Lifetimes of high spin states in 168Yb

Lifetimes of high spin states in 168Yb have been extracted using a Doppler shift Attenuation Method and a loss of collectivity has been found at the highest spins. A possible explanation, involving a reduction of deformation due to changes of intrinsic structure, is discussed. In addition a Doppler Shift Attenuation Method has been applied to the ridge structure resulting from the E2 quasi-continuum in an Eγ,x - Eγ,y matrix. Strong collective enhancement is found to persist for transitions a few meV above the yrast line, but the transition rates of γ-rays with energies of approximately 1 MeV are modified by a gain in alignment, which is probably associated with the creation of two quasi-protons. (author)