A germanium-based coded aperture imager

We describe a coded-aperture-based gamma-ray imager that uses a unique hybrid germanium detector system. A planar, germanium strip detector, 11 mm thick, is followed by a coaxial detector. The 19×19 strip detector (2-mm pitch) is used to determine the location and energy of low-energy events. The location of high-energy events is determined from the location of the Compton scatter in the planar detector. The energy is determined from the sum of the coaxial and planar energies. With this geometry, we obtain useful photopeak quantum efficiency in a position-sensitive mode out to 500 keV The detector is used with a 19×17 URA coded aperture to obtain spectrally resolved images in the gamma-ray band. We discuss the performance of the planar detector, the hybrid system, and present images taken of laboratory sources.