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1 Introduction Strontium-90 (90Sr) is an anthropogenic radionuclide, which, due to its radiological relevance, has been most intensively monitored in the past. In terms of initial activity, over 630 PBb of this radioisotope have been distributed globally from stratospheric fallout of bomb-testing, and there are more localized contributions from test, accidents, and releases from reprocessing plants.[1] Despite of the massive spike of 90Sr from global fall-out has been very difficult to measure in the ocean, due to the massive dilution in the oceans and the low atom detection efficiency of decay counting measurements. Massive sample sizes (up to 100 l of seawater or 100 g of coral aragonite) were required even right after the peak period of global fall-out from bomb testing. On the other hand, the high amount of strontium dissolved in seawater complicates the use of mass spectrometric methods, as an isotopic abundance sensitivity of at least 1·10-15 is required to detect the estimated main signal. Here we report on the results of successful measurements of such samples using a new Accelerator Mass Spectrometry (AMS) technique [2]. 2 Samples and Methods Our interest in this study lies in the determination of 90Sr as geochemical and ocean current tracer in conjunction with another anthropogenic tracer isotope, 236U. Both the respective elements both get build into marine carbonates such a coral samples, and both are present in significant amounts in seawater. While 236U is a well-established isotope and can be measured at very low levels ( |
