Recent experimental results in sub- and near-barrier heavy ion fusion reactions

TL;DR

This paper reviews recent experimental and theoretical advances in sub- and near-barrier heavy-ion fusion reactions, focusing on transfer channels, fusion hindrance, and implications for astrophysics, highlighting progress with radioactive beams and coupled-channels models.

Contribution

It provides a comprehensive review of experimental results and theoretical interpretations, especially on fusion hindrance and the role of transfer channels in heavy-ion fusion.

Findings

Transfer channels significantly influence fusion cross sections.

Fusion hindrance occurs at deep sub-barrier energies and may be linked to the Pauli exclusion principle.

Recent radioactive beam experiments offer new insights into fusion dynamics.

Abstract

Recent advances obtained in the field of near and sub-barrier heavy-ion fusion reactions are reviewed. Emphasis is given to the results obtained in the last decade, and focus will be mainly on the experimental work performed concerning the influence of transfer channels on fusion cross sections and the hindrance phenomenon far below the barrier. Indeed, early data of sub-barrier fusion taught us that cross sections may strongly depend on the low-energy collective modes of the colliding nuclei, and, possibly, on couplings to transfer channels. The coupled-channels (CC) model has been quite successful in the interpretation of the experimental evidences. Fusion barrier distributions often yield the fingerprint of the relevant coupled channels. Recent results obtained by using radioactive beams are reported. At deep sub-barrier energies, the slope of the excitation function in a semi-logarithmic plot keeps increasing in many cases and standard CC calculations over-predict the cross sections. This was named a hindrance phenomenon, and its physical origin is still a matter of debate. Recent theoretical developments suggest that this effect, at least partially, may be a consequence of the Pauli exclusion principle. The hindrance may have far-reaching consequences in astrophysics where fusion of light systems determines stellar evolution during the carbon and oxygen burning stages, and yields important information for exotic reactions that take place in the inner crust of accreting neutron stars.