Calibration methodology for near-field neutron sensitivity of large-scale plastic scintillators
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摘要: 针对大尺寸塑料闪烁体（Φ100 mm×100 mm）在近场（＜1 m）脉冲中子测量中因标定与测量几何差异导致的中子灵敏度偏差问题，本研究提出基于实验和蒙特卡洛模拟的双外推动态标定方法。建立蒙特卡洛模拟模型，量化距离对灵敏度的影响规律。模拟结果表明：当源距小于80 cm时，需要考虑距离对于中子灵敏度的影响，当源距缩短至20 cm时，中子灵敏度修正系数达到8.44%。通过近场实验分析，提出了一种散射本底外推方法，较为准确地测量了近场中子探测器的灵敏度，实验结果验证了理论模拟的准确性。研究建立的修正方法能够在平方反比定律不适用的条件下，有效降低传统单点标定法在近场测量中的系统偏差，扩展了中子探测器的测量范围，为脉冲堆瞬态诊断、聚变装置等强辐射场环境下的精确中子计量提供了新的技术途径。Abstract:
Background In near-field pulsed neutron measurements (＜1 m), large-sized plastic scintillators (Φ100 mm × 100 mm) exhibit neutron sensitivity deviation due to geometric discrepancies between calibration and measurement, and the inverse-square law has limited applicability under close-proximity conditions, hindering accurate metrology.Purpose To address this deviation, reduce systematic errors from traditional single-point calibration, and extend neutron sensitivity calibration range, this study proposes a dual-extrapolation dynamic calibration method combining experimental extrapolation with Monte Carlo (MC) simulation.Methods An MC model was established to quantify distance’s effect on sensitivity, and a scattering background extrapolation method was developed via near-field experiments for close-proximity sensitivity measurement.Results MC results show source-to-detector distance ＜80 cm significantly impacts sensitivity, with an 8.44% correction factor at 20 cm; experiments validated simulation accuracy.Conclusions This method effectively mitigates sensitivity deviation, clarifies the inverse-square law’s limitations under close proximity, extends calibration scope, and provides a new technical pathway for precise neutron metrology in harsh environments like pulsed reactor transient diagnostics and fusion devices. -
图 3 MCNP模拟不同距离反推值与模拟值的差异
Figure 3. The discrepancy between the extrapolated values and MCNP simulation results at different distances
图 5 中国原子能科学研究院E高压倍加器实验平台布局图
Figure 5. Layout diagram of the China Institute of Atomic Energy high-voltage multiplier experimental platform
表 1 MCNP模拟结果
Table 1. MCNP simulation results
distance/cm proton deposited
energy(Epro)electron deposited
energy(Eelec)total deposited
energyinverse-square-law-derived
distance datarelative
deviation/%150 6.05E-04 2.59E-05 6.48E-04 6.53E-04 −0.73 100(reference) 1.37E-03 5.91E-05 1.47E-03 1.47E-03 0 80 2.15E-03 9.48E-05 2.31E-03 2.29E-03 0.54 60 3.85E-03 1.74E-04 4.14E-03 4.08E-03 1.59 40 7.77E-03 3.61E-04 8.37E-03 8.13E-03 3.01 20 3.68E-02 1.80E-03 3.98E-02 3.67E-02 8.44 
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表 2 基准区散射系数实验结果
Table 2. Experimental results of scattering coefficients in reference region
distance from crystal center /cm source neutron yield net signal/nA scattering coefficient 106.9 2.62E+09 37.65 1.44E-08 121.6 2.12E+09 24.75 1.17E-08 137.7 2.17E+09 21.81 1.01E-08 155.7 1.39E+09 12.47 8.97E-09 202.6 2.01E+09 13.54 6.74E-09
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表 3 MCNP模拟结果与实验结果对比
Table 3. Comparison between MCNP simulations and experimental results
distance from crystal center /cm measured sensitivity measured deviation % simulated deviation % （simulated - measured）/% 32.3 1.228E-11 5.09 4.78 −0.31 41.1 1.203E-11 2.95 3.47 0.52 75.8 1.171E-11 0.17 1.04 0.87 112.2(Reference) 1.169E-11 0 0 0
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表 4 拟合曲线在不同实验距离对应的不确定度
Table 4. Uncertainty distribution of fitting curves across experimental distances
distance/cm standard uncertainty of
fitting curvesoutput signals corresponding to
experimental yields/nAdirect irradiation signals corresponding to
experimental yields/nAuncertainty components of
fitting curves/%32.3 8.79×10−9 5.53 1245.30 0.44 41.1 5.07×10−9 4.23 1000.70 0.42 75.8 9.35×10−10 0.76 279.05 0.27 112.2 3.38×10−11 0.06 300.04 0.02
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表 5 不同实验距离对应的总不确定度
Table 5. The total uncertainty corresponding to different experimental distances
distance/
cmuncertainty components of
fitting curves/%uncertainty components of
distance measurement/%uncertainty components of
neutron fluence rate monitoring/%uncertainty components of
electrometer signal/%combined standard
uncertainty(k=1)/%32.3 0.44 0.62 1.5 1 2.05 41.1 0.42 0.48 1.5 1 1.97 75.8 0.27 0.26 1.5 1 1.86 112.2 0.02 0.18 1.5 1 1.82
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