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2007 Nuclear Science Symposium and Medical Imaging Conference (2007 NSS/MIC), Honolulu : États-Unis (2007)
Single electron Response and Energy Resolution of a Micromegas Detector
V. Lepeltier1, B. Genolini2, J. Pouthas2, T. Zerguerras2

In gaseous detectors, spatial and energy resolutions are limited by the gain fluctuations. We have measured the single electron response of a Micromegas detector and also its energy resolution as a function of the number of electrons by means of a point-like electron source. A pulsed nitrogen UV laser is focused on the drift electrode made of a thin metal layer deposited on a quartz lamina, creating with an accuracy of 1 micron a spot of an adjustable and well known number of photoelectrons, with a transverse size smaller than 100 microns. With a drift distance of 3 mm, and a Ne-isobutane (90-10%) gas mixture the transverse diffusion is 200 microns rms. The avalanche in the multiplication gap induces charge on the anode made of 128 strips with a 338 microns pitch. For the single electron measurements, the total number of electrons is about 150, in such a way that the corresponding number of electrons contributing to a signal on a strip located at a transverse distance of 4-5 standard deviations from the spot is never greater than one.
1 :  LAL - Laboratoire de l'Accélérateur Linéaire
2 :  IPNO - Institut de Physique Nucléaire d'Orsay
Physique/Physique/Instrumentations et Détecteurs