Spectral response of antimony-caesium photocathodes

Abstract

Measurements have been made of the relative photoelectric quantum efficiency η(λ) of SbCs3 cathodes of photomultipliers with Pyrex and quartz windows, from λ = 200-650 mμ. η(λ) depends on the window transmittance W(λ), the cathode absorbance A(λ, d), the absolute photoelectric quantum efficiency Q0(λ) and the photoelectron escape probability f(λ, d). Comparison with other data has allowed the separation of these factors, yielding inter alia the absorption spectrum of SbCs3 down to λ = 220 mμ, and the absolute photoelectric threshold curve Q0(λ) plotted against λ. The optimum thickness for a thin cathode is d = 200 A. Errors in other published data are noted, and methods of increasing η(λ) and of improving scintillation detectors are discussed.