Multiplicity counters are a traditional non-destructive analysis technique to measure plutonium in containers for safeguards. We will discuss a technique we call correlated fast neutron counting which uses segmented liquid scintillator well counter with nanosecond timing. With this detector, we have measured 10~ 5 discrimination of neutrons and gamma-rays above 500 keV. Used passively, this fast neutron counter can detect isolated fission chain bursts in the presence of high backgrounds, such as in storage areas or where the signal is dominated by (alpha,n) or spontaneous fission backgrounds. It will be useful in quantifying total fissile mass. Used actively, in conjunction with 60-keV neutron interrogation to induce fission, it detects the high-energy fission neutrons and is blind to the interrogating beam. The 60 keV beam energy will enable us to preferentially fission ~ 235U and ~ 239Pu over ~ 244Cm.
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