Transition Probabilities: a key to prove the X(5) symmetry

The lifetimes of excited states in Gd-154 were measured using the recoil distance Doppler-Shift (RDDS) method. The experiment was performed at Cologne FN Tandem accelerator where a beam of S-32 with an energy of 110 MeV was used to Coulomb excite states of 154Gd. The determined transition probabilities as well as the low-spin level scheme of 154Gd demonstrate a good agreement with the predictions of the critical point symmetry X(5). Comparison of specific experimental observables for the N = 90 rare earth isotones with the calculations of the X(5) model clearly show that Gd-154 is one of the best examples of the realization of the X(5) dynamical symmetry. In addition, the experimental data are compared to fits in the framework of the IBA and the General Collective Model (GCM).