X-ray fluorescence

X-ray fluorescence (XRF) is the phenomenon where a material is exposed to X-rays of high energy, and as the X-ray (or photon) strikes an atom (or a molecule) in the sample, energy is absorbed by the atom. If the energy is high enough, a core electron is ejected out of its atomic orbital.

Related Topics:
X-ray - Energy - Photon - Atom - Molecule - Electron - Atomic orbital

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An electron from an outer shell then drops into the unoccupied orbital, to fill the hole left behind. This transition gives off an X-ray of fixed, characteristic energy that can be detected by a fluorescence detector. The energy needed to eject a core electron is characteristic of each element, and so is the energy emitted by the transition. The transition of an L shell electron dropping into the K shell is termed a Kα transition, while an M shell electron dropping into the K shell is a Kβ transition.

Related Topics:
Hole - Fluorescence - Shell

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When the energy source is a synchrotron, the X-ray beam can be very small and very intense, and atomic information on the sub-micrometer scale can be obtained.

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Typically the lightest element that can be analysed is beryllium (Z = 4), but due to instrumental limitations and low x-ray yields for the light elements, it is often difficult to quantify elements lighter than sodium (Z = 11).

Related Topics:
Beryllium - Sodium

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There are two types of spectrometer:

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• wavelength dispersive spectrometers (WDX or WDS): the photons are separated by diffraction on a single crystal before being detected;
• energy dispersive spectrometers (EDX or EDS): the detector allows the determinaion of the energy of the photon when it is detected; the EDX spectrometers are smaller (even portable), cheaper, the measurement is faster, but the resolution and the detection limit is far worse than the WDX spectrometers.
 
X-ray fluorescence: Other spectroscopic methods using the same principle ►