A study of the deformation potentials of 232Th and 238U by photofission

Angular distributions and yields measurements of subthreshold photofission of 232Th and 238U are analysed in terms of transition states configurations. The method of analysis is based on the doorway states model applied to the fission through a double-humped barrier. The data of 232Th are consistent with a triple humped barrier with a third mass asymmetric shallow minimum caused by the split of the normal second maximum. Puzzling results on the isotropic component of photofission need further investigations both theoretical and experimental for a satisfactory understanding of low energy fission of 232Th.