Strong residual correlations between neutrons and protons in N approximate to 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 As-66. 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 As-67, 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. (c) 2005 Elsevier B.V. All rights reserved.
展开▼
