Measurement of Uranium Isotopes in Particles of U3O8 by Secondary Ion Mass Spectrometry–Single-Stage Accelerator Mass Spectrometry (SIMS–SSAMS)

Research progress on the analysis and application of radioactive hot particle

Radioactive hot particle is the particulate form of nuclear material that exists in the environment. The U, Pu, Am, Cs, and other radionuclides isotope in the hot particle contain abundant and accurate fingerprint information, such as the origin and age of the nuclear material. The acquisition and analysis of the key information in the hot particle can be equivalent to the analysis of bulk nuclear material, which could directly reflect the real situation of nuclear activities. Therefore, the single particle analysis of hot particles has become an irreplaceable key technology in nuclear safeguards inspection. The rapid identification, screening, locating, and accurate isotope analysis of hot particles from a large number of particles dispersed in environmental media or on the surface of other materials are one of the most important research field in nuclear emergency. In this review, the research process of the analytical methods for hot particles in the last decade was summarized, including the physical character of hot particles, and the techniques of localization, screening, and extraction of hot particles. Furthermore, we also focused on the mass spectrometry technology for the analysis of hot particle. The advantages and disadvantages of the most used mass spectrometry were summarized. Finally, the research trend for hot particle analysis methods was proposed.

Evaluation of Graphene Oxide as a Thermal Ionization Enhancer for Plutonium in TIMS Measurement

Thermal ionization mass spectrometry (TIMS) has been extensively employed for the assessment of plutonium (Pu) isotopes in nuclear forensics and environmental monitoring. Recently, great efforts have been made to improve the ionization efficiency (IE) of Pu to achieve better accuracy and precision for trace-level analysis. Herein, the thermal ionization enhancement effect for plutonium of graphene oxide (GO) was investigated and the corresponding mechanism was discussed. The GO layers were homogeneously mounted on the filament's central surface to promote pg-level Pu ion emission. With the excellent structural property of GO, a greatly promoted ionization efficiency of 0.44% for Pu was obtained, and the initial ionization temperature for Pu was remarkably reduced from 1610 to 1390 °C. Average boosts in IE compared to the classical double-filament mode and graphite-loaded single-filament mode were 1640 and 520%, respectively. The analytical accuracy and precision based on the GO-loaded single-filament mode were validated using Pu isotopic certified reference materials. This work demonstrates the excellent property of GO as an ion source additive for Pu ionization, as it provided an interface for the promotion of energy transfer and Pu carbide formation. The operation of GO loading is quite simple and can be finished within 5 min. This rapid filament carburization approach has great potential for improving the measurement precision of trace-level plutonium isotopes and can be applied in nuclear safeguards, nuclear forensics, and environmental monitoring.

U-Pu Mixed Oxide Particle Analysis by NAUTILUS and Implications for Next-Generation Verification Challenges

Precise and accurate measurement of U and Pu isotopes from micrometer-sized particles represents new verification challenges for the International Atomic Energy Agency. The U and Pu isotopes and U-Pu elemental ratio provide valuable information about the intended use, the production process, and the purification process of Pu and mixed oxide (MOX) fuels. We demonstrate the ability to directly measure U and Pu isotopes from MOX fuel particles using the U.S. Naval Research Laboratory's Naval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS). Reactor-grade MOX reference materials with well-characterized U and Pu isotopic composition (e.g., UKMOX10 and UKMOX100) were prepared using standard sample preparation methods for large geometry-secondary ion mass spectrometry (LG-SIMS). The results show that the NAUTILUS can discriminate the 238U1H+ signal from 239Pu+, enabling the accurate measurement of the 240Pu/239Pu ratio for MOX particles within 2σ of the certificate value for U-Pu ratios from 3:1 to 300:1. The accuracy of previously reported LG-SIMS measurements was limited to U-Pu ratios <15:1. Using the NAUTILUS, the 234U/238U, 235U/238U, 236U/238U, 240Pu/239Pu, and 242Pu/239Pu ratios for UKMOX10 and UKMOX100 can all be measured accurately within 2σ of the reference values, directly, without correction. The application of the NAUTILUS to the accurate and precise determination of the elemental and isotopic composition of MOX particles in environmental samples may unravel some emerging verification challenges in international safeguards.

An overview of NRL's NAUTILUS: a combination SIMS-AMS for spatially resolved trace isotope analysis

We present a description of the capabilities and performance of the NAval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS) at the U.S. Naval Research Laboratory. The NAUTILUS combines secondary ion mass spectrometry (SIMS) and single-stage accelerator mass spectrometry (SSAMS) into a single unified instrument for spatially resolved trace element and isotope analysis. The NAUTILUS instrument is essentially a fully functional SIMS instrument with an additional molecule-filtering detector, the SSAMS. The combination of these two techniques mitigates the drawbacks of each and enables new measurement paradigms for SIMS-like microanalysis. Highlighted capabilities include molecule-free raster ion imaging for direct spatially resolved analysis of heterogeneous materials with or without perturbed isotopic compositions. The NAUTILUS' sensitivity to trace elements is at least 10× better than commercial SIMS instruments due to near-zero background conditions. We describe the design and construction of the NAUTILUS, and its performance applied to topics in nuclear materials analysis, cosmochemistry, and geochemistry.

Rapid paper spray mass spectrometry characterization of uranium and exemplar molecular species

RATIONALE

The ability to detect and quantify the presence of specific inorganic elements and complexes is essential for environmental monitoring and nuclear safeguards applications. In this work, paper spray ionization mass spectrometry was used for the rapid chemical and isotopic characterization of trace inorganic species collected on cotton swipe substrates. The direct analysis of cotton swipes using this ambient ionization technique led to fast sample analysis that retained original chemical information of the source material with minimal sample preparation.

METHODS

Mass spectra were collected with an atmospheric pressure ionization, high-resolution mass spectrometer for solutions containing uranyl acetate, uranyl chloride, uranyl nitrate, and uranyl tri-n-butylphosphate complexes. Gadolinium nitrate was used as an internal standard for the quantitative analysis of uranium. To demonstrate the ability to characterize inorganic contaminants in the presence of uranium, a multi-element inorganic standard containing U, Bi, Pb, Cd, Fe, and Zn was deposited onto cotton substrates and directly analyzed without purification.

RESULTS

All elements doped on the cotton substrate were detected with strong signal-to-noise ratios (ca 1000 for UO₂ ⁺ on multi-element doped swipes) and high integrated intensities (>10⁵ counts) from collection periods of approximately 1 min. Limits of detection were determined to be approximately 94 ng for UO₂ ⁺ and uranyl acetate through the measurement of ppb level solutions.

CONCLUSIONS

The rapid analysis of uranium and other inorganic-containing samples while still retaining original chemical information (e.g. uranyl complexation) was demonstrated. Qualitative detection and speciation were achieved in less than 1 min of analysis. For uranium isotopic quantitation, longer accumulations (>15 min) can be sustained to improve the accuracy of minor ²³⁵ U isotopic abundance measurements to approximately 1% error.

Direct, uncorrected, molecule-free analysis of 236U from uranium-bearing particles with NAUTILUS: a new kind of mass spectrometer

We demonstrate use of the Naval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS) at the U.S. Naval Research Laboratory (NRL) to measure 236U directly from uranium-bearing particles free from molecular isobaric interferences. Particles with 235U enrichments in the range of 0.32% to 3.28% and 236U enrichments from no enrichment to 0.015% provided by the International Atomic Energy Agency (IAEA) were analyzed directly using the NAUTILUS. We report the experimental data here without correcting for molecular hydrides and/or applying any other background subtractions. The results from all samples agreed with the certified values within standard error save for the 236U composition of the IRMM 023, which suffered from a combination of insufficient particle sizes and sub-μmol mol-1 236U concentrations. We were able, however, to directly measure as low as three μmol mol-1 of 236U in individual particles regardless of the 235U concentration. Our results are comparable with Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS) and serve as baseline for a more comprehensive comparison between LG-SIMS and the NAUTILUS in the future. Moreover, we demonstrate the ability of the NAUTILUS to generate raster ion images with the same ease as traditional LG-SIMS instruments. By combining our ability to measure 236U directly with raster ion imaging, we were able to detect a low intensity, small uranium-bearing particle in the presence of high molecular backgrounds for a non-ideal sample. This discovery could lead to more targeted and, therefore, less time intensive particle screening methodologies.

Discovery of fissionogenic Cs and Ba capture five years after Oklo reactor shutdown

Understanding the release and sequestration of specific radioactive signatures into the environment is of extreme importance for long-term nuclear waste storage and reactor accident mitigation. Recent accidents at the Fukushima and Chernobyl nuclear reactors released radioactive ¹³⁷Cs and ¹³⁴Cs into the environment, the former of which is still live today. We have studied the migration of fission products in the Oklo natural nuclear reactor using an isotope imaging capability, the NAval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS) at the US Naval Research Laboratory. In Oklo reactor zone (RZ) 13, we have identified the most depleted natural U of any known material with a ²³⁵U/²³⁸U ratio of 0.3655 ± 0.0007% (2σ). This sample contains the most extreme natural burnup in ¹⁴⁹Sm, ¹⁵¹Eu, ¹⁵⁵Gd, and ¹⁵⁷Gd, which demonstrates that it was sourced from the most active Oklo reactor region. We have discovered that fissionogenic Cs and Ba were captured by Ru metal/sulfide aggregates shortly following reactor shutdown. Isochrons from the Ru aggregates place their closure time at 4.98 ± 0.56 y after the end of criticality. Most fissionogenic ¹³⁵Ba and ¹³⁷Ba in the Ru migrated and was incorporated as Cs over this period. Excesses in ¹³⁴Ba in the Ru point to the burnup of ¹³³Cs. Cesium and Ba were retained in the Ru despite local volcanic activity since the reactor shutdown and the high level of activity during reactor operation.