Oscillations above the barrier in the fusion of 28Si + 28Si

TL;DR

This study measures fusion cross sections of 28Si + 28Si above the barrier, observes regular oscillations, and demonstrates that coupled-channel models with a shallow potential can reproduce these phenomena, highlighting the role of channel couplings.

Contribution

It is the first to reproduce oscillations and sub-barrier cross section trends within the same theoretical framework using a shallow M3Y+repulsion potential.

Findings

Regular oscillations observed in fusion cross sections.

Coupled-channel model reproduces oscillations and sub-barrier trends.

Channel couplings significantly influence oscillation appearance.

Abstract

Fusion cross sections of 28Si + 28Si have been measured in a range above the barrier with a very small energy step (DeltaElab = 0.5 MeV). Regular oscillations have been observed, best evidenced in the first derivative of the energy-weighted excitation function. For the first time, quite different behaviors (the appearance of oscillations and the trend of sub-barrier cross sections) have been reproduced within the same theoretical frame, i.e., the coupled-channel model using the shallow M3Y+repulsion potential. The calculations suggest that channel couplings play an important role in the appearance of the oscillations, and that the simple relation between a peak in the derivative of the energy-weighted cross section and the height of a centrifugal barrier is lost, and so is the interpretation of the second derivative of the excitation function as a barrier distribution for this system, at energies above the Coulomb barrier.