Proton Single-Particle States aboveZ=64

Abstract

From a (${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, $3n$) in-beam study of the one-particle nucleus ${}_{}{}^{147}{}_{}{}^{}\mathrm{Tb}$ the 1.6-h isomer is assigned at ½+ which is attributed to the $\pi s_{\frac{1}{2}}$ shell-model state. The $\pi d_{\frac{3}{2}}$ level lies at 253 keV, and the $\pi {d_{\frac{5}{2}}}^{-1\mathrm{}}{j_0}^2$ and $\pi {g_{\frac{7}{2}}}^{-1\mathrm{}}{j_0}^2$ states are found at 354 and 719 keV, respectively. These observations provide a clear and consistent picture of the single-proton states in this region. The discontinuity of the observed quasiparticle energies between ${}_{63}{}^{145}{}_{}{}^{}\mathrm{Eu}_{82}^{}{}_{}{}^{}$ and ${}_{65}{}^{147}{}_{}{}^{}\mathrm{Tb}_{82}^{}{}_{}{}^{}$ provides support for a large single-particle energy gap at $Z=64\mathrm{}$, estimated to be ∼ 2.3 MeV.