Chemical procedure for extracting ~(129)I, ~(60)Fe and ~(26)Al from marine sediments: Prospects for detection of a ～2.8 My old supernova

摘要

For the past three years, we have been developing a procedure to measure carrier-free ~(129)I/I in gram size quantities of marine sediments containing microgram quantities of iodine. Potential applications involve dating of old (>10 My) sediments and the detection of ~(129)I (t_(1/2) = 15.7 My) from a purported supernova (SN) explosion ～2.8 million years ago, that has been inferred from a ~(60)Fe (t_(1/2) = 1.5 My) 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 NH_2OH · HCl-HOAc mixture, extraction of iodine from the organic phase with TMAH, separation and purification using anion-exchange chromatography, and coprecipitation as AgI-Ag_2O. We realized the washing step, which extracts authigenic iron and aluminum, could also be used to measure ~(60)Fe/~(56)Fe and ~(26)Al/~(27)Al 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 ~(129)I/~(127)I ratio in pre-anthropogenic marine sediments, and that derived from experimental measurements.