Program Listings

Session Chair: Abdallah Lyoussi, CEA / French Atomic Energy Commission, France

Neutron multiplicity counters are used in safeguards to provide rapid assay of plutonium bearing items. With appropriate detector design, the neutron single, double, and triple coincidence events can be used to extract information of three unknown parameters such as the 240Pu-effective mass, the sample self-multiplication, and the (α,n) rate. Alternatives to 3He have been investigated for next-generation neutron multiplicity counters. A project at PNNL is using nickel-quenched 6LiF/ZnS neutron-scintillator sheets and wavelength shifting plastic for light pipes in place of 3He. A combination of laboratory and modeling work predicts a LiF/ZnS-based system to be able to match or exceed the performance of the best 3He-based systems available. Also, the Ni-quenched material is expected to allow for improved neutron/gamma-ray discrimination at twice the event rate relative to the non-Ni-quenched LiF/ZnS. A new system based on the LiF/ZnS material is under construction and components are being used to optimize the detection efficiency and neutron/gamma-ray discrimination properties. The full-scale system has been extensively modeled to better understand the impact of all the various components. The new system is under construction and parts are undergoing performance testing utilizing high-speed digitizers with field programmable gate arrays to perform the neutron/gamma-ray discrimination. The performance status of the new partial system will be presented and along with the expected performance of the full-scale system due for completion in 2016.