First gamma-ray spectroscopy of Fe-49 and Ni-53: Isospin-breaking effects at large proton excess

Isospin-breaking effects have been studied for the first time in T=3/2 isobaric analog states. Gamma decays have been observed from Tz=-3/2 nuclei, 49Fe and 53Ni, presented here in new level schemes, and mirror energy differences have been computed following observation of analog states in 49V and 53Mn, respectively. Shell-model calculations in the fp shell are in good agreement with the data and reveal the importance of non-Coulomb isospin-breaking effects in T=3/2 isobaric analog states. A two-step fragmentation process was developed to allow access to highly proton-rich nuclei and to produce each member of a mirror pair via mirrored fragmentation of a 56Ni secondary beam. This work represents the first study using this technique and demonstrates the power of this approach for future studies of isobaric analog states in very proton-rich systems