HREXI calibration facility: mapping out subpixel-level responses from high-resolution cadmium zinc telluride imaging x-ray detectors

Abstract

The High-Resolution Energetic X-ray Imager (HREXI) cadmium zinc telluride (CZT) detector development program at Harvard is aimed at developing tiled arrays of finely pixelated CZT detectors for use in wide-field coded aperture 3 to 200 keV x-ray telescopes. A pixel size of ∼600 μm has already been achieved in the ProtoEXIST2 (P2) detector plane with CZT readout by the NuSTAR application-specific integrated circuits. This paves the way for even smaller than 300-μm pixels in the next-generation HREXI detectors. We describe a new HREXI calibration facility (HCF) that enables a high-resolution subpixel-level (100 μm) two-dimensional (2D) scan of a 256-cm2 tiled array of 2 × 2 cm2 CZT detectors illuminated by a bright x-ray AmpTek Mini-X tube source at timescales of around a day. HCF is a significant improvement from the previous apparatus used for scanning these detectors, which took ∼3 weeks to complete a one-dimensional (1D) scan of a similar detector plane. Moreover, HCF has the capability to scan a large tiled array of CZT detectors (32 × 32 cm2) at 100-μm resolution in the 10- to 50-keV energy range, which was not possible previously. We describe the design, construction, and implementation of HCF for the calibration of the P2 detector plane.