Recent improvements in on-site detection and identification of radioactive/nuclear material

To prevent and detect illicit trafficking of radioactive or nuclear material sensitive mobile detection systems are mandatory in addition to fixed monitors installed at border crossings, or at the gateway of nuclear and industrial facilities. This paper is about investigations of characteristics of recently fielded promising instruments for out of-laboratory operation. The Inspector 1000 (manufactured by Canberra) system with lanthanum bromide (LaSr) scintillator offers high efficiency at reasonable cost combined with enhanced resolution compared to NaI. Scintillators of LaBr can be produced with virtually any size and are therefore comparable to the wide-spread NaI scintillators. LaBr offers a 2 to 3 times better resolution than NaI. Uranium-Plutonium-Analysis, normally only feasible with high resolution Germanium detectors, come into view. There are also fairly new detection systems with high resolution gamma crystals available, which are now more compact and easier to use as for example the DetectivEX (manufactured by Ortec). A disadvantage of such systems is still there, the very high price. The n-Probe (manufactured by BTI) enables neutron spectroscopy with a hand-held detection systems. This system contains a NE213 liquid scintillator and a He-3 tube and thereby covers the energy range from 0 to 18 MeV. Energy information for neutrons may be very helpful to categorize radioactive material. The system is rather inexpensive. Neutron coincidence and to some extent even multiplicity information also can be gained with a portable, hand pulled system, e.g., the fission meter (manufactured by Ortec) [2]. It consist of 30 He--3 tubes with a PE-moderator on one side. This system allows categorization of material in fissionable and non-fissionable. This is done by analyzing the multiplicity structure of the neutron events and comparing it to a Poisson distribution which would arise from a random source. In addition, the system can to some extent discover shielding material located between source and detector by Feynman variance plots. The presence of shielding material is often important information for the evaluation of neutron measurements. One disadvantage of such systems remains: They are very expensive. All of the detection systems mentioned above were investigated in the author's institute, their benefits indicated and constraints and limitations were figured out. These types of instruments enhance the possibility to detect radioactive material out of regulatory control and to bring it into a safe and secure environment and thereby reduce the risks of this material becoming used for malicious purposes.