Evidence of a new shell closed nucleus governing slow quasi-fission

TL;DR

This paper presents evidence that a new shell-closed nucleus influences slow quasi-fission, showing consistent mass distribution features across reactions, with implications for nuclear structure and super-heavy element synthesis.

Contribution

It provides the first experimental evidence of a shell effect involving a new doubly magic nucleus in slow quasi-fission processes.

Findings

Mass distributions are double peaked with fixed centroid positions.

Quasi-fission yield decreases with increasing projectile energy.

The lighter fragment peak is around A ~ 96, indicating shell effects.

Abstract

Mass distributions of fission fragments arising from the slow quasi-fission process have been derived by comparing the measured distributions with the theoretical distributions based on compound nuclear fission model for several reactions. The mass-distributions corresponding to quasi-fission events for all the systems show the following common features: (1) they are double peaked with fixed peak-centroids and nearly same width at different incident energies, (2) the yield of quasi-fission events decreases with the increasing projectile energy, and (3) peak corresponding to lighter fragment is observed at A $\sim$ 96 for all the systems, whereas the peak of heavier fragment increases linearly with the mass of the di-nuclear system. All the above observations are quite similar to the ones observed in well known asymmetric fission of actinides, thus providing clear evidences of shell effect in slow quasi-fission where the lighter fragment is possibly nuclei around $^{96}$Zr, a new doubly magic nucleus. This finding has great implications in the study of nuclear reactions, structure and particularly in super-heavy element synthesis where quasi-fission is synonymous.