A novel isotope analysis of oxygen in uranium oxides: comparison of secondary ion mass spectrometry, glow discharge mass spectrometry and thermal ionization mass spectrometry

The natural variation of the oxygen isotopic composition is used among geol ogists to determine paleotemperatures and the origin of minerals. In recent studies, oxygen isotopic composition has been recognized as a possible too l for identification of the origin of seized uranium oxides in nuclear fore nsic science. In the last 10 years, great effort has been made to develop n ew direct and accurate n(O-18)/n(O-16) measurements methods. Traditionally, n(O-18)/n(O-16) analyses are performed by gas mass spectrometry. In this w ork, a novel oxygen isotope analysis by thermal ionization mass spectrometr y (TIMS), using metal oxide ion species (UO+), is compared to the direct me thods: glow discharge mass spectrometry (GDMS) and secondary ion mass spect rometry (SIMS). Because of the possible application of the n(O-18)/n(O-16) ratio in nuclear forensics science, the samples were solid, pure UO2 or U3O 8 particles. The precision achieved using TIMS analysis was 0.04%, which is similar or even better than the one obtained using the SIMS technique (0.0 5%), and clearly better if compared to that of GDMS (0.5%). The samples use d by TIMS are micrograms in size. The suitability of TIMS as a n(O-18)/n(O- 16) measurement method is verified by SIMS measurements. In addition, TIMS results have been confirmed by characterizing the n(O-18)/n(O-16) ratio of UO2 sample also by the traditional method of static vacuum mass spectrometr y at the University of Chicago. (C) 2001 Elsevier Science B.V. All rights r eserved.