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Natural uranium is, in most text books and tables, described as having an isotopic composition of 0.0055 % 234U, 0.72 % 235U, 99.2745 % 238U. However, small variations in the isotopic composition have been observed by numerous researchers. The present investigation aims at establising an isotopic fingerprint of natural uranium of different origins. A number of natural uranium reference materials and natural uranium samples collected at various places in the world were subjected to highly accurate measurements. After conversion to UF(6) the 235U/238U ratio of the samples was measured using a MAT 511 gas mass spectrometer and calibrating the measurements by means of synthetic isotope mixtures using the double standard method. The 234U/235U ratio was determined by thermal ionisation mass spectrometry (ThIMS) using the previously determined 235U/238U ratio as internal standard. ThIMS measurements were performed on a Finnigan MAT 262 RPQ (high abundance sensitivity) instrument. The presence/absence of 236U was also checked during the measurements.

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Authors: MAYER K, JRC Geel (BE);DE BOLLE W, JRC Geel (BE);DE BIEVRE P, JRC Geel (BE)
Bibliographic Reference: Paper presented: ESARDA Symposium 1993, Roma (IT), May 11-13, 1993
Availability: Text not available
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