Band crossings in 170Os

Excited states in the neutron-deficient nucleus Os were identified up to spin (24) in the yrast band and to spin (23) in the lowest negative-parity band. Deformation systematics implied by the 2 state energies for the very light osmium isotopes are compared with theory. Band-crossing frequencies, alignments and alignment gains are compared with cranked shell-model calculations. Deformation changes are required to obtain detailed agreement. A three-band mixing approach is invoked to explain the low-spin yrast anomaly in Os and to reproduce the yrast band in Os. The excitation energy of the postulated "intruder" band in Os and Os is deduced