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Title: Exploitation of Geometric Occlusion and Covariance Spectroscopy in a Gamma Sensor Array

The National Security Technologies, LLC, Remote Sensing Laboratory has recently used an array of six small-footprint (1-inch diameter by 3-inch long) cylindrical crystals of thallium-doped sodium iodide scintillators to obtain angular information from discrete gamma ray–emitting point sources. Obtaining angular information in a near-field measurement for a field-deployed gamma sensor is a requirement for radiological emergency work. Three of the sensors sit at the vertices of a 2-inch isosceles triangle, while the other three sit on the circumference of a 3-inch-radius circle centered in this triangle. This configuration exploits occlusion of sensors, correlation from Compton scattering within a detector array, and covariance spectroscopy, a spectral coincidence technique. Careful placement and orientation of individual detectors with reference to other detectors in an array can provide improved angular resolution for determining the source position by occlusion mechanism. By evaluating the values of, and the uncertainties in, the photopeak areas, efficiencies, branching ratio, peak area correction factors, and the correlations between these quantities, one can determine the precise activity of a particular radioisotope from a mixture of radioisotopes that have overlapping photopeaks that are ordinarily hard to deconvolve. The spectral coincidence technique, often known as covariance spectroscopy, examines the correlations and fluctuations inmore » data that contain valuable information about radiation sources, transport media, and detection systems. Covariance spectroscopy enhances radionuclide identification techniques, provides directional information, and makes weaker gamma-ray emission—normally undetectable by common spectroscopic analysis—detectable. A series of experimental results using the concept of covariance spectroscopy are presented.« less
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Journal Name: Proc. SPIE 8852, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XV, 88520H; Journal Volume: 8852; Conference: SPIE Conference Optics + Photonics; August 26, 2013; San Diego, CA
Research Org:
Nevada Test Site/National Security Technologies, LLC (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA), Office of Emergency Operations (NA-40)
Country of Publication:
United States
occlusion, covariance spectroscopy, correlations, fluctuations, Compton scattering