Calculation of gamma-ray buildup factors for two-layered shields made of water, concrete and iron and application of approximating formula

Gamma-ray buildup factors that are the basic data for the point kernel calc ulations were calculated up to 40 mean free path (mfp) for double-layered s hields consisting of water, concrete and iron by the EGS4 code using a spec ial splitting technique at gamma-ray energies of 0.1, 0.3, 0.6, 1, 3, 6 and 10 MeV. The assumed shields were 40 mfp monolayer, 5 mfp first layer + 35 mfp second layer, 10 mfp first layer + 30 mfp second layer and 20 mfp first layer + 20 mfp second layer of these materials. All the possible combinati ons of single- and double-layered shields made up of two materials from wat er, concrete and iron were assumed in the calculations. The calculated data were parameterized by an empirical formula based on the transmission matri x method of recently proposed by the authors. The formula reproduced very w ell the reference data in all cases, except for those at 0.1 MeV where the small disagreement is now under investigation. (C) 2001 Elsevier Science Lt d. All rights reserved.