  In this paper, measurement results and experimental methodology are presented
on the determination of multiplication distributions of avalanches initiated by
single electron in GEM foils. The measurement relies on the amplification of
photoelectrons by the GEM under study, which is subsequently amplified in an
MWPC for signal enhancement and readout. The intrinsic detector resolution,
namely the sigma-over-mean ratio of the multiplication. distribution is also
elaborated. Small gain dependence of the shape of the avalanche response
distribution is observed in the range of net effective gain of 15 to 100. The
distribution has an exponentially decaying tail at large amplitudes. At small
amplitudes, the applied working gas is seen to have a well visible effect on
the shape of the multiplication distribution. Equivalently, the working gas has
an influence on the intrinsic detector resolution of GEMs via suppression of
the low amplitude responses. A sigma-over-mean ratio of 0.75 was reached using
a neon based mixture, whereas other gases provided an intrinsic detector
resolution closer to 1, meaning a multiplication distribution closer to the
low-field limit exponential case.

Instrumentation and Detectors;High Energy Physics - Experiment;Nuclear Experiment