Dissipative dynamics in quasi-fission

TL;DR

This study uses time-dependent density functional theory to analyze quasi-fission in heavy-ion collisions, revealing how calcium isotope differences influence the likelihood of forming superheavy elements.

Contribution

First microscopic calculation of excitation energy distribution in quasi-fission, linking initial neutron-proton asymmetry to reaction outcomes.

Findings

Quasi-fission is reduced with $^{48}$Ca projectiles.

$^{40}$Ca reactions reach quasi-thermal equilibrium.

Initial neutron-proton asymmetry affects energy sharing.

Abstract

Quasi-fission is the primary reaction mechanism that prevents the formation of superheavy elements in heavy-ion fusion experiments. Employing the time-dependent density functional theory approach we study quasi-fission in the systems $^{40,48}$Ca+$^{238}$U. Results show that for $^{48}$Ca projectiles the quasi-fission is substantially reduced in comparison to the $^{40}$Ca case. This partly explains the success of superheavy element formation with $^{48}$Ca beams. For the first time, we also calculate the repartition of excitation energies of the two fragments in a dynamic microscopic theory. The system is found in quasi-thermal equilibrium only for reactions with $^{40}$Ca. The differences between both systems are interpreted in terms of initial neutron to proton asymmetry of the colliding partners.