This award provides partial support to complete development of technology necessary for measuring the abundance of two rare krypton isotopes, Kr-81 and Kr-85. These isotopes, whose concentration in the atmosphere is stable and known, are potentially ideal tracers for a variety of environmental studies. Kr-81, with a 229,000 year half-life, can determine how long ancient ice or ground water has been isolated from the atmosphere in the 20,000 to 1,000,000 year time range. Similarly, Kr-85, with its 10.8 year half-life, can determine isolation times in the 1 to 50 year time range. These type of measurements can, for instance, provide important insight into the movement of groundwater, identify pathways for pollution infiltration, and provide input to overall resource management. Being chemically inert, it is anticipated that the krypton isotopes will provide more reliable results than other, chemically active tracers, by eliminating the complexity of interactions with the underground environment. The work sponsored by this grant includes completion of the necessary improvements to existing instrumentation, and application of the technique to several important groundwater problems to highlight its utility. ***
