Groundwater dating with Atom Trap Trace Analysis of³⁹Ar

We report on the realization of Atom Trap Trace Analysis for 39 Ar and its first application to dating of groundwater samples. The presented system achieves an atmospheric 39 Ar count rate as high as 3.58 ± 0.10 atoms/h allowing for the determination of the 39 Ar concentration in less than a day. We demonstrate that the measured count rates are proportional to the 39 Ar concentration by intercomparison with Low‐Level Counting results and by measurements on prepared argon samples with defined concentration. For a geophysical application, we degas three different groundwater samples and gas chromatographically extract the argon. The 39 Ar ages inferred from the count rates extend over the accessible dating range and are in agreement with the Low‐Level Counting results as well as with complementary isotope data.