1. Introduction

Neutron activation analysis (NAA) is a state-of-the-art analytical technique used for identification of elements and determination of the elemental concentration in different applications. With the development of accurate and fast gamma spectrometric techniques, advanced electronics and automation in data analysis, the method has gained active application in diverse field of basic research. Non-destructive or instrumental NAA has also become popular for varied industrial application due to its ease in handling. With the development of high-power neutron source, precise and fast neutron detectors and sophisticated electronics, NAA has

© 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 IntechOpen. 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.

achieved ultralow minimum detection limit (MDL). As a result the method has turned out to be one of the best choices for quantification of trace elements in a wide variety of samples geological, archaeological, biological and environmental samples.

where N is the number of target atoms available for interaction, σ<sup>i</sup> is the cross section for production of the ith isotope, φð Þ E is the neutron fluence rate at energy E, λ<sup>i</sup> is the decay

Neutron Activation Analysis: Application in Geology and Medicine

http://dx.doi.org/10.5772/intechopen.76726

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Gamma spectrometric analysis of the irradiated sample helps one to determine the elemental composition and impurity of the sample. There are different types of NAA that can be used for

In many applications the sample under study is irradiated in a reactor or by a neutron source, and the exposed sample is analysed for gamma emission. No chemical treatment of the sample is carried out between irradiation and counting. This type of NAA is called instrumental neutron activation analysis or INAA. This is also known as non-destructive neutron activation analysis. In the second method, the sample after irradiation with neutrons is treated chemically in order to separate different constituents depending on their solubility or other physical properties. The separated constituents are then counted separately for their characteristic gamma emission. This method is called radiochemical neutron activation analysis (RNAA). INAA can again be carried out in more than one way—prompt gamma neutron activation analysis (PGNAA) and delayed gamma neutron activation analysis (DGNAA). In the first method, gamma counting is done online when the sample is irradiated. The neutron interacts with the target nucleus, and the latter goes to an excited state which thereby decays to the lower energy states with the emission of gamma radiation. The reaction time is of the order of 10�<sup>15</sup> s. Analysis of these gamma rays provides information on the incident neutron flux as well as the composition of the sample. In DGNAA gamma spectrometry of the irradiated sample is carried out after the irradiation is over. In this method the decay gammas from the product radioisotopes are counted. The k0-NAA is one of the most accepted standardisation methods for quantitative multielemental analysis of the sample through gamma spectrometry. In this method one standard or reference material with known amount of an isotope and a single comparator are irradiated and counted along with the sample under the identical conditions. The quantity of the different elements present in the sample is estimated using the k-factors determined from the analysis of the standard and the comparator. The varied forms

of NAA are applied for quantitative analysis of different types of samples.

Different variant of NAA is employed for detection and quantification of the trace and ultratrace level of elemental concentration in different geological formation, uranium ore, etc.

NDNAA and Compton-suppressed NAA are efficiently used for analysis of geological samples (i) for uranium content measurement in phosphate rocks and surrounding geology and (ii) in trace elemental analysis of rock samples. Trace elemental analysis of rock samples is particularly important as these rocks can find a novel use as the coarse aggregate in varieties of

concrete that may be developed for shielding of accelerator and reactor facilities [1].

3. Neutron activation in geology

constant for the ith isotope, tI is the time of irradiation.

the analysis of a sample.

Varied analysis devices for neutron activation studies have made it a preferred choice for the analysis of construction material, coal, environmental, geological and archaeological samples and biological material, security monitoring and academic studies. Since its inception around the middle of last century, different variants of NAA such as prompt gamma neutron activation analysis (PGNAA), pulsed fast neutron analysis (PFNA), pulsed fast/thermal neutron analysis (PFTNA) and associated particle imaging (API) have been developed. Nondestructive NAA is one of the most preferred methods of sample analysis as it requires minimal processing of the activated sample. In the semiconductor industry, NAA is used to determine ultra-trace concentration of impurities, or dopant as impurity concentration even at 1 ppb can affect the performance of the semiconductor. NAA-induced associated particle imaging (API) efficiently used for security monitoring has several advantages over other conventional scanning methods.

Different forms of NAA offer good choice over other techniques for application in geology and medicine. NAA is used for quantitative analysis of trace elements in rock samples which serves as an important tool for modelling geochemical processes and also helps in sample selection for other applications. Pai et al. [1] have used instrumental NAA (INAA) for trace element analysis in different rock samples to determine its suitability for use in the coarse aggregate for concrete in shielding material. Over the last several years, NAA has made important inroads in the field of medical science. The method is used in production of radiotracers which are used in situ for evaluation of new pharmaceuticals for their distribution, time release, clearance, etc. Neutron-stimulated emission computed tomography (NSECT) is a newly developed imaging method that non-invasively maps the concentration of an isotope in the body [2]. Multiple pencil beams of fast neutrons are developed for early diagnosis of breast cancer through NAA using differential femto-oximetry (DFO) [3]. This chapter will discuss application of different forms of NAA in geology and medicine and related recent advancements.

## 2. Method

Neutron activation analysis (NAA) is a procedure employed for analysing the elemental composition of a material and for determining the concentrations of elements at the trace and ultra-trace level in a vast majority of samples. In this method the sample is irradiated with neutron from the reactor when nuclear reaction is induced in the sample. The gamma rays emitted from the isotope as a result of this reaction is detected and counted and the reaction analysed. The activity of the ith isotope induced in the sample is given by

$$A\_i = N \left[ \int \sigma\_i(E) \varphi(E) dE \right] \left(1 - e^{\lambda\_i t\_l} \right) \tag{1}$$

where N is the number of target atoms available for interaction, σ<sup>i</sup> is the cross section for production of the ith isotope, φð Þ E is the neutron fluence rate at energy E, λ<sup>i</sup> is the decay constant for the ith isotope, tI is the time of irradiation.

Gamma spectrometric analysis of the irradiated sample helps one to determine the elemental composition and impurity of the sample. There are different types of NAA that can be used for the analysis of a sample.

In many applications the sample under study is irradiated in a reactor or by a neutron source, and the exposed sample is analysed for gamma emission. No chemical treatment of the sample is carried out between irradiation and counting. This type of NAA is called instrumental neutron activation analysis or INAA. This is also known as non-destructive neutron activation analysis. In the second method, the sample after irradiation with neutrons is treated chemically in order to separate different constituents depending on their solubility or other physical properties. The separated constituents are then counted separately for their characteristic gamma emission. This method is called radiochemical neutron activation analysis (RNAA). INAA can again be carried out in more than one way—prompt gamma neutron activation analysis (PGNAA) and delayed gamma neutron activation analysis (DGNAA). In the first method, gamma counting is done online when the sample is irradiated. The neutron interacts with the target nucleus, and the latter goes to an excited state which thereby decays to the lower energy states with the emission of gamma radiation. The reaction time is of the order of 10�<sup>15</sup> s. Analysis of these gamma rays provides information on the incident neutron flux as well as the composition of the sample. In DGNAA gamma spectrometry of the irradiated sample is carried out after the irradiation is over. In this method the decay gammas from the product radioisotopes are counted. The k0-NAA is one of the most accepted standardisation methods for quantitative multielemental analysis of the sample through gamma spectrometry. In this method one standard or reference material with known amount of an isotope and a single comparator are irradiated and counted along with the sample under the identical conditions. The quantity of the different elements present in the sample is estimated using the k-factors determined from the analysis of the standard and the comparator. The varied forms of NAA are applied for quantitative analysis of different types of samples.
