Research On Sourceless Efficiency Calculation For Airborne Gamma-ray Spectrometer

Aviation ? detection is of great significance in the fields of mineral exploration,nuclear accident exploration and measurement of radon concentration in buildings.At present,the research of sourceless efficiency calibration technology in China is mainly based on Monte Carlo simulation.,but it takes a long time because of the large size of the model.The use of variance reduction techniques is likely to cause bias in the efficiency calibration.At the same time,the NaI(Tl)crystal used in aviation ? detection has a large size,and the counts of full-energy-peak formed by multiple scattering of the ?-ray in the detector are difficultly counted by the numerical algorithm.Therefore,direct numerical calculation methods are difficult to achieve practical purposes.This paper relies on national key R&D projects: high-resolution aviation gamma spectroscopy and airborne imaging spectroscopy(2017YFC0602100),National Natural Science Foundation of China: high-resolution aerial gamma spectroscopy and 3D quantitative inversion techniques(41774190)Conducting research on sourceless efficiency calculation for airborne gamma-ray spectrometer.Based on the ? radiation field distribution characteristics of aeronautical ?-measuring objects,formulas for calculating detection efficiency of square and cylindrical typical detectors for point source,surface Source and volume source is established by the idea of micro-emission field integration.Based on the theoretical calculation,Monte Carlo method is proposed to solve the influence of particle scattering on the full-energy-peak counts of the detector and improve the accuracy of the calculation results.At the same time,combined with the theoretical formula to establish the land ? radiation field model,to improve the Sampling Efficiency of Monte Carlo Program.According to the derived mathematical model,this paper compiles a sourceless efficiency calibration software on MATLAB platform,and realizes the detection efficiency calculation of the full-energy-peaks of the three typical detectors for the three characteristic sources.The calibration case of HPGe and NaI(Tl)detectors proves that the software can be used for the detection efficiency calculation of conventional ?-ray spectrometer.It also demonstrates that the theoretical model has good adaptability and accuracy.At the end of the paper,the theoretical model and the sourceless efficiency calibration software are applied to calculate the detection efficiency of the Airborne ?-ray spectrometer,and the theoretical model and software calculation results are verified by the experimental data.The results show that the theoretical model derived from this paper is effective for Airborne ?-ray spectrometer.At the same time,this method has high computational efficiency,and can carry out detection efficiency calculation of airborne ?-ray spectrometer on PC platform.