Measurement of fission product yields in the spectrum averaged neutron-induced fission of 232Th

Abstract

Cumulative yields of various fission products within the mass range of 77–151 have been measured in the spectrum averaged 4.93 and 8.31 MeV neutron induced fission of ²³²Th by using an off-line γ-ray spectrometric technique. The neutron beams were obtained from the ⁷Li(p,n) reaction with the proton energies of 7 and 15 MeV. Since the cumulative yield is not for the end mass fission product of an isobaric chain, charge distribution correction was applied to obtain the mass chain yield. From the mass chain yield data, the peak-to-valley (P/V) ratio, the average value of light mass (<A_L>), heavy mass (<A_H>) and the average number of neutrons (<ν>) were obtained. The data from the present work and literature in the ²³²Th(n, f) reaction at various neutron energies were compared with the similar data in the ²³²Th(γ, f) reaction. In both the reactions, it was found that the mass yield distribution are asymmetric with triple humps. The fission product yields for A = 133–134, A = 138–140, and A = 143–144 and their complementary products are higher than the yields of other fission products, which is the role of nuclear structure effect. The yields of symmetric products increase with excitation energy, which causes the decrease of peak-to-valley (P/V) ratio. The <A_L>, <A_H> and <ν> values at comparable excitation energy show a similar trend with a surprising differences in between the ²³²Th(n, f) and ²³²Th(γ, f) reactions.