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

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/CH4(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.