New signature of non-equilibrium fission from pre-scission alpha-particle emission

The pre-scission alpha-particle multiplicity (alpha(pre)), measured in O-16 (96 MeV) + Th-232 reaction, is observed to be significantly lower than the global trend reported earlier. Statistical model calculations also show a much shorter fission-time to reproduce the experimental alpha(pre). By assimilating the previous measurements, it is observed that the alpha(pre) makes a changeover from high to a very low value while crossing the Businaro Gallone point in mass asymmetry in the entrance channels in heavy-ion induced fission of Th-232. Similar discontinuous behavior with respect to the entrance channel mass asymmetry was observed earlier in fission fragment angular anisotropy data, and it was attributed to "pre-equilibrium fission". The present results on alpha(pre) provide compelling evidence for an admixture of non-equilibrium fission which depends on the entrance channel dynamics. (C) 2022 The Authors. Published by Elsevier B.V.