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| Titel |
A con-focal setup for micro-XRF experiments using diamond anvil cells |
| VerfasserIn |
Max Wilke, Karen Rickers, Laszlo Vincze, Christian Schmidt, Manuela Borchert, Sakura Pascarelli |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043924
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| Zusammenfassung |
| In this contribution we introduce an experimental setup to perform con-focal micro X-ray
fluorescence measurements in situ in samples at high temperatures and pressures in diamond
anvil cells (DAC) (e.g. Schmidt et al. 2007). The con-focal arrangement is used to suppress
the background in X-ray fluorescence (XRF) spectra that stems from elastic and inelastic
scattering of the diamond anvils. The setup is based on a focusing optic in the incident
beam that reaches a spot of 5-10 μm and a focusing poly-capillary in front of an
energy-dispersive solid-state detector. The detector poly-capillary is designed to work at a
very long working distance of 50 mm in order to collect the radiation from the center of
the DAC at 90° to the incident beam. The probing volume is defined by the two
foci and has a size of ca. 300 μm at 8 keV and 150 μm at 19 keV as measured by
scans through thin metal foils. Comparison of XRF spectra acquired with a usual
detector collimator and spectra recorded with the detector capillary shows a strong
suppression of XRF signal generated outside the probed volume, i.e. XRF from the gasket
material and signal from elastic and Compton scattering by the diamond anvils. The
ratio of the Zr K-alpha fluorescence peak to the peak of the Compton scattering
changes from 0.5 (collimator) to 1.26 (detector capillary) for a ca. 1000 ppm Zr
standard solution and an incident beam energy of 20 keV. For a standard solution
containing ca. 1000 ppm Hf, the ratio of the L-alpha to the Compton signal increases
to 6 using the detector capillary and an incident beam energy of 9.7 keV. Thus,
the con-focal setup substantially improves the fluorescence to background ratio.
This will result in higher sensitivities for dilute elements in the sample chamber
of the DAC. Furthermore, the possibilities of interference of the sample’s signal
with signal from the sample environment are greatly reduced. In a broader sense,
the setup can also be applied to other confined samples that require long working
distances.
Schmidt et al. (2007) Lithos 95, 87-102 |
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