Particle Analysis by Inorganic Mass Spectrometry

Of special interest in the mass spectrometric determination of transuranium elements is the characterization of microparticles stemming from different radioactivity release scenarios. Such microparticles bearing radionuchdes, in particular uranium, plutonium, neptunium and americium, can enter the environment and therefore the human food chain through different processes which can be related to the nuclear fuel cycle as well as to clandestine nuclear activities. In addition, nuclear safeguards programmes seek to determine the uranium isotope abundances of individual p,m sized particles. Anomalous amounts of or may indicate that artificial isotope enrichment 

Danes et al3 applied SIMS, in addition to X-ray fluorescence imaging, by using a microbeam (p,-XRF) and scanning electron microscope equipped with an energy dispersive X-ray fluorescence analyzer (SEM-EDXRF) to characterize soil samples and to identify small DU particles collected in Kosovo locations where depleted uranium (DU) ammunition was employed during the 1999 Balkan conflict. Knowledge of DU particles is needed as a basis for the assessment of the potential environmental and health impacts of military use of DU, since it provides information on possible resuspension and inhalation. The measurements indicated spots where hundreds of thousands of particles may be present in a few mg of contaminated soil. The particle size distribution showed that most of the DU particles were 5 p,m in diameter and more than 50 % of the particles had a diameter of 1.5 p.m.  

Six plutonium containing particles stemming from soil (Marshall Island) were characterized by SIMS, SEM-EDX-WDX and sychrotron radiation by Jernstrom et al. AU the particles were identified as nuclear fuel fragments of exploded weapons components. Since they contained plutonium with a low °Pu/ Pu atomic ratio (less than 0.065), which corresponds to weapons grade plutonium or a detonation with low fission yield, the particles were identified as originating from the safety test and low yield tests conducted on Runit Island.  

Resonant and non-resonant laser post-ionization of sputtered uranium atoms using SIRIS (sputtered initited resonance ionization spectroscopy) and SNMS (secondary neutral mass spectrometry) in one instrument for the characterization of sub-pm sized single microparticles was suggested by Erdmann et al Resonant ionization mass spectrometry allows a selective and sensitive isotope analysis without isobaric interferences as demonstrated for the ultratrace analysis of plutonium from bulk samples. Unfortunately, no instrumental equipment combining both techniques is commercially available. 

Comparative studies of neodymium measurements in UOj fuel for the future application of local burn up calculations have been carried out by the SIMS analysis of a Nd implanted UOj single crystal. Samples for a round robin test were produced by the implantation of Nd (5 x 10 ° at cm , 400 keV) in a UOj single crystal. Different depth profiles of the Nd / U+ ratio and especially the NdO /Nd, UO+/U+ and U02 /U+ ratios obtained by SIMS are not constant over time and indicate evidence of some fluctuations during the analysis. SIMS plays a dominant role for particle analysis, but also LA-ICP-MS with lower spatial resolution can be applied to identify anomalies in the isotopic composition of radionuclides. 

Becker, J. S. and Dietze H. J., Encyclopedia Analytical Chemistry, A. Meyers (ed.). John Wiley Sons, Ltd, Chichester, 12947 (2000). 

Giinther-Leopold, I., Kobler Waldis, J., Wernli, B. and Kopajtic, Z., Int. J. Mass Spectrom., 242, 197 (2005). 

Karpas, Z., Lorber, A., Sela, H. etal., Radiation Protection Dosimetry, 118, 106 (2006). 

---