Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Only approved publications

32228 Publications
Nutzbarmachung der List-Mode Akquisition an der PET-Kamera ECAT EXACT HR+
Just, U.; Will, E.; Beuthien-Baumann, B.; Bühler, P.; van den Hoff, J.;
  • Abstract in refereed journal
    Nuklearmedizin (2003) 42 p. A93

Publ.-Id: 5978 - Permalink


Korrektur bewegungsbedingter Fehlortung individueller Koinzidenzereignisse in der PET
Bühler, P.; Just, U.; Will, E.; Zührl, K.; Kotzerke, J.; van den Hoff, J.;
  • Abstract in refereed journal
    Nuklearmedizin (2003) 42 p. A26
  • Lecture (Conference)
    41. Jahrestagung der DGN, 2.-5. April 2003, Essen

Publ.-Id: 5977 - Permalink


Untersuchung des Glukosestoffwechsels bei Patienten mit HIV-Infektion unter hochaktiver antiretroviraler Therapie (HAART) mittels quantitativer dynamischer FDG-PET
van den Hoff, J.; Börner, A.; Behrens, G.; Meyer, G. J.; Knapp, W. H.;
  • Abstract in refereed journal
    In: Nuklearmedizin als Paradigma molekularer Bildgebung, ed. I Brink, S Högerle, E Moser, p. 16, Blackwell Verlag, Berlin (2002)

Publ.-Id: 5976 - Permalink


Dynamische 15O-H2O-PET zur Erzeugung quantitativer 3D-Polar-Maps der Myokardperfusion
van den Hoff, J.; Fricke, H.; Wielepp, P.; Burchert, W.;
  • Abstract in refereed journal
    Nuklearmedizin (2003) 42 p. A27

Publ.-Id: 5975 - Permalink


P0316 - Anordnung zur Röntgentomographie milt einem elektronisch abgelenkten Elektonenstrahl
Prasser, H.-M.; Hampel, U.;
Aufgabe der Erfindung ist es, eine Anordung zur schnellen Tomographie mit elektronisch abgelenktem Elektronenstrahl vorzuschlagen, die es ermöglicht, Projektionen der Dichteverteilung eines zeitlich veränderlichen Messobjekts aus einer genau definierten Messebene zu ermitteln, deren Orientierung im Raum sich bei Veränderung der Durchstrahlungsrichtung während des Messzyklus nicht ändert.
  • Patent
    DE 103 56 601 A1
  • Patent
    DE 103 56 601 B4 - 2008.11.27

Publ.-Id: 5974 - Permalink


Quantenkaskadenlaser
Dekorsy, T.; Helm, M.; Georgiev, N.; Künzel, H.;
Es wird ein Quantenkaskadenlaser mit einer Emissionswellenlänge unterhalb von 3,4 um und oberhalb von 1,5 um vorgeschlagen.
  • Patent
    DE 103 55 949 A1
  • Patent
    EP 1536531

Publ.-Id: 5973 - Permalink


P0313 - Verfahren zur Erzeugung verbesserter heteroepitaktischer gewachsener Siliziumkarbidschichten auf Siliziumsubstraten
Skorupa, W.; Panknin, D.; Ferro, G.; Gebel, T.; Yankow, R.;
Aufgabe der Erfindung ist ein Verfahren, mit dem es möglich ist, die in der unteren Schicht vorhandenen gewünschten Eigenschaften der mit Lichtimpulsen behandelten Substrate für den weiteren Prozess verwertbar zu machen und die Welligkeit der Schicht zu verringern oder zu vermeiden.
  • Patent
    DE 103 44 986 A1
  • Patent
    WO 2005/031825 A1
  • Patent
    DE 103 44 986 B4 - 23. Okt. 2008

Publ.-Id: 5971 - Permalink


3-O-Methyl-6-[18F]Fluoro-L-DOPA and its Evaluation in Brain Tumour Imaging
Beuthien-Baumann, B.; Bredow, J.; Burchert, W.; Füchtner, F.; Bergmann, R.; Alheit, H.-D.; Reiss, G.; Hliscs, R.; Steinmeier, R.; Franke, W.-G.; Johannsen, B.; Kotzerke, J.;
  • European Journal of Nuclear Medicine and Molecular Imaging (2003) 30: 1004-1008

Publ.-Id: 5970 - Permalink


Synthesis and Characterization of [11C]SMe-ADAM as a Potential Radiotracer for Imaging the Serotonin Transporter with PET
Zessin, J.; Kretzschmar, M.; Pawelke, B.; Bergmann, R.; Deuther-Conrad, W.; Brust, P.; Wüst, F.; Steinbach, J.; Johannsen, B.;
  • Poster
    15th International Symposium on Radiopharmaceutical Chemistry, Sydney, Australia, 2003

Publ.-Id: 5969 - Permalink


Sex Differences in the Uptake of [18F]FMe-McN in Rat Brain
Marjamäki, P.; Eskola, O.; Haaparanta, M.; Grönroos, T.; Fagerholm, V.; Bergman, J.; Lehikoinen, P.; Savisto, N.; Zessin, J.; Solin, O.;
  • Lecture (Conference)
    15th International Symposium on Radiopharmaceutical Chemistry, Sydney, Australia, 2003

Publ.-Id: 5968 - Permalink


Comparison of [11C](+)-MCN5652 and S-([18F]Fluoromethyl)-(+)-MCN5652 for PET Imaging of the Serotonin Transporter
Brust, P.; Zessin, J.; Solin, O.; Steinbach, J.;
  • Lecture (Conference)
    15th International Symposium on Radiopharmaceutical Chemistry, Sydney, Australia, 2003

Publ.-Id: 5967 - Permalink


S-[18F]fluoromethyl-(+)-McN5652, a PET Tracer for the Serotonin Transporter: Evaluation in Rats
Marjamäki, P.; Zessin, J.; Eskola, O.; Grönroos, T.; Haaparanta, M.; Bergman, J.; Lehikoinen, P.; Forsback, S.; Brust, P.; Steinbach, J.; Solin, O.;
The [18F]fluoromethyl analog of (+)-McN5652 ([18F]FMe-NcN) for imaging serotonin transporter (SERT) with positron emission tomography (PET) has recently been synthesized. We describe here the biological evaluation of [18F]FMe-NcN in rats. Biodistribution studies of [18F]FMe-McN in rat brain ex vivo after an intravenous injection showed a high accumulation of radioactivity in the regions rich in SERT, such as raphe nuclei, hypothalamus, thalamus, substantia nigra, locus coeruleus, and amygdala. Region-to-cerebellum ratios reached a muximum value of 9 in raphe nuclei within 3.5 h after administration. The specificity and selctivity of [18F]FMe-McN binding to SERT was studied by preinjecting blocking doses of serotonin, norepinephrine, and dopamine transporter inhibitors. Fluoxetine, a specific inhibitor for SERT, decreased the specific binding of [18F]FMe-McN in raphe nuclei by 91 plus minus 4 %; in other regions rich in SERT, similar results were obtained GBR12909 and nisoxetine, selective inhibitors for dopamine transporter (DAT) and norepinephrine transporter (NET), respectively, showed no significant effects on the uptake of [18F]FMe-McN. Our studies show that [18F]FMe-McN has a clear potential as a tracer for studies with PET or SERT function in humans.
Keywords: [18F]FMe-(+)-McN5652; serotonin transporter; positron emission tomography; 18F
  • Synapse (2003) 47: 45-53

Publ.-Id: 5966 - Permalink


18F-Labelling of the CCR1 antagonist ZK811460 for the diagnosis of the Alzheimer´s disease
Mäding, P.;
  • Lecture (others)
    Technical Exchange Meeting on Alzheimer Imaging, Berlin, 30.10.2003

Publ.-Id: 5965 - Permalink


Investigation of the Complexation and the Migration Behavior of Actinides and Non-Radioactive Substances with Humic Acids under Geogenic Conditions - Complexation of Humic Acids with Actindies in the Oxidation State IV Th, U, Np
Sachs, S.; Schmeide, K.; Brendler, V.; Krepelova, A.; Mibus, J.; Geipel, G.; Heise, K.-H.; Bernhard, G.;
Objective of this project was the study of basic interaction and migration processes of actinides in the environment in presence of humic acids (HA). To obtain more basic knowledge on these interaction processes synthetic HA with specific functional properties as well as 14C-labeled HA were synthesized and applied in comparison to the natural HA Aldrich. One focus of the work was on the synthesis of HA with distinct redox functionalities. The obtained synthetic products that are characterized by significantly higher Fe(III) redox capacities than Aldrich HA were applied to study the redox properties of HA and the redox stability of U(VI) humate complexes. It was confirmed that phenolic OH groups play an important role for the redox properties of HA. However, the results indicate that there are also other processes than the single oxidation of phenolic OH groups and/or other functional groups contributing to the redox behavior of HA. A first direct-spectroscopic proof for the reduction of U(VI) by synthetic HA with distinct redox functionality was obtained.
The complexation behavior of synthetic and natural HA with actinides (Th, Np, Pu) was studied. Structural parameters of Pu(III), Th(IV), Np(IV) and Np(V) humates were determined by X-ray absorption spectroscopy (XAS). The results show that carboxylate groups dominate the interaction between HA and actinide ions. These are predominant monodentately bound. The influence of phenolic OH groups on the Np(V) complexation by HA was studied with modified HA (blocked phenolic OH groups). The blocking of phenolic OH groups induces a decrease of the number of maximal available complexing sites of HA, whereas complex stability constant and Np(V) near-neighbor surrounding are not affected.
The effects of HA on the sorption and migration behavior of actinides was studied in batch and column experiments. Th(IV) sorption onto quartz and Np(V) sorption onto granite and its mineral constituents are affected by the pH value and the presence of HA. HA exhibits a significant influence on the transport of U(IV) and U(VI) in a laboratory quartz sand system.
In order to provide the basis for a more reliable modeling of the actinide transport, the metal ion complexation with HA has to be integrated into existing geochemical speciation codes. Within this project the metal ion charge neutralization model was embedded into the geochemical modeling code EQ3/6. In addition to that, a digital data base was developed which covers HA complexation data basing on the charge neutralization model.
Keywords: Humic Substances, Humic Acids, Model Substances, Redox Properties, Actoinides, Thorium, Uranium, Neptunium, Plutonium, Complexation, Structure, Sorption, Migration, Repository, Modeling, Data Base
  • Other report
    Final Report, BMWA Project No. 02 E 9299
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf, FZR-399 2004
  • Other report
    In: C.M. Marquardt (Ed.): Investigations on the Complexation Behaviour of Humic Acids and their Influence on the Migration of Radioactive and Non-radioactive Substances under Conditions Close to Nature. Final Report, Forschungszentrum Karlsruhe, Wissenschaftliche Berichte FZKA 6999, Karlsruhe 2004

Downloads:

Publ.-Id: 5964 - Permalink


18F-markierte Corticosteroide als Liganden für die Darstellung von Glucocorticoidrezeptoren (GR) im Gehirn mittels PET
Wüst, F.;
  • Lecture (others)
    Gemeinsames Institutskolloquium der Klinik und Poliklinik für Nuklearmedizin und des Instituts für Interdisziplinäre Isotopenforschung Leipzig, 23.10.2003

Publ.-Id: 5962 - Permalink


Fraktografie an radioaktiven Proben mit der Abdrucktechnik
Müller, G.;
Die direkte Fraktografie auf Bruchflächen von bestrahlten oder radioaktiv kontaminierten Proben ist nur an speziell für einen solchen Einsatz dedizierten Rasterelekt-ronenmikroskopen (REM) möglich. Eine Alternative bietet die Anwendung der Abdrucktechnik, mit deren Hilfe auch fraktografische Untersuchungen an herkömmli-chen REMs durchgeführt werden können. Die Methode muss genügend Details wie-dergeben, unter den Bedingungen einer heißen Zelle handhabbar sein und im Endabdruck kontaminationsfrei arbeiten.

Abdrucktechniken werden von einschlägigen Firmen vorzugsweise auf der Basis von Folien angeboten. Für rauhe, duktile Bruchflächen sind sie ungeeignet. Auch die Verwendung von Filmmaterialien und Wachsen ist unter den gegebenen Bedingungen nicht geeignet. Am erfolgreichsten erweist sich ein einstufiger Negativ-Abdruck mit duktilen, additionsvernetzenden Silikonen.

Dieses Verfahren wurde an Bruchflächen von Proben aus Reaktordruckbehälterstäh-len und -schweißmetall erfolgreich getestet. Zielstellung war vor allem der Nachweis von interkristallinen Bruchanteilen an vorzugsweise spröd und duktil gebrochenen Charpy-Proben. An den unbestrahlten RDB-Stählen A 533-B Cl. 1 und 15 CrMoV2 sowie dem Schweißmetall 10 CrMnNiMo2 konnte ein relativ großer Anteil interkristallinen Bruchs nachgewiesen werden. Die Anwendung des Verfahrens auf bestrahlte Proben des Schweißmetalls 10 CrMnNiMo2 erbrachte, je nach der Zähig-keit der Proben, differierende Anteile an transkristallinem Spalt- und Wabenbruch und nur sehr vereinzelten interkristallinen Bruch.
Keywords: Abdrucktechnik, Bruchfläche, Provil Novo, Reaktordruckbehälterstähle, radioaktiv, kontaminiert
  • Lecture (Conference)
    Sonderbände der Praktischen Metallographie, Band 35, Fortschritte in der Metallographie, S. 371-376, Sonderdruck und Internetbericht durch Fa. Heraeus Kulzer GmbH & Co. KG
  • Contribution to external collection
    Sonderbände der Praktischen Metallographie, Band 35, Fortschritte in der Metallographie, S. 371-376, Sonderdruck und Internetbericht durch Fa. Heraeus Kulzer GmbH & Co. KG

Downloads:

Publ.-Id: 5961 - Permalink


Comment on "Identification of lattice vacancies on the two sublattices of SiC"
Kuriplach, J.; Brauer, G.; Anwand, W.; Skorupa, W.;
no abstract !
Keywords: silicon carbide, positron annihilation, defects

Publ.-Id: 5958 - Permalink


Percolation of Electron Tunneling between Si Nanocrystals Synthesized in Thin SiO2 Films by Ion Implantation
Müller, T.; Heinig, K.-H.;
The controlled fabrication of a narrow layer of Si nanocrystals (NCs) in thin SiO2 films for multi-dot non-volatile memories (NC memory) is still a considerable materials issue, which will be addressed in this contribution. The synthesis of NCs by Si+ implantation of SiO2 followed by a thermal treatment aims at an optimum NC density. A NC density being as high as possible is required in order to achieve a substantial threshold voltage shift of the MOS transistor. On the other hand, the advantages of the NC memory, as good scalability and data retention, are lost at too high NC densities. Then NC’s charge can spread over neighboring NCs by direct e- tunneling, i.e. due to electrical in-plane percolation paths. One single oxide defect could discharge several electrically percolated NCs.
This contribution is devoted to the trade-off between these two optimization routes. The Si NC formation by nucleation, growth and Ostwald ripening in low-energy Si+ implanted SiO2 is predicted by kinetic lattice Monte Carlo simulations. On the basis of these simulations, the dependence of the Si NC density, the distribution of the NC spacing as well as the threshold for extended electron tunneling paths are predicted. Thus, process conditions could be identified, where NCs align in narrow layer at high density but are sufficiently electrically isolated.
  • Poster
    Fall Meeting of the Materials Research Society, December 1-5, 2003, Boston, USA

Publ.-Id: 5957 - Permalink


Comparison of Kinetic MC Simulations and EFSTEM Observations of Phase Separation in Si Implanted Thin SiO2 Films
Müller, T.; Heinig, K.-H.; Bonafos, C.; Coffin, H.; Ben Assayag, G.; Schamm, S.; Zanchi, G.; Claverie, A.; Colliex, C.; Tencé, C.;
Studies on the ion beam synthesis of narrow Si nanocrystal (NC) layers in thin SiO2 films are presented. Very low-energy Si+ implantation into gate oxides for MOS transistors followed by thermal annealing allows for the fabrication of novel Si NC floating gate based non-volatile charge storage devices.
Small and isolated Si NCs at high density are required to obtain a large threshold voltage shift of the memory transistor. However, former work shows that the characterization of the Si NCs embedded in SiO2 by conventional Transmission Electron Microscopy (TEM) is difficult. It requires careful con-siderations and special imaging conditions [1] due to the weak contrast be-tween Si and SiO2 .
In this contribution, Energy Filtered Scanning Transmission Electron Micros-copy (EFSTEM) investigations on the morphology of phase separated Si in SiO2 are presented, which overcome the contrast limitations of the conven-tional TEM. Furthermore, a comparison of the observed Si pattern with pre-dictions of kinetic lattice Monte Carlo (MC) simulations [2] is performed. The Si precipitates were synthesized by 1 keV Si+ implantation into 10 nm thick SiO2 and by furnace annealing in N2 (or N2 + O2). Varying fluences from 5E15 to 2E16 Si+ cm-2 were used in order to adjust the Si excess in the SiO2. For these conditions, dynamical binary collision simulations (TRIDYN) of high-fluence implantation were combined with kinetic Monte Carlo simula-tions of NC formation by phase separations. For low Si excess, NCs are pre-dicted to form by nucleation, growth and Ostwald ripening. On the other hand, at high Si excess, phase separation proceeds via spinodal decomposition, were elongated NCs are found in our computer experiment. At even higher flu-ences, structural percolation occurs and a random connected Si mesh forms. Thus, the morphology of the phase separated Si changes with increasing ion fluence from isolated, spherical NCs to percolated structures as observed by EFSTEM. The pattern of the phase separated Si predicted by kinetic Monte Carlo simulations and observed by Electron Microscopy agree remarkably well.
  • Lecture (Conference)
    Fall Meeting of the Matrials Research Society 2003, December 1-5, Boston, USA

Publ.-Id: 5955 - Permalink


Range and mixing distributions of low-energy carbon ions as a base for subplantation growth models
Dollinger, G.; Neumaier, P.; Bergmaier, A.; Görgens, L.; Eckstein, W.; Fischer, R.; Hofsäss, H.; Jäger, H. U.; Kröger, H.; Ronning, C.;
Subplantation was early recognised as being the basic process in low-energy ion growth of diamondlike materials and has also to be considered for the description of bias enhanced diamond nucleation. A number of theories modelling the evolution of diamondlike phases have been proposed. However, the precise details of the subplantation and relaxation processes remain unclear. The problem in testing the complex models is that experimental information other than film structure versus ion energy is missing to a large extent. Mixing and range distributions of low-energy carbon ions are ideal data to model diamond-like film growth. Here we present measurements of range and mixing distributions for carbon ions at energies in the relevant energy range between 12 eV and 692 eV in carbon. The substrates are grown at the identical energies using 12C ions by mass separated ion beam deposition. Less than a monolayer of 13C was implanted each for the range distributions and as a marker layer for the mixing profiles. The 13C depth profiles are measured by high-resolution elastic recoil detection (ERD). These data are directly compared to calculations based on the binary collision approximation (TRIDYN) and to molecular dynamics (MD) simulations which consider atomic interactions on a time scale up to 15 ps including the thermal spike phase. Additionally, mixing distributions are derived from a transport calculation based on the measured range distributions. The measured range profiles show bimodal structures for energies below 200 eV which are significantly broader than the calculated profiles.The mixing profiles are also significantly broader than respective TRIDYN and MD calculations at these low energy. However, mixing profiles are in good agreement with transport calculations based on the measured range profiles showing the relevance of the measured range structures. Three reasons for the observed differences between the measured and theoretical range and mixing distributions are discussed in the paper: thermal induced self diffusion during thermal spike, mobility solely of the deposited ion after the collisional stage and a 3-dimensional surface structure of the carbon films on atomic scale. The experiment allows a crucial test for models of the subplantation scheme and may serve as input for improved calculations.
  • Invited lecture (Conferences)
    MRS 2003 Fall Meeting, Dec. 1 - 5, Boston, USA; Symp.R: Radiation Effects and Ion Beam Processing of Materials; contr. R12.1, invited talk

Publ.-Id: 5954 - Permalink


Conserved high-affinity ligand binding and membrane association in the native and refolded extracellular domain of the human glycine receptor alpha 1 subunit
Breitinger, U.; Breitinger, H.-G.; Bauer, F.; Fahmy, K.; Glockenhammer, D.; Becker, C.-M.;
  • Journal of Biological Chemistry 279(2004)4, 1627-1636

Publ.-Id: 5953 - Permalink


Analysis of buoyancy driven coolant mixing by using the code TRIO_U
Höhne, T.; Bieder, U.;
A generic investigation of the influence of density differences between the primary loop inventory and the ECC water on the mixing in the downcomer was made at the ROCOM Mixing Test Facility at Forschungszentrum Rossendorf (FZR). For the validation of the Trio_U code an experiment with 5% constant flow rate in one loop (magnitude of natural circulation) and 10% density difference between ECC and loop inventory was taken. Trio_U is a CFD code developed by the CEA France, aimed to supply an efficient computational tool to simulate transient thermal-hydraulic single -phase turbulent flows encountered in the nuclear systems as well as in the industrial processes. For this study, a LES approach was used for mesh sizes between 1–2 million control volumes. The study showed, that density effects play an important role during natural convection with ECC injection in pressurized water reactors. Further-more it was important to point out, that Trio_U is able to cope the main flow and mixing phenomena.
Keywords: Boron Dilution, COOLANT MIXING, ROCOM Test FACILITY, Computational Fluid Dynamics, LES, Trio_U
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 25.-27.05.2004, 2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 25.-27.05.2004, 2004, Düsseldorf, Germany, CD-ROM

Publ.-Id: 5952 - Permalink


Validation of TRIO_U – Numerical Simulations of a ROCOM Buoyancy Driven Test Case
Höhne, T.; Bieder, U.; Prasser, H.-M.; Kliem, S.;
A generic investigation of the influence of density differences between the primary loop inventory and the ECC water on the mixing in the downcomer was made at the ROCOM Mixing Test Facility at Forschungszentrum Rossendorf (FZR)/Germany.
ROCOM is designed for experimental coolant mixing studies over a wide variety of possible scenarios. It is equipped with advanced instrumentation, which delivers high-resolution information characterizing either temperature or boron concentration fields in the investigated pressurized water reactor.
For the validation of the Trio_U code an experiment with 5% constant flow rate in one loop (magnitude of natural circulation) and 10% density difference between ECC and loop water was taken.
Trio_U is a CFD code developed by the CEA France, aimed to supply an efficient computational tool to simulate transient thermal-hydraulic single-phase turbulent flows encountered in the nuclear systems as well as in the industrial processes. For this study a LES approach was used for mesh sizes according to between 300000 – 2 million control volumes.
The results of the experiment as well as of the numerical calculations show, that a streak formation of the water with higher density is observed. At the upper sensor, the ECC water covers a small azimuthal sector. The density difference partly suppresses the propagation of the ECC water in circumferential direction. The ECC water falls down in an almost straight streamline and reaches the lower downcomer sensor position directly below the affected inlet nozzle. Only later, coolant containing ECC water appears at the opposite side of the downcomer.
The study showed, that density effects play an important role during natural convection with ECC injection in pressurized water reactors. Furthermore it was important to point out, that Trio_U is able to cope the main flow and mixing phenomena.
Keywords: BORON DILUTION, COOLANT MIXING, ROCOM TEST FACILITY, COMPUTATIONAL FLUID DYNAMICS, LES, TRIO_U
  • Lecture (Conference)
    12th International Conference on Nuclear Engineering, 25.-29.05.2004, Washington D.C., United States
  • Contribution to proceedings
    12th International Conference on Nuclear Engineering, 25.-29.05.2004, Washington D.C., United States, Book of Abstracts, S. 278

Publ.-Id: 5951 - Permalink


Radiation enhanced silicon self-diffusion and the silicon vacancy at high temperatures
Bracht, H.; Fage, J. P.; Zangenberg, N.; Nylandsted, A. L.; Haller, E. E.; Lulli, G.; Posselt, M.;
We report proton radiation enhanced self-diffusion (RESD) studies on Si-isotope heterostructures. Self-diffusion experiments under irradiation were performed at temperatures between 780 0C and 872 0C for various times and proton fluxes. Detailed modeling of RESD provides direct evidence that vacancies at high temperatures diffuse with a migration enthalpy of HmV = (1.8±0.5 eV) significantly more slowly than expected from their diffusion at low temperatures, which is described by HmV < 0.5 eV. We conclude that this diffusion behavior is a consequence of the microscopic configuration of the vacancy whose entropy and enthalpy of migration increase with increasing temperature.
Keywords: defects, silicon, vacancy, interstitial, diffusion, ion implantation
  • Physical Review Letters 91 (2003) 245502

Publ.-Id: 5950 - Permalink


Monte-Carlo-Methoden für den Elektronentransport mit Einzelstreumodellen
Reichelt, U.; Henniger, J.; Enghardt, W.;
Die Abbremsung eines Elektrons bis zu seiner vollständigen Thermalisierung ist durch eine sehr große Anzahl von Wechselwirkungen gekennzeichnet. Deshalb basieren Monte-Carlo-Algorithmen für den Elektronentransport derzeit noch fast ausschließlich auf der Anwendung von zwei Mehrfachstreumodellen. Die Vielfachstreutheorie nach MOLIERE versagt bei kleinen räumlichen Strukturen und Dichtesprüngen. Das Modell nach GOUDSMIT-SAUNDERSON führt für diese Fälle praktisch zum Einzelstreumodell und erfordert dabei aber einen enormen numerischen Aufwand.
An dieser Stelle soll ein Monte-Carlo-Algorithmus vorgestellt werden, der genuin auf Einzelstreuakten basiert. Die Strahlverfolgung (ray tracing) sowie das Erheben von Stichproben für freie Weglängen und Eigenschaften der Streuteilchen müssen mit effektiven numerischen Verfahren behandelt werden. Insbesondere die stark anisotropen Streuprozesse erschweren dieses Anliegen erheblich.
Diese Methodik ist ins Transportprogramm AMOS implementiert. Ein Vergleich mit experimentell bestimmten Daten und anderen Transportrechnungen zeigt zufriedenstellende Übereinstimmungen.
Keywords: Strahlungstransport, Einzelstreumodell, Monte-Carlo-Algorithmus
  • Lecture (Conference)
    68. Physikertagung der Deutschen Physikalischen Gesellschaft 2004, Frühjahrstagung der Arbeitskreise Atome, Moleküle, Quantenoptik und Plasmen (AMOP)

Publ.-Id: 5949 - Permalink


Measurements of gamma and neutron flux spectra in iron-water configurations
Böhmer, B.; Grantz, M.; Hansen, W.; Hinke, D.; Konheiser, J.; Noack, K.; Mehner, H.-C.; Stephan, I.; Unholzer, S.;
Neutron and gamma spectra were measured behind and inside of modules consisting of variable iron and water slabs which were installed in radial beams of the zero-power training and research reactors AKR of the Technical University Dresden and ZLFR of the University of Applied Sciences Zittau/Görlitz. The applied NE-213 scintillation spectrometer allowed the measurement of gamma and neutron fluence spectra in the energy regions 0.3 - 10 MeV for photons and 1.0 - 20 MeV for neutrons. Measurements with thermoluminescence dosemeters (TLD) between slabs supplied additional information about the space distribution of energy integrated fluxes. The paper describes the experiments and presents some important results of the measurements. They will be compared with the results of transport calculations made by means of MCNP and TRAMO in another paper.
Keywords: neutron spectra, gamma spectra, spectrum measurements, coupled neutron/gamma transport calculations, NE-213 scintillation spectrometer, TLD-measurements
  • Kerntechnik 68 (2003) 5-6

Publ.-Id: 5948 - Permalink


Theorien und Experimente zum hydromagnetischen Dynamoeffekt
Stefani, F.;
Die Magnetfelder von Planeten, Sternen und Galaxien entstehen hauptsächlich durch Selbsterregung in strömenden elektrisch leitfähigen Fluiden. Falls die Strömung stark genug ist und ein gewisses Mass an Schraubenförmigkeit aufweist, können die unter der Wirkung eines angenommenen Magnetfeldes induzierten elektrischen Ströme genau jenes Magneteld reproduzieren. Die Theorie hydromagnetischer Dynamos wird anhand der Induktionsgleichung sowie eines äquivalenten Integralgleichungssystems auf Basis des Biot-Savart-Gesetzes skizziert. Der Schwerpunkt des Vortrages liegt auf dem experimentellen Nachweis des Effektes, der Ende 1999 nahezu zeitgleich an zwei Natriumanlagen in Riga und Karlsruhe erfolgte. Die Ergebnisse des Rigaer Experimentes werden ausführlicher dargestellt und mit numerischen Resultaten verglichen.
  • Lecture (others)
    Physikalisches Kolloquium, Brandenburgische Technische Universität Cottbus, 13. 01.2004, Cottbus, Germany

Publ.-Id: 5947 - Permalink


Free-Electron Lasers in Physics
Dekorsy, T.;
The topic of this chapter is a survey on the main applications of free-electron lasers (FELs) in physical sciences. The merits of FELs are discussed with respect to other available laser sources. For the wavelength ranges, where FELs contributed significantly to advances in physical sciences, specific examples of the research with FELs are given.
Keywords: free-electron lasers, applications of FELs, spectroscopy, time-resolved
  • Contribution to external collection
    Encyclopedia of Modern Optics, Eds. B.D. Guenther and D.G. Steel, Elsevier (2004), 164-169

Publ.-Id: 5946 - Permalink


Light-emitting silicon pn diodes
Dekorsy, T.; Sun, J.; Skorupa, W.; Schmidt, B.; Helm, M.;
We report on the electrical and optical characteristics of silicon light-emitting pn diodes. The diodes are prepared by ion implantation of boron at high doses and subsequent high-temperature annealing. Under forward bias, the diodes emit infrared electroluminescence close below the bandgap of bulk Si. We present a rate equation model for bound excitons, free excitons and free carriers which successfully describes the electrical and optical behaviour of the diodes at low temperatures. Especially an electrical bistability observed below 50 K is shown to be based on the interplay of bound excitons, free excitons, and free carriers in the active area of the diodes. The ionization of bound excitons is the origin of an improved electroluminescence from the diodes
at higher lattice temperatures.
Keywords: silicon based optoelectronics, light emission, pn diode, ion implantation
  • Applied Physics A 78(2004), 471-475

Publ.-Id: 5945 - Permalink


Discussion of the Behaviour of Different RPV-Steels in Vessel Creep Failure Experiments
Willschütz, H.-G.; Müller, G.; Altstadt, E.;
Considering the hypothetical core melt down scenario for a light water reactor the failure mode of the reactor pressure vessel (RPV) has to be investigated to deter-mine the loadings on the containment. Experimental and numerical work is performed worldwide to get insights about possible consequences. To validate the developed computational tools numerical simulations of Lower Head Failure experi-ments like OLHF or FOREVER are conducted.
An interesting question to be solved in this frame is the reason for the different shape of the failure site even under comparable loading conditions and for the same material: In some experiments like LHF-7 and EC-FOREVER-3B a rough crack surface was found at the failure site while in others like OLHF-1 a rather ductile behaviour was observed resulting in nearly blade-like edges on both sides of the vessel opening.

Keywords: lower head failure experiments, LHF, OLHF, FOREVER, creep failure, FEM simulation
  • 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 519-522

Publ.-Id: 5944 - Permalink


Fluid-Structure Interaction Investigations for Pipelines
Altstadt, E.; Carl, H.; Weiß, R.;
The influence of the fluid-structure interaction on the magnitude fo the loads on pipe walls and support structures is not yet completely understood. In case of a dynamic load caused by a pressure wave, the stresses in pipe walls, especially in bends, are different from the static case.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-393 Dezember 2003

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Publ.-Id: 5943 - Permalink


Characterization of Radiation Effects in Reactor Pressure Vessel Steels by means of Small Angle Neutron Scattering
Ulbricht, A.; Böhmert, J.;
The influence of deleterious elements on the microstructural evolution in materials due to neutron irradiation was investigated by small angle neutron scattering experiments.
The study compares properties of ASTM and VVER RPV steels after different exposure levels.
Keywords: SANS, RPV steel, radiation defect
  • 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 pp. 515-518,

Publ.-Id: 5942 - Permalink


Kolloidgetragene Schadstoffe in oxischen Bergwerkswässern
Zänker, H.; Ulrich, K.-U.; Jenk, U.; Moll, H.; Richter, W.;
Ausgehend von drei grundsätzlichen Fällen werden die Konsequenzen der Vernachlässigung des kolloidgetragenen Transports von toxischen und radiotoxischen Schadstoffen in stillgelegten Bergwerken für die Prognose der Auswirkungen der Bergwerke auf die Umwelt diskutiert. Zunächst werden Messungen zur Bestimmung des Kolloidinventars in einem typischen "sauren Porenwasser" (Lettenwasser Freiberg) und einem typischen "Bulk-Wasser" (Stollenwasser Rothschönberg) beschrieben. Sodann wird ein Neutralisationsversuch vorgestellt, bei dem innerhalb von fünf Tagen 6 Liter sauerstoffarmes saures Flutungswasser aus einem Uranbergwerk mit etwa 100 Liter oxischem Grundwasser aus einem in der Nähe gelegenen Grundwasserleiter gemischt wurden, um die Flutung der Grube unter oxischen Bedingungen (Begasung mit Sauerstoff) bis in ihr Endstadium zu simulieren. Der Versuch zeigt, dass ab pH > 4 zunehmende Mengen des in dem Flutungswasser enthaltenen Urans in einen kolloidgetragenen Zustand übergehen. Die Natur der Uranbindung in den Kolloiden wird auf spektroskopischem Wege (Tieftemperatur-EXAFS an der Rossendorfer Beamline ROBL der ESRF in Grenoble) noch direkt bestimmt.
Keywords: Kolloide, Bergwerke, Uran, Flutung
  • Poster
    Jahrestagung der Wasserchemischen Gesellschaft in der GDCh, Bad Saarow, 17. - 19. Mai 2004
  • Contribution to proceedings
    Jahrestagung Wasserchemische Gesellschaft, 17.-19.05.2004, Bad Saarow, Deutschland
    Kurzreferate, Wächtersbach: PM-GrafikDesign, 3-936028-24-9, 181-185

Publ.-Id: 5941 - Permalink


Imaging Si Nanoclusters in Thin SiO_2 Layers by XTEM using Contrast Enhancing Decoration with Ge
Röntzsch, L.; Heinig, K. H.; Schmidt, B.;
The Multidot Nano-flash Memory suggested by Tiwari [APL69(1996)1232] is a promissing candidate for succeeding the common Floating Gate Flash Memory.

Its most challenging configurational feature is a layer of insulated Si nanoclusters (NCs) within the oxide of a MOS-like structure.

Here, we present experimental evidence that the theoretical concept predicting the self-organization of delta-layers of Si NCs at ion irradiated interfaces is valid (cf. Heinig [APA77(2003)17]).

In this approach of ``bottom-up" structuring, unconventionally, a 15nm thin buried SiO_2 layer, which is enclosed by a 50nm poly-Si capping layer and the Si substrate, is irradiated with Si ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiO_x (x<2) -- where x is a function of depth -- is formed which is not stable.

During annealing, the system relaxes towards equilibrium, i.e. phase separation (via spinodal decomposition and nucleation) sets in. Within a certain time window of annealing, the structure of the system matches with a structure similar to the Multidot Memory device, the principal character of which is a 2D layer of Si nanoclusters of (d~3nm) which is embedded in a 3D SiO_2 matrix at a distance of ~3nm from the Si substrate.

The experimental handicap that tiny Si NCs (d<3nm) which are embedded in SiO_2 are not visible in common XTEM is resolved by a novel method which applies Ge as contrast enhancing element in TEM studies of tiny Si NCs.

Keywords: Ion Irradiation, Si Nanoclusters, Ge decoration, Multidot Flash Memory
  • Poster
    Conference contribution to Trends in Nanotechnology, Sept. 2003, Salamanca, Spain

Publ.-Id: 5939 - Permalink


Velocity measuring techniques at FZR and status of MULTIMAG
Galindo, V.; Cramer, A.; Eckert, S.; Gerbeth, G.;
A review will be given on the present status of the facility MULTIMAG and the possibilities to measure local velocities in metal or semiconductor melts. The use of MULTIMAG or the measuring techniques for applications in crystal growth modeling will be discussed.
  • Lecture (Conference)
    Use of magnetic fields in crystal growth, Workshop, Riga (Lettland), 5.-6.12.2003

Publ.-Id: 5938 - Permalink


In vivo Measurement of the Serotonin Transporter with (S)-([18F]fluoromenthyl)-(+)-McN5652
Brust, P.; Hinz, R.; Kuwabara, H.; Hesse, S.; Zessin, J.; Pawelke, B.; Stephan, H.; Bergmann, R.; Steinbach, J.; Sabri, O.;
The radiolabeled serotonin transporter (SERT) ligand [11C](+)-McN5652 has recently been used in clinical positron emission tomography (PET) studies for SERT imaging. However, this radioligand offers disadvantages in routine clinical settings because of its short radioisotope half-life (eg PET facilities within hospitals without a cyclotron need to acquire such radioligands from distant cyclotron units for clinical use). S-([18F]fluoromenthyl)-(+)-McN5652 ([18F](+)-FMe-McN5652) is an analogue which has been synthesized newly, and has a significant longer radioisotope half-life. In the porcine brain, it demonstrates the same characteristic distribution pattern of serotonin-uptake sites like the 11C-labeled congener with the highest binding in the midbrain and thalamus and the lowest in the cerebellum and occipital cortex. It shows a 30 % higher blood-brain transfer and a slower peripheral metabolism than [11C](+)-McN5652. Rather uniform brain binding was observed after injection of the pharmacologically inactive radiolabeled enantiomer, or after pretreatment with the highly selective SERT inhibitor citalopram. The norepinephrine uptake inhibitor maprotiline did not show any inhibitory effect. Using a one-tissue compartment model (K1, k´´2) or a two tissue compartment model (K1, k4) with or without constraints for calculation, the regional binding parameters of [11C](+)-McN5652 and [18F](+)-FMe-McN5652 are highly correlated among each other and with the SERT density, as determined by in vivo binding of [3H]citalopram. Using constraints to correct for the free fraction and nonspecific binding of the radiotracers, a considerable increase of the midbrain-occipital cortex ratios with higher values for [18F](+)-FMe-McN5652 compared to [11C](+)-McN5652 was revealed. It is concluded that [18F](+)-FMe-McN5652 has better features than [11C](+)-McN5652 for SERT imaging with PET.
Keywords: serotonin transporter; receptor imaging; positron emission tomography; kinetic modeling; [18F](+)-FMe-McN5652; citalopram
  • Neuropsychopharmacology (2003) 28, 2010-2019

Publ.-Id: 5937 - Permalink


Local flow structures in liquid metals measured by ultrasonic Doppler velocimetry
Cramer, A.; Zhang, C.; Eckert, S.;
Ultrasound Doppler velocimetry (UDV) has been successfully applied to measure local velocities in mercury and the eutectic alloy InGaSn. Two different kinds of magnetic fields established the fluid motion in a cylindrical vessel. For both, the rotating and the traveling field, agreement with expectations from theory and local measurements employing different techniques was achieved.
The deliverance of a profile by UDV instead of one value at one fixed co-ordinate, typical for almost any other method, allowed for the determination of the topology in a plane covered by the ultrasonic beam while the sensor was traversed. These area-wide results are, by nature, time averaged respectively mean velocities.
The range of flow regimes regarding the magnitude of velocity which is detectable by means of the Doppler procedure begins already in the turbulent region. For the case of the rotating magnetic field spectral distributions of time series of velocity signals measured at different positions in the fluid volume will be presented.

  • Flow Measurement and Instrumentation 15(2004), 145-153

Publ.-Id: 5936 - Permalink


Cathodoluminescence Decay Kinetics in Ge+, Si+, O+ Implanted SiO2 Layers
Trukhin, A. N.; Jansons, J.; Fitting, H.-J.; Barfels, T.; Schmidt, B.;
Cathodoluminescence spectra shapes and respective band decay times show no similarity between luminescence centers in different crystal and amorphous modifications of SiO2 and GeO2. On the other hand, the additionally produced red luminescence centers (650 nm) by oxygen implantation into SiO2 layers are of the same nature as in stoichiometric SiO2 and are attributed to the non-bridging oxygen hole center (NBOHC). Moreover, the elevated blue (460 nm) luminescence in Si implanted SiO2 belongs to the silicon related oxygen deficient center (SiODC) as in stoichiometric layers too. Ge implantation into SiO2 and thermal post-annealing leads to a huge violet luminescence (400 nm) with a first rapid decay of t = 24 ns followed by a slow hyperbolic decay with (t)-0.15 ... (t)-0.54. The last 10% show again an exponential decay with a mean life time t = 125 µs. This complex luminescent center is related to the GeODC center formed during the thermal treatment by Ge cluster formation
Keywords: Cathodoluminesence, ion implantation, nanocluster, glass
  • Journal of Non-Crystalline Solids 331(2003) 91-99

Publ.-Id: 5935 - Permalink


DYN3D Calculations Compared to the Measurements in the V-1000 Test Facility
Grundmann, U.; Mittag, S.;
The full-scale zero power facilitlity V-1000 was build at the Russian Research Centre ?Kurtschatov Institute? for the investigation of neutron-physical parameters of the VVER-1000 core[1]. Two steady-state measurements and two transient experiments at the V-1000 were made available in the frame of EU project VALCO for the valida-tion of three-dimensional neutron kinetic codes. The results of the DYN3D code [2] by using three different libraries of two group constants generated with the cell codes HELIOS [3], CASMO [4] and WIMS [5] are compared with the measurements. The C/E comparisons of the radial power distribution at the axial detector position for the two steady-states with all control rods out of core and with inserted bank 10 are pre-sented in the next section. A single control rod of bank 9 is moved in the core and reverse in the transient experiment 1. The experiment 2 consists of a scram with a delayed motion of one stuck cluster The results of the calculations with the three li-braries are compared with the incore detectors signals and the signals of two ioniza-tion chambers in section 3. The reactivity calculated by inverse point kinetics from the ionization chambers signals and from the calculated core averaged fluxes are pre-sented.
Keywords: neutron kinetics three-dimensional validation codes steady states transients zero power reactor VVER-1000 experiments nodal methods
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 25.-27.05.2004, Düsseldorf, Germany, CD-ROM 17-20

Publ.-Id: 5934 - Permalink


Stress measurements of germanium nanocrystals embedded in silicon oxide
Wellner, A.; Paillard, V.; Bonafs, C.; Coffin, H.; Claverie, A.; Schmidt, B.; Heinig, K.-H.;
Ge nanocrystals embedded in thermal SiO2 on top of a Si substrate are investigated using Raman spectroscopy and transmission electron microscopy. We observe that the Raman peak frequency of the Ge nanocrystals is strongly affected by compressive stress. In the case of large particles for which the phonon confinement-induced Raman shift can be neglected, the stress is measured taking into account isotopic composition effects induced by the ion implantation process used to produce
the nanocrystals. The stress is proposed to originate from a liquid¿solid phase transition in Ge.
Keywords: Ge nanocrystals, Raman spectroscopy, stress

Publ.-Id: 5933 - Permalink


Nanostructures by Ion Beam Synthesis
Schmidt, B.;
Ion beams are widely used in research and development as well as in different fields of industrial applications, for example for doping of semiconductors in microelectronics. Furthermore, among other techniques ion beams exhibit a great potential for synthesis of new materials as well as for the self-organization of nanostructures. Two of the goals of materials research using ion beams are the ion beam synthesis (IBS) of nanocrystals (NC´s) and the self-organization of NCs under ion irradiation in a solid matrix, for example the formation of semiconducting or metallic NCs in insulating films for applications microelectronics and optoelectronics, respectively.
Semiconducting NCs embedded in the gate oxide of a MOS field effect transistor can be charged/decharged by tunnelling of electrons from/to the Si substrate, caused by an appropriate voltage pulse applied to the gate. There is a difference in the source/drain current for charged and neutral NCs which can be used for the storage of information. The basis of this memory concept is quite simple. However, the fabrication of tiny NCs (~2 nm) placed at the right position within the very thin (< 20 nm) gate oxide is a strong challenge. Different ion beam processes are being developed for realization: i) low energy ion implantation into the thin gate silicon oxide and ii) medium energy ion irradiation through the gate oxide. The two approaches will be described from the physical and technological point of view and experimental results of charge storage behaviour in NC MOS transistors fabricated by the two ion beam processes will be presented.
Another effort is currently devoted to the application of ion beam synthesized metallic NCs in optoelectronics. The fabrication of NCs by IBS requires usually a thermal treatment for phase separation of implanted impurity atoms and for damage annealing. This annealing leads inevitably to broad NC size distribution. Due to the broad size distribution of NCs fabricated by IBS, their size- depending characteristics, e.g. absorption and luminescence, can be obscured. Thus the potential for tailoring of size and size distribution of NCs by IBS is rather limited. It will be shown that size and size distribution can be tailored by high-energy ion irradiation through an ensemble of NCs.
Finally, in the outlook the lecture will address new trends of IBS for nanostructure fabrication, e.g. self-organization at ion implantation into templates and IBS of nanostructures by using focused ion beams (FIB).

Keywords: Ion beam synthesis, nanocluster, nanocluster memory
  • Lecture (Conference)
    13th International Summer School on Vacuum, Electron and Ion Technologies (VEIT 3003), September 15-19, 2003, Varna, Bulgaria

Publ.-Id: 5932 - Permalink


Local structure of Sn implanted in thin SiO2 films
Spiga, S.; Montovan, R.; Franciulli, M.; Ferretti, N.; Boscherini, F.; Schmidt, B.; Grötzschel, R.; Mücklich, A.;
The formation and the structural properties of Sn nanocrystals produced by ion implantation in thin SiO2 films was investigated by 119Sn conversion electron Moessbauer spectroscopy (CEMS), x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). Sn ion implantation was performed at 80 keV with a fluence of 1x1016 cm2, positioning the peak of the implantation profile in the middle of the SiO2. The annealing treatments were performed in the temperature range 800–1100 °C by rapid thermal processing. CEMS and XAS provided unique information on the local atomic and electronic environment of Sn in SiO2 allowing a detailed investigation of the effect of different annealing conditions. In the as-implanted state all Sn ions are oxidized (with both Sn2+ and Sn4+ oxidation states present), while annealing induces the formation of beta-Sn nanoclusters. TEM showed that cluster sizes are in the range 7–17 nm. For clusters with average diameter ,10 nm, XAS detected a reduction in coordination number and interatomic distances. Both XAS and CEMS indicate an increase in the static disorder in the metallic clusters. The investigated annealing treatments do not lead to a complete precipitation of Sn atoms in the metallic phase, leaving a fraction of them oxidized.
Keywords: Sn nanocluster, ion implantation, CEMS, XAS, TEM, RBS

Publ.-Id: 5931 - Permalink


Nanocrystals by ion beams - from fundamentals to application in non-volatile memories
Möller, W.; Schmidt, B.; Heinig, K.-H.;
Ion beams are widely used in research and development as well as in different fields of industrial applications, for example for doping of semiconductors in microelectronics. Furthermore, among other techniques ion beams exhibit a great potential for synthesis of new materials. One of the goals of materials research using ion beams is the ion beam synthesis (IBS) of nanocrystals (NC´s) in a solid matrix, for example the synthesis of semiconducting or metallic NC´s in insulating films.
NC´s embedded in the gate oxide of a MOS field effect transistor can be charged/decharged by tunnelling of electrons from/to the Si substrate, caused by an appropriate voltage pulse applied to the gate. There is a difference in the source/drain current for charged and neutral NCs which can be used for the storage of information. The basis of this memory concept is quite simple. However, the fabrication of tiny NCs (~2 nm) placed at the right position within the very thin (< 20 nm) gate oxide is a strong challenge. Different processes are being developed for realization. Among these, only ion implantation of impurity atoms into the gate oxide followed by their precipitation during subsequent annealing is completely compatible with CMOS technology.
The lecture will first address the fundamentals governing ion beam synthesis NC´s in extremely thin SiO2 layers, with well-controlled size and position tailoring. The results of the fundamental investigations form the base for technology transfer to the production of non-volatile memories. In the frame of national and international R&D projects and in strong collaboration with local microelectronics industries, the viability of a new technology route to memory device fabrication is demonstrated.

Keywords: Ion beam synthesis, Si nancluster, nanocluster memory
  • Lecture (Conference)
    International Conference Nanofair 2003, November 20-21, 2003, Dresden, Germany

Publ.-Id: 5930 - Permalink


Atomistische Computersimulation von Ionenimplantation und ionenstrahlinduzierter Defektbildung und –evolution in Si und SiC
Posselt, M.;
kein Abstrakt
  • Lecture (others)
    Seminar des Instituts für Materialphysik an der Universität Münster, Münster, Germany, December 1, 2003

Publ.-Id: 5929 - Permalink


Control of flow separation using electromagnetic forces
Weier, T.; Gerbeth, G.; Mutschke, G.; Lielausis, O.; Lammers, G.;
Introduction

If a fluid is electrically conductive, its flow may be controlled using electromagnetic forces. Meanwhile, this technique is a recognized tool even on an industrial scale for handling highly conductive materials like liquid metals. However, also fluids of low electrical conductivity as considered in the present study, like sea--water and other electrolytes, permit electromagnetic flow control. Experimental results on the prevention of flow separation by means of a streamwise, wall parallel Lorentz force acting on the suction side of inclined flat plates and hydrofoils will be presented.

Force Configuration
The stripwise arrangement of permanent magnets and electrodes of alternating magnetization direction and polarity shown in Fig. 1 was proposed by Gailitis and Lielausis (1961). It generates a wall parallel force with a maximum value directly at the wall, decaying exponentially with the wall distance. Due to the low electrical conductivity, both electric and magnetic fields have to be applied to generate a Lorentz force of adequate strength. The width of the electrodes is equal to that of the magnets and
determines the penetration of the force into the flow. The ratio of electromagnetic to inertial force can be characterized by the interaction parameter. In analogy to the terminology used in separation control by blowing, one may also define an electrohydrodynamic momentum coefficient.

Results and Discussion
A downstream directed force adds momentum to the flow and accelerates the fluid in the vicinity of the wall. This flow acceleration may be used to counteract the energy loss due to friction and adverse pressure gradients. Actually, a streamwise Lorentz force has already been successfully applied to control the flow around a circular cylinder in Weier et al. (1998). The two inserts in Fig. 2 show the flow around an inclined flat plate. In the lower left photograph, the unforced separated flow is visible, whereas the upper subfigure depicts the fully attached flow under the action of a suction side Lorentz force. The graph indicates that the interaction
parameter, necessary to completely suppress separation, decreases with increasing chord length Reynolds number. The effect of a suction side Lorentz force on lift and drag of NACA--0017--like hydrofoils has been quantified by means of force balance measurements. Depending on the inclination angle, two different effects are observed. At small angles of incidence, a moderate lift increase due to additional circulation is observed. Simultaneously, caused by the added momentum, the drag is decreased. At higher angles of attack, where the unforced hydrofoil would normally stall, a more pronounced lift increase occurs. Fig. 3 shows the lift gained by the suction side Lorentz force at a fixed inclination angle of 17. Here delta CL is the difference of the lift coefficients of the forced and the unforced hydrofoil at the specified chord length Reynolds number. The shape of the curve as well as the total values of the lift gain and the momentum coefficient resemble the behavior found in separation control experiments with steady blowing. In the presentation, a complementary discussion on scaling issues based on experiments with a NACA 0015 hydrofoil will be given.
  • Flow, Turbulence and Combustion, Vol. 71, No. 1-4, pp. 5-17

Publ.-Id: 5928 - Permalink


Proteinoxidation und Krankheit
Pietzsch, J.; Bergmann, R.; Wüst, F.; van den Hoff, J.;
Proteine zeichnen sich durch eine hohe Suszeptibilität gegenüber dem Angriff reaktiver Sauerstoffspezies (ROS) aus. Die oxidative Modifikation von Proteinen kann zur Veränderung ihrer Struktur und zur Beeinträchtigung ihrer biologischen Funktion führen. Diese Veränderungen sind beim Menschen eng mit der Ätiologie, Manifestation und Progression verschiedener Krankheiten assoziiert. Durch neue Methoden zur Charakterisierung und quantitativen Beschreibung der Bildung und des Metabolismus spezifischer Oxidationsprodukte werden Hinweise auf die Art und Weise der Schädigung sowie Schutzmöglichkeiten des Organismus gewonnen.
  • Contribution to HZDR-Annual report
    FZR-Jahresbericht 2003. In: Johannsen, B.; Joehnk, P. (Eds.) Research Center Rossendorf: Annual Report/Wissenschaftlich-Technische Berichte (Annual Report) 2003 (FZR-398). Research Centre Rossendorf, Dresden. 52-61

Downloads:

Publ.-Id: 5926 - Permalink


Characterization of the unoccupied and partially occupied states of TTF-TCNQ by XANES and first-principles calculations
Fraxedas, J.; Lee, Y. J.; Jimenez, I.; Gago, R.; Nieminen, R. M.; Ordejon, P.; Canadell, E.;
We report a combined experimental and theoretical study of the unoccupied electronic states of the neutral molecular organic materials TTF (tetrathiafulvalene) and TCNQ (7,7,8,8-tetracyano-p-quinodimethane) and of the one-dimensional metallic charge transfer salt TTF-TCNQ. The experimental density of states (DOS) is obtained by x-ray absorption near edge spectroscopy (XANES) with synchrotron light and the predicted DOS by means of first-principles density functional theory calculations. Most of the experimentally derived element specific XANES features can be associated to molecular orbitals of defined symmetry. Because of the planar geometry of the TTF and TCNQ molecules and the polarization of the synchrotron light, the energy dependent sigma or pi character of the orbitals can be inferred from angular dependent XANES measurements. The present work represents the state of the art analysis of the XANES spectra of this type of materials and points out the need for additional work in order to elucidate the governing selection rules in the excitation process.
Keywords: 71.20.Rv, 71.15.Mb, 61.10.Ht

Publ.-Id: 5925 - Permalink


Biologische Funktionen - ihre Aufklärung mit Hilfe von Metallkomplexverbindungen
Johannsen, B.;
  • Lecture (others)
    Adlershofer Analytisches Kolloquium der BAM, Adlershof, 25.11.2003

Publ.-Id: 5924 - Permalink


Radiopharmazeutika - gestern, heute und morgen
Johannsen, B.;
  • Lecture (others)
    Bad Berkaer Gespräch Nuklearmedizin, Bad Berka, 12.11.2003

Publ.-Id: 5923 - Permalink


Zur Zulassungsproblematik und spezifischen Anwendung von GMP bei PET-Radiopharmaka
Johannsen, B.;
  • Lecture (Conference)
    Arbeitstagung der pharmazeutischen und veterinärmedizinischen Überwachungsbeamtinnen und -beamten der Länder, Workshop Radiopharmazeutika, Erfurt, 24.09.2003

Publ.-Id: 5922 - Permalink


CFD modelling of subcooled boiling
Krepper, E.;
Heat transfer and boiling are key phenomena for power generation facilities. Whereas for 1D thermalhydraulic system codes modeling of boiling was state aof the art from the beginning of their development, the 3D modelling of boiling has not yet reached this maturity. In the paper the boiling model implemented in the CFD-code CFX-4 was applied, to analyse lots of experiments, their results were published in the literature. The validity of the implemented correlations is examined. In many cases the model yields a good agreement to experiments. The modelling of subcooled boiling in the section of a BWR fuel rod element is presented as an application example.
Keywords: CFD, boiling model, comparison with experiments, BWR fuel rod
  • 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

Publ.-Id: 5921 - Permalink


Novel Procedures for Preparing 99mTc(III) Complexes with Tetradentate/Monodentate Coordination of Varying Lipophilicity and Adaptation to 188Re Analogues
Seifert, S.; Künstler, J.-U.; Pietzsch, H.-J.; Pawelke, B.; Bergmann, R.; Spies, H.;
Improved methods are presented for the preparation of 99mTc and 188Re mixed-ligand complexes with tetradentate and monodentate ligands of the general formula [MIII(L1)(L2)] (M = Tc, Re; L1 = NS3 or NS3-COOH; L2 = isocyanide or phosphine). To avoid the unrequested formation of reduced-hydrolyzed species of both metals the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal NS3 ligand and the monodentate isocyanide or phosphine ligand to the so-called ‘4+1’ complex. Copper(I) isocyanide complexes are used for preparing the ‘4+1’ complexes. That facilitates storage stability and allows kit formulations. Moreover, using that stabilized form of isocyanides enables the formation of 188Re complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed and that results in high specific activity labeling of interesting molecules. The lipophilicity of complexes can be controlled by introducing a carboxyl group into the tetradentate ligand and/or derivatization of the monodentate ligands. Furthermore, the carboxyl group enables the conjugation of biomolecules. As an example, the neurotensin derivative CN-NT(8-13) was prepared and labeled with 99mTc according to the ‘4+1’ approach and its behavior in vivo was studied.

Publ.-Id: 5920 - Permalink


TRANSIENT SIMULATIONS IN VVER-1000 – COMPARISON BETWEEN DYN3D-ATHLET AND DYN3D-RELAP5
Kozmenkov, Y.;
Simulations of a real transient of an operating VVER-1000 power plant have been performed using DYN3D-ATLET and DYN3D-RELAP5 code systems in the frame of activities aimed at a validation of the coupled neutronic / thermal-hydraulic codes. The problem chosen for simulation is a main coolant pump (MCP) switching off, when three of the four MCPs of the plant are in operation (transient scenario of the VALCO project). The same nodalization models of the plant (except the core) but two different libraries of macroscopic cross-sections have been used in calculations. Additionally, the compared code systems are based on the different - external and internal - coupling techniques. This paper contains a brief description of the coupled codes and the plant model as well as a comparison between results from simulations.
Keywords: coupled code, DYN3D, RELAP5, validation, VALCO project
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany, Proceedíngs CD-ROM paper 104

Publ.-Id: 5919 - Permalink


Analysis of MSR Benchmark by Using the Code DYN1D-MSR
Krepel, J.; Grundmann, U.; Rohde, U.;
A one-dimensional code DYN1D-MSR for transient analysis of Molten Salt Reactors – MSR was developed in FZR. The code is based on the well know three-dimensional code DYN3D. The neutron kinetics routines for axial direction calculation from DYN3D are combined with new models of delayed neutrons production and thermal-hydraulic. The results from the Molten salt Reactor Experiment were used to validate the code. After the successful validation several transients typical for the liquid fuel system were analyzed using the design data of the Molten Salt Breeder Reactor. The results of all transients (overcooling of fuel at core inlet, reactivity insertion, and fuel pump coast-down) have shown that the dynamic behavior of MSR is stable when the coefficients of thermal feedback are negative.
Keywords: Molten, Salt, Reactor, Breeder, MSRE, MSBR, MSR
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany, Proceedíngs CD-ROM paper 104 , paper 105
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany

Publ.-Id: 5918 - Permalink


Electron beam diagnostic and the undulator field adjustment of the ELBE IR-FEL
Evtushenko, P.; Gippner, P.; Grosse, E.; Michel, P.; Seidel, W.; Wohlfahrt, D.; Wolf, A.; Wolf, U.; Wünsch, R.; Wustmann, B.; van der Geer, C. A. J.;
For the electron beam diagnostic in the undulator of the ELBE FEL two systems are completed. The first one consists of insertable OTR (Optical Transition Radiation)view screens. The same view screens will be used for the FEL optical resonator alignment. This is why there are very strong requirements on the long-term positioning reproducibility of the view screens. The second system is based on a single moveable YAG (Yttrium Aluminum Garnet activated by Cerium) screen, which can travel within the undulator vacuum chamber such that the electron beam position can be measured at any place in the undulator. Both systems are completed and successfully tested. Results of the tests as well as design ideas are presented. After transporting two undulator units to Rossendorf and installing the stainless steel vacuum chamber the magnetic field has been measured again and adjusted applying the pulsed-wire method. Irregularities of the undulator magnetic field could affect gain and wavelength of the FEL. Such effects were analyzed using numerical simulations.
  • Poster
    25th International Free Electron Laser Conference, and the 10th FEL Users Workshop 2003, 08.-12.09.2003, Tsukuba, Ibaraki, Japan
  • Contribution to proceedings
    25th International Free Electron Laser Conference, and the 10th FEL Users Workshop, Part II, 08.-12.09.2003, Tsukuba, Ibaraki, Japan
    Extended Abstracts, book edition of the proceedings, 0-444-52727-8, II-29

Publ.-Id: 5917 - Permalink


Gas and liquid velocity measurements in bubble chain driven two-phase flow by means of UDV and LDA
Zhang, C.; Eckert, S.; Gerbeth, G.;
The goal of our work is to apply the UDV technique for investigations of liquid metal two-phase flows. In the present paper UDV is validated for its capability of measuring both gas and liquid velocities in transparent two-phase flow. The results are discussed with references to the existing knowledge and parallel measurements by Laser Doppler Anemometry (LDA).
Keywords: UDV, LDA, bubble chain, two-phase flow, phase discrimination
  • Lecture (Conference)
    5th International Conference of Moultiphase Flow (ICMF), 30.05.-04.06.2004, Yokohama, Japan
  • Contribution to external collection
    5th International Conference of Multiphase Flow (ICMF), 30.05.-04.06.2004, Yokohama, Japan, CD-ROM ICMF2004, paper 260

Publ.-Id: 5916 - Permalink


Chromium recoil implantation into SAE 1020 steel by nitrogen bombardment
Gomes, G. F.; Ueda, M.; Reuther, H.; Richter, E.; Beloto, A. F.;
Chromium recoil implantation into SAE 1020 steel by nitrogen bombardment
  • Poster
    X Latin American Workshop on Plasma Physics, São Pedro, Brasilien, 30.11. - 5.12.2003
  • Open Access LogoBrazilian Journal of Physics 34(2004)4b, 1629-1631

Publ.-Id: 5915 - Permalink


Results from experiments on hybrid plasma immersion ion implantation / nitriding processing of materials
Ueda, M.; Kostov, K.; Gomes, G. F.; Reuther, H.; Lepienski, C. M.; Soares Jr., P. C.; Takai, O.; Silva, M. M.;
Results from experiments on hybrid plasma immersion ion implantation / nitriding processing of materials
  • Lecture (Conference)
    X Latin American Workshop on Plasma Physics, São Pedro, Brasilien, 30.11. - 5.12.2003
  • Open Access LogoBrazilian Journal of Physics 34(2004)4b, 1632-1637

Publ.-Id: 5914 - Permalink


Chromium implantation into ABNT 1020 steel by nitrogen PIII and ion beam recoil
Gomes, G. F.; Ueda, M.; Beloto, A. F.; Reuther, H.;
Chromium implantation into ABNT 1020 steel by nitrogen PIII and ion beam recoil
  • Lecture (Conference)
    XXIV Congresso Brasileiro de Aplicacoes de Vacuo na Industria e na Ciencia, Bauru, Brasilien, 28 - 30.7.2003

Publ.-Id: 5913 - Permalink


Annealing effects on silicon oxynitride layer synthesized by N plasma immersion ion implantation
Ueda, M.; Reuther, H.; Beloto, A. F.; Kuranaga, C.; Abramof, E.;
Annealing effects on silicon oxynitride layer synthesized by N plasma immersion ion implantation
  • Lecture (Conference)
    20th International Conference on Amorphous and Microcrystalline Semiconductors - Science and Technology, Campos do Jordao, Brasilien, 25 - 29.9.2003
  • IEEE Transactions on Plasma Science 34(2006)4, 1080-1083

Publ.-Id: 5912 - Permalink


Grazing incidence X-ray diffraction of SS304 steel surfaces modified by high and low pressure ion nitriding processes
Ueda, M.; Gomes, G. F.; Abramof, E.; Reuther, H.;
Grazing incidence X-ray diffraction of SS304 steel surfaces modified by high and low pressure ion nitriding processes
  • Poster
    VIIth International Workshop on Plasma-Based Ion Implantation (PBII),San Antonio, USA,16 - 19 September 2003

Publ.-Id: 5911 - Permalink


Nitrogen recoil chromium implantation into construction steel SEA 1020 steel by means of ion beam or plasma immersion ion implantation
Gomes, G. F.; Ueda, M.; Beloto, A. F.; Reuther, H.;
Nitrogen recoil chromium implantation into construction steel SEA 1020 steel by means of ion beam or plasma immersion ion implantation
  • Poster
    XIIIth International Conference on Surface Modification of Materials by Ion Beams (SMMIB), San Antonio, USA, 21 - 26 September 2003

Publ.-Id: 5910 - Permalink


Beam loss detection at Radiation Source ELBE
Michel, P.; Teichert, J.; Schurig, R.;
The Rossendorf superconducting Electron Linac of high Brilliance and low Emittance (ELBE) delivers an 40 MeV, 1 mA cw-beam for different applications such as bremsstrahlung production, electron channeling, free-electron lasers or secondary particle beam generation. In this energy region in case of collisions of the electron beam with the pipe nearly all beam power will be deposited into the pipe material. Therefore a reliable beam loss monitoring is essential for machine protection at ELBE. Different systems basing on photo multipliers, compton diodes and long ionisazion chambers were studied. The pros and cons of the different systems will be discussed. Ionisazion chambers based on air-isolated RF cables installed some cm away parallel to the beam line turned out to be the optimal solution. The beam shut-off threshold was adjusted to 1 µC integral charge loss during a 100 ms time interval. Due to the favourable geometry the monitor sensitivity varies less than +/- 50 % along the beam line (different shielding conditions).
  • Lecture (Conference)
    6th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators, 05.05. – 07.05.2003, Mainz, Germany
  • Contribution to proceedings
    6th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators, 65 - 67, 05, 05.-07.05.2003, Main, Deutschland, 65-67

Downloads:

Publ.-Id: 5909 - Permalink


The temperature dependence of the energy distribution of the beam emitted by a Au82Si18 liquid metal field-ion emitter
Aidinis, C. J.; Mair, G. L. R.; Bischoff, L.; Londos, C. A.; Akhmadaliev, C.; Ganetsos, T.;
The energy distribution of the monomer ion species is studied as a function of emitter temperature for a Au82Si18 eutectic liquid metal alloy ion source (LMAIS). Secondary peaks, or shoulders, in the distribution of some of the species are explained in terms of Hornsey's model, which involves the fast movement of the jet in conjunction with a space-charge energy broadening mechanism within the beam. Moreover, the results confirm an earlier conclusion that whereas Au+, Si+ and Si++ are emitted by direct field-evaporation from the liquid surface, Au++ forms by the post ionization of Au+.
Keywords: liquid metal ion source, alloy, temperature, energy distribution

Publ.-Id: 5908 - Permalink


Optische Untersuchungen an Stickstoff-implantiertem GaAs
Sinning, S.; Dekorsy, T.; Helm, M.;
Seit mehreren Jahren werden verdünnte Legierungen aus III-V Halbleitern und Stickstoff intensiv untersucht. Eine hervorstechende Eigenschaft dieser Systeme ist die starke Reduktion der Bandlücke mit steigendem Stickstoffgehalt. Neben epitaktischem Wachstum ist Ionenimplantation eine weitere Methode zur Herstellung solcher Materialien.
Wir untersuchen die optischen Eigenschaften und deren Abhängigkeit von den Implantations- und Ausheilbedingungen für GaNxAs1-x (x<0,04). Es zeigt sich, dass unter entsprechenden Bedingungen der von der Implantation verursachte Schaden minimiert und die Bandkantenverschiebung maximiert werden kann. Eine in Photoreflexion beobachtete Bandlückenverschiebung von 63meV konnte bei einer implantierten N-Konzentration von 1% beobachtet werden. Der Einfluss der modifizierten Bandstruktur auf die Ladungsträgerdynamik wird in Femtosekunden zeitaufgelösten pump-probe Experimenten untersucht.
Keywords: GaNAs Stickstoff Implantation zeitaufgelöst Ladungsträgerdynamik pump-probe Reduktion Bandlücke
  • Lecture (Conference)
    DPG-Tagung, Frühjahrs-Tagung des Arbeitskreises Festkörperphysik; Dresden 2003

Publ.-Id: 5907 - Permalink


Effect of hydrodynamics on microstructure evolution of Nd-Fe-B alloys
Hermann, R.; Gerbeth, G.; Filip, O.; Priede, J.; Shatrov, V.;
The influence of melt convection on the microstructure formation of Nd-Fe-B alloys, mainly the volume fraction and grain size of the a-Fe phase, has been investigated experimentally using the electromagnetic levitation technique and a specially designed floating-zone arrangement. Samples were subjected to a strong rotation during levitation and compared to fixed samples without additional sample rotation in the levitation facility. A controlled influence on the melt flow is possible via tailored magnetic fields which enable enhancement or suppression of the melt convection using the floating-zone arrangement. A specially designed magnetic two-phase stirrer offers a strong influence on the melt flow in the floating-zone facility. The microstructure pattern, mainly the volume fraction and grain size of the a-Fe phase, vary strongly with the strength of the internal flow motion in both types of experiments. The melt flow in a levitated droplet was studied numerically under the additional effect of a global sample rotation resulting in a strong suppression of internal motions. The electromagnetically driven flow in the inductively heated melt zone of the floating-zone arrangement turned out to be of strong influence on the resulting microstructure. Numerical simulations are essential in order to understand and design the various flow structures.
  • Contribution to external collection
    Dieter M. Herlach: Solidification and Crystallization, Weinheim: WILEY-VCH Verlag, 2004, 3-527-31011-8, 185-193

Publ.-Id: 5906 - Permalink


Near infrared intersubband transitions in InGaAs-AlAs-InAlAs double quantum wells
Semtsiv, M. P.; Georgiev, N.; Dekorsy, T.; Helm, M.; Masselink, W. T.;
not available
Keywords: intersubband transitions, quantum wells, infrared
  • Poster
    7th Int. Conference on Intersubband Transitions in Quantum Wells, Evolene, Switzerland, Sept. 1-5, 2003 (auf CD-ROM publiziert)
  • Contribution to proceedings
    7th Int. Conference on Intersubband Transitions in Quantum Wells, Evolene, Switzerland, Sept. 1-5, 2003 (auf CD-ROM publiziert)

Publ.-Id: 5903 - Permalink


Alternated high- and low-pressure nitriding of austenitic stainless steel: Mechanisms and results
Gomes, G. F.; Ueda, M.; Reuther, H.;
A combined surface modification treatment consisting of ion nitriding at high pressure and high temperature, followed by a cycle at low pressure, both cycles using a gas mixture of (N-2/H-2):(50/50) in pressure, was applied to stainless-steel AISI 304. In the first cycle, in a glow discharge at 4x10(-1) mbar and temperatures of 400- 450 degreesC, high-pressure nitriding was applied to the samples. In the second cycle, in a glow discharge at 8x10(-4) mbar, low-pressure nitriding was applied to the samples. Applying this sequential hybrid treatment alternately, good nitriding was obtained. X-ray diffraction (XRD) measurements showed the effects of this hybrid ion nitriding in the AISI 304 surface, indicating thick nitrided layers, confirmed by Auger electron spectroscopy (AES). Conversion electron Mossbauer spectroscopy, combined with AES and XRD, showed phases and compounds induced by such treatments. Vickers hardness measurements showed great enhancement in the surface hardness. Applying other combinations of gas mixtures and cycles, produced diverse results in the surface, like the induction of alpha- and epsilon-phases.

Publ.-Id: 5902 - Permalink


Facility Management in Forschungseinrichtungen - Anforderungen, Umsetzung, Erfahrungen
Joehnk, P.;
  • Lecture (Conference)
    Workshop Facility-Management, Slowakische Technische Universität, Bratislava, 29.9.2003 Smolenice, Slowakische Republik

Publ.-Id: 5901 - Permalink


The bremsstrahlung facility at the ELBE accelerator
Rusev, G.; Schwengner, R.; Schilling, K. D.; Wagner, A.; Käubler, L.; Dönau, F.; Mallion, S.; Grosse, E.; Junghans, A. R.; Erhard, M.; Schulze, W.; Hartmann, A.;
A superconducting electron linear accelerator of high brilliance and low emittance has been constructed in the Forschungszentrum Rossendorf in order to deliver cw electron beams with a maximum average current of 1 mA. The accelerator will be used to produce different kinds of secondary radiation, neutrons and positrons. Bremsstrahlung produced at ELBE will be used for nuclear-structure and nuclear-astrophysics experiments employing photon-induced reactions such as (y,y) (nuclear-resonance-fluorescence), (y,n), (y,p) (nuclear photo effect) and photon-induced fission. These experiments will be carried out with electron energies up to 20 MeV at a specially designed bremsstrahlung facility. In order to optimize the design of components of the bremsstrahlung facility and to reduce background radiation, simulations using the code GEANT were performed. We describe the main elements of the bremsstrahlung facility, such as the thin water-cooled radiator, the beam hardener, the photon beam collimator, the HPGe-detector setup. Furthermore, we present a comparison of simulations with measurements and report on first experiments with the new facility.
  • BgNS Transactions 9(2004), 173

Publ.-Id: 5900 - Permalink


Diagnostics of a N2/Ar direct current magnetron discharge for reactive sputter deposition of fullerene-like carbon nitride thin films
Neidhardt, J.; Hultman, L.; Abendroth, B.; Gago, R.; Moeller, W.;
Plasma probe measurements and energy selective mass spectrometry were used to characterize the composition and energetic conditions of the ion flux of a direct current, N2 /Ar, unbalanced magnetron sputtering plasma in front of a graphite target, depending on the total pressure and gas composition. It is shown that the flux of ionized film-forming species consist predominantly of CxNy (x,y<2) species. The total number of C-containing ions strongly depends on the N2 fraction in the discharge and can be increased by almost one order of magnitude scaling with the availability of N2 as the discharge gas. This finding suggests that besides C and N atoms and ions, other species, like preformed CxNy particles, play an important role during growth of fullerene-like (FL) carbon nitride (CNx) thin films. It is proposed that such clusters have a direct effect as growth templates or nucleation sites on the evolution of curved and cross-linked FL structures. The carbon target was identified as the main source of preformed C-containing species, following from the pressure dependence of the ion energy distributions of the most abundant CxNy (x,y<2) ions.
  • Journal of Applied Physics 94/11 (2003) 7059
    DOI: 10.1063/1.1625091
  • Virtual Journal of Nanoscale Science & Technology 8/21 (Compilation of links to selected articles covering a focused area of frontier research published by the American Institute of Physics and the American Physical Society)

Publ.-Id: 5899 - Permalink


High-Fluence C-Implantation into 3C-SiC: Synthesis of Buried Diamond-Nanocrystals
Weishart, H.; Heera, V.; Pécz, B.; Tóth, L.; Skorupa, W.;
Their outstanding properties, such as wide band gap, high thermal conductivity and saturated electron drift velocity, make silicon carbide and diamond useful semiconductors for applications under harsh conditions. A combination of both materials on a microscopic scale may be a promising way to novel devices.
Ion Beam Synthesis (IBS) is an excellent method for creating precipitates inside any matrix without thermodynamic constraints. We previously demonstrated the synthesis of nanocrystalline 3C-SiC inside diamond by high-fluence Si implantation. In this work we investigate phase formation in carbon-implanted 3C-SiC substrates. Implantations were performed with different fluences ranging form 3x1017 cm-2 to 3x1018 cm-2. Additionally, the influence of implantation temperature and dose rate was studied using X-ray diffraction (XRD), Raman spectrometry and high-resolution cross-sectional transmission electron microscopy (HRTEM).
Low implantation temperatures and high dose rates favor the formation of graphite precipitates in a textured form, while in all other cases epitaxial diamond nanocrystals grow. Hence, a critical temperature for diamond formation exists, which depends on dose rate. Increasing the fluence leads to bigger nanocrystals. Diamond platelets of up to 20 nm length were found.

Keywords: Ion Beam Synthesis, silicon carbide, diamond
  • Lecture (Conference)
    Verhandlungen der Deutschen Physikalischen Gesellschaft 2004, Fachverband Dünne Schichten, Sitzung DS 18.2, Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 8.-12.03.2004, Regensburg, Deutschland

Publ.-Id: 5898 - Permalink


VALIDATION OF COUPLED CODES IN VALCO WP1 USING MEASURED VVER DATA
Hämäläinen, A.; Vanttola, T.; Weiss, F.-P.; Mittag, S.; Kliem, S.; Kozmenkov, Y.; Keresztúri, A.; Hádek, J.; Strmensky, C.; Stefanova, S.; Kuchin, A.; Hlbocky, P.; Siko, D.; Danilin, S.;
The collection of measured data from transients in VVER type NPPs has been used for the validation of coupled thermal hydraulics / neutron kinetics codes in the previous PHARE project SRR1/95 and continuing now in the Work Package 1 of the VALCO project with new types of transients and new data. Firstly, a collection of five transients was made, then two transients; ‘Drop of control rod at nominal power at Bohunice-3’ for VVER-440 reactors and ‘Coast-down of 1 from 3 working MCPs at Kozloduy-6’ for VVER-1000 reactors, were used in code validation. Eight institutes participated with ten calculations for the code validation with five different combinations of coupled codes. Used thermal hydraulic codes were ATHLET, SMABRE and RELAP5 and the neutron kinetic codes DYN3D, HEXTRAN, KIKO3D and BIPR8.

The amount of collected data in WP1 was excessive. Simultaneous calculation of the selected transients brought up additional specification needs for data, which improved its quality. Further, the ability to interpret plant data has increased among the participants. The general behaviour of both transients was quite well calculated with all the codes and as a result more information in some special phenomena was received. The differences between the calculations pave the way for future needs of more accurate fuel models in the coupled codes.
  • Lecture (Conference)
    13. Symposium of AER, Dresden, 22-26 September, 2003, pp. 555-576
  • Contribution to proceedings
    13. Symposium of AER, Dresden, 22-26 September, 2003, pp. 555-576

Publ.-Id: 5897 - Permalink


Self-Organization of Nanocluster delta-Layers at Ion-Beam-Mixied Si-SiO2 Interfaces
Röntzsch, L.; (Editor)
This diploma thesis presents experimental evidence of a theoretical concept which predicts the self-organization of delta-layers of silicon nanoclusters in the buried oxide of a MOS-like structure. This approach of "bottom-up" structuring might be of eminent importance in view of future semiconductor memory devices.

Unconventionally, a 15nm thin SiO2 layer, which is enclosed by a 50nm poly-Si capping layer and the Si substrate, is irradiated with Si+ ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiOx (x<2) - where x is a function of depth - is formed which is not stable.

During annealing, the system relaxes towards equilibrium, i.e. phase separation (via spinodal decomposition and nucleation) sets in. Within a certain time window of annealing, the structure of the system matches with a structure similar to the multidot non-volatile memory device, the principal character of which is a 2D layer of Si nanoclusters of ~3nm in diameter which is embedded in a 3D SiO2 matrix at a distance of ~3nm from the Si substrate.

The physical mechanisms of ion mixing of the two Si-SiOx interfaces and subsequent phase separation, which result in the desired sample structure, are elucidated from the viewpoint of computer simulation. In addition, experimental evidence is presented based on various methods, including TEM, RBS, and SIMS. Of particular importance is a novel method of Si nanocluster decoration which applies Ge as contrast enhancing element in TEM studies of tiny Si nanoclusters.
Keywords: ion-mixing, self-organization, phase separation, Si nanocluster, non-volatile memory, Si-SiO2 interface, Ge decoration
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-392 Oktober 2003

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Publ.-Id: 5896 - Permalink


Redox and electrocatalytic activity of Ni ion-implanted Ti
Pham, M. T.; Maitz, M. F.; Reuther, H.; Richter, E.; Matz, W.; Muecklich, A.; Chevtchenko, N.; Prokert, F.;
Ni-Ti surface alloy was prepared by ion-implanting Ni into Ti. The surface film was amorphous having a Ni surface content of 10 - 40 at. %. The material was compared with a Ni-Ti bulk alloy (44.08:55.9) regarding their redox and electrocatalytic behaviour in NaOH by cyclic voltammetry. The surface was characterized by X-ray photoelectron spectroscopy, X-ray and electron diffraction, and electron and atomic force microscopy. The ion-implantated material revealed an enhanced activity toward the redox conversion of Ni(OH)2 " NiOOH and the anodic oxidation of glucose. The effect was discussed considering the enhanced generation of active Ni surface sites from amorphous Ni and the stabilization of higher valence Ni by Ti.
Keywords: Ni-Ti alloy electrodes, electrocatalysis, glucose, surface alloying, ion implantation
  • Journal of Materials Research 19(2004), 1249-1256

Publ.-Id: 5895 - Permalink


Modifications in cell cycle kinetics and in expression of G1 phase-regulating proteins in human amniotic cells after exposure to electromagnetic fields and ionizing radiation
Lange, S.; Viergutz, T.; Simkó, M.;
Low-frequency electromagnetic fields are suspected of being involved in carcinogenesis, particularly in processes that could be related to cancer promotion. Since development of cancer is associated with deregulated cell growth and we previously observed a MF-induced decrease in DNA synthesis (Lange et al. 2002), this study aims to document the influence of 50 Hz, 1 mT magnetic fields (MF), with or without initial gamma-ionizing radiation (IR), on the following cell proliferation-relevant parameters in AFC cells: cell cycle distribution, expression of the G1 phase-regulating proteins Cdk4, cyclin D1, p21CIP1, and p16INK4a, and Cdk4 kinase activity. While IR induced a G1 delay as well as a dose-dependent G2 arrest, no discernible changes in cell cycle kinetics were observed due to MF exposure. Significant alterations in the protein expression of cyclin D1, p21CIP1, and p16INK4a could be detected after exposure to MF and/or IR, respectively, whereas only a slight diminution of Cdk4 kinase activity was noticed. Consequently, Cdk4 appears not to act as mediator of MF- or IR-induced changes in the cell cycle of AFC cells. Combined exposure to MF/IR affected neither cell cycle distribution nor protein expression or kinase activity additionally or synergisticly and, therefore, MF seems not to modify the mutagenic potency of IR.
Keywords: electromagnetic field, ionizing radiation, cell cycle regulation, Cdk4, cyclin D1, p16INK4a, p21CIP1
  • Cell Proliferation 37(2004)5, 337-349

Publ.-Id: 5894 - Permalink


Reactor Dosimetry: Accurate Determination and Benchmarking of Radiation Field Parameters, relevant for Pressure Vessel Monitoring (REDOS)
Ballesteros, A.; Garcia, G.; Böhmer, B.; OšMera, B.; Keresztúri, A.; Ilieva, K.; Acosta, B.; Smutný, V.; Polke, E.; Zaritsky, S.; Ortego, P.;
Radiation embrittlement of reactor pressure vessel (RPV) steels is a degradation mechanism that requires crucial consideration for the safe operation of aged nuclear power plants. Plant life management needs a reliable estimation of radiation field parameters, including their uncertainty, to avoid the use of conservative approaches.
The particular objectives of the REDOS project are the improvements of the RPV monitoring, the improvement of the neutron-gamma calculation methodologies through the LR-0 engineering benchmarks for VVER-1000 and VVER-440, and the accurate determination of radiation field parameters in the vicinity and over the thickness of the RPV.
The REDOS project started in November 2001 and has a duration of three years. At its mid term stage in the project, all the required NPP experimental data have been collected. A review of the available experimental data of Kozloduy RPV unit 1 has been performed and the attenuation coefficients through the vessel wall have been estimated. The collection of the available revised data for VVER-440 Mock-up have been completed. Furthermore, the existing data for the VVER-1000 Mock-up have been reviewed and the preparatory work for subsequent measurement and experimental data analysis was carried out.

Measurements of the space-energy distribution of the mixed neutron-gamma field in the VVER-1000 model have been performed over the RPV simulator. The photon and neutron spectra have being measured simultaneously with the stilbene scintillator and the multiparameter technique, and the thermal neutron flux has been measured in several points with a He-3 miniature chamber. The most important improvements in the experimental techniques used are the multiparameter spectrometer and a new low noise precise monitoring system in the LR-0 reactor, developed for this type of measurements. The calculational models of the benchmark exercise were prepared by the project participants using their respective codes.



Keywords: Radiation embrittlement, reactor pressure vessel, VVER-1000, VVER-440, LR-0, reactor mock-up, neutron-gamma calculation, radiation field parameters, photon and neutron spectra measurements, stilbene scintillator, multiparameter spectrometer, He-3 miniature chamber
  • Lecture (Conference)
    FISA-2003 - Symposium on EU Research in Reactor Safety, 10-13 November 2003, Luxembourg
  • Contribution to proceedings
    FISA-2003 - Symposium on EU Research in Reactor Safety, 10-13 November 2003, Luxembourg

Publ.-Id: 5892 - Permalink


Electrohydrodynamic instabilities on a liquid anode displaying an anomalous surface tension coefficient
Mair, G. L. R.; Akhmadaliev, C.; Bischoff, L.; Ganetsos, T.; Aidinis, C. J.;
In the search for a deeper understanding of the factors governing the stability of liquid metal field-ion emitters, the behaviour of a liquid anode with an anomalous surface tension coefficient is studied.The main parameter in this experimental study is the emitter temperature. At the conclusion of the work an important result emerged: apart from the surface tension coefficient, space-charge effects constitute a major factor in influencing emitter stability.
Keywords: liquid metal ion source, surface tension coefficient, temperature,instabilities

Publ.-Id: 5891 - Permalink


Synthesis, Characterization, and Biological Evaluation of Neutral Nitrido Technetium(V) Mixed Ligand Complexes Containing Dithiolates and Aminodiphosphines. A Novel System for Linking Technetium to Biomolecules
Bolzati, C.; Benini, E.; Cazzola, E.; Jung, C.; Tisato, F.; Refosco, F.; Pietzsch, H.-J.; Spies, H.; Uccelli, L.; Duatti, A.;
A new biomolecule labeling method that utilizes the [99mTc(N)(PNP)]2+m metal fragment is presented. Thus, a series of nitrido mixed-ligand M(V) complexes (M = 99mTc, 99gTc, Re), [M(N)(Ln)(PNP)], where Ln is the dianionic form of a dithiolate or substituted-dithiolate ligand and PNP is an aminodiphosphine, is described. 99mTc complexes can be prepared using either a two-step or a three-step procedure starting from generator-eluted pertechnetate through a pre-reduced mixture of [99mTc(N)] containing species, followed by contemporary or sequential addition of the relevant dithiolate and aminodiphosphine. The reaction of 2,3-dimercapto propionic acid (H2L1) with [Tc(N)(PNP)]2+ was investigated in detail. It was found that this bidentate ligand coordinated the metal fragment through the [S-,S-] donor atom pair, to yield neutral mixed-ligand complexes [99mTc(N)(L1)(PNP)] in high specific activity. The additional carboxylic functional group was not involved in metal coordination, thus remaining available for conjugation to target-specific molecules. Dithiolates incorporating pendant functional group(s) gave rise to a 1:1 diastereoisomeric mixture of syn-[M(N)(Ln)(PNP)] and anti-[M(N)(Ln)(PNP)] derivatives, depending on the relative orientation of the dithiolate substituent(s) with respect to the terminal nitrido group, and no isomeric conversion was detected. 99mTc species had been proven to be identical with the 99gTc complexes prepared at the macroscopic level by comparison of the corresponding radiometric and UV/vis HPLC profiles. Challenge experiments with cysteine or glutathione indicated that these physiological agents had no effect on the stability of this class of mixed-ligand 99mTc-complexes. Biodistribution studies in rats of selected 99mTc-complexes showed a rapid clearance from the blood and tissues after 60 min. p.i..
  • Bioconjugate Chemistry 15(2004), 628-637

Publ.-Id: 5890 - Permalink


Finite-width QCD sum rules for rho and omega mesons
Kämpfer, B.; Zschocke, S.;
We present a combined analysis of the behavior of rho and omega mesons within the Borel QCD sum rule taking into account finite widths.
Keywords: vector mesons, in-medium modification, condensates
  • Progress in Particle and Nuclear Physics 53(2004), 317-327

Publ.-Id: 5888 - Permalink


Quantum design and synthesis of a boron-oxygen-yttrium phase
Music, D.; Chirita, V.; Kreissig, U.; Czigany, Z.; Schneider, J. M.; Helmersson, U.; (Editors)
Ab initio calculations are used to design a crystalline boron–oxygen–yttrium (BOY) phase. The essential constituent is yttrium substituting for oxygen in the boron suboxide structure (BO0.17) with Y/B and O/B ratios of 0.07. The calculations predict that the BOY phase is 0.36 eV/atom more stable than crystalline BO0.17 and experiments confirm the formation of crystalline thin films. The BOY phase was synthesized with reactive rf magnetron sputtering and identified with x-ray and selected area electron diffraction. Films with Y/B ratios ranging from 0.10 to 0.32, as determined via elastic recoil detection analysis, were grown over a wide range of temperatures (300–600 °C) and found to withstand 1000 °C.

Keywords: PACS: 81.15.Cd, 68.55.Jk, 62.20.Dc, 68.60.Bs, 81.40.Jj

Publ.-Id: 5887 - Permalink


Structure and energetics of defects: A comparative study of 3C- and 4H-SiC
Gao, F.; Posselt, M.; Belko, V.; Zhang, Y.; Weber, W. J.;
The structures, formation energies and stable configurations of elementary defects (vacancies, antisite defects and self interstitials) in 3C- and 4H-SiC are studied using classical molecular dynamics simulation with a recently developed interatomic potential. The defect structures in 3C-SiC are relative simple, but those in 4H-SiC are more complicated. The interstitials between hexagonal and trigonal rings are characteristic for 4H-SiC and other hexagonal polytypes, but not for 3C-SiC. The number of non-equivalent defects in 4H-SiC is much higher than in 3C-SiC, and a considerable difference is found for some complex and anisotropic defects, in particular for the dumbbells D1Si-Si, D1Si-C and D2Si-C. The lattice deformation beyond the first nearest neighbor shell, which depends strongly on the polytype structure, plays an important role on these effects. However, the polytypism does not have a significant influence on the structure and energetics of the more compact and isotropic defects, such as vacancies and antisite defects. Despite the complexity of defect configurations, the tetrahedral interstitials have very similar properties in 3C- and 4H-SiC because their first, second and third nearest neighbor shells are equal.
Keywords: computer simulation, SiC, defects
  • Lecture (Conference)
    12th Int. Conf. on Radiation Effects in Insulators (REI-12),Gramado, Brazil, August 31 - September 5, 2003

Publ.-Id: 5884 - Permalink


HADES tracking system: First In-beam Experience.
Kanaki, K.; Dohrmann, F.; Enghardt, W.; Garabatos, C.; Grosse, E.; Hutsch, J.; Kämpfer, B.; Kondyurin, A.; Kotte, R.; Naumann, L.; Sadovsky, A.; Stroth, J.; Sobiella, M.;
The High Acceptance Di-Electron Spectrometer (HADES) at the heavy ion synchrotron SIS of GSI, Darmstadt, is a high-resolution second generation detector system for lepton pair spectroscopy. Its low-mass tracking system consists of two pairs of planes of trapezoidally shaped Multiwire Drift Chambers (MDC), installed on either side of a superconducting toroidal magnet. This paper summarizes some experiences with the construction and the in-beam operation of the six large-area chambers produced by Forschungszentrum Rossendorf. Studies on creeping of aluminum wires over a period of three years are presented. In addition, the observation of growth of filaments with various shapes and sizes in one of the chambers used in-beam will be discussed in detail.
Keywords: aging, drift chambers, energy dispersive x-ray (EDX) spectrometry, filaments, infrared spectroscopy, rubber sealants, wire tension

Publ.-Id: 5883 - Permalink


Water hammer and condensation hammer scenarios in power plants using new measurement system
Dudlik, A.; Schönfeld, S. B. H.; Hagemann, O.; Carl, H.; Prasser, H.-M.;
This contribution presents experimental results of the investigation of water hammer and cavitation hammer at the pipeline test facility at Fraunhofer UMSICHT in the context of the EURATOM project WAHALoads. The main objective of this running project is the prediction of the strain on equipment and support structures caused by water and condensation hammer. Thus, some typical scenarios of power plants are conducted. For this purpose the test facility at Fraunhofer UMSICHT (PPP) was modified in order to simulate a piping system and associated supports that are typical of a power plant.

For a better understanding of thermohydraulic processes, new wire mesh sensors with thermocouples for the measurement of condensation heat transfer, and other innovative transient measurement techniques were implemented into PPP additionally.

Keywords: water hammer, cavitation collapse, fast acting valve, pipeline, two-phase flow, mesh sensor
  • Lecture (Conference)
    9th International Conference on Pressure Surges, 24.-26.03.2004, Chester, Great Britain
  • Contribution to proceedings
    9th International Conference on Pressure Surges, 24.-26.03.2004, Chester 2004, UK, proceedings part I, pp. 151 - 165

Publ.-Id: 5882 - Permalink


Correlation between irradiation-induced changes of microstructural parameters and mechanical properties for RPV steels
Böhmert, J.; Viehrig, H.-W.; Ulbricht, A.;
Radiation hardening, displayed by the yield stress increase, and radiation embrittlement, described by the Charpy transition temperature shift, were experimentally determined for a broad variety of irradiation probes machined from different reactor pressure vessel base and weld materials and irradiated in several VVER-type reactors. Additionally, the same probes were investigated by small angle neutron scattering. The analysis of the neutron scattering data suggests the presence of nanoscaled radiation defects. The volume fraction of these defects depends from the neutron fluence and the material. Both radiation hardening and radiation embrittlement correlate with the square root of the defect volume fraction linearly. However, a generally valid proportionality is only a rough approximation; in detail chemical composition and technological pretreatment clearly affect the correlation.

Publ.-Id: 5881 - Permalink


Modeling of flashing-induced instabilities in the start-up phase of natural-circulation BWRs using the code FLOCAL
Manera, A.; Rohde, U.; Prasser, H.-M.; van der Hagen, T. H. J. J.;
This paper reports on the modeling and simulation of flashing-induced instabilities in natural circulation systems, with special emphasis on natural circulation Boiling Water Reactors (BWRs). For the modeling the 4-equation two-phase code FLOCAL (Rohde, 1986), developed at the Forschungzentrum Rossendorf (FZR, Germany), has been used. The model allows for the liquid and vapor to be in thermal non-equilibrium and, via drift-flux models, to have different velocities. The phenomenology of the instability has been studied and the dominating physical effects have been revealed. The results of the simulations have been compared qualitatively and quantitatively with experiments (Manera et al., 2002) that have been carried out within the framework of a European project (NACUSP) on the CIRCUS facility. The facility, built at the Delft University of Technology in The Netherlands, is a water/steam 1:1 height-scaled loop of the Dutch natural-circulation-cooled BWR Dodewaard.
Keywords: Flashing, natural circulation, flow oscillations, BWRs
  • Lecture (Conference)
    The 10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10), Seoul, Korea, October 5-9, 2003; conference-CD: A00506
  • Contribution to proceedings
    The 10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10), Seoul, Korea, October 5-9, 2003; conference-CD: A00506

Publ.-Id: 5880 - Permalink


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
  • Lecture (Conference)
    The 10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10), Seoul, Korea, October 5-9, 2003; conference-CD: A00108
  • Contribution to proceedings
    The 10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10), Seoul, Korea, October 5-9, 2003; conference-CD: A00108

Publ.-Id: 5879 - Permalink


Institute of Safety Research; Annual Report 2002
Weiß, F.-P.; Rindelhardt, U.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-380 Juni 2003

Downloads:

Publ.-Id: 5878 - Permalink


Use of Bacteria for Cleaning Radioactive Wastewaters
Raff, J.; Selenska-Pobell, S.;
Saxony and Thuringia are mountainous German states featuring quaint villages, carved nutcrackers and centuries-old castles. But there is another side to this region. Decades of uranium mining to fuel former Soviet Union nuclear weapons and European nuclear power plants have devastated the region, which spills into the Czech Republic and Poland. Since the fall of the Berlin Wall, most mines have fallen into disuse, leaving an ominous legacy to threaten the long-term safety of the soil, subsoil and groundwater in nearby residential areas. Preliminary investigations in Thuringia and Saxony mining towns show elevated incidences of lung cancer in the men who worked the mines as well as in women who reside there.
These findings have raised fears about leaching and seepage of radionuclides from acid mine drainage waters and about contaminants from abandoned uranium waste rock piles dumped on valley slopes. Unfortunately, these environmental hazards are not limited to this region. Similar problems threaten the health of people in uranium mining areas in Hungary, Bulgaria, Estonia, Romania and Slovenia.
Closure, remediation and recultivation of former mining sites in Saxony and Thuringia have been underway since 1991. Conventional chemical and physical removal methods are useful for high concentrations of radionuclides and heavy metals, but not for low concentrations. After the initial remediation treatment, the remaining concentrations of these compounds are still above allowed limit values. So, scientists at Forschungszentrum Rossendorf Institute of Radiochemistry in Dresden, Germany are searching for alternative decontamination methods. They hope to develop a selective, yet effective process for completely removing metals and radionuclides from polluted effluents, wastewater, sediments and soils based on microorganisms.
Bacteria are the most frequent organisms on earth. They are able to live in extreme environments where higher organisms such as plants and animals are not able to survive, e.g. hot springs, antarctic ice, deep sea and deserts. For this reason it is not surprising, that researchers have found bacteria also in highly contaminated environments such as uranium mining waste piles. Above that the latter are big reservoirs for bacteria that are resistant to heavy metals. Many of the microorganisms living under these difficult conditions have developed different strategies to resist mobility and toxicity of metals and radionuclides. Bacteria interact not only with organic but also with inorganic compounds such as heavy metals. Some of them are able to solubilize metals or metalsulfides by oxidation. Others makes the opposite, they precipitate metals by reduction. Beside that many bacteria accumulate cobalt, molybdenum, lead, mercury, copper, manganese, aluminium, cadmium, gallium, barium and other toxic metals and transport them out of contaminated areas. All these properties offer interesting options for solving the above mentioned problems.
  • Genomics/Proteomics Technology 22(2004)2, 32L-32N

Publ.-Id: 5877 - Permalink


Bacterial and archaeal diversity in waters at the Siberian deep-well monitoring site Tomsk-7
Nedelkova, M.; Selenska-Pobell, S.;
Microbial diversity was studied in water samples collected at depths of 290 to 324 m from the monitoring site S15 near the city of Tomsk, Siberia, Russia. The 16S rDNA retrieval was applied, in order to overcome the problems of culturability of the bacteria and archaea indigenous for that extreme habitat. The biomass from the samples was concentrated via consequent filtration on a glass-fibre filter and on filters with pore sizes of 0.45 and 0.22 µm. In this work two bacterial clone libraries were analysed: one constructed for the DNA isolated from the biomass collected on the filter with a size of 0.45µm and another one for those of the 0.22µm filter. In addition, an archaeal clone library was generated for the total DNA extracted simultaneously from all the tree filters (unfractioned DNA). Comparative analyses of the two bacterial libraries revealed significant differences in the predominant groups and in the species composition. In the 0.45µm clone library a dominance of Dechlorosoma spp. populations was found. This result is in agreement with our previous study on bacterial diversity in water at the site S15 which was performed by using total unfractioned DNA (1). However, in contrast of that previous analysis, now the predominance of the Dechlorosoma spp. was not too strong and we were able to find a larger variety of species from: d-subclass of Proteobacteria, Gramm positive bacteria, and in addition members of Candidate divisions OP8, TM7 and the Termite group. In the 0.22µm clone library Dechlorosoma sp. was not identified any more. In this case populations of Chrysobacterium spp. from the Cytophaga/Flavobacterium/Bacteroides group were predominant. There were some common Proteobacterial and Actinobacterial species, which were identified in both the 0.45µm and the 0.22µm libraries. Interestingly, relatively dense and diverse populations of deeply branched not yet cultured Cyanobacteria were found in both bacterial clone libraries. The phylogenetic analysis of Archaeal populations in the S15 sample revealed the presence of sequences which belong to Crenarchaeota and Euryarchaeota. The members of the latter were methanogens and some of them were related to clones identified in metal-rich freshwaters by others (2). Most of the Crenarchaeota 16S rDNA sequences were also similar to those found in other metal-rich environments (3).
Our analysis indicates that microbial communities at the monitoring site S15 are rather complex and diverse. The 0.45µm clone library exhibits greater overall diversity than the 0.22µm clone library. The archaeal populations are represented mainly by clones affiliated with organisms found in other metal pollutd environments.

References:
1. Nedelkova, M., et al. (2003) Environmental Geology (in press).
2. Stein, L. et al. (2001) Env. Microb. 3(1) : 10-18.
3. Stein, L. et al. (2002) FEMS Microb. Ecol. 42 : 431-440.
  • Poster
    Workshop Umweltmikrobiologie Freiberg 5.-7.10.2003

Publ.-Id: 5876 - Permalink


Uranium contaminated environments as a reservoir of unusual bacteria prospective for bioremediation and nanotechnology
Selenska-Pobell, S.;
Microbial communities were studied in several uranium mining wastes in Germany and in the USA by using the rDNA retrieval applying several sets of amplification primers flanking different regions of the rrn operons (1, 2). The bacterial populations in the studied soil samples were rather dense and extremely diverse. In the water samples a lower grade of bacterial diversity was found. Despite the fact that the composition of the bacterial communities was site-specific, several bacterial groups including also novel lineages seem to be characteristic for the studied heavy-metal-polluted environments. The archaeal populations, in contrast, were not very dense and were limited to several not yet cultured Crenarchaeotae lineages which were identified in other metal contaminated environments as well.
In parallel to the above mentioned direct molecular approach, the method of enrichment culturing was applied in order to recover and study particular bacterial strains indigenous for the U wastes. Bacterial isolates belonging to different species representing diverse bacterial groups were recovered and characterized (1). The resistance and the interactions of these isolates with U and with other heavy metals were demonstrated to be species- and even strain-specific. The atomic structures and the cellular location of the complexes formed with U(VI) by the isolates were studied using EXAFS spectroscopy, TEM, and EDX analyses. In all cases phosphate groups were predominantly implicated in the complexation of uranium but the structural parameters and the cellular location of the complexes differed between the studied bacterial groups (3).
Many of the studied strains possess unusual characteristics as the isolate JG-A12, for instance, which accumulates selectively U, Cu, Pb, Al, and Cd (4). This strain as well as its intrinsic S-layer are forming U(VI)-complexes with identical structural parameters in which phosphorous residues in addition to the carboxyl groups are involved. ICP-MS demonstrated that the S-layer of JG-A12 is phosphorylated. This can explain its high ability to complex uranium and other metals. The latter seems to give an advantage to the strain to survive in environments heavily polluted with uranium and other toxic metals from which it was recovered.
Sol-gel ceramics with high and reversible metal binding capacity were prepared via homogeneous dispersion and embedding of B. sphaericus JG-A12 vegetative cells (5, 6). This biological ceramics are very perspective for bioremediation of heavy metal contaminated water wastes.
In addition, Pd nanoclusters were also successfully grown on the surface of these bacteria. The latter is of interest for the nanotechnology. Interestingly, the above mentioned S-layer of JG-A12 possesses an unusual primary structure which indicates that lateral transfer was involved in the evolution of its gene.
References
1. Selenska-Pobell, S. (2002) Interactions of Microorganisms with Radionuclides p. 225-253; Elsevier, Oxford
2. Selenska-Pobell, S., et al. (2001) Antonie van Leeuwenhoek 79, 149-161.
3. Merroun M. et al. (2003) FZR-Report No. 364, p. 26-30
4. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67
5. Raff, J. et al. (2003) Chem. Mater. 15 (1): 240-244.
6. Soltmann et al. (2003) J Sol-Gel Science and Technology 26, 1209-1212.
  • Lecture (Conference)
    Workshop Umweltmikrobiologie Freiberg 5.-7.10.2003

Publ.-Id: 5875 - Permalink


Uranium mining waste pile isolate Bacillus sphaericus JG-A12 and its technological applications
Pollmann, K.; Raff, J.; Merroun, M.; Schnorpfeil, M.; Selenska-Pobell, S.;
The strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt. The drain water and the soil of this environment are highly contaminated with heavy metals and radionuclides. The cells of B. sphaericus JG-A12 are capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters (1). It was demonstrated that the strain JG-A12 is enveloped by a surface layer protein (S-layer) which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date (2). The highly ordered crystalline S-layers are one of the most common cell envelope structures of bacteria and archaea (3). They are composed of identical protein monomers which possess an ability to self-assemble into two-dimensional crystalline arrays. The highly regular structure of the S-layers with many pores of identical size offers good binding sites for many different metals and nucleation sites for the formation of metal nanoclusters or minerals. EXAFS-analyses of the uranium complexes formed by the S-layer of JG-A12 showed that this metal is coordinated to carboxyl and phosphate groups of the latter (4). Analyses of the amino acid composition of the C-terminus showed a high content of serine and treonine residues which are potential phosphorylation sites. These characteristic features of the S-layer of B. sphaericus JG-A12 make the strain perspective for bioremediation and nanotechnological applications.
In this work we are presenting the formation of Pd nanoclusters on the cells of B. sphaericus JG-A12 in the presence of H2 as a reducing agent. These nanoclusters are interesting for the development of bionanocatalysts and biosensors. Further, by embedding cells, spores or S-layers using sol-gel techniques bioceramics particles were produced (5, 6). These bioceramics can be used for bioremediation of heavy metal contaminated waters.

References
1. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67
2. Raff, J. (2002) "Wechselwirkungen der Hüllproteine von Bakterien aus Uranabfallhalden mit Schwermetallen" PhD thesis, FZR-Report No. 358.

3. Sleytr, U. et al. (1997) FEMS Microbiol. Rev. 20, 47-97.
4. Merroun M. et al. (2003) FZR-Report No. 364, p. 26-30
5. Raff, J. et al. (2003) Chem. Mater. 15 (1): 240-244.
6. Soltmann et al. (2003) J Sol-Gel Science and Technology 26, 1209-1212.
  • Poster
    Workshop Umwelttechnologie Freiberg 5.-7.10.2003

Publ.-Id: 5874 - Permalink


Archaeal and bacterial populations in soil and water samples from the uranium mill tailings Gittersee/Coschütz
Radeva, G.; Flemming, K.; Satschanska, G.; Selenska-Pobell, S.;
Bacterial and archaeal populations in soil and water samples of the uranium mill tailings Gittersee/Coschütz were studied by using the rDNA retrieval applying different sets of PCR amplification primers. Bacterial communities found in both soil and water samples had similar composition as estimated via analyses of the constructed 16S rDNA43F-1404R and 16S rDNA7F-1513R clone libraries. They consisted of proteobacteria (mainly from the gamma-subclass) and of representatives of the Cytophaga/Flavobacterium/Bacteroides (CFB) group. In the soil samples Gram-positive bacteria were found as well. These results are in contrast to those obtained by the analysis of the samples collected from the uranium mining waste pile near the town of Johanngeorgenstadt where members of the alpha proteobacteria and of the Holophaga/Acidobacterium phylum were found to be predominant by using the same 16S rDNA PCR amplification primers (1, 2, 3).
The analysis of the water samples applying the ribosomal intergenic spacer amplification rDNA retrieval using the 16S rDNA968F and 23S rDNA130R PCR primers revealed much higher diversity. In addition to the members of the Proteobacteria and of the CFB, populations of Nitrospira, Verrucomicrobia, Planctomycetales, Actinobacteria and also of several novel bacterial divisions were found (4). This result is due to the primer structures (5).
The identified archaeal populations, in contrast to those of the bacteria, were not very diverse in the studied environment. In the archaea-specific 16S rDNA21F-958R clone libraries constructed for the above mentioned soil and water samples only a few populations of not yet cultured Crenarchaeota were found (6).
Most of the 16S rDNA sequences obtained in this work showed no close phylogenetic affiliation to cultured bacteria or archaea. For this reason, it is difficult to predict the phenotypic properties and the ecological role of the corresponding organisms. However, it is interesting that the most related 16S rDNA sequences found in the Gene Bank were retrieved in environments with geologic and ecological properties similar to those of the uranium wastes, such as gold mine and other acid mine drainage systems (7, 8).
Efforts to culture representatives from some of the most predominant microbial populations are in progress.

References

1. Selenska-Pobell, S. et al. (2002) Bacterial communities in uranium mining waste piles and their interaction with heavy metals, p.455-464; In Uranium in the aquatic environment. Springer-Verlag.
2. Selenska-Pobell, S., et al. (2001) Antonie van Leeuwenhoek 79, 149-161.
3. Geißler, A. (2003) Molekulare Analyse der bakteriellen Diversität in Uranabraumhalden. Diploma Thesis, FZR-Report No. 377
4. Selenska-Pobell, S. (2002) Diversity and activity of bacteria in uranium waste piles, p. 225-253; In, Interactions of Microorganisms with Radionuclides. Elsevier Sciences, Oxford, UK.
5. Derakshani, M., et al. (2001) Appl. Environ. Microbiol. 67: 623-631.
6. Radeva, G. and Selenska-Pobell, S. (2003) FZR-Report No. 373, p. 29
7. Takai, K., et al. (2001) Appl. Env. Microbiol. 67, 5750-5760.
8. Stein, L., et al. (2002) FEMS Microb. Ecol. 42, 431-440.
  • Poster
    Umweltmikobiologie Workshop Freiberg 5.-7.10.2003

Publ.-Id: 5873 - Permalink


Bacterial diversity and monitoring of Geobacter sp. in uranium contaminated soils
Geißler, A.; Tzvetkova, T.; Selenska-Pobell, S.;
Bacterial diversity was investigated by using the 16S rDNA retrieval in soil samples collected from a uranium mining waste pile called Haberland situated near the town of Johanngeorgenstadt, Germany, and from one uranium mill tailings in the USA, namely Shiprock, New Mexico. Significant differences were found in the composition of the bacterial communities at the studied sites. Alpha-Proteobacteria and representatives of the Holophaga/Acidobacterium phylum are predominant at the uranium mining waste pile Haberland, whereas the Shiprock uranium mill tailings is mainly occupied by Bacillales, g-Proteobacteria, and Green non-sulfur bacteria. The observed differences in the composition of the bacterial communities in the two studied environments are most probably connected to their different grade of contamination with heavy metals, and also to their different geographic and geologic origin (1).
Representatives of the Geobacter genus were found in both samples studied, but mainly by using Geobacter specific primers. This indicates that the Geobacter populations are probably not predominant in the studied environments. The exact quantification of these populations will be performed by using Real-Time PCR (work in progress). Geobacteracea are involved in reduction of heavy metals (e.g. iron) and radionuclides (e.g. uranium). Because these bacteria can significantly influence the mobility of the mentioned metals (2) their quantification in the uranium wastes is of great importance.

References:
1. Geißler, A. (2003) Molekulare Analyse der bakteriellen Diversität in Uranabraumhalden. Diploma Thesis,
Wissenschaftlich-Technische Berichte des Forschungszentrums Rossendorf FZR-377.

2. Lovley, D. R. et al. (1993) Archives of Microbiology 159: 336-344.
  • Poster
    Workshop Umweltmikrobiologie Freiberg 5.-7.10.2003

Publ.-Id: 5872 - Permalink


Investigation of a tin liquid metal ion source
Bischoff, L.; Akhmadaliev, C.; Mair, A. W. R.; Mair, G. L. R.; Ganetsos, T.; Aidinis, C. J.;
A Sn liquid metal ion source was prepared employing a Ni needle to anchor the liquid ion emitter. The main source properties, i.e., the I-V curve, the mass spectra, the energy spread for the main species, as well as the long term source stability were systematically studied. Moreover, a new etching technique for Ni tips has been developed. The mass spectra show a large amount of Sn clusters, apart from the dominant species, Sn+ and Sn++. The source was stable down to 1µA emission current, corresponding to an energy spread for the singly-charged ions of 7 eV. Theoretical arguments strongly suggest that both Sn+ and Sn++ are emitted by direct field-evaporation from the liquid surface.
Keywords: tin liquid metal ion source, Ni emitter assembly needle, mass spectra, energy spread

Publ.-Id: 5871 - Permalink


Azimuthal Dependence of Collective Expansion for Symmetric Heavy-Ion Collisions
Stoicea, G.; Petrovici, M.; Andronic, A.; Herrmann, N.; Alard, J. P.; Barret, V.; Basrak, Z.; Bastid, N.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Hildenbrand, K. D.; Hong, B.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Korolija, M.; Kotte, R.; Kress, T.; Lebedev, A.; Leifels, Y.; Lopez, X.; Merschmeyer, M.; Neubert, W.; Pelte, D.; Rami, F.; Reisdorf, W.; Schüll, D.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, S.; Stockmeier, M.; Wisniewski, K.; Wohlfarth, D.; Yushmanov, I.; Zhilin, A.; Danielewicz, P.;
Detailed studies of the azimuthal dependence of the mean fragment and flow energies in the Au+Au and Xe+CsI systems are reported as a function of incident energy and centrality. Comparisons between data and model calculations show that the flow energy values along different azimuthal directions could be viewed as snapshots of the fireball expansion with different exposure times. For the same number of participating nucleons more transversally elongated participant shapes from the heavier system produce less collective transverse energy. Good agreement with Boltzmann-Uehling-Uhlenbeck calculations is obtained for a soft nuclear equation of state.

Publ.-Id: 5870 - Permalink


The pseudo-Hermiticity of MHD dynamo operators
Günther, U.;
The presentation provides a short introduction to MHD dynamos and to the pseudo-Hermiticity properties of the matrix differential operator of the spherically symmetric α2-dynamo.
In the first part of the lecture, the underlying physics is described starting from a discussion of the homopolar disk dynamo, of field reversals of the Earth's magnetic field and of the dynamo experiments in Riga and Karlsruhe. Furthermore, a sketchy outline of the helicity based meanfield technique for the MHD induction equation is presented and the closing of the dynamo cycle is discussed.
In the second part, attention is paid to the derivation of the matrix differential operator for the spherically symmetric α2-dynamo and its associated quadratic operator pencil. Boundary conditions, pseudo-Hermiticity and Krein-space features are used to heuristically explain the level-crossing properties of the spectrum. Along the lines of [1], the derivation of a constructive no-go theorem for isospectral dynamo configurations is described and interesting open problems are listed.

[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: 5869 - Permalink


Intertwiners of pseudo-Hermitian 2×2-block-operator matrices and a no-go theorem for isospectral MHD dynamo operators
Günther, U.;
Pseudo-Hermiticity as a generalization of usual Hermiticity is a rather common feature of (differential) operators emerging in various physical setups. Examples are Hamiltonians of PT- and CPT-symmetric quantum mechanical systems [1] as well as the operator of the spherically symmetric α²-dynamo [2] in magnetohydrodynamics (MHD). In order to solve the inverse spectral problem for these operators, appropriate uniqueness theorems should be obtained and possibly existing isospectral configurations should be found and classified. As a step toward clarifying the isospectrality problem of dynamo operators, we discuss an intertwining technique for η-pseudo-Hermitian 2×2-block-operator matrices with second-order differential operators as matrix elements. The intertwiners are assumed as first-order matrix differential operators with coefficients which are highly constrained by a system of nonlinear matrix differential equations. We analyze the (hidden) symmetries of this equation system, transforming it into a set of constrained and interlinked matrix Riccati equations. Finally, we test the structure of the spherically symmetric MHD α²-dynamo operator on its compatibility with the considered intertwining ansatz and derive a no-go theorem.

[1] Bender C.M. and Boettcher S., Real spectra in non-Hermitian Hamiltonians having PT symmetry, Phys. Rev. Lett. 80, 1998, 5243, physics/9712001; Znojil M., PT-symmetric harmonic oscillators, Phys. Lett. A259, 1999, 220, quant-ph/9905020; Bender C.M., Brody D.C. and Jones H.F., Complex extension of quantum mechanics, Phys. Rev. Lett. 89, 2002, 270401, quant-ph/0208076.

[2] 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.
Keywords: MHD, dynamo, discrete symmetry, Krein space, Supersymmetry, operator intertwining technique, matrix Riccati equation
  • Lecture (Conference)
    Fifth International Conference "Symmetry in Nonlinear Mathematical Physics" June 23-29, 2003, Institute of Mathematics, National Academy of Sciences of Ukraine, Kyiv (Kiev), Ukraine
  • Proceedings of the Institute of Mathematics of the National Academy of Sciences of Ukraine 50(2004, 780-787

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Publ.-Id: 5868 - Permalink


Riga dynamo experiment and its theoretical background
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.;
It is widely believed that almost all magnetic fields in a natural environment are the result of the dynamo process - the field generation in moving nearly homogeneous electro-conducting fluids. This dynamo process occurs in the depths of celestial bodies such as the Earth, most of the planets, the Sun, other stars, and even galaxies.The Riga dynamo experiment is not intended as a model of any particular celestial body. It aims at demonstrating the basic dynamo mechanism - that the intense motion in a large volume of a good electro-conducting liquid creates a magnetic field. In the present paper, the set-up and the main results of this experiment are presented, with some focus on the theoretical interpretation of the data.
  • Physics of Plasmas 11(2004), 2828-2843

Publ.-Id: 5867 - Permalink


Influence of the pipe diameter on the structure of the gas-liquid interface in a vertical two-phase pipe flow
Prasser, H.-M.; Beyer, M.; Böttger, A.; Carl, H.; Lucas, D.; Schaffrath, A.; Schütz, P.; Weiß, F.-P.; Zschau, J.;
Two-phase flow tests in a 194.1 mm diameter vertical pipe (DN200) with an air-water mixture are reported. Close to the upper end of a 9 m tall test section a wire-mesh sensor is installed that delivers instantaneous void fraction distributions over the entire cross section with time resolution of 2500 frames per second. The sensor disposes of 64x64 measuring points, which corresponds to a spatial resolution of 3 mm. Beside an fast flow visualisations, void-fraction profiles and bubble size distributions were obtained. Earlier, similar experiments were carried out in a pipe of 51.2 mm inner diameter (DN50). A comparison of the data from the two different facilities allows to study the scaling effects on void fraction profiles, bubbles size distributions and the flow patterns. In the small pipe, the increase of the air flow rate leads to a transition from bubbly via slug to churn turbulent flow.
The transition to slug flow is accompanied by the appearance of a second peak in the bubble size distribution that corresponds to the class of large Taylor bubbles. A similar qualitative behaviour was found in the large pipe, though the large bubble fraction has a significantly bigger mean diameter at identical superficial velocities, the peak is less tall but wider. Bubbles move more freely than in the small pipe, since the confining action of the pipe walls to the flow is less pronounced, while the large Taylor bubbles occupy almost the entire cross section in case of the small pipe. Furthermore, the bubbles show much more deformations in the large pipe. Shapes of such large bubbles were characterised in three dimensions for the first time. They can rather be complicated and far from the shape of ideal Taylor bubbles. Also the small bubble fraction tends to bigger sizes in the large pipe.

Keywords: two-phase flow, vertical upwards flow, wire-mesh sensor, flow pattern, bubble size
  • Lecture (Conference)
    10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10), Seoul, Korea, October 5-9, 2003; conference-CD: A00308
  • Contribution to proceedings
    10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10), Seoul, Korea, October 5-9, 2003; conference-CD: A00308

Publ.-Id: 5866 - Permalink


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