Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The MHD activities at FZR are summarized. Main focus is put on applied MHD projects like in crystal growth, metal casting, electromagnetic levitation or metal fibre extraction. For basic research activities, the dynamo project and the studies on seawater flow control are presented.

The basic idea of tailored magnetic field solutions is outlined, and examples from crystal growth and metallurgical applications are given for this approach. The importance of a combined approach is pointed out consisting of numerical simulations and cold liquid metal model experiments.

Um die künftigen Redoxbedingungen, die durch den natürlichen Holzabbau in gefluteten Gruben entstehen, zu charakterisieren, wurde das Wasser eines Hochmoors im Erzgebirge untersucht. Das Redoxpotential im Moorwasser, gemessen mit einer Platinelektrode, sank von der Oberfläche bis in einen Meter Tiefe von etwa 600 mV auf -100 mV. Aus der Tiefenwasseranalyse und der Untersuchung des Sumpfgases, das aus dem Grund extrahiert wurde, errechnete sich ein Redoxpotential von -119  5 mV. Charakteristisch für das stark reduzierende Milieu ist das Auftreten von Methan und Schwefelwasserstoff im Sumpfgas. Aus der Kenntnis dieses Zustands kann für die künftige Situation in der gefluteten Grube die Schlussfolgerung gezogen werden, dass Uran(VI) und Arsen(V) im Laufe der Zeit reduziert werden und als Uran(IV)-Hydroxid und Arsen(III)-Sulfid ausgeschieden werden. Auf diese Weise findet ein natürlicher Reinigungsprozess im Grubenwasser statt.

To characterize the future redox milieu caused by natural degradation of wood in flooded uranium mines the aquifer of a highland bog ground was studied as a natural analogue site. Going from the surface to a depth of one meter in the bog water the redox potential measured with a platinum electrode changes from about 600 mV to -100 mV. From the depth-water analyses and analyses of bog gas extracted from the ground an Eh value of -119  5 mV could be calculated. Methane and hydrogen sulfide were found in the gas characterizing the strongly reducing condition in the bog ground. From that the conclusion for the future mine situation can be drawn that uranium(VI) and arsenic(V) will be reduced and precipitated as U(OH)4 and As2S3. In that way decontamination of the mine water takes place as a consequence of a natural attenuation process.

We determined Sb speciation in 9 soil samples from 6 Swiss shooting ranges using Sb K-edge EXAFS spectroscopy and advanced statistical data analysis methods (ITFA). Despite the high variability in Geology, pH (3.1 - 7.5) and Sb concentrations (1000 - 17000 mg/kg), we found only two species: metallic Sb(0) and Sb(V) forming inner-sphere sorption complexes on Fe oxide surfaces. The relative amount of Sb(0) ranged from 0 to 75 %, the relative amount of Sb(V) ranged from 25 to 100 %. Distribution between the two species was not explained by any of the measured variables. No evidence for Sb(III) was found in the bulk samples. To the best of our knowledge this is the first quantitative determination of the chemical Sb forms in bulk soil samples.

Electroluminescence with power efficiencies larger than 0.1 % is observed from silicon pn diodes prepared by boron implantation. The implanted boron concentration is above the solubility limit for the post-implantation annealing temperature leading to the formation of boron clusters during annealing. The electroluminescence from electron-hole pairs exhibits an anomalous increase in the total intensity with increasing temperature. This behavior is explained by the thermal release of carriers trapped at local potential minima related to the boron clusters.

The flow field in the pressure vessel of a PWR is of turbulent nature. Statistical fluctuations occurring under quasi-stationary and transient flow conditions influence the mixing of coolant with different quality. It can be assumed, that the resulting boron concentrations and coolant temperatures at the inlet of the fuel assemblies are influenced by these fluctuations, too. Experiments at the ROCOM test facility for a hypothetical boron dilution event following the inadvertent start-up of the first main coolant pump were carried out with the goal to provide boundary conditions for core calculations. The core behaviour is simulated with the reactor dynamic code DYN3D. The influence of statistical fluctuations of the coolant and its consequences are investigated. Several simulations are performed with different core boundary conditions based on average values, a single measurement and values which are the boundaries of given confidence intervals of the measurements. Considering the different simulations the influence of the turbulent fluctuations on the reactor power and its distribution cannot be neglected. It can be important for similar transients, if safety parameters are close to the given limits.

Cone-beam type X-ray CT is a potential mehtod to measure three-dimensional phase-distribution in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. Such data is highly valuable for the assessment and evaluation of chemical processes, for optimisation of the reactor and stirrer design, and for evaluation of computational fluid dynamics codes used to model the fluid flow and heat transer in reactive systems. However, there are considerable difficulties for accurate quantitative measurements, for instance of average gas fraction in a fluid, due to beam hardening and radiation scattering effects. In a theoretical and experimental work we have investigated the non-linear effect of both physical phenomena and developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate void fraction measurement with X-ray cone-beam tomography.

A new ion beam facility for slow highly charged ions is presented that will provide low and medium energetic highly charged ions. An Electron Cyclotron Resonance (ECR) ion source delivers high currents of low and medium charged ions whereas very highly charged ions at lower ion currents are supplied by an Electron Beam Ion Trap(EBIT). The new ion beam facility will provide an experimental environment for basic research in atomic and solid state physics, as well as applied research in areas such as surface engineering, nanostructuring and nanobiotechnology.

In the interaction of highly charged ions with solid surfaces a main interest lies in the study of the dissipation channels for the potential energy. A large amount of information about secondary electron emission and X-ray emission has been collected in the past, enlightening the physics of the relaxation process of HCIs at surfaces. Calculating the amount of energy, which is dissipated into these channels only 10% to 15% is obtained. Less information is available about the absolute amount of the potential energy, which is deposited into the surface. In view of possible applications of HCIs for surface modifications the knowledge of this amount is essential.
In order to study the energy retention of the potential energy of HCIs into solid surfaces, we apply a calorimetric approach [1]. The ions (charge state q=2 .. 8) are extracted from an ECR ion source with 5 kV and decelerated to final kinetic energies down to 60 eV x q after beam transport and charge state separation. By using a liquid-nitrogen cooled calorimetric setup the retention of the total energy, kinetic and potential, is determined via the temperature increase during the bombardment. Measuring the energy retention at kinetic energies from 200 – 60 eV and extrapolating to 0 eV kinetic energy the separated potential energy is obtained. The experiments were done on clean Cu, Si, and SiO2 surfaces.
Here, we present a comparative study of the relative retention coefficients of the potential energy for the metallic, semiconductor, and insulator surfaces. In addition, measurements of the secondary electron yield are taken into consideration for a detailed picture of the energy dissipation channels.
[1] U. Kentsch, G. Zschornack, H. Tyrroff, and W. Möller, Phys. Rev. Lett. 87, 105504 (2001)

The secondary electrons emitted during the interaction of highly charged ions with solid surfaces carry detailed information about the complex interaction mechanism. In the past, the study of the secondary electrons emitted from the interaction with metal surfaces revealed the fascinating dynamics of the hol-low atoms formed above and below the surface. However, in the case of the interaction with insulating surfaces there is still some controversy whether the relaxation dynamics is the same as for metals. In addition, the microscopic and macroscopic charging of the insulating surfaces, which constitutes an im-portant part of the interaction mechanisms, makes these studies difficult.
Here, we report on the emission of electrons from Ne9+ interacting with thin SiO2 films. The typical LMM and KLL Auger electrons resulting from the last steps in the neutralisation process are observed on top of a broad secondary electron background. The mean peak positions of the Auger electrons are shifted to lower energies compared to the Auger electrons from metal sur-faces. Two mechanisms will be discussed for the interpretation of this obser-vation: the macroscopic charging of the SiO2 surface and a weaker screening of the ions in the SiO2 film.

Es werden Substanzen vorgeschlagen, die radioaktive Metalle mit hoher Stabilität binden und deren Metallkonjugate nach Applikation in den Körper metabolisch stabil sind, außerdem ein Verfahren zur Herstellung der Substanzen

Es wird eine Blitzlampenspiegelanordnung vorgestellt, die eine homogene und schnelle Erwärmung von Halleitersubstraten bei unwesentlich höheren Anlagenkosten ermöglicht.

Various magnetic properties like the saturation magnetization, the Curie temperature, the coercivity and the magnetic damping behavior can easily be modified by means of ion irradiation and implantation. In combination with focused ion beam techniques even a pure magnetic patterning without changing the surface topography becomes feasible. A magnetic domain pattern can be imprinted by using ion irradiation in an applied magnetic field. Thus doping of magnetic materials opens a route to a new class of artificial magnetic materials with adjustable magnetic properties.
Here, as an example, we report on the tailoring of the magnetic properties of Permalloy (20 nm Ni81Fe19) by means of 30 keV Cr implantation. Due to the doping the Curie temperature of the Permalloy film decreases with the implantation fluence and drops below room temperature at an averaged Cr concentration of about 7 at-%. Also the saturation magnetization and the uniaxial anisotropy decrease. However the magnetic damping behavior of Cr implanted Permalloy films is strongly enhanced which is due to a combination of structural changes and alloying effects in the thin film. In order to clarify the basic mechanism for the enhancement the chemical and structural contributions to the magnetic damping parameter are separated by a comparison to results of 30 keV Ni implantation.

Owing to its large magneto-crystalline anisotropy energy, L1_0 ordered tetragonal FePt is among the most intensively discussed materials when it comes to pushing the superparamagnetic limit towards minimum particle sizes for future ultra-high density magnetic data storage media. Depending on the preparation technique, however, the formation of the L10 thermodynamic equilibrium phase is often impeded by either a lack of thermodynamic driving forces or a lack of diffusivity.
Recently it has been shown that gas phase prepared FePt nanoparticles can exhibit a very narrow size distribution with a mean diameter of roughly 6 nm. Together with a packing density of 2.8 x 10^12 particles / cm^2 a potential data storage density of 18 Tbit / inch^2 could be achieved. Unfortunately these particles are superparamagnetic at room temperature due to their multiply twinned icosahedral structure. Therefore it is of essential importance to transform these nanoparticles into the favourable L10 phase in a post-deposition treatment.
In the present study, post-deposition 5 keV He irradiation has been employed in order to perform the phase transformation of such gas phase prepared FePt nanoparticles. Structural characterization of the samples was carried out by means of High Resolution Transmission Electron Microscopy (HRTEM). After ion irradiation the previously multiply twinned icosahedral particles have transformed mostly into the single crystalline fcc structure. However, no indication for the chemically ordered L10 phase is found. This might be due to the fact that either the particles investigated are already smaller than a critical particle size below which the L10 phase is no longer the thermodynamic equilibrium phase in FePt, or kinetic aspects may be of increasing importance at these length scales.

Im Rahmen des Planfeststellungsverfahrens für die Stilllegung des ERAM wurden standortspezifische Sorptions- und Löslichkeitsexperimente durchgeführt, um die potentielle Rückhaltung von Radionukliden belastbar in einer Sicherheitsanalyse berücksichtigen zu können. An ausgewählten Verschließmaterialien (Salzbeton und Magnesiabinder) des Endlagers für radioaktive Abfälle Morsleben (ERAM) für die Radionuklide Uran und Kohlenstoff-14 (als Carbonat) sowie am Grauen Salzton für die Radionuklide Plutonium, Americium, Uran, Radium und Kohlenstoff (als [¹⁴C]-Carbonat) wurden belastbare Sorptionsdaten aus Sorptionsexperimenten ermittelt, die für Modellrechnungen zur Ausbreitung von Radionukliden im Nah- und Fernbereich des ERAM verwendet werden können.
Als flüssige Phase für die Sorptionsexperimente wurden zwei endlagertypische gesättigte Salzlösungen eingesetzt: Lösung 1, eine quinäre Salzlösung, und Lösung 3, die hauptsächlich Natriumchlorid enthält.
Zusätzlich zur Sorption der Radionuklide wurden die Löslichkeiten der Radionuklide in den mit dem jeweiligen Bodenkörper konditionierten Salzlösungen bestimmt.

Beta decays of _94,96Ag and ₁₀₃Sn nuclei into Proton Channels have been studied in the recent experiments at the GSI-ISOL facility

Release of reactive (phosphate-like) phosphorus (P) from fresh water sediments represents a significant internal P source for many lakes.
Hypolimnetic P release occurs under reducing conditions that cause reductive dissolution of ferric hydroxide (Fe(OH)3). This hypolimnetic P release may be naturally low or artificially reduced by sediment with naturally high or artificially elevated concentrations of aluminum hydroxide (Al(OH)3). We present field and laboratory data for a common extraction analysis of sediments from 43 lakes differing in trophic status, pH regime, climate, and P loading. The results indicate that a simple sequential extraction of sediment may be a useful predictor of sediment’s ability to release P. Sequential extractions of sediment P, Al, and Fe using water (H2O), bicarbonate-dithionite (BD), and NaOH (at
25°C) showed that negligible amounts of P would be released from lake sediments during hypolimnetic anoxia if either: (1) the molar AlNaOH~25:FeBD ratio is >3, or (2) the molar AlNaOH~25:P(H2O+BD) ratio is >25. These ratios can be used as operational targets for estimation of sediment P release potential and Al dosing of P-rich sediment to prevent hypolimnetic P release under anoxic conditions.

The common concept of heavy metal migration in the hydrosphere differentiates between solid and liquid phase, considered as immobile and mobile. Colloidal phases are often neglected, which may have the following consequences on environmental hazard prognosis (Zänker et al. 2003):

a) The contaminant is regarded as mobile in the model, but it adsorbs on colloids which aggregate and settle (‘natural attenuation’): the prognosis is too pessimistic.
b) The contaminant is regarded as immobile in the model due to adsorption on the host rock, but in part it adsorbs on colloids which are transported: the prognosis is too optimistic.
c) Only if the contaminant is fully mobile, i.e. it is not adsorbed onto solid phases: colloidal transport is irrelevant and the model description is correct.
This study is focused on the incidence of colloids and their binding of toxic metals in streams of the Erzgebirge (Germany), a low mountain region which strongly suffered in the past from mining activities, e.g. uranium mining, and from acid rain loads exceeding the buffering reaction by weathering. Mildly acidic conditions (pH 5-6.5), which may occur in the runoff from dumps or arise on the reversal from stronger acidification (Ulrich and Meybohm 2005), or by mixing of waters with different loads of protons and metals, favor the generation of colloids by hydrolysis of iron (Fe) and aluminum (Al) or by dissolution of clay minerals and precipitation of secondary ferric oxides.
Based on samples from the confluence of two forest streams in the Erzgebirge, 27Al MAS NMR spectroscopy showed that Al-rich colloids contain distinct Al(O)4 centers similar to the -Keggin polyoxocation AlO4Al12(OH)24(H2O)127+(aq) [Al13] (left Fig.). These colloids form via aggregation of the Al13 nanoclusters (Furrer et al. 2002) and bear a high surface density of functional groups capable of accumulating heavy metal cations.
Fe-rich colloids (right Fig.), which often consist of metastable ferrihydrite, exhibit similar properties. Such colloids form when acidic seepage (e.g. from a uranium mine or dump) mixes with near-neutral surface water. Uranium (U), which is soluble under strongly acidic (UO22+) and alkaline (uranyl carbo-nate complexes) conditions, will be scavenged and immobilized by colloids which aggregate and settle in the slightly acidic pH region. On the other hand, contaminants that are usually immobile (As, Cu, Pb), can be mobilized by colloids. The molecular structure of some sorption complexes derived from EXAFS and ATR FT-IR spectroscopy is discussed.

References
Furrer, G., Phillips, B.L., Ulrich, K.-U., Pöthig, R. and Casey, W.H. (2002) The origin of aluminum flocs in polluted streams. Science 297, 2245-2247.
Ulrich, K.-U. and Meybohm, A. (2005) Reservoir ecosystems recover from atmospheric acidification: I. Trends of chemical reversal. ACID RAIN 2005, Conference Proceedings, 000.
Zänker, W., Richter, W., Hüttig, G. (2003) Scavenging and immobilization of trace contaminants by colloids in the waters of abandoned ore mines. Coll. Surf. A 217, 21-31.

Most of the atmospherically acidified drinking-water reservoirs in the Erzgebirge (Germany, southern Saxony) responded more rapidly to the strong reduction of oxidized sulfur and nitrogen emissions than surface waters from other siliceous mountain ranges in Germany (Ulrich and Meybohm 2005). The substantial decrease of proton concentration and toxic forms of aluminum provided a basis for the recovery of sensitive aquatic organisms. Three of four reservoirs which were monitored over a decade showed significantly (p<0.01) falling trends of chlorophyll a and phytoplankton biovolume, mainly due to the decline of dinophyceae. Biovolumes of diatoms and picoplankton slightly increased in the Werda and Muldenberg Reservoir. The zooplankton biocoenosis was dominated by rotifers and small phyllopods, the genus Daphnia was still lacking.
Since 1999 and 2002, small perch (Perca fluviatilis) and sunbleak (Leucaspius delineatus) occurred in the Muldenberg and Werda Reservoir, respectively. The zooplanktivorous sunbleak population showed an extremely high fluctuation of abundance (1,000 67,000 individuals per hectare) and biomass (1 29 kg ha-1, Fig.). Even a population crash due to increased natural mortality happened. The fish individuals revealed a very low factor of corpulence, which indicates limited energy supply and high intraspecific competition on food resources (i.e. on zooplankton, Fig.). Severe top-down control may further delay the recovery of bigger zooplankton species (e.g. Daphnia) and consecutive planktonic groups of the food web. Introduction of predatory fishes could help to control zooplanktivorous fish populations and to prevent mass mortality.

References
Ulrich, K.-U. and Meybohm, A. (2005) Reservoir ecosystems recover from atmospheric acidification: I. Trends of chemical reversal. ACID RAIN 2005, Conference Proceedings, 000.

In Saxony, about two million people are supplied with drinking-water from reservoirs, of which 16 suffered from atmospheric acidification. After the German reunification, the waterworks were modernized and adjusted on the treatment of acidic soft waters. But the emissions of oxidized sulfur (SO2) and nitrogen (NOx) compounds strongly declined within the 1990s. Whereas lakes of the Bohemian Mountains responded rapidly by chemical reversal from acidification (Kopáček et al., 2002), siliceous low mountain ranges in Germany showed a delayed or even no response (Alewell et al., 2001).
This paper presents major trends of chemical water composition monitored for 11 years in 7 acidified drinking water reservoirs and 22 tributaries of the Erzgebirge (Germany), and statistically evaluated by the Seasonal Kendall Test. About 85% of these surface waters showed significantly (p<0.05) declining concentrations of protons (-76%), nitrate ( 55%), sulfate (-26%), and reactive aluminum (Al, 104% on average). The strong decrease of toxic forms of Al provided a basis for recovery of sensitive aquatic organisms like fish (Meybohm and Ulrich, 2005).
Dependent on each initial acidification stage which differed, the study waters shifted one or two stages towards neutrality within a decade, thereby passing through a transitional stage of seasonally (episodically) fluctuating pH regime as illustrated by the Figure. The concentrations of dissolved organic carbon, ammonium, chloride, calcium, magnesium, manganese, and iron showed no trend in 60-75% of the investigated waters. But four reservoirs showed rising trends of iron, probably due to increased microbial activity in the sediment favoring anoxic release of ferrous iron.
The rapid chemical response of the study waters is attributed to the very high level and thus intense reduction of industrial SO2 and NOx emissions, which declined by 99% and 82% in southern Saxony between 1993 and 1999. Deposition rates of protons and sulfate decreased by a factor of ~3, but total N deposition remained almost constant. Soil protection liming, which was performed as a measure of forest remediation, contributed positively to the chemical reversal in about 20% of the surface waters, in particular of those where the cumulative dolomite supply on the total drainage area exceeded 7 t ha-1.

References
Alewell, C., Armbruster, M., Bittersohl, J., Evans, C.D., Meesenburg, H., Moritz, K. and Prechtel, A. (2001) Are there signs of acidification reversal in freshwaters of the low mountain ranges in Germany? Hydrol. Earth System Sci. 5(3), 367-378.
Kopáček, J., Stuchlík, E., Veselý, J., Schaumburg, J., Anderson, I., Fott, J., Hejzlar, J. and Vrba, J. (2002) Hysteresis in reversal of Central European mountain lakes from atmospheric acidification. Water Air Soil Pollut.: Focus 2, 91-114.
Meybohm, A. and Ulrich, K.-U. (2005) Reservoir ecosystems recover from atmospheric acidification: II. Signs of biological recovery. ACID RAIN 2005, Conference Proceedings, 000.

Die Nutzung biologischer Strukturen für die Nanotechnologie ist auf Grund der Größe vieler wichtiger Biomoleküle ein naheliegender Ansatz. S-Layer (engl.: surface layer) sind als äußerste parakristalline Proteinschicht bei vielen Bakterien und Archaea zu finden. Die Untereinheiten dieser Schichten, Protein- oder Glykoproteinmonomere, haben die Fähigkeit zur Selbstorganisation als monomolekulare gitterartige Schicht und eignen sich deshalb bestens zur Funktionalisierung von Oberflächen und zur Herstellung von Ultrafiltrationsmembranen. Einige S-Layer von bakteriellen Isolaten aus Schwermetall- und Radionuklid-belasteten Umgebungen haben außerdem die Eigenschaft, bestimmte Metalle zu binden und können deshalb zur Herstellung von Nanostrukturen, Metallclustern definierter Größe oder als selektive Bindungsmatrix in Filter zur Reinigung kontaminierter Wässer eingesetzt werden.

It is shown that the α²-dynamo of Magnetohydrodynamics, the hydrodynamic Squire equation as well as an interpolation model of PT-symmetric Quantum Mechanics are closely related as spectral problems in Krein spaces. For the α²-dynamo and the PT-symmetric model the strong similarities are demonstrated with the help of a 2×2 operator matrix representation, whereas the Squire equation is re-interpreted as a rescaled and Wick-rotated PT-symmetric problem. Based on recent results on the Squire equation the spectrum of the PT-symmetric interpolation model is analyzed in detail and the Herbst limit is described as spectral singularity.

Bubble Columns are widely used in the process industry and their scale-up from laboratory scale units to industrial units have been a subject of extensive study. The void fraction distribution in the bubble column is affected by the column size, superficial velocity of the dispersed phase, height of the liquid column, size of the gas bubbles, flow regime, sparger design and geometry of the bubble column. The void fraction distribution in turn affects the interfacial momentum transfer in the bubble column. The void fraction distribution in a rectangular bubble column 10cm wide and 2 cm deep, has been measured using Wire-Mesh Tomography. Experiments were performed in an air-water system with the column operating in the dispersed bubbly flow regime. The experiments also serve the purpose of studying the performance of wire-mesh sensors in batch flows. A ‘wall peak’ has been observed in the measured void fraction profiles, for the higher gas flow rates. This ‘wall peak’ seems to be unique as this distribution has not previously been reported in bubble column literature. Low gas flow rates yielded the conventional ‘center peak’ void profile. The effect of column height and superficial gas velocity on the void distribution has been investigated. Wire-mesh Tomography also facilitates the measurement of bubble size distribution in the column. This paper presents the measurement principle and the experimental results for a wide range of superficial gas velocities.

The objective of the ECORA project is the evaluation of computational fluid dynamics (CFD) software for reactor safety applications, resulting in best practice guidelines (BPG) for an efficient use of CFD for reactor safety problems. The project schedule is as follows: (i) establishment of BPGs for use of CFD codes, for judgement of CFD calculations and for assessment of experimental data; (ii) assessment of CFD simulations for three-dimensional flows in LWR primary systems and containments; (iii) quality-controlled CFD simulations for selected UPTF and SETH PANDA test cases; and (iv) demonstration of CFD code customisation for PTS analysis by implementation and validation of improved turbulence and two-phase flow models. The project started in October 2001 and is for a period of 36 months. The project consortium consists of 12 partners combining thermal-hydraulic experts, code developers, safety experts and engineers from nuclear industry and research organizations. At mid-term, the following results were achieved: (i) BPGs are available for simulations of reactor safety relevant flows. These BPGs have found interest in the European projects FLOMIX-R, ASTAR and ITEM; (ii) important flow phenomena for PTS and containment flows have been identified; (iii) experimental data featuring these phenomena have been selected and described in a standardised manner suitable for simulation with CFD methods; (iii) surveys of existing CFD calculations and experimental data for containment and primary loop flows have been performed and documented; (iv) first results for simulations of PTS-relevant single-phase and two-phase flow cases are available.
Documentation is available via the internet at http://domino.grs.de/ecora/ecora.nsf. The models developed within the project are implemented in industrial and commercial CFD software packages and are therefore accessible by industry and research institutions.

Microbial diversity was studied in water samples collected at depths of 290 to 324 m from the Siberian deep-well radioactive disposal site S15 near the Russian city of Tomsk. For this molecular and cultivation approaches were applied. The biomass from the samples was concentrated via consequent filtration on filters with pore sizes of 1.2, 0.45, and 0.22 µm. For one of the samples 16S rDNA bacterial and archaea clone libraries were constructed from the total DNA (S15A) recovered from the biomass collected on the three filters. For another parallel sample two bacterial clone libraries S15B and S15D were generated from the DNA extracted individually from 0.45 and 0.22 µm filters, respectively. The analysis of the libraries demonstrated that the estimation of the diversity strongly depends on the way of collecting the biomass. About 65% of the clones in the S15A bacterial library were affiliated to ß-proteobacterial Dechlorosoma species. The rest of the clones represent very diverse bacterial groups. In the S15B library the Dechlorosoma sp. represented 30% of the total number of clones. This result indicates a possible dominance of Dechlorosoma sp. in the S15 samples [1]. Another 20% of the clones from the S15B library were affiliated with a low identity to a novel cyanobacteria-related lineage. Sequences representing the same “cyanobacteria-like” group were also found in the 0.22 µm library. However, populations of Cytophagales were the most predominant in the latter library and represented about 55% of the clones.
In addition, Euryarchaeota and Crenarchaeota 16S rDNA sequences were identified in the S15A total DNA as well. Most of them were affiliated to 16S rRNA genes of not jet cultured archaeons, found in different metal-rich habitats.

Autotrophic microorganisms were retrieved in the S15 samples by using primer pairs specific for the form I [2,3] and form II [4] of RubisCO gene. Some of the identified sequences from the form I were affiliated with RubisCO genes of Proteobacteria, which were related to those identified previously in the same samples via the 16S rDNA approach. Interesting is also the result that more than 80% of the form I sequences were affiliated with the RubisCO genes of different species from the β-subclass of Proteobacteria. The 16S rDNA approach indicated a dominance of β-proteobacterial species in the same samples as well. The retrieved form II sequences were affiliated with α-proteobacterial RubisCO genes.

Several oligotrophic bacteria were isolated under aerobic conditions from the 0.22 µm filter. They were related to -Proteobacterial and to Actinobacterial species. Three of the isolates, affiliated to Microbacterium oxydans possess microdiverse 16S rDNA stretches. The ability of these isolates to tolerate and sorb uranium and other heavy metals was studied. The results demonstrated that the resistance to and binding of heavy metals are strain-specific for these isolates.

Acknowledgements
This work was partly supported by grant FIKW-CT-2000-00105 (BORIS) from the European Community. We thank A. Zubkov, E. Zaharova, E. Kamenev and A. Rybalchenko for the supplying of the S15 samples.

References
[1] M. Nedelkova, G. Radeva and S. Selenska-Pobell. (2005) In: Underground Injection Science and Technology, Elsevier Science, (in press).
[2] A. Alfreider, C. Vogt, D. Hoffmann and W. Babel. Microbial Ecology 45 (2003), p. 17-328
[3] K. Nanba, G.M. King and K. Dunfield. Appl. Environ. Microbiology 70 (2004), p. 2245-2253
[4] H. Elsaied and T. Naganuma. Appl. Environ. Microbiology 67 (2001), p. 1751-1765

Uranium ores are very common in several regions of Germany, e.g. Saxony, Thuringia and Bavaria. Weathering and ore mining are processes which result in mobilization of uranium. So far only a general radiation dose limit for drinking water exists in Germany but no limit value for uranium itself. The latter is a radioactive and also toxic element and therefore discussions have raised to adopt a limit value for uranium in Germany. Against this background the development of novel strategies for cleaning uranium contaminated water became an increasingly interesting subject. In the past the Bacillus sphaericus strain JG-A12, recovered from the uranium mining waste pile “Haberland” nearby the town of Johanngeorgenstadt, was demonstrated to bind selectively several heavy metals including uranium [1]. Molecular and structural analyses of the uranium complexes formed by the cells, spores and the surface layer (S-layer) protein of B. sphaericus JG-A12 via extended X-ray absorption fine structure (EXAFS) spectroscopy identified carboxyl and phosphate groups as binding sites for uranium [2]. Moreover sol-gel techniques were used for immobilization of B. sphaericus JG-A12 cells in a porous silicate matrix. [4, 5]. The obtained biological ceramic (biocer) is particularly suitable for the use as selective filter material for the immobilization of uranium from polluted industrial waters.

This work is aimed to investigate the capability of biocers containing B. sphaericus JG-A12 cells to remove uranium from contaminated drinking water. For the experiments four different tap water samples supplemented with 30 µg uranium per liter and one Hungarian mineral water with a uranium content of 142 µg uranium per liter were selected. Uranium sorption by the biocer showed the removal of over 99% of dissolved uranium from the tap water samples. In the case of the heavy metal containing and highly saline mineral water 86% of uranium and 76% of zinc were immobilized.

In order to improve the uranium binding capacity of the biocers, the uranium sorption by B. sphaericus JG-A12 cells was tested depending on the amount of phosphorus present in the growth medium. Highest binding capacities were achieved with biomass grown in phosphate rich media, containing at least 1.4 mM phosphorus. In contrast, the binding capacity was remarkably lower with biomass grown in phosphate limited medium. Furthermore uranium binding of the isolated and purified S-layer of B. sphaericus JG-A12 was investigated. Interestingly, the S-layer of B. sphaericus JG-A12 possesses even at low concentration of uranium higher affinity to uranium than the S-layer protein of its closest relative B. sphaericus NCTC 9602 or the reference protein bovine serum albumine. Recent analyses of the S-layer genes of B. sphaericus JG-A12 [6] allow to perform in future genetic modifications of the cell surface of B. sphaericus JG-A12. This displays a further possibility to enhance the capacity and the selectivity of the uranium binding by the next generation of biocers.

Acknowledgement
This work was founded through Project DFG SE 671/7-2 from the German Research Community (DFG) and trough EC grant GRD1-2001-40424. We thank R. Getzlaff and I. Plumeier (GBF Braunschweig) for their assistence and U. Soltmann (GMBU, Dresden) for the preparation of the biocer.

References
[1] S. Selenska-Pobell et al. 1999. FEMS Microbiology Ecology 29, 59-67
[2] J. Raff et al. 2004. In: R.B. Wanty and R.R. Seal II. Water-Rock Interaction. 1, 697-701
[4] J.Raff et al. 2003. Chemistry of Materials 15, 240-244
[5] U. Soltmann et al. 2003. Journal of Sol-Gel Science and Technology 26, 1209-1212
[6] K. Pollmann et al. (in preparation)

An experimental study with respect to the influence of a rotating magnetic field (RMF) on the unidirectional solidification of Pb-Sn alloys is reported. The magnitude of the bulk flow in the melt generated by the RMF varies with the magnetic Taylor number Ta. The forced convection causes distinct modifications of the temperature and concentration field such as a reduction of the temperature gradient ahead of the solidification front. Without electromagnetic stirring the alloy solidifies solely in form of dendrites aligned parallel to the heat flow direction. In contrast, a transition from a columnar to an equiaxed growth (CET) is observed if the solidifying ingot is exposed to an RMF. The position of the CET is shifted towards the bottom of the casting by increasing the Ta number. The CET was found to occur for a cooling rate of about 0.4 K/s and temperature gradients in the range between 0.6 and 1.0 K/mm

In processes involving electrically conducting liquids, the application of an external magnetic field offers efficient opportunities for a contactless flow control and fluid handling. However, for a well-aimed optimisation of the flow structure local information about flow quantities like velocity, pressure, temperature, concentration or void fraction are necessary. In case of liquid metals the choice of a suitable measuring technique is a crucial problem, because the user is confronted not only with the opaqueness but also with high temperatures as well as a strong chemical reactivity of the fluid against many materials. Therefore, measuring techniques well-known from ordinary hydrodynamics generally fail for liquid metal applications. As a consequence, no commercial measuring systems are available for liquid metal applications.
During the last years experimental activities of FZR were focussed on the development and qualification of techniques to measure the velocity in liquid metal flows. Various liquid metal model experiments with various liquid melts at different temperatures have been performed to test and evaluate local sensors as well as integral methods.

Measurements of the cross sectional distribution of gas fraction and bubble size distributions were conducted in a vertical pipe with an inner diameter of 51.2 mm and a length of about 3 m for air/water bubbly and slug flow. The use of a wire-mesh sensor allows a high resolution of the gas fraction data in space as well as in time. From these data time averaged values for the two-dimensional gas fraction profiles decomposed according to a large number of bubble size classes were calculated. This allows to extract data for the radial gas fraction profiles for a given range of bubble sizes as well as data for local bubble size distributions. The structure of the flow is characterized by these data. The measurements were done for up to 10 different inlet lengths and for about 100 combinations of gas and liquid volume flow rates. The data are very useful for the development and validation of meso-scale models for the forces acting on a bubble in a shear field of the liquid flow and models for bubble coalescence and break-up. Such models are necessary for the qualification of CFD codes for the simulation of bubbly flows.

Hydrogen solubility has been studied in hydrogenated amorphous silicon (a-Si:H) prepared by plasma-enhanced chemical vapour deposition with hydrogen-diluted silane. Post-hydrogenation experiments have been carried out using hydrogen plasma and hydrogen ion implantation. Thermal annealing and silicon ion implantation have been used to change the defect density in the amorphous silicon network. Hydrogen concentration has been established by means of nuclear reaction analysis and infrared spectroscopy. It has been shown that the hydrogen solubility in a-Si:H is strongly related to the density of the hydrogen trapping sites in the silicon network and the value of the solubility limit is determined by the material structure and consequently by the a-Si:H preparation conditions. The ratio between the hydrogen concentration and its solubility limit has been discussed in the context of the light-induced degradation of a-Si:H.

The production of K+-mesons in pA (A = D: Q Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotroii COSY-Julich for beam energies T-p = 1.0-2.3 GeV. Double differential inclusive p C cross-sections at forward angles theta(K+) < 12&DEG; as well as the target mass dependence of the K+ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at T-NN = 1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target mass dependence of the cross-sections at higher energies, the repulsive in-medium potential of the K+--mesons can be deduced. Using pN cross-section parameterisations from the literature and our measured pD data we derive a cross-section ratio σ(pn --> K+X)/sigma(pp --> K+X) similar to (3-4).

The QCD sum rule approach to in-medium modifications of the omega meson in nuclear matter is reviewed with emphasis of its relation to 4-quark condensates and chiral symmetry restoration. Possible implications of the CB-TAPS experiment for the reaction gamma A -> A' omega (-> pi⁰ gamma) are sketched and the particularly important role of di-electron probes, accessible with HADES, is highlighted. A brief update of a parametrization of the previous dilepton and photon probes from CERES and WA98 of heavy-ion collisions at CERN-SPS energies is presented.

The time-dependent flux over the fission barrier of an excited nucleus under the influence of dissipation is investigated. Characteristic features of the evolution of the amplitude of the probability distribution and the velocity profile at the fission barrier are derived. Analytical results are compared to numerical Langevin calculations and used to develop a new analytical approximation to the solution of the Fokker¿Planck equation for the time-dependent fission-decay width. This approximation is
shown to be more realistic than previously proposed descriptions, which were widely used in the past.

Forty years of uranium mining in the German state of Saxony have left a legacy of uranium-contaminated pits, waste piles, mine tailings and surrounding soils. Since 1963, and more extensively since 1989, contaminated sites were covered in order to protect people and environment. Little is known on the further fate of uranium at these buried sites. Therefore, we investigated two mine tailing samples from hydrochloric-acid ore-extraction, which were buried for 30 years under several meters of mine and communal waste.
The two samples were collected at depths of 5 m (sample 1) and 12 m (sample 2) below the surface. Due to the neutralizing influence of the waste cover, the upper sample 1 had a pH of 8, while the lower sample 2 had a pH of 4. Both samples were retrieved from oxic redox conditions. Chemical extractions showed that U is predominantly water soluble and/or ion exchangeable in sample 1, while U is predominantly bound in weakly soluble solid phases in sample 2. To further identify the uranium species, we applied a combination of Synchrotron-based methods, namely Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy of bulk samples, micro X-Ray Diffraction (µ-XRD) and micro X-Ray Fluorescence (µ-XRF) spectroscopy. In sample 1, uranium predominates homogeneously distributed at concentrations in the mg/kg range in aggregates with a diameter of tens to hundreds of µm. The aggregates consist of layer silicates (muscovite, kaolinite, illite), jarosite and gypsum. Chemical extractability, EXAFS, µ-XRD, and µ-XRF strongly suggest that U(VI) is adsorbed on edge sites of the layer silicates. In sample 2, U is heterogeneously distributed among single crystals and small aggregates with very high U concentrations (g/kg) and variable elemental composition. Besides the matrix minerals muscovite, kaolinite, illite and quartz, we identified pitchblende and coffinite, and found evidence for other uranyl hydroxide and vanadate solids. In addition, a smaller amount of uranium seems to be adsorbed to mineral surfaces as in sample 1.
The results suggest that a substantial amount of uranium remained in the buried tailings as relatively mobile, adsorbed U(VI) species. No clear evidence for secondary uranium mineral precipitates was found.

Silizium ist zwar die Basis für nahezu die gesamte Mikroelektronik, die Integration mit optischer Funktionalität ist jedoch nur eingeschränkt möglich, da Silizium als indirekter Halbleiter ein schlechter Lichtemitter ist. Andere optoelektronische Komponenten, wie Dektektoren, Modulatoren oder Wellenleiter können aus Silizium hergestellt werden, ein Siliziumlaser hat sich bisher aber allen Realisierungsversuchen widersetzt. In den letzten Jahren hat es jedoch rasante Fortschritte bei der Effizienz Silizium-basierter Lichtemitter gegeben, sogar optischer Gewinn (gain) wurde berichtet. Ich möchte diese Entwicklung zusammenfassen und dann unsere Unterschungen an Bor-implantierten Si pn Dioden und an mit seltenen Erd-Ionen implantierte MOS-Strukturen präsentieren, deren Effizienzen schon nahe zum anwendungsrelevanten Bereich kommen.

Chrombeschichtung von Baustahl mittels Ionenstrahlbehandlung

The evolution of reactive gas uptake at the target surface has been investigated by real-time in situ diagnostics during magnetron sputtering. Using a planar circular dc magnetron for reactive sputter deposition of TiN from a Ti target in an argon/nitrogen gas mixture, the target uptake of nitrogen was determined at varying gas flows of nitrogen using the 14N(d,)12C nuclear reaction, directly demonstrating the target "poisoning" effect. The expected hysteresis behavior at increasing/decreasing nitrogen gas flow is confirmed. Within the precision of the measurement, the nitrogen content remains unaltered after switching off the magnetron, indicating the absence of a significant mobile fraction of nitrogen in the target. The maximum amount of retained nitrogen significantly exceeds one adsorbed monolayer, which is attributed to nitrogen ion implantation and recoil implantation of adsorbed nitrogen. This is quantitatively reproduced by TRIDYN collisional computer simulations.

Bulk nickel samples, produced by electrodeposition, resulting in different initial structure properties, were experimentally studied by X-ray diffraction, as well as by scanning and transmission electron microscopy. Attempts are made to correlate the mechanical behaviour during cyclic plastic deformation with the response of the microstructure. A special effort is made to examine the influence of grain size and internal stresses on the deformation processes.

Combined external Ion Beam Analysis (IBA) measurements, consisting of Proton Induced X-ray Emission–Proton Induced Gamma-ray Emission–Rutherford Back-Scattering (PIXE-PIGE-RBS) have been performed on several obsidian fragments with archaeological significance at the Rossendorf tandem accelerator using a 3.85 MeV proton beam. A comparison was made between these external IBA results and the ones previously obtained on the same obsidian samples using Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS). The purpose of the study was to assess the potentiality of external IBA for provenance studies on archaeological obsidian, especially as a non-destructive alternative to the LA-ICP-MS method. As an example, the source attribution of an archaeological obsidian fragment from Transylvania to Tokay Mountains/Slovakian range flow is discussed.

Structural modifications of solid Si (0 0 1) targets exposed to the XUV TESLA free lectron laser radiation were studied. The samples were irradiated with the photon energy centered at 14 eV, in short pulses of only 80 fs and of peak power up to 1 GW. The FEL beam was focused on sample surfaces to microspots of size 10–100m. The energy density in the spots varied from below the ablation threshold up to far above this threshold. The structural modifications induced with the irradiation were studied by AFM, Nomarski contrast microscopy and by X-ray diffraction methods. A variety of morphological structures created in the damaged areas was found. The maps of the X-ray diffracted intensity distribution recorded around chosen spots on the Si surface made it possible to probe the damage distribution range around the spots. The observed features are related to the FEL irradiation fluencies applied.

EDXRF analysis with subsequent multivariate data analysis proves useful for the determination of the authenticity of iridescent glass artifacts. Thus, clusters of the glass groups investigated were formed which can be associated with the glass manufacturers. By means of ion beam analysis with the external proton beam the producing technology of iridescent glass objects of the Art Nouveau glass manufacturer Loetz/Austria with so-called Papillon pattern was characterised in a non-destructive way. Due to the simultaneous application of PIXE and RBS the glass structure including a sequence of glass layers covered with a SnO2-layer of approximately 50 nm thickness on the surface could be described.

The dispersion of bubbles in a vertical two-phase flow is studied experimentally by means of wire-mesh sensors and high-speed video camera. The first technique is applied to a 200 mm pipe with flow patterns ranging from bubbly to slug/churn flow. The latter technique is instead applied to a rectangular bubble columns at low void-fractions. The experimental results are compared with numerical investigations.

For the investigation of air/water stratified flow, a horizontal channel with rectangular cross-section was build at Forschungszentrum Rossendorf. The channel allows the investigation of air/water co- and counter-current flows under atmospheric pressure, especially the slug behaviour.
Optical measurements were performed with a high-speed video camera, and were complemented by simultaneous dynamic pressure measurements. Further, an interface capture technique was developed and possible applications (e.g. plot of the time dependent water level in a cross-section, recognition of the slug position) presented.

During last decades magnetohydrodynamic (MHD) effects have attracted growing interest because of its potential impact on numerous industrial technologies. In processes involving electrically conducting liquids, the application of an external magnetic field offers efficient opportunities for a contactless flow control and fluid handling. However, for a well-aimed optimisation of the flow structure local information about flow quantities like velocity, pressure, temperature, concentration or void fraction is necessary. In case of liquid metals the choice of a suitable measuring technique is a crucial problem, because the user is confronted with the problems of opaque fluids, high temperatures as well as a strong chemical reactivity of the fluid against many materials. Therefore, measuring techniques well-known from ordinary hydrodynamics generally fail for liquid metal applications. As a consequence, no commercial measuring systems are available for liquid metal applications.
We present a summary of our R&D activities on velocity measuring techniques for liquid metal flows. Various model experiments with various liquid melts at different temperatures have been performed to test and evaluate local sensors as well as integral methods.
A mechano-optical probe was developed which has to be positioned directly inside the liquid metal flow. The measuring principle is based on the separation of a direct mechanical interaction between flow and sensor tip and the optical acquisition and processing of the signal. The insensitivity of the system to electrical noise and external magnetic fields can be considered as an important advantage. Until now, the sensor has been tested in metallic melts up to temperatures of about 450 °C, but an extension up to 800°C should be straightforward. The ultrasound Doppler velocimetry (UDV) represents a powerful tool since it delivers a full velocity profile along the ultrasonic beam. It can operate with a direct contact to the melt, but also through a channel wall. To overcome the thermal restriction of the ultrasonic transducers an acoustic wave guide has been used. The acoustic wave guide and the piezoelectric element are combined in form of an integrated sensor. This approach allowed the first successful application of the ultrasound Doppler technique in liquid metals at temperatures above 200°C. The feasibility of this integrated sensor concept was demonstrated in experiments in metallic melts as sodium, PbBi, CuSn or aluminium.
In some applications even a coarse knowledge of the flow topology and the direction of the main eddies would be of high value. We study the possibility of velocity reconstruction in electrically conducting fluids from external measurements of induced magnetic fields. The method is based on the fact that an external magnetic field is deformed by the motion of the fluid. Applying the primary magnetic field in two different directions and measuring the related induced magnetic fields at an array of Hall probes, the three-dimensional velocity field can be reconstructed. Besides some theoretical basics, we present experimental results of a demonstration experiment.

The mould filling process of aluminum investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment. Several types of filters are already in use for the purpose of inclusion filtering but velocity reduction, too.
We present results on the design and application of a DC magnetic field to control the pouring velocity. Numerical calculations were performed to simulate the filling process and the effect of the magnetic field. The free surface problem which occurs in the riser of the casting unit was taken into account by a Volume-of-Fluids Method. 3d transient calculations using the commercial finite- element code FIDAP (FLUENT Inc.) were carried out for a simplified model system as well as for the real aluminum casting unit. The term for the electromagnetic force was implemented into the code via a user defined subroutine, and an additional equation for the electrical potential was solved. End effects due to the limited size of the magnet poles were taken into account. In that way, results from three-dimensional transient simulations of the filling process were obtained.
Parallel to the simulations model experiments have been performed using the low melting eutectic InGaSn. The casting unit was modelled by a plexiglas model. The ultrasonic Doppler velocimetry was applied to carry out detailed velocity measurements in the model. Such measurements delivered the basis to validate the numerical calculations. A comparison between numerical and experimental results showed an excellent agreement, allowing scaling up the simulations to the realistic aluminium casting process.
Real tests have been performed at an industrial investment caster with molten aluminium. The primary action of the magnetic field, i.e. the reduction of the velocity peaks at the beginning of the process, was clearly shown. In a second set of experiments the amplitude of the DC field was tuned during the process. At the beginning the maximum braking force was applied, whereas the field strength was reduced with increasing fluid level in the casting unit. In this regime, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time.

TOPFLOW stands for Transient TwO Phase FLOW. The new thermal-fluiddynamic test facility of FZR was built for generic and applied studies of transient two phase flow phenom-ena in power and process industries. It is used as experimental basis to develop and validate three-dimensional CFD, in particular for an application to safety relevant flow simulations in the field of nuclear reactor safety. The work is carried out in a close and very fruitful coopera-tion with the code developer ANSYS-CFX. Object of the experimental studies is a gas-liquid two-phase flow. In the field of nuclear technology, the introduction of CFD is connected with high expectations concerning the quality of the predictions compared to the established one-dimensional thermal hydraulic analyses, since CFD allows to substitute geometry-dependent empirical closure relations by more physically justified closure laws that are formulated on the scale of the structures of the gas-liquid interface. In this way, modelling becomes much more independent from geometrical and thermodynamic boundary conditions and the scale-up to the real reactor scale becomes more reliable than in case of traditional thermal hydraulic codes.

TOPFLOW is not a dedicated integral test modelling a specific reactor type. It was rather de-signed as a multi-purpose facility for different single-effect experiments. This offers numer-ous possibilities for experiments to study basic two-phase flow phenomena as well as to per-form applied research for the industries. The latter includes, for instance, investigations of innovative and passive safety systems for nuclear reactors, like the emergency condenser for boiling water reactors, a model of which is a major component of TOPFLOW. A carefully designed instrumentation including advanced two-phase flow sensors of own development delivers experimental data of high quality, that reflect the addressed phenomena and processes in the necessary detail.

An important role plays the availability of measuring information from wire-mesh sensors with a high spatial resolution of 3 mm, which deliver sequences of complete two-dimensional gas fraction distributions from the entire cross section of both pipes DN50 and DN200 with a frame rate of 2500 Hz. These sensors were upgraded to operational parameters of 280 °C and 65 bar. First results on void profiles and bubble size distributions as well as the evolution of the flow structure along a vertical pipe obtained in this parameter range will be presented.

Another new method used at TOPFLOW is the strategy to install a test facility inside a tank pressurized with air of up to 50 bar and operate if in pressure equilibrium with the inner at-mosphere of the tank. The advantages can be summarised as follows: (1) the test facility itself can have strange shapes that are unfeasible for pressurised components, (2) the manufacture of the test itself will be cheap, since no pressure carrying components are needed, (3) thin walls make it easy to apply instrumentation, for instance optical measurements through glass walls or temperature field measurements by directing an infrared camera to a thin metal wall, (4) no expensive and time consuming licensing procedures are necessary, because the test is housed in the tank designed for the maximum overpressure.

Bacteria can interact in different ways with uranium. Therefore, they play a major role in biogeochemical cycling of this element. Natural bacterial communities were studied of several different soil samples collected from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt (Saxony, Germany). The 16S rDNA retrieval showed that the communities were predominated by members of -Proteobacteria and Holophaga/ Acidobacterium. In order to analyse the influence of U(VI) on the natural bacterial community structure, one of the studied soil samples, containing originally 40 mg/kg U, was supplemented with nearly 60 mg/kg U(VI) as uranyl nitrate. After four weeks of incubation, selective sequential extractions revealed, that most of the added U(VI) was weakly complexed, hence remained bioavailable. The predominant bacterial populations were shifted from -Proteobacteria and Holophaga/Acidobacterium to Pseudomonas sp., Arthrobacter sp. and Geobacter sp.. Column experiments are in progress in our laboratory, which will help to improve our understanding of the influence of U(VI) on the natural bacterial community. The influence of aeration was also studied on the changes of the bacterial community structure induced by the addition of U(VI).

The strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. The cells of this strain are capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters. It was demonstrated that this strain is enveloped by a surface layer protein (S-layer) which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date. The highly regular structure of the S-layers with many pores of identical size offers good binding sites for different kind of molecules and also nucleation sites for formation of metal nanoclusters like Pd, for example. In this study we demonstrate that the cells of B. sphaericus JG-A12 and their purified and recrystallized S-layer are capable to bind effectively Au(III) from salt solutions. Moreover, in the presence of reducing agents such as molecular H2, Au(III) is reduced to metallic nanoclusters. Reduced gold nanoclusters were regularly distributed and sized according to the pores of the protein lattice. The metallic nature of the clusters was confirmed by different techniques such as EXAFS, XANES, UV-Vis spectroscopy and by X-ray powder diffraction. The size of the gold nanoparticles was estimated to be about 10 Å. Changes in functional groups in the cells and S-layer due to gold binding were observed by FT-IR microscopy. The cellular localization of the deposited Au(III) and of the gold nanoclusters was defined using transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). The results demonstrated that B. sphaericus JG-A12 might be used to prepare gold nanoparticles that can be tailor-made for particular applications.

Bacteria have evolved several different mechanisms to tolerate uranium or to use U(VI) as terminal electron acceptor in anaerobic respiration. Because of this, bacteria play a major role in geomicrobiological cycling of uranium and can be used for the bioremediation of uranium-contaminated sites. In this work natural bacterial communities were investigated by the use of 16S rDNA retrievals in several soil samples from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt (Saxony, Germany). Inductively coupled plasma mass spectrometry (ICP-MS) and selective sequential extraction (SSE) analysis were used for the geochemical characterization of the soil samples. The 16S rDNA analysis showed that the natural bacterial communities were predominated by -Proteobacteria and Acidobacteria. SSE analysis demonstrated that the uranium was weakly complexed and bound by Mn(hydr)oxides or Fe(hydr)oxides. The soil samples contain in addition to uranium also other heavy metals like arsenic for example. In order to understand how U(VI) influences the structure of natural bacterial community, one of the studied samples with the lowest indigenous amount of U was supplemented with 60 mg/kg U(VI) in form of uranyl nitrate. After four weeks of incubation, SSE analysis and 16S rDNA retrieval were done in parallel. The SSE analysis demonstrated that most of the supplemented uranium was weakly complexed and remained probably bioavailable. The 16S rDNA retrieval showed that populations of Pseudomonas, Arthrobacter and Geobacter were stimulated by the addition of U(VI) to the soil sample. For more profound understanding of the influence of U(VI) on natural bacterial community, column experiments are running in our laboratory.

The sorption complexes of uranium to colloidal ferrihydrite (Fh) were investigated by EXAFS and ATR FT-IR spectroscopy in mildly acidic solution (pH 5.5) in presence and in absence of atmospheric CO2. EXAFS has shown that sulfate, silicate, and carbonate are not involved as ligands bidentately bound onto the adsorbed U. Hence a new surface bond structure of U on hydrous ferric oxides is proposed which tightly fits the experimental EXAFS data. However, ATR FT-IR spectra suggest ternary uranyl carbonato surface complexes under these conditions open to the atmosphere. The conflicting spectroscopic results can be harmonized by proposing a monodentate linkage of the carbonate ligands.

Various developments of velocity measuring techniques, their test in different liquid metals, and applications in hot melts are reported. A Mechano-Optical Probe (MOP) performing local measurements up to temperatures of about 700°C has been developed and successfully tested. The Ultrasound Doppler Velocimetry (UDV) can be considered as another attractive technique to get velocity data from opaque flows. To extend the application range to higher temperatures and to abrasive liquids a new integrated ultrasonic sensor with an acoustic wave guide has been designed. First successful measurements in a CuSn melt of about 620°C and in liquid Al of about 750°C were carried out. A fully contactless investigation of the mean velocity field is possible by magnetic tomography. Local measurements of the induced magnetic field and the application of inverse reconstruction techniques allow an analysis of the flow structure. A first demonstration experiment showing the feasibility of this approach for the reconstruction of the three-dimensional mean velocity structure is presented.

iIon irradiation induced interface mixing was used to generate silicon nanoclusters at the SiO2-Si interface of metal-oxide-semiconductor (MOS) structures aiming at electronic memory applications. No particular processing issues have been encountered during integration of this technique in standard submicronic C-MOS technology. The memory properties of the fabricated structures as a function of the Si+-irradiation dose and post-irradiation temperature and time have been examined through electrical measurements of capacitors and transistors. Low-voltage operating devices that can endure more than 106 programming/erasing cycles have been successfully achieved. While excellent device uniformity and reproducibility have been observed over 6-inch wafers, more research is still required to improve charge retention and ensure the standard 10-year retention time needed for true non-volatile memory applications.

The remediation of contaminated areas and facilities of the former uranium mining and milling in Saxony and Thuringia (Germany) requires detailed knowledge on the uranium migration in natural aquifer systems. Humic acids (HA), polyelectrolytic organic macromolecules, are of importance for the mobilization of radiotoxic and toxic metals in the environment due to their ability for complex and colloid formation. In addition, HA are characterized by redox properties that can influence the oxidation state of metal ions which effects their speciation and consequently their migration behavior.

In order to improve the knowledge on the interaction between HA and uranium we characterized the redox properties of different HA (Eh values, Fe(III) redox capacities) and studied the stability of the oxidation state of U(VI) in presence of HA on a time-scale of several weeks. We obtained a spectroscopic proof for the reduction of U(VI) to U(IV) by HA with pronounced redox functionalities applying laser-induced photoacoustic spectroscopy.

This demonstrates a possible relevance of HA for the migration of tetravalent actinides. Therefore, we investigated the transport behavior of the redox couple U(IV)/U(VI) in presence of HA in quartz sand by column experiments. Retardation factors and eluate recoveries were determined. We found that HA influences the transport of both, U(IV) and U(VI). In presence of HA both redox species migrate nearly as fast as the groundwater flow. In case of U(VI) HA exhibits a significant mobilizing effect. There are strong indications for a similar impact on the U(IV) transport.

The ability of hydroxyapatite Ca10(OH)2(PO4)6 (HAP) to immobilize metal ions, particularly lanthanides and actinides, is well known. The long-term stability of this fixation is proven by natural analogue studies. Thus, HAP is a potential filling material in engineered barriers in abandoned mining areas as well as in the near-field of underground repositories for nuclear and toxic waste.
The interaction of U(VI) with HAP was studied in batch and unsaturated column experiments and by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We investigated a seepage water from Schlema (Saxony) with a Uranium concentration of 10-5 M and a syn-thetic HAP packed in a matrix of purified quartz sand.
The batch sorption experiments show 100 % adsorption of UO22+. The break-through curves measured in the column experiments with continuous pulse injection yield a retardation factor Rf = 33.2 ± 1.5 compared to the conservative tracer tritiated water. This value corresponds to the strong adsorption behavior. An elution of the column with ten pore volumes of a uranium-free solution revealed a distinct tailing and a uranium recovery near unity. Thus, the sorption process proved reversible. The TRLFS measurements facilitate a differentiation of uranium bound to the HAP surfaces and to the quartz matrix. Furthermore, the surface speciation of uranium could be identified. Finally, a numerical model using the reactive transport code Crunch describes the transport behavior of uranium.

Natural aquatic and terrestrial environments exert large variations in redox state due to oxygen diffusion on one hand and microbial processes on the other hand. Actinides with their large number of oxidation states are especially susceptible to these redox changes, forming different aqueous complexes which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their thermodynamic metastability. Therefore, we developed a new spectro-electrochemical cell, which allows to study the structure and speciation of aqueous actinide complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential. Due to the specific safety requirements for handling of radioactive materials the electrochemical cell is gas tight. The spectro-electrochemical cell comprises two safety compartments and a special electrode arrangement. First U LIII-edge X-ray absorption spectra have been obtained from aqueous solutions of U(VI) and U(IV) in high concentrated chloride solutions.

Dokumentation zu einem IDL-basierten Steuerprogramm für die Prozesssteuerung einer MBE-Anlage

The small punch test (SPT) is a suitable miniaturized test method to determine the actual and local material state in structural components under operating conditions. A combined experimental-numerical approach is presented to identify material parameters of plastic deformation and ductile damage behaviour from the SPT. Neural networks (NN) are generated and trained by finite element simulations to obtain the relation between a load displacement curve of the SPT and the matching material parameters. These parameters, identified from the SPT, are validated by reference values determined from smooth and notched tensile specimens. Next, the same parameters are used to simulate the ductile crack growth in fracture specimens by means of finite elements. This way, even fracture thoughness data J_Ic of the materials could be successfully predicted. These findings substantiate the feasibility to gain comprehensive material characteristics from the SPT and their transferibility to quantify the ductile failure of strucural components.

Die Studie beinhaltet die Sichtung, Zusammenstellung und Bewertung der zur Bearbeitung sicherheitstechnischer Fragestellungen benötigten Daten für die Modellierung geochemischer Prozesse. Der Abschlussbericht basiert auf den im Rahmen dieses Projektes erstellten Zwischenberichten. Die nach Sichtung und, soweit möglich, kritischer Begutachtung ausgewählten Daten sind in einem separaten Anhang in tabellarischer Form zusammengestellt.

In photothermal beam deflection (PTBD) spectroscopy generating and detection of thermal waves occur generally in the sub-millimeter length scale. Therefore, PTBD provides spatial information about the surface of the sample and permits imaging and/or microspectrometry. Recent resulrs of PTBD experiments are presented with a high spatial resolution which is near the diffraction limit of the infrared pump beam.

Die auf dem “Master-Curve” (MC)-Konzept basierende ASTM-Prüfvorschrift E 1921 ist für die Ermittlung einer Referenztemperatur T0 homogener Stähle mit einer kubisch-raumzentrierten (ferritischer) Grundstruktur konzipiert. In der Realität sind große Schmiederinge, Grobbleche und insbesondere Schweißverbindungen makroskopisch oft nicht homogen. Aus diesem Grund wurden auf dem MC-Konzept basierende Verfahren entwickelt, mit denen sich Referenztemperaturen von inhomogenen Stähle ermitteln lassen. An russischen Reaktordruckbehälterstählen des Typs 15Kh2MFA werden J-Integral basierte Bruchzähigkeitswerte KJc beim Ein-satz von Spaltbruch gemessen und nach der Standard MC-Methode und den modifi-zierten Verfahren ausgewertet.
The Master Curve (MC) approach of defining reference transition temperature, T0, has been standardized in ASTM Standard Test Method E 1921. The basic MC approach for analysis of fracture test results is intended for macroscopically ho-mogeneous steels with a body centred (ferritic) structure only. In reality, the steels are seldom fully macroscopically homogeneous. In this paper, new comparatively simple extensions of the MC are applied on forgings of Russian reactor pressure vessel steel 15Kh2MFA. J-integral based fracture toughness values KJc measured at the onset of cleavage fracture were evaluated with the basic MC evaluation, the lower tail modification of the SINTAP procedure, a bimodal estimation and a maxi-mum likelihood estimation of the random inhomogeneity.

The successful quasi-particle model is compared with recent lattice data of the coefficients in the Taylor series expansion of
the excess pressure at finite temperature and baryon density. A chain of approximations, starting from QCD to arrive at the model expressions for the entropy density, is presented.

Non-invasive imaging of genes which are introduced into cells is a useful method for gene therapy monitoring. The labeling of acyclic purine and pyrimidine nucleoside derivatives with fluorine-18 required for the HSV-1 tk imaging approach with Positron Emission Tomography (PET) 18 is described. The methoxytritylated and tosylated precursors were radiolabeled using a K[¹⁸F]F/kryptofix 2.2.2^TM complex, followed by removal of the protecting groups under acidic conditions and HPLC purification. The radiochemical yields of the ¹⁸F-tracers amount to 5 - 15 % (decay corrected) after a synthesis time of 85 - 95 min, the radiochemical purity was > 98 % with an average specific activity of 19 GBq/μmol at the end of synthesis.

Molecular speciation is a prerequisite for reliable assessment of contaminant migration in the environment. We use sophisticated techniques for concentrating colloids (e.g. ultracentrifugation, ultrafiltration) in combination with Extended X-ray Absorption Fine Structure (EXAFS) and Attenuated Total Reflectance Infrared (ATR IR) spectroscopy to investigate the speciation of colloid-borne uranium in waters which occur in abandoned ore mines. Mine flooding was simulated in a 100 L scale by mixing acid mine water of elevated U concentration and near-neutral groundwater from an aquifer above the mine until pH~5.5 was reached. The generated colloids adsorbed 95% of the total uranium and consisted mainly of 2-line ferrihydrite (Fh) besides traces of aluminum, sulfur, sil-ica, and carbon compounds. EXAFS analysis at the U-LIII absorption edge suggested a bidentate surface complex of UO22+ on FeO6 octahedra, but two minor backscattering contributions in the vicinity of the absorber remained unexplained. Since only Al could be excluded as backscattering atom, we studied U sorption on Fh at pH 5.5 in presence and in absence of sulfate, silicate, and atmospheric CO2 to clarify the bond structure.

EXAFS showed the unknown backscattering contributions in all the sorption samples regardless of the presence or absence of the tested components. Contrary to structural models in the literature, bidentately complexed carbonate ligands cannot explain the results when using U concentrations around 0.1 mM. But ATR-IR spectra showed that U(VI) carbonato complexes must be involved in the sorption of uranyl on Fh. These results are not contradictory if the carbonate ligands were bound monodentately, which is currently being studied. Nevertheless, carbon cannot act as backscattering atom in carbonate-free samples prepared in N2 atmosphere. Monte-Carlo Target Transform Factor Analysis was employed to test if the EXAFS spectra could be fitted by a struc-ture including exclusively Fe, U, and O atoms. We propose a new model in which the bidentately bridged UO22+ is oriented in a way that yields a distance of ~2.9 Å to the O atom of an adjacent, edge-shared FeO6 octahedron. This model predicts a second Fe shell at ~4.35 Å which tightly fits the experimental data.

Summarizing, uranium may form different sorption complexes with colloidal Fh: a binary bidentate uranyl complex with modified orientation, and ternary U carbonato complexes with monodentate linkage of the carbonate ligands, depending on specific conditions.

The performance of the normalization method (NM) is evaluated and compared with the standard unloading-compliance method of fracture-toughness analysis for a broad spectrum of different materials and specimen geometries. The critical J-integral values based on the normalization method are summarized and compared with the results of unloading compliances tests. The results demonstrate the applicability of the normalization method for the J-R curve determination for a range of steels. The normalization method yields results, which deviate as much as 15 % from the values obtained with the unloading compliance method, and thus results of acceptable accuracy can e attained with this method.

This paper provides a summary of Master Curve fracture toughness test results on small surveillance-type single- edge bend (SE(B)) and one-inch thick compact tension (1T-CT) specimens of the IAEA reference reactor pressure vessel (RPV) steel JRQ and other national RPV steels from numerous laboratories throughout the world. The JRQ test blocks distributed to the different laboratories were mainly from test plate 6JRQ. The mean fracture toughness of the 6JRQ plate material generally can be described satisfactorily with the standard Master Curve method from ASTM E 1921-02. The mean T0 values shows in accordance with previous investigations that a bias of around 10 K exists between the T0 values of CT and SE(B) specimen types so that CT specimens give higher T0. The analyses of both JRQ and national RPV steels confirm that the procedures specified in ASTM E 1921-02, as well as the SINTAP procedure, are generally valid and applicable for characterizing RPV type steels and even steels showing distributed inhomogeneity.

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The capabilities and limitations of wavelet analysis are demonstrated for the illustrative case of two practial applications: investigation of magneto-tunneling signals and the extended x-ray absorption fine structure (EXAFS) of uranium. A brief introduction to wavelet analysis is given. The term "window size" of the mother wavelet function is defined; this concept underlies one of the ideas for a criterion of optimal choice of the mother wavelet function. The capabilities of a software package developed by the authors are demonstrated; this software was used for all the calculations done in the course of this study.

Extended Xray absorption fine structure data evaluation usually begins with the Fourier transform of the spectrum. We suggest the wavelet transform as a complement to the Fourier transform. While the Fourier transform analyzes the distances to the backscattering atoms, wavelet transform additionally reveals the wavenumber dependence of the scattering. Thus wavelet analysis can differentiate between heavier and lighter backscattering atoms, even if they are almost equidistant from the central atom. First the method of operation and the advantage of the wavelet analysis will be demonstrated by simple models. Then it is applied to the interpretation of extended Xray absorption fine structure spectra concerning the complexation of UraniumVI with the carboxylic groups acetic, formic, and glycolic acid. The wavelet transform analysis suggests clearly for the system Uraniumformic acid both, UU and UCC, structural elements. In contrast to the clear separation of different scattering paths by wavelet transform, Fourier transform analysis was not able to resolve the two different backscattering processes.

Surface Complexation Models (SCM) can describe sorption processes at the mineral-fluid interface on a scientific, quasi-thermodynamic basis. The effect of parameter uncertainty in blind predictions is illustrated by the example of Np(V) sorption onto hematite.
The Diffuse Double Layer (DDL) model was chosen as SCM submodel to keep the number of parameters at a minimum. From the surface species reported so far, =FeOH₂ ⁺, =FeO^-, =FeONpO₂, =FeONpO₂(HCO₃)₂ ^2-, =FeOHCO₂, and =FeOCO₂ ^- were selected with their normalized DDL reaction constants log K_n, taken from the RES³T database (Brendler et al., 2003).
The modeling was performed with the FITEQL code, version 3.2. The predictions were evaluated by comparison with the experimental results by Kohler et al. (1999), comprising of 52 data points for the Np(V) sorption at varied pH, ionic strength, solid/liquid ratio, Np content, and air P_CO2. When focusing on the conventional distribution coefficient K_D, the maximum deviation for all data subsets is less than one order of magnitude, a spreading considered to be reasonable in performance assessment applications.
Because the protolysis constants can not be varied independently, the point of zero charge (PZC) and delta pK were calculated based on experimental pK₁ and pK₂. Consequential we generated 20 independent pK data sets with the aid of Gaussian-distributed random numbers. None of these parameter sets did deliver unacceptable blind predictions for the distribution coefficients.
The formally large scatter of pK values as extracted from literature is actually not critical. Even the use of inconsistent values from other electrostatic models will yield similar results. For well-defined mineral systems, provided a suitable database is accessible, the SCM approach seems to be promising.
(References: Brendler V. et al. (2003), J. Cont. Hydrol., 61, 281-291.; Kohler M. et al. (1999), Radiochim. Acta, 85, 33-48.)

The relations linking structure, microhardness and adhesion were studied for ion-beam mixed tungsten layers deposited on the surface of high-speed steel. The 45 nm thick W layer were mixed with 340 keV Kr ions at temperatures ranging fro, RT up to 450°C. The increase of mixing temperature results in partial crystallization of the layers and the increase of the layer hardness. Substantial increase of layer adhesion has been observed in scratch tests for all mixed samples.

To gain a better understanding of the behavior of the reactor pres
sure vessel lower head in case of a core meltdown scenario in a light water reactor experiments have been conducted worldwide. Especially for experiments including a heated melt pool in the lower head like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes and the dislocation of the melt pool due to the expanding vessel.
Therefore a 2D Finite Element Model with 3 different sub models is developed based on the code ANSYS® Multiphysics. A thermal sub model includes planar and contact elements for conductive heat transfer. Additional surface elements are used to simulate convection and radiation from outer surface areas and a radiation matrix is used to account for internal radiative heat exchange. Normally a CFD-simulation would have been required for the natural convective heat transfer in the melt pool, but at very high internal Rayleigh numbers there is no turbulence model that correctly simulates the heat transfer. Therefore an Effective Conductivity Convectivity Model is implemented to simulate the heat transfer from the melt pool to its boundaries.
The resulting temperature field of the vessel wall is applied to the mechanical sub model of the vessel. To describe the visco-plastic deformation a numerical creep data base was developed where the creep strain rate is evaluated in dependence on the current total strain, temperature, and equivalent stress. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The third sub model uses hyperelasticity and contact elements to move the melt pool along with the creeping vessel wall.
In this paper the differences between the results of a simple coupled and a recursive coupled FE-simulation are highlighted. Due to the thermal expansion at the beginning and the accumulating creep strain later on the shape of the melt pool and of the vessel wall are changing. Despite the fact that these relative small geometrical changes take place relatively slowly over time, the effect on the temperature field is rather significant concerning the mechanical material behavior and the resulting failure time. Assuming the same loading conditions the change in the predicted failure time between the simple and the recursive coupled model is in the order of magnitude of the total failure time of the simple model. The comparison with results from the FOREVER-experiments shows that the recursive coupled model is closer to reality than the single step model.

The aim of this work is to illustrate the effect of parameter uncertainty (protolysis constants) in surface complexation modeling. As example the blind prediction of Np(V) sorption onto hematite was selected, applying the Diffuse Double Layer Model (DDLM).
None of the pK parameter sets randomly generated within a space of two standard deviations did deliver unacceptable predictions for the distribution coefficients. Thus the formally large spreading of the pK values as extracted from literature (even after normalization and extrapolation to infinite dilution) is actually not critical. For well-defined mineral systems, provided a suitable database is accessible, the DDLM approach seems to be promising.

Den gestiegenen Anforderungen bei der Herstellung immer komplexerer, dünnwandigerer und auch größerer Feingussteile kann mit der gezielten elektromagnetischen Strömungsbeeinflussung der Schmelze über magnetische Felder begegnet werden. Hierbei kann auf kontaktlose Weise die Zuströmung hinsichtlich einer optimalen Füllung der Gießform kontrolliert werden. Die aufgabenspezifische Auswahl aus einer Vielzahl technisch realisierbarer Feldarten und die Parametrierung erfordert die Kenntnis der typenspezifischen Wirkungsweise auf die Strömung und der jeweils zu erwartenden Stärke des Einflusses. Das erste Kapitel liefert deshalb einen Einstieg in die Grundlagen der Strömungskontrolle mit Magnetfeldern.

Im realen Prozess sind in-situ Untersuchungen der Strömungsvorgänge in der Regel nicht möglich. Eine Beurteilung des Endproduktes kann zwar, in begrenztem Umfang, den Einfluss magnetischer Felder auf dessen Qualität liefern, nicht aber die Wirkkette oder gar ein umfassendes Verständnis. Die Auslegung der Felder stützt sich von daher meist auf numerische Strömungssimulationen oder Modellexperimente. Warum etwa Wasserexperimente für die weitaus meisten metallurgischen Prozesse ungeeignet und numerische Simulationen alleine nicht ausreichend sind, wird in Kapitel zwei beschrieben.

Auch in den vergleichsweise „kalten“ Modellexperimenten bleibt die für die Optimierung des Magnetfeldeinsatzes erforderliche Bestimmung von Strömungsgeschwindigkeiten weiterhin problematisch. Die für transparente Flüssigkeiten kommerziell verfügbaren Methoden LDA (Laser Doppler Anemometrie), PIV (Particle Image Velocimetry) oder auch das Einbringen von Farbstoffen und/oder Schwebeteilchen zur Visualisierung sind auf Grund der Undurchsichtigkeit von Metallschmelzen nicht anwendbar. Kapitel 3 gibt einen Überblick über die für Flüssigmetallströmungen geeigneten Messtechniken.

Im Hauptkapitel 4, welches sich mit Beispielanwendungen beschäftigt, wird zunächst über den erfolgreichen Einsatz einer Magnetfeldbremse, von der Auslegung des Feldes bis hin zur Implementierung, im industriellen Aluminium-Feinguss berichtet. Dem schließt sich eine Beschreibung einer weitergehenden Prozessoptimierung mittels eines linearen Mehrphasen-Wechselfeldes an, welche das Potenzial des „Maßschneiderns“ von Magnetfeldern demonstriert. Den Abschluss bildet die Erstarrung im rotierenden Magnetfeld, die als ein weiteres Beispiel für die Vielfalt der elektromagnetischen Kontrolle im Bereich der Metallurgie dienen möge.

For a physical modelling of hot and chemically aggressive metallic melts in industrial processes, the according experiments are done mostly on water. Besides the fact that the important influence of magnetic fields on the flow cannot be studied at all, the majority of these results are meaningless owing to the non-matching similarity criteria, such as for instance the Prandtl number in the case when thermal gradients are involved. Realistic models rely on low melting point metals the flow of which is not easily measurable by „of the shelf“ equipment.
Rather than giving a systematic review of the measuring techniques available for liquid metal flows, the presentation will concentrate on electric potential probes (EPP) and the up and coming ultrasonic Doppler velocimetry (UDV). These methods will be compared with respect to their applicability and characteristics such as sensitivity, dynamic range, and spatial as well as temporal resolution. Several practically orientated examples have been selected to demonstrate the state of the art performance of both these techniques.
In crystal growth processes rotating magnetic fields (RMFs) are often employed for homogenisation purposes while it is mandatory to keep the flow almost stationary. Well below the threshold of linear stability, the transition from the Stokes-regime to a laminar boundary layer flow was quantified by EPP.
The flow mapping capabilites of UDV have turned out to be a powerful tool for the determination of topological details of the convective pattern.
Scaling laws known from theory may be proved by precision measurements. This was done for the ~Ta2/3-dependence in the RMF by EPP and the ~B-characteristic in a single-phase AC (pulsating) magnetic field by UDV.
Whereas „Kolmogorov-like“ spectra were obtained from the swirling flow, large scale structures with the according low frequency oscillations were found within the recirculation. A video prepared from a sequence of the correlated velocity information contained in each UDV-profile impressively shows the spatio-temporal behaviour of such coherent structures.
To complete with the modern developments in velocity measuring techniques in electrically conduction fluids, the principles of the inverse reconstruction from measurements of the flow-induced magnetic field outside the fluid volume will be outlined. A first benchmark of this method clearly shows its robustness and the ranges of applicability.

Intruduction

We present direct numerical simulations (DNS) of the flow in a finite cylinder driven by a rotating magnetic field. The main idea is that externally applied magnetic field can be used to control the motion of the liquid during the growth of single crystals in a good electrical conductors. The experiments have demonstrated that rotating magnetic field produced much better solid-solution or alloyed crystals and reduce small-scale spatial oscillations of the additive concentration in nearly pure crystal. The subject is complicated by the fact that the Taylor-Görtler instability of the side layer and the instability of the Bödewadt-type horizontal layer occur in the flow depending on the aspect ratio and magnetic Taylor number Employing the rigid-body and low-frequency approximations the mathematical model reduces to the Navier-Stokes equations with a priori known Lorentz force. A second-order finite-element method combined with Adams-Bashforth time integrations is used for discretization.
The transient and early turbulent flow regimes have been investigated in detail by numerical computation. Some characteristic features such as dominating large structures and homogenous rotating core have been identified in flow. Furthermore, weak secondary flow appear near the top and bottom of the walls due to existence of the Bödewadt layers.

It is already known that the microstructure of a metallic alloy can be affected in a significant way due to the convection in the liquid phase during solidification. A time varying magnetic field can be applied to produce a flow field in the melt which influences the nucleation and growth processes. The aim of our research program is to find an strategy to refine the microstructure of castings by an optimal combination of magnetic field intensity, field frequency and cooling rate. Furthermore, the basic mechanisms controlling the solodification by magnetic fields are investigated.

This work is concerned with the convection in a finite cylinder driven by a rotating magnetic field. Both direct numerical simulation (DNS) and experiments have been carried out to study the characteristics of this kind of confined flows. A decoupling of the mathematical model into the Navier-Stokes equations and an a priori known Lorentz force was achieved in the usual manner by employing the rigid-body and the low-frequency approximations. Adams-Bashforth time integration has been combined with a second-order finite element method for the discretisation. Utilising the upcoming technique of Ultrasonic Doppler Velocimetry (UDV) allowed for a mapping of the meridional velocity components throughout an entire section of the container. In a more quantitative fashion potential difference measurements (PDM) were performed to support and validate the numerical results.

Two cases are considered in order to study possible drag reductions due to the action of electromagnetic forces.
1. A direct numerical simulation of a turbulent channel flow is performed. The unsteady Navier-Stokes equations and Poisson electric potential equation are solved at a Reynolds number Re=3000 and 6000, based on the laminar centreline velocity V0 and channel half-width d. The tau-collocation spectral method developed by J. Kim. et al. is used. The Crank-Nikolson method for the viscous and a third-order Runge-Kutta method for the nonlinear term and the Lorentz force are applied. The resolution was 64x65x64 in the streamwise, wall-normal and spanwise directions. For an electromagnetic actuator consisting basically of a spanwise oscillating force, we analysed the drag reduction and its efficiency for various load number. It is shown that a load number of order one leads to a significant increase of the efficiency in comparison to the standard case of high small load number.

2. For the flow around a sphere we found an internal alternating electromagnetic field source which leads to a strong drag reduction. The analysis is done in the Stokes approximation analytically and then at Reynolds number Re ~ 300 numerically using a pseudospectral code. A simple gradient-type optimisation was applied in order to tailor the magnetic field source for the purpose of a reduced drag. We considered the simplified case (decoupling of fluid flow and electromagnetic fields) of large load numbers, with the drawback that the strong drag reductions obtained are certainly inefficient from the energetical point of view.

The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC longitudinal magnetic field was examined. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4×10-13. The liquid metal was in a cylindrical container at rest. Bubble and liquid velocities were measured using the Ultrasound Doppler Velocimetry (UDV). The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. Whereas for small bubbles (de £ 4.6 mm) an increase of the drag coefficient with increasing magnetic interaction parameter was observed, the application of the magnetic field reduces the drag coefficient of larger bubbles (de ³ 5.4 mm). The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddies in the wake. The Strouhal number St decreases with increasing magnetic interaction parameter.

Electromagnetic levitation is a well-known technique for containerless processing of metals and alloys both in the solid and in the molten state. In experiments the levitated bodies often times show different types of instabilities resulting in a rotating and oscillating motion of the sample. We present results on the reason of such spontaneous instabilities. The theoretical predictions are verified by model experiments using solid Al or Mg spheres. These instabilities can obviously be avoided by system parameters below the corresponding non-dimensional threshold. If this is not possible, an active damping method using DC magnetic fields has been developed. The DC field can either be produced by permanent magnets or by an electromagnetic superposition to the levitation coils. Experiments will be shown demonstrating the stabilization effect due to the DC magnetic fields.
Numerical simulations for the flow inside the molten levitated sample will be given as well as results for the linear stability of this internal flow. Flow and flow stability are also analyzed for the case of a molten droplet subject to a global rotation. It is shown that the global rotation may have a significant stabilizing influence on the internal flow field.

We performed silicon diffusion experiments with sol-gel derived isotopically enriched silica glasses at temperatures between 1050°C and 1300°C. The diffusion profiles were measured by means of time-of-flight secondary ion mass spectrometry. Samples annealed in closed silica ampoules under argon or dry air reveal enhanced Si diffusion compared to Si diffusion in fused silica. On the other hand, annealing in a large alumina tube under ¹⁸O₂ ambient yields Si and O diffusion coefficients which approach the results for thermally grown SiO₂. The enhanced Si diffusion in sol-gel derived glass is proposed to be due to water residues which lead to the formation of silanol SiOH groups.

Electromagnetic fields provide a tool to influence the flow and, in turn, the heat & mass transfer in electrically conducting fluids. An attractive feature for metallurgical or crystal growth applications is the contact-less form of this control. There have been many studies in the past analysing the changes in the transport phenomena which take place by application of some type of magnetic field. In general, steady magnetic fields suppress flows and alternating magnetic fields drive some motion. The variety of magnetic field actions is very big which allows for an inverse approach: a pre-defined flow control is possible by tailored magnetic field systems. There is a basic fluiddynamic interest in such type of flow control, but applications in crystal growth, solidification, metal casting, welding, seawater flow control and others are very close, too.
On the other hand, there is a growing community dealing from a theoretical and computational point of view with optimization, optimal or sub-optimal control and flow control in general. We expect that Magnetohydrodynamics (MHD) establishes an interesting example for it as it provides an active, well-controllable influence on the flow which can directly be tested in experiments. The flow itself is often not of direct interest but acts as a kind of intermediate agent for more general goals like the resulting heat & mass transfer, the resulting microstructure in solidification, or integral results as drag of lift. Hence, it is in many cases a highly non-trivial question which flow field might be a desirable one for the more general objectives of the various processes.
Such type of inverse MHD approach has not yet been realized on its full scale, i.e., starting from a theoretical optimization problem and its numerical implementation up to the experimental demonstration. However, several examples exist of partly addressing this approach, and some of them will be shortly presented: Cz-Si crystal growth with AC and DC magnetic fields, aluminum investment casting with magnetic field control, tailored DC field stabilization of the melt extraction process for metallic fibres, electromagnetic levitation with DC field sample stabilization, seawater flow control for drag reduction and lift enhancement, and float-zone crystal growth with a tailored magnetic field control in order to shape the solid-liquid phase boundary. The latter case will be presented in more detail demonstrating its capabilities for the float-zone crystal growth and solidification studies with NdFeB alloys.

A multiple velocity multiple size group (NxM MUSIG) model was developed for inhomogeneous poly-dispersed multiphase flows in cooperation with ANSYS CFX. The model is constructed by incorporating the population balance equation into the multi-fluid modeling framework. The dispersed phase is allowed to be classified into $N$ continuum fields (velocity groups) according to their hydrodynamic behaviors; each group allowing an arbitrary number of sub-size classes. This model has generalized all possible class model variants and is applicable to large-scale computations. As a pre-investigation for the CFX5.8 development, the Nx1 variant was implemented based on CFX5.7 and applied to investigate as-liquid flows in a vertical pipe. The results confirm that this model is capable of predicting the separation of bubbles of different sizes and the development of the gas volume fraction along the pipe.

A detailed experimental database, obtained for a large pipe with an inner diameter of 195 mm and length of 9 m was used for the validation of models applied in CFD codes for the simulation of bubbly flow. Since the bubbles were injected via holes at the pipe wall, especially very useful information on the bubble migration from the pipe wall towards the pipe center were obtained by measurements at different distances between gas injection and measuring plane. The bubble migration is determined by the forces acting on the bubbles. A simplified model, introduced earlier, but with some new extensions, described in this paper, was used to analyze the data. The comparison of results from a simulation and the experimental findings give the advice, that the turbulent dispersion force according to the FAD model is too strong compared with the radial drag. Up to now no appropriate models for bubble coalescence and break-up are available, which can be applied for a wide range of gas and liquid volume flow rates. Nevertheless for selected combinations of volume flow rates, the calculated bubble size distributions and radial gas volume fraction profiles show an acceptable agreement with the experimental data.

The concept of the Synthesised Hot Ion Plasmoid (SHIP) experiment at the gas dynamic trap (GDT) facility of the Budker Institute Novosibirsk was already presented at the 29th EPS Conference. During the last year several numerical simulations were made by means of the Integrated Transport Code System (ITCS) to determine the best experimental scenario for getting high plasma parameters. This contribution presents important results of the recent numerical simulations of SHIP by means of the ITCS modules which had to be partly modified.

In dem Seminarvortrag mit Lehrcharakter wird einleitend auf die Bedeutung von Actinidenkolloiden in der Radioökologie und Methoden der Kolloidforschung eingegangen. Detailliert wird die LIBD abgehandelt, gegliedert nach physikalischen Grundlagen, experimentellen Anordnungen, wobei das Gerätesystem des Instituts für Radiochemie vorgestellt wird und Anwendungen der LIBD. Dazu werden Beispiele aus der Literatur und eigene Messungen an natürlichen Wässern und zur Bestimmung der U(IV)-Löslichkeit vorgestellt. Abschließend werden die Anwendung der LIBD zur Aerosoldetektion und die Laser-Induzierte Breakdown Spektroskopie diskutiert.

The capabilities of the in-house code FLOCAL and of the code ATHLET (developed by GRS, Germany) to reproduce instabilities of natural circulation BWRs at low pressure will be shown. FLOCAL consists of a 4-equations two-phase model. This code is the thermalhydraulic module of the three-dimensional neutronic codes DYN3D, also in-house development of FZR. The code ATHLET is a general-purpose thermalhydraulic code which has the possibility of using 4, 5 or 6-equations two-phase model. This code has been coupled with DYN3D. The results of the simulation obtained with the two codes are compared with experiments carried out with facilities built at Delft University of Technology (The Netherlands) and at Paul Scherrer Institute (PSI, Switzerland). The phenomenology of the instabilities is very well reproduced by the two codes. Good quantitative agreement is found as well.

An abstract was not required.

Nanoparticles embedded in a host matrix are systems with a high internal structural gradient which exhibit exciting electronic, optical, and/or magnetic properties. With regard to applications, the position of the nanoparticles, their size and their size distribution have to be well defined which has been a severe challenge for materials scientists. "Bottom-up" approaches are promising alternatives to the conventional "top-down". Usually, they are driven by self-organization mechanisms of matter.
Aiming at novel non-volatile flash memories [1], we have studied the synthesis of Si nanoclusters (NCs) in a thin SiO₂ layer which is embedded between the (100)-Si substrate and a poly-Si capping layer. For this application, Si NCs of equal size are required which are located in the buried oxide layer at a given distance from the Si-SiO₂ interface. In a previous work [2] we presented a theoretical concept which suggests that such a Si multi-dot structure can be achieved in a two-step process. At first, the layer stack poly-Si/SiO₂/(100)Si is irradiated with Si ions of medium energy (50keV) which leads to ion mixing of the Si-SiO₂ interfaces. During annealing, phase separation takes place in the course of which the Si-SiO₂ interfaces recover rapidly. Excess Si of the tails of the mixing profiles remains in the oxide, precipitates, and – in a self-organizing manner – grows up to a Si NC delta-layer which is ~3nm apart from the Si-SiO₂. Because of the very low mass contrast of Si NCs to the surrounding SiO₂ and their tininess, the Si NC delta-layer structure is outside the visibility limit of common XTEM.

In this contribution, we present for the first time experimental evidence which proves the mechanism of Si NC delta-layer formation addressed above. For this purpose, the sample structure portrayed previously was modified. In order to enhance the mass contrast of the Si NCs we "decorate" the Si NCs with Ge. A 5nm thin Ge layer was inserted in between the capping and the oxide layer. In the course of annealing, Ge diffuses through the oxide and attaches to the growing Si precipitates due to the energetically favourable Si-Ge bond. Differently from delta-layer of pure Si NCs, the Si_xGe_1-x NC delta-layer is indeed observable in XTEM because of the considerably higher mass contrast to the surrounding SiO₂. Without the presence of Si NCs, which act as seeds to which Ge monomers attach, no NC delta-layer would be visible at the position of interest. Consequently, the existence of Si NCs which align in a collective manner at a distinct distance of ~3nm from the Si channel is successfully proven.

This work was supported by the GROWTH Program of the European Community (GRD1-2000-25619).

[1] S. Tiwari, F. Rana, H. Hanafi, A. Hartstein, E. F. Crabbe, and K. Chan, "A Silicon nanocrystals based memory", Appl. Phys. Lett. 68, 1377 (1996).
[2] K.-H. Heinig, T. Müller, B. Schmidt, M. Strobel, and W. Möller, "Interfaces under ion irradiation: growth and taming of nanostructures", Appl. Phys. A 77, 17 (2003).

The Multidot Nano-flash Memory suggested by Tiwari [APL69(1996)1232] is a promissing candidate for succeeding the common Floating Gate Flash Memory.
Its most challenging configurational feature is a layer of insulated Si nanoclusters (NCs) within the oxide of a MOS-like structure.
Here, we present experimental evidence that the theoretical concept predicting the self-organization of delta-layers of Si NCs at ion irradiated interfaces is valid (cf. Heinig [APA77(2003)17]).
In this approach of "bottom-up" structuring, unconventionally, a 15nm thin buried SiO₂ layer, which is enclosed by a 50nm poly-Si capping layer and the Si substrate, is irradiated with Si ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiO_x (x<2) -- where x is a function of depth -- is formed which is not stable.
During annealing, the system relaxes towards equilibrium, i.e. phase separation (via spinodal decomposition and nucleation) sets in. Within a certain time window of annealing, the structure of the system matches with a structure similar to the Multidot Memory device, the principal character of which is a 2D layer of Si nanoclusters of (d~3nm) which is embedded in a 3D SiO₂ matrix at a distance of ~3nm from the Si substrate.
The experimental handicap that tiny Si NCs (d<3nm) which are embedded in SiO₂ are not visible in common XTEM is resolved by a novel method which applies Ge as contrast enhancing element in TEM studies of tiny Si NCs.

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. The cells of this strain are enveloped by a highly ordered crystalline proteinaceous surface layer (S-layer) with an ability to bind uranium and other heavy metals. By using a phosphoprotein specific staining, Inductive Coupled Plasma- Mass Spectrometry (ICP-MS) analysis and a colorimetric method, purified and recrystallized S-layer proteins were shown to be phosphorylated. We used Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to determine the structural parameters of the uranium complexes formed by purified and recrystallized S-layer sheets of B. sphaericus JG-A12. In addition, the complexation of uranium by the vegetative bacterial cells was studied. The EXAFS analysis demonstrated that in all samples studied, the U(VI) is coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.88 ± 0.02 Å, and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.62 ± 0.02 Å. Transmission Electron Microscope (TEM) analysis showed that the uranium accumulated by the cells of this strain is located at the cell surface as dense deposits.

Development of biological methods for removal of heavy metals and actinides are a subject of a great interest due to their low cost and high efficiency at moderate metal concentrations. Many bacterial strains have been isolated that sorb actinides usually at the cell surface. In this paper we describe the isolation of bacterial strains from extreme habitats (such as uranium mining wastes and Siberian deep-well radioactive disposal sites). Phylogenetic analysis of these strains revealed that they are related to α-Proteobacteria and to Actinobacteria. Some of these strains possess the ability to accumulate and tolerate uranium and other heavy metals. Thus, a strain of Microbacterium oxydans (SW3) which was isolated from a uranium contaminated water sample tolerates a concentration of U up to 4 mM and accumulates high amounts (up to 110 mg U/dry biomass at pH 4.5 and an initial uranium concentration of 0.25 mM). X-ray absorption near-edge structure analysis showed that the cells of these strains precipitate U(VI) as autunite-like phase (inorganic uranyl phosphate) at pH 4.5, probably due to the release of inorganic phosphate from the cells. However, at pH 2 uranium formed complexes with organically bound phosphate of the cell surface. At pH 3, both organic and inorganic phosphate uranyl species occur together. We applied Iterative Target Test Factor Analysis /1/ to determine the speciation at different pH values quantitatively from the EXAFS spectra. Transmission electron microscopy and energy dispersive X-ray analysis revealed strain-specific extracellular and/or intracellular uranium accumulations to varying degrees.

References:

/1/ Rossberg, A. et al. 2004. Anal. Bioanal. Chem. 376:631

wird nachgereicht

Synchrotron radiation excited X-ray microprobe techniques (-XRF/XAS, -XRD, imaging/tomography) give unique possibility for non-destructive, in situ investigation of several sample characteristics (elemental- and crystalline composition, chemical speciation, morphology) and different chemical, environmental processes within inhomogeneous samples. The ID22 X-ray microprobe beamline of the European Synchrotron Radiation Facility (ESRF, Grenoble, France) offers the simultaneous use of these techniques with m spatial resolution in the 6-30 keV energy range.

Material and environmental sciences are two scientific fields often requiring the combined investigation of the elemental distribution, chemical speciation, and crystalline structure of large number of samples with (sub)-micron spatial resolution. The new developments of the ID22 beamline can readily fulfill these requirements, as will be illustrated by the presented examples. The high 1010-5x1011 ph/s intensity of the micro-beam (depending on the spot-size, energy and focusing device) allows for continuous scanning -XRF measurements of sample areas of up to 1 mm2 with 0.6-2 m spatial resolution within <10-12 hours measurement time in case of high enough characteristics X-ray line intensities. Combination of scanning -XRF with -XANES (-EXAFS) gives information about the dependence of the oxidation state/chemical speciation of a given element from the elemental composition. The achromaticity of the commonly used KB focusing mirror makes the change of the excitation energy possible in the 7-18 keV energy region without significant change of the size and position of the focused beam. Thus, XANES measurements at different absorption edges are achievable, which allow to study the correlation among chemical speciation of different elements. Correlation between the chemical characteristics and the crystalline structure of the sample can be investigated by combining these techniques with -X-ray diffraction measurements.

We employed a combination of selective sequential extractions and bulk XAFS spectroscopy, and extracted spectral XAFS components and their concentrations by iterative transformation factor analysis (ITFA), in order to determine the Zn speciation in a smelter-contaminated, acidic soil. We compared the speciation by ITFA with one we performed earlier using principal component analysis and linear combination fit. ITFA identified 4 different species, two different franklinite-type phases (Zn-Fe spinels), sphalerite (Zn sulfide) and Zn oxalate, the latter forming as a precipitate during chemical extraction with oxalate solution. The second spinel-type phase could be extracted with the help of ITFA, although no appropriate reference sample was available. Spinel 1 and 2 have Zn-O distances of 1.96 and 1.99 Å, and Zn-Fe distances of 3.53 and 3.48 Å, respectively. The results from ITFA gave much better fits of experimental spectra and are better in line with elemental mapping and XAFS microspectroscopy. The major advantage of investigating XAFS data with ITFA is the possibility to derive all species even when part of the references are not available.

The Rossendorf Beamline is in full operation since 1999. Its X-ray absorption spectroscopy station dedicated to actinide research is unique in Europe, and has served for about 80 different experiments in the past four years. An overview on the current status of operation modes, technical details and access conditions is presented.

Humic substances are important sorbents for organic and inorganic contaminants such as heavy metals or radionuclides. They participate in many geochemical processes, affecting the quality of ground and surface waters, or the uptake of nutrients by plants. This property is due to their high surface area, the sorption of ions at charged hydrophilic functional groups and the sorption of non-polar organic compounds by hydrophobic surface sites [1,2].
The bulk chemical porperties of of humic substances can be investigated with a variety of methods like solid-state CP-MAS 13C-NMR spectroscopy, FT-IR spectroscopy, pyrolysis coupled with mass spectrometry or acid-base titrations. Although all of those methods have been applied widely to characterize colloids and their interaction with contaminants, methods which provide both in-situ imaging as well as spectroscopic characterization are rare. The Scanning Transmission X-ray Microscope (STXM) at beamline X1-A at the National Synchrotron Light Source (NSLS) is one of the few methods that may fill in this gap. Carbon X-ray absorption near-edge structure (C-1s XANES) as well as X-ray microscopy was employed to systematically monitor the chemical properties of humic substances. Furthermore, the colloidal fraction of different soil types was extracted and analyzed with C-1s XANES spectroscopy. The objectives of this study are (i) to characterize the spectroscopic features of humic substances and mobile soil colloids with C-XANES spectroscopy and X-ray microscopy and (ii) to evaluate a qualitative as well as quantitative comparison with other spectroscopic methods like solid-state CP-MAS 13C-NMR spectroscopy or FT-IR spectroscopy.

References
[1] Pignatello J.J., and Xing B. (1996) Environ. Sci. Technol. 30, 1-11.
[2] Grolimund, D., Elimelech, M., Borkovec, M., Barmettler, K., Kretzschmar, R., and Sticher, H. (1998) Environ. Sci. Technol. 32, 3562-3569.