Precompound-model analysis of photonuclear reactions

A large body of photonuclear-reaction data has been compared with predictions of the hybrid-plus-evaporation model. The data are for monoenergetic photons of energy from 25 to 132 MeV on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, Sn, Ce, Ta, and Pb targets, measured by the Saclay group. A quasideuteron absorption mechanism was assumed to give the primary excitation, and the hybrid-plus-evaporation model was used to predict the excitation functions, the neutron-emission widths and multiplicities, and the number of fast neutrons and protons emitted per absorbed photon versus photon energy for Sn, Ce, Ta, and Pb. The parameters used in the calculations were the global set recently selected for nucleon-induced reactions. The calculated results are in excellent agreement with the experimental data over the entire energy range. Additional experiments are suggested in order to make possible stricter tests of the precompound-decay models to provide further information on the details of the primary excitation process.