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

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, $B(E2;0^{+}\to 2^{+})$. 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.

Comments: accepted PRL