Effects of the Photon Cross Sections and Energy-Absorption Coefficients of Air to the Gamma-Ray Point Isotropic Exposure Buildup Factors

The effects of using different photon cross-section libraries and energy-absorption coefficients on the gamma-ray point isotropic exposure buildup factors up to 40 mean free path (mfp) were studied using the EGS4 Monte Carlo code for water‚ iron, and lead from the 0.1- to 10-MeV energy regions., Differences due to the cross sections used exist‚ but are small‚ < 10%, except those for lead at 0.1 and 10 MeV. The differences in the case of lead increase along with an increase in the depth and are nearly 30% at 40 mfp depth. The effects of using different energy-absorption coefficients of air are <2%