STRUCTURAL AND CHEMICAL MODIFICATIONS OF MICROSAMPLES INDUCED DURING PIXE ANALYSIS

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