Structural and chemical modifications of microsamples induced during PIXE analysis

Mass losses caused by proton bombardment in the course of PIXE analyses have been frequently reported in the case of biological samples but only very little information on the damage of rock targets is available. With the Heidelberg Proton Microprobe we scanned seven approximate to 100 mu m fragments of a sheet silicate using various proton currents and doses that - after the PIXE analysis - were analysed with transmission electron microscopy (TEM). The effects of the proton bombardment range from intact lattice to a totally amorphous structure. Our results demonstrate the necessity to limit the proton current and dose to below certain values that have to be experimentally determined for a given sheet silicte in order to maintain intactness. Time resolved PIXE measurements of the alkali (Na, K) contents of feldspar and alkali glass fragments do not result in volatilisation losses which often are observed in SEM and EMPA studies.