Applications
Non-destructive elemental analysis of solid or liquid samples for major and minor constituents. Used in
routine analysis of metallurgical and mineral samples. Most suited to the determination of heavy
elements in light matrices (e.g. Br or Pb in petroleum). Well suited for on-stream, routine analysis.
Electron beam excitation methods valuable in surface studies in combination with electron microscopy.
Detection limits generally in the range 10–100 ppm. Relative precision, 5–10%.
Disadvantages
Matrix absorption, secondary fluorescence and scattering phenomena limit sensitivity and precision in
many cases, especially with dense matrices. The sensitivity falls off with atomic number; elements with
Z < 15 are particularly difficult to analyse. Analysis is characteristic of surface layers (5– 500 μm depth)
only for a solid specimen. Instruments are often large, complicated and costly.
X-ray Processes
Electronic transitions within the inner shells of an atom involve energy changes consistent with the
absorption or emission of electromagnetic radiation of high energy (short wavelength). Analytical
techniques based on an exploitation of these changes have a number of potential advantages:
(1) The possible electronic rearrangements are limited in number, and the energy levels are widely
spaced. This leads to the production of simple uncomplicated spectra, which are characteristic of the
elements present within the specimen.
(2) The electrons involved are in the core of the atom and should be much less affected by external
influences such as chemical bonding which greatly modify the properties of the outer electrons. For
light elements however the K and L electrons may also be the valency electrons and significant effects
may be observed.
(3) The radiations involved with these low lying energy changes are energetic and highly penetrating. In
these circumstances the analysis of solid samples without prior treatment becomes a real possibility and
time consuming stages such as dissolution may well be eliminated.
The Emission of Primary X-rays
Primary X-rays may be produced by the bombardment of a target with a stream of high energy particles
such as 20–50 keV electrons or nuclear particles from a radioactive source such as^241 Am. The impact
of the bombarding particles on the target is non-selective and produces a wide range of energy
transitions and consequently a continuum of X-ray emissions. Because of the wide range of
wavelengths which are involved the