Improvement of photonuclear reaction model below 140 MeV in the PHITS code

Abstract

The photonuclear reaction model in the particle and heavy ion transport code system (PHITS) code is improved for incident photon energies below 140 MeV. Japanese Evaluated Nuclear Data Library (JENDL) Photonuclear Data File 2004 (JENDL/PD-2004) is adopted to determine the total reaction cross section. The statistical decay model after excitation of the nucleus in PHITS is improved by modifying the decay widths for light nuclei under the isospin selection rule to reasonably reproduce the proton and neutron emission in the de-excitation process. The quasideuteron disintegration process is newly introduced into PHITS to handle the photonuclear reaction up to 140 MeV of incident photon energy. The accuracy of the improvements was verified by comparison with the experimental literature data. The improved PHITS can contribute to various practical applications such as neutron dose estimation in X-ray therapy.