Some Factors Affecting the Decay of Secondary Electron Emission of SilVer-Magnesium Alloys

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The secondary emission yield is observed to decay very rapidly under electron bombardment especially during the exhaust process using oil diffusion pump. In this paper, factors affecting the decay, a method of remedy to make the decayed yield to recover, and effects of various gases and vapors on the yield are discussed. A major cause of the secondary yield decay is attributed to the deposition of amorphous carbon, which is produced on the dynode surface through the decomposition of hydrocarbon or carbon-containing gases by the electron beam. Heating the contaminated dynode at high temperatures in oxygen atmosphere for some period results in a recovery of the yield. Keeping the dynode at high temperatures during electron bombardment is effective in bringing about a marked decrease in the decay. From the data on the temperature dependence of the decay, the heat of adsorption of a gas which is considered to be the source of contamination, is calculated to be about 1.6kcal mole. N_2, CO and CO_2 do not exert any harmful effects upon activated dynodes, while H_2 exerts somewhat harmful effects, and, particularly, electric discharge in H_2 should be avoided. The most unfavorable gas is the grease vapor. The process of contamination is briefly discussed.
社団法人日本物理学会の論文
1957-07-05