The latter can be divided in two types. The first group contains transitions which are so fast that they are not candidates for the observation of hyperfine interactions of the corresponding nuclear level. Their widths of a few eV are, however, still exceptionally small in comparison with the energy band which can be obtained by electronic scattering methods. There are for example K, Gd and Zn. The resonance of K was observed but is hardly used for research as there is no radioactive source and the excitation of the level by a nuclear reaction is difficult.
Potassium ions are, however, under the most interesting ions in biological environments.
The other two nuclei mentioned have transitions of exceptional small energetic width. Gravitational experiments will be possible and in the case of zinc also biological experiments with the highest resolution can be expected. The pulse length of 120ps typical for dedicated storage rings will be reduced to 80fs. This shortening by a factor of 1500 will decrease the possible observation time of fast quantum beats correspondingly. However,with presently available detectors they would not be observable.