Nuclear Forensic Science: Correlating Measurable Material Parameters to the History of Nuclear Material

Laser-Induced Plasmas of Plutonium Dioxide in a Double-Walled Cell

Plutonium research has been stifled by the significant number of administrative controls and safety procedures, space and instrumentation limitations in radiological gloveboxes, and the potential for personnel and equipment contamination. To address the limited number of spectroscopic studies in Pu-bearing compounds in the current scientific literature, this work presents the use of double-walled cells (DWCs) in "clean" buildings/laboratories as an alternative to research in radiological gloveboxes. This study reports the first laser-induced breakdown spectroscopy (LIBS) experiments of a PuO2 pellet contained within a DWC, where the formation of elemental (atomic and ionic) species as well as the evolution from elemental to molecular products (PuxOy) was measured. Raman spectroscopy was also used to characterize the surface of the ablated pellet and the particulates deposited on the window of the inner cell. The full width half-maximum of the T2g band enabled us to obtain an estimate of the temperature at the pellet surface after the ablation pulse and the particulates based on the crystal lattice disorder. Particulates deposited on the window of the DWC during laser ablation were characterized using scanning electron microscopy, where molten irregular particulates and spheroids were observed. This exciting research conducted in a DWC describes our initial attempts to incorporate LIBS in the arsenal of spectroscopic tools for nuclear forensics applications.

Interrogating a Mixed Actinide Basket Using High-Resolution γ-Ray Spectrometry: A Nuclear Forensic Perspective on Possible Smuggling Scenarios

The total fissile content in seized nuclear materials is of immense importance and needs to be estimated with reasonable accuracy as a part of nuclear forensics for early decision-making in legal proceedings. High-resolution γ-ray spectrometry (HRGRS), because of its nondestructive nature, is a powerful tool for the assay of such samples to reach a quick "on-site" decision on the severity, intended use, and associated radiological threat. If the seized package contains fissile isotopes of more than one actinide in a multicompartmental heterogeneous mixture, analogous to the most likely scenario of a "smuggled mixed actinide basket", its "on-site" quantification can be extremely challenging. This makes up an increasing share of the absolute HRGRS in nuclear forensics and demands for fundamentally new approaches. In the present work, the challenges associated with varying attenuation experienced by γ-rays of different actinides at different subcontainments of the heterogeneous sample matrix have been addressed by an iterative efficiency transfer approach from "point" to "extended" source for individual actinides and demonstrated for the assay of four mock-up samples and a legacy packet, mimicking seized packages containing nuclear materials. An absolute isotopic inventory of the fissile and other radioisotopes has been obtained within <10% along with the assay of total U and Pu within <3% of the expected values with measurement uncertainty <10% for the majority. The present approach has a good potential for "on-site" nuclear forensics in nuclear smuggling scenarios and also can be adapted easily for a wide variety of other applications.

Exploring band-free Raman microspectrometry combined with PCA and MCR-ALS for size-resolved forensic analysis of uranium in aerosols in a model nuclear atmosphere

Achieving non-destructive micrometer-scale molecular and structural analysis of uranic materials in atmospheric aerosols with traditional methodologies is a challenge. Spatially resolved analysis of uranium in actinide-bearing aerosols is critical for nuclear forensics. Although laser Raman microspectrometry enables this, for the normally low uranium concentrations in the aerosols the spectra are indiscernible (band-free) against pronounced background: trace analysis requires a push in analytical strategy. We combined laser Raman microspectrometry (utilizing two lasers (λ = 532 nm, λ = 785 nm)) with principal component analysis (PCA) and multivariate curve resolution-alternate least squares (MCR-ALS) to perform size-resolved analysis of uranium in aerosols. Uranium-specific Raman scatter bands corresponding to uranyl nitrate (860 cm-1), uranium sulphate (868 cm-1), uranyl chloride (816 cm-1) and uranium trioxide (839 cm-1) were detected. The 816 cm-1, 854 cm-1, 868 cm-1 bands were resolved by MCR-ALS and used to identify and map uranium in PM4.5 size aerosols. Based on spectral feature selection of the signature bands, PCA identified two sources of aerosol particles in model nuclear atmosphere - Sea spray for PM4.5 and re-suspension of 'nuclear' dust from a rare earth element (REE) mine for PM2.5. The MCR-ALS-resolved uranium bands showed the potential for attributive nuclear forensic analysis.

Age dating of liquid 90Sr-90Y sources

In the context of age dating of 90Sr, the selective adsorption of zirconium ions from the mixture with strontium and yttrium by adsorbents based on TiO2 with a chemically modified surface was investigated. The general features of the separation process of strontium, yttrium, and zirconium in batch conditions were determined. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to analyze the initial and residual concentrations of the studied cations. Separation of 90Zr and 90Sr from a liquid source containing 90Sr-90Y using adsorbents based on TiO2 was performed for the first time. The ratio of 90Zr/90Sr was measured, and the age of liquid 90Sr-90Y sources was determined. In addition, we studied the age dating of 90Sr-90Y sources using a combination of liquid-scintillation counting of 90Sr and ICP-MS measurement. The results of both methods - the method of age-dating with the chemical separation of isotopes and the combination of LSC and ICP-MS analysis - agree very well and thus serve for cross-validation. Moreover, the combination of the two methods increases the confidence in the age-dating results of 90Sr-90Y sources.

Multi-element isotopic analysis of hot particles from Chornobyl

Microscopic fuel fragments, so-called "hot particles", were released during the 1986 accident at the Chornobyl nuclear powerplant and continue to contaminate the exclusion zone in northern Ukraine. Isotopic analysis can provide vital information about sample origin, history and contamination of the environment, though it has been underutilized due to the destructive nature of most mass spectrometric techniques, and inability to remove isobaric interference. Recent developments have diversified the range of elements that can be investigated through resonance ionization mass spectrometry (RIMS), notably in the fission products. The purpose of this study is to demonstrate the application of multi-element analysis on hot particles as relates to their burnup, particle formation in the accident, and weathering. The particles were analysed with two RIMS instruments: resonant-laser secondary neutral mass spectrometry (rL-SNMS) at the Institute for Radiation Protection and Radioecology (IRS) in Hannover, Germany, and laser ionization of neutrals (LION) at Lawrence Livermore National Laboratory (LLNL) in Livermore, USA. Comparable results across instruments show a range of burnup dependent isotope ratios for U and Pu and Cs, characteristic of RBMK-type reactors. Results for Rb, Ba and Sr show the influence of the environment, retention of Cs in the particles and time passed since fuel discharge.

Take a Swipe at Actinide Bioavailability: Application of a New In Vitro Method

ABSTRACT

Filter swipe tests are used for routine analyses of actinides in nuclear industrial, research, and weapon facilities as well as following accidental release. Actinide physicochemical properties will determine in part bioavailability and internal contamination levels. The aim of this work was to develop and validate a new approach to predict actinide bioavailability recovered by filter swipe tests. As proof of concept and to simulate a routine or an accidental situation, filter swipes were obtained from a nuclear research facility glove box. A recently-developed biomimetic assay for prediction of actinide bioavailability was adapted for bioavailability measurements using material obtained from these filter swipes. In addition, the efficacy of the clinically-used chelator, diethylenetriamine pentaacetate (Ca-DTPA), to enhance transportability was determined. This report shows that it is possible to evaluate physicochemical properties and to predict bioavailability of filter swipe-associated actinides.

Simultaneous isotopic analysis of fission product Sr, Mo, and Ru in spent nuclear fuel particles by resonance ionization mass spectrometry

Fission product Sr, Mo, and Ru isotopes in six 10-μm particles of spent fuel from a pressurized water reactor were analyzed by resonance ionization mass spectrometry (RIMS) and evaluated for utility in nuclear material characterization. Previous measurements on these same samples showed widely varying U, Pu, and Am isotopic compositions owing to the samples' differing irradiation environments within the reactor. This is also seen in Mo and Ru isotopes, which have the added complication of exsolution from the UO₂ fuel matrix. This variability is a hindrance to interpreting data from a collection of particles with incomplete provenance since it is not always possible to assign particles to the same batch of fuel based on isotopic analyses alone. In contrast, the measured ⁹⁰Sr/⁸⁸Sr ratios were indistinguishable across all samples. Strontium isotopic analysis can therefore be used to connect samples with otherwise disparate isotopic compositions, allowing them to be grouped appropriately for interpretation. Strontium isotopic analysis also provides a robust chronometer for determining the time since fuel irradiation. Because of the very high sensitivity of RIMS, only a small fraction of material in each of the 10 μm samples was consumed, leaving the vast majority still available for other analyses.

Propagation and variation of material characteristics during the uranium ore concentrate production at Dolní Rožinka, Czech Republic

In the framework of the European Commission Support Programme to the International Atomic Energy Agency (EC SP task A1753) 20 samples were obtained from the Dolní Rožínka (DIAMO, Czech Republic) uranium milling facility. The sampling procedure followed stepwise the uranium production and purification from the U ore to uranium ore concentrate (yellow cake) end-product. Elemental concentrations, rare-earth elemental pattern, anion concentrations, morphology and isotope abundance ratios of S, Sr, Pb and U were measured at each sampling stage. The purpose of the measurements was to investigate the applicability of various material characteristics for authentication, propagation and variation of these parameters, and to identify the relevant signatures for nuclear forensics and safeguards during the uranium production.

In View of "On-Site" Nuclear Forensics and Assay of Fissile Materials in Sealed Packages by High-Resolution γ-Ray Spectrometry

Several incidences of nuclear smuggling during the past few decades have raised the demand for the development of a strong "on-site" nuclear forensic infrastructure. High-resolution γ-ray spectrometry (HRGRS) plays an important role in nuclear forensics. However, the existing methodologies, developed primarily for nuclear fuel cycle applications, are relative and rely on the availability of a standard, limiting their use for the absolute assay of special nuclear materials in nonstandard geometry samples with an unknown matrix, which is vital to make a quick "on-site" decision on the severity, potential radiological threat, and intended use of an interdicted package. In this work, a methodology has been developed using HRGRS for quantifying fissile (²³⁵U, ²³⁹Pu) and other radioisotopes, which is applicable to sealed packages without requiring the knowledge of the sample geometry and the matrices. By combining experiments and Monte Carlo simulations, an iterative methodology has been proposed for "point" to "extended" source absolute efficiency transformation and demonstrated further for the absolute isotopic assay of uranium and plutonium standards, mock-up nuclear forensic samples, and an unknown nuclear material mixture with a nonstandard geometry, compound matrices, and a wide variation in the elemental and isotopic compositions with a view to imitate an "on-site" experience. The present methodology requires an assay time of only a few minutes to an hour and thus promises "on-site" nuclear forensic analysis of suspected flagged packages at borders and ports using high-resolution γ-ray spectrometry. Furthermore, the present methodology is versatile and can also be adopted for wider applications, beyond nuclear forensics.

A Review on Spike and Recovery Method in Analytical Method Development and Validation

In multidisciplinary science, Analytical approaches based on spike and recovery (SAR) play a substantial role in analytical testing. The spike and recovery method is an important technique for analyzing and accessing the accuracy of analytical methods. The goal of this review seeks to provide clarity on the role of SAR methods in the forensic science discipline. Recent literature has been searched from numerous databases like Google, Web of Sciences, Scopus, PubMed, Google Scholar, and SciFinder. Websites like Science Direct are critically explored to gather scientific reports related to SAR utility. This review discusses the applications and current role of the SAR methods in Forensic Toxicology. It is suggested as one of the major parameters in the validation of the analytical method. SAR methodology is extremely important for the identification and quantitation of analytes in the sample matrix. Moreover, the extension of SAR methods to any scientific discipline is equally important for quality assurance. All relevant processes like method development and its optimization, quality control, and assurance rely on SAR-based studies. However, the method requires better apprehension and needs to be utilized using standard guidelines.

Analysis of solid uranium particulates on cotton swipes with an automated microextraction-ICP-MS system

An automated microextraction method coupled to an inductively coupled plasma - mass spectrometer (ICP-MS) was developed for the direct analysis of solid uranium particulates on the surface of cotton swipes. The microextraction probe extracts particulates from the sample surface, in a flowing solvent, and directs the removed analyte to an ICP-MS for isotopic determination. The automated system utilizes a mechanical XY stage that is software controlled with the capability of saving and returning to specific locations and a camera focused to the swipe surface for optimal viewing of the extracted locations (i.e., material present). Here, particulates (n = 135) were extracted and measured by ICP-MS, including 35 depleted uranyl nitrate hexahydrate (UN) (used for mass bias corrections), 50 uranyl fluoride (UO₂F₂), and 50 uranyl acetate (UAc) particulates. Blank extractions were performed on the cotton swipes between triplicate sample analyses. Between each swipe extraction, the probe was sent between two wells containing 10% and 5% HNO₃ to clean the probe head and to eliminate any analyte carryover between particulates. The measured ²³⁵U/²³⁸U and ²³⁴U/²³⁸U isotope ratios for the UO₂F₂ particulates were 0.00725(8) and 0.000054(4), a percent relative difference (% RD) of -0.041% and -1.7% from the reference isotope ratios determined in-lab through multi-collector ICP-MS analysis of dissolved aliquots of the U material. The UAc samples had a measured ²³⁵U/²³⁸U isotope ratio of 0.00206(7), a -0.96% relative difference from the reference value of 0.00208(1). The ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios were 0.000008(1) and 0.000031(4), -5.1% RD and -4.3% RD, respectively. The automated sample stage enabled seamless and rapid particle analysis, leading to a significant increase in throughput versus what was previously possible. Additionally, the saved location capability reduced user sampling error as sampling locations were easily stored and recalled. Analysis of U particles on the swipe surface - including blanks, mass bias, and triplicate extractions - was completed in less than an hour without any sample preparation necessary.

Laser ablation inductively coupled plasma mass spectrometry analysis of isotopically heterogeneous uranium materials

A reliable and accurate laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) method was developed for analysis of inhomogeneous samples containing uranium particles or aggregates of various enrichments. For the method development, a mixed solid standard was prepared using 1% and 3% 235U enriched certified reference materials. After screening and localization of the particles of interest, the U isotopic composition was analysed for a 5-µm sample spot determining accurately and precisely the various constituents. Besides the LA-MC-ICP-MS, the standard was also measured by large-geometry secondary ion mass spectrometry (LG-SIMS) for additional verification.

Determination of 241Am in Environmental Samples: A Review

The determination of ²⁴¹Am in the environment is of importance in monitoring its release and assessing its environmental impact and radiological risk. This paper aims to give an overview about the recent developments and the state-of-art analytical methods for ²⁴¹Am determination in environmental samples. Thorough discussions are given in this paper covering a wide range of aspects, including sample pre-treatment and pre-concentration methods, chemical separation techniques, source preparation, radiometric and mass spectrometric measurement techniques, speciation analyses, and tracer applications. The paper focuses on some hyphenated separation methods based on different chromatographic resins, which have been developed to achieve high analytical efficiency and sample throughput for the determination of ²⁴¹Am. The performances of different radiometric and mass spectrometric measurement techniques for ²⁴¹Am are evaluated and compared. Tracer applications of ²⁴¹Am in the environment, including speciation analyses of ²⁴¹Am, and applications in nuclear forensics are also discussed.

Oxygen Isotopic Composition of U3O8 Synthesized From U Metal, Uranyl Nitrate Hydrate, and UO3 as a Signature for Nuclear Forensics

Triuranium octoxide (U₃O₈) is one of the main compounds in the nuclear fuel cycle. As such, identifying its processing parameters that control the oxygen isotopic composition could be developed as a new signature for nuclear forensic investigation. This study investigated the effect of different synthesis conditions such as calcination time, temperature, and cooling rates on the final δ¹⁸O values of U₃O₈, produced from uranium metal, uranyl nitrate hydrate, and uranium trioxide as starting materials. The results showed that δ¹⁸O of U₃O₈ is independent of the above-listed starting materials. δ¹⁸O values of 10 synthetic U₃O₈ were similar (9.35 ± 0.46‰) and did not change as a function of calcination time or calcination temperature. We showed that the cooling rate of U₃O₈ at the end of the synthesis process determines the final oxygen isotope composition, yielding a significant isotope effect on the order of 30‰. Experiments with two isotopically spiked 10 M HNO₃, with a difference of δ¹⁸O ∼75‰, show that no memory of the starting solution oxygen isotope signature is expressed in the final U₃O₈ product. We suggest that the interaction with atmospheric oxygen is the main process parameter that controls the δ¹⁸O value in U₃O₈. The uranium mass effect, the tendency of uranium ions to preferentially incorporate ¹⁶O, is expressed during the solid-gas oxygen exchange, which occurs throughout cooling of the system.

A new way to ensure selective zirconium ion adsorption

This work studies the adsorption of zirconium ions by mesoporous titanium dioxide with surface arsenate groups. Experimental maximal adsorption values of zirconium ions were found to be 109.6 mg/g in neutral medium. This process depends on the interaction time, the equilibrium concentration of zirconium ions, and the acidity of the solution. Adsorption kinetics fit well into the kinetic model based on the pseudo-second-order equation (R 2 = 0.9984). Equilibrium adsorption of zirconium ions is well described by Langmuir’s adsorption theory (R 2 = 0.9856 and χ 2 = 1.307). Although zirconium ions are less actively adsorbed from a neutral medium than strontium or yttrium ions, in the 2% nitric acid only zirconium is adsorbed out of the mixture of zirconium, strontium, and yttrium. The results obtained by inductively coupled plasma mass spectrometry have shown that the investigated adsorbent selectively adsorbs zirconium ions from their mixture with strontium and yttrium in the range of solution acidity pH = 0–1. The average percentage of maximum extraction of zirconium ions is 94.3 ± 2.4%, and the highest percent of zirconium ions taken up from the mixture with strontium and yttrium is ∼98.4%. Investigated titanium dioxide selectively separate 90Zr from 90Sr with the presence of 1000-fold excess of stable 88Sr in radioactive liquid β − source. This fact is extremely valuable for the age dating of 90Sr-containing device in nuclear forensics or the determination of 90Sr in low activity background samples.

Phase Analysis of Australian Uranium Ore Concentrates Determined by Variable Temperature Synchrotron Powder X-ray Diffraction

The chemical speciation of uranium oxides is sensitive to the provenance of the samples and their storage conditions. Here, we use diffraction methods to characterize the phases found in three aged (>10 years) uranium ore concentrates of different origins as well as in situ analysis of the thermally induced structural transitions of these materials. The structures of the crystalline phases found in the three samples have been refined, using high-resolution synchrotron X-ray diffraction data. Rietveld analysis of the samples from the Olympic Dam and Ranger uranium mines has revealed the presence of crystalline α-UO₂(OH)₂, together with metaschoepite (UO₂)₄O(OH)₆·5H₂O, in the aged U₃O₈ samples, and it is speculated that this forms as a consequence of the corrosion of U₃O₈ in the presence of metaschoepite. The third sample, from the Beverley uranium mine, contains the peroxide [UO₂(η²-O₂)(H₂O)₂] (metastudtite) together with α-UO₂(OH)₂ and metaschoepite. A core-shell model is proposed to account for the broadening of the diffraction peaks of the U₃O₈ evident in the samples.

Effect of Diel Cycling Temperature, Relative Humidity, and Synthetic Route on the Surface Morphology and Hydrolysis of α-U3O8

The speciation and morphological changes of α-U₃O₈ following aging under diel cycling temperature and relative humidity (RH) have been examined. This work advances the knowledge of U-oxide hydration as a result of synthetic route and environmental conditions, ultimately giving novel insight into nuclear material provenance. α-U₃O₈ was synthesized via the washed uranyl peroxide (UO₄) and ammonium uranyl carbonate (AUC) synthetic routes to produce unaged starting materials with different morphologies. α-U₃O₈ from UO₄ is comprised of subrounded particles, while α-U₃O₈ from AUC contains blocky, porous particles approximately an order of magnitude larger than particles from UO₄. For aging, a humidity chamber was programmed for continuous daily cycles of 12 "high" hours of 45 °C and 90% RH, and 12 "low" hours of 25 °C and 20% RH. Samples were analyzed at varying intervals of 14, 24, 36, 43, and 54 days. At each aging interval, crystallographic changes were measured via powder X-ray diffraction coupled with whole pattern fitting for quantitative analysis. Morphologic effects were studied via scanning electron microscopy and 12-way classification via machine learning. While all samples were found to have distinguishing morphologic characteristics (93.2% classification accuracy), α-U₃O₈ from UO₄ had more apparent change with increasing aging time. Nonetheless, α-U₃O₈ from AUC was found to hydrate more quickly than α-U₃O₈ from UO₄, which can likely be attributed to its larger surface area and porous starting material morphology.

Stable isotope signatures of hydration water in secondary mineralization on UO2

Hydrated secondary mineralization readily forms on the surface of UO₂ particles exposed to humidity in an oxidizing environment. The oxygen stable isotope composition of the secondary uranium oxide may reflect that of the water vapor, as well as the hydrogen and oxygen stable isotopic composition of the mineral hydration water. The geospatial organization of δ²H and δ¹⁸O values of atmospheric humidity and precipitation is increasingly well understood, which suggests that the hydrogen and oxygen stable isotopes in secondary mineral hydration water may yield information on the environment in which the mineralization formed. UO₂ powders were exposed to air with constant 30%, 61%, and 91% relative humidity, and constant H and O stable isotope composition. Aliquots were sampled from the UO₂ materials at intervals of 1-10 days through the total humidity exposure duration of 180 days. Scanning electron microscopy, transmission electron microscopy, and x-ray diffraction analysis of the humidity-exposed UO₂ indicates that schoepite/metaschoepite [(UO₃)•2H₂O] secondary phases had formed on the underlying UO₂. The δ²H and δ¹⁸O values of mineral hydration waters were determined by thermogravimetry-enabled isotope ratio infrared spectroscopy (TGA-IRIS). Results indicate that hydrogen in the surface sorbed and mineral hydration waters is exchangeable and thus their δ²H values are difficult to interpret. However, oxygen in these waters is less exchangeable, and thus the oxygen stable isotope composition of the schoepite/metaschoepite hydration water is likely to be related to that of the exposure water vapor. After formation of schoepite/metaschoepite, the δ¹⁸O values of the hydration water in schoepite/metaschoepite does not change in response to changes in exposure vapor δ¹⁸O values, which suggests that the δ¹⁸O values of the hydration water is relatively durable. These findings suggest that information about the origin and storage history of a UO₂ sample may be discernable from δ¹⁸O values of schoepite/metaschoepite hydration water.

Progress in Uranium Chemistry: Driving Advances in Front-End Nuclear Fuel Cycle Forensics

The front-end of the nuclear fuel cycle encompasses several chemical and physical processes used to acquire and prepare uranium for use in a nuclear reactor. These same processes can also be used for weapons or nefarious purposes, necessitating the need for technical means to help detect, investigate, and prevent the nefarious use of nuclear material and nuclear fuel cycle technology. Over the past decade, a significant research effort has investigated uranium compounds associated with the front-end of the nuclear fuel cycle, including uranium ore concentrates (UOCs), UF₄, UF₆, and UO₂F₂. These efforts have furthered uranium chemistry with an aim to expand and improve the field of nuclear forensics. Focus has been given to the morphology of various uranium compounds, trace elemental and chemical impurities in process samples of uranium compounds, the degradation of uranium compounds, particularly under environmental conditions, and the development of improved or new techniques for analysis of uranium compounds. Overall, this research effort has identified relevant chemical and physical characteristics of uranium compounds that can be used to help discern the origin, process history, and postproduction history for a sample of uranium material. This effort has also identified analytical techniques that could be brought to bear for nuclear forensics purposes. Continued research into these uranium compounds should yield additional relevant chemical and physical characteristics and analytical approaches to further advance front-end nuclear fuel cycle forensics capabilities.

Characterizing the solid hydrolysis product, UF4(H2O)2.5, generated from neat water reactions with UF4 at room temperature

Uranium tetrafluoride (UF₄) is an important intermediate in the production of UF₆ and uranium metal. Room temperature hydrolysis of UF₄ was investigated using a combination of Fluorine-19 nuclear magnetic resonance spectroscopy (¹⁹F NMR), Raman and infrared spectroscopy, powder X-ray diffraction, and microscopy measurements. UF₄(H₂O)_2.5 was identified as the primary solid hydrolysis product when anhydrous UF₄ was stirred in deionized water. Static NMR and ¹⁹F magic angle spinning NMR measurements revealed that a small amount of uranyl fluoride can also form when anhydrous UF₄ is left in water, although this species comprises less than 5% of the total sample with the remaining parts being UF₄(H₂O)_2.5. Since UF₄ is generally considered to be stable under ambient conditions, these findings mark the first time that a room temperature reaction between UF₄ and water has been detected and analyzed without interference from additional chemical reagents. The Raman characterization of UF₄(H₂O)_2.5 presented herein is the first on record. Since UF₄ is one of the most used intermediates during chemical conversion of uranium ore to uranium metal for nuclear fuel and weapons, the results presented herein are applicable to numerous nuclear science fields where solid state detection of uranium is of value, including nuclear nonproliferation, nuclear forensics, and environmental remediation.

A new nondestructive iterative method for forensics characterization of uranium-bearing materials by HRGS

In addition to the isotopic composition of a radioactive material, the high-resolution gamma spectrometry (HRGS) allows one to quantify physical characteristics of the material, which are important for nuclear forensics. A quantitative assessment of these characteristics requires two input parameters: the sample density and the mass fraction of radioactive material in the matrix. A method is proposed to determine these parameters provided that the enrichment and the total mass of the material are known. The method is formulated as an iterative quasi-Newton Broyden algorithm for finding roots of two functions in two variables. The developed method is applied to certified reference materials based on the powder uranium octaoxide in the range of enrichments from 0.3% to 93%. It is shown that the matrix density and the uranium mass fraction found experimentally well agree with the declared data in certificates, and the deviations do not exceed 4% up to an enrichment value of 93%.

Isotopic and Compositional Variations in Single Nuclear Fuel Pellet Particles Analyzed by Nanoscale Secondary Ion Mass Spectrometry

The Collaborative Materials Exercise (CMX) is organized by the Nuclear Forensics International Technical Working Group, with the aim of advancing the analytical capabilities of the participating organizations and providing feedback on the best approaches to a nuclear forensic investigation. Here, model nuclear fuel materials from the 5^th CMX iteration were analyzed using a NanoSIMS 50L (CAMECA) in order to examine inhomogeneities in the ²³⁵U/²³⁸U ratio and trace element abundance within individual, micrometer scale particles. Two fuel pellets were manufactured for the exercise and labelled CMX-5A and CMX-5B. These pellets were created using different processing techniques, but both had a target enrichment value of ²³⁵U/²³⁸U = 0.01. Particles from these pellets were isolated for isotopic and trace element analysis. Fifteen CMX-5A particles and 20 CMX-5B particles were analyzed, with both sample types displaying inhomogeneities in the U isotopic composition at a sub-micrometer scale within individual particles. Typical particle diameters were ∼1.5 to 41 μm for CMX-5A and ∼1 to 61 μm for CMX-5B. The CMX-5A particles were shown to be more isotopically homogeneous, with a mean ²³⁵U/²³⁸U atom ratio of 0.0130 ± 0.0066. The CMX-5B particles showed a predominantly depleted mean ²³⁵U/²³⁸U atom ratio of 0.0063 ± 0.0094, which is significantly different to the target enrichment value of the pellet and highlights the potential variation of ²³⁵U/²³⁸U in U fuel pellets at the micrometer scale. This study details the successful application of the NanoSIMS 50L in a mock nuclear forensic investigation by optimizing high-resolution imaging for uranium isotopics.

Hydration of α-UO3 following storage under controlled conditions of temperature and relative humidity

Experimental measurements and theoretical evaluation of changes in chemical speciation of α-UO₃ using XRD, EXAFS, TGA, and DFT calculations.

Spatially-resolved uranium isotopic analysis of contaminated scrap metal using laser ablation multi-collector ICP-MS

LA-MC-ICP-MS is a fast and quasi non-destructive technique to reveal possible U isotopic inhomogeneity in scrap metal samples, filling the gap between bulk isotopic analysis and particle analysis.

Identifying surface morphological characteristics to differentiate between mixtures of U3O8 synthesized from ammonium diuranate and uranyl peroxide

In the present study, surface morphological differences of mixtures of triuranium octoxide (U3O8), synthesized from uranyl peroxide (UO4) and ammonium diuranate (ADU), were investigated. The purity of each sample was verified using powder X-ray diffractometry (p-XRD), and scanning electron microscopy (SEM) images were collected to identify unique morphological features. The U3O8 from ADU and UO4 was found to be unique. Qualitatively, both particles have similar features being primarily circular in shape. Using the morphological analysis of materials (MAMA) software, particle shape and size were quantified. UO4 was found to produce U3O8 particles three times the area of those produced from ADU. With the starting morphologies quantified, U3O8 samples from ADU and UO4 were physically mixed in known quantities. SEM images were collected of the mixed samples, and the MAMA software was used to quantify particle attributes. As U3O8 particles from ADU were unique from UO4, the composition of the mixtures could be quantified using SEM imaging coupled with particle analysis. This provides a novel means of quantifying processing histories of mixtures of uranium oxides. Machine learning was also used to help further quantify characteristics in the image database through direct classification and particle segmentation using deep learning techniques based on Convolutional Neural Networks (CNN). It demonstrates that these techniques can distinguish the mixtures with high accuracy as well as showing significant differences in morphology between the mixtures. Results from this study demonstrate the power of quantitative morphological analysis for determining the processing history of nuclear materials.