PROTON CONFIGURATIONS AND PAIRING CORRELATIONS AT THE N=80 SUPERDEFORMED SHELL CLOSURE - STUDY OF TB-145

A superdeformed band has been observed in the N = 80 nucleus Tb-145 wh ich was produced with the reactions Sn-112(Cl-37,2p2n) and Sn-118(P-31 ,4n) at bombarding energies of 187 and 160 MeV, respectively. Since su perdeformed bands also exist in the three lighter N = 80 isotones Sm-1 42, Eu-143, and Gd-144, it is now possible to understand the valence-p roton configurations of these bands in a systematic way. The J((2)) dy namic moment of inertia in Tb-145 shows no evidence for the N = 6 quas iproton crossing that is observed in Gd-144. Comparison with cranked W oods-Saxon and total Routhian surface calculations suggests that the p roton configuration in Tb-145 is 6(1)x[404](2)(9/2+). in which the qua siproton crossing is blocked. Furthermore, like Eu-143 and Sm-142, the re is no evidence in the J((2)) for the N = 6 quasineutron crossing pr edicted by the calculations. This may indicate that static neutron pai ring correlations are quenched at the N = 80 superdeformed shell closu re.