Micro-PIXE technique

Ghazvini, P. T. M. Mashkani, S. G. (2009). Effect of salinity on vanadate biosorption by Halomonas sp. GT-83 Preliminary investigation on biosorption by micro-PIXE technique. Bioresour Technol, 100, 2361-2368. 

PIGE is a rapid, non-destructive technique that is employed in the analysis of light elements such as lithium (10-100 ppm limit of detection), boron (500-1000 ppm limit of detection), and fluorine (1-10 ppm limit of detection), which are often difficult to determine by other analytical means. Because the technique is based upon specific nuclear reactions, the sensitivity of PIGE varies greatly from isotope to isotope, and this non-uniformity of sensitivity has limited its widespread use as a complementary technique to micro-PIXE. 

Kramer U, Grime GW, Smith JAC, Hawes CR, Baker AJM. Micro-PIXE as a technique for studying nickel localization in leaves of the hyperaccumulator plant Alyssum lesbiacum. Nucl Instr Methods B 1997 130 346-350. 

In 2006, Lobinski et al.1 reported on the imaging and speciation analysis of trace elements to study the element distribution, oxidation state, metal site and metal structure in biological environments using mass spectrometric techniques (LA-ICP-MS, SIMS, MALDI-MS) and non-mass-spectrometric techniques such as micro-PIXE (proton induced X-ray emission), XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) -the latter two techniques are very sensitive due the use of a more intense synchrotron beam.1... 

An important variant on PIXE is micro-PIXE. By using a proton beam whose spatial dimension is 0.5 pm (rather than the usual 10 mm), one can determine the trace-element content of a small portion of the sample, giving one a trace-element microscope. This application is important in probing samples of medical interest. A related technique is used in the electron microprobe where the ionization is caused by electron impact. 

The following example is a illustration of how photon and charged particles techniques like the micro-PIXE and micro-Raman spectrometry can be combined to solve an important archaeological issue, namely to unveil the intriguing provenance of the red gemstones mounted on barbarian jewels from the early Middle-Ages [11]. 

Electrical trees are essentially breakdown channels whose size, typically 50 to 200 microns, together with the large variations in impurity concentrations in the surrounding polyethylene, makes the identification of the impurities associated with both kinds of trees very difficult by traditional techniques. The use of micro-PIXE for the location and analysis of trace elements in electrical and water trees found in the polyethylene insulation of high voltage cables will be described. 

More work remains to be done to better understand the role of impurities on water tree growth and we feel that micro-PIXE is a very powerful technique for such measurements since it has the required sensitivity and spatial resolution to provide detailed contour maps of the impurity concentrations, which can then be correlated with the visual tree. Our present micro-PIXE equipment with its 20 micron diameter beamspot is ideally suited for such measurements as it is very easy to use and provides online data. However, the use of only a few point measurements could miss essential components of the tree, and raster scans of the whole tree area would provide more complete information, and at the same time reduce beam induced damage. 

Tadic, T, Jaksic, M., Bogdanovic, I., Fazinic, S., Dujmic, D. 1997. Proton micro-PIXE control of standard reference materials for PIXE environmental applications. In Proceedings of the Symposium on the Harmonization of Health-related Environmental Measurements using Nuclear and Isotopic Techniques, Hyderabad, India, 4-7 November 1996. IAEA Proc. Series STI/PUB/1006, ISBN 92-0-103697-3, pp. 251-264. 

Microbeam Particle Induced X-ray Emission (PIXE), often called micro-PIXE, was used for single particle analysis. The greatest advantage of this system is excellent detection limits in the order of 10 -10 g. It also has the merit of a multielement non-destmctive technique with a wide range of elements for various samples. 

As mentioned above, it is possible to maintain insoluble particles, which were scavenged by raindrop, on individual raindrop replicas by collodion film technique. These insoluble particles are the target of micro-PIXE analysis. An example of the elemental map for Si, S, Cl, K, Ca, and Fe is drawn in Fig. 8. Each elemental map was drawn on the 128 x 128 pixels by scanning of about 1 pm micro beam on the sample surface. Because the residual particles were retained on a raindrop replica as several clusters, we could not radiate the microbeam to individual residual particles. However, the visualized elemental maps of six element types in several particle clusters enable us to estimate the chemical mixing state of raindrop residual particles. In addition, it is also presumed that the chemical transformation of dust particles is made by wet scavenging processes. 

Micro-PIXE offers a powerful nondestructive analytical method of micrometer-scale lateral resolution for research in art and archeology. Among other fields of application studies in corrosion processes, searching for characteristic features of painting and fabrication techniques, identification of art objects through trace element qualifications, and testing of restoration methods can be mentioned here. 

In addition to the applications mentioned above, a wide variety of lesser activities in all branches of science are studied using PIXE. In all cases where it is beneficial to use a trace element analytical technique that combines a lateral resolution of 1 pm with trace element detection limits (l-10pgg =10 -10 g), micro-PIXE is an option well worth considering. 

Particle-induced X-ray emission (PIXE) is an elemental analysis technique that employs a beam of energetic heavy charged particles (usually protons of 1-4 MeV) to induce element-specific X-ray emission. Depending on the sample material and thickness and on the conditions of the analysis, the technique offers detection limits at the 0.1-10 mg kg concentration level for low-Z matrices. Applied in nuclear microprobes, micro-PIXE combines a high sensitivity with the possibility of providing elemental maps with a lateral resolution in the sub-micrometer range. 

By using a highly focused proton beam wliich is scanned over a sample, it is possible to produce elemental imaging of a microscopic specimen, in which the spatial intensities of individual X-ray emission hnes are displayed. Clearly, there are many applications of this micro-probe technique to medical, toxicological, environmental, semiconductor and forensic science monitoring. An example of an elemental PIXE image is shown in Fig. 5.8, showing the distribution of different elements in a human hair. 

The features mentioned above show that IBA techniques and particularly PIXE, because of its high sensitivity, constitute an extremely useful tool for the knowledge and the preservation of cultural heritage. A decisive improvement has been achieved in developing an experimental set-up permitting the direct analysis of objects without sampling. This is carried out by means of a 20-pm diameter micro-beam extracted in air through an ultra-thin exit window, as shown in fig. 3 [10],... 

Valkovic, V., Zeisler, R., Berasconi, G. and Danesi, P.R., Reference materials for micro-analytical nuclear techniques. Int. J. PIXE, 2 (1992) 651-664. 

To measure Pb concentrations in small particles such as aerosols, or to study the variation in Pb concentrations within sohds such as mineral grains, there is a range in available techniques such as micro-beam XRF (including synchrotron methods), proton induced X-ray emission spectrometry (PIXE), secondary ionization mass spectrometry (SIMS), and laser ablation ICP-MS (LA-ICP-MS). These methods have been used for high spatial resolution even in 3-D, as well as for rapid analyses of biological or geological structures growing incrementally [39-43] or small, specihc phases [44]. 

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