Thermionic Emission from an Oxide-Coated Cathode

The properties of thermionic emission from a cathode coated with barium oxide are studied. The cathode is indirectly heated and its temperature is measured by a thermocouple. It is found that the emitted electrons have a Maxwellian distribution corresponding closely to the temperature of the cathode. The emission is studied with accelerating voltages up to 1300 volts. The current rises more steeply than predicted by Schottky's theory but begins to bend at the upper end. The variation of the work function and the factor A with the state of the cathode is studied by glowing the cathode at different temperatures. It is found that both the work function and the factor A vary. No appreciable decay of emission with time is observed. The effect of drawing emission on the work function and the factors A is small.