Mass distributions in monoenergetic-neutron-induced fission ofTh232

Physical Review C1980Vol. 22(1), pp. 152–159

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L.E. Glendenin, J.E. Gindler, I. Ahmad, Deborah J. Henderson, J.W. Meadows

Abstract

Fission product yields for 38 masses were determined for the fission of $^{232}\mathrm{Th}$ with essentially monoenergetic neutrons of 2.0, 3.0, 4.0, 5.9, 6.4, 6.9, 7.6, and 8.0 MeV. Fission product activities were measured by Ge(Li) $\ensuremath{\gamma}$-ray spectrometry of irradiated $^{232}\mathrm{Th}$ foils and by chemical separation of the fission product elements followed by $\ensuremath{\beta}$ counting. The mass yield data for $^{232}\mathrm{Th}(n, f)$ show a sensitive increase of fission yields in the near-symmetric mass region (valley) with increasing incident neutron energy ${E}_{n}$ and a pronounced dip in yield at the onset of second-chance fission just above the neutron binding energy (at \ensuremath{\sim} 6 MeV) where the excitation energy is lowered by competition with neutron evaporation prior to fission. The effect of second-chance fission is also seen in the yields of asymmetric peak products. A distinct third peak is observed at symmetry in the valley of the mass distribution, and enhanced yields are observed in the asymmetric peaks at masses associated with even $Z$ (proton pairing effect). The fission yields of $^{232}\mathrm{Th}(n, f)$ are compared with those of $^{238}\mathrm{U}(n, f)$ and $^{232}\mathrm{Th}(n, f)$.NUCLEAR REACTIONS, FISSION $^{232}\mathrm{Th}(n, f)$ ${E}_{n}=2.0, 3.0, 4.0, 5.9, 6.4, 6.9, 7.6, \mathrm{and} 8.0$ MeV; measured mass yields.

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Abstract

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