The PIXE Technique - It's History and Theory 

In the analytical world Proton Induced X-ray Emission (PIXE) is a relatively new technique. PIXE was first introduced at the Lund Institute of Technology in 1970, following the advent of Lithium drifted [Si(Li)] detectors in the late1960's. 

It was this detector technology which stimulated the development PIXE and other energy dispersive spectroscopic techniques . Like other spectroscopic techniques used for elemental analysis, PIXE is based upon the physics of the atom, rather than its chemistry. It involves the excitation of the atoms in the sample to produce characteristic X-rays and a means of detection. In order to identify and quantify the X-ray intensities produced, known standards are used in conjunction with computer software to establish sensitivities for each element. The X-ray spectrum is initiated by irradiating a sample with a proton beam produced from pure Hydrogen by, in our case, a 2.5 MeV Van der Graff accelerator. 

When a sample is irradiated with the proton beam, the protons interact with the electrons to create inner-shell vacancies in the atoms present in the sample material. The energies of the X- rays which are emitted when these vacancies are filled again are characteristic of the elements from which they originate. The number of X-rays of a certain energy is proportional to the mass of the corresponding element found in the sample. A Lithium drifted Silicon detector is used for data acquisition, allowing for the simultaneous analysis of the elements form Sodium through Uranium. Data reduction is then accomplished using computer software which normalizes the detected sample X-ray intensities against those measured from pure standards for each element. Thus, elements are easily identified and quantified. 

Below is a schematic movie of the X-ray production and the Energy Level Transitions Diagram. 

The cyan balls are the protons, the red balls are the electrons, the arrow is an X-ray emitted. 

Below is an PIXE spectrum of an aerosol sample collected at the Italian Antarctic site (PNRA Project). The sample was irradiated for 12 minutes using a 1.8 MeV proton beam. 

A Wide Variety of Analytical Applications

Two significant advantages of PIXE analysis are its diversity and extreme flexibility, which make this technique ideally suited for applications ranging from routine
quality assurance / quality control for industrial processes to environmental monitoring and specialized research and development. In addition, the non-destructive
nature of the technique also offers the advantage of analysis without the necessity of time consuming digestions, thereby minimizing the potential for errors
resulting from sample digestion, dilution and preparation.