ABSTRACT The analysis method of Fast Neutron Multiplicity Counting (FNMC) plays an increasingly important role in the measurement of nuclear material properties. Based on the assumption of point model, fast neutron multiplicity measurement equation is derived which can be used to measure the mass of Pu sample. However, the deviation of the simulated measurement of 1 kg Pu sample reaches 16.6% and increases with mass. Because nonpoint source samples of different shapes do not fully satify the hypothesis. To correct this deviation, a set of fast neutron multiplicity counters was built by Geant4 to simulate and study the mass attribute of Pu samples.The cylindrical sources of different shapes and different masses were simulated, the self-multiplication factor and α coefficient were corrected.And the corresponding third-order polynomial fitting equation was obtained, the goodness of fit was greater than 0.970. In the same way, the spherical and spherical shell source samples in the mass range of 0–5 kg were analyzed, the corrected mass deviation of samples was less than 10% in this interval. The results show that the combination of the fast neutron multiplicity counter and parameter correction can accurately measure the sample mass attribute.

中文翻译：

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样品形状对Pu测量结果影响的分析与改进

摘要 快速中子多重计数（FNMC）分析方法在核材料特性测量中发挥着越来越重要的作用。基于点模型假设，推导了快速中子多重性测量方程，可用于测量Pu样品的质量。然而，1 kg Pu 样品的模拟测量偏差达到 16.6%，并且随着质量的增加而增加。因为不同形状的非点源样本并不完全满足假设。为了纠正这种偏差，Geant4构建了一套快速中子多重计数器来模拟和研究Pu样品的质量属性。模拟不同形状和不同质量的圆柱源，修正自倍增因子和α系数。并得到相应的三阶多项式拟合方程，拟合优度大于0.970。同理分析了0-5 kg质量范围内的球体和球壳源样品，该区间样品的校正质量偏差小于10%。结果表明，将快中子多重性计数器与参数校正相结合，可以准确测量样品质量属性。