AN ALL-SKY SURVEY FOR TENS OF KEV

The HEXIS (High Energy X-Ray Imaging Spectrometer) is a MIDEX-class mi ssion concept to perform a deep survey and continuous monitoring of ne arly the entire sky in the 5-200 keV band. It uses arrays of position- sensitive Cadmium-Zinc Telluride (CZT) detectors and coded masks to ac hieve 26/ resolution and a 5 sigma sensitivity (> 20 keV) of 4 milliCr ab in one day and 0.2 milliCrab in one year. With these capabilities i t is estimated that similar to 5000 sources can be discovered and loca lized and have their spectra and variability characterized. Hundreds o f gamma-ray bursts would be detected each year and localized to < 20/. HEXIS also contains a narrow field, 5 degrees, coded mask imager for detailed studies of selected regions. This has three are minute resolu tion and is seven times more sensitive than the all-sky system. The HE XIS detector concept uses crossed strip readout to achieve 0.5 mm reso lution pixels for large area arrays, similar to 400 cm(2). This techni que is under development at UCSD and Washington University. Detectors have been studied with tuneable monochromatic x-ray beams and mapped w ith finely collimated 30 micron beams. These results show that the cro ssed strip readout has the necessary spatial and spectral characterist ics. The HEXIS concept is described and results are presented on the d etectors' spatial and spectral properties.