High-spin collectivity in A∼40 nuclei

Recent experiments with large gamma-ray detector arrays coupled to 4pi charged-particle detectors have enabled the detailed spectroscopic study of higly- and super-deformed rotational bands in a number of N approximate to Z nuclei in the A similar to 40 mass region. In the context of the Nilsson scheme, these rotational structures are associated with the shell gaps at large prolate deformation for particle numbers N, Z = 16, 18, 20, while in the spherical shelf model context they are described in terms of multi-particle multi-hole excitations across the N, Z = 20 spherical shell grip. In analogy with rotational bands in heavy nuclei, these highly collective structures involve active valence particles in two major shells for both protons and neutrons, yet their 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.