Uranium Isotope Ratios Research Articles

Chernobyl fuel microparticles: uranium oxidation state and isotope ratio by HERFD-XANES and SIMS

Chernobyl fuel microparticles: uranium oxidation state and isotope ratio by HERFD-XANES and SIMS

Exploration of metallic interferences pertinent to nuclear safeguards related uranium isotope ratio measurement on the Neoma MC-ICP-MS platform without the MS/MS option

In this paper we present basic observations regarding the formation and effect of various polyatomic metallic interferences (combinations of Pb, Al, Si, Mo, W, Fe, Sn, Ti, Ba, and Pt) on uranium isotopic ratios measured via a new Multi Collector – Inductively Coupled Plasma – Mass Spectrometer (MC-ICP-MS) platform: The ThermoFisher Scientific™ Neoma® (without the MS/MS® collision cell option). Our approach is to dope a uranium isotopic standard (IRMM-2020) with various quantities of the metallic elements, all of which have been previously identified as posing isobaric interferences during uranium isotope measurement, and then perform analyses in solution mode and by laser ablation (LA) MC-ICP-MS. As expected, there is considerable variability between the different elementally doped solution and the degree of perturbation exhibited by the uranium isotope standard. However, Pt appears to induce the most drastic shift for 234U/238U, 235U/238U, and 236U/238U. One unexpected result is that the presence of Pb, whether alone or in combination with Al and Si, appears to result in a reduction of the expected uranium signal. This effect was observed (and re-confirmed using a different cup configuration) on the Neoma® MC-ICP-MS during wet plasma analysis, but was not observed during dry plasma conditions (e.g. laser ablation sampling of dried IRMM-2020 containing Pb). Furthermore, the phenomenon was also not observed during dry plasma analysis on a NeptunePlus®. Further experiments will be necessary to fully understand the origin of this signal attenuation, and the results of our study highlight the need for continued investigation of the polyatomic interference issue as new MC-ICP-MS platforms are developed since our results clearly demonstrate that they can drastically skew the observed isotope ratios in sometimes unexpected directions. Lastly, the use of N2 during LA sampling appears to slightly increase the magnitude of the interferences compared to when only Ar is utilized as the carrier gas. This observation further highlights the importance of plasma conditions on interference formation.

Comparative evaluation of uranium isotope ratios by peak-jumping and static multi-collector measurements in thermal ionization mass spectrometry

The 235U/238U isotope ratios of uranium standard reference materials and an environmental uranium sample recovered from seawater were measured by thermal ionization mass spectrometry using the single-collector peak-jumping and static multi-collection modes. All the 235U/238U isotope ratios measured in the peak-jumping mode were systematically lower than the values obtained in the static measurements. The lowering of the measured isotope ratios became more remarkable with the decrease in the 235U isotopic abundance, resulting in the maximum 2.2‰-lower value comparable to isotope mass fractionation. The lowering of isotope ratios is not due to the apparent loss of 235U ion currents caused by the time constant of the Faraday amplifier used but attributable to the actual decrease of ion currents by ion-beam changes in the mass switching step of peak-jumping mode. Furthermore, the proper collection of ion beams to the Faraday cup was achieved by allowing sufficient delay time for eliminating the effect of ion-beam changes, which was significantly longer than the time needed for the response of the amplifiers.

Application of ATONA Amplifiers to the Measurement of Uranium Isotopic Ratios by Thermal Ionization Mass Spectrometry.

Uranium isotopic composition can provide valuable information about the history and provenance of a nuclear material; therefore, uranium isotopic analyses are frequently made in the nuclear forensics, safeguards, and environmental monitoring communities. These measurements have always presented challenges due to the extreme variability in the relative abundance between the major (235U, 238U) and minor (233U, 234U, 236U) isotopes of uranium. The recently developed ATONA (Atto- to Nano-Amp) amplification system paired with Faraday cup detectors has a large dynamic range and low noise floor making it ideal for measuring uranium isotopic ratios in materials of both natural and anthropogenic origin. A wide variety of certified reference materials were analyzed to investigate the utility of the ATONA amplification system for determining uranium isotopic composition in samples ranging from depleted to highly enriched. The ATONA amplifiers provide nearly an order of magnitude improvement in external reproducibility over 1011 Ω amplifiers when measuring the minor 234U/238U ratio in isotopically natural and depleted samples and when paired with a secondary electron multiplier can measure very low relative abundance uranium isotopes (i.e., 236U).

Investigation of potential polyatomic interferences on uranium isotope ratio measurements for the LS-APGD-Orbitrap MS system

The determination of actinide (e.g., U and Pu) content and isotopics is of importance to the nuclear forensics and safeguards communities. However, in the analysis of environmental samples, such as those collected by the International Atomic Energy Agency, uranium measurements can be complicated by isobaric interferences from polyatomic variants of heavy elements (e.g., Pb). This leads to complex, time-consuming sample manipulations (i.e., separations) before determining isotope ratios. An alternative strategy to sample pretreatment is to use high-resolution mass spectrometric platforms during the analysis to fully resolve the uranium isotopes from potential polyatomic interferences, negating the need for prior chemical separation. The liquid sampling - atmospheric pressure glow discharge (LS-APGD) coupled with an Orbitrap mass spectrometer provides a high-resolution (>70,000 m/Δm at m/z 200) inorganic mass spectrometry platform. As a demonstration of the power of this instrumental platform, and indeed, the high-resolution approach in general, uranium isotope ratios were determined in the presence of elemental impurities (e.g., Pb, Pt, Ta, W) commonly encountered with environmental sample swipe analysis, without any prior treatment. Even at elemental impurity concentrations of 1000–5000× relative to uranium, no interference was observed with the 235U or 238U signal. In addition, the 235U/238U isotope ratio for the samples with the concomitants present are within 2 standard deviations of the values obtained without their addition, indicating that these impurities do not impact the determined uranium isotope ratio. These findings represent a significant first step in leveraging the high resolution of the LS-APGD-Orbitrap-MS to overcome isobaric and molecular interferences instead of relying on chemical separations.

Assessment of the radiation quality of groundwater with an increased uranium isotope ratio 234U/238U (Pre-Volga region, European Russia)

Assessment of the radiation quality of groundwater with an increased uranium isotope ratio 234U/238U (Pre-Volga region, European Russia)

Quantifying uranium radio-isotope ratios in riverine suspended particulate matter: Insights into natural and anthropogenic influences in the glacial-fed river system of the NE Tibetan Plateau

The analysis of uranium isotope ratio 235U/238U in environmental media serves as a reliable method to distinguish between natural and anthropogenic sources of uranium, playing a crucial role in assessing the extent of contamination with anthropogenic uranium and disturbances in its biogeochemical cycle. In this study, we focus on the northeastern Tibetan Plateau to examine the atomic ratio of 235U and 238U in riverine suspended particulate matter (SPM) across eight glacial watersheds. Results reveal that the 235U/238U atomic ratio in the suspended load ranges from 0.007247 to 0.007437 (with an average value of 0.00727 ± 0.00003), which closely aligns with the ratio found in natural uranium (0.00725). The highest mean ratio (0.00729 ± 0.00007) is observed in the upper glacial basin of the Ningchan River. Results suggest the negligible influence of isotopically altered in relation to human nuclear activities. When considering different environmental media, such as soil, snow/cryoconite, and riverine suspended particulate matter in the study area, the 235U/238U ratio in surface soil presents the highest values, pointing to a slight enrichment of 235U. This may be attributed to the fact that soil retains the cumulative signals of uranium atmospheric deposition, including the deposition of 235U-enriched airborne particulate matter deposited after atmospheric nuclear tests carried out in the second half of the 20th century. On the contrary, riverine suspended particulate matter and glacial sediments are more influenced by the natural 235U/238U signature under modern environmental conditions. This confirms that the northeastern Tibetan Plateau is still relatively pristine with respect to biogeochemical disturbances related to human activities.

Anthropogenic influence on groundwater geochemistry in Horn Creek Watershed near the Orphan Mine in Grand Canyon National Park, Arizona, USA

Breccia pipe deposits of the Grand Canyon region contain ore grade copper and uranium. Horn Creek is located near the Orphan Mine mineralized breccia pipe deposit, and groundwater emerging from the bedrock in the headwaters of Horn Creek has the highest uranium concentrations in the region. Uranium decreases an order of magnitude between the groundwater at the top of the watershed and the groundwater emerging from the alluvial material lower in the watershed. Horn Creek water has low sulfur and uranium isotopic ratios which may suggest interaction with sulfide and uranium minerals found in mineralized breccia pipe deposits. Per- and polyfluoroalkyl substances were found in low concentrations in groundwater from the bedrock and may be related to mining process materials or other anthropogenic activities. PHREEQC modelling suggests that water that is elevated in uranium emerging from the bedrock in the upper watershed may mix with other groundwater and atmospheric precipitation infiltrated into the alluvial material in the lower watershed. Tritium is elevated in Horn Creek groundwaters, suggesting a component of modern water, some of which may have interacted with Orphan Mine workings. Additional studies could build on this understanding of chemistry changes in the waters of Horn Creek to provide more direct evidence of the contribution of water moving through the Orphan Mine. Supplementary material: Chemical data for this paper are available at https://doi.org/10.5066/F7P55KJN , PHREEQC geochemical simulations are available at https://doi.org/10.5066/P9X17FKG and groundwater chemistry from south of Grand Canyon, AZ is available at https://doi.org/10.6084/m9.figshare.c.6747638 Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits

Substantial incorporation of isotopically heavy reduced U species into marine carbonate sediments

The uranium (U) isotope ratio (238U/235U, reported as δ238U) in marine carbonates is an important proxy for reconstructing changes in past oceanic redox conditions, based on the essential assumption that U in carbonates originates from dissolved U(VI) in seawater. However, diagenetic processes may induce the addition of isotopically heavy U(IV) into the carbonates, complicating the application of the U isotope proxy. So far, the valence states of trace amounts of U and its relation with U isotope composition in marine carbonate sediments have not been directly studied. In this study, we have calibrated an ion-exchange chromatographic method to separate U(IV) from U(VI) in geological carbonate samples (e.g., modern and fossil corals, stalagmites, cold seep carbonates) and quantified their contents by mass spectrometry. Our study confirms that modern coral carbonates are faithful archives of U(VI) sourced from seawater. Surprisingly, drill core samples from a modern coral carbonate platform, which bear no sign of alteration inferred from conventional diagenetic proxies (e.g., Mn/Sr), show significant positive correlation between U(IV) fraction and bulk carbonate δ238U, suggesting U(IV) is present in the marine carbonates and drives δ238U toward higher values than that of seawater. We therefore suggest that coupled valence and isotope analyses of U in marine carbonates could provide critical constraints toward reliable reconstruction of marine redox evolution in the Earth’s history.

Faraday detector uranium isotope ratio measurement: Insights from solution- and laser ablation-based sampling methodologies on the Neoma MC-ICP-MS

In this study we utilize an all-faraday cup detector configuration on the Neoma MC-ICP-MS to perform uranium isotope ratio determinations from certified reference materials and a nuclear fuel precursor material via solution and laser ablation based sampling methodologies. The goal in performing these measurements is primarily to demonstrate that the all-faraday cup method can produce highly precise and accurate isotope ratios even at relatively low signal intensity levels while also developing a preliminary understanding of how the complex interplay between different amplifier resistor levels (e.g. 1011 vs 1013 Ω) and integration times impacts the precision and accuracy of different types of measurements. Our results show that the faraday cups with 1013 Ω resistors in their amplifier feedback loops can be used to produce accurate and relatively precise isotope ratios for ion beams down to ∼5 K cps. However, at the lower end of the signal intensities observed in this study, longer integration times are necessary to mitigate the impact of ion beam instability that can occur during laser ablation based sampling. Despite this potential limitation, the all-faraday cup method is highly versatile as exemplified by the analysis of a collection of uranium reference materials with highly variable uranium isotopic compositions.

Initial Characterization and Optimization of the Liquid Sampling-Atmospheric Pressure Glow Discharge Ionization Source Coupled to an Orbitrap Mass Spectrometer for the Determination of Plutonium.

Plutonium measurements are essential to the nuclear forensics and safeguards community. The liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma ionization source coupled with an Orbitrap mass spectrometer is a proven platform for uranium isotope ratio determinations. This work expands the LS-APGD-Orbitrap platform capabilities by reporting the first-ever analysis of plutonium with the LS-APGD and the first-ever measurement of elemental plutonium with an Orbitrap mass spectrometer. This coupling has the potential to dramatically reduce the complex sample manipulations required for traditional analysis techniques employed for actinide isotope ratio determinations. As a first step toward the goal of simultaneous uranium and plutonium isotope ratio determinations, the initial characterization and optimization of the platform for the detection of plutonium are reported. Collision-induced dissociation modality settings were optimized to reduce water-related and other molecular clusters containing plutonium, maximizing 242Pu16O2+ responses. A design of experiments study was conducted to optimize the discharge conditions of the dual-electrode LS-APGD toward the responsivity of 242Pu16O2+. The measurement sensitivity was determined from a Pu response curve, yielding a limit of detection of 10 fg (absolute) of total analyte when data was collected and processed with a Spectroswiss FTMS Booster X2 data acquisition system. Additionally, plutonium and uranium were measured in a simultaneous acquisition, and each analyte remained unaffected by the other. It is believed that the LS-APGD-Orbitrap platform could be a valuable addition to the nuclear forensics' toolbox and, indeed, other scientific disciplines and regulatory communities in which rapid, high-resolution plutonium determinations are paramount.

Rare Earth Elements Geochemistry and 234U/238U, 235U/238U Isotope Ratios of the Kanyakumari Beach Placer Deposits: Occurrence and Provenance

Geochemical studies of rare earth elements (REEs) as well as major and trace elements were conducted on the beach placer sands from the Kanyakumari coastal region, a well-known high background natural radiation area (HBNRA). For the first time, uranium isotope ratios (234U/238U and 235U/238U) were determined in the study area to investigate the provenance and leaching of U from the beach sands. Inductively coupled plasma mass spectrometry was used for the measurement of REEs and trace elements whereas thermal ionization mass spectrometry (TIMS) was used for the measurement of U isotope ratios. ∑REEs were found to be in the range of 778.93 to 15,007. 54 µg/g, whereas ∑Light REEs were in the range of 770.58 to 14,860.80 µg/g and ∑Heavy REEs varied from 8.35 to 146.74 µg/g. The enrichment factor showed the LREEs Th and U were extremely enriched in the Kanyakumari beach placer sands. The 235U/238U isotope ratios were similar to the natural terrestrial ratio value. The 234U/238U activity ratio varied from 0.995 to 1.071, and showed the prevailing secular equilibrium among them. The δ238U results could, to some extent, explain the U fractionation and source.

Preliminary investigation of an uncertainty budget for uranium isotope ratio analysis using a liquid sampling—atmospheric pressure glow discharge—orbitrap mass spectrometer system

Preliminary investigation of an uncertainty budget for uranium isotope ratio analysis using a liquid sampling—atmospheric pressure glow discharge—orbitrap mass spectrometer system

Uranium Isotope Ratios of Twenty‐nine Geological Rock Reference Materials Measured by MC‐ICP‐MS

Uranium isotope ratios are reported for twenty‐nine geological reference materials (RMs) including igneous, metamorphic and sedimentary rocks, as well as sediments. Measurements were conducted on a multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS) using the 233U‐236U double spike technique. These RMs possess a wide range of matrices with U mass fractions ranging from 0.11 μg g‐1 to 18.7 μg g‐1. The δ234/238U values (relative to the n(234U)/n(238U) ratio at secular equilibrium) show minor fluctuations around the secular equilibrium value except for two Pleistocene speleothem RMs. The δ238/235U values (relative to the value for NBL CRM 112a (NBS SRM 960)) of igneous rocks and metamorphic rocks are within the range of the continental crust value (‐0.29 ± 0.03‰, 95% CI). The δ238/235U value for sedimentary rock and sediment RMs spans a wide range of 0.98‰, suggesting significant 238U/235U isotopic fractionation in low temperature environments. The range of δ238/235U RMs reported in this study (‐0.63‰ to 0.35‰) exceeds that of previous RMs (‐0.61‰ to 0.17‰), allowing inter‐laboratory calibration of wider ranges of geological and environmental samples.

Oceanic redox conditions during the terminal Cambrian extinction event

Marine animal diversity during the late Cambrian was reduced by a series of extinctions that have generally been attributed to oceanic anoxic events associated with positive carbon isotope excursions. Here we present carbon and uranium isotope ratios (δ13C and δ238U values) as proxies for global carbon cycle and oceanic redox conditions, respectively, from carbonate rocks of the Wa'ergang section, South China. The dataset spans an interval that includes the last major negative δ13C excursion (TOCE) of the Cambrian Period. The TOCE is a globally documented event, recovery from which corresponds to the terminal Cambrian extinction event. The δ13C and δ238U values covary through the section, shifting initially to lower values, with δ238U falling below the modern open-ocean seawater value from the start to the middle of the profile, followed by a shift to higher values towards the end of the Cambrian. Neither the co-occurrence of δ13C and δ238U negative excursions, nor the association of rising δ238U with extinction have been commonly reported. Here we argue that robust positive coupling of δ13C and δ238U relates to the existence of extensive intermediate reducing settings (from low-O2 suboxia to intermittent anoxia) during the late Cambrian alongside low atmospheric pO2 and a greenhouse climate. Similarly, a stepwise increase in the δ238U baseline in carbonates across the Ediacaran−Cambrian boundary is consistent with the growing importance of an intermediate reducing sink through that interval. We propose further that divergent trends in lower and upper ocean redox conditions could have driven the parallel isotope excursions. An expansion of intermediate reducing conditions, rather than persistent anoxic euxinia, is consistent with the recovery of δ13C and δ238U to higher values, as well as the presence of benthic fauna and shoreward extension of deeper-water fauna that may have had a greater tolerance against hypoxia.

Controls on Speleothem Initial 234U/238U Ratios in a Monsoon Climate

AbstractSpeleothem initial uranium isotope ratios ((234U/238U)i) can be influenced by processes along the seepage water flow‐path including alpha‐recoil into porewater during 238U decay and hostrock weathering, the balance of which can reflect the infiltration rate. Thus, speleothem (234U/238U)i may provide information about past changes in rainfall amounts. However, the utility of (234U/238U)i as a paleo‐infiltration proxy has only been explored in a limited set of rainfall regimes. We present a speleothem (234U/238U)i record from Mawmluh Cave in northeast India, an area influenced by the Indian Summer Monsoon, covering 1964–2012 CE. Speleothem (234U/238U)i was relatively constant from 1964 to 1984 but then linearly increased by 0.05 over ∼15 years, a trend that does not correspond with observed rainfall changes. To evaluate potential drivers of (234U/238U)i variability, we model the evolution of water (234U/238U) in a simple karst system using an advection‐reaction model parameterized by Mawmluh Cave variables. Although varying infiltration influences modeled water (234U/238U), the larger, sustained change observed in the speleothem record can only be modeled by varying the U concentration and (234U/238U) of the weathering hostrock. This suggests that larger shifts in speleothem (234U/238U)i may result from flow path changes, bringing waters in contact with hostrock of variable U characteristics. Consideration of published Mawmluh Cave records suggests that these mechanisms may also explain variability in stalagmite (234U/238U)i on precessional timescales. Further examination of speleothems (234U/238U)i from climates characterized by high rainfall and extensive weathering is warranted to better constrain the controls on (234U/238U)i in these dynamic environments.

234U/238U disequilibrium and 235U/238U ratios measured using MC-ICP-MS in natural high background radiation area soils to understand the fate of uranium

The Chhatrapur-Gopalpur coastal area in Odisha, India is a well-known natural high background radiation (HBRA) area due to the abundance of monazite (a thorium bearing radioactive mineral) in beach sands and soils. Recent studies on Chhatrapur-Gopalpur HBRA groundwater have reported high concentrations of uranium and its decay products. Therefore, the soils of the Chhatrapur-Gopalpur HBRA are reasonably suspected as the sources of these high uranium concentrations in groundwater. In this report, first the uranium concentrations in soil samples were measured using inductively coupled plasma mass spectrometry (ICP-MS) and they were found to range from 0.61 ± 0.01 to 38.59 ± 0.16 mg kg−１. Next, the 234U/238U and 235U/238U isotope ratios were measured to establish a baseline for the first time in Chhatrapur-Gopalpur HBRA soil. Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) was used for measurement of these isotope ratios. The 235U/238U ratio was observed to be the normal terrestrial value. The 234U/238U activity ratio, was calculated to understand the secular equilibrium between 234U and 238U in soil and it varied from 0.959 to 1.070. To understand the dynamics of uranium in HBRA soil, physico-chemical characteristics of soil were correlated with uranium isotope ratios and this correlation of 234U/238U activity ratio indicated the leaching of 234U from Odisha HBRA soil.

Comparison of AMS, TIMS, and SIMS techniques for determining uranium isotope ratios in individual particles.

The determination of isotope ratios in individual uranium particles is very important for nuclear safeguards. In this work, accelerator mass spectrometry (AMS), thermal ionization mass spectrometry (TIMS), and secondary ion mass spectrometry (SIMS) were applied to isotope ratio analysis of individual uranium particles and compared in terms of background, measurement accuracy, and efficiency. Several individual uranium particles (1-7μm) from certified reference materials were used as samples. The results show that the average values of blank counting rate of 235 U for AMS, FT-TIMS (FT: fission track), SEM-TIMS (SEM: scanning electron microscope), and SIMS were 7.3, 7.8, 2.7 and 2.2cps, respectively. The relative error of 234 U/235 U and 234 U/236 U isotope ratios of the particles from U200 for AMS were within 10% and 20%, whereas the results of FT-TIMS and SIMS were within 5% and 10%, respectively. The relative error and external precision of 234 U/238 U and 235 U/238 U of the particles from U850 for the method of AMS, SEM-TIMS, and SIMS were within 10% and 5%, respectively. For 236 U/238 U, the average values of the relative error and external precision measured by AMS were within 5%, which measured by SEM-TIMS and SIMS were all within 10%. AMS has advantages in measuring 236 U/238 U. The measurement time of AMS and SEM-TIMS was shorter than that of FT-TIMS and longer than that of SIMS. It is considered that AMS and SEM-TIMS have a certain development prospect, and it is necessary to research deeply.

Determination of uranium isotopes in marine sediments and seawaters by SF ICP-MS after rapid chemical separation using TK200 resin.

This work provided a novel analytical procedure for rapid and precise uranium isotopic determination in marine sediment and seawater, using a new type of extraction resin, TK200 resin, in combination with microwave digestion (for marine sediments), Fe(OH)3 co-precipitation (for seawater), and single collector sector field-inductively coupled plasma mass spectrometry (SF ICP-MS) measurement. The removal ability of TK200 extraction chromatography for the interfering elements (IEs) Hg, Pb, Th, Pt, Tl, and the matrix rare earth elements (REEs) was carefully investigated. High decontamination factors (DFs) were obtained for IEs and REEs. Accurate quantification of uranium isotope ratios was accomplished based on a "double-cycle" ICP-MS measurement method. The analytical method was optimized and validated with isotopic standards (IRMM-187), matrix-containing certified reference marine sediments (IAEA-384, IAEA-385, and IAEA-412), and seawater reference material (IAEA-443). A stable chemical recovery of ~ 90% was obtained for both types of marine environmental samples, and the method showed great efficiency with a total analytical time of less than 6h. The proposed procedure was validated following ISO/IEC 17025 guidelines. The important factors affecting the isotope ratio results (instrument background, procedural blank, memory effects, peak tailing, mass discrimination, dead time, and hydride interferences) were considered in the estimation of combined uncertainties. This work provides an alternative way for the determination of trace uranium isotope ratios and can be applied in the emergency monitoring of nuclear accidents and marine environmental analysis.

Coupling of the Liquid Sampling-Atmospheric Pressure Glow Discharge to Orbitrap Mass Analyzers for Uranium Isotope Ratio Analysis: Evolution of the Methodology and Implications to the Field.

Just over a decade ago, a truly outside-of-the-box approach to isotope ratio mass spectrometry (IRMS) was undertaken between research groups at Clemson University and the Pacific Northwest National Laboratory. The original motivation dealt with projections as to whether or not microplasmas could be developed into practical elemental ionization sources, perhaps for transportable analysis applications. In particular, the use of the liquid sampling-atmospheric pressure glow discharge (LS-APGD) was pursued. Its interfacing to an ultra-high resolution Orbitrap platform, proved not only facile, but opened up a wealth of potential applications. Here, we lay out a historical, tutorial description of the interfacing and the evolution of the methodology regarding IRMS of uranium. Practical challenges and opportunities are described, which hopefully provide guidance to further applications in high resolution IRMS. It is hoped that, while detailed and lengthy, the didactic nature of the presentation provides experimental insights and tips, and also serves as an homage to our very good friend, Professor Gary M. Hieftje, whose scientific inspiration and comradery have been immeasurably important in our own careers.