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

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

Assessment of residual radionuclide levels at the Bokak and Bikar Atolls in the northern Marshall Islands.

The Bikar and Bokak Atolls, located in the northern Marshall Islands, are extremely isolated and consist of pristine marine and terrestrial ecosystems. Both atolls may have experienced significant radioactive deposition following the nuclear weapon testing conducted at Bikini and Enewetak proving grounds. Here we report activity concentrations of artificial radionuclides (239Pu, 240Pu, 241Pu, 241Am, 137Cs and 90Sr) in marine and terrestrial samples collected from Bikar and Bokak Atolls. Artificial radionuclides in soil from the Majuro Atoll are also reported and form a radiological baseline against which the levels at the other atolls can be compared. We observed low levels of artificial radionuclides in soil from Majuro and Bokak, but significantly higher levels in soil from Bikar. The residual radioactivity in the Bikar environment is comparable to the levels previously reported for other nearby atolls, including Taka and Utrik, but lower than for Rongerik, Rongelap, Bikini and Enewetak. An analysis of 240Pu/239Pu isotope ratios and estimations of the dates of contamination from 241Am/241Pu activity ratios both indicated that the Bikar Atoll was contaminated mainly by radioactive fallout from the Castle Bravo test in 1954. We compare the results of our measurements at Bikar and Bokak to data from other atolls in the Marshall Islands and to regions of the world affected by both global and regional fallout from atmospheric nuclear weapons testing and nuclear accidents.

236U, 237Np and 239,240Pu as complementary fingerprints of radioactiveeffluents in the western Mediterranean Sea and in the Canada Basin (Arctic Ocean).

The aim of this study was to assess the potential of combining the conservatively behaving anthropogenic radionuclides 236U and 237Np to gain information on the origin of water masses tagged with liquid effluents from Nuclear Reprocessing Plants. This work includes samples collected from three full-depth water columns in two areas: i) the Arctic Ocean, where Atlantic waters carry the signal of Sellafield (United Kingdom) and La Hague (France) nuclear reprocessing facilities; and ii) the western Mediterranean Sea, directly impacted by Marcoule reprocessing plant (France). This work is complemented by the study of the particle-reactive Pu isotopes as an additional fingerprint of the source region. In the Canada Basin, Atlantic waters showed the highest concentrations and 237Np/236U ratios in agreement with the estimated values for North Atlantic waters entering the Arctic Ocean and tagged with the signal of European Nuclear Reprocessing Plants. These results may reflect the impact of the documented releases for the 1990s. In the Mediterranean Sea, an excess of 236U presumably caused by Marcoule is reflected in the lower 237Np/236U ratios compared to the Global Fallout signal in all the studied samples. On the contrary, the 239,240Pu profiles were mainly governed by the Global Fallout. The impact of Marcoule as a local source is further corroborated when comparing the temporal evolution of these ratios between 2001 and 2013. The lowest 237Np/236U ratios observed in 2001 at the surface reflect a previous local input that is no longer observed in 2013 as it had been homogenized through the whole water column. This work presents the use of 237Np as a new ocean tracer. A more accurate characterization of the main sources is still needed to optimize the use of 236U-237Np as a new tool to understand transient oceanographic processes.

Simple and fast method for the analysis of 236U, 237Np, 239Pu and 240Pu from seawater samples by Accelerator Mass Spectrometry.

A simple and fast radiochemical procedure for the sequential extraction of U, Np and Pu from small-volume seawater samples (<10 L) is presented. The method has been developed and optimized for the final determination of 236U, 237Np, 239Pu and 240Pu by Accelerator Mass Spectrometry (AMS). It is based on the use of 242Pu as tracer for both Np and Pu isotopes. Samples are pre-concentrated by Fe(OH)2 co-precipitation. TEVA® and UTEVA® resins are used in a very simplified way for the final purification of the Pu+Np and U fractions, respectively. The radiochemical yields of the three elements have been investigated in detail by alpha spectrometry (AS) and gamma spectrometry (GS). The obtained results indicate high and robust chemical yields for the three elements and similar ones for Pu and Np. Furthermore, the use of 242Pu as tracer for 237Np is validated by analyzing a reference seawater sample (IAEA-443) by radiometric techniques. We demonstrated that, if chemicals are properly chosen, processed blank levels can be kept at the same level of the extremely low detection limits that can be achieved by AMS (105-106 atoms/sample). The procedure is finally applied for the study by AMS of a reference seawater sample from the Mediterranean Sea (IAEA-418).

Artifact Induced by a Transponder During In Vivo Magnetic Resonance Imaging on Horse Brain.

Magnetic resonance imaging (MRI) is now widely used in equine veterinary practice. However, the mandatory European legislation regarding horse identification imposes the implantation of a transponder within the fatty tissue of the neck cervical ligament. While performing brain MRI for scientific purposes in ponies, we faced artifacts produced by such transponder and reported here this problem. Indeed, pony mares were anesthetized for 2 hours and placed, bedded on their back, in a 3T MRI scanner. A four-element flexible antenna positioned around the head was used. Three MRI sequences were performed on each animal: three-dimensional T1, three-dimensional T2, and two-dimensional T1. The anesthesia allowed the acquisition of MRI for 2 hours. The images for the three MRI sequences for each pony exhibited great quality on all the anterior parts of the brain but began to become distorted posteriorly to the pineal pituitary axis and completely disappeared at the level of the cerebellum. To find the origin of the artifact, the transponder used for the identification of the animal was inserted in an inert gel and imaged in the same conditions as the ponies. The images obtained looked similar to the observed artifact. Our study thus advocates for the further exploration of such kind of artifact when using 3T MRI in brain imaging in horses.

On the use of MnO2 cartridges for the plutonium determination in seawater.

To analyze plutonium (Pu) in open ocean waters can be challenging due to the low seawater concentrations. In this study we compared two techniques for Pu determination, one in-situ MnO2 cartridge system and the more commonly used MnO2 precipitation technique. During the pre-pilot GEOTRACES cruise ANT XXX-1 (2005) we tested MnO2 cartridges for the pre-concentration of Pu from seawater at 19 sampling stations on a transect in the southeastern Atlantic Ocean between Vigo (Spain) and Cape Town (South Africa). Our in-situ sampling setup consisted of one particle cartridge followed by three MnO2 cartridges in a series. Through the system we pumped between 956 and 2700 l of surface seawater with a flow rate between 1.6 and 5.2 l/min. We found that the adsorption efficiency of a single MnO2 cartridge to adsorb Pu was rather constant and on average a 58 ±â€¯7%. The adsorption efficiency was also found to be independent of seawater: temperature in the range of 18.3-29.2 °C, salinity range 34.2-37.1‰, and conductivity in the range of 46.8-58.4 mS/cm. In parallel with the in-situ sampling, discrete surface water samples between 259 and 281 l were taken and Pu was pre-concentrated using the MnO2 precipitation method. We find a good agreement between the Pu concentrations determined with the two different techniques. The in-situ pre-concentration technique requires more radiochemical work in the laboratory but has the advantage that large seawater volumes can be sampled without the necessity for radiochemical processing on-board the ship. The much larger volumes sampled with the in-situ technique compared with the precipitation technique, enables accurate determination of Pu-isotopic ratios with a low relative standard deviation. We have shown in this study that in-situ MnO2 cartridge technique can be used in a reliable way for the determination of dissolved Pu seawater concentration in open ocean waters.

Distribution of natural and anthropogenic radionuclides in northwest Mediterranean coastal sediments.

The distribution of radionuclides in NW Mediterranean coastal sediments, and the processes controlling their abundance were investigated in three cores taken near the island of Porquerolles and one offshore Monaco. The sediments collected near Porquerolles were strongly anoxic due to diagenetic processes involved in the decomposition of organic matter, whereas they transitioned from oxic to anoxic at a depth of 4 cm beneath the seawater interface at Monaco. Organic carbon (OC) was more abundant in sediments at Porquerolles (by about a factor of 3-5) than at Monaco and elsewhere in the coastal NW Mediterranean. Sediment cores collected NE of Porquerolles also possessed elevated uranium concentrations that correlated with high OC content and strong reducing conditions. The 239,240Pu and 241Am activities in surficial sediments ranged from 1 to 5.7 Bq kg-1 and 0.3 to 1 Bq kg-1, respectively, while the 137Cs activity ranged from 0.3 to 6.2 Bq kg-1. The mean activity ratios of 241Am/239,240Pu and 238Pu/239,240Pu in Porquerolles and Monaco sediments were similar to the global fallout ratios. Sediment inventories of global fallout 239,240Pu (430-800 Bq m-2) and 241Am (150-285 Bq m-2) were by about a factor of 5-10 higher at Porquerolles, whereas the inventory of 137Cs (430-1000 Bq m-2) was substantially lower at the investigated stations than have been reported elsewhere at similar latitudes. Specific local conditions characterised by high OC sediment loads due to the growth and mortality of Posidonia oceanica have been responsible for deposition of large amounts of seagrass tissues at the NE corner of Porquerolles, which have had a profound effect on the distribution of radionuclides in the sediments.

Determination of low-level plutonium in seawater by sector field inductively coupled plasma mass spectrometry: method validation.

Sources of plutonium isotopes to the marine environment are well defined, both spatially and temporally which makes plutonium (Pu) a potential tracer for oceanic processes. This paper presents the optimisation and validation of an analytical procedure for ultra-trace determination of Pu isotopes (239Pu and 240Pu) in seawater based on the external calibration and sector field inductively coupled plasma mass spectrometry (SF ICP-MS) determination. Additionally, method for Pu isotope ratio (240Pu/239Pu) in marine samples is also discussed. A combination of two-step anion exchange (AG1-X8) and one-step extraction chromatography (TEVA) was very efficient resulting in uranium (U) decontamination factor of 5 × 106-1 × 108. A full validation approach in line with ISO 17025 standard and Eurachem guidelines was followed. With this in mind, blanks, recovery (87 ± 8 %, k = 2), within-laboratory repeatability (5.6 %), limits of detection (0.12 and 0.08 fg mL-1 for 239Pu and 240Pu, respectively) and expanded uncertainty (13 %, k = 2) were systematically assessed. The procedure was applied for the determination of 239Pu and Pu in seawater sample coming from Mediterranean Sea. Obtained results were in good agreement with results obtained with alpha spectrometry, applied on the same seawater sample. Pu/239Pu atom ratio in seawater sample from the Mediterranean Sea was also determined. The precision and accuracy of 240Pu/239Pu isotopic ratio analysis were carefully examined using NBS-947 isotopic standard. 240Pu/239Pu ratio was found to be 0.187 ± 0.006 and is in agreement with accepted ratios for the global fallout of Pu.

Main results of the 2012 joint Norwegian-Russian expedition to the dumping sites of the nuclear submarine K-27 and solid radioactive waste in Stepovogo Fjord, Novaya Zemlya.

This paper reports the main results of the 2012 joint Norwegian-Russian expedition to investigate the radioecological situation of the Stepovogo Fjord on the eastern coast of Novaya Zemlya, where the nuclear submarine K-27 and solid radioactive waste was dumped. Based on in situ gamma measurements and the analysis of seawater and sediment samples taken around the submarine, there was no indication of any leakage from the reactor units of K-27. With regard to the radioecological status of Stepovogo Fjord, activity concentrations of all radionuclides in seawater, sediment and biota in 2012 were in general lower than reported from the previous investigations in the 1990s. However in 2012, the activity concentrations of (137)Cs and, to a lesser extent, those of (90)Sr remained elevated in bottom water from the inner part of Stepovogo Fjord compared with surface water and the outer part of Stepovogo Fjord. Deviations from expected (238)Pu/(239,240)Pu activity ratios and (240)Pu/(239)Pu atom ratios in some sediment samples from the inner part of Stepovogo Fjord observed in this study and earlier studies may indicate the possibility of leakages from dumped waste from different nuclear sources. Although the current environmental levels of radionuclides in Stepovogo Fjord are not of immediate cause for concern, further monitoring of the situation is warranted.