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UP: Fachverband Umweltphysik

UP 2: Bodenphysik und Ozeanographie

UP 2.1: Vortrag

Dienstag, 11. März 2008, 11:45–12:00, 3B

Detection of rare noble gas radioisotopes by atom trap trace analysis (ATTA) — •Joachim Welte¹, Anna Wonneberger², Markus Oberthaler¹, and Werner Aeschbach-Hertig² — ¹Kirchoff-Institut für Physik, Universität Heidelberg — ²Institut für Umweltphysik, Universität Heidelberg

The noble gas radioisotopes ³⁹Ar, ⁸¹Kr and ⁸⁵Kr have a great potential as dating tools in hydrology and oceanography, but are extremely rare and thus difficult to measure. Atom trap trace analysis (ATTA) provides a new way to detect these isotopes. The resonant scattering of many photons in laser cooling results in superb isotopic selectivity. Single atoms are trapped in a magneto-optical trap (MOT) and counted by detection of their fluorescence. The feasibility of ATTA for ⁸¹Kr dating of groundwater has been demonstrated.

The aim of our project is to develop ATTA for the detection of ³⁹Ar, an isotope that opens an otherwise inaccessible time window for water dating. ³⁹Ar has successfully been used for the dating of groundwaters and oceanic deep waters, but its application has been severely limited by the excessive sample size required for ultra low-level counting. ATTA promises to overcome this limitation. We have realised a test setup based on an existing laser cooling system for metastable ⁴⁰Ar atoms and have successfully detected single atoms. We now plan to build a dedicated system optimised for the efficient trapping and detection of ³⁹Ar. Furthermore, new efficient methods for water degassing by membrane contactors as well as for the separation of Ar from the extracted gas are currently being developed.