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

TL;DR

This study measures ion-induced secondary electron emission from various photocathodes and assesses its impact on gaseous photomultiplier operation, providing experimental data and theoretical estimates relevant for device optimization.

Contribution

It introduces a simple indirect method to measure effective ion-induced secondary-electron emission coefficients and compares experimental results with theoretical predictions for different photocathodes.

Findings

Effective ion-induced secondary-electron emission coefficients range from 0.02 to 0.03 in gas.

Vacuum secondary-electron emission coefficients are approximately 0.47 to 0.49.

The gas medium reduces secondary electrons by about 94%.

Abstract

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, $\gamma_+^{eff}$ was developed. The experimental results with visible-sensitive K-Cs-Sb, Na-K-Sb and Cs-Sb photocathodes, yielded $\gamma_+^{eff}$ - 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, $\gamma_+$, 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 $\gamma_+^{eff}$ and vacuum $\gamma_+$ IISEE coefficients, calculated to be $\sim$0.06, is the fraction of secondary electrons surmounted the backscattering in the gas media.