无人机航空γ测量中地面人工核素定量反演关键技术研究

UAV airborne gamma-ray spectrum detection technology is irreplaceable on the field of nuclear accident emergency radiation monitoring because of reducing radiation dose to staff, weakening the effect of topographic relief, increasing detection limit by low altitude flight. It is far away from forming the semi-infinite calibration models for significant short-lived artificial radionuclides because of the short half-life periods of most artificial radionuclides, potential radiation hazards, high cost, and so on. Monte Carlo simulation will be used to solve the above problem at enhancing nuclear accident emergency radiation monitoring capability of Sino-European conference in 2016. According to the disadvantage in the previous research, experiment coupled with Monte Carlo simulation will be used to establish Monte Carlo simulation optimization model of UAV airborne gamma-ray spectrometer. Based on the above optimization model, detection efficiency of UAV airborne gamma-ray spectrometer for infinite ground include artificial nuclide and the correction model for flight altitude and gamma-ray energy will be obtained. Meanwhile, those stripping coefficients of scattering contribution from artificial nuclide and natural radioactivity nuclide in surface layer of soil and the correction model for flight altitude will be calculated. And the above simulation results will be proved by experiments. In the end, the program will establish a quantitative inversion for artificial nuclide in surface layer of soil from UAV airborne gamma-ray spectrum. And it provides a valid technical support to for monitoring artificial radionuclides by UAV airborne gamma-ray spectrum which have high social and scientific significance.

无人机航空γ能谱探测技术因能最大限度地降低工作人员所受辐射剂量、削弱地形起伏影响、低空飞行提高探测限等使其在核应急监测领域的作用日渐凸显。但因辐射安全性、造价昂贵及半衰期短等原因导致诸多人工放射性核素的半无限大尺寸实物刻度模型难以实现。2016年“提升核应急航空监测能力”中欧技术研讨会确定采用Monte Carlo模拟方法解决上述难题。针对以往研究中的不足，本项目拟采用实验与Monte Carlo模拟耦合的方法获取无人机航空γ谱仪探测效率MC模拟优化模型，建立任意人工核素无限大地面上无人机航空γ谱仪探测效率随探测高度及特征γ射线能量间的函数关系、地表层天然及人工核素间散射成分剥离系数及高度校正模型，并实验验证上述反演参数的可靠性。最终编制一套核事故情况下基于无人机航空γ能谱人工核素定量反演软件，为核应急状态下无人机航空γ谱仪的有效应用提供技术支撑，具有较大的学术价值与社会意义。

近年来，放射源丢失事件屡见不鲜、福岛核事故的危害亦未解除，人工地面普查速度慢、耗资高，无人机航空γ能谱测量则能很好地解决上述问题。本项目对无人机航空γ测量中地面人工核素定量反演关键技术进行研究，重点开展了如下研究并取得如下成果：1）将γ谱仪、气象测量系统、GPS定位装置和激光高度计集成到无人机上搭建了一套无人机航空γ谱仪；设计了一款数字化多道脉冲幅度分析器，并将推导的直线成形方法应用于FPGA中分析数字化核脉冲，验证结果表明该方法提升了无人机航空γ谱仪的计数率。2）通过购置导轨滑台和步进电机，搭建了一套点源三维运动精确定位装置。3）优化了无人机航空γ谱仪中探头几何结构，实验验证了优化后的γ谱仪几何模型GEANT4软件模拟结果的可靠性；模拟半无限大地表面分别均匀分布的典型人工放射性核素上空不同高度的无人机航空γ谱仪探测效率值，建立了其探测效率随高度的变化规律。4）模拟半无限大地层分别均匀分布平衡铀系、钍系和K-40源上空不同高度的无人机航空γ能谱，确定其对人工核素能窗的散射成分剥离系数随高度的变化规律，同时建立典型人工放射性核素间散射成分剥离系数随高度的变化规律。5）设计了一套无人机航空γ谱仪对地人工核素定量反演方法，基于MATLAB平台编写相应代码，在两个测区上进行实验验证，对点源的反演活度与实测值间相对偏差为3.49%、大面源的反演活度与实测值间相对偏差为-9.95%～7.67%，充分证实了所设计的反演方法的可行性。项目研究成果为核应急状态下无人机航空γ谱仪的有效应用奠定了一定的研究基础。