In the light rare-earth region, seven new neutron-deficient radioactive isotopes have been produced by proton bombardment in the 184-in. cyclotron and the linear accelerator; their radiations have been studied by absorption curve and magnetic counter methods. The new isotopes and their half-lives are ${\mathrm{La}}^{134}$, 6.5±0.25 min; ${\mathrm{Ce}}^{133}$, 6.30±0.1 hr; ${\mathrm{Ce}}^{134}$, 72.0±0.5 hr; ${\mathrm{Pr}}^{138}$, 120±5 min; ${\mathrm{Pr}}^{139}$, 4.50±0.2 hr; ${\mathrm{Nd}}^{138}$, 22±2 min; ${\mathrm{Nd}}^{139}$, 5.50±0.2 hr. Additional data have been obtained for the isotopes, ${\mathrm{Ce}}^{135}$ and ${\mathrm{Ce}}^{137}$.

• Received 18 August 1950

DOI:https://doi.org/10.1103/PhysRev.81.8