Neutron-deficient isotopes of bismuth and lead have been produced in various heavy-ion—induced reactions. Argon and krypton ions were used as projectiles on ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$, ${}_{}{}^{155}{}_{}{}^{}\mathrm{Gd}$, and ${}_{}{}^{109}{}_{}{}^{}\mathrm{Ag}$. We observed $\alpha$ emission from bismuth nuclides and isomers with $A=190-197\mathrm{}$ and from lead isotopes with $A=186-190\mathrm{}$. We give results on mass assignments, $\alpha$-decay energies, half-lives, and $\alpha$ branching ratios. Two new lead isotopes were found: ${}_{}{}^{187}{}_{}{}^{}\mathrm{Pb}$, $E_{\alpha }=6.08\mathrm{}$ MeV, $t_{\frac{1}{2}}=17.5\mathrm{}$ sec; and ${}_{}{}^{186}{}_{}{}^{}\mathrm{Pb}$, $E_{\alpha }=6.32\mathrm{}$ MeV, $t_{\frac{1}{2}}=7.9\mathrm{}$ sec. No $\alpha$-emitting isotopes of thallium were found, and upper limits significantly below 1% can be set on the $\alpha$ branching ratios of T1 isotopes with $A=182-187\mathrm{}$.

• Received 10 July 1972

DOI:https://doi.org/10.1103/PhysRevLett.29.958