Maria Wallenius

Application of Lead and Strontium Isotope Ratio Measurements for the Origin Assessment of Uranium Ore Concentrates

Lead and strontium isotope ratios were used for the origin assessment of uranium ore concentrates (yellow cakes) for nuclear forensic purposes. A simple and low-background sample preparation method was developed for the simultaneous separation of the analytes followed by the measurement of the isotope ratios by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The lead isotopic composition of the ore concentrates suggests applicability for the verification of the source of the nuclear material and by the use of the radiogenic (207)Pb/(206)Pb ratio the age of the raw ore material can be calculated. However, during data interpretation, the relatively high variation of the lead isotopic composition within the mine site and the generally high contribution of natural lead as technological contamination have to be carefully taken into account. The (87)Sr/(86)Sr isotope ratio is less prone to the variation within one mine site and less affected by the production process, thus it was found to be a more purposeful indicator for the origin assessment and source verification than the lead. The lead and strontium isotope ratios measured and the methodology developed provide information on the initial raw uranium ore used, and thus they can be used for source attribution of the uranium ore concentrates.

Determination of rare-earth elements in uranium-bearing materials by inductively coupled plasma mass spectrometry

A novel and simple analytical procedure has been developed for the trace-level determination of lanthanides (rare-earth elements) in uranium-bearing materials by inductively coupled plasma sector-field mass spectrometry (ICP-SFMS). The method involves a selective extraction chromatographic separation of lanthanides using TRU resin followed by ICP-SFMS analysis. The limits of detection of the method proposed is in the low pg g(-1) range, which are approximately two orders of magnitude better than that of without chemical separation. The method was validated by the measurement of reference material and applied for the analysis of uranium ore concentrates (yellow cakes) for nuclear forensic purposes, as a potential application of the methodology.

Origin assessment of uranium ore concentrates based on their rare-earth elemental impurity pattern

Abstract The rare-earth element pattern was used as an additional tool for the identification and origin assessment of uranium ore concentrates (yellow cakes) for nuclear forensic purposes. By this means, the source of an unknown material can be straightforwardly verified by comparing the pattern with that of a known or declared sample. In contrast to other indicators used for nuclear forensic studies, the provenance of the material can also be assessed in several cases even if no comparison sample is available due to the characteristic pattern. The milling process was found not to change the pattern and no significant elemental fractionation occurs between the rare-earth elements, thus the pattern in the yellow cakes corresponds to that found in the uranium ore.

Measurement of the sulphur isotope ratio (34S/32S) in uranium ore concentrates (yellow cakes) for origin assessment

A novel method has been developed for the measurement of the 34S/32S isotope ratio in uranium ore concentrate (yellow cake) samples for origin assessment in nuclear forensics. The leachable sulphate is separated and pre-concentrated by anion exchange separation followed by the 34S/32S ratio measurement by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The effect of sample composition on the accuracy was investigated and optimized. Matching of the sample to the bracketing standard was necessary to obtain accurate results. The method was validated by the measurement of standard reference materials (IAEA-S-2, IAEA-S-3 and IAEA-S-4) and the δ34S value could be determined with an uncertainty between 0.45‰ and 1.9‰ expressed with a coverage factor of 2. The method was then applied for the analysis of uranium ore concentrates of world-wide origin. In the studied materials distinct 34S/32S isotope ratios could be observed, which can be a promising signature for the nuclear forensic investigations to identify the source of unknown nuclear materials.

Development and validation of a methodology for uranium radiochronometry reference material preparation.

The paper describes a methodology for a reference material preparation to be used for the determination of the production date (i.e. the time elapsed since the last chemical processing) of uranium materials based on the (230)Th/(234)U radiochronometer. The reference material was prepared from highly enriched uranium by a complete separation of thorium decay products, thus zeroing the initial daughter nuclide concentration at known time. The complete elimination of thorium from the starting material was verified by gamma spectrometric measurements and by addition of a (232)Th tracer to the material and its re-measurement in the final product after the separation. The validation of the methodology was carried out subsequently by comparing the ingrown daughter nuclide (230)Th and the measured (230)Th/(234)U ratio after recorded times following the last chemical separation with the calculated values obtained on the basis of their respective half-lives. The prepared reference material can be used as a quality control material for age determination of uranium in nuclear forensics and safeguards as well as for method validation.

Application of neodymium isotope ratio measurements for the origin assessment of uranium ore concentrates

A novel procedure has been developed for the measurement of (143)Nd/(144)Nd isotope ratio in various uranium-bearing materials, such as uranium ores and ore concentrates (UOC) in order to evaluate the usefulness and applicability of variations of (143)Nd/(144)Nd isotope ratio for provenance assessment in nuclear forensics. Neodymium was separated and pre-concentrated by extraction chromatography and then the isotope ratios were measured by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The method was validated by the measurement of standard reference materials (La Jolla, JB-2 and BCR-2) and the applicability of the procedure was demonstrated by the analysis of uranium samples of world-wide origin. The investigated samples show distinct (143)Nd/(144)Nd ratio depending on the ore type, deposit age and Sm/Nd ratio. Together with other characteristics of the material in question, the Nd isotope ratio is a promising signature for nuclear forensics and suggests being indicative of the source material, the uranium ore.

Characterization and classification of uranium ore concentrates (yellow cakes) using infrared spectrometry

Abstract In this work the applicability of Fourier-transform infrared spectrometry (FTIR) for nuclear forensic studies of uranium ore concentrates (UOC) are investigated. The technique was used for the identification of the type of uranium compound and various process-related impurities, which can give information on the production method of the material. The measured spectra were evaluated also by statistical means, using the soft independent modelling of class analogy (SIMCA) technique to reveal less apparent similarities between the measured UOC samples.

Interviewing a Silent (Radioactive) Witness through Nuclear Forensic Analysis

Nuclear forensics is a relatively young discipline in science which aims at providing information on nuclear material of unknown origin. The determination of characteristic parameters through tailored analytical techniques enables establishing linkages to the materials processing history and hence provides hints on its place and date of production and on the intended use.

Investigation of the 236U/238U Isotope Abundance Ratio in Uranium Ores and Yellow Cake Samples

Abstract Uranium ores and yellow cake samples of known geographic origin were investigated for their n(236U)/n(238U) isotope abundance ratio. Samples from four different uranium mines in Australia, Brazil and Canada were selected. Uranium was separated by UTEVA® Resin and was measured by Accelerator Mass Spectrometry (AMS) at the Vienna Environmental Research Accelerator (VERA). The measurement of the isotope abundance ratio n(236U)/n(238U) will be used to investigate possible correlations between the original mineral (uranium ore) and the intermediate product (yellow cake). Such correlations are useful indicators for nuclear forensic or for non-proliferation purposes.

Unveiling the history of seized plutonium through nuclear forensic investigations

Abstract Illicit incidents involving nuclear or other radioactive materials and the threat of nuclear terrorism are reasons for serious concern. Since 1993 more than 1300 incidents have been reported to the IAEA Illicit Trafficking Database. Only a small number of cases involve plutonium or plutonium containing materials. However, these cases are attributed particular attention in view of the proliferation aspects and of the radiotoxicity associated with plutonium. Efforts focus on prevention, detection and response to cases of illicit trafficking of nuclear material. If the place of theft or diversion of the material can be identified, then measures of safeguards and physical protection can be implemented to prevent future thefts. Nuclear Forensic Science aims at providing clues on the origin and intended use of nuclear or other radioactive material involved in illicit incidents. The paper provides a brief description of the nuclear forensic methodology and describes in detail the challenges associated with age determination of plutonium materials.