Real-time, fast neutron coincidence assay of plutonium with a 4-channel multiplexed analyzer and organic scintillators

The design, principle of operation and the results of measurements made with a four-channel organic scintillator system are described. The system comprises four detectors and a multiplexed analyzer for the real-time parallel processing of fast neutron events. The function of the real-time, digital multiple-channel pulse-shape discrimination analyzer is described together with the results of laboratory-based measurements with $^{252}{hbox{Cf}}$, $^{241}hbox{Am–Li}$ and plutonium. The analyzer is based on a single-board solution with integrated high-voltage supplies and graphical user interface. It has been developed to meet the requirements of nuclear materials assay of relevance to safeguards and security. Data are presented for the real-time coincidence assay of plutonium in terms of doubles count rate versus mass. This includes an assessment of the limiting mass uncertainty for coincidence assay based on a 100 s measurement period and samples in the range 0–50 g. Measurements of count rate versus order of multiplicity for $^{252}{hbox{Cf}}$ and $^{241}hbox{Am–Li}$ and combinations of both are also presented