Statistical Model of Heavy-Ion Fusion-Fission Reactions

TL;DR

This paper presents a statistical model for heavy-ion fusion-fission reactions that accurately predicts fission lifetimes and challenges previous assumptions about nuclear viscosity's temperature dependence.

Contribution

It introduces a Kramers-modified statistical model incorporating collective motion, temperature effects, and orientation, providing improved fission lifetime estimates.

Findings

Fission data align with fully equilibrated system models.

Standard lifetime calculations are inadequate for excitation-energy dependence.

No evidence supports temperature-dependent nuclear viscosity.

Abstract

Cross-section and neutron-emission data from heavy-ion fusion-fission reactions are consistent with the fission of fully equilibrated systems with fission lifetime estimates obtained via a Kramers-modified statistical model which takes into account the collective motion of the system about the ground state, the temperature dependence of the location and height of fission transition points, and the orientation degree of freedom. If the standard techniques for calculating fission lifetimes are used, then the calculated excitation-energy dependence of fission lifetimes is incorrect. We see no evidence to suggest that the nuclear viscosity has a temperature dependence. The strong increase in the nuclear viscosity above a temperature of approximately 1.3 MeV deduced by others is an artifact generated by an inadequate fission model.