A sealed large area neutron detector based on boron-lined MWPC
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摘要: 针对核环境安全监测、聚变脉冲中子测量等需求，研究了基于镀硼多丝正比室的密闭型大面积中子探测器。利用 Geant4 软件模拟了镀硼厚度对探测器效率的影响、次级粒子在工作气体中的能量沉积及系统的 γ 射线灵敏度，制作了镀硼厚度 1.6 μm、有效面积 10 cm×10 cm 的双层密闭型探测器，并通过中子源对其输出信号脉冲幅度谱和中子探测效率进行了实验测试。模拟结果显示，镀硼厚度在 0.1 μm～2.5 μm 时，热中子探测效率为 1%～7%；能量阈值为 100 keV 时，γ 射线灵敏度小于 5×10−6。中子源测试结果表明，探测器脉冲幅度谱与模拟的能量沉积相一致。探测器测得的中子波长谱与标准3He管相对比，通过本底扣除后测得对 1.8Å热中子的探测效率为4.2%，对 2.9Å和4.8Å 中子的探测效率分别为 6.0% 和 9.4%。Abstract:
Background Efficient neutron detectors are widely used in national security, neutron scattering, and nuclear energy development. The 3He proportional tube, a commonly used neutron detector, faces a global shortage of 3He resources. Meanwhile, existing alternative detectors like BF3 proportional tubes have low efficiency and toxicity, and most large-area boron-lined gas detectors adopt a flow-gas design requiring gas cylinders, causing inconvenience in use and maintenance.Purpose To address the above issues, this study aims to develop a sealed large-area neutron detector based on a boron-lined multi-wire proportional chamber (MWPC) for nuclear environment safety monitoring and fusion pulsed neutron measurement.Methods The Geant4 software with the FTFP_BERT_HP physics library was used to simulate the effect of boron coating thickness on detection efficiency, energy deposition of secondary particles in the working gas, and γ-ray sensitivity. A double-layer sealed detector with a 1.6 μm boron coating and 10 cm×10 cm effective area was fabricated. Performance tests (pulse height spectrum and neutron detection efficiency) were conducted at the 20th beamline (BL20) of the China Spallation Neutron Source (CSNS), using a self-developed readout electronics system and a standard 3He tube as a reference.Results Simulation showed that thermal neutron detection efficiency was 1%-7% when boron coating thickness was 0.1-2.5 μm, and γ-ray sensitivity was < 5×10−6 at a 100 keV energy threshold. Experimental results indicated the detector's pulse height spectrum matched the simulated energy deposition. After background subtraction, its detection efficiencies for 1.8 Å, 2.9 Å, and 4.8 Å neutrons were 4.2%, 6.0%, and 9.4%, respectively, consistent with the 10B neutron absorption cross-section law.Conclusions The developed sealed large-area boron-lined MWPC neutron detector avoids complex gas circulation systems. Future optimization of boron coating thickness and conversion layer number can further improve efficiency, providing a new solution for nuclear safety monitoring and fusion pulsed neutron measurement.-
Key words:
- boron-lined /
- MWCP /
- sealed /
- neutron detector /
- γ-ray sensitivity
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图 2 （a）次级粒子在工作气体中的能量沉积，（b）不同转换层厚度下的中子探测效率。
Figure 2. (a) Energy deposition in the gas volume. (b) Neutron detection efficiency as a function of the boron layer thickness
图 3 不同能量γ射线产生的电子在工作气体中的能量沉积
Figure 3. Energy deposition of the gamma rays in the gas volume
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