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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 Me V质子静电加速器上,利用T(p,n)3He反应产生的483 ke V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 e Xtended)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2.884 2 g金属铀含5.712 8×1021个238U原子,实验结果的不确定度是4.1%。
As an important fissile material, the accurate determination of 238U is of great significance in fission yield data measurement. In the 2.5 Me V proton electrostatic accelerator at Sichuan University, a single-neutron detector of 483 ke V produced by T (p, n) 3He irradiation was used to irradiate metallic uranium samples to measure the γ-ray characteristic of 239Np radionuclide after irradiation. Known 238U (n, gamma) capture cross section data enables accurate measurement of 238U content. The factors affecting the accuracy of the measurement results are analyzed in detail. The Monte Carlo method MCNPX (Monte Carlo N-Particle e Xtended) is used to correct the multiple scattering effect and the neutron flux attenuation effect. The γ-ray self-absorption in the sample was also corrected. The corrected experimental result is 2.884 2 g of uranium containing 5.712 8 × 1021 238 U atoms. The uncertainty of experimental results is 4.1%.