A 48×48 CdZnTe array with multiplexer readout

We report results of gamma-ray imaging and energy-resolution tests of a 48×48 CdZnTe array. Our detectors have 125 μm square pixel electrodes produced by photolithography and are indium-bump-bonded to a multiplexer readout circuit. Using a collimated beam of 140 keV gamma rays of 120 μm diameter centered on one pixel, we found that the majority of events produced significant charge deposition in nearby pixels. Charge and energy are transported out of the pixel by charge diffusion, photoelectron range, Compton scattering, and escape of K X-rays. These effects also distort single-pixel spectra, although photopeaks are still discernible at 140 keV. When signals from neighboring pixels are summed together to correct for this charge spreading, an energy resolution of 10 keV is obtained at 140 keV. Corrections will be simpler and energy resolution should be better for the 380 μm pixels of the 64×64 CdZnTe arrays we are constructing for an ultra-high-resolution brain imager