Gamow-Teller transitions and magnetic properties of nuclei and shell evolution

New aspects of quenching of Gamow-Teller ~GT! transitions and magnetic moments are investigated forp-shell nuclei using an improved shell-model Hamiltonian with enhanced spin-flip proton-neutron interactionand modified single-particle energies. The present shell-model Hamiltonian thus obtained is used in the configurationspace up to ~2–3!\v excitations, and GT transitions and magnetic moments are calculated with bareg factors and bare axial-vector coupling constant. Manifestation of variable quenching due to changing gapbetween 0p3/2 and 0p1/2 is presented in GT transitions such as 12C!12N, 11B!11Be, and 9Li!9Be. A similareffect is shown for magnetic moments. Better agreement with experimental values is obtained systematicallyby using the present Hamiltonian for GT transitions and magnetic moments in most of p-shell nuclei, as wellas for energy levels. Thus, the shell structure is changing from nucleus to nucleus in an orderly way ~i.e., shellevolution!, the inclusion of which leads us to an improved description of the GT and magnetic properties. It isstressed that the anomalous shell structure of exotic nuclei and the GT/magnetic properties of stable and exoticnuclei are linked through the same underlying mechanism.status: publishe