用活化法无损测定金属铀样品中238U的含量

摘要

238U 作为一种重要的裂变材料，其含量的准确测定在裂变产额数据测量中具有重要意义。在四川大学2.5 MeV质子静电加速器上，利用T(p,n)3He反应产生的483 keV单能中子照射金属铀样品，对照射后生成放射性核素239Np的特征γ射线进行测量，利用已知的238U(n,γ)俘获截面数据实现了对238U含量的准确测量。对影响测量结果准确性的因素做了细致分析，采用蒙特卡罗方法应用软件 MCNPX (Monte Carlo N-Particle eXtended)对中子的多次散射效应和中子注量衰减效应进行了修正，对γ射线在样品中的自吸收也进行了修正，修正后的实验结果是2.8842 g金属铀含5.7128×1021个238U原子，实验结果的不确定度是4.1%。%Background: As a kind of important fission material, the accurate quantification of 238U is of great significance in the measurement of fission yield data. Purpose:The aim is to nondestructively measure the content of 238U by using the activation method. Methods:Neutron of 483-keV produced by the reaction of T(p,n)3He induces 238U occurring radiative capture reaction on the 2.5-MeV electrostatic accelerator of Sichuan University. The atomic number of 238U in uranium samples is measured by using 278-keV gamma ray of 239Np on the detector of high purity germanium (HPGe) and the data of capture cross section. Results: The deflections which were caused by multiple scattering and self-shielding of the target and sample in the experiment were corrected with MCNPX (Monte Carlo N-Particle eXtended). The result of the experiment is that the atomic number of 238U in the 2.884 2-g metal uranium is 5.712 8×1021. Conclusion:The uncertainty of the experimental result is 4.1%. We can reduce the effect of multiple scattering effects and self-shielding by decreasing the thickness of the bottom lining, target tube, water layer and cladding material of the sample.