The Submarine In-situ X-ray Fluorescence Detection System

Submarine in-situ X-ray fluorescence detection technology is based on the energy dispersive X-ray fluorescence analysis principle, the submarine X-ray probe should be put on the submarine sediment, and then we use the drag way to deal with the submarine sediment constituents for in-situ, real-time measurement, and the multi-element content data of submarine sediments should be quickly got. This paper discusses the development of submarine in-situ X-ray fluorescence detection system and technique research achievements, including the development of the digital submarine x-ray probe, submarine sediment moisture effect correction model, the quantitative analysis model and survey analysis software, etc. This paper comes from: National High Technology Research and Development Program (863 program) project: "research on submarine in-situ X-ray probe analysis system" (project number: 2006AA09Z219) and China Geological Survey subject "submarine in-situ X-ray fluorescence detection system" (subject Numbers:HKWT-2010-026).The paper results can provide new equipment and technology for China’s Marine mineral resources survey; the equipment and technology will also improve the equipment level and technical level on China’s ocean geophysical exploration.The paper main achievements obtained are as follows:Submarine probe has to work in hundreds of meters and even thousands of meters deep water with high pressure. Therefor it requires the ability of water-pressure resistance and anti-seep to make X-ray go in and out freely. We design the "bullet" shell of submarine exploratory tube with 2A12 duralumin, make the X-ray detection window with 1.5 mm beryllium, we combine them in vacuum environment, submarine exploratory tube will be sealed up with double "O" structure and got pressure experiment in the Pressure lab of Chongqing geological instrument plant, there should be no deformation and seepage phenomenon in the 12 Mpa pressure (equivalent to water depth is 1200 meters) within 2 hours.It’s the first time to design the excitation detection device of ocean bottom in-situ X-ray fluorescence detection system with a miniature X-ray tube and high resolution electric refrigeration Si-PIN semiconductor detector, we confirm the angle between the X-ray tube and sample is 70°～75°by original level X-ray scattering theory analysis and test verification, at the same time we can get the best peak to background. According to the X-ray tube original level X-ray spectrum intensity distribution and the X-ray intensity distribution of target material, we take research on the best working voltage and current of X-ray tube in measuring Ti, Cr, Co, Cu, Mo respectively. Considering the excitation efficiency and higher peak to background of all elements detected by submariner X-ray fluorescence in-situ measurement, we determine the working voltage of X-ray tube is 30 kV, the working current is 4 uA, and achieve the efficient excitation and detection on submarine sediment samples.Through the output signal analysis on charge sensitive preamplifier of detector, we take low noise digital nuclear pulse processor which is based on the digital pulse shaping filter, digital baseline estimation and recovery, digital pulse accumulation of resistance and count rate correction, digital pulse wave form screening in the system, the counting-pass percentage can be up to 40kcps with the assurance of the system energy resolution. We develop long distance high fidelity data transmission communication interface circuit based on the CAN bus technologies, theoretically data transmission distance can reach 10km, we also realize the ship control system to control the submarine exploratory tube and acquire data, provide the hardware to make sure of realization of submarine X-ray fluorescence in-situ measurements.We take the original level spectrum scattering background deduct technology based on the Fourier transform method and characteristic X-ray differential spectral analysis technology based on maximum likelihood estimation to the experiment, the result of the measured differential spectrum line of prepared sediment samples of Cu, Ni, Pb, Zn indicates the method can effectively deduct scattering background, analytic energy difference is two-thirds of the FHWM of overlapping spectrum peak and this method can also provide feature information.We study the mathematical model of water effect, establish the correction equation of water in submarine sediments, the result of experiment of saturated water effect correction of Fe and Cu shows that the relative error of corrected content is less than 5%. Through the submarine sediment sample matrix effect research, we build the matrix effect correction quantitative analysis model based on counting rate power factor method and characteristic-scattering ratio power factor method "classification-characteristic-scattering ratio-parameters-nonlinear correction" and through the comparison of the geochemical standard substance of low content (10μg/g), high content (100g/g) and ore samples with Cu, Ni, Pb, Zn, Ti and Fe, we get a very good correction effect.We design the eccentric aggravate device in order to make the submarine exploratory tube detection window always contact closely to sediments in in-situ detection. At the same time, we research count rate difference of the original level X-ray scattering peak between water medium and sediment samples, take experiment to different matrix in the simulation of sediment samples in laboratory flume, according to the difference of the scattering peak count rate, we realize the dynamic monitoring of submarine exploratory tube detection window.based on the above hardware development and the method study of technology, we develop the intelligent submarine in-situ X-ray fluorescence detection system measurement control and data processing software based on LabWindows/CVI platform. We carry out in-situ X-ray fluorescence point measurement and continuous drag measurement test in Yan lake bottom of ChengDu university of technology and shallow seabed of GuangXi BeiHai, through sampling analysis of the bottom sediment samples and comparative analysis of fixed point measurement and continuous drag measuring, it shows that both fixed point measurement and continuous drag measurement submarine of in-situ X fluorescence detection system can realize qualitative and quantitative analysis.Research results show that the submarine X-ray fluorescence analysis system can use fixed point measurement or continuous measurement way to measure submarine sediments with the Ti, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sr, Mo,et, al. at the same time in the 1000-meter depth of water environment, and it can also do real-time guidance marine mineral resources investigation.