Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35872 Publications

Spéciation des complexes du technétium par couplage SAX - Electrochimie

Poineau, F.; Fattahi, M.; Grambow, B.; Den Auwer, C.; Hennig, C.

Le couplage SAZ - Elèctrochimie s'avère être une méthode pour la spéciation des espèces réduites du technetium. Cette méthode pourra être étendue à l'étude des espèces instables des actinides et des produits de fission.

  • Poster
    Journée de Radiochimie, 5.-6.2.2004, Avignon, France

Publ.-Id: 6361

Polarized EXAFS of uranium L1 and L3 edges - A comparison

Hennig, C.; Scheinost, A.

Uranium(VI) consists predominantly of two double bonded oxygen atoms in axial direction (Oax) and 4, 5 or 6 oxygen atoms in the equatorial plane (Oeq). This anisotropic coordination leads to a strong polarization dependence of XAFS. Responsible for the polarization dependence are the electron waves with different impulse-momentum at the L1 and L3 edges. We investigated this effect by comparing experimental data with the theory. The Theory and experiment are in good agreement. The polarization dependence of L1 edge is significantly stronger that of L3 edge.

  • Poster
    14th ESRF User Meeting, 10./11.02.2004

Publ.-Id: 6360

Pre-irradiation memory effect on the photoluminexcence intensity of Ge-implanted SiO2 layers

Lopes, J. M. J.; Zawislak, F. C.; Fichtner, P. F. P.; Behar, M.; Rebohle, L.; Skorupa, W.

  • Nuclear Instruments and Methods in Physics Research B 218(2004), 438-443

Publ.-Id: 6358

Evidence for the Interaction of Technetium colloids with humic substances by X-ray absorption spectroscopy

Maes, A.; Geraedts, K.; Bruggeman, C.; Vancluysen, J.; Rossberg, A.; Hennig, C.

Spectroscopic extended X-ray absorption fine structure (EXAFS) evidence was obtained on the chemical environment of 99Tc(IV) atoms formed upon introduction of TcO4 - into four types of laboratory-scale synthetic and natural systems which mimic in situ natural reducing conditions in humicrich geochemical environments: (a) magnetite/pyrite in synthetic groundwater in the absence of humic substances (HSs), (b) magnetite/pyrite in natural Gorleben groundwater in the presence of HSs, (c) Boom clay sediment mixed with synthetic groundwater, and (d) Gorleben sand mixed with natural Gorleben groundwater. The investigated systems obey to pH 8-9 conditions, and all measured samples show similar EXAFS spectra for Tc, which could be fitted by a hydrated TcO2¿ xH2O phase. The results are interpreted as follows: upon introduction of high concentrations (millimolar to micromolar) of TcO4 to chemically reducing environments, small Tc(IV) oxidic polymers are formed, which either may aggregate into larger units (colloids) and finally precipitate or may interact in their polymeric form with (dissolved and immobile) humic substances. This latter type of interactionsTc(IV) colloid sorption onto HSssdiffers significantly from the generally accepted metal-humate complexation and therefore offers new views on the possible reaction pathways of metals and radionuclides in humic-rich environments.

  • Environmental Science & Technology 38(2004), 2044-2051

Publ.-Id: 6357

X-ray absorption spectroscopy studies of reactions of technetium, uranium and neptunium with mackinawite

Livens, F.; Jones, M.; Hynes, A.; Charnock, J.; Mosselmans, J.; Hennig, C.; Steele, H.; Collins, D.; Vaughan, D.; Et, A.

Technetium, uranium and neptunium may all occur in the environment in more than one oxidation state (IV or VII, IV or VI and IV or V respectively). The surface of mackinawite, the first-formed iron sulfide: phase in anoxic conditions, can promote redox changes so a series of laboratory experiments were carried out to explore the interactions of Tc, U and Np with this mineral. The products of reaction were characterised using X-ray absorption spectroscopy. Technetium, added as TcO4-, is reduced to oxidation state IV and forms a TcS2-like species. On oxidation of the mackinawite in air to form goethite, Tc remains in oxidation state IV but in an oxide, rather than a sulfide environment. At low concentrations, uranium forms uranyl surface complexes on oxidised regions of the-mackinawite surface but at higher concentrations, the uranium promotes surface oxidation and forms a mixed oxidation state oxide phase. Neptunium is reduced to oxidation IV and forms a surface complex with surface sulfide ions. The remainder of the Np coordination sphere is filled with water molecules or hydroxide ions.

  • Journal of Environmental Radioactivity 74(2004), 211-219

Publ.-Id: 6356

Structure of uranium sorption complexes at montmorillonite edge sites

Hennig, C.; Reich, T.; Dähn, R.; Scheidegger, A. M.

Extended X-ray absorption fine structure (EXAFS) spectroscopy at the uranium LIII-edge was used for determining the structural environment of aqueous uranyl sorbed onto montmorillonite. The study reveals that uranyl uptake at pH ~ 5- ~ 7 and at an initial uranyl concentration of 5×10-5 M takes place at amphoteric surface hydroxyl sites as inner-sphere complex. The measured bond distances between uranium and the equatorial oxygen atoms are in the range of 2.34 Å and 2.37 Å indicating an inner-sphere coordination. At ~ 3.4Å the presence of a U-Al backscattering pair was determined. This backscattering pair indicates that the binding of the uranyl unit to amphoteric surface hydroxyl sites occurs preferred as a bidentate inner-sphere complex on aluminol groups.

Keywords: Montmorillonite; Uranium; Sorption; EXAFS

  • Radiochim. Acta 90, 653-657 (2002)

Publ.-Id: 6355

EXAFS and XRD investigations of zeunerite and meta-zeunerite

Hennig, C.; Reck, G.; Reich, T.; Rossberg, A.; Kraus, W.; Sieler, J.

In this paper EXAFS was used to determine bond lengths in the structures of zeunerite and meta-zeunerite. The atomic distances between heavy and light scatterers observed using EXAFS in meta-zeunerite deviate approximately 0.1 _A from literature data of single-crystal X-ray diffraction measurements. Because this difference is significant higher than the error limits of EXAFS measurements, the complete crystal structure of meta-zeunerite, Cu[UO2AsO4]2 _ 8 H2O, is revised by X-ray structure analysis. The bond length determinations by EXAFS and the revised XRD data agree within the experimental error limits. In this study EXAFS spectroscopy has proven to be an useful tool for determining precise local bond lengths in the environment of heavy atoms. Moreover, the crystal structure of zeunerite, Cu[UO2AsO4]2 _ 12 H2O, hitherto not been described in the literature, was investigated. Reflex broadening effects and intergrowth relationship between zeunerite and meta-zeunerite show that meta-zeunerite grows in nature due to dehydration of zeunerite. The structural transition from zeunerite to meta-zeunerite is connected with a change in the uranyl arsenate layer arrangement and the crystal water content.

  • Z. Kristallogr. 218 (2003) 37-45

Publ.-Id: 6354

An EXAFS and TRLFS study of the sorption of trivalent actinides onto smectite and kaolinite

Stumpf, T.; Hennig, C.; Bauer, A.; Denecke, M. A.; Fanghänel, T.

The structure parameters of the Am3+ aquo ion and of Am(III) sorbed onto smectite and kaolinite at varying pH are analyzed using EXAFS. An Am-O distance of 2.47-2.49 Å is found and a coordination number of 8-9 oxygen atoms is observed for the Am3+ and its hydration sphere. Combined TRLFS (Cm(III)) and EXAFS (Am(III)) results show that An(III) sorbs onto smectite at pH 4, forming an outer-sphere complex and retains its complete primary hydration sphere. With increasing pH, inner-sphere sorption onto smectite and kaolinite occurs. The overall number of oxygen atoms coordinating the actinide ion remains about the same at pH 6, with four water molecules being replaced by oxygen atoms from the mineral surface during inner-sphere complex formation. The coordination number of sorbed Am(III) at pH 8 exhibits an apparent decrease, which may be affected by the formation of ternary OH-/Am/clay mineral surface species.

Keywords: Actinides; Clay minerals; EXAFS; Surface complexation; TRLFS

  • Radiochimica Acta 92(2004), 133-138

Publ.-Id: 6352

"Programme & Projekte - Beispiele für das Management in einer Forschungseinrichtung"

Joehnk, P.

  • Lecture (others)
    Vortrag Technische Universität, Bergakademie Freiberg, 27.05.2004

Publ.-Id: 6351

Grundlagen der Gestaltungslehre als Voraussetzung für gute (wissenschaftliche) Präsentationen

Joehnk, P.

  • Lecture (others)
    Doktorandenklausur, TU Szezcin, TU Lódz, IFW Dresden, Sklarska, Poreba, Polen. - 17.05.2004

Publ.-Id: 6350

n-type conductivity in high-fluence Si-implanted diamond

Weishart, H.; Heera, V.; Skorupa, W.

Epitaxial SiC nanocrystals are fabricated by high-fluence Si-implantation into natural diamond at elevated temperatures between 760 °C and 1100 °C. Fluences under investigation range from 4.5 to 6.2 x 1017 Si cm-2 . This implantation scheme yields a buried layer rich of epitaxial aligned SiC- nanocrystals within slightly damaged diamond. The generation of a small fraction of graphitic sp2-bonds of up to 15 % in the diamond host matrix can not be avoided. Unintentional coimplantation with nitrogen results in a very high doping level of more than 1021 cm-3 . Resistivity and Hall measurements in van der Pauw geometry reveal a high, thermally stable n-type conductivity with electron concentrations exceeding 1020 cm-3and mobilities higher than 2 cm2/Vs. It is supposed, that both the SiC regions as well as the diamond matrix exhibit n-type conductivity and that the electron transport occurs across the low-resistivity SiC nanograins. In the SiC nanocrystals the electrons originate from nitrogen donors whereas in diamond defects are responsible for the electron conductivity. The formation of disordered graphite, which leads to low electron mobility, is substantially reduced.

Keywords: Ion implantation; thin films; Heterostructures; electronic properties; Ion radiation effects

  • Journal of Applied Physics 97(2005), 103514.

Publ.-Id: 6349

Nonlinear Charakteristics of Gas-Liquid Two-phase Flow and Verification of Extended Two-Fluid Model

Misawa, M.; Suzuki, A.; Morikawa, Y.; Minato, A.; Prasser, H.-M.

Void fraction distributions of air-water two-phase flow in 3 different diameter vertical tubes (0.042 m, 0.1 m, and 0.2 m) were measured by 16x16 wire-mesh sensors with a sampling frequency of 1 kHz. Also, predictions under the same flow conditions were made by a 3D extended two-fluid model, generating a time-series of cross-section averaged void fraction at the same frequency with the experiment. Fluctuation characteristics from experiments and simulations were analysed in view of the probability density function, frequency spectrum, and Trajectory Parallel Measures (TPM). The analyses of TPM showed that dynamics is well-established for large nunnles whose fiameter is on the order of Taylor wave length in an air-water system, although small bubble void fraction signal is almost random in dynamical point of view. It is shown that the fluctuation component in void fraction time series can be used as one of criteria for validation of numerical models.

Keywords: two-fluid model; gas-liquid flow; wire-mesh sensor; statistical analysis; trajectory parallel measures; code validation

  • Lecture (Conference)
    5th International Conference on Multiphase Flow, ICMF'04, 30.05.-04.06.2004, Yokohama, Japan
  • Contribution to proceedings
    5th International Conference on Multiphase Flow, ICMF'04, 30.05.-04.06.2004, Yokohama, Japan, paper 213.

Publ.-Id: 6348

NuclearReactor - Reaktorphysik populär im Internet - ein Versuch, den Internetauftritt der KTG attraktiver zu machen

Prasser, H.-M.

Die Ortssektion Sachsen der Kerntechnischen Gesellschaft bemüht sich kontinuierlich um eine aktuelle und attraktive Präsens im Internet. Mit der eigenen Internetseite "", die seit Oktober 2001 besteht, wird versucht, neben der Information für die Mitglieder - in erster Linie Ankündigungen und Auswertungen von Veranstaltungen - mit Diskussionsbeiträgen zur Kernenergie ein breiteres Publikum zu erreichen. Dabei werden unter der Rubrik ARGUMENTE Themen, wie Nachhaltigkeit, CO2-Emissionen und Energieressourcen berührt. Unter der Überschrift NEWS wird über aktuelle Ereignisse informiert. Insgesamt
bleibt die Resonanz auf diese Internetseite jedoch gering. Nur sehr selten trifft Post ein, die auf die publizierten Argumente eingeht oder auch Widerspruch anmeldet. Um die Attraktivität der Internetseite zu erhöhen und dabei gleichzeitig einen Beitrag zum allgemeinen Informationsstand über die physikalischen Grundlagen der Reaktortechnik in der Bevölkerung zu leisten, wurde im November 2003 ein neuer Weg beschritten. Es wurde ein Programm zur On-line Simulation der Kettenreaktion in einem Kernreaktor entwickelt und ins Netz gestellt. Die Ortssektion Sachsen strebt damit die folgenden Ziele an:
(1) Durch eine attraktive Darstellung der physikalischen Prozesse in einem Kernreaktor, die durch interaktive Eingriffe über die Steuerorgane beeinflusst werden können, entsteht eine Art Computerspiel, mit dem es gelingen soll, interessierten Personen - insbesondere Kindern und Jugendlichen - Einblicke in die Reaktorphysik zu ermöglichen. Dabei wird Wert darauf gelegt, die Grundprozesse qualitativ möglichst korrekt und umfassend darzustellen, um einen hohen Bildungseffekt zu erreichen.
(2) Durch die spielerische Erschließung des Stoffes soll die emotionale Barriere, die häufig gegenüber der Kerntechnik besteht, abgebaut werden, um die Besucher der Internetseite an weitergehenden Informationen zu interessieren und die Aufgeschlossenheit für weitere Diskussionen und Argumente zu erhöhen.
(3) Durch ständige Weiterentwicklung sollen in monatlichen Abständen jeweils neue Versionen des Programms mit erweiterten Möglichkeiten angeboten werden, um eine Art Fangemeinde entstehen zu lassen, die der Internetseite ihre Treue hält. Das Programm wurde in der Programmiersprache DELPHI erstellt. Der unter WINDOWS ausführbare Code (EXE) kann zusammen mit einem Manual, welches die physikalischen
Hintergründe in populärwissenschaftlicher Weise beschreibt und dem Anwender numerische Experimente vorschlägt, von der Webseite heruntergeladen werden.

Keywords: Education; Reactor Physics; Public Relation; Monte-Carlo Simulation

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2004, 25. - 27. Mai 2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2004, 25. - 27. Mai 2004, Düsseldorf, Germany, paper 495-500

Publ.-Id: 6347

Effect of excess vacancies in ion beam synthesis of SiC nanoclusters

Kögler, R.; Eichhorn, F.; Mücklich, A.; Skorupa, W.; Serre, C.; Perez-Rodriguez, A.

SiC nanoclusters are synthesized in Si by simultaneous dual implantation using two ion beams, of C and Si ions. This implantation mode is associated with extra excess vacancy generation. The effect of vacancies on SiC synthesis is investigated in this study. The amount of synthesized SiC is compared for different implantation modes, simultaneous and sequential ones. Sequential pre-deposition of vacancy defects in Si before the C implantation is performed by additional Si and He implantation. The simultaneous dual beam implantation is found to be the only method to improve SiC synthesis. The introduction of vacancies, both excess vacancies and He induced vacancies, by a sequential implantation process is disadvantageous for SiC nanocluster formation. The pre-deposition of vacancy defects is accompanied with higher crystal damage and/or the defects are annealed out during the subsequent C implantation at temperatures above 400oC. Vacancies must be created “in-situ” during C implantation to achieve enhanced output of SiC.

Keywords: Ion implantation; Simultaneous dual implantation; SiC; Si; Ion beam synthesis

  • Vacuum 78(2005)2-4, 177-180

Publ.-Id: 6346

Excess vacancies induced by ion beam implantation into silicon

Kögler, R.; Eichhorn, F.; Peeva, A.; Voelskow, M.; Mücklich, A.; Serre, C.; Skorupa, W.

The process of formation of excess vacancies by ion implantation is explained. Moreover, the simulation of the process, the experimental detection of excess vacancies and their application for defect engineering is described.

Keywords: Ion implantation; Silicon; Excess vacancies; Electron microscopy; Positron annihilation spectrometry

  • Lecture (Conference)
    V th international conference on ion implantation and other applications of ions and electrons, ION2004, June 14-17, 2004, Kazimierz Dolny, Poland

Publ.-Id: 6345

Generation eines Pseudomonas aeruginosa Biofilms auf Biotit und dessen mikroskopische Charakterisierung.

Großmann, K.; Arnold, T.; Bernhard, G.; Garske, B.; Krawietz, R.

Zum Studium der Wechselwirkungen von Schwermetallen mit Biofilmen in der Umwelt ist die reproduzierbare Präparation und detaillierte Charakterisierung von Biofilmen auf Mineral- und Gesteinsoberflächen notwendig. Die initialen Aufwachsstadien von auf Biotit erzeugten Pseudomonas aeruginosa Biofilmen wurden mit Rasterelektronenmikroskopie (SEM) und Rasterkraftmikroskopie (AFM) visualisiert. Zum Studium des reifen Biofilms wurden Fluoreszenzmikroskopie und konfokale Fluoreszenzmikroskopie (CLSM) eingesetzt. Die Unterscheidung zwischen lebenden und toten Bakterien erfolgte mit Hilfe eines LIVE/DEAD - Kit. Zur Visualisierung von Polysacchariden innerhalb der EPS wurden Lektine gekoppelt mit Fluoreszenzfarbstoffen verwendet. Hierbei konnten die einzelnen Polysaccharide der EPS unterschieden werden in solche, die direkt an Zellwände der Bakterien gebunden sind und weitere, die eine diffuse Verteilung der EPS im Biofilm aufzeigen. Die Dicke der erzeugten Biofilme auf den Biotitoberflächen wurde mit CLSM bestimmt. Sie schwankte zwischen 5,3 µm für Biofilme, die unter Nährstoffmangel angezogen wurden, und 16,6 µm bei ausgereiften Biofilmen.

Keywords: Biofilm; Pseudomonas aeruginosa; Mikroskopie; Fluoreszenzfarbstoffe; Lectine

  • GWF-Wasser/Abwasser 146(2005) 2, 113-118

Publ.-Id: 6344

Validation of models for bubble forces

Lucas, D.; Krepper, E.; Prasser, H.-M.

Closure laws are needed for the qualification of CFD codes for two-phase flows. In case of bubbly and slug flow, the momentum transfer between the phases is usually modelled by forces acting on the bubbles. These forces depend on the liquid flow field as well as on the size and the shape of the bubbles. To validate models for these forces a detailed database for vertical pipe flow is used. It contains not only the information on the radial distribution of bubbles of different size, but also information on the bubble size distribution. Measurements were done for a large number of combinations of gas and liquid superficial velocities and for two different pipe diameter (DN50 and DN200). An one-dimensional model, which resolves the variables in radial direction and which considers a large number of bubble size classes to account for the size effect, is used for an analysis of models for these forces. The results obtained by this model were compared to 3D results obtained by the commercial code CFX-5.7 for simplified cases with only one bubble class. The effect of the number of bubbles classes as well as the effect of the lateral extension of the bubbles were analysed. For the validation of the bubble forces measured bubble size distributions were taken as an input for the model. On basis of the assumption of an equilibrium of the lateral bubble forces, radial volume fraction profiles were calculated separately for each bubble class. In the result of the validation of different models for the bubble forces, a set of Tomiyama lift and wall force and the Favre averaged turbulent dispersion force was found to reflect the experimental data with best agreement. Some discrepancies remain at high liquid superficial velocities.

Keywords: Two-phase flow; bubble; bubble forces; modelling; CFD

  • Lecture (Conference)
    42nd European Two-Phase Flow Group Meeting, 23.-25.06.2004, Genua, Italy
  • Contribution to proceedings
    42nd European Two-Phase Flow Group Meeting, 23.-25.06.2004, Genua, Italy, paper E1

Publ.-Id: 6342

Atomic computer simulations of defect migration in 3C and 4H-SiC

Gao, F.; Weber, W. J.; Posselt, M.; Belko, V.

Knowledge of the migration of intrinsic point defects is crucial to understand defect recovery, various annealing stages and microstructural evolution after irradiation or ion implantation. Molecular dynamics (MD) and the nudged-elastic band method have been applied to investigate long-range migration of point defects in SiC over the temperature range from 0.36 to 0.95 Tm , and the defect diffusion coefficient, activation energy and defect correlation factor have been determined. The results show that the activation energies for C and Si interstitials in 3C-SiC are about 0.74 and 1.53 eV, respectively, while it is about 0.77 eV for a C interstitial in 4H-SiC. The minima energy paths reveal that the activation energies for C and Si vacancies are about 4.1 and 2.35 eV, respectively. Finally, the results are discussed and compared with experimental observations and available ab initio data.

Keywords: Defect diffusion; activation energy; molecular dynamics; nudged-elastic band method

  • Contribution to external collection
    Materials Science Forum, 457-460; Part 1 (2004), 457-460

Publ.-Id: 6341

Development of a SAXS-Method to characterize the damage zone around a crack tip in metals

van Ouytsel, K.; Müller, G.

The aim was to characterize the damage zone ahead a crack tip in technical aluminium alloys using Small Angle X-ray Scattering. Experiments were conducted at the Austrian beamline at ELETTRA in Trieste from 18th-24th of February 2003. Four specimens of 2024-T351 aluminium alloy, different in shape, deformation condition and grain size, were investigated. Anisotropic grain boundary scattering of the CT-specimen was observed.

Keywords: Small Angle X-ray Scattering (SAXS); damage zone; crack tip

  • Contribution to external collection
    Austrian Small Angle X-ray Scattering (SAXS) Beamline at ELETTRA, Annual Report 2003, published 2004, 51-52

Publ.-Id: 6340

Simultaneous Determination of 226Ra, 233U and 237Np by Liquid Scintillation Spectrometry

Nebelung, C.; Baraniak, L.

A method has been developed for the simultaneous determination of 226Ra, 233U and 237Np by liquid-scintillation (LS) spectrometry. This method consists in the evaluation of strongly overlapped multi peak spectra by a special peak fit function, considering the deviation of the LS-peak shape from the pure Gaussian distribution. First 237Np is determined using its daughter 233Pa by analyzing the ß-spectrum. 226Ra follows from the α-spectrum recorded 6 weeks after sample preparation. The peak of the three short-lived daughters 222Rn, 218Po and 214Po corresponds to the 226Ra activity under radioactive equilibrium conditions. Finally the 233U activity results from the joint α-peak at 4.8 MeV of the deconvoluted spectrum by subtracting the activity of 226Ra and 237Np. A second option uses the characteristic double peak of 237Np near 4.8 MeV. Due to the fact that the position is accurately known the pure α-spectrum can be analyzed for the determination of the given nuclides.

Keywords: Liquid scintillation; Alpha-Beta- Separation; Deconvolution of Multielement spectra

  • Applied Radiation and Isotopes, 65 (2007) 209-217

Publ.-Id: 6337

Molecular Bacterial Diversity in Water at the Deep-Well Monitoring Site Tomsk-7

Nedelkova, M.; Radeva, G.; Selenska-Pobell, S.

Bacterial diversity was studied in a water sample collected from a depth of 290-324 m below the land surface from the monitoring site S15 near the city of Tomsk, Siberia, Russia. In order to overcome the problems of culturability of bacteria, we applied a direct molecular approach based on PCR amplification and cloning of the 16S rDNA of the members of the natural bacterial communities. 65% of the cloned sequences were almost identical to the 16S rRNA genes of Dechlorosoma sp. belonging to the Rhodocyclus group of b-subclass of Proteobacteria. Relatively high was the number of the sequences which shared high identities with the 16S rRNA genes of some cultured g-Proteobacteria (6.9%), a-Proteobacteria (4.6%) and with the sequences of mostly uncultured members of Cytophaga/Flavobacterium/Bacteroides (5.4%), Actinobacteria (4.6%) and Planctomycetales (2.3 %). The rest of the retrieved sequences were clustered in small groups, each containing about 1 % of the total number of clones, and they matched with 16S rDNA sequences of Bacillales, Holophaga/Acidobacteria, Nitrospira, and d-Proteobacteria, respectively.

  • Contribution to external collection
    Chin-Fu Tsang and John A. Apps: Developments in Water Science, Underground Injection Science and Technology, Netherlands: Elsevier, 2005, 978-0-444-52068-5, 521-536

Publ.-Id: 6336

Time-Dependent Kinematic Dynamos in Finite Cylinders as Treated with the Integral Equation Approach

Xu, M.; Stefani, F.; Gerbeth, G.

Dynamo action is generally accepted as the source of cosmic magnetic fields, such as the fields of planets, stars and galaxies. The understanding of dynamos has considerably progressed during the last decades. Recently, the hydromagnetic dynamo effect has been demonstrated experimentally in large liquid sodium facilities in Riga and Karlsruhe.
The electrically conducting fluid is usually confined to a finite domain which is surrounded by an insulator. For only a few cases, such as spheres or cylinders with infinite length, the boundary conditions for the magnetic field are easily implementable. In most cases, including finite cylinders which are relevant for the liquid sodium experiments in Riga, Karlsruhe, Cadarache and New Mexico, the correct handling of the non-local boundary conditions is far from trivial. We have re-formulated Pre-Maxwell's equations to an integral equation system under the assumption that the velocity field is stationary.
The main advantage of this approach is that the numerical solution of the integral equation system does not require any discretization of the exterior region.
In the present work, the integral equation approach is performed on a group of Beltrami flows (and some modifications) with the topologies s2t2, s2t1 and s1t1 in a finite cylinder. Beltrami flows are characterized by maximum helicity for a given magnetic Reynolds number. Due to the axisymmetry of these flows, the integral equation system in the cylindrical system is reduced to a two-dimensional form.
The calculated results show a good agreement with those obtained by a differential equation approach. This integral equation approach exhibits attractive features such as robustness and stability.
The impact of a stagnant conducting layer surrounding the cylinder is also investigated. Such a layer can reduce the critical magnetic Reynolds number significantly, and it can even transform no-dynamos into dynamos. Interestingly, the presence of a layer can also change an oscillatory dynamo to a steady dynamo.

  • Lecture (Conference)
    7th MHD-Days, Technische Universität Ilmenau, 20.-21.09.2004, Ilmenau, Germany

Publ.-Id: 6335

Application of gamma tomography to the measurement of fluid distributions in a hydrodynamic coupling

Hampel, U.; Hoppe, D.; Diele, K.-H.; Fietz, J.; Höller, H.; Kernchen, R.; Prasser, H.-M.; Zippe, C.

Gamma tomography has been used to investigate the fluid distribution within multiple axial planes of a hydrodynamic test coupling under operating conditions. The tomographic data was obtained by phase correlated averaging of projections from the homogeneously rotating parts of the coupling. By application of the filtered backprojection reconstruction technique to the data we reconstructed average fluid fraction distributions in the transversal planes at different operating points of the coupling.

Keywords: gamma tomography; hydrodynamic coupling; two-phase flow measurement

  • Flow Measurement and Instrumentation 16(2005), 85-90

Publ.-Id: 6334

Overview of the present status of the SRF gun design and construction

Teichert, J.; Evtushenko, P.; Janssen, D.; Lehmann, W.-D.; Lehnert, U.; Michel, P.; Schneider, C.; Stephan, J.; Volkov, V.; Will, I.

A status report on the SRF photo-injector activities at FZR within the CARE/PHIN project will be given. The new SRF gun has been designed for CW operation at the ELBE linac with an average current of 1 mA, 77 pC bunch charge, and 10 MeV energy. The basic concept of the gun, operating a normal conducting, thermally insolated photo-cathode within a superconducting cavity, have been taken from the first SRF half-cell gun [1] which was successfully tested. In this report the design layout of the SRF photo-injector, the parameters of the superconducting cavity and the expected electron beam parameters are presented. The SRF gun will have a 31/2-cell niobium cavity working at 1.3 MHz and will be operated at 2 K. The cavity consists of three full cells with TESLA-like shapes and a half-cell in which the photocathode is situated.

Keywords: SRF photo-injector; electron source; superconductivity; niobium cavity; electron acceleration

  • Lecture (Conference)
    1st Workshop of ELAN, 04.-06.05. 2004, Frascati, Rom, Italy
  • Contribution to proceedings
    1st Workshop of ELAN, 04.-06.05.2004, Frascati, Italy CARE-Note-2004-010-ELAN

Publ.-Id: 6333

Study of e+,e production in elementary and nuclear collisions near the production threshold with HADES

Salabura, P.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bellia, G.; Belvers, D.; Bielcik, J.; Böhmer, M.; Bokemeyer, H.; Boyard, J.; Braun-Munzinger, P.; Chepurnov, V.; Chernenko, S.; Christ, T.; Coniglione, R.; Diaz, J.; Djeridi, R.; Dohrmann, F.; Duran, I.; Eberl, T.; Emeljanov, V.; Fabbietti, L.; Fateev, O.; Fernandez, C.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Fuentes, B.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzalez, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Hoffmann, J.; Holzmann, R.; Ierusalimov, A.; Iorii, J.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanakir, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kotte, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Kurtukian-Nieto, T.; Lang, S.; Lehnert, J.; Maiolino, C.; Marn, J.; Markert, J.; Metag, V.; Montes, N.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Panebratsev, Y.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Przygoda, W.; Rabin, N.; Ramstein, B.; Reshetink, A.; Ritmanh, J.; Rodriguez-Prieto, G.; Roy-Stephan, M.; Rustamov, A.; Sabin-Fernandez, J.; Sadovsky, A.; Sailer, B.; Sanchez, M.; Smolyankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; C., S.; Sudol, M.; Titov, A.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Vazquez, A.; Volkov, Y.; Wagner, V.; Walus, W.; Winkler, S.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.

HADES is a second generation experiment designed to study dielectron production in proton, pion, and heavy ion induced reactions at the GSI accelerator facility in Darmstadt. The physics programme of HADES is focused on in-medium properties of the light vector mesons. In this contribution we present status of the HADES experiment, demonstrate its capability to identify rare dielectron signal, show first experimental results obtained from C+C reactions at 2 A GeV and shortly discuss physics programme of up-coming experimental runs.

  • Progress in Particle and Nuclear Physics 53(2004), 49

Publ.-Id: 6329

Uranium binding by the natural isolate Bacillus Sphaericus JG-A12 and its application for bioremediation

Raff, J.; Merroun, M.; Rossberg, A.; Foerstendorf, H.; Selenska-Pobell, S.

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. Similarly to some other Bacillus isolates from this site, cells and spores of B. sphaericus JG-A12 bind selectively and reversibly large amounts of different toxic metals, such as uranium /1/. The cells of the B. sphaericus strain JG-A12 are covered by a surface layer (S-layer) protein. The latter forms a highly ordered lattice with distinct structural and chemical properties. Because it was shown that S-layers may work as protective coat, matrix for biomineralization, molecular sieve or as ion and molecule trap /2, 3, 4/ their special importance for the interaction of cells with radionuclides and heavy-metals in the surrounding environment is evident. As a consequence of the above mentioned properties, B. sphaericus JG-A12 was investigated with regard to its suitability to work as a binding matrix for bioremediation of uranium mining waste waters. A fundamental requirement for biotechnological application is the complete immobilization of the biomass in a porous structure. In this work, sol-gel techniques were used for embedding B. sphaericus JG-A12 cells, spores and S-layer protein in a SiO2-matrix in order to obtain a novel kind of biological ceramic (biocer) /5/. To select the appropriate filter material, uranium sorption and desorption experiments were carried out with free and immobilized cells, spores and S-layer protein of B. sphaericus JG-A12. Besides quantification of the available binding sites, the formed uranium complexes were investigated also by using infrared and extended X-ray absorption fine structure (EXAFS) spectroscopy. The latter revealed that the binding of uranium by free cells, spores and S-layer occurred via phosphate and carboxyl groups. The presence of phosphate groups was confirmed by different methods not only for cells and spores but also for the S-layer protein. The spectroscopic analysis of the uranium complexes formed by the biocer demonstrates the metal binding via phosphate groups and the formation of a uranium precipitate, what is of special interest for the binding capacity of the biocer. In case of the xerogel uranium was bound to silanol groups. Analyses of the uranium sorption by cells, spores and S-layer protein of B. sphaericus JG-A12 and of the xerogel itself (without biocomponent) showed highest binding capacity for spores followed by cells, S-layer protein and xerogel. In case of embedded biocomponents only the binding capacity of spores is significantly reduced and is lower than for cell- and S-layer-ceramics. Uranium bound to biocers can be completely removed by washing with citric acid.

1. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67
2. Beveridge, T.J. 1979 J. Bacteriol. 139 (3): 1039-1048
3. Schultze-Lam, S. et al. (1992) J. Bacteriol. 174 (24): 7971-7981
4. Sára, M. & Sleytr, U.B. 1987. J. Bacteriol. 169 (6): 2804-2809
5. Raff, J. et al (2003) Chem. Mater 2003; 15(1):240-4

  • Lecture (Conference)
    Biometals 2004, 03.-05.09.2004, Garmisch-Partenkirchen, Germany
  • Contribution to proceedings
    Biometals 2004, 03.-05.09.2004, Garmisch-Partenkirchen, Germany

Publ.-Id: 6328

Bacterial Diversity in a Soil Sample from a Uranium Mining Waste Pile as estimated via a Culture-Independent 16S rDNA Approach

Satchanska, G.; Golovinski, E.; Selenska-Pobell, S.

Bacterial diversity was studied in a soil sample collected from a uranium mining waste pile situated near the town of Johanngeorgenstadt, Germany. As estimated by ICP-MS analysis the studied sample was highly contaminated with Fe, Al, Mn, Zn, As, Pb and U. The 16S rDNA retrieval, applied in this study, demonstrated that more than the half of the clones of the constructed 16S rDNA library were represented by individual RFLP profiles. This indicates that the composition of the bacterial community in the sample was very complex. However, several 16S rDNA RFLP groups were found to be predominant and they were subjected to a sequence analysis. The most predominant group, which represented about 13% of the clones of the 16S rDNA library, was affiliated with the Holophaga/Acidobacterium phyllum. Significant was also the number of the proteobacterial sequences which were distributed in one predominant alpha-proteobacterial cluster representing 11% of the total number of clones and in two equal-sized beta- and gamma-proteobacterial clusters representing each 6% of the clones. Two smaller group representing both 2% of the clones were affiliated with Nitrospira and with the novel division WS3. Three of the analysed sequences were evaluated as a novel, not yet described lineage and one as a putative chimera.

  • Comptes Rendues del Ácademie bulgare des Sciences 57(2004)5, 75-82


Publ.-Id: 6327

Molecular analysis of bacterial populations in water samples from two uranium mill tailings by using a RISA retrieval

Radeva, G.; Selenska-Pobell, S.

A ribosomal intergenic spacer amplification (RISA) retrieval was applied to analyze the natural bacterial communities in drain waters of two uranium mill tailings - Gittersee/Coschütz in Germany and Shiprock in the USA. About 35% of the clones from the RISA library constructed for the samples of the German tailings represented a microdiverse population of Planctomycetales. The rest of the clones were affiliated with rather diverse bacterial groups including g- and d- Proteobacteria, Cytophaga/Flavobacterium/Bacteroides (CFB), Nitrospira, Verrucomicrobia and Actinobacteria. 8% of the cloned sequences represented a novel bacterial lineage from the recently described division NC3.
Bacterial diversity in the Shiprock mill tailings was found to be significantly lower. The RISA library constructed for those samples contained only two larger groups of clones, representing b-proteobacterial species and one small group, which was affiliated with d-Proteobacteria.

  • Comptes Rendues de l´Academie bulgare des Sciences 57(2004)6, 111-115

Publ.-Id: 6326

Combined Analysis of Threshold-Near Production of ω and φ Mesons in Nucleon-Nucleon Collisions

Kaptari, L. P.; Kämpfer, B.

Vector meson (V=ω , φ) production in threshold-near elementary nucleon-nucleon collisions pp to ppV, pn to pnV and pn to dV is studied within an effective meson-nucleon theory.
It is shown that a set of effective parameters can be established to explain fairly well the available experimental data on angular distributions and the energy dependence of the total cross sections without explicit implementation of the Okubo-Zweig-Iisuka rule violation. Isospin effects are considered in details and compared with experimental data whenever available.

Keywords: bector mesons; OZI rule; hadron reactions

  • Eur. Phys. Journal A 23 (2005)291-304

Publ.-Id: 6324

Bacterial diversity in water samples from uranium wastes as demonstrated by 16S rDNA and RISA retrievals

Radeva, G.; Selenska-Pobell, S.

Bacterial diversity was assessed in water samples collected from several uranium mining wastes in Germany and in the USA by using 16S rDNA and RISA retrievals.
The results obtained using the 16S rDNA retrieval showed that the samples collected from the uranium mill tailings Schlema/Alberoda, Germany, were predominated by Nitrospina-like bacteria, whereas those from the mill tailings Shiprock, New Mexico, USA, were predominated by g-Pseudomonas and Frateuria spp. Additional smaller populations of CFB, a-, and d-proteobacteria were identified in the Shiprock samples as well. Proteobacteria and CFB were also predominant in the third uranium mill tailings studied, Gittersee/Coschütz in Germany, but the groups of the predominant clones were rather small. Most of the clones of the Gittersee/Coschütz samples represented individual sequences that indicated a high level of bacterial diversity. The samples from the fourth uranium waste studied, namely Steinsee Deponie B1 in Germany, were predominantly occupied by Acinetobacter spp.
The RISA retrieval provided results complementary to those obtained by the 16S rDNA analyses. For instance, in the Shiprock samples an additional predominant bacterial group was identified and affiliated to Nitrosomonas sp., whereas in the Gittersee/Coschütz samples Anammox-populations were identified which were not retrieved by the used 16S rDNA approach.

Keywords: bacterial diversity; 16S rDNA; ribosomal intergenic spacer amplification (RISA); uranium wastes

  • Canadian Journal of Microbiology 51(2005)11, 910 - 923

Publ.-Id: 6323

Migration of Uranium (IV)/(VI) in the Presence of Humic Acids in Quartz Sand: A Laboratory Column Study

Mibus, J.; Sachs, S.; Nebelung, C.; Bernhard, G.

The migration behavior of U(IV)/U(VI) in the presence of humic acids was studied in a laboratory quartz sand system by column experiments. It was found that humic acid influences the transport of U(IV) and U(VI). In presence of humic acid both redox species migrate nearly as fast as the groundwater flow. Retardation factors of 1.11 ± 0.03 and 1.14 ± 0.03 as well as eluate recoveries of 0.83 ± 0.09 and 0.65 ± 0.07 were determined for U(VI) and U(IV), respectively. In case of U(VI) humic acid exhibits a clear mobilizing effect compared to the humic acid-free system. There are also strong indications for a similar effect on the U(IV) transport.
The present study demonstrates that humic acids can play an important role in the migration of tetravalent actinides. Consequently, the humic colloid-borne transport of actinides has to be taken into account in performance assessment.

Keywords: Uranium(IV); Uranium(VI); Humic Acids; Quartz Sand; Migration; Adsorption

  • Journal of Contaminant Hydrology 89 (2007) 199 - 217 DOI 10.1016/j.jconhyd.2006.08.005

Publ.-Id: 6322

Biotechnological potential of bacteria from extreme environments

Raff, J.

  • Lecture (Conference)
    Internationales Sales-Meeting, 17.-18.6.2004, Lampertheim, Germany

Publ.-Id: 6320

Synthesis of a 11C-labelled Nonsteroisal Glucocorticoid Receptor Ligand as Potential Radiotracer for Imaging Brain Glucocorticoid Receptors with Positron Emission Tomography (PET)

Wüst, F.; Kniess, T.; Bergmann, R.

  • Lecture (Conference)
    12th Workshop of the Central European Division e. V. of the International Isotope Society, 17.-18.06.2004, Bad Soden, Germany
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmceuticals 47(2004), 1051-1052

Publ.-Id: 6318

18F-Labelling of a Potent Nonpeptide CCR1 Antagonist for the Diagnosis of the Alz-heimer’s Disease

Mäding, P.; Füchtner, F.; Hilger, C. S.; Halks-Miller, M.; Horuk, R.

Objectives: PET imaging of cardiac reporter gene expression holds promise for noninvasive monitoring of gene therapy. Two approaches based on herpesviral thymidine kinase gene(HSV1-tk) habe been applied. Wild-type HSV1-tk was imaged with 2´-fluoro-2´-deoxy-5[124I]-iodo-arabinofuranosyluracil([124I]FIAU), and mutant HSV1-sr39tk was imaged with 9-[4-[18F]-fluoro-3-(hydroxymethylbutyl)guanine([18F]FHBG).
Methods: Adenovirus expressing wild-type HSV1-tk(Adtk), mutant HSV1-sr39tk (Adsr39tk), or control gene (AdLacZ) were directly injected into myocarcardium of 24 rats and 8 pigs. Two days later, dynamic PET imaging was performed for 120 min after injection of [124I]FIAU or [18F]FHBG with a clinical scanner. Imaging with [13N]-ammonia was performed to identify cardiac regions of interest. Pig hearts were sliced into 5 short-axis slices for ex vivo imaging, and regional tracer uptake was analyzed.
Results: For [124I]FIAU, the largest difference of cardiac uptake between Adtk rats and controls was found at 10-30 min after injection (1.7±0.25 vs 0.87±0.22 %dose/ml, p=0.035). No difference was observed at later imaging times due to [124I]FIAU washout. For [18F]FHBG, difference between Adsr39tk rats and controls continuously increased over time and was largest at 105-120 min (1.45±0.45 vs 0.35±0.05 %dose/ml, P=0.0066). Global cardiac reporter probe kinetics in rats was confirmed by regional myocardial analysis in pigs. Transgene expression was specifically visualized by both approaches. Highest target/background ratio of [124I]FIAU in Adtk infected myocardium was 1.50±0.20 vs 2.64±0.49 for [18F]FHBG in Adsr39tk infected areas (P=0.01). In vivo results of rats were confirmed by ex vivo counting and autoradiography. In vivo segmental reporter probe uptake in pigs correlated well with those in ex vivo images.
Conclusions: Both combinations were feasible for PET of cardiac transgene expression in different species. Specific probe kinetics suggests different myocardial handling of pyrimidine ([124I]FIAU) and acycloguanosine ([18F]FHBG) derivatives. Results are in favour of [18F]FHBG because of continuous accumulation over time and higher imaging contrast.

  • Lecture (Conference)
    12th Workshop of the Central European Division e. V. of the International Isotope Society, 17.-18.06.2004, Bad Soden, Germany
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 47(2004), 1053-1054

Publ.-Id: 6317

No-carrier added synthesis of 18F-labelled nucleosides using Stille cross-coupling reactions with 4-[18F]fluoroiodobenzene

Wüst, F.; Knieß, T.

The radiosyntheses of 5-(4´-[18F]fluorophenyl)-uridine [18F]-11 and 5-(4´-[18F]fluorophenyl)-2´-deoxy-uridine [18F]-12 are described. The 5-(4´-[18F]fluoro-phenyl)-substituted nucleosides were prepared via a Stille cross-coupling reaction with 4-[18F]fluoroiodobenzene followed by basic hydrolysis using 1 M potassium hydroxide. The Stille cross-coupling rreaction was optimized by screening various palladium complexes, additives and solvents. By using optimized labelling conditions (Pd2(dba)3/CuI/AsPh3 in DMF/dioxane (1:1), 20 min at 65 °C), 550 MBq of [4-18F]fluoroiodobenzene could be converted into 120 MBq (33 %, decay-corrected) of 5-(4´-[18F]fluorophenyl)-2´-deoxy-uridine [18F]-12 within 40 min, including HPLC purification.

Keywords: Stille cross-coupling; 4-[18F]fluoroiodobenzene; nucleosides; uridine

  • Journal of Labelled Compounds and Radiopharmaceuticals 47(2004), 457-468
    DOI: 10.1002/jlcr.834

Publ.-Id: 6316

Migration of di- and tri-interstitials in silicon

Posselt, M.; Gao, F.; Zwicker, D.

A comprehensive study on the migration of di- and tri-interstitials in silicon is performed using classical molecular
dynamics simulations with the Stillinger–Weber potential. The initial di- and tri-interstitial configurations with the lowest
formation energies are determined, and then, the defect migration is investigated for temperatures between 800 and
1600 K. The defect diffusivity and the self-diffusion coefficient per defect are calculated. Compared to the mono-interstitial,
the di-interstitial migrates faster, whereas the tri-interstitial diffuses slower. The migration mechanism of the diinterstitial
shows a pronounced dependence on the temperature. Like in the case of the mono-interstitial, the mobility of
the di-interstitial is higher than the mobility of the lattice atoms during the defect diffusion. On the other hand, the triinterstitial
mobility is lower than the corresponding atomic mobility. The implications of the present results for the
analysis of experimental data on defect evolution and migration are discussed.

Keywords: Defects; diffusion; silicon; computer simulations

Publ.-Id: 6315

Electrochemical behaviour of nickel surface-alloyed with copper and titanium

Pham, M. T.; Maitz, M.; Richter, E.; Reuther, H.; Prokert, F.; Muecklich, A.

Ni was surface-alloyed with Cu, Ti or Cu + Ti by ion implantation. This material was examined for its redox and electrocatalytic activity by cyclic voltammetry. The surface was characterized by X-ray photoelectron spectroscopy, X-ray and electron diffraction, and electron and atomic force microscopy. This type of materials exhibited a unique voltammetric response of Ni and was shown to stabilize the ß modification of the Ni oxide/hydroxide. Cu modified the anodic oxidation of glucose and the oxygen evolution to a higher degree than Ti. The morphology and microstructure differed from those of bulk materials.

Keywords: Cu-Ti-Ni alloy electrodes; electrocatalysis; glucose; surface alloying; ion beams

  • Journal of Electroanalytical Chemistry 572 (2004) 185-193

Publ.-Id: 6314

On the modelling of bubbly flow in vertical pipes

Krepper, E.; Lucas, D.; Prasser, H.-M.

To qualify CFD codes for two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. Information on the local structure of the flow is also required by 1D thermal-hydraulic codes. Gas-liquid flow in vertical pipes is a very good object for studying the corresponding phenomena. Here, the bubbles move under clear boundary conditions, resulting in a shear field of nearly constant structure where the bubbles rise for a comparatively long time. The evolution of the flow within the pipe depends on a very complex interaction between bubble forces and bubble coalescence and break-up. E.g. the Lift-force, which strongly influences the radial distribution of the bubbles, changes its sign depending on the bubble diameter. Basing on extensive experimental data with a high resolution in space and time the applicability and the limits for the simulation of bubble flow with current CFD-codes are demonstrated, using the simulation of vertical pipe flow with CFX-4 as an example. Using a simplified model, parametric studies can be conducted. They give an indication for necessary improvements of the codes. Finally a possible way for the improvement of the CFD-codes is shown.

Keywords: two phase flow; bubbly flow; bubble size; vertical pipe flow; computational fluid dynamics

  • Nuclear Engineering and Design 235(2005), 597-611

Publ.-Id: 6313

Experimental and Numerical Investigations for Fragmentation and Insulation Particle Transport Phenomena in Water Flow

Hampel, R.; Kästner, W.; Alt, S.; Seeliger, A.; Krepper, E.; Grahn, A.

The paper includes the description of separate effect test facilities used for investigations with regard to the fragmentation and the transport behaviour of different insulation materials in multidimensional aqueous flow. The instrumentation of the rigs is specified, in particular modern digital image processing technologies. First experimental results are shown and discussed generated at three acrylic glass test facilities. The experimental data will be use for CFD-modelling and validation. The anticipated modeling concepts are presented and their feasibility is demonstrated. During the ongoing work further results are expected.

Keywords: debris generation; debris transport; debris sedimentation; strainer clogging; experiments; computational fluid dynamics models

  • Poster
    5th International Conference on Multiphase Flow, Yokohama, Japan, May 30–June 4, 2004, Paper No. 555
  • Contribution to proceedings
    5th International Conference on Multiphase Flow, 30.05.-04.06.2004, Yokohama, Japan, Paper No. 555

Publ.-Id: 6312

TOPFLOW tests on the structure of the gas-liquid interface in a large vertical pipe

Prasser, H.-M.; Beyer, M.; Böttger, A.; Carl, H.; Lucas, D.; Schaffrath, A.; Schütz, P.; Weiss, F.-P.; Zschau, J.

TOPFLOW is a new thermal fluid-dynamic multipurpose test facility designed for generic and applied studies of transient two phase flow phenomena.
The paper presents results obtained in air-water tests which were started in December 2002. The experiments aimed at studying the structure of a gas-liquid two phase flow in pipes of large diameter. The experimental data is used for the visualisation of the two phase flow structure as well as to obtain void fraction profiles and bubble size distributions. Additionally, a new visualisation technique is presented, that consists in the creation of virtual side projection of the flow.

Keywords: TOPFLOW; two phase flow; wire-mesh sensor; void fraction profile; bubble size distribution

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany, CD-ROM 69 - 74

Publ.-Id: 6311

Electrochemical activities in the Rossendorf MHD group

Hüller, J.; Weier, T.; Gerbeth, G.

Momentum and mass transfer during electrochemical reactions in a small cell can be significantly influenced by Lorentz forces. Depending on the magnetic field configurations, a multitude of flow fields with an accordingly large range of mass transfer conditions can be arranged. The moderate magnetic field of simple permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. The interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.

Our activities were directed to the investigation of some diffusion controled electrochemical reactions like [Fe(CN)6]3+/[Fe(CN)6]4+, Ce4+/Ce3+ and the electrodeposition of Cu2+.

Since Faradaic currents are inherently coupled to electrochemical processes, the mass transfer enhancement attainable by Lorentz force induced convection does not increase the running costs. Therefore it seems attractive to perform further studies in order to determine the underlying scaling laws.

In a second part of the discussion a fluidic microsystem is presented. The silicon-glass wafer system is produced in a micromechanic planar technology and consists of a network of microfluidic channels. The microsystem can be coupled with microsensors and actuators.

  • Lecture (Conference)
    COST F2 Symposium "Electrochemical Flow Measurements and Microfluidics", 01.-03.07.2004, Poitiers, France

Publ.-Id: 6310

The Effect of Parameter Uncertainty on Blind Prediction of Np(V) Sorption onto Haematite using Surface Complexation Modelling

Richter, A.; Brendler, V.; Nebelung, C.

Still, the KD concept of empirical distribution coefficients is the most often utilized approach for description of sorption phenomena. However, as an empirical concept it can not correctly portray the complex processes on the surfaces. A better approach is a Surface Complexation Models (SCM) capable of describing the sorption processes at the mineral-fluid interface on a scientific, quasi-thermodynamic basis. SCM are available in various versions, in which the Diffuse Double Layer Model (DDL), Constant Capacitance Model (CC) and Triple Layer Model (TL) are the most important and applied submodels.
Certainly, during the next decade SCM will replace KD only in some simple systems or systems dominated by one mineral. However, SCM can help to verify measured KD's, to identify the most sensitive experimental parameters, to assign uncertainty limits, to fill gaps difficult to access in sorption experiments, and to help to gain a better process understanding.
RES³T [1]– the Rossendorf Expert System for Surface and Sorption Thermodynamics - is a digitized version of a thermodynamic sorption database as required for the parametrisation of SCM, namely in risk assessment studies.
As an example to illustrate the effect of parameter uncertainty in blind predictions the Np(V) sorption onto haematite was selected.

Keywords: surface complexation modelling; uncertainty analysis; RES3T; blind prediction; Np(V) soerption

  • Lecture (Conference)
    NRC 6 - Sixth International Conference on Nuclear and Radiochemistry, 29.08.-03.09.2004, Aachen, Germany
  • Contribution to external collection
    Advances in Nuclear and Radiochemistry, Schriften des FZ Jülich, 3(2004), 493-495

Publ.-Id: 6307

Slow positron annihilation spectroscopy – a tool to characterize vacancy-type damage in ion-implanted 6H-SiC

Brauer, G.; Anwand, W.; Coleman, P. G.; Skorupa, W.

Slow Positron Implantation Spectroscopy (SPIS), based on the generation, implantation and subsequent annihilation of mono-energetic positrons in a sample, is used to study depth dependent vacancy-type damage in ion-implanted 6H-SiC. The derivation of physical information from the Doppler-broadened annihilation lineshape is exemplified. It is found that the depth profile of vacancy-type damage formed in SiC co-implanted by Al+ and N+ at 800 °C, and subsequently annealed at 1200 °C and 1650 °C, strongly depends on the sequence of implantations and on annealing conditions. These studies show that annealing at 1650 °C for 10 minutes is not sufficient to remove the vacancy-type damage created by ion implantation.

Keywords: ion implantation; silicon carbide; depth dependent defect profile; positron

  • Vacuum 78(2005), 131-136

Publ.-Id: 6305

Annual Report 2003 - Institute of Radiochemistry

Bernhard, G.; Engelmann, H.-J.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-400 2004
    ISSN: 1437-322X


Publ.-Id: 6302

Annual Report 2003 - Institute of Ion Beam Physics and Materials Research

von Borany, J.; Heera, V.; Helm, M.; Jäger, H. U.; Möller, W.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-396 2004
    ISSN: 1437-322X


Publ.-Id: 6301

The MHD α2-dynamo: operator pencil, pseudo-Hermiticity, level crossings, spectral phase transitions

Günther, U.; Stefani, F.; Gerbeth, G.

The lecture is splitted into three parts. In its first part, a brief introduction is presented into the underlying physics of the dynamo effect of magnetohydrodynamics (MHD), in order to make clear the motivation of the subsequent mathematical considerations. Paleomagnetic evidences for fields reversals of the geomagnetic field are discussed, as well as the results of the Riga dynamo experiment. Special emphasis is laid on the planned next generation dynamo experiments.

In the second part of the lecture, the basic operator-theoretic properties of the 2×2 operator matrix of the spherically symmetric α2-dynamo are discussed: its pseudo-Hermiticity in the case of idealized boundary conditions (with corresponding representation of the operator in a Krein space as indefinite generalization of a Hilbert space), and the general lack of symmetry and Hermiticity for physically realistic boundary conditions. A brief summary is given of the results of Ref. [1] on testing the operator struture on its compatibility with an operator intertwining technique as descriptive tool for possibly existing isospectral classes of dynamo operators. A corresponding no-go theorem is discussed for first-order differential operators as intertwiners.

Subject of the third part of the lecture are recent results on spectral phase transitions. Such phase transtions from non-oscillating dynamo regimes to oscillating regimes occur at two-fold degenerate level-crossing points of the spectrum (exceptional points), where two real-valued branches of the spectrum cross and leave the real axis to develop as pair of complex conjugate branches. Some general properties of the spectrum in the vicinity of the exceptional points are discussed. For this purpose, the linear eigenvalue problem of the 2×2 operator matrix is reformulated as equivalent eigenvalue problem of an associated quadratic operator pencil. Special emphasis is laid on the differences of exceptional points for quantum mechanical operators in Hilbert spaces and for pseudo-Hermitian operators in Krein spaces.

The lecture is completed by a discussion of open operator theoretic problems with relevance for the planned next generation dynamo experiments.

[1] Günther U. and Stefani F., Isospectrality of spherical MHD dynamo operators: pseudo-Hermiticity and a no-go
theorem, J. Math. Phys. 44, 2003, 3097, math-ph/0208012.

Publ.-Id: 6300

Machbarkeitstudie für einen industriellen supraleitenden Table Top Elektronenbeschleuniger

Schneider, C.; Büttig, H.; Enghardt, W.; Gabriel, F.; Janssen, D.; Michel, P.; Pobell, F.; Prade, H.; Kudryavtsev, A.; Haberstroh, C.; Sandner, W.; Will, I.

At the Forschungszentrum Rossendorf the build-up of the superconducting 1.3 GHz accelerator ELBE is still in progress. Furthermore a new sc photo injector (SRF gun) is under development, which should accelerate electrons up to 10 MeV at 1.3 GHz frequency. The use of electron accelerators is also more and more interesting for applications where the destructive potential of the electrons are used like sterilization of medical waste and medical products, food irradiation or decontamination of sewage. For these processes a high power is required to achieve a high product throughput in a plant. The aim is therefore to use beam powers of around 100 kW or more. Since the applications of electron accelerators in industrial environments are steadily increasing one can speculate about transferring the above named state of the arte technology to industrial electron accelerators. At the FZR a feasibility study of such a table top electron accelerator (TTE) has been performed to investigate its technical limits and marketabilitys.

Keywords: Industrieller Beschleuniger; Fotoemissionskatode; Laser induzierte Emission; Präparationskammer zur Katodenbedampfung; Fotokatode in Beschleunigungskavität; supraleitender Resonator; superconducting cavity; Strahlleistung 50 kW; Strahlenergie 10 MeV; Kryostat; Sterilisation; Entkeimung; Lebensmittelbestrahlung; Lebensmittelpasteurisierung; Beseitigung organischer Schadstoffe; Kunststoffvernetzung

  • Open Access Logo Wissenschaftlich-Technische Berichte FZR-410 2004
    ISSN: 1437-322X


Publ.-Id: 6299

Performance of differently orientated PV modules - results of a long time measuring program

Rindelhardt, U.; Futterschneider, H.

For 10 years an irradiation measuring field has been operated at FZR near Dresden. It consisted of 12 modules with different tilt and azimuth angles. The yearly mean values of the generated DC-energy are presented and directly compared with the predictions of the PEREZ model. The main result of the measurements is the providing of typical module DC power distributions. This distributions can be used to determine the optimal module/inverter power ratio of grid connected PV plants. For nearly optimal orientated generators this ratio should be one. Further a revision of the widely used “European Efficiency” of inverters is suggested, which is based on new weighting factors derived from the measurements. For PV plants a maximum performance ratio of 84% could be estimated. Finally the matching of the daily electricity load with PV plants in Germany is discussed. The load peak in Germany can be covered by an installed PV capacity of 45 GW.

Keywords: PV modules; grid connected; performance

  • Poster
    19th European Photovoltaic Solar Energy Conference and Exhibition, 07.-11.06.2004, Paris, France
  • Contribution to proceedings
    Proceedings on. 19th European Photovoltaic Solar Energy Conference and Exhibition, 07.-11.06.2004, Paris, France

Publ.-Id: 6297

Chrombeschichtung von Baustahl mittels Ionenstrahlbehandlung

Reuther, H.; Richter, E.; Prokert, F.; Ueda, M.; Beloto, A. F.; Gomes, G. F.

Zur Verbesserung des Korrosionsverhaltens von Baustahl wurde versucht, durch Rückstoßimplantation bzw. Ionenstrahlmischen seine Oberfläche mit einer chromreichen Schicht zu versehen. Dazu wurde polierter Baustahl (SAE 1020) mit Chrom bedampft und anschließend mit Stickstoffionen bestrahlt. Der Ionenbeschuß erfolgte sowohl durch direkte Ionenimplantation als auch durch Plasmaimmersions-Ionenimplantation.

Die so hergestellten Proben wurden mittels Augerelektronenspektroskopie, Konversionselektronen-Mößbauerspektroskopie und Röntgendiffraktometrie untersucht. Die Kombination dieser Verfahren gestattete eine ausreichende Charakterisierung der erzeugten Oberflächenschichten. Während die Schichtung Chrom/Stahl durch die direkte Ionenimplantation kaum verändert wurde, entstand durch die Plasmaimmersions-Ionenimplantation eine (Eisen/Chrom)-Nitridschicht auf der Stahloberfläche.

Nach der Behandlung wurden die Oberflächenhärte und das Korrosionsverhalten bestimmt und mit dem Ausgangszustand verglichen. Während sich bei den direkt implantierten Proben nur die Härte leicht erhöhte, nahm bei den durch Plasmaimmersions-Ionenimplantation behandelten Proben die Korrosionsbeständigkeit zu, so dass für den gewünschten Zweck dieses Verfahren das geeignetere ist.

  • Lecture (Conference)
    13. Arbeitstagung Angewandte Oberflächenanalytik (AOFA 13), 14.-17. September 2004, Dresden, Deutschland

Publ.-Id: 6296

Tomografische Rekonstruktion zweier asynchron rotierender Objekte am Beispiel einer hydrodynamischen Kupplung

Hoppe, D.; Hampel, U.; Zippe, C.; Prasser, H.-M.; Kernchen, R.

Zwei asynchron rotierende Objekte sollen gemein-sam tomografisch rekonstruiert werden. Dafür werden tomografische Projektionen immer nur dann vorgenommen, wenn beide Objekte eine bestimmte Relativposition zueinander aufweisen. Die Objekte erscheinen dadurch wie fest miteinander verbunden. Vorhandene radiale Symmetrien der Objekte können ausgenutzt werden. Als praktisches Anwendungsbeispiel dient eine hydrodynamische Kupplung.

Keywords: Tomografie; asynchrone Drehungen; hydro-dynamische Kupplung

  • Technisches Messen 2004(2004)12, 634-639

Publ.-Id: 6295

Virtuelle tomografische Rekonstruktionsbilder infolge ungeeigneter Abtastraten

Hoppe, D.

Bei tomografischen Bildrekonstruktionen können zu große Detektorabstände oder zu wenige Projektionen Aliasing-Artefakte hervorrufen. Betrachtet werden Objekte, die eine drehsymmetrische Struktur enthalten. Von ihr entsteht neben dem reellen auch ein virtuelles tomografisches Abbild. Gezeigt wird, dass es schwierig sein kann, ein solches virtuelles Abbild als Aliasing-Artefakt zu identifizieren.

Keywords: Tomografie; Drehsymmetrie; Nyquist-Frequenz; Aliasing-Artefakte

  • Technisches Messen 2004(2004)12, 640-642

Publ.-Id: 6294

New possibilities for velocity measurements in liquid metals by potential probes

Varshney, K.; Cramer, A.; Gerbeth, G.

The improved resolution of potential probe measurements allowed to investigate the turbulent properties of flows driven by various types of alternating magnetic fields. Results will be presented on the turbulent spectra of such flows and the spatio-temporal changes of the mean velocity profiles.

  • Lecture (Conference)
    International. Workshop on "The History of Magnetohydrodynamics", 26.-28.05.2004, Coventry, Great Britain

Publ.-Id: 6293

Magnetic field control in aluminum investment casting and the problem of electromagnetic flow rate measurements

Buchenau, D.; Eckert, S.; Witke, W.; Gerbeth, G.

The magnetic control of aluminium investment casting is presented as an example of metallurgical applications of external magnetic fields.

  • Lecture (Conference)
    International. Workshop on "The History of Magnetohydrodynamics", 26.-28.05.2004, Coventry, Great Britain

Publ.-Id: 6292

Electromagnetic seawater flow control - from old ideas to recent results

Gerbeth, G.; Weier, T.; Shatrov, V.; Mutschke, G.

Recent results on separation control with steady and unsteady Lorentz forces will be presented, embedded into the 40 years history of electromagnetic seawater flow control.

  • Lecture (Conference)
    International. Workshop on "The History of Magnetohydrodynamics", 26.-28.05.2004, Coventry, Great Britain

Publ.-Id: 6291

Overview of the WWER-440 Benchmark Results

Boehmer, B.

The preliminary results of the REDOS project participants for neutron and gamma fluence spectrum integrals obtained for two VVER-440 pressure vessel benchmarks at the LR-0 reactor in Rez have been analyzed. The results of different calculations have been compared with each other and with experiments. The influence of the scintillation detectors on the measurement results was discussed.

  • Lecture (Conference)
    REDOS Progress Meeting, 01.-02.04.2004, Budapest, Hungary

Publ.-Id: 6290

Hydrogen in a natural Pd-O compound from Gongo Soco, Minas Gerais, Brazil

Cabral, A. R.; Lehmann, B.; Grambole, D.; Herrmann, F.

The existence of hydrogen in Pd–O-bearing aggregates, which together with iron oxides form the characteristic dark encrustation of an ouro preto nugget of Gongo Soco, Minas Gerais, Brazil, is confirmed by elastic recoil detection analysis with a heavy-ion microbeam (micro-ERDA). Hydrogen is lost from Pd–O-bearing areas during the micro-analyses, but not from goethite.
The data indicate that the Pd–O–H phase is unstable compared to goethite, giving support to previous observations that it is a transient phase in a transformation to native palladium.

Keywords: : hydrogen; elastic recoil detection analysis; Pd–O-bearing compound; ouro preto nugget; Gongo Soco; Minas Gerais; Brazil

  • Canadian Mineralogist 42(2004), 689-694

Publ.-Id: 6289

Summary of the WWER-1000 Benchmark Results

Boehmer, B.

The final results of the REDOS project participants for neutron and gamma fluence spectrum integrals obtained for the VVER-1000 pressure vessel benchmark at the LR-0 reactor in Rez had been analyzed. The comparison of different calculations with each other and of calculations with experiments showed in both cases reasonable agreement.

Keywords: Benchmark; LR-0 reactor; neutron and gamma spectrum calculation and measurement; VVER-1000 reactor

  • Lecture (others)
    REDOS Progress Meeting, April 1-2, 2004, Budapest, Hungary

Publ.-Id: 6288

Results of TRAMO-Calculations of WWER-440 Mock-up Experiments in the LR-0 Reactor

Konheiser, J.

Neutron and gamma fluence results for the VVER-440 mock-up at the LR0-reactor in Rez, that were calculated with the Monte Carlo Code TRAMO had been compared with measured data. A reasonable agreement between calculation results and experimental data was reached.

  • Lecture (others)
    REDOS Progress Meeting, April 1-2 2004 Budapest, Hungary

Publ.-Id: 6287

Shielding Design of the PANDA Spectrometer at the Munich High-Flux Reactor FRM-II

Noack, K.; Pyka, N.; Rogov, A.; Steichele, E.

The start-up of the Munich high-flux reactor FRM-II is going on. At the beam tube SR-2 the spectrometer PANDA has been installed. It is a three-axis neutron spectrometer looking onto a slightly under-moderated cold neutron source. For polarization analysis PANDA is equipped with a vertical cryo-magnet producing fields up to 14.5 Tesla at the sample. To get an appropriate shielding of the high-intensity instrument one had to take into account the large cross-section of the primary beam, several restrictions using magnetic materials, limitations in loading the site and, finally, one had to keep the lateral extent of the shielding small to allow for high scattering angles. The shielding has been designed on the base of results which were achieved by the combined use of both the Monte Carlo code MCNP-4B2 and an analytical method based on one-dimensional dose transmission functions.

Keywords: Shielding Design; Neutron/Gamma Transport; High-Flux Reactor FRM-II; PANDA Spectrometer; Monte Carlo Calculations; MCNP Code

  • Lecture (Conference)
    International Conferences ICRS-10/RPS 2004, 09.-14.05.2004, Funchal, Madeira Island Portugal
  • Radiation Protection Dosimetry 115(2005)1-4, 262-267
    DOI: 10.1093/rpd/nci158

Publ.-Id: 6286

Results of TRAMO-Calculations of WWER-1000 Mock-up Experiments in the LR-0 Reactor

Konheiser, J.

Neutron and gamma fluence results for the VVER-1000 mock-up at the LR0-reactor in Rez, that were calculated with the Monte Carlo Code TRAMO had been compared with measured data. A reasonable agreement between calculation results and experimental data was reached. Additionally, results obtained with different energy group structures were compared.

Keywords: Monte Carlo calculation TRAMO LR-0; mock-up VVER-1000

  • Lecture (others)
    REDOS Progress Meeting, September 3-6 2003, Elena Bulgaria

Publ.-Id: 6285

Creation and evaluation of the VVER-1000 Balakovo-3 ex-vessel dosimetry benchmark for the NEA SINBAD data base

Borodkin, G.; Boehmer, B.; Noack, K.; Khrennikov, N.

A new neutron dosimetry benchmark of the NEA SINBAD Data Base is described. This full-scale reactor benchmark, based on VVER-1000 ex-vessel neutron activation measurements performed at the Balakovo NPP, Unit 3 (Balakovo-3), is a result of several years of thorough measurements and calculations. With regard to evaluation of measured and calculated results an international intercomparison study played a key role. This interlaboratory comparison produced the reference measured data expressed as end-of-irradiation activities of reaction products of the reactions: 237Np(n,f), 238U(n,f), 93Nb(n,n'), 58Ni(n,p), 54Fe(n,p), 46Ti(n,p) and 63Cu(n,a). A comprehensive analysis of reactor data used for creating the computational models has been performed. Special attention was paid to the analysis of the reliability of the absolute neutron source distributions. Results of calculations performed by various discrete ordinates and Monte Carlo codes have been used for the benchmark evaluation. It turned out that these calculation results are in agreement within 12 % with the reference measured data. The experience gained by creation and evaluation of the full-scale power reactor benchmark is discussed in the paper.

Keywords: neutron activation measurements; fast neutron benchmark; data base; reactor pressure vessel embrittlement; verification of neutron fluence calculations

  • Lecture (Conference)
    ICRS-10 / RPS 2004 Conferences, 09.-14.05.2004, Funchal, Madeira, Portugal

Publ.-Id: 6284


Prasser, H.-M.; Böttger, A.; Zschau, J.; Baranyai, G.; Ezsöl, G.

  • Lecture (Conference)
    11th International Conference on Nuclear Engineering Tokyo, JAPAN, April 20-23,2003, Proceedings ICONE11-36310
  • Contribution to proceedings
    11th International Conference on Nuclear Engineering Tokyo, JAPAN, April 20-23,2003, Proceedings ICONE11-36310

Publ.-Id: 6282

Range and mixing distributions of low-energy carbon ions as a base for subplantation growth models

Dollinger, G.; Neumaier, P.; Bergmaier, A.; Eckstein, W.; Fischer, R.; Hofsaess, H.; Kroeger, H.; Ronning, C.; Jaeger, H. U.

  • Lecture (Conference)
    European Materials Research Society 2004 Spring Meeting, Symposium J: Synthesis, Characterisation and Advanced Applications of Amorphous Carbon films, contr. J-I.3, 24-28 May 2004, Strasbourg, France

Publ.-Id: 6281

In-situ studies of Shape Memory Alloy (SMA) Ni-Ti thin films

Martins, R. M. S.; Schell, N.; Braz Fernandez, F. M.; Silva, R.

Ni-Ti thin films (SMA) formed by sputtering have been attracting great interest as powerful actuators in microelectromechanical systems (MEMS) such as microvalves, microfluidic pumps and micromanipulators. Successful implementation of Ni-Ti micro-actuactors requires a good understanding of the relationship among processing, microstructure and proprieties of Ni-Ti thin films. At the ROssendorf BeamLine (ROBL-CRG) at the ESRF, we carried out a series of experiments that clearly illustrate the benefit of in-situ studies, not only during annealing, but also during sputtering. The in-situ annealing experiments, using a Be-dome furnace installed into the six-circle diffractometer of the Materials Research Hutch (MRH) allowed us to determine the kinetics of the phenomena, to identify the sequence of precipitation and to correlate the build-up of the final structure with the processing conditions. The in-situ sputtering experiments during film growth were performed using a magnetron sputter deposition chamber also installed into the six-circle diffractometer [1]. This facility allowed us to follow, almost in “real time”, the structural evolution of the deposited thin film as a consequence of changing deposition parameters.

Keywords: magnetron sputtering; in-situ XRD; real-time structural design; shape memory alloy NiTi

  • Lecture (Conference)
    4th Conference on Synchrotron Radiation in Materials Science (SRMS-4), August 23-25, 2004, Grenoble, France

Publ.-Id: 6280

Real-time and in-situ structural design of functional NiTi SMA thin films

Schell, N.; Martins, R. M. S.; Braz Fernandez, F. M.

The real-time structural design of magnetron sputtered NiTi SMA (shape memory alloy) thin films is reported. During deposition the phase content was followed in situ by synchrotron x-ray diffraction and controlled by varying the power of co-sputtering NiTi plus Ti for otherwise fixed deposition parameters. This method allows an optimization of the thin film in respect to its functional properties like phase transition temperature or adhesion as well as an understanding of the actual growth process by revealing temporary intermediate growth states (precipitates) and diffusion processes during film growth. The method is neither restricted to the sputter material (NiTi) nor to the controlling parameter (power) chosen, but immediately applicable to a large class of materials as well as general enough for other deposition parameters.

Keywords: magnetron sputtering; in-situ XRD; real-time structural design; shape memory alloy NiTi

  • Applied Physics A 81(2005)7, 1441-1445; DOI: 10.1007/s00339-004-3201-1

Publ.-Id: 6279

Microchanneling Investigation of ß-FeSi2-Structures

Dagkaldiran, Ü.; Grambole, D.; Herrmann, F.; Schreiber, H.-U.; Meijer, J.

Semiconducting ß-FeSi2 has currently attracted scientific interest, due to the fact that ß-FeSi2 has a direct band gap of 0.8 eV [1,2]. This property makes it a special candidate for e.g. silicon-based micro-LED’s. Single crystalline ß-FeSi2- layers would even open possibilities for devices like micro-laserdiodes. However, the synthesis of these structures is experimentally extremely delicate.

The temperature during implantation, the energy of the beam, the annealing procedures as well as the fluence and current density of the beam, the structure size of the layer etc. are all key process parameters and have to be optimized with respect to one another.

The first micro channeling analyses of FeSi2-structures, which were produced with an ion energy of 800 keV and sample sizes between 70-190 µm in diameters, were carried out. The combination of the two set-ups, the ion projector at the Ruhr University of Bochum and the micro-channeling set-up at the research centre Rossendorf, allows a fast synthesis as well as the analysis of the samples.

The implantation temperature of the samples was varied between 50 – 350 °C. The results show that bulk formation by Ostwald maturing depends on implantation temperature and structure size. Even if the layers do not show the desired crystalline characteristics, the investigations permit to draw conclusions about the damage of the surface layer with consideration of the bulk formation. This is of enormous interest, in order to optimize and model the embedding into a pn-structure as a step towards the development of a LED.

Additional Raman measurements showed clear fingerprints of ß-FeSi2 [3].

[1]: N.E. Christensen;
Electronic structure of ß-FeSi2;
Phys. Rev. B42, 1990, p. 7148-7153

[2]: D. Pankin, F. Eichhorn, E. Wieser, W. Skorupa, W. Henrion, J. Albrecht;
Electrical and optical properties of ß-FeSi2 after Co implantation and annealing;
Nucl. Instrum. Methods Phys. Res. B84, 1994, p. 172-175

[3]: A.G. Birdwell, R. Glosser, D.N. Leong, K.P. Homewood;
Raman investigation of ion beam synthesized ß-FeSi2 ;
J. Appl. Phys., Vol. 89, No. 2, 2001, p. 965- 972

  • Lecture (Conference)
    9th International Conference on Nuclear Microprobe Technology and Applications (ICNMTA-2004), Sept. 13 -17 2004, Cavtat, Dubrovnik, Croatia

Publ.-Id: 6278

Porous silicon as an intermediate layer for heterojunction solar cells on p-type Si crystalline substrates

Ulyashin, A.; Bilyalov, R.; Carnel, L.; van Nieuwenhuysen, K.; Grambole, D.; Bruck, A.; Scherff, M.; Monakhov, E.; Kuznetsov, A. Y.; Svensson, B. G.; Beaucarne, G.; Poortmans, J.

The study of the influence of ITO deposition process on the defect formation in the interface region of heterojunctions (HJ) is done. The role of intrinsic a-Si:H and as an alternative a thin porous Si buffer layer is analyzed. It is shown that a thin porous Si as a buffer layer in HJ solar cells leads to the improvement of the HJ solar cells efficiency since this layer serves as a protection one of the Si substrate during the ITO deposition process. By DLTS method it is observed that damages created during the deposition of ITO layer can be essentially suppressed by a thin a-Si:H or thin porous Si buffer layers. In case of porous silicon formation by the electrochemical etching the process is “softer” and this thin intermediate layer has similar properties as a-Si:H concerning the hydrogen concentration and the characteristics of Si-H bonds. This conclusion was derived from the Nuclear Reaction Analysis (NRA) and Raman measurements, which are performed on porous-Si/crystalline Si structures. It is concluded that the main role of a thin porous Si layer in a Si based heterojunction structure is the improvement of the interface properties of HJ solar cells due to a protection of the Si substrate during the depositions of a-Si:H and ITO layers.

Keywords: heterojunction; silicon; passivation

  • Lecture (Conference)
    19th European Photovoltaic Solar Energy Conference, 7 - 11 June, 2004, Paris, France
  • Contribution to proceedings
    19th European Photovoltaic Solar Energy Conference, 07.-11.06.2004, Paris, France, 588

Publ.-Id: 6277

Bonding in hydrogenated diamond-like carbon by Raman spectroscopy

Casiraghi, C.; Piazza, F.; Ferrari, A. C.; Grambole, D.; Robertson, J.

We study the 514 and 244 nm Raman spectra of a wide variety of hydrogenated amorphous carbons (a-C:H). The hydrogen content can be estimated from the slope of the photoluminescence background (PL) of the spectra measured at 514.5 nm. Generally, the evolution of the sp(2) and sp(3) phases is not independent for as-deposited a-C:H samples. This, in principle, allows us to derive their structural and optical properties just by studying the visible Raman spectra. For highly hydrogenated samples, the PL background overshadows the visible Raman spectra, and UV excitation is the only way to measure a Raman spectrum.

[1] A. C. Ferrari, J. Robertson, Phys. Rev. B 64 (2001) 075414.
[2] T. Schwarz-Selinger, A. von Keudell, W. Jacob, J. Appl. Phys. 86
(1999) 3988
[3] A. C. Ferrari, J. Robertson, M. G. Beghi, C. E. Bottani, R. Ferulano,
R. Pastorelli, Appl. Phys. Lett. 75 (1999) 1893.

  • Lecture (Conference)
    15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides & Silicon Carbide (Diamond 2004), 12 -17 September 2004, Riva Del Garda, Italy
  • Diamond and Related Materials 14(2005)3 - 7, 1098-1102

Publ.-Id: 6276

Protective diamond-like carbon coatings for future optical storage disks

Piazza, F.; Grambole, D.; Schneider, D.; Casiraghi, C.; Ferrari, A. C.; Robertson, J.

Diamond-like carbon (DLC) is a promising protective coating for future optical storage technologies. The requirements place conflicting constraints on the nature of the DLC. It must be transparent at 400 nm, hard and wear-resistant, uniform, pinhole-free, have a low stress and be deposited at high rate without a high heat load on a plastic substrate. In order to optimise the films under these constraints, we have studied in detail the band gap, stress, density and Young's modulus of hydrogenated amorphous carbon (a-C:H) films deposited by plasma enhanced chemical vapour deposition using a large area electron cyclotron wave resonance source of 14 in. diameter and a variety of hydrocarbon gas sources. We have been able to produce wear-resistant carbon coatings with a high transparency at 400 nm without damaging the plastic disks. We also show that for these films the refractive index can be used as a rapid empirical means of property correlation.

[1] F. Piazza, D. Grambole, L. Zhou, F. Talke, C. Casiraghi, A.C. Ferrari,
J. Robertson, Diamond Related Mater., in press.

Keywords: Hydrogenated amorphous carbon; ECWR plasma beam source; protective coatings

  • Lecture (Conference)
    15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides & Silicon Carbide (Diamond 2004), 12 -17 September 2004, Riva Del Garda, Italy
  • Diamond and Related Materials 14(2005)3 - 7, 994-999

Publ.-Id: 6275

Micro RBS-channeling measurements to study damage accumulation in silicon by ion implantation

Grambole, D.; Herrmann, F.; Dagkaldiran, Ü.; Meijer, J.

Ion implantation is the key technology for electrical doping of silicon. There are many studies of the amorphization of silicon by ion implantation. To extend the investigation of the damage accumulation in silicon to very high ion fluxes, Si samples were implanted with 600 keV Si+ ions of a current density of 360 µA/cm² (2.2 x 1015 Si /(s x cm²)) at different substrate temperatures up to a fluence of 1 x 1018 Si/cm² by the Bochum super conducting ion projector [1]. The damage of the Si crystal in the implanted circular areas of 185 µm diameter was investigated by micro RBS-channeling with 3 MeV He ions using the Rossendorf nuclear microprobe. For micro channeling measurements a second chamber with a precisely justified 4-axis goniometer was installed behind the chamber used normally for micro ion beam analysis. It allows to investigate the crystal structure in regions down to a size of about 10 µm, keeping the crystal damage during the analysis in check. For this high Si ion flux a significant dependence of the damage accumulation and of the Si amorphization on the implantation temperature and fluence was observed. It was shown that the model of the current density dependence on the amorphization temperature used also by R.D. Goldberg et al. [2] can not be extrapolated to very high ion current densities.

[1] J. Meijer, A. Stephan, Microelec. Eng. 41/42 (1998) 257
[2] R.D. Goldberg, R.G. Elliman, J.S. Williams, Nucl. Instr. and Meth. B 80/81 (1993) 596

  • Poster
    9th International Conference on Nuclear Microprobe Technology and Applications (ICNMTA-2004), Sept. 13 -17 2004, Cavtat, Dubrovnik, Croatia

Publ.-Id: 6274

Hydrogen behaviour in novel materials for spintronic: GaFeN codoped with Mg, Si and Al

Turos, A.; Abdul-Kader, A. M.; Podsiadlo, S.; Strojek, B.; Strzalkowski, I.; Grambole, D.

Hydrogen plays an important role in GaN and related alloys. It is often a part of the growth environment and can be incorporated in GaN during different processing steps. Its behaviour is rather complicated and poorly understood. GaN doped with Fe has currently gained an increasing interest as a suitable magnetic semiconductor for spintronic applications. Here, we report results of the study on GaN doped with Fe and codoped with Mg for deep acceptors, Si for shallow donors and isoelectronic Al. Samples were grown by the chemical transport process in the form of small (~ 0.3 mm) crystallites and subsequently pressed to form platelets. As-grown samples and after annealing in different atmospheres (successively with N2 and NH3) were studied. Hydrogen concentration were determined by NRA using the 15N profiling method. Hydrogen release due to the analysing beam was evaluated using the molecular recombination model. Effective H-release cross-section was found to be the same for all GaFeN samples, independently of codoping. The lowest concentration of hydrogen among as-grown materials was revealed in GaFeN samples. Codoped materials showed higher hydrogen concentration, increasing in the following sequence: Mg, Si and Al. Hydrogen concentration can be substantially reduced by annealing in N2 atmosphere, whereas subsequent annealing in NH3 produces hydrogenation, however, to concentrations below that for pristine samples. The model of these processes has been proposed.

Keywords: Spintronics; Gallium nitride; Hydrogen; Nuclear reaction analysis

  • Lecture (Conference)
    Vth International Conference Ion Implantation and Other Applications of Ions and Electrons, June 14-17, 2004, Kazimierz Dolny, Poland
  • Vacuum 78(2005)2-4, 285-290

Publ.-Id: 6273

Experimentelle Untersuchungen zur reaktionsgetriebenen Druckentlastung

Kryk, H.; Schmitt, W.; Hessel, G.; Tefera, N.

Die Qualität der Simulationsergebnisse existierender Computercodes zur dynamischen Simulation von Druckentlastungsvorgängen (z.B. SAFIRE/ Vent, BRICK) ist von der Genauigkeit der Untermodelle zur Berücksichtigung von Wärme- und Stofftransport, Reaktionskinetik, Mischphasenthermodynamik sowie Aufwall- und Schaumverhalten abhängig. Die Untersuchungen dienen einer verbesserten Modellierung dieser Teilprozesse unter Berücksichtigung der spezifischen Prozessbedingungen der Druckentlastung. Hierzu sind sowohl reaktionsgetriebene Druckentlastungsexperimente in Rührkesselreaktoren unter prozessnahen Bedingungen als auch zusätzliche Experimente zur Ermittlung von apparate- und prozessspezifischen Parametern durchzuführen. Die Ergebnisse liefern den Prozessdaten-Pool zur Weiterentwicklung und Validierung von Simulationssoftware für Druckentlastungsprozesse in Batch-Reaktoren. Ziel ist die Simulation des Gesamtprozesses vom Reaktionsstart über die hydro- und thermodynamischen sowie die prozesskinetischen Vorgänge während der Druckentlastung bis hin zu Nachreaktionen.
Als Modellprozess wurde die Veresterung von Essigsäureanhydrid mit Methanol gewählt. Zur Berücksichtigung der stofflichen und wärmetechnischen Einflüsse der Reaktion auf den Druckentlastungsprozess wurde ein reaktionskinetisches Modell entwickelt, das die thermischen und chemischen Reaktionsverläufe über weite Temperatur- und Konzentrationsbereiche unabhängig von der Prozessführung wiedergibt.
Hauptgegenstand der experimentellen Untersuchungen sind reaktive Druckentlastungsexperimente unter prozessnahen Bedingungen. Die Experimente werden unter isoperibolen Prozessbedingungen in mantelgekühlten Rührkesselreaktoren aus Glas und Edelstahl durchgeführt. Die Reaktorvolumina betragen 1 bis 10 Liter. Bei Verwendung der Glasreaktoren kann, bedingt durch die Positionierung des kritischen Querschnittes (wechselbare Lochblende) in Höhe des Reaktordeckels, das Einströmverhalten in die Blende mittels High-Speed-Videotechnik beobachtet werden. Zusätzliche elektrische Heizpatronen im Reaktor gestatten die Bestimmung von Wärmeübergangskoeffizienten und anderen Prozess- und Anlagenkennwerten. Die für den Druckentlastungsprozess signifikantesten Signale werden mit einer Abtastrate von max. 200 Hz aufgezeichnet. Zur Ermittlung der dynamischen Phasenanteile in der Druckentlastungsleitung wurde eine spezielle nadelförmige Leitfähigkeitssonde mit integrierter Temperaturmessung entwickelt. Durch Verwendung von Rührkesselreaktoren mit Mantelkühlung in Verbindung mit elektrischen Kalibrierheizungen ist die thermodynamische Charakterisierung des Systems durch Wärmebilanzierung realisierbar. Zur stofflichen Charakterisierung der Reaktionsgemische wird die FTIR-Spektroskopie eingesetzt.
Gegenstand der Präsentation bilden die Versuchsanlagen, die experimentelle Strategien zur Modellierung und Simulation von Druckentlastungsszenarien sowie die konkreten Versuchsabläufe zur Realisierung reproduzierbarer reaktionsgetriebener Druckentlastungsprozesse. Erste Versuchsergebnisse werden gezeigt und ein Ausblick auf weitere experimentelle und modelltheoretische Untersuchungen wird gegeben.

Keywords: Anlagensicherheit; Druckentlastung; chemische Reaktion; Rührkesselreaktor; Modellierung

  • Lecture (Conference)
    7. Fachtagung "Anlagen-, Arbeits- und Umweltsicherheit" 04.-05.2004, Köthen, Germany
  • Contribution to proceedings
    7. Fachtagung "Anlagen-, Arbeits- und Umweltsicherheit" 04.-05.2004, Köthen, Germany, CD-ROM

Publ.-Id: 6272

Strömungskontrolle bei Formfüllung mittels Magnetfeldern

Eckert, S.; Galindo, V.; Gerbeth, G.; Witke, W.; Buchenau, D.; Gerke-Cantow, R.; Nicolai, H.-P.; Steinrücken, U.

Es ist aus theoretischen Überlegungen und praktischen Untersuchungen bekannt, daß beim Feinguß eine in die Form einströmende Schmelze eine in ihrem exakten Zahlenwert unbekannte Maximalgeschwindigkeit (Näherungswert: 0,5 m/s) nicht übersteigen darf. Füllt die Schmelze den Formhohlraum mit einer höheren Geschwindigkeit, ergeben sich Verwirbelungen und Oxideinschlüsse, die sich nachteilig auf die mechanischen Eigenschaften des Gussteils auswirken. Es gibt Hinweise an Gussteilen, die diese Theorien stützen. Da eine Form als oben offener Hohlraum betrachtet werden kann, muß das Metall immer aus einer Höhe eingefüllt werden, die durch die Höhe des Gussteils und zusätzlicher gießtechnischer Anordnungen vorbestimmt ist. Damit resultiert die Maximalgeschwindigkeit der Schmelze am tiefsten Punkt aus den geometrischen und flüssigkeitsdynamischen Gegebenheiten. Eine kontaktlose Regelung der Schmelzströmung, welche durch Einsatz elektromagnetischer Felder realisiert werden kann, ist offensichtlich wünschenswert und vorteilhaft im Vergleich zu mechanischen Lösungen.

Keywords: Feinguss; Formfüllung; Flüssigmetall; elektromagnetische Strömungskontrolle; Magnetfeld

  • Lecture (Conference)
    Deutscher Giessereitag 2004, 03.-04.06.2004, München, Germany
  • Giesserei 92(2005)5, 26-31

Publ.-Id: 6271

Calculations of K+, K- and Phi Production in Near-Threshold Proton-Nucleus Collisions

Barz, H.-W.; Kämpfer, B.; Naumann, L.; Wolf, G.; Zetenyi, M.

K+, K- and phi meson production in proton-nucleus (pA) collisions has been calculated within a BUU transport model. It is shown that the nucleon-hyperon strangeness transfer channel is essential. The role of three-body reactions has been investigated within the medium.
The mass dependence of phi production is predicted to give important information on the in-medium properties of all three mesons.

  • Acta Physica Hungarica A 22(2005)3-4, 231-237

Publ.-Id: 6270

Modelling of bubble flow in vertical pipes

Krepper, E.; Lucas, D.; Shi, J.

To qualify CFD codes for two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. Information on the local structure of the flow is also required by 1D thermal-hydraulic codes. Gas-liquid flow in vertical pipes is a very good object for studying the corresponding phenomena. Here, the bubbles move under clear boundary conditions, resulting in a shear field of nearly constant structure where the bubbles rise for a comparatively long time. The evolution of the flow within the pipe depends on a very complex interaction between bubble forces and bubble coalescence and break-up. E.g. the Lift-force, which strongly influences the radial distribution of the bubbles, changes its sign depending on the bubble diameter. Basing on extensive experimental data with a high resolution in space and time the applicability and the limits for the simulation of bubble flow with current CFX-codes are demonstrated, using the simulation of vertical pipe flow with CFX-4 as an example. Using a simplified model, parametric studies can be conducted. They give an indication for necessary improvements of the codes. Finally a possible way for the improvement of the CFD-codes is shown.

Keywords: two phase flow; bubble flow; bubble size; vertical pipe flow; CFD

  • Lecture (Conference)
    Multiphase Flows in Industrial Applications CFX-Germany, FZ-Rossendorf 28.-30.04.03

Publ.-Id: 6269

CFD Modelling of subcooled boiling

Krepper, E.

Heat transfer and boiling are key phenomena in critical equipment used in power generation facilities. Modelling of boiling in 1D thermal hydraulic codes was state of the art right from the beginning of their development, whereas boiling models in 3D thermal hydraulic codes are far from reaching this level of maturity. In this paper, the boiling model implemented in the CFD code CFX-4 was applied, to analyse several boiling experiments, the results of which are published in literature. The validity of the implemented correlations is examined. In many cases the model yields a good agreement with experiments. However, especially in the low pressure region, the steam volume fraction is under predicted. The models implemented in CFX are critically reviewed and compared to alternative solutions. The sensitivity of the calculated results on different parameters are compared. The need for improvements in the model and for further experiments are derived. Main attention should be focused on measuring and modelling of the correct size of the steam bubbles generated.

Keywords: CFD; boiling; experiments

  • Lecture (Conference)
    XIII. AER-Symposium on VVER Physics and Reactor Safety, Dresden, Germany, September 23-26, 2003, Proceedings pp. 819-833
  • Contribution to proceedings
    XIII. AER-Symposium on VVER Physics and Reactor Safety, Dresden, Germany, September 23-26, 2003, Proceedings pp. 819-833

Publ.-Id: 6268

Coupled Fluid-Structure Analysis with EUROPLEXUS Fast Dynamics Software of the CWHTF Experiment

Potapov, S.; Altstadt, E.

The present paper aims at the validation of modelling capacities of the EUROPLEXUS fast dynamics software in the domain of condensation-induced water hammers and Fluid-Structure Interaction (FSI). Two numerical models of EUROPLEXUS accounting for FSI effects are considered and compared throughout modelling and computation. The first model is a simplified pipeline model using intrinsically coupled pipeline elements. The second FSI model is a mixed model; it contains both pipeline and 3D parts and uses a special interface model between the 3D fluid volume and the shell mesh of the piping. Numerical results are compared with experimental data obtained on the Cold Water Hammer Test Facility (CWHTF) at Forschungszentrum Rossendorf, within the WAHALoads European project. In this experiment water hammer is generated by accelerated water bouncing against a lid flange.

Keywords: Water Hammer Experiment; Fluid-Structure Interaction; EUROPLEXUS fast dynamics software

  • Lecture (Conference)
    6th International Conference on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-6), 04.-08.10.2004, Nara, Japan
  • Contribution to proceedings
    6th International Conference on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-6), 04.-08.10.2004, Nara, Japan

Publ.-Id: 6267

NIR Spectroscopic Study of the Complexation of Neptunium(V) with Humic Acids: Influence of Phenolic OH Groups on the Complex Formation

Sachs, S.; Bernhard, G.

The influence of phenolic OH groups on the Np(V) complexation by humic acids was studied at pH 7 and pH 8 under nitrogen atmosphere applying chemically modified humic acids with blocked phenolic OH groups in comparison to their corresponding unmodified humic acids. The studies were performed by near-infrared (NIR) absorption spectroscopy using the metal ion charge neutralization model for evaluation of the experimental data. For all humic acids under investigation comparable complexation constants were determined. However, the studied modified humic acids Aldrich and M42 show significantly lower loading capacities for NpO2+ ions (e.g., pH 7: 7.2 ± 1.1 % and 5.3 ± 1.0 %, respectively) than the corresponding unmodified humic acids (e.g., pH 7: 10.0 ± 1.5 % and 11.2 ± 1.1 %, respectively). This result points to a lower amount of maximal available humic acid ligand sites after blocking of phenolic OH groups. From that, it can be concluded that humic acid phenolic OH groups contribute to the interaction between humic acid and Np(V) under the studied conditions. The comparison of the loading capacities obtained for unmodified and modified Aldrich humic acid at pH 7 and pH 8 shows that the impact of phenolic OH groups on the Np(V) complexation by humic acids is increased with increasing pH value.

Keywords: Humic acid; Synthetic humic acid; Modified humic acid; Phenolic OH groups; Complexation; Neptunium(V)

  • Radiochimica Acta 93(2005), 141-145

Publ.-Id: 6266

In-situ investigations of the amorphous-to-crystalline transformation of ITO films by synchrotron X-ray scattering

Shevchenko, N.; Rogozin, A.; Schell, N.; Cantelli, V.; Vinnichenko, M.; Prokert, F.; Kolitsch, A.

Amorphous tin-doped indium oxide (ITO) films were grown by reactive pulsed middle frequency dual magnetron sputtering on Si (100) substrates covered with 500 nm SiO2. Changes in the microstructure and the resistivity of the ITO films during annealing in vacuum (p ~ 10-6 mbar) were characterized by in-situ synchrotron XRD analysis and simultaneous four-point probe measurements at ROssendorf Beam Line (ROBL). The in-situ experiments are performed at isothermal (temperature range of 210 - 240 °C) and non-isothermal (T-ramp: 2.5 - 10 K/min) annealing modes.
At non-isothermal annealing the XRD data reveal a rapid crystallization in the temperature range of 240 - 280°C. The heating rate does not influence on the temperature of the crystallization onset (T=240 ± 10 °C).
At isothermal annealing increase of the temperature leads to decrease of the time of crystallization onset and the total time of amorphous-to-crystalline transformation and, therefore the crystallization rate increases. Using the Kolmogorov-Avrami-Johnson-Mehl equation [f ~ 1-exp(-ktn)] for the dependence of the crystalline fraction f on the annealing time, the kinetic parameters of crystallization were determined. On the condition that the coherently diffracting domain size (~65 nm) is smaller than the film thickness (~130 nm) a three-dimensional crystallization process was indicated.
Even in amorphous films the resistivity significantly decreases with increasing temperature, likely by the generation of oxygen vacancies. The rapid crystallization leads to further reduction of the resistivity probably due to Sn donor activation.

Keywords: ITO; crystallization; annealing; in-situ

  • Poster
    The Conference on Synchrotron Radiation in Materials Science (SRMS-4), France, 23-25 August 2004

Publ.-Id: 6265

Ion implantation of NiTi alloy: surface processes and properties

Shevchenko, N.; Pham, M.-T.; Richter, E.; Maitz, M. F.

The superelastic or memory shape NiTi alloy has big potential for biomedical applications, but due to the high nickel content there are restrictions against it. It has been shown, that ion implantation is a very versatile method to reduce the surface nickel content and modify the structure, by this improve the surface properties for biomaterials applications. The understanding of the mechanism of the Ni depleted layer formation and growth is still limited, but it is a key for achieving control and optimization of the process. The aim of this contribution is to study the surface processes of TiNi alloys during ion implantation, especially the phenomena of Ni depletion of NiTi surface to improve the biocompatibility.
N, O and Ar ion implantation of the NiTi samples was performed by means of plasma immersion ion implantation at different parameters: ion energy (20 - 40 keV and 200 keV), fluence (10 17 - 10 18 cm -2), substrate temperature (RT - 400 °C). The implanted layers were examined by Auger electron spectroscopy, grazing incidence X-ray diffraction analysis and transmission electron microscopy. The corrosion resistance and biocompatibility were investigated by the electrochemical corrosion analysis, cell culture and blood compatibility tests, respectively.
Nickel depleted surface layers of TiOx or TiNx are formed during oxygen or nitrogen implantation, respectively. Below this a nickel enriched zone up to 300 nm is found, with the possible phases Ni4Ti3 and Ni2.67Ti1.33. This indicates a reactive diffusion process as main control mechanism of Ni transport. Finally, any correlation of corrosion, chemical and microstructure properties of modified NiTi surfaces to the biocompatibility are discussed.

Keywords: NiTi; modified surface; ion implantation

  • Poster
    7th International Conference on Modification of Materials with Particle Beams and Plasma Flows, Tomsk, Russia, July 25 -30, 2004

Publ.-Id: 6264

Microstructural and Mechanical Characterization of the Radiation Effects in Model Reactor Pressure Vessel Steels

Ulbricht, A.; Boehmert, J.; Viehrig, H.-W.

This paper presents results of radiation-induced nanoscal microstructural changes measured by Small-Angle Neutron Scattering (SANS) on ASTM-type reactor pressure vessel (RPV) steels. Five different base metals and one weld metal were investigated. The irradiation was performed in a VVER-type power reactor on 3 different dose levels, maximally 0.14 dpa, at an irradiation temperature of 255 °C. The volume content of the micostructural features measured is correlated with the irradiation hardening and embrittlement.
In every case clear radiation-related hardening, embrittlement and microstrucural effects are proven. Radiation produces nanoscaled scattering defects of a radius between 0 < R < 3 nm with the maximum near R = 1 nm. Fluence and chemical composition do not or hardly change the shape of the size distribution but strongly the volume content. The radiation sensitivity is mainly controlled by the copper content. Copper also increases the A-ratio. There are good correlations between volume content of the nanoscaled radiation defects and the radiation hardening or embrittlement, respectively.
Annealing at 475 °C produces almost full recovery of the mechanical properties. However, the original microstructure of the unirradiated state is not completely reproduced.

Keywords: microstructure; SANS; radiation hardening; radiation embrittlement

  • Lecture (Conference)
    STP 1475: Effects of Radiation on Materials, 22nd Symposium, 08.-10.06.2004, Boston, Massachusetts, United States
  • Journal of ASTM International 2(2005)10, 14, Paper ID JAI12385
  • Contribution to proceedings
    STP 1475: Effects of Radiation on Materials, 22nd Symposium, 08.-10.06.2004, Boston, United States
    STP 1475, West Conshohocken, PA: ASTM International, 978-0-8031-3401-0, 151-164


Publ.-Id: 6263

Ion implanted NiTi surfaces for biomedical applications

Shevchenko, N.; Pham, M.-T.; Richter, E.; Maitz, M. F.

  • Poster
    16th International Vacuum Congress IVC-16/ ICSS-12/ NANO-8, Venice, Italy, June 28 - July 2, 2004

Publ.-Id: 6262

In situ monitoring of the ITO film structure and properties during annealing

Shevchenko, N.; Rogozin, A.; Vinnichenko, M.; Prokert, F.; Cantelli, V.; Kolitsch, A.; Moeller, W.

Keywords: ITO; in situ; annealing

  • Lecture (Conference)
    16th International Vacuum Congress IVC-16/ ICSS-12/ NANO-8, June 28 - July 2, 2004, Venice, Italy

Publ.-Id: 6261

Ni depletion of a NiTi surface by ion implantation for biomedical applications

Shevchenko, N.; Maitz, M.

The NiTi alloy is interesting for medical applications because of its either superelastic or memory shape properties. However, clinical acceptance of the alloy still is limited due to its high nickel content.
The aim of this work is to reduce the Ni concentration in a NiTi surface by ion implantation and study the influence on surface stability and biocompatibility.
Modification of the NiTi samples was performed by N or/ and Ar ion implantation at different parameters: ion energy (20 - 40 keV and 200 keV), fluence (10 17 - 10 18 cm -2), substrate temperature (RT - 400 °C). The modified layers were examined by Auger electron spectroscopy, grazing incidence X-ray diffraction analysis and transmission electron microscopy. The corrosion resistance and biocompatibility were investigated by the electrochemical corrosion analysis and cell culture tests with bone forming cells, respectively.
Ion implantation could reduce the surface nickel content down to ~0.5 at%. Below the Ni depleted surface a Ni enriched zone is formed, which indicates an increased mobility either of Ni from the surface to the bulk or of Ti from the sub-surface to the surface. A reactive diffusion mechanism for the nickel depletion in this system is discussed. The corrosion stability increases by this treatment. In preliminary studies with bone forming cells no decrease in biocompatibility was seen by this treatment.

Keywords: NiTi; biocompatibility; ion implantation

  • Lecture (Conference)
    DPG - spring meeting, March 8-12, 2004, Regensburg, Deutschland

Publ.-Id: 6260

Nucleation of calcium phosphate by surface-bound extracellular matrix

Pham, M. T.; Maitz, M.; Reuther, H.; Muecklich, A.; Prokert, F.; Steiner, G.

The native extracellular matrix (ECM) laid down on silicon and titanium surfaces by osteoblast-like SAOS-2 cells was exposed by selective removing of cells. This type of material surface ECM-Si, ECM-Ti was shown to promote the nucleation of calcium phosphate from a simulated body fluid (SBF). Microscopic and spectroscopic results revealed the effect being associated with a collagen fibre-free extracellular matrix.

Keywords: osteoblasts; extracellular matrix; silicon; titanium; mineralization

  • Journal of Biomedical Materials Research 71A(2004), 16-24.

Publ.-Id: 6259

Application of Advanced Monte Carlo Methods in Numerical Dosimetry

Reichelt, U.; Henniger, J.; Lange, C.

Many tasks in different sectors of dosimetry are very complex and highly sensitive to changes of the radiation field, e. g. dose estimations in microdosimetry. Often experimental measurements are only available for particular conditions or at single target points. Thus only the simulation of radiation transport is capable of describing the radiation field completely. Different approaches for solving the radiation transport problem as e.g. FEM can be used. In particular the Monte Carlo (MC) method is very useful for high-dimensional problems, and it is accepted as a standard method for this purpose.
Down to sub cellular dimensions the energy deposition by cascades of secondary electrons is the main pathway for damage induction in matter. A high number of interactions is taking place until such an electron is slowed down to thermal energies. For this reason the non-analog Monte Carlo program AMOS has been developed for photon and electron transport. The advanced MC algorithms implemented are able to handle a large number of histories at reasonable performance even for time consuming single scattering models. They facilitate the calculation of photon dose distributions at up to 10^6 points.
Modeling the dose distribution of a 125-I brachytherapy source has proven the high efficiency of this MC approach. Further on results achieved by AMOS for the transport of electrons with low energies (E < 100 keV) in matter with low atomic numbers were compared to measured data from the literature. It has been proven that the program code produces results in rather well agreement to the experiments also for small target structures of about one micrometre. This is especially important for the application to cell irradiation experiments as they are carried out at the FZ Rossendorf. As another example of application a simulation of the whole spectral detector response of an HPGe detector will be presented.

  • Poster
    14 International Conference on Solid State Dosimetry (2004)
  • Radiation Protection Dosimetry 119(2006), 479-482
    DOI: 10.1093/rpd/nci682

Publ.-Id: 6258

Coherent phonons in NdBa2Cu3O7-x single crystals: Optical-response anisotropy and hysteretic behavior

Misochko, O. V.; Lebedev, M.; Georgiev, N.; Dekorsy, T.

Femtosecond pump-probe measurements of reflection from crystallographic planes are performed to investigate lattice relaxation dynamics in the NdBa2Cu3O7-x high-temperature superconductor. Ultrafast phonon response is examined over a wide temperature range for various orientations of the pump and probe polarization vectors with respect to particular crystallographic axes. The initial phases of coherent phonons are measured, and hysteretic behavior is revealed in the transition between two temperature regions above T-c for the ac plane.

Keywords: coherent phonons; high temperature superconductors

  • Journal of Experimental and Theoretical Physics 98(2004), 341-347

Publ.-Id: 6256

Umklapp process in observation of coherent folded longitudinal acoustic phonons in a GaAs/AlAs long-period superlattice

Mizoguchi, K.; Hino, T.; Nakayama, M.; Dekorsy, T.; Bartels, A.; Kurz, H.; Nakashima, S.

Coherent folded longitudinal acoustic phonons in a GaAs/AlAs long-period superlattice (SL) have been investigated by using a reflection-type two-color pump-probe technique under the condition that the wave vector of the probe pulse in the sample exceeds the mini-Brillouin zone. The coherent oscillations observed in the time-domain signals indicate the propagation of the phonon wave packet through the whole SL layer. The Fourier transform spectrum of the time-domain signals is compared with the dispersion relation of the folded longitudinal acoustic phonons in the long-period SL calculated using a transfer matrix method on the bases of an elastic continuum model. This comparison indicates that the folded longitudinal acoustic phonons in the long-period SL are observed through the umklapp process.

Keywords: coherent phonons; superlattices; femtosecond; umklapp process

  • Physica E 21(2004), 646-650

Publ.-Id: 6255

Investigation of the Damage Around a Crack Tip in Metals using Small Angle X-ray Scattering

Müller, G.; van Ouytsel, K.; Böhmert, J.; Dolbnya, I.; Bergner, F.

Structural materials, such as ferritic and austenitic steels and aluminium alloys, as used in the nuclear and aircraft industry are subject to external stresses which may lead to the nucleation of cracks. The damage zone ahead of a crack tip introduced as a result of static deformation was investigated in an Al-2024 and Al-6013 alloy and in a 10 CrMo9 10 reference steel by means of small angle X-ray scattering. A robust parameter, the anisotropy parameter, describing the damage region was developed. Further parameters were exployed. The data, supported by electron microscopy investigations point to large oriented dislocation networks. Finite element calculations show a good correspondence in the shape and size of the damage zone.

Konstruktionswerkstoffe, z.B. ferritische Stähle, austenitische Stähle und Aluminiumlegierungen mit Anwendung in der Kernenergie- und Luftfahrttechnik, sind hohen äußeren Belastungen ausgesetzt, die zur Rissbildung führen können. Die Schädigungszone vor der Spitze von Rissen, die durch quasistatische Belastung in Materialproben der Aluminiumlegierungen Al-2024 und Al-6013 und des warmfesten Stahls 10 CrMo9 10 eingebracht worden waren, wurde mittels Röntgenkleinwinkelstreuung punktweise erfasst und abgerastert. Aus den Streubildern wurden mehrere verschiedene Streuparameter abgeleitet, von denen sich der Anisotropieparameter als besonders robust erwies. Die Ergebnisse deuten, gestützt durch elektronenmikroskopische Untersuchungen, auf grobe orientierte Versetzungsnetzwerke. Finite-Elemente-Rechnungen zeigen eine gute Übereinstimmung hinsichtlich Form und Größe der Schädigungszone.

Keywords: SAXS; Al-alloy; steel; crack; damage; synchrotron radiation; dislocations; microvoids

  • MP Materials Testing 50(2008)4, 191-198

Publ.-Id: 6254

Suitability of drift-flux models, void-fraction evolution and 3D flow pattern visualization during stationary and transient flashing flow in a vertical pipe

Manera, A.; Prasser, H.-M.; van der Hagen, T. H. J. J.

An assessment of void fraction correlations and drift-flux models applied to stationary and transient flashing flows in a vertical pipe has been performed. Experiments have been carried out on a steam/water loop that can be operated both in forced and natural-circulation conditions. Advanced instrumentation, namely wire-mesh sensors, has been used to obtain a detailed picture of the void-fraction development in the system. On the basis of experimental data collected, three-dimensional flow-pattern visualization was achieved.

Keywords: Drift-flux models; flashing; void fraction; natural circulation

  • Nuclear Technology, 152(2005)1, 38-53

Publ.-Id: 6253

Benchmark of Dynamics Simulation Tool for Molten Salt Reactors

Delpech, M.; Dulla, S.; Garzenne, C.; Kophazi, J.; Krepel, J.; Lebrun, C.; Lecarpentier, D.; Mattioda, F.; Ravetto, P.; Rineiski, A.; Schikorr, M.; Szieberth, M.

A benchmark of some codes developed for the neutronic analysis of molten-salt reactors is presented. The results of the calculations are compared to the experimental data reported for the Molten Salt Reactor Experiment performed at Oak Ridge National Laboratory in the 60's. Both static and time-dependent situations are considered. The phenomena connected to the motion of the multiplying material are investigated. The results presented show a good agreement among the codes and with the available experimental data, thus providing the adequateness of the computational tools for the simulation of molten-salt system.

Keywords: Molten; Salt; Reactor; MSR; MSRE; Benchmark; Transient

  • Contribution to proceedings
    Proceedings of the international conference GLOBAL 2003, 2182-2187, New Orleans, LA, November 2003

Publ.-Id: 6252

Investigation of flashing-induced instabilities at the CIRCUS test facility using the code ATHLET

Schäfer, F.; Manera, A.

The CIRCUS test facility has been built to study the start-up phase of a natural-circulation BWR. During the start-up so called flashing-induced instabilities can arise. These instabilities are induced by flashing, due to steam production in the long adiabatic riser section, which is placed above the core to enhance the flow rate. Flashing occurring in the riser causes an unbalance between driving force and pressure losses in the natural-circulation loop, giving rise to flow oscillations.

This paper gives an overview about experimental results and the physics of the instabilities. The thermo-hydraulic code ATHLET is used to investigate the dynamic behavior of the CIRCUS test facility and the results of the calculations are compared with the experimental data.

This work is part of the NACUSP project (Natural Circulation and Stability Performance of BWRs) within the European-Union 5th Framework Programme.

Keywords: BWR; ATHLET; CIRCUS; flow instabilities

  • Lecture (Conference)
    29th International Meeting on Reactor Noise, 17.-19.05.2004, Budapest, Hungary
  • Contribution to proceedings
    29th International Meeting on Reactor Noise, 17.-19.05.2004, Budapest, Hungary, CD-ROM

Publ.-Id: 6251

Untersuchung der Kühlmittelvermischung an der Versuchsanlage ROCOM - Experimente und Modellierung

Prasser, H.-M.; Höhne, T.; Kliem, S.; Rohde, U.; Weiß, F.-P.

Die experimentellen Arbeiten zur Kühlmittelvermischung in einem Druckwasserreaktor vom Typ KONVOI an der Versuchsanlage ROCOM werden vorgestellt. Weiterhin sind die parallel zu den Experimenten durchgeführten theoretischen Arbeiten zur Anwendung und Validierung des CFD-Codes CFX-4 Bestandteil des Beitrages.

  • Lecture (Conference)
    Fachsitzung "Experimentelle und theoretische Untersuchungen zu Borverdünnungstransienten in DWR" auf der Jahrestagung Kerntechnik 2003, Berlin, 20.-22. Mai 2003, Berichtsheft S.57-83
  • Contribution to proceedings
    Fachsitzung "Experimentelle und theoretische Untersuchungen zu Borverdünnungstransienten in DWR" auf der Jahrestagung Kerntechnik 2003, Berlin, 20.-22. Mai 2003, Berichtsheft S.57-83

Publ.-Id: 6249

Fabrication of Schottky barrier MOSFETs on SOI by a self-assembly CoSi2-patterning method

Zhao, Q. T.; Kluth, P.; Winnerl, S.; Mantl, S.

  • Solid State Electronics 47 (2003) 1183

Publ.-Id: 6248

X-ray studies of Al(x)GA(1-x)As implanted with 1.5 meV As ions

Wierzchowski, W.; Wieteska, K.; Graeff, W.; Turos, A.; Grötzschel, R.

  • Vacuum 70 (2003) 115

Publ.-Id: 6247

Resistance to high temperature oxidation in B+Si implanted TiN coatings on steel

Werner, Z.; Piekoszewski, J.; Grötzschel, R.; Richter, E.; Szymczyk, W.

  • Vacuum 70 (2003) 93

Publ.-Id: 6246

Raman and HRTEM investigations of Ge nanocrystals produced by Ge+ ion implantation of SiO2 films and subsequent high pressure annealing

Tyschenko, I. E.; Talochkin, A. B.; Cherkov, A. G.; Zhuravlev, K. S.; Misiuk, A.; Yankov, R. A.; Skorupa, W.

  • Contribution to external collection
    Proc. SPIE Int. Soc. Opt. Eng. 5136 (2003) 236

Publ.-Id: 6245

Jahresbericht 2003 - Forschung für Mensch und Umwelt

Bohnet, C.; (Editor)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-398 2004
    ISSN: 1437-322X


Publ.-Id: 6244

Properties of Ge nanocrystals formed by implantation of Ge+ ions into SiO2 films with subsequent annealing under hydrostatic pressure

Tyschenko, I. E.; Talochkin, A. B.; Cherkov, A. G.; Zhuravlev, K. S.; Misiuk, A.; Yankov, R. A.; Skorupa, W.

  • Semiconductors 37 (2003) 462

Publ.-Id: 6243

Strong blue light emission from ion implanted Si-SiO2 structures

Skorupa, W.; Rebohle, L.; Gebel, T.; Helm, M.

  • Contribution to external collection
    in: L. Pavesi et al. (eds.), "Towards the First Silicon Laser", NATO Sciences Series, Kluwer Academic Publishers, Dordrecht, 2003, p. 69

Publ.-Id: 6242

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