Mass distribution in the quasi-mono-energetic neutron-induced fission of ²³²Th

Abstract.

The cumulative yields of various fission products in ²³²Th(n, f) with average neutron energies of 6.35, 8.53 and 10.09 MeV have been determined using an off-line $\gamma$-ray spectrometric technique. The neutron beam was produced from the ⁷Li(p, n) reaction. From the cumulative fission yields, the mass chain yields were obtained by using charge distribution correction of medium energy. The peak-to-valley ($P/V$) ratio, the average value of light mass ($\langle A_{L}\rangle$), heavy mass ($\langle A_{H} \rangle$) and the average number of neutrons ($\langle\nu \rangle$) at the three different neutron energies of the present work and at other energies from the literature in the ²³²Th(n, f) reaction were obtained from the mass yield data. The present and the existing literature data in the ²³²Th(n, f) reaction at various excitation energies were compared with similar data in the ²³⁸U(n, f) reaction. The fine structure in the mass yield distribution was interpreted from the point of nuclear structure effect such as shell closure proximity and even-odd effect. The role of standard I and standard II asymmetric mode of fission was discussed. The different types of mass-yield distributions between ²³²Th(n, f) and ²³⁸U(n, f) reactions were explained from different types of the potential energy between the two fissioning systems. The role of excitation energy was also investigated.