Alleviating the inconsistencies in modelling decay of fissile compound nuclei

TL;DR

This paper enhances the modeling of fissile compound nucleus decay by incorporating key physical effects and systematically comparing with extensive experimental data, reducing previous inconsistencies in predictions.

Contribution

It introduces a comprehensive model including shell effects, dissipation, and collective enhancements, with minimal parameter tuning, to better match experimental decay data across a wide mass range.

Findings

Reasonable fits to evaporation residue and fission cross sections.

Underestimation of pre-scission neutron multiplicities beyond ACN~200.

Qualitative agreement in proton and alpha-particle multiplicities.

Abstract

This work attempts to overcome the existing inconsistencies in modelling decay of fissile nucleus by inclusion of important physical effects in the model and through a systematic analysis of a large set of data over a wide range of CN mass (ACN). The model includes shell effect in the level density (LD) parameter, shell correction in the fission barrier, effect of the orientation degree of freedom of the CN spin (Kor), collective enhancement of level density (CELD) and dissipation in fission. Input parameters are not tuned to reproduce observables from specific reaction(s) and the reduced dissipation coefficient is treated as the only adjustable parameter. Calculated evaporation residue (ER) cross sections, fission cross sections and particle, i.e. neutron, proton and alpha-particle, multiplicities are compared with data covering ACN = 156-248. The model produces reasonable fits to ER and fission excitation functions for all the reactions considered in this work. Pre-scission neutron multiplicities are underestimated by the calculation beyond ACN~200. An increasingly higher value of pre-saddle dissipation strength is required to reproduce the data with increasing ACN. Proton and alpha-particle multiplicities, measured in coincidence with both ERs and fission fragments, are in qualitative agreement with model predictions. The present work mitigates the existing inconsistencies in modelling statistical decay of the fissile CN to a large extent.