A Universal Damping Mechanism of Quantum Vibrations in Deep Sub-Barrier Fusion Reactions

TL;DR

This paper reveals a universal damping mechanism of quantum vibrations during deep sub-barrier fusion reactions, demonstrated through calculations of transition strengths in a heavy-mass asymmetric nuclear system, linking quantum damping to fusion hindrance.

Contribution

It applies the random-phase approximation to a heavy asymmetric system to show quantum vibration damping near the touching point, a novel approach in this context.

Findings

Quantum octupole vibrations are damped near the touching point.

Damping correlates with fusion hindrance phenomena.

Damping appears universal in deep sub-barrier fusion reactions.

Abstract

We demonstrate the damping of quantum octupole vibrations near the touching point when two colliding nuclei approach each other in the mass-asymmetric $^{208}$Pb + $^{16}$O system, for which the strong fusion hindrance was clearly observed. We, for the first time, apply the random-phase approximation method to the heavy-mass asymmetric di-nuclear system to calculate the transition strength $B$(E3) as a function of the center-of-mass distance. The obtained $B$(E3) strengths are substantially damped near the touching point, because the single-particle wave functions of the two nuclei strongly mix with each other and a neck is formed. The energy-weighted sums of $B$(E3) are also strongly correlated with the damping factor which is phenomenologically introduced in the standard coupled-channel calculations to reproduce the fusion hindrance. This strongly indicates that the damping of the quantum vibrations universally occurs in the deep sub-barrier fusion reactions.