Lawrence Berkeley National Laboratory

The recent experimental observation of isospin symmetry breaking (ISB) in the ground states of the T=3/2 mirror pair Sr73-Br73 is theoretically studied using large-scale shell-model calculations. The large valence space and the successful PFSDG-U effective interaction used for the nuclear part of the problem capture possible structural changes and provide a robust basis to treat the ISB effects of both electromagnetic and nonelectromagnetic origin. The calculated shifts and mirror-energy differences are consistent with the inversion of the Iπ=1/2-,5/2-states between Sr73 and Br73 and suggest that the role played by the Coulomb interaction is dominant. An isospin breaking contribution of nuclear origin is estimated to be ≈25keV.