Exploring asymmetric fission in 180Hg⁎ compound nucleus using dynamical cluster-decay model

Abstract

The observed asymmetric fission of the ¹⁸⁰Hg^⁎ compound nucleus challenges conventional expectations of symmetric fission, which are attributed to the presence of shell closures at Z=40 (semi-magic) and N=50 (magic). To comprehend this novel phenomenon, the dynamical cluster-decay model has been employed. For the first time, this model incorporates the bulk and neutron-proton asymmetry coefficients of the nuclear shape-dependent mass excess formula which are tuned recently to the ground state mass excess data of AME2020 and/or FRDM(2012) along with the temperature dependence for the nuclear shape and the surface energy coefficient of the nuclear proximity potential. The calculations have considered nuclear shapes as both spherical and deformed (quadrupole), with and without temperature dependence for the quadrupole deformation. A new minimum appears in the symmetric mass region of the fragmentation potential for masses (80, 100), when the fragments are deformed and optimally oriented, at an energy lower than that obtained for masses (90, 90) where the fragments are assumed to be spherical or nearly spherical at higher temperatures. This new minimum seems equivalent to the appearance of a new shell gap with deformation and is responsible for the asymmetric fission of ¹⁸⁰Hg^⁎. The most probable fission channel and the transition from asymmetric to symmetric mass distribution at higher excitation energies are consistent with experiments for the current temperature dependence assigned to the quadrupole deformation parameter.