Use of secondary ion mass spectrometry in nuclear forensic analysis for the characterization of plutonium and highly enriched uranium particles

The application of secondary ion mass spectrometry (SIMS) analysis is described for the characterization of plutonium and highly enriched uranium (HEU) particles with a diameter to 10 mu m. Applying a method previously described, particles of HEU could be detected in a scrap material, together with natural uranium. The isotopic composition of the particles was measured with a typical accuracy and precision of 0.5%. The spectrum of the trace elements in the uranium particles was also recorded. From the results it was possible to deduce that the uranium oxide, as UO2, was produced via a pyrochemical process. In a sample consisting of a mixture of three different species of particles, two of these were identified as plutonium particles. They were characterized according to their isotopic ratio 239/240 as well as to their dimension and shape. The results obtained by SIMS for the isotopic ratio were compared with those obtained analyzing the particles by Thermal Ionization Mass Spectrometry (TIMS). The shape and dimensions were confirmed by the analysis with Scanning Electron Microscopy (SEM). In both the cases the results obtained by SIMS were in good agreement with those from TIMS and SEM.