Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

31629 Publications
Hydrodynamic characterization of transient multiphase flows in monolithic structures using ultrafast X-ray tomography
Schäfer, T.; Wagner, M.; Hampel, U.; Weiß, M.; Meitzner, C.; Lange, R.;
Detailed hydrodynamic characterization of transient multiphase flows is significant in the field of process engineering. The ultrafast X-ray tomography system ROFEX was used to analyze the complex transient multiphase flow and its hydrodynamic characteristics in monolithic structures. Introducing the applied tomography system and the particular experimental set-up, selected experiments and investigations will be explained. Furthermore several methods for the computation and visualization of gas and liquid phase distribution, the calculation of liquid holdup and the characterization of the occurring flow structures will be presented. As a conclusion a selection of achieved results and the derivable information will be summarized.
Keywords: ultrafast X-ray tomography; multi-phase flow; flow structure; flow properties; monolith
  • Contribution to proceedings
    7th World Congress on Industrial Process Tomography, WCIPT7, 02.-05.09.2013, Kraków, Poland
    Proceedings of WCIPT7
  • Lecture (Conference)
    7th World Congress on Industrial Process Tomography, WCIPT7, 02.-05.09.2013, Kraków, Poland

Publ.-Id: 18990 - Permalink


Entwurf eines Personalinformationssystems für den Einsatz in Forschungseinrichtungen
Joehnk, P.;
  • Other report
    Bratislava: Slowakische Technische Universität in Bratislava, 1999
    83 Seiten

Publ.-Id: 18989 - Permalink


Budgetierung, KLR, Zielvereinbarung und Controlling - neue Steuerungselemente für Forschungseinrichtungen
Joehnk, P.;
  • Lecture (others)
    Vortrag Forschungszentrum Rossendorf, 10.03.1999, Dresden Rossendorf, Deutschland

Publ.-Id: 18988 - Permalink


Datenverarbeitung: Ordnung im Reich der Drittmittel
Joehnk, P.;
  • WGL-Journal (1997)1, 15

Publ.-Id: 18987 - Permalink


Mit der Principal-Agent-Theorie von der Input-Orientierung zur Output-Steuerung
Joehnk, P.;
  • Lecture (others)
    Seminarvortrag, 03.-05.03.1999, Holzhau, Deutschland

Publ.-Id: 18986 - Permalink


Ziele und Elemente des neuen Modells der Ressourcensteuerung in Forschungseinrichtungen
Joehnk, P.;
  • Lecture (others)
    Seminarvortrag, Gewerkschaft Öffentliche Dienste, Transport und Verkehr, 11.-12.01.1999, Undeloh, Deutschland

Publ.-Id: 18985 - Permalink


Moderné informacné systémy v správe vedecko-technických grantov na priklade systému PROMAN-W
Joehnk, P.; Moravcik, O.; Michalconok, G. F.; Petrik, D.;
  • ATP - Administrative Theory & Praxis (1998)12, 54-55

Publ.-Id: 18984 - Permalink


Erfahrungen beim Neubau von Laborgebäuden
Joehnk, P.;
  • Lecture (Conference)
    Fachtagung "Arbeitssicherheit in Hochschulen und wissenschaftlichen Institutionen", 18.-20.05.1998, Dresden, Deutschland

Publ.-Id: 18983 - Permalink


Berufsperspektiven für Naturwissenschaftler - Realität und Vision
Joehnk, P.;
  • Lecture (others)
    Gewerkschaft ÖTV, Schulungszentrum, 01.10.1997, Undeloh, Deutschland

Publ.-Id: 18982 - Permalink


Moderne DV-Instrumente in der Wissenschaftsadministration am Beispiel von "PROMAN-W"
Joehnk, P.;
  • Lecture (others)
    Forschungsforum Leipzig, 01.09.1997, Leipzig, Deutschland

Publ.-Id: 18981 - Permalink


Konfiguration und Optimierung der Software-Anwendungsentwicklung vom Typ Client-Server für das Management von (Drittmittel-)Projekten
Joehnk, P.; Moravcik, O.; Michalconok, G. F.; Misut, M.;
  • Contribution to proceedings
    42. Internationales Wissenschaftliches Kolloquium, 22.-25.09.1997, Illmenau, Deutschland
    Tagungsband 1, 78-83

Publ.-Id: 18980 - Permalink


Software-Anwendungsentwicklung vom Typ Klient-Server für das Management von Projekten
Moravcik, O.; Joehnk, P.; Michalconok, G. F.; Misut, M.;
  • Contribution to external collection
    in: Wissenschaftliche Berichte der Slowakischen Technischen Universität Bratislava 5, Bratislava: Slowakische Technische Universität Bratislava, 1997, 171-177

Publ.-Id: 18979 - Permalink


Moderne Instrumente in der Administration - PROMAN-W: Ein DV-System zum Management von Projekten
Joehnk, P.; Bernhardt, M.;
  • Contribution to external collection
    in: IFW Jahresbericht 20, Dresden: IFW, 1997

Publ.-Id: 18978 - Permalink


Zuwenden und Fördern - das andere Sponsoring
Joehnk, P.;
  • Communication & Media Relations
    Broschüre, Förderverein Gymnasium Coswig 01.11.1996

Publ.-Id: 18977 - Permalink


First FEL lasing driven by SRF gun at Rossendorf
Teichert, J.; Xiang, R.; Arnold, A.; Büttig, H.; Justus, M.; Lehnert, U.; Lu, P.; Michel, P.; Murcek, P.; Schurig, R.; Seidel, W.; Vennekate, H.; Will, I.; Rudolph, J.; Kamps, T.;
We present in this talk the first experiment of IR-FEL production driven by ELBE SRF gun.
Keywords: free electron laser, SRF gun
  • Invited lecture (Conferences)
    PITZ collaboration meeting 2013, 11.-12.06.2013, DESY, 15738 Zeuthen, Germany

Publ.-Id: 18976 - Permalink


Neubau = Zukunft
Joehnk, P.;
  • Communication & Media Relations
    Broschüre IFW Dresden 01.11.1996

Publ.-Id: 18975 - Permalink


Kosten-Nutzen-Relation in Bezug auf die stärkere Nutzung elektronischer Informationsdienste
Joehnk, P.;
  • Lecture (others)
    Workshop "Modernes Informationsmanagement in deutschen Forschungseinrichtungen - Stand und Zukunft", 01.10.1996, Bonn, Deutschland

Publ.-Id: 18974 - Permalink


Bewirtschaftung von Drittmittelressourcen
Joehnk, P.;
  • Lecture (Conference)
    Finanzmanagement und Drittmittelressourcen - Nöte und Chancen der wissenschaftlichen Forschungseinrichtungen, 01.10.1996, Hamburg, Deutschland

Publ.-Id: 18973 - Permalink


Wir leben von der Substanz / Interview
Joehnk, P.;
  • ÖTV-Report Wissenschaft und Forschung (1996)

Publ.-Id: 18972 - Permalink


Finanz- und Kostenmanagement am Beispiel der Produktpalette MACH
Joehnk, P.;
  • Lecture (others)
    Vortrag, Ministerium der Finanzen, 01.06.1996, Stuttgart, Deutschland

Publ.-Id: 18971 - Permalink


Festansprache
Joehnk, P.;
  • Lecture (others)
    Festansprache aus Anlaß des 10-järigen Jubiläums der Fakultät für Werkstoffe und Technologie Slowakische Technische Universität Bratislava, 01.05.1996, Trnava, Slowakei

Publ.-Id: 18970 - Permalink


Vorwort: Hans Gille - ein Wanderer zwischen den Welten?
Joehnk, P.;
  • Book chapter
    in: Deutschland - in vier Teilen erlebt, o.A.: Eigen-Verl., 1996

Publ.-Id: 18969 - Permalink


Spectroscopic identification of binary and ternary surface complexes of Np(V) on gibbsite
Gückel, K.; Rossberg, A.; Müller, K.; Brendler, V.; Bernhard, G.; Foerstendorf, H.;
Detailed molecular information of the Np(V) sorption species on amorphous and crystalline gibbsite were obtained for the first time by in situ time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy under environmentally relevant conditions. The results consistently demonstrate the formation of mononuclear inner sphere complexes of the NpO2+ ion irrespective of the prevailing atmospheric condition. In particular, the impact of the presence of atmospheric equivalent added carbonate on the speciation in solution and on the surfaces becomes evident from vibrational data. Whilst the 1:1 aqueous carbonato species (NpO2CO3−) was found to become predominant in the circumneutral pH range, it is most likely that this species is sorbed onto the gibbsite surface as an inner sphere ternary surface complex where the NpO2+ moiety is directly coordinated to the functional groups of the gibbsite’s surface. These findings are corroborated by results obtained from EXAFS spectroscopy. The identification of the Np(V) surface species on gibbsite constitutes a basic finding for a comprehensive description of the dissemination of neptunium in groundwater systems.

Publ.-Id: 18968 - Permalink


Wissenschaftsgemeinschaft Blaue Liste - eine Standortbestimmung
Joehnk, P.;
  • Lecture (others)
    Klausurtagung der Mitglieder des Stadtrates Dresden, 01.04.1996, Bad Schandau, Deutschland

Publ.-Id: 18967 - Permalink


Kosten-/Leistungsrechnung, Controlling und Berichtswesen in Ministerien und oberen Bundesbehörden
Joehnk, P.;
  • Lecture (others)
    Software-Praxistag, 01.03.1996, Bonn, Deutschland

Publ.-Id: 18966 - Permalink


Wie sind Mitarbeiter einer Forschungseinrichtung motivierbar?
Joehnk, P.;
  • Lecture (others)
    Vortrag, 20.02.1996, Dresden, Deutschland

Publ.-Id: 18965 - Permalink


Finanzbuchhaltung und Controlling-Instrumente unter Windows
Joehnk, P.;
  • Lecture (others)
    Fachinformationszentrum Karlsruhe, 30.11.1995, Karlsruhe, Deutschland

Publ.-Id: 18964 - Permalink


Virtuelle Bibliotheken - Handlungsbedarf für die Wissenschaftsgemeinschaft Blaue Liste?
Joehnk, P.;
  • Lecture (others)
    Verwaltungsausschuss der WBL, 02.05.1995, Greifswald, Deutschland

Publ.-Id: 18963 - Permalink


Einführung eines integrierten Finanz- und Kostenmanagement-Systems
Joehnk, P.;
  • Lecture (others)
    Gesellschaft für Mathematik und Datenverarbeitung, Projektträger Fachinformation, 09.10.1994, Darmstadt, Deutschland

Publ.-Id: 18962 - Permalink


Standortbestimmung des IFW Dresden
Joehnk, P.;
  • Lecture (others)
    Vortraf, 31.03.1994, Dresden, Deutschland

Publ.-Id: 18961 - Permalink


Praxis der Projektförderung des Sächsischen Ministers für Umwelt und Landwirtschaft
Joehnk, P.;
  • Lecture (others)
    Seminar für Ministeriumsmitarbeiter und Projektträger, 23.-27.03.1992, Bad Schandau, Deutschland

Publ.-Id: 18960 - Permalink


Einführungsseminar für Projektträger
Joehnk, P.;
  • Lecture (others)
    Seminarvortrag, Einführungsseminar für Projektträger, 30.09.-02.10.1991, Boppard, Deutschland

Publ.-Id: 18959 - Permalink


Projektförderung des BMFT auf Kostenbasis
Joehnk, P.; Donau, J. J.; Schneider, G.;
  • Book (Authorship)
    St. Augustin: Joehnk-Stadelmayer, 1991
    278 Seiten

Publ.-Id: 18958 - Permalink


Einführungsseminar füe neue Mitarbeiter bei Projektträgern des BMFT
Joehnk, P.;
  • Lecture (others)
    Seminarvortrag bei Projektträgern des BMFT, 11.-14.03.1991, Winterscheid, Deutschland

Publ.-Id: 18957 - Permalink


Der Umwelt im sächsischen Raum gemeinsam schnell und wirksam helfen
Joehnk, P.;
  • Dresdner Universitätsjournal (1991)2

Publ.-Id: 18956 - Permalink


Näher den Kunden im Osten
Joehnk, P.;
  • KfK-Hausmitteilungen (1991)

Publ.-Id: 18955 - Permalink


Posterbeitrag Gewässerschutzseminar
Joehnk, P.; Knobel, K.-P.;
  • Poster
    Magdeburger Gewässerschutzseminar, 28.-30.11.1990, Magdeburg, Deutschland

Publ.-Id: 18954 - Permalink


Einführungsseminar für neue Mitarbeiter bei der VDI/VDE
Joehnk, P.;
  • Lecture (others)
    Seminar bei der VDI/VDE, 29.-31.10.1990, Berlin, Deutschland

Publ.-Id: 18953 - Permalink


Posterpräsentation Umweltforschung
Joehnk, P.; Robel, W.;
  • Poster
    Deutsch-deutsches Symposium Umweltforschung in der DDR, 01.09.1990, Berlin, Deutschland

Publ.-Id: 18952 - Permalink


Seminarvortrag
Joehnk, P.;
  • Lecture (others)
    Bundesakademie für öffentliche Verwaltung , Projektgruppe Fortbildung DDR (für Minister und Staatsekretäre der DDR), 21.-25.05.1990, Boppard, Deutschland

Publ.-Id: 18951 - Permalink


Jahresbericht 1989 des Projektträgers des BMFT für Wassertechnologie, Abwasser- und Schlammbehandlung
Joehnk, P.; (Editor)
  • Other report
    Karlsruhe: Kernforschungszentrum Karlsruhe, 1990
    137 Seiten

Publ.-Id: 18950 - Permalink


Praxis der Projektförderung des Bundesministeriums für Forschung und Technologie
Joehnk, P.; Vollmer, S.;
  • Other report
    Karlsruhe: Kernforschungszentrum Karlsruhe, 1989
    169 Seiten

Publ.-Id: 18949 - Permalink


Einführungsseminar für neue PT-Mitarbeiter
Joehnk, P.;
  • Lecture (others)
    Seminarvortrag BMFT, 29.05.-01.06.1989, Winterscheid, Deutschland

Publ.-Id: 18948 - Permalink


Die Projektförderung des Bundesministeriums für Forschung und Technologie - eine Darstellung der finanziellen, rechtlichen, administrativen und organisatorischen Rahmenbedingungen
Joehnk, P.;
  • Lecture (others)
    Industrie- und Handelskammer Mannheim, 01.08.1988, Mannheim, Deutschland

Publ.-Id: 18947 - Permalink


Die Information als wichtigster Produktionsfaktor
Joehnk, P.;
  • Markt & Technik 20(1986)

Publ.-Id: 18946 - Permalink


Sponge-like Si-SiO2 nanocomposite – morphology studies of spinodally decomposed silicon-rich oxide
Friedrich, D.; Schmidt, B.; Heinig, K. H.; Liedke, B.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.; Mikolajik, T.;
Sponge-like Si nanostructures embedded in SiO2 were fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide with a stoichiometry close to that of silicon monoxide. After thermal treatment a mean feature size of about 3 nm was found in the phase-separated structure. The structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography, and atom probe tomography, which revealed a percolated Si morphology. It was shown that the percolation of the Si network in 3D can also be proven on the basis of 2D EFTEM images by comparison with 3D kinetic Monte Carlo simulations.
Keywords: Silicon rich oxide, spinodal decomposition, silicon sponge, EFTEM, nanocomposite

Publ.-Id: 18945 - Permalink


Plasma-based nanotechnology against corrosion of organ pipes
Pelic, B.; Bregolin, F.; Prucnal, S.; Skorupa, W.; Yankov, R.;
Aggressive environments contribute to the corrosion of pipe organs, which causes flaking, losing the voice and final collapse of the old century’s pipes. Additional factor is dezincification of brass (CuZn) containing more than 15 at.% of Zn in the presence of oxygen and moisture. In this approach, the nanotechnology treatment of the CuZn24 (reed organ pipes) is proposed. The conservation strategy based on two stages Pulsed Laser Deposition (PLD) followed by Plasma Immersion Ion Implantation (PIII) were performed. The brass coupons were coated with the protective oxide-films (Al2O3, SiO2, and ZnO) using PLD technique, and implanted with nitrogen ions of energy 20 keV for 200 seconds. The influence of the deposited and implanted coatings, on the corrosion phenomena, has been evaluated by exposing the coupons to the laboratory air with the high concentration of 2% acetic acid (CH3COOH), as aggressive agent. The areal density of the deposited films was measured using Rutherford Backscattering Spectroscopy (RBS). The composition and depth profiling of the sample’s elements was analyzed with Auger Electron Spectroscopy (AES). The average roughness (Ra) of the as coated and implanted specimens was measured using Dektak Stylus Profilometry in 2 and 3 dimensions. Those results were compared with the roughness measurements performed after the corrosion test. A significant improvement in the corrosion resistance with acetic acid action has been achieved by applying aluminum oxide film (30 nm) and introducing nitrogen ions into the near surface and the interphase regions. This gives a light to introduce the nanotechnology into the greatest and best sounding objects of the cultural heritage.
Keywords: Plasma Immersion Ion Implantation, Pulsed Laser Deposition, corrosion of organ pipes
  • Lecture (Conference)
    The 12th International Workshop on Plasma-Based Ion Implantation and Deposition (PBII&D), 01.-05.07.2013, Poitiers, France

Publ.-Id: 18944 - Permalink


Protection of organ pipes using plasma-based nanotechnology
Pelic, B.; Bregolin, F.; Prucnal, S.; Wiesenhütter, K.; Yankov, R.; Skorupa, W.;
The present historical organs are musical instruments, which provide sound impression of divine music spanning six centuries. Unfortunately, organ pipes, traditionally made of PbSn alloys, have been severely affected by corrosion in the last couple of centuries, and particularly over the last decades. A major threat to the historical organs is harmful indoor environments. Thus, it is necessary to develop a method of protecting the organ pipes, so that the significant cultural heritage obtained over many centuries does not get lost. A new conservation concept based on nanotechnology using plasma immersion ion implantation (PIII) is proposed here for the protection of PbSn alloys exposed to high levels of acetic acid vapors. Samples of organ-pipe quality PbSn alloys with compositions were processed by PIII of either nitrogen or SF6 for different times and bias voltages. The PIII-treated specimens were subsequently studied by Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy to study the concentration/depth profiles of the implanted elements. The implant profiles were also simulated with the aid of the SRIM code. Samples were finally examined using an accelerated corrosion tests in an acetic acid ambient. Both the alloy composition and the implant dose were found to strongly influence the corrosion behavior of the PbSn alloys. The best corrosion resistance was obtained for samples consisting of Pb-Sn15-Sb10 and Pb-Sn28, after the implantation of nitrogen to a dose of1E16cm-2.It was revealed that plasma immersion ion implantation can play an important role in the corrosion prevention of the organ pipes in the acetic acid atmosphere. A protection mechanism was accordingly proposed and discussed.
Keywords: Plasma Immersion Ion Implantation, corrosion of organ pipes, PbSn alloy
  • Lecture (Conference)
    E-MRS 2013 SPRING MEETING, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 18943 - Permalink


Einfluss der Bestrahlung mit energiereichen Teilchen auf die Härte von Fe-Cr-Legierungen
Heintze, C.;
Ferritisch/martensitische Cr-Stähle und deren oxiddispersionsverfestigte Varianten gehören zu den potenziellen Konstruktionswerkstoffen für Komponenten zukünftiger kerntechnischer Einrichtungen, wie z. B. Fusionsreaktoren und Spalt-reaktoren der IV. Generation, die Strahlungsfeldern mit hohem Neutronenfluss aus-gesetzt sind. Ein Hauptproblem dieser Materialgruppen ist das Auftreten des Spröd-duktil-Übergangs und dessen maßgeblich durch die Strahlenhärtung verursachte Verschiebung zu höheren Temperaturen.
In der vorliegenden Arbeit wird das Bestrahlungsverhalten von binären Fe-Cr-Modelllegierungen untersucht, die ein vereinfachtes Modell für ferritisch/martensitische Cr-Stähle darstellen. Dabei werden Bestrahlungen mit Eisenionen zur Simulation der durch Neutronen hervorgerufenen Schädigung verwendet. Die auf wenige Mikrometer begrenzte Eindringtiefe der Ionen macht es erforderlich, dass für dünne Schichten geeignete Charakterisierungsmethoden ein-gesetzt werden. Im Rahmen dieser Arbeit sind das Nano¬härte¬messungen und Transmissions¬elektronen¬mikroskopie (TEM).
Im Ergebnis liegen die bestrahlungsinduzierte Härteänderung der Schicht in Ab-hängig¬keit von Chromgehalt, Bestrahlungsfluenz und –temperatur sowie, für aus-gewählte Zustände, quantitative TEM-Analysen vor. Zusammen mit begleitenden Ergebnissen von Neutronenkleinwinkelstreuexperimenten an neutronen-bestrahlten Proben der gleichen Werkstoffe ermöglichen sie die Identifizierung von bestrahlungsinduzierten Versetzungsringen und nm-großen α’-Ausscheidungen als Quellen der Strahlenhärtung. Im Rahmen eines vereinfachten Modells, das auf Orowan zurückgeht, werden die Hindernis¬stärken dieser Gitterbaufehler für das Gleiten von Versetzungen abgeschätzt.
Darauf aufbauend erfolgt ausblickartig eine Erweiterung des Untersuchungsgegenstands auf komplexere Situationen hinsichtlich der Bestrahlungs-bedingungen und des Werkstoffs. Durch das Einbeziehen simultaner und sequentieller Bestrahlungen mit Eisen- und Heliumionen kann gezeigt werden, dass der Effekt von Helium auf die Strahlenhärtung von der Bestrahlungs-reihenfolge abhängt und dass der simultane Eintrag fusionsrelevanter Mengen von Helium zu einer Verstärkung der Strahlenhärtung führt, die auf einem synergistischen Effekt beruht. Für Cr-Stähle mit 9 % Cr und deren oxiddispersions-verfestigte Varianten wird kein grundlegend anderes Bestrahlungsverhalten beobachtet als für binäres Fe-9at%Cr. Es gibt jedoch Hinweise, dass Oxid-dispersionsverfestigung die Strahlenhärtung unter bestimmten Bedingungen reduzieren kann.
Im Ergebnis der Arbeit zeigt sich, dass Ionenbestrahlungen in Kombination mit Nanohärtemessungen zu einem vertiefenden Verständnis der Strahlenhärtung in Werkstoffen auf Fe-Cr-Basis sowie zu einer effektiven Materialvorauswahl beitragen können. Voraussetzung ist, dass der Eindruckgrößeneffekt und der Substrateffekt auf geeignete Weise in Rechnung gestellt werden.
Keywords: Fe-Cr-Legierungen, Ionenbestrahlung, Neutronenbestrahlung, Nanohärte, SANS, TEM
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-037 2013

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Publ.-Id: 18942 - Permalink


Probing the surface speciation of U(VI) on iron (hydr)oxides by in situ ATR FT-IR spectroscopy
Foerstendorf, H.; Jordan, N.; Heim, K.;
The surface speciation of uranium(VI) on maghemite (γ-Fe2O3) was elucidated at the spectroscopic level for the first time. By means of in situ ATR FT-IR measurements, the formation of uranium(VI) outer-sphere complexes was revealed under anoxic conditions and in ambient atmosphere at mildly acid conditions. This type of complexation was verified by the frequency of the ν3(UO2) mode observed for the surface species, the impact of the ionic strength of the background electrolyte on U(VI) sorption and by the high reversibility of the sorption process monitored by on line spectroscopy. The impact of carbonate ions from atmospherically derived CO2 on U(VI) sorption on maghemite was investigated. Although the surface speciation of the carbonate ions presumably change from a monodentate coordination on maghemite to a bidentate coordination in the ternary sorption system, the U(VI) speciation is not changed. A contrasting juxtaposition of comparable results obtained from maghemite and ferrihydrite reveal a basically different type of U(VI) complexation, namely outer and inner spheric coordination.

Publ.-Id: 18941 - Permalink


Migration-induced field-stabilized polar phase in strontium titanate single crystals at room temperature
Hanzig, J.; Zschornak, M.; Hanzig, F.; Mehner, E.; Stöcker, H.; Abendroth, B.; Röder, C.; Talkenberger, A.; Schreiber, G.; Rafaja, D.; Gemming, S.; Meyer, D. C.;
Local reversible structural changes in SrTiO3 single crystals in an external electric field are induced by oxygen redistribution. We present in-situ X-ray diffraction measurements during and immediately after electroformation. Several reflections are monitored and show an elongation of the cubic unit cell of strontium titanate. Raman investigations verify that the expansion of the unit cell involves a transition from the centro-symmetric to a lower symmetry phase. During a complete formation cycle, including the hold time of the electric field and relaxation time without field, two different dynamics are observed for the reversible transitions from cubic symmetry to tetragonal distortion: a slow one during the increase of the lattice constant in field direction and a fast one after switching off the electric field. Based on the experimental data we propose the formation of a polar strontium titanate unit cell at room temperature stabilized by the electric field, which is referred to as migration-induced field-stabilized polar (MFP) phase.
Keywords: ferroic, density-functional, DFT, strontium titanate, STO, migration, RAMAN, oxide

Publ.-Id: 18940 - Permalink


Microbial influence on the migration behaviour of radionuclides
Krawczyk-Bärsch, E.;
In an underground rock characterization facility, the ONKALO tunnel in Finland, massive 5–10-mm thick biofilms were observed attached to tunnel walls where groundwater was seeping from bedrock fractures at a depth of 70 m. In laboratory experiments performed in a flow cell with detached biofilms to study the effect of uranium on the biofilm, uranium was added to the circulating groundwater obtained from the fracture feeding the biofilm. The final uranium concentration was adjusted to 4.25×10–5 M. EF-TEM studies indicated that uranium in the biofilm was immobilized intracellularly in microorganisms by the formation of metabolically mediated uranyl phosphate, similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6 H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O). At the Äspö HRL (Sweden) Gallionella ferruginea dominated biofilms associated with bacteriogenic iron oxides (BIOS) and groundwater were sampled from an in situ continuous flow cell. In laboratory sorption experiments UO2(ClO4)2 and NpO2(ClO4) were added to the BIOS biofilms in groundwater under aerobic conditions adjusting a final U(VI) concentration of 1.9×10-5 M. U(VI) and 3.27×10-5 M Np(V). The results showed a substantial decrease of uranium and neptunium in the groundwater of approximately 85 % and 95 %, respectively. Thermodynamic calculation of the theoretical predominant field of uranium species was performed using the analytical data of the uranium-contaminated groundwater. Under the given pH and Eh the formation of the aqueous uranium carbonate species Ca2UO2(CO3)3(aq) is predicted due to the high concentration of carbonate in the groundwater. In the BIOS biofilm the ferrous iron-oxidizing and stalk-forming bacterium Gallionella ferruginea is dominating the sorption process. The stalk represents an organic surface upon which Fe oxyhydroxides can precipitate. Under the given pH conditions the uptake of U and Np depends predominantly on the high amount of ferrihydrite precipitated onto the stalks. Conclusively, the combination of this biological material and iron oxides creates an abundant surface area for adsorption of radionuclides.
Keywords: biofilm, U(VI), Np(V), Äspö, ONKALO, sorption
  • Lecture (Conference)
    Coordination Meeting at Äspö, 26.04.2013, Äspö, Sweden

Publ.-Id: 18939 - Permalink


Microbial experiments at URL sites: Influence on radionuclide
Krawczyk-Bärsch, E.;
At the Äspö HRL (Sweden) Gallionella ferruginea dominated biofilms associated with bacteriogenic iron oxides (BIOS) and groundwater were sampled from an in situ continuous flow cell, which has been installed in a cavity of the main access tunnel at 2200 A site, 300 m below sea level In laboratory sorption experiments UO2(ClO4)2 and NpO2(ClO4) were added to the BIOS biofilms in groundwater under aerobic conditions adjusting a final U(VI) concentration of 1.9×10-5 M. U(VI) and 3.27×10-5 M Np(V). The analysis showed a substantial decrease of uranium and neptunium in the groundwater of approximately 85 % and 95 %, respectively. Under the given pH and Eh the formation of the aqueous uranium carbonate species Ca2UO2(CO3)3(aq) is predicted due to the high concentration of carbonate in the groundwater. In the BIOS biofilm the ferrous iron-oxidizing and stalk-forming bacterium Gallionella ferruginea is dominating the sorption process.
Keywords: biofilm, Äspö, U(VI), Np(V), sorption
  • Lecture (Conference)
    Final Workshop of the Crock Project "Crystalline rock retention processes", 14.-16.05.2013, Karlsruhe, Germany

Publ.-Id: 18938 - Permalink


Reverse Epitaxy of Ge: Ordered and Faceted Surface Patterns
Ou, X.; Keller, A.; Helm, M.; Fassbender, J.ORC; Facsko, S.
Normal incidence ion irradiation at elevated temperatures, when amorphization is prevented, induces novel nanoscale patterns of crystalline structures on elemental semiconductors by a reverse epitaxial growth mechanism: on Ge surfaces irradiation at temperatures above the recrystallization temperature of 250°C leads to self-organized patterns of inverse pyramids. Checkerboard patterns with fourfold 2 symmetry evolve on the Ge (100) surface, whereas on the Ge (111) surface, isotropic patterns with a sixfold symmetry emerge. After high-fluence irradiations, these patterns exhibit well-developed facets. A deterministic nonlinear continuum equation accounting for the effective surface currents due to an Ehrlich-Schwoebel barrier for diffusing vacancies reproduces remarkably well our experimental observations.
Keywords: ion irradiation, pattern formation, negative epitaxy

Publ.-Id: 18937 - Permalink


Formation and coarsening of sponge-like Si-SiO2 nanocomposites
Liedke, B.; Heinig, K.-H.; Mücklich, A.; Schmidt, B.;
It has been recently found by energy filtered transmission electron microscopy (EFTEM) that metastable SiOx≈1 films decay into a Si nanowire network embedded in SiO2 by spinodal decomposition during thermal treatment. To have a guideline for nanocomposites fabrication, the details of the morphology evolution have been studied by comparison of EFTEM images with kinetic Monte-Carlo (kMC) simulations. Pair correlation functions calculated by kMC have been adjusted to that extracted from EFTEM. This comparison allows to conclude about characteristic lengths of 3D morphologies. Combining kMC with EFTEM delivers the understanding for tailoring the properties like quantum confinement of the spongy Si
Keywords: sponge-like silicon nanostructure annealing kinetic Monte-Carlo

Publ.-Id: 18936 - Permalink


A spectroscopic study on U(VI) biomineralization in cultivated Pseudomonas fluorescens biofilms isolated from granitic aquifers
Krawczyk-Bärsch, E.; Lütke, L.; Moll, H.; Bok, F.; Steudtner, R.; Rossberg, A.;
The interaction between the Pseudomonas fluorescens biofilm and U(VI) were studied using extended X-ray absorption fine structure spectroscopy (EXAFS), and time-resolved laser fluorescence spectroscopy (TRLFS). In EXAFS studies, the formation of a stable uranyl phosphate mineral, similar to autunite (Ca[UO2]2[PO4]2•2–6H2O) or meta-autunite (Ca[UO2]2[PO4]2•10–12H2O) was observed. This is the first time such a biomineralization process has been observed in P. fluorescens. Biomineralization occurs due to phosphate release from the cellular polyphosphate, likely as a cell’s response to the added uranium. It differs significantly from the biosorption process occurring in the planktonic cells of the same strain. TRLFS studies of the uranium-contaminated nutrient medium identified aqueous Ca2UO2(CO3)3 and UO2(CO3)3 4− species, which in contrast to the biomineralization in the P. fluorescens biofilm, may contribute to the transport and migration of U(VI). The obtained results reveal that biofilms of P. fluorescens may play an important role in predicting the transport behavior of uranium in the environment. They will also contribute to the improvement of remediation methods in uranium-contaminated sites.
Keywords: EXAFS; Meta-autunite; Pseudomonas fluorescens; TRLFS; Uranium

Publ.-Id: 18935 - Permalink


Polyatomic bismuth impacts into germanium: Molecular dynamics study
Anders, C.; Heinig, K.-H.; Urbassek, H.;
Using molecular dynamics simulations, we study the effects induced by the impact of Bin (n≤5) clusters with energies in the range of a 3–20 keV/atom into a Ge target. The target consists of Ge including a 10% contribution of randomly distributed Bi atoms. The impacting polyatomic clusters create a long-lived melt pool at the surface. After resolidification, the surface shows a characteristic meniscuslike depression; it is caused both by the missing sputtered atoms and by the volume change of Ge upon melting and amorphization. During cooling, Bi is driven towards the center of the melt pool. A large precipitate forms at the surface (for polyatomic impact) or in the center of the molten pocket (for monatomic impact). The remainder of the resolidified amorphous zone is purified from Bi. We argue that the reason for the demixing of Bi and Ge is the thermophoretic or Soret effect which is caused by the different diffusivities of Bi and Ge in the melt. Bi is sputtered preferentially from the sample. The extent of surface modification, the amount of Bi collected on the surface, the concentration of Bi, and structure of Bi precipitates in the former melt pool are analyzed in their dependence on projectile size, impact energy, and direction.
Keywords: atomistic computer simulation, germanium, polyatomic ions, melting

Publ.-Id: 18934 - Permalink


Advanced Numerical and Experimental Studies to Turbulent Buoyancy Driven Flow in the Primary Circuit of Pressurized Water Reactors
Höhne, T.;
Validated and accurate advanced simulation tools, in particular advanced Computational Fluid Dynamics (CFD) simulation methods, are required to further improve the economics and safe operation of future nuclear power plants.
These methods will be beneficiary for Generation III+ and Generation IV reactors.
Buoyancy driven flows are of relevance for boron dilution transients or pressurized thermal shock scenarios.
Therefore, a combined numerical and experimental study of buoyant mixing processes is planned in the project using existing experiments of the HZDR test facility ROCOM.
A systematic determination of the advantages, disadvantages, and accuracy of these advanced CFD simulation methods for application to NRS assessments is planned.
This will contribute to the development of Generation III+ and IV nuclear reactors, and thereby to the utilization of more efficient and more economical nuclear power in the future.
Keywords: HZDR, ROCOM, NRS, CFD
  • Invited lecture (Conferences)
    IAEA Workshop, 17.-19.07.2013, Wien, Österreich

Publ.-Id: 18933 - Permalink


Linear excitation of short propagating spin waves via a pair of layered vortex cores
Wintz, S.; Weigand, M.; Tyberkevych, V. S.; Slobodianiuk, D. V.; Stoll, H.; Raabe, J.; Neudert, A.; Erbe, A.; Lindner, J.; Slavin, A. N.; Fassbender, J.ORC
The investigation of spin wave dynamics in nanomagnetic systems is one of the key topics in modern magnetism. To excite short spin waves, it is typically necessary either to use transducers of the size of a wavelength (micro-striplines or point-contacts) or to excite the spin waves parametrically by a double-frequency spatially uniform microwave signal. Here we demonstrate that the efficient linear excitation of short propagating spin waves is possible in a trilayer in which the magnetic layers form a vortex pair with opposite circulations and parallel cores. Such spin waves are directly observed by time-resolved x-ray microscopy upon application of microwave magnetic fields of appx. 1 mT. We find that for excitation frequencies in the GHz regime, the resulting spin wavelength is continuously tunable in a range between 50 nm and 500 nm by this frequency. Here, the radial spin wave propagation direction depends on the total handedness of the two vortex circulations, revealing a clear non-reciprocity of the spin waves observed. Both, analytic theory and micromagnetic simulations show that such a nanomagnetic system supports a gapless spin wave branch with linear dispersion and strong nonreciprocity, and that the propagating spin waves belonging to this branch can be excited by a spatially uniform microwave signal. Other excitation mechanisms, such as spin-transfer torques or thermal gradients, could be utilized to generate spin waves in the system presented.
  • Poster
    Gordon Research Conferences: Spin Dynamics in Magnetic Nanostructures, 18.08.2013, Hong Kong, China

Publ.-Id: 18932 - Permalink


Results of Testing of Calculation Procedure for Neutron Fluence and Spectrum on the VVER-440 RPV during Operation with new Fuel Compositions
Borodkin, P. G.; Borodkin, G. I.; Adeev, V. A.; Konheiser, J.;
In accordance to PNAE G-7-008-89 [1] on the NPP since starting-up should be accounted neutron fluence of RPV, which determines the RPV life-time in accordance to strength calculations. Detailization of these PNAE G-7-008-89 [1] requirements has been represented in the RB-007-99 [2]. Recently elaborated procedure for accounting and prediction of RPV fast neutron fluence has been regulated by normative document RD EO 1.1.2.29.0913-2012 [3].
During NPP unit operation some modernizations have been realized, for example, using of new types of fuel assemblies and new kind of fuel. Changes in the reactor core loading, especially on the core periphery, give influence in the fast neutron fluence on the RPV, which should be evaluated by neutron fluence calculations. The reliability of these calculations should be validated by ex-vessel neutron-activation measurements at NPPs with VVER.
Paper deals with the results of calculations and measurement of fast neutron fluence on the RPV for last fuel cycles of Kola NPP power units, with using new type of fuel, and gives some recommendations for improvement of routine fluence calculation procedures.
Keywords: VVER, neutron fluence, RPV
  • Lecture (Conference)
    Safety Assurance of NPP with WWER, 28.-31.05.2013, Podolsk, Russia
  • Contribution to proceedings
    Safety Assurance of NPP with WWER, 28.-31.05.2013, Podolsk, Russia
    Conference proceedings

Publ.-Id: 18931 - Permalink


Synchrotron X-ray tomography of a Taylor bubble
Boden, S.; Hampel, U.;
A profound understanding of the transfer processes in capillary multiphase flow is of primary importance from the viewpoint of fundamental science as well as for practical design and operation of new chemical reaction devices. The desired flow regime in such small channel geometries is surface tension dominated Taylor bubble flow. Still today the lack of precise morphological data on such Taylor bubble capillary two-phase flows calls for the development of adequate measurement techniques providing the necessary spatial resolution for the investigation of the flow structures moving at moderate speeds. Experiments to reveal the shape of moving Taylor bubbles were performed at the ANKA synchrotron radiation source in Karlsruhe, Germany, in capillaries with a hydraulic diameter of dh = 2 mm. The careful examination of the bubble positions in the dataset enabled the generation of consecutive projection images necessary for application of a computerized tomographic reconstruction algorithm to reveal the cross-sectional shape of the Taylor bubble.
Keywords: Taylor bubble flow, X-ray tomography, synchrotron
  • Lecture (Conference)
    7th World Congress on Industrial Process Tomography, 02.-05.09.2013, Krakow, Poland

Publ.-Id: 18930 - Permalink


Thermal-Hydraulic Investigations for Safety Related Tasks
Höhne, T.;
The session „Thermal-Hydraulic Investigations for Safety Related Tasks“ was chaired by Thomas Höhne (Helmholtz-Zentrum Dresden - Rossendorf ).
The first presentation on „Comparative analysis of a LOCA for a German PWR with ASTEC and ATHLET-CD“, from Nils Reinke (Co-authors: H.-W. Chan, M. Sonnenkalb, all from the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH, Köln) presented calculations with the German-French severe accident integral code ASTEC for the early phase of the accident, thereby focusing on thermal-hydraulics mainly. He explained that the purpose of this work was mainly to assess the ASTEC code behavior in modeling thermal-hydraulics in the coolant circuit in the early phase of a hypothetical severe accident. This is in particular interesting, since the early phase of the accident determines core heat-up and the subsequent core degradation phase. A comparison is done versus the more mechanistic code system ATHLET-CD/COCOSYS, developed at GRS, too.
Keywords: KTG, Jahrestagung Kerntechnik, Thermal-Hydraulic, CFD
  • atw - International Journal for Nuclear Power 58(2013)10, 587-588

Publ.-Id: 18929 - Permalink


Ortsaufgelöste Analyse von Uranspezies mittels einem gekoppelten System aus CLSM und LIFS
Großmann, K.; Arnold, T.; Brockmann, S.;
Die fluoreszierenden Eigenschaften des Urans bei Anregung mit UV-Licht werden zunehmend für spektroskopische Analysen von Uranspezies innerhalb wässriger Proben eingesetzt. Dabei spielen neben den Fluoreszenzeigenschaften der sechswertigen Oxidationsstufe auch zunehmend die der vier- und fünfwertigen Oxidationsstufe eine wichtige Rolle. Bei Fluoreszenzmessungen von Uranverbindungen sind die Emissionsbandenlagen sowie die Fluoreszenzlebenszeit (die Abklingzeit der Fluoreszenzlichtemission nach der Anregung) wichtige Parameter. Durch Abgleich der ermittelten Peaklagen und Lebenszeiten mit denen von Referenzverbindungen lassen sich somit Aussagen zur vorhandenen Uranspezies treffen. Die Detektion von Fluoreszenzemissionsspektren an festen bzw. biologischen Proben mittels (zeitaufgelöster) laserinduzierter Fluoreszenzspektroskopie (TRLFS bzw. LIFS) hat jedoch den Nachteil, dass keine Aussagen zur räumlichen Lokalisation des Urans möglich sind. Gerade in komplexen, biologischen Proben, wie Biofilmverbänden oder mikrobiellen Zellen, sind jedoch Aussagen zum Ort der Urananreicherung in der Probe erwünscht um z.B. zwischen intra- und extrazellulären Urananbindungen unterscheiden zu können.
Die Fluoreszenzeigenschaften der Uran(VI)verbindungen und –minerale können auch zu deren Lokalisation innerhalb von komplexen Proben genutzt werden. So stellt die Anwendung fluoreszenzmikroskopischer Messmethoden eine Möglichkeit dar, Uranpräzipitate und Anreicherungen z.B. in biologischen Proben wie Biofilmen oder Zellen zu lokalisieren und zu visualisieren. Die konfokale Laser-scanning Mikroskopie (CLSM) eignet sich hierbei besonders, da diese Methode eine dreidimensionale Darstellung fluoreszierender Bereiche in komplexen Probenstrukturen ermöglicht. Durch Anwendung geeigneter Fluoreszenzfarbstoffe kann auch die sonstige Probenstruktur abseits der fluoreszierenden Schwermetalle abgebildet werden, wodurch eine räumliche Einordnung innerhalb der Probengeometrie ermöglicht wird [1].
Eine Kopplung der konfokalen Laser-scanning Mikroskopie (CLSM) mit der laserinduzierten Fluoreszenzspektroskopie (LIFS) ermöglicht es Fluoreszenzsignale räumlich, dreidimensional zu lokalisieren und zu visualisieren sowie gleichzeitig entsprechende ortsaufgelöste, fluoreszenz-spektroskopische Daten zu detektieren [2]. Verschiedene erfolgreiche Anwendungen an biologischen Proben aber auch an Mineraloberflächen zeigen, dass es sich bei dieser kombinierten Methode aus Mikroskopie und Spektroskopie um eine zukunftsweisende Technik zur zerstörungsfreien Detektion von fluoreszierenden Schwermetallen und besonders der Uran(VI)spezies handelt. Diese Methode ist besonders vielversprechend hinsichtlich der Detektion von Uran(VI)akkumulationen innerhalb von komplexen Probensystemen deren Struktur und Aufbau durch die Analyse der Uranspezies nicht zerstört werden soll. Dabei zeichnet sich diese Technik durch relativ niedrige Nachweisgrenzen von bis zu 1∙10-6 M für Uran(VI)verbindungen innerhalb des konfokalen Volumens aus.
  • Poster
    7. Workshop RCA, 10.-11.06.2013, Rossendorf, Deutschland

Publ.-Id: 18928 - Permalink


Growth of a three-dimensional anisotropic lattice of Ge quantum dots in an amorphous alumina matrix
Buljan, M.; Roshchupkina, O.; Santic, A.; Holy, V.; Baehtz, C.; Mücklich, A.; Horak, L.; Vales, V.; Radic, N.; Bernstorff, S.; Grenzer, J.;
Simple processes for the preparation of semiconductor quantum dot lattices embedded in dielectric amorphous matrices play an important role in various nanotechnology applications. Of particular interest are quantum dot lattices with properties that differ significantly in different directions parallel to the material surface. Here, a simple method is demonstrated for the fabrication of an anisotropic lattice of Ge quantum dots in an amorphous Al2O3 matrix by a self-assembly process. A specific deposition geometry with an oblique incidence of the Ge and Al2O3 adparticles was used during magnetron sputtering deposition to achieve the desired anisotropy. The observed Ge quantum dot ordering is explained by a combination of directional diffusion of adparticles from the Ge and Al(2)O(3)targets and a shadowing process which occurs during deposition as a result of the specific surface morphology. The prepared material shows a strong anisotropy of the electrical conductivity in different directions parallel to the sample surface.
Keywords: Ge quantum dots; self-assembly; conductivity; anisotropy; magnetron sputtering; synthesis

Publ.-Id: 18927 - Permalink


The neutron-proton charge-exchange amplitudes measured in the dp -> ppn reaction
Mchedlishvili, D.; Barsov, S.; Carbonell, J.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Engels, R.; Gebel, R.; Glagolev, V.; Grigoryev, K.; Goslawski, P.; Hartmann, M.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Stein, H.; Steffens, E.; Stockhorst, H.; Stroher, H.; Tabidze, M.; Trusov, S.; Uzikov, Y.; Valdau, Y.; Wilkin, C.;
The unpolarised differential cross section and the two deuteron tensor analysing powers A(xx) and A(yy) of the (d) over right arrowp -> {pp}(s)n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27 GeV, data were obtained for small momentum transfers to a {pp}(s) system with low excitation energy. The results at the three lower energies are consistent with impulse approximation predictions based upon the current knowledge of the neutron-proton amplitudes. However, at 2.27 GeV, where these amplitudes are far more uncertain, agreement requires a reduction in the overall double-spin-flip contribution, with an especially significant effect in the longitudinal direction. These conclusions are supported by measurements of the deuteron-proton spin-correlation parameters C-x,C-x and C-y,C-y that were carried out in the (d) over right arrow(p) over right arrow -> {pp}(s)n reaction at 1.2 and 2.27 GeV. The values obtained for the proton analysing power A(y)(p) also suggest the need for a radical re-evaluation of the neutron-proton elastic scattering amplitudes at the higher energy. It is therefore clear that such measurements can provide a valuable addition to the neutron-proton database in the charge-exchange region.

Publ.-Id: 18926 - Permalink


The ternary system U(VI) / humic acid / Opalinus Clay
Joseph, C.;
The storage of nuclear waste in deep geological formations is discussed worldwide as the main strategy for nuclear waste management. To ensure the confinement of the nuclear waste, a multiple barrier system which consists of engineered, geo-engineered, and geological barriers will be applied. Thereby, in Germany the definition of the isolating rock zone represents an important safety function indicator.
Clay rock is internationally investigated as potential host rock for a repository and represents a part of the geological barrier. In the present work, the natural clay rock Opalinus Clay from the Mont Terri rock laboratory, Switzerland, was studied.
In Germany, the direct disposal of the spent nuclear fuel without the reprocessing of the spent fuel is preferred. In case of water ingress, radionuclides can be released from the nuclear waste repository into its surroundings, namely the host rock of the repository. Humic acids, ubiquitous in nature, can be found associated with the inorganic components in natural clay rock (1.5×10–3 wt.% in Opalinus Clay). They can be released under certain conditions. Due to their variety of functional groups, humic acids are very strong complexing agents for metal ions. They have inherent redox abilities and a colloidal conformation in solution. Because of these characteristics, humic acids can affect the mobility of metal ions such as actinides. Furthermore, in the near-field of a repository elevated temperatures have to be considered due to the heat production resulting from the radioactive decay of the various radionuclides in the nuclear waste.
This work focuses on the interaction of uranium, as main component of spent nuclear fuel, with Opalinus Clay and studies the influence of humic acid and elevated temperature on this interaction. For investigation of the retention behavior of the clay and the mobility of U(VI) in the system, batch sorption and diffusion experiments were performed. To clarify which U(VI) and humic acid species were present under the applied conditions, aqueous speciation modeling was used. Additionally, the U(VI) speciation in solution and on the clay surface was investigated by spectroscopic methods.

Prior to the investigation of the ternary system U(VI) / humic acid / clay, the applied batches of Opalinus Clay were characterized (e.g., specific surface area, carbon content, cation exchange capacity, elemental composition, particle size distribution). Leaching studies with Opalinus Clay in synthetic Opalinus Clay pore water (pH 7.6, It = 0.34 mol/L) and in NaClO4 (pH 3 – 10, I = 0.1 mol/L) were performed to identify the competing ions and their concentrations in the background electrolytes. These data were used to calculate the U(VI) and humic acid speciation in solution. Calcium and carbonate ions are present under pore water conditions as well as in 0.1 mol/L NaClO4 from pH 7 to 8.5, due to dissolution of calcite (mineral fraction in Opalinus Clay). Thus, the U(VI) speciation is dominated by the aquatic Ca2UO2(CO3)3 complex. In the case of pore water, Ca2UO2(CO3)3(aq) is also the dominant U(VI) species in the presence of humic acid, which was corroborated by time-resolved laser-induced fluorescence spectroscopic measurements. A significantly changed speciation was found in 0.1 mol/L NaClO4 in the presence of humic acid. At pH > 7, the negatively charged UO2(CO3)2HA(II)4– complex determines the U(VI) speciation, thus repressing the Ca2UO2(CO3)3(aq) complex. In addition, the speciation of humic acid is influenced from ions leached out from Opalinus Clay. The CaHA(II) complex is the dominating humic acid species in solution.
Batch sorption experiments in 0.1 mol/L NaClO4 showed that Opalinus Clay has the strongest retardation effect on U(VI) in the pH range from pH 4.5 to 7. However, under environmentally relevant conditions (pH > 7), the sorption of U(VI) onto Opalinus Clay is very weak. Under pore water conditions, a distribution coefficient (Kd) of 0.0222 ± 0.0004 m3/kg was determined, which was shown to be independent of solid-to-liquid ratios ≥ 60 g/L. In addition, in pore water, the U(VI) sorption onto Opalinus Clay is not influenced by humic acid, which is supported by the speciation results. Extended X ray absorption fine-structure investigations confirmed this batch sorption result.
The U(VI) diffusion experiments performed in pore water at 25 °C with Opalinus Clay bore core samples confirmed the Kd value obtained by batch sorption experiments. In the diffusion experiments at 60 °C, a change in the U(VI) speciation occurred. Beside Ca2UO2(CO3)3(aq), a colloidal U(VI) species was formed. Almost equivalent apparent diffusion coefficient (Da) values were determined for the diffusion of the aqueous U(VI) species at 25 and 60 °C through Opalinus Clay. Thus, based on the investigations in the present study the breakthrough of U(VI) through Opalinus Clay is expected to be independent of the temperature and should occur nearly at the same time. Modeling calculations showed that it would take about 10 years until a detectable amount of 233U(VI) (1×10–9 mol/L) migrates through an 11 mm thick Opalinus Clay sample.
Two distinct humic acid size fractions – a large- and a small-sized colloid fraction – diffused through the Opalinus Clay samples. Within three months, the high molecular size humic acid colloids migrated only about 500 µm into the clay, whereas the low molecular size fraction diffused through the entire Opalinus Clay samples and were consequently detected in the receiving reservoirs. These findings demonstrate a filtration effect of the compacted clay. The diffusion experiments revealed that the effect of humic acid on U(VI) diffusion is negligible and, under the studied conditions, independent of temperature.
The obtained results contribute to data bases used for modeling of interaction and migration processes in uranium / clay rock systems. Thus, the collected sorption and diffusion data are not only relevant for safety assessment of nuclear waste repositories but also for any clay-containing system present in the environment, where the geochemical interaction with uranium contaminated water plays a role.
Concerning the suitability of Opalinus Clay as host rock for a nuclear waste repository, it can be concluded, that Opalinus Clay has a relatively high retardation potential for U(VI). In case of water ingress U(VI) as part of the nuclear waste is released into the clay formation. Under near-neutral pH conditions, it will be complexed by calcium and carbonate ions leached out from Opalinus Clay, whereby Ca2UO2(CO3)3(aq) is formed. This complex is only weakly retarded by sorption onto the clay, which can contribute to an enhanced mobility of U(VI) in the host rock. However, the U(VI) migration through the clay rock is governed by molecular diffusion. This decelerates the migration of Ca2UO2(CO3)3(aq) through Opalinus Clay and thus it represents the decisive retardation process in the investigated system. Additionally, under environmentally relevant conditions, humic acid has no significant influence on U(VI) / Opalinus Clay interaction even at an elevated temperature of 60 °C. This was shown by speciation, sorption, as well as diffusion experiments.
Keywords: uranium(VI), humic acid, Opalinus Clay, sorption, diffusion, speciation
  • Doctoral thesis
    TU Dresden, 2013
    163 Seiten

Publ.-Id: 18925 - Permalink


Embrittlement of TiAl after high temperature exposure
Paul, J.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Masset, P.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schimansky, F.-P.; Schumacher, P.; Schütze, M.; Wolf, G.; Yankov, R.;
It is well known that the room temperature ductility of gamma-based titanium aluminide alloys is significantly reduced after exposure to elevated temperatures. In some cases exposure can even lead to brittle fracture on reloading of an initially ductile alloy. However the original ductility can be restored if around 30 to 50 µm of the exposed surface is removed before testing. In an attempt to reduce this problem, the effect of coatings combined with halogen treatment on the tensile behaviour of cast + HIPed Ti-48Al-2Cr-2Nb has been investigated. This talk will give a general outline of the embrittlement problem and present current ideas that have been postulated to explain the embrittlement mechanism. Additionally the protective coating methods used in the study will be presented; mechanical test results of specimens that had undergone protective coating treatments are compared to those obtained for un-treated specimens after being oxidised at 900°C for 100 hours.
Keywords: titanium aluminides, oxidation protection, coating
  • Lecture (others)
    International Workshop on Gamma Alloy Technology (GAT 2013), 11.-14.06.2013, Toulouse, France

Publ.-Id: 18924 - Permalink


Shielding and activation calculations for the FASTEF-MYRRHA ADS design in the subcritical operation mode
Ferrari, A.; Di Maria, S.; Sarotto, M.; Stankovskiy, A.;
Accelerator-driven systems (ADS) are one of the options studied for transmutation of nuclear waste in the European Community. The present study has been done in the frame of the FP7 European project Central Design Team (CDT), which in the years 2009-2012 worked to design the FAst Spectrum Transmutation Experimental Facility (FASTEF) with the goal to demonstrate efficient transmutation of high level waste and associated ADS technology. On this design will be based the MYRRHA reactor at SCK•CEN in Mol (Belgium), which should enter the construction phase in 2015. The heart of the system is a lead-bismuth eutectic (LBE) cooled reactor, working both in critical and in sub-critical operation modes. The neutrons needed to sustain fission in the subcritical mode are produced via spallation processes by a 600 MeV, 4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core. The use of high energy/high current proton beams, in combination with a nuclear reactor core operating in subcritical or critical mode, presents many challenges for various aspects of the design, being radiation shielding and minimization of the induced activation key points.
Keywords: Accelerator Driven Systems, Reactor safety, Monte Carlo, Shielding
  • Contribution to proceedings
    2013 ANS Winter Meeting, Session "Best of ICRS/RSPD 2012" (invited), 10.-14.11.2013, Washington, DC, USA
    Transactions of the American Nuclear Society, Volume 109, La Grange Park, Illinois: American Nuclear Society, ISSN:0003-018X, 1249-1251

Publ.-Id: 18923 - Permalink


Surface complexation and oxidation of SnII by nano-magnetite
Dulnee, S.; Banerjee, D.; Merkel, B.; Scheinost, A. C.;
The long-lived fission product 126Sn is of substantial interest in the context of nuclear waste disposal in deep underground repositories. However, the prevalent redox state (di- or tetravalent), the aqueous speciation as well as the reactions at the mineral-water interface under the expected anoxic conditions are still a matter of debate. We therefore investigated the reaction of SnII with a relevant redox-reactive mineral, magnetite (FeIIFeIII2O4) at < 2 ppmv O2, and monitored Sn uptake as a function of pH and time. Tin redox state and local structure was monitored by Sn-K X-ray absorption spectroscopy (XAS). We observed a rapid (< 30 min) uptake and oxidation of SnII to SnIV in the presence of magnetite. The local structure determined by XAS showed two Sn-Fe distances of about 3.15 and 3.60 Å in line with edge and corner sharing arrangements between octahedrally coordinated SnIV and the magnetite surface, indicative of formation of tetradentate inner-sphere complexes between pH 3 and 9, in line with the strong sorption (logRd >5 from pH 3 to 9). Based on the EXAFS-derived surface structure, we could successfully model the sorption data with two different complexes, (Magn_sO)4Sn(OH)2-2 ( -14.97±0.35) prevailing from pH 2 to 9, and (Magn_sO)4Sn(OH)2Fe ( -17.72±0.50), which forms at pH > 9 by co-adsorption of FeII, thereby increasing sorption at this high pH.
Keywords: Sn Redox Surface complexation Nuclear waste magnetite EXAFS XANES XRD TEM

Publ.-Id: 18922 - Permalink


Mineralogical characterization of REE mineralization in Norra Kärr alkaline complex, Sweden
Atanasova, P.; Krause, J.; Gutzmer, J.;
Alkaline complexes comprise one of the most promising future sources for rare earth element supply. They are particularly enriched in heavy rare earth elements. However, the often complex and highly unusual mineralogy of REE-enriched ores from alkaline complexes pose particular challenges for beneficiation. A geometallurgical approach is required to quantify mineralogical and textural diversity and variability. Based on a geometallurgical model, a suitable approach to beneficiation can be developed. Scanning electron microscope (SEM)-based image analysis can be used to characterize ores as well as beneficiation products. A wide range of tangible mineralogical and textural parameters are constrained for every ore type, including mineral abundance, grain size, and liberation. SEM-based image analysis combined with a quantitative analysis of the chemical composition of the ore minerals is illustrated here for the case of the Norra Kärr alkaline complex, Sweden. Current research focuses on quantitative mineralogical and textural constraints for different lithological domains recognized in the HREE-Zrmineralized zones of the complex. Based on the results, a geometallurgical model will be developed that will be based on the processing characteristics of the different portions of the mineralized zones.
Keywords: rare earth elements, alkaline complex, geometallurgy, eudialyte, nepheline-syenite
  • Contribution to proceedings
    Mineral Deposit Research for a High-tech World: 12th SGA Biannial Meeting, 12.-15.08.2013, Uppsala, Sweden
    Mineral Deposit Research for a High-tech World: 12th SGA Biannial Meeting, 978-91-7403-207-9, 298-301
  • Lecture (Conference)
    Mineral Deposit Research for a High-tech World: 12th SGA Biannial Meeting, 12.-15.08.2013, Uppsala, Sweden
  • Lecture (others)
    FEI User Group Meeting, 08.-09.10.2013, Eindhoven, Holland

Publ.-Id: 18921 - Permalink


Block Kriging for geometallurgical optimization
Tolosana-Delgado, R.; Mueller, U.; van den Boogaart, K. G.; Ward, C.;
Adpative processing is often related to the mineral composition of the mining block currently processed. The portions of waste, ore and secondary product minerals considered are always positive and typically sum to 100%, i.e. a composition. A typical solution to predict block averages of spatially dependent quantities would be block kriging. However, kriging is based on spatial correlations and it has been repeatedly shown that correlations of compositional data are spurious and blurred by the constant sum constraint.

Aitchison (1982) proposed a general solution for compositional problems, based on transforming the compositional data to a set of logarithms of ratios of components, and analysing the transformed scores. The transform is chosen to be invertible to ensure that no information is lost in the process. This methodology avoids spurious correlation problems and ensures coherence between results obtained with different subcompositions. Pawlowsky-Glahn and Olea (2004) already adapted the approach for point-support geostatistics, allowing the prediction of point compositions from spatially neighbouring data, without the artefacts induced by using standard multivariate cokriging. Unfortunately upscaling the results of this approach with block kriging is not straightforward, because of the nonlinearity of logratio transforms. Furthermore, we have to consider those nonlinearities created by the dependence on the block composition of extraction efficiency and processing costs of the possible processing choices.

This paper proposes a solution for predicting the conditional expectations of the benefit of processing the block with each processing choice using geostatistical simulations of the local values of the composition and the resulting block integrals. The computation for a large number of blocks can be done efficiently using Cholesky decomposition. The approach also allows the calculation of prediction errors for expected compositions and expected benefit at almost no additional computational cost. Such compositional approach is necessary, e.g.: when processing choices depend on proportions of certain minerals after other components have been removed; or if processing alters the composition in a multiplicative way, by partially removing a portion of some components.
Keywords: Compositional data analysis,optimization, negative bias, uniform conditioning
  • Contribution to proceedings
    23rd World Mining Congress, 11.-15.08.2013, Montreal, Canada

Publ.-Id: 18920 - Permalink


Regression between compositional data sets
Tolosana-Delgado, R.; van den Boogaart, K. G.;
Linear regression where both the explained and the explanatory variables form compositions are naturally tractable within the log-ratio framework. Fitting such models does not imply any diculty: they can be t in a standard way after applying any one-to-one logratio transformation to each compositional set. Problems arise to test and display the model, due to the large dimension of the model parameters space, and the dicult interpretation of classical hypotheses in terms of the original components. This contribution proposes two graphical representations of the model: in the form of a biplot, parallel to redundacy analysis, and as condence ellipses on the parameters projected onto a set of subcompositions. Each of these representations brings also associated a way to test for certain subcompositional independence hypotheses. An exact, general, Scheffé-like test of independence (for the whole composition or any subcomposition) can be derived from a generalized eigenvalue problem of the matrix of regression coecients and its estimation covariance matrix. For certain hypotheses of independence, classical tests based on Hotelling's T2 or X2 distributions can also be adapted. Any of these tests can be used to calculate the radii of condence ellipses on the parameters, in order to visualize the corresponding tests. This provides a toolbox to reduce the complexity of compositional-to-compositional regression, and enables a structured way of exploring and testing which components of the explanatory set influence which components of the explained set.
  • Open Access LogoContribution to proceedings
    the 5th International Workshop on Compositional Data Analysis, 03.-07.06.2013, Vorau, Österreich
    Proceedings of the 5th International Workshop on Compositional Data Analysis, 978-3-200-03103-6, 164-188

Publ.-Id: 18919 - Permalink


Compositional regression with unobserved components or below detection limit values
van den Boogaart, K. G.; Tolosana-Delgado, R.; Hron, K.; Templ, M.; Filzmoser, P.;
The typical way to deal with zeroes and missing values in compositional data sets is to impute them with a reasonable value, and then the desired statistical model is estimated with the imputed data set, e.g. a regression model. This contribution aims at presenting alternative approaches to this problem within the framework of Bayesian regression with a compositional response. In a first step, a compositional data set with missing data is considered to follow a normal distribution on the simplex, which mean value is given as an Aitchison ane linear combination of some fully-observed explanatory variables. Both the coecients of this linear combination and the missing values can be estimated with standard Gibbs sampling techniques. In a second step, a normally-distributed additive error is considered superimposed on the compositional response, and values are taken as \below the detection limit" (BDLs) if they are \too small" in comparison with the additive standard deviation of each variable (usually, a 3 rule is applied here). Within this framework, the regression parameters and all missing values (including BDLs) can be estimated, albeit this time with a less ecient Metropolis-Hastings algorithm. Both methods estimate the regression coecients without need of any preliminary imputation step, and adequately propagate the uncertainty derived from the fact that the missing values and BDLs are not actually observed, something imputation methods cannot achieve.
  • Open Access LogoContribution to proceedings
    CoDaWork'2013: the fifth international Workshop on Compositional Data Analysis, 03.-07.06.2013, Vorau, Österreich
    Proceedings of CoDaWork'2013: the fifth international Workshop on Compositional Data Analysis, 978-3-200-03103-6, 10-19

Publ.-Id: 18918 - Permalink


The challenges of adaptive processing to geostatistical prediction
van den Boogaart, K. G.; Konsulke, S.; Tolosana Delgado, R.;
Adaptive Processing as proposed in geometallurgy has to rely on spatially interpolated information on geometallurgical parameters like phase composition, size distributions of particles of different phases, grain shape parameters, and portions of value elements in different grains. Using the geostatistically predicted values for adaptive processing, e.g. for the selection of milling diameters, thresholds in physical separation, or choices on using an extra pre-separation step, is typically not optimal. Mathematically this effect is introduced by two forms of nonlinearities: 1) The nonlinear scales of compositions, distributions, and shapes have special properties with respect to geostatistics. Classical geostatistics creates some artefacts for these nonlinear scales. On the other hand, modern geostatistical procedures adapted to these scales do not provide unbiased results with respect to linear transformations of the data (e.g. biased block estimates). 2) Neither economic nor ecological effects (e.g. monetary gain) of processing decisions are linear in the interpolated geometallurgical parameters. These nonlinear transforms are not unbiasedly estimated by the likewise transformed unbiased geostatistical predictions of the geometallurgical parameters. Furthermore, we need to optimize the conditional expectation of the gain, rather than obtain an unbiased estimate. Standard geostatistics as such does not provide the "right sort" of estimates for adaptive processing. A nonlinear kriging procedure is needed to approximate the nonlinearities mentioned before.

We propose to solve these problems simultaneously using a nonlinear geostatistical technique for predicting the target function (the monetary gain), rather than to predict the geometallurgical parameters and compute the gain from them. The optimization can then be performed directly on this estimated function.
It can be shown that this optimization performed on the conditional expectations, not on unbiased predictions, would yield the best possible processing choice. We propose a procedure choosing the processing parameters on an approximation of the conditional expectation. The difficulties with the classical approach and the effectiveness of this new approach are illustrated by a simplified simulation example with a single processing parameter and a simple dependence on the microstructure.
Keywords: geometallurgy, nonlinear geostatistics, optimisation, processing
  • Contribution to proceedings
    23rd World Mining Congress, 11.-15.08.2013, Montreal, Canada
    23rd World Mining Congress 2013 Proceedings, 978-1-926872-15-5

Publ.-Id: 18917 - Permalink


Chemical Equilibria in Compositional Data
van den Boogaart, K. G.; Tolosana-Delgado, R.; Konsulke, S.;
Chemical equilibria are typically formulated in terms of concentrations and depend on temperature and thermodynamical constants. In simple systems (e.g. aqueous diluted solutions), these equilibria are governed by the chemical master equation or equilibrium constant. In natural systems the chemical composition is often observed incompletely and relative, i.e. according to the compositional principles. This contribution shows how the chemical master equation is related to the geometry of the Aitchison simplex. If the reaction in equilibrium preserve the amount of matter, the equilibrium defines a hyperplane in the Aitchison simplex. When the reaction does not preserve the amount of matter, the equilibrium can be used to infer the total matter per unit volume.
Keywords: chemical master equation, thermodynamical equilibria, Aitchison simplex
  • Contribution to proceedings
    15th Annual Conference of the International Association for Mathematical Geosciences, 02.-06.09.2013, Madrid, Espana
    Mathematics of Planet Earth - Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences: Springer, 978-3-642-32408-6, 107-111
    DOI: 10.1007/978-3-642-32408-6_26

Publ.-Id: 18916 - Permalink


Testing for microhomogeneity in reference materials for microanalytical methods
Tolosana-Delgado, R.; Renno, A. D.; Michalak, P. P.; van den Boogaart, K. G.;
It is assumed that reference materials for analytical methods must be homogeneous, i.e. have the same concentration of the relevant element(s) overall, to ensure that they can be used reliably to get comparison values during the analysis with non absolute methods. To ensure such homogeneity becomes increasingly difficult with increasing resolution, up to the point that it is not possible for several microanalytical methods. We propose a way to get reliable comparison values with some types of inhomogeneous material. This is based on multiple probing the reference material. The minimal number of probing spots required for a certain precision level can be derived from the variance calculations. However, using adequate models of local heterogeneity can greatly reduce that number: Geostatistics can be used in random, systematic and periodic heterogeneities, while robust methods are useful in cases of nugget heterogeneities.
Keywords: inhomogeneity, microanalytical methods, calibration, simple kriging
  • Contribution to proceedings
    15th Annual Conference of the International Association for Mathematical Geosciences, 02.-06.09.2013, Madrid, Espana
    Mathematics of Planet Earth - Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences: Springer, 978-3-642-32408-6, 27-32
    DOI: 10.1007/978-3-642-32408-6_7

Publ.-Id: 18915 - Permalink


Compositional Block Cokriging
Tolosana-Delgado, R.; Mueller, U.; van den Boogaart, K. G.; Ward, C.;
Estimates of a whole block composition may be useful for improving the assessment and mining of resources, especially if the economic viability depends on more than just one metal or component. Banded Iron Formation (BIF) represents such a case, where optimal exploitation requires evaluation of Fe content, as well as waste and penalty elements. Block cokriging of the whole composition may yield these estimates. To avoid the spurious correlation problem, this should be based on log-ratios of the composition. But due to the non-linearity of the log-ratio transformations, this does not yield a direct change-of-support model. This contribution explores the approximation of this block average compositional cokriging by means of geostatistical simulation within the block. This methodology is illustrated with a BIF deposit of Western Australia.
Keywords: ALN, alr, compositional kriging, LU simulation
  • Contribution to proceedings
    15th Annual Conference of the International Association for Mathematical Geosciences, 02.-06.09.2013, Madrid, Espana
    Mathematics of Planet Earth - Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences: Springer, 978-3-642-32408-6, 713-716
    DOI: 10.1007/978-3-642-32408-6_154

Publ.-Id: 18914 - Permalink


Radiation field characterization and shielding studies
Ferrari, A.; Amato, E.; Margarone, D.;
The achieved performances in terms of energy and brightness of laser-accelerated particle beams require a proper shielding assessment for the primary and secondary ionizing radiation, especially when high intensity laser systems operate in repetition rate (typically in the range 0.1-10 Hz). In the frame of the ELI Beamlines project a general shielding study for both the 10 PW (0.016 Hz) and 2 PW (10 Hz) laser beamlines, dedicated to the high energy electron and proton acceleration, has been performed. All the work has been done keeping in mind that we deal with a rapidly evolving field, where not all the parameters that characterize the radiation fields can be completely set at this stage: the precise description of the source particle distributions, double-differential in energy and in angle, can evolve with the improved knowledge, and on the other hand the workload (in terms of shots/day), could be optimized in the future with the increased experience and technological improvements. The general philosophy has been therefore to maintain a realistic approach, always conservative, and adopt where possible flexible solutions. In the present work a summary of the analysis done and the solutions proposed for the longitudinal containment of the radiation in the proton acceleration experimental area is illustrated and discussed.
Keywords: Laser-particle acceleration, Monte Carlo, Shielding
  • Lecture (Conference)
    2nd ELIMED Workshop and Panel, 18.-19.10.2012, Catania, Italy
  • AIP Conference Proceedings 1546(2013), 57-62
    DOI: 10.1063/1.4816607

Publ.-Id: 18913 - Permalink


Effects of dopaminergic treatment on striatal dopamine turnover in de novo Parkinson disease
Storch, A.; Wolz, M.; Beuthien-Baumann, B.; Loehle, M.; Herting, B.; Schwanebeck, U.; Oehme, L.; van den Hoff, J.; Perick, M.; Graehlert, X.; Kotzerke, J.; Reichmann, H.;
Objective: To evaluate the effects of levodopa and the dopamine D2 agonist cabergoline on striatal dopamine turnover estimated as the inverse of the effective dopamine distribution volume ratio (EDVR) measured by F-18-dopa PET in de novo Parkinson disease (PD).

Methods: Single-center, parallel-group, randomized, observer-blinded study of cabergoline (3 mg/day) and levodopa (300 mg/day) over 12 weeks in patients with de novo PD. Primary efficacy measure was the change of the side-to-side averaged putaminal EDVR comparing baseline and end-of-maintenance period.

Results: Thirty-five out of 39 randomized patients were assigned to the primary efficacy analysis (cabergoline, n = 17; levodopa, n = 18). At the end of treatment period, mean EDVRs were significantly lower compared to baseline solely in the levodopa group (relative change -1.0 +/- 13.0% in cabergoline [p = 0.525 when compared to baseline], -8.3 +/- 11.8% in levodopa group [p = 0.006]) with a nonsignificant trend between groups (mean relative difference: 7.3% (95% confidence interval -1.2% to 15.8%; p = 0.091). There was significant clinical improvement in both groups at 12 weeks compared to baseline, but no significant differences between groups in clinical and PET secondary outcome measures. Both pharmacologic treatments and PET scanning were well-tolerated and safe.

Conclusion: Putaminal dopamine turnover is increased by levodopa treatment in de novo PD. The nonsignificant trend toward a larger influence by levodopa compared to cabergoline is supported by ancillary statistical analyses. This augmentation of early compensatory events by levodopa might contribute not only to its symptomatic effects, but also to its induction of motor complications.

Publ.-Id: 18912 - Permalink


Pairs of Effective Spin Merons in Ferromagnetic Multilayer Elements
Wintz, S.; Bunce, C.; Neudert, A.; Körner, M.; Strache, T.; Buhl, M.; Erbe, A.; Gemming, S.; Raabe, J.; Quitmann, C.; Fassbender, J.ORC
We report on pairs of diverging/converging spin vortices in Co/Rh/Ni81Fe19 disks. The lateral magnetization distribution of these effective spin merons [1] is directly imaged by means of element-selective x-ray microscopy. By this method, both the circulation and divergence states of the individual layers are identified as antisymmetric [2] (see Figure 1). Magnetization reversal measurements of corresponding continuous films reveal that biquadratic interlayer exchange coupling is the origin for the formation of such effective meron pairs. Furthermore, the effective meron pair’s three-dimensional magnetic structure is determined via micromagnetic simulations. We find that the perpendicular magnetization component is distributed nonhomogeneously, namely M is partially circulating on a flux-closing torus. This toroidal topology enforces a symmetry break, which ties the core polarities to the divergence configuration. Upon excitation, such topology-induced core stabilization could lead to enhanced maximum amplitudes of steady gyration compared to single layer vortices, as the meron pair’s core switching onset velocity is expected to be higher than that of a single vortex.
  • Lecture (Conference)
    58th Conference on Magnetism and Magnetic Materials (MMM), 04.-08.11.2013, Denver, USA

Publ.-Id: 18911 - Permalink


Economic surface treatment of Ti-alloys to improve their resistance against environmental high temperature attack
Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.;
High temperature Ti-alloys are usually sophisticated and hence expensive. To allow the use of cheaper alloys at elevated temperatures an economic and easy to apply procedure was developed to improve their high temperature capability. The treatment consists of a combination of Alenrichment in a shallow surface region plus additional fluorination. The Al-enrichment at elevated temperatures leads to the formation of intermetallic TiAl-phases. These phases improve the oxidation resistance of Ti-alloys but not to a sufficient extent. An additional fluorine treatment of the Al-enriched surface leads to the formation of a protective alumina scale due to the fluorine effect. In this paper results from high temperature exposure tests performed on different Ti-alloys without any treatment and with a combination of Al-treatment plus fluorination are presented. The results are discussed in the view of the use of the optimized Ti-components for several high temperature applications.
Keywords: titanium, embrittlement, oxidation

Publ.-Id: 18910 - Permalink


Precise study of the supernova reaction 40Ca(α,γ) 44Ti by activation and in-beam γ-spectroscopy
Schmidt, K.; Akhmadaliev, C.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Degering, D.; Dietz, M.; Dressler, R.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Marta, M.; Menzel, M.-L.; Munnik, F.; Schumann, D.; Schwengner, R.; Szücs, T.; Wagner, A.; Yakorev, D.; Zuber, K.;
The radioactive nuclide 44Ti is believed to be produced in the α-rich freezeout preceding supernova explosions. The γ-rays from its decay have been observed in space-based γ-observatories for the Cassiopeia A and very recently also SN 1987A supernova remnants. The rates of the nuclear reactions governing the production and destruction of 44Ti should therefore be known with high precision. Over the last years there have been various studies of the 40Ca(α,γ)44Ti reaction, which is dominating the 44Ti production in supernovae. Those studies have been performed using in-beam γ-spectroscopy, activation, accelerator mass spectrometry (AMS), and recoil mass spectrometry via inverse kinematics. However, there are still discrepancies in the resulting reaction rates. Using an α-beam of 1-2 A intensity the strengths of the strongest 40Ca(α,γ)44Ti resonances from 3.5 to 4.5 MeV laboratory α-energy have been studied by in-beam γ-counting and activation. The samples have been analyzed in the ultra-low-background underground γ-counting facility "Felsenkeller Dresden". The target stoichiometry has been determined by nuclear reactions and by elastic recoil detection analysis (ERDA). An AMS measurement of the activated samples is in preparation.
Keywords: alpha rich freeze-out, capture reaction, hydrogen depth profiling
  • Lecture (Conference)
    Workshop on "Open problems and future directions in heavy element nucleosynthesis", 10.-12.04.2013, Debrecen, Hungary
  • Lecture (Conference)
    25th International Nuclear Physics Conference (INPC 2013), 02.-07.06.2013, Firenze, Italy

Publ.-Id: 18909 - Permalink


Electron-induced damage of biotin studied in the gas phase and in the condensed phase at a single-molecule level
Keller, A.; Kopyra, J.; Gothelf, K.; Bald, I.;
Biotin is an essential vitamin that is on the one hand relevant for the metabolism, gene expression, and in the cellular response to DNA damage, and on the other hand finds numerous applications in biotechnology. The functionality of biotin is due to two particular sub-structures, the ring structure and the side chain with carboxyl group. The heterocyclic ring structure results in the capability of biotin to form strong intermolecular hydrogen and van-der-Waals bonds with proteins such as streptavidin, whereas the carboxyl group can be employed to covalently bind biotin to other complex molecules. Dissociative electron attachment (DEA) to biotin results in a decomposition of the ring structure and the carboxyl group, respectively, within resonant features in the energy range 0-12 eV, thereby preventing the capability of biotin for intermolecular binding and covalent coupling to other molecules. Specifically, the fragment anions (M-H)-, (M-O)-, C3N2O-, CH2O2-, OCN-, CN-, OH- and O- are observed, and exemplarily the DEA cross section of OCN- formation is determined to be 3·10-19 cm2. To study the response of biotin to electrons within a complex condensed environment we use the DNA origami technique and determine a dissociation yield of (1.1 ± 0.2)·10-14 cm2 at 18 eV electron energy, which represents the most relevant energy for biomolecular damage induced by secondary electrons. The present results thus have important implications for the use of biotin as a label in radiation experiments.

Publ.-Id: 18908 - Permalink


Bildung Zn-haltiger Korrosionsprodukte bei einem Kühlmittelverluststörfall
Hoffmann, W.; Kryk, H.;
Im Kühlmittel eines DWR können nach einem Störfall mit Kühlmittelverlust während des Sumpfumwälzbetriebs höhere Konzentrationen an gelöstem Zink auftreten, die durch Korrosion verzinkter Einbauten des Containments verursacht werden. Bei höheren Temperaturen werden feste Korrosionsprodukte ausgeschieden. Die Ausscheidung lief im Batchversuch mit einer Verzögerung ab, was auf komplexe Vorgänge bei der Partikelbildung hinweist. Unterschiede in der chemischen Zusammensetzung zu Produkten, die an Heizelementen entstehen, lassen einen Einfluss der Bildungsbedingungen auf den Reaktionsmechanismus erkennen. Durch die im Notkühlkreislauf vorliegenden Temperaturgradienten können die korrosionsbedingte Zn-Auflösung und Partikelbildung gleichzeitig ablaufen. Die Bildung und Ablagerung von Zn-Korrosionsprodukten im Kern soll durch weiterführende Arbeiten im Rahmen des Projektes untersucht werden.
Keywords: LOCA, Zn corrosion, boric acid, deposition of corrosion products
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2013, 14.-16.05.2013, Berlin, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2013, 14.-16.05.2013, Berlin, Deutschland
    CD-ROM

Publ.-Id: 18907 - Permalink


Simulation of particle deposition and multilayer formation between periodic steps
Lecrivain, G.; Drapeau-Martin, S.; Barth, T.; Hampel, U.;
In a pebble-bed high temperature reactor core where thousands of pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust eventually deposits in the primary circuit of the reactor. The numerical prediction of graphite dust deposition is therefore a key safety issue and needs investigation. The deposition of aerosol graphite particles in a turbulent channel flow obstructed by periodic steps is here numerically investigated at Reynolds number Re = 8,000. Particles in the size range d = 1...100μm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. A two dimensional quasi-static simulation is performed. The quasi-static assumption is motivated by the time duration of the experimental test which lasts several hours. The iterative process is decomposed as follows: a Reynolds Averaged Navier Stokes turbulence model is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After sufficient deposition of the particulate matter, the build-up of the dust layer is computed using mechanics of dry granular material. The wall boundaries of the computational domain are then updated prior to the next flow simulation. The procedure is repeated until the dust layer reaches appropriate growth. The result of the multi-layer deposition matches reasonably well that of the experimental test performed on-site
  • Lecture (Conference)
    Cluster Workshop on Thermal Hydraulics of Innovative Nuclear Systems, 06.-07.02.2013, Stockholm, Sweden

Publ.-Id: 18906 - Permalink


Simulation of particle bed formation between obstacles
Lecrivain, G.; Hampel, U.;
In a pebble-bed high temperature reactor core where thousands of pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust eventually deposits in the primary circuit of the reactor. The numerical prediction of graphite dust deposition is therefore a key safety issue and needs investigation. The deposition of aerosol graphite particles in a turbulent channel flow obstructed by periodic steps is here numerically investigated at Reynolds number Re = 10,000. Particles in the size range d = 1...20µm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. A two dimensional quasi-static simulation is performed. The quasi-static assumption is motivated by the time duration of the experimental test which lasts several hours. The iterative process is decomposed as follows: a Reynolds Averaged Navier Stokes turbulence model is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After sufficient deposition of the particulate matter, the build-up of the dust layer is computed using mechanics of dry granular material. The wall boundaries of the computational domain are then updated prior to the next flow simulation. The procedure is repeated until the dust layer reaches appropriate growth. The result of the multi-layer deposition matches reasonably well that of the experimental test performed on-site
  • Lecture (others)
    2nd Ph.D. Reactive Transport Modeling Meeting, 26.03.2013, Leipzig, Dresden

Publ.-Id: 18905 - Permalink


Simulation of graphite dust resuspension in a turbulent square dust flow
Lecrivain, G.; Loyseau, X.; Hampel, U.;
In a pebble-bed High Temperature Reactor (HTR) core where thousands of graphite pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the coolant gas and deposits in the primary circuit of the reactor. In the event of a Loss of Coolant Accident (LOCA) radioactive carbonaceous dust may be resuspended and escape the system boundaries. There is therefore a need to predict the dust resuspension during a LOCA.
A resuspension model is here presented and coupled with computational fluid dynamics. A Reynolds-averaged Navier–Stokes is employed to simulate the turbulent flow in a wall-bounded channel flow. Micro-sized graphite particles are initially placed on the bottom wall surface of the virtual channel flow. The gas velocity is gradually increased and the resuspended fraction is plotted as a function of the wall shear velocity. The number of reentrained particles increases with gas velocity. The overall resuspended fraction matches experimental data available from the literature. It is found that particles far from the side walls reenter the turbulent flow much faster than those near the corner.
Findings from this study can be used for the prediction of carbonaceous dust resuspension in a HTR during a LOCA.
  • Open Access LogoContribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-15.05.2013, Pisa, Italy

Publ.-Id: 18904 - Permalink


Infrared ellipsometry for improved laterally resolved analysis of thin films
Hinrichs, K.; Furchner, A.; Sun, G.; Gensch, M.; Rappich, J.; Oates, T.;
In the present article we discuss developments towards increasing the spatial resolution of infrared ellipsometry and ellipsometric microscopy for the study of thin films. Relevant aspects in the interpretation of observed peaks in the infrared (ellipsometric) spectra are discussed. In particular anisotropic effects in dependence of molecular orientations in organic films and the excitation of a macroscopic wave, the Berreman mode, in thin silicon oxide films are addressed. For correct interpretation of measured data optical simulations are essential to avoid incorrect conclusions on band frequency and assignments.
Keywords: FTIR-microscopy, Infrared spectroscopic ellipsometry, molecular orientation, thickness, polymer film, silicon oxide

Publ.-Id: 18903 - Permalink


Speciation of iodine isotopes inside and outside of a contaminant plume at the Savannah River Site
Schwehr, K. A.; Otosaka, S.; Merchel, S.; Kaplan, D. I.; Zhang, S.; Xu, C.; Li, H.-P.; Ho, Y.-F.; Yeager, C. M.; Santschi, P. H.; Aster, T.;
A primary obstacle to understanding the fate and transport of the toxic radionuclide 129I (a thyroid seeker) is an accurate method to distinguish it from its stable isotope, 127I, and to quantify its various species at environmentally relevant concentrations (~10-8 M). A pH-dependent solvent extraction and combustion method was paired with accelerator mass spectrometry (AMS) to measure ambient levels of 129I/127I isotope ratios and iodine speciation (iodide (I-), iodate (IO3-), and organo-I (OI)) in aquatic systems. The method exhibits an overall uncertainty of 10% or less for iodide and iodate, and less than 20% for organo-I species concentrations and enabled 129I measurements as low as 0.5 Bq/L in groundwater from the Savannah River Site (SRS) in South Carolina, USA along a pH, redox potential (Eh), and organic carbon gradient. The data confirmed that the 129I/127I ratios and species distribution were strongly pH dependent, consistent with our knowledge that the 129I was emanating from a strongly acidic source. Low 129I concentrations detected in samples collected outside the known 129I plume, as delineated by the Maximum Contaminant Level (MCL) of 1 pCi/L129I (0.037 Bq/L), were still orders of magnitude higher than ambient 129I concentration typically found in the USA groundwater. This is likely due to past atmospheric releases of volatile 129I species by SRS nuclear reprocessing facilities near the study site. The results confirmed the existence of 129I as not only iodide, but as organic iodine and iodate species. This study underscores the importance of understanding a contaminant’s biogeochemistry at multiple concentrations, concentrations below and above regulatory MCLs.
Keywords: Radioiodine (I-129), Iodide, Iodate, Organo-iodine, Accelerator mass spectrometry, AMS, Iodine speciation

Publ.-Id: 18902 - Permalink


Crystallization induced by thermal annealing with millisecond pulses in silicon-on-insulator films implanted with high doses of hydrogen ions
Tyschenko, I. E.; Volodin, V. A.; Voelskow, M.;
The crystallization of silicon-on-insulator films, implanted with high doses of hydrogen ions, upon annealing with millisecond pulses is studied. Immediately after hydrogen-ion implantation, the formation of a three-phase structure composed of silicon nanocrystals, amorphous silicon, and hydrogen bubbles is detected. It is shown that the nanocrystalline structure of the films is retained upon pulsed annealing at temperatures of up to similar to 1000A degrees C. As the temperature of the millisecond annealing is increased, the nanocrystal dimensions increase from 2 to 5 nm and the fraction of the nanocrystalline phase increases to similar to 70%. From an analysis of the activation energy of crystal phase growth, it is inferred that the process of the crystallization of silicon films with a high (similar to 50 at %) hydrogen content is limited by atomic-hydrogen diffusion.
Keywords: Crystallization, Flash Lamp Annealing, Hydrogen Implantation, SOI

Publ.-Id: 18901 - Permalink


A new approach to chemical imaging with PIXE using an X-ray colour camera
Munnik, F.; Hanf, D.; Ziegenrücker, R.; Renno, A. D.;
Summary:
A new approach using poly-capillaries has been used for laterally resolved PIXE.
Promising for large area surveys.
The experimental setup is ready and works.

Outlook:
Start of a Ph.D. student in the framework of the Marie-Cure project SPRITE.
Some technical extensions have still to be installed.
Development data-reduction protocols and image reconstruction.
Development of integrated control and analysis software.
Keywords: PIXE, CCD camera
  • Lecture (Conference)
    Workshop „Ionenstrahlen – Forschung und Anwendung“, 12.-13.06.2013, Leipzig, Deutschland

Publ.-Id: 18900 - Permalink


Prozessführung und Echtzeit-Monitoring von Grignard-Reaktionen
Kryk, H.;
Als Grignard-Reaktionen werden chemische Reaktionen zwischen einem organischen Halogenid und Magnesium zur entsprechenden magnesium-organischen Verbindung (Grignard-Reagenz) bezeichnet, welche große Bedeutung als Zwischenprodukte für organische Synthesen in der Feinchemie und der pharmazeutischen Industrie haben. Grignard-Reaktionen besitzen aufgrund des spezifischen Prozessverhaltens der stark exothermen Bildungsreaktionen und der hohen Reaktivität der Grignard-Reagenzien ein erhöhtes Gefahrenpotenzial. Hauptgefahrenquellen sind das verzögerte Starten der Reaktion bei unzulässig hoher Halogenid-Konzentration und Halogenid-Akkumulationen im Rührkesselreaktor während des Semibatch-Prozesses durch hohe Dosierraten und/ oder sinkende Reaktionsgeschwindigkeiten. Von großer Bedeutung für die Prozesssicherheit sind deshalb industriell anwendbare Methoden für eine objektive Detektion des Reaktionsstarts und für die Echtzeit-Verfolgung von Edukt-Akkumulationen im Reaktionsgemisch.
In Form eines Übersichtsvortrages werden online-spektroskopische Methoden zur Reaktionsverfolgung mittels FTIR sowie am HZDR entwickelte, auf gekoppelten Energie- und Stoffbilanzen basierende echtzeitfähige Verfahren zur Reaktionsstart-Detektion und zur Verfolgung der Edukt- und Produktkonzentrationen im Reaktionsgemisch eines Rührkesselreaktors vorgestellt und im Detail erläutert. Weiterhin erfolgt der Vergleich zwischen industriell etablierten Detektionsmethoden unter Nutzung konventioneller Prozesssignale sowie analytik- und bilanzbasierten Verfahren, wobei die Vor- und Nachteile der einzelnen Methoden dargestellt werden. Aus den Ergebnissen der bilanzbasierten Reaktionsverfolgung können sicherheitstechnische Kenngrößen abgeleitet werden, die eine inhärent sichere Prozessführung bei gleichzeitiger Erhöhung der Prozesseffizienz ermöglichen.
Keywords: Grignard, process control, FTIR, real-time monitoring, heat balance, process safety, inherent safety
  • Invited lecture (Conferences)
    Firmen-Kolloquium der Saltigo GmbH, 13.06.2013, Leverkusen, Deutschland

Publ.-Id: 18899 - Permalink


Impact of Triaxiality on the Emission and Absorption of Neutrons and Gamma Rays in Heavy Nuclei
Grosse, E.; Junghans, A. R.; Massarczyk, R.;
For many spin-0 target nuclei neutron capture measurements yield information on level densities at the neutron separation energy. Also the average photon width has been determined from capture data as well as Maxwellian average cross sections for the energy range of unresolved resonances. Thus it is challenging to use this data set for a test of phenomenological prescriptions for the prediction of radiative processes. An important ingredient for respective calculations is the photon strength function for which a parameterization was proposed using a fit to giant dipole resonance shapes on the basis of theoretically determined ground state deformations including triaxiality. Deviations from spherical and axial symmetry also influence level densities and it is suggested to use a combined parameterization for both, level density and photon strength. The formulae presented give a good description of the data for low spin capture into 124 nuclei with 72 Keywords: Nuclear triaxiality; level density; average radiative width; Maxwellian averaged cross sections; nuclear waste transmtation

Publ.-Id: 18898 - Permalink


Geometallurgical Classification of REE Mineralisation in Alkaline Complexes
Atanasova, P.; Gutzmer, J.; Leijd, M.;
Alkaline complexes comprise one of the most promising future sources for future rare earth element supply. They are particularly enriched in heavy rare earth elements. However, the often complex and highly unusual mineralogy of REE-enriched ores from alkaline complexes pose particular challenges for beneficiation. A geometallurgical approach is required to quantify mineralogical and textural diversity and variability. Based on a geometallurgical model, a suitable approach to beneficiation can be developed. SEM-based image analysis can be used to characterize ores as well as beneficiation products. A wide range of tangible mineralogical and textural parameters are constrained for every ore type, including mineral abundance, grain size, and liberation. The use of such an approach is illustrated here for the case of the Norra Kärr alkaline complex, Sweden. The complex is highly deformed and metamorphosed and known currently to contain resources of 41.6 Mt @ 0.57 % TREO with 51 % HREO/TREO and 1.7 % ZrO2 (indicated) and 16.5 Mt @ 0.64 % TREO with 49% HREO/TREO and 1.7 % Zr2O (inferred). Mineralization is hosted by aegirine nepheline-syenites that show a considerable textural and compositional diversity. REE-bearing minerals include eudialyte group minerals and very minor mosandrite and cerite. Zr is hosted by Zr-silicates catapleiite and eudialyte. Current research focuses to provide quantitative mineralogical and textural constraints for different lithological domains recognized in the HREE-Zr-mineralized zones of the complex. Based on the results, a geometallurgical model will be developed that will be based on the processing characteristics rather of the different portions of the mineralized zones.
Keywords: rare earth elements, alkaline complex, geometallurgy,
  • Lecture (Conference)
    Critical Minerals 2013, 04.-05.06.2013, Perth, Australia
  • Contribution to proceedings
    Critical Minerals 2013, 04.-05.06.2013, Perth, Australia
    Critical Minerals Conference 2013 - Conference Proceedings, Australia: Australasian Institute of Mining and Metallurgy, 978 1 921522 88 8

Publ.-Id: 18897 - Permalink


Transient increase of the energy gap in superconducting NbN thin Films excited by resonant narrow-band terahertz pulses
Beck, M.; Rousseau, I.; Klammer, M.; Leiderer, P.; Mittendorff, M.; Winnerl, S.; Helm, M.; Gol’tsman, G. N.; Demsar, J.;
Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Δ=h. Utilizing intense, narrowband picosecond THz pulses, tuned to just below and above 2Δ=h of a BCS superconductor NbN, we demonstrate that superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced non-thermal electron distribution persisting on a 100 ps timescale.
Keywords: radiation-enhanced superconductivity, NbN, Time resolved spectroscopy

Publ.-Id: 18896 - Permalink


Fast relaxation of free carriers in compensated n- and p-type germanium
Deßmann, N.; Pavlov, S.; Mittendorff, M.; Winnerl, S.; Zhukavin, R.; Tsyplenkov, V.; Shengurov, V.; Shastin, V.; Abrosimov, N.; Riemann, H.; Hübers, H.-W.;
The relaxation of free holes and electrons in compensated germanium doped by gallium (p-Ge:Ga:Sb) and antimony (n-Ge:Sb:Ga) has been studied by a pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. The relaxation times vary between 20-300 ps and depend on the incident THz intensity and compensation level. The relaxation times are about five times shorter than previously obtained results for uncompensated n-Ge:Sb and p-Ge:Ga. The results support the development of fast photoconductive detectors in the THz frequency range.
Keywords: Time resolved spectroscopy, THz
  • Lecture (Conference)
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665867

Publ.-Id: 18895 - Permalink


The computation of lipophilicities of 64Cu PET systems based on a novel approach for fluctuating charges
Comba, P.; Martin, B.; Sanyal, A.; Stephan, H.;
A QSPR scheme for the computation of lipophilicities of 64Cu complexes was developed with a training set of 24 tetraazamacrocylic and bispidine-based CuII compunds and their experimentally available 1-octanol/water distribution coefficients. A minimum number of physically meaningful parameters was used in the scheme, and these are primarily based on data available from molecular mechanics calculations, using an established force field for CuII complexes and a recently developed scheme for the calculation of fluctuating atomic charges. The developed model was also applied to an independent validation set and found to accurately predict distribution coefficients of potential 64Cu PET (positron emission tomography) systems. A possible next step would be the development of a QSAR-based biodistribution model to track the uptake of imaging agents in different organs and tissues of the body. It is expected that such simple, empirical models of lipophilicity and biodistribution will be very useful in the design and virtual screening of positron emission tomography (PET) imaging agents.

Publ.-Id: 18894 - Permalink


Ultra-fast transistor-based detectors for precise timing of near infrared and THz signals
Preu, S.; Mittendorff, M.; Winnerl, S.; Lu, H.; Gossard, A. C.; Weber, H. B.;
A whole class of two-color experiments involves intense, short Terahertz radiation pulses. A fast and moderately sensitive detector capable to resolve both near-infrared and Terahertz pulses at the same time is highly desirable. Here we present the first detector of this kind. The detector element is a GaAs-based field effect transistor operated at room temperature. THz detection is successfully demonstrated at frequencies up to 4.9 Hz. The THz detection time constant is shorter than 30 ps, the optical time constant is 150 ps. This detector is ideally suited for precise, simultaneous resolution of optical and THz pulses and for pulse characterization of high-power THz pulses up to tens of kW peak power levels. The dynamic range of the detector is as large as 65 ± 3 dB/√Hz, enabling applications in a large variety of experiments and setups, also including table-top systems.
Keywords: ultrafast detector, THz detection

Publ.-Id: 18893 - Permalink


Resonance triplet at Eα = 4.5 MeV in the 40Ca(α,γ)44Ti reaction
Schmidt, K.; Akhmadaliev, S.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Degering, D.; Dietz, M.; Dressler, R.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Marta, M.; Menzel, M.-L.; Munnik, F.; Schumann, D.; Schwengner, R.; Szücs, T.; Wagner, A.; Yakorev, D.; Zuber, K.;
The 40Ca(α,γ)44Ti reaction is believed to be the main production channel for the radioactive nuclide 44Ti in core-collapse supernovae. Radiation from decaying 44Ti has been observed so far for two supernova remnants, and a precise knowledge of the 44Ti production rate may help improve supernova models. The 40Ca(α,γ)44Ti astrophysical reaction rate is determined by a number of narrow resonances. Here, the resonance triplet at Eα = 4497, 4510, and 4523 keV is studied both by activation, using an underground laboratory for the counting, and by in-beam spectrometry. The target properties are determined by elastic recoil detection analysis and by nuclear reactions. The strengths of the three resonances are determined to ωγ = (0.92 ± 0.20), (6.2 ± 0.5), and (1.31 ± 0.24) eV, respectively, a factor of two more precise than before. The strengths of this resonance triplet may be used in future works as a point of reference. In addition, the present new data directly affect the astrophysical reaction rate at relatively high temperatures, above 3.5GK.
Keywords: alpha rich freeze-out, capture reaction, hydrogen depth profiling

Publ.-Id: 18892 - Permalink


InGaAs-based Large Area Photoconductive Emitters For 1.55 µm Excitation
Xu, M.; Mittendorff, M.; Dietz, R.; Göbel, T.; Schneider, H.; Helm, M.; Winnerl, S.;
We present a scalable large-area terahertz (THz) emitter designed for excitation with 1.55 µm pump radiation. It is based on an InGaAs heterostructure combined with a microstructured electrode pattern. Electric fields of more than 2.5 V/cm in the THz focus are reached, the spectrum of the pulses extends up to 3 THz.
Keywords: photoconductive THz emitter, 1.55 µm excitation, InGaAs-based THz emitter
  • Poster
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665436

Publ.-Id: 18891 - Permalink


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