2080
Anal. Chem. 1981, 53, 2060-2067
RECEIVED for review March 2,1981. Accepted August 20,1981. This work was supported by the Department of Defense, United States Air Force, Air Force Systems Command, Aerospace Medical Division, USAF School of Aerospace Med-
icine, Brooks AFB, TX, under Contract F33615-78-D-06170030 and Army Research Office Contract DAAG-29-80-K-002, This paper has been reviewed by the USAF Office of Public Affairs and is approved for publication.
Isotopic Determination of Uranium in Picomole and Subpicomole Quantities J. H. Chen and G. J. Wasserburg" Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 9 1 125
A procedure for the separation of U and measurement of U isotopes in meteorltic, lunar, and terrestrlal samples is described. Accurate 23'U/235Uratios and U concentration measurements can be done on a routine basis at the level of mol of U by isotope dilution using a double tracer composed of 233Uand n3eU. Precise determination of the number of U atoms in a sample can be done at the level of 108-10s atoms. The technique involves careful control of the chemical procedures to ellmlnate laboratory contamination and precise calibration of the mass spectrometer in order to obtain high reproducibliity. The 238U/23sU ratios were measured on a wide variety of samples which include (1) bulk meterorltes, (2) lunar samples, (3) coarse-grained Ca-AITI-rich inclusions and (4) fine-grained AI-Mg-Na-rich inclusions from the Aliende meteorlte, and (5) phosphates from three meteorites. The results show the same Isotopic values withln limits of errors as that measured on normal terrestrial U to within 4%0. Ail 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 247Cmwas
