  Controlled etching of copper electrodes in Gas Electron Multiplier foils
allows a reduction of the material budget by more than a factor of two for a
triple-GEM detector. Detectors making use of thinned foils provide performances
similar to those obtained with standard devices: a gain above 10^4 for a
double-GEM, with energy resolution of 27 % fwhm for 5.9 keV X-rays.

Instrumentation and Detectors