Abstract
For the past three years, we have been developing a procedure to measure carrier-free 129I/I in gram size quantities of marine sediments containing microgram quantities of iodine. Potential applications involve dating of old (>10My) sediments and the detection of 129I (t1/2=15.7My) from a purported supernova (SN) explosion ∼2.8 million years ago, that has been inferred from a 60Fe (t1/2=1.5My) signal in a deep-sea ferromanganese crust [K. Knie, G. Korschinek, T. Faestermann, E.A. Dorfi, G. Rugel, A. Wallner, Phys. Rev. Lett. 93 (2004) 171103]. The procedure consists in washing the sediment with a NH2OH·HCl–HOAc mixture, extraction of iodine from the organic phase with TMAH, separation and purification using anion-exchange chromatography, and coprecipitation as AgI–Ag2O. We realized the washing step, which extracts authigenic iron and aluminum, could also be used to measure 60Fe/56Fe and 26Al/27Al in this phase of the same sediment sample. We outline here the chemical procedures developed, and briefly comment on their possible application to the supernova problem. We also point out a large discrepancy between the theoretically calculated 129I/127I ratio in pre-anthropogenic marine sediments, and that derived from experimental measurements.
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