Developments of a field gas extraction device and krypton purification system for groundwater radio-krypton dating at...

The long-lived radio-krypton isotope ⁸¹Kr (t_1/2 = 2.29 × 10⁵ yr) is an ideal tracer for old groundwater age dating in the range of 10⁵-10⁶ years which goes beyond the reach of radio-carbon (¹⁴C) age dating. Analytical breakthrough made over the last two decades in Atom Trap Trace Analysis (ATTA) has enabled the use of this isotope with extremely low abundance (⁸¹Kr/Kr = 6 × 10^-13) to be used as a practical dating tool for very old groundwater. The International Atomic Energy Agency aims to provide this new isotope tool for better groundwater resource management of Member States and developed a field sampling device to collect dissolved gas samples from groundwater and a system to separate and purify trace amounts of krypton from the gas samples for the ATTA analysis. The design, setup and performances of our sampling and purification systems are described here. Our system can produce a high purity aliquot of about 5 μL of krypton from 5 L of air sample (recovery yield of >90%). The samples made by our system were confirmed to be acceptable for the ATTA analysis.