Firstγ-ray spectroscopy ofFe49andNi53: Isospin-breaking effects at large proton excess

Abstract

Isospin-breaking effects have been studied for the first time in $T=\frac{3}{2}$ isobaric analog states. Gamma decays have been observed from ${T}_{z}=\ensuremath{-}\frac{3}{2}$ nuclei, $^{49}\mathrm{Fe}$ and $^{53}\mathrm{Ni}$, presented here in new level schemes, and mirror energy differences have been computed following observation of analog states in $^{49}\mathrm{V}$ and $^{53}\mathrm{Mn}$, respectively. Shell-model calculations in the $\mathit{fp}$ shell are in good agreement with the data and reveal the importance of non-Coulomb isospin-breaking effects in $T=\frac{3}{2}$ 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 $^{56}\mathrm{Ni}$ 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.