Isomers and alignments in ¹⁹¹Ir and ¹⁹²Os

Abstract

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 i13/2 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 (τm ∼8s) and probably arises from coupling of the h11/2 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.