This volume deals with the interaction between moments of excited or radioactive nuclei and electromagnetic fields. The experimental techniques developed for the observation of this hyperfine interaction are governed by the lifetime of the nuc lear states in question. The dynamics of the interaction are reflected by the time dependence of the spatial distribution of the radioactive decay radiation. Basically, the experiments yield information on the energy shifts and/or splittings of the nuc lear levels. These quantities are determined essentially by the product of the nuc lear moment and the...