Shape changes in the mirror nuclei $^{70}$Kr and $^{70}$Se

TL;DR

This study investigates unexpected shape changes in mirror nuclei $^{70}$Kr and $^{70}$Se, revealing a novel violation of isospin symmetry in electromagnetic transition matrix elements that challenges current nuclear structure theories.

Contribution

It provides the first experimental evidence of isospin symmetry violation at the transition matrix element level in mirror nuclei, suggesting shape changes contrary to existing models.

Findings

Observed a 3σ deviation from expected linearity in electromagnetic matrix elements.

First detection of isospin symmetry violation at this level in mirror nuclei.

Heuristic explanation proposes shape change as the cause of the anomaly.

Abstract

We studied the proton-rich $T_z=-1$ nucleus $^{70}$Kr through inelastic scattering at intermediate energies in order to extract the reduced transition probability, $B(E2;\;0^+ \rightarrow 2^+)$. Comparison with the other members of the $A=70$ isospin triplet, $^{70}$Br and $^{70}$Se, studied in the same experiment, shows a $3\sigma$ deviation from the expected linearity of the electromagnetic matrix elements as a function of $T_z$. At present, no established nuclear structure theory can describe this observed deviation quantitatively. This is the first violation of isospin symmetry at this level observed in the transition matrix elements. A heuristic approach may explain the anomaly by a shape change between the mirror nuclei $^{70}$Kr and $^{70}$Se contrary to the model predictions.