Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32227 Publications
Radionuclide binding to Cetuximab - a promising approach for the treatment of Squamous Cells/Radionuklidbindung an Cetuximab – ein vielversprechender Ansatz für die Behandlung von Plattenepithelkarzinomzellen
Eke, I.; Förster, C.; Ingargiola, M.; Kunz-Schughart, L.; Baumann, M.; Runge, R.; Kotzerke, J.; Heldt, J.-M.; Steinbach, J.; Cordes, N.;
Zielgerichtete Therapiestrategien gegen den epidermalen Wachstumsfaktorrezeptor (EGFR) mittels Cetuximab verbessern in Kombination mit Bestrahlung das Überleben und die lokale Tumorkontrolle bei Patienten mit Plattenepithelkarzinomen (SCC) des Kopf/Hals-Bereiches. Trotz dieses Behandlungserfolgs machen auftretende Tumorresistenzen eine weitere Optimierung dieser Therapie notwendig. In unserer Studie untersuchten wir das Überleben von SCC Zellen nach Behandlung mit einem Konjugat aus Cetuximab und dem Radionuklid Yttrium-90 ([90Y]Y-CHX-A´´-DTPA-Cetuximab).
In vier verschiedene humane SCC Zelllinien (FaDu, SAS, UTSCC14, A431) wurden EGFR-Hemmung und nachgeschalteter Signalmoleküle mittels Western blot und die Bindung von Cetuximab an EGFR durch Fluorochrom-markiertes Cetuximab analysiert. Das Überleben nach Behandlung mit 90Y, [90Y]Y-CHX-A´´-DTPA-Cetuximab (beide ca. 5–15 MBq äquivalent zu 2–6 Gy), Cetuximab-DTPA oder Cetuximab alleine oder in Kombination mit externer Bestrahlung (Röntgenstrahlen; 200 kV, 20 mA, 1.3 Gy/min; 2–6 Gy) wurde im Koloniebildungstest bestimmt. Zusätzlich wurden Adhäsions- und gammaH2AX-Foci-Assays durchgeführt.
Obwohl Cetuximab-Behandlung zu einer Hemmung von EGFR und nachgeschalteten Signalmolekülen führte, zeigte keine der verwendeten Zelllinien eine Strahlensensibilisierung. Fluorochrom-markiertes Cetuximab blieb zellmembranständig ohne Hinweise auf Internalisierung oder Abbau. 90Y]Y-CHX-A´´-DTPA-Cetuximab verringerte das klonogene Überleben signifikant stärker und in Abhängigkeit der EGFR-Expression als alleiniges 90Y. Zellen, die mit 90Y plus externe Bestrahlung behandelt wurden, überlebten deutlich besser als Zellen nach [90Y]Y-CHX-A´´-DTPA-Cetuximab plus externe Bestrahlung. Das klonogene Überleben konnte mit strahleninduzierten gammaH2AX-Foci korreliert werden. Ein Einfluss von Cetuximab auf die Zelladhäsion war nicht zu verzeichnen.
Unsere Daten zeigen, dass eine Verbindung aus Cetuximab und einem Radionuklid das Überleben von SCC Zellen deutlich stärker reduziert als das unkonjugierte Radionuklid oder externe Bestrahlung. Weitere In-vitro- und In-vivo-Studien sind nötig, um zu untersuchen, inwieweit derartige Konjugate in Therapiestrategien im Rahmen einer Strahlentherapie eingebunden werden können.
  • Poster
    DEGRO 2012 18. Jahreskongress der Deutschen Gesellschaft für Radioonkologie , 07.-10.06.2012, Wiesbaden, D
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 188(2012), 121

Publ.-Id: 18178 - Permalink

Effect of He+ irradiation on Fe–Cr alloys: Mössbauer-effect study
Dubiel, S. M.; Cieslak, J.; Reuther, H.;
Effect of He ions irradiation on three model Fe100−xCrx alloys (x = 5.8, 10.75 and 15.15) was investigated with the conversion electron Mössbauer spectroscopy. The study of the alloys irradiated with 25 keV ions revealed that the strongest effect occured in the Fe84.85Cr15.15 sample where an inversion of a short-range-order (SRO) parameter was found.

Publ.-Id: 18177 - Permalink

Flow cytometric cell-based assay to preselect antibody constructs for radionuclide conjugation
Ingargiola, M.; Dittfeld, C.; Runge, R.; Zenker, M.; Heldt, J.-M.; Steinbach, J.; Cordes, N.; Baumann, M.; Kotzerke, J.; Kunz-Schughart, L.;
Radiolabeled antibodies (Abs) are an attractive tool for targeting and delivering particle emitters for therapy or imaging applications. The labeling of Abs with metal radionuclides requires chelating agents and can cause loss of binding to their ligands. The aim of the present approach was to design an easy-handling flow cytometric cell-based assay to evaluate Ab-binding capacity of conjugates of the therapeutic Ab Cetuximab and to verify the most promising candidate in a competitive radioactive binding experiment. The final setup for flow cytometric assessment of cellular binding capacities of epidermal growth factor receptor (EGFR)/ErbB1-directed Ab conjugates is based on (a) the selection of a robust cell line model (b) the definition of nonsaturated staining concentrations for the unconjugated reference Ab Cetuximab plus implementation of a reasonable isotype control, and (c) the calculation of relative Ab affinities based on the flow cytometric data. Two (FaDu, SAS) out of the three cell lines with different total and cell surface expression levels of EGFR turned out to be adequate models but the application of one cell line was sufficient to estimate reduced binding capacities of conjugates relative to Cetuximab. Only 1/11 conjugate Abs exhibited a fluorescence signal comparable to unconjugated Cetuximab and was applied for radiolabeling with Yttrium-90. Unaltered binding affinity of this conjugate was proven in a competitive radioactive Ab-binding study. We conclude that the flow cytometric assay is reliable and that the relative binding capacity of Cetuximab is neither affected by covalent modification with CHX-A″-DTPA (N-[(R)-2-Amino-3-(p-isothiocyanato-phenyl) propyl]-trans-(S,S)-cyclohexane-1,2-diamine-N,N,N′,N″,N″-pentaacetic acid) with a final chelator-to-Ab ratio of 5 nor by subsequent radiolabeling. [90Y]Y-CHX-A″-DTPA-Cetuximab thus qualifies for preclinical treatment testing as a prerequisite for therapeutic application.
Keywords: EGFR/ErbB1; cell-based assay; antibody binding; radionuclide; chelators; flow cytometry; 2-D cell culture; competitive binding

Publ.-Id: 18176 - Permalink

Electronic Griffiths Phase in the Te-Doped Semiconductor FeSb2
Hu, R.; Wang, K.; Ryu, H.; Lei, H.; Choi, E. S.; Uhlarz, M.; Wosnitza, J.; Petrovic, C.;
We report on the emergence of an electronic Griffiths phase in the doped semiconductor FeSb2, predicted for disordered insulators with random localized moments in the vicinity of a metal-insulator transition. Magnetic, transport, and thermodynamic measurements of Fe(Sb1-xTex)2 single crystals show signatures of disorder-induced non-Fermi liquid behavior and a Wilson ratio expected for strong electronic correlations. The electronic Griffiths phase states are found on the metallic boundary between the insulating state (x = 0) and a long-range albeit weak magnetic order (x ≥ 0.075).

Publ.-Id: 18175 - Permalink

Towards Fluid Flow Estimation from Tomographic Images
Korn, N.;
  • Lecture (others)
    KOMPOST2012, 13.12.2012, Rossendorf, Deutschland

Publ.-Id: 18174 - Permalink

Fabrication of nanostructure arrays by ion beam irradiation
Ou, X.; Kögler, R.; Facsko, S.;
Periodic semiconductor nanostructure arrays have the potential for nano-electronic and nano-optoelectronic application. The broad ion beam erosion is a simple and potentially mass productive technique to fabricate the nanostructure patterns on semiconductor surface as it avoids conventional lithographic steps.[1] The present work reports the fabrication of horizontal silicon nanowire arrays on insulator by Xe+ ion beam erosion of Si-on-insulator substrate. [3] A periodic ripple surface pattern of the Si surface is created by irradiation with Xe+ ions and the transfer of this pattern to the oxide interface as shown in figure 1a. This procedure results in an array of disconnected parallel ordered Si nanowires. A more recent achievement concerns nanopattern of single crystal Ge substrate which is based on a “negative epitaxy”. Vacancies created during ion beam sputtering will diffuse and rearrange according to the crystallographic anisotropy of the substrate which results in orientation-dependent pattern formation of the Ge surface.
Figure 1 (a) Schematic of Si NWs array fabricated by Xe+ beam irradiation on Si-on-insulator substrate. (b)Atomic Froce Miroscopy (AFM) images showing the nanostructure and pattern fabricated on Ge (100) and Ge (111) surface based on “negative epitaxy” process. The scale is 100 nm
[1] S. Facsko et al. Science 285, (1999) 1551.
[2] C. S. Madi et al. Physical Review Letters, 106, (2011) 066101.
[3] X. Ou et al. AIP Advances, 1, (2011) 042174.
Keywords: Irradiation, nanostructure
  • Lecture (others)
    Lecture at University of Konstanz, 12.-15.11.2012, Konstanz, Germany

Publ.-Id: 18173 - Permalink

Fluid Dynamics Research at HZDR
Hampel, U.;
The presentation gives an overview over current research topics, methods and results in research at the Institute of Fluid Dynamics at HZDR. The talk covers both research topics in nuclear reactor safety and efficient processes and described among other the development and application of advanced two-phase flow measurement techniques and computation afluid dynamics tools.
Keywords: fluid dynamics, multiphase flow, CFD
  • Invited lecture (Conferences)
    HIF Seminar Series, 07.01.2013, Freiberg, Germany

Publ.-Id: 18172 - Permalink

Tailoring the properties of semiconductor nanowiresfor thermoelectric applicationsby means of metal-assisted chemical etching
Geyer, N.; Tonkikh, A. A.; Ou, X.; Kögler, R.; Skorupa, W.; Werner, P.; Keywords: metal-assisted etching, semiconductor nanowires, silicon, thermoelectrics
  • Lecture (Conference)
    31th International and 10th European Conference on Thermoelectrics, 09.-12.07.2012, Aalborg, Denmark

Publ.-Id: 18171 - Permalink

AMS of 36Cl with the VERA 3 MV tandem accelerator
Martschini, M.; Andersson, P.; Forstner, O.; Golser, R.; Hanstorp, D.; Lindahl, A. O.; Kutschera, W.; Pavetich, S.; Priller, A.; Rohlén, J.; Steier, P.; Suter, M.; Wallner, A.;
Recent progress with compact ionization chambers has opened new possibilities for isobar suppression in accelerator mass spectrometry (AMS). Separation of 36Cl (t1/2 = 0.30 Ma) at natural isotopic levels from its stable isobar 36S became feasible at particle energies of 24 MeV, which are also accessible for mediumsized tandem accelerators with 3 MV terminal voltage like VERA (Vienna Environmental Research Accelerator). Investigations with an ionization chamber revealed how physics favors isobar separation even at energies below the maximum of the Bragg curve. The strong energy focusing effect at high energy losses reduces energy straggling significantly and isobar separation steadily increases up to almost full energy loss. With an optimized detection setup, sulfur suppression factors of 2 × 104 have been achieved.
Refraining from the additional use of degrader foils has the benefit of high transmission to the detector (~16%), but requires a low sulfur output from the ion source. Therefore several backing materials have been screened for sulfur content. The dependence of the sulfur output on the AgCl sample size has been investigated as well.
Precision and accuracy have been thoroughly assessed over the last two years. Since drifts in the spectra are efficiently corrected by monitoring the position of the 36S peak, the reproducibility for high ratio samples (36Cl/Cl > 10-12) is better than 2%. Our blank value of 36Cl/Cl ≈ (5 ± 5) × 10-16 is competitive to other labs. 36Cl has become a routine AMS-isotope at VERA.
Recently we also explored novel techniques for additional sulfur suppression already in the ion source. While results with a small gas reaction cell in front of the sputter target were discouraging, a decrease in the sulfur/chlorine ratio by one order of magnitude was achieved by directing 300mW continuous wave laser beam at 445 nm towards the cathode in the ion source.
Keywords: AMS, 36Cl, Isobar separation, Energy loss straggling, Cesium sputter ion source

Publ.-Id: 18170 - Permalink

Extraktionsuntersuchungen von umweltrelevanten Radionukliden mit modifizierten Calix[4]arenen
Poetsch, M.; Mansel, A.; Schnorr, R.; Haupt, S.; Kersting, B.;
Im Rahmen eines vom BMBF geförderten Projektes beschäftigt sich die Abteilung „Reaktiver Transport“ des HZDR in Wechselwirkungsstudien mit der Komplexbildung und dem Transportverhalten von d- und f-Elementen mit makrozyklischen Chelatliganden.
Als kurzlebige Analoga für langlebige, umweltrelevante Radionuklide kommen in den Studien 56Co, 64Cu, 65Zn und 85Sr zum Einsatz. Diese werden am hauseigenen Zyklotron hergestellt. Die makrozyklischen Liganden basieren auf funktionalisierten Calix[4]arenen.
Das Komplexierungsverhalten der Calix[4]arene bezüglich der genannten Radionuklide wurde in Extraktionsstudien in flüssig-flüssig Systemen untersucht. Dabei lag der Fokus auf den Reaktionsbedingungen, unter denen eine erfolgreiche Extraktion realisierbar war. Die Extraktionswirkung der Calix[4]arene wurde mit Hilfe der Radiotracertechnik verfolgt.
Unter alkalischen Bedingungen konnten für zwei spezielle Calix[4]arene Extraktionsausbeuten von >90 % erreicht werden. Die entstandenen Komplexe wurden hinsichtlich ihres Bindungsverhaltens spektroskopisch untersucht. Weiterhin konnten Aussagen zur Reversibilität der Reaktionen getroffen werden.
Basierend auf den Reaktionsbedingungen konnten die Extraktionsversuche der Calix[4]arene bezüglich der erwähnten Radionuklide erfolgreich auf reale Wasserproben mit komplexeren Matrizes übertragen werden.
  • Lecture (Conference)
    Anakon 2013, 04.-07.03.2013, Essen, Deutschland

Publ.-Id: 18169 - Permalink

Stand der CFD-Modellierung von Siedevorgängen am Beispiel des NUPEC-Heisskanaltests (PSBT)
Rzehak, R.; Krepper, E.;
Die NUPEC “PWR Subchannel and Bundle Tests” (PSBT) waren zur Untersuchung kritischer Wärmestromphänomene in Brennelementbündeln und zur Validierung von Heißkanalcodes ausgelegt. Einige der Tests sind zur Validierung von CFD-Wandsiedemodellen geeignet. Der Vortrag präsentiert CFD-Analysen der Gasgehaltsverteilung unter Verwendung des CFD-Codes ANSYS CFX-12.1. Zunächst werden die wichtigsten Aspekte des implementierten Modells und Unsicherheiten der Modellparameter herausgestellt. Es kann gezeigt werden, dass die gemessenen querschnittsgemittelten Messwerte mit einem Satz im Rahmen der Mo-dellunsicherheiten kalibrierter Modellparameter reproduziert werden kann. Für die Reproduktion der Verteilungsmuster des Dampfgehaltes im Kanalquerschnitt muss die Modellierung der Turbulenz beachtet werden. Nur ein Turbulenzmodell, das die turbulenten Sekundärströ-mungen auflösen kann, ist in der Lage, die beobachteten Verteilungsmuster zu reproduzieren.
Keywords: CFD, two fluid model, wall boiling, PSBT, turbulence
  • Lecture (Conference)
    Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland: "Kondensationsinduzierte Druckstöße" und "Sieden in DWR", 11.-12.10.2012, Rossendorf, Deutschland

Publ.-Id: 18168 - Permalink

Sorption von U(VI) und Np(V) an Äspö-Granit unter anaeroben und aeroben Bedingungen
Gürtler, S.;
Eine Anforderung an das Wirtsgestein eines möglichen Endlagers für radioaktive Abfälle in tiefen geologischen Formationen ist dessen Funktion als geologische Barriere zur Herabsetzung der Mobilität von im Störfall freigesetzten Actiniden.
Zur Untersuchung des Rückhaltevermögens von Granit gegenüber Actiniden wurde in der Diplomarbeit die Sorption von U(VI) und Np(V) an Granit aus dem Untertagelabor in Äspö (Äspö Hard Rock Laboratory, Äspö HRL, Schweden) untersucht. Die Wechselwirkungen wurden in Batch-Sorptionsversuchen im Labor simuliert und beschrieben. Um den endlagerspezifischen Bedingungen und der geplanten Einlagerung von wärmeentwickelnden, hochradioaktiven Abfällen gerecht zu werden, wurde dabei der Einfluss der Korngrößen des Granits, der Einfluss der Ionenstärke des Hintergrundelektrolyten und der Einfluss der Temperatur unter anaeroben und aeroben Bedingungen ermittelt. Die Konzentration von U(VI) und Np(V) in der wässrigen Phase wird mittels Flüssigszintillation bestimmt. Der Oxidationszustand der Actinide wird durch Flüssig-Flüssig-Extraktion mit 2-Thenoyltrifluoroaceton in Xylol ermittelt. Durch Schwingungsspektroskopie (ATR FT-IR) wurde die Speziation der Oberflächenkomplexe bestimmt.
Keywords: Uran(VI), Neptunium(V), Sorption, Granit
  • Diploma thesis
    Hochschule Fresenius, University of Applied Sciences, Zwickau, 2012
    73 Seiten

Publ.-Id: 18167 - Permalink

The Composition and Depositional Environments of Mesoarchean Iron Formations of the West Rand Group of the Witwatersrand Supergroup, South Africa
Smith, A. J. B.; Beukes, N. J.; Gutzmer, J.;
This paper documents the sedimentological setting, mineralogy, and geochemistry of several iron formation units interbedded with siliciclastic strata of the Mesoarchean Witwatersrand Supergroup, well known for its world-class conglomerate-hosted Au-U deposits. Four major iron formation beds, with associated magnetic mudstones, are present in two distinctly different lithostratigraphic associations, namely shale- and diamictite-associated iron formation. The shale association is represented by the Water Tower and Contorted Bed iron formations in the Parktown Formation of the Hospital Hill Subgroup in the lower part of the succession and the diamictite association by the Promise and Silverfield iron formations in the overlying Government Subgroup. The iron formation units have been subjected to lower greenschist facies metamorphism. Oxide (magnetite and limited hematite), carbonate, and silicate facies iron formations are recognized. The iron formations typically overlie major transgressive flooding surfaces in the succession and, in turn, form the base of progradational coarsening-upward increments of sedimentation comprising magnetic mudstone, nonmagnetic shale, and interbedded siltstone-quartzite. The upward transition from iron formation into magnetic mudstone is accompanied by a change in mineralogical composition from hematite-magnetite iron formation at the base in the most distal setting through magnetite-siderite- and siderite-facies iron formation in the transition zone to magnetic mudstone. The siderite with associated ankerite displays highly depleted 13C values, suggesting crystallization via iron respiration in presence of organic carbon. The iron formations display positive post-Archean Australian shale-normalized Eu and Y anomalies with depletion in light rare-earth elements relative to heavy rare-earth elements, indicating precipitation from marine water with a high-temperature hydrothermal component. Integration of sedimentological, petrographic, and geochemical results indicates that the shale-associated iron formation was deposited during the peak of transgression, when reduced iron-rich hydrothermal waters entered the Witwatersrand Basin over a limited vertical extent due to neutral buoyancy, with the top of the plume occurring below the photic zone. It is suggested that chemolithoautotrophic iron-oxidizing bacteria, which would have been able to exploit the difference in chemistry between the iron-enriched plume water and ambient ocean water to fuel metabolic activity in the presence of limited free molecular oxygen, were responsible for precipitation of initial ferric iron oxyhydroxides. The vertical facies associations in the iron formations most likely developed in response to the limited vertical extent of the hydrothermal plume, with (from distal to proximal) hematite preserved where the base of the plume was not in contact with the basin floor, magnetite where the plume water was in contact with bottom sediment, iron-rich carbonates where organic carbon input was high, iron-rich alumosilicates where siliciclastic input became significant in more proximal settings, and iron-poor sediment above the top of the plume. Diamictite-associated iron formations in the Witwatersrand are inferred to have been deposited in a fashion similar to the shale-associated iron formations, with the exception that major transgressions and hydrothermal plume invasion were preceded by glacial ice cover. The climate warming and increased volcanic activity required could have been related to increased tectonic activity inferred for the Witwatersrand Supergroup during deposition of the glacially associated iron formations.
Keywords: no keywords

Publ.-Id: 18166 - Permalink

CFD analysis of a void distribution benchmark of the NUPEC PSBT tests - model calibration and influence of turbulence modelling
Krepper, E.; Rzehak, R.;
The NUPEC “PWR Subchannel and Bundle Tests” (PSBT) were designed to investigate critical heat flux phenomena in rod bundles and yield data to validate hot channel codes. Some of the tests are suitable for validating a CFD wall boiling model. The paper presents CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns. Furthermore the influence of bubble forces on the calculated void distribution is investigated.
Keywords: CFD, two fluid model, wall boiling, PSBT, turbulence
  • Contribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH15, 12.-15.05.2013, Pisa, Italy
  • Lecture (Conference)
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH15, 12.-15.05.2013, Pisa, Italy

Publ.-Id: 18165 - Permalink

CFD model of wall boiling considering the bubble size distribution
Krepper, E.; Rzehak, R.; Lifante, C.; Frank, T.;
New developments in the framework of a common project simulating subcooled boiling are described. The computational model used combines the Euler / Euler two-phase flow description with heat flux partitioning. Main achievements were a comprehensive study of the boiling process itself and a better description of the interfacial area by coupling of wall boiling with a population balance model. The paper presents validations and shows the capabilities of the model extensions. A careful calibration of correlations used in the wall boiling model is necessary to obtain agreement with the measured data. For the demonstration, DEBORA tests were used. During these tests radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size were measured.
Keywords: CFD, two fluid model, wall boiling, populatioon balance, MUSIG, DEBORA experiments
  • Contribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH15, 12.-15.05.2013, Pisa, Italy
  • Lecture (Conference)
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH15, 12.-15.05.2013, Pisa, Italy

Publ.-Id: 18164 - Permalink

Verbundprogramm Modellierung, Simulation und Experimente zu Siedevorgängen in DWR
Krepper, E.;
Der Vortrag fasst den Wissensgewinn und das Fazit des Projektverbundes zusammen
Keywords: CFD, model development, model validation, experiments
  • Invited lecture (Conferences)
    Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland: "Kondensationsinduzierte Druckstöße" und "Sieden in DWR", 11.-12.10.2012, Rossendorf, Deutschland

Publ.-Id: 18163 - Permalink

Modellierung, Simulation und Experimente zu Siedevorgängen in DWR – Relevanz für die Kerntechnik
Krepper, E.;
Die Simulation des kritischen Wärmestromes spielt eine wichtige Rolle bei der sicheren und effektiven Auslegung von Anlagen zur Energieerzeugung. CFD-Modelle sind hierfür sehr gut geeignet, da sie es prinzipiell ermöglichen, Strömungsvorgänge unabhängig von der konkreten Geometrie in einem weiten Bereich der thermohydraulischen Parameter zu simulieren.
Ein im Rahmen des Förderprogramms "Energie 2020+" durch das Bundesministerium für Bildung und Forschung geförderten Verbundprojektes, in dem 4 Universitäten, 2 Forschungszentren sowie der Codeentwickler ANSYS zusammenarbeiten, wird durch das HZDR koordiniert. Das Projekt ist auf die Entwicklung und Validierung von CFD-Modellen für Siedevorgänge in Druckwasserreaktoren vom unterkühlten Sieden bis hin zum kritischen Wärmestrom gerichtet. Das Projekt ist auf die Grundlagenforschung orientiert und richtet sich auf die Modellentwicklung sowie die Durchführung von Experimenteten in verschiedenen Größenordnungen. Ein wichtiges Ziel ist die Ausbildung aund Aufrechterhaltung der Kompetenz in der Kerntechnik.
Keywords: boiling, critical heat flux, CFD, two fluid model, experiments
  • Invited lecture (Conferences)
    Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland: Kondensationsinduzierte Druckstöße und Sieden in DWR, 11.-12.10.2012, Rossendorf, Deutschland

Publ.-Id: 18162 - Permalink

Modelling, simulation and experiments on boiling processes in pressurized water reactors
Krepper, E.;
A collaborative project funded by the Federal Ministry of Education and Research (BMBF) in the framework of the R&D program "Energie 2020+" by four Universities, two Research Centres and ANSYS is coordinated by Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The project is directed towards the development and validation of CFD models of boiling processes in PWR in the range from subcooled nucleate boiling up to the critical heat flux. The work is oriented towards basic research and focused on model development, simulation and experiments on different scales. An important objective is the education and maintaining of competence in nuclear technology.
Keywords: CFD, wall boiling, models, experiments
  • Kerntechnik 78(2013)1, 35-37

Publ.-Id: 18161 - Permalink

CFD analysis of a void distribution benchmark in a rod bundle
Krepper, E.; Rzehak, R.;
The NUPEC “PWR Subchannel and Bundle Tests” (PSBT) were designed to investigate criti-cal heat flux phenomena in rod bundles and yield data to validate hot channel codes. Some of the tests are suitable for validating a CFD wall boiling model. The paper presents CFD calcu-lations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncer-tainties in several model parameters. It is then shown that the measured cross sectionally av-eraged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections atten-tion has to be focussed on the modelling of turbulence in the narrow channel. Only a turbu-lence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns.
Keywords: CFD, two-fluid model, wall boiling, model validation, PSBT, rod bundle
  • Kerntechnik 78(2013)1, 38-42

Publ.-Id: 18160 - Permalink

CFD-modelling of subcooled boiling
Krepper, E.; Rzehak, R.; Lifante, C.; Frank, T.;
In this paper new developments in the framework of a common project simulating subcooled boiling are described. The computational model used combines the Euler / Euler two-phase flow description with heat flux partitioning. Main achievements were a comprehensive study of the boiling process itself and a better description of the interfacial area by coupling of wall boiling with a population balance model. The model extensions are validated and the present capabilities of CFD for wall boiling are investigated.
Keywords: CFD, two fluid model, wall boiling, population balance model, DEBORA tests
  • Kerntechnik 78(2013)1, 43-49

Publ.-Id: 18159 - Permalink

Simulation und Messung der Hochfrequenzeigenschaften einer supraleitenden Photo-Elektronenquelle
Arnold, A.;
Der Erfolg zukünftiger Synchrotronstrahlungsquellen und Hochleistungs-IR-FELs wird eng mit der Entwicklung einer geeigneten Elektronenquelle verbunden sein. Einen vielversprechenden Ansatz, die dafür erforderliche Brillanz und den hohen mittleren Strom zu erzeugen, stellt der supraleitende Hochfrequenz-Photoinjektor (SRF-Gun) dar. Im Rahmen dieser Arbeit konnte die bislang einzige, an einem Elektronen-Linearbeschleuniger betriebene Quelle dieses Typs erfolgreich in Betrieb genommen sowie wesentliche Eigenschaften theoretisch und praktisch untersucht werden.

The success of future synchrotron radiation sources and high power IR free-electron lasers (FELs) largely depends on the development of an appropriate electron source. At the moment, the superconducting radio frequency photoinjector (SRF gun) seems to be a promising approach to achieve the required brightness and the high average current at the same time. Within the present thesis a SRF gun was brought into operation and essential characteristics were investigated. At the time of printing, it was the only source equipped with all components and operated at a linear accelerator.
Keywords: superconducting radio frequency photo gun; SRF gun; electron injector; electron source; radiation source ELBE; supraleitender Hochfrequenz-Photoinjektor; Elektronenquelle; Strahlungsquelle ELBE
  • Doctoral thesis
    Fakultät für Informatik und Elektrotechnik der Universität Rostock, 2012
    293 Seiten


Publ.-Id: 18158 - Permalink

Incorporation dosimetry of F-18-Flubatine – Comparison of animal model data with first-in-man results
Sattler, B.; Kranz, M.; Patt, M.; Donat, C.; Deuther-Conrad, W.; Hoepping, A.; Sattler, T.; Brust, P.; Steinbach, J.; Sabri, O.;
Objectives: (-HF-18]-Flubatine (former NCFHEB) is a new tracer for neuroimaging of !l4ß2 nAChRs with PET. To assess the radiation risk, its biodistribution, organ doses (00) and effective dose (EO) were determined in pigs and compared to earlier results in mice and humans [SNM20J J No. 1454, 1459J.
Methods: For whole body dosimetry, 5 female piglets (age: 44±3.0d, weight: 13.7±1.7kg) were narcotized (20 mglkg Ketamine, 2mglkg Azaperone; 1.5% Isoflurane in 70% N20/30% 02) and sequentially imaged up to 5h post i.v. injection of 186.6±7.4MBq F1ubatine on a PET/CT-system with 7 bed positions (BP) per frame, J .5-6min/BP, CT-attenuation correction and iterative reconstruction. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activitydata (%ID/g, and %IO/organ). Time and mass were adapted to the human scale. The OOs were calculated using the adult male model with OLINOA. The EO was calculated using tissue weighting factors as published in the ICRPI03.
Results: The highest 00 was received by the urinary bladder (49.0± 19.4j.1SvIMBq*) and the kidneys (39.9±6. J *). The highest contribution to the EO was by the urinary bladder (2.0±0.7*) and the stornach (1.5±0.3*). The EO to humans after i.v. injection of(-)-Flubatine is 14.6±3.2*.
Conclusions: As true for other PET-Tracers, preclinical dosimetry potentially underestimates the EO to humans. The EO by F1ubatine yielded from pig-(this study) and mice-(14.2j.1SvIMBq) studies compared to human dosimetry (22.6±0.68j.1Sv/MBq) show that animal dosimetry underestimates the potential radiation exposure to humans by 35-37%. This fact needs to be considered in the assessment ofthe EO to humans prior early phase clinical trials.
Research Support: The study was supported by Strahlenschutzseminar in Thüringen e. V
  • Abstract in refereed journal
    Journal of Nuclear Medicine 53(2012)1, 1503

Publ.-Id: 18157 - Permalink

Hydrodynamic studies in slurry bubble columns: An experimental and numerical study
Rabha, S.; Schubert, M.; Hampel, U.;
To overcome the current difficulties in designing a slurry bubble column reactor with respect to the effect of particle properties, the influence of solid concentration (Cs) on the hydrodynamics of a slurry bubble column was studied experimentally using ultrafast electron beam X-ray tomography. Experiments were carried out for dP = 100 µm at Cs = 0 – 0.36 at superficial gas velocity UG = 0.02 – 0.05 m/s in a slurry bubble column of diameter DT = 0.07 m. The real time gas flow structure, average bubble diameter and average gas hold-up as a function of UG and Cs have been reported. Corresponding three-phase simulations were also performed using the Euler-Euler multi-fluid model implemented in CFX 14. The bubble size distribution was calculated using the MUSIG model. The predicted gas hold-up and bubble size distribution also show dependence on UG and Cs and agree quite well with the measurements.
Keywords: Slurry bubble column, three-phase flow, solid concentration, ultrafast electron beam X-ray tomography, Euler-Euler modeling

Publ.-Id: 18156 - Permalink

Ferromagnetic Behavior of Fe+ Implanted Si(100) Semiconductor
Yilgin, R.; Yurtisigi, M.; Parabas, A.; Turksoy, M.; Ozdemir, M.; Aktas, B.; Kolitsch, A.;
Fe ions have been implanted into Si (100) single crystals using ion implantation technique. The Fe ions have been accelerated to 45 keV with a dose of 5x10(17) ion/cm(2) at room temperature. The ions have been sent to the substrate's surface at normal incidence. The temperature dependence of magnetization measurement was explored at the temperature range of 10-300 K. The implanted Si substrate was studied with Ferromagnetic Resonance (FMR) technique and Vibrating Sample Magnetometer (VSM). The FMR spectra were recorded by applying external magnetic field in different experimental geometries. FMR spectra were analyzed and the magnetic properties, which are the g-factor, effective magnetization and uniaxial anisotropy parameter, were estimated by simulation of the experimental data. The sample showed two-fold magnetic anisotropic symmetry. By fitting the Si-2p region obtained through XPS measurements it is observed that Fe and Fe compounds are present in the material.

Publ.-Id: 18155 - Permalink

Intrinsic flow behaviour in a slurry bubble column: A comprehensive study on the effect of particle properties
Rabha, S.; Schubert, M.; Hampel, U.;
There is a strong controversy in the literature on the effect of particle properties which limit reliable design of slurry bubble columns. Thus, the influence of particle size (dP) and solid concentration (Cs) on the hydrodynamics of a slurry bubble column was studied experimentally using ultrafast electron beam X-ray tomography. Experiments were carried out for dP = 50 - 150 µm at Cs = 0 – 0.20 and superficial gas velocity UG = 0.02 – 0.05 m/s in a slurry bubble column of diameter DT = 0.07 m. The real time gas flow structure, average bubble diameter and averaged gas hold-up were found to be independent of dP and Cs at small particle size and low solid concentration. However, at large dP and high Cs, strong dependency on dP and Cs was observed. Corresponding three-phase simulations were also performed using the Euler-Euler multi-fluid model implemented in CFX 14. The bubble size distribution was calculated using the MUSIG model. The predicted gas hold-up and bubble size distribution also shows dependence on dP and agreed quite well with the measurements and previous studies
Keywords: Slurry bubble column, three-phase flow, gas hold-up, ultrafast electron beam X-ray tomography, Euler-Euler modeling, MUSIG model

Publ.-Id: 18154 - Permalink

Gamma-ray computed tomography for imaging of multiphase flows
Bieberle, A.; Härting, H.-U.; Rabha, S.; Schubert, M.; Hampel, U.;
Multiphase flows are omnipresent in the chemical industry. The flow phenomena in multiphase reactors strongly affect the processes performance. Nonetheless, even basic information on flow patterns, flow regimes and effects of internals etc. is often not available, which is a strong obstacle for a reliable design and scale-up. Non-invasive tomographic techniques are promising measurement tools to visualize opaque multiphase flows. The contribution provides a short survey about today’s tomographic imaging techniques and introduces the principles of radiation-based tomography. In particular, two gamma-ray computed tomography designs and their application for a sparger performance studies in large bubble columns and for flow regime determination in inclined rotating fixed bed reactors is presented.
Keywords: gamma-ray computed tomography, flow imaging, bubble column, gas sparger, inclined rotating fixed bed reactor

Publ.-Id: 18153 - Permalink

High-resolution two-phase flow measurement techniques for the generation of experimental data for CFD code qualification
Hampel, U.; Krepper, E.; Lucas, D.; Beyer, M.; Szalinski, L.; Banowski, M.; Barthel, F.; Hoppe, D.; Bieberle, A.; Barth, T.;
Computational fluid dynamics simulations for two-phase flows are important in different fields of engineering and science. Since two-phase flows are inherently complex, also CFD modeling development requires special attention. The validation of model implementation and the derivation of physics based models for momentum, heat, and mass transfer in two-phase flow require experiments with generation of high-resolution measurement data. This, however, is a great challenge, since most standard flow measurement tools used in single phase flow situations, are not suited for multiphase flows.
In this article we report on advanced imaging and measuring methods for two-phase flow ex-periments, which have been extensively used in the recent past to conduct experiments for two-phase flows at the Helmholtz-Zentrum Dresden-Rossendorf. In particular the application of wire-mesh sensors, ultrafast X-ray tomography, gamma ray tomography and positron emis-sion tomography will be introduced and discussed.
Keywords: multiphase flow measurement, computational fluid dynamics
  • Kerntechnik 78(2013)1, 9-15

Publ.-Id: 18152 - Permalink

Editorial for Special Issue IWPT-4 in Flow Measurement and Instrumentation
Hampel, U.;
In the past years a growing community of measurement scientists and engineers has been struggling with new and optimized measurement and imaging techniques for process engineering applications. This research and development is mainly driven by needs in industry and fundamental science to obtain quantitative parameters from industrial processes. The commonality behind these needs is the fact, that many industrial processes are governed by multiphase flows of educts and products, whose parameters must be obtained in many places of plants and facilities. Most prominent examples of such are multiphase chemical reactors, separation units and solids processing units, thermal hydraulic circuits in nuclear reactors and solar power plants, as well as multiphase streams in mineral oil production. Moreover, there is also a constant pressure from fundamental flow mechanical science to have high resolution experimental data from multiphase flows available for the validation of CFD codes.

Tomographic imaging techniques naturally provide a good basis for multiple parameter measurements, though the requirements for high resolution in space and time, robustness with respect to harsh process conditions and cost issues are difficult to meet, particularly within one instrument or technique. Hence the field of process tomography has been seen to develop continuously since almost 30 years. Mature concepts of robust and non-intrusive tomographic imaging techniques, such as electrical resistance (ERT), capacitance (ECT) or impedance (EIT) tomography, are today constantly improved regarding particular needs of industrial applications, such as real-time monitoring and parameter extraction, 3D imaging and sensor data fusion. Now, however, they become more and more complemented by new techniques, such as electromagnetic tomography (EMT), electromagnetic flow metering with distributed sensors and industrial hard field imaging techniques. Furthermore, emerging process and environmental technologies, like carbon capture and storage, ionic liquids for chemical engineering applications, geothermal energy harvesting and new routes of mineral oil and gas production, such shale gas exploitation, deep-water offshore oil production and processing of high viscosity crudes and and oil sands, demand also new ideas and sensors from industrial process tomography.

The 4th International Workshop on Industrial Process Tomography IWPT-4 held in Chengdu, China, Sept. 21st-23rd, 2011 was a platform for specialists to present and discuss their most recent advancements in the development and application of process tomography techniques. The workshop was the fourth in a successful series of workshops held in Beijing and Hangzhou (2005), Macau (2006), and Tokyo (2009). It was organized by the International Society for Industrial Process Tomography (ISIPT) together with the Institute of Mechanics of the Chinese Academy of Science and hosted by Southwest Petroleum University.
Keywords: process tomography

Publ.-Id: 18151 - Permalink

Die Helmholtz-Energie-Allianz “Energieeffiziente Chemische Mehrphasenprozesse”
Hampel, U.; Dittmeyer, R.; Patyk, A.; Wetzel, T.; Lange, R.; Freund, H.; Schwieger, W.; Grünewald, M.; Schlüter, M.; Petasch, U.;
Die Energieeffizienz großtechnischer Prozesse ist ein wichtiges Ziel von Forschungs- und Entwicklungsaktivitäten in Unternehmen und Forschungsinstitutionen. Zum einen sichern Maßnahmen zur Erhöhung der Energieeffizienz unmittelbar die Wettbewerbsfähigkeit von Unternehmen, zum anderen besteht ein gesellschaftlicher Konsens über die Notwendigkeit der Erreichung klima- und energiepolitischer Zielstellungen, insbesondere zur Reduktion der produktionsbedingten Treibhausgasemissionen. Die politischen Ziele dazu sind ehrgeizig und wurden insbesondere in Deutschland durch den im Jahr 2011 beschlossenen Umbau der Energieversorgung durch schrittweise Abschaltung der deutschen Kernkraftwerke bis 2022 und eine deutliche Steigerung der Energieerzeugung aus erneuerbaren Energiequellen neu justiert. Mit dem Umbau der Energieversorgung sind eine Reihe technischer, wirtschaftlicher und gesellschaftlicher Probleme zu lösen. Dies betrifft die effiziente Gewinnung, Speicherung und Verteilung von elektrischer Energie aus erneuerbaren Energiequellen ebenso wie ein bedarfs- und angebotsoptimiertes Netz- und Lastmanagement im Energienetz. Parallel dazu sind weitere umfassende Maßnahmen zur Senkung des Primärenergieverbrauchs durch eine Steigerung der Energieeffizienz in Wirtschaft, Privathaushalten und im Transportsektor unerlässlich.
Die Helmholtz-Gemeinschaft deutscher Forschungszentren (HGF) stellt sich dieser Aufgabe durch verstärkte Investitionen in Forschungsinfrastrukturen und eine weitere Vernetzung der Forschungsaktivitäten zwischen Helmholtz-Zentren und Universitäten. Im Hinblick auf die neuen energiepolitischen Rahmenbedingungen in der Bundesrepublik Deutschland startete die Helmholtz-Gemeinschaft deutscher Forschungszentren im Jahr 2011 eine Initiative zur Förderung neuer Themen der Energieforschung. Die in diesem Beitrag vorgestellte Helmholtz-Energie-Allianz ist ein Forschungsverbund, der Kompetenzen und Forschungsaktivitäten im Bereich der chemischen Verfahrenstechnik bündelt. Die Ziele des auf drei Jahre angelegten Forschungsvorhabens bestehen in der Weiterentwicklung von Entwurfs- und Auslegungsmethoden sowie numerischen und experimentellen Techniken zur Effizienzsteigerung chemischer Mehrphasenprozesse, die in der chemischen Produktion von herausragender Bedeutung sind.
Keywords: energy efficiency, multiphase reaction engineering

Publ.-Id: 18150 - Permalink

Chemical ordering of FePt films using millisecond flash-lamp annealing
Brombacher, C.; Schubert, C.; Daniel, M.; Liebig, A.; Beddies, G.; Schumann, T.; Skorupa, W.; Donges, J.; Häberlein, S.; Albrecht, M.;
The structural and magnetic properties of 20-nm-thick FexPt100-x films that were processed by 20 ms flash-lamp annealing were investigated. A maximum in coercivity of (10.4 ± 0.5) kOe was achieved for a composition of Fe53Pt47, which shows also a high degree of L10 chemical order. A variation of the chemical composition toward either higher or lower Fe content leads to a lowering of the coercivity, which can be attributed to a reduction in L10 ordered volume fraction. Thus, in the millisecond time regime, the fastest ordering transformation occurs for slightly Fe-rich FePt films.
Keywords: Flash lamp annealing, FePt-films, magnetic properties, microstructure

Publ.-Id: 18149 - Permalink

Radiation damage in YSZ simulated by single and double beam ion irradiation
Ou, X.; Kögler, R.; Zhou, H. B.; Anwand, W.; Grenzer, J.; Voelskow, M.; Butterling, M.; Mücklich, A.; Zhou, S.; Skorupa, W.;
YSZ (yttria-stabilized zirconia) with cubic phase is a promising nuclear material. YSZ has excellent radiation resistance and chemical stability and can be applied for the inter matrix layer of fuel cells or for the covering and storage of nuclear waste. The effect of irradiation on YSZ has been intensively investigated in recent years via single beam implantation.[1,2] Most of experimental works were performed to simulate the radiation damage from alpha particles by He+ implantation [2] or to simulate the neutron radiation damage and the damage introduced from alpha recoils by implantation of heavy ions. [1] In fact, the radiation damages created by the simultaneous dual beam implantation of Zr+ and He+ ions is much more adequate to reflect the real irradiation conditions. However this case is rarely reported in the literature due to the experimental restrictions. In this work the dual beam facility in Rossendorf is used for the investigation of the radiation damage in YSZ created either by simultaneous implantation of Zr+ & He+ or by separate single beam implantation. The samples were analyzed by a variety of methods such as Rutherford backscattering spectrometry in channeling mode, high resolution x-ray diffraction, positron annihilation spectroscopy, nanointendation and transmission electron microscopy.
The results show that the excitation by the additional Zr+ implantation can activate and enhance the out diffusion of the simultaneously implanted He. The release of He.from YSZ substrate, instead to be trapped by implantation induced vacancies generated by the heavy Zr+ ions, avoids the formation and growth of He bubbles. Such bubbles make the material hard and brittle. In this way the ability of YSZ for the stable inclusion of nuclear waste in the long term is verified. Possible mechanisms are discussed.

[1] S. Moll et al., Journal of Applied Physics 105, 023512 (1999).
[2] G. Velisa et al., Journal of Nuclear Materials 402, 87 (2010).
Keywords: Radiation damage, double beam ion irradiation
  • Poster
    The 18th International Conference on Ion Beam Modifications of Materials (IBMM2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 18148 - Permalink

Tuning resistive switching behavior of BiFeO3 by Ar+ irradiation
Ou, X.; Shuai, Y.; Luo, W. B.; Reuther, H.; Zhou, S.; Schmidt H;
The resistive switching (RS) of functional oxide thin films has attracted tremendous interest recently due to its promising application as building blocks in non-volatile memory devices. [1] By applying voltage pulses, the functional oxide films are switched between different resistance states and may store information, which is the basis of resistance random access memory (RRAM). However, the RS performance of the oxides still needs improvement for a future commercial application, and the physical mechanism of the RS is not fully understood yet. The point defects, especially oxygen vacancies, play an important role on determining the electrical conduction of oxide thin films. [2] This work reports a low cost and effective approach to tune the resistive switching behavior of BiFeO3 films which have been deposited by pulsed laser deposition [3] and irradiated with low energy Ar+ ions. Due to the preferential sputtering of BiFeO3 films, oxygen vacancies as well as the surface morphology can be tuned by low energy irradiation in a controllable way to enhance the RS performance. The obvious improvement of key switching parameters, i.e. the resistance stability and retention, was observed in the irradiated BiFeO3 (Figure 1). These improvements give an opportunity to design a nonvolatile memory with a multilevel RS function which is more scalable than a memory based on bistable RS reported by most of studies [3]. The changing of the conduction mechanism in the BiFeO3 from Poole-Frenkel to space-charged-limited conduction after irradiation will be discussed. The combination of the microstructure analysis and the electrical characterization of the irradiated BiFeO3 will gain an insight into the resistive switching mechanism.

Figure 1(a) I-V characteristic curves showing a significant improvement of the stability of resistive switching in BiFeO3 film after irradiation. The distinguishable neighboring resistance states in the irradiated sample allow for designing multilevel RS memory devices based on BiFeO3 films. (b) Retention test showing the nonvolatile resistance states in irradiated BiFeO3 film on an extrapolated time scale of 10 years.

[1] R. Waser et al., Nature Materials 6, (2007) 833.
[2] D. W. Reagor et al., Nature Materials 4, (2005) 593.
[3] Y. Shuai et al., Applied Physics Letters 98, (2011) 232901.
[4] Y. Shuai X. Ou et al., Journal of Applied Physics 111, (2012) 07D906.
Keywords: Irradiation, Resistive switching
  • Poster
    The 18th International Conference on Ion Beam Modifications of Materials (IBMM2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 18147 - Permalink

Fabrication of Si and Ge nanostructure arrays
Ou, X.; Kögler, R.; Wei, X.; Mücklich, A.; Skorupa, W.; Facsko, S.; Wang, X.;
The periodical semiconductor nanostructure arrays have the potential for nano-electronic and nano-optoelectronic application. Comparing to the conventional low efficiency lithographic techniques broad ion beam erosion is a simple and potentially mass productive technique to fabricate the nanostructure patterns on semiconductor surface.[1] Based on a “self-organized” erosion process, periodical nanoripple, nanohole, nanodot and nanotip arrays can be created due to the interplay of different processes.[2] As the ion beam erosion is performed on Si /Ge thin layer on insulator substrate and precisely ceased when the nanopattern moves to the interface of the buried oxide layer, an array of separate nanostructure can be fabricated on insulator. This work reports the fabrication of the horizontal silicon nanowire arrays on insulator by Xe+ beam erosion of Si-on-insulator substrate [3] (figure 1a). A periodic ripple surface pattern on Si is created by ion irradiation with Xe+ at an incidence angle of 67o to the surface normal. The transfer of the pattern to the oxide interface results in an array of disconnected parallel ordered Si nanowires.The electrical doping behaviour of the fabricated Si nanowire was investigated by scanning spreading resistance microscopy (SSRM). Meanwhile, we will also report our recent discover of single crystal Ge nanopattern formation based on “negative epitaxy” process (figure 1b). The vacancies created during the ion beam sputtering will be distributed according to the crystallographic anisotropy, which results in the orientation-dependent pattern formation on single crystal Ge surface. The mechanism of this novel process will be discussed.
[1] Stefan Facsko et al. Science 285, 1551 (1999).
[2] C. S. Madi et al. Phys. Rev. Lett. 106, 066101 (2011).
[3] Xin Ou et al. AIP Advances, 1, 042174 (2011).
Keywords: Irradiation, nanopatterning
  • Lecture (Conference)
    The 18th International Conference on Ion Beam Modifications of Materials (IBMM2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 18146 - Permalink

Fabrication of Si and Ge nanostructure arrays by ion beam irradiation
Ou, X.; Kögler, R.; Mücklich, A.; Skorupa, W.; Facsko, S.; Helm, M.;
The periodical semiconductor nanostructure arrays have the potential for electronic and optoelectronic application. Comparing to the conventional low efficiency lithographic techniques broad ion beam erosion is a simple and potentially mass productive technique to fabricate the nanostructure patterns on semiconductor surface.[1] Based on a “self-organized” erosion process, periodical nanoripple, nanohole, nanodot and nanotip arrays can be generated due to the interplay of different processes.[2] As the ion beam erosion is performed on Si /Ge thin layer on insulator substrate and precisely ceased when the nanopattern moves to the interface of the buried oxide layer, an array of separate nanostructure can be fabricated on insulator. This work reports the fabrication of the horizontal silicon nanowire arrays on insulator by ion beam erosion of Si-on-insulator substrate [3] and the fabrication of different single crystal Ge nanopattern and nanostructure based on novel “negative epitaxy” process induced by ion beam erosion. The electrical doping behaviour of the fabricated Si nanowire and formation mechanism of the Ge nanopattern will be discussed.
[1] Stefan Facsko et al. Science 285, 1551 (1999).
[2] C. S. Madi et al. Phys. Rev. Lett. 106, 066101 (2011).
[3] Xin Ou et al. AIP Advances, 1, 042174 (2011).
Keywords: irradiation, nanostructure
  • Lecture (Conference)
    International Conference on Superlattices, Nanostructures and Nanodevices (ICSNN 2012), 22.-27.07.2012, Dresden, Germany

Publ.-Id: 18145 - Permalink

Nonvolatile Multilevel Resistive Switching in Ar+ Irradiated BiFeO3 Thin Films
Shuai, Y.; Ou, X.; Luo, W.; Du, N.; Wu, C.; Zhang, W.; Bürger, D.; Mayr, C.; Schüffny, R.; Zhou, S.; Helm, M.; Schmidt, H.;
Low-energy Ar+ ion irradiation has been applied to an Au/BiFeO3/Pt capacitor structure before deposition of the Au top electrode. The irradiated thin film exhibits multilevel resistive switching (RS) without detrimental resistance degradation, which makes the intermediate resistance states more distinguishable, as compared with the nonirradiated thin film. The stabilization of resistance states after irradiation is discussed based on the analysis of the conduction mechanism during the RS, which was investigated by means of temperature-dependent current–voltage measurement from room temperature to 423 K
Keywords: Irradiation, rectifying, resistive switching (RS)

Publ.-Id: 18144 - Permalink

Copper(II) chemistry of the functionalized macrocycle cyclam tetrapropionic acid
Comba, P.; Emmerling, F.; Jakob, M.; Kraus, W.; Kubeil, M.; Morgen, M.; Pietzsch, J.; Stephan, H.;
The CuII complex of H4TETP (H4TETP = 1,4,8,11-tetraazatetradecane-1,4,8,11-tetrapropionic acid) is five-coordinate with a distorted square-pyramidal structure (τ = 0.45; i.e. the geometry is nearly half-way between square-pyramidal and trigonal-bipyramidal) and a relatively long Cu–N and a short Cu–O bond; the comparison between powder and solution electronic spectroscopy, the frozen solution EPR spectrum and ligand-field-based calculations (angular overlap model, AOM) indicate that the solution and solid state structures are very similar, i.e. the complex has a relatively low “in-plane” and a significant axial ligand field with a dx2−y2 ground state. The ligand-enforced structure is therefore shown to lead to a partially quenched Jahn–Teller distortion and to a relatively low complex stability, lower than with the corresponding acetate-derived ligand H4TETA. This is confirmed by potentiometric titration and by the biodistribution with 64Cu-labeled ligands which show that the uptake in the liver is significantly increased with the H4TETP-based system.

Publ.-Id: 18143 - Permalink

Polyoxometalates as versatile enzyme inhibitors
Stephan, H.; Kubeil, M.; Emmerling, F.; Müller, C. E.;
Polyoxometalates (POMs) are inorganic cluster compounds that have been shown to possess a number of pharmacological properties, including antidiabetic, antibacterial, antiprotozoal, antiviral and anticancer activities. Their molecular mechanism of action is largely unknown. However, several studies indicate that many of their activities may be due to the inhibition of enzymes, in particular, of those enzymes that are accessible from the extracellular space and do not require the penetration of cell membranes. In this review, we describe the recent progress in the preparation and optimization of POMs, and an evaluation of their use as inhibitors of different families of enzymes. The next important steps in this area of research will be to gain a better understanding of the interactions of POMs with enzymes on a structural level through an X-ray crystallographic study of enzyme–POM complexes and the analysis of structure–activity relationships. Furthermore, POMs with increased stability and in vivo half-lives have to be prepared. Surface modification may allow the targeting of POM drugs at their sites of action.

Publ.-Id: 18142 - Permalink

Multimodal MRI-PET iron oxide nanoparticles as imaging agents for cancer
Barreto, J.; Graham, B.; Stephan, H.; Spiccia, L.;
The search for new methods of cancer diagnosis is leading to the development of multimodal imaging agents that may be detected by techniques such as Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET). A new bimodal imaging agent has been prepared which can be used for dual mode detection of cancer by both MRI and PET imaging. The imaging agent consists of an azamacrocyclic ligand, 1,4-bis (2-pyridilmethyl)-1,4,7-triazacyclononane (DMP-TACN), linked to iron oxide nanoparticles through polyethylene glycol (PEG) chains (Mn ~ 600) that are attached to the nanoparticle surface by silanization. The azamacrocyclic ligands serve as complexing agents for radioactive copper (64Cu) for PET imaging, while the iron oxide nanoparticles work both as a carrier and an imaging agent for MRI. The iron oxide nanoparticles have been synthesized by thermal decomposition from iron oleate. The functionalized nanoparticles have sizes ranging between 7–10 nm, as determined by TEM, whilst Nanoparticle Tracking Analysis (NTA) experiments suggest an average hydrodynamic diameter of 50 nm. 64Cu labeling experiments revealed that the nanoparticles loaded with DMP-TACN have a labeling yield of around 10%. MRI experiments in rats showed the nanoparticles accumulate in the liver 15 min after intravenous administration. 64Cu labeling and breast tumor cell labeling studies are currently being performed using the new nanoparticles.
Keywords: iron oxide, azamacrocycle, PET/MRI cancer imaging
  • Poster
    40th ICCC (International Conference on Coordination Chemistry), 09.-13.09.2012, Valencia, Spain

Publ.-Id: 18141 - Permalink

TACN-derived ligands as highly stable biofunctionalizable chelators for copper(II)
Stephan, H.; Hesse, J.; Ruffani, A.; Viehweger, K.; Steinbach, J.;
The tridentate macrocycle 1,4,7-triazacyclononane (TACN) forms stable complexes especially with Cu(II) whereby the metal ion lying out of the plane defined by the three nitrogen atoms. The donor atoms are oriented in such a way as to maximize orbital overlap and thereby produce complexes with very high stabilities. The introduction of further donor groups on the ligand skeleton, such as pyridine units, significantly influences the thermodynamic stability as well as the kinetic inertness of the metal complexes formed. We have developed a ligand scaffold based on bis(2-pyridylmethyl)triazacyclononane (DMPTACN) [1]. This structure allows for the introduction of linker groups, such as carboxylic acids, maleimide or isothiocyanate, thereby facilitating coupling of targeting molecules (see Figure).
TACN ligands containing one or two pendant 2-picolyl arms prefer the formation of square-pyramidal coordination geometry with copper(II). A hexadentate ligand with two picoline coordination groups as well as a carboxylic functionality (DMPTACN-COOH) enforces a six-coordinate copper(II) complex having a distorted octahedral structure. It has been found that relevant peptide conjugates of this hexadentate bis(2-pyridylmethyl)-TACN-acetic acid derivative can readily form radiocopper complexes under physiologically relevant conditions and show high in vivo stability. Such radiolabeled peptides are thus attractive candidates for radiopharmaceutical applications.
We want to present the synthesis of peptide conjugates with DMPTACN derivatives capable of gastrin releasing peptide receptor (GRPR) and epidermal growth factor receptor (EGFR) targeting. Both types of receptors are overexpressed on different cancer cells. In vitro binding characteristics of [64Cu]CuII-labeled DMPTACN-peptide conjugates in GRPR and EGFR overexpressing cancer cells (PC-3, FaDu, A431) will be presented. Small animal PET studies confirmed a high extent of tumor accumulation in NMRI nu/nu mice bearing the human prostate tumor PC-3. Derived from that, it can be concluded that 64CuII complexes of DMPTACN-peptide conjugates have considerable potential for tumor imaging, since these peptide derivatives can effectively display receptor-rich tissue in vivo.
[1] G. Gasser, L. Tjioe, B. Graham, M. J. Belousoff, S. Juran, M. Walther, J.-U. Künstler, R. Bergmann, H. Stephan, L. Spiccia, Bioconjugate Chem. 2008, 9, 719-730.
Keywords: copper(II), bioconjugation, radiolabeling
  • Poster
    40th ICCC (International Conference on Coordination Chemistry), 09.-13.09.2012, Valencia, Spain

Publ.-Id: 18140 - Permalink

Development of an ion source for volatile elements
Pavetich, S.; Akhmadaliev, S.; Merchel, S.; Rugel, G.;
No abstract needed
Keywords: AMS, DREAMS, 36Cl, long-term-memory-effect, ion source, volatile elements
  • Lecture (others)
    Vortrag im Rahmen von gemeinsamen Messungen in Wien am Vienna Enviromental Research Accelerator, 20.11.2012, Wien, Österreich

Publ.-Id: 18139 - Permalink

Ion source memory in 36Cl accelerator mass spectrometry
Pavetich, S.; Akhmadaliev, S.; Arnold, M.; Aumaître, G.; Bourlès, D.; Buchriegler, J.; Golser, R.; Keddadouche, K.; Martschini, M.; Merchel, S.; Rugel, G.; Steier, P.;
Since the DREAMS (Dresden Accelerator Mass Spectrometry) facility went operational in 2011, constant effort was put into enabling routine measurements of long-lived radionuclides as 10Be, 26Al and 41Ca. For precise AMS-measurements of the volatile element Cl the key issue is the minimization of the long term memory effect [1]. For this purpose one of the two original HVE sources was mechanically modified, allowing the usage of bigger cathodes with individual target apertures. Additionally a more open geometry was used to improve the vacuum level. To evaluate this improvement in comparison to other up-to-date ion sources, a small interlaboratory comparison had been initiated.
The long-term memory effect in the Cs sputter ion sources of the AMS facilities VERA, ASTER and DREAMS had been investigated by running samples of natural 35Cl/37Cl-ratio and samples containing highly enriched 35Cl (35Cl/37Cl > 500). Primary goals of the research are the time constants of the recovery from the contaminated sample ratio to the initial ratio of the sample and the level of the long-term memory effect in the sources.
[1] R. Finkel et al., NIMB 294 (2013) 121.
Keywords: accelerator mass spectrometry, DREAMS, 36Cl, long-term-memory-effect, ion source, volatile elements
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 18.-22.03.2013, Hannover, Deutschland

Publ.-Id: 18138 - Permalink

Interlaboratory study of the ion source memory effect in 36Cl accelerator mass spectrometry
Pavetich, S.; Akhmadaliev, S.; Arnold, M.; Aumaître, G.; Bourlès, D.; Buchriegler, J.; Golser, R.; Keddadouche, K.; Martschini, M.; Merchel, S.; Rugel, G.; Steier, P.;
In 2011 the DREAMS (Dresden Accelerator Mass Spectrometry) facility [1] based on a HVE 6 MV Tandetron went operational. Since then constant effort was put into enabling routine measurements of long-lived radionuclides such as 10Be, 26Al and 41Ca. In the case of 36Cl the main focus was set on understanding and minimization of the ion source memory effect, which is the key issue for precise AMS-measurements of volatile elements like Cl and I [2,3]. For this purpose, one of the two original HVE sources was mechanically modified. The new design has a more open geometry to improve the vacuum level and a modified target loading and positioning system, which allows exchanging the individual cathode aperture with each target.
To evaluate this improvement in comparison to other up-to-date ion sources, a small interlaboratory comparison had been initiated. The long-term memory effect in the four Cs sputter ion sources of VERA [3] (Vienna Environmental Research Accelerator, NEC ion source: MC-SNICS), ASTER [4] (Accélérateur pour les Sciences de la Terre, Environnement, Risques, modified HVE SO110) and DREAMS (original HVE and modified HVE ion source) [1] had been investigated by running samples of natural 35Cl/37Cl-ratio and samples containing highly enriched 35Cl (35Cl/37Cl > 500).
Primary goals of the research are the time constants of the recovery from the contaminated sample ratio to the initial ratio of the sample and the level of the long term memory effect in the sources.

[1] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5.
[2] R. Finkel et al., Nucl. Instr. Meth. B 294 (2013) 121.
[3] M. Arnold et al., Nucl. Instr. Meth. B 294 (2013) 24.
[4] M. Martschini et al., Nucl. Instr. Meth. B 269 (2011) 3188.
Keywords: accelerator mass spectrometry, DREAMS, 36Cl, volatile elements, long-term-memory-effect, ion source
  • Lecture (Conference)
    Heavy Ion Accelerator Symposia on Fundamental and Applied Science, 08.-12.04.2013, Canberra, Australien

Publ.-Id: 18137 - Permalink

Geologische Karte des Freistaates Sachsen 1:25 000 - Blatt 5047 Freital
Alexowsky, W.; Berger, H.-J.; Horna, F.; Jaschke, I.; Kurze, M.; Renno, A.; Stanek, K.; Schneider, J. W.; Tröger, K.-A.;
Geologische Karte mit Erläuterungen des Freistaates Sachsen 1 : 25000 (Blatt 5047 Freital)
Keywords: Geology, Saxony, Freital, Döhlener Becken
  • Book (Authorship)
    Dresden: Staatsbetrieb Geobasisinformation und Vermessung Sachsen (GeoSN), 2012
    180 Seiten

Publ.-Id: 18136 - Permalink

Super-radiant coherent THz Sources: Challenges and Opportunities
Gensch, M.;
At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at the prototype THz pump probe facility at FLASH [1,2] the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses. The pulse energies are expected to exceed the 100 microJ limit at scalable repetition rates between 1 and 200 KHz (cw), thereby the coherent THz facility will represent a worldwide unique facility. Besides user experiments the laboratory is also foreseen as a test bed for THz-based electron bunch diagnostics (arrival time, bunch form, …) on cw linear accelerators. The current status of the project and planned experiments are presented.
[1] M. Gensch et. al., The new THz undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[2] U. Fruehling, M. Wieland, M. Gensch et. al., Single-shot Terahertz-field driven Streak camera, Nature Photonics 3 (2009), 523.
[3] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch et. al., Few Femtosecond Timing at 4th Generation X-ray light sources, Nature Photonics 5 (2011), 162."
  • Invited lecture (Conferences)
    Frontiers of THz Science, 05.-06.09.2012, Stanford, USA

Publ.-Id: 18135 - Permalink

Life Sciences in High THz fields: Challenges and Opportunities
Gensch, M.;
The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow-bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4th Generation X-ray Light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges for in particular the life sciences will be discussed on the example of recent pilot experiments.

[1] G.L. Carr et. al., High power terahertz radiation from relativistic electrons, Nature 420 (2002), 153.
[2] M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[3] U. Fruehling et. al., Single-Shot THz-field-driven X-ray streak camera, Nat. Photon. 3 (2009), 523.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Light sources, Nat. Photon. 5 (2011), 162.
[5] D. Daranciang et. al., Single-cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent transition radiation, Appl. Phys. Lett. 99 (2011), 141117.
Keywords: Super-radiant, coherent, THz, life sciences, X-FEL
  • Invited lecture (Conferences)
    Visegrad Retreat of the HAS-ELTE Molecular Biophysics Research Group, University of Budapest, 04.-05.01.2013, Budapest, Hungary

Publ.-Id: 18134 - Permalink

Fluid-induced magmatic and post-magmatic zircon and monazite patterns in granitoid pluton and related rhyolitic bodies
Lisowiec, K.; Bartosz, B.; Słaby, E.; Renno, A. D.; Götze, J.;
Zircon and monazite from the Stolpen granite and related rhyolitic dyke show magmatic as well as post-magmatic textures. The magmatic textures are overprinted by post-magmatic fluid interaction which is indicated by elevated contents of Y, P, Th, and U in altered zircon domains. This can be observed both in the granite and rhyolite; however these processes were less intensive in the rhyolite. Patchy zoning in primary monazite from the granite also suggests fluid-induced alterations. High Ca, Pb, and Si contents and depletion in Th, as well as porous, spongy textures in monazite from the rhyolite are results of fluid-induced alterations that caused also crystallization of cheralite. Zircon and monazite from the granite are accompanied by fluorite, Y-rich and Nb-rich minerals. The alteration of primary, magmatic accessory minerals and formation of secondary minerals is interpreted as related to magmatic fluids, which origin cannot be defined precisely on the base of the present data, however their composition suggests some mantle contribution. The presence of fluorine and CO2 which promoted the transport of some HFSE and LILE accounts for their enrichment in the accessory minerals. Fluids that affected the accessory minerals from the rhyolite show different features (silica- and Ca-enrichment) and most probably came from another source
Keywords: Zircon, monazite, Stolpen granite, electron microprobe

Publ.-Id: 18133 - Permalink

Ziegenrücker, R.;
Vorstellung des technischen Konzepts und der analytischen Möglichkeiten der Super-SIMS.
Keywords: Super-SIMS
  • Lecture (others)
    Short course - Introduction to Secondary Ion Mass Spectrometry in the Earth Sciences, 22.-26.10.2012, Potsdam, Deutschland

Publ.-Id: 18132 - Permalink

Some pitfalls in chemical sample preparation for accelerator mass spectrometry
Merchel, S.;
Sophisticated sample preparation including the determination of stable nuclides are an essential prerequisite for high-accuracy accelerator mass spectrometry (AMS) data. Improvements in the low-level regime already paid back [1], however, some pitfalls still exist or are (re-) appearing due to recent developments:
1.) As most samples prepared for 10Be-AMS need the addition of 9Be in the form of a liquid solution of known 9Be-concentration and commercial solutions contain too much 10Be, solutions from minerals originating from deep mines have been established. Special attention has recently been paid to the preparation of such a 9Be-carrier by the determination of the 9Be-value by an interlaboratory comparison. It could be shown that deviations between different labs exist, thus, it is strongly advised to have such solutions analysed at more than a single lab to prevent incorrect 10Be-results.
2.) In our approach to analyse as many radionuclides as possible in a single meteorite sample, small changes in the established chemical separation [2] have been tested. Though, the secondary formation of partially insoluble compounds of Mg and Al by the pressure digestion is strongly influenced, thus, yielding to too low 27Al-results in the taken aliquot and overall incorrect 26Al-results.
Ackn.: DREAMS-team and colleagues performing 9Be- and 27Al-measurements (BAM, GFZ, HZDR, CEREGE, TUBAF, U Cologne, VKTA). Ref.: [1] NIMB 266 (2008) 4921. [2] RCA 84 (1999) 215.
Keywords: AMS, stable nuclides, radionuclides
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 18.-22.03.2013, Hannover, Deutschland


Publ.-Id: 18131 - Permalink

Current-voltage characteristics of single-molecule diarylethene junctions measured with adjustable gold electrodes in solution
Briechle, B. M.; Kim, Y.; Ehrenreich, P.; Erbe, A.; Sysoiev, D.; Huhn, T.; Groth, U.; Scheer, E.;
We report on an experimental analysis of the charge transport through sulfur-free photochromic molecular junctions. The conductance of individual molecules contacted with gold electrodes and the current-voltage characteristics of these junctions are measured in a mechanically controlled break-junction system at room temperature and in liquid environment. We compare the transport properties of a series of molecules, labeled TSC, MN, and 4Py, with the same switching core but varying side-arms and end-groups designed for providing the mechanical and electrical contact to the gold electrodes. We perform a detailed analysis of the transport properties of TSC in its open and closed states. We find rather broad distributions of conductance values in both states. The analysis, based on the assumption that the current is carried by a single dominating molecular orbital, reveals distinct differences between both states. We discuss the appearance of diode-like behavior for the particul!
ar species 4Py that features end-groups, which preferentially couple to the metal electrode by physisorption. We show that the energetic position of the molecular orbital varies as a function of the transmission. Finally, we show for the species MN that the use of two cyano end-groups on each side considerably enhances the coupling strength compared to the typical behavior of a single cyano group.
Keywords: molecular electronics, mechanically controllable break junctions

Publ.-Id: 18130 - Permalink

Lumineszenz von Seltenen Erden in SiO2
Rebohle, L.; Prucnal, S.; Lehmann, J.; Germer, S.; Skorupa, W.;
Seltenerdbasierte MOS Emitter zeigen bei elektrischer Anregung die für Seltene Erden typischen Lumineszenzspektren. Die Anregung erfolgt über Stoßanregung heißer Elektronen, die aber gleichzeitig zu einer Degradation des Oxides führt. Die für die Elektronen erforderliche Beschleunigungsstrecke in der Größenordnung von 10-20 nm begrenzt die Dicken- und Spannungsskalierung nach unten. Mögliche Strategien zur Optimierung von Effizienz und Betriebslebensdauer beinhalten u.a. die Verwendung von Sensitizern zur Erhöhung des Anregungsquerschnittes bzw. das Einfügen einer SiON-Pufferschicht. Anwendungsmöglichkeiten liegen in der Sensorik mittels integrierter, optoelektronischer Chips.
Keywords: Elektrolumineszenz Seltene Erden MOS Struktur Ionenimplantation
  • Lecture (Conference)
    EFDS Seminar “Struktur und Eigenschaften dielektrischer Schichten für die Optik”, 07.11.2012, Jena, Deutschland

Publ.-Id: 18129 - Permalink

Schwingungsspektroskopische Untersuchungen der Sorption von Np(V) an Mineraloxiden (Al2O3, SiO2, TiO2) in wässriger Lösung.
Gröschel, A.;
Neptunium ist eines der wichtigsten Radionuklide in der Problematik der Endlagerung nuklearer Abfälle. Obwohl die Np-Konzentrationen im radioaktiven Abfall aus der Energiegewinnung gering sind, zählt es aufgrund seiner hohen Halbwertszeit (2x106 Jahre), seiner physiologischen Verfügbarkeit und seiner potenziell gesundheitlichen Schadwirkung zu den gefährlichsten Nukliden [1].

Die Sorption von Neptunium an der Wasser-Mineral Grenzfläche spielt eine wesentliche Rolle in der Abschätzung seines Migrationsverhaltens in der Umwelt. Frühere Untersuchungen zeigen, dass die Np(V) Sorption an Tonmineralen durch eine Vielzahl verschiedener Faktoren beeinflusst wird, z.B. pH-Wert, Np-Konzentration, Vorhandensein anderer Kationen und Ionenstärke. Bekannte Sorptionseigenschaften wurden vorrangig mittels Batch Versuchen erhalten [2-4]. Aussagen über die Struktur und Stöchiometrie der bei der Sorption entstandenen Neptuniumkomplexe konnten bisher nur über die Modellierung von Sorptions- und thermodynamischen Daten gewonnen werden und sind durch geeignete spektroskopische Methoden zu überprüfen [4].

Die Infrarotspektroskopie kann durch die Erfassung von charakteristischen Schwingungsfrequenzen von funktionellen Gruppen (z.B. NpO2+) Informationen zur Struktur von Molekülen bzw. von Molekülkomplexen liefern [5]. In wässrigem Milieu werden diese Untersuchungen mittels der „Attenuated Total Reflection“-Technik (ATR) durchgeführt. Somit kann die Sorption von Ionen an mineralischen Phasen in situ (z.B. in Durchfluss-experimenten) eingehend studiert werden. Durch das definierte Einstellen physikalisch-chemischer Parameter der wässrigen Lösung (pH-Wert, Ionenstärke, etc.) lassen sich definierte, naturnahe Reaktionsbedingungen schaffen.
Als Modellsystem für komplexe Tonminerale soll sich diese Untersuchung mit der Np Sorption an verschieden Mineraloxiden (z. B. Al2O3, SiO2, TiO2) beschäftigen. Die zu erhaltenden IR-Spektren sind von großer Bedeutung, um die Komplexierung der NpO2+ Kationen mit den Aluminol-, Silanol- oder Titanol- Oberflächengruppen zu verstehen und dienen als Basis für spätere Untersuchungen komplexerer Mineralsysteme.

[1] Kaszuba, J.P. et al. (1999) Environ. Sci. Technol. 33, 4427-4433.
[2] Li, W.J. et al. (2003) J. Colloid Interface Sci. 267, 25-31.
[3] Del Nero, M. et al. (2004) Chem. Geol. 211, 15-45.
[4] Tochiyama, O. et al. (1995) Radiochim. Acta 68, 105-111.
[5] Müller, K. et al. (2009) Environ. Sci. Technol. 43, 7665-7670.

Geplante Arbeiten:
FT-IR Durchflussexperimente zur Sorption von Np(V) an Al2O3, SiO2, TiO2 bei Variation sorptionsbestimmender Parameter (pH, Np(V)-Konzentration, Ionenstärke, Anwesenheit von anorganischen Liganden, z.B. Carbonat)
  • Bachelor thesis
    HTW Dresden, 2013
    50 Seiten

Publ.-Id: 18128 - Permalink

Untersuchungen der Sorptionsprozesse von Uran(VI) an Mineraloxiden bei höheren Temperaturen
Kruse, C.;
Die vorliegende Diplomarbeit entstand vom 15.04.2012 bis zum 15.10.2012 in der Abteilung Grenzflächenprozesse des Instituts für Ressourcenökologie des Helmholtz-Zentrums Dresden-Rossendorf.
Für abgebrannte Brennelemente aus Kernkraftwerken wird neben der Wiederaufarbeitung vor allem die direkte Endlagerung als Entsorgungskonzept verfolgt. Die Endlagerbehälter korrodieren während der Einlagerungszeit, sodass der uranhaltige Abfall in die Geosphäre eintreten kann und dort physikalischen und chemischen Einflüssen ausgesetzt ist. Hohe Bedeutung kommt hier der Bildung von Hydroxo- und Carbonatokomplexen des Uranyl-Ions (UO22+) zu, welche die Chemie des Urans in wässrigen Systemen (Grundwasser) dominieren.
Die einzelnen Komplexe weisen dabei je nach Zusammensetzung unterschiedliche Affinität zu natürlichen Oberflächen – wie zum Beispiel Mineraloberflächen – auf, wobei die Beschaffenheit sowohl dieser Grenzflächen als auch der Koordinationssphäre des UO22+-Ions starke Temperatur- und pH-Anhängigkeiten zeigen. In der vorliegenden Arbeit wurde vorrangig der Temperatureinfluss auf die Sorptionsprozesse des Uran(VI) an Mineraloxidoberflächen im Temperaturbereich zwischen 25 °C und 60 °C eingehend untersucht. Dies wurde mittels zweier experimenteller Ansätze bewerkstelligt: Die Infrarot-Spektroskopie liefert Informationen zu Art und Struktur der infolge Sorption gebildeten Oberflächenkomplexe, während klassische Batch-Versuche zur Betrachtung des Verteilungsgleichgewichts zwischen gelöstem und sorbiertem Uran nützlich sind. Als Modelloberflächen für natürliche Gesteine und Minerale dienten verschiedene Metalloxide wie TiO2, SiO2, α-Fe2O3, γ-Al2O3 und γ-Al(OH)3.
Die schwingungsspektroskopischen Versuche wurden im schwach sauren pH-Bereich von 5 bis 6 durchgeführt. Es konnte gezeigt werden, dass sich die Zusammensetzung der Oberflächenkomplexe in Abhängigkeit von der Temperatur stark ändert: Bei höheren Temperaturen nimmt der Anteil koordinativ gebundener Komplexe gegenüber elektrostatisch gebundenen zu. Auch zwischen den einzelnen Oxiden wurden deutliche Unterschiede festgestellt: Während z. B. bei TiO2 elektrostatisch gebundene Komplexe von U(VI) vorherrschen, sind bei α-Fe2O3 und γ-Al(OH)3 eher die koordinativ gebundenen Komplexe zu finden. Der Carbonat-Anteil in den sorbierten Komplexen nimmt mit steigender Temperatur meist ab, lediglich α-Fe2O3 zeigte hier ein abweichendes Verhalten. Auch in den Batch-Versuchen verhielten sich die untersuchten Oxide im pH-Bereich von 2,5 bis 7 recht unterschiedlich: Wurde beispielsweise bei TiO2 eine verbesserte Sorption bei höherer Temperatur gefunden, war es bei SiO2 umgekehrt, während das Verteilungsgleichgewicht zwischen Fest- und Flüssigphase bei γ-Al(OH3), γ-Al2O3 und α-Fe2O3 durch die Temperatur eher schwach beeinflusst wurde. Grundsätzlich wurde bei steigendem pH-Wert eine Verschiebung des Gleichgewichts in Richtung Festphase beobachtet, nur bei γ-Al2O3 war ein Minimum bei pH ≈ 3 zu verzeichnen.
Die im Rahmen dieser Arbeit durchgeführten Experimente konnten die Temperatur- und pH-Abhängigkeit der Sorption von U(VI)-Komplexen an verschiedenen Oxiden weiter beleuchten, aber es besteht noch ein großer Bedarf an weiteren Experimenten, insbesondere zur Untersuchung der Sorptionsvorgänge in stark saurem oder basischem Milieu.
  • Diploma thesis
    Hochschule Zittau / Görlitz, 2012
    60 Seiten

Publ.-Id: 18127 - Permalink

Spektroskopische Untersuchungen von Uran(VI)-Oberflächenprozessen in Gegenwart von Citronen- und Oxalsäure an den Modelloxiden SiO2 und α-Fe2O3
Meyer, R.;
Für die Sicherheitsanalyse eines Endlagers für radioaktive Stoffe ist es notwendig, das Verhalten von Uran im wässrigen Medium und im Boden zu kennen. Während der Wiederaufarbeitung oder eines Störfalls, einer unkontrollierten Freisetzung, kann Uran mit organischen Säuren im Boden oder im radioaktiven Abfall in Kontakt kommen. Speziationsuntersuchungen der Systeme Uran(VI)-Citronensäure und Uran(VI)-Oxalsäure in equimolarer Konzentration (c = 10 mM) und umweltrelevanter Ionenstärke (I = 0,1 M) bestätigten zum Teil bekannte Uranspezies, wurden aber auch durch noch nicht beschriebene Komplexe erweitert. Dazu wurde die Methode der ATR FT-IR Spektroskopie verwendet. Uran(VI) und Citronensäure bilden zwischen pH 2,5 und 5 den bekannten Komplex (UO2)2(cit)22-. Zwischen pH 5 und 6,5 ist der gemischte Uranyl-Citrat-Hydroxo-Komplex (UO2)2(cit)2OH3- und oberhalb von pH 6,5 der Komplex (UO2)3(cit)3(OH)58- zu finden, welche noch nicht in der Literatur beschrieben sind. Im System U(VI)-Oxalsäure wurde zwischen pH 1 bis etwa pH 5 der bekannte Komplex (UO2)(ox) bestätigt. Oberhalb von pH 5 bis pH 8 konnte eine neue Spezies festgestellt werden, der Komplex (UO2)2(ox)2OH-. Diese Urankomplexe zeigen eine erhöhte Migrationsfähigkeit aufgrund der Löslichkeit bis hin in den basischen pH Wert (pH 8). Das Sorptionsverhalten von U(VI) wurde an den Modelloxiden Hämatit und SiO2 in Anwesenheit der o. g. Liganden untersucht. Bereits eine equimolare Konzentration von U(VI) und Citronensäure (c = 20 µM) hemmt die Sorption von Uran an Hämatit durch Komplexierung im wässrigen Medium. Bei Beladung der Hämatitoberfläche mit U(VI) entstehen durch Kontakt mit Citronensäure kurzzeitig ternäre Oberflächenkomplexe, die durch stärkere Komplexierung im wässrigen Medium wieder abgebaut werden. U(VI) und Oxalsäure bilden ebenfalls kurzzeitig einen U(VI)-Oxalat-Hämatit-Oberflächenkomplex. SiO2 bildet mit U(VI) und den organischen Liganden keinen ternären Oberflächenkomplex. Eine uranbeladene SiO2-Oberfläche neigt zur Desorption und wässrigen Komplexierung des Schwermetalls durch die organischen Liganden. Die Immobilisierung von Uran durch Sorption an Hämatit oder SiO2 wird durch Anwesenheit von Citronen- oder Oxalsäure gehemmt.
For a reliable safety assessment of final repositories of nuclear waste, knowledge the behaviour, i.e. molecular reactions of uranium in aqueous solutions and at mineral-water interfaces is of major concern. During an accidental release, uranium may interact with organic acids and geologic material in the near- and far-field of the nuclear waste repository.
In this work the speciation of U(VI)-citric acid and U(VI)-oxalic acid in equimolar concentration (c = 10 mM) and at environmentally relevant ionic strength (I = 0.1 M) was investigated by ATR FT-IR spectroscopy. The obtained data confirm previously described uranium complexes, however, new species could be identified as well. Between pH 2.5 and 5 the known species (UO2)2(cit)22- was found. For the first time, the mixed uranyl-citrate-hydroxo-species (UO2)2(cit)2OH3- (pH 5 – 6.5) and (UO2)3(cit)3(OH)58- (> pH 6.5) were detected. These species have not been described in the literature so far. In the system U(VI)-oxalic acid between pH 1 to 5 the known species (UO2)(ox) was confirmed. Above pH 5 to pH 8 there was a new species identified, (UO2)2(ox)2OH-. The mixed uranyl-organic ligand-hydroxo-species increase the U(VI) migration behavior, because of their high solubility till pH 8.
The sorption behavior of U(VI) was investigated on the model oxides hematite and silicon dioxide in presence of above mentioned organic ligands. Equimolar concentration of U(VI) and citric acid (c = 20 µM) decrease uranium sorption on hematite through complexation in aqueous solution. A U(VI) loaded mineral oxide surface in contact with citric acid forms an intermediate ternary surface complex with citric acid and U(VI). The complexation in aqueous medium is stronger than the ternary surface complex, hence, U(VI) desorption occurs. U(VI) and oxalic acid forms also an intermediate ternary surface complex with hematite. Silica forms no ternary surface complex with U(VI) and the organic acids. An uranium loaded silica surface desorbs U(VI) und forms aquatic species with the organic acids. The immobilization of uranium through sorption on hematite and silicon dioxide is inhibited in the presence of citric- and oxalic acid.
  • Master thesis
    HTW Dresden, 2012
    70 Seiten

Publ.-Id: 18126 - Permalink

Schwingungsspektroskopische Untersuchung der Speziation von U(VI) in Löosungen und an der Oberfläache von Titandioxid bei hohen Temperaturen
Meusel, T.;
Ziel der Arbeit war die schwingungsspektroskopische Identifizierung und Charakterisierung der Hydrolyseprodukte des Uran(VI) in wässriger Lösung und von U(VI) Oberflächenkomplexen an der Fest-Flüssig Grenzfläche bei erhöhten Temperaturen. Diese Spezies des U(VI) können mithilfe der ATR FT-IR Spektroskopie in situ untersucht werden. Anhand charakteristischer Schwingungsfrequenzen bestimmter funktioneller Gruppen, z.B. UO22+, werden somit strukturelle Informationen über die jeweilige Bindungsform auf molekularer Ebene erhalten.

Zunächst sollte im Rahmen der Masterarbeit die bisher genutzte Durchflussapparatur für ATR FT-IR spektroskopische Untersuchungen für Experimente bei erhöhten Temperaturen weiterentwickelt werden. Bei der Verwendung der Differenzspektroskopie hat die Temperaturkonstanz eine entscheidende Bedeutung, da schon Unterschiede von einigen wenigen Grad Celsius zu Instabilitäten der Basislinie und damit zu schwer interpretierbaren bis hin zu nicht auswertbaren Infrarotspektren führen. Das von Herrn Meusel entwickelte Messsystem besteht zum Einen aus einem thermostatisierbaren Block zur Präparation und Lagerung der Proben vor und während der IR Messungen. Dabei stellen die exakte Einstellung der pH-Werte als auch die Volumenänderung der Proben durch Evaporation kritische Faktoren dar. Zum Anderen gehören ein thermostatisierbarer Metallring zum Erwärmen der direkten Umgebung des ATR-Kristalls, als auch eine Durchflusszelle mit integriertem Temperatursensor zum weiterentwickelten Aufbau. Des Weiteren wurden eine Isolation der Schlauch- und Verbindungsstücke realisiert und eine detaillierte Bedienvorschrift entwickelt. Während des Zeitraumes der Masterarbeit wurde dieser Aufbau soweit optimiert, dass eine ausreichende Grundlinienstabilität über mehrstündige Reaktionszeiträume für Untersuchungen bei Temperaturen von bis zu 70°C gewährleistet wird.

Somit konnten erstmalig die U(VI)-Hydrolysereaktionen bei erhöhten Temperaturen schwingungsspektroskopisch erfasst werden. Es wurden U(VI)-Lösungen im milli- und mikromolaren Konzentrationsbereich bei 25, 40 und 60°C untersucht. Die erhaltenen IR Spektren zeigen, dass sich mit steigender Temperatur das Hydrolysegleichgewicht zu niedrigeren pH-Werten verschiebt. Des Weiteren wurde in Lösungen mit erhöhter U(VI) Konzentration und bei Temperaturen über 25°C eine geringere Löslichkeit des U(VI) beobachtet.

Ein weiterer Aufgabenschwerpunkt der vorliegenden Masterarbeit bestand in Untersuchungen zur Komplexierung von U(VI) an der Mineraloxid-Wasser Grenzfläche in Abhängigkeit der Temperatur. Als Modellmineral wurde Titandioxid (TiO2) ausgewählt. TiO2 zeigt eine hohe thermodynamische Stabilität und wurde zudem in früheren spektroskopischen Untersuchungen am IRC intensiv hinsichtlich seiner U(VI) Retentionskapazitäten untersucht. Im Rahmen der Masterarbeit wurde der Einfluss der Temperatur bis 70°C in situ und in zeitaufgelösten Experimenten ermittelt. Im Vergleich zu Sorptionsprozessen bei 25°C verlaufen die Oberflächenreaktionen bis 50°C kinetisch beschleunigt, die U(VI) Speziesverteilung an der TiO2 Oberfläche ändert sich jedoch wenig. Anhand der erhaltenen Spektren konnten ein stark gebundener innersphärischer Komplex bei geringer Oberflächenbeladung (z.B. im frühen Sorptionsstadium) und ein weniger stark gebundener außersphärischer Komplex bei hoher Oberflächenbeladung (z.B. im späten Sorptionsstadium) nachgewiesen werden. Bei Temperaturen oberhalb 50°C deuten die Ergebnisse auf eine drastische Änderung der Sorptionsprozesse hin. Während der innersphärische Komplex vermutlich kinetisch gehemmt und die Bildung des außersphärischen Komplexes nicht mehr beobachtet wird, konnte eine neue polymere Spezies identifiziert werden. Möglicherweise handelt es sich hier um eine U(VI) Oberflächenausfällung deren spektralen Charakteristika denen von U(VI) Kolloiden in Lösung und Sorptionsprozessen an anderen Mineraloxidoberflächen (Al2O3) sehr ähneln. Die Ergebnisse belegen die entscheidende Rolle der Temperatur auf die Grenzflächenprozesse, die das Migrationsverhalten von (radioaktiven) Schwermetallen in der Umwelt maßgeblich beeinflussen.
  • Master thesis
    TU Dresden, 2011
    60 Seiten

Publ.-Id: 18125 - Permalink

Introducing ferromagnetism into semiconductors by ion beams
Zhou, S.;
In this talk, the following topics will be discussed:
(1) Why magnetic semiconductors are important;
(2) Diluted magnetic semiconductors by ion implantation: successful cases and pit-falls;
(3) Defect-induced ferromagnetism in semiconductors: ion beam irradiation provides a controllable approach.
  • Invited lecture (Conferences)
    18th International Conference on Ion Beam Modifications of Materials, 02.-07.09.2012, Qingdao, China

Publ.-Id: 18124 - Permalink

Annealing induced colossal magnetocapacitance and colossal magnetoresistance in In-doped CdCr2S4
Xie, Y.; Yang, Z.; Li, L.; Yin, L.; Hu, X.; Huang, Y.; Jian, H.; Song, W.; Sun, Y.; Zhou, S.; Zhang, Y.;
The correlation between colossal magnetocapacitance (CMC) and colossal magnetoresistance (CMR) in CdCr2S4 system has been revealed. The CMC is induced in polycrystalline Cd0.97In0.03Cr2S4 by annealing in cadmium vapor. At the same time, an insulator-metal transition and a concomitant CMR are observed near the Curie temperature. In contrast, after the same annealing treatment, CdCr2S4 displays a typical semiconductor behavior and does not show magnetic field dependent dielectric and electric transport properties. The simultaneous occurrence or absence of CMC and CMR effects implies that the CMC in the annealed Cd0.97In0.03Cr2S4 could be explained qualitatively by a combination of CMR and Maxwell-Wagner effect.

Publ.-Id: 18123 - Permalink

The influence of microorganisms on the speciation and mobilization of uranium in acid mine drainage and crystalline rock environments.
Krawczyk-Bärsch, E.;
In the uranium mine Königstein (Saxony, Germany) the uranium production was achieved by leaching the sandstone with sulphuric acid in the past. As a consequence the geochemical nature of the deposit was changed with an increase of sulphate and heavy metals, (especially uranium) in acidic, sulfate-rich waters. Since 2001 the mine has been flooded for remediation processes. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO2SO4). According to thermodynamic calculations a retention of uranium from the AMD water by forming solid uranium(VI) or uranium(IV) species will be inhibited until the pH will increase to > 4.8.
In the underground rock characterization facility tunnel "ONKALO" in Finland massive biofilms were observed attached to the fractured bedrock at a depth of 70 m. Experiments were performed in the laboratory to study the effect on the behavior of uranium in biofilms by adding uranium to the fracture water with a final uranium concentration (410-5 M) relevant for what can be expected from an injured and leaking waste canister in the far-field during a nuclear event in a HLW repository. The results obtained by analysis, microsensor measurements, TRLFS investigation, EF-TEM/EELS studies and thermodynamic calculations clearly indicate that biofilms have to be considered as microenvironments, which differ significantly from the surrounding medium. EF-TEM investigations showed that in the biofilm uranium was immobilized intracellular in bacteria by a biologically mediated uranyl phosphate formation similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O). In contrast, TRLFS studies of the contaminated fracture water showed aqueous uranium carbonate species, most likely (Ca2UO2[CO3]3), which was formed using the available high amount of carbonate from the water. The results are in agreement with the thermodynamic calculation of the theoretical predominance field of uranium species, formed in the uranium contaminated fracture water at the measured geochemical parameters.
Keywords: uranium, biofilm, TRLFS, thermodynamic calculation, EF-TEM
  • Lecture (others)
    Eingeladener Vortrag im Institute of Geology of Ore Deposits (IGEM), Laboratory of Radiogeology, Russian Academy of Science und bei SUE SIA "RADON"., 22.-23.11.2012, Moscow, Russia

Publ.-Id: 18122 - Permalink

Simultaneous probing of phase transformations in Ni-Ti thin film Shape Memory Alloy by synchrotron radiation-based X-ray diffraction and Electrical Resistivity
Braz Fernandes, F. M.; Mahesh, K. K.; Martins, R. M. S.; Silva, R. J. C.; Baehtz, C.; von Borany, J.;
Nickel-Titanium (Ni-Ti) thin film shape memory alloys (SMAs) have been widely projected as a novel material, which can be utilized in microdevices. Characterization of their physical properties and its correlation with phase transformations has been a challenging issue. In the present study, X-ray beam diffraction has been utilised to obtain the structural information at different temperatures while cooling. Simultaneously, electrical resistivity (ER) was measured in the phase transformation temperature range. The variation of ER and integral area of the individual diffraction peaks of the different phases as a function of temperature have been compared. A mismatch between the conventional interpretation of ER variation and the results of the XRD data has been clearly identified.
Keywords: Ni-Ti, shape memory alloys, thin film, XRD, electrical resistivity

Publ.-Id: 18120 - Permalink

Clarification of the sorption behavior of uranium onto mica and feldspar
Richter, C.; Stockmann, M.; Brendler, V.; Großmann, K.;
As part of long-term safety assessments for radioactive waste disposals, scenarios have to be considered, which lead to the mobilization of radionuclides from the waste and to their transport through the repository system. Any repository sites (such as Gorleben) the sedimentary overburden is an important barrier for radionuclide transport. For most radionuclides the transport is retarded by sorption on mineral phases. Mica and feldspars are major components of the Gorleben sediments. However, almost no sorption parameters are available (³t [1]) for these systems.
The WEIMAR-project (Further Development of the Smart Kd-Concept for Long-Term Safety Assessment) shall address these shortcomings. Batch sorption experiments and spectroscopic investigations will allow the assessment, the evaluation as well as the processing of sorption data for U, Np, La(III) onto muscovite and orthoclase. Generally, the amount of sorption can depend on the pH-value, ionic strength, redox potential, concentrations of the contaminant as well as of the sorbent, of complexing ligands and competing ions. All batch experiments are carried out under ambient atmosphere and with 0.01 M NaClO4 as background electrolyte.
For muscovite and orthoclase the background concentration of the sorbing elements, the tendency of wall sorption and the dissolution behavior has to be determined. For both minerals an optimal solid-to liquid ratio has to be optimized. This means that the sorption is neither too low nor too high, so the sorption has to be between 5 and 95%. All those problems will be illustrated for the case of U(VI) sorption.

This project is funded by the German Federal Ministry of Economics and Technology (BMWi) under contract number 02 E 11072B

[1] Brendler, V. et al. (2003), J. Cont. Hydrol. 61, 281-291.
  • Poster
    JCF Frühjahrssymposium 2013, 06.-09.03.2013, Berlin, Deutschland

Publ.-Id: 18119 - Permalink

Investigation of actinide(IV)-silica colloids at near-neutral pH
Husar, R.; Weiß, S.; Dreißig, I.; Hennig, C.; Brendler, E.; Zänker, H.;
Knowledge of the migration and mobility of actinides is an important issue to predict potential release of radiotoxic elements from nuclear waste repositories. Under the reducing conditions expected for the disposal zone, the tetravalent form of the actinides An (An = Th, U, Np) is predominant. Due to the low solubility at neutral pH, An(IV) are considered as immobile under these conditions. Nevertheless, high environmental mobility has been found. This fact is obviously related with the formation of An(IV) eigencolloids or the sorption on other colloids.
We report some examples of investigated colloids of An(IV) ( An= Th, U, Np): An(IV) silica colloids.
The main characteristic properties (eg. particlesize distribution, longterm monitored time stability, surfacecharge) of these colloids are presented.
Keywords: An(IV), tetravalent actinides, silica, colloids, nanoparticles
  • Poster
    PhD Seminar Schöneck, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 18118 - Permalink

Investigations into the formation of neptunium(IV)-silica colloids
Husar, R.; Weiß, S.; Zaenker, H.; Bernhard, G.;
Knowledge of the migration and mobility of actinides is an important issue to predict potential release of radiotoxic elements from nuclear waste repositories. Under the reducing conditions expected for the disposal zone, the tetravalent form of the actinides An (An = Th, U, Np, Pu) is predominant. Due to the low solubility at neutral pH, An(IV) are considered as immobile under these conditions. Nevertheless, high environmental mobility has been found. This fact is related with the formation of An(IV) eigencolloids or the sorption on other colloids.

Here Neptunium(IV) forms silicate-containing colloids when the limit of solubility is exceeded in presence of soluble silicate.
The formation and stability of Np(IV)-silica colloids was investigated by liquid LSC, ICP-MS, UV-Vis spectroscopy and light scattering
Keywords: Neptunium, tetravalent actinides, silica, colloids, nanoparticles
  • Poster
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2012), 05.-07.11.2012, Dresden, Germany

Publ.-Id: 18117 - Permalink

The potential of historic rock avalanches and man-made structures as chlorine-36 production rate calibration sites
Merchel, S.; Braucher, R.; Alfimov, V.; Bichler, M.; Bourlès, D. L.; Reitner, J. M.;
Samples from three medieval rock avalanches from the French (Le Claps, Mont Granier) and Austrian Alps (Dobratsch) and a man-made structure, i.e. the Stephansdom in Vienna, have been analysed for in-situ produced 36Cl by accelerator mass spectrometry (AMS). All four sampling sites of independently known exposure duration turned out to be not appropriate as calibration sites for the determination of the 36Cl production rate from Ca. Indeed, the determination of short exposure ages for dating rock avalanches and man-made structures by 36Cl is hindered dramatically by inheritance production, especially for samples characterized by high natCl concentrations. Generally, there are hints that the theoretical calculation of 36Cl production from epithermal and thermal neutron-capture on 35Cl is highly underestimated in all existing models, thus, asking for particular precaution if working on high-Cl samples for any project. Hence, this work evidences that potential high inheritance, even for samples reasonably shielded before exhumation, has to be considered especially when dealing with recently exposed surfaces such as glacially polished rocks, alluvial terraces, fault scarps etc.
Keywords: terrestrial cosmogenic nuclides (TCN); Cosmogenic nuclide exposure dating; Production rate, Accelerator mass spectrometry, calibration site; rock avalanche

Publ.-Id: 18116 - Permalink

Magnetic properties and crystal structure of Sr3CoIrO6 and Sr3NiIrO6
Mikhailova, D.; Schwarz, B.; Senyshyn, A.; Bell, A. M. T.; Skourski, Y.; Ehrenberg, H.; Tsirlin, A. A.; Agrestini, S.; Rotter, M.; Reichel, P.; Chen, J. M.; Hu, Z.; Li, Z. M.; Li, Z. F.; Tjeng, L. H.;
We have studied the magnetic properties and crystal structure of Sr3CoIrO6 and Sr3NiIrO6 as a function of temperature. Two characteristic temperatures, T1 = 90 K and T2 = 25 K for Sr3CoIrO6, and T1 = 85 K and T2 = 15 K for Sr3NiIrO6, were observed. Below T1 a significant increase of magnetization and below T2 a weak temperature dependence of magnetization in the field-cooled and practically zero magnetization values in the zero-field-cooled mode were detected for both compounds. The existence of Ir4+ in Sr3CoIrO6 was confirmed by an Ir-LIII x-ray absorption measurement. Magnetoelastic effects have been observed in the temperature dependence of the lattice parameters of Sr3CoIrO6 and Sr3NiIrO6. The magnetic structure of Sr3CoIrO6 in zero fields can be described as a commensurate modulated antiferromagnet with a propagation vector k = (0,0,1). Neutron powder diffraction with polarized neutrons gave evidence of short-range magnetic order, above and below the magnetic ordering temperature.

Publ.-Id: 18115 - Permalink

Order-disorder transition and magnetic quantum oscillations in the vortex state of strong type-II superconductors
Maniv, A.; Maniv, T.; Zhuravlev, V.; Bergk, B.; Wosnitza, J.; Canfield, P. C.; Sonier, J. E.;
We present results of μSR, dHvA, and SQUID magnetization measurements on borocarbide superconductors, which show a remarkable correlation between an order-disorder transition of the vortex lattice, observed in the μSR measurements, and enhanced additional damping of dHvA oscillations in the peak-effect region. It is, therefore, concluded that an important mechanism of additional damping of dHvA oscillations in the superconducting state should be associated with enhanced scattering of quasi particles by the pair potential in disordered vortex lattices.

Publ.-Id: 18114 - Permalink

The Phase of Iron Catalyst Nanoparticles during Carbon Nanotube Growth
Wirth, C. T.; Bayer, B. C.; Gamalski, A. D.; Esconjauregui, S.; Weatherup, R. S.; Ducati, C.; Baehtz, C.; Robertson, J.; Hofmann, S.;
We study the Fe-catalyzed chemical vapor deposition of carbon nanotubes by complementary in situ grazing-incidence X-ray diffraction, in situ X-ray reflectivity, and environmental transmission electron microscopy. We find that typical oxide supported Fe catalyst films form widely varying mixtures of bcc and fcc phased Fe nanoparticles upon reduction, which we ascribe to variations in minor commonly present carbon contamination levels. Depending on the as-formed phase composition, different growth modes occur upon hydrocarbon exposure: For γ-rich Fe nanoparticle distributions, metallic Fe is the active catalyst phase, implying that carbide formation is not a prerequisite for nanotube growth. For α-rich catalyst mixtures, Fe3C formation more readily occurs and constitutes part of the nanotube growth process. We propose that this behavior can be rationalized in terms of kinetically accessible pathways, which we discuss in the context of the bulk iron−carbon phase diagram with the inclusion of phase equilibrium lines for metastable Fe3C. Our results indicate that kinetic effects dominate the complex catalyst phase evolution during realistic CNT growth recipes.
Keywords: carbon nanotube, CVD, Fe, carbide, catalyst, XRD, ETEM

Publ.-Id: 18113 - Permalink

DNA origami
Keller, A.;
DNA origami: from shape to functionality
  • Lecture (others)
    Topical Problems in Theoretical Physics, 12.12.2012, Chemnitz, Deutschland

Publ.-Id: 18112 - Permalink

Nanostrukturierung von Oxidoberflächen mit Ionenstrahlen: Einfluss auf Zelladhäsion und -proliferation
Keller, A.;
  • Invited lecture (Conferences)
    12. Sitzung des Arbeitskreises Biokeramik, 16.11.2012, Aachen, Deutschland

Publ.-Id: 18111 - Permalink

A diffusion-induced transition in the phase separation of binary fluid mixtures subjected to a temperature ramp
Benczik, I.; Vollmer, J.;
Demixing of binary fluids under slow temperature ramps shows repeated waves of nucleation which arise as a consequence of the competition between generation of supersaturation by the temperature ramp and relaxation of supersaturation by diffusive transport and flow. Here, we use an advection-reaction-diffusion model to study the oscillations in the weak- and strong-diffusion regime. There is a sharp transition between the two regimes, which can only be understood based on the spatial distribution of the composition, rather than in terms of the average composition. Our results shed light on the parameter drift and secondary features observed in phase separating fluids subjected to a temperature ramp, and they bear intriguing communalities with macroscopic oscillations due to synchronization of life cycles in ageing populations.

Publ.-Id: 18110 - Permalink

A scintillator-based online detector for the angularly resolved measurement of laser-accelerated proton spectra
Metzkes, J.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Richter, C.; Schürer, M.; Sobiella, M.; Stiller, N.; Zeil, K.; Schramm, U.;
In recent years, a new generation of high repetition rate (∼10 Hz), high power (∼100 TW) laser systems has stimulated intense research on laser-driven sources for fast protons. Considering experimental instrumentation, this development requires online diagnostics for protons to be added to the established offline detection tools such as solid state track detectors or radiochromic films. In this article, we present the design and characterization of a scintillator-based online detector that gives access to the angularly resolved proton distribution along one spatial dimension and resolves 10 different proton energy ranges. Conceived as an online detector for key parameters in laser-proton acceleration, such as the maximum proton energy and the angular distribution, the detector features a spatial resolution of ∼1.3 mm and a spectral resolution better than 1.5 MeV for a maximum proton energy above 12 MeV in the current design. Regarding its areas of application, we consider the detector a useful complement to radiochromic films and Thomson parabola spectrometers, capable to give immediate feedback on the experimental performance. The detector was characterized at an electrostatic Van de Graaff tandetron accelerator and tested in a laser-proton acceleration experiment, proving its suitability as a diagnostic device for laser-accelerated protons.

Publ.-Id: 18109 - Permalink

Neue photokatalytisch aktive Verbundmaterialien zur Eliminierung von pharmazeutischen Reststoffen - Interaktion zwischen S-Layer-Proteinen und photokatalytischem System
Schmoock, C.; Börnick, H.; Worch, E.; Vogel, M.; Lehmann, F.; Bobeth, C.; Matys, S.; Kutschke, S.; Raff, J.;
Untersuchung der S-Layer-Proteine bezüglich Stabilität und Auswirkungen der Hydroxylradikale auf deren Molekülstruktur, Radikalfängereigenschaften und Verminderung der Hydroxylradikalausbeute im photokatalytischen System sowie den Gesamteinfluss auf die Hydroxylradikalbildung.
Identifizierung der Einflussgrößen und Aufklärung der Einflussgrößenordnung der S-Layer-Hüllproteine auf die Bildung von Hydroxylradikalen und deren katalytisch nutzbare Ausbeute im photokatalytischen System (Suspension mit kommerziellem ZnO). Desweiteren wurden die Auswirkungen der Hydroxylradikale auf die S-Layer-Proteine im photokatalytischen System und mit Diamantelektrode untersucht und verglichen. Es konnte die Stabilität der S-Layer-Proteine im Rahmen verschiedener bioanalytischer Untersuchungen nachgewiesen werden. So wird die Stabilität der Proteinschicht im photokatalytischen System durch Radikaleinwirkung durch intermolekulare Vernetzung erhöht. Weitere Untersuchungen zur Langzeitstabilität der Proteine gegenüber Radikalen sind geplant
Keywords: S-layer, hydroxyl radical, photocatalyst
  • Poster
    3. Clustertreffen der BMBF-Fördermaßnahmen NanoCare und NanoNature, 14.-15.01.2013, Frankfurt am Main, Deutschland

Publ.-Id: 18108 - Permalink

Nanoarchitecture of a III-V semiconductor-on-silicon platform made by ion implantation and millisecond flash lamp annealing
Prucnal, S.; Zhou, S. Q.; Ou, X.; Fritzsche, M.; Reuther, H.; Grebing, J.; Liedke, M. O.; Liedke, B.; Mücklich, A.; Helm, M.; Zuk, J.; Turek, M.; Drozdziel, A.; Skorupa, W.;
The downscaling and stressor technology of Si based devices is extending the performance of the silicon channel to its limits. One solution for the performance progress which can overcome the downsizing limit in the silicon technology is the integration of different functional optoelectronic elements within one chip. For the on-chip optical interconnections a different material has to be used, e.g. a direct band gap III-V compound semiconductor material. Besides efficient light emission many of the binary semiconductors exhibit much larger carrier mobility than silicon. This feature is crucial for a further performance enhancement of advanced devices.
Recently we have demonstrated a compact, CMOS compatible and fully integrated solution for the integration of III-V semiconductor nanocrystals with silicon technology for optoelectronic applications. They are synthesized in silicon using combined ion beam implantation and millisecond flash lamp annealing (FLA) techniques [NanoLett. 11, 2814 (2011)]. FLA appears to be the most suitable technique for this purpose. The energy budget introduced to the sample during FLA is sufficient to recrystallize silicon amorphized during ion implantation and to form III-V nanocrystals (NCs) via the liquid phase processes. Microstructural, optical and electrical properties of III-V nanostructures (InAs, GaAs and InP) formed in silicon or on SOI wafers will be presented. The evolution of the III-V nanostructures growth during FLA and the influence of the annealing parameters on theirs crystallographic orientation, shape and size will be explored. Moreover, a self-organization of the III-V nano-objects on the SOI wafers after flashing will be presented. A unique nano-swelling effect appearing during ion implantation of the SOI wafers combined with millisecond range liquid phase epitaxy leads to the evolution of the III-V semiconductors from the quantum dots to the nano-films. Conventional selective etching was used to form the n-III-V/p-Si heterojunction. Current-voltage measurements confirm the heterojunction diode formation between n-type III-V quantum dots and p-type Si substrate. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based self-powered photronic devices.
Keywords: III-V quantum dots, silicon, ion implantation, flash lamp annealing
  • Poster
    18th International Conference on Ion Beam Modifications of Materials (IBMM2012), 02.09.-07.12.2012, Qingdao, China

Publ.-Id: 18107 - Permalink

III-V compound semiconductors integrated with silicon for functional optoelectronic devices
Prucnal, S.; Facsko, S.; Mücklich, A.; Zhou, S. Q.; Ou, X.; Liedke, M. O.; Turek, M.; Zuk, J.; Skorupa, W.;
The downscaling and stressor technology of Si based devices is extending the performance of the silicon channel to its limits. The further downsizing of CMOS devices below 16 nm will need to solve some of the practical limits caused by one of the integration issues, such as chip performance, cost of development and production, power dissipation, reliability, etc. One solution for the performance progress which can overcome the downsizing limit in silicon technology is the integration of different functional optoelectronic elements within one chip.
We propose to realize a compact, CMOS compatible and fully integrated solution for the integration of III-V compound semiconductors with silicon technology for optoelectronic applications. The III-V nanostructured semiconductors are synthesized in silicon using the combined ion beam implantation and millisecond flash lamp annealing (FLA) techniques [1]. The FLA appears to be the most suitable one for this purpose. The energy budget introduced to the sample during FLA is sufficient to recrystallize silicon amorphized during the ion implantation and to form III-V nanocrystals (NCs). In this paper we will present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs and InP) formed in silicon. Conventional selective etching was used to form the n-III-V/p-Si heterojunction. The current-voltage measurement confirms the heterojunction diode formation between n-type III-V quantum dots and p-type Si. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based photronic devices.
[1] S. Prucnal, S. Facsko, Ch. Baumgart, et al. NanoLett. 11, 2814 (2011).
Keywords: Ion implantation, FLA, quantum dots, silicon
  • Lecture (Conference)
    Workshop Ionenstrahlphysik 2012 Universität Augsburg, 10.-11.07.2012, Augsburg, Germany

Publ.-Id: 18106 - Permalink

InP nanocrystals on silicon for optoelectronic applications
Prucnal, S.; Zhou, S.; Ou, X.; Reuther, H.; Liedke, M. O.; Mücklich, A.; Helm, M.; Zuk, J.; Turek, M.; Pyszniak, K.; Skorupa, W.;
One of the solutions enabling performance progress, which can overcome the downsizing limit in silicon technology, is the integration of different functional optoelectronic devices within a single chip. Silicon with its indirect band gap has poor optical properties, which is its main drawback. Therefore, a different material has to be used for the on-chip optical interconnections, e.g. a direct band gap III-V compound semiconductor material. In the paper we present the synthesis of single crystalline InP nanodots (NDs) on silicon using combined ion implantation and millisecond flash lamp annealing techniques. The optical and microstructural investigations reveal the growth of high quality (100) oriented InP nanocrystals. The photocurrent and current-voltage measurements confirm the formation of n-p heterojunction between the InP NDs and silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based self-powered electronic devices.
Keywords: heterojunction, flash lamp annealing, InP, quantum dots, ion implantation

Publ.-Id: 18105 - Permalink

Broadband Laser Cooling of Relativistic Ion Beams
Bussmann, M.; Seltmann, M.; Siebold, M.; Schramm, U.; Wen, W.; Winters, D. F. A.; Beck, T.; Rein, B.; Walther, T.; Tichelmann, S.; Birkl, G.; Sanchez-Alarcon, R. M.; Ullmann, J.; Lochmann, M.; Nörtershäuser, W.; Clark, C.; Kozhuharov, C.; Steck, M.; Dimopoulou, C.; Nolden, F.; Zhang, D.; Ma, X.; Stöhlker, T.;
We present first results on the laser cooling of relativistic ion beams at the Experimental Storage Ring, ESR, at GSI using a cw laser with a broad frequency scanning range.
Keywords: laser cooling, ion beams, relativistic, storage ring
  • Invited lecture (Conferences)
    9th International Topical SPARC Workshop, 26.-28.11.2012, Wien, Österreich

Publ.-Id: 18104 - Permalink

Fast Simulations of Fast Processes - How GPUs Give Insight Into the Interaction of Light and Matter
Bussmann, M.;
Laser-driven radiation sources can potentially help us to cure cancer or understand the dynamics of matter on the atomistic scale. With GPUs we today can simulate these sources at a frames-per-second rate. This in turn enables us to make them affordable to more users than ever before.
Keywords: gpu, picongpu, particle in cell, simulation
  • Invited lecture (Conferences)
    SC12, The International Conference for High Performance Computing, Networking, Storage and Analysis, 10.-16.11.2012, Salt Lake City, United States of America

Publ.-Id: 18103 - Permalink

Optical Free Electron Lasers - It's all a matter of dispersion
Bussmann, M.; Debus, A.; Steiniger, K.; Pausch, R.; Couperus, J. P.; Jochmann, A.; Irman, A.; Kraft, S.; Siebold, M.; Schramm, U.; Cowan, T. E.; Sauerbrey, R.;
In our talk we show that optical SASE FELs are in reach with next generation short-pulse Petawatt Lasers and low-energy electron accelerators.
We discuss the fundamental problems of optical undulators compared to standard magnetic undulators and present ideas on how to solve these problems.
We furthermore provide insight into the generation of high-energy electron beams with lasers and how this can help to reach X-ray FEL operation on a much smaller scale than with conventional accelerator techniques.
Finally, we try to highlight problems of modelling classical SASE FELs using computer simulations, that migh also occur when modelling FELs in the quantum regime.
Keywords: travelling wave thomson scattering twts electron beam laser pulse free electron laser fel
  • Invited lecture (Conferences)
    Theoretisch-Physikalisches Kolloquium, 05.11.2012, Ulm, Deutschland

Publ.-Id: 18102 - Permalink

Forward and inverse problems in fundamental and applied magnetohydrodynamics
Giesecke, A.; Stefani, F.; Wondrak, T.; Xu, M.;
This Minireview summarizes the recent efforts to solve forward and inverse problems as they occur in different branches of fundamental and applied magnetohydrodynamics. As for the forward problem, the main focus is on the numerical treatment of induction processes, including self-excitation of magnetic fields in non-spherical domains and/or under the influence of non-homogeneous material parameters. As an important application of the developed numerical schemes, the functioning of the von-K\'{a}rm\'{a}n-sodium (VKS) dynamo experiment is shown to depend crucially on the presence of soft-iron impellers.
As for the inverse problem, the main focus is on the mathematical background and some first practical applications of the Contactless Inductive Flow Tomography (CIFT), in which flow induced magnetic field perturbations are utilized for the reconstruction of the velocity field. The promises of CIFT for flow field monitoring in the continuous casting of steel are substantiated by results obtained at a test rig with a low melting liquid metal. While CIFT is presently restricted to flows with low magnetic Reynolds numbers, some selected problems of non-linear inverse dynamo theory, with possible application to geo- and astrophysics, are also discussed.
Keywords: Dynamo Magnetohydrodynamics Inverse Problems
  • European Physical Journal - Special Topics 220(2013), 9-23
    DOI: 10.1140/epjst/e2013-01793-3
  • Lecture (Conference)
    International Symposium on Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry, 25.-27.03.2013, Dresden, Germany

Publ.-Id: 18101 - Permalink

Ionenstrahlbasierte Oberflächenmodifizierung von TiAl-Werkstoffen
Kolitsch, A.; Yankov, R.;
Titanium aluminide (TiAl) alloys are attractive lightweight materials for medium-temperature (500°-750°C) structural applications including components such as jet engine and industrial gas turbine blades, turbocharger rotors and automotive engine valves. However, envisaged service temperatures for future advanced applications will have to be in the range of 750° to 1000°C, over which these alloys suffer from both oxidation and oxygen embrittlement. Therefore, development of surface-engineering techniques for preventing high-temperature environmental damage is critical in exploiting the advantages of TiAl alloys to their fullest extent.

Two efficient approaches to protecting candidate TiAl alloys from high-temperature (>750°C) environmental degradation have been developed at HZDR. The first technique involves a single step, namely treating TiAl alloy components directly by plasma immersion ion implantation (PIII) of fluorine using a mixture of difluoromethane and argon (CH2F2 + 25% Ar) as the precursor gas. The oxidation performance of the fluorine-implanted alloys has been evaluated by thermal gravimetric analysis (TGA) over the temperature range of 750° to 1050°C under conditions of both isothermal and thermal cyclic oxidation in air, and for times as long as 6000 h. This type of surface modification has been shown to produce a stable, adherent and highly protective alumina scale. The second technique involves the fabrication of a durable protective coating in a two-step process, namely formation of a thin aluminum-rich TiAl layer (Ti-60Al) by chemical vapor deposition (CVD) employing a mixture of inorganic precursors, followed by PIII of fluorine. Subsequent long-term oxidation exposures to air at 900°C of a GE 4822 alloy (Ti-48Al-2Cr-2Nb; alloy composition qualified for aerospace applications) have shown that the coating so developed is able to successfully prevent oxidation damage to the base material while maintaining up to 90% of its initial mechanical properties (strength and ductility).
Keywords: Titanium; Titanium-base alloys; Oxidation protection; Fluorine
  • Invited lecture (Conferences)
    3. Dresdner Werkstoffsymposium 2012, 06.-07.12.2012, Dresden, Germany

Publ.-Id: 18100 - Permalink

Enhancing the High Temperature Capability of Ti-Alloys
Donchev, A.; Schutze, M.; Kolitsch, A.; Yankov, R.;
Titanium is a widely used structural material for applications below approximately 500 degrees C but right now it cannot be used at higher temperatures. Titanium forms a fast growing rutile layer under these conditions. Furthermore enhanced oxygen uptake into the metal subsurface zone leads to embrittlement which deteriorates the mechanical properties. To overcome this problem a combined Al- plus F-treatment was developed. The combination of Al-enrichment in the surface zone so that intermetallic TixAly-layers are produced which form a protective alumina layer during high temperature exposure plus stabilization of the Al2O3-scale by the fluorine effect led to significantly improved resistance against increased oxidation and embrittlement in high temperature exposure tests of several Ti-alloys. In this paper, the experimental procedures and achieved improvements are described. The results will be discussed for the use of Ti-alloys at elevated temperatures.
Keywords: Titanium; Titanium-base alloys; Oxidation protection; Fluorine
  • Steel Research International 83(2012)10, 938-942
    DOI: 10.1002/srin.201100281
  • Invited lecture (Conferences)
    Dresdner Werkstoffsymposium 2012, 06.-07.12.2012, Dresden, Germany

Publ.-Id: 18099 - Permalink

Ladungsträger-Tiefenprofilierung an ultra-flachen pn-Übergängen
Schmidt, B.; Philipp, P.; Zier, M.; Zimmermann, L.;
Die Stufenweise Oxidationsprofilierung (SWOP) wurde zur Ladungsträgertiefenprofilierung an Bor-implantierten Silizium eingesetzt. Das Meßverfahren basiert auf einer alternierenden elektrischen Messung des Schichtwiderstandes mit van-der-Pauw (VDP)-Strukturen zwischen jeweils einem Si-Schichtabtrag durch elektrochemische anodische Oxidation. Es konnte gezeigt werden, dass die SWOP-Profile sehr gut mit SIMS-Referenzprofilen übereinstimmen und eine Tiefenauflösung von 1 nm sowie eine Nachweisgrenze 1•1016cm-3 erreicht wird.
Keywords: ion implantation, van der Pauw structures, sheet resistance measurement, charge carrier depth profiles, anodic oxidation

Publ.-Id: 18098 - Permalink

Control over surface and bulk atomistic processes in carbon-transition metal films
Abrasonis, G.;
Control over surface and bulk atomistic processes in carbon-transition metal films
  • Lecture (others)
    Seminars at TU Chemnitz Topical Problems in Theoretical Physics (WS11/12), 25.01.2012, Chemnitz, Germany

Publ.-Id: 18097 - Permalink

Low temperature plasma nitriding induced decomposition in AISI 304L austenitic stainless steel
Abrasonis, G.; Martinavicius, A.; Scheinost, A. C.; Danoix, R.; Danoix, F.; Stinville, J. C.; Templier, C.; Gemming, S.; Möller, W.;
Plasma nitriding of austenitic stainless steel (ASS) at moderate temperature (~400°C) produces a modified near surface layer, often called S phase, which shows significantly improved tribological properties, conserved or improved (electro)chemical properties and induced ferromagnetism. Here, the study of the nature of the S phase in nitrided ASS 304L is presented. A combination of global probes (X-ray diffraction (XRD), nuclear reaction analysis, glow discharge optical emission spectroscopy) and local probes (field ion microscopy, extended x-ray absorption fine structure spectroscopy) is employed to reveal the phase structure, morphology, atomic ordering and chemical environment. While XRD shows only the presence of the presence of the S phase, the local analysis techniques
consistently demonstrate the heterogeneous nature of the nitrided layer. It consists of nanometric CrN precipitates embedded in a Fe4N-like matrix. The size of the CrN precipitates is found to be larger at the surface than at the nitrided layer-steel interface. Moreover, X-ray spectroscopic investigations disclose three different intermetallic distances and different chemical environments for Fe, Cr and Ni, accompanied with a large static disorder. These findings suggest that the presence of the interstitial nitrogen can destabilize the homogeneous matrix element distribution in ASS 304L even at the rather low temperature of 400°C. Based on the heterogeneous nature of the S phase revealed in plasma nitrided ASS 304L, an alternative insight into its remarkable combination of properties is presented.
Keywords: plasma nitriding austenitic stainless steel
  • Poster
    13th International Conference on Plasma Surface Engineering, 10.-14.09.2012, Garmisch-Partenkirchen, Germany

Publ.-Id: 18096 - Permalink

Stability of the electrically induced flow between two hemispherical electrodes
Shatrov, V.; Gerbeth, G.;
The stability of the steady laminar flow driven by the meridional electromagnetic force due to an electric current from a hemispherical electrode to a hemispherical cavity surface is studied using a multi-domain pseudospectral method. The analysis is performed for a broad ratio of electrode and cavity radii. The most unstable azimuthal wave number is found as m=4, which differs from literature results for the flow in a cone with a point-electrode where the most unstable wave number was found as m=0. In the presence of an external uniform magnetic field the fluid rotates in azimuthal direction. Already for a rather low strength of the external magnetic field, the meridional flow in the main toroidal eddy changes its direction from counter-clockwise to clockwise
Keywords: meridional electromagnetic
  • Magnetohydrodynamics 48(2012)3, 469-483

Publ.-Id: 18095 - Permalink

Atom probe tomography characterization of the decomposition in austenitic stainless steels 304L and 316L induced by low temperature plasma nitriding
Martinavičius, A.; Danoix, R.; Danoix, F.; Abrasonis, G.; Drouet, M.; Templier, C.; Hannoyer, B.;
Nitriding of austenitic stainless steel (ASS) at moderate temperatures (~400°C) leads to the formation of a modified layer which shows increased hardness and induced magnetism without compromising the corrosion resistance. In this study, a three-dimensional atomic characterization of plasma nitrided ASS 304L and 316L has been achieved with atom probe tomography (APT). While only a single phase, usually called the S phase or expanded austenite, can be detected by the X-ray diffraction, the APT reveals the formation of nanometric CrN precipitates. The precipitates have irregular oblate-spheroid-like shape. Small CrN clusters of only few nanometers in diameter have been observed close to the nitrided layer-steel interface as well as close to the surface. The regions which have been under nitrogen supersaturated conditions during the entire process, i.e. the regions close to the surface, exhibit also larger precipitates with a diameter more than 10 nm. In addition, preferential precipitation of CrN precipitates at grain boundaries and dislocations has been observed. These observations suggest that incorporation of large amounts of N provides strong driving force for CrN formation even at 400°C, a rather low temperature.
Keywords: austenitic stainlees steel nitriding atom probe tomography CrN precipitation
  • Lecture (Conference)
    13th International Conference on Plasma Surface Engineering - PSE 2012, 10.-14.09.2012, Garmisch-Partenkirchen, Germany

Publ.-Id: 18094 - Permalink

Ion-assisted deposition of carbon-transition metal nanocomposite thin films
Abrasonis, G.; Krause, M.; Gemming, S.; Bilek, M. M. M.; Möller, W.;
Ion assistance during film growth provides unique opportunities (i) toinfluence the film microstructure due to energy transfer and (ii) impose the directionality due to momentum transfer effects. Ion induced displacements occur in a thin surface layer of the growing film where they increase the atomic mobility. Therefore the ion assistance can be used to control the phase separation occurring during co-deposition of materials with low miscibility, and hence the resulting nanocomposite morphology. As the structure at the nanoscale determines the properties at the macroscale, the control over the microstructure is a key issue in nanomaterials science. In this contribution, a comparison of the growth-structure relationship of carbon-transition metal (Ni, Cu) nanocomposite films grown by ion beam assisted deposition (IBAD) and pulsed filtered cathodic vacuum arc (PFCVA) is reported. The formation of elongated nickel nanoparticles is strongly promoted by temperature and ion beam assistance. Moreover, the metal nanocolumns no longer align with the advancing surface, as in the case without ion assistance, but with the incoming ions. Although the energy in PFCVA is carried by film forming ions themselves while for IBAD it is delivered by a separate ion beam, both deposition techniques show a window of deposition conditions where the ion assistance leads to the formation of regular nanopatterns. As the dominating factors (ion induced ballistic effects) are of physical origin, this approach might be applicable to other materials systems with limited solubility.
Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379, and by DEEWR, Australia, in the framework of Endeavour Research Fellowship (Contract No. 837_2008), is gratefully acknowledged.
Keywords: ion beam assisted deposition ionized PVD nanocomposite
  • Lecture (Conference)
    13th International Conference on Plasma Surface Engineering - PSE 2012, 10.-14.09.2012, Garmisch-Partenkirchen, Germany

Publ.-Id: 18093 - Permalink

Ion-guided Phase Separation of Carbon-Nickel Composite Films during Ion Beam Assisted Deposition: 3D Sculpting at the Nanoscale
Abrasonis, G.; Krause, M.; Oates, T. W. H.; Mücklich, A.; Facsko, S.; Baehtz, C.; Shalimov, A.; Gemming, S.;
Ion assistance during film growth provides unique opportunities to influence the microstructure due to energy transfer and imposed directionality. During nanocomposite film growth at low temperatures, phase separation occurs at the growing film surface. Ion-assistance is a key parameter to control the surface processes during multiphase film growth, and hence the resulting nanocomposite morphology. A systematic study of ion irradiation as a pure energy and momentum transfer agent in the context of surface diffusion assisted phase separations is, however, lacking. Here the influence of low energy (50-130 eV) assisting Ar+ ion irradiation on the morphology of C-Ni thin films will be reported. Ion-beam assisted deposition (IBAD) promotes the columnar growth of carbon encapsulated metallic nano-columns at low deposition temperatures for Ar+ ion energy ranges of 50-100 eV. Moreover, the momentum transfer results in a tilting of the columns relative to the film surface. The potential to grow complex matrix encapsulated metallic structures such as chevrons is demonstrated. Furthermore, a window of deposition conditions will be reported where the ion assistance leads to the formation of regular 3D nanopatterns with well-defined periodicity. The influence of such anisotropic film morphology on the optical properties is highlighted.
Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379, is gratefully acknowledged.
  • Lecture (Conference)
    AVS 59th International Symposium & Exhibition, 28.10.-02.11.2012, Tampa, Florida, United States of America

Publ.-Id: 18092 - Permalink

Optical velocity measurements of electrolytic boundary layer flows influenced by magnetic fields
König, J.; Neumann, M.; Mühlenhoff, S.; Tschulik, K.; Albrecht, T.; Eckert, K.; Uhlemann, M.; Weier, T.; Büttner, L.; Czarske, J.;
Magnetic fields are applied to electrically conducting fluids, in order to influence electrochemical processes by leveraging the magnetohydrodynamic effect. Various phenomena, e.g. on electrodeposited metal layers, were observed, which can be attributed to forced convections. To provide information about acting forces, the laser Doppler velocity profile sensor was applied to measure the transition layer of a Lorentz force influenced backward-facing step and the velocity boundary layer during copper-deposition. With this sensor, the electrolyte convection is revealed within < 500 μm of an electrode with a spatial resolution down to 15 μm. The interaction of buoyant, Lorentz and magnetic field gradient force is studied by measuring the velocities down to 10 μm in front of the cathode. It is shown that complex electrolyte convection is induced inside the concentration boundary layer, which varies not only in time but also in its structure, depending on the present forces and their temporal influence. At inhomogeneous magnetic field configurations, the magnetic field gradient force dominates the velocity boundary layer at steady state and transports electrolyte toward regions of high magnetic gradients, where maximum deposit thicknesses are found. In this way, the measurements confirm the predicted influence of the magnetic field gradient force on the structuring of copper-deposits.
Keywords: Laser Doppler Velocity Profile Sensor, Particle Image Velocimetry, backward facing step, copper deposition

Publ.-Id: 18091 - Permalink

The two-phase flow at gas-evolving electrodes: bubble-driven and Lorentz-force-driven convection
Weier, T.; Landgraf, S.;
We observe electrolysis with gas evolution, a phenomenon occurring in a number of industrial scale electrochemical processes. Here, water electrolysis takes place in a small undivided electrolysis cell consisting of vertical electrodes embedded in a larger glass vessel which contains a dilute NaOH solution. Fluid flow velocities are measured by Particle Image Velocimetry with fluorescent tracers, while size distribution and velocities of the bubbles are determined from bubble shadow images obtained with a high speed camera. Coalescence phenomena are observed in the flow and explain the relatively wide distribution of bubble sizes.
Depending on the gap width and the current density, bubbles ascending near the electrodes form two discernible bubble curtains (low average void fraction, wide gaps) or a flow profile more akin to a channel flow (high average void fraction, small gaps). If the flow consists of separate bubble curtains, instabilities develop not unlike to that of a single phase wall jet.
Finally, the influence of different wall parallel Lorentz force configurations on the velocity distribution in the cell is investigated. These Lorentz forces are generated by permanent magnets mounted behind the electrodes. Depending on gap width, current density, and magnet configuration, liquid phase velocities can be increased by several times compared to the baseline case.
Keywords: water electrolysis, Lorentz force, Particle Image Velocimetry

Publ.-Id: 18089 - Permalink

Numerical simulation of the Tayler instability in liquid metals
Weber, N.; Galindo, V.; Stefani, F.; Weier, T.; Wondrak, T.;
The electrical current through an incompressible, viscous and resistive liquid conductor produces an azimuthal magnetic field that becomes unstable when the corresponding Hartmann number exceeds a critical value in the order of 20. This Tayler instability, which is not only discussed as a key ingredient of a non-linear stellar dynamo model (Tayler-Spruit dynamo), but also as a limiting factor for the maximum size of large liquid metal batteries, was recently observed experimentally in a column of a liquid metal.
On the basis of an integro-differential equation approach, we have developed a fully three-dimensional numerical code, and have utilized it for the simulation of the Tayler instability at typical viscosities and resistivities of liquid metals. The resulting growth rates are in good agreement with the experimental data. We illustrate the capabilities of the code for the detailed simulation of liquid metal battery problems in realistic geometries.
Keywords: Tayler instability, Biot-Savart, liquid metal battery

Publ.-Id: 18088 - Permalink

Volcanic glass under fire - A comparison of three complementary analytical methods
Eder, F. M.; Neelmeijer, C.; Pearce, N. J. G.; Bichler, M.; Sterba, J. H.; Ntaflos, T.; Merchel, S.;
The two obsidian sources from the island of Melos (Greece), Agia Nychia and Demenegakion, are chemically characterized by three complementary analytical techniques. Ion beam analysis (IBA) comprising of particle induced X-ray emission (PIXE) and particle induced gamma-ray emission (PIGE), neutron activation analysis (NAA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are applied to the same set of geological obsidian samples.
The combination of methods allows a more complete characterisation of obsidian sources and reveals a highly specific chemical composition, the so-called chemical fingerprint. This multi-methodical approach checks also the self-consistency of the analytical results and shows the most reliable and characteristic key elements Co and Sc, but also Fe, Ca and Ti of Melos obsidian deposits. NAA contributes the largest number of reliable elements to the most unambiguous chemical fingerprint comprising in total of 41 elements. Therefore, NAA is the most suitable analytical method for a clear identification of Melos obsidian deposits.
Moreover, the accuracy of methods is demonstrated by the excellent correspondences (calculated correlation coefficient R2=1.00 for IBA and NAA, R2=0.99 for LA-ICP-MS) between determined analytical results obained by IBA, NAA and LA-ICP-MS and certified values of the reference glass BAM-S005B.
Keywords: PIXE, PIGE, neutron activation analysis, LA-ICP-MS

Publ.-Id: 18087 - Permalink

Dual-Plane Ultrasound Flow Measurements in Liquid Metals
Büttner, L.; Nauber, R.; Burger, M.; Räbiger, D.; Franke, S.; Eckert, S.; Czarske, J.;
An ultrasound measurement system for dual-plane, two-component flow velocity measure-ments especially in opaque liquids is presented.
Present-day techniques for measuring local flow structures in opaque liquids disclose consid-erable drawbacks concerning a line-wise measurement of single ultrasound probes. For study-ing time-varying flow patterns, conventional ultrasound techniques are either limited by a time-consuming mechanical traversing or by the sequential operation of single probes.
The measurement system presented within this paper employs 4 transducer arrays with a total of 100 single elements which allows for a flow-mapping without mechanical traversing. A high frame rate of several 10 Hz has been achieved due to an efficient parallelization scheme using time division multiplex realized by a microcontroller-controlled electronic switching matrix.
The functionality and capability of the measurement system is demonstrated at a liquid metal flow at room temperature inside a cube driven by a rotating magnetic field (RMF). For the first time, the primary and the secondary flow have been studied in detail and simultaneously using a configuration with two crossed measurement planes. The experimental data confirm predictions made by numeric simulation. After a sudden switching on of the RMF inertial oscillations of the secondary flow were observed by means of a time-resolved measurement with a frame rate of 3.4 Hz.
The experiments demonstrate that the presented measurement system is able to investigate complex and transient flow structures in opaque liquids. Due to its ability to study the tem-poral evolution of local flow structures, the measurement system could provide a considerable progress for fluid dynamics research, in particular for applications in the food industry or liq-uid metal technologies.
Keywords: ultrasound Doppler method, ultrasound sensor arrays, flow measurements, liquid metal flow, magnetohydrodynamics

Publ.-Id: 18086 - Permalink

Novel ultrasound array measurement system for flow mapping of complex liquid metal flows
Nauber, R.; Burger, M.; Büttner, L.; Franke, S.; Räbiger, D.; Eckert, S.; Czarske, J.;
In magnetohydrodynamics, model experiments are commonly conducted to investigate the interaction between magnetic fields and electrically conductive fluids. The available flow instrumentation for opaque fluids usually lacks the ability to capture and visualize a velocity field in one shot. We present a multidimensional ultrasound array Doppler velocimeter that employs multiple line arrays of transducers and allows to resolve small scale structures in complex flows. The system archives a lateral resolution up to 3mm, an axial resolution of approx. 1:4mm and frame rates up to 30Hz in metal melts at room temperature. A flexible sensor arrangement allows for various measurement configurations, e.g. four planes can be measured simultaneously with one velocity component, two planes with two components or two lines with three components. We present an experiment in a square shaped container driven by a rotating magnetic field and results of a model experiment for continuous steel casting. The measurement system has proven to be a powerful tool for research in magnetohydrodynamics.

Publ.-Id: 18085 - Permalink

Carrier dynamics in graphene near the Dirac point
Helm, M.; Winnerl, S.; Mittendorff, M.; Schneider, H.; Winzer, T.; Malic, E.; Knorr, A.; Orlita, M.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.;
We discuss pump-probe experiments on multilayer graphene over a wide range of photon energies (10-250 meV), hereby unveiling the relevant electronic relaxation mechanisms. A slowing down is observed for smaller photon energies and lower temperature, in accord with microscopic calculations. Remarkably we observe a sign change of the probe signal, when the photon energy becomes smaller than twice the Fermi energy. This crossover from induced bleaching to induced absorption is related to the interplay between inter- and intraband absorption. Applying an additional magnetic field we have recently measured the relaxation dynamics between Landau levels, showing a strong dependence on the circular polarization of the light.
Keywords: graphene, infrared, terahertz, free electron laser, relaxation, absorption
  • Invited lecture (Conferences)
    Joint Dresden-Japan Workshop on Molecular Scale and Organic Electronic Materials, 11.-13.12.2012, Dresden, Deutschland

Publ.-Id: 18084 - Permalink

Cfd simulation of flashing boiling flow in the containment cooling condenser system of kerena reactor
Liao, Y.; Lucas, D.; Krepper, E.; Rzehak, R.;
The KERENA™ reactor is a generation III+ BWR concept, which was originally proposed by AREVA and is currently being developed jointly by AREVA and German utility E.ON (AREVA, 2010). It aims to achieve a cost competitive plant with enhanced safety features and an optimal BWR balance of active and passive safety systems. The containment cooling condensers (CCC) belong to such kind of passive features, which require neither electric power nor switching operations to begin functioning. The CCC unity is connected to a shielding/storage pool, which is located above it, via an inlet to the lower end and a discharge line at the upper end. In case of overpressure or overtemperature, steam in the containment will condense at the outside wall of the condensers. Heat released by steam will be transferred to the cooling water inside the tubes. As it is heated, the cooling water will remove heat from the containment to the water of the shielding/storage pool through a natural circulation.

The performance of the complete CCC system has been investigated experimentally on the full-scale INKA test facility of AREVA in Karlstein (Leyer and Wich, 2012). During the experiment, strong flow instability or water hammer caused by the formation and subsequent destruction of steam bubbles inside the discharge line was observed. In other words, the formation of steam will have a significant influence on the safety operation and heat removal capacity of the system, which requires further investigation. In this case, the mechanism of phase change from water to steam is different from that of the traditional boiling as a result of wall heating. Due to the elevation difference between the CCC and the upper end of the discharge line, which is about 12 m, the drop of hydrostatic pressure along the discharge line exceeds 1bar. The formation of steam is a result of depressurization instead of wall-heating, which is called flashing boiling in contrast to the traditional boiling.
Keywords: KERENA™ reactor, Containment Cooling Condensers (CCC), Flashing boiling, CFD simulation
  • Open Access LogoContribution to proceedings
    21st International Conference On Nuclear Engineering, 29.07.-02.08.2013, Chengdu, China
    Proceedings of the 21st International Conference On Nuclear Engineering
  • Lecture (Conference)
    21st International Conference On Nuclear Engineering, 29.07.-02.08.2013, Chengdu, China

Publ.-Id: 18083 - Permalink

Cfd simulation of water evaporation under pressure release transients
Liao, Y.; Lucas, D.; Krepper, E.; Rzehak, R.;
Water evaporation (flashing) inside a vertical pipe under pressure release transients is investigated by CFD simulations based on the Eulerian two-fluid model. Important assumptions made in the current work are: a) constant bubble diameter; b) no nucleation and c) mass transfer caused only by thermal heat transfer between phases. The predicted evolution of steam volume fraction and water temperature is compared with the measured one, respectively. The results show that the applied model setup in principle can reproduce the flashing process. Whether the evaporation of superheated water can start depends on the initial guess of steam volume fraction and especially the presumed bubble size. A large initial steam volume fraction and a small bubble size will favor the inception of evaporation. Once the flashing is successfully triggered, the maximum evaporated steam is determined by the pressure drop ultimately. Furthermore, the increase of steam volume fraction per unit evaporated mass reduces drastically at high pressure levels due to a large steam to water density ratio. As a result, a relatively small value has to be presumed for bubble size under high pressure conditions in order to launch the evaporation. In addition, the predicted maximum steam volume fraction at a pressure of 65bar is much lower than the measured one. In this case besides the interphase thermal heat transfer consideration of nucleation and bubble growth due to mechanical non-equilibrium across the interface might be helpful.
Keywords: Flashing, Evaporation, CFD, Two-Fluid Model, Mono-dispersed
  • Open Access LogoContribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH15, 12.-17.05.2013, Pisa, Italy
  • Lecture (Conference)
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH15, 12.-17.05.2013, Pisa, Italy

Publ.-Id: 18082 - Permalink

Few Femtosecond level electron bunch diagnostic at quasi-cw electron accelerators
Green, B.; Kuntzsch, M.; Kovalev, S.; Al-Shemmary, A.; Hauser, J.; Findeisen, S.; Schneider, C.; Kaya, C.; Stojanovic, N.; Michel, P.; Gensch, M.;
At the SRF based prototype cw accelerator ELBE a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1-200 KHz regime and with pC bunch charge and repetition rates of 13 MHz, is currently being constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class lasers and the generation of broad and narrow bandwidth coherent THz pulses. Discussed here are ideas for novel online diagnostics of the electron bunch properties (e.g. arrival time and bunch form) based on the time and frequency domain analysis of the emitted coherent THz radiation, but also based on direct measurements by e.g. electro-optic sampling. The suitability of ELBE as a testbed for diagnostic of future cw X-ray photon sources (e.g. energy recovery linacs) will be discussed.
  • Poster
    77. Jahrestagung der DPG und DPG Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18081 - Permalink

TELBE - the super-radiant THz test-facility at ELBE
Green, B.; Kovalev, S.; Hauser, J.; Kuntzsch, M.; Al-Shemmary, A.; Schneider, H.; Winnerl, S.; Seidel, W.; Zvyagin, S.; Wall, S.; Radu, I.; Eng, L. M.; Lehnert, U.; Helm, M.; Stojanovic, N.; Heberle, J.; Cavalleri, A.; Michel, P.; Gensch, M.;
It has been shown recently that relativistic electron bunches can be utilized for the generation of super-radiant coherent THz radiation by one single pass through an undulator, bending magnet, or CDR/CTR screens. However, the high THz fields have all been achieved at large accelerators that allow for high electron beam energies. A crucially important research topic for the next years at the HZDR is therefore to investigate whether an equally fine control over highly charged electron bunch form can be routinely achieved in a low electron beam energy accelerator like ELBE. If successful this development would allow the generation of high field THz fields by linear accelerators at considerably reduced cost. Given stable operation can be provided, TELBE, could also become a world-wide unique research facility for high field THz science. The current status and an outlook on future developments are presented.
  • Poster
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18080 - Permalink

Novel Drift compensation for a femtosecond laser system at a quasi-cw electron accelerator
Green, B.; Kuntzsch, M.; Kovalev, S.; Gensch, M.;
A method for electron beam/THz to femtosecond (fs) - laser synchronization drift correction at the quasi-cw linear electron accelerator ELBE is presented, which is utilizing THz radiation generated by a CDR/CTR screen and an undulator respectively. Measurements of these pulses will allow for compensation of slow drifts in the arrival time on millisecond timescales between the THz and the fs-laser pulses. The method requires two electro-optic detection setups which allow for the sampling of a single THz pulse, at two different working points. Given a consistent pulse shape these two data points can provide information on the sign of the arrival time drift relative to the laser. This information can be used both for providing feedback on fs laser arrival time in a potential THz time domain experiment as well as the electron bunch arrival time in the accelerator.
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Germany

Publ.-Id: 18079 - Permalink

Driving magnetization dynamics via mid-infrared phonon excitation
Mährlein, S.; Radu, I.; Gensch, M.; Kimel, A.; Kalashnikova, A.; Kampfratth, T.; Wolf, M.;
The fundamental interactions between electrons, spins and the lattice of a solid have always been subject of large scientific interest. Here, we investigate the coupling between phonons and the ordered spin system of ferrimagnetic oxides on ultrashort time scales, an elusive and actively debated issue of modern ultrafast magnetism.
For this purpose, we use intense electromagnetic pulses at terahertz (THz) frequencies, from both table-top and accelerator-based sources, to resonantly excite a specific phonon mode. The impact of this vibrational excitation on the spin system is monitored by detecting the transient Faraday rotation of a subsequently arriving optical probe pulse. As such, we obtain access to the magnetization dynamics with a time resolution of down to 10fs.
These mode-selective pumping experiments show a response of the spin system on a timescale of few picoseconds and thus indicate an (ultra)fast spin-lattice interaction. The possible underlying coupling mechanisms will be discussed.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18078 - Permalink

Analysis and Applications of a Two-Fluid Multi-Field Hydrodynamic Model for Churn-Turbulent Flows
Montoya, G.; Liao, Y.; Lucas, D.; Krepper, E.;
Today Computational Fluid Dynamic (CFD) codes are widely used for industrial applications in the case of single phase flows as in automotive or aircraft industries, but multiphase flow modeling had gain an increasing importance in the last years. Safety analyses on nuclear power plants require reliable prediction on steam-water flows in case of different accident scenarios. This is particularly true for passive safety systems as the GEKO component of the KERENA reactor. Here flashing may occur in the riser. In such a case high gas volume fractions and the churn-turbulent flow regime may occur. So far, the codes for the prediction of churn-regime have not shown a very promising behavior in the past. In this paper, a two-fluid multi-field hydrodynamic model has been developed based in the Euler-Euler framework. The main emphasis of this work has been on the modeling and applicability of various interfacial forces between dispersed gaseous phases and the continuous liquid, as well as bubble-bubble interactions, and the evolution of different bubble sizes in an adiabatic vertical pipe inside the churn-turbulent flow regime. All the expected mechanistic models that intervene in this flow pattern have been taken into account including drag force, wall force, lift force, turbulent dispersion, and bubble induced turbulence. Bubble breakup and coalescence has been defined (Liao et al., 2011), and in order to design a polydispersed model related to reality, the inhomogeneous MUSIG approach (Krepper et al., 2008) has been used to defined an adequate number of bubble size fractions, each with their own velocity field. Based on these models, a series of simulations were made on the framework of ANSYS CFX 14.0, and all of the calculations were further validated with experimental data extracted from the TOPFLOW facility at the Helmholtz-Zentrum Dresden-Rossendorf. Different water and gas flow rates were used inside the churn-turbulent flow regime, as well as for the transition from bubbly to churn flow. The calculated cross-section averaged bubble size distributions, gas velocities, and time averaged radial profile for the gas fraction have shown a promising agreement with the experimental data. Nevertheless there are also clear deviations which indicate shortcomings of the present modelling. In order to further improve the modeling of this flow regime, a discussion based on the results will be used to shown a series of limitations of the actual modeling and possible solutions to be implemented in future works.

Best Paper Award
Keywords: Computational, Fluid, Dynamics, CFD, churn-turbulent, flow, GEKO, KERENA, safety, nuclear, Euler-Euler, MUSIG, TOPFLOW, churn
  • Contribution to proceedings
    21st International Conference on Nuclear Engineering - ICONE 21, 29.07.-02.08.2013, Chengdu, China
    Proceedings of the 21st International Conference on Nuclear Engineering (ICONE 21)
  • Poster
    21st International Conference on Nuclear Engineering - ICONE 21, 29.07.-02.08.2013, Chengdu, China
  • Lecture (Conference)
    21st International Conference on Nuclear Engineering - ICONE 21, 29.07.-02.08.2013, Chengdu, China

Publ.-Id: 18077 - Permalink

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