Shape Evolution in Rotating ¹⁷⁸Os

In order to investigate the evolution of X(5) in rotating ¹⁷⁸Os, an experiment populating ¹⁷⁸Os via the fusion evaporation reaction ¹⁵⁴Sm(²⁹Si,5n)¹⁷⁸Os was performed at the HI−13 tandem accelerator at the China Institute of Atomic Energy (CIAE). Lifetimes of excited states above 8⁺ in the yrast band in ¹⁷⁸Os have been measured using the Doppler shift attenuation method. Lifetimes above 12⁺ states were measured for the first time. The deduced transitional quadruple moments (Q_t), together with the previous data using the recoil distance Doppler shift (RDDS) method are compared with theoretical calculations based on the X(5) model and the interaction Boson model (IBM). Above the 10⁺ states, the Q_t values fit well with the X(5) predictions. The present result suggests that the shape of a nucleus ¹⁷⁸Os keeps X(5) critical point symmetry as spin increases to at least 14⁺. The shape change of ¹⁷⁸Os with spin increasing is similar to that of ¹⁷⁶Os.