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I am curious whether or not every element can be equally well detected by using X-Ray-fluorescence-spectroscopy. Might there be any contitions or circumstances that make it hard/impossible to detect a certain element in a probe?

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In a very very broad reasoning, XRF is much more sensitive to the "mid-range" elements.

Elements below Na are generally not detectable.

  • The x-ray tubes must have a beryllium window to seal the tubs which absorbs the low energy x-rays.
  • The lower the atomic number the less the fluorescent yield.
  • Low energy x-rays don't penetrate from the sample efficiently.
  • Low energy x-rays tend to be absorbed in the detector windows.

For the very heavy elements the detectability is poor too. Say anything about lanthanum.

  • The K x-rays are so energetic that a high voltage on the x-ray tube is needed to excite them.
  • The lanthanides and actinides tend to behave similarly chemically so geological samples tend to contain a mixture which creates peak overlaps.
  • Higher energy detection of x-rays is poor. EDS because the x-rays penetrate the detector. WDS because the available crystals don't diffract high energies well.
  • The L x-rays are not quite as useful because the greater number of x-rays leads to more peak overlap.
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