Isotopes of actinium lighter than mass 216 were studied at the Berkeley heavy-ion linear accelerator by bombardment of ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, enriched ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$ and ${}_{}{}^{203}{}_{}{}^{}\mathrm{Tl}$ with ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ with ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$. Silicon (Au) surface-barrier detectors were used in on-line measurements to determine $\alpha$-decay characteristics. Mass-number assignments of ${}_{}{}^{209}{}_{}{}^{}\mathrm{Ac}$ through ${}_{}{}^{215}{}_{}{}^{}\mathrm{Ac}$ were made on the basis of excitation functions, genetic relationships with radium isotopes, and systematic trends in $\alpha$-decay energies. Half-lives and $\alpha$-particle energies were determined.

• Received 6 October 1967

DOI:https://doi.org/10.1103/PhysRev.167.1094