Evolution Of The X(5) Critical-Point Symmetry In Rotating Os-176

Lifetimes of excited states above 10(+) in the yrast band in Os-176 have been measured using the Doppler shift attenuation method, via the fusion evaporation reaction Sm-152(Si-28, 4n) Os-176. Lifetimes of states over 12(+) were measured for the first time. The deduced transitional quadruple moments (Q(t)), together with the previous data using a recoil distance method, are compared with theoretical calculations based on the X(5) model and the interaction boson model. For the states below spin 10(+), the data of previous work support an X(5)-like structure, but for the states above 10(+), the value of Qt remains almost constant, being the characteristic of a symmetric rotor. The present result suggests that the shape of the nucleus Os-176 changes from X(5) critical-point symmetry to an axially deformed rotor with increasing spin.