High-pressure GEM operation aiming at thermal neutron detection

Experiments at the anticipated intense spallation neutron sources require neutron detection with typically millimeter position resolution. We are investigating the possibility of applying the gas electron multiplier (GEM) for this purpose. For efficient detection, ³He gas at up to 10 bar is required with some stopping gas at a differential pressure of 3-5 bar, i.e., high enough to sufficiently reduce the range of the neutron capture reaction products to achieve the required resolution. Due to the large initial charge deposition in the gas, only a small gain (10-100) is necessary. However, at the high pressures involved, it is not clear if even this can be achieved. We present first results of experiments using a range of gases, pressures, and, in this case, GEM hole sizes of 60 and 80 μm to investigate this question. We observed the highest gain in an Ar/DME mixture, but this mixture does not meet the resolution criterion. The use of Xe (an effective stopping gas) in a Xe/DME mixture is ruled out, as no signal can be detected at pressures above 2 bar