Fission properties of 233Th

Abstract

The fission fragment kinetic energy and mass distributions as a function of incident neutron energy were investigated for the 232Th(n, f) reaction. The neutron energy range studied, from 1.35 to 5.30 MeV, includes the fission threshold region where some large structures in the fission cross section are observed, which are attributed to vibrational states in the second (or third) well of the fission barrier. The variation of the mean total kinetic energy of the primary fragments with incident neutron energy is consistent with the results of recent measurements of the variation of the mean number of prompt neutron emitted per fission. Two distinct behaviors are observed, depending upon whether or not the fission proceeds below the barrier (through vibrational states). Information concerning the fission fragment mass dependance of the fragment kinetic energy variation as a function of neutron energy, is also presented. A possible explanation of the results is given in terms of a near adiabatic behavior of the 232Th(n, f) process. It is the first time that such a behavior is observed in the actinide region.