Year
2016
Abstract
Technological advances in the ability to verify, account, and control special nuclear materials (SNM) are needed to support the aims of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). Neutron multiplicity counting is a widely used technique to verify and safeguard SNM; however, these systems traditionally rely heavily on He-3. Recently, the decreasing He-3 supply has driven research efforts to provide alternative detection systems. Fast neutron detectors have shown promises as an alternative, because they do not require moderation of the incoming neutrons. Additionally, coincidence windows on the order of tens of nanoseconds are possible, compared to the microsecond time-scales of moderated systems. These shorter windows lower the rate of accidentals, thus allowing a more precise measurement of fissile mass. Direct detection of the fast neutrons also enables spectroscopic capabilities, which are impossible in traditional systems. We present a fast neutron multiplicity counter that consists of eight 7.62 cm x 7.62 cm EJ-309 liquid organic scintillators and eight 5.08 cm x 5.08 cm stilbene scintillators configured in a cylindrical array. Two sets of metal plutonium fuel plates were measured at Idaho National Laboratory to quantify the mass of Pu-240 by detection of neutron-neutron correlations. The full paper will show the results of this experimental campaign and presents an analysis of the effect of neutron cross-talk on the accuracy of plutonium mass estimation.