The isotopic composition and the atomic weight of zirconium

Abstract

The isotopic composition of zirconium in the normal shelf reagent and in two terrestrial rock standards, W-1 and G-2, has been determined. In the course of this study, the mass spectrometric measurements were checked by artificla mixtures of 90Zr-, 91Zr-, 92Zr- and 94Zr-enriched isotopes. The absolute isotopic abundance obtained in this work is as follows (atom%); 90Zr: 51.449 ± 0.059; 91Zr: 11.320 ± 0.015; 92Zr: 17.189 ± 0.021; 94Zr: 17.283 ± 0.021; and 96Zr: 2.759 ± 0.004. Because of the higher accuracy, these abundances should replace the currently accepted values. The corresponding atomic weight of zirconium was calcualted to be 91.219. This shows good agreement with the currently accepted value of 91.22 by IUPAC (1975), although the isotopic composition differs slightly from the IUPAC “intrim” values. From nine chondrites, belonging to various classes, zirconium was extracted and the isotopic composition was determined. By the present technique, the limit of the experimental error for a single measurement of each sample, 2σ ≈ 0.5%, prevents detection of possible incomplete mixing during and after nucleosynthesis and following the formation of the solar system.