2-D imaging with cascaded GEM/MHSP multipliers

The imaging properties of cascaded-GEM (Gas Electron Multiplier) and cascaded-GEM/MHSP (Micro-Hole and Strip Plate) gaseous electron multipliers, equipped with 2-D Wedge and Strip (W and S) readout electrodes, are presented. The W and S electrode was capacitively coupled to the electron multiplier through a resistive electrode, to adapt the charge-cloud size to the 1.6 mm readout pitch. The studies were carried out with soft X-rays and single UV-photons in Ar/5%CH4 gas mixture at atmospheric pressure. Spatial resolutions of ∼225μm and ∼250μm (FWHM) were reached, with 5.9 keV X-rays, in 3-GEM and 2-GEM/MHSP based detectors, respectively. Single photoelectrons, emitted from a CsI photocathode deposited on the top electrode of the first GEM in the cascade, were localized with resolution of ∼ 170μm (FWHM) in a 4-GEM gaseous photomultiplier