Development of the EXITE Detector: A New Imaging Detector for 20 - 300 keV Astronomy

We report on the development and testing of a detector to be used in the Energetic X-ray Imaging Telescope Experiment (EXITE). It consists of a 34 cm diameter NaI(Tl) cyrstal coupled directly to a single large image intensifier tube with associated silicon PIN diode readout. The measured spatial and energy resolutions at 122 keV are 6mm (FWHM) and 9% (FWHM), respectively. This energy resolution is ~50% better than that of any previously flown hard x-ray experiment. These resolutions decrease with the square root of the energy of the incident x-ray, indicating that they are determined by the number of photons emitted in the NaI(Tl) scintillator light flash.