <sup>ρ</sup>bmi

i

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

vuut <sup>≈</sup>

<sup>i</sup> � <sup>ρ</sup>b<sup>k</sup>

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>k</sup>

Figure 4. Illustration of distributions D<sup>H</sup><sup>0</sup> (left curve) and D<sup>H</sup><sup>1</sup> (right curve) and construction rules of the hypothesis test.

<sup>i</sup>ð Þ k þ 1 Δt � �

� � � � , the distribution of the difference random variable with its

� � <sup>¼</sup> 0 (cf. left curve in Figure 4). A decision threshold (DT) is determined

ð Þ ð Þ <sup>k</sup> <sup>þ</sup> <sup>1</sup> <sup>Δ</sup><sup>t</sup> <sup>2</sup>

will finite statistics [1]. The variances associated with both uncorrelated random processes are

<sup>i</sup> ð Þ mi <sup>þ</sup> <sup>1</sup> <sup>Δ</sup><sup>t</sup> � � � <sup>1</sup>

ð Þ k þ 1 Δt

� � � � (18)

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

i

s

is the quantile of the error function (err) with a confidence

<sup>P</sup> <sup>ρ</sup>b<sup>k</sup>

� � <sup>¼</sup> <sup>Δ</sup><sup>θ</sup> between times (<sup>i</sup> � mi)Δ<sup>t</sup> and <sup>i</sup>Δt. Moreover,

<sup>i</sup> , as common in nuclear counting experiments

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ρbmi i ð Þ mi þ 1 Δt

<sup>i</sup>ð Þ k þ 1 Δt

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159

. According to the equality between

<sup>þ</sup> <sup>ρ</sup>b<sup>k</sup> i ð Þ <sup>k</sup> <sup>þ</sup> <sup>1</sup> <sup>Δ</sup><sup>t</sup> (19)

<sup>i</sup> ¼ pð Þ H1jH0 . DT is defined in the follow-

Among FIR filters, the exponential moving average (EMA) remains widespread [7, 8], but do not fully deals with the tread-off issue between accuracy and precision.

The algorithm translation of the actualization of mi is the building of infinite impulse response (IIR) dedicated to nuclear counting [9]. Such nonlinear filtering requires a hypothesis test to detect the changes in count rate ρ. The null hypothesis H0 and the detection hypothesis H1 are formalized as follows:

$$\mathbf{H}\_{\mathbf{0}} \colon \forall \mathbf{j} \in [\mathbf{i} - m\_i; \mathbf{j}] \,\rho\_j = \theta\_0 \tag{15}$$

$$\mathbf{H}\_{\mathbf{I}} \colon \exists j \in [\mathbf{i} - m\_i; \mathbf{i}] \,\rho\_j = \theta\_1 \tag{16}$$

In a first approach [10], a sequential probability ratio test (SPRT) has been assessed under the assumption that θ<sup>1</sup> is a known value. Later, generalized tests in which θ<sup>1</sup> is an unknown parameter have been introduced, notably the generalized likelihood ratio test (GLR) [11] and the centered significance test (CST) [12]. In these change detection algorithms, several estimations of the current count rate are calculated using different temporal depths k such as:

$$\widehat{\rho \rho}\_i^k = \frac{1}{(k+1)\Delta t} \sum\_{j=i-k}^i N\_j \tag{17}$$

In the rest of the discussion, we will conventionally use notation <sup>ρ</sup>b<sup>k</sup> <sup>i</sup> to designate both the underlying random variable and its actual values.

In the CST test, the vector <sup>ρ</sup>bk, <sup>1</sup> <sup>≤</sup> <sup>k</sup> <sup>≤</sup> mi <sup>i</sup> is scanned to find a potential change in the true rate ρ. For every temporal depth <sup>k</sup><sup>∈</sup> ⟦1; mi⟧, the difference between count rate estimations <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> <sup>¼</sup> <sup>ρ</sup>bmi <sup>i</sup> � <sup>ρ</sup>b<sup>k</sup> i is the quantity which will be tested for significance.

The method is based on a comparison between actual and expected distributions of <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> under H0 and H1, respectively [13]. The distribution <sup>D</sup> of <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> is the difference between two weighted Poisson distributions

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems http://dx.doi.org/10.5772/intechopen.71233 159

$$\Delta \hat{\rho}\_i^k \sim \mathfrak{D} = \left\{ \frac{1}{(m\_i + 1)\Delta t} \mathcal{P}\left(\hat{\rho}\_i^{m\_i} \left(m\_i + 1\right)\Delta t\right) - \frac{1}{(k+1)\Delta t} \mathcal{P}\left(\hat{\rho}\_i^k (k+1)\Delta t\right) \right\} \tag{18}$$

The expectation <sup>E</sup> <sup>Δ</sup>ρb<sup>k</sup> i � � <sup>¼</sup> <sup>E</sup> <sup>ρ</sup>bmi i � � � <sup>E</sup> <sup>ρ</sup>b<sup>k</sup> i � � <sup>¼</sup> <sup>Δ</sup><sup>θ</sup> between times (<sup>i</sup> � mi)Δ<sup>t</sup> and <sup>i</sup>Δt. Moreover, we will make use of assumption <sup>Δ</sup>θ<sup>b</sup> <sup>¼</sup> <sup>ρ</sup>bmi <sup>i</sup> � <sup>ρ</sup>b<sup>k</sup> <sup>i</sup> , as common in nuclear counting experiments will finite statistics [1]. The variances associated with both uncorrelated random processes are summed to obtain a cumulative standard deviation for <sup>Δ</sup>ρb<sup>k</sup> i . According to the equality between expectation and variance, we obtain:

optimal value for mi is a function of the temporal behavior of the rate ρ at the time ti: <sup>d</sup><sup>ρ</sup>

more weight to recent than older count values such as Eq. (12) become:

not fully deals with the tread-off issue between accuracy and precision.

<sup>ρ</sup>b<sup>i</sup> <sup>¼</sup>

First approaches consist in the implementation of preset count filter providing a fixed variance

P i j¼i�m

ð Þ m þ 1 Δt

Among FIR filters, the exponential moving average (EMA) remains widespread [7, 8], but do

The algorithm translation of the actualization of mi is the building of infinite impulse response (IIR) dedicated to nuclear counting [9]. Such nonlinear filtering requires a hypothesis test to detect the changes in count rate ρ. The null hypothesis H0 and the detection hypothesis H1 are

In a first approach [10], a sequential probability ratio test (SPRT) has been assessed under the assumption that θ<sup>1</sup> is a known value. Later, generalized tests in which θ<sup>1</sup> is an unknown parameter have been introduced, notably the generalized likelihood ratio test (GLR) [11] and the centered significance test (CST) [12]. In these change detection algorithms, several estima-

> X i

j¼i�k

<sup>i</sup> is scanned to find a potential change in the true rate ρ. For

tions of the current count rate are calculated using different temporal depths k such as:

<sup>i</sup> <sup>¼</sup> <sup>1</sup> ð Þ k þ 1 Δt

every temporal depth <sup>k</sup><sup>∈</sup> ⟦1; mi⟧, the difference between count rate estimations <sup>Δ</sup>ρb<sup>k</sup>

The method is based on a comparison between actual and expected distributions of <sup>Δ</sup>ρb<sup>k</sup>

ρbk

In the rest of the discussion, we will conventionally use notation <sup>ρ</sup>b<sup>k</sup>

underlying random variable and its actual values.

is the quantity which will be tested for significance.

H0 and H1, respectively [13]. The distribution <sup>D</sup> of <sup>Δ</sup>ρb<sup>k</sup>

In the CST test, the vector <sup>ρ</sup>bk, <sup>1</sup> <sup>≤</sup> <sup>k</sup> <sup>≤</sup> mi

Poisson distributions

� �, or finite impulse response (FIR) filters in which a kernel function ϑ is used to assign

ϑ<sup>i</sup>�jNj

Pm j¼1 ϑj

H0: ∀j∈ i � mi ½ � ; i , ρ<sup>j</sup> ¼ θ<sup>0</sup> (15)

H1: ∃j∈ i � mi ½ � ; i , ρ<sup>j</sup> ¼ θ<sup>1</sup> (16)

Nj (17)

<sup>i</sup> is the difference between two weighted

<sup>i</sup> to designate both the

<sup>i</sup> <sup>¼</sup> <sup>ρ</sup>bmi

<sup>i</sup> � <sup>ρ</sup>b<sup>k</sup> i

<sup>i</sup> under

or dρ dt � � � t¼ti > 0.

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>i</sup>

158 Ionizing Radiation Effects and Applications

formalized as follows:

dt � � � t¼ti ¼ 0

(14)

$$\sigma\left(\Delta\widehat{\rho}\_{i}^{k}\right) = \sqrt{\frac{\sigma^{2}\left(\widehat{\rho}\_{i}^{m\_{i}}(m\_{i}+1)\Delta t\right)}{\left((m\_{i}+1)\Delta t\right)^{2}} + \frac{\sigma^{2}\left(\widehat{\rho}\_{i}^{k}(k+1)\Delta t\right)}{\left((k+1)\Delta t\right)^{2}}} \approx \sqrt{\frac{\widehat{\rho}\_{i}^{m\_{i}}}{(m\_{i}+1)\Delta t} + \frac{\widehat{\rho}\_{i}^{k}}{(k+1)\Delta t}}\tag{19}$$

We will note <sup>D</sup> <sup>E</sup> <sup>Δ</sup>ρb<sup>k</sup> i � �; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup> i � � � � , the distribution of the difference random variable with its first and second order moments.

Under H0, <sup>E</sup> <sup>Δ</sup>ρb<sup>k</sup> i � � <sup>¼</sup> 0 (cf. left curve in Figure 4). A decision threshold (DT) is determined in compliance with a given risk of false detection α<sup>k</sup> <sup>i</sup> ¼ pð Þ H1jH0 . DT is defined in the following formula, where Q<sup>1</sup>�α<sup>k</sup> i is the quantile of the error function (err) with a confidence level 1 � <sup>α</sup><sup>k</sup> i :

Figure 4. Illustration of distributions D<sup>H</sup><sup>0</sup> (left curve) and D<sup>H</sup><sup>1</sup> (right curve) and construction rules of the hypothesis test.

$$\alpha\_i^k = \int\_{DT} \mathfrak{D}\_{H\_0} \left( 0, \sigma \left( \Delta \widehat{\rho}\_i^k \right) \right) d\Delta \widehat{\rho}\_i^k \approx err \left( \mathbb{Q}\_{1-d\_i^k} \right) \tag{20}$$

DLk

DLk <sup>i</sup> <sup>¼</sup> <sup>Q</sup><sup>2</sup>

Li ¼ dim arg

At every elementary time step <sup>Δ</sup>t, the retained count rate estimate <sup>ρ</sup>b<sup>∗</sup>

ρb∗

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>∗</sup> i � � <sup>¼</sup> <sup>1</sup>

<sup>i</sup> <sup>¼</sup> <sup>1</sup>

<sup>i</sup> with a smoothing parameter δ<sup>i</sup> such as:

i

ρb1 <sup>i</sup> <sup>¼</sup> <sup>δ</sup>iρb<sup>∗</sup>

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>1</sup> i � � <sup>¼</sup> <sup>δ</sup>i<sup>σ</sup> <sup>ρ</sup>b<sup>∗</sup>

ð Þ mi þ 1 Δt

ð Þ ð Þ mi <sup>þ</sup> <sup>1</sup> <sup>Δ</sup><sup>t</sup> <sup>2</sup>

This nonlinear approach performs advantageously in comparison with conventional linear filters [12, 14], allowing to maintain sufficient precision while rate changes in the signal occur. Remaining high-frequency fluctuations can now be reduced using a second, recursive smoother, for instance a Brown's double exponential filter [14]. A first exponential smoothing

<sup>i</sup> <sup>þ</sup> ð Þ <sup>1</sup> � <sup>δ</sup><sup>i</sup> <sup>ρ</sup>b<sup>∗</sup>

� � � � <sup>2</sup> <sup>þ</sup> ð Þ <sup>1</sup> � <sup>δ</sup><sup>i</sup> <sup>σ</sup> <sup>ρ</sup>b<sup>∗</sup>

i�1

The number Li of significant changes recorded into memory <sup>Δ</sup>ρb<sup>k</sup>

<sup>i</sup> , hypothesis H1 is accepted with a confidence level 1 � β = γ.

k, <sup>1</sup> <sup>≤</sup> <sup>k</sup> <sup>≤</sup> mi

If Li = 0, true rate ρ is considered to remain constant and historical depth may be extended

true rate ρ is considered to change and the historical depth needs to be reduced mi + 1 = mi � Li,

When y! ∞,

<sup>i</sup> <sup>≥</sup> DL<sup>k</sup>

to the benefit of σ bt

value of temporal depth mi + 1:

mi + 1 <sup>=</sup> mi + 1, to the benefit of a reduction of <sup>σ</sup> <sup>ρ</sup><sup>b</sup>

� � (better accuracy).

over an adaptable temporal depth mi, Eq. (17) becoming:

If <sup>Δ</sup>ρb<sup>k</sup>

With

ρb1

With

<sup>i</sup> is performed on <sup>ρ</sup>b<sup>∗</sup>

i,<sup>0</sup> <sup>¼</sup> <sup>2</sup>Qγσ <sup>Δ</sup>ρb<sup>k</sup>

<sup>γ</sup> <sup>þ</sup> <sup>2</sup>Q<sup>γ</sup> <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

Δρbk i � � �

� � � <sup>&</sup>gt; DLk i

X i

j¼i�mi

X i

j¼i�mi

i

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

i

� � (26)

http://dx.doi.org/10.5772/intechopen.71233

161

� � (27)

h i ( ) (28)

� � (better precision). On the other hand, if Li > 0,

<sup>i</sup> is used to calculate the next

<sup>i</sup> is therefore calculated

Nj (29)

Nj (30)

<sup>i</sup>�<sup>1</sup> (31)

� � � � <sup>2</sup> (32)

In practice, for embedded implementations, it is impossible to sample and interpolate distributions Q<sup>1</sup>�α<sup>k</sup> i <sup>¼</sup> <sup>f</sup> <sup>α</sup><sup>k</sup> i � � for every value of <sup>i</sup> and <sup>k</sup>. Moreover, when <sup>E</sup> <sup>ρ</sup>bmi i � � and <sup>E</sup> <sup>ρ</sup>b<sup>k</sup> i � � are large enough, distribution <sup>D</sup>H0 may be approximated as <sup>N</sup> <sup>0</sup>; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup> i � � � � , with <sup>N</sup> the Normal law. Under this assumption, for every value of i and k, α<sup>k</sup> <sup>i</sup> ¼ α and Q<sup>1</sup>�α<sup>k</sup> i ¼ Q<sup>1</sup>�<sup>α</sup>, where Q<sup>1</sup> � <sup>α</sup> is a quantile of N and err becomes:

$$err(Q\_{1-a}) = 2 - 2\Phi(Q\_{1-a})\tag{21}$$

where Φ is the cumulative distribution function of the centered Normal law.

As illustrated in Figure 4, DT can be calculated thanks to the weighting of the standard deviation by Q<sup>1</sup> � <sup>α</sup> such as:

$$DT\_i^k = Q\_{1-\alpha} \, \sigma \left(\Delta \widehat{\rho}\_i^k\right) \tag{22}$$

If <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> <sup>≤</sup> DT<sup>k</sup> <sup>i</sup> , hypothesis H<sup>0</sup> is accepted with a confidence level equal to 1 � α.

Under H1, <sup>D</sup>H1 <sup>E</sup> <sup>Δ</sup>ρb<sup>k</sup> i � �; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup> i � � � � <sup>≈</sup><sup>N</sup> DLk <sup>i</sup> ; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> <sup>þ</sup> DL<sup>k</sup> i � � � � (cf. right curve in Figure 4), where DL is defined as the detection limit. DL is determined in compliance with a given risk of non-detection β = p(H0| H1). DL is obtained in the following formula:

$$\beta = \int\_{-\infty}^{DT} \mathcal{N}\left(DL\_i^k, \sigma\left(\Delta\widehat{\rho}\_i^k + DL\_i^k\right)\right) d\theta = err\left(Q\_{1-\beta}\right) \tag{23}$$

As illustrated in Figure 4, DL can be calculated thanks to the weighting of the associated standard deviation by the quantile Q<sup>1</sup> � <sup>β</sup> of the error function erf such as:

$$DL\_i^k = DT\_i^k + \mathbb{Q}\_{1-\beta} \sigma \left(\Delta \widehat{\rho}\_i^k + DL\_i^k\right) \tag{24}$$

An equivalent confidence level 1 � α = 1 � β = γ is considered, and Eq. (23) is solved recursively such as:

$$\forall y \in [1; \infty]$$

$$DL\_{i,y}^k = \mathcal{Q}\_{\boldsymbol{\gamma}} \left[ \sigma \left( \Delta \hat{\boldsymbol{\rho}}\_i^k \right) + \sigma \left( \Delta \hat{\boldsymbol{\rho}}\_i^k + DL\_{i,y-1}^k \right) \right] \tag{25}$$

With

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems http://dx.doi.org/10.5772/intechopen.71233 161

$$D L\_{i,0}^k = \mathcal{Q} \mathcal{Q}\_\mathcal{\boldsymbol{\gamma}} \sigma \left(\Delta \hat{\boldsymbol{\rho}}\_i^k\right) \tag{26}$$

When y! ∞,

αk <sup>i</sup> ¼ ð ∞

Under this assumption, for every value of i and k, α<sup>k</sup>

butions Q<sup>1</sup>�α<sup>k</sup>

If <sup>Δ</sup>ρb<sup>k</sup>

such as:

With

<sup>i</sup> <sup>≤</sup> DT<sup>k</sup>

Under H1, <sup>D</sup>H1 <sup>E</sup> <sup>Δ</sup>ρb<sup>k</sup>

i � �

β ¼

� � � �

; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup> i

> DT ð

�∞

DL<sup>k</sup>

i <sup>¼</sup> <sup>f</sup> <sup>α</sup><sup>k</sup> i

160 Ionizing Radiation Effects and Applications

quantile of N and err becomes:

deviation by Q<sup>1</sup> � <sup>α</sup> such as:

DT

enough, distribution <sup>D</sup>H0 may be approximated as <sup>N</sup> <sup>0</sup>; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

where Φ is the cumulative distribution function of the centered Normal law.

DT<sup>k</sup>

≈N DLk

<sup>i</sup> ; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

� � � �

of non-detection β = p(H0| H1). DL is obtained in the following formula:

N DLk

standard deviation by the quantile Q<sup>1</sup> � <sup>β</sup> of the error function erf such as:

<sup>i</sup> <sup>¼</sup> DT<sup>k</sup>

i, <sup>y</sup> <sup>¼</sup> <sup>Q</sup><sup>γ</sup> <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

DLk

<sup>D</sup><sup>H</sup><sup>0</sup> <sup>0</sup>; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

i � � � �

In practice, for embedded implementations, it is impossible to sample and interpolate distri-

As illustrated in Figure 4, DT can be calculated thanks to the weighting of the standard

<sup>i</sup> <sup>¼</sup> <sup>Q</sup><sup>1</sup>�<sup>α</sup> <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

<sup>i</sup> ; <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

<sup>i</sup> <sup>þ</sup> DL<sup>k</sup> i

As illustrated in Figure 4, DL can be calculated thanks to the weighting of the associated

<sup>i</sup> <sup>þ</sup> <sup>Q</sup><sup>1</sup>�<sup>β</sup> <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

An equivalent confidence level 1 � α = 1 � β = γ is considered, and Eq. (23) is solved recursively

∀y ∈½ � 1; ∞ ,

<sup>þ</sup> <sup>σ</sup> <sup>Δ</sup>ρb<sup>k</sup>

h i � �

i � �

where DL is defined as the detection limit. DL is determined in compliance with a given risk

� � � �

<sup>i</sup> , hypothesis H<sup>0</sup> is accepted with a confidence level equal to 1 � α.

i � �

> <sup>i</sup> <sup>þ</sup> DL<sup>k</sup> i

> > dθ ¼ err Q<sup>1</sup>�<sup>β</sup>

<sup>i</sup> <sup>þ</sup> DLk i

<sup>i</sup> <sup>þ</sup> DL<sup>k</sup>

i,y�1

� �

� �

� � for every value of <sup>i</sup> and <sup>k</sup>. Moreover, when <sup>E</sup> <sup>ρ</sup>bmi

<sup>d</sup>Δρb<sup>k</sup>

<sup>i</sup> <sup>≈</sup> err Q<sup>1</sup>�α<sup>k</sup>

i � �

i � � � �

err Q<sup>1</sup>�<sup>α</sup> ð Þ¼ 2 � 2Φ Q<sup>1</sup>�<sup>α</sup> ð Þ (21)

i

<sup>i</sup> ¼ α and Q<sup>1</sup>�α<sup>k</sup>

i

� � and <sup>E</sup> <sup>ρ</sup>b<sup>k</sup>

i � �

, with N the Normal law.

¼ Q<sup>1</sup>�<sup>α</sup>, where Q<sup>1</sup> � <sup>α</sup> is a

(cf. right curve in Figure 4),

(20)

are large

(22)

(23)

(24)

(25)

$$\mathcal{D}\mathcal{D}\_i^k = \mathbb{Q}\_\gamma^2 + \mathcal{D}\mathbb{Q}\_\gamma \sigma \left(\Delta \widehat{\rho}\_i^k\right) \tag{27}$$

If <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> <sup>≥</sup> DL<sup>k</sup> <sup>i</sup> , hypothesis H1 is accepted with a confidence level 1 � β = γ.

The number Li of significant changes recorded into memory <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> is used to calculate the next value of temporal depth mi + 1:

$$L\_i = \dim \left\{ \underset{k\_i \ 1 \le k \le m\_i}{\text{arg}} \left[ \left| \Delta \widehat{\rho}\_i^k \right| > DL\_i^k \right] \right\} \tag{28}$$

If Li = 0, true rate ρ is considered to remain constant and historical depth may be extended mi + 1 <sup>=</sup> mi + 1, to the benefit of a reduction of <sup>σ</sup> <sup>ρ</sup><sup>b</sup> � � (better precision). On the other hand, if Li > 0, true rate ρ is considered to change and the historical depth needs to be reduced mi + 1 = mi � Li, to the benefit of σ bt � � (better accuracy).

At every elementary time step <sup>Δ</sup>t, the retained count rate estimate <sup>ρ</sup>b<sup>∗</sup> <sup>i</sup> is therefore calculated over an adaptable temporal depth mi, Eq. (17) becoming:

$$
\widehat{\rho}\_i^\* = \frac{1}{(m\_i + 1)\Delta t} \sum\_{j=i-m\_i}^i N\_j \tag{29}
$$

With

$$\sigma^2 \left( \hat{\rho}\_i^\* \right) = \frac{1}{\left( (m\_i + 1)\Delta t \right)^2} \sum\_{j=i-m\_i}^i N\_j \tag{30}$$

This nonlinear approach performs advantageously in comparison with conventional linear filters [12, 14], allowing to maintain sufficient precision while rate changes in the signal occur.

Remaining high-frequency fluctuations can now be reduced using a second, recursive smoother, for instance a Brown's double exponential filter [14]. A first exponential smoothing ρb1 <sup>i</sup> is performed on <sup>ρ</sup>b<sup>∗</sup> <sup>i</sup> with a smoothing parameter δ<sup>i</sup> such as:

$$
\widehat{\rho}\_i^1 = \delta\_i \widehat{\rho}\_i^\* + (1 - \delta\_i) \widehat{\rho}\_{i-1}^\* \tag{31}
$$

With

$$
\sigma^2 \left( \hat{\rho}\_i^1 \right) = \left[ \delta\_l \sigma(\hat{\rho}\_i^\*) \right]^2 + \left[ (1 - \delta\_l) \sigma(\hat{\rho}\_{i-1}^\*) \right]^2 \tag{32}
$$

A last exponential smoothing <sup>ρ</sup>b<sup>2</sup> <sup>i</sup> is eventually performed on <sup>ρ</sup>b<sup>1</sup> <sup>i</sup> under the form:

$$
\widehat{\rho}\_i^2 = \delta\_i \widehat{\rho}\_i^1 + (1 - \delta\_i) \widehat{\rho}\_{i-1}^1 \tag{33}
$$

With

$$
\sigma^2 \left( \widehat{\rho}\_i^2 \right) = \left[ \delta\_l \sigma \left( \widehat{\rho}\_i^1 \right) \right]^2 + \left[ (1 - \delta\_i) \sigma \left( \widehat{\rho}\_{i-1}^1 \right) \right]^2 \tag{34}
$$

The parameter δ<sup>i</sup> changes as a function of the parameter mi and its strength is set with the parameter W:

$$\delta\_i = 1 - \exp\left(-\frac{1}{W(m\_i - 1)}\right) \tag{35}$$

Finally, the Brown's estimation <sup>ρ</sup>b∗∗ <sup>i</sup> is calculated such as:

$$
\hat{\rho}\_i^{\*\*} = \mathbf{2}\hat{\rho}\_i^1 - \hat{\rho}\_i^2 \tag{36}
$$

compared to moving average filters set with m = 50 samples (soft) and m = 500 samples (hard). Figure 5 shows that nonlinear filtering offers a better compromise between precision and accuracy, though the detection of small changes within large statistical fluctuation remains

Such nonlinear smoothing algorithms, easily embedded into programmable components, have for instance been implemented into a Geiger-Müller dosimeter fixed on a wireless robot used for radiological threat detection [15]. This algorithmic building block is plays a key role in the nuclear counting methods studied in the next sections, namely compensation measurements

In many cases, radiation monitoring requires the counting of a signal from a first radiation source within an interference signal induced by a second particle emitter, namely α/β vs. γ; n vs. γ, γ vs. γ … The most efficient techniques consist in the recognition of the particle origin associated with each individual pulse event by coincidence/anti-coincidence, pulse height discrimination (PHD) or pulse shape discrimination (PSD) [16]. However, event-by-event discrimination techniques may be found unreliable in particular mixed field configurations. Compensation methods are an alternative solution when addressing such limitations [17, 18]: their principle lies within measuring count rates ρ<sup>A</sup> from a first detector A, sensitive to all particles, and comparing the result with count rates ρ<sup>B</sup> from a second detector B, only significantly sensitive to background contributions (typically gamma rays). The estimation ρ<sup>C</sup> of the count rate associated with particles of interest is obtained by subtraction of ρ<sup>A</sup> with ρ<sup>B</sup> such as:

<sup>i</sup> <sup>&</sup>gt; DL<sup>k</sup> i

Figure 6. Behavior of smoothing filters over a 20% rate variation at 500 counts per sample.

� �. At higher count rates (Figure 6), nonlinear filtering permits the

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

http://dx.doi.org/10.5772/intechopen.71233

163

� � and ensures a significant gain, operating both faster

unreachable <sup>Δ</sup>ρb<sup>k</sup>

<sup>i</sup> <sup>≤</sup> DL<sup>k</sup> i

and more precisely than both moving averages.

detection of the rate change <sup>Δ</sup>ρb<sup>k</sup>

and sensor network processing.

4. Compensation measurement

With

$$
\sigma^2(\hat{\rho}\_i^{\*\*}) = 4\sigma^2(\hat{\rho}\_i^1) + \sigma^2(\hat{\rho}\_i^2) \tag{37}
$$

Figures 5 and 6 illustrate the advantage of the hereby described nonlinear filters over conventional, moving average filters with a 20% rate variation, respectively, in a low count rate configuration (5 counts per sample) and in a higher count rate configuration (500 counts per sample). The nonlinear filter has been set with parameters Q<sup>γ</sup> = 1.645 (γ = 90%) and W = 0.2 and

Figure 5. Behavior of smoothing filters over a 20% rate variation at 5 counts per sample.

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems http://dx.doi.org/10.5772/intechopen.71233 163

Figure 6. Behavior of smoothing filters over a 20% rate variation at 500 counts per sample.

compared to moving average filters set with m = 50 samples (soft) and m = 500 samples (hard). Figure 5 shows that nonlinear filtering offers a better compromise between precision and accuracy, though the detection of small changes within large statistical fluctuation remains unreachable <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> <sup>≤</sup> DL<sup>k</sup> i � �. At higher count rates (Figure 6), nonlinear filtering permits the detection of the rate change <sup>Δ</sup>ρb<sup>k</sup> <sup>i</sup> <sup>&</sup>gt; DL<sup>k</sup> i � � and ensures a significant gain, operating both faster and more precisely than both moving averages.

Such nonlinear smoothing algorithms, easily embedded into programmable components, have for instance been implemented into a Geiger-Müller dosimeter fixed on a wireless robot used for radiological threat detection [15]. This algorithmic building block is plays a key role in the nuclear counting methods studied in the next sections, namely compensation measurements and sensor network processing.

#### 4. Compensation measurement

A last exponential smoothing <sup>ρ</sup>b<sup>2</sup>

162 Ionizing Radiation Effects and Applications

Finally, the Brown's estimation <sup>ρ</sup>b∗∗

With

With

parameter W:

<sup>i</sup> is eventually performed on <sup>ρ</sup>b<sup>1</sup>

The parameter δ<sup>i</sup> changes as a function of the parameter mi and its strength is set with the

<sup>δ</sup><sup>i</sup> <sup>¼</sup> <sup>1</sup> � exp � <sup>1</sup>

<sup>i</sup> is calculated such as:

ρb∗∗ <sup>i</sup> <sup>¼</sup> <sup>2</sup>ρb<sup>1</sup>

� � <sup>¼</sup> <sup>4</sup>σ<sup>2</sup> <sup>ρ</sup>b<sup>1</sup>

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ i

Figure 5. Behavior of smoothing filters over a 20% rate variation at 5 counts per sample.

<sup>i</sup> <sup>þ</sup> ð Þ <sup>1</sup> � <sup>δ</sup><sup>i</sup> <sup>ρ</sup>b<sup>1</sup>

<sup>þ</sup> ð Þ <sup>1</sup> � <sup>δ</sup><sup>i</sup> <sup>σ</sup> <sup>ρ</sup>b<sup>1</sup>

W mð Þ <sup>i</sup> � 1 � �

> <sup>þ</sup> <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>2</sup> i � �

<sup>i</sup> � <sup>ρ</sup>b<sup>2</sup>

i � �

Figures 5 and 6 illustrate the advantage of the hereby described nonlinear filters over conventional, moving average filters with a 20% rate variation, respectively, in a low count rate configuration (5 counts per sample) and in a higher count rate configuration (500 counts per sample). The nonlinear filter has been set with parameters Q<sup>γ</sup> = 1.645 (γ = 90%) and W = 0.2 and

h i � � <sup>2</sup>

i�1

ρb2 <sup>i</sup> <sup>¼</sup> <sup>δ</sup>iρb<sup>1</sup>

<sup>¼</sup> <sup>δ</sup>i<sup>σ</sup> <sup>ρ</sup>b<sup>1</sup> i h i � � <sup>2</sup>

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b<sup>2</sup> i � � <sup>i</sup> under the form:

<sup>i</sup>�<sup>1</sup> (33)

<sup>i</sup> (36)

(34)

(35)

(37)

In many cases, radiation monitoring requires the counting of a signal from a first radiation source within an interference signal induced by a second particle emitter, namely α/β vs. γ; n vs. γ, γ vs. γ … The most efficient techniques consist in the recognition of the particle origin associated with each individual pulse event by coincidence/anti-coincidence, pulse height discrimination (PHD) or pulse shape discrimination (PSD) [16]. However, event-by-event discrimination techniques may be found unreliable in particular mixed field configurations. Compensation methods are an alternative solution when addressing such limitations [17, 18]: their principle lies within measuring count rates ρ<sup>A</sup> from a first detector A, sensitive to all particles, and comparing the result with count rates ρ<sup>B</sup> from a second detector B, only significantly sensitive to background contributions (typically gamma rays). The estimation ρ<sup>C</sup> of the count rate associated with particles of interest is obtained by subtraction of ρ<sup>A</sup> with ρ<sup>B</sup> such as:

$$
\rho\_{\mathbb{C}} = \rho\_A - \omega \rho\_B \tag{38}
$$

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ C,i � � <sup>¼</sup> <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗

nq Pnq q¼1

positive and significant values of <sup>ρ</sup>bC,i

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi <sup>2</sup>σ<sup>2</sup> <sup>ρ</sup>b∗∗ C,i <sup>r</sup> � �,

A, <sup>q</sup> ρb∗∗ B, <sup>q</sup>

The estimation of ω and σ<sup>2</sup>

compensation factors <sup>ω</sup><sup>q</sup> <sup>¼</sup> <sup>ρ</sup>b∗∗

an empirical mean <sup>ω</sup> <sup>¼</sup> <sup>1</sup>

Algorithm 1:

C,i > Q<sup>γ</sup>

C,i <sup>¼</sup> <sup>ρ</sup>b∗∗

If <sup>ρ</sup>b∗∗

Then <sup>ρ</sup>b∗∗∗

Else <sup>ρ</sup>b∗∗∗

<sup>ρ</sup>b∗∗∗

A, <sup>q</sup> and <sup>ρ</sup>b∗∗∗

A,i � � <sup>þ</sup> <sup>ω</sup><sup>2</sup>

<sup>ω</sup><sup>q</sup> and variance <sup>σ</sup><sup>2</sup>ð Þ¼ <sup>ω</sup> <sup>1</sup>

to apply an envelope coverage factor Q<sup>γ</sup> associated with a confident level γ as:

Figure 7 synthetizes the principle, inputs, and outputs of the compensation technique.

The method improves the reliability of compensation measurement with the use of a recorded

ticles of interest are optimized using an adaptive filter, smoothing individual channels while suppressing all negative or non-significant values. The approach described in the present section has been successfully implemented in varied applications, such as α/β contamination

As a perspective, it has been demonstrated that the multiplication of channels, such as illustrated in Figure 8, allows the system to learn a prior distribution for the signal over a set of pixels as a function of incident energy and spatial origin of background particles. Dispatching

B, <sup>q</sup> data along (X > 1) dimensions induces a reduction of detection threshold

C,i (detection hypothesis H<sup>1</sup> is accepted)

C,i ¼ 0 (detection hypothesis H<sup>1</sup> is rejected)

database. Moreover, accuracy and decision threshold Q<sup>γ</sup>

meters or gadolinium-based neutron detectors [20, 21].

Figure 7. Principle of the compensation technique.

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ B,i � � <sup>þ</sup> <sup>ρ</sup>b∗∗

> nq Pnq q¼1

eters. An approach is proposed in [19, 20], in which a database is built from measures acquired in representative areas and in absence of the signal particle of interest: ρ<sup>C</sup> = 0. In these conditions,

Based on the generalized variance expressed in Eq. (43), a hypothesis test is built to select

presence of particles of interest is detected in compliance with a confidence level γ governing the test. Most of the time, ω<sup>q</sup> values can be considered to follow a Normal law, which allows us

B,i � �<sup>2</sup>

are obtained for each measurement point (1 ≤ q ≤ nq), allowing for

(ω) is complicated by the experimental dependence of these param-

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

σ2

<sup>ω</sup><sup>q</sup> � <sup>ω</sup> � �<sup>2</sup> to be estimated.

. Algorithm 1 presents the detection test in which the

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi <sup>2</sup>σ<sup>2</sup> <sup>ρ</sup>b∗∗ C,i

<sup>r</sup> � � associated with the par-

ð Þ ω (44)

165

http://dx.doi.org/10.5772/intechopen.71233

where ω is a correction factor taking in account the fact that detector B is not strictly equivalent to detector A in terms of response as a function of the energy and spatial localization of incident background particles. Three challenges are to be faced in compensation measurement:


Values of ρA, <sup>i</sup>Δt and ρB, <sup>i</sup>Δt at the time ti are described by Poisson processes, as already stated in the third section of this chapter. Therefore, if ω = 1, values of ρC, <sup>i</sup>Δt are described by a Skellam process Sk ρA,i Δt; ρB,i Δt � � such as:

$$
\rho\_{\mathbb{C},i} \Delta t \sim \mathcal{S} \, k \Big( \rho\_{A,i} \Delta t, \rho\_{B,i} \Delta t \Big) \tag{39}
$$

The expectation and the variance of the random variable <sup>ρ</sup>bC,i <sup>Δ</sup><sup>t</sup> are, respectively, <sup>E</sup> <sup>ρ</sup>bC,i Δt � � <sup>¼</sup> <sup>ρ</sup>bA,i <sup>Δ</sup><sup>t</sup> � <sup>b</sup>ρB,i Δt ¼ ρA,i Δt � ρB,i <sup>Δ</sup><sup>t</sup> and <sup>σ</sup><sup>2</sup> <sup>ρ</sup>bC,i Δt � � <sup>¼</sup> <sup>ρ</sup>bA,i <sup>Δ</sup><sup>t</sup> <sup>þ</sup> <sup>b</sup>ρB,i Δt ¼ ρA,i Δt þ ρB,i Δt under the same assumption as in Section 4. The variance definition highlights an increase of fluctuation level in comparison with single-channel measurement. It is therefore required to reduce this variance using a suitable smoothing filter, such as the CST a nonlinear filter described in the previous section (cf. Eqs. (36) and (37)):

$$\mathbb{E}\left[\widehat{\rho}\_{A,i}^{\*\*};\sigma\left(\widehat{\rho}\_{A,i}^{\*\*}\right)\right] = \mathbb{C}ST\left(\widehat{\rho}\_{A,i}\right) \tag{40}$$

$$\left[\widehat{\rho}\_{B,i}^{\*\*}; \sigma\left(\widehat{\rho}\_{B,i}^{\*\*}\right)\right] = \text{CST}\left(\widehat{\rho}\_{B,i}\right) \tag{41}$$

Reduced variances <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ A,i � � and <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ B,i � � calculated according to Eq. (36) are used to determine <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ C,i � � as:

$$
\sigma^2 \left( \hat{\rho}\_{\mathbb{C},i}^{\*\*} \right) = \sigma^2 \left( \hat{\boldsymbol{n}}\_{A,i}^{\*\*} \right) + \sigma^2 \left( \hat{\rho}\_{B,i}^{\*\*} \right) \tag{42}
$$

If the compensation factor ω remains constant but different from 1, Eq. (42) becomes:

$$
\sigma^2 \left( \widehat{\rho}\_{\mathbb{C},i}^{\*\*} \right) = \sigma^2 \left( \widehat{\rho}\_{A,i}^{\*\*} \right) + \omega^2 \sigma^2 \left( \widehat{\rho}\_{A,i}^{\*\*} \right) \tag{43}
$$

In practice, the factor ω is not constant, due to the impact of energy and spatial distributions of incident particles. We then introduce notations ω and σ<sup>2</sup> (ω) for the expectation and variance of the variable ω. A resulting variance is therefore calculated by taking into account both statistical error and bias such as:

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems http://dx.doi.org/10.5772/intechopen.71233 165

$$
\sigma^2 \left( \widehat{\rho}\_{C,i}^{\*\*} \right) = \sigma^2 \left( \widehat{\rho}\_{A,i}^{\*\*} \right) + \overline{\sigma}^2 \sigma^2 \left( \widehat{\rho}\_{B,i}^{\*\*} \right) + \left( \widehat{\rho}\_{B,i}^{\*\*} \right)^2 \sigma^2(\omega) \tag{44}
$$

The estimation of ω and σ<sup>2</sup> (ω) is complicated by the experimental dependence of these parameters. An approach is proposed in [19, 20], in which a database is built from measures acquired in representative areas and in absence of the signal particle of interest: ρ<sup>C</sup> = 0. In these conditions, compensation factors <sup>ω</sup><sup>q</sup> <sup>¼</sup> <sup>ρ</sup>b∗∗ A, <sup>q</sup> ρb∗∗ B, <sup>q</sup> are obtained for each measurement point (1 ≤ q ≤ nq), allowing for an empirical mean <sup>ω</sup> <sup>¼</sup> <sup>1</sup> nq Pnq q¼1 <sup>ω</sup><sup>q</sup> and variance <sup>σ</sup><sup>2</sup>ð Þ¼ <sup>ω</sup> <sup>1</sup> nq Pnq q¼1 <sup>ω</sup><sup>q</sup> � <sup>ω</sup> � �<sup>2</sup> to be estimated.

Based on the generalized variance expressed in Eq. (43), a hypothesis test is built to select positive and significant values of <sup>ρ</sup>bC,i . Algorithm 1 presents the detection test in which the presence of particles of interest is detected in compliance with a confidence level γ governing the test. Most of the time, ω<sup>q</sup> values can be considered to follow a Normal law, which allows us to apply an envelope coverage factor Q<sup>γ</sup> associated with a confident level γ as:

Algorithm 1:

ρ<sup>C</sup> ¼ ρ<sup>A</sup> � ωρ<sup>B</sup> (38)

<sup>Δ</sup><sup>t</sup> are, respectively, <sup>E</sup> <sup>ρ</sup>bC,i

Δt þ ρB,i

Δt ¼ ρA,i

calculated according to Eq. (36) are used to deter-

(ω) for the expectation and variance of

(39)

¼

(40)

(41)

(42)

(43)

Δt � �

Δt under the

where ω is a correction factor taking in account the fact that detector B is not strictly equivalent to detector A in terms of response as a function of the energy and spatial localization of incident background particles. Three challenges are to be faced in compensation measurement:

Values of ρA, <sup>i</sup>Δt and ρB, <sup>i</sup>Δt at the time ti are described by Poisson processes, as already stated in the third section of this chapter. Therefore, if ω = 1, values of ρC, <sup>i</sup>Δt are described by a Skellam

> Δt; ρB,i Δt

� �

<sup>¼</sup> <sup>ρ</sup>bA,i

<sup>¼</sup> CST <sup>ρ</sup>bA,i � �

<sup>¼</sup> CST <sup>ρ</sup>bB,i � �

> <sup>þ</sup> <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ B,i � �

> > <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ A,i � �

<sup>þ</sup> <sup>ω</sup><sup>2</sup>

<sup>Δ</sup><sup>t</sup> <sup>þ</sup> <sup>b</sup>ρB,i

Δt � Sk ρA,i

Δt � �

same assumption as in Section 4. The variance definition highlights an increase of fluctuation level in comparison with single-channel measurement. It is therefore required to reduce this variance using a suitable smoothing filter, such as the CST a nonlinear filter described in the

• loss of reliability (impact of energy and anisotropy of the background signal).

• increase in fluctuation level;

164 Ionizing Radiation Effects and Applications

Δt; ρB,i Δt

� �

Δt ¼ ρA,i

Reduced variances <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗

as:

C,i � �

cal error and bias such as:

mine <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗

previous section (cf. Eqs. (36) and (37)):

process Sk ρA,i

<sup>Δ</sup><sup>t</sup> � <sup>b</sup>ρB,i

<sup>ρ</sup>bA,i

• apparition of negative count rates without physical sense;

such as:

The expectation and the variance of the random variable <sup>ρ</sup>bC,i

Δt � ρB,i

A,i � � ρC,i

<sup>Δ</sup><sup>t</sup> and <sup>σ</sup><sup>2</sup> <sup>ρ</sup>bC,i

ρb∗∗ A,i ; <sup>σ</sup> <sup>ρ</sup>b∗∗ A,i h i � �

ρb∗∗ B,i ; <sup>σ</sup> <sup>ρ</sup>b∗∗ B,i h i � �

and <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ C,i � �

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ C,i � �

incident particles. We then introduce notations ω and σ<sup>2</sup>

B,i � �

> <sup>¼</sup> <sup>σ</sup><sup>2</sup> ̃ bn ∗∗ A,i � �

If the compensation factor ω remains constant but different from 1, Eq. (42) becomes:

<sup>¼</sup> <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ A,i � �

In practice, the factor ω is not constant, due to the impact of energy and spatial distributions of

the variable ω. A resulting variance is therefore calculated by taking into account both statisti-

$$\text{If } \widehat{\rho}\_{\mathbb{C},i}^{\*\*} > \mathbb{Q}\_{\prime} \sqrt{2\sigma^2 \left(\widehat{\rho}\_{\mathbb{C},i}^{\*\*}\right)} \tau$$

Then <sup>ρ</sup>b∗∗∗ C,i <sup>¼</sup> <sup>ρ</sup>b∗∗ C,i (detection hypothesis H<sup>1</sup> is accepted)

Else <sup>ρ</sup>b∗∗∗ C,i ¼ 0 (detection hypothesis H<sup>1</sup> is rejected)

Figure 7 synthetizes the principle, inputs, and outputs of the compensation technique.

The method improves the reliability of compensation measurement with the use of a recorded database. Moreover, accuracy and decision threshold Q<sup>γ</sup> ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi <sup>2</sup>σ<sup>2</sup> <sup>ρ</sup>b∗∗ C,i <sup>r</sup> � � associated with the particles of interest are optimized using an adaptive filter, smoothing individual channels while suppressing all negative or non-significant values. The approach described in the present section has been successfully implemented in varied applications, such as α/β contamination meters or gadolinium-based neutron detectors [20, 21].

As a perspective, it has been demonstrated that the multiplication of channels, such as illustrated in Figure 8, allows the system to learn a prior distribution for the signal over a set of pixels as a function of incident energy and spatial origin of background particles. Dispatching <sup>ρ</sup>b∗∗∗ A, <sup>q</sup> and <sup>ρ</sup>b∗∗∗ B, <sup>q</sup> data along (X > 1) dimensions induces a reduction of detection threshold

Figure 7. Principle of the compensation technique.

Figure 8. Principle of the compensation technique for pixelated detectors.

Qγ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi <sup>2</sup>σ<sup>2</sup> <sup>ρ</sup>b∗∗ C,i <sup>r</sup> � � and thus an improvement of measurement reliability. Compensation factors ωj, <sup>k</sup> and variances σ<sup>2</sup> (ωj, <sup>k</sup>) are determined for every 1 ≤ j ≤ X A-type detector, and every 1 ≤ k ≤ X B-type detector. Resulting count rates ρC, <sup>i</sup> are estimated as:

$$
\widehat{\rho}\_{\mathbb{C},i}^{\*\*} = \sum\_{j=1}^{X} \left[ \widehat{\rho}\_{A,i,j}^{\*\*} - \sum\_{k=1}^{X} \overline{\omega}\_{j,k} \widehat{\rho}\_{B,i,k}^{\*\*} \right] \tag{45}
$$

DT ¼ Q<sup>1</sup>�<sup>α</sup> σ θb<sup>0</sup> � θ<sup>0</sup>

θ<sup>1</sup> � DT σ θð Þ <sup>1</sup> þ θ<sup>0</sup> � �

θ<sup>1</sup> � Q<sup>1</sup>�<sup>α</sup>

detected with a non-detection risk:

If ω < 1, Eq. (48) becomes:

even for ω ≈ 1.

βω¼<sup>1</sup> <sup>¼</sup> err

βω<<sup>1</sup> ¼ err

hoping for gain in flexibility [24]. The latter is described below.

the random variable ρiΔt�P(θTΔt) at each time ti such as:

slope state Di with values between �1 and 1 such as:

ρb∗∗ <sup>i</sup> ; <sup>σ</sup> <sup>ρ</sup>b∗∗ i � � � � <sup>¼</sup> CST <sup>ρ</sup>b<sup>i</sup>

<sup>ρ</sup>^\_ <sup>i</sup> <sup>¼</sup> ð Þ <sup>1</sup> � <sup>α</sup><sup>1</sup>

calculating, at each time step ti, the filtered logarithmic derivative <sup>ρ</sup>^\_<sup>i</sup> of the signal:

with α<sup>1</sup> and l being, respectively, a smoothing parameter and the derivative depth.

filter, minimizing the high-frequency variance σ<sup>2</sup>

� � <sup>¼</sup> <sup>Q</sup><sup>1</sup>�<sup>α</sup>

During the passage of a dense vehicle, θ<sup>0</sup> will decrease due to gamma-ray attenuation as the vehicle acts as a radiation shield. Such baseline alteration is noted ωθ0, where ω e [0; 1] is the attenuation factor. An added count rate from a source with intrinsic rate θ1, put onboard the vehicle, will thus lead to a total signal θ<sup>T</sup> = ωθ<sup>0</sup> + θ1. If ω = 1 and θ<sup>1</sup> > DT, the source is

¼ err

p σ θð Þ <sup>1</sup> þ ωθ<sup>0</sup> " #

This effect, so-called "shadow effect," induces a significant loss in detection capability (β↗)

Many works have been done in order to restore the baseline (ω! 1) and all of them use a database recorded when a representative sample of void vehicle in passing through the RPM [22, 23]. An alternative method based on time series analysis has been developed to restore the baseline without using any prior knowledge about the vehicle and the experimental conditions

In the first place, the minimization of DT requires the implementation of an efficient smoothing

serving the temporal shape of the signal of interest θ1(ti). Thus, the nonlinear filter CST (Eqs. (36) and (37)) has proven efficient for this purpose. The single-channel RPM estimates

Estimations are continuously recorded into an historical memory with a depth m allowing

∀i ∈½ � 1; m ,

ρb∗∗ <sup>i</sup> � <sup>ρ</sup>b∗∗ i�l ρb∗∗ i

The trend of the signal, which can be constant, decreasing or increasing, is represented by a

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2σ<sup>2</sup>ð Þ θ<sup>0</sup>

> ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2σ<sup>2</sup>ð Þ θ<sup>0</sup>

<sup>&</sup>gt; βω¼<sup>1</sup> (49)

http://dx.doi.org/10.5772/intechopen.71233

(θ0) and subsequently the β risk, while pre-

� � (50)

� <sup>α</sup>1ρ^\_<sup>i</sup>�<sup>1</sup> (51)

p σ θð Þ <sup>1</sup> þ θ<sup>0</sup> " # (47)

167

(48)

q

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

θ<sup>1</sup> � Q<sup>1</sup>�<sup>α</sup>

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2σ<sup>2</sup>ð Þ ωθ<sup>0</sup>

$$\sigma^{2}\left(\widehat{\rho}\_{\mathbb{C},i}^{\ast\ast}\right) = \sum\_{j=1}^{X} \left\{ \sigma^{2}\left(\widehat{\rho}\_{A,i,j}^{\ast\ast}\right) - \sum\_{k=1}^{X} \left[\overline{\boldsymbol{\sigma}}\_{\mathbb{H},k} \sigma\left(\widehat{\boldsymbol{\rho}}\_{B,i,k}^{\ast\ast}\right)\right]^{2} + \left[\widehat{\rho}\_{B,i,k}^{\ast\ast} \sigma\left(\boldsymbol{\omega}\_{\mathbb{H},k}\right)\right]^{2} \right\} \tag{46}$$

#### 5. Moving source detection

Radiation portal monitors (RPM) are implemented to detect radioactive sources, carried by a vehicle in motion, through the monitoring of a count rate measured by large-volume detectors. Two main issues arise in RPM development: correcting the shadow shielding effect observed when the vehicle is dense enough to impact the baseline of the signal, and improving the detection capability (increasing true detection minus false alarm detection probability).

RPM detection strategy is based on a hypothesis test where the estimated signal <sup>ρ</sup>b<sup>i</sup> at the time ti is continuously compared to a threshold h, itself determined in comparison with the signal distribution under H0. Let θ<sup>0</sup> be the expected background count rate without any vehicle in the environment surrounding the RPM. A decision threshold (DT) is set, following the same philosophy as presented previously (Eqs. (20)–(26)), as a function of variance σ<sup>2</sup> (θ0) and a confidence level associated with a false detection risk α

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems http://dx.doi.org/10.5772/intechopen.71233 167

$$DT = Q\_{1-a} \sigma \left(\hat{\theta}\_0 - \theta\_0\right) = Q\_{1-a} \sqrt{2\sigma^2(\theta\_0)}\tag{47}$$

During the passage of a dense vehicle, θ<sup>0</sup> will decrease due to gamma-ray attenuation as the vehicle acts as a radiation shield. Such baseline alteration is noted ωθ0, where ω e [0; 1] is the attenuation factor. An added count rate from a source with intrinsic rate θ1, put onboard the vehicle, will thus lead to a total signal θ<sup>T</sup> = ωθ<sup>0</sup> + θ1. If ω = 1 and θ<sup>1</sup> > DT, the source is detected with a non-detection risk:

$$\beta\_{w=1} = \text{err}\left[\frac{\theta\_1 - DT}{\sigma(\theta\_1 + \theta\_0)}\right] = \text{err}\left[\frac{\theta\_1 - Q\_{1-a}\sqrt{2\sigma^2(\theta\_0)}}{\sigma(\theta\_1 + \theta\_0)}\right] \tag{48}$$

If ω < 1, Eq. (48) becomes:

Qγ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi <sup>2</sup>σ<sup>2</sup> <sup>ρ</sup>b∗∗ C,i r � �

166 Ionizing Radiation Effects and Applications

ωj, <sup>k</sup> and variances σ<sup>2</sup>

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ C,i � �

5. Moving source detection

B-type detector. Resulting count rates ρC, <sup>i</sup> are estimated as:

Figure 8. Principle of the compensation technique for pixelated detectors.

<sup>¼</sup> <sup>X</sup> X

j¼1

confidence level associated with a false detection risk α

ρb∗∗ C,i <sup>¼</sup> <sup>X</sup> X

<sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗ A,i,j � �

j¼1

ρb∗∗ A,i,j �<sup>X</sup> X

�<sup>X</sup> X

k¼1

Radiation portal monitors (RPM) are implemented to detect radioactive sources, carried by a vehicle in motion, through the monitoring of a count rate measured by large-volume detectors. Two main issues arise in RPM development: correcting the shadow shielding effect observed when the vehicle is dense enough to impact the baseline of the signal, and improving the detection capability (increasing true detection minus false alarm detection probability).

RPM detection strategy is based on a hypothesis test where the estimated signal <sup>ρ</sup>b<sup>i</sup> at the time ti is continuously compared to a threshold h, itself determined in comparison with the signal distribution under H0. Let θ<sup>0</sup> be the expected background count rate without any vehicle in the environment surrounding the RPM. A decision threshold (DT) is set, following the same

philosophy as presented previously (Eqs. (20)–(26)), as a function of variance σ<sup>2</sup>

and thus an improvement of measurement reliability. Compensation factors

k¼1

<sup>ω</sup>j, <sup>k</sup><sup>σ</sup> <sup>ρ</sup>b∗∗ B,i, k h i � � <sup>2</sup>

( )

" #

(ωj, <sup>k</sup>) are determined for every 1 ≤ j ≤ X A-type detector, and every 1 ≤ k ≤ X

<sup>ω</sup>j, <sup>k</sup>ρb∗∗ B,i, k

<sup>þ</sup> <sup>ρ</sup>b∗∗

B,i, <sup>k</sup>σ ωj, <sup>k</sup> � � h i<sup>2</sup> (45)

(46)

(θ0) and a

$$\beta\_{\omega < 1} = err \left[ \frac{\theta\_1 - Q\_{1-\alpha} \sqrt{2\sigma^2(\omega \theta\_0)}}{\sigma(\theta\_1 + \omega \theta\_0)} \right] > \beta\_{\omega = 1} \tag{49}$$

This effect, so-called "shadow effect," induces a significant loss in detection capability (β↗) even for ω ≈ 1.

Many works have been done in order to restore the baseline (ω! 1) and all of them use a database recorded when a representative sample of void vehicle in passing through the RPM [22, 23]. An alternative method based on time series analysis has been developed to restore the baseline without using any prior knowledge about the vehicle and the experimental conditions hoping for gain in flexibility [24]. The latter is described below.

In the first place, the minimization of DT requires the implementation of an efficient smoothing filter, minimizing the high-frequency variance σ<sup>2</sup> (θ0) and subsequently the β risk, while preserving the temporal shape of the signal of interest θ1(ti). Thus, the nonlinear filter CST (Eqs. (36) and (37)) has proven efficient for this purpose. The single-channel RPM estimates the random variable ρiΔt�P(θTΔt) at each time ti such as:

$$\mathbb{E}\left[\widehat{\rho}\_{i}^{\*\*};\sigma(\widehat{\rho}\_{i}^{\*\*})\right] = \mathbb{C}ST(\widehat{\rho}\_{i})\tag{50}$$

Estimations are continuously recorded into an historical memory with a depth m allowing calculating, at each time step ti, the filtered logarithmic derivative <sup>ρ</sup>^\_<sup>i</sup> of the signal:

$$\forall i \in [1, m].$$

$$\hat{\boldsymbol{\rho}}\_i = (1 - \alpha\_1) \frac{\hat{\boldsymbol{\rho}}\_i^{\*\*} - \hat{\boldsymbol{\rho}}\_{i-l}^{\*\*}}{\hat{\boldsymbol{\rho}}\_i^{\*\*}} - \alpha\_1 \hat{\boldsymbol{\rho}}\_{i-1} \tag{51}$$

with α<sup>1</sup> and l being, respectively, a smoothing parameter and the derivative depth.

The trend of the signal, which can be constant, decreasing or increasing, is represented by a slope state Di with values between �1 and 1 such as:

$$
\hat{\phi}\_i < -\alpha\_2 \Rightarrow D\_i = -1 \tag{52}
$$

Knowing the state of the system, the baseline of the signal can be restored. The upper level (UL) (state 1) and the lower level LL (state 6) are firstly estimated in a recorded time series at

ð Þ Si�<sup>k</sup> ¼ 1 (55)

ð Þ Si�<sup>k</sup> ¼ 6 (56)

<sup>i</sup>�<sup>k</sup> (57)

http://dx.doi.org/10.5772/intechopen.71233

169

<sup>i</sup>�<sup>k</sup> (58)

<sup>i</sup>�<sup>k</sup> (59)

<sup>i</sup>�<sup>k</sup> <sup>þ</sup> UL � LL (60)

zUL ¼ arg 1 ≤ k ≤ ξ

zLL ¼ arg 1 ≤ k ≤ ξ

dimð Þ ZUL

dimð Þ ZLL

Si�<sup>k</sup> <sup>∈</sup>f g <sup>1</sup>; <sup>2</sup>; <sup>3</sup>; <sup>4</sup> , <sup>ρ</sup>b∗∗∗

dim X ð Þ ZUL

dim X ð Þ ZLL

<sup>i</sup>�<sup>k</sup> <sup>¼</sup> <sup>ρ</sup>b∗∗

Figure 11 illustrates the baseline restoration: the correction algorithm enables the detection of a source originally hidden by shadow effect. A simulation study has shown the significant gain

The conception of a RPM primarily consists in designing detection blocks with a maximized sensitivity according to the application view and cost-effectiveness strategies. Signal processing is then to be implemented in the system in order to tune its detection capabilities.

k¼1

k¼1

ρb∗∗

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

ρb∗∗

<sup>i</sup>�<sup>k</sup> <sup>¼</sup> <sup>ρ</sup>b∗∗

UL <sup>¼</sup> <sup>1</sup>

LL <sup>¼</sup> <sup>1</sup>

The baseline is restored to obtain corrected count rate estimations <sup>b</sup>ρ∗∗∗ such as:

Si�<sup>k</sup> <sup>∈</sup>f g <sup>5</sup>; <sup>6</sup>; <sup>7</sup>; <sup>8</sup> , <sup>ρ</sup>b∗∗∗

in detection probability with the maintaining of a stable false detection rate [24].

Figure 11. Signal and state evolutions over the simulation of a source passing into a dense vehicle.

time ti:

∀k ∈⟦1; ξ⟧,

$$\left|\hat{\dot{\rho}}\_{i}\right| \le \alpha\_2 \Rightarrow D\_i = 0 \tag{53}$$

$$
\hat{\phi}\_i > \alpha\_2 \Rightarrow D\_i = 1 \tag{54}
$$

with α<sup>2</sup> > 0 being a parameter for variation significant.

The state of the signal Si is labeled by a number between 1 and 8, defined as illustrated in Figure 9. The first line describes the passage of a vehicle containing a source without shadow effect; the second line corresponds to the passage of a dense vehicle with no source; and the third one to the passage of a dense vehicle containing a radioactive source (shadow shielding).

States Si can be determined with knowledge of Di and Si � <sup>1</sup> using a sequential logic algorithm detailed under the form of a state diagram in Figure 10. To solve the problem, states 3 and 8 automatically pass to state 1 after a preset watchdog time τw.

Figure 9. Schematic view of possible states of the system.

Figure 10. State diagram of the state determination algorithm.

Knowing the state of the system, the baseline of the signal can be restored. The upper level (UL) (state 1) and the lower level LL (state 6) are firstly estimated in a recorded time series at time ti:

$$\tau\_{\rm LL} = \underset{1 \le k \le \xi}{\text{arg}} \left( \mathbb{S}\_{i-k} = 1 \right) \tag{55}$$

$$z\_{LL} = \underset{1 \le k \le \xi}{\text{arg}} \left( \mathbb{S}\_{i-k} = \mathfrak{G} \right) \tag{56}$$

$$\text{LIL} = \frac{1}{\text{dim}(Z\_{\text{UL}})} \sum\_{k=1}^{\text{dim}(Z\_{\text{UL}})} \hat{\rho}\_{i-k}^{\*\*} \tag{57}$$

$$LL = \frac{1}{\dim(Z\_{IL})} \sum\_{k=1}^{\dim(Z\_{IL})} \widehat{\rho}\_{i-k}^{\*\*} \tag{58}$$

The baseline is restored to obtain corrected count rate estimations <sup>b</sup>ρ∗∗∗ such as:

∀k ∈⟦1; ξ⟧,

<sup>ρ</sup>^\_<sup>i</sup> <sup>&</sup>lt; �α<sup>2</sup> ) Di ¼ �<sup>1</sup> (52)

≤ α<sup>2</sup> ) Di ¼ 0 (53)

<sup>ρ</sup>^\_<sup>i</sup> <sup>&</sup>gt; <sup>α</sup><sup>2</sup> ) Di <sup>¼</sup> <sup>1</sup> (54)

ρ^\_i 

The state of the signal Si is labeled by a number between 1 and 8, defined as illustrated in Figure 9. The first line describes the passage of a vehicle containing a source without shadow effect; the second line corresponds to the passage of a dense vehicle with no source; and the third one to the passage of a dense vehicle containing a radioactive source (shadow shielding).

States Si can be determined with knowledge of Di and Si � <sup>1</sup> using a sequential logic algorithm detailed under the form of a state diagram in Figure 10. To solve the problem, states 3 and 8

with α<sup>2</sup> > 0 being a parameter for variation significant.

168 Ionizing Radiation Effects and Applications

automatically pass to state 1 after a preset watchdog time τw.

Figure 9. Schematic view of possible states of the system.

Figure 10. State diagram of the state determination algorithm.

$$S\_{i-k} \in \{1; 2; 3; 4\}, \hat{\rho}\_{i-k}^{\*\*} = \hat{\rho}\_{i-k}^{\*\*} \tag{59}$$

$$S\_{i-k} \in \{5; 6; 7; 8\}, \hat{\rho}\_{i-k}^{\*\*} = \hat{\rho}\_{i-k}^{\*\*} + \text{UL} - \text{LL} \tag{60}$$

Figure 11 illustrates the baseline restoration: the correction algorithm enables the detection of a source originally hidden by shadow effect. A simulation study has shown the significant gain in detection probability with the maintaining of a stable false detection rate [24].

The conception of a RPM primarily consists in designing detection blocks with a maximized sensitivity according to the application view and cost-effectiveness strategies. Signal processing is then to be implemented in the system in order to tune its detection capabilities.

Figure 11. Signal and state evolutions over the simulation of a source passing into a dense vehicle.

σ<sup>2</sup> R<sup>ϕ</sup>

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2σ<sup>2</sup> R<sup>ϕ</sup> q � �

The detection test reads:

Algorithm 2:

variance σ<sup>2</sup>

σ<sup>2</sup> R<sup>ϕ</sup>

with

� � <sup>k</sup> <sup>¼</sup> <sup>σ</sup><sup>2</sup> <sup>R</sup><sup>ϕ</sup> � � � � �

channel j and the phase ϕ reads:

If R<sup>ϕ</sup><sup>0</sup> > R þ Q<sup>1</sup>�<sup>α</sup>

Then H1 is accepted Else H0 is accepted

The use of the empirical variance σ<sup>2</sup>

in the following recursive formula:

�

<sup>k</sup>�<sup>1</sup> <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗

� � <sup>¼</sup> <sup>n</sup> � <sup>1</sup>

ξ � 1 � � <sup>X</sup> <sup>ξ</sup>�<sup>1</sup> b c <sup>n</sup>�<sup>1</sup>

challenging signal-to-noise ratios [27, 28]. However, an algorithmic refinement is achieved with the introduction of a Normal law a priori on count rate distributions [29]. Thus, a modified

nonlinear filter (cf. Eq. (37)) for every detector j and memory slot i. Its calculation is presented

� �<sup>2</sup> � � <sup>þ</sup> <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗

<sup>k</sup>�<sup>1</sup> <sup>¼</sup> <sup>ρ</sup>b∗∗

<sup>1</sup> <sup>¼</sup> <sup>σ</sup><sup>2</sup> <sup>ρ</sup>b∗∗

The detection algorithm mixes the detection according to each individual channel with the detection using the correlation factor. In both cases, a decision threshold (DT) is calculated as a function of a false detection risk α. Let DTj,<sup>ϕ</sup> the decision threshold associated with the

1,i�1

ξ � 1 n � 1 � � � � � � ,

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

j,i�ð Þ j�1 φþ1

<sup>2</sup>σ<sup>2</sup> <sup>ρ</sup>b∗∗

ξ � 1 n � 1 � � � � � � ,

k,i�ð Þ k�1 ϕþ1

(Rϕ) is obtained by the estimation of individual variances σ<sup>2</sup>

∀k ∈½ � 2; n & ∀φ ∈ 1;

R<sup>φ</sup> � �

∀j∈½ � 1; n & ∀φ ∈ 1;

And let DTR<sup>ϕ</sup> be the decision threshold associated with the correlation factor R<sup>ϕ</sup> such as

DTj,<sup>φ</sup> ¼ Q<sup>1</sup>�<sup>α</sup>

σ<sup>2</sup> R<sup>φ</sup> � �� �

k,i�ð Þ k�1 ϕþ1 � � <sup>þ</sup> <sup>ρ</sup>b∗∗

φ¼1

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

<sup>R</sup><sup>φ</sup> � <sup>R</sup> � �<sup>2</sup> (63)

http://dx.doi.org/10.5772/intechopen.71233

(ρj, <sup>i</sup>) provides by the

� � k�1 � �<sup>2</sup>

(64)

171

k,i�ð Þ k�1 ϕþ1 � � <sup>R</sup><sup>ϕ</sup>

<sup>1</sup>,<sup>1</sup> (65)

� � (66)

<sup>r</sup> � � (67)

(Rϕ) ensures a significant gain in detection capability under

Figure 12. Schematic of a system based on correlation detection.

The improvement of RPM performance forms an active topic of research. It has notably been established that the spectral analysis of the signal, even for unresolved detectors, allows a gain in detection performance [25]. Another upgrade can be achieved by time series analysis techniques, especially when RPM are deployed in a network, which allows the implementation of correlation methods [26]. Figure 12 presents the schematic of a RPM network implementing n channels and dedicated to moving source detection.

The network configuration enables two complementary types of detection: the first one based on traditional temporal analysis of individual channel H1∣ρb1, …, <sup>b</sup>ρn, the second one based on frequency analysis, searching for a phase ϕ maximizing the correlation between channels H1∣φρ^<sup>1</sup> ,…,ρ^<sup>n</sup> . When the network is linear and the source carrier has a constant velocity, this phase corresponds to the periodic echo of the signal increase on the first channel as seen on the other channels. The difference in nature between both methods introduces a quantitative information gain, and thus a potential improvement in detection capability [27–29].

A correlation vector R<sup>φ</sup> is calculated by scanning the product of all channels with phase φ such as:

$$\begin{aligned} \forall \phi \in [1; \left\lfloor \frac{\zeta - 1}{n - 1} \right\rfloor] \end{aligned}$$

$$\begin{aligned} R\_{\psi} &= \widehat{\rho}\_{1, i - 1}^{\ast \ast \ast} \widehat{\rho}\_{2, i - (\varphi + 1)}^{\ast \ast \ast} \widehat{\rho}\_{3, i - (2\varphi + 1)}^{\ast \ast \ast} \cdots \widehat{\rho}\_{j, i - [(j - 1)\varphi + 1]}^{\ast \ast \ast} \cdots \widehat{\rho}\_{n, i - [(n - 1)\varphi + 1]}^{\ast \ast \ast} \\ R\_{\psi} &= \prod\_{j = 1}^{n} \widehat{\rho}\_{j, i - [(j - 1)\varphi + 1]}^{\ast \ast \ast} \end{aligned} \tag{61}$$

For the vehicle passing from detectors 1 to n.

The algorithm firstly determines a phase φ<sup>0</sup> maximizing Rφ, then the significance of the associated temporal correlation is evaluated with a hypothesis test in which H0 is the null hypothesis (no echo detected) and H1 is the detection hypothesis (echo detected). Values of R<sup>φ</sup> are compared to the mean and variance of their distribution. Mean R and empirical variance σ2 (Rφ) are calculated according to:

$$\overline{R} = \left\lfloor \frac{n-1}{\xi -1} \right\rfloor \sum\_{\wp=1}^{\left\lfloor \frac{\zeta}{n-1} \right\rfloor} R\_{\wp} \tag{62}$$

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems http://dx.doi.org/10.5772/intechopen.71233 171

$$\sigma^2(\mathcal{R}\_\phi) = \left\lfloor \frac{n-1}{\xi -1} \right\rfloor \sum\_{\varphi=1}^{\left\lfloor \frac{\xi-1}{n-1} \right\rfloor} \left( \mathcal{R}\_\varphi - \overline{\mathcal{R}} \right)^2 \tag{63}$$

The detection test reads:

Algorithm 2:

The improvement of RPM performance forms an active topic of research. It has notably been established that the spectral analysis of the signal, even for unresolved detectors, allows a gain in detection performance [25]. Another upgrade can be achieved by time series analysis techniques, especially when RPM are deployed in a network, which allows the implementation of correlation methods [26]. Figure 12 presents the schematic of a RPM network

The network configuration enables two complementary types of detection: the first one based on traditional temporal analysis of individual channel H1∣ρb1, …, <sup>b</sup>ρn, the second one based on frequency analysis, searching for a phase ϕ maximizing the correlation between channels

phase corresponds to the periodic echo of the signal increase on the first channel as seen on the other channels. The difference in nature between both methods introduces a quantitative

A correlation vector R<sup>φ</sup> is calculated by scanning the product of all channels with phase φ such as:

<sup>3</sup>,i�ð Þ <sup>2</sup>φþ<sup>1</sup> …ρb∗∗∗

The algorithm firstly determines a phase φ<sup>0</sup> maximizing Rφ, then the significance of the associated temporal correlation is evaluated with a hypothesis test in which H0 is the null hypothesis (no echo detected) and H1 is the detection hypothesis (echo detected). Values of R<sup>φ</sup> are compared to the mean and variance of their distribution. Mean R and empirical variance

φ¼1

information gain, and thus a potential improvement in detection capability [27–29].

<sup>R</sup><sup>φ</sup> <sup>¼</sup> <sup>Y</sup><sup>n</sup> j¼1 ρb∗∗∗ j,i�½ � ð Þ j�1 φþ1

<sup>R</sup> <sup>¼</sup> <sup>n</sup> � <sup>1</sup> ξ � 1 � � <sup>X</sup> <sup>ξ</sup>�<sup>1</sup> b c <sup>n</sup>�<sup>1</sup>

. When the network is linear and the source carrier has a constant velocity, this

j,i�½ � ð Þ <sup>j</sup>�<sup>1</sup> <sup>φ</sup>þ<sup>1</sup> …ρb∗∗∗

n,i�½ � ð Þ n�1 φþ1

R<sup>φ</sup> (62)

(61)

implementing n channels and dedicated to moving source detection.

Figure 12. Schematic of a system based on correlation detection.

170 Ionizing Radiation Effects and Applications

H1∣φρ^<sup>1</sup>

∀φ ∈ 1; <sup>ξ</sup>�<sup>1</sup>

σ2

n�1 � � � � � � ,

<sup>R</sup><sup>φ</sup> <sup>¼</sup> <sup>ρ</sup>b∗∗∗

For the vehicle passing from detectors 1 to n.

(Rφ) are calculated according to:

<sup>1</sup>,i�<sup>1</sup>ρb∗∗∗

<sup>2</sup>,i�ð Þ <sup>φ</sup>þ<sup>1</sup> <sup>ρ</sup>b∗∗∗

,…,ρ^<sup>n</sup>

$$\text{If } \mathcal{R}\_{\phi\_0} > \overline{\mathcal{R}} + Q\_{1-a} \sqrt{2\sigma^2(\mathcal{R}\_{\phi})}$$

Then H1 is accepted

Else H0 is accepted

The use of the empirical variance σ<sup>2</sup> (Rϕ) ensures a significant gain in detection capability under challenging signal-to-noise ratios [27, 28]. However, an algorithmic refinement is achieved with the introduction of a Normal law a priori on count rate distributions [29]. Thus, a modified variance σ<sup>2</sup> (Rϕ) is obtained by the estimation of individual variances σ<sup>2</sup> (ρj, <sup>i</sup>) provides by the nonlinear filter (cf. Eq. (37)) for every detector j and memory slot i. Its calculation is presented in the following recursive formula:

$$\forall k \in [2; n] \,\text{let} \,\forall \varphi \in \left[1; \left\lfloor \frac{\xi - 1}{n - 1} \right\rfloor\right],$$

$$\left[\sigma^2(\mathbb{R}\_{\phi})\right]\_k = \sigma^2(\mathbb{R}\_{\phi})|\_{k - 1} \left[\sigma^2\left(\widehat{\rho}\_{k, i - (k - 1)\phi + 1}^{\*\*}\right) + \left(\widehat{\rho}\_{k, i - (k - 1)\phi + 1}^{\*\*}\right)^2\right] + \sigma^2\left(\widehat{\rho}\_{k, i - (k - 1)\phi + 1}^{\*\*\*}\right)\left(\mathbb{R}\_{\phi}|\_{k - 1}\right)^2 \tag{64}$$

with

$$\left.R\_{\psi}\right|\_{k-1} = \widehat{\rho}\_{1,1}^{\*\*}\tag{65}$$

$$
\sigma^2(\mathcal{R}\_\psi)\big|\_1 = \sigma^2\Big(\hat{\rho}\_{1,i-1}^{\*\*}\Big)\tag{66}
$$

The detection algorithm mixes the detection according to each individual channel with the detection using the correlation factor. In both cases, a decision threshold (DT) is calculated as a function of a false detection risk α. Let DTj,<sup>ϕ</sup> the decision threshold associated with the channel j and the phase ϕ reads:

$$\forall j \in [1; n] \& \forall \varphi \in \left[1; \left\lfloor \frac{\xi - 1}{n - 1} \right\rfloor \right],$$

$$DT\_{j, \varphi} = Q\_{1 - \alpha} \sqrt{2\sigma^2 \left(\widehat{\rho}\_{j, i - (j - 1)\varphi + 1}^{\*\*} \right)} \tag{67}$$

And let DTR<sup>ϕ</sup> be the decision threshold associated with the correlation factor R<sup>ϕ</sup> such as

$$\forall \varphi \in \left[1; \left\lfloor \frac{\xi - 1}{n - 1} \right\rfloor \right],$$

$$DT\_{R\_{\phi}} = Q\_{1 - \alpha} \sqrt{2\sigma^{2} \left(R\_{\psi}\right)|\_{n}} \tag{68}$$

6. Conclusion

RPM network.

References

704 & 66-85

Computers, 1997:85-90

princeton.edu/wws509/notes/

Author details

suited for post-processing analyses.

Romain Coulon\* and Jonathan Dumazert

\*Address all correspondence to: romain.coulon@cea.fr

tions on Nuclear Science. 2017;68(8):2423-2432

Different count rate processing methods have been presented in this chapter: an adaptive smoother, a background discrimination method and two algorithms improving the detection of moving sources. In these algorithms, frequentist inferences are realized on the basis of measured data. These types of approaches are well suited for real-time processing, allowing taking decision with very few iterations, compared to Bayesian inferences which are more

Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

http://dx.doi.org/10.5772/intechopen.71233

173

The nonlinear smoother is proved to be a key building block in radiation monitors, delivering a fine estimation of count rate expectation with a minimized associated variance. Both expectation and variance estimations are used to apply hypothesis tests addressing many problematics in radiation monitoring such as for instance those already developed hereby: compensation and

French Alternative Energies and Atomic Energy Commission, Gif-sur-Yvette, France

[1] Knoll GF. Radiation Detection and Measurement. 4th ed. Hoboken: Wiley; 2010. p. 625-

[2] Jordanov VT, Knoll GF, Huber AC, Pantazis JA. Digital techniques for real-time pulse shaping in radiation measurements. Nuclear Instruments and Methods A. 1994;353:261-264

[3] French M, Thevenin M, Hamel M, Montbarbon E. A histogram-difference method (HDM) for neutron/gamma discrimination using liquid and plastic scintillators. IEEE Transac-

[4] Rohée E, Coulon R, Carrel F, Dautremer T, Barat E, Montagu T, et al. Benchmark of the non-parametric Bayesian deconvolution method implemented in the SINBAD code for

[6] Rodriguez G. Lecture Notes on Generalized Linear Models. 2007. URL: http://data.

[7] Londen-Thurgood RM, Pople J. A new ratemeter concept for radiation measuring instru-

ments. Nuclear Instruments and Methods. 1981;184(2–3):533-536

X/γ rays spectra processing. Nuclear Instruments and Methods A. 2016;836:91-97 [5] Timmermann KE, Nowak RD. Multiscale Bayesian estimation of Poisson intensities. In: Conference Record of the Thirty-First Asilomar Conference on Signals, Systems and

Algorithm 2 presents the mechanism of the cumulative detection.

Algorithm 3:

$$\text{If } \forall j \in [1; n] \& \forall \varphi \in \left[1; \left\lfloor \frac{\le -1}{n - 1} \right\rfloor\right], DT\_{j, \varphi} - \widehat{\rho}\_{j, i - (j - 1)6 + 1}^{\*\*} \le 0.$$

And if ∀φ ∈ 1; <sup>ξ</sup>�<sup>1</sup> n�1 � � � � � , DTRφ� <sup>R</sup><sup>φ</sup> <sup>≤</sup> 0,

Then, the detection hypothesis H0 is accepted and the hypothesis H1 is rejected,

Else if ∃ϕ∈ 1; <sup>ξ</sup>�<sup>1</sup> n�1 � � � � &∃j 0 <sup>∈</sup>½ � 1; <sup>n</sup> , DTj,<sup>φ</sup> � <sup>ρ</sup>b∗∗ j,i�ð Þ <sup>j</sup>�<sup>1</sup> <sup>φ</sup>þ<sup>1</sup> <sup>&</sup>gt; 0,

Then, the detection hypothesis H1 is accepted and the hypothesis H0 is rejected,

$$\text{Or if } \exists \varphi' \in \left[1; \left\lfloor \frac{\xi - 1}{r - 1} \right\rfloor\right], DT\_{R\_{\varphi'}} - R\_{\varphi'} > 0, \text{ }$$

Then, the detection hypothesis H1 is accepted and the hypothesis H0 is rejected,

And, the velocity of the source is equal to <sup>L</sup> φ0 <sup>Δ</sup><sup>t</sup> where L is the distance between detectors.

It has been proven in [27–29], the largely significant added-value in term of detection capability permits by the implementation of the correlation based detection. The true detection rate is increased while maintaining very low false alarm rate. Figure 13 presents a system realized by the CEA which implements the correlation method [30].

All of these algorithms will be implemented in a dedicated DSP card [3] and the compliance of the RPM system will the standard ANSI42-35 will be tested in due course [31].

Figure 13. Photography of the RPM prototype (Katrina) developed by the CEA in the framework of the SECUR-ED project funded by the European Commission [30].

## 6. Conclusion

∀φ ∈ 1;

DTR<sup>ϕ</sup> ¼ Q<sup>1</sup>�<sup>α</sup>

j,i�ð Þ <sup>j</sup>�<sup>1</sup> <sup>o</sup>€þ<sup>1</sup> <sup>≤</sup> 0,

Then, the detection hypothesis H0 is accepted and the hypothesis H1 is rejected,

Then, the detection hypothesis H1 is accepted and the hypothesis H0 is rejected,

Then, the detection hypothesis H1 is accepted and the hypothesis H0 is rejected,

the RPM system will the standard ANSI42-35 will be tested in due course [31].

φ0

It has been proven in [27–29], the largely significant added-value in term of detection capability permits by the implementation of the correlation based detection. The true detection rate is increased while maintaining very low false alarm rate. Figure 13 presents a system realized by

All of these algorithms will be implemented in a dedicated DSP card [3] and the compliance of

Figure 13. Photography of the RPM prototype (Katrina) developed by the CEA in the framework of the SECUR-ED

<sup>∈</sup>½ � 1; <sup>n</sup> , DTj,<sup>φ</sup> � <sup>ρ</sup>b∗∗

Algorithm 2 presents the mechanism of the cumulative detection.

Algorithm 3:

If <sup>∀</sup>j∈½ � 1; <sup>n</sup> &∀φ<sup>∈</sup> <sup>1</sup>; <sup>ξ</sup>�<sup>1</sup>

172 Ionizing Radiation Effects and Applications

And if ∀φ ∈ 1; <sup>ξ</sup>�<sup>1</sup>

Else if ∃ϕ∈ 1; <sup>ξ</sup>�<sup>1</sup>

Or if ∃φ<sup>0</sup> ∈ 1; <sup>ξ</sup>�<sup>1</sup>

n�1

� � � � � � , DTRφ� <sup>R</sup><sup>φ</sup> <sup>≤</sup> 0,

0

� � � � � � , DTR<sup>φ</sup><sup>0</sup> � <sup>R</sup><sup>φ</sup><sup>0</sup> <sup>&</sup>gt; 0,

the CEA which implements the correlation method [30].

And, the velocity of the source is equal to <sup>L</sup>

project funded by the European Commission [30].

n�1

n�1 � � � � &∃j

n�1

� � � � � , DTj,<sup>φ</sup> � <sup>ρ</sup>b∗∗

ξ � 1 n � 1 � � � � � �

q

j,i�ð Þ <sup>j</sup>�<sup>1</sup> <sup>φ</sup>þ<sup>1</sup> <sup>&</sup>gt; 0,

<sup>Δ</sup><sup>t</sup> where L is the distance between detectors.

,

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2σ<sup>2</sup> R<sup>φ</sup> � �� � n

(68)

Different count rate processing methods have been presented in this chapter: an adaptive smoother, a background discrimination method and two algorithms improving the detection of moving sources. In these algorithms, frequentist inferences are realized on the basis of measured data. These types of approaches are well suited for real-time processing, allowing taking decision with very few iterations, compared to Bayesian inferences which are more suited for post-processing analyses.

The nonlinear smoother is proved to be a key building block in radiation monitors, delivering a fine estimation of count rate expectation with a minimized associated variance. Both expectation and variance estimations are used to apply hypothesis tests addressing many problematics in radiation monitoring such as for instance those already developed hereby: compensation and RPM network.

## Author details

Romain Coulon\* and Jonathan Dumazert

\*Address all correspondence to: romain.coulon@cea.fr

French Alternative Energies and Atomic Energy Commission, Gif-sur-Yvette, France

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## *Edited by Boualem Djezzar*

The benefits of ionizing radiations have been largely demonstrated through many achievements of human life. Understanding the fundamental elementary interactions of ionizing radiations with material has allowed the development of various applications needed by different industries. This book draws some facets of their applications, such as hardening process for semiconductor devices, biomedical imaging by radiation luminescent quantum dots, hydrogen gas detection by Raman lidar sensor for explosion risk assessment, water and wastewater purification by radiation treatment for environment, doping by the neutron transmutation doping for the semiconductor industry, and polymerization by irradiation, which is useful for industries requiring resistant and protective coating. I wish the chapters of this book can provide some helpful information on ionizing radiation applications.

Photo by Job Savelsberg / Unsplash

Ionizing Radiation Effects and Applications

Ionizing Radiation Effects

and Applications