PIXE (Proton Induced X-Ray Emission)

PIXE was first introduced at the Lund Institute of Technology in 1970. It is a relatively simple, powerful analytical technique that can be used to identify and quantify trace elements in a sample. Samples are irradiated by 2-3 MeV proton beam of a Van de Graaff (or other kind of) accelerator. Protons interact with the electrons in the atoms of the sample, creating inner (K and L) shell vacancies. When the vacancies are refilled with electrons from higher shells, X-rays are emitted. Energy of X-rays are characteristic of the element from which they originate, and the number of X-rays is proportional to the amount of the corresponding element within the sample. X-ray detection is usually done by Si(Li) energy dispersive semiconductor detectors.

The details of the PIXE technique and its applications can be found in the following books:

S.A.E. Johansson, J.L. Campbell, PIXE: A Novel Technique for Elemental Analysis, Wiley, New York, 1988.

Description of our PIXE set-up

Our PIXE analytical set-up is installed on one of the beam lines of the 5 MV Van de Graaff accelerator of the Institute. This chamber is fitted with a diffuser foil to obtain homogeneous beam profile, exchangeable collimators to define the beam size, and X-ray absorbers. A built in electron source is used to reduce enhanced electron bremsstrahlung appearing on insulating samples as a consequence of their charging up during proton bombardment. A semiautomatic system with a rotating disk is used for sample changing. The chamber itself forms a Faraday cup insulated from the ground. Characteristic X-rays are detected by a Canberra Si(Li) detector, and electronic signals are processed by an NZ-881 digital signal processor. Spectra are evaluated with the PIXEKLM program package. K and L line calibration has been performed for the PIXE setup by independent use of experimental and theoretical methods (References: Borbély-Kiss 21, Gy. Szabó 107).

An example of a PIXE spectrum obtained from aerosol sample and evaluated by the PIXEKLM is shown here. This spectrum was accumulated using 2.0 MeV protons with 39 µC charge.