Hindrance of ^{16}O+^{208}Pb fusion at extreme sub-barrier energies

TL;DR

This study investigates the hindrance of ^{16}O+^{208}Pb fusion at deep sub-barrier energies, demonstrating that a corrected M3Y potential with enhanced transfer coupling explains the observed fusion suppression.

Contribution

The paper introduces a modified M3Y potential with a repulsive term and emphasizes the importance of transfer channel couplings in modeling fusion hindrance.

Findings

Hindrance explained by M3Y+repulsion potential

Transfer coupling strength increased by 25% improves data fit

Fusion data at high energies better reproduced with M3Y+repulsion and imaginary potential

Abstract

We analyze the fusion data for $^{16}$O+$^{208}$Pb using coupled-channels calculations. We include couplings to the low-lying surface excitations of the projectile and target and study the effect of the ($^{16}$O,$^{17}$O) one-neutron pickup. The hindrance of the fusion data that is observed at energies far below the Coulomb barrier cannot be explained by a conventional ion-ion potential and defining the fusion in terms of ingoing-wave boundary conditions (IWBC). We show that the hindrance can be explained fairly well by applying the M3Y double-folding potential which has been corrected with a calibrated, repulsive term that simulates the effect of nuclear incompressibility. We show that the coupling to one-neutron transfer channels plays a crucial role in improving the fit to the data. The best fit is achieved by increasing the transfer strength by 25% relative to the strength that is required to reproduce the one-neutron transfer data. The larger strength is not unrealistic because the calculated inelastic plus transfer cross section is in good agreement with the measured quasielastic cross section. We finally discuss the problem of reproducing the fusion data at energies far above the Coulomb barrier. Here we do not account for the data when we apply the IWBC but the discrepancy is essentially eliminated by applying the M3Y+repulsion potential and a weak, short-ranged imaginary potential.