Contribution of bremsstrahlung to buildup factor of shielding materials: a MCNP study

The buildup factors of different γ-rays energy, shielding thickness or shielding materials, including bremsstrahlung radiations, for a point isotropic source have been calculated using MCNP code. The simulation results show that when the energy of γ-ray is less than 2 MeV, contribution of the bremsstrahlung to buildup factor is very small; when the energy of γ-ray is more than 6 MeV, contribution of the bremsstrahlung to buildup factor is very large. With the increasing of γ-ray energy, shielding thickness or shielding materials atomic number Z, the contribution of the bremsstrahlung to buildup factor is getting lager. The buildup factors with or without bremsstrahlung calculated by MCNP shows good agreement with the calculation value. (authors)