Isospin symmetry breaking at high spins in the mirror pairSe67andAs67

Recent experimental data have revealed large mirror energy differences (MED) between high-spin states in the mirror nuclei {sup 67}Se and {sup 67}As, the heaviest pair where MED have been determined so far. The MED are generally attributed to the isospin symmetry breaking caused by the Coulomb force and by the isospin-nonconserving part of the nucleon-nucleon residual interaction. The different contributions of the various terms have been extensively studied in the fp shell. By employing large-scale shell-model calculations, we show that the inclusion of the g{sub 9/2} orbit causes interference between the electromagnetic spin-orbit and the Coulomb monopole radial terms at high spin. The large MED are attributed to the aligned proton pair excitations from the p{sub 3/2} and f{sub 5/2} orbits to the g{sub 9/2} orbit. The relation of the MED to deformation is discussed.