A New Active Neutron Multiplicity Measurement Device for Uranium Assay Utilizing a Portable D-D Neutron Generator

摘要: Ensuring the safeguards and monitoring of enriched uranium is crucial for preventing its illegal theft, destruction, or transfer under arms control. Non-destructive analysis techniques for uranium quantification play a vital role in this effort. The Am-Li source is widely used as an excitation source in Active Uranium Non-destructive Analysis Techniques. However, as acquiring Am-Li becomes increasingly challenging, controllable accelerator-based neutron sources have emerged as a promising alternative due to their superior energy monochromaticity, controlled yield, and on-demand operational capabilities. This study develops an optimized neutron multiplicity measurement system based on a D-D neutron generator, using metallic uranium samples with varying ²³⁵U content. Key parameters, including the distance between the neutron generator and a two-layer ³He detector array, ³He tube length, and the material and thickness of the reflector, were optimized via Monte Carlo simulations. The detection efficiency and neutron decay time of the optimized system were evaluated, followed by experimental validation through the quantification of uranium samples with different ²³⁵U enrichments and masses. The results indicate that for highly enriched uranium (²³⁵U enrichment >50%), the M-C coupling curve yielded a measurement relative deviation of less than 10%, while for other enrichment levels, deviations remained within 100 g. Furthermore, by analyzing fission neutron detection efficiency (ε_f) and spatial fission rate variations within the sample chamber, a correction factor (k) was introduced using partial least squares regression to account for sample geometry, density, and ²³⁵U abundance, reducing the average relative deviation from 20.67% to 8.18%. This research provides a foundation for further development and experimental validation of neutron multiplicity measurement devices utilizing D-D neutron generators.