Survival of Pairing Correlations and Shell Effects at Scission in Finite-Temperature Nuclear Fission: Implications for Odd-Even Staggering

TL;DR

This study examines how pairing and shell effects evolve with temperature during nuclear fission, highlighting their deformation dependencies and implications for odd-even staggering in fragment yields.

Contribution

It provides a detailed finite-temperature analysis of pairing and shell effects near scission, emphasizing their separate deformation and temperature dependencies.

Findings

Pairing remains deformation-dependent at scission and varies with pairing strength prescriptions.

Shell correction is significant at low temperature and diminishes with increasing excitation energy.

Results support pairing correlations as a cause of odd-even staggering in fragment charge yields.

Abstract

We investigate the finite-temperature evolution of microscopic free-energy corrections in nuclear fission, focusing on pairing and shell effects near scission. The analysis is based on a finite-temperature BCS treatment combined with the Strutinsky method and is performed for representative deformation points along the fission path. Both pairing and shell contributions exhibit regular thermal attenuation, but their deformation dependencies differ substantially. In particular, pairing remains strongly deformation-dependent in the scission region, and its free-energy contribution differs markedly between the constant and surface-dependent pairing-strength prescriptions. The shell correction near scission is also significant at low temperature and is progressively suppressed with increasing excitation energy. These results support the interpretation of odd-even staggering in fragment charge yields as a manifestation of pairing correlations surviving into the strongly deformed pre-scission configuration. They also show that pairing and shell effects should be treated separately in finite-temperature dynamical calculations, with distinct deformation- and temperature-dependent attenuation laws.