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The CZT detector on the InFOCµS hard X-ray telescope is a pixellated solid-state device capable of imaging spectroscopy by measuring the position and energy of each incoming photon. The detector sits at the focal point of an 8 m focal length multilayered grazing incidence X-ray mirror which has significant effective area between 20-40 keV. The detector has an energy resolution of 4.0 keV at 32 keV, and the InFOCµS telescope has an angular resolution of 2.2 arcminute and a field of view of about 10 arcminutes. InFOCµS flew on a balloon mission in July 2001 and observed Cygnus X-1. We present results from laboratory testing of the detector to measure the uniformity of response across the detector, to determine the spectral resolution, and to perform a simple noise decomposition. We also present a hard X-ray spectrum and image of Cygnus X-1, and measurements of the hard X-ray CZT background obtained with the SWIN detector on InFOCµS.

The energy resolution of CdTe and CdZnTe detectors is usually limited by the poor transport properties of holes. Devices segmented into small pixels have been observed to exhibit improved energy resolutions. Simulations have shown that this small pixel effect is due to the fact that small pixels are mostly sensitive to carriers moving close to the pixel, within a distance of the order of the pixel size. In this paper, signals are calculated for CdZnTe strip detectors in order to determine to what extent a similar small electrode effect is produced by strips. The free carrier density distributions following the absorption of a y-ray are calculated by solving the continuity equations. Combined with the strip weighting field, this provides the signal induced in the strip. Simulations are made for various detector geometries and for both the anode and cathode strips. Simulated signals are compared with actual signaIs measured on CdZnTe detectors.

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