Research On Standard-less Quantitative XRF Analysis Technology Of Field Geological Samples

Field XRF analysis technology refers to the rapid elemental qualitative and quantitative analysis of samples using a portable X-ray fluorescence analyzer(PXRFA)in the field.The most important feature of the energy dispersion analysis method used in this technology is that the instrument is light,fast,more analytical elements,and low cost.It can be directly non-destructive or in-situ analyzed in the field.Its working principle is based on Moseley's law,the characteristic X-ray energy emitted by the target element atoms in the sample is proportional to the square of the atomic number of the target element.The characteristic X-ray intensity is positively correlated with the content of the target element in the sample.The PXRFA instrument which based on X-ray tube is widely used,but the high-precision fluorescence spectrum analysis and quantitative analysis are important issues in the current application.Aiming at the problems of unknown matrix,difficulty in stripping overlapping peaks and time-consuming instrument calibration in XRF analysis of geological samples,the in-situ XRF standard-less analysis method for geological samples was studied.The main contents of this paper are as follows:Based on the theoretical formula derivation and research of the calculation of primary fluorescence and secondary fluorescence intensity in X-ray fluorescence analysis,a standard-less quantitative analysis model of XRF geological samples in the field was established.According to the established XRF standard-free quantitative analysis model,a corresponding nuclear physics database was constructed,including the calculation process of absorption limit transition factor,spectral line fraction,fluorescence yield and mass absorption coefficient,which solved the basic physics parameters in the model.In view of the complex and variable matrix of geological samples,there is a“black matrix”that cannot be analyzed by full element.The in-site XRF technology based on the traditional basic parameter method can't realize the problem of quantitative analysis without standard.The characteristics of incident X-ray coherent scatter and incoherent scatter are proposed.Peak count rate ratio(R)to determine the effective atomic number(Z_eff)of different geological samples,establish the mathematical relationship between Z_effand R,and use stepwise iterative method to obtain the effective atomic number of different matrix geological samples,solve How to calculate the mass energy absorption coefficient of the geological sample matrix in the standard-free quantitative analysis model.Accurately obtain the X-ray tube output spectrum and the geometry of the instrument.In this paper,the X-ray tube output spectral function acquisition is studied.The simulation results of X-ray tube output spectrum using MCNP and GEANT4 are compared.The GEANT4 simulation software is selected as the output spectrum simulation software.The method of solving the parameters such as instrument geometry factor Gi and detection efficiency is established,and the relationship between Gi value and energy is established too.The Gi value corresponding to the corresponding energy is obtained by interpolation.Aiming at the limited energy resolution of existing energy spectrum detectors,sometimes it is not effective to distinguish the characteristic X-ray energy between elements,and the overlapping peaks formed are difficult to be accurately stripped.A new quantitative analysis method for energy spectrum analysis is proposed—full spectrum matching algorithm,which combines the energy spectrum analysis with the quantitative analysis process,and solves the effects of spectrum overlap and matrix effect in the existing energy spectrum analysis,and solves the spectrum under the energy resolution of the existing detector.The problem has been solved for the integration of line analysis and quantitative analysis of content.Research on spectrum analysis methods was carried out.For the full-spectrum matching algorithm,the scattering background subtraction method is evaluated in this paper.The energy deposition spectrum and simulate easurement spectrum of six soil standards are obtained by Monte Carlo numerical simulation.Four kinds of SNIP,FFT,Air PLS and AIMA are used.The typical background subtraction algorithm performs the scattering background subtraction on the measured spectrum,and verifies the deduction effect and accuracy of the four consecutive background subtraction algorithms by comparing the relative errors.The Air PLS algorithm is selected to subtract the scattering background.The paper realized in-site XRF spectrum analysis software and verified the feasibility of the algorithm with 13national standard soil samples.The results show that the algorithm can be used for standard-less XRF quantitative analysis of geological samples.Based on the proposed and established field-based XRF standard-less quantitative analysis method,the application demonstration is carried out.The numerical model verification of 17 different rock sample bases equipped with Cu element as the main element was carried out.The results show that the influence of the XRF analysis results of the rock sample matrix on the site is not completely controlled by rock classification or rock mass elements.The correlation between the X-ray intensity of the elemental features and the main parameters of the spectral line is used to classify the similar matrix effects of the rock mass.In addition,in combination with the geological and mineral survey special project“Demonstration Application and Promotion of Field Rapid Analysis Equipment”,the field XRF non-standard quantitative analysis method was used to carry out geological minerals in Duobao Mountain,Fengshan Township in Heilongjiang,Wulagai in Inner Mongolia and Wulagai in Inner Mongolia.Investigate and apply the demonstration,and demonstrate the application of anomaly verification in the Mengmara area of West Tianshan,Xinjiang,and compare the analysis results with the analysis results of the vehicle EDXRF and the analysis results of the indoor WDXRF,and obtain a good application effect.Also the result is provided to verify the feasibility and practicality of the method technology.In summary,through theoretical derivation,model establishment and calculation,this paper studies and implements the standard-less quantitative analysis method technology applicable to XRF geological samples in the field,and applies the method technology to field geological sample analysis.It provides a reference for the further application and promotion of XRF analysis methods in the field.