Fragmentation of the yrast band in Os-186 at I pi=18(+) and disappearance of the collective minimum

High-spin states in Os-186 have been populated by the W-186(He-4,4n)-reaction at 55 MeV. The emitted gamma-radiation was detected with the OSIRIS spectrometer. The yrast band; for which the nucleus has a prolate shape, was found to terminate at I-pi=18(+). The gamma-ray intensity is then distributed between several irregular sequences. Different to other cases of band termination, the minimum in the total routhian surface corresponding to a collective shape is calculated to disappear in this spin region, although the available spin of the valence nucleons is far from being exhausted. A different structure, which is dominated by non-collective states becomes yrast.