The $\beta$-rays emitted by the isotopes ${\mathrm{Ga}}^{70}$, ${\mathrm{As}}^{76}$, ${\mathrm{Br}}^{80}$, ${\mathrm{Br}}^{82}$, ${\mathrm{Rb}}^{86}$, ${\mathrm{Rh}}^{104}$, ${\mathrm{Ag}}^{108}$, ${\mathrm{In}}^{116}$, ${\mathrm{Sb}}^{122}$, ${\mathrm{Sb}}^{124}$, ${\mathrm{I}}^{128}$, ${\mathrm{Re}}^{186}$, and ${\mathrm{Au}}^{198}$ have been examined for positrons by the "trochoidal" method of Thibaud. ${\mathrm{Br}}^{80}$ is the only one of the above isotopes which was found to emit positrons as well as electrons. In studying Rb, a new activity of about 40-day half-life was found.

• Received 13 August 1947

DOI:https://doi.org/10.1103/PhysRev.72.1156