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An upper limit on anthropogenic 81Kr in the atmosphere
1Hefei National Research Center for Physical Sciences at the Microscale, School of Physical Sciences, University of Science and Technology of China, Hefei, 230026, China.
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The cosmogenic radionuclide 81Kr (half-life 229 ka) is widely used to date groundwater and ice on 104-106 year timescales. Anthropogenic nuclear activities can lead to an increase of 81Kr in the atmosphere, but this contribution has not been tightly constrained experimentally. We report a precise measurement of the anthropogenic contribution using Atom Trap Trace Analysis (ATTA). A pre-nuclear atmospheric krypton sample collected in the 1940s was measured alongside a present-day atmospheric sample, acquiring over one million 81Kr atom counts for each sample. Given the measured difference of δ = (0.09 ± 0.14)% and after correcting for the cross-sample contamination, we obtain an upper limit of 0.43% (90% confidence level) for the anthropogenic contribution, validating the stability of the atmospheric 81Kr baseline for high-precision dating applications.
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