Fast atom-trap analysis of Ar-39 with isotope pre-enrichment

We demonstrate fast analysis of Ar-39/Ar at the 10(-16) 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-40 by two orders of magnitude while preserving both the rare tracer isotope Ar-39 and a minor stable isotope Ar-38 for control purposes. Measurements of both natural and enriched samples with atom trap trace analysis demonstrate that the Ar-39/Ar-38 ratios change less than 10%, while the overall count rates of Ar-39 are increased by one order of magnitude. By overcoming the analysis-speed bottleneck, this advance will benefit large-scale applications of Ar-39 dating in the earth sciences, particularly for mapping ocean circulation.