重屏蔽条件下铀材料丰度的时间关联测量分析

针对高原子序数物质屏蔽下的铀材料，提出了一种新的技术方法来估算其铀丰度。首先，用D-T中子发生器的14 MeV中子对铀材料及屏蔽层进行主动质询，同时利用裂变射线探测器得到裂变中子/γ射线时间关联测量谱。然后，利用成像探测器建立的断层扫描图像得到铀材料及屏蔽层的几何和材料参数，并调用不同的铀丰度参数进行蒙特卡罗模拟计算，得到时间关联计算谱。最后，寻找与测量谱最匹配的模拟谱，确定铀材料的实际铀丰度。通过对比裂变射线探测器实验测量得到的所有裂变中子/γ射线时间关联谱，结果发现在各种屏蔽层状态下，高浓铀材料与贫化铀材料的时间关联谱均存在显著差异，可用时间关联谱作为区分不同铀材料丰度的重要技术特征；对于相同铀丰度和屏蔽状态下的铀材料，模拟谱与测量谱吻合较好，表明时间关联谱的模拟与实验分析可为铀材料铀丰度的估算提供技术基础。

Time Correlation Measurement Analysis of Enrichment of Uranium Material Shielded by Heavy Matter

For uranium materials shielded by the high Z matters, a new method was proposed to estimate their enrichments. Firstly, uranium materials and shieldings were irradiated by 14 MeV neutrons of a D-T neutron generator, and fission neutron/gamma time correlation spectra were obtained by fission radiation detectors at the same time. Secondly, geometry and material parameters were acquired by the tomographic images from imaging detectors. Monte Carlo simulations of different uranium enrichments were conducted with these parameters, and so simulation spectra of time correlation were got. Lastly, the actual uranium enrichments were fixed by searching the simulation spectra that match the measurement spectra. By analyzing all fission neutron/gamma time correlation spectra measured by fission radiation detectors, it is shown that the time correlation spectra of high-enriched uranium and depleted uranium are obviously different under each shielding condition. Thus, time correlation spectra can be a key technical feature to distinguish different enrichments of uranium materials. For uranium materials with the same enrichment and shielding, the simulation results coincide with the measurement results. So simulation and measurement analysis of the time correlation spectra can build technical basis for enrichment estimation of the uranium materials.