High-spin collectivity in A ∼ 40 nuclei

Abstract

Recent experiments with large gamma-ray detector arrays coupled to 4π charge-particle detectors have enabled the detailed spectroscopic study of highly- and super-deformed rotational bands in a number of N ≈ Z nucleic in the A ∼ 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 shell model context they are described in terms of multi-particle multi-hole excitations across the N, Z = 20 spherical shell gap. 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 comparison between experimental data and both microscopic and macroscopic models of collective motion in nuclei.