A Simulation Framework for Evaluating Detector Performance in Cargo Screening Applications

Deployed radiation portal monitor systems (RPMs) screen gamma-ray signatures of cargo at international border crossings with the goal of detecting illicit radiological materials. Estimating the detection sensitivity of these systems requires an in-depth understanding, and quantification, of RPM response to both benign and illicit sources. Benign sources of radioactivity include background, alterations of the background due to the presence of vehicles and cargo, as well as sources that frequently cause nuisance alarms. These nuisance sources, for example those consisting of naturally occurring radioactive materials (NORM) and medical isotopes, frequently limit system performance. Advanced detector technology promises to increase the capability of deployed systems to discriminate illicit from nuisance sources. Presented here is a framework developed to assess the performance of these passive detection technologies. Due to the difficulty in obtaining empirical data for emerging technologies, the foundation of this comparison framework lies on a simulated benign source population to create a comprehensive set of data representing cargo vehicles driving through the RPM. Quantification of performance stems from injecting simulated signatures from illicit sources and comparing probabilities of detection via case and population studies.