Abstract
Gas Electron Multiplier based detectors have been recently used for neutron measurement at spallation sources and for fusion relevant applications. The present work is meant to characterize the detector sensitivity to γ-ray background which often can represent the main background source associated to neutron measurements. The γ-ray sensitivity has been measured as a function of detector gain and it has been found to be lower than 10−7at the typical gain used for neutrons detection. Coincidence measurements, giving the possibility to select mono-energetic photons and to suppress background events, allowed to measure the absolute sensitivity at a well defined γ-ray energy and at low interaction rates. The mechanism of interaction and energy deposition of γ-rays in the detector has been studied using MCNPX Monte Carlo simulations.