Disproportionately High Contributions of 60 Year Old Weapons-137Cs Explain the Persistence of Radioactive Contamination in Bavarian Wild Boars.

Radionuclides released from nuclear accidents or explosions pose long-term threats to ecosystem health. A prominent example is wild boar contamination in central Europe, which is notorious for its persistently high 137Cs levels. However, without reliable source identification, the origin of this decades old problem has been uncertain. Here, we target radiocesium contamination in wild boars from Bavaria. Our samples (2019-2021) range from 370 to 15,000 Bq·kg-1 137Cs, thus exceeding the regulatory limits (600 Bq·kg-1) by a factor of up to 25. Using an emerging nuclear forensic fingerprint, 135Cs/137Cs, we distinguished various radiocesium source legacies in their source composition. All samples exhibit signatures of mixing of Chornobyl and nuclear weapons fallout, with 135Cs/137Cs ratios ranging from 0.67 to 1.97. Although Chornobyl has been widely believed to be the prime source of 137Cs in wild boars, we find that "old" 137Cs from weapons fallout significantly contributes to the total level (10-68%) in those specimens that exceeded the regulatory limit. In some cases, weapons-137Cs alone can lead to exceedances of the regulatory limit, especially in samples with a relatively low total 137Cs level. Our findings demonstrate that the superposition of older and newer legacies of 137Cs can vastly surpass the impact of any singular yet dominant source and thus highlight the critical role of historical releases of 137Cs in current environmental pollution challenges.

Identification of a chemical fingerprint linking the undeclared 2017 release of 106Ru to advanced nuclear fuel reprocessing.

The undeclared release and subsequent detection of ruthenium-106 (106Ru) across Europe from late September to early October of 2017 prompted an international effort to ascertain the circumstances of the event. While dispersion modeling, corroborated by ground deposition measurements, has narrowed possible locations of origin, there has been a lack of direct empirical evidence to address the nature of the release. This is due to the absence of radiological and chemical signatures in the sample matrices, considering that such signatures encode the history and circumstances of the radioactive contaminant. In limiting cases such as this, we herein introduce the use of selected chemical transformations to elucidate the chemical nature of a radioactive contaminant as part of a nuclear forensic investigation. Using established ruthenium polypyridyl chemistry, we have shown that a small percentage (1.2 ± 0.4%) of the radioactive 106Ru contaminant exists in a polychlorinated Ru(III) form, partly or entirely as ß-106RuCl3, while 20% is both insoluble and chemically inert, consistent with the occurrence of RuO2, the thermodynamic endpoint of the volatile RuO4 Together, these findings present a clear signature for nuclear fuel reprocessing activity, specifically the reductive trapping of the volatile and highly reactive RuO4, as the origin of the release. Considering that the previously established 103Ru:106Ru ratio indicates that the spent fuel was unusually young with respect to typical reprocessing protocol, it is likely that this exothermic trapping process proved to be a tipping point for an already turbulent mixture, leading to an abrupt and uncontrolled release.

Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017.

In October 2017, most European countries reported unique atmospheric detections of aerosol-bound radioruthenium (106Ru). The range of concentrations varied from some tenths of µBq·m-3 to more than 150 mBq·m-3 The widespread detection at such considerable (yet innocuous) levels suggested a considerable release. To compare activity reports of airborne 106Ru with different sampling periods, concentrations were reconstructed based on the most probable plume presence duration at each location. Based on airborne concentration spreading and chemical considerations, it is possible to assume that the release occurred in the Southern Urals region (Russian Federation). The 106Ru age was estimated to be about 2 years. It exhibited highly soluble and less soluble fractions in aqueous media, high radiopurity (lack of concomitant radionuclides), and volatility between 700 and 1,000 °C, thus suggesting a release at an advanced stage in the reprocessing of nuclear fuel. The amount and isotopic characteristics of the radioruthenium release may indicate a context with the production of a large 144Ce source for a neutrino experiment.

Measurements of extinct fission products in nuclear bomb debris: Determination of the yield of the Trinity nuclear test 70 y later.

This paper describes an approach to measuring extinct fission products that would allow for the characterization of a nuclear test at any time. The isotopic composition of molybdenum in five samples of glassy debris from the 1945 Trinity nuclear test has been measured. Nonnatural molybdenum isotopic compositions were observed, reflecting an input from the decay of the short-lived fission products (95)Zr and (97)Zr. By measuring both the perturbation of the (95)Mo/(96)Mo and (97)Mo/(96)Mo isotopic ratios and the total amount of molybdenum in the Trinity nuclear debris samples, it is possible to calculate the original concentrations of the (95)Zr and (97)Zr isotopes formed in the nuclear detonation. Together with a determination of the amount of plutonium in the debris, these measurements of extinct fission products allow for new estimates of the efficiency and yield of the historic Trinity test.

Uranium from German Nuclear Power Projects of the 1940s--A Nuclear Forensic Investigation.

Here we present a nuclear forensic study of uranium from German nuclear projects which used different geometries of metallic uranium fuel. Through measurement of the (230)Th/(234)U ratio, we could determine that the material had been produced in the period from 1940 to 1943. To determine the geographical origin of the uranium, the rare-earth-element content and the (87)Sr/(86)Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of (236)U and (239)Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence.

Separation of gold from irradiated actinide material utilizing a 2- thenoyltrifluoroacetone extraction resin.

Post-detonation nuclear forensics capabilities depend on the ability to rapidly isolate radionuclides to improve measurement quality. In this work an extraction chromatography resin was developed utilizing thenoyltrifluoroacetone and 1-octanol supported on Eichrom prefilter resin. The resin was tested in nitric and hydrochloric acid matrices. In nitric acid the resin was able to extract zirconium, while in hydrochloric acid matrices it was possible to extract iron and gallium. In all acid conditions tested, gold was retained but can be eluted from the column with 10 % thiourea.

A new method for quantifying 64Cu in nuclear debris samples.

Quantifying 64Cu in post-detonation nuclear debris samples can provide important diagnostic information regarding the structural materials used within a nuclear device. However, this task is challenging due to the weak gamma emissions associated with the decay of 64Cu, its short half-life (12.701 h), and the presence of interfering fission product radioisotopes. Large quantities of debris sample are generally needed to accurately quantify 64Cu, which can be problematic in sample-limited scenarios where other radiometric analyses are required. Herein, we present a new method for the separation of 64Cu from solutions of mixed fission products and demonstrate the quantification of its activity through use of gas-flow proportional beta counting. The new method was validated through a series of rigorous tests and was shown to improve the detection limit of 64Cu by over two orders of magnitude, from 2.5 × 106 to 1.3 × 104 atoms/sample for 100 min measurements.

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.

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.

Diffuse Reflectance Spectroscopy and Principal Component Analysis to Retrospectively Determine Production History of Plutonium Dioxide.

Diffuse reflectance spectroscopy measurements in the shortwave infrared (930-1600 nm) spectral region were acquired for Pu2(C2O4)3•9H2O and its thermal decomposition product, PuO2. We analyzed a total of eight PuO2 samples that were produced at different calcination temperatures (300, 350, 450, 525, 600, 675, 750, and 900 °C). Our goal was to identify spectroscopic fingerprints that could be used to gain retrospective information regarding the production parameters of these important nuclear compounds. The diffuse reflectance spectrum of Pu2(C2O4)3•9H2O features several broad bands that currently preclude detailed analysis. However, all PuO2 samples produced relatively sharp spectral features that got sharper and more intense for samples that were produced at higher calcination temperatures. The electronic band observed at 1433 nm in the diffuse reflectance spectra of PuO2 was found to be a sensitive indicator of crystallinity; a result that is corroborated by ancillary Raman spectroscopy measurements. Principal component analysis of diffuse reflectance spectra was able to clearly rank and categorize PuO2 samples based on the calcination temperature that was employed during their production. Thus, we show herein that important retrospective information pertaining to the process history of PuO2 can be gained through the relatively simplistic combination of diffuse reflectance spectroscopy and principal component analysis. This discovery presents a new method for determining the provenance and process history of PuO2 and should have an impact in the fields of nuclear forensics and nuclear nonproliferation.

Separation of protactinium from uranium-niobium alloys for 231Pa-235U radiochronometry in nuclear forensic investigations.

The isolation and purification of protactinium from uranium materials is essential for 231Pa-235U radiochronometry, but separating Pa from uranium-niobium alloys, a common material in the nuclear fuel cycle, is challenging due to the chemical similarity of Pa and Nb. Here we present three resin chromatography separation techniques for isolating Pa from U and Nb which were independently developed by three different laboratories through ad hoc adaptations of standard operating procedures. Our results underscore the need for and value of purification methods suitable for a diversity of uranium-based materials to ensure the operational readiness of nuclear forensics laboratories. Supplementary Information: The online version contains supplementary material available at 10.1007/s10967-023-08928-y.

Chemical separation and measurement of platinum activation products.

A method has been developed to purify and measure platinum radioisotopes in the presence of fission products and environmental constituents. The method uses a combination of cation exchange and anion exchange chromatography and selective precipitation steps to remove other radioisotopes from the sample. The addition of stable platinum carrier allows for a gravimetric determination of the chemical yield of the procedure. Overall, the method is fast, simple, and potentially applicable for rapid turnaround of unknown samples. Using this method, multiple platinum radioisotopes were measured in two different irradiation experiments. The measured ratios of the platinum radioisotopes clearly reflect the neutron spectrum of the irradiation, suggesting that platinum radioisotopes could be valuable signatures in nuclear forensic analyses.

Gamma spectrometric measurement of uranium isotopic composition and mass in sintered UO2 pellets using the efficiency transfer method.

Gamma spectrometric measurements to determine the isotopic composition and total uranium mass in UO2 pellets (D = 7.5 mm; H = 3.5 mm, ρ = 10 g/cm3) were carried out. The required efficiency curve was obtained by applying the efficiency transfer method from a calibration standard (D = 65 mm; H = 20 mm) of a slightly acidified water solution. The average isotopic composition of ten UO2 pellets was consistent with values of natural uranium given by IUPAC. The average relative bias for the 235U/238U amount ratio was -0.73% using the 1001 keV gamma line for 238U and 0.50% using the 63 keV gamma line (186 keV was always used for 235U). For the total uranium mass, the mean deviation as compared to mass determinations using a balance was 5.5% using the 1001 keV gamma line for 238U and 4.3% using the 63 keV gamma line.

Rapid separation of americium from complex matrices using solvent impregnated triazine extraction chromatography resins.

Several novel extraction chromatography resins (EXC) have been synthesised by solvent impregnation of the triazine ligands 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[1,2,4]triazin-3-yl)-2,2'-bipyridine (CyMe4BTBP) and 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazin-3-yl)-1,10-phenanthroline (CyMe4BTPhen) into Amberlite XAD7 and Amberchrom CG300 polymer supports. The resins have been physically characterised by a suite of spectroscopic, analytical and imaging techniques. The resins have also been evaluated in terms of their ability to selectively extract americium from complex matrices intended to simulate those typical of spent nuclear fuel raffinate, environmental samples and nuclear forensics samples. The resins have been compared with previously reported attempts to generate EXC resins based on CyMe4BTBP and CyMe4BTPhen. Previously reported resins all rely on complex synthesis for the formation of a covalent bond between extractant and support by contrast with the simpler solvent impregnation method reported here. The Amberchrom supported CyMe4BTBP resin achieved a weight distribution ration (DAm) of 170 within 60 min and a decontamination factor (DF) of >1000 for americium over lanthanides by column chromatography. The Amberchrom CyMe4BTPhen resin achieved a DAm of 540 within 30 min and a DF for americium from lanthanides of 60-160.

A simple method for Ce-Nd separation using nano-NaBiO3: Application in the isotopic analysis of U, Sr, Pb, Nd, and Hf in uranium ores.

U, Sr, Pb, Nd, and Hf isotope ratios can provide basic and important information of nuclear materials. We established a simple and efficient column chemistry method using nano-NaBiO3, as both oxidizer and adsorbent, to completely separate Ce from rare earth elements (REEs). This new method exhibited a high decontamination (Ce/Nd < 10-5) ability and was easy to conducted, thereby providing clear advantages compared to traditional liquid-liquid and solid phase micro-extraction techniques. Additionally, a rapid four-column separation procedure, based on Sr, TUR, Ln resins and nano-NaBiO3, was developed to isolate U, Sr, Pb, Nd, and Hf in ore samples. The entire procedure could be completed in 4-5 hrs. The robustness of the proposed method was demonstrated by analyzing the 235U/238U, 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 142Nd/144Nd, 143Nd/144Nd, and 176Hf/177Hf isotopic ratios of two certified reference materials (CRMs). The analytical results obtained using this method showed good agreement with previously published data. The feasibility of this method was extended to the determination of isotope ratios in uranium ores. The results obtained from the two samples with different regions indicated that they have different isotopic ratios information. These findings indicate the potential for the use of this new method in nuclear forensic science.

Polyamidoxime-based membranes for the rapid screening of uranium isotopes in water.

Traditional radiochemistry approaches for the detection of trace-level alpha-emitting radioisotopes in water require lengthy offsite sample preparations and do not lend themselves to rapid quantification. Therefore, a novel platform is needed that combines onsite purification, concentration, and isotopic screening with a fieldable detection system. This contribution describes the synthesis and characterization of polyamidoxime membranes for isolation and concentration of uranium from aqueous matrices, including high-salinity seawater. The aim was to develop a field portable screening method for the rapid quantification of isotopic distribution by alpha spectroscopy. Membranes with varying degree of modification were prepared by chemical conversion of nitrile groups to amidoxime groups on the surface of polyacrylonitrile ultrafiltration (UFPAN) membranes. Attenuated total reflectance Fourier-transform infrared spectroscopy was used to analyze changes in surface chemistry. Flow through filtration experiments conducted using deionized (DI) water and simulated seawater solutions indicated that the modified membrane was effective in capturing more than 95% of the uranium in the solution prior to breakthrough even in the presence of salt ions. Batch uptake experiments were conducted and compared with the flow through experimental data to elucidate likely binding mechanisms. Alpha spectra of uranium loaded membranes were analyzed, and the effects of solution matrix and degree of modification on peak energy resolution were studied. Peak energy resolutions of 24 ± 2 keV and 32 ± 6 keV full width at half maximum (FWHM) were obtained by loading uranium from DI and seawater solutions onto modified membranes. Full width at 10% maximum of the same spectra were calculated to be 63 ± 9 keV and 160 ± 34 keV to quantify differences seen in peak tailing. Calculations performed based on the results show that it would take less than 3 h of analysis time to screen a sample provided enough volumes of solution are available. This work offers a facile method to prepare polyamidoxime-based membranes for uranium separation and concentration at circumneutral pH values, enabling the rapid, onsite screening of unknown samples.

Integrating the theory of sampling into a nuclear forensic investigation.

We present a study case where the theory of sampling (TOS) is used to make defensible inferences in a nuclear forensic investigation. The forensic investigations focused on five suspicious radioactive materials seized in 2019. All errors introduced by sampling and sub-sampling the radioactive materials are evaluated according to TOS. A maximum sampling error of 35% was tolerated. The uses of TOS enabled the forensic team to make inferences about the seized materials and therefore make confidence-based statements about the exceeding of limits established in the Swiss Radiological Protection Ordinance for radioactive substances. The analysis of the isotope and activity ratios allowed the team to exclude some potential sources of the radioactive contamination; however, it was not possible to determine its origin precisely.

Development of a rapid method for extraction of uranium from uranium bearing materials using ionic liquid as extracting agent from basic media.

The paper presents the development of a rapid method for the direct determination of uranium using liquid scintillation analysis in uranium bearing materials with different uranium concentrations and with different impurity levels (U-ore, Uranium ore concentrate (UOC) and U-metal). Uranium extraction was carried out using hydrophobic ionic liquid Aliquat-336 thiosalicylate, ([A-336][TS]) from diluted samples in basic medium followed by liquid scintillation counting (LSC). Extraction efficiencies for uranium from aqueous medium was studied with very small volumes of ionic liquid under varying volume, pH and uranium concentration of the aqueous medium. Maximum extraction efficiency was achieved near pH 8-11. Uranium was successfully re-extracted from organic medium with nitric acid and electroplated onto stainless steel planchette for alpha spectrometry determination. Maximum re-extraction efficiency with 1 M HNO3 combined with electroplating efficiency observed was 80%. The methodology was applied for real samples. The uranium extraction efficiency using ionic liquid was about 85% for U-metal and UOC samples with comparatively low impurity level; whereas extraction efficiency for U-ore samples was found to be less than 40%. The technique can be applied for nuclear forensic applications as well as nuclear emergency scenarios for a quick initial assessment and isotopic analysis of uranium in the samples.

Objective colour analysis from digital images as a nuclear forensic tool.

A digital colour image may be composed of hundreds of thousands of pixels, every pixel exhibiting a single colour. Each colour can be described as a combination of red, green and blue (RGB) components, of discrete values between 0-255. The RGB data contained within the pixels of an image could, therefore, be used to quantitatively establish the colour of nuclear material powders from digital images, particularly for use in nuclear forensics applications, where there is a need for consistent, objective analysis. This paper sets out a standard method for the photography and analysis of digital images of uranium oxide powder, for the objective quantification of colour by mean RGB values. Eight heat treated (up to 550°C) powder samples of studtite ([(UO2)(O2)(H2O)2]·2H2O) were photographed at room temperature and analysed by the RGB method. Hue, saturation and value of the coloured samples were obtained alongside mean RGB values, both of which were used to successfully determine the heating temperatures of unknown specimens of studtite.

Application of gamma-ray spectrometry, neutron multiplicity counting and calorimetry for non-destructive assay of U-Pu mixed samples.

This paper presents a standardless non-destructive method for simultaneous assay of uranium and plutonium in mixed samples relevant to nuclear safeguards, forensics and fuel cycle. The method is based on an in-situ absolute efficiency calibration of a γ-ray detector using plutonium γ-rays that can subsequently be used for quantification of uranium in the sample. The method was tested by assaying U-Pu samples with known amounts of U and Pu with varying mass, geometry, composition, reactor type, age and fissile isotope enrichment.