Development The Micro-beam And Micro-area X-ray Fluorescence Mineral Probe

Observation and determination for mineral components at micro-level and sub-micro level are of great significance in the field of geosciences and mineral resources exploration. As an important analytical tool, micro-beam and micro-area X-ray fluorescence (Micro-XRF) mineral probe which aims to combine both a large area of scanning and micro-area analysis is capable of meeting the requirements for the analysis and detection of mineral composition and elements distribution at micrometer scale, it can also be further extended to the metal study, electronics science, medicine, biology, environmental monitoring and other fields. From the basic principle of X-ray interaction with matter, setting out to study the key analytical technology of micro-beam X-ray fluorescence for the minerals, the dissertation elaborates the design and development of a kind of micro-beam and micro-area X-ray fluorescence (Micro -XRF) mineral probe. The main contents and the innovative research results are as follows:1. Developed the first micro-beam and micro-area X-ray fluorescence mineral probe at home. Implemented micro-beam irradiation (spot diameter is about 30μm ~50μm) and micro-area excitation; micro-area precision positioning and control; microscopic magnification and imaging; obtaining accurate information of characteristic X-ray energy spectrum for micro-area analysis, multi-elements qualitative and quantitative analysis for minerals within micro-area. The major technical indicators have reached that of similar foreign products, part of them surpass the foreign advanced level.2. Design and Implementation of Micro-beam X-ray source. Designed X-ray optical path and established the technical association between the focusing X-ray optics and micro-area X-ray fluorescence analysis . The micro-beam X-ray source combined both the Oxford advanced side's window low-power X-ray tube with 70μm micro-spot and Monolithic X-ray Lens made in china which have reached the international advanced level. The measured spatial resolution on NiKαline spot diameter is 34μm, which effectively raised the target element characteristic X-ray fluorescence excitation efficiency, reduced the background scattering, then laid the foundation for micro-beam and micro-area multi-element qualitative analysis and highsensitivity quantitative measurement. 3. Designed a kind of three-dimensional precision micro-displacement stage targeting at the distribution characteristic of micro-beam X-ray energy and intensity. Research into its space micrometer precision positioning technology in order to improve the moving stability and accuracy for the mechanical components under the low speed effectively. Based on exploring the three-dimensional layout of the overall structure, built up a dynamic model for the mechanical transmission system in series which consists of high-precision motor and high precision mechanical transmission components. Using Hertz contact theory to execute the theoretical derivation for transmission chain rigidity of mechanical transmission system. Analyzed the reasons of unstability at low speed and the positioning errors of micro-platform. At the same time, used parametric modeling software combined with finite element analysis method to optimize the design of the mechanical structure. The three-dimensional micro-displacement stage, which was designed less than 180mm3 in overall size and achieved ten to tens of millimeter stroke in spatial orientation with±1μm positioning accuracy and 1.5μm average step, can provide a precise movement for the target point positioning and the surface scanning in Micro-probe system.4. Considering on the special requirements of micro-beam sources and micro-area analysis, studied the access technology of information from the micro-area on mineral sample(including image information and energy spectrum characteristic information of X-ray). Adopting Si-PIN semiconductor detector and a microscopic magnification systems which consists the 20 to 40 times optical magnifier and 300 million pixel CCD industrial digital camera, the Mineral probe can collect the information of the micro-area image and characteristic X-ray energy spectrum of target elements in real-time. Meanwhile, the micro-area to be analyzed can be precisely located in space when linking the operation of microscopic magnification systems and the three-dimensional moving platform. Obtained the optimal source - sample - probe-CCD geometric design based on the theoretical analysis and physical experiments, which reduced detection limits of micro-beam and micro-area X-ray fluorescence analysis, improved the sensitivity of elemental analysis and provided technical guarantee of the accuracy.5. Carried out the testing for the main technical indicators of mineral probe. Presented scientific differential and integral experimental methods to measure the focal spot size of micro-beam and micro-area X-ray mineral probe. In the micron scale, measuring the NiKαX-ray characteristics peak area of nickel-chromium wire (diameter 10μm) by step moving can get the differential curve of the spot , however measuring the CuKαX-ray characteristics peak area of copper slice by step can get the integral curve of spot. Under a certain level of confidence, analyzing the differential curve and the integral curves further will finally access the spot size of the instrument. The test results showed that at 0.317 confidence level, the focal spot diameter of micro-beam and micro-area X-ray fluorescence minaral probe is 34μm.6. Developed preliminary mineral tests on the micro-beam and micro-area X-ray fluorescence mineral probe system, which operated on the sample of massive zinc ore (sphalerite) and iron ore (pyrite). The results showed that micro-beam and micro-area X-ray fluorescence mineral probe system can effectively distinguish mineral particles varying from 10μm to 30μm from matrix. The analysis accuracy for elements content in single mineral is 4.21% (RSD).With the characteristic of lower costs, simple sample preparation, fast speed of analysis, the micro-beam and micro-area X-ray fluorescence mineral probe instrument is satisfactory for qualitative and quantitative multi-element micro-area analysis, which can be used in the geological mineral samples, crystalline or cryptocrystalline mineral composition, powder materials, massive, thin, tinsel materials. Hence, developing the micro-beam and micro-area X-ray fluorescence mineral probes and investigating the key technologies of them will accelerate the pace of manufacturing domestic silimar production, fill the empty of development the low-cost, automated, high precision Micro-XRF and application in the mineral exploration within micro-region at home; Meanwhile, break the monopoly situation by foreign device at domestic market. All of that will improve the equipment level and technical level of mineral exploration at home.