Building large area CZT imaging detectors for a wide-field hard X-ray telescope—ProtoEXIST1

We have constructed a moderately large area (32cm2), fine pixel (2.5mm pixel, 5mm thick) CZT imaging detector which constitutes the first section of a detector module (256cm2) developed for a balloon-borne wide-field hard X-ray telescope, ProtoEXIST1. ProtoEXIST1 is a prototype for the High Energy Telescope (HET) in the Energetic X-ray imaging Survey Telescope (EXIST), a next generation space-borne multi-wavelength telescope. We have constructed a large (nearly gapless) detector plane through a modularization scheme by tiling of a large number of 2cm×2cm CZT crystals. Our innovative packaging method is ideal for many applications such as coded-aperture imaging, where a large, continuous detector plane is desirable for the optimal performance. Currently we have been able to achieve an energy resolution of 3.2keV (FWHM) at 59.6keV on average, which is exceptional considering the moderate pixel size and the number of detectors in simultaneous operation. We expect to complete two modules (512cm2) within the next few months as more CZT becomes available. We plan to test the performance of these detectors in a near space environment in a series of high altitude balloon flights, the first of which is scheduled for Fall 2009. These detector modules are the first in a series of progressively more sophisticated detector units and packaging schemes planned for ProtoEXIST2 & 3, which will demonstrate the technology required for the advanced CZT imaging detectors (0.6mm pixel, 4.5m2 area) required in EXIST/HET.