Lifetime measurements of yrast states inYb162andHf166

Lifetime measurements of yrast levels in 162Yb and 166Hf were performed using the recoil distance Doppler-shift method in coincidence mode. Excited states in 162Yb and 166Hf were populated via the reactions 116Cd(50Ti, 4n) and 122Sn(48Ti, 4n), respectively. The resulting B(E2) values are compared with the X(5) critical point model predictions and interacting boson approximation (IBA) model calculations. The X(5) model provides a reasonable description of the yrast B(E2) values in 166Hf, whereas the IBA fails to reproduce the transition strengths from the higher spin levels. In 162Yb, some transitions agree with the X(5) predictions while others are more consistent with the predictions of the IBA or a deformed symmetric rotor.