An improved instrument for ³⁹Ar dating of water samples

A cosmogenic radioisotope with 269-year half-life and a unique age span, ³⁹Ar is an ideal tracer for age-dating glaciers, oceans, and groundwater. It can help scientists better understand the global water cycle and Earth’s climate history.

Typically, ³⁹Ar is difficult to detect due to its extremely low isotopic abundance. To this end, Tong et al. developed an instrument to measure the ³⁹Ar isotope in environmental water samples with greater precision using an analytical method called atom trap trace analysis (ATTA).

“Detection of ³⁹Ar at its natural abundance level with ATTA was first demonstrated in 2011,” said author Wei Jiang. “After that work, this method is evolving steadily thanks to the efforts from the research groups in Germany and China. Now, we aim to further perfect the ATTA method for ³⁹Ar.”

ATTA is a laser-based method capable of detecting individual atoms of a particular isotope in a sample. At its heart, a magneto-optical trap can capture and count atoms. The measured atom count rate is then converted to isotopic abundance, which is used to calculate age in radiometric dating applications.

Tong et al. implemented a series of upgrades, including a more powerful laser system with a different repumping scheme, a high-efficiency spin-flip Zeeman slower, an improved vacuum system with higher atomic flux, and a RF source cooled to liquid nitrogen temperatures.

“Analyzing ³⁹Ar with this new instrument is not only much faster but also more precise,” said Jiang. “The dating range is expanded considerably with smaller uncertainties and covers some of the geological periods that are interesting to paleoclimate studies, including the little ice age and medieval warm period.”

Source: “An atom trap for ³⁹Ar dating with improved precision,” by Amin L. Tong, Ji-Qiang Gu, Guo-Min Yang, Shui-Ming Hu, Wei Jiang, Zheng-Tian Lu, and Florian Ritterbusch, Review of Scientific Instruments (2021). The article can be accessed at http://doi.org/10.1063/5.0050620 .