Sub-barrier fusion enhancement due to positive Q-value four-neutron transfer

TL;DR

This paper systematically investigates how positive Q-value four-neutron transfer enhances sub-barrier fusion cross sections, showing that neutron transfer effects reduce barriers and improve predictive accuracy in fusion models.

Contribution

It introduces an empirical method incorporating PQ4NT effects to better predict sub-barrier fusion cross sections, highlighting the role of neutron transfer in fusion enhancement.

Findings

PQ4NT reduces barrier heights and enhances sub-barrier capture cross sections.

Inclusion of PQ4NT effects decreases prediction deviations by 20%.

Larger neutron pickup probabilities are observed in reactions with positive Q-value four-neutron transfer.

Abstract

The influence of positive $Q$-value four-neutron transfer (PQ4NT) effects on the sub-barrier capture cross sections is systematically investigated using the empirical barrier distribution (EBD2) method. For 13 fusion reactions with $Q_{4n}>0$, sustained neutron-pair transfer is found to reduce barrier heights and enhance capture cross sections at sub-barrier energies. In contrast, reactions such as $^{18}$O+$^{58}$Ni, which have $Q_{2n}>0$ but $Q_{4n}<0$, exhibit no enhancement due to the stalling of subsequent neutron-pair transfer after the initial 2n transfer. By incorporating PQ4NT effects into EBD2 for systems with $Q_{4n}>0$, the average deviation between predicted and experimental capture cross sections (113 datasets) is significantly reduced by $20\%$. Additionally, comparing with the systems induced by $^{48}$Ca ($Q_{4n}<0$), much larger neutron pickup probabilities are observed in the quasi-elastic scattering of $^{40}$Ca-induced reactions ($Q_{4n}>0$) from the time-dependent Hartree-Fock (TDHF) calculations.