The effect of irradiation on the breakdown voltage of sphere-gaps in air under direct and alternating voltages

Breakdown voltages have been measured with and without the irradiation from 0.5 mg of radium. Spheres of diameters 2 to 25 cm were used and some experiments were made with parallel-plate electrodes. The irradiation lowered the breakdown voltage by as much as 4% in some circumstances. A maximum effect was obtained with a particular gap length, and this length depended on the size of the sphere electrodes.