RADIATION-DAMAGE OF MYLAR FOILS BY A NUCLEAR MICROPROBE

Mylar foils have been irradiated under typical PIXE conditions using the Bochum nuclear microprobe. The induced radiation damage was investigated with the HEIS technique for studies of the chemical composition and the STIM technique for studies of the extent of axial and lateral damage. The data show that the current density of the microbeam influences the extent of axial and lateral damage in the foils, while the fluence of the microbeam causes changes in chemical composition: more than one-half of the original H and O abundances are lost, while the C abundance - after a 15% drop within the first few seconds - increases slowly with fluence. Furthermore, the thickness of the foil affects the final chemical composition of the sample only at large fluences. The results indicate that some caution is necessary in the interpretation of PIXE analyses of trace elements in biological or medical samples using nuclear microprobes.