Speaker
Description
A photonuclear reaction consists of the photoabsorption and particle emission. Once the photon is absorbed, the excited nucleus decays via direct, preequilibrium and compound (evaporation) mechanisms. Photoneutron production yields and production mechanisms were investigated by comparing results of the well-known estimation methods. Differential photoneutron yields from 𝑛𝑎𝑡Pb,197Au, 𝑛𝑎𝑡Sn and 𝑛𝑎𝑡Cu targets irradiated with 16.6 MeV photons were calculated using PHITS-3.1, FLUKA 4-2.1, and MCNP6.1. JENDL/PD-2004 library was used in PHITS for photoabsorption cross section and neutron emission was handled by generalized evaporation model (GEM). FLUKA uses the IAEA photonuclear cross section library as well as other experimental data and neutron emission is calculated by PreEquilibrium Approach to NUclear Thermalization (PEANUT) model. The ENDF/B-VII.0 and IAEA/PD-2019 photonuclear libraries were used in MCNP6.1 and compared together. The results were compared with experimental data in the literature. Compound, preequilibrium and direct reaction contributions to neutron double differential cross sections were calculated by TALYS. All Monte Carlo codes generated the compound part of neutron spectra well but failed at higher energy range. MCNP6.1 using ENDF/B-VII.0 and IAEA/PD-2019 libraries were more reasonable than PHITS and FLUKA. MCNP6.1 with ENDF/B-VII.0 reproduced the neutron spectra up to 8 MeV for 197Au target and agreed well with experimental data. The preequilibrium mechanism significantly contributed to the photoneutron production for the natPb, 197Au and natSn above 4 MeV, while for the natCu target, compound mechanism was dominant over the whole neutron emission energies.
Results in this study showed the necessity of improvement of nuclear data libraries or nuclear models implemented in the codes for describing photonuclear reactions beyond the evaporation part, namely preequilibrium and direct mechanisms