Isotope Measurements Research Articles

An inversion model for burnup history of spent fuels in pebble bed HTGR based on optimization algorithm

The measurement of transuranic isotopes in spent nuclear fuel is a crucial technique for nuclear material accounting and nuclear non-proliferation. In a pebble bed high-temperature gas-cooled reactor, numerous fuel spheres circulate through the reactor core multiple times, making it unfeasible to document the power histories of individual fuel spheres. This complexity renders it impossible to employ traditional methods, such as solving the forward burnup equations used in conventional reactors, to calculate the transuranic isotopes.In this approach, optimization algorithms were coupled with the data obtained from the BUrnup Measurement System to establish a power history inversion model, which was used to solve for the power history of fuel spheres and subsequently calculate the transuranic isotopes.The paper also compared the pros and cons of coupling the inversion model with different optimization algorithms and evaluated models using various schemes of activity vector. This process helped determine the most suitable optimization algorithm and scheme of activity vector. Sensitivity analysis revealed that the established inversion model exhibited a degree of tolerance to noise in input data and the underlying physical model.

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.

Oxygen diffusion coefficient in the γ phase of a TiAl GE alloy determined by SIMS

First reliable experimental oxygen diffusion coefficient data have been obtained in a Ti48.3Al47.7Cr1.9Nb2.1 near-γ GE alloy through secondary ion mass spectrometry (SIMS) depth profiling measurements of 18O isotopes between 500 °C and 700 °C. The following expression of diffusion coefficient D has thus been derived: D(m2/s)=10−10.6±1∙exp(−107±10kJ.mol−1/RT). These data have been compared with theoretical calculations from literature, showing reasonable agreement concerning the activation energy, but significant discrepancy regarding the D values.

Exploring Burial and Dietary Patterns at the Copper Age Necropolis of Selvicciola (Viterbo, Italy): New Perspectives from 14C and Stable Isotope Data

The Selvicciola necropolis is a large burial site dated to the Copper Age, located on the mid-Tyrrhenian side of Central Italy, in the Fiora river valley. Despite post-depositional disturbances, 32 prehistoric tombs were found, generally in a good state of preservation, with a total number of 119 individuals identified. In the present study, radiocarbon and stable isotope measurements on bone collagen are combined with skeletal data for 71 of these individuals. We aim to investigate possible changes in food practices and burial patterns throughout time. In detail, the results allowed us to define a timeframe for the use of the cemetery of at least 2000 years, with the two most ancient individuals found in tomb 17 and dated to around 3950 cal BC, assigning this a necropolis chronological investigation of the so-called Rinaldone culture. Stable carbon and nitrogen isotope analysis confirmed a predominantly agropastoral subsistence strategy for this prehistoric community. Although the plant intake consisted mainly of C3 species, we further discuss the fact that the stable isotope data suggest an increase in the consumption of C4 plants over time. The integration of radiocarbon and isotopic data with the skeletal evidence and material culture provides an interesting insight into the funerary world of this community, highlighting the importance of Selvicciola for the understanding of life in the Mediterranean at the transition between the fourth and the third millennia BC.

Unravelling instrumental mass fractionation of MC-ICP-MS using neodymium isotopes

Since the initial discovery of the non-exponential mass fractionation (non-EMF) of Nd isotopes analysis in 2002, similar deviations from an EMF pattern have been reported for measurements of a number of isotope systems (e.g., Si, Ge, Sr, Sn, Ba, Yb, W, Os, Hg and Pb) with MC-ICP-MS. However, the previous controversial reports on the magnitude of the deviations from EMF suggest that instrumental mass bias behaviour of MC-ICP-MS is neither fully understood nor well-characterised. Consequently, the standard approach of using a mass dependent fractionation (MDF) correction model (e.g., exponential law) may lead to both inaccurate and imprecise results. In this study, we systematically characterise the instrumental mass fractionation of MC-ICP-MS using Nd isotope measurements carried out under different plasma conditions, quantified using the normalised argon index (NAI) as an estimate of plasma temperature. Our results indicate that the mass bias of MC-ICP-MS is not always a simple exponential function of mass but shows systematic deviations from an EMF behaviour, which are closely associated with decreased NAIs. As a result, the conventional exponential correction yields a 143Nd/144Nd value of 0.512257 for the reference material BHVO-2 when the NAI is low, which is 722 ppm lower than the reported value of 0.512979. By tuning the plasma to higher NAIs (higher plasma temperatures), the deviations from the EMF array are systematically attenuated and the exponential correction is able to correct for the instrumental mass bias under high NAIs. In contrast, a regression correction model for Nd isotopes is developed to account for the observed mass fractionation behaviour that does not follow EMF under low NAIs, given that the regression correction relies on the observed loglinear fractionation of different isotope pairs and does not require both isotope ratios to undergo EMF. We expect that the analytical protocol and fundamental insights gained in this study are applicable to a wide range of other isotope measurements with MC-ICP-MS.

Simultaneous measurement of 13C-,18O-, and 17O- isotopes of CO2 using a compact mid-infrared hollow waveguide gas sensor

A compact gas sensor has been developed for the first time employing a quantum cascade laser (QCL) with a central wavelength of 4.32 μm, combined with direct absorption spectroscopy technology and a hollow waveguide. The sensor could measure the concentrations of four isotopic molecules (16O12C16O, 18O12C16O, 16O13C16O, and 17O12C16O) in CO2 gas simultaneously, thereby obtaining the relative isotope ratios of δ13C, δ18O, and δ17O. By adjusting the incident light path, the anomalous absorption peaks in the system have been effectively suppressed, and a compact feedback function generator has been integrated to ensure control of the laser output wavelength to eliminate the loss of measurement precision caused by wavelength fluctuations. Under the two conditions of free-running and wavelength-controlled, a standard CO2 sample with a concentration of 5 % was measured continuously. The results showed that under wavelength-controlled conditions, the precision of the four isotopic molecule concentration measurements was improved by a minimum of 1.8 times, and the measurement precision could be further improved after filtering. According to the Allan variance analysis, the detection precision for δ13C, δ18O, and δ17O were 0.7 ‰, 0.62 ‰, and 1.58 ‰, respectively, at the optimal integration time of 98 seconds. This study has the potential for respiratory diagnosis to detect simultaneously the values of δ13C, δ18O, and δ17O in exhaled samples.

Determination of silicon isotopic composition in soil using gas-source isotope ratio mass spectrometry by thermal decomposition of barium hexafluorosilicate

Determining the Si isotopic compositions of samples of the Earth’s surface is crucial to understanding the implications of the biogeochemistry cycling of Si. This study established an alternative method for high-precision Si isotopic measurement in soil samples using gas-source isotope ratio mass spectrometry, which involved the conversion of Si in the samples into SiF4 gas, which was purified cryogenically and collected for isotopic analysis. The proposed method was applied to determine the Si isotopic composition of two reference materials (GBW04421 and GBW04422), and the results were found to be in good agreement with the certified values. Moreover, the proposed method exhibited a long-term measurement precision of 0.05 ‰–0.08 ‰ (2 s) for the δ30Si values. The δ30Si values obtained from ten soil reference materials ranged from −1.84 ‰ to −0.17 ‰, which were within the range of the values reported in the literature (−1.82 ‰ to −0.15 ‰). The sample preparation and analysis method in this study provided an easy and effective approach to determining the Si isotopic composition of solid samples and offers to the promise of being applicable to biogeochemical analyses of the Earth’s surface processes.

Introducing Isotòpia: A stable isotope database for Classical Antiquity.

We present Isotòpia, an open-access database compiling over 36,000 stable isotope measurements (δ13C, δ15N, δ18O, δ34S, 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 207Pb/206Pb, and 208Pb/206Pb) on human, animal, and plant bioarchaeological remains dating to Classical Antiquity (approximately 800 BCE - 500 CE). These were recovered from different European regions, particularly from the Mediterranean. Isotòpia provides a comprehensive characterisation of the isotopic data, encompassing various historical, archaeological, biological, and environmental variables. Isotòpia is a resource for meta-analytical research of past human activities and paleoenvironments. The database highlights data gaps in isotopic classical archaeology, such as the limited number of isotopic measurements available for plants and animals, limited number of studies on spatial mobility, and spatial heterogeneity of isotopic research. As such, we emphasise the necessity to address and fill these gaps in order to unlock the reuse potential of this database.

Condensation of refractory minerals on igneous compact type A Ca‐Al‐rich inclusion from Northwest Africa 7865 CV chondrite

AbstractA melilite‐rich, compact type A Ca‐Al‐rich inclusion (CAI), KU‐N‐02, from the reduced CV3 chondrite Northwest Africa 7865, is mantled by an åkermanite‐poor layer. We carried out a combined study of petrographic observations and in situ O and Al–Mg isotopic measurements for KU‐N‐02. The core shows a typical texture of igneous compact type A CAIs. The mantle consists of spinel, åkermanite‐poor melilite, and perovskite. Individual mantle melilite crystals show reverse zoning toward the crystal grain boundary, in contrast to core melilite crystals showing normal zoning. The O isotopic compositions of the minerals in KU‐N‐02 plot along the carbonaceous chondrite anhydrous mineral line on a three O‐isotope diagram. The mantle and core spinel crystals are uniformly 16O‐rich (Δ17O ~ −23‰). The mantle melilite crystals exhibit variable O isotopic compositions ranging between Δ17O ~ −2‰ and −9‰, in contrast to the uniformly 16O‐poor (Δ17O ~ −2‰) core melilite. The mantle melilite crystals also exhibit variable δ25Mg values (δ25MgDSM‐3 ~ −2‰ to +3‰) compared with the nearly constant δ25Mg values of the core melilite (δ25MgDSM‐3 ~ +2‰). The mantle minerals are likely to have formed by condensation from the solar nebular gas after core formation. The Al–Mg mineral isochrons of the core and mantle give initial 26Al/27Al ratios of (4.66 ± 0.15) × 10−5 and (4.74 ± 0.14) × 10−5, respectively. The age difference between the core and mantle formation is estimated to be within ~0.05 Myr, implying that both melting and condensation processes in the variable O isotopically solar nebular environments occurred within a short time during single CAI formation.

Influence of the type of fuel used on the content of gamma radionuclides in the soot from the smoke ducts of the home furnaces

Abstract This paper presents the results of the measurements of gamma radioactive isotopes in soot samples from 15 different chimneys of household furnaces fired with various types of solid fuel. Soot samples were collected by the chimney sweep during the mandatory periodic cleaning of the chimneys. The γ-spectrometry technique using the high-purity germanium (HPGe) detector was employed for radiometry of the above-mentioned soot. It was found that the determined activity of gamma isotopes in soot is at a level similar to that in fly ash from power plants around the world. Artificial 137Cs was detected only in the soot from the combustion of biofuel or mixed fuel. The results obtained were chemometrically analyzed to find the relationship between the fuel used and the gamma isotope content in the soot. The analysis of 137Cs, 40K, 228Th, and 226Ra is sufficient to differentiate between the soot obtained and tested, and it varied with the fuel type burned (fossil fuels/biofuels).

A self-made tube cracker coupled to an EA-IRMS-AGE3 system

AbstractThe automatic graphitization system (AGE3) by IonPlus is very popular among radiocarbon dating laboratories. Usually, solid samples are burnt in an elemental analyzer (EA), and the gaseous CO2 is transferred for graphitization. Our system is coupled also with an isotope ratio mass spectrometer (IRMS), which measures the δ13C and δ15N of that gas. Some less routine pretreatment protocols require the production of gaseous samples and prevent the possibility of using the EA-AGE3 system, as the EA is used for solid samples only. In order to use that system, including the measurements of stable isotopes, we developed a glass tube cracker that connects to the EA. The device is routinely used in our laboratory and is mainly built from Swaglok catalog parts. We show that the background (blank) levels of a marble standard are indistinguishable between using the cracker and burning solid marble using the EA. We further demonstrate that the δ13C values are consistent and that the extraction efficiency when using the device is above 93%. Full descriptions, drawings, and working protocol are supplied.

Spring buds of European woody plants have old 14C age

Trees and shrubs maintain carbon reserves to support their functions during periods when metabolic demand exceeds carbon supply, such as during the dormant season. To gain a better understanding of carbon storage and utilisation dynamics of eight woody plant species in temperate Central Europe, bud scale and leaf samples were collected to determine the radiocarbon age of fresh sprouts in trees and shrubs, at three background sites avoiding local emissions that may influence affect the observed 14C/12C ratio. The accelerator mass spectrometry-based bomb-radiocarbon approach, to determine the age of the mobilized carbon in the plant bud samples from storage, was complemented by stable carbon isotope measurements. The bomb-radiocarbon dating technique was used to determine the age of the samples, while a northern hemispheric atmosphere 14CO2 dataset was used to calibrate the radiocarbon ages of the plant samples. The youngest observed calibrated radiocarbon age of the buds was over 4 years, and the oldest was even 9 years old. There was no significant difference between the ages of bud scales and embryonal leaf laminas. Our results show that there is a considerable amount of stored older carbon in the woody stems that can be used to produce buds in spring, which is a complex mixture of stored carbon of different ages, but there is no relationship between the radiocarbon age and the stable carbon isotope composition. The observed results show that not only the tree species, but shrubs also can store and use significantly older carbon pools, the carbon storage intensity is similar for trees with trunks and short-stemmed shrubs branching directly above the ground, i.e. carbon storage starts in young twigs and continues in ageing branches.

Reconstruction of Cenozoic δ11Bsw Using a Gaussian Process

AbstractThe boron isotope ratio of seawater (δ11Bsw) is a parameter which must be known to reconstruct palaeo pH and CO2 from boron isotope measurements of marine carbonates. Beyond a few million years ago, δ11Bsw is likely to have been different to modern. Palaeo δ11Bsw can be estimated by simultaneously constraining the vertical gradients in foraminiferal δ11B (Δδ11B) and pH (ΔpH). A number of subtly different techniques have been used to estimate ΔpH in the past, all broadly based on assumptions about vertical gradients in oxygen, and/or carbon, or other carbonate system constraints. In this work we pull together existing data from previous studies, alongside a constraint on the rate of change of δ11Bsw from modeling. We combine this information in an overarching statistical framework called a Gaussian Process. The Gaussian Process technique allows us to bring together data and constraints on the rate of change in δ11Bsw to generate random plausible evolutions of δ11Bsw. We reconstruct δ11Bsw, and by extension palaeo pH, across the last 65Myr using this novel methodology. Reconstructed δ11Bsw is compared to other seawater isotope ratios, namely , , and δ7Li, which we also reconstruct with Gaussian Processes. Our method provides a template for incorporation of future δ11Bsw constraints, and a mechanism for propagation of uncertainty in δ11Bsw into future studies.

Isotopic constraints on the late Pleistocene glacial water and sediment inputs to the central Arctic ocean

The Quaternary history of the Arctic Ocean reflects pronounced periodic changes in marine and glacial environments. This variability is an important component of the Arctic paleoclimatic system. For more insight, we use isotopic measurements on the detrital (Nd-Sr-Pb) and authigenic (Nd) phases of the Quaternary sediments from the central Arctic Ocean. We analyze core ICE4 from ∼3 km water depth off the Lomonosov Ridge. This core was previously studied for other sedimentary proxies (Dong et al., 2022). The analyzed record is estimated to cover major Late Pleistocene Weichselian/Wisconsinian glaciations occurring over the last ∼100–200 ka. Our results provide new evidence that glacially-derived waters from the glaciated margins reached the bottom of the deep Arctic basins. We infer that these waters were delivered to the deep basins by hyperpycnal flows originating from subglacial outbursts accompanying overflow meltwater and iceberg discharge during glacial/deglacial events. Voluminous outbursts during the older, presumed Early/Middle Weichselian glaciation, ca. 115-35 ka, are traced to the West Siberian margin impacted by the Eurasian Ice Sheet. Similar sedimentary layers are found in longer records from the central Arctic Ocean at older stratigraphic intervals. Sediments constrained to the Last Glacial Maximum have less pronounced glacigenic inputs with a stronger Laurentide Ice Sheet signature. The circulation patterns were likely dependent on the interplay of the timing and extent of the Laurentide and Eurasian ice sheets.

Precise measurement of Fe isotopes in marine and biological samples by pseudo-high-resolution multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS).

This paper introduces an enhanced technique for analyzing iron isotopes in complex marine and biological samples. A dedicated iron purification method for biological marine matrices, utilizing three ion exchange columns, is validated. The MC-ICPMS in pseudo-high-resolution mode determines precise iron isotopic ratios, with sensitivity improved through the DSN-100 desolvating nebulizer system and Apex-IR. Only 2µg of iron on DSN versus 1µg on Apex is needed for six replicates (30-60 times improvement) while 10 to 20µg is required for a single measurement on awet system considering the resolution power (Rp) is maintained at 11,000-13,000. The Ni-doping method with a Fe/Ni ratio of 1 yields more accurate isotopic ratios than standard-sample bracketing alone. Measurement reproducibility of triplicate samples from marine biological experiments on MC-ICPMS is ± 0.03‰ (2SD) for δ56Fe and ± 0.07‰ for δ57Fe (2SD). This study introduces a novel iron purification process specifically designed for marine and biological samples, enhancing sensitivity and enabling more reliable measurements with smaller sample sizes and reduced uncertainties. It proposes iron isotopic compositions for biological reference materials, offering a valuable reference dataset in diverse scientific disciplines.

Optimizing Zr-doped MC-ICP-MS sample-standard bracketing to simultaneously determine 87Sr/86Sr and δ88Sr for high sample-throughput

In recent years, the increasing demand for extensive strontium (Sr) datasets across various scientific fields has prompted the development of fast, precise, and reliable protocols. These protocols aim to achieve high sample-throughput without compromising data quality. A novel method termed the zirconium (Zr) doped sample-standard bracketing (SSB) has been recently introduced for isotope measurements using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). This method allows for simultaneous acquisition of 87Sr/86Sr and δ88Sr data without the need for sample spiking. However, the reliability of this method in handling large datasets and ensuring long-term reproducibility requires additional documentation. A comprehensive examination of the reliability of Sr isotope data over two years involves the implementation of systematic tests on reference materials from the National Institute of standards and technology (NIST) with the standard reference material (SRM) numbers: 1400, 1515, 987, 2910b, 1486, as well as a Hawaiian volcano observatory basalt (BHVO-1). The results of this study lead to the definition of a set of quality control parameters. The developed protocol applies various controls to ensure precise matching of Sr and Zr concentrations for both the samples and the bracketing standard (NIST SRM 987), along with the identification of instrumental biases. The outlined quality control ensures the reproducibility of the results (87Sr/86Sr = 0.710247 ± 0.000026, 2SD, n = 557; and δ88Sr = 0.001 ± 0.053 ‰, 2SD, n = 537 for NIST SRM 987), proving invaluable for archaeological, geological, and ecological studies requiring the fast acquisition of extensive datasets (n > 100) to create isotopic baselines.

Lower crustal control in the iron isotope systematics of plutonic xenoliths from Adak Island, Central Aleutians, with implications for arc magma geochemistry

We present bulk-rock and mineral Fe isotope data of ultramafic to mafic xenoliths and basaltic to andesitic lavas from Adagdak Volcano (Adak Island, Central Aleutians) to study the effects of early differentiation on the Fe isotopic evolution of island arc basalts and their crystallization products. The Fe isotope composition of ultramafic cumulate xenoliths increases from dunite (δ56Fe = –0.09 to –0.02 ‰) to clinopyroxenite (δ56Fe = +0.06 to +0.09 ‰), consistent with higher modal proportions of clinopyroxene (δ56Fe = –0.05 to +0.11 ‰) relative to olivine (δ56Fe = –0.10 to +0.06 ‰) in the latter. Mid-crustal cumulate amphibole gabbro and hornblendite cumulates also record heavier Fe isotope compositions (δ56Fe = +0.04 to +0.08 ‰) due to the abundance of isotopically heavy amphibole (δ56Fe = +0.07 to +0.09 ‰) and magnetite (δ56Fe = +0.11 to +0.13 ‰) in these rocks. High inter-mineral fractionations observed in spinel-olivine and spinel-clinopyroxene pairs (Δ56Fespl-ol = +0.12 to +0.28 and Δ56Fespl-cpx = +0.06 to +0.19) suggest that spinel is not recording equilibrium crystallization conditions for the ultramafic assemblages, likely due to subsolidus Fe-Mg exchange. Our data also include Fe isotope measurements of one mantle dunite (δ56Fe = +0.03 ± 0.05 ‰). Five Adagdak lavas, spanning from basalts to andesites, yield a narrow range of δ56Fe between +0.03 and +0.06 ‰. Our results highlight the potential of amphibole in driving the Fe isotope depletion trends observed in many erupted arc lavas, as amphibole hosts 28–99 % of the FeOT budget in the amphibole gabbro and hornblendite cumulates. This is also supported by single-crystal synchrotron Mössbauer spectroscopy of two amphibole grains, the first from an amphibole gabbro and the second from a hornblendite, which yield Fe3+/ΣFe ratios of 0.55 ± 0.06 and 0.58 ± 0.02, respectively. Water content and hydrogen isotope compositions determined by secondary-ion mass spectrometry from the same amphibole grains indicate partial dehydrogenation. Using Rayleigh fractionation modeling to account for oxidation during post-crystallization dehydrogenation, we calculate magmatic Fe3+/ΣFe ratios of 0.41 ± 0.04 for the amphibole gabbro and 0.30 ± 0.05 for the hornblendite. These data are then used to estimate an appropriate Fe force constant for Adagdak amphibole and quantitatively evaluate the effects of amphibole fractionation. Through a fractional crystallization model, we show how arc melts may experience periods of increasing δ56Fe during olivine-dominated fractionation, followed by decreasing δ56Fe once magnetite and amphibole saturate as cumulate phases. Notably, this dichotomy between fractionation of isotopically light versus heavy cumulate assemblages and its effects on the Fe isotope evolution of arc magmas is not captured by the Adagdak lava record, highlighting the utility of cumulates in chronicling the early isotopic evolution of magmatic systems.

Hydrologic Connectivity Regulates Riverine N2O Sources and Dynamics.

Indirect nitrous oxide (N2O) emissions from streams and rivers are a poorly constrained term in the global N2O budget. Current models of riverine N2O emissions place a strong focus on denitrification in groundwater and riverine environments as a dominant source of riverine N2O, but do not explicitly consider direct N2O input from terrestrial ecosystems. Here, we combine N2O isotope measurements and spatial stream network modeling to show that terrestrial-aquatic interactions, driven by changing hydrologic connectivity, control the sources and dynamics of riverine N2O in a mesoscale river network within the U.S. Corn Belt. We find that N2O produced from nitrification constituted a substantial fraction (i.e., >30%) of riverine N2O across the entire river network. The delivery of soil-produced N2O to streams was identified as a key mechanism for the high nitrification contribution and potentially accounted for more than 40% of the total riverine emission. This revealed large terrestrial N2O input implies an important climate-N2O feedback mechanism that may enhance riverine N2O emissions under a wetter and warmer climate. Inadequate representation of hydrologic connectivity in observations and modeling of riverine N2O emissions may result in significant underestimations.

Micro-sample Nd isotopic measurement on reference rock powders via the thermal ionization mass spectrometer Nd+ mode

The Sm–Nd isotopic system has been broadly utilized for dating and tracing in earth and planetary sciences. However, low Nd+ ionization efficiency permanently hinders precise and accurate measurements on small amounts of Nd samples. So far, isotopic measurement of micro-amount Nd sample via thermal ionization mass spectrometry (TIMS) Nd+ mode was mostly performed on Nd reference solutions, but less on natural rock or mineral samples. In the present study, analytical procedures to measure isotopic composition via the TIMS Nd+ mode were designed for natural rock powders by using 1–5 ng pure Nd. The analytical technique was refined through low-blank sample digestion, small-column chemistry for Nd extraction from matrix elements, loading Nd using purified H3PO4 solution, and careful heating of filaments before data acquisition. Measurements on small Nd amounts (1 ng–5 ng) of either the JNdi-1 reference solution or four reference rock powders yielded satisfactory results of 143Nd/144Nd value with respect to precision and accuracy. The analytical results agree well with the recommendation values of the reference materials within analytical errors and the internal precision is better than ±0.005 % (2RSE). When using 1 ng or 2 ng Nd amounts, 144Nd ion flow can remain stable in a signal intensity of >100 mV, and without the assistance of an additional ionization enhancer. Therefore, the analytical procedure, featured by low procedural blank (about 10–22 pg), high Nd+ ionization efficiency, and easy operation, has broad prospects for the application of Nd isotope in single-grain minerals or micro-samples.

Fully resolved high-precision measurement of 36S for sulfur reference materials.

Advances in sulfur isotope measurement techniques have led to increased analytical precision. However, accurate measurement of 36S remains a challenge. This difficulty arises primarily from unresolved isobaric interferences of 36SF5 + at m/z = 131u, 186WF4 2+ and 12C3F5 +, which lead to scale compression. Theoretically, unresolved interference with 2% relative intensity could cause 1‰ underestimation in a sample with real δ36S = +60‰. Our study develops an interference-free four-sulfur isotope measurement method by using the high-resolution mass spectrometer Panorama. The mass resolving power of Panorama allows the distinction of 186WF4 2+ and 12C3F5 + from 36SF5 +. The 186WF4 2+ relative intensity was initially 9.4% that of 36SF5 + but reduced to 1.5% through tuning, while 12C3F5 + relative intensity dropped from 74% to 40% after flushing with air. Three IAEA standards were analyzed with both Panorama and MAT 253. We obtained Δ36SIAEA-S-2 = 1.238 ± 0.040‰ and Δ36SIAEA-S-3 = -0.882 ± 0.030‰, relative to IAEA-S-1, from Panorama, and Δ36SIAEA-S-2 = 0.18 ± 0.02‰ and Δ36SIAEA-S-3 = 0.11 ± 0.14‰ from MAT 253, while δ34S values from the two instruments are consistent. The measurement discrepancies on 36S between Panorama and MAT 253 highlight the impact of scale compression due to unresolved isobaric interferences. Resolving this problem is crucial for accurate 36S analysis. We recommend replacing the filament material with rhenium, tuning the filament voltage, and avoiding carbon in instruments to eliminate or mitigate interferences. We propose future systematic efforts to calibrate the δ33S, δ34S, and δ36S of IAEA-S-1, IAEA-S-2, and IAEA-S-3 and advise bracketing all three reference materials in the measurement sequences, to enable calibration.