Nuclear Level Structure Of Er-169

Levels in $^{169}\mathrm{Er}$ have been studied through the reactions $^{168}\mathrm{Er}(d,p)^{169}\mathrm{Er}$ and $^{170}\mathrm{Er}(d,t)^{169}\mathrm{Er}$, using 12-MeV deuterons, and via thermal-neutron capture in $^{168}\mathrm{Er}$. Over 40 states below 1.5 MeV are populated in the charged-particle reactions. These data, coupled with the $\ensuremath{\approx}150$ capture $\ensuremath{\gamma}$ rays observed, lead to a level scheme that includes the following spectroscopic assignments (rotational band-head energy in keV, followed by the Nilsson single-particle state believed to be dominant): 0.0, ${\mathrm{\textonehalf{}}}^{\ensuremath{-}}$[521], with associated rotational band to spin ${\frac{11}{2}}^{\ensuremath{-}}$, 92.2, ${\frac{5}{2}}^{\ensuremath{-}}[512]$, with band to ${\frac{11}{2}}^{\ensuremath{-}}$; 243.7, ${\frac{7}{2}}^{+}[633]$, with band to ${\frac{13}{2}}^{+}$; 562.1, ${\mathrm{\textonehalf{}}}^{\ensuremath{-}}$[510], with band to ${\frac{7}{2}}^{\ensuremath{-}}$; 714.5, ${\frac{3}{2}}^{\ensuremath{-}}[521]$, with band to ${\frac{11}{2}}^{\ensuremath{-}}$; 823, ${\frac{7}{2}}^{\ensuremath{-}}$ [514], with band to ${\frac{9}{2}}^{\ensuremath{-}}$; 850, ${\frac{5}{2}}^{\ensuremath{-}}[523]$, with band to ${\frac{11}{2}}^{\ensuremath{-}}$; and 1081.8, ${\frac{3}{2}}^{\ensuremath{-}}[512]$, with band to ${\frac{7}{2}}^{\ensuremath{-}}$. In addition, a level at 860.2 keV is assigned as the head of a ${K}^{\ensuremath{\pi}}={\frac{3}{2}}^{+}$ band that is mainly the ($K\ensuremath{-}2$) $\ensuremath{\gamma}$-vibrational state associated with ${\frac{7}{2}}^{+}[633]$. The data suggest that the 562.1-, 714.5-, and 1081.8-keV bands also have significant vibrational admixtures. Several features of the level scheme, including certain $\ensuremath{\gamma}$-ray branching ratios, are interpreted in terms of Coriolis mixing. The neutron separation energy for $^{169}\mathrm{Er}$ is determined as 6003.1 \ifmmode\pm\else\textpm\fi{} 0.3 keV, and the $Q$ value for the $^{170}\mathrm{Er}(d,t)^{169}\mathrm{Er}$ reaction is found to be -950 \ifmmode\pm\else\textpm\fi{} 30 keV.