Hyperfine-Structure Anomalies of Stable Ytterbium Isotopes

Hyperfine-structure anomalies of the stable ytterbium isotopes Yb¹⁷¹ (I=1/2) and Yb¹⁷³ (I=5/2) have been measured in the two lowest-lying ³P₁ states of the Yb atom. For the (4f)¹⁴6s6p³P₁ level Δ=-0.367(9)%, while for the (4f)¹³5d(6s)²³P₁ level Δ=+0.084(22)%. 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×{}10⁵ G. Byproducts of our work have been the lifetimes of the two excited electronic states. We find τ(6s6p³P₁)=7.6(8)×10^-7 sec and τ(f^-1ds²³P₁)=1.7(2)×10^-8 sec.