Yrast states in ¹⁹⁴Os: The prolate-oblate transition region

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