Long-lived three-quasiparticle isomers in ¹⁹¹Ir and ¹⁹³Ir with triaxial deformation

Deep-inelastic reactions have been used to populate high-spin states in the iridium isotopes. New results include the identification of particularly long-lived three-quasiparticle isomers in ¹⁹¹Ir and ¹⁹³Ir, with mean-lives of 8.2(7) s and 180(3) μs respectively, decaying into newly identified states of the h _11/2 proton bands and into other structures. Spins and parities of J ^π=31/2 ⁺ are suggested for both, consistent with coupling of the 11/2 ^-[505] proton to the 10 ^- two-neutron excitations in the cores. These and other configurations are discussed in the context of configuration constrained potential-energy-surface calculations. All calculated intrinsic states are expected to be associated with triaxial shapes and the extreme isomerism observed is attributed to spin-trapping rather than K-hindrance.