Borggreen and Hyde recently reported the discovery of three new $\alpha$-emitting osmium isotopes, ${}_{}{}^{172}{}_{}{}^{}\mathrm{Os}$, ${}_{}{}^{173}{}_{}{}^{}\mathrm{Os}$, and ${}_{}{}^{174}{}_{}{}^{}\mathrm{Os}$. The present study deals with a search for osmium nuclides with $A<\mathrm{}172\mathrm{}$. These osmium isotopes were produced by bombarding ${}_{}{}^{156}{}_{}{}^{}\mathrm{Dy}$ with the 160-MeV ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}_{}^{6+}{}_{}{}^{}$ beam from the Oak Ridge isochronous cyclotron. With the use of $\alpha$ spectroscopy and the helium gas-jet technique, two new $\alpha$ groups were observed. Their mass assignments and decay characteristics are as follows: (1) ${}_{}{}^{170}{}_{}{}^{}\mathrm{Os}$, $E_{\alpha }=5.40\mathrm{}\pm 0.01$ MeV, $T_{\frac{1}{2}}=7.1\mathrm{}\pm 0.5$ sec; and (2) ${}_{}{}^{171}{}_{}{}^{}\mathrm{Os}$, $E_{\alpha }=5.24\mathrm{}\pm 0.01$ MeV, $T_{\frac{1}{2}}=8.2\mathrm{}\pm 0.8$ sec.

• Received 13 March 1972

DOI:https://doi.org/10.1103/PhysRevC.5.2060