On the two-quasineutron rotational band in Ba-128

The lifetimes of five levels of the two-quasineutron band in Ba-128 populat ed via the Cd-116(O-16, 4n) reaction were measured for the first time by me ans of the recoil-distance Doppler-shift method. For the data-analysis, a n ew version of the differential decay-curve method in singles-like mode was developed which takes into account the velocity distribution of the recoils and the effect of the Doppler-shift attenuation in the stopper. The high v alues of (K-2) and K-eff characterising the band are confirmed by the deter mined B(E2, I --> I - 2) and B(M1, I --> I - 1) transition strengths. At th e same time, the rigid-rotor model is not able to describe the behaviour of the experimental B(E2, I --> I - 1) and B(M1, I --> I - 1) values, A new t heoretical effort seems to be needed for a consistent explanation of the in traband transition strengths within two-quasiparticle bands in gamma-soft n uclei. (C) 2000 Elsevier Science B.V. All rights reserved.