Photon-counting energy-sensitive micropattern gas detector for digital radiography

A photon counting energy sensitive micro-pattern gaseous detector is being developed for projection radiography. Two cascaded gas electron multipliers (GEMs) are used as gain stages following a drift region that acts as an absorption volume. Active area of the detector is 7cm x 7cm and the signal is read out by 0.2 mm pitch strips. An aluminum pressure vessel was designed as an integral part of the detector, which operates at pressures up to 10 atm. Voltage-gain curves were obtained for Ar and Kr mixtures. Energy resolution for a 5.9 keV Fe-55 was determined to be 20% FWHM. Energy spectra for a conventional x-ray generator operating at various voltages were also obtained. Detector MTF and DQE were calculated using linear systems analysis. The effect of primary electron range, a dominant factor in determining spatial resolution, and the effect of fluorescent photon reabsorption were studied. Operation of the detector for imaging at higher pressures with Kr and Xe mixtures is in progress.

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