Synchrotron Radiation Confocal X-ray Fluorescence Imaging Method And Its Applications In The Study Of Biology And Geology

Based on the properties of characteristic X-ray,X-ray fluorescence(XRF)analysis has developed into an efficient and multi-elemental analytical technique,which can provide accurate quantitative information on the elemental composition of sample in a non-destructive manner.The rapid developments of the synchrotron radiation light source,X-ray focusing optical technology and X-ray detection technology has greatly promoted the development of X-ray fluorescence spectroscopy.However,there is no restriction on the direction of detector in the conventional synchrotron radiation micro X-ray fluorescence(μ-SRXRF)experiment,the XRF emitted from the samples of different depths in the incident beam path can be detected by the detector.Therefore,the two-dimensional(2D)XRF maps do not provide any depth resolution information.The confocal SRXRF is a three-dimensional(3D)non-destructive analytical method with the advantages of depth-sensitive,high spatial resolution,and high sensitivity.It has been applied in the research fields of biology,geology,material science,archaeology and so on.However,there are still some problems to be solved.During the depth-scanning analysis,the confocal volume will move at varying depths within the sample.The absorption difference of the detected XRF at varying depths may falsify the results of XRF intensity distribution maps.Therefore,the absorption correction or quantitative calculation methods is required for the depth-dependent XRF intensity distribution from confocal SRXRF imaging experiment before relevant analysis.Focusing on the shortcomings of conventional μ-SRXRF,the innovative explorations were made on the confocal SRXRF imaging method and its applications.The details are as follows:1.The confocal μ-SRXRF platform was built at the hard X-ray micro-focusing beamline(BL15U1)of Shanghai Synchrotron Radiation Facility(SSRF).The depth resolution and transmission efficiency of the polycapillary optics were discussed.A quantitative method based on the fundamental parameter method was improved to calculate the XRF data collected by the confocal μ-SRXRF imaging,which promotes the accuracy of elemental three-dimensional spatial distribution.The results of the physical properties of the polycapillary optics show that the confocal μ-SRXRF setup has high spatial resolution,and can be used to determine the 3D elemental distribution with depth resolution.The test results of National Institute of Standards and Technology(NIST)standard reference material(SRM)611 show that the initial inhomogeneous XRF intensity distribution maps form rather homogeneous concentration distribution maps after quantitative calculation,which demonstrates that the absorption difference of XRF at varying depths was effectively corrected,and the elemental distribution maps at varying depths were effectively compensated after quantitative calculation.The average calculated concentrations are close to the nominal concentrations.These verify the effectiveness and correctness of the quantitative calculation method.The first quantitative confocal μ-SRXRF imaging analysis was realized at the SSRF.2.The confocal SRXRF was applied in the biological research,including the specific application of confocal μ-SRXRF in the study of model plant(Arabidopsis thaliana seed)and the specific applications of the combination of confocal μ-SRXRF and in-situ cryogenic device in the study of environmental model organism(Daphnia magna)were introduced.Compared with the results obtained by the conventional μ-SRXRF,the spatial distributions of chemical elements for in vivo Arabidopsis thaliana seed without slicing were directly obtained by confocal μ-SRXRF.The specific distribution of chemical elements in plant tissues or organs was more accurately obtained.In addition,the spatial distributions of chemical elements for in vivo Daphnia magna without slicing or drying were directly obtained by the combination of confocalμ-SRXRF and in-situ cryogenic device.It not only avoids the problem of false results caused by surface adsorption or contamination,but also observes the absorption and distribution characteristics of chemical elements in biological organisms more carefully.The results show that the confocal μ-SRXRF can be used to directly and effectively analyze the spatial distribution of chemical elements within biological samples.Meanwhile,it can be expanded to analyze the heat-sensitive biological samples and chemical elements by equipping with in-situ cryogenic device,which provids a powerful in-situ characterization technique for the life and environment research.3.The confocal SRXRF and quantitative calculation method was applied in the study of fluid inclusion.The confocal μ-SRXRF was exploited to analyze an intact individual fluid inclusion within a natural beryl crystal,and the quantitative calculation method was applied to the concentration calculation of the individual fluid inclusion.The 3D concentration distributions of trace elements in beryl were obtained.Compared with the results obtained by the conventional μ-SRXRF,the confocal μ-SRXRF can provide more spatially resolved informations and thus avoid the problems associated with projecting the full 3D distribution image into a single 2D plane and the absorption difference of the detected XRF at varying depths.The results show that non-destructive3 D XRF analysis by the confocal μ-SRXRF imaging technique will be effective for depth-structural and multi-elemental studies of many materials,and allows to study more complicated phenomena,providing a powerful in-situ characterization technique for the geological research.