Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published August 1978 | public
Journal Article

Ca isotope fractionation on the Earth and other solar system materials


It is demonstrated that differences in the ^(40)Ca/^(44)Ca ratio due to mass dependent isotope fractionation in nature are clearly resolvable to a level of 0.5‰. This precision is obtained (a) by using the double spike technique; (b) by using a mass-dependent law for correction of instrumental mass fractionation; and (c) by eliminating fractionation effects identified as due to differential elution of isotopes through ion exchange resins. We have determined the following uniform Ca isotopic composition after removing small natural fractionation effects: ^(40)Ca/^(44)Ca = 47.153 ± 3, ^(42)Ca/^(44)Ca = 0.31221 ± 2, ^(43)Ca/^(44)Ca = 0.06486 ± I, ^(46)Ca/^(44)Ca = 0.00152 ± I, ^(48)Ca/^(44)Ca = 0.08871 ± 2, where the errors correspond to the last figures shown. This yields an atomic weight of 40.076 ± 0.001. The data indicate the absence in the studied samples of detectable, distinct nuclear components in Ca similar to those observed for oxygen. In the samples studied, there is a distinct but small degree of Ca isotope fractionation. Overlapping ranges of fractionation of 2.5‰ for ^(40)Ca/^(44)Ca (four atomic mass units) are observed in meteorites, lunar, and terrestrial samples. Means by which isotope fractionation could arise for Ca are discussed, but the small range of effects and the lack of systematic variations do not permit at present the identification of the mechanisms responsible for the fractionation observed in the suite of samples. Ca in the biological cycle does not show fractionation effects larger than observed for non-biogenic samples. In contrast to these results, we have observed large effects of up to 13‰, for industrially purified Ca.

Additional Information

© 1978 Published by Elsevier Ltd. Received 23 August 1977, Accepted in revised form 16 March 1978, Available online 25 March 2003. We thank G. J. WASSERBURG for his interest and support of this work. H. A. LOWENSTAM shared his insight and enthusiasm on biological processes and provided us with interesting samples. We benefited from discussions with H. G. THODE, L. MARGULIS, S. EPSTEIN and G. R. ROSSMAN. A. J. GANCARZ provided valuable discussions about alternate fractionation Jaws. Meteorite samples were provided by F. BEGEMANN, K. KEIL, C. B. MOORE and P. PELLAS; H. G. THODE provided us with the two gypsum samples and R. ELIAS with the squirrel tooth. W. R. KELLY, R. LETOLLE, C. E. REES and S. M. SAVIN provided helpful suggestions regarding the manuscript. This work was supported by NSF grant PHY76-83685.

Additional details

August 19, 2023
October 20, 2023