Electron-Nuclear Potential Fields from Hyperfine Structure

Theoretical predictions for the effects of nuclear size on hyperfine structure are compared with experimental data. New data show that isotope shifts of $\mathrm{ns}$ levels in Tl III are proportional to ${\psi }^2\mathrm{}\left(0\right)\mathrm{}$ as predicted. The fractional change in nuclear radius for the addition of two neutrons, determined from $s$ electron shifts in Hg II, Tl III, Pb IV, is the same for the three elements. Köhler's results for Tl II are consistent with those for Tl III when allowance is made for the mutual screening of the valence electrons.