Shape coexistence or particle alignment in the light osmium isotopes ¹⁷¹Os, ¹⁷²Os and ¹⁷³Os

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.