Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Estimation of field amplitudes during the operation of the 1.5 cell photoelectron RF gun of the PITZ collaboration
Janssen, D.;
The present paper discuss the posibility to obtain information about the field flatness of a 1.5 cell normal conducting RF gun cavity during the running of the gun. By measurements of the microwave network parameters at room temperature and by measurement of the passband frequencies in the running regime of the gun it is possible to estimate the perturbation of field flatness, caused by an inhomogeneous temperature distribution.
  • Other report
    Hamburg: DESY, 2005
    7 Seiten

Publ.-Id: 7183 - Permalink


[11C]SMe-ADAM, an imaging agent for the brain serotonin transporter: Synthesis, pharmacological characterization and microPET studies in rats
Zessin, J.; Deuther-Conrad, W.; Kretzschmar, M.; Wüst, F.; Pawelke, B.; Brust, P.; Steinbach, J.; Bergmann, R.;
N,N-Dimethyl-2-(2-amino-4-methylthiophenylthio)benzylamine (SMe-ADAM, 1) was found to be a highly potent and selective inhibitor of the serotonin transporter (SERT). This compound was labelled with carbon-11 by methylation of the S-desmethyl precursor 10 with [11C]methyl iodide to obtain the potential positron emission tomography radiotracer [11C]SMe-ADAM. Radiochemical yield was 27  5 % and the specific radioactivity was 26 – 40 GBq/µmol at the end of synthesis . Ex vivo and in vivo biodistribution experiments in rats demonstrated a rapid accumulation of the radiotracer in brain regions known to be rich in SERT, such as the thalamus/hypothalamus region (3.59 ± 0.41 %ID/g at 5 min after injection). This is the highest brain uptake ever reported for this type of radiotracer in rats. The specific uptake reached a thalamus to cerebellum ratio of 6.74 ± 0.95 at 60 min post injection. The [11C]SMe-ADAM uptake in the thalamus was significantly decreased by pre-treatment with fluoxetine to 45 ± 9 % of the control values. Furthermore, no metabolites of [11C]SMe-ADAM could be detected in the SERT rich regions of the rat brain. It is concluded that [11C]SMe-ADAM may be a suitable PET ligand for SERT imaging in the living brain.
Keywords: [11C]SMe-ADAM, [11C]methyl iodide, serotonin transporter, microPET
  • Nuclear Medicine and Biology 33(2006)1, 53-63

Publ.-Id: 7181 - Permalink


Motion of single gas bubbles rising in a liquid metal exposed to a DC magnetic field
Zhang, C.; Eckert, S.; Gerbeth, G.;
The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC magnetic field was examined. The magnetic field lines were aligned either in longitudinal or in transverse direction. 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 = 2.4e-13. The liquid metal was in a cylindrical container at rest. The Ultrasound Doppler Velocimetry (UDV) was applied to determine bubble and liquid velocities simultaneously. The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Within the present interaction number range (N < 2), the applied magnetic field can either increase or decrease the bubble drag coefficient depending on the bubble size and the magnetic interaction parameter. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddy structures in the wake. In case of the longitudinal magnetic field the Strouhal number St decreases with increasing magnetic interaction parameter.
Keywords: Single bubble, Liquid metal, Magnetic field, Terminal velocity, Drag coefficient, Bubble wake, Ultrasound Doppler Velocimetry
  • Poster
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
    1(2005), 195-198

Publ.-Id: 7178 - Permalink


Flow structures during solidification of metallic alloys affected by a rotating magnetic field
Willers, B.; Nikritjuk, P. A.; Eckert, K.; Eckert, S.;
In order to improve the microstructure of casting ingots a rotating magnetic field (RMF) is widely used to stir the liquid phase during solidification. Usually, the interaction between the solidification process and the RMF driven flow has been discussed only in terms of the flow pattern well-known from the laminar, isothermal case being a superposition of a primary swirling flow in azimuthal direction and a secondary flow occurring as a double vortex in the r-z plane. Effects arising from the propagation of the solidification front, the extension of the mush zone or the spin-up of the flow at higher cooling rates are almost not taken into account. We present experimental and numerical investigations concerning the influence of a RMF driven flow on the momentum, heat and mass transfer within a binary Sn-Pb alloys solidified directionally.
Solidification experiments were carried out using a Sn-15wt%Pb alloy in a cylindrical mold positioned on a water-cooled copper chill. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification. The temperature field was monitored using thermocouples. The set-up was enclosed by an inductor providing the RMF. The Taylor numbers Ta were varied between 10e5 and 10e8.
The continuum formulation based model has been adopted for numerical simulations using the following assumptions: all transport properties, such as thermal and electrical conductivity or viscosity, are assumed to be constant; the density of solid phase equals the density of liquid phase; the phases are in local thermodynamic equilibrium; the velocity of solid phase in the upper part of the mushy zone is equal to the velocity of the liquid phase. The mushy region is modeled using a mixture viscosity formulation. The Lorentz force in the Navier-Stokes equation has been calculated by means of an analytical solution for the time-averaged Lorentz force for a finite cylinder. The resulting set of eqiuations is discretized by an implicit finite-volume, finite-difference based method, and solved by using the SIMPLE algorithm.
Our results show that the velocity field undergoes distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case.
Keywords: solidification, Pb-Sn alloy, Fluid flow, Electromagnetic stirring, Rotating magnetic field
  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
    Proceedings 2(2005), 269-272

Publ.-Id: 7177 - Permalink


Synthesis and Binding Properties of Dendritic Oxybathophenanthroline Ligands towards Copper(II)
Stephan, H.; Geipel, G.; Bernhard, G.; Comba, P.; Rajaraman, G.; Hahn, U.; Vögtle, F.;
Dendritic oxybathophenanthroline ligands (generation 0 to 3) have been synthesized by treatment of 4,7-bis(4´-hydroxyphenyl)-1,10-phenanthroline with the corresponding Fréchet-type dendrons carrying a benzylic bromide function at the focal point. The complexation of copper(II) has been studied by liquid-liquid extraction using the radioisotope 64Cu and time-resolved laser-induced fluorescence (TRLFS) measurements in organic media proving the formation of 1:3 complexes (Cu : dendritic ligand). The stability of the copper complexes is mainly determined by the 1,10-phenanthroline core element. The stability constants of the 1:3 complexes were found to be in the order of log K ~ 16 in CHCl3. On the other hand, increasing generation of the dendritic Fréchet-type branches leads to enhanced shielding of the copper ion from the environment. Additional information about this behaviour was obtained by the fluorescence lifetimes which are much less influenced upon addition of copper(II) salt to solutions of the higher generation ligands.

Publ.-Id: 7176 - Permalink


A study on the mixing behaviour of different density liquids in a stirred tank reactor by passive and reactive tracers
Hessel, G.; Hristov, H. V.; Kryk, H.; Prasser, H.-M.; Schmitt, W.;
Mixing in stirred vessels of different density liquids is common operation in the process industry. The hydrodynamic behaviour of such a system could be crucial for the overall process performance. The aim of this work is to numerically predict the dynamics of the mixing process of initially stratified system of two different density liquids. Stratified conditions could occur in the stirred vessel, especially in the case of impeller malfunctioning, i.e. impeller breakdown. This effect might prove to be of significant importance, particularly in the case of reacting liquids for large-scale reactors operating in the industry.
The CFD analyses were performed for a non-baffled stirred vessel reactor, mechanically agitated by the Pfaudler impeller. The two main cases of passive and reactive tracer mixing behaviour were numerically predicted by the means of the CFD software CFX 5.7. In both cases the system of two miscible liquids with different densities was dynamically predicted in 3D from an initially stratified to a complete mixing condition. The full 3D simulation was applied in order to capture the flow instabilities associated with the impeller blade passage, especially pronounced in the first few seconds after the impeller start. In order to study the effect of the free surface deformation on the mixing process, the gas phase was also involved into the system via the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. In the case of the reactive tracer mixing, the alkali was diluted in the lighter liquid. The simulations were performed on different grids in order to obtain grid independent results.
The accuracy of the numerical simulations was evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one which were initially stratified were brought into motion by the rotating impeller. In the case of the passive tracer mixing, the alcoholic phase was coloured by blue dye whereas in the case of the reactive mixing a phenolphthalein indicator was applied. The mixing process was captured by a digital camcorder and subsequently the images were digitally processed. The mixing of different initial lighter phase concentrations was visually investigated to obtain the colour calibration curve. The numerical predictions were evaluated against several locations, close to vessel central line and wall, for which the optical distortion was minimal.
  • Lecture (Conference)
    GVC/DECHEMA Jahrestagung, 06.-08.09.2005, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 77(2005)8, 1057-1058

Publ.-Id: 7175 - Permalink


Untersuchungen zur sicheren Prozessführung von Grignard-Reaktionen
Hessel, G.; Kryk, H.; Schmitt, W.; Tefera, N.;
Die Grignard-Chemie erlebt eine Renaissance bei der industriellen Herstellung neuer pharmazeutischer Wirkstoffe, Lebensmitteladditive und Feinchemikalien. Sicherheitsprobleme können aufgrund der sehr großen Exothermie und der hohen Reaktivität der Grignard-Reagenz beim Scale-up in den großtechnischen Maßstab auftreten. Die Hauptgefahrenquelle ist das spontane Starten der Grignard-Reaktion, wenn bereits eine kritische Menge an organischem Halogenid akkumuliert ist, und dann die durchgehende Startreaktion durch den starken Druckanstieg zur Stofffreisetzung führt. Die genaue Bestimmung der reaktionstechnischen Prozessparameter zur Auslegung des Kühlsystems für das Produktions-Betriebsregime wird an einem ge-schlossenen Reaktionskalorimeter mit integriertem in-situ FTIR-Spektrometer für eine industrielle Grignard-Reaktion beschrieben. Weiterhin werden Möglichkeiten zur Detektion des Reaktionsstarts und zur Verfolgung der Halogenid-Akkumulation vorgestellt. Durch den Einsatz der in-situ FTIR-Spektroskopie läßt sich einerseits der Re-aktionsstart eindeutig detektieren, andererseits können sowohl der Verbrauch des organischen Halogenids als auch der Aufbau der Grignard-Reagenz in Echtzeit überwacht werden. Neben den Online-Konzentrationsmessungen können an einem geschlossenen Rührkesselreaktor auch die steilen Anstiege der Reaktortemperatur und des Druckes sowie die Wärmebilanz zum Nachweis des Reaktionsstarts genutzt werden. Durch Online-Konzentrationsmessungen und/oder Wärmebilanzmessungen ist es außerdem möglich, das Einschlafen der Hauptreaktion durch Verunreinigungen zu erkennen und das spätere Wiederstarten zu verhindern. Darüber hinaus konnte nachgewiesen werden, daß im geschlossenen Reaktionskalorimeter die reaktionstechnischen Parameter, wie Induktionszeit, Dauer des Startprozesses und Reaktionsenthalpie, wesentlich genauer als im offenen Reaktor gemessenen werden können. Ferner werden Untersuchungen dieser Grignard-Reaktion im adiabatischen Reaktionskalorimeter (PhiTecII) diskutiert, das auch zur Dimensionierung von Notentlastungssystemen dienen kann.
  • Lecture (Conference)
    GVC/DECHEMA Jahrestagung 2005, 06.-08.09.2005, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 77(2005)8, 1123-1123

Publ.-Id: 7174 - Permalink


The influence of the density difference on the mixing process in mechanically agitated reactor
Hessel, G.; Hristov, H. V.; Kryk, H.; Prasser, H.-M.; Schmitt, W.;
A non-baffled stirred vessel reactor was investigated computationally with CFX-5 numerical package. The mixing of two miscible liquids with different densities was dynamically predicted from an initially stratified to a complete mixing condition. Although for a non-baffled vessel an axi-symmetric behaviour can be expected, the process was regarded as three dimensional in order to demonstrate the local instabilities associated with the blade passage. Additionally, the gas phase was involved into the simulations to investigate the effect of the free surface deformation on the mixing process. The two-phase gas-liquid interactions were modelled using the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. The grid elements size was kept relatively low because of the dynamic behaviour of the liquid surface central vortex. Furthermore, the available turbulence models were considered to obtain the closest possible match with the experimental observations. In such a way, the stirred vessel hydrodynamics was dynamically calculated in 3-D in order to study the effect of the density difference.
The numerical simulations were evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one, which were initially stratified, were brought into motion by the means of the rotating impeller and the mixing process was captured by digital camcorder and subsequently the images were digitally processed. Several points, close to vessel central line and wall, for which the optical distortion was minimal were considered for evaluation of the numerical predictions.
The hydrodynamics of the above described system is of particular concern for many chemical and biochemical reactions engineered to take place in stirred vessel reactor. Although the initial conditions were to some extend idealised in order to avoid some complications raised by the presence on an injection, the studies showed strong influence on the density difference on the homogenisation. Such so called idealised conditions, however, also might occur in the stirred vessel, especially in the case of impeller malfunctioning. In case of impeller stoppage, i.e. breakdown, different density liquids present in the vessel might get stratified. This effect might prove to be of significant importance, especially in the case of reacting liquids for large-scale reactors operating in the industry.
  • Contribution to proceedings
    Conference on Computational Fluid Dynamics in Chemical Reaction Engineering IV, 19.-24.06.2005, Barga, Italy
    CD-ROM
  • Lecture (Conference)
    Conference on Computational Fluid Dynamics in Chemical Reaction Engineering IV, 19.-24.06.2005, Barga, Italy

Publ.-Id: 7173 - Permalink


Sonne in der Schule: Betriebsergebnisse aus den Programmen in Bayern, Sachsen und Norddeutschland
Becker, G.; Schiebelsberger, B.; Rindelhardt, U.; Weber, W.;
Seit 10 Jahren wird in Deutschland das Programm "Sonne in der Schule" durchgeführt. An mehr als 1000 Schulen wurden dabei netzgekoppelte Photovoltaik-Anlagen errichtet. Im Beitrag werden die erreichten Betriebsergebnisse dieser Anlagen dargestellt. Darüber hinaus wird auf die Nutzung der Anlagen im Unterricht eingegangen.
Keywords: Photovoltaik-Anlagen
  • Poster
    20. Symposium Photovoltaische Solarenergie, 09.-11.03.2005, Staffelstein, Deutschland
  • Contribution to proceedings
    20. Symposium Photovoltaische Solarenergie, 09.-11.03.2005, Staffelstein, Germany

Publ.-Id: 7172 - Permalink


Athermal germanium migration in strained silicon layers during junction formation with solid-phase epitaxial regrowth
Vandervorst, W.; Janssens, T.; Brijs, B.; Delhougne, R.; Loo, R.; Caymax, M.; Pawlak, B. J.; Posselt, M.;
The formation of a thin strained Si layer on top of a strain-relaxed SiGe buffer is a recent approach to improve the drive current of complementary metal-oxide-semiconductor devices by inducing strain within the transistor channel. At the same time, advanced process technologies require junction formation processes with minimal diffusion and very high dopant activation. Solid-phase epitaxial regrowth is a low temperature process based on preamorphization and subsequent regrowth leading to highly activated and shallow junctions. In this letter, we investigate the stability of the thin strained Si layer, during solid-phase epitaxial regrowth process by monitoring the Ge redistribution/strain after the preamorphization step (without any anneal) and after the thermal regrowth process.
Keywords: strained silicon, germanium, silicon germanium, junction formation, athermal migration
  • Applied Physics Letters 86(2005), 081915

Publ.-Id: 7168 - Permalink


Wire-mesh sensors and tomography methods developed by FZR
Prasser, H.-M.;
The Institute of Safety Research of the Forschungszentrum Rossendorf, Germany, has developed electrode-mesh sensors, which allow the measurement of the electrical conductivity distribution in a flow duct. This can be used either for the detection of the gaseous phase in a gas-liquid flow or for mixing studies in single phase flow, when the components have different electric conductivities. Due to the high measuring rate each bubble is mapped in several successive instantaneous frames. This allows to obtain bubble size distributions as well as bubble-size resolved gas fraction profiles beside the visualisation and the calculation of profiles of the time-averaged void fraction. The sensor is widely used to study the evolution of the flow pattern in an upwards air-water flow. The experiments aim at closure equations describing forces acting on bubbles as well as coalescence and fragmentation frequencies for the implementation in CFD-codes. Some other prominent examples of the application of wire-mesh sensors were given, like (1) boiling water reactor stability studies, (2) the visualization of cavitation at fast-acting cut-off valves, (3) the visualization of the flow structure behind a closing globe valve, and finally (4) mixing studies in single-phase flow at the ROCOM test facility in Rossendorf, which are aimed at the mixing of deborated slugs during boron dilution transients.

Second subject of the paper is radiation tomography. A gamma-tomography setup for imaging a periodically changing density field is described. It is based on a time-resolved acquisition of the detector signals. It was used to visualize the gas fraction distribution within the impeller of an axial turbo-pump operating at about 1500 rpm, that delivered a gas-liquid mixture, as well as to a hydraulic clutch (coupling). In the field of X-ray tomography, the status of the development of an ultra-fast system based on a scanning electron beam is presented. An electron beam is linearly deflected over a tungsten target with a frequency of 1 kHz. X-rays generated by the traveling focus penetrate the object and arrive at a detector line placed behind the object. The detectors are read-out with a sufficiently high speed in order to obtain projections of the density distribution in different projecting directions, which change thanks to the scanning. First results showing tomographic image sequences of a phantom consisting of small spheres kept in arbitrary motion in a cylindrical test box will be presented. Moving spheres of 3 mm diameter with cylindrical holes of 1 mm diameter were resolved at a framing rate of 1 kHz.
Keywords: Wire-mesh sensor, X-ray tomography, gamma tomography, gas-liquid flow
  • Invited lecture (Conferences)
    Seminar, 29.11.2004, Darmstadt, Germany

Publ.-Id: 7167 - Permalink


Irrtümer über Kernenergie
Prasser, H.-M.;
Der Vortrag plädiert für einen Mix aus Atomenergie und erneuerbaren Energien, um die Versorgung für die Zukunft sicher zu stellen. Kernkraftwerke sind ebenso wirtschaftlich, wie heute die Energiegewinnung aus fossilen Brennstoffen, jedoch mit wesentlich geringeren Stoffströmen verbunden: Der Ertrag aus der Spaltung von einem Kilogramm Uran 235 oder Plutonium 239 entspricht dem aus der Verbrennung von rund 2800 Tonnen Steinkohle. Dies ist die Stärke der Kernenergie, denn dadurch ist sie die einzige Primärenergiequelle, bei der die Abfälle vollständig erfasst und geordnet entsorgt werden können. Unrealistisch ist die Vorstellung, Deutschland könne seinen Energiebedarf bis 2050 zur Hälfte aus regenerativen Quellen decken. Speichermöglichkeiten sind begrenzt, weshalb bei idealen Witterungsbedingungen Überkapazitäten auftreten würden, die nicht verwertet werden könnten. Bei einer Flaute oder bedecktem Himmel wiederum müsste Strom importiert oder beispielsweise aus fossilen Kraftwerken eingespeist werden. Beides würde den ohnehin schon hohen Strompreis aus diesen Quellen in unvertretbare Höhen treiben. Weiterhin betrachtet werden die Verfügbarkeit von Spaltmaterial, der erreichte Stand bei der Sicherheit der Kernkraftwerke sowie die Endlagerproblematik.
Keywords: nuclear energy, energy strategy, nuclear safety, nuclear waste disposal, nuclear fuel
  • Lecture (others)
    Thematischer Abend, 19.11.2004, Darmstadt, Germany

Publ.-Id: 7166 - Permalink


Kernkraft - eine Energiequelle der Zukunft - auch für Deutschland
Prasser, H.-M.;
Gefährlich, riskant, umweltschädigend, gesundheitsschädlich, unverantwortbar, unwirtschaftlich, unsozial, nicht nachhaltig - das sind Adjektive, mit der die Nutzung der Kernenergie zur Stromversorgung häufig belegt wird. Tatsächlich tragen die Kernkraftwerke jedoch stabil zur kostengünstigen Stromversorgung bei. In Deutschland haben sie einen Anteil von 30 %, in einigen Ländern mehr. Unter dem Eindruck spürbar anwachsender Brennstoffpreise bei den fossilen Energieträgern und immer deutlicher werdender Folgen der Klimaveränderungen mehren sich die Stimmen, die eine Renaissance der Kernenergie für notwendig halten. In einer solchen Situation ist es wichtig, die Potenzen der Energiegewinnung durch Kernspaltung zu kennen und die wichtigsten Behauptungen der Kernenergiegegner kritisch zu hinterfragen. Speziell für Deutschland wird ein Blick auf die gängigen Konzeptionen zur Energiestrategie der nächsten 50 Jahre geworfen. Letztendlich wird der Schluss gezogen, dass langfristig ein Umsteuern auf einen Mix aus nuklearen und regenerativen Energiequellen erfolgen muss, um zu einer nachhaltigen und ökonomisch, sozial und ökologisch vertretbaren Energieversorgung zu gelangen.
Keywords: nuclear energy, sustainability, energy strategy, acceptance of nuclear energy
  • Lecture (others)
    Industrieclub Sachsen, 05.10.2004, Dresden, Schloss Eckberg, Germany

Publ.-Id: 7165 - Permalink


Turbulent dispersion of bubbles in poly-dispersed gas-liquid flows in a vertical pipe
Shi, J.-M.; Burns, A.; Prasser, H.-M.;
The turbulence of the liquid phase has a signi cant dispersion e ect on the migration of bubbles in a vertical ow. Based on a double averaging approach and by adopting the Favre averaged velocity, a generalized model, called the Favre Averaged Drag (FAD) Model, was developed for the turbulent dispersion force for Eulerian simulations of multiphase ows [Burns et al., 2004]. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the inter phase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation makes the sense of the double averaging approach straightforward. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will signi cantly increase the computational e ciency. We also provide validation and evaluation for this model by numerical and experimental investigations of bubbly ows in a vertical pipe. The experimental data were obtained by using the wire-mesh sensor technique. The computations were carried out by applying poly-dispersed models. The emphasis is to examine the model applicability under various ow conditions including bubbly ows with a wall peak and a core peak of the gas volume fraction, ows in the transition region between them, and in the nely dispersed ow regime. The e ect of the drag force model on the turbulent dispersion force was also examined.
Keywords: Turbulent dispersion force, non-drag force model, bubbly flow, CFD
  • Contribution to proceedings
    13th International Conference on Nuclear Engineering, 15.-20.05.2005, Beijing, China

Publ.-Id: 7163 - Permalink


DYN1D-MSR dynamics code for molten salt reactors
Krepel, J.; Rohde, U.; Grundmann, U.; Weiss, F.-P.;
This paper reports about the DYN1D-MSR code development and dynamics studies of the molten salt reactors (MSR) – one of the ‘Generation IV International Forum’ concepts. In this forum the graphite-moderated channel type MSR based on the previous Oak Ridge National Laboratory research is considered.
The liquid molten salt serves as a fuel and coolant, simultaneously and causes two physical peculiarities: the fission energy is released predominantly directly into the coolant and the delayed neutrons precursors are drifted by the fuel flow. The drift causes the spread of delayed neutrons distribution to the non-core parts of primary circuit and it can lead to a reactivity loss or gain in the case of fuel flow acceleration or deceleration, respectively. Therefore, specific 3D tool based on in house code DYN3D was developed in FZR. The code DYN3D-MSR is based on the solution of two-group neutron diffusion equation by the help of a nodal expansion method and it includes models of delayed neutrons drift and specific MSR heat release distribution.
In this paper the development and verification of 1D version DYN1D-MSR of the code is described. The code has been validated with the experimental data gained from the molten salt reactor experiment performed in the Oak Ridge and after the validation it was applied to several typical transients (overcooling of fuel at the core inlet, reactivity insertion, and the fuel pump trip).
Keywords: MSR, Molten, Salt, Reactor, Dynamics, DYN3D, DYN1D-MSR, liquid, fuel

Publ.-Id: 7162 - Permalink


Thermo-mechanical FE-modelling of in-vessel retention
Willschuetz, H.-G.; Altstadt, E.;
Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. At the Institute of Safety Research of the FZR a finite element model has been developed simulating the thermal processes and the viscoplastic behaviour of the vessel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal hydraulic and the mechanical calculations are sequentially and recursively coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool. The model was applied to pre-and post test calculations for the FOREVER test series of the KTH Stockholm. First calculations for a PWR geometry were performed to work out differences and commonalities between prototypic scenarios and scaled experiments.
Keywords: Finite-Element-Model, In-vessel melt retention, Light Water Reactor, Creep, Convection, Fracture
  • Lecture (Conference)
    SARNET - First Annual Review Meeting, 15.02.2005, Köln, Germany

Publ.-Id: 7161 - Permalink


Links of SARNET with the ISTC program - presentation of the contact expert group of severe accident management
Altstadt, E.;
General information on the ISTC program are given. The working procedures of the CEG-SAM are explained and the currently running ISTC projects related to SAM are presented in brief.
Keywords: Severe accident management, International Science and Technology Center (ISTC)
  • Invited lecture (Conferences)
    SARNET - First Annual Review Meeting of Corium Topic, 15.02.2004, Köln, Germany

Publ.-Id: 7160 - Permalink


Studies of the Interaction Behavior of Humic Acids with Actinides in the Environment
Sachs, S.; Schmeide, K.; Geipel, G.; Mibus, J.; Bernhard, G.;
Due to their abilities for complex and colloid formation as well as their redox properties, humic acids influence the migration of actinides in the environment. Therefore, risk assessments, related to the behavior of actinides in the environment, require basic knowledge on the interaction of humic acids with metal ions. Thus, the interaction of humic acids with actinides is studied, e.g., the Np(V)-humic acid-complexation and the redox stability of uranium(VI) humate complexes, applying synthetic and natural humic acids.
Keywords: Humic Acids; Model Substances, Actinides; Complexation; Migration; Redox Processes
  • Poster
    8. German-American Frontiers of Engineering Symposium, 04.-07.05.2005, Potsdam, Germany

Publ.-Id: 7159 - Permalink


First analysis of anisotropic flow with Lee-Yang zeroes
Bastid, N.; Andronic, A.; Barret, V.; Basrak, Z.; Benabderrahmane, M. L.; Caplar, R.; Cordier, E.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasparic, I.; Gobbi, A.; Grishkin, Y.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Koczon, P.; Korolija, M.; Kotte, R.; Kress, T.; Lebedev, A.; Leifels, Y.; Lopez, X.; Mangiarotti, A.; Manko, V.; Merschmeyer, M.; Moisa, D.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolarkiewicz, M. M.; Smolyankin, V.; Soliwoda, I. J.; Stockmeier, M. R.; Stoicea, G.; Tyminski, Z.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z.; Yushmanov, I.; Zhilin, A.;
We report on the first analysis of directed and elliptic flow with the new method of Lee-Yang zeroes. Experimental data are presented for Ru+Ru reactions at 1.69A GeV measured with the FOPI detector at SIS/GSI. The results obtained with several methods, based on the event-plane reconstruction, on Lee-Yang zeroes, and on multi-particle cumulants (up th 5th order) applied for the first time at SIS energies, are compared. They show conclusive evidence that azimuthal correlations between nucleons and composite particles at this energy are largely dominated by anisotropic flow.

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Publ.-Id: 7158 - Permalink


Turbulent dispersion force -- physics, model derivation and evaluation --
Shi, J.-M.; Frank, T.; Burns, A.;
Turbulence dispersion has a significant dispersion effect on the migration of bubbles in a vertical flow. Based on a double averaging approach and by adopting the Favre averged velocity, we developed the Favre Averaged Drag (FAD) turbulent dispersion force model for Eulerian simulations of multiphase flows. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the interphase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation explains the physical mechanism and makes the sense of the double averaging approach straightford. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will significantly increase the computational efficiency.

We also provide a systematic model evaluation based on numerical simulations of bubbly flows in a vertical pipe using both mono- and poly-dispersed flow models. The numerical results for the radial distribution of the gas concentration were compared with the experimental data measured by using the wire-mesh sensor technique. The results confirm that the bubble size and the liquid flow Reynolds number have a strong effect on the turbulent dispersion as is shown in the model derivation.
Keywords: turbulent dispersion, bubbly flow, CFD, model
  • Lecture (Conference)
    FZR-ANSYS CFX Workshop on Multiphase Flow, 29.-30.06.2004, Dresden, Germany

Publ.-Id: 7157 - Permalink


Uranyl Complexation in Fluorinated Acids (HF, HBF4, HPF6, HTf2N): ACombined Experimental and Theoretical Study
Gaillard, C.; El Azzi, A.; Billard, I.; Bolvin, H.; Hennig, C.;
The aim of this work is to characterize the complexation ability of F-, BF4 -, PF6 -, and Tf2N- toward uranyl ions in aqueous solution. These anions were chosen as they represent the anionic part of the most studied roomtemperature ionic liquids. Time-resolved emission spectroscopy and X-ray absorption spectroscopy were used to retrieve structural data on the complexes formed. The results obtained were compared with computational data.
Tf2N- does not complex uranyl, even at high concentration. Other fluorinated acids form inner-sphere complexes with U(VI), in a monodentate fashion in the case of BF4 and PF6.
  • Inorganic Chemistry 44(2005), 852-861

Publ.-Id: 7155 - Permalink


Predictive Atomistic Computer Simulations on Synthesis and Stability of Single-crystalline Nanowires
Röntzsch, L.; Heinig, K.-H.;
In this contribution, results of predictive atomistic computer simulations are presented which describe the ion beam synthesis of single-crystalline CoSi2 nanowires (NWs) embedded in Si. In order to simulate the Co implantation, the binary collision codes TRIDYN and TRIM were adapted to the particular experimental situation of a finely focused Co ion beam of a few tens of nanometers in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described.
Due to the systems tendency towards a reduction of interfacial free energy (Rayleigh instability), it will be demonstrated that the orientation of the Co implantation profile to the Si matrix influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)/Si(111) interface, faceting forces occur if the Co implantation profile is not aligned with the Si-[011] direction. Thus, intentional misalignment is a possible way to a controlled decay of the NW into a chain of monodisperse and equidistant nanoclusters which is applicable as plasmon waveguide.
Keywords: nanowire, CoSi2, Rayleigh instability, faceting, kinetic Monte-Carlo
  • Poster
    342. WE-Heraeus Seminar "Science and Technology of Inorganic Nanowires", 13.-16.02.2005, Bad Honnef, Deutschland

Publ.-Id: 7154 - Permalink


X-ray Tomography
Hampel, U.;
The presentation discusses the application of X-ray micro-tomography to the measurement of size, shape and porosity of polymer particles.
Keywords: X-ray, micro-tomography, polymer processing
  • Invited lecture (Conferences)
    DPI PO Day, 10.02.2005, Enschede, Netherlands

Publ.-Id: 7153 - Permalink


Application of computer tomography in microelectronic packaging
Speck, M.; Wolter, K.-J.; Danczak, M.; Daniel, D.;
In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.
Keywords: computer tomography, nondestructive testing, microelectronic packaging, limited angle tomography
  • Contribution to proceedings
    9th International Symposium on NDE for Health Monitoring and Diagnostics, 15.-17.03.2004, San Diego, United States
    5392(2004), 194-202
  • Lecture (Conference)
    9th International Symposium on NDE for Health Monitoring and Diagnostics, 15.-17.03.2004, San Diego, United States

Publ.-Id: 7152 - Permalink


Optical measurement of nasal swellings
Hampel, U.; Schleicher, E.; Wüstenberg, E. G.; Hüttenbrink, K.-B.;
We introduce a new method to noninvasively and continuously measure the swelling process of the nasal mucosa. Thereby we use light of different wavelengths in the near infrared range which is transilluminated through the nasal tissue and whose extinction is recorded as a function of time. From the temporal and spectral extinction data we are able to extract characteristic parameters that describe the swelling process quantitatively by means of a regression type parameter estimation algorithm. Furthermore, we show the capability of the method to quantify hemoglobin saturation in the surplus blood volume and introduce a bilateral measurement approach that allows us to examine the swelling process in both nasal cavities simultaneously. The method has been applied to the nasal allergen provocation test and verified on a limited number of volunteers.
Keywords: allergy diagnostics, nasal provocation test, optical sensor, NIR spectroscopy
  • IEEE Transactions on Biomedical Engineering 51(2004)9, 1673-1679

Publ.-Id: 7151 - Permalink


X-ray computed tomography for experimental investigations of multi-phase flows
Hampel, U.;
The presentation discusses the application of conventional X-ray CT, X-ray cone beam CT and ultrafast limited angle X-ray CT to the measurement of phase distributions in multiphase flow problems.
Keywords: X-ray tomography, multiphase flows
  • Contribution to proceedings
    Multi-phase Flow: Simulation, Experiment and Applications, ANSYS-CFX / FZR workshop, 28.-30.06.2004, Dresden, BRD

Publ.-Id: 7150 - Permalink


K6H2[TiW11CoO40]×13H2O, with a monotitanoundecatungstocobaltate(II) anion
Kraus, W.; Stephan, H.; Röllich, A.; Matéjka, Z.; Reck, G.;
Hexapotassium dihydrogen monotitanoundecatungstocobaltate(II) tridecahydrate, K6H2[TiW11CoO40]×13H2O, crystallizes from aqueous solution in the cubic space group P43m. The structure was refined as an inversion twin. The [TiW11CoO40]8- anion has a Keggin structure with one W-atom site occupied by titanium and a central tetrahedral CoO4 group.
  • Open Access LogoActa Crystallographica Section E 61(2005), i35-i37

Publ.-Id: 7149 - Permalink


New concepts for short-wavelength quantum cascade lasers and few-cycle THz emitters
Helm, M.;
I will discuss two recent advances related to semiconductor light sources in the infrared and THz regions. One example is a quantum cascade laser operating at a wavelength shorter than 4 microns above room temperature with high peak power. It is based on strained InGaAs/InAlAs on InP, with the addition of high barriers of pure AlAs for better confinement and strain compensation. In a novel few-cycle THz emitter we try to combine the advantages of the high electric bias field in photoconductive antennas with a large active area. This is achieved with an interdigitated electrode structure, partially covered in order to mask one field polarity. As a result no destructive interference of the emitted THz wave occurs, which allows upscaling of the device area.
Keywords: THz emitter, quantum cascade laser
  • Invited lecture (Conferences)
    Japan-Germany Colloquium 2005: Semiconductor Physics and Technology, 14.-16.02.2005, Dresden, Deutschland

Publ.-Id: 7148 - Permalink


Study of the Influence of Humic Acid on the U(VI) Sorption onto Kaolinite
Krepelova, A.; Sachs, S.; Reich, T.; Rossberg, A.; Bernhard, G.;
Humic acids (HA) comprise an important part of natural organic materials. Due to their interactions with organic and inorganic pollutants produced by human activity, they play a significant role in biochemical cycles of ecosystems. By the formation of soluble anionic complexes with the range of more or less toxic metals, including radionuclides, HA can affect the transport of these contaminants. Therefore, the understanding of their impact on the actinide migration in geologic environments is essential for a reliable safety assessment of nuclear waste disposal sites. In the present study the influence of HA on the U(VI) sorption onto kaolinite was studied. Kaolinite represents a well-defined model substance for clay-rich host formations.
Batch experiments were combined with EXAFS spectroscopy to obtain molecular-level information on the interaction of U(VI) with HA (14C-labeled HA) and kaolinite (KGa-1b).
Three kinds of batch experiments were performed under different experimental conditions: HA sorption in the absence of U(VI), U(VI) sorption in the absence and U(VI) sorption in the presence of HA. The sorption curves have shown that the U(VI) sorption on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 and HA presence. U(VI) sorption increases with pH up to pH 8.5, then it decreases. In the absence of CO2, no decrease is observed. In the presence of CO2 HA effects U(VI) adsorption onto kaolinite over the entire pH range. At pH < 5 the presence of HA enhances the U(VI) uptake relative to the HA-free system because the adsorbed HA forms additional binding sites for U(VI). In the pH range between pH 5 and pH 8.5 the U(VI) sorption decreases in the presence of HA due to desorption of HA from the kaolinite surface resulting in the formation of dissolved U(VI)-HA complexes. At pH > 8.5 uranium sorption increases again relative to the HA-free system (Fig.1).
We performed EXAFS measurements with U(VI)-HA-kaolinite sorbates in order to characterize the surface complexes of U(VI) in the presence of HA. Results of the spectroscopic measurements are interpreted and compared with the EXAFS results in the binary system without HA [1] to obtain information on the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.
Keywords: Humic Acid, Uranium, Sorption, EXAFS, Kaolinite
  • Lecture (Conference)
    GDCh Jahrestagung 2005, 11.-14.09.2005, Düsseldorf, Germany
  • Contribution to proceedings
    GDCh - Jahrestagung 2005, Chemie schafft neue Strukturen, 11.-14.09.2005, Düsseldorf, Germany
    Kurzreferate, 3-936028-36-2, 500

Publ.-Id: 7147 - Permalink


Interpretation of TOF-SIMS depth profiles from ultrashallow high-K dielectric stacks assisted by hybrid collisional computer simulation
Ignatova, V. A.; Möller, W.; Conard, T.; Vandervorst, W.; Gijbels, R.;
The TRIDYN collisional computer simulation has been modified to account for emission of ionic species and molecules during sputter depth profiling, by introducing a power law dependence of the ion yield as a function of the oxygen surface concentration, and by modelling the sputtering of monoxide molecules. The results are compared to experimental data obtained with dual beam TOF-SIMS depth profiling of ZrO2/SiO2/Si high-k dielectric stacks with thicknesses of the SiO2 interlayer of 0.5, 1, and 1.5 nm. Reasonable agreement between experiment and computer simulation is obtained for most of the experimental features, demonstrating the effects of ion-induced atomic relocation, i.e. atomic mixing and recoil implantation, and preferential sputtering. The depth scale of the obtained profiles is significantly distorted by recoil implantation and the depth-dependent ionization factor. A pronounced double peak structure in the experimental profiles related to Zr is not explained by the computer simulation, and is attributed to ion-induced bond breaking and diffusion, followed by a decoration of the interfaces by either mobile Zr or O.
  • Applied Physics A 81(2005)1, 71-77

Publ.-Id: 7146 - Permalink


Uncertainty and sensitivity analysis for the modeling of transients with interaction of thermal hydraulics and neutron kinetics
Kliem, S.; Mittag, S.; Weiß, F.-P.; Langenbuch, S.;
The GRS methodology to assess the uncertainty of the calculation results of computer simulation codes was applied to the coupled code system DYN3D/ATHLET, consisting of a 3D neutron kinetic core model and a thermal hydraulic system code. It was used to make a statistical analysis of the result parameters from the output data of the DYN3D/ATHLET-calculation. A number of variation calculations with randomly distributed input parameters within given boundaries was carried out. On that basis, time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations.
  • Lecture (Conference)
    11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
    Proceedings CDROM paper 461

Publ.-Id: 7145 - Permalink


Polarization effects at the Uranium L1 and L3 edges – Theory and Applications
Hennig, C.;
The polarization dependence of U L1 edge EXAFS spectra is relatively simple because the photoelectron is excited from ground state (l = 0) to one excited state (l = 1). By contrast, the polarization dependence is more complicated at the L2 and L3 edges were the photoelectron is excited from p ground state into final states s (l = 0) and d (l = 2). The EXAFS expression of L2 and L3 edges comprises here pure s, pure d and coupled s-d states. The polarization effect at the U L1 and L3 edges was investigated using a single crystal of Ca[UO2PO4]2•6H2O. The high symmetry in the equatorial shell allows to compare successful the measurements with the theory. In a second part two types of applications will be discussed. It will be shown, that powder samples have a texture which can lead to an erroneous determination of coordination numbers. A use of the magic angle allows to avoid this problem. A second example will be discussed where the polarization dependency can be used to determine the orientation of actinyl ions sorbed at mineral surfaces.
  • Lecture (Conference)
    Actinides 2005, 04.-08.07.2005, Manchester, Great Britain
  • Contribution to proceedings
    Actinides 2005, 03.-09.07.2005, Manchester, Great Britain
    Recent Advances in Actinide Science, Editors: May, I., Alvares, R., Bryan, N.: The Royal Society of Chemistry 2006, 0-85404-678-X, 716-718

Publ.-Id: 7144 - Permalink


Ion irradiation in exchange bias systems
Fassbender, J.ORC
Lecture on the present status of ion irradiation in exchange bias systems.
Keywords: magnetism, ion irradiation, exchange bias
  • Invited lecture (Conferences)
    EU-RTN-Meeting Nexbias, 17.-18.02.2005, Kaiserslautern, Deutschland

Publ.-Id: 7141 - Permalink


Uranium speciation in 30-year old Freital mine tailings: An EXAFS, μ-XRD, and μ-XRF Study
Scheinost, A.; Hennig, C.; Somogyi, A.; Martinez-Criado, G.; Knappik, R.;
Risk assessments of actinide-contaminated soils and sediments require detailed knowledge of actinide speciation and its long-term kinetics. Former Saxonian mine tailings, which have been covered but else left undisturbed, are ideally suited to study changes in uranium speciation over timescales of decades. We investigated the major uranium species in two samples from buried mine tailings using a combination of Synchrotron-based microfocus-techniques (μ-XRF, μ-XRD with micrometer resolution), bulk EXAFS spectroscopy, and chemical extractions.
In sample F1 (5 m depth, oxic, pH 8, U=440 mg/kg, high Ca, S, Pb, Cu, Zn concentrations), uranium is diffusely distributed among aggregates of layer silicates (muscovite, illite and kaolinite). The chemical extractions and EXAFS results confirm that uranium is sorbed to these minerals, but is not incorporated into their crystal structure. Sorption is also in line with the high pH and low carbonate concentrations in pore water. In sample F3 (12 m depth, oxic, pH 4, U=430 mg/kg), the combination of μ-XRF and μ-XRD enabled us to identify several U(IV) and U(VI) containing minerals like coffinite, uraninite, uranyl hydroxide, and vanuralite. Only a minor part of U is sorbed to layer silicates as confirmed by chemical extractions and EXAFS spectroscopy.
At smaller depth (F1, 5 m), sulfuric acid from the ore extraction procedure was completely neutralized by the construction waste used as cover material, resulting in precipitation of jarosite and gypsum. Even 30 years after the ore extraction, uranium remains highly soluble. At greater depth (F3, 12 m), the low pH from ore extraction was conserved. The presence of U(IV) minerals suggest either precipitation of secondary (IV) minerals due to microbial redox activity, or incomplete dissolution of primary (IV) minerals due to ore processing inefficiency of these older sediments. The U(IV) minerals were recalcitrant during chemical extractions, suggesting low uranium solubility even at oxic redox conditions. The results demonstrate a very high variability of uranium speciation and hence potential mobility, which seems to depend on geochemical parameters and site history, but shows little influence of time.
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Lecture (Conference)
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7140 - Permalink


Dilepton Analysis in the HADES Spectrometer for C+C at 2 AGeV
Otwinowski, J.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Atkin, E.; Balanda, A.; Bellia, G.; Belver, D.; Bielcik, J.; Böhmer, M.; Bokemeyer, H.; Boyard, J.; Braun-Munzinger, P.; Chepurnov, V.; Chernenko, S.; Christ, T.; Coniglione, R.; Daues, H.; Diaz, J.; Djeridi, R.; Dohrmann, F.; Duran, I.; Eberl, T.; Emelianov, V.; Fabbietti, L.; Fateev, O.; Fernandez, C.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Fuentes, B.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hehner, J.; Heinz, T.; Hennino, T.; Hlavac, S.; Hoffmann, J.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kopf, U.; Kotte, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Kutukian-Nieto, T.; Lang, S.; Lehnert, J.; Maiolino, C.; Marin, J.; Markert, J.; Mishin, Y.; Montes, N.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Ott, W.; Pachmayer, Y.; Panebrasev, Y.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Pvrzygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Rodrigez Pieto, G.; Roy-Stephan, M.; Rustamov, A.; Sabin, F. J.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Sapienza, P.; Schmah, A.; Schroeder, C.; Schwab, E.; Senger, P.; Simon, R.; Smolyankin, V.; Smykov, L.; Spataro, S.; Stelzer, H.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Titov, A.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Vazquez, A.; Volkov, Y.; Wagner, V.; Walus, W.; Wang, Y.; Winkler, S.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zovinec, D.; Zumbruch, P.;
The light meson dilepton identification in the HADES detection system is based on an invariant mass reconstruction of their decay into e+e- pairs. Methods of the dilepton signal reconstruction in the HADES spectrometer and preliminary dilepton spectra for C+C reactions at 2 AGeV are presented in this paper. In the signal reconstruction particularly important is the reduction of the huge combinatorial background arising from wrong combinations of electrons and positrons into un-like sign pairs. A purity of the dilepton signal is determined by using GEANT simulation with the full HADES geometry and a realistic detector response.
  • Contribution to proceedings
    XLII International Winter Meeting on Nuclear Physics ON NUCLEAR PHYSICS, 25.01.-01.02.2004, Bormio, Italy
    Ricerca Scientifica ed Educazione Permanente Supplemento, 180-189

Publ.-Id: 7138 - Permalink


FELBE - a new facility providing coherent radiation for infrared spectroscopic investigations in actinide research
Foerstendorf, H.; Seidel, W.; Bernhard, G.;
FELBE is an acronym for the free-electron laser (FEL) at the Electron Linear accelerator with high Brilliance and Low Emittance (ELBE) located at the Forschungszentrum Rossendorf in Dresden, Germany. This FEL is a source of pulsed, coherent light which is continuously tunable over the infrared wavelength range from 5 to 25 µm. This will be enlarged to about 150 µm in late 2006.
At the FELBE facility a laboratory suitable for radiochemistry research was installed. This lab is classified as a controlled zone for investigations of certain radionuclides obeying to all aspects of radiation protection. The maximum activity of the investigated radioactive samples can add up to 105 times of the admissible limit. A glove box provides the possibility to perform experiments on sensitive samples which have to be kept in an inert gas atmosphere.
The time structure of the pulsed FEL beam is related to the frequency of the electron pulses of the accelerator which offers a 13 MHz repetition rate in macropulses of a few 100 μs at up to 25 Hz. A continuous 13 MHz regime is also available as well as single pulse selection down to a frequency of 1 Hz. The energy of the infrared pulses is up to 1 µJ/pulse depending on the wavelength.
The FELBE facility is a member in the Integrated Infrastructure Initiative (I3) on synchrotron and free-electron laser science (IA SFS) within the 6th framework programme of the EU. With this grant, external users of FELBE can be financially supported ("transnational access").
In our first experiment we use the FEL beam for investigation of mineral surfaces by Phototermal Beam Deflection (PTBD) spectroscopy. The PTBD technique is based on the theory of photothermal spectroscopy which describes the conversion of absorbed energy of a light beam incident on a sample into heat by nonradiative de-excitation processes. In typical PTBD experiments the magnitude signal is proportional to the slope of the induced displacement of the sample surface. There is a direct proportionality between the observed signal and the absorption coefficient of the material under investigation which provides a direct access to infrared absorption spectra with a very low detection limit is provided.
Furthermore, the PTBD technique is capable to gain spatial information (microspectrometry) of the sample’s surface since generation and detection of the thermal wave occurs generally in the submillimeter length scale. This may result in a microspectrometric technique for determining the distribution e.g. of sorbed metal species on mineral surfaces.
  • Contribution to proceedings
    Migration 2005, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 18.-23.09.2005, Avignon, France

Publ.-Id: 7137 - Permalink


Characterization of the Binding Mechanisms of Uranium to Different Isolated Bacteria in Function of pH
Merroun, M.; Nedelkova, M.; Raff, J.; Roßberg, A.; Hennig, C.; Scheinost, A.; Selenska-Pobell, S.;
The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive wastes. The mobility of this radionuclide is controlled by its interactions with ions, minerals and microorganisms present in nature. As a consequence of their small size and diverse metabolic activities, bacteria are able to interact intimately with uranium and other metal ions present in their environment. Assessment of the potential hazard posed by the presence of uranyl-bacterial complexes, as well as the development and application of accurate contaminant transport models, requires an understanding of the speciation of uranium associated with bacteria. This paper summarizes the effect of pH on the speciation of uranium bound by about fifteen bacterial strains isolated from uranium mining wastes. Microbiological methods in combination with Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Infrared (IR) spectroscopy, Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) were applied. EXAFS analysis showed that the cells of the most bacterial strains studied precipitate U(VI) as m-autunite-like phase at pH 4.5, probably due to the release of the inorganic phosphate from the cells as result of the acidic phosphatase activity. However, at pH 2 uranium formed complexes with organically bound phosphates of the cell surface. At pH 3, both organic and inorganic phosphate uranyl species occur together. No structural differences of the uranium complexes formed by three types of Acidithiobacillus ferrooxidans at above mentioned pH values were found, indicating the implication of organic phosphate moieties in the complexation. However, in the case of B. sphaericus JG-A12 the uranium bonding was consistent with the formation of complexes with organic bound phosphate and carboxylate groups of the cell surface. We applied Iterative Target Test Factor Analysis to determine the speciation at different pH values quantitatively from the EXAFS spectra. Transmission electron microscopy and energy dispersive X-ray analysis revealed species and even strain-specific extracellular and/or intracellular uranium accumulations to varying degrees. Different hypothesis explaining the different coordination chemistry of uranium to bacteria in function of the pH of the uranium solution in terms of solubility of m-autunite and/or microbial activity will be discussed.
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7136 - Permalink


Di-electron measurements in C+C reactions at 2GeV*A with HADES
Eberl, T.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bellia, G.; Bielcik, J.; Böhmer, M.; Boyard, J.; Braun-Munzinger, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Djeridi, R.; Dohrmann, F.; Duran, I.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kotte, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Lang, S.; Lehnert, J.; Maiolino, C.; Markert, J.; Metag, V.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Novotny, J.; Otwinowski, J.; Ott, W.; Pachmayer, Y.; Pant, L. M.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Pvrzygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Sapienza, P.; Schmah, A.; Simon, R.; Smolyankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zovinec, D.; Zumbruch, P.;
The High Acceptance DiElectron Spectrometer HADES has been recently commissioned at GSI, Darmstadt. It has been designed for systematic studies of hadron properties inside nuclear matter. We report first preliminary results on invariant masses of e+e--pairs which were measured in 12C + 12C collisions at Ekin=2 GeV*A. The analysis methods are briefly outlined and a comparison with detailed Monte-Carlo simulations is shown.

Publ.-Id: 7135 - Permalink


Dilepton analysis in the HADES spectrometer for 12C + 12C at 2 AGeV
Otwinowski, J.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bellia, G.; Belver, D.; Bielcik, J.; Böhmer, M.; Bokemeyer, H.; Boyard, J.; Braun-Munzinger, P.; Chepurnov, V.; Chernenko, S.; Christ, T.; Coniglione, R.; Daues, H.; Diaz, J.; Djeridi, R.; Dohrmann, F.; Duran, I.; Eberl, T.; Emelianov, V.; Fabbietti, L.; Fateev, O.; Fernandez, C.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Fuentes, B.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hehner, J.; Heinz, T.; Hennino, T.; Hlavac, S.; Hoffmann, J.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kopf, U.; Kotte, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Kutukian-Nieto, T.; Lang, S.; Lehnert, J.; Maiolino, C.; Marin, J.; Markert, J.; Mishin, Y.; Montes, N.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Ott, W.; Pachmayer, Y.; Panebrasev, Y.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Pvrzygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Rodrigez Pieto, G.; Roy-Stephan, M.; Rustamov, A.; Sabin, F. J.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Sapienza, P.; Schmah, A.; Schroeder, C.; Schwab, E.; Senger, P.; Simon, R.; Smolyankin, V.; Smykov, L.; Spataro, S.; Stelzer, H.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Titov, A.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Vazquez, A.; Volkov, Y.; Wagner, V.; Walus, W.; Wang, Y.; Winkler, S.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zovinec, D.; Zumbruch, P.;
The identification of light mesons in the HADES spectrometer is based on an invariant mass reconstruction of their decay into e+e- pairs. In the delepton (e+e) signal reconstruction particularly important is the reduction of a combinatorial background arising from wrong combinations of e+ and e- to unlike sign pairs. The purity of the dilepton signal is determined by using GEANT simulations. The analysis methods of the dilepton signal and combinatorial background reconstruction will be presented.
  • International Journal of Modern Physics A 20(2005), 602-605

Publ.-Id: 7134 - Permalink


Probing of in-medium hadron structure with HADES
Salabura, P.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bellia, G.; Bielcik, J.; Böhmer, M.; Boyard, J.; Braun-Munzinger, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Djeridi, R.; Dohrmann, F.; Duran, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kotte, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Lang, S.; Lehnert, J.; Maiolino, C.; Markert, J.; Metag, V.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Novotny, R.; Otwinowski, J.; Pachmayer, Y.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Pvrzygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Sanchez, M.; Sapienza, P.; Schmah, A.; Smolyankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zovinec, D.; Zumbruch, P.;
The High Acceptance DiElectron Spectrometer (HADES) has been recently commissioned at GSI Darmstadt. It has been designed to study hadron properties inside nuclear matter via measurements of dielectron decays in proton, pion and heavy ion induced reactions in 1−2 AGeV energy range. We report first preliminary results on invariant masses of e+e pairs measured in 12C + 12C collisions at E=2 AGeV and compare them to simulations based on UrQMD transport model. In summary we present and discuss planned experiments.

Publ.-Id: 7133 - Permalink


Interaction of Uranium(VI) and Humic Acid under Neutral pH Conditions
Sachs, S.; Geipel, G.; Brendler, V.; Bernhard, G.;
Due to their strong ability for complex and colloid formation, humic acids influence the speciation and consequently the migration behavior of actinide ions in the environment. In order to perform a trustworthy risk assessment for the conception of future nuclear waste repositories as well as for the remediation of former uranium mining and milling areas, reliable thermodynamic data on the interaction of uranium with humic acids under geogenic conditions are necessary.
The U(VI) complexation by humic acids was already the subject of a number of previous investigations. However, these studies were predominately performed in the acidic pH range, were the hydrolysis of the uranyl ion can be neglected. Only few studies exist on the interaction of U(VI) with humic acids under neutral pH conditions where ternary U(VI) humate complexes are formed.
In the present study we investigate the complexation of U(VI) by purified Aldrich humic acid at pH 7 under exclusion of CO2 ([HA]: 2 mg/L; [U]: 1·10-6-1·10-5 M, I: 0.1 M NaClO4). Under the studied experimental conditions and in absence of humic acid, U(VI) occurs in form of the following species: UO2OH+, UO2(OH)2(aq), (UO2)3(OH)5+, (UO2)4(OH)7+. The speciation is dominated by 62-73 % of (UO2)3(OH)5+. Based on this speciation, the formation of ternary uranyl hydroxy humate complexes is assumed. For determination of the U(VI) and humic acid speciation in solution we apply the conventional time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses, respectively. For identification and quantification of the U(VI) species in solution, fluorescence spectra were measured for the relevant U(VI) hydrolysis species. The experimental data are evaluated applying the metal ion charge neutralization model [1], which describes the metal ion complexation by humic acids.

[1] Kim, J.I., Czerwinski, K.R.: Complexation of Metal Ions with Humic Acids: Metal Ion Charge Neutralization Model. Radiochim. Acta 73, 5 (1996).
Keywords: Humic acids, complexation, uranium, migration
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7132 - Permalink


Investigation of the Influcence of Humic Acid on the Interaction of U(VI) with Kaolinite: Sorption and Spectroscopic Studies
Krepelova, A.; Sachs, S.; Reich, T.; Roßberg, A.; Bernhard, G.;
Humic acids (HA) comprise an important part of natural organic materials. By the formation of soluble complexes with radionuclides, HA can affect the transport of these contaminants. Therefore, the understanding of the impact of HA on the actinide migration in geologic environments is essential for a reliable safety assessment of nuclear waste disposal sites. In the present study we investigated the influence of HA on the U(VI) sorption onto kaolinite. Kaolinite represents a well-defined model substance for clay-rich host formations.
Batch experiments were combined with EXAFS spectroscopy to obtain molecular-level information on the interaction of U(VI) with HA (14C-labeled) and kaolinite (KGa-1b) in natural systems.
From our batch experiments it is known that the sorption of U(VI) on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 and HA presence. U(VI) sorption increases with pH up to pH 7.5, then it decreases. In the absence of CO2, no decrease is observed. In the presence of CO2 HA effects U(VI) adsorption onto kaolinite over the entire pH range. At pH < 5 the presence of HA enhances the U(VI) uptake relative to the HA-free system because the adsorbed HA forms additional binding sites for U(VI). In the pH range between pH 5 and pH 8.5 the U(VI) sorption decreases in the presence of HA due to desorption of HA from the kaolinite surface resulting in the formation of dissolved U(VI)-HA complexes. At pH > 8.5 uranium sorption increases again relative to the HA-free system.
Previously, EXAFS spectroscopy was applied to study the structure of the U(VI) adsorbed on kaolinite [1], but no EXAFS was measured in the system U(VI)-HA-kaolinite. Therefore, we performed EXAFS measurements with U(VI)-HA-kaolinite sorbats in order to characterize the surface complexes of U(VI) in the presence of HA. Results of the spectroscopic measurements are interpreted and compared with the EXAFS results in the binary system without HA to obtain the information on the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.
Keywords: Humic Acid, Uranium, Kaolinite, Sorption, EXAFS
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7131 - Permalink


Application of a spectro-electrochemical cell for speciation of U(IV) by EXAFS
Hennig, C.;
An electrochemical cell was developed for in situ investigations of radioactive materials using X-ray absorption spectroscopy. Due to the specific safety requirements for handling of radioactive materials the electrochemical cell had to be gas tight. The spectro-electrochemical cell comprises two safety compartments and a special electrode arrangement in order to avoid any gas release.
Keywords: EXAFS, XANES, spectro-elechtrochemical cell, uranium, U(IV)
  • Invited lecture (Conferences)
    Vortrag (Einladung), 21.01.2005, Stockholm, Sweden

Publ.-Id: 7130 - Permalink


Interaction of Desulfovibrio äspöensis with plutonium
Moll, H.; Merroun, M.; Hennig, C.; Rossberg, A.; Den Auwer, C.; Selenska-Pobell, S.; Bernhard, G.;
Microbes are widely distributed in nature and they can strongly influence the migration of actinides in the environment. Microorganisms in concentrations of 1x103 to 5x106 cells ml-1 were estimated by Pedersen et al. in the aquifer system of the Äspö Hard Rock Laboratory (Äspö HRL) in Sweden. The number of sulfate-reducing bacteria (SRB) was between 101 to 2x104 cells ml-1. We investigated the interaction of the SRB Desulfovibrio äspöensis, DSM 10631T, with plutonium. The 242Pu was provided as a mixture of ca. 46% Pu(VI) and ca. 34% Pu(IV)-polymer. Interactions between bacteria and plutonium in mixed oxidation states were not yet intensively investigated.
In this study, accumulation experiments were performed in order to obtain information about the amount of the Pu bound by bacteria in dependence on the contact time and the [Pu]initial at pH 5. We used liquid-liquid-extractions and absorption spectroscopy to determine the Pu speciation. In agreement with the results obtained with U(VI) [2] and Np(V), we found a strong dependence of the amount of accumulated Pu with [Pu]initial. Based on our results and taking into consideration the findings of Panak et al. [3], we developed a model describing the interaction of Pu(VI) and Pu(IV)-polymers with D. äspöensis. In a first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. The Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 24 h of contact time. Most of the formed Pu(V) dissolves due to the weak complexing properties. The dissolved Pu(V) disproportionates to Pu(IV) and Pu(VI) which are then interacting with functional groups of the cell surface structure. Indications were found also for a penetration of Pu species inside the bacterial cells.

[1] Pedersen, K.: Microbial processes in radioactive waste disposal. SKB Technical Report TR-00-04 (2000).
[2] Moll, H.; Merroun, M.; Stumpf, Th.; Geipel, G.; Selenska-Pobell, S.; Hennig, C.; Roßberg, A.; Bernhard, G.: Interaction of Desulfovibrio äspöensis with Actinides, presented at the MIGRATION’03, Gyeongju, Korea (2003).
[3] Panak, P. J.; Nitsche, H.: Radiochim. Acta 89, 499 (2001).

This work was funded by the BMWi under contract number: 02E9491.
Keywords: Plutonium, Bacteria, Desulfovibrio äspöensis
  • Lecture (Conference)
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7129 - Permalink


Redox Stability of Neptunium(V) in the Presence of Humic Substances of Varying Functionality
Schmeide, K.; Geipel, G.; Bernhard, G.;
Naturally occurring aquatic humic substances (humic and fulvic acids) are known to effect the speciation and thus, the migration behavior of actinide contaminants in environmental systems due to their complexing and redox properties and their ability to form colloids. Therefore, to understand and predict the mobility of actinides in natural aquifer systems, amongst others, information on their redox stability in the presence of humic substances is necessary.
In the present work, the time dependence of the reduction of Np(V) to Np(IV) by humic substances of varying functionality has been studied under anaerobic conditions between pH 3.5 and pH 9. Synthetic humic acids with pronounced redox functionality (type Cat-Gly and Hyd-Glu) [1] were studied in comparison to natural humic substances (Aldrich humic acid, Kranichsee fulvic acid). For Np speciation in solution liquid-liquid extraction, laser-induced photoacoustic spectroscopy (LIPAS), NIR absorption spectroscopy, and ultrafiltration were applied. In comparison to the natural humic substances, the synthetic humic acids lead to a much stronger reduction of Np(V) to Np(IV) [2]. The Np(IV) formed in the course of the experiments is stabilized as Np(IV) humate. The tetravalent oxidation state remained constant for several months.
The redox capacities of the synthetic humic acids, which are significantly higher than those of the natural humic substances, can be attributed to their higher phenolic/acidic OH group contents compared to natural humic substances. The dominating role of phenolic/acidic OH groups for the reduction of Np(V) by humic substances could be verified applying a synthetic humic acid with blocked phenolic/acidic OH groups (type Hyd-Glu-PB). Furthermore, the influence of NO3- on the Np(V) reduction by humic substances was studied.
The results have shown that by application of the synthetic humic acids with distinct redox functionalities actinides can be stabilized in lower oxidation states, e.g. in complexation and sorption studies.

[1] Sachs, S., Schmeide, K., Brendler, V., Krepelová, A., Mibus, J., Geipel, G., Heise, K.H., Bernhard, G.: Investigation of the Complexation and the Migration of Actinides and Non-radioactive Substances with Humic Acids under Geogenic Conditions. Complexation of Humic Acids with Actinides in the Oxidation State IV Th, U, Np. FZR-399, Wissenschaftlich-Technische Berichte, Forschungszentrum Rossendorf, Dresden 2004.
[2] Schmeide, K., Geipel, G., Bernhard, G.: Study of the Neptunium(V) Reduction by Various Natural and Synthetic Humic Substances. In: FZKA 7070, Wissenschaftliche Berichte (G. Buckau, ed.). Forschungszentrum Karlsruhe, Karlsruhe 2005, 19-31.
Keywords: Neptunium, Reduction, Tetravalent, Humic acid, Redox processes
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7128 - Permalink


Diffusion of humic colloids in compacted clay and the influence on uranium migration
Mibus, J.; Sachs, S.;
The diffusion of humic acid (HA) in Georgia kaolinite KGa-1B was studied. The compacted clay plug was conditioned with a 0.01 M NaClO4 + 1 mM NaN3 solution at pH 5.2. The effective porosity ε and the effective diffusion coefficient De of water were determined using tritiated water (HTO). A synthetic 14C-labeled HA type M42 with a concentration of 11.0 mg/L and a specific activity of (17.0 ± 0.5) MBq/g was used as tracer. We applied a steady-state through-diffusion technique with constant gradient. The particle size distribution of HA was determined by ultrafiltration.

The migration of HA in compacted clay is governed by diffusion. However, compared to an ionic tracer some characteristics are observed. The De values found for HA (2·10^13 to 2·10^12 m^2/s) are about two to three orders of magnitude lower than that of HTO. Likewise the rock capacity factor α(HA) amounts to only 10 % to 50 % of ε. The spatial extension of the humic colloids constricts their mobility in the narrow pore space thus increasing the tortuosity of the diffusion path and decreasing the pore volume accessible for HA. This phenomenon is referred to as size exclusion effect. In [1] a significant adsorption of HA on KGa-1B was found (Kd = 680 ml/g at pH 5.2) which would result in a value for α above unity. Obviously, the size exclusion dominates the HA migration.
The particle size distributions of the high and the low concentration reservoir differ significantly. The mean particle size shifts from about 50 kD in the high to less than 1 kD in the low concentration reservoir. Only small particles are able to pass the pore system. This is in agreement with the HA distribution in the clay plug where most of the tracer was found at the high concentration boundary.
Keywords: Humic Acid, Uranium, Kaolinite, Diffusion
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7127 - Permalink


Functional Imaging of the Brain in Patients with Liver Cirrhosis.
Weissenborn, K.; Bokemeyer, M.; Ahl, B.-R.; Fischer-Wasels, D.; Giewekemeyer, K.; van den Hoff, J.; Köstler, H.; Berding, G.;
Brain imaging techniques have provided substantial insight into the pathophysiology of hepatic encephalopathy (HE). Magnetic resonance imaging gave hint to the fact that there is an increased deposition of manganese especially in the basal ganglia. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) showed that the preference of the basal ganglia might be due to differences in regional cerebral blood flow and an additional redistribution of blood flow from the cortex to subcortical regions in cirrhotics. PET studies using ammonia as tracer showed that the cerebral metabolism of ammonia and the permeability of the blood brain barrier for ammonia is increased in cirrhotic patients compared to healthy controls. The regional ammonia supply is in accordance with the regional blood flow. In accordance with these findings fluorodesoxyglucose-PET-studies of the brain in cirrhotics showed characteristic alterations of glucose utilisation in the patients with a relative decrease of the glucose utilisation of the cingulate gyrus, the frontomedial, frontolateral, and parieto-occipital cortex, while the glucose utilisation of the basal ganglia, the hippocampus, and the cerebellum was relatively increased. These findings fit well with the clinical characteristics of early stages of HE such as deficits in attention, visuo-spatial orientation, visuo-constructive abilities, motor speed, and accuracy.
  • Metabolic Brain Disease 19(2004), 269-280

Publ.-Id: 7124 - Permalink


Effect of the hypoxic cell sensitizer isometronidazole on local control of two human Squamous Cell Carcinomas after fractionated irradiation.
Schreiber, A.; Krause, M.; Zips, D.; Dörfler, A.; Richter, K.; Vettermann, S.; Petersen, C.; Beuthien-Baumann, B.; Thümmler, D.; Baumann, M.;
BACKGROUND AND PURPOSE: Hypoxia of clonogenic tumor cells is a major reason for radioresistance and hence local failure in radiotherapy. The objective of the present study was to test the efficacy of the hypoxic cell sensitizer isometronidazole (ISO) during fractionated irradiation in two different human squamous cell carcinomas. MATERIAL AND METHODS: Local control was evaluated for FaDu (radiobiological hypoxic fraction [rHF] 7%) and GL tumors (rHF 0.1%) after single-dose (SD) irradiation under ambient conditions and after 30 fractions within 6 weeks (30 f/6 w). ISO was applied 60 min before SD irradiation at a concentration of 100 mg/kg body weight (b.w.) or 750 mg/kg b.w. in both tumors. During fractionated irradiation, ISO was applied daily 60 min before each fraction (100 mg/kg b.w., in FaDu also 750 mg/kg b.w.). RESULTS: 100 mg/kg b. w. ISO did not improve local control after SD irradiation or 30 f/6 w in both tumor models. Application of 750 mg/kg b. w. ISO significantly decreased the SD-TCD(50) in FaDu tumors (dose-modifying factor [DMF] = 1.2; p = 0.01) but not in the better oxygenated GL tumor. ISO at 750 mg/kg b.w. also significantly improved local control of FaDu tumors after 30 fractions in 6 weeks (DMF = 1.2; p = 0.01), indicating that hypoxic clonogenic cells in FaDu tumors are not only present before start of irradiation but also limit the efficacy of treatment during a fractionated course of radiotherapy. CONCLUSION: ISO at a concentration of 750 mg/kg b.w. shows an efficacy as a hypoxic cell sensitizer in severely hypoxic FaDu tumors but not in less hypoxic GL tumors. This supports the principle of hypoxic cell sensitization and improvement of local control of hypoxic tumors by nitroimidazole derivatives. However, doses of 750 mg/kg b. w. before each fraction may be difficult to achieve in the clinical situation. This, in light of the fact that other well-tolerable hypoxic cell sensitizers such as nimorazole with clinically proven efficacy at daily oral doses of < 3 g are available, limits the potential usefulness of ISO for radiation oncology.
  • Strahlentherapie und Onkologie 180(2004), 1196-1201

Publ.-Id: 7123 - Permalink


Peritoneal strumosis.
Brogsitter, C.; Wonsak, A.; Würl, K.; Kotzerke, J.;
  • European Journal of Nuclear Medicine and Molecular Imaging 31(2004), 1057-1058

Publ.-Id: 7122 - Permalink


Synthesis of 18F-labelled COX-2 inhibitors via Stille Reaction with 4-[18F]fluoro-iodobenzene.
Wüst, F.; Höhne, A.; Metz, P.;
The Stille reaction with 4-[(18)F]fluoroiodobenzene as a novel approach for the synthesis of radiotracers for monitoring COX-2 expression by means of PET has been developed. Optimized reaction conditions were elaborated by screening of various catalyst systems and solvents. By using optimized reaction conditions (18)F-labelled COX-2 inhibitors [(18)F]- and [(18)F]- could be obtained in radiochemical yields of up to 94% and 68%, respectively, based upon 4-[(18)F]fluoroiodobenzene.
  • Organic & Biomolecular Chemistry 3(2005), 503-507

Publ.-Id: 7121 - Permalink


Fluorine-18 radiolabeling of low-density lipoproteins: a potential approach for characterization and differentiation of metabolism of native and oxidized low-density lipoproteins in vivo.
Pietzsch, J.; Bergmann, R.; Rode, K.; Hultsch, C.; Pawelke, B.; Wüst, F.; van den Hoff, J.;
Oxidative modification of low-density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Assessing the metabolic fate of oxidized LDL (oxLDL) in vivo with radiotracer techniques is hindered by the lack of suitable sensitive and specific radiolabeling methods. We evaluated an improved methodology based on the radiolabeling of native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 ((18)F) by conjugation with N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB). We investigated whether radiolabeling of LDL induces adverse structural modifications. Results suggest that radiolabeling of both nLDL and oxLDL using [(18)F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively. Thus, radiolabeling of LDL using [(18)F]SFB could prove to be a promising approach for studying the kinetics of oxLDL in vivo.
  • Nuclear Medicine and Biology 31(2004), 1043-1050

Publ.-Id: 7120 - Permalink


Etch rate retardation of Ga+ ion beam irradiated silicon
Schmidt, B.; Oswald, S.; Bischoff, L.;
Surface chemistry during wet chemical etching in alkaline KOH solution and dry etching in SF6/O2 plasma of high dose Ga+ implanted Si has been investigated by means of secondary ion mass spectroscopy (SIMS) and x-ray induced photoelectron spectroscopy (XPS). During wet chemical etching in a KOH/H2O solution a thin layer of GaOx of < 1 nm thickness is formed, which has been investigated more in detail by angle-resolved XPS.. In the case of dry reactive ion etching the surface chemistry is quite different. In this case a more enhanced oxidation of Ga takes place due to the high reactivity of atomic oxygen from the SF6/O2 plasma. SIMS results show that during RIE a Ga rich surface layer forms and therefore an enhanced Ga oxidation takes place leading to a thicker GaOx layer compared to wet chemical treatment. XPS depth profiling points at a stoichiometry of nearly completely oxidized Ga (Ga2O3) layer free from Si with a thickness of about 5 ... 10 nm. The etch rate lowering in Ga+ as- implanted silicon is ascribed to the formation of gallium oxide at the Si surface during the etch processes.
Keywords: ion implantation, wet and dry etching, SIMS and XPS
  • Journal of the Electrochemical Society 152(2005)11, G875-G879

Publ.-Id: 7119 - Permalink


Bonding characteristics of DC magnetron sputtered B-C-N thin films investigated by FTIR and XPS
Linss, V.; Rodil, S.; Reinke, P.; Garnier, G.; Oelhafen, P.; Kreissig, U.; Richter, F.;
B-C-N thin films of a wide composition range were deposited by reactive d.c. magnetron sputtering of targets with different B/C ratio in an Ar/N2 atmosphere. The bonding characteristics of these amorphous films were investigated by Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy. The results of both characterisation methods indicate that real ternary compounds in which all three elements are bound to each other are only formed when at least one element has a low concentration in the film (and therefore could be considered as an impurity). Otherwise the deposited material tends to a phase separation into binary compounds and single phases.
Keywords: BCN, Bonding characteristics, FTIR, XPS
  • Thin Solid Films 467(2004), 76-87

Publ.-Id: 7118 - Permalink


He-RBS, He-ERDA and heavy ion-ERDA analysis of Si/Ta 70Å/CoFe 35Å/ HfAlO /CoFe 35Å/Ta 30Å systems
Barradas, N. P.; Matias, V.; Sequeira, A. D.; Soares, J. C.; Kreissig, U.; Wang, J. U.; Freitas, P. P.;
Low resistance spin-dependent tunnel junctions are investigated for read-head applications due to their large tunneling magnetoresistance effect and low junction resistance-area product. Typical full junction structures can be Ta 70Å/NiFe 70Å/MnIr 80Å/CoFe 35Å/Hf(x)Al(y)O(z) t/CoFe 35Å/NiFe 40Å/Ta 30Å, with t around 10 Å, annealed to temperatures up to 250ºC. We analysed simpler structures with RBS experiments at a grazing angle of incidence in order to study the junction only. Heavy ion- and He-ERDA experiments were also done. The composition of the HfAlO barrier is determined, showing that a slightly substoichiometric oxide is formed. On annealing at 240ºC, the interfaces of the barrier become sharper. TEM results confirm that the barrier is continuous after annealing. This is related to an increase in the tunnel magnetoresistance signal from 4% to 13.5% after annealing.
Keywords: RBS, ERDA, tunnel junctions, magnetoresistive materials
  • Nuclear Instruments and Methods in Physics Research B 219-220(2004), 742-746

Publ.-Id: 7117 - Permalink


CFD calculation of a mixing experiment in the VVER-1000 reactor model
Höhne, T.; Bezrukov, Y.;
A study of the mixing of a deborated slug during start-up of the first coolant pump in VVER-1000 type reactors was performed with the commercial CFD package CFX-5.7 using experimental results of the 1:5 scaled test facility. The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor CFX-5 and contains 2.5 Mio. tetrahedral elements. The CAD geometry and the grid model include the inlet nozzles, the downcomer incl. spacer elements and the lower plenum with the elliptical sieve plate and internals. Parts of the complicated lower plenum structures were modeled with the porous media approach in CFX-5, which uses directed resistance coefficients.

The output of the Best Practice Guidelines for optimizing the numerical studies of boron dilution transients in different reactor types was used in the numerical simulation. The discretisation scheme in time was set to second order Euler and in space to High Resolution. The SST turbulence model was taken.

The modeled deborated slug first arrives at the core inlet of the reactor pressure vessel in the neighboring areas at the outer case of the starting loop. Later the slug is almost homogenously distributed over the core inlet plane. The minimum averaged deboration value in the experiment and the CFD calculation is in good agreement when using a constant wall temperature (72%). The existing time offset in the numerical calculation could not been clarified.
Keywords: Boron Dilution, Coolant Mixing, VVER-1000, CFD
  • Contribution to proceedings
    The 4-th International Conference Safety Assurance of OF Nuclear Power Plants with WWER, 23.-26.05.2005, Podolsk, Russian Federation
  • Lecture (Conference)
    The 4-th International Conference Safety Assurance of OF Nuclear Power Plants with WWER, 23.05.2005, Podolsk, Russian Federation

Publ.-Id: 7116 - Permalink


Ferromagnetic coupling field reduction in CoFeB tunnel junctions deposited by Ion Beam
Cardoso, S.; Ferreira, R.; Freitas, P. P.; Mackenzie, M.; Chapman, J.; Ventura, J. O.; Sousa, J. B.; Kreissig, U.;
In this work, junctions with reduced Hf coupling were fabricated by ion beam deposition and oxidation, using CoFeB electrodes. The CoFeB layer has a strong (110) texture that can be the origin of lower Hf and coercivity when compared with CoFe. Junctions processed down to 2x4 um2 with 40Å thick CoFeB bottom electrodes have 42% of tunneling magnetoresistance (TMR), (R x A ~400 Ohm um2), Hc of ~10 Oe and Hf of ~2 Oe. CoFe-based junctions (R x A ~500W Ohm um2) have lower TMR (~35%) and larger Hf (~5-6 Oe) and Hc (~12-14 Oe). Local chemical composition analysis of the cross section indicated Fe-O segregation without Co grown on top of the barrier for CoFe-based junctions and not for CoFeB ones.
Keywords: Ion beam deposition, tunnel junctions, ferromagnetic coupling, CoFeB electrodes
  • IEEE Transactions on Magnetics 40(2004)4, 2272-2274

Publ.-Id: 7115 - Permalink


Domain structure of magnetically micro-patterned PtMn/NiFe exchange bias bilayers
Potzger, K.; Bischoff, L.; Liedke, M. O.; Hillebrands, B.; Rickart, M.; Freitas, P.; McCord, J.; Fassbender, J.ORC
A PtMn/NiFe exchange bias system with an exchange bias field of 180 Oe was magnetically patterned by means of a low fluence focused ion beam. A 1 µm wide stripe pattern with the long axis (1000 µm) oriented parallel to the exchange bias field direction has been irradiated by 2x1014 Ga+/cm2. In the irradiated area the coercivity is reduced and the exchange bias field vanishes, while in the nominally non-irradi-ated region between the irradiated stripes the exchange bias field is reduced to approximately 35 Oe. This reduction is attributed to the magnetic coupling of the irradiated stripes to their intervening non-irradiated regions. Magnetic domain imaging by means of Kerr microscopy and magnetic force microscopy support this interpretation.
Keywords: magnetism, exchange bias, focused ion beam, FIB, ion irradiation, local modification, magnetic patterning, magnetic force microscopy, MFM, Kerr microscopy

Publ.-Id: 7113 - Permalink


Results from experiments on hybrid plasma immersion ion implantation/nitriding processing of materials
Ueda, M.; Gomes, G.; Kostov, K.; Reuther, H.; Lepienski, C.; Soares, P.; Takai, O.; Silva, M.;
To improve the performance of critical part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments mixing PIII and ion nitriding processes. A combination of high pressure (4 x 10(1)Pa), moderate temperature (up to 450degreesC) glow discharge nitriding with low pressure (8 x 10(-2)Pa) and low DC bias voltage ion nitriding (or DC PIII) was implemented. Depending on the particular conditions of the treatment and the depth probed, mixed phases of gamma(N) and epsilon were measured in the treated SS304 steel sample. This near surface modification resulted in an improved hardness (up to a factor of 2.7 x) of the sample which could also enhance its wear properties. Surface modification of T16Al4V alloy and SS304 steel by a combination of PIII and subsequent ion nitriding was investigated as well. Nitrogen ions were implanted into the specimens at 15 keV and then ion nitrided at ! low pressure (7 x 10(-2)Pa) with a bias of -800 V. Compared to the untreated samples, the hardness of Ti6Al4V alloy and the steels could be improved significantly. AES results indicated high retained doses in both samples, confirming the high efficiency of this hybrid process.
  • Open Access LogoBrazilian Journal of Physics 34(2004)4b, 1632-1637

Publ.-Id: 7111 - Permalink


Investigation of Environmentally Relevant Colloids by Laser-Induced Breakdown Detection (LIBD)
Opel, K.; Hübener, S.; Weiß, S.; Zänker, H.; Bernhard, G.;
An apparatus for laser-induced breakdown detection (LIBD) was established, which is aimed at in-situ detection of aquatic colloids of a particle size down to < 50 nm and a particle concentration down to the ppt range. LIBD is based on the generation of dielectric breakdown events on individual colloid particles by pulses of a focused laser (cf. [1]). A diode pumped Nd:YAG laser is used as light source and is operated at maximum power for stability reasons. The pulse energy is controlled by a combination of two Fresnel rhombs and a calcite polarizer. The beam is focused into a quartz cell containing the particle suspension to be analyzed. The breakdown events are simultaneously observed by a CCD camera and by piezoelectric detectors.

Polystyrene latex standards of different particle size were diluted with de-ionized water (Membrapure) to mass concentrations of the ppt and ppb range. These solutions were used for the calibration of the LIBD system.

Two particle systems of environmental relevance were studied by LIBD.
First, a nearly particle-free spring water of a small stream was investigated. Photon correlation spectroscopy, an alternative technique of particle detection, was too insensitive to find particles in this water. Both the raw sample of this stream water and centrifugates/filtrates of the water could be successfully investigated and consistent results were provided by LIBD. Second, uranium(IV) colloids were generated in a glove box (N2 atmosphere) by cathodic reduction of uranium(VI) followed by the successive increase of the pH by coulometric titration. The formation of these colloids was traced by LIBD.

[1] Walther, C., Bitea, C., Hauser, W., Kim, J.I. and Scherbaum, F.J.
Laser Induced Breakdown Detection for the Assessment of Colloid Mediated Radionuclide Migration. Nucl. Instr. and Meth. B 195 (2002) 374-388
Keywords: colloids, laser-induced breakdown detection, libd, particle sizing, uranium, colloid generation
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7110 - Permalink


Feasibility study of wrist watched based radiation survey meter
Wolf, A.;
Feasibility study of wrist watched based radiation survey meter
  • Invited lecture (Conferences)
    Research Coordination Meeting, 04.-08.10.2004, Sochi, Russische Förderation

Publ.-Id: 7108 - Permalink


Mechanische und optische Anforderungen an die Cavity des FEL
Wolf, A.;
Mechanische und optische Anforderungen an die Cavity des FEL
  • Lecture (others)
    Studiengruppe für Elektronische Instrumentierung, 27.09.2004, Rossendorf, Deutschland

Publ.-Id: 7107 - Permalink


A startup procedure for natural circulation boiling Water Reactors
Manera, A.;
A start-up procedure for natural-circulation Boiling Water Reactors is illustrated. The procedure, developed in order to avoid flashing-induced instabilities at low pressures and low powers, does not require any additional system. The reactor vessel is pressurized while steam is produced outside the core and riser sections. In this way, the firsts stage of the pressurization takes place with the reactor operating in single-phase natural-circulation conditions, thus without occurrence of flashing-induced flow oscillations. At the same time, a smooth steam production and pressurization of the system is achieved. A simple analytical model is applied to the ESBWR of General Electric to have a first impression on the order of magnitude of the parameters involved and to verify whether the start-up of the reactor can be achieved in reasonable times. The feasibility of the procedure is then studied in details by means of the ATHLET code (Lerchi and Austregesilo, 2003), developed by GRS (Germany). This code has been successfully qualified against low-pressure flashing-induced instabilities within the framework of the EU project NACUSP
Keywords: Startup procedure, BWR, natural circulation, flashing
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France

Publ.-Id: 7106 - Permalink


Formation of Colloids by the Weathering of Rock Material
Zänker, H.; Arnold, T.; Hüttig, G.; Nitsche, H.; Bernhard, G.;
Colloids can either stimulate or retard the transport of actinides. Environmental colloids are formed by a variety of mechanisms. The most important one is the precipitation of secondary phases. There have already been several publications on colloid generation within water bod-ies due to chemical reactions after the mixing of waters of different chemical composition or after access of air. Much less information exists about a different mechanism of colloid for-mation in the nature – the direct production of secondary mineral colloids at the water-rock interface by the weathering of rock material.

The formation of colloids during the weathering of ground phyllite from an abandoned ura-nium mine and the sorption of uranium(VI) onto these colloids were studied. Centrifugation and ultrafiltration were applied. A method to differentiate between the primary mineral col-loids of the phyllite and the precipitated secondary mineral colloids was developed.

Significant amounts of colloids of the 101 to 102 nm size class were found in the suspension of ground phyllite after weathering times of 87 h to 792 h. Considerable fractions (up to 10 mg/L) of these 101 to 102 nm colloids consisted of secondary minerals. The following compo-sition of the freshly precipitated colloids is to be expected: Ferihydrite, aluminosilicates, amorphous Al(OH)3, gibbsite, possibly iron silicates, possibly iron-alumino silicates. It should be emphasized that a significant fraction of the secondary mineral colloids was composed of iron(III) compounds which is of relevance for the sorption behaviour of these colloids. A more detailed mineralogical characterization of the colloids is underway. The 101 to 102 nm secondary mineral colloids were relatively stable and remained in colloidal suspension over longer periods of time.

The direct formation of secondary mineral colloids at the mineral-water interface by the weathering of rock material is an alternative to the well-known mechanism of colloid forma-tion by the mixture of different water bodies or by aeration of a water body. This direct mechanism of colloid production occurs during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine dumps. Colloids produced by this mechanism can influence the transport of actinides since they have a large specific surface area and a high sorption affinity for heavy metals. This was demonstrated for uranium(VI).
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7105 - Permalink


Spectroscopic Studies on Colloid-borne Uranium(VI)
Ulrich, K.-U.; Roßberg, A.; Weiß, S.; Foerstendorf, H.; Brendler, V.; Scheinost, A.; Zänker, H.;
Information on molecular speciation provides a basis for the reliable assessment of actinide migration in the environment. We use several methods for the separation of colloids from liquids (e.g. ultracentrifugation, ultrafiltration) in combination with spectroscopic techniques (EXAFS, ATR-FTIR, Mössbauer) and modeling of surface complexation reactions. This enables us to investigate the speciation of colloid-borne uranium in waters occurring in or escaping from abandoned uranium mines during the remediation process. Mine flooding was simulated on a 100 L scale by mixing acid mine water of elevated U concentration with oxic, near-neutral groundwater until pH~5.5 was reached. The freshly formed colloids adsorbed 95% of the total uranium and consisted mainly of 2-line ferrihydrite (Fh) besides traces of aluminum, sulfur, silica, 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 close vicinity to 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 proposed in the literature, bidentately complexed carbonate ligands do not explain our experimental EXAFS data. But ATR-IR spectra showed that U-carbonato complexes must be involved in the sorption of uranyl on Fh. These results are not contradictory if the carbonate ligands were bound monodentately. Nevertheless, carbon cannot act as backscattering atom in carbonate-free samples prepared in N2 atmosphere. We propose a new structural model including exclusively Fe, H, and O atoms in which the bidentately bound 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.

In summary, uranium may form different sorption complexes with colloidal ferric hydroxides: a binary bidentate uranyl complex with modified orientation, and ternary U-carbonato complexes with monodentate linkage of the carbonate ligand. The affinity of carbonate and uranyl to form such complexed surface species will increase when sorption sites with high affinity, as provided by colloidal Fh, are present.
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Publ.-Id: 7104 - Permalink


Studies and Codes on Molten Salt Reactors
Koch, R.; Křepel, J.; Grundmann, U.; Rohde, U.;
The renewed interest on MSR systems has stimulated the development of computational tools assigned for analysis and simulation of MSR systems. The code system is a tool developed at Forschungszentrum Rossendorf for the analysis of burn-up behavior and transient simulation of Molten Salt Reactors. The computing method is based on the coupling between the well-known Monte Carlo transport code MCNP-4C2 and the burn-up code ORIGEN 2.1. In the second part the contribution shows applications of the system DYN3D-MSR dynamics code for Molten Salt Reactors, which is based on FZR two groups diffusion code DYN3D designed for dynamics calculation of light water reactors.
Keywords: Molten-Salt Reactor, MSR, Monte-Carlo Code, MCNP, Burnup, ORIGEN, Reactor Dynamics, DYN3D
  • Lecture (Conference)
    Technical Meeting of the Co-ordinated Research Project on " ... Incineration of Radioactive Waste", 22.-26.11.2004, Hefei, China

Publ.-Id: 7103 - Permalink


Applications of Code HELIOS at Research Center Rossendorf and some Remarks to Formal Innovations of the Code
Koch, R.;
This contribution shows some applications of code HELIOS at Research Center Rossendorf. These are: A cell assembly models of the European Pressurized Water Reactor (EPR), including burnup calculations, with HELIOS Version 1.6, and applications of a typical pressurized water reactors of the type KONVOI with HELIOS Version 1.6 & 1.7 and comparisons with the lattice transport and burnup code CASMO 4. The second part gives remarks what can be done better in future codes.
Keywords: Neutronen-Transportcode, Code HELIOS, Code ZENITH, Fuel Assembly, Neutron Flux, Burnup, Actinide Molten Salt Transmuter, AMSTER
  • Lecture (Conference)
    Core/Fuel Management Software, European Users Group Meeting 2004, 19.-21.04.2004, Turku, Finland

Publ.-Id: 7102 - Permalink


A review of MHD activities at Forschungszentrum Rossendorf
Gerbeth, G.;
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.
  • Invited lecture (Conferences)
    JSPS Meeting, 29.01.2005, Nagoya, Japan

Publ.-Id: 7101 - Permalink


Process control by tailored magnetic fields - examples from crystal growth, metal casting and solidification
Gerbeth, G.;
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.
  • Invited lecture (Conferences)
    JSPS Meeting, 28.01.2005, Nagoya, Japan

Publ.-Id: 7100 - Permalink


Moorwasser als natürliches Analogon für künftige Redoxvorgänge in gefluteten Uranerzgruben
Abraham, A.; Baraniak, L.; Bernhard, G.;
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.
  • Wissenschaftliche Zeitschrift der Technischen Universität Dresden (2013)

Publ.-Id: 7098 - Permalink


Chemical Forms of Antimony in Shooting Range Soils: An X-Ray Absorption Spectroscopy Study
Scheinost, A.; Roßberg, A.; Vantelon, D.; Kretzschmar, R.; Johnson, C. A.;
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.
  • Invited lecture (Conferences)
    1st International Workshop on Antimony in the Environment, 16.-19.05.2005, Heidelberg, Germany

Publ.-Id: 7097 - Permalink


Origin of Efficient Light Emission from Si pn Diodes Prepared by Ion Implantation
Dekorsy, T.; Sun, J. M.; Skorupa, W.; Mücklich, A.; Schmidt, B.; Helm, M.;
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.
Keywords: Silicon photonics, silicon light emitters, electroluminescence
  • Contribution to proceedings
    27th International Conference on the Physics of Semiconductors, 26.-30.07.2004, Flagstaff, AZ, USA
    American Institute of Physics Conference Proceedings 772(2005), 1539-1540
  • Poster
    27th Int. Conf. on the Physics of Semiconductors, Flagstaff, AZ, USA, July 26-30, 2004, 26.-30.07.2004, Flagstaff, AZ, USA

Publ.-Id: 7096 - Permalink


The influence of the coolant flow fluctuations on the consequences of a hypothetical boron dilution event
Grundmann, U.; Kliem, S.; Mittag, S.; Rohde, U.;
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.
Keywords: reactor dynamics three-dimensional measurements hypothetical boron dilution event mixing problems fluctuations transient simulations accident analysis safety limits
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany
    CD-ROM

Publ.-Id: 7095 - Permalink


Quantitative Measurement of Gas Distributions in a Stirred Chemical Reactor with Cone-Beam X-ray Computed Tomography
Boden, S.; Hampel, U.; Speck, M.;
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.
Keywords: cone-beam CT, gas distribution, stirred chemical reactor, X-ray tomography
  • Contribution to proceedings
    4th World Congress on Industrial Process Tomography, 05.-08.09.2005, Aizu, Japan
    Proceedings, 0 85316 255 7, 813-818

Publ.-Id: 7093 - Permalink


A new ion beam facility for slow highly charged ions
Zschornack, G.; Landgraf, S.; Facsko, S.; Kost, D.; Möller, W.; Tyrroff, H.; Großmann, F.; Kentsch, U.; Ovsyannikov, V.; Schmidt, M.; Ullmann, F.;
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.
Keywords: highly charged ions, ECR ion source, EBIT
  • Contribution to proceedings
    9th European Particle Accelerator Conference 2004, 05.-09.07.2004, Luzern, Schweiz
    Proceedings of EPAC (2004), 1189-1191

Publ.-Id: 7092 - Permalink


Potential energy retention of highly charged ions in solid surfaces
Facsko, S.; Kost, D.; Möller, W.; Zschornack, G.; Hellhammer, R.; Stolterfoht, N.;
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)
Keywords: highly charged ions
  • Lecture (Conference)
    12th International Conference on the Physics of Highly Charged Ions, 06.-11.09.2004, Vilnius, Lithuania

Publ.-Id: 7091 - Permalink


Electron emission from Ne9+ interacting with thin SiO2 films
Facsko, S.; Pesic, Z.; Hellhammer, R.; Stolterfoht, N.; Kost, D.; Möller, W.;
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.
Keywords: highly charged ions, electron spectrsocopy, silicon oxide
  • Lecture (Conference)
    24th Werner Brandt Workshop, 12.-14.07.2004, Berlin, Deutschland

Publ.-Id: 7090 - Permalink


Radioaktive Metallkomplexe von Chelatbildnern und deren Verwendung für die nuklearmedizinische Diagnostik und Therapie sowie Verfahren zur Herstellung der Metallkomplexe
Comba, P.; Juran, S.; Kerscher, M.; Pietzsch, H.-J.; Spies, H.; Stephan, H.;
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
  • Patent
    Patentanmeldung 10 2004 062 568.9

Publ.-Id: 7089 - Permalink


Blitzlampenspiegelanordnung
Voelskow, M.; Anwand, W.; Skorupa, W.;
Es wird eine Blitzlampenspiegelanordnung vorgestellt, die eine homogene und schnelle Erwärmung von Halleitersubstraten bei unwesentlich höheren Anlagenkosten ermöglicht.
  • Patent
    Patentanmeldung 10 2004 060 557.2

Publ.-Id: 7088 - Permalink


Doping magnetic materials - tunable properties due to ion implantation
Fassbender, J.ORC; McCord, J.; Mattheis, R.; Potzger, K.; Mücklich, A.; von Borany, J.
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.
Keywords: magnetic films, doping, ion implantation, anisotropy, damping, Curie temperature
  • Lecture (Conference)
    Euromat 2005, 05.-08.09.2005, Prague, Czech Republic

Publ.-Id: 7087 - Permalink


Structural phase transformation of FePt nanoparticles by ion irradiation
Dmitrieva, O.; Rellinghaus, B.; Liedke, M. O.; Fassbender, J.ORC
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.
Keywords: FePt, nanoparticle, high anisotropy, magnetic, L10-phase, structure, TEM, ion irradiation
  • Lecture (Conference)
    Euromat 2005, 05.-08.09.2005, Prague, Czech Republic

Publ.-Id: 7086 - Permalink


Nuklidmigration im Deckgebirge des ERAM (DGL) Abschlußbericht zum BfS-Auftrag 9M 212 230-62 FZK-INE 14/03, 2004, 225 Seiten
Vejmelka, P.; Lützenkirchen, J.; Kelm, M.; Bohnert, E.; Gompper, K.; Nebelung, C.; Baraniak, L.;
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.
Keywords: Sorption, solubility, uranium, radium, americium, plutonium,[14C]-Carbonat, waste disposal Morsleben, backfilling material, rock material
  • Other report
    Karlsruhe: FZK-INE 14/03, 2004
    225 Seiten

Publ.-Id: 7085 - Permalink


Studies of β-delayed proton decays of N≈Z nuclei around 100Sn at the GSI-ISOL facility
Mukha, I.; Batist, L.; Becker, F.; Blazhev, A.; Brüchle, A.; Döring, J.; Gorska, M.; Grawe, H.; Fästermann, T.; Hoffmann, C.; Janas, Z.; Jungclaus, A.; Karny, M.; Kavatsyuk, M.; Kavatsyuk, O.; Kirchner, R.; La, C.; Mazzocchi, M.; Plettner, C.; Plochocki, C.; Roeckl, A.; Romoli, E.; Schädel, M.; Schwengner, R.; Tabor, R.; Wiedeking, S. L.;
Beta decays of 94,96Ag and 103Sn nuclei into Proton Channels have been studied in the recent experiments at the GSI-ISOL facility

Publ.-Id: 7084 - Permalink


Aluminum Control of Phosphorus Sorption by Lake Sediments
Kopacek, J.; Borovec, J.; Hejzlar, J.; Ulrich, K.-U.; Norton, S.; Amirbahman, A.;
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.
  • Environmental Science & Technology 39(2005)22, 8784-8789

Publ.-Id: 7083 - Permalink


Heavy metals and colloids in streams impaired by acid rain
Ulrich, K.-U.; Zänker, H.; Roßberg, A.; Furrer, G.;
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.
Keywords: colloid migration, heavy metals, uranium, sorption, EXAFS
  • Poster
    Acid Rain 2005, 7th International Conference on Acid Deposition, 12.-17.06.2005, Prague, Czech Republic
  • Contribution to proceedings
    Acid Rain 2005, 7th International Conference on Acid Deposition, 12.-17.06.2005, Prague, Czech Republic
    Acid Rain 2005 Conference Abstracts, 613

Publ.-Id: 7082 - Permalink


Reservoir ecosystems recover from atmospheric acidification: II. Signs of biological recovery
Meybom, A.; Ulrich, K.-U.;
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.
Keywords: Zooplankton biomass on wet weight basis (black bars) and estimated sunbleak biomass (triangles: littoral biomass by electro-fishing, circles: pelagic biomass by vertical and horizontal hydroacoustics) in the Werda drinking-water reservoir in 2002 and 2003
  • Contribution to proceedings
    Acid Rain, 12.-17.06.2005, Prague, Czech Republic
    Acid Rain 2005 Conference Abstracts, 80-86690-25-3, 558
  • Poster
    Acid Rain 2005, 7th International Conference on Acid Deposition, 12.-17.06.2005, Prague, Czech Republic

Publ.-Id: 7081 - Permalink


Reservoir ecosystems recover from atmospheric acidification: I. Trends of chemical reversal
Ulrich, K.-U.; Meybohm, A.;
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.
Keywords: acidification reversal, emissions abatement, forest soil liming, hydrochemistry, trend analysis
  • Contribution to proceedings
    Acid Rain 2005, 7th International Conference on Acid Deposition, 12.-17.06.2005, Prague, Czech Republic
    Acid Rain 2005 Conference Abstracts, 80-86690-25-3, 545
  • Poster
    Acid Rain 2005, 7th International Conference on Acid Deposition, 12.-17.06.2005, Prague, Czech Republic

Publ.-Id: 7080 - Permalink


S-Layer? Biomolekulare Template zur Erzeugung von Nanostrukturen
Raff, J.;
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.
  • Lecture (others)
    Lehrerfortbildung 2004 / 2005, 11.02.2005, Dresden, Germany

Publ.-Id: 7079 - Permalink


MHD α²-dynamo, Squire equation and PT-symmetric interpolation between square well and harmonic oscillator
Günther, U.; Stefani, F.; Znojil, M.;
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.
Keywords: MHD dynamo, Squire equation, Couette flow, PT-symmetric Quantum Mechanics, Krein space, operator theory, spectral analysis, exceptional points, phase transitions, singularities, Herbst limit

Publ.-Id: 7078 - Permalink


Wire-Mesh Tomography Measurements of Void Fraction in Rectangular Bubble Columns
Reddy, V. B. N.; Zaruba, A.; Prasser, H.-M.; Krepper, E.; Lopez, D. B. M. A.;
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.
Keywords: void fraction measurement, wire-mesh tomography, bubble size distribution, bubbly flow
  • Contribution to proceedings
    2004 International Congress on Advances in Nuclear Power Plants (ICAPP '04), 13.-17.06.2004, Pittsburgh, United States

Publ.-Id: 7077 - Permalink


Evaluation of computational fluid dynamic methods for reactor safety analysis (ECORA)
Scheuerer, M.; Heitsch, M.; Menter, F.; Egorov, Y.; Toth, I.; Bestion, D.; Pigny, S.; Paillere, H.; Martin, A.; Boucker, M.; Krepper, E.; Willemsen, S.; Muhlbauer, P.; Andreani, M.; Smith, B.; Karlsson, R.; Henriksson, M.; Hemstrom, B.; Karppinen, I.; Kimber, G.;
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.
Keywords: nuclear reactor safety analysis, computational fluid dynamics
  • Nuclear Engineering and Design 235(2005)2-4, 359-368

Publ.-Id: 7076 - Permalink


Bacterial and Archaeal Diversity in Groundwaters of the Siberian Deep-Well Radioactive Disposal Site TOMSK-7
Nedelkova, M.; Merroun, M.; Radeva, G.; Selenska-Pobell, S.;
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
  • Poster
    BioMicroWorld 2005, 15.-18.03.2005, Badajoz, Spain
  • Contribution to proceedings
    BioMicroWorld 2005, 15.-18.03.2005, Badajoz, Spain

Publ.-Id: 7075 - Permalink


Immobilization of Uranium from Drinking Water by Bacillus Sphaericus JG-A12
Raff, J.; Pollmann, K.; Selenska-Pobell, S.;
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)
  • Contribution to proceedings
    BioMicroWorld 2005, International Conference on Environmental, Industrial and Applied Microbiology, 15.-18.03.2005, Badajoz, Spain, 693-693
  • Poster
    BioMicroWorld 2005, International Conference on Environmental, Industrial and Applied Microbiology, 15.-18.03.2005, Badajoz, Spain

Publ.-Id: 7074 - Permalink


The columnar-to-equiaxed transition in Pb-Sn alloys affected by electromagnetically driven convection
Willers, B.; Eckert, S.; Michel, U.; Haase, I.; Zouhar, G.;
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
Keywords: Solidification, Pb-Sn alloy, Columnar-to-equiaxed transition (CET), Fluid flow, Electromagnetic stirring, Rotating magnetic field

Publ.-Id: 7073 - Permalink


Velocity measurements in metallic melts: New developments and applications
Eckert, S.; Gerbeth, G.; Stefani, F.;
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.
Keywords: Velocity measurements, liquid metal, Ultrasound Doppler velocimetry, Magnetic flow tomography, Mechano-Optical Probe, Inductive Flowmeter
  • Invited lecture (Conferences)
    Annual meeting of JSPS, 27.-28.01.2005, Nagoya, Japan

Publ.-Id: 7072 - Permalink


Development of co-current air-water flow in a vertical pipe
Lucas, D.; Krepper, E.; Prasser, H.-M.;
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.
Keywords: bubble flow, vertical pipe flow, experimental database, bubble size distribution
  • International Journal of Multiphase Flow 31(2005), 1304-1328

Publ.-Id: 7070 - Permalink


Hydrogen solubility limit in hydrogenated amorphous silicon
Danesh, P.; Pantchev, B.; Schmidt, B.; Grambole, D.;
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.
Keywords: a-Si:H, ion implantation, hydrogen concentration, NRA
  • Semiconductor Science and Technology 19(2004)12, 1422-1425

Publ.-Id: 7069 - Permalink


Inclusive K+ Meson Production in Proton Nucleus Interactions
Büscher, M.; Koptev, V.; Nekipelov, M.; Rudy, Z.; Ströher, H.; Valdau, Y.; Barsov, S.; Hartmann, M.; Hejny, V.; Kleber, V.; Lang, N.; Lehmann, I.; Mikirtychiants, S.; Ohm, 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).

Publ.-Id: 7068 - Permalink


Electromagnetic Probes of Strongly Interacting Matter: Probes of Chiral Symmetry Restoration?
Thomas, R.; Gallmeister, K.; Zschocke, S.; Kämpfer, B.;
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.
Keywords: In-Medium Modifications, QCD Sum Rules, Chiral Symmetry, Four-Quark Condensates, Electromagnetic Probes
  • Contribution to proceedings
    Workshop on In-Medium Hadron Physics, 11.-13.11.2004, Giessen, Deutschland
  • Acta Physica Hungarica A 27(2006)1, 35-45

Publ.-Id: 7067 - Permalink


A critical analysis of the modelling of dissipation in fission
Jurado, B.; Schmitt, C.; Schmidt, K.-H.; Benlliure, J.; Junghans, A. R.;
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.
Keywords: Nuclear fission; Dissipation effects; Time-dependent fission-decay width; Langevin equation; Fokker–Planck equation; Analytical approximation

Publ.-Id: 7065 - Permalink


Uranium speciation in two Freital mine tailing samples: EXAFS, µ-XRD, and µ-XRF results
Scheinost, A. C.; Hennig, C.; Somogyi, A.; Martinez-Criado, G.; Knappik, R.;
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.
  • Lecture (Conference)
    Uranium Mining and Hydrogeology IV, 11.-16.09.2005, Freiberg, Germany
  • Poster
    15th Users Meeting, 08.-11.02.2005, Grenoble, France

Publ.-Id: 7064 - Permalink


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