Tracking of fissile material by means of coincident neutron detection - Fission Meter vs. Slab Counter

In the context of fissile material detection, discrimination between changes of the natural neutron background, industrial material, and a real neutron source, indicating the presence of nuclear material, is tremendously important. The negligence of such material may lead to drastic if not fatal consequences to the general public in case the material in question is used in explosive devices such as Improvised Nuclear Devices (IND). To achieve the discrimination required, measurements of coincident neutrons are feasible because only fissile material emits coincident neutrons. Two neutron detection systems, the Fission Meter by Ametek/Ortec and the Slab Counter by Canberra, were tested concerning their quality of detecting nuclear material as mentioned above, using primarily a variety of Plutonium sources with different isotopic compositions provided by the Institute of Transuranium Elements (ITU) of the Joint Research Centre at Ispra, Italy, where the measurements were performed. We also examined the influence of shielding effects of the materials which would possibly be part of an IND. The results of these measurements and an assessment of the reliability of the two detection systems concerning fissile material verification will be presented.