Decay Properties of Neutron Deficient Osmium and Rhenium Isotopes. I. Decay Modes of ${\mathrm{Re}}^{179}$, ${\mathrm{Re}}^{180}$, ${\mathrm{Os}}^{180}$, and ${\mathrm{Os}}^{181}$

Scintillation and semiconductor detectors have been used to investigate the decay properties of neutron-deficient osmium and rhenium isotopes which were produced in proton and helium-ion bombardments of tantalum and tungsten targets. ${\mathrm{Re}}^{179}$ decays by electron capture with a half-life of 19.7±0.5 min; the energies, and relative intensities of 14 $\gamma$ rays emitted in ${\mathrm{Re}}^{179}$ decay are reported. The positron decay branch previously assigned to 20-hr ${\mathrm{Re}}^{180}$ has been shown to occur in the decay of 13-h ${\mathrm{Re}}^{182}$, and no evidence for a ${\mathrm{Re}}^{180}$ isomer having a half-life longer than a few minutes was found. The existence of 2.45-min ${\mathrm{Re}}^{180}$ has been confirmed; it decays predominantly by electron capture with the emission of intense 902.2- and 103.6- keV $\gamma$ rays. By establishing its genetic relationship with 2.45-min ${\mathrm{Re}}^{180}$, a new isotope ${\mathrm{Os}}^{180}$, decaying by electron capture with a 21.7±0.6 min half-life, has been identified. The half-life for the electron capture decay of ${\mathrm{Os}}^{181}$ has been determined to be 105±3 min, in disagreement with previous values reported for this isotope. An intense 238.6-keV $\gamma$ ray is characteristic of ${\mathrm{Os}}^{181}$ decay and the energies and relative intensities of other ${\mathrm{Os}}^{181}$ $\gamma$ rays are reported. Reasons are advanced for believing that the ${\mathrm{Re}}^{179}$, ${\mathrm{Os}}^{180}$, and ${\mathrm{Os}}^{181}$ activities identified here have been observed previously by other workers, but have been incorrectly assigned to ${\mathrm{Re}}^{180}$, ${\mathrm{Os}}^{181}$, and ${\mathrm{Os}}^{183m}$, respectively.