Contribution of compound, preequilibrium and direct reactions to photoneutron emission spectrum from various targets induced by 16.6-MeV monoenergetic photons

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, FLUKA, and MCNP. 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 and were discussed. 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. Results in this study showed the necessity of improvement of nuclear data libraries or nuclear models implemented in the codes for describing photonuclear reactions above the energy related to the compound, particularly.