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The Character Of Airborne Gamma-ray Spectrometry And The Method For Spectrum Analysis

Posted on:2011-01-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q X ZhangFull Text:PDF
GTID:1100360308959180Subject:Nuclear Resources and nuclear exploration project
Abstract/Summary:PDF Full Text Request
Airborne gamma-ray spectrometry survey is detecting the gamma-ray spectrum released form the terrene which the airborne gamma-ray detecor is fixed in airplane. It can get U, Th and K contents of the terrene directly when the airplane flying. Airborne gamma-ray spectrometry survey is widely applied, such as mineralization exposure, environment radiation evaluation and nucleus emergency. The gamma-ray spectrum characteristics and spectrum analysis is the key of improving the precision of U, Th, K content measurement. At present, the researchers pay attention to the spectrum measured by instrument and radionuclides released, hardly consider the sperctrum disturbution which effected by geologic body. As for the spectrum analysis, the conventional method is the tripping-ratio, few regarding the full spectrum analysis. Influencing factor of the airborne gamma-ray spectrometry survey is the key of the survey result inversion. In view of the research insufficiency the airborne gamma-ray spectrum, airborne gamma-ray spectrum characteristic and spectrum analysis have been studied in this paper.In the paper, the author gets the characteristic of airborne gamma-ray spectrometry by theoretic analysis and Monte Carlo method. The character such as:â‘ The gamma-ray spectrometry in the air is consecutive, it is different from the gamma-ray spectrometry from the the radioactive nuclear. The gamma-ray spectrometry construct of charactertic gamma-ray and the baseline of Compton Scattering.â‘¡The character of gamma-ray spectrometry in air, especially the Compton Scattering peak, is relationship to medium composition. In the paper, the character of gamma-ray spectrometry is studied upon the simplex element medium, granite, gritstone, limestone and basalt. We can use the variable of S1/S2 to distinguish the effective atom number so we can distinguish the lithology.â‘¢The effect of water in the soil on the gamma-ray spectrometry measuring on the surfer of ground. With the increase of the water content, the flux of gama-ray decrease on the surfer of ground. In the paper, author established the correction model of wate content in the soil. By the Monte Carlo simulation, the parameters of the correction model had been acquired. Moreover, the model can correct the influence of water by experimentation test and the error is less than 2%.In the thesis, the influence mechanism of landform to the airborne gamma-ray spectrometry survey has been analysised, and the micro elment landform correction method has been put forwarded. Based on the numerical calculation, the landform correction on the airborne gamma-ray sepectrometry survey has been achieved; furthermore, the program code has been completed. There are nine typical landform had bed considerated and corresponding correction factors has been calculated. As a consequence, there is the new method for the landform correction of airborne gamma-ray sepectrometry survey.For the unsatisfactory energy resolution of the NaI(Tl) crystal, the problem of scattered rays in airborne gamma-ray sepectrometry and the defect of conventional tripping-ratio method, Author put forward the analysis mehod of gamma-ray spectrum for airborne gamma-ray spectrometry.â‘ The method of fourier transform approach background by step (FTABS) is been adopted to estimate the scattered rays background for airborne spectrum. FTABS can estimate the scattered rays effectively only by the response function matrix which is established by gaussian function. Using this method, the response function is simpler and has higher practicality in full spectrum analysis. By the simulation spectrum test, the error of background estimation is less than 15%.â‘¡Profits from the concept of response function matrix, author establish the relation between spectrometry and input spectrum. The spectrum have been restructured by maximum likelihood method and direct demodulate method. A FWHM-discrepant overlapping peak has been separated by the spectrum restructured technology, and the area of peaks maintains invariable.â‘¢The spectrum analysis algorithm is applied to gamma-ray spectrometry calibration, the relation between net peak area of characteristic gamma-ray and the content of U, Th and K has been established. Using spectrum analysis algorithm, spectrometer calibration process can be simplified. In the experiment of content calibration processing prove that the spectrum analysis algorithm can effectively improve the precision of element content calibration. Calibrating on the saturated gamma model, the mixed model content by measurement described as fellow: comparing with conventional tripping-ratio method, the error of K element content from 9.74% reduces to 8.73%, the error of U element content from -8.25% reduces to -0.96% and the error of Th element content from 10.51% reduces to -3.13%.â‘£The 137Cs measurement which detected by NaI(Tl) crystal using spectrum analysis algorithm has been discussed. Experiment proves that NaI(Tl) crystal detector can measure the activity of 137Cs by spectrum analysis. The determination coefficient between the net area and activity of 137Cs is 0.99.For the rearch in the thesis, measuring accuracy of U, Th and K content has been improved and calibration process has been simplified. The rearch provides the basis of geologic interpretation of prospecting by airborne gamma-ray spectrometry survey, which have high practical value and scientific significance and expanded application scope.
Keywords/Search Tags:airborne gamma-ray spectrum, geologic body, gamma-ray spectrum distribution character, landform correction, spectrum analysis
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