Abstract

To address the international community’s needs for the safeguarding and monitoring of enriched uranium materials and to prevent the illicit theft, destruction, and transfer of such materials, it is crucial to explore non-destructive analytical techniques for measuring uranium content in enriched uranium materials. Currently, the Am-Li source is commonly used as an excitation source in active uranium measurement methods. However, as the acquisition of Am-Li becomes increasingly challenging, controllable accelerator-based neutron sources have emerged as preferred alternatives due to their superior energy monochromaticity, controlled yield, and on-demand operational capabilities. This study is based on the neutron multiplicity device using a portable D-D neutron generator instead of an Am Li source. It focuses on the optimization of the device structure and the performance simulation. Monte Carlo simulation software was used to evaluate critical measurement parameters, including the distance between the neutron generator and the two-layer He-3 detection array, the length of the He-3 tubes, and the materials and thicknesses of the reflective layers. Following the design phase, simulations were conducted to determine the detection efficiency and neutron decay time of the new device. Additionally, the device’s performance was evaluated through simulated measurements and quantification of uranium materials with different U-235 abundances and masses. The results indicate that for samples with U-235 enrichment exceeding 50%, the relative deviation of the measurements is less than 10%, and deviations for other enrichment levels are less than 100 g. Finally, the sources of quantification error in the device were examined, and corrections were made to the calculation of the neutron leakage multiplication using the fission neutron detection efficiency. This research lays the groundwork for the study and experimental validation of the neutron multiplicity device based on D-D neutron generators.

Instructions:

This study introduces a neutron multiplicity device based on a portable portable D-D neutron generator, optimized through Monte Carlo simulations focusing on reflector configuration and layout of He-3 tubes. The new device features a polyethylene main body, standing 115 cm tall with an 86 cm diameter. It incorporates 43 He-3 tubes, with 42 tubes evenly distributed in two rings within the polyethylene moderator, and one tube positioned at the bottom to monitor the yield of the portable D-D neutron generator, thereby stabilizing its output. Building upon the new device, comprehensive simulations using Monte Carlo software were conducted to study its overall performance. The device achieved a total detection efficiency of 32%, with a neutron decay time of 49.58 μs. When the portable D-D neutron generator’s yield stabilized at 1×10^5 s^-1, the count rate at the bottom He-3 tube remained at 270 s^-1. The device obtained Monte Carlo coupled M-C calibration curves for highly enriched uranium materials, facilitating preliminary quantification of uranium in materials with varying U-235 enrichments. Quantitative discrepancies between calculated and theoretical values were less than 100 g, and for samples with U-235 enrichment exceeding 50%, measurement relative deviations were below 10%. The study also addresses the sources of quantitative errors in the apparatus and corrects the neutron leakage multiplication by incorporating the actual fission neutron detection efficiency. Based on the fission characteristics of the unit U-235 metal sphere within the sample chamber, it was observed that the new apparatus features a flux-stable region only with a side length of 5.0 cm at the center of the sample chamber. To further enhance measurement precision, additional optimization of either the sample chamber structure or the spatial distribution of fission neutrons is required. Through Monte Carlo simulations, the neutron multiplicity device based on portable D-D Neutron Generator has demonstrated strong feasibility and practicality for industrial applications. This study provides a reference for the design of future active neutron multiplicity uranium mass measurement instruments and quantitative methods for uranium assessment.

Funding Agency:

East China University of Technology

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Data for A New Neutron Multiplicity Device Based on Portable D-D Neutron Generator

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