Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

Fast Neutron Cross-Section Measurements with the nELBE Neutron Time-of-Flight Facility

Wagner, A.; Bemmerer, D.; Beyer, R.; Birgersson, E.; Ferrari, A.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kögler, T.; Marta, M.; Matic, A.; Nolte, R.; Schilling, K. D.; Schramm, G.; Schwengner, R.; Weiss, F.-P.; Yakorev, D.

At the Forschungszentrum Dresden-Rossendorf a new neutron time-of-flight facility has been set up. Fast neutrons in the energy range from 0.1 MeV to 10 MeV are produced using pulsed electron beams from a superconducting electron linear accelerator. Short beam pulses of less than 10 ps allow high-resolution time-of-flight experiments with the aim to determine interaction cross sections of neutrons with reactor structural materials and actinides at energies matching the neutron energies in fast reactors. Following experiments using a thermionic electron injector a new superconducting radio-frequency injector has been built which will allow average beam currents of 0.5 mA at a repetition rate of 500 kHz.
Meanwhile, first experiments on inelastic neutron scattering cross sections on 56Fe and total neutron cross sections on aluminium and tantalum have been performed as benchmark experiments. While photons from the de-exciting transitions are being detected using a 16-element BaF2 scintillator array, neutrons are measured with five low-threshold plastic scintillation detectors. Beam normalisation is done using a calibrated 235U fission chamber. The preparation of actinide targets for neutron induced fission cross section measurements is under way.

Keywords: neutron time-of-flight superconducting electron linear accelerator interaction cross sections reactor structural materials actinides inelastic neutron scattering

  • Contribution to proceedings
    18th International Seminar on Interaction of Neutrons with Nuclei: "Neutron Spectroscopy, Nuclear Structure, Related Topics", 26.-29.05.2010, Dubna, Russia
    ISINN-18: Neutron Spectroscopy, Nuclear Structure, Related Topics, Dubna, Russia: Joint Institute for Nuclear Research, 978-5-9530-0277-6, 127-134
  • Lecture (Conference)
    18th International Seminar on Interaction of Neutrons with Nuclei: "Fundamental Interactions & Neutrons, Nuclear Structure, Ultracold Neutrons, Related Topics", 26.05.2010, Dubna, Russia

Publ.-Id: 14491

Grain growth induced by focused ion beam irradiation in thin magnetic films

Roshchupkina, O. D.; Grenzer, J.; Strache, T.; Fritzsche, M.; Fassbender, J.

Focused ion beam irradiation can be used as a tool for creation of magnetic nanos-tructures. Previous studies have shown that FIB irradiation of thin metallic films could induce significant grain growth and therefore modify magnetic properties [1-2]. In this work we compare X-ray diffraction studies with magnetic properties that were characterized by magneto-optic Kerr effect sensing both the in-plane and the out-of-plane components of the magnetization.
A 50nm thick permalloy layer (Ni80Fe20) irradiated with different fluences of Ga+ ions was chosen for the investigations of grain size and microstrain. Due to the small irradiated areas produced by FIB irradiation XRD measurements were carried out on an optimized X-ray laboratory setup with a focused X-ray beam of 200µm as well as on the ESRF ID01 facility using a 1µm focused beam. Figure 1a shows rocking curves of the (111) permalloy reflection and demonstrates the material texturing with increase of ion fluence as there is a narrowing in FWHM and a rise of intensity. Low irradiation fluences up to 6.24*10E15 ions/cm2 modify the material and induce crystal-lite growth, whereas larger fluences completely destroy the crystalline structure. A further material crystallization should improve the magnetic properties. Due to the incorporation of Ga+ ions into the lattice additional softening of the permalloy film occurs and leads to the degradation of magnetic properties. In figure 1b a corre-sponding saturation Kerr rotation measurement is shown. It demonstrates a decrease of the magnetic moment with increasing ion fluence.

[1] C.M. Park and J. A. Bain., J. of Appl. Phys. 91, 6830 (2002).
[2] W.M. Kaminsky et al., Appl. Phys. Lett. 78, 1589 (2001).

Keywords: Focused ion beam irradiation; permalloy

  • Poster
    XTOP 2010 / 10th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, 20.-23.09.2010, University of Warwick, UK

Publ.-Id: 14490

Transporting radioactive samples from the laboratory to the ESRF

Venault, L.; Den Auwer, C.; Moisy, P.; Colomp, P.; Scheinost, A. C.; Hennig, C.

Desription of safety efforts required to transport radioactive samples

Keywords: The Rossendorf beamline; EXAFS; XANES; radionuclides; actinides

  • Communication & Media Relations
    ESRF News Nr. 54 15.06.2010
    1 Seiten

Publ.-Id: 14487

High-field metamagnetic transitions in Rare-Earth Transition-metal ferrimagnets

Skourski, Y.

hat nicht vorgelegen

  • Lecture (Conference)
    Joint European Magnetic Symposia (JEMS 2010), 23.-28.08.2010, Krakow, Poland

Publ.-Id: 14486

3D-observation of heterogeneous transport and comparison to Lattice-Boltzmann modelling

Wolf, M.

This thesis is located at the Institute of Radiochemistry, FZD Research Site Leipzig for Interdisciplinary Isotope Research, Reactive Transport Division (FWRT). The main focus of this division is the investigation of transport processes in geosystems by means of radiotracer applications. The main topic of the thesis is the visualization of transport processes in geologic material by means of the in-house development of the GeoPET-method. This work is conducted as part of the scientific joint venture: „Dynamik abgesoffener oder gefluteter Salzbergwerke und ihres Deckgebirgsstockwerks“ („Dynamic of drowned or flooded salt mines and their overburden“), coordinated by the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR).

Since the late 19. century drowned salt mines cause severe mining damages in the city of Stassfurt (Saxony-Anhalt). Sink hole depressions and subsidence of the surface below the groundwater table destroyed large parts of the down town. The general causation was lack of experience with salt mines and mining in gypsum karst in the 19. century. The causation in detail why and how exactly salt rock has washed out is more complicated to identify, as streaming mechanisms at the small scale level are partly still unclear; the general fluid dynamics at small scales is partly unknown.

To reveal these processes and mechanisms the behaviour of salt brines at the millimetre scale in drilling cores of the different geological units of the salt rock and its surrounding is examined by three-dimensional visualization of the distribution of radioactive labelled water measured with PET. Mechanisms at millimetre scale control mechanisms at the kilometre scale and are of utmost importance for the principal understanding of fluid dynamics. In the laboratory you can have „a look into the rock“. In the field this is not possible this way.

Combining PET data with high resolution CT-scans of the samples (conducted by the cooperation partners JGU Mainz and BAM Berlin) allows an alignment of processes of the fluid flow and its associated hydraulic pathway structures. This matching is important for understanding and for generalized conclusion about ongoing processes and is a necessary preparatory work for computer modelling.

Lattice-Boltzmann-simulations of velocity fields and streaming patterns based on CT-data are compared with PET-data derived from the same samples. This comparison of the flow patterns is done by means of geostatistic methods that allows scale independant spatial correlation of the patterns and therefore provide scale indpendant parameters like correlation lengths that are a necessity for upscaling.

Short term objective is the improvement and validation of parameters and fluid flow concepts derived from small scale simulations. Long term objective is the improvement of upscaling of parameters and concepts to the field scale and a better understanding and prediction of mining damages and groundwater behaviour.

  • Lecture (others)
    FZD Doktorandenseminar, 22.-24.09.2010, Krögis (Meissen), Deutschland

Publ.-Id: 14485

Environmental Sciences at the ESRF

Cotte, M.; Auffan, M.; Degruyter, W.; Fairchild, I.; Newton, M.; Morin, G.; Sarret, G.; Scheinost, A. C.

In the past several years, environmental sciences have increased their share in the research portfolios of many synchrotrons, not least for their topicality from a societal point of view. As this field overlaps with many other disciplines, the ESRF decided to establish, in 2005, a dedicated Review Panel for Environmental Science and Cultural Heritage.
This facility report summarizes recent trends and results from the ESRF to highlight the different disciplines, techniques and topics. It should also be noted that environmental studies encompass both a better understanding of natural phenomena and monitoring the impact of human activity on nature.

Keywords: synchrotron radiation; XAFS; environmental research

Publ.-Id: 14483

The use of ionization chambers for short-pulsed radiation fields with high pulse dose

Karsch, L.; Richter, C.; Pawelke, J.

no abstract available

Keywords: ionization chamber; saturation correction

  • Abstract in refereed journal
    Strahlentherapie und Onkologie 186(2010)Suppl. 1, 93-93
  • Poster
    16. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 03.-06.06.2010, Magdeburg, Deutschland

Publ.-Id: 14482

Characterization and optimization of the imaging and dosimetric properties of a image-guided precision irradiation device for small animals

Tillner, F.; Hietschold, V.; Khaless, A.; Pawelke, J.; Thute, P.; Enghardt, W.

no abstract available

Keywords: IGRT; small animal

  • Abstract in refereed journal
    Strahlentherapie und Onkologie 186(2010)Suppl. 1, 105-105
  • Poster
    16. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 03.-06.06.2010, Magdeburg, Deutschland

Publ.-Id: 14481

The Influence of the temperature on the carbonate complexation of Uranium(VI) - a spectroscopic study

Götz, C.; Geipel, G.; Bernhard, G.

The interaction of uranium(VI) with carbonate ions was studied with absorption spectroscopy and time resolved laser induced fluorescence spectroscopy due to the importance of these complexes in environmental relevant waters. In the pH range from 2 to 11 the influence of the temperature on the spectra was studied to check changes in the abundances of several binding forms. It was found that several binding forms are predominant at different temperatures and pH values. This observation can be explained by speciation changes due to the dependence of chemical equilibria on the temperature.
Furthermore photoluminescence spectra of aqueous solutions of uranyl carbonate complexes were observed at ambient temperatures for the first time and single component absorption spectra of the uranyl carbonate complexes UO2(CO3)34- and UO2(CO3)22- were derived.

Keywords: Uranium(VI); carbonate complexation; absorption spectroscopy; time resolved laser induced fluorescence spectroscopy; temperature; chemical equilibrium

Publ.-Id: 14479

Instantaneous shape sampling: A model for the gamma-absorption cross section of transitional nuclei

Bentley, I.; Brant, S.; Dönau, F.; Frauendorf, S.; Kämpfer, B.; Schwengner, R.; Zhang, S. Q.

The influence of the quadrupole shape fluctuations on the dipole vibrations in transitional nuclei is investigated in the framework of the instantaneous-Shape Sampling (ISS) Model, which combines the Interacting Boson Model for the slow collective quadrupole motion with the Random Phase Approximation for the rapid dipole vibrations. Coupling to the complex background configurations is taken into account by folding the results with a Lorentzian with energy dependent width (collisional damping CD).
The low-energy energy portion of the gamma absorption cross section, which is important for photo-nuclear processes, is studied for the isotop series of Kr, Xe, Ba, and Sm. The experimental cross sections are well reproduced. The low-energy dipole strength is determined by the Landau fragmentation of the dipole strength and its redistribution caused by the shape fluctuations. CD only wipes out fluctuations of the absorption cross section, generating the smooth energy dependence observed in experiment. In the case of semi magical nuclei, shallow pygmy resonances are found in correspondence with experiment.

Keywords: Dipole strength; absorption cross section; interacting boson model; quasiparticle random-phase-approximation

  • Physical Review C 83(2011), 014317

Publ.-Id: 14478

Experimentelle und analytische Untersuchungen zu passiven Komponenten des KERENA TM Konzeptes im Versuchsstand INKA

Willschütz, H.-G.; Diercks, F.; Leyer, S.; Krüssenberg, A.-K.; Schäfer, F.; Hristov, H. V.

Das KERENA TM - Konzept ist eine kontinuierliche Weiterentwicklung der seit Jahren bewährten (deutschen) Siedewassertechnologie der "Baulinie 72". Die Kombination von betriebserprobten aktiven Sicherheitssystemen mit neu hinzugekommenen passiven Sicherheitssystemen setzt die Forderungen der "Defense in Depth"-Philsophie konsequent um. Insbesondere für die neu eingeführten passiven Sicherheitssysteme muss das Betriebsverhalten durch experimentelle Untersuchungen validiert und die thermohydraulischen Berechnungsprogramme müssen qualifiziert werden, so dass sie die auftretenden Naturumlaufphänomene korrekt berechnen können. Mit den vorliegenden Arbeiten wird die Eignung des Thermohydraulikprogrammsystems ATHLET der Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH als ein Programm, das im Genehmigungs- und Aufsichtsverfahren in verschiedenen Ländern eingesetzt wird, zur Berechnung des Betriebsverhalten der passiven Komponenten untersucht. Dazu wurde ein Modell für die Versuchsanlage INKA (INtegral test facility in KArlstein) entwickelt, mit dem sowohl Vorausrechnungen des Kennfelds der passiven Komponenten Notkondensator und Gebäudekondensator als auch Nachrechnungen zu Experimenten durchgeführt wurden.

Keywords: KERENA; ATHLET; Boiling Water Reactor

  • Contribution to proceedings
    42. Kraftwerkstechnisches Kolloquium 2010, 12.-13.10.2010, Congress Center Dresden, Deutschland
    Experimentelle und analytische Untersuchungen zu passiven Komponenten des KERENA TM Konzeptes im Versuchsstand INKA
  • Lecture (Conference)
    42. Kraftwerkstechnisches Kolloquium 2010, 12.-13.10.2010, Congress Center Dresden, Deutschland

Publ.-Id: 14476

4D-in-beam-PET für periodisch bewegte Phantome bei Bestrahlung mit einem mitbewegten 12C-Strahl

Laube, K.; Bert, C.; Chaudhri, N.; Fiedler, F.; Parodi, K.; Rietzel, E.; Saito, N.; Enghardt, W.

In-beam-PET ist die bislang einzige Methode zur in vivo und in situ Überwachung der Dosisapplikation bei der Ionenstrahltherapie. Sie wurde in einem Pilotprojekt am GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt bei der 12C-Bestrahlung von über 400 Patienten mit unbeweglichen Tumoren im Kopf-Halsbereich erfolgreich eingesetzt. Die geplante Anwendung der Ionenstrahltherapie auf, v. a. atmungsbedingt, intrafraktionell bewegliche Tumoren erfordert eine Erweiterung der in-beam-PET-Datenrekonstruktion. Die Notwendigkeit einer zeitaufgelösten (4D) Auswertung und die Qualität der damit reproduzierbaren Aktivitätsverteilung werden anhand experimenteller Daten dargestellt.

Ein PMMA-Phantom wurde mittig im Gesichtsfeld des Doppelkopf-PET-Scanners BASTEI am ehemaligen medizinischen Bestrahlungsplatz der GSI positioniert und senkrecht zur Einstrahlrichtung periodisch (sinusförmig, Amplitude = 10 mm, Periode ≈ 3,5 s) ausgelenkt. Mit einem monoenergetischen 12C-Bleistiftstrahl wurde eine im Bereich des Bragg-Peaks homogene, linienförmige Dosisverteilung parallel zur Bewegungsrichtung im Target appliziert. Für die Bestrahlung wurde ein neuartiges Tracking-System benutzt, welches die Strahlrichtung der aktuellen Phantomauslenkung anpasst. Im Verlauf der Bestrahlung entsteht durch Kernfragmentierungen eine der Dosisverteilung ähnliche +-Aktivitätsverteilung aus v. a. 11C und 15O. Die entsprechende Annihilationsstrahlung sowie die Targetbewegung werden während der Bestrahlung (≈ 85 s) und weitere 5 min danach detektiert. Die gemessenen Ereignisse werden unter Berücksichtigung der Detektoreffektivität und einer Schwächungskorrektur rückprojiziert und mit einer Referenzaktivität aus einer zweiten, identischen Bestrahlung und Aktivitätsmessung jedoch ohne Phantombewegung verglichen. Für eine 4D-Auswertung werden zuerst in einem zusätzlichen Zwischenschritt die Koinzidenzen entsprechend der Bewegungsamplitude oder -phase sortiert und die einzelnen Rückprojektionen werden anschließend zusammengeführt.

Ohne Berücksichtigung der Phantombewegung ist die Aktivitätsverteilung entlang der Bewegungsrichtung über die Targetgrenzen hinaus verschmiert. Sie weicht im Hochdosisbereich bis zu 22 % von der statischen Referenz ab und die Breite des lateralen 80–20%-Aktivitätsabfalls vergrößert sich von 7,6 mm für die Referenz auf 17,2 mm. Bei der 4D-in-beam-PET bleibt diese mit 8,3 mm innerhalb der Fehlergrenzen erhalten und der maximale Unterschied zur Referenz beträgt nur 4 %.

Bereits bei geringen Bewegungsamplituden ist eine 4D-Rekonstruktion erforderlich, da andernfalls nicht die tatsächlich applizierte Dosisverteilung verifiziert werden kann. Bei genauer Kenntnis des Bewegungsverlaufes reproduziert die vorgestellte 4D-in-beam-PET die Aktivitätsverteilung im Phantom innerhalb statistischer Schwankungen. Weitere Experimente für komplexe Targetgeometrien, Dosisverteilungen und Bewegungsabläufe sind erforderlich.

Keywords: in-beam PET; moving targets; ion beam therapy

  • Poster
    16. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 03.-06.06.2010, Magdeburg, Deutschland

Publ.-Id: 14475

Atomic Layer Deposition of CaB2O4 Films Using Bis(tris(pyrazolyl)borate)calcium as a Highly Thermally Stable Boron and Calcium Source

Saly, M. J.; Munnik, F.; Winter, C. H.

The atomic layer deposition of CaB2O4 was carried out using bis(tris(pyrazolyl)borate)calcium (CaTp2) and water as precursors. CaTp2 melts at 280 °C, undergoes solid state thermal decomposition at 385 °C, and sublimed on a preparative scale at 180 °C/0.05 Torr in about 3 hours with 99.7% recovery and 0.2% nonvolatile residue. Self-limited ALD growth was established at 350 °C with CaTp2 pulse lengths of ≥ 2.0 s. An ALD window was observed from 300 to 375 °C, in which the growth rate was between 0.34 and 0.36 Å/cycle. The thin film compositions were assessed by elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). The B/Ca ratios for CaB2O4 films deposited at 275, 325, 350, and 400 °C were 1.84(11), 1.85(11), 1.89(13), and 1.42(10), respectively, as determined by ERDA. Within the ALD window, hydrogen concentrations ranged from 0.22(2) to 0.35(4) atom % and the carbon and nitrogen concentrations were below the detection limits. XPS analyses on representative CaB2O4 thin films showed all expected ionizations. X-ray diffraction experiments revealed that the as-deposited films were amorphous. The surface morphology was assessed by atomic force microscopy and scanning electron microscopy. The rms surface roughness of a typical 2 μm x 2 μm area for films deposited at 325 and 350 °C was 0.3 nm. Scanning electron micrographs of these films showed no cracks or pinholes.

Keywords: group 2 ALD precursors; calcium borate; tris(pyrazolyl)borate; bimetallic ALD precursors; atomic layer deposition

Publ.-Id: 14474

All-Optical Ion Beam Cooling and Online Diagnostics at Relativistic Energies

Bussmann, M.; Schramm, U.; Nörtershäuser, W.; Novotny, C.; Geppert, C.; Walther, T.; Birkl, G.; Winters, D. F. A.; Kühl, T.; Kozhuharov, C.; Steck, M.; Nolden, F.; Dimopoulou, C.; Stöhlker, T.

Recent experiments at the Experimental Storage Ring (ESR) at GSI have shown that relativistic Li-like C3+ ion beams can be cooled to an unprecedented momentum spread of dp=p ~ 10-7 using a single-frequency laser tuned to the Doppler-shifted 2S1/2 -> 2P1/2 and 2S1/2 -> 2P3/2 atomic transitions. Although these results encourage the application of laser cooling to beams of other Li-like and Na-like ions at even higher energies as will be available at future storage rings at FAIR (Facility for Antiproton and Ion Research), two major concepts have to be demonstrated experimentally: First, efficient laser cooling of ion beams with large initial momentum spread, thus avoiding additional electron cooling to match the large momentum spread to the usually small momentum acceptance of the laser force. Second, all-optical measurements of the relevant beam parameters, thus overcoming the limited resolution of standard storage ring detectors such as the Schottky pickup electrode at ultra-low momentum spreads. The aim of this paper is to discuss the technical realization of these concepts as planned for an upcoming beam time at ESR.

Keywords: laser cooling; relativistic; energy beam; ion; laser; optical diagnostics; storage ring; esr; gsi; c3+

  • Contribution to proceedings
    Workshop on Beam Cooling and Related Topics 2009, COOL 2009, 31.08.-04.09.2009, Lanzhou, China
    All-Optical Ion Beam Cooling and Online Diagnostics at Relativistic Energies: Atomic Energy Press, 978-7-5022-4871-0, 22-26

Publ.-Id: 14473

DREAMS at FZD: The new accelerator mass spectrometry facility

Akhmadaliev, S.; Heller, R.; Kolitsch, A.; Merchel, S.; Möller, W.

The installation of a new 6 MV-Tandetron accelerator opens a new topic of research at FZ Dresden-Rossendorf: Accelerator mass spectrometry (AMS). The Dresden AMS facility (DREAMS) will be mainly used for measurements of the long-lived radionuclides 10Be, 26Al, 36Cl, 41Ca and 129I (T1/2 = 0.1-15.7 Ma) in the isotopic ratio range of 10-10- 10-16. The same accelerator will be partially also used for spatial- and depth-resolved chemical analysis using ion beam techniques such as Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection (ERD), Particle-induced X-ray and Gamma-ray emission (PIXE/PIGE) and Nuclear Reaction Analysis (NRA). Using these methods, we are able to measure nondestructively "all natural" elements, i.e. H to U; most elements with lateral, some in 3D resolution. Additionally, materials modification via high energy ion implantation is possible.
The AMS injector consist of two Cs-sputter ion sources SO-110 with wheels for up to 200 sputter targets, a 54° electrostatic analyzer (ESA) and a 90° bouncer magnet for sequential acceleration of stable isotopes and radionuclides. In contrast to common low-energy AMS facilities, which have mainly specialized in radiocarbon analyses (14C), the FZD-AMS is the first modern type facility in the EU that will run at a terminal voltage of 6 MV. The electrostatic accelerator operates with a Cockcroft-Walton type high voltage cascade for generating the terminal voltage. The high-energy part of the system consists of a 90° analyzing magnet, a set of precise Faraday cups with energy slits for measuring the stable nuclides and stabilising the terminal voltage, a set of absorber foils for isobar suppression, a 35° ESA, and a 30° vertical magnet for suppressing interfering species. The radionuclides will be finally detected by a ΔE/E gas ionisation chamber containing four anodes. There is a main advantage of us-ing a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses (e.g. isobars) are nearly completely eliminated. Thus, AMS provides much lower detection limits compared to conventional mass spectrometry.
The benefits from using AMS for radiation protection, nuclear safety, nuclear waste, radioecology, phytology, nutrition, toxicology, and pharmacology research are obvious and manifold: Smaller sample sizes, easier and faster sample preparation, higher sample throughput and the redundancy for radiochemistry la-boratories will largely reduce costs. Lower detection limits will widen applications to shorter and longer time scales and to sample types which could never been investigated before. Especially in environmental and geosciences, the determination of long-lived cosmogenic radionuclides like 10Be, 26Al, and 36Cl became more and more important within the last decades. Using these nuclides dating of suddenly occurring prehistoric mass movements, e.g. volcanic eruptions, rock valanches, tsunamis, meteor impacts, earth quakes and glacier movements, is possible. Additionally, glacier movements and data from ice cores give hints for the reconstruction of historic climate changes and providing information for the validation of climate model predicting future changes. Taking the advantage of location into account DREAMS will soon also focus on applications of radionuclides of anthropogenic origin such as plutonium isotopes and 129I.
Investment and maintenance costs of a high-energy AMS facility are much higher compared to e.g. methods determining radionuclides via their decay. All methods including AMS need sophisticated radiochemical separation procedures. However, for several nuclides the requirements with respect to the purity of the final sample to be measured are much lower for AMS. As it is the case for most destructive analytical methods AMS chemical sample preparation takes much longer and is more expensive that the actual measurement, which takes about 10 - 60 min.

Keywords: AMS; Ion Beam Analysis; Tandetron

  • Lecture (Conference)
    6. Workshop Radiochemische Analytik bei Betrieb und Rückbau kerntechnische Anlagen, der Deklaration von Abfällen und im Schtrahlenschutz und 23.Seminar Aktivierungsanalyse und Gammaspektroskopie, 06.-08.09.2010, Dresden, Deutschland

Publ.-Id: 14472

Simulation of advanced, laser-driven radiation sources at FZD

Bussmann, M.

In this talk I will present an overview of the activities at the Forschungszentrum Dresden-Rossendorf (FZD) focusing on laser ion acceleration, x-ray generation via Thomson scattering and medical beam line design for tumor therapy with laser-driven particle beams.
Optimization and precise control of the properties of laser-driven radiation sources using large-scale realistic simulations and direct comparison to experiment play a key role in the research program at FZD.
I will show some recent results obtained at FZD and give an outlook on future work, with an emphasis on the development of new simulation tools.

Keywords: laser; particle; acceleration; x-ray; radiation; source; overview; simulation

  • Invited lecture (Conferences)
    Seminar of the Shanghai Institute of Optics and Fine Mechanics (SIOM), 30.08.2010, Shanghai, China

Publ.-Id: 14471

Experimental Design of Traveling-Wave Thomson Scattering

Debus, A.; Bussmann, M.; Jochmann, A.; Siebold, M.; Cowan, T.; Schramm, U.; Sauerbrey, R.

Traveling-wave Thomson scattering is a novel interaction design that allows circumventing the Rayleigh limit in optical undulators, which is interesting for possible realizations of Thomson scattering sources with photon yields per pulse that are orders of magnitudes beyond current designs. The resulting radiation reaction could even be strong enough for driving an FEL instability. Here we present details on how a Traveling-wave setup has to be implemented in experiment. An emphasis is put on the use of varied-line spacing (VLS) gratings for spatio-temporal beam shaping at large interaction angles to achieve optimal overlap. At the FZD we are using the high-power laser system DRACO (250TW) to realize a Thomson source with electrons from the linear accelerator ELBE or laser-plasma accelerated electrons. We present the current status and further progress towards a head-on Thomson source and a Traveling-Wave Thomson scattering source aiming for high photon yields per pulse.

Keywords: Traveling-wave Thomson scattering; free electron laser; FEL; xray; EUV

  • Poster
    32nd International Free Electron Laser Conference FEL 2010, 23.-27.08.2010, Malmö, Sweden

Publ.-Id: 14470

Traveling-wave Thomson scattering for scaling optical undulators towards the FEL regime

Debus, A. D.; Bussmann, M.; Jochmann, A.; Siebold, M.; Cowan, T.; Schramm, U.; Sauerbrey, R.

We present a novel concept for optical undulators that avoids the restrictions by the Rayleigh limit and thus allows to define interaction length and diameter independent of each other. With an ultrashort, high-power laser pulse in an oblique angle scattering geometry using tilted pulse fronts, electrons and laser remain overlapped while both beams travel over distances much longer than the Rayleigh length. For small scattering angles (<10°), where dispersive effects become negligible and interaction lengths scale up to the meter range, we discuss with the help of 1D-calculations the possibility of entering the SASE-FEL regime using optical undulators driven by existing lasers.

Keywords: Traveling-wave Thomson scattering; free electron laser; xray; EUV

  • Poster
    32nd International Free Electron Laser Conference FEL 2010, 23.-27.08.2010, Malmö, Sweden

Publ.-Id: 14469

A Virtual Firefighting Simulator

Schmeißer, N.

A simulator will be presented which employs VR techniques in order to provide a training environment for re-ghters. While existing systems for re-brigade training do focus on tactics and command training, this simulator targets the training of the re attack group. It provides scenarios for search & rescue operations, direct reghting using water and foam as well as radiation source search operations. Visual, audio and haptic feed-back is provided. The system supports immersive displays (HMD) as well as standard techniques (monoscopic big-wall). It implements a walking paradigm, which enables the trainee to move around freely. The simulator uses extended reality features in order to improve the handling (nozzles, dose meter, ...). The trainee can use the system fully equipped, even using the respiratory protection, in order to provide a realistic feeling. Several physical models are used to provide eects closed to reality, namely:

  • heat release rate is used to model the energetic behavior of a fire, fl ame size etc.
  • a simple energetic model for re-extinction by cooling
  • water and foam ejection (depending on pressure, volume, form of jet, agent)
  • a smoke system (visibility equivalent to height of eye)
  • superposition of radiation sources (no shielding) and detection by Teleprobe FH40G
The simulation is supervised by an instructor, each action, e.g. radio traffc, movements is logged for analysis.

Keywords: simulation fire fire-fighting extinction radioton search rescue

  • Contribution to proceedings
    3rd International Workshop "Innovation in Information Technologies - Theory and Practice", September 6th-10th, Dresden, Germany, 2010, 06.-10.9.2010, Dresden, BRD
    A Virtual Firefighting Simulator, Dresden: Forschungszentrum-Rossendorf e. V., 978-3-941405-10-3, 76-82

Publ.-Id: 14468

Cold quark stars from hot lattice QCD

Schulze, R.; Kämpfer, B.

Based on a quasiparticle model for \beta stable and electrically neutral deconfined matter we address the possibility of pure quark stars. The model is adjusted to recent hot lattice QCD results for 2+1 flavors with almost physical quark masses. Using stability and binding arguments general statements can be made concerning the existence of such compact stellar objects.

Keywords: QCD; quasiparticle model; quark stars; quark gluon plasma

  • Invited lecture (Conferences)
    Hot and Cold Baryonic Matter 2010, 15.-20.08.2010, Budapest, Hungary

Publ.-Id: 14467

Schlagende Herzen und rasante Strömungen - Schnelle bildgebende Messverfahren in Technik und Medizin

Hampel, U.

Der Vortrag gibt einen Einblick in die Nutzung schneller tomographischer Bildgebungsverfahren in der Medizin und Technik.

Keywords: fast tomography methods; medicine; engineering

  • Invited lecture (Conferences)
    Dresdner Seniorenakademie, 09.09.2010, Dresden, Germany

Publ.-Id: 14465

Steam bubble condensation in polydispersed flow experiments and CFD simulations

Krepper, E.; Schmidtke, M.; Lucas, D.; Beyer, M.

Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
Experiments on steam bubble condensation in vertical co-current steam/water flows have been carried out in a 8m long vertical DN200 pipe. Steam is injected into the pipe and the development of the bubbly flow is measured at different distances to the injection using a wire mesh sensor. By varying the steam nozzle diameter the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore condensate slower. Steam pressures between 1-2 MPa and sub-cooling temperatures from 2 to 6 K were applied. Due to the drop of hydrostatic pressure along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section. The experimental configurations are simulated with the CFD code CFX using an extended MUSIG approach, which includes the bubble shrinking or growth due to condensation or re-evaporation. The development of the vapour phase along the pipe with respect to vapur void fractions and bubble sizes is qualitatively well reproduced in the simulations. For a better quantitative reproduction, reliable models for the heat transfer at high Reynolds number as well as for bubble breakup and coalescence are needed.

Keywords: two phase flow; experiments; CFD simulation; population balance models; mass transfer

  • Contribution to proceedings
    Int. Conf. "Nuclear Energy for New Europe", 06.09.-09.10.2010, Portoz, Slovenien
  • Lecture (Conference)
    Int. Conf. "Nuclear Energy for New Europe", 06.-09.09.2010, Portoz, Slovenien

Publ.-Id: 14464

Computing the KPZ Equation Using GPU Acceleration

Schulz, H.; Odor, G.; Kelling, J.; Heinig, K.-H.; Liedke, B.; Schmeißer, N.

In this talk we present an approach for fast parallel computation of the Kardar-Parisi-Zhang equation (KPZ). Acceleration of these computations is always a major task since the run time of the simulations representing sequential algorithms is in the range of several months. We developed an implementation for the KPZ equation on graphics processing units (GPU) using the Compute Unified Device Architecture (CUDA). Experimental results show a significant speed-up compared to implementations on conventional processors.

  • Contribution to proceedings
    Innovation Information Technologies - Theory and Practice, 06.-10.09.2010, Dresden, Deutschland
    Computing the KPZ Equation Using GPU Acceleration, Dresden: FZD, 978-3-941405-10-3, 46-48

Publ.-Id: 14463

Raster-Kelvinkraft-Mikroskopie zur quantitativen Dotierprofilierung an dotiertem Silizium und Mn-implantiertem Germanium

Baumgart, C.; Zhou, S.; Helm, M.; Schmidt, H.

Am Beispiel von dotierten Halbleitern konnte gezeigt werden, dass es mit Hilfe der korrekten Interpretation von KPFM-Daten möglich ist, die gemessene KPFM-Spannung mit der Ladungsträger-Konzentration in den untersuchten Halbleitern zu korrelieren. Die präsentierten Ergebnisse an dotiertem Silizium und Mn-implantiertem Germanium legen nahe, dass die Modellierung der KPFM-Spannung auf alle dotierten Halbleitermaterialien angewandt werden kann, solange die intrinsische Ladungsträgerkonzentration geringer als die Dotierkonzentration ist. Wir erwarten, dass in Zukunft die KPFM-Methode auch zur quantitativen Untersuchung der elektrischen Eigenschaften anderer Materialsysteme eingesetzt wird. Grundlage dafür ist immer das Verständnis der Ursache der mittels KPFM detektierten elektrostatischen Kräfte und die damit verbundene korrekte Interpretation der KPFM-Spannung.

Publ.-Id: 14462

Enhanced nucleation of vortices in soft magnetic disks prepared by silica nanosphere lithography

Martin, N.; Bigall, N. C.; Mönch, I.; Gemming, T.; Eychmüller, A.; Mattheis, R.; Schäfer, R.; Schultz, L.; McCord, J.

Magnetic vortices show promise as data storage structures, however the vortex formation process imposes a lower limit on the element’s size. In this article a technique is presented, which application increases the probability of nucleating of magnetic vortices in sub-micron sized soft magnetic thin film elements. By tailoring the edge geometry of the elements, the symmetry of their magnetic configuration is broken in a manner which favors vortex nucleation. Micromagnetic simulations are presented, which demonstrate this effect in soft-magnetic disks with beveled edges. The favored edge geometry was realized by applying nanosphere lithography directly on top of a ferromagnetic thin film material. The resulting magnetic reversal loops show that in both magnetically isolated as well as in closely packed arrays of beveled disks, vortex formation takes place. The technique presented facilitates the vortex formation even in closely packed and small elements. The lowering of the minimum critical diameter for vortex formation enables a significant increase of data storage density in devices based on magnetic vortices.

Keywords: nanoparticles; patterned arrays; magnetic materials; thin films; magnetic vortex

Publ.-Id: 14459

Synthesis and Radiofluorination of Iodophenyl Esters as Tool for the Traceless Staudinger Ligation

Pretze, M.; Flemming, A.; Köckerling, M.; Mamat, C.

A new synthetic pathway for the preparation of ω-functionalized 2-iodophenyl esters as starting materials for the synthesis of substituted phosphanes is described. A radiolabeling of these esters with fluorine-18 has led to building blocks which were reacted with HPPh2 in a Pd-catalyzed P-C cross coupling to establish new phosphanes. These compounds can be applied as mild and bioorthogonal radiolabeling agents by means of the traceless Staudinger ligation. A route to access this class of compounds has been established.

Keywords: Staudinger Ligation; Traceless; Bioorthogonal; Radiofluorination; PET; X-Ray Structure

  • Zeitschrift für Naturforschung Section B - A Journal of Chemical Sciences 65(2010), 1128-1136

Publ.-Id: 14458

A Compton Imager for in-vivo Dosimetry of Proton Beams

Enghardt, W.; Golnik, C.; Kormoll, T.; Wüstemann, J.; Fiedler, F.; Müller, A.; Schöne, S.

no abstract available

Keywords: in-vivo dosimetry; proton irradiation; ion irradiation

  • Lecture (others)
    WP 3 Meeting, ENVISION, 04.09.2010, Stockholm, Schweden

Publ.-Id: 14457

High-precision ( p,t) reaction to determine 25Al( p,γ )26Si reaction rates

Matic, A.; van den Berg, A. M.; Harakeh, M. N.; Wörtche, H. J.; Berg, G. P. A.; Couder, M.; Görres, J.; Leblanc, P.; O’Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.; Shimbara, Y.; Fujita, H.; Wakasa, T.; Brown, B. A.; Schatz, H.

Since the identification of ongoing 26Al production in the universe, the reaction sequence 24Mg(p,γ )25Al(β+ν)25Mg(p,γ )26Al has been studied intensively. At temperatures where the radiative capture on 25Al (t1/2 = 7.2 s) becomes faster than the β+ decay, the production of 26Al can be reduced due to the depletion of 25Al. To determine the resonances relevant for the 25Al(p,γ )26Si bypass reaction, we measured the 28Si(p,t )26Si reaction with high-energy precision using the Grand Raiden spectrometer at the Research Center for Nuclear Physics, Osaka. Several new energy levels were found above the p threshold and for known states excitation energies were determined with smaller uncertainties. The calculated stellar rates of the bypass reaction agree well with previous results, suggesting that these rates are well established.

Keywords: 26Al 24Mg(p; γ )25Al(β+ν)25Mg(p; γ )26Al Grand Raiden spectrometer

Publ.-Id: 14456

Analysis of Design Basis Accidents

Weiss, F.-P.; Schaefer, F.; Kliem, S.; Tusheva, P.

The safety philosophy of nuclear reactors aims at maintaining the barriers for the retention of radioactivity. The safety functions required to achieve this fundamental protection goal are implemented by the operational and safety systems. All these systems are elements in a staggered safety concept, known as the defence in depth (DiD) concept which is meant to optimize the interaction of the manifold systems in respect to their effect on the safety of the nuclear power plant. On the first two levels of the DiD concept, i.e. at normal and abnormal or disturbed operation, the operational as well as the limitation and protection systems are designed to keep the plant at normal operation or to return to normal operation after a disturbance had occurred. Only in case of a failure of these systems or by effect of external events, an operational disturbance might develop into an accident. Accident scenarios which have been considered in the plant design are called design basis accidents. Safety systems and measures are arranged at level 3 of the DiD concept to control the design basis accidents and to bring the reactor back to a safe state.

  • Lecture (Conference)
    FJOH Summer School 2010, 24.-26.08.2010, Aix-en-Provence, Frankreich
  • Contribution to proceedings
    Analysis of Design Basis Accidents, 24.-26.08.2010, Aix-en Provence, Frankreich

Publ.-Id: 14455

Experiments and numerical simulations of horizontal two-phase flow regimes using an interfacial area density model

Höhne, T.; Vallee, C.

Stratified two-phase flow regimes can occur in the main cooling lines of Pressurized Water Reactors, Chemical plants and Oil pipelines. A relevant problem occurring is the development of wavy stratified flows, which can lead to slug generation. In the last decade, stratified flows have increasingly been modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. Recent improvements of the multiphase flow modelling in the ANSYS CFX code, now make it possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, a high spatial and temporal resolution of measurement data are required. For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built. The channel allows in particular the study of air/water slug flow under atmospheric pressure. Parallel to the experiments, CFD calculations were carried out. The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model based on the implemented mixture model was introduced, which allows the detection of the morphological form of the two-phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result, this model can distinguish between bubbles, droplets and the free surface using the local value of the volume fraction of the liquid phase. The behaviour of slug generation and propagation was qualitatively reproduced by the simulation, while local deviations require a continuation of the work.


  • Contribution to proceedings
    ANSYS Conference & 28. CADFEM Users´ Meeting 2010, 03.-05.11.2010, Aachen, Deutschland
  • Invited lecture (Conferences)
    ANSYS Conference & 28. CADFEM Users´ Meeting 2010, 03.-05.11.2010, Aachen, Deutschland
  • The Journal of Computational Multiphase Flows 2(2010)3, 131-143

Publ.-Id: 14454

Thermodynamical limits of diluted (magnetic) semiconductors

Bürger, D.; Seeger, M.; Zhou, S.; Skorupa, W.; Helm, M.; Schmidt, H.

The incorporation of transition metal dopants in semiconductors above their solubility limit is the main challenge for the fabrication of diluted magnetic semiconductors. Dietl et al. have predicted the Curie temperature of different p-type conducting semiconductors alloyed with 5 at. % Mn [1]. This work motivated experimental efforts focused on the fabrication of highly diluted magnetic semiconductors. Unfortunately, such highly diluted magnetic semiconductors are metastable alloys and try to reach their thermodynamical equilibrium by the diffusion of the incorporated magnetic dopants leading to spinodal decomposition and secondary phase formation. There exist classical models which describe the kinetics of phase transitions and secondary phase formation for large clusters consisting of 100, 1000 or more atoms. However, electronic properties like carrier concentration strongly depend on the fraction of unclustered dopant atoms. Especially, in diluted magnetic semiconductors the formation of such clusters has to be prevented and growth techniques far from thermodynamical equilibrium are necessary.
Besides the LT-MBE process, the magnetic dopant implantation followed by pulsed laser annealing (PLA) appears to be a promising route for the fabrication of ferromagnetic semiconductors. The fast temperature quenching during PLA suppresses the diffusion of magnetic dopant atoms, i.e. diffusion via random hopping of these dopants is frozen and metastable diluted magnetic semiconductors are formed.
In this contribution we present the results from combined random-walk simulations and heat-flow calculations to describe the initial cluster formation for different magnetic semiconductors being characterized by a large variation of diffusion coefficients of the magnetic dopants. Under the assumption that the de-clustering probability of neighbouring dopants is lower than the clustering probability, we can explain the successful fabrication of GaAs:Mn and the impossibility to fabricate diluted ferromagnetic Si:Mn with LT-MBE or Mn implantation followed by PLA. Especially, our modelling approach can be used to estimate first clustering events during the re-crystallization after PLA. Within this picture, we conclude that for the preparation of diluted ferromagnetic semiconductors the basic diffusion parameters and the room temperature solubility of the magnetic dopants are reasonable parameters to estimate the chance for a successful preparation of different kinds of diluted systems.
[1] T. Dietl et al. Science 287 1019 (2000)

Keywords: ferromagnetic semiconductors; pulsed laser annealing; metastable; manganese

  • Poster
    30th International Conference on the Physics of Semiconductors (ICPS 2010), 25.-30.07.2010, Seoul, Südkorea

Publ.-Id: 14453

Characterization of mesoporous ZnO:SiO2 films obtained by the sol-gel method

Martins, R. M. S.; Musat, V.; Mücklich, A.; Franco, N.; Fortunato, E.

ZnO:SiO2 films are intensively investigated for optical and electronic applications. Additionally, porous ZnO:SiO2 films are of great interest as catalyst and gas-sensing materials. The sol–gel method is an efficient and low-cost process for the deposition of meso- and microporous silica-based films. The present paper studies the effect of the withdrawal speed on the microstructure and optical properties of mesoporous ZnO:SiO2 films obtained by the sol–gel method. The morphology of the films was investigated by atomic force microscopy and the overall structure was studied by X-ray diffraction. The structure and size of the zinc oxide nanoparticles embedded in the silica matrix were investigated in more detail by transmission electron microscopy. These techniques showed ZnO:SiO2 films with crack-free mesoporous morphology and highly efficient embedding of ZnO nanoparticles with (100) preferred orientation. Furthermore, the optical transmittance (in the visible and near infrared regions) and the optical band gap value were observed to vary with withdrawal speed. It is shown that ZnO:SiO2 nanocomposites films which possess ZnO particles exhibiting a (100) orientation, with possible special applications in non-linear optics, could be prepared by the low-temperature crystallization sol–gel method.

Keywords: sol–gel; Zinc oxide; nanoparticles; silica matrix; thin films; mesoporous films; optical and electrical properties; X-ray diffraction; atomic force microscopy

Publ.-Id: 14450

3D QSAR study, synthesis and in vitro evaluation of (+)-5-FBVM as potential PET radioligand for the Vesicular AcetylCholine Transporter (VAChT)

Kovac, M.; Mavel, S.; Deuther-Conrad, W.; Méheux, N.; Glöckner, J.; Wenzel, B.; Anderluh, M.; Brust, P.; Guilloteau, D.; Emond, P.

Located in presynaptic cholinergic nerve terminals, the vesicular acetylcholine transporter (VAChT) represents a potential target for quantitative visualization of early degeneration of cholinergic neurons in Alzheimer´s disease using PET. Benzovesamicol derivatives are proposed as radioligands for this purpose. We report QSAR studies of vesamicol and benzovesamicol derivatives taking into account the stereoselectivity of the VAChT binding site. Use of different data sets and different models in this study revealed that both enantiomers of 5-fluoro-3-(4-phenyl-piperidin-1-yl)-1,2,3,4-tetrahydro-naphthalen-2-ol (5-FBVM) are promising candidates, with predicted VAChT affinities between 6.1 and 0.05 nM. The synthesis of enantiopure (R,R)- and (S,S)-5-FBVM and their corresponding triazene precursors for future radiofluorination is reported. Both enantiomers exhibited high in vitro affinity for VAChT [(+)-5-FBVM: Ki = 6.95 nM and (-)-5-FBVM: Ki = 3.68 nM] and were selective for s2 receptors (~70-fold), only (+)-5-FBVM is selective for s1 receptors (~5-fold). These initial results suggest that (+)-(S,S)-5-FBVM warrants further investigation as a potential radioligand for in vivo PET imaging of cholinergic nerve terminals.

Keywords: Benzovesamicol derivative; VAChT; triazene; fluoro-dediazoniation, 3D QSAR

Publ.-Id: 14449

Actinide Interactions with Bacteria

Moll, H.; Bernhard, G.

Microbes are widely distributed in nature also under harsh conditions (e.g., high salinity; low permeability; high and low temperatures). They can strongly influence the migration of hazardous actinides in the environment once they have been released. This is demonstrated by an increased interest in studies exploring the interaction processes involving actinides and bacteria during the last years. However, worldwide only little detailed information is available about the biodiversity and microbial influences on radionuclide migration under the conditions of a deep nuclear repository.
The presentation covers the broad topic of actinide interactions with bacteria. A short overview about the determination of the microbial diversity giving the dominant bacterial strains will be given. In more detail, the manifold interaction process of bacteria with actinides will be highlighted based on selected examples.
With this presentation we want to point out the importance of actinide-microbe interactions for the disposal of nuclear waste.

Keywords: microbes; actinides; nuclear waste disposal

  • Lecture (Conference)
    Actinide and Brine Chemistry in a Salt-Based Repository (ABC-SALT) International Workshop, 15.-17.09.2010, Carlsbad, New Mexico, USA

Publ.-Id: 14448

Terahertz nonlinear optics using intraexcitonic quantum well transitions: sideband generation and AC Stark splitting

Wagner, M.; Schneider, H.; Stehr, D.; Winnerl, S.; Andrews, A. M.; Schartner, S.; Strasser, G.; Helm, M.

Intense THz electric fields coupling to intraband excitations can modify the interband absorption of semiconductors. A classical nonlinear mixing process is the sideband generation, where a ps NIR laser beam is mixed with the THz beam to generate sidebands at ωNIR ± n × ωTHz (integer n). In an undoped GaAs/AlGaAs multi quantum well film (substrate etched away) we observe several even-order sidebands using an all-normal-incidence geometry for the NIR and THz laser pulses [1]. Varying THz and NIR frequencies, we identify several resonances, where the intraexciton 1s-2p transition (at ~9 meV) makes the strongest contribution. Fig. 1(a) shows a typical NIR transmission spectrum with the NIR fundamental at the hh(1s) state and the resulting even-order sidebands.
In a second experiment we monitor the sample’s broadband transmission under THz pumping. THz light can couple and “dress” two resonant states, giving rise to the Autler-Townes or AC Stark effect [2, 3]. Fig. 1(b) shows the measured transmission spectra without (dashed line) and with (solid line) THz light at a THz peak intensity of 220 kW/cm² for THz pumping above (14 meV), near (10.5 meV) and below (6.1 meV) resonance. Near resonance (10.5 meV) we observe a distinct line splitting (see arrows), which represents the first clear evidence of the Autler-Townes effect in an intraexcitonic transition. Above and below resonance, low- and high-energy shoulders, respectively, are observed (see arrows). We discuss our findings on the basis of a simple two-level model that describes the situation surprisingly well near resonance up to a THz field strength of 10 kV/cm, corresponding to a Rabi energy of 0.6 times the 1s-2p transition energy. This is already well beyond the rotating-wave approximation of our model. Observed deviations would have to be addressed within a full many-body theory dealing with the complete set of excitonic states as well as with the possibility of exciton field ionization. Note that for the above parameters the ponderomotive energy is 3 meV, comparable to the exciton transition/ionization energy and the Rabi energy, an extremely non-perturbative regime with a Keldysh parameter near unity.

[1] M. Wagner et al., Appl. Phys. Lett. 94, 241105 (2009).
[2] S. H. Autler and C. H. Townes, Phys. Rev. 100, 703 (1955).
[3] S. G. Carter et al., Science 310, 651 (2005).

Keywords: AC Stark effect; Autler Townes effect; excitons; terahertz; sideband generation; nonlinear optics

  • Lecture (Conference)
    NOEKS 10 - 10th International workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors, 16.-19.08.2010, Paderborn, Deutschland

Publ.-Id: 14447

Terahertz induced intra-excitonic Autler-Townes effect in semiconductor quantum wells

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

When light is resonant with a material excitation the optical Stark or Autler-Townes (AT) effect couples the involved energy states and alters their energy, i.e. the states get “dressed” by the light-matter interaction. This fundamental quantum-mechanical feature of light-matter interaction was originally observed in atomic spectroscopy [1]. However, despite some theoretical work, it took a long time to the first observation of the AT effect for terahertz (THz) light coupled to hole [2] and electron [3] intersubband transitions in semiconductor quantum wells.
Here, we report clear evidence of the intra-excitonic AT effect. In our experimental work we study the NIR transmission at low temperature of a GaAs/AlGaAs multiple quantum well film (substrate etched away) exposed to strong picosecond THz pulses from the free-electron laser (FEL) at FZD. NIR spectra are recorded for a series of different THz frequencies and intensities. When tuning the THz photon energy in the range from 6 to 17 meV around the 1s-2p intra-excitonic transition energy that lies at ~9 meV, we observe a line splitting when pumping near resonance, and low- and high-energy shoulders, respectively, when pumping off resonance. This behavior is consistent with the AT effect. In Fig. 1 the measured absorption around the heavy-hole 1s exciton is displayed for different THz photon energies, showing the two dressed states and their expected anticrossing behavior. We discuss our experimental evidence of a coupling between the NIR “bright” 1s state and the NIR “dark” 2p state on the basis of a two-level model. Near resonance (10.5 meV) we find that our simplified model describes the situation surprisingly well up to a THz field strength of 10 kV/cm (I = 650 kW/cm2), corresponding to a Rabi energy of 0.6 times the 1s-2p transition energy. This is already well beyond the limits of the rotating-wave approximation. At the highest field strengths, the Rabi sidebands appear to start interacting with other exciton states. A full many-body theory would have to deal with the complete manifold of excitonic states as well as with the possibility of exciton field ionization. Note that for the above parameters in our case the ponderomotive energy is 3 meV and thus of the same order as the exciton transition/ionization energy (i.e. Keldysh parameter near unity) and the Rabi energy, an extremely non-trivial regime.
Using picosecond THz pulses we finally demonstrate that the induced absorption change occurs adiabatically only during the THz pulse. This ultrashort change that corresponds to an up to 20-fold increase in transmission can in principle be exploited in NIR modulators or switches.

[1] S. H. Autler and C. H. Townes, Phys. Rev. 100, 703 (1955).
[2] S. G. Carter et al., Science 310, 651 (2005).
[3] J. F. Dynes, M. D. Frogley, M. Beck, J. Faist, and C. C. Phillips, Phys. Rev. Lett. 94, 157403 (2005).

Keywords: AC Stark effect; Autler Townes effect; excitons; terahertz; sideband generation; nonlinear optics

  • Lecture (Conference)
    ICPS 2010, 30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul, Südkorea
  • Contribution to proceedings
    ICPS 2010, 30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul, Südkorea
    AIP Conference Proceeding 1399 (2011) 479-480; doi: 10.1063/1.3666462

Publ.-Id: 14446

Interaction of U(VI) with Schizophyllum commune

Günther, A.; Roßberg, A.; Raff, J.; Bernhard, G.

Biosorption processes of heavy metals and actinides like uranium by fungal cells play an important role in the mobilisation or immobilisation of these elements in nature. Different sorption experiments of U(VI) with Schizophyllum commune at different initial uranium concentrations and therewith connected varying initial uranium speciation showed high uranium sorption capacities in the pH range from 4 to 7. Formed uranium complexes were investigated by means of time-resolved laser-induced fluorescence spectroscopic measurements (TRLFS). The obtained spectra show clearly differences between the emissions properties of the uranium species on fungi and the dissolved uranium species in the initial mineral medium. While the oxidation state of uranium remained unchanged during the sorption process, the uranium speciation changes significantly. Extra- and/or intracellular phosphate groups are the predominant binding places of uranium due to our first spectroscopic results. X-ray absorption fine structure spectroscopic measurements (EXAFS) were performed for a structural characterisation of formed uranium-fungi species and a verification of the TRLFS results.

Keywords: Uranium(VI); fungi; TRLFS; EXAFS

  • Lecture (Conference)
    9th Symposium on remediation in Jena, "Jenaer Sanierungskolloquium", 04.-05.10.2010, Jena, BRD

Publ.-Id: 14445

Nanostructuring of BaF2 (111) surfaces by single slow highly charged ions

El-Said, A. S.; Heller, R.; Facsko, S.

The creation of surface nanostructures in BaF2 (111) surfaces was studied after irradiation with slow highly charged Xe ions from the Dresden-EBIT (Electron Beam Ion Trap). After irradiation, the crystals were investigated by scanning force microscopy (SFM). Using specific ion parameters, the topographic images show nanohillocks emerging from the surface. Additionally, we used the technique of selective chemical etching to reveal the lattice damage created by ion energy deposition below and above threshold needed for surface hillocks formation. The role of both potential and kinetic energy as well as a comparison with results for swift heavy ion irradiations of BaF2 single crystals are presented.

Keywords: highly charged ions; nanostructures

  • Nuclear Instruments and Methods in Physics Research B 269(2011), 901-904

Publ.-Id: 14444

Ion-Induced Nanoscale Ripple Patterns on Si Surfaces - Theory and Experiment

Keller, A.; Facsko, S.

Nanopatterning solid surfaces by low-energy ion bombardment has received considerable interest in the recent years. This interest was partially motivated by promising applications of nanopatterned substrates in the production of functional surfaces. Especially nanoscale ripple patterns on Si surfaces have attracted attention both from a fundamental and an application related point of view. This paper summarizes the theoretical basics of ion-induced pattern formation and compares the predictions of the various continuum models to experimental observations with special emphasis on the morphology development of Si surfaces during sub-keV ion sputtering.

Keywords: nanopatterning; ion sputtering; surface morphology; continuum theory

Publ.-Id: 14443

Vibrational spectroscopy of actinyl sorption complexes

Gückel, K.

Information about motivation and objectives as well as first results of the PhD thesis

  • Poster
    FZD PhD Seminar, 22.-24.09.2010, Krögis, Deutschland

Publ.-Id: 14442

Stofftransport bei Bergbaufolgeschäden und Altlastensanierung

Wolf, M.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    GEOforum Leipzig, 08.06.2010, Leipzig, Deutschland

Publ.-Id: 14441

Geochemische Wechselwirkungen bei Anwesenheit von Huminstoffen in Untertagedeponien

Fellmer, F.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    GEOforum 2010, 08.06.2010, Leipzig, Deutschland

Publ.-Id: 14439

Ultrafast three-dimensional X-ray computed tomography

Bieberle, M.; Hampel, U.; Barthel, F.; Menz, H.-J.; Mayer, H.-G.

X-ray computed tomography (CT) is nowadays a well established 2D and 3D visualization technique in medicine and non-destructive testing. An increasing number of scientific and engineering problems requires three-dimensional imaging capabilities, since structures of growing complexity are seldom seizable by a cross-section only. Because CT scanning requires sampling of radiographic projections from different viewing angles around an object, typically mechanical rotation mechanisms, either for the source-detector compound or the object, are employed by common CT systems. Hence, they are quite slow and their application in the study of fast processes, such as multiphase flows or live animals, was so far impossible.
Here we introduce a new ultrafast three-dimensional X-ray CT method based on electron beam scanning, which achieves imaging rates of 500 volume images per second. It represents an extension of a two-dimensional ultrafast electron beam CT modality presented earlier1. Although this 2D CT system reaches cross-sectional frame rates of up to 10,000 images per second, the new system is superior for the analysis of processes and moving objects, where structural changes occur in three dimensions. With an experimental study that is reported here we could demonstrate the capability of this new method to recover the structure of typical gas-solid and gas-liquid two-phase flows. Thus, ultrafast three-dimensional X-ray CT forms a practical alternative to high-speed videometry and furthermore provides non-superimposed density distributions even from opaque media.

Keywords: ultrafast; X-ray; 3D; computed tomography

Publ.-Id: 14437

Molecular and microscopical characterization of the algae mat from the „Gessenhalde“ (Ronneburg/Eastern Thuringia) and the proof of the retention of uranium

Zirnstein, I.; Krawczyk-Bärsch, E.; Arnold, T.; Röske, I.

Next to the test-field site of the former uranium leaching dump “Gessenhalde” (Ronneburg/Eastern Thuringia), which is part of a research program of the Friedrich-Schiller University, biofilms were sampled from a creek and investigated by PCR and cloning, light microscopy, CLSM and TEM/EDX. The molecular and microscopical characterization of the eukaryote diversity showed a wide spectrum of free living eukaryote microorganism, like the filamentary green algae Microspora and Klebsormidium as the dominant eukaryote. Flagellates, ciliates and rotaroria are present as representatives of the protozoa in minor amount. The water of the creek is characterized by a low pH of 3.3 – 3.9 and a uranium concentration, which ranges seasonally between 1x10-6 M/L and 6x10-6 M/L. Following up the question if the algae mat may have immobilized uranium by biosorption or bioaccumulation the filamentary algae were selected and investigated microscopically and spectroscopically by CLSM and TEM/EDX. Since the results did not provide any microscopic and spectroscopic evidence for the presence of uranium immobilization, the filamentary algae were cultured in rain water with a pH adjusted to 6,0. After the addition of uranium as UO2(ClO4)2 in the ecologically relevant concentration of 1x10-5 M/L the algae showed characteristic fluorescence spectra in the wavelength range of 480-560 nm, which is typical for uranium (VI). The results demonstrated that the actual in-situ geochemical conditions of the creek from the "Gessenhalde" inhibit the retention of uranium by the algae mat. The removal of uranium from the aqueous phase requires the cultivation of algae in a neutral media.

Keywords: biofilm; algae; uranium

  • Poster
    9. Sanierungskolloquium, 04.-05.10.2010, Jena, Deutschland

Publ.-Id: 14436

Interaction of Selected Actinides with Microorganisms Relevant to Nuclear Waste Disposal

Frost, L.; Moll, H.; Krawczyk-Bärsch, E.

The sorption behavior/ retardation of actinides (uranium) in deep geological formations like clay, granite or salt is determined by the constitution of the host rock material and the presence of bioligands and microbes. To which extent can bioligands and microbes lead to a mobilisation of the respective actinyl ion?
By presenting results of our current research categorical examples for the interaction of uranium(VI) with above mentioned interaction partners are given:
- Interaction with host rock material: the anaerobic sorption of U(VI) onto Opalinus Clay
- Interaction with bioligands: interaction of U(VI) with the model ligand benzoic acid investigated by UV-vis spectroscopy and cryo-TRLFS
- Interaction with microbes: interaction of U(VI) with the Äspö bacterium Pseudomonas fluorescens (HAADF-TEM measurements and uranium accumulation experiments)

Keywords: Uranium; Opalinus Clay; Pseudomonas fluorescens; UV-vis spectroscopy; cryo-TRLFS

  • Poster
    5th FZD Ph.D. Seminar, 22.-24.09.2010, Krögis, Deutschland

Publ.-Id: 14435

Analysis of the influence of different arrangements for ZrH moderator material on the performance of a SFR core

Merk, B.; Weiß, F. P.

The structure for the development of a fuel element design with reduced sodium void achieved by the use of the moderating material ZrH is investigated. In the study the sodium void effect, as well as the major feedback coefficients are analyzed. Besides the feedback coefficients, the influence on the operational parameters like neutron flux distribution, power distribution, and burnup distribution is investigated for the different possibilities of arranging the moderating material in the fuel element. Additionally, the fuel cycle parameters breeding and minor actinide production are analyzed. For a first evaluation of the behavior during transients the influence of temperature changes in the ZrH and the consequences of dissociation of the ZrH on the fuel element power are studied.

Keywords: Sodium void; fast reactor; zirconium hydride

Publ.-Id: 14434

Electromagnetic induction in non-uniform domains

Giesecke, A.; Stefani, F.; Gerbeth, G.

Numerical simulations of the electromagnetic induction equation are carried out applying a grid based finite volume method where insulating boundaries are treated by the boundary element method. A prescribed flow of liquid sodium provides the energy source for self-generation of a magnetic field and the influences of non-uniform material properties on the induction process are examined by means of internal assemblies and outer container walls with high conductivity or high permeability.

High permeability material even if localized in a small volume like the flow driving impellers in the French VKS dynamo experiment, essentially determines the field generation process (decrease of the effective critical magnetic Reynolds number and enforcing of internal boundary conditions on material interfaces). Permeability caused facilitation of dynamo action might be important as well for the helical flow in cooling circuits of fast breeders. Preliminary simulations for a model flow in and around soft-iron sub-assemblies (that comprise the nuclear fuel pins) show a reduction of the critical magnetic Reynolds number for the onset of dynamo action by a factor of 2.

The third examined configuration is motivated by an application of the contactless inductive flow tomography (CIFT) in a continuous casting model experiment. Consideration of the finite conductivity of the copper container walls results in a quantitative modification of the current distribution within the solid material. An enhanced current yields an amplified induced magnetic field outside of the container which must be considered in the reconstruction of the fluid velocity field.

Keywords: Dynamo; Conductivity; Permeability; Induction

  • Lecture (Conference)
    Workshop on Numerical Simulations of MHD flows, 18.-20.10.2010, Karlsruhe, Deutschland

Publ.-Id: 14433

Ein Modell zur Beschreibung der Kühlmittelvermischung und seine Anwendung auf die Analyse von Borverdünnungstransienten in Druckwasserreaktoren

Kliem, S.

Es wurde ein Modell zur realistischen Beschreibung der Kühlmittelvermischung innerhalb des Reaktordruckbehälters eines Druckwasserreaktors entwickelt und validiert. Dieses schnell rechnende Modell basiert auf dem Prinzip der linearen Superposition der Antwortfunktionen auf Dirac-Impuls-ähnliche Störungen der Kühlmittelparameter. Es wurde in den gekoppelten Programmkomplex DYN3D/ATHLET als Schnittstelle zwischen dem eindimensionalen Thermohydraulikprogramm ATHLET und dem dreidimensionalen neutronenkinetischen Kernmodell DYN3D eingebunden und simuliert in effizienter Weise die Vermischung des Kühlmittels innerhalb des RDB.
Für die Analyse von hypothetischen Borverdünnungsstörfallen wurde eine Methodik entwickelt, die auf dem neuen Modell zur Beschreibung der Kühlmittelvermischung basiert. Diese Methodik besteht aus einer Kombination von stationären und transienten Rechnungen, in denen die Vermischung der deborierten Pfropfen auf dem Weg zum Reaktorkern in realistischer Weise simuliert wird. Über die Variation der Größe des deborierten Kühlmittelpfropfens kann der gewünschte Grad an Konservativität für die Analysen vorgegeben werden.
Diese neue Methodik wurde erfolgreich auf zwei verschiedene Borverdünnungsstörfalle angewandt. Neben dem Start der ersten Hauptkühlmittelpumpe bei Vorhandensein eines deborierten Kühlmittelpfropfens im kalten Strang des Primärkreislaufes wurde ein Deborierungsstörfall im Nachkühlbetrieb betrachtet. In beiden Fällen zeigten die Ergebnisse der Parameterstudie für eine generische Kernkonfiguration, dass es selbst bei Annahme des maximal möglichen Pfropfenvolumens zwar zur Rekritikalität des abgeschalteten Reaktors aber nicht zu einer unzulässigen Erhöhung der Hüllrohrtemperatur kommt. Wesentliche Ursache dafür ist die Verwendung realistischer zeitabhängiger Verteilungen der Borkonzentration am Eintritt in jedes Brennelement.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-539 2010
    ISSN: 1437-322X


Publ.-Id: 14432

Aqueous curium(III) phosphate species characterized by time-resolved laser-induced fluorescence spectroscopy

Moll, H.; Brendler, V.; Bernhard, G.

The formation of aqueous Cm(III) phosphate complexes was studied at room temperature by time-resolved laser-induced fluorescence spectroscopy (TRLFS) in 0.1 M NaClO4 solutions. The experiments were perfomed at a fixed total Cm(III) concentration of 3x10-7 or 2x10-8 M by varying the phosphoric acid concentration (3x10-5 - 0.1 M) and the pH (1.4 - 6.0). The red shift of the excitation and emission spectra, as well as the increase of luminescence lifetimes clearly showed the influence of phosphate on the aqueous Cm(III) speciation. In acidic phosphate solutions ([H3PO4] < 0.1 M, pH 1.4 - 2.6) an increase in luminescence intensity was detected due to complexation with H2PO4 -. At [H3PO4] > 4x10-4 M and between pH 4.0 and 6.0 in general a decrease in luminescence intensity affiliates the complexation with HPO42-. Two Cm(III)-phosphate complexes could be identified from the emission data, CmH2PO4 2+ and CmHPO4+, having peak maxima at 599.6 and 600.8 nm, respectively. TRLFS in combination with ultra-filtration (1 kD) showed that the formation of CmHPO4+ is affiliated by the generation of Cm(III)-phosphate colloids especially at [H3PO4] > 0.002 M and pH > 5. Cm(III)-phosphate colloids formed at pH 5 and 6 are characterized by an emission maximum at 603.1 nm. Based on the factor analysis of the emission data the stability constants of the two complexes were calculated to be log ß121 = 20.23 ± 0.13 and log ß111 = 16.54 ± 0.80 at an ionic strength of 0.1 M (NaClO4).

Keywords: Curium(III); Phosphoric acid; Stability constant; Speciation; Complexation; TRLFS; Ultra-filtration

Publ.-Id: 14431

Test site Gessenwiese: Results in TRLFS investigations on surface water and pore waters, and preliminary results on plant saps concerning uranium speciation

Baumann, N.; Arnold, T.

Plants may take up uranium from contaminated sites and thus may represent a potential risk. To evaluate the risk of uranium being transferred from the environment into the human food chain knowledge concerning the uranium speciation is essential since reactivity and toxicity of uranium largely depend on its speciation.
Plants take up their nutrients from the soil in dissolved form and thus uranium may enter plants as dissolved species. To study this process the speciation of uranium in a uranium contaminated site, i.e. Gessenheap near Ronneburg in Saxony/Germany was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) in the aqueous phase, i.e. in surface water (drainage channel on the Gessenheap) and in pore water (approximately 0.5 – 1 m below surface of test site Gessenwiese). In both waters uranium sulfate species dominate the uranium speciation and clearly show that uranium sulfate species are in contact with plant components.
In a second step we determined the uranium concentration in the plants obtained from the test field Gessenheap by ICP-MS. For these analyses cell saps of birch leaves, of a birch boletus, and of compartments of butterbur (leaves, roots, and sprouts) were obtained by ultra centrifugation. The highest uranium concentration was found in sap samples from roots of butterbur with 39.3 ppb uranium (approximately 1.5 • 10-7 M uranium); in the sap samples of birch leaves 18.1 and 16.6 ppb uranium, respectively were detected. In all other sap samples the uranium contents were below 4 ppb uranium. The uranium content in the studied dried plant materials were less than 2.2 ppb, and dried birch leaves contains less than 0.1 ppb uranium.
The above listed uranium concentrations turned out to be too low to be successfully analyzed by TRLFS. In addition, we have to mention that plant sap may contain substances which quench the fluorescence signal of uranium (VI), e. g. some heavy metal ions or organic compounds. For future studies plant samples containing higher uranium concentrations are used for TRLFS investigations, possibly mosses or lichens.

Keywords: TRLFS; uranium speciation

  • Lecture (Conference)
    9th Symposium on remediation in Jena "Jenaer Sanierungskolloqium", 04.-05.10.2010, Jena, Germany
  • Contribution to proceedings
    9th Symposium on remediation in Jena "Jenaer Sanierungskolloqium", 04.-05.10.2010, Jena, Germany

Publ.-Id: 14430

Terahertz activated luminescence of trapped carriers in InGaAs/GaAs quantum dots

Bhattacharyya, J.; Wagner, M.; Helm, M.; Hopkinson, M.; Wilson, L. R.; Schneider, H.

Optical properties and interdot transfer dynamics of trapped carriers in InGaAs quantum dots (QDs) are investigated. Time resolved photoluminescence (PL) was measured for time-delayed interband and intraband excitations. Terahertz activated luminescence (TAL) from trapped carriers having lifetimes of ~250 ns at 8 K, was observed. Spectral shift of the TAL with respect to the PL showed the trionic nature of the PL in the n-doped QDs. With increasing terahertz excitation intensity, the TAL increased and reached saturation. The activation energy associated with the trapped carrier decay was quite close to the intersublevel transition energy (~20 meV) indicating trapping in the QDs.

Keywords: Quantum dots; Photoluminescence quenching; trapped carriers

Publ.-Id: 14427

Development of the coupled 3D neutron kinetics/thermal-hydraulics code DYN3D-HTR for the simulation of transients in block-type HTGR

Rohde, U.; Baier, S.; Duerigen, S.; Fridman, E.; Merk, B.; Weiss, F.-P.

At the Forschungszentrum Dresden-Rossendorf (FZD), the Light Water Reactor (LWR) dynamics code DYN3D is extended and adopted for the application to block-type High temperature gas-cooled reactor (HTGR). DYN3D is a two-group diffusion code for 3D steady-state and transient core calculations based on nodal expansion methods. In addition to the neutron kinetics, it disposes of a thermal-hydraulics model for flow in parallel coolant channels. Macroscopic cross section data libraries precalculated with variation of burn-up, reactor poisons concentrations and thermal-hydraulic feedback parameters are linked to the code. Recently, a multi-group version of the code was developed.
In this paper, we give an overview of the latest developments of DYN3D concerning block-type HTGR.
The SP3 transport approximation is implemented into the multi-group DYN3D code to take anisotropy of the neutron flux and heterogeneity of the core more precisely into account. The SP3 method previously implemented into DYN3D for square fuel element geometry of LWR is being extended for hexagonal geometry of the graphite blocks, where the hexagons are subdivided into triangular nodes to be able to perform a systematic mesh refinement.
The main challenge in cross section generation for the HTGR core calculations is the treatment of the so-called “double heterogeneity”. The Reactivity equivalent Physical Transformation (RPT) approach is applied in order to eliminate the double-heterogeneity of HTGR fuel elements in HELIOS calculations. The full core analysis of the reference simplified HTGR core is performed with DYN3D using macroscopic nodal cross sections provided by HELIOS. The DYN3D results are verified against full core Monte Carlo simulations.
A 3D heat conduction module coupled with a channel-type coolant flow model is implemented to take into account the temperature reactivity feedback to neutronics physically correctly. It is shown that there is significant redistribution of the produced heat by heat conduction between the graphite blocks.

Keywords: high temperature reactor; reactor dynamics; computer code; double heterogeneity; SP3 transport approximation; heat conduction; temperature reactivity feedback; computer code

  • Lecture (Conference)
    5th Topical Meeting in High Temperature Reactor Technology, 18.-20.10.2010, Prague, Czech Republic
  • Contribution to proceedings
    5th Topical Meeting on High Temperature Reactor Technology, 18.-20.10.2010, Pargue, Czech Republic
    Conference Website, Paper #036

Publ.-Id: 14426

Very large DPSS lasers are coming

Toepfer, T.; Neukum, J.; Hein, J.; Siebold, M.

New alcaline-earth fluoride laser materials and ever-improving diode-laser module technology are bringing very high-energy, moderate-to high-repetition-rate DPSS lasers for research closer to reality.

Keywords: High-energy; diode-pumped; solid-state lasers

  • Open Access Logo Laser Focus World 46(2010)10, 64-67

Publ.-Id: 14425

Excitation wavelength dependence of phase matched terahertz emission from a GaAs slab

Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.

We report on phase matched THz emission from GaAs using the anomalous dispersion introduced by optical phonon absorption at the reststrahlenband in GaAs. For this system tunability of the emitted THz frequencies by changing the near infrared excitation wavelength is predicted. We investigate this phenomenon for an oversized double metallized GaAs waveguide. A shift in the THz spectra is observed when the near-infrared wavelength is varied. Enhanced emission is found when phase matching is achieved at 1.4 µm.

Keywords: Terahertz; far infrared; ultrafst nonlinear optics

  • Open Access Logo Optics Express 18(2010)19, 19574-91580

Publ.-Id: 14424

Longitudinal Fields in Focused Radially Polarized Terahertz Beams

Winnerl, S.; Hubrich, R.; Peter, F.; Schneider, H.; Helm, M.

We study the spatial and temporal structure of focused THz beams of radial polarization. Strong longitudinal field components localized at the axis of propagation are observed. The phase of the longitudinal field components is shifted by pi/2 with respect to the transverse field components.

Keywords: Terhertz; vector beams

  • Invited lecture (Conferences)
    35th International Conference on Infrared, Millimeter and Terahertz Waves, 05.-10.09.2010, Rome, Italy
  • Contribution to proceedings
    35th International Conference on Infrared, Millimeter and Terahertz Waves, 05.-10.09.2010, Rome, Italy
    Conference Digest of the 35th International Conference on Infrared, Millimeter and Terahertz Waves

Publ.-Id: 14423

Thermal Emittance Measurement of the Cs2Te Photocathode in FZD Superconducting RF Gun, WEPB22

Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.

The thermal emittance of the photocathode is an interesting physical property for the photoinjector, because it decides the minimum emittance the photoinjector can finally achieve. In this paper we will report the latest results of the thermal emittance of the Cs2Te photocathode in FZD Superconducting RF gun. The measurement is performed with solenoid scan method with very low bunch charge and relative large laser spot on cathode, in order to reduce the space charge effect as much as possible, and meanwhile to eliminate the wake fields and the effect from beam halos

  • Poster
    FEL 2010 Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    FEL 2010 Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010

Publ.-Id: 14422

QCD sum rules for D mesons in dense and hot nuclear matter

Hilger, T.; Schulze, R.; Kämpfer, B.

Open charm mesons (pseudo-scalar and scalar as well as axial-vector and vector) propagating or resting in nuclear matter display an enhanced sensitivity to the chiral condensate. This offers new prospects for seeking signals of chiral restoration, in particular in pA and \bar{p}A reactions as envisaged in first-round experiments by the CBM and PANDA collaborations at FAIR. Weinberg-type sum rules for charming chiral partners are presented, and the distinct in-medium modifications of open-charm mesons are discussed. We also address the gluon condensates near Tc and their impact on QCD sum rules.

Publ.-Id: 14420

[18F]NS10743: Characterisation Of A Selective a7 Nicotinic Acetylcholine Receptor (a7 nAChR) Radioligand In Pig Brain By PET

Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Funke, U.; Østergaard Nielsen, E.; Brunicardi Timmermann, D.; Steinbach, J.; Peters, D.; Brust, P.

Introduction: Alterations of a7 nAChR have been observed in schizophrenia, brain trauma and neurodegenerative diseases. For PET imaging of a7 nAChR [18F]NS10743 has been successfully developed evaluated in mice by tissue distribution and specificity studies. Here we report on baseline and blocking PET studies with [18F]NS10743 in pig brain.
Methods: [18F]NS10743 was synthesized with high specific activity (>150 GBq/μmol) and radiochemical purity (>99%). Dynamic PET scanning was performed in anaesthetized female piglets (13-15 kg), intravenously injected with ~ 330 MBq [18F]NS10743 (total mass ~ 472 ng) for 120 min. Three animals additionally received 3 mg/kg of the a7 nAChR partial antagonist NS6740 at 10 min pre-tracer injection followed by a continuous infusion (1 mg/kg/h). Plasma samples were taken and metabolite-corrected input functions were estimated. Individual regions of interest were defined using an MRI-based template of pig brain. SUV and distribution volume (VT = K1/k2) were estimated. The ratio of specifically bound radioligand and non-displaceable radioligand in brain tissue was calculated from the VT values by BPND = (VT region - VT reference)/VT reference.
Results: [18F]NS10743 readily passed the blood-brain barrier and the uptake of radioactivity peaked with SUV = 2.23 ± 0.71 at 8 min in the baseline scan while in NS6740-blocking studies the radioactivity levels peaked significantly earlier (SUV = 3.02 ± 1.28 at 5 min) and decreased faster. At the end of study (between 90 and 120 min p.i.) SUV was significantly decreased by NS6740 in allinvestigated brain regions except olfactory bulb, which was chosen as reference region for calculation of BPND. At baseline, a VT value of 6.07 ± 1.54 was estimated for the whole brain with the highest radiotracer accumulation in the temporal, parietal, and occipital lobe, thalamus, striatum, and middle cortex (VT = 7.27 ± 1.95 – 7.10 ± 1.58). Intermediate binding was observed in hippocampus, colliculi, midbrain, frontal lobe, and ventral cortex (VT = 6.76 ± 1.71 – 6.09 ± 1.05), and lowest values were assessed in the cerebellum, pons, and olfactory bulb (VT = 5.71 ± 1.18 – 4.11 ± 0.96). Baseline BPND values for high (temporal lobe), median (hippocampus) and low specific binding (cerebellum) were 0.76 ± 0.07, 0.54 ± 0.08, and 0.39 ± 0.08, respectively. NS6740 significantly reduced the binding potential BPND in regions with high [18F]NS10743 binding (temporal lobe: -29 %, p = 0.01; midbrain: -35 %, p = 0.02) while the decrease in regions with low binding was not significant (cerebellum: -16 %, p = 0.2).
Conclusion: These data make [18F]NS10743 a reasonable candidate for further development of in vivo a7 nAChR imaging by PET. The challenge to improve the binding potential of [18F]NS10743, limited mainly by the low density of a7 nAChR expression in the brain and reflected by rather small regional differences in baseline uptake of [18F]NS10743, will be met by further modifications of the NS10743 core structure intended to increase the target affinity of the tracer compound.
the target affinity of the tracer compound.

Keywords: [18F]NS10743; a7 nAChR; PET

  • Lecture (Conference)
    NRM2010 (Neuroreceptor Mapping Congress), 22.-24.07.2010, Glasgow, Großbritannien
  • Abstract in refereed journal
    NeuroImage 52(2010)1
    DOI: 10.1016/j.neuroimage.2010.04.230

Publ.-Id: 14418

Extension of CFD codes - application to two-phase flow safety problems, phase 2

Bestion, D.; Anglart, H.; Mahaffy, J.; Lucas, D.; Song, C. H.; Scheuerer, M.; Zigh, G.; Andreani, M.; Kasahara, F.; Heitsch, M.; Komen, E.; Moretti, F.; Morii, T.; Mühlbauer, P.; Smith, B. L.; Watanabe, T.

This document is an extension of the NEA/SEN/SIN/AMA(2006)2 report produced by the Writing Group 3 on the extension of CFD to two-phase flow safety problems, which was formed following the recommendations made at the “Exploratory Meeting of Experts to Define an Action Plan on the Application of Computational Fluid Dynamics (CFD) Codes to Nuclear Reactor Safety Problems” held in Aix-en-Provence, in May 2002. Extension of CFD codes to two-phase flow is a chance for safety investigations, by giving some access to smaller scale flow processes which were not seen by present tools. Using such tools as part of a safety demonstration may bring a better understanding of physical situations, more confidence in the results, and an estimation of safety margins. The increasing computer performance allows a more extensive use of 3D modelling of two-phase Thermalhydraulics with finer nodalization. However, models are not as mature as in single phase flows and a lot of work has still to be done on the physical modelling and numerical schemes in such two-phase CFD tools. The Writing Group listed and classified the NRS problems where extension of CFD to two-phase flow may bring real benefit and also classified different modelling approaches. First ideas were reported about the specification and analysis of needs in terms of validation and verification.

Keywords: CFD; two phase flow; nuclear safety research

  • Other report
    OECD: Report NEA/CSNI/R(2010)2, 2010
    137 Seiten

Publ.-Id: 14416

Studies on the patterning effect of copper deposits in magnetic gradient fields

Tschulik, K.; Sueptitz, R.; Koza, J.; Uhlemann, M.; Mutschke, G.; Weier, T.; Gebert, A.; Schultz, L.

Electrochemical Cu deposition was performed from electrolytes containing 0.1 M to 1 M CuSO4 in a well-defined magnetic gradient field. Patterned deposits resulted in all cases showing a strong correlation to this gradient field. It was observed that with increasing Cu2+ concentration the structuring effect decreases in terms of differences in topography and morphology. An explanation of this effect is presented based on local convection induced by the magnetic field gradient force which is dependent on the concentration gradient established during the deposition. Superimposed effects of Lorentz force driven convection were observed for high Cu2+ concentrations, and their influence on the deposition process is discussed.

Keywords: magnetic gradient field; deposit patterns; Lorentz force

Publ.-Id: 14415

The EPOS system at the radiation source ELBE at For-schungszentrum Dresden-Rossendorf

Krause-Rehberg, R.; Butterling, M.; Jungmann, M.; Krille, A.; Anwand, W.; Brauer, G.; Rogov, A.; Noack, K.; Cowan, T.; Wagner, A.

The heart of the radiation source ELBE at the Forschungszentrum Dresden-Rossendorf (FZD) is a 40-MeV LINAC with an average current of 1 mA. Due to its superconducting technology, the time structure is different from conventional LINACs. Electron bunches as short as 2 ps with a 26 MHz repetition rate can be used in continuous operation (cw) mode. This is an ideal host for an intense positron source. After organizing SLOPOS-9 in Rossendorf, it was decided to add EPOS (ELBE Positron Source) to the existing experiments at ELBE. EPOS consists of two LINAC-based setups, Gamma-induced Positron Spectroscopy (GiPS) and Monoenergetic Positron Spectroscopy (MePS). The GiPS setup, where positrons are produced inside the whole sample volume by pair production using a pulsed gamma beam, is unique so far. Here, bulky samples such as coarse powders, dispersions, but also liquids or whole devices of non-destructive testing can be investigated by all positron techniques important for materials science (lifetime spectroscopy, age-momentum correlation, and coincidence Doppler broadening spectroscopy). The same techniques will be applied at the MePS setup, where slow, mono-energetic positrons will be generated by moderation to study near-surface layers. This system is still under construction. The EPOS system will be completed by two conventional setups, a continuous slow positron beam and a positron lifetime/ Doppler spectrometer, both operated by 22Na sources.

Keywords: Positron spectroscopy; Positron Annihilation; Monoenergetic Positrons; Gamma-induced Positrons; LINAC-based

  • Contribution to proceedings
    Proceedings of the International School of Physics "E. Fermi" - Physics with many positrons, 07.-17.07.2009, Varenna, Italia
    The EPOS system at the radiation source ELBE at For-schungszentrum Dresden-Rossendorf, Amsterdam: IOS Press Amsterdam

Publ.-Id: 14413

Pu recycling in a full Th-MOX PWR core: Part I - steady state analysis

Fridman, E.; Kliem, S.

Current practice of Pu recycling in existing LWRs in the form of U-Pu mixed oxide fuel (MOX) is not efficient due to continuous Pu production from U-238. The use of Th-Pu mixed oxide (TOX) fuel will considerably improve Pu consumption rates because virtually no new Pu is generated from thorium. In this study, the feasibility of Pu recycling in a typical pressurized water reactor (PWR) fully loaded with TOX fuel is investigated.
Detailed 3-dimensional 100% TOX and 100% MOX PWR core designs are developed. The full MOX core is considered for comparison purposes. The design stages included determination of Pu loading required to achieve 18-month fuel cycle assuming three-batch fuel management scheme, selection of poison materials, development of the core loading pattern, optimization of burnable poison loadings, evaluation of critical boron concentration requirements, estimation of reactivity coefficients, core kinetic parameters, and shutdown margin.
The performance of the MOX and TOX cores under steady-state condition and during selected reactivity initiated accidents (RIA) is compared with that of the actual uranium oxide (UOX) PWR core.
Part I of this paper describes the full TOX and MOX PWR core designs and reports the results of steady state analysis. The TOX core requires a slightly higher initial Pu loading than the MOX core to achieve the target fuel cycle length. However, the TOX core exhibit superior Pu incineration capabilities.
The significantly degraded worth of control materials in Pu cores is partially addressed by the use of enriched soluble boron and B4C as a control rod absorbing material. Wet annular burnable absorber (WABA) rods are used to flatten radial power distribution. The temperature reactivity coefficients of the TOX core were found to be always negative. The TOX core has a slightly reduced, as compared to UOX core, but still sufficient shutdown margin.
In the TOX core βeff is smaller by about a factor of two in comparison to the UOX core and even lower than that of the MOX core. The combination of small βeff and reduce control materials worth may potentially deteriorate the performance under RIA conditions and requires an additional examination. The behavior of the considered cores during the most limiting RIAs, such as rod ejection, main steam line break, and boron dilution, is further investigated and reported in Part II of the paper.

Keywords: Pu recycling; PWR; Thorium; MOX; three-dimensional core analysis

Publ.-Id: 14412

The superconducting RF photoelectron source for the ELBE accelerator at Rossendorf

Teichert, J.

Most of the proposed electron accelerator projects for future FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. The ideal candidate for it is the superconducting RF photogun (SRF gun) which can be easily operated in CW like a DC photogun and may reach the beam quality of a normal conducting RF photogun. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high-average power into the gun and finally the risk of beam excitation of higher order cavity modes. At the FZ Dresden-Rossendorf a SRF gun has been developed and installed at the ELBE superconducting linac. The SRF gun is designed for an average current of 1 mA and an maximum electron energy of 9 MeV. The 1.3 GHz cavity consists of three full cells with TESLA geometry, a specially designed half-cell where the photocathode is placed. The photocathode with a Cs2Te photoemission layer is normal-conducting and cooled by liquid nitrogen. In the talk an overview of the technical concept, the RF properties, the photo cathode development, and beam parameter measurements will be given.

  • Lecture (others)
    ANKA Seminar, 08.02.2010, Karlsruhe, Deutschland

Publ.-Id: 14411

A new hexanuclear rhenium cluster complex with six terminal acetate ligands: Synthesis, structure, and properties of K4[Re6S8(CH3COO)6]·8H2O

Brylev, K. A.; Mironov, Y. V.; Fedorov, V. E.; Kim, S.-J.; Pietzsch, H.-J.; Stephan, H.; Ito, A.; Kitamura, N.

A room-temperature reaction between [Re6S8(OH)6]4− and acetic acid in an aqueous solution resulted in the substitution of all terminal hydroxo groups by acetate ligands, affording a new hexanuclear anionic rhenium cluster complex [Re6S8(CH3COO)6]4−. The complex was isolated as a potassium salt with the composition of K4[Re6S8(CH3COO)6]·8H2O (1) and characterized by X-ray single-crystal diffraction and elemental analyses, IR, 1H NMR, UV–Vis, and luminescence spectroscopies.

Keywords: Synthesis; Cluster compounds; Rhenium; Carboxylate ligands; Luminescence


Publ.-Id: 14409

Traveling-wave Thomson scattering and optical undulators for high-yield EUV and X-ray sources

Debus, A. D.; Bussmann, M.; Siebold, M.; Jochmann, A.; Schramm, U.; Cowan, T. E.; Sauerbrey, R.

We present a novel high-yield Thomson scattering geometry that takes advantage of compact electron bunches, as available in advanced, low-emittance linear accelerators or laser wakefield accelerators. In order to avoid the restrictions on the X-ray photon yield imposed by the Rayleigh limit, we use ultrashort, pulse-front tilted laser pulses in a side-scattering geometry. Such a traveling-wave setup allows an overlap of electron and laser beams, even after propagating over distances much longer than the Rayleigh length. Experimental designs are discussed and optimized for different scattering angles. Specifically, to minimize group delay dispersion at large scattering angles > 10° degrees, we propose the use of varied-line spacing (VLS) gratings for spatio-temporal laser pulse shaping. Compared to head-on (180° degrees) Thomson scattering, interaction lengths are in the centimeter to meter range and photon numbers for ultrashort X-ray pulses can increase by several orders of magnitudes.

Keywords: Thomson Scattering; Traveling-Wave Thomson Scattering; Xray; EUV; VLS gratings

  • Applied Physics B 100(2010)1, 61-76
    DOI: 10.1007/s00340-010-3990-1
  • Lecture (others)
    WIP Seminar, 21.05.2010, FZD, Deutschland

Publ.-Id: 14408

Novel 99mTc '4 + 1' peptide conjugates: Tuning the biodistribution by variation of coligands

Künstler, J.-U.; Seidel, G.; Bergmann, R.; Gniazdowska, E.; Walther, M.; Schiller, E.; Decristoforo, C.; Stephan, H.; Haubner, R.; Steinbach, J.; Pietzsch, H.-J.

A sophisticated coligand strategy is presented for peptide-derived radioconjugates based on 99mTc '4 + 1' mixed-ligand complexes. The new pharmacologically active coligands are assessed for 99mTc-labeling of the RGD-peptide cyclo(Arg-Gly-Asp-D-Tyr-Lys) which is an established vehicle to target avß3 integrins playing a crucial part in tumor pathogenesis.
Complexes of the general formula [99mTc(NS3R)X] were synthesized and evaluated, in which Tc(III) is coordinated by NS3R, a derivative of the tetradentate chelator 2,2´,2´´-nitrilotriethanethiol (NS3), and by X, a monodentate binding isocyanide bearing the biomolecule. The novel tetradentate chelators (NS3R = NS3crown, NS3en, NS3(COOH)3) constitute NS3 with a crown ether, an amine or a tricarboxylic acid as pharmacological modifiers. The isocyanides (X = L2-RGD, L2-Lys) contained the linker isocyanobutanoic acid (L2) coupled to N6-Lys of the RGD-peptide and additionally to a single Lys.
The lipophilicity (distribution coefficient log DO/W, pH = 7.4) of the RGD-containing radiotracers decreased in the order of the coligands NS3crown (-1.7 +/- 0.1), NS3en (-2.7 +/- 0.1) and NS3(COOH)3 (-3.3 +/- 0.1). In the same order of the coligands, the biodistribution of the series [99mTc(NS3R)(L2-RGD)] in normal rats showed a decrease of hepatobiliary and an increase of urinary excretion.
The ratio of specifically to unspecifically uptaken activity (sum of surface bound and internalized activity) in avß3 integrin-expressing M21 cells was in the range of approximately 4-5 and comparable for all [99mTc(NS3R)(L2-RGD)] tracers. The biodistribution of [99mTc(NS3en)(L2-RGD)] in v/v mice bearing M21 and M21L (control) tumor xenografts exhibited a specific tumor uptake with a low target-background ratio.
The metabolic stability of the [99mTc(NS3R)(L2-RGD)] tracers in normal rats was high, since 75-87% of the radioactivity in the plasma extract was assigned to the injected radiotracers 60 min after intravenous
application in a rat. The hypothetical metabolites [99mTc(NS3R)(L2-Lys)] were not found.
These results demonstrate a considerable improvement of in vivo properties of 99mTc '4 + 1' peptide conjugates and open up the possibility of applying the labeling approach for further radiodiagnostic peptides.

Keywords: Technetium; '4 + 1' Mixed-ligand complex; Peptide; RGD

Publ.-Id: 14407

Advanced Materials Research - Biennial Scientific Report 2007-2008 / Volume 1

Bohnet, C.; Bartho, A.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-507 2010
    ISSN: 1437-322X


Publ.-Id: 14405

Cancer Research - Biennial Scientific Report 2007-2008 / Volume 2

Bohnet, C.; Bartho, A.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-508 2010
    ISSN: 1437-322X


Publ.-Id: 14404

Nuclear Safety Research - Biennial Scientific Report 2007-2008 / Volume 3

Bohnet, C.; Bartho, A.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-509 2010
    ISSN: 1437-322X


Publ.-Id: 14403

The sorption of uranium(VI) and neptunium(V) onto surfaces of selected metal oxides and alumosilicates studied by in situ vibrational spectroscopy

Müller, K.

The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces.
Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral – water interfaces of oxides of titania, alumina, silica, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
From the infrared spectra, a significant change of the U(VI) speciation is derived upon lowering the U(VI) concentration from the milli- to the micromolar range, strongly suggesting the dominance of monomeric U(VI) hydrolysis products in the micromolar solutions. In contradiction to the predicted speciation, monomeric hydroxo species are already present at pH ≥ 2.5 and become dominant at pH 3. At higher pH levels (> 6), a complex speciation is evidenced including carbonate containing complexes.
For the first time, spectroscopic results of Np(VI) hydrolysis reactions are provided in the submillimolar concentration range and at pH values up to 5.3, and they are comparatively discussed with U(VI). For both actinides, the formation of similar species is suggested at pH ≤ 4, whereas at higher pH, the infrared spectra evidence structurally different species. At pH 5, the formation of a carbonate-containing dimeric complex, that is (NpO2)2CO3(OH)3^-, is strongly suggested, whereas carbonate complexation occurs only under more alkaline conditions in the U(VI) system.
The results from the experiments of the sorption processes clearly demonstrate the formation of stable U(VI) surface complexes at all investigated mineral phases. This includes several metal oxides, namely TiO2, Al2O3, and SiO2, serving as model systems for the elucidation of more complex mineral systems, and several alumosilicates, such as kaolinite, muscovite and biotite. From a multiplicity of in situ experiments, the impact of sorbent characteristics and variations in the aqueous U(VI) system on the sorption processes was considered.
A preferential formation of an inner-sphere complex is derived from the spectra of the TiO2 and SiO2 phases. In addition, since the in situ FT-IR experiments provide an online monitoring of the absorption changes of the sorption processes, the course of the formation of the U(VI) surface complexes can be observed spectroscopically. It is shown that after prolonged sorption time on TiO2, resulting in a highly covered surface, outer-sphere complexation predominates the sorption processes. The prevailing crystallographic modification, namely anatase and rutile, does not significantly contribute to the spectra, whereas surface specific parameters, e.g. surface area or porosity are important.
A significant different surface complexation is observed for Al2O3. The formation of innerspheric species is assumed at low U(VI) surface coverage which is fostered at low pH, high ionic strength and short contact times. At proceeded sorption the surface complexation changes. From the spectra, an outer-spheric coordination followed by surface precipitation or polymerization is deduced. Moreover, in contrast to TiO2, the appearance of ternary U(VI) carbonate complexes on the γ-Al2O3 surface is suggested.
The first results of the surface reactions on more complex, naturally occurring minerals (kaolinite, muscovite and biotite) show the formation of U(VI) inner-sphere sorption complexes. These findings are supported by the spectral information of the metal oxide surfaces.
In this work, first spectroscopic results from sorption of aqueous Np(V) on solid mineral phases are provided. It is shown that stable inner-sphere surface species of NpO2 ^+ are formed on TiO2. Outer-sphere complexation is found to play a minor role due to the pH independence of the sorption species throughout the pH range 4 – 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2, and ZnO indicate structurally similar bidentate surface complexes.
The multiplicity of IR spectroscopic experiments carried out within this study yields a profound collection of spectroscopic data which will be used as references for future investigations of more complex sorption systems in aqueous solution. Furthermore, from a methodological point of view, this study comprehensively extends the application of ATR FT-IR spectroscopic experiments to a wide range in the field of radioecology.
The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V/VI), in the environment. Consequently, more reliable predictions of actinides migration which are essential for the safety assessment of nuclear waste repositories can be performed.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-535 2010
    ISSN: 1437-322X


Publ.-Id: 14401

Self-organization of Ge nanopattern under erosion with heavy Bi monomer and cluster ions

Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Facsko, S.; Pilz, W.

The self-organisation of periodic pattern on (001)Ge by bombardment with different heavy ion species (Bi+, Bi++, Bi2+, Bi3+, Bi3++) obtained from a liquid metal ion source in a mass separating 30 kV FIB system was studied. Aspect ratios exceeding values reported so far for elemental semiconductors substantially were found after cluster irradiation. An excellent regular self-ordering of dot (40 nm in height, interdistance of ~50 nm) and ripple pattern was achieved. Despite of high ion fluence, Raman measurements prove a crystalline surface layer. This result deviates drastically from monomer irradiation, where similar to former ion irradiation of Ge a spongy amorphous surface layer is formed. For the transition from the usual behaviour to the unexpected pronounced pattern formation a threshold of the energy density deposited by the collision cascade was identified: If the deposited energy density exceeds the melting threshold, dot or ripple pattern appear. In our model we assume that the ion-impact-induced deposition of energy per volume (estimated by SRIM) must exceed the energy needed for melting. Thus, Bi segregation during re-solidification of the melted pool and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.

Keywords: Bi-cluster; germanium; FIB; nanopattern

  • Poster
    17th International Conference on Ion Beam Modification of Material - IBMM 2010, 22.-27.08.2010, Montreal, Canada
  • Nuclear Instruments and Methods in Physics Research B 272(2012), 198-201
    DOI: 10.1016/j.nimb.2011.01.064

Publ.-Id: 14400

FZD intern 57

Bartho, A.; Bohnet, C.

Hauszeitung des FZD

  • Communication & Media Relations
    Hauszeitung des FZD 06.08.2010
    8 Seiten

Publ.-Id: 14399

The effect of rare-earth clustering on charge trapping and electroluminescence in rare-earth implanted metal-oxide-semiconductor light-emitting devices

Nazarov, A. N.; Tiagulskyi, S. I.; Tyagulskyy, I. P.; Lysenko, V. S.; Rebohle, L.; Lehmann, J.; Prucnal, S.; Voelskow, M.; Skorupa, W.

The effect of rare-earth clustering in dielectric media on the electroluminescence (EL) intensity, the charge trapping and the EL quenching was investigated using the example of Tb and Eu-implanted SiO2 layers. It was shown that the increase in the REOX cluster size induced by an increase in the furnace annealing temperature resulted in an increase in the concentration of electron traps with capture cross sections from 2 x 10-15 to 2 x 10-18 cm2. This is probably associated with an increase in the concentration of oxygen deficiency centers as well as with strained and dangling bonds in the SiO2 matrix which leads to an enhanced scattering of hot electrons and a decrease in the excitation cross section of the main EL lines of RE3+ ions. For the main EL lines of Tb3+ and Eu3+ ions the relation of the EL quenching to negative and positive charge generation in the SiO2 was considered. It was demonstrated that in case of REOX nanoclusters with small sizes (up to 5 nm) the E!
L quenching process can mainly be explained by a defect shell model which suggests the formation of negatively charged defect shells around the nanoclusters leading to a Coulomb repulsion of hot electrons and a suppression of the RE3+ excitation. At high levels of the injected charge (more than 2 x 1020 e/cm2) a second stage of the EL quenching was observed which was contributed to a positive charge accumulation in the SiO2 at a distance beyond the tunneling distance from the SiO2-Si interface. In case of Eu-implanted SiO2 the quenching of the main EL line of Eu3+ is mostly correlated with positive charge trapping in the bulk of the dielectric. A model of EL quenching of the main Eu3+ line is proposed. (C) 2010 American Institute of Physics.

Keywords: Electroluminescence; rare earth; MOS capacity; charge trapping; ion implantation

  • Journal of Applied Physics 107(2010)12, 123112

Publ.-Id: 14397

New sensors for the velocity measurement in liquid metal processes

Timmel, K.; Eckert, S.; Wondrak, T.; Stefani, F.; Gerbeth, G.

In many technological processes involving liquid metals or semiconductor melts the velocity fields cannot be measured due to the lack of commercial measuring techniques for opaque melts. We present two measuring techniques which have proven recently as providing reliable velocity measurements in liquid metals, at least in the temperature range up to about 700°C: the ultrasonic Doppler Velocimetry (UDV) and the contactless inductive flow tomography (CIFT). UDV is capable of delivering velocity profiles along the ultrasonic beam with a time-resolution of about 20 Hz. CIFT is based on the flow-induced modification of some externally applied magnetic field, which is measured by some array of magnetic field sensors outside of the melt. We present measurements with both techniques at the small-scale liquid metal model Mini-LIMMCAST of the continuous steel casting process. Both measuring methods give consistent results for the jets evolving from the nozzle outlets.

Keywords: continuous casting; liquid metal model; magnetic field; mould flow; Ultrasound Doppler Method; industrial tomography

  • Lecture (Conference)
    2011 TMS Annual Meeting & Exhibition, 27.02.-03.03.2011, San Diego, Californien, USA
  • Contribution to proceedings
    2011 TMS Annual Meeting & Exhibition, 27.02.-03.03.2011, San Diego, Californien, USA
    Sensors, Sampling, and Simulation for Process Control: Wiley, 978-1-118-03618-1, 43-50

Publ.-Id: 14396

Competition of two-ion and single-ion anisotropy in rare-earth systems: Large anisotropy example of Tb5Ge3

Doerr, M.; Haase, A.; Loewenhaupt, M.; Rotter, M.; Bartkowiak, M.; Daou, R.; Kampert, E.; Perenboom, J.; Tsutaoka, T.

The standard model of rare-earth magnetism assumes that magnetic anisotropy is mainly caused by single-ion effects. The importance of two-ion anisotropy is still disputed. For a number of materials this two-ion anisotropy is in the same order of magnitude and strongly influences the magnetic properties. Single crystalline Tb5Ge3 has a high moment and low symmetry and, because of this, a large anisotropy is expected. In the present study the influence of the two-ion interaction was investigated. Magnetization and magnetostriction were measured in high magnetic fields up to 60 T. The magnetic phase diagram constructed for the main crystallographic directions shows antiferromagnetism in zero field and a number of magnetic phases at higher fields. The exchange interaction was evaluated based on a model calculation of these phase diagrams. We conclude that a huge anisotropy in the two-ion interaction is present, which overwhelms the single-ion effects.

  • Physical Review B 82(2010), 024422

Publ.-Id: 14395

Manganese implanted Germanium: from clustering to carrier-mediated ferromagnetism

Zhou, S.; Bürger, D.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.

Mn doped Ge (Ge:Mn) is a promising candidate for a ferromagnetic semiconductor compatible with silicon technology, since Mn acts as a magnetic ion as well as a double acceptor. Whereas ferromagnetism above room temperature has been evidenced by magnetization measurements, the transport behavior is entirely different from the GaAs:Mn system [1], the prototype of a ferromagnetic semiconductor.

We have prepared a series of Ge:Mn layer by Mn ion implantation into near-intrinsic Ge substrates, at 350 °C (resulting in Mn5Ge3 clusters) and -40 °C (without precipitates) [1-4]. The Mn concentration ranges from 0.004% to 10%. For samples with 10% Mn, flash lamp and pulsed laser annealing (PLA) has been applied. We obtained three kinds of samples: (1) very dilute Ge:Mn where no ferromagnetic coupling can be expected [1]; (2) nanocrystalline Mn5Ge3 embedded inside the Ge matrix [2]; and (3) diluted Ge:Mn together with Mn-rich spinodal phases [3]. Indeed all samples show p-type conductivity with a hole concentration ranging from 1018 to 1020 cm3. The highest concentrations above 1020 cm3 can only be achieved by PLA. In the sample with the largest hole concentration of 2.1×1020 cm3, we observed a one-to-one correspondence between the hysteresis in magnetization, magnetoresistance and Hall resistance below 10 K [3, 4]. We argue that the hole concentration is the critical parameter to establish carrier mediated ferromagnetism in Ge:Mn [4]. In addition to the compatibility to Si technology, ion implantation followed by PLA is an established scalable chip technology and may have a significant industry impact.

[1] S. Zhou et al., APL, 95, 172103 (2009).
[2] S. Zhou et al., APL, 95, 192505 (2009).
[3] S. Zhou et al., PRB 81, 165204 (2010).
[4] S. Zhou et al., APL, in press (2010).

  • Lecture (Conference)
    The 17th International Conference on Ion Beam Modification of Materials, 22.-27.08.2010, Montreal, Canada

Publ.-Id: 14392

Manganese doped Germanium: from clustering to carrier-mediated ferromagnetism

Zhou, S.; Bürger, D.; Baumgart, C.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.

Manganese doped Germanium (Ge:Mn) is a promising candidate for a ferromagnetic semiconductor compatible with silicon technology, since Mn acts as a magnetic ion as well as a double acceptor. In recent years, Ge:Mn thin layers as well as nanostructures have been fabricated, mostly by LT-MBE, and analyzed [1-4]. Whereas ferromagnetism above room temperature has been evidenced by magnetization measurements, the transport behavior (magnetoresistance: MR, anomalous Hall effect: AHE) is entirely different from the GaAs:Mn system, the prototype of a ferromagnetic semiconductor. For instance, the previously reported AHE in Ge:Mn (i) was observed at temperatures above 10 K, (ii) but exhibited no hysteresis, and (iii) changed the sign of its slope. This behavior has been ascribed to Mn-diluted Ge [2, 4], Mn-rich spinodal decomposed phases [3] and MnGe precipitates [5], respectively. We argue that the origin of these observations lies in the less effective substitution of Mn at Ge sites, which results in too low a hole concentration, making carrier-mediated ferromagnetism impossible. The hole concentrations realized in Ge:Mn grown by LT-MBE are mostly well below 1019 cm-3.

We have prepared a series of Ge:Mn layer by Mn ion implantation into near-intrinsic, n-type Ge substrates, at 350 °C (resulting in Mn5Ge3 clusters) and -40 °C (without precipitates) [6-8]. The Mn concentration ranges from 0.004% to 10%. For samples with 10% Mn, several annealing procedures have been applied, namely ms flash lamp annealing and nsec pulsed laser annealing with various optical fluences. By this systematic preparation, we obtained three kinds of samples: (1) very dilute Ge:Mn where no ferromagnetic coupling can be expected [6]; (2) nanocrystalline Mn5Ge3 embedded inside the Ge matrix [7]; and (3) diluted Ge:Mn together with Mn-rich spinodal phases [8]. Indeed all samples show p-type conductivity with a hole concentration ranging from 1018 to 1020 cm-3. The highest concentrations above 1020 cm-3 can only be achieved with the help of pulsed laser annealing. A careful characterization of structure, magnetic and transport properties, leads us to the following conclusions.

(1) From 20 to 10 K the resistance of samples with a hole concentration of >1018 cm-3 increases in an activated manner with an activation energy of 4 meV, but below 10 K it saturates, i.e. the sample behaves metallic.
(2) We evoke the consideration of a two-band-like conduction in Ge:Mn. Above 10 K another conducting channel with different mobility is active, resulting in the drop of resistivity and the anomalous Hall resistance. The latter can be well described over a wide of parameters by considering two types of carriers with different mobility and population (see Ref. 6).
(3) In the sample with the largest hole concentration of 2×1020 cm-3, we observed, for the first time to our knowledge, a one-to-one correspondence between the hysteresis in magnetization, magnetoresistance and Hall resistance below 10 K. This is our key result, shown in Fig. 1, and is a strong evidence for carrier-mediated ferromagnetism. Note however that considering mere magnetization data, ferromagnetism remains present up to >100 K.

In summary, we present the magnetic and magnetotransport properties of a series of Ge:Mn samples with hole concentrations ranging from 1018 to 2x1020 cm-3. The hole concentration is the critical parameter to establish carrier mediated ferromagnetism in Ge:Mn, similar as is known for GaAs:Mn. A high-concentration co-doping with a shallow acceptor may allow to increase the hole concentration further, possibly resulting in a dramatically increased Curie temperature. In addition to the compatibility to Si technology, ion implantation followed by pulsed laser annealing is an established scalable chip technology and therefore may have a significant industry impact.

[1] Y. D. Park et al., Science 295, 651 (2002).
[2] F. Tsui et al., Phys. Rev. Lett. 91, 177203 (2003).
[3] M. Jamet et al., Nature Mater. 5, 653 (2006).
[4] C. Zeng, et al., Phys. Rev. Lett. 100, 066101 (2008).
[5] O. Riss, et al., Phys. Rev. B 79, 241202(R) (2009).
[6] S. Zhou et al., Appl. Phys. Lett. 95, 172103 (2009).
[7] S. Zhou et al., Appl. Phys. Lett. 95, 192505 (2009).
[8] S. Zhou et al., Phys. Rev. B (2010), submitted.

  • Lecture (Conference)
    International Conference on Physics and Applications of Spin Related Phenomena in Semiconductors (PASPS-VI), 01.-04.08.2010, Tokyo, Japan
  • Invited lecture (Conferences)
    Invited talk at the Institute of Physics, Chinese Academy of Sciences, 13.04.2010, Beijing, China

Publ.-Id: 14391

Hysteresis in the magneto-transport of Manganese-doped Germanium: evidence for carrier-mediated ferromagnetism

Zhou, S.; Bürger, D.; Baumgart, C.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.

The III-V compound GaMnAs is considered as being the prototype diluted ferromagnetic semiconductor (FMS), exhibiting negative magnetoresistance (MR) and anomalous Hall effect (AHE) related to carrier-mediated ferromagnetism. However, it would be very desirable to have a group-IV FMS, being compatible with silicon technology. In particular manganese-doped germanium prepared using low-temperature molecular beam epitaxy (LT-MBE) has proven to be a very promising material [1]. Still, no direct correspondence between transport and magnetization data has been reported yet to date. The reported MR and AHE in Ge:Mn are likely caused by (super)paramagnetic Mn ions or precipitates or by two-band-like conduction [2]. We believe that the origin of these observations lies in the less effective substitution of Mn at Ge sites, which results in too low a hole concentration, making carrier-mediated ferromagnetism impossible. The hole concentrations realized in Ge:Mn grown by LT-MBE are mostly well below 1019 cm-3, which indicates the possible unsuitability of LT-MBE to achieve a large hole concentration in Ge:Mn.

In this contribution, we show that the hole concentration can be increased by two orders of magnitude, from 1018 to 1020 cm-3, through Mn-ion implantation into Ge followed by pulsed laser annealing [3]. In Mn-doped Ge with a hole-concentration of around 2.1×1020 cm-3, we observe that the longitudinal (Fig. 1c) and the Hall (Fig. 1b) resistance exhibit the same hysteresis as the magnetization (Fig. 1a) at temperatures below 10 K. This hysteresis in magneto-transport is usually considered as a direct evidence of carrier-mediated ferromagnetism. In sharp contrast to this, such effects are absent in Mn-doped Ge with a smaller hole-concentration. Below 10 K, the resistance of Ge:Mn films is nearly constant, i.e., quasi metallic, while from 10 to 20 K it decreases steeply with an activation energy of 4 meV. The magnetic and magneto-transport properties can be qualitatively well explained within a picture of dopant segregation and the formation of bound magnetic polarons. We will present a comprehensive correlation between the magnetic, transport and structural properties of Ge:Mn samples with different hole concentrations, as well as a comparison with literature. Note that ion implantation followed by pulsed laser annealing is an established scalable chip technology and may have a significant industry impact.

[1] Y. D. Park et al., Science 295, 651 (2002); M. Jamet et al., Nature Mater. 5, 653 (2006).
[2] S. Zhou et al., Appl. Phys. Lett. 95, 172103 (2009); Appl. Phys. Lett. 95, 192505 (2009).
[3] S. Zhou et al., Phys. Rev. B (2010), submitted.

  • Lecture (Conference)
    30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul,, korea

Publ.-Id: 14390

Rate theory and SANS study of phase separation in a neutron irradiated Fe-12.5at%Cr model alloy

Gokhman, A. R.; Bergner, F.; Küchler, R.

Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr-precipitates in neutron irradiated Fe-12.5at%Cr alloy at the irradiation doses up to 12 dpa, fluence about 140 ndpa/s and T=300 C. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data [1,2] on the defect structure of this material irradiated at the doses of 0.6 and 1.5 dpa are used to calibrate the model. It was found the saturation behaviour of free vacancy and free SIA concentrations, number density of SIAC and Cr-precipitates volume fraction for neutron expose great than 0.006 dpa; strong peak of SIAC with the average diameter about 0.5 nm and presence of VC with radius less 0.5 nm.

Keywords: Cluster dynamics; neutron irradiation; chromium iron alloys; defects

  • Invited lecture (Conferences) Research Workshop Nucleation Theory and Applications, 10.-17.04.2010, Dubna, Russia

Publ.-Id: 14389

The MoS2 nanotubes with defect-controlled electric properties

Remskar, M.; Mrzel, A.; Virsek, M.; Godec, M.; Krause, M.; Kolitsch, A.; Singh, A.; Seabaugh, A.

We describe a two-step synthesis of pure multiwall MoS2 nanotubes with a high degree of homogeneity in size. The Mo6S4I6 nanowires grown directly from elements under temperature gradient conditions in hedgehog-like assemblies were used as precursor material. Transformation in argon-H2S/H2 mixture leads to the MoS2 nanotubes still grouped in hedgehog-like morphology. The described method enables a large scale production of MoS2 nanotubes and their size control. X-ray diffraction, optical absorption and Raman spectroscopy, scanning electron microscopy with wave dispersive analysis, and transmission electron microscopy were used to characterize the starting Mo6S4I6 nanowires and the MoS2 nanotubes. The unit cell parameters of the Mo6S4I6 phase are proposed. Blue shift in optical absorbance and metallic behaviour of MoS2 nanotubes in two-probe measurement are explained by a high defect concentration.

Keywords: inorganic fullerenes; layered compounds; nanotubes; nanowires

Publ.-Id: 14388

Ultrashort pulse laser accelerated proton beams for first radiobiological applications

Schramm, U.; Zeil, K.; Richter, C.; Beyreuther, E.; Bussmann, M.; Cowan, T. E.; Enghardt, W.; Karsch, L.; Kluge, T.; Kraft, S.; Laschinsky, L.; Metzkes, J.; Naumburger, D.; Pawelke, J.; Sauerbrey, R.

We report on the generation of proton pulses with maximum energies exceeding 15MeV bymeans of the irradiation of few micron thick metal foils by ultrashort (30 fs) laser pulses at a power level of 100 TW. In contrast to the well known situation for longer laser pulses, here, a near linear scaling of the maximum proton energy with laser power can be found. Aiming for radiobiological applications the long and short term stability of the laser plasma accelerator as well as a compact energy selection and dosimetry system is presented. The first irradiation of in vitro tumour cells showing dose dependent biological damage is demonstrated paving the way for systematic radiobiological studies.

Keywords: laser proton acceleration; first cell irradiation

  • Contribution to proceedings
    14th Workshop on Advanced Accelerator Concepts, 13.-19.06.2010, Annapolis, MD, USA, USA
    AIP Conference Proceedings, Advanced Esselerator Concepts, 1299: AIP, 731

Publ.-Id: 14382

Physikalische Modellierung des Stranggussprozesses mit niedrig schmelzenden Legierungen

Timmel, K.; Galindo, V.; Miao, X.; Eckert, S.; Gerbeth, G.

Die Strömung in der Metallschmelze hat einen wesentlichen Einfluss auf die Produktqualität beim Stranggießen. Probleme entstehen beispielsweise durch Einschlüsse von Oxiden, intermetallischen Verbindungen oder Gasblasen, die durch eine unkontrollierte Strömung in die Erstarrungszone gelangen. Die Optimierung dieser Strömung basierte bisher vor allem auf numerischen Simulationen und Modellexperimenten mit Wasser. Obwohl die Strömungsuntersuchungen an diesen Wassermodellen signifikante Erkenntnisgewinne über die Strömung und die optimale Auslegung z.B. des Tauchrohrs oder der Eintauchtiefe des Tauchrohrs gebracht haben, stoßen diese Modelle für eine Reihe von Fragestellungen an ihre physikalischen Grenzen, da Flüssigmetalle z.B. sehr hohe Oberflächenspannungen und sehr kleine Prandtl-Zahl besitzen, und Wasser offensichtlich für Untersuchungen des Einflusses von Magnetfeldern völlig ungeeignet ist.
In den vergangenen Jahren wurden am Forschungszentrum Dresden-Rossendorf experimentelle Versuchsanlagen mit niedrig schmelzenden Legierungen für die physikalische Modellierung des Stranggussprozesses aufgebaut. Ziel ist die systematische Untersuchung der Flüssigmetallströmungen und Transportprozesse in Verteiler, Tauchrohr und Kokille. Dabei steht insbesondere die Wirkung elektromagnetischer Felder, wie sie in Form von elektromagnetischen Bremsen oder Rührern bereits im industriellen Einsatz sind, im Mittelpunkt. Außerdem bieten die Versuchsanlagen gute Bedingungen für die Erprobung neuer Messtechniken und Anlagenkomponenten. Die Versuchsanlage „CONCAST-LMM“ (Continuous Casting Liquid Metal Model) ist 2009 fertig gestellt worden und arbeitet mit einer Sn60Bi40-Legierung als Modellfluid im Temperaturbereich von 200°C bis 400°C. Ein kleineres Modell mit der eutektischen GaInSn-Legierung wird bei Raumtemperatur betrieben. Die Strömungseigenschaften werden mit Hilfe lokaler Sonden sowie modernen Ultraschall und elektromagnetischen Methoden vermessen.
Im Rahmen dieses Beitrages werden Strömungsmessungen in einer einphasigen Flüssigmetallströmung in der Kokille unter Einwirkung eines statischen Magnetfeldes vorgestellt und mit entsprechenden numerischen Simulationen verglichen. Es zeigt sich, dass das Magnetfeld den aus dem Tauchrohr in die Kokille austretenden Jet ablenkt und lokale Rezirkulationsgebiete verstärkt. Die bremsende Wirkung des Magnetfeldes stellt sich als äußerst komplex dar. Eine gleichmäßige Reduktion der Strömungsgeschwindigkeit im gesamten Volumen wird nicht beobachtet.

Keywords: continuous casting; liquid metal model; magnetic field; mould flow; Ultrasound Doppler Method

  • Lecture (Conference)
    Symposium Stranggießen, 15.-17.11.2010, Neu-Ulm, Deutschland
  • Contribution to proceedings
    Symposium Stranggießen, 15.-17.11.2010, Neu-Ulm, Deutschland

Publ.-Id: 14381

Structural evolution of magnetron sputtered shape memory alloy Ni–Ti films

Martins, R. M. S.; Schell, N.; von Borany, J.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.

Near equiatomic and Ti-rich Ni–Ti polycrystalline films have been deposited by magnetron co-sputtering using a chamber installed at a synchrotron radiation beamline. The in situ X-ray diffraction studies enabled the identification of different steps of the structural evolution during film processing.
The depositions on a 140 nm amorphous SiO2 buffer layer heated at 520°C (without applying bias voltage, Vb, to the substrate) led to a preferential growth of <100> oriented grains of the Ni–Ti B2 phase from the beginning of film growth until the end of the deposition.
Films exhibiting a preferential growthof <110> oriented grains of the Ni–Ti B2 phase from the beginning of the deposition were obtained (without and with a Vb of - 45 V) by using a TiN coating with a topmost layer formed by <111> oriented grains. Those trends have been observed for the growth of near equiatomic (~50.0 at.% Ti–Ni) and Ti-rich (~50.8 at.% Ti–Ni) Ni–Ti films.
Additionally, an ion gun had been commissioned, which allows ion bombardment during sputter deposition or post-deposition ion irradiation. In this first series of experiments, a Ni–Ti film was irradiated with He ions after deposition (without exposing the film to the atmosphere, i.e., avoiding surface oxide formation), thus modifying deliberately the microstructure of the film locally.

Keywords: Deposition by sputtering; Ni–Ti Shape memory alloy (SMA); In situ X-ray diffraction (XRD); Texture development; Ion bombardment

Publ.-Id: 14380

Quantitative KPFM Measurements on Silicon Nanowire Structures

Baumgart, C.

This workshop focus on the electrical characterization of vertical and horizontal Si nanowires.

  • Lecture (others)
    Workshop FZD/FZJ: Silicon Nanowire Structures, 29.04.2010, Dresden, Germany

Publ.-Id: 14379

Quantitative Kelvin probe force microscopy imaging on locally doped Si

Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.

Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface
potential. Since KPFM was developed in 1991 the measured KPFM signal was attributed to the contact potential difference (CPD) between conductive probe and sample. We show that the CPD is not suitable to describe the measured Kelvin bias in semiconductors quantitatively and introduce a unique KPFM model [1] which successfully correlates the measured Kelvin bias with the difference between Fermi energy and respective band edge. Quantitative dopant profiling is demonstrated on cross-sectionally prepared Si epilayer structures and on a Si dynamic random access memory cell.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80 (2009) 085305.

  • Poster
    DPG Frühjahrstagung, 21.-26.03.2010, Regensburg, Germany

Publ.-Id: 14378

Shallow acceptor and hydrogen impurity in p-type arsenic-doped ZnMgO films grown by radio frequency magnetron sputtering

Fan, J.; Ding, G.; Fung, S.; Xie, Z.; Zhong, Y.; Wong, K.; Brauer, G.; Anwand, W.; Grambole, D.; Ling, C.

Arsenic-doped ZnMgO films were fabricated on SiO2 by the radio frequency magnetron sputtering technique at different substrate temperatures during growth. The yielded films were characterized by room temperature Hall measurement, x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, secondary ion mass spectroscopy, nuclear reaction analysis and low-temperature photoluminescence. As-doped samples grown at low substrate temperature (350 degrees C) were n-type conducting (n similar to 1018 cm-3), with evidence showing that the hydrogen impurity was an important shallow donor associated with the observed n-type conduction. Conversion of n-type to p-type conduction being observed at the substrate temperature of similar to 400 degrees C was associated with the formation of the AsZn(VZn)2 shallow acceptor complex and the drastic reduction of the hydrogen content.

Publ.-Id: 14377

Quantitative Kelvin probe force microscopy on semiconductors

Baumgart, C.; Helm, M.; Schmidt, H.

Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to locally doped semiconductors. Quantitative dopant profiling by means of KPFM is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions [2].
In addition, the frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer on top [3]. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).

  • Lecture (others)
    2. Wissenschaftliches Seminar des Dresdner Fraunhofer-Clusters Nanoanalytik, 05.08.2010, Dresden, Germany

Publ.-Id: 14375

Quantitative Kelvin probe force microscopy imaging on locally doped semiconductors

Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.

Failure analysis and optimization of nanoelectronic devices demand knowledge of their electrical properties. Especially, quantitative profiling of dopant concentrations is essential for process and device engineering in semiconductor industry. The most straightforward nanometrology technique is the Kelvin probe force microscopy (KPFM) where electrostatic forces are detected.
Quantitative dopant profiling by means of KPFM measurements is successfully shown on a conventional static random access memory (SRAM) cell and on
cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different pulsed laser annealed Mn-implanted Ge samples by revealing a strong variation of the Fermi level position on the micrometer scale in dependence on
the annealing conditions after Mn implantation [2].
In addition, the frequency dependence of the KPFM bias is discussed. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, the frequency dependence is samplespecific and KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor are

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm,
and H. Schmidt, Phys. Rev. B 81 (2010), 165204.

  • Lecture (Conference)
    Nano 2010, 13.-17.09.2010, Rome, Italy

Publ.-Id: 14374

Quantitative Kelvin probe force microscopy on semiconductors under ambient conditions

Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.

Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to locally doped semiconductors. Quantitative dopant profiling by means of KPFM is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions [2].
In addition, the frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer on top [3]. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).

  • Lecture (Conference)
    Nanofair 2010, 06.-07.07.2010, Dresden, Germany

Publ.-Id: 14373

Revealing the role of anchoring groups in the electrical conduction through single-molecule junctions

Zotti, L. A.; Kirchner, T.; Cuevas, J.-C.; Pauly, F.; Huhn, T.; Scheer, E.; Erbe, A.

A combined experimental and theoretical study is presented revealing the influence of metal-molecule coupling on electronic transport through single-molecule junctions. Transport experiments through tolane molecules attached to gold electrodes via thiol, nitro, and cyano anchoring groups are performed. By fitting the experimental current-voltage characteristics to a single-level tunneling model, we extract both the position of the molecular orbital closest to the Fermi energy and the strength of the metal-molecule coupling. The values found for these parameters are rationalized with the help of density-functional-theory-based transport calculations. In particular, these calculations show that the anchoring groups determine the junction conductance by controlling not only the strength of the coupling to the metal but also the position of the relevant molecular energy levels.

Keywords: anchoring groups; break junctions; density functional theory; molecular electronics; molecular wires

Publ.-Id: 14372

Density reduction and diffusion in driven two-dimensional colloidal systems through microchannels

Henseler, P.; Erbe, A.; Köppl, M.; Leiderer, P.

The behavior of particles driven through a narrow constriction is investigated in experiment and simulation. The system of particles adapts to the confining potentials and the interaction energies by a self-consistent arrangement of the particles. It results in the formation of layers throughout the channel and of a density gradient along the channel. The particles accommodate to the density gradient by reducing the number of layers one by one when it is energetically favorable. The position of the layer reduction zone fluctuates with time while the particles continuously pass this zone. The flow behavior of the particles is studied in detail. The velocities of the particles and their diffusion behavior reflect the influence of the self-organized order of the system.

Keywords: Colloids; Nonlinear dynamics and chaos; Computer simulation of molecular and particle dynamics; Studies of specific magnetic materials

Publ.-Id: 14370

Observation of negative differential resistance in DNA molecular junctions

Kang, N.; Erbe, A.; Scheer, E.

The mechanically controllable break junction technique is used to study charge transport through suspended DNA molecules. The current-voltage (I-V) characteristics in an aqueous solution display series of negative differential resistance (NDR) and hysteresis behavior. Under high-vacuum conditions, the peak positions of NDR shift to lower voltage, and the amplitude is reduced dramatically. The observed NDR behavior is consistent with the polarization mechanism in DNA molecular junctions, which demonstrates a change in the coupling of the molecular level to a polaron mode under different environment.

Keywords: DNA electronics; molecular electronics; mechanically controllable break junctions

Publ.-Id: 14369

Leitlinie für SPECT-Untersuchungen mit dem 123I-markierten Dopamintransporter-Liganden FP-CIT (DaTSCANTM)

Tatsch, K.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Grünwald, F.; Kuwert, T.; Krause, B. J.; Sabri, O.

Es ist kein Abstract vorhanden.

Keywords: SPECT; 123I; Dopamintransporter Ligand; FP-CIT; DaTSCAN

  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners, Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 100-107

Publ.-Id: 14368

Leitlinie für SPECT-Untersuchungen mit dem 123I-markierten Dopamin-D2-Rezeptor Liganden IBZM

Tatsch, K.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Grünwald, F.; Kuwert, T.; Krause, B. J.; Sabri, O.

Es ist kein Abstract vorhanden.

Keywords: SPECT; 123I; Dopamin-D2-Rezeptor; Ligand; IBZM

  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners; Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 108-115

Publ.-Id: 14367

Leitlinie für die Hirnperfusions-SPECT mit 99mTc-Radiopharmaka

Menzel, C.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Krause, B. J.; Kuwert, T.; Sabri, O.; Schreckenberger, M.; Tatsch, K.; Grünwald, F.

Es ist kein Abstract vorhanden.

Keywords: Hirnperfusions-SPECT; 99mTc

  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners; Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 87-91

Publ.-Id: 14366

Dose-dependent biological damage of tumour cells by laser-accelerated proton beams - online diagnostics

Schramm, U.

Talk on the status of laser proton acceleration and online dosimetry with respect to radiobiological applications.

  • Invited lecture (Conferences)
    First Workshop on Instrumentation for Diagnostics and Control of Laser Accelerated Proton Beams, 09.-10.08.2010, Abingdon / Oxford, UK

Publ.-Id: 14365

Slip ratio in dispersed viscous oil-water pipe flow

Rodriguez, I. H.; Yamaguti, H. K. B.; de Castro, M. S.; Da Silva, M. J.; Rodriguez, O. M. H.

In this article, dispersed flow of viscous oil and water is investigated. The experimental work was performed in a 26.2-mm-i.d. 12-m-long horizontal glass pipe using water and oil (viscosity of 100 mPa.s and density of 860 kg/m3) as test fluids. High-speed video recording and a new wire mesh sensor based on capacitance (permittivity) measurements were used to characterize the flow. Furthermore, holdup data were obtained using quick-closing-valves technique (QCV). An interesting finding was the oil-water slip ratio greater than one for dispersed flow at high Reynolds number. Chordal phase fraction distribution diagrams and images of the holdup distribution over the pipe cross-section obtained via wire-mesh sensor indicated a significant amount of water near to the pipe wall for the three different dispersed flow patterns identified in this study: Oil-in-water Homogeneous Dispersion (o/w H), Oil-in-water Non-homogeneous Dispersion (o/w NH) and Dual continuous (Do/w & Dw/o). The phase slip might be explained by the existence of a water film surrounding the homogeneous mixture of oil in water in a hidrofilic-oilfobic pipe.

Keywords: Liquid-liquid flow; oil-water flow; viscous oil; dispersed flow; slip ratio; wire-mesh sensor

Publ.-Id: 14364

Marangoni convection in molten salts - physical modelling toward lower Prandtl numbers

Cramer, A.; Landgraf, S.; Beyer, E.; Gerbeth, G.

Marangoni convection is involved in many technological processes. The substances of industrial interest are often governed by diffusive heat transport and their physical modelling is limited with respect to the Prandtl number Pr. The present paper addresses this deficiency. Studies were made on molten salts having Pr values in an intermediate range well below that of the typically employed organics. Since some of the selected species have a relatively high melting point, a high-temperature facility which allows studying thermocapillary convection at temperatures in excess of 1000°C was built. The results presented here were obtained in a cylindrical geometry, although the equipment that was built is not restricted to this configuration because of its modular construction. Modelled after some applications, the fluid was heated centrically on top. The bulk was embedded in a large thermostatically controlled reservoir so as to establish the lower ambient reference temperature. A characteristic size of the experimental cell was chosen such that, on the one hand, the dynamic Bond number Bo did not become too high; on the other hand, the liquid had to have a certain depth to allow particle image velocimetry. The complicated balance between body forces and thermocapillary forces in the case of intermediate Bo was found to result in a distinct local separation into a bulk motion governed by natural convection with a recirculating Marangoni flow on top. In contrast to low viscosity organics, the vapour pressure of which increases considerably with decreasing Pr, high values of the Marangoni number can be reached. Comparisons of the topology of Marangoni vortices between molten salts with 2.3 <= Pr <= 6.4 and a silicone oil with Pr typically one order of magnitude higher suggest that the regime of non-negligible heat diffusion is entered.

Keywords: Marangoni convection; surface tension driven flow; molten salts; Prandtl number; physical modelling

Publ.-Id: 14363

On the prediction of boron dilution using the CMFD code TRANSAT: the ROCOM test case

Labois, M.; Panyasantisuk, J.; Lakehal, D.; Höhne, T.; Kliem, S.

This contribution aims at introducing a new multiscale, multicomponent CFD/CMFD approach for the simulation of thermal-hydraulics flows evolving in complex component-scale configurations. In this novel approach, the flow system could involve one or two fluids, convective and conductive heat transfer in solids, and phase-change heat transfer. This is made possible thanks to the Immersed Surfaces Technology (IST), a methods inspired from Interface Tracking techniques for two-phase flow, whereby solid bodies contained in the system are defined using a solid level set function to describe their surfaces, transcending conventional unstructured and body-fitted grids (BFC). In a typical two-phase flow, material properties of the fluids and the solid are segregated based on the gas-liquid and solid Level-Set functions. The technique helps solve conjugate heat transfer problems without resorting to explicit jump conditions. Selected validation test-cases are presented here. The main application includes steady and transient solutions of the boron dilution in the ROCOM test case.


  • Contribution to proceedings
    CFD4NRS-3, 14.-16.09.2010, Washington, USA
  • Lecture (Conference)
    CFD4NRS-3, 14.-16.09.2010, Washington, USA

Publ.-Id: 14362

Controlling blue-violet electroluminescence of Ge-rich Er-doped SiO2 layers by millisecond annealing using flash lamps

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Helm, M.; Skorupa, W.

Systematic evolution of the 400 nm electroluminescence (EL) with increasing flash lamp annealing (FLA) temperature from 800 to 1100 °C in an Er-doped Ge-rich metal-oxide semiconductor structure is presented. No significant change in the 1535 nm Er EL is observed with increasing FLA temperature. Enhancement of the 400 nm EL decay time with rising FLA temperature is found to be associated with recrystallization of the damaged Ge clusters in the absence of Ge outdiffusion. The 400 nm EL quenching with continuous charge injection process is also discussed within the device operation time.

Keywords: electroluminescence; flash lamp annealing; Er-doped Ge-rich metal-oxide semiconductor

Publ.-Id: 14361

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