Proton configurations and pairing correlations at the N=80 superdeformed shell closure: Study of Tb145

A superdeformed band has been observed in the N=80 nucleus Tb145 which was produced with the reactions Sn112(37Cl,2p2n) and Sn118(31P,4n) at bombarding energies of 187 and 160 MeV, respectively. Since superdeformed bands also exist in the three lighter N=80 isotones Sm142, Eu143, and Gd144, it is now possible to understand the valence-proton configurations of these bands in a systematic way. The T(2) dynamic moment of inertia in Tb145 shows no evidence for the N = 6 quasiproton crossing that is observed in Gd144. Comparison with cranked Woods-Saxon and total Routhian surface calculations suggests that the proton configuration in Tb145 is 61-[404]9/2+2 in which the quasiproton crossing is blocked. Furthermore, like Eu143 and Sm142, there is no evidence in the T (2) for the N=6 quasineutron crossing predicted by the calculations. This may indicate that static neutron pairing correlations are quenched at the N=80 superdeformed shell closure.