Particle Induced X-ray emission, or PIXE, is a very useful analytical
tool used to identify constituent materials in an obect. Its technique is similar to that of the XRF
in that it too relies on the ejection of an inner-shell electron
s, but wheras the XRF induces electron emission through high energy x-ray photon
s, the PIXE makes use of accelerated proton
s or occasionally helium
ions directed towards a sample area.
As the charged particle moves through the material, it transfers energy to inner shell electrons of the K and L orbitals, causing them to be ejected. This creates an overall instability in the atom, and electrons in the higher orbitals will move down to fill the vacancies and re-achieve stabilty. This causes energy in the form of a photon to be released - this photon is proportional to orbital distance, and is characteristic to each element, and therefore can be used to identify it. This x-ray emission is measured and compared to databases, and the instrument will produce a spectrum, identifying and quantifying constituent elements.
The PIXE tool is extremely useful in that it does not require sampling and is thus non-destructively analytical. For this reason it is used as on-site analysis for archeological, geological, biological or material science purposes. It is also highly precise and may detect constituent elements in trace quantities from 1-100 ppm.