Evidence for X(5) critical point symmetry in 128Ce

Lifetimes of excited states in Ce-128 were measured using the recoil distance Doppler-shift (RDDS) and the Doppler-shift attenuation (DSAM) methods. The experiments were performed at the Wright Nuclear Structure Laboratory of Yale University. Excited states of Ce-128 were populated in the Mo-100(Si-32,4n) reaction at 120 MeV and the nuclear gamma decay was measured with an array of eight Clover detectors positioned at forward and backward angles. The deduced yrast transition strengths together with the energies of the levels within the ground-state (gs) band of Ce-128 are in agreement with the predicted values for the X(5) critical point symmetry. Thus, we suggest Ce-128 as a benchmark X(5) nucleus in the mass A approximate to 130 region.