The Disintegration Voltage

Author: J.B. Hoag

Atoms from which electrons have been ejected are called positive ions. If these ions have been created in the region between the filament and the plate of a gas-filled tube, then the positive potential of the plate repels them toward the cathode. If the energy which they acquire by the time they strike the cathode is sufficiently small they will not damage the cathode. If, however, their energy exceeds 20 to 25 volts, for inert gases and mercury vapor, then the positive ion bombardment will disintegrate the sensitized coatings on the filament and render it a poor emitter of electrons.

The working range of voltages across a gas-filled tube is given as the difference between the disintegration voltage and the ionizing potential. If the voltage across the tube is less than the ionizing potential, the gas will not be ionized, and if the voltage exceeds the disintegration voltage, the cathode willsoon be ruined. It is possible, within limits, to control the voltage drop across a tube by choosing its dimensions properly so that it is below the disintegration value.