Geant4 Monte Carlo code application in photon interaction parameter of composite materials and comparison with XCOM and experimental data

Transcription

1 Indian Journal of Pure & Applied Physics Vol. 54, Februray 2016, pp Geant4 Monte Carlo code application in photon interaction parameter of composite materials and comparison with XCOM and experimental data M E Medhat 1,2 & V P Singh 3,4 * 1 Experimental Nuclear Physics Department., Nuclear Research Centre, P.O.13759, Cairo, Egypt 2 Institute of High Physics, CAS, Beijing , China 3 Department of Physics, Karnatak University, Dharwad , India 4 Health Physics Section, Kaiga Atomic Power Station-3&4, NPCIL, Karwar , India Received 7 November 2013; revised 25 February 2014; accepted 8 September 2015 In the present work, the applicability of Geant4 Monte Carlo code for mass attenuations of different types of composite materials such as building materials, glasses, plastics and water matrix at photon energies 59.5, 80, 356, 661.6, and kev has been tested. The Geant4 simulated results of mass attenuation coefficients of composite materials have been compared with the experimental and theoretical XCOM data and a good agreement has been observed. The results indicate that this simulation process can be followed to determine the data on the gamma rays interaction parameters with the several energies in different types of materials. The modeling for photon interaction has been standardarised for any type of composite samples. The Geant4 code can be utilized for gamma ray mass attenuation coefficients for each sample at different energies, which may sometimes be impractical by experiment investigation. Keywords: Composite material, Mass attenuation coefficient, Geant4 simulations 1 Introduction Geant4 is widely used toolkit for the Monte Carlo simulation of the passage of particles through the matter. It is based on object-oriented programming and allows user to derive classes to describe the detector geometry, primary particle generator and physics processes models along electromagnetic, hadronic and decay physics based on theory, experimental data or parameterizations. Most of physics processes models include multiple scattering, ionization, Bremsstrahlung, positron annihilation, photoelectric effect, Compton and Rayleigh scattering, pair production, synchrotron and transition radiation, Cherenkov effect, refraction, reflection, absorption, scintillation, fluorescence, and Auger electrons emission 1-4. The validation of Geant4 physics models with respect to experimental data is a critical subject to test the applicability of Geant4 based Monte Carlo simulations. The most important parameter which can be applied for testing electromagnetic packages of Geant4 is mass attenuation coefficients of gamma ray through the matter. It characterizes the penetration and diffusion of gamma radiation in materials *Corresponding author ( kudphyvps@rediffmail.com) which represents the probability of a photon-atom interaction (scattered/absorbed) per unit path length. It is the fundamental parameter to derive several other parameters of dosimetric and shielding interest such as mass-energy absorption coefficient, molecular, atomic and electronic cross-sections, effective atomic numbers, electron densities, shielding effectiveness (half-value layer/tenth-value layer thickness) 5-8. The testing and validation of Geant4 electromagnetic models of Geant4 based Monte Carlo simulations to demonstrate its success in radiation interactions and to derive the interaction parameters using mass attenuation coefficients, have been studied in the present paper. It was applied in calculating principle interaction parameter, mass attenuation coefficients in different types of materials (building materials, glasses, plastics and water matrix) and compared with their experimental measurements and the theoretical data obtained by XCOM program. This study is very useful for application in gamma ray interaction with the matter and deriving various interaction parameters analogous to experiment at various photon energies. The standard modeling of the present work for estimation of photon interaction parameters can be utilized for any type of sample/complex material.

2 138 INDIAN J PURE & APPL PHYS, VOL 54, FEBRUARY Monte Carlo Model and Simulation Modeling the photon attenuation through materials in computer environment gives flexibility and ease of use, instead of performing an experimental determination of mass attenuation of different composite materials. For this reason, the application would be useful for further experiments where material and incident photon energy are changed. Then, instead of performing photon attenuation for each type of material, which may sometimes be impractical, the model can be used through macro file to calculate mass attenuation coefficients at different energies. The physics of Geant4 simulation depends on narrow beam geometry with the various photon energies. The experimental set-up of the simulation, consisting of a mono-energetic photon beam impinging on a slab of one of the selected materials, the mass attenuation coefficients of investigated materials are determined by the transmission method according to Beer Lambert s law (I = I 0 e -µ m x ), where I 0 and I are the incident and attenuated photon intensity, respectively, µ m (cm 2.g -1 ) is the mass attenuation coefficient and x is the thickness of the slab. The thickness of the target is optimized according to the energy of the incident beam to avoid that all the photons are absorbed in the target or traverse the slab without interacting. The primary photons emerging unperturbed from the slab are counted. The energy range of incident photons varied between 1 kev and 100 GeV. Attenuation of photons is calculated by simulating all relevant physical processes and interactions before and after inserting the investigated sample. Some Geant4 code simulation studies for attenuation of gamma rays for compounds and scintillation detectors have been reported The Physics processes defined in Physics List are low-energy electromagnetic processes with valid energy range down to 250 ev. This variant is based on the use of experimental data parameterizations using databases developed by Lawrence Livermore National Laboratory: Evaluated Photon Data Library (EPDL97), Evaluated Electron Data Library (EEDL) and Evaluated Atomic Data Library (EADL). Photon interactions include photoelectric effect, Compton scattering, pair production, Rayleigh scattering and electrons interactions include Bremsstrahlung, multiple scattering and ionization. Atomic effects after photoelectric effect, as X-rays emission and Auger effect are included. So it is possible to have a vertex from photoelectric effect Materials and Methods In the present work, an investigation on availability of Geant4 Monte Carlo code for calculation of gamma-ray attenuation coefficients of some composite materials and to test the code validity on this subject by comparison of simulation results with the theoretical XCOM results and the available experimental data, has been carried out. The composite materials studied here were chosen to cover different wide range of materials such as building materials, glasses, plastics and water matrices as given in Table 1. The composite material samples were irradiated by 59.5, 81.0, 356.5, 661.6, and kev photons emitted through 241 Am (2.78 GBq), 133 Ba (2.92 GBq), 137 Cs (3.14 GBq), and 60 Co (3.7 GBq) radioactive point sources, respectively. For each sample intensities of incident and attenuated photons Table 1 Chemical compositions of the composite materials Category Material Elemental Concentrations (% weight) Building BM1 C(0.558), Na(0.023), Mg(0.001), Al(0.082), Si(0.082), Ca(0.246), Fe(0.008) Materials BM2 O(0.37), Mg(0.004), Al(0.209), Si(0.021), Ca(0.279), Fe (0.117) BM3 H(0.009), C(0.001), O(0.536), Na(0.005), Mg(0.001), Al(0.013), Si(0.367), S(0.001), K(0.003), Ca(0.056), Fe (0.006) Glasses G1 O(0.532), Si(0.467) G2 G3 B(0.041),O(0.54),Na(0.028),Al(0.012 ),Si(0.38), K(0.0033) O(0.468), Na(0.096), Mg(0.001), Al(0.007), Si(0.345), S(8 10-4), K(0.003), Ca(0.075), Ti(6 10-4), Fe(0.003) Plastics P1 H(0.066), C(0.525), O(0.408) Water Matrix P2 P3 WM1 WM2 WM 3 H(0.031), C(0.285), N(0.111), O(0.571) H(0.055), C(0.755), O(0.189) H(0.102), N(0.010), O(0.844), Mn(0.008), Cu(0.0042), Pb(0.031) H(0.105), N(0.009), O(0.864), Cu(0.017), Zn(0.004) H(0.106), N(0.004), O(0.858), Pb(0.0312)

3 MEDHAT & SINGH: GEANT4 MONTE CARLO CODE APPLICATION IN PHOTON INTERACTION 139 were measured by HPGe detector coupled with a personal computer analyzer (PCA) and Genie 2000 for data acquisition and analysis. The measurements for all samples were carried out three times for each energy value with a sufficiently large fixed preset time to reduce the statistical uncertainties. The experimental set-up is shown in Fig Results and Discussion In order to calculate values for the mass attenuation coefficient from the measured incident and transmitted gamma-ray intensities, it is necessary to Fig. 1 Experimental set-up for mass attenuation coefficients of composite materials know the thickness and bulk density of each sample of the system. Bulk densities were determined by traditional method. Masses were determined by a sensitive balance and the volume of the samples measured with digital caliper. The mass attenuation coefficients of the samples were determined at 59.5, , 661.6, and kev photons by using gamma transmission method. The experimental error was estimated by combining errors for the product of linear attenuation coefficient and thickness, density and thickness measurements in quadrature. In addition, systematic errors may occur because of deviations from good narrow-beam geometry. Calculations of the mass attenuation coefficients of all investigated composite materials were carried out by the XCOM program theoretically. It can generate cross-sections and attenuation coefficients for elements, compounds or mixtures in the energy range between 1 kev and 100 GeV in the form of total cross-sections and attenuation coefficients as well as partial cross-sections of the following processes: incoherent scattering, coherent scattering, photoelectric absorption and pair production in the field of the atomic nucleus and in the field of the atomic electrons 13. The results of our presented Geant4 simulation were compared with the theoretical values obtained using XCOM database and the obtained experimental results are shown in Tables 2-5. Table 2 Calculated and measured mass attenuation coefficients of the some building materials BM1 BM2 BM ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.009 Table 3 Calculated and measured mass attenuation coefficients of the some glass materials G1 G2 G ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.010

4 140 INDIAN J PURE & APPL PHYS, VOL 54, FEBRUARY Calculated and measured mass attenuation coefficients of the some plastics P 1 P 2 P ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.009 Table 5 Calculated and measured mass attenuation coefficients of the some water matrices WM1 WM2 WM ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.009 Fig. 2 Comparison of mass attenuation calculated by Geant4 and XCOM with respect to experiment according to relative deviation in some building materials

5 MEDHAT & SINGH: GEANT4 MONTE CARLO CODE APPLICATION IN PHOTON INTERACTION 141 It is clear that there is satisfactory agreement between experiment and theory, although the experimental values tend to be lower than the theoretical values. Discrepancy in the values of the calculated and the experimental mass attenuation coefficients could be due to deviations from narrow beam geometry in the source-detector arrangements. The relative deviations (RD) between the experimental and theoretical values are lower than the corresponding values of XCOM for most of the composite materials at different photon energies as shown in Figs 2-5. It is clear that the representative Geant4 Monte Carlo simulation generated data for mass attenuation coefficients of all the composite materials are a function of incident photon energy and the chemical compositions. The mass attenuation coefficients of the selected composite materials are different based on the chemical compositions of the elements. Fig. 3 Comparison of mass attenuation calculated by Geant4 and XCOM with respect to experiment according to relative deviation in some glasses

6 142 INDIAN J PURE & APPL PHYS, VOL 54, FEBRUARY 2016 Fig. 4 Comparison of mass attenuation calculated by Geant4 and XCOM with respect to experiment according to relative deviation in some plastics Fig. 5 Comparison of mass attenuation calculated by Geant4 and XCOM with respect to experiment according to relative deviation in some water matrices

7 MEDHAT & SINGH: GEANT4 MONTE CARLO CODE APPLICATION IN PHOTON INTERACTION Conclusions Monte Carlo simulation is a powerful tool in studying interaction of gamma ray in the materials. The applicability of this method is greatly dependent on the accuracy of geometry model, composition and density distribution of the sample matrix. The Geant-4 simulation toolkit was used to calculate mass attenuation coefficients of different wide varieties of materials in the kev photon energy range. The simulations show that the calculated mass attenuation values are close to experimental values better than obtained by theoretical XCOM database. These results conclude that Geant4 Monte Carlo simulation can be applied to estimate the fundamental parameter mass attenuation for various attenuator and energies. Therefore, it is concluded that the Geat4 Monte Carlo simulation toolkit is better theoretical method for evaluation of photon interaction parameters of the various types of materials. Acknowledgement One author (ME Medhat) would like to thank all member of Iinstitute of High Physics (IHEP) during hosting his postdoctoral fellowships presented by Chinese Academy of Science (CAS), China. This work was supported by the Chinese Academy of Sciences Fellowships for Young International Scientists. References 1 Agostinelli S et al., Nucl Instrum Methods Phys Res A, 506 (2003) CERN, Geant-4 toolkit web site. 4 Allison J et al., IEEE Trans Nucl Sci, 53 (2006) Hubbell J H, Phys Med Biol, 51 (2006) Medhat M E, J Radioanal Nucl, 293 (2012) Medhat M E, Ann Nucl, 40 (2012) Medhat M E, Ann Nucl, 38 (2011) Cirrone et al. G A P, Nucl Instr Methods, A 618 (2010) Medhat M E, Ann Nucl, 62 (2013) Singh V P, Medhat M E & Badiger N M, Ann Nucl, 68 (2014) Amako K et al., IEEE Trans Nucl Sci, 52 (2005) Berger M J, Hubbell J H, Seltzer S M, Chang J, Coursey J S, Sukumar R, Zucker D S & Olsen K, (2010). nist.gov/pml/data/xcom/index.cfm.