Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of ²²⁹Th

In the epi-cadmium neutron-induced fission of ²²⁹Th, cumulative yields of relatively long-lived fission products within the mass range of 77 to 151 were measured by using an off-line gamma-ray spectrometric technique. The mass yields were obtained from the cumulative fission product yields by using charge distribution correction. The peak-to-valley (P/V) ratio, full-width at tenth-maximum of light and heavy mass wings, average light mass <A_L> and heavy mass <A_H>, and average neutron number <ν> were obtained. The P/V ratio was obtained for the first time and was found to be about three times lower in the epi-cadmium neutron fission than in the thermal neutron fission of ²²⁹Th, which shows the role of excitation energy. The fine structure of the mass yield distribution in the ²²⁹Th(n_f,f) reaction was explained from the viewpoint of nuclear structure effect and the Standard I and Standard II asymmetric modes of fission.