**Natural Occurring Radionuclide Materials**

Raad Obid Hussain and Hayder Hamza Hussain

*College of Science/Kufa University Iraq* 

### **1. Introduction**

The stellar material, from which the earth was formed, about 4.5 billion years ago, contained many unstable nuclides (Scholten and Timmermans, 1996). Some of the original primordial nuclides, whose half-lives are about as long as the earth's age, are still present. Radiation comes from outer space (cosmic), the ground terrestrial, and even from within over bodies. It present in the air we breathe, the food we eat, the water we drink and in the construction materials used to build our houses. So, radiation is all around us, it is naturally in our environment and it has been since the birth of our planet (Maher and Raed, 2007). Radioactivity of soil environment is one of the major sources of exposure to human (Abusini, 2007).

The 235U, 232Th series and natural 40K are the main source of natural radioactivity in soil (Yasir et al., 2007; Vosniakos et al., 2002). Since these natural occurring radio nuclides materials, (NORMs) such as 238U, 232Th, 235U, and 40K have very long half- lives (up to 1010 years), their presence of soils and rocks can simply be considered as permanent. The geological and geographical conditions are the major factors effects, the natural environmental radioactivity and the associated external exposure due to gamma radiation. Thus these radiation levels appear at different levels in the soil of each region in the world (UNSCEAR, 2000).

Issue in terms of radiological protection exposure to natural source of radiation becomes an important. In 1992 the national radiological protection Board (NRPB), estimated that radon accounts for approximately 50% of annual dose of radiation from all sources in the most of the world (Ibrahim, 1999).

An average person receives a radiation dose of about 300 millirem per year from natural sources compared to a dose of about 50 millirem from produced material source of radioactive materials such as medical x-ray (UNSCEAR, 1988). Exposure of public to radiation from any sources is unlikely. The European committee has issued a draft proposal for revision of the basic safety standards for the protection of workers and the general against the dangers of ionizing radiation (Marcelo and Pedro, 2007).

The United Nations Scientific Committee on the Effects of Atomic Radiation established that the world mean dose from natural radiation sources of normal area is estimated to be 2.4 mSv.y-1 while for all man- made sources including exposure, is about 0.8 mSv.y-1 (UNSCEAR, 1993; Valter at el., 2008). Thus 75% of the radiation dose received by humanity is come from natural radiation source. It is clear that the assessment of gamma radiation dose from natural source is of particular importance as natural radiation is the largest contributor to the external dose of the world population (UNSCEAR, 1988).

Natural Occurring Radionuclide Materials 5

Uranium and thorium are not stable; they decay mainly by alpha-particle emission to nuclides that themselves are radioactive. Natural uranium is composed of three long lived isotopes, 238U, a smaller proportion of 235U and an even smaller proportion of 234U, the decay-series daughter of 238U. Natural thorium has one single isotope, 232Th. Each of these nuclides decays to an unstable daughter leading, in turn, to a whole series of nuclides that terminate in one or other of the stable isotopes of lead. Under normal circumstances, in a natural material, the

Gamma spectrometry of materials containing these nuclides can only be effectively done

The products of the decay are called radioactivity series. This series starts with the Uranium-238 isotope, which has a half-life 4.5×1010 year as shown in Figure 1 (Henery and John, 1972; Littlefield and Thorley, 1974). Since nuclides have very long half-life, this chain is still present today. The radionuclide 238U decays into 234Th emitting an alpha-particle, the newly formed nuclide is also unstable and decay further (Figure 1). Finally, after total of 14 such steps, emitting 8 alpha particles and 6 Beta particles, accompanied by gamma radiation, stable lead is formed. This series is said to be in secular equilibrium because all their daughters following

This decay series includes the 226Ra which has half-lives of 1600 year and chemical properties clearly different from those of uranium. 226Ra decay into 222Rn which is an inert noble gas that not form any chemical bonds and can escape into the atmosphere and attacks rapidly to aerosols and dust particles in the air deposited. The radiation emitted at the decay

It is also known as Uranium-235 series and starts with 235U and by successive transformations and up in a stable lead 207Pb. It comprises 0.72% of natural uranium. Although only a small proportion of the element, its shorter half-life means that, in terms of radiations emitted, its spectrometric significance is comparable to 238U. The decay series, shown in (Figure 2), involves 12 nuclides in 11 decay stages and the emission of 7 alpha particles (ignoring a number of minor decay branches). Since its abundance is very small, it

Within this series, only 235U itself can readily be measured, although 227Th, 223Ra and 219Rn can be measured with more difficulty. Even though the uncertainties may be high, measurement of the daughter nuclides can provide useful support information confirming

Natural thorium is 100% 232Th. The decay series is shown in (Figure 3). Six alpha particles are emitted during ten decay stages. Four nuclides can be measured easily by gamma spectrometry: 228Ac, 212Pb, 212Bi and 208Tl. The decay of 212Bi is branched – only 35.94% of decays produce 208Tl by alpha decay. The beta decay branch produces 212Po that cannot be measured by gamma spectrometry. If a 208Tl measurement is to be used to estimate the thorium activity, it must be divided by 0.3594 to correct for the branching (Harb, 2004).

the direct 235U measurement or giving insight into the disruption of the decay series.

235U/238U ratio will be fixed and all nuclides in each of the series will be in equilibrium.

with a detailed understanding of the decay chains of the nuclides involved.

238U have shorter half-life than the parent nuclide 238U (Benenson, 2002).

of these products, can cause damage to the deep lungs.

dose not taken into account in the measurements (Harb, 2004).

**2.1 The NORM decay series** 

**2.1.1 Uranium series** 

**2.1.2 Actinium series** 

**2.1.3 Thorium series** 

Since predominate part of the environmental radiation is found in the upper soil layer, this knowledge ensures radiological control. The 238U, 232Th and 40K have a non-negligible radioactivity (WHO, 1993; José at el., 2005). The high radioactivity of 226Ra and 228Ra and their pressure in soil require particular attention. It is known that even a small amount of a radiation substance may produce a damaging biological effects and that ingested and inhaled radiation can be a serious health risk (Rowland, 1993).

The radiological impact of natural radio nuclides is due to the gamma ray exposure of the body and irradiation of lung tissue from inhalation of radon and its daughters. In general exposure to ionizing radiation often comes from medical diagnosis and therapy application in just food and air and environmental sources. The radiation from the last one cannot be switched of thus the environmental radioactivity surveillance becomes, therefore a necessity. Generally, in Iraq and especially in the middle region area, there is a lack of the scientific information on radioactivity contents of naturally occurring radioactive materials in soil especially in terms of environmental radiological studies.

Based on these facts, one can certify that the knowledge of natural occurring radionuclide materials (MORMs), such as 238U, 232Th and 40K, is an important pre-requisite for evaluation of the rate of exposure absorbed dose by the population in order to estimate their radiological impacts and to establish a data base which will be used as reference to radiation observer in the studied area (NCRP, 1987).

#### **2. Background**

According to the source of radiation, radioactivity in the environment may be classified into two general categories; artificial and natural. Natural radioactivity comes from naturallyoccurring, Uranium, Thorium and Actinium radioactive series as well as from radioisotopes like Rubidium-87, Indium-115, Lanthanum-138, Neobynium-144, Samarian-147, Luteium-176, Hafinium-174, Vanadium-150, Gadolinium-152, Platinum-190 and 192, Rhenium-187 and Potassium-40. Except for K-40 these non-series radioisotopes occur scarcely. In contrast, K-40 is ubiquitous (Vosnikos et al., 2003). In the other hand artificial activity arises mainly from discarded sources, radioactive wastes, and radioactive fallout in the nature.

There are four distinct natural series: Uranium, Actinium, thorium, and Neptunium as listed in (Table 1). Only uranium, actinium, and thorium series are found in natural. Since the isotope 237Np has a half-life much shorter than the age of the earth (about 5 billion of years), virtually all neptunium decayed within the first 50 millions of years after the earth formed.

Only uranium, actinium, and thorium series are found in natural. Since the isotope 237Np has a half-life much shorter than the age of the earth (about 5 billion of years), virtually all neptunium decayed within the first 50 millions of years after the earth formed.


Table 1. Natural series of uranium, actinium, thorium and neptunium

#### **2.1 The NORM decay series**

4 Radioisotopes – Applications in Physical Sciences

Since predominate part of the environmental radiation is found in the upper soil layer, this knowledge ensures radiological control. The 238U, 232Th and 40K have a non-negligible radioactivity (WHO, 1993; José at el., 2005). The high radioactivity of 226Ra and 228Ra and their pressure in soil require particular attention. It is known that even a small amount of a radiation substance may produce a damaging biological effects and that ingested and

The radiological impact of natural radio nuclides is due to the gamma ray exposure of the body and irradiation of lung tissue from inhalation of radon and its daughters. In general exposure to ionizing radiation often comes from medical diagnosis and therapy application in just food and air and environmental sources. The radiation from the last one cannot be switched of thus the environmental radioactivity surveillance becomes, therefore a necessity. Generally, in Iraq and especially in the middle region area, there is a lack of the scientific information on radioactivity contents of naturally occurring radioactive materials

Based on these facts, one can certify that the knowledge of natural occurring radionuclide materials (MORMs), such as 238U, 232Th and 40K, is an important pre-requisite for evaluation of the rate of exposure absorbed dose by the population in order to estimate their radiological impacts and to establish a data base which will be used as reference to radiation

According to the source of radiation, radioactivity in the environment may be classified into two general categories; artificial and natural. Natural radioactivity comes from naturallyoccurring, Uranium, Thorium and Actinium radioactive series as well as from radioisotopes like Rubidium-87, Indium-115, Lanthanum-138, Neobynium-144, Samarian-147, Luteium-176, Hafinium-174, Vanadium-150, Gadolinium-152, Platinum-190 and 192, Rhenium-187 and Potassium-40. Except for K-40 these non-series radioisotopes occur scarcely. In contrast, K-40 is ubiquitous (Vosnikos et al., 2003). In the other hand artificial activity arises mainly

There are four distinct natural series: Uranium, Actinium, thorium, and Neptunium as listed in (Table 1). Only uranium, actinium, and thorium series are found in natural. Since the isotope 237Np has a half-life much shorter than the age of the earth (about 5 billion of years), virtually all neptunium decayed within the first 50 millions of years after the earth formed. Only uranium, actinium, and thorium series are found in natural. Since the isotope 237Np has a half-life much shorter than the age of the earth (about 5 billion of years), virtually all

from discarded sources, radioactive wastes, and radioactive fallout in the nature.

neptunium decayed within the first 50 millions of years after the earth formed.

Uranium 238U 4.5×109 206Pb Actinium 235U 7.10×108 207Pb Thorium 232Th 1.39×1010 208Pb Neptunium 237Np 2.14×106 209Bi

Table 1. Natural series of uranium, actinium, thorium and neptunium

**Series First Isotope Half-life(years) Last Isotope** 

inhaled radiation can be a serious health risk (Rowland, 1993).

in soil especially in terms of environmental radiological studies.

observer in the studied area (NCRP, 1987).

**2. Background** 

Uranium and thorium are not stable; they decay mainly by alpha-particle emission to nuclides that themselves are radioactive. Natural uranium is composed of three long lived isotopes, 238U, a smaller proportion of 235U and an even smaller proportion of 234U, the decay-series daughter of 238U. Natural thorium has one single isotope, 232Th. Each of these nuclides decays to an unstable daughter leading, in turn, to a whole series of nuclides that terminate in one or other of the stable isotopes of lead. Under normal circumstances, in a natural material, the 235U/238U ratio will be fixed and all nuclides in each of the series will be in equilibrium.

Gamma spectrometry of materials containing these nuclides can only be effectively done with a detailed understanding of the decay chains of the nuclides involved.

#### **2.1.1 Uranium series**

The products of the decay are called radioactivity series. This series starts with the Uranium-238 isotope, which has a half-life 4.5×1010 year as shown in Figure 1 (Henery and John, 1972; Littlefield and Thorley, 1974). Since nuclides have very long half-life, this chain is still present today. The radionuclide 238U decays into 234Th emitting an alpha-particle, the newly formed nuclide is also unstable and decay further (Figure 1). Finally, after total of 14 such steps, emitting 8 alpha particles and 6 Beta particles, accompanied by gamma radiation, stable lead is formed. This series is said to be in secular equilibrium because all their daughters following 238U have shorter half-life than the parent nuclide 238U (Benenson, 2002).

This decay series includes the 226Ra which has half-lives of 1600 year and chemical properties clearly different from those of uranium. 226Ra decay into 222Rn which is an inert noble gas that not form any chemical bonds and can escape into the atmosphere and attacks rapidly to aerosols and dust particles in the air deposited. The radiation emitted at the decay of these products, can cause damage to the deep lungs.

#### **2.1.2 Actinium series**

It is also known as Uranium-235 series and starts with 235U and by successive transformations and up in a stable lead 207Pb. It comprises 0.72% of natural uranium. Although only a small proportion of the element, its shorter half-life means that, in terms of radiations emitted, its spectrometric significance is comparable to 238U. The decay series, shown in (Figure 2), involves 12 nuclides in 11 decay stages and the emission of 7 alpha particles (ignoring a number of minor decay branches). Since its abundance is very small, it dose not taken into account in the measurements (Harb, 2004).

Within this series, only 235U itself can readily be measured, although 227Th, 223Ra and 219Rn can be measured with more difficulty. Even though the uncertainties may be high, measurement of the daughter nuclides can provide useful support information confirming the direct 235U measurement or giving insight into the disruption of the decay series.

#### **2.1.3 Thorium series**

Natural thorium is 100% 232Th. The decay series is shown in (Figure 3). Six alpha particles are emitted during ten decay stages. Four nuclides can be measured easily by gamma spectrometry: 228Ac, 212Pb, 212Bi and 208Tl. The decay of 212Bi is branched – only 35.94% of decays produce 208Tl by alpha decay. The beta decay branch produces 212Po that cannot be measured by gamma spectrometry. If a 208Tl measurement is to be used to estimate the thorium activity, it must be divided by 0.3594 to correct for the branching (Harb, 2004).

Natural Occurring Radionuclide Materials 7

In 1905, J.J. Thompson discovered the radioactivity in 40K is what makes everybody radioactive, it is present in body tissue. This radionuclide can be decayed by three general

In first mode, 40K radionuclide disintegrates directly into the ground state of 40Ca by the emission of Beta- particle of energy 1321 keV in probability of 88.8% of the decays and no

Through the second mode, 40K nuclide can be transformed into stable state (ground state) of 40Ar by two ways, in the first one, 40K disintegrates directly with one jump into ground state of 40Ar with sixteen hundredths of the decays go by electron capture. In the second way, 40K nuclide can be decayed indirectly into the ground state of 40Ar by two stages. firstly, 40K decay into the first excited state of 40Ar. Secondly, the excited nuclide 40Ar, decayed into ground state, accompanied by gamma radiation of 1460 keV energy in probability of 11% of the 40K atoms undergo this change. In the last one (beta emission), a proton will be decayed

The study of the biological effects of radiation is a very complex and difficult task for two

1. The human body is a very complicated entity with many organs of different sizes,

gamma emission is associated with this type of formation (Podgorsak, 2005).

into positron and 40K changed into 40Ar by probability of 0.0011%.

2. Pertinent experiments are practically impossible with humans.

Fig. 3. A schematic diagram of the Thorium-232 series.

**2.1.4 Potassium radionuclide** 

**2.2 Biological effects of radiation** 

functions, and sensitivities.

main reasons.

a. Positron emission. b. K- electron capture. c. Beta emission.

modes:

Fig. 1. Schematic diagram of the Uranium-238 series.

Fig. 2. A schematic diagram of Uranium-235 series (actinium).

Fig. 1. Schematic diagram of the Uranium-238 series.

Fig. 2. A schematic diagram of Uranium-235 series (actinium).

Fig. 3. A schematic diagram of the Thorium-232 series.

#### **2.1.4 Potassium radionuclide**

In 1905, J.J. Thompson discovered the radioactivity in 40K is what makes everybody radioactive, it is present in body tissue. This radionuclide can be decayed by three general modes:


In first mode, 40K radionuclide disintegrates directly into the ground state of 40Ca by the emission of Beta- particle of energy 1321 keV in probability of 88.8% of the decays and no gamma emission is associated with this type of formation (Podgorsak, 2005).

Through the second mode, 40K nuclide can be transformed into stable state (ground state) of 40Ar by two ways, in the first one, 40K disintegrates directly with one jump into ground state of 40Ar with sixteen hundredths of the decays go by electron capture. In the second way, 40K nuclide can be decayed indirectly into the ground state of 40Ar by two stages. firstly, 40K decay into the first excited state of 40Ar. Secondly, the excited nuclide 40Ar, decayed into ground state, accompanied by gamma radiation of 1460 keV energy in probability of 11% of the 40K atoms undergo this change. In the last one (beta emission), a proton will be decayed into positron and 40K changed into 40Ar by probability of 0.0011%.

#### **2.2 Biological effects of radiation**

The study of the biological effects of radiation is a very complex and difficult task for two main reasons.


Natural Occurring Radionuclide Materials 9

The water represents nearly 80% of the human body. When a body exposed to an ionized radiation, the large effect will be happened on the water molecules. The break up of water molecule may Produce (. OH .) on that is highly reactive chemically and may attack the

If, at the same time, there is adjacent damage to the other cell that may be errors in the repair process. The cell may die or damage to cell which cause later uncontrolled cell division. The incident radiation on the body, the water molecule will be ionized the water molecule and free electron will be liberated. The mechanism of this process can be summarized in the

2OH <sup>2</sup> eOH

e) is called dried electron, its energy proportional with the incident radiation energy. This dried electron will be losses its energy through its path in the body and caused some

At low energy some water molecules shall be capture these dried electrons produced water electron which denoted by e- symbol. The velocity of water electron e- in the human cells is

<sup>2</sup> 2OHOH 3OHOH

3OHe <sup>2</sup> HOH It is found that the effectiveness of free hydroxyl root five times of that of free hydrogen root. This free root will be interacting with the organic molecules and other constituent of the cell causing change in their chemical properties which leads to distortion in their functions which may be lead to death. The effect degree of ionizing radiation depends on the type, energy and

The germ cells in human are the most sensitive in the body if they exposed to radiation, in a dolts these cells presents in double number as compared with children in infancy this

During division there are spindle-like particulars cells as chromosomes that reveal a hung number of granulated particles with a special arrangement called as genes the later are the responsible for the individually inherited character. the destruction or change of the geneses or chromosomes many reveal a character that not previously present in parents this change

Radiation will increase the probability of occurring of genetic mutation and childhood abnormalities or infection with certain genetic discuses. If the divided cell exposed to radiation, these cells may undergo abnormal cell division, in the same time these cells may have the capacity proof reading of genetic mistakes that faced with hence may repair any

intensity of radiation and exposure time. The body effective classified into two types:

increase related to cell division and generation of completely similar new cells.

2OH ) will be interacts with the free Hydrogen according to the

3OH reduced water and free hydrogen root

DNA molecule.

following equations.

The water positive ion (

**2.2.2 The early effectiveness** 

called as genetic mutation .

following equation:

ionizing and excitation of other atoms and nuclides.

The water electron e- will be interacting with

less than of dried electrons by factor of 105 times (Podgorsak, 2005).

(-

( H ):

The existing human data on the biological effects of radiation come from accidents, through extrapolation from animal studies, and from experiments in vitro. How and why does radiation produce damage to biological material? To answer the question, one should consider the constituents and the metabolism of the human body. In terms of compounds, about 61 percent of the human body is water. Other compounds are proteins, nucleic acids, fats, and enzymes. In terms of chemical elemental composition, the human body is, by weight, about 10 percent H, 18 percent C, 3 percent N, 65 percent 0, 1.5 percent Ca, 1 percent P, and other elements that contribute less than 1 percent each. To understand the basics of the metabolism, one needs to consider how the basic unit of every organism, which is the cell, functions.

The understandings of natural radiation concepts are essential for radiation protection purpose. The presences of radionuclides in soil affect the common people immensely. Since, the natural radionuclides form 10% of the average annual dose to the human body from all other types of radiation (UNSCEAR, 1993) and exposure to ionizing radiation, in generally considered undesirable at all levels.

Researchers drew attention to the low level exposure; there are three ways, through which the radio nuclides enter the human body: (1) direct inhalation of air born particulates, (2) ingestion through the mouth and (3) entry through the skin (Dipak et al., 2008). Direct exposure to skin is also responsible for radioactive contamination. Some of radionuclide which inters the lung by inhalation affects the blood. Their effectiveness, depend primarily upon two factors:


The effects of radioactive in take depend upon the physical and chemical form and the root through which the radionuclide inter the body. These effects may cause damage to genetic organs, and eye defects and skin smear and destroy the circulatory system and lung cancer.

Exposure to low radiation ray lead to somatic infirmities like cancer and genetic defects such as mutation and chromosome aberrations. Gene modifications may result such conditions and diseases as asthma, diabetes, anemia. Genetic changes are passed on from one generation to another (Gerrado, 1974).

When people are exposed to certain levels of 238U, 232Th and 40K for a long period of time cancer of the bone and hazard cavity may result (Nour, 2004). When radium inters the body by ingestions and inhalation, its metabolic behavior in similar to that of calcium faction of it will be deposited in bone where the remaining fraction being distributed uniformly in the soft tissues, thus the most radiotoxic and most important, among the several radionuclide in the radioactive decay chain the two natural series of uranium and thorium are 226Ra and 228Ra. The biological radiation effectiveness can be dividing into two types:

#### **2.2.1 Body effectiveness**

Cell is the basic unit of living tissue. Cells are complex structures enclosed by a surface membrane. DNA (deoxyribonucleic acid) is existed in the central of nucleus and considered as code of the structure, function, and replication of the cell. The famous "double helix" of the DNA molecule has a diameter of about (2nm). The induction of cancer or of hereditary disease by low levels of ionizing radiation is believed to be related to damage of the DNA molecules. This can be happen direct by ionization of the molecule, or indirectly through ionization of the water molecules in the cell (Cottingh and Greenwood, 2001). A single broken start and of DNA is rapidly repaired by cellular enzyme system, the unbroken strand of the DNA acting as template.

The existing human data on the biological effects of radiation come from accidents, through extrapolation from animal studies, and from experiments in vitro. How and why does radiation produce damage to biological material? To answer the question, one should consider the constituents and the metabolism of the human body. In terms of compounds, about 61 percent of the human body is water. Other compounds are proteins, nucleic acids, fats, and enzymes. In terms of chemical elemental composition, the human body is, by weight, about 10 percent H, 18 percent C, 3 percent N, 65 percent 0, 1.5 percent Ca, 1 percent P, and other elements that contribute less than 1 percent each. To understand the basics of the metabolism, one needs to consider how the basic unit of every organism, which is the cell, functions. The understandings of natural radiation concepts are essential for radiation protection purpose. The presences of radionuclides in soil affect the common people immensely. Since, the natural radionuclides form 10% of the average annual dose to the human body from all other types of radiation (UNSCEAR, 1993) and exposure to ionizing radiation, in generally

Researchers drew attention to the low level exposure; there are three ways, through which the radio nuclides enter the human body: (1) direct inhalation of air born particulates, (2) ingestion through the mouth and (3) entry through the skin (Dipak et al., 2008). Direct exposure to skin is also responsible for radioactive contamination. Some of radionuclide which inters the lung by inhalation affects the blood. Their effectiveness, depend primarily

The effects of radioactive in take depend upon the physical and chemical form and the root through which the radionuclide inter the body. These effects may cause damage to genetic organs, and eye defects and skin smear and destroy the circulatory system and lung cancer. Exposure to low radiation ray lead to somatic infirmities like cancer and genetic defects such as mutation and chromosome aberrations. Gene modifications may result such conditions and diseases as asthma, diabetes, anemia. Genetic changes are passed on from one

When people are exposed to certain levels of 238U, 232Th and 40K for a long period of time cancer of the bone and hazard cavity may result (Nour, 2004). When radium inters the body by ingestions and inhalation, its metabolic behavior in similar to that of calcium faction of it will be deposited in bone where the remaining fraction being distributed uniformly in the soft tissues, thus the most radiotoxic and most important, among the several radionuclide in the radioactive decay chain the two natural series of uranium and thorium are 226Ra and

Cell is the basic unit of living tissue. Cells are complex structures enclosed by a surface membrane. DNA (deoxyribonucleic acid) is existed in the central of nucleus and considered as code of the structure, function, and replication of the cell. The famous "double helix" of the DNA molecule has a diameter of about (2nm). The induction of cancer or of hereditary disease by low levels of ionizing radiation is believed to be related to damage of the DNA molecules. This can be happen direct by ionization of the molecule, or indirectly through ionization of the water molecules in the cell (Cottingh and Greenwood, 2001). A single broken start and of DNA is rapidly repaired by cellular enzyme system, the unbroken

228Ra. The biological radiation effectiveness can be dividing into two types:

considered undesirable at all levels.

upon two factors:

1. Kind of the radionuclide.

2. Physiological of the exposed person

generation to another (Gerrado, 1974).

strand of the DNA acting as template.

**2.2.1 Body effectiveness** 

The water represents nearly 80% of the human body. When a body exposed to an ionized radiation, the large effect will be happened on the water molecules. The break up of water molecule may Produce (. OH .) on that is highly reactive chemically and may attack the DNA molecule.

If, at the same time, there is adjacent damage to the other cell that may be errors in the repair process. The cell may die or damage to cell which cause later uncontrolled cell division. The incident radiation on the body, the water molecule will be ionized the water molecule and free electron will be liberated. The mechanism of this process can be summarized in the following equations.

2OH <sup>2</sup> eOH

( e) is called dried electron, its energy proportional with the incident radiation energy. This dried electron will be losses its energy through its path in the body and caused some ionizing and excitation of other atoms and nuclides.

At low energy some water molecules shall be capture these dried electrons produced water electron which denoted by e- symbol. The velocity of water electron e- in the human cells is less than of dried electrons by factor of 105 times (Podgorsak, 2005).

The water positive ion ( 2OH ) will be interacts with the free Hydrogen according to the following equation:

$$\text{H}\_2\text{O}^+ + \text{H}\_2\text{O} \xrightarrow{\text{H}\_2\text{O}} \text{OH} + \text{H}\_3\text{O}^+$$

The water electron e- will be interacting with 3OH reduced water and free hydrogen root ( H ):

$$\mathrm{^{-}e} + \mathrm{H\_{3}O} + \xrightarrow{-} \longrightarrow \mathrm{H\_{2}O} + \mathrm{H\_{4}}$$

It is found that the effectiveness of free hydroxyl root five times of that of free hydrogen root. This free root will be interacting with the organic molecules and other constituent of the cell causing change in their chemical properties which leads to distortion in their functions which may be lead to death. The effect degree of ionizing radiation depends on the type, energy and intensity of radiation and exposure time. The body effective classified into two types:

#### **2.2.2 The early effectiveness**

The germ cells in human are the most sensitive in the body if they exposed to radiation, in a dolts these cells presents in double number as compared with children in infancy this increase related to cell division and generation of completely similar new cells.

During division there are spindle-like particulars cells as chromosomes that reveal a hung number of granulated particles with a special arrangement called as genes the later are the responsible for the individually inherited character. the destruction or change of the geneses or chromosomes many reveal a character that not previously present in parents this change called as genetic mutation .

Radiation will increase the probability of occurring of genetic mutation and childhood abnormalities or infection with certain genetic discuses. If the divided cell exposed to radiation, these cells may undergo abnormal cell division, in the same time these cells may have the capacity proof reading of genetic mistakes that faced with hence may repair any

Natural Occurring Radionuclide Materials 11

standard sources of gamma rays were used (Table 2). The relative intensities of the photo-

Twenty five soil samples were collected in area of approximately 40000 m2, located around the uranium mine at Najaf governorate. The latitude and longitude of this area are 31o 52′ 254" N and 22o 26′ 221" E. We used systematic grid sampling system involves subdividing the area of concern by using a square and collecting samples from the nodes (intersections of the grid lines). The origin and direction for placement of the grid is done, where the mine was centred in grid. From that point, a coordinate axis and grid is constructed over the whole site. The distance between sampling locations was 50 m (Figure 4). Systematic grid sampling is often used to delineate the extent of contamination

In order to measure the NORMs in soil surface, 25 soils samples were collected, one sample average from each point, was taken by digging a hole at a depth of 35 cm before the ground surface. The soil texture for all samples was very similar. The collected samples were transferred to labeled closed polyethylene bags and taken to the laboratory of radiation detection and measurement in the physics department, collage of science, university of Kufa. In this work a 1.4 litter polyethylene marinelli beaker was used as a sampling and measuring container. Before use, the containers were washed with dilute hydrochloric acid

276.39 302.85 356 383.85 34 7.16 18.3 62 8.9

peaks corresponding to their gamma rays lines have been measured.

22Na 1274.5 99.95 133B 80.99

85.6 10.88

99.97 99.98

and to define contaminant concentration gradients (IAEA, 2004).

57Co 122.1

60Co 1173.2

136.4

1332.5

**3.2 Study area and sampling** 

Fig. 4. Systematic grid sampling method

Isotope E (keV) I % Isotope E (keV) I %

109Cd 88.03 3.6 137Cs 661.6 85.1 Table 2. Energies and transition probabilities of standard sources (Heath, 1997)

Biological disturbance. The radiation in this harm, but in accordance, they have new characters that may transform to embryos ending with exposed obvious genetic mutations. These genetic mutations not always harmful, in contrast, may result in favorable characters like the gain a good quality fruits in shape or size in the same time, animal's cell if exposed to genetic mutation may result in improved characters.

This type take place when the whole body expressed to radiation for high dose through short time some results can be appear in a few days or weeks, likes, reducing in weigh change in the blood cells hair loss and redness of the skin, and sometime the death is probable.

#### **3. Experimental study**

#### **3.1 Gamma spectrometer**

In this study we used gamma spectroscopy to determine the 238U, 232Th and 40K in surface soil layer around the uranium mine at Najaf city.

Gamma spectroscopy is one of many famous techniques are used to measure the NORMs contents in the different environmental elements. It has many advantages such as high accuracy, measure wide energy range and different type samples and not need a chemical method in sample preparation. Beside these advantages gamma spectrometry of NORM is still difficult for a number of reasons. First, the activity levels are low and, if statistically significant results are to be obtained, need long count periods, ideally on a gamma spectrometer whose construction and location are optimized for low activity measurements. The second difficulty is the matter of spectrometer background (i.e. a large number of peaks that one might see in background spectra). Many of these are due to the NORM nuclides in the surroundings of the detector. Any activity in the sample itself must be detected on top of all that background activity. In many cases, it will be necessary to make a peakedbackground correction in addition to the normal peak background continuum subtraction. All of those difficulties are then compounded by the fact that there are a large number of mutual spectral interferences between the many nuclides in the decay series of uranium and thorium.

The gamma rays levels were measured by integral counting using a spectrometer consist of a scintillation detector NaI(Tl) of ( 22 ) crystal dimension with resolution value of 6.48% for line energy of 662 keV, scalar, shielding and specially designed sample container that allowed the sample to surround the scintillation detector at the top and on the sides. This system was computer controlled. The detector was connected to the amplifier through preamplifier unit; an analog to digital converter (ADC) of 4096 channels was assembled to the system. The spectroscopic measurements and analysis were performed via the CASSAY software into the PC of the laboratory.

In order to reduce the background radiation due to different radiation hazard, the detector was maintained in vertical position and shield by a cubic chamber of two layers starting with copper of 2mm thick followed by lead of 10 cm thick. The cosmic rays, photons and electrons, are reduced to a very low level by the 10 cm of lead shielding. This interaction will produced x-ray with low energy which can be suppressed by the copper layer (Aziz, 1981). The x-rays can be also come from radioactive impurities like antimony in the lead.

The spectrometer was calibrated for energy by acquiring a spectrum from radioactive standard sources of known energies like 60Co (1332 keV, 1773 keV) and 137Cs (662 keV). To measure the counting efficiency of the system, 22Na, 57Co, 60Co, 109Cd, 133Ba and 137Cs

Biological disturbance. The radiation in this harm, but in accordance, they have new characters that may transform to embryos ending with exposed obvious genetic mutations. These genetic mutations not always harmful, in contrast, may result in favorable characters like the gain a good quality fruits in shape or size in the same time, animal's cell if exposed

This type take place when the whole body expressed to radiation for high dose through short time some results can be appear in a few days or weeks, likes, reducing in weigh change in the blood cells hair loss and redness of the skin, and sometime the death is

In this study we used gamma spectroscopy to determine the 238U, 232Th and 40K in surface

Gamma spectroscopy is one of many famous techniques are used to measure the NORMs contents in the different environmental elements. It has many advantages such as high accuracy, measure wide energy range and different type samples and not need a chemical method in sample preparation. Beside these advantages gamma spectrometry of NORM is still difficult for a number of reasons. First, the activity levels are low and, if statistically significant results are to be obtained, need long count periods, ideally on a gamma spectrometer whose construction and location are optimized for low activity measurements. The second difficulty is the matter of spectrometer background (i.e. a large number of peaks that one might see in background spectra). Many of these are due to the NORM nuclides in the surroundings of the detector. Any activity in the sample itself must be detected on top of all that background activity. In many cases, it will be necessary to make a peakedbackground correction in addition to the normal peak background continuum subtraction. All of those difficulties are then compounded by the fact that there are a large number of mutual spectral interferences between the many nuclides in the decay series of uranium and

The gamma rays levels were measured by integral counting using a spectrometer consist of a scintillation detector NaI(Tl) of ( 22 ) crystal dimension with resolution value of 6.48% for line energy of 662 keV, scalar, shielding and specially designed sample container that allowed the sample to surround the scintillation detector at the top and on the sides. This system was computer controlled. The detector was connected to the amplifier through preamplifier unit; an analog to digital converter (ADC) of 4096 channels was assembled to the system. The spectroscopic measurements and analysis were performed via the CASSAY

In order to reduce the background radiation due to different radiation hazard, the detector was maintained in vertical position and shield by a cubic chamber of two layers starting with copper of 2mm thick followed by lead of 10 cm thick. The cosmic rays, photons and electrons, are reduced to a very low level by the 10 cm of lead shielding. This interaction will produced x-ray with low energy which can be suppressed by the copper layer (Aziz, 1981).

The spectrometer was calibrated for energy by acquiring a spectrum from radioactive standard sources of known energies like 60Co (1332 keV, 1773 keV) and 137Cs (662 keV). To measure the counting efficiency of the system, 22Na, 57Co, 60Co, 109Cd, 133Ba and 137Cs

The x-rays can be also come from radioactive impurities like antimony in the lead.

to genetic mutation may result in improved characters.

soil layer around the uranium mine at Najaf city.

software into the PC of the laboratory.

probable.

thorium.

**3. Experimental study 3.1 Gamma spectrometer** 


standard sources of gamma rays were used (Table 2). The relative intensities of the photopeaks corresponding to their gamma rays lines have been measured.

Table 2. Energies and transition probabilities of standard sources (Heath, 1997)

#### **3.2 Study area and sampling**

Twenty five soil samples were collected in area of approximately 40000 m2, located around the uranium mine at Najaf governorate. The latitude and longitude of this area are 31o 52′ 254" N and 22o 26′ 221" E. We used systematic grid sampling system involves subdividing the area of concern by using a square and collecting samples from the nodes (intersections of the grid lines). The origin and direction for placement of the grid is done, where the mine was centred in grid. From that point, a coordinate axis and grid is constructed over the whole site. The distance between sampling locations was 50 m (Figure 4). Systematic grid sampling is often used to delineate the extent of contamination and to define contaminant concentration gradients (IAEA, 2004).

Fig. 4. Systematic grid sampling method

In order to measure the NORMs in soil surface, 25 soils samples were collected, one sample average from each point, was taken by digging a hole at a depth of 35 cm before the ground surface. The soil texture for all samples was very similar. The collected samples were transferred to labeled closed polyethylene bags and taken to the laboratory of radiation detection and measurement in the physics department, collage of science, university of Kufa. In this work a 1.4 litter polyethylene marinelli beaker was used as a sampling and measuring container. Before use, the containers were washed with dilute hydrochloric acid

Natural Occurring Radionuclide Materials 13

equivalent of 1.5 mSv/y, which we assumed to be the maximum permissible dose to human

Absorbed dose rate defined as the ratio of an incremental dose (dD) in a time interval

Gamma dose rate in air, one meter above the ground, is used for the description of terrestrial radiation, and is usually expressed in nGy/h or pGy/h. the absorbed dose rate due to gamma radiation of naturally occurring radionuclide (238U, 232Th, and 40K), were

<sup>U</sup> Th A0417.0A621.0A462.0)h/nG(AD <sup>K</sup>

Where 0.462, 0.621 and 0.0417 are the conversion factors for 238U, 232Th and 40K assuming that the contribution natural occurring radionuclide can be neglected as they contribute very

To estimate annual effective doses, account must be taken of (a) the conversion coefficient from absorbed dose in air to effective dose and (b) the indoor occupancy factor. The average numerical values of those parameters vary with the age of the population and the climate at the location considered. In the UNSCEAR 1993 Report, the Committee used 0.7 Sv.Gy/y for the conversion coefficient from absorbed dose in air to effective dose received by adults and 0.8 for the indoor occupancy factor, i.e. the fraction of time spent indoors and outdoors is 0.8 and 0.2, respectively. These values are retained in the present analysis. From the data summarized in this Chapter, the components of the annual effective dose are determined as

Indoor (nSv) = absorbed dose nGy/h × 8760 h × 0.8 × 0.7 SvG/y

Outdoor (nSv) = absorbed dose nGy/h × 8760 h × 0.2 × 0.7 SvG/y The resulting worldwide average of the annual effective dose is 0.48 mSv, with the results for individual countries being generally within the (0.3 - 0.6) mSv range. For children and infants, the values are about 10% and 30% higher, in direct proportion to an increase in the

To reflect the external exposure, a widely used hazard index, called the external hazard

259 A

370 <sup>A</sup> <sup>H</sup> <sup>U</sup> Th <sup>K</sup> ex

4810 A

value of the conversion coefficient from absorbed dose in air to effective dose.

dt dD AD

from their exposure to natural radiation from soil in one year.

calculated on guidelines provided by (UNSCEAR, 2000).

little to total dose from environmental background.

**3.5 Absorbed does rate in air** 

**3.6 Annual effective doses** 

follows: (UNSCEAR, 1993).

**3.7 Hazard index** 

index (Hex), which is defined as following:

(dt).

and rinsed with distilled water. The soil samples were prepared for analysis by drying, sieving and kept moisture free by keeping 24 hours in the oven at 100Co. They were mechanically crushed and sieved through of 0.8 mm pore size diameter sieved to get homogeneity (R2).

To remove completely the air from sample, the later was pressed on by light cap of the marinelli beaker. The respective net weights were measured and record with a high sensitive digital weighting balance with a percent of ±0.01%. After that about 1 kg of each sample was then packed in a standard marinelli beaker that was hermetically sealed and dry weighted. The sample was placed in face to face geometry over the detector for along time measurement.

#### **3.3 Specific activity**

The definition of activity refers to the number of transformations per unite time. Since the fundamental unite time is the second the quantity activity is measured in disintegrations per second or (dps). In 1950, the international joint commission on standards Unit and constants of radioactivity define the curie by accepting 37 billion dps as curie of radioactivity regardless of its source or characteristics. The SI derived unit of activity is the Becquerel (Bq) and is that quantity of radioactive material in which one atom is formed per second or under goes one disintegration per second (1 dps).

The activity of 238U was estimated from the 1765 keV gamma transition energy of 214Bi (17% possibility). Also the activity of 232Th was measured from the 2614 keV gamma transition energy of 208Tl (100% possibility) whereas 40K activity was determined using the 1460 keV gamma ray line (10.7% possibility) (Vosniakos, 2003).

The specific activity is defined as activity per unite mass of radioactive substance and the reported in units such as Curie per gram or Becquerel per kilogram (Bq/kg). The specific activity of each radionuclide was calculated using the following equation (UNSCEAR, 2000).

$$\mathbf{A} = \frac{\mathbf{A'}}{\mathbf{c} \cdot \mathbf{I}\_{\chi} \cdot \mathbf{m} \cdot \mathbf{t}}$$

Where A the specific activity of the radionuclide in Bq/kg, A the liquid count, ε the counting efficiency, I the percentage of gamma emission probability of the radionuclide under study, t the counting time in second and m the mass of the sample in kg.

#### **3.4 Radium equivalent activity**

To represent the activity levels of 238U, 232Th and 40K which take into account the radiological hazards associated with them, a common radiological index has been introduced. This index is called radium equivalent activity (Raeq) and is mathematically defined by (UNSCEAR, 2000).

$$\text{Ra}\_{\text{eq}} \text{(Bq/kg)} = \text{A}\_{\text{U}} + 1.4 \text{\AA}\_{\text{Th}} + 0.077 \text{A}\_{\text{K}}$$

Where AU, ATh and AK are the specific activities of Uranium, Thorium, and potassium respectively. This equation is based on the estimation that 10 Bq/kg of 238U equal 7 Bq/kg of 232Th and 130 Bq/kg of 40K produced equal gamma dose. The maximum value of Raeq must be less than 370 Bq/kg. Also the Raeq value of 370 Bq/kg is equivalent to the annual dose

and rinsed with distilled water. The soil samples were prepared for analysis by drying, sieving and kept moisture free by keeping 24 hours in the oven at 100Co. They were mechanically crushed and sieved through of 0.8 mm pore size diameter sieved to get

To remove completely the air from sample, the later was pressed on by light cap of the marinelli beaker. The respective net weights were measured and record with a high sensitive digital weighting balance with a percent of ±0.01%. After that about 1 kg of each sample was then packed in a standard marinelli beaker that was hermetically sealed and dry weighted. The sample was placed in face to face geometry over the detector for along time

The definition of activity refers to the number of transformations per unite time. Since the fundamental unite time is the second the quantity activity is measured in disintegrations per second or (dps). In 1950, the international joint commission on standards Unit and constants of radioactivity define the curie by accepting 37 billion dps as curie of radioactivity regardless of its source or characteristics. The SI derived unit of activity is the Becquerel (Bq) and is that quantity of radioactive material in which one atom is formed per second or

The activity of 238U was estimated from the 1765 keV gamma transition energy of 214Bi (17% possibility). Also the activity of 232Th was measured from the 2614 keV gamma transition energy of 208Tl (100% possibility) whereas 40K activity was determined using the 1460 keV

The specific activity is defined as activity per unite mass of radioactive substance and the reported in units such as Curie per gram or Becquerel per kilogram (Bq/kg). The specific activity of each radionuclide was calculated using the following equation (UNSCEAR,

<sup>A</sup> <sup>A</sup> Where A the specific activity of the radionuclide in Bq/kg, A the liquid count, ε the counting efficiency, I the percentage of gamma emission probability of the radionuclide

under study, t the counting time in second and m the mass of the sample in kg.

tmI

To represent the activity levels of 238U, 232Th and 40K which take into account the radiological hazards associated with them, a common radiological index has been introduced. This index is called radium equivalent activity (Raeq) and is mathematically defined by (UNSCEAR,

eq <sup>U</sup> Th A077.0A43.1A)kg/Bq(Ra <sup>K</sup>

Where AU, ATh and AK are the specific activities of Uranium, Thorium, and potassium respectively. This equation is based on the estimation that 10 Bq/kg of 238U equal 7 Bq/kg of 232Th and 130 Bq/kg of 40K produced equal gamma dose. The maximum value of Raeq must be less than 370 Bq/kg. Also the Raeq value of 370 Bq/kg is equivalent to the annual dose

homogeneity (R2).

measurement.

2000).

2000).

**3.3 Specific activity** 

under goes one disintegration per second (1 dps).

gamma ray line (10.7% possibility) (Vosniakos, 2003).

**3.4 Radium equivalent activity** 

equivalent of 1.5 mSv/y, which we assumed to be the maximum permissible dose to human from their exposure to natural radiation from soil in one year.

#### **3.5 Absorbed does rate in air**

Absorbed dose rate defined as the ratio of an incremental dose (dD) in a time interval (dt).

$$\text{AD} = \frac{\text{dD}}{\text{dt}}$$

Gamma dose rate in air, one meter above the ground, is used for the description of terrestrial radiation, and is usually expressed in nGy/h or pGy/h. the absorbed dose rate due to gamma radiation of naturally occurring radionuclide (238U, 232Th, and 40K), were calculated on guidelines provided by (UNSCEAR, 2000).

$$\rm{AD(nG/h)} = 0.462A\_{\rm{U}} + 0.621A\_{\rm{Th}} + 0.0417A\_{\rm{K}}$$

Where 0.462, 0.621 and 0.0417 are the conversion factors for 238U, 232Th and 40K assuming that the contribution natural occurring radionuclide can be neglected as they contribute very little to total dose from environmental background.

#### **3.6 Annual effective doses**

To estimate annual effective doses, account must be taken of (a) the conversion coefficient from absorbed dose in air to effective dose and (b) the indoor occupancy factor. The average numerical values of those parameters vary with the age of the population and the climate at the location considered. In the UNSCEAR 1993 Report, the Committee used 0.7 Sv.Gy/y for the conversion coefficient from absorbed dose in air to effective dose received by adults and 0.8 for the indoor occupancy factor, i.e. the fraction of time spent indoors and outdoors is 0.8 and 0.2, respectively. These values are retained in the present analysis. From the data summarized in this Chapter, the components of the annual effective dose are determined as follows: (UNSCEAR, 1993).

Indoor (nSv) = absorbed dose nGy/h × 8760 h × 0.8 × 0.7 SvG/y

$$\text{Outdoor (nSv)} = \text{absorbed dose nGy/h} \times 8760 \text{ h} \times 0.2 \times 0.7 \,\text{SvG/y}$$

The resulting worldwide average of the annual effective dose is 0.48 mSv, with the results for individual countries being generally within the (0.3 - 0.6) mSv range. For children and infants, the values are about 10% and 30% higher, in direct proportion to an increase in the value of the conversion coefficient from absorbed dose in air to effective dose.

#### **3.7 Hazard index**

To reflect the external exposure, a widely used hazard index, called the external hazard index (Hex), which is defined as following:

$$\mathbf{H}\_{\rm ex} = \frac{\mathbf{A}\_{\rm U}}{370} + \frac{\mathbf{A}\_{\rm Th}}{259} + \frac{\mathbf{A}\_{\rm K}}{4810}.$$

Natural Occurring Radionuclide Materials 15

specific activity (Bq/kg) Raeq

S11 72.17±4.43 3.38±0.69 253.19±8.79 96.49 46.00 S12 59.37±4.02 0.28±0.20 184.47±7.51 73.97 35.29 S13 213.24±7.62 5.63±0.89 238.84±8.54 239.68 111.97 S14 39.76±3.29 0.28±0.20 174.70±7.30 53.61 25.82 S15 480.12±11.43 8.02±1.06 415.06±11.26 523.54 244.10 S21 138.07±6.13 2.81±0.63 176.23±7.34 155.65 72.88 S22 645.42±13.26 10.13±1.19 521.04±12.61 700.02 326.20 S23 312.64±9.23 6.47±0.95 409.87±11.19 353.45 165.54 S24 249.18±8.24 4.08±0.76 283.43±9.30 276.83 129.47 S25 37.31±3.19 3.66±0.72 132.25±6.36 52.72 25.02 S31 122.82±5.78 2.39±0.58 153.63±6.85 138.06 64.63 S32 285.95±8.82 12.94±1.35 219.60±8.19 321.36 149.30 S33 122.82±5.78 5.35±0.87 153.52±6.85 142.29 66.46 S34 273.97±8.64 6.47±0.95 211.96±8.05 299.54 139.43 S35 78.43±4.62 4.08±0.76 232.12±8.42 102.13 48.44 S41 142.43±6.23 4.92±0.83 205.85±7.93 165.31 77.44 S42 324.07±9.39 7.03±0.99 264.49±8.99 354.48 165.11 S43 860.29±15.31 13.65±1.39 678.33±14.39 932.04 434.21 S44 175.38±6.91 3.80±0.73 229.67±8.38 198.49 92.96 S45 1112.47±17.41 18.57±1.62 459.96±11.85 1189.84 553.01 S51 167.48±6.75 7.32±1.01 302.06±9.60 201.20 94.51 S52 276.69±8.68 10.41±1.21 156.98±6.92 303.66 140.84 S53 139.16±6.16 7.32±1.01 158.21±6.95 161.81 75.43 S54 85.78±4.83 7.88±1.05 201.27±7.84 112.54 52.91 S55 288.94±8.87 10.27±1.20 320.38±9.89 328.29 153.22 Min. 37.31 0.28 132.25 52.72 25.26 Max. 1112.47 18.57 678.33 1189.84 553.01 mean 268.16 6.68 277.49 299.09 139.61

Table 3. Specific activity, Radium equivalent activity and absorbed dose rate of soil samples.

238U 232 nG/h Th 40K

(Bq/kg)

AD

Sample code

There is another hazard index called internal hazard index (Hin), which is given by equation.

$$\mathbf{H}\_{\rm in} = \frac{\mathbf{A}\_{\rm U}}{185} + \frac{\mathbf{A}\_{\rm Th}}{259} + \frac{\mathbf{A}\_{\rm K}}{4810}$$

The values of the index must be less than the unity in order to keep the radiation hazard to be insignificant unity corresponds to the upper limit of radiation equivalent activity (370 Bq/kg).
