Ion-induced secondary electron emission from K-Cs-Sb, Na-K-Sb, and Cs-Sb photocathodes and its relevance to the operation of gaseous avalanche photomultipliers

摘要

The operation of visible-sensitive gaseous and to some extent, vacuum-photomultipliers is critically affected by secondary electrons originating from ion impact on the photocathode. A simple method for indirect measurement of the effective ion-induced secondary-electron emission (IISEE) coefficient from the photocathode into a gas medium γ_+~(eff) was developed. The experimental results with visible-sensitive K-Cs-Sb, Na-K-Sb, and Cs-Sb photocathodes, yielded γ_+~(eff)-values between 0.02 and 0.03 in Ar/CH_4(95/5) at 700 mbar; these are in good agreement with theoretical calculations. The corresponding vacuum IISEE coefficients γ_+ were estimated, based on a theoretical model, to be 0.47, 0.49, and 0.47 for K-Cs-Sb, Na-K-Sb, and Cs-Sb photocathodes, respectively. The ratio of gas γ_+~(eff) and vacuum γ_+ IISEE coefficients, calculated to be ～0.06, is the fraction of secondary electrons surmounted the backscattering in the gas media.