The Isotope Shift in Hyperfine Structure

The effect of deviations of the nuclear field from the inverse square law such as are suggested by the theory of radioactive disintegration is calculated. The isotope shift due to a change of the nuclear radius by 1 percent is found to be larger than those observed. The spectrum of T1 appears not to fit any simple modification of the theory. The isotope shifts in Pb I and Pb II can be explained roughly on the supposition that the deviations of the nuclear field from the inverse square law are local but that for the valence electrons these deviations should be taken to be smaller than is usually supposed in the theory of radioactive disintegration.