Sub-barrier fusion of 32S+90,96Zr: semi-classical coupled-channels approach

TL;DR

This study investigates sub-barrier fusion of 32S with Zr isotopes, showing that neutron transfer channels significantly influence fusion enhancement, with semi-classical coupled-channels models partially explaining experimental data.

Contribution

It introduces a simple model incorporating neutron transfer effects to better explain sub-barrier fusion cross sections for 32S+96Zr.

Findings

Sub-barrier fusion cross sections are larger for 32S+96Zr than for 32S+90Zr.

Coupled-channels calculations with two-phonon excitations explain 32S+90Zr data but not 32S+96Zr.

Neutron transfer channels with positive Q-values are important for understanding fusion enhancement.

Abstract

The fusion excitation functions have been measured with rather good accuracy for 32S+90Zr and 32S+96Zr near and below the Coulomb barrier. The sub-barrier cross sections for 32S+96Zr are much larger compared with 32S+90Zr. Semi-classical coupled-channels calculations including two-phonon excitations are capable to describe sub-barrier enhancement only for 32S+90Zr. The remaining disagreement for 32S+96Zr comes from the positive Q-value intermediate neutron transfers in this system. The comparison with 40Ca+96Zr suggests that couplings to the positive Q-value neutron transfer channels may play a role in the sub-barrier fusion enhancement. A rather simple model calculation taking neutron transfers into account is proposed to overcome the discrepancies of 32S+96Zr.