Two-Quasiparticle States inTb158

Abstract

Thirty-four levels in ${\mathrm{Tb}}^{158}$ have been observed up to an excitation energy of 1166 keV utilizing 12-MeV deuterons and the reaction ${\mathrm{Tb}}^{159}(d,t){\mathrm{Tb}}^{158}$. The ground-state $Q$ value was determined to be -1870 \ifmmode\pm\else\textpm\fi{} 15 keV. The spectrum has been interpreted in terms of the coupling of the [$411\ensuremath{\uparrow}$] Nilsson proton orbital with the neutron orbitals prominent in the ($d,t$) spectrum of ${\mathrm{Gd}}^{157}$. This interpretation has resulted in the determination of relative energies due to the residual neutron-proton interaction for eight different configurations. The observed singlet-triplet splitting energies for the [$521\ensuremath{\uparrow}$], [$402\ensuremath{\downarrow}$], and [$400\ensuremath{\uparrow}$] neutron orbitals coupled to the [$411\ensuremath{\uparrow}$] proton orbital were measured to be +132, -111, and +136 keV, respectively. Theoretical calculations of these energies made for a zero-range spin-dependent central potential gave values of +174, -186, and +136 keV, respectively.