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 ${\mathrm{Tb}}^{159}\mathrm{}(d,t)\mathrm{}{\mathrm{Tb}}^{158}$. The ground-state $Q$ value was determined to be -1870 ± 15 keV. The spectrum has been interpreted in terms of the coupling of the [$411\uparrow$] 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 [$521\uparrow$], [$402\downarrow$], and [$400\uparrow$] neutron orbitals coupled to the [$411\uparrow$] 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.