# The Nuclear Physics of Precise Atomic
Spectroscopy

##
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
^{3}He^{+} atoms. The leading-order nuclear mechanism
contributing to hyperfine
structure is a charge-magnetic correlation that was sketched by Bohr, derived
by Low, and extended recently. Detailed calculations based on this mechanism
provide a good description of the nuclear corrections to hyperfine structure
in light hydrogenic atoms and ions.