Electron emission from cold magnesium oxide

A porous layer of magnesium oxide may be used as a cold source of electrons in a vacuum tube, the emission depending upon the maintenance of a positive electric field through the oxide layer. Methods of making and processing cathodes of this type are described, and it is shown that stable emission is obtained only from cathodes in a fully oxidized state. The behaviour of these cathodes under various experimental conditions has been examined with particular reference to voltage and temperature effects.