Isotopic Determination of Uranium in Picomole andSubpicomole Quantities
TL;DR: In this paper, a procedure for the separation of U and measurement of UIsotopes in meteoritic, lunar, and terrestrial samples is described, and the results show the same Isotopic values within limits of errors as that measured on normal terrestrial U to within 4
Abstract: A procedure for the separation of U and measurement of U
Isotopes in meteoritic, lunar, and terrestrial samples Is described. Accurate ^(238)U/^(235)U ratios and U concentration measurements can be done on a routine basis at the level of ~ 10^(-13) mol of U by Isotope dilution using a double tracer composed of ^(233)U and ^(238)U. Precise determination of the number of U atoms In a sample can be done at the level of 10^8-10^9 atoms. The technique Involves careful control of the chemical procedures to eliminate laboratory contamination and precise calibration of the mass spectrometer In order to obtain high reproducibility. The ^(238)U/^(235)U ratios were measured
on a wide variety of samples which Include bulk
meterorltes, lunar samples, coarse-grained Ca-AITI-
rlch Inclusions and fine-grained AI-Mg-Na-rich Inclusions from the Allende meteorite, and phosphates from three meteorites. The results show the same Isotopic values within limits of errors as that measured on normal terrestrial U to within 4‰. All of the analyzed meteorite samples are very ancient and several of them show large fractionations of U relative to Th and Nd. These data Imply that ^(247)Cm was not abundant In the early solar system (^(247)Cm/^(235)U « 4 X 10^(-3)) and that the last major "r" process terminated at ~ 10^8 years prior to the formation of the solar system.
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Cites methods from "Isotopic Determination of Uranium i..."
...In this kind of mixture, the 238 Ur235U ratio can be mea- sured, using the known 233Ur236 U ratio to normalize Žfor mass fractionation see Chen and Wasserburg, 1981 for an extensive set of these sorts of measure.ments ....
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...233scribed by Chen and Wasserburg 1981 ....
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TL;DR: In this paper, Krogh et al. developed a simple procedure for the decomposition of zircon and the extraction of U and Pb for isotopic age determinations.
2,527 citations
TL;DR: In this paper, the ultramafic pyroxenite Angra dos Reis meteorite was estimated to have an internal isochron age of 4.55 plus or minus 0.04 eons.
228 citations
167 citations
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