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Abstract

A set of six examples, collected World Wide from various uranium ore mining facilities, was analysed for uranium isotopic composition by high accuracy isotope mass spectrometry. The goal was to measure isotopic variation between samples of different geographical origin. In the first step, the molar ratio of the isotopes (235)U and (238)U, n(235U) /n (238U), was measured using a UF(6)-gas-inlet isotope mass spectrometer (VARIAN MAT 511). This instrument was calibrated by gravimetrically prepared synthetic isotope mixtures and SI-traceable measurements were made. The "minor" isotope ratios n(234U) /n(238U) and n(236U) /n(238U) were determined in a second step using a thermal ionization mass spectrometer with high abundance sensitivity (Finnigan MAT262-RPQ-PLUS). The mass fractionation correction was done internally using the result of the n(235U) /n (238U) measurement. As a result, the complete measured uranium isotopic composition is traceable to the SI system. For all ratios n(234U) /n(238U), n(235U) /n(238U) and n(236U) /N(238U) significant differences for samples of different origin were found. Regarding the n(2369U) /n(238U) results, only 2 samples, one of them from the Oklo reactor on Gabon, showed significant presence of (236)U. For all other samples am upper limit for n (236U) /n(238U) of about 6:10(-10), mainly dependent on the instrumentation, was found. Using results of this study suggestions are made for the "Best measurement from a Single Terrestrial Source" and the "Range of Natural Variations" in the IUPAC-table of the "Isotopic Composition of the Elements."

Additional information

Authors: RICHTER S, Institute for Reference materials and measurements, Geel (BE);ALONSO A, Institute for Reference materials and measurements, Geel (BE);DE BOLLE W, Institute for Reference materials and measurements, Geel (BE);WELLUM R, Institute for Reference materials and measurements, Geel (BE);TAYLOR P, Institute for Reference materials and measurements, Geel (BE)
Bibliographic Reference: Article: International Journal on Mass, Spectrometry and Ion Processes, 1-29
Record Number: 199910350 / Last updated on: 1999-03-12
Category: PUBLICATION
Original language: en
Available languages: en
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