ジョンソン形電顕球によるトリウムタングステン線のエミッション像の研究

抄録

Some thoriated tungsten filaments used in vacuum tubes have abnormally high evaporation of emissive matter at initial stage of aging process, which however does not affect the normal emission characteristics, though occasionally faulty grid emission leads to breakdown of the tubes. In order to investigate the cause of such abnormality, experimental tubes with thoriated tungsten filaments in varied conditions are prepared and emission patterns are examined with a Johnson type emission microscope. Of all the filaments tested, only those that had the said abnormality were found to undergo reversal of emission pattern, dark area of the pattern becoming bright in initial stage of aging process. This reversal of pattern occurs readily when the tube vacuum deteriorates. Under optical microscope, those responsible filaments alone show cracks in their carburized surface layer, probably produced either before or during the carburization. The reversal of pattern is therefore explained as related to abnormal evaporation and cracking in carburized surface layer of the filament.