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In order to improve the analytical methods used in the field of particle analysis in nuclear safeguards, monodispersed micrometre-sized particles with certified uranium isotopic composition and uranium amount per particle are highly useful. In this study, picogram amounts of uranium in particle form were quantified in a candidate particle reference material for certification. The uranium amount per particle was determined using optical microscopy combined with Isotope Dilution Thermal Ionisation Mass Spectrometry (ID-TIMS). The uranium amount was verified using Isotope Dilution Multi Collection-Inductively Coupled Plasma Mass Spectrometry (ID-MC-ICPMS). The uranium amount per particle agreed well between the two techniques within the associated uncertainties. Both techniques are suitable for quantification of picogram amounts of uranium in particulate reference materials. The uranium particle material in this study was later used in a proficiency test (NUSIMEP-9) and eventually certified for the uranium isotopic composition of particles and the uranium amount per particle. [ABSTRACT FROM AUTHOR]

The IRMM-2019-2029 series of uranium nitrate solutions was certified for the isotopic composition. The solutions were originally prepared for the certification of the IRMM-019-029 series of uranium hexafluoride (UF6) materials in 2014, for which certification measurements were performed by thermal ionization mass spectrometry after conversion of UF6 into uranyl nitrate solutions. Analyses were performed using the modified total evaporation method and for some materials with low 236U abundances, the n(235U)/n(238U) ratio was measured using a n(233U)/n(236U) double spike. The integrity of the certified values after dilution and ampouling of the original solutions was checked through process control measurements. [ABSTRACT FROM AUTHOR]

The IRMM-1000a and IRMM-1000b uranium reference materials, of 20 and 50 mg uranium, respectively, were produced by the European Commission Joint Research Centre's Institute for Reference Materials and Measurements (EC-JRC-IRMM) in collaboration with the Institute for Transuranium Elements (EC-JRC-ITU). They are novel uranium reference materials certified for the production date based on the Th/U radiochronometer, i.e. the date of the last chemical separation of these two radionuclides. The certified reference value and its uncertainty, homogeneity and stability of the material were established in accordance with the ISO Guide 34:2009 and the 'Guide to the Expression of Uncertainty in Measurement'. [ABSTRACT FROM AUTHOR]

For nuclear safeguards purposes, two new uranium oxide micro-particle isotope reference materials were certified, IRMM-2329P and IRMM-2331P, with 235U enrichments of 3% and 5%, and 236U abundances of 30 µg·g1and 60 µg·g1, respectively. The isotopic compositions of the base materials were measured by TIMS. The production of the uranium oxide particles was achieved using a vibrating orifice aerosol generator (VOAG) and the particles deposited on carbon planchets. Process control verification measurements on dissolved uranium oxide particles were performed by MC-ICPMS. For IRMM-2329P also the uranium amount per particle was certified by TIMS/IDMS and verified by MC-ICPMS/IDMS. [ABSTRACT FROM AUTHOR]

Abstract: In the context of the KErguelen Ocean and Plateau compared Study (KEOPS, 19 January–13 February 2005), particle dynamics were investigated using thorium isotope measurements over and off the Kerguelen plateau. Dissolved and particulate 230Th and 232Th samples were collected at nine stations. Dissolved excess 230Th concentrations (230Thxs) vary from 0.5 to 20.8fg/kg and particulate 230Thxs concentrations from 0.1 to 10.0fg/kg. Dissolved and particulate 232Th concentration ranges are 16.8–450.2pg/kg and 3.8–502.8pg/kg, respectively. The 230Thxs concentrations increase linearly with depth down to the bottom at most of the plateau stations and down to 1000m at the off-plateau stations. This linear trend is observed down to the bottom (1550m) at Kerfix, the open-ocean “upstream” station located west of the Kerguelen plateau. A simple reversible scavenging model applied to these data allowed the estimation of adsorption rate constant (k 1≈0.2–0.8year−1), desorption rate constant (k −1≈1–8year−1) and partition coefficients (average K=0.16±0.07). Calculated particle settling velocities S deduced from this simple model are ca. 500m/year at most of the plateau stations and 800m/year at all the off-plateau stations. The plateau settling velocities are relatively low for such a productive site, compared to the surrounding HNLC areas. The difference might reflect the fact that lateral advection is neglected in this model. Taking this advection into account allows the reconstruction of the observed 230Thxs linear distributions, but only if faster settling velocities are considered. This implies that the 1D model strongly underestimates the settling velocity of the particles. In the deep layers, the occurrence of intense boundary scavenging along the escarpment due to bottom sediment re-suspension and interaction with a nepheloid layer, yielding a removal of ∼50% of the Th stock along the northwestward transect, is suggested. [Copyright &y& Elsevier]

The history of uranium isotopic reference materials from JRC-Geel during the last 50 years is reviewed by presenting certification methods and relevant applications. The certified isotope ratios are traceable to the SI via gravimetrical preparation, either directly through gravimetrical mixing of highly enriched materials, or indirectly using existing gravimetrically prepared reference materials for calibration of mass spectrometers used for certification measurements. Due to developments of mass spectrometers and analytical methods, certification measurements have improved regarding precision, uncertainties and accuracy. This has led to a comprehensive set of uranium isotopic reference materials available for nuclear safety, security and the scientific community. [ABSTRACT FROM AUTHOR]

Abstract: Uncertainty propagation formulae are presented for age dating in support of nuclear forensics. The age of radioactive material in this context refers to the time elapsed since a particular radionuclide was chemically separated from its decay product(s). The decay of the parent radionuclide and ingrowth of the daughter nuclide are governed by statistical decay laws. Mathematical equations allow calculation of the age of specific nuclear material through the atom ratio between parent and daughter nuclides, or through the activity ratio provided that the daughter nuclide is also unstable. The derivation of the uncertainty formulae of the age may present some difficulty to the user community and so the exact solutions, some approximations, a graphical representation and their interpretation are presented in this work. Typical nuclides of interest are actinides in the context of non-proliferation commitments. The uncertainty analysis is applied to a set of important parent–daughter pairs and the need for more precise half-life data is examined. [Copyright &y& Elsevier]