Exploring fission mode transitions in fermium isotopes

Fission mode transitions have been explored by analyzing the mass and charge yield distributions and the average total kinetic energy of the fission fragments in the spontaneous fission of fermium isotopes using the quantum mechanical fragmentation theory, considering fragments in their optimum hot-compact and cold-elongated orientations. The fragmentation potential used for mass yield calculations includes a nuclear shape-dependent mass excess term, with its bulk and neutron–proton asymmetry coefficients tuned to match the ground state mass excess data AME2020 or, where unavailable, adjusted to match FRDM (2012) data. The mass and charge distributions of the yield, in the case of the optimum hot orientations of the fragments, are found to be asymmetric for lighter isotopes ([Formula: see text]Fm) and symmetric for [Formula: see text]Fm. However, in the case of the optimum cold orientations, the distributions are asymmetric for all Fm isotopes considered in this study, except for [Formula: see text]Fm, where the symmetric fission mode dominates. This trend is further supported by the calculated average total kinetic energy of the fission fragments, which provides a clear picture of the dominant symmetric and asymmetric fission modes of Fm isotopes. These fission modes are closely linked to various spherical and/or deformed shell closures and large deformations. The mass and charge distributions of the calculated fission yields, their correlation with shell effects, the transition from asymmetric to symmetric fission with increasing mass number, the average total kinetic energy of the fission fragments, and the mass yield distributions percentage all align well with available experimental and theoretical results in the literature.