Microscopic quasifission dynamics of the ${}^{54}\text{Cr}+{}^{243}\text{Am}$ reaction

TL;DR

This study uses microscopic simulations to analyze quasifission dynamics in the $^{54}$Cr+$^{243}$Am reaction, revealing how shell effects and collision geometry influence fragment formation and energy dependence, informing superheavy element synthesis.

Contribution

It provides a detailed microscopic analysis of quasifission mechanisms in a key reaction for superheavy element creation, emphasizing the roles of orientation and energy.

Findings

Shell effects drive fragment formation towards specific nuclear closures.

Interaction times are shorter for shell-stabilized, rigid fragments.

Energy dependence shows a transition from octupole to shell-driven regimes.

Abstract

Synthesizing superheavy elements (SHEs) like $Z=119$ is severely hindered by the dominant quasifission (QF) channel, which prevents compound nucleus formation. Understanding QF dynamics is thus essential for future experiments. We investigate the QF mechanisms in the $^{54}\text{Cr}+^{243}\text{Am}$ reaction, a key candidate system for SHE 119, emphasizing the roles of projectile orientation and incident energy. Calculations are performed using the fully microscopic time-dependent Hartree-Fock theory based on the Skyrme energy density functional. We conduct systematic simulations covering a broad set of initial orientations of the deformed $^{54}\text{Cr}$ and $^{243}\text{Am}$ nuclei, alongside a finely spaced range of incident energies extending from below to well above the Coulomb barrier. Our fixed-energy results show that projectile side collisions are governed by shell effects driving heavy and light fragments toward spherical $Z=82$ and deformed $N=52\text{--}56$ closures, respectively, whereas tip collisions exhibit weaker shell influence. These shell-dominated reactions are characterized by shorter interaction times, attributed to the enhanced rigidity of shell-stabilized fragments accelerating neck rupture. The energy dependence reveals a complex evolution where the system transitions from an octupole-stabilized regime ($Z \approx 88$) to a spherical shell-driven regime, with specific energy windows exhibiting suppressed shell influence. Our study demonstrates that the manifestation of shell effects in QF is a dynamical outcome sensitively dependent on both collision geometry and incident energy. Systematically probing this energy sensitivity is crucial for identifying optimal incident energies where the QF process exhibits suppressed shell influence, thereby potentially enhancing the fusion probability and improving the prospects for synthesizing new SHEs.