Spectroscopy on the proton drip-line: Probing the structure dependence of isospin nonconserving interactions

Abstract

The recoil-$\ensuremath{\beta}$ tagging technique was used to identify transitions associated with the decay of the ${\mathrm{2}}^{+}$ and, tentatively, the ${\mathrm{4}}^{+}$ excited states in $^{74}\mathrm{Sr}$. Combining these results with published data for the $A=74$ isobars, triplet energy differences (TEDs) have been extracted, the heaviest case for which these values have been evaluated. State-of-the-art shell-model calculations using the JUN45 interaction and incorporating a $J=0$ isospin nonconserving (INC) interaction with an isotensor strength of 100 keV can reproduce the trend in the TED data, with particularly good agreement for the ${\mathrm{2}}^{+}$ state. This agreement for the TED data taken together with the fact that agreement has also been shown between shell-model calculations with the same strength of INC interaction in the ${f}_{7/2}$ shell and recently for $A=66$ strongly suggests that such an interaction exists throughout the nuclear chart and cannot have a strong dependence on details of nuclear structure such as which nuclear orbitals are occupied. It also supports the hypothesis that only a $J=0$ component of the INC interaction need be included to explain the observed TEDs.