Effect of Radiation on the Breakdown of Homogeneous Field and Sphere Gaps

Abstract

Hadiation effects on the breakdown voltage of homogeneous field and sphere gaps were investigated by mounting homogeneous-field electrodes in a glass chamber. The voltage was accurately stabilized and controlled by means of a helical potentiometer. A 0.001-microfarad condenser was charged through a 100-M OMEGA resistor, which was in turn counected to one electrode by a 10-M OMEGA resistor. This arrangement ensured that, when a spark occurred in the chamber, the voltage was chopped and the condenser had to recharge before another spark could occur. The number of discharges per minute was counted for different values of applied voltage for electrode gaps of 1 and 2 cm at pressures of 76 cm and 38.8 cm of mercury in air. The source of radiation was 0.1 mg of radium. In all cases there was an increase in the number of sparks per minute when the gap was irradiated, and there were larger differences between the spark counts as the intensity of irradiation was increased. A comparison was made between the performance of sphere and plane electrodes, and the results indicate that the breakdown voltage of a uniform field gap of 1 cm was about 2 per cent less than for the samemore » spacing between 5-cm spheres. The separation of the spheres was reduced to 0.975 cm so that both gaps broke down at the same voltage. The gaps were cornected in parallel and placed so that the radium was 30 cm from both. The apparent reduction of the breakdown voltage by irradiation was about 0.1 per cent for the uniform field and about 1 per cent for the spheres. (J.H.M.)« less