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

The pre-scission α-particle multiplicity (αpre), measured in 16O (96 MeV) + 232Th 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 αpre. By assimilating the previous measurements, it is observed that the αpre 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 232Th. 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 αpre provide compelling evidence for an admixture of non-equilibrium fission which depends on the entrance channel dynamics.