Three-Dimensional Trace Element Analysis by Confocal X-ray Microfluorescence Imaging

Abstract

A three-dimensional (3D) variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF). The method is based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector. The experimental arrangement represents a significant generalization of regular two-dimensional (2D) scanning micro-XRF and employs a detector half-lens whose focus coincides with that of the focused incoming beam. The detection volume defined by the intersection of the exciting beam and the energy-dependent acceptance of the polycapillary optics is 100-350 mum(3). Minimum detection limits are sub-ppm, and sensitivities are comparable with regular scanning XRF. Next to the reduction of in-sample single/multiple scattering, the setup provides the possibility of sample depth scans with an energy-dependent resolution of 10-35 mum in the energy range of 3-23 keV and the possibility of performing 3D-XRF analysis by simple XYZ linear scanning. This provides a suitable alternative to X-ray fluorescence tomography. The method is illustrated with results of the analysis of solid inclusions in diamond and fluid inclusions in quartz.

Confocal micro-x-ray fluorescence spectrometer for light element analysis

“…By overlapping the two foci of the optics on the sample a well-defined measurement volume is created. [3][4][5][6][7] This allows for depth resolved measurements which has two advantages: First, it solves the problem of the larger information depth for elements with a higher Z leading to wrong coincidences in the images. 8 Second, it allows for measurements into the sample by performing depth profiling or even full 3D analysis 6 without the need to use a reconstruction algorithm.…”

Spatially resolved 3D micro-XANES by a confocal detection scheme

“…These unique diamonds and their inclusions form the only direct source of information available on the physical and chemical conditions in the deep Earth down to at least the upper part of the lower mantle. [7][8][9][10][11][12][13][14][15][16][17] In order to preserve the enclosed nature of the inclusions a non-destructive in situ analysis method is desired. In this respect X-ray techniques like XRF, XRD and XAS can be very useful.…”

“…Indeed, confocal m-XRF has been shown to allow the 3D visualisation of main and trace elements within a B150 mm large mineral inclusion. 17 Conventional Fig. 4 Elemental detection limits determined using the NIST SRM1577b standard for an incoming X-ray energy of 9.027 keV and a measuring time of 300 s for the conventional micro-fluorescence detection mode, left: corresponding absolute detection limits; right: corresponding relative detection limits (the error bars represent AE 1 SD).…”

“…and confocal m-XRF spectra recorded on the same mineral inclusion studied in ref. 17 are given in Fig. 7.…”

Confocal X-ray Fluorescence Imaging and XRF Tomography for Three-Dimensional Trace Element Microanalysis

“…In case of the latter, instead of using computed tomography techniques, direct local information from an arbitrary microscopic volume-element within the sample can be obtained (limited in depth by signal self-absorption) by employing a polycapillary half-lens in front of the energy-dispersive detector [1][2]. This optical element restricts the XRF-spectra to be detected only from the microscopic intersection volume of the incoming microbeam and the coinciding focus of the polycapillary lens.…”