# The Nuclear Physics of Precise Atomic
Spectroscopy

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By trading 12 orders of magnitude in electron energy for roughly the same factor
in experimental precision, atomic measurements of some deuteron quantities can
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,
which 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 are known to at least three significant figures 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 and derived by Low. Detailed calculations based on this
mechanism provide a good description of the nuclear corrections.