Interplay between quantum shells and orientation in quasi-fission

TL;DR

This study investigates how the orientation of deformed nuclei and quantum shell effects influence the quasi-fission process, revealing that specific orientations favor either quasi-fission or fusion in heavy nuclear collisions.

Contribution

It combines experimental fragment mass-angle correlation measurements with microscopic quantum calculations to uncover the interplay between nuclear orientation and shell effects in quasi-fission.

Findings

Tip collisions produce fragments with magic Z=82

Side collisions are more likely to lead to fusion

Quantum shell effects significantly influence quasi-fission outcomes

Abstract

The quasi-fission mechanism hinders fusion in heavy systems through breakup within zeptoseconds into two fragments with partial mass equilibration. Its dependence on the structure of both the collision partners and the final fragments is a key question. Our original approach is to combine an experimental measurement of the fragments' mass-angle correlations in $^{40}$Ca$+^{238}$U with microscopic quantum calculations. We demonstrate an unexpected interplay between the orientation of the prolate deformed $^{238}$U with quantum shell effects in the fragments. In particular, calculations show that only collisions with the tip of $^{238}$U produce quasi-fission fragments in the magic $Z=82$ region, whilst collisions with the side are the only one which may result in fusion.