# The Nuclear Physics of precise atomic spectroscopy

**Jim Friar**

T-16, LANL

By trading 10-12 orders of magnitude in electron energy for roughly the same factor in experimental precision, atomic measurements of some deuteron observables can successfully compete with accelerator measurements. The deuteron matter radius, for example, is most accurately determined by the isotope shift in the 1S-2S level splittings of H and D. The precision of this determination is adequate to provide a window on small relativistic corrections and meson-exchange currents in the deuteron that is unattainable in accelerator measurements. The theory of QED corrections for hyperfine structure in hydrogenic atoms has recently advanced to the point that differences with experiment can be interpreted as nuclear corrections, which can be determined to at least three significant-figure accuracy for the H, D, T and 3He+ atoms. The leading-order nuclear mechanism contributing to hyperfine structure is a charge-magnetic correlation that was sketched by Bohr and derived by Low. Detailed calculations based on this mechanism provide a good description of the nuclear corrections to hyperfine structure in light hydrogenic atoms and ions.