The feeding times and lifetimes of high-spin levels in ytterbium doubly even isotopes

The intensities, lifetimes and feeding times of rotational bands with spins up to 10-20h/2π have been measured for four doubly even isotopes, 160-166Yb, formed in the reactions 124-13052Te(4018Ar,4n), using the recoil-distance Doppler-shift method. The obtained values of rotational are compared with the predictions of the rigid-rotor model. For the isotopes 164166Yb a small retardation (by a factor of 1.2-1.4) of transitions in the backbending region is found. Intrinsic quadrupole moments and deformation parameters are deduced as a function of spin for all the four isotopes. The results are discussed in terms of different backbending concepts. The mean-square angular momenta of the levels populated are obtained. Some conclusions on the nature of the γ-ray cascade leading to the feeding of rotational bands are drawn. (Auth.)