Development of gaseous neutron detector with GEM

We are developing a new gaseous neutron detector with Gas Electron Multiplier (GEM) as a detector for material science using thermal (cold) neutrons at high intensity pulsed neutron sources. For a detection of neutron, Boron is coated on the both surfaces of one GEM foil. In order to obtain higher detection efficiency, several GEM foils are stacked in a chamber. A prototype chamber was constructed with 100 mm x 100 mm GEM foils and several beam tests were performed at a research reactor in Japan. Results show the detection efficiency is 30% for 0.22 nm thermal neutrons and the position resolution is around 1 mm. Uniform 2D position measurement without distortion can be obtained. Diffraction pattern for a single crystal can be clearly observed. (author)