地形对就地γ谱仪技术注量活度比测量影响的模拟研究

Simulation Research on the Influence of landform on the Measurement of Fluence Ac-tivity Ratio in in-Situ γ-Ray Spectrometer

摘要: 本文简要比较了几种不同地形对就地γ谱仪中注量活度比测量的影响，分析其可近似使用Beck公式直接计算的条件。通过几何平移变换、源偏倚抽样、简化模型等方法提高蒙特卡洛模拟效率以获得山包、冲沟和粗糙表面等不同土壤模型下的注量活度比数值，比较其与理论注量活度比的偏差。结果表明，当放射性核素衰变光子能量在0.354 MeV到2.614 MeV范围内，且山包和冲沟的坡角小于5˚，粗糙表面模型面源粗糙度小于0.5 cm，体源粗糙度小于10 cm时，都可以忽略地形对就地γ谱仪注量活度比测量的影响，直接使用Beck公式进行简便计算。

Abstract: This paper briefly compared the influence of landforms on the fluence activity ratio of in-situ γ-ray spectrometer, and analyzes the conditions in which the fluence activity ratio can be approximated by Beck’s formula. This paper uses some variance reduction methods to improve the efficiency of Monte Carlo simulation, including geometric transformation method, source bias sampling method and simplified model method. Then it compares the simulated fluence activity ratios of different landforms such as mountain, gully and rough-surface ground with the theoretical values given by Beck’s formula. The result shows that when the energy of decay photon is in the range of 0.354 MeV to 2.614 MeV, the following cases can ignore the influence of landforms on the fluence activity ratio and use Beck’s formula to calculate the value directly: the slope angle of mountain and gully is less than 5˚; the roughness is less than 0.5 cm under surface source distribution in rough-surface flat ground model; the roughness is less than 10 cm under volume source distribution in rough-surface flat ground model.