Reconstruction of the Spatial Distribution of Surface Activity Concentration for an In-Situ, Gamma-Ray, Truck-Borne Survey

In 2012, a radiological dispersal device (RDD) was detonated at the experimental proving ground of Defence Research and Development Canada, in Suffield, Alberta. The Nuclear Emergency Response Team of Natural Resources Canada conducted two mobile surveys to reconstruct the distribution of surface activity concentration of the deposited material, lanthanum-140. One of these surveys involved using a truck-borne, directional spectrometer, which contained four, standing, NaI(Tl) detectors. The Electron Gamma Shower code of the National Research Council (EGSnrc) was used to find the averaged activity concentration for a gamma-emitting disc source, with a radius at the threshold of the spectrometer sensitivity. In addition, a spatial deconvolution method was used to reconstruct the distributed source around a sample of survey path. It involved pixelizing a field of interest, and representing the distributed source by pixel sources, based on array responses for EGSnrc simulations and the respons from the Suffield dataset.