Abstract
Abstract The effect of chlorine, bromine, and oxygen on the emission of thermal positive ions from tungsten filaments has been studied. When a tungsten filament is heated in a vacuum, positive ion emission is always observed, and it cannot be removed completely by flashing the filament at high temperatures. This background ion emission increases greatly in halogen or oxygen. Main positive ions are K+ and Na+. The increase cannot be explained by the increase of the work function of tungsten by the formation of adsorbed layer of halogen or oxygen atoms. It is ascertained that the tungsten surface reacts with these gases and the reaction products evaporate as neutral particles. As the reaction proceeds, tungsten surface is removed successively and alkali metal atoms in the bulk are exposed to the surface and contribute to the positive ion emission.
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