PIXE

B1.24 Rutherford backscattering, resonance scattering, PIXE and forward (recoil) scattering... 

By inserting a semiconductor x-ray detector into the analysis chamber, one can measure particle induced x-rays. The cross section for particle induced x-ray emission (PIXE) is much greater than that for Rutherford backscattering and PIXE is a fast and convenient method for measuring the identity of atomic species within... 

This overview covers the major teclnhques used in materials analysis with MeV ion beams Rutherford backscattering, chaimelling, resonance scattering, forward recoil scattering, PIXE and microbeams. We have not covered nuclear reaction analysis (NRA), because it applies to special incident-ion-target-atom combinations and is a topic of its own [1, 2]. 

The relative simplicity of tlie method and the penetrative nature of the x-rays, yield a technique that is sensitive to elements with Z > 10 down to a few parts per million (ppm) and can be perfonued quantitatively from first principles. The databases for PIXE analysis programs [21, 22 and 23] are typically so well developed as to include accurate fiindamental parameters, allowing the absolute precision of the technique to be around 3% for major elements and 10-20% for trace elements. A major factor m applying the PIXE teclmique is that the bombardmg energy of the... 

Typically, PIXE measurements are perfonned in a vacuum of around 10 Pa, although they can be perfonned in air with some limitations. Ion currents needed are typically a few nanoamperes and current is nonnally not a limiting factor in applying the teclmique with a particle accelerator. This beam current also nonnally leads to no significant damage to samples in the process of analysis, offering a non-destmctive analytical method sensitive to trace element concentration levels. 

Figure Bl.24.15. An example of a PIXE spectmm. This spectmm was obtained from the analysis of a piece of ivory to establish whether the origm of the ivory could be detennined from trace element concentrations.

The quantitative imaging capability of the NMP is one of the major strengtiis of the teclmique. The advanced state of the databases available for PIXE [21, 22 and 23] allows also for the analysis of layered samples as, for example, in studying non-destmctively the elemental composition of fluid inclusions in geological samples. 

Figure Bl.24.16. An example of the applieation of the PIXE teelmique using the NMP in the imaging mode. The figures show images of the eross seetion tlirough a root of the Phaseolus vulgaris L. plant. In this ease the material was seetioned, freeze-dried and mounted in vaeuiim for analysis. The seales on the right of the figures indieate the eoneentrations of the elements in ppm by weight. It is elear that the transports of the elements tlirough the root are very different, not only in the eases of the major elements Ca and K, but also in the ease of the traee element Zn.

Ryan C G, Cousins D R, Sie S H, Griffin W L, Suter G F and Ciayton E 1990 Quantitative PiXE mioroanaiysis of geoiogioai materiai using the CSiRO proton mioroprobe Nucl. Instrum. Methods B 47 55... 

Ryan C G and Jamieson D N 1993 Dynamio anaiysis—oniine quantitative PiXE mioroanaiysis and its use in overiap-resoived eiementai mapping Nucl. Instrum. Methods B 77 203... 

Maxweii J A, Campbeii J L and Teesdaie W J 1989 The Gueiph PiXE software paokage Nucl. Instrum. Methods B 43 218... 

Campbeii J L, Russeii S B, Faiq S, Souite C W, Oiierhead R W and Gingerioh R R 1981 Optimization of PiXE sensitivity for biomedioai appiioations A/oc/. Instrum. Methods 181 285... 

Johanssen S A E and Campbeii J L 1988 FIXE A Novel Technique for Elemental Analysis (Chichester Wiiey) Covers PiXE in detaii and is a good reference for graduate students and researchers. 

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