Radiokrypton Dating with Atom Trap Trace Analysis

The long-lived noble-gas isotope 81Kr is the ideal tracer for old water and ice in the age range of 105 - 106 years, a range beyond the reach of 14C. 81Kr-dating, a concept pursued over the past four decades by numerous laboratories employing a variety of techniques, is now available for the first time to the earth science community at large. This is made possible by the development of an atom counter based on the Atom Trap Trace Analysis (ATTA) method, in which individual atoms of the desired isotope are selectively captured and detected with a laser-based atom trap. ATTA possesses superior selectivity, and is thus far used to analyze the environmental radioactive isotopes 81Kr, 85Kr, and 39Ar. These three isotopes have extremely low isotopic abundances in the range of 10-16 to 10-11, and cover a wide range of ages and applications. In collaboration with earth scientists, we are dating groundwater in major aquifers around the world as well as polar ice from Antarctica. A new radiokrypton dating center is planned at University of Science and Technology of China to meet the increasing demands from the earth science community.