Isomers and alignments in ¹⁹¹Ir and ¹⁹²Os

Deep-Inelastic reactions have been used to populate high-spin states in the even-even osmium isotopes and in the iridium neighbors. New isomers have been identified in ¹⁹⁰Os, ¹⁹²Os, ¹⁹⁴Os, ¹⁹¹Ir and ¹⁹³Ir. These include a 2 ns 12⁺ state at 2865 keV and a 295 ns, 20⁺ state at 4580 keV in ¹⁹²Os. Although a number of multi-quasiparticle states arising from prolate and triaxial deformations are expected in these nuclei, the main structures in ¹⁹²Os can be interpreted as a two-stage alignment of i_13/2 neutrons at oblate deformation, in close analogy with similar structures in the isotones ¹⁹⁴Pt and ¹⁹⁶Hg. The isomers are attributed to low-energy E2 transitions at the point of the alignment gains. The isomer observed in ¹⁹¹Ir is long-lived (τ_m ∼8s) and probably arises from coupling of the h_11/2 proton to the 10 ^-ν/9/2^- [505]11/2⁺ [615] prolate configuration that gives rise to long-lived isomers in ¹⁹⁰Os and ¹⁹²Os, although potential-energy-surface calculations indicate that the resultant three-quasiparticle state will be triaxial.