Barrier penetration and rotational damping of thermally excited superdeformed nuclei

We construct a microscopic model of thermally excited superdeformed states that describes both the barrier penetration mechanism, leading to the decay-out transitions to normal deformed states, and the rotational damping causing fragmentation of rotational E2 transitions. We describe the barrier penetration by means of a tunneling path in the two-dimensional deformation energy surface, which is calculated with the cranked Nilsson-Strutinsky model. The individual excited superdeformed states and associated E2 transition strengths are calculated by the shell-model diagonalization of the many-particle-many-hole excitations interacting with the delta-type residual two-body force. The effects of the decay-out on the excited superdeformed states are discussed in detail for ¹⁵²Dy, ¹⁴³Eu and ¹⁹²Hg. The model predicts that the decay-out brings about a characteristic decrease in the effective number of excited superdeformed rotational bands.