Figure 8.34
(a) Diagram showing the additional absorption path that X-rays must take when
operation is at a low take-off angle, as compared to operation at a high
take-off angle.
(b) Relationship between absorption correction factor and take-off angle.The Absorption and Fluorescent Emission of X-rays
When primary X-rays are directed on to a secondary target, i.e. the sample, a proportion of the incident
rays will be absorbed. The absorption process involves the ejection of inner (K or L) electrons from the
atoms of the sample. Subsequently the excited atoms relax to the ground state, and in doing so many
will lose their excess energy in the form of secondary X-ray photons as electrons from the higher
orbitals drop into the 'hole' in the K or L shell. Typical transitions are summarized in Figures 8.35 and
8.36. The reemission of X-rays in this way is known as X-ray fluorescence and the associated analytical
method as X-ray fluorescence spectrometry. The relation between the two principal techniques of X-ray
emission spectrometry is summarized in Figure 8.37.
Not all excited atoms will relax by the re-emission of X-rays and the