Dynamical effects in fusion with exotic nuclei

TL;DR

This study uses microscopic theories to explore how exotic nuclear structures, like neutron skins and charge transfer, influence fusion reactions near the barrier, revealing that dynamical effects and transfer processes can hinder fusion despite static expectations.

Contribution

It provides a detailed microscopic analysis of fusion involving exotic calcium isotopes, highlighting the roles of dynamical effects and charge transfer, which were not fully understood before.

Findings

Neutron skin development lowers static fusion barriers.

Dynamical effects hinder fusion in neutron-rich isotopes.

Charge transfer processes can suppress fusion by increasing Coulomb repulsion.

Abstract

[Background] Reactions with stable beams have demonstrated a strong interplay between nuclear structure and fusion. Exotic beam facilities open new perspectives to understand the impact of neutron skin, large isospin, and weak binding energies on fusion. Microscopic theories of fusion are required to guide future experiments. [Purpose] To investigate new effects of exotic structures and dynamics in near-barrier fusion with exotic nuclei. [Method] Microscopic approaches based on the Hartree-Fock (HF) mean-field theory are used for studying fusion barriers in $^{40-54}$Ca+$^{116}$Sn reactions for even isotopes. Bare potential barriers are obtained assuming frozen HF ground-state densities. Dynamical effects on the barrier are accounted for in time-dependent Hartree-Fock (TDHF) calculations of the collisions. Vibrational couplings are studied in the coupled-channel framework and near-barrier nucleon transfer is investigated with TDHF calculations. [Results] The development of a neutron skin in exotic calcium isotopes strongly lowers the bare potential barrier. However, this static effect is not apparent when dynamical effects are included. On the contrary, a fusion hindrance is observed in TDHF calculations with the most neutron rich calcium isotopes which cannot be explained by vibrational couplings. Transfer reactions are also important in these systems due to charge equilibration processes. [Conclusions] Despite its impact on the bare potential, the neutron skin is not seen as playing an important role in the fusion dynamics. However, the charge transfer with exotic projectiles could lead to an increase of the Coulomb repulsion between the fragments, suppressing fusion. The effect of transfer and dissipative mechanisms on fusion with exotic nuclei deserve further studies.