The Research Of Stratum Radioactive Elements Low Energy Natural Gamma Ray Spectrum Processing Method

Compared with other gamma detectors,LaBr₃（Ce）scintillator detector is not high in environmental conditions,and the price is moderate,which is an important trend of the future.The detection efficiency for high energy gamma-ray decreases as the size decreases of LaBr₃（Ce）crystal,so selecting the low energy peaks to research gamma spectrometry is meaningful.In this paper,using the small size LaBr₃（Ce）scintillator detector to obtain the formation natural gamma spectra,Select the low energy gamma characteristic peak with high energy spectrum response,to study the data processing method for quantitative analysis of radioactive elements in stratified strata.This article has mainly carried on the following work:1.According to the principle of choiceγ-ray spectrum and analyze the measured data,the ²¹⁴Bi0.609MeV,²²⁸Ac0.908MeV,⁴⁰K1.460MeVcharacteristic energy is confirmed to alibrated the content of U,Th,K.2.This paper using the method of centroid and least square fitting to smooth the spectral data.The results show that the best smooth method is 7 points centroid.3.Using the SNIP method and fourier transform method to subtract the background.It proves that the SNIP method not suitable to subtract the background for the whole spectrum and choose different iterations for erery characteristic energy peak.The effect of selecting different step size will be different for fourier transform method.4.Analysing the gaussian fit algorithm in theory,least square gaussian fit method were used to reduce error in the original data processing.The test use the gaussian fit method to dispose the single peak of ⁴⁰K-1.46MeV,²²⁸Ac-0.908MeV and resolve the overlapped peaks ²¹⁴Bi-0.609MeV,²⁰⁸Tl-0.583MeV in the double gaussian function fit.The analysis results accorded with the original data.5.Determining the peak region,get the fitting data,then fit them.Finally determine peak region by setting the probability of peak interval（99.7%）.6.At last,integrate the function on that region and calculate the peak area.Get the content of U,Th,K by inverse matrix method.After subtracte the background,the errors are less than10%.But,the error of potassium content is big,because the test is not allowance theeffectof¹³⁸LafromLa Br₃（Ce）crystalfor the restrictions in experimental conditions.This method is feasible and accuracy requirements for exploration acceptable in precision.Theresearchresultsshowthatitispossibletochoice the²¹⁴Bi-0.609MeV,²²⁸Ac-0.908MeV,⁴⁰K-1.460MeV to calibrated the content of U,Th,K use theΦ1.5×2 inch LaBr₃（Ce）crystal.The tests prove the superiority and feasibility of the square least gaussian function fit and resolve the overlapped peaks,solve the difficulties of background subtraction,gaussian fitting and decomposition of overlapping peaks.The research provides a new way of thinking for data processing for quantitative analysis of formation radioactive elements.