Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Phase-Resolved X-ray Ferromagnetic Resonance Measurements of Spin Pumping in Spin Valve Structures
Marcham, M. K.; Shelford, L. R.; Cavill, S. A.; Keatley, P. S.; Yu, W.; Shafer, P.; Neudert, A.; Childress, J. R.; Katine, J. A.; Arenholz, E.; Telling, N. D.; van der Laan, G.; Hicken, R. J.;
Element-specific phase-resolved x-ray ferromagnetic resonance (FMR) was used to study spin pumping within Co50Fe50(3)/ Cu(6)/ Ni80Fe20(5) (thicknesses in nm) spin valve structures with large areas, so that edge effects typical of nanopillars used in standard magnetotransport experiments could be neglected. The phase of precession of the Co50Fe50 fixed layer was recorded as FMR was induced in the Ni80Fe20 free layer. The field dependence of the fixed layer phase contains a clear signature of spin transfer torque (STT) coupling due to spin pumping. Fitting the phase delay yields the spin mixing conductance, the quantity that controls all spin transfer phenomena. The STT coupling is destroyed by insertion of Ta into the middle of the Cu layer.
Keywords: XMCD, FMR, XFMR

Publ.-Id: 18580 - Permalink


Sorption of selenium oxyanions onto hematite
Jordan, N.; Domaschke, S.; Foerstendorf, H.; Scheinost, A. C.; Weiß, S.; Heim, K.;
The 79Se isotope, which is a long-lived (t1/2 ~ 3.27 × 105 years[1]) and radiotoxic fission product found in spent nuclear fuels, is of high importance in the context of geological disposal facilities. Safety calculations assessments have shown it to be one of the most contributing isotopes to the total radioactivity that could be potentially released to the biosphere. Selenium has a quite complex speciation, with four main oxidation states, depending on both the pH and the redox potential of the surrounding environment. The concentration, the bioavailability, the mobility, the distribution and the oxidation state of selenium in the environment are greatly influenced by the pH, nature of mineral sorbent as well as potential redox reactions at mineral surfaces. Among the mechanisms which enable selenium retardation and reduces its migration, adsorption processes onto solid surfaces (iron, alumina, titanium oxides) has been extensively investigated at room temperature [2-4].
Our study focuses on selenium(VI) and selenium(IV) sorption onto hematite (α-Fe2O3), which was so far not thoroughly characterized yet. By means of EXAFS and ATR FT-IR spectroscopic studies, it was observed that selenium(VI) forms purely monodentate inner-sphere complexes onto hematite, but the study was only performed at pD 3.5 [5]. To our knowledge, the only spectroscopic characterization of the binary selenium(IV)/hematite system concluded the formation of bidentate bridging inner-sphere complexes onto single hematite crystal using x-ray standing wave (XSW), but the measurements were only performed at pH 4.0 [6]. Hematite was chosen because it is a ubiquitous iron oxide mineral present in the environment. In addition, it is an iron phase often found in rocks and soils in the vicinity of underground repositories [7]).
At the macroscopic level, the effect of pH and ionic strength was studied by means of batch experiments. Sorption of both oxyanions was found to decrease with increasing pH. An increase of the ionic strength (from 0.01 M to 0.1 M) impacted the sorption of selenium(VI), while the selenium(IV) uptake was found to be not significantly affected. Electrophoretic mobility measurements revealed that selenium(IV) sorption shifted the isoelectric point (pHIEP) of hematite to lower pH values, while the pHIEP was not significantly modified upon selenium(VI) sorption. At the molecular level, in situ ATR FT-IR measurements revealed the formation of inner-sphere complexes during selenium(IV) sorption onto hematite, while the sorption of selenium(VI) proceeded via the formation of outer-sphere complexes. Complementary information about the Se reactivity at the hematite surface is provided by EXAFS spectroscopy.
High level and long-lived radioactive wastes are well-known to increase the temperature at the vicinity of the waste disposal site. Such a thermal effect raises the question how the retention of selenium is influenced at elevated temperatures. By means of batch sorption experiments, electrophoretic mobility measurements and in situ ATR FT-IR spectroscopic studies, information and insights about mechanisms involved at higher temperatures (from 25 °C to 60 °C) are provided.

[1] G. Jörg, R. Buhnemann, S. Hollas, N. Kivel, K. Kossert, S. Van Winckel, C.L.V. Gostomski, Appl. Radiat. Isotopes 68 (2010) 2339.
[2] E.J. Elzinga, Y.Z. Tang, J. McDonald, S. DeSisto, R.J. Reeder, J. Colloid Interface Sci. 340 (2009) 153.
[3] N. Jordan, A. Ritter, H. Foerstendorf, A.C. Scheinost, S. Weiss, K. Heim, J. Grenzer, A. Mucklich, H. Reuther, Geochim. Cosmochim. Acta 103 (2013) 63.
[4] A.C. Scheinost, L. Charlet, Environmental Science & Technology 42 (2008) 1984.
[5] D. Peak, D.L. Sparks, Environ. Sci. Technol. 36 (2002) 1460.
[6] J.G. Catalano, Z. Zhang, P. Fenter, M.J. Bedzyk, J. Colloid Interface Sci. 297 (2006) 665.
[7] F. Claret, B.A. Sakharov, V.A. Drits, B. Velde, A. Meunier, L. Griffault, B. Lanson, Clay Clay Min. 52 (2004) 515.
Keywords: selenium; sorption; hematite; ATR FT-IR; EXAFS; temperature
  • Contribution to proceedings
    14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 08.-13.09.2013, Brighton, United Kingdom
    Proceedings of the Migration Conference 2013

Publ.-Id: 18579 - Permalink


Study of Europium and Nickel interaction with calcite - batch experiments and spectroscopic characterization
Sabău, A.; Jordan, N.; Lomenech, C.; Marmier, N.; Brendler, V.; Barkleit, A.; Surblé, S.; Toulhoat, N.; Pipon, Y.; Moncoffre, N.; Giffaut, E.;
Interactions between cations and natural or synthetic calcite may include incorporation processes, resulting in the irreversibility of some sorption reactions. Calcite is present in soil and sediment materials, and in particular in the Callovo-Oxfordian clay samples from of the French underground laboratory of Bure (France), studied in the context of an underground repository for radioactive waste. Europium has been chosen to be investigated by TRLFS due to its fluorescent properties and because it can serve as an analogue for trivalent actinides. Nickel is toxic as a heavy metal as well as in its radioactive form. Few experimental studies have been made to define its interaction with soil and sediment minerals in general and only a handful of articles report investigations of Ni interaction with calcite. To investigate these irreversible processes, we have chosen to work on the Eu-CO2-NaCl-CaCO3 and Ni-CO2-NaCl-CaCO3 systems at pH 8.4, buffered by calcite under atmospheric conditions.
Our study combines macroscopic batch experiments with spectroscopic investigations (Time Resolved Laser Fluorescence Spectroscopy - TRLFS and Rutherford Backscattering Spectrometry - RBS) to comprehensively characterize these systems.

First, appropriate material for sorption experiments were selected based on characterization studies. Eventually, a calcite powder from SOLVAY (SOCAL U1-R) with a particle size of 0.2 μm for TRLFS investigations was chosen, mainly due to its large BET specific surface area (i.e. 18.4 m2/g). In addition, a calcite powder from OMYA (BL 200), with a bigger particle size (56 μm) and a lower specific surface area (0.7 m2/g) was used for Rutherford Backscattering Spectrometry (RBS) measurements, due to the specific requirements of this technique.
For both powders, Diffuse Reflectance Infra-Red Fourier Transform Spectroscopy (DRIFT), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and elementary analysis confirmed the absence of polymorphic CaCO3 compounds (i.e. vaterite and aragonite).
In order to get a better understanding of incorporation of cations in the structure of calcite, we compared our results obtained on powders with studies on millimetric calcite single crystals from Alfa Aesar, performed under the same experimental conditions as for powders.
The sample preparation consists in open reactor experiments under atmospheric conditions (pCO2 = 10-3.5 atm) in 0.1 M NaCl media. The studied concentrations range from 10-6 to 10-3 M. The experiments were carried out for contact times ranging from 4 hours to 6 months for europium and from 4 hours up to 3 months for nickel. For europium, ICP-AES/ICP-MS analysis of the supernatants showed a strong retention by calcite whatever the initial concentration, contrary to nickel where the retention is depending on the initial concentration.

The second step of the work involved efforts to better understand the time-dependence of Eu and Ni sorption and respective mechanisms.
For each concentration of europium investigated by TRLFS, two species are identified and their fluorescence lifetime increases as the initial concentration decreases and time goes on, corresponding to a gradual loss of water molecules surrounding the europium. For higher concentrations, the species identified appear to correspond to a (co-) surface precipitate and possibly an inner-sphere surface complex with two water molecules retained in the hydration sphere. For lower concentrations, the longer lifetimes observed for one of the two species suggest the incorporation of europium in calcite [1,2].
Rutherford Backscattering Spectrometry (RBS) experiments have been carried out using an alpha particle millibeam at the 4MV Van de Graaff accelerator of IPNL and also on nuclear microprobe of CEA-Saclay. This technique is well adapted to discriminate sorption processes such as: (i) adsorption or co precipitation at the mineral surfaces or (ii) incorporation into the mineral structure (through diffusion for instance). The interpretation of the results shows different sorption behaviors for Ni and Eu. Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation, which confirms the hypothesis of the surface precipitate, and (ii) incorporation up to depths greater than 160 nm after 1 month of sorption. Complementary Scanning Electron Microscopy (SEM) observations of the mineral surfaces at low voltage have also been carried out, which confirmed the heterogeneities detected by RBS measurements.

[1] Fernandes, M. M.; Schmidt, M.; Stumpf, T.; Walther, C.; Bosbach, D.; Klenze, R.; Fanghänel, Th., Journal of Colloid and Interface Science (2008), 321(2), 323-331.
[2] Piriou, B; Fedoroff, M.; Jeanjean, J.; Bercis, L., Journal of Colloid and Interface Science (1997), 194, 440-447.
Keywords: Europium; Nickel; calcite; incorporation; diffusion; TRLFS; RBS
  • Poster
    14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 08.-13.09.2013, Brighton, United Kingdom

Publ.-Id: 18578 - Permalink


On the geological availability of germanium
Frenzel, M.; Ketris, M. P.; Gutzmer, J.;
Based on a detailed statistical analysis of chemical data published in the scientific literature, estimates were made of the minimum amounts of recoverable Ge contained within sulphidic zinc ores and coals, given current processing technologies. It is expected that at least 119 kt (∼7 kt in zinc ores and ∼112 kt in coal) of recoverable germanium exist within proven reserves (at present stage of knowledge) at grades in excess of 100 ppm in sphalerite and 200 ppm in coal, while at least 440 kt (∼50 kt in zinc ores and ∼390 kt in coal) should become recoverable in the future, being associated to coal reserves at 8–200 ppm Ge and zinc resources containing in excess of 100 ppm Ge in sphalerite. Mississippi Valley Type (MVT) deposits are expected to be the most important hosts of germanium-rich sphalerite, while both brown and hard coals are expected to be equally important as hosts of germanium. The approach taken in this publication shows that reliable minimum estimates for the availability of by-product metals lacking suitable reserve/resource data may be attained by using robust statistical methods and geochemical data published in the scientific literature.
Keywords: critical metals, resources, reserves, sphalerite, coal

Publ.-Id: 18577 - Permalink


Analyse von aquatischen und sorbierten Actinidspezies mittels Abgeschwächte Totalreflexion (ATR) FT-IR Spektroskopie
Gückel, K.; Foerstendorf, H.; Kruse, C.; Müller, K.;
1. Motivation
Die Ausbreitung der Actinide in der Umwelt ist in den letzten Jahrzehnten verstärkt in den Fokus der Wissenschaft gerückt, da diese aufgrund ihrer Gewinnung und Wiederaufarbeitung im Zusammenhang mit der zivilen Nutzung der Kernkraft aber auch durch in der Vergangenheit durchgeführten Atomwaffentest sowie durch nukleare Unfälle zu weit verbreiteten Schadstoffen geworden sind.
Das Migrationsverhalten dieser Schwermetalle in Grundwassersystemen wird hauptsächlich von der aquatischen Speziation und von Sorptionsprozessen an der Mineral-Wasser-Grenzfläche bestimmt. Daher ist die Untersuchung der aquatischen Spezies sowie der Wechselwirkungen von Actiniden mit Metalloxiden, die als Modellsyteme für komplexe, natürliche Minerale in wässrigen Lösungen dienen, für die Sicherheitsbewertung von nuklearen Endlagern essentiell. Neben verschiedenen festen Phasen, wie Fe(OOH)x, TiO2, oder SiO2, sind Aluminiumoxide und –hydroxide von besonderem Interesse, da sie Hauptbestandteile von Ton und Tonmineralen sind, die als Wirtsgestein für nukleare Endlager in Frage kommen.

2. Aufgabe
Abgeschwächte Totalreflexion (ATR) FT-IR-Spektroskopie ist eine leistungsfähige Technik zur in-situ und zeitaufgelösten Untersuchung der Speziation und von Sorptionprozessen an der Mineral-Wasser-Grenzflächen bei geringen (µM) Actinylionenkonzentrationen. Die ATR FT IR ermöglicht die Untersu-chung von stark IR-absorbierenden oder optisch dichten Medien und gestattet somit die Analyse von wässrigen Proben.
In dieser Arbeit wird die Wechselwirkung von Uran und Neptunium mit mineralen Modellsystemen, die relevant für das Nah- und Fernfeld von Endlagern sind, in wässrigen Lösungen vorgestellt. Vorrangig konzentriert sich die Arbeit auf den Einfluss von ausgesuchten Anionen auf die Sorptionsprozesse von U und Np. Außerdem wurde die aquatische Speziation von Uran bei erhöhten Temperaturen bestimmt. Die ternären Systeme und der Einfluss der Temperatur auf die Speziation und Sorption wurden untersucht, um strukturelle Informa-tionen über die während der Sorption gebildeten Oberflächenkomplexe zu erhalten.
  • Poster
    7. Workshop RCA; Hürden und Fallstricke bei der Charakterisierung von Abfall-Gebinden, 10.-11.06.2013, Dresden, Deutschland

Publ.-Id: 18576 - Permalink


Uranium(VI) sorption on montmorillonite in high ionic strength media
Fritsch, K.; Schmeide, K.;
Of the three main choices for radioactive waste repository host rock—salt dome, argillaceous rock and crystalline rock—Germany has deposits of two eligible rock types. Salt dome, present in Northern Germany, has long been investigated as host rock and in recent years argillaceous rock has come to attention. There are two areas in Germany with sizable clay deposits: In the more populated south of Germany there is a deposit of the already well-researched Opalinus clay (OPA) and in the north of Germany there are clay deposits whose pore waters have a salt concentration of up to 4 mol L-1, ten times that of OPA. The aim of this work is to determine the sorption and diffusion properties of uranium(VI) on/in model clays and OPA at increased salinities in NaCl, KCl, CaCl2 and MgCl2. The basis for this work is formed by sorption experiments with Wyoming montmorillonite (SWy-2) in several strong electrolyte solutions. This also includes leaching experiments.
Keywords: nuclear waste repositories, uranium sorption, argillaceous rock,clay, uranium, montmorillonite, high ionic strength
  • Lecture (Conference)
    ABC-Salt Workshop III, 15.-17.04.2013, Santa Fe, USA

Publ.-Id: 18575 - Permalink


Investigation of the mobility of uranium(VI) in argillaceous rock at higher salinity
Fritsch, K.; Schmeide, K.; Bernhard, G.;
Argillaceous rock is considered as one of the possible host rock types for radioactive waste repositories. Therefore, it is necessary to examine the retention behaviour of argillaceous rock towards long-lived radionuclides, such as uranium. In this study, the 2:1 clay montmorillonite, consisting of an octahedral alumina sheet sandwiched by two tetrahedral silicate sheets, is used. The sorption of uranium(VI) onto montmorillonite is studied in NaCl, KCl, CaCl2, and MgCl2.
Keywords: nuclear waste repositories, uranium sorption, argillaceous rock,clay, uranium, montmorillonite, high ionic strength
  • Poster
    Migration 2013, 08.-13.09.2013, Brighton, United Kingdom

Publ.-Id: 18574 - Permalink


Investigations of Byzantine glass bracelets from Nufaru, Romania using external PIXE-PIGE methods
Bugoi, R.; Poll, I.; Manucu-Adamesteanu, G.; Neelmeijer, C.; Eder, F.;
The chemical composition of 20 glass bracelet fragments found in Nufaru, a Byzantine site from 10th - 13th centuries A.D., nowadays located on Romania's territory, has been determined using Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE) in external beam mode. Most of the Byzantine bracelet fragments were identified as "mixed natron-plant ash" soda-lime-silica glasses. The obtained chemical compositions indicated that the manufacturing of these finery items was performed using similar raw materials and techniques, in most of the cases involving colored glass recycling. PIXE-PIGE results highlighted the glass chromophores (cobalt, manganese, copper and iron ions) and provided hints about the mineral pigments used to paint the external surface of some bracelets.
Keywords: Byzantine glass, glass bracelets, Chemical analysis, PIXE, PIGE, Pigments

Publ.-Id: 18573 - Permalink


14N(p,γ)15O-Wirkungsquerschnitte für 1-2 MeV Strahlenergie
Wagner, L.; Bemmerer, D.; Anders, M.; Marta, M.; Junghans, A.; Elekes, Z.; Reinhardt, T.; Reinicke, S.; Schmidt, K.; Schwengner, R.; Wagner, A.; Zuber, K.;
Die 14N(p,γ)15O-Reaktion bestimmt als langsamste Kernreaktion die Rate des Bethe-Weizsäcker-Zyklus. Für eine präzise Extrapolation des Wirkungsquerschnitts zu niedrigen Energien ist die genaue Kenntnis der Anregungsfunktion über einen weiten Energiebereich notwendig. Am 3 MV Tandetron des Helmholtz-Zentrums Dresden-Rossendorf wurde der nichtresonante Wirkungsquerschnitt der 14N(p,γ)15O-Reaktion im Bereich von 1-2 MeV Strahlenergie neu untersucht. In dem Vortrag werden vorbereitende Simulationen, erste experimentelle Daten sowie ein Ausblick präsentiert.
Keywords: Nuclear Astrophysics, solar fusion, CNO cycle, 3MV Tandetron, non resonant cross sections, 14N(p,γ)15O
  • Lecture (Conference)
    DPG Frühjahrstagung, Fachgruppe Hadronen und Kerne, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18572 - Permalink


Untersuchung der 40Ca(𝛼,𝛾)44Ti-Reaktion mittels Aktivierungsmessung im Felsenkeller Dresden
Schmidt, K.; Akhmadaliev, C.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Dietz, M.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Marta, M.; Menzel, M.-L.; Schwengner, R.; Szücs, T.; Wagner, A.; Wagner, L.; Yakorev, D.; Zuber, K.;
Modelle einer Kernkollaps-Supernova sagen vorher, dass Titan-44 (Halbwertszeit = 58,9 a) produziert wird. Dementsprechend werden mehrere Titan-44-Gammastrahlungsquellen in unserer Galaxie erwartet. Jedoch konnte Titan-44 bisher nur in den Supernovaüberresten Cassiopeia A und SN 1987A nachgewiesen werden. 40Ca(𝛼,𝛾)44Ti ist die wichtigste Reaktion, die Titan-44 erzeugt. Ihre Reaktionsrate wird durch mehrere Resonanzen dominiert. Am 3.3 MV Tandetron des Helmholtz-Zentrums Dresden-Rossendorf werden die Verzweigungsverhältnisse mittels in-beam 𝛾-Spektrometrie untersucht und anschließend die Resonanzstärken durch eine Aktivierungsmessung im Niederniveaumesslabor Felsenkeller bestimmt.
Keywords: core collapse supernova, Titanium-44, gammaray, supernova remnant, Cassiopeia A, SN 1987A, 40Ca(𝛼,𝛾)44Ti, reaction rate, resonance strength, 3.3 MV Tandetron, activation measurement, ultra-low-background facility Felsenkeller Dresden
  • Lecture (Conference)
    DPG Frühjahrstagung Dresden 2013, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18571 - Permalink


Big Bang nucleosynthesis and the results of the 2H(α,γ)6Li experiment at LUNA
Anders, M.; for the LUNA collaboration;
Observations of the 6Li abundance in very metal-poor stars, if confirmed, show a level of 6Li that is several orders of magnitude larger than the production of this nuclide in standard Big Bang nucleosynthesis. The 2H(α,γ)6Li nuclear reaction is believed to dominate 6Li production in the Big Bang, but there are no directly measured data at relevant energies yet. The reaction has been studied at the LUNA 0.4 MV accelerator, deep underground in the Gran Sasso laboratory in Italy, using an intensive He+ beam and a windowless deuterium gas target. The conclusions from the final data analysis of the experiment will be presented. – Supported in part by DFG (BE 4100/2-1).
Keywords: Big-Bang nucleosynthesis, LUNA, Nuclear Astrophysics, Gran Sasso, Gas Target
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18570 - Permalink


Structural characterization of the aqueous dimeric uranium(VI) species: (UO2)2CO3(OH)3−
Gückel, K.; Tsushima, S.; Foerstendorf, H.;
A combined theoretical and spectroscopic approach was used to refine structural data of the aqueous dimeric U(VI) species, (UO2)2CO3(OH)3−. Several isomer structures of this complex were already derived from previous X-ray absorption and NMR experiments (Szabó, Z. et al. J. Chem. Soc.-Dalton Trans., 2000, 3158-3161) but due to unequivocal results a distinct structure could not be determined and uncertainties remain. In this work, the Gibbs energies and U–U distances obtained from density functional theory (DFT) calculations predict two isomers, one with a carbonate ligand and one with two hydroxo groups as bridiging groups, as most likely structures. The experimental IR spectrum indicates a bidentate coordination of the carbonate ion and the presence of two spectroscopically specifiable uranyl moieties as it also is predicted by the spectra computed on the base of DFT. Taken together theoretical and experimental results the isomer with a carbonate ligand bridging the two uranyl units appears most likely to represent the predominat structure. Contributions to a small extent of an isomer with a non-bridging carbonate anion can not be completely ruled out.
Keywords: Speciation, ATR FT-IR, DFT calculations

Publ.-Id: 18569 - Permalink


Isotopenaustausch-Studien zur Reversibilität der Metall-Huminstoff-Komplexbildung
Lippold, H.;
Kein Abstract zur Veranstaltung. Inhaltliche Zusammenfassung:

Die Wechselwirkung mehrwertiger Metalle mit natürlichem organischem Material kann kinetischen Stabilisierungseffekten unterliegen, was zu Unsicherheiten im Hinblick auf die Anwendbarkeit thermodynamischer Konstanten in Transportmodellierungen führt. Die Reversibilität des Prozesses wurde deshalb in Isotopenaustausch-Studien erstmals direkt und über einen längeren Zeitraum untersucht. Hierzu wurden Bindungsisothermen für [160Tb]Tb(III) an Huminstoff-Flockulaten aufgenommen, wobei 160Tb als Radiotracer simultan oder nachträglich (nach verschiedenen Alterungszeiten des Komplexes von 1 bis 90 Tagen) eingeführt wurde. In allen Fällen wurde im Sättigungszustand ein ungehindertes dynamisches Austausch-Gleichgewicht festgestellt. Langzeitprozesse zulasten der Reversibilität treten also offenbar nicht generell auf.
  • Lecture (others)
    4. Workshop zum Verbundprojekt "Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen", 11.-12.04.2013, Karlsruhe, Deutschland

Publ.-Id: 18567 - Permalink


Studies on interactions and reactive transport of higher-valent metals in clay, considering organic carriers and high ionic strengths
Poetsch, M.; Lippold, H.; Kulenkampff, J.; Lippmann-Pipke, J.;
Colloid-borne transport of radiotoxic metals in the subsurface hydrosphere is a topic of major interest in view of long-term risk assessments for nuclear waste repositories. In particular, interaction with natural organic complexants such as humic substances can be decisive for the mobility of higher-valent metals. Depending on geochemical parameters, migration can be both enhanced and reduced. The respective conditions need to be identified, and models must be able to describe such complex systems by few parameters.

According to the Linear Additive Model, total metal adsorption in the presence of humic matter can be calculated by linking parameters for adsorption of both components and for their interaction with each other. The basics of this approach are also implicit in reactive transport models where humic carriers are considered. The applicability is, however, not unanimously accepted, and modelling results are in part not satisfactory.

Clay rock is being discussed as a potential host formation for a final repository, mainly because of its high adsorption capacity. This barrier function may, however, be subverted by charge screening or competition effects due to the high salt contents of pore waters. Complexation of radionuclides with humic-like clay organics could cause an additional mobilisation. So far, the effect of high ionic strengths on interactions of such organic carriers is unknown.

Within the framework of the planned PhD thesis, these processes will be investigated in detail, using radioactive tracers for interaction studies at high salt contents and for 3D imaging of transport processes by means of Positron Emission Tomography. The Linear Additive Model will be tested for static and dynamic systems, aiming at a specification of criteria for its applicability. To describe the effects of high salinities on a molecular level, mechanistic models for metal-humic interaction and surface complexation will be employed as well. An outline of this topic shall be presented at the meeting.
  • Lecture (others)
    2nd Meeting of the PhD Initiative "Reactive Transport Modelling", 26.03.2013, Leipzig, Deutschland

Publ.-Id: 18566 - Permalink


The dp-elastic cross section measurement at the deuteron kinetic energy of 2.5 GeV
Kurilkin, P.; Agakishiev, G.; Behnke, C.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Blume, C.; Böhmer, M.; Cabanelas, P.; Chernenko, S.; Dritsa, C.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gill, K.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Holzmann, R.; Huck, P.; Höhne, C.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krebs, E.; Krizek, F.; Kuc, H.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, L.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
New results on the differential cross section in deuteron-proton elastic scattering are obtained at the deuteron kinetic energy of 2.5 GeV with the HADES spectrometer. The angular range of 69° – 125° in the center of mass system is covered. The obtained results are compared with the relativistic multiple scattering model calculation using the CD-Bonn deuteron wave function. The data at fixed scattering angles in the c.m. are in qualitative agreement with the constituent counting rules prediction.

Publ.-Id: 18565 - Permalink


Preparation of Equiatomic FeRh Thin Films by MBE
Heidarian, A.; Potzger, K.; Lindner, J.; Heller, R.; Wilhelm, R.; Grenzer, J.; Reuther, H.; Bali, R.;
Equiatomic FeRh thin films with varying thickness have been prepared on MgO (100) substrates via molecular beam epitaxy (MBE). The optimization of the stoichiometry was monitored using XRD, RBS and AES while the magnetic properties were probed using SQUID magnetometry. XRD results evidence a well ordered CsCl-type crystal structure. By increasing the annealing temperature of the films, the structural quality of the films also increases. Moreover, the known first order phase transition at ~350 K from an antiferromagnetic (AF) to a ferromagnetic (FM) state slightly shifts towards higher temperatures. M-H loops of films annealed at 800 ∘C or 850 ∘C recorded at 300 K show an opening, which is likely related to the magnetic field-induced AFM-FM phase transition. Residual low-temperature ferromagnetic moments are of unknown origin, but likely related to strain or diffusion effects at the surface or interface.
Keywords: FeRh thin films, Magnetic properties, Lattice structure, SQUID
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18564 - Permalink


Magnetic and defect-properties of Co implanted TiO2
Yildirim, O.; Cornelius, S.; Vinnichenko, M.; Butterling, M.; Wagner, A.; Smekhova, A.; Potzger, K.;
The magnetic and structrual properties of the potential diluted magnetic oxide (DMO), i.e. Co implanted TiO2 thin films have been investigated. These films have been grown by magnetron sputtering on SrTiO3 single crystals. Avoidence of possible magnetic contamination has been verified by magnetometry measurements after substrate preparation and deposition. For magnetic doping, implantations of Co+ ions have been performed at atomic concentrations of 0.5%, 2.5% and 3% respectively. The dependencies between the fluence implanted, defect creation and ferromagnetic properties have been investigated using magnetometry, positron annihilation spectroscopy and structural characterisation.
This work is supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz-Russia Joint Research Group HRJRG−314, and the Russian Foundation for Basic Research, RFBR #12 − 02 − 91321 − 𝑆𝐼𝐺 − 𝑎
Keywords: Magnetic Semiconductors, Diluted Magnetic Oxides
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland
  • Poster
    International Conference on Nanoscale Magnetism, 02.-06.09.2013, Istanbul, Turkey

Publ.-Id: 18563 - Permalink


Spin Torque Ferromagnetic Resonance in MgO-based Magnetic Tunnel Junctions
Aleksandrov, Y.; Deac, A. M.; Bernert, K.; Fowley, C.; Sluka, V.; Kowalska, E.; Lindner, J.; Fassbender, J.ORC
Spin polarized currents can exert a torque on a ferromagnetic layer‘s magnetic moment leading to switching or steady-state precession. Spintorque driven ferromagnetic resonance (ST-FMR) is a unique method to measure the magnetic anisotropy, saturation magnetization and damping in a nanoscale structure. ST-FMR can also be used to determine the bias dependence of spin-transfer torques in magnetic tunnel junctions [1- 3]. For different values of applied RF power and DC bias, we swept the RF frequency from 1 to 15 GHz and measured the resulting mixing voltage across our MgO-based tunnel junctions. Not only the low-frequency fundamental mode was observed, but also a higher order mode. We find that the mixing voltage peak shifts with applied DC-field and increases with RF power. Finally, we separate the fieldlike torque contribution from that of the in-plane spin-transfer torque and determine their bias dependence.
Keywords: Spin Excitations, Spin Torque
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18562 - Permalink


Electrical detection of inverse spin Hall effect induced by spin pumping
Aleksandrov, Y.; Lindner, J.; Farle, M.; Rod, I.; Zähres, H.;
Spin pumping driven by ferromagnetic resonance (FMR) injects a spin current through a simple ferromagnetic (FM)/paramagnetic (PM) interface into a PM layer [1]. Due to the inverse spin Hall effect (ISHE), arising from the spin-orbit coupling in the PM layer, the spin current is converted into a charge current. As a result transverse electromotive force perpendicular to the applied magnetic field and to the microwave field is produced [2]. Here we present direct measurements of the ISHE induced by spin pumping in Py/Pt bilayer. We observe a 4mT FMR linewidth broadening for the samples with Pt capping layers due to spin pumping. We also find that the electromotive force varies systematically with changing microwave power and frequency, magnetic-field angle, or temperature. This is consistent with the predictions based on the Landau-Lifshitz-Gilbert equation combined with the models of the ISHE and spin pumping.
Keywords: Spin-dependent Transport Phenomena
  • Lecture (Conference)
    Frühjahrstagung der SKM der DPG, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18561 - Permalink


Influence of a Dy overlayer on the precessional dynamics of a ferromagnetic thin film
Marcham, M. K.; Yu, W.; Keatley, P. S.; Shelford, L. R.; Shafer, P.; Cavill, S. A.; Qing, H.; Neudert, A.; Childress, J. R.; Katine, J. A.; Arenholz, E.; Telling, N. D.; van der Laan, G.; Hicken, R. J.;
Precessional dynamics of a Co50Fe50(0.7)/Ni90Fe10(5)/Dy(1)/Ru(3) (thicknesses in nm) thin film have been explored by low temperature time-resolved magneto-optical Kerr effect and phase-resolved x-ray ferromagnetic resonance measurements. As the temperature was decreased from 300 to 140 K, the magnetic damping was found to increase rapidly while the resonance field was strongly reduced. Static x-ray magnetic circular dichroism measurements revealed increasing ferromagnetic order of the Dy moment antiparallel to that of Co50Fe50/Ni90Fe10. Increased coupling of the Dy orbital moment to the precessing spin magnetization leads to significantly increased damping and gyromagnetic ratio of the film while leaving its magnetic anisotropy effectively unchanged.
Keywords: magnetization dynamics, XMCD-FMR, TR-MOKE

Publ.-Id: 18560 - Permalink


Two-magnon scattering in Permalloy thin films due to rippled substrates
Körner, M.; Lenz, K.; Gallardo, R. A.; Fritzsche, M.; Mücklich, A.; Facsko, S.; Lindner, J.; Landeros, P.; Fassbender, J.ORC
We report on the influence of correlated substrate roughness on the two-magnon scattering in 30 nm Ni81Fe19 thin films. Using ion beam erosion periodically modulated substrates (ripple) were produced with wavelengths between 20 nm and 432 nm. This surface corrugation is adopted by magnetic layers grown on top yielding dipolar stray fields if magnetization and ripple ridges are aligned perpendicular. In case of λ ≥ 222 nm the evolving periodic field pattern trigger two-magnon scattering, which depends strongly on the direction of magnetization with respect to the ripple pattern. In-plane broadband ferromagnetic resonance reveals prominent peaks in the frequency dependent linewidth measured perpendicular to the ripple ridges. These peaks can be switched off if the magnetization is aligned along the ripple ridges.
Keywords: magnetic relaxation, ferromagnetic resonance, two-magnon scattering, periodic nanostructures, magnetization dynamics

Publ.-Id: 18559 - Permalink


Interaction of Polyatomic Bi Ions with Ge and Si
Liedke, B.; Böttger, R.; Heinig, K.-H.; Bischoff, L.; Hübner, R.; Pilz, W.;
Si and Ge surfaces were irradiated with polyatomic Bi ions at normal incidence with energies between 10 and 20 keV per atom. For comparison, irradiation with monatomic ions was performed. The resulting surface morphologies were studied by SEM, XTEM and AFM. A variety of surface patterns were revealed, which are based on different formation mechanisms. Irradiation of Ge with Bi3 , Bi3 and Bi2 at RT results in a surface morphology of hexagonally ordered dots. They have an aspect ratio close to one, which has not been reported for elemental semiconductors so far [1]. For comparison, Ge irradiated with monatomic Bi ions at RT leads to well-known sponge-like surface layers, whereas with increasing substrate temperature similar dot patterns appear [2]. On Si irradiated at RT with monatomic or polyatomic Bi ions, no dot patterns have been found, which holds for Bi even for T>RT. On Si dot patterns appear only after polyatomic Bi irradiation well above RT.
The surface patterns will be explained by models based on vacancy kinetics and the liquid-solid phase transition. The sponge formation, as suggested in literature, results from vacancy kinetics, and will be demonstrated by kinetic Monte-Carlo simulations. The dot patterns are consistently modeled by ion-induced transient local melt pools, using TRIM simulations and heat conduction calculations.
Keywords: FIB, polyatomic irradiation, KMC, TRIM, Bi ions, Ge, Si, surface patterning
  • Invited lecture (Conferences)
    E-MRS 2013 Spring Meeting, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 18558 - Permalink


Stabilizing and destabilizing perturbations of PT-symmetric indefinitely damped systems
Kirillov, O.;
Eigenvalues of a potential dynamical system with damping forces that are described by an indefinite real symmetric matrix can behave as those of a Hamiltonian system when gain and loss are in a perfect balance. This happens when the indefinitely damped system obeys parity–time (PT ) symmetry. How do pure imaginary eigenvalues of a stable PT -symmetric indefinitely damped system behave when variation in the damping and potential forces destroys the symmetry? We establish that it is essentially the tangent cone to the stability domain at the exceptional point corresponding to the Whitney umbrella singularity on the stability boundary that manages transfer of instability between modes.
Keywords: indefinite damping, PT -symmetry, Krein signature, dissipation-induced instabilities, exceptional point, modulational instability

Publ.-Id: 18557 - Permalink


Exchange of oxygen in uranyl(VI) and water: two binuclear scenarios in acid and in base
Tsushima, S.; Rossberg, A.; Moll, H.;
The mechanism of exchange between oxygen in UO22+ and that in solvent water has been disputed over last 50 years. It is well–known that the rate of “yl”–oxygen exchange depends heavily on pH, and that there is virtually no exchange at low pH. With increase of pH (pH > 2) the exchange becomes appreciable, and under highly alkaline solution there is a rapid oxygen exchange. These observations led to an idea that there are at least two different exchange mechanisms; one dominating under weakly acidic to neutral pH and another mechanism at very high pH. Szabó and Grenthe [1, 2] used NMR spectroscopy to identify the species involved in “yl”–oxygen exchange and they suggested two binuclear complexes as key species; (UO2)2(OH)22+ at low pH and [(UO2(OH)42-)(UO2(OH)53-)] at high pH. How the oxygen exchange takes place in these complexes in atomic scale, however, remains unidentified because the lifetimes of the intermediate species and the transition states of the oxygen exchange are too short to be detected spectroscopically. That is to say, we know they (dimer complexes) did it but we do not know how they managed to do it. Our attempt here is to identify the “yl”–oxygen exchange pathways in these complexes using quantum chemical method thereby proving that oxygen exchange through these complexes are indeed possible – thereby bringing end to the long–disputed arguments over the “yl”–oxygen exchange mechanisms.
First, we studied the “yl”–oxygen exchange pathway via (UO2)2(OH)22+ [3]. We used hybrid density functional theory (DFT) with Becke’s three–parameter hybrid functional and Lee–Yang–Parr’s gradient–corrected correlation functional (B3LYP) employing conductor–like polarizable continuum model (CPCM) using Gaussian 09 program (Gaussian Inc.). The small core effective core potential and corresponding basis set was used on uranium and oxygen. Direct proton transfer from the hydroxo bridge or from the coordinating water to the “yl”–oxygen in (UO2)2(OH)22+ can be ruled out because we found exceedingly high activation barrier (~170 kJ mol–1) through these mechanisms. The exchange mechanism in (UO2)2(OH)22+ can be described by a multi–step proton transfer pathway that involves the formation of an oxo bridge between the two uranyl(VI) centres (U–Oyl–U bridge). The activation enthalpy of the reaction obtained at the B3LYP level is 94.7 kJ mol–1 and is somewhat larger than the experimental value of 80 ± 14 kJ mol–1. However, the discrepancy is at the acceptable level.
Second, we tried to identify the oxygen exchange pathway through [(UO2(OH)42-)(UO2(OH)53-)]. For this attempt, we first studied the speciation of uranyl(VI) in highly alkaline solution by quantum chemical calculations as well as X–ray absorption spectroscopy (XAS). Although various previous studies assumed that hydrolysis of UO2(OH)42– produces UO2(OH)53–, our B3LYP calculations together with previous theory work by others [4,5] suggest that hydrolysis of UO2(OH)42– yields UO3(OH)33–. We studied this point further using XAS at the Rossendorf Beamline (ROBL) in ESRF, Grenoble, France, and we found evidence of the existence of new species UO3(OH)33– in XANES spectra. The sample which contained further hydrolyzed species showed clear shift of the uranium LIII absorption edge compared to the sample containing only UO2(OH)42–.Similar energy shift was observed in Pa(V) when speciation changed from spherical Pa5+ to mono–oxo PaO3+ [6]. Therefore the species beyond UO2(OH)42– is better assigned to UO3(OH)33– rather than UO2(OH)53–. Likewise, the complex described as [(UO2(OH)42-)(UO2(OH)53-)] by Szabó and Grenthe should better be written as [(UO2(OH)42-)(UO3(OH)33-)]. We then studied the “yl”–oxygen pathway within [(UO2(OH)42-)(UO3(OH)33-)] by DFT, and found a realistic pathway which has the activation Gibbs energy of 56.3 kJ mol–1 at the B3LYP level, which is again in good agreement with the experimental value of 60.8 ± 2.4 kJ mol–1 obtained by Szabó and Grenthe [2].
Our calculations confirm the “yl”–oxygen exchange mechanisms through (UO2)2(OH)22+ and [(UO2(OH)42-)(UO3(OH)33-)], and underscores the role of binuclear species. The formation of U–Oyl–U bridge seems to play a key role in facilitating intramolecular proton shuttling among the oxygen atoms thereby contributing to faster “yl”–oxygen exchange.

[1] Szabó, Z. and Grenthe, I., Inorg. Chem. 2007, 46, 9372–9378.
[2] Szabó, Z. and Grenthe, I., Inorg. Chem. 2010, 49, 4928–4933.
[3] Tsushima, S., Inorg. Chem. 2012, 51, 1434–1439.
[4] Shamov, G. A. and Schreckenbach, G., J. Am. Chem. Soc. 2008, 130, 13735–13744.
[5] Bühl, M. and Schreckenbach, G., Inorg. Chem. 2010, 49, 3821–3827.
[6] Le Naour, C. et al., Inorg. Chem. 2005, 44, 9542–9546.
  • Lecture (Conference)
    14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (Migration 2013), 08.-13.09.2013, Brighton, United Kingdom

Publ.-Id: 18556 - Permalink


WKB instability thresholds of the magnetized cylindrical Couette-Taylor flow in helical magnetic fields
Kirillov, O.; Stefani, F.; Fukumoto, Y.;
We consider a cylindrical Couette-Taylor (CT) flow of an electrically conducting viscous and resistive fluid in an external helical magnetic field. Local stability of the flow is studied with respect to three-dimensional perturbations within a short-wavelength approximation. Maximization of the critical Rossby number at the instability threshold is performed with respect to the non-dimensional parameters of the problem characterizing hydrodynamic and magnetic effects. Quite surprisingly, it is found that the critical Rossby number at the threshold of magnetorotational instability in the case of infinitesimally small magnetic Prandtl number is universally bounded from above by a quantity 2 − 2√2 known as the Liu limit, which is below that of Keplerian rotation (−3/4).
Keywords: Magnetorotational instability, Tayler instability, short-wavelength approximation, Keplerian flow
  • Lecture (Conference)
    IUTAM Symposium on Vortex Dynamics: Formation, Structure and Function, 10.-14.03.2013, Fukuoka, Japan

Publ.-Id: 18555 - Permalink


Temperature dependent emission and absorption cross section of Yb3+ doped yttrium lanthanum oxide (YLO) ceramic and its application in diode pumped amplifier
Banerjee, S.; Koerner, J.; Siebold, M.; Yang, Q.; Ertel, K.; Mason, P.; Phillips, J.; Loeser, M.; Zhang, H.; Lu, S.; Hein, J.; Schramm, U.; Kaluza, M.; Collier, J.;
Temperature dependent absorption and emission cross-sections of 5at% Yb3+ doped yttrium lanthanum oxide (Yb:YLO) ceramic between 80K and 300K are presented. In addition, we report on the first demonstration of ns pulse amplification in Yb:YLO ceramic. A pulse energy of 102mJ was extracted from a multi-pass amplifier setup. The amplification bandwidth at room temperature confirms the potential of Yb:YLO ceramic for broad bandwidth amplification at cryogenic temperatures.
Keywords: laser amplifiers, Lasers, ytterbium

Publ.-Id: 18554 - Permalink


Numerical analysis of the dynamics in gas-solid fluidized beds and experimental validation using ultra-fast X-ray tomography
Verma, V.; Deen, N. G.; Padding, J. T.; Kuipers, J. A. M.; Bieberle, M.; Barthel, F.; Wagner, M.; Hampel, U.;
Bubble characteristics in a cylindrical gas-solid fluidized bed have been studied with a two-fluid model (TFM) based on Kinetic theory of granular flow and validated with experiments performed with X-ray computed tomography (XRT). It is shown that the equivalent bubble diameter increases with height from the gas distributor plate. Experimental and TFM results are in good agreement for glass particles. Darton et al. (1) and Werther (2) correlation slightly over-predict bubble size. XRT and simulations results show similar trend for LLDP and glass particles. KTGF theory performs better for glass particles, and is in good agreement with XRT results.
Keywords: gas solid fluidized bed, numerical analysis, ultra fast x-ray CT
  • Contribution to proceedings
    Fluidization XIV, 26.-31.05.2013, Noordwijkerhout, The Netherlands
  • Lecture (Conference)
    Fluidization XIV, 26.-31.05.2013, Noordwijkerhout, The Netherlands

Publ.-Id: 18553 - Permalink


Aspects of the core shielding assessment for the FASTEF-MYRRHA design
Ferrari, A.; Di Maria, S.; Fernandez, R.; Konheiser, J.; Ottolini, M.; Sarotto, M.; Stankovskiy, A.;
In the frame of the FP7 European project Central Design Team (CDT), an extensive simulation study has been done to assess the main shielding problems in view of the construction of the MYRRHA accelerator-driven system at SCK•CEN in Mol (Belgium). A method based on the combined use of the two Monte Carlo codes MCNPX and FLUKA has been developed, with the goal to characterize realistic neutron fields around the core barrel and build complex source terms, to be used in detailed analyses of the radiation fields due to the system in operation, and of the coupled residual radiation. The results evidenced a powerful way to analyze the shielding and activation problems, with direct and clear implications on the design solutions.
Keywords: Accelerator Driven Systems, Shielding, Monte Carlo
  • Contribution to proceedings
    Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios, 04.-07.03.2013, Paris, France
    Proceedings of FR13, Wien: IAEA Publishing
  • Poster
    Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios, 04.-07.03.2013, Paris, France

Publ.-Id: 18552 - Permalink


Aspects of the core shielding assessment for the design of FASTEF-MYRRHA
Ferrari, A.;
To support the construction of the MYRRHA accelerator driven system at SCKCEN in Mol (Belgium), in the years 2009-2012 the FP7 European project Central Design Team (CDT) worked at the design of the Fast Spectrum Transmutation Experimental Facility (FASTEF), to demonstrate efficient transmutation of high level waste and associated technology. The heart of the system is a lead-bismuth eutectic (LBE) cooled reactor, working both in critical and subcritical mode. The neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV,  4 mA proton beam, which hits a LBE spallation target located inside the reactor core. Between the many challenges of the design, radiation shielding and minimization of induced activation are key points. To assess the shielding of the reactor core, both critical and sub-critical operation modes have been studied. Since in FASTEF the reactor is foreseen to operate at 100 MW core power in the critical mode and at 94 MW in the subcritical one, the critical mode exhibits the highest lateral neutron fluence at the fuel level, and can be reasonably considered the conservative case for the lateral radiation containment. At the contrary, because of the backscattered radiation from the spallation target and due to the presence of the beam pipe channel, the subcritical operation drives the vertical design. Starting from the MCNPX Monte Carlo models of the core defined in CDT in both the operation modes, neutron spectra have been fully characterized on suitable surfaces and used as input of a second row of FLUKA simulations, where complex source terms have been used. FLUKA has the unique possibility to compute, in the same simulation, the transport of the radiation due to the system in operation and the coupled residual fields, due to the activated materials. The FLUKA/MCNPX comparison of the neutron fluence rates inside the external vessel at different radial and vertical distances from the core barrel shows a very good agreement - at the percent level - and has been used to validate the FLUKA analysis. Dose distributions have been then evaluated from the core barrel to the external containment and the shielding walls in the horizontal direction, up to the last magnet of the proton beam-line and the final roof in the vertical one. Moreover, the activation of key materials has been characterized for typical irradiation patterns. This simulation addressed the optimization of key elements of the design, from the cover plate to the local shielding structure above the last magnet.
Keywords: ADS, shielding, Monte Carlo
  • Poster
    Nuclear Physics Data for the Transmutation of Nuclear Waste/ 525. WE-Heräus-Seminar, 25.-27.02.2013, Bad Honnef, Germany

Publ.-Id: 18551 - Permalink


Röntgentomographische Studien zu Zweiphasenströmungen in einem vertikalen Rohr
Banowski, M.; Hoppe, D.; Lucas, D.; Hampel, U.;
Gas-Flüssigkeits-Zweiphasenströmungen in Rohrleitungen sind für die Entwicklung und Validierung zweiphasiger CFD-Codes ein geeigneter generischer Untersuchungsgegenstand. Der Grad an strömungsmorphologischer Komplexität ist relativ hoch, was sich insbesondere in der Ausprägung charakteristischer Strömungsregime mit ihren jeweils spezifischen Impulstransferbeziehungen an der Phasengrenze in Abhängigkeit von Leerrohrgeschwindigkeiten und Stoffwerten äußert. An der TOPFLOW-Versuchsanlage des HZDR werden gegenwärtig umfangreiche experimentelle Studien zu Zweiphasenströmungen in senkrechten Testsektionen für Wasser/Luft- und Wasser/Dampf-Strömungen bis 65 bar Druck durchgeführt. Diese Experimente dienen vordergründig der Erhebung von Messdaten für die CFD-Codeentwicklung. Bei aktuellen Studien an einer DN50 Testsektion kommt die ultraschnelle Röntgentomographie als Messverfahren zum Einsatz. Diese ermöglicht es, den Strömungsquerschnitt mit Bildraten von 2500 Bildern/Sekunde und einer räumlichen Auflösung von etwa 1 mm in zwei jeweils 10 mm entfernten Abbildungsebenen zu visualisieren. Verschiedene Strömungsregime werden durch Wahl der Leerohrgeschwindigkeiten für die Gas- und die Flüssigphase am Versuchsstand eingestellt. Neben der Aufklärung des Strömungsregimes und der Erfassung interessanter Detailstrukturen der Strömung, wie Flüssigkeitslamellen zwischen Gasblasen, Wandfilmstrukturen und Kleinblasenverteilungen im Großblasennachlauf, können radiale Gasgehaltsprofile ebenso wie Gasphasengeschwindigkeiten durch automatisierte Auswerteroutinen extrahiert werden. Fernerhin wird derzeit an Auswertealgorithmen zur Vermessung von Einzelblasen, zur Bestimmung der Phasengrenzflächendichte sowie zur Ermittlung lokaler Flüssigphasengeschwindigkeiten gearbeitet. Im Beitrag werden Ergebnisse ausgewählter Studien zu aufwärtsgerichteten Gleichströmungen sowie Gegenströmungen der Gas- und Flüssigphase vorgestellt.
Keywords: X-ray tomography, bubbles, two-phase flow, TOPFLOW
  • Poster
    DECHEMA ProcessNet Jahrestreffen Extraktion und Mehrphasenströmungen, 19.-20.03.2013, Baden-Baden, Deutschland

Publ.-Id: 18550 - Permalink


Enhanced Laser Ion Acceleration from Solids
Kluge, T.;
This thesis presents results on the theoretical description of ion acceleration using ultra-short ultra-intense laser pulses. It consists of two parts. One deals with the very general and underlying description and theoretic modeling of the laser interaction with the plasma, the other part presents three approaches of optimizing the ion acceleration by target geometry improvements using the results of the first part. In the first part, a novel approach of modeling the electron average energy of an over-critical plasma that is irradiated by a few tens of femtoseconds laser pulse with relativistic intensity is introduced.
The first step is the derivation of a general expression of the distribution of accelerated electrons in the laboratory time frame. As is shown, the distribution is homogeneous in the proper time of the accelerated electrons, provided they are at rest and distributed uniformly initially. The average hot electron energy can then be derived in a second step from a weighted average of the single electron energy evolution. This result is applied exemplary for the two important cases of infinite laser contrast and square laser temporal profile, and the case of an experimentally more realistic case of a laser pulse with a temporal profile sufficient to produce a preplasma profile with a scale length of a few hundred nanometers prior to the laser pulse peak. The thus derived electron temperatures are in excellent agreement with recent measurements and simulations, and in particular provide an analytic explanation for the reduced temperatures seen both in experiments and simulations compared to the widely used ponderomotive energy scaling.
The implications of this new electron temperature scaling on the ion acceleration, i.e. the maximum proton energy, are then briefly studied in the frame of an isothermal 1D expansion model. Based on this model, two distinct regions of laser pulse duration are identified with respect to the maximum energy scaling. For short laser pulses, compared to a reference time, the maximum ion energy is found to scale linearly with the laser intensity for a simple flat foil, and the most important other parameter is the laser absorption efficiency. In particular the electron temperature is of minor importance. For long laser pulse durations the maximum ion energy scales only proportional to the square root of the laser peak intensity and the electron temperature has a large impact. Consequently, improvements of the ion acceleration beyond the simple flat foil target maximum energies should focus on the increase of the laser absorption in the first case and the increase of the hot electron temperature in the latter case.
In the second part, exemplary geometric designs are studied by means of simulations and analytic discussions with respect to their capability for an improvement of the laser absorption efficiency and temperature increase. First, a stack of several foils spaced by a few hundred nanometers is proposed and it is shown that the laser energy absorption for short pulses and therefore the maximum proton energy can be significantly increased. Secondly, mass limited targets, i.e. thin foils with a finite lateral extension, are studied with respect to the increase of the hot electron temperature. An analytical model is provided predicting this temperature based on the lateral foil width. Finally, the important case of bent foils with attached flat top is analyzed. This target geometry resembles hollow cone targets with flat top attached to the tip, as were used in a recent experiment producing world record proton energies. The presented analysis explains the observed increase in proton energy with a new electron acceleration mechanism, the direct acceleration of surface confined electrons by the laser light. This mechanism occurs when the laser is aligned tangentially to the curved cone wall and the laser phase co-moves with the energetic electrons. The resulting electron average energy can exceed the energies from normal or oblique laser incidence by several times. Proton energies are therefore also greatly increased and show a theoretical scaling proportional to the laser intensity, even for long laser pulses.
  • Doctoral thesis
    Helmholtz-Zentrum Dresden-Rossendorf, 2012
    203 Seiten

Publ.-Id: 18549 - Permalink


Die wundersame Wandlung des Elements Administratium – was hat HWM im Wissenschaftssystem schon bewirkt und was ist für die Professionalisierung weiter zu tun?
Joehnk, P.;
Hochschul- und Wissenschaftsmanagement
  • Invited lecture (Conferences)
    10. Osnabrücker Kolloquium zum Hochschul- und Wissenschaftsmanagement, 21.02.2013, Osnabrück, Deutschland

Publ.-Id: 18548 - Permalink


Ökologie und Ökonomie vereinbaren -Beispielhafte Übersetzung von Nachhaltigkeit während der Sanierung eines Forschungsstandortes
Joehnk, P.;
Nachhaltigkeit und deren Umsetzung in Wissenschaftscampi unter dem Begriff Green Campus ist ein allgegenwärtiges Thema. Beides - Nachhaltigkeit und Green Campus - sind keine Erfindungen der letzten Jahre, bis heute aber konnten die Begriffe nicht eindeutig definiert werden. Während das Thema "Green Campus" wohl eher unter Marketinggesichtspunkten beim Wettstreit um die besten Köpfe in den USA erfunden und nach Europa übergeschwappt ist, dürfte als erster verbriefter Beschreiber der Nachhaltigkeit ein Sachse sein. Der Begriff Nachhaltigkeit wurde durch den sächsischen Oberberghauptmann Carl von Carlowitz in seinem Werk "Sylvicultura oeconomica" (1713) erstmalig erwähnt.
Keywords: sustainability, masterplan, Green Campus
  • Open Access LogoWissenschaftsmanagement 6(2012), 14-15

Publ.-Id: 18547 - Permalink


Decision Support System for the Alumni Management
Iskhakova, L.; Yusupova, N.; Hilbert, A.; Joehnk, P.; Hoffmann, S.;
Workshop on computer science and information technologies
  • Invited lecture (Conferences)
    7th International Scientific and Technical Conference "Computer Sciences and Informations Technologies" (CSIT’2012), 20.-24.11.2012, Lviv, Ukraine

Publ.-Id: 18546 - Permalink


Großes für Kleines – wie der Betrieb von wissenschaftlichen Großgeräten die Arbeitsbedingungen in Forschungseinrichtungen verändert
Joehnk, P.;
Wissenschaft im Dialog – Kooperative Forschungsstelle Technikstress (KFT) – Arbeit und Technik im Wandel
  • Book chapter
    Annette Hoppe: Arbeit und Technik im Wandel, Aachen: Shaker, 2012, 978-3-8440-1410-5, 46-55

Publ.-Id: 18545 - Permalink


Comparative simulations of free surface flows using VOF-methods and a new approach for multi-scale interfacial structures
Hänsch, S.; Lucas, D.; Höhne, T.; Krepper, E.; Montoya, G.;
This paper presents free surface flow simulations using different VOF-like interface capturing methods. Both the interFoam solver available in OpenFOAM and the Free Surface Model implemented in ANSYS CFX are applied for the collapse of a water column hitting an obstacle. The computational results of these established methods are compared to a new multi-field concept which is developed for flow situations with multi-scale interfacial structures. The new concept extends the inhomogeneous MUltiple SIze Group (MUSIG)-Model for polydispersed flows by adding a large-scale continuous gas phase. It represents the largest gas structures whose filtered gas-liquid interfaces are captured within the computational domain. Adequate interfacial transfer formulations are introduced for area density and drag and allow the use of different closure models depending on the local morphology. By including appropriate models for the mass transfer, transitions between dispersed and continuous gas morphologies can be described. Thus not only gas-liquid interfaces for large gas structures are detected, but also small scale bubbles that are entrained under the free surface can be described properly taking into account coalescence- and breakup processes. The concept further improves free surface simulations by including sub-grid information about small waves and instabilities at the free surface. Therefore a new treatment of turbulent kinetic energy is applied via source terms at the free surface.
The application of this concept to the dambreak-case with an obstacle demonstrates the breakup of a continuous gas phase and the appearance of polydispersed gas. The collapse of the water column is accompanied by trapping of gas which breaks up to smaller structures. The quality of interface detection during the simulation is compared to the above mentioned VOF-methods. Furthermore the formation of a bubble size distribution underneath the surface serves as a demonstration of the possible benefit using such an averaged multi-field approach.
Keywords: multi-scale, interface capturing, free surface, CFX, OpenFOAM
  • Contribution to proceedings
    ASME 2013 Fluids Engineering Division Summer Meeting (FEDSM2013), 07.-11.07.2013, Incline Village, USA
    Proceedings of the ASME 2013 Fluids Engineering Division Summer Meeting Vol. 1C
  • Lecture (Conference)
    ASME 2013 Fluids Engineering Division Summer Meeting (FEDSM2013), 07.-11.07.2013, Incline Village, USA

Publ.-Id: 18544 - Permalink


Application of a multi-field concept to the dam-break case with an obstacle
Hänsch, S.; Lucas, D.; Höhne, T.; Krepper, E.; Montoya, G.;
This paper presents new results for a generalized approach developed for the simulation of two-phase flow problems with multi-scale interfacial structures. The inhomogeneous Multiple Size Group (MUSIG)-model (Krepper et al., 2008) is extended by a large-scale continuous gas phase whose filtered gas-liquid interface is captured within the Eulerian approach. In the framework of the coalescence- and breakup processes desribed by the MUSIG-model, mass transfers between the continuous gas phase and the bubble size groups have to be modelled additionally. The new concept enables transitions between dispersed and continuous gas morphologies, including the evanescence and appearance of a particular phase. Adequate interfacial transfer formulations, which are consistent with such an approach, are introduced for area density and drag. Following the free surface drag-formulation proposed by Höhne and Vallée (2010) shear stresses are considered within the free surface area.
The application of the concept to the dambreak-case demonstrates the breakup of continuous gas into a polydispersed phase consisting of different bubble sizes due to the collapse of a water column. Both resolved free surface structures as well as the entrainment of bubbles and their coalescence and breakup underneath the surface can be described. The computational results will be compared with experiments of Koshizuka et al. (1995). Simulations have been performed with the CFD-code CFX 14.0.
The paper will further investigate the possible improvement of such free surface simulations by including sub-grid information about small waves and instabilities at the free surface. Therefore a new treatment of turbulent kinetic energy at the free surface via source terms will be applied according to the proposal of Brocchini and Peregrine (2001). A comparison of the results will be used for a discussion of possible new mass transfer models between filtered free surface areas and dispersed bubble size groups as part of the future work.
Keywords: multi-scale, MUSIG, free surface, air entrainment, sub-grid turbulence
  • Contribution to proceedings
    NURETH-15 - 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-17.05.2013, Pisa, Italy
    Proceedings of the 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics
  • Lecture (Conference)
    NURETH-15 - 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-17.05.2013, Pisa, Italy

Publ.-Id: 18543 - Permalink


Demonstration of a multi-field approach for different scales of interfacial structures
Hänsch, S.;
A new concept for generalized two-phase flows (GENTOP) is presented which combines the idea of the inhomogeneous MUSIG-model and the AIAD-approach. It is used for the simulation of transitions between multi-scale interfacial structures. It is demonstrated using three different exemplary cases: the impinging jet with air entrainment, a bubble column and the dambreak case with an obstacle. Main principles are introduced and recent developments on this concept are presented, including a new source term for sub-grid wave turbulence.
Keywords: multi-scale, MUSIG, AIAD, gas-liquid interface, turbulence
  • Lecture (Conference)
    CFD-Verbundtreffen, 06.-07.03.2013, Garching, Deutschland

Publ.-Id: 18542 - Permalink


Investigations to the System Ln(III)/An(III)-B(OH)3-Organics
Schott, J.; Acker, M.; Kretzschmar, J.; Barkleit, A.; Taut, S.; Brendler, V.; Bernhard, G.;
Boric acid (B(OH)3) and (poly)borates are of great interest regarding the mobilization of trivalent actinides in nuclear waste repositories, particularly in salt deposits.
This work describes approaches to determine the stability constant in the Eu(III)-borate system. The stability constant between Eu(III) and borates is in the order of magnitude of 1...2, and with it the borate complexation is very weak.
Furthermore, in presence of polyborates at pH 6 the formation of a solid Eu borate species is observed. The formation rate of the solid Eu borate species depends on the polyborate concentration and salt concentration/type (NaClO4/NaCl). Some structural information of the solid Eu borate were provided from IR spectroscopy, solid-state NMR (11B) and solid-state TRLFS.
Keywords: europium, boric acid, borates, polyborates
  • Contribution to proceedings
    14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 08.-13.09.2013, Brighton, United Kingdom
  • Lecture (Conference)
    14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 08.-13.09.2013, Brighton, United Kingdom

Publ.-Id: 18540 - Permalink


Linear excitation of short propagating spin waves in a pair of layered vortices with opposite circulation
Wintz, S.; Weigand, M.; Tyberkevych, V. S.; Slobodianiuk, D. V.; Stoll, H.; Raabe, J.; Erbe, A.; Lindner, J.; Slavin, A. N.; Fassbender, J.ORC
The investigation of spin wave excitations in nano-magnetic systems is one of the key topics in modern magnetism. Typically, to excite short spin waves it is necessary either to use transducers of the size of a wavelength (micro-striplines or point-contacts) or to excite 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 tri-layer in which the magnetic layers form a vortex pair with opposite circulations.
Keywords: magnetism, spin waves, vortex
  • Lecture (Conference)
    International Symposium on Spin Waves 2013, 09.-15.06.2013, St. Petersburg, Russland

Publ.-Id: 18539 - Permalink


Radiotracer exchange studies on the reversibility of interaction processes related to humic-bound metal transport
Lippold, H.; Lippmann-Pipke, J.;
The mobility of actinides or other contaminants in the subsurface hydrosphere is considerably influenced by their interaction with natural colloids. Besides inorganic particles, aquatic humic substances are ubiquitous in natural waters, and their complexing ability can dominate the speciation of toxic or radioactive metals [1, 2]. Since humic carriers are subject to a solid-liquid distribution depending on geochemical parameters, an adequate assessment of migration processes needs thorough consideration of all interactions within the ternary system metal – humic substance – solid surface, including adsorption / retardation of humic colloids. Reactive transport models have been developed, taking all these processes into account [3-5]. As a prerequisite, reversibility is commonly assumed.

There is, however, a lack of clarity as to whether full reversibility is actually given for the whole ternary system, especially concerning interactions of humic matter with mineral surfaces and metals. For adsorption of humic substances, strong hysteresis has been observed (hardly any desorption upon dilution) [6-8], and recoveries in column experiments have been found to be far from complete [9, 10]. Regarding metal-humic interaction, it has been reported that complexation of higher-valent metals is accompanied by slow processes leading to an increase in complex inertness, i.e., a growing resistance towards dissociation in the presence of competing ligands or metals [11-13].

In view of these uncertainties, the aim of the present study was to elucidate the reversible / irreversible character of processes controlling humic-bound transport. For this purpose, the principle of tracer exchange was employed to gain insight into the dynamics of equilibria within the ternary system. In case of reversibility, a dynamic equilibrium exists, i.e., a permanent run of adsorption and desorption (or complex formation and dissociation) at equal rates. Such an exchange can be detected by introducing a radiotracer into pre-equilibrated systems where all binding sites are occupied.

The chosen model system for these experiments consisted of terbium(III) (as an analogue of trivalent actinides), humic acid (Aldrich) or fulvic acid (isolated from bog water), and kaolinite (KGa-1b standard material). 160Tb as a radioisotope was produced by neutron activation of 159Tb at the TRIGA Mark II reactor of the University of Mainz. Humic and fulvic acids were radiolabelled by an azo coupling reaction with [14C]aniline [14].

To investigate the dynamics of adsorption equilibria, kaolinite suspensions were first contacted with non-radioactive Tb(III) or humic / fulvic acid at a range of concentrations, covering an adsorption isotherm including the plateau region. Subsequent to a pre-equilibration phase, a small amount of the radiotracer (160Tb(III) or 14C-labelled humic / fulvic acid, respectively) was added. After admitting different time periods for equilibration, tracer exchange was evaluated from the concentration decrease in the supernatant. In additional batch experiments, desorption of humic and fulvic acid upon dilution was examined within a comparable time frame.

Reversibility of Tb(III)-humate complexation was investigated in a similar way. Since humic acid precipitates completely on loading with Tb(III), adsorption systems were generated. Here, times for tracer exchange were kept constant, and pre-equilibration times were varied instead.

As expected, adsorption of Tb(III) onto kaolinite was found to be a fast dynamic equilibrium process. Identical adsorption isotherms were obtained regardless of whether the radiotracer was introduced instantaneously together with the non-radioactive metal or subsequently after 2 days of pre-equilibration. For humic and fulvic acid, such dynamic exchange was proven to exist as well, but at considerably lower rates. In case of subsequent tracer addition, the plateau sections of the isotherms were significantly lowered (notably, not to zero). When equilibration times were increased (from 6 hours to 4 weeks), the plateaus approached the respective isotherm for instantaneous tracer addition. Finally, both isotherms coincided, i.e., the dynamic equilibrium was quantitatively represented by the tracer.

In desorption experiments with humic or fulvic acid, initiated by diluting the supernatant after an adsorption phase, no release was observed in the course of 4 weeks, which seems to be contradictory to the above results. One may conclude that the absence of desorption upon dilution is not necessarily indicative of a static equilibrium without any exchange. Thus, models for humic-bound transport are certainly applicable under appropriate conditions. Nonetheless, when comparing the kinetics of exchange to the kinetics of adsorption for humic / fulvic acid, rate constants differ by one order of magnitude [15]. This discrepancy must be taken into account when conditions of a steady local equilibrium are assigned to a maximum flow velocity.

For complexation of Tb(III) with humic acid, we did not find any indications of stabilisation processes affecting the reversibility. Increasing complex inertness has been observed for a variety of metals such as Al(III), Eu(III), Am(III), Th(IV) or U(VI), on time scales ranging from 2 days up to several months (see [13] for a review). In our tracer exchange experiments, Tb(III)-humate complexes were pre-equilibrated for 1 to 90 days before 160Tb(III) was added and a subsequent equilibration period of 1 day was admitted. In all cases, the binding isotherms were indistinguishable from the binding isotherm obtained for instantaneous tracer addition, i.e., an unresisted dynamic exchange was indicated by the tracer, even after long contact times prior to its introduction. Obviously, increasing complex inertness is not a general phenomenon occurring across all higher-valent metals.

[1] J. P. L. Dearlove et al., Radiochim. Acta 52/53, 83 (1991).
[2] J. I. Kim et al., Radiochim. Acta 58/59, 147 (1992).
[3] L. Lührmann et al., Water Resour. Res. 34, 421 (1998).
[4] N. D. Bryan et al., J. Environ. Monit. 7, 196 (2005).
[5] M. Kim and S. B. Kim, Environ. Technol. 28, 205 (2007).
[6] E. M. Murphy et al., Sci. Total Environ. 117/118, 413 (1992).
[7] B. Gu et al., Environ. Sci. Technol. 28, 38 (1994).
[8] M. J. Avena and L. K. Koopal, Environ. Sci. Technol. 32, 2572 (1998).
[9] F. M. Dunnivant et al., Soil Sci. Soc. Am. J. 56, 437 (1992).
[10] H. Weigand and K. U. Totsche, Soil Sci. Soc. Am. J. 62, 1268 (1998).
[11] R. Artinger et al., J. Contam. Hydrol. 35, 261 (1998).
[12] H. Geckeis et al., Environ. Sci. Technol. 36, 2946 (2002).
[13] H. Lippold et al., Appl. Geochem. 27, 250 (2012).
[14] A. Mansel and H. Kupsch, Appl. Radiat. Isot. 65, 793 (2007).
[15] H. Lippold et al., in preparation (2013).
  • Poster
    14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (MIGRATION 2013), 08.-13.09.2013, Brighton, United Kingdom

Publ.-Id: 18538 - Permalink


Design and calibration of ultra-short, broadband (200nm-12µm), single-shot spectrometer for ultrashort electron bunch durations diagnostics
Zarini, O.; Debus, A.; Bussmann, M.; Couperus, J. P.; Irman, A.; Seidel, W.; Schramm, U.;
The properties of electron bunch based on the Laser-Wakefield accelerators (LWFA) vary from shot to shot due to changes in the environment, such as gas jet profile or laser pointing. In order to understand the properties of these ultrashort electron bunches like bunch duration and bunch substructure in the range of 0.7 to 40 fs we are building a broadband-spectrometer for measuring coherent and incoherent transition radiation (TR).
Our TR-spectrometer is able to measure the TR-spectrum from a thin Al-foil in a single shot experiment from UV (200 nm) to mid-IR (12µm) by means of a CCD detector for the UV to VIS range and two array detectors for the NIR and MIR range. In this poster we present our design and calibration results of the detectors.
Keywords: Laser-wakefield accelerator, UV, VIS, NIR, mid-IR, spectrometer, coherent transition radiation
  • Lecture (Conference)
    DPG-Frühjahrstagung 2013, Dresden, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18537 - Permalink


The TRAKULA joint research project
Hannaske, R.; Trakula-Kollaboration;
TRAKULA is a BMBF joint research project in the framework “Energie 2020+” that aims for precise measurements of nuclear data relevant for nuclear transmutation technologies. The collaboration consists of the University of Cologne, the Technical University Dresden, the Johannes-Gutenberg University Mainz, the Technical University Munich, the Physikalisch-Technische Bundesanstalt Braunschweig, and the Helmholtz-Zentrum Dresden-Rossendorf. The topics covered are the production and experimental use of fast neutrons to study nuclear reactions, the spectroscopy with photon beams in the MeV range, the development of a high resolution Compton camera, the measurement of low radioactivities including accelerator mass spectroscopy, and the production of homogeneous thin actinide targets for neutron-induced fission measurements. Graduate seminars have been organized to maintain competencies in the field of nuclear safety and radiation research. All topics are connected to each other by their application to nuclear transmutation and nuclear waste management. The progress of the various topics will be explained and results will be presented. Experiments at the neutron-time-of-flight facility nELBE and measurements of fast neutron induced reactions will be discussed in detail. TRAKULA is supported by the German Federal Ministry of Education and Research (Contract 02NUK13A).
Keywords: Transmutation, TRAKULA
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18536 - Permalink


Simulation des Neutronenspektrums beim Deuteronen-Photodissoziations-Experiment an ELBE
Ferrari, A.; Hannaske, R.; Junghans, A. R.;
Die für die primordiale Nukleosynthese wichtige Reaktion 𝑑(𝛾, 𝑛)𝑝 wurde am supraleitenden Elektronen-Linearbeschleuniger ELBE mit Bremsstrahlung bei einer Endpunktenergie von 5,0 MeV untersucht [1]. Neutronen mit einer kinetischen Energie von 20 − 1400 keV wurden mit Hilfe der Flugzeit-Detektoren RoLAND (Rossendorf Low-Amplitude- Neutron Detector) nachgewiesen. Wechselwirkungen der emittierten Neutronen mit dem Targetmaterial (23 Schichten aus Aluminium und deuteriertem Polyethylen) und anderen Teilen des Expermientaufbaus (HPGe- und BGO-Detektoren, Bleiabschirmungen, Strahlfänger, Betonwände) haben einen nicht zu vernachlässigenden Einfluss und wurden daher mit FLUKA [2] simuliert. Zusammen mit der experimentell bestimmten Detektoreffektivität erhält man einen Flugzeit-abhängigen Korrekturfaktor für das gemessene Neutronenspektrum. Der Aufbau und die Ergebnisse der Simulation sowie die Bestimmung des Korrekturfaktors und dessen Einfluss auf den ermittelten 𝑑(𝛾, 𝑛)𝑝 Wirkungsquerschnitt werden präsentiert.
[1] R. Hannaske et al., PoS(NIC XI)090 (2010). [2] www.fluka.org
Gefördert durch die DFG (JU 2705/1-1).
Keywords: Big Bang nucleosynthesis, bremsstrahlung, neutron time-of-flight, nuclear astrophysics, neutron detector, efficiency
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18535 - Permalink


NeuLAND time of flight detector for 0.2-1.0 GeV neutrons: status 2013
Bemmerer, D.;
The status of the NeuLAND time of flight detector for 0.2-1.0 GeV neutrons for FAIR is reviewed.
Keywords: Time of flight, neutron detection, SiPM, scintillator, single electron beam, ELBE, detector test
  • Invited lecture (Conferences)
    Kick-off meeting of the NEutron DEtector developments for Nuclear Structure, Astrophysics and Applications (NEDENSAA), 20.-22.02.2013, Acireale, Italy

Publ.-Id: 18534 - Permalink


Status und Programm für den 5 MV Pelletron-Beschleuniger im Dresdner Felsenkeller
Bemmerer, D.; Zuber, K.;
Die Modellierung astrophysikalischer Szenarien benötigt Eingabepara- meter, deren Präzision besser als die Genauigkeit der entsprechenden astronomischen Beobachtungen ist. Da für einige solche Szenarien wie die Urknall-Nukleosynthese, die Sonne, rote Riesensterne und Superno- vae in unserer Milchstraße inzwischen eine Vielzahl von Beobachtun- gen vorliegen, wird es notwendig, die Raten der dort stattfindenden Kernreaktionen im Labor neu und präzise zu vermessen. Ein probates Mittel für leichte Kerne sind beschleunigergestützte Experimente bei den astrophysikalisch relevanten Energien, die wegen der beobachteten sehr geringen Zählraten allerdings nur dann Aussicht auf Erfolg haben, wenn die Experimente in von der Höhenstrahlung geschützte unterir- dische Labors verlegt werden. Zur Zeit gibt es nur einen Untertage- Ionenbeschleuniger weltweit, die LUNA 0.4MV Maschine am Gran Sasso (Italien).
Im Sommer 2012 wurde ein gebrauchtes 5 MV Hochstrom-Pelletron gekauft und nach Dresden transportiert. Es soll 2013 im Dresdner Untertagelabor Felsenkeller installiert werden und wird durch seinen Energiebereich einzigartig sein. Der Felsenkeller ist durch eine 47m dicke Felsdecke von der Atmosphäre getrennt. In dem Vortrag werden das wissenschaftliche Programm und der Status des Projekts zusam- mengefasst. – Unterstützt von NAVI.
Keywords: Nuclear Astrophysics, Underground experiments, Felsenkeller, LUNA, Big Bang Nucleosynthesis, solar fusion, helium burning, carbon burning, supernovae
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18533 - Permalink


Rezisztívlap-kamra, mint gyorsneutron-detektor
Elekes, Z.;
  • Open Access LogoFizikai Szemle 63(2013)2, 42-46

Publ.-Id: 18532 - Permalink


Nuclear reactions for astrophysics studied at LUNA and in the Dresden Felsenkeller
Bemmerer, D.;
Nuclear reactions power our Sun, and they create the chemical ele- ments that are necessary for human life. In order to correctly under- stand what happens in stars, one needs astronomical observations, but also nuclear physics data. For a number of astrophysical scenarios such as the Big Bang and our Sun, precise astronomical data are now avail-able. This calls for new nuclear reaction data of similar precision.
The nuclear reactions that are important for hydrogen burning in the Sun and for Big Bang nucleosynthesis have to be studied by low- energy experiments with intensive beams of stable ions. Due to the low cross sections involved, the experiments are usually performed in a low-background environment, such as an underground laboratory. The results obtained in the last decade at the pioneering LUNA 0.4 MV accelerator deep underground in the Gran Sasso laboratory, Italy, will be summarized, as well as related studies at surface-based ion accelerators.
New, higher-energy underground accelerators are necessary to ex- tend the energy range of the solar fusion data, and to address stellar helium and carbon burning. Relevant projects are underway both at LUNA and at the Dresden Felsenkeller.
Keywords: LUNA, Felsenkeller, Nuclear Astrophysics, underground experiments, Big Bang Nucleosynthesis, solar fusion
  • Invited lecture (Conferences)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18531 - Permalink


Nuclear Physics in the Big Bang
Bemmerer, D.;
The nuclear physics processes taking place in the first three minutes of the universe are reviewed, from an experimental perspective
Keywords: Nuclear Astrophysics, Big Bang Nucleosynthesis, LUNA, Felsenkeller, cosmic lithium problem
  • Invited lecture (Conferences)
    HGS-HIRe Lecture Week on Nuclear Structure and Astrophysics, 23.-25.01.2013, Manigod, Frankreich

Publ.-Id: 18530 - Permalink


The nuclear physics of our Sun
Bemmerer, D.;
The nuclear fusion processes in the center of our Sun are reviewed
Keywords: LUNA, Felsenkeller, Nuclear Astrophysics, solar fusion, solar neutrinos
  • Invited lecture (Conferences)
    HGS-HIRe Lecture Week on Nuclear Structure and Astrophysics, 23.-25.01.2013, Manigod, Frankreich

Publ.-Id: 18529 - Permalink


micro-Raman spectroscopic imaging of copper ores
Kostudis, S.; Hof, M.; Kutschke, S.; Pollmann, K.;
The large deposits of Kupferschiefer in Middle Europe involve the northeastern part of Saxony, the Upper Lusatia. The regional copper shale raised again interest of both industry and science because it’s copper content constitutes the most important natural copper resource in this region. Due to the complex composition of the shale including copper and sulfide rich ores, carbonates and organic compounds, there is no efficient biotechnological approach applied yet. Bioleaching, which means the use of microorganisms and their metabolites to extract metals from their ores, reduces costs of high energy input and avoids the usage of toxic chemicals thus benefitting environment (Narayan 2009) and employees.
Raman spectroscopy enables a fast and specific chemical identification of minerals and ores (Hope 2001) as well as changes e.g. caused by oxidation (García-Meza 2012). Also Raman spectroscopic imaging of biotic components such as biofilms has already been performed (Virdis 2012).
We aim to use Raman spectroscopy to investigate the interactions of microorganisms and ore surface: Different polished sections of bornite, chalcopyrite (both from Henderson Mine, Namagualand, South Africa), chalcosite (Japan) and copper shale (Polkovice, Poland) were analysed by polarising microscopy to ensure correct spectra assignment (Fig. 1/2). Subsequently identic areas were analysed by Raman imaging using 2D scanning function (Fig. 3 - 5). After incubation with microorganisms the sections will be investigated again in order to evaluate chemical changes of the ore surfaces, biofilm formation and to monitor bioleaching processes.
  • Poster
    Conference on Raman and Luminescence Spectroscopy in the Earth Sciences, 03.-06.07.2013, Wien, Österreich

Publ.-Id: 18528 - Permalink


Nuclear reactions, solar neutrinos, and the importance of the CNO cycle
Bemmerer, D.;
The state of the art of nuclear physics for solar neutrinos is reviewed.
Keywords: LUNA, Felsenkeller, solar fusion, nuclear astrophysics, solar neutrinos, underground experiments
  • Invited lecture (Conferences)
    522. Wilhelm und Else Heraeus Seminar: Exploring the neutrino sky and fundamental particle physics on the Megaton scale, 21.-23.01.2013, Bad Honnef, Deutschland

Publ.-Id: 18527 - Permalink


Kluge Köpfe. Die Zukunft unserer Welt
Joehnk, P.; Toepfer, K.;
  • Innovation 1(2012)20

Publ.-Id: 18526 - Permalink


The Importance of Unified Financal Control to Preserve a Financal Situation of a Holding
Hoduliková, P.; Joehnk, P.; Šnircová, J.;
Workshop - eingeladener Vortrag
  • Invited lecture (Conferences)
    Workshop “Innovation Information Technologies: Theory and Practice”, 01.04.2011, Ufa, Russland

Publ.-Id: 18525 - Permalink


The Importance of the Unified Financal Control in the Mechanical Engineering Management-Holding
Hoduliková, P.; Drozdova, A.; Joehnk, P.; Šnircová, J.;
  • Invited lecture (Conferences)
    EBES 2012 Conference - Antalya, 13.-14.01.2012, Antalya, Turkey

Publ.-Id: 18524 - Permalink


Alumni Management System: Methods and Models of the Information Processing
Joehnk, P.; Iskhakova, L.; Smetanin, Y. G.; Smetanina, O.;
Veröffentlichung
  • Invited lecture (Conferences)
    Workshop on computer science and information technologies CSIT`2011, 27.09.-02.10.2011, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 18523 - Permalink


Leistungs- und Schnittstellenstufung: Objektmanagement – am Praxisbeispiel der Restrukturierung eines Forschungsstandortes
Joehnk, P.;
Vortrag im Rahmen des FM – Nutzerkongresses, Düsseldorf
  • Invited lecture (Conferences)
    FM – Nutzerkongress 2012, 24.-25.04.2012, Düsseldorf, Deutschland

Publ.-Id: 18522 - Permalink


Die perfekte Sekretärin
Joehnk, P.;
  • Lecture (others)
    Sekretärinnen-Seminar UFZ, 02.05.2011, Leipzig, Deutschland

Publ.-Id: 18521 - Permalink


Bacterial diversity in Mont Terri Opalinus Clay and the influence of the bacterial Sporomusa sp. isolate on plutonium speciation
Moll, H.; Lütke, L.; Bachvarova, V.; Geissler, A.; Selenska-Pobell, S.; Bernhard, G.;
The concept of geological disposal of nuclear waste comprises a detailed knowledge concerning potential host rock formations. One of such formations is the Opalinus Clay geologic layer of the Mont Terri Underground Rock Laboratory (Switzerland). Dominant bacterial strains from sites destined for future nuclear waste deposition have to be identified and investigated regarding their interaction mechanisms with soluble actinide ions.
For the first time microbial total DNA (tDNA) was isolated from 50 g unperturbed Mont Terri Opalinus Clay. Analysis of the tDNA revealed that the bacterial community of the unperturbed Opalinus Clay is dominated by representatives of Firmicutes, Betaproteobacteria, and Bacteriodetes. Representatives of Firmicutes completely overgrow the other members of the community after treatment of the clay with R2A medium. Bacteria isolated from Mont Terri Opalinus Clay on R2A medium were affiliated with different Sporomusa spp., Paenibacillus spp., and Clostridium spp..
After isolation, characterization, and cultivation, we studied the unknown interaction between plutonium in mixed oxidation states and cell-suspensions of one of the Sporomusa sp. MT-2 isolates. Accumulation experiments were performed in order to obtain information about the amount of Pu bound by the bacteria in dependence on the contact time and the initial plutonium concentration. The 242-Pu present in blank (no cells added), supernatant, and washed biomass suspension at pH 0 was analyzed using UV-vis-NIR spectroscopy, solvent extraction, and liquid scintillation counting (LSC). In addition experiments were performed by adding an electron donor (Na-pyruvate) in two concentrations 0.1 mM and 10 mM.
The amount of Pu sorbed by Sporomusa sp. cells increased with time. Steady state conditions were reached after approximately 200 h. The data could be successfully fitted to a bi-exponential law. The amount of Pu associated with Sporomusa sp. cells depends on the initial 242-Pu concentration. In the first step, a fast binding of the Pu(VI) and Pu(IV)-polymers onto the biomass occurred. Solvent extractions showed that 92 % of the initially present Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 48 h of contact time (no electron donor added). The corresponding redox potential in the cell suspensions dropped down to 300 mV compared to 780 mV measured in the blanks. Most of the formed Pu(V) dissolves from the cell envelope back to the aqueous solution due to the weak complexing properties of Pu(V). Good binding properties of Pu(IV)-polymers on functional groups of the Sporomusa sp. cell envelope were found (immobilization). In contrast to earlier measurements with Pseudomonas fluorescens (CCUG 32456A) cells clear indications for increased amounts of Pu(IV) and Pu(III) on the Sporomusa biomass were observed. The Pu oxidation state distributions as a function of time will be discussed in detail and the results of the system without addition of electron donors will be compared with the electron donor supplemented systems. Here differences in the Pu interaction mechanism were found.
Keywords: plutonium, bacteria, Sporomusa, speciation, absorption spectroscopy, solvent extraction
  • Contribution to proceedings
    MIGRATION 2013 - 14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 08.-13.09.2013, Brighton, United Kingdom
    Proceedings of MIGRATION 2013
  • Poster
    MIGRATION 2013 - 14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 08.-13.09.2013, Brighton, United Kingdom

Publ.-Id: 18520 - Permalink


Spectral methods for measuring ultrashort electron bunch durations from Laser-wakefield accelerators
Debus, A.; Zarini, O.; Bussmann, M.; Couperus, J. P.; Irman, A.; Seidel, W.; Schramm, U.;
Laser-wakefield accelerators (LWFA) feature electron bunch durations ranging from several fs to tens of fs. Knowledge and control of the electron bunch duration is vital to the design of future table-top, X-ray
light-sources for laser-synchronized pump-probe experiments, ranging from betatron radiation, Thomson scattering to FELs. Due to the nonlinear nature of the laser-wakefield electron injection and small changes in initial experimental conditions the electron bunch properties are often subject to large shot-to-shot variations, which requires diagnostics working not only at ultrashort time-scales but also at single-shot.
We aim for measurements of the LWFA electron bunch duration and bunch substructure at single-shot by analysing the coherent and incoherent transition radiation spectrum. Our ultra-broadband spectrometer ranges from the UV (200 nm) to the mid-IR (12 µm), which allows to resolve time-scales from 0.7 to 40 fs. The prims and grating-based spectrometer divides and maps the spectrum onto three detector systems (UV/VIS;NIR;MIR) of staggered, increasing resolution towards lower wavelengths. Here we present the experimental approach, scope and current status of our spectrometer project.
Keywords: Laser-wakefield acceleration, UV, VIS, NIR, mid-IR, spectrometer, coherent transition radiation
  • Lecture (Conference)
    DPG-Frühjahrstagung, Dresden 2013, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18519 - Permalink


Human resource development – challenges and opportunities for universities and research institutes
Joehnk, P.; Runow, A.; Gilge, B.;
  • Invited lecture (Conferences)
    ISTU Izhevsk, 19.-22.04.2010, Izhevsk, Russland

Publ.-Id: 18518 - Permalink


Incorporation of Europium and Nickel in calcite studied by Rutherford Backscattering Spectrometry
Toulhoat, N.; Pipon, Y.; Moncoffre, N.; Sabau, A.; Lomenech, C.; Jordan, N.; Barkleit, A.; Marmier, N.; Brendler, V.; Surblé, S.; Giffaut, E.;
This study aims at elucidating the mechanisms leading to the incorporation of cations (Eu and Ni) into carbonates (CaCO3). These minerals are present in the French Callovo Oxfordian shales where the radioactive waste should be disposed of. Europium is a long lived fission product that can also be used as analogue of trivalent actinides. Nickel is a long lived activation product. Therefore, for safety reasons, the evaluation of the retention capabilities of calcite with respect to these radionuclides has to be checked. Calcite powders or calcite single crystals (some mm sized) have been put into contact with inactive Europium or Nickel enriched solutions. The concentrations ranged from 10-3 to 10-5 mol/L for Eu and 10-3 mol/L for Ni and the sorption durations ranged from one week to one month. In order to elucidate the incorporation mechanisms of these elements on calcite, Rutherford Backscattering Spectrometry (RBS) experiments have been carried out using an alpha particle millibeam at the 4 MV Van de Graaff accelerator of IPNL. This technique is well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance). For the single crystals, complementary Scanning Electron Microscopy (SEM) observations of the mineral surfaces at low voltage have also been carried out. Moreover, for Europium incorporation, using its fluorescence properties, the results have been compared to those obtained by Time-resolved laser fluorescence spectroscopy (TRLFS). Results on single crystals show different sorption behavior for Ni and Eu. Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160 nm after 1 month of sorption.
Keywords: incorporation; RBS; Eu; Ni; calcite
  • Poster
    21st International Conference on Ion Beam Analysis, 23.-28.06.2013, Seattle, USA

Publ.-Id: 18517 - Permalink


Simultaneous measurement of AMR and observation of magnetic domains
Osten, J.; Langer, M.; Lenz, K.; Linder, J.; Fassbender, J.ORC
Anisotropic magneto resistance (AMR) sensors are widely used in daily life. Nevertheless, the influence of magnetic domains on the AMR is still not fully understood. AMR depends on the angle between applied current and the direction of the internal magnetization, which is equal to the sum of all magnetic domains. For the understanding of the AMR it is important to know the domain structure.
In this experiment Kerr microscopy is used for the observation of the magnetic domains while at the same time the AMR is measured. The investigated permalloy films are stripe patterned by Cr+ implantation. Amongst other effects the implantation leads to a lower saturation magnetization in the implanted stripes compared to the non-implanted ones.
Our measurements show a clear correlation between AMR and the magnetic domain structure. It is also possible to correlate stripe parameters to different domain types.
This work is supported by DFG grant FA316/3-2.
Keywords: AMR Kerr microscopy
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18516 - Permalink


Design of two-phase inductor circuit for the floating-zone crystal growth
Priede, J.; Gerbeth, G.; Hermann, R.;
The present work is concerned with the growth of small-diameter single intermetallic compound crystals by the floating-zone method using a radio frequency RF induction heating. In order to maintain a convex solidification interface, which is required for the growth of single crystals, we have developed a novel two-phase inductor comprising a secondary coil, which is short-circuited through capacitor and resistor. The former is adjusted to have resonance in the secondary circuit, which results in a 90 degrees phase lag of the secondary current relative to the primary one. However, it is not always possible to tune the secondary circuit into the resonance as it turns out to be incompatible with the operation of contemporary self-tuning RF-generators. We show that the resonance frequency is unstable unless the resistance of the secondary circuit is made high enough. Analytical results are confirmed by both numerical simulation of the circuit system using the Simulink and measurements on the floating-zone crystal growth facility equipped with a two-phase inductor.
  • Journal of Iron and Steel Research International 19(2012)Suppl., 700-704

Publ.-Id: 18515 - Permalink


Influence of Rippled Substrate Morphology on the Interlayer Exchange Coupling in Fe/Cr/Fe Thin Films
Körner, M.; Lenz, K.; Liedke, M. O.; Strache, T.; Mücklich, A.; Keller, A.; Facsko, S.; Fassbender, J.ORC
We have investigated the interlayer exchange coupling in Fe (4nm)/Cr (x nm)/Fe (4nm) thin film trilayers (x=0–5 nm) deposited on rippled amorphous silicon substrates. The substrate surface was periodically modulated (periods of 22 nm and 37 nm) by Ar+ ion erosion. The influence of the resulting surface and interface structure on the magnetic properties has been investigated by magneto-optical Kerr effect (MOKE). We found an orange peel type coupling, predicted by N´eel’s theory and, due to the morphology of the magnetic layers, a strong uniaxial magnetic anisotropy in the system.
This work is supported by DFG grant FA 314/6-1.
  • Poster
    The Nanoscale Modification of Surfaces and Thin Films workshop, 30.08.-03.09.2009, Rathen, Deutschland

Publ.-Id: 18514 - Permalink


Effects of the TiO2 buffer thickness on SrTiO3 (111) epitaxial films grown on GaN (0002)
Luo, W.; Zhu, J.; Shuai, Y.; Zhang, W.; Zhang, Y.; Zhou, S.; Gemming, S.; Schmidt, H.;
SrTiO3 (STO) films have been grown on TiO2-buffered GaN(0002) substrates. The deposition process was in-situ monitored by reflective high energy electron diffraction (RHEED). The deposition rate and in-plane lattice parameter of TiO2 were calculated from the oscillation curve and RHEED patterns, respectively. It was found that the TiO2 lattice parameter changed as the thickness increased, which indicated a strain relaxation process of TiO2 buffer layers during the deposition. We show that the thickness of TiO2 can significantly influence the STO growth mode, surface morphology and crystalline quality. As the TiO2 thickness increased, the STO growth mode is changed from 3D island to 2D growth mode and finally to S.K mode as revealed by RHEED. The growth mode evolution shows close relation with the surface morphology and crystalline quality of STO. STO films deposited on 2nm thick TiO2 film show 2D growth mode and have smoothest surface and smallest full width at half magnitude of the STO rocking curve. Our investigation hints towards to a general approach to optimize the crystalline quality of STO can be optimized by adjusting the strain state of TiO2 buffer layer.

Publ.-Id: 18513 - Permalink


Does electron dynamics in Traveling-Wave Thomson-Scattering allow for an optical FEL?
Steiniger, K.; Pausch, R.; Widera, R.; Debus, A.; Bussmann, M.; Sauerbrey, R.;
In the Travelling-wave Thomson-scattering (TWTS) scheme ultrashort and narrow-band light pulses in the X-Ray region of the spectrum are created by scattering high intensity laser pulses from relativistic electron bunches. TWTS uses lasers with a pulse front tilt in a side-scattering geometry to scale the interaction length into the centimeter to meter range. This is crucial for allowing the scattered radiation to act back on the electrons which eventually can lead to coherent amplification of the radiation as in a free electron laser (FEL). We study the electron dynamics in the laser field including back reaction effects and discuss the applicability of TWTS as a SASE-FEL.
Keywords: traveling wave, thomson scattering, free electron laser, laser pulse, x-ray
  • Lecture (Conference)
    DPG-Frühjahrstagung Dresden 2013, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18512 - Permalink


Höchstsensitiver Nachweis von Radionukliden mit der Dresdner AMS (DREAMS)
Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.; Renno, A.; Ziegenrücker, R.;
Beschleunigermassenspektrometrie (AMS, accelerator mass spectrometry) ist eine höchstsensitive Methode, um langlebige Radionuklide mit einer Halbwertszeit von 100 Jahren und länger zu messen. Der Aufbau der AMS-Anlage DREAMS (DREsden AMS), die seit August 2011 in Betrieb ist, ist in Abbildung 1 dargestellt.
Aus der zu analysierenden – bereits chemisch aufbereiteten – Probe werden in einer Cäsium-Sputterionenquelle negative Ionen (Moleküle oder Elemente) extrahiert. Diese einfach negativ geladenen Ionen werden in einem Niederenergie-Massenspektrometer nach ihrer Energie und Masse analysiert und gelangen nachfolgend in den Tandem-Beschleuniger, wo sie durch eine positive Hochspannung (im Bereich von MV) beschleunigt werden. Beim Durchgang durch Argon-Gas werden den Ionen Elektronen abgestreift, dadurch Moleküle zerstört, und die nun positiven Ionen ein zweites Mal beschleunigt. Im Hochenergie-Massenspektrometer werden die Radionuklide dann mit einem geeigneten Detektionssystem identifiziert. Mit diesem Aufbau lassen sich Isobare effizient, sowie molekularer Untergrund vollständig unterdrücken.
Momentan werden an DREAMS Routinemessungen der Nuklide 10Be, 26Al und 41Ca durchgeführt [1]. Die Nachweisgrenze liegt im Bereich von 10-15 – 10-16 Radionuklid zu stabilem Nuklid, was Aktivitäten im Bereich von nBq entspricht. Zu Messungen volatiler Elemente wie Chlor (36Cl) siehe [2].
DREAMS wird um eine Flugzeitstrecke (time-of-flight (TOF)) erweitert, um schwere Nuklide wie Aktinide messen zu können. Neben der vollständigen Molekülunterdrückung und dem geringeren Präparationsaufwand von Proben liegt der Vorteil der AMS darin, Isotope wie 239Pu und 240Pu unterscheiden zu können, was mittels Alphaspektrometrie nicht möglich ist.
Durch den Anbau einer kommerziellen SIMS (SIMS = Secondary ion mass spectrometry) Anlage an den Beschleuniger wird DREAMS zu einer Super-SIMS erweitert. Damit sollen Verhältnisse stabiler Elemente im Bereich von 10-9-10-12 unter Beibehaltung der Ortsauflösung einer SIMS-Anlage gemessen werden.
[1] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5.
[2] S. Pavetich, Poster, 7. Workshop RCA.
  • Lecture (Conference)
    7. Workshop RCA, 10.-11.06.2013, Dresden, Rossendorf, Deutschland

Publ.-Id: 18511 - Permalink


Positron Annihilation Spectroscopy at a Superconducting Electron Accelerator
Wagner, A.;
High-power superconducting linear electron accelerators allow producing a variety of secondary beams. At the Helmholtz-Zentrum Dresden-Rossendorf a 40 MeV superconducting electron accelerator is operated at beam currents up to 1.6 mA in continous-wave mode delivering neutrons from photo-production off lead, tunable coherent laser light from free-electron lasers, intense Bremsstrahlung for nuclear (astro-) physics, and positrons from pair production. New developments now enable for the first time positron annihilation lifetime experiments in bulk materials, fluids, gases and organic tissue. A 3-D tomographic annihilation lifetime imaging systems has been developped for new classes of experiments for quantitative and qualitative crystal-defect characterizations, chemsitry of positronium in insulators and porous materials. Some recent applications will be presented.
Keywords: superconducting linear electron accelerator positron annihilation lifetime tomography imaging positronium
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18510 - Permalink


How to excite oscillating modes in the kinematic mean-field α2-dynamo: A Krein space-related perturbation approach
Kirillov O.; Stefani F.; Gunther U.;
We consider equations of the kinematic mean-field alpha^2-dynamo with the spherically-symmetric alpha-profile that depends only on the radial coordinate. We study spectrum of the non-self-adjoint boundary eigenvalue problem for the corresponding operator matrix with the boundary conditions associated either with a perfect electrically conducting surrounding or with an insulating one. In the first case we demonstrate that the operator is self-adjoint in a Hilbert space with the indefinite metric (i.e. in the Krein space). Moreover, if, additionally, the alpha-profile is constant (the problem A), the eigenvalues are real-valued linear functions of alpha; hence, only non-oscillatory instability is possible. However, with non-constant alpha-profiles and insulating boundary conditions, oscillatory dynamo regimes can become dominant (the problem B). With the use of the perturbation theory of multiple eigenvalues we explicitly demonstrate how from the real spectrum of the problem A one can get the complex eigenvalues of the problem B due to variation of alpha-profile and interpolation between the two types of boundary conditions.
Keywords: MHD, dynamo, boundary eigenvalue problem, Krein signature, instability
  • Poster
    Les Houches Winter school "Waves and Instabilities in Geophysical and Astrophysical Flows", 03.-08.02.2013, Les Houches, France

Publ.-Id: 18509 - Permalink


WKB thresholds of standard, helical, and azimuthal magnetorotational instability
Kirillov O.; Stefani, F.;
We consider rotating flows of an electrically conducting, viscous and resistive fluid in an external magnetic field with arbitrary combinations of axial and azimuthal components. Within the short-wavelength approximation, the local stability of the flow is studied with respect to perturbations of arbitrary azimuthal wavenumbers. In the limit of vanishing magnetic Prandtl number (Pm) we find that the maximum critical Rossby number (Ro) for the occurrence of the magnetorotational instability (MRI) is universally governed by the Liu limit which is below the value for Keplerian rotation.
Keywords: Magnetorotational instability; WKB approximation; accretion disks

Publ.-Id: 18508 - Permalink


Schnelle Röntgentomographie zur zeitlich aufgelösten Messung von Geschwindigkeiten in Strömungen
Hoppe, D.;
Ein gegebener schneller Röntgentomograph mit zwei parallelen Messebenen dient zur örtlich aufgelösten Messung von Geschwindigkeiten. Seine Aufgabe soll ohne technischen Zusatzaufwand auf zeitlich aufgelöste Messungen ausgedehnt werden. Der Ebenenabstand ist dafür aber zu groß. Deshalb wird zusätzlich eine indirekte Messebene definiert, indem diejenige Strahlung ausgenutzt wird, die sich im Tomographen zwischen den regulären Ebenen ausbreitet. Die neue Messebene hat zu einer der regulären Ebenen einen genügend kleinen Abstand. Wie damit gemessen werden kann, verdeutlicht ein praktisches Beispiel.

A given fast X-ray tomograph with two parallel measuring planes is used for spatially resolved measurements of flow velocities by design. Now it is to be extended to time-resolved measurements avoiding any additional technical effort. But the spacing between the planes is too big. Thus, an additional indirect measuring plane is defined utilizing radiation which propagates between the regular planes during the tomographic scan. This indirect plane is close enough to one of the regular planes. A practical example illustrates the mode of measurement using the new method.
Keywords: Short time cross correlation, measuring planes, bubble flow, Rofex
  • Technisches Messen 80(2013)9, 261

Publ.-Id: 18507 - Permalink


The reactor dynamics code DYN3D and its trigonal-geometry nodal diffusion model
Duerigen, S.; Rohde, U.; Bilodid, Y.; Mittag, S.;
The reactor dynamics code DYN3D is a three-dimensional best-estimate tool for simulating steady states and transients of light-water reactors and innovative reactor designs. An overview of the DYN3D features is provided. This paper further focuses on the recently developed trigonal-geometry diffusion model DYN3D-TRIDIF including a description of the underlying nodal approach and the characteristics of trigonal geometries. Via a mesh refinement study by means of a VVER-1000-type core benchmark using a fine-mesh diffusion reference solution, DYN3D-TRIDIF shows spatial convergence. Furthermore, the performance of DYN3D-TRIDIF is verified by means of a single-assembly problem on pin-cell level. Good agreement between DYN3D-TRIDIF and the detailed-geometry transport reference is achieved with an average deviation in power of less than 1 %.
Keywords: DYN3D, nodal method, diffusion, trigonal, triangular, hexagonal
  • Kerntechnik 78(2013)4, 310-318

Publ.-Id: 18506 - Permalink


Magnetic semiconductors: created and modified by ion beams
Zhou, S.;
In this talk, I will introduce our work on magnetic semiconductors using ion beams. We can (1) prepare ferromagnetic III-V:Mn with different bandgaps and (2) change the hole concentration while keeping Mn concentration constant by ion irradiation. Both possibilities are unique and may lead to a better understanding of magnetic semiconductors.
  • Lecture (Conference)
    Seminar at Institut für Physik, Technische Universität Chemnitz, 06.03.2013, Chemnitz, Germany

Publ.-Id: 18505 - Permalink


Ridge waveguide lasers in Nd:YAG crystals produced by combining swift heavy ion irradiation and precise diamond blade dicing
Jia, J.; Rüter, C. E.; Akhmadaliev, S.; Zhou, S.; Chen, F.; Kip, D.;
Ridge waveguides have been fabricated in Nd:YAG crystals by using ion irradiation and precise diamond blade dicing. Continuous-wave lasers at ~1064 nm have been realized in the ridge waveguides through optical pumping at 808 nm at room temperature. The ridge guiding structure shows superior lasing performance with respect to the planar counterpart with a slope efficiency of 43% and a maximum output power of 84 mW.
Keywords: Laser materials, Waveguides, channeled, Ion irradiation

Publ.-Id: 18504 - Permalink


Ga-68- and Cu-64-Labeled NOTA-Albumin Conjugates for PET Sentinel Lymph Node Imaging
Schiller, E.; Bergmann, R.; Wunderlich, G.; Andreeff, M.; Jacob, A.; Pietzsch, H.-J.;
Our objective was to develop and evaluate Ga-68- and Cu-64-labeled albumin conjugates for PET imaging of sentinel lymph nodes. Four different albumin conjugates were prepared starting from NOTA-HSA.The lymph node uptake of Ga-68- and Cu-64-labeled albumin conjugates was investigated after subcutaneous injection into the foot pad of Wistar rats. A pig model was utilized for further biological evaluation of the lymph node uptake. For all the four conjugates, radiolabeling with Ga-68 and Cu-64 resulted in >95% radiochemical yield. Denatured and mannosylated Ga-68 NOTA-HSA revealed the highest popliteal lymph node uptake in rats (2.78%±0.38% IDand 6.13%±1.13%ID 10 min and 60 min p.i., resp.).Thepopliteal lymph node reached its maximumactivity after approximately 120 min and remained constant for denatured and mannosylated Cu-64 NOTA-HSA at least up to 240 min p.i. In a pig model, 2% of the injected dose of this compound was found in the sentinel lymph node 60 min after subcutaneous injection. In conclusion, PET imaging of sentinel lymph nodes with Ga-68- and Cu-64-labeled denatured NOTA-Man-HSA could be successfully demonstrated and deserves further investigations.

Publ.-Id: 18503 - Permalink


Simulating electromagnetic radiation from laser-wakefield acceleration plasmas
Pausch, R.; Debus, A.; Steiniger, K.; Widera, R.; Bussmann, M.;
Measuring the transient plasma density structures of Laser-wakefield accelerators (LWFA) that are shorter than the drive laser on a µmfs-scale is experimentally challenging, which complicates comparisons of these results with numerical models from 3D-PIC simulations. Radiation spectra from LWFA plasmas on the other hand are straightforward to measure, but hard to calculate in realistic detail because it is computationally expensive (both CPU and memory) to calculate the radiation emitted by a complete PIC simulation. However, it would be very useful to know where to look for "good" radiation signatures that show quantitative details on the electron dynamics at electron injection.
Here we present a highly-scalable, classical radiation code based on Liénard-Wiechert potentials, which runs on high-performance computing clusters using GPUs. The memory and disk-space footprint is reduced by directly integrating into the 3D-PIC code PIConGPU. With this new code, it is possible to calculate logarithmic-scaled spectra from IR to X-ray wavelengths in arbitrary observation directions. In this talk we put the emphasis on the code architecture, the verification of the physics and on some first results.
Keywords: laser-wakefield acceleration, LWFA, radiation spectra, radiation signatures, Liénard-Wiechert potentials, GPU, PIConGPU
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18502 - Permalink


Modern Developments in FIB Application
Bischoff, L.;
In the last decade focused ion beams (FIB) became an irrecoverable instrument in research and industry. Sample preparation, local ion implantation and ion analysis are the main application topics. Most of the systems are equipped with a gallium liquid metal ion source (LMIS). But, modern trends in nanotechnology require more extended properties like variable ion species, non-contaminating milling at higher rates or higher lateral resolution in the field of ion microscopy.
In this presentation the assembly and the mode of operation as well as the application of alloy LMIS in mass separated FIB systems are introduced. A brief survey about the history and fabrication technology of LMIS is given. Finally, new developments including sources in the field of FIB applications in the nanotechnology are discussed.
Keywords: focused ion beam; liquid metal ion source; nano pattern; new trends
  • Lecture (others)
    Instituts-Seminar, 28.02.2013, Wien, Österreich

Publ.-Id: 18501 - Permalink


Microorganisms in metal- and radionuclide-contaminated environments and potential nuclear waste disposals
Geissler, A.; Reitz, T.; Tschikov, J.; Lütke, L.; Moll, H.; Bachvarova, V.; Merroun, M.; Selenska-Pobell, S.;
Microorganisms in a soil sample from the uranium mining waste Johanngeorgenstadt, Germany and an Opalinus clay sample from the Mont Terri rock laboratory were investigated by culture-independent and culture-dependent methods. In addition, the interactions of an Arthrobacter sp. from the uranium mining waste and a Sporomusa sp. clay isolate with Uranium(VI) will be shown. The studies demonstrated that different microorganisms are present in these two different environments and in both cases indigenous microorganisms have the potential to interact with heavy metals and uranium.
Keywords: microbial diversity, bacterial isolates, uranium(VI)
  • Lecture (Conference)
    Higrade‐Module Introduction to Research in Environmental Technology, 08.03.2013, Leipzig, Deutschland

Publ.-Id: 18500 - Permalink


Coupling of side chain hydration and protonation to membrane protein structure: time-resolved FTIR and fluorescence studies of rhodopsin
Fahmy, K.; Reeves, P.; Eichler, S.;
Membrane proteins fulfil vital functions in cellular signalling and ion exchange across cell membranes. Their function originates in well defined structural transitions of transmembrane and extramembraneous protein domains. The latter experience aqueous and hydrophobic solvation forces, respectively. We have used time-resolved FTIR spectroscopy coupled to static fluorescence measurements to study how this solvation balance at the membrane water interface affects membrane protein structure. Transmembrane peptides derived from rhodopsin, a prototypical G protein-coupled receptor (GPCRs), exhibit solvent-accessible stretches which couple protonation and hydration to local helical structure: protonation of a conserved cytosolic site in helix 3 (Glu-134) causes side chain partitioning at the water lipid interface [1]. Vice versa, the side chain charge affects structural transitions that are induced by transients (seconds) of interfacial water potential. These local processes depend on the hydrophobic context of the amino acid sequence. Opsin mutants containing amino acid replacements of the same carboxyl side chain also exhibit altered responses of their structure to water potential. The data indicate that the conserved carboxyl in helix 3 of GPCRs is a protonation-controlled hydration site that regulates the partial entry of water at the protein lipid interface, thereby contributing to the free enthalpy difference between active and inactive structures of the receptor.
Keywords: GPCR FTIR membrane protein rhodopsin
  • Invited lecture (Conferences)
    Meeting of the British and German Biophysical Society, 21.-23.03.2013, Hünfeld, Germany
  • Poster
    9th European Biophysics Congress, 13.-17.07.2013, Lissabon, Portugal
  • Open Access LogoAbstract in refereed journal
    European Biophysics Journal 42(2013)1, S149
    DOI: 10.1007/s00249-013-0917-x

Publ.-Id: 18499 - Permalink


Preclinical dose assessment of (S)-(–)-[18F]fluspidine and (R)-(+)-[18F]fluspidine, new PET tracers for imaging of σ1 receptors
Kranz, M.; Sattler, B.; Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Donat, C. K.; Wünsch, B.; Steinbach, J.; Sabri, O.; Brust, P.;
  • Poster
    OncoRay-Retreat 2013, 07.-08.03.2013, Rossendorf, Deutschland

Publ.-Id: 18498 - Permalink


Silicon Films with Gallium Rich Nanograins - from Superconductor to Insulator
Heera, V.; Fiedler, J.; Hübner, R.; Schmidt, B.; Voelskow, M.; Skorupa, W.; Skrotzki, R.; Herrmannsdörfer, T.; Wosnitza, J.; Helm, M.;
Si films sputter deposited on SiO2 substrates are enriched with Ga by ion implantation through a capping SiO2 layer. The morphology and the electrical transport properties of these films are investigated after rapid thermal annealing. Amorphous, Ga rich nanograins are embedded in a nanocrystalline Si matrix. The nanograins are metallic in the normal state and superconducting below 7 K. They form a random network of junctions to heavily doped Si crystallites. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. Ga rich Si films show a wealth of low-temperature transport phenomena which have been known until now only from granular metals or high temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current controlled sheet resistance. The possibility to fabricate and tailor films of Ga rich Si with microelectronics compatible technology make it a promising material for the integration of superconducting circuits into Si devices.
Keywords: Silicon-Gallium-Film, Granular Composite, Superconductor-Insulator Transition, Hopping Conduction, Electric Current Effect

Publ.-Id: 18497 - Permalink


Radiolabelling of engineered nanoparticles – alternative strategies for Ag0-NP, TiO2-NPs and CNTs
Schymura, S.; Hildebrand, H.; Franke, K.;
As nanotechnology increasingly finds its way into everyday applications the risk assessment of a potential nanoparticle (NP) release into the environment becomes mandatory. Though, NPs are notoriously difficult to trace in such complex environments as the geosphere, ground and surface waters or organisms, especially at the predicted low concentrations that nevertheless might be environmentally relevant. Radiolabeling of NPs provides a possibility to overcome this problem. However, radiolabeling itself bears the danger of changing the particle properties, leading to uncertainties in the interpretation of experimental results. We here present radiolabelling strategies for TiO2, Ag0 nanoparticles and carbon nanotubes (CNTs) that were developed with a minimum of NP property alteration in mind.

TiO2 and Ag0 NPs were radiolabeled using an in-diffusion technique resulting in the incorporation of radionuclides of the respective element in the NPs. Briefly, radionuclide stock solutions containing 45Ti or 110mAg were applied to dry nanoparticle powder followed by a low temperature annealing for diffusive introduction of the radionuclides into the NPs. A stable radiolabeling was achieved with no significant change in particle properties detectable in the range of our experimental conditions.

CNTs were radiolabelled using the one-pot Iodogen reaction for introduction of radioactive iodine 125/131I onto the CNT side wall. The radiolabel proved to be stable in the absence of light and no changes of the particle properties could be measured. The potential employment of 124I opens the possibility for positron emission tomography studies and therefore the localisation of radiolabeled CNTs in complex matrices such as rock materials.
Keywords: Radiolabelling, carbon nanotubes, titanium dioxide, silver, nanoparticles
  • Poster
    2nd QNano Integrating Conference, 27.02.-01.03.2013, Prague, Czech Republic

Publ.-Id: 18496 - Permalink


Radiolabelling of engineered nanoparticles – different strategies for Ag0-NP, TiO2-NP and MWCNTs
Schymura, S.; Hildebrand, H.; Cydzik, I.; Bulgheroni, A.; Simonelli, F.; Holzwarth, U.; Kozempel, J.; Bilz, E.; Freyer, A.; Franke, K.; Gibson, N.;
The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles (NPs) in applications outside of research laboratories a careful risk assessment of their release into the environment becomes mandatory. However the monitoring of nanoparticles in such complex natural systems as geological formations or ground water is nearly impossible using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research. We present here two different radiolabelling strategies for Ag0-NP, TiO2-NP and MWCNTs.

Both strategies involve proton bombardment using a cyclotron and cause the incorporation of radioactive isotopes inside the NPs. The first option is to directly activate the NPs by proton irradiation, which proved useful for MWCNTs and TiO2-NP. 12C gets activated using a (p,3d) nuclear reaction to 7Be while 48Ti gets activated to 48V by a (p,n) reaction.
The second option, which is generally adoptable for NPs that do not show useful nuclear reactions, is to mix the NP powder with a lithium containing compound like LiH and irradiate it to create 7Be out of 7Li via a (p,n) reaction. The recoil of the 7Be from the nuclear reaction causes the incorporation of the radiotracer into the structure of the NP.
The methods were tested for labelling yield, achievable activity concentration, pH-dependent stability of the labeling and the influence on NP-properties. Data thus obtained enables the selection of a radiolabelling method appropriate for different experimental conditions.
48V labeled TiO2-NPs were successfully employed to study the NP release out of surface coatings not measurable using conventional methods.
Keywords: Radiolabelling, cyclotron, carbon nanotubes, silver, Titanium dioxide, nanoparticles
  • Lecture (Conference)
    2nd QNano Integrating Conference, 27.02.-01.03.2013, Prag, Tschechien

Publ.-Id: 18495 - Permalink


Small-Angle Neutron Scattering study of WWER-440 Cr-Mo-V alloyed RPV steels
Ulbricht, A.; Bergner, F.; Viehrig, H.-W.; Keiderling, U.; Dewhurst, C.; Mathon, M.-H.; Török, G.; Gillemot, F.; Valo, M.;
Der Vortrag fasst Ergebnisse zu mikrostrukturellen Untersuchungen an neutronenbestrahlten WWER440 RDB-Stählen mittels Neutronen-Kleinwinkelstreuung zusammen.
Keywords: The presentation summarizes results of microstructural invetigations on WWER440 -type RPV steels by means of SANS.
  • Lecture (Conference)
    21st Workshop on Iron-Chromium Alloys an 3rd Workshop on nuclear Fe alloys: modelling and experiments, 29.-31.10.2012, Alicante, Spain

Publ.-Id: 18494 - Permalink


A brief comparison of Pitzer databases for nuclear waste disposal modeling
Bok, F.; Voigt, W.; Bube, C.; Wilhelm, S.; Moog, H.;
For the modeling of different chemical aspects of a salt repository for nuclear waste, the Pitzer formalism is necessary. Therefore, a comprehensive database with the relevant aqueous and mineral species, the corresponding reaction constants and associated ion-ion interaction parameters are required.
A number of different Pitzer databases are available for, or even delivered with various geochemical speciation codes such as EQ3/6, PHREEQC, Geochemist’s Workbench® (GWB) or ChemApp. In this work we performed comparative calculations for well-defined chemical systems on the base of these Pitzer databases. In Addition, for a more comprehensive view experimentally measured values from the literature were included in the comparisons.
Keywords: THEREDA, Thermodynamic Reference Database, Benchmark calculation, Pitzer, databases, geochemical modeling, nuclear waste disposal
  • Lecture (Conference)
    Actinide and Brine Chemistry in a Salt Repository Workshop (III), 15.-17.04.2013, Santa Fe, USA

Publ.-Id: 18493 - Permalink


Small-angle neutron scattering of low-Cu RPV steels neutron-irradiated at 255 degrees C and post-irradiation annealed at 290 degrees C
Wagner, A.; Bergner, F.; Ulbricht, A.; Dewhurst, C. D.;
Fast neutron irradiation of low-Cu reactor pressure vessel (RPV) steels gives rise to the formation of solute clusters and a degradation of mechanical properties. A remarkable acceleration of cluster formation was identified in a previous investigation of low-Cu steels irradiated at 255 degrees C. The thermal stability of the observed features at a typical RPV operation temperature (290 degrees C) is of particular interest. Small-angle neutron scattering experiments for three low-Cu materials irradiated at 255 degrees C and exposed to post-irradiation annealing at 290 degrees C are reported. The results indicate stability of the irradiation-induced features at a temperature of 290 degrees C for all three materials. In two cases, even an increase in scattering intensity upon post-irradiation annealing has been observed. The effect of the annealing treatment on the nature of clusters is discussed and a model of the cluster-matrix interface is introduced to rationalize the observed increase in scattering intensity. The role of the residual elements is discussed.
  • Poster
    NuMat 2012: The Nuclear Materials Conference, 21.-25.10.2012, Osaka, Japan
  • Journal of Nuclear Materials 441(2013), 487-492
    DOI: 10.1016/j.jnucmat.2013.06.032

Publ.-Id: 18492 - Permalink


Robust Monte-Carlo fitting of small-angle neutron scattering curves for determining cluster-size distributions
Wagner, A.; Ulbricht, A.; Bergner, F.;
Reactor pressure vessel (RPV) steel, when exposed to fast neutron irradiation, leads to the formation of nano-sized clusters [1]. These clusters can cause an overall degradation in mechanical properties, which is a safety issue. Small-angle neutron scattering (SANS) is a commonly used technique to determine the irradiation-induced cluster volume fraction and cluster size distribution in the material.
However, in the case of modern RPV steels, standard data treatment [2] for back-transforming the SANS scattering curves to real space can lead to unstable results. These are highly dependent on renormalisation parameters to be chosen by the user.
Here, a Monte Carlo fitting (MCF) algorithm based on [3] is presented. No renormalisation parameter is needed. The algorithm is optimized to get a robust determination of small cluster volume fractions (≈ 0.01 %) and cluster radii (≈ 0.7 nm), which are typical for modern RPV steels. The significance of the resulting data can be evaluated by an automatic error analysis. Using simulated scattering curves, the MCF is able to deliver a good reconstruction of the cluster size distribution and volume fraction in the vicinity of the SANS detection limit. Furthermore, the algorithm is tested with experimental scattering curves of neutron-irradiated RPV steels. The MCF transformation yields in physical meaningful, non-divergent results. Comparisons between analyses performed by the standard methods [2] and the MCF algorithm are drawn. The stability of the results and the limits of information to be extracted from the experimental data are discussed.

References
[1] G.R. Odette, B.D. Wirth, Handbook of Materials Modeling, Springer Netherlands, 999–1037 (2005)
[2] S. Hansen, J.S. Pedersen, J.Appl.Crystallogr. 24, 541–548 (1991)
[3] S. Martelli, P.E. Di Nunzio, Part.Part.Syst.Char. 19, 247–255 (2002)
  • Poster
    German Neutron Scattering Conference, 24.-26.09.2012, Bonn, Deutschland

Publ.-Id: 18491 - Permalink


Microstructural properties of Spark Plasma Sintered ODS Fe-14Cr steels
Schönitz, I.; Heintze, C.; Bergner, F.; García-Junceda, A.; Weißgärber, T.;
Fe-14 Cr based ODS alloys are candidates for nuclear applications such as cladding tubes. One of the main issues is the fabrication of dense material with uniformly dispersed nanometer-size oxide particles. In order to investigate the influence of the fabrication route on the microstructure of the material the samples with Yttria contents of 0…0.6wt% were produced by mechanical alloying and subsequent consolidation via spark plasma sintering (SPS). The microstructure was characterized concerning the grain and particle size by means of electron backscatter diffraction (EBSD) and atom probe tomography (APT).
Keywords: EBSD, spark plasma sintering, APT, ODS, ferritic steel
  • Poster
    ODS Alloys workshop, 24.-26.09.2012, Oxford, United Kingdom

Publ.-Id: 18490 - Permalink


Fabrication and Characterization of ODS Fe14Cr-Alloys for Nuclear Applications
Schönitz, I.; Bergner, F.; Weißgärber, T.; Shariq, A.;
Ferritic Fe14Cr based oxide dispersion strengthened (ODS) alloys are promising candidates for components of GEN IV reactors. Due to their high Cr content high corrosion resistance is provided and the austenite phase transformation is prevented. Matrix compositions containing Ti in combination with yttria as reinforcing constituent tend to the formation of complex Y-Ti oxides that are known for their small particle sizes. High creep resistance and yield strength as well as an improved resistance against radiation induced He embrittlement are expected improvements to be achieved by ODS.
The considered fabrication process consists of a mechanical alloying step and the subsequent consolidation. During these steps an evolution of the added yttria particles (≈30 nm) towards much smaller Ti-Y-O nanoclusters (2-5 nm) has been observed [ ; ]. However, the mechanisms of dissolution and especially the re-precipitation during the consolidation process are not well known yet.
In order to evaluate the influence of the processing parameters, powders of different compositions (0….0.6wt% Y2O3) are fabricated applying different milling times (20h; 30h). These powders are consolidated via spark plasma sintering (SPS). The sintered material has been characterized with respect to porosity, microstructure, spatial distribution of composition and Vickers hardness. Ongoing research is focussed on the characterization of the oxide particles at the nanometre scale.
Keywords: ODS, ferritic steel, spark plasma sintering, nanoclusters
  • Poster
    International School on Materials UNder Extreme COnditions (MUNECO), 11.-15.06.2012, Madrid, Spain

Publ.-Id: 18489 - Permalink


Interfacial reactions of Sn(II) with anatase (TiO2): EXAFS and surface complexation modeling
Dulnee, S.; Merkel, B.; Scheinost, A. C.;
Sn(II) is a contaminant of general environmental interest, but little is known about its interaction and retention by mineral surfaces. We have selected the redox-inactive mineral anatase (TiO2) to study the surface complexation mechanism by combining EXAFSderived surface structures with surface complexation modeling to model the macroscopic sorption behavior. Three adjustable parameters required for diffuse double layer model were determined in this study: the surface site density (16 sites/nm2), and two log K+ values (4.76 ± 0.36 and −9.90 ± 0.42) of the protolysis reactions. EXAFS spectra show Sn(II)–Ti distances at 3.26 and 3.60 Å indicating the formation of monodentate and bidentate inner-sphere sorption complexes. Four surface complexes, Anat_sOSn+, Anat_sSnOH,
Anat_sOH(Anat_sO)Sn+, and (Anat_sO)2Sn, with log K values of 3.66, 3.68, 4.63, and 4.41, respectively,
were required to model the sorption data.
Keywords: Sn(II) surface complexation; surface complexation models; anatase (TiO2); adsorption
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-030 Januar 2013, 44-44

Publ.-Id: 18488 - Permalink


Anticorrosion studies for pipe organ-related materials using plasma processing
Pelic, B.; 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.
Keywords: Plasma immersion ion implantation, PbSn alloys, corrosion of organ pipes
  • Lecture (Conference)
    Internationale Konferenz zur Korrosion in Pfeifen von historischen Orgeln, 21.02.2013, Bremen, Germany

Publ.-Id: 18487 - Permalink


Millisecond flash lamp annealing for LaLuO3 and LaScO3 high-k dielectrics
Lehmann, J.; Hübner, R.; Skorupa, W.; von Borany, J.; Mikolajick, T.; Schäfer, A.; Schubert, J.; Mantl, S.;
LaLuO3 and LaScO3 high-k layers were treated by flash lamp annealing (FLA) at temperatures between 1000°C and 1200°C for 3 or 20 ms. This procedure mimics the effect of an source/drain activation annealing by FLA on the electrical and microstructural properties of these alternative high-k dielectrics in a gate-first processing sheme. Related MOS capacitors with a TiN metal gate were processed in a gate first like processing scheme. It is shown that 3 nm thick oxide layers resist crystallization even at 1200°C for 3 ms, while nanocrystallites are formed in thicker layers. The influence of the FLA treatment on capacitance-voltage (C-V) and current-voltage (I-V) characteristics are investigated. From these measurements, the effects on the relative dielectric constant (k), the fixed oxide charge density (Qox) as well as the leakage current through the insulators are deduced.
Keywords: High-k gate dielectrics, Higher-k gate dielectrics, Ternary high-k oxides, Rare-earth based gate oxides, Electrical properties
  • Microelectronic Engineering 109(2013), 381-384
    DOI: 10.1016/j.mee.2013.04.021
  • Lecture (Conference)
    18th Conference of "Insulating Films on Semiconductors", 25.-28.06.2013, Kraków, Polen

Publ.-Id: 18485 - Permalink


CFD-Simulation of Bubble Columns
Ziegenhein, T.; Rzehak, R.; Krepper, E.; Lucas, D.;
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. A large body of work using different closure relations of varying degree of sophistication exists, but no complete, reliable, and robust formulation has been achieved so far.
As a step towards this goal, an attempt is made here to collect the best available description for all aspects known to be relevant for adiabatic bubbly flows where only momentum is exchanged between liquid and gas phases. Apart from interest in its own right, results obtained for this restricted problem also provide a good starting point for the investigation of more complex situations including heat and mass transport and possibly phase change or chemical reactions.
Aspects requiring closure for the case under consideration are: (i) the exchange of momentum between liquid and gas phases, (ii) the effects of the dispersed bubbles on the turbulence of the liquid carrier phase, and (iii) processes of bubble coalescence and breakup that determine the distribution of bubble sizes. All of these aspects are coupled and therefore in principle have to be considered as a whole.
To validate the overall model, simulation results are compared against experimental data taken from the literature for bubble columns in various settings. In the present study the focus is on the homogeneous regime where the assumption of a monodisperse bubble size distribution is reasonable and coalescence and breakup need not be considered. From the observed level of agreement between simulation and experiment, issues requiring further investigation will be identified. Necessary extensions to the heterogeneous regime will be discussed but remain to be worked out in the future.
Keywords: bubble column, CFD simulation, gas liquid multiphase flow, Euler Euler two fluid model, model validation
  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Agglomerations- und Schüttguttechnik und Computational Fluid Dynamics, 04.-06.03.2013, Weimar, Deutschland

Publ.-Id: 18484 - Permalink


Ion Beam Shaping of Nanomaterials
Schmidt, B.;
The talk gives an overview about high energy ion-induced anisotropic deformation of nanostructures, also called ion beam shaping, especially of different nanoparticles embedded in silica. For selected examples, swift-heavy-ion-induced deformation of spherical Au and Ge nanoclusters (NCs) embedded in SiO2 was studied experimentally and theoretically. Ge NC shaping is size dependent under irradiation with 38 MeV iodine ions and with 89 and 185 MeV gold ions. Large NCs don’t deform, smaller ones become discus-shaped, and very small ones show Ge loss at their equator. Small Au NCs deform into rods and wires, and, rather exotic, at critical NC size Au wires are squeezed out of the poles of the Au spheres.
Experimental results are compared with modeling and atomistic computer simulations. The model describes the ion-induced shape evolution of different elements for different ion species, energies and fluences even quantitatively, where only one fit parameter describes all experiments. It is based on classical thermodynamics and hydrodynamics only.
  • Lecture (Conference)
    3rd SPIRIT Workshop “Ion Beams as a Tool for Nanotechnology”, 19.-20.07.2012, Lisbon, Portugal

Publ.-Id: 18483 - Permalink


Feasibility studies with GeoPET: microbial processes tomography in geological environments
Mickein, K.; Kutschke, S.; Pollmann, K.; Kulenkampff, J.; Lippmann-Pipke, J.;
Positron emission tomography (PET) is widely used in radiology to visualized cancer cells and infections in human tissue. This functional imaging technique is commonly used in order to visualize processes in the body with the help of radioactive substances. In addition, this method has been used for the investigation of transport processes in geological materials [1].
The aim of our work is the development of a method for the application of PET for geo-microbial research. We will use this technique for the spatio-temporal visualization of the mobility of bacteria in geological matrices. The visualization of the formation of biofilms and their influence on flow paths in different matrices is an important aspect as well. In addition, it offers the possibility to get insights into microbial processes (e.g. bioleaching) in opaque materials.
Some basic investigations for the experimental set-up are necessary. First, the method requires an efficient non-toxic method that allows the selective labeling of bacteria without interfering with the geological matrix. Currently, we are investigating a selection of antimicrobial peptides for their use as appropriate marker. Second, appropriate bacteria are selected for further investigation. Pseudomonas fluorescens and Lysinibacillus sphaericus JG-A12 were chosen as typical organisms living in soil. Third, the interactions of the different compounds and the influence of experimental parameters need to be tested. For further experiments it is very important to examine the stability of the label as well as adsorption and desorption processes of the PET nuclides and of the labeled substances in conjunction with different matrices. The characterisation of model columns that are filled with quartz gravel or copper ore needs to be investigated as well. Fluid dynamics and structural parameters like porosity and the internal surface area have to be investigated.
In this study we present our recent results on the development of a PET-method that allows the in-situ labeling of bacteria and the visualization of their mobility in geological matrices.

[1] Gründig, M., M. Richter, et al. (2003). Positron Emission Tomography for investigation of water flow in soil columns. Geochemical Processes in Soil and Groundwater. H. D. Schulz. Weinheim, Wiley-VCH: 550-559.
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 11.-13.03.2013, Bremen, Deutschland

Publ.-Id: 18482 - Permalink


Interactions of the Mont Terri Opalinus Clay isolate Sporomusa sp. MT-2.99 with curium(III) and europium(III)
Moll, H.; Lütke, L.; Geissler, A.; Selenska-Pobell, S.; Bernhard, G.; Bachvarova, V.;
Bacterial cell walls have great potential to influence the speciation and mobility of actinides and lanthanides in the environment. This study explores the unknown interaction between Cm(III)/Eu(III) and cell-suspensions of Sporomusa sp. MT-2.99, a novel isolate originating from Opalinus Clay (Mont Terri, Switzerland).
The Cm(III)/Eu(III) binding by the cell surface functional groups was studied by potentiometry combined with time-resolved laser-induced fluorescence spectroscopy (TRLFS). This paper provides stability constants of Cm(III)/Eu(III) complexed by cell surface functional groups. It could be shown that as a function of pH Cm(III)/Eu(III) binding occurred to hydrogen phosphoryl, carboxyl and deprotonated phosphoryl sites. Both metals showed a similar interaction process consisting of surface complexation (major) with high thermodynamic stability and immobilization within the cell envelope (minor).
Keywords: curium; europium; Sporomusa sp.; bacteria; TRLFS; potentiometry; complexation

Publ.-Id: 18481 - Permalink


A fluoro versus a nitro derivative - a high-performance liquid chromatography study of two basic analytes with different RP and silica phases as basis for the separation of a positron emission tomography radiotracer
Wenzel, B.; Günther, R.; Brust, P.; Steinbach, J.;
To optimize the semi-preparative separation of a 18F-labeled PET radiotracer from its nitro precursor in a recently developed radiosynthesis, we performed an analytical HPLC study using the unlabeled reference compound and the corresponding nitro precursor. Several RP phases as well as a bare silica column were investigated with ACN and MeOH as organic modifiers and aqueous NH4OAc because of the basic character of the analytes. Four types of separation were observed based on different interaction mechanisms. When ACN/20 mM NH4OAc aq. was used mainly cationic-exchange and hydrophobic interactions contribute to the retention. A reversal of elution order could be observed starting from 95% ACN and subsequent increasing of the water content. This phenomenon was observed for all RP phases and seems to be independent of the different spacers bound to the silica. By contrast, using MeOH/20 mM NH4OAc aq. the elution order depends on the phase material. Two columns with the potential to perform π-π interactions showed different separation behavior compared to the other RP phases.
Keywords: Basic analytes, Cationic-exchange, RP phases, Silanol sites, VAChT

Publ.-Id: 18479 - Permalink


Wear in tetrahedral amorphous carbon induced by sp3/sp2 phase transition
Kunze, T.; Seifert, G.; Posselt, M.; Gemming, S.; von Lautz, J.; Pastewka, L.; Moseler, M.;
Tetrahedral amorphous carbon (ta-C) coatings have attracted high scientific attention in recent years due to their outstanding low friction coefficients in lubricated environments and their superior resistance to abrasive as well as adhesive wear. Consequently, they are highly suitable as protective coatings in automotive components such as combustion engines to reduce wear and friction. Nevertheless, ta-C abrade under extreme conditions and an atomistic understanding of the wear processes in ta-C is crucial for optimizing its wear resistance. The present study employs atomic-scale simulations to investigate the basic principles of wear between hydrogen- free tetrahedral-amorphous carbon (ta-C) films, which are modeled state-of-the-art by an improved version of the well-known Brenner bond-order potential. During tribological contact, these mainly sp3 hybridized films tend to form an amorphous carbon (a-C) tribomaterial mainly consisting of carbon atoms in sp2 configuration. Furthermore, the observed tribolayer grows faster than the a-C between diamond surfaces under similar conditions, which can be explained by easy breaking of weak bonds in a finite ta-C region triggered by plasticity in the adjacent a-C while the diamond/a-C transition occurs at an atomically sharp interface. The difference in the a-C tribofilm formation between ta-C and diamond is in agreement with near-edge x-ray absorption fine structure spectroscopy (NEXAFS) studies published recently.
  • Poster
    PSI-K ADGLASS Workshop 2012 - Atomistic modelling for Industrial product development, 14.-16.11.2012, Bremen, Deutschland

Publ.-Id: 18478 - Permalink


Tribosimulation of ta-C nanocoatings - Friction and wear on the atomic scale
Kunze, T.; Posselt, M.; Gemming, S.; von Lautz, J.; Pastewka, L.; Moseler, M.; Seifert, G.;
Nanocoatings have the potential to improve the surface properties of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed automotive engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency. The present study employs atomic-scale simulations to investigate the basic principles of wear and friction between hydrogen-free tetrahedral-amorphous carbon (ta-C) films. The ta-C films are modeled state-of-the-art by an improved version of the well-known Brenner bond-order potential, which had been successfully applied to elucidate the wear processes during diamond polishing.

We start our work by the preparation of the ta-C film structure, which is then characterized with respect to local and global film properties in comparison to experiments. After validating our ta-C nanocoatings with the help of experimental data, we perform computational sliding experiments to investigate mechanisms of friction and wear between interacting ta-C surfaces. During tribological contact, these diamond-like films (mainly sp3 hybridized) tend to form a soft-amorphous or graphite-like tribomaterial mainly consisting of carbon atoms in sp2 configuration. The sp3 to sp2 transition originates from atom-by-atom extraction events occurring at the sp3/sp2 interface. We discuss the underlying mechanisms by focusing on associated triboreactions and tribological properties such as shear forces.
  • Poster
    Gordon Research Conference 2012 - Tribology, 08.-13.07.2012, Waterville, USA

Publ.-Id: 18477 - Permalink


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