MISTI imaging and source localization

MISTI (Mobile Imaging and Spectroscopic Threat Identification) provides both excellent gamma-ray spectroscopic and imaging capabilities to maximize the detection sensitivity of localized sources while at the same time minimizing the false alarm rate. The truck-based instrument is currently under construction and will detect and locate, in both position and range, a 1 mCi 137 Cs at 100 m in 20 s with typical background levels. This performance is achieved using a hybrid system that combines the superb spectroscopic capabilities of germanium detectors for sensitive detection with the large collecting power available using scintillation detectors for producing gamma-ray images. Once an isotope of interest is detected by the germanium system, the NaI imager generates gamma-ray images for that energy that are overlaid based on the truck location at the time of acquisition. The overlayed images are calculated at a number of distance from the truck and the location and range of the source is determined by locating the reconstructed position and range with the maximum flux. The fully coded field of view, where all detectors contribute to the image, covers 92° × 29° using 9 × 3 pixels with the larger coverage in the horizontal direction.