Semiclassical origin of asymmetric nuclear fission: nascent-fragment shell effect in periodic-orbit theory

Abstract

The origin of the asymmetry in the fragment mass distribution of low-energy nuclear fission is considered from the semiclassical point of view. Using the semiclassical periodic-orbit theory, one can define and quantify the shell effect associated with spatially localized nascent-fragment (prefragment) part of the potential. We investigate the roles of prefragments in the deformed shell effect using a simple cavity potential model, but with realistic shape degrees of freedom for describing the fission processes. The results suggest that the prefragment magic numbers play essential roles in determining the shapes at the fission saddles, which should have a close relation to the fragment mass distribution.

Octupole deformation of nuclei near the spherical closed-shell configurations

“…The idea of this work has been brought about by our recent works, in which we discussed the prefragment shell effect of the nuclei in fission [8][9][10]. In the fission process, nucleus is elongated and a neck is formed which gradually separate the system into two subsystems called prefragments.…”

Efficient method for estimation of fission fragment yields of r-process nuclei

“…This early development of the prefragments is a manifestation of the freeze-out of single particle energies along the fission path [28][29][30][31] as the system tries to maintain its microscopic configuration to avoid level crossings. The suggestion that the prefragment particle numbers play essential roles in determining the fission fragment distribution can be traced back to strong shell effects in prefragments in the semiclassical periodic-orbit theory [32,33].…”