SGER: Redetermining the Half-Life of 187 Re

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Peucker-EhrenbrinkEAR-0228307In contrast to many widely used geochronometers, the uncertainty in the experimentally determined half-life of 187 Re (4.23 plus or minus 0.13 x 10E10 yr; Lindner et al., 1986, 1989) is large (~3%). This uncertainty currently limits the application of the Re-Os system as a precise chronometer. This proposal requests support for an experimental determination of the 187 Re half-life using 1 kg of Re originally used by Lindner et al. (1986, 1989) in their experimental determination of the 187 Re half-life. The aliquots will be sealed in glass stills equipped with break seals to prevent loss of volatile Os during storage. Storage periods of 0.5-2.5 years are sufficient to generate 187 Os/ 188 Os 1 in all except the first experiment, ensuring that the precision on the 187 Os/ 188 Os is not limited by the abundance of radiogenic 187 Os. Five independent determinations of the 187 Re half-life will be made using plasma ionization multicollector mass spectrometry on initially Os-free perrhenic acid. The expected overall uncertainty of the 187 Re half-life using this approach is 0.4%.