Tracking of weak radioactive sources in crowded venues

Monitoring for the clandestine transport of nuclear and radiological materials at large public gatherings or special events, such as the presidential inauguration, is one element in a strategy for preventing their subsequent dispersal. Being able to track these materials as they approach or move through such a venue can provide law-enforcement personnel with important information. The focus of this paper is on methods developed by the authors to meet the challenges inherent in the tracking problem. Results of laboratory experiments performed using the RadTrac prototype system are described.