We report on recent three-dimensional imaging performance and detection efficiency measurements obtained with 5 mm thick prototype CdZnTe detectors fabricated with orthogonal coplanar anode strips. In previous work, we have shown that detectors fabricated using this design achieve both very good energy resolution and sub-millimeter spatial resolution with fewer electronic channels than are required for pixel detectors. As electron-only devices, like pixel detectors, coplanar anode strip detectors can be fabricated in the thickness required to be effective imagers for photons with energies in excess of 500 keV. Unlike conventional double-sided strip detectors, the coplanar anode strip detectors require segmented contacts and signal processing electronics on only one surface. The signals can be processed to measure the total energy deposit and the photon interaction location in three dimensions. The measurements reported here provide a quantitative assessment of the detection capabilities of orthogonal coplanar anode strip detectors.

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We report new performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector under study as a prototype imaging spectrometer for astronomical X-ray and 7-ray observations. The prototype is 1.5 mm thick with 375 micron strip pitch in both the x and y dimensions. Previously reported work included demonstrations of half-pitch spatial resolution ( 190 microns) and good energy resolution and spectral uniformity. Strip detector efficiency measurements have also been presented. A model that includes the photon interaction, carrier transport and the electronics was developed that qualitatively reproduced the measurements.The new studies include measurements of the CdZnTe transport properties for this prototype in an effort to resolve quantitative discrepancies between the measurements and the simulations. Measurements of charge signals produced by laser pulses and a-rays are used to determine these transport properties. These are then used in the model to predict 7-ray efficiencies that are compared with the data. The imaging performance of the detector is studied by scanned laser and gamma beam spot measurements. The results support the model's prediction of nearly linear sharing of the charge for interactions occurring in the region between electrodes. The potential for strip detectors with spatial resolution much finer than the strip pitch is demonstrated. A new design scheme for strip detectors is shortly discussed.

We are working on the development of a new balloon-borne telescope, MARGIE (Minute-of-Arc Resolution Gamma ray Imaging Experiment). It will be a coded aperture telescope designed to image hard X-rays (in various configurations) over the 20-600 keV range with an angular resolution approaching one arc minute. MARGIE will use one (or both) of two different detection plane technologies, each of which is capable of providing event locations with sub-mm accuracies. One such technology involves the use of Cadmium Zinc Telluride (CZT) strip detectors. We have successfully completed a series of laboratory measurements using a prototype CZT detector with 375 micron pitch. Spatial location accuracies of better than 375 microns have been demonstrated. A second type of detection plane would be based on CsI microfiber arrays coupled to a large area silicon CCD readout array. This approach would provide spatial resolutions comparable to that of the CZT prototype. In one possible configuration, the coded mask would be 0.5 mm thick tungsten, with 0.5 mm pixels at a distance of 1.5 m from the central detector, giving an angular resolution of 1 arc-minute and a fully coded field of view of 12 degrees. We review the capabilities of the MARGIE telescope and report on the status of our development efforts and our plans fora first balloon flight.