基于中子/瞬发γ射线联合测量的中子剂量监测模拟研究

Simulation Study on Neutron Dose Monitoring Based on Joint Measurement of Neutron and Prompt Gamma-Rays

  • 摘要: 辐射场下的中子周围剂量当量率监测具有重要意义,其可以反应核设施运行状况以及辐射防护信息。目前常用的监测仪器为基于单探测器、单慢化体的A-B型剂量当量率仪,其响应曲线与“中子注量-周围剂量当量转换系数”有较大的差异,导致测量结果误差较大。为提升中子剂量仪测量结果的准确性,对基于中子和瞬发γ射线联合监测中子剂量率开展研究。利用铅块、含硼聚乙烯、有机玻璃和氯化钠组合而成的转换材料,通过蒙特卡罗模拟计算B、H、Cl、Pb、C和O元素对不同能量中子的响应,利用响应曲线结合LB6411型剂量仪的响应曲线进行线性拟合,得到与“中子注量-周围剂量当量转换系数”更为接近的响应曲线。通过差分进化算法计算得到线性拟合系数,结果显示,新的响应曲线在1×10−8~16 MeV能量区间内与h_\phi 响应曲线更贴近,二者的相对偏差在50%之内。联合测量中子与瞬发γ射线对中子周围剂量当量率进行监测可行,为中子剂量仪校准和研发提供了新的方向和支持。

     

    Abstract: The monitoring of neutron ambient dose equivalent rate in a radiation field is of significant importance as it can reflect the operational status of nuclear facilities and provide radiation protection information. Currently, the commonly used monitoring instrument is the A-B type dose equivalent rate meter based on a single detector and a single moderator. However, its response curve differs from the “neutron fluence-ambient dose equivalent conversion coefficient,” leading to measurement errors. In this study, in order to improve the accuracy of neutron dosimeter measurement, a feasibility study was carried out on the joint monitoring of neutron dose rate based on neutrons and instant γ-rays. Lead, borated polyethylene, polymethyl methacrylate, and sodium chloride were used to establish a conversion object. Monte Carlo simulations were performed to calculate the neutron responses of elements B, H, Cl, Pb, C and O. Then, these response curves were combined with the response curves of the LB6411 dosimeter to obtain a new response curve closer to the “neutron fluence-ambient dose equivalent conversion coefficient”. The linear fitting coefficients were calculated by using the differential evolution algorithm. The results demonstrate that the modified response curve is closely to the h_\phi response curve. The relative discrepancies are within 50% for the energy range of 1×10−8-16 MeV. The study indicates the feasibility of joint measurement of neutron and prompt gamma-ray for monitoring neutron ambient dose equivalent rate, providing new directions and support for neutron dosimeter calibration and development.

     

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