Lifetime measurements for continuum gamma rays in 164Yb and 170Hf

Lifetimes of states associated with the ridges in the Eγ-Eγ correlation spectrum of 164Yb and 170Hf were measured by the Doppler-shift attenuation method. The results indicate a reduction of the quadrupole collectivity associated with γ-rays with energy from 0.7 to 0.9 MeV and an enhancement of collectivity for those above 0.9 MeV. The reduced and the enhanced collectivity can be understood as rotationally-induced modifications of the occupation of high-j orbitals originating from below and above the Fermi surface, respectively. The effect of rotational damping on the lifetimes of continuum states is also discussed.