Active interrogation involves directing nuclear radiation into a closed container and measuring secondary radiations to gain information about the contents of the container.
Typically neutrons or high-energy photons are used as the impinging radiation. Active interrogation has a greater potential for detection of small quantities of Special Nuclear Material than passive detectors. It also holds the promise of detection and identification of non-nuclear materials, such as hazardous chemicals and explosives, including Vehicle-Borne Improvised Explosive Devices (VBIED). NIST has lead the drafting committee that wrote and successfully balloted ANSI Standard: N42.41 - Minimum Performance Criteria for Active Interrogation Systems used for Homeland Security.
Active interrogation is a highly active area of research and development. The selection of correct techniques for further development, and, ultimately, the selection of appropriate systems, requires a consistent set of standards for comparing the various techniques.
Image Description: An ISO Standard Cargo Container has been outfitted with the four cargo regions specified in N42.41. The section filled with hollow steel cubes can be seen. Part of each cargo region is on tracks to permit access to the central rack for threat specimens or stimulants. (Photograpy by: NI&D Group)