Detection of fissile material using cold neutron interrogation combined with neutron coincidence counting

A variety of neutron interrogation techniques exists for the identification and characterization of fissile materials. Typically the sample is irradiated continuously or in pulses, and the neutron or gamma response is used for the characterization of the sample. Active neutron coincidence counting is one of these techniques, based on the detection of correlated prompt neutrons from induced fission in 235U, in order to quantify uranium. Typically AmLi neutron sources are used for the interrogation so far. In this study we used for the first time a guided cold neutron beam for interrogation, which is a far more intense source of uncorrelated neutrons. A pilot neutron coincidence setup was installed at a neutron beam of the Budapest Neutron Centre, and samples of small volumes and various uranium contents were measured. It was proven that the detection of fission events (Doubles) is feasible even for micrograms of 235U and the detector response is proportional to the fissile content of the sample.