The Research On Stabilizationfor Airborne Gamma-ray Spectrometry System

Airborne gamma-ray spectrometry survey is to detect the radiation from terrenewhich the airborne gamma-ray spectrometry is fixed on airplane. Furthermore, we candetermine the U, Th and K contents of the terrene from the count of those energywindows. Airborne gamma-ray spectrometry survey is main supportive technologiesforradioactive mineral exploration, geological mapping, environment radiationevaluation and nucleus emergency. The paper comes from "the eleventh five-yearplan"–the research and development on Airborne gamma-ray spectrometry surveysupported by National863Program of China（Project Number:2006AA06A207）andNational Natural Science Foundation of China “The research on Natural gamma rayfield in the nuclear geophysics”（Project Number:40774063）. This article takesspectral drift of airborne gamma spectroscopy system as the research object，systematically analyzed the reason of spectrum drift about the detector with the largeSodium iodide crystal. The experiment about law between drift and temperature iscarred out. The result of experiment provide the experimental basis and experimentalbasis to stabilize the airborne gamma-ray spectrometry system.A new method of fuzzyself-tuning PID stabilizer, combined with the software and hardware, is established.The achievement about the research can improve the stability and quality of theairborne gamma-ray spectrometry system which have high practical value andscientific significance.It is carried out the research and investigation about the airborne gamma-rayspectrometry technology and gamma spectroscopy spectrum stabilization methods athome and abroad. The paper introduces the research. 1)The mechanism of the airborne gamma energy spectrum instrument spectrumis probed. And the reason of the spectrum drift is revealed. The experiment is carriedout about the gamma spectroscopy drift experiments and temperature drift law. Thisexperiment takes the gamma-ray detector with crystal NaI (Tl) scintillation asexperimental object.Theexperimental result provide theoretical and experimental basisfor for airborne gamma spectroscopy spectrum stabilization.2)The PID control algorithm is taked to stabilize the airborne gamma-rayspectrometry system.The paper introduces the definition of stable spectral parameters,the fuzzy control tuning method, and avariety of control algorithm. So the newlystabilization system for airborne gamma ray spectroscopy is set up which is combinedwith the hardware and software.3)The method to stabilize the spectral are developed by the software. It containsthe digital shift method, sample rate conversion and the GMM model for correctingthe spectrum. These methods provide a mathematical model to correct the spectrum.4) The research about how to smooth the data,reduce the noise, deduct thebackground and extract the drift of the spectrum. Research findings provide thetechnology to achieve high-quality instrument spectrum.5)The stabilization system is applied into the airborne gamma-ray spectrometryto check up the effect.In the paper, the author gets the result such as:1)Based on the analysis of airborne gamma-ray instrument spectrum formed toexplore the causes of the instrument spectral drift. Temperature effect is in the processof airborne gamma-ray spectrometry, aviation NaI (Tl) scintillation counter theairborne gamma spectroscopy drift factors; by indoor physical experiments show that,aviation NaI (Tl) scintillation counter temperature effect can be generated canspectrum positive shift3-order polynomial function to describe, the fittingcoefficients better than0.99. Theexperimental result provide theoretical andexperimental basis for for airborne gamma spectroscopy spectrum stabilization.2) Based on the heoretical study and numerical simulation, the fuzzy self-tuningPID spectrum stabilization technology is proposed which is combined about thehardware and software. According the spectrum drift, the proporional element and theintegral element will bring the phase-lead quantity. And the differentiation element isused to diminish the steady-state error in the system.According the fuzzy controlalgorithm, the stabilization system can obtain proper coefficient by the spectrum driftand the variance ratio of the spectrum drift. 3)Effective for airborne gamma-ray instrument spectral peaks net peak area, putforward the wavelet multiple iterations buckle the background technology. Themethod uses the idea of wavelet multi-resolution, multiple iterations to achieve thededuction on the bottom. For simulated spectral data showed that: the peak intensity(peak height) when a change occurs, the impact on the bottom net of the effect, whenthe Gaussian peak intensity from time20to5, the variation of the peak area and theactual peak area changes compared to less than5%; when peak20fixed time, plus thenoise from the unit noise (from0to1, Gaussian distributed random noise) to1times4times the noise when the theory with the estimated bottom end of the present thedeviation is less than5%, the method does not appears in the spectral data in thebottom of the net of the present process, no physical meaning of the negative.4)The spectrum stabilization method based on signal processing is proposed torelease self-stabilization. Three methods are proposed to correct the spectrum. Thereare digital translations, sampling rate conversion and gauss function fitting. Afterdeducting the linear background, the peak location obtains by gaussian function fittingto get peak location. The result show that the diversification of the peak location isless than1channel;compared with the cross reference, the absolute value of therelative deviation of the peak area is less than5%.5)The fuzzy self-tuning PID stabilizer is used in airborne gamma spectroscopysystem. The result in the laboratory tests show that airborne gamma spectrometer canstabilize in±1channel（channel256） for the characteristic peak of40K-1.46MeVwhen the system started at29seconds. When the spectrum is adjusted to deviate thestandard, the system will stabize between±2channels（channel1024）for thecharacteristic peak of40K-1.46MeV in the180seconds and between±1channels（channel1024）in240seconds. Vehicle experiment and field test data show that,under the condition of complex dynamic, the movement of the characteristic peakposition of40K-1.46MeV is between±1channel（channel256）.AGS-863Airbornegamma spectrometer carry out trial production of20,000line km flight in a pilot areain Inner Mongolia. The result shows that the method to stabilize the spectroscopy isEffective to stabilize the system and elineation of the strata of the test area.