A gamma ray camera, based principally on position-sensitive silicon detectors, is proposed as a means to imaging the radioactive materials in the background. In order to maximize its utility, the background imager should be able to sense environmental alterations out to reasonable ranges, be of relatively low cost so that it can be widely deployed, and finally, it should have a large active volume so that statistical fluctuations in the count do not out-compete the environmental fluctuations of interest. In general, the qualities 'low cost' and 'large volume' are mutually exclusive, especially if the solid-state detectors with the best energy and spatial resolution are deployed; however, if batch-processed silicon-based detectors can be deployed, then greater detector areas can be realized, at the cost of mass attenuation and absorption probability. We will compensate for the reduced differential detection efficiency by building layers of silicon detectors, in which each individual component detector will be 3D position-sensitive, in which the interaction depth is sensed via drift time measurements, and the 2D lateral position measured via charge sharing techniques. The silicon scatter layers will be coupled with position-sensitive scintillator sensors that we are currently developing, if a high Z, high-density stopping detector is required.
Keywords: RADIATION DETECTION, COMPTON CAMERA, INTERNAL IMAGING, ENVIRONMENTAL ANALYSIS, SILICON DETECTORS, GAMMA RAY SOURCES
