Study of the Gyromagnetic Resonance Damping in Relaxing Rare Earth Substituted YGd2Fe5O12 Garnets

The influence of magnetic state (saturated or unsaturated states) on the gyromagnetic resonance damping in relaxing rare earth substituted Y1-xDyxGd2Fe5O12 garnets (with x=0;0.15;0.3;0.6) has been studied. The damping parameter α, as defined by Landau-Lifshitz equation, has been determined either by FMR at 10GHz (saturated state) or by measurement of the frequency dependence of the complex initial permeability in the 0.1GHz-10GHz band (unsaturated state). On the one hand, the damping parameter αsat has been calculated by fitting the FMR spectra of single crystals with the theoretical lorentzian shape. On the other hand, the damping parameter αunsat of polycrystals has been calculated using models which take into account the interaction between magnetic domains. In the fully magnetized state the introduction of relaxing rare earth (Dy) is found to increase significantly αsat values (from 0.02 to 0.3 when x varies from 0 to 0.6). On the contrary, the introduction of Dy hardly increases αunsat values. It appears that the difference between αsat and αunsat values stems not only from the interaction between magnetic domains but also from the modification of the damping in each magnetic domain owing to the presence of magnetic domain walls

Distributions and fluxes of 226^{226}Ra and 228^{228}Ra in the Irish Sea and in the English channel, in relation to hydrological conditions and sediment interactions

International audienceDistribution of $^{226}$Ra activities and $^{228}$Ra/$^{226}$Ra activity ratios were measured in the surface waters of the Irish Sea and in the English Channel. 226Ra activities vary from 0.001 Bq.l$^{−1}$ for the Atlantic water to 0.002 Bq.l$^{-1}$ for coastal waters, whereas $^{228}$Ra/$^{226}$Ra activity ratios increase from 0.18 to 2.18. The coastal waters are clearly dominated by radium injection from nearshore sediments

Distribution of Technetium-99 in sub-tidal sediments of the Irish Sea

To date, relatively little attention has been given to the accumulation of 99Tc discharged from Sellafield in the subtidal sediments of the Irish Sea. The potential implications for secondary seafood contamination from contaminated sediment has driven the UK Food Standards Agency to commission further research into this pathway. The work reported here reviews existing data and provides new measurements of 99Tc specific activity in surface and sub-surface sediments of the Irish Sea, together with environmental K d values. The results are used to assess the spatial and temporal evolution of 99Tc in the seabed after 8 years of enhanced Sellafield discharges (between 1994 and 2002), of the aforementioned radionuclide. The information is discussed with reference to other studies, in an attempt to infer the processes controlling 99Tc uptake and release from seabed sediments. The average environmental Kd value for 99Tc in the Irish Sea (1.9×103) was more than an order of magnitude greater than the presently recommended value of 102 [IAEA, 2004. Sediment distribution coefficients and concentration factors for biota in the marine environment. Technical Report Series No. 422, IAEA, Vienna]. Comparison with results from laboratory studies indicates that the observed distribution may represent metastable binding rather than thermodynamic equilibrium. Activities in surface sediments decreased with increasing distance from Sellafield but were also dependent upon the nature of the underlying substrate, being greater on muddy material. Preliminary measurements of grain-size distribution indicated that the observed variation in activities was probably not due to surface area effects. There is an emerging body of evidence from other studies that indicate the differences were most likely due to variations in redox regimes between the different substrates. Vertical profiles were significantly irregular, probably due to the effects of variable sediment mixing processes. Comparison of profiles, close to the Sellafield pipeline, with a core taken over 20 years earlier (pre-EARP) indicated that the increase in the cumulative Sellafield discharge and redissolution from surficial sediment were required to explain the temporal variation. Since the surveys reported here were completed, substantial progress has been made in reducing 99Tc discharges from Sellafield. Assuming that the rate and extent of 99Tc remobilisation follows a similar pattern to that previously observed for caesium (137Cs), then the half-time for redissolution of 99Tc bound to sedimentary material in the Irish Sea is likely to be of the order of several tens of years. It is probable that small but nevertheless measurable 99Tc contamination of local seafood will persist for several decades, due to this secondary source. Crown Copyright © 2006 Published by Elsevier Ltd. All rights reserved

The dynamics of

From 1990 to 2000, 60Co, a radionuclide released into the English Channel by the La Hague reprocessing plant, has been measured in the deposited sediments of the Seine estuary. Since 1990, the 60Co concentrations have slowly increased from some tenths of Bq.kg-1 to ca 10 Bq.kg-1. This transient signal was used to bring the evidence of the input of marine particles far upstream in the estuary, ca 80 km from the river mouth. The dynamics of this process have been deciphered by comparing several sets of data obtained in the years 1990 to 2000. An average velocity of about 10 km.y-1 was found for this incoming sediment pool. These observations are conformable with calculated of suspended sediment fluxes performed along the river

Plutonium measurements at NEA’s North East Atlantic dumpsites

Surface, intermediate and near-bottom water samples were collected at two of the North East Atlantic radioactive waste dumping sites (47∘ 14’N, 05∘ 33’W and 45∘ 27’N, 06∘ 16’W) in the course of a sampling campaign in June–July 1998. Analysis of 239,240Pu concentrations show no significant differences with respect to measured concentrations in waters taken from control (background) stations well removed from the dumping sites

Molecular quantification of sulfate-reducing microorganisms (carrying dsrAB genes) by competitive PCR in estuarine sediments

In this study, we describe a competitive polymerase chain reaction (PCR) for the quantification of the sequences of dsrAB in sulfate-reducing microorganisms. We used the dsr1F/dsr4R set of primers, previously designed by Wagner et al. (1998), and a competitor sequence was constructed from the dsrAB genes of Desulfovibrio vulgaris. The detection limit of competitive PCR corresponded to 45 copies of the dsrAB genes per ng of extracted DNA, and most of the dsrAB sequences amplified and cloned from DNA extracted from Seine estuary sediments were amplified with a similar efficiency. Competitive PCR was then used to assess the abundance of dsrAB genes in the total DNA extracted from the sediment of the Seine estuary mudflats. We observed that the abundance of dsrAB coincided with the variation in the sulfate reduction rate with the depth of the sample, confirming the importance of 'dsrAB' sulfate-reducing microorganisms in sulfidogenesis in anoxic environments. We obtained values ranging from 0.045×103 to 6.63×103 copies of dsrAB per ng of extracted DNA, and values of the sulfate reduction rate ranging from 35 to 158 nmol cm-3 day-1. These results are similar to those obtained in other studies using molecular biology techniques. © 2003 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved

Post-depositional reactivity of the plutonium in different sediment facies from the English Channel - an experimental approach

The post-depositional reactivity of the plutonium was investigated in bottom sediments collected in the central English Channel using an experimental approach. Medium to coarse grained surficial sediments and fine-grained undisturbed sediment cores were spiked with 238Pu. After a one-month incubation, pore waters were extracted under strictly anoxic conditions and dissolved plutonium was analysed by liquid scintillation techniques. Kd values ranged from 102 to 105 in surficial sediments undergoing oxic diagenesis, and were shown to be grain-size dependant. In fine-grained sediments undergoing anoxic diagenesis, Kd values ranged between 103 and 105. Kd profile suggests an active recycling of the plutonium in the topmost sediment layers, and subsequent efficient uptake process at depth, tentatively acido-volatile sulphide (AVS) precipitation. This hypothesis was further confirmed by a correlation between the AVS content and the loosely bound plutonium extracted using an oxidising/complexing solution from sediment subsamples. In surficial sediments, by contrast, loosely bound plutonium was likely to be associated with the carbonate phase as surface complexes

Higher-order crystal field and rare-earth magnetism in rare-earth– Co 5 intermetallics

International audienc

Multi-isotopic determination of plutonium (239Pu, 240Pu, 241Pu and 242Pu) in marine sediments using sector-field inductively coupled plasma mass spectrometry

cited By 26International audienceAmong the transuranic elements present in the environment, plutonium isotopes are mainly attached to particles, and therefore they present a great interest for the study and modelling of particle transport in the marine environment. Except in the close vicinity of industrial sources, plutonium concentration in marine sediments is very low (from 10-4 ng kg-1 for 241Pu to 10 ng kg-1 for 239Pu), and therefore the measurement of 238Pu, 239Pu, 240Pu, 241Pu and 242Pu in sediments at such concentration level requires the use of very sensitive techniques. Moreover, sediment matrix contains huge amounts of mineral species, uranium and organic substances that must be removed before the determination of plutonium isotopes. Hence, an efficient sample preparation step is necessary prior to analysis. Within this work, a chemical procedure for the extraction, purification and pre-concentration of plutonium from marine sediments prior to sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS) analysis has been optimized. The analytical method developed yields a pre-concentrated solution of plutonium from which 238U and 241Am have been removed, and which is suitable for the direct and simultaneous measurement of 239Pu, 240Pu, 241Pu and 242Pu by SF-ICP-MS. © 2007 Elsevier B.V. All rights reserved