Calculation of gamma-ray buildup factors up to depths of 100 mfp by the method of invariant embedding, (i)

Abstract

The method of invariant embedding has been applied to calculations of gamma-ray buildup factors for point isotropic sources in infinite homogeneous media up to depths of 100 mean free paths (mfp) without bremsstrahlung. A comprehensive survey of buildup factors was performed to estimate errors due to energy, angle and space meshes adopted in the transport calculations by the present method. It is confirmed numerically that the exposure buildup factors can be calculated up to depths of 100 mfp with an error less than 10% by using the present method. The exposure buildup factors for water, iron and lead for typical source energies of 10 MeV, 1.0 MeV and 0.1 MeV are provided up to depths of 100 mfp. Those buildup factors are found to agree well with other data including the moments method calculations and the Monte Calro calculations by EGS4. These results indicate that the method of invariant embedding is able to provide gamma-ray buildup factor up to depths of 100 mfp with an accuracy enough to be used in shielding calculations. © 2002 Taylor and Francis Group, LTD.