PIXE analysis

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... 

For the preceding modes, the discussion implicitly assumed the normal conditions for PIXE analysis (i.e., few mm-diameter beam, approximately constant beam current, and specimen in vacuum), and ignored the crystallographic nature of the specimen. However, some of the most interesting PIXE results have been obtained using other modes. 

Szymozyk, S., Kajfosz, J., Dutkienwicz, E., and Borkowski, J. (1986). Pixe analysis of selenium in nutrition and environment. /. Spurenelem. Symp. 5, 598-604. 

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. 

Figure 4.17. Schematic diagram of the arrangement for PIXE analysis.

The advantage of p-PIXE analysis over the scanning electron microprobe arises from the presence of a strong Bremsstrahlung background in the latter, which tends to mask the characteristic X-ray peaks. There is thus a striking difference in sensitivity between the two techniques the detection limits are of the order of 0.1% for the electron microprobe and 0.001% for p-PIXE. 

Figure 4.19. PIXE X-ray spectra collected by i-PIXE analysis in a new in-vacuum experimental set-up from a fragment of cobalt-blue glass. Upper spectra from a UTW detector and lower spectra from a Be-window detector. (Reproduced by permission of Uzonyi et al. 2001.)...

A matrix of light elements (e.g. plastic, or organic tissue) containing a large number of trace elements constitutes an ideal sample for PIXE analysis, and air pollution samples provide a good example of the technique. 

Faiz et al. (1996) have applied micro-PIXE analysis to study solute distributions in a single crystal sample of YiBa2Cu307 5 high temperature superconductor (YBCO) of dimensions 1.3 mm x 1.5 mm x 75 pm. It contained a small secondary crystal overgrowth of dimensions 340 x 340 x 100 pm3. The interface region between the smaller crystal and the base crystal was covered with a material which appeared to be residual flux. The instrument employed a 2.5 MeV focused proton beam of about 4 pm resolution, which could scan an area of 500 x 500 pm2 on the sample surface. The microbeam current was kept low (typically about 30 pA) to avoid any damage to the sample. 

Christensen, M., Calligaro, T., Consigny, S., et al. (1998). Insight into the usewear mechanism of archaeological flints by implantation of a marker ion and PIXE analysis of experimental tools. Nuclear Instruments and Methods in Physics Research B 136 869-874. 

Gersch, H. K., Robertson, J. D., Henderson, A. G., Pollack, D., and Munson, C. A. (1998). PIXE analysis of prehistoric and protohistoric Caborn-Welbom phase copper artifacts from the lower Ohio River Valley. Journal of Radioanalytical and Nuclear Chemistry 234 85-90. 

Gosser, D. C., Ohnersorgen, M.A., Simon, A.W., and Mayer, J. W. (1998). PIXE analysis of Salado polychrome ceramics of the American Southwest. Nuclear Instruments and Methods in Physics Research B 136-138 880-887. 

Beck L, Alloin E, Berthier C, Reveillon S, Costa V (2008) Silver surface enrichment controlled by simultaneous RBS for rehable PIXE analysis of ancient coins. Nucl Instmm Methods Phys Res B 266 2320-2324. 

Mannermaa, J. P, Raisanen, J., Hyvonen-Dabek, M., Spring, E., and Yliruusi, J. (1994), Use of proton-induced X-ray emission (PIXE) analysis in the evaluation of large volume parenteral rubber stoppers, Int. J. Pharm., 103,125-129. 

One of the most successful applications of PIXE has been in the analysis of air pollution particulate matter. Atmospheric particulate matter is typically collected by impaction on a filter paper, which provides an ideal thin sample for PIXE analysis. Another aspect of PIXE that is very important for the analysis of aerosol samples is the ability to analyze a large number of samples in a short time. PIXE analyses typically take less than a minute, and the entire irradiation, counting, sample changing, and analysis procedure can be automated. 

Figure 13.5 Detection limits in a pixE analysis of a biological sample. [From anc Morita (1990).]...

FIGURE 5.4 An x-ray spectrum from a normal skin sample obtained by PIXE-analysis. Detectable peaks are seen above the continuous background (Bremsstrahlung) radiation. Note that the Na peak is not detectable (due to absorption in the sample and the detector window). 

From what was given earlier, it is clear that PIXE analysis of tissue physiology requires cryo-methods for tissue preparation. But are the data obtained with PIXE compatible with those given by the EMP (XRMA) ... 

The PIXE analysis has a sensitivity that allows analysis of most of the physiologically important elements down to 1 ppm level with the notable exception of Na. The characteristic x-ray quanta from Na have a low energy and are, therefore, to a great extent, suffering self-absorption within the... 

The heavy particles in the probe used in PIXE analysis are not as easily retarded as electrons by biological materials, and this results in a negligible background production allowing even weak secondary x-rays to be detected, hence the high sensitivity of 1 ppm. 

Kurtz, K. et al., PIXE analysis in different stages of psoriatic skin, J. Invest. Dermatol., 88, 223, 1987. 

Pallon, J. et al., Pixe analysis of pathological skin with special reference to psoriasis and atopic dry skin, Cell. Mol. Biol. (Noisy-le-grand), 42, 111, 1996. 

Combustion of coal produces ash that can be transported through the air. Slagging and fouling problems can also be predicted from elemental analysis. Therefore, elemental analysis of both the coal as well as the ash are important. Procedures for dissolution and analysis of coal and combustion products of coal have been reported [334-336]. Laser ablation sampling has been successfully used for coal and combusted materials [337,338]. The direct introduction of slurries has also been used [339]. Comparison of ICP-MS and PIXE analysis of coal combustion aerosols showed that analysis errors can occur in ICP-MS if particle vaporization is incomplete in the ICP [340]. 

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