Isotopic discrimination in a Cameca IMS-3f ion microprobe has been measured as a function of mass, and of primary and secondary ion energy. Discrimination factors were determined for a series of elements (Pb, Mo, Cu, Ni, Cr, Ti and Si) as metallic targets, using an O2+ primary beam. The results show a trend of isotope ratio, and by inference of the fraction of atoms ionized, proportional to M-0.75. Energy-range selection was used to identify a dependence of the measured isotope ratios on the secondary ion energy, favoring the lighter isotopes, ions of lower energy being more fractionated. A small variation with primary ion energy from 0.5 to 13 ke V was also observed fractionation increasing with decreasing primary beam energy. These effects, together with those due to possible instrumental discrimination, must be taken into account for a complete understanding of isotopic measurements obtained by secondary ion mass spectrometry.
|Original language||English (US)|
|Number of pages||7|
|Journal||International Journal of Mass Spectrometry and Ion Physics|
|State||Published - Jan 1982|