Detailed Behavior of Exposure Buildup Factor in Stratified Shields for Plane-Normal and Point Isotropic Sources, Including the Effects of Bremsstrahlung and Fluorescent Radiation

Exposure buildup factors, energy spectra, and angular flux distributions for plane-normal incident and point isotropic source gamma rays of 0.1, 0.5, 1, 3, 6, and 10 MeV penetrating two-layer water-lead and lead-water shields are calculated with the point Monte Carlo code EGS4 The effects of bremsstrahlung and fluorescent radiation are included. The value of the buildup factor in the second layer lies between those for infinite media of both materials in two source geometries in the 0.5- to 3-MeV energy range. However, this behavior varies remarkably and is enhanced with a bremsstrahlung contribution, when the source energy is higher than that corresponding to the minimum in the attenuation coefficient of lead. This varies equally with the fluorescent contribution when the source energy is close to the K edge of lead.