Ion microprobe PIXE and PIGE analysis of standards’ trace elements for electron microprobe calibration.

The purpose of this study is, with the recorded data, to be able to calibrate microanalytical methods, in particular electron microprobe with high precision chemical data standards. Analysis on selected standards by ion microprobe Particle-Induced-X-ray-Emission (PIXE) and Particle-Induced-Gamma-ray-Emission (PIGE) are used to detect and quantify the trace and light elements present in these samples. The presence of those elements makes a specific calibration of the machines necessary.
Electron- and X-ray measurements need good standards for a good quantification of the elements of interest. Actually, certified reference materials for microanalytical methods are very rare. In addition they are mainly glass samples. Utilisation of chosen minerals fixed in a matrix instead of glasses for calibration makes possible the application of the matrix-matched principle and the detection and quantification of trace elements in natural minerals for a resource technology application.
The widespread utilisation of Smithsonian Microbeam Standards makes this study relevant. That is why a 10 sample selection has been made in this collection. The samples’ theoretical compositions in major and trace elements are very important for the achievement of the analysis. In addition to the given element concentrations [1], a bibliographic study has also been performed for each standard in order to find possible trace elements which could be detected.
The standards received from the Smithsonian Institute are composed of crushed particles (500 µm diameter). The sample preparation is also essential. It consists in the fixation of three particles with epoxy resin into a 3 mm diameter messing cylinder.
The analyses are performed with an incident proton beam of 3.5 MeV in order to acquire simultaneously X- and Gamma-ray spectra. The data analysis is performed with GeoPIXE in order to add qualitative and quantitative data about trace elements to the given composition of the major elements. Preliminary results on apatite (NMNH 104021) are in agreement with the literature and show the presence of vanadium, arsenic, strontium, yttrium and light Rare Earth Elements such as lanthanum, cerium and neodymium. These trace elements are important for mineral resources analysis. Elemental mapping is also achieved in order to check the homogeneity of the samples’ particles.

Acknowledgements: Special thanks to Andreas Bartzsch, from the sample’s preparation laboratory of the Helmholtz Institute Freiberg, Germany, for his expertise.

[1] E. Jarosewich, J. A. Nelen, J. A. Norberg, Geostandards Newsletter 4 1980, p. 43-47