Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Innovative Experimente an der TOPFLOW Versuchsanlage zur Verfikation und Validierung von CFD Codes
Lucas, D.; Hampel, U.; Beyer, M.; Weiß, F.-P.;
There is an increasing interest to apply beside system codes also Computational Fluid Dynamics (CFD) codes for special analyses related to Nuclear Reactor Safety (NRS). Presently CFD codes are frequently used in practical applications for single phase flows, e.g. in automobile or aviation industries. Also in nuclear reactor research CFD codes are successfully applied single phase flows, e.g. for problems related to boron mixing in the primary circuit of Pressure Water Reactors. On the other hand two-phase flow simulations using CFD codes are not yet mature due to the complex interactions between the phases. Examples are poly-dispersed bubbly flows which require a multi bubble size modelling or models for separated flows in horizontal or near horizontal channels which are characterized by large interfaces. For two-phase CFD codes additional closure models are needed to describe mass, momentum and energy transfer between the phases. Such models should consider only local flow parameters, i.e. correlations available for system codes cannot be transferred in general for the use in CFD codes. Instead closure models have to be developed and validated basing on new experimental data with high resolution in space and time. Due to the independency of CFD codes on the geometry and scale it is not necessary to do such experiments in real geometries, but the local flow conditions should be similar the ones expected in praxis. TOPFLOW is a unique thermal hydraulic test facility for such two-phase flow studies. Experiments can be carried out for air-water or steam-water two phase flows at pressures up to 7 MPa. For steam production up to 4 MW heating power are available. This allows to conduct experiments at condition which are close to the nuclear application. On the other hand local data characterizing the micro- or meso-scale structure of the flow are required. For this reason unique measurement devices, such as high-pressure wire-mesh sensors and fast X-ray tomography are applied in TOPFLOW experiments. They provide CFD like data, which means data in high resolution in space and time. The TOPFLOW facility was used for different types of flow experiments in vertical test sections and a large pressure chamber. New experimental setups are currently under preparation. The paper gives a general overview on the experiments done at the facility and their importance for CFD model development and validation for two-phase flows. This is illustrated in detail on the example of poly-dispersed bubbly flows. In addition examples for experimental data useful for the CFD code qualification in case of stratified flows are given. Finally the complex flow situation in case two-phase Pressurized Thermal Shock (PTS) is discussed.
Keywords: two-phase flow, bubble, pipe flow, CCFL, experiment, CFD, wire-mseh sensor, X-ray tomography
  • Invited lecture (Conferences)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 12754 - Permalink


Innovative experiments at the Rossendorf TOPFLOW facility for verification and validation of two-phase flow CFD Codes
Lucas, D.; Hampel, U.; Beyer, M.; Vallée, C.; Weiß, F.-P.;
For special analyses related to Nuclear Reactor Safety (NRS), there is an increasing interest to apply beside system codes also Computational Fluid Dynamics (CFD) codes. Presently CFD codes are frequently used in practical applications for single phase flows, e.g. in automobile or aviation industries. Also in the field of nuclear safety research CFD codes are successfully applied to single phase flows, e.g. for problems related to boron mixing in the primary circuit of Pressure Water Reactors. On the other hand two-phase flow simulations using CFD codes are not yet mature due to the complex interactions between the phases. Examples are poly-dispersed bubbly flows which require a multi bubble size modelling or models for separated flows in horizontal or near horizontal channels which are characterized by large interfaces. For two-phase CFD codes, additional closure models are needed to describe mass, momentum and energy transfer between the phases. Such models should consider only local flow parameters, i.e. correlations available for system codes cannot be transferred in general for the use in CFD codes. Instead, closure models have to be developed and validated basing on new experimental data with high resolution in space and time. Due to the independency of CFD codes on the geometry and scale, it is not necessary to do such experiments in real geometries, but the local flow conditions should be similar the ones expected in praxis. TOPFLOW is a unique thermal hydraulic test facility for such two-phase flow studies. Experiments can be carried out for air-water or steam-water two-phase flows at a pressure up to 7 MPa. For steam production, up to 4 MW heating power are available. This allows to conduct experiments at conditions close to the nuclear application. On the other hand, local data characterizing the micro- or meso-scale structure of the flow are required. For this reason unique measurement devices, such as high-pressure wire-mesh sensors and fast X-ray tomography are applied in TOPFLOW experiments. They provide CFD like data, which means data in high resolution in space and time. The TOPFLOW facility was used for different types of experiments in vertical test sections and in a large pressure chamber. New experimental setups are currently under preparation. The paper gives a general overview on the experiments done at the facility and their importance for CFD model development and validation for two-phase flows. This is illustrated in detail on the example of poly-dispersed bubbly flows. In addition, examples for experimental data useful for the CFD code qualification in case of stratified flows are given.
Keywords: two-phase flow, bubble, pipe flow, CCFL, experiment, CFD, wire-mseh sensor, X-ray tomography
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 12753 - Permalink


Untersuchungen zur Fluoreszenz von Lactat bei Raumtemperatur und tiefen Temperaturen
Wimmer, C.; Arnold, T.; Großmann, K.;
Die Fluoreszenzeigenschaften einer 0,1 M Lactatlösung wurden bei Raumtemperatur und im gefrorenen Zustand bei 200, 100, und 10 K bei einer Anregungswellenlänge von 266 nm durch Kopplung der zeitaufgelösten Laser-induzierten Fluoreszenzspektroskopie (TRLFS) mit einem Kryostatensystem untersucht. Bei Raumtemperatur konnte keine Fluoreszenz nachgewiesen werde. Allerdings war es mit abnehmender Temperatur möglich eine stark zunehmende Fluoreszenzintensität und -lebensdauer zu detektiert. Es konnte ein Intensitätsmaximum bei 472 ± 2 nm und bei 10 K eine Lebensdauer von 6737,5 ± 1,6 ns ermittelt werden.
Keywords: fluorescence lifetime, lactate, laser-induced fluorescence spectroscopy
  • Chemie Ingenieur Technik 81(2009)4, 501-504
    DOI: 10.1002

Publ.-Id: 12752 - Permalink


Quality assurance in accelerator mass spectrometry: Results from international round-robin exercises for 10Be and 36Cl
Merchel, S.; Bremser, W.;
Driven by the overall progress in the field of accelerator mass spectrometry (AMS) and its spreading application within the geosciences, measurements of increasing numbers of samples with low isotopic ratios of 10Be/9Be and 36Cl/Cl will be required in the future. In order to check the quality of measurements at low 10Be concentrations, we have examined the linearity of 10Be/9Be as a function of isotope ratio. For this purpose we have prepared small quantities of three secondary standards and distributed these to nine AMS laboratories. Ratios can be calculated relative to the diluted NIST SRM 4325 after taking account of the 10Be contribution of the 9Be carrier (10Be/9Be=(1.24±0.23)x10-14) @ ASTER, Gif, VERA). As the initial 10Be/9Be of the primary standard is under discussion, results of the secondary standards (~3x10-12/-13/-14) will be discussed relatively to the primary standard ratio only.
The problem of low ratio samples is even more crucial for 36Cl due to the high volatility of chlorine. Thus, we have prepared large quantities of three 36Cl/Cl solutions from a certified 36Cl activity (NIST SRM 4943) by step-wise dilution with NaCl (MERCK CertiPUR®, Cl traceable to NIST SRM 999a). AgCl precipitated from these solutions has been distributed to nine AMS laboratories. Calculated 36Cl/Cl ratios are 1x10-11/-12/-13.
Results for each nuclide show that these interlaboratory exercises are very valuable, as they show maximum differences between individual AMS labs up to 35% for 10Be, and 25% for 25Cl, respectively. Possible reasons for these discrepancies are standard-like materials in use for calibration and cross-contamination in the ion sputter source. A full statistical data evaluation is in preparation and might help to identify more clearly error sources at individual AMS facilities. Thus, we are taking a step forward on the long way of improving quality assurance systems in the AMS community.
Acknowledgments: This round-robin could not have taken place without the interest and team effort of the participating AMS laboratories, as there are: Laboratory for Ion Beam Physics/ETH Zurich, PRIME Lab/Purdue University, The Australian National University/Canberra, CAMS/Lawrence Livermore National Laboratory, Scottish Universities Environmental Research Centre/East Kilbride, Centro Nacional de Aceleradores/University of Seville, University of Tsukuba/Ibaraki, Vienna Environmental Research Accelerator/Universität Wien. This work was partially funded by CRONUS-EU (Marie-Curie Action, 6th FP #511927).
Keywords: AMS, QM, cosmogenic nuclides, reference materials
  • Lecture (Conference)
    19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, UK

Publ.-Id: 12751 - Permalink


Glaciation history of Queen Maud Land (Antarctica) using in situ produced cosmogenic 10Be, 26Al and 21Ne
Altmaier, M.; Herpers, U.; Delisle, G.; Merchel, S.; Ott, U.;
We have determined exposure ages of more than 50 quartz rich samples primarily from the Wohlthat Massiv / Queen Maud Land, Antarctica, via in situ produced 10Be (T1/2 = 1.51 Ma) and 26Al (T1/2 = 0.7 Ma) using accelerator mass spectrometry (AMS). Measured radionuclide concentrations vary from extremely low values up to saturation. For a scenario with extremely low erosion and minimal tectonic uplift 10Be and 26Al surface exposure ages are generally in good agreement. Long exposure ages up to >8 Ma were confirmed by measurement of stable 21Ne using noble gas mass spectrometry.
Our data call for a decisively higher ice stand in the Wohlthat Massiv / Queen Maud Land about 0.3 Ma ago, the ice level being 200 400 m higher than today. The following successive reduction of the glaciation down to the present level was essentially completed 0.1 Ma ago. Low level changes during the last glacial maximum occurred about 0.02 Ma ago and did affect only a region located close to the present shelf ice. As the extremely low erosion rates (<5 cm Ma-1) inferred for several samples can only exist under extremely cold and hyperarid conditions, we exclude a scenario featuring a prolonged period with warm and humid climatic conditions within the last 8 Ma.
Keywords: Antarctica, Queen Maud Land, landscape evolution, glaciation history, cosmogenic nuclides, AMS

Publ.-Id: 12750 - Permalink


Thermal design feasibility of Th-233U PWR breeder
Fridman, E.; Volaski, D.; Shwageraus, E.;
This study explores the basic thermal-hydraulic feasibility of a self-sustainable Th-U233 fuel cycle that can be adopted in the current generation of Pressurized Water Reactors. In previous studies we explored some fuel design strategies to achieve (or to approach as closely as possible) a sustainable fuel cycle, including the use of heterogeneous seed-blanket fuel assembly design. Preliminary neutronic analysis suggested that net breeding of U233 is feasible in principle within a typical PWR operating envelope. However considerable core design tradeoffs such as a reduction of core power density would be necessary to achieve such performance. The purpose of this work is to establish the maximum achievable power density for breeding core by evaluation of limiting thermal hydraulic parameters.
  • Contribution to proceedings
    GLOBAL 2009, 06.-11.09.2009, Paris, France
    Thermal design feasibility of Th-233U PWR breeder
  • Lecture (Conference)
    GLOBAL 2009, 06.-11.09.2009, Paris, France

Publ.-Id: 12749 - Permalink


Laser-driven soft-X-ray undulator source
Fuchs, M.; Weingartner, R.; Popp, A.; Major, Z.; Becker, S.; Osterhoff, J.; Cortrie, I.; Hoerlein, R.; Tsakiris, G. D.; Schramm, U.; Rowlands-Rees, T. P.; Hooker, S. M.; Habs, D.; Krausz, F.; Karsch, S.; Gruener, F.;
Synchrotrons and free-electron lasers (FELs) are the most powerful sources of Xray radiation. They constitute invaluable tools for a broad range of research in physics, biology, materials science, chemistry, and medicine. However, their dependence on large-scale radio-frequency electron accelerators restricted diversification of these X-ray sources to only several sites worldwide. Laser-driven plasma-wave accelerators provide dramatically increased accelerating fields and hence offer the potential to shrink the size and cost of these X-ray sources to the university-laboratory scale. Here we demonstrate the generation of soft-X-ray undulator radiation with laser-plasma-accelerated electron beams. The wellcollimated beams deliver soft-X-ray pulses with an expected pulse duration of ~10 fs, inferred from the physics of plasma-wave accelerators. Our source draws on a dedicated 30-cm-long undulator and a 1.5-cm-long accelerator delivering stable electron beams5 with energies of ~210 MeV. The spectrum of the generated undulator radiation typically consists of a main peak centered at a wavelength of ~18 nm (fundamental), a second peak near ~9nm (second harmonic) and a highenergy cutoff at ~7 nm. Magnetic quadrupole lenses ensure efficient electron beam transport and demonstrate an enabling technology for reproducible generation of tunable soft-X-ray undulator radiation. The source is scalable to shorter wavelengths by increasing the electron energy. Our results open the prospect of brilliant, ultrashort-pulsed X-ray sources becoming available in smallscale laboratories
Keywords: table top FEL, laser driven undulator radiation, EUV

Publ.-Id: 12748 - Permalink


Linear and Non-Linear Thomson-Scattering X-Ray Sources Driven by Conventionally and Laser Plasma Accelerated Electrons
Debus, A.; Bock, S.; Bussmann, M.; Cowan, T. E.; Jochmann, A.; Kluge, T.; Kraft, S. D.; Sauerbrey, R.; Zeil, K.; Schramm, U.;
Compact tuneable sources of ultrashort hard x-ray pulses can be realized by Thomson scattering, taking advantage of the comparatively short wavelength of a scattered laser pulse with respect to the period length of conventional undulators. Here, we present a detailed analysis and optimization of the efficiency of linear and non-linear Thomson scattering when the process is driven with relativistic laser pulses and when the conventional accelerator is replaced by a laser-plasma wakefield accelerator.
Keywords: laser driven x-ray sources, Thomson scattering
  • Contribution to proceedings
    SPIE Europe, Optics and Optoelectronics, 21.-22.4.2009, Prag, Czech Republic
    Harnessing Relativistic Plasma Waves as Novel Radiation Sources from THz to X-rays and beyond, Bellingham, WA (USA): Proceedings of SPIE, 9780819476333, 735908-1-735908-12
  • Invited lecture (Conferences)
    SPIE Europe Optics and Optoelectronics, 21.-22.4.2009, Prag, Czech Republic

Publ.-Id: 12747 - Permalink


Measurement of hydrodynamic non-uniformities and their dynamics in porous particle packings using capacitance wire-mesh sensors
Schubert, M.; Schäfer, T.; Da Silva, M. J.; Thiele, S.; Hessel, G.; Kryk, H.; Hampel, U.;
Despite intensive work in the past decades, hydrodynamics of the widely used trickle bed reactors are still on the focus of today’s research. There are a lot of questions and obstacles to be solved and simple but accurate and reliable measurement devices to be developed. In this study we present a new capacitance wire-mesh sensor system applied to a trickle bed reactor to investigate steady-state and dynamic hydrodynamic characteristics allowing to get new insights into the temporal and spatial behaviour of the trickle flow and pulse flow.
Keywords: capacitance wire-mesh sensor, trickle bed reactor, liquid distribution, liquid saturation, pulse characteristics, flow visualization
  • Poster
    9th International Conference on Gas-Liquid, Liquid-Solid, Gas-Liquid-Solid Reactor Engineering, GLS-9, 23.-27.08.2009, Montreal, Canada
  • Contribution to proceedings
    9th International Conference on Gas-Liquid, Liquid-Solid, Gas-Liquid-Solid Reactor Engineering, GLS-9, 23.-27.08.2009, Montreal, Canada
    Conference Proceedings of the 8th World Congress of Chemical Engineering

Publ.-Id: 12746 - Permalink


Hydrodynamic effects of inclination angle on co-current gas-liquid packed beds
Schubert, M.; Hamidipour, M.; Duchesne, C.; Larachi, F.;
The incidence of inclination angle on the hydrodynamic behaviour of cocurrent gas-liquid flows through a packed bed is investigated experimentally in terms of liquid holdup, pressure gradient, and cross-wise and stream-wise gas-liquid segregation. Electrical capacitance tomography was applied for the analysis of the dynamic features of the two-phase flow as well as liquid saturation distribution. As a result of inclination angle, a segregated flow emerged in packed bed as a new flow regime intertwined between the trickle and the pulse flow regimes. Both segregated flow regime and pulse flow regimes were characterized and their relevant hydrodynamic features discussed.
Keywords: inclined bed, packed bed, hydrodynamics, pulse flow, segregated flow
  • Lecture (Conference)
    9th International Conference on Gas-Liquid, Liquid-Solid, Gas-Liquid-Solid Reactor Engineering, GLS-9, 23.-27.08.2009, Montreal, Canada
  • Contribution to proceedings
    9th International Conference on Gas-Liquid, Liquid-Solid, Gas-Liquid-Solid Reactor Engineering, GLS-9, 23.-27.08.2009, Montreal, Canada
    Conference Proceedings of the 8th World Congress of Chemical Engineering

Publ.-Id: 12745 - Permalink


Hydrodynamic studies in trickle bed reactors using wire mesh sensors
Schubert, M.; Da Silva, M. J.; Kryk, H.;
Multiphase flows exist in many commercial areas such as the manufacture of petroleum-based products and fuels, the production of commodity and specialty chemicals, pharmaceuticals, production of polymers and pollution abatement. The trickle bed reactor (TBR) with a random packing operated in gas-liquid co-current downflow mode is the most widely used multiphase reactor in the chemical, biochemical and waste treatment industry.
There are several advantages of the downflow operation mode, including a wide operating range for gas/liquid flow rates, high capacities as well as high efficiencies. However, due to improper initial gas/liquid distributors, external bed porosity variations, wall effects, partial catalyst wetting and surface tension related effects, intricate problems arise which amongst others are non-uniformities in liquid distribution, liquid velocity and liquid holdup and their dynamics.
A new capacitance wire-mesh sensor for flow imaging is presented which succeeded in overcoming previous difficulties such as applicability for organic liquid flows in porous particle packings, velocity measurements, acquisition time etc. to explore dynamic hydrodynamic features in trickle bed reactors.
  • Lecture (Conference)
    Workshop on Multi-Phase Flows: Simulation, Experiment and Application, 26.-28.05.2009, Dresden, Deutschland
  • Contribution to proceedings
    Workshop on Multiphase Flows: Simulation, Experiment and Application, 26.-28.05.2009, Dresden, Deutschland
    Proceedings of "Multiphase Flows: Simulation, Experiment and Application"

Publ.-Id: 12744 - Permalink


Nicht-Newtonsche schäumende Flüssigkeiten in Rieselbettreaktoren – Hydrodynamische Charakterisierung und effiziente Schaumbegrenzung
Aydin, B.; Schubert, M.; Lange, R.; Larachi, F.;
Hydrodynamische Studien in Rieselbettreaktoren unter erhöhten Drücken und Temperaturen beschäftigen sich hauptsächlich mit koaleszierenden, also nicht-schäumenden, Systemen. Obwohl in zahlreichen industriellen Prozessen schäumende Flüssigkeiten angewandt werden, ist keine aussagekräftige Datenbasis vorhanden. Für die verlässliche Auslegung und den sicheren Betrieb von Reaktoren wurden die Effekte von Temperatur und Druck auf die hydrodynamischen Kenngrößen für Newtonsche und nicht-Newtonsche schaumbildende Systeme untersucht. Außerdem wurde eine neue operative Methode entwickelt, bei der der Rieselbettreaktor alternierend zyklisch betrieben wird und die ohne die Dosierung von chemischen Zusätzen effektiv zur Begrenzung der Schaumbildung eingesetzt werden kann.

Publ.-Id: 12743 - Permalink


Rieselbettreaktoren unter Filtrationsbedingungen – Mechanismus der Ablagerung, Hydrodynamische Folgen, Methoden zur Begrenzung der Filterwirkung
Hamidipour, M.; Schubert, M.; Larachi, F.;
Schüttungen in Rieselbettreaktoren wirken gegenüber Feinpartikeln als Filter. Sowohl in Festbettbioreaktoren als auch bei petrochemischen Anwendungen wird durch die reduzierte Permeabilität und die damit verbundenen Druckverluste die Wirtschaftlichkeit der Prozesse stark beeinträchtigt. Obwohl den Anwendern das Problem bewusst ist, sind die Kenntnisse zur Filterwirkung von Rieselbettreaktoren bisher nicht intensiv erforscht.
Die Mechanismen der Ablagerung und die Auswirkungen auf die Hydrodynamik wurden am Beispiel von Kaolin-Feinpartikeln, die ein dominierender Bestandteil in den nachgelagerten Behandlungsstufen bei der Verarbeitung von Athabasca-Ölsanden sind, untersucht. Zusätzlich werden effektive technische Lösungen und operative Methoden zur Begrenzung der Ablagerungen vorgestellt.

Publ.-Id: 12742 - Permalink


Rieselbettreaktoren unter künstlichem Schwerkrafteinfluss – Prinzip, Umsetzung, Auswirkung und Anwendung
Munteanu, M. C.; Schubert, M.; Larachi, F.;
Die Anwendung von Magnetfeldern hat sich als vielversprechender Ansatz zur Beeinflussung von Gas/Flüssig-Strömungen erwiesen. Obwohl organische Flüssigkeiten gewöhnlich kein magnetisches Verhalten zeigen, kann durch starke Gradienten-Magnetfelder mittels supraleitender Magneten auch in katalytischen Mehrphasenreaktoren, wie zum Beispiel Rieselbettreaktoren, der Schwerkraft entgegengewirkt und damit die Strömung einer erdgebundenen Mikrogravitation ausgesetzt werden. Unter diesen Bedingungen können der Flüssigkeitsanteil in der Katalysatorschüttung und der Benetzungsgrad an der Katalysatoroberfläche effektiv beeinflusst und damit Stofftransport und Umsatz einer katalytischen Reaktion deutlich gesteigert werden.

Publ.-Id: 12741 - Permalink


Native aluminum: Does it exist?
Dekov, V. M.; Arnaudov, V.; Munnik, F.; Boycheva, T. B.; Fiore, S.;
A number of papers reporting exotic native elements have been published within the last few decades. The "native" occurrences described are rather dubious in view of the lack of solid proof of their relationships with the host-rock minerals. Consequently, the genetic models proposed ranging from bio-reduction to the influence of deep-mantle, strongly-reduced fluids, are somewhat speculative. Here we present data for a unique Al0 flake protruding from the phlogopite matrix of a rock specimen collected from a desilicated pegmatite vein. The geologic setting suggests two processes that might have played a key role in the Al0 formation: (1) desilication of pegmatite, resulting in its Al residual enrichment; and (2) serpentinization of an ultramafic body, providing a strongly reduced front (H2 and hydrocarbons) towards the serpentinite/pegmatite contact. These processes have presumably led to the reduction of Al to Al0 at discrete sites of alumina-rich minerals.
Keywords: Native Al, serpentinization, desilication, reduction, pegmatite

Publ.-Id: 12740 - Permalink


Phase holdups in three-phase semi-fluidized beds and the generalized bubble wake model
Schubert, M.; Larachi, F.;
A new experimental measurement methodology was proposed to characterize the hydrodynamics in gas-liquid-solid semi-fluidized beds. Using pressure drop measurements in the lower fluidized bed section and a tracer response technique in the upper fixed bed portion, the six phase holdup components of the reactor were determined simultaneously. Available models for macroscopic predictions of holdups, initially proposed for three-phase fluidization, were extended and their applicability was discussed concerning semi-fluidized beds. Special attention was paid to the parameters of the generalized bubble wake model and their predictability with an artificial neural network. Phenomenological observations identified an additional interface region between both beds, which, viewed as an inchoate freeboard region determines the mechanisms of attachment and release of particles from the fluidized bed to the fixed bed portion.
Keywords: gas-liquid-solid semi-fluidization, hydrodynamics, tracer response technique, bubble wake model

Publ.-Id: 12739 - Permalink


Two color pump-probe studies of intraminiband relaxation in doped GaAs/AlGaAs superlattices
Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.;
In this work we investigate the miniband relaxation dynamics of electrons in doped GaAs/AlGaAs superlattices by two-color infrared pump-probe experiments using a free electron laser synchronized to a table top broadband IR source. In contrast to single color experiments, by this technique we are able to separate the different contributions from inter- and intraminiband relaxation to the transient behavior after an ultrafast excitation. In particular, the intraminiband relaxation is studied for different miniband widths, below and above the optical phonon energy of GaAs. For minibands wider than this critical value we find fast relaxation, nearly constant for different excitation intensities whereas for narrow minibands, a strong temperature and intensity dependence of the relaxation is found. The results are in good agreement with previously published Monte Carlo simulations.
Keywords: superlattice, intersubband, intrasubband, miniband, ultrafast spectroscopy, relaxation, two-color.
  • Invited lecture (Conferences)
    SPIE Photonics West, 24.-29.01.2009, San Jose, CA, USA
  • Contribution to proceedings
    SPIE Photonics West, 24.-29.01.2009, San Jose, Ca, USA
    Two color pump-probe studies of intraminiband relaxation in doped GaAs/AlGaAs superlattices

Publ.-Id: 12738 - Permalink


Efficiency calibration of the ELBE nuclear resonance fluorescence setup using a proton beam.
Trompler, E.; Bemmerer, D.; Beyer, R.; Broggini, C.; Caciolli, A.; Erhard, M.; Fülöp, Z.; Grosse, E.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Marta, M.; Menegazzo, R.; Nair, C.; Schwengner, R.; Szücs, T.; Wagner, A.; Yakorev, D.;
The nuclear resonance fluorescence (NRF) setup at ELBE uses bremsstrahlung with endpoint energies up to 20 MeV. The setup consists of four 100% high-purity germanium detectors, each surrounded by a BGO escape-suppression shield and a lead collimator. The detection efficiency up to E = 12 MeV has been determined using the proton beam from the FZD Tandetron and well-known resonances in the 11B(p,gamma)12C, 14N(p,gamma)15O, and 27Al(p,gamma)28Si reactions. The deduced efficiency curve allows to check efficiency curves calculated with GEANT. Future photon-scattering work can be carried out with improved precision at high energy. — This work has been supported in part by the European Union (FP6 AIM RITA 025646).
Keywords: ELBE; HPGe efficiency calibration; Tandetron
  • Lecture (Conference)
    Frühjahrstagung des DPG - Fachverbands Hadronen und Kerne and European Nuclear Phyisics Conference (EuNPC), 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 12737 - Permalink


The 15N(p,gamma )16O reaction studied at LUNA.
Bemmerer, D.; Caciolli, A.; Bonetti, R.; Broggini, C.; Confortola, F.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Formicola, A.; Fulop, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyurky, G.; Junker, M.; Limata, B.; Marta, M.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Alvarez, C. R.; Somorjai, E.; Straniero, O.;
The 15N(p,gamma)16O reaction lies at the intersection of the first and second CNO cycle of hydrogen burning. Recent R-matrix extrapolations suggest that its cross section may be lower by about a factor two with respect to previous work. Here we show new, direct experimental data on this reaction obtained at the LUNA 400 kV accelerator deep underground in the Gran Sasso laboratory in Italy.
Keywords: Nuclear astrophysics; Nova burning; CNO cycle; gas target; BGO detector; LUNA
  • Poster
    Frühjahrstagung des DPG - Fachverbands Hadronen und Kerne and European Nuclear Phyisics Conference (EuNPC), 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 12736 - Permalink


Thermoelectromagnetic convection - an alternative stirring technique in metallurgy
Cramer, A.; Zhang, X.; Gerbeth, G.;
Thermoelectromagnetic convection in electrically conducting cubic containers was studied experimentally. Two opposing side walls were cooled and heated, respectively, to produce a uniform temperature gradient. Inhomogeneous magnetic field distributions were achieved either with a small permanent magnet located above the melt layer, or with specifically shaped pole shoes of the magnetic system. Ultrasonic Doppler velocimetry measurements demonstrated that even a moderate temperature gradient may drive a distinct convection. Two different flow regimes were investigated with the permanent magnet. When it was positioned in the vicinity of an isothermal wall, with its direction of magnetization parallel to the temperature gradient, a single vortex spreading the whole container developed while the flow might be assessed as relatively stable. Moving the magnet to the center led to a modified distribution of the magnetic field, which altered the flow structure. The convective pattern changed to four vortices and the velocity fluctuations were intensified. A more generic case was realized with the pole shoes providing a gradient of the magnetic field only in one direction. Since the strength of the field could be raised significantly above that provided by the small permanent magnet and the area of impact onto the melt was larger, developed turbulent regimes were accomplished. Numerical results obtained for the Lorentz force and the rotor thereof support the experimental findings.
  • Contribution to proceedings
    International Symposium on Liquid Metal Processing and Casting, 20.-23.09.2009, Santa Fe, New Mexico, 978-0-87339-743-8
  • Lecture (Conference)
    International Symposium on Liquid Metal Processing and Casting, 20.-23.09.2009, Santa Fe, New Mexico

Publ.-Id: 12735 - Permalink


Laser-Driven-Protons and Their Future in Oncology
Burris, T.;
The advancement of high power (1e20 W/cm^2), short pulse (25 fs) laser systems has allowed for the production of high field gradients (~1e12 V/m) on the rear side of micron thick targets. This high field gradient is responsible for accelerating protons up to tens of MeV. This poster gives an overview of the work being performed at Forschungszentrum Dresden to study and develop the technique of proton laser acceleration into an Oncology based therapy unit, and it presents the first planned relative biological effectiveness experiments along with the associated dosimetry and beam transport.
Keywords: laser accelerated protons relative biological effectiveness
  • Poster
    Workshop on Hadron Beam Therapy of Cancer, Erice Italy, 24.04.-01.05.09, Erice, Italy

Publ.-Id: 12734 - Permalink


Strength, decay branching ratios, and angular distribution of the 0.987MeV resonance in the 14N(p,gamma )15O reaction.
Marta, M.; Bemmerer, D.; Beyer, R.; Broggini, C.; Caciolli, A.; Erhard, M.; Fülöp, Z.; Grosse, E.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Menegazzo, R.; Nair, C.; Schwengner, R.; Szücs, T.; Trompler, E.; Wagner, A.; Yakorev, D.;
The 14N(p,gamma)15O reaction controls the rate of the hydrogen burning CNO cycle. This reaction has recently been re-studied at E < 500keV at different facilities, including LUNA. However, also data at higher energy play a role in determining the extrapolated cross section in the R-matrix framework. Here we report on a new measurement of the absolute strength, decay branching ratio, and angular distribution of the E = 0.987 MeV (E_x = 8.284 MeV) resonance carried out at the high-current FZD Tandetron. --- This work has been supported in part by the European Union (FP6 AIM RITA 025646).
Keywords: Nuclear astrophysics; CNO cycle; Tandetron; TiN solid target
  • Lecture (Conference)
    Frühjahrstagung des DPG - Fachverbands Hadronen und Kerne and European Nuclear Phyisics Conference (EuNPC), 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 12733 - Permalink


Determination of the Saturation Magnetization from Perpendicular Magnetic Anisotropy Measurements of Ion Irradiated Multilayers
Markó, D.; Strache, T.; Lenz, K.; Fassbender, J.ORC; Kaltofen, R.
Thin films and superlattices of Py/Ta with an overall Py thickness of 20 nm and different number of Py/Ta stacks were irradiated with Ne ions in order to study the influence of interfacial mixing on their magnetic properties. With both, increasing ion fluence and increasing number of Py/Ta interfaces, a decrease of saturation magnetization and an increase of damping can be observed. However, the small uniaxial anisotropy of the samples remains unaffected. The critical ion fluence at which ferromagnetism, depending on the number of interfaces, vanishes has been determined.
Keywords: Magnetic Multilayers, Magnetic Anisotropy, Ferromagnetic Resonance

Publ.-Id: 12731 - Permalink


Epitaxial 3C-SiC nanocrystal formation at the SiO2 /Si interface by combined carbon implantation and annealing in CO atmosphere
Pécz, B.; Stoemenos, J.; Voelskow, M.; Skorupa, W.; Dobos, L.; Pongrácz, A.; Battistig, G.;
High quality 3C-SiC nanocrystallites were epitaxially formed on 100 Si wafers covered by a 150 nm thick SiO2 capping layer after low dose carbon implantation and high temperature annealing in CO atmosphere. Carbon implantation is used to introduce nucleation sites by forming silicon-carbon clusters at the SiO2 / Si interface acting as nucleation sites for the growth of 3C-SiC nanocrystallites. The formation of the nucleation clusters as well as the morphology, the size, and the density of the nanocrystals were systematically studied by conventional and high resolution transmission electron microscopy. The nanocrystallites were developed following two different modes of growth: The first develops facets along the <100> crystallographic direction giving tetragonal grains and the second facets along the <110> direction resulting in elongated nanocrystallites. The formation mechanism of the nanocrystallites and the strain related with them are also discussed
Keywords: nanocrystals, carbon implantation, annealing, CO, TEM, microstructure
  • Journal of Applied Physics 105(2009), 083508-1-083508-8

Publ.-Id: 12730 - Permalink


Memory effect of magnetic nanoparticle systems originating from particle size distribution
Zhang, G.; Potzger, K.; Zhou, S.; Mücklich, A.; Ma, Y.; Fassbender, J.ORC
Magnetic characteristics of both interacting and noninteracting Fe nanoparticle systems synthesized inside LaAlO3 matrices were investigated, utilizing SQUID magnetometry. The origin of the magnetic memory effect was explored. We found that not the interaction between magnetic nanoparticles but the size distribution is mainly responsible for that effect. Transmission electron micrographs support the finding by recording the FC/ZFC magnetization to evidence our illumination.
Keywords: Magnetic nanoparticles; Ion implantation

Publ.-Id: 12729 - Permalink


Defect engineering in the MOSLED structure by the ion implantation
Prucnal, S.; Wójtowicz, A.; Pyszniak, K.; Drozdziel, A.; Zuk, J.; Turek, M.; Rebohle, L.; Skorupa, W.;
When amorphous silica is bombarded with energetic ions, various types of defects are created as a consequence of ion-solid interaction (peroxy radicals POR, oxygen deficient centres ODC, non-bridging oxygen hole centres NBOHC, E’-centres, etc.). The intensity of the electroluminescence from oxygen deficiency centres at 2.7 eV, non-bridging oxygen hole centres at 1.9 eV and defect centres with emission at 2.07 eV can be easily modified by the ion implantation of the different elements (H, N, O) into the full processed MOSLED structure. Nitrogen implanted into the SiO2:Gd layer reduces the concentration of the ODC and NBOHC while the doping of the oxygen increases the EL intensity observed from POR defect and NBOHC. Moreover, after oxygen or hydrogen implantation into the SiO2:Ge structure fourfold or fifth fold increase of the germanium related EL intensity was observed.
Keywords: MOSLED, ion implantation, defect engineering, electroluminescence
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1311-1313

Publ.-Id: 12728 - Permalink


Ex-situ n and p doping of vertical epitaxial short silicon nanowires by ion implantation
Das Kanungo, P.; Kögler, R.; Nguyen-Duc, K.; Zhakarov, N.; Werner, P.; Gösele, U.;
Epitaxial silicon nanowires (Si NWs) grown by molecular beam epitaxy on Si <111> substrates were separately doped p and n-type ex situ by implanting with B, P and As ions at room temperature with doses in the order of 1013 - 1014 cm-2. No implantation damage was observed in the B-implanted NWs after a rapid thermal annealing at 850°C for 30 s whereas the same could not heal out the P and As-implanted NWs completely. Electrical measurements showed that the desired doping concentrations were achieved for the B implanted NWs (p-type) while for the P and As implanted NWs (n-type) the measured carrier concentrations fell four orders of magnitude short of the intended. Incomplete electrical activation of the dopant atoms and out-diffusion/segregation at defects of dopants during annealing are probably responsible for such discrepancies in carrier concentrations in the n-type (P and As doped) NWs.
Keywords: Ion implantation, Doping, Si-nanowires
  • Nanotechnology 20(2009), 165706-165713

Publ.-Id: 12727 - Permalink


Spectroscopic characterization of Au-complexation and nanoparticle formation on S-layer protein of L. sphaericus JG-A12
Jankowski, U.; Fahmy, K.; Selenska-Pobell, S.; Merroun, M.;
The strain Lysinibacillus sphaericus JG-A12, isolated from the uranium mining waste pile “Haberland” in Saxony (Germany), is capable of selective and reversible accumulation of radionuclides and toxic metals. It was demonstrated that metal binding is caused generally by the surface layer of the protein. This S-layer possesses a highly ordered lattice structure and can serve as a template spatially confined metal nanoparticle growth.
Our aim was to elucidate binding modes of Au to S-layer protein from L. sphaericus JG-A12.
In this study Au-complexes were produced by sorption of Au(III) on S-layer and reduction of these complexes to Au(0) nanoparticles. Au(III) complexes and Au(0) nanoparticles were studied by means of FTIR and EXAFS techniques.
EXAFS reveals the short range environment of the metal. No significant differences between the Au(III) and Au(0) were observed. Furthermore, EXAFS can only distinguish between elements in the short range order around the metal, the detected elements N, O and C cannot further be assigned to specific chemical groups.
FTIR measurements have shown that side chain carboxylates play a different role in Au(0) complex formation as compared to the complexation of Pd(II) or Pt(II).
For Au a weakening of asymmetric (1560 cm-1) and symmetric (1400 cm-1) carboxylate stretching mode indicates a different binding mode of Au to protein, probably involving stabilization of the protonated state of the carboxyls.
Hypothesize that Au causes hydrophobic burial, and thus protonation of carboxylic side chains rather than ionic interactions as found for Pd.
The results let us conclude that the binding mode of Au to S-layer from L. sphaericus JG-A12 is remarkably different from that of Pt or Pd.
  • Poster
    The European conference on the Spectroscopy of Biological Molecules, 28.08.-02.09.2009, Palermo, Italien

Publ.-Id: 12726 - Permalink


Progress towards lightning control using lasers
Kasparian, J.; Ackermann, R.; Andre, Y. B.; Mechain, G.; Mejean, G.; Prade, B.; Rohwetter, P.; Salmon, E.; Stelmaszczyk, K.; Mysyrowicz, A.; Sauerbrey, R.; Woeste, L.; Wolf, J. P.;
Lightning research needs on-demand lightning strikes, because of the random character of natural lightning. Lasers have been proposed as alternatives to the current technique using rocket-pulled wires, because they would expectedly provide more flexibility. However, high-energy, nanosecond lasers cannot provide long connected plasma channels. In contrast, we recently reported the triggering of electric events in thunderclouds using ultrashort laser pulses. Further improvements of the laser pulse sequence and experimental geometry are discussed.

Publ.-Id: 12724 - Permalink


The age of the Monturaqui impact crater
Valenzuela, M.; Rochette, P.; Bourlès, D. L.; Braucher, R.; Faestermann, T.; Finkel, R. C.; Gattacceca, J.; Korschinek, G.; Merchel, S.; Morata, D.; Poutivtsev, M.; Rugel, G.; Suavet, C.;
Introduction: The Monturaqui crater is the only meteorite impact related structure yet found in Chile. The simple crater of ~400 m diameter and ~34 m of depth [1] is localized at 3015 m altitude in the precordillera near the southern end of Salar de Atacama. The crater age was estimated as older than 0.1 Ma with an appreciable error by [2] by thermoluminescence analysis. We are reporting the first absolute ages of the Monturaqui impact following two approaches: a) the terrestrial age of the impactor by measuring the residual activities of 10Be, 26Al, 36Cl, 41Ca, 59Ni, 60Fe, and 53Mn in iron shale samples, which corresponds to the altered fragments of the impactor (coarse octahedrite - group I - deduced from Fe-Ni-spherules found in impact melt ejecta [2,3]), and b) surface exposure ages by measuring in-situ produced 10Be in the granite outcrops exposed to cosmic radiation on Earth.
Experimental: Accelerator mass spectrometry of 10Be and 26Al took place at ASTER, 36Cl at CAMS, and 53Mn at the Maier-Leibnitz-Laboratory. Other nuclides are foreseen soon.
Results: Measured concentrations are compared with depth-depending production rates (PRs) from theoretical Monte-Carlo calculations [priv.com., I. Leya]. As these PRs are based on the chemical composition (in space), remaining fragments are highly altered and precise chemical analyses could not yet be achieved, certain assumptions are influencing the discussion of our, thus preliminary, data.
The longest-lived radionuclide53Mn (t1/2=3.7 Ma), normalized to a fully corroded Fe2O3-sample, is the least sensitive nuclide to a varying terrestrial age, thus, providing us with the best value for a shielding depth: 62-71 cm. The best fit of the measured shortest-lived radionuclide 36Cl (t1/2=0.3 Ma) with theoretical PRs at that depth is for a terrestrial age of 500-600 ka. The 26Al-activity (t1/2=0.7 Ma) validates that age. The measured 10Be is far too high compared to theoretical PRs (based on a C-content of 0.1%, as Canyon Diablo). This goes along with earlier studies [4,5] demonstrating the big influence of inhomogeneously distributed traces as C, S, and P on the production of light nuclides.
Our second approach, using terrestrial 10Be, leads to a minimum in-situ exposure age of two quartz-rich samples from the crater wall of 200-250 ka. However, a larger age is very likely due to the subsequent erosion of the crater walls.
Preliminary paleomagnetic measurements of the granite within the crater revealed mixed normal and reverse magnetic field polarities suggesting a possible age for the impact remag-netization older than 780 ka.
Acknowledgements: CRONUS-EU, CNRS-CONICYT, M. Arnold, G. Aumaître, L. Benedetti, and I. Leya.
References: [1] Ugalde H. et al. 2007. Meteoritics & Planetary Science 42:2153. [2] Buchwald V. F. 1975. Handbook of iron meteorites 1:262. [3] Bunch P. E. and Cassidy W. 1972. Contrib. Mineral. Petrol. 36:95. [4] Leya I. and Michel R. 1998. Abstract #1172. 29th Lunar and Planetary Science Conference. [5] Leya I. et al. 1997. Meteoritics & Planetary Science 32:A78.
Keywords: accelrator mass spectrometry, terrestrial cosmogenic nuclides, AMS, TCN
  • Abstract in refereed journal
    Meteoritics & Planetary Science 44(2009)7 Suppl., 5185
  • Poster
    72nd Annual Meeting of the Meteoritical Society, 13.-18.07.2009, Nancy, France

Publ.-Id: 12723 - Permalink


Hydrodynamische Untersuchungen in Rieselbettreaktoren mittels kapazitiver Gittersensoren
Kryk, H.; Schubert, M.; Schäfer, T.; Da Silva, M. J.; Thiele, S.;
Rieselbettreaktoren sind von besonderer technischer Bedeutung für kontinuierliche Gas/Flüssig-Reaktionsprozesse. Voraussetzung für die strömungstechnische Analyse und Optimierung von Rieselbettprozessen ist die Kenntnis örtlich und zeitlich aufgelöster hydrodynamischer Parameter wie Phasen- und Geschwindigkeitsverteilung im Strömungsquerschnitt sowie Pulsfrequenz, -geschwindigkeit und Pulsform bei höheren Strömungsgeschwindigkeiten. Diese Aufgaben stellen hohe Anforderungen an neuartige Messsysteme.
Die Untersuchungen dieser charakteristischen Parameter wurden in einem Rieselbettreaktor im Pilotmaßstab (D = 100 mm, H = 1,4 m, Al2O3-Packung) durchgeführt. Als Messsysteme kamen 4 neuartige Gittersensoren zum Einsatz, die in verschiedenen Ebenen des Reaktors angeordnet sind. Die Sensoren bestehen aus zwei Ebenen, bei denen je 16 Edelstahldrähte rechtwinklig zueinander angeordnet sind, wodurch sich 208 Messpunkte je Sensor im Strömungsquerschnitt ergeben. Das kapazitive Messprinzip erlaubt die Anwendung industrierelevanter organischer Flüssigkeiten.
Durch eine hohe Abtastrate von bis zu 1000 Hz können auch transiente Strömungen im Reaktor, z.B. im Pulsregime oder bei instationärer Prozessführung, visualisiert werden. Die Verwendung eines Doppel-Gittersensors ermöglicht außerdem die Untersuchung von Strömungs- und Pulsgeschwindigkeiten mithilfe von Tracern. Die Untersuchungen dienen der Optimierung von Prozessführung und Apparatedesign sowie der Validierung von CFD-Simulationen.
  • Poster
    ProcessNet-Jahrestagung 2009, 08.-10.09.2009, Mannheim, Deutschland
  • Abstract in refereed journal
    Chemie Ingenieur Technik 81(2009)8, 1117-1117

Publ.-Id: 12722 - Permalink


Antiproton evolution in little bangs and in the Big Bang
Schade, H.; Kämpfer, B.;
The abundances of antiprotons and protons are considered within momentum-integrated Boltzmann equations describing Little Bangs, i.e., fireballs created in relativistic heavy-ion collisions. Despite of a large antiproton annihilation cross section we find a small drop of the ratio of antiprotons to protons from 170 MeV (chemical freeze-out temperature) until 100 MeV (kinetic freeze-out temperature) for CERN-SPS and BNL-RHIC energies thus corroborating the solution of the previously exposed ”antiproton puzzle”. In contrast, the Big Bang evolves so slowly that the antibaryons are kept for a long time in equilibrium resulting in an exceedingly small fraction. The adiabatic path of cosmic matter in the phase diagram of strongly interacting matter is mapped out.

Publ.-Id: 12721 - Permalink


Chiral symmetry and open-charm mesons
Hilger, T.; Kämpfer, B.;
Pseudo-scalar and scalar D mesons are considered within the QCD sum rule approach. We present an analysis of the mass splitting of the pseudo-scalar D - D mesons and the relation to QCD condensates. Weinberg type sum rules are derived for chiral partners which highlights the role of the chiral condensate.
  • Open Access LogoIl Nuovo Saggiatore Italian Physical Society (2009)
  • Contribution to proceedings
    XLVII International Winter Meeting on Nuclear Physcis, 26.-30.01.2009, Bormio, Italien
    Conference Proceedings Vol. 99

Publ.-Id: 12720 - Permalink


Uncertainty analyses of coupled thermal hydraulic/neutron kinetic code calculations for transients at NPPs with VVER reactors
Kliem, S.; Langenbuch, S.; Weiß, F.-P.;
The transition from the application of conservative models to the use of best-estimate models raises the question about the uncertainty of the obtained results. This question becomes especially important, if the best-estimate models should be used for safety analyses in the field of nuclear engineering. Different methodologies were developed to assess the uncertainty of the calculation results of computer simulation codes. One of them is the methodology developed by Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) which uses the statistical code package SUSA. In the past, this methodology was applied to the calculation results of the advanced thermal hydraulic system code ATHLET. In the frame of the recently finished EU FP5 funded research project VALCO, that methodology was extended and successfully applied to different coupled code systems, including the uncertainty analysis for neutronics. These code systems consist of a thermal hydraulic system code and a 3D neutron kinetic core model. Six different working groups applying different coupled code systems performed calculations. The involved system codes were ATHLET and SMABRE. They were used for the calculations together with the 3D neutron kinetic core models DYN3D, KIKO3D, BIPR8 and HEXTRAN.
Two real transients at NPPs with VVER-type reactors documented within the VALCO project were selected for analyses. One was the load drop of one of two turbines to house load level at the Loviisa-1 NPP (VVER-440), the second was a test with the switching-off of one of two main feed water pumps at the VVER-1000 Balakovo-4 NPP. Based on the relevant physical processes in both transients, lists of possible sources of uncertainties were compiled. They are specific for the two transients. Besides control parameters like control rod movement and thermal hydraulic parameters like secondary side pressure, mass flow rates, pressurizer sprayer and heater performance, different neutron kinetic parameters were included into the list of possible sources of uncertainties. These are the burn-up state of the core, the control rod efficiency for different control rod groups and the coefficients for Doppler and moderator density feed back. By use of the SUSA package, sets of input data with statistical variation of the relevant parameter values were generated for a large number of runs of the coupled codes for each transient.
Time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. First of all, these are the core power, upper plenum pressure, core outlet and loop temperatures. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations. This list gives indications for further model improvements and code developments.
  • Lecture (Conference)
    OECD Benchmark for Uncertainty Analysis in Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs - Third Workshop, 29.04.-01.05.2009, State College, USA

Publ.-Id: 12719 - Permalink


Validation of the coupled code system DYN3D/ATHLET on the basis of transients at NPPs with VVER reactors
Kliem, S.; Rohde, U.; Weiß, F.-P.;
In the presentation, an overview on the validation activities for the coupled 3D neutron kinetic / thermal hydraulic system code DYN3D/ATHLET is given.
  • Lecture (Conference)
    OECD Benchmark Workshop for Kalinin-3 VVER-1000 Coupled Code Calculations, 27.-28.04.2009, State College, USA

Publ.-Id: 12718 - Permalink


Ion sputtering of Si surfaces at normal incidence: roughening versus smoothening
Zhou, J.; Facsko, S.; Keller, A.; Möller, W.;
Ion sputtering of Si surfaces at normal incidence has been studied with and without metal codeposition. Metal impurities are necessary for dot pattern formation. Normal incidence ion sputtering of Si without metal codeposition has a smoothening instead of a roughening effect. The smoothening effect is effected by the presence of metal impurities and differs from „classical“ relaxation mechanisms where the decay coefficient has a power law dependence on the wavenumber.
  • Lecture (others)
    Treffen der DFG-Forschergruppe 845 "Selbstorganisierte Nanostrukturen durch niederenergetische Ionenstrahlerosion", 31.3.2009, Köln, Deutschland

Publ.-Id: 12717 - Permalink


Investigations of the beltline welding seam and base metal of a WWER-440 first generation reactor pressure vessel from the former Greifswald NPP
Schuhknecht, J.; Rindelhardt, U.; Viehrig, H.-W.;
The paper presents results of the circumferential core weld SN0.1.4 and the base metal ring 0.3.1 of the RPV from the unit 1 of the Greifswald WWER-440/230. The investigated trepans represent the irradiated-annealed-re-irradiated (IAI) condition. The working program is focussed on the characterisation of the RPV steels through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921 to determine the fracture toughness in different thickness locations.
Keywords: WWER, reactor pressure vessel steel, weld metal, base metal, trepans, welding seam, fracture toughness, Master Curve, Charpy-V
  • Lecture (Conference)
    Structural Integrity and Life of NPP Equipment: SIL 2009, 20.-22.05.2009, Kiev, Ukraine
  • Contribution to proceedings
    Structural Integrity and Life of NPP Equipment: SIL 2009, 20.-22.05.2009, Kiev, Ukraine
    Abstracts "SIL-2009", Kiev, 978-966-02-5224-0, 10-11

Publ.-Id: 12716 - Permalink


Wasserkraftnutzung an der Saale
Rindelhardt, U.;
Im Beitrag wird die Entwicklung der Laufwasserkraftnutzung an der Saale dargestellt. Einem starken Ausbau in der ersten Hälfte des 20. Jahrhunderts folgte ein Niedergang bis 1990. Heute arbeiten in Thüringen und Sachsen-Anhalt 32 Laufwasserwasserkraftanlagen mit einer Leistung von etwa 28 MW (Arbeit 120 GWh/a). Dazu kommen 110 GWh/a Strom aus regenerativer Wasserkraft von den PSW Bleiloch und Hohenwarthe I. Am bayrischen Oberlauf der Saale arbeiten 11 WKA mit einer Leistung von 0,7 MW (Arbeit 2 GWh/a). Unter den aktuellen Rahmenbedingungen kann noch mit einem Zubau von etwa 6 MW (24 GWh/a) gerechnet werden.
The development of the run-of-river hydropower on the river Saale is described. The extensive use in the first half of the last century was followed by a strong decrease between 1960 and 1990. Today 32 hydropower plants are again operating in Thuringia and Saxony-Anhalt with total power of 28 MW (120 GWh/a). The PSP Bleiloch and Hohenwarthe I additionally provide a renewable hydropwer generation of 110 GWh/a. Further 11 plants operate in Bavaria (power 0,7 MW, energy 2 GWh/a). A power increase of about 6 MW (corresponding to 24 GWh/a) can be expected taking into account the actual framework conditions.
Keywords: potential hydro power, Saale river
  • EW : Das Magazin für die Energiewirtschaft (2009)19, 44-49

Publ.-Id: 12715 - Permalink


High-spin level structure of 94,95Mo
Zhang, Y. H.; Hasegawa, M.; Guo, W. T.; Liu, M. L.; Zhou, X. H.; de Angelis, G.; Axiotis, T. M.; Gadea, A.; Marginean, N.; Martinez, D. R. N.; Rusu, C.; Podolyak, Z.; Ur, C.; Bazzacco, D.; Brandolini, F.; Lunardi, S.; Lenzi, S. M.; Menegazzo, R.; Schwengner, R.; Gargano, A.; von Oertzen, W.; Tazaki, S.;
High-spin level structures of 94,95Mo have been reinvestigated via the 16 O(82 Se, xn )94,95 Mo (x = 4, 3) reactions at E(82Se) = 460 MeV. The previously reported level schemes of these two nuclei have been largely modified up to 11 MeV in excitation energy due to identifications of some important linking transitions. Shellmodel calculations have been made in the model space of pi(p1/2 , g9/2 , d5/2 )4 and nu(d5/2 , s1/2 , d3/2 , g7/2 , h11/2 )2(3) and compared with the modified level schemes. The structures of the newly assigned high-spin states in 94,95Mo have been discussed.
Keywords: Nuclear Structure. Gamma-ray spectroscopy. Shell model.

Publ.-Id: 12714 - Permalink


Interaction of uranium(VI) with nitrogen containing model ligands studied by laser-induced fluorescence spectroscopy
Raditzky, B.; Schmeide, K.; Sachs, S.; Geipel, G.; Bernhard, G.;
The complexation of uranium(VI) with two nitrogen containing organic ligands, representing model substances for humic acid building blocks, has been investigated at pH values between 1.5 and 4.5 and an ionic strength of 0.1 M (NaClO4). Using two independent fluorescence spectroscopic methods, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses (fs-TRLFS), the complex formation of uranium(VI) with anthranilic and nicotinic acid in aqueous solution was studied. In both systems a decrease in the luminescence intensity was observed with increasing ligand or metal ion concentration. Uranium(VI) complexes of the type MxLyHz were identified. Anthranilic acid forms a 1:1 complex under the given experimental conditions with a stability constant of log ß111 = 8.00 ± 0.10. For the uranium(VI) nicotinate system 1:1 and 1:2 complexes could be identified. The corresponding formation constants were calculated to be log ß111 = 8.60 ± 0.08 and log ß122 = 17.29 ± 0.10.
Keywords: uranium(VI), complexation, anthranilic acid, nicotinic acid, TRLFS, fs-TRLFS

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Publ.-Id: 12713 - Permalink


Novel U(VI) Complexes of Bis(2-hydroxyaryl)imine Ligands: Synthesis, Structural Characterization, and Extraction Studies
Tanh Jeazet, H.; Doert, T.; Gloe, K.; Tsushima, S.; Geipel, G.; Gloe, K.; Bernhard, G.;
The coordination chemistry of uranium in differen toxidation states has recently gernerated much attention due to several reasons. The most important reason is the separation of U(VI) presentin radioactive waste, but also the effects of U(VI) on our environment. The extraction and separation of U(VI) and other actinides, especially the separation from lanthanides, is most difficult due to their similar chemical behaviour...
  • Contribution to proceedings
    GDCh Jahrestagung, Fachbereich Nuklearchemie, 30.08.-02.09.2009, Frankfurt, Deutschland

Publ.-Id: 12711 - Permalink


Zeitaufgelöste PIV-Untersuchungen zur Strömungskontrolle mittels elektromagnetischer Kräfte in schwach leitfähigen Fluiden
Cierpka, C.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-516 2009

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Publ.-Id: 12710 - Permalink


Untersuchung der Wechselwirkung von Uran (VI) mit der Grünalge Chlorella vulgaris in Abhängigkeit von pH-Wert und metabolischer Aktivität
Vogel, M.; Günther, A.; Raff, J.; Bernhard, G.;
Die Grünalgen (Chlorophyta) gehören zur Gruppe der aquatischen „niederen“ Pflanzen, die in Süß-, Salzwasser und im Boden leben können. Aufgrund der weiten Verbreitung der Algen ist deren Einfluss auf die Migrationsprozesse von Uran und anderen Aktiniden in der Umwelt von grundlegendem Interesse. Außerdem spielen Algen eine wirtschaftlich relevante Rolle als Nahrungsmittel sowie Nahrungsergänzungsstoff, so dass von der Alge aufgenommene Schwermetalle und Aktiniden in die Nahrungskette gelangen und so auch eine Gesundheitsgefahr für den Menschen darstellen können.
Die einzellige Grünalge Chlorella vulgaris besitzt die Fähigkeit im pH-Wertbereich von 3 bis 7 größere Mengen an Uran (VI) zu binden.[1][2] Ziel dieser Studie war es die Wechselwirkung von Uran (VI) mit der Alge C. vulgaris quantitativ und strukturell insbesondere unter Einwirkung umweltrelevanten Urankonzentrationen bei metabolischer Aktivität der Zellen zu charakterisieren. Bei pH 4,4 wurde Uran (10-4 M, 5x10-6 M) sowohl von lebenden als auch toten Zellen unter den gegebenen experimentellen Bedingungen nahezu vollständig gebunden. Die Untersuchung der Wechselwirkung von Algen mit Uran bei Anfangs-pH-Werten von 4,4 bis 7 und niedriger Urankonzentration zeigte zunächst ebenfalls eine vollständige Sorption von Uran an die Zellen. Interessanterweise wird in Ansätzen mit metabolisch aktiven Algen ein Teil des gebundenen Urans im Verlauf der Inkubation wieder freigesetzt. Eine mögliche Erklärung dafür ist die Wechselwirkung des Urans mit Ausscheidungs¬produkten der Algen und eine dadurch bedingte Desorption. Für die Charakterisierung der in den Lösungen und an der Biomasse gebildeten Uranylspezies wurde die Laser-induzierte Fluoreszenzspektroskopie und die Röntgenabsorptionsspektroskopie genutzt. Die spektroskopischen Untersuchungen zeigen Unterschiede bei den gebildeten Komplexen zwischen Uran und der Algenbiomasse in Abhängigkeit von der metabolischen Aktivität der Algenzellen und der Uranspeziation in den Ausgangslösungen. Für die Bindung von Uran an die Algenzellen scheinen insbesondere Phosphatgruppen verantwortlich zu sein. Eine Beteiligung von Karboxylgruppen kann zum gegenwärtigen Zeitpunkt nicht eindeutig ausgeschlossen werden.

Literatur:

[1] A. Günther et al., Biometals 2008, 21, 333. [2] M. Vogel et al., Uranium, Mining and Hydrogeology 2008, 693.
Keywords: Chlorella vulgaris, algae, uranium(VI), biosorption, TRLFS
  • Poster
    GDCh-Wissenschaftsforum Chemie 2009, 30.08.-02.09.2009, Frankfurt am Main, Deutschland

Publ.-Id: 12709 - Permalink


New age estimation of the Monturaqui impact crater
Valenzuela, M.; Bourlès, D. L.; Braucher, R.; Faestermann, T.; Finkel, R. C.; Gattacceca, J.; Korschinek, G.; Merchel, S.; Morata, D.; Poutivtsev, M.; Rochette, P.; Rugel, G.; Suavet, C.;
The Monturaqui impact crater is the only meteorite impact related structure yet found in Chile. It is localized at 3,015 m altitude in the precordillera near the southern end of Salar de Atacama. It is a simple crater of ~400 m diameter and ~34 m of depth [1], first referred as an impact crater by [2]. The age of the crater was estimated as older than 0.1 Ma by [3] by thermoluminiscence analysis.
We are reporting the first absolute ages of the Monturaqui impact crater following two approaches: a) the terrestrial age of the impactor by measuring the residual activities of 10Be, 26Al, 36Cl, 41Ca, 59Ni, 60Fe, and 53Mn in selected iron shale samples, which corresponds to the remaining altered fragments of the impactor, inferred to be an iron meteorite, and b) in-situ ages obtained through the use of long-lived terrestrial cosmogenic radionuclides 10Be and 26Al in the granite outcrops exposed to cosmic radiation starting after the impact.
Chemical preparation of targets suitable for accelerator mass spectrometry (AMS) have been performed after [4] (for the iron meteorite sample) and a combination of slight modifications of [4] and [5] (for the granite samples).
AMS measurements of 10Be and 26Al have been performed at the French 5 MV-AMS facility ASTER, 36Cl at CAMS, LLNL, USA, and 53Mn at the Maier-Leibnitz-Laboratory (MLL).
We can compare our measured radioactivities with depth-depending production rates from sophisticated theoretical Monte-Carlo calculations [priv.com. I. Leya]. As these production rates are a function of the chemical composition (of the impactor in space), remaining fragments are highly altered and precise chemical analyses could not yet be achieved, certain further assumptions are influencing the following discussion of our, thus preliminary, data.
The longest-lived radionuclide 53Mn (t1/2=3.7 Ma), normalized to a fully corroded Fe2O3-sample, is the least sensitive nuclide to a varying terrestrial age, thus, providing us with a shielding depth of 62-71 cm. The best fit of the measured shortest-lived radionuclide 36Cl (t1/2=0.3 Ma) with theoretical production rate at that depths is for a terrestrial age of 500-600 ka. The 26Al-activity goes along with that age. Though, the measured 10Be-concentration is far too high in comparison to the theoretical production rate, which are based on an average carbon-content of 0.1% (as Canyon Diablo). As earlier studies [6,7] demonstrated the great influence of inhomogeneous distributed trace elements like C, S, and P on the production rates of lighter cosmogenic radionuclides in iron meteorite samples. Finally, under the contrary assumption of no corrosion of the impactor, the whole discussion changes only slightly: Deeper shielding position (66-80 cm), but as production rates of 53Mn and 36Cl are influenced the same way, the terrestrial age will not change.
Our second approach using terrestrial cosmogenic radionuclides leads to concordant results for 10Be only: The minimum in-situ exposure age of two samples from the crater wall could be calculated to 200-250 ka. A larger age of excavation is very likely due to the subsequent erosion of the crater walls.
We are looking forward to measurements of the most sensible 41Ca (t1/2=0.1 ka) that might improve the accuracy of this age.

References: [1] H. Ugalde et al., MAPS 42 (2007) 2153. [2] J. Sanchez, W. Cassidy, J. Geophys. Res. 71 (1966) 4891. [3] V.F. Buchwald, Handbook of iron meteorites, Univ. of California Press, Berkeley. Vol. 1 (1975) 262. [4] S. Merchel, U. Herpers, RCA 84 (1999) 215. [5] E. T. Brown et al., GCA 55 (1991) 2269. [6] I. Leya, Michel R., Lunar Planet. Sci. 29 (1998) #1172. [7] I. Leya et al., MAPS 32 (1997) A78.
Keywords: impact, terrestrial cosmogenic nuclides, accelerator mass spectrometry, meteorite, exposure age
  • Contribution to external collection
    in: Annual report of the Maier-Leibnitz-Laboratorium für Kern- und Teilchenphysik der Ludwig- Maximilians-Universität München und der Technischen Universität München (MLL), München: Maier-Leibnitz-Laboratorium, 2008, 27

Publ.-Id: 12708 - Permalink


Ultra-fast evolution via PT-symmetry and entanglement: extending the BBJM brachistochrone
Günther, U.; Samsonov, B.;
The basics of quantum mechanical brachistochrones are briefly sketched for Hermitian systems as well as for PT-symmetric systems --- as the latter have been recently proposed by Bender, Brody, Jones and Meister (BBJM) in [C. M. Bender et al, Phys. Rev. Lett. 98, 040403 (2007)]. Using a mainly geometric approach, the hidden new features of this PT-symmetric brachsistochrone with its close relation to non-diagonalizable operator realizations with non-trivial Jordan block structures and spectral singularities (spectral exceptional points) are discussed. Furthermore the Naimark dilation technique as basic tool for an extension toward possible experimental implementations is explained. The remarkable links to wormhole-type setups and entangled states (Einstein's 'spooky action') are highlighted and sketched geometrically. The talk is mainly based on [Phys. Rev. Lett. 101, 230404 (2008)].
Keywords: quantum brachistochrone, quantum computing, PT quantum mechanics, strongly non-Hermitian regime, exceptional point, Anandan-Aharonov lower bound, ultra-fast evolution, POVM, Naimark dilation, Naimark extension, entangled state, two-qubit system, wormhole, Einstein's spooky action
  • Invited lecture (Conferences)
    Arbeitsgruppenseminar "Theoretische Quantenoptik", Institut für Theoretische Physik, TU Dresden, 08.05.2009, Dresden, Deutschland

Publ.-Id: 12707 - Permalink


Numerical simulations of liquid metal experiments on cosmic magnetic fields
Stefani, F.; Giesecke, A.; Gerbeth, G.;
Cosmic magnetic fields, including the fields of planets, stars, and galaxies, are produced by the hydromagnetic dynamo effect in moving electrically conducting fluids. They play also an active role in cosmic structure formation by enabling outward transport of angular momentum in accretion disks via the magnetorotational instability (MRI). The last ten years have seen tremendous efforts in studying both effects in liquid metal experiments. This paper is focused on the numerical attempts that were undertaken to understand, optimize, and analyze those experiments.

Publ.-Id: 12706 - Permalink


Helical magnetorotational instability in a Taylor-Couette flow with strongly reduced Ekman pumping
Stefani, F.; Gerbeth, G.; Gundrum, T.; Hollerbach, R.; Priede, J.; Rüdiger, G.; Szklarski, J.;
The magnetorotational instability (MRI) is thought to play a key role in the formation of stars and black holes by sustaining the turbulence in hydrodynamically stable Keplerian accretion discs. In previous experiments the MRI was observed in a liquid metal Taylor-Couette flow at moderate Reynolds numbers by applying a helical magnetic field. The observation of this helical MRI (HMRI) was interfered with a significant Ekman pumping driven by solid end-caps that confined the instability only to a part of the Taylor-Couette cell. This paper describes the observation of the HMRI in an improved Taylor-Couette setup with the Ekman pumping significantly reduced by using split end-caps. The HMRI, which now spreads over the whole height of the cell, appears much sharper and in better agreement with numerical predictions. By analyzing various parameter dependencies we conclude that the observed HMRI represents a self-sustained global instability rather than a noise-sustained convective one.

Publ.-Id: 12705 - Permalink


Inferring basic parameters of the geodynamo from sequences of polarity reversals
Fischer, M.; Gerbeth, G.; Giesecke, A.; Stefani, F.;
The asymmetric time dependence and various statistical properties of polarity reversals of the Earth's magnetic field are utilized to infer some of the most essential parameters of the geodynamo, among them the effective (turbulent) magnetic diffusivity, the degree of supercriticality, and the relative strength of the periodic forcing which is believed to result from the Milankovic cycle of the Earth's orbit eccentricity. A time-stepped spherically symmetric alpha2 dynamo model is used as the kernel of an inverse problem solver in form of a downhill simplex method which converges to solutions that yield a stunning correspondence with paleomagnetic data.

Publ.-Id: 12704 - Permalink


Liquid metal experiments on helical MRI
Stefani, F.;
The magnetorotational instability (MRI) plays a key role in the formation of stars and black holes. By destabilizing hydrodynamically stable Keplerian flows, the MRI triggers turbulence and enables outward transport of angular momentum in accretion discs. The Potsdam Rossendorf Magnetic InStability Experiment (PROMISE) is devoted to the experimental study of the so-called helical MRI. Preliminary experiments had confirmed the prediction that combined axial and azimuthal magnetic fields allow the investigation of the MRI in liquid metal Taylor-Couette flows at moderate Reynolds and Hartmann numbers. A drawback of these experiments was that the travelling MRI wave ceased at the radial jet that results from the Ekman pumping at the end-caps of the Taylor-Couette cell. However, by using split end-caps the Ekman pumping is strongly reduced so that the MRI wave can travel freely through the entire height. Consequently, the transition to MRI appears much sharper and in improved agreement with numerical predictions. By analyzing various parameter dependencies of the MRI wave we conclude that it represents a global instability and not a noise-triggered convective one.
  • Invited lecture (Conferences)
    The Astrophysics of the Magnetorotational Instability and Related Processes, 14.-18.04.2009, Tegernsee, Germany

Publ.-Id: 12703 - Permalink


Liquid metal experiments on dynamo action and magnetic instabilities
Stefani, F.;
The talk comprises a short summary of liquid metal experiments on dynamo action that have been carried out during the last decade. Its main focus, however, will be on recent experiments on the magnetorotational instability (MRI). The prospects for future experiments on dynamo action, MRI, and Tayler instability, as well as for possible combinations will also be discussed.
  • Invited lecture (Conferences)
    Frontiers in Dynamo Theory, 16.-20.03.2009, Paris, France

Publ.-Id: 12702 - Permalink


Mechanical properties of spark plasma sintered Fe-Cr compacts strengthened by nanodispersed yttria particles
Franke, P.; Heintze, C.; Bergner, F.; Weissgärber, T.;
Oxide dispersion strengthening of high-Cr steels is a well-recognized way to extend the application window including nuclear applications for this class of materials. The experimental investigation of model alloys of less complexity is important in order to separate individual influence factors and to understand the irradiation behaviour. The present work is devoted to the mechanical properties of ODS Fe-9wt%Cr alloys produced by means of spark plasma sintering. The range of material conditions covers contents of nanodispersed yttria of 0 (reference), 0.3 wt% and 0.6 wt% as well as variations of the milling time. Results obtained for the density, elastic properties, hardness, tensile behaviour and brittle-ductile transition are reported and the effect of ODS content and PM process parameters is discussed.
  • MP Materials Testing 52(2010), 133-138

Publ.-Id: 12701 - Permalink


Liquid metal experiments on cosmic magnetic fields
Stefani, F.;
In the talk we summarize the experimental activities to study dynamo action and the magnetorotational instability in the liquid metal laboratory. Both processes are thought to play a key role in the understanding of accretion disks and jets in which ultra-high energy cosmic particles are believed to be produced.
  • Invited lecture (Conferences)
    Ultra-high Energy Cosmic Rays and Magnetic Fields in the Universe, 11.-14.02.2009, Tegernsee, Germany

Publ.-Id: 12700 - Permalink


Surface diffusion assisted phase separation during the growth of carbon:transition metal nanocomposite thin films
Abrasonis, G.;
Encapsulated nanostructures formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices, high density magnetic storage media, multifunctional coatings, as large scale templates for nanowire fabrication. In this talk our activities concerning the investigation of the growth mechanisms of carbon: transition metal (TM=V,Co,Ni,Cu) thin films grown in the in the substrate temperature range of RT- RT-500 C will be summarized [1-5]. Vanadium (copper) is in the carbidic(metallic) state in the whole temperature range while Co and Ni undergo a transition from a carbidic towards a metallic state [3]. The vanadium carbide nanoparticles exhibit a globular shape independently on the growth temperature, while the other metals show a transition from a globular towards a columnar growth when the substrate temperature increases. At a fixed temperature, the morphology of Ni nanocolumns significantly depends on the substrate type which points out that the initial stages of the film growth determine the structure of the subsequently grown film [5]. The use of the hyperthermal species introduces an additional complexity in the phase separation process and allows obtaining a significantly larger variety of nanostructures due to the intperlay of vertical and lateral phase separation processes (disordered array of nanoparticles, self-organized multilayers, nanocolumns or liquid-like coalescence) [4].


[1] G. Abrasonis, M .Krause, A. Mucklich, K. Sedlackova, G. Radnoczi, U. Kreissig, A. Kolitsch, W. Moller, “Growth regimes and metal enhanced 6-fold ring clustering of carbon in carbon-nickel composite thin films”, Carbon 45, 2995 (2007).

[2] G. Abrasonis, A.C. Scheinost , S. Zhou, R. Torres, R. Gago, I. Jimenez, K. Kuepper, K. Potzger, M. Krause, A. Kolitsch, W. Moeller, S. Bartkowski, M. Neumann, R. R. Gareev, “X-ray spectroscopic and magnetic investigation of C : Ni nanocomposite films grown by ion beam cosputtering”, J. Phys. Chem. C 112, 12628 (2008).

[3] G. Abrasonis, M. Berndt, M. Krause, K. Kuepper, F. Munnik, A. Kolitsch, W. Moller, “Soft X-ray Absorption and Emission Spectroscopic Investigation of Carbon and Carbon: Transition Metal Composite Films”, J. Phys. Chem. C 112, 17161 (2008).

[4] G. Abrasonis, G. Kovacs, L. Ryves, M. Krause, A. Mucklich, F. Munnik, M. Bilek, W. Moller, “Phase separation in carbon-nickel films during hyperthermal ion deposition“, J. Appl. Phys. submitted.

[5] G. Abrasonis, A. Mucklich, G. Kovacs, D. Babonneau, A. Martinavicius, M. Berndt, F. Munnik, M. Vinnichenko, K. H. Heinig, J. Grenzer, A. Kolitsch, W. Moller, ”Substrate Effect on the Surface Diffusion Assisted Phase Separation during the Growth of C:Ni Nanocomposite Films”, J. Phys. Chem. C submitted.
  • Invited lecture (Conferences)
    Second Plasma-Nano International workshop at CSIRO, Lindfield, Australia, 09.02.2009, Lindfield, Australia

Publ.-Id: 12699 - Permalink


Phase separation in carbon-nickel films during hyperthermal ion deposition
Abrasonis, G.; Kovács, G. J.; Ryves, L.; Krause, M.; Mücklich, A.; Munnik, F.; Oates, T. W. H.; Bilek, M. M. M.; Möller, W.;
Microstructure evolution as function of the substrate temperature and metal content of C:Ni nanocomposite films grown by hyperthermal ion deposition is investigated. The films were grown by pulsed filtered cathodic vacuum arc on thermally oxidized Si substrates held at temperatures in the range from room temperature (RT) to 500 °C and with the metal content ranging from 7 to 40 at. %. The elemental depth profiles and composition were determined by elastic recoil detection analysis. The film morphology and phase structure were studied by means of cross-sectional transmission electron microscopy and selected area electron diffraction. For RT deposition a transition from repeated nucleation dominated toward self-organized growth of alternating carbon and crystalline nickel carbide layers is observed at a Ni threshold content of ~40 at. %. The surface diffusion increases concomitantly with the growth temperature resulting in the formation of elongated/columnar structures and a complete separation of the film constituents into the coexisting carbon and fcc Ni phases. At the highest growth temperature (500 °C) Ni shows a tendency to segregate at the surface of the growing film and to form a continuous layer for integrated Ni contents of =>30 at. %. A corresponding structure zone model diagram is presented, and the results are discussed on the basis of the ion induced atomic displacement, temperature activated adatom diffusion, and the metallic island coalescence processes whose complex interplay results in the observed variety of the microstructures.

Publ.-Id: 12698 - Permalink


Substrate Effects on the Morphology of Carbon Encapsulated Nickel Nanoparticles Grown by Surface Diffusion Assisted Phase Separation
Abrasonis, G.; Kovacs, G. J.; Mucklich, A.; Zhou, S. Q.; Babonneau, D.; Martinavicius, A.; Berndt, M.; Munnik, F.; Vinnichenko, M.; Heinig, K. H.; Grenzer, J.; Kolitsch, A.; Schmidt, H.; Moller, W.;
Encapsulated nanoparticles formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices or as large scale templates for nanowire fabrication. In this study, substrate type influence on the morphology of encapsulated metal nanoparticles in C:Ni films grown by ion beam cosputtering is investigated. C:Ni (∼15 atom %) nanocomposite thin films (∼50-70 nm thick) were grown at 400 °C on amorphous SiO2 and Nb2O5, polycrystalline TiN, and single crystalline MgO (001) substrates. Combined diagnostics using transmission electron microscopy, grazing incidence smallangle X-ray scattering, and superconducting quantum interference device magnetometry demonstrate that all the films exhibit metallic nanoparticles elongated along the film growth direction, while the substrate material strongly influences their morphology even far away from the film/substrate interface despite the fact that repeated nucleation occurs in all the films. The mean nanoparticle diameter is strongly substrate dependent and ranges from ∼2 to ∼18 nm in the sequence SiO2 < MgO < Nb2O5 < TiN. In addition, the substrate type influences strongly the vertical film constituent distribution, resulting in a homogeneous metal constituent distribution for the films grown on the SiO2 and MgO substrates while causing the metal segregation at the film surface for the films grown on the Nb2O5 and TiN substrates. The results strongly suggest that the metal diffusivity, not that of carbon, is the limiting factor determining the film structure. The results are consistent with the nucleation and growth mechanism, with the repeated nucleation events being correlated with the preceding film morphology, rather than that of spinodal decomposition. Furthermore, the findings suggest that a controlled growth of encapsulated nanoparticles may be achieved with an ordinary cosputtering technique by changing the substrate type or state or by applying a variety of prepatterning recipes.
  • Journal of Physical Chemistry C 113(2009)20, 8645-8651

Publ.-Id: 12697 - Permalink


Terrestrial cosmogenic radionuclides and the new AMS facility DREAMS
Merchel, S.;
no abstract necessary
Keywords: terrestrial cosmogenic nuclides, accelerator mass spectrometry
  • Lecture (others)
    Seminar über aktuelle Themen aus Kosmochemie und Astrophysik, 06.05.2009, Mainz, Deutschland

Publ.-Id: 12696 - Permalink


P0706 - Gittersensor
Schleicher, E.; Sühnel, T.; Boden, D.; Fischer, F.; Futterschneider, H.;
Aufgabe der vorliegenden Erfindung ist es, einen Gittersensor vorzuschlagen, mit dem der Aufwand des Fertigungsprozesses sowie die Einbau- und Betriebskosten für den Gittersensor deutlich verringert und die Haltbarkeit sowie Druck- und Temperaturfestigkeit des Gittersensors gegenüber bisherigen Gittersensoren deutlich erhöht werden können.
Die technische Lösung beinhaltet im Wesentlichen, dass vom Rand des Messquerschnitts (2) aus Kanäle (3) mit einer Breite von mehr als dem Durchmesser der Drahtelektroden (6) und mit einer Tiefe von weniger als der halben Dicke der Sensorplatine (1) in dieser nach außen verlaufen, dass die Kanäle (3) mit einer Metallschicht (5) ausgekleidet sind, dass die Drahtelektroden (6) mit ihren beiden Enden jeweils in einem der gegenüberliegenden Kanäle (3) an der Peripherie des Messquerschnitts (2) eingelegt und in den Kanälen (3) mittels leitfähiger Verschlussmasse (8) fixiert sind, dass die leitfähige Verschlussmasse (8) in jedem Kanal (3) mit der Oberseite der Sensorplatine (1) plan abschließt und dass die Sensorplatine (1) zwischen zwei Spannplatten (10) eingespannt ist.
Fig. 2
  • Patent
    DE102007019926 - Erteilung: 09.04.2009, Nachanmeldungen: WO, EP (validiert in 12 Ländern), US

Publ.-Id: 12695 - Permalink


Probing the impact of microstructure on the electroluminescence properties of Ge-nanocrystal enriched Er-doped SiO2 layers
Kanjilal, A.; Rebohle, L.; Baddela, N. K.; Zhou, S.; Voelskow, M.; Skorupa, W.; Helm, M.;
We present the microstructural evolution in Ge-rich SiO2 doped with Er under different fabrication conditions. At sufficiently high Er contents and annealing temperatures, the Er2O3 and Er2Ge2O7 phases are eventually formed, leading to an electroluminescence quenching of Ge-related oxygen-deficiency centers. The correlation between the microstructure and electroluminescence is discussed based on: (i) an Er doping dependent fragmentation/amorphization of Ge nanocrystals, (ii) a temperature dependent Ge diffusion toward the Si/SiO2 interface, and (iii) the formation of different Er phases.
Keywords: EL, XRD, RBS, Ge NCs, Er

Publ.-Id: 12694 - Permalink


Correlation between the microstructure and electroluminescence properties of Er-doped metal-oxide semiconductor structures
Kanjilal, A.; Rebohle, L.; Skorupa, W.; Helm, M.;
Optical response of a rare earth (RE)-doped SiO2 layer is known to deteriorate markedly at room temperature due to RE clustering. The key challenge is therefore to probe the ongoing processes at the microscopic level and the subsequent impact on the luminescence properties with increasing RE concentration. Here, we report how the Er electroluminescence in a metal-oxide-semiconductor structure has been affected by increasing Er content. Our results indicate that the Er oxide clustering is anticipated by the formation of Si-based oxygen-deficiency centers during postimplantation annealing and leads to a strong quenching of the short-wavelength (350–500 nm) Er electroluminescence.
Keywords: Electroluminescence, Er, TEM

Publ.-Id: 12693 - Permalink


Comparative evaluation of coolant mixing experiments at the ROCOM and the Gidropress test facilities
Kliem, S.; Höhne, T.; Rohde, U.; Bykov, M.; Lisenkov, E.;
Coolant mixing inside the nuclear reactor is the most important inherent safety mechanism against boron dilution or overcooling transients and in the case of pressurized thermal shock scenarios. In the frame of the TACIS Project R2.02/02 coolant mixing experiments have been performed at the 1:5 scaled Gidropress mixing test facility. This experimental facility consists of a model of the reactor pressure vessel (RPV) with four circulating loops. The RPV model is made of steel and reproduces in the given scale practically all the geometrical features of the RPV of the VVER-1000 at the NPP Novovoronezh-5 which are affecting the in-vessel mixing phenomena up to the core inlet, particularly the internal components such as the barrel, the lower ellipsoidal perforated shell, the core support columns and the lower core plate. In the carried-out experimental series the mixing processes during reactor coolant pump (RCP) start-up, during natural circulation conditions with the variation of density ratio differences and during stationary flow conditions with different number of RCP in operation were investigated.
At Forschungszentrum Dresden-Rossendorf, the 1:5 scaled mixing test facility ROCOM (Rossendorf Coolant Mixing Model) has been in operation since ten years. This facility models the primary circuit of the German PWR KONVOI with all four loops. The vessel of the facility is made from Perspex. The geometrical similarity between the model and the original reactor is fully respected within the region in-between the bends in the cold legs, which are closest to the reactor inlet and the core entrance. The geometry of the inlet nozzles with their diffuser segments and the curvature radius of the inner wall at the junction with the pressure vessel were modeled in detail. Similarity is also taken into account for the core support plate with the orifices for the coolant and the perforated sieve drum (flow skirt below the core barrel) in the lower plenum. Beside others, experiments have been performed at the ROCOM test facility for the first and the third classes mentioned above for the Gidropress test facility. That allows comparing the experimental results obtained at both test facilities.
The analysis of the slug mixing experiments showed comparable flow behavior. The first part of the tracer is found on the opposite side in regard to the position of the starting-up loop. In this region, the maximum tracer is measured in both facilities. These maximum values differ by about the same value as the initial slug sizes in the experiments.
In stationary experiments at both test facilities a clear sector formation at the core inlet could be observed. Coolant from the loop with the perturbation arrives nearly unmixed in both cases at single measurement positions at the core inlet. In one of the Gidropress experiments an additional counterclockwise swirl was found which is responsible for moving the sector. In the corresponding ROCOM experiment such an additional swirl is fully absent. Contrary to that, a shift of the sector is found in a four-loop experiment at reduced flow rate.
  • Contribution to proceedings
    6th International Conference "Safety Assurance of NPP with WWER", 26.-29.05.2009, Podolsk, Russland
    Proc. of the 6th International Conference "Safety Assurance of NPP with WWER", CDROM, paper 008, Podolsk: OKB Gidropress Podolsk, 9785948830926
  • Lecture (Conference)
    6th International Conference "Safety Assurance of NPP with WWER", 26.-29.05.2009, Podolsk, Russland

Publ.-Id: 12692 - Permalink


Ripple rotation in the anisotropic Kuramoto-Sivashinsky equation
Keller, A.; Nicoli, M.; Cuerno, R.; Facsko, S.; Möller, W.;
The formation of regular nanopatterns during low energy ion sputtering of solid surfaces has become a topic of intense research. This research is mainly motivated by promising applications of nanopatterned surfaces e.g. in thin film growth. On the other hand, these surfaces represent an interesting example of spontaneous pattern formation in non-equilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1].
According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and diffusional smoothing of the surface. Since the local erosion rate is higher in troughs than on crests, the eroded surface is unstable against any periodic perturbances. In the presence of a smoothing mechanism, however, wave vector selection occurs and a periodic pattern with a characteristic spatial frequency is observed. During recent years, several nonlinear extensions of the linear BH model have been proposed with the stochastic Kuramoto-Sivashinsky (KS) equation having played a prominent role [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation.
In this work, we have investigated the influence of anisotropy on the morphology evolution in numerical integrations of the aKS equation. For a strong nonlinear anisotropy, a rotation by 90° of the initially formed ripple pattern was observed for intermediate and long integration times. Comparison with analytical predictions indicates that the observed rotated ripple pattern arises from anisotropic renormalization properties of the aKS equation. This result may also offer an explanation for the recent observation of transient structures in high-temperature experiments on Si(111) [4].

[1] W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3] R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)
[4] A.-D. Brown, J. Erlebacher, W.-L. Chan, and E. Chason, Phys. Rev. Lett. 95 056101 (2005)
  • Lecture (Conference)
    MRS Spring Meeting, 13.-17.04.2009, San Francisco, USA

Publ.-Id: 12691 - Permalink


Introducing artificial length scales to tailor magnetic properties
Fassbender, J.ORC; Strache, T.; Liedke, M. O.; Marko, D.; Wintz, S.; Lenz, K.; Keller, A.; Facsko, S.; Mönch, I.; McCord, J.
Magnetism is a collective phenomena. Hence, a local variation on the nanoscale of material properties which act on the magnetic properties affect the overall magnetism in an intriguing way. In particular important are the length scales on which a material property changes. These might be related to the exchange length, the domain wall width, a typical roughness correlation length or a length scale introduced by patterning of the material. Here we report on the influence of two artificially created length scales: i) Ion erosion templates which serve as a source of a predefined surface morphology and hence allow for the investigation of roughness phenomena, ii) Ion implantation through a lithographically defined mask which is used for a magnetic property patterning on various length scales. The resulting magnetic properties are neither present in non-implanted nor in homogeneously implanted films. In both cases the magnetic properties, the magnetization reversal process as well as the magnetic domain configurations depend sensitively on the artificially introduced length scale.
Keywords: magnetism, ion implantation, ripples, ion erosion, self-organization, magnetic anisotropy, domains

Publ.-Id: 12690 - Permalink


Hydrodynamic modeling of mineral wool fiber suspensions in a two-dimensional channel flow
Cartland Glover, G. M.; Krepper, E.; Weiss, F.-P.; Zacharias, F.; Kratzsch, A.; Alt, S.; Kaestner, W.;
A consequence of a loss of coolant accident is the damage of adjacent insulation materials (IM). IM may then be transported to the containment sump strainers where water is drawn into the ECCS (emergency core cooling system). Blockage of the strainers by IM lead to an increased pressure drop acting on the operating ECCS pumps. IM can also penetrate the strainers, enter the reactor coolant system and then accumulate in the reactor pressure vessel.
An experimental and theoretical study that concentrates on mineral wool fiber transport in the containment sump and the ECCS is being performed. The study entails fiber generation and the assessment of fiber transport in single and multi-effect experiments. The experiments include measurement of the terminal settling velocity, the strainer pressure drop, fiber sedimentation and resuspension in a channel flow and jet flow in a rectangular tank. An integrated test facility is also operated to assess the compounded effects. Each experimental facility is used to provide data for the validation of equivalent computational fluid dynamic models.
The channel flow facility allows the determination of the steady state distribution of the fibers at different flow velocities. The fibers are modeled in the Eulerian-Eulerian reference frame as spherical wetted agglomerates. The fiber agglomerate size, density, the relative viscosity of the fluid-fiber mixture and the turbulent dispersion of the fibers all affect the steady state accumulation of fibers at the channel base. In the current simulations, two fiber phases are separately considered. The particle size is kept constant while the density is modified, which affects both the terminal velocity and volume fraction. The relative viscosity is only significant at higher concentrations. The numerical model finds that the fibers accumulate at the channel base even at high velocities; therefore, modifications to the drag and turbulent dispersion forces can be made to reduce fiber accumulation.
Keywords: Mineral Wool Agglomerates, Containment Sump, Computational Fluid Dynamics, Multiphase Flow
  • Lecture (Conference)
    The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa, Japan
  • Contribution to proceedings
    The 13th International Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa, Japan
    Proceedings of 13th International Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13)

Publ.-Id: 12689 - Permalink


Quasimonoenergetic electron acceleration in the self-modulated laserr wakefield regime
Hidding, B.; Geissler, M.; Pretzler, G.; Amthor, K.-U.; Schwoerer, H.; Karsch, S.; Veisz, L.; Schmid, K.; Sauerbrey, R.;
Details on the generation of multiple quasimonoenergetic electron bunches in the self-modulated laser wakefield acceleration SMLWFA regime are presented. This type of laser-plasma interaction can result in pronounced longitudinal laser pulse fragmentation, dependent on plasma density and laser intensity. It is shown by experiments and particle-in-cell simulations that these laser pulse fragments can be powerful enough to trigger nonlinear plasma wave breaking, injection, and acceleration of electrons to quasimonoenergetic energies. With high plasma densities, selfmodulation is promoted, and the advantages of SMLWFA such as especially high accelerating fields and short electron bunches (<5 fs) can be harvested. In addition, more than one quasimonoenergetic electron bunch can be created, with a temporal spacing between each bunch of only few tens of femtoseconds, again governed by plasma density.

Publ.-Id: 12688 - Permalink


Hydrodynamic modeling of mineral wool fiber suspensions in a two-dimensional flow
Cartland Glover, G. M.; Grahn, A.; Krepper, E.; Weiss, F.-P.; Alt, S.; Hampel, R.; Kaestner, W.; Kratzsch, A.; Zacharias, F.;
A consequence of a loss of coolant accident is that the local insulation material is damaged and maybe transported to the containment sump where it can penetrate and/or block the sump strainers. An experimental and theoretical study, which examines the transport of mineral wool fibers via single and multi-effect experiments is being performed. This paper focuses on the experiments and simulations performed for validation of numerical models of sedimentation and resuspension of mineral wool fiber agglomerates in a racetrack type channel. Three velocity conditions are used to test the response of two dispersed phase fiber agglomerates to two drag correlations and to two turbulent dispersion coefficients. The Eulerian multiphase flow model is applied with either one or two dispersed phases.
  • Contribution to proceedings
    17th International Conference on Nuclear Engineering, 12.-16.07.2009, Brussels, Belgium
    Proceedings of ICONE17 17th International Conference on Nuclear Engineering
  • Lecture (Conference)
    17th International Conference on Nuclear Engineering, 12.-16.07.2009, Brussels, Belgium

Publ.-Id: 12687 - Permalink


Mapping of 2+1 dimensional KPZ growth onto driven lattice gas model of dimers
Odor, G.; Liedke, B.; Heinig, K.-H.;
We confirm by numerical simulations that the scaling exponents of the dimer model are in agreement with those of the 2+1 dimensional KPZ class.
Surface pattern form if we include Mullins diffusion in the simulation.
Keywords: KPZ equation, ion erosion, surface pattern formation
  • Poster
    International Seminar on Many-body systems far from equilibrium: Fluctuations, slow dynamics and long-range interactions, 16.-27.02.2009, Dresden, Germany

Publ.-Id: 12686 - Permalink


Mapping two-dimensional surface patterns and scaling onto driven lattice gases
Odor, G.; Liedke, B.; Heinig, K.-H.;
We show that a (2+1)-dimensional discrete surface growth model exhibiting Kardar-Parisi-Zhang (KPZ) class scaling can be mapped onto a two-dimensional conserved lattice gas model of directed dimers. The KPZ height anisotropy in the surface model corresponds to a driven diusive motion of the lattice gas dimers. We conrm by numerical simulations that the scaling exponents of the dimer model agree with those of the (2+1)-dimensional KPZ class. This suggests that the dimension dependence has a topological (exclusion) origin. The mapping opens up the possibility of analyzing growth models via reaction-diusion models and allow much more ecient computer simulations (see [1]). In particular we provide very precise surface scaling exponents for d = 2; 3; 4; 5 dimensions obtained by ecient bit-coded algorithms and discuss the problem of the debated upper-critical dimension of KPZ. Furthermore if we supplement this model with conserved, competing surface diusion reactions we can obtain various, coarsening dot or ripple patterns (see image), which are important in self-organizing nano-structure research (see http://www.iom-leipzig.de/for845/).
[1] G. Odor, B. Liedke, and K.-H. Heinig, Phys. Rev. E 79 (2009) 021125.
Keywords: KPZ equation, ion erosion, surface pattern formation
  • Lecture (Conference)
    34th Conference of the Middle European Cooperation in Statistical Physics, 30.03.-01.04.2009, Leipzig, Germany

Publ.-Id: 12685 - Permalink


KPZ growth mapping onto driven lattice gas model of n-mers
Odor, G.; Liedke, B.; Heinig, K.-H.;
We show that a 2+1 dimensional discrete surface growth model exhibiting KPZ class scaling can be mapped onto a two dimensional conserved lattice gas model of directed dimers. In case of KPZ height anisotropy the dimers follow driven diffusive motion. We confirm by numerical simulations that the scaling exponents of the dimer model are in agreement with those of the 2+1 dimensional KPZ class. This opens up the possibility of analyzing growth models via reaction-diffusion models, which allow much more efficient computer simulations.
Keywords: layer growth, ion erosion, scaling behavior, KPZ equation
  • Lecture (Conference)
    Workshop on Statistical Physics, 16.04.2009, Kisterem, Budapest Roosevelt tér 9, Hungary

Publ.-Id: 12684 - Permalink


Yb:CaF2 - a new old laser crystal
Siebold, M.; Bock, S.; Schramm, U.; Xu, B.; Doualan, J. L.; Camy, P.; Moncorgé, R.;
Here is presented and discussed the history, the spectroscopic, the thermo-mechanical and the laser properties of the new old laser crystal Yb:CaF2, of its Sr and Ba isotypes as well as of an Yb and Na codoped compound. It will be shown that Yb:CaF2 is a very particular luminescent material, in which the laser active center probably consists of a complex hexameric cluster, that it is the most promising Yb doped °uoride material for large scale high power and high energy laser systems and that it can compete in several aspects with the currently used Yb doped oxide crystals and glasses. The opportunity of operating the crystals at cryogenic temperatures and the recently achieved improvements in the¯eld of femtosecond pulsed laser operation and high peak power laser amplication is highlighted and evaluated.

Publ.-Id: 12683 - Permalink


Implications of a non-uniform permeability distribution on the generation of magnetic fields in the Von-K\'arm\'an-Sodium dynamo experiment.
Giesecke, A.;
Numerical simulations of the kinematic induction equation have been carried out in a setup that resembles the configuration of the VKS dynamo experiment. Primary objective are investigations of the impact of the non-uniform permeability distribution introduced by the ferrous impellers that drive a flow of liquid sodium in the experiment. It is shown that a high-permeability domain favours the axisymetric field mode whereas the first non-axisymmetric mode remains nearly unaffected. However, to circumvent the restrictions of Cowling's theorem, still an alpha-effect is required to explain the axisymmetric field as it is observed in the experiment.
Keywords: VKS Dynamo Induction MHD
  • Invited lecture (Conferences)
    Seminar am Laboratoire d'Informatique pour la Mécanique et les Sciences de l'Ingénieur (LIMSI), 05.05.2009, Paris, Frankreich

Publ.-Id: 12682 - Permalink


Electronic and magnetic structure of RScO3 (R=Sm,Gd,Dy) from x-ray spectroscopies and first-principles calculations
Raekers, M.; Kuepper, K.; Bartkowski, S.; Prinz, M.; Postnikov, A. V.; Potzger, K.; Zhou, S.; Arulraj, A.; Stüßer, N.; Uecker, R.; Yang, W. L.; Neumann, M.;
The electronic structures of SmScO3, GdScO3, and DyScO3 are investigated by means of x-ray photoelectron spectroscopy, x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS). A strong hybridization between Sc 3d and O 2p is found, and a contribution of the rare-earth 5d states to this hybridization is not excluded. The band gaps of the compounds are determined by combining XES and XAS measurements. For SmScO3, GdScO3, and DyScO3 the band gaps were determined to be 5.6, 5.8, and 5.9 eV, respectively. Magnetization versus temperature measurements reveal antiferromagnetic coupling at 2.96 (SmScO3), 2.61 (GdScO3), and 3.10 K (DyScO3). For DyScO3 a Rietveld refinement of a 2 K neutron-diffraction data set gives the spin arrangement of Dy in the Pbnm structure (Shubnikov group: Pbnm).
Keywords: ab initio calculations, antiferromagnetism, dysprosium compounds, energy gap, magnetic structure, magnetisation, neutron diffraction, samarium compounds, scandium compounds, X-ray absorption spectra, X-ray emission spectra, X-ray photoelectron spectra

Publ.-Id: 12681 - Permalink


Implantation induced point defects and their role in silicon-on-insulator (SOI) materials processing
Kögler, R.;
The origin of the distribution of ion implantation induced point defects in Si and their effect on the oxygen redistribution during SIMOX processing is discussed.
Keywords: Ion implantation, SOI, SIMOX
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-08.04.2009, Jena, Deutschland

Publ.-Id: 12680 - Permalink


Effects of film thickness and Co doping on the magnetism of Pd structures
Pankoke, V.; Gemming, S.;
Palladium in its ground-state has a non magnetic fcc structure. We suggest that it can be forced to get ferro-magnetic by an expansion of the lattice constant, or in case of thin films by a varying number of atomic layers. Another option to induce magnetism is to dope the Pd structures with 3d transition metals. We used first principles methods to calculate the magnetization density of different Co doped and undoped Pd structures. Calculations were carried out with the projector augmented waves (PAW) method in the LDA+U approximation and a plane wave basis set. In addition the linear augmented plane waves (LAPW) method was used and compared with the PAW results. Both methods show, that doping with 3d transition metals leads to magnetic moment at the Pd sites of the crystal. In case undoped Pd films the PAW results are similar to existing LAPW calculations.
Keywords: magnetism, doping, quantum well states, transition metals, stoner criterion
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12679 - Permalink


Analysis of severe accidents in VVER-1000 reactors using the integral code ASTEC
Tusheva, P.; Reinke, N.; Altstadt, E.; Schaefer, F.; Weiss, F.-P.; Hurtado, A.;
The studies presented are aiming at a detailed investigation of the behaviour of a VVER-1000/V-320 reactor and the containment structures during a postulated severe accident, including the ways and means by which these accidents may be prevented or mitigated.
A hypothetical station blackout scenario (loss of the offsite electric power system concurrent with a turbine trip and unavailability of the emergency AC power system), belonging to the typical beyond design basis accidents, has been investigated. Station blackout results in reactor shut down, loss of feed water and trip of all reactor coolant pumps. Continuous evaporation of the secondary side leads to steam generators’ depletion followed by heating up of the core. In case of unavailability of essential safety systems the core will be severely damaged and finally the reactor pressure vessel (RPV) might fail.
The analyses are performed using the integral code ASTEC commonly developed by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH).
Code-to-code comparative analyses for the early thermal-hydraulic phase have been performed with the GRS code ATHLET. A large number of sensitivity calculations have been done regarding the axial core power distribution, heat losses, and RPV lower head modelling. The analyses have shown that, despite the considerable differences in the codes themselves, the calculation results are similar in terms of thermal hydraulic response. There are discrepancies in timings of phenomena, which are within the limitations of the physical models and the applied nodalizations.
It was one objective of this investigation to evaluate the Severe Accident Management (SAM) procedures for VVER-1000 reactors, by for instance estimating the time available for taking appropriate decisions and preparing counter-measures. To evaluate the effect of possible operator actions, a SAM procedure (primary side depressurization) is included into the simulation. Without SAMs, the simulation provides plastic rupture of the RPV after approximately 4.3 h, while with SAMs, a prolongation of the vessel failure time is obtained by approximately 90 minutes.
Currently, the late phase of the accident is investigated in more detail by comparing the lower head behaviour as simulated by ASTEC with results from dedicated finite element calculations.
The work contributes to the reliability of the ASTEC code by means of plant applications.
Keywords: safety analysis, severe accidents, accident management measures, ASTEC, ATHLET, ANSYS
  • Contribution to proceedings
    17th International Conference on Nuclear Engineering ICONE17, 12.-16.07.2009, Brussels, Belgium
    Proceedings of the 17th International Conference on Nuclear Engineering ICONE17
  • Lecture (Conference)
    17th International Conference on Nuclear Engineering ICONE17, 12.-16.07.2009, Brussels, Belgium

Publ.-Id: 12678 - Permalink


IAEA coordinated research project on Master Curve approach to monitor fracture toughness of RPV steels: effect of loading rate
Viehrig, H.-W.; Lucon, E.; Server, W. L.;
The Master Curve (MC) approach procedure standardised in ASTM E1921 is defined for quasi-static loading conditions. However, the extension of the MC method to dynamic testing is well-established. The effect of loading rate can be broken down into two distinct aspects: 1) the effect of loading rate on Master Curve To values for loading rates within the loading rate range specified in ASTM E1921 for quasi-static loading, and 2) the effect of loading rate on Master Curve To values for higher loading rates. The IAEA CRP8 includes both aspects, but primarily focuses on the second element of loading rate effects, i.e. loading rate ranges above the upper limit of the E1921 standard and it comprises:
- results of a round-robin exercise to validate the application of the Master Curve approach to precracked Charpy (PCC) specimens tested in the ductile-to-brittle transition region using an instrumented pendulum,
- Master Curve data obtained at different loading rates on various RPV steels, in order to assess the loading rate dependence of To and compare it with an empirical model proposed by Wallin, and
- the comparison of results from unloading compliance and monotonic loading in the quasi-static range.
Keywords: reactor pressure vessel steels, fracture toughness, Master Curve approach, loading rate
  • Contribution to proceedings
    2009 ASME Pressure Vessels and Piping Division Conference, 26.-30.07.2009, Prague, Czech Republic
    Proceedings of the 2009 ASME Pressure Vessels and Piping Division Conference, New York: ASME Technical Publishing Department
  • Lecture (others)
    2009 ASME Pressure Vessels and Piping Division Conference, 26.-30.07.2009, Prague, Czech Republic

Publ.-Id: 12676 - Permalink


QCD equation of state and compact stellar objects from Hard Thermal Loops
Schulze, R.; Kämpfer, B.;
● QPM with ImΠi ≠ 0, plasmons and plasminos from HTL
● extrapolation of lattice QCD to large baryon densities, e.g. CBM@FAIR
● EOS for hydrodynamic phase of heavy-ion collisions (RHIC, LHC, SPS) and quark stars
Keywords: quasiparticle model, equation of state, hard thermal loops, QCD
  • Lecture (Conference)
    Gemeinsame DPG Frühjahrstagung mit der European Physical Society (EuNPC), 16.3.2009, Bochum, Deutschland

Publ.-Id: 12675 - Permalink


QCD equation of state and compact stellar objects from Hard Thermal Loops
Schulze, R.; Kämpfer, B.;
We present a quasiparticle model based on a two-loop effective action equipped with hard thermal loop (HTL) dispersion relations and an effective running coupling strength. The model allows for an extrapolation of present QCD lattice results at small or zero chemical potential to larger baryon densities. The resulting QCD Equation of State is combined with the hadron sector to arrive at a usable form for hydrodynamical simulations of heavy-ion collisions over a large energy interval. The EoS is shown for several regions of the phase diagram and implications for quark/neutron stars are discussed.
Keywords: QCD, compact stellar matter, hard thermal loops, quasiparticle model, equation of state
  • Invited lecture (Conferences)
    Phases of Strongly Interacting Matter 2009, 08.-13.3.2009, Paris-Orsay, France

Publ.-Id: 12674 - Permalink


QCD Equation of State and compact stellar objects from Hard Thermal Loops
Schulze, R.; Kämpfer, B.;
We present a quasiparticle model based on a two-loop effective action equipped with hard thermal loop (HTL) dispersion relations and an effective running coupling strength. The model allows for an extrapolation of present QCD lattice results at small or zero chemical potential to larger baryon densities. The resulting QCD Equation of State is combined with the hadron sector to arrive at a usable form for hydrodynamical simulations of heavy-ion collisions over a large energy interval. The EoS is shown for several regions of the phase diagram and implications for quark/neutron stars are discussed.
Keywords: QCD, equation of state, quasiparticle model
  • Poster
    Schladming Winter School 2009, 27.02.-8.3.2009, Schladming, Österreich
  • Poster
    Quark Matter 2009, 29.03.-6.4.2009, Knoxville, TN, USA

Publ.-Id: 12673 - Permalink


Simultaneous structural and electrical measurements on Si-doped Ge2Sb2Te5 for PCRAM applications
Wilde, L.; Bähtz, C.; von Borany, J.; Krügener, J.; Teichert, S.;
Ge2Sb2Te5 (GST) based materials can be easily transformed between amorphous and crystalline phase and vice versa. The dramatic differences in the electrical resistance of these structural states make these materials suitable for non-volatile memory applications (phase change RAM or PCRAM). In order to tune these materials to the desired working point (e.g. low melting temperature, fast crystallization speed), dopants such as Si, N or O are used. In this study, we investigated the influence of PVD deposited Si dopants in 100 nm thin GST films on the crystallisation temperature and on the electrical resistance as well. The dopant concentration was varied between 0% and 3.5% by tunig the RF sputtering power on the SiO2 target. The XRD measurements (ESRF: ROBL beamline @ 12keV) were carried out in a high temperature chamber equipped with a Be dome, that allowed simulaneous determination of the sheet resistance by an electrical 4-point measurement. The samples were heated up to 450°C under vacuum conditions.
All samples were amorphous after deposition. Depending on the Si content, all samples crystallize in a cubic phase in the range between 160°C – 200°C. At the crystallisation temperature the electrical resistance drops by two orders of magnitude. A second transformation to a hexagonal phase was observed only for samples with a Si concentration below 1.0%. The temperature of this phase transformation depends significantly on the Si content. The electrical measurements show a further decline of the resistance upon this phase transformation. The cooling curve of the resistance measurements indicates, that the hexagonal phase exhibits metallic behaviour, whereas the cubic phase exhibits semiconducting properties.
Keywords: phase change memory; phase transformation; high temperature XRD
  • Poster
    12th International Conference on the Formation of Semiconductor Interfaces, 05.-10.07.2009, Weimar, Germany

Publ.-Id: 12672 - Permalink


Formation of Uranium(IV) Nanoparticles
Zänker, H.; Weiß, S.; Dreissig, I.; Opel, K.;
Uranium(IV) is usually regarded as sparingly soluble at near-neutral pH values. It should, therefore, be immobile in anoxic groundwaters. However, indications are that UO2 is able to form stable colloids (nanoparticles) [1] and the question arises if such nanoparticles might counteract the immobility of U(IV) in natural waters. Attempts were made by us to produce U(IV) colloids that are stable at environmentally relevant (i.e. near-neutral or slightly alkaline) pH values. It turned out that U(IV) colloids which are stable over many months can be produced by electrochemical reduction of U(VI) at alkaline pH, adding silicate and titration to the near-neutral region from the alkaline side of the pH scale.
Keywords: uranium(IV), nanoparticles, silicate
  • Invited lecture (Conferences)
    Russian-German Symposium on Actinide nano-Particles, 21.-22.05.2009, Moskwa, Rossia

Publ.-Id: 12671 - Permalink


Spectroscopic investigations of uranyl reduction by Fe-bearing clays
Chakraborty1, S.; Boivin, F. F.; Gehin, A.; Banerjee, D.; Scheinost, A. C.; Greneche, J. M.; Mullet, M.; Bardelli, F.; Charlet, L.;
Ferrous iron in clay is a potential natural reductant in anoxic environments. The reduction of UVI by FeII could be an important pathway for the immobilization of uranium in natural subsurface environments as well as in high-level nuclear waste (HLW) repositories. In the present study, we employed three dithionite-bicarbonate-citrate (DCB) treated, Ca-exchanged, Fe-bearing clays viz. montmorillonite (FeSM), Fe-rich smectite (Swa-1) and nontronite (NAu-2) with varying Fe content, and studied the reactivity of structural and readsorbed (surface complexed) Fe(II) species with respect to U sorption and/or reduction at pH 6 in a CO2-free anoxic atmosphere (<1 ppm O2 (v/v)) by using XPS, EXAFS and Mӧssbauer spectroscopies. The surface complexed Fe(II) species on untreated, Ca-exchanged clays were not found to be reactive in uranyl reduction. All three partially (17-45%) reduced, Ca-exchanged clays remove U from solution with a fast rate (minutes-hours), followed by a slow (months) reduction step. EXAFS analysis showed that UVI forms a mononuclear bidentate surface complex with FeIII in the untreated, Ca-exchanged clays which is the pre-requisite of heterogeneous reduction of U by their analogue in DCB treated clays. The adsorbed U was present as partially reduced mixed valence state (UVI and UIV) after 15 and 30 days. After 3 months, XANES spectra showed a substantial increase of UIV (20-50%) at the expense of UVI in case of reduced (DCB treated) FeSM, Swa-1 and complete reduction occurred (100%) in case of reduced NAu-2. The U4f5/2 XPS spectra were deconvoluted into two components, a higher binding energy (393.2±0.2 eV) for UVI and a lower binding energy (391.5±0.2 eV) for UIV. Despite the presence of abundant structural and readsorbed Fe(II) species and favourable reducing condition, the slow reduction of U might be due to (1) the stabilization of Ca in the clay interlayer inhibiting the cation release into solution which is coupled to the electron transfer process (2) that not all structural FeII species are potentially reactive at pH 6 and accessible to U for coordination.
Keywords: Uranium, reduction, clays, EXAFS, XPS
  • Lecture (Conference)
    Goldschmidt Conference, "Challenges to Our Volatile Planet", 21.-26.06.2009, Davos, Switzerland
  • Geochimica et Cosmochimica Acta 73(2009)13, A205-A205

Publ.-Id: 12670 - Permalink


Molecular imaging of α7 nicotinic acetylcholine receptors: design and evaluation of the potent radioligand [18F]NS10743
Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Ostergaard Nielsen, E.; Brunicardi Timmermann, D.; Steinbach, J.; Sabri, O.; Peters, D.; Brust, P.;
Purpose
The outstanding diversity of cellular properties mediated by neuronal and nonneuronal α7 nicotinic acetylcholine receptors (α7 nAChR) points to the diagnostic potential of quantitative nuclear molecular imaging of α7 nAChR in neurology and oncology. It was our goal to radiolabel the α7 nAChR agonist 4-[5-(4-fluoro-phenyl)-[1,3,4]oxadiazol-2-yl]-1,4-diaza-bicyclo[3.2.2]nonane(NS10743) and to assess the selectivity of [18F]NS10743 binding site occupancy in animal experiments.

Methods
[18F]NS10743 was synthesized by nucleophilic substitution of the nitro precursor. In vitro receptor affinity and selectivity were assessed by radioligand competition and autoradiography. The radiotracer properties were
evaluated in female CD-1 mice by brain autoradiography and organ distribution. Target specificity was validated after treatment with SSR180711 (10 mg/kg, intraperitoneal), and metabolic stability was investigated using radio-HPLC.

Results
The specific activity of [18F]NS10743 exceeded 150 GBq/μmol at a radiochemical purity >99%. In vitro, NS10743 and [18F]NS10743 showed high affinity and specificity towards α7 nAChR. The brain permeation of
[18F]NS10743 was fast and sufficient with values of 4.83 and 1.60% injected dose per gram and brain to plasma ratios of 3.83 and 2.05 at 5 and 60 min after radiotracer administration. Brain autoradiography and organ distribution showed target-specific accumulation of [18F]NS10743 in brain substructures and various α7 nAChR-expressing organs. The radiotracer showed a high metabolic stability in vivo with a single polar radiometabolite, which did not cross the blood–brain barrier.

Conclusion
The good in vitro and in vivo features of [18F] NS10743 make this radioligand a promising candidate for quantitative in vivo imaging of α7 nAChR expression and encourage further investigations.
Keywords: Alpha7 nicotinic acetylcholine receptors . PET. Diagnostic imaging . Nonneuronal . Oncology . Neurology. Diazabicyclononane

Publ.-Id: 12669 - Permalink


Magnetic properties of Mn-doped ZnO Nanowires
Granovsky, S. A.; Gaidukova, I. Y.; Markosyan, A. S.; Lu, J. G.; Chien, C. J.; Doerr, M.; Papageorgiou, T.; Wosnitza, J.;
Structural, magnetic and transport properties of undoped and Mn-doped quasi onedimensional ZnO nano-wires formed as dendrite crystals of different width have been studied. All Mn-doped nanowires (Mn content 16% and 27 %) exhibit a ferromagnetic behavior, which is significantly temperature dependent. A small magnetic signal detected up to the room temperature is supposed to be due to small amounts of magnetic impurities. Analysis of the temperature dependencies of magnetization shows that the observed magnetic properties can be caused by the host ferromagnetic matrix with Curie temperature TC = 40 K.
  • Solid State Phenomena 152-153(2009), 303-306

Publ.-Id: 12668 - Permalink


Isostructural transition coupled with spin ordering in CsCuCl3: A spatially frustrated spiral crystal lattice
Plakhty, V. P.; Wosnitza, J.; Martin, N.; Marchi, Y.; Smirnov, O. P.; Grenier, B.; Gavrilov, S. V.;
By means of single-crystal neutron diffraction, an isostructural transition is observed at the Néel temperature of CsCuCl3, a quasi-one-dimensional antiferromagnet with a helically modulated crystal structure that is built out of six Cu2+ layers. Abrupt atomic displacements of about 0.01 A minimize the ferromagnetic interlayer superexchange interaction via the path Cu-Cl1-Cu that enters also the antiferromagnetic path Cu-Cl1-Cl2-Cu. The latter couples only one pair of Cu2+ ions in each chlorine layer since all the other intralayer bonds either have much longer interatomic distances or include more than two intermediate Cl ions and, therefore, can be neglected. Thus, a spatial geometric frustration in this helically modulated stacked triangular lattice is provided by three Cu layers. Influences of the atomic displacements on the exchange energy, as well as the critical behavior of this spatially frustrated material, are discussed.
  • Physical Review B 79(2009), 012410

Publ.-Id: 12666 - Permalink


Low-dimensional compounds containing cyano groups. XVII. Crystal structure, spectroscopic, thermal and magnetic properties of [Cu(bmen)2][Pt(CN)4] (bmen = N,N´-dimethylethylenediamine)
Potocnák, I.; Vavra, M.; Cizmar, E.; Kajnaková, M.; Radváková, A.; Steinborn, D.; Zvyagin, S. A.; Wosnitza, J.; Feher, A.;
The synthesis, structural analysis, spectroscopic studies, susceptibility and specific-heat measurements of {[Cu(bmen)2][Pt(CN)4]}n (bmen = N,N'-dimethylethylenediamine) are presented. X-ray crystalstructure analysis revealed that the [Pt(CN)4]2- building blocks are combined with [Cu(bmen)2]2+ units to form a chain-like structure along the a axis. The Cu(II) atoms are hexacoordinated by four nitrogen atoms in the equatorial plane belonging to two molecules of bidentate bmen ligands with average Cu–N distance of 2.043(18) A . The axial positions are occupied by two nitrogen atoms from bridging [Pt(CN)4]2- anions at a longer axial Cu–N distance of 2.490(4) A . The compound is characterized by the presence of a weak antiferromagnetic exchange coupling J/kB = 0.6 K. Despite the one-dimensional (1D) character of the structure, the analysis of the magnetic properties and specific heat at very low temperatures shows that [Cu(bmen)2][Pt(CN)4] behaves as a two-dimensional (2D) square-lattice Heisenberg magnet with weak interlayer coupling.
  • Journal of Solid State Chemistry 182(2009), 196-202

Publ.-Id: 12665 - Permalink


Low-energy excitations in DTN below Tc: ESR studies
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.; Glazkov, V. N.; Sosin, S. S.; Smirnov, A. I.;
NiCl2-4SC(NH2)2 (known as DTN) is an S = 1 system with an easy-plane anisotropy dominating over the exchange interaction and exhibiting a field-induced antiferromagnetic ordering with critical fields Bc1 = 2.1 T, Bc2 = 12.6 T and temperature Tmaxc = 1.2 K. A systematic study of the low-energy excitation spectrum of DTN in the ordered phase at temperatures down to 0.45 K is presented. It is showed that two observed gapped modes can be consistently interpreted within a four-sublattice antiferromagnet model with a weak isotropic corner-center interaction of magnetic ions in the body-centered tetragonal lattice.
  • Open Access LogoJournal of Physics: Conference Series 150(2009), 042244

Publ.-Id: 12664 - Permalink


Ultrasonic investigation of NiCl2-4SC(NH2)2 in the vicinity of the quantum critical points
Zherlitsyn, S.; Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Zvyagin, A. A.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.;
We report results of sound-velocity and sound-attenuation measurements in the quantum S = 1 spin-chain magnet NiCl2-4SC(NH2)2 that shows a field-induced antiferromagnetic (AF) ordering and two corresponding quantum critical points at Hc = 2.1 T and Hs = 12.6 T. The longitudinal acoustic c33 mode modulates the in-chain exchange interaction and shows a softening in the vicinity of the quantum critical points, accompanied by energy dissipation in the acoustic wave. We discuss our results with a model where the main contribution to the spin-lattice interaction arises from the exchange-striction coupling within one-dimensional spin-chains.
  • Open Access LogoJournal of Physics: Conference Series 145(2009), 012069

Publ.-Id: 12663 - Permalink


Magnetic properties of the S = 1/2 Heisenberg spin-chain material (6MAP)CuCl3
Ozerov, M.; Cizmar, E.; Wosnitza, J.; Zvyagin, S. A.; Xiao, F.; Landee, C. P.; Turnbull, M. M.;
Magnetic properties of the S = 1/2 Heisenberg spin-chain material (6MAP)CuCl3 have been probed by means of magnetization, specific-heat and electron spin resonance (ESR) measurements. A pronounced low-temperature Curie-like tail in the magnetic susceptibility was found at low temperatures. As recently suggested, such a behavior could originate from staggered magnetization effects, responsible also for the field-induced gap opening in S = 1/2 chains with broken translational symmetry. We found a clear anomaly in the specific heat having a broad maximum at Tmax = 2.3 K, accompanied by a significant ESR line broadening and g-factor shift. The specific-heat anomaly is magnetic-field independent, indicating that its origin is not related to the field-induced transverse staggered magnetization effects
  • Open Access LogoJournal of Physics: Conference Series 150(2009), 042159

Publ.-Id: 12662 - Permalink


One-dimensional (Mo3S3)n Clusters: building blocks of clusters materials and ideal nanowires for molecular electronics
Gemming, S.; Seifert, G.; Bertram, N.; Fischer, T.; Götz, M.; Ganteför, G.;
The geometric and electronic structures of gas phase Mo3nS3n+2 and Mo3n-1S3n+5 clusters are studied experimentally using mass and photoelectron spectroscopy. The experimental results are compared with calculations based on density-functional theory. Although such clusters have been known for decades as main constituents of Chevrel phases, we here report their first gas phase synthesis for sizes up to n=17 (Mo51S53). The smallest entities are Mo6S8 and Mo5S11 with HOMO-LUMO gaps of 0.9eV and 0.5eV. With increasing n, the clusters grow 1-dimensional and form nanowires with a vanishing gap. The sulfur atoms at both ends may easily bind to Au electrodes making these clusters promising components of future nanoelectronic devices.
Keywords: molybdenum sulfide, clusters, Chevrel compounds, density-functional theory

Publ.-Id: 12661 - Permalink


Interface and border trap relaxation in Si/SiO2 structures witzh Ge nanocrystals examined by transient capacitance spectroscopy
Beyer, R.; von Borany, J.; Burghardt, H.;
The formation of interface and border states in metal-oxide-semiconductors structures associated with the generation of embedded germanium nanocrystals in 20 nm SiO2-layers by means of ion implantation and a subsequent annealing was examined. Deep level transient spectroscopy and related time-domain techniques were applied in order to study the charge trapping and emission at the Si-SiO2 interface. A significant dependence of the interface state density Dit on the conditions of the cluster generation was found. Any Ge-implanted sample features a pronounced level at about 0.31 eV above the valence band edge and a concentration above 1e13 /cm²eV, likely related to a Pb-center.
A systematic variation of the filling pulse parameters was utilized in order to separate the response of fast and slow states, and to substantiate the existence of border traps located in the vicinity of the Si-SiO2 interface. The role of interface and border traps for the relaxation of the trapped charge in the nanocrystals is illustrated.
Keywords: nanocrystals, Si-SiO2 interface states, capacitance transient spectroscopy
  • Poster
    16th Conference of Insulating Films on Semiconductors (INFOS 2009), 29.06.-01.07.2009, Cambridge, United Kingdom
  • Microelectronic Engineering 86(2009)7-9, 1859-1862

Publ.-Id: 12660 - Permalink


Annual Report 2008 Institute of Ion Beam Physics and Materials Research
von Borany, J.; Heera, V.; Helm, M.; Möller, W.; (Editors)
Outstanding scientific results and statistical overview of the Institute of Ion Beam Physics and Materials Research in 2008
Keywords: Selected Publications, Statistics
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-512 2009

Downloads:

Publ.-Id: 12659 - Permalink


Discontinuous Superconducting Transitions in the Paramagnetic limit: a Non-Perturbative approach
Maniv, T.; Zhuravlev, V.; Wosnitza, J.;
The unusual superconducting (SC) phase transitions occuring under competing orbital and spin pair breaking, which characterize clean strongly type-II superconductors at low temperatures, are investigated within a non-perturbative approach, which avoides the difficulties encountered in various perturbative approaches and enables comparison with recent experimental data. It is shown that in a 3D system with strong spin-splitting, a spatial (FFLO) modulation of the order parameter along the magnetic-field direction preserves the continuous nature of the SC transition. However, at a magnetic field slightly below Hc2 the FFLO state becomes unstable, transforming discontinuously into a uniform SC state via a first-order phase transition. Our calculation shows that the entropy jump at the first-order phase transition is siginificantly larger than its total variation in the continuous region between the two transitions, in agreement with recent thermal-conductivity measurements performed on the heavy-fermion compound URu2Si2.
  • Open Access LogoJournal of Physics: Conference Series 150(2009), 052151

Publ.-Id: 12658 - Permalink


Diameter and Morphology Dependent Raman Signatures of WS2 Nanostructures
Krause, M.; Virsek, M.; Remskar, M.; Salacan, N.; Fleischer, N.; Chen, L.; Hatto, P.; Kolitsch, A.; Möller, W.;
WS2 fullerene particles and nanotubes show a diameter and morphology dependent Raman response, see figure showing response for WS2 nanotubes of 290 nm and 50 nm diameter. This enables the classification of WS2 nanotubes, fullerenes, and nanocrystals, and the estimation of geometric properties (Table of Contents).
Keywords: inorganic fullerenes, layered compounds, nanotubes, Raman spectroscopy, tribological thin films

Publ.-Id: 12657 - Permalink


Magnetic properties of the Zn-doped Haldane-gap material NENB
Cizmar, E.; Ozerov, M.; Wosnitza, J.; Zvyagin, S. A.; Krzystek, J.; Landee, C. P.; Landry, B. R.; Turnbull, M. M.; Wikaira, J. L.;
Experimental studies of the spin-1 Haldane-chain material [Ni(C2H8N2)2NO2](BF4) (NENB) doped with diamagnetic Zn(II) ions in a range up to nominally 5% by means of the magnetic-susceptibility and the electron-spin resonance (ESR) techniques are reported. The presence of fractional S = 1/2 chain-end states, revealed by ESR and susceptibility measurements is found to be responsible for spin-glass freezing effects. It is suggested that a higher doping with Zn ions suppresses the spin-glass behaviour by creating shorter and isolated chain fragments.
  • Open Access LogoJournal of Physics: Conference Series 150(2009), 042017

Publ.-Id: 12656 - Permalink


Erste Phantommessungen für eine prätherapeutische Dosimetrie mit Y-86-DOTATOC an einem PET/CT (Biograph 16, Siemens, Erlangen)
Andreeff, M.; Hartmann, H.; Oehme, L.; Kotzerke, G.; Walther, M.; Kotzerke, J.;
Ziel/Aim:
Für die Therapie mit Y-90-DOTATOC wird obligatorisch eine posttherapeutische Dosimetrie unter Gammakamera durchgeführt, wobei die Nutzung der Bremsstrahlung für die Quantifizierung viele Limitationen mit sich bringt, so dass häufig als Surrogatmarker In-111-DOTATOC verwendet wird. Seit längerer Zeit wird eine prätherapeutische Dosimetrie mit Y-86-DOTATOC favorisiert. Phantom- und Patientenuntersuchungen für singuläre PET-Geräte älterer Bauart existieren. Aber es fehlen dezidierte Untersuchungen für moderne Hybrid-Geräte. An einem PET/CT-Gerät sollen Phantomuntersuchungen die Möglichkeiten zur Dosimetrie aufzeigen.

Methodik/Methods:
Für die Kalibrierung und mögliche Korrekturen wurde ein mit Aktivität füllbares Zylinderphantom (Durchmesser: 20cm, Länge: 20cm) mit 3 inaktiven Zylindereinsätzen (Teflon, Wasser und Luft) verwendet. Die Untersuchung wurde an einem konventionell kalibrierten PET/CT (Normalisierung mit F-18), LSO HiRes Biograph 16 (Siemens, Erlangen) durchgeführt. Zur genauen Aktivitätsbestimmung wurde ein Aktivitätsmessgerät ISOMED 2000 (MED Dresden) über die PTB Braunschweig für Y-86 kalibriert. Das Phantom wurde mit 5,8 kBq/ml Y-86 gefüllt. 3D-Aufnahmen erfolgten mit 10min pro Bettposition, AC-CT, Iterative Rekonstruktion (8i,4s, FWHM=5mm, Streukorrektur).

Ergebnisse/Results:
Die ROI-Auswertung am Phantom ergab eine Überbewertung ("falsche" Aktivitätsanreicherung) in den inaktiven Zylindern, bezogen auf die Aktivitätskonzentration im aktiven Zylinderbereich (Teflon +0,3%, Luft +22% und Wasser +2%). Mit der konventionellen PET-Normalisierung, Schwächungs- und Streukorrektur wurde die zu erwartende Aktivitätskonzentration im Zylinder um 45% reduziert wiedergegeben. Ein Rekonstruktionsvergleich mit und ohne Streukorrektur zeigte, dass der konventionelle Streukorrekturalgorithmus für Y-86 falsche Ergebnisse liefert. Für die weitere Quantifizierung ohne Streukorrektur wurde eine Crosskalibrierung vorgenommen und ein Kalibrierfaktor von 0,9 cps(Siemens)/Bq für Y-86 bestimmt.

Schlussfolgerungen/Conclusions:
Für eine prätherapeutische Dosimetrie mit Y-86 an einem PET/CT-Gerät, kann mit der konventionellen Kalibrierung (Normalisierung mit F-18) eine Quantifizierung vorgenommen werden. Die besten Ergebnisse sind bei Rekonstruktion ohne Streukorrektur (artefaktfrei) zu erreichen. Eine separate Crosskalibrierung für Y-86 ist notwendig. Die Überbewertung bei Luft ist sicherlich auf das ungünstige Emissionsspektrum von Y-86 zurückzuführen. Die gemessenen Überbewertungen (Reko: ohne Streukorrektur) für dieses 3D-PET Gerät (PET/CT, LSO) ist moderater als dies Pentlow [1] für einen 3D-BGO-GE-Scanner (Advance) (Teflon +161%, Luft -20%% und Wasser +56%) ermittelt hat.

Literatur/References:
[1] Pentlow, K.S., Finn, R.D., Larson, St.M. et.al., Quantitative Imaging of Y-86 with PET: The Occurrence and Correction of Anomalous Apparent Activity in High Density Regions; Clinical Positron Imaging, Vol.3, No.3, 2000
  • Poster
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A94

Publ.-Id: 12655 - Permalink


Präzisionsmessung der rekonstruierten Bildauflösung mit dem IEC/NEMA Ganzkörper Kugelphantom für verschiedene PET- und PET/CT-Scanner
Mix, M.; Eckerle, S.; van den Hoff, J.; Weber, W.;
Ziel/Aim:
Für Multi-Center Studien mit unterschiedlichen PET-Scannern ist ein einfach anwendbares und robustes Verfahren zur Bestimmung der rekonstruierten Bildauflösung entscheidend um vergleichbare Ergebnisse bei der quantitativen Auswertung und Volumenbestimmung zu erzielen. Ziel dieser Arbeit war deshalb die präzise Bestimmung der Auflösung innerhalb des rekonstruierten Bildes mit Hilfe von Messungen am weit verbreiteten IEC/NEMA Ganzkörperphantom in Abhängigkeit vom Target zu Hintergrund Kontrast und der Zählstatistik.

Methodik/Methods:
Datengrundlage bildeten Messungen eines IEC Ganzkörperphantoms (Kugeleinsätze 10-37mm Durchmesser) an 7 Scannersystemen (2 BGO-, 3 LSO- und 2 GSO-Scanner) die im 3D und, wenn möglich, 2D Modus für unterschiedliche Messzeiten (1 bis 10min) und Kontrastverhältnisse zwischen Kugeln und Hintergrund (1:0,6:1/3:1/1,5:1) akquiriert und jeweils mit dem herstellerseitig empfohlenen Ganzkörperprotokoll rekonstruiert wurden. Die rekonstruierte Ortsauflösung im Bild wurde für jede der 5 Kugeln im Phantom durch Anpassung des entsprechenden Modells, d.h. durch Faltung der Objektfunktion (Kugel+Wand+Untergrund) mit einer Gauss-förmigen Point Spread Function an die vollständigen als Radialprofil aufgetragenen 3D-Messdaten (je nach Größe der Kugel ca. 103-104Datenpunkte pro Kugel) bestimmt.

Ergebnisse/Results:
Mit dem vorgestellten Regressionsverfahren kann unter klinikähnlichen Messbedingungen die rekonstruierte Bildauflösung FWHM [mm] anhand der Kugeln mit einer sehr hohen statistischen Genauigkeit von (2,8 +/- 0,1)% bestimmt werden (Mittelwert über 593 Kugeln). Für kleine Kugeln von 10-16mm Durchmesser ist die stat. Genauigkeit mit 3-5% etwas schlechter als mit ~2% für große Kugeln mit 22-37mm Durchmesser. Die Resultate zeigen, dass mit dem Ganzkörper-Standardprotokoll die rekonstruierte Bildauflösung bei allen Systemen deutlich unter der mit NEMA spezifizierten Geräteauflösung liegt. Sie ist i.w. unabhängig von der Messzeit (1-10min), sinkt aber mit fallendem Target zu Hintergrund Kontrast (gegenüber dem 1:0 Kontrast um 30% bei Kontrast 6:1, um 54% bei Kontrast 3:1 und um 80% bei Kontrast 1,5:1). Diese Auflösungsverschlechterung hat bei Strukturengrößen unterhalb dem Dreifachen der Bildauflösung direkten Einfluss auf die Quantifizierung und auf die das Volumen repräsentierende Aktivitätsschwelle.

Schlussfolgerungen/Conclusions:
Um eine auch für kleine Zielstrukturen über unterschiedliche Scanner gültige Quantifizierung und valide Methode zur Volumenbestimmung in der PET zu etablieren, muss zwingend die tatsächliche, rekonstruierte Bildauflösung einbezogen werden. Der hier beobachteten Abhängigkeit der Ortsauflösung vom Kontrast ist dabei Rechnung zu tragen.
  • Poster
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A93

Publ.-Id: 12654 - Permalink


Ultrasonic Investigation of NiCl2-4SC(NH2)2
Chiatti, O.; Zherlitsyn, S.; Sytcheva, A.; Wosnitza, J.; Zvyagin, A. A.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.;
We report results of ultrasonic investigations of the quantum S = 1 spin-chain magnet NiCl2-4SC(NH2)2, also known as DTN, in magnetic fields up to 18 T and temperatures down to 0.3 K. A field H along the [001] direction induces a transition into an antiferromagnetic phase with TmaxN = 1.2 K. Accordingly, at T = 0 there are two quantum critical points at ~2.1 T and at ~12.6 T. The acoustic c33 mode, propagating along the spin chains, shows a pronounced softening close to the phase transition, accompanied by energy dissipation of the sound wave. The H-T phase diagram obtained from our measurements is compared with results from other experimental investigations and the low-temperature acoustic anomalies are traced up to T > TN. We also report frequency-dependent effects, which open the possibility to investigate the spin fluctuations in the critical regions. Our observations show an important role of the spin-phonon coupling in DTN.

Publ.-Id: 12653 - Permalink


The pulsed magnetic field facility at Dresden
Wosnitza, J.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S.;
Since 2007, the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD) operates as a user facility, providing unique experimental possibilities in pulsed fields. The HLD offers various experimental techniques, such as electrical transport, magnetization, ultrasound, and magnetic resonance. A particular feature of the laboratory is the next-door free-electron-laser installation used for high-field infrared spectroscopy and electron spin resonance in pulsed fields. Additionally, nuclear magnetic resonance and specific-heat measurement techniques are being developed in pulsed magnetic field. As the only laboratory in Europe, the HLD has reached magnetic fields of about 87 T allowing now to perform experiments in this field range for modern materials research. Several 60 and 70 Tesla magnets are regularly used by researchers. A two-coil 100 T prototype magnet and a long-pulse (1000 ms) 60 T magnet are ready for their first tests. Some recent scientific results will be highlighted.
  • Lecture (Conference)
    International Conference on Magnetism (ICM 2009), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 12652 - Permalink


Antiferromagnetic Resonance of the Ho subsystem in Multiferroic HoMnO3
Kamemskiy, D.; Ozerov, M.; Cizmar, E.; Wosnitza, J.; Zvyagin, S. A.; Zhou, H. D.; Wiebe, C. R.;
Multiferroic HoMnO3 is ferroelectric below Tc = 875 K and antiferromagnetically ordered below TN(Mn) = 75 K (Mn subsystem). In addition, at TN(Ho) approximately 5 K the Ho subsystem undergoes a transition into an antiferromagnetically ordered state. The coupling between the ferroelectric and antiferromagnetic order parameters in HoMnO3 has not yet been unambiguously explained, revealing the importance of geometrical frustrations and a complex interplay between the Ho and Mn magnetic subsystems. High-quality single-crystalline samples of HoMnO3 were studied by means of X-band (9.3 GHz) electron spin resonance spectroscopy. A relatively strong absorption was found below 5 K, which corresponds to the temperature of the magnetic ordering of the Ho subsystem. The observed mode exhibits a very pronounced anisotropic behavior and can be interpreted as an excitation within the antiferromagnetically ordered Ho subsystem.
  • Poster
    International Conference on Magnetism (ICM 2009), 26.-31.07.2009, Karlsruhe, Deutschland

Publ.-Id: 12651 - Permalink


THz-range free-electron laser ESR spectroscopy: techniques and applications in high magnetic fields
Ozerov, M.; Cizmar, E.; Kamenskyi, D.; Zherlitsyn, S.; Herrmannsdörfer, T.; Wosnitza, J.; Zvyagin, S. A.;
The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave THz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The unique combination of two linac-based FELs (covering the wavelength range of 4 - 250 μm) with high magnetic fields at the Research Center Dresden-Rossendorf (FZD) allows for tunable-frequency ESR spectroscopy in an extraordinary broad frequency range of 1.2 - 75 THz in magnetic fields up to ~70 T. The new approach is of particular importance for studying magnetic excitations in materials exhibiting field-induced phenomena (including magnetic phase transitions) and in spin systems with a large zero-field splitting. The performance of the spectrometer is illustrated with ESR spectra obtained in the low-dimensional organic material (C6H9N2)CuCl3 and the multiferroic compound YMnO3 This work was made in collaboration with R. Wünsch, W. Seidel, H.D. Zhou, C. Wiebe.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM)2009, 22.-27.03.2009, Dresden, Deutschland
  • Poster
    Terahertz spectroscopy and its high-field applications & EuroMagNET II user meeting, 14.-16.06.2010, Dresden, Deutschland

Publ.-Id: 12650 - Permalink


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