Sealed gas UV-photon detector with a multi-GEM multiplier

A sealed gas photon detector with a gas electron multiplier (GEM) cascade coupled to a semitransparent CsI photocathode has been studied. High gains, reaching 10/sup 6/, and fast anode signals, of a width of 15 ns, were obtained with this GEM-photomultiplier in Ar-CH/sub 4/ (95/5), in a photon counting mode. The lifetime of this first prototype detector under high photon flux and large anode currents is provided.