Isospin symmetry in the $T = 1, A = 62$ triplet

TL;DR

This study investigates isospin symmetry in the $T=1$, $A=62$ triplet by measuring excited states in $^{62}$Ga and $^{62}$Ge using relativistic radioactive ion beams and fusion-evaporation reactions, providing new experimental data and analysis.

Contribution

The paper provides the first identification of the first excited $T=1$, $J^ = 2^+$ states in $^{62}$Ga and $^{62}$Ge, and compares experimental results with shell-model calculations to analyze symmetry breaking.

Findings

Identified first excited $2^+$ states at 979 keV in $^{62}$Ga and 965 keV in $^{62}$Ge.

Observed states beyond the first $2^+$ state in $^{62}$Ge for the first time.

Confirmed the shrinkage of $p$-orbit radii when occupied by nucleons.

Abstract

Excited states in the $T_z = 0, -1$ nuclei $^{62}$Ga and $^{62}$Ge were populated in direct reactions of relativistic radioactive ion beams at the RIBF. Coincident \grays were measured with the DALI2$^+$ array and uniquely assigned to the $A=62$ isobars. In addition, $^{62}$Ge was also studied independently at JYFL-ACCLAB using the ${}^{24}$Mg(${}^{40}$Ca,$2n$)${}^{62}$Ge fusion-evaporation reaction. The first excited $T=1, J^\pi =2^+$ states in $^{62}$Ga and $^{62}$Ge were identified at $979(1)$ and $965(1)$~keV, respectively, resolving discrepant interpretations in the literature. States beyond the first $2^+$ state in $^{62}$Ge were also identified for the first time in the present work. The results are compared with shell-model calculations in the $fp$ model space. Mirror and triplet energy differences are analyzed in terms of individual charge-symmetry and charge-independence breaking contributions. The MED results confirm the shrinkage of the $p$-orbits' radii when they are occupied by at least one nucleon on average.