NUCLEAR SIZES AND THE ISOTOPE SHIFT

Darwin-Foldy nuclear-size corrections in electronic atoms and nuclear radii are discussed from the nuclear-physics perspective. The interpre tation of precise isotope-shift measurements is formalism dependent, a nd care must be exercised in interpreting these results and those obta ined from relativistic electron scattering from nuclei. We strongly ad vocate that the entire nuclear-charge operator be used in calculating nuclear-size corrections in atoms rather than relegating portions of i t to the nonradiative recoil corrections. A preliminary examination of the intrinsic deuteron radius obtained from isotope-shift measurement s suggests the presence of small meson-exchange currents (exotic bindi ng contributions of relativistic order) in the nuclear charge operator , which contribute approximately 1/2%. [S1050-2947(97)04312-6].