PIXE
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PIXE (Particle-Induced X-ray Emission or Proton Induced X-ray Emission) is a technique used in the determining of the elemental make-up of a material or sample. When a material is exposed to an ion beam, atomic interactions occur that give off EM radiation of wavelengths in the x-ray part of the electromagnetic spectrum specific to an element.
Particle-induced X-ray emission (PIXE), is a powerful yet non-destructive elemental analysis technique now used routinely by geologists, archaeologists, art conservators and others to help answer questions of provenience, dating and authenticity.
Quantum theory states that orbiting electrons of an atom must occupy discrete energy levels in order to be stable. Bombardment with ions of sufficient energy (usually MeV protons) produced by an ion accelerator, will cause inner shell ionization of atoms in a specimen. Outer shell electrons drop down to replace inner shell vacancies, however only certain transitions are allowed. X-rays of a characteristic energy of the element are emitted. An energy dispersive detector is used to record and measure these X-rays and the intensities are then converted to elemental concentrations.
Recent extensions of PIXE using tightly focused beams (down to 1 μm) gives the additional capability of microscopic analysis. This technique, called microPIXE, can be used to determine the distribution of trace elements in a wide range of samples such as aerosols or fly ash. Other applications include determining the elemental composition of liquid and crystalline proteins, as microPIXE can quantify the metal content of protein molecules with a relative accuracy of between 10% and 20%Template:Ref.
Notes and references
- Template:Note Garman, E.F. and Grime, G.W. Elemental analysis of proteins by microPIXE. Progress in Biophysics and Molecular Biology, vol. 89/2, October 2005, 173-205.