Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41347 Publications

Influence of hydrogen on the toughness of irradiated reactor pressure vessel steels

Müller, G.; Uhlemann, M.; Ulbricht, A.; Böhmert, J.

The influence of hydrogen on the mechanical behaviour of different reactor pressure vessel (RPV) steels was investigated by tensile tests in correla-tion to the chemical composition, the neutron fluence, the hydrogen charg-ing condition, the strain rate, and the temperature. Small-angle neutron scattering (SANS) experiments, hydrogen analyses and thermal desorp-tion investigations were performed to prove the evidence of hydrogen trapping at irradiation defects. An increasing susceptibility to hydrogen embrittlement indicated by reduction of area was observed at room tem-perature with in-situ hydrogen-charged specimens when loaded by low strain rates or with specimens, which had been irradiated at low tempera-ture. Generally, the susceptibility increases with increasing strength of the steels. At 250°C hydrogen embrittlement was not evident. The results do neither prove that irradiation defects are favoured traps for hydrogen nor give evidence that hydrogen affects the RPV integrity under normal oper-ating conditions.

Keywords: hydrogen embrittlement; reactor pressure vessel steel; irradiation; fluence; tensile test; toughness; hydrogen charging

Publ.-Id: 8645

Preparation and Biological Characterization of Isomeric 188Re(V) Oxocomplexes with Tetradentate S4 Ligands Derived from DMSA for Labeling of Biomolecules

Seifert, S.; Heinrich, T.; Jentschel, C.; Smuda, C.; Bergmann, R.; Pietzsch, H.-J.

A new type of tetradentate S4 ligand has been synthesized by bridging two molecules of meso 2,3-dimercapto succinic acid for stable binding and easy conjugation of rhenium-188 to biologically interesting structures. The stereoisomeric tetrathiolato S4 ligands form very robust anionic five-coordinated oxorhenium(V) and oxotechnetium(V) complexes. Two routes for the preparation of the 188Re(V) oxocomplexes with (iBu)2N(O)C-C(SH)-C(SH)-C(O)NH-(CH2)3–NH-(CH2)3–NHC(O)-C(SH)-C(SH)-C(O)N(iBu)2 (ligand 1) and its hydrophilic crown ether derivative (ligand 2) were tested and optimized. Several isomers were separated by HPLC from the preparation solutions and characterized in vitro and in vivo. The identity of the species obtained was determined by comparison with the HPLC profiles of reference 185/187Re analogues which were characterized by ESI-MS. All of them were absolutely stable in rat and human plasma solutions. Challenge experiments with cysteine corroborated the high inertness of the isomers towards ligand exchange reactions. Various in vivo samples, taken off at different times from blood, intestine and urine of rats, confirmed the high in vivo stability of the 188Re-S4 complexes. Biodistribution studies using male Wistar rats were performed and resulted in a high uptake and fast clearance from the liver of the more lipophilic cis and trans isomers of complex I (log Po/w between 1.5 and 1.7), whereas the isomers of the hydrophilic complex II (log Po/w about -1.75) were rapidly excreted via the renal and the hepatobiliary pathway. The low level of radioactivity in the stomach confirms good in vivo stability. Thus, these new 188Re-S4 complexes fulfill the requirements for a stable and high specific activity labeling of biomolecules with rhenium-188.

Publ.-Id: 8644

Safety aspects of the process control of Grignard reactions

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

Grignard reactions comprise considerable hazard potentials due to the spontaneous heat release during the initiation of the exothermic reactions and the high reactivity of the Grignard compounds. To establish industrially applicable methods for an objective detection of the reaction start-up and for the accumulation of the organic halide during the process, calorimetric studies of a special Grignard reaction in a pressurised vessel were carried out using several on-line monitoring methods. In general, the process signal profiles, FTIR measurements and balance-based on-line monitoring systems are applicable to provide the operator with additional information on the process state. Further experiments at adiabatic and isothermal conditions show significant influences of impurities (i.e. water) on the thermal process behaviour.

Keywords: Chemical processes; Grignard reaction; On-line monitoring; Process control; Safety; Chemical analysis

  • Poster
    ISCRE 19, 19th International Symposium on Chemical Reaction Engineering, 03.-06.09.2006, Potsdam, Germany
  • Contribution to proceedings
    ISCRE 19, 19th International Symposium on Chemical Reaction Engineering, 03.-06.09.2006, Potsdam, Germany
    Book of Abstracts, 362-363
  • Chemical Engineering Science 62(2007), 5198-5200

Publ.-Id: 8643

Colloid Generation and Stability in Simulated Reduced Groundwaters

Zänker, H.; Weiß, S.; Sachs, S.

The focus was on the investigation of U(IV) colloids during this phase of the project. First, a technique to reduce U(VI) to U(IV) was developed. Colloid formation and solubility of U(IV) in acidic HClO4/NaClO4 solutions were investigated by coulometric titration. Quantification of traces of U(VI) by laser fluorescence spectroscopy proved that the tetravalent state of uranium had been maintained. Laser-induced breakdown detection (LIBD) was applied for the detection of traces of uranium colloids as the pH was increased. The pH values at the onset of colloid formation were used for thermodynamic calculations aimed at determining the solubility products of crystalline and amorphous uranium dioxides. In acidic solutions, the UO2·xH2O(am) colloids showed colloidal stability over a period of at least 10 months during which they did not aggregate and precipitate. Relatively high zeta potentials were found for the UO2 colloids in the acidic and in the alkaline pH regions; the point of zero charge was at 6.9. No indications of the formation of mixed U(IV)-Al(III) complexes were found. There was also no influence of Al(III) on the UO2(cr) solubility.

Keywords: Uranium(IV); intrinsic colloids; pseudocolloids

  • Lecture (others)
    2nd FUNMIG RTDC-2 Progress Meeting Karlsruhe, August 2, 2006, 02.08.2006, Karlsruhe, Germany

Publ.-Id: 8641

Synthesis and biological evaluation of tricarbonyl Re(I) and Tc(I) complexes anchored by poly(azolyl)borates: application on the design of radiopharmaceuticals for the targeting of 5-HT1A receptors

Garcia, R.; Gano, L.; Maria, L.; Paulo, A.; Santos, I.; Spies, H.

Keywords: Technetium; Rhenium; Poly(azolyl)borates; 5HT1A receptor; Bivalent approach

Publ.-Id: 8640

Properties of p- and w-mesons in dense and hot nuclear matter near the critical pion mode softening

Bunatian, G.; Kämpfer, B.

  • Open Access Logo Forschungszentrum Rossendorf; FZR 08 1992
    ISSN: 1436-3976


Publ.-Id: 8639

Velocity measurements and concentration field visualizations in copper electrolysis under the influence of Lorentz forces and buoyancy

Weier, T.; Cierpka, C.; Hüller, J.; Gerbeth, G.

Velocity measurements and shadowgraph visualizations for copper electrolysis under the influence of a magnetic field are reported. Experiments in a rectangular cell show the expected strong correlation between flow features and limiting current density. The flow can be understood as driven by the interplay of Lorentz forces and buoyancy. For a cylindrical cell with only slightly non-parallel electric and magnetic field lines, the presence and importance of the Lorentz force is demonstrated by velocity measurements.

Keywords: electrolysis; Lorentz force; copper deposition

  • Magnetohydrodynamics 42(2006)4, 379-387
    ISSN: 0024-998X

Publ.-Id: 8638

Development of dendritic ligands for binding metallic radionuclides

Röhrich, A.; Noll, S.; Stephan, H.; Steinbach, J.; Bergamini, G.; Balzani, V.

Two star-like cyclam derivatives 1 and 2 possessing four sugar units on the periphery have been prepared. UV-vis measurements point to slow formation of stable 1:1 complexes of Cu(II) with 1 and 2. Preliminary studies show that the dendritic ligands also complex 99mTc.

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGEditoriali, 2006, 88-89884-04-5, 233-234

Publ.-Id: 8637

Synthesis, characterization and evaluation of novel chelating agents for copper radionuclides

Stephan, H.; Juran, S.; Walther, M.; Steinbach, J.; Born, K.; Comba, P.

Three different hexadentate bispidine ligands L4 – L6 have been prepared. Studies which have been performed to label these ligands with 67Cu indicate a rapid formation of stable complexes under mild conditions (room temperature, aqueous solution). Challenge experiments of these complexes in the presence of a high excess of competing ligands such as glutathione, histidine and cyclam gave no evidence of radiocopper exchange. The 67Cu complexes of the bispidine ligands investigated are also stable in rat plasma at least for 24 h.

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGEditoriali, 2006, 88-89884-04-5, 219-222

Publ.-Id: 8636

Stability aspects of higher dimensional gravitational models with nonlinear scalar curvature coupling R4

Günther, U.

Subject of the talk is a multidimensional gravitational model with scalar curvature nonlinearity R4. It is assumed that the higher dimensional spacetime manifold of this model undergoes a spontaneous compactification to a manifold with warped product structure. The main attention is paid to the stability of the extra-dimensional factor spaces and it is shown that for certain parameter regions the system allows for a freezing stabilization of these spaces. The most interesting fact, which is demonstrated, is a dependence of the stability region (in parameter space) on the total dimension D=dim(M) of the higher dimensional spacetime M. For D>8 the stability region consists of a single (absolutely stable) sector which is shielded from a conformal singularity (and an antigravity sector beyond it) by a potential barrier of infinite height and width. This sector is smoothly connected with the stability region of a curvature-linear model. For D<8 an additional (metastable) sector exists which is separated from the conformal singularity by a potential barrier of finite height and width so that systems in this sector are prone to collapse into the conformal singularity. This second sector is not smoothly connected with the first (absolutely stable) one. Several limiting cases and the possibility for inflation are discussed. The talk is mainly based on:

Class. Quantum Grav. 22, (2005), 3135-3167, hep-th/0409112

Keywords: cosmology; higher dimensional gravity; stabilization of extra dimensions; conformal singularity; gravitational collapse

  • Invited lecture (Conferences)
    Eleventh Marcel Grossmann Meeting on recent developments in theoretical and experimental general relativity, gravitation and relativistic field theories., 23.-29.07.2006, Berlin, Germany

Publ.-Id: 8635

Mn-silicide nanoparticles: the origin of ferromagnetism in Mn-implanted Si?

Zhou, S.; Potzger, K.; Zhang, G.; Mücklich, A.; Eichhorn, F.; Grötzschel, R.; Schmidt, B.; Skorupa, W.; Helm, M.; Fassbender, J.

Recently Si and Ge semiconductors doped with Mn are reported to be ferromagnetic [1, 2]. The ferromagnetism is attributed to the coupling between Mn ions and carriers. However some MnxSiy and MnxGey compounds are ferromagnetic. A careful structural analysis is crucial to clarify the ferromagnetism in Mn doped Si or Ge. In this work, Mn ions were introduced to p-Si by ion implantation. Structural and ferromagnetic properties of Mn-implanted Si were investigated by Rutherford backscattering, x-ray diffraction (XRD), transmission electron microscopy (TEM) and superconducting quantum interference device magnetometer (SQUID). Synchrotron irradiation XRD and TEM revealed the formation of Mn4Si7 nanoparticles already in the as implanted samples (Fig. 1). Depending on the Mn-fluence they grew up from 5 nm to 20 nm upon rapid thermal annealing. No significant evidence is found for Mn substituting Si sites either in the as-implanted or annealed samples. By SQUID, hysteretic loops were observed, while the coecivity and remanence are drastically decreased with increasing temperature. The magnetization upon zero-field cooled and field cooled procedure shows a characteristic of a magnetic nanoparticle system. Together with structural analysis, we attributed the observed ferromagnetism to Mn-silicides nanoparticles.

(1) Y. D. Park, et al., Science 295, 651 (2002).
(2) M. Bolduc, et al., Phys. Rev. B 71, 033302 (2005).

  • Poster
    IBMM 2006, 18.-22.09.2006, Taormina, Italy

Publ.-Id: 8634

A brane model, its AdS-dS states and their agitated extra dimensions

Günther, U.; Vargas Moniz, P.; Zhuk, A.

We consider multidimensional gravitational models with a nonlinear scalar curvature term and form fields. It is assumed that the higher dimensional spacetime undergoes a spontaneous compactification to a warped product manifold. Particular attention is paid to models with quadratic scalar curvature terms and a Freund-Rubin-like ansatz for solitonic form fields. It is shown that for certain parameter ranges the extra dimensions are stabilized for any sign of the internal space curvature, the bulk cosmological constant and of the effective four-dimensional cosmological constant. Moreover, the effective cosmological constant can satisfy the observable limit on the dark energy density.

Keywords: cosmology; higher dimensional gravity; stabilization of extra dimensions

Publ.-Id: 8633

Remarks on dimensional reduction of multidimensional cosmological models

Günther, U.; Zhuk, A.

Multidimensional cosmological models with factorizable geometry and their dimensional reduction to effective four-dimensional theories are analyzed on sensitivity to different scalings. It is shown that a non-correct gauging of the effective four-dimensional gravitational constant within the dimensional reduction results in a non-correct rescaling of the cosmological constant and the gravexciton/radion masses. The relationship between the effective gravitational constants of theories with different dimensions is discussed for setups where the lower dimensional theory results via dimensional reduction from the higher dimensional one and where the compactified space components vary dynamically.

Keywords: cosmology; higher dimensional gravity; stabilization of extra dimensions

Publ.-Id: 8632

Boron Dilution Transients during natural circulation flow in PWR – experiments and CFD simulations

Höhne, T.; Kliem, S.; Rohde, U.; Weiss, F.-P.

Partial depletion of the primary circuit during a postulated small break loss of coolant accident can lead to the interruption of one-phase flow natural circulation. In this case, the decay heat is removed from the core in the reflux-condenser mode. In case of the partial non-availability of the safety injection system, weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive this safety injection. After refilling of the primary circuit, natural circulation re-establishes and the lower-borated slugs are shifted towards the reactor pressure vessel (RPV). Mixing in the downcomer and the lower plenum is an important phenomenon mitigating the reactivity insertion into the core in this postulated scenario. Therefore, mixing of the lower-borated slugs with the ambient coolant in the RPV was investigated at the four loop 1:5 scaled ROCOM mixing test facility. In these experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied. From the test matrix an experiment with 2% density difference between the de-borated slugs and the ambient coolant was used to validate the CFD software ANSYS CFX. To model the effects of turbulence on the mean flow a Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used. The experiment and CFD calculation show a stratification in the downcomer. The less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core. The validation proves that ANSYS CFX is able to simulate appropriately the flow field and mixing effects of coolant with different densities.

Keywords: PWR; CFD; ROCOM; Boron Dilution

Publ.-Id: 8631

Einfluss von Uran auf die Archae-Diversität in Bodenproben aus der Haberlandhalde

Reitz, T.

Der Einfluss von Uranylnitrat und Natriumnitrat auf eine in einer Uranabfallhalde natürlich vorkommende archaeale Gemeinschaft wurde mit Hilfe molekularbiologischer Methoden auf der Grundlage der 16S rRNA-Genanalyse untersucht. Es zeigte sich, dass sich die archaeale Diversität der Originalprobe auf einige wenige Abstammungslinien mesophiler Crenarchaeota begrenzte.
In allen Versuchsansätzen, unabhängig von der zugegebenen Menge des Uranyl- bzw. Natriumnitrats, der Inkubationsdauer und der Sauerstoffverfügbarkeit, konnte eine Verschiebung der archaealen Populationen zu einer Gruppe eng verwandter, mikrodiverser Crenarchaeota nachgewiesen werden.
Unterschiedliche Nährmedien wurden hergestellt um Vertreter dieser Gruppe anzureichern und zu isolieren. Dabei gelang es mesophile Crenarchaeota der oben genannten Gruppe in zwei Nährmedien zu kultivieren. Die bakterielle Begleitflora beider Archaea-Kulturen war geprägt durch Vertreter der Klassen Bacilli und Clostridia.
In einem weiteren Teil der Arbeit wurde die Biosorptionskinetik von Uran(VI) an den Zellen des hyperthermophilen Crenarchaeons Pyrobaculum islandicum (DSM 4184) sowie des bakteriellen Haldenisolats Paenibacillus sp. JG35+U4-B1 untersucht. Es konnte gezeigt werden, dass bei beiden Stämmen eine schnelle Sättigung (< 30 min) der Zelloberflächen mit Uran bei Raumtemperatur eintritt. Die Uranbindungskapazität von P. islandicum lag mit etwa 28 mg pro g Trockenmasse deutlich unter der des bakteriellen Isolats Paenibacillus sp. JG35+U4-B1 mit 65 mg Uran/g TM. Ein Grund dafür könnte sein, dass die Versuchsbedingungen nicht dem physiologischen Temperaturoptimum des hypothermophilen Archaeons entsprechen.

  • Other report
    Technische Universität Dresden: Diplomarbeit (Studiengang Biologie), 2006
    83 Seiten

Publ.-Id: 8630

Winzlinge im Kampf gegen Uran

Bittner, D.; Flemming, K.; Raff, J.

Im Rahmen der Praktikumsarbeit "Winzlinge im Kampf gegen Uran" wurde ein Internetbeitrag zu „Forschung populär – Von Schülern für Schüler“ über die Arbeiten zur Identifizierung von Bakterien, der Untersuchung ihrer Wechselwirkungen mit Schwermetallen und Radionukliden sowie deren Nutzung zur Reinigung belasteter Abwässer erstellt. Ziel ist es, einzelne Arbeitsgebiete einem breiten Publikum vorzustellen.

Publ.-Id: 8629

FZR activities on in-vessel melt retention

Altstadt, E.; Willschütz, H.-G.

An overview of the modelling activities of FZR in the field of in-vessel corium melt retention (IVR) is given. The thermal and mechanical models and their application to various IVR scenarios are described. The thermo-chemical interaction between molten corium and reactor vessel steel is considered in the calculations.

Keywords: In-vessel melt retention; Finite element model; corrosion; VVER-1000; FOREVER experiments

  • Lecture (others)
    2nd meeting of the ISTC-project "Reactor Core Melt", 05.07.2006, Moskva, Russia

Publ.-Id: 8628

Monocrystalline spinel nanotube fabrication based on the Kirkendall effect

Fan, H. J.; Knez, M.; Scholz, R.; Nielsch, K.; Pippel, E.; Hesse, D.; Zacharias, M.; Gösele, U.

There is a deep interest in methods to fabricate hollow anocrystals for potential application as high-efficiency catalysts or drug-delivery agents. Tubular one-dimensional nanocrystals have been prepared for a wide variety of materials, including semiconductors1,2, metals3,4, ferroelectrics5,6 and magnetite7. They can be produced by rolling up layered materials or via an axial growth in a rolled-up form8–10, coating pores in templates11 or by eliminating the core of a core–shell nanowire1,7. The Kirkendall effect, a classical phenomenon in metallurgy12, was recently applied to explain the formation of hollow spherical nanocrystals13–17. Although the experimental demonstration and theoretical treatment mainly concern binary compounds and planar interfaces or nanoscale spherical interfaces, the fabrication route provided by the Kirkendall effect should be generic, and should also work for high-aspect-ratio hollow cylinders (that is, nanotubes) or even more complex superstructures. In this letter, we report, for the first time, on ultra-long single-crystal ZnAl2O4 spinel nanotubes (total diameter: ∼40 nm, wall thickness: ∼10 nm) fabricated through a spinel-forming interfacial solid-state reaction of core–shell ZnO–Al2O3 nanowires involving the Kirkendall effect. Our results simultaneously represent an extension of applying the Kirkendall effect in fabricating hollow nano-objects from zero-dimensional to multidimensional, and from binary to ternary systems.

Keywords: nanowires; nanotubes; kirkendall effect

Publ.-Id: 8627

Synthesis and radiopharmacological characterization of 2β-carbo-2’-[18F]fluoroethoxy-3β-(4-bromo-phenyl)tropane ([18F]MCL-322) as a potential PET radiotracer for imaging the dopamine transporter (DAT)

Wüst, F.; Berndt, M.; Strobel, K.; van den Hoff, J.; Peng, X.; Neumeyer, J. L.; Bergmann, R.

The fluoroalkyl-containing tropane derivative 2β-carbo-2’-fluoroethoxy-3β-(4-bromo-phenyl)tropane (MCL-322) is a highly potent and selective ligand for the dopamine transporter (DAT). The compound was labeled with the short-lived positron emitter 18F in a single step by nucleophilic displacement of the corresponding tosylate precursor MCL-323 with n.c.a. [18F]fluoride. The positron emission tomography (PET) radiotracer 2βcarbo-2’-[18F]fluoroethoxy-3β-(4-bromo-phenyl)tropane [18F]MCL-322 was obtained in decay-corrected radiochemical yields of 30-40 % at a specific radioactivity of 1.6-2.4 Ci/µmol (60-90 GBq/µmol) at the end-of-synthesis (EOS). Small animal PET, ex vivo and in vivo biodistribution experiments in rats demonstrated a high uptake in the striatum (3.2 % ID/g) 5 min after injection, which increased to 4.2 % ID/g after 60 min. The uptake in the cere¬bellum was 1.8 % ID/g and 0.6 % ID/g after 5 min and 60 min post injection, respectively. Specific binding to DAT of [18F]MCL-322 was confirmed by blocking ex¬periments using the high affinity DAT ligand GBR 12909. The radiopharmacological characterization was completed with metabolite and autoradiographic studies confirming the highly selective uptake of [18F]MCL-322 in the striatum.
It is concluded that the simple single-step radiosynthesis of [18F]MCL-322 and the promising radiopharmacological data make [18F]MCL-322 an attractive candidate for the further development of a PET radiotracer potentially suitable for clinical DAT imaging in the human brain.

Publ.-Id: 8626

Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland - KTG-Fachtagung 2006

Grauf, E.; Stoll, U.; Teschendorff, V.; Weiß, F.-P.

Der Fachtag fand am 03. und 04. April 2006 im Forschungszentrum Rossendorf (FZR) e.V. bei Dresden statt.
Die Veranstaltung griff mit der Borverdünnung in Druckwasserreaktoren bzw. mit der Verstopfung der Sumpfansaugsiebe durch freigesetztes Isolationsmaterial zwei Themen der Reaktorsicherheit auf, die auch in aktuellen Aufsichtsverfahren eine Rolle spielen. Eingebettet in den internationalen Kontext beleuchteten die Veranstalter die sicherheitstechnische Bedeutung dieser Themen für die deutschen Anlagen und stellten die Auswirkungen auf die zu erbringenden Sicherheitsnachweise und den Anlagenbetrieb dar. Dabei kamen Gutachter, Vertreter der Forschung, Hersteller und Betreiber gleichermaßen zu Wort.
Der Fachtag vermittelte den Teilnehmern aber insbesondere, welche Beiträge die privat und öffentlich finanzierte Reaktorsicherheitsforschung zur Aufklärung der jeweiligen Ereignisabläufe und ihrer sicherheitstechnischen Bedeutung geleistet hat.
In diesem Forschungskontext spielen, auch international, die Methoden der so genannten Computational Fluid Dynamics (CFD) eine zunehmende Rolle. Deshalb war eine Sitzung den Grundlagen, Möglichkeiten und Grenzen von CFD-Methoden gewidmet. Dabei wurden u. a. Anwendungen zur Borvermischung und zum Verhalten von Mineralwolle im Sumpf präsentiert.

  • atw - International Journal for Nuclear Power (2006)6, 405-409

Publ.-Id: 8625

Strong improvement of the electroluminescence stability of SiO2:Gd layers by potassium co-implantation.

Prucnal, S.; Sun, J. M.; Reuther, H.; Skorupa, W.; Buchal, C.

Metal-Oxide-Silicon-Based light emitting diodes with Gd implanted SiO2 layers exhibit strong ultraviolet electroluminescence at 316 nm coming from Gd3+ ions. Co-implantation of potassium ions into the SiO2:Gd layer leads to elimination of the luminescent peak from point defects in SiO2 layers. The electropositive potassium ions compensate the negative charge trapping in the gate oxide and thus improve the electrical stability of the ultraviolet emission from Gd3+ ions. The operating time of the devices was increased more than 30 times by using potassium co-implantation and millisecond flash lamp annealing.

Keywords: ion implantation; MOSLEDs; electroluminescence; silicon dioxide

  • Electrochemical and Solid State Letters 10(2007), 330

Publ.-Id: 8624

Dipole-strength distributions up to the particle-separation energies and photodissociation of Mo isotopes

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

Dipole-strength distributions in the nuclides 92$Mo, 98Mo and 100Mo have been investigated in photon-scattering experiments at the superconducting electron accelerator ELBE of the Forschungszentrum Rossendorf.
A simulation of gamma cascades was performed in order to estimate the distribution of inelastic transitions to low-lying states and thus to deduce the correct dipole-strength distributions up to the neutron-separation energies. The obtained absorption cross sections connect smoothly to (gamma,n) cross sections and give novel information about the low-energy tail of the Giant Dipole Resonance below the neutron-separation energies. The experimental cross sections are compared with predictions of a Quasiparticle-Random-Phase Approximation in a deformed basis.

Photoactivation experiments were performed at various electron energies to study the 92Mo(gamma,n), 92Mo(gamma,p) and 92Mo(gamma,alpha) reactions. The deduced activation yields are compared with theoretical predictions.

Keywords: Photon scattering; photoabsorption cross section; dipole strength; Random-Phase-Approximation; photoactivation; p-nuclei; reaction yields

  • Contribution to proceedings
    International Conference on Collective Motion in Nuclei under Extreme Conditions, 20.-23.6. 2006, Sankt Goar, Deutschland
  • Nuclear Physics A 788(2007), 331c-336c

Publ.-Id: 8623

Excess vacancy generation in SiGe

Kögler, R.

The excess vacancy generation in SiGe by ion implantation was investigated. In contrast to theory the excess vacancy generation in SiGe was observed to be higher than in Si. The reason is the incomplete vacancy-interstitial recombination of defects in SiGe.

Keywords: Ion implantation; implantation defects; excess defects; vacancies; Si; SiGe

  • Lecture (Conference)
    Europien Materials Research Society Conference 2006 - E-MRS2006 -, 29.05.-02.06.2006, Nizza, France

Publ.-Id: 8622

Ion beam Engineering in the initial stage of SIMOX processing

Kögler, R.

Different modes of defect engineering were applied for synthesis of SiO2 nanoclusters in Si. In particular He ion pre-implantation and simultaneous dual-implantation of Si and O ions were performed. It was demonstrated that He pre-implantation is especially suitable for creation of a well defined narrow oxide layer.

Keywords: Silicon-on-insulator; SOI; SiO2 nanocluster; defect engineering; ion beam synthesis

  • Lecture (Conference)
    Ion Implantation - Jahrestagung, 16.-17.05.06, Berlin, Deutschland

Publ.-Id: 8621

Kinetics of precipitation in neutron irradiated steel

Gokhman, A.; Bergner, F.; Ulbricht, A.

Gegenstand der Vortrags ist die ratentheoretische Modellierung der Entwicklung der Größenverteilung von Cu-reichen Defekt-Fremdatom-Clustern in Cu-angereicherten Fe-Basis-Modelllegierungen unter Neutronenbestrahlung. Die berechneten Clustergrößenverteilungen werden mit Ergebnissen von Neutronenkleinwinkelstreumessungen verglichen.

  • Lecture (Conference)
    Mathematical problems to describe the phase transformation of the 1-st kind, 02.-08.07.2006, Bugas, Ukraina

Publ.-Id: 8620

A novel needle probe based on high-speed complex permittivity measurements for investigation of dynamic fluid flows

Da Silva, M. J.; Schleicher, E.; Hampel, U.

For the investigation of multiphase or multicomponent flows, which are of interest, for instance, in oil extraction and processing or in chemical engineering, there are only few suitable measuring techniques. For this reason, we have developed a high-speed complex permittivity needle probe. Such probes are able to distinguish the different phases or components of a flow by measuring the complex value of the electrical permittivity at a high data rate (up to 20000 samples/s). The performance of the system, as well as its ability to differentiate organic substances, has been analyzed. A time-resolved experiment in an oil–water–gas flow, as well as a two-substance mixing experiment in a stirred tank, is presented.

Keywords: complex permittivity measurement; heterogeneous mixture; multiphase flow; multicomponent flow; needle probe


Publ.-Id: 8619

EXAFS investigation of U(VI), U(IV) and Th(IV) sulfato complexes in aqueous solution

Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Scheinost, A.

The structures of U(VI), U(IV) and Th(IV) sulfato complexes were investigated by LIII edge EXAFS spectroscopy in aqueous solutions with total sulfate concentrations, [SO42-]total, ranged from 0.05 to 3 M in the pH range 1.0-2.7. In equimolar U(VI)/[SO42-]total solutions, the species distribution is dominated by monodentate sulfate coordination with a U-Smon distance of 3.57±0.02 Å. With increasing U(VI)/[SO42-]total ratio bidentate coordination becomes dominant with a U-Sbid distance of 3.11±0.02 Å. The aqueous Th(IV) sulfate comprises both, monodentate and bidentate coordination with Th-S distances of 3.14±0.02 and 3.81±0.02 Å, respectively. A similar coordination is obtained for U(IV) sulfato complexes at pH 1 with U-S distances of 3.08±0.02 Å and 3.67±0.02 Å. By increasing the pH value to 2, a U(IV) precipitate occurs, where sulfate act exclusively as bridging ligand with a U-S distance 3.67±0.02 Å.

Keywords: EXAFS; uranium; thorium; sulfate; coordination

  • Inorganic Chemistry 46(2007)15, 5882-5892
  • Poster
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
  • Contribution to proceedings
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
    Speciation Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources: OECD, 978-92-64-99006-7, 219-224

Publ.-Id: 8618

Evidence for double-electron excitations in X-ray absorption spectra of actinides

Hennig, C.

A systematic investigation of double-electron resonances in L3 edge X-ray absorption spectra of actinides in aqueous solution is presented. Actinide species in valence states IV and III were investigated by using experimental data of Th4+, U4+, Np4+, Pu3+, and Am3+ hydrates. The double-electron excitation was identified as a L3N6,7 shake-up effect. Energy positions of the double-electron features were found in good agreement with the Z+1 approximation. The double-electron resonances undergo a larger chemical shift as the L3 edge.

Keywords: double-electron excitation; shake-up; Z+1 approximation; actinides

Publ.-Id: 8617

Enhanced local void and temperature measurements for highly transient two-phase flows

Schleicher, E.; Da Silva, M. J.; Hampel, U.

Abstract: Local void fractions measurements in two-phase flow phenomena are commonly carried out by the use of needle probes. The measuring principle of these probes is based on conductivity or optical measurements. In the past advanced needle probes with integrated micro-thermocouples have been introduced by Prasser et al., making possible to measure local temperatures at the same position where the void fractions are determined because the sheath of the micro-thermocouple serves as the measuring electrode for the conductivity measurement. Thereby - in principle - the temperatures of the two different phases (e. g. steam and water) can be distinguished. The big disadvantage of this technique is the relative long time constant (~20 ms) of mineral-insulated sheathed thermocouples. The usage of this type of thermocouples was necessary because the electronic was not able to separate the two signals (temperature and conductivity) from each other. Measuring of high-transient two phase flows were impossible due to the slow time response. Additionally the two signals had to be sampled sequentially because of influence of the rectangular excitation signal into the small temperature voltage. Investigations of temperature changing in the interfacial area between gas and liquid were therefore very difficult. To solve this problem we have developed a new combined temperature and conductivity needle probe measuring system, which is able to handle grounded or direct sheathed thermocouples (where the thermocouple wires are electrically-joined to the protective sheath) as well as open thermocouples (exposed junction).

Keywords: needle probe; temperature measurement; two-phase flows; micro-thermocouple

Publ.-Id: 8614

Improving Resolution in k and r Space: A FEFF-based Wavelet for EXAFS Data Analysis

Funke, H.; Chukalina, M.; Voegelin, A.; Scheinost, A.

Applying the wavelet analysis of Extended X-Ray Absorption Fine Structure (EXAFS) spectra to a Zn-Al layered double hydroxide, we could unequivocally identify the presence of Al and Zn atoms at the same distance of r ≈ 3 Å from the central Zn atom. The focused paths (including MS) at r ≈ 5 - 6 Å (2nd and 3th metal shell) show also both Al and Zn for all LDH spectra. With the newly developed FEFF-Morlet wavelet it is possible to resolve the two shells individually. The result is, that the 2nd shell not contains Al. This confirms directly the homogeneity of the Al - Zn distribution. No significant differences were found by shell fit- and wavelet analysis between the EXAFS spectra of pure Zn-,Co- or Ni LDH on the one hand and the mixed Zn/Co and Zn/Ni LDH on the other hand.

Keywords: EXAFS; wavelet analysis; layered double hydroxides

  • Lecture (Conference)
    13th International Conference on X-ray Absorption Fine Structure (XAFS13), 09.-14.07.2006, Stanford, United States
  • Contribution to proceedings
    13th International Conference on X-ray Absorption Fine Structure (XAFS13), 09.02.-14.07.2006, Stanford, United States
    AIP Conference Proceedings, Vol. 882, Melville, N.Y., 72-74

Publ.-Id: 8613

Influence of carbonate on U(VI) aqueous speciation and adsorption to ferrihydrite investigated by advanced EXAFS data analysis methods

Rossberg, A.; Ulrich, K.-U.; Brendler, V.; Scheinost, A.

At alkaline pH conditions, formation of soluble uranyl carbonato complexes commonly prevents U(VI) sorption to mineral surfaces, thereby promoting uranium migration in the liquid phase. Microbial activity may increase the partial CO2 pressure by several orders of magnitude in relation to the atmosphere, hence negatively charged carbonato complexes may play a significant role even at acidic pH values, where sorption to positively charged surfaces may compete with formation of binary inner-sphere sorption complexes. Therefore, we studied by EXAFS the sorption of UO22+ on ferrihydrite in aqueous solution as a function of pH and at elevated carbonate concentrations. We used iterative target transformation factor analysis (ITFA) [1] to derive the spectra of the pure species from the EXAFS spectral mixtures. Then we applied Monte Carlo simulations (MCTFA) [2] to determine the three-dimensional structure of the pure species and the radial pair distribution functions of the single and multiple scattering paths. The spectra of the mixtures can be described by a linear combination of two species. Species 1 is an inner-sphere binary U(VI)-ferrihydrite complex, with U(VI) coordinating to the edge of an Fe octahedron. In species 2, U(VI) is coordinated to two or three carbonato ligands, suggesting formation of [(UO2)(CO2)2]2- or [(UO2)(CO2)3]4- complexes associated with the ferrihydrite solid.

[1] Rossberg, A., Reich, T. & Bernhard, G. Complexation of uranium(VI) with protocatechuic acid - application of iterative transformation factor analysis to EXAFS spectroscopy. Analytical and Bioanalytical Chemistry 376, 631-638 (2003).
[2] Rossberg, A. & Scheinost, A. C. Three-dimensional modeling of EXAFS spectral mixtures by combining Monte Carlo Simulations and Target Transformation Factor Analysis. Analytical and Bioanalytical Chemistry 383(1), 56-66 (2005).

  • Poster
    13th International Conference on X-ray Absorption Fine Structure (XAFS13), 09.-14.07.2006, Stanford, United States

Publ.-Id: 8612

Modified spectro-electrochemical cell for experiments with ionic liquids

Hennig, C.

The presentation concludes the technical development of a spectro-electrochemical cell for actinide research. Electrolysis can be applied with an electrode of second order or by using a diaphragm to seperate catodic and anodic space. The results of chloro and sulfato coordination in presence of U(VI) and U(IV) will be discussed.

Keywords: EXAFS; spectro-electrochemistry; uranium

  • Invited lecture (Conferences)
    Actinet Meeting "Actinides and lanthanides solution chemistry in water stable Room Temperature Ionic Liquids", 08.-09.06.2006, Strasbourg, France

Publ.-Id: 8611

The Structure Of Uranyl Sulfate In Aqueous Solution - Monodentate versus Bidentate Coordination

Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Scheinost, A. C.

The structure of U(VI) aquo sulfato complexes has been investigated by LIII edge EXAFS spectroscopy. A monodentate coordination with a U-Smon distance of 3.57±0.02 Å prevail in equimolar [SO42-]total/U(VI) solutions. With increasing [SO42-]total/U(VI) ratio, bidentate coordination with a U-Sbid distance of 3.11±0.02 Å becomes dominant.

Keywords: EXAFS; U(VI); aquo sulfato complex

  • Contribution to proceedings
    13th International Conference on X-ray Absorption Fine Structure (XAFS13), 09.-14.07.2006, Stanford, United States
    API - Special Edition

Publ.-Id: 8610

Coordination of uranium aquo chloro and sulfato complexes under different redox conditions

Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Scheinost, A. C.

Natural aquatic systems may exert large variations in actinide oxidation states because of limited oxygen diffusion, and microbially and inorganic (surface catalyzed) redox processes. Redox state and coordination hence is a key variable controlling uranium mobility at former uranium mining areas. We have developed a spectro-electrochemical cell, which allows to study the structure speciation of aqueous U(VI) and U(IV) complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential [1]. Here we present data on the influence of redox state on the uranium coordination by chloride and sulfate. The reduction of U(VI) to U(IV) involves an electron transfer and a chemical reaction transforming the trans-dioxo cation to the spherically coordinated U4+ cation. With [Cl] increasing from 0 to 9 M, we observed for U(VI) the complexes UO2(H2O)52+, UO2(H2O)4Cl+, UO2(H2O)3Cl20 and UO2(H2O)2Cl3, and for U(IV) the complexes U(H2O)94+, U(H2O)8Cl3+, U(H2O)6-7Cl22+ and U(H2O)5Cl3+ [1]. Elevated sulfate concentrations have been monitored at the former uranium mine Königstein/Germany, where uranium was leached by sulfuric acid. We observed that tetra- and hexavalent uranium forms both monodentate and bidentate complexes with sulfate. However, with increasing [SO42-] concentration the bidentate coordination prevails. The observed formation of soluble U(IV) sulfato complexes may prevent uraninite precipitation even at low pH, thus increasing the mobility of uranium even under reducing conditions.

Keywords: EXAFS; U(VI); U(IV); electrochemistry

  • Poster
    XAFS-13 Conference, 09.-14.07.2006, Stanford, USA

Publ.-Id: 8609

The problem to account for processes on different time scales in the investigation of neutron embrittlement

Gokhman, A.; Bergner, F.; Ulbricht, A.

Neutrons with energy of about 1 МeV or higher, to which reactor pressure vessel steels are exposed under service conditions of nuclear power plants, can stimulate the phenomenon of so-called neutron embrittlement. The reason is the irradiation-induced formation and evolution of precipitates and solute/defect clusters. The set of experimental methods to investigate the nanostructure, including X- ray and neutron small angle scattering, atom probe field ion microscopy method, TEM as well as direct determination of the mechanical properties of the reactor vessel is usually carried out after irradiation intervals of the order of one year.
Therefore a project called virtual test reactor has been started recently within the framework of the European program “PERFECT”. Experimental data obtained for neutron irradiated pressure vessel steels are used as the reference for working out and study theoretical models of the kinetics of neutron embrittlement.
In the cascade stage, following the interaction of a neutron with a so-called primary knock-on atom, the recoil energy transferred to the crystal lattice causes a local increase of the temperature to beyond the melting temperature and the formation of defects. A typical time scale for these processes is picoseconds. Such processes are studied by the molecular dynamics and Monte-Carlo methods.
Unlike the case of electron irradiation, where only Frenkel pairs are formed, point defect clusters and Cu-precipitates are produced in the case of neutron irradiation. The evolution of these clusters can be studied in the rate theory approach, in particular by cluster dynamics method. This method allows for the determination of the time dependence of the number density of clusters (precipitates) via integration of the system of ordinary differential equations with the initial data as the final data of the cluster number density after cascade stage. The characteristic relaxation time depends on the kind of the irradiated feature. For example for point defect clusters this time is about 1 day but for Cu-precipitates the relaxation time is about one month. Hence the problem to integrate the master equation of cluster dynamics is the problem of integration of so-called stiff ordinary differential equations.
The objective of our present investigation is the comparative analysis of software tools applied to the cluster dynamics modeling. The most effective one, namely the code D02EJF from the licensed Fortran NAG Library has been used to investigate the kinetics of the following three kinds of neutron irradiated features in reactor pressure vessel steels:

  • The system of free and clustering vacancies (V) and interstitials (I), denoted (V+I)-system,
  • The system of the Cu-precipitates favoured because of irradiation-enhanced Cu diffusivity, denoted (V+I)=>Cu system,
  • The (V+I)óCu system, when the effect of Cu-precipitates on the sink strength in the first and second model is additionally considered.
The comparison of the experimental and cluster dynamics data has been carried out on the basis of low-Cu and Cu-enriched mock-up alloys after neutron irradiation.
  • Lecture (Conference)
    4-th Russian Symposium "Physics Problems of Ultrashort Phenomena in Strongly Non-Equilibrium Media", 22.07.-01.08.2006, New Athos, Russia

Publ.-Id: 8608

CFD-simulation of OECD V1000CT2 with advanced turbulence models

Höhne, T.

CFD calculations have been performed for the themalhydraulic benchmark V1000CT-2.
The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor ANSYS CFX and contains 4.7 Mio. tetrahedral elements Different advanced turbulence models were used in the numerical simulation The best agreement with the Kozloduy experiment at the core inlet shows the DES simulation. Strong fluctuations occur in the downcomer of the RPV.
The results show a clear sector formation of the affected loop at the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%
Deficits: Estimation of experimental values at the core outlet to the core inlet, interpolation

Keywords: OECD; VVER-1000; CFD

  • Lecture (Conference)
    Annual meeting of Working Group C and G of AER, 22.-23.05.2006, Balatonfüred, Hungary

Publ.-Id: 8607

Fluid mixing and flow distribution ín a primary circuit of a nuclear pressurized water reactor – Validation of CFD codes

Rohde, U.; Höhne, T.; Kliem, S.; Hemström, B.; Scheuerer, M.; Toppila, T.; Aszodi, A.; Boros, I.; Farkas, I.; Muehlbauer, P.; Vyskocil, V.; Klepac, J.; Remis, J.; Dury, T.

The EU project FLOMIX-R was aimed at describing the mixing phenomena relevant for both safety analysis, particularly in steam line break and boron dilution scenarios, and mixing phenomena of interest for economical operation and the structural integrity.
This report will focus on the Computational Fluid Dynamics (CFD) code validation. Slug mixing tests simulating the start-up of the first main circulation pump have been performed with two 1:5 scaled facilities: The Rossendorf coolant mixing model ROCOM and the VATTENFALL test facility. Additional data on slug mixing in a VVER-1000 type reactor gained at a 1:5 scaled metal mock-up at EDO Gidropress are provided. Experimental results on mixing of fluids with density differences obtained at ROCOM and the FORTUM PTS test facility were made available. Concerning mixing phenomena of interest for operational issues and thermal fatigue, flow distribution data available from commissioning tests have been used together with the data from the ROCOM facility as a basis for the flow distribution studies. CFD calculations have been accomplished for selected experiments with two different CFD codes (CFX-5, FLUENT). Best practice guidelines (BPG) were applied in all CFD work when choosing computational grid, time step, turbulence models, modelling of internal geometry, boundary conditions, numerical schemes and convergence criteria. The strategy of code validation based on the BPG and a matrix of CFD code validation calculations have been elaborated. Based on the “best practice solutions”, conclusions on the applicability of CFD for turbulent mixing problems in PWR were drawn and recommendations on CFD modelling were given.


Publ.-Id: 8606

Surface speciation of uranyl(VI) on gibbsite: A combined spectroscopic approach

Arnold, T.; Scheinost, A.; Baumann, N.; Brendler, V.

Sorption phenomena are important immobilization processes to be considered in the design of nuclear waste repositories. Confidence in respective performance assessments requires a mechanistic understanding of the dominant surface reactions. Highly sensitive and non-invasive techniques such as Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS) and Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy are valuable tools to reveal the true surface speciation.
Here TRLFS and EXAFS were applied to study the species of uranyl(VI) adsorbed onto gibbsite particles. This system is important as a model for the characterization of the edge sites of aluminosilicates, relevant as potential host rock and as part of engineered barrier systems.
The experiments were performed with both normal and CO2-free atmosphere, in the pH range 4 to 9, with a total uranium concentration of 10 µM, an ionic strength of 0.01 M (NaClO4), a solid concentration of 4.15 and 12.5 g/L, and using a grain size of 0.2 – 12 µm.
TRLFS at room temperature provided evidence for two adsorbed uranium(VI) surface species. The two species showed similar positions of the fluorescence emission bands and different fluorescence lifetimes indicating a different coordination environment for the two species. The first surface species with the shorter fluorescence lifetimes was assigned to a mononuclear surface complex, where EXAFS indicated (AlO)2UO2 distance of 3.6 Å. The second species with the longer fluorescence lifetimes was attributed to polynuclear surface species supported by a U – U distance of 4.2 Å obtained by EXAFS at cryogenic temperature. Cryogenic TRLFS experiments at 10 K implied the presence of a third surface species. The significant shift of the fluorescence emission bands to shorter wavelength (approximately 16 nm) points to a ternary uranyl carbonato surface species, supported by an EXAFS-derived U – C distance of 2.9 Å. These results will help to formulate more realistic surface reactions on aluminosilicates.

  • Lecture (Conference)
    2006 Fall Meeting, 27.11.-01.12.2006, Boston, United States
  • Contribution to proceedings
    2006 Fall Meeting, 27.11.-01.12.2006, Boston, United States

Publ.-Id: 8605

Analytische und experimentelle Untersuchungen zur Modellierung der Fluid-Struktur-Wechselwirkung in einem 2D-Ringspalt

Grunwald, G.; Altstadt, E.

  • Open Access Logo Forschungszentrum Rossendorf; FZR 1 1993
    ISSN: 1436-3976


Publ.-Id: 8604

Complexation of uranium(VI) with aromatic acids in aqueous solution – A comparison of hydroxamic acids and benzoic acid

Glorius, M.; Moll, H.; Bernhard, G.

The complex formation of uranium(VI) with salicylhydroxamic, benzohydroxamic, and benzoic acid in 0.1 M NaClO4 was studied by UV-vis spectroscopy at pH 3 and 4. Uranium(VI) species of the type MpLqHr were identified from the UV-vis spectra in all three systems. An increase in the absorption combined with a blue shift of the absorption maxima in comparison to the bands of the free uranyl ion of 22.5 ± 2 nm was observed in the uranium (VI)-salicylhydroxamic acid-system. Besides indications for a 1:2 complex, the formation of a 1:1 complex with a stability constant of log β111= 17.12 ± 0.10 could be demonstrated by its individual absorption spectrum and molar absorption coefficient. Also in the uranium(VI)-benzohydroxamic acid-system a blue shift of the absorption maxima in comparison to the bands of the free uranyl ion of 27 ± 1.4 nm indicate the complex formation. The stability constants are log β110 = 7.96 ± 0.05 for UO2[C6H4CONHO]+ and log β120 = 15.25 ± 0.11 for UO2[C6H4CONHO]2. In contrast to the hydroxamic acids, benzoic acid shows a red shift of the absorption maxima of 2.5 ± 2 nm. Only the 1:1 complex UO2[C6H4COO]+ with a stability constant of log β110 = 3.37 ± 0.14 is existent. An estimate is made in order to discuss the dependencies observed in the absorption spectra in relation to possible coordination modes of uranium(VI). The strength of the complex formation between uranyl and the three aromatic acids is discussed.

Keywords: Uranyl; Hydroxamic acid; Spectroscopy; UV-vis spectra; Complexation

Publ.-Id: 8603

ROSY - Rossendorfer Synchrotronstrahlungsquelle, Vorschlag für die Errichtung einer Synchrotronstrahlungsquelle für die Materialforschung im Forschungszentrum Rossendorf

Einfeld, D.; Matz, W.

Der Projektvorschlag für eine kompakte Synchrotronstrahlungsquelle der 3. Generation ROSY wird beschrieben. Die Quelle sol1 für die Materialforschung dediziert sein, die für die Forschung im regionalen Umfeld von Rossendorf prägend ist.
Bei einer Speicherringenergie von 3 GeV wird Synchrotronstrahlung im harten Röntgenbereich mit einer kritischen Energie des Spektrums von Ec = 8,4 keV (hc=0,14 nm) emittiert. Mit einer naturlichen Emittanz von 28 n nm rad wird eine sehr brillante Strahlung zur Verfügung gestellt. Neben der Strahlung aus Ablenkmagneten kann Strahlung aus Wigglern und Undulatoren genutzt werden. Für diese insertion devices sind 8 Einbaumöglichkeiten vorhanden, von denen 4 in nichtdispersionsfreien geraden Strecken liegen. Der Speicherring hat eine vierfache Symmmetrie, einen Umfang von 148 m und ist als modifizierte FODO-Struktur konzipiert. Ein nachträglicher Einbau von supraleitenden Ablenkmagneten zur Erzeugung eines harteren Spektrums und
damit zur Ausweitung des Anwendungsbereiches ist möglich.
Der Teil I enthält die wissenschaftliche Begründung fur ROSY und eine Darstellung der Nutzungsmöglichkeiten. Im Teil II werden das Speicherringkonzept und die technischen Details der einzelnen Komponenten beschrieben.

  • Open Access Logo Forschungszentrum Rossendorf; FZR 10 1992
    ISSN: 1436-3976


Publ.-Id: 8602

Electronegativity and point defect formation in ion implanted SiO2 layers

Prucnal, S.; Sun, J.; Reuther, H.; Skorupa, W.; Buchal, C.

The Metal-Oxide-Silicon (MOS) diode structure containing ion implanted electropositive (M+) and electronegative (M-) ions is one of the most promising candidates for a new type of high-efficiency electroluminescence (EL) devices which can be integrated with standard silicon CMOS technology. The implantation process creates defects in the SiO2 layer. After implantation an annealing process leads to the diffusion of the implanted elements and a broadening of the SiO2/Si interface. The influence of the different implanted ions (Gd, F, K) was investigated by electroluminescence measurements and correlated to different defects in the oxide layer. Implanted electronegative ions (such as F) lead defects comprising O2 molecules and peroxy radicals (POR). On the other hand, the electropositive ions (Gd and K) increase the number of the oxygen vacancy defects.

Keywords: ion implantation; electronegativity; electroluminescence

  • Vacuum 81(2007)10, 1296-1300

Publ.-Id: 8601

Annual Report 1992, Institute of Nuclear and Hadronic Physics

Dönau, F.; Prade, H.; (Editors)

  • Open Access Logo Forschungszentrum Rossendorf; FZR 10 1993
    ISSN: 1436-3976


Publ.-Id: 8600

Evolution of interfacial area concentration in a vertical air-water flow measured by wire-mesh sensors

Prasser, H.-M.

An application of wire-mesh sensors to obtain the interfacial area concentration in vertical pipes is presented as an alternative to widely used multiple-tip electrical or optical fibre probes. The measuring data of a mesh sensor consists in a three-dimensional matrix of local instantaneous gas fractions measured at each crossing point of the wires and recorded as a time sequence. Bubbles are clearly reflected in this data matrix, since they represent regions of interconnected elements containing the gaseous phase. The method to deduce the interfacial area concentration from this data is based on a full reconstruction of the gas-liquid interface, where the interfacial area of each bubble is recovered as the sum of the surface area of all surface elements belonging to the given bubble. The new method can be applied to large bubbles with an arbitrary shape. To study the change of the interfacial area concentration along the pipe the distance between sensor and gas injection was varied. Obtained results were compared to the findings reported in literature.

Keywords: two-phase flow; flow pattern; interfacial area concentration; vertical upwards flow; wire-mesh sensors

  • Nuclear Engineering and Design 237(2007), 1608-1617

Publ.-Id: 8599

CFD modelling of subcooled boiling – concept, validation and application to fuel assembly design

Krepper, E.; Koncar, B.; Egorov, Y.

The paper describes actual CFD (Computational Fluid Dynamics) approaches to subcooled boiling and investigates their capability to contribute to fuel assembly design. In a prototype version of the CFD code CFX a wall boiling model is implemented based on a wall heat flux partition algorithm. It can be shown, that the wall boiling model is able to calculate the cross sectional averaged vapour volume fraction of vertical heated tubes tests with good agreement to published experimental data. The most sensitive parameters of the model are identified. Needs for more detailed experiments are established which are necessary to support further model development. The model is applied for investigation of the phenomena inside a hot channel of a fuel assembly. Here the essential phenomenon is the critical heat flux. Although subcooled boiling represents only a preliminary state towards the critical heat flux occurrence, essential parameters like swirl, cross flow between adjacent channels and concentration regions of bubbles can be determined. By calculating the temperature of the rod surface the critical regions can be identified which may later on lead to departure from nucleate boiling and possible damage of the fuel pin. The application of up-to-date CFD with a subcooled boiling model for the simulation of a hot channel enables the comparison and the evaluation of different geometrical designs of the spacer grids of a fuel rod bundle.

Keywords: CFD; bubbly flow; boiling; code validation; fuel rod bundle

Publ.-Id: 8597

Picosecond dynamics of interminiband transitions in doped GaAs/AlGaAs superlattices

Stehr, D.; Winnerl, S.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.

Semiconductor superlattices are an essential component of novel infrared devices such as detectors and quantum cascade lasers and their optical and transport properties have been investigated extensively during the past two decades. However, unlike for quantum well structures where considerable knowledge on the intersubband relaxation dynamics has been obtained, so far no experimental work has been published on the interminiband relaxation dynamics in superlattices.

In this work we have studied the transient transmission of a doped GaAs/Al0.3Ga0.7As superlattice in pump-probe experiments [1]. The superlattice with thickness of 9.0 nm and 2.5 nm of the wells and barriers, respectively, was n-doped in the center of the wells, resulting in a doping density of 1.51016 cm-3 averaged over one superlattice period. Picosecond infrared pulses with energies up to 100 nJ in the range from 4 µm to 22 µm were generated at 13 MHz repetition rate by the free-electron laser FELBE at the Forschungszentrum Rossendorf. In particular, the experiments were performed at the absorption maxima of the superlattice at 9.0 µm and 15.8 µm (compare Fig. 1). These wavelengths are the spectral positions of the van Hove singularities of the joint density of states in the center and at the edge of the mini-Brillouin zone, respectively.

The measured pump-probe signals shown in Fig 2 consist of a fast component due to the bleaching of the interminiband transition and subsequent relaxation and thermalization, and a slower component due to cooling of the heated electron system. The fast component decays typically around 2-2.5 ps, in reasonable agreement with published theoretical values [2]. The slower component due to cooling is positive for excitation at 9.0 µm and negative at 15.8 µm and shows a strong temperature and excitation density dependence with cooling times ranging from 5 to 50 ps. This behavior is consistent with the temperature dependence of the linear absorption spectrum, i.e. yielding higher or lower transmission for increasing electron temperature. The effect provides an internal thermometer for the miniband electrons on a picosecond timescale.

[1] D. Stehr et al., Appl. Phys. Lett. (in print)
[2] F. Compagnone, A. Di Carlo, and P. Lugli, Appl. Phys. Lett. 80, 920 (2002)

  • Lecture (Conference)
    POISE Summer School, 25.-30.06.2006, Cortona, Italia

Publ.-Id: 8596

Nanocluster formation in Fe implanted GaN

Talut, G.; Reuther, H.; Mücklich, A.; Eichhorn, F.; Potzger, K.

The formation of Fe-clusters in wurtzite GaN implanted with 200 keV 57Fe ions at 350 ±C was investigated. Cluster sizes from few nanometers up to several 100 nm depending on ion fluence, implantation and annealing temperature have been observed for ion fluences between 4·1016 cm−2 and 1.6·1017 cm−2. A clear epitaxial relation between Fe and GaN was determined. X-ray diffraction, conversion electron Mössbauer spectroscopy, transmission electron microscopy and Auger electron spectroscopy were used for the characterization of the implanted samples. Mössbauer spectroscopy shows that precipitation of Fe occurs already during implantation.

Keywords: Fe; clusters; GaN; DMS; Mössbauer

Publ.-Id: 8595

Magnetohydrodynamic drag reduction and its efficiency

Shatrov, V.; Gerbeth, G.

We present results of direct numerical simulations of a turbulent channel flow influenced by electromagnetic forces. The magnetohydrodynamic Lorentz force is created by the interaction of a steady magnetic field and electric currents fed to the fluid via electrodes placed at the wall surface. Two different cases are considered. At first, a time-oscillating electric current and a steady magnetic field create a spanwise time-oscillating Lorentz force. In the second case, a stationary electric current and a steady magnetic field create a steady, mainly streamwise Lorentz force. Besides the viscous drag, the importance of the electromagnetic force acting on the wall is figured out. Regarding the energetic efficiency it is demonstrated that in all cases a balance between applied and flow induced electric currents improves the efficiency significantly. But even then, the case of a spanwise oscillating Lorentz force remains with a very low efficiency, whereas for the self-moved regime in case of a steady streamwise force much higher efficiencies are found. Still, no set of parameters has yet been found for which an

energetic breakthrough, i.e. a saved power exceeding the used power, is reached.

  • Physics of Fluids 19, 035109(2007)

Publ.-Id: 8594

Study of crystal damage by ion implantation using micro RBS/Channeling

Grambole, D.; Herrmann, F.; Heera, V.; Meijer, J.

The combination of microbeam implantation and in-situ micro RBS/Channeling analysis in the Rossendorf nuclear microprobe facility enables crystal damage studies with high current densities not achievable in standard ion implantation experiments. Si(100) samples were implanted with 600 keV Si+ ions and a fluence of 1 x 1016 Si/cm². Using a beam spot of 200 µm x 200 µm current densities from 4 to 120 µA/cm² were obtained. The substrate temperature was varied between RT and 265 °C. The implanted regions were subsequently analysed by micro RBS/Channeling with a 3 MeV He+ beam having a spot size of 50 µm x 50 µm.
Crystal damage up to amorphisation was obtained in dependence on the substrate temperature. Above a critical temperature TC no amorphisation occurs. TC was determined for each series of samples implanted with the same ion current density j. It was found that the empirical Arrhenius relation j ~ exp(- Em/ kTC), known from standard implantation experiments, is also valid at high current densities. The observed Arrhenius law can be derived from a model of epitaxial crystallisation stimulated by defect diffusion.

Keywords: Nuclear microprobe; Micro RBS/Channeling; Experimental setup; Ion implantation; Si ions; Silicon; Ion current density; Radiation damage; Amorphisation; Critical temperature

  • Invited lecture (Conferences)
    10th International Conference on Nuclear Microprobe Technology and Applications, 10.-14.07.2006, Singapore, Singapore
  • Nuclear Instruments and Methods in Physics Research B 260(2007), 276-280

Publ.-Id: 8592

Ion beam analysis by nuclear microprobes

Grambole, D.; Herrmann, F.

The nuclear microprobe is extensively applied to a wide research field, due to the combination of the good ability of the ion beam analysis and the spatial resolution in the range of a few micrometer.
The nuclear microprobe at the 3MV Tandetron accelerator of the Forschungs-zentrum Rossendorf is one of very few probes about the world, at which all ion beam analytical methods are availably:

  • micro Rutherford Backscattering Spectrometry (µRBS) for detection of mainly heavier elements,
  • micro RBS – Channeling (µRBS/Channeling) to investigate the crystal structure and damage in small regions,
  • micro Elastic Recoil Detection Analysis (µERDA) for profiling of light elements,
  • micro Particle Induced X-ray Emission (µPIXE) for mapping of especially trace elements and
  • micro Nuclear Reaction Analysis (µNRA) for detection of special light isotopes.
In order to demonstrate the generally analytical performance of nuclear microprobes a selection of various uses of the Rossendorf microprobe for ion beam analysis will be presented and discussed.
  • Invited lecture (Conferences)
    6th International Conference "Ion Implantation and other Applications of Ions and Electrons" ION 2006, 26.-29.06.2006, Kazimierz Dolny, Poland

Publ.-Id: 8591

Steam bubble condensation in sub-cooled vertical pipe flow

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

Detailed experimental data on the evolution of a two-phase flow along a vertical pipe with an inner diameter of 195 mm and a length of 8 m were obtained for adiabatic air-water mixture as well as for steam-water mixture under adiabatic and non-adiabatic conditions at different pressure. The experiments were performed at the TOPFLOW facility of our institute. The measurements were carried out using the wire-mesh sensor technology. The data include local gas volume fraction values (lateral resolution: 3 mm) as well as bubble size distributions and local volume fraction distributions decomposed according to bubble size classes. A slight sub-cooling of the water (max. 4 K) was achieved by throttling the globe valve at the upper end of the vertical test section.

Since the wire-mesh sensor disturbs the flow in downflow direction (but still measures the undisturbed flow!) it doesn’t make sense to place a number of wire-mesh sensors behind each other in order to investigate the evolution of the flow along the pipe. Because of the large dimensions of the facility it is also not applicably to shift a single sensor to different height positions by dismantling the facility each time. For this reason the measuring plane was fixed at the upper end of the test section and a variable gas injection was used. The gas was injected by rings of holes at the pipe wall, which are placed at different height positions 1 mm and 4 mm holes can be used for the injection.

The previously developed Multi-Bubble-Size-Group Test Solver was extended to consider the phase transfer. The large number of bubble classes (50) in the simulation allows the investigation of the influence of the bubble size distribution. The interfacial area density is calculated according to the bubble size distributions and the assumption of ellipsoidal bubbles with a deformation according to the well-known Wellek-correlation. Simulations show, that there are clear differences in the condensation process along the pipe for poly-dispersed flow in comparison with the assumption of mono-dispersed flow is discussed.

The results of the simulations show a good agreement with the experimental data. The condensation process is clearly slower, if large bubbles are injected (4 mm holes). Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some unsureness arises from the unknown interfacial area for large bubbles and possible uncertainties of the heat transfer coefficient.

Keywords: Condensation; Bubbly Flow; Phase Transfer

  • Lecture (others)
    44rd European Two-Phase Flow Group Meeting, 07.-09.06.2006, Lausanne, Schwizerland

Publ.-Id: 8590

The traveling wave MRI in cylindrical Taylor-Couette flow: comparing wavelengths and speeds in theory and experiment

Rüdiger, G.; Hollerbach, R.; Stefani, F.; Gundrum, T.; Gerbeth, G.; Rosner, R.

We study experimentally the flow of a liquid metal confined between differentially rotating cylinders, in the presence of externally imposed axial and azimuthal magnetic fields. For increasingly large azimuthal fields a wave-like disturbance arises, traveling along the axis of the cylinders. The wavelengths and speeds of these structures, as well as the field strengths and rotation rates at which they arise, are broadly consistent with theoretical predictions of such a traveling wave magnetorotational instability.

Publ.-Id: 8589

QWIP Camera Development and Applications

Schneider, H.

Quantum well infrared photodetector (QWIP) technology opens up new opportunities to realize focal plane arrays (FPA) for high-performance thermal imaging. Large infrared detector arrays with excellent thermal and spatial resolution, low fixed-pattern noise, low 1/f noise, and high pixel yield can thus be realized at moderate cost.
In this tutorial, I will report on typical QWIP structures optimized for thermal imaging applications, the development of focal plane arrays, and the performance of state-of-the-art QWIP cameras. Dual-band QWIP FPAs detecting simultaneously in different spectral bands will also be addressed.
In most cases, a successful novel technology is not only suitable for existing applications; it will also create its new applications. Talking about applications of QWIP FPAs, I will show that QWIP technology has in fact lead to new and interesting opportunities, in particular in the medical market.

Keywords: quantum well infrared photodetector; QWIP; dual-band QWIP; photovoltaic QWIP; thermal imaging; focal plane array; noise-equivalent temperature difference; GaAs/AlGaAs

  • Invited lecture (Conferences)
    International Workshop on Quantum Well Infrared Photodetectors (QWIP2006), 18.-24.06.2006, Kandy, Sri Lanka

Publ.-Id: 8588

Autocorrelation measurements of free-electron laser radiation using a two-photon QWIP

Schneider, H.; Drachenko, O.; Winnerl, S.; Helm, M.; Maier, T.; Walther, M.

The two-photon QWIP approach involves three equidistant subbands, namely two bound states localized in the quantum well and an extended state in the continuum. Here the intermediate state generates a huge optical nonlinearity, six orders of magnitude larger than in usual bulk semiconductors, which makes this device very promising for quadratic autocorrelation measurements of pulsed mid-infrared lasers. In addition, temporal resolution is only limited by the sub-ps intrinsic time constants of the quantum wells, namely the intersubband relaxation time and the dephasing time of the intersubband polarization [1]. We will report here on autocorrelation measurements of ps optical pulses from a free-electron laser (FEL). Due to the intense nonlinear signal, two-photon QWIP operation is possible at room temperature. The device is thus ideally suited for standard diagnostics of the FEL pulse shape.
[1] H. Schneider, T. Maier, H. C. Liu, M. Walther, P. Koidl, Ultra-sensitive femtosecond two-photon detector with resonantly enhanced nonlinear absorption, Optics Letters 30, 287 (2005).

Keywords: quantum-well infrared photodetector; QWIP; quadratic autocorrelation; GaAs/AlGaAs; free-electron laser

Publ.-Id: 8587

Consideration of steel corrosion rates from the MASCA / METCOR-tests to the RPV strength under IVR conditions

Willschuetz, H.-G.; Altstadt, E.

Physicochemical interaction of prototypic UO2-ZrO2-Zr corium melt and VVER vessel steel was examined during the 2nd Phase of the ISTC METCOR Project. Rasplav-3 test facility was used for conducting four tests, in which the Zr oxidation degree and interaction front temperature were varied; in one of the tests, stainless steel was added to the melt.
Direct experimental measurements and posttest analyses were used for determining corrosion kinetics and maximum corrosion depth, as well as the steel temperature conditions during the interaction, and finally the structure and composition of crystallized ingots, including the interaction zone. The minimum temperature on the interaction front boundary, which determined its final position and maximum corrosion depth was ~1090°С. An empirical correlation for calculation of corrosion kinetics has been derived.
In this presentation the impact of the so called "corrosion" is compared to calculations without a consideration of the corrosion. The evaluated scenario considers the In-Vessel-Retention for a VVER-1000 with a stratified melt pool and with a homogeneous melt pool.

Keywords: In-Vessel-Retention; VVER-1000; vessel wall corrosion; homogeneous and stratified melt pool

  • Invited lecture (Conferences)
    Seminar at the Division of Nuclear Power Safety, 26.06.2006, Stockholm, Sveden

Publ.-Id: 8586

Innovationspool Natur: Bakterien und Bionik

Raff, J.

Ein Ziel der heutigen Forschung ist es, neue und innovative Wege zur Lösung technischer Fragestellungen zu erschließen. In der Bionik wird dazu versucht, von der Natur zu lernen. Höchst erfolgreiche Beispiele dafür sind der Lotuseffekt, der Klettverschluss oder die Nutzung der Struktur der Haifischschuppe zur Reduktion des Luftwiderstandes bei Flugzeugen. Aber nur wenige wissen, dass auch die kleinsten Lebewesen unseres Planten, die Bakterien, hier einen großen Beitrag leisten können.

  • Lecture (others)
    Vortrag anlässlich des Besuch der Berufschulzentrum Technik, Bautzen, 26.01.2006, Dresden, Germany
  • Lecture (others)
    Vortrag anlässlich des Besuch des Leistungskurses Physik des Vizthum-Gymnasiums Dresden, 19.06.2006, Dresden, Germany

Publ.-Id: 8585

Measurement of porosity in polyolefin particles using X-ray microtomography

Boden, S.; Bieberle, M.; Hampel, U.

The morphology of polymer macroparticles is directly linked to the various parameters of the polymerisation process. X-ray cone beam microtomography is a tool to provide key information on internal structure like morphology, porosity and interfacial area of such particles to the process engineers. By further application of image processing tools to the reconstructed tomograms, we were able to identify different characteristic morphologies within different polyolefin samples and to detect enclosed voids, which will ultimately not contribute to the active surface area.

Keywords: microstructure; polymer; polyolefin; macroparticle; microtomography; X-ray

  • Contribution to proceedings
    4th International Symposium on Process Tomography in Poland, 14.-15.09.2006, Warsaw, Poland
    Proceedings, 83-60660-01-8, 102-105

Publ.-Id: 8584

Isospin dependence of relative yields of K+ and K0 mesons at 1.528 AGeV

Lopez, X.; Kim, Y. J.; Herrmann, N.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Caplar, R.; Cordier, E.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasparic, I.; Gobbi, A.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kirejczyk, M.; Kis, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Merschmeyer, M.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Ryu, M. S.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stoicea, G.; Tyminski, Z.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z.; Yushmanov, I.; Zhilin, A.; Ferini, G.; Gaitanos, T.

New results of K+ and K0 meson production in Ru+Ru and Zr+Zr collisions at beam energy of 1.528 AGeV, measured with the FOPI detector at GSI Darmstadt, are presented as a possible probe of isospin effects in high density nuclear matter. The measured double ratio (K+/K0)Ru/K+/K0)Zr is compared with a thermal model and a Relativistic Mean Field transport model using two different collision scenarios and under different assumptions on the stiffness of the symmetry energy. We found a good agreement with the thermal model predictions and the assumption of a soft symmetry energy for infinite nuclear matter.

Publ.-Id: 8583

Si Nanocrystals for nanoelectronic applications

Zacharias, M.; Gösele, U.

First experimental results more than one decade ago demonstrated the visible room temperature luminescence of Si nanocrystals in implanted SiO2 or porous Si which triggered the strong interest in Si nanocrystal based systems and their properties. Basic fundamental questions concerning quantum confinement effects in indirect semiconductors as well as potential applications such as light emission from electrically excited Si nanocrystals, energy transfer to Er 3+ ions, and non volatile Si NC based memories also stimulated the broad scientific interest in this material system. For clarifying the origin of the observed luminescence signal as well as for applications, tight control over the size of the nanocrystals is essential. The talk will give an overview about ways for size controlled Si nanocrystals. Basic properties as well as various applications including memory applications will be discussed in details.

Keywords: Si nanocrystals; optical properties; electronic properties

  • Invited lecture (Conferences)
    E-MRS Spring Meeting 2006, Symposium C, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8582

Ordered Arrays of ZnO Nanowires: Piezoelectric properties and stimulated emission from single wires

Fan, H. J.; Alexe, M.; Hauschild, R.; Kalt, H.; Zacharias, M.

The current interest in ZnO nanostructures is based on its possible applications in UV optoelectronics. In particular, ZnO nanowires (NWs) appear to be promising candidates for the realization of dense arrays of nanosized lasers.
ZnO NW arrays were grown by a modified vapor liquid solid process which results in the Au catalyst remaining at the base of the nanowires. The fabrication process is template assisted involving a gold nanodisk array. This allows a site-specific growth of the ZnO NWs in an ordered hexagonal arrangement. The typical separation of the wires is around 500 nm, the NWs have a narrow size distribution centered at 300 nm and a typical height of 1.5 mm. The effective piezoelectric coefficient of individual ZnO NWs will be shown for various sizes and length. High-excitation phenomena, in particular excitonic nonlinearities and lasing will be reported. Under low excitation the NWs show bulk-like PL spectra. However, there is still a one-dimensional confinement of exciton-polaritons resulting in the absence of the P-band emission resulting from polariton-polariton scattering in thin wires. Stimulated emission is observed in single NWs up to 150 K. Upon raising the excitation fluency a spectrally and temporally narrow emission peak shows up while the P-band emission is quenched. We will show that free carriers are involved in the laser emission. We observe, that the lasing is influenced by details of the wire geometry. Calculations show the increasing leakage of the guided modes into the vacuum when decreasing the wire diameter. There is also a significant leakage of the resonator modes into the substrate. This loss can be reduced significantly by introducing thin layers of gold at the resonator facets as done here.

Keywords: nanowire; stimulated emission; piezoelectric effect

  • Lecture (Conference)
    E-MRS, Symposium E, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8581

Computer Simulations of Epitaxial Recrystallization and Amorphous-to-Crystalline Transition in 4H-SiC

Gao, F.; Zhang, Y.; Devanathan, R.; Posselt, M.; Weber, W. J.

Molecular dynamics (MD) methods have been employed to study the epitaxail recrystallization and amorphous-to-crystalline (a-c) transition in 4H-SiC, with simulation times of up to a few hundred ns and at temperatures ranging from 1000 to 2000 K. Three nano-sized amorphous layers with the normal of a-c interfaces along the [-12-10], [-1010] and [0001] directions, respectively, were created within a crystalline cell to investigate the anisotropies of recrystallization processes. The amorphous structures were analyzed using a topological method, which indicates the complete loss of long-rang order, and the existing short-range disorder is quantified by the fraction of homonuclear bonds. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layers. The amorphous layer with the a-c interfaces normal along the [-12-10] direction can be completely recrystallized at the temperatures of 1500 and 2000 K, but the recrystallized region is defected with dislocations and stacking faults. The temperatures required for complete recrystallization are in good agreement with those observed at experiments. On the other hand, the recrystallization processes for the a-c interfaces normal along [-1010] and [0001] directions are hindered by the nucleation of polycrystalline phases. These secondary ordered phases have been identified as 4H- and 3C-SiC with different crystallographic orientations to the original 4H-SiC. The bond mismatches at the interfaces between different microcrystals result in the formation of number stacking faults. The temperature is an important parameter to control the nucleation of secondary ordered phase, whereas the size of amorphous region has a significant effect on their growth. These results are in good agreement with the previous experimental observations. One of the most important results is that the epitaxial recrystallization of amorphous layer with a-c interface along the c axis is much slower than those long the basal plane, which provides atomic-level insights into the anisotropies in the different activation energies for recrystallization.
Based on a model developed in the previous annealing simulations of 3C-SiC, the activation energy spectra for recrystallization along the three directions have been determined. In general, the activation spectra show that there is a number of activation energy peaks associated with different recrystallization processes. These activation energy values for full recrystallization are in the range of from 1.2 to 1.7 eV for the amorphous layers with the a-c interfaces along [-12-10] and [-1010] directions, and 1.1 to 2.3 eV for the amorphous layer with the a-c interfaces along [0001] direction. However, the highest activation energy of 2.3 eV is consistent with the experimental value of 2.1±0.5 eV reported for 6H-SiC. The internal energy distribution provides a detailed analysis of energy paths to recrystallization, and the nucleation and growth of the secondary ordered phases.

Keywords: SiC; atomistic simulation; recrystallization

  • Poster
    8th Int. Conf. on Computer Simulation of Radiation Effects in Solids (COSIRES 2006), 18.-23.06.2006, Richland, WA, USA

Publ.-Id: 8580

An improved interatomic potential for Ge

Geßner, H.; Posselt, M.

Two classes of interatomic potentials for germanium are presently available: (i) a Stillinger-Weber-type potential with different parametrizations, and (ii) a Tersoff-type potential. The evaluation shows that one group of potentials overestimates the melting temperature considerably, whereas the other group does not give the correct values for the lattice parameter and the cohesive energy. In the present work an improved Stillinger-Weber-type potential is developed by adjusting the two three-body parameters in such a manner, that the potential yields the correct lattice constant and the correct cohesive energy, and the melting point and other properties are reproduced satisfactorily. The influence of the three-body parameters on the structural and thermal properties is investigated in detail. Besides the lattice constant, the cohesive energy, and the melting point, the elastic constants and the thermal expansion coefficient of the diamond structure are considered. Furthermore, the properties of the liquid and the amorphous state as well as different crystalline structures of Ge are studied. Particular attention is paid to point defects and self-diffusion in the diamond structure. The influence of the three-body parameters on the formation and migration energies of vacancies and self-interstitials is investigated.

Keywords: Ge; atomistic simulations; interatomic potential

  • Lecture (Conference)
    8th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2006), 18.-23.06.2006, Richland, WA, USA

Publ.-Id: 8579

Interstitial contribution to self-diffusion in Si: Dependence of the correlation factor on the migration mechanism

Posselt, M.

Self-diffusion in Si is determined by the concentration and the mobility of both vacancies and self-interstitials. The self-diffusion coefficient is usually given by Dsd = fV CV DV + fI CI DI, where CV and CI are the relative concentrations of vacancies and self-interstitials, respectively; DV and DI denote the diffusivities. The quantities fV and fI describe the correlation between the migration of Si atoms and the migration of vacancies and self-interstitials; fV and fI are therefore called correlation factors. The statistical theory of diffusion allows the determination of these factors if certain atomic mechanisms for vacancy and self-interstitial migration are assumed. On the other hand, the self-diffusion coefficient per point defect as well as the point defect diffusivity can be calculated by molecular dynamics (MD) simulations. The ratio of both quantities yields the correlation factors fV and fI. In this manner, they can be determined without any assumption about the atomic migration mechanisms. In the present work, point defect migration and the related atomic mobility are investigated by MD simulations using the interatomic potentials of Stillinger-Weber and Tersoff. It is shown that the value for fV obtained by MD simulations is identical with that determined by the statistical diffusion theory, since the simple atomic mechanism assumed in the theory is also found by the simulations. The mechanisms of self-interstitial migration are more complex. The detailed study, including a visual analysis and investigations with the nudged elastic band method, reveals a variety of transformations between different self-interstitial configurations. MD simulations with the Stillinger-Weber potential show, that the self-interstitial migration is dominated by the dumbbell mechanism, whereas in the case of the Tersoff potential the interstitialcy mechanism prevails. The corresponding values of the correlation factor fI are different.

Keywords: diffusion Si defects atomistic simulations

  • Lecture (Conference)
    8th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2006), 18.-23.06.2006, Richland, WA, USA

Publ.-Id: 8578

Effect of electron-Beam Treatment on Subsequent Titanium Alloy Nitriding

Markov, A. B.; Gunzel, R.; Reuther, H.; Shevchenko, N.; Rotshtein, V. P.; Akhmadeev, Y. K.; Schanin, P. M.

  • Electrotehnica, Elektronica 5-6(2006), 230-233
  • Lecture (Conference)
    8th International conference on Electron Beam Technologies, 05.-10.06.2006, Varna, Bulgaria

Publ.-Id: 8577

Atomic-level simulation of epitaxial recrystallization and phase transformation in SiC

Gao, F.; Devanathan, R.; Zhang, Y.; Posselt, M.; Weber, W. J.

A nano-sized amorphous layer embedded in an atomic simulation cell was used to study the amorphous-to-crystalline (a-c) transition and subsequent phase transformation by molecular-dynamics computer simulations in 3C–SiC. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layer, which is hindered by the nucleation of a polycrystalline 2H–SiC phase. The kink sites and triple junctions formed at the interfaces between 2H– and 3C–SiC provide low-energy paths for 2H–SiC atoms to transform to 3C–SiC atoms. The spectrum of activation energies associated with these processes ranges from below 0.8 eV to about 1.9 eV.

Keywords: SiC; atomistic simulation; recrystallization

Publ.-Id: 8576

Thermohydraulische Modellierung der Kondensation von Dampf in einer unterkühlten Flüssigkeitsströmung

Gregor, S.; Prasser, H.-M.; Beyer, M.

Nach einer kurzen technischen Beschreibung der Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW und der verwendeten Messtechnik werden die theoretischen Grundlagen zur Modellierung der Kondensation von Dampf in einer Wasserströmung erläutert. Dabei gehen die Autoren besonders auf die Auswahl geeigneter Modelle zur Beschreibung des Wärmeübergangs und der Zwischenphasengrenzfläche im Druckbereich zwischen 10 und 65 bar detailliert ein. Außerdem werden verschiedene Drift-Flux-Modelle auf ihre Tauglichkeit anhand von experimentellen Daten geprüft.
Da Veränderungen thermodynamischer und strömungstechnischer Parameter hauptsächlich in axialer Richtung stattfinden, wurden diese Modelle in einen eindimensionalen Code eingebettet, mit dem der Strömungsverlauf entlang einer vertikalen Rohrleitung mit einer Länge von 8 m und einem Nenndurchmesser von 200 mm berechnet werden kann. Anschließend werden Aufbau und Funktion dieses Programms vorgestellt.
Nachfolgend vergleichen die Autoren experimentelle und berechnete Strömungsverläufe bei der Kondensation von Dampf sowohl in einer unterkühlten Wasserströmung als auch nahe der Siedetemperatur. Dabei wird der Einfluss wichtiger Randbedingungen, wie z. B. Druck oder Primärblasengröße, auf die Kondensationsintensität analysiert.
Eine Einschätzung der Fehlerbanden für die experimentellen Daten, die verwendeten Gittersensoren und die numerische Simulation schließen den Bericht ab.

Keywords: multi-phase flow; condensation; wire-mesh sensor; interfacial area; heat transfer; TOPFLOW

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-440 2006
    ISSN: 1437-322X


Publ.-Id: 8575

Melt extraction of short metallic filaments: fibre formation process revisited

Cramer, A.; Gerbeth, G.

This article presents experimental results of the extraction of metallic fibres from the surface of a melt pool. A low-melting alloy was used in a model facility to produce filaments of equal length. Operational parameters such as e.g. wheel speed and feed rate were varied to yield thin fibres. The analysis of the fibre cross-section showed, if ever, only a small decrease with increasing wheel speed. Highspeed video recording of the meniscus region was employed to investigate this falling short of expectation with respect to the commonly accepted tendencies. The recordings revealed that short fibres may only be produced during duty cycles. As available literature does not provide explanation of the observations, also a simple model was developed.

  • Journal of Materials Processing Technology 204(2008), 103-110

Publ.-Id: 8573

MHD turbulence in electromagnetic processing of materials

Gerbeth, G.

The basics of AC field driven flows will be presented. Examples of turbulent AC driven flows will be discussed

  • Invited lecture (Conferences)
    Graduate School and Workshop on Instabilities and Turbulence in MHD Flows, 26.-30.06.2006, University of Warwick, Great Britain

Publ.-Id: 8572

Use of magnetic fields in aluminum investment casting

Gerbeth, G.; Eckert, S.; Galindo, V.; Willers, B.; Hewelt, U.; Katz, H.-W.; Ziemann, M.

The mould filling process of aluminum investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment. We present results on the design and application of a DC magnetic field in order to control this pouring process. Based on numerical simulations and modeling cold metal pre-experiments, DC fields were designed and installed in various casting processes under industrial conditions. The statistics of the casting products show a significant improvement of the casting parts quality. In addition, modeling studies have been performed for an AC magnetic field which may serve for a melt braking at the beginning of the casting process, but a pumping of the melt in a later stage, too.

  • Invited lecture (Conferences)
    EPM 2006, 23.-27.10.2006, Sendai, Japan
  • Contribution to proceedings
    EPM 2006, 23.-27.10.2006, Sendai, Japan
    Proceedings, Tokyo: The Iron and Steel Institute of Japan, 4-930980-55-0 C3057, 323-328

Publ.-Id: 8571

Periodic chains of gold nanoparticles and the role of oxygen during the growth of silicon nanowires

Kolb, F. M.; Berger, A.; Hofmeister, H.; Pippel, E.; Gösele, U.; Zacharias, M.

The introduction of oxygen during the SiO-VLS growth of silicon nanowires causes a shift in SiOx stoichiometry resulting in an increased formation of SiO2 at the nanowire surface. This leads to instabilities of the usual cylindrical nanowire core-shell structure, where the liquid Au/Si alloy droplet at the nanowire tip is incorporated inside a SiO2 nanowire in form of a periodic array of nanoparticles. The structure and the composition of the resulting nanostructure are investigated in detail using high-resolution and analytical transmission electron microscopy. The influence of the oxygen is investigated experimentally and supports our model of the formation mechanism.

Keywords: nanowires; vapor liquid solid growth; self organization

  • Applied Physics Letters (2007)

Publ.-Id: 8570

Laser Interference Lithography Tailored for Highly symmetric arranged ZnO nanowire arrays

Kim, D. S.; Ji, R.; Fan, H. J.; Bertram, F.; Scholz, R.; Dadgar, A.; Nielsch, K.; Krost, A.; Christen, J.; Gösele, U.; Zacharias, M.

Highly symmetric arranged ZnO nanowire arrays are produced by laser interference lithography and chemical vapor transport process. The resulting ZnO nanowires show a narrow diameter distribution as well as a uniform spacing. Liquid-phase assistant vapor-solid mechanism is proposed for one-to-one synthesized ZnO nanowires growth. Scanning cathodoluminescence microscopy is used to characterize the optical properties.

Keywords: Arrays; Chemical vapor transport; Lithography; Nanowires; Semiconductors

  • Small (2007)

Publ.-Id: 8569

Fluorescence Analysis of Actinides: Instrumentation, Applications, Quantification, Future Trends and Quality Assurance

Geipel, G.; Billard, I.

Since the discovery of uranium, the impact of actinides has dramatically increased in our every-day life, firstly through the naturally occurring elements Th, Pa and U, (that were first used mainly as color pigments or cancer-treatment) and secondly through the artificial ones, produced along all steps of the nuclear power process (mostly Pu, Np, Am and Cm). Considering the huge problem of providing safe and sustainable energy in order to supply the fast increasing world demand in the near future, nuclear power will be one of the major concerns of this century. It is therefore of tremendous importance to tackle associated problems, that are related either to the remediation of old mining and milling sites, to the control of fissile products throughout the nuclear power production cycle and finally to the long term disposal of generated wastes. In this field and according to the public concern, quantification and quality assurance are of outmost importance. However, owing to the radioactive properties of actinides, these objectives are liable to even more difficulties than for other, stable elements. Other problems that need to be overcome are mainly related to the complexity of the chemical behaviour of actinides, that display numerous oxidation states, a large tendency to hydrolysis, and, for the short-lived ones (mostly, elements above Cm), handling problems. Furthermore, the range of concentration of these elements which can be found in the environment (as a consequence of mining, milling, nuclear bomb testing and accidents, mainly) limit the use of speciation techniques, that need to be safe, fast, reliable and very sensitive. Fortunately enough, some major actinides display luminescence properties, which can be used for the determination of complex stabilities as well as for the direct detection of the formed species in different environments in a wide concentration range, from ultra traces to chemical usable concentrations up to reprocessing conditions.
In this chapter, we will present an overview of the field of actinide luminescence analysis (Time-Resolved Laser Induced Fluorescence Spectroscopy, TRLIFS), focussing on applications related to the nuclear fuel cycle, from reprocessing to validation of nuclear waste repositories. However, it is not possible to include all publications in this contribution and a personally influenced selection has been made, that highlights applications in solution. Also it should be mentioned that the contribution of laser-induced spectroscopy to actinide speciation has been reviewed recently in several publications [1-6]. Owing to the limited place allocated, the reader is also referred to books on basic actinide chemistry [7] and reviews [8].

Keywords: actinides; luminescence; fluorescence; laser-induced; spectroscopy

  • Contribution to external collection
    Resch-Genger, Ute: Standardization and Quality Assurance in Fluorescence Measurements State of the Art and Future Challenges Series: Springer Series on Fluorescence, Vol. 5, Heidelberg: Springer Verlag, 2008, 978-3-540-75206-6, 465-492

Publ.-Id: 8568

Bromo(tricarbonyl) (15-{[2-(methylthio-S)ethylthio-S} pentadecanoic acid)rhenium(l)

Kraus, W.; Walther, M.; Jung, C. M.; Emmerling, F.; Pietzsch, H.-J.

The title compound, C21H36BrO5ReS2, was synthesized and characterized as non-radioactive surrogate of a novel Tc-containing fatty acid derivative prepared according to the tricarbonyl/dithioether design with the objective to develop new Tc-based radio-pharmaceuticals für the non-invasive diagnosis of myocardial metabolism. The Re chelate contains the metal core in the oxidation state +1 and is attached to the terminal position of a fatty acid. The complex formation was accomplished by ligand exchange reaction using [NBu4]2[Re(CO)3Br3] as starting material

Publ.-Id: 8567

Characterization of deformed and undeformed Al-alloys

Frielinghaus, H.; Ulbricht, A.; Bergner, F.

The experiment is aimed to characterize the nature of the material damage in a mechanically loaded specimen of a ductile aluminium alloy in order to get the input needed for damage mechanics based evaluation of structural components. In the first step the as-received and the homo¬geneously deformed conditions of the aluminium alloy shall be investigated by SANS. The objective is to identify and separate the main features responsible for the measured scattering effects and especially to find out the nature of the additional defects introduced by the mechanical loading procedure.

Keywords: SANS; Al-alloy

  • Contribution to external collection
    T. Brückel, D. Richter, R. Zorn: Neutron Scattering at FRJ-2, Experimental Reports 2005/6, Jülich: Forschungszentrum Jülich GmbH, 2006, 457-458

Publ.-Id: 8566

Magnetic and structural properties of Fe implanted GaN

Talut, G.; Reuther, H.; Eichhorn, F.; Mücklich, A.; Potzger, K.; Stromberg, F.; Zhou, S.

In order to investigate the possibility to create and stabilize a DMS behavior in the (Ga,Fe)N-system, p-doped GaN was implanted with 200 keV 57Fe+ ions at 350°C, RT and -30°C with fluences Φ = 1*10^16 cm^-2 - 1.6*10^17 cm^-2. Magnetic electronic and structural properties of as implanted as well as subcequently annealed samples were investigated by AES, CEMS, TEM, SQUID and XRD techniques.

Keywords: DMS; Mößbauer; GaN; Fe; Cluster

  • Poster
    Sixth Workshop on Mössbauer Spectroscopy, 07.-11.06.2006, Seeheim, Deutschland

Publ.-Id: 8565

Structural investigation on uranium mine water colloids and their interaction with UO22+

Ulrich, K.-U.; Rossberg, A.; Scheinost, A.; Reuther, H.; Zaenker, H.

Flooding abandoned uranium mines normally involves mixing of shallow groundwater with acidic, iron-rich pore water. A simulation experiment in mesocosm scale showed that nanoparticles of 2-line ferrihydrite formed and took up about 97% of total uranium between pH 5-7. The molecular topology of ferrihydrite and the U(VI) surface complex structure were investigated by EXAFS and ATR-FTIR spectroscopy. The contribution of carbonate to surface sorption was studied by preparing reference samples at varied CO2 partial pressure and pH conditions, and by applying iterative target transformation factor analysis on EXAFS spectra. Surface sorbed UO22+ delayed the thermally induced aqueous phase transformation of ferrihydrite to hematite, shown by Mössbauer spec-troscopy. Desorption of U(VI) from the solid phase was less effective for original colloid and sediment samples from a uranium mine and for aged reference samples than for fresh U(VI)-ferrihydrite precipitates, suggesting that part of the uranium was fixed within the mineral lattice.

  • Lecture (Conference)
    232nd ASC National Meeting, 10.-14.09.2006, San Francisco, United States

Publ.-Id: 8564

Cooling dynamics in multi-fragmentation processes

Liu, T. X.; Lynch, W. G.; van Goethem, M. J.; Liu, X. D.; Shomin, R.; Tan, W. P.; Tsang, M. B.; Verde, G.; Wagner, A.; Xi, H. F.; Xu, H. S.; Friedman, W. A.; Souza, S. R.; Donangelo, R.; Beaulieu, L.; Davin, B.; Larochelle, Y.; Lefort, T.; de Souza, R. T.; Yanez, R.; Viola, V. E.; Charity, R. J.; Sobotka, L. G.

Fragment energy spectra of neutron-deficient isotopes are significantly more energetic than those of neutron-rich isotopes of the same element. This trend is well beyond what can be expected for the bulk multi-fragmentation of an equilibrated system. It can be explained, however, if some of these fragments are emitted earlier through the surface of the system while it is expanding and cooling.

Keywords: Thermal and statistical models; Multifragment emission and correlations

Publ.-Id: 8563

Indirect Radioiodination Increases In Vivo Stability and Tumor Uptake of I-125-L19-SIP

Rother, A.; Sieger, S.; Berndorff, D.; Cyr, J.; Dinkelborg, L.


The extradomain B of fibronectin (ED-B-FN) is an angiogenesis-associated marker of the tumoral extracellular matrix, which can be targeted by the human recombinant, high-affinity antibody fragment L19-SIP. By I-131-labeling L19-SIP becomes a radiotherapeutic agent, which is effective in several tumor models. In this study indirect and direct radioiodination methods were compared with regard to tumor uptake and in vivo stability of the obtained L19-SIP derivatives.


L-19-SIP was directly radioiodinate using the Iodogen methods, as well as indirectly by conjugation of I-125-Boltron Hunter reagent (I-125-BH) or I-125-succinimidylbenzoate (I-125-SIB). Pharmacokinetics and tumor accumulation of the iodinated L19-SIP derivatives were investigated in tumor bearing mice up to 72 h (F9, murine teratocarcinoma and U251, human glioblastoma) with subsequent dosimetry for the therapeutic isotope I-131.


In biodistribution studies the directly iodinated L-19-SIP showed increasing thyroid uptake over time due to dehalogenation of I-125 in vivo, whereas the indirectly iodinated L19-SIP showed improved stability of the iodine label. I-125-BH-L19-SIP and I-125-SIB-L19-SIP exhibited longer retenation in the tumor compared to I-125-L19-SIP. Tumor-to-blood ratios were significantly higher for the indirectly labelled compounds at later time points. It was calculated that activities of 48 MBq I-131-L19-SIP (Iodogen), 47 MBq I-131-BH-L19-SIP and 64 MBq I-131-SIB-L19-SIP could be injected per mouse before reaching the maximum tolerated dose of 2.5 Gy in the bone marrow, and would lead to doses of 42 Gy, 40 Gy and 144 Gy in 100 mg F9-tumors, respectively. The calculated tumor doses were comparable in both tumor models.


I-125-SIB-L19-SIP shows considerably higher in vivo stability and longer tumor retention compared to directly labelled L19-SIP leading to a substantially higher tumor dose.

  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A95
    ISSN: 0029-5566

Publ.-Id: 8562

Eine Untersuchung zur Beschreibung kleiner Luftblasen durch Ellipsoide / An investigation concerning the description of small bubbles by ellipsoids

Hoppe, D.; Zaruba, A.

In ruhendem Wasser emporsteigende Luftblasen werden oft durch zweiachsige Ellipsoide beschrieben, ohne dass dies näher begründet wird. Eine Rechtfertigung dafür soll dadurch gefunden werden, dass eine reale Blase erst als dreiachsiges Ellipsoid modelliert und dann geprüft wird, ob sie zu einem zweiachsigen Ellipsoid vereinfacht werden kann. Für diesen Zweck erfolgen zunächst drei orthogonale optische Projektionen der Blase. Diese ebenen Abbildungen werden durch drei Ellipsen beschrieben, aus denen anschließend das gesuchte dreiachsige Ellipsoid berechnet wird.

Bubbles ascending in resting water are often described without further explanation using biaxial ellipsoids. Justification of this practice can be found via primarily modelling a real bubble as triaxial ellipsoid and subsequently checking if it can be reduced to a biaxial ellipsoid. For this purpose three orthogonal optical projections are produced at first. These plane maps are expressed by three ellipses from which in a second step the required triaxial ellipsoid is calculated.

Keywords: Bubble; Three-Axis Ellipsoid; Spheroid

  • Technisches Messen 1(2007), 29-35

Publ.-Id: 8561

Experimental Evidence for Magnetorotational Instability in a Taylor-Couette Flow under the Influence of a Helical Magnetic Field

Stefani, F.; Gundrum, T.; Gerbeth, G.; Rüdiger, G.; Schultz, M.; Szklarski, J.; Hollerbach, R.

A recent Letter [R. Hollerbach and G. Rüdiger, Phys. Rev. Lett. 95, 124501 (2005)] has shown that the threshold for the onset of the magnetorotational instability in a Taylor-Couette flow is dramatically reduced if both axial and azimuthal magnetic fields are imposed. In agreement with this prediction, we present results of a Taylor-Couette experiment with the liquid metal alloy GaInSn, showing evidence for the existence of the magnetorotational instability at Reynolds numbers of order 1000 and Hartmann numbers of order 10.

Publ.-Id: 8560

Contribution of Mössbauer Spectroscopy to the Exploration of Diluted Magnetic Semiconductors

Reuther, H.

Worldwide, semiconductor spin transfer electronics (spintronics) is of strongly increasing interest. One intention is the use of the spin for data storage to increase the possible storage density, another one is to overcome the fundamental limits of the computing speed. To realize such devices polarized carriers can be injected from a ferromagnetic metal into a diluted magnetic semiconductor (DMS). DMS are “conventional” semiconductors doped with transition metal or rare-earth ions which are diluted within the host matrix and ferromagnetically aligned via an indirect magnetic coupling. For applications, it is important that such DMS could be used at practical temperatures, i.e. above room temperature, and that they can base upon an already existing materials technology.

From theory, wide band gap semiconductors like GaN, ZnO, InN, AlP or SiC are the most promising candidates. Doping could be performed by Mn, V, Fe, Co or Ni with concentrations in the range of some %. The magnetism may originate either from a more or less random alloy in which the doping ion substitutes a host atom as interstitial or from small clusters. In the case of 57Fe as doping ion, Mössbauer spectroscopy can be used to investigate how it is built in the host matrix. The 57Fe ion acts both as doping and probe.

In the present study ion implantation is used as doping technique. 57Fe ions were implanted into GaN, ZnO and SiC. The produced layers were investigated by Mössbauer spectroscopy however this method is insufficient for a full characterization. Therefore, samples were studied by transmission electron microscopy, Auger electron spectroscopy, Zero-field-cooled/field-cooled SQUID measurements and by X-ray diffraction too. Depending on the implantation temperature and the annealing conditions diluted magnetic semiconductors could be obtained.

  • Invited lecture (Conferences)
    Sixth workshop on Mössbauer spectroscopy Seeheim, 07.-11.06.2006, Seeheim, Deutschland

Publ.-Id: 8559

RBE of 25 kV X-rays for the Survival and Induction of Micronuclei in the Human Mammary Epithelial Cell Line MCF-12A

Lehnert, A.; Lessmann, E.; Pawelke, J.; Dörr, W.

The broad application of low energy X-rays below about 50 keV in radiation therapy and diagnostics and especially in mammography substantiates the precise determination of their relative biological effectiveness (RBE). A quality factor of 1 is stated for photons of all energies in the ICRP Recommendations. However, the RBE of low-energy X-rays compared to high-energy photons was found to be dependent on photon energy, cell line and endpoints studied, hence varying from less than 1 up to about 4. In the present study, the human mammary epithelial cell line MCF-12A has been chosen due to the implementation of the results in the estimation of risk from mammography procedures. The RBE of 25 kV X-rays (W anode, 0.3 mm Al filter) relative to 200 kV X-rays (W anode, 0.5 mm Cu filter) was determined for clonogenic survival and micronuclei induction. The RBE for clonogenic survival was found to be significantly higher than 1 for surviving fractions in the range between 0.005 and 0.2. The RBE decreased with increasing survival, with an RBE0.1 at 10 % survival of 1.13 ± 0.03. The effectiveness of soft X-rays for micronuclei induction was found to be 1.40 ± 0.07 for the fraction of binuclear cells (BNC) with micronuclei (MN) and 1.44 ± 0.17 for the number of MN per BNC. In contrast, the RBE determined from the number of MN per MN-bearing BNC was found to be 1.08 ± 0.32. This indicates that the effectiveness of 25 kV X-rays results from an increase in the number of damaged cells, which, however, do not have higher number of micronuclei per cell.

Keywords: Soft X-rays; clonogenic survival; micronuclei; human mammary epithelial cells; MCF-12A; RBE

Publ.-Id: 8558

Electronic structure and x-ray spectra of defect oxides LixCoO2

Galakhov, V. R.; Ovechkina, N. A.; Shkvarin, A. S.; Shamin, S. N.; Kurmaev, E. Z.; Kuepper, K.; Takács, A. F.; Raekers, M.; Robin, S.; Neumann, M.; Gavrila, G.-N.; Semenova, A. S.; Kellerman, D. G.; Käämbre, T.; Nordgren, J.

X-ray absorption, resonant x-ray emission, and x-ray photoelectron spectra of the valence band
and core levels have been measured for LixCoO2 (0.6 < x < 1.0). Resonant O K x-ray emission
spectra of LiCoO2 showed localized excitonic states due to a dd transition between unoccupied and
occupied Co 3d states. On the base of measurements of Co 3s x-ray photoelectron and Co 2p and
O 1s x-ray absorption spectra it was established that in defective cobaltites the electronic holes are
localized mainly in O 2p states. Metallic character of conductivity of defective cobaltites LixCoO2 is
confirmed by a combination of x-ray photoelectron and O 1s x-ray absorption spectra. An evidence
of phase separation in LixCoO2 has been found.

Keywords: PACS numbers: 79.60.-i; 78.70.Dm; 78.70.En; 71.28.+d

Publ.-Id: 8557

Ion beam modifications of magnetic films

Fassbender, J.

In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.

1. J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
2. J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
3. J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B 73, 184410 (2006).
4. J. Fassbender, J. McCord, Appl. Phys. Lett. in press (2006).

Keywords: magnetism; magnetic film; ion irradiation; ion implantation

  • Invited lecture (Conferences)
    23rd Summer School and International Symposium on the Physics of Ionized Gases, 28.08.-01.09.2006, Kopaonik, Serbia
  • Invited lecture (Conferences)
    Workshop on Ion Beam Applications for Materials Modification and Analysis, 02.09.2006, Belgrade, Serbia

Publ.-Id: 8556

Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland

Weiß, F.-P.; (Editor)

Die Veranstaltung widmete sich mit der Borverdünnung in Druckwasserreaktoren bzw. mit der Verstopfung der Sumpfansaugsiebe durch freigesetztes Isolationsmaterial schwerpunktmäßig zwei Themen der Reaktorsicherheit, die auch in aktuellen Aufsichtsverfahren eine Rolle spielen. Eingebettet in den internationalen Kontext wollten die Veranstalter die sicherheitstechnische Bedeutung dieser Themen für die deutschen Anlagen beleuchten und die Auswirkungen auf die zu erbringenden Sicherheitsnachweise und den Anlagenbetrieb darstellen. Dabei kamen Gutachter, Vertreter der Forschung, Hersteller und Betreiber gleichermaßen zu Wort.
Der Fachtag sollte den Teilnehmern aber insbesondere vermitteln, welche Beiträge die privat und öffentlich finanzierte Reaktorsicherheitsforschung zur Aufklärung der jeweiligen Ereignisabläufe und ihrer sicherheitstechnischen Bedeutung geleistet hat.
In diesem Forschungskontext spielen, auch international, die Methoden der so genannten Computational Fluid Dynamics (CFD) eine zunehmende Rolle. Deshalb widmete sich eine Sitzung den Grundlagen, Möglichkeiten und Grenzen von CFD-Methoden.
Dabei wurden u. a. Anwendungen zur Borvermischung und zum Verhalten von Mineralwolle im Sumpf präsentiert.

Keywords: reactor safety; emergency core cooling system reliability; cooling sump performance; boron mixing; boron dilution transients; computational fluid dynamics (CFD); CFD methods

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-455 2006
    ISSN: 1437-322X


Publ.-Id: 8555

Coupled fluid-flow and magnetic-field simulation of the Riga dynamo experiment

Kenjeres, S.; Hanjalic, K.; Renaudier, S.; Stefani, F.; Gerbeth, G.; Gailitis, A.

Magnetic fields of planets, stars, and galaxies result from self-excitation in moving electro-conducting fluids, also known as dynamo effect. This phenomenon was recently experimentally confirmed in the Riga dynamo experiment, consisting of a helical motion of sodium in a long pipe followed by a straight back-flow in a surrounding annular passage, which provided adequate conditions for magnetic field self-excitation. We report here on the first attempt to simulate computationally the Riga experiment. The velocity and turbulence fields are modelled by a finite-volume Navier-Stokes solver using a Reynolds-Averaged-Navier-Stokes (RANS) turbulence model. The magnetic field is computed by an Adams-Bashforth finite-difference solver. The coupling of the two computational codes, although performed sequentially, provides an improved understanding of the interaction between the fluid velocity and magnetic fields in the saturation regime of the Riga dynamo experiment under realistic working conditions.

Publ.-Id: 8554

Wo stehen wir bei der Integration der PET in die Bestrahlungsplanung der perkutanen Strahlentherapie aus physikalisch-technischer Sicht der Nuklearmedizin?

van den Hoff, J.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany

Publ.-Id: 8553

Untersuchungen mittels PET bei onkologischen Fragestellungen

van den Hoff, J.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Workshop: Einsatz der PET in der Bestahlungsplanung, 11.-12.03.2005, Homburg/Saar, Deutschland

Publ.-Id: 8552

Annual Report 2005 - Institute of Nuclear and Hadron Physics

Enghardt, W.; Fahmy, K.; Grosse, E.; Kämpfer, B.; Schneidereit, C.; Wagner, A.; Wünsch, R.; (Editors)

The Forschungszentrum Rossendorf (FZR) at Dresden is a multidisciplinary research center within the Wissenschafts-Gemeinschaft G. W. Leibniz (WGL), one of the German agencies for extra-university research. The center is active in investigations on the structure of matter as well as in the life sciences and in environmental research. The Institute of Nuclear and Hadron Physics (IKH) within the FZR avails for its research the coupling of radiation to matter in subatomic dimensions as well as to tissue, to cells, and to their components. Its research in the field of Subatomic Physics is part of the FZR-program Structure of Matter and its investigations concerning the interaction of Biostructures and Radiation contribute to the bf Life Science program of the FZR. In this field the IKH exploits possibilities for transfer and introduction of experimental and theoretical techniques from particle and nuclear physics to projects in radiobiology and biophysics. Much of this kind of interdisciplinary transfer is connected to the Radiation Source ELBE at the FZR. With its superconducting accelerator for relativistic electrons this large installation provides photons in the wide wavelength range from fm to mm - i.e. bremsstrahlung for the investigation of photonuclear processes, hard X-rays for radiobiological and other studies and infrared light for research on the structural dynamics of biomolecules. The investigation of radiation-induced processes not only dominates the projects in nuclear astrophysics as pursued at ELBE, it also is a central theme of the experimental and theoretical research performed by the IKH in close connection to the heavy ion synchrotron SIS and the upcoming FAIR facility at Darmstadt. ELBE also will deliver compact bunches of secondary neutrons and fission fragments; both offer new possibilities in laboratory studies related to the cosmic breeding of the chemical elements thus complementing the astrophysics-motivated studies with bremsstrahlung photons...

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-442 2006
    ISSN: 1437-322X


Publ.-Id: 8551

CFD simulations and X-ray measurements of the local gas hold-up in a stirred tank reactor agitated by a gas-inducing turbine

Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.

The experimental and the numerically studies were applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions.
The cone-beam type X-Ray tomography is a potential method to measure the phase-distributions in stirred vessels. Three-dimensional information can be gathered within only one tomographic scan. The reconstruction of a rotationally symmetric distribution-field is even possible from a single radiographic image. Such an experimental approach was carefully examined and applied to obtain the quantitative measurements of gas-fraction profiles in a stirred tank reactor. Additionally, a moving slit technique was adapted to estimate the inherent scattered radiation offset, which emerges while un-collimated x-rays penetrate the fluid-filled tank. An additional reference measurement was introduced and used to remove beam hardening artefacts. An absolute quantification was possible due to the knowledge of the ratio of the fluids and the reference-materials x-ray absorption coefficients. Phantom-measurements inside the vessel were conducted for performance evaluation. A systematic measurement error of less then 1.5% absolute gas fraction for local gas fractions up to 30% was achieved while maintaining a spatial resolution of better then 1 mm.
The computational fluid dynamics analyses of the stirred tank reactor were performed in 3D with CFX 10.0 numerical software. Five steady state simulations, at stirrer speeds corresponding to the ones at which the measurements were performed, were conducted to be compared with the experimental observations. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid and the liquid phase as continuous fluid. Different turbulence models and their suitability were considered in the simulations.

  • Lecture (Conference)
    ANSYS-FZR Multiphase Flow: Simulation, Experiment and Application, 26.-29.06.2006, Dresden, Germany
  • Contribution to proceedings
    ANSYS-FZR Multiphase Flow: Simulation, Experiment and Application, 26.-29.06.2006, Dresden, Deutschland
    Proceedings, CD-ROM

Publ.-Id: 8550

Experimental and numerical assessment of the phase distribution in a stirred tank reactor agitated by a gas-inducing turbine

Hristov, H. V.; Boden, S.; Hampel, U.; Kryk, H.; Schmitt, W.; Hessel, G.

Over the last century two-phase flow mixing, engineered to take place in mechani-cally agitated tank reactors, has become one of the most common operations in the industry. Traditionally the gas-phase is supplied via a single pipe or a ring sparger mounted beneath the rotating impeller. The gas-inducing impellers provide an alter-native gas injection, in which case the gas is fed directly in the stirrer region.
A non-baffled laboratory-scale tank reactor mechanically agitated by a gas inducing turbine was experimentally and numerically studied. Above a certain impeller speed, at the investigated experimental conditions, the stirrer becomes able to induce gas and consequently disperse it into the bulk liquid phase. The two-phase system under examination comprises air as gas phase into isopropanol as liquid phase at room temperature. The gas-phase distribution was assessed at five different impeller speeds starting from 1000 rpm, at which gas inducement occurs.
The cone-beam type X-Ray tomography, which can provide three-dimensional infor-mation on the gas-phase distribution, was employed to experimentally study the two-phase system. The reconstruction of a rotationally symmetric distribution-field is pos-sible from a single radiographic image. Such an experimental approach was applied to obtain the quantitative measurements of gas-fraction profiles. Additionally, a mov-ing slit technique was adapted to estimate the inherent scattered radiation offset, which emerges while un-collimated X-rays penetrate the fluid-filled tank. An addi-tional reference measurement was introduced and used to remove beam hardening artefacts. An absolute quantification was possible due to the knowledge of the ratio of the fluids and the reference-materials X-ray absorption coefficients. Phantom-measurements inside the vessel were conducted for performance evaluation.
The computational fluid dynamics analyses of the stirred tank reactor were performed with CFX 10.0 numerical software. The numerical predictions at 1000 rpm used pre-vious simulation results at lower impeller speed as an initial guess. Starting from 1000rpm, five simulations were performed at stirrer speed thresholds of 50 rpm to be compared with X-Ray cone beam tomography experimental observations. The tetra-hedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer de-scribed by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid with a mean diame-ter of 1 mm and the liquid phase as continuous fluid.
The results demonstrate the X-Ray cone beam tomography and the CFD capabilities to capture the two-phase flow in detail, which can provide valuable information for the industry. In particular the special gas phase distribution can have a crucial impact on the reactor performance. This can be in detail predicted by the computational fluid dynamic software, which can prove to be an essential tool for the reactor optimisation and scale-up.

  • Poster
    DECHEMA 2006 - GVC/DECHEMA-Jahrestagungen 2006, Rhein-Main-Hallen, Wiesbaden, 26.-28.09.2006, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 78(2006)9, 1274

Publ.-Id: 8549

Contactless electromagnetic induction flowmeter based on phase shift measurements

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

This study is concerned with a conceptual design of a new contactless AC induction flowmeter for liquid metal flows. The basic idea is to make use of the fact that the fluid flow disturbs not only the amplitude but also the phase distribution of an applied AC magnetic field. The goal is to consider the possibility of using the fluid flow induced phase shift of an AC magnetic field to measure the flow rate. In order to figure out the basic characteristics of such a flowmeter we consider several simple theoretical models where the liquid flow is approximated by a solid body motion. Based on these ideas a laboratory model of such a flowmeter has been built and tested at a liquid metal flow.

  • Contribution to proceedings
    EPM 2006, 23.-27.10.2006, Sendai, Japan
    Proceedings, Tokyo: The Iron and Steel Institute of Japan, 4-930980-55-0 C3057, 735-740
  • Lecture (Conference)
    EPM 2006, 23.-27.10.2006, Sendai, Japan

Publ.-Id: 8548

Hyperon production in the channel pp→K+Λp near the reaction threshold

Abd El-Samad, S.; Bilger, R.; Böhm, A.; Brinkmann, K.-T.; Clement, H.; Dshemuchadse, S.; Eyrich, W.; Erhardt, A.; Fanara, C.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Geyer, R.; Hauffe, J.; Hassan, A.; Herrmann, P.; Hesselbarth, D.; Jakob, B.; Kilian, K.; Koch, H.; Kress, J.; Kuhlmann, E.; Marcello, S.; Marwinski, S.; Metzger, A.; Michel, P.; Möller, K.; Morsch, H. P.; Naumann, L.; Roderburg, E.; Schamlott, A.; Schönmeier, P.; Schulte-Wissermann, M.; Schroeder, W.; Steinke, M.; Stinzing, F.; Sun, G. Y.; Wächter, J.; Wagner, G. J.; Wagner, M.; Wilms, A.; Wirth, S.; Zielinski, U.

Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of var epsilon=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the Nasterisk operator(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.

Keywords: Associated strangeness production; Total cross-section; Angular distribution; Dalitz plot

  • Physics Letters B 632(2006)1, 27-34

Publ.-Id: 8547

Complex formation of uranium(VI) with the amino acids L-glycine and L-cysteine: A fluorescence emission and UV-vis absorption study

Günther, A.; Geipel, G.; Bernhard, G.

The complexation of uranium(VI) with the amino acid L-glycine and L-cysteine has been investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and UV-vis spectroscopy at low pH range. The identified 1:1 and 1:2 uranyl-L-glycine complexes fluoresce and have similar absorbance properties. In contrast to the glycine system, uranyl forms with L-cysteine two different non-fluorescent 1:1 complexes showing individual absorbance properties under the given experimental conditions.The corresponding complex formation constants were calculated using the spectroscopic data.

Keywords: uranium; complexation; amino acid; TRLFS; UV-vis spectroscopy

  • Polyhedron 26(2007), 59-65

Publ.-Id: 8546

Effect of an external magnetic field on the flow in a liquid metal bubble plume

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

Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids, especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications. In the range of small or moderate void fractions the UDV technique delivers both the bubble and the liquid velocity.
In our experiments we investigated the consequences of an application of both DC and AC magnetic fields on the velocity field of bubble plumes. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. The application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction. AC magnetic fields can be applied to generate flow structures being different from the recirculating flow known from classical bubble plumes. A tailoring of the flow using magnetic fields obviously allows a control of the heat and mass transfer in bubble plumes.

Keywords: bubble plume; DC magnetic field; AC travelling magnetic field; electromagnetic stirring; velocity measurements; ultrasound Doppler technique

  • Lecture (Conference)
    CHISA 2006, 27.-31.08.2006, Praha, Czech Republic
  • Contribution to proceedings
    17th International Congress of Chemical and Process Engineering, CHISA 2006, 27.-31.08.2006, Praha, Czech Republic

Publ.-Id: 8545

Upper limits on resonance contributions to proton-proton elastic scattering in the c.m. mass range 2.05-2.85 GeV/c^2

Rohdjeß, H.; Altmeier, M.; Bauer, F.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Busch, M.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Ernst, J.; Eversheim, P. D.; Eyser, K. O.; Felden, O.; Gebel, R.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Langkau, R.; Lindlein, J.; Maier, R.; Mosel, F.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schulz-Rojahn, F.; Schwandt, F.; Schwarz, V.; Scobel, W.; Trelle, H.-J.; Ulbrich, K.; Weise, E.; Wellinghausen, A.; Woller, K.; Ziegler, R.

Recently published excitation functions in proton-proton (pp) elastic scattering observables in the laboratory energy range 0.5-2.5GeV provide an excellent data base to establish firm upper limits on the elasticities ηel = Γel/Γtot of possible isovector resonant contributions to the nucleon-nucleon (NN) system. Such contributions have been predicted to arise from dibaryonic states, with c.m. masses between 2.1-2.9GeV/c2, but have not been confirmed experimentally. A method to determine quantitatively the maximum value of ηel compatible with experimental data is presented. We use energy-dependent phase shift fits to the pp data base to model the non-resonant interaction. Based upon the differential cross-section data measured by the EDDA Collaboration an unbiased statistical test is constructed to obtain upper limits on ηel, that exclude larger values with a 99% confidence level. Results in the c.m. mass range 2.05-2.85GeV/c2 and total widths of 10-100MeV/c2 in the partial waves 1S0, 1D2, 3P0, 3P1, and 3F3 are presented and discussed.

Keywords: PACS. 25.40.Cm Elastic proton scattering; 13.75.Cs Nucleon-nucleon interactions (including antinucleon and deuterons etc.); 14.20.Pt Dibaryons; 11.80.Et Partial-wave analysis

Publ.-Id: 8544

Determining beam parameters in a storage ring with a cylindrical hodoscope using elastic proton–proton scattering

Rohdjeß, H.; Albers, D.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Eversheim, P. D.; Gasthuber, M.; Greiff, J.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Igelbrink, M.; Langkau, R.; Maier, R.; Mosel, F.; Müller, M.; Münstermann, M.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schirm, N.; Schwandt, F.; Scobel, W.; Trelle, H. J.; Wellinghausen, A.; Wiedmann, W.; Woller, K.; Ziegler, R.

The EDDA-detector at the cooler-synchrotron COSY/Jülich has been operated with an internal CH2 fiber target to measure proton–proton elastic scattering differential cross-sections. For data analysis knowledge of beam parameters, like position, width and angle, are indispensable. We have developed a method to obtain these values with high precision from the azimuthal and polar angles of the ejectiles only, by exploiting the coplanarity of the two final-state protons with the beam and the kinematic correlation. The formalism is described and results for beam parameters obtained during beam acceleration are given.

Keywords: Vertex reconstruction; Fiber target; Elastic proton–proton scattering; Storage ring

Publ.-Id: 8543

Radiation damage of polypropylene fiber targets in storage rings

Rohdjeß, H.; Albers, D.; Bisplinghoff, J.; Bollmann, R.; Büßer, K.; Diehl, O.; Dohrmann, F.; Engelhardt, H.-P.; Eversheim, P. D.; Greiff, J.; Groß, A.; Groß-Hardt, R.; Hinterberger, F.; Igelbrink, M.; Langkau, R.; Maier, R.; Mosel, F.; Müller, M.; Münstermann, M.; Prasuhn, D.; von Rossen, P.; Scheid, H.; Schirm, N.; Schwandt, F.; Scobel, W.; Trelle, H. J.; Wellinghausen, A.; Wiedmann, W.; Woller, K.; Ziegler, R.

Thin polypropylene fibers have been used for internal experiments in storage rings as an option for hydrogen targets. The change of the hydrogen content due to the radiation dose applied by the circulating proton beam has been investigated in the range 1 × 106–2 × 108 Gy at beam momenta of 1.5–3 GeV/c by comparing the elastic pp-scattering yield to that from inelastic p-carbon reactions. It is found that the loss of hydrogen as a function of applied dose receives contributions from a fast and a slow component.

Keywords: Radiation damage; Polypropylene; Fiber target; Elastic proton–proton scattering; Storage ring

Publ.-Id: 8542

Determination of the flow structure in bubble-driven liquid metal flows using ultrasound Doppler method

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

The ultrasound Doppler velocimetry (UDV) was validated for its capability to measure both gas and liquid velocities in transparent as well as opaque two-phase flows. A special threshold method has been tested successfully for processing of UDV data acquired from bubble-driven flows. Our experimental work presented here is focused on the influence of a transverse static magnetic field on a bubble plume in a cylindrical vessel. The liquid flow field has been measured by means of the ultrasound Doppler velocimetry. Despite the well-known damping effect of a DC magnetic field, it was observed, that the application of a moderate magnetic field may also cause an intensification of the liquid recirculation. The global flow field was found to be dominated by quasi-two-dimensional large scale vortex structures, whose axes are parallel aligned with the magnetic field direction. Therefore, the time-averaged flow field shows a distinct anisotropy. Local recirculating zones are found in the meridional plane perpendicular to the magnetic field lines, while velocity distributions become more uniform in the other plane parallel to the magnetic field.

Keywords: bubble plume; liquid metal; magnetic field; ultrasound Doppler velocimetry

  • Lecture (Conference)
    5th International Symposium on Ultrasound Doppler Methods (ISUD), 12.-14.09.2006, Zürich, Swizerland
  • Contribution to proceedings
    ISUD5, 5th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics, 12.-14.09.2006, Zürich, Swizerland
    Proceedings: ETH Zürich, 51-54

Publ.-Id: 8541

Electron beam monitoring for channeling radiation measurements

Neubert, W.; Azadegan, B.; Enghardt, W.; Heidel, K.; Pawelke, J.; Wagner, W.

A secondary emission monitor and an auxiliary Faraday cup necessary for calibration purposes have been constructed and installed at the radiation physics beam line of the electron accelerator ELBE. These devices are to be applied for the precise beam-current monitoring in measurements of channeling radiation. Miscellaneous simulations of underlying interactions of the beam electrons with the target material as well as with the materials of the monitor equipment have been performed to optimize the design and to evaluate possible correction factors inherent to transmission monitoring.

Keywords: electron beam monitor; secondary electrons; channeling radiation

  • Nuclear Instruments and Methods in Physics Research B 254(2007), 319-328

Publ.-Id: 8540

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