Gamma ray shielding characteristics and exposure buildup factor for some natural rocks using MCNP-5 code

The mass attenuation coefficient μm for eight rock samples having different chemical composition was simulated using the MCNP 5 code in energy range (0.002MeV≤E≤10MeV). Moreover, the μm for the studied rock samples was computed theoretically using XCOM database. The comparison between simulated and computed data for all selected rock samples showed a good agreement with differences varied between 0.01 and 8%. The highest μm was found for basalt rocks M2 and M1 and the lowest one is reported for limestone rocks Dike. The simulated values of the μm then were used to calculate other important shielding parameters such as the mean free path, effective electron density and effective atomic number. The exposure buildup factor EBF was also computed for the selected rocks with the contribution of G-P fitting parameters and the highest EBF attended by the basalt sample Sill and varied between 1.022 and 744 in the energy range between (0.015≤E≤15MeV) but the lowest EBF achieved by basalt sample M2 and varied between 1.017 and 491 in the same energy range. Keywords: Gamma ray, Shielding properties, Natural rocks, MCNP, Buildup factor