A new series of radioactive isotopes has been produced by deuteron and helium ion bombardments of thorium. The identity and the properties of the five members of this series, which is a branch of the uranium-radium series and joins it at RaC′, are shown to be the following: $\left\{{\mathrm{Pa}}^{230}\underset{17d}{\stackrel{{\beta }^{-}}{\to }}{\mathrm{U}}^{230}\underset{20.8d}{\stackrel{\alpha \left(5.86\mathrm{}\mathrm{MeV}\right)}{\to }}{\mathrm{Th}}^{226}\underset{30.9m}{\stackrel{\alpha \left(6.3\mathrm{}\mathrm{MeV}\right)}{\to }}\right\}\left\{{\mathrm{Ra}}^{222}\underset{38s}{\stackrel{\alpha \left(6.5\mathrm{}\mathrm{MeV}\right)}{\to }}{\mathrm{Em}}^{218}\underset{0.019s}{\stackrel{\alpha \left(7.1\mathrm{}\mathrm{MeV}\right)}{\to }}\mathrm{Ra}{\mathrm{C}}^{\prime }\underset{1.5\times {10}^{-4\mathrm{}}}{\stackrel{\alpha }{\to }}\right\}\left\{\mathrm{RaD}\underset{22y}{\stackrel{{\beta }^{-}}{\to }}\mathrm{RaE}\underset{5d}{\stackrel{{\beta }^{-}}{\to }}\mathrm{RaF}\underset{140d}{\stackrel{\alpha }{\to }}\mathrm{RaG}\right(\mathrm{stable}\left)\right\}$

A simple electronic device was developed to measure the short half-life of ${\mathrm{Em}}^{218}$.

• Received 20 May 1948

DOI:https://doi.org/10.1103/PhysRev.74.591