Reconstructing the chronology of the natural and anthropogenic uranium isotopic signals in a marin sediment core from beppu bay, Japan

The long-lived U isotopes, ²³³U and ²³⁶U, have been used increasingly in recent years as marine circulation tracers and for identifying sources of uranium contamination in the environment. The sedimentation histories of these two U isotopes in combination with natural ²³⁸U were reconstructed for an anoxic sediment core collected from Beppu Bay, Japan, in the western North Pacific Ocean showing good time resolution (less than 2.6 y/sample). The ²³³U/²³⁶U atom ratio showed a prominent peak of (3.20 ± 0.30) × 10^-2 around 1957 which can be attributed to the input from atmospheric nuclear weapons tests including thermonuclear tests conducting in the Equatorial Pacific. The integrated ²³³U/²³⁶U ratio of (1.64 ± 0.08) × 10^-2 for the sediment was found to be in relatively good agreement with the representative ratio published for global fallout (∼1.4 × 10^-2). A prominent increase in the authigenic ratio of ²³³U/²³⁸U_a,s in the leached fraction (1.39 ± 0.11 × 10^-11) and the bulk digestion (1.36 ± 0.10 × 10^-11) was also observed around 1957. This reflects the input supply of ²³³U to the seawater which is known to have a relatively constant ²³⁸U content. The authigenic ²³⁶U/²³⁸U_a,s ratio (0.18 ± 0.02 × 10^-9) obtained for 1921 increased from the early 1950's to a maximum of (6.59 ± 0.60) × 10^-9 around 1962. The variation in this ratio represents well the introduction history of U into the surface environment without site-specific U contamination and the time profile is also consistent with the ¹³⁷Cs signature. This work thus provides a benchmark for the long-term use of the isotopic U composition as an input parameter for seawater circulation tracers and as a chronological marker for anoxic sediments and sedimentary rocks. Especially the ²³³U/²³⁶U ratio may serve as a key-marker for the new geological age Anthropocene.

Tracing Atlantic water transit time in the subarctic and Arctic Atlantic using 99Tc-233U-236U

The pathway and transport time of Atlantic water passing northern Europe can be traced via anthropogenic radioisotopes released from reprocessing of spent nuclear fuels at Sellafield (SF) and La Hague (LH). These reprocessing derived radioisotopes, with extremely low natural background, are source specific and unique fingerprints for Atlantic water. This study explores a new approach using ⁹⁹Tc-²³³U-²³⁶U tracer to estimate the transit time of Atlantic water in the coast of Greenland. We isolate the reprocessing plants (RP) signal of ²³⁶U (²³⁶U_RP) by incorporating ²³³U measurements and combine this with ⁹⁹Tc which solely originates from RP, to estimate the transit time of Atlantic water circulating from Sellafield to the coast of Greenland-Iceland-Faroe Islands. Both being conservative radioisotopes, the temporal variation of ⁹⁹Tc/²³⁶U_RP ratio in Atlantic water is only influenced by their historic discharges from RP, thus ⁹⁹Tc/²³⁶U_RP can potentially be a robust tracer to track the transport of Atlantic water in the North Atlantic-Arctic region. Based on our observation data of ⁹⁹Tc-²³³U-²³⁶U in seawater and the proposed ⁹⁹Tc/²³⁶U_RP tracer approach, Atlantic water transit times were estimated to be 16-22, 25 and 25 years in the coast of Greenland, Iceland and Faroe Island, respectively. Our estimates from northeast Greenland coastal waters agree with earlier results (17-22 years). Therefore, this work provides an independent approach to estimate Atlantic water transit time with which to compare estimates from ocean modelling and other radiotracer approaches.

Understanding source terms of anthropogenic uranium in the Arctic Ocean - First 236U and 233U dataset in Barents Sea sediments

This work reports the first dataset of ²³⁶U and ²³³U in sediment cores taken from the Barents Sea, with the aim to better understand the source terms of anthropogenic uranium in the Arctic region. Concentrations of ²³⁶U and ²³³U along with ¹³⁷Cs, and ²³³U/²³⁶U atomic ratio were measured in six sediment profiles. The cumulative areal inventories of ²³⁶U and ²³³U obtained in this work are (3.50-12.7) × 10¹¹ atom/m² and (4.92-21.2) × 10⁹ atom/m², with averages values of (8.08 ± 2.93) × 10¹¹ atom/m² and (1.08 ± 0.56) × 10¹⁰ atom/m², respectively. The total quantities of ²³⁶U and ²³³U deposited in the Barents Sea bottom sediments were estimated to be 507 ± 184 g and 7 ± 3 g, respectively, which are negligible compared to the total direct deposition of ²³⁶U (6000 g) and ²³³U (40-90 g) from global fallout in the Barents Sea. The integrated atomic ratios of ²³³U/²³⁶U ranging in (0.98-1.57) × 10^-2 reflect the predominant global fallout signal of ²³⁶U in the Barents Sea sediments and the highest reactor-²³⁶U contribution accounts for 30 ± 14 % among the six sediment cores. The reactor-²³⁶U input in the Barents Sea sediments is most likely transported from the European reprocessing plants rather than related to any local radioactive contamination. These results provide better understanding on the source term of anthropogenic ²³⁶U in the Barents Sea, prompt the oceanic tracer application of ²³⁶U for studying the dynamics of the Atlantic-Arctic Ocean and associated climate changes. The ²³⁶U-²³³U benchmarked age-depth profiles seem to match reasonably well with the reported input function history of radioactive contamination in the Barents Sea, indicating the high potential of anthropogenic ²³⁶U-²³³U pair as a useful tool for sediment dating.

Deciphering sources of U contamination using isotope ratio signatures in the Loire River sediments: Exploring the relevance of 233U/236U and stable Pb isotope ratios

A broad range of contaminants has been recorded in sediments of the Loire River over the last century. Among a variety of anthropogenic activities of this nuclearized watershed, extraction of uranium and associated activities during more than 50 years as well as operation of several nuclear power plants led to industrial discharges, which could persist for decades in sedimentary archives of the Loire River. Highlighting and identifying the origin of radionuclides that transited during the last decades and were recorded in the sediments is challenging due to i) the low concentrations which are often close or below the detection limits of routine environmental surveys and ii) the mixing of different sources. The determination of the sources of anthropogenic radioactivity was performed using multi-isotopic fingerprints (²³⁶U/²³⁸U, ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) and the newly developed ²³³U/²³⁶U tracer. For the first time ²³³U/²³⁶U data in a well-dated river sediment core in the French river Loire are reported here. Results highlight potential sources of contamination among which a clear signature of anthropogenic inputs related to two accidents of a former NUGG NPP that occurred in 1969 and 1980. The ²³³U and ²³⁶U isotopes were measured by recent high performance analytical methods due to their ultra-trace levels in the samples and show a negligible radiological impact on health and on the environment. The determination of mining activities by the use of stable Pb isotopes is still challenging probably owing to the limited dissemination of the Pb-bearing material marked by the U-ore signature downstream to the former U mines.

Retrospective determination of U and Pu isotopes and atom ratios in lung samples from Vienna, Austria

Uranium and plutonium isotope concentrations as well as ²³⁶U/²³⁸U and ²⁴⁰Pu/²³⁹Pu atom ratios were measured by AMS in human lung samples from the early 1960s. The ²³⁶U concentrations as well as the ²³⁶U/²³⁸U atom ratios show a maximum in 1964, ²³⁹Pu and ²⁴⁰Pu concentrations are increasing continually from 1962 to 1965. ²³⁶U/²³⁸U atom ratios are lower by two orders of magnitude compared to corresponding aerosol data from Vienna, probably due to older ²³⁸U deposited in the lungs, enhanced ²³⁸U concentrations in the city air, and activity partition within different particle sizes. The ²³⁶U/²³⁹Pu atom ratios in lung samples are also lower than expected from the aerosol data, while ²⁴⁰Pu/²³⁹Pu atom ratios lie well within the range typical for nuclear bomb fallout.

Correction: Novel 90Sr analysis of environmental samples by Ion-Laser InterAction Mass Spectrometry

Correction for 'Novel ⁹⁰Sr analysis of environmental samples by Ion-Laser InterAction Mass Spectrometry' by Maki Honda et al., Anal. Methods, 2022, 14, 2732-2738, https://doi.org/10.1039/D2AY00604A.

Novel 90Sr analysis of environmental samples by Ion-Laser InterAction Mass Spectrometry

The sensitive analysis of ⁹⁰Sr with accelerator mass spectrometry (AMS) was developed to advance environmental radiology. One advantage of AMS is the ability to analyze environmental samples with ⁹⁰Sr/⁸⁸Sr atomic ratios of 10^-14 in following a simple chemical separation. Three different IAEA samples with known ⁹⁰Sr concentrations (moss-soil, animal bone, Syrian soil: 1 g each) were analyzed to assess the validity of the chemical separation and the AMS measurement. The ⁹⁰Sr measurements were conducted on the AMS system VERA combined with the Ion Laser InterAction Mass Spectrometry (ILIAMS) setup at the University of Vienna, which has excellent isobaric separation performance. The isobaric interference of ⁹⁰Zr in the ⁹⁰Sr AMS was first largely removed by chemical separation. The separation factor of Zr in two-step column chromatography with Sr resin and anion exchange resin was 10⁶. The ⁹⁰Zr remaining in the sample was effectively suppressed by ILIAMS. This procedure achieved a limit of detection <0.1 mBq in the ⁹⁰Sr AMS, which is lower than typical β-ray detection. The agreement between AMS measurements and nominal values for the ⁹⁰Sr concentrations of IAEA samples indicated that the new highly-sensitive ⁹⁰Sr analysis in the environmental samples with AMS is reliable.

Anthropogenic 236U and 233U in the Baltic Sea: Distributions, source terms, and budgets

The Baltic Sea receives substantial amounts of hazardous substances and nutrients, which accumulate for decades and persistently impair the Baltic ecosystems. With long half-lives and high solubility, anthropogenic uranium isotopes (²³⁶U and ²³³U) are ideal tracers to depict the ocean dynamics in the Baltic Sea and the associated impacts on the fates of contaminants. However, their applications in the Baltic Sea are hampered by the inadequate source-term information. This study reports the first three-dimensional distributions of ²³⁶U and ²³³U in the Baltic Sea (2018-2019) and the first long-term hindcast simulation for reprocessing-derived ²³⁶U dispersion in the North-Baltic Sea (1971-2018). Using ²³³U/²³⁶U fingerprints, we distinguish ²³⁶U from the nuclear weapon testing and civil nuclear industries, which have comparable contributions (142 ± 13 and 174 ± 40 g) to the ²³⁶U inventory in modern Baltic seawater. Budget calculations for ²³⁶U inputs since the 1950s indicate that, the major ²³⁶U sources in the Baltic Sea are the atmospheric fallouts (∼1.35 kg) and discharges from nuclear reprocessing plants (> 211 g), and there is a continuous sink of ²³⁶U to the anoxic sediments (589 ± 43 g). Our findings also indicate that the limited water renewal endows the Baltic Sea a strong "memory effect" retaining aged ²³⁶U signals, and the previously unknown ²³⁶U in the Baltic Sea is likely attributed to the retention of the mid-1990s' discharges from the nuclear reprocessing plants. Our preliminary results demonstrate the power of ²³⁶U-¹²⁹I dual-tracer in investigating water-mass mixing and estimating water age in the Baltic Sea, and this work provides fundamental knowledge for future ²³⁶U tracer studies in the Baltic Sea.

Deciphering anthropogenic uranium sources in the equatorial northwest Pacific margin

This work reports the first high-resolution deposition records of anthropogenic uranium (²³⁶U and ²³³U) in a sediment core taken at the continental slope of the Philippine Sea off Mindanao Island in the equatorial northwest Pacific Ocean. Two notable peaks were observed in both profiles of ²³⁶U and ²³³U concentrations, with a narrower peak in 1951-1957 corresponding to close-in Pacific Proving Grounds (PPG) signal, and a broader peak in 1960s-1980s corresponding to the global fallout from nuclear weapons testing. ²³⁶U and ²³³U areal cumulative inventories in the studied sediment core are (2.79 ± 0.20) ∙ 10¹² atom ∙ m^-2 and (3.12 ± 0.41) ∙ 10¹⁰ atom ∙ m^-2, respectively, about 20-30% of reported ²³³U and ²³⁶U inventories from the direct global fallout deposition. The overall ²³³U/²³⁶U atomic ratios obtained in this work vary within (0.3-3.5) ∙ 10^-2, with an integrated ²³³U/²³⁶U atomic ratio of (1.12 ± 0.17) ∙ 10^-2. The contribution from global fallout and close-in PPG fallout to ²³⁶U in the sediment core is estimated to be about 69% and 31%, respectively. We believe the main driving process for anthropogenic uranium deposition in the Philippine sediment is continuous scavenging of dissolved ²³⁶U from the surface seawater by sinking particles.

Revisiting the Middle and Upper Palaeolithic archaeology of Gruta do Caldeirão (Tomar, Portugal)

Gruta do Caldeirão features a c. 6 m-thick archaeological stratification capped by Holocene layers ABC-D and Ea, which overlie layer Eb, a deposit of Magdalenian age that underwent significant disturbance, intrusion, and component mixing caused by funerary use of the cave during the Early Neolithic. Here, we provide an updated overview of the stratigraphy and archaeological content of the underlying Pleistocene succession, whose chronology we refine using radiocarbon and single-grain optically stimulated luminescence dating. We find a high degree of stratigraphic integrity. Dating anomalies exist in association with the succession’s two major discontinuities: between layer Eb and Upper Solutrean layer Fa, and between Early Upper Palaeolithic layer K and Middle Palaeolithic layer L. Mostly, the anomalies consist of older-than-expected radiocarbon ages and can be explained by bioturbation and palimpsest-forming sedimentation hiatuses. Combined with palaeoenvironmental inferences derived from magnetic susceptibility analyses, the dating shows that sedimentation rates varied in tandem with the oscillations in global climate revealed by the Greenland oxygen isotope record. A steep increase in sedimentation rate is observed through the Last Glacial Maximum, resulting in a c. 1.5 m-thick accumulation containing conspicuous remains of occupation by people of the Solutrean technocomplex, whose traditional subdivision is corroborated: the index fossils appear in the expected stratigraphic order; the diagnostics of the Protosolutrean and the Lower Solutrean predate 24,000 years ago; and the constraints on the Upper Solutrean place it after Greenland Interstadial 2.2. (23,220–23,340 years ago). Human usage of the site during the Early Upper and the Middle Palaeolithic is episodic and low-intensity: stone tools are few, and the faunal remains relate to carnivore activity. The Middle Palaeolithic is found to persist beyond 39,000 years ago, at least three millennia longer than in the Franco-Cantabrian region. This conclusion is upheld by Bayesian modelling and stands even if the radiocarbon ages for the Middle Palaeolithic levels are removed from consideration (on account of observed inversions and the method’s potential for underestimation when used close to its limit of applicability). A number of localities in Spain and Portugal reveal a similar persistence pattern. The key evidence comes from high-resolution fluviatile contexts spared by the site formation issues that our study of Caldeirão brings to light—palimpsest formation, post-depositional disturbance, and erosion. These processes. are ubiquitous in the cave and rock-shelter sites of Iberia, reflecting the impact on karst archives of the variation in climate and environments that occurred through the Upper Pleistocene, and especially at two key points in time: between 37,000 and 42,000 years ago, and after the Last Glacial Maximum. Such empirical difficulties go a long way towards explaining the controversies surrounding the associated cultural transitions: from the Middle to the Upper Palaeolithic, and from the Solutrean to the Magdalenian. Alongside potential dating error caused by incomplete decontamination, proper consideration of sample association issues is required if we are ever to fully understand what happened with the human settlement of Iberia during these critical intervals, and especially so with regards to the fate of Iberia’s last Neandertal populations.

70-Year Anthropogenic Uranium Imprints of Nuclear Activities in Baltic Sea Sediments

A strongly stratified water structure and a densely populated catchment make the Baltic Sea one of the most polluted seas. Understanding its circulation pattern and time scale is essential to predict the dynamics of hypoxia, eutrophication, and pollutants. Anthropogenic ²³⁶U and ²³³U have been demonstrated as excellent transient tracers in oceanic studies, but unclear input history and inadequate long-term monitoring records limit their application in the Baltic Sea. From two dated Baltic sediment cores, we obtained high-resolution records of anthropogenic uranium imprints originating from three major human nuclear activities throughout the Atomic Era. Using the novel ²³³U/²³⁶U signature, we distinguished and quantified ²³⁶U inputs from global fallout (45.4-52.1%), Chernobyl accident (0.3-1.8%), and discharges from civil nuclear industries (46.1-54.3%) to the Baltic Sea. We estimated the total release of ²³³U (7-15 kg) from the atmospheric nuclear weapon testing and pinpointed the ²³³U peak signal in the mid-to-late 1950s as a potential time marker for the onset of the Anthropocene Epoch. This work also provides fundamental ²³⁶U data on Chernobyl accident and early discharges from civil nuclear facilities, prompting worldwide ²³³U-²³⁶U tracer studies. We anticipate our data to be used in a broader application in model-observation interdisciplinary research on water circulation and pollutant dynamics in the Baltic Sea.

First dataset of 236U and 233U around the Greenland coast: A 5-year snapshot (2012-2016)

We report the first combined dataset of ²³⁶U and ²³³U in the Greenland marine environment during the period of 2012-2016. Results are discussed in terms of time evolution and spatial distribution of ²³⁶U concentration, and atomic ratios of ²³⁶U/²³⁸U and ²³³U/²³⁶U. ²³⁶U concentrations along the Greenland coast are distributed within a relatively narrow range of (0.7-12.9) × 10⁷ atom/L, corresponding to ²³⁶U/²³⁸U atomic ratios of (1.1-15.5) × 10^-9. The ²³³U/²³⁶U atomic ratios obtained vary from 0.12 × 10^-2 to 1.16 × 10^-2, with the majority distributed in the range of (0.2-0.7) × 10^-2. We applied ²³³U/²³⁶U and ²³⁶U/²³⁸U atomic ratios in a binary mixing model to identify possible ²³⁶U source terms. The results indicate that anthropogenic ²³⁶U and ²³³U in Greenland surface seawater originated from the direct global fallout (DGF) and the Sellafield and La Hague reprocessing plants (RP) is diluted by a third endmember, mostly likely natural ocean water (NOW), containing marginal ²³⁶U and ²³³U. A preliminary estimation of the source terms of ²³⁶U using ²³³U/²³⁶U atomic ratios indicate that, for both eastern and western Greenland seawater, contributions from global fallout (GF) constitute about 30% of ²³⁶U. The dominating source for ²³⁶U, i.e. 70 %, is associated to reactor ²³⁶U including discharges from RP and local reactor input in the Arctic Ocean.

Radiocarbon analysis of carbonaceous aerosols in Bratislava, Slovakia

Aerosols dispersed in the atmosphere represent important factors influencing not only the environment, but also human health. Carbonaceous aerosols are one of the main components of total atmospheric aerosols, and their sources are of great interest. Radiocarbon analysis provides an excellent way to determine the fraction of fossil and non-fossil aerosols in the atmosphere. Over the period of one year (June 2017-June 2018), we sampled atmospheric aerosols with size greater than 0.3 μm in Bratislava, Slovakia and used the exposed quartz filters for radiocarbon analysis of the elemental carbon (EC) aerosol fraction. The results show that on average the fossil fuel combustion is the dominant source of EC aerosol particles in Bratislava. In summer months, they represent more than half (65-80%) of the total EC aerosols. The relative amount of EC particles derived from biomass burning was 20-35% in summer, which increased to 40-55% in winter months. The dominance of fossil fraction is caused by high degree of industrialization and urbanization of the city. The increase of biomass fraction in winter is probably caused by domestic wood burning in areas surrounding the Bratislava city.

Pushing Limits of ICP-MS/MS for the Determination of Ultralow 236U/238U Isotope Ratios

Determination of uranium isotope ratios is of great expedience for assessing its origin in environmental samples. In particular, the ²³⁶U/²³⁸U isotope ratio provides a powerful tool to discriminate between the different sources of uranium (uranium ore, geochemical background, and uranium from anthropogenic activities). However, in the environment, this ratio is typically below 10^-8. This low abundance of ²³⁶U and the presence in large excess of major isotopes (mainly ²³⁸U and ²³⁵U) complicates the accurate detection of ²³⁶U signal by mass spectrometry and thus highly sensitive analytical instruments providing high abundance sensitivity are required. This work pushes the limits of triple quadrupole-based ICP-MS technology for accurate detection of ²³⁶U/²³⁸U isotope ratios down to 10^-10, which is so far mainly achievable by AMS. Coupled with an efficient desolvating module, N₂O was used as the reaction gas in the collision reaction cell of the ICP-MS/MS. This configuration allows a significant decrease of the uranium polyatomic interferences (²³⁵UH⁺ ions) and an accurate determination of low ²³⁶U/²³⁸U isotope ratios. This new methodology was successfully validated through measurements of certified reference material from 10^-7 to 10^-9 and then through comparisons with AMS measurement results for ratios down to 10^-10. This is the first time that ²³⁶U/²³⁸U isotope ratios as low as 10^-10 were determined by ICP-MS/MS. The possibility of measuring low ²³⁶U/²³⁸U isotope ratios can offer a large variety of geochemical applications in particular for the determination of uranium sources in the environment.

The movements of Alpine glaciers throughout the last 10,000 years as sensitive proxies of temperature and climate changes

A brief review of the movements of Alpine glaciers throughout the Holocene in the Northern Hemisphere (European Alps) and in the Southern Hemisphere (New Zealand Southern Alps) is presented. It is mainly based on glacier studies where 14C dating, dendrochronology and surface exposure dating with cosmogenic isotopes is used to establish the chronology of advances and retreats of glaciers. An attempt is made to draw some general conclusions on the temperature and climate differences between the Northern and Southern Hemisphere.

The quest for AMS of 182Hf – why poor gas gives pure beams

The long-lived radioisotope 182Hf (T1/2 = 8.9 Ma) is of high astrophysical interest as its potential abundance in environmental archives would provide insight into recent r-process nucleosynthesis in the vicinity of our solar system. Despite substantial efforts, it could not be measured at natural abundances with conventional AMS so far due to strong isobaric interference from stable 182W. Equally important is an increase in ion source efficiency for the anions of interest.

The new Ion Laser InterAction Mass Spectrometry (ILIAMS) technique at VERA tackles the problem of elemental selectivity in AMS with a novel approach. It achieves near-complete suppression of isobar contaminants via selective laser photodetachment of decelerated anion beams in a gas-filled radio-frequency quadrupole (RFQ) ion cooler. The technique exploits differences in electron affinities (EA) within elemental or molecular isobaric systems neutralizing anions with EAs smaller than the photon energy. Alternatively, these differences in EA can also facilitate anion separation via chemical reactions with the buffer gas.

We present first results with this approach on AMS-detection of 182Hf. With He +O2 mixtures as buffer gas in the RFQ, suppression of 182WF5− vs 180HfF 5− by >105 has been demonstrated. Mass analysis of the ejected anion beam identified the formation of oxyfluorides as an important reaction channel. The overall Hf-detection efficiency at VERA presently is 1.4% and the W-corrected blank value is 182Hf/180Hf = (3.4 ± 2.1)×10−14. In addition, a survey of different sample materials for highest negative ion yields of HfF 5− with Cs-sputtering has been conducted.

Radionuclides in surface waters around the damaged Fukushima Daiichi NPP one month after the accident: Evidence of significant tritium release into the environment

Following the Fukushima nuclear accident (2011), radionuclides mostly of volatile elements (e.g., ¹³¹I, ^134,137Cs, ¹³²Te) have been investigated frequently for their presence in the atmosphere, pedosphere, biosphere, and the Pacific Ocean. Smaller releases of radionuclides with intermediate volatility, (e.g., ⁹⁰Sr), have been reported for soil. However, few reports have been published which targeted the contamination of surface (fresh) waters in Japan soon after the accident. In the present study, 10 surface water samples (collected on April 10, 2011) have been screened for their radionuclide content (³H, ⁹⁰Sr, ¹²⁹I, ¹³⁴Cs, and ¹³⁷Cs), revealing partly unusually high contamination levels. Especially high tritium levels (184 ± 2 Bq·L^-1; the highest levels ever reported in scientific literature after Fukushima) were found in a puddle water sample from close to the Fukushima Daiichi nuclear power plant. The ratios between paddy/puddle water from one location only a few meters apart vary around 1% for ¹³⁴Cs, 12% for ¹²⁹I (¹³¹I), and around 40% for both ³H and ⁹⁰Sr. This illustrates the adsorption of radiocesium on natural minerals and radioiodine on organic substances (in the rice paddy), whereas the concentration differences of ³H and ⁹⁰Sr between the two waters are mainly dilution driven.

Radiocarbon re-dating of contact-era Iroquoian history in northeastern North America

A time frame for late Iroquoian prehistory is firmly established on the basis of the presence/absence of European trade goods and other archeological indicators. However, independent dating evidence is lacking. We use 86 radiocarbon measurements to test and (re)define existing chronological understanding. Warminster, often associated with Cahiagué visited by S. de Champlain in 1615-1616 CE, yields a compatible radiocarbon-based age. However, a well-known late prehistoric site sequence in southern Ontario, Draper-Spang-Mantle, usually dated ~1450-1550, yields much later radiocarbon-based dates of ~1530-1615. The revised time frame dramatically rewrites 16th-century contact-era history in this region. Key processes of violent conflict, community coalescence, and the introduction of European goods all happened much later and more rapidly than previously assumed. Our results suggest the need to reconsider current understandings of contact-era dynamics across northeastern North America.

Limits on Supernova-Associated ^{60}Fe/^{26}Al Nucleosynthesis Ratios from Accelerator Mass Spectrometry Measurements of Deep-Sea Sediments

We searched for the presence of ^{26}Al in deep-sea sediments as a signature of supernova influx. Our data show an exponential dependence of ^{26}Al with the sample age that is fully compatible with radioactive decay of terrigenic ^{26}Al. The same set of samples demonstrated a clear supernova ^{60}Fe signal between 1.7 and 3.2 Myr ago. Combining our ^{26}Al data with the recently reported ^{60}Fe data results in a lower limit of 0.18_{-0.08}^{+0.15} for the local interstellar ^{60}Fe/^{26}Al isotope ratio. It compares to most of the ratios deduced from nucleosynthesis models and is within the range of the observed average galactic ^{60}Fe/^{26}Al flux ratio of (0.15±0.05).

The increase of soil organic carbon as proposed by the "4/1000 initiative" is strongly limited by the status of soil development - A case study along a substrate age gradient in Central Europe

During COP 21 in Paris 2015, several states and organizations agreed on the "4/1000" initiative for food security and climate. This initiative aims to increase world's soil organic carbon (SOC) stocks by 4‰ annually. The influence of soil development status on SOC dynamics is very important but usually not considered in studies. We analyse SOC accumulation under forest, grassland and cropping systems along a soil age gradient (10-17,000years) to show the influence of soil development status on SOC increase. SOC stocks (0-40cm) and accumulation rates along a chronosequence in alluvial soils of the Danube River in the Marchfeld (eastern Austria) were analysed. The analysed Fluvisols and Chernozems have been used as forest, grassland and cropland for decades or hundreds of years. The results showed that there is a fast build-up of OC stocks (0-40cm) in young soils with accumulation of ~1.3tha^-1a^-1 OC in the first 100years and ~0.5tha^-1a^-1 OC between 100 and 350years almost independent of land use. Chernozems with a sediment deposition age older than 5.000years have an accumulation rate<0.01tOCha^-1a^-1 (0-40cm). Radiocarbon dating showed that the topsoil (0-10cm) consists mainly of ">modern" and "modern" carbon indicating a fast carbon cycling. Carbon in subsoil is less exposed to decomposition and OC can be stored at long-time scales in the subsoil (¹⁴C age of 3670±35 BP). In view of the '4/1000' initiative, soils with constant carbon input (forest & grassland) fulfil the intended 4‰ growth rate of SOC stocks only in the first 60years of soil development. We proclaim that under the present climate in Central Europe, the increase of SOC stocks in soil is strongly affected by the state of soil development.

Precise dating of the Middle-to-Upper Paleolithic transition in Murcia (Spain) supports late Neandertal persistence in Iberia

The late persistence in Southern Iberia of a Neandertal-associated Middle Paleolithic is supported by the archeological stratigraphy and the radiocarbon and luminescence dating of three newly excavated localities in the Mula basin of Murcia (Spain). At Cueva Antón, Mousterian layer I-k can be no more than 37,100 years-old. At La Boja, the basal Aurignacian can be no less than 36,500 years-old. The regional Middle-to-Upper Paleolithic transition process is thereby bounded to the first half of the 37th millennium Before Present, in agreement with evidence from Andalusia, Gibraltar and Portugal. This chronology represents a lag of minimally 3000 years with the rest of Europe, where that transition and the associated process of Neandertal/modern human admixture took place between 40,000 and 42,000 years ago. The lag implies the presence of an effective barrier to migration and diffusion across the Ebro river depression, which, based on available paleoenvironmental indicators, would at that time have represented a major biogeographical divide. In addition, (a) the Phlegraean Fields caldera explosion, which occurred 39,850 years ago, would have stalled the Neandertal/modern human admixture front because of the population sink it generated in Central and Eastern Europe, and (b) the long period of ameliorated climate that came soon after (Greenland Interstadial 8, during which forests underwent a marked expansion in Iberian regions south of 40°N) would have enhanced the “Ebro Frontier” effect. These findings have two broader paleoanthropological implications: firstly, that, below the Ebro, the archeological record made prior to 37,000 years ago must be attributed, in all its aspects and components, to the Neandertals (or their ancestors); secondly, that modern human emergence is best seen as an uneven, punctuated process during which long-lasting barriers to gene flow and cultural diffusion could have existed across rather short distances, with attendant consequences for ancient genetics and models of human population history.

Multiactinide Analysis with Accelerator Mass Spectrometry for Ultratrace Determination in Small Samples: Application to an in Situ Radionuclide Tracer Test within the Colloid Formation and Migration Experiment at the Grimsel Test Site (Switzerland)

The multiactinide analysis with accelerator mass spectrometry (AMS) was applied to samples collected from the run 13-05 of the Colloid Formation and Migration (CFM) experiment at the Grimsel Test Site (GTS). In this in situ radionuclide tracer test, the environmental behavior of ²³³U, ²³⁷Np, ²⁴²Pu, and ²⁴³Am was investigated in a water conductive shear zone under conditions relevant for a nuclear waste repository in crystalline rock. The concentration of the actinides in the GTS groundwater was determined with AMS over 6 orders of magnitude from ∼15 pg/g down to ∼25 ag/g. Levels above 10 fg/g were investigated with both sector field inductively coupled plasma mass spectrometry (SF-ICPMS) and AMS. Agreement within a relative uncertainty of 50% was found for ²³⁷Np, ²⁴²Pu, and ²⁴³Am concentrations determined with the two analytical methods. With the extreme sensitivity of AMS, the long-term release and retention of the actinides was investigated over 8 months in the tailing of the breakthrough curve of run 13-05 as well as in samples collected up to 22 months after. Furthermore, the evidence of masses 241 and 244 u in the CFM samples most probably representing ²⁴¹Am and ²⁴⁴Pu employed in a previous tracer test demonstrated the analytical capability of AMS for in situ studies lasting more than a decade.

Anthropogenic 236U in Danish Seawater: Global Fallout versus Reprocessing Discharge

This work focuses on the occurrence of ²³⁶U in seawater along Danish coasts, which is the sole water-exchange region between the North Sea-Atlantic Ocean and the Baltic Sea. Seawater collected in 2013 and 2014 were analyzed for ²³⁶U (as well as ²³⁸U and ¹³⁷Cs). Our results indicate that ²³⁶U concentrations in Danish seawater are distributed within a relatively narrow range of (3.6-8.2) × 10⁷ atom/L and, to a certain extent, independent of salinity. ²³⁶U/²³⁸U atomic ratios in Danish seawater are more than 4 times higher than the estimated global fallout value of 1× 10^-9. The levels of ²³⁶U/²³⁸U atomic ratios obtained are comparable to those reported for the open North Sea and much higher than several other open oceans worldwide. This indicates that besides the global fallout input, the discharges from the two major European nuclear reprocessing plants are dominating sources of ²³⁶U in Danish seawater. However, unexpectedly high ²³⁶U/²³⁸U ratios as well as high ²³⁶U concentrations were observed at low-salinity locations of the Baltic Sea. While this feature might be interpreted as a clue for another significant ²³⁶U input in the Baltic Sea, it may also be caused by the complexity of water currents or slow turnover rate.

Vertical distribution of 236U in the North Pacific Ocean

The first extensive study on ²³⁶U in the North Pacific Ocean has been conducted. The vertical distribution of ²³⁶U/²³⁸U isotopic ratios and the ²³⁶U concentrations were analysed on seven depth profiles, and large variations with depth were found. The range of ²³⁶U/²³⁸U isotopic ratios was from (0.09 ± 0.03) × 10^-10 to (14.1 ± 2.2) × 10^-10, which corresponds to ²³⁶U concentrations of (0.69 ± 0.24) × 10⁵ atoms/kg and (119 ± 21) × 10⁵ atoms/kg, respectively. The variations in ²³⁶U concentrations could mainly be attributed to the different water masses in the North Pacific Ocean and their formation processes. Uranium-236 inventories on the water column of each sampling station were calculated and varied between (3.89 ± 0.08) × 10¹² atoms/m² and (7.03 ± 0.50) × 10¹² atoms/m², which is lower than in former studies on comparable latitudes in the North Atlantic Ocean and the Sea of Japan. The low inventories of ²³⁶U found for the North Pacific Ocean in this study can be explained by the lack of additional input sources of artificial radionuclides, apart from global and regional/local fallout. This study expands the use of ²³⁶U as oceanographic circulation tracer to yet another ocean basin and shows that this isotope can be used for tracing circulation patterns of water masses in the Pacific Ocean.

Plutonium Isotopes (239-241Pu) Dissolved in Pacific Ocean Waters Detected by Accelerator Mass Spectrometry: No Effects of the Fukushima Accident Observed

The concentration of plutonium (Pu) and the isotopic ratios of ²⁴⁰Pu to ²³⁹Pu and ²⁴¹Pu to ²³⁹Pu were determined by accelerator mass spectrometry (AMS) in Pacific Ocean water samples (20 L each) collected in late 2012. The isotopic Pu ratios are important indicators of different contamination sources and were used to identify a possible release of Pu into the ocean by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. In particular, ²⁴¹Pu is a well-suited indicator for a recent entry of Pu because ²⁴¹Pu from fallout of nuclear weapon testings has already significantly decayed. A total of 10 ocean water samples were prepared at the Radiochemie München of the TUM and analyzed at the Vienna Environmental Research Laboratory (VERA). Several samples showed a slightly elevated ²⁴⁰Pu/²³⁹Pu ratio of up to 0.22 ± 0.02 compared to global fallout (²⁴⁰Pu/²³⁹Pu = 0.180 ± 0.007), whereas all measured ²⁴¹Pu-to-²³⁹Pu ratios were consistent with nuclear weapon fallout (²⁴¹Pu/²³⁹Pu < 2.4 × 10^-3), which means that no impact from the Fukushima accident was detected. From the average ²⁴¹Pu-to-²³⁹Pu ratio of 8_-2⁺³ ×10^-4 at a sampling station located at a distance of 39.6 km to FDNPP, the 1-σ upper limit for the FDNPP contribution to the ²³⁹Pu inventory in the water column was estimated to be 0.2%. Pu, with the signature of weapon-grade Pu was found in a single sample collected around 770 km off the west coast of the United States.

First study on 236U in the Northeast Pacific Ocean using a new target preparation procedure for AMS measurements

We succeeded in obtaining the depth profile of ²³⁶U for a sampling station in the Northeast Pacific Ocean using only one litre of seawater sample from each depth. For this purpose, a new procedure was developed that allowed for the preparation of accelerator mass spectrometry targets for trace uranium using only 100 μg of iron carrier material. The ²³⁶U concentrations in water samples from the Northeast Pacific Ocean showed large variations from (9.26 ± 0.42) × 10⁶ atoms/kg at 60 m depth to (0.08 ± 0.02) × 10⁶ atoms/kg at a depth of 3000 m. The high ²³⁶U concentrations in surface water reflect the input of ²³⁶U by global and local fallout from nuclear weapons tests. The low ²³⁶U concentrations in seawater from 1500 m and below are an indicator for the low vertical diffusion of surface water to deeper layers in the North Pacific Ocean. The total inventory of ²³⁶U on the water column was (8.35 ± 0.23) × 10¹² atoms/m², which is lower compared to those of other ocean regions solely affected by global fallout on comparable latitudes. This study represents the first dataset for ²³⁶U in the Pacific Ocean and shows the possibility of downsizing sample volumes which may help in future applications of ²³⁶U as tracer for large ocean areas.

Sphagnum-dominated bog systems are highly effective yet variable sources of bio-available iron to marine waters

Iron is a micronutrient of particular interest as low levels of iron limit primary production of phytoplankton and carbon fluxes in extended regions of the world's oceans. Sphagnum-peatland runoff is extraordinarily rich in dissolved humic-bound iron. Given that several of the world's largest wetlands are Sphagnum-dominated peatlands, this ecosystem type may serve as one of the major sources of iron to the ocean. Here, we studied five near-coastal creeks in North Scotland using freshwater/seawater mixing experiments of natural creek water and synthetic seawater based on a (59)Fe radiotracer technique combined with isotopic characterization of dissolved organic carbon by Accelerator Mass Spectrometry. Three of the creeks meander through healthy Sphagnum-dominated peat bogs and the two others through modified peatlands which have been subject to artificial drainage for centuries. The results revealed that, at the time of sampling (August 16-24, 2014), the creeks that run through modified peatlands delivered 11-15μg iron per liter creek water to seawater, whereas the creeks that run through intact peatlands delivered 350-470μg iron per liter creek water to seawater. To find out whether this humic-bound iron is bio-available to marine algae, we performed algal growth tests using the unicellular flagellated marine prymnesiophyte Diacronema lutheri and the unicellular marine green alga Chlorella salina, respectively. In both cases, the riverine humic material provided a highly bio-available source of iron to the marine algae. These results add a new item to the list of ecosystem services of Sphagnum-peatlands.

European roe deer antlers as an environmental archive for fallout (236)U and (239)Pu

Anthropogenic (236)U and (239)Pu were measured in European roe deer antlers hunted between 1955 and 1977 which covers and extends beyond the period of intensive nuclear weapons testing (1954-1962). The antlers were hunting trophies, and hence the hunting area, the year of shooting and the approximate age of each animal is given. Uranium and plutonium are known to deposit in skeletal tissue. Since antler histology is similar to bone, both elements were expected in antlers. Furthermore, roe deer shed their antlers annually, and hence antlers may provide a time-resolved environmental archive for fallout radionuclides. The radiochemical procedure is based on a Pu separation step by anion exchange (Dowex 1 × 8) and a subsequent U purification by extraction chromatography using UTEVA(®). The samples were measured by Accelerator Mass Spectrometry at the VERA facility (University of Vienna). In addition to the (236)U and (239)Pu concentrations, the (240)Pu/(239)Pu isotopic ratios were determined with a mean value of 0.172 ± 0.023 which is in agreement with the ratio of global fallout (∼0.18). Rather high (236)U/(238)U ratios of the order of 10(-6) were observed. These measured ratios, where the (236)U arises only from global fallout, have implications for the use of the (236)U/(238)U ratio as a fingerprint for nuclear accidents or releases from nuclear facilities. Our investigations have shown the potential to use antlers as a temporally resolved archive for the uptake of actinides from the environment.

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

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

Method for (236)U Determination in Seawater Using Flow Injection Extraction Chromatography and Accelerator Mass Spectrometry

An automated analytical method implemented in a flow injection (FI) system was developed for rapid determination of (236)U in 10 L seawater samples. (238)U was used as a chemical yield tracer for the whole procedure, in which extraction chromatography (UTEVA) was exploited to purify uranium, after an effective iron hydroxide coprecipitation. Accelerator mass spectrometry (AMS) was applied for quantifying the (236)U/(238)U ratio, and inductively coupled plasma mass spectrometry (ICPMS) was used to determine the absolute concentration of (238)U; thus, the concentration of (236)U can be calculated. The key experimental parameters affecting the analytical effectiveness were investigated and optimized in order to achieve high chemical yields and simple and rapid analysis as well as low procedure background. Besides, the operational conditions for the target preparation prior to the AMS measurement were optimized, on the basis of studying the coprecipitation behavior of uranium with iron hydroxide. The analytical results indicate that the developed method is simple and robust, providing satisfactory chemical yields (80-100%) and high analysis speed (4 h/sample), which could be an appealing alternative to conventional manual methods for (236)U determination in its tracer application.

Abundance of live ²⁴⁴Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis

Half of the heavy elements including all actinides are produced in r-process nucleosynthesis, whose sites and history remain a mystery. If continuously produced, the Interstellar Medium is expected to build-up a quasi-steady state of abundances of short-lived nuclides (with half-lives ≤100 My), including actinides produced in r-process nucleosynthesis. Their existence in today’s interstellar medium would serve as a radioactive clock and would establish that their production was recent. In particular ²⁴⁴Pu, a radioactive actinide nuclide (half-life=81 My), can place strong constraints on recent r-process frequency and production yield. Here we report the detection of live interstellar ²⁴⁴Pu, archived in Earth’s deep-sea floor during the last 25 My, at abundances lower than expected from continuous production in the Galaxy by about 2 orders of magnitude. This large discrepancy may signal a rarity of actinide r-process nucleosynthesis sites, compatible with neutron-star mergers or with a small subset of actinide-producing supernovae.

The build-up of short-lived nuclides in the interstellar medium tells us about production frequency and yield of heavy elements by nucleosynthesis. Wallner et al. find a low abundance of live interstellar 244Pu detected from the deep-sea floor, suggesting a rarity for r-process nucleosynthesis sites.

Novel method to study neutron capture of 235U and 238U simultaneously at keV energies

The neutron capture cross sections of the main uranium isotopes, (235)U and (238)U, were measured simultaneously for keV energies, for the first time by combining activation technique and atom counting of the reaction products using accelerator mass spectrometry. New data, with a precision of 3%-5%, were obtained from mg-sized natural uranium samples for neutron energies with an equivalent Maxwell-Boltzmann distribution of kT ∼ 25 keV and for a broad energy distribution peaking at 426 keV. The cross-section ratio of (235)U(n,γ)/(238)U(n,γ) can be deduced in accelerator mass spectrometry directly from the atom ratio of the reaction products (236)U/(239)U, independent of any fluence normalization. Our results confirm the values at the lower band of existing data. They serve as important anchor points to resolve present discrepancies in nuclear data libraries as well as for the normalization of cross-section data used in the nuclear astrophysics community for s-process studies.

Airborne Plutonium and non-natural Uranium from the Fukushima DNPP found at 120 km distance a few days after reactor hydrogen explosions

Plutonium (Pu) and non-natural uranium (U) originating from the Fukushima Daiichi Nuclear Power Plant (FDNPP) were identified in the atmosphere at 120 km distance from the FDNPP analyzing the ratio of number of atoms, following written as n(isotope)/n(isotope), of Pu and U. The n((240)Pu)/n((239)Pu), n((241)Pu)/n((239)Pu), n((234)U)/n((238)U), n((235)U)/n((238)U) and n((236)U)/n((238)U) in aerosol samples collected before and after the FDNPP incident were analyzed by accelerator mass spectrometry (AMS) and inductively coupled plasma mass spectrometry (ICPMS). The activity concentrations of (137)Cs and (134)Cs in the same samples were also analyzed by gamma spectrometry before the destructive analysis. Comparing the time series of analytical data on Pu and U obtained in this study with previously reported data on Pu, U, and radioactive Cs, we concluded that Pu and non-natural U from the FDNPP were transported in the atmosphere directly over a 120 km distance by aerosol and wind within a few days after the reactor hydrogen explosions. Effective dose of Pu were calculated using the data of Pu: (130 ± 21) nBq/m(3), obtained in this study. We found that the airborne Pu contributes only negligibly to the total dose at the time of the incident. However the analytical results show that the amount of Pu and non-natural U certainly increased in the environment after the incident.

Isotopic compositions of (236)U and Pu isotopes in "black substances" collected from roadsides in Fukushima prefecture: fallout from the Fukushima Dai-ichi nuclear power plant accident

Black-colored road dusts were collected in high-radiation areas in Fukushima Prefecture. Measurement of (236)U and Pu isotopes and (134,137)Cs in samples was performed to confirm whether refractory elements, such as U and Pu, from the fuel core were discharged and to ascertain the extent of fractionation between volatile and refractory elements. The concentrations of (134,137)Cs in all samples were exceptionally high, ranging from 0.43 to 17.7 MBq/kg, respectively. (239+240)Pu was detected at low levels, ranging from 0.15 to 1.14 Bq/kg, and with high (238)Pu/(239+240)Pu activity ratios of 1.64-2.64. (236)U was successfully determined in the range of (0.28 to 6.74) × 10(-4) Bq/kg. The observed activity ratios for (236)U/(239+240)Pu were in reasonable agreement with those calculated for the fuel core inventories, indicating that trace amounts of U from the fuel cores were released together with Pu isotopes but without large fractionation. The quantities of U and (239+240)Pu emitted to the atmosphere were estimated as 3.9 × 10(6) Bq (150 g) and 2.3 × 10(9) Bq (580 mg), respectively. With regard to U, this is the first report to give a quantitative estimation of the amount discharged. Appreciable fractionation between volatile and refractory radionuclides associated with the dispersal/deposition processes with distance from the Fukushima Dai-ichi Nuclear Power Plant was found.

A review on 129I analysis in air

A review of literature focused on (129)I determination in air is provided. (129)I analysis in the environment represents a vital tool for tracing transport mechanisms, distribution pathways, safety assessment and its application as environmental tracer. To achieve that, specific chemical extraction methods and high sensitivity analytical techniques have been developed. This paper is intended to give an overview about the sample collection, extraction and distribution of (129)I in the air. Sensitivity of available measurement techniques for the determination of (129)I is compared. The article also provides the summary of current worldwide distribution of (129)I in air and respective radiation exposure of man.

Investigation of the isotopic ratio 129I/I in petrified wood

In fossil specimens, measurements of the natural isotopic ratio (129)I/I may provide a method to estimate the age of sample. The motivation for measuring the isotopic composition ((129)I/I) of petrified wood samples collected from Austria was to check this feasibility. Alkaline fusion together with anion exchange was used to extract iodine from the sample. Typical sample size for this study was 10-90 g. An atomic ratio as low as 10(-14) was determined using accelerator mass spectrometry (AMS). Uranium concentrations measured by instrumental neutron activation analysis (INAA) and α-spectrometry were found to be less than 3 mg kg(-1), therefore the contribution from fissiogenic (129)I was small and an estimation of ages was based on the decrease of the initial ratio (due to decay of the cosmogenic (129)I in a closed system) after subtraction of the fissiogenic (129)I. The value of the prenuclear ratio is crucial for the use of the (129)I system for dating purposes in the terrestrial environment. From the preanthropogenic (initial) ratio of 1.5 × 10(-12) of the hydrosphere and the results of the present study for the samples from Altenburg (1.05 × 10(-12)) and Fuerwald (6.16 × 10(-13)), respective ages of 8 ± 2.2 and 20.2 ± 2.2 million years were derived. Since samples were collected from a stratum deposited in the Upper Oligocene/Ergerien period (~25-30 million years ago), it can be concluded that these isotopic ratios do not show ages but an elapsed time since fossil wood was isolated from mineral rich water. Paleontological investigation shows that samples from Altenburg had mixed characteristics of old and modern Tertiary plants, thus an origin from a younger stratum re-sedimented with Oligocene cannot be excluded. However, the sample from Drasenhofen reflects that the (129)I/I system might not always be suitable for the dating of petrified wood sample due to fixation of anthropogenic (129)I into surface fractures.

Measurements of ²³⁶U in ancient and modern peat samples and implications for postdepositional migration of fallout radionuclides

(236)U was analyzed in an ombrotrophic peat core representing the last 80 years of atmospheric deposition and a minerotrophic peat sample from the last interglacial period. The determination of (236)U at levels of 10(7) atoms/g was possible by using ultraclean laboratory procedures and accelerator mass spectrometry. The vertical profile of the (236)U/(238)U isotopic ratio along the ombrotrophic peat core represents the first observation of the (236)U bomb peak in a terrestrial environment. A constant level of anthropogenic (236)U with an average (236)U/(238)U isotopic ratio of (1.24 ± 0.08) × 10(-6) in the top layers of the core was observed. Comparing the abundances of the global fallout derived (236)U and (239)Pu along the peat core, the post depositional migration of plutonium clearly exceeds that of uranium. However, the cumulative (236)U/(239)Pu ratio of 0.62 ± 0.31 is in agreement with previous studies on the global fallout uranium and plutonium. In the interglacial peat samples a (236)U/(238)U isotopic ratio of (3.3 ± 0.7) × 10(-12) was detected; although this measurement is an upper limit, it constitutes a significant step forward in the experimental determination of the natural (236)U abundance and represents a true background sample for the ombrotrophic peat core.

Iodine-129 in seawater offshore Fukushima: distribution, inorganic speciation, sources, and budget

The Fukushima nuclear accident in March 2011 has released a large amount of radioactive pollutants to the environment. Of the pollutants, iodine-129 is a long-lived radionuclide and will remain in the environment for millions of years. This work first report levels and inorganic speciation of (129)I in seawater depth profiles collected offshore Fukushima in June 2011. Significantly elevated (129)I concentrations in surface water were observed with the highest (129)I/(127)I atomic ratio of 2.2 × 10(-9) in the surface seawater 40 km offshore Fukushima. Iodide was found as the dominant species of (129)I, while stable (127)I was mainly in iodate form, reflecting the fact that the major source of (129)I is the direct liquid discharges from the Fukushima NPP. The amount of (129)I directly discharged from the Fukushima Dai-ichi nuclear power plant to the sea was estimated to be 2.35 GBq, and about 1.09 GBq of (129)I released to the atmosphere from the accident was deposited in the sea offshore Fukushima. A total release of 8.06 GBq (or 1.2 kg) of (129)I from the Fukushima accident was estimated. These Fukushima-derived (129)I data provide necessary information for the investigation of water circulation and geochemical cycle of iodine in the northwestern Pacific Ocean in the future.

Determination of (239)Pu, (240)Pu, (241)Pu and (242)Pu at femtogram and attogram levels - evidence for the migration of fallout plutonium in an ombrotrophic peat bog profile

The isotopic composition of plutonium ((239)Pu, (240)Pu, (241)Pu and (242)Pu) was investigated in a ∼0.5 m long peat core from an ombrotrophic bog (Black Forest, Germany) using clean room procedures and accelerator mass spectrometry (AMS). This sophisticated analytical approach was ultimately needed to detect reliably the Pu concentrations present in the peat samples at femtogram (fg) and attogram (ag) levels. The mean (240)Pu/(239)Pu isotopic ratio of 0.19 ± 0.02 (N = 32) in the peat layers, representing approximately the last 80 years, was in good agreement with the accepted value of 0.18 for the global fallout in the Northern Hemisphere. This finding is largely supported by the corresponding and rather constant (241)Pu/(239)Pu (0.0012 ± 0.0005) and (242)Pu/(239)Pu (0.004 ± 0.001) ratios. Since the Pu isotopic composition characteristic of the global fallout was also identified in peat samples pre-dating the period of atmospheric atom bomb testing (AD 1956-AD 1980), migration of Pu within the peat profile is clearly indicated. These results highlight, for the first time, the mobility of Pu in a peat bog with implications for the migration of Pu in other acidic, organic rich environments such as forest soils and other wetland types. These findings constitute a direct observation of the behaviour of Pu at fg and ag levels in the environment. The AMS measurements of Pu concentrations (referring to a corresponding activity of (240+239)Pu from 0.07 mBq g(-1) to 5 mBq g(-1)) essentially confirm our a priori estimates based on existing (241)Am and (137)Cs data in the investigated peat core and agree well with the global fallout levels from the literature. Exclusively employing the Pu isotope ratios established for the peat samples, the date of the Pu irradiation (AD 1956, correctable to AD 1964) was calculated and subsequently compared to the (210)Pb age of the peat layers; this comparison provided an additional hint that global fallout derived Pu is not fixed in the peat column, but has migrated downwards along the peat profile to layers preceding the nuclear age.

236U/238U and 240Pu/239Pu isotopic ratios in small (2 L) sea and river water samples

Accelerator Mass Spectrometry (AMS) and alpha spectrometry were used to determine uranium ((236)U, (238)U, (234)U) and plutonium isotopes ((239)Pu, (240)Pu) in sea and river water samples. Plutonium was separated by Dowex(®) 1 × 8 resin and UTEVA(®) resin was used for uranium purification. The measured (236)U/(238)U isotopic ratios for surface water from the Atlantic Ocean, the Pacific Ocean and the Black Sea were in the order of 10(-9), while values for river water were in the order of 10(-8). These contaminations may be attributed to global fallout. A sample of the reference material IAEA-443, collected from the Irish Sea, showed, in accordance to the reference value, a ratio that was 10(3) times higher due to effluents from the reprocessing plant at Sellafield. These results underline the good suitability of (236)U/(238)U as a tracer for hydrology and oceanography, and show that relatively small water samples are sufficient for the determination of (236)U by AMS, which is not the case for plutonium with present techniques. The plutonium concentrations in our water samples could only be measured with large uncertainties and were in the order of 10(-3) mBq/L (with the exception of the Irish Sea sample).