Microprobe X-ray Fluorescence CT And Its Application On The Quantitative Analysis To Rare Earth Elements

Synchrotron-based X-ray micro-fluorescence compute tomography (-XFCT) isan emerging imaging modality with high sensitivity and high spatial resolution thatallows for the nondestructive reconstruction of the internal distribution of elementswithin a sample. X-ray fluorescence CT was firstly proposed by Boisseau in1986. Thefluorescence signal excited along the route of monochromatic pencil beams thatilluminated the sample was captured. It is a combination of the synchrotron-based X-ray fluorescence (XRF) and CT technology. The-XFCT has been widely applied inthe research field of phytology, materialology, geology, and particularly in biomedicalstudies, because of the high quality of X-ray source provided by the third generationsynchrotron radiation device.With the deepening of these research fields, the people have the furtherrequirements to the development of-XFCT. Especially for detection of trace elementsin biological tissue, it is hoped that-XFCT has higher sensitivity and better spatialresolution. Also the long exposure under X-ray not only will suffer high does, but alsocould destroy the structure of the biological samples. At present, the study of-XFCTmainly focused on the detection of low atomic number elements, as a result of thelimitation of synchrotron radiation device’s spectral range. While the study of high Zelements with-XFCT has been in a blank. This thesis is dedicated to the X-ray Imaging and Biomedical Application beamlineof Shanghai Synchrotron Radiation Facility (SSRF), then the above relevant problemsabout-XFCT were studied as follows:1. Development of the-XFCT analysis system with capillary focusing element.Several focal characteristics of the capillary were researched in this system. In addition,the detection limit of the-XFCT system was obtained.2. Study of the accelerated XFCT reconstruction algorithm. In this paper, wepresent an accelerated OSEM algorithm by increasing the step size of the correctionitem and show its convergence characteristics with various subsets and acceleratedfactors. It has also proven to be much fast and reliably in reconstruction by computersimulation and test samples.3. In this study, based on high energy X-ray at BL13W1of the SSRF, we employedhigh-energy excitation for tomographic imaging of the heavy metals (rare earthelements) in fish teeth from deep-sea sediments on the micrometer scale using K-shellX-ray fluorescence. The virtual cross sectional distribution of La, Ce, Pm, Pr, Nd, andSm were obtained, and it is concluded that the chemical zoning of REEs in fish teethoccurred, thereby providing a feasible approach for analyzing the enrichmentmechanism of rare earth elements.