B. Bochev

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

Abstract The intensities, lifetimes and feeding times of rotational bands with spins up to 10–20ħ have been measured for four doubly even isotopes, 160–166 Yb, formed in the reactions 124–130 52 Te ( 40 18 Ar, 4n), using the recoil-distance Doppler-shift method. The obtained values of rotational level lifetimes, τ I , are compared with the predictions of the rigid-rotor model. For the isotopes 164, 166 Yb 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 meansquare 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.

Feeding and lifetimes of yrast levels in Hf nuclei

Abstract Feeding intensities and times, as well as lifetimes of yrast levels in doubly even 166, 168, 170 Hf nuclei have been measured. The reactions 122, 124 Sn( 48, 50 Ti, 4n) 166–170 72 Hf have been investigated using the recoil-distance Doppler-shift method. The lifetimes, and hence the B ( E 2) values measured, show the same trends of rather small deviations from the rigid rotor as in the known 68 Er and 70 Yb cases. In addition to the fast feeding component, showing behaviour rather similar to that of the Yb nuclei, another type of slow feeding, related to the low spin yrast levels, is observed.