PROTON EXCITATIONS ACROSS THE Z=64 GAP IN THE DOUBLY MAGIC SUPERDEFORMED NUCLEUS GD-144

Five superdeformed (SD) bands have been identified in Gd-144 with the GASP array using the reaction Mo-100 + Ti-48. The J((2)) moments of in ertia of the four excited SD bands are flat as a function of rotationa l frequency, indicating the blocking of the N = 6 proton crossing obse rved in the yrast SD band. According to cranked shell model calculatio ns, the excited bands have two-quasiproton configurations with one pro ton in the N = 6 orbital and the other in each signature partner of th e [404]9/2(+) or [411]3/2(+) orbitals, lying above the Z = 64 gap. The interpretation of the excited SD bands in terms of proton excitations points to the high stability of the N = 80 shell closure at SD shapes . The population of the yrast SD band as a function of the beam energy has been also investigated. Our data shows that the intensity of the yrast SD band is not configuration dependent, being comparable to that of yrast SD bands in the neighboring nuclei. By comparing experimenta l and theoretical alignments, spins and configurations are assigned to all observed SD bands in the A = 140-150 region. (C) 1997 Elsevier Sc ience B.V.