Characterization of Smithsonian microbeam standards by micro-PIXE and -PIGE methods.

High quality and certified standards are necessary to perform accurate and reliable measurements. However, it is complicated to find certified mineral reference materials to calibrate analytical devices like electron microprobe. The aim of the study is to characterize with a high accuracy and precision existing mineral standards in order to perform these calibrations. Standards are coming from the Smithsonian Institute collections at Washington D.C. (U.S.A). Last results of analyzes performed of these standards have been published in 1980 and have been achieved by chemical wet analyzes. It is necessary to perform further investigations to characterize these standards from the chemical and mineralogical point of view in order to use them. 10 mineral standards have been selected in the Smithsonian Microbeam Standard collection according to chemical, crystallographic and geologic criteria. The 3 target are, first to find new trace elements which have not been detected yet, then to quantify all the elements in the standards and at last to check the homogeneity of the samples, an important parameter for performing high quality measurements. Therefore, 2 methods have been selected. They are based on an X- and Gamma-ray emission of samples atoms after collision with an incident proton beam. They are called PIXE and PIGE. They are used respectively for heavy (Z>18) and light (Z<18) element analyzes. An ion microprobe has been used with a particle accelerator in order to provide a 3.54 MeV proton beam to perform analyzes. Results are raw PIXE and PIGE spectra. They are processed with different methods to reach the targets of the study. New trace elements have been found and quantified thanks to data processing. Quantification is irrelevant for minerals with high light elements concentrations because they cannot be quantified. Statistics have been performed on elements distribution through the analyzed particles. Further analyses, and in particular X-ray fluorescence, have to be achieved in order to bring more precisions about the obtained data.