SHAPE COEXISTENCE OR PARTICLE ALIGNMENT IN THE LIGHT OSMIUM ISOTOPES OS-171, OS-172 AND OS-173

Decay schemes of the nuclei 171Os, 172Os and 173Os were studied using the reactions 144Sm(30Si,3n)171Os, 144Sm(31P, p2n)172Os and 149Sm(28Si, 4n)173Os. The 5- 2[523] and i 13 2 bands were identified in the odd nuclei. Low-spin properties of these bands are analyzed using the particle-rotor model, while band-crossing frequencies and alignments are examined with the aid of the cranked shell model. A low-frequency band crossing was found in the 5- 2 [523] band of 173Os. At higher frequencies, the measured B(M1) B(E2) transition rates and signature splittings in the 5- 2[523] bands of both nuclei are consistent with a neutron alignment. In the i 13 2 band of 173Os, an upbend, in the unfavoured sequence, possibly due to the AD crossing, occurs at a lower frequency than a similar upbend, presumably from the BC crossing, in the favoured sequence. These crossings were also analyzed with phenomenological three-band-mixing calculations. © 1990.