Oblate-prolate shape competition in Z = 34 to 38 nuclei

Now magic numbers for deformed shapes are established at N and Z of 38 and N of 60. These shell gaps at large deformation (β ≅ 0.4) are magic when the proton and neutron shell gaps reinforce each other. Other shell gaps for 34 and 36 are predicted to be important for oblate deformation. The competition between these oblate and the 38 prolate gaps as well as the 40 spherical shell gap are considered. In 71Se coexistence of oblate (β ≅ -0.24) and large prolate (β ≅ 0.4) shapes are observed. In 72Se the excited prolate band with large deformation which coexists with the near-spherical ground state is found to dominate the yrast spectrum to 28+. The moment of inertia of this band is essentially that of a rigid body. This moment of inertia supports the suggestion that the ''super deformation'', β ≅ 0.4, being observed in this region may be associated with a collapse of pairing