Ion Beam Analysis - Proton Induced X-ray Emission
What it measures
Energetic protons can also eject inner-shell electrons and the subsequent electron transitions to fill the empty, inner shell orbitals also produce characteristic x-ray energies. Photons, electrons and protons lead to the production of characteristic energy x-rays that can be used to identify elements in pigments or in metallic artifacts.
Most common uses in conservation
analysis of manuscript ink, small statues, metallic plate, coins
In PIXE the proton beam irradiates a relatively small area of the artifact (beam sizes are approx. 1mm x 1mm down to 0.1mm x 0.1mm - the diameter of a paper clip wire or smaller) thus small enough to lie well within a line of ink on a manuscript or a well defined ara of a painting. Additionally one of the advantages of PIXE is that calibration of the amount of pigment is easier than with other techniques (e.g. XRF). PIXE (requires an ion acelerator which is a large, fixed piece of equipment and so unlike with XRF the painting or artifact must be brought to the equipment in the lab.