Asymmetric to symmetric fission transition in 180 Hg * : Effects of excitation energy and angular momentum

The transition from asymmetric to symmetric fission in the 180Hg* nucleus, formed in the 36 Ar + 144 Sm reaction, as a function of excitation energy and angular momentum has been investigated. Using the dynamical cluster-decay model, the fragmentation potential, preformation probability, and cross-sections have been analyzed for asymmetric (80, 100) and symmetric (90, 90) mass fission channels, considering both the optimum hot and cold orientations of the fragments, as well as the case of symmetric mass fission channel with fragments assumed to be spherical. The calculations reveal that deformed proton and neutron shell closures favour asymmetric fission at lower excitation energies, while a transition to symmetric fission occurs near 40 MeV of excitation energy due to changes in fragment deformation with excitation energy. These findings are consistent with the available experimental observations and theoretical predictions. The transition also occurs with increasing angular momentum, but only for optimum hot orientations.