Journal of Spectroscopy

Volume 2017, Article ID 9792816, 9 pages

https://doi.org/10.1155/2017/9792816

## A Comprehensive Study on Gamma Rays and Fast Neutron Sensing Properties of GAGOC and CMO Scintillators for Shielding Radiation Applications

^{1}Department of Physics, Faculty of Science, University of Tabuk, Tabuk, Saudi Arabia^{2}Department of Physics, Faculty of Science, Al-Azhar University, Cairo, Egypt^{3}Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia^{4}Materials Synthesis and Characterization Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

Correspondence should be addressed to K. A. Matori; ym.ude.mpu@lurimahk

Received 3 April 2017; Revised 10 July 2017; Accepted 26 July 2017; Published 26 September 2017

Academic Editor: Tino Hofmann

Copyright © 2017 Shams A. M. Issa et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

The WinXCom program has been used to calculate the mass attenuation coefficients (*μ _{m}*), effective atomic numbers (

*Z*

_{eff}), effective electron densities (

*N*

_{el}), half-value layer (HVL), and mean free path (MFP) in the energy range 1 keV–100 GeV for Gd

_{3}Al

_{2}Ga

_{3}O

_{12}Ce (GAGOC) and CaMoO

_{4}(CMO) scintillator materials. The geometrical progression (G-P) method has been used to compute the exposure buildup factors (EBF) and gamma ray energy absorption (EABF) in the photon energy range 0.015–15 MeV and up to a 40 penetration depth (mfp). In addition, the values of the removal cross section for a fast neutron have been calculated. The computed data observes that GAGOC showed excellent

*γ*-rays and neutrons sensing a response in the broad energy range. This work could be useful for nuclear radiation sensors, detectors, nuclear medicine applications (medical imaging and mammography), nuclear engineering, and space technology.

#### 1. Introduction

Due to the great importance of inorganic scintillator materials in the field of ionizing nuclear radiation detection, they are a very suitable to utilize in many applications such as technology of space, the design of nuclear devices, and medicinal diagnostics [1]. To develop the new scintillator materials, the knowledge of mass attenuation coefficient (*μ _{m}*) is very considered for scintillators because the results of

*μ*show the probability of interaction. Furthermore, when the gamma ray interacts with the material, the half-value layer (HVL), mean free path (MFP), effective atomic number (

_{m}*Z*

_{eff}), effective electron density (

*N*

_{el}), exposure buildup factors (EBF), and gamma ray energy absorption (EABF) are the fundamental quantities required to explain the penetration of nuclear radiation in matter. HVL, MFP,

*Z*

_{eff},

*N*

_{el}, EBF, and EABF parameters can be computed utilizing the values of

*μ*[2]. Precise

_{m}*μ*values are wanted to provide fundamental results in many nuclear radiation fields like computerized tomography, radiation shielding, nuclear radiation dosimeter, fluorescence of gamma ray, and safety inspection [3]. Various other researchers reported the properties of gamma radiation shielding for alloys, multielemental materials, soils, solutions, polyvinyl alcohol, and biological materials [4–11].

_{m}Hine [12] suggested a number of composite changes with energy called effective atomic number (*Z*_{eff}) to characterize the atomic number of mixed materials with energy. Due to the high light yield, speedy decay time, high density, high *Z*_{eff}, and good energy resolution of GAGOC scintillator materials, it is a great nominee for many applications like gamma spectroscopy and position emission tomography (PET) [13]; furthermore, GAGOC does not have natural radioactivity [14]. Because there is lack of knowledge of gamma ray and neutron interaction with GAGOC and CMO scintillator materials, *μ _{m}*, HVL, MFP,

*Z*

_{eff},

*N*

_{el}, EBF, and EABF have been investigated in a broad energy range. The values have been computed for

*μ*, HVL, MFP,

_{m}*Z*

_{eff}, and

*N*

_{el}in the energy range 1 keV–100 GeV and for EBF and EABF in the energy range 0.015–15 MeV using the WinXCom program. Also, the macroscopic fast neutron removal cross section has been calculated.

#### 2. Theory

Photoelectric effect, Compton scattering, and pair production mechanisms can explain the interaction of photons with the GAGOC and CMO scintillator materials. If the intensity of the initial beam penetrates the sample which is *I*_{0}, the intensity of the beam will be attenuated and exponentially decreased to *I* according to the Beer–Lambert law.
where *I*_{0} is the intensity of bombarding beam, *I* is the intensity of transmitting beam, *ρ* is the density of scintillator samples (g/cm^{3}), and *d* is the thickness of the samples (cm). The total photon interaction cross section (*σ _{t}*) of the samples has been calculated with the help of the

*μ*according to the following equation: where the molecular weight of the sample,

_{m}*A*is the atomic weight of the

_{i}*i*th element,

*n*is the number of the formula units of a molecule, and

_{i}*N*

_{A}is the Avogadro’s number. Effective atomic cross section,

*σ*, has been calculated using the following equation:

_{a}Total electronic cross section, *σ _{e}*, has been calculated by
where

*f*indicates to the fractional abundance of the element

_{i}*i*and

*Z*the atomic number of the constituent element. The

_{i}*Z*

_{eff}is related to

*σ*and

_{a}*σ*through the following equation:

_{e}The effective electron densities (*N*_{el}) of GAGOC and CMO have been calculated from the following:

Half-value thickness (HVL) is the thickness of any given material where 50% of the incident energy has been attenuated and has been computed utilizing the linear attenuation coefficient (*μ*) through the following equation:

One of the other values that are calculated in this study of GAGOC and CMO is the mean free path (MFP) which is described in [15, 16]. For the detailed knowledge on calculations of the parameters of G-P fitting, exposure buildup factor and energy absorption buildup factor, the element G-P fitting parameters have been taken from the ANSI/ANS 6.4.3 [17].

Finally, the removal cross sections for fast neutrons for GAGOC and CMO materials can be calculated using the following equations:
where *ρ _{i}* is the partial density and is the mass removal cross section of the

*i*th element which is taken from Kaplan and Chilten [18, 19].

#### 3. Results and Discussion

##### 3.1. Mass Attenuation Coefficient (*μ*_{m})

_{m}

Coherent scattering, incoherent scattering, photoelectric absorption, nuclear pair production, and electron pair production are the interaction processes of photon energy with matter. These interaction processes can explain the dependency of total mass attenuation coefficient (*μ _{m}*) on the photon energy, as shown in Figure 1 for GAGOC. This figure shows that the low photon energy range (E < 0.3 MeV), intermediate photon energy range (0.3 < E < 5 MeV), and high photon energy range (E > 5 MeV) are the three photon energy ranges in interaction processes. Figure 2 shows the calculated

*μ*values of GAGOC and CMO scintillator materials. As shown in Figure 2, the

_{m}*μ*values of the samples decrease quickly, from 3.50 × 10

_{m}^{3}to 1.68 × 10

^{−1}cm

^{2}/g and 4.81 × 10

^{3}to 1.17 × 10

^{−1}cm

^{2}/g for GAGOC and CMO, respectively, as the photon energy increases up to 0.3 MeV. In this photon energy range, the K-, L-, and M-absorption edges have been observed of Al, Ca, Ga, Mo, Ce, and Gd as shown in Table 1 due to the photoelectric effect. This behavior of

*μ*with photon energy may be attributed to the photoelectric absorption cross section which is relative to E

_{m}^{3.5}. In the photon energy range 0.3 < E < 5 MeV, the

*μ*values of GAGOC and CMO scintillator materials change slowly, form 0.01179 to 0.0345 cm

_{m}^{2}/g and 0.0971 to 0.0317 cm

^{2}/g for GAGOC and CMO, respectively. The difference of the

*μ*values becomes approximately equal to zero as shown in Figure 2. This is because the process of Compton scattering is a predominant mechanism [20]. Since, the Compton scattering cross-section process is relative to E

_{m}^{−1}and linearly changes with the

*Z*number. Figure 2 shows that, as the photon energy increases from 5 MeV to 100 GeV, the values of

*μ*increase slowly, becoming constant and highly dependent on the composition of samples. This may be attributed to the fact that the pair production process is a predominant mechanism. The results show that the GAGOC scintillator material has higher

_{m}*μ*than CMO.

_{m}