Atom-trap trace analysis of 41Ca/Ca down to the 10-17 level

The cosmogenic isotope Ca-41 with a half-life of 99,000 years can, in principle, serve as a tracer for environmental processes at an age scale beyond the reach of C-14. With accelerator mass spectrometry, the ratio of Ca-41/Ca has been measured down to the 10(-15) level in natural samples. A wide range of potential applications, such as the burial dating of bones and exposure dating of rocks, require measuring even smaller Ca-41/Ca ratios in the range of 10(-16) to 10(-15). Here we achieved this by employing the atom-trap trace analysis method in which individual Ca-41 atoms are selectively captured in a magneto-optical trap and counted by detecting their fluorescence. We realized a precision of 12% on the Ca-41/Ca ratio at the level of 10(-16) and achieved a detection limit at the level of 10(-17), which is below the distribution of natural abundances. We verified the accuracy of the Ca-41/Ca results through a series of measurements of reference samples, and performed demonstration analyses on bone, rock and seawater samples. Our table-top method has the potential to explore the suitability of Ca-41 as a tracer. The calcium isotope Ca-41 is a promising candidate to complement dating methods relying on radiocarbon. Small levels of Ca-41 can be measured with atom-trap trace analysis, which brings the use of Ca-41 a step closer to applications.

Automated summary

In this study, the atom-trap trace analysis method was used to measure Ca-41/Ca ratios at the level of 10(-16) and achieved a detection limit at the level of 10(-17). This method has the potential to explore the suitability of Ca-41 as a tracer.