Development of New Instrumentation for Laser Atom-Trap Analysis of Radiokrypton

University Of Chicago, Chicago IL

Investigators

Abstract

The Atom Trap Trace Analysis (ATTA) method has revolutionized our ability to measure radiokrypton isotopes, 81Kr (half-life = 229,000 yr) and 85Kr (half-life = 10.8 yr), in samples of natural material. This in turn opens the door to a wide range of new applications in the earth sciences. The first demonstration of ATTA using the prototype instrument, having an efficiency of 10E-7, to measure both 81Kr and 85Kr in pure Kr gas was published in 1999 [Chen et al., Science 286, 1999]. Through modifications to the instrument, the efficiency of ATTA was subsequently improved to ~10E-4, whereby the first earth science applications became feasible using the current generation instrument, ATTA-2 [Du et al., Geophys. Res. Lett. 30, 2003]. 81Kr measurements of groundwater samples from the Nubian Aquifer in the Western Desert of Egypt showed residence times approaching one million years, in good agreement with 36Cl data and numerical hydrodynamic models [Sturchio et al., Geophys. Res. Lett. 31, 2004]. However, a water sample of >1,000 liters was required for each of these measurements, making the method inconvenient for routine scientific applications. Recent developments in our lab, in particular, the demonstration of a metastable Kr* atomic beam produced via two-step optical excitation, have made it possible to further improve both the counting rate and counting efficiency of the ATTA method. This project will develop the next generation instrument, ATTA-3, which will reduce sample size requirements into the 10-liter range for radiokrypton analysis of groundwater and glacial ice.