Calculation of total mass attenuation coefficients, effective atomic numbers and effective electron density for some shielding materials

In this study, the total mass attenuation coefficients, μm, the effective atomic number, Zeff , and the effective electron density, Neff, of 5 shielding materials: (Pure Polyethylene, Lithium Polyethylene, Borated Polyethylene, Bismuth-loaded Polyethylene and Borated-lead Polyethylene) have been calculated for the photon energy of 1 keV to 100 GeV. The values of μm were calculated using WinXCom program. The Zeff and the Neff have been calculated using the values of μm. The variation of these parameters with the incident photon energy and the dependence on chemical composition are discussed. During its passage through material medium, a photon undergoes several interactions such as photoelectric absorption, Coherent scattering, scattering Incoherent and Pair Production. If a photon beam having an initial intensity penetrates the matter, it will be attenuated and its intensity decreases exponentially according to the exponential law. This is called the Beer-Lambert law. The formulas used to calculate Zeff and Neff have been given in some previous studies. The mass attenuation coefficient (μm) of Pure Polyethylene, 5 pour cent Borated Polyethylene, 30 pour cent Borated Polyethylene and Lithium Polyethylene, were calculated using the program WinXCom. The results obtained show that (μm) depends on the incident photon energy and chemical composition of materials. The variation of (μm) with the incident photon energy for all materials is almost identical. In the low incident photon energies (1-30keV), the (μm) decreases rapidly when the incident photons energy increases. In the intermediate energies (30 keV-20 MeV), it decreases slowly. Finally, in high energy regions (20MeV < E), it increases slowly and is almost constant. This behavior can be explained by the fact that the dominance of different interaction processes of photon with the matter. In the low energy region, the photoelectric absorption is the dominant process and its effective cross section is inversely proportional to the incident photon energy and is proportional to the atomic number (Z4). In the intermediate incident photon energies, the Compton scattering becomes the dominant mechanism, its cross section is inversely proportional to the incident photons energy (E-1) and it varies linearly with the atomic number Z. Finally, in the high energy region, the pair-production process becomes dominant; its effective cross section doesn't depend on the energy but is proportional to (Z2). Also, it can be seen from this figure that Lithium olyethylene has the highest value of (μm). In effect, this material contains higher concentration of O (57.76 pour cent) and C (26.13 pour cent). The effective atomic number, Zeff, and the effective electron density, Neff of the materials considered in this work were determined using the values of the mass attenuation coefficients (μm). The behaviours of Zeff and Neff with energy for all materials are similar: initially, they are almost constant and then decrease steadily, and in the intermediate energies, they become constant again, finally in high energies, they increase slowly and then they become constant. These behaviours are due to the dominance of different interaction processes of photon with the matter. We can conclude from this work that K-resin is a good material for gamma rays shielding applications, it show the best properties with respect to the radiation attenuation properties, it has higher values of (μm) and Zeff. (Author)