1. Introduction

The gamma rays are emitted from a nucleus or from the annihilation of positron with electrons. The most intense sources of gamma rays are radioactive sources. The photons resulting from de-excitation of nuclei have energies ranging from less than 1 to about 20 MeV.

#### Use of Gamma Radiation Techniques in Peaceful Applications

The photons resulting from annihilations event can have much larger energy: the neutral pion (π<sup>0</sup> ), for example, produce two photons of about 70 MeV.

• Production of meson π<sup>0</sup>

DOI: http://dx.doi.org/10.5772/intechopen.85503

3. Gamma attenuation

detecting it. The meson (π<sup>0</sup>

We have to introduce the attenuation notion.

energy and nature of the absorber.

3.1 Attenuation law

given by:

111

density (in g/cm<sup>3</sup>

pair production (with a threshold energy of 1022 keV).

types:

: A meson can be produced during reactions of several

) then disintegrates into two photons.

◦ Collision between two protons or a proton and alpha (helium nucleus).

Gamma Rays: Applications in Environmental Gamma Dosimetry and Determination Samples…

◦ Collision between a proton and an antiproton; if the antimatter exists in the Universe, the observation of the gamma radiation produced is a method for

• Nucleus de-excitation: Just like an atom or a molecule, a nucleus has energy levels whose transitions between the least excited levels give rise to gamma radiation. Such nucleus de-excitation may occur either during the interaction of a nucleus with neutrinos or during certain thermonuclear reactions.

Unlike charged particles that gradually loses up their energy to matter, when gamma rays traverse matter, some are absorbed, some pass through without interaction, and some are scattered as lower energy photons. Electromagnetic radiation vanishes brutally as a result of interaction. We can no longer talk about a slowdown.

Although a large number of possible interaction mechanisms are known, when monoenergetic gamma rays are attenuated in the matter, only four major effects are important: photoelectric effect, Compton effect, elastic or Rayleigh scattering and

The probability which has a photon of energy given to undergo an interaction during the penetrating in a given material is represented by the attenuation coefficient for this material absorber. The more range of gamma rays in the absorber is long, the more the interaction probability increases. The attenuation coefficient is the sum of coefficients of the various interaction modes (Compton, photoelectric, pair production), the proportion of each of these effects varying with the radiation

When a narrow beam of N0 (number of photons/unit area) monoenergetic photons with energy E0 passes through an homogeneous absorber of thickness x, the number of photons that reach a depth (in cm) without having an interaction is

where μ (in cm) is the linear attenuation coefficient for material of physical

The total linear attenuation coefficient can be decomposed into the contribu-

where μph, μC, μcoh and μ<sup>p</sup> are the attenuation coefficient for photoelectric effect, Compton scattering, Rayleigh scattering and pair production respectively. Although linear attenuation coefficients are convenient for engineering applications and

�μ ρð Þ ;Z;<sup>E</sup> <sup>x</sup> (1)

μtot ¼ μph þ μ<sup>C</sup> þ μcoh þ μ<sup>p</sup> (2)

N ¼ N0e

) and atomic number Z.

tions from each above described mode of photon interaction as:

Gamma rays are ionizing electromagnetic radiation, obtained by the decay of an atomic nucleus. Gamma rays are more penetrating, in matter, and can damage living cells to a great extent. Gamma rays are used in medicine (radiotherapy), industry (sterilization and disinfection) and the nuclear industry. Shielding against gamma rays is essential because they can cause diseases to skin or blood, eye disorders and cancers.

The interaction of gamma rays with matter may be divided into three main categories depending on the energy of the photon. These three mechanisms are the photoelectric effect, Compton scattering and pair production. All results in the energy of the photon being transferred to electrons which subsequently lose energy by further interactions.

#### 2. Origin of the gamma rays

The gamma radiations are constituted by photons, characterized by their energy, inversely proportional to their wavelength. The gamma rays come from the nuclei during the nuclear reactions, it is monoenergetics for a given characteristic reaction. So, the β-decay of the 137Cs to 137Ba produces a gamma radiation of 660 keV. The β-decay of the 60Co to 60Ni produces a double radiation emission of 1.17 and 1.33 MeV.

Natural gamma radiation sources can be easily divided into three groups according to their origin. The first group includes potassium (40K) with a half-life of 1.3 109 years, uranium-238 (238U) with a half-life of 4.4 109 years, uranium-235 (238U) with a halflife of 7.1 108 years and thorium (232Th) with a half-life of 1.4 1010 years.

The second group includes radioactive isotopes from the first group. Those have half-lives ranging from small fractions of a second to 10<sup>4</sup> to 10<sup>5</sup> years. The third group will include it isotopes created by external causes, such as the interaction of cosmic rays with the earth and its atmosphere.

#### 2.1 Gamma radiation production mechanism

The Gamma rays are produced in number of ways:


Gamma Rays: Applications in Environmental Gamma Dosimetry and Determination Samples… DOI: http://dx.doi.org/10.5772/intechopen.85503

	- Collision between two protons or a proton and alpha (helium nucleus).
	- Collision between a proton and an antiproton; if the antimatter exists in the Universe, the observation of the gamma radiation produced is a method for detecting it. The meson (π<sup>0</sup> ) then disintegrates into two photons.

#### 3. Gamma attenuation

The photons resulting from annihilations event can have much larger energy: the

), for example, produce two photons of about 70 MeV. Gamma rays are ionizing electromagnetic radiation, obtained by the decay of an

atomic nucleus. Gamma rays are more penetrating, in matter, and can damage living cells to a great extent. Gamma rays are used in medicine (radiotherapy), industry (sterilization and disinfection) and the nuclear industry. Shielding against gamma rays is essential because they can cause diseases to skin or blood, eye

Use of Gamma Radiation Techniques in Peaceful Applications

The interaction of gamma rays with matter may be divided into three main categories depending on the energy of the photon. These three mechanisms are the photoelectric effect, Compton scattering and pair production. All results in the energy of the photon being transferred to electrons which subsequently lose energy

The gamma radiations are constituted by photons, characterized by their energy, inversely proportional to their wavelength. The gamma rays come from the nuclei during the nuclear reactions, it is monoenergetics for a given characteristic reaction. So, the β-decay of the 137Cs to 137Ba produces a gamma radiation of 660 keV. The β-decay of the 60Co to 60Ni produces a double radiation emission of 1.17 and 1.33 MeV. Natural gamma radiation sources can be easily divided into three groups according to their origin. The first group includes potassium (40K) with a half-life of 1.3 109 years, uranium-238 (238U) with a half-life of 4.4 109 years, uranium-235 (238U) with a half-

The second group includes radioactive isotopes from the first group. Those have half-lives ranging from small fractions of a second to 10<sup>4</sup> to 10<sup>5</sup> years. The third group will include it isotopes created by external causes, such as the interaction of

• Thermal radiation: Only an extremely hot medium (T = 10<sup>8</sup> K) is likely to produce gamma radiation. Such media are extremely rare, and this process is

• Inverse Compton effect: During a collision with low energy photon, a

relativistic electron can transfer to it a significant part of its energy, the photon

• The Synchrotron radiation: A relativistic electron spiraling through the force lines of a magnetic field radiates electromagnetic energy. Thus, energy electrons 3 <sup>10</sup><sup>8</sup> MeV in a magnetic field of 3 <sup>10</sup><sup>6</sup> Gauss will create a gamma radiation. But, by radiating the electrons lose energy: their lives are

• Bremsstrahlung or braking radiation: An electron passing near a nucleus is influenced by its Coulombian field. The deceleration of the electron is accompanied by a loss of energy in the form of gamma radiation when the

life of 7.1 108 years and thorium (232Th) with a half-life of 1.4 1010 years.

neutral pion (π<sup>0</sup>

disorders and cancers.

by further interactions.

2. Origin of the gamma rays

cosmic rays with the earth and its atmosphere.

2.1 Gamma radiation production mechanism

can then have an energy of 100 MeV.

electron has a relativistic speed.

therefore limited.

110

The Gamma rays are produced in number of ways:

not fundamental to the production of this radiation.

Unlike charged particles that gradually loses up their energy to matter, when gamma rays traverse matter, some are absorbed, some pass through without interaction, and some are scattered as lower energy photons. Electromagnetic radiation vanishes brutally as a result of interaction. We can no longer talk about a slowdown. We have to introduce the attenuation notion.

Although a large number of possible interaction mechanisms are known, when monoenergetic gamma rays are attenuated in the matter, only four major effects are important: photoelectric effect, Compton effect, elastic or Rayleigh scattering and pair production (with a threshold energy of 1022 keV).

The probability which has a photon of energy given to undergo an interaction during the penetrating in a given material is represented by the attenuation coefficient for this material absorber. The more range of gamma rays in the absorber is long, the more the interaction probability increases. The attenuation coefficient is the sum of coefficients of the various interaction modes (Compton, photoelectric, pair production), the proportion of each of these effects varying with the radiation energy and nature of the absorber.

#### 3.1 Attenuation law

When a narrow beam of N0 (number of photons/unit area) monoenergetic photons with energy E0 passes through an homogeneous absorber of thickness x, the number of photons that reach a depth (in cm) without having an interaction is given by:

$$N = N\_0 e^{-\mu(\rho, Z, E) \mathbf{x}} \tag{1}$$

where μ (in cm) is the linear attenuation coefficient for material of physical density (in g/cm<sup>3</sup> ) and atomic number Z.

The total linear attenuation coefficient can be decomposed into the contributions from each above described mode of photon interaction as:

$$
\mu\_{\rm tot} = \mu\_{\rm ph} + \mu\_C + \mu\_{\rm coh} + \mu\_p \tag{2}
$$

where μph, μC, μcoh and μ<sup>p</sup> are the attenuation coefficient for photoelectric effect, Compton scattering, Rayleigh scattering and pair production respectively. Although linear attenuation coefficients are convenient for engineering applications and

shielding calculations, they are proportional to the density of the absorber, which depends on the physical state of the material.

The relationship (1) can be written as:

$$N = N\_0 e^{-\left(\frac{\rho(Z,\rho)}{\rho}\right)\rho x} \tag{3}$$

where μ/ρ (in cm<sup>2</sup> /g) is the mass attenuation coefficient.

If the absorber is a chemical compound or mixture, its mass attenuation coefficient μ/ρ can be approximately evaluated form the coefficients for the constituent elements according to the weights sum

$$
\left(\frac{\mu}{\rho}\right)\_{compound} = \sum\_{i} \left(\frac{\mu}{\rho}\right)\_{i} w\_{i} \tag{4}
$$

where wi is the proportion by weight of the ith constituent the material.

The mass attenuation coefficient of a compound or a mixture can be, therefore, calculated from the mass attenuation coefficient of the components [1].

The total linear attenuation coefficient, μcompound or mixture of the compound or mixture can then be simply found by multiplying the total mass attenuation coefficient, (μ/ρ)compound with its density, ρ. Thus,

$$
\mu\_{compound} = \left(\frac{\mu}{\rho}\right)\_{compound} \times \rho \tag{5}
$$

Figure 1 shows the linear attenuation of solid sodium iodide, a common material used in gamma-ray detectors.

#### 3.2 Attenuation coefficients versus atomic number and physical density

The total mass attenuation coefficient μ/ρ is also proportional to the total cross section per atom σ<sup>2</sup> tot. His relation is:

$$\frac{\mu}{\rho} = \sigma\_{\text{tot}}^2 \left( \frac{cm^2}{atom} \right) . \left( \frac{N\_A}{A} \right) \left( \frac{atoms}{g} \right) \tag{6}$$

3.3 Calculation of HVL, TVL and relaxation length (λ)

N<sup>0</sup> <sup>2</sup> <sup>¼</sup> <sup>N</sup>0<sup>e</sup>

HVL <sup>¼</sup> ln <sup>2</sup>

The HVL of a given material thus characterizes the quality (penetrance or

Figure 2 shows the relationship between the linear attenuation coefficient and

The average distance between two successive interactions is called the relaxation

length (λ) or the photon mean free path which is determined by the equation:

when � = HVL, <sup>N</sup><sup>0</sup>

and pair production [2].

Figure 1.

hardness) of a gamma beam.

the HVL for a soft tissue [3].

113

3.4 Calculation of relaxation length (λ)

<sup>N</sup> <sup>¼</sup> <sup>1</sup> 2 . From Eq. (3) it can be shown that:

The linear attenuation coefficient is inversely proportional to a quantity called a half-value layer (HVL), which is the material thickness needed to attenuate the intensity of the incident photon beam to half of its original value. This means that

Linear attenuation coefficient of NaI showing contributions from photoelectric absorption, Compton scattering,

Gamma Rays: Applications in Environmental Gamma Dosimetry and Determination Samples…

DOI: http://dx.doi.org/10.5772/intechopen.85503

�μHVL

(7)

<sup>μ</sup> <sup>¼</sup> <sup>0</sup>:<sup>693</sup> μ

where NA = 6.03 � <sup>10</sup><sup>23</sup> is Avogadro's number and A is the atomic mass of the absorber (in g).

Since there are Z electrons per atom:

$$\frac{\mu}{\rho} = \sigma\_{tot}^2 \left( \frac{Z N\_A}{A} \right) = \sigma\_{tot}^2 \delta\_{\epsilon}$$

where σ<sup>2</sup> tot (cm2 /electron) is the total cross section per electron and the term ZNA A represents the electron density (number of electrons per g).

For all elements except hydrogen, <sup>δ</sup><sup>e</sup> approximately equals NA/2 = 3 � <sup>10</sup>23, because Z/A = ½. For hydrogen, δ<sup>e</sup> is equal to NA, and is therefore twice the « normal » value.

This indicates that atomic composition dependence of <sup>μ</sup> <sup>ρ</sup> is uncorrelated to the term δe, and is related to the term σ<sup>2</sup> tot. The linear attenuation coefficient μ is, therfore, approximately depending on Z in the physical density term ρ and expressly depending on Z in term σ<sup>2</sup> tot.

Gamma Rays: Applications in Environmental Gamma Dosimetry and Determination Samples… DOI: http://dx.doi.org/10.5772/intechopen.85503

#### Figure 1.

shielding calculations, they are proportional to the density of the absorber, which

/g) is the mass attenuation coefficient. If the absorber is a chemical compound or mixture, its mass attenuation coefficient μ/ρ can be approximately evaluated form the coefficients for

> ¼ ∑ i

The mass attenuation coefficient of a compound or a mixture can be, therefore,

The total linear attenuation coefficient, μcompound or mixture of the compound or

ρ 

Figure 1 shows the linear attenuation of solid sodium iodide, a common material

The total mass attenuation coefficient μ/ρ is also proportional to the total cross

: NA A

where NA = 6.03 � <sup>10</sup><sup>23</sup> is Avogadro's number and A is the atomic mass of the

tot: ZN<sup>A</sup> A 

For all elements except hydrogen, <sup>δ</sup><sup>e</sup> approximately equals NA/2 = 3 � <sup>10</sup>23, because Z/A = ½. For hydrogen, δ<sup>e</sup> is equal to NA, and is therefore twice the

therfore, approximately depending on Z in the physical density term ρ and

tot.

atoms

<sup>¼</sup> <sup>σ</sup><sup>2</sup> tot:δ<sup>e</sup>

/electron) is the total cross section per electron and the term

tot. The linear attenuation coefficient μ is,

g 

compound

μ ρ 

i

� <sup>μ</sup>ð Þ <sup>Z</sup>;<sup>ρ</sup> ð Þ <sup>ρ</sup> <sup>ρ</sup><sup>x</sup> (3)

wi (4)

� ρ (5)

<sup>ρ</sup> is uncorrelated to the

(6)

N ¼ N0e

compound

calculated from the mass attenuation coefficient of the components [1].

<sup>μ</sup>compound <sup>¼</sup> <sup>μ</sup>

mixture can then be simply found by multiplying the total mass attenuation

3.2 Attenuation coefficients versus atomic number and physical density

cm<sup>2</sup> atom 

where wi is the proportion by weight of the ith constituent the material.

depends on the physical state of the material. The relationship (1) can be written as:

Use of Gamma Radiation Techniques in Peaceful Applications

the constituent elements according to the weights sum

coefficient, (μ/ρ)compound with its density, ρ. Thus,

tot. His relation is:

μ <sup>ρ</sup> <sup>¼</sup> <sup>σ</sup><sup>2</sup> tot

> μ <sup>ρ</sup> <sup>¼</sup> <sup>σ</sup><sup>2</sup>

represents the electron density (number of electrons per g).

This indicates that atomic composition dependence of <sup>μ</sup>

Since there are Z electrons per atom:

μ ρ 

where μ/ρ (in cm<sup>2</sup>

used in gamma-ray detectors.

section per atom σ<sup>2</sup>

absorber (in g).

where σ<sup>2</sup>

« normal » value.

ZNA A

112

tot (cm2

term δe, and is related to the term σ<sup>2</sup>

expressly depending on Z in term σ<sup>2</sup>

Linear attenuation coefficient of NaI showing contributions from photoelectric absorption, Compton scattering, and pair production [2].

#### 3.3 Calculation of HVL, TVL and relaxation length (λ)

The linear attenuation coefficient is inversely proportional to a quantity called a half-value layer (HVL), which is the material thickness needed to attenuate the intensity of the incident photon beam to half of its original value. This means that when � = HVL, <sup>N</sup><sup>0</sup> <sup>N</sup> <sup>¼</sup> <sup>1</sup> 2 .

From Eq. (3) it can be shown that:

$$\begin{aligned} \frac{N\_0}{2} &= N\_0 e^{-\mu H VL} \\ H \text{VL} &= \frac{\ln 2}{\mu} = \frac{0.693}{\mu} \end{aligned} \tag{7}$$

The HVL of a given material thus characterizes the quality (penetrance or hardness) of a gamma beam.

Figure 2 shows the relationship between the linear attenuation coefficient and the HVL for a soft tissue [3].

#### 3.4 Calculation of relaxation length (λ)

The average distance between two successive interactions is called the relaxation length (λ) or the photon mean free path which is determined by the equation:

Use of Gamma Radiation Techniques in Peaceful Applications

$$
\lambda = \frac{\int\_0^\infty x e^{-\mu x} dx}{\int\_0^\infty e^{-\mu x} dx} = \frac{1}{\mu} \tag{8}
$$

treatment of cancers. Cancers cells divided more quickly are more sensitive, than normal cells to ionizing radiation. By sending these cells a certain dose of radiation,

Gamma Rays: Applications in Environmental Gamma Dosimetry and Determination Samples…

• Irradiation of surgical and food material: Irradiation is a privileged means to

destroy micro-organisms (fungi, bacteria, virus…). As a result, many applications radiation exists for sterilization of objects. For example, most medical-surgical equipment (disposable syringes, etc.) is today radio-sterilized by specialized industrialists. Similarly, the treatment by irradiation of food ingredients allows improve food hygiene: sterilization spices, elimination of salmonella from shrimp and frog legs. This technics is also known as food

• Irradiation of art objects: Treatment with gamma rays helps to eliminate larvae, insects or bacteria lived inside objects, to protect them from degradation. This technics is used in the treatment of conservation and restoration of arts objects, ethnology and archaeology. It is applicable to

• Elaboration of materials: Irradiation causes, under certain conditions, chemical reactions that allow the development of more resistant materials,

The development of γ-spectrometry began with the development of nuclear sciences and technology to meet the needs for the control, characterization and analysis of radioactive materials. This measurement technics exploits a fundamental property observed for unstable nuclei: the emission of radiation from the process of nuclear decay. It is thus known as non-destructive because it respects the integrity

The interest in γ spectrometry has continued to grow over the years, both from a point of view metrological and a point of view applications. This development was made possible by a better understanding of the process of photon interaction with matter, and especially by the appearance of semiconductor detectors in the 1960s. Spectrometry γ then became a powerful tool for studying decay patterns. It is now used in a wide variety of sectors (for example: dating, climatology, astrophysics,

Photon spectrometry is a commonly used nuclear measurement technique to

The radionuclides measured by this method emit gamma photons of specific energies and their interactions with the detector depend on several variables (geometry or conditioning: physical shape of the object, density, measured quantity, container type, emission energy, size, shape, nature of the detector, etc.).

identify and quantify gamma emitting radionuclides in a sample. It is nondestructive and does not require specific sample preparation. Conventional spectrometers are designed around semiconductor detectors, usually with high purity

different types of materials: wood, stone, leather, etc.

more lightweight, capable of superior performance.

medicine) and in virtually all stages of the fuel cycle.

it is possible to kill them and eliminate the tumor.

DOI: http://dx.doi.org/10.5772/intechopen.85503

4.2 Sterilization of objects by gamma radiation

ionization.

4.3 Industrial applications

4.4 Gamma rays spectrometry

of the object to be analyzed [4].

germanium (hyper-pure germanium).

115

where μ is the linear attenuation coefficient and x is the absorber thickness. N.B: The relaxation length is the thickness of a shield for which the photon intensity in a narrow beam is reduced to 1/e (or 0.37) of its original value.

Figure 2.

Relationship between the linear attenuation coefficient and the HVL for a soft tissue.
