Nuclear Levels ofYb169Populated in theYb168(n,γ)Reaction

The level structure of ${}_{}{}^{169}{}_{}{}^{}\mathrm{Yb}$ has been studied using the thermal-neutron capture reaction ${}_{}{}^{168}{}_{}{}^{}\mathrm{Yb}(n,\gamma ){}_{}{}^{169}{}_{}{}^{}\mathrm{Yb}$. The $\gamma$-ray spectrum from this reaction has been studied in the energy intervals 60-1500 keV and 5200-7000 keV with Si(Li) and Ge(Li) spectrometer systems. Targets of isotopically separated ${}_{}{}^{168}{}_{}{}^{}\mathrm{Yb}$ and ${}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}$ and of natural ytterbium were used to provide definitive identification of transitions occurring in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Yb}$. The results of this investigation are compared with the published results from studies of the ($d,p$) and ($d,t$) reactions, radioactive decay, and the neutron-capture internal-conversion electron spectrum. The levels observed in the ($n,\gamma$) studies include: the ${\frac{7}{2}}^{+}$ and ${\frac{9}{2}}^{+}$ members of the [$633\uparrow$] ground-state rotational band; the 5 lowest members of the [$521\downarrow$] band, based at 24.3 keV; the ${\frac{5}{2}}^{-}$, ${\frac{7}{2}}^{-}$, and ${\frac{9}{2}}^{-}$ members of the [$512\uparrow$] band, based at 191.2 keV; the ${\frac{5}{2}}^{-}$ and ${\frac{7}{2}}^{-}$ members of the [$523\downarrow$] band, based at 569.8 keV; the two lowest members of the [$521\uparrow$] band, based at 659.8 keV; the ${\frac{3}{2}}^{+}$ and ${\frac{5}{2}}^{+}$ members of a $K^{\pi }={\frac{3}{2}}^{+}$ band, based at 720.0 keV, believed to be partly vibrational and partly [$651\uparrow$]; and the 4 lowest members of a $K^{\pi }={\frac{1}{2}}^{-}$ band, based at 813.2 keV, believed to involve large components of both [$510\uparrow$] and the vibrational configuration ${\left[512\mathrm{}\uparrow \right]}_{\gamma -\mathrm{v}\mathrm{i}\mathrm{b}}$. In addition, specific configurational assignments are proposed for several of the levels observed above 850 keV. Details of the level structure are discussed in the light of recent theoretical calculations by Soloviev et al. and by Bés and Cho. Emphasis is placed on the possible structure of the previously unobserved 720.0-keV ${\frac{3}{2}}^{+}$ band, and Coriolis calculations involving this band are presented.