Structure of isomeric states in 66As and 67As

Abstract

Strong residual correlations between neutrons and protons in N ≈ Z systems can lead to unusual structure. Using the spherical shell model, we show that a low-excitation shape isomer can occur in the odd–odd N = Z nucleus 66As. This extends the picture of shape coexistence beyond even–even nuclei. Furthermore, it is demonstrated that in 66As and in the N = Z + 1 nucleus 67As, a new type of isomer, which we term j-isomer, can be formed. The underlying mechanism for the isomerism formation is structure change in the isomeric states, which involves either an alignment of a neutron–proton pair from the high- j intruder orbitals, or a simultaneous occupation of these neutron and proton high- j orbitals.