Low-lying collective quadrupole and octupole strengths in even-even nuclei

The B(E2){↑} values for the first 2⁺ state of even-even nuclei in the Z{≥}50 region are compared with the predictions of several theoretical models. Comparative estimates of the overall agreement with the data are provided. Gaps and discrepancies in the data and examples that show interesting features such as shape changes are discussed. The B(E2){↑} values are examined critically to search for the dynamical Pauli effects predicted by the fermion dynamic symmetry model. The empirical B(E2){↑} and B(E3){↑} systematics are employed to obtain a measure of the harmonicity of the quadrupole and octupole vibrations. The fraction of the energy-weighted sum-rule strength exhausted by the sum of all known low-lying 2⁺ states below 2.3 MeV is found to be surprisingly constant in the 60A250 region except near closed shells.