Particle-induced X-ray emission spectrometry

Principles and Characteristics Particle-induced X-ray emission spectrometry (PIXE) is a high-energy ion beam analysis technique, which is often considered as a complement to XRF. PIXE analysis is typically carried out with a proton beam (proton-induced X-ray emission) and requires nuclear physics facilities such as a Van der Graaff accelerator, or otherwise a small electrostatic particle accelerator. As the highest sensitivity is obtained at rather low proton energies (2-4 MeV), recently, small and relatively inexpensive tandem accelerators have been developed for PIXE applications, which are commercially available. Compact cyclotrons are also often used. 

PIXE is not a true nuclear analytical method, because it is based on the interaction of fast ions with the electron clouds of the atoms. In fact, PIXE is based on X-ray 

PIXE is a primary analytical technique, like NAA, and permits absolute determinations of concentrations. The basis for quantitative PIXE is, as in all X-ray methods, that there exists a relationship between the net peak area of an X-ray line in the spectrum and the amount of element in the sample. One of two methods can be applied to calibration  

A correction for matrix effects is usually required. Difficulties in PIXE quantitation may be relieved by complementary information from RBS [290], or FTIR and elastic backscattering (EBS) analysis [291], FTIR can give a rough estimation of the elemental composition, while EBS or RBS can deliver information on the major-element composition. 

With charged-particle microprobes, the samples must be stained and thinned to improve both contrast and signal-to-noise ratio coated with a thin conducting layer to reduce charging effects and improve spatial resolution and be in vacuum to maintain the charged-particle beams. Finally, information on the chemical state of the detected elements is difficult to obtain using techniques based on charged particles. 

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Vol. 133. Particle-Induced X-Ray Emission Spectrometry. By Sven A. E. Johansson, John L. Campbell, and Klas G. Malmqvist... 

Although sophisticated methods may constitute the core methods for certification it is useful to include good, well executed routine methods. In order to further minimize systematic error, a conscious purposeful attempt should be made to get methods and procedures with wide-ranging and different sample preparation steps, including no decomposition as in instrumental neutron activation analysis and particle induced X-ray emission spectrometry. 

Johansson, S.A., Campbell, J.L. Malmqvist, K.G. (1995) Particle-Induced X-Ray Emission Spectrometry (PIXE), John Wiley Sons, New York, Chichester. 

Johansson SAL (1995) Introduction to PIXE. In Johansson SAL, Campbell JL and Malmqvist KG, eds. Particle-induced X-ray emission spectrometry (PIXE) (Vol 133 in Chemical Analysis), pp. 1-17. John Wiley Sons, New York. 

PIXE particle induced X-ray emission spectrometry (variant of XRF for thin surface layers)... 

Figure 1 Energy dispersed X-ray spectra from the same sample excited by 20 keV electrons (top) and 2.5 MeV protons (bottom). The enhancement of the detection limit for the trace elements caused by the absence of primary Bremsstrahlung in the PIXE spectrum can be seen clearly. Reproduced with permission of Wiley from Johansson SAE, Campbell JL and Malmqvist KG (1995) Particle-Induced X-ray Emission Spectrometry. New York Wiley.

Johansson SAE and Campbell JL (1988) PIXE, A Novel Technique for Elemental Analysis. Chichester Wiley. Johansson SAE, Campbell JL and Malmqvist KG (1995) Particle-Induced X-ray Emission Spectrometry. New York Wiley. 

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