Shape coexistence phenomena in medium mass nuclei

We review the theoretical interpretation of experimental results on low and high spin states in some even mass A=60-80 nuclei within the complex versi ons of the Excited Vampir and Fed Vampir variational approaches. The coexis tence of oblate and prolate deformed configurations and their mixing at low spin are found to be responsible for the irregular sequences of states and the isomeric decays identified at low excitation energy in even-even nucle i. This behaviour is determined essentially by the isoscalar neutron-proton interaction. At higher spins the coexistence of states with different defo rmations causes complicated multiple band structures and strong fragmentati on of the B(E2) strengths. It also influences the occurence of almost ident ical bands at normal deformation in some even mass nuclei. In some odd-odd nuclei the shape coexistence furthermore suggests a possible mechanism to p opulate high spin isomeric states. For the ground state properties of N=Z n uclei the competition between neutron-proton and like-nucleon isovector pai ring plays an important role. With increasing angular momentum the neutron- proton alignment dominates the like-nucleon one in the ground bands of odd- odd N=Z nuclei while in the doubly even N=Z nuclei both types of alignment are of comparable importance.