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Isotopic Measurements of Inorganic Material by Time-Of-Flight SIMS

Isotopic measurements via Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) have generally not been considered as practical because of the low duty cycle at which ToF-SIMS instruments operate and the corresponding low data rate. The recent discovery of pre-solar material in meteorites has shown that large variations in isotopic ratios (several orders of magnitude for some elements) exist in small (∼1 μm), refractory meteoritic grains. These grains are ideal candidates for ToF-SIMS, which consumes little sample material, compared to dynamic, magneticsector SIMS. ToF-SIMS also allows for parallel detection of all species present in the sample; thus, multiple isotopic systems can be studied in one measurement. As a prerequisite to studying the isotopic composition of meteoritic materials, preliminary determinations of ratios for a number of elements have been made on materials of known isotopic composition. This allows us to investigate problems that may be unique to ToF-SIMS for the measurement of isotopic ratios.