Hyperfine interactions-un peu d'histoire

The history of hyperfine interactions is outlined from the first observations by optical spectroscopy, through magnetic resonance in the solid state and in atomic beams, to the use of lasers. For lanthanide atoms and ions, a number of hyperfine structure corrections are discussed, with particular reference to the problem of <r ⁻³>. The various contributions to the nuclear electric quadrupole interaction are reviewed, including shielding effects. Results deduced from electronic spectra are compared with those involving the use of negative muons.