DETECTION AND IDENTIFICATION OF NUCLEAR MATERIALS BY RADIOGRAPHIC METHODS

The paper describes novel imaging detectors intended for prevention of illicit trafficking of nuclear sources and materials including materials of nuclear fuel cycle: 1) CCD— detector for simultaneous X-ray and fast neutron imaging, 2) CCD-detector for detection and identification of fast neutron sources and 3) Hodoscopic detector. The mentioned CCD detectors are based on special composite luminescent screens made of scintillating fibers and powder phosphors. Images produced by neutrons and X-rays at the screen surface of the first detector come into view in different regions of visible spectrum. Corresponding optical filters allow separating these images and registering them independently of one another on different CCD matrixes. The composite screen of the second detector provides imaging not only fast neutrons but also thermal neutrons produced in the screen due to fast neutrons moderation. Matrix form of the thermal neutron screen allows separating signals produced by fast and thermal neutrons. Spatial distribution of the signal produced by fast neutrons is used for detecting position of the source. Ratio of thermal-to-fast neutrons signals depends on the average energy of incoming neutrons thus allowing to discern between sources with different mean energy. The hodoscopic detector is composed of layered (crosshatched) scintillating fast neutron sensors. Additional sensors for ã-rays and thermal neutrons provide higher reliability of the radiation source detection and identification. Potential applications for the described detectors include passive radiation detection or detecting the presence of hidden nuclear materials, large area monitoring (e.g. ensuring the security of a storage area for nuclear materials), screening of small objects, packages or containers (e.g. at an airport or postal substation) and monitoring the integrity of pipes used in the transfer of radioactive materials (e.g. at a reprocessing facility).