Position sensing in a cylindrical ionization detector with a resistive cathode

Position sensing in cylindrical ionization detectors is essential for imaging applications and can be used to improve energy resolution. We propose a readout design that incorporates a resistive cathode and external pickup electrodes. Signals induced in each electrode are used to predict the radial and azimuthal coordinates of interaction vertices. A prototype detector, 25.4 mm in diameter, made of quartz fiber composite and containing xenon at 10 atm, was built to test the proposed readout design. Data collected using an 241Am alpha source show a spatial resolution of 1.9 mm (FWHM). In addition, Monte Carlo simulations of gamma interactions over a range of energies, predict values that are in good agreement with the experiment. Using the position data to remove the geometrical dependence, energy resolution at 140 and 511 keV is predicted to be 8.2% and 2.3% FWHM, respectively (ENC of 60 electrons). These values represent a significant improvement over conventional crystal detectors, such as NaI. The proposed technique can be applied in a large volume position sensitive detector.