The energy levels of hydrogen-like atomic systems are shifted
slightly by the complex structure of the nucleus, in particular by the
finite size of the nucleus. These energy shifts are vastly magnified in
muonic atoms and ions, i.e. the hydrogen-like systems formed by a negative
muon and a nucleus. By measuring the 2S-2P energy splitting in muonic
hydrogen, muonic deuterium and muonic helium, we have been able to
deduce the p, d, ^33He
and ^44He
nuclear charge radii to an unprecedented accuracy. These radii provide
benchmarks for hadron and nuclear theories, lead to precision tests of
bound-state QED in regular atoms and to a better determination of the
Rydberg constant.
Muonic atoms with extreme nuclear charge