Application of Secondary Ion Mass Spectrometry to the Identification of Single Particles of Uranium and their Isotopic Measurement.

An instrumental method based on the use of secondary ion mass spectrometry (SIMS) is presented for the identification of uranium particles, and the determination of their isotopic composition. The particles collected on swipe samples were transferred to a special adhesive sopport for analysis by SIMS> Charging effects duringanalysis were avoidedby a coating with 20 nm carbon. For the measurements of the isotope ratios a mass resolution of 1000 was sufficient. At this resolution flat top peaks were obtained which greatly improve the accuracy of the measurement. A detection limit in the ng/g - range was obtained by optimising different instrumental parameters, such as the acquisition time. Blank samples, consisting only of the adhesive support and of swipes collected in an environment where uranium was absent, were employed for the evaluation of the background signals in the mass range 233-240. The level of background was eliminated by applying a voltage offset. From the results obtained on simulated swipe samples containing certified enriched uranium, the approach used was found to be very promising and after further improvements has been applied for the routine analysis of uranium particles in swipe samples.JRC.E-Institute for Transuranium Elements (Karlsruhe