Application of the EGS4 Monte Carlo code to a study of multilayer gamma-ray exposure buildup factors of up to 40 mfp

Multilayer gamma-ray exposure buildup factors of up to 40 mfp were calculat ed using an electron-photon cascade Monte Carlo code, EGS4, as a point isot ropic source. A kind of splitting technique was used in the EGS4 calculatio ns in order to obtain reasonable results at very deep penetration problems, such as 40 mfp. The double-layer gamma-ray exposure buildup factors were calculated for com binations of water, iron and lead for 0.1, 0.3, 0.6, 1.0, 3.0, 6.0 and 10 M eV gamma-rays. The thickness of the first medium was set to 1, 5, 10 or 20 mfp. As typical triple-layered shields, the calculations were performed for 4 different configurations of water, iron and lead. The behavior of multilayer buildup factors for deep penetration problems wa s studied using the obtained results. Buildup factors after the bounday sho w the tendency to vary largely depending on the material combination and th e source energy of gamma-rays.