Gamma-Ray Buildup Factors for a Point Isotropic Source in the Single Layer Shield by Using BERMUDA Code

Abstract

In order to modify the standard data of gamma-ray buildup factors for a point isotropic source in the single layer, the applicability of the direct integration method code BERMUDA to buildup factor calculations was surveyed. In this code, group-angle transfer matrix of photons is calculated by numerically integrating the Klein-Nishina formula for Compton scattering taking the energy-angle correlation into account. In the low energy region, the four K-shell fluorescence are considered whose isotropic emission intensity can be calculated from the primary photon intensity, the K-shell absorption cross section data and fluorescence yield. In the higher energy region for high-Z materials, the Bremsstrahlung is considered whose energy-angle production correlation matrixes were obtained by EGS4 code. The exposure buildup factors of lead for low energy photons calculated by using BERMUDA code without and with fluorescence were good agreement with those by EGS4 and PALLAS codes. Those of lead for high energy photons without Bremsstrahlung were also good agreement with those by EGS4 and PALLAS codes, but those with Bremsstrahlung were smaller than those by EGS4 code.