Progress in development of a 6LiF/ZnS-based neutron multiplicity counter

Neutron multiplicity counters are used in safeguards to provide rapid assay of samples which contain an unknown amount of plutonium in a potentially unknown configuration. Alternatives to the use of ³He for the detection of thermal neutrons are being investigated. 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. A project at PNNL has investigated replacing ³He-based tubes with LiF/ZnS neutron-scintillator sheets and wavelength shifting plastic for light pipes. A demonstrator system was constructed and is being used to test potential data acquisition system options and neutron/gamma-ray discrimination algorithms for a larger-scale system. A full-scale system has been extensively modeled to better understand the impact of all the various components. The results of the current testing and modeling effort will inform the final design of a full scale system which is expected to match the performance of existing ³He-based neutron multiplicity counters. A review of the current effort and the most recent findings will be presented.