Study Of Non-destructive Assay For Nuclear Material By Gamma-ray Passive Measurement

Non-destructive Assay technology of passive measurement of uranium materials was widely used in the field of nuclear security.There were many methods of the technology.The enrichment meter principle,which relied on the characteristic ray generated by the spontaneous decay of uranium to complete the uranium enrichment measurement,with lots of researches and applications,was one of the most classic methods.However,the enrichment meter principle still suffered from the disadvantages of the thickness of the container and the position of the detection device.Therefore,this dissertation optimized the enrichment meter principle by introducing the container thickness correction factor to improve the measurement accuracy.The main research content was summarized as follows:Firstly,a small-angle Compton scattering method for determining the thickness of uranium material containers was simulated.Based on the analysis of the principle of Compton scattering between photons and container materials,the relationship between the container thickness and the response values of Compton plateaus,which was on both sides of the omnipotent peak at 185.72 keV,were proposed.The influences of container thickness,uranium enrichment,and container material on the response value were studied by using the control variable method.The simulation results showed that the response value was only related to the parameters of the container material itself and varied linearly with the thickness of the container.The slope was determined by the type of container material and was not affected by the enrichment of uranium materials.In the National Nuclear Security Technology Center,experiments were performed on the small-angle Compton scattering method.The problem of anomalies in the initial energy spectrum was solved by the energy calibration method to improve the accuracy of feature extraction.The experimental results were consistent with the simulation results.Then,the infinite thickness method was simulated,and the realization principle of the infinite thickness method was analyzed,and the accuracy of the double region of interest algorithm was verified,and the thickness of the container was used as a correction factor to introduce the double region of interest algorithm,which solved the problem that the measurement accuracy was greatly affected by the thickness of the container.The simulation results showed that the introduction of container thickness correction significantly improved the measurement accuracy.Especially when the samples with high enrichment were measured,the relative error and relative deviation of the results were within 10%,which provided theoretical support for improving the experimental accuracy of the infinite thickness method.In addition,as the thickness of the container increased,the accuracy of the corrected measurement results decreased,indicating that the container thickness should only correct the measurement results to some extent.Finally,experiments on the enrichment meter principle were conducted.HPGe detector was used to measure the energy spectrum.The enrichment degree measurement was performed on a single sample scale.The correction effect of the container thickness on the measurement results was verified,and the data with higher correction and enrichment degree were emphatically analyzed.The cause of the larger error provided a new idea for the selection of scale samples.