Hyperfine Spectroscopy of Radioactive Alkali Isotopes

Systematic experimental studies of long series of radioactive isotopes of the same element are now becoming a rapidly developing area. The results obtained in the case of Hg isotopes for instance [1], give a good idea of the attractiveness of such a type of investigation. Moreover, similar studies of radioactive Na isotopes of mass number 21 to 31 have already been performed using high resolution laser spectroscopy [2], and have shown for the first time for such a light element, an appreciable volume shift contribution to the total isotope shift. Obviously, hyperfine results, as well as nuclear spin determinations and precise isotope shift measurements give an ensemble of data that seem to be of crucial importance to a better understanding of nuclear properties and suggest new refinements in theoretical models. The further the isotopes are from magic numbers, the larger the nuclear deformations are expected to be. One has therefore to deal with essentially short-lived species, which requires one to work on-line behind the accelerators where they are produced. In the previously mentioned case of Na atoms for instance, the nuclei were obtained by fission reactions of uranium targets bombarded by 20 GeV protons delivered by the PS synchrotron of C.E.R.N..