Point Source Detection using Sodium Iodide Detectors for Radiation Portal Monitoring

Radiation detection systems are deployed at U.S. borders to guard against entry of illicit radioactive material. Nuisance alarms due to naturally occurring radiation (NORM) limit detection probabilities (DPs) for threat sources. Strategies to recognize common NORM such as cat litter or ceramics depend on the sensor energy resolution. This paper uses data from one site to evaluate to what extent sodium iodide (NaI) gamma detectors deployed in primary screening can detect threat point sources, with attention to background suppression effects, and assuming that NORM sources are more spatially distributed than a point source. The approach taken uses the variation of spectral shape over time as a moving vehicle is screened