Zheng-tian Lu
Argonne National Laboratory
Atom Trap, Krypton-81, and Egypt

Since radio-carbon dating was first demonstrated in 1949, the field of trace analysis of long-lived radioactive isotopes has seen steady growth on both analytical methods and applicable isotopes. The impact of such analyses has reached a wide range of scientific and technological areas. A new method, named Atom Trap Trace Analysis (ATTA), was developed by our group and used to analyze 81Kr (t1/2 = 2.3 105 years, isotopic abundance ~ 1 10-12) in environmental samples. In this method, individual 81Kr atoms are selectively captured and detected with a laser-based atom trap. 81Kr is produced in the upper atmosphere by cosmic-ray induced spallation and neutron activation of stable krypton isotopes. It is the ideal tracer for dating ice and groundwater in the age range of 104106 years. As the first real-world application of ATTA, we have determined the mean residence time of the old groundwater in the Nubian Aquifer located underneath the Western Desert of Egypt.