The Research On The Processing Technology Of Nuclear Pulse Signal And Instrument Spectrum For Airborne Gamma Spectrum

Because of the advantages such as high efficiency,low cost,unrestricted by topographic factors and wide working area,airborne gamma spectrometry technology has played an important role in the exploration of uranium mines,potash salts,rare polymetallic deposits,oil and gas resources related to radioactive feature.With the progress and de Velopment of nuclear energy and nuclear technology in recent years,airborne gamma spectrometry measurement technology has been gradually applied to the investigation and e Valuation of environmental radioactive pollution,nuclear facility monitoring,nuclear accident emergency monitoring and other fields.This paper selectes a topic from the National Key Research Project �high-resolution aerial gamma spectrum measurement and airborne imaging spectral measurement technology�(grant number: 2017 yfc0602105)and the National Natural Science Fund �high resolution aerial gamma ray detector array group of spectrum response research�(grant number: 41774147),and is supported by the project funding.This paper focuses on the research of nuclear pulse signal processing technology and instrument spectrum processing technology of airborne gamma-ray spectrum,and implements the de Velopment of high-performance airborne gamma-ray spectrometer.The main research contents and results are provided as follows:(1)The Mexican straw hat wavelet forming technology is proposed to effectively solve the problem of the existence of electronic noise,ballistic deficit and baseline change of digital nuclear pulse signal in the acquisition and processing of airborne gamma spectrum.Taking the airborne gamma ray spectrometer of Na I(Tl)scintillation counter as the research object,the paper discusses the characteristics of the output nuclear pulse signal of Na I(Tl)scintillation counter,and puts forward the Mexican straw hat wavelet forming technology,focusing on its waveform characteristics,noise characteristics and "ballistic deficit".Mexican straw hat wavelet is obtained by taking the second derivative of the gaussian forming system function.For the linear baseline of exponential nuclear pulse signal superposition,the baseline is identical to 0 after Mexican straw hat wavelet forming,which has the simple and unique advantage of baseline deduction.According to the time difference T and amplitude difference h between the two minimums in the waveform after the formation of Mexican straw hat wavelet,a mathematical model of time difference T,amplitude difference h and pulse amplitude h is established to measure and compensate the degree of ballistic loss.Mexico straw hat wavelet forming is to complete the filtering forming function through convolution calculation,and the filtering forming,spectral drift extraction and stability control algorithms can be processed in real time by using multi-arithmetic logic processing unit array,so as to meet the application requirements of nuclear pulse signal amplitude analysis of airborne gamma spectrum measurement system.(2)Using the Mexican straw hat wavelet analysis technology,the calculation of the full energy peak,the net peak area and the full width at half maximum of the airborne gamma spectrum instrument is implemented.Based on the unique effect of wavelet analysis in characterizing the signal distortion,the center location of total energy peak is found exactly by using Mexican straw wavelet analysis and regarding the peak as the distortion signal.According to the physical basis that the full energy peak is superposed by the Compton scattering background count,this count is firstly regarded as a linear curve on the full energy gaussian peak,and then is removed by secondary smoothing of Mexican straw hat analysis.Finally,the net peak area and the full width at half maximum are calculated successively,accomplishing the real-time e Valuation of the energy resolution of airborn gamma spectrum measurement system.(3)A novel digital airborne gamma spectrometry measurement system based on Mexican straw hat wavelet forming technology is designed and de Veloped,including the core circuit design and implementation of airborn gamma spectrometer,the design and implementation of arithmetic logic unit for the nuclear pulse Mexican hat wavelet shaping algorithm,the design and implementation of the circuit control unit,and the de Velopment of energy spectrum data processing software.According to the actual measurement,the energy resolution of the new digital airborne gamma spectrometer reaches to 7.49%(with regard to FWHM,0.661 Me V)by taking use of Na I(Tl)scintillation counter as gamma ray detector.For the same measurement point,multiple continuous measurements are implemented and the duration time of each measurement is 600 s.For each measurement,fast count,slow count,Tc,Cs,K,U,Th channel and cosmic ray are calculated.The test results show that the relative standard de Viations of the above parameters are separately 0.13%,0.13%,0.13%,0.20%,0.19%,0.33%,0.27%,0.82%,meaning superior repeatability.For continuous measurement of the same measuring point,each measurement time is set as 3600 s.The variances of the above parameters in 3600 s are all far less than 1%,which means the better stability for the de Veloped spectrometer under the conditions of long-time operation.