The GEM photomultiplier operated with noble gas mixtures

We present the results of detailed investigations of the Gas Electron Multi plier (GEM)-based photomultiplier, consisting of a solid CsI photocathode c oupled to a cascade of GEM elements. The detector is filled with non-ageing mixtures based on noble gases: Ar, Ne, Ar + Ne, Ar + Xe, Ar + CH4 and Ar N-2. Very high gas gains, reaching 10(6), and rather fast anode pulses, of a width of 10 ns, were observed in some mixtures. Various phenomena and ph ysical processes, found to affect the device operation, are discussed here: additional gain due to secondary scintillation; mixtures with enhanced ion ization efficiency. improvement of pulse-height resolution due to avalanche confinement in the GEM holes; avalanche extension outside the GEM holes: g ain limitation due to ion feedback and charging-up of GEM electrodes: photo electron backscattering. (C) 2000 Elsevier Science B.V. All rights reserved .