Coulomb Excitation of $^{80}$Sr and the limits of the $N = Z = 40$ island of deformation

TL;DR

This study uses Coulomb excitation to investigate the deformation of 0Sr, revealing it is not strongly prolate deformed, thus constraining the region of deformation around N=Z=40 to specific nuclei.

Contribution

It provides the first experimental measurement of 0Sr's quadrupole moment, challenging theoretical predictions of strong prolate deformation in this region.

Findings

0Sr is inconsistent with significant axial prolate deformation.

The region of strong deformation is limited to 6,78Sr and 8,80Zr.

The results refine the understanding of nuclear shape evolution near N=Z=40.

Abstract

The region of $N\approx Z\approx 40$ has long been associated with strongly deformed nuclear configurations. The presence of this strong deformation was recently confirmed through lifetime measurements in $N\approx Z$ Sr and Zr nuclei. Theoretically, however, these nuclei present a challenge due to the vast valence space required to incorporate all deformation driving interactions. Recent state-of-the-art predictions indicate a near axial prolate deformation for $N=Z$ and $N=Z+2$ nuclei between $N=Z=36$ and $N=Z=40$. In this work we investigate the shores of this island of deformation through a sub-barrier Coulomb excitation study of the $N=Z+4$ nucleus, \textsuperscript{80}Sr. Extracting a spectroscopic quadrupole moment of $Q_s(2^+_1) = 0.45^{+0.83}_{-0.88}$~eb, we find that \textsuperscript{80}Sr is inconsistent with significant axial prolate deformation. This indicates that the predicted region of strong prolate deformation around $N=Z=40$ is tightly constrained to the quartet of nuclei: \textsuperscript{76,78}Sr and \textsuperscript{78,80}Zr.