Multi-Nucleon Exchange in Quasi-Fission Reactions

TL;DR

This paper investigates nucleon exchange in quasi-fission reactions using the Stochastic Mean-Field approach, revealing diffusion processes that influence the formation of heavy elements in nuclear collisions.

Contribution

It introduces a microscopic diffusion model for nucleon exchange in quasi-fission, providing new insights into the process at energies below the fusion barrier.

Findings

Diffusion coefficients for nucleon exchange are derived from microscopic calculations.

Long interaction times lead to charge equilibration and drift toward symmetry.

Diffusion may facilitate formation of trans-uranium elements in collisions.

Abstract

Nucleon exchange mechanism is investigated in the central collisions of ${}^{40}$Ca + ${}^{238}$U and ${}^{48}$Ca + ${}^{238}$U systems near the quasi-fission regime in the framework of the Stochastic Mean-Field (SMF) approach. Sufficiently below the fusion barrier, di-nuclear structure in the collisions is maintained to a large extend. Consequently, it is possible to describe nucleon exchange as a diffusion process familiar from deep-inelastic collisions. Diffusion coefficients for proton and neutron exchange are determined from the microscopic basis of the SMF approach in the semi-classical framework. Calculations show that after a fast charge equilibration the system drifts toward symmetry over a very long interaction time. Large dispersions of proton and neutron distributions of the produced fragments indicate that diffusion mechanism may help to populate heavy trans-uranium elements near the quasi-fission regime in these collisions.