Negative Ion Emission From Oxide Coated Filaments

Abstract

Using a tube described by ${\mathrm{Smyth}}^1$, it was discovered that oxide-coated, platinum filaments emit negative ions as well as electrons. These ions were shown to be due not to gas in the tube or to gas absorbed by the filament, but to disintegration of the oxide coating itself. Electro-magnetic analysis of these ions, described in this paper, gave the value of $\frac{m}{e}$ as about 33 with reference to hydrogen ions and indicated that they consisted only of negative, singly charged, molecular oxygen ions. No evidence of the emission of any positive ions was obtained. This negative ion emission apparently begins at a lower temperature than electronic emission, and increases with temperature, but less rapidly than the electronic. The contribution of the negative ions to the space charge is appreciable because of their relatively large mass, causing the space charge limited current for a given voltage to be less than for a similar non-coated platinum filament. Certain observations by other experimenters are discussed and shown to be in support of the above conclusions.