Progress in MHSP electron multiplier operation

The Micro-Hole & Strip-Plate gas electron multiplier (MHSP) was studied as a stand-alone device or in combination with a cascade of Gas Electron Multipliers (GEMs), for x-ray and UV-photon detection. An MHSP operating in Ar/5%Xe yielded gains above 10/sup 4/ and energy resolutions of about 14% FWHM for 5.9-keV x-rays. Gains as high as 10/sup 7/ were reached in a 3-GEM/MHSP gaseous photomultiplier operating in an Ar/5%CH/sub 4/; the ion-backflow fraction to the top of the first GEM could be reduced down to ∼2% 2D-imaging performed using signals induced by avalanche ions on a Wedge-and-Strip readout cathode, placed at close proximity of the anode strips yielded position resolutions of the order of 200 to 250 μm FWHM for 5.9-keV x-rays.