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

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.

Laser-Based Metastable Krypton Generation

We demonstrate the generation of metastable krypton in the long-lived 1s^{5} state using laser excitation. The atoms are excited through a two-photon absorption process into the 2p^{6} state using a pulsed optical parametric oscillator laser operating near 215 nm, after which the atoms decay quickly into the metastable state with a branching ratio of 75%. The interaction dynamics are modeled using density matrix formalism and, by combining this with experimental observations, we are able to calculate photoionization and two-photon absorption cross sections. When compared to traditional approaches to metastable production, this approach shows great potential for high-density metastable krypton production with minimal heating of the sample. Here, we show metastable production efficiencies of up to 2% per pulse. The new experimental results gained here, when combined with the density matrix model we have developed, suggest that fractional efficiencies up to 30% are possible under optimal conditions.