Development of a Prototype Fast Neutron Active Coincidence Collar for Safeguards

The International Atomic Energy Agency has developed a prototype liquid scintillator-based neutron coincidence collar in collaboration with the European Commission (EC) Joint Research Centre in ISPRA and Hybrid Instruments, Ltd. (UK). The fast-neutron detection capabilities are particularly beneficial for coincidence counting safeguards applications. Detection of neutrons from fission events does not require a thermalization process, thus neutrons coming from the same event are detected with almost zero delay. This feature makes possible the minimization of the detector coincidence gate to ~60 ns, and thus a three orders of magnitude reduction in accidentals. This enables the system to work in a low-signal condition (e.g., fast-mode fresh fuel interrogation) with an acceptable signalto- noise ratio. This results in significantly lower measurement statistical error compared to the standard 3He-based thermal neutron detectors. This activity has been partly sponsored by the UK, Netherlands, and EC Support Programs to IAEA Safeguards.