X-Ray Fluorescence

The radiation provided by a source of X-rays is allowed to fall on the sample to be analysed. The energy of the radiation must be sufficient to displace electrons in the K, L or M-shells of the atoms present in the sample.
When an electron from the K-shells is displaced it leaves a vacancy which destabilises the energy structures of the atom.
An electron from a higher-energy level will fall into this vacancy. Such an electron can be provided by the L-shell, the energy associated with this transfer corresponds to that of the emission of a photon Ka with energy equal to the difference in energy possessed by electrons of the K and L shells. Such a transfer results also in a vacancy being created in the L-orbital which in turn is filled by transfer of an electron from the M-orbital, with emission of a photon L. This allows the atom to return to a more stable energy-state. The spectrum of wavelengths resulting from the energy-level-jumps of the electrons into the K-orbital is called the "K-series". Those originating in the L and M-orbitals are similarly called the "L and M series".
For a given atom, the principal wavelength of each series has an intensity that is well defined and constant, subject to the laws of probability and to small variations which depend on the atomic number. The radiation emitted in these transitions appears in the X-ray part of the electromagnetic spectrum and is specific to each element in the periodic table. The energy of the emission is not influenced by the chemical bonding of the atom. The fluorescence effect is concerned only with the internal structure of the atom, and is not affected by the arrangement of the surrounding molecular orbitals.
Using a solid-state detector it is now possible to detect all the elements in the periodic table from sodium to uranium simultaneously. By including a known quantity of a reference element in the sample, quantitative measurements of the other elements present can be obtained.