IDENTIFICATION OF RADIOLOGICAL/NUCLEAR THREAT SOURCES

We have designed, developed, and tested automated radiation detection systems for detecting and identifying illicit radioactive sources in transit along public highways and waterways. Because many legitimate industrial, medical, and naturally occurring radioactive sources are transported, especially on highways, an automated radioactive source alarm system must be able to discriminate between illicit and legitimate sources to be useful on heavily traveled routes. The configuration, shielding, and isotopes used in possible threat sources are unknown, making automatic recognition algorithms for threat sources difficult to construct. On the other hand, the number of different types of legitimate sources, though large, is finite, and therefore these can be characterized. A strategy to deal with this situation includes training the system to recognize sources that fit patterns archived for legitimate sources, and triggering further investigation of detected events that do not fit recognized patterns. The success criterion of this technique is to reduce the number of unrecognized sources to an acceptably small percentage of encountered legitimate ones while not filtering out any true threats.