Low-temperature nuclear orientation: possibilities, results, perspectives

The theoretical expressions, which describe the directional distribution of γ rays emitted by oriented nuclei and the de-orientation coefficients, have been analyzed, and the generalization of these expressions was made for the case of the level population from any number of the initially oriented nuclear states. The possibilities and also restrictions of the low-temperature nuclear orientation method are shown and are illustrated by our experimental and theoretical results. The most possibilities offered by the nuclear orientation study were used. For example, hundreds of spin values, I, Ii, and If, and of the E2/M1, M2/E1, E3/M2 and E0/E2 mixing ratios, the mechanisms of orientation of EuGd and YbGd, the magnitudes of the magnetic dipole moments of the 147Gd and 149Gd ground states, the attenuation factors of orientation of the excited states in 171Yb, the E2/M1 mixing ratio sign change when going from 169Yb to 171Yb (observation of the space reflection property), the intensities of the components with different multipolarities in the β transition from 154EuFe and so on were determined. The studied nuclei were interpreted in the frame of the quasiparticle-phonon model of Solov'ev, of this model with a Coriolis interaction, of the IBA models and of the dynamic deformation model. Some future developments and possibilities are shown. (author)