Calculation of gamma-ray exposure buildup factors up to 40 mfp using the EGS4 Monte Carlo code with a particle splitting

Abstract

Gamma-ray exposure buildup factors up to 40 mfp have been calculated using the Monte Carlo code EGS4 for water, iron and lead for point isotropic sources. The new algorithm which applies particle-splitting at each preset depth to simulate almost same number of particles from the preset depth is developed in order to obtain reasonable results with EGS4 at deep-penetrations. Comparisons of these results to the standard data calculated with the moments method or the discrete ordinates code PALLAS show good agreements if the same cross section data and energy absorption coefficients are used. The EGS4 calculations with this new algorithm will be a useful tool for future studies of gamma-ray buildup factors including the review of the standard data.