快中子多重性分析技术是当前核材料衡算领域的热门研究方向。针对中子伽马脉冲形状甄别的效果在探测距离很近时明显变差的实验现象展开了研究。使用GEANT4工具箱模拟了液体闪烁体探测器测量裂变中子伽马的粒子输运过程，并基于计算机模拟数据分析了使用BC－501 A液体闪烁体探测器测量裂变中子时，裂变物质与探测器的距离（几何效率）对中子－伽马甄别效果的影响。分析的结果与实验现象相符，表明在基于液体闪烁体探测器的核材料属性测量中，若单个探头的探测效率较高，裂变中子伽马脉冲叠加会严重影响甄别结果和测量计数。%Fast Neutron Multiplicity Counting has drawn much attention from nuclear material accounting .The reason of bad pulse shape discrimination (PSD) result in near detection is studied .With GEANT4 toolkit, a simulation of the particle transport process of detecting fission neutron and gamma with liquid scintillator was re -alized .Based on the simulation data , the impact of the distance between nuclear material and the detector ( ge-ometry efficiency ) on the PSD in measuring fission neutron by BC -501 A liquid scintillator is discussed in de-tail.The analysis result is generally consistent with the experiment .The analysis show that if the detection effi-ciency of single detector is high , the pile up neutron and gamma may seriously affect the discrimination result and measurement counts.
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