MEASUREMENT OF OIL DEPOSIT RESULTING FROM BACKSTREAMING IN A DIFFUSION PUMP SYSTEM BY PROTON ELASTIC-SCATTERING

A brief survey of methods of oil contamination measurements in diffusion pump systems is given. An ion probe system using protons with energies up to 2.5 MeV is briefly described. Backscattering spectroscopy is a suitable method for qualitative and quantitative measurements of thin layers. The mass resolution at low masses is very good and the carbon peak is well defined in a backscattering spectrum. Using the resonant elastic scattering of protons on the carbon atoms C-12 (p, p) C-12 the sensitivity for carbon detection better than 10(16) atoms cm-2 can be reached.