Isotope shifts in medium-heavy elements

Abstract

Isotope shifts in the atomic spectra of elements covering the range between the magic neutron numbers 50 and 82 are discussed in terms of nuclear charge distribution. A com­parison with evidence obtained from Coulomb excitation experiments shows that for some elements, the variation of field shifts within the sequences of even-even isotopes cannot be due solely to deformation effects, whether static or vibrational. A quantitative treatment shows that the increase of nuclear volume, or the change of nuclear charge distribution due to purely radial, as distinct from deformation, effects, occurs in markedly unequal steps as neutron pairs are added. The evidence is particularly striking in Sn and Cd, where deformations are small, and vary little among the even isotopes. Values of radial changes are obtained from the isotope shift results and com pared with the values predicted from electron scattering data. It also appears that the odd-even staggering cannot always be attributed to deformation effects.