Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Riga dynamo experiments
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.;
A review of the Riga dynamo experiment is given focusing mainly on the measured turbulent properties of the flow-induced magnetic field.
  • Invited lecture (Conferences)
    Joint 15th Riga and 6th PAMIR International Conference on MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on MHD, 27.06.-01.07.2005, Riga, Latvia
    1(2005), 15-24

Publ.-Id: 7748 - Permalink


Applications of AC and DC magnetic fields in metallurgical and crystal growth processes
Cramer, A.; Eckert, S.; Galindo, V.; Priede, J.; Gerbeth, G.;
A summary on magnetic field applications in the fields of melt extraction, aluminum casting, electromagnetic levitation and float-zone crystal growth is given.
  • Contribution to external collection
    H. Wada, H.J. Schneider-Muntau (Hrsg.): Materials Processing in Magnetic Fields, Singapore: World Scientific Publishing, 2005, 157-168

Publ.-Id: 7747 - Permalink


How to actualize reversals in dynamo experiments?
Xu, M.; Gerbeth, G.; Günther, U.; Stefani, F.;
The theoretical connection between field reversals and the occurrence of exceptional points in the dynamo operator spectrum is examined.
  • Poster
    IGA 2005 Scientific Assembly, 18.-29.07.2005, Toulouse, France

Publ.-Id: 7746 - Permalink


Magnetic field details of the Riga dynamo experiment
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Gundrum, T.; Stefani, F.;
The back-reaction mechanism of the Riga dynamo is examined. It shows in particular a leading action of the induced magnetic field on the azimuthal velocity component, which finally results in a very smart increase of the motor power in case of the finally saturated magnetic field.
  • Invited lecture (Conferences)
    IAGA 2005 Scientific Assembly, 18.-29.07.2005, Toulouse, France

Publ.-Id: 7745 - Permalink


Uranium speciation in two Freital mine tailing samples: EXAFS, micro-XRD, and micro-XRF results
Scheinost, A.; Hennig, C.; Somogyi, A.; Martinez-Criado, G.; Knappik, R.;
We investigated the uranium speciation in a former WISMUT mine tailing, which was buried for 30 years under mine and construction debris.
Chemical extractions, EXAFS, -XRD, and -XRF reveal two major U pools. The first with a relatively high potential mobility was identified as U(VI) sorbed to layer silicates by inner-sphere complexation; the second pool is represented by the relatively insoluble U(IV) minerals pitchblende and coffinite, and by the U(VI) solids uranyl hydroxide and vanuralite.
Distribution between the two pools seems to be con-trolled by pH. Evidence for reductive precipitation of uraninite was found.
  • Contribution to proceedings
    Uranium Mining and Hydrogeology UMH IV, 11.-16.09.2005, Freiberg, Germany
    Uranium in the Environment. Mining Impact and Consequences (B.J. Merkel, A. Hasche-Berger, eds.), Berlin: Springer, 117-126

Publ.-Id: 7744 - Permalink


Uncertainty and sensitivity analyses of the Kozloduy pump trip test using coupled thermal-hydraulic 3D kinetics code
Bousbia Salah, A.; Kliem, S.; Rohde, U.; D’Auria, F.; Petruzzi, A.;
The modeling of complex transients in Nuclear Power Plants (NPP) remains a challenging topic for Best Estimate three-dimensional coupled code computational tools. This technique is, nowadays, extensively used since it allows decreasing conservatism in the calculation models and performs more realistic simulation and more precise consideration of multidimensional effects under complex transients in NPPs. Therefore, large international activities are in progress aiming to assess the capabilities of coupled codes and the new frontiers for the nuclear technology that could be opened by this technique. In the current paper a contribution to the assessment and validation of coupled code technique through the Kozloduy VVER100 pump trip test is performed. For this purpose, the coupled RELAP5/3.3-PARCS/2.6 code is used. The code results were assessed against experimental data. Deviations between code predictions and measurements are mainly due to the used models for evaluating and modeling of the Doppler feedback effect. Further investigations through the use of two “antagonist” uncertainty GRS and the CIAU methods, were considered in order to evaluate and quantify the origin of the observed discrepancies. It was revealed on one hand that relative error quantification discrepancies exist between the two approaches, and further enhancements for both methods are needed

Publ.-Id: 7743 - Permalink


Wire-mesh sensors for high-resolving two-phase flow studies at high pressures and temperatures
Pietruske, H.; Prasser, H.-M.;
Wire-mesh sensors are used for a high-speed visualization of a gas-liquid flow as well as for the measurement of void fraction profiles, bubble size distributions and gas velocity distributions. Recent progress was made in designing and constructing such sensors for an application in a hot steam-water mixture. Two types are presented: (1) a sensor with an inner diameter of 52.3 mm with a measuring matrix of 16x16 and (2) a sensor of 195 mm inner diameter with 64x64 measuring points. Both devices can be operated at 7 MPa and a temperature of max. 286 °C. The spatial and temporal resolutions are equal to earlier used sensors for air-water flow at ambient conditions (3 mm, 2500 fps). In the paper, the function of the sensors is illustrated by presenting flow visualizations obtained at two vertical test sections of the Rossendorf TOPFLOW facility. The pipes are approximately 9 m long and have inner diameters equal to the diameters of the measuring cross sections mentioned above. The results show how the flow structure depends on the thermodynamic parameters by comparing measurements performed at 1, 2, 4 and 6.5 MPa and 180, 212, 250 and 280 °C, correspondingly, under adiabatic conditions with earlier air-water tests.
Keywords: two-phase flow, flow pattern, vertical upwards flow, wire-mesh sensors
  • Flow Measurement and Instrumentation 18(2007)2, 87-94
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
    CD-ROM, Paper 533

Publ.-Id: 7742 - Permalink


Determination of In concentration in InGaAs/GaAs 001 epilayers in the early stage of anisotropic stress relaxation
Sass, J.; Mazur, K.; Eichhorn, F.; Strupinski, W.; Turos, A.; Schell, N.; (Editors)
A method has been developed for determination of In concentration in strained layers of InGaAs/GaAs heterostructures. Chemical composition and lattice strain were evaluated from the reciprocal space maps obtained for asymmetric reflections. It was observed that beginning of
relaxation of the In0.13Ga0.87As/GaAs (0 0 1) system with lattice misfit Delta-a/a = 9.3×10−3 and the critical thickness tc(MB) = 15 nm can be detected for layers of thickness exceeding t∼
70 nm ∼ 4.5tc(MB). The principal relaxation mechanism is due to the slipping of 60° misfit dislocations on the tilted (1 1 1) glide planes. The accuracy of indium concentration measurements was estimated to Delta-x =±0.01.
Keywords: X-ray diffraction; Lattice strain; InxGa1−x As/GaAs (0 0 1) heterostructures

Publ.-Id: 7741 - Permalink


Toxic avengers
Raff, J.; Selenska-Pobell, S.;
Live adapts to survive in the most forbidding conditions - even in former uranium mining and production sites. If man could understand how microbes handle radionuclides, he might one day harness a natural force for remediation.
  • Nuclear Engineering International 51(2006)619, 34-36

Publ.-Id: 7740 - Permalink


Radiopharmakaforschung: Trends und neue Konzepte
Wüst, F.;
Die Leistungsfähigkeit der Nuklearmedizin in der Diagnostik, Therapie und medizinischen Forschung hängt entscheidend vom Fortschritt bei der Entwicklung neuer geeigneter Radiopharmaka ab. Die Auswahl, die Herstellung und die präklinische Evaluation dieser neuen Radiopharmaka ist Gegenstand der radiopharmazeutischen Chemie. Vor dem Hintergrund der rasanten Entwicklungen auf den Gebieten der Biowissenschaften im Post-Genom Zeitalter und der technologischen Fortschritte bei der Instrumentierung der bildgebenden nuklearmedizinischen Verfahren SPECT und PET hat sich die Radiopharmakaforschung in den letzten Jahren zu einer komplexen chemischen Wissenschaft entwickelt. Die Schwerpunkte der aktuellen Radiopharmakaforschung umfassen dabei besonders neue koordinationschemische Entwicklungen auf dem Gebiet der [99mTc]Technetium Radiopharmaka, die Herstellung von sogenannten Nicht-Standard Radionukliden für die PET sowie die Synthese von 11C- und 18F-markierten Radiopharmaka mit hoher spezifischer Radioaktivität.
Weitere wichtige Entwicklungen zeichnen sich durch die zunehmende Ausrichtung der Radiopharmakaforschung auf die Entwicklung von Radiotherapeutika und die Einbeziehung der PET in die Arzneimittelentwicklung und -evaluation ab.
Keywords: [99mTc]Technetium; Nicht-Standard-PET-Radionuklide; spezifische Radioaktivität; Radiotherapeutika; Arzneimittelforschung

Publ.-Id: 7739 - Permalink


In vivo metabolism of oxidized low density lipoproteins: Insights from small animal positron emission tomography (PET) studies
Pietzsch, J.; Bergmann, R.; Wüst, F.; van den Hoff, J.;
The human organism is exposed to numerous processes that generate reactive oxygen or nitrogen species may directly or indirectly cause oxidative modification and damage of proteins. Protein oxidation is regarded as a crucial event in the pathogenesis of various diseases ranging from rheumatoid arthritis to Alzheimer's disease and atherosclerosis. The importance of protein oxidation in respect of altered function is exemplified by oxidation of low density lipoproteins (LDL) which causes altered receptor recognition and, e.g., plays a key role in atherogenesis. However, data concerning the role of circulation oxidized LDL (oxLDL) in the development and outcome of disease are scarce. One reason for this is the shortage of methods for direct assessment of the metabolic fate of circulation oxLDL in vivo. As an attractive alternative to, e.g., LDL iodination methods, a novel methodology based on the radiolabeling of apoB-100 of native LDL (nLDL) and oxLDL, respectively, with the positron emitter fluorine-18 (18F]SFB) was developed. In cotrast to most protein radioiodination methods, radiolabeling of both nLDL and oxLDL using [18F]SFB caused neither additional oxidative structural modifications of LDLlipids and proteins nor alteration of their biological activity and functionality, respectively, in virto. The method was further evaluated with respect to the radiopharmacological properties to both [18F]fluorobenzoylated nLDL and oxLDL by biodistribution and dynamic positron emission tomography (PET) studies in male Wistar rats. These studies demonstrated the methodology to be of value to characterize and to discriminate the kinetics and the metabolic fate of nLDL and oxLDL in small animals in vivo.
  • Recent Research Developments in Molecular & Cellular Biochemistry 2(2005), 153-177

Publ.-Id: 7738 - Permalink


Synthesis of a 11C-labelled taxane derivative by [1-11C]acetylation
Mäding, P.; Zessin, J.; Pleiß, U.; Füchtner, F.; Wüst, F.;
The 11C-labelling of the taxane derivative BAY 59-8862 (1), a potent anticancer drug, was carried out as a module-assisted automated multi-step synthesis procedure. The radiotracer [11C]1 was synthesized by reacting [1-11C]acetyl chloride (6) with the lithum salt of the secondary hydroxy group of precursor 3 followed by deprotection. After HPLC purification of the final product [11C]1, its solid phase extraction, formulation and sterile filtration, the decay-corrected radiochemical yield of [11C]1 was in the range between 12 and 23% (related to [11C]CO2; n = 10). The total synthesis time was about 54 min after EOB. The radiochemical purity of [11C]1 was greater than 96% and the chemical purity exceeded 80%. The specific radioactivity was up to 20 GBq/µmol at EOS starting from 80 GBq of [11C]CO2.
Keywords: taxane, anticancer drug, [1-11C]acetyl chloride, [11C]BAY 59-8862, positron emission tomography
  • Journal of Labelled Compounds and Radiopharmaceuticals 49(2006), 357-365
    DOI: 10.1002/jlcr.1059

Publ.-Id: 7737 - Permalink


Influence of sputtering conditions and electron energy on XPSdepth profiling of Ge in SiO2
Oswald, S.; Schmidt, B.; Heinig, K.-H.;
Ge nanocluster formation in SiO2 is of growing interest for new electronic applications. Ion beam synthesis using high-energy Ge implantation connected with thermal annealing is one possible preparation method of such clusters. In addition to investigations of electrical and structural changes during the cluster formation process we also studied chemical changes in the samples using x-ray photoelectron spectroscopy (XPS). This was done with low-energy noble gas ion sputtering for depth profiling. Binding state information one can get from the XPS data by means of factor analysis (FA) in combination with other structural investigations.
However, mixed bonding states probably created by ion beam damage during sputter erosion are dominating the results. It is shown, that by changing the experimental conditions (ion beam impact depth during sputtering, electron information depth during XPS measurement) these mixed states are influenced in an appropriate manner. It is concluded that useful chemical information on the behavior of the implanted Ge can be derived despite of the ion beam damage.
Keywords: XPS, depth profile, data analysis, ion beam effects.
  • Crystal Research and Technology 40(2005)12, 1134-1138

Publ.-Id: 7736 - Permalink


Untersuchung des Einflusses von Gallussäure auf das Redoxverhalten von Uran (VI)
Steudtner, R.;
Im Mittelpunkt der Uranforschung stehen die Wechselwirkungen des Urans mit natürlichen Organika, wie Huminstoffen und Holzabbauprodukte. Diese entstehen durch den natürlichen Zersetzungsprozess und sind teilweise hochmolekulare organische Substanzen mit mehreren funktionellen Gruppen.
Es ist bekannt, dass diese Stoffe einen Einfluss auf den Oxidationszustand des Urans haben. Ein bedeutender Unterschied zwischen den verschiedenen Oxidationsstufen liegt in der Löslichkeit des vierwertigen und sechswertigen Urans begründet. Die sehr geringe Löslichkeit des vierwertigen Urans gegenüber dem sechswertigen Uran führt zu einer Immobilisierung des Urans. Bei der Reduktion durch natürliche Organika könnte es so zu einer lokalen Anreicherung an Uran im Boden führen.

Das Ziel der vorliegenden Arbeit ist es, den Einfluss der Gallussäure (3, 4, 5-Trihydroxybenzoesäure) auf das Redoxverhalten von Uran(VI) zu untersuchen und eine mögliche Reduktion des Uran(VI) zu Uran(IV) spektroskopisch nachzuweisen.

Die Gallussäure wurde dabei als vereinfachte Modellvorstellung für Huminstoffe betrachtet, weil sie eine organische Substanz mit mehreren funktionellen Gruppen ist und reduzierende Eigenschaften gegenüber Metallionen aufweist].
  • Other report
    Hochschule Zittau / Görlitz: Diplomarbeit (Studiengang Chemie), 2005
    65 Seiten

Publ.-Id: 7735 - Permalink


Investigation of insulated buried layers obtained by ion implantation in AlGaAs with various Al concentration
Wierzchowski, W.; Wieteska, K.; Graeff, W.; Gawlik, G.; Turos, A.; Mücklich, A.;
The important element of modern AlxGa1-xAs semiconductor lasers is an insulating buried layer introduced by selective implantation with He or H ions. The difficulty in obtaining of such layers is connected with controlling of strain and defects introduced by implantation, which may disturb the action of the laser. The strain may be however controlled in less complicated laterally homogeneous structures or even single implanted layer.
The insulated buried layers obtained by implantation of 150 keV He ions to AlxGa1-xAs with various concentration of Al and GaAs were studies with different synchrotron diffraction methods exploring both white and monochromatic beam.The selected samples were studied with high resolution transmission electron microscopy. The implantation were performed at room temperature, 80°C and 120°C. The doses were in the range from 2x1016 to 6x1016 cm-2. The synchrotron experiment included taking local rocking curves using small 50x50 µm2 probe beam. The rocking curves exhibit characteristic sequence of interference maxima and enabled the analysis of the strain profiles by fitting the theoretical rocking curves obtained by numerical integration of the Takagi-Taupin equations. The white beam synchrotron back reflection topography revealed a sequence of strain modulation fringes similar to the main interference maxima in the rocking curves. They also confirm the uniformity of applied dose and lack of extended crystallographic defects which could be caused by implantation. The characteristic feature of the evaluated profiles was the existence of the deformed region close to the surface which points that the deformation is mainly caused by point defects produced by incident ions and recoils. The other feature increasing with the temperature of implantation was the flattening of top part of the strain maximum corresponding to the insulating buried layer.
  • Poster
    E-MRS 2005 Fall Meeting, 05.-09.09.2005, Warsaw, Poland

Publ.-Id: 7734 - Permalink


Strain Profiles in the Insulated Buried Layers Obtained by He Implantation in AlGaAs
Wierzchowski, W.; Wieteska, K.; Graeff, W.; Gawlik, G.; Turos, A.; Maurin, J.; Mücklich, A.;
The insulated buried layers formed by 150 keV ions to AlxGa1-xAs with various concentration of Al were studied with synchrotron diffraction methods. Some samples were studied with HRTEM. The implantations were performed at RT, 80 and 120°C. The doses varied from 2x1016 to 6x1016 cm-2. The measurements included taking local rocking curves using small 50x50 µm2 probe beam. The rocking curves exhibited characteristic interference maxima and enabled the analysis of the strain profiles by fitting the theoretical rocking curves obtained by numerical integration of the Takagi-Taupin equations. The white beam synchrotron back reflection topography revealed a sequence of strain modulation fringes similar to the main interference maxima in the rocking curves. The evaluated profiles exhibited the deformed region close to the surface indicating that the deformation is mainly caused by the point defects produced by incident ions and the recoils. The other feature increasing with the temperature of implantation was the flattening of top part of the strain maximum corresponding to the insulating buried layer. This flattening was more distinct for lower concentration of Al. The HRTEM patterns revealed characteristic small gaseous inclusions appeared in the most deformed region in the samples implanted with the highest applied doses.
Keywords: strain, ion implantation, diffraction
  • Contribution to proceedings
    XX Congress of the International Union of Crystallography, 23.-31.08.2005, Florence, Italy
    Acta Crystallographica (2005), A61, C449

Publ.-Id: 7733 - Permalink


Methodenentwicklung zur Analyse von Störfallszenarien mit Frischdampfleck und Borverdünnung mit Hilfe des Codesystems ATHLET-DYN3D - Abschlussbericht Teil 2
Kliem, S.; Grundmann, U.; Rohde, U.;
Es wurde ein Modell zur realistischen Beschreibung der Kühlmittelvermischung innerhalb des Reaktordruckbehälters von Druckwasserreaktoren in den gekoppelten Programmkomplex DYN3D/ATHLET implementiert. Diese Modell basiert auf dem Prinzip der linearen Superposition Dirac-Impuls-ähnlicher Störungen und kann für die Modellierung der Vermischung von Kühlmittel unterschiedlicher Temperatur und/oder unterschiedlicher Borsäurekonzentration eingesetzt werden. Der um das Vermischungsmodell erweiterte Programmkomplex DYN3D/ATHLET wurde für Analyse von Borverdünnungsstörfällen und Frischdampflecks angewandt. Für den Fall „Start der ersten Hauptkühlmittelpumpe bei Vorhandensein eines minderborierten Pfropfens im kalten Strang“ zeigten die Ergebnisse der durchgeführten Parame-terstudie, dass es selbst bei Annahme des maximal möglichen Pfropfenvolumens nicht zu einer Schädigung des Brennstoffes kommt. Mit den Analysen zu einem generischen Frischdampfleckszenario wurde die Anwendbarkeit des Programmkomplexes DYN3D/ATHLET auf die zweite Störfallklasse, in der die Kühlmittelvermischung eine wichtige Rollen spielt, demonstriert.
Im Rahmen der Arbeiten zum Projekt wurde außerdem gezeigt, dass der Einfluss der turbulenten Schwankungen des Geschwindigkeitsfeldes innerhalb des Reaktordruckbehälters auf neutronenkinetische Parameter im Nominalbetrieb und unter Störfallbedingungen nicht zu vernachlässigen ist.

A model for the realistic description of the coolant mixing inside the pressure vessel of pressurized water reactors was implemented into the coupled code complex DYN3D/ATHLET. This model is based on the linear superposition Dirac-pulse-like perturbations. The model can be applied to the mixing of coolant of different temperature and/or boron concentration. The coupled code complex DYN3D/ATHLET with the newly implemented model was applied to the analysis of boron dilution and steam line break accidents. The results of a parameter study for the case “Start-up of the first main coolant pump with a slug of lower borated water in the cold leg” have shown, that even under the conditions of the maximum slug volume there is no fuel damage. The applicability to the second class of accidents, where the coolant mixing has to be considered, was demonstrated by the analysis of a generic main steam line break scenario.
Further it was shown, that the influence of turbulent fluctuations of the velocity inside the reactor pressure vessel during nominal and accident conditions on neutron-kinetic parameters cannot be neglected.
Keywords: pressurized water reactor, accident analysis, coupled neutronics-thermohydraulic codes, boron dilution, main steam line break, coolant mixing
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-438 2005

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Publ.-Id: 7732 - Permalink


Direct evidence of self-aligned Si nanocrystals formed by ion irradiation of Si/SiO2 interfaces
Röntzsch, L.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.; Thomas, J.; Gemming, T.;
Energy-filtered transmission electron microscopy proves di-rectly, that ion irradiation and post-irradiation annealing of a Si/SiO2 interface results in the formation of a narrow layer of monodisperse Si nanocrystals in the oxide at a tunnel distance from the interface. Position and size of the Si nanocrystals are in agreement with predictive atomistic computer simulations.
Keywords: Ion Irradiation, Phase Separation Si-SiO2 Interface, Si Nanocluster, Non-volatile Memory

Publ.-Id: 7731 - Permalink


Verhalten des Reaktordruckbehälters bei einem unterstellten Kernschmelzunfall
Willschuetz, H.-G.; Altstadt, E.;
Für das unwahrscheinliche Szenario eines Kernschmelzunfalls in einem Leichtwasserreaktor mit Bildung eines Schmelzesees in der Bodenkalotte des Reaktordruckbehälters (RDB) ist es notwendig, mögliche Versagensformen des RDB sowie Versagenszeiträume zu ermitteln, um die daraus resultierende mögliche Belastung des Sicherheitsbehälters bestimmen zu können. Es wurde ein integrales Modell entwickelt, das die Vorgänge im unteren Plenum beschreibt. Dabei sind zwei prinzipielle Modellbereiche zu unterscheiden: Das Temperaturfeld in der Schmelze und im RDB wird mit einem thermodynamischen Modell berechnet, während für die Strukturanalyse des RDB ein mechanisches Modell verwendet wird.
Zunächst wird das betrachtete Unfallszenario dargestellt.
Das thermodynamische und das mechanische Modell können rekursiv gekoppelt werden, wodurch die wechselseitige Beeinflussung berücksichtigt werden kann. Insbesondere werden damit neben der Temperaturabhängigkeit der Materialparameter und den thermisch induzierten Spannungen im mechanischen Modell auch die Rückwirkungen der Behälterverformung auf das Temperaturfeld selber erfasst.
Als Ergebnis der Arbeiten lässt sich festhalten, dass das gekoppelte Modell prinzipiell in der Lage ist, die Behälterdeformation im Falle der skalierten FOREVER-Experimente exakt zu beschreiben bzw. vorherzusagen. Unsicherheiten bezüglich der Versagenszeit resultieren aus nicht exakt bekannten Materialparametern und Randbedingungen.
Die wesentlichen Ergebnisse lassen sich wie folgt zusammenfassen: Aufgrund des thermodynamischen Verhaltens eines großen Schmelzesees mit inneren Wärmequellen erfolgt die höchste thermomechanische Belastung des RDB im oberen Drittel der Bodenkalotte. Dieser Bereich wird als heißer Fokus bezeichnet. Der untere Bereich der Kalotte weist hingegen eine höhere Festigkeit auf und verlagert sich deswegen bei entsprechender Belastung des RDB im wesentlichen senkrecht nach unten. Bei einer externen Flutung besteht auch bei hohen Innendrücken für einen Reaktor großer Leistung (KONVOI) die Möglichkeit, die Schmelze im RDB zurückzuhalten. Ohne interne oder externe Flutung besteht für das betrachtete Szenario keine Aussicht für eine Schmelzerückhaltung im RDB.
Abweichend von bisherigen Annahmen kann im Hinblick auf die Entwicklung zukünftiger Baulinien festgehalten werden, dass eine Kernschmelzerückhaltung im Reaktordruckbehälter auch für Reaktoren größerer Leistung möglich ist.
Keywords: core melt down, in vessel retention, coupled thermal and mechanical FE-model
  • Invited lecture (Conferences)
    Seminar Energieverfahrenstechnik WS 2005/2006, 20.10.2005-26.01.2006, Dresden, Deutschland

Publ.-Id: 7730 - Permalink


Simulation of the FOREVER experiments: enhancement and approach to a prototypic scenario
Willschuetz, H.-G.;
For the simulation of experiments investigating the behavior of the lower head of a nuclear power station in case of a core meltdown scenario like FOREVER it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model with 3 different submodels is developed based on the code ANSYS® Multiphysics.
A thermal submodel was build up including planar and contact elements for conductive heat transfer, additional surface elements to simulate convection and radiation from outer surface areas and a radiation matrix to account for internal radiative heat exchange. Normally a CFD-simulation would have been required for the natural convective heat transfer in the melt pool, but at very high internal Rayleigh numbers no turbulence model is capable for a correct simulation. Therefore an Effective Conductivity Convectivity Model (ECCM) was developed to simulate the heat transfer from the melt pool to its environment.
The resulting temperature field of the vessel wall is applied to the mechanical submodel. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided.
The third submodel is a kind of fictitious physics environment: it uses hyperelasticity and contact to move the melt pool along with the creeping vessel wall.
In this presentation problems on the numerical side are explained and differences between the results of a simple coupled and a kinematically coupled FE-simulation are highlighted. The final comparison with the experiments shows that the kinematically coupled model is closer to reality than the single step model.
Keywords: core melt down accident, thermal and mechanical simulation, recursive coupling
  • Invited lecture (Conferences)
    Seminar at the chair of Nuclear Power Safety, 12.10.2005, Stockholm, Sveden

Publ.-Id: 7729 - Permalink


Electron-optical-phonon interaction in the In0.73Ga0.27As–AlAs intersubband laser
Drachenko, O.; Galibert, J.; Léotin, J.; Tomm, J. W.; Semtsiv, M. P.; Ziegler, M.; Dressler, S.; Müller, U.; Masselink, W. T.;
The magnetic-field dependence of the operation of a quantum-cascade intersubband laser (QCL) is used to investigate the energetic relaxation of injected electrons through phonon emission. The QCL emits at 3.8mkm and incorporates a strain-compensated active region with a large degree of internal strain. Energies of the relevant electron-phonon scattering responsible for the depopulation of the upper laser level are determined from the analysis of the Landau-level spectra. A comparison of those energies with the Raman spectrum of the active region is used to identify which phonon is primarily involved in the electron-phonon scattering. In spite of the low Ga-content in the (In,Ga)As quantum wells and high Al-content in the AlAs/ (In,Al)As composite barriers, the depopulation of the upper laser level appears to be dominated by the resonant electron-GaAs-likelongitudinal-phonon intersubband scattering. In particular, the contribution due to AlAs-like modes is negligible
Keywords: Quantum Cascade Lasers, Intersubband Magnetophonon Resonance, Phonon spectroscopy
  • Applied Physics Letters (2005)87, 072104-1-072104-3

Publ.-Id: 7728 - Permalink


Reactive plasma immersion ion implantation for surface passivation
Yankov, R. A.; Shevchenko, N.; Rogozin, A.; Maitz, M. F.; Richter, E.; Möller, W.; Donchev, A.; Schütze, M.;
Plasma immersion ion implantation (PIII) using halogen or oxygen plasmas has been employed for the surface passivation of advanced alloys with a view to their applications for high-temperature oxidation protection and in medicine. Special devices have been designed to ensure efficient plasma generation and reduce sample contamination arising from the interaction of the aggressive plasmas with the chamber components under bias. The paper addresses two main applications of PIII, namely oxidation protection of gamma-titanium aluminides (γ-TiAl), and modification of the surface properties of shape-memory superelastic nickel titanium (NiTi) alloys. TiAl intermetallics are of great interest for advanced automobile, aerospace and power generation applications due to their low specific weight and high strength. However, excessive oxidation occurring in these materials at temperatures above 700°C has hindered their widespread use. Samples of technical γ-TiAl alloys have been treated by both beamline implantation of Cl or F, and PIII of Cl using an Ar/Cl gaseous blend or alternative precursor gases. High-temperature oxidation behavior has been examined under conditions of either isothermal or thermocyclic oxidation at 900°C. Optimized implantation processing produces marked improvement in the oxidation behavior of the γ-TiAl samples. On the basis of these results, a commercially viable process for enhancing the high-temperature oxidation resistance of γ-TiAl alloys using PIII of halogens is being developed. NiTi alloys are promising materials for use in biomedicine, provided that the release of Ni ions into the body environment can be sufficiently reduced. Oxygen PIII at substrate temperatures below 250°C results in the formation of a transparent rutile TiO2 surface layer with a Ni content down to below 1 at%. This layer in turn serves as a barrier to the corrosion and out-diffusion of Ni ions. Biocompatibility tests show superior in vitro blood compatibility in comparison with untreated NiTi samples.
Keywords: TiAl alloys, shape-memory NiTi alloys, oxidation protection, biocompatibility, ion implantation, plasma immersion ion implantation
  • Surface & Coatings Technology 201(2007), 6752-6758

Publ.-Id: 7725 - Permalink


Small-angle neutron scattering study of post-irradiation annealed neutron irradiated pressure vessel steels
Ulbricht, A.; Bergner, F.; Dewhurst, C. D.; Heinemann, A.;
Neutron irradiated reactor pressure vessel steel of two different Cu contents exposed to isochronal post-irradiation annealing treatments at stepwise increasing levels of temperature have been investigated. Results of small-angle neutron scattering experiments are reported and compared with the respective unirradiated and as-irradiated conditions. Volume distributions of scatterers and ratios of total to nuclear scattering intensities (A-ratio) were calculated from the measured differential macroscopic scattering cross sections. Finally, total volume fractions of scatterers, peak radii of the volume distribution and partial information on the composition of scatterers were extracted and discussed as a function of annealing temperature. Our measurements indicate that there is a temperature regime characterized by essentially complete dissolution of the irradiation-induced Cu-enriched clusters and another temperature regime characterized by a competition of dissolution and coarsening. An Arrhenius type of behaviour and a remarkable reversibility of the irradiation-induced cluster distribution are observed in the complete dissolution regime.
  • Journal of Nuclear Materials 353(2006), 27-34

Publ.-Id: 7724 - Permalink


Uranium(VI) Adsorption onto Synthetic Humic Substance-Kaolinite Sorbates
Sachs, S.; Bernhard, G.;
The reliable risk assessment of future nuclear waste repositories requires knowledge on the actinide migration behavior in potential host rock formations. Clay formations as possible host rocks are closely associated with natural organic matter, e.g., humic substances, which are known as efficient complexing agents for metal ions. Therefore, the immobilization as well as the release of humic substances by clays can affect the mobilization of actinide ions in the environment.
The impact of humic acid on the U(VI) sorption onto kaolinite was investigated in the ternary model system U(VI) – kaolinite - synthetic humic acid [1]. In the present work, the U(VI) sorption onto a synthetic kaolinite sorbate with humic substances is studied in order to approach natural conditions. For that, we synthesized humic acid M42 [2] in presence of Georgia kaolinite KGa-1b. As synthesis product we obtained a synthetic humic substance - kaolinite sorbate (M42-KS). Due to the fact that this humic substance - kaolinite sorbate was formed during the humic acid synthesis, a different composition of the humic material and different interactions between the humic substances and the kaolinite can be expected compared to the model system investigated in [1]. However, these conditions are probably closer to those found in natural clay systems.
The organic carbon content of two synthetic humic substance - kaolinite sorbates was determined with 5 and 24 mg C/g representing about 9 and 44 mg humic substances/g, respectively. To quantify the influence of the humic material associated with kaolinite we studied the U(VI) sorption onto M42-KS ([U(VI)]: 1· 10-6 M, S/L: 4 g/L, I: 0.01 M NaClO4) in the pH range between pH 3.0 and pH 10.0 by batch experiments. Compared to the humic substance-free system the U(VI) adsorption onto M42-KS is significantly increased between pH 3 and pH 5 which is ascribed to the association of humic substances with kaolinite. Up to pH 8 the U(VI) sorption onto M42-KS is reduced in contrast to the system without humic materials. Under these conditions M42-KS releases humic acid resulting in the formation of soluble U(VI) humate complexes. A further reduction of the U(VI) sorption was observed between pH 8 and 10. This is attributed to the formation of soluble U(VI) humate complexes and/or the formation of U(VI) carbonato complexes that dominate the U(VI) sorption in absence of humic material under these conditions. Differences were found for the U(VI) sorption onto humic substances - kaolinite sorbates with various contents on organic carbon. In addition to that, the U(VI) sorption onto M42-KS differs from that observed in the ternary model system U(VI) – kaolinite - humic acid M42. Probably, these dissimilarities are due to a different composition of the humic materials resulting in different functionalities of the humic substances. These can effect a varying interaction behavior in the system U(VI) - humic substance – kaolinite. Our results indicate that the release of humic materials from natural clays can play an important role for the mobilization of U(VI).

[1] Křepelova, A. et al., In: Forschungszentrum Rossendorf, Wissenschaftlich-Technische Berichte, FZR-419, Rossendorf 2005, p. 50.
[2] Pompe, S. et al., Radiochim. Acta 74, 135 (1996).
Keywords: Humic substances, humic acid, clay, kaolinite, uranium(VI), uranium, sorption
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 46-46
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7722 - Permalink


Investigation of gettering effects in CZ-silicon with SIMS
Krecar, D.; Fuchs, M.; Kögler, R.; Hutter, H.;
Abstract:
The ion implantation is a well-known standard procedure in electronic device technology for precise and controlled introduction of dopants into silicon. Damages caused by implantation act as effective gettering zones, collecting unwanted metal impurities. In this work, the consequences of high-energy ion implantation into silicon and of subsequently annealing were analysed by means of secondary ion mass spectrometry (SIMS). The differences in impurities gettering behaviour were studied in dependence of the implantation dose and annealing time at T = 900 degrees C.
Keywords: Ion implantation, silicon, phosphorus, gettering, Rp-effect, trans-Rp-effect, SIMS

Publ.-Id: 7721 - Permalink


SIMS investigation of gettering centres produced by phosphorus MeV ion implantation.
Krecar, D.; Fuchs, M.; Kögler, R.; Hutter, H.;
Damage caused by ion implantation act as effective gettering region, collecting unwanted metal impurities. In this study the consequences of high-energy ion implantation into silicon and subsequent annealing were analysed by means of secondary ion mass spectrometry (SIMS). The differences in impurity gettering behaviour were studied in dependence of the implantation dose and annealing time at T= 900oC.
Keywords: ion implantation, silicon, metal impurities, secondary ion mass spectrometry, SIMS
  • Contribution to proceedings
    13th Applied Surface Analysis Workshop, AOFA 13(2004), 30.09.2004, Dresden, Deutschland
  • Applied Surface Science 252(2005)1, 278-281

Publ.-Id: 7720 - Permalink


Influence of Humic Acid on U(VI) Sorption Onto Kaolinite Studied by TRLFS and EXAFS
Krepelova, A.; Sachs, S.; Reich, T.; Roßberg, A.; Brendler, V.; Baumann, N.; Bernhard, G.;
Understanding the migration behavior of actinides is important for the reliable long-term risk assessment of potential nuclear waste repositories. Depending on geochemical conditions different materials and processes can influence the behavior of such pollutants in natural aquifer systems. Humic acids (HA) comprise an important part of natural organic materials. HA are soluble in the pH range of natural waters and have the ability for complex and colloid formation. Due to these properties HA can affect the speciation of actinide ions, and therefore, their migration in the environment. In the present study we investigated the influence of HA on the U(VI) sorption onto kaolinite.
Results from our previous batch experiments were combined with spectroscopic measurements to obtain molecular-level information on the interaction of U(VI) with HA and kaolinite (KGa-1b) in natural systems.
From our batch experiments resulted that the sorption of U(VI) on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 presence and HA concentration. HA affects 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 due to the formation of 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 because of 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. Possibly, ternary U(VI)-humate complexes, e.g. uranyl-carbonato-humate complexes, are formed, which can interact with the kaolinite surface and therefore, enhance the U(VI) sorption onto kaolinite in the presence of HA in this pH region.
We used time-resolved laser-induced fluorescence spectroscopy (TRLFS) in order to characterize the species of U(VI) adsorbed onto kaolinite in the absence and presence of HA. Two adsorbed U(VI) surface species on kaolinite were identified in the pH range of pH 5.0 to pH 8.5. No EXAFS was measured in the system U(VI)-HA-kaolinite, therefore we performed also EXAFS measurements under different experimental conditions with U(VI)-HA-kaolinite sorbates in order to improve the knowledge about the surface complexes of U(VI). Results of the spectroscopic measurements are interpreted and compared with the results in the binary system without HA [1] to study the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes. Obtained results help to improve the understanding of the geochemical interactions of hexavalent actinides in environment.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.
Keywords: EXAFS, TRLFS, Humic Acid, Uranium, Sorption, Kaolinite
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 45-45
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Marianske Lazne, Czech Republic

Publ.-Id: 7719 - Permalink


Migration of Caesium in Bentonite: Influence of the Pore Water Composition
Brockmann, S.; Mibus, J.; Nebelung, C.;
The transferability of empirical distribution coefficients (KD) derived from batch sorption experiments to compacted systems is evaluated in this study. Sorption pa-rameters of Cs+ on bentonite (Wyoming type MX-80) were studied at different dry bulk densities of the clay (1.3, 1.6, 1.9 g/cm3) in both batch tests and diffusion ex-periments. Here, an innovative approach developed at Paul Scherrer Institute (CH) was used for modelling the pore water composition of the compacted clay [1]. The obtained parameters shall be used for long-term prognoses of diffusion processes in the near-field of final repositories of nuclear waste.
The KD values derived from batch and diffusion tests, respectively, differ by ap-proximately 20 to 40 %. This result is acceptable, when taking into consideration the experimental uncertainties of both methods. The use of batch derived KD’s to de-scribe the migration behaviour of Cs+ can be recommended, provided that an ade-quate pore water composition is used.
In contrast, the effective diffusion coefficients (De) of Cs+ in compacted ben-tonite exceed the De’s of tritiated water (HTO) significantly. This effect is attributed to a phenomenon described in the literature as “surface diffusion” indicating an addi-tional diffusive flux of adsorbed species.
Hence, the combination of diffusion coefficients of HTO and batch derived KD’s systematically underestimates the diffusive flux of Cs+. In order to implement this ap-proach in the future, the surface diffusion phenomenon has to be elucidated by ad-vanced spectroscopic methods and to be quantified.
Deviations in the KD are only related to the transient state of the diffusion proc-ess. Thus, they influence the initial state of the transport process. The batch derived KD’s are transferable to the compacted system. However, the use of an adequate diffusion coefficient De is of extreme importance for any prediction of long-term pre-dictions in risk assessment.
Keywords: cesium, bentonite, pore water, sorption, diffusion
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 50-50
  • Poster
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7718 - Permalink


Simulation of condensation in a sub-cooled bubbly steam-water flow along a large vertical pipe
Lucas, D.; Prasser, H.-M.;
Detailed experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into sub-cooled water and condenses during the upwards flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process is clearly slower, if large bubbles are injected (4 mm holes). Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some unsureness arises from the unknown interfacial area for large bubbles and possible uncertainties of the heat transfer coefficient.
Keywords: bubbly flow, phase transfer, bubble size distribution, vertical pipe
  • Open Access LogoArchives of Thermodynamics 26(2005)4, 49-59

Publ.-Id: 7717 - Permalink


Migration of Uranium(VI) in a Phosphate Environment: Column Experiments and Modeling
Mibus, J.; Brendler, V.; Pfingsten, W.;
The ability of hydroxyapatite Ca10(OH)2(PO4)6 (HAP) to immobilize metal ions, particularly lanthanides and actinides, is well known. The long-term stability of this fixation is proven by natural analogue studies. Thus, HAP is a potential filling material in engineered barriers in abandoned mining areas as well as in the near-field of un-derground repositories for nuclear and toxic waste.
The interaction of U(VI) with HAP was studied in batch and unsaturated column experiments and by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We investigated a seepage water from Schlema (Saxony) with a uranium concentra-tion of 10-5 M and a synthetic HAP packed in a matrix of purified quartz sand.
In common batch sorption experiments, a strong interaction of uranium with the HAP surface was observed. The sorption of uranyl ions onto phosphate groups is eventually as important as their sorption onto silanol groups, outweighing the low phosphate content. From the interpretation of the TRLFS spectra, two surface spe-cies could be distinguished. On the basis of their fluorescence decay time and the shift of the peak maxima related to the free uranyl ion, these two species could be associated with uranium adsorbed to phosphate and silanol surface groups, respec-tively.
The breakthrough curves (BTC’s), measured at different vertical positions of the column, exhibit a strong retardation of uranium compared to the conservative tracer. The breakthrough (i.e., exceeding 50 % of the starting concentration) occurs after about 30 pore volumes. However, the elution part of the BTC’s features a pro-nounced tailing. The release of uranium is controlled by two processes of different rates. We assign the faster sorption/desorption scheme to the uranyl silanol surface species, exhibiting an almost full reversibility. The second observed process creating the long and pronounced tailing in the BTC’s can be explained by the much stronger binding of the uranyl moiety to the phosphate sites.
Keywords: uranium, hydroxy apatite, sorption, transport, modeling
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 238-238
  • Poster
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7716 - Permalink


Evidence for In-Medium Changes of Four-Quark Condensates
Thomas, R.; Zschocke, S.; Kämpfer, B.;
Utilizing the QCD sum rule approach to the behavior of the omega meson in nuclear matter we derive evidence for in-medium changes of particular four-quark condensates from the recent CB-TAPS experiment for the reaction gamma + A -> A' + omega (-> pi0 gamma) with A = Nb and LH2.
Keywords: In-Medium Modifications, QCD Sum Rules, Chiral Symmetry, Four-Quark Condensates

Publ.-Id: 7715 - Permalink


Atomistic computer simulation of ion implantation, ion-beam-induced defect formation and defect migration
Posselt, M.;
Ion implantation and subsequent thermal annealing are the standard processes for the electrical doping of semiconductors. Ion implantation is characterized by fast ballistic processes which lead to the deposition of the implanted atoms and to displacements of the target atoms. After the fast relaxation of the displaced atoms a (meta)stable defect structure is formed. Long-term thermally activated processes, especially during thermal annealing, cause defect reduction, rearrangement, and migration. In my talk I will show that computer simulations on the atomic level are a useful tool for the theoretical description of the different physical processes occurring during ion implantation and thermal annealing. The ballistic processes are simulated by the Crystal-TRIM code which is based on the binary collision approximation (BCA). This code is part of different process simulators. Classical molecular dynamics (MD) simulations are employed to investigate defect migration over a period of 10 - 100 ns. The defect diffusivity as well as the microscopic migration mechanisms are studied. A combination of BCA and MD simulations is used to determine the complex defect morphology after the fast relaxation processes are finished. This method allows the effective calculation of the total number and the depth distribution of different defect species (e.g. isolated vacancies and self-interstitials as well as more complex defects) formed on average per incident ion.
Keywords: computer simulation, implantation, defects, Si
  • Lecture (others)
    eingeladener Vortrag am CEA-LETI, 11.10.2005, Grenoble, France

Publ.-Id: 7713 - Permalink


Modelling of in-vessel retention after relocation of corium into the lower plenum
Altstadt, E.; Willschuetz, H.-G.; Sehgal, B. R.; Weiss, F.-P.;
Considering the unlikely 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. Worldwide several experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work.
At the Institute of Safety Research of the FZR a finite element model has been de-veloped simulating the thermal processes and the viscoplastic behaviour of the ves-sel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal and the mechanical calculations are sequentially and recursively coupled. The model is capable of evalu-ating 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 se-ries representing the lower head RPV of a PWR in the geometrical scale of 1:10. These experiments were performed at the Royal Institute of Technology in Stock-holm. The results of the calculations can be summarised as follows:

• The creeping process is caused by the simultaneous presence of high tem-perature (>600 °C) and pressure (>1 MPa)
• The hot focus region is the most endangered zone exhibiting the highest creep strain rates.
• The exact level of temperature and pressure has an influence on the vessel failure time but not on the failure position
• The failure time can be predicted with an uncertainty of 20 to 25%. This uncer-tainty is caused by the large scatter and the high temperature sensitivity of the viscoplastic properties of the RPV steel.
• Contrary to the hot focus region, the lower centre of the vessel head exhibits a higher strength because of the lower temperatures in this zone. The lower part moves down without significant deformation. Therefore it can be assumed, that the vessel failure can be retarded or prevented by supporting this range.
• The development of a gap between melt crust and vessel wall could not be proofed.

First calculations for a PWR geometry were performed to work out differences and commonalities between prototypic scenarios and scaled experiments. The results of the FOREVER-experiments cannot be transferred directly to PWR geometry. The geometrical, mechanical and thermal relations cannot be scaled in the same way. Because of the significantly higher temperature level, a partial ablation of the vessel wall has to be to expected in the PWR scenario, which is not the case in the FOREVER tests. But nevertheless the FOREVER tests are the only integral in-vessel retention experiments up to now and they led to a number of important insights about the behaviour of a vessel under the loading of a melt pool and pressure.
Keywords: In-vessel retention, Reactor pressure vessel, Core melt down accident, Creep, Damage, ECCM, FEM
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-437 2005

Downloads:

Publ.-Id: 7712 - Permalink


Einfluss von Huminsäure auf die Np(V)-Sorption an Kaolinit
Schmeide, K.;
Die Np(V)-Sorption an Kaolinit in Abwesenheit und Gegenwart von Huminsäure wird mittels Batch-Experimenten untersucht.
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Migration von Actiniden im System Ton, Huminstoff, Aquifer", 04.-05.10.2005, Leipzig, Germany

Publ.-Id: 7711 - Permalink


CORPHAD and METCOR ISTC projects
Bechta, S. V.; Khabensky, V. B.; Granovsky, V. S.; Kroushinov, E. V.; Vitol, S. A.; Gusarov, V. V.; Almiashev, V. I.; Mezentseva, L. P.; Petrov, Y. B.; Lopukh, D. B.; Fischer, M.; Bottomley, D.; Tromm, W.; Barrachin, M.; Altstadt, E.; Piluso, P.; Fichot, F.; Hellmann, S.; Defoort, F.;
The ongoing CORPHAD Project (Phase Diagrams for Multicomponent Systems Containing Corium and Products of its Interaction with NPP Materials) started in August 2001. The main aim of the project is to experimentally determine the relevant physicochemical data on phase diagrams of binary, ternary, quaternary and prototypic multi-component systems, which are important for analysis and modelling of a severe accident (SA) and efficient planning of severe accident management (SAM) measures. The data should be directly used for the European NUCLEA database development and validation. The following systems are in the focus of the project: (1) UO2 – FeO, (2) ZrO2 – FeO, (3) SiO2– Fe2O3, (4) UO2 – SiO2, (5) UO2 – ZrO2-FeO, (6) UO2 – ZrO2-FeOy, (7) U-O-Fe, (8) Zr-O-Fe, (9) U-O-Zr, (10) U-Zr-Fe-O, (11) complex corium mixtures.
The experimentally determined data of the listed diagrams include: coordinates of characteristic points (eutectics, peritectics and others); liquidus and solidus concentration curves; component solubility limits in the solid phase; tie line coordinates and temperature-concentration regions of the miscibility gap. Different methodologies are used for the phase diagram study. Classical methods of thermal analysis, like DTA and DSC are combined with methods specifically developed for corium studies.
The METCOR project (Investigation of Corium Melt Interaction with NPP Reactor Vessel Steel) started in April 1999. The objectives of the project are to qualify and to quantify physico-chemical phenomena of corium melt interaction with reactor vessel steel cooled from the outside. The variable parameters of the interaction tests are: oxygen potential in the system, corium composition, interaction interface temperature and heat flux from corium to steel. The medium scale tests with corium mass of about 2 kg are carried out by using high-frequency induction heating of the corium melt in a cold crucible.
The METCOR&CORPHAD work-packages are performed by Russian partners in close collaboration with leading European scientific institutes in the area of corium research as well as with the European nuclear industry.
This paper briefly describes the results obtained in both projects and their possible application for SA analysis and SAM. The paper concludes with recommendations for future research activities in the frame of METCOR and CORPHAD projects.
Keywords: Corium, Phase diagram, Corium-structure interaction, Reactor vessel steel
  • Contribution to proceedings
    ERMSAR 2005, 14.-16.11.2005, Aix en Provence, France

Publ.-Id: 7710 - Permalink


Vessel rupture: Synthesis of the FOREVER interpretation activity
Altstadt, E.; Willschütz, H.-G.; Sehgal, B. R.; Weiß, F.-P.;
At FZR an integral axisymmetric finite element model has been developed for simulat-ing the late phase of core melt down scenarios in a RPV. The model allows for the calculation of the failure time and the failure mode of a vessel with a heated melt pool. In the thermal submodel the transient temperature field of the melt and of the vessel wall is evaluated. This can be done either with a CFD model or with the Effective Conduction Convection Model (ECCM). Within the mechanical submodel the viscoplastic deformation of the vessel wall is simulated. By use of the material damage the failure time and position can be deter-mined. An additional mechanical submodel is used to evaluate the melt pool deformation. The thermal and the mechanical submodels are recursively and sequentially coupled, i.e. for each time step a thermal dynamic and a mechanical solution is calculated considering a mutual feedback. Besides of the temperature dependence of the material parameters and the thermally induced stresses, which are considered in the mechanical model, also the consequences of the vessel deformation for the temperature calculation are included (change of melt pool geometry, melt level drop, change of heat resistance of the vessel wall through thickness reduction, increase of the effective surface for heat radiation and convection). For the mechanical model a creep data base has been developed based on experimental results of projects of the 4th frame work programme of the EU. The viscoplastic calculation is coupled with the material damage. The creep data base was validated using two pipe rupture experiments. The coupled model for vessel failure was for pre- and post test calculations of the FOREVER experiments performed at the KTH Stockholm. In general, a good agreement of the calculation and the experimental results could be achieved. The FE model can be considered as validated for medium scaled vessel tests. Some sensitivity studies are done to evaluate the influence of the design peculi-arities of the FOREVER experiments in comparison with the prototypic scenarios.
Keywords: In-vessel retention, Reactor pressure vessel, Finite element model, Creep, Damage, Effective conduction convection model
  • Contribution to proceedings
    ERMSAR 2005, 14.-16.11.2005, Aix en Provence, France
  • Lecture (Conference)
    ERMSAR 2005, 14.-16.11.2005, Aix en Provence, France

Publ.-Id: 7709 - Permalink


Ripple structure of ion beam induced Si wafers
Pietsch, U.; Grenzer, J.; Hazra, S.; Chini, T. K.; Sanyal, M. K.;
Ion beam induced ripple formation in Si wafers was studied by atomic force microscopy (AFM) and non-destructive depth-resolved x-ray grazing incidence diffraction (GID). The formation of ripple structure at high doses (7x1017 ions/cm2), starting from initiation at low doses (1x1017 ions/cm2) of ion beam is evident from AFM, while that in the buried crystalline region below a partially crystalline top layer is evident from GID study. The GID technique reveals that these periodically modulated wave-like buried crystalline features become highly regular and strongly correlated as one increases the Ar ion beam energy from 60 keV to 100 keV. The vertical density profile obtained from the analysis of Vineyard profile shows that the density in the upper top part of ripples is decreased to about 15% of the crystalline density. The partially crystalline top layer at low dose, transforms to a completely amorphous layer for high doses and the top morphology was found to be conformal with the underlying crystalline ripple. Inspection of the amorphous scattering shows that the amorphous form factor of the damaged top layer is strongly textured in azimuth and scales with the ion dose.
Keywords: ion beam errosion, grazing incidence diffraction
  • Lecture (Conference)
    IUCr2005 XX Congress of the International Union of Crystallography, 23.-31.08.2005, Florence, Italy

Publ.-Id: 7708 - Permalink


Grazing-incidence Diffraction and Small angle X-ray scattering
Grenzer, J.;
X-ray grazing incidence diffraction and small angle scattering are a scattering method which combines out-of plane reflectivity under the condition of X-ray total external reflection with in-plane Bragg diffraction and small angle scattering, respectively. The formation of an evanescent wave propagating parallel but close below the sample surface opens the possibility to probe structures at a sample surfaces or close below it.
Keywords: x-ray granzing incidence diffraction, grazing incidence small angle scattering
  • Invited lecture (Conferences)
    6th Autumn School on X-ray scattering from surfaces and thin layers, 18.-21.09.2005, Smolenice, Slovenia

Publ.-Id: 7707 - Permalink


X-ray investigation of focused ion-beam induced semiconductor surfaces - How to make a lateral nanostructure
Grenzer, J.; Bischoff, L.; Pietsch, U.;
We report on the strain and defect analysis of lateral nanostructures created in Ga and Si substrates which was performed utilizing the method of X-ray grazing-incidence diffraction. The substrates were patterned by focused ion beam implantation technique using a Ga or AuGeSi liquid metal ion source.
Keywords: ion beam implantation, grazing incidence diffrtaction
  • Lecture (Conference)
    348. WE-Heraeus-Seminar, Ions at Surfaces: Patterns and Processes, 19.-23.06.2005, Bad Honnef, Germany

Publ.-Id: 7706 - Permalink


X-ray investigation of low-energy ion-beam induced lateral surface nanostructures on semiconductor surfaces
Grenzer, J.; Hazra, S.; Chini, T. K.; Bischoff, L.; Pietsch, U.; Sanyal, M. K.;
Low energy ion beams are widely used to alter the surface properties of semiconductors. We have used two different ways to create lateral nanostructures, either using an artificial patterning by a focused ion beam or by a tilted non-focused ion beam achieving a self-organizing ripple formation. X-ray grazing-incidence diffraction is a powerful tool to investigate such lateral nano-structures. Choosing the angle of incidence smaller or slightly larger as the critical angle of total external reflection one can probe the fine structure of an in-plane Bragg diffraction in a depth between about 5 to several 100 nm.
Keywords: ion beam implantation, ion beam errosion, x-ray diffraction
  • Invited lecture (Conferences)
    IUMRS ICA2004, 16.-18.11.2004, Hsinchu, Taiwan

Publ.-Id: 7705 - Permalink


Depth resolved strainanalysis of lateral nanostrucutres by x-ray grazing incidence diffraction
Grenzer, J.;
Quantum well semiconductor heterostructures are increasingly important systems in the development of smaller, faster and more efficient electronic and optoelectronic devices. One way to modify the electronic band structure is to exploit quantum size effects requiring device engineering on a nanometer length scale. In particular, the lateral patterning of a strained stressor layer allows to achieve a lateral carrier confinement in a buried single quantum well as a result of the strain relaxation. The strain relaxation at free surfaces of the stressor layer induces a lateral inhomogeneous strain distribution and subsequently a lateral change of the optical properties within the single SQW. To exploit this effect in a device the structure has to be planarized by a second epitaxial step. The lateral carrier confinement of the initially free standing nanostructure can almost be maintained using a two step overgrowth process. The layout of the lateral nano structure (layer thicknesses and composition, shape) is predicted by finite element calculations of the strain distribution. The achieved optical properties are measured by photoluminescence; the strain field is probed by X-ray grazing-incidence diffraction.
Keywords: x-ray diffraction
  • Lecture (others)
    eingeladener Vortrag am Institut für experimentelle Physik, 11.05.2005, Warschau, Polen

Publ.-Id: 7704 - Permalink


A modified rf ion source with a ceramic bottle
Friedrich, M.;
The generation of negative He ions for acceleration at tandem accelerators requires an ion source with alkali vapor charge exchange canal. The diffusion of the Li or Rb vapor into the surrounding vacuum chamber limits the operation time of the ion source and increases the necessary maintenance. On the other hand, the modified rf ion source at the Rossendorf single ended 2 MV Van de Graaff accelerator has a life time of some thousands hours. The installation of this ion source inside the terminal of the Rossendorf 5 MV tandem accelerator would allow high-energy implantation of He ions in the energy range of 1-5 MeV without the difficulties of the charge-exchange canal. To reduce the risk for breaking of the ion source glass bottle under the pressure of the insulating gas a ceramic source bottle has been tested. First results of its operation at the 2 MV VdG are presented.
Keywords: Ion sources, Electrostatic accelerators, Helium ions
  • Lecture (Conference)
    39th Symposium of Northeastern Accelerator Personnel (SNEAP), 16.-20.10.2005, Port Jefferson, USA

Publ.-Id: 7703 - Permalink


Investigation of WWER RPV steel and cladding from Greifswald NPP
Rindelhardt, U.; Konheiser, J.; Viehrig, H.-W.;
The investigation of the well documented different irradiation/annealing states of the four former NPP Greifswald units are a special advantage to assess the reactor pressure vessel integrity and to check the corresponding rules and codes.
The results of new, more accurate calculations of the neutron fluence will be given. Further, the change of the RPV dismantling strategy required a new approach for the trepanning procedure. The new procedure will be shortly described and the cold test results of the new developed drilling machine are shown. Finally some aspects of the material investigation program are discussed.
Keywords: RPV steel, embrittlement, NPP Greifswald
  • Invited lecture (Conferences)
    IAEA-Workshop “Improved Reactor Pressure Vessels (RPV) Structural Integrity Assessment for NPPs”, 18.-21.10.2005, Madrid, Spain

Publ.-Id: 7702 - Permalink


Die Erholung der sächsischen Talsperrenökosysteme von der atmosphärischen Versauerung im Vergleich zu hydrochemischen Trends im Einzugsgebiet der Talsperre Kleine Kinzig (Nordschwarzwald)
Ulrich, K.-U.; Meybohm, A.; Hoehn, E.;
Aufgrund des enormen Ausstoßes an Schwefeldioxid und Stickoxiden sowie des basenarmen Grundgesteins von Erzgebirge und Vogtland litten zahlreiche sächsische Staugewässer etwa seit Mitte der 1960er Jahre unter der atmosphärischen Versauerung. Dies betraf auch einige Trink¬wassertalsperren. Nach der Wiedervereinigung wurden weder Kosten noch Aufwand gescheut, um geeignete Technologien zur Aufbereitung des weichen, sauren Rohwassers zu entwickeln, die Wasserwerke zu modernisieren und auf die Einhaltung der geforderten Grenzwerte einzustellen.
Innerhalb des letzten Jahrzehnts verringerten sich die Schwefeldioxid-Emissionen beträchtlich. Der Literatur zufolge gibt es große regionale Unterschiede bei der Erholung der Oberflächengewässer von der atmosphärischen Versauerung. Entsprechende Trends sind in vielen deutschen Mittelgebirgen nur schwach ausgeprägt oder überhaupt nicht nachweisbar. Dies begründet die Motivation, den Datenbestand der Landestalsperrenverwaltung Sachsen am Beispiel von sieben versauerten Talsperren und 22 Zuflüssen hinsichtlich der Trends ausge¬wählter hydrochemischer Parameter für 11 Jahre (1993-2003) mit dem Saisonalen Mann-Kendall Test statistisch auszuwerten und mit anderen Regionen zu vergleichen. Beispielsweise stehen im Nordschwarzwald für die Zuflüsse der Trinkwassertalsperre Kleine Kinzig entsprechende Datensätze aus den Jahren 1989 bis 2003 zur Verfügung.
Der Vortrag stellt die charakteristischen Trends im Zusammenhang mit der regionalen Entwicklung der Emissions- und Depositionssituation und vor dem Hintergrund forstlicher Bodenschutzkalkung dar. Als Hauptfaktor für den in 85% der untersuchten sächsischen Gewässer signifikanten Konzentrationsrückgang von Protonen und Sulfat wird die Abnahme der Depositionsraten um mindestens Faktor 3 angesehen. In etwa 20% der Gewässer, bei denen die insgesamt applizierte Dolomitdosis im Einzugsgebiet 7 t ha-1 überschritt, fanden sich steigende Trends der Calcium- und/oder Magnesiumkonzentration, die jedoch nicht signifikant waren. Der direkte Beitrag der Bodenschutzkalkung zur Entsäuerung und nachhaltigen Erhöhung des Pufferungsvermögens der Oberflächengewässer wird als relativ gering eingeschätzt. Der starke Konzentrationsrückgang von Protonen und damit einhergehend von toxischen Aluminiumver¬bindungen bildet die Grundlage für eine Wiederbesiedelung der Gewässer durch säure¬empfindliche Organismen. Veränderungen in der Dominanzstruktur des Phytoplanktons gab es bereits in mehreren Talsperren im Vogtland. Dort hat sich auch gezeigt, dass mit dem Auftreten einer planktivoren Fischart extreme Schwankungen im Bestand bis hin zu Massensterben durch zeitweise Erschöpfung der Nahrungsressourcen einhergehen. Die Räuber-Beute-Effekte sowie episodisch auftretende Säureschübe können die Etablierung von größerer planktischer Filtrierer (z.B. Daphnien) stark verzögern.
  • Invited lecture (Conferences)
    15. Limnologisches Gespräch des Zweckverbandes Wasserversorgung Kleine Kinzig (WKK), 20.10.2005, Alpirsbach-Reinerzau, Germany

Publ.-Id: 7701 - Permalink


Perturbation theory for non-selfadjoint operator matrices and its application to the MHD α²-dynamo
Günther, U.; Kirillov, O.;
We consider singular boundary value problems for linear non-selfadjoint m-th order N×N matrix differential operators on the interval (0,1]∋ x. The coefficient matrices in the differential expressions and the matrix boundary conditions are assumed to depend on the spectral parameter λ as well as on a vector-valued parameter distribution p(x). For simplicity, we restrict our attention to setups with a (boundary) singular point (x=0) of regular (Fuchsian) type.

Based on a bi-orthogonal solution ansatz, we study perturbations of simple and multiple eigenvalues under small variations of the parameter distribution p(x). Special attention is paid to perturbations of semi-simple multiple eigenvalues (diabolical points; characterized by coinciding geometric and algebraic multiplicity and corresponding diagonal spectral decomposition of the operator) as well as to perturbations of non-derogatory eigenvalues (branch points, exceptional points; with non-trivial Jordan structures in the spectral decomposition) with one eigenvector (geometric multiplicity one) and several associated vectors forming a Keldysh chain of length equal to the algebraic multiplicity of the eigenvalue. Explicit formulae describing the bifurcation of the eigenvalues are derived.

As application, the general technique is utilized for the investigation of the spectral properties of spherically symmetric MHD α²-dynamos. Specifically, we provide an analytical description for the occurrence of spectral branch points under transitions from idealized boundary conditions to physically realistic boundary conditions. Furthermore, we develop a gradient technique with respect to the α-profile α(x) of the dynamo which allows us to search for most efficient α-perturbations to trigger magnetic field reversals.
Keywords: non-selfadjoint matrix differential operators, singular boundary value problems, perturbation theory, spectral analysis, spectral bifurcations, branch points, diabolical points, exceptional points, magnetohydrodynamics, dynamo theory
  • Lecture (Conference)
    4th International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 23.-25.11.2005, Stellenbosch, South Africa

Publ.-Id: 7700 - Permalink


Bundle stratification of PT-symmetric 4×4 matrix systems and fourth-order spectral branch points of MHD α²-dynamos
Günther, U.; Kirillov, O.; Stefani, F.;
The spectra of PT-symmetric quantum systems are, in general, highly complicated complex varieties over the parameter spaces of these systems. Parameter space regions of exact PT-symmetry with purely real eigenvalues adjoin other regions with broken PT-symmetry and pairwise complex conjugate eigenvalues. The boundaries between different regions correspond to (exceptional) hypersurfaces in the parameter space and have certain system defined codimensions. Hypersurfaces (strata) of lower codimension may intersect at sub-hypersurfaces (sub-strata) of higher codimension forming in this way a hierarchical structure of dimensionally nested hypersurfaces of increasing codimension (and increasing "exceptionality"), i.e. they form a so called stratified manifold.

In case of matrix systems, the most general parameter space can be identified with the matrix space itself. Endowing this space with a natural fiber bundle structure, regarding matrix orbits (equivalence classes) over a given Jordan structure as fibers, the hierarchical hypersurface structure of the spectral variety can be studied with the help of nested Jordan structures. As result, one arrives at a so called bundle stratification.

We perform such a bundle stratification explicitly for a PT-symmetric 4×4 matrix systems and use the obtained results to comparatively analyze the spectral structure of the spherically symmetric α²-dynamo of magnetohydrodynamics in the vicinity of a fourth-order branch point.
Keywords: non-selfadjoint operators, spectral theory, branch points, exceptional points, fiber bundles, stratification, PT-symmetric quantum mechanics, magnetohydrodynamics, dynamo theory
  • Lecture (Conference)
    4th International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 23.-25.11.2005, Stellenbosch, South Africa

Publ.-Id: 7699 - Permalink


High-speed complex admittance/permittivity needle probe for investigation of multiphase flows
Da Silva, M. J.; Brückner, F.; Schleicher, E.; Hampel, U.;
For the investigation of three- or multiphase flows, which are of interest for instance in the chemical engineering or in oil extraction and processing, there are only few suitable measuring techniques. For this reason we have developed a high-speed complex admittance/permittivity needle probe. Such probes are able to distinguish the different phases or components of a flow by measuring the complex value of the electrical admittance/permittivity at a high data rate (up to 10,000 samples/s). The performance of the system as well as its ability to differentiate some organic substances has been analyzed. A preliminary time resolved experiment in a gasoline-air-water flow is also presented.
Keywords: needle probe, admittance measurement, permittivity measurement, multiphase flow
  • Contribution to proceedings
    23rd IEEE Instrumentation and Measurement Technology Conference, 24.-27.04.2006, Sorrento, Italy
    Proceedings, 0-7803-9360-0, 1937-1941
  • Lecture (Conference)
    IEEE Instrumentation and Measurement Technology Conference, 24.-27.04.2006, Sorrento, Italy

Downloads:

Publ.-Id: 7698 - Permalink


Influence of Mg, Ca, Sr and Ba on formation of geochemical relevant uranyl species
Geipel, G.;
The uranyl tricarbonato complex is one of the most important uranyl species under environmental conditions. The tendency to form stable metal-uranyl tricarbonato complexes was found particularly for the interaction with alkaline earth elements. However, under comparable chemical conditions the formation of these complexes is very different. While magnesium tends mainly to the formation of a MgUO2(CO3)32+ - complex, in the case of calcium the Ca2UO2(CO3)3(aq.) complex is the most stable and the formation of the CaUO2(CO3)32+ - complex is very limited. In the corresponding systems with strontium as well as for barium only the MeUO2(CO3)32+ - complex is formed. The stability constants of the MeUO2(CO3)32+ - complexes increase in the series Mg, Ca , Sr and Ba. The formation of Me2UO2(CO3)3 – complexes for Mg, Sr and Ba occurs only in a small concentration range and the formed complexes tends to precipitate. The Me2UO2(CO3)3 – complexes for Mg and Ca form stable minerals as bayleyite and liebigite. However several other mineral modifications as zellerite, fontanite, sharpite and rabbittite underline the geochemical importance of this class of compounds.
Analogous phenomena can be expected in the alkaline earth uranyl phosphate systems and results for the formation of species of the type Mex(UO2PO4)y will be presented.
Keywords: Uranium, TRLFS, minerals, complex formation
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 36-36
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7697 - Permalink


Atomistic study of the mobility of small interstitial clusters in silicon
Posselt, M.; Gao, F.;
In this work a comprehensive atomistic study is performed in order to get a better understanding of the mechanisms of di- and tri-interstitial diffusion at different temperatures and to obtain more data for their diffusivities and migration barriers. A classical potential approach is employed since it allows the investigation of defect migration under relatively realistic conditions, by considering a large computational cell, a very long simulation time, and different initial conditions. In order to test the potential employed, at first the structure and energetics of di- and tri-interstitials are determined and the results are compared with the data obtained by tight-binding and density-functional-theory calculations.
The migration of mono-, di- and tri-interstitials is investigated for temperatures between 800 and 1600 K. The defect diffusivity, the self-diffusion coefficient per defect and the corresponding effective migration barriers are calculated. Compared to the mono-interstitial, the di-interstitial migrates faster, whereas the tri-interstitial diffuses slower. The mobility of the di- and the mono-interstitial is higher than the mobility of the lattice atoms during the diffusion of these defects. On the other hand, the tri-interstitial mobility is lower than the corresponding atomic mobility. The migration mechanism of the di-interstitial shows a pronounced dependence on the temperature. At low temperature a high mobility on zigzag-like lines along a <110> axis within a {110} plane is found, whereas the change between equivalent <110> directions or equivalent {110} planes occurs seldom and requires a long time. At high temperature a frequent change between equivalent <110> directions or {110} planes is observed. During the diffusion within {110} planes the di-interstitial moves like a wave packet so that the atomic mobility is lower than that of the defect. On the other hand, the change between equivalent {110} migration planes is characterized by frequent atomic rearrangements. The visual analysis of the tri-interstitial diffusion reveals complex migration mechanisms and a high atomic mobility. The implications of the present results for the explanation of experimental data on defect evolution and migration are discussed.

[1] P. Pichler, D. Stiebel, Nucl. Instr. Meth. B 186 (2002) 256.
[2] M. J. Caturla, T. Diaz de la Rubia, L. A. Marques, G. H. Gilmer, Phys. Rev. B 54 (1996) 16683.
[3] M. Posselt, Mater. Res. Soc. Symp. Proc. 647 (2001) O2.1.1.
[4] G. H. Gilmer, T. Diaz de la Rubia, D. M. Stock, M. Jaraiz, Nucl. Instr. Meth. B 102 (1995) 247.
[5] S. K. Estreicher, M. Gharaibeh, P. A. Fedders, P. Ordejon, Phys. Rev. Lett. 86 (2001) 1247.
Keywords: Si, intrinsic defects, diffusion, simulations
  • Poster
    11th Int. Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technology (GADEST), 25.-30.09.2005, Giens, France

Publ.-Id: 7696 - Permalink


A modified concerted exchange mechanism for antisite pair recombination in cubic and hexagonal silicon carbide
Posselt, M.; Gao, F.;
The antisite pair is one of the defect species which can be formed during ion beam processing of SiC. It consists of two neighboring atoms on “wrong” lattice sites, namely a Si atom on a C site and a C atom on a Si site. In general the experimental analysis of the different defect types formed during ion irradiation is difficult. Theoretical investigations on defect kinetics and defect evolution can be therefore very helpful to interpret the results of the annealing experiments with the irradiated samples. The antisite pair could not yet be identified unambiguously by experimental methods. Recently, the DI low temperature photoluminescence (PL) center has been correlated with the antisite pair [1]. In that theoretical work it is assumed that the antisite pair is stable up to a temperature of 2000 K. However, the thermal stability of the antisite pair has not yet been investigated. To our knowledge, there is only one work that is related to this topic [2]. Based on Pandey’s concerted exchange originally proposed for silicon [3], the antisite pair formation is studied by static potential energy calculations.

This work shows results of a systematic atomistic study on the thermal stabilty of the antisite pair and on the mechanisms of recombination in cubic (3C) and hexagonal (4H) SiC. At first the structure and energetics of the antisite pair is determined for T = 0 K. The results are compared with literature data which were obtained by the density-functional theory (DFT). The comparison shows that the interatomic potential used in the atomistic simulations yields reasonable data. The thermal stability of the antisite pair was investigated by molecular dynamics (MD) simulations at temperatures between 800 and 2500 K. Due to the statistical nature of the recombination process, it was necessary to perform several statistically independent simulations at every temperature. This was done by using different initial random numbers. The lifetime of the antisite pair was determined by different methods: (i) The evolution of the potential energy of the atoms which belong to the antisite pair and/or the potential energy of the atoms belonging to the defect and to the defect environment were analyzed. (ii) The time dependence of the recombination parameter was followed. (iii) The defect configuration was monitored visually. It is found that the thermal stability of the antisite pair is relatively low. It can be therefore not correlated with the DI low temperature PL center which is stable up to 2000 K. These results are confirmed by DFT-based MD simulations. The detailed study of the atomic rearrangements during the antisite pair recombination revealed a modified concerted exchange mechanism. Due to the different atomic sizes in SiC, this process is not identical with the concerted exchange proposed for Si [3] and considered by Rauls et al. [2] in order to explain the antisite pair formation in cubic SiC. Investigations of antisite pair recombination in hexagonal (4H) SiC yield results which are slightly different to those obtained for the cubic polytype.

[1] A. Gali, P. Deak, E. Rauls, N. T. Son, I. G. Ivanov, F. H. C. Carlsson, E. Janzen,
W. I. Choyke, Phys. Rev. B 67 (2003) 155203.
[2] E. Rauls, Z. Hajnal, A. Gali, P. Deak, T. Frauenheim, Materials Science Forum
353-356 (2001) 435.
[3] K. C. Pandey, Phys. Rev. Lett. 57 (1986) 2287.
[4] F. Cargnoni, C. Gatti, L. Colombo, Phys. Rev. B 57 (1998) 170.
[5] M. Tang, L. Colombo, J. Zhu, T. Diaz de la Rubia, Phys. Rev. B 55 (1997) 14279.
Keywords: SiC, intrinsic defects, simulations
  • Poster
    11th Int. Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technology (GADEST), 25.-30.09.2005, Giens, France

Publ.-Id: 7695 - Permalink


X-ray absorption spectroscopy - experimental possibilities and limitations
Hennig, C.;
X-ray absorption spectroscopy allows to investigate the electronic structure (XANES) and interatomic distances and coordination numbers (EXAFS) not only in solid compounds aut also in non-crystalline and liquid samples. Basic principles and limitations of the technique will be discussed. The use of NEXAFS in comparison with XPS will be demonstrated.
Keywords: XAS, XPS, EXAFS, XANES, NEXAFS, Actinides
  • Invited lecture (Conferences)
    ACTINET - Theoretical User Lab: Experiment / Theory Workshop, 24.10.2005, Karlsruhe, Germany

Publ.-Id: 7694 - Permalink


Structure investigation of actinides in solution by combining EXAFS with electrochemistry
Hennig, C.;
Natural aquatic and terrestrial environments comprise large variations in redox states. Actinides with their variable oxidation states are especially susceptible to these redox conditions. They form aqueous complexes which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their thermodynamic metastability.

Therefore, we developed a spectro-electrochemical cell to study the speciation and structure of aqueous actinide complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential. Due to the specific safety requirements for handling radioactive materials the electrochemical cell is equipped with two safety compartments and a special electrode arrangement.
  • Invited lecture (Conferences)
    eingeladener Vortrag am ITU Karlsruhe, 21.10.2005, Karlsruhe, Deutschland

Publ.-Id: 7693 - Permalink


P0503-Verfahren zur Behandlung von Halbleiter-Substratoberflächen, die mittels intensiven Lichtimpulsen kurzzeitig aufgeschmolzen werden
Voelskow, M.; Skorupa, W.; Anwand, W.;
Es soll der Vertikalaufbau der mittels der Lichtimpulsbestrahlung zu schmelzenden Oberflächenschichten so modifiziert werden, dass eine weitgehend ebene und nicht facetierte Schmelzfront erreicht wird.
  • Patent
    DE 10 2005 036 669 A1
  • Patent
    EP 06013986

Publ.-Id: 7692 - Permalink


Sättigbarer Absorber
Dekorsy, T.; Neuhaus, J.; Helm, M.;
Mit der Erfindung soll ein sättigbarer Absorber realisiert werden, der aus einer Halbleiter-Heterostrukur mit mindestens einem Quantenfilm besteht und dessen charakteristische Absorptionswellenlänge im Bereich des intraroten elektromagnetischen Spektrums liegt und abgestimmt werden kann.
  • Patent
    DE 10 2005 022 436 A1

Publ.-Id: 7691 - Permalink


P0501 - Gittersensor
Pietruske, H.; Sühnel, T.; Prasser, H.;
Es wird ein Gittersensor vorgeschlagen, welcher auch für den Einsatz bei hohen und wechselnden Temperaturen und Drücken geeignet ist.
  • Patent
    DE102005019739.6: Erteilung-26.10.2006; Nachanmeldung WO (EP,JP,US); EP (CH,DE,ES,FI,FR,GB,IT,NL.SE)

Publ.-Id: 7690 - Permalink


On the detector arrangement for in-beam PET for hadron therapy monitoring
Crespo, P.; Shakirin, G.; Enghardt, W.;
In-beam positron emission tomography (in-beam PET) is currently the only method for an in-situ monitoring of highly tumour-conformed charged hadron therapy. At the experimental carbon ion tumour therapy facility, running at the Gesellschaft fuer Schwerionenforschung, Darmstadt, Germany, all treatments have been monitored by means of a specially adapted dual-head PET scanner.
The positive clinical impact of this project triggered the construction of a hospital-based hadron therapy facility, with in-beam PET expected to monitor more delicate radiotherapeutic situations.
Therefore, we have studied possible in-beam PET improvements by optimising the arrangement of the gamma-ray detectors.
For this, a fully 3D, rebinning-free, maximum likelihood expectation maximization algorithm applicable to several closed ring or dual-head tomographs has been developed. The analysis of beta+ activity distributions simulated from real-treatment situations and detected with several detector arrangements allows to conclude that a dual-head tomograph with narrow gaps yields in-beam PET images with sufficient quality for monitoring head and neck treatments.
For monitoring larger irradiation fields, e.g. treatments in the pelvis region, a closed-ring tomograph was seen to be highly desirable. Finally, a study of the space availability for patient and bed, tomograph and beam
portal proves the implementation of a closed-ring detector arrangement for in-beam PET to be feasible.
  • Physics in Medicine and Biology 51(2006), 2143-2163

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Publ.-Id: 7689 - Permalink


Complex Formation of Curium(III) with the Amino Acids L2-Aminobutyric Acid and L-Threonine and the Corresponding Phosphate Ester O-Phospho-L-Threonine
Moll, H.; Bernhard, G.;
The complex formation of curium(III) with L2-Aminobutyric acid, L-Threonine and O-Phospho-L-Threonine was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (3x10-7 M). The concentrations of L2-Aminobutyric acid and L-Threonine were varied between 0.001 and 0.25 M in the pH range of 2 to 9.6 using 0.5 M NaCl as background electrolyte. In the case of O-Phospho-L-Threonine, lower concentrations were applied varying from 1x10-4 to 0.025 M in the pH range 2.8 to 7.6 using 0.154 M NaCl as background electrolyte.
Curium species of the type MpHqLr were identified from the fluorescence emission spectra. Three Cm–L2-Aminobutyrate complexes could be determined: (i) CmL2+ with a peak maximum at 596.0 nm, (ii) CmL2+ with a peak maximum at 600.8 nm, and (iii) CmL3 with a peak maximum at 603.8 nm. The corresponding formation constants were calculated from TRLFS measurements to be log β101 = 5.17 ± 0.07, log β102 = 9.00 ± 0.07, and log β103 = 11.30 ± 0.09. In the Cm–Threonine system, also three different species could be characterized: (i) CmThr2+ with a peak maximum at 599.6 nm, (ii) CmThr2+ with a peak maximum at 603.2 nm, and (iii) CmThr2- with a peak maximum at 605.7 nm. These species show the following formation constants: log β101 = 6.72 ± 0.07, log β102 = 10.22 ± 0.09, and log β1-22 = -(7.22 ± 0.19). Two species could be identified in the Cm–Phosphothreonine system: (i) CmH2PThr2+ with a peak maximum at 597.0 nm and (ii) CmHPThr+ with a peak maximum at 601.0 nm. The formation constants of the Cm-Phosphothreonine complexes were calculated to be log β121 = 18.03 ± 0.13 and log β111 = 14.17 ± 0.09. Possible structures of the identified curium species will be discussed on the basis of the fluorescence lifetime measurements.
For a better understanding of the actinide interaction processes in biological systems such as microbes and plants on a molecular level, it is essential to explore their complexation with selected bioligands of relevant functionalities as model compounds.

This work was funded by the BMWi under contract number: 02E9985.
Keywords: Amino acids; L2-aminobutyric acid; L-Threonine; O-Phospho-L-Threonine; Aqueous solution; TRLFS; Curium; Complexation
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 223-223
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7688 - Permalink


Manufacturing and characterization of Pd-nanoparticles formed on immobilized bacterial cells
Pollmann, K.; Merroun, M.; Raff, J.; Hennig, C.; Selenska-Pobell, S.;
Biological ceramic composites (biocers) were used as a template to produce Pd(0)-nanoparticles. The metal binding cells of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 were used as biological component of the biocers and immobilized by using sol-gel technology. Vegetative cells and surface layer proteins of this strain are known to bind high amounts of Pd(II) that can be reduced to Pd(0) particles by the addition of a reducing agent. After embedding into sol-gel ceramics, the cells retained their Pd(II)-binding capability. Pd(0)-nanoclusters were produced by the addition of hydrogen as reducing agent after the sorption of Pd(II). The formed Pd(0) nanoparticles were investigated by EXAFS-spectroscopy. The particles had a size of 0.6-0.8 nm. The thus immobilized Pd nanoparticles possess very interesting physical and chemical properties and are of interest for technical applications.
  • Letters in Applied Microbiology 43(2006)1, 39-45

Publ.-Id: 7687 - Permalink


Interaction of Uranium(VI) and colloidal Iron(III) oxyhydroxide in an abandonded uranium mine
Ulrich, K.-U.; Rossberg, A.; Scheinost, A.; Reuther, H.; Zänker, H.;
Acid mine drainage and process water from the in-situ leaching by sulfuric acid applied on uranium mines usually contain high amounts of iron, uranium, and sulfate besides other elements such as aluminum, manganese, zinc, calcium and silicon. Flooding of abandoned U mines by shallow groundwater initiates de-acidification, oxidation, and hydrolysis reactions by which colloids are formed, dominated by X-ray amorphous Fe(III) oxyhydroxide phases. Previous investigation on a flooding scenario has given spectroscopic evidence that the high affinity of U(VI) onto this type of colloids is due to the formation of mononuclear, inner-sphere surface complexes on 2-line ferrihydrite (Fh) where we suppose two types of coordination: (i) edge-sharing linkage of the UO22+ cation to an Fe(O,OH)6 octahedron stabilized by a hydrogen bond between one axial oxygen atom and the Fh surface, occurring in absence of CO2 and other ligands [1], and (ii) double-corner sharing linkage of the UO22+ cation to two Fe(O,OH)6 octahedra, occurring in the presence of atmospheric CO2 at pH ≤ 8 at the expense of the type (i) surface complex owing to competitive adsorption of carbonate on the Fh surface. Whereas a ternary sorption complex with monodentate linkage of carbonate to the adsorbed UO22+ cannot be ruled out at the tested conditions, ternary complexes with other ligands such as sulfate, nitrate, and silicate could be excluded [1].
The retarding impact of colloids on the transport of U(VI) does not only depend on the structure, but also on the long-term stability of the covalent bond between U(VI) and the solid phase. We started a series of desorption experiments in a simulated groundwater medium and a dilute NaHCO3 solution to study the kinetics of U(VI) desorption from U-loaded Fh. On a longer time scale of decades to centuries, the transformation of Fh to more crystalline phases such as hematite and goethite must be considered as well. We use the common approach of gently heating the samples to accelerate the crystallization of Fh in order to quantify the amount of U(VI) that will be incorporated in the lattice during the aging process as shown for instance by Duff et al. [2]. Recent results of these experiments will be presented.
In conclusion, our results show that the interaction of U(VI) and the highly reactive surface of ferric oxyhydroxide colloids plays a major role in lowering or delaying the release of radiotoxic uranium from flooded U mines into adjacent groundwater aquifers or surface water.


References
[1] Ulrich K.-U., Rossberg A., Scheinost A.C., Foerstendorf H., Zänker H., Jenk U. (2006), in: Merkel B.J., Hasche-Berger A. (Eds.), Uranium in the Environment. Mining Impact and Consequences. Springer, pp. 137-147.
[2] Duff M.C., Coughlin J.U., Hunter D.B. (2002), Geochim. Cosmochim. Acta 66, 3533-3547.
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University, 80-01-03474-7, 47-47
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7686 - Permalink


Addition of U(VI) to uranium mining waste pile soil samples and resulting changes of natural bacterial community structure
Selenska-Pobell, S.;
Changes of natural bacterial community structure induced by addition of uranyl or sodium nitrate to weakly contaminated soil samples from a uranium mining waste pile were studied using the 16S rDNA retrieval. Our results demonstrated that both treatments caused drastic changes in bacterial composition of the studied samples resulting in strongly reducing the originally predominant Acidobacteria and Alphaproteobacteria. The addition of sodium nitrate induced a strong propagation of denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes. The treatment of the samples with uranyl nitrate demonstrated that most part of the mentioned Bacteroidetes and some of the actinobacterial populations do not tolerate high U(VI) concentrations. Most interesting is the strong propagation of Gamma-Pseudomonas spp. capable to accumulate significant amounts of U(VI) and to build biofilms, hence being able to protect the community from the added toxic metal. At the initial stages of incubation (four weeks after the addition of uranyl nitrate) also U(VI) reducing Geobacter spp. appeared. However, at the later stages of incubation (fourteen weeks after the supplementation) no Geobacter populations were detected anymore. The latter indicated that no biological reduction of U(VI) occurred in these samples most probably because of the lack of electron donors to support this reaction. Interestingly, different U-sensitive Bacteroidetes and alphaproteobacterial populations propagated in the U(VI) treated samples at these late stages of incubation. That indicated that the added U(VI) was immobilized and did not disturb anymore the studied bacterial community.
The drastic changes induced by the addition of U(VI) indicate that bacterial communities are able to protect their members from the toxicity of this radionuclide by propagation of resistant and capable to interact with U(VI) populations. On the other hand, the large number of dead bacteria liberates phosphate-rich and other biopolymers capable to bind U(VI). Hence, bacteria together with the abiotic soil components such as minerals and humic acids play a key role in the immobilization of U(VI) in nature.
  • Lecture (others)
    Kolloquium im Institut für Molekulare Biologie der BAW, 10.10.2005, Sofia, Bulgaria

Publ.-Id: 7685 - Permalink


Addition of U(VI) to a Uranium Mining Waste Sample and Resulting Changes in the Indigenous Bacterial Community
Geissler, A.; Selenska-Pobell, S.;
Changes of natural bacterial community structure induced by addition of uranyl or sodium nitrate to weakly contaminated soil samples from a uranium mining waste pile were studied using the 16S rDNA retrieval. Our results demonstrated that both treatments caused drastic changes in bacterial composition of the studied samples resulting in strongly reducing the originally predominant Acidobacteria and Alphaproteobacteria. The addition of sodium nitrate induced a strong propagation of denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes. The treatment of the samples with uranyl nitrate demonstrated that most part of the mentioned Bacteroidetes and some of the actinobacterial populations do not tolerate high U(VI) concentrations. Most interesting is the strong propagation of Gamma-Pseudomonas spp. capable to accumulate significant amounts of U(VI) and to build biofilms, hence being able to protect the community from the added toxic metal. At the initial stages of incubation (four weeks after the addition of uranyl nitrate) also U(VI) reducing Geobacter spp. appeared. However, at the later stages of incubation (fourteen weeks after the supplementation) no Geobacter populations were detected anymore. The latter indicated that no biological reduction of U(VI) occurred in these samples most probably because of the lack of electron donors to support this reaction. Interestingly, different U-sensitive Bacteroidetes and alphaproteobacterial populations propagated in the U(VI) treated samples at these late stages of incubation. That indicated that the added U(VI) was immobilized and did not disturb anymore the studied bacterial community.
The drastic changes induced by the addition of U(VI) indicate that bacterial communities are able to protect their members from the toxicity of this radionuclide by propagation of resistant and capable to interact with U(VI) populations. On the other hand, the large number of dead bacteria liberates phosphate-rich and other biopolymers capable to bind U(VI). Hence, bacteria together with the abiotic soil components such as minerals and humic acids play a key role in the immobilization of U(VI) in nature.

Publ.-Id: 7684 - Permalink


On the temperature dependence of the mass spectra of AuGe and AuGeSi liquid metal alloy ion sources
Bischoff, L.; Pilz, W.; Ganetsos, T.; Akhmadaliev, C.; Aidinis, C. J.; Londos, C. A.;
This reports on an extensive study of the characteristics of AuGe and AuGeSi liquid metal alloy ion sources as a model system for new semiconductor compatible FIB sources. Such characteristics include ion beam mass spectra. A careful investigation has been undertaken where the emitter temperature is the main variable parameter. This work concerns the temperature dependence of the mass spectra of two needle-type liquid metal alloy ion sources (LMAISs), namely Au77Ge14Si9 (Tm=364°C) and Au73Ge27 (Tm=365°C). The sources are importan for producing SiGe layers. The experimental results, in conjunction with existing theories, strongly points towards the co-existance of twomechanisms for the emission of doubly-charged monomer ions: direct field-evaporation and post-ionisation.
Keywords: liquid metal alloy ion source, temperature, mass spectra
  • Contribution to proceedings
    Second Conference on Microelectronics, Microsystems and Nanotechnology, 14.-17.11.2004, Athens, Greece
    Journal of Physics: Conference Series 10(2005), 214-217, Bristol and Philadelphia: Institute of Physics Publishing, ISSN 1742-6588

Publ.-Id: 7683 - Permalink


11C-C bond formation by palladium-mediated cross-coupling of alkenylzirconocenes with [11C]methyl iodide
Wüst, F. R.; Berndt, M.;
A novel 11C-C bond formation based on the palladium-mediated cross-coupling reaction of alkenylzirconocenes with [11C]methyl iodide is described. The conversion of internal alkynes into the corresponding alkenylzirconocenes followed by transmetalation with Pd(PPh3)4 and subsequent cross-coupling with [11C]methyl iodide gave several 11C-labelled alpha,alpha’-dimethyl substituted alkenes. The palladium complex Pd(PPh3)4 proved to be superior to Pt(PPh3)4 or Ni(PPh3)4 as transition metal complex.
The scope and limitations of the novel palladium-mediated cross-coupling reaction of alkenylzirconocenes with [11C]methyl iodide were tested with various internal alkynes. Radiochemical yields of up to 75% (based upon [11C]methyl iodide) could be achieved
  • Journal of Labelled Compounds and Radiopharmaceuticals 49(2006)2, 91-100

Publ.-Id: 7682 - Permalink


Synergism effects between Ni and Cu on the radiation susceptibility of RPV model alloys
Ulbricht, A.; Keiderling, U.;
After the formation of a high point-defect content of vacancies and self- or solute interstitial atoms during neutron-induced displacement cascade processes, the radiation susceptibility of a reactor pressure vessel (RPV) steel is expressed in its capability of defect clustering. These fine-scaled features are the essential microstructural changes and the reason for the enhanced material ageing under irradiation. Small-angle neutron scattering (SANS) provides statistically reliable results about their size distributions and contents in macroscopic volumina. A possible cluster composition can be derived from their magnetic and nuclear scattering intensities.
The content of Cu is the most essential parameter controlling the radiation susceptibility. Ni rich alloys have a higher radiation susceptibility as Ni poor steels with the same content of deleterious elements as Cu. The synergism of Ni and Cu has a catalytical effect on the radiation defect formation. Cu precipitates were not found.
Keywords: SANS, radiation defects, RPV steel
  • Contribution to external collection
    Y. Kirschbaum, A. Brandt, M. Tovar, D. Bischoff, R. Michaelsen: BENSC Experimental Reports 2004, Berlin: Hahn-Meitner-Institut, HMI - B 601(2005), 2005, ISSN 0936 - 0891, 155

Publ.-Id: 7681 - Permalink


Changes in zinc speciation in field soil after contamination with zinc oxide
Voegelin, A.; Pfister, S.; Scheinost, A.; Marcus, M.; Kretzschmar, R.;
Recent studies on the speciation of Zn in contaminated soils confirmed the formation of Zn-layered double hydroxide (LDH) and Zn-phyllosilicate phases. However, no information on the kinetics of the formation of those phases under field conditions is currently available. In the present study, the transformation of Zn in a field soil artificially contaminated with ZnO containing filter dust from a brass foundry was monitored during 4 years using extended X-ray absorption fine structure (EXAFS)
spectroscopy. Soil sections were studied by í-X-ray fluorescence (í-XRF) and í-EXAFS spectroscopy. EXAFS spectra were analyzed by principal component analysis (PCA) and linear combination fitting (LCF). The results show that ZnO dissolved within 9 months and that half of the total Zn reprecipitated. The precipitate was mainly of the Zn- LDH type (>75%). Only a minor fraction (<25%) may be of Zn-phyllosilicate type. The remaining Zn was adsorbed to soil organic and inorganic particles. No significant
changes in Zn speciation occurred from 9 to 47 months after the contamination. Thermodynamic calculations show that both Zn-LDH and Zn-phyllosilicate may form in the presence of ZnO but that the formation of Zn-phyllosilicate would be thermodynamically favored. Thus, the dominance of Zn-LDH found by spectroscopy suggests that the formation of the Zn precipitates was not solely controlled by thermodynamics but also contained a kinetic component. The rate-limiting step could be the supply of Al and Si from soil minerals to the Zn-rich solutions around dissolving ZnO grains.
  • Environmental Science & Technology 39(2005)17, 6616-6623

Publ.-Id: 7680 - Permalink


Spektroskopische Untersuchungen zur Wechselwirkung von U(VI) mit Huminsäure unter neutralen pH-Bedingungen
Sachs, S.;
Im Vortrag werden Studien zur U(VI)-Komplexierung durch Huminsäuren bei pH 7 vorgestellt. Die Untersuchungen erfolgten mittels konventioneller zeitaufgelöster laser-induzierter Fluoreszenzspektroskopie (TRLFS) sowie mittels Femtosekunden-TRLFS (fs-TRLFS).
Keywords: Humic acid, complexation, uranium, spectroscopy, ternary complexes
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Migration von Actiniden im System Ton, Huminstoff, Aquifer", 04.-05.10.2005, Leipzig, Germany

Publ.-Id: 7679 - Permalink


Magnetic-field induced band-structure change in CeBiPt
Kozlova, N.; Hagel, J.; Doerr, M.; Wosnitza, J.; Eckert, D.; Muller, K.; Schultz, L.; Opahle, I.; Elgazzar, S.; Richter, M.; Goll, G.; von Lohneysen, H.; Zwicknagl, G.; Yoshino, T.; Takabatake, T.;
We report on a field-induced change of the electronic band structure of CeBiPt as evidenced by electrical-transport measurements in pulsed magnetic fields. Above similar to 25 T, the charge-carrier concentration increases nearly 30% with a concomitant disappearance of the Shubnikov-de Haas signal. These features are intimately related to the Ce 4f electrons since for the non-4f compound LaBiPt the Fermi surface remains unaffected. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.
  • Physical Review Letters 95(2005), 086403

Publ.-Id: 7677 - Permalink


Comparative assessment of coupled RELAP5/PARCS and DYN3D/RELAP5 codes against the Kozloduy-6 pump trip test
Kozmenkov, Y.; Grundmann, U.; Kliem, S.; Rohde, U.;
The modeling of complex transients in Nuclear Power Plants (NPP) remains a challenging topic for Best Estimate (BE) three-dimensional coupled code computational tools. Nowadays, this technique is extensively used since it allows decreasing conservatism in the calculation models by performing more realistic simulations based on a more precise consideration of multidimensional effects under complex transients in NPPs. This paper represents a contribution to the assessment and validation of coupled code technique through the Kolzoduy VVER-1000 pump trip test. The coupled REALP5/3.3-PARCS/2.6 and DYN3D/3-RELAP5/3.3 code systems are used in simulations. The obtained results are assessed against experimental data and also through the code-to-code comparison.

The DYN3D/RELAP5 computational model of VVER-1000 has been developed and adjusted for simulations with the parallel running scheme (PVM) of RELAP5/PARCS. Also, the macroscopic cross-section library used in the DYN3D/RELAP5 calculations has been adapted to meet the input requirements of PARCS. Prior to the test simulations, the RELAP5/PARCS model of the plant has been assessed in the standalone PARCS and RELAP5 test calculations.
A reasonably good agreement between the experimental data and the calculated results is obtained. For the initial state, the observed discrepancies are mainly due to the absence of ADF correction and the evaluation of the Doppler feedback effect. During the transient, the deviations are mainly due to the combined effect of the measurement uncertainty in the control rod axial position and the estimation of the Doppler effect.
Keywords: Coupled codes, 3D neutron kinetics, code assessment, VVER-1000, plant-measured data, main coolant pump
  • Contribution to proceedings
    International Top. Meeting on Mathematics and Computation, Supercomputing, Reactor Physics and Nuclear Applications, 12.-15.09.2005, Avignon, France

Publ.-Id: 7676 - Permalink


Uncertainty and sensitivity analyses of the Kozloduy pump trip test by coupled RELAP5/PARCS code
Bousbia Salah, A.; Kliem, S.; Rohde, U.;
The modeling of complex transients in Nuclear Power Plants (NPP) remains a challenging topic for Best Estimate three-dimensional coupled code computational tools. This technique is, nowadays, extensively used since it allows decreasing conservatism in the calculation models and performs more realistic simulating and more precise consideration of multidimensional effects under complex transients in NPPs. In the current paper a contribution to the assessment and validation of coupled code technique through the Kolzoduy VVER100 pump trip test is performed. For this purpose, the coupled REALP5/3.3-PARCS/2.6 code is used. The code results were assessed against experimental data and the comparison study shows good agreements between the calculations and the global kinetic and thermal-hydraulic aspects observed experimentally. Further investigations through the uncertainty and sensitivity GRS method, covering kinetic and thermal-hydraulic parameters, have been carried out in order to assess the origin of the observed discrepancies.
Keywords: Coupled Codes, Uncertainty and Sensitivity Analyses, GRS Method
  • Invited lecture (Conferences)
    International Top. Meeting on Mathematics and Computation, Supercomputing, Reactor Physics and Nuclear Applications, 12.-15.09.2005, Avignon, France
  • Contribution to proceedings
    International Top. Meeting on Mathematics and Computation, Supercomputing, Reactor Physics and Nuclear Applications, 12.-15.09.2005, Avignon, France
    Proceedings

Publ.-Id: 7675 - Permalink


EXAFS Investigations of U(IV) species in aqueous solutions with a newly developed spectro-electrochemical cell
Hennig, C.; Tutschku, J.; Palladino, G.; Poineau, F.; Schmeide, K.; Rossberg, A.; Scheinost, A.; Bernhard, G.;
Actinides with their large number of oxidation states are susceptible to redox conditions, forming different aqueous complexes which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their thermodynamic metastability. Therefore, we developed a new spectro-electrochemical cell which allows to study the structure and speciation of aqueous actinide complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential.
The safety regulations for handling of radioactive materials at the ESRF prohibit any gas release from samples containing radionuclides. Therefore the electrochemical cell is air-tight and the applied reduction process prevents a water decomposition. The electrochemical cell comprises a double confinement. A well-defined anodic reaction is applied by using Ag as anode in equilibrium with hardly soluble AgCl. Formal cathodic potentials Ecs of the U(VI)/U(IV) couple were verified by cyclic voltammetry. The potential Ecs+E was then kept constant for the subsequent reduction process of U(VI) to U(IV).
The coordination of the U(VI) species before reduction and the electrochemically stabilized U(IV) ions in presence of different ligand systems has been studied by U LIII-edge EXAFS spectroscopy. In non-complexing perchloric acid the U(IV) aquo ion was obtained with 9 spherically arranged atoms in a distance of 2.41 Å. In concentrated chloride solutions we observed between 3 to 9 M [Cl] the complexes U(H2O)8Cl3+, U(H2O)6-7Cl22+ and U(H2O)5Cl3+ with U-O distances of 2.41 Å and U-Cl distances of 2.71 Å [1]. In presence of sulfuric acid, the coordination with SO42- seems to change from bidentate with U(VI) to monodentate fashion with U(IV) at low pH. We observed in presence of formic acid tetranuclear U(IV) species with U-U distances of 3.85 Å. Investigations in carbonate solutions are in progress.
[1] C. Hennig, J. Tutschku, A. Rossberg, G. Bernhard, A.C. Scheinost, Comparative EXAFS investigation of U(VI) and U(IV) aquo chloro complexes in solution using a newly developed spectro-electrochemical cell, Inorg. Chem., submitted
  • 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: 7674 - Permalink


Molekulare Wechselwirkungsmechanismen an der Grenzfläche zwischen Geosphäre und Biosphäre
Raff, J.;
Detailkenntnisse der mikroskopischen Prozesse an der Grenzfläche zwischen Biosphäre und Geosphäre sind notwendig für das Verständnis des makroskopischen Verhaltens von Schwermetallen und Radionukliden in der Umwelt. Darauf aufbauend erlaubt die Untersuchung komplexer Systeme die Beurteilung der Relevanz der einzelnen Reaktionen unter natürlichen Bedingungen. Die erhaltenen Ergebnisse sind sowohl für die Risikobeurteilung als auch für die Entwicklung innovativer Sanierungs­verfahren von entscheidender Bedeutung. Anhand ver­schiedener Unter­suchungen zur Immobilisierung von Uran durch Bakterien werden existierende Wechselwirkungs­mechanismen aufgezeigt sowie deren Bedeutung und Anwendungspotential diskutiert.
  • Invited lecture (Conferences)
    Plenarvortrag im Rahmen des 4. Jenaer Sanierungskolloquiums, 29.-30.09.2005, Jena, Germany

Publ.-Id: 7673 - Permalink


Modification of temperature and solute distribution during directional solidification caused by electromagnetically-driven convection
Willers, B.; Eckert, S.; Nikrityuk, P. A.; Eckert, K.;
The application of time varying magnetic fields can be considered as an effective tool to organize a well-defined flow structure in the liquid phase affecting the nucleation and solidification parameters. Once a flow occurs in the liquid melt during solidification, nucleation and grain growth are mainly governed by the convective transport of heat and solute. The consequences on the structure of solidified ingots are widely discussed in the literature. So it is known, that the application of mechanical or electromagnetic stirring promotes the formation of fine, equiaxed grains [1-4].
Solidification experiments as well as numerical simulations were carried out considering the directional solidification of Pb Sn alloys from a water cooled copper chill. A rotating magnetic field (RMF) was applied for melt agitation. Thermocouples were used to measure the temperature field during solidification. Profiles of the velocity in the liquid phase were determined by means of Ultrasound Doppler velocimetry (UDV) [5].
Numerical simulations are based on the classical mixture formulation [6]. To calculate the viscosity in the mushy region the model proposed by Roplekar and Dantzig [7] was implemented into the code. The amplitude of the electric currents induced by the RMF are altered if the electrical conductivity of the growing solid phase deviates from that of the liquid phase. Previous investigations [8] showed that for such a situation numerical predictions of the velocity field using a stationary Lorentz force term become questionable. For our calculations presented here the Lorentz force term has been recalculated for each time step.
The comparison between numerical simulations and solidification experiments delivered a good agreement. Due to the permanent changes both of the aspect ratio of the fluid volume and the material properties during solidification the flow field shows a transient behaviour being more complex as known from the stationary, isothermal case. Our results disclose that the forced convection causes distinct modifications of the temperature and concentration field. The electromagnetic stirring promotes the columnar-to-equiaxed transition and causes a considerable grain refinement. Modifications of the grain structure and effects of macrosegregation are discussed with respect to the details of the flow field.

[1] D.B. Spencer, R. Mehrabian, M.C. Flemings (1972), Met. Trans. 3, 1925-1932
[2] W.C. Johnston, G.R. Kofler, S. O?Hara, H.V. Ashcom, W.A. Tiller (1965), Trans. Met. Soc. AIME 233, 1856-1860
[3] W.D. Griffiths, D.G. McCartney (1996), Mater. Sci. Eng. A 216, 47-60
[4] B. Willers, S. Eckert, U. Michel, I. Haase, G. Zouhar (2005), Mater. Sci. Eng. A, article in press
[5] S. Eckert, B. Willers, G. Gerbeth (2005), Met. Mat. Trans. 36A, 267-270
[6] W.D. Bennon and F.P. Incropera (1987), Int. J. Heat Mass Trans. 30, 2161-2170
[7] J.K. Roplekar, J.A. Dantzig (2001), Int. J. Cast Metals Research 14, 79-98
[8] S. Eckert, B. Willers, P.A. Nikritjuk, K. Eckert, U. Michel, G. Zouhar (2005), International Conference on Advanced Solidification Processes, Stockholm, Sweden
Keywords: solidification, PbSn alloys, forced convection, rotating magnetic field
  • Contribution to proceedings
    MCWASP Conference, Modeling of Casting, Welding and Advanced Solidification Processes XI, 28.05.-02.06.06, Opio, France
  • Lecture (Conference)
    MCWASP Conference, Modeling of Casting, Welding and Advanced Solidification Processes XI, 28.05.-02.06.2006, Opio, France

Publ.-Id: 7672 - Permalink


Ferromagnetic Gd-implanted ZnO single crystals
Potzger, K.; Zhou, S.; Eichhorn, F.; Helm, M.; Skorupa, W.; Mücklich, A.; Fassbender, J.ORC; Herrmannsdörfer, T.; Bianchi, A.
In order to introduce ferromagnetic properties, ZnO single crystals have been implanted with Gd ions at 180 keV ion energy and two different fluences. Magnetization reversal hysteresis loops have been recorded for as-implanted as well as annealed samples using a superconducting quantum interference device (SQUID). It was found that for a fluence of 5x1015 Gd+/cm2 post implantation annealing leads to an increase of the saturation moment up to 1.8 B/Gd at exactly 300 K thus excluding Gd, ZnGd or Gd2O3 secondary phases to be formed. The increase of the saturation moment can be explained along with changes in resistivity due to the annealing reported elsewhere.
Keywords: rare earths, diluted magnetic semiconductors, ZnO, ion beams, doping
  • Journal of Applied Physics 99(2006), 063906

Publ.-Id: 7671 - Permalink


Multimodal luminescence spectra of ion-implanted silica
Fitting, H.-J.; Salh, R.; Barfels, T.; Schmidt, B.;
Thermally oxidized SiO2 layers have been implanted by oxygen and sulfur ions up to an atomic dopant fraction of about 4 at%. The cathodoluminescence spectra of these ion implanted layers show besides the characteristic bands an identical sharp and intensive multimodal structure in the green up to near IR region. The energy step differences of the luminescence sublevels in average amount to 120 meV and indicate vibronic transitions in terms of a configuration coordinate potential model. A most probable candidate for these spectra are O2– interstitial molecules, as we could demonstrate by respective configuration coordinate data. These assumptions are contrary to photonic crystal models for the multimodal spectra as well as to models of quantum size effects, both discussed recently in literature.
Keywords: Cathodoluminescence, Sulfur and oxygen, ion implantation, silica
  • Physica Status Solidi (A) 202(2005)13, R142-R144

Publ.-Id: 7670 - Permalink


Pressure studies on a low-resistance variant of the quasi2D organic superconductor κ-(ET)2Cu[N(CN)2]Br
Lang, M.; Strack, C.; Akinci, C.; Wolf, B.; Schlueter, J. A.; Wosnitza, J.; Schweitzer, D.;
Measurements of the interlayer resistivity, ρ(T), under hydrostatic pressure have been performed on a low (LR)- and high (HR)-resistance variant of the title organic superconductor. While the HR sample, synthesized according to the standard procedure, shows a semimetallic-like ρ(T) behavior at high temperatures followed by the pronounced maximum around 90 K, the LR crystal, which is the result of a somewhat modified synthesis route, remains metallic for . Common to both variants is, however, an almost abrupt change in ρ(T) around , consistent with a density-wave-type instability, which below coexists with superconductivity, and a ρAT2 dependence for TcTT0. While T* and Tc are sample independent, the values for A and T0 were found to differ markedly between both variants, inconsistent with the T2 dependence originating from coherent Fermi-liquid excitations.
Keywords: Organic superconductors; Resistivity measurements; Pressure studies

Publ.-Id: 7669 - Permalink


Why dynamos are prone to reversals
Stefani, F.; Gerbeth, G.; Günther, U.; Xu, M.;
In a recent paper (Phys. Rev. Lett. 94 (2005), 184506) it was shown that a simple mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha can exhibit a number of features which are typical for Earth's magnetic field reversals. In particular, the model produces asymmetric reversals (with a slow decay of the dipole of one polarity and a fast recreation of the dipole with opposite polarity), a positive correlation of field strength and interval length, and a bimodal field distribution. All these features are attributable to the magnetic field dynamics in the vicinity of an exceptional point of the spectrum of the non-selfadjoint dynamo operator where two real eigenvalues coalesce and continue as a complex conjugated pair of eigenvalues. Usually, this exceptional point is associated with a nearby local maximum of the growth rate dependence on the magnetic Reynolds number. The negative slope of this curve between the local maximum and the exceptional point makes the system unstable and drives it to the exceptional point and beyond into the oscillatory branch where the sign change happens. A weakness of this reversal model is the apparent necessity to fine-tune the magnetic Reynolds number and/or the radial profile of alpha in order to adjust the operator spectrum in an appropriate way. In the present paper, it is shown that this fine-tuning is not necessary in the case of higher supercriticality of the dynamo. Numerical examples and physical arguments are compiled to show that, with increasing magnetic Reynolds number, there is strong tendency for the exceptional point and the associated local maximum to move close to the zero growth rate line where the indicated reversal scenario can be actualized. Although exemplified again by the spherically symmetric alpha^2 dynamo model, the main idea of this ''self-tuning'' mechanism of saturated dynamos into a reversal-prone state seems well transferable to other dynamos. As a consequence, reversing dynamos might be much more typical and may occur much more frequently in nature than what could be expected from a purely kinematic perspective.

Publ.-Id: 7668 - Permalink


Untersuchung posttranslationaler Modifikationen bakterieller HÜllproteine (S-Layer) von Uranabfallhaldenisolaten und deren Einfluss auf die Bindung von Uran
Berger, S.;
Die vorliegende Arbeit untersucht bakterielle S-Layer hinsichtlich ihrer posttranslationalen Modifikationen und deren Einfluss auf die Bindung von Uran. Dabei konnten bei 9 Haldenisolaten der Gattung /Bacillus /S-Layer nachgewiesen und bei den Isolaten B5T, B7, B12, B35, B41, B53 und B62 erfolgreich isoliert werden. Mit Hilfe der 16S rDNA-Analyse konnten die Isolate phylogenetisch identifiziert und unter Berücksichtigung der mikroskopischen Ergebnisse eingeordnet werden. Die Untersuchung der S-Layer auf das Vorhandensein von Glykosylierungen mit einer spezifischen Färbung der Blot-Membran ergab ein negatives Ergebnis.
Jedoch konnte mit Hilfe der colorimetrischen Bestimmung des Phosphatgehaltes bei allen untersuchten S-Layern Phosphorylierungen nachgewiesen werden. Besonders interessant verhielt sich der S-Layer des Isolates B12. Er konnte vollständig gereinigt werden, zeigte mit 2,5 mol Phosphat pro mol S-Layer den höchsten Phosphatgehalt und wies mit 291,5 µg Uran pro mg S-Layer die größte Uranbindungskapazität auf.
  • Other report
    Hochschule für Wirtschaft und Technik Dresden: Praktikumsbericht, Fachbereich Chemieingenieurwesen, 2005
    38 Seiten

Publ.-Id: 7667 - Permalink


Modifizierung bakterieller Hüllproteine (S-Layer) zur Erhöhung der Metallbindungskapazität und -selektivität
Kaufmann, M.;
wird nachgereicht
  • Other report
    Technische Universität Dresden: Bericht zur Interdisziplinären Projektarbeit,Fakultät Maschinenwesen, FB Bioverfahrenstechnik, 2004
    80 Seiten

Publ.-Id: 7666 - Permalink


Measurement of bubble velocity profiles and turbulent diffusion coefficients of the gaseous phase in rectangular bubble column using image processing
Zaruba, A.; Krepper, E.; Prasser, H.-M.; Schleicher, E.;
The flow in a rectangular bubble column with a cross-section of 100x20 mm and a height of 1500 mm was studied using a high-speed video system. Series of the images were taken at a frequency of 500 Hz at different elevations. The images were treated by means of a bubble recognition algorithm. It allows the tracking of most of the individual bubbles in a bubble swarm. Time-averaged velocity profiles and turbulent diffusion coefficients were derived as a function of the superficial gas velocity.
To measure the turbulent diffusion coefficient of the gaseous phase the lateral displacement of bubbles traveling over a certain vertical distance was transformed into a probability density distribution. It was found that the shape of distributions fits well to a Gaussean standard distribution. Dispersion coefficients were found to grow nearly proportionally to the square root of the vertical distance. Diffusion coefficients were calculated from the proportionality factor and were compared to correlations from the literature. Experiments were performed at superficial gas velocities ranging from 0.5 to 4 mm/s. The bubbles were generated either by a porous sparger or a set of capillaries placed at the bottom of the column. Measurements were taken at heights between 1 and 1.5 m, where the bubble cloud was occupying the entire cross section.
Keywords: bubble column, turbulence, high-speed imaging, image processing, turbulent dispersion, bubble size, bubble velocity
  • Experimental Thermal and Fluid Science 29(2005), 851-860

Publ.-Id: 7665 - Permalink


QCD matter within a quasi-particle model and the critical end point
Kämpfer, B.; Bluhm, M.; Schulze, R.; Seipt, D.; Heinz, U.;
We compare our quasi-particle model with recent lattice QCD results for the equation of state at finite temperature and baryo-chemical potential. The inclusion of the QCD critical end point into models is discussed. We propose a family of equations of state to be employed in hydrodynamical calculations of particle spectra at RHIC energies and compare with the differential azimuthal anisotropy of strange and charm hadrons
  • Nuclear Physics A 774(2006), 757-760

Publ.-Id: 7663 - Permalink


Beta decay of 103Sn
Kavatsyuk, O.; Kavatsyuk, M.; Batist, L.; Banu, A.; Becker, F.; Blazhev, A.; Brüchle, W.; Döring, J.; Faestermann, T.; Górska, M.; Grawe, H.; Janas, Z.; Jungclaus, A.; Karny, M.; Kirchner, R.; La Commara, M.; Mandal, S.; Mazzocchi, C.; Mukha, I.; Muralithar, S.; Plettner, C.; Płochocki, A.; Roeckl, E.; Romoli, M.; Schädel, M.; Schwengner, R.; Żylicz, J.;
The β decay of 103Sn, a three-neutron-particle nucleus with respect to the 100Sn core, was investigated at the GSI on-line mass separator using an array of 17 germanium crystals and a total absorption spectrometer. A total of 31 β-delayed γ-rays (29 new) of the 103Sn →103 In decay were observed and, on the basis of β-γ-γ coincidences, the 103Sn decay scheme was established for the first time. By means of total absorption spectroscopy, β intensities, the Gamow-Teller strength distribution and the summed Gamow-Teller strength value of 3.5±0.5 were determined for this decay. Its half-life and QEC value were found to be 7.0±0.2 s and 7.64±0.7 MeV, respectively. The β-delayed proton branching ratio was measured to be 1.2±0.1%. The results are discussed in comparison with shell-model predictions based on realistic and empirical interactions.
  • European Physical Journal A 25(2005)2, 211-222

Publ.-Id: 7662 - Permalink


The local structure of U(VI)-Ferrihydrite sorption complexes revisited: EXAFS spectroscopy and Monte Carlo Simulations
Roßberg, A.; Ulrich, K. U.; Scheinost, A. C.;
EXAFS analysis of actinyl sorption complexes is a complicated task due to the presence of overlapping shells, structural disorder and the presence of multiple scattering paths due to the specific actinyl structure. Hence often controversial interpretations arise from conventional shell fitting. A typical example is the proposed formation of ternary uranyl carbonato surface complexes on ferrihydrite, where a peak at ~2.4 Å in the Fourier transform is explained by backscattering carbon atoms at 2.86-2.94 Å. While such ternary carbonate complexes have been confirmed by complementary techniques like FTIR and electrophoretic mobility measurements, the EXAFS peak shows even up in those uranyl ferrihydrite systems, where great care has been taken to keep the system carbonate-free, rendering an EXAFS fit with carbon meaningless.
To overcome this common problem of EXAFS shell fitting, we developed a new analysis approach based on Monte-Carlo simulations coupled to theoretical EXAFS modeling using FEFF. Here, the position of the uranyl atom is first refined in relation to a given ferrihydrite surface structure. In a second step, the whole complex structure is refined to allow for e.g. surface relaxation effects. Using this approach, a match to the experimental EXAFS spectra of U(VI) ferrihydrite complexes without carbonate could be achieved. The local structure indicates a mononuclear bidentate (edge-sharing) surface complex, which was identified for the first time by EXAFS spectroscopy. Further fits were performed to elucidate the influence of carbonate and other anions on the structure of the surface complex. The results demonstrate the potential of the Monte-Carlo approach for determining the structure of actinyl surface complexes.
  • 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: 7660 - Permalink


Electronic structure of LaSrMnO4: XPS and XES studies
Kuepper, K.; Klingeler, R.; Reutler, P.; Büchner, B.; Neumann, M.;
We present a comprehensive investigation of the valence band of the single layered manganite LaSrMnO4. X-ray photoelectron spectroscopy (XPS) and x-ray emission emission spectroscopy (XES) were used to reveal a detailed picture of the total and partial densities of states in this compound. The results are discussed in the light of available theory.
Keywords: La1-xSr1+xMnO4, electronic structure, x-ray photoelectron spectroscopy, x-ray emission spectroscopy, valence band
  • Journal of Applied Physics 99(2006)8, 08Q308-1-08Q308-3
    DOI: 10.1063/1.2151792
  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA

Publ.-Id: 7659 - Permalink


Magnetic and electronic properties of the iron-containing polyoxotungstate [Fe4(H2O)10(β-SbW9O33)2]6-
Prinz, M.; Takács, A.; Schnack, J.; Balasz, I.; Burzo, E.; Kortz, U.; Kuepper, K.; Neumann, M.;
The magnetic and X-ray photoelectron spectroscopy (XPS) studies on the transition metal substituted, dimeric polyoxotungstate [Fe4(H2O)10(β-SbW9O33)2]6- are reported. The magnetic data were analysed by using an isotropic Heisenberg Hamiltonian. The ground state of the frustrated molecule has a total spin of S = 2. The XPS Fe 2p spectra suggest a 2+ formal valence state. The deviation from the contained Fe3+ ions can be explained by charge-transfer e®ects.
Keywords: magnetic molecules, polyoxotungstates, Heisenberg model, magnetization measurements, x-ray photoelectron spectroscopy
  • Journal of Applied Physics 99(2006), 08J505-1-08J505-3
    DOI: 10.1063/1.2173613
  • Poster
    Magnetism and Magnetic Materials Conference, 30.10.-03.11.2005, San Jose, USA

Publ.-Id: 7658 - Permalink


Ion beam synthesis of Fe nanoparticles in MgO
Potzger, K.; Reuther, H.; Zhou, S.; Mücklich, A.; Eichhorn, F.; Grötzschel, R.; Fassbender, J.ORC
MgO(001) single crystals were irradiated with 57Fe at an energy of 100 keV and an ion fluence of 6x1016cm-2 at implantation temperatures between 25°C(RT) and 1000°C.
Analysis was carried out by means of CEMS, XRD, RBS and TEM. We found that the implantation temperature plays the important role for the formation of Fe nanoparticles. The fraction of metallic Fe (CEMS Fe0 signal) increases from 28% for RT implantation to 60% for 800°C implantation, while the Fe profile remains unchanged (Rp ¡Ö 50 nm). The nanoparticles formed after 800°C implantation are about 5 nm in size and exhibit fcc-structure with an orientation relationship of Fe(111)/MgO(111) and Fe(220)/MgO(220). The nanoparticles exhibit paramagnetism at room temperature.
At an implantation temperature of 1000°C the Fe implantation profile smears out completely and 92% of the Fe atoms are found in the Fe3+
oxidation state.
Keywords: embedded nanoparticles, magnetism, ion beam synthesis
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-427 Januar 2005, 52-52

Publ.-Id: 7657 - Permalink


Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet
Takács, A.; Neumann, M.; Postnikov, A. V.; Kuepper, K.; Scheurer, A.; Sperner, S.; Prince, K. C.; Saalfrank, R. W.;
The electronic structure of the single molecule magnet system {M[Fe(L1)2]3}*4CHCl3, (M = Fe, Cr; L1 = CH3N(CH2CH2O)2 2-) has been studied using X-ray photoelectron spectroscopy,X-ray absorption spectroscopy, soft X-ray emission spectroscopy, as well as theoretical density functional-based methods. There is good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 eV and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O, N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron atom, giving a high spin state molecule with a total S=5 effective spin for the case of M = Fe.
Keywords: PACS numbers: 75.50.Xx, 31.15.Ar, 33.20.Rm, 33.60.Fy

Publ.-Id: 7656 - Permalink


Fe implanted ferromagnetic ZnO
Potzger, K.; Zhou, S. Q.; Reuther, H.; Mücklich, A.; Eichhorn, F.; Schell, N.; Skorupa, W.; Fassbender, J.ORC; Helm, M.; Herrmannsdörfer, T.; Papageorgiou, T. P.
The origin of ferromagnetism in ZnO single crystals implant-doped with Fe is investigated using X-ray diffraction, transmission electron microscopy, superconducting quantum interference device magnetometry and Mössbauer spectroscopy. For an ion fluence of 4×1016 ions per cm2 and an implantation temperature of 620 K, Fe nanoparticles are responsible for room-temperature ferromagnetism of the ZnO single crystals. On the other hand Fe ions implanted with an ion fluence of 4×1015 ions per cm2 at a temperature of 253 K develop a ferromagnetic coupling within the host matrix. Consequently only high resolution methods allow to rule out secondary phases in doped magnetic semiconductors.
Keywords: diluted magnetic semiconductors, ZnO, implant doping
  • Applied Physics Letters 88(2006)5, 052508

Publ.-Id: 7655 - Permalink


Effects of implantation of magnetic ions into ZnO
Potzger, K.; Zhou, S.; Reuther, H.; Brauer, G.; Anwand, W.; Eichhorn, F.; Bischoff, L.; Herrmann, F.; Grambole, D.; Groetzschel, R.; Fassbender, J.ORC
Recent achievements in the field of diluted magnetic semiconductors are summarized. Then, effects of the implantation of magnetic ions into ZnO single crystals are studied by various highly sensitive analysis methods. It is found that the implantation of Fe ions at elevated temperatures (620 K) yields the formation of small ferromagnetic Fe particles. Moreover, the host lattice exhibits open-volume type damage confined at the near surface region. Both effects strongly depend on the ion fluence. On the other hand, after 25 keV focused ion beam implantation of Co+ no magnetic domains could be detected on a ZnO single crystal surface. However, unscreened electric charges are locally introduced effectuating a contrast within a lift mode-operated atomic force microscope that can easily be confused with magnetic field gradients.
Keywords: ZnO, diluted magnetic semiconductors, ion implantation, magnetism
  • Lecture (Conference)
    HeT-SiC-05, 26.04.-01.05.2005, Krippen, Deutschland

Publ.-Id: 7652 - Permalink


Magnetic Materials and Ion Irradiation - New topics in Rossendorf
Potzger, K.;
An introduction on new topics at the institute for ion beam physics and materials research concerning magnetic materials is given. Especially the field of ion beam synthesis of ferromagnetic nanoparticles in oxide host materials, magnetic patterning of exchange bias thin films and magnetic doping of ZnO is discussed.
Keywords: embedded ferrmoagnetic nanoparticles, diluted magnetic semiconductors, exchange bias, ion beam synthesis
  • Lecture (others)
    Abteilungsseminar, 28.01.2005, Leipzig, Deutschland
  • Lecture (others)
    Abteilungsseminar, Prof. W. Brewer, 10.02.2005, Berlin, Deutschland

Publ.-Id: 7651 - Permalink


Fabrication of Si nanocrystals for memory application by ion irradiation through SiO2/Si-interfaces
Schmidt, B.; Heinig, K.-H.; Roentzsch, L.; Mücklich, A.; Stegemann, K.-H.; Votintseva, E.; Klimenkov, M.;
This contribution addresses self-assembling of Si-nanocrystals (NCs) in gate oxides, with special emphasis on size and position tailoring and their application as discrete charge storage centers in nanocrystal memories. The Si NCs for these multi-dot floating-gate memories have been produced by ion irradiation through SiO2/Si-interfaces. Si excess within SiO2 is formed by ion beam mixing of Si from the Si substrate and from the poly-Si capping layer into the gate oxide. Ion irradiation with 3x1015 -10x1015 Si+ cm-2 at 50-100 keV through 50 nm poly-Si and 15 nm SiO2 on (001)Si results in a considerable Si excess. At the upper and lower interfaces of the gate oxide, this ion irradiation forms a metastable SiOx composition. Si NCs are formed by phase separation into Si and SiO2 during post-irradiation thermal treatment. Adjacent to the recovering interfaces, narrow SiO2 zones becomes denuded of excess Si. More distant excess Si precipitates as Si NCs in the gate oxide. This approach was applied to nMOSFET-NC-memory fabrication in the standard CMOS line at ZMD. MOSFET characteristics in terms of write/erase voltage, duration of the programming time, endurance and retention have been evaluated.
Keywords: Si nanocrystals, ion iradiation, interface mixing, memory devices
  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Berlin, 04.03.-09.03.2005, 04.-09.03.2005, Berlin, Deutschland

Publ.-Id: 7650 - Permalink


Luminescent Defect dynamics in amorphous SiO2:H
Fitting, H.-J.; Ziems, T.; Salh, R.; Voncharnowski, A.; Schmidt, B.;
The main luminescent centers in SiO2 are the red luminescence R(1.85eV) of the non-bridging oxygen hole center (NBOHC) and the oxygen deficient center (ODC) with a blue B(2.7eV) and a UV band (4.4eV). Implanted hydrogen diminishes the red luminescence but increases the blue and the UV bands. Thus hydrogen passivates the NBOHC and keeps the ODC's in active emission states. A preliminary model of luminescence center transformation is based on radiolytic dissociation and re-association of mobile oxygen and hydrogen at the centers as well as formation of interstitial H2, O2, and H2O molecules.
Keywords: Luminescence, SiO2, hydrogen ion implantation
  • Physica Status Solidi (C) 2(2005)1, 693-698

Publ.-Id: 7649 - Permalink


On the Determination of the Optical Constants of Very Thin (Lambda/50) Films
Gushterova, P.; Sharlandjiev, P.; Schmidt, B.; Pham, M.;
The improvement of a recently developed spectrophotometric method for the determination
of the complex refractive index (ñ) and physical thickness (d) of very thin films (d = Lambda/50, Lambda is the wavelength in the visible and near infrared) is presented. The thin film transmittance (Tf), front side reflectance (Rf) and back side reflectance (Rf') are used for the estimation of (ñ, d). Utilizing the nanothickness of the films, we derive analytical expressions for Rf, Rf' and Tf, by development of the Abelès characteristic matrix elements up to the 4th order in ñd/Lambda. An optimization procedure is used to estimate (ñ, d). Thus, the problem related to multiple or lack of solutions is overcome. The method is applied to Au films, deposited on transparent glass substrates. For comparison of the resulting (ñ, d), Veriable Angle Spectroscopic Ellipsometry is used as an independent technique.
Keywords: Spectrophotometry, Ellipsometry, thin Au layers
  • Journal of Optoelectronics and Advanced Materials 7(2005)1, 305-308

Publ.-Id: 7648 - Permalink


Studies on the interaction of actinides with biomolecular and mineral surfaces and their contribution to long-term assessment
Raff, J.;
An overview of our work concerning the interaction of actinides with the biosphere and the geosphere is given and possible contributions to long-term assessment were discussed.
  • Lecture (Conference)
    GBIZ, 12.-14.09.2005, Barcelona, Spain

Publ.-Id: 7647 - Permalink


Cathodoluminescence of wet, dry, and hydrogen-implanted silica films
Fitting, H.-J.; Ziems, T.; Salh, R.; Zamoryanskaya, M. V.; Kolesnikova, K. V.; Schmidt, B.; von Czarnowski, A.;
The main luminescent centers in SiO2 films are the red luminescence R (1.85 eV) of the non-bridging oxygen hole center (NBOHC), a blue B (2.7 eV) band of the oxygen deficient centers (ODC's), a UV (4.3 eV),band, and a yellow Y (2.2 eV) band appears especially in hydrogen-implanted silica after longer time of irradiation. By means of pulsed electron beam excitation and a new track-stop technique we have investigated the luminescence life time as well as the initial luminescence properties at the beginning of irradiation. Thus the dose dependence of the red (R) luminescence in wet and dry oxide differs, decreasing in wet oxide from an initial level and increasing in dry oxide from almost zero at room temperature. Additionally, implanted hydrogen diminishes the red luminescence in wet oxide but increases the blue and the UV bands. Thus hydrogen passivates the NBOHC and keeps the ODC's in active emission states. A preliminary, model of luminescence center transformation is based!
A model of luminescensecenter transformation is based on radiolytic dissociation and re-association of mobile oxygen and hydrogen at the centers as well as formation of interstitial H-2, O-2, and H2O molecules. A comparison with the CL of ice layers shows that the H2O molecules should be the origin of the yellow (Y) luminescence.
Keywords: Cathodoluminescence, SiO2, ion implantation
  • Journal of Non-Crystalline Solids 351(2005)27-29, 2251-2262

Publ.-Id: 7646 - Permalink


Iron nanoparticles in amorphous SiO2: X-ray emission and absorption spectra
Kurmaev, E. Z.; Zatsepin, D. A.; Cholakh, S. O.; Schmidt, B.; Harada, Y.; Tokushima, T.; Osawa, H.; Shin, S.; Takeuchi, T.;
The local structure of the chemical bond of iron ions implanted into SiO2 glasses (implantation energy, 100 keV; fluence, 1 x 10(16) cm(-2)) is investigated using x-ray emission and absorption spectroscopy. The Fe L x-ray emission and absorption spectra are analyzed by comparing them with the corresponding spectra of reference samples. It is established that iron nanoparticles implanted into the SiO2 vitreous matrix are in an oxidized state. The assumption is made that the most probable mechanism of transformation of iron nanoparticles into an oxidized state during implantation involves the breaking of Si-O-Si bonds with the formation of Si-Si and Fe-O bonds.
Keywords: Nanoparticles, ion implantation, X-ray absorption and emission spectroscopy
  • Physics of The Solid State 47(2005)4, 754-757

Publ.-Id: 7645 - Permalink


Complex formation of U(VI) with the amino acid L-threonine and the corresponding phophate ester O-Phopho-L-threonine
Günther, A.; Geipel, G.; Bernhard, G.;
The complex formation of uranium(VI) with L-threonine and O-Phospho-L-threonine was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). An increase in fluorescence emission intensity and a corresponding red shift of the bands in the spectra compared to the free uranyl cation indicate a complex formation between UO22+ and the non- and phosphorylated amino acid threonine. The complex formation constants for a 1:1 and 1:2 complex in the case of L-threonine were determined to be logß111 = 10.33 ± 0.26 at ionic strength I = 0.1 M, logß111 = 10.25 ± 0.25 and logß122 = 19.94 ± 0.01 at ionic strength I = 0.5 M. The calculated constants of the different 1:1 uranyl complexes with O-Phospho-L-threonine are logß113 = 20.28 ± 0.11, logß112 = 18.94 ± 0.29 and logß111 = 15.02 ± 0.23 at I = 0.1 M.
Keywords: uranium, complexation, TRLFS, amino acid, phosphorylated amino acid, speciation
  • Radiochimica Acta 94(2006), 845-851

Publ.-Id: 7644 - Permalink


Identifizierung und Charakterisierung von U(VI)-Komplexen in höheren Pflanzen
Günther, A.;
Zusammenfassende Darstellung der bisherigen Ergebnisse der Untersuchungen zur chmeischen Speziation von Uran in Pflanzen und Vorstellung der dafür notwendigen Modellkomplexierungen (ausgewählte Beispiele)
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7643 - Permalink


EXAFS-Untersuchungen von U(VI)-Komplexlösungen mit ausgewählten Aminosäuren und Peptiden
Günther, A.; Roßberg, A.; Merroun, M.; Raff, J.;
Darstellung neuster EXAFS-Ergebnisse zur Aufklärung der Bindungsverhältnisse von U(VI) an verschiedenen Aminosäuren und Peptiden
  • Lecture (others)
    ROBL-Radiochemie Workshop, 13.12.2004, Dresden, Germany

Publ.-Id: 7642 - Permalink


Spektroskopische Charakterisierung von U-Spezies in Pflanzen
Günther, A.; Roßberg, A.;
Darstellung von Resultaten verschiedener TRLFS - und EXAFS Messungen an uranhaltigen Pflanzenproben
  • Lecture (others)
    ROBL-Radiochemie-Workshop, 08.12.2003, Dresden (Rossendorf), Deutschland

Publ.-Id: 7641 - Permalink


Interaction of Desulfovibrio äspöensis with selected actinides
Moll, H.; Merroun, M.; Selenska-Pobell, S.; Bernhard, G.;
Darstellung neuer Aspekte der Wechselwirkung von ausgewählten Aktiniden mit Desulfovibrio äspöensis.
Keywords: Actinides, Bacteria, Desulfovibrio äspöensis, Biosorption, Bioreduction, Bioaccumulation
  • Lecture (others)
    FZR - FSU Jena Workshop, 27.-28.07.2005, Dresden, Germany

Publ.-Id: 7640 - Permalink


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