ArTTA-10mL: An instrument for 39Ar-dating of small ice and water samples

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The noble gas radioisotope 39Ar is of great interest for dating applications in oceanography, glaciology, and hydrogeology, because it is the only isotope to cover the important age range between about 50 and 1000 yr. The fundamentally new analytical technique of Atom Trap Trace Analysis (ATTA), which for the first time has rendered 81Kr dating possible, has the potential to revolutionize the application of 39Ar, by reducing sample size requirements by a factor of 100 to 1000. In a previous project we have for the first time demonstrated that 39Ar analysis of natural samples by ATTA is possible, although we still needed the usual tons of water. Very recently, using samples from first pilot projects targeting ocean water and alpine ice, we have demonstrated that 39Ar-ATTA (ArTTA) analysis on samples of about 25 L of water or 10 mL of Ar or even less is feasible. This achievement enables completely new perspectives for the application of 39Ar-dating, providing highly valuable information so far not accessible. The demand for such analyses, in particular in the field of tracer oceanography, is well established and documented by support letters of our current partners for ArTTA applications. This proposal will enable us to construct the worldwide first ArTTA instruments targeted at routine operation with small samples. We aim at building a 39Ar dating platform that meets the needs for dating in the fields of groundwater research, oceanography and glacier research. In order to enable meaningful applications in tracer oceanography, a capacity of at least 200 samples per year is required. This new instrument for research will enable long-sought applications which otherwise would not be possible. Based on previous research we have a clear plan for setting up a complete platform for ArTTA operation: A new sample preparation line based on gettering of reactive gases enables the separation of up to 10 mL of pure Ar from small (< 25 L of water or 10 kg of ice) environmental samples in a few hours. These samples are transferred to the ArTTA apparatus, which consists of 2 modules: the optics module produces the proper laser frequencies and laser power, the atomic module is the part where the atoms are detected employing the atom optical tools realized in the prototype from the previous project. As far as possible the apparatus will be built from reliable, high-performance commercial parts. The system will be installed in highly controlled container environment offering a modular setup which in the future can be installed at different places.