Research On The Technology Of UAV Ultra-low Altitude Dual Energy Directional Gamma Spectrum Sampling

The UAV ultra-low altitude dual energy directional gamma spectrum sampling technology is a method that the dual energy directional gamma spectrum sampler is installed on the UAV to measure the gamma ray energy and intensity released from rock(ore)or soil,and calculate the content of radionuclides in rock(ore)or soil according to the obtained gamma spectrum data.In the process of uranium exploration and mining,the UAV ultra-low altitude dual energy directional gamma spectrum sampling technology can be used to obtain the uranium grade of rock(ore)on geological engineering or mining face,such as trench,stripping,tunnel wall and open pit,calculate the line reserve,guide exploration engineering and mining engineering.Compared with traditional directional gamma radiation sampling technology,UAV ultra-low altitude dual energy directional gamma spectrum sampling can save manpower,improve work efficiency,guide uranium exploration engineering and open-pit uranium mining,realize digital mine construction,and avoid and eliminate the radiation dose of workers in the process of radiation sampling.In this paper,the research of UAV ultra-low altitude dual energy directional gamma spectrum sampling technology is carried out,and the national key research and development plan "high resolution aviation gamma spectrum measurement and airborne imaging spectrum measurement technology"(Project No.: 2017yfc0602100)and the National Natural Science Foundation Project "high resolution aviation gamma array detector group spectral response research"(Project No.: 41774147)and The research results are as follows.1)The working principle and mathematical model of UAV ultra-low altitude dual energy directional gamma spectrum sampling are proposed.The traditional directional gamma radiation sampling method can be divided into two kinds: the second gamma radiation sampling method and the first gamma radiation sampling method.Among them,the secondary gamma radiation sampling method is to measure the gamma ray fluence rate at each point to be measured when the detector has lead sleeve and lead-free sleeve,and eliminate the interference of surrounding gamma rays by using the difference between the two measurement results,so as to achieve the purpose of directional gamma sampling;the primary gamma sampling is to wrap the secondary detector around the main detector(such as FD-42 directional gamma radiometer),and In the last measurement of the point to be measured,the directional gamma radiation sampling is realized through the gamma ray flux obtained by the main and auxiliary detectors.For UAV ultra-low altitude directional gamma radiation sampling,because it is a continuous measurement,only one gamma radiation sampling method can be used.The dual energy directional gamma spectrum sampling uses the cerium bromide scintillation counter as the gamma ray detector with an energy resolution of 4%(relative to FWHM,0.661mev).The detector is surrounded by a thin layer of lead sheath.The gamma rays with high and low energy are selected as the detection objects.The significant difference of mass attenuation coefficient between the high and low energy gamma rays in the thin layer of lead sheath is used to obtain the detection results The high or low energy gamma ray flux directly below the detector can eliminate the interference of gamma rays around the detector.According to the above working principle,the basic equation of the dual energy directional gamma spectrum sampling is established,and the directional proportion coefficient of the dual energy directional gamma spectrum sampling probe is defined.According to the interaction between photon and matter and the superposition theory of the uranium ore body gamma field,the mathematical equation of the gamma ray fluence rate and the uranium content of the uranium ore body recorded by the directional gamma spectrum detector is derived,and the directional dual energy gamma is defined Conversion factor of the horse energy spectrum sampling system.2)A dual energy directional gamma spectrum sampling probe is designed.Using the recommended algorithm in ICRU Report No.53,the effective detection radii of 0.352 mev,0.609 mev ?-photons are 1.2m,2.5m,3.6m,5.1m,1.4m,3M,4.5m,6.2m,respectively,when the gamma ray flux ratio is 60%,80%,85%,90%.Using Monte Carlo numerical simulation method(mcnp5.0 software),under the body source model with depth of 0.6m and radius of 6m,one unit point in the body source is taken out to integrate the gamma ray fluence of cebr3 detector,and then the total gamma ray fluence is calculated by integrating the unit point source as the body source,taking 0.352 mev and 0.609 mev as the detection objects,with 80% photon flux accounting for 80% Under specific conditions,the optimal thickness and length of two groups of lead orienteers were obtained: lead orienteer was 4.5cm long and 0.2cm thick,its real shape was 17 cm long and 4.5cm wide and 0.2cm thick lead skin,the directional proportion coefficient a = 0.65,a = 0.33;lead orienteer was 5.5cm long and 0.3cm thick,its real shape was 17.6cm long and 5.5cm thick and 0.3cm thick lead skin,the directional proportion coefficient a = 0.55,a = 0.32.3)Data processing of directional gamma spectrometer.Seven point center of gravity smoothing method and full peak area method are used to obtain the net peak area of characteristic gamma ray all-round peak.Double Gaussian fitting least square method is used to solve the problem of 0.609 mev and 0.583 mev heavy peak.The average relative error within the fitting range is 7.28%,and the fitting effect is good.4)4)The uranium content calibration method of the UAV ultra-low altitude dual energy directional gamma spectrum sampling system is established.The calibration of uranium content is carried out on the radioactive standard model.According to the uranium content of the radioactive u,th and K models and the net peak area count of the corresponding 0.609 mev and 0.352 mev gamma ray characteristic peaks,the least square method is used to solve the conversion coefficient ?,?,? and ? in the formula of conclusion 1,and the net peak area of the conversion count result and the 0.609 mev and 0.352 mev gamma ray characteristic peaks of the mixed model are calculated The uranium content calculated by counting and compared with the uranium content of mixed model,the relative error of calculation is required to be less than 10%.