Dynamical approach to heavy-ion induced fission using actinide target nuclei at energies around the Coulomb barrier

TL;DR

This paper presents a dynamical model combining coupled-channels and fluctuation-dissipation approaches to analyze heavy-ion fusion and fission reactions involving actinide nuclei near the Coulomb barrier, explaining experimental fragment mass distributions.

Contribution

The study introduces a novel combined model that accounts for nuclear orientation and dynamical evolution, providing new insights into quasi-fission processes in actinide-induced reactions.

Findings

Different quasi-fission time scales for $^{30}$Si and $^{36}$S projectiles.

Deformation differences at scission influence mass asymmetry.

Model successfully reproduces experimental mass distributions.

Abstract

In order to describe heavy-ion fusion reactions around the Coulomb barrier with an actinide target nucleus, we propose a model which combines the coupled-channels approach and a fluctuation-dissipation model for dynamical calculations. This model takes into account couplings to the collective states of the interacting nuclei in the penetration of the Coulomb barrier and the subsequent dynamical evolution of a nuclear shape from the contact configuration. In the fluctuation-dissipation model with a Langevin equation, the effect of nuclear orientation at the initial impact on the prolately deformed target nucleus is considered. Fusion-fission, quasi-fission and deep quasi-fission are separated as different Langevin trajectories on the potential energy surface. Using this model, we analyze the experimental data for the mass distribution of fission fragments (MDFF) in the reactions of $^{34,36}$S+$^{238}$U and $^{30}$Si+$^{238}$U at several incident energies around the Coulomb barrier. We find that the time scale in the quasi-fission as well as the deformation of fission fragments at the scission point are different between the $^{30}$Si+$^{238}$U and $^{36}$S+$^{238}$U systems, causing different mass asymmetries of the quasi-fission.