Evidence for the Importance of Soft Deformation Potentials in Strongly Deformed Nuclei

Excited states of 168Hf were populated using the 124Sn(48Ti,4n) fusion evaporation reaction at the WNSL of Yale University. The lifetimes of the Jp = 4+,6+,8+, and 10+ levels along the ground state band of 168Hf were measured by means of the recoil distance Doppler shift (RDDS) method using the New Yale Plunger Device (NYPD) and the SPEEDY Ge detector array. The new lifetime values are sufficiently precise to clearly prove the increase of quadrupole collectivity as a function of angular momentum in the deformed nucleus 168Hf. The data agree with the predictions from the geometrical Confined b-Soft (CBS) rotor model that involves centrifugal stretching in a soft potential. Relative and absolute E0 transition strengths [r2(E0)] on the transitional path between X(5) and the Rigid Rotor Limit have been evaluated within the framework of the CBS rotor model, too. Relative inter-band E0 transition strengths decrease with increasing angular momentum for a given potential stiffness, while for increasing potential stiffness, the absolute E0 transition strengths decrease with increasing angular momentum and increasing potential stiffness.