Scintillation and semiconductor detectors have been used to investigate the decay properties of neutrondeficient osmium and rhenium isotopes which were produced in proton and helium-ion bombardments of tantalum and tungsten targets. Re 179 decays by electron capture with a half-life of 19.7db0.5 min; the energies, and relative intensities of 14 y rays emitted in Re 179 decay are reported. The positron decay branch previously assigned to 20-hr Re 180 has been shown to occur in the decay of 13-h Re 182 , and no evidence for a Re 180 isomer having a half-life longer than a few minutes was found. The existence of 2.45-min Re 180 has been confirmed; it decays predominantly by electron capture with the emission of intense 902.2-and 103.6-keV 7 rays. By establishing its genetic relationship with 2.45-min Re 180 , a new isotope 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 Os 181 has been determined to be 105±3 min, in disagreement with previous values reported for this isotope. An intense 238.6-keV y ray is characteristic of Os 181 decay and the energies and relative intensities of other Os 181 7 rays are reported. Reasons are advanced for believing that the Re 179 , Os 180 , and Os 181 activities identified here have been observed previously by other workers, but have been incorrectly assigned to Re 180 , Os 181 , and Os 183w , respectively.

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