Setting a Limit on Anthropogenic Sources of Atmospheric 81Kr through Atom Trap Trace Analysis

TL;DR

This paper establishes a 2.5% upper limit on human-made 81Kr in the atmosphere using advanced laser-based atom counting, enhancing the reliability of 81Kr dating for earth sciences.

Contribution

It introduces a precise measurement of anthropogenic 81Kr contribution, improving the accuracy of 81Kr dating methods in geoscience research.

Findings

Anthropogenic 81Kr contribution limited to 2.5% at 90% confidence

Achieved 1% relative uncertainty in 81Kr/Kr measurements

Removed a systematic constraint for 81Kr dating

Abstract

We place a 2.5% limit on the anthropogenic contribution to the modern abundance of 81Kr/Kr in the atmosphere at the 90% confidence level. Due to its simple production and transport in the terrestrial environment, 81Kr (halflife = 230,000 yr) is an ideal tracer for old water and ice with mean residence times in the range of 10^5-10^6 years. In recent years, 81Kr-dating has been made available to the earth science community thanks to the development of Atom Trap Trace Analysis (ATTA), a laser-based atom counting technique. Further upgrades and improvements to the ATTA technique now allow us to demonstrate 81Kr/Kr measurements with relative uncertainties of 1% and place this new limit on anthropogenic 81Kr. As a result of this limit, we have removed a potential systematic constraint for 81Kr-dating.