Study Of Influence Factors Of Heavy Metal Elements EDXRF Detection Accuracy In Ecological Environment

The spectroscopy by using the energy-dispersive X-ray fluorescence(EDXRF) is widely applied in every industry or trade such as the metal smelting, geological survey, mining exploitation, petrochemical engineering, bio-medical, criminal investigation and archaeological identification, especially it can be used to make the full spectrum analysis for the samples to be tested in the site environment and online instant analysis and get a variety of data as well, the results and effects which can get could not be achieved by using other means of analysis. It does not need the analyzing crystal and the system of angular measurement when using the EDXRF spectrometer, which means that the complex structures are not needed between the detector and samples, thus the stereo angle of the detector receiving the fluorescence radiation will be wider, resulting in the improvement of the receiving efficiency of the detector, therefore it still can get the counting rate meeting the detector demand when using the low-energy roentgen tube as the excitaton source, the high power supply and heavy cooling system are not needed anymore when using EDXRF system, resulting in smaller volume.With the continuous development of computer technology and continuous progress of the technological level, the spectroscopy using the energy-dispersive X-ray fluorescence(EDXRF) will play an more important role in the site environmental detection and analysis.The expanding industrial production scale leads to the enviromental contamination more seriously which endangers the human health gradually, especially the heavy metal contamination has made many heavy pollution disaster areas pay a painful price. For example, “Blood lead” children’ s events happened in Fengxiang Shaanxi and other places, “Red River” events happened in Beijiang Guangdong and other places and so on, all those events show the high harmfulness of the heavy metals to the eco-enviromental contamination. The heavy metals enter into the eco-enviroments mainly by three industrial wastes, then enter into animals and plants by environmental carriers such as soil and rivers, as a result continue to accumulate there and endanger the human health finally. More seriously, the heavy metals could not be eliminated fundamentally, they can be controlled strictly and managed effectively only in order to reduce its harmfulness. At the moment, the carriers of the main samples tested for the heavy metal contamination include soil, water and plants. The main purpose of this paper is how to detect accurately the heavy metal contents existed in soil and plants by using EDXRF spectroscopy(The water samples have not been considered in this paper.) in order to provide a convenient and effective elemental analysis method for the enviromental contamination mornitoring.The EDXRF spectroscopy used to detect the heavy metals in soil and plants leads to the low probability and yield of the produced characteristic X-ray fluorescence because of the low contents of the heavy metals, which makes the effective spectrum signals to be covered by the noises from the system and background, bringing the difficulties to detect the elements accurately. There are more factors impacting the detection accuracy in the EDXRF spectrometer system with different causes. For this reason the detection of the heavy metals contented in soil and plants by using the EDXRF spectroscopy has been achieved in this paper through the improvement of the hardware circuit, structural parameter simulation and spectral line data processing. The main research items achieved in this paper are as following:1. X-ray flare intensity distribution in the sample surface certified by Monte Carlo simulation established on the theoretical structure and simulated is random with a Gaussian. The yield of the characteristic X-ray fluorescence has a close association with the divergence angle of the incident X-rays and the X-ray intensity. The trends of X-ray parameter have been investigated by the improvement of the systematic structure parameters, the simulated production of the X-ray and its operation process with substance and tracing the trajectory of charged particles, which is used as the reference of the systematic structure optimization in order to promote the detecting ability of the system to the traces of heavy metals.2. The analysis circuit structure of the high-speed pulse amplitude has been redesigned based on the analysis of the data signal processing circuit in the EDXRF system and comparative analysis of the performance parameters of pulse amplitude analyzers against the dead time generation principle of the multi- channel pulse amplitude analysis module in order to improve the detecting ability of the system to the weak signals.3. Based on the spectral line processing algorithms, the spectral line noise interference caused by the continuous background spectrum, characteristic X-ray spectrum, escape peak and doublet peak generated because of the sum peak superimposed with the excessive metal adjacent spectral lines in X-ray fluorescence spectrometry has been solved with the least square method of spectral line smoothing, symmetrical zero area peak search method, background subtraction of stripping peak method and fundamental parameter method.4. By investigating the heavy metal content in tea and stream sediment(bottom sediment) respectively, EDXRF system studies on the heavy metal elements content test of soil and plants in the ecological environment. By means of comparing heavy metal contents of standard samples, we could draw a conclusion on the EDXRF system detection precision evaluation.