Properties of the GEM, double GEM and GEM plus MGC combination

We have examined the operation of a GEM, double GEM and GEM + MGC combinati on in several counting gases, including argon/DME 60/40, 90/10, xenon/DME 9 0/10, xenon/CO2 90/10 as well as pure argon and pure xenon. In a cascaded G EM configuration, large gains are recorded, around 10(5) in argon/DME 90/10 . Energy resolution is < 25% FWHM for 5.9 keV photons. The collected electr on cloud size is limited to a maximum of similar to 10(7) electrons, depend ing somewhat on the voltage across the last amplifying GEM. For the MGC in combination with the GEM this maximum, the Raether limit, is found to be 2. 7 x 10(7) electrons. This corresponds to a gain for the GEM + MGC of 1.5 x 10(5) for 5.9 keV photons in Ar/DME 60/40. In pure argon and xenon the maxi mum gain is, respectively, 4000 and 7000 for the double GEM, with energy re solutions of, respectively, 40% and 25% FWHM. Special attention is paid to behaviour of the gain with respect to the electric field strengths before a nd after the GEM, as well as between two GEMs, in view of a better understa nding of the processes of charge collection into the hole and ejection out of the hole. (C) 2000 Elsevier Science B.V. All rights reserved.