Calculation Of The Effective Atomic Number In Geological Samples

For geological samples are concerned, the matrix consists mainly three rock types (magmatite, metamorphic and sedimentary rocks), the composition mainly are silica, aluminum, oxygen, sulfur and calcium and the like. In X ray fluorescence measurement, the change of matrix's composition brings the change of test sample's density, effective atomic number, then causes the change of scattering and absorption conditions, and brings direct impact to test elements'X ray eminence and linear relationship between its content.There are many scholars at home and abroad who did some related experiments about the change of matrix's composition which brings the change of test sample's effective atomic number. By measuring scattering and incoherent coherent ratio of the scattering count and determine the relations with sample's effective atomic number, Then to analysis the substance composition. This method was validated in actual analysis work of simple inorganics, organics, glass and alloy specimens. In China some scholars have used Si (Li) detectors, and use 238Pu source to test rock samples and determine relationship of scattering rate and average atomic number. But the research work of using Si PIN detector, 238Pu radioactive isotopes source excitation to determine the geological samples'effective atomic number is not much.In view of the present limitation of study in this field, this paper bases on usage of IED 2000P portable multi elements X ray fluorescence analyzer (Si PIN detector, 238Pu radioactive isotopes source), developed by the college of nuclear technology and automation engineering institute of Chengdu University of Technology, to study the relationship between scattering rate and effective atomic number. This subject comes from China Aero Geophysical Survey & Remote Sensing Center for Land and Resources's project"Application of X fluorescence analyzer in the West Tianshan of aeromagnetic anomaly verification"and national 863 high tech research project"Research of airborne gamma ray spectrometry exploration system". 1. In this paper, electronic shells binding energy's atomic number correction factor is fitted. The fitting scope is 4 to 20 elements. And get a curve relationship of K layer correction coefficient and atomic number. The correlation coefficient of fitting is 0.9999. And some elements relatively outer layers L layer, M layer electronic binding energy atomic number correction factors is also fitted.2. By Monte Carlo Simulation method, we get the relationship between density and effective atomic number of analysis pure samples SiO₂ and Al₂O₃ which have very close effective atomic number with geological samples. Through different quality test of boric acid reagents which are commonly used in solid presser sample, and get the density increment after the samples are pressed. And compare to Monte Carlo Simulation results, calculated the density increment of SiO₂ and Al₂O₃ (the increment of powder samples and powder presser samples), and got the results of effective atomic number's increment of SiO₂ and Al₂O₃ is only 0.00115and 0.00054, this influence for the calculation results of effective atomic number is limited.3. For the measurements of portable isotope radioactive sources X fluorescence analyzer, scattering Angle is a very important parameter. Different scattering Angle will have a big impact on results. And X fluorescence analyzer's scattering Angle inspired by isotopic source is difficult to accurately determine. This paper roughly shows the calculated best scattering Angle of IED 2000P portable multi elements X ray fluorescence analyzer, by a lot of experiments of analysis pure samples SiO₂ and Al₂O₃ whose effective atomic number is very close to geological samples.4. In in depth researchof the relationship of scattering peak and effective atomic number. And get a method of calculating samples'effective atomic number (spectral lines scattering method), and apply to xinjiang tianshan, Mengmala and Touxun these three work area. Comparing to effective atomic number measured by Wavelength dispersive X fluorescence spectrometer (wavelength dispersion Method), it has a smaller relative error, and good results were obtained.1) In the whole work area of Hongshanzui, effective atomic number calculated by spectral lines scattering method is 13.23, and for wavelength dispersion Method, it's 13.45. The relative error is 1.67%.2) In the whole work area of Mengmala, effective atomic number calculated by spectral lines scattering method is 12.93, and for wavelength dispersion Method, it's 13.20. The relative error is 2.06%.3) In the whole work area of Tuoxun, effective atomic number calculated by spectral lines scattering method is 13.14, and for wavelength dispersion Method, it's 13.17. The relative error is 0.32%.