Collectivity in the yrast band of 168Yb

The lifetimes of four low-lying levels of the yrast band in 168Yb, populated via the 154Sm(18O,4n) reaction, were measured for the first time by means of the recoil-distance Doppler-shift method. For the data-analysis we applied the differential decay-curve method in a version where gates are set on both shifted and unshifted components. The reduced transition probabilities indicate some reduction of the collectivity for states above the 6+ level, i.e. well below the band-crossing, which may be understood as the result of an interaction between the rotational ground-state band and yet unknown part of the two-quasiparticle ((ν13/2)) spin-aligned S-band or alternatively, as changes in the internal structure induced by the rotation.