Collective motions and band structures in A = 60 to 80, even--even nuclei

Evidence for and the theoretical understanding of the richness of the collective band structures as illustrated by at least seven bands seen in levels of 68Ge, 74Se are reviewed. The experimental data on even-even nuclei in the A = 60 to 80 region have now revealed a wide variety of collective bands with different structures. The even parity yrast cascades alone are seen to involve multiple collective structures. In addition to the ground-state bands, strong evidence is presented for both neutron and proton rotation-aligned bands built on the same orbital, (g9/2)2, in one nucleus. Several other nuclei also show the crossing of RAL bands around the 8+ level in this region. Evidence continues to be strong experimentally and supported theoretically that there is some type of shape transition and shape coexistence occurring now both in the Ge and Se isotopes around N = 40. Negative parity bands with odd and even spins with very collective nature are seen in several nuclei to high spin. These bands seem best understood in the RAL model. Very collective bands with ΔI = 1, extending from 2+ to 9+ are seen with no rotation-alignment. The purity of these bands and their persistence to such high spin establish them as an independent collective mode which is best described as a gamma-type vibration band in a deformed nucleus. In addition to all of the above bands, new bands are seen in 76Kr and 74Se. The nature of these bands is not presently known. 56 references