Design and testing of a prototype pixellated CZT detector and shield for hard- x-ray astronomy

We report on the design and laboratory testing of a prototype imaging CZT detector intended for balloon flight testing in April 2000. The detector test several key techniques needed for the construction of large-area CZT arrays, as required for proposed hard x-ray astronomy missions. Two 10 mm X 10 mm X 5 mm CZT detectors, each with a 4 X 4 array of 1.9 mm pixels on a 2.5 mm pitch, will be mounted in a 'flip chip' fashion on a printed circuit board carrier card; the detectors will be placed 0.3 mm apart in a tiled configuration such that the pixel pitch is preserved across both crystals. One detector is eV Products high-pressure Bridgman CZT, and the other is IMARAD horizontal Bridgman material. A passive shield/collimator surrounded by plastic scintillator surrounds the detectors on five sides and provides an approximately 45 degree field of view. The background spectrum recorded by this instrument will be compared to that measured by a single-element CZT detector fitted with the same passive/plastic collimator but including an active BGO shield to the rear. This detector has been previously flown by us completely shielded by a passive cover. We describe preliminary laboratory result for the various systems, discuss initial background simulations, and describe our plans for balloon flight tests.