Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Povedenie germanii, implantirovannovo v SiO2 vblisi granizui sraschivania kremnii na isolatore Behavior of Germanium Ion-implanted into SiO2 Near the Bonding Interface of a Silicon-on-Insulator Structure

in Russian

Popov, V. P.; Tyschenko, E.; Voelskow, M.; Cherkov, A. G.

issledovanui svoistva germanii, implantirovannovo v sloi SiO2
The properties of germanium implanted into the SiO2 layers in the vicinity of the bonding interface of silicon-on-insulator structures are studied. It is shown that, under conditions of high-temperature (1100 °C) annealing, germanium nanocrystals are not formed, while the implanted Ge atoms segregate at the Si/SiO2 bonding interface. It is established that, in this case, Ge atoms are found at sites that are coherent with the lattice of the top silicon layer. In this situation, the main type of traps is the positive-charge traps; their effect is interpreted in the context of an increase in the surface-state density due to the formation of weaker Ge–O bonds. It is found that the slope of the drain–gate characteristics of the back MIS transistors increases; this increase is attributed to an increased mobility of holes due to the contribution of an intermediate germanium layer formed at the Si/SiO2 interface.

Keywords: ion implantation; germanium; SiO2

  • Fizika i Tekhnika Poluprovodnikov 41(2007)3, 301-303
  • Semiconductors 41(2007)3, 291-296

Permalink: https://www.hzdr.de/publications/Publ-11796
Publ.-Id: 11796


Transport and noise in organic field effect devices

Morawetz, K.; Gemming, S.; Luschtinetz, R.; Kunze, T.; Lipavský, P.; Eng, L. M.; Seifert, G.; Milde, P.; Pankoke, V.

The transport and fluctuation properties of organic molecules ordered parallel between two Au contact leads are investigated by the method of surface Green function. From first-principles simulation the relevant hopping parameters are extracted and used to calculate nonlinear transport coefficients with respect to an external bias voltage. A staggering of conductance is found in dependence on the number of molecules squeezed in-between the contacts. The thermal properties show an anomalous behavior whenever the voltage reaches the values of the molecular energy levels active for transport. The thermoelectric figure of merit shows a resonance allowing to reach values even larger than one.

  • Physical Review B 79(2009)085405, 1-12

Permalink: https://www.hzdr.de/publications/Publ-11795
Publ.-Id: 11795


Pattern competition in homogeneously heated fluid layers

Cartland Glover, G. M.; Generalis, S. C.

Simulations examining pattern competition have been performed on a horizontal homogeneously heated layer that is bounded by an isothermal plane above an adiabatic plane. Several different circulation patterns arose as the heating regime applied to the horizontal layer was modified. The sequence of the patterns formed as the Grashof number was increased had the following order: laminar, rolls, squares, hexagons and pentagons, pentagons and then two square modes of differing orientations. Fourier analysis was used to determine how the key modes interact with each pattern.

Keywords: Convection; Horizontal Layer; Heat Transfer; Stability

  • Open Access Logo Engineering Application of Computational Fluid Mechanics 3(2009)2, 164-174

Permalink: https://www.hzdr.de/publications/Publ-11794
Publ.-Id: 11794


Ultra fast electron beam x-ray CT scanner for industrial process tomography

Fischer, F.; Hampel, U.; Mattausch, G.

In many industrial fields, there is a strong interest in the understanding of inner structure and transient behaviour of multi-phase flows. This is relevant for process control and optimisation in chemical industry or has influence on design of safety components in nuclear engineering, for example. The qualification of computational fluid dynamics codes dedicated to simulation of the stationary and transient flows in complex three dimensional geometries requires in-depth knowledge of the details of the real flow structure under various conditions. To extend our measurement capabilities beyond the wire mesh sensor and needle probes used so far [1], we have developed a high-speed x-ray tomography system recently [2]. This new technique offers the opportunity to perform non-intrusive flow measurements with a high frame rate and also at high temperatures and pressures. The basic principle of the system is similar to the EB CT being used in cardiac diagnostics [3]. The scanner consists of an electron beam gun with triode-type cathode system delivering up to 65 mA beam current at 150 kV acceleration voltage. Using fast electron-optical units, the electron beam is focussed onto a semicircular metal target and swept at a frequency of up to 10 kHz along the target thus producing a rapidly moving x-ray spot. A circular x-ray detector comprising 240 CZT pixels measures the x-ray power transmitted through the object which is placed in the center of the scanner head. The detector readings are recorded at a data acquisition rate of 1 MS/s and subsequently used for image reconstruction. Frame rates of up to 7.000 2D slices per second can be achieved in this way. Typical object diameters are up to 120 mm. Spatial resolution is currently in the range of 1 mm feature size but will be improved in the future.

  • Lecture (Conference)
    1st ITG International Vacuum Electronics Workshop, 10.-11.11.2008, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11793
Publ.-Id: 11793


Air-water experiments in a vertical DN200-pipe

Beyer, M.; Lucas, D.; Kussin, J.; Schütz, P.

The extensive experimental results presented in this report provide a high-quality database for air-/water flows in a vertical pipe with a nominal diameter of 200 mm. This database can be used for the development and validation of CFD-like models for two-phase flows, e.g. for bubble coalescence and fragmentation. In particular, the investigations aim on the evolution of the two-phase flow along the pipe height. Therefore, up to 18 single measurements with varying distances between the gas injection and measurement plane were realised for each of the 92 combinations of gas and water flow rates. The pressure at the position of the activated gas injection was kept constant at 0.25 MPa(a). This boundary condition has the advantage that the measured data represent exactly the evolution of the flow along the pipe, i.e. they reflect a configuration at which the gas injection is at a fixed height position, while the measurement plane varies. Important results of this test series are time averaged radial profiles of the gas fraction, and the gas velocity, as well as the time and cross-section averaged bubble size distributions. Furthermore, gas fraction data resolved regarding the bubble size and spatial distribution are presented. As in previous test series, flow patterns were analysed, whereby the classification results from the bubble size. A substantial part of these new air/water experiments were quality and plausibility checks of the measured data. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. The influence of the orifice diameter of the gas injection on flow patterns is also discussed in the report.
Freigabe ab 2011

Keywords: Two-phase flow; Gas bubbles; Gas volume fraction distribution; Gas velocity

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-505 2008
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-11792
Publ.-Id: 11792


Luft-Wasser Experimente im vertikalen DN200-Rohr

Beyer, M.; Lucas, D.; Kussin, J.; Schütz, P.

Die im Rahmen dieser Versuchsserie erzielten umfangreichen experimentellen Ergebnisse bilden eine hochwertige Datenbasis für Luft-Wasser-Strömungen in einem vertikalen DN200-Rohr, die für die Entwicklung und Validierung von CFD-Modellen, beispielweise bzgl. Blasenkoaleszenz und -fragmentierung, genutzt werden können. Besonderes interessant ist die Untersuchung der Entwicklung der Zweiphasenströmung über der Rohrhöhe. Aus diesem Grund wurden für jede der 92 betrachteten Kombinationen aus Gas- und Wasser-Volumenstromdichten bis zu 18 Messungen mit variablen Abständen zwischen Gaseinspeisung und Messebene durchgeführt. Dabei wurde der Druck an der Gaseinspeisestelle konstant auf 0,25 MPa(a) gehalten. Diese Randbedingung bietet den Vorteil, dass die so gemessenen Daten die Entwicklung der Strömung über der Rohrhöhe widerspiegeln, d.h. eine Konfiguration beschreiben, bei der das Gas an einer festen Höhenposition eingespeist wird und die Messungen in verschiedenen darüberliegenden Ebenen erfolgen. Wesentliche Ergebnisse dieser Messserie sind radiale zeitgemittelte Profile für den Gasgehalt und die Gasgeschwindigkeit sowie zeit- und querschnittsgemittelte Blasengrößenverteilungen. Außerdem liegen blasengrößen- und ortsaufgelöste Gasgehaltsdaten vor. Wie bereits bei früheren Versuchsserien wurden auch in diesem Fall die Strömungsformen analysiert, wobei die Klassifizierung anhand der Blasengröße erfolgte. Ein wesentlicher Bestandteil dieser neuen Luft/Wasser-Versuche war die Qualitäts- und Plausibilitätsprüfung der Messdaten. Es konnte festgestellt werden, dass die Daten einen eindeutigen, widerspruchsfreien Trend bzgl. ihrer Entwicklung mit zunehmendem Abstand von der Gaseinspeisung aufweisen. Zur Plausibilitätsprüfung wurden Vergleiche des Gasgehaltsverlaufes über der Rohrhöhe mit theoretisch zu erwartenden Kurven durchgeführt. Zusätzlich zu diesen Ergebnissen enthält der Bericht eine Einschätzung des Einflusses des Bohrungsdurchmessers an der Gaseinspeisung auf die sich einstellende Strömung.
Freigabe ab 2011

Keywords: Two-phase flow; Gas bubbles; Gas volume fraction distribution; Gas velocity

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-504 2008
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-11791
Publ.-Id: 11791


Miniature conductivity wire mesh sensor for gas-liquid two-phase flow measurement

Hampel, U.; Otahal, J.; Boden, S.; Beyer, M.; Schleicher, E.; Zimmermann, W.; Jícha, M.

A miniature conductivity wire mesh sensor for gas-liquid two-phase flow measurement in small channels is introduced. The sensor design is similar to the conventional wire mesh sensor for larger flow cross sections with wire electrodes stretched across the flow channel in two adjacent planes and with perpendicular wire orientation between planes. Conductivity measurement is performed by special electronics which consecutively applies bipolar voltage pulse excitation to the sender wires and measures electrical current flow in the wire crossings at the receiver wires. The new design is based on printed circuit board technology. A prototypical sensor made of 2 x 16 stainless steel wires each of 50 µm diameter was manufactured and applied to two-phase flow measurement inside the mixing chamber of an effervescent atomizer. Accuracy of the sensor was studied for static liquid distributions using microscope photography and for dynamic two-phase flow by comparison of wire mesh data with radial gas fraction profiles obtained from X-ray microtomography measurements.

Keywords: wire-mesh sensor; atomizer; two-phase flow; X-ray microtomography

Permalink: https://www.hzdr.de/publications/Publ-11790
Publ.-Id: 11790


Vacancy-type defects in 6H–silicon carbide induced by He-implantation: a positron annihilation spectroscopy approach

Zhu, C. Y.; Ling, C. C.; Brauer, G.; Anwand, W.; Skorupa, W.

Six-fold helium ion implantation was carried out on nitrogen doped n-type 6H–SiC epi samples. A box-shaped He-implantation profile and damage region was thus introduced. Vacancy-type defects in the implanted region were studied by positron annihilation spectroscopy using a monoenergetic positron beam. The average size of the vacancy-type defect detected in the as-He-implanted sample was the divacancy (V2). Thermal annealing had the effect of shrinking the defective region. Annealing at temperatures lower than 900 ◦C had the effect of removing vacancy-type defects in the defective region. While the annealing temperature is above 900 ◦C, the size of the vacancy-type defects in the defective region increased with annealing temperature. At the annealing temperature of 1600 ◦C, the defectiveregion reduced to ∼100 nm and the vacancy-type defects within the region agglomerated to clusters having an average size of 14 V2.

  • Journal of Physics D: Applied Physics 41(2008), 195304

Permalink: https://www.hzdr.de/publications/Publ-11789
Publ.-Id: 11789


Ionenstrahlen – ein Werkzeug zur Herstellung von Nanostrukturen

Schmidt, B.

Es wird ein Überblich über die Möglichkeiten des Einsatzes von Ionenstrahltechniken zur Erzeugung von Nanostrukturen sowohl auf Festkörperoberflächen als auch vergraben im Festkörper gegeben. Besonders wird dabei auf die Ionenstrahlsynthese von Nanoclustern in SiO2 und die Synthese von Nanodrähten mittels feinfokussierten Ionenstrahlen eingegangen. Zum Schluss wird die Herstellung von Si-Nanodrähten und Nano-Elektro-Mechanischen Systemen (NEMS) beschrieben, die auf der Kombination von lakaler Ga+ FIB-Implantation mit einer selektiven Ätztechnik beruht.

Keywords: ion implantation; ion beam synthesis; nanocluster; nanowire; NEMS

  • Invited lecture (Conferences)
    Internationale Fachmesse für Feinwerktechnik, Ultrapräzision, Micro- und Nanotechnologien -MiNat, MiNat Hot Spot WGL - Nanotechnologie in der Leibnizgesellschaft (WGL), 07.-08.10.2008, Stuttgart, Germany

Permalink: https://www.hzdr.de/publications/Publ-11788
Publ.-Id: 11788


Cluster growth and luminescence in ion-implanted silica

Fitting, H.-J.; Salh, R.; Kourkoutis, L.; Schmidt, B.

Scanning electron microscopy (SEM) and cathodoluminescence (CL) in
combination with scanning transmission electron microscopy (STEM) have been used
to investigate thermally grown amorphous silicon dioxide layers implanted
isoelectronically with group IV ions (C+, Si+, Ge+, Sn+, Pb+) as well as with group VI
ions (O+, S+, Se+).

Keywords: Cathodoluminescence; Silica layers; Ion implantation

  • Lecture (Conference)
    14th European Microscopy Congress, 01.-05.09.2008, Aachen, Germany
  • Contribution to proceedings
    14th European Microscopy Congress, 01.-05.09.2008, Aachen, Germany
    S. Richter, A. Schwedt (Eds.):EMC 2008, Vol. 2: Materials Science, Berlin Heidelberg: Springer-Verlag, 17-18

Permalink: https://www.hzdr.de/publications/Publ-11787
Publ.-Id: 11787


Ecological problems in Saxony related to the former uranium mining activities – fluorescence spectroscopy, a tool for analyzing the uranium binding form

Baumann, N.; Arnold, T.

As a consequence of extensive and reckless uranium mining in Eastern Germany by the Soviet mining company WISMUT between 1945 and 1990, numerous mining residues exist including important ecological problems in Saxony and Thuringia today. A main topic is washing out mobile uranium species from the rock piles and for-mer mines by surface water. It is necessary to control the pathway, the species, and the amount of migrating ura-nium compounds, and to investigate the interactions between solid mineral phases and mobile uranium species such as sorption, precipitation and forming secondary uranium minerals.
One tool for analyzing tiny amounts of U(VI) species (but also in a minor way U(IV) and U(V) species) is time-resolved laser-induced fluorescence spectroscopy (TRLFS). This method is well established in the Institute of Radiochemistry (IRC) from the Forschungszentrum Dresden-Rossendorf (FZD), especially in case of problems connected with uranium. TRLFS delivers a fluorescence signal with characteristic features in dependence of concentration and speciation of the fluorescent species in the sample. These features are the positions of the peak maxima, and, secondary, characteristic lifetimes of the signals. This technique is applicable in case of U(VI) spe-cies in water solutions, but also in case of thin U(VI) mineral coatings on solid phases.
In that lecture results of investigations of adsorbed uranium species onto mineral surfaces like from gibbsite and from muscovite are presented. Spectroscopic characterisation of several secondary uranium minerals (e.g. bolt-woodite and compreignacite) by determination of the positions of the peak maxima and the lifetimes from the TRLFS signals are presented. The spectroscopic signatures of these uranium (VI) minerals are useful for identi-fying U(VI) mineral species as colloids, as thin coatings on rocks, as minor components in soils, or as alteration products of nuclear waste. Additionally the interaction between an aqueous solution and metallic uranium was investigated by TRLFS: The identification of an ultra-thin secondary mineral film on a disk of metallic depleted uranium (DU) originated from a British tank shell, which was in contact with a phosphate containing solution, will be showed. This example demonstrates the high sensitivity of TRLFS regarding solid U(VI) phases.

Keywords: Uranium mining; U(VI); TRLFS

  • Lecture (others)
    Seminar, 27.10.2008, Hiroshima, Japan

Permalink: https://www.hzdr.de/publications/Publ-11786
Publ.-Id: 11786


Thermo-mechanische Finite-Elemente-Modellierung zur Schmelzerückhaltung im RDB nach Verlagerung von Corium in das untere Plenum Thermo-mechanical finite element modelling of in-vessel melt retention after corium relocation into the lower plenum

Altstadt, E.; Abendroth, M.; Willschütz, H.-G.

Bezüglich eines hypothetischen Kernschmelzeszenarios in einem Leichtwasserreaktor ist es notwendig, mögliche Versagensformen des Reaktordruckbehälters sowie Versagenszeiträume zu untersuchen, um die Belastung für das Containment bestimmen zu können.
Vom Institut für Sicherheitsforschung des FZD wurden Finite-Elemente-Modelle erstellt, die sowohl die Temperaturfeldberechnung für die Wand als auch die elastoplastische Mechanik der Behälterwand beschreibt. Die thermischen und mechanischen Berechnungen sind gekoppelt. Das Modell ist in der Lage, Versagenszeit und Versagensposition eines Behälters mit beheiztem Schmelzepool zu berechnen. Es existieren Modelle für die Druckwasserreaktortypen KONVOI und WWER-1000. Es wurden prototypische Szenarien mit und ohne externe Flutung des RDB untersucht, wobei die homogen und die segregierte Schmelzepoolkonfiguration betrachtet wurden. Zusätzlich wurde eine bruchmechanische Bewertung des Thermoschocks, der durch die externe Flutung entsteht, vorgenommen. Auf Grundlage der Experimente im Rahmen des ISTC-Projekts METCOR wurde außerdem die Auswirkung der thermochemischen Wechselwirkung zwischen Corium-Schmelze und RDB-Wand auf das Versagensverhalten des RDB untersucht. Das wichtigste Ergebnis ist, dass eine erfolgreiche Schmelzerückhaltung im RDB auch bei größeren Reaktoren möglich erscheint, wenn eine rechtzeitige Flutung der Reaktorgrube gelingt. Mittels einer statistischen Analyse wurden die Empfindlichkeiten von Ergebnissen gegenüber den Eingangsparametern
und die Unsicherheiten der Ergebnisse quantifiziert.

Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Several experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work. At the Institute of Safety Research of the FZD finite element models have been developed simulating the thermal processes and the viscoplastic behaviour of the vessel wall. The thermal hydraulic and the mechanical calculations are coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool. Models exist for the pressurised water reactor types KONVOI and VVER-1000. Prototypic scenarios with and without external flooding were investigated with consideration of homogeneous and segregated melt pool configurations. Additionally a fracture mechanic evaluation of the thermal shock, originating from the external flooding, was performed. Based on the experimental results of the ISTC project METCOR, the effects of the thermal chemical interaction between corium melt and vessel steel were investigated in the IVR scenarios. An important result of the project is that a successful in-vessel melt retention seems to be possible even for large reactors if the reactor pit can be filled with water before the corium melt is relocated to the lower plenum. By means of statistical analysis the sensitivity of results against input parameter variations was studied. The uncertainty of results was quantified.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-503 2008
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-11785
Publ.-Id: 11785


The immobilization of uranium in multispecies biofilms studied by microsensors and confocal microscopy

Krawczyk-Baersch, E.; Arnold, T.

Multispecies biofilms were cultured in standard culture media (Sifin; TN 1171) with a pH of approximately 7.2, and in air atmosphere condition at room temperature (20 °C). The culture media were pumped through three annular reactors for two months with a flow-rate of 15.2 ml/min, and an inner cylinder rotation speed of 14 rpm. Inside the reactors biofilms were grown on glass slides to a thickness of approximately 600 µm. Two reactors were fed with UO2(ClO4)2 to adjust the total uranium concentration in the culture medium in ecological relevant concentration (5×10-5 M and 5×10-6 M). After three weeks the cultured multispecies biofilms were used for microscopical and spectroscopical studies (CLSM) as well as for O2 microsensor studies.
Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in a living multispecies biofilm grown on biotite plates. These particles ranged between 1 and 7 µm in width and up to 20 µm in length and were located at the bottom and at the edges of biofilms colonies. Anaysis of amplified 16S rRNA fragments and fluorescence in situ hybridization were used to characterize the biofilm communities. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilms. The detection of uranium(V) in a multispecies biofilm was interpreted as a short-lived intermediate of the uranium(VI) to uranium(IV) redox reaction. Its presence clearly documents that the uranium(VI) reduction is not a two electron step but that only one electron is involved.
Concentration profiles of oxygen versus biofilm depths were measured in the biofilms by electrochemical microsensors with a tip diameter of 10µm. A motor-driven micromanipulator was used for moving downwards through the biofilm in 20 or 50µm steps. The microsensor results clearly showed that the vertical profiles of the O2 concentration within the biofilms are affected by the presence as well as by the concentration of U(VI) in the culture media. In the absence of uranium the O2 concentration in the well aerated biofilm decreased slightly. In contrast, O2 concentrations in the biofilms, which were exposed to different concentrations of uranium, decreased with increasing uranium concentration.

  • Lecture (Conference)
    4th Semi-Annual RTDC-2 Meeting of FUNMIG, 29.-30.04.2008, Larnaca, Cyprus

Permalink: https://www.hzdr.de/publications/Publ-11784
Publ.-Id: 11784


The influence of microbes on the mobility and immobilization of radionuclides e.g. U(VI) in surface and subsurface environments: A microscopical and geochemical study

Krawczyk-Baersch, E.

The effect of uranium added in ecologically relevant concentrations (1×10-5 M and 1×10-6 M) to stable multispecies biofilms was studied by electrochemical oxygen microsensors with tip diameters of 10 µm and by confocal laser scanning microscopy (CLSM). The results show the different influences of microorganisms on the migration of uranium due to redox processes taking place within biofilm. For the first time the reduction of the U(VI) to metastable U(V) by a one-electron transfer was proved by using a combination of confocal laser microscopy (CLSM) and fluorescence spectroscopy. The microsensor profile measurements in the stable multispecies biofilms exposed to uranium indicated that the bacteria in the top region of the biofilms, i.e. the metabolically most active biofilms zone, battle the toxic effects of aqueous uranium with an increased respiratory activity and high consumption rates. As analysis of the amplified 16S rRNA gene fragments showed, the addition of uranium in ecologically relevant concentrations did not change the bacterial diversity in the stable multispecies biofilms. Adaptation and detoxification mechanisms allow them to resist concentrations of toxic elements. The increased respiratory activity and high consumption rates of the microbes results in larger zones of O2 depletion in the biofilms. These zones may trigger redox processes leading to precipitation of U(IV) solids and consequently to an increased removal and immobilization of uranium from the surrounding bulk solution.

  • Invited lecture (Conferences)
    Institute Seminar, Institute of Chemistry, Cyprus University, 02.05.2008, Nicosia, Cyprus

Permalink: https://www.hzdr.de/publications/Publ-11783
Publ.-Id: 11783


The response of biofilms to uranium impacts

Krawczyk-Baersch, E.; Brockmann, S.; Arnold, T.; Hofmann, S.; Wobus, A.

The effect of uranium added in ecologically relevant concentrations (1×10-5 M and 1×10-6 M) to stable multispecies biofilms was studied by electrochemical oxygen microsensors with tip diameters of 10 µm and by confocal laser fluorescence microscopy (CLSM). The microsensor profile measurements in the stable multispecies biofilms exposed to uranium showed that the oxygen concentration decreased faster with increasing biofilm depth compared to the uranium free biofilms. In the uranium containing biofilms, the oxygen consumption, calculated from the steady-state microprofiles, showed high consumption rates of up to 61,7 nmol cm-3s-1 in the top layer (0 - 70 µm) and much lower consumption rates in the lower zone of the biofilms. Staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI) confirmed the high respiratory activities of the bacteria in the upper layer. Analysis of the amplified 16S rRNA gene fragments showed that the addition of uranium in ecologically relevant concentrations did not change the bacterial diversity in the stable multispecies biofilms and is therefore not responsible for the different oxygen profiles in the biofilms. The fast decrease in the oxygen concentrations in the biofilm profiles showed that the bacteria in the top region of the biofilms, i.e. the metabolically most active biofilm zone, battle the toxic effects of aqueous uranium with an increased respiratory activity. This increased respiratory activity results in O2 depleted zones closer to the biofilm/air interface which may trigger uranium redox processes, since suitable redox partners, e.g. extracellular polymeric substance (EPS) and other organics (e.g. metabolites), are sufficiently available in the biofilm porewaters. Such redox reactions may lead to precipitation of uranium(IV) solids and consequently to a removal of uranium from the aqueous phase.

  • Lecture (Conference)
    7. Jenaer Sanierungskolloquium, 22.-23.09.08, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11782
Publ.-Id: 11782


The increase of metabolic activity in biofilms caused by uranium

Krawczyk-Baersch, E.; Brockmann, S.; Arnold, T.; Wobus, A.; Diessner, S.

Most surface and subsurface environments are inhabited by microorganisms, which do not usually occur as single individual cells in nature but rather in multicellular communities called biofilms. Such biofilms attached to mineral surfaces may considerably influence the migration of toxic and/or radioactive heavy metals in contaminated environments. In our studies multispecies biofilms, which were cultured in air atmosphere on glass slides in biofilm reactors were exposed to uranium in ecologically relevant concentrations, i.e. a total U concentration of 1×10-5 mol/l and 5×10-6 M, respectively. The resulting response of the microbial biofilm community to the added uranium was studied by oxygen microsensors in biofilms. In addition staining methods such as CTC and the DNA-binding DAPI were used in combination with confocal laser microscopy (CLSM). The results reveal that the addition of uranium in ecologically relevant concentrations to stable biofilms has a strong effect on the oxygen concentration and consumption rates in biofilms due to a stimulation of the metabolism of the microbes and, consequently, on their respiratory activity and oxygen consumption. The addition of uranium (VI) in ecologically relevant concentrations (1×10-5 M and 1×10-6 M) to stable multispecies biofilms induced a fast decrease of the oxygen concentration with increasing biofilm depth, which is dependent on the uranium concentration. The microbial response to the addition of uranium occurred within two to three hours and resulted in oxygen concentration profiles similar to the profiles measured three weeks after the uranium addition.

  • Lecture (Conference)
    Biofilms III, 3rd International Conference, 06.-08.10.2008, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11781
Publ.-Id: 11781


In-situ Measurements on Suspended Nanoparticles with Visible Laser Light, Infrared Light and X-rays

Zänker, H.

The presence of engineered nanoparticles (ENPs) in the water cycle is a subject of discussion amongst scientists, producers of nanomaterials, environmentalists and politicians. At this stage the influence of ENPs on the environment is still minimum and there is also hardly any experience with measuring such artificial nanoparticles within the complex matrices of environmental samples. However, there is experience with measuring natural nanoparticles in environmental waters. An overview is given on measuring methods with the focus on in-situ methods. They are aimed at studying particle size, particle size distribution, electric charge or binding type of environmental contaminants on the nanoparticles. Examples of use are given for methods such as photon correlation spectroscopy, laser-induced breakdown detection, laser Doppler velocimetry, time-resolved laser fluorescence spectroscopy, Fourier transform infrared spectroscopy and X-rax absorption spectroscopy with synchrotron radiation. The examples show the general strategies of such measurements, indicate typical problems and difficulties and demonstrate how such difficulties can be overcome.

Keywords: Nanoparticles; environmental contaminants; photon correlation spectroscopy; laser-induced breakdown detection; laser Doppler velocimetry; time-resolved laser fluorescence spectroscopy; Fourier transform infrared spectroscopy; X-rax absorption spectroscopy

  • Contribution to external collection
    Nießner, R.; Frimmel, F.H.: Nanoparticles in the Water Cycle. Properties, Analysis and Environmental Relevance., Berlin, Heidleberg, New York: Springer, 2010, 3-642-10317-0, 117-138

Permalink: https://www.hzdr.de/publications/Publ-11780
Publ.-Id: 11780


The effect of spatial discretization in LWR cell calculations with HELIOS 1.9

Merk, B.; Koch, R.

Cell and lattice calculations are the basis for all deterministic static and transient 3D full core calculations. The spatial discretization used for the cell and lattice calculations influences the results for these transport solutions significantly. The arising differences in the neutron flux distribution due to different spatial discretization are demonstrated. These differences in the flux distribution cause significant changes in the kinf value. An evaluation of the kinf value for the case of infinitely fine discretization is made. The influence of the discretization on the calculation of homogenized few group cross sections which are forwarded to the 3D full core calculations is investigated. Strategies for improving the discretization are developed and their influence on the calculation time is evaluated.

Keywords: Spatial Discretization; Neutron Transport; HELIOS; Collision Probabilities; Flat-Flux-Approximation

  • Contribution to proceedings
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary
    Proceedings of the 18th Symposium of AER, 9789633726389, 257-266
  • Lecture (Conference)
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary

Permalink: https://www.hzdr.de/publications/Publ-11779
Publ.-Id: 11779


Character of magnetic excitations in a quasi-one-dimensional antiferromagnet near the quantum critical points: Impact on magnetoacoustic properties

Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Zherlitsyn, S.; Zvyagin, A. A.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.

We report results of magnetoacoustic studies in the quantum spin-chain magnet NiCl2-4SC(NH2)2 (DTN) having a field-induced ordered antiferromagnetic (AF) phase. In the vicinity of the quantum critical points (QCPs) the acoustic c33 mode manifests a pronounced softening accompanied by energy dissipation of the sound wave. The acoustic anomalies are traced up to T>TN, where the thermodynamic properties are determined by fermionic magnetic excitations, the “hallmark” of one-dimensional (1D) spin chains. On the other hand, as established in earlier studies, the AF phase in DTN is governed by bosonic magnetic excitations. Our results suggest the presence of a crossover from a 1D fermionic to a three-dimensional bosonic character of the magnetic excitations in DTN in the vicinity of the QCPs

  • Physical Review B 78(2008), 094406

Permalink: https://www.hzdr.de/publications/Publ-11778
Publ.-Id: 11778


Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal

Wosnitza, J.; Gvozdikov, V. M.; Hagel, J.; Ignatchik, O.; Bergk, B.; Meeson, P. J.; Schlueter, J. A.; Davis, H.; Winter, R. W.; Gard, G. L.

We report on an anomalous behavior of the spin-splitting zeros in the de Haas–van Alphen (dHvA) signal of a quasi-two-dimensional organic superconductor. The zeros as well as the angular dependence of the amplitude of the second harmonic deviate remarkably from the standard Lifshitz–Kosevich (LK) prediction. In contrast, the angular dependence of the fundamental dHvA amplitude as well as the spin-splitting zeros of the Shubnikov–de Haas (SdH) signal follow the LK theory. We can explain this behavior of the dHvA signal by small chemical-potential (CP) oscillations and find a very good agreement between theory and experiment. A detailed wave-shape analysis of the dHvA oscillations corroborates the existence of an oscillating CP. We discuss the absence of the above spin-zero effect in the SdH signal and argue that in k-(BEDT-TTF)2SF5CH2CF2SO3 it can be explained by an incoherent variable range hopping interlayer transport which is insensitive to the small CP oscillations.

  • Open Access Logo New Journal of Physics 10(2008), 083032

Permalink: https://www.hzdr.de/publications/Publ-11777
Publ.-Id: 11777


Spectral-history modeling in DYN3D burnup calculations

Bilodid, Y.; Mittag, S.

Reactor dynamics codes such as DYN3D use two-group cross sections (XS) which depend on local burnup, given in terms of the energy produced per fuel mass (MWd/kgHM). However, a certain burnup value can be reached under different spectral conditions depending on moderator density and other local parameters. Neglecting these spectral effects, i.e. applying the summary-burnup value only, can cause considerable errors in the calculated power density. In some cases with a high burnup the inaccuracy can reach 20%.
This paper describes a way to take into account spectral-history effects. It is shown that the respective XS correction linearly depends on the actual Pu-239 concentration. The applicability of the method was proved not only for usual uranium oxide fuel, but also for mixed uranium/plutonium oxide (MOX) and fuel assemblies with burnable absorber. A test version of an extended data library containing history coefficients was created. The code DYN3D was extended by new subroutines that calculate the actual distribution of Pu-239 in the core and apply a spectral-history correction for the cross sections.

Keywords: DYN3D; spectral-history effects; burnup history effect; burnup; cross sections

  • Contribution to proceedings
    18th AER Symposium on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary
    Proceedings of 18th AER Symposium on VVER Reactor Physics and Reactor Safety, Budapest, 978-963-372-639-6, 467-481
  • Lecture (Conference)
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary

Permalink: https://www.hzdr.de/publications/Publ-11776
Publ.-Id: 11776


The importance of the intracellular glutathione pool of rape cells exposed to heavy metal stress

Viehweger, K.; Geipel, G.

Uranium is a widespread radioactive toxic heavy metal, released into the biosphere mostly by military purposes and nuclear industry. It is taken up by plant root systems and its chemical toxicity is much more dangerous than the radiological. Thus cell suspensions of rape (Brassica napus) revealed similar intracellular defence reactions after uranium exposure like it is described for other heavy metals (1).
Glutathion is one of the key players in this network, because of its ability to complex xenobiotics via the action of glutathione-S-transferase, its redox-capacity, and/or as precursor in the biosynthesis of heavy metal-binding peptides, e.g. phytochelatines.
Rape cells react with a decrease of the cytoplasmic glutathione pool, revealed by HPLC and TLC, respectively. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) measurements gave an insight in interactions between glutathione and uranium. The possible reduction of the soluble uranium(VI) to an insoluble oxidation state of (IV) by glutathione can be excluded, because of lacking uranium(IV) in the cytoplasm, detected by photoacustic measurements. These findings and the time course of dropping the glutathione pool suggest an involvement in the biosynthesis of pytochelatines, which is proven by HPLC. Experiments addressing the physiological relevance of these parts of cellular defence mechanisms are under way, especially to elucidate whose impact on intracellular heavy metal sequestration.

(1) Clemens, S. (2001). "Molecular mechanisms of plant metal tolerance and homeostasis." Planta V212 (4): 475-486.

Keywords: Glutathion; uranium

  • Contribution to proceedings
    The American Society for Cell Biology 48th Annual Meeting, 13.-17.12.2008, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-11775
Publ.-Id: 11775


Experimental two-phase flow measurement using ultra fast limited-angle-type electron beam X-ray computed tomography

Bieberle, M.; Fischer, F.; Schleicher, E.; Koch, D.; Menz, H.-J.; Mayer, H.-G.; Hampel, U.

We report on an experimental evaluation of a novel limited-angle-type ultra fast electron beam X-ray computed tomography approach for the visualization and measurement of a gas-liquid two-phase flow. With this method a simple linear electron beam scan is used to produce radiographic views of a live two-phase flow in a pipe segment of a flow loop. Electron beam scanning can be performed very rapidly, thus a frame rate of 5 kHz is achieved. Radiographic projections are recorded by a very fast detector arc made of CZT elements. This detector records the X-ray radiation passing through the object with a sampling rate of 1 MHz. The reconstruction of slice images from the recorded detector data is a limited angle problem since in our scanning geometry the object’s Radon space is only incompletely sampled. We investigated, whether this technology is able to produce accurate gas fraction data from bubbly two-phase flow. Experiments were performed both on a Perspex phantom with known geometry and an experimental flow loop operated under vacuum conditions in an electron beam processing box.

Keywords: flow measurement; two-phase flow; electron beam tomography; X-ray tomography

Permalink: https://www.hzdr.de/publications/Publ-11774
Publ.-Id: 11774


Uranium sorption onto opalinus clay and uranium complexation with model ligands - New results.

Joseph, C.; Schmeide, K.; Sachs, S.

An anaerobic opalinus clay sample was characterized (BET, TC, TOC, CEC, XRD, IR). No significant differences between the aerobic and the anaerobic clay could be determined.
The uranium(VI) sorption onto aerobic opalinus clay (S/L = 60 g/l) in opalinus clay pore water in absence and presence of humic acid was investigated and compared with the according uranium(VI)-kaolinite sorption results.
The model ligands mandelic acid and glycolic acid were chosen for the uranium(IV) complexation. The complex formation constants for the uranium(IV) complexation were determined applying UV-Vis absorption spectroscopy. Thereby, the hydrogen ion concentration was varied.
Sulfur-containing humic acid model substances were synthesized and characterized (S-content, PEC, FTIR, XPS). First investigations of the uranium(VI) complexation of humic acid type M1-S1 were performed.

Keywords: anaerobic opalinus clay; characterization; uranium(VI); sorption; humic acid; mandelic acid; glycolic acid; U(IV)-complexation; tetravalent; synthesis

  • Lecture (others)
    5th Workshop of the joint project "Interaction and transport of actinides in natural argillaceous rock considering humic substances and clay organics", 07.-08.10.2008, Speyer, Germany

Permalink: https://www.hzdr.de/publications/Publ-11773
Publ.-Id: 11773


Mn - implanted, polycrystalline indium tin oxide and indium oxide films

Scarlat, C.; Vinnichenko, M.; Xu, Q.; Bürger, D.; Zhou, S.; Kolitsch, A.; Grenzer, J.; Helm, M.; Schmidt, H.

Polycrystalline conducting, ca. 250 nm thick indium tin oxide (ITO) and indium oxide (IO) films grown on SiO2/Si substrates using reactive magnetron sputtering, have been implanted with 1 and 5 at% of Mn at 120 keV, 60 keV and 20 keV, followed by annealing in nitrogen for 10 s at 650oC (rapid thermal annealing, RTA) or in vacuum for 2 h at 200oC (vacuum thermal annealing, VTA). The effect of the post-growth treatment on the structural, electrical, magnetic, and optical properties has been studied. The roughness of implanted films ranges between 3 and 15 nm and XRD measurements revealed a polycrystalline structure. A smaller negative magnetoresistance (MR) has been probed on unimplanted ITO and IO films. By magnetotransport measurements at 5 K and 3 T, the positive MR of the IO film implanted with 1 at% Mn, VTA, and an electron concentration of 1.9×1020 cm-3 amounts to 3%. Spectroscopic ellipsometry has been used to prove the existence of midgap electronic states in the Mn implanted ITO and IO films reducing the transmittance below 80%.

Keywords: diluted magnetic semiconductor; ITO; magnetoresistance; optical constants

  • Poster
    IBMM 2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009)8-9, 1616-1619
    DOI: 10.1016/j.nimb.2009.01.158

Permalink: https://www.hzdr.de/publications/Publ-11772
Publ.-Id: 11772


AER working group D on VVER safety analysis – report of the 2008 meeting

Kliem, S.

The AER Working Group D on VVER reactor safety analysis held its 17th meeting in Garching, Germany during the period 31 March-01 April 2008. The meeting was hosted by the GRS Garching. Altogether 19 participants attend the meeting of the working group D, 16 from AER member organizations and 3 guests from non-member organizations. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations. The given presentations and the discussions can be attributed to the following topics:
• Code benchmarking
• Safety analysis methodology and results
• Reactor pressure vessel thermal hydraulics
• Future activities
New solutions for the second and the third AER benchmarks were presented and discussed. The second dynamic AER benchmark considers a control rod ejection at hot zero power with Doppler feedback, only. The third AER benchmark concerns the same transient and includes additionally the modeling of thermal hydraulics in the core. S. Kliem (FZD) presented an overview on available solutions for the second benchmark. Additionally, results were presented by G. Alekhin (EDO Gidropress) obtained with the KAMAZ-code and J. Hádek (NRI Řež) using the DYN3D code. S. Bznumi (Nuclear and Radiation Centre Yerevan) presented results for the third and C. Parisi (UniPisa) for the first dynamic AER benchmarks. Two further benchmarks calculated in the frame of the EU-NURESIM project were presented by J. Hádek. K. Velkov (GRS) showed preliminary results on a new coupled code benchmark based on Kalinin-3 data (VVER-1000). A summary of the results of the OECD VVER-1000 coolant transient benchmark was given by N. Kolev (INRNE Sofia) and S. Kliem presented the results of a PWR boron dilution benchmark.
M. Bykov (EDO Gidropress) gave an overview on the results of coolant mixing experiments performed at a VVER-1000 test facility. A new CFD model of a VVER-440 reactor pressure vessel was presented by B. Kiss (TU Budapest). A. Kotsarev (Kurchatov Institute) presented the outline of a envisaged coolant mixing benchmark.
E. Syrjälahti (VTT Helsinki) gave an overview on the real time 3D core model of the new Loviisa training simulator. RIA analyses for the Generation IV HPLWR using KIKO3D/ATHLET were presented by A. Keresztúri (AEKI Budapest) and I. Panka (also AEKI Budapest) presented different hot channel calculation methodologies.

  • Contribution to proceedings
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary
    Proceedings of the 18th Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest, 9789633726389, 307-314
  • Lecture (Conference)
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary

Permalink: https://www.hzdr.de/publications/Publ-11771
Publ.-Id: 11771


Kernenergieforschung mit schnellen Neutronen

Junghans, A.; Wagner, A.

Die Kernenergie ist eine Energiequelle, die nur sehr geringe Emissionen von Treibhausengasen verursacht. Auf internationaler Ebene wird die Entwicklung neuer Kernkraftwerkstypen der 4. Generation betrieben, so dass die Kernenergie auch in Zukunft genutzt werden kann. Dabei wird auch das Problem des langlebigen radioaktiven Abfalls betrachtet. An der Neutronenquelle „nELBE" im Forschungszentrum Dresden-Rossendorf soll in Zukunft untersucht werden, wie langlebiger radioaktiver Abfall, der weltweit in Kernkraftwerken entsteht, so umgewandelt werden kann, dass er nur noch für historisch überschaubare Zeiten in ein Endlager eingeschlossen werden muss. Durch Beschuss mit schnellen Neutronen können langlebige schwere Atomkerne wie etwa Curium oder Neptunium umgewandelt werden und in kurzlebige oder sogar stabile Reaktionsprodukte zerfallen. Bei dieser „Transmutation“ werden also langlebige, radioaktive Atomkerne in kurzlebigere umgewandelt. Nach weniger als 1.000 Jahren haben sie dann das natürliche Radioaktivitätsniveau erreicht.
An nELBE können 100 000 mal pro Sekunde kurze Pulse von schnellen Neutronen produziert werden, mit denen die inelastische Streuung, der Neutroneneinfang und Kernspaltung untersucht werden können. Im Vortrag werden die internationalen Entwicklungen auf dem Gebiet der Transmutation
vorgestellt sowie die neue Neutronenquelle „nELBE“ und unsere ersten Experimente dort gezeigt.

  • Lecture (others)
    6. Dresdner Lange Nacht der Wissenschaften, 04.07.2008, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11770
Publ.-Id: 11770


nELBE - eine Anlage f¨ur die Transmutationsforschung mit schnellen Neutronen

Beyer, R.; Grosse, E.; Junghans, A.; Rouki, C.; Schilling, K.-D.; Schwengner, R.; Wagner, A.

An der Strahlungsquelle ELBE in Rossendorf wurde eine Flugzeitanlage aufgebaut für Neutronen aus dem von Elektronen induzierten Kern-Photoeffekt in Blei, das in einem Flüssigmetall-Kreislauf auch die bis zu 30 kW Strahlleistung abführt. Durch konsequente Vermeidung wasserstoffhaltiger Materialien und andere Konstruktionsdetails wird ein Neutronenspektrum erzeugt, das nur schnelle Neutronen enthält und das darüber hinaus sehr ähnlich ist dem Spektrum von Neutronen aus der Spaltung von Aktiniden. Ein solches Spektrum ist günstig für die Transmutation von Radionukliden und fast alle der in der internationalen Initiative zur wissenschaftlichen Vorbereitung einer vierten Kernreaktor-Generation untersuchten Konzepte beruhen auf schnellen Neutronen. Für die Reduktion der Radiotoxizität der Abfälle wichtige und oft nur ungenau bekannte Wirkungsquerschnitte zur Transmutation von Spaltfragmenten und von in Reaktoren gebildeten Aktiniden sollen innerhalb der EU-Initiative EFNUDAT bestimmt werden. [Gefördert durch DFG-Gr1674/2 und EU-FP6]

  • Lecture (Conference)
    DPG Frühjahrstagung, 10.-14.03.2008, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11769
Publ.-Id: 11769


Visualization of uranium in living biofilms in relation to biofilm structure and geochemical conditions

Brockmann, S.; Großmann, K.; Krawczyk-Bärsch, E.; Arnold, T.; Wobus, A.

The speciation of uranium in environmentally relevant concentrations of 1×10-5 mol/l in biofilms was investigated by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach. The microbial communities in the biofilms were determined by analysis of the amplified 16S rRNA gene fragments. No changes of the microbiological diversity were observed in the biofilms in contact with uranium and without. The respiratory activity was microscopically investigated by staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI). It was found that in the presence of uranium (1×10-5 mol/l added as UO2(ClO4)2) the biofilm responded with a higher respiratory activity of the bacteria in the upper layer, leading to changes of geochemical gradients within the biofilms with corresponding effects on the uranium geochemistry. These effects include a change in oxidation state and precipitation of respective uranium phases.
Laser fluorescence spectroscopy was used to identify in-situ and in a non-invasive fashion the speciation of uranium within the biofilms. A fluorescence signal in the wavelength range of 415-475 nm was indicative for metastable uranium- (V) and a fluorescence signal in the range of 480-560 nm was identified as uranium(VI), clearly showing that redox processes take place within the biofilms.
We found that aqueous uranium in environmentally relevant concentrations may trigger higher O2 consumption rates which lead to larger reducing zones within the biofilms. Consequently, such zones may be responsible for an increased immobilization of uranium from the surrounding bulk solution. Our studies indicated that the microbial influence on the migration behavior of uranium in the environment has to be included in performance assessment studies to predict more realistic uranium migration scenarios.

Keywords: Biofilm; uranium; metabolism; staining; CLSM

  • Poster
    Biofilm III, 3rd International Biofilms Conference, 06.-08.10.2008, Garching, Germany

Permalink: https://www.hzdr.de/publications/Publ-11768
Publ.-Id: 11768


The nELBE time of flight facility

Junghans, A. R.; Altstadt, E.; Beckert, C.; Beyer, R.; Galindo, V.; Grosse, E.; Hannaske, R.; Klug, J.; Legrady, D.; Naumann, B.; Rouki, C.; Schilling, K. D.; Schneider, S.; Schlenk, R.; Schwengner, R.; Wagner, A.; Weiss, F.-P.; Nolte, R.; Röttger, S.

The nELBE time of flight facility has become operational at the ELBE superconducting linear accelerator at Forschungszentrum Dresden-Rossendorf. The commissioning started with a beamtime in November 2007 and again in February 2008. With a short flight path of approximately 5 m a 100 kHz repetition rate of the electron beam was used to measure neutron time of flight in the energy range of 0.1 – 10 MeV. The electron beam energy was 25, and 33 MeV with 1-5 A of average electron current. The electron beam intensity was kept low to allow in-beam single particle counting.
The beam profile of neutrons and photons was determined with two plastic scintillators mounted on a translation stage. The neutron time of flight spectrum was determined with plastic scintillators with a low detection threshold of ca. 25 keV and with a 235-U fission chamber from PTB, which also allowed to measure the absolute neutron fluence and estimate the background of low energy neutrons. The transmission of the electron beam line was optimized to reduce the bremsstrahlung background not coming from the photo-neutron source. First transmission measurements of total neutron cross sections were made.
Beam time at nELBE is available as of now and all potential users are invited to submit proposals for experiments. TAA funding through EFNUDAT can be provided.

  • Lecture (Conference)
    Workshop on modern methods using fast neutrons for research related to the transmutation of nuclear waste, 13.-15.02.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11767
Publ.-Id: 11767


Gamma-ray strength-function measurements at ELBE

Schwengner, R.

Dipole-strength functions up to the neutron-separation energies S_n of the N=50 isotones 88Sr, 89Y, 90Zr and the even-mass Mo isotopes from 92Mo to 100Mo have been studied in photon-scattering experiments using the bremsstrahlung facility at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf. To estimate the distribution of inelastic transitions from high-lying levels at high level density to low-lying levels, simulations of gamma-ray cascades were performed. On the basis of these simulations intensities of inelastic transitions were subtracted from the experimental intensity distributions, including the resolved peaks as well as a continuous part formed by unresolved transitions, and the intensities of elastic transitions to the ground state were corrected for their branching ratios. The combination of our gamma,gamma data with (gamma,n) data gives novel information about the dipole-strength functions in the whole energy range from about 4 MeV up to the giant dipole resonance (GDR). They show that
(i) there is extra strength in the energy range from about 6 to about 12 MeV with respect to simple Lorentzian-like approximations of the tail of the GDR,
(ii) the accumulated dipole-strength in the energy range from about 6 to 12 MeV grows with increasung neutron number in the chain of Mo isotopes.
Calculations in the framework of a quasiparticle-random-phase approximation (QRPA) in a deformed Woods-Saxon basis describe the increase of strength towards the heavier Mo isotopes as a consequence of growing nuclear deformation.

Keywords: Nuclear structure; photon scattering; gamma-ray strength-functions; random-phase-approximation

  • Invited lecture (Conferences)
    Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, 08.-11.07.2008, Athens, Ohio, USA

Permalink: https://www.hzdr.de/publications/Publ-11766
Publ.-Id: 11766


nELBE: A new facility to produce high brilliance pulses of fast neutrons for transmutation research by time of flight.

Junghans, A.; Klug, J.; Wagner, A.; Weiss, F. P.; Grosse, E.

The Radiation Source ELBE at Forschungszentrum Dresden-Rossendorf (FZD), with electron energies up to 40 MeV, will be used to produce intense pulses of fast neutrons. The neutron radiator consists of a liquid lead circuit where bremsstrahlung photons generated from the electron beam at ELBE produce neutrons in (γ,n) reactions. Monte Carlo simulations with MCNP4C3/MCNP5 were performed to characterise neutron and photon intensities as well as time and energy distributions, and to optimise the neutron beam. The short beam pulses provide the basis for an excellent time resolution for neutron time-of-flight experiments, giving an energy resolution of about < 2 % with a flight path of ~ 5 m.

  • Lecture (Conference)
    NEMEA-4 - Neutron Measurements, Evaluations and Applications, 16.-18.10.2007, Prag, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-11765
Publ.-Id: 11765


Die experimentellen Versuchsanlagen des Instituts für Sicherheitsforschung

Lucas, D.

Im Vortrag werden verschiedene Versuchsanlagen des Instituts für Sicherheitsforschung zur Untersuchung von Strömungen vorgestellt. Ziel der Versuche ist die Bereitstellung von Daten in hoher Orts- und Zeitauflösung, die für die Entwicklung und Validierung von CFD-Modellen geeignet sind. Daher werden in allen vorgestellten Versuchseinrichtungen innovative Messtechniken eingesetzt. Die ROCOM-Anlage dient der Untersuchung einphasiger Vermischungsvorgänge im Primärkreislauf von Kernreaktoren. Am horizontalen Strömungskanal werden geschichtete Luft-Wasser-Strömungen untersucht. Die TOPFLOW (Transient TwO Phase FLOW) dient der Untersuchung von Dampf-Wasser-Strömungen bei Dücken bis 7 MPa. Mit eine 4 MW Dampferzeuger können bei diesem Druck bis zu 1,5 kg Dampf pro Sekunde erzeugt werden. Die Experimente an vertikalen Teststrecken und im TOPFLOW-Drucktank werden diskutiert.

Keywords: mixing; two phase flow; bubbles; stratified flow; CFD; experimental facilities

  • Lecture (Conference)
    3. Workshop "Strömungssimulation" der Technischen Universität Dresden und des Forschungszentrums Dresden-Rossendorf, 25.09.2008, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11764
Publ.-Id: 11764


Experiment and simulation of the compositional evolution of Ti-B thin films deposited by sputtering of a compound target

Neidhardt, J.; Mrátz, S.; Schneider, J. M.; Strub, E.; Bohne, W.; Liedke, B.; Möller, W.; Mitterer, C.

The evolution of the coating stoichiometry with pressure, target-substrate distance, and angle was analyzed for dc sputtering of TixB (x=0.5, 1, 1.6) compound targets by elastic recoil detection analysis. For an investigation of the underlying fundamental processes primarily Ar was used as sputter gas. Additionally, the effect of a reactive gas (N2) as well as bias voltage (floating up to −200 V) was briefly cross-checked. For deposition along the target normal (90°) a pronounced Ti-deficiency of up to 20% is detected. Increasing the pressure or distance from 0.5 to 2 Pa and from 5 to 20 cm, respectively, leads to an almost equivalent linear increase in Ti/B ratio surpassing even the target composition. Off-axis depositions at lower angles (30° and 60°) on the other hand result in a higher Ti/B ratio. This is consistent with results obtained from Monte Carlo simulations combining the respective emission characteristics from the sputter process as well as the gas-phase transport. Hence, the pressure, distance, and sample position induced changes in chemical film composition can be understood by considering gas scattering and the angular distribution of the sputtered flux. The theoretically determined transition from a directional flux to thermal diffusion
was experimentally verified by mass-energy analysis of the film-forming atoms.

  • Journal of Applied Physics 104(2008), 063304

Permalink: https://www.hzdr.de/publications/Publ-11763
Publ.-Id: 11763


P0707 - Anordnung zur zweidimensionalen Messung des Geschwindigkeitsfeldes in Strömungen

Hampel, U.

Aufgabe der vorliegenden Erfindung ist es, eine Anordnung zur Messung der Geschwindigkeitsverteilung in einem Messquerschnitt anzugeben, mit der vor allem Flüssigkeits- oder Gasströmungen untersucht werden können und die über ein möglichst effizientes elektronisches Anregungs- und Messschema verfügt. Der Kern der Erfindung ist die Verwendung und Modifizierung eines Gittersensors, bei dem
- die Anregungselektroden (2) und die Empfängerelektroden (3) in jedem Kreuzungspunkt des Gitters durch einen Festkörper mit temperaturabhängem ohmschen Widerstand, dem Hitzeelement (4), elektrisch miteinander verbunden sind,
- die zugeordnete Messelektronik, zusätzlich zu der den Anregungselektroden (2) vorgeschalteten Heizspannungsquelle (5), über eine den Anregungselektroden (2) vorgeschaltete Messspannungsquelle (6) verfügt und
- jede Anregungselektrode (2) mit einem dreipoligen Analogschalter (7) verbunden ist, der die Elektrode wahlweise mit der Heizspannungsquelle (5), der Messspannungsquelle (6) oder Massepotenzial verbindet, sowie jede Empfängerelektrode (3) mit einem Analogschalter (7) verbunden ist, der die Empfängerelektrode (3) wahlweise mit einem festen Bezugspotenzial (zum Beispiel Masse-Potenzial) oder einem Strom-Spannungs-Wandler (8) verbindet.
(Fig 1)

  • Patent
    DE 10 2007 019 927 B3 - 2008.09.25

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-11762
Publ.-Id: 11762


Electrical properties and structure of transparent conductive oxide films deposited by pulsed reactive magnetron sputtering

Vinnichenko, M.; Rogozin, A.; Cornelius, S.; Shevchenko, N.; Munnik, F.; Gago, R.; Mücklich, A.; Kolitsch, A.; Möller, W.

Sn-doping of InOx and Al-doping of ZnO is extensively used to create transparent thin film electrodes. However, the mechanisms of donor impurity incorporation and its electrical activation, especially in relation to the film structure and phase composition, are not properly understood. In order to have a deeper insight into these processes, InOx, InOx:Sn, ZnO and ZnO:Al films were grown by reactive pulsed magnetron sputtering from In, In:Sn, Zn and Zn:Al targets, respectively, at substrate temperatures ranging from 40 °C to 580 °C, and characterized by spectroscopic ellipsometry, Hall effect measurements, X-ray diffraction (XRD) and, in case of ZnO and ZnO:Al films, by X-ray absorption near edge spectroscopy (XANES). For InOx:Sn, the film crystallinity always improves with increasing substrate temperature or during isothermal annealing, with the electrical resistivity decreasing. This is explained by Sn donor activation during the film amorphous-to-crystalline transition. In contrast, the electrical resistivity of ZnO:Al films shows a clear minimum at a certain substrate temperature, which correlates with a maximum in crystallinity (grain size). Here, the lower resistivity is due to an increased density and free electron mobility. Increasing the Zn/O2 flux ratio decreases this optimum temperature from 350 °C to 250 °C. At higher temperature, the film electrical properties and crystalline quality decrease due to the formation of a new metastable phase, which is identified as homologous (ZnO)3(Al2O3) by XANES and XRD for low and high Zn/O2 ratio, respectively. The optimization of the oxygen partial pressure, the substrate temperature and the Al concentration allows to minimize the ZnO:Al resistivity down to 2.3-2.5x10^-4 Ohm cm at a significantly improved free electron mobility.

Keywords: transparent conductive oxides; tin-doped indium oxide; aluminum doped zinc oxide

  • Invited lecture (Conferences)
    The Eleventh International Conference on Plasma Surface Engineering, 15.-19.09.2008, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-11761
Publ.-Id: 11761


Uranium in Biofilms

Arnold, T.

Biofilms show a complex architecture of heterogeneously distributed sessile bacteria embedded in extracellular polymeric substances (EPS), made of polysaccharides, proteins, lipoproteins and glycoproteins, which are interspersed by open water channels. Biofilms are made of 50-95% water and dissolved substances and are thus considered as hydrogels. Through these water channels nutrients and possibly toxic heavy metals from the surrounding bulk solution effectively infuse into the biofilms to the microorganisms and metabolites and exudates of the microorganisms are transported away.
The attachment of microbial cells to surfaces during biofilm formation leads to major changes in metabolism, resistance, and survivability and therefore the retention of radionuclides by biofilms is probably different from the interactions with single cell suspensions of only one type of bacterial species.
In this study particulate uranium in a multi-spezies biofilm grown at the solid/liquid interface was visualized within the biofilm and spectroscopically identified by a combination of confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy as uranium(VI) and metastable uranium(V). The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium-(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilm. The detection of uranium(V) in a multispecies biofilm was interpreted as a short-lived intermediate of the uranium(VI) to uranium-(IV) redox reaction. Its presence clearly documents that the uranium(VI) reduction is not a two electron step but that only one electron is involved.

Keywords: uranium; biofilms

  • Invited lecture (Conferences)
    7th symposium on remediation in Jena Metal stress: biotic and abiotic factors, 22.-23.09.2008, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11760
Publ.-Id: 11760


Simulation-based investigation of spatial sensitivity distribution of wire-mesh sensors

Wagner, M.; Da Silva, M. J.; Thiele, S.; Hampel, U.

The wire-mesh sensor is capable of generating images of multiphase flows in pipes and vessels with high spatial and temporal resolution. This paper investigates the spatial sensitivity distribution of the capacitance wire-mesh sensor using numerical field simulation. The results will support further developments of the image and data processing.

Keywords: wire-mesh sensor; spatial sensitivity; numerical field simulation

  • Contribution to proceedings
    COMSOL Conference 2008, 04.-06.11.2008, Hannover, Deutschland
    Proceedings of COMSOL Conference 2008, Paper No. 5448
  • Lecture (Conference)
    COMSOL Conference 2008, 04.-06.11.2008, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11759
Publ.-Id: 11759


Ultra fast electron beam x-ray tomography and its application to multi phase flow measurement

Hampel, U.; Fischer, F.

An ultra fast electron beam CT scanner is introduced which has been developed for flow measurement applications. Its basic design comprises an electron gun with beam optics and fast electromagnetic deflection system and an ultra fast X-ray detec-tor based on room-temperature semiconductor converters. As in other tomographic imaging modalities radiographic projections are generated by a moving X-ray source, in this case the focal spot of the focused electron beam on a circular tungsten target, which circulates across the target by virtue of electromagnetic beam deflection. The electron beam parameters are 150 kV acceleration voltage, max. 10 kW beam power, 1 mm focal spot size and 7 kHz maximum beam sweeping frequency. The detectors with 1.5 mm pitch allow a spatial resolution of about 1 mm. Maximum object size is 120 mm and maximum imaging rate is 7000 cross-sectional images per second. The scanner has been employed for multiphase flow measurement studies and may also be used for small animal scanning. In the presentation we will discuss a few applica-tion examples in the fields of flow measurement and small animal diagnostics.

Keywords: ultra fast x-ray tomography; electron beam tomography; multiphase flow

  • Lecture (Conference)
    IEEE Dresden 2008 - Workshop on X-Ray Micro Imaging of Materials, Devices, and Organisms, 22.-24.10.2008, Dresden, Germany
  • Contribution to proceedings
    IEEE Dresden 2008 - Workshop on X-Ray Micro Imaging of Materials, Devices, and Organisms, 22.-24.10.2008, Dresden, Germany
    IEEE NSS/MIC/RTSD Conference Record

Permalink: https://www.hzdr.de/publications/Publ-11758
Publ.-Id: 11758


Observation of melt flow effects and dendritic growth during directional solidification of Ga-In alloys by X-ray radioscopy

Boden, S.; Willers, B.; Eckert, S.; Gerbeth, G.

Capabilities of the X-ray attenuation contrast radioscopy were used to provide a real-time diagnostic technique for the observations of dendritic growth and the melt flow during directional solidification of a Ga-30wt%In alloy. The metal alloy was contained in the 150 µm wide gap between the two quartz glass plates of a solidification cell. The solidification process was visualised using a microfocus X-ray radioscopy setup. At typical frame repetition rates of one frame per second, the experimental assembly enables both the observation of the evolution of the dendritic network at length scales of several micrometers as well as the simultaneous observation of the melt convection at nearly millimeter length scale. The Optical Flow approach was used to derive information about the velocity field ahead of the solidification front and in the mushy zone from the observed displacement of the brightness patterns between consecutively acquired X-ray image frames. Growth rates of single primary dendrite trunks were obtained by means of a tip tracking algorithm. Therewith, aspects of the complex interaction mechanisms between melt flow and dendritic growth have been elucidated. Experiments have been carried out to solidify the Ga-In alloy unidirectionally either starting from the bottom or the top of the specimen. The first case is significantly affected by solutal convection. Dendritic fragmentation can be observed during the solidification in the reverse top-down direction.

  • Lecture (Conference)
    IEEE 2008 - Workshop on X-Ray Micro Imaging of Materials, Devices, and Organisms, 22.-24.10.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11757
Publ.-Id: 11757


Identification of Yrast high-K intrinsic states in 188Os

Modamio, V.; Jungclaus, A.; Podolyak, Z.; Shi, Y.; Xu, F. R.; Algora, A.; Bazzacco, D.; Escrig, D.; Fraile, L. M.; Lenzi, S.; Marginean, N.; Martinez, T.; Napoli, D. R.; Schwengner, R.; Ur, C. A.

The high-spin structure of the Z=76 nucleus 188 Os has been studied using the incomplete fusion reaction 7 Li +186 W. A K = 10+ band has been established up to spin (24+ ) and its crossing with the ground state band studied. In addition, intrinsic high-K states have been identified and on top of two of them, K = 7- and K = 10- , regular bands have been observed. The K =16+ and K =18+ states are Yrast while the K =14+ level lies only 33 keV above the Yrast line and decays with a low reduced hindrance of f < 1.3 to the ground state band (K=14). The results are discussed by means of a systematic comparison with the even-even neighbouring nucleus 186 Os. Configurationconstrained multi-quasiparticle potential-energy-surface calculations have been performed in order to identify the configurations of multi-quasiparticle states.

Keywords: Nuclear structure; gamma-ray spectroscopy; high-spin states; potential-energy-surface calculations

Permalink: https://www.hzdr.de/publications/Publ-11756
Publ.-Id: 11756


Influence of electron irradiation on hydrothermally grown zinc oxide single crystals

Lu, L. W.; So, C. K.; Zhu, C. Y.; Gu, Q. L.; Li, C. J.; Fung, S.; Brauer, G.; Anwand, W.; Skorupa, W.; Ling, C. C.

The resistivity of hydrothermally grown ZnO single crystals increased from similar to 10(3) Omega cm to similar to 10(6) Omega cm after 1.8 MeV electron irradiation with a fluence of similar to 10(16) cm(-2), and to similar to 10(9) Omega cm as the fluence increased to similar to 10(18) cm(-2). Defects in samples were studied by thermally stimulated current (TSC) spectroscopy and positron lifetime spectroscopy (PLS). After the electron irradiation with a fluence of 10(18) cm(-2), the normalized TSC signal increased by a factor of similar to 100. A Zn vacancy was also introduced by the electron irradiation, though with a concentration lower than expected. After annealing in air at 400 degrees C, the resistivity and the deep traps concentrations recovered to the levels of the as-grown sample, and the Zn vacancy was removed.

  • Semiconductor Science and Technology 23(2008)9, 095028

Permalink: https://www.hzdr.de/publications/Publ-11754
Publ.-Id: 11754


Development of an ultra fast scanned electron beam X-ray CT

Fischer, F.; Hoppe, D.; Bieberle, M.; Schleicher, E.; Hampel, U.; Mattausch, G.; Flaske, H.; Bartel, R.

Electron beam X-ray CT is a promising technique for a fast measurement of multiphase flows with frame rates of at least 1000 images per second. Thus, X-ray tomography in principle gives quantitatively accurate images of the flow at high resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement application we devised and built a fast scanned electron beam X-ray tomography scanner. The heart of the scanner is a medium power electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current. The system further comprises all the typical components of an electron beam device, such as beam adjustment, beam focussing and beam deflection unit and the vacuum system. X-ray radiation is produced on a circular tungsten target that is water cooled. For X-ray detection we use a fast circular CZT detector comprising 240 elements of 1.5 mm x 1.5 mm active pixel area. The photonic converters are connected to a state-of-the-art detector electronics with gain selectable amplifiers, fully parallel analogue-to-digital conversion and online data storage within a 4 GB dynamic RAM. The whole system is controlled by an industrial PC via LabVIEW.

Keywords: Ultra fast X-ray CT; multi phase flow measurement; scanned electron beam CT

  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography, 03.-06.09.07, Bergen, Norway
  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography, 03.-06.09.07, Bergen, Norwegen

Permalink: https://www.hzdr.de/publications/Publ-11753
Publ.-Id: 11753


An ultra fast electron beam x-ray tomography scanner

Fischer, F.; Hoppe, D.; Schleicher, E.; Mattausch, G.; Flaske, H.; Bartel, R.; Hampel, U.

This paper introduces the design of an ultra fast x-ray tomography scanner based on electron beam technology. The scanner has been developed for two-phase flow studies where frame rates of 1 kHz and higher are required. Its functional principle is similar to that of the electron beam x-ray CT scanners used in cardiac imaging. Thus, the scanner comprises an electron beam generator with a fast beam deflection unit, a semicircular x-ray production target made of tungsten alloy and a circular x-ray detector consisting of 240 CZT elements with 1.5 mm × 1.5 mm × 1.5 mm size each. The design is optimized with respect to ultra fast imaging of smaller flow vessels, such as pipes or laboratory-scale chemical reactors. In that way, the scanner is capable of scanning flow cross-sections at a speed of a few thousand frames per second which is sufficient to capture flows of a few meters per second velocity.

Keywords: electron beam tomography; x-ray tomography; multiphase flow measurement

Permalink: https://www.hzdr.de/publications/Publ-11751
Publ.-Id: 11751


Fracture mechanical investigation of a thermo shock scenario for a VVER-440 RPV

Altstadt, E.; Abendroth, M.

The paper describes the modelling and evaluation of a pressurized thermal shock (PTS) scenario in a VVER-440 reactor pressure vessel due to an emergency cooling. An axially oriented semi-elliptical crack is assumed to be located in the core welding seam. Two variants of fracture mechanical evaluation are performed: the analysis of a sub-cladding crack and of a surface crack. Three-dimensional finite element (FE) models are used to compute the global transient temperature and stress-strain fields. By using a three-dimensional submodel, which includes the crack, the local crack stress-strain field is obtained. Within the subsequent postprocessing using the J integral technique the stress intensity factors KI along the crack front are obtained. The FE results are compared to analytical calculations proposed in the VERLIFE code. The stress intensity factors are compared to the fracture toughness curve of the weld material.

Keywords: Fracture mechanichs; thermal shock; crack; reactor pressure vessel

  • Contribution to proceedings
    34. MPA-Seminar, 09.-10.10.2008, Stuttgart, Deutschland
    34. MPA-Seminar “Werkstoff- & Bauteilverhalten in der Energie- & Anlagentechnik”

Permalink: https://www.hzdr.de/publications/Publ-11750
Publ.-Id: 11750


Interactions of microorganisms with U(VI).

Reitz, T.; Merroun, M. L.; Selenska-Pobell, S.

The release of uranium into the environment is a subject of great public concern due to the chemical and radiological toxicity of this radionuclide. For the development of effective remediation strategies and reliable risk assessment, consolidated knowledge about the uranium behavior in contaminated sites is necessary. Beside the interactions with inorganic soil components, an important role in the migration behavior of uranium play the naturally occurring microorganisms. A high number of studies were dedicated to elucidate the bacterial processes responsible for the binding of uranium. However, little is known about the processes implicated in the complexation of this radionuclide by representatives of the second microbial domain of life, the “Archaea”. The objective of the present work was to investigate whether the structural differences between the cell surfaces of representatives of archaea and bacteria influence the cellular localization and the molecular environment of U(VI) bound by the two kinds of organisms. For this, Transmission Electron Microscopy (TEM), Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS), and X-ray Absorption Spectroscopy (XAS) were used.

  • Poster
    3rd PhD Seminar of the Forschungszentrum Dresden/Rossendorf, 27.-29.08.2008, Limbach, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11749
Publ.-Id: 11749


Interactions of Paenibacillus sp. JG-TB8 and Sulfolobus acidocaldarius with U(VI)

Reitz, T.; Merroun, M. L.; Selenska-Pobell, S.

Microorganisms are interacting in multiple ways with radionuclides. A high number of studies were dedicated to elucidate the bacterial mechanisms of uranium binding. However, little is known about the complexation of this radionuclide by representatives of archaea. The objective of the present work was to investigate whether the structural differences between the cell walls of archaea and bacteria influence the cellular localization and the molecular environment of U(VI) bound by the two kinds of organisms. For this, Transmission Electron Microscopy (TEM), Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS), and X-ray Absorption Spectroscopy (XAS) were used

  • Poster
    12th International Symposium on Microbial Ecology, 17.-22.08.2008, Cairns, Australien

Permalink: https://www.hzdr.de/publications/Publ-11748
Publ.-Id: 11748


Uranium biomineralization by uranium mining waste isolates: a multidisciplinary approach study

Merroun, M.; Hennig, C.; Selenska-Pobell, S.

- wird nachgereicht

  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 723-723

Permalink: https://www.hzdr.de/publications/Publ-11747
Publ.-Id: 11747


Dipole strength in 89Y up to the neutron-separation energy

Benouaret, N.; Schwengner, R.; Rusev, G.; Dönau, F.; Beyer, R.; Erhard, M.; Grosse, E.; Junghans, A. R.; Kosev, K.; Nair, C.; Schilling, K. D.; Wagner, A.; Bendjaballah, N.

Photoexcitation of the N = 50 nucleus 89Y has been performed at the bremsstrahlung facility at the superconducting electron accelerator ELBE at electron energies of E = 9.5 MeV and 13.2 MeV. About 250 levels up to the neutron-separation energy were identified. Statistical methods were applied to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from (gamma,n) data and provides information about the extension of the giant dipole resonance toward energies below the neutron-separation energy. An enhancement of E1 strength has been found in the range from about 6 MeV to 11 MeV. The experimental photoabsorption cross sections of 89Y and of the neighboring N = 50 isotones 88Sr and 90Zr are compared with predictions of the quasiparticle-random-phase approximation.

Keywords: Nuclear structure; photon scattering; gamma-ray strength functions; absorption cross sections; random-phase-approximation

Permalink: https://www.hzdr.de/publications/Publ-11746
Publ.-Id: 11746


Begleitende Untersuchungen zur Pilotierung eines Verfahrens zur elektrochemischen Aufbereitung saurer Wässer aus Tagebaurestseen / 3. Zwischenbericht

Kryk, H.; Schubert, M.; Hessel, G.

Das vom VKTA entwickelte elektrochemische Verfahren zur Aufbereitung schwefelsaurer Wässer aus Tagebau-Restseen (RODOSAN®) befindet sich zurzeit in der Phase der Pilotierung. Hierzu wurde vom VKTA im Gebiet des Lausitzer Braunkohlen-Tagebaureviers eine Grubenwasserreinigungs-Pilotanlage errichtet. Durch das FZD wurden prozessbegleitende Untersuchungen sowohl zur Optimierung des Elektolyseprozesses als auch zur Aufbereitung der Koppelprodukte durchgeführt.
Schwerpunkte waren experimentelle Untersuchungen zum Einfluss des Elektrolyseprozesses (Gasblasenbildung) auf die Verweilzeitverteilung der Flüssigkeit im Katodenraum unter Verwendung der laserinduzierten Fluoreszenz (LIF). Dazu wurde die Strömung im Katodenraum der Elektrolysezelle bei laufender Elektrolyse unter Anwendung verschiedener Stromdichten untersucht. Die Messungen stellen eine informative Basis zur Optimierung der Strömungsstruktur in der Zelle dar.
Im Mittelpunkt des Projektes stand weiterhin eine Machbarkeitsstudie zur Abtrennung des Koppelproduktes Ammoniumperoxodisulfat aus der Anolyt-Lösung. Hierzu wurden thermodynamische Kristallisationsparameter ermittelt und Verfahrensvorschläge für die großtechnische Koppelproduktaufbereitung erarbeitet. Ziel ist die optimale Verwertung der beim Elektrolyseprozess entstehenden Koppelprodukte zur Erhöhung der Wirtschaftlichkeit des Gesamtverfahrens.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\04
    0069 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11745
Publ.-Id: 11745


Begleitende Untersuchungen zur Pilotierungeines Verfahrens zur elektrochemischen Aufbereitung saurer Wässer aus Tagebaurestseen / 2. Zwischenbericht

Kryk, H.; Schubert, M.; Hessel, G.

Das vom VKTA entwickelte elektrochemische Verfahren zur Aufbereitung schwefelsaurer Wässer aus Tagebau-Restseen (RODOSAN®) befindet sich zurzeit in der Phase der Pilotierung. Hierzu wurde vom VKTA im Gebiet des Lausitzer Braunkohlen-Tagebaureviers eine Grubenwasserreinigungs-Pilotanlage errichtet. Durch das FZD wurden prozessbegleitende Untersuchungen sowohl zur Optimierung des Elektolyseprozesses als auch zur Aufbereitung der Koppelprodukte durchgeführt.
Schwerpunkte waren experimentelle Untersuchungen zum Einfluss des Abstandgitters, der beweglichen Membran sowie der Volumenströme auf die Verweilzeitverteilung der Flüssigkeit im Katodenraum unter Verwendung der laserinduzierten Fluoreszenz (LIF). Außerdem gibt die Visualisierung durch die Verwendung fluoreszierender Tracer Informationen über Strömungsasymmetrien durch die Einlassgeometrie, das Abstandsgitter sowie den Aufbau der Zelle. Dazu wurde die Strömung im Katodenraum der Elektrolysezelle in unterschiedlichen Konfigurationen untersucht. Die Messungen stellen eine informative Basis zur Optimierung der Strömungsstruktur in der Zelle dar. Ziel der Untersuchung war, das Verweilzeitverhalten besser zu charakterisieren und damit Rückschlüsse auf das Elektrolyseergebnis ziehen zu können.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\01
    0042 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11744
Publ.-Id: 11744


Melt flows in combined rotating and traveling magnetic fields

Gerbeth, G.; Grants, I.; Zhang, C.; Eckert, S.

The liquid metal flow in a cylinder driven by poloidal and azimuthal magnetic body forces is studied experimentally. For this purpose we apply the ultrasound Doppler velocimetry in the bulk and a particle image velocimetry on the free surface. The body forces are generated by axial traveling and rotating magnetic fields of considerably different frequencies. The transition between poloidal to azimuthal force governed states proceeds in two intermediate stages. At first, a pronounced swirl enhancement and concentration is observed. As the azimuthal forcing is further increased the axial vorticity accumulates on a ring inside of which the poloidal flow changes its direction. This transition occurs at a surprisingly low azimuthal forcing of just about one per cent of its poloidal counterpart. The two characteristic velocity components, in turn, have comparable magnitude. The disproportionality of both force strengths is, thus, a consequence of a considerably higher hydraulic resistance for the poloidal flow. The observed swirl concentration during the regime change is explained by the phenomenon of vortex stretching.

  • Lecture (Conference)
    79th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM2008), 02.-04.04.2008, Bremen, Germany

Permalink: https://www.hzdr.de/publications/Publ-11743
Publ.-Id: 11743


On the efficiency of MHD drag reduction

Shatrov, V.; Gerbeth, G.

Recently, permanent magnets and high electric current densities are often used to achieve reasonable Lorentz forces for a magnetohydrodynamic (MHD) flow control. This choice, however, usually leads to a low energetic efficiency for the flow control of seawater. We present results of direct numerical simulations of turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by a permanent magnetic field and an electric current from electrodes placed at the bottom wall. The investigations are restricted to the two cases of a spanwise oscillating force and a streamwise steady force. The lecture to be presented extends the results recently published by the authors.

  • Lecture (Conference)
    European Drag Reduction and Flow Control Meeting, 08.-11.09.2008, Ostritz, Germany

Permalink: https://www.hzdr.de/publications/Publ-11742
Publ.-Id: 11742


Tridiagonal factorization algorithm for Chebyshev-tau method with an exponential coordinate mapping

Priede, J.; Grants, I.; Gerbeth, G.

Spectral numerical methods, which involve seeking the solution in terms of a series of known, smooth functions such as, for example, Chebyshev polynomials, are well known in Computational Fluid Mechanics for their superior accuracy. However, the practical use of spectral methods depends critically on the efficiency of algorithms for solution of the resulting systems of algebraic equations. Spectral methods often yield systems of linear equations with dense matrices whose solution may be considerably less cost efficient in comparison to the band matrices resulting from finite element or finite difference techniques. Exception is the Chebyshev-tau method which combined with the recurrence relations for derivatives of Chebyshev polynomials results in tri- and penta-diagonal matrices for approximation of second derivative operators in Cartesian and polar coordinates, respectively.
In the present study we derive a similar reduction to a tridiagonal matrix for a Chebyshev-tau approximation of the second derivative operator in a transformed coordinatemapping a semi-infinite domain which is useful for the numerical solution of boundary layer equations. This approach combined with FFT results in a cost-efficient and accurate algorithm for a direct numerical simulation of boundary layer flows. Application of this algorithm is demonstrated for a turbulent Hartmann-layer flow of an electrically conducting liquid in a transverse magnetic field.

  • Lecture (Conference)
    8th World Congress on Computational Mechanics (WCCM8), 01.-05.07.2008, Venice, Italy

Permalink: https://www.hzdr.de/publications/Publ-11741
Publ.-Id: 11741


Linear stability analysis of an alternating magnetic field driven flow in a spinning container

Gerbeth, G.; Shatrov, V.; Hermann, R.

We present a numerical analysis of the free surface liquid metal flow driven by an alternating (AC) magnetic field in a spinning cylindrical container. The axysimmetric flow structure is analyzed for various values of the magnetohydrodynamic interaction parameter N and the Ekman number E. The governing hydrodynamic equations are solved by a spectral collocation method. The alternating magnetic field distribution is found by a boundary-integral method. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface. The upper free boundary was found simultaneously with the flow by a Newton method. It is found that in all considered parameter ranges the flow contains four main toroidal eddies. This is caused by the non-uniformity of the magnetic field near the edges of the liquid volume. The interaction parameter N controls the intensity of the flow. The additional container spinning leads to a deformation of the flow structure. At Ekman number E < 1 ´ 10-2 the meridional flow is reduced. The secondary azimuthal flow has its maximum in the Ekman number range of E ~ 10-3 - 10-2, at smaller Ekman number the azimuthal flow is suppressed too.
The three-dimensional stability analysis of the flow showed that the spinning leads mainly to a destabilization of the base flow. Only at very small Ekman numbers E the flow in the spinning container is more stable than in the non-spinning case. The instability at large Ekman numbers is of oscillatory type and the most unstable azimuthal wave number is m = 3. At smaller Ekman numbers the azimuthal wave number increased to m = 5, m = 6, etc. At E < 2.1 ´ 10-4 the most unstable wave number is m = 16. Except the narrow Ekman number range of 1.935 ´ 10-2 < E < 2.376 ´ 10-2 where the instability is of oscillatory type, at all other values of Ekman number E < 4.6136 ´ 10-2 the instability is of steady type.

  • Lecture (Conference)
    8th World Congress on Computational Mechanics (WCCM8), 01.-05.07.2008, Venice, Italy

Permalink: https://www.hzdr.de/publications/Publ-11740
Publ.-Id: 11740


The flow around an electromagnetically self-propelled sphere

Shatrov, V.; Gerbeth, G.

We present a numerical analysis of the flow behind an electromagnetically self-propelled sphere. Two cases are considered. In the first part the sphere contains the electromagnetic coil system which creates a traveling magnetic field on the sphere surface. The control parameter of the problem is the interaction parameter N of the traveling field. For a given value of N the sphere moves in an electrically conducting fluid with some velocity, which defines the corresponding Reynolds number. It is found that in the self-propelled regime when the hydrodynamic drag force and the electromagnetic thrust force balance each other, the flow behind the sphere has a much smaller separation bubble than in the absence of the Lorentz force. The size of the separation bubble depends from the distribution of the electromagnetic field near the sphere surface and the value of the interaction parameter N. Vortex separation can be fully suppressed. We study the linear stability of the axisymmetric flow. It is found that the 3D instability occurs at much larger Reynolds numbers than in the absence of the Lorentz force. For the unstable 2D flow case we calculated a full 3D flow behind the sphere. It is found that even in this unstable case the drag of the sphere can be smaller than the drag of the sphere without Lorentz force.
In the second part we studied a so-called conductive system. The sphere contains a system of sectioned electrodes on the surface and a coil system inside. The Lorentz force is three-dimensional now and the flow behind the sphere is three-dimensional too, due to the 3D Lorentz forcing. We calculated the 3D flow behind a sphere in the self-propelled regime and found that the drag can be significantly reduced. We consider the energy consumption due to the drag reduction as well.

  • Lecture (Conference)
    8th World Congress on Computational Mechanics (WCCM8), 01.-05.07.2008, Venice, Italy

Permalink: https://www.hzdr.de/publications/Publ-11739
Publ.-Id: 11739


Morphology and structure of C:Co, C:V and C:Cu nanocomposite films

Berndt, M.; Abrasonis, G.; Krause, M.; Mücklich, A.; Munnik, F.; Kolitsch, A.; Möller, W.

The influence of transition metals (TM) type on the encapsulating carbon (C) medium during the growth of C:TM composite films is investigated. The C:V(~30 at.%), C:Co(~30 at.%) and C:Cu (~30 at. %) thin films have been grown by ion beam co-sputtering in the temperature range of RT-500°C. The films have been investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy at two excitation wavelengths (532 nm and 632 nm). For comparison reasons, pure carbon films have been grown in the same temperature range.
XRD reveals that the nanoparticles in C:V and C:Cu films are in carbidic and metallic state over the whole temperature range of this study, respectively. In contrast, in C:Co films a phase transition from carbide phase, present for growth temperatures of RT-300°C, to the metallic phase above 300°C occurs. According to the TEM observations, cobalt or cobalt carbide nanoparticles embedded in a carbon matrix have an elongated shape in the direction of the thin film growth with both length and diameter increasing with growth temperature (the latter from 2 up to 5 nm). However, in C:V films the nanoparticles exhibit globular shapes with diameters of ~ 2 nm at RT, which only slightly increases with temperature. Raman spectroscopy shows that all three metals enhance 6-fold ring clustering of the carbon phase independent of the nanoparticle type, size, shape and phase.

Keywords: carbon; transition metal; sputter deposition; transmission electron microscopy; raman spectroscopy

  • Lecture (Conference)
    Eleventh International Conference on Plasma Surface Engineering, 15.-19.09.2008, Garmisch-Partenkirchen, Germany
  • Plasma Processes and Polymers 6(2009)Suppl., S902-S906

Permalink: https://www.hzdr.de/publications/Publ-11738
Publ.-Id: 11738


Some new results on liquid metal measuring techniques and instrumentation

Gerbeth, G.; Eckert, S.; Weiss, F.-P.

Liquid metal cooling or liquid metal targets belong to innovative reactor concepts such as the sodium cooled fast breeder reactor or the lead-bismuth target in a transmutation system. The safe and reliable operation of liquid metal systems requires corresponding measuring systems and control units, both for the liquid metal single-phase flow as well as for gas bubble liquid metal two-phase flows. We report on some recent developments in this field. Integral flow rate measurements are an important issue. We describe two new, fully contactless electromagnetic solutions and related test measurements at available sodium and lead loops. One of the sensors is of particular interest since its operation does not depend on the electrical conductivity of the liquid metal, hence it is independent on the melt temperature. A development of the past decade is the local velocity measurement by application of the Ultrasound Doppler Velocimetry (UDV). It provides the velocity profile along the ultrasonic beam, and has the capability to work even through some channel wall. We report on measurements in liquid sodium at 150°C. For higher temperatures, an integrated ultrasonic sensor with an acoustic wave-guide has been developed to overcome the limitation of ultrasonic transducers to temperatures lower than 200°C. This sensor can presently be applied at maximum temperatures up to 1000°C. Stable and robust measurements have been performed in various PbBi flows in our laboratory at FZD as well as at the THESYS loop of the KALLA laboratory of Forschungszentrum Karlsruhe (FZK). We will present experimental results obtained in a PbBi bubbly flow at 250...300°C. Argon bubbles were injected through a single orifice in a cylindrical container filled with stagnant PbBi. Velocity profiles were measured in the bubble plume. At the THESYS loop of FZK, stable velocity profiles were measured in a round tube of diameter 60 mm during a period of about 72 hours at temperatures between 180°C and 350°C. Further, we report on the development of a contactless magnetic tomography of the mean flow in liquid metals. This method gives the full three-dimensional mean velocity distribution in a liquid metal volume. Results from a laboratory demonstration experiment will be presented. Finally, a heat exchanger design will be presented working with an intermediate liquid metal in order to avoid the possible contact between a hot liquid metal and cooling water. It is installed at FZD at a lead loop where liquid lead of up to 500°C circulates. The room temperature liquid alloy GaInSn is used as intermediate melt, the heat flux is controlled by regulating the height of this melt in a gap separating the flowing lead from the cooling water.

  • Lecture (Conference)
    THIRS Workshop, 14.-16.04.2008, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-11737
Publ.-Id: 11737


Auswirkungen von verschiedenen Brennstoffzyklusoptionen auf die anfallenden Aktinidenmengen im deutschen Reaktorpark

Merk, B.; Broeders, C. H. M.

On the basis of the legally stipulated total volume of electricity to be generated in Germany an estimate is given of the amounts of residues arising from reactor operation in terms of spent uranium fuel, plutonium, and minor actinides. Various idealized scenarios are considered as limiting criteria and compared with a realistic scenario in an attempt to show the impacts of various fuel cycle options on the remaining plant life. The case of plutonium reduction by using mixed oxide (MOX) fuels is analyzed in particular. While consistent direct disposal at the end of plant life leaves approx. 160 t of plutonium (upper bound), this quantity can be reduced by some 40 t merely by recycling once. Recycling twice could reduce the amount of plutonium by nearly 60 t (lower bound). Present boundary conditions already reduce the remaining amount of plutonium by some 17 t, which level could be raised to something close to the possible value of 40 t by resuming reprocessing. An additiona!
l scenario considered are the impacts on actinide production of plant life extension for all scenarios as a basis for future discussions of the kind already going on in other countries.

Keywords: Lifetime Extension; Cycle Studies; Plutonium Management; MOX Fuel

  • atw - International Journal for Nuclear Power 53(2008)6, 404-412

Permalink: https://www.hzdr.de/publications/Publ-11736
Publ.-Id: 11736


Magnetfelder optimieren Metalllegierungen: Forschen für das optimale Gefüge

Schue, A.; Eckert, S.

In der Arbeitsgruppe Magnetohydrodynamik am Forschungszentrum Dresden-Rossendorf (FZD) werden Wechselwirkungen zwischen elektrisch leitfähigen Flüssigkeiten und magnetischen Feldern eingesetzt, um Strömungsverhalten und Erstarrungsprozesse flüssiger Metalllegierungen kontrolliert zu steuern. Ziel sind optimierte Produktionsprozesse für die Gießereitechnik. Zur Analyse setzt man ein System aus High-End-Mikroskop und Power-Mosaic-Bildaufnahme ein, das große Probenoberflächen in hochaufgelösten Einzelbildern abrastert und ein präzises Gesamtbild für quantitative Auswertungen liefert.

Keywords: metal alloys; solidification; electromagnetic stirring; microstructure

  • Quality Engineering (2008)10, 47-49

Permalink: https://www.hzdr.de/publications/Publ-11735
Publ.-Id: 11735


Improvement of structural, electronic, and magnetic properties of Co2MnSi thin films by He+-irradiation

Gaier, O.; Hamrle, J.; Hillebrands, B.; Kallmayer, M.; Pörsch, P.; Schönhense, G.; Elmers, H. J.; Fassbender, J.; Gloskovskii, A.; Jenkins, C. A.; Felser, C.; Ikenaga, E.; Sakuraba, Y.; Tsunegi, S.; Oogane, M.; Ando, Y.

The influence of 30 keV He+ ion irradiation on structural, electronic and magnetic properties of Co2MnSi thin films with B2 order was investigated. It was found, that irradiation with light ions can improve the local chemical order. This provokes changes of the electronic structure and elementspecific magnetization towards the bulk properties of the well-ordered Co2MnSi Heusler compound with L21 structure.

Keywords: magnetism; ion irradiation; Heusler alloy; ordering; chemical order

Permalink: https://www.hzdr.de/publications/Publ-11734
Publ.-Id: 11734


A literature review on mechanisms and models for the coalescence process of fluid particles

Liao, Y.; Lucas, D.

This paper presents a literature review on mechanisms and models for the coalescence process of fluid particles (bubbles and drops). For the mechanisms, five categories are summarized, namely, turbulence fluctuation, viscous shear stress, capture in turbulent eddies, buoyancy and wake interaction. Models for the collision frequency and coalescence efficiency of bubbles or drops in turbulent liquid are reviewed thoroughly. The development and limitation of the existing models are studied and possible improvements are proposed.

Keywords: Population balance equation; Bubble size distribution; Coalescence mechanisms; Coalescence models

Permalink: https://www.hzdr.de/publications/Publ-11733
Publ.-Id: 11733


Analysis of scattered radiation cross-talk in a high-resolution gamma ray tomography detector with GATE Monte-Carlo simulation

Kiessling, N.; Bieberle, A.; Hampel, U.

Limited energy resolution in scintillation type gamma ray detectors leads to systematic errors in photon counting because the pulse height discrimination stages cannot accurately discriminate interactions with full respectively partial deposition of isotopic emission energy. The resulting error is a systematic positive count rate offset originating from erroneously counted scattered photons. The origin of scattering may be the detector itself (scintillation crystals and other construction material) as well as components of the setup, including the object of investigation. In this article results of a simulation study are presented which was carried out to assess the role of different design parameters for the count rate accuracy of a high resolution gamma ray detector used for transmission tomography. Thereby the simulation software Geant4 Application for Emission Tomography (GATE) was used. As a target parameter we evaluated the radiation cross-talk, which is the amount of erroneously counted interactions from photons which have undergone Compton scattering in neighbouring crystals. For the given detector design it was found that cross-talk obtained from the simulated data is in good agreement with experimentally determined cross-talk. It could further be shown by virtual detector design changes that radiation cross-talk can be reduced only to a degree that would still require additional software correction measures, such as scattering correction algorithms, if quantitative accuracy it demanded.

Keywords: GATE; Monte-Carlo simulation; scintillation detector; gamma ray tomography

Permalink: https://www.hzdr.de/publications/Publ-11732
Publ.-Id: 11732


Numerical study of the turbulent two-phase flow in a steel mould

Miao, X.; Galindo, V.; Gerbeth, G.; Ren, Z.

Magnetic fields are an attractive contactless possibility in order to influence the liquid steel flow in the mould of the continuous casting process. In slab casting, argon bubbles are commonly introduced through the submerged entry nozzle into the liquid steel in order to reduce nozzle clogging. However, argon gas bubbles are very influential on the upper recirculation zone. Argon gas bubbles give rise to the entrapment of mould flux while bursting out at the free surface between the molten steel and the mould flux. On the other hand, several reports show that argon gas bubbles ascend near the nozzle due to their buoyancy, and such ascending argon bubbles induce an upstream of the molten steel. Thus, argon gas bubbling is thought to be able to affect the flow pattern of molten steel and subsequently exert an influence on the initial solidification in the meniscus region. Therefore, it is essential not only to prevent the steel defects which are caused by both the entrainment of mould flux and the gas bubbles, but to control the two-roll flow pattern. In our presentation, a multi-phase model is adopted to simulate the effect of argon gas bubbles on the flow pattern in the slab mould compared with water model experiments. The calculations show that argon gas bubbling increases the probability of an asymmetric instability and even unbalances the two-roll flow pattern in the slab mould.

Keywords: magnetic control; continuous casting

  • Lecture (Conference)
    8th. World Congress on Computational Mechanics (WCCM8) / 5th. European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2008), 30.06.-04.07.2008, Venice, Italy

Permalink: https://www.hzdr.de/publications/Publ-11731
Publ.-Id: 11731


Detailed Analysis Concerning the Biodistribution and Metabolism of Human Calcitonin-Derived Cell-Penetrating Peptides

Neundorf, I.; Rennert, R.; Franke, J.; Közle, I.; Bergmann, R.

The interest in using small peptides for therapeutic and diagnostic in vivo applications is based on several advantageous features such as good penetration into tissues and rapid clearance from the body. Because of their size, they can easily be synthesized chemically. The recently discovered cell-penetrating peptides (CPP) and among them CPP derived from the native peptide hormone human calcitonin (hCT) could meet these requirements.
Therefore, they are nowadays widely used as delivery vectors for a variety of bioactive molecules. However, the knowledge about the distribution and metabolism of CPP in vivo is very limited. Hence, evaluation of the pharmacological features of any promising peptide is a crucial challenge in its development process. Herein, we studied the in vivo radiopharmacology of 68Ga radiolabeled DOTA-modified, hCT-derived CPP in rats using small animal PET. Furthermore, the arterial blood at different time points and urine were analyzed for radiometabolites. It was shown that D-amino acid modifications of the sequence hCT(9-32) resulted in an increased in vivo stability and lower retention in the kidney cortex of this peptide.

Permalink: https://www.hzdr.de/publications/Publ-11730
Publ.-Id: 11730


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.

Keywords: SiC; implantation; thermal wave measurement

  • Contribution to proceedings
    Third International Workshop on Nondestructive Testing and Computer Simulations in Science and Engineering, 07.-11.06.1999, St. Petersburg, Russia
    Proceedings of the Third International Workshop on Nondestructive Testing and Computer Simulations in Science and Engineering, ISSN:0277-786X ( print )

Permalink: https://www.hzdr.de/publications/Publ-11729
Publ.-Id: 11729


Model experiments on macroscopic thermoelectromagnetic convection

Zhang, X.; Cramer, A.; Lange, A.; Gerbeth, G.

Thermoelectromagnetic convection (TEMC) in a generic configuration is studied experimentally. The experimental results demonstrate that even a moderate temperature gradient can produce distinct convection. When the magnet was positioned close to an isothermal wall with its direction of magnetization parallel to , a relatively stable vortex developed throughout the whole container. Moving the magnet to the center led to a modified distribution of the magnetic field, while, in turn, altered the flow topology into four-vortex structure. Numerical results support the experimental findings.

Keywords: Thermoelectromagnetic Convection; Thermoelectric Power; Temperature Gradient; Container

  • Contribution to proceedings
    7th PAMIR International Conference on fundamental and applied MHD, 08.-12.09.2008, Presqu'Île de Giens, France, 495-499
  • Poster
    7th PAMIR International Conference on fundamental and applied MHD, 08.-12.09.2008, Presqu'Île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11728
Publ.-Id: 11728


Develompent of a modeling approach for bubble entrainment

Schmidtke, M.; Lucas, D.

This final report presents the work done for the numerical prediction of the plunging jet configuration including the air entrainment below the surface by the jet. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. Various drag models are tested and their influence on the gas void fraction below the water level is discussed. For the quantification of the gas entrainment and for the description of the plume geometry diverse measures are developed. The results of simulations are compared with experimental correlations and are discussed with respect to physical plausibility, e.g. in terms of mass conservation, bubble entrainment and the penetration depth of the gas plume below the water level.
If the gas is treated as dispersed phase everywhere in the domain and the grace drag law is applied, the gas entrainment is overestimated substantially. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free surface drag coefficient. The gas entrainment can be controlled (tuned) via this parameter. So the AIAD approach can be used in future for the implementation of models (e.g. correlations) for the gas entrainment, since the physical details of the bubble generation generally can not be resolved in Euler-Euler simulations of large multiphase configurations.

Keywords: bubble; entrainment; jet; plunging; impinging; interface area density; AIAD; ECC; PTS

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    NURESIM-SP2-TH-D2.1.3.2
    0026 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11727
Publ.-Id: 11727


Impedance sensors for fast multiphase flow measurement and imaging

Da Silva, M. J.

In this work, the use of electrical impedance techniques for multiphase flow measurement has been investigated. Three different impedance sensor systems to quantify and monitor multiphase flows have been developed, implemented and metrologically evaluated. The first one is a complex permittivity needle probe which can detect the phases of a multiphase flow at its probe tip by simultaneous measurement of the electrical conductivity and permittivity at up to 20 kHz repetition rate. Two-dimensional images of the phase distribution in pipe cross section can be obtained by the newly developed capacitance wire-mesh sensor. The sensor is able to discriminate fluids with different relative permittivity (dielectric constant) values in a multiphase flow and achieves frame frequencies of up to 10,000 frames per second. The third sensor introduced in this thesis is a planar array sensor which can be employed to visualize fluid distributions along the surface of objects and near-wall flows. The planar sensor can be mounted onto the wall of pipes or vessels and thus has a minimal influence on the flow. It can be operated by a conductivity-based as well as permittivity-based electronics at imaging speeds of up to 10,000 frames/s. All three sensor modalities have been employed in different flow applications which are discussed in this thesis. The main contribution of this research work to the field of multiphase flow measurement technology is therefore the development, characterization and application of new sensors based on electrical impedance measurement. All sensors present high-speed capability and two of them allow for imaging phase fraction distributions. The sensors are furthermore very robust and can thus easily be employed in a number of multiphase flow applications in research and industry.

Keywords: impedance sensors; multiphase flow; flow imaging; tomography

  • Book (Authorship)
    Dresden: TUDpress, 2008
    154 Seiten

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-11725
Publ.-Id: 11725


SIMS investigation of Gex(4H-SiC)1-x solid solutions synthesized by Ge-ion implantation up to x=0.2

Peyre, H.; Pezoldt, J.; Voelskow, M.; Skorupa, W.; Camassel, J.

Ge-ion implantation in SiC is of interest for fundamental damage studies and hetero-junction device applications. For instance, a thin Ge-implanted layer has already been used as base for hetero-structure bipolar transistors [5]. Germanium is also a widely used solvent in VLS (Vapor-Liquid-Solid) growth technology and shedding more light on the incorporation of Ge in the SiC lattice is of interest [6]. Recently, high dose / high temperature ion-implantations have been done in 4H-SiC samples which, when investigated by RBS (Rutherford Backscattering Spectroscopy) techniques, suggested that up to 50% of the initial dose could be lost for targeted concentrations in the range of 10 to 20%. In this work we present a comparative investigation of the Ge concentration distributions carried out by SIMS and RBS and highlight the effects affecting the depth distribution and measurement results.

Keywords: SiC; Ge Ion implantation; SIMS; RBS

  • Lecture (Conference)
    7th European Conference on Silicon Carbide and Related Materials, 07.-11.09.2008, Barcelona, Spain
  • Materials Science Forum 615-617(2009), 465-468

Permalink: https://www.hzdr.de/publications/Publ-11724
Publ.-Id: 11724


Meson and di-electron production with HADES

Fröhlich, I.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krása, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Lopes, L.; Maier, L.; Mangiarotti, A.; Marín, J.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Mishra, D.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pérez Cavalcanti, T.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Simon, R.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Veretenkin, I.; Wagner, V.; Wen, H.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.

The HADES experiment, installed at GSI, Darmstadt, measures di-electron production in A+A, p/pi+N and p/pi+A collisions. Here, the pi0 and eta Dalitz decays have been reconstructed in the exclusive p+p reaction at 2.2 GeV to form a reference cocktail for long-lived di-electron sources. In the C+C reaction at 1 and 2 GeV/u, these long-lived sources have been subtracted from the measured inclusive e+e- yield to exhibit the signal from the early phase of the collision. The results suggest that resonances play an important role in dense nuclear matter.

  • Contribution to proceedings
    MESON2008, 10th International Workshop On Meson Production, Properties And Interaction, 06.-10.06.2008, Cracow, Poland
    Int. J. Mod. Phys. A 24 (2009) 317-326, Singapore: World Scientific Publ., ISSN: 0217-751X
  • Contribution to WWW
    arXiv:0809.2764: http://de.arxiv.org/abs/0809.2764

Permalink: https://www.hzdr.de/publications/Publ-11723
Publ.-Id: 11723


Epitaxial 3C-SiC nanocrystal formation at the SiO2/Si interface after carbon implantation and annealing in CO atmosphere

Voelskow, M.; Pécz, B.; Stoemenos, J.; Skorupa, W.

High quality 3C-SiC nanocrystallites were epitaxially formed on a single crystalline Si surface covered by a 150 nm thick SiO2 capping layer after low dose carbon implantation and subsequent high temperature annealing in CO atmosphere. Carbon implantation is used to introduce nucleation sites by forming silicon-carbon clusters at the SiO2/Si interface facilitating the growth of 3C-SiC nanocrystallites.

Keywords: nanocrystallites; 3C-SiC; carbon implantation

  • Poster
    IBMM 08 - 16th International Conference on ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1364-1367

Permalink: https://www.hzdr.de/publications/Publ-11722
Publ.-Id: 11722


Nanometer-thick SGOI structures produced by Ge+ ion implantation of SiO2 film and subsequent hydrogen transfer of Si layer

Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.

Strong decrease in the carrier mobility of the nanometer-thick silicon films imposes a limitation on the application of silicon-on-insulator (SOI) structures in the current silicon planar CMOS technology. The formation of SiGe-heterostructures-on-insulator (SGOI) is a way to increase the hole mobility in the nanometer-scale layers. In this work, we present the results on the interface mediated endotaxial growth of nanometer-thick Ge film from the Ge+-ion implanted SiO2 layer of the SOI structure

Keywords: SOI; SiGe; SGOI; Ge implantation

  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1277-1280

Permalink: https://www.hzdr.de/publications/Publ-11721
Publ.-Id: 11721


Comparative simulations of bubble entrainment cases with NURESIM_CFD and CFX-11

Schmidtke, M.; Lucas, D.

This progress report presents the work done for the numerical prediction of the plunging jet configuration. A study case is simulated with both the NURESIM_CFD_1.0.5 code and with CFX-11 and the results for the gas entrainment near the jet are compared. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. In this study the SIMMER model is applied for the drag. This model assumes bubbly flow where the gas void fraction is low and droplets in air, where the gas void fraction is high. The influence of the drag model and particle diameters for droplets and bubbles on the gas entrainment is studied.
For the drag, the Grace law (constant drag coefficient) and the Schiller Naumann law are tested. The particle diameter also has an influence on the drag. A variation of the drag force does not have an obvious effect on the gas entrainment in the simulations performed with the SIMMER model. The gas entrainment is overestimated in all simulations and there is no free parameter inside the SIMMER model which allows an adjustment of the entrainment in the simulation.

Keywords: Bubble entrainment; jet; impinging; plunging; PTS; ECC

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    NURESIM-SP2-TH-D2.1.3.3
    12 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11720
Publ.-Id: 11720


Endotaxial growth of InSb nanocrystals at the bonding interface of the In+ and Sb+ ion implanted SOI structure

Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.

The formation of heterostructures-on-insulator is a way to increase the carrier mobility in the nanometer-scale layers. The electron mobility in InSb is about 50 times higher than that in bulk silicon. The formation of Si/InSb on insulator heterostructures may provide an increase of effective electron mobility in the nanometer scale SOI films. In this work, we present the results on the interface mediated endotaxial growth of InSb nanocrystalline phase at the Si/SiO2 bonding interface of silicon-on-insulator (SOI) structure.

Keywords: SOI; mobility; InSb; heterostructures

  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1360-1363

Permalink: https://www.hzdr.de/publications/Publ-11719
Publ.-Id: 11719


Controlled localised melting in silicon by high dose germanium implantation and flash lamp annealing

Voelskow, M.; Pezoldt, J.; Kups, T.; Skorupa, W.

The annealing of semiconductor surfaces via pulsed laser melting has been practised since the 70 ' s. During the process a thin surface layer is molten up to a depth of mkm and recrystallises, after the pulse is over, epitaxially on the non molten substrat.
Depending on the segregation coefficient of additionally admixed atoms completely different doping profiles can be achieved. Typical for all pulse irradiation techniques is, that the melting process starts near the surface. The aim of the present work is to overcome this phenomen and to force a buried melting by large area flash lamp irradiation using an additional Ge admixture. The addition of Germanium locally leads to a reduction of the silicon melting temperature so that separated melting in the bulk of silicon can be observed. During cooling down of the sample the buried liquid layer recrystallises epitaxially on the non molten bulk material and for the case of additional doping of the layer special profiles can be observed. Ion implantation at high doses and high energies was used to produce structures with a buried germanium enriched layer. The pulse irradiation was performed at the Rossendorf flash lamp apparatus using intense light pulses with a duration of 20 ms from a field of Xe flash tubes. The energy density at the sample surface was varied within wide limits. For the determination of the Ge profiles after the flash lamp irradiation the RBS technique was used. The microstructure of the recrystallised films was observed by cross sectional TEM. It could be shown that buried melting takes place whereby the width of the molten zone depends on the energy density. Deep facetted melting, typical for virgin silicon material, was not observed.

Keywords: flash lamp annealing; buried melting; germanium; RBS TEM

  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1269-1272

Permalink: https://www.hzdr.de/publications/Publ-11718
Publ.-Id: 11718


Gamma flashes from relativistic electron-positron plasma droplets

Mustafa, G. M.; Kämpfer, B.

Ultra-intense lasers are expected to produce, in near future, relativistic electron-positron plasma droplets. Considering the local photon production rate in complete leading order in quantum electrodynamics (QED), we point out that these droplets are interesting sources of gamma ray flashes.

Permalink: https://www.hzdr.de/publications/Publ-11717
Publ.-Id: 11717


Synthesis of a precursor for an alumina ceramic reinforced by zirconium dioxide from inorganic compounds in the presence of urea

Zharnylskaya, A. L.; Volkhin, V. V.; Shcherban, M. G.; Reuter, H.

Samples of a precursor for an alumina ceramic reinforced by zirconium dioxide were synthesized. The samples have a uniform structure and are characterized by high ratios of the tetragonal and monoclinic modifications of ZrO2, tlm, after a thermal treatment (1250 degrees C). The structure of samples in the system Al2O3-ZrO2 is formed under conditions favorable for deposition of products of hydrolysis of Al(III) ions on the surface of ZrO2 sol particles in decomposition of urea. The coating of ZrO2 sol particles by products of hydrolysis of Al(III) salts was confirmed by electrophoresis. The size distribution of particles of the in?dividual ZrO2 sol was determined by small-angle X-ray scattering. The structure of the products formed in thermal treatment of samples of mixed oxides Al2O3-ZrO2 was characterized by X-ray phase analysis and scanning electron microscopy. The porosity and specific surface area of a thermally treated sample was determined by measuring nitrogen absorpt!

  • Russian Journal of Applied Chemistry 81(2008)7, 1147-1152

Permalink: https://www.hzdr.de/publications/Publ-11716
Publ.-Id: 11716


Force-free and contactless electromagnetic flow rate sensors

Priede, J.; Buchenau, D.; Gerbeth, G.

We present a novel design of flowmeter using a single cylindrical permanent magnet magnetized perpendicularly to its axis about which it can freely rotate, and placed close the duct with liquid metal flow. The electromagetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. However, the equilibrium rotation rate, which attained at vanishing net electromagnetic torque on the magnet, depends only on the flowrate and geometry of the system while it is independent of the electromagnetic torque itself. A laboratory model of a such flowmeter has been built and tested at a liquid metal flow.

Keywords: flowmeter

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 815-819
  • Poster
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11715
Publ.-Id: 11715


Experimental study of traveling magnetic field driven instability in a thermally stratified liquid gallium cylinder

Klyukin, A.; Grants, I.; Gerbeth, G.

A liquid gallium cylinder is subject to a stable vertical thermal stratification (hot top and cold bottom) and an upward traveling magnetic field (TMF). The instability, which arises due to the combined action of magnetic field and temperature gradient, is investigated experimentally.

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 627-631
  • Poster
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11714
Publ.-Id: 11714


Nonstationary electrovortex flows in a long shallow channel with conducting fluid

Kolesnichenko, I.; Khripchenko, S.; Buchenau, D.; Gerbeth, G.

This paper describes our investigations into the generation of the electro-vortex flow of a conducting fluid in a plane long layer in the unstable regime. In the context of the present problem we consider the velocity field and the amplitude and frequency of velocity oscillations of this flow. The pressure drop in the channel with inclined ferromagnetic plates induced by both the direct and alternating electrical currents is studied. The obtained results can be used in developing metallurgical devices having the maximum possible stability of the flow-rate.

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 369-373
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11713
Publ.-Id: 11713


Helical magnetorotational instability in a TaylorCouette flow

Priede, J.; Gerbeth, G.

We analyze numerically the magnetorotational instability (MRI) of a hydrodynamically stable Taylor-Couette flow with a helical external magnetic field in the inductionless approximation defined by a zero magnetic Prandtl number. The Chebyshev collocation method is used to calculate the eigenvalue spectrum for small amplitude perturbations. Besides the convective instability threshold also an absolute one is found implying that this type of MRI might be experimentally observable in a system of sufficiently large but finite axial extension.

Keywords: magnetorotational instability

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 251-255
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11712
Publ.-Id: 11712


Vertical Gradient Freeze growth in a combined magnetic AC/DC field

Pätzold, O.; Lantzsch, R.; Grants, I.; Stelter, M.; Gerbeth, G.

The Vertical Gradient Freeze (VGF) method is an important technology for the melt growth of bulk compound semiconductors. The structural perfection of the crystals and the distribution of dopants in the material are closely connected to the conditions of heat and mass transport in the liquid phase. The application of external magnetic fields allows for tailoring the melt flow and, hence, gives the possibility to optimize the quality of the crystals and the yield of the growth process.
In this paper experimental and numerical results are presented, showing the influence of a combined traveling magnetic field (TMF) and steady axial magnetic field (DC) on the VGF growth of semiconducting GaAs and Ge single crystals. The quality of the crystals is characterized in terms of the interface deflection, axial/radial macrosegregation and microsegregation. The numerical simulations of the VGF growth are performed using the commercial code CrysMAS. The TMF melt flow and its influence on the interface deflection as well as the resulting local v. Mises stress are calculated on the basis of a global thermal model of the equipment.

Keywords: Vertical Gradient Freeze; crystal growth; traveling magnetic field

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 633-635
  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11711
Publ.-Id: 11711


An alternating magnetic field driven flow in a spinning cylindrical container and its three-dimensional linear stability analysis

Shatrov, V.; Gerbeth, G.; Hermann, R.

We present a numerical analysis of the free surface liquid metal flow and its three-dimensional linear stability. The flow is driven by an alternating magnetic field in a spinning cylindrical container. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface.

Keywords: free surface liquid metal flow; three-dimensional linear stability

  • Lecture (Conference)
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 525-529

Permalink: https://www.hzdr.de/publications/Publ-11710
Publ.-Id: 11710


Numerical modeling of the growth of small-diameter intermetallic compound crystals by a two-phase RF floating zone method

Krauze, A.; Priede, J.; Hermann, R.; Gerbeth, G.

We model numerically the growth of small–diameter single crystals of intermetallic compounds by the floating zone technique using two-phase radio-frequency (RF) electromagnetic heating. An axisymmetric quasi-stationary numerical model is implemented as several coupled computer programs for modeling electromagnetic fields, heat source and force density distributions, heat transfer, and turbulent melt flow. The results of model calculations are presented for the growth of Ni crystals of 2 mm in diameter. It is found that the stable molten zone exists in a very narrow range of inductor currents.

Keywords: crystal growth; electromagnetic heating; floating zone technique

  • Contribution to proceedings
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France
    Fundamental and Applied MHD, Reims: Universite de Reims Champagne-Ardenne, 851-855
  • Poster
    7th International PAMIR Conference on Fundamental and Applied MHD, 08.-12.09.2008, Presqu´île de Giens, France

Permalink: https://www.hzdr.de/publications/Publ-11709
Publ.-Id: 11709


Interfacial heat and mass tansfer models

Krepper, E.; Scheuerer, G.

The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.

Keywords: CFD; Two fluid model; heat transfer; mass transfer; boiling; cavitation

  • Invited lecture (Conferences)
    6th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 24.-26.06.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11708
Publ.-Id: 11708


Practical calculation of bubble column flow with CFX-11

Frank, T.; Lifante, C.; Krepper, E.

The lesson 6 of the "Short Course on Multiphase Flow Modelling" describes the practical simulation of the flow in a bubble column. The necessiy of the correct simulation of the momentum exchange between the phases is shown comparing different results with experiments.

Keywords: CFD; two fluid model; dispersed gaseous phase; drag bubble forces; non drag bubble forces; bubble column

  • Invited lecture (Conferences)
    6th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 24.-26.06.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11707
Publ.-Id: 11707


Finite-time thermodynamics of shear flows - modelling attractors of simple to complex dynamics

Schlegel, M.; Noack, B.; Ahlborn, B.; Mutschke, G.; Morzynski, M.; Comte, P.; Tadmor, G.

A finite-time thermodynamics formalism is proposed to compute mean flow and fluctuation levels of unsteady incompressible flows. The formalism builds upon a Galerkin model framework (see Noack et al., J. Noneqilib. Thermodyn. 33 (2008) 103-148) and is applied to a periodic vortex shedding regime behind a circular cylinder, homogeneous shear turbulence and the Burgers equation.

Keywords: finite-time thermodynamics; Galerkin methods; turbulence

  • Poster
    Dynamics Days Europe 2008, 25.-29.08.2008, Delft, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-11706
Publ.-Id: 11706


Periodically modulated surfaces and interfaces: Introducing artificial length scales to tailor magnetic properties

Fassbender, J.; Liedke, M. O.; Strache, T.; Marko, D.; Lenz, K.; Keller, A.; Facsko, S.; Tibus, S.; Springer, F.; Albrecht, M.; Rohrmann, H.

In thin magnetic films different intrinsic length scales affect the magnetic properties, e.g., the exchange correlation length determined by the exchange constant and the anisotropy of the material or the grain size of polycrystalline materials determined mainly by the growth conditions and substrates used. In the latter case also the intergranular coupling influences the magnetic properties.

Introducing an artificial extrinsic length scale in the range 10 – 100 nm allows an additional degree of freedom to tailor the overall magnetic properties of the material of choice. This length scale is established by means of low energy ion erosion of semiconductor surfaces which lead to a periodically modulated surface (ripple structure). The periodicity and amplitude can easily be varied by means of the ion erosion parameters [1]. Hence upon thin film deposition modulated surfaces and interfaces of the magnetic films result.

Two different examples will be discussed. i) Induced magnetic anisotropies in soft magnetic films deposited on rippled substrates [2]. The microscopic origin can be extrinsic, due to dipolar stray fields, as well as intrinsic, due to spin-orbit coupling phenomena at monoatomic steps. The relative contribution of both microscopic effects to the macroscopically measurable material properties depend sensitively on the introduced ripple wavelength and amplitude. ii) Magnetic properties of hard magnetic CoCrPt-SiO2 perpendicular recording media [3]. Due to a combination of deposition on a modulated surface and post-deposition ion irradiation a predefined number of grains can be exchange coupled to act as one magnetic entity required for bit patterned media. The physical mechanisms will be discussed.

Support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

[1] S. Facsko, H. Kurz, T. Dekorsy, Energy dependence of quantum dot formation by ion sputtering, Phys. Rev. B 63, 165329 (2001).
[2] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mücklich, S. Facsko, J. Fassbender, Induced anisotropies in exchange-coupled systems on rippled substrates, Phys. Rev. B 75, 220407(R) (2007).
[3] T. Strache, S. Tibus, F. Springer, H. Rohrmann, M. Albrecht, J. Fassbender, Tuning coercivity in CoCrPt-SiO2 hard disk material, OR15-4, International Conference on Ion Beam Modification of Materials, IBMM08, 31.08.-05.09.2008, Dresden, Germany

Keywords: magnetism; ion erosion; ion irradiation; modulated surfaces; MBE; intergranular coupling; induced anisotropies

  • Lecture (others)
    Seminar, National Institute of Standards and Technology, 03.11.2008, Boulder, USA
  • Invited lecture (Conferences)
    2nd International Conference on Physics at Surfaces and Interfaces, 23.-27.02.2009, Puri, Orissa, Indien
  • Lecture (others)
    Seminar, Institut für Physik, TU Ilmenau, 30.10.2008, Ilmenau, Deutschland
  • Invited lecture (Conferences)
    Symposium "Ion Beams and Nano-Engineering", MRS Spring Meeting, 13.-17.04.2009, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-11705
Publ.-Id: 11705


Application of GATE to detector optimisation in transmission gamma ray tomography

Hampel, U.; Kiessling, N.; Bieberle, A.

We present results of a simulation study on the role of different design parameters for the count rate accuracy of a high resolution gamma ray detector used for transmission tomography. The considered gamma ray tomography system is operated with a Cs-137 isotopic source and a special detector composing 320 single elements, made of LYSO scintillators coupled to APD. Typically, energy resolution of the detector elements (geometry 2mm x 2mm x 24mm) is limited to about 25% which leads to erroneous counting of photons which have been Compton scattered before detection in other parts of the detector and the object. This introduces a linearity error into the tomographic data which leads to artefacts and errors in the reconstructed images. We therefore performed a theoretical analysis with the GATE simulation software. Simulation of the count rate error for the existing configuration shows good agreement with measured detector cross-talk. In the following we assessed different virtual design changes regarding crystal geometry, separation, shielding and arrangement. Results show that further increase in accuracy is possible.

Keywords: Monte Carlo simulation; GATE; scattered radiation; radiation cross-talk; gamma ray tomography

  • Lecture (Conference)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
    IEEE NSS/MIC/RTSD Conference Record

Permalink: https://www.hzdr.de/publications/Publ-11704
Publ.-Id: 11704


Ultra fast electron beam X-ray computed tomography for two-phase flow measurement

Fischer, F.; Hampel, U.

Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focussing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm x 1.5 mm x 1.5 mm active pixel
area. X-ray radiation is produced on a circular water cooled tungsten target The CT system achieves up to 7000 frames per second with a spatial resolution of 1 millimetre. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. On the basis of these data we developed image processing algorithms which enable to extract information on bubble shapes, bubble size distributions and interfacial area density distribution. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in the future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.

Keywords: Two-phase flow; electron beam tomography; CFD code validation

  • Contribution to proceedings
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
    Proceedings of XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety
  • Lecture (Conference)
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 12.09.2008, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-11703
Publ.-Id: 11703


Quadratic detection and autocorrelation measurements with two-photon quantum well infrared photodetectors

Schneider, H.; Winnerl, S.; Liu, H. C.; Drachenko, O.; Helm, M.; Walther, M.; Faist, J.

The two-photon quantum well infrared photodetector (QWIP) comprises three equidistant subbands, two of which are bound in the quantum well, and the third state in the continuum. This results in a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in usual semiconductors. In addition, temporal resolution is only limited by the sub-ps intrinsic time constants of the quantum wells, namely the intersubband relaxation time and the dephasing time of the intersubband polarization. Both properties make this device very promising for quadratic autocorrelation measurements of pulsed mid-infrared sources, including modelocked quantum cascade lasers, radiation obtained by nonlinear optical frequency conversion, and free-electron lasers (FEL).
We have performed autocorrelation measurements of ps optical pulses from the free-electron laser (FEL) facility FELBE at the Forschungszentrum Rossendorf. Using a rapid-scan autocorrelation scheme at a scan frequency of 20 Hz, high-quality quadratic autocorrelation traces are obtained, yielding ratios close to the theoretically expected value of 8:1 between zero delay and large delay for interferometric autocorrelation, and 3:1 for intensity autocorrelation. Thus, two-photon QWIPs provide an excellent new approach to online pulse monitoring of the FEL. In addition, we have investigated the saturation mechanism of the photocurrent signal, which is due to internal space charges generated in the detector. We will also report on room temperature operation of two-photon QWIPs.

Keywords: quantum well infrared photodetector; two-photon absorption; intersubband transition; quadratic autocorrelation; GaAs/AlGaAs

  • Lecture (Conference)
    9th International Conference on Mid-Infrared Optoelectronics: Materials and Devices (MIOMD-IX), 07.-11.09.2008, Freiburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-11702
Publ.-Id: 11702


Spannungs- und Ermüdungsanalyse für den Sicherheitsbehälter des KKW Krümmel

Altstadt, E.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\07
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11701
Publ.-Id: 11701


Spannungs- und Ermüdungsanalyse für die RDB-Einbauten des KKW Krümmel

Altstadt, E.; Werner, M.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\06
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11700
Publ.-Id: 11700


Spannungs- und Ermüdungsanalyse für den RDB-Boden des Kernkraftwerks Krümmel

Altstadt, E.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\05
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-11699
Publ.-Id: 11699


In-beam Positron Emission Tomography for Ion Therapy Monitoring

Fiedler, F.; Laube, K.; Möckel, D.; Parodi, K.; Pawelke, J.; Priegnitz, M.; Shakirin, G.; Enghardt, W.

Due to the special characteristics of ion beams and delicate treatment situations, i.e. in close vicinity to organs at risk, a three-dimensional, in-vivo and in-situ monitoring of the dose delivery is highly desirable. At present, in-beam PET is the only method meeting these requirements. An in-beam PET system has been implemented for clinical application at the carbon ion therapy facility of the Gesellschaft für Schwerionenforschung (GSI) Darmstadt. So far, more than 400 patients have been monitored with this system. It could be demonstrated that this PET technique is capable of assessing relevant parameters for quality assurance of carbon ion therapy, measuring the particle range in tissue, the position of the irradiated volume with respect to anatomical landmarks, and estimating local deviations between the planned and applied dose. In-beam PET has become a tool providing valuable clinical feedback.
The implementation of the in-beam PET system at the medical beamline at GSI will be described. Clinical results will be shown with examples. Furthermore, the application of in-beam PET for protons, 3-He, 7-Li and 16-O shows promising results and will be presented.

Keywords: in-beam PET; ion therapy

  • Invited lecture (Conferences)
    IGRT Vienna 2008 - Visions and Perspectives in Image Guided Radiation Oncology, 24.-26.09.2008, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-11698
Publ.-Id: 11698


From multiply twinned to fcc nanoparticles via irradiation-induced transient amorphization

Järvi, T. T.; Pohl, D.; Albe, K.; Rellinghaus, B.; Schultz, L.; Fassbender, J.; Kuronen, A.; Nordlund, K.

We present experimental evidence for structural trransformation of multiply twinned CuAu nanoparticles to single crystalline morphology by 0.5 keV helium irradiation. This finding is unexpected as the stability of twin boundaries should not be affected by ion-beam induced Frenkel pairs. Molecular dynamics simulations reveal, however, a new transformation mechanism based on transient amorphization of the particle. By comparing with irradiation simulations of elemental nanoparticles, as well as alloyed bulk samples and surface cascades, we show that this transformation route is only present in alloyed particles. Moreover, the observed amorphization is more efficient for twinned than single-crystalline particles. This, together with the fast recrystallization kinetics in CuAu, explains the experimentally observed untwinning process.

Keywords: ion irradiation; nanoparticles; binary alloys; structural transformation; ordered phases

Permalink: https://www.hzdr.de/publications/Publ-11697
Publ.-Id: 11697


The effect of ion irradiation and annealing on exchange spring magnets

Fassbender, J.; Grenzer, J.; Roshchupkina, O.; Choi, Y.; Jiang, J. S.; Bader, S. D.

It is demonstrated that both the nucleation field and the irreversible switching field of Sm2Co7/Fe exchange spring bilayers is decreased by means of 10 keV He ion irradiation. The reduction is attributed to interfacial mixing and irradiation induced softening of the hard magnetic layer. By lowering the energy to 0.8 keV the ions do not penetrate the hard magnetic layer and consequently no softening is observed. However, although irradiation induced interfacial mixing is still present it is not large enough to create a graded interface layer and the nucleation field decreases. In contrast conventional annealing under appropriate conditions leads to an increase of the nucleation field. This distinct discrepancy can be explained by detailed investigation of the layer structure by x-ray reflectivity measurements.

Keywords: magnetism; ion irradiation; exchange spring; hard magnets

Permalink: https://www.hzdr.de/publications/Publ-11696
Publ.-Id: 11696


Simulation analysis of the spatial sensitivity of a wire-mesh sensor

Thiele, S.; Da Silva, M. J.; Wagner, M.; Hampel, U.

The wire-mesh sensor is an imaging instrument which is able to generate cross-sectional phase distribution images with high spatial and temporal resolutions, thus being very well suitable for the investigation of multiphase flows. It has successfully been used in several research and industrial applications. In this article, we present the results of the precise simulation analysis of the spatial sensitivity of this device, which support further developments of the image data processing.

Keywords: wire-mesh sensor; spatial sensitivity; numerical field simulation

  • Contribution to proceedings
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany
    EUROSENSORS XXII, Duesseldorf: Verein Deutscher Ingenieure e.V. (VDI), 978-3-00-025217-4, 157-160
  • Poster
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-11695
Publ.-Id: 11695


Intraminiband relaxation in doped GaAs/AlGaAs superlattices studied by two-color infrared pump-probe experiments

Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.

no abstract available

Keywords: superlattice; free electron laser; infrared

  • Poster
    29th International Conference on the Physics of Semiconductors, 27.07.-01.08.2008, Rio de Janeiro, Brazil

Permalink: https://www.hzdr.de/publications/Publ-11694
Publ.-Id: 11694


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