Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32227 Publications
Comparison of numerical and experimental flow data from a liquid-metal model of a continuous casting mould
Maiwald, A.; Timmel, K.; Schwarze, R.; Gerbeth, G.;
Detailed knowledge of the flow fields in continuous casting moulds is of major importance, e.g., for the steel and the copper industry. Because there are only limited possibilities for measurements at real plant mould flows, model experiments and numerical simulations have been extensively used in the past for the inspection of mould flows. However, most data which are available in the literature are obtained at water model experiments, and most validation studies are based on those data sets. Recently, a new liquid-metal model of a continuous casting mould has been installed at the Forschungszentrum Dresden-Rossendorf. The facility allows for the first time flow measurements in liquid metal mould flows. The paper presents a first comparison of the experimental data with results from a numerical model of the mould flow. The numerical grid includes the submerged entry nozzle (SEN) and the mould. Simulations are performed with boundary conditions which fit to the operating parameters of the experiment. The Reynolds number based on the mean velocity and the hydraulic diameter of the SEN ports is about 4 x 104, the Reynolds number based on the mean velocity and the hydraulic diameter of the mould cross section area is about 3 x 103. The numerical model is based on the Reynolds-averaged Navier-Stokes (RANS) equations.
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, pp. 239-242
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland

Publ.-Id: 13812 - Permalink


Conductivity in DFT
Gemming, S.;
In nanostructured materials spatial confinement effects lead to structure-dependent modifications of the bulk transport properties. In part, such modifications can be accounted for by a classical master equation approach for the transport of the different charge carrier species. The rather large quantity of parameters, which enter such an approach, can more or less easily be adjusted to the dimensional characteristics and the electronic settings of the system as well as to temperature effects. On the other hand, a microscopically more detailed and mostly parameter-free picture is obtained from a quantum-mechanical treatment on the basis of the density-functional theory. An extension by a Green's function formalism allows the determination and analysis of electronic transport through contacted nanostructures. Examples will be given to demonstrate the applicability of the different approaches for dissipative and hopping transport through a regular array of nanostructures, for a mechanically triggered metal-insulator transition in nanowires, and for the enhanced conductivity at multiferroic domain walls.
Keywords: DFT, conductivity
  • Lecture (Conference)
    Wilhelm-und-Else-Heraeus Physics School on Density Functional Theory and its Applications in Crystallography, 07.-11.02.2010, Aachen, Deutschland

Publ.-Id: 13811 - Permalink


Density-functional theory within multi-scale modelling
Gemming, S.;
Modeling the changes in materials during everyday use requires a thorough understanding of processes on length and time scales which span several orders of magnitude. Standard simulation techniques are commonly restricted to much smaller ranges in length and time, thus a method hierarchy is desirable to join the virtues of approaches at different scales and employ this synergy for a scale-adapted description of modifications which materials undergo during processing and use. Electronic interactions including optical, magnetic and transport phenomena range at the shortest, the nanoscopic time and length scales. Their proper description provides the basis for more average meso- and macro-scale quantities, thus a precise nano-scale modelling provides the basis for a detailed and quantitative understanding of the macroscopic material piece. Density-functional theory is a computationally efficient numerical tool which provides fast access to the ground-state electronic properties and perturbation expansions yield also observables for more complex physical interactions. Determination of relevant processes at the atomistic scale and suitable averaging then yields input parameters for more meso-/macro-scale particel-based or continuum approaches.
Keywords: multiscale modelling, density functional theory, DFT
  • Lecture (Conference)
    Wilhelm-und-Else-Heraeus Physics School on Density Functional Theory and its Applications in Crystallography, 07.-11.02.2010, Aachen, Deutschland

Publ.-Id: 13810 - Permalink


DNS and LES of separation control using oscillating Lorentz forces
Albrecht, T.; Marlow, F.; Metzkes, H.; Stiller, J.;
The separated flow around an inclined flat plate at a Reynolds number 10↑4 has been computed using Direct Numerical and Large Eddy Simulation. A Lorentz force oscillates near the leading edge to reduce the separated flow region and increase the lift coefficient. Since no theory on relevant spanwise length scales of this flow is known to the authors, different mesh sizes have been investigated. Lift and drag coefficients seem to converge for ratio of spanwise length to chord ≥ 0.3. Although a comparison with PIV measurements is already quite satisfactory, simulation time should be extended to allow for more reliable statistics.
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland, pp. 688-691

Publ.-Id: 13809 - Permalink


Dosimetric characterization of laser-accelerated particles
Richter, C.;
kein Abstract vorhanden
  • Lecture (others)
    5th Meeting of the Scientific Advisory Board of OncoRay, 04.03.2010, Dresden, Deutschland

Publ.-Id: 13808 - Permalink


Auf dem Weg zu systematischen radiobiologischen Experimenten mit laserbeschleunigten Protonen: Entwicklung, Charakterisierung und Einsatz eines integrierten Dosimetrie- und Zellbestrahlungssystems
Richter, C.; Akhmadaliev, S.; Beyreuther, E.; Dammene, Y.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Naumburger, D.; Schürer, M.; Sobiella, M.; Weber, A.; Pawelke, J.; Baumann, M.;
Abstract too long (9790) - is not allowed from system
Keywords: laser, radiooncology, cell irradiation, laser particle acceleration
  • Lecture (Conference)
    19. Symposium - Experimentelle Strahlentherapie und Klinische Strahlenbiologie, 04.-06.03.2010, Dresden, Deutschland
  • Experimentelle Strahlentherapie und klinische Strahlenbiologie 19(2010), 192-195

Publ.-Id: 13807 - Permalink


Development of Diode-pumped lasers for ultra-high peak-power
Röser, F.; Siebold, M.; Loeser, M.; Kroll, F.; Schramm, U.; Sauerbrey, R.;
100J-class diode-pumped lasers (HEC-DPSSLs)
Laser materials
Spectroscopic & thermo-mech. properties
Optical Quality
PW-Laser development @ FZD
Applications
Laser electron acceleration
Laser ion acceleration
Keywords: HEC-DPSSL, diode,pumped,solid,state,laser,PW project
  • Lecture (others)
    PS&A Seminar Series, 04.02.2010, Livermore, CA, USA

Publ.-Id: 13806 - Permalink


Optical absorption, luminescence, and electron paramagnetic resonance (EPR) spectroscopy of crystalline to metamict zircon: Evidence for formation of uranyl, manganese, and other optically active centers
Kempe, U.; Thomas, S.-M.; Geipel, G.; Thomas, R.; Plötze, M.; Böttcher, R.; Grambole, G.; Hoentsch, J.; Trinkler, M.;
wird nachgereicht

Publ.-Id: 13805 - Permalink


Untersuchungen zum Einfluss von Huminsäuren auf die Migration von Actiniden in der Umwelt
Sachs, S.;
Huminsäuren (HS), ubiquitär vorkommende organische Makromoleküle, spielen eine wichtige Rolle in geochemischen Wechselwirkungsprozessen von Metallionen. HS sind löslich im pH-Bereich natürlicher Wässer und zeigen die Fähigkeit Metallionen zu komplexieren und Kolloide zu bilden. Außerdem sind HS durch ein ausgeprägtes Redoxverhalten charakterisiert. Aufgrund dieser Eigenschaften können HS die Speziation und somit auch den Transport von Metallionen, z.B. Actinidionen, in der Umwelt beeinflussen. Detaillierte Kenntnisse der geochemischen Wechselwirkungsprozesse von HS mit Actiniden sind z.B. für Langzeitsicherheitsanalysen für zukünftige Endlager hochradioaktiver Abfälle sowie zur Sanierung kontaminierter Flächen und Einrichtungen des ehemaligen Uranbergbaus erforderlich.
Im Vortrag werden am Beispiel von Uran detaillierte Untersuchungen zur Komplexierung von Actiniden mit HS vorgestellt. Der Einfluss der Uran-HS-Komplexierung auf die Uranspeziation wird anhand von Speziationsdiagrammen diskutiert. Weiterhin wird anhand von Ergebnissen aus Sorptions- und Transportuntersuchungen der mögliche Einfluss von HS auf Immobilisierung und Migration von Uran im Tongestein diskutiert und mit anderen Actiniden verglichen.
Keywords: Humic acid, uranium, complexation, speciation, migration, sorption, environment, clay, actinides
  • Invited lecture (Conferences)
    Umwelttechnisches Fachseminar "Wissenschaft&Praxis" des Instituts für Verfahrensentwicklung, Torf- und Naturstoff-Forschung (iTN), 31.03.2010, Zittau, Germany

Publ.-Id: 13804 - Permalink


Saturation of the filament density of ultrashort intense laser pulses in air
Henin, S.; Petit, Y.; Kasparian, J.; Wolf, J.-P.; Jochmann, A.; Kraft, S. D.; Bock, S.; Schramm, U.; Sauerbrey, R.; Nakaema, W. M.; Stelmaszczyk, K.; Rohwetter, P.; Wöste, L.; Soulez, C.-L.; Mauger, S.; Bergé, L.; Skupin, S.;
We experimentally and numerically characterize multiple filamentation of laser pulses with incident intensities of a few TW/cm2. Propagating 100 TW laser pulses over 42 m in air, we observe a new propagation regime where the filament density saturates. As also evidenced by numerical simulations in the same intensity range, the total number of filaments is governed by geometric constraints and mutual interactions among filaments rather than by the available power in the beam.
Keywords: High power laser propagation in air, filamentation, multiple filamentation

Publ.-Id: 13803 - Permalink


Chemical bonds and formation process of actinide(IV) oligomers and colloids
Hennig, C.; Takao, K.; Takao, S.; Ikeda-Ohno, A.; Banerjee, D.; Weiss, S.; Zaenker, H.; Kraus, W.; Emmerling, F.; Scheinost, A. C.;
Tetravalent actinides show a strong tendency towards hydrolysis followed by the formation of oligomers and colloids. This formation process was investigated on Th(IV), U(IV) and Np(IV) species with EXAFS, LIBD, XPS, HEXS, UV-Vis, NMR and XRD. We investigated the involved chemical bonds, the local structure and structure development as well as the formation mechanism.
We observed that the oligomerization of tetravalent actinides was limited by the presence of chelating ligands. The presence of carboxylic acids, for example, resulted in hexanuclear complexes [1]. Such polynuclear species consist of a framework made of oxo and hydroxo bonds which is terminated by chelating carboxylic acids. In absence of such terminating ligands, the polymerization often continues until stable colloids are formed [2]. This formation process is kinetically hindered due to several reasons related with (a) the limited number of OH groups in the An(OH)n4-n precursor and (b) terminating water molecules. The polymerization comprises of olation and oxolation processes. At a later stage, the initially amorphous structure of the colloides undergoes an ordering process during which hydroxo groups are systematically replaced by oxo groups. Zeta potential measurements indicated that the colloidal particles carry positive charge at acidic pH and negative charge at alkaline pH. We found that silicate is able to stabilize such colloids at near-neutral pH through modification of the inner structure and by influencing the electrostatic repulsion caused by an enhanced negative surface charge.
UV/Vis, EXAFS spectroscopy and light scattering proved to be sensitive tools to differentiate between hydolysis species, oligomers and colloids.

[1] Takao et al. (2009) Eur. J. Inorg. Chem. 32, 4771-4775.
[2] Ikeda-Ohno et al. (2009) Inorg. Chem. 48, 7201-7210.
Keywords: UV/Vis, EXAFS, light scattering, hydolysis species, oligomers, colloids
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 74(2010), A400-A400
  • Lecture (Conference)
    Goldschmidt Conference, 13.-18.06.2010, Knoxville, USA

Publ.-Id: 13802 - Permalink


Homogeneity study for obsidian provenancing by ion beam analysis
Eder, F.; Neelmeijer, C.; Bichler, M.; Merchel, S.;
Obsidian is a natural volcanic glass which was one of the most appreciated materials by of ancient man for cutting tools and has been found by researchers in many locations, far away from any natural source. Reliable provenancing can provide evidence of contacts over a certain distance and information about exchange patterns and mobility of prehistoric people.
The application of analytical methods can solve the problem of obsidian provenancing by means of its highly specific chemical composition, the “chemical fingerprint”. Combined external Ion Beam Analysis (IBA) measurements, consisting of Proton Induced X-ray Emission (PIXE), Proton Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), are frequently used due to the high sensitivity and the non-destructive beam mode. Our study has been carried out at the 5 MV Tandem accelerator of the Ion Beam Centre of FZD, where a number of quantitative glass analyses has been performed simultaneously with all three external ion beam techniques [1-5].
Obsidian usually exhibits a very uniform appear-ance and is generally described as a relatively homogeneous material. Banded obsidians can be observed also, and the question was raised, if these bands are caused by differences in the chemical composition or if these changes in the optical properties are related to inclusions of clouds of gas bubbles, microphenocrysts or similar features without significant compositional influence. Therefore, a systematic investigation of a banded obsidian sample from Demengakion (Milos, Greece) has been carried out in order to check the actual variation range of the chemical composition. (Fig. 1).
To investigate the influence of different preparation techniques on the analytical results, we produced an obsidian in-house reference sample (Fig. 2). This specimen originates from the highly homogeneous obsidian source Hrafntinnuhryggur (Iceland) and features three different surfaces: natural fracture, ground finish (1200 diamond lap) and polished [6].
This study is part of a project which aim is to apply selected analytical methods, in particular IBA, Neutron Activation Analysis (NAA) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), to detect a maximum of compositional differences between easily available samples of the natural obsidian sources in Europe. This knowledge should enable to decide, which least invasive analytical method should be chosen for the analysis of a specific archaeological artefact, on a case by case basis.
References: [1] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136–146. [2] Mäder M. et al. NIMB 239 (2005) 107-113. [3] Mäder M. and Neelmeijer C. NIMB 226 (2004) 110–118. [4] Jembrih D. et al. NIMB 181 (2001) 698–702. [5] Mäder M. et al. NIMB 136-138 (1998) 863–868. [6] Tuffen H. and Castro J. M. Journal of Volcanology and Geothermal Research 185 (2009) 352–366.
Keywords: archeometry, RBS, PIXE, PIGE
  • Poster
    Ionenstrahlphysik-Workshop 2010, 29.-31.03.2010, Dresden-Rossendorf, Deutschland

Publ.-Id: 13801 - Permalink


Landweber-EXAFS structural analysis of aqueous polynuclear U(VI) complexes with tartaric acid
Rossberg, A.; Lucks, C.; Tsushima, S.; Scheinost, A. C.;
In coordination chemistry, an open question is if the structure of an aqueous metal complex is equal to the structure of its solid form. While the structure of the solid can usually be determined with great reliability and precision by XRD, determination of the structure in solution by EXAFS may be much more biased. An intrinsic problem of EXAFS shell fitting is that the radial pair distribution function (RPDF) is approximated by Gaussians functions imitating the coordination shells. Different combinations of shells can yield different structures with similar fit quality, thereby making the structural solution non-unique. Even the so-called F-test often does not allow obtaining a unique solution.
Therefore, we developed two methods which enable the direct calculation of the RPDF and the spatial structure of metal complexes in solution. Solely based on the FEFF scattering theory, the Landweber inverse method [1] yields the RPDF for the aqueous bi- and tri-nuclear U(VI)-tartaric acid complexes without predefined assumptions about the form of the RPDF. With this information and density functional theory (DFT) calculations, the spatial structures of the complexes are refined by Monte Carlo Target Transformation Factor Analysis [2], which also include the calculation of higher order scattering events. Using this combinatorial structural analysis, we were able to show that in the (UO2)3(H-1Tar)3(OH)25- complex a central equatorial oxygen atom at a radial U-O distance of 2.22 Å connects the three uranium atoms symmetrically. Consequently, the formula of the aqueous complex corresponds to its stoichiometric equivalent (UO2)3(mue3-O)(H-1Tar)35-.

[1] Rossberg & Funke (2010), J. Synchr. Rad. 17, 280-288.
[2] Rossberg et al. (2005), Anal. Bioanal. Chem. 383, 56-66.
Keywords: Landweber iteration, EXAFS, uranium, tartaric acid, aqueous, complexes, radial pair distribution function
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 74 Suppl.1(2010)12, A884
  • Poster
    Goldschmidt 2010, 13.-18.06.2010, Knoxville, USA

Publ.-Id: 13800 - Permalink


Ion Beam Analysis at FZD: Achievements and Perspectives
Munnik, F.; Heller, R.;
There are many applications for which it is important to know the composition of surface layers and even to know the composition as a function of depth. Such information is needed for (ultra) shallow implantation profiles and the damage caused by implantation, diffusion barriers for IC technology, interface mixing in IBAD processing, multilayers for X-ray mirrors, magnetic multilayer structures, etc.
Ion Beam Analysis (IBA) can provide answers through a variety of methods for the compositional analysis of surface layers. In this presentation, the principles of (IBA) are presented with the emphasis on those methods useful for materials science like Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA). The possibilities of analysis with our equipment is shown by means of examples of applications.
  • Lecture (others)
    Materials Science Seminar, 19.01.2010, Dresden, Germany

Publ.-Id: 13799 - Permalink


Autonomous sensor particle for parameter tracking in large vessels
Thiele, S.; Da Silva, M. J.; Hampel, U.;
We developed a neutrally buoyant self-powered sensor particle for the measurement of spatially distributed process parameters in large vessels. One intended application is the measurement of flow parameters in stirred fermentation biogas reactors. The prototype sensor particle is a robust and neutrally buoyant capsule with integrated measurement electronics which performs logging of temperature, absolute pressure (immersion depth) and 3D-acceleration data. In an initial flow experiment the autonomous operation of the developed prototype was successfully proven, showing feasibility for future application in fermentation reactors and other industrial processes.
Keywords: Autonomous Sensing, Parameter Tracking, Multi-Parameter Measurement, Neutral Buoyancy, Sensor Particle

Publ.-Id: 13798 - Permalink


Reaction of Pu(III) and (V) with magnetite and mackinawite: a XANES/EXAFS investigation
Kirsch, R.; Fellhauer, D.; Altmaier, M.; Neck, V.; Rossberg, A.; Charlet, L.; Scheinost, A. C.;
Plutonium is the major transuranium actinide in nuclear waste and a highly toxic environmental contaminant. As iron(II) minerals are ubiquitous and known to reduce a range of metal(loid)s, including As, Cr, Se, Pu and Np, through surface-mediated redox reactions, we investigated here the reactivity of magnetite (Fe3O4) and mackinawite (FeS) towards Pu(III) and (V) using XAFS to analyse the oxidation state and molecular structure of the reaction products.
Experimental Conditions
Mineral syntheses and reactions were carried out under anoxic conditions in N2 or Ar glove-boxes. Fe3O4 and FeS were reacted for 40 days in 0.1 M NaCl with Pu (1x10-5M) at approx. pH 8. 242Pu was added as electrolytically prepared Pu(V) to Fe3O4 and FeS, and as Pu(III) to Fe3O4.
Results and Discussion
The spectra obtained from tri- and pentavalent Pu reacted with magnetite are nearly identical; shell fitting yielded a Pu-O distance of 2.50 Å, indicative of Pu(III). Using Monte Carlo modeling of the EXAFS spectra (MC) [1], we were able to unequivocally identify a distinct Pu(III) surface complex wherein Pu(III) is connected via three oxygen atoms to three edge-sharing FeO6-octahedra of the Fe3O4 {111} face. This result is in disagreement with [2], where in the absence of spectroscopic methods Pu(IV) had been determined as the oxidation state resulting from reduction of Pu(V) by magnetite under anoxic conditions. After reaction of Pu(V) with mackinawite, Pu(IV) was identified as the prevalent Pu oxidation state by both XANES and EXAFS shell fitting. The EXAFS spectrum closely ressembles that of PuO2 solids and colloids. Our study demonstrates that under reducing conditions in geological environments both Pu(IV) and Pu(III) species may be relevant and migration as eigen-colloids or adsorbed species may play an important role in controlling Pu mobility.
Keywords: Plutonium, XAFS, XANES, EXAFS, magnetite, mackinawite, redox reaction, surface complex
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 74 Suppl.1(2010)12, A520

Publ.-Id: 13796 - Permalink


Measurement of the hydrogen concentration in indium oxide tubular nanostructures
Voelskow, M.; Grambole, D.; Skorupa, W.; Kanjilal, A.; Kumar, M.; Chatterjee, R.; Milikisiyants, S.; Lakshmi, K. V.; Singh, J. P.;
Hydrogen is ubiquitous and it is often difficult to remove hydrogen from synthesis of nano-materials. Therefore, studying interaction of hydrogen with metals and semiconductors is of immense interest owing to the development of efficient materials for the storage of hydrogen and gas-sensing devices.
Keywords: Hydrogen, indium oxide, nuclear methods
  • Poster
    Workshop Ionenstrahlphysik, 29.-31.03.2010, Dresden, BRD

Publ.-Id: 13795 - Permalink


Photon Counting System for Time-resolved Experiments in Multibunch Mode
Puzic, A.; Korhonen, T.; Kalantari, B.; Raabe, J.; Quitmann, C.; Juellig, P.; Bommer, L.; Goll, D.; Schuetz, G.; Wintz, S.; Strache, T.; Koerner, M.; Marko, D.; Bunce, C.; Fassbender, J.ORC
Photon Counting System for Time-resolved Experiments in Multibunch Mode
Keywords: photon counting, synchrotron radiation, multibunch, time-resolved, magnetic imaging

Publ.-Id: 13794 - Permalink


Spektroskopische Bestimmung der Bindungsform von Europium(III) und Curium(III) im menschlichen Urin
Heller, A.; Barkleit, A.; Bernhard, G.; Ackermann, J.-U.;
Das Institut für Radiochemie des Forschungszentrums Dresden-Rossendorf e.V. beschäftigt sich mit der Aufklärung des Schicksals von radioaktiven Schwermetallen in der Umwelt. Hierzu werden u.a. sowohl die Bindung an natürlich vorkommende Liganden untersucht, als auch die komplexeren Wechselwirkungen in Pflanzen- und Bakterienzellen oder in Biofluiden. Die vorgestellte Promotionsarbeit befasst sich dabei mit der spektroskopischen Aufklärung der Bindungsform von Curium(III) und Europium(III) in natürlichem, menschlichem Urin.
Curium und Europium sind zwei f-Elemente, deren Metabolismus im Biosystem bis heute nicht vollständig geklärt ist. Da Curium innerhalb des Kernbrennstoffzyklus gebildet wird und nur radioaktive Isotope aufweist, stellt es im Falle einer Kontamination oder unfallbedingter Freisetzung in die Umwelt eine ernste Gefahr für die Gesundheit dar. Um mögliche Dekontaminationsmittel zu erforschen, müssen daher sein Metabolismus und die Bindungsform in Biofluiden bekannt sein. Im Gegensatz dazu ist Europium nicht radioaktiv und gewinnt in der Medizin immer mehr an Bedeutung als Bestandteil von Kontrastmitteln in der bildgebenden Diagnostik. Trotz seiner wachsenden Applikation ist auch der Metabolismus dieses Metalls bisher unbekannt. Beide Elemente weisen ähnliche Eigenschaften auf, da sie in Form ihrer dreiwertigen Ionen vergleichbare Elektronenkonfigurationen besitzen. Aufgrund seiner besseren Handhabbarkeit wird Europium daher oft als Analogon für Curium verwendet. Darüber hinaus zeigen beide Elemente einzigartige Fluoreszenzeigenschaften. Dies erlaubt Untersuchungen mittels (zeitaufgelöster) laserinduzierter Fluoreszenzspektroskopie im Spurenkonzentrationsbereich.
Urin ist das Hauptausscheidungsmedium im menschlichen Körper und besteht zu über 90 % aus Harnstoff. Mögliche Reaktionen mit dieser Matrixkomponente wurden daher zuerst untersucht. Weitere biologisch relevante, organische Liganden, deren Komplexbildungsvermögen gegenüber Curium(III) und Europium(III) ebenfalls untersucht wurde, sind Citronensäure und Aminosäuren. Die Ergebnisse zeigen, dass die Komplexirung mit Harnstoff vernachlässigbar gering ist und Aminosäuren bei physiologisch relevanten pH-Werten ebenfalls nur schwache Komplexe bilden. Demgegenüber bildet Citronensäure starke Komplexe mit beiden Metallen.
Erste Aufnahmen von Lumineszenzspektren natürlicher, menschlicher Urinproben, die in vitro mit einem der beiden Elemente versetzt wurden, zeigen, dass bei niedrigeren pH-Werten Komplexe mit Citronensäure dominieren. Im Gegensatz dazu scheinen bei höheren pH-Werten Komplexe mit anorganischen Liganden, vorzuherrschen.
Keywords: Eu(III), Cm(III), Biofluide, Komplexierung, TRLFS, Speziation von Schwermetallen
  • Lecture (others)
    Umweltkolloquium, 01.04.2010, Dresden, Deutschland

Publ.-Id: 13793 - Permalink


Relaxation dynamics in graphene investigated in the mid- and far-infrared spectral range
Winnerl, S.; Helm, M.; Malic, E.; Knorr, A.;
We describe experiments and microscopic modelling based on density matrix theory to study the relaxation dynamics in graphene. Experiments using the free-electron laser at FZD include also experiments in magnetic fields which will show how Landau quantization can quench relaxation channels.
Keywords: graphene, relaxation dynamics
  • Poster
    Begutachtungskolloquium zum Schwerpunktprogram "Graphen" der DFG, 21.-22.01.2010, Bad Honnef, Germany

Publ.-Id: 13792 - Permalink


Large Scale and Small Scale Terahertz Sources for Spectroscopy
Winnerl, S.;
We present FELBE, the free-electron laser at FZD and discuss time-resloved experiemnts using its radiation. Furthermore we discuss tabletop terahertz sources based on surface emitters and scalable photoconductive emitters.
Keywords: Terahertz, free-electron laser, photoconductive emitter
  • Lecture (others)
    Seminarvortrag in der Gruppe von K. von Klitzing, 21.12.2009, Stuttgart, Germany

Publ.-Id: 13791 - Permalink


Efficiency, energy, and power scaling of diode-pumped, short-pulse laser amplifiers using Yb-doped gain media
Siebold, M.; Loeser, M.; Koerner, J.; Wolf, M.; Hein, J.; Wandt, C.; Klingebiel, S.; Karsch, S.; Schramm, U.;
We present a novel approach to overcome efficiency limitations of nanosecond lasers based on Yb-doped materials. Furthermore, we introduce a combination of bulk and thin-disk design for power scaling of diode-pumped lasers.
  • Lecture (Conference)
    Advanced Solid-State Photonics (ASSP), 31.01.-03.02.2010, San Diego, USA
  • Contribution to proceedings
    Advanced Solid-State Photonics (ASSP), 31.01.-03.02.2010, San Diego, USA
    Efficiency, Energy, and Power Scaling of Diode-Pumped, Short-Pulse Laser Ampliers Using Yb-Doped Gain Media: OSA Technical Digest Series, AWB19

Publ.-Id: 13790 - Permalink


Humic acid model substances with pronounced redox functionality for the study of environmentally relevant interaction processes of metal ions in the presence of humic acid
Sachs, S.; Bernhard, G.;
Humic acid (HA) model substances with pronounced redox functionality were synthesized by oxidation of hydroquinone or catechol in the presence of glycine or glutamic acid and characterized concerning their elemental, structural and functional properties. In order to characterize the redox properties of the synthetic products, formal redox potentials and Fe(III) reducing capacities were determined and compared to purified Aldrich HA (AHA). Furthermore, the reduction of U(VI) in the presence of HA was studied.
The synthetic products show elemental, functional and structural properties comparable to natural HA, however, they are characterized by high amounts of phenolic/acidic OH groups. Furthermore, the synthetic HA show significantly higher reducing capacities for Fe3+ and [Fe(CN)6]3- at pH 3.0 and at pH 9.2, respectively, than AHA. The highest reducing capacities were obtained for HA Cat-Gly, an oxidation product from catechol and glycine, which is characterized by the lowest formal redox potential of all studied HA. Indications for a slight reduction of U(VI) in the presence of HA were observed, whereby, HA Cat-Gly exhibits again the highest reducing capacity. Using modified HA with blocked phenolic/acidic OH groups the importance of these functional groups for the redox behavior of HA was confirmed.
Synthetic HA with pronounced redox functionality can be used to study the redox behavior of HA and the redox stability of metal ions in the presence of HA and furthermore, to stabilize redox-sensitive metal ions against oxidation in complexation and transport studies with HA. This contributes to a better understanding of interaction processes of metal ions with humic substances in soils, sediments and waters.
Keywords: Humic acid, humic acid model substances, synthesis, characterization, redox behavior, redox potential, reducing capacity, iron(III), uranium(VI)

Publ.-Id: 13789 - Permalink


Degradation of cover SiO2 on Ge during Ga implantation
Fiedler, J.; Heera, V.; Bischoff, L.; Facsko, S.; Heinig, K.-H.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Voelskow, M.; Wündisch, C.; Skorupa, W.; Gobsch, G.;
Germanium is currently considered as a potential replacement for silicon devices [1]. The formation of heavily doped, shallow junctions in Ge by ion im-plantation and appropriate annealing techniques is under investigation [2, 3]. In contrast to Si the Ge surface is severely affected by irradiation damage. Im-plantation into the uncovered Ge surface leads to sur-face roughening and even porous layers [3]. Therefore, the Ge surface must be protected by a thin cover layer, which is commonly a sputtered SiO2-layer between 10 and 30 nm. This cover layer remains on the Ge sample also during annealing. For light dopants like B or P this oxide layer remains stable and smooth. However, with increasing ion mass and fluence surface erosion and oxide degradation can occur. A relatively heavy ion of interest is Ga [3]. It is a shallow acceptor with a high solid solubility in Ge. We studied the effect of Ga im-plantation through a SiO2 cover layer.
Keywords: doping of germanium, cover SiO2, Ga implantation, surface degradation
  • Poster
    Workshop Ionenstrahlphysik, 29.-31.03.2010, Dresden-Rossendorf, Deutschland

Publ.-Id: 13788 - Permalink


Non-termination of yrast bands at maximum configuration spin in 73Kr
Steinhardt, T.; Eberth, J.; Thelen, O.; Schnare, H.; Schwengner, R.; Plettner, C.; Käubler, L.; Dönau, F.; Algora, A.; de Angelis, G.; Gadea, A.; Napoli, D. R.; Hausmann, M.; Jungclaus, A.; Lieb, K. P.; Müller, G. A.; Jenkins, D. G.; Wadsworth, R.; Wilson, A. N.;
High-spin states in 73Kr were studied at the XTU tandem accelerator of the Laboratori Nazionali di Legnaro using the reaction 40Ca(40 Ca,2pn) at a beam energy of 185 MeV. Gamma rays were detected with the EUROBALL spectrometer. Particle detection enabled us to identify the reaction channel leading to 73Kr. The yrast bands of positive and negative parity were established up to probable spins of 61/2+ and 63/2- , respectively. The energies of the two identified bands agree well with the predictions of the configuration-dependent Cranked Nilsson-Strutinsky approximation and indicate that the nucleus remains collective up to the maximum spins of the respective high-spin configurations. The positive-parity band represents one of the rare cases where band non-termination at the highest spin of the configuration could be established experimentally.
Keywords: Nuclear structure, gamma-ray spectroscopy, particle detection, EUROBALL, Cranked Nilsson-Strutinsky calculations.

Publ.-Id: 13787 - Permalink


Two models of PT Quantum Mechanics and their behavior in the vicinity of spectral singularities
Günther, U.; Samsonov, B.; Rotter, I.; Graefe, E.-M.; Korsch, H.-J.; Niederle, A.;
The last ten years witnessed a strong research activity into so called PT Quantum Mechanics (PTQM) --- a Quantum Mechanics whose Hamiltonians are allowed to be non-Hermitian but PT-symmetric. In general, PTQM has sectors of exact PT-symmetry with purely real energy spectrum as well as sectors of spontaneously broken PT-symmetry with pairwise complex conjugate energy branches. Sectors of exact PT-symmetry can be isomorphically mapped into models of conventional (von Neumann) Quantum Mechanics (possibly of highly nonlocal type). Sectors of spontaneously broken PT-symmetry might have realizations as certain effective quantum systems. Varying the coupling parameters of PTQM models the corresponding quantum system can undergo phase transitions from exact PT symmetry to spontaneously broken PT-symmetry. Such PT phase transitions are associated with branch points (exceptional points) of the energy spectrum --- so called spectral singularities.

In the talk two PTQM models and their behavior in the vicinity of spectral singularities will be discussed.

In the first part of the talk, I will report on the quantum brachistochrone problem for PTQM, i.e. the problem of finding a PT-symmetric Hamiltonian which minimizes the time needed for evolving a given initial state into a predefined final state (e.g. for a spin-flip). This problem was solved by Bender, Brody, Jones and Meister in 2007. It turned out that in PTQM the evolution time for a spin flip can be tended toward zero so that the Aharonov-Anandan lower bound on the evolution time for Hermitian systems would be violated --- a kind of "quantum wormhole" effect. In 2007 we showed that this effect occurs in the vicinity of a PT phase transition (a spectral singularity). A still open problem at that time was a possible scheme for an experimental realization, because one somehow would have to switch between PTQM and experimental setups based on conventional QM. In [Phys. Rev. Lett. 101, 230404, 2008] we solved this switching problem by embedding the PTQM brachistochrone into a higher dimensional Hilbert space. In this way we found a realization of the PTQM brachistochrone evolution as a special kind of tuned unitary evolution in a highly asymmetrically entangled two-qubit setup --- which in principle might be realized experimentally in the nearest future.

The second part of the talk will be devoted to a non-Hermitian PT-symmetric two-mode Bose Hubbard model which might describe e.g. a BEC in a double-well potential with additional well-balanced gain-loss couplings. The main focus is laid on the unfolding of the higher-order spectral singularities typical for this kind of models. A perturbative Newton polygon technique allows us to qualitatively explain the numerically obtained branching behavior of the energy spectrum. It turns out that the Hessenberg type of the effective coupling matrix is responsible for the special Galois structure of the occurring eigenvalue rings in the complex energy plane.
Keywords: PT quantum mechanics, spectral singularity, exceptional point, quantum brachistochrone, spin flip, Naimark dilation, two-qubit state, Bose Hubbard model, Bose Einstein condensate, Newton polygon technique, Galois structure, eigenvalue ring, singularity unfolding, Hessenberg type
  • Lecture (Conference)
    Many-Body Open Quantum Systems: From Atomic Nuclei to Quantum Dots, 22.-26.02.2010, Trento, Italy

Publ.-Id: 13786 - Permalink


XPS and XAS investigation of Sb(V) reduction on mackinawite: Effect of pH and surface loading
Banerjee, D.; Kirsch, R.; Scheinost, A. C.;
Sb exists in nature in a wide range of oxidation states and can be a potential hazardous contaminant depending on its speciation and reactivity. In this study we employed cryogenic-XPS and XAS techniques in order to understand the reduction of SbV at the surface of mackinawite (FeS) as a function of pH and surface loading.
Experimental Conditions
Nanoparticulate, Mackinawite samples were prepared and stored as suspensions under strictly anoxic conditions (~ 1 ppmv O2) in a Jacomex glovebox. Sorption experiments at pH 5 and pH 8 with increasing Sb concentrations (0.1, 0.3, 0.6, 0.8 mM) were also conducted in the same glovebox under anoxic conditions [1, 2]. X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) measurements were conducted on frozen wet pastes of reacted mackinawite samples.
Results and Discussion
Sb3d XPS spectra of reacted sample series at pH 5 revealed presence of increasing amounts of SbIII at the surface suggesting that the rate of reduction of SbV was directly proportional to surface loading. Corresponding Fe 2p ans S 2p spectra of the same samples showed significant increase in the proportion of FeIII species and presence of S0 at the surface. However, the proportion of S0 remained constant suggesting that Fe is the dominant redox partner in this sytem. At pH 8, presence of SbIII was only observed at higher surface loadings indicating that adsorption and redox processes both occur at much slower rate compared to that at pH 5. In addition, increased contribution of surface monosulfide group at pH 5 suggest that Sb is most likely bound to S atoms at the surface, which was confirmed by Sb K-edge EXAFS spectra. In contrast, at pH 8, such increase in surface monosulfide contributions are absent, suggesting Sb is most likely bound to O atoms at the surface.
Keywords: XPS, mackinawite, redox processes, surface loading, EXAFS
  • Lecture (Conference)
    Goldschmidt 2010, 13.-18.06.2010, Knoxville, USA
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 74(2010)11, A47-A47

Publ.-Id: 13785 - Permalink


N-Doped Photocatalytic Titania Thin Films on Active Polymer Substrates
Tavares, C. J.; Marques, S. M.; Lanceros-Méndez, S.; Rebouta, L.; Alves, E.; Barradas, N. P.; Munnik, F.; Girardeau, T.; Riviére, J.-P.;
Active polymer substrates have found their way in the semiconductor industry as a base layer for flexible electronics, as well as in sensor and actuator applications. The optimum performance of these systems may be affected by dirt adsorbed on its surface, which can also originate mechanisms for the degradation of the polymer. Titanium dioxide (titania) semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron sputtering on one of the most applied and investigated electroactive polymer: poly(vinilidene fluoride), PVDF In order to increase the photocatalytic efficiency of the titania coatings, a reduction of the semiconductor band-gap has been attempted by using a nitrogen doping. Rutherford Backscattering Spectroscopy was used in order to assess the composition of the titania thin films, whereas Heavy Ion Elastic Recoil Detection Analysis provided the evaluation of the doping level of nitrogen. X-ray Photoelectron Spectroscopy provided valu!
able information about the cation-anion binding within the semiconductor lattice. The photocatalytic performance of the titania films have been characterized by decomposing an organic dye illuminated with combined UV/visible light.

Publ.-Id: 13784 - Permalink


P0805 Erhöhung der Hochtemperaturoxidationsbeständigkeit von TiAl-Legierungen und daraus bestehenden Bauteilen durch Pl3
Kolitsch, A.; Yankov, R.; Donchev, A.; Schütze, M.;
Die Plasma-Immersion-Ionen-Implantation (Pl3) von Fluor, das aus z. B. einem CH2F2-Plasma generiert wurde, in die Oberfläche von TiAl-Bauteilen kann deren Oxidationsbeständigkeit im Temperaturbereich von 700 bis 1100°C an trockener und feuchter Luft oder anderen oxidierenden Atmosphären auch unter Temperaturwechselbeanspruchung gegenüber unbehandelten TiAl-Legierungen deutlich erhöhen. Entgegen dem bisherigen Kenntnisstand, wo nur die reinen Halogene verwendet wurden, lässt sich durch Verwendung von z. B. Difluormethan oder Tetrafluorkohlenstoff ein deutlich vereinfachter Ionen-Implantationsprozess durchführen als bei reiner Fluorimplantation, ohne eine Beeinträchtigung des positiven Fluoreffekts zu erzielen. Das Fluor wird in kontrollierbaren Mengen in die Oberflächenrandzone von TiAl-Bauteilen implantiert, wo es seinen positiven Effekt auf den Oxidationswiderstand entfaltet.
  • Patent
    DE102008028990A1: Offenlegung-11.01.2010; Erteilung-08.10.2013

Publ.-Id: 13783 - Permalink


P0809 Vorrichtung und Verfahren zur Auswertung einer Aktivitätsverteilung sowie Bestrahlungsanlage
Rietzel, E.; Bert, C.; Parodi, K.; Enghardt, W.;
Die Erfindung betrifft eine Vorrichtung zur Auswertung einer in einem bewegten Zielobjekt auftretenden Aktivitätsverteilung, welche durch einen mit einer Bestrahlungseinrichtung erzeugten Strahl erzeugbar ist, aufweisend:
- einen Positronen-Emissions-Tomographen, welcher ausgebildet ist zum Aufzeichnen von durch den Strahl im Zielobjekt erzeugten Photonen und zur Erzeugung von Messdaten, welche Entstehungsorte der Photonen repräsentieren,
- eine Bewegungserfassungseinrichtung, welche ausgebildet ist, ein Bewegungssignal zu erzeugen, das die Bewegung des Zielobjekts repräsentiert,
- eine Auswertungseinheit, welche ausgebildet ist, die Entstehungsorte der gemessenen Photonen zu Positionen im Zielobjekt unter Verwendung des Bewegungssignals zuzuordnen, wodurch eine räumliche Charakteristik der tatsächlich im Zielobjekt erzeugten Aktivitätsverteilung über die durch den Strahl erzeugten Photonen auswertbar ist, sowie eine Bestrahlungsanlage und ein Verfahren, in welchen eine derartige Vorrichtung eingesetzt wird.
  • Patent
    DE 102008036478 A1 - 11.01.2010
  • Patent
    Anmeldung: WO 2010015358 A1 2010/02/11

Publ.-Id: 13782 - Permalink


Ions and X-rays: Unique partners for accurate stopping power determination of 15N ions in Si for hydrogen depth profiling
Zier, M.; Reinholz, U.; Riesemeier, H.; Radtke, M.; Munnik, F.;
In many areas of material sciences hydrogen analysis is of particular importance. For example, hydrogen is most abundant as impurity in thin-film materials - depending on the deposition process - and has great influence on the chemical, physical and electrical properties of many materials. Therefore, it is necessary to monitor the H-concentration by depth profiling. Best-suited methods for depth-resolved hydrogen analysis are ion beam techniques such as elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). In principle, both methods can be performed as primary - reference material free - methods.
The most common method, NRA, makes use of the 6385 keV resonance of the 1H(15N,αγ)12C nuclear reaction. The correct quantification of the depth scale in the measured hydrogen profiles essentially relies on accurate stopping power values, i.e. any imperfection in the stopping power values is influencing all H-values provided by NRA. For the determination of the accurate stopping power of ~6.4 MeV 15N ions in hydrogen-containing amorphous Si-layers (a-Si:H), we have, therefore, combined NRA with X-ray reflectometry (XRR), also a primary method.
The samples are prepared by magnetron sputtering of a-Si in an Ar/H2-atmosphere on a Cr-layer, which is needed as contrast material for XRR. The energy loss in the layers is measured by NRA at FZD. The layer thickness, density and roughness are determined by XRR using synchrotron radiation. XRR measurements were performed at the electron storage ring BESSY at the hard X-ray beamline BAMline. The beam was monochromatised to 10 keV using a Si [111]-double-crystal monochromator. The reflected photons of the θ-2θ-scans from the 6-circle goniometer are counted by a scintillation detector and a photodiode, respectively. Data analysis is performed by the IMD 4.1 software package.
The unique combination of results from NRA and XRR allows the accurate calculation of the mass stopping power independent of the density of the material. Our preliminary results show significant discrepancies in the order of 15-20% to the commonly used stopping powers calculated by the well accepted SRIM program (version 2006). These discrepancies have to be considered, if transforming the energy loss scale to a depth scale in hydrogen profiles. Thus, further work for confirmation is absolutely needed.
Acknowledgments: The help of D. Grambole and S. Merchel (FZD) is greatly appreciated.
Keywords: Stopping power hydrogen depth profiling NRA XRR synchrotron radiation
  • Poster
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten (SNI2010), 24.-26.02.2010, Berlin, Deutschland

Publ.-Id: 13781 - Permalink


GDCh Arbeitskreis Analytik mit Radionukliden und Hochleistungsstrahlenquellen
Eberhardt, K.; Henkelmann, R.; Merchel, S.; Denecke, M. A.;
Der Arbeitskreis „Analytik mit Radionukliden und Hochleistungsstrahlenquellen“ (ARH) wird gemeinsam von den GDCh-Fachgruppen „Nuklearchemie”, „Analytische Chemie”, „Makromolekulare Chemie“, „Festkörperchemie und Materialforschung“ und der „Wöhler-Vereinigung für Anorganische Chemie“ getragen. Der ARH Vorstand setzt sich aus Synchrotron-, Neutronen- und Ionen-Experten zusammen und steht hiermit in direktem Bezug zum SNI2010. Der Arbeitskreis setzt sich die Förderung und den Einsatz von Radionukliden zur Qualitätssicherung von Analysenverfahren und die Analytik mit Großgeräten zum Ziel. Zurzeit strebt der ARH-Vorstand insbesondere eine Vertiefung von Kontakten zu anderen wissenschaftlichen Vereinigungen wie dem „Komitee für Synchrotronstrahlung“ (KFS) und dem Komitee Forschung mit nuklearen Sonden und Ionenstrahlen (KFSI) an. Ein weiterer Schwerpunkt ist die (Fort-)Bildung sowie der Wissenstransfer und der Erfahrungsaustausch in Form von wissenschaftlichen Tagungen und Seminaren. Zum Beispiel finden das 23. SAAGAS („Seminar Aktivierungsanalyse und Gammaspektroskopie“) im September 2009 und der Workshop „Ionenstrahlphysik“ im März 2010 in Dresden statt. In dieser Posterpräsentation werden der Arbeitskreis ARH, seine Arbeitsschwerpunkte und Ziele sowie zukünftige
Aktivitäten dargestellt.
Keywords: nuclear analytics, synchrotron radiation, neutrons, ion accelerator
  • Poster
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten (SNI2010), 24.-26.02.2010, Berlin, Deutschland

Publ.-Id: 13780 - Permalink


Ungeduldige Wissenschaftler: Bestimmung langlebiger Radionuklide mittels Beschleunigermassenspektrometrie (AMS)
Merchel, S.;
Das Forschungszentrum Dresden-Rossendorf (FZD) erweitert diesen Sommer sein Portfolio um eine weitere hochsensitive analytische Methode: die Beschleunigermassenspektrometrie (accelerator mass spectrometry, AMS). Die AMS ermöglicht insbesondere die Bestimmung langlebiger Radionuklide mit Halbwertszeiten im Bereich von ka bis Ma.

Entgegen der sonst allgemein üblichen Zerfallszählung warten die „ungeduldigen AMS-Wissenschaftler“ dabei nicht auf den Zerfall des Radionuklids und die Detektion des durch den Zerfall emittierten Teilchens bzw. der Strahlung. Vielmehr werden die noch nicht zerfallenen Radionuklide wesentlich effizienter massenspektrometrisch bestimmt. Die AMS besitzt allerdings gegenüber der konventionellen Massenspektrometrie den Vorteil, dass sie Störsignale, hervorgerufen von Molekülionen oder Ionen ähnlicher Masse, insbesondere Isobare, effektiver unterdrücken kann. Die AMS liefert somit weitaus niedrigere Nachweisgrenzen als die konventionellen Methoden.

Im Gegensatz zu den in Deutschland und Europa gängigen niederenergetischen AMS-Anlagen, die sich hauptsächlich auf die Bestimmung des Radiokohlenstoffs (14C) spezialisiert haben, wird die AMS-Anlage des FZD - DREAMS (DREsden AMS) - als erste moderne Anlage in der EU mit einer Terminalspannung von 6 MV betrieben werden. Sie ist somit prädestiniert zur effizienten und hochempfindlichen Analyse der Radionuklide 10Be, 26Al, 36Cl, 41Ca und 129I (t1/2=0,1-15,7 Ma).

Die Einführung der AMS wird die interne Vernetzung der FZD-Forschungsaktivitäten im Bereich Materialforschung, Strahlenphysik, Radiochemie und Radiopharmazie vorantreiben. Darüber hinaus wird die AMS aber auch externen Nutzern zur Verfügung stehen. Die möglichen Arbeitsgebiete sind vielfach und multidisziplinär. So haben die instrumentellen Weiterentwicklungen auf dem Gebiet der AMS, die Anwendungsfelder der Methode stark ausgeweitet. Die anfänglich bevorzugt untersuchten Proben aus der Kosmochemie, Astrophysik und Kernreaktionsdaten, werden zunehmend von Proben aus den Bereichen Strahlenschutz, Nuklearsicherheit, Nuklearentsorgung, Radioökologie, Phytologie, Ernährungswissenschaften, Toxikologie und Pharmakologie verdrängt.

Zudem hat die AMS vor allem in den Geo- und Umweltwissenschaften in den letzten Jahren an Bedeutung gewonnen. Mittels kosmogener Radionuklide können relativ plötzlich aufgetretene prähistorische Ereignisse wie Vulkanausbrüche, Bergstürze, Tsunamis, Meteoriteneinschläge und Erdbeben datiert werden. Die Quantifizierung von geomorphologischen Vorgängen wie Erosion und Flusseinschnitte über lange Zeiträume, sowie hydrogeologische Studien sind ebenfalls möglich. Mittels der Datierung von Gletscher-bewegungen und Untersuchungen an Eisbohrkernen können zudem Klimaveränderungen rekonstruiert und Klimamodelle für die Zukunft validiert werden.

Nach dem Motto „Ready for dreams for DREAMS“ sehen wir gespannt den neuen AMS-Möglichkeiten am FZD und den damit verbundenen interdisziplinären Kooperationen, vor allen Dingen auch im Bereich der Helmholtz-Gemeinschaft, entgegen.
Keywords: cosmogenic radionuclides, TCN, AMS, accelerator mass spectrometry
  • Lecture (others)
    Glaziologie-Seminar, Alfred-Wegener-Institut für Polar- und Meeresforschung, 18.02.2010, Bremerhaven, Deutschland

Publ.-Id: 13779 - Permalink


Linear and non-linear stability of a thermally stratified magnetically driven rotating flow in a cylinder
Grants, I.; Gerbeth, G.;
The stability of a thermally stratified liquid metal flow is considered numerically. The flow is driven by the rotating magnetic field in a cylinder heated from above and cooled from below. The stable thermal stratification turns out to destabilise the flow. This is explained by the fact that a stable stratification suppresses the secondary meridional flow, thus indirectly enhancing the primary rotation. The instability in the form of Taylor-Görtler rolls is consequently promoted. It is known from earlier studies that these rolls can be only excited by finite disturbances in the isothermal flow. A sufficiently strong thermal stratification transforms this non-linear bypass instability into a linear one reducing, thus, the critical value of the magnetic driving force. A weaker temperature gradient delays the linear instability but makes the bypass transition more likely. We quantify the non-normal and non-linear components of this transition by direct numerical simulation of the flow response to noise.
It is observed that the flow sensitivity to finite disturbances increases considerably under the action of a stable thermal stratification. The capabilities of the random forcing approach to identify disconnected coherent states in a general case are discussed.
  • Physical Review E 82(2010), 016314

Publ.-Id: 13778 - Permalink


Stellarator-Mirror Based Fusion Driven Fission Reactor
Moiseenko, V.; Noack, K.; Agren, O.;
The version of fusion driven system (FDS), a sub-critical fast fission assembly with a fusion plasma neutron source, theoretically investigated here is based on a stellarator with a small mirror part. In the magnetic well of the mirror part, fusion reactions occur from collision of an RF heated hot ion component (tritium), with high perpendicular energy with cold background plasma ions. The hot ions are assumed to be trapped in the magnetic mirror part. The stellarator part which connects to the mirror part provides confinement for the bulk (deuterium) plasma. Calculations based on a power balance analysis indicate the possibility to achieve a net electric power output with a compact FDS device. For representative thermal power output of a power plant (P (th) a parts per thousand P (fis) = 0.5-2 GW) the computed electric Q-factor is in the range Q (el) = 8-14, which indicates high efficiency of the FDS scheme.
  • Journal of Fusion Energy 29(2010)1, 65-69

Publ.-Id: 13777 - Permalink


Filamentous E. coli induced by heterologous expression of surface layer proteins
Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.;
Bacterial envelope proteins, so called surface layers (S-layer) are widely spread paracrystalline surface structures which coat the cells of lots of bacterial strains and as universal attribute of all archaea. They are mostly composed of protein monomers which form via self-assembling high regular two dimensional arrays on the cells as well as on surfaces and interfaces after their isolation. The S-layer proteins we investigate are from bacterial strains recovered from the uranium mining waste pile “Haberland” in Saxony, Germany. Their special S-layer proteins selectively bind uranium and protect the cells from its toxicity. These special S-layer characteristics make them interesting for many technological applications such as filter materials, biosensors, as functional surfaces, or for example as drug containers.
In order to produce surface layer proteins in a high efficient way a heterologous expression in Escherichia coli is essential. In our study, the S-layer-like protein SllB of Lysinibacillus sphaericus JG-A12 was expressed in E. coli Bl21 (DE3). Noteworthy, recombinant protein production resulted in a high stability of the cells against mechanical and chemical treatment. These unusual cells were analyzed by light microscopy, AFM and TEM.
All methods demonstrated a total changed cell morphology. The cells formed long filaments in the beginning of the exponential growth stage and started to form 5-200 µm long tube like transparent structures at the end of the exponential growth stage, which contained E. coli single cells. These tube-like structures were isolated and analyzed by SDS-PAGE, N-terminal sequencing and infra red spectroscopy. The analyses showed that the tube-like structures consist of outer membrane associated with recombinant surface layer proteins. These findings point to a disordered cell division. However, the underlying mechanisms of these morphological changes are not known and will be analyzed in future. Investigations of supernatant proteins and proteins of periplasmic space in combination with enzyme assays demonstrate a transport of recombinant proteins that is not caused by cell damage. The long filaments, in combination with high expression level, good growth and high stability make these unusual E. coli cells interesting for biotechnological applications. In addition, these results cast a new light on one of the best studied microorganisms.
Keywords: Escherichia coli, S-layer proteins, Outer membrane, tube-like structures
  • Poster
    Bacterial Cell Surfaces, 27.06.-02.07.2010, New London, NH, USA

Publ.-Id: 13776 - Permalink


Future perspectives at SIS-100 with HADES-at-FAIR
Fröhlich, I.;
Currently, the HADES spectrometer undergoes un upgrade program to be prepared for measurements at the upcoming SIS-100 synchrotron at FAIR. We describe the current status of the HADES di-electron measurments at the SIS-18 and our future plans for SIS-100.
  • Contribution to proceedings
    xLVII International Winter Meeting on Nuclear Physics, 01.02.2010, Bologna, Italien
    Conference Proceedings Vol. 99
  • Invited lecture (Conferences)
    47th International Winter Meeting on Nuclear Physics, 26.-30.01.2009, Bormio, Italy
  • Contribution to WWW
    arXiv:0906.0091v2 [nucl-ex]

Publ.-Id: 13775 - Permalink


Scanning Probe Microscopy-based Characterization of ZnO Nanorods
Teichert, C.; Hou, Y.; Beinik, I.; Chen, X.; Hsu, Y. F.; Djurisic, A. B.; Anwand, W.; Brauer, G.;
Abstract-We apply scanning probe microscopy (SPM) to study the morphology and electrical properties of vertical zinc oxide nanorods grown by hydrothermal methods on silicon substrates. It is demonstrated that – against the intuition – SPM techniques can indeed be used to study such fragile high-aspect ratio semiconductor nanorods. Atomic-force microscopy (AFM) operating in tapping mode yields - via the analysis of the height histograms calculated from AFM images - easy access to the height fluctuations in the nanorod ensemble. High-resolution AFM images reveal the three-dimensional shape of the nanorods including transition facets between the (0001) top terrace and the {10-10} side facets. Further, we were able to acquire currentvoltage curves of individual nanorods by conductive atomic force microscopy (CAFM) operating in contact mode.
  • Lecture (Conference)
    IEEE International nanoElectronics Conference (INEC 2010), 03.-08.01.2010, Hong Kong, China

Publ.-Id: 13774 - Permalink


Defect studies of nanocrystalline zirconia powders and sintered ceramics
Cizek, J.; Melikhzova, O.; Prochazka, I.; Kuriplach, J.; Kuzel, R.; Brauer, G.; Anwand, W.; Konstantinova, T. E.; Danilenko, I. A.;
The main objective of the present paper is to communicate a study of defects behavior in zirconia-based nanomaterials—pressure-compacted yttria-stabilized zirconia (YSZ) nanopowders with different contents of Y2O3 and ceramics obtained by sintering the YZS nanopowders. In addition, YZS single crystals were also investigated. Positron annihilation techniques including positron lifetime and coincidence Doppler broadening with a conventional positron source and Doppler broadening experiments on a monoenergetic positron beam were involved in this study as the principal tools. These techniques were supplemented with transmission electron microscopy and x-ray diffraction observations. In order to get better support of the experimental data interpretation, the state-of-art theoretical calculations of positron parameters were performed for the perfect ZrO2 lattice and selected defect configurations in the YSZ. Theoretical calculations have indicated that neither the oxygen vacancies nor their neutral complexes with substitutional yttrium atoms are capable of positron trapping. On the other hand, the zirconium vacancies are deep positron traps and obviously are responsible for the saturated positron trapping observed in the YSZ single crystals. In the compacted YSZ nanopowders, a majority of positrons is trapped either in the vacancylike defects situated in the negative space-charge layers along grain boundaries (τ1≈185 ps) or in vacancy clusters at intersections of grain boundaries (τ2≈370 ps). The intensity ratio I2/I1 was found to be correlated with the mean grain size d as I2/I1∼d−2. A small fraction of positrons (≈10%) form positronium in large pores (τ3≈2 ns, τ4≈30 ns). A significant grain growth during sintering of the YSZ nanopowders above 1000 °C was observed.
  • Physical Review B 81(2010), 024116

Publ.-Id: 13773 - Permalink


Nature of vacancy complexes associated with hydrogen ion-induced splitting of bulk GaN
Moutanabbir, O.; Scholz, R.; Gösele, U.; Guittoum, A.; Jungmann, M.; Butterling, M.; Krause-Rehberg, R.; Anwand, W.; Egger, W.; Sperr, P.;
We present a detailed study of the thermal evolution of H ion-induced vacancy related complexes and voids in bulk GaN implanted under ion-cut condition. By using transmission electron microscopy, we found that the damaged band in as-implanted GaN is decorated with a high density of nanobubbles of ~1-2 nm in diameter. Variable energy Doppler broadening spectroscopy showed that this band contains vacancy clusters and voids. In addition to vacancy clusters, the presence of VGa, VGa-H2, and VGaVN complexes was evidenced by pulsed low energy positron lifetime spectroscopy. Subtle changes upon annealing in these vacancy complexes were also investigated. As a general trend, a growth in open volume defects is detected in parallel to an increase in both size and density of nanobubbles. The observed vacancy complexes appear to be stable during annealing. However, for temperatures above 450ºC, unusually large lifetimes were measured. These lifetimes are attributed to the formation of positronium in GaN. Our finding contradicts the prevalent belief that the formation of postronium is not possible in a semiconductor. Based on the Tao-Eldrup model, the lattice opening during thermal annealing was quantified. We found that a wall spacing of 0.4 nm is induced by annealing at 600ºC. The role of these complexes in the sub-surface microcraking is discussed.
Keywords: GaN, hydrogen ion-induced splitting, thermal evolution of H ion-induced vacancy related complexes and voids, TEM, PAS
  • Physical Review B 81(2010), 115205

Publ.-Id: 13772 - Permalink


Contactless inductive flow tomography for a model of continuous steel casting
Wondrak, T.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Stefani, F.; Timmel, K.;
The contactless inductive flow tomography (CIFT) aims at reconstructing the velocity field in electrically conducting melts from externally measured induced magnetic fields. One of its possible applications is the velocity reconstruction in the continuous casting process. In this paper, we apply this method to the flow field in a small model (containing approximately 1.4 liters of the eutectic alloy GaInSn) of a mould for thin slab casting. It is shown that the flow structure in general, and the jet position and intensity in particular, can be reliably determined from magnetic field data using only a modest number (in the order of 5) of sensors.
  • Measurement Science and Technology 21(2010), 045402

Publ.-Id: 13771 - Permalink


Determination of Uranium Speciation in Aqueous Samples by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS)
Bernhard, G.; Geipel, G.;
wird nachgereicht
Keywords: -
  • Contribution to external collection
    Lahiri, Susanta: Advanced Trace Analysis, New Delhi: Narosa Publishing House, 2010, 978-81-8487-029-9, 127-147

Publ.-Id: 13770 - Permalink


Effects of posture on regional pulmonary blood flow in rats as measured by PET
Richter, T.; Bergmann, R.; Pietzsch, J.; Közle, I.; Hofheinz, F.; Schiller, E.; Ragaller, M.; van den Hoff, J.;
Using small animal PET with 68Ga-radiolabeled human albumin microspheres (Ga-68-microspheres), we investigated the effect of posture on regional pulmonary blood flow (PBF) in normal rats. This in vivo method is noninvasive and quantitative, and it allows for repeated longitudinal measurements. The purpose of the experiment was to quantify spatial differences in PBF in small animals in different postures. Two studies were performed in anesthetized, spontaneously breathing Wistar rats. Study 1 was designed to determine PBF in the prone and supine positions. Ga-68-microspheres were given to five prone and eight supine animals. We found that PBF increased in dorsal regions of supine animals (0.75) more than in prone animals (0.70; P = 0.037), according to a steeper vertical gradient of flow in supine than in prone animals. No differences in spatial heterogeneity were detected. Study 2 was designed to determine the effects of tissue distribution on PBF measurements. Because microspheres remained fixed in the lung, PET was performed on animals in the position in which they received Ga-68-microsphere injections and thereafter in the opposite posture. The distribution of PBF showed a preference for dorsal regions in both positions, but the distribution was dependent on the position during administration of the microspheres. We conclude that PET using Ga-68-microspheres can detect and quantify regional PBF in animals as small as the rat. PBF distributions differed between the prone and supine postures and were influenced by the distribution of lung tissue within the thorax.
Keywords: pulmonary blood flow; positron emission tomography; 68Ga radiolabel; human serum albumin microspheres; prone position; supine position; small animal

Publ.-Id: 13769 - Permalink


Comment on “Developing DCE-CT to Quantify Intra-Tumor Heterogeneity in Breast Tumors With Differing Angiogenic Phenotype”
Abramyuk, A.; Wolf, G.; Hietschold, V.; Haberland, U.; van den Hoff, J.; Abolmaali, N.;
In our comment some essential issues concerning determination of arterial input function (AIF), cardiac and respiratory related motion artifacts, contrast agent application and compartmental model fitting done by Cao et al., 2009 are discussed.

Publ.-Id: 13768 - Permalink


PET-based investigation of cerebral activation following intranasal trigeminal stimulation
Hummel, T.; Oehme, L.; van den Hoff, J.; Gerber, J.; Heinke, M.; Boyle, J. A.; Beuthien-Baumann, B.;
The present study aimed to investigate cerebral activation following intranasal trigeminal chemosensory stimulation using O15-H2O-PET. A total of 12 healthy male participants underwent a PET scan presented with four scanning conditions; two left-sided intranasal CO2-stimuli and two matched baseline conditions consisting of odorless air. CO2 was used as it produces burning and stinging sensations. Stimulation started 20 s before intravenous injection of the isotope and lasted for the first 60 s of the 5 min scan time. A comparison between CO2 and baseline showed a pronounced activation of the trigeminal projection area at the base of the postcentral gyrus (primary and secondary somatosensory cortex) which was more intense for the right hemisphere, contralateral to the side of stimulation. In addition, activation was also found in the piriform cortex which is typically activated following odor presentation and thus thought of as primary olfactory cortex. In conclusion, and in line with previously published work, our data suggest that intranasal trigeminal stimulation not only activates somatosensory projection areas, but that it also leads to activation in cerebral areas associated with the processing of olfactory information. This may be interpreted in terms of the intimate relation between the intranasal chemosensory systems.
Keywords: pain • stinging • nose • anosmia • olfaction • positron emission tomography • 15O-H2O

Publ.-Id: 13767 - Permalink


RP-HPLC zur Trennung von DNA Bausteinen
Förster, C.;
kein Abstract verfügbar
  • Lecture (others)
    3. Workshop Möglichkeiten und Grenzen der HPLC in den Lebenswissenschaften, 29.01.2010, Dresden- Rossendorf, D

Publ.-Id: 13766 - Permalink


Effects of cold sphere walls in PET phantom measurements on the volume reproducing threshold
Hofheinz, F.; Dittrich, S.; Pötzsch, C.; van den Hoff, J.;
We studied quantitatively the effects of the discontinuity introduced in an otherwise homogeneous background by the cold walls of the standard spherical glass inserts commonly used in phantom measurements for calibration of
threshold-based approaches to volumetric evaluation of PET investigations. We concentrated especially on the question of threshold-based volume determination. We computed analytically the convolution of an isotropic Gaussian point-spread function with the insert geometry (hot sphere + cold wall + warm background) and derived the theoretical background dependence of the volume reproducing threshold. This analysis shows a clear wall-related reduction of the optimal threshold with increasing background. The predictions of our theoretical analysis were verified in phantom measurements at background fractions between 0 and 0.29. Defining the background-corrected relative threshold T = Tabs−B ./. A−B (Tabs: absolute volume reproducing threshold, A: measured activity at centre, B: background), we find that for a wall-less sphere T is independent of the background level. In the presence of cold walls, T drops (for not too small spheres, where recovery at the centre approaches 100%) from about 43% at B/A = 0 to about 25% at B/A = 0.5. Applying these thresholds towall-less spheres leads to sizeable overestimates of the true volumes (43% at B/A = 0.5 for a sphere of 6 ml volume). We conclude that phantom measurements with standard sphere inserts for calibration of optimal thresholding algorithms introduce a systematic bias if performed at finite background levels. The observed background dependence is an artefact of the measurement procedure and does not reflect the conditions present in actual patient investigations.

Publ.-Id: 13765 - Permalink


Radiomarkierte Verbindungen: Anwendungsmöglichkeiten in Analytik und Medizin
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Freie Universität Berlin, Institut für Chemie und Biochemie, 03.02.2010, Berlin, Deutschland

Publ.-Id: 13763 - Permalink


Molekulare Bildgebung zum Aufspüren von Tumorerkrankungen
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Hochschule Görlitz/Zittau, 05.11.2009, Zittau, Deutschland

Publ.-Id: 13762 - Permalink


E1 strength in Pb-208 within the shell model
Schwengner, R.; Massarczyk, R.; Brown, B. A.; Beyer, R.; Dönau, F.; Erhard, M.; Grosse, E.; Junghans, A. R.; Kosev, K.; Nair, C.; Rusev, G.; Schilling, K. D.; Wagner, A.;
The dipole response of the doubly-magic 208Pb was studied in a photon-scattering experiment at the electron linear accelerator ELBE with bremsstrahlung produced at a kinetic electron energy of 14.0 MeV. The present (gamma,gamma') data combined with (gamma,n) data from literature are compared with results of calculations using a quasiparticle random-phase approximation and with results of shell-model calculations. It turns out that the shell model describes the experimental low-lying E1 strength as well as the giant dipole resonance well by applying a small spreading width only.
Keywords: Photon scattering, nuclear spectroscopy, nuclear structure, gamma strength function, random-phase approximation, shell model
  • Physical Review C 81(2010)5, 054315

Publ.-Id: 13761 - Permalink


An overall assessment of abnd model for large-scale bubbly flows
Duan, X.; Cheung, S. C. P.; Yeoh, G. H.; Tu, J.; Krepper, E.; Lucas, D.;
For increasing the predictability of equipment and improving efficiency of production, there is a high demand to develop a compact and efficient mathematical model capable of modelling the complex bubbly flow structures which frequently occur in large-scale industrial engineering systems. A generalized Average Bubble Number Density (ABND) transport equation model in conjunction with three forms of bubble coalescence and breakage kernels was implemented and incorporated into commercial software ANSYS CFX 11. The main focus of this paper is to assess the overall performance of the ABND model and the three different bubble mechanism kernels under a large-scale gas-liquid bubbly flow system. Based on the high-quality TOPFLOW database for airwater two-phase flows in a large vertical pipe with nominal diameter of 195.3mm, experimental data were strategically selected for model validation. To examine the relative merits and drawbacks of three forms of coalescence and breakage kernels, model predictions of
local radial distributions of bubble rise velocity, volume fraction and bubble size were compared against experimental results. The capabilities in predicting the “core peak” volume fraction profiles and evolution process of bubble rise of different kernels were discussed.
Keywords: CFD, two phase flow, bubble population balance model, model validation
  • Contribution to proceedings
    7th International Conference on CFD in the Minerals and Process Industries CSIRO, Melbourne, Australia, 09.-11.12.2009, Melbourne, Australia
  • Lecture (Conference)
    7th International Conference on CFD in the Minerals and Process Industries CSIRO, 09.-11.12.2009, Melbourne, Australia

Publ.-Id: 13760 - Permalink


Nanostructured Biocomposites - Chances and Perspectives for Water Treatment
Raff, J.;
Bacterial surface layer protein polymers (S-layers) are excellently suited for the development of a wide range of novel nano-structured biocomposite materials. The presentation summarizes current developments at the Institute of Radiochemistry as starting point for an intensive discussion of their application potential, marketability and general market needs.
Keywords: S-layer biocomposites
  • Lecture (others)
    "Nanostructured biocomposites - chances and perspectives for water management" Workshop, 02.02.2010, Dresden, Deutschland

Publ.-Id: 13759 - Permalink


Coordination behaviour of bis-pyridylimine ligads: polymers, metallamocrocycles and helicates
Gloe, K.; Tanh Jeazet, H. B.; Gloe, K.; Doert, T.; Kataeva, O. N.; Bernhard, G.;
wird nachgereicht
  • Lecture (Conference)
    International Conference on Coordination Chemistry ICCC39, 25.-30.07.2010, Adelaide, Australia

Publ.-Id: 13758 - Permalink


Neue UO22+-Komplexe von Bis(2-hydroxyaryl)imin-Liganden: Synthese, Struktur und Extraktionseigenschaften
Tanh Jeazet, H. B.; Doert, T.; Gloe, K.; Geipel, G.; Bernhard, G.; Gloe, K.;
wird nachgereicht
  • Lecture (Conference)
    Jahrestreffen des ProcessNet-Fachausschusses Extraktion, 18.-19.03.2010, Kaiserslautern, Deutschland

Publ.-Id: 13757 - Permalink


P0807 Verfahren zur Herstellung von Halbleiterstrukturen auf Silizium-Germanium-Basis mit erhöhter Effizienz
Voelskow, M.; Kanjilal, A.; Skorupa, W.;
Die Erfindung beschreibt ein Herstellungsverfahren von Halbleiterstrukturen auf Silizium-Germanium-Basis. Durch die Germanium-Ionenimplantation und die anschließende Bestrahlung mit einem Lichtimpuls können die Germanium legierten Gebiete kurzzeitig und lokal aufgeschmolzen werden und die entstandenen Schäden während der Implantation an den Profilkanten ausgeheilt werden. Dadurch wird eine erhöhte Effizienz und rationellere Produktion erreicht, die vor allem bei der Produktion von Solarzellen verwendet werden kann. Weiterhin können mit diesem Verfahren verspannte Silizium-Halbleiterstrukturen hergestellt werden.
  • Patent
    DE 10 2008 035 846 A1 - 04. Febr. 2010

Publ.-Id: 13756 - Permalink


Radiation damage in focused ion beam implantation
Hausmann, S.; Bischoff, L.; Teichert, J.; Voelskow, M.; Moller, W.;
Compared to conventional ion implantation, focused ion beam (FIB) implantation works with a current density which is up to five orders of magnitude higher. This has an effect on the accumulated radiation damage during the implantation process. The present work shows how the radiation damage is influenced by the dwell-time in the case of focused ion beam synthesis (IBS) of cobalt disilicide. If the accumulated damage during implantation is not too high the use of conventional ion implantation IBS results in single-crystalline CoSi2 layers
Keywords: focused ion beam
  • Contribution to proceedings
    Microprocesses and Nanotechnology '99, 06.-08.07.1999, Yokohama, Japan
    Proceedings of the 1999 International Microprocesses and Nanotechnology Conference, 4930813972

Publ.-Id: 13755 - Permalink


Computer simulation and RBS/C studies of high-dose N + and Al + co-implantation in 6H-SiC
Kharlamov, V. S.; Kulikov, D. V.; Truschin, Y. V.; Tsigankov, D. N.; Voelskow, M.; Skorupa, W.; Pezoldt, J.;
Computer simulation and RBS/C studies of high-dose N + and Al + co-implantation in 6H-SiC
Keywords: Computer simulation, RBS, ion implantation, 6H-SiC
  • Proceedings of SPIE 3345(1998), 260

Publ.-Id: 13754 - Permalink


High-temperature high-dose implantation of N- and Al+ ions in 6H–SiC
Yankov, R. A.; Voelskow, M.; Kreissig, W.; Kulikov, D. V.; Pezoldt, J.; Skorupa, W.; Trushin, Y. V.; Kharlamov, V. S.; Tsigankov, D. N.;
A series of experimental and theoretical investigations has been initiated for 6H–SiC samples sequentially implanted with high doses of N+(65 keV) + N+(120 keV) + Al+(100 keV) + Al+(160 keV) ions at temperatures between 200 and 800 °C. Nitrogen and carbon distribution profiles are measured by ERD and structural defect distributions are measured by Rutherford backscattering with channeling. A comparison between the experimental data and the results of computer simulation yields a physical model to describe the relaxation processes of the implanted SiC structure, where the entire implanted volume is divided into regions of different depth, having different guiding kinetics mechanisms.
Keywords: 6H-SiC, ion implantation
  • Technical Physics Letters 23(1997)8, 617-620

Publ.-Id: 13753 - Permalink


Photothermal measurements of Al+ and Al+/N+ implanted 6H-SiC
Pezoldt, J.; Teichert, G.; Panknin, D.; Voelskow, M.;
Thermal wave measurements on 6H-SiC with a particular emphasis on Al+ and Al+/N+ implanted 6H-SiC was carried out. The 6H-SiC wafers were implanted at different substrate temperatures. The photothermal measurements of the conversion coefficient K and the reflectivity R show a strong dependence on the implantation temperature. This result is discussed in relation to Rutherford backscattering spectrometry/ion channeling measurements. The behaviour of the reflectivity in dependence on the implantation conditions could be modelized by using a simple two layer optical model. The carried out investigations of the implanted SiC demonstrate, that photothermal methods are suitable for both research and on-line production use.
Keywords: thermal wave, silicon carbide
  • Contribution to proceedings
    International workshop on nondestructive testing and computer simulations in science and engineering No3, St. Petersburg , RUSSIA, 07.06.1999, St. Petersburg, Russia

Publ.-Id: 13752 - Permalink


Hochgenaue Gammastrahlen-Computertomographie für industrielle Anwendungen
Bieberle, A.; Schleicher, E.; Hampel, U.;
Im Rahmen eines Promotionsvorhabens wurde erstmalig ein hochpräziser und räumlich hochauflösender Computertomograph für industrielle Anwendungen entwickelt. Das Messsystem umfasst eine leistungsstarke Cs-137 Isotopenquelle, einen hochgenauen, driftfreien 320-kanaligen Gammastrahlendetektor sowie eine automatisierte rotatorisch-translatorische Stelleinheit. Der Computertomograph dient vorrangig der Untersuchung von Strömungsprozessen in technischen Anlagen und Strömungsmaschinen und kommt darüber hinaus auch in der zerstörungsfreien Prüfung schwerer Bauteile zur Anwendung. Der Schwerpunkt im Systemdesign wurde auf eine hohe Nachweiseffizienz des Strahlendetektors sowie Unempfindlichkeit gegenüber elektromagnetischen Feldern und Umgebungstemperaturänderungen gelegt.
Keywords: räumlich hochauflösende Computertomographie, Gammastrahlung
  • Poster
    Ideas to Market - Dresdner Materialinnovationen für die Praxis & Verleihung "Dresden Barkhausen Award 2009", 15.01.2010, Dresden, Deutschland

Publ.-Id: 13751 - Permalink


Crystallization and surface erosion of SiC by ion irradiation at 500°C
Heera, V.; Stoemenos, J.; Kögler, R.; Voelskow, M.; Skorupa, W.;
The effects of high dose ion irradiation through an amorphous surface layer on single crystalline 6H–SiC at 500°C are studied in detail. Material swelling, subsequent densification, surface erosion and recrystallization are quantified. The results demonstrate that undisturbed epitaxial regrowth of an amorphous surface layer on (0001)-oriented 6H–SiC cannot be achieved at this temperature by ion irradiation. The shift of the amorphous/crystalline interface observed by RBS/C analysis is a consequence of columnar regrowth and surface erosion. The columnar growth starts inside the heavily damaged transition region between the amorphous surface layer and the single crystalline bulk material. It is stopped by random nucleation. Neither the interface roughness nor the kind of impurity atoms influence the thickness of the columnar layer.
Keywords: Ion implantation, Recrystallization, SiC, Surface erosion
  • Materials Science and Engineering B 61-62(1999), 358-362

Publ.-Id: 13750 - Permalink


Ion-Beam-Assisted Nanocrystal Formation in Silicon Implanted with High Doses of Pb+ and Bi+ Ions
Kalitzova, M.; Zollo, G.; Yankov, R.; Angelov, C.; Simov, S.; Pizzuto, C.; Faure, J.; Kilian, L.; Bonhomme, P.; Manno, D.; Voelskow, M.; Vitali, G.;
In this paper we discuss ion-beam-assisted nanocrystal nucleation in amorphized silicon (a-Si) layers produced by high-dose implantation of Pb+ and Bi+. (100)-oriented Si wafers were implanted at room temperature (RT) with 50 keV Pb+ and Bi+ ions at doses ranging from 5E13 to 1E18 cm−2 and a constant ion current density of 10μAcm−2. The resulting structures were studied by conventional transmission electron microscopy (CTEM), high resolution transmission electron microscopy (HRTEM) and Rutherford backscattering spectroscopy (RBS) in combination with computer simulations. The dynamics of the ion-beam-induced crystallization of new phases and precipitates evolution in the implanted layer were studied as a function of implant dose. It is established that the front of the new phase crystallization (cubic Pb and hexagonal Bi nanocrystals) starts approximately at the peaks of the implanted species profiles; the crystallography of the nucleated nanocrystal is examined as a function of the dose.
Keywords: ion implantation, precipitation, nanoclusters, silicon, electron microscopy
  • Japanese Journal of Applied Physics 40(2001)10, 5841-5849

Publ.-Id: 13749 - Permalink


Transient enhanced diffusion and electrical activation of As in Si during rapid thermal annealing
Koegler, R.; Wieser, E.; Voelskow, M.; Otto, G.;
(100) Si was implanted at 150 or 100 keV with fluences from 5 E 15 to 2 E16 cm-2. The samples were processed by rapid thermal annealing at temperatures between 1000 and 1200°C and dwell times at T(max) from 1 to 30 s. As depth distributions were measured by RBS and SIMS. By comparison of experimental profiles with computer simulations based on the diffusion model proposed by Tsai et al. and including a time independent enhancement factor or a transient enhancement according to Fair a transient enhanced diffusion has been found. The influence of As clustering or precipitation on the diffusion behaviour of high concentrations is discussed. The comparison of samples implanted through 30 nm SiO2 or in bare Si shows an enhanced As concentration at the SiO2 interface and a decreased diffusivity for the former case. These effects are explained by an interaction of As with oxygen recoil atoms.
Keywords: transient enhanced diffusion, RTA, implantation
  • Nuclear Instruments and Methods in Physics Research B 19-20(1987), 516-520

Publ.-Id: 13748 - Permalink


Epitaxial lateral overgrowth of amorphous CVD silicon films induced by ion irradiation
Voelskow, M.; Skorupa, W.; Wollschlaeger, K.; Matthaei, J.; Knothe, P.; Heinig, K.-H.;
Amorphous silicon layers deposited by chemical vapour deposition on monocrystalline silicon substrates partly covered with silicon dioxide to produce SOl structures were epitaxially recrystallised by ion beam induced epitaxial crystallisation at 400 C after preamorphisation of the transition region layer/substrate. The implantation with a dose of 5E17 cm-2 into the wafers with SOl structure resulted in a 1.5 um wide overgrown crystalline layer.
Keywords: CVD, epitaxy, ion irradiation
  • Applied Surface Science 43(1989)1-4, 196-199

Publ.-Id: 13747 - Permalink


MeV carbon implantation into silicon: microstructure and electrical properties
Skorupa, W.; Kögler, R.; Voelskow, M.; Schmalz, K.; Morgenstern, G.; Gaworzewski, P.;
Doping effects after carbon implantation at 0 .33 and 10 MeV were investigated at silicon wafers with different oxygen content. No distinct influence of the oxygen concentration on the carbon induced doping effect was found for rapid thermal annealing at 1250°C for 30 s whereas for furnace annealing at 1000°C the doping effect is higher for Czochralski-grown silicon wafers with their higher oxygen content. The gettering efficiency of a buried carbon implanted layer for additionally introduced iron atoms was investigated by deep level transient spectroscopy. Gettering sets in at a dose of 10E14 cm2 and is completed for a carbon dose of 1E16 cm2 for iron doses up to 1E13 cm2. The microstructure of such a buried layer is characterised by a narrow band of dark contrast containing mainly stacking faults of the extrinsic type .
Keywords: MeV ion implantation, DLTS
  • Nuclear Instruments and Methods in Physics Research B 68(1992)1-4, 408-412

Publ.-Id: 13746 - Permalink


Model experiments on thermo-electromagnetic convection
Cramer, A.; Zhang, X.; Gerbeth, G.;
Thermoelectromagnetic convection in electrically conducting cubic containers was studied experimentally. Two opposing side walls were cooled and heated, respectively, to produce a uniform temperature gradient. Inhomogeneous magnetic field distributions were achieved either with a small permanent magnet located above the melt layer, or with specifically shaped pole shoes of the magnetic system. Ultrasonic Doppler velocimetry measurements demonstrated that even a moderate temperature gradient may drive a distinct convection. Two different flow regimes were investigated with the permanent magnet. When it was positioned in the vicinity of an isothermal wall, with its direction of magnetisation parallel to the temperature gradient, a single vortex spreading the whole container developed while the flow might be assessed as relatively stable. Moving the magnet to the centre led to a modified distribution of the magnetic field which, in turn, altered the flow structure. The convective pattern changed to four vortices and the velocity fluctuations were intensified. A more generic case was realised with the pole shoes providing a gradient of the magnetic field only in one direction. Since the strength of the field could be raised significantly above that provided by the small permanent magnet and the area of impact onto the melt was larger, developed turbulent regimes were accomplished. Numerical results obtained for the Lorentz force and the rotor thereof support the experimental findings.
Keywords: Thermoelectricity, Model experiments, Magnetohydrodynamics, Liquid Metals, Thermocurrent, Electromagnetic stirring
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials EPM 2009, 19.-23.10.2009, Dresden, Deutschland
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials EPM 2009, 19.-23.10.2009, Dresden, Deutschland
    Proceedings of the EPM 2009, 978-3-936104-65-3, 94-97

Publ.-Id: 13745 - Permalink


Ion beam synthesis by tungsten-implantation into 6H-silicon carbide
Weishart, H.; Steffen, H. J.; Matz, W.; Voelskow, M.; Skorupa, W.;
Synthesis of a highly conductive surface layer on 6H-silicon carbide was achieved by high-dose, room temperature implantation of tungsten at 200 keV. Subsequently, the samples were annealed in two steps, namely at 500°C and 950°C. ‘I%e influence of both dose and annealing on the reaction of W with Sic was investigated. Rutherford Backscattering Spectrometry (RBS), X-Ray Diffraction (XRD) and Auger Electron Spectroscopy (AES) contributed to study the structure and composition of the layer as well as the chemical states of the elements. During implantation sputtering becomes significant for doses exceeding 1.0 X 10” cm- ‘. Formation of tungsten carbide and silicide is already observed in the as-implanted state. An annealing temperature of 950°C is necessary to crystallize tungsten carbide. However, tungsten silicide remains amorphous at this temperature. Therefore, a mixture of polycrystalline tungsten carbide and amorphous tungsten silicide develops under these conditions. The resistivity of such a layer implanted with 1.0 E17 W+ cm2 and annealed at 950°C is 565 uohmcm.
Keywords: Ion beam synthesis, 6H-SiC
  • Nuclear Instruments and Methods in Physics Research B 112(1996)1-4, 338-341

Publ.-Id: 13744 - Permalink


A novel (SiC)1-x(AlN)x compound synthesized using ion beams
Pezoldt, J.; Yankov, R. A.; Mücklich, A.; Fukarek, W.; Voelskow, M.; Reuther, H.; Skorupa, W.;
The formation of a novel (SiC)1-x(AlN)x compound (x=0.2) at low temperatures within the miscibility gap of the SiC/AlN phase diagram by hot, high-dose co-implantation of N+ and Al+ ions into 6H±SiC substrates is investigated. The compound layers have been studied by Rutherford backscattering spectrometry/ion channelling (RBS/C), Auger electron spectroscopy (AES), polarized infrared re¯ection spectroscopy (PIRR) and cross sectional electron microscopy (XTEM) and the temperature dependence of their fabrication has been examined. An optimum temperature window has been established within which the structure of the synthesized material retains good crystallinity during implantation.
Keywords: Ion beam synthesis, Silicon carbide; Aluminum nitride; Solid solutions; Polytypism
  • Nuclear Instruments and Methods in Physics Research B 147(1999)1-4, 273-278

Publ.-Id: 13743 - Permalink


Characterisation of defects in ion implanted SiC by slow positron implantation spectroscopy and Rutherford backscattering
Anwand, W.; Brauer, G.; Coleman, P. G.; Voelskow, M.; Skorupa, W.;
SiC(1-x)AlN(x) has been prepared by ion co-implantation of Nqand Alqinto a 6H-SiC n-type wafer. The substrate temperature during implantation was varied from 200°C to 800°C in order to reduce the damage created by ion implantation. The obtained structures have been investigated by Slow Positron Implantation Spectroscopy (SPIS). and Rutherford Backscattering and Ion Channeling (RBS). Both methods are sensitive to different kinds of defects and the results are complementary. The defect structures determined by SPIS and RBSrC are presented and the influence of the variation of the substrate temperature is discussed.
Keywords: Silicon carbide; Ion implantation; Vacancy-like defects; Defect profiles
  • Applied Surface Science 149(1999)1-4, 148-150

Publ.-Id: 13742 - Permalink


Theoretical and experimental investigations of defect evolution in silicon carbide during N+ and Al+ ion implantation taking into account internal stress fields
Rybin, P. V.; Kulikov, D. V.; Trushin, Y. V.; Yankov, R. A.; Voelskow, M.; Scharmann, F.; Pezoldt, J.;
A theoretical model is developed which allows to describe the defect evolution in silicon carbide implanted with high doses of nitrogen and aluminium ions and subsequently annealed to form a solid solution. The diffusion of defects, the formation of complexes of defect clusters and the influence of the internal elastic stress fields produced by the implanted ions and the complexes formed are taken into account. Results from the simulations have been correlated with data obtained by Rutherford backscattering spectrometry/ion channelling (RBS/C).
Keywords: Ion-beam synthesis; Computer simulation; Defect production; Kinetics of defects; Influence of stress
  • Nuclear Instruments and Methods in Physics Research B 178(2001)1-4, 269-274

Publ.-Id: 13741 - Permalink


Vertrieb von Forschungsleistungen am Beispiel des FZD
Joehnk, P.;
Vortrag im Rahmen der Reihe Dresdner Vertriebsfrühstück
  • Lecture (others)
    Vertriebsfrühstück, 29.01.2010, Dresden, Deutschland

Publ.-Id: 13740 - Permalink


Melt flow stabilisation in bulk crystal growth by means of external magnetic fields
Pätzold, O.; Lantzsch, R.; Greif, A.; Galindo, V.; Grants, I.; Gerbeth, G.; Stelter, M.;
Several approaches to suppress a non-stationary melt flow and related fluctuations of the temperature and the dopant concentration in bulk crystal growth by means of external magnetic fields are presented. The paper includes results of model and growth experiments carried out in Bridgman- or Czochralski-like configurations under the influence of different fields (rotating, traveling, axial steady, cusp, combinations of which). It is shown that both time-dependent and steady fields can be used to stabilize a melt. The impact of a magnetic field on the melt flow, however, depends strongly on the configuration and thermal conditions of the growth. Therefore, type and parameters of the applied field have to be properly adjusted to the particular setup under consideration to achieve an optimal damping of fluctuations and to avoid unfavorable effects.
Keywords: bulk crystal growth, external magnetic fields
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany, 978-3-936104-65-3, 849-862
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany

Publ.-Id: 13738 - Permalink


Comparison of various contactless flow rate sensors
Buchenau, D.; Gerbeth, G.; Priede, J.;
We consider three versions of recently developed contactless flowrate sensors: the well-known magnetic flywheel, a newly developed phase-sift sensor based on an applied alternating magnetic field, and a new force-free sensor based on a rotating single magnet. Comparative measurements were performed at a GaInSn-loop.
Keywords: Liquid metal, GaInSn-loop, Magnetic flywheel, Phase-shift sensor, Rotating magnet
  • Contribution to proceedings
    6th Int. Conf. on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, BRD, pp. 383-386
  • Lecture (Conference)
    6th Int. Conf. on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, BRD

Publ.-Id: 13737 - Permalink


Numerical Simulation of Two-phase Flow in a Slab Mold by MUSIG Model
Miao, X.; Galindo, V.; Lucas, D.; Gerbeth, G.; Ren, Z.;
An Euler-Euler approach has been employed to investigate the effects of varying flow rate of argon gas and static magnetic field on the flow pattern in a slab mold. The mathematical model is based on the k − ǫ turbulence model and coupled with the MHD model in CFX. In this work, three dimensional localized DC magnetic fields were constructed and calculated by a finite element method and then imported into CFX. The results show that a static magnetic field does not always slow down the bulk flow, but occasionally gives rise to large eddies for increasing magnetic field strengths. In principle, the injection of Argon gas is able to suppress the fluctuation of the free surface and to reduce the penetration depth significantly. However, gas bubbles may produce a reversed flow surrounding the nozzle at the meniscus if large bubbles float up rapidly in the case the flow rate ratio of argon gas to molten steel reaches a certain value. The MUSIG (multiple size group) model considering coalescence and breakup of bubbles provides an effective tool to solve the multiphase flow and to get insight into the flow pattern in a continuous casting mold with argon gas injection.
Keywords: two-phase flow, continuous castig, musig model
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany, 978-3-936104-65-3, 579-582
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany

Publ.-Id: 13735 - Permalink


Numerical calculations for steam-water CCFL tests using the 1/3rd scale rectangular channel simulating a PWR hot leg
Kinoshita, I.; Murase, M.; Utanohara, Y.; Lucas, D.; Vallée, C.; Tomiyama, A.;
In reflux cooling, steam generated in the reactor core and water condensed in a steam generator (SG) form a countercurrent flow in a hot leg, which consists of a horizontal pipe, an elbow and an inclined pipe. At Forschungszentrum Dresden-Rossendorf (FZD), both countercurrent air-water and steam-water tests were previously carried out using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility. In this paper, in order to evaluate the effects of fluid properties, numerical calculations for the steam-water CCFL tests at FZD were conducted using the CFD code, FLUENT6.3.26. The numerical calculation region included the reactor vessel simulator, hot leg and SG inlet chamber, in order to avoid uncertainties of boundary conditions at both ends of the hot leg. The VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. The CCFL characteristics calculated by the 2F and VOF models agreed with the steam-water CCFL data at FZD and showed the same trends with the data for fluid properties.
Keywords: CCFL, stratified flow
  • Contribution to proceedings
    The 8th International Conference on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-8), paper N8P0044, 10.-14.10.2010, Shanghai, China

Publ.-Id: 13733 - Permalink


Ultra large coercivity in barium ferrite thin films prepared by magnetron sputtering
Zhang, W.; Peng, B.; Zhang, W.; Zhou, S.; Schmidt, H.;
Hexagonal barium ferrites were deposited onto sapphire substrates by radio frequency magnetron sputtering. The composition, microstructure, and magnetic properties of these isotropic thin films were investigated with Rutherford backscattering spectroscopy, X-ray diffraction, atomic force microscopy, magnetic force microscopy and SQUID magnetometry. The intrinsic coercivity of the films reaches about 11.5 kOe at room temperature. The mechanism of the coercivity is proposed to be nucleation in the decoupled single domain nanometer particles as shown by the characteristics of the magnetic domains and the virgin magnetization curves.
Keywords: Barium ferrite; Coercivity; Nucleation

Publ.-Id: 13732 - Permalink


Numerical calculations for air-water tests on CCFL in different-scale models of a PWR hot leg
M. Murase, M.; Kinoshita, I.; Utanohara, Y.; Lucas, D.; Vallée, C.; Tomiyama, A.;
Air-water CCFL (countercurrent flow limitation) tests were previously carried out at Kobe University using the 1/5th scale rectangular channel and 1/15th scale circular tube simulating a PWR hot leg. Then numerical calculations for these tests and full-scale PWR conditions were made using the CFD code, FLUENT6.3.26. At Forschungszentrum Dresden-Rossendorf (FZD), similar tests were previously carried out for both air-water and steam-water flows using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility.
In this paper, numerical simulations for the air-water CCFL tests of FZD using FLUENT6.3.26 are presented and compared with the experimental data obtained at Kobe University and FZD. In the calculations, the VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. Calculation parameters were the air flow rates and air inlet locations, which were at the top of the reactor vessel simulator simulating the FZD test facility (inlet 1) and the opposite side of the hot leg junction simulating the test loops at Kobe University (inlet 2). Conclusions were as follows : (1) the calculated CCFL characteristics using the 2F model for the FZD tests agreed well with the 1/15th scale circular tube data obtained at Kobe University and the calculated results for full-scale PWR conditions, which supported the validity of the 1/3rd scale rectangular channel to simulate CCFL in circular tubes; (2) there were no significant differences between the calculated CCFL characteristics with the air inlet 1 and inlet 2, which indicated that the air inlet location did not influence CCFL behavior in a hot leg; and (3) comparison with the FZD data showed that the calculations using the 2F and VOF models overestimated the water flow rates for deflooding.
Keywords: CCFL, air-water, stratified flow
  • Contribution to proceedings
    18th International Conference on Nuclear Engineering (ICONE18), paper ICONE18-29092, 17.-21.05.2010, Xi’an, China
    Proceedings of the 18th International Conference on Nuclear Engineering

Publ.-Id: 13731 - Permalink


Extension of the Inhomogeneous MUSIG model for bubble condensation
Lucas, D.; Frank, T.; Lifante, C.; Zwart, P.; Burns, A.;
Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modeling of the condensation process. The effect of bubble sizes was clearly shown in experimental investigations done previously at the TOPFLOW facility of FZD. Steam bubbles were injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices were used to vary the initial bubble size distribution. Measurements were done using a wire-mesh sensor. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. Recently the Inhomogeneous MUSIG model was implemented into the CFD code CFX from ANSYS enabling the simulation of poly-dispersed flows including the effects of separation of small and large bubbles due to bubble size dependent lift force inversion. It allows to divide the dispersed phase into size classes regarding the mass as well as regarding the momentum balance. Up to now transfers between the classes in the mass balance can be considered only by bubble coalescence and breakup (population balance). Here an extension of the model is proposed to include the effects due to phase transfer. The paper focuses on the derivation of equations for the extension of the Inhomogeneous MUSIG model and presents some first results for verification and validation.
Keywords: two-phase flow, condensation, bubbly flow, poly-dispersion, CFD, MUSIG

Publ.-Id: 13730 - Permalink


Recent results from HADES on electron pair production in relativistic heavy-ion collisions
Galatyuk, T.; Hades Collaboration;
Systematic investigations of dilepton production are performed at the SIS accelerator of GSI with the HADES spectrometer. The goal of this program is a detailed understanding of di-electron emission from hadronic systems at moderate temperatures and densities. New results obtained in HADES experiments focussing on electron pair production in elementary collisions are reported here. They pave the way to a better understanding of the origin of the so-called excess pairs earlier on observed in heavy-ion collisions by the DLS collaboration and lately confirmed in two measurements of the HADES collaboration using C+C and Ar+KCl collisions. Results of these studies are discussed.
  • Contribution to proceedings
    5th International Workshop on Critical Point and Onset of Deconfinement - CPOD 2009, 08.-12.06.2009, New York, USA
    arXiv:0911.2411

Publ.-Id: 13729 - Permalink


Omega and Eta (Eta-prime) mesons from NN and ND collisions at intermediate energies
Kaptari, L. P.; Kämpfer, B.;
The production of pseudo scalar, Eeta, Eta-prime, and vector, Omega, Rho, Phi, mesons in NN collisions at threshold-near energies is analyzed within a covariant effective meson-nucleon theory. It is shown that a good description of cross sections and angular distributions, for vector meson production, can be accomplished by considering meson and nucleon currents only, while for pseudo scalar production an inclusion of nucleon resonances is needed. The di-electron production from subsequent Dalitz decay of the produced mesons, eta' to gamma gamma^* to gamma e^+e^- and omega to pi gamma^* to pi e^+e^- is also considered and numerical results are presented for intermediate energies and kinematics of possible experiments with HADES, CLAS and KEK-PS.
We argue that the transition form factor omega to gamma^* pi as well as eta' to gamma^* gamma can be defined in a fairly model independent way and the feasibility of an experimental access to transition form factors is discussed.

Publ.-Id: 13728 - Permalink


Ionen als Agenten und Detektive
Neelmeijer, C.;
Dieser Vortrag für Schüler zeigt auf, wie Protonenstrahlanalytik an Atmosphäre erfolgt, welcher Informationsgehalt durch die Kombination von PIGE-PIXE-RBS gewonnen wird und welche typische Fragestellungen damit beantwortrt werden können.
Keywords: zerstörungsfreie Analyse, Kunstwerke, Unikate, mikroelektronische Strukture
  • Lecture (others)
    Schülervortrag, 01.02.2010, Dresden, Deutschland

Publ.-Id: 13727 - Permalink


Laser proton acceleration - First experiments
Zeil, K.; Kraft, S.; Metzkes, J.; Richter, T.; Bock, S.; Bussmann, M.; Kluge, T.; Schramm, U.; Cowan, T.; Sauerbrey, R.;
In this talk first experiments of proton acceleration with the Draco laser are presented.
  • Lecture (Conference)
    American Physical Society: 51st Annual Meeting of the Division of Plasma Physics, 03.11.2009, Atlanta, United States of America

Publ.-Id: 13725 - Permalink


The Role of Transferrin in Actinide(IV) Uptake: Comparison with Iron(III)
Jeanson, A.; Ferrand, M.; Funke, H.; Hennig, C.; Moisy, P.; Solari, P. L.; Vidaud, C.; Den Auwer, C.;
The impact of actinides on living organisms has been the subject of numerous studies since the 1950s. From a general point of view, these studies show that actinides are chemical poisons as well as radiological hazards. Actinides in plasma are assumed to be mainly complexed to transferrin, the iron carrier protein. This paper casts light on the uptake of actinides(IV) (thorium, neptunium, plutonium) by transferrin, focusing on the pH dependence of the interaction and on a molecular description of the cation binding site in the protein. Their behavior is compared with that of iron(III), the endogenous transferrin cation, from a structural point of view. Complementary spectroscopic techniques (UV/Vis spectrophotometry, microfiltration coupled with g spectrometry, and X-ray absorption fine structure) have been combined in order to propose a structural model for the actinide-binding site in transferrin. Comparison of our results with data available on holotransferrin suggests some similarities between the behavior of FeIII and NpIV/PuIV/ NpIV is not complexed at pH <7, whereas at pH ≈7.4 complexation can be regarded as quantitative. This pH effect is consistent with the in vivo transferrin “cycle”. PuIV also appears to be quantitatively bound by apotransferrin at around pH ~7.5, whereas ThIV was never complexed under our experimental conditions. EXAFS data at the actinide edge have allowed a structural model of the actinide binding site to be elaborated: at least one tyrosine residue could participate in the actinide coordination sphere (two for iron), forming a mixed hydroxo–transferrin complex in which actinides are bound with transferrin both through An–tyrosine and through An-OH bonds. A description of interatomic distances is provided.
Keywords: Actinides, Transferrin, EXAFS

Publ.-Id: 13724 - Permalink


Influence of air entrainment on the liquid flow field caused by a plunging jet and consequences for fibre deposition
Krepper, E.; Weiß, F.-P.; Alt, S.; Kratzsch, A.; Renger, S.; Kästner, W.;
Plunging jets play an important role in nuclear reactor safety research. In the present paper the case of the strainer clogging issue is considered. Entrained air caused by a plunging jet has an influence of the liquid flow field and on the fibre transport in the sump. In the paper the amount of entrained air is given as an inlet boundary condition according to correlations in the literature and confirmed by own experiments. The influence of entrained air on the fibre deposition pattern at the bottom of a tank and on the mixing procedure for the case of temperature differences between jet and tank water are investigated by Computational Fluid Dynamics (CFD) calculations and compared to experiments.
The presented work is part of a joint research project performed in cooperation between the University of Applied Science Zittau/Görlitz and Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow in Zittau and the development of CFD models for its simulation in Rossendorf Whereas an overview and a description of the main concepts of this project are described by Krepper et al. 2008, 2009, the focus of the actual paper is directed on the different aspects of a jet.
The entrained air has a remarkably influence on the generation of swirls und therefore on the transport and deposition of fibres. At least qualitative conclusions concerning main effects, critical regions of fibre deposition and design improvements avoiding undesired fibre deposition can be drawn. The CFD simulation of the sump flow conditions during a real accident scenario over several 1000 seconds however will fail caused by the large computational effort.
Keywords: fibres, experiments, cfd, multiphase flow

Publ.-Id: 13723 - Permalink


Electron bunch length measurements from laser-accelerated electrons using single-shot THz time-domain interferometry
Debus, A. D.; Bussmann, M.; Schramm, U.; Sauerbrey, R.; Murphy, C. D.; Major, Z.; Hörlein, R.; Veisz, L.; Schmid, K.; Schreiber, J.; Witte, K.; Jamison, S. P.; Gallacher, J. G.; Jaroszynski, D. A.; Kaluza, M. C.; Hidding, B.; Kiselev, S.; Heathcote, R.; Foster, P. S.; Neely, D.; Divall, E. J.; Hooker, C. J.; Smith, J. M.; Ertel, K.; Langley, A. J.; Norreys, P.; Collier, J. L.; Karsch, S.;
Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches with and unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment.
We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5J, 45fs, 800nm laser and a ZnTe-based electro-optical setup we demonstrate the duration of laser-accelerated, quasi-monoenergetic electron bunches (best fit of 32fs (FWHM) with a 90% upper confidence level of 38fs) to be shorter than the drive laser pulse, but similar to the plasma period.
Keywords: electron bunch length measurement coherent transition radiation laser plasma wakefield acceleration
  • Physical Review Letters 104(2010), 084802
    DOI: 10.1103/PhysRevLett.104.084802
  • Lecture (Conference)
    DPG Tagung 2010, 08.-12.03.2010, Hannover, Deutschland
  • Lecture (Conference)
    TR18-Treffen Bad Breisig, 04.03.-05.05.2010, Bad Breisig, Deutschland

Publ.-Id: 13722 - Permalink


Absolute charge calibration of scintillating screens for relativistic electron detection
Buck, A.; Zeil, K.; Popp, A.; Schmid, K.; Jochmann, A.; Kraft, S.; Hidding, B.; Kudyakov, T.; Sears, C.; Veisz, L.; Karsch, S.; Pawelke, J.; Sauerbrey, R.; Cowan, T.; Krausz, F.; Schramm, U.;
We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower detection limit in our setup for the most sensitive scintillating screen (KODAK Biomax MS) was 10 fC / mm2. The screens showed a linear photon-to-charge dependency over several orders of magnitude. An onset of saturation effects starting around 10 - 100 pC / mm2 was found for some of the screens. Additionally, a constant light source was employed as a luminosity reference, to simplify the transfer of a one-time absolute calibration to different experimental setups.

Publ.-Id: 13720 - Permalink


Absolute response of Fuji imaging plate detectors to picosecond-electron bunches
Zeil, K.; Kraft, S. D.; Jochmann, A.; Kroll, F.; Jahr, W.; Schramm, U.; Karsch, L.; Pawelke, J.; Hidding, B.; Pretzler, G.;
The characterization of the absolute number of electrons generated by laser wakefield acceleration often relies on absolutely calibrated FUJI imaging plates (IP), although their validity in the regime of extreme peak currents is untested. Here, we present an extensive study on the dependence of the sensitivity of BAS-SR and BAS-MS IP to picosecond electron bunches of varying charge of up to 60 pC, performed at the electron accelerator ELBE, making use of about three orders of magnitude of higher peak intensity than in prior studies. We demonstrate that the response of the IPs shows no saturation effect and that the BAS-SR IP sensitivity of 0.0081 photostimulated luminescence per electron number confirms surprisingly well data from previous works. However, the use of the identical readout system and handling procedures turned out to be crucial and, if unnoticed, may be an important error source.
  • Review of Scientific Instruments 81(2010)1, 013307

Publ.-Id: 13719 - Permalink


P0803 - Verfahren zur Herstellung für Kohlenstoffnanoröhrchen, durch das Verfahren hergestellte Kohlenstoffnanoröhrchen und deren Verwendung
Abrasonis, G.; Pollmann, K.; Raff, J.;
Die Erfindung betrifft ein Verfahren, mit dessen Hilfe Kohlenstoffnanoröhrchen mit definiertem Durchmesser auf einem Substrat in gleichmäßiger Ausrichtung hergestellt werden können. Bei dem erfindungsgemäßen Verfahren wird die Eigenschaft von selbstorganisierenden Molekülen, geordnete Schichten auszubilden, ausgenutzt, um einheitliche Nanopartikel auf einem Trägersubstrat geordnet zu erzeugen und damit Nanokohlenstoffröhrchen mit definierter Anordnung auf diesem Trägersubstrat zu synthetisieren. Dazu bringt man zunächst eine Schicht aus selbstorganisierenden Molekülen auf ein Trägersubstrat auf und erzeugt auf der Schicht aus selbstorganisierenden Molekülen anorganische Nanopartikel. Anschließend wird die Schicht aus selbstorganisierenden Molekülen entfernt, wobei die anorganischen Nanopartikel auf dem Trägersubstrat zurückbleiben und an den Nanopartikeln Nanokohlenstoffröhrchen synthetisiert werden. Mit dem erfindungsgemäßen Verfahren können Kohlenstoffröhrchen mit definierter Größe in hoher Ausbeute und Einheitlichkeit hergestellt werden.
  • Patent
    DE 10 2008 023 229 A1 - 12.11.2009
  • Patent
    EP 2123602 A1 - 25.11.2009
  • Patent
    EP2123602B1: Erteilung-16.01.2013; Validierung in DE, FR, GB

Publ.-Id: 13717 - Permalink


2d-2c ultrasound Doppler array velocimeter for flow investigations in liquid metals
Franke, S.; Lieske, H.; Fischer, A.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.;
In magnetohydrodynamics ultrasound Doppler velocimetry (UDV) is applied for flow field investigations of liquid metal flows. Thereto, commercial UDV instruments are available. However, their application possibility for multi-dimensional, multi-componential flow mapping with high measurement rates is highly limited since these features cannot be applied simultaneously. Hence, we have developed an ultrasound Doppler velocimeter for measuring the two-dimensional two-componential (2d-2c) flow field of magnetically driven liquid metal. The velocimeter utilizes two identical linear ultrasound Doppler arrays arranged orthogonally to each other to facilitate the 2d-2c flow mapping in a plane of 70 x 70 mm². Each ultrasound array providing a centre frequency of 8 MHz comprises 25 transducer elements each with a piezo element size of 2.5 x 5 mm². In operation two adjacent elements are combined to a square transducer pair of 5 x 5 mm² allowing a small lateral scanning step width of 2.5 mm on the one hand and a low divergence of the ultrasound beam and accordingly a better lateral resolution up to 2 mm on the other hand. To achieve a high temporal resolution concurrently to the high spatial resolution, the measurement is parallelized as much as possible by simultaneous operation of four transducer pairs which are controlled by a special multiplex control unit. The operation principle, design considerations and the characterisation of the ultrasound Doppler array velocimeter will be reported. Flow mapping of a swirling flow in a cubic vessel with GaInSn generated by a rotating magnetic field were performed. Measurement results of a stationary as well as a periodically reversed flow will be presented.
Keywords: Ultrasound Doppler method, sensor array, liquid metal, rotating magnetic field
  • Lecture (Conference)
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.2010, Göteborg, Schweden
  • Contribution to proceedings
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.10, Göteborg, Schweden
    Proceedings of the 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 89-92

Publ.-Id: 13716 - Permalink


Ultrasonic flow measurements in a low temperature liquid metal model of the continuous steel casting process
Timmel, K.; Eckert, S.; Gerbeth, G.;
Fluid flow in the mould cavity of the continuous casting process can be controlled by the application of magnetic fields. Experiments have been performed at room temperature using a small-scale experimental set-up with the eutectic alloy GaInSn. The ultrasound Doppler method was applied for measuring the fluid velocity in the mould. An arrangement of 10 transducers was used to determine a two-dimensional distribution of the horizontal velocity component. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied. Our measurements deliver an authentic reproduction of the location and extension of the emergent jet and disclose the temporal behaviour of the flow inside the jet as well as in the recirculating zones. An important result of our study was the feature that a static magnetic field may give rise to non-steady, non-isotropic large-scale flow perturbations. Likewise, the flow measurements presented here did not confirm the expectation of a smooth reduction of the velocity fluctuations at the nozzle outlet due to the magnetic field. This problem requires further investigation, because the concept of an EMBR in the continuous casting process relies on a reliable damping effect of the applied magnetic field. The combination of liquid metal cold models and the ultrasound Doppler method as a powerful flow measuring technique in liquid metals appears as an important tool for an experimental investigation of such open questions and provides valuable experimental data for the validation of numerical flow simulations.
Keywords: continuous casting, liquid metal model experiment, flow measurements, Ultrasound Doppler Velocimetry
  • Lecture (Conference)
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.2010, Göteborg, Schweden
  • Contribution to proceedings
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.10, Göteborg, Schweden
    Proceedings of the 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 93-96

Publ.-Id: 13715 - Permalink


Investigations of the bulk flow inside a cylindrical liquid metal column generated by diverse AC magnetic fields
Räbiger, D.; Zhang, C.; Grants, I.; Eckert, S.; Gerbeth, G.;
This presentation considers various situations where the flow inside a liquid metal column is driven by different configurations of AC magnetic fields. The ultrasonic Doppler method has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both a swirling flow in the horizontal planes and the flow pattern in the radial-meridional plane. In the first part we consider the transient liquid metal flow which is generated inside a cylindrical container by the discontinuous application of a rotating magnetic field (RMF) and the alternating application of subsequent RMF and TMF pulses, respectively. Such new approaches have been recently suggested for melt stirring during solidification of metal alloys in order to control the heat and mass transfer at the solidification front. The second part is concerned with an RMF-driven flow which is influenced by an oxide layer at the free surface of the metallic melt. The oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls. A complex interaction occurs if the both forces are in the same order of magnitude. In that case, our measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk flow. Finally, we study the combination of a travelling and a rotating magnetic field which may generate a specific flow phenomenon in form of a concentrated vortex with properties similar to a tornado. The travelling magnetic field (TMF) creates an intense converging flow at one end of the cylinder whereas the additionally superimposed rotating magnetic field (RMF) with a substantially different frequency sets the flow into rotation. The angular momentum conservation forces the rotation to intensify towards the centre of the converging flow. This phenomenon may be useful to stir floating particles into the melt.
Keywords: liquid metal, electromagnetic stirring, mixing, Ultrasound Doppler Velocimetry
  • Lecture (Conference)
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.2010, Göteborg, Schweden
  • Contribution to proceedings
    6th Annual European Rheology Conference (AERC2010), ISUD7, 07.-09.04.10, Göteborg, Schweden
    Proceedings of the 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 81-84

Publ.-Id: 13714 - Permalink


Experimental modeling of the continuous casting process of steel using low melting point metal alloys - the LIMMCAST program
Timmel, K.; Eckert, S.; Gerbeth, G.; Stefani, F.; Wondrak, T.;
This paper presents the new experimental facility CONCAST which was designed for modeling fluid flow and transport processes in the continuous casting of steel. The facility operates at temperatures of 200°C - 400°C by using the low melting point alloy SnBi. The main parameters of the facility, including the dimensions of the test sections, will be given. The resultant possibilities with respect to flow investigations in the tundish, in the submerged entry nozzle, and in the mould will be discussed. Over the period of assembling and commissioning the CONCAST facility, the small-scale set-up Mini-CONCAST was employed which uses the alloy GaInSn that is liquid at room temperatures. At this precursory facility an experimental program was started which is focused on quantitative flow measurements in the mould and in the submerged entry nozzle (SEN). The Ultrasound Doppler Velocimetry (UDV) and the Contactless Inductive Flow Tomography (CIFT) were applied to determine the flow structure within the mould. First experimental results will be presented here for a single and a two-phase flow in which argon gas bubbles were injected at the inlet of the SEN. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the emergent jet flow from the SEN has been studied.
Keywords: continuous casting, liquid metal model experiments, flow measurements, two-phase flow, electromagnetic brake

Publ.-Id: 13713 - Permalink


P0710 - Verfahren zur Reduzierung von Temperaturfluktuationen in Schmelzen
Grants, I.; Gerbeth, G.;
Die Erfindung betrifft ein Verfahren zur Reduzierung von Temperaturfluktuationen in Halbleiter- oder Metall-Schmelzen. Das Hauptinteresse gilt vor allem Schmelzen in Kristallzüchtungsprozessen wie Gallium-Arsenid (GaAs), Indium-Phosphid (InP) oder Silizium (Si).
Mit der Erfindung werden große Temperaturfluktuationen in der Schmelze unterdrückt, die den Prozess des Kristallwachstums stören bzw. teilsweise unmöglich machen.
Durch den Einsatz dieses Verfahrens können deutlich größere Schmelzvolumina als heute üblich verwendet werden.
  • Patent
    DE 10 2007 036 944 A1 - 05/02/09
  • Patent
    EP 2090679 A1 - 19/08/09

Publ.-Id: 13712 - Permalink


P0712 - Verfahren und Einrichtung zum elektromagnetischen Rühren von elektrisch leitenden Flüssigkeiten
Eckert, S.; Räbiger, D.; Willers, B.; Gerbeth, G.; Nikrityuk, P. A.; Eckert, K.; Grundmann, R.;
Die Erfindung betrifft ein Verfahren und eine Einrichtung zum elektromagneti-schen Rühren elektrisch leitfähiger Flüssigkeiten (2) unter Verwendung eines in der horizontalen Ebene rotierenden Magnetfeldes RMF (34) und eines dazu in vertikaler Richtung wandernden Magnetfeldes WMF (47).

Die Aufgabe besteht darin, dass unsymmetrische Strömungsstrukturen in mit Schmelzen gefüllten Behältern, insbesondere zu Beginn und während des Ver-laufs der Erstarrung vermieden werden. Außerdem sollen eine effektive Durch-mischung der Flüssigkeit und/oder eine kontrollierte Erstarrung metallischer Le-gierungen unter Vermeidung der Ausbildung von Entmischungszonen im Erstar-rungsgefüge erreicht werden.

Die Lösung besteht darin, dass sowohl das rotierende Magnetfeld RMF (34) als auch das wandernde Magnetfeld WMF (47) diskontinuierlich in Form von zeitlich begrenzten und einstellbaren Periodendauern (TP,RMF,TP,WMF) und abwechselnd zeitlich nacheinander über zugehörige Induktionsspulen (31,32,33;41,42,43,44, 45,46) zugeschaltet werden.
  • Patent
    Patent DE 10 2007 038 281 B4 - 2009/06/18
  • Patent
    DE 10 2007 038 281 A1 - 19/02/2009
  • Patent
    WO 2009/018810 - 12/02/2009

Publ.-Id: 13711 - Permalink


P0711 - Verfahren und Einrichtung zum elektromagnetischen Rühren von elektrisch leitenden Flüssigkeiten
Eckert, S.; Räbiger, D.; Willers, B.; Gerbeth, G.; Nikrityuk, P. A.; Eckert, K.; Grundmann, R.;
Die Erfindung betrifft ein Verfahren und eine Einrichtung zum elektromagnetischen Rühren von elektrisch leitenden Flüssigkeiten (2,21,22) im flüssigen Zustand und/oder im Zustand des Beginns der Erstarrung der Flüssigkeit (2,21,22) unter Verwendung eines in der horizontalen Ebene eine Lorentzkraft (FL) erzeugenden, rotierenden Magnetfeldes.
Die Aufgabe besteht darin, dass eine intensive dreidimensionale Strömung im In-nern der Flüssigkeit zum Durchmischen im flüssigen Zustand bis in die unmittelbare Umgebung von Erstarrungsfronten erreicht und gleichzeitig eine ungestörte, freie Oberfläche der Flüssigkeit gewährleistet werden. ...
  • Patent
    DE102007037340A1: Offenlegung-19.02.2009; Nachanmeldung WO (nationalisiert in US, EP, JP, US)
  • Patent
    Patent DE102007037340B4 2010/02/25

Publ.-Id: 13710 - Permalink


P0709 - Flüssigmetall-Ionenquelle zur Erzeugung von Lithium-Ionenequelle
Bischoff, L.; Akhmadaliev, S.;
Die Erfindung betrifft eine Flüssigmetall-Ionenquelle (LMIS) zur Erzeugung von Lithiumionenstrahlen, insbesondere das den Emitter benetzende Quellenmaterial einer derartigen Ionenquelle.
Die Erfindung beinhaltet Flüssigmetall-Ionenquellen, deren Emitter mit einer definierten Legierung aus Lithium und einem oder mehreren der Elemente Gallium, Indium und Wismut als Quellenmaterial benetzt ist.
Mit derart ausgestatteten Flüssigmetall-Ionenquellen ist es möglich, langzeitig einen stabilen Ionenstrom, der im ausreichendem Maße aus Lithiumionen besteht, zu erhalten.
Die Bestandteile der Legierung im Zusammenspiel mit dem niedrigen Schmelzpunkt führen dazu, dass keine chemischen Reaktionen mit dem Emitter- und Heizermaterial auftreten sowie die Legierungsoberfläche relativ langsam an Luft korrodiert.
  • Patent
    DE 10 2007 027 097 A1

Publ.-Id: 13709 - Permalink


Combined Computational and Experimental Study of Uranyl(VI) 1:2-Complexation by Aromatic Acids
Wiebke, J.; Weigand, A.; Weißmann, D.; Glorius, M.; Moll, H.; Bernhard, G.; Dolg, M.;
The bis(salicylhydroxamato), bis(benzohydroxamato), and bis(benzoato) complexes of UO22+ in aqueous solution have been investigated in a combined experimental and computational effort using extended X-ray absorption fine structure and UV−vis spectroscopy, and density functional theory (DFT) techniques, respectively. Experimental data indicates 5-fold UO22+ coordination with mean equatorial U−O distances of 2.42 and 2.40 Å for the salicyl- and benzohydroxamate systems, respectively. DFT calculations on microsolvated model systems [UO2L2OH2] indicate UO22+ eta-2-chelation via the hydroxamate and benzoate oxygen atoms in excellent agreement with experimental data; calculated complex stabilities support that UO22+ prefers hydroxamate over carboxylate coordination. The 414 nm absorption band of UO22+ in aqueous solution is blue-shifted to 390 and 386 nm upon complexation by salicyl- and benzohydroxamate, respectively. Calculated time-dependent DFT excitation energies of [UO2L2OH2], however, occasionally fail to reproduce accurately experimental UV−vis spectra, which are dominated by L− -to- UO22+ charge-transfer contributions. We additionally show that the UVI large-core pseudopotential approximation recently developed by some of the authors can routinely be applied for electronic structure calculations not involving uranium 5f occupations significantly different from UVI.
Keywords: Density-Functional Theory, Uranyl-Ion, Electronic-structures, Molecular-Structure, Hydroxamic acids, Benzoic acid

Publ.-Id: 13708 - Permalink


Burning plutonium and minimizing radioactive waste in existing PWRs
Mittag, S.; Kliem, S.;
Plutonium and other long-lived radioactive actinides are produced in light water reactors (LWR) using conventional fuel. "Innovative" fuel matrices may reduce the breeding of these nuclides. However, essential LWR safety features have to be preserved, which restricts the possibilities for new fuel-carrying matrices. Respective fuel-assembly and LWR-core safety studies indicate practicable new fuel options for the near future.

Publ.-Id: 13706 - Permalink


Radiotracer studies on interaction processes related to humic-bound transport of radionuclides
Lippold, H.; Lippmann-Pipke, J.;
Colloid-borne transport of actinides in aquifer systems is a topic of major interest in view of long-term risk assessments for underground radwaste repositories. In particular, complexation with aquatic humic substances can be decisive for the mobility of radiotoxic metals [1,2]. Depending on geochemical parameters, migration can be both enhanced and reduced. The respective conditions need to be identified, and models must be able to describe such complex systems by few parameters. According to the Linear Additive Model [3], total metal adsorption in the presence of humic matter can be calculated by linking parameters for the adsorption of both components and their interaction with each other. The basics of this approach are also implicit in advanced transport models [4].
In our study, the influence of humic acid on metal adsorption onto three clay materials (montmorillonite, illite, Opalinus clay) as a function of pH was investigated for Tb(III) as an analogue of trivalent actinides. 160Tb and 131I-labelled humic acid were used as radiotracers, allowing experiments at very low concentrations to mimic realistic conditions. For all clay materials under study, the presence of humic acid caused an increase in metal adsorption at neutral and acidic pH, i.e., metal desorption from clay barriers in consequence of acidification processes is generally counteracted in the presence of humic matter. Based on the pH-dependences of humic acid adsorption and Tb-humate complexation, this can be qualitatively explained by co-adsorption of humic-bound Tb. Quantitative estimates by means of the Linear Additive Model were, however, not successful.
In equilibrium models (Kd models), it is presumed that reaction rates for adsorption and desorption are both high enough to ensure a steady local equilibrium under flow conditions. Regarding the adsorption of humic substances onto geological materials, however, there is a lack of clarity concerning the dynamic character of this process. Recoveries in column experiments suggest a limited reversibility. In order to gain direct insight into the dynamics of the adsorption-desorption equilibrium, we conducted tracer exchange experiments with 14C-labelled humic acid. A negligible amount of the radiotracer was contacted with equilibrated systems of kaolinite and non-labelled humic acid for different periods of time. Tracer exchange at surface saturation provided evidence of a reversible process, but the time needed until the dynamic equilibrium was quantitatively represented by the tracer turned out to be much longer than the time needed to attain the overall adsorption equilibrium. This discrepancy between exchange kinetics and adsorption kinetics, which is indicative of a very slow desorption rate, has to be taken into consideration when the equilibrium condition is assigned to a maximum flow rate in transport systems.
  • Lecture (Conference)
    11th International Symposium on Environmental Radiochemical Analysis, 15.-17.09.10, Chester, United Kingdom

Publ.-Id: 13705 - Permalink


Counter-current flow limitation in a model of the hot leg of a PWR - comparison between air/water and steam/water experiments
Vallée, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.; Pietruske, H.; Schütz, P.; Carl, H.;
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Helmholtz-Zentrum Dresden Rossendorf (HZDR). The hot leg model is devoted to optical measurement techniques, therefore, a flat test section design was chosen and equipped with large windows. In order to enable the operation at high pressures, the test section is installed in the pressure chamber of the TOPFLOW test facility of HZDR, which is used to perform the experiments under pressure equilibrium with the inside atmosphere. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux-condenser cooling mode appearing in small break LOCA scenarios. The fluids used were air and water at room temperature and pressures of up to 3.0 bar, as well as steam and water at pressures of up to 50 bar and the corresponding saturation temperature of 264°C. One selected 50 bar experiment is presented in detail: the observed behaviour is analysed and illustrated by typical high-speed camera images of the flow.

Furthermore, the flooding characteristics obtained from the different experimental runs are presented in terms of the Wallis parameter and Kutateladze number, which are commonly used in the literature. However, a discrepancy was first observed between the air/water and steam/water series. Further investigations show that the steam was probably wet due to heat losses and to liquid entrainment from the heater circuit. Consequently, a correction of the steam measurements was required. The amount of parasitic water was evaluated indirectly over the zero liquid penetration noticed in the CCFL diagram. Finally, the experimental results confirm that the Wallis similarity is appropriate to scale flooding in the hot leg of a pressurised water reactor over a wide range of pressure and temperature conditions.
Keywords: two-phase flow, counter-current flow limitation, flooding, hot leg, pressurised water reactor

Publ.-Id: 13704 - Permalink


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