Experimental Investigation of the Structure of Medium Mass Neutron-Deficient Atomic Nuclei at High Angular Momentum.

The gamma decays from high spin states in three atomic nuclei of the deformed A = 70-80 region, _sp{36}{76}Kr _{40}, _sp{36 }{78}Kr_{42} , and _sp{34}{73} Se_{39}, were investigated via gamma ray spectroscopy. Many new levels in several rotational bands of each nucleus are reported. A cranked shell model analysis aided by the results of Cranked-Woods -Saxon-Strutinsky calculations is performed, and band crossings due to quasi-particle alignment and various shape phenomena are discussed within this context. In addition, the nuclear rotational moments of inertia in _sp{36 }{76}Kr_{40} and _sp{36}{78} Kr_{42} are found to have values close to that of a rigid body. Moments of inertia are typically reduced from this value by the existence of superfluid pair correlations. The observation of rigid rotation is interpreted as the result of a significant reduction in the coherent pair correlations. This reduction may be explained by the low level density at the Fermi level for large deformation in nuclei of this region, reinforcement of this effect from Pauli blocking by excited quasi-particles, and the antipairing effects of the Coriolis force in the rotating system.