Highly-Deformed Rotational Structures In A ～ 40 Nuclei

摘要

Recent experiments with GAMMASPHERE and the MICROBALL charged-particle detector array have led to the identification, and have enabled the detailed spectroscopic study, of highly-deformed and superdeformed rotational bands in a number of A ～ 40, N ? Z nuclei. These rotational bands are built on multi-particle multi-hole excitations across the N, Z = 20 shell gap from the sd to the pf shell and, in the context of the Nilsson scheme, are associated with the shell gaps formed at large prolate deformation for particle numbers N, Z = 16, 18,20 as pf-shell intruder orbitals are occupied. In analogy with well-developed rotational motion in heavy nuclei, these highly collective rotational structures involve active valence particles in two major shells for both protons and neutrons, yet the A ～ 40 bands possess the unique advantage that the valence space dimension remains small enough to be approached from a shell-model perspective. These rotational bands thus provide an ideal opportunity for detailed comparisons between experimental data and both microscopic and macroscopic models of collective motion in nuclei.