A number of heavy alpha-particle emitting nuclides, members of decay chains which are "collateral" to the heavy radioactive series, have been observed and their radioactive properties characterized. Some of these undergo branching decay by orbital electron capture. The parent isotopes are produced in bombardments of thorium with high energy deuterons or helium ions in the 184-inch cyclotron. Chemical identification has been made in all cases where needed, and the alpha-particle energies have been measured through the use of an alpha-pulse analyzer apparatus. The following are the collateral series which have been studied: ${\mathrm{Pa}}^{226}\to {\mathrm{Ac}}^{222}\to {\mathrm{Fr}}^{218}\to {\mathrm{At}}^{214} (4n+2\mathrm{} \mathrm{mass}\mathrm{type})$; ${\mathrm{Pa}}^{227}\to {\mathrm{Ac}}^{223}\to {\mathrm{Fr}}^{219}\to {\mathrm{At}}^{215} \mathrm{}(4n+3)\mathrm{}$; ${\mathrm{Pa}}^{228}\to {\mathrm{Ac}}^{224}\to {\mathrm{Fr}}^{220}\to {\mathrm{At}}^{216} \mathrm{}\left(4n\right)\mathrm{}$; ${\mathrm{U}}^{228}\to {\mathrm{Th}}^{224}\to {\mathrm{Ra}}^{220}\to {\mathrm{Em}}^{216} \mathrm{}\left(4n\right)\mathrm{}$; ${\mathrm{U}}^{229}\to {\mathrm{Th}}^{223}\to {\mathrm{Ra}}^{221}\to {\mathrm{Em}}^{217} \mathrm{}(4n+1)\mathrm{}$.

• Received 7 November 1950

DOI:https://doi.org/10.1103/PhysRev.81.782