Influence of complete energy sorting on the characteristics of the odd-even effect in fission-fragment element distributions

TL;DR

This paper models how energy sorting influences the odd-even effect in fission fragment distributions, highlighting the role of pairing correlations and entropy in shaping nuclear fission outcomes.

Contribution

It introduces a statistical mechanics-based model that explains the odd-even effect considering energy sorting and pairing correlations in fission fragments.

Findings

The odd-even effect varies with fissioning nucleus mass and asymmetry.

Energy sorting causes unpaired nucleons to favor the heavy fragment.

The model links the odd-even effect to the energy-sorting process in fission.

Abstract

The characteristics of the odd-even effect in fission-fragment Z distributions are compared to a model based on statistical mechanics. Special care is taken for using a consistent description for the influence of pairing correlations on the nuclear level density. The variation of the odd-even effect with the mass of the fissioning nucleus and with fission asymmetry is explained by the important statistical weight of configurations where the light nascent fission fragment populates the lowest energy state of an even-even nucleus. This implies that entropy drives excitation energy and unpaired nucleons predominantly to the heavy fragment. Therefore, within our model, the odd-even effect appears as an additional signature of the recently discovered energy-sorting process in nuclear fission.