Investigation of a large change in deformation for the gamma-soft nucleus Sm-136

Lifetimes of excited states of the ground-state rotational band in the Sm-136 nucleus have been measured up to I-pi = 20(+) using the Doppler-shift attenuation method. The states were populated in the reaction Ag-107(S-32, 1p2n) at 145-MeV beam energy and the gamma rays emitted from the excited states were detected using the Indian National Gamma Array at the Tata Institute of Fundamental Research, Mumbai. The extracted transitional quadrupole moments indicate a reduction of collectivity with increasing spin after the band crossing. The results have been compared with the predictions of the cranked shell model as well as the triaxial projected shell-model calculations and indicate that the nucleus evolves from prolate gamma-soft to a stable triaxially deformed shape after the first and the second crossing involving pi h(11/2)(2) and pi h(11/2)(2) circle times nu h(11/2)(2) configurations, respectively.