热中子分析探雷的中子源慢化装置设计与优化
Design and Optimization of Neutron Moderation Device for Thermal Neutron Analysis Landmine Detection
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摘要: 与传统的地雷探测技术相比，热中子分析(Thermal Neutron Analysis，简称TNA) 探雷技术具有准确率高、虚警率低和对环境适应性强的特点，但探测速度较慢，制约了其广泛应用。为了提高地雷位置处的慢热中子通量，缩短探测时间，提出了一种基于252Cf 的中子源慢化装置设计构型，主要包含中子慢化层、中子反射层、本底 屏蔽层和侧向中子吸收层4 个部分。采用数值模拟的方法比较了4种常用中子慢化(反射) 材料的性能，优选高密度聚乙烯作为慢化材料，石墨作为反射材料。同时，为了满足辐射安全要求，对屏蔽材料的结构进行了优化计算。按照设计构型搭建了TNA 探雷实验平台。在104 n/s 中子源强下优化了慢化层和反射层的厚度，测试了装置慢化效能，在107 n/s 中子源强下评估了装置辐射安全性能。结果表明，采用该装置可使地雷位置处的慢热中子通量提升11 倍以上，并能有效保障辐射安全。Compared with the traditional landmine detection methods, Thermal Neutron Analysis (TNA) landmine detection has the advantages of high accuracy, low false alarm rate and strong adaptability to the environmental change.But the long detection time restrict the wide application of this technology. In order to shorten the detection time, one possible design of neutron moderation device based on 252Cf neutron source is proposed to enhance the moderated neutron
flux in mine position. The device consists of four parts, the neutron moderator, the neutron reflector, the background shield and the useless neutron absorbing layer. Then, the performance of four widely used materials in neutronics was compared with MCNP5 code, and HDPE was chosen as the neutron moderator material, graphite as the neutron reflector material. The thickness of the useless neutron absorbing layer was optimized at the same time. Finally, an experimental platform of 252Cf neutron moderation device was assembled on the basis of simulation results, and a series of experiments were carried out to optimize the geometric dimensions and evaluate the dose equivalent with two different strengths neutron source, 104 and 107 n/s. The results indicate that this device can effectively enhance the thermal neutron flux at mine position by more than 11 times and ensure the radiation safety.Abstract: Compared with the traditional landmine detection methods, Thermal Neutron Analysis (TNA) landmine detection has the advantages of high accuracy, low false alarm rate and strong adaptability to the environmental change.But the long detection time restrict the wide application of this technology. In order to shorten the detection time, one possible design of neutron moderation device based on 252Cf neutron source is proposed to enhance the moderated neutron
flux in mine position. The device consists of four parts, the neutron moderator, the neutron reflector, the background shield and the useless neutron absorbing layer. Then, the performance of four widely used materials in neutronics was compared with MCNP5 code, and HDPE was chosen as the neutron moderator material, graphite as the neutron reflector material. The thickness of the useless neutron absorbing layer was optimized at the same time. Finally, an experimental platform of 252Cf neutron moderation device was assembled on the basis of simulation results, and a series of experiments were carried out to optimize the geometric dimensions and evaluate the dose equivalent with two different strengths neutron source, 104 and 107 n/s. The results indicate that this device can effectively enhance the thermal neutron flux at mine position by more than 11 times and ensure the radiation safety.
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