Fission modes of mercury isotopes

TL;DR

This study uses advanced nuclear density functional theory to analyze fission modes in mercury isotopes 180 Hg and 198 Hg, revealing the influence of shell effects on fragment mass asymmetry and predicting a transition towards more symmetric fission in heavier isotopes.

Contribution

It provides a detailed theoretical analysis of fission pathways in mercury isotopes using self-consistent density functional theory, highlighting the role of shell effects and predicting fission fragment distributions.

Findings

Asymmetric fission valleys are identified in both isotopes.

A transition from asymmetric to more symmetric fission is predicted from 180 Hg to 198 Hg.

Most probable fission splits are identified for both isotopes.

Abstract

Background: Recent experiments on beta-delayed fission in the mercury-lead region and the discovery of asym- metric fission in 180 Hg [1] have stimulated theoretical interest in the mechanism of fission in heavy nuclei. Purpose: We study fission modes and fusion valleys in 180 Hg and 198 Hg to reveal the role of shell effects in pre-scission region and explain the experimentally observed fragment mass asymmetry and its variation with A. Methods: We use the self-consistent nuclear density functional theory employing Skyrme and Gogny energy density functionals. Results: The potential energy surfaces in multi-dimensional space of collective coordinates, including elongation, triaxiality, reflection-asymmetry, and necking, are calculated for 180 Hg and 198 Hg. The asymmetric fission valleys - well separated from fusion valleys associated with nearly spherical fragments - are found in in both cases. The density distributions at scission configurations are studied and related to the experimentally observed mass splits. Conclusions: The energy density functionals SkM\ast and D1S give a very consistent description of the fission process in 180 Hg and 198 Hg. We predict a transition from asymmetric fission in 180 Hg towards more symmetric distribution of fission fragments in 198 Hg. For 180 Hg, both models yield 100 Ru/80 Kr as the most probable split. For 198 Hg, the most likely split is 108 Ru/90 Kr in HFB-D1S and 110 Ru/88 Kr in HFB-SkM\ast.