Yrast states in Os-194: The prolate-oblate transition region - art. no. 011304

Previously unidentified states in the neutron-rich nucleus Os-194 have been populated following a deep inelastic reaction using a 780 MeV Xe-136 beam on a thick Pt-198 target. gamma-gamma coincidence events were collected usi ng the 8 pi detector array. The yrast band in Os-194 has been observed up t o I-pi=(10(+)), for the first time. This represents the heaviest osmium nuc leus where in-beam gamma -ray spectroscopy has been performed to date. The excitation energies of the new levels are compared to the systematics of th e lighter even-even osmium nuclei. The evidence for a transition from prola te to oblate-deformed ground states in the heavy osmium nuclei is discussed and total Routhian surface calculations are presented. An alignment analys is together with cranked shell model calculations, suggest that the yrast s tates have a prolate shape, in contrast to earlier interpretations. Predict ions for the neighboring even-even tungsten isotopes are also described.