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Session 48 - Gamma Rays & X-ray Instrumentation.
Display session, Thursday, January 08
Exhibit Hall,
CZT (Cadmium Zinc Telluride), a room-temperature semiconductor, is a very promising detector material for high energy X-ray astronomy. It can operate from <10 keV to >200 keV, and give sub-keV energy resolution and sub-mm spatial resolution. Thus it is attractive for both focusing instruments with small fields of view, <1^\circ, and coded mask instruments with large fields of view, >10^\circ. We report recent progress on CZT detectors by the UCSD/WU collaboration. Three detectors were used: a 25 x 25 x 1.4 mm^3 detector with orthogonal crossed strip readout using 375 micron pitch electrodes, manufactured by Digirad, (2) a 12 x 12 x 2 mm^3 detector with orthogonal crossed strip readout using 500 micron pitch electrodes plus "steering electrodes" to improve the anode charge collection, manufactured by eV Products, and (3) a standard 12 x 12 x 2 mm^3 planar detector manufactured by eV Products. The eV Products crossed strip detector achieved \sim4.5 keV resolution with no tailing at 60 keV using commercial electronics. Uniformity of spectral response versus position and absolute accuracy of spatial response were measured with a finely collimated, 30 micron diameter, X-ray beam. Inaccuracies of inferred interaction positions of a few 100 microns were often observed. The latter 2 detectors were tested on a balloon flight to determine their energy resolution and background with several passive shielding schemes. Model calculations were made of charge collection and the effects of the steering electrodes' bias and compared with laboratory results. We also report on future plans which include the integration of detectors, bias networks, and readout ASICs to form the "plug-in module" which is planned to be tested on a balloon flight in March 1998.
