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31745 Publications
Actinide Interactions with Bacteria
Moll, H.; Bernhard, G.;
Microbes are widely distributed in nature also under harsh conditions (e.g., high salinity; low permeability; high and low temperatures). They can strongly influence the migration of hazardous actinides in the environment once they have been released. This is demonstrated by an increased interest in studies exploring the interaction processes involving actinides and bacteria during the last years. However, worldwide only little detailed information is available about the biodiversity and microbial influences on radionuclide migration under the conditions of a deep nuclear repository.
The presentation covers the broad topic of actinide interactions with bacteria. A short overview about the determination of the microbial diversity giving the dominant bacterial strains will be given. In more detail, the manifold interaction process of bacteria with actinides will be highlighted based on selected examples.
With this presentation we want to point out the importance of actinide-microbe interactions for the disposal of nuclear waste.
Keywords: microbes, actinides, nuclear waste disposal
  • Lecture (Conference)
    Actinide and Brine Chemistry in a Salt-Based Repository (ABC-SALT) International Workshop, 15.-17.09.2010, Carlsbad, New Mexico, USA

Publ.-Id: 14448 - Permalink


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

References:
[1] M. Wagner et al., Appl. Phys. Lett. 94, 241105 (2009).
[2] S. H. Autler and C. H. Townes, Phys. Rev. 100, 703 (1955).
[3] S. G. Carter et al., Science 310, 651 (2005).
Keywords: AC Stark effect, Autler Townes effect, excitons, terahertz, sideband generation, nonlinear optics
  • Lecture (Conference)
    NOEKS 10 - 10th International workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors, 16.-19.08.2010, Paderborn, Deutschland

Publ.-Id: 14447 - Permalink


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

[1] S. H. Autler and C. H. Townes, Phys. Rev. 100, 703 (1955).
[2] S. G. Carter et al., Science 310, 651 (2005).
[3] J. F. Dynes, M. D. Frogley, M. Beck, J. Faist, and C. C. Phillips, Phys. Rev. Lett. 94, 157403 (2005).
Keywords: AC Stark effect, Autler Townes effect, excitons, terahertz, sideband generation, nonlinear optics
  • Lecture (Conference)
    ICPS 2010, 30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul, Südkorea
  • Contribution to proceedings
    ICPS 2010, 30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul, Südkorea
    AIP Conference Proceeding 1399 (2011) 479-480; doi: 10.1063/1.3666462

Publ.-Id: 14446 - Permalink


Interaction of U(VI) with Schizophyllum commune
Günther, A.; Roßberg, A.; Raff, J.; Bernhard, G.;
Biosorption processes of heavy metals and actinides like uranium by fungal cells play an important role in the mobilisation or immobilisation of these elements in nature. Different sorption experiments of U(VI) with Schizophyllum commune at different initial uranium concentrations and therewith connected varying initial uranium speciation showed high uranium sorption capacities in the pH range from 4 to 7. Formed uranium complexes were investigated by means of time-resolved laser-induced fluorescence spectroscopic measurements (TRLFS). The obtained spectra show clearly differences between the emissions properties of the uranium species on fungi and the dissolved uranium species in the initial mineral medium. While the oxidation state of uranium remained unchanged during the sorption process, the uranium speciation changes significantly. Extra- and/or intracellular phosphate groups are the predominant binding places of uranium due to our first spectroscopic results. X-ray absorption fine structure spectroscopic measurements (EXAFS) were performed for a structural characterisation of formed uranium-fungi species and a verification of the TRLFS results.
Keywords: Uranium(VI), fungi, TRLFS, EXAFS
  • Lecture (Conference)
    9th Symposium on remediation in Jena, "Jenaer Sanierungskolloquium", 04.-05.10.2010, Jena, BRD

Publ.-Id: 14445 - Permalink


Nanostructuring of BaF2 (111) surfaces by single slow highly charged ions
El-Said, A. S.; Heller, R.; Facsko, S.;
The creation of surface nanostructures in BaF2 (111) surfaces was studied after irradiation with slow highly charged Xe ions from the Dresden-EBIT (Electron Beam Ion Trap). After irradiation, the crystals were investigated by scanning force microscopy (SFM). Using specific ion parameters, the topographic images show nanohillocks emerging from the surface. Additionally, we used the technique of selective chemical etching to reveal the lattice damage created by ion energy deposition below and above threshold needed for surface hillocks formation. The role of both potential and kinetic energy as well as a comparison with results for swift heavy ion irradiations of BaF2 single crystals are presented.
Keywords: highly charged ions, nanostructures
  • Nuclear Instruments and Methods in Physics Research B 269(2011), 901-904

Publ.-Id: 14444 - Permalink


Ion-Induced Nanoscale Ripple Patterns on Si Surfaces - Theory and Experiment
Keller, A.; Facsko, S.;
Nanopatterning solid surfaces by low-energy ion bombardment has received considerable interest in the recent years. This interest was partially motivated by promising applications of nanopatterned substrates in the production of functional surfaces. Especially nanoscale ripple patterns on Si surfaces have attracted attention both from a fundamental and an application related point of view. This paper summarizes the theoretical basics of ion-induced pattern formation and compares the predictions of the various continuum models to experimental observations with special emphasis on the morphology development of Si surfaces during sub-keV ion sputtering.
Keywords: nanopatterning; ion sputtering; surface morphology; continuum theory

Publ.-Id: 14443 - Permalink


Vibrational spectroscopy of actinyl sorption complexes
Gückel, K.;
Information about motivation and objectives as well as first results of the PhD thesis
  • Poster
    FZD PhD Seminar, 22.-24.09.2010, Krögis, Deutschland

Publ.-Id: 14442 - Permalink


Stofftransport bei Bergbaufolgeschäden und Altlastensanierung
Wolf, M.;
Es ist kein Abstract vorhanden.
  • Lecture (others)
    GEOforum Leipzig, 08.06.2010, Leipzig, Deutschland

Publ.-Id: 14441 - Permalink


Geochemische Wechselwirkungen bei Anwesenheit von Huminstoffen in Untertagedeponien
Fellmer, F.;
Es ist kein Abstract vorhanden.
  • Lecture (others)
    GEOforum 2010, 08.06.2010, Leipzig, Deutschland

Publ.-Id: 14439 - Permalink


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

Publ.-Id: 14437 - Permalink


Molecular and microscopical characterization of the algae mat from the „Gessenhalde“ (Ronneburg/Eastern Thuringia) and the proof of the retention of uranium
Zirnstein, I.; Krawczyk-Bärsch, E.; Arnold, T.; Röske, I.;
Next to the test-field site of the former uranium leaching dump “Gessenhalde” (Ronneburg/Eastern Thuringia), which is part of a research program of the Friedrich-Schiller University, biofilms were sampled from a creek and investigated by PCR and cloning, light microscopy, CLSM and TEM/EDX. The molecular and microscopical characterization of the eukaryote diversity showed a wide spectrum of free living eukaryote microorganism, like the filamentary green algae Microspora and Klebsormidium as the dominant eukaryote. Flagellates, ciliates and rotaroria are present as representatives of the protozoa in minor amount. The water of the creek is characterized by a low pH of 3.3 – 3.9 and a uranium concentration, which ranges seasonally between 1x10-6 M/L and 6x10-6 M/L. Following up the question if the algae mat may have immobilized uranium by biosorption or bioaccumulation the filamentary algae were selected and investigated microscopically and spectroscopically by CLSM and TEM/EDX. Since the results did not provide any microscopic and spectroscopic evidence for the presence of uranium immobilization, the filamentary algae were cultured in rain water with a pH adjusted to 6,0. After the addition of uranium as UO2(ClO4)2 in the ecologically relevant concentration of 1x10-5 M/L the algae showed characteristic fluorescence spectra in the wavelength range of 480-560 nm, which is typical for uranium (VI). The results demonstrated that the actual in-situ geochemical conditions of the creek from the "Gessenhalde" inhibit the retention of uranium by the algae mat. The removal of uranium from the aqueous phase requires the cultivation of algae in a neutral media.
Keywords: biofilm, algae, uranium
  • Poster
    9. Sanierungskolloquium, 04.-05.10.2010, Jena, Deutschland

Publ.-Id: 14436 - Permalink


Interaction of Selected Actinides with Microorganisms Relevant to Nuclear Waste Disposal
Frost, L.; Moll, H.; Krawczyk-Bärsch, E.;
The sorption behavior/ retardation of actinides (uranium) in deep geological formations like clay, granite or salt is determined by the constitution of the host rock material and the presence of bioligands and microbes. To which extent can bioligands and microbes lead to a mobilisation of the respective actinyl ion?
By presenting results of our current research categorical examples for the interaction of uranium(VI) with above mentioned interaction partners are given:
- Interaction with host rock material: the anaerobic sorption of U(VI) onto Opalinus Clay
- Interaction with bioligands: interaction of U(VI) with the model ligand benzoic acid investigated by UV-vis spectroscopy and cryo-TRLFS
- Interaction with microbes: interaction of U(VI) with the Äspö bacterium Pseudomonas fluorescens (HAADF-TEM measurements and uranium accumulation experiments)
Keywords: Uranium, Opalinus Clay, Pseudomonas fluorescens, UV-vis spectroscopy, cryo-TRLFS
  • Poster
    5th FZD Ph.D. Seminar, 22.-24.09.2010, Krögis, Deutschland

Publ.-Id: 14435 - Permalink


Analysis of the influence of different arrangements for ZrH moderator material on the performance of a SFR core
Merk, B.; Weiß, F. P.;
The structure for the development of a fuel element design with reduced sodium void achieved by the use of the moderating material ZrH is investigated. In the study the sodium void effect, as well as the major feedback coefficients are analyzed. Besides the feedback coefficients, the influence on the operational parameters like neutron flux distribution, power distribution, and burnup distribution is investigated for the different possibilities of arranging the moderating material in the fuel element. Additionally, the fuel cycle parameters breeding and minor actinide production are analyzed. For a first evaluation of the behavior during transients the influence of temperature changes in the ZrH and the consequences of dissociation of the ZrH on the fuel element power are studied.
Keywords: Sodium void, fast reactor, zirconium hydride

Publ.-Id: 14434 - Permalink


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

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

The third examined configuration is motivated by an application of the contactless inductive flow tomography (CIFT) in a continuous casting model experiment. Consideration of the finite conductivity of the copper container walls results in a quantitative modification of the current distribution within the solid material. An enhanced current yields an amplified induced magnetic field outside of the container which must be considered in the reconstruction of the fluid velocity field.
Keywords: Dynamo Conductivity Permeability Induction
  • Lecture (Conference)
    Workshop on Numerical Simulations of MHD flows, 18.-20.10.2010, Karlsruhe, Deutschland

Publ.-Id: 14433 - Permalink


Ein Modell zur Beschreibung der Kühlmittelvermischung und seine Anwendung auf die Analyse von Borverdünnungstransienten in Druckwasserreaktoren
Kliem, S.;
Es wurde ein Modell zur realistischen Beschreibung der Kühlmittelvermischung innerhalb des Reaktordruckbehälters eines Druckwasserreaktors entwickelt und validiert. Dieses schnell rechnende Modell basiert auf dem Prinzip der linearen Superposition der Antwortfunktionen auf Dirac-Impuls-ähnliche Störungen der Kühlmittelparameter. Es wurde in den gekoppelten Programmkomplex DYN3D/ATHLET als Schnittstelle zwischen dem eindimensionalen Thermohydraulikprogramm ATHLET und dem dreidimensionalen neutronenkinetischen Kernmodell DYN3D eingebunden und simuliert in effizienter Weise die Vermischung des Kühlmittels innerhalb des RDB.
Für die Analyse von hypothetischen Borverdünnungsstörfallen wurde eine Methodik entwickelt, die auf dem neuen Modell zur Beschreibung der Kühlmittelvermischung basiert. Diese Methodik besteht aus einer Kombination von stationären und transienten Rechnungen, in denen die Vermischung der deborierten Pfropfen auf dem Weg zum Reaktorkern in realistischer Weise simuliert wird. Über die Variation der Größe des deborierten Kühlmittelpfropfens kann der gewünschte Grad an Konservativität für die Analysen vorgegeben werden.
Diese neue Methodik wurde erfolgreich auf zwei verschiedene Borverdünnungsstörfalle angewandt. Neben dem Start der ersten Hauptkühlmittelpumpe bei Vorhandensein eines deborierten Kühlmittelpfropfens im kalten Strang des Primärkreislaufes wurde ein Deborierungsstörfall im Nachkühlbetrieb betrachtet. In beiden Fällen zeigten die Ergebnisse der Parameterstudie für eine generische Kernkonfiguration, dass es selbst bei Annahme des maximal möglichen Pfropfenvolumens zwar zur Rekritikalität des abgeschalteten Reaktors aber nicht zu einer unzulässigen Erhöhung der Hüllrohrtemperatur kommt. Wesentliche Ursache dafür ist die Verwendung realistischer zeitabhängiger Verteilungen der Borkonzentration am Eintritt in jedes Brennelement.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-539 2010
    ISSN: 1437-322X

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Publ.-Id: 14432 - Permalink


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

Publ.-Id: 14431 - Permalink


Test site Gessenwiese: Results in TRLFS investigations on surface water and pore waters, and preliminary results on plant saps concerning uranium speciation
Baumann, N.; Arnold, T.;
Plants may take up uranium from contaminated sites and thus may represent a potential risk. To evaluate the risk of uranium being transferred from the environment into the human food chain knowledge concerning the uranium speciation is essential since reactivity and toxicity of uranium largely depend on its speciation.
Plants take up their nutrients from the soil in dissolved form and thus uranium may enter plants as dissolved species. To study this process the speciation of uranium in a uranium contaminated site, i.e. Gessenheap near Ronneburg in Saxony/Germany was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) in the aqueous phase, i.e. in surface water (drainage channel on the Gessenheap) and in pore water (approximately 0.5 – 1 m below surface of test site Gessenwiese). In both waters uranium sulfate species dominate the uranium speciation and clearly show that uranium sulfate species are in contact with plant components.
In a second step we determined the uranium concentration in the plants obtained from the test field Gessenheap by ICP-MS. For these analyses cell saps of birch leaves, of a birch boletus, and of compartments of butterbur (leaves, roots, and sprouts) were obtained by ultra centrifugation. The highest uranium concentration was found in sap samples from roots of butterbur with 39.3 ppb uranium (approximately 1.5 • 10-7 M uranium); in the sap samples of birch leaves 18.1 and 16.6 ppb uranium, respectively were detected. In all other sap samples the uranium contents were below 4 ppb uranium. The uranium content in the studied dried plant materials were less than 2.2 ppb, and dried birch leaves contains less than 0.1 ppb uranium.
The above listed uranium concentrations turned out to be too low to be successfully analyzed by TRLFS. In addition, we have to mention that plant sap may contain substances which quench the fluorescence signal of uranium (VI), e. g. some heavy metal ions or organic compounds. For future studies plant samples containing higher uranium concentrations are used for TRLFS investigations, possibly mosses or lichens.
Keywords: TRLFS, uranium speciation
  • Lecture (Conference)
    9th Symposium on remediation in Jena "Jenaer Sanierungskolloqium", 04.-05.10.2010, Jena, Germany
  • Contribution to proceedings
    9th Symposium on remediation in Jena "Jenaer Sanierungskolloqium", 04.-05.10.2010, Jena, Germany

Publ.-Id: 14430 - Permalink


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

Publ.-Id: 14427 - Permalink


Development of the coupled 3D neutron kinetics/thermal-hydraulics code DYN3D-HTR for the simulation of transients in block-type HTGR
Rohde, U.; Baier, S.; Duerigen, S.; Fridman, E.; Merk, B.; Weiss, F.-P.;
At the Forschungszentrum Dresden-Rossendorf (FZD), the Light Water Reactor (LWR) dynamics code DYN3D is extended and adopted for the application to block-type High temperature gas-cooled reactor (HTGR). DYN3D is a two-group diffusion code for 3D steady-state and transient core calculations based on nodal expansion methods. In addition to the neutron kinetics, it disposes of a thermal-hydraulics model for flow in parallel coolant channels. Macroscopic cross section data libraries precalculated with variation of burn-up, reactor poisons concentrations and thermal-hydraulic feedback parameters are linked to the code. Recently, a multi-group version of the code was developed.
In this paper, we give an overview of the latest developments of DYN3D concerning block-type HTGR.
The SP3 transport approximation is implemented into the multi-group DYN3D code to take anisotropy of the neutron flux and heterogeneity of the core more precisely into account. The SP3 method previously implemented into DYN3D for square fuel element geometry of LWR is being extended for hexagonal geometry of the graphite blocks, where the hexagons are subdivided into triangular nodes to be able to perform a systematic mesh refinement.
The main challenge in cross section generation for the HTGR core calculations is the treatment of the so-called “double heterogeneity”. The Reactivity equivalent Physical Transformation (RPT) approach is applied in order to eliminate the double-heterogeneity of HTGR fuel elements in HELIOS calculations. The full core analysis of the reference simplified HTGR core is performed with DYN3D using macroscopic nodal cross sections provided by HELIOS. The DYN3D results are verified against full core Monte Carlo simulations.
A 3D heat conduction module coupled with a channel-type coolant flow model is implemented to take into account the temperature reactivity feedback to neutronics physically correctly. It is shown that there is significant redistribution of the produced heat by heat conduction between the graphite blocks.
Keywords: high temperature reactor, reactor dynamics, computer code, double heterogeneity, SP3 transport approximation, heat conduction, temperature reactivity feedback, computer code
  • Lecture (Conference)
    5th Topical Meeting in High Temperature Reactor Technology, 18.-20.10.2010, Prague, Czech Republic
  • Contribution to proceedings
    5th Topical Meeting on High Temperature Reactor Technology, 18.-20.10.2010, Pargue, Czech Republic
    Conference Website http://www.htr2010.eu/authors-area/upload/docs/htr2010_pdfonly.rar, Paper #036

Publ.-Id: 14426 - Permalink


Very large DPSS lasers are coming
Toepfer, T.; Neukum, J.; Hein, J.; Siebold, M.;
New alcaline-earth fluoride laser materials and ever-improving diode-laser module technology are bringing very high-energy, moderate-to high-repetition-rate DPSS lasers for research closer to reality.
Keywords: High-energy, diode-pumped, solid-state lasers
  • Open Access LogoLaser Focus World 46(2010)10, 64-67

Publ.-Id: 14425 - Permalink


Excitation wavelength dependence of phase matched terahertz emission from a GaAs slab
Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.;
We report on phase matched THz emission from GaAs using the anomalous dispersion introduced by optical phonon absorption at the reststrahlenband in GaAs. For this system tunability of the emitted THz frequencies by changing the near infrared excitation wavelength is predicted. We investigate this phenomenon for an oversized double metallized GaAs waveguide. A shift in the THz spectra is observed when the near-infrared wavelength is varied. Enhanced emission is found when phase matching is achieved at 1.4 µm.
Keywords: Terahertz, far infrared, ultrafst nonlinear optics
  • Open Access LogoOptics Express 18(2010)19, 19574-91580

Publ.-Id: 14424 - Permalink


Longitudinal Fields in Focused Radially Polarized Terahertz Beams
Winnerl, S.; Hubrich, R.; Peter, F.; Schneider, H.; Helm, M.;
We study the spatial and temporal structure of focused THz beams of radial polarization. Strong longitudinal field components localized at the axis of propagation are observed. The phase of the longitudinal field components is shifted by pi/2 with respect to the transverse field components.
Keywords: Terhertz, vector beams
  • Invited lecture (Conferences)
    35th International Conference on Infrared, Millimeter and Terahertz Waves, 05.-10.09.2010, Rome, Italy
  • Contribution to proceedings
    35th International Conference on Infrared, Millimeter and Terahertz Waves, 05.-10.09.2010, Rome, Italy
    Conference Digest of the 35th International Conference on Infrared, Millimeter and Terahertz Waves

Publ.-Id: 14423 - Permalink


Thermal Emittance Measurement of the Cs2Te Photocathode in FZD Superconducting RF Gun, WEPB22
Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.;
The thermal emittance of the photocathode is an interesting physical property for the photoinjector, because it decides the minimum emittance the photoinjector can finally achieve. In this paper we will report the latest results of the thermal emittance of the Cs2Te photocathode in FZD Superconducting RF gun. The measurement is performed with solenoid scan method with very low bunch charge and relative large laser spot on cathode, in order to reduce the space charge effect as much as possible, and meanwhile to eliminate the wake fields and the effect from beam halos

http://www.maxlab.lu.se/maxlab/conference/fel2010/index.html
  • Poster
    FEL 2010 Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    FEL 2010 Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010

Publ.-Id: 14422 - Permalink


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

Publ.-Id: 14420 - Permalink


[18F]NS10743: Characterisation Of A Selective a7 Nicotinic Acetylcholine Receptor (a7 nAChR) Radioligand In Pig Brain By PET
Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Funke, U.; Østergaard Nielsen, E.; Brunicardi Timmermann, D.; Steinbach, J.; Peters, D.; Brust, P.;
Introduction: Alterations of a7 nAChR have been observed in schizophrenia, brain trauma and neurodegenerative diseases. For PET imaging of a7 nAChR [18F]NS10743 has been successfully developed evaluated in mice by tissue distribution and specificity studies. Here we report on baseline and blocking PET studies with [18F]NS10743 in pig brain.
Methods: [18F]NS10743 was synthesized with high specific activity (>150 GBq/μmol) and radiochemical purity (>99%). Dynamic PET scanning was performed in anaesthetized female piglets (13-15 kg), intravenously injected with ~ 330 MBq [18F]NS10743 (total mass ~ 472 ng) for 120 min. Three animals additionally received 3 mg/kg of the a7 nAChR partial antagonist NS6740 at 10 min pre-tracer injection followed by a continuous infusion (1 mg/kg/h). Plasma samples were taken and metabolite-corrected input functions were estimated. Individual regions of interest were defined using an MRI-based template of pig brain. SUV and distribution volume (VT = K1/k2) were estimated. The ratio of specifically bound radioligand and non-displaceable radioligand in brain tissue was calculated from the VT values by BPND = (VT region - VT reference)/VT reference.
Results: [18F]NS10743 readily passed the blood-brain barrier and the uptake of radioactivity peaked with SUV = 2.23 ± 0.71 at 8 min in the baseline scan while in NS6740-blocking studies the radioactivity levels peaked significantly earlier (SUV = 3.02 ± 1.28 at 5 min) and decreased faster. At the end of study (between 90 and 120 min p.i.) SUV was significantly decreased by NS6740 in allinvestigated brain regions except olfactory bulb, which was chosen as reference region for calculation of BPND. At baseline, a VT value of 6.07 ± 1.54 was estimated for the whole brain with the highest radiotracer accumulation in the temporal, parietal, and occipital lobe, thalamus, striatum, and middle cortex (VT = 7.27 ± 1.95 – 7.10 ± 1.58). Intermediate binding was observed in hippocampus, colliculi, midbrain, frontal lobe, and ventral cortex (VT = 6.76 ± 1.71 – 6.09 ± 1.05), and lowest values were assessed in the cerebellum, pons, and olfactory bulb (VT = 5.71 ± 1.18 – 4.11 ± 0.96). Baseline BPND values for high (temporal lobe), median (hippocampus) and low specific binding (cerebellum) were 0.76 ± 0.07, 0.54 ± 0.08, and 0.39 ± 0.08, respectively. NS6740 significantly reduced the binding potential BPND in regions with high [18F]NS10743 binding (temporal lobe: -29 %, p = 0.01; midbrain: -35 %, p = 0.02) while the decrease in regions with low binding was not significant (cerebellum: -16 %, p = 0.2).
Conclusion: These data make [18F]NS10743 a reasonable candidate for further development of in vivo a7 nAChR imaging by PET. The challenge to improve the binding potential of [18F]NS10743, limited mainly by the low density of a7 nAChR expression in the brain and reflected by rather small regional differences in baseline uptake of [18F]NS10743, will be met by further modifications of the NS10743 core structure intended to increase the target affinity of the tracer compound.
the target affinity of the tracer compound.
Keywords: [18F]NS10743; a7 nAChR; PET
  • Lecture (Conference)
    NRM2010 (Neuroreceptor Mapping Congress), 22.-24.07.2010, Glasgow, Großbritannien
  • Abstract in refereed journal
    NeuroImage 52(2010)1
    DOI: 10.1016/j.neuroimage.2010.04.230

Publ.-Id: 14418 - Permalink


Extension of CFD codes - application to two-phase flow safety problems, phase 2
Bestion, D.; Anglart, H.; Mahaffy, J.; Lucas, D.; Song, C. H.; Scheuerer, M.; Zigh, G.; Andreani, M.; Kasahara, F.; Heitsch, M.; Komen, E.; Moretti, F.; Morii, T.; Mühlbauer, P.; Smith, B. L.; Watanabe, T.;
This document is an extension of the NEA/SEN/SIN/AMA(2006)2 report produced by the Writing Group 3 on the extension of CFD to two-phase flow safety problems, which was formed following the recommendations made at the “Exploratory Meeting of Experts to Define an Action Plan on the Application of Computational Fluid Dynamics (CFD) Codes to Nuclear Reactor Safety Problems” held in Aix-en-Provence, in May 2002. Extension of CFD codes to two-phase flow is a chance for safety investigations, by giving some access to smaller scale flow processes which were not seen by present tools. Using such tools as part of a safety demonstration may bring a better understanding of physical situations, more confidence in the results, and an estimation of safety margins. The increasing computer performance allows a more extensive use of 3D modelling of two-phase Thermalhydraulics with finer nodalization. However, models are not as mature as in single phase flows and a lot of work has still to be done on the physical modelling and numerical schemes in such two-phase CFD tools. The Writing Group listed and classified the NRS problems where extension of CFD to two-phase flow may bring real benefit and also classified different modelling approaches. First ideas were reported about the specification and analysis of needs in terms of validation and verification.
Keywords: CFD, two phase flow, nuclear safety research
  • Other report
    OECD: Report NEA/CSNI/R(2010)2, 2010
    137 Seiten

Publ.-Id: 14416 - Permalink


Studies on the patterning effect of copper deposits in magnetic gradient fields
Tschulik, K.; Sueptitz, R.; Koza, J.; Uhlemann, M.; Mutschke, G.; Weier, T.; Gebert, A.; Schultz, L.;
Electrochemical Cu deposition was performed from electrolytes containing 0.1 M to 1 M CuSO4 in a well-defined magnetic gradient field. Patterned deposits resulted in all cases showing a strong correlation to this gradient field. It was observed that with increasing Cu2+ concentration the structuring effect decreases in terms of differences in topography and morphology. An explanation of this effect is presented based on local convection induced by the magnetic field gradient force which is dependent on the concentration gradient established during the deposition. Superimposed effects of Lorentz force driven convection were observed for high Cu2+ concentrations, and their influence on the deposition process is discussed.
Keywords: magnetic gradient field, deposit patterns, Lorentz force

Publ.-Id: 14415 - Permalink


The EPOS system at the radiation source ELBE at For-schungszentrum Dresden-Rossendorf
Krause-Rehberg, R.; Butterling, M.; Jungmann, M.; Krille, A.; Anwand, W.; Brauer, G.; Rogov, A.; Noack, K.; Cowan, T.; Wagner, A.;
The heart of the radiation source ELBE at the Forschungszentrum Dresden-Rossendorf (FZD) is a 40-MeV LINAC with an average current of 1 mA. Due to its superconducting technology, the time structure is different from conventional LINACs. Electron bunches as short as 2 ps with a 26 MHz repetition rate can be used in continuous operation (cw) mode. This is an ideal host for an intense positron source. After organizing SLOPOS-9 in Rossendorf, it was decided to add EPOS (ELBE Positron Source) to the existing experiments at ELBE. EPOS consists of two LINAC-based setups, Gamma-induced Positron Spectroscopy (GiPS) and Monoenergetic Positron Spectroscopy (MePS). The GiPS setup, where positrons are produced inside the whole sample volume by pair production using a pulsed gamma beam, is unique so far. Here, bulky samples such as coarse powders, dispersions, but also liquids or whole devices of non-destructive testing can be investigated by all positron techniques important for materials science (lifetime spectroscopy, age-momentum correlation, and coincidence Doppler broadening spectroscopy). The same techniques will be applied at the MePS setup, where slow, mono-energetic positrons will be generated by moderation to study near-surface layers. This system is still under construction. The EPOS system will be completed by two conventional setups, a continuous slow positron beam and a positron lifetime/ Doppler spectrometer, both operated by 22Na sources.
Keywords: Positron spectroscopy, Positron Annihilation, Monoenergetic Positrons, Gamma-induced Positrons, LINAC-based
  • Contribution to proceedings
    Proceedings of the International School of Physics "E. Fermi" - Physics with many positrons, 07.-17.07.2009, Varenna, Italia
    The EPOS system at the radiation source ELBE at For-schungszentrum Dresden-Rossendorf, Amsterdam: IOS Press Amsterdam

Publ.-Id: 14413 - Permalink


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

Publ.-Id: 14412 - Permalink


The superconducting RF photoelectron source for the ELBE accelerator at Rossendorf
Teichert, J.;
Most of the proposed electron accelerator projects for future FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. The ideal candidate for it is the superconducting RF photogun (SRF gun) which can be easily operated in CW like a DC photogun and may reach the beam quality of a normal conducting RF photogun. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high-average power into the gun and finally the risk of beam excitation of higher order cavity modes. At the FZ Dresden-Rossendorf a SRF gun has been developed and installed at the ELBE superconducting linac. The SRF gun is designed for an average current of 1 mA and an maximum electron energy of 9 MeV. The 1.3 GHz cavity consists of three full cells with TESLA geometry, a specially designed half-cell where the photocathode is placed. The photocathode with a Cs2Te photoemission layer is normal-conducting and cooled by liquid nitrogen. In the talk an overview of the technical concept, the RF properties, the photo cathode development, and beam parameter measurements will be given.
  • Lecture (others)
    ANKA Seminar, 08.02.2010, Karlsruhe, Deutschland

Publ.-Id: 14411 - Permalink


A new hexanuclear rhenium cluster complex with six terminal acetate ligands: Synthesis, structure, and properties of K4[Re6S8(CH3COO)6]·8H2O
Brylev, K. A.; Mironov, Y. V.; Fedorov, V. E.; Kim, S.-J.; Pietzsch, H.-J.; Stephan, H.; Ito, A.; Kitamura, N.;
A room-temperature reaction between [Re6S8(OH)6]4− and acetic acid in an aqueous solution resulted in the substitution of all terminal hydroxo groups by acetate ligands, affording a new hexanuclear anionic rhenium cluster complex [Re6S8(CH3COO)6]4−. The complex was isolated as a potassium salt with the composition of K4[Re6S8(CH3COO)6]·8H2O (1) and characterized by X-ray single-crystal diffraction and elemental analyses, IR, 1H NMR, UV–Vis, and luminescence spectroscopies.
Keywords: Synthesis; Cluster compounds; Rhenium; Carboxylate ligands; Luminescence

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Publ.-Id: 14409 - Permalink


Traveling-wave Thomson scattering and optical undulators for high-yield EUV and X-ray sources
Debus, A. D.; Bussmann, M.; Siebold, M.; Jochmann, A.; Schramm, U.; Cowan, T. E.; Sauerbrey, R.;
We present a novel high-yield Thomson scattering geometry that takes advantage of compact electron bunches, as available in advanced, low-emittance linear accelerators or laser wakefield accelerators. In order to avoid the restrictions on the X-ray photon yield imposed by the Rayleigh limit, we use ultrashort, pulse-front tilted laser pulses in a side-scattering geometry. Such a traveling-wave setup allows an overlap of electron and laser beams, even after propagating over distances much longer than the Rayleigh length. Experimental designs are discussed and optimized for different scattering angles. Specifically, to minimize group delay dispersion at large scattering angles > 10° degrees, we propose the use of varied-line spacing (VLS) gratings for spatio-temporal laser pulse shaping. Compared to head-on (180° degrees) Thomson scattering, interaction lengths are in the centimeter to meter range and photon numbers for ultrashort X-ray pulses can increase by several orders of magnitudes.
Keywords: Thomson Scattering, Traveling-Wave Thomson Scattering, Xray , EUV, VLS gratings
  • Applied Physics B 100(2010)1, 61-76
    DOI: 10.1007/s00340-010-3990-1
  • Lecture (others)
    WIP Seminar, 21.05.2010, FZD, Deutschland

Publ.-Id: 14408 - Permalink


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

Publ.-Id: 14407 - Permalink


Advanced Materials Research - Biennial Scientific Report 2007-2008 / Volume 1
Bohnet, C.; Bartho, A.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-507 2010

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Publ.-Id: 14405 - Permalink


Cancer Research - Biennial Scientific Report 2007-2008 / Volume 2
Bohnet, C.; Bartho, A.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-508 2010

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Publ.-Id: 14404 - Permalink


Nuclear Safety Research - Biennial Scientific Report 2007-2008 / Volume 3
Bohnet, C.; Bartho, A.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-509 2010

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Publ.-Id: 14403 - Permalink


The sorption of uranium(VI) and neptunium(V) onto surfaces of selected metal oxides and alumosilicates studied by in situ vibrational spectroscopy
Müller, K.;
The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces.
Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral – water interfaces of oxides of titania, alumina, silica, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
From the infrared spectra, a significant change of the U(VI) speciation is derived upon lowering the U(VI) concentration from the milli- to the micromolar range, strongly suggesting the dominance of monomeric U(VI) hydrolysis products in the micromolar solutions. In contradiction to the predicted speciation, monomeric hydroxo species are already present at pH ≥ 2.5 and become dominant at pH 3. At higher pH levels (> 6), a complex speciation is evidenced including carbonate containing complexes.
For the first time, spectroscopic results of Np(VI) hydrolysis reactions are provided in the submillimolar concentration range and at pH values up to 5.3, and they are comparatively discussed with U(VI). For both actinides, the formation of similar species is suggested at pH ≤ 4, whereas at higher pH, the infrared spectra evidence structurally different species. At pH 5, the formation of a carbonate-containing dimeric complex, that is (NpO2)2CO3(OH)3^-, is strongly suggested, whereas carbonate complexation occurs only under more alkaline conditions in the U(VI) system.
The results from the experiments of the sorption processes clearly demonstrate the formation of stable U(VI) surface complexes at all investigated mineral phases. This includes several metal oxides, namely TiO2, Al2O3, and SiO2, serving as model systems for the elucidation of more complex mineral systems, and several alumosilicates, such as kaolinite, muscovite and biotite. From a multiplicity of in situ experiments, the impact of sorbent characteristics and variations in the aqueous U(VI) system on the sorption processes was considered.
A preferential formation of an inner-sphere complex is derived from the spectra of the TiO2 and SiO2 phases. In addition, since the in situ FT-IR experiments provide an online monitoring of the absorption changes of the sorption processes, the course of the formation of the U(VI) surface complexes can be observed spectroscopically. It is shown that after prolonged sorption time on TiO2, resulting in a highly covered surface, outer-sphere complexation predominates the sorption processes. The prevailing crystallographic modification, namely anatase and rutile, does not significantly contribute to the spectra, whereas surface specific parameters, e.g. surface area or porosity are important.
A significant different surface complexation is observed for Al2O3. The formation of innerspheric species is assumed at low U(VI) surface coverage which is fostered at low pH, high ionic strength and short contact times. At proceeded sorption the surface complexation changes. From the spectra, an outer-spheric coordination followed by surface precipitation or polymerization is deduced. Moreover, in contrast to TiO2, the appearance of ternary U(VI) carbonate complexes on the γ-Al2O3 surface is suggested.
The first results of the surface reactions on more complex, naturally occurring minerals (kaolinite, muscovite and biotite) show the formation of U(VI) inner-sphere sorption complexes. These findings are supported by the spectral information of the metal oxide surfaces.
In this work, first spectroscopic results from sorption of aqueous Np(V) on solid mineral phases are provided. It is shown that stable inner-sphere surface species of NpO2 ^+ are formed on TiO2. Outer-sphere complexation is found to play a minor role due to the pH independence of the sorption species throughout the pH range 4 – 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2, and ZnO indicate structurally similar bidentate surface complexes.
The multiplicity of IR spectroscopic experiments carried out within this study yields a profound collection of spectroscopic data which will be used as references for future investigations of more complex sorption systems in aqueous solution. Furthermore, from a methodological point of view, this study comprehensively extends the application of ATR FT-IR spectroscopic experiments to a wide range in the field of radioecology.
The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V/VI), in the environment. Consequently, more reliable predictions of actinides migration which are essential for the safety assessment of nuclear waste repositories can be performed.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-535 2010
    ISSN: 1437-322X

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Publ.-Id: 14401 - Permalink


Self-organization of Ge nanopattern under erosion with heavy Bi monomer and cluster ions
Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Facsko, S.; Pilz, W.;
The self-organisation of periodic pattern on (001)Ge by bombardment with different heavy ion species (Bi+, Bi++, Bi2+, Bi3+, Bi3++) obtained from a liquid metal ion source in a mass separating 30 kV FIB system was studied. Aspect ratios exceeding values reported so far for elemental semiconductors substantially were found after cluster irradiation. An excellent regular self-ordering of dot (40 nm in height, interdistance of ~50 nm) and ripple pattern was achieved. Despite of high ion fluence, Raman measurements prove a crystalline surface layer. This result deviates drastically from monomer irradiation, where similar to former ion irradiation of Ge a spongy amorphous surface layer is formed. For the transition from the usual behaviour to the unexpected pronounced pattern formation a threshold of the energy density deposited by the collision cascade was identified: If the deposited energy density exceeds the melting threshold, dot or ripple pattern appear. In our model we assume that the ion-impact-induced deposition of energy per volume (estimated by SRIM) must exceed the energy needed for melting. Thus, Bi segregation during re-solidification of the melted pool and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.
Keywords: Bi-cluster; germanium; FIB; nanopattern
  • Poster
    17th International Conference on Ion Beam Modification of Material - IBMM 2010, 22.-27.08.2010, Montreal, Canada
  • Nuclear Instruments and Methods in Physics Research B 272(2012), 198-201
    DOI: 10.1016/j.nimb.2011.01.064

Publ.-Id: 14400 - Permalink


FZD intern 57
Bartho, A.; Bohnet, C.;
Hauszeitung des FZD
  • Communication & Media Relations
    Hauszeitung des FZD 06.08.2010
    8 Seiten

Publ.-Id: 14399 - Permalink


The effect of rare-earth clustering on charge trapping and electroluminescence in rare-earth implanted metal-oxide-semiconductor light-emitting devices
Nazarov, A. N.; Tiagulskyi, S. I.; Tyagulskyy, I. P.; Lysenko, V. S.; Rebohle, L.; Lehmann, J.; Prucnal, S.; Voelskow, M.; Skorupa, W.;
The effect of rare-earth clustering in dielectric media on the electroluminescence (EL) intensity, the charge trapping and the EL quenching was investigated using the example of Tb and Eu-implanted SiO2 layers. It was shown that the increase in the REOX cluster size induced by an increase in the furnace annealing temperature resulted in an increase in the concentration of electron traps with capture cross sections from 2 x 10-15 to 2 x 10-18 cm2. This is probably associated with an increase in the concentration of oxygen deficiency centers as well as with strained and dangling bonds in the SiO2 matrix which leads to an enhanced scattering of hot electrons and a decrease in the excitation cross section of the main EL lines of RE3+ ions. For the main EL lines of Tb3+ and Eu3+ ions the relation of the EL quenching to negative and positive charge generation in the SiO2 was considered. It was demonstrated that in case of REOX nanoclusters with small sizes (up to 5 nm) the E!
L quenching process can mainly be explained by a defect shell model which suggests the formation of negatively charged defect shells around the nanoclusters leading to a Coulomb repulsion of hot electrons and a suppression of the RE3+ excitation. At high levels of the injected charge (more than 2 x 1020 e/cm2) a second stage of the EL quenching was observed which was contributed to a positive charge accumulation in the SiO2 at a distance beyond the tunneling distance from the SiO2-Si interface. In case of Eu-implanted SiO2 the quenching of the main EL line of Eu3+ is mostly correlated with positive charge trapping in the bulk of the dielectric. A model of EL quenching of the main Eu3+ line is proposed. (C) 2010 American Institute of Physics.
Keywords: Electroluminescence, rare earth, MOS capacity, charge trapping, ion implantation
  • Journal of Applied Physics 107(2010)12, 123112

Publ.-Id: 14397 - Permalink


New sensors for the velocity measurement in liquid metal processes
Timmel, K.; Eckert, S.; Wondrak, T.; Stefani, F.; Gerbeth, G.;
In many technological processes involving liquid metals or semiconductor melts the velocity fields cannot be measured due to the lack of commercial measuring techniques for opaque melts. We present two measuring techniques which have proven recently as providing reliable velocity measurements in liquid metals, at least in the temperature range up to about 700°C: the ultrasonic Doppler Velocimetry (UDV) and the contactless inductive flow tomography (CIFT). UDV is capable of delivering velocity profiles along the ultrasonic beam with a time-resolution of about 20 Hz. CIFT is based on the flow-induced modification of some externally applied magnetic field, which is measured by some array of magnetic field sensors outside of the melt. We present measurements with both techniques at the small-scale liquid metal model Mini-LIMMCAST of the continuous steel casting process. Both measuring methods give consistent results for the jets evolving from the nozzle outlets.
Keywords: continuous casting, liquid metal model, magnetic field, mould flow, Ultrasound Doppler Method, industrial tomography
  • Lecture (Conference)
    2011 TMS Annual Meeting & Exhibition, 27.02.-03.03.2011, San Diego, Californien, USA
  • Contribution to proceedings
    2011 TMS Annual Meeting & Exhibition, 27.02.-03.03.2011, San Diego, Californien, USA
    Sensors, Sampling, and Simulation for Process Control: Wiley, 978-1-118-03618-1, 43-50

Publ.-Id: 14396 - Permalink


Competition of two-ion and single-ion anisotropy in rare-earth systems: Large anisotropy example of Tb5Ge3
Doerr, M.; Haase, A.; Loewenhaupt, M.; Rotter, M.; Bartkowiak, M.; Daou, R.; Kampert, E.; Perenboom, J.; Tsutaoka, T.;
The standard model of rare-earth magnetism assumes that magnetic anisotropy is mainly caused by single-ion effects. The importance of two-ion anisotropy is still disputed. For a number of materials this two-ion anisotropy is in the same order of magnitude and strongly influences the magnetic properties. Single crystalline Tb5Ge3 has a high moment and low symmetry and, because of this, a large anisotropy is expected. In the present study the influence of the two-ion interaction was investigated. Magnetization and magnetostriction were measured in high magnetic fields up to 60 T. The magnetic phase diagram constructed for the main crystallographic directions shows antiferromagnetism in zero field and a number of magnetic phases at higher fields. The exchange interaction was evaluated based on a model calculation of these phase diagrams. We conclude that a huge anisotropy in the two-ion interaction is present, which overwhelms the single-ion effects.
  • Physical Review B 82(2010), 024422

Publ.-Id: 14395 - Permalink


Manganese implanted Germanium: from clustering to carrier-mediated ferromagnetism
Zhou, S.; Bürger, D.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.;
Mn doped Ge (Ge:Mn) is a promising candidate for a ferromagnetic semiconductor compatible with silicon technology, since Mn acts as a magnetic ion as well as a double acceptor. Whereas ferromagnetism above room temperature has been evidenced by magnetization measurements, the transport behavior is entirely different from the GaAs:Mn system [1], the prototype of a ferromagnetic semiconductor.

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

[1] S. Zhou et al., APL, 95, 172103 (2009).
[2] S. Zhou et al., APL, 95, 192505 (2009).
[3] S. Zhou et al., PRB 81, 165204 (2010).
[4] S. Zhou et al., APL, in press (2010).
  • Lecture (Conference)
    The 17th International Conference on Ion Beam Modification of Materials, 22.-27.08.2010, Montreal, Canada

Publ.-Id: 14392 - Permalink


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

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

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

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

References:
[1] Y. D. Park et al., Science 295, 651 (2002).
[2] F. Tsui et al., Phys. Rev. Lett. 91, 177203 (2003).
[3] M. Jamet et al., Nature Mater. 5, 653 (2006).
[4] C. Zeng, et al., Phys. Rev. Lett. 100, 066101 (2008).
[5] O. Riss, et al., Phys. Rev. B 79, 241202(R) (2009).
[6] S. Zhou et al., Appl. Phys. Lett. 95, 172103 (2009).
[7] S. Zhou et al., Appl. Phys. Lett. 95, 192505 (2009).
[8] S. Zhou et al., Phys. Rev. B (2010), submitted.
  • Lecture (Conference)
    International Conference on Physics and Applications of Spin Related Phenomena in Semiconductors (PASPS-VI), 01.-04.08.2010, Tokyo, Japan
  • Invited lecture (Conferences)
    Invited talk at the Institute of Physics, Chinese Academy of Sciences, 13.04.2010, Beijing, China

Publ.-Id: 14391 - Permalink


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

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

[1] Y. D. Park et al., Science 295, 651 (2002); M. Jamet et al., Nature Mater. 5, 653 (2006).
[2] S. Zhou et al., Appl. Phys. Lett. 95, 172103 (2009); Appl. Phys. Lett. 95, 192505 (2009).
[3] S. Zhou et al., Phys. Rev. B (2010), submitted.
  • Lecture (Conference)
    30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul,, korea

Publ.-Id: 14390 - Permalink


Rate theory and SANS study of phase separation in a neutron irradiated Fe-12.5at%Cr model alloy
Gokhman, A. R.; Bergner, F.; Küchler, R.;
Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr-precipitates in neutron irradiated Fe-12.5at%Cr alloy at the irradiation doses up to 12 dpa, fluence about 140 ndpa/s and T=300 C. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data [1,2] on the defect structure of this material irradiated at the doses of 0.6 and 1.5 dpa are used to calibrate the model. It was found the saturation behaviour of free vacancy and free SIA concentrations, number density of SIAC and Cr-precipitates volume fraction for neutron expose great than 0.006 dpa; strong peak of SIAC with the average diameter about 0.5 nm and presence of VC with radius less 0.5 nm.
Keywords: Cluster dynamics, neutron irradiation, chromium iron alloys, defects
  • Invited lecture (Conferences)
    XIV.th Research Workshop Nucleation Theory and Applications, 10.-17.04.2010, Dubna, Russia

Publ.-Id: 14389 - Permalink


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

Publ.-Id: 14388 - Permalink


Ultrashort pulse laser accelerated proton beams for first radiobiological applications
Schramm, U.; Zeil, K.; Richter, C.; Beyreuther, E.; Bussmann, M.; Cowan, T. E.; Enghardt, W.; Karsch, L.; Kluge, T.; Kraft, S.; Laschinsky, L.; Metzkes, J.; Naumburger, D.; Pawelke, J.; Sauerbrey, R.;
We report on the generation of proton pulses with maximum energies exceeding 15MeV bymeans of the irradiation of few micron thick metal foils by ultrashort (30 fs) laser pulses at a power level of 100 TW. In contrast to the well known situation for longer laser pulses, here, a near linear scaling of the maximum proton energy with laser power can be found. Aiming for radiobiological applications the long and short term stability of the laser plasma accelerator as well as a compact energy selection and dosimetry system is presented. The first irradiation of in vitro tumour cells showing dose dependent biological damage is demonstrated paving the way for systematic radiobiological studies.
Keywords: laser proton acceleration, first cell irradiation
  • Contribution to proceedings
    14th Workshop on Advanced Accelerator Concepts, 13.-19.06.2010, Annapolis, MD, USA, USA
    AIP Conference Proceedings, Advanced Esselerator Concepts, 1299: AIP, 731

Publ.-Id: 14382 - Permalink


Physikalische Modellierung des Stranggussprozesses mit niedrig schmelzenden Legierungen
Timmel, K.; Galindo, V.; Miao, X.; Eckert, S.; Gerbeth, G.;
Die Strömung in der Metallschmelze hat einen wesentlichen Einfluss auf die Produktqualität beim Stranggießen. Probleme entstehen beispielsweise durch Einschlüsse von Oxiden, intermetallischen Verbindungen oder Gasblasen, die durch eine unkontrollierte Strömung in die Erstarrungszone gelangen. Die Optimierung dieser Strömung basierte bisher vor allem auf numerischen Simulationen und Modellexperimenten mit Wasser. Obwohl die Strömungsuntersuchungen an diesen Wassermodellen signifikante Erkenntnisgewinne über die Strömung und die optimale Auslegung z.B. des Tauchrohrs oder der Eintauchtiefe des Tauchrohrs gebracht haben, stoßen diese Modelle für eine Reihe von Fragestellungen an ihre physikalischen Grenzen, da Flüssigmetalle z.B. sehr hohe Oberflächenspannungen und sehr kleine Prandtl-Zahl besitzen, und Wasser offensichtlich für Untersuchungen des Einflusses von Magnetfeldern völlig ungeeignet ist.
In den vergangenen Jahren wurden am Forschungszentrum Dresden-Rossendorf experimentelle Versuchsanlagen mit niedrig schmelzenden Legierungen für die physikalische Modellierung des Stranggussprozesses aufgebaut. Ziel ist die systematische Untersuchung der Flüssigmetallströmungen und Transportprozesse in Verteiler, Tauchrohr und Kokille. Dabei steht insbesondere die Wirkung elektromagnetischer Felder, wie sie in Form von elektromagnetischen Bremsen oder Rührern bereits im industriellen Einsatz sind, im Mittelpunkt. Außerdem bieten die Versuchsanlagen gute Bedingungen für die Erprobung neuer Messtechniken und Anlagenkomponenten. Die Versuchsanlage „CONCAST-LMM“ (Continuous Casting Liquid Metal Model) ist 2009 fertig gestellt worden und arbeitet mit einer Sn60Bi40-Legierung als Modellfluid im Temperaturbereich von 200°C bis 400°C. Ein kleineres Modell mit der eutektischen GaInSn-Legierung wird bei Raumtemperatur betrieben. Die Strömungseigenschaften werden mit Hilfe lokaler Sonden sowie modernen Ultraschall und elektromagnetischen Methoden vermessen.
Im Rahmen dieses Beitrages werden Strömungsmessungen in einer einphasigen Flüssigmetallströmung in der Kokille unter Einwirkung eines statischen Magnetfeldes vorgestellt und mit entsprechenden numerischen Simulationen verglichen. Es zeigt sich, dass das Magnetfeld den aus dem Tauchrohr in die Kokille austretenden Jet ablenkt und lokale Rezirkulationsgebiete verstärkt. Die bremsende Wirkung des Magnetfeldes stellt sich als äußerst komplex dar. Eine gleichmäßige Reduktion der Strömungsgeschwindigkeit im gesamten Volumen wird nicht beobachtet.
Keywords: continuous casting, liquid metal model, magnetic field, mould flow, Ultrasound Doppler Method
  • Lecture (Conference)
    Symposium Stranggießen, 15.-17.11.2010, Neu-Ulm, Deutschland
  • Contribution to proceedings
    Symposium Stranggießen, 15.-17.11.2010, Neu-Ulm, Deutschland

Publ.-Id: 14381 - Permalink


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

Publ.-Id: 14380 - Permalink


Quantitative KPFM Measurements on Silicon Nanowire Structures
Baumgart, C.;
This workshop focus on the electrical characterization of vertical and horizontal Si nanowires.
  • Lecture (others)
    Workshop FZD/FZJ: Silicon Nanowire Structures, 29.04.2010, Dresden, Germany

Publ.-Id: 14379 - Permalink


Quantitative Kelvin probe force microscopy imaging on locally doped Si
Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.;
Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface
potential. Since KPFM was developed in 1991 the measured KPFM signal was attributed to the contact potential difference (CPD) between conductive probe and sample. We show that the CPD is not suitable to describe the measured Kelvin bias in semiconductors quantitatively and introduce a unique KPFM model [1] which successfully correlates the measured Kelvin bias with the difference between Fermi energy and respective band edge. Quantitative dopant profiling is demonstrated on cross-sectionally prepared Si epilayer structures and on a Si dynamic random access memory cell.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80 (2009) 085305.
  • Poster
    DPG Frühjahrstagung, 21.-26.03.2010, Regensburg, Germany

Publ.-Id: 14378 - Permalink


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

Publ.-Id: 14377 - Permalink


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


[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).
  • Lecture (others)
    2. Wissenschaftliches Seminar des Dresdner Fraunhofer-Clusters Nanoanalytik, 05.08.2010, Dresden, Germany

Publ.-Id: 14375 - Permalink


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

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm,
and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
  • Lecture (Conference)
    Nano 2010, 13.-17.09.2010, Rome, Italy

Publ.-Id: 14374 - Permalink


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


[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).
  • Lecture (Conference)
    Nanofair 2010, 06.-07.07.2010, Dresden, Germany

Publ.-Id: 14373 - Permalink


Revealing the role of anchoring groups in the electrical conduction through single-molecule junctions
Zotti, L. A.; Kirchner, T.; Cuevas, J.-C.; Pauly, F.; Huhn, T.; Scheer, E.; Erbe, A.;
A combined experimental and theoretical study is presented revealing the influence of metal-molecule coupling on electronic transport through single-molecule junctions. Transport experiments through tolane molecules attached to gold electrodes via thiol, nitro, and cyano anchoring groups are performed. By fitting the experimental current-voltage characteristics to a single-level tunneling model, we extract both the position of the molecular orbital closest to the Fermi energy and the strength of the metal-molecule coupling. The values found for these parameters are rationalized with the help of density-functional-theory-based transport calculations. In particular, these calculations show that the anchoring groups determine the junction conductance by controlling not only the strength of the coupling to the metal but also the position of the relevant molecular energy levels.
Keywords: anchoring groups, break junctions, density functional theory, molecular electronics, molecular wires

Publ.-Id: 14372 - Permalink


Density reduction and diffusion in driven two-dimensional colloidal systems through microchannels
Henseler, P.; Erbe, A.; Köppl, M.; Leiderer, P.;
The behavior of particles driven through a narrow constriction is investigated in experiment and simulation. The system of particles adapts to the confining potentials and the interaction energies by a self-consistent arrangement of the particles. It results in the formation of layers throughout the channel and of a density gradient along the channel. The particles accommodate to the density gradient by reducing the number of layers one by one when it is energetically favorable. The position of the layer reduction zone fluctuates with time while the particles continuously pass this zone. The flow behavior of the particles is studied in detail. The velocities of the particles and their diffusion behavior reflect the influence of the self-organized order of the system.
Keywords: Colloids, Nonlinear dynamics and chaos, Computer simulation of molecular and particle dynamics, Studies of specific magnetic materials

Publ.-Id: 14370 - Permalink


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

Publ.-Id: 14369 - Permalink


Leitlinie für SPECT-Untersuchungen mit dem 123I-markierten Dopamintransporter-Liganden FP-CIT (DaTSCANTM)
Tatsch, K.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Grünwald, F.; Kuwert, T.; Krause, B. J.; Sabri, O.;
Es ist kein Abstract vorhanden.
Keywords: SPECT; 123I; Dopamintransporter Ligand; FP-CIT; DaTSCAN
  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners, Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 100-107

Publ.-Id: 14368 - Permalink


Leitlinie für SPECT-Untersuchungen mit dem 123I-markierten Dopamin-D2-Rezeptor Liganden IBZM
Tatsch, K.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Grünwald, F.; Kuwert, T.; Krause, B. J.; Sabri, O.;
Es ist kein Abstract vorhanden.
Keywords: SPECT; 123I; Dopamin-D2-Rezeptor; Ligand; IBZM
  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners; Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 108-115

Publ.-Id: 14367 - Permalink


Leitlinie für die Hirnperfusions-SPECT mit 99mTc-Radiopharmaka
Menzel, C.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Krause, B. J.; Kuwert, T.; Sabri, O.; Schreckenberger, M.; Tatsch, K.; Grünwald, F.;
Es ist kein Abstract vorhanden.
Keywords: Hirnperfusions-SPECT; 99mTc
  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners; Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 87-91

Publ.-Id: 14366 - Permalink


Dose-dependent biological damage of tumour cells by laser-accelerated proton beams - online diagnostics
Schramm, U.;
Talk on the status of laser proton acceleration and online dosimetry with respect to radiobiological applications.
  • Invited lecture (Conferences)
    First Workshop on Instrumentation for Diagnostics and Control of Laser Accelerated Proton Beams, 09.-10.08.2010, Abingdon / Oxford, UK

Publ.-Id: 14365 - Permalink


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

Publ.-Id: 14364 - Permalink


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

Publ.-Id: 14363 - Permalink


On the prediction of boron dilution using the CMFD code TRANSAT: the ROCOM test case
Labois, M.; Panyasantisuk, J.; Lakehal, D.; Höhne, T.; Kliem, S.;
This contribution aims at introducing a new multiscale, multicomponent CFD/CMFD approach for the simulation of thermal-hydraulics flows evolving in complex component-scale configurations. In this novel approach, the flow system could involve one or two fluids, convective and conductive heat transfer in solids, and phase-change heat transfer. This is made possible thanks to the Immersed Surfaces Technology (IST), a methods inspired from Interface Tracking techniques for two-phase flow, whereby solid bodies contained in the system are defined using a solid level set function to describe their surfaces, transcending conventional unstructured and body-fitted grids (BFC). In a typical two-phase flow, material properties of the fluids and the solid are segregated based on the gas-liquid and solid Level-Set functions. The technique helps solve conjugate heat transfer problems without resorting to explicit jump conditions. Selected validation test-cases are presented here. The main application includes steady and transient solutions of the boron dilution in the ROCOM test case.
Keywords: CFD, ASCOMP, FZD, ROCOM, TRANSAT
  • Contribution to proceedings
    CFD4NRS-3, 14.-16.09.2010, Washington, USA
    CD-ROM
  • Lecture (Conference)
    CFD4NRS-3, 14.-16.09.2010, Washington, USA

Publ.-Id: 14362 - Permalink


Controlling blue-violet electroluminescence of Ge-rich Er-doped SiO2 layers by millisecond annealing using flash lamps
Kanjilal, A.; Rebohle, L.; Voelskow, M.; Helm, M.; Skorupa, W.;
Systematic evolution of the 400 nm electroluminescence (EL) with increasing flash lamp annealing (FLA) temperature from 800 to 1100 °C in an Er-doped Ge-rich metal-oxide semiconductor structure is presented. No significant change in the 1535 nm Er EL is observed with increasing FLA temperature. Enhancement of the 400 nm EL decay time with rising FLA temperature is found to be associated with recrystallization of the damaged Ge clusters in the absence of Ge outdiffusion. The 400 nm EL quenching with continuous charge injection process is also discussed within the device operation time.
Keywords: electroluminescence, flash lamp annealing, Er-doped Ge-rich metal-oxide semiconductor

Publ.-Id: 14361 - Permalink


Ultrasound investigations of some frustrated and low-dimensional magnets
Zherlitsyn, S.; Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Zvyagin, A. A.;
The investigation of the correlations between magnetic and lattice degrees of freedom provides a better understanding of the underlying physics of frustrated and low-dimensional spin systems. Ultrasound experiments are proven to be a powerful tool to probe the spin-lattice interactions and lattice instabilities. Here, we will present some recent outcome of our ultrasound studies performed at high magnetic fields. We report results of our investigations of the frustrated spin system CdCr2O4 [1]. This material shows a wide magnetization plateau, from 28 to 58 T, at one half of the full moment of S = 3/2 Cr3+. We further present results for the low-dimensional quantum antiferromagnets Cs2CuCl4 [2] and NiCl2-4SC(NH2)2 [3]. The spin-strain coupling is discussed in frame of the exchange-striction mechanism.
  • Poster
    Strongly Correlated Electron Systems 2010 (SCES 2010), 27.06.-02.07.2010, Santa Fe, USA

Publ.-Id: 14360 - Permalink


Electronic band structure of superconducting PrPt4Ge12
Wosnitza, J.; Bergk, B.; Ignatchik, O.; Polyakov, A.; Gumeniuk, R.; Leithe-Jasper, A.; Schnelle, W.; Nicklas, M.; Rosner, H.; Grin, Y.;
Recently, the new skutterudite superconductor PrPt4Ge12 with the comparably high transition temperature of Tc = 7.9 K was discovered [1]. First experiments gave evidence for strong coupling and hint at point-like nodes of the order parameter [2]. The Sommerfeld coefficient is rather low and indicates that PrPt4Ge12 is not a heavy-fermion superconductor. Here, we present results of a de Haas-van Alphen (dHvA) study performed on a high-quality single crystal. Several dHvA frequencies could be resolved over a broad angular range. The small band-resolved effective masses (less than half the free-electron mass) confirm the non-heavy-fermion character of the electron system. To get insight into the nature of the mass renormalization, the experimental data are compared with state-of-the-art band-structure calculations
  • Poster
    Strongly Correlated Electron Systems 2010 (SCES2010), 27.06.-02.07.2010, Santa Fe, USA

Publ.-Id: 14359 - Permalink


High-field ultrasound investigations of frustrated and low-dimensional magnets
Zherlitsyn, S.;
es hat kein Abstract vorgelegen.
  • Invited lecture (Conferences)
    International Workshop "Perspectives in Highly Frustrated Magnetism", 19.-23.04.2010, Dresden, Deutschland

Publ.-Id: 14358 - Permalink


Influence of vanadium concentration on the microstructure and magnetic properties of V-doped ZnO thin films
Naydenova, T.; Atanasov, P.; Koleva, M.; Nedialkov, N.; Perriere, J.; Defourneau, D.; Fukuoka, H.; Obara, M.; Baumgart, C.; Zhou, S.; Schmidt, H.;
Vanadium doped ZnO thin films (Zn1−xVxO, where x=0.05 or x=0.13) were grown on c-cut sapphire substrates using pulsed laser deposition technique. Their structure and magnetic properties were examined in relation to the doping concentration. All deposited films were highly oriented along the c-axis and exhibited ferromagnetic behavior with a Curie temperature up to 300 K. The crystal structure was found to be better for layers with lower vanadium concentration. The films had a porous fine-grained microstructure and a column-like character as the V concentration was reduced. A weak dependence of magnetization on temperature was observed. The saturation magnetization was found to be strongly dependent on the crystal structure, grain size and V-ion concentration.
Keywords: ZnO, Vanadium doping, Thin films, PLD, DMS
  • Thin Solid Films 518(2010), 5505-5508

Publ.-Id: 14357 - Permalink


Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6
Zvyagin, S. A.;
We report on high-field magnetization, specific-heat and electron spin resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes below TN \approx 4.38 K is described in the frame of the mean-field theory. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the inter/intra-plane exchange-interaction ratio, J'/J = 1/16. It is argued that despite of onset of 3D long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and nonmonotonic field dependence of the Neel temperature) are strongly affected by two-dimensional spin correlations.
  • Poster
    International Workshop on "Perspectives in Highly Frustrated Magnetism", 19.-23.04.2010, Dresden, Deutschland

Publ.-Id: 14356 - Permalink


Room temperature ferromagnetism in Ni-doped HfO2 thin films
Sharma, M.; Kanjilal, A.; Voelskow, M.; Kanjilal, D.; Chatterjee, R.;
In this paper detailed studies on modification of structural and magnetic properties of Ni-doped hafnium oxide (HfO2) thin films are reported. We used 200 keV Ni beam for doping of Ni. For homogeneous dispersion and activation of doped Ni ions, 120 MeV Ni swift heavy ions (SHI) irradiation was used. This unique combination of Ni doping by ion beam and dispersing and activating by Ni SHI irradiation of HfO2 films is reported for the first time. The origin of ferromagnetism in the Ni-doped HfO2 thin films is investigated. We demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization versus temperature data. Rutherford backscattering data are used to establish that Ni ions are implanted in the HfO2 matrix at the predicted location. Dispersion of implanted Ni and lattice defects such as oxygen vacancies are attributed to be the main source of ferromagnetism.
Keywords: magnetic clusters, Ni-doped hafnium oxide (HfO2), swift heavy ion irradiation

Downloads:

Publ.-Id: 14355 - Permalink


Antiferromagnetic resonance in the multiferroic frustrate YMnO3
Kamenskyi, D.;
Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Using THz-range FEL- and BWO-based electron spin resonance (ESR) spectroscopy techniques, the frequency-field dependence of magnetic excitations in the hexagonal multiferroic YMnO3 in the antiferromagnetically (AFM) ordered phase has been studied. A slope of the frequency-field dependences of AFM resonance modes, ~ 0.5 cm−1/T, is explaned in terms of the triangular AFM model. A gap in the excitation spectrum, ~ 42 cm−1, was observed directly. A fine structure of AFM resonance absorption observed by as is a clear signature of a finite interaction between the neighboring Mn3+ layers. The interplane exchange interactions constants, J1 = -510 mK and J2 = -350 mK, have been estimated.
  • Poster
    International Workshop on "Perspectives in Highly Frustrated Magnetism" (PHFM10), 19.-23.04.2010, Dresden, Deutschland

Publ.-Id: 14354 - Permalink


New experimental study of low-energy (p,gamma) resonances in magnesium isotopes
Limata, B.; Strieder, F.; Formicola, A.; Imbriani, G.; Junker, M.; Becker, H. W.; Bemmerer, D.; Best, A.; Bonetti, R.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Dileva, A.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Lemut, A.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Salvo, C.; Somorjai, E.; Straniero, O.; Terrasi, F.; Trautvetter, H.-P.;
Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H shell burning. In particular, the strengths of low-energy resonances with E < 200 keV in 25Mg(p,gamma)26Al determine the production of 26Al and a precise knowledge of these nuclear data is highly desirable. Absolute measurements at such low-energies are often very difficult and hampered by gamma-ray background as well as changing target stoichiometry during the measurements. The latter problem can be partly avoided using higher energy resonances of the same reaction as a normalization reference. Hence the parameters of suitable resonances have to be studied with adequate precision. In the present work we report on new measurements of the resonance strengths omega_gamma of the E = 214, 304, and 326 keV resonances in the reactions 24Mg(p,gamma)25Al, 25Mg(p,gamma)26Al, and 26Mg(p,gamma)27Al, respectively. These studies were performed at the LUNA facility in the Gran Sasso underground laboratory using multiple experimental techniques and provided results with a higher accuracy than previously achieved.

Publ.-Id: 14353 - Permalink


Low-Temperature Elastic Properties of Non-Kramers Doublet Compound PrMg3
Araki, K.; Mitsumoto, K.; Akatsu, M.; Nemoto, Y.; Suzuki, H. S.; Tanida, H.; Takagi, S.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Goto, T.;
We have investigated low-temperature elastic properties of PrMg3 with a non-Kramers Gamma3 doublet ground state using ultrasonic measurements. Although the Gamma3 doublet possesses electric quadrupoles Ou and Ov with Gamma3-symmetry and magnetic octupole Txyz with Gamma2, PrMg3 reveals no sign of symmetry breaking long-range ordering down to 20 mK. [1] The elastic constant of (C11-C12)/2 in PrMg3 exhibits remarkable softening below 8 K, which is well described in terms of a Curie-type quadrupole susceptibility for the Gamma3 doublet. An appreciable upturn in (C11-C12)/2 below 800 mK in PrMg3 may indicate an transition into an exotic ground state due to the quadrupole Kondo state being screened by conduction electrons. Frequency dependence in (C11-C12)/2 and its attenuation coefficients at low temperature in PrMg3 suggests quadrupole fluctuations possessing a characteristic relaxation time tau = tau0exp(E/kT) with tau0 = 6x10-11 sec and an activation energy E = 410 mK. The low-temperature behavior in (C11-C12)/2 of PrMg3 under magnetic fields is also presented.
  • Poster
    Strongly Correlated Electron Systems 2010 (SCES 2010), 27.06.-02.07.2010, Santa Fe, USA

Publ.-Id: 14352 - Permalink


Die Jagd nach dem Feldrekord: Forschung in hohen Magnetfeldern
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Lecture (others)
    Eröffnungsvortrag zum Tag des offenen Labors des Forschungszentrum Dresden-Rossendorf, 04.07.2010, Dresden, Deutschland

Publ.-Id: 14351 - Permalink


Research at the Dresden High Magnetic Field Laboratory
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Seminar at the National High Magnetic Field Laboratory, Los Alamos, 25.06.2010, Los Alamos, USA
  • Invited lecture (Conferences)
    Seminar at the Institute for Solid State Physics, University of Tokyo, 17.09.2010, Kashiwa, Japan

Publ.-Id: 14350 - Permalink


Das Hochfeld-Magnetlabor Dresden – Forschung und Infrastruktur
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Klausurtagung des SFB 609 „Elektromagnetische Strömungsbeeinflussung in Metallurgie, Kristallzüchtung und Elektrochemie", 11.-12.03.2010, Schmochtiz, Deutschland

Publ.-Id: 14349 - Permalink


Evidence for a novel superconducting state in layered organic superconductors
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    International Conference of the SFB/TR 49 „Novel states in correlated matter - from model systems to real materials", 02.-04.03.2010, Berlin, Deutschland

Publ.-Id: 14348 - Permalink


Die Jagd nach dem Feldrekord – Forschung in hohen Magnetfeldern
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Gemeinsames Kolloquium des KIT und der Universität Heidelberg, 29.01.2010, Karlsruhe, Deutschland

Publ.-Id: 14347 - Permalink


High-frequency and high-field ESR in quantum spin systems
Zvyagin, S. A.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Terahertz spectroscopy and its high-field applications & EuroMagNET II user meeting, 14.-16.06.2010, Dresden, Deutschland

Publ.-Id: 14346 - Permalink


Optical conductivity of Ba(Fe0.9Co0.1)2As2 and LuNi2B2C in the terahertz range
Pronin, A. V.; Fischer, T.; Wosnitza, J.; Schachinger, E.; Iida, K.; Kurth, F.; Haindl, S.; Niemeier, T.; Schultz, L.; Holzapfel, B.;
es hat kein Abstract vorgelegen.
  • Poster
    Low-Energy Electrodynamics in Solids 2010 (LEES 2010), 05.-10.07.2010, Les Diablerets, Schweiz

Publ.-Id: 14345 - Permalink


Nuclear data needs for underground accelerators
Bemmerer, D.;
The nuclear data needs for underground accelerators will be reviewed, with a focus on the present and future LUNA program.
  • Lecture (Conference)
    Data needs for nuclear astrophysics, 25.-27.07.2010, Darmstadt, Deutschland

Publ.-Id: 14344 - Permalink


The 14N(p,gamma)15O cross section at 0.5-1.5 MeV
Bemmerer, D.;
The 14N(p,g)15O reaction is the bottleneck of the carbon-nitrogen-oxygen (CNO) cycle, thus determining its speed. The precise knowledge of its cross section is necessary to address the recently discovered discrepancy for elemental abundances in the standard solar model, the so-called solar abundance problem. Several experimental efforts are underway to improve the precision, among them lifetime measurements of excited states in the 15O compound nucleus. The seminar talk will report on a different approach, namely a direct cross section measurement at comparatively high energy, 0.5-1.5 MeV, recently performed at the Dresden Tandetron.
  • Invited lecture (Conferences)
    Seminar INFN Laboratori Nazionali di Legnaro, Italy, 30.07.2010, Legnaro, Italien

Publ.-Id: 14343 - Permalink


Dissipative Taylor-Couette flows under the influence of helical magnetic fields
Rüdiger, G.; Gellert, M.; Schultz, M.; Hollerbach, R.;
The linear stability of magnetohydrodynamic Taylor-Couette flows in axially unbounded cylinders is considered for magnetic Prandtl number unity. Magnetic background fields varying from purely axial to purely azimuthal are imposed, with a general helical field parametrized by beta=B-phi/B-z. We map out the transition from the standard magnetorotational instability (MRI) for beta=0 to the nonaxisymmetric azimuthal magnetorotational instability for beta ->infinity. For finite beta, positive and negative wave numbers m, corresponding to right and left spirals, are no longer degenerate. For the nonaxisymmetric modes, the most unstable mode spirals in the opposite direction to the background field. The standard (beta=0) MRI is axisymmetric for weak fields (including the instability with the lowest Reynolds number) but is nonaxisymmetric for stronger fields. If the azimuthal field is due in part to an axial current flowing through the fluid itself (and not just along the central ax! is), then it is also unstable to the nonaxisymmetric Tayler instability which is most effective without rotation. For purely toroidal fields the solutions for m=+/- 1 are identical so that in this case no preferred helicity results. For large beta the wave number m=-1 is preferred, whereas for beta less than or similar to 1 the mode with m=-2 is most unstable. The most unstable modes always spiral in the same direction as the background field. For background fields with positive and not too large beta the kinetic helicity of the fluctuations proves to be negative for all the magnetic instabilities considered.
  • Physical Review E 82(2010), 016319

Publ.-Id: 14342 - Permalink


Laser-Based Particle Acceleration for Future Ion Therapy: Current Status of the Joint Project onCOOPtics with Special Focus On Beam Delivery and Dosimetry
Richter, C.; Beyreuther, E.; Dammene, Y.; Enghardt, W.; Kaluza, M.; Karsch, L.; Laschinsky, L.; Lessmann, E.; Naumburger, D.; Nicolai, M.; Sauerbrey, R.; Schlenvoigt, H. P.; Schürer, M.; Sobiella, M.; Weber, A.; Pawelke, J.; Baumann, M.;
Purpose: Before the novel technology of laser-based particle acceleration can be used for clinical applications, several requirements have to be fulfilled. These are the supply of stable and reliable particle beams with reproducible properties, sufficient particle intensity and useable energy spectra. Additionally, a precise dose delivery in an appropriate time and the exposure of a desired irradiation field are needed. Beside these demands, consequences on dosimetry as well as on the radiobiological effect have to be investigated for ultra-short pulsed laser-accelerated particle beams. Method andMaterials: The joint project onCOOPtics, an interdisciplinary and multicenter institution focusing on the development of a laser particle accelerator for radiation oncology, is introduced. The worldwide first systematic in vitro irradiations with laser-accelerated electrons performed with the JeTi laser system will be presented focusing on the experimental setup, practical experiences and on dosimetric and radiobiological results. In a next step, cell irradiation experiments with laser-accelerated protons have been prepared. Therefore, a dedicated dosimetric system was developed. It is integrated into a device that can be installed at different laser and conventional accelerators and serves also as cell or animal irradiation device. Results: A laser accelerator was successfully optimized for systematic radiobiological experiments performed over 3 months. No significant differences between laser-accelerated and conventional 6 MeV electron beams were found. An integrated dosimetry and cell irradiation device for systematic in vitro and in vivo experiments with laser-accelerated protons was developed, characterized, calibrated and successfully tested with both continuous and pulsed proton beams. Cell irradiations with protons have been started. Conclusion: Laser accelerators can be used for radiobiological experiments, meeting all necessary requirements like homogeneity, stability and precise dose delivery. Nevertheless, before fulfilling the much higher requirements for clinical application, several improvements concerning i.e. proton energy, spectral shaping and patient safety are necessary. Supported by BMBF (03ZIK445).
  • Abstract in refereed journal
    Medical Physics 37(2010)6, 3292-3292
    DOI: 10.1118/1.3468857
  • Poster
    AAPM 2010, 18.-22.07.2010, Philadelphia, USA

Publ.-Id: 14340 - Permalink


Tilting of self-organized layered arrays of encapsulated metal nanoparticles in C:Ni nanocomposite films by means of hyperthermal ion deposition
Abrasonis, G.; Oates, T. W. H.; Kovacs, G. J.; Grenzer, J.; Persson, P. O. A.; Heinig, K. H.; Martinavicius, A.; Jeutter, N.; Baehtz, C.; Grötzschel, R.; Tucker, M.; Rosen, J.; Bilek, M. M. M.; Möller, W.;
Self-organization at the nanoscale is a key issue in modern material science as it promises a potential route to commercially scalable production of functional nanomaterials. Here we present the growth-structure study of self-organized layered arrays of carbon encapsulated Ni nanoparticles grown by means of pulsed filtered cathodic vacuum arc deposition. Influence of the oblique ion incidence and Ni content on the film morphology is investigated. The film morphology has been determined by transmission electron microscopy (TEM) and grazing incidence small angle x-ray scattering (GISAXS) while C/Ni ratio was determined by means of nuclear reaction analysis. The C:Ni films with the Ni content in the range of ~6-50 at.% are considered. The results show that for the perpendicular incoming depositing ion incidence the C:Ni film structure consists of alternating self-organized nickel carbide and carbon layer oriented parallel to the film surface. However, for the oblique ion incidence the layered structure tilts in relation to the surface. The tilting angle and periodicity strongly depends on the deposition angle as well as on the Ni content. Combined TEM and GISAXS analysis shows that the film cross-sections can be described by two density modulation waves advancing with the growing film surface – one towards the incoming ions, another one with the weaker amplitude moving in roughly perpendicular direction. The results are discussed on the basis of the interplay between thermodynamically driven phase separation and energetic ion induced ballistic effects. Such structures show significant anisotropy which can be considered for tribological, optical, magnetic or magnetotransport applications.
  • Lecture (Conference)
    ICMCTF 2010 38th International Conference on Metallurgical Coatings & Thin Films, 02.-06.05.2010, San Diego, California, United States of America

Publ.-Id: 14339 - Permalink


(i)PVD growth of carbon-transition metal nanocomposites: from energetic condensation to periodic precipitation patterns
Abrasonis, G.;
(i)PVD growth of carbon-transition metal nanocomposites: from energetic condensation to periodic precipitation patterns
  • Invited lecture (Conferences)
    Nanofair 2010, 06.-07.07.2010, Dresden, Germany

Publ.-Id: 14338 - Permalink


High-energy break-up of 6Li as a tool to study the Big-Bang nucleosynthesis reaction D(alpha,gamma)6Li
Hammache, F.; Heil, M.; Typel, S.; Galaviz, D.; Sümmerer, K.; Coc, A.; Uhlig, F.; Attallah, F.; Caamano, M.; Cortina, D.; Geissel, H.; Hellström, M.; Iwasa, N.; Kiener, J.; Koczon, P.; Kohlmeyer, B.; Mohr, P.; Schwab, E.; Schwarz, K.; Schümann, F.; Senger, P.; Sorlin, O.; Tatischeff, V.; Thibaud, J. P.; Vangioni, E.; Wagner, A.; Walus, W.;
The recently claimed observations of non-negligible amounts of 6Li in old halo stars have renewed interest in the Big-Bang Nucleosynthesis (BBN) of 6Li. One important ingredient in the predicted BBN abundance of 6Li is the low-energy D(alpha,gamma)6Li cross section. Up to now, the only available experimental result for this cross section showed an almost constant astrophysical S-factor below 400 keV, contrary to theoretical expectations. We report on a new measurement of the D(alpha,gamma)6Li reaction using the break-up of 6Li at 150 A MeV. Even though we cannot separate experimentally the Coulomb contribution from the nuclear one, we nd clear evidence for Coulomb-nuclear interference by analyzing the scattering-angular distributions. This is in-line with our theoretical description which indicates a drop of the S24-factor at low energies as predicted also by most other models. Consequently, we find even lower upper limits for the calculated primordial 6Li abundance than before.
Keywords: 6Li halo stars Big-Bang Nucleosynthesis BBNcross section astrophysical S-factor break-up

Publ.-Id: 14337 - Permalink


Modification of the Reactivity Equivalent Physical Transformation Method for HTGR Fuel Element Analysis
Fridman, E.; Merk, B.;
The so called “double-heterogeneity”, characterizing High Temperature Gas cooled Reactors (HTGR) block type fuel elements, presents a challenge for existing deterministic lattice codes that were originally developed for LWR applications. A large number of TRISO particles randomly dispersed in the fuel compact introduces an additional complexity into the modeling. The Monte Carlo (MC) based codes, which are capable of simulating complex geometries of HTGR fuel elements, are mainly used for the reference calculations. The use of MC codes as production tools for a few-group cross section generation for 3D nodal codes is still very limited due to the high computational costs.
Recently a new few-group cross section generation methodology for a full core analysis of HTGRs was proposed. This methodology is based on homogenization approach called Reactivity equivalent Physical Transformation (RPT). The RPT methodology combines high spatial resolution of MC codes with superior computational speed of deterministic lattice codes. At the first stage, a MC code is used to simulate an HTGR fuel element with explicitly described TRISO particles at the beginning of life (BOL) and at the nominal operational conditions. At the second stage the TRISO particles are homogenized with the fuel compact graphite to get rid of double-heterogeneity problem. It is well known that a simple volume-weighted homogenization of TRISO particles in the graphite matrix results in the underestimation of the self-shielding effect. However, according to the RPT approach, TRISO particles are homogenized in a smaller central volume rather than in entire fuel compact. The volume of the smeared region is adjusted in such way that k-inf of homogenized geometry matches that of the reference heterogeneous one obtained from MC reference calculations. Since the radius of the smeared zone was determined at the beginning of life (BOL) it is kept constant and is used for depletion and branch-off calculations by lattice codes.
The main disadvantage of the RPT approach is the fact that TRISO particles are smeared together with the compact graphite and constitute one homogeneous material. Keeping in mind that the fuel and graphite temperatures may significantly vary during the reactor operation, these temperatures should be decoupled during a few-group cross section generation. However in the majority of lattice codes temperatures are assigned to the regions (e.c. HELIOS code) or to the homogeneous materials (e.c. CASMO code) rather than to particular nuclides like in the MC codes. In order to overcome this disadvantage the RPT methodology has been modified in a way that only TRISO particles are smeared in the central compact region while all compact graphite is concentrated in the remained outer compact region. This modification allows assigning different temperatures to the fuel and as well as to the compact matrix graphite.
The main objective of this study is to verify the modified RPT methodology. A set of depletion calculations of a prismatic block-type HTGR fuel lattice of fuel and coolant channels was performed. Two models of prismatic fuel assembly are considered: 1) 3D model with explicitly described TRISO particles; 2) 2D model, in which TRISO particles are homogenized using the modified RPT approach. 3D calculations are performed with MCNP based depletion code BGCore. 2D calculations are carried out with BGCore code and deterministic lattice code HELIOS 1.9. The comparison between 3D and 2D results is reported. Conclusions regarding validity of modified RPT approach are drawn.
Keywords: HTGR, double-heterogeneity treatment, BGCore, HELIOS
  • Contribution to proceedings
    5th International Topical Meeting on High Temperature Reactor Technology, 18.-20.10.2010, Prague, Czech Republic
    Modification of the Reactivity Equivalent Physical Transformation Method for HTGR Fuel Element Analysis
  • Lecture (Conference)
    5th International Topical Meeting on High Temperature Reactor Technology, 18.-20.10.2010, Prague, Czech Republic

Publ.-Id: 14336 - Permalink


Preliminary analysis of HTGR core with DYN3D nodal diffusion code
Fridman, E.; Kliem, S.; Rohde, U.;
DYN3D is an advanced nodal code for the three-dimensional steady-state and transient analysis of LWR cores with quadratic and hexagonal fuel assemblies. Although a new version of DYN3D for the simulation of block type High Temperature Gas cooled Reactors (HTGR) is currently under development, the main objective of this work is to demonstrate the applicability of the standard DYN3D version for the steady-state analysis of HTGR core. A preliminary reactor physic analysis procedure in which few group cross section sets are generated using HELIOS 1.9 transport lattice code and full core calculations are performed by DYN3D will be established. The Reactivity equivalent Physical Transformation (RPT) approach will be applied in order to eliminate the double-heterogeneity of HTGR fuel elements in HELIOS calculations. The full core analysis of the reference simplified HTGR core will be performed with DYN3D using macroscopic nodal cross sections provided by HELIOS. At this stage thermo-hydraulic feedback is not considered. The results of DYN3D calculations such as neutron multiplication factor, radial and axial power distribution, will be compared with those obtained from reference full core MCNP simulation.
Keywords: HTGR full core analysis, DYN3D, MCNP, HELIOS
  • Contribution to proceedings
    5th International Topical Meeting on High Temperature Reactor Technology, 18.-20.10.2010, Prague, Czech Republic
    Preliminary analysis of HTGR core with DYN3D nodal diffusion code
  • Lecture (Conference)
    5th International Topical Meeting on High Temperature Reactor Technology, 18.-20.10.2010, Czech Republic, Prague

Publ.-Id: 14335 - Permalink


Die Verwendung von Thorium in Druckwasserreaktoren
Fridman, E.;
Die Verwendung von Th-basierten Brennstoffkreisläufen als Alternative zum U-Brennstoffkreislauf wurde ausgiebig in den Anfangsjahren der Kernenergienutzung zwischen Mitte der 1950er und Mitte der 1970er Jahre erforscht. Obwohl der Nachweis zur Nutzung von Th in einer Reihe von thermischen und schnellen Systemen erbracht wurde, ist es nicht zur kommerziellen Anwendung von Th-Brennstoffen gekommen, bis das Interesse an Th-Brennstoffkreisläufen in den 1980er Jahren schließlich einschlief, vor allem wegen der großen Uranreserven und der Furcht vor nuklearer Proliferation. Die neuerliche Wiederbelebung des Interesses an Th-Kreisläufen, insbesondere in kommerziell betriebenen Druckwasserreaktoren (DWR), ist in erster Linie auf ihr Potential zur Lösung von Proliferationsrisiken, bei der Schonung natürlicher Uranvorkommen und bei der Entsorgungsproblematik im konventionellen Urankreislauf zurückzuführen. Der vorliegende Artikel gibt eine Übersicht über einige der neuesten Studien, die sich mit Implementierungsszenarien und den zu erwartenden Vor- und Nachteilen von Th-basierten Brennstoffen in der aktuellen DWR-Generation auseinandersetzen.
  • Contribution to proceedings
    Kraftwerkstechnischen Kolloquium, 12.-13.10.2010, Dresden, Germany
    Die Verwendung von Thorium in Druckwasserreaktoren
  • Lecture (Conference)
    Kraftwerkstechnischen Kolloquium, 12.-13.10.2010, Dresden, Germany

Publ.-Id: 14334 - Permalink


Electrical transport in Al doped ZnO grown by reactive pulsed magnetron sputtering
Cornelius, S.; Vinnichenko, M.; Kolitsch, A.; Möller, W.;
The synthesis of transparent conductive oxides (TCO) with high transmittance in the near infrared (IR) spectral range is a key requirement for increasing the power conversion efficiency in thin film solar cells. As the absorption at energies close to the Si band gap (1.1 eV) is caused by the free electron plasma it is necessary to maximize their mobility at moderate densities (~5x1020 cm-3) in order to simultaneously reach low resistivities of ~2x10-4 Ohm*cm and improve the IR transmittance.
Therefore a reactive magnetron sputtering method using metallic Zn/Al alloy targets was developed to achieve high carrier mobilities (~45 cm2/Vs) in ZnO:Al thin films. The influence of growth temperature, oxygen partial pressure and target Al concentration on the electrical film properties has been investigated systematically by Hall effect measurements.
Additionally XRD, X-TEM, AFM, ERDA, RBS and spectroscopic ellipsometry were employed to reveal film structure, composition and optical properties. The experimentally observed limit of mobility in polycrystalline ZnO:Al is discussed in terms of ionized impurity scattering and clustering as well as grain boundary limited transport.
Keywords: transparent conductive oxides, TCO, reactive magnetron sputtering, ZnO:Al, AZO, electrical properties, mobility, ionized impurity scattering, grain boundary limited transport
  • Lecture (Conference)
    5th Forum on New Materials (in the framework of 12th International Conference on Modern Materials and Technologies - CIMTEC 2010), 13.-18.06.2010, Montecatini Terme, Italien

Publ.-Id: 14333 - Permalink


Optical conductivity of LuNi2B2C in the terahertz range
Fischer, T.; Pronin, A. V.; Wosnitza, J.; Lobo, R. P. S. M.; Niemeier, T.; Holzapfel, B.;
es hat kein Abstract vorgelegen.
  • Poster
    Terahertz spectroscopy and its high-field applications & EuroMagNET II user meeting, 14.-16.06.2010, Dresden, Deutschland

Publ.-Id: 14332 - Permalink


Spin-orbit interaction in chiral carbon nanotubes probed in pulsed magnetic fields
Jhang, S. H.; Marganska, M.; Skourski, Y.; Preusche, D.; Witkamp, B.; Grifoni, M.; van der Zant, H.; Wosnitza, J.; Strunk, C.;
The magnetoconductance of an open carbon nanotube (CNT)-quantum wire was measured in pulsed magnetic fields. At low temperatures, we find a peculiar split magnetoconductance peak close to the chargeneutrality point. Our analysis of the data reveals that this splitting is intimately connected to the spin-orbit interaction and the tube chirality. Band-structure calculations suggest that the current in the peak regions is highly spin polarized, which calls for application in future CNT-based spintronic devices.
  • Physical Review B 82(2010), 041404(R)

Publ.-Id: 14331 - Permalink


Spin dynamics in S= 1/2 chains with next-nearest-neighbor exchange interactions
Ozerov, M.; Zvyagin, A. A.; Cizmár, E.; Wosnitza, J.; Feyerherm, R.; Xiao, F.; Landee, C. P.; Zvyagin, S. A.;
Low-energy magnetic excitations in the S= 1/2 chain compound [(C6H9N2)CuCl3]CuCl3 [known as (6MAP)CuCl3] are probed by means of tunable-frequency electron spin resonance. Two modes with asymmetric (with respect to the hnu =gµBB line) frequency-field dependences are resolved, illuminating the striking incompatibility with a simple uniform S= 1/2 Heisenberg chain model. The unusual ESR spectrum is explained in terms of the recently developed theory for S= 1/2 chains, suggesting the important role of next-nearest-neighbor interactions in this compound. Our conclusion is supported by model calculations for the magnetic susceptibility of (6MAP)CuCl3, revealing a good qualitative agreement with experiment
  • Physical Review B 82(2010), 014416

Publ.-Id: 14330 - Permalink


Einfluss der Al-Konzentration auf Struktur und elektrische Eigenschaften von mittels reaktivem gepulstem Magnetronsputtern gewachsenen ZnO:Al Schichten
Cornelius, S.; Vinnichenko, M.; Shevchenko, N.; Kolitsch, A.; Möller, W.;
Reactive pulsed magnetron sputtering (RPMS) is employed to grow Al-doped ZnO (AZO) films on fused silica and epitaxially on Al2O3(001). The RPMS process window for obtaining highly transparent and conductive AZO with high mobility and the influence of process parameters such as oxygen partial pressure and substrate temperature are discussed. It is shown that the optimum electrical properties depend stronly on the Al concentration of the sputtering target and that mobility on fused silica is limited to about 45 cm²/Vs. The relations between depostion conditions and film microstructure, stochiometry and electrical properties are investigated, pointing to an enrichment of Al with increasing substrate temperature leading to a deterioration of crystalline structure and carrier mobility.
Finally the observed limitations of electrical properties are categorized and discussed in terms of ionized impurity scattering and grain boundary limited transport.
Keywords: reactive pulsed magnetron sputtering, Al-doped ZnO, AZO, mobility, ionized impurity scattering, grain boundary limited transport
  • Lecture (Conference)
    Workshop „Transparente leitfähige Oxide – Festkörperphysikalische Grundlagen und Technologie“, 01.-02.06.2010, Dresden, Deutschland

Publ.-Id: 14329 - Permalink


Design and Performance of Non-Destructive Pulsed Magnets at the Dresden High Magnetic Field Laboratory
Zherlitsyn, S.; Herrmannsdörfer, T.; Wustmann, B.; Wosnitza, J.;
In this paper we consider various issues of design, fabrication, and performance of non-destructive pulsed magnets at the Dresden High Magnetic Field Laboratory. Currently, a variety of pulsed magnets are in operation in the laboratory. A 70 T/8.5 MJ magnet, having a 24 mm bore and generating field pulses of about 150 ms duration serves as a workhorse for external users and for in-house research. Smaller 60–65 T/1.5 MJ magnets with a bore of 20 mm and pulse duration of 25 ms have been proven to be very reliable in operation. In addition, a new 90 T/9MJdual-coil magnet has recently achieved 87.2 T in a 20 mm bore. A 60 T/43 MJ longpulse magnet is currently tested. Questions of magnet longevity, coil monitoring, as well as magnetic-field measurements are addressed. Further magnet-technology developments and the route to 100 T are discussed.
  • IEEE Transactions on Applied Superconductivity 20(2010), 672

Publ.-Id: 14328 - Permalink


Spin relaxation and resonant phonon trapping in [Gd2(fum)3(H2O)4]·3H2O
Orendáč, M.; Sedláková, L.; Cizmár, E.; Orendácová, A.; Feher, A.; Zvyagin, S. A.; Wosnitza, J.; Zhu, W. H.; Wang, Z. M.; Gao, S.;
Results of ac-susceptibility, specific-heat, magnetization, and electron-spin-resonance studies of a [Gd2(fum)3(H2O)4]·3H2O (fum=fumarate, C4H2O4) powder samples are reported. The results of these measurements enabled us to identify the studied compound as a three-dimensional S = 7/2 Heisenberg magnet with TN = 0.19 K and dominant crystal-field anisotropy. The susceptibility studies conducted at audio frequencies and temperatures from 2 to 30 K revealed that the application of static magnetic fields induces a slow spin relaxation. The relaxation is not associated with an anisotropy energy barrier and is explicable assuming resonant phonon trapping. The magnetic field dependence of the relaxation time is consistent with the proposed scenario and suggests that a strong spin-lattice interaction may be the mechanism governing the relaxation properties in the studied system
  • Physical Review B 81(2010), 214410

Publ.-Id: 14327 - Permalink


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