Systematics of the ratio of electric quadrupole moments Q(21+) to the square root of the reduced transition probabilities B(E2;01+→21+) in even-even nuclei

A survey of even-even nuclei in the nuclear chart showed regularities in the values of the ratio Q(21+)/(B(E2) for each nucleus for which independent measurements of both the electric quadrupole moment of the 21+ state, Q(21+), and the reduced transition probability B(E2;01+→21+) exist. As predicted by the rotational model, this ratio was found to be close to unity for the deformed nuclei in the rare-earth region. For non-rotational nuclei the absolute value of this ratio is almost always considerably lower. This latter observation can be interpreted within different models for different classes of nuclei as illustrated by a set of schematic IBA model calculations. A general mixing model and simple geometrical models are also suitable for collective non-rotational nuclei. Near magic nuclei a mechanism within the seniority scheme is compatible with the observed small value of RQB.