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Natural uranium samples from different origins may show small differences in isotopic composition. These differences may arise from natural isotope fractionation or nuclear reactions. The aim of the present work was the accurate determination of isotope ratios in natural uranium reference materials. Although natural uranium consists of 234U, 235U and 238U, all samples were also measured for their 236U isotope abundance. The measurements were performed using two different types of mass spectrometer: a VARIAN MAT 511 gas mass spectrometer for determination of the n(235U)/n(238U) molar isotope ratio, and a Finnigan MAT 262 RPQ thermal ionisation mass spectrometer for the determination of the minor abundant isotopes. The latter is equipped with a decelerating system for improved abundance sensitivity and ion counting for precise measurement of the ion beam intensities of the minor abundant isotopes. Results from UF(6) measurements and thermal ionisation measurements were combined to give a final result. The results show that samples of natural uranium from different origins differ significantly not only in their n(235U)/n(238U) molar isotope ratio but also in the 234U abundance. Also, non-negligible amounts of 236U were found in some samples.

Additional information

Authors: MAYER K ET AL., JRC Geel (BE)
Bibliographic Reference: Paper presented: 3rd International Conference on Nuclear and Radiochemistry, Wien (AT), September 7-11, 1992
Availability: Text not available
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