Studies of Decay Schemes in the Osmium-Iridium Region. III. Decay of 15.8-HourIr186

Abstract

The decay of 15.8-h ${\mathrm{Ir}}^{186}$ was studied with a double-focusing electron spectrometer, a lens spectrometer, and scintillation spectrometers. Several coincidence experiments were also performed. About two-thirds of the 101 transitions observed could be fitted into a level scheme for ${\mathrm{Os}}^{186}$ consisting of a ground-state ($K=0$) band, a $K=2$ (gamma-vibrational) band, and several other levels. The positron spectrum shows at least two branches; the branch with the highest end-point energy (1.94\ifmmode\pm\else\textpm\fi{}0.02 MeV) populates the $I=6$, $K=0$, state at 0.869 MeV. The total positron intensity is (2.5\ifmmode\pm\else\textpm\fi{}0.7)%. The most probable spin assignment for ${\mathrm{Ir}}^{186}$ (15.8-h) is 7. Energies of the collective levels of ${\mathrm{Os}}^{186}$, and relative transition probabilities, are discussed in the framework of the existing knowledge of other even-$A$ osmium isotopes, and are compared with the predictions of the band-mixed strong coupling model and of various versions of the asymmetric rotor model. An appendix gives data accumulated during the course of this work on transitions following the decay of ${\mathrm{Ir}}^{185}$ and of ${\mathrm{Ir}}^{187}$.