High resolution PIXE analyses of interplanetary dust particles with the new Heidelberg proton microprobe

Besides meteorites and lunar material, interplanetary dust particles (IDPs) collected in the stratosphere represent another form of extraterrestrial matter available for studies in the laboratory. One major goal of IDP research activities is the search for an IDP classification scheme based on their chemical composition that is obtained by modern microanalytical methods, to ascertain the source and perhaps also the specific history of individual IDPs. Excitation of characteristic X-rays in a sample by 2–4 MeV protons (Proton-Induced X-ray Emission, PIXE) enables the non-destructive detection of elements with Z > 11 with high sensitivity. If a focused proton beam is provided as with a proton microprobe, measurements with a spatial resolution in the micrometer range are possible. This method turns out to be useful to study the chemical composition of individual IDPs with high spatial resolution and with sensitivities down to ppm levels for elements between Mg and Br. Between 1990 and 1992 in Heidelberg a new proton microprobe was developed and constructed. Here we will report some of its properties, especially those which are necessary to perform PIXE analyses of small particles. We will then present the first bulk and high resolution PIXE results on IDPs using the new machine.