Performance of high pressure Xe/TMA in GEMs for neutron and X-ray detection

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 addition of several bars of He to these gases has been determined. It has been found that a Penning mixture of Xe/TMA has the highest gain. At a pressure of 7 bar Xe+2.5% TMA a gain of 10 could still be obtained for a 50 /spl mu/m thick GEM with 80 /spl mu/m holes. A gain of 100 is possible in a mixture of 4 bar Xe, 2.5% TMA and 6 bar He, which makes the above mentioned position resolution possible. In addition it has been found that the Xe/TMA mixture scintillates around 300 nm in the multiplication process in the GEM. The light yield per secondary electron depends only slightly on the Xe pressure or the TMA concentration.