Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can ...

ETH Zurich

Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle.

Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model.

It is difficult to obtain fossil data from the 10% of Earth's terrestrial surface that is covered by thick glaciers and ice sheets, and hence, knowledge of the paleoenvironments of these regions has remained limited. We show that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores, enabling reconstructions of past flora and fauna. We show that high-altitude southern Greenland, currently lying below more than 2 kilometers of ice, was inhabited by a diverse array of conifer trees and insects within the past million years. The results provide direct evidence in support of a forested southern Greenland and suggest that many deep ice cores may contain genetic records of paleoenvironments in their basal sections.

Ancient biomolecules from deep ice cores reveal a forested southern Greenland.

Atom ratios of the isotopes (239)Pu, (240)Pu, (241)Pu and (244)Pu were determined in sediments and soils from Bikini atoll using low energy Accelerator Mass Spectrometry. All samples had been contaminated by local fallout from nuclear weapon testing between 1946 and 1958 and show significant variations in the isotopic composition, which are ascribed to the different yields of single tests and to the mixture of material from various devices. Differences in the (244)Pu/(239)Pu ratio (2.8-5.7x10(-4)) are more pronounced than in the (240)Pu/(239)Pu ratio of the same samples and provide complementary information to distinguish the sources of contamination.

Isotopic signature of plutonium at Bikini atoll.

Understanding the temporal variation of cosmic radiation and solar activity during the Holocene is essential for studies of the solar-terrestrial relationship. Cosmic-ray produced radionuclides, such as (10)Be and (14)C which are stored in polar ice cores and tree rings, offer the unique opportunity to reconstruct the history of cosmic radiation and solar activity over many millennia. Although records from different archives basically agree, they also show some deviations during certain periods. So far most reconstructions were based on only one single radionuclide record, which makes detection and correction of these deviations impossible. Here we combine different (10)Be ice core records from Greenland and Antarctica with the global (14)C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution (10)Be record from Dronning Maud Land obtained within the European Project for Ice Coring in Antarctica in Antarctica. The new cosmic radiation record enables us to derive total solar irradiance, which is then used as a proxy of solar activity to identify the solar imprint in an Asian climate record. Though generally the agreement between solar forcing and Asian climate is good, there are also periods without any coherence, pointing to other forcings like volcanoes and greenhouse gases and their corresponding feedbacks. The newly derived records have the potential to improve our understanding of the solar dynamics and to quantify the solar influence on climate.

9,400 years of cosmic radiation and solar activity from ice cores and tree rings.

Comprendre la variation temporelle des rayonnements cosmiques et l&#39;activit&eacute; solaire au cours de l&#39;Holoc&egrave;ne est essentiel pour l&#39;&eacute;tude de la relation soleil-terre. &Ecirc;tre des radionucl&eacute;ides produits des rayons cosmiques, par exemple (10) et (14) C qui sont stock&eacute;s dans des carottes de glaces polaires et anneaux d&#39;arbre, offrir une opportunit&eacute; unique pour reconstituer l&#39;histoire des rayonnements cosmiques et l&#39;activit&eacute; solaire pendant plusieurs mill&eacute;naires. Bien que le chronogramme de diff&eacute;rentes archives fondamentalement d&#39;accord, ils montrent aussi certains &eacute;carts par rapport au cours de certaines p&eacute;riodes. Jusqu&#39;&agrave; pr&eacute;sent la plupart des reconstructions reposaient sur seul enregistrement seul radionucl&eacute;ide, ce qui rend impossible la d&eacute;tection et la correction de ces d&eacute;viations. Ici, nous combinons diff&eacute;rentes (10) glace chronogramme au Groenland et en Antarctique avec le global (14) C de base enregistrement de bague arbre &agrave; l&#39;aide d&#39;analyse en composantes principales. Cette approche n&#39;est possible en raison d&#39;une nouvelle haute r&eacute;solution (10) &ecirc;tre record de Dronning Maud Land obtenus au sein du projet europ&eacute;en for Ice Coring in Antarctica en Antarctique. Le nouveau record de rayonnement cosmique permet de d&eacute;river l&#39;irradiance solaire totale, qui est ensuite utilis&eacute; comme indicateur de l&#39;activit&eacute; solaire pour identifier l&#39;empreinte solaire dans un enregistrement de climat asiatique. Bien que l&#39;accord entre le for&ccedil;age solaire et le climat asiatique est g&eacute;n&eacute;ralement bonne, il y a aussi des p&eacute;riodes sans aucune coh&eacute;rence, pointant aux autres for&ccedil;ages comme les volcans et les gaz &agrave; effet de serre et leurs r&eacute;troactions correspondantes. Les enregistrements nouvellement d&eacute;riv&eacute;es ont le potentiel d&#39;am&eacute;liorer notre compr&eacute;hension de la dynamique solaire et de quantifier l&#39;influence solaire sur le climat.

9 400 ans des rayonnements cosmiques et l&#39;activit&eacute; solaire de carottes de glace et les cernes.

Capire la variazione temporale della radiazione cosmica e attivit&agrave; solare durante l&#39;Olocene &egrave; essenziale per gli studi del rapporto solare-terrestre. Essere prodotte radionuclidi raggi cosmici, come ad esempio (10) e (14) C che sono memorizzati nelle carote di ghiaccio polare e dell&#39;albero anelli, offrono l&#39;opportunit&agrave; unica di ricostruire la storia della radiazione cosmica e attivit&agrave; solare sopra molti millenni. Anche se fondamentalmente d&#39;accordo record da archivi diversi, essi mostrano anche alcune deviazioni in determinati periodi. Finora la maggior parte delle ricostruzioni erano basate su un solo record singolo radionuclide, che rende impossibile la rilevazione e la correzione di queste deviazioni. Qui combiniamo diversi (10) essere ice core records dalla Groenlandia e Antartide con il globale (14) C record di anello albero utilizzando analisi delle componenti principali. Questo approccio &egrave; possibile solo a causa di una nuova ad alta risoluzione (10) essere record da Dronning Maud Land ottenuti nell&#39;ambito del progetto europeo per Ice Coring in Antarctica in Antartide. Il nuovo record di radiazione cosmica consente di derivare irradianza solare totale, che viene quindi utilizzato come proxy dell&#39;attivit&agrave; solare per identificare l&#39;impronta solare in un record di clima asiatico. Anche se l&#39;accordo tra forzatura solare e clima asiatico &egrave; generalmente buona, ci sono anche periodi senza alcuna coerenza, puntando ad altre forzanti come vulcani e gas serra e loro feedback corrispondente. Il record recente derivata hanno il potenziale per migliorare la nostra comprensione delle dinamiche solari e di quantificare l&#39;influenza solare sul clima.

9.400 anni di radiazione cosmica e attivit&agrave; solare da carote di ghiaccio e anelli degli alberi.

An analytical method was developed for simultaneous determination of ultratrace level plutonium (Pu) and neptunium (Np) using iron hydroxide coprecipitation in combination with automated sequential injection extraction chromatography separation and accelerator mass spectrometry (AMS) measurement. Several experimental parameters affecting the analytical performance were investigated and compared including sample preboiling operation, aging time, amount of coprecipitating reagent, reagent for pH adjustment, sedimentation time, and organic matter decomposition approach. The overall analytical results show that preboiling and aging are important for obtaining high chemical yields for both Pu and Np, which is possibly related to the aggregation and adsorption behavior of organic substances contained in urine. Although the optimal condition for Np and Pu simultaneous determination requires 5-day aging time, an immediate coprecipitation without preboiling and aging could also provide fairly satisfactory chemical yields for both Np and Pu (50-60%) with high sample throughput (4 h/sample). Within the developed method, (242)Pu was exploited as chemical yield tracer for both Pu and Np isotopes. (242)Pu was also used as a spike in the AMS measurement for quantification of (239)Pu and (237)Np concentrations. The results show that, under the optimal experimental condition, the chemical yields of (237)Np and (242)Pu are nearly identical, indicating the high feasibility of (242)Pu as a nonisotopic tracer for (237)Np determination in real urine samples. The analytical method was validated by analysis of a number of urine samples spiked with different levels of (237)Np and (239)Pu. The measured values of (237)Np and (239)Pu by AMS exhibit good agreement (R(2) ≥ 0.955) with the spiked ones confirming the reliability of the proposed method.

Sequential injection approach for simultaneous determination of ultratrace plutonium and neptunium in urine with accelerator mass spectrometry.

The contamination of Japan after the Fukushima accident has been investigated mainly for volatile fission products, but only sparsely for actinides such as plutonium. Only small releases of actinides were estimated in Fukushima. Plutonium is still omnipresent in the environment from previous atmospheric nuclear weapons tests. We investigated soil and plants sampled at different hot spots in Japan, searching for reactor-borne plutonium using its isotopic ratio ²⁴⁰Pu/²³⁹Pu. By using accelerator mass spectrometry, we clearly demonstrated the release of Pu from the Fukushima Daiichi power plant: While most samples contained only the radionuclide signature of fallout plutonium, there is at least one vegetation sample whose isotope ratio (0.381 ± 0.046) evidences that the Pu originates from a nuclear reactor (²³⁹⁺²⁴⁰Pu activity concentration 0.49 Bq/kg). Plutonium content and isotope ratios differ considerably even for very close sampling locations, e.g. the soil and the plants growing on it. This strong localization indicates a particulate Pu release, which is of high radiological risk if incorporated.

Plutonium release from Fukushima Daiichi fosters the need for more detailed investigations.

Activation measurements of materials exposed to nuclear bomb explosions are widely used to reconstruct the neutron flux for retrospective dosimetry. In this study the applicability of coral CaCO3 as a biogenic neutron fluence dosimeter is tested. The long-lived radioisotopes (41)Ca, (14)C and (10)Be, which had been produced in nuclear bomb explosions, are measured in several coral sand samples from the Bikini atoll at the 600 kV and 200 kV AMS facilities of ETH Zurich. Elevated concentrations of all studied isotopes are found in a sample from the crater that was initially formed by the high-yield nuclear explosion Castle Bravo in 1954 and that had been used as site for several tests afterward. The observed (14)C concentration is considered too large to originate from neutron irradiation of CaCO3 alone. The relatively low concentration of (10)Be found in the crater sample indicates that production of (10)Be during nuclear bomb testing is generally minor. A simple neutron fluence reconstruction is performed on basis of the (41)Ca/(40)Ca ratio.

41Ca, 14C and 10Be concentrations in coral sand from the Bikini atoll.

By focusing high-intensity laser pulses on carbonate samples carbon dioxide is generated and can be directly introduced into the gas ion source (GIS) of an Accelerator Mass Spectrometer (AMS). This new technique allows rapid radiocarbon analyses at high spatial resolution. The design of the deignated laser ablation cell as well as first results on a stalagmite sample are presented.

Rapid revelation of radiocarbon records with laser ablation Accelerator Mass Spectrometry.

The Fukushima nuclear accident (March 11, 2011) caused the widespread contamination of Japan by direct deposition of airborne radionuclides. Analysis of weekly air filters revealed sporadic releases of radionuclides long after the Fukushima Daiichi reactors have been stabilized. One major discharge was observed in August 2013 in monitoring stations north of the Fukushima Daiichi nuclear power plant (FDNPP). During this event, an air monitoring station in this previously scarcely contaminated area suddenly reported (137)Cs activity levels that were 30-fold above the background. Together with atmospheric dispersion and deposition simulation, radionuclide analysis in soil indicated that debris removal operations conducted on the FDNPP site on August 19, 2013 are likely to be responsible for this late release of radionuclides. One soil sample in the center of the simulated plume exhibited a high (90)Sr contamination (78±8 Bq kg(-1)) as well as a high (90)Sr/(137)Cs ratio (0.04); both phenomena have usually been observed only in very close vicinity around the FDNPP. We estimate that through the resuspension of highly contaminated particles in the course of these earthmoving operations, a gross (137)Cs activity of ca. 2.8×10(11)Bq has been released.

Marcus Christl

Laboratory of Ion Beam Physics

ETH Zurich

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

Marcus Christl

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Laboratory of Ion Beam Physics

ETH Zurich

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

Laboratory of Ion Beam Physics