Proton configurations and pairing correlations at theN=80 superdeformed shell closure: Study ofTb145

Abstract

A superdeformed band has been observed in the N=80 nucleus ${}_{}{}^{145}{}_{}{}^{}\mathrm{Tb}$ which was produced with the reactions ${}_{}{}^{112}{}_{}{}^{}\mathrm{Sn}$ ${(}^{37}$Cl,2p2n) and ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$ ${(}^{31}$P,4n) at bombarding energies of 187 and 160 MeV, respectively. Since superdeformed bands also exist in the three lighter N=80 isotones ${}_{}{}^{142}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{143}{}_{}{}^{}\mathrm{Eu}$, and ${}_{}{}^{144}{}_{}{}^{}\mathrm{Gd}$, it is now possible to understand the valence-proton configurations of these bands in a systematic way. The ${\mathcal{T}}^{\mathrm{}\left(2\right)\mathrm{}}$ dynamic moment of inertia in ${}_{}{}^{145}{}_{}{}^{}\mathrm{Tb}$ shows no evidence for the N = 6 quasiproton crossing that is observed in ${}_{}{}^{144}{}_{}{}^{}\mathrm{Gd}$. Comparison with cranked Woods-Saxon and total Routhian surface calculations suggests that the proton configuration in ${}_{}{}^{145}{}_{}{}^{}\mathrm{Tb}$ is $6^1$⊗[404${]}_{9/2^{+}}^2$ in which the quasiproton crossing is blocked. Furthermore, like ${}_{}{}^{143}{}_{}{}^{}\mathrm{Eu}$ and ${}_{}{}^{142}{}_{}{}^{}\mathrm{Sm}$, there is no evidence in the T ${\mathrm{}}^{\mathrm{}\left(2\right)\mathrm{}}$ 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.