Hyperfine-Structure Anomalies of Stable Ytterbium Isotopes

Abstract

Hyperfine-structure anomalies of the stable ytterbium isotopes ${\mathrm{Yb}}^{171}$ ($I=\frac{1}{2}$) and ${\mathrm{Yb}}^{173}$ ($I=\frac{5}{2}$) have been measured in the two lowest-lying ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ states of the Yb atom. For the ${\mathrm{}\left(4f\right)\mathrm{}}^{14}6s6p{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ level $\Delta =-0.367\mathrm{}\left(9\right)\%$, while for the ${\mathrm{}\left(4f\right)\mathrm{}}^{13}5d{\mathrm{}\left(6s\right)\mathrm{}}^2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ level $\Delta =+0.084\mathrm{}\left(22\right)\%$. The former result is the first conclusive evidence that the Nilsson model can account for the distribution of nuclear magnetism in highly deformed nuclei. The second result, in conjunction with the first, can be used to establish the amount of unpaired $s$-electron spin density in a state explicitly lacking in unpaired $s$ electrons. If we neglect other forms of configuration interaction, we calculate that the core-polarization magnetic field produced by the $5d$ electron at the nuclear site is -1.7×${10}^5$ G. Byproducts of our work have been the lifetimes of the two excited electronic states. We find $\tau \left(6s6p{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}\right)=7.6\mathrm{}\left(8\right)\mathrm{}\times {10}^{-7\mathrm{}}$ sec and $\tau \left(f^{-1\mathrm{}}d{s}^2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}\right)=1.7\mathrm{}\left(2\right)\mathrm{}\times {10}^{-8\mathrm{}}$ sec.