Direct Comparison ofmefor the Positron and the Electron

A relativistic, double-focusing mass spectrometer has been built to operate with 55-kev electrons. It has reversible electric field and fixed magnetic field. Positrons from ${\mathrm{Na}}^{22}$ and electrons from a hot filament alternately follow identical trajectories in opposing directions. The magnitude of the electric field required to focus is used as the measure of $\frac{m}{e}$. Seventeen positron runs were made intermediate in time between twelve electron runs. The rms deviation of the data lies within the standard deviation associated with positron counting. The result is $\frac{{\left(\frac{m}{e}\right)}^{-}-{\left(\frac{m}{e}\right)}^{+}}{\frac{m}{e}}=(26\mathrm{}\pm 71)\times {10}^{-6\mathrm{}},$ where the uncertainty is the standard deviation.