Imager prototype for gamma-ray astronomy: functional performance

A prototype module for the imager on INTEGRAL (International Gamma Ray Astrophysics Laboratory) has been constructed for laboratory and space tests by means of a balloon launch. The main detector is designed to operate in the energy range from 0.25 to 10 MeV and consists of 96 CsI(Tl) bars, each 15 cm in length. At 662 keV, the typical performance is 1.5 cm full width half maximum (FWHM) spatial resolution (1 sigma ) along the bar, and 15% energy resolution. The work carried out during instrument construction and calibration is described, with emphasis on the simple method which has been implemented to normalize the nonuniformity of the performance of the bars. The measurements of energy threshold and energy and position resolution are presented and discussed.<
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