Evidence for competing bi-faceted compound nucleus fission modes in 232Th(α,f) reaction

Abstract

Relative isotopic yield distributions have been extracted for nine correlated fission fragment pairs following a detailed analysis of prompt γ−γ coincidence events from 232Th(α,f) reaction at Elab = 30 MeV. Simultaneously, the charge and mass yield distributions of the even-even fission fragments have been obtained from the measured relative isotopic yields. The onset of a triple-hump structure is seen in the extracted charge as well as mass yield distributions of the fragments. The results are consistent with the two-mode fission hypothesis of compound nucleus and in good agreement with the theoretical predictions, based on relevant fission models. The detailed results provide experimental evidence for the presence of two distinct compound nucleus fission modes, where the asymmetric and symmetric fission components are 83% and 17%, respectively. An average neutron multiplicity value of 4.60 ± 0.09 has been obtained, and the extracted neutron multiplicity distribution pattern corroborates the observed features of the multifaceted fission modes. Comparing the measured yield distributions following the 232Th(α,f) surrogate reaction, which produces 236U⁎ at an excitation energy of 21.5 MeV, with that of the direct reaction of 14 MeV neutron induced fission of 235U, an increase of about 11% in the yield of the symmetric component has been observed.