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 for p-shell nuclei using an improved shell-model Hamiltonian with enhanced spin-flip proton-neutron interaction and modified single-particle energies. The present shell-model Hamiltonian thus obtained is used in the configuration space up to (2-3)(h) over bar omega excitations, and GT transitions and magnetic moments are calculated with bare g factors and bare axial-vector coupling constant. Manifestation of variable quenching due to changing gap between 0p(3/2) and 0p(1/2) is presented in GT transitions such as C-12-->N-12, B-11-->Be-11, and Li-9-->Be-9. A similar effect is shown for magnetic moments. Better agreement with experimental values is obtained systematically by using the present Hamiltonian for GT transitions and magnetic moments in most of p-shell nuclei, as well as for energy levels. Thus, the shell structure is changing from nucleus to nucleus in an orderly way (i.e., shell evolution), the inclusion of which leads us to an improved description of the GT and magnetic properties. It is stressed that the anomalous shell structure of exotic nuclei and the GT/magnetic properties of stable and exotic nuclei are linked through the same underlying mechanism.