Characteristic radiation arises from the electronic transition in an excited atom. Excitation consists in removal of an electron from an inner shell. It requires energy that can be provided by fast electrons (as it occurs in the x-ray tube or in a scanning electron microscope). In x-ray fluorimetry (XRF), excitation energy is as a rule provided in the form of an x-ray beam generated by an x-ray source.
 

1) Excitation: an electron in the K shell is ejected from the atom by an external primary excitation x-ray, creating a vacancy.

2) The K lines.An electron from the L or M shell “jumps in” to fill the vacancy. In the process, it emits a characteristic x-ray unique to this element and in turn, produces a vacancy in the L or M shell.

3) The L lines. When a vacancy is created in the L shell by either the primary excitation x-ray or by the previous event, an electron from the M or N shell “jumps in” to occupy the vacancy. In this process, it emits a characteristic x-ray unique to this element and in turn, produces a vacancy in the M or N shell.

F. G. Banica, 09-03-25