X-Ray Fluorescence Analytical Techniques - CNSTN : Centre ...

Figure I.7: Schematic description of photoelectric principle.
Figure I.8: Absorption edges for different shells.
The Figure I.8 supplies the following:
• The overall progression of the coefficient decreases as energy increases, i.e. the higher the
energy of the X-ray quants, the less they are absorbed.
• The rapid changes in the mass attenuation coefficient reveal the binding energies of the
electrons in the appropriate shells. If an X-ray quant has a level of energy that is equivalent
to the binding energy of an atomic shell electron in an appropriate shell, it is then able to
transfer all its energy to this electron and displace it from the atom. In this case, absorption
increases sharply. Quants whose energy is only slightly below the absorption edge are
absorbed far less rapidly.
III.7.2 Compton Effect
Also known as incoherent scattering, Compton effect is the interaction of a photon with
a free electron that is considered to be at the rest. The weak binding of electrons to atoms may