Photon Cross Section Data in Absorbed Dose Calculations

Air kerma data and the relative response of the new HPA TLD are calculated for Narrow Series X-ray distribution and Cs photon sources using the general purpose Monte Carlo code MCNP5, and the results are compared to those obtained using its predecessor, MCNP4c2. It is found that the results differ at low energies (< 0.1 MeV) by up to ~10 %. This disparity is mainly ascribed to differences in the default photon interaction data used by the two codes, and derives ultimately from the influence on absorbed dose of the recent updates to the photoelectric effect cross sections. The sources of these data are reviewed, and their differences explored. The cross sections used to derive the commonly-used mass attenuation and mass-energy absorption coefficients, as well as air kerma to personal dose equivalent conversion coefficients, are also discussed, and the implications of these considered.