Thermal neutron detection with a high-pressure Xe/TMA//sup 3/He gas electron multiplier

In the framework of development of a single-GEM detector for thermal neutron detection, with a position resolution of 1 mm, the charge multiplication in the GEM has been studied for different stopping gases at pressures up to 8 bar. The effect on the gain of adding ~1-~9 bars of He has been determined as well. It has been found that a Penning mixture of Xe/TMA results in the highest gain. At a pressure of 7 bar Xe/2.8% TMA a gain of 10 could still be obtained for a 50 mum thick GEM with 80 mum holes. A gain of 100 is possible in a mixture of 4 bar Xe/2.5% TMA/6 bar He, which makes 1 mm position resolution possible. We measured thermal-neutron pulse height spectra in 4 bar Xe/0.1 bar TMA/0.8 bar ³He/0-8.5 bar ⁴He