Uranium Isotope Ratios Research Articles

Uranium reduction and isotopic fractionation in reducing sediments: Insights from reactive transport modeling

Uranium concentrations and isotopic ratios (238U/235U, denoted as δ238U) have been used to provide quantitative information about the degree of oxygenation and de-oxygenation of past oceans. The potential to constrain changes in global redox conditions, in contrast to many other proxies that reflect local conditions, is a particular strength of the uranium isotope approach. Because uranium reduction primarily occurs in sediments underlying anoxic water columns rather than in the anoxic water column itself, the removal of uranium in organic-rich shales is the largest lever on seawater δ238U. Accordingly, accumulation and isotopic fractionation are modulated by local variations in productivity, basin connectivity, sedimentation rate, and bottom-water redox conditions. To isolate the processes at the sediment-water interface that control δ238U and uranium accumulation in reducing sediments, we constructed a reactive transport model that couples biogeochemical reactions to diffusive transport and the burial of solutes and minerals.Using the model framework, we test the sensitivity of authigenic uranium isotopic fractionation and accumulation to oxygenation, permeability, sedimentation rate, organic carbon delivery, and basin restriction. Our results demonstrate that these external forcings produce diagnostic patterns in isotopic fractionation. Specifically, the model predicts that authigenic δ238U is sensitive to productivity because of the associated organic carbon burial rate. Moreover, our results suggest that the isotopic offset does not vary significantly due to changing bottom-water O2 concentrations, but the amount of accumulation does—a result that differs from previous estimates. Water column uranium reduction adds additional complexity to the ultimate δ238U value. The predictive patterns derived from model results can offer insight into local depositional conditions, such as sedimentation patterns. Collectively, these effects—including bottom-water redox conditions and related reducing sediments—alter the isotopic signature of the overlying water column according to the authigenic δ238U value and the diffusive fluxes arising from porewater concentration gradients. More broadly, this work provides important new constraints on the major controls on the δ238U of sediments while also supporting its use as a proxy for global marine redox conditions.

Determination of 234U/238U, 235U/238U, 236U/238U Isotope Ratios in Uranium Oxide by Sector-Field ICP-MS

Influence of mass bias effect, isobaric and polyatomic interferences on the results of 234U/238U, 235U/238U, 236U/238U isotope ratio determination in uranium oxide by sector-field ICP-MS was studied. Uranium isotopic standards CRM U100, CRM U200 based on triuranium octoxide (U3O8) and single-collector mass spectrometer ICP-SFMS ELEMENT 2 were used for research. It has been demonstrated that the mass bias effect has most influence on the results of uranium isotope ratios determination. To investigate the influence of the mass bias effect on the determinations of uranium isotope ratios, the external standardization calibration was used with three models (linear, power, exponential) describing the behavior of the specific discrimination coefficient β versus the mass of measured isotopes. The mass discrimination factor has been found to vary from 6.00 ´ 10-3 to 1.20 ´ 10-2. The advantage for using the (power/exponential)-law models of the β=F(Δm) relationship for correcting measured isotope ratios was justified. In case of polyatomic interferences, the efficiency of uranium hydride ion (235U1H+) formation is 3.54 ´ 10-5, while the impact of isobaric overlapping due to the contribution of scattered 238U ions to the intensities of less abundant 236U and 235U ions reaches 8.17 ´ 10-6. The relative measurement error for the 234U/238U, 236U/238U , ratios was found to be < 0.5 %, and for the 235U/238U, ratio less than 0.1 %. The calculated standard uncertainty u of the 234U/238U, 235U/238U, 236U/238U isotope ratio measurements in the CRM U100 was 0.563, 0.322 and 0.856 %, respectively. These are reasonable estimates in comparison with the uncertainties of certified values of 0.296, 0.097 and 0.265 %.

A comparative study of ultra-trace-level uranium by thermal ionization mass spectrometry with continuous heating: Static and peak-jumping modes

For ensuring nuclear safeguards, we report the analytical signal-detection performance of thermal ionization mass spectrometry (TIMS) with continuous heating for the measurement of isotopic ratios in samples containing ultra-trace amounts of uranium. As methods for detecting uranium signals, peak-jumping mode using a single detector and static mode using multiple detectors were examined with U100 (10% 235U-enriched) uranium standard samples in the femtogram-to-picogram range. Uranium isotope ratios, n(235U)/n(238U), were measured down to levels of 1 fg and 3 fg in static and peak-jumping modes, respectively, while n(234U)/n(238U) and n(236U)/n(238U) values were measured down to levels of 100 fg in both modes. In addition, the dependency of the 238U signal intensity on sample quantity exhibited similar tendencies in both modes. The precisions of the isotope ratios obtained in the static mode over all sample ranges used in this study were overall slightly higher than those obtained in peak-jumping mode. These results indicate that isotope ratio measurements by TIMS with continuous heating are almost independent of the detection method, i.e., peak-jumping mode or static mode, which is characteristic of isotope-ratio measurements using the TIMS method with continuous heating. TIMS with continuous heating is advantageous as it exhibits the properties of multiple detectors within a single detector, and is expected to be used in various fields in addition to ensuring nuclear safeguards.

Chemical alteration processes for uranium migration and their significance on uranium isotopic ratio changes

ABSTRACT Gabal Abu Garadi area is covered by metasediments, alkali feldspar granites and stream sediments. Geochemically, silicification, desilicification, sericitisation, fluoritisation and Na-metasomatism are the main alteration features of alkali feldspar granites. The activity concentration of 238U in alkali feldspar granites ranged between 1.7 ± 0.1 Bq g−1 and 3.9 ± 0.3 Bq g−1; between 1.7 ± 0.2 Bq g−1 and 9.4 ± 1.4 Bq g−1 for 234U and between 0.012 ± 0.0002 Bq g−1 and 0.09 ± 0.0001 Bq g−1 for 235U. The activity concentration of 228Th ranges between 1.3 ± 0.1 Bq g−1 and 3.6 ± 0.8 Bq g−1; between 1.5 ± 0.2 Bq g−1 and 2.7 ± 0.7 Bq g−1 for 230Th and between 1.8 ± 0.3 Bq g−1 and 4.1 ± 0.4 Bq g−1 for 232Th. The variability in Chemical Index of Alteration (CIA) with U, Th, 230Th/238U and 230Th/234U for the studied altered granite indicates that U and Th concentrations increased with increasing alteration especially in the silicified and desilicified samples. Changes in U, Th, 230Th/238U and 230Th/234U suggest the role of alteration processes in uranium and thorium mobilisation though thorium is geochemically less mobile or immobile. Thorium mobilisation could be controlled by adsorption in the alteration products of Abu Garadi granites such as clay minerals, manganese and iron oxides. In contrast, 230Th/238U and230Th/234U decreased with increasing CIA values suggesting uranium accumulation. 234U/238U ratios were in equilibrium in most samples; this might suggest the effect of severe chemical weathering or alteration processes that leads to the leachability of the two radionuclides (234U, 238U) with the same ratio probably during kaolinisation processes. In contrast, 230Th/238U and230Th/234U>1 were in disequilibrium, suggesting the changes in the physicochemical conditions accompanying the different alteration processes.

A NanoSIMS 50 L Investigation into Improving the Precision and Accuracy of the 235U/238U Ratio Determination by Using the Molecular 235U16O and 238U16O Secondary Ions

A NanoSIMS 50 L was used to study the relationship between the 235U/238U atomic and 235U16O/238U16O molecular uranium isotope ratios determined from a variety of uranium compounds (UO2, UO2F2, UO3, UO2(NO3)2·6(H2O), and UF4) and silicates (NIST-610 glass and the Plesovice zircon reference materials, both containing µg/g uranium). Because there is typically a greater abundance of 235U16O+ and 238U16O+ molecular secondary ions than 235U+ and 238U+ atomic ions when uranium-bearing materials are sputtered with an oxygen primary ion beam, the goal was to understand whether use of 235U16O/238U16O has the potential for improved accuracy and precision when compared to the 235U/238U ratio. The UO2 and silicate reference materials showed the greatest potential for improved accuracy and precision through use of the 235U16O/238U16O ratio as compared to the 235U/238U ratio. For the UO2, which was investigated at a variety of primary beam currents, and the silicate reference materials, which were only investigated using a single primary beam current, this improvement was especially pronounced at low 235U+ count rates. In contrast, comparison of the 235U16O/238U16O ratio versus the 235U/238U ratio from the other uranium compounds clearly indicates that the 235U16O/238U16O ratio results in worse precision and accuracy. This behavior is based on the observation that the atomic (235U+ and 238U+) to molecular (235U16O+ and 238U16O+) secondary ion production rates remain internally consistent within the UO2 and silicate reference materials, whereas it is highly variable in the other uranium compounds. Efforts to understand the origin of this behavior suggest that irregular sample surface topography, and/or molecular interferences arising from the manner in which the UO2F2, UO3, UO2(NO3)2·6(H2O), and UF4 were prepared, may be a major contributing factor to the inconsistent relationship between the observed atomic and molecular secondary ion yields. Overall, the results suggest that for certain bulk compositions, use of the 235U16O/238U16O may be a viable approach to improving the precision and accuracy in situations where a relatively low 235U+ count rate is expected.

Graphene Oxide Carburization Enhanced Ionization Efficiency for TIMS Isotope Ratio Analysis of Uranium at Trace Level.

Isotope analysis of trace uranium is important in nuclear safeguards and nuclear forensics, which requires the analytical methodologies with high sensitivity, accuracy, and precision. As one of the most powerful techniques in isotopic measurement, thermal ionization mass spectrometry (TIMS) usually suffers from its relatively low sensitivity in ultratrace measurements. To overcome this limitation, we have developed a new filament carburization technique for TIMS, with graphene oxide (GO) as the ionization enhancer. A high and steady ionization efficiency of ∼0.2% for uranium was achieved in single-filament mode, which was 10× the classical double-filament method. With total evaporation (TE) measurements, this method was validated with certified reference materials (CRMs) at the picogram level, and the relative uncertainties for n(235U)/ n(238U) were as low as the ∼1% level. The enhancement mechanism of GO's promoting effect on uranium ionization was attributed to the uniform microstructure facilitating energy transfer and formation of carbides. This approach provides an alternative simple and rapid method for trace uranium isotope analysis with high sensitivity and excellent repeatability. Filament carburization and uranium loading could be accomplished within 10 min. This technique has great advantage in analysis of trace uranium isotope ratios and can be applied in the researches of environmental analysis and nuclear forensics.

Analytical considerations in the determination of uranium isotope ratios in solid uranium materials using laser ablation multi-collector ICP-MS

Validated analytical measurement protocols for the fast and accurate determination of the uranium (U) isotopic composition (234U, 235U, 236U, 238U) of solid nuclear materials were developed employing ns-laser ablation (LA) coupled to multi-collector ICP-MS. The accuracy of the analytical procedure was assured by frequent (n = 65) analysis of a pressed pellet of certified isotopic reference material CRM U-030 (∼3 wt% 235U). The expanded uncertainty (k = 2) for the n(235U)/n(238U) ratio was as low as 0.05%, rising to 0.62% and 1.09% for n(234U)/n(238U) and n(236U)/n(238U) ratios, respectively. LA-MC-ICP-MS measurements of a pressed pellet of certified isotopic reference material CRM U-020 (∼2 wt% 235U) before analysis of each sample allowed calculation of the ion counter gains and mass bias correction. Both individual spot analysis and line scan analysis were used to measure n(234U)/n(238U), n(235U)/n(238U), and n(236U)/n(238U) ratios in two low-enriched UO2 pellets from the fourth Collaborative Materials Exercise (CMX-4), four seized low-enriched UO2 pellets intercepted from illicit trafficking and one metal sample consisting of depleted U. LA-MC-ICP-MS results of all investigated samples matched well with U isotope ratios obtained by thermal ionisation mass spectrometry (TIMS). This independent confirmation of the LA-MC-ICP-MS results by TIMS underpinned the high quality of generated analytical data. Acquisition of several thousand data points within a couple of minutes during line scan analysis yielded detailed information on the spatial distribution of the U isotopic composition of selected UO2 pellets, revealing straightforwardly their (in˗)homogeneity on the μm-scale. Calculating skewness and half width of the frequency distributions of the n(235U)/n(238U) amount ratio allowed the quantitative assessment of the (in-)homogeneity of the investigated samples. This information allows drawing conclusions on the starting materials used for the production of the pellets. From a nuclear forensics perspective, LA-MC-ICP-MS provides quick, accurate results on the spatial distribution of major and minor U isotopes while preserving the sample i.e. piece of evidence, essentially intact.

More than Five Percent Ionization Efficiency by Cavity Source Thermal Ionization Mass Spectrometry for Uranium Subnanogram Amounts.

Numerous applications require the precise analysis of U isotope relative enrichment in sample amounts in the subnanogram to picogram range; among those are nuclear forensics, nuclear safeguards, environmental survey, and geosciences. However, conventional thermal ionization mass spectrometry (TIMS) yields U combined ionization and transmission efficiencies (i.e., ratio of ions detected to sample atoms loaded) of less than 0.1% or 2% depending on the loading protocol, motivating the development of sources capable of enhancing ionization. The new prototype cavity source TIMS at ETH Zürich offers improvements from 4 to 15 times in combined ionization and transmission efficiency compared to conventional TIMS, yielding up to 5.6% combined efficiency. Uranium isotope ratios have been determined on reference standards in the 100 pg range bound to ion-exchange or extraction resin beads. For natural U standards, n(235U)/ n(238U) ratios are measured to relative external precisions of 0.5-1.0% (2RSD, 2 < n < 11, conventional source) or 2.0% (2RSD, n = 6, cavity source) and accuracies of 0.2-0.7% (conventional source) or 0.4-0.9% (cavity source). Meanwhile, n(234U)/ n(238U) ratios are determined to relative external precisions of 1.7-3.6% (2RSD, 2 < n < 11, conventional source) or 5.6% (2RSD, n = 6, cavity source) and accuracies of 0.1-2.5% (conventional source) or 0.5-8.3% (cavity source), which would benefit further from in-run organic interference and peak tailing corrections.

Sediment residence time reveals Holocene shift from climatic to vegetation control on catchment erosion in the Balkans

Abstract Understanding the evolution of soil systems on geological time scales has become fundamentally important to predict future landscape development in light of rapid global warming and intensifying anthropogenic impact. Here, we use an innovative uranium isotope-based technique combined with organic carbon isotopes and elemental ratios of sediments from Lake Ohrid (North Macedonia/Albania) to reconstruct soil system evolution in the lake's catchment during the last ~16,000 cal yr BP. Uranium isotopes are used to estimated the paleo-sediment residence time, defined as the time elapsed between formation of silt and clay sized detrital matter and final deposition. The chronology is based on new cryptotephra layers identified in the sediment sequence. The isotope and elemental data are compared to sedimentary properties and pollen from the same sample material to provide a better understanding of past catchment erosion and landscape evolution in the light of climate forcing, vegetation development, and anthropogenic land use. During the Late Glacial and the Early Holocene, when wide parts of the catchment were covered by open vegetation, wetter climates promoted the mobilisation of detrital matter with a short paleo-sediment residence time. This is explained by erosion of deeper parts of the weathering horizon from thin soils. Detrital matter with a longer paleo-sediment residence time, illustrating shallow erosion of thicker soils is deposited in drier climates. The coupling between climatic variations and soil erosion terminates at the Early to Mid-Holocene transition as evidenced by a pronounced shift in uranium isotope ratios indicating that catchment erosion is dominated by shallow erosion of thick soils only. This shift suggests a threshold is crossed in hillslope erosion, possibly as a result of a major change in vegetation cover preventing deep erosion of thin soils at higher elevation. The threshold in catchment erosion is not mirrored by soil development over time, which gradually increases in response to Late Glacial to Holocene warming until human land use during the Late Holocene promotes reduced soil development and soil degradation. Overall, we observe that soil system evolution is progressively controlled by climatic, vegetation, and eventually by human land use over the last ~16,000 years.

Determination of the isotopic composition of single sub-micrometer-sized uranium particles by laser ablation coupled with multi-collector inductively coupled plasma mass spectrometry.

A multi-collector inductively coupled plasma (MC-ICP) mass spectrometer coupled to a UV ns-laser ablation (LA) system was used to measure uranium isotopic ratios (234 U/238 U, 235 U/238 U and 236 U/238 U) in single uranium particles of various sizes and isotopic compositions, including home-made sub-micrometric natural uranium particles of narrow size distribution (415 ± 60 nm). The LA-ICP mass spectrometer was operated in wet plasma conditions thanks to simultaneous injection of the laser aerosol and water vapor through a desolvating nebulizer. The isotopic ratios were corrected for mass bias and gain factors between detectors. The 236 U/238 U ratios were also corrected for the presence of 235 U hydrides and tailing of the 238 U+ peak. 236 U/238 U ratios were successfully measured in micrometer-sized particles from the NBS U050 certified standard material with a 236 U/238 U ratio of ~5 × 10-4 . The analysis of 77 natural uranium sub-μm-sized particles yielded a very good trueness with respect to the expected 234 U/238 U and 235 U/238 U ratios, while the measurement errors for single particles ranged from -2.7% to +2.1% for 235 U/238 U and from -17% to +33% for the 234 U/238 U ratios. Their relative combined standard uncertainties ranged from 3.3% to 32.8% and from 0.4% to 4.0% for 234 U/238 U and 235 U/238 U ratios, respectively. In addition, extremely low detection limits, in the attogram range, were achieved. This study demonstrates that coupling of a ns-laser ablation system with a MC-ICP mass spectrometer allows measurements of the isotopic composition in natural uranium particles of a few hundreds of nm with very good trueness, average combined standard uncertainties of ~1% for 235 U/238 U ratios and 12% for 234 U/238 U ratios, and detections limits of a few ag for minor isotopes.

Development and comparison of high accuracy thermal ionization mass spectrometry methods for uranium isotope ratios determination in nuclear fuel

This study presents the development and the comparison of high accuracy methods for uranium isotope determination by thermal ionization mass spectrometry. Two methods for uranium minor isotope ratio determination were compared in term of accuracy, analysable quantity, analysis time and versatility: the total evaporation and the classical method with multi-dynamic sequences. The mathematical correction of the abundance sensitivity and the detector calibration within the classical method helps decreasing the uncertainties and the biases compared to the total evaporation method. This comparative study was conducted within the framework of the “2017 Nuclear Material Round Robin” participation organized by the International Atomic Energy Agency.

Considerations for uranium isotope ratio analysis by atmospheric pressure ionization mass spectrometry.

The accurate measurement of uranium isotope ratios from trace samples lies at the foundation of achieving nuclear nonproliferation. These challenging measurements necessitate both the continued characterization and evaluation of evolving mass spectrometric technologies as well as the propagation of sound measurement approaches. For the first time in this work, we present the analysis of uranium isotope ratio measurements from discrete liquid injections with an ultra-high-resolution hybrid quadrupole time-of-flight mass spectrometer. Also presented are important measurement considerations for evaluating the performance of this type and other atmospheric pressure and ambient ionization mass spectrometers for uranium isotope analysis. Specifically, as the goal of achieving isotope ratios from as little as a single picogram of solid material is approached, factors such as mass spectral sampling rate, collision induced dissociation (CID) potentials, and mass resolution can dramatically alter the measured isotope ratio as a function of mass loading. We present the ability to accurately measure 235UO2+/238UO2+ down to 10s of picograms of solubilized uranium oxide through a proper consideration of mass spectral parameters while identifying limitations and opportunities for pushing this limit further.

A laser ablation resonance ionisation mass spectrometer (LA-RIMS) for the detection of isotope ratios of uranium at ultra-trace concentrations from solid particles and solutions

A commercial MALDI mass spectrometer coupled with a tunable laser ionisation system can be used for the detection of uranium isotope ratios at trace levels.

Optimization of the sample preparation and measurement protocol for the analysis of uranium isotopes by MC-ICP-MS without spike addition

This study elucidates the importance of assessing mass biases due to sample pre-treatment for uranium isotope ratio analysis.

Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans

Anoxic and iron-rich oceanic conditions prevailed throughout most of the Archean and Proterozoic (4000 to c.540 million years ago, Ma), but the oceans are hypothesised to have become progressively oxygen-rich during the Ediacaran–Cambrian transition interval, coincident with the rise of animal life. We utilise the uranium isotope ratio of seawater (238U/235U; reformulated as δ238U), an effective tracer of oceanic redox conditions, as a proxy for changes in the global proportion of anoxic seafloor. We present a new δ238U dataset for carbonate rocks from the Lower Nama Group, Namibia, deposited in a shelf ramp succession during the terminal Neoproterozoic (∼550 to ∼547 Ma). These data capture a transition from δ238U similar to the modern ocean towards persistently low δ238U (average = −0.81 ± 0.06‰). Such low δ238U are consistent with enhanced U drawdown from the water column under anoxic conditions, and the preferential export of ‘heavy’ 238U to sediments following U(VI)–U(IV) reduction. Placing our results into a steady state ocean box model suggests at least a third of the global seafloor was covered by anoxic bottom waters compared with only 0.3% in today's oxygenated oceans. Comparison with δ238U from older sediments deposited in other basins further supports an expansion of anoxic bottom waters towards the end of the Ediacaran. Our data are consistent with an emerging picture of a dominantly anoxic Ediacaran ocean punctuated by brief ocean oxygenation events. In the Nama Group, the transition towards globally widespread anoxic conditions post-dates the first appearance of both skeletal metazoans and soft-bodied fauna of the Nama Assemblage. This suggests that the global expansion of anoxia did not coincide with the decline of the Ediacaran biota, or drive the biotic turnover between the White Sea and Nama Assemblages. The impact of this global redox change on metazoan ecosystems is unclear, since the expansion of anoxia, if contained mainly within deeper waters, may not have impinged significantly upon continental shelves that host the majority of biodiversity.

Simultaneous Determination of Uranium and Depleted Uranium Isotopic Ratio Using Inductively Coupled Mass Spectrometry.

We have developed and validated a method for the simultaneous quantitative measurement of total uranium (TU) and uranium 235 U/238 U isotopic ratio (UIR) in urine by inductively coupled plasma mass spectrometry (ICP-MS) using a Thermo Scientific iCAP-Q instrument. The performance characteristics of the assay were determined to be in compliance with clinical laboratory standards. The assay was linear in the concentration range of 1.0 to 500.0 ng/liter TU. The method was precise and accurate with limits of detection of 2.5 ng/liter for TU and 9.8 ng/liter for UIR. The accuracy was >93% and the coefficient of variation (% CV) was <5.0% for both TU and UIR. All results were within established guidelines and agreed-upon criteria, and the results fell within the certified range for the reference controls. The method has thus been shown to be effective as a simple, precise, and sensitive analytical technique for testing urine samples. © 2018 by John Wiley & Sons, Inc.

Actinides AMS on the VEGA accelerator

The VEGA 1MV accelerator at ANSTO is designed to be a highly versatile AMS instrument. In this paper we focus on describing those aspects of the system that are designed to optimise its performance for actinides isotopic analysis, in particular the implementation of fast isotope cycling and multiple isotope detection methods to enable isotope detection across a wide range of rates and currents. Charge state yields are reported in the energy range from 0.3 to 1.0 MeV with helium gas stripping, showing that the highest yield for the 3+ charge state occurs around 1 MeV and exceeds 40%. Accuracy and precision for uranium isotope ratios are shown to approach 1% over a wide range of concentrations and isotope ratios. The ionisation efficiency for plutonium is shown to exceed 3%, leading to overall detection efficiency over 1%. In the absence of background, this leads to sub-attogram detection limits for several Pu isotopes including 244Pu.

Uranium oxide microparticle suspensions for the production of reference materials for micro-analytical methods

To support the nuclear safeguards particle analysis, a method was developed to produce micrometer-sized uranium oxide microspheres with a known uranium content and isotope ratio, which are intended to be characterized as certified reference material. To simplify handling of the produced particles, the collected particles have been transferred into ethanol suspensions. In addition to a demonstration of the suitability and new capabilities of such particle suspensions, such as the preparation of particle mixtures, the stability of the particles has been investigated and demonstrated with regard to dissolution and isotopic exchange.

Application of laser ionization mass spectrometry for measurement of uranium isotope ratio in nuclear forensics and nuclear safeguards

The uranium isotope ratio of both bulk material and individual particles provides important information for nuclear safeguards and nuclear forensics. As a rapid in situ analytical technique, laser ionization mass spectrometry (LIMS) was used to determine the uranium isotope ratio of solid bulk samples and single particles of U3O8. The results of measuring bulk samples showed excellent agreement with certified values. The deviation was less than 1% and the uncertainty of measurement was less than 5%. The uranium isotope ratio of single particles with diameters of about 50 μm was measured by scanning electron microscopy (SEM) combined with LIMS. According to our research, LIMS has demonstrated promising uses in uranium isotope analysis in nuclear forensics and nuclear safeguards.

The use of carbon dioxide as the reaction cell gas for the separation of uranium and plutonium in quadrupole inductively coupled plasma mass spectrometry (ICP-MS) for nuclear forensic samples

The use of carbon dioxide (CO2) as a reaction cell gas for separation and trace analysis of uranium and plutonium by inductively coupled plasma mass spectrometry was investigated. For the analysis of the resultant UO2+ product ion, it was shown that quantitative determination of uranium concentration was achievable within ± 7% uncertainty for samples containing plutonium. In addition, uranium isotope ratios were measured within ± 12% for standard reference materials of several enrichments. This was achieved in both nitric acid and digested cellulose filter paper solutions—a common nuclear forensic sample substrate. However, non-linearity and long term signal instability was observed for plutonium at the high flow rate of CO2 and tuning parameters required to minimise uranium interferences. Therefore, plutonium analysis was not achievable.