Systematic study of prescission neutron multiplicity: Revealing the role of entrance channel magicity

The prescission neutron multiplicities (vpre) are studied for a systematic understanding of the influence of entrance-channel shell closure in fusion-fission dynamics. The existing vpre data are analyzed for reactions with a wide variety of target and projectile combinations. For completeness, the measured vpre data for the fusion-fission reactions with the doubly closed shell 16O projectile on the targets having either proton (204,206Pb) or both proton and neutron (208Pb) shell closure is reanalyzed. Although the measured vpre for 224Th disagree with the available data reported by Rossner et al. (1992) [1], our results are found to be more consistent and follow a systematic trend as described in this letter. Theoretical analysis is performed within the standard statistical model framework, where dissipation strength is used as a tunable parameter. It is observed that irrespective of the compound nuclear excitation energy, the entrance channel magicity imparts an intriguing impact on the dissipation strength. A similar entrance channel effect in the evaporation residue cross-section is also demonstrated. In conclusion, the present analysis establishes an entanglement of the exit channel observables with the entrance channel shell closure. It contradicts the hypothesis of complete equilibrium in compound nuclear reactions.& COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.

Automated summary

This study investigates the influence of entrance-channel shell closure on fusion-fission dynamics by analyzing existing data for various target and projectile combinations. The reanalysis of measured data for fusion-fission reactions with 16O projectile and targets with proton or both proton and neutron shell closure shows consistent results, contradicting previous data. Theoretical analysis within the statistical model framework reveals that the magicity of the entrance channel significantly affects the dissipation strength, with similar effects observed in the evaporation residue cross-section. This analysis establishes a relationship between exit channel observables and entrance channel shell closure, challenging the hypothesis of complete equilibrium in compound nuclear reactions.