The removal of thorium from the surface of a thoriated tungsten filament by positive ion bombardment: K. H. Kingdon and Irving Langmuir. (Phys. Rev., Aug., 1923.)
✍ Scribed by G.F.S
- Publisher
- Elsevier Science
- Year
- 1924
- Tongue
- English
- Weight
- 54 KB
- Volume
- 197
- Category
- Article
- ISSN
- 0016-0032
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✦ Synopsis
The Removal of Thorium from the Surface of a Thoriated Tungsten Filament by Positive Ion Bombardment. K. H. KINGDON and IRVING LANGMUIR. (Phys. Rev., Aug., 1923. )-" Langmuir has shown that by subjecting a tungsten filament containing a small percentage of thorium oxide to suitable thermal treatment, it is possible to obtain a complete layer of thorium one atom deep over the surface of the tungsten. At a temperature of 15OO ° K. the electron emission from this thorium surface is about IOO,OOO times that from an equal area of pure tungsten. Hence removal of thorium from the surface by ion bombardment or otherwise exposes the tungsten underneath and decreases the electron emission of the filament." This paper is a study of the knocking off of the thorium layer by the impact of positive ions of various gases. For each gas a certain threshold voltage was necessary in order that the disintegration ("sputtering") of the thorium cathode should commence. For Ar, Cs, Hg and Ne ions about 50 volts sufficed, but for hydrogen 6oo volts were too small. At I5O volts quite different numbers of impinging ions of the several gases were needed to remove one atom of thorium. It took about 700o helium ions or 12 argon ions to take one thorium atom from the surface. G.F.S.