  Darwin-Foldy nuclear-size corrections in electronic atoms and nuclear radii
are discussed from the nuclear-physics perspective. Interpretation of precise
isotope-shift measurements is formalism dependent, and care must be exercised
in interpreting these results and those obtained from relativistic electron
scattering from nuclei. We strongly advocate that the entire nuclear-charge
operator be used in calculating nuclear-size corrections in atoms, rather than
relegating portions of it to the non-radiative recoil corrections. A
preliminary examination of the intrinsic deuteron radius obtained from
isotope-shift measurements suggests the presence of small meson-exchange
currents (exotic binding contributions of relativistic order) in the nuclear
charge operator, which contribute approximately 1/2%.
