µXRF of light elements

Micro X-ray Fluorescence (Micro-XRF) is a well established tool to determine the spatial distribution of major, minor and trace elements in a sample. It is widely used to investigate samples from different fields (biology, geology, life science, etc.). The method is non-destructive, requires little sample preparation and allows simultaneous multi-element detection. Most available Micro-XRF spectrometers operate in air which does not allow the analysis of low-Z elements (Z ≤ 14). To extend the analytical range down to light elements (Z ≥ 6) a special micro-XRF spectrometer has been designed.

The new spectrometer offers improved excitation and detection conditions, necessary for light element analysis. The thin window (125µm) of the low power (50W) x-ray tube allows both, the molybdenum L-lines and K-lines to sufficiently excite the sample over a wide energy range. An optinal beam filter can be used to modify the primary radiation and reduce background. The beam is focused onto the sample using a polycapillary x-ray optics, offering a focal spot of about 31µm for Mo-Ka radiation and 71µm FWHM for the Cu-L edge. Detection of the low energetic characteristic radiation is possible due to the ultra thin window of the energy dispersive Si(Li) detector. To eliminate absorption of the exciting and fluorescent radiation in air the system operates under vacuum condition.

 

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Fig.1: Spectrum showing excitation of F and Na by the Mo-L lines
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Fig.2: Area scan of a NaF droplet on a Kapton foil