Recent major advances in Accelerator Mass Spectrometry (AMS) at the Vienna Environmental Research Accelerator (VERA) regarding detection efficiency and isobar suppression have opened possibilities for the analysis of additional long-lived radionuclides at ultra-low environmental concentrations. These radionuclides, including 233U, 135Cs, 99Tc, and 90Sr, will become important for oceanographic tracer application due to their generally conservative behavior in ocean water. In particular, the isotope ratios 233U/236U and 137Cs/135Cs have proven to be powerful fingerprints for emission source identification as they are not affected by elemental fractionation. Improved detection efficiencies allowed us to analyze all major long-lived actinides, i.e., 236U, 237Np, 239,240Pu, 241Am as well as the very rare 233U, in the same 10 L water samples of a depth profile from the northwest Pacific Ocean. For this purpose, a simplified and very flexible chemical purification procedure based on extraction chromatography (a single UTEVA® column) was implemented which can be extended by a DGA® column for Am purification. The procedure was validated with the reference materials IAEA-381/385. With the additional increase in ionization efficiency expected for the extraction of actinides as fluoride molecules from the AMS ion source, a further reduction of chemical processing may become possible. This method was successfully applied to an exemplary set of air filter samples. In order to determine the quantitative 237Np concentration reliably, a 236Np spike material is being developed in collaboration with the University of Tsukuba, Japan. Ion-Laser Interaction Mass Spectrometry (ILIAMS), a novel technique for the efficient suppression of stable isobaric background, has been developed at VERA and provides unprecedented detection sensitivity for the fission fragments 135Cs, 99Tc, and 90Sr. The corresponding setup is fully operational now and the isobar suppression factors of >105 achieved, in principle, allow for the detection of the mentioned radionuclides in the environment. Especially for 90Sr analysis, this new approach has already been validated for selected reference materials (e.g., IAEA-A-12) and is ready for application in oceanographic studies. We estimate that a sample volume of only (1–3) L ocean water is sufficient for 90Sr as well as for 135Cs analysis, respectively.

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Developing Accelerator Mass Spectrometry Capabilities for Anthropogenic Radionuclide Analysis to Extend the Set of Oceanographic Tracers

The application of multiple radiochronometers in a forensic investigation of bulk uranium provides increased confidence for interpreting age-dating results We have developed a streamlined method for the purification of Pa and Th from bulk uranium and have applied this method in analyzing uranium certified reference materials (CRMs) IRMM-1000 and CRM U100, using the 231Pa–235U and 230Th–234U radiochronometers Our improved 233Pa spike calibration technique has replaced the time-intensive, conventional calibration using geologic rock standards Paired Pa–U and Th–U age-dating analyses of CRM U100 produce concordant results In contrast, analyses of IRMM-1000 demonstrate reproducibly-discordant Th–U and Pa–U age-dates

Improved protactinium spike calibration method applied to 231 Pa– 235 U age-dating of certified reference materials for nuclear forensics

Application of the 231Pa/235U radiochronometer for nuclear forensic investigations is challenged by a lack of certified reference materials with 231Pa/235U model purification dates. The Japan Atomic Energy Agency, Los Alamos National Laboratory, and Lawrence Livermore National Laboratory completed an interlaboratory study measuring 231Pa/235U model ages of New Brunswick Laboratory CRM U100. Results from independent laboratories were combined to calculate a consensus 231Pa/235U model purification date for CRM U100 of March 26, 1959 ± 237 days. This 231Pa/235U consensus date for CRM U100 may be used by the nuclear forensic community for quality control of 231Pa/235U radiochronometry measurements of unknown materials.

An interlaboratory collaboration to determine consensus 231Pa/235U model ages of a uranium certified reference material for nuclear forensics

Hyphenation of capillary electrophoresis with MC-ICP-MS - A novel tool for uranium age dating.

From introduction: The purposes of this paper are to tabulate and discuss the results of a number of complete disequilibrium analyses, to illustrate a proposed classification of disequilibrium patterns, to study these disequilibria as clues to the understanding of the geochemical history of the samples and of the deposits, and to point out some of the difficulties when simply comparing radioactivity and chemical uranium assays for interpreting equilibrium or disequilibrium in samples.

https://digital.library.unt.edu/ark:/67531/metadc304665/m2/1/high_res_d/metadc304665.pdf

Uranium Series Disequilibrium in Radioactive Ores

In 2014 the United States Department of Energy and the China Institute of Atomic Energy collaborated in a study measuring the model ages of uranium certified reference materials. Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL), and the Chinese Institute of Atomic Energy (CIAE) determined 230Th–234U model ages for uranium certified reference materials U010 and U850. The aim of this work was to collaborate with CIAE and compare methods for measuring the age of bulk uranium materials using the 230Th–234U radiochronometer. Accurate results for age-dating depend on the accurate calibration of the tracer materials (e.g., 229Th and 233U) used for the isotope dilution mass spectrometry (IDMS) analyses. To facilitate inter-comparison of results, samples of a 230Th standard reference material were distributed to each laboratory for 229Th tracer inter-calibration. The resulting 230Th–234U model ages from this collaboration for U010 ranged from March 1956 to January 1959, which agree with the known material production date of June 5th, 1958. The determined model ages for U850 were from December 1955 to October 1957, which agree with the material production date of December 31, 1957. All three laboratories used independent methods to determine model ages for uranium standards that agree with known production ages and with previously reported results.

US-DOE and CIAE international cooperation in age-dating uranium standards

High-precision measurement of U-Pu-Np-Am concentrations and isotope ratios in environmental reference materials by mass spectrometry.

This interlaboratory study measured thorium concentrations and isotope compositions in uranium ore concentrates from different geographical locations to examine whether thorium impurities may be useful forensic signatures for uranium ore concentrates found out of regulatory control. Measured 230Th/232Th in fifteen uranium ore concentrates record over three orders of magnitude of compositional variation. Results demonstrate that 230Th/232Th used in combination with U/Th ratios resulted in a unique signature for individual uranium ore concentrates from different processing locations. Data presented here suggest potential for 230Th/232Th and U/Th to be used as comparative signatures to investigate the provenance of seized uranium ore concentrates.

Annelise M. R. Cardon

Papers

US-DOE and CIAE international cooperation in age-dating uranium standards

High-precision measurement of U-Pu-Np-Am concentrations and isotope ratios in environmental reference materials by mass spectrometry.

Exploring the use of thorium isotope compositions and concentrations as nuclear forensic signatures for uranium ore concentrates

Rapid response in vitro bioassay method for the determination of Pu isotopes in urine samples