Fast atom-trap analysis of Ar with isotope pre-enrichment.

We demonstrate fast analysis of Ar/Ar at the 10 level using a mass spectrometer for isotope pre-enrichment and an atom trap for counting. An argon gas sample first passes through a dipole mass separator that reduces the dominant isotope Ar by two orders of magnitude while preserving both the rare tracer isotope Ar and a minor stable isotope Ar for control purposes. Measurements of both natural and enriched samples with atom trap trace analysis demonstrate that the Ar/Ar ratios change less than 10%, while the overall count rates of Ar are increased by one order of magnitude. By overcoming the analysis-speed bottleneck, this advance will benefit large-scale applications of Ar dating in the earth sciences, particularly for mapping ocean circulation.