Photonuclear reactions of actinide and pre-actinide nuclei at intermediate energies

Photonuclear reaction is described with an approach based on the quasideuteron nuclear photoabsorption model followed by the process of competition between light particle evaporation and fission for the excited nucleus. Thus fission process is considered as a decay mode. The evaporation-fission process of the compound nucleus is simulated in a Monte-Carlo framework. Photofission reaction cross sections are analysed in a systematic manner in the energy range $\sim$~50-70 MeV for the actinides $^{232}$Th, $^{233}$U, $^{235}$U, $^{238}$U and $^{237}$Np and the pre-actinide nuclei $^{208}$Pb and $^{209}$Bi. The study reproduces satisfactorily well the available experimental data of photofission cross sections at energies $\sim$~50-70 MeV and the increasing trend of nuclear fissility with the fissility parameter $Z^2/A$ for the actinides and pre-actinides at intermediate energies [$\sim$~20-140 MeV].