Nuclear Deformability and Quadrupole Moments

A survey of the present phenomenological theory of collective excited states in spherical and non-spherical even-even nuclei is made. It is shown that the character of excited states depends essentially upon the two parameters specifying the nuclear equilibrium shape in the ground state as well as two other dimensionless parameters specifying the longitudinal and transversal deformability of the nuclear surface. Relative to these parameters the nuclei are subdivided into rigid and soft nuclei. In the soft nuclei the rotations are not separated from the vibrations. The above parameters are computed from the data concerning energies of three excited levels. The reduced transition probabilities for E2-transitions between excited states are also expressed in terms of these parameters. Sum rules for reduced E2-transition probabilities and expectation values of quadrupole moments in excited states are discussed. It is shown that the theory of non-spherical deformable nuclei yields expectation values of the quadrupole electric moments of the first 2+ excited state in good agreement with experimental data for isotopes of the nuclei Cd, Ba, Sm and Gd. (author)