X-Ray Fluorescence - The Basic Process

X-Ray Fluorescence (XRF) can be considered in a simple three step process occurring at the atomic level:

  1. An incoming X-Ray knocks out an electron from one of the orbitals surrounding the nucleus within an atom of the material.
  2. A hole is produced in the orbital, resulting in a high energy, unstable configuration for the atom.
  3. To restore equilibrium, an electron from a higher energy, outer orbital falls into the hole. Since this is a lower energy position, the excess energy is emitted in the form of a fluorescent X-Ray.

The energy difference between the expelled and replacement electrons is characteristic of the element atom in which the fluorescence process is occurring – thus, the energy of the emitted fluorescent X-Ray is directly linked to a specific element being analyzed. It is this key feature which makes XRF such a fast analytical tool for elemental composition.

In general, the energy of the emitted x-ray for a particular element is independent of the chemistry of the material. For example, a calcium peak obtained from CaCO3, CaO and CaCl2 will be in exactly the same spectral position for all three materials.