Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39537 Publications

Synthesis of S-Layer Conjugates and Evaluation of Their Modifiability as a Tool for the Functionalization and Patterning of Technical Surfaces

Weinert, U.; Pollmann, K.; Barkleit, A.; Vogel, M.; Günther, T.; Raff, J.

Chemical groups of surface layer (S-layer) proteins were chemically modified in order to evaluate the potential of S-layer proteins for the introduction of functional molecules.
S-layer proteins are structure proteins that self-assemble to regular arrays on surfaces. One general feature of S layer proteins is their high amount of carboxylic and amino groups. These groups are potential targets for linking functional molecules thus producing reactive surfaces.
In this work these groups were conjugated with the amino acid tryptophan. In another approach, SH-groups were chemically inserted in order to extend the spectrum of modifiable groups. The amount of modifiable carboxylic groups was further evaluated by potentiometric titration in order to evaluate the efficiency of S-layer proteins to work as matrix for bioconjugations. The results proved that S-layer proteins can work as matrizes for the conjugation of different molecules. The advantage of using chemical modification methods over genetic methods lies in its versatile usage enabling the attachment of biomolecules as well as fluorescence dyes and inorganic molecules. Together with their self-assembling properties S-layer proteins are suitable as targets for bioconjugates, thus enabling a nanostructuring and bio-functionalization of surfaces which can be used for different applications like biosensors, filter materials or (bio)catalytic surfaces.

Keywords: EDC; Modified Surface-layer proteins; Potentiometric titration; Modification rate; Bio-functionalization of surfaces; Chemical modification; Immobilization


Publ.-Id: 21020

Atomistic modeling of ion-beam induced processes in Si and Ge

Liedke, B.; Heinig, K.-H.; Böttger, R.; Anders, C.; Urbassek, H.; Facsko, S.; Posselt, M.

Modeling of ion-beam induced processes includes ion beam – solid interactions as well as solid state physics. Thus, a rather broad field of physics has to be considered which can be approached using a large variety of modeling techniques. Atomistic models of ion-induced materials modification can be classified as follows: (i) including the ion-induced collision cascade, molecular dynamics (MD) simulations provide the most accurate way to simulate a single or a few ion impacts. The predictive power of MD simulations depends on the accuracy of the interatomic potentials in the wide energy range from meV to keV. (ii) For energetic ions, with the Binary Collision Approximation (BCA) properties like the ion range can be predicted with similar precision like with MD, but thermally activated processes following the collision cascade cannot be simulated; (iii) kinetic Monte-Carlo (KMC) simulations can be used very efficiently and with an acceptable accuracy for modelling of diffusion, relaxation and precipitation of defects and impurities.
Here we will address all of three types of atomistic simulations: (i) With our recently developed TRIDER program, which unifies the BCA and KMC methods [1], low-energy irradiation of a-Si surface has been accurately simulated, in particular the rotation of self-organized surface ripples with the angle of ion incidence. (ii) The BCA, KMC and MD simulation methods have been employed to study the surface stability of Ge and Si under irradiation with heavy ion. [2]. KMC simulations show that the hole-like and sponge-like morphologies results from the vacancy kinetics. The origin of dot-like patterns after irradiation with poly-atomic ions or at elevated substrate temperatures has been revealed by a model based on TRIM and MD simulations: Single ion impacts induce tiny, short-living melt pools. Each meltpool generates a local surface minimization which leads, together with the high ion erosion rate, to a pronounce surface instability. (iii) Swift-heavy-ions change drastically the shape of spherical nanoparticles embedded in silica: Metal clusters become rods, whereas e.g. Ge clusters form to discs. [3]. A model has been developed which is based on transient melting of the nanoparticles by single ion hits, and the volume change of the metal/Ge upon this phase transition. Our KMC program has been modified to simulate the ion-induced shape evolution of different elements for different ion species, energies and fluences even quantitatively, where finally just one fit parameter describes all experiments.
1. Liedke, B.; Heinig, K.-H.; Möller, W.; Nucl. Instr. Meth. B 316, 56 (2013)
2. Böttger, R.; Heinig, K.-H.; Bischoff, L.; Liedke, B.; Facsko, S.; Appl. Phys. A 113, 53 (2013)
3. Schmidt, B.; Heinig, K.-H.; Mücklich, A.; Akhmadaliev,; Nucl. Instr. Meth. B 267, 1345 (2009)

Keywords: molecular dynamics; kinetic Monte-Carlo; TRIM; TRIDER; surface patterning; ion-beam shaping

Related publications

  • Invited lecture (Conferences)
    Swift Heavy ions in Materials Engineering and Characterization (SHIMEC 2014), 14.-17.10.2014, New Delhi, India

Publ.-Id: 21019

First Investigation of the two-phase oxidation of isobutane by a micro reactor.

Willms, T.; Kryk, H.

The micro reactor, the principal structure and components of the lab facility and the most important challenges of its construction are presented. As a proof of functionality, the first two-phase flow oxidation experiment of isobutane to t-Butyl hydroperoxide (TBHP) in a micro reactor was accomplished. Challenges of the gas chromatographic analytics (GC) of the reaction are discussed.
The chromatogram of the reaction mixture obtained by the first experiment has been interpreted.
Furthermore a device has been developed to allow the analysis of the gaseous products in a high pressure steel crucible for Differential scanning calorimetry (DSC).
It has been used to analyze the gases resulting from the decomposition of TBHP at higher temperatures by GC.

Keywords: micro reactor; isobutane oxidation; gas chromatography

  • Lecture (others)
    Halbjahresmeeting Helmholtz-Energie-Allianz, 09.-10.10.2014, Hamburg, Duetschland

Publ.-Id: 21018

Untersuchung von Kopplungseffekten und magnetischer Anisotropie in Fe3Si-Dreifachlagen mittels ferromagnetischer Resonanz

Schneider, T.

Im Rahmen dieser Arbeit wurden Einzelfilme und Dreifachlagen bestehend aus Fe3Si mittels ferromagnetischer Resonanz untersucht. Das Hauptaugenmerk lag hierbei auf der Bestimmung der Interlagenaustauschkopplungskonstanten J1 . Außerdem sollen g-Faktor und Anisotropiekonstanten bestätigt werden. Hierbei kann aufgrund des breitbandigen Aufbaus auf die Linienbreite der Signale über einen großen Frequenzbereich eingegangen werden. Bei dem verwendeten Probensystemen Fe3Si/MgO/Fe3Si/MgO/GaAs(001) wurde die Dicke der MgO-Schicht variiert, um einerseits den Einfluss der verschiedenen Lagen aufeinander und andererseits das gekoppelte Verhalten zu untersuchen. Dabei konnte festgestellt werden: (i) Die in dieser gemessenen Parameter stimmen gut mit vorher bestimmten überein. (ii) Das dynamische Verhalten wird durch Zwei-Magnonen-Streuung und Einflüsse der Mosaizität geprägt. (iii) Die Kopplungkonstante J1 wurde bei beiden verwendeten MgO-Zwischenschichtdicken bestimmt. (iv) Der Ursprung der uniaxialen Anisotropie ist durch Grenzflächeneffekte zwischen Fe3Si/GaAs und Fe3Si/MgO bedingt.

Keywords: Interlayer exchange coupling; FMR; Fe3Si

Related publications

  • Bachelor thesis
    TU Dresden, 2013
    Mentor: Fassbender, Jürgen
    54 Seiten

Publ.-Id: 21017

Investigation of interlayer exchange coupling and magnetic anisotropy of Fe3Si-trilayers using ferromagnetic resonance

Schneider, T.; Hübner, R.; Lenz, K.; Lindner, J.; Fassbender, J.

In this thesis, magnetic properties of single Fe3Si-films und trilayer structures are investigated by ferromagnetic resonance. Using this technique, it is possible to determine the magnetic anisotropy energy and interlayer exchange coupling J1 in absolute units. Further on, values for the magnetic anisotropy constants and the g-factor should be confirmed in this work. Due to the use of a broad band setup, it is possible to investigate the linewidth of the measured signals. The measurements are carried out using structures containing two Fe3Si films separated by one MgO-layer. The MgO thickness is varied to obtain two different samples. In one of these samples both layers can be considered as decoupled. In the second sample both layers are coupled due to interlayer exchange coupling (IEC). The main results of this thesis are: (i) The obtained parameters for magnetic anisotropy and the g-factor match former results quite well. (ii) The investigation of the resonance linewidth shows contributions of two-magnon-scattering and inhomogeneous broadening due to the mosaicity. (iii) For both used layer thicknesses the interlayer exchange coupling can always be neglected. (iv) The origin of the uniaxial anisotropy is given by effects at the interfaces between the Fe3Si and MgO or the Fe3Si and GaAs layers.

Keywords: Interlayer exchange coupling; FMR; Fe3Si

Related publications

  • Lecture (others)
    Gruppenseminar AG Wende, 14.01.2014, Duisburg, Deutschland

Publ.-Id: 21016

Taktsynchronisierung und Zeitmessung in einem verteilten Datenerfassungssystem

Födisch, P.; Sandmann, J.; Lange, B.; Kaever, P.

Die Zeitmessung mit einem verteilten Datenerfassungssystem erfordert die Synchronisierung der einzelnen Teilsysteme. Eine dedizierte Taktverteilung ist für diese Anwendung eine einfache und präzise Lösung, erfordert aber zusätzlichen Installationsaufwand und bereitet vor allem bei der Skalierung des Gesamtsystems Probleme. Stattdessen können auch die vorhandenen Datenlinks der einzelnen Module für eine Rückgewinnung des Systemtaktes verwendet werden. Hier wird gezeigt, wie mit industriellen Komponenten (FPGA und Gigabit-Ethernet PHY) die Synchronisierung auf eine gemeinsame Taktfrequenz realisiert wird. Der Abgleich der Uhren erfolgt anschließend protokollbasiert über die Ethernet-Schnittstelle. Es werden die hardwareseitigen Anforderungen, die Umsetzung sowie die experimentellen Ergebnisse vorgestellt. Das implementierte System erreicht Genauigkeiten im Sub-Nanosekunden Bereich mit einer 1000BASE-T Punkt-zu-Punkt Verbindung.

  • Open Access Logo Contribution to proceedings
    105. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2014, 10.-12.03.2014, Geesthacht, Deutschland, Hamburg: Verlag Deutsches Elektronen-Synchrotron, 978-3-935702-85-0, 238-242


Publ.-Id: 21015

Ferromagnetic InMnAs with perpendicular magnetic anisotropy synthesized by ion implantation

Yuan, Y.; Khalid, M.; Wang, Y.; Weschke, E.; Skorupa, W.; Helm, M.; Zhou, S.

Due to the great potential application in spintronic device, III-Mn-V dilute magnetic semiconductors (DMS) have drawn significant attention during the past two decades. Although of the model member GaMnAs (mostly be prepared by low-temperature molecule beam epitaxy: LTMBE) have been comprehensively investigated, the challenge for preparing other DMS such as InMnAs still exists. Therefore, the understanding about the full family III-Mn-V DMS is far from satisfaction. Ferromagnetic DMS GaMnAs and GaMnP were firstly obtained alternatively by Mn ion implantation and pulsed laser annealing [1, 2], a method rather than LTMBE. The Mn concentration and depth could be controlled through implanting fluence and implanting energy, respectively. When annealing under pulsed laser, due to high temperature gratitude, the large regrowth velocity could trap Mn atoms into the substitutional sites, which is quite effective to obtain high quality laser with less defects which can act as double donors and be harmful to ferromagnetism.
We prepared ferromagnetic InMnAs with different Mn concentrations by ion implantation and pulsed laser annealing. The formation of an epitaxial InMnAs on InAs substrates was proved by Rutherford Backscatting/Channeling and X-ray diffraction. The Curie temperature could be as high as around 75 K when the Mn concentration is around 8%. The out-of-plane direction is the easy axis, originating from the compreassive strain along the perpendicular direction, as expected from the case of GaMnAs [3, 4]. The perpendicular anisotropy is particularly useful for exploiting spintronics functionalities, such as current induced magnetization switching.

[1] M. A. Scarpulla et al. Phys. Rev. Lett., 95, 207204 (2005)
[2] M. A. Scarpulla et al. Appl. Phys. Lett., 82, 1251 (2003)
[3] Shengqiang Zhou et al. APEX, 5, 093007 (2012)
[4] K. W. Edmonds et al. Phys. Rev. Lett., 96 117207 (2006)

Keywords: InMnAs; Ferromagnetic Semiconductors; Ion implantation

Related publications

  • Poster
    International Conference on Ion Beam Modification of Materials, 14.-19.09.2014, leuven, Belgium
  • Lecture (Conference)
    DPG Frühjahrstagung 2015, 15.-20.03.2015, Berlin, Germany

Publ.-Id: 21014

Laser-Induced Spectroscopy of Actinides – From simple metal systems to species in living cells

Geipel, G.; Viehweger, K.

Application of laser-induced methods allow the direct determination of uranium speciation at extremely low concentrations. First tunable solid state laser in an actinide chemistry lab was installed in 1993 in Dresden-Rossendorf under Heino Nitsche’s directorship. Later the installation of the first fs-laser system allowed us to study the interaction of organic compounds with actinides.
U(VI) released anthropogenically, e.g. through mining activities, can be accumulated for instance in plants and consequently can enter further parts of the food chain. Uranium as a redox-active heavy metal can cause also various redox imbalances in plant cells.
Recently we have shown that uranium can be taken up by plant cells. Fractionation studies showed that the uranium was present in nearly all cell compartments.
One of the major remaining questions concerns to the ways of uranium uptake. Recently published work proposed that the uranium uptake is influenced by the iron uptake. As it is known that the iron uptake occurs via reduction of the iron(III) into iron(II), we conclude that uranium uptake should also by accompanied by a redox process.
The evaluation of Laser-Induced Photoacoustic Spectra (LIPAS) in the wavelength range 620 nm to 680 nm gave evidence for the formation of both reduced oxidation states in the media studied. The uranium(V) is assigned to an absorption at around 637 nm, while uranium(IV) absorbs light at ~660 nm.

Keywords: Laser-Induced Spectroscopy; uranium, plants

  • Invited lecture (Conferences)
    ACS Annual Spring Meeting Denver, 22.-26.03.2015, Denver, USA

Publ.-Id: 21013

Mikrobiologische Verfahren in der Hydrometallurgie

Kutschke, S.; Raff, J.; Pollmann, K.

Die Vorbereitung von Erzen zur Verhüttung kann mit hydrometallurgischen Verfahren erfolgen. Dazu zählen Extraktionsverfahren mit wässrigen Lösungen, die Flotation, Sink-Schwimmtrennung und Fällungen. Diese Verfahren finden häufig in äußerst aggressiver Umgebung statt. Für einige dieser Prozesse stehen interessante Alternativen zur Verfügung. Die untersuchten und dargestellten Methoden werden durch Mikroorganismen oder ihre Stoffwechselprodukte unterstützt.
Seit 1980 wird Bioleaching im industriellen Maßstab in Chile eingesetzt. Zur Laugung trägt in diesen Anlagen die Oxidation der sulfidischen Erze durch Acidithiobacillus sp. bei. Oxidische oder carbonatische Erze können auf diesem Weg nicht gelaugt werden. Untersuchungen zeigen, dass in diesen Fällen der Einsatz von Pilzen und Bacillus sp. zur Freisetzung von Metallen aus diesen Erzen beiträgt. Dabei spielen die von Mikroorganismen gebildeten organischen Säuren eine entscheidende Rolle.
Für Sink- Schwimmtrennungen und Fällungen können weitere biologische Komponenten verwendet werden. Zum einen sind es Phagen mit speziell gestalteten Oberflächen. Diese Oberflächen können so konstruiert werden, dass sie spezifisch für einzelne Metalle sind. Durch weitere Variationen der Phagenoberfläche kann die Hydro¬phobi¬zität der mikroskopisch kleinen Partikel an die Anforderungen zum Beispiel einer Flotation angepasst werden. Zum anderen sind es calciumbindende Proteine, die über spezifische und unspezifische Bindungsstellen verfügen und darüber einzelne industrierelevante Metalle sehr selektiv binden können. Die letzten beiden Ideen werden in anderen Bereichen bereits genutzt, zeigen aber auch ein sehr hohes Anwendungspotential bei der Aufbereitung von Erzen.

  • Lecture (Conference)
    Jahrestagung 2013 „Aufbereitung und Recycling“, 13.-14.11.2013, Freiberg, Deutschland

Publ.-Id: 21012

Tilting column and 3D pattern formation during ion beam assisted growth of carbon:nickel nanocomposite films

Krause, M.; Buljan, M.; Möller, W.; Facsko, S.; Zschornak, M.; Wintz, S.; Heller, R.; Endrino, J. L.; Gemming, S.

Ion assistance provides unique opportunities to influence the microstructure of growing films due to energy and momentum transfer. Here, ion effects on the microstructure of C:Ni nanocomposite thin films grown at RT to 500°C by ion-beam sputtering with assisting oblique incidence angle Ar+ ion beam irradiation (50 – 130 eV) are studied by SEM, (c)AFM, TEM, GISAXS, and TRI3DYN simulations. Two types of ordered metallic nanostructures in an amorphous carbon matrix are identified and characterized: i) tilted parallel columns [1] and ii) rippled, periodic three-dimensional nanoparticle arrays [2]. For the former one, the tilt angle and diameter of the nanocolumns are controlled by the deposition parameters. Ion-enhanced diffusivity and ion-induced surface drift are responsible for the tilted column microstructure. Complex secondary structures like chevrons with partially epitaxial junctions are grown by sequential deposition. For a given composition of the depositing flux, the transition from the columnar growth to the 3D pattern formation regime as a function of the assisting ion energy is demonstrated. The 3D pattern is attributed to the transfer of compositionally modulated surface ripples into the bulk of the C:Ni thin film. The essential experimental features are reproduced by three-dimensional binary collision computer simulations. This agreement points to ion-induced preferential displacements as the driving force for the 3D pattern formation.

Keywords: Nanocomposites; Ion assistance; pattern formation

Related publications

  • Poster
    14th International Conference on Plasma Surface Engineering, 15.-19.09.2014, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 21011

P1311 - Anordnung zur schnellen Elektronenstrahl-Röntgencomputertomographie

Barthel, F.

Aufgabe der Erfindung ist es, eine Anordnung zur Elektronenstrahl-Röntgen-Computertomographie anzugeben, die ohne die erhebliche axiale Ausdehnung des Elektronenstrahlers auskommt, und weitgehend auf elektronenoptische Strahlführungselemente verzichtet. Die Erfindung umfasst, dass ein Röntgendetektorbogen (6) und das Target (4) um den Untersuchungsquerschnitt innerhalb einer Bestrahlungsebene angeordnet sind, und ein im Elektronenstrahlerzeuger generierter Elektronenstrahl in den Durchflutungsbereich einer oder mehrerer Längsspulen radial eingebracht wird, und durch das Magnetfeld auf eine Kreisbahn gezwungen wird. Durch periodisches Verstellen der Feldstärke wird der Radius der Kreisbahn vergrößert, was dazu führt, dass der Elektronenstrahl das Target (4) in einem tangential wandernden Brennfleck (7) trifft. Vom das Target umgebenden Röntgendetektor(6) werden Durchstrahlungsprojektionen des in der Mitte der Anordnung befindlichen Objekts (8) aufgenommen. Der Elektronenstrahlerzeuger (1) kann sowohl innerhalb als auch außerhalb der Längsspulen (3) angeordnet sein. Darüber hinaus kann die Target- und Röntgendetektorebene mit oder ohne Axialversatz angeordnet sein.

  • Patent
    DE102013206252 - Offenlegung 09.10.2014, Nachanmeldung WO, EP, JP, US

Publ.-Id: 21010

Tetrahedral amorphous carbon coatings for friction reduction of the valve train in internal combustion engines

Götze, A.; Makowski, S.; Kunze, T.; Hübner, M.; Zellbeck, H.; Weihnacht, V.; Leson, A.; Beyer, E.; Joswig, J.-O.; Seifert, G.; Abrasonis, G.; Posselt, M.; Fassbender, J.; Gemming, S.; Krause, M.

Tetrahedral amorphous carbon (ta-C) is studied as a tribological coating for the valve train’s exhaust camshaft of a combustion engine. The coated camshafts were installed in a non-fired engine, tested in a computerized component test bench under practice-relevant conditions and analyzed for their frictional behavior. A notable reduction of the valve train’s drive torque on the test bench is demonstrated. Namely, on a roller cam system with ta-C coated camshaft the reduction is about 15% in average within the entire engine-map. The ta-C coatings were extensively characterized under laboratory conditions before and after the investigations on the test bench. Mechanistic understanding of the tribological behavior of ta-C coatings under dry or starving lubricated conditions was achieved by atomistic simulations of the tribological contact. Industrial utilization of these results would lead to a significant increase of the energy efficiency of combustion engines.

Keywords: tribological coatings; tetrahedral amorphous carbon (ta-C); combustion engines; atomistic simulations

Related publications

Publ.-Id: 21009

Heterogeneous nucleation in cfd simulation of flashing flows in converging-diverging nozzle

Janet, J. P.; Liao, Y.; Lucas, D.

Flashing flow is an important industrial phenomenon present in many contexts. In flashing flow, a liquid boils in response to a depressurization. CFD is used to simulate the complex two-phase nature of flow, but nucleation is frequently neglected in these simulations. In this work, 3 models for wall nucleation in flashing flow are tested and compared against experimental data. The models are implemented as source terms at the walls only, consistent with experimental observations. The model proposed by Blinkov et al. (1993) is found to provide the best agreement with no parameter fitting. Axial properties and mass flow can be well predicted, but matching the radial profiles requires the addition of a bulk heterogeneous nucleating term, which is small in comparison to wall nucleation and has little impact on average properties but has a large effect on the vapour structure. Additionally, other effects such as coalescence influencing bubble size should be taken into account, since radial distribution of the vapour phase depends directly on the bubble size.

Keywords: Flashing; Nozzle; CFD; Nucleation; Depressurization

Publ.-Id: 21008

Imaging systems for dose monitoring in particle therapy

Fiedler, F.

no abstract available

  • Invited lecture (Conferences)
    Interdisciplinary Symposium ''Precision, Speed and Flexibility: New radiation detection methods for ion beam radiotherapy, 23.-25.10.2014, Heidelberg, Deutschland

Publ.-Id: 21007

Particle Therapy Positron Emission Tomography (PT-PET) for Treatment Verification

Fiedler, F.

Radiation therapy is an important treatment modality in cancer therapy. New radiation species, like protons and light ions have the potential of increasing tumor conformality of irradiation. Because of the way these particles deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the damage of the surrounding normal tissue.
High precision radiotherapy treatment requires efficient quality assurance techniques. Even small changes in the irradiated volume will lead to a mismatch of the deposited dose maximum and the tumor. This causes missing dose in the tumor volume and potential damage to normal tissue. Therefore, a treatment verification system is highly desirable. Between 1997 and 2008, the in-beam Positron Emission Tomography (PET) method was used at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany to monitor the dose delivered by 12C beams [1]. This method makes use of the β+-activity produced via nuclear interactions between the therapeutic beam and the patient tissue. The results and experiences of the clinical application of in-beam PET for carbon ions GSI will be shown. Based on this experience several approaches to improve the significance of the result have been studied.
Since the dose delivery is evaluated by means of a comparison between measured and simulated data a reliable prediction of β+-activity is crucial. To model the positron emitter production accurately, cross sections for all possible nuclear reactions occurring in the tissue during irradiation which lead to positron emitters are required. Since these cross sections are available only for a few reaction channels in the required energy range, a novel approach for estimating the positron emitter production from experimental data is introduced [2].
Up to now the comparison of the distributions is performed by well-trained observers (clinicians, physicists). This process is very time consuming and low in reproducibility. Therefore, a semi-automatic method has been developed evaluating the range and including a cavity filling detection algorithm. System inherent uncertainties are handled by means of a statistical approach [3, 4].
The Particle Therapy (PT)- PET method has been approved for static tumors under clinical conditions. However, also for intra-fractionally moving targets, the 4D simulation [5] as well as the 4D reconstruction [6] of PT-PET data has been established. By means of dedicated 4D-PET experiments the results of the comparison between measured and anticipated activities have been investigated.
[1] W. Enghardt, et al., Nucl. Instr. Meth A 525, 2004.
[2] M. Priegnitz, et al., IEEE Trans. Nucl. Sci. 59, 2012.
[3] S. Helmbrecht, et al., Phys. Med. Biol. 57, 2012.
[4] P. Kuess, et al., Med. Phys. 39, 2012.
[5] K. Laube, et al., Phys. Med. Biol. 58, 2013.
[6] K.Stützer, Phys. Med. Biol. 58, 2013.

  • Invited lecture (Conferences)
    Workshop on Range Assessment and Dose Verification in Particle Therapy, 29.-30.09.2014, Dresden, Deutschland

Publ.-Id: 21006

Identifizierung der Oberflächenkomplexe von Radionukliden an Mineralphasen – Schwingungsspektroskopische Echtzeitexperimente

Foerstendorf, H.

Für eine verlässliche Beschreibung des Migrationsverhaltens von Radionukliden in der Umwelt ist unter anderem eine genaue Kenntnis der molekularen Prozesse an Mineraloberflächen in Aquiferen unverzichtbar. Unter den spektroskopischen Methoden, die sich auf diesem Forschungsfeld etabliert haben, hat sich die in situ Infrarotspektroskopie für Untersuchungen von Grenzflächenprozessen gelöster Schwermetallionen an festen Mineralphasen als besonders wertvoll erwiesen, da aus den schwingungsspektroskopischen Daten komplementäre Informationen auf molekularer Ebene erhalten werden. In diesem Vortrag soll ein Überblick über aktuelle Ergebnisse der Sorptionsreaktionen von Uran(VI) und Selen(VI) an Metalloxiden gegeben werden.
Mit Hilfe der in situ IR Spektroskopie lassen sich die Sorptions- und Desorptionsprozesse in Echtzeit unter umweltrelevanten Bedingungen untersuchen und somit können Rückschlüsse über die Art der Oberflächenkomplexe über die Reversibilität der Sorptionsreaktionen gezogen werden. Für das Uran wurde beispielsweise eine signifikant unterschiedliche Oberflächenkomplexierung an verschiedenen eisenhaltigen Mineralphasen beobachtet. Zudem lassen sich die Bildung ternärer Oberflächenkomplexe des Urans mit Carbonat- oder Phosphatliganden beobachten, womit weitere Einblicke in den Ablauf komplexerer Sorptionsprozesse gewonnen werden.
Das Selenatanion (SeVIO4 2−) zeigt generell schwache, überwiegend elektrostatische Wechselwirkungen (Physisorption) mit Mineralphasen im neutralen pH Bereich. Es hat sich jedoch gezeigt, dass diese Wechselwirkungen, die sog. außersphärische Komplexierung, auf verschiedenen Arten von Oberflächenkomplexen basieren kann. Auf Grund der hohen Selektivität der IR Spektroskopie bezüglich der Molekülsymmetrie, zeigen die Sorptionsexperimente des Se(VI) mit verschiedenen Mineralphasen die Bildung zweier unterschiedlicher Arten außersphärischer Komplexe.

  • Lecture (others)
    Institutsseminar des Instituts für Kernchemie, Universität Mainz, 02.02.2015, Mainz, Deutschland

Publ.-Id: 21005

Hyperdoping Si with chalcogen: solid vs. liquid phase epitaxy

Liu, F.; Prucnal, S.; Gao, K.; Khalid, M.; Skorupa, W.; Helm, M.; Zhou, S.

Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in Si, the materials were previously only realized by femtosecond or nanosecond laser annealing of implanted Si or bare Si in certain background gases. The high energy density deposited on the Si surface renders it into a liquid phase and the fast recrystallization velocity allows trapping of S/Se/Te into the Si matrix. However, this method encounters a problem of S/Se/Te surface segregation. In this Letter, we propose a solid phase processing by flash lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed Se-implanted Si shows a substitutional rate of more than 70% with the implanted concentration up to 1-2%. The resistivity is lower and the carrier mobility is higher than those of laser annealed samples. Our results show that flash lamp annealing is superior laser annealing in preventing surface segregation and in allowing scalability.

Keywords: Chalcogen elements; pulsed laser annealing

Related publications

  • Poster
    E-MRS 2014 FALL MEETING, 15.-18.09.2014, Warsaw, Poland

Publ.-Id: 21003

Hyperdoping Si with deep level impurities by ion implantation and short-time annealing

Liu, F.; Prucnal, S.; Gao, K.; Khalid, M.; Skorupa, W.; Helm, M.; Zhou, S.

Impurities play an important role in determining the electrical, optical and structural properties of semiconductors. It has been proposed that deep level impurities, such as Titanium (Ti) or chalcogens in Si, can induce an impurity band inside the bandgap at high enough doping concentration [1, 2]. The insertion of an impurity band can enhance the absorption at a broader wavelength range and leads to applications in the so-called intermediate band solar cell [3]. In the present work, we use ion implantation combined with short-time annealing to realize hyperdoping of Ti and chalcogens in Si. The structural, electrical and optical properties were determined by X-raydiffraction and Rutherford backscattering spectroscopy/channeling, electrical transport measurement and Raman spectroscopy. Analysis shows that the implanted Si layer can be recrystallized by both flashlamp and pulsed laser annealing. Ti ions mainly occupy the interstitial sites, while S and Se ions substitute the Si in the lattice. The consequent changes in electrical properties are also observed.

[1] J. Olea, G. González-Díaz, D. Pastor, I. Mártil, A. Martí, E. Antolín, and A. Luque, J. Appl. Phys. 109, 063718 (2011).
[2] Brion P. Bob, Atsushi Kohno, Supakit Charnvanichborikarn, Jeffrey M. Warrender, Ikurou Umezu, Malek Tabbal, James S. Williams, and Michael J. Aziz J. Appl. Phys. 107, 123506 (2010)
[3] A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997).

Keywords: Ion implantation; deep level impurities

Related publications

  • Lecture (Conference)
    ION, 23.-26.06.2014, Kazimierz Dolny, Poland

Publ.-Id: 21002

Hyperdoping Si with deep level impurities by ion implantation and short-time annealing

Liu, F.; Prucnal, S.; Gao, K.; Khalid, M.; Skorupa, W.; Helm, M.; Zhou, S.

Impurities play an important role in determining the electrical, optical and structural properties of semiconductors. It has been proposed that deep level impurities, such as Titanium (Ti) or chalcogens in Si, can induce an impurity band inside the bandgap at high enough doping concentration [1, 2]. The insertion of an impurity band can enhance the absorption at a broader wavelength range and leads to applications in the so-called intermediate band solar cell [3]. In the present work, we use ion implantation combined with short-time annealing to realize hyperdoping of Ti and chalcogens in Si. The structural, electrical and optical properties were determined by X-raydiffraction and Rutherford backscattering spectroscopy/channeling, electrical transport measurement and Raman spectroscopy. Analysis shows that the implanted Si layer can be recrystallized by both flashlamp and pulsed laser annealing. Ti ions mainly occupy the interstitial sites, while S and Se ions substitute the Si in the lattice. The consequent changes in electrical properties are also observed.

[1] J. Olea, G. González-Díaz, D. Pastor, I. Mártil, A. Martí, E. Antolín, and A. Luque, J. Appl. Phys. 109, 063718 (2011).
[2] Brion P. Bob, Atsushi Kohno, Supakit Charnvanichborikarn, Jeffrey M. Warrender, Ikurou Umezu, Malek Tabbal, James S. Williams, and Michael J. Aziz J. Appl. Phys. 107, 123506 (2010)
[3] A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997).

Keywords: Ion implantation; deep level impurities

Related publications

  • Poster
    Deutsche Physikalische Gesellschaft, 30.03.-04.04.2014, Dresden, Germany

Publ.-Id: 21001

Ferromagnetic GaMnP prepared by ion implantation and pulsed laser annealing

Y, Yuan.

We present the magnetic, transport and structural properties of GaMnP with different Mn concentrations prepared by ion implantation and pulsed laser annealing. The Curie temperature increases with Mn concentration and the samples show in-plane magnetic anisotropy due to the in-plane compressive strain in the GaMnP layer. Anomalous Hall effect and negative magnetoresistance are observed, indicating the carrier mediated nature of the ferromagnetism in GaMnP. According to the micro-Raman spectroscopy data after pulsed laser annealing the implanted layer has been fully recrystallized and the carrier concentration (hole) increases with Mn concentration.

Keywords: Ferromagnetic semiconductors; GaMnP; Ion Implantation; Pulsed laser annealing

Related publications

  • Lecture (Conference)
    IEEE International Magnetics Conference, 04.-08.05.2014, Dresden, Germany

Publ.-Id: 21000

Possible defect-induced ferromagnetism in Cr doped SiC single crystals

Liu, Y.; Zhou, S.; Wang, G.; Wang, S.; Sun, W.; Chen, X.

Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.

Keywords: defect-induced ferromagnetism; SiC; Cr doping; semiconductors

  • Poster
    The 19th International Conference on Ion Beam Modification of Materials (IBMM 2014), 14.-19.09.2014, Leuven, Belgium

Publ.-Id: 20999

Possible defect-induced ferromagnetism in Cr doped SiC single crystals

Liu, Y.; Zhou, S.; Wang, G.; Wang, S.; Sun, W.; Chen, X.

Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.

Keywords: defect-induced ferromagnetism; SiC; Cr doping; semiconductors

  • Poster
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France

Publ.-Id: 20998

XFM studies of plutonium dispersed in an arid environment

Ikeda-Ohno, A.; Johansen, M. P.; Payne, T. E.; Hotchkis, M. A. C.; Child, D. P.

The soil particles collected at a former British nuclear test site in Australia were investigated by synchrotron-based X-ray fluorescence microscopy (XFM), in order to determine the chemical speciation of radioactive nuclides retained in the particles. The results demonstrate that the particles contain a high concentration of Pu which derives from the original nuclear bomb material. The outcomes of this study would have a potential impact on the safety and environmental assessment associated with the former nuclear test sites.

Keywords: actinides; plutonium; synchrotron; X-ray fluorescence microscopy; environment; speciation

  • Lecture (Conference)
    12th International Conference on X-Ray Microscopy (XRM 2014), 26.-31.10.2014, Melbourne, Australia

Publ.-Id: 20997

Ferromagnetic InMnAs prepared by Ion implantation and pulsed laser annealing

Yuan, Y.; Wang, Y.; Khalid, M.; Weschke, E.; Skorupa, W.; Helm, M.; Zhou, S.

Ferromagnetic InMnAs has been previously prepared by low temperature MBE. In this contribution, we present an alternative method what combines Mn ion implantation and pulsed laser annealing to achieve In1-xMnxAs (x = 0.04 and 0.08) [1], and to obtain a remarkably high Curie Temperature (TC) up to 80 K compared to InMnAs with the same Mn concentration as prepared by MBE. The advantage of pulsed laser annealing is its high process temperature within the nano-second range, eliminating n-type defects which can decrease its magnetization and TC. The saturation magnetization is ~2.6μB / Mn by consideration of all implanted Mn ions. The out-of-plane [001] is the easy axis displaying a nearly square like hysteresis loop. Our results suggest that InMnAs prepared by ion implantation and pulsed laser annealing shows a promising prospect to get high TC DMS after optimizing the preparation parameters.

Keywords: Ferromagnetic Semiconductors; Ion Implantation; Pulsed laser annealing

Related publications

  • Poster
    DPG-Frühjahrstagung, 30.03.-04.04.2014, Dresden, Germany

Publ.-Id: 20996

Local instabilities in magnetized rotational flows: A short-wavelength approach

Kirillov, O.; Stefani, F.; Fukumoto, Y.

We perform a local stability analysis of rotational flows in the presence of a constant vertical magnetic field and an azimuthal magnetic field with a general radial dependence. Employing the short-wavelength approximation we develop a unified framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive setup, our main focus is on the case of small magnetic Prandtl numbers which applies, e.g., to liquid metal experiments but also to the colder parts of accretion disks. We show that the inductionless versions of MRI that were previously thought to be restricted to comparably steep rotation profiles extend well to the Keplerian case if only the azimuthal field slightly deviates from its current-free (in the fluid) profile. We find an explicit criterion separating the pure azimuthal inductionless magnetorotational instability from the regime where this instability is mixed with the Tayler instability. We further demonstrate that for particular parameter configurations the azimuthal MRI originates as a result of a dissipation-induced instability of the Chandrasekhar's equipartition solution of ideal magnetohydrodynamics.

Keywords: magnetorotational instability; Chandrasekhar's equipartition solution; dissipation-induced instabilities; diffusive instabilities; magnetohydrodynamics

Publ.-Id: 20995

Electronical and structural changes induced by the incorporation of Am into conventional fuels

Prieur, D.; Carvajal-Nunez, U.; Vigier, J.-V.; Somers, J.; Bes, R.; Martin, P.; Lebreton, F.; Caisso, M.; Delahaye, T.; Scheinost, A. C.; Hennig, C.; Pruessmann, T.; Vitova, T.; Kvashnina, K. O.

241Am is one of the most hazardous actinide isotopes present in the spent fuel Transmutation in fast neutrons reactors :

conversion of highly radioactive elements into short-lived isotopes
Dramatic reduction of the nuclear waste inventory (< 300 years)
Two strategies :
Homogeneous transmutation : Incorporation of MA in low concentration (<5%) to the conventional MOX fuel Am-MOX, Np-MOX, etc.
Heterogeneous transmutation : Incorporation of MA in high concentration (5-30%) in dedicated assemblies at the core periphery
(U,Am)O2, (Pu,Am)O2, etc.

Keywords: Transmutation; americium; XAFS

Related publications

  • Lecture (Conference)
    NUMAT 2014, 27.-30.10.2014, Hilton Clearwater, Florida, U.S.A.

Publ.-Id: 20994

Ion beam synthesis of the full spectrum of III-V:Mn ferromagnetic semiconductors

Zhou, S.

Ferromagnetic semiconductors have been under intensive investigation during the last decade. Until now, III-Mn-V based compound semiconductors are the only well accepted class of materials. The prototype ferromagnetic semiconductor GaMnAs has revealed a variety of unique features induced by the combination of its magnetic and semiconducting properties. To prepare ferromagnetic semiconductors, one needs to dope the host with up to 5-10% Mn, which is far beyond the solid solubility of Mn in III-V compounds. As a non-equilibrium process, ion implantation can introduce enough dopants as required. However, the activation of dopants remains challenging due to the clustering of implanted ions during post-annealing. The solubility limit is a fundamental barrier for dopants incorporated into a specific semiconductor. On the other hand, one notes that the solubility limit in the liquid phase is generally much larger than that in the solid phase. Short-time annealing in the millisecond or nanosecond regime allows the epitaxial growth from a liquid phase. The mature development and commercialization of ion implantation promise the versatility. The approach combining ion implantation and pulsed laser melting allows us to prepare ferromagnetic semiconductors covering the full spectrum of III-V compound semiconductors. We have successfully synthesized ferromagnetic Mn doped III-V from InAs and GaAs to InP and GaP with different bandgaps. The results of magnetization, magnetic anisotropy, resistivity, anomalous Hall effect, magnetoresistance and x-ray magnetic circular dichroism obtained from the synthesized samples confirm the intrinsic origin and the carrier-mediated nature of the ferromagnetism. Moreover, in different III-V hosts we observe distinct differences regarding the magnetic anisotropy and conduction mechanism which are related with the intrinsic parameters such as the lattice mismatch, energy gap and the acceptor level of Mn. These results could allow a panorama-like understanding of III-V:Mn based ferromagnetic semiconductors.
[1] D. Bürger, S. Zhou, et al., Phys. Rev. B 81, 115202 (2010).
[2] S. Zhou, et al., Appl. Phys. Lett. 96, 202105 (2010).
[3] S. Zhou, et al., Appl. Phys. Express 5, 093007 (2012).
[4] M. Khalid et al., Phys. Rev. B., 89, 121301(R) (2014).
[5] Y. Yuan, et al, IEEE Tran. Magn., in press (2014).

Keywords: Magnetic semiconductors; Ion implantation

Related publications

  • Invited lecture (Conferences)
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France
  • Invited lecture (Conferences)
    The Moscow International Symposium on Magnetism 2014, 29.06.-03.07.2014, Moscow, Russia
  • Invited lecture (Conferences)
    X-th International Conference - Ion Implantation and Other Applications of Ions and Electrons, 23.-26.06.2014, Kazimierz Dolny, Poland

Publ.-Id: 20993

Surface protection of titanium and titanium-aluminum alloys against environmental degradation at elevated temperatures

Yankov, R.; von Borany, J.; Munnik, F.; Donchev, A.; Schütze, M.

Ti and its alloys with Al are a class of lightweight materials, which find extensive use in a number of advanced aerospace, automotive and power generation applications. These materials, however, are limited in applicability by their poor oxidation resistance at elevated temperatures (> 500°C for Ti, and > 750°C for TiAl).
We have developed a technique for protecting the above-mentioned materials against high-temperature environmental degradation (oxidation and embrittlement). In the case of TiAl alloys of an Al content of about 40 to 60 at.% , the technique has involved a single step, i.e. plasma immersion ion implantation (PIII) of fluorine, making use of the so-called “fluorine effect”. Optimum process parameters have been established under which the F-implanted TiAl alloys acquire a stable, adherent and highly protective alumina scale upon subsequent high-temperature oxidation in air. The extent of oxidation protection has been evaluated by testing F-implanted TiAl samples either isothermally or under conditions of thermal cyclic oxidation at temperatures ranging from 900° to 1050°C, and for times as long as 6000 hours. Results from characterization by elastic recoil detection analysis (ERDA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and Rutherford backscattering spectrometry (RBS) have proven the possibility of forming a protective alumina scale on both laboratory coupons and machine components such as jet turbine blades and turbochargers. In the case of Ti and low-Al-content Ti-Al alloys, e.g. Ti3Al, the technique has involved two steps, namely Al enrichment (aluminization) of the material’s near-surface, and introduction of F by PIII to activate the fluorine effect. Under optimized process conditions, the Ti and Ti3Al samples so modified have shown marked environmental stability at temperatures as high as 700°C and for extended oxidation times due to the presence of a protective alumina layer.

Keywords: titanium; titanium aluminides; high-temperature oxidation protection

Related publications

  • Lecture (Conference)
    28th International Conference on Surface Modification Technologies (SMT), 16.-18.06.2014, Tampere, Finland

Publ.-Id: 20992

Improvement of the resistance of titanium aluminides to environmental embrittlement

Masset, P. J.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Paul, J.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schumacher, P.; Schütze, M.; Wolf, G.; Yankov, R. A.

Aluminum enriched coatings have been developed for titanium aluminide alloys. It has been shown that Metal Organic Chemical Vapor Deposition (MO-CVD) and Physical Vapor Deposition (PVD) processes combined with fluorination of the coating enables to reduce significantly the embrittlement of TiAl alloys through oxidation. Even after oxidation at 900 °C for 100h, the coatings exhibit suitable adhesion and 90 % of the fracture toughness and ductility of the alloy are maintained.

Related publications

Publ.-Id: 20991

GGR Biennial Critical Review: Analytical Developments Since 2012

Wiedenbeck, M.; Bédard, P. L.; Bugoi, R.; Horan, M.; Linge, K.; Merchel, S.; Morales, L. F. G.; Savard, D.; Souders, A. K.; Sylvester, P.

Advances in the chemical, crystallographic and isotopic characterization of geological and environmental materials can often be ascribed to technological improvements in analytical hardware or to innovative approaches to data acquisition and/or its interpretation. This biennial review addresses key laboratory methods that form much of the foundation for analytical geochemistry; again this contribution is presented as a compendium of laboratory techniques. We highlight advances that have appeared since January 2012 and which are of particular significance for the chemical and isotopic characterization of geomaterials. Prominent scientists from the selected analytical fields present publications they judge to be particular noteworthy, providing background information about the method and assessing where further opportunities might be anticipated. In addition to well established technologies such as thermal ionization mass spectrometry and plasma emission spectroscopy, this publication also presents new or rapidly growing methods such as electron backscattered diffraction analysis and atom probe tomography – a very sensitive method providing atomic scale information.

Keywords: ICPMS; laser ablation; mass spectrometry; ICP-AES; microwave plasma source; TIMS; isotopic analysis; geochronology; trace element analysis; calibration; XRF; environmental sampling; AMS; Ion Beam Analysis; radionuclides; SIMS; ion probe; microanalysis; FIB; EBSD; atom probe tomography

Publ.-Id: 20990

Generation of few-group constants with Serpent: Application examples

Fridman, E.

The purpose of this presentation is to demonstrate the capability of the Serpent Monte Carlo code to generate few-group constants for existing and innovative reactor systems

  • Invited lecture (Conferences)
    PHYSOR 2014, Workshop on new features and capabilities in the Serpent 2 Monte Carlo code, 28.09.-03.10.2014, Kyoto, Japan

Publ.-Id: 20989

Development of new coatings to prevent environmental embrittlement of titanium aluminides

Masset, P.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Paul, J.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schumacher, P.; Schütze, M.; Wolf, G.; Yankov, R.

Abstract: For temperatures above 750°C, TiAl alloys still show insufficient oxidation resistance and suffer from environmental embrittlement. This work focuses on the surface modification of alloys and development of coatings against environmental embrittlement, as well as on testing of mechanical properties after high temperature oxidation. Aluminum enriched coatings (between 50 and 60 at.%) containing alloying elements, i.e. Cr, Nb, Si, Y, to improve the oxidation behavior and the corrosion resistance have been produced by MO-CVD, CVD, PVD and thermal spraying techniques (HVOF, APS), and have subsequently been chemically modified with halogen elements, notably fluorine. The mechanical properties have been studied by means of 4-point bending and tensile tests on coated samples after 100h oxidation at 900 °C in laboratory air. The CVD process combined with fluorine treatment using plasma immersion implantation (PI³) of F offers the best combination to remedy environmental embrittlement. It has been shown in particular that 90% of the initial fracture strain and fracture stress can be maintained.

Keywords: titanium; titanium aluminides; high-temperature oxidation; protective coatings

Related publications

  • Lecture (Conference)
    TMS 2014, 143rd Annual Meeting & Exhibition, 16.-20.02.2014, San Diego, United States

Publ.-Id: 20988

Protection of Ti-alloys against high temperature environmental attack by a two step process, aluminization + fluorination

Donchev, A.; Galetz, M.; Schütze, M.; Yankov, R.; Kolitsch, A.

Ti-alloys cannot be used at elevated temperatures above approximately 600°C in oxidizing environments. They suffer from accelerated oxidation and oxygen uptake in the subsurface zone, which deteriorates the mechanical properties. The addition of Al (usually < 10%) into standard Ti-alloys is not enough to form a protective alumina layer. Aluminization of technical Ti-alloys and formation of intermetallic Al-rich phases (e.g. TiAl3) change the oxidation behavior from fast and non-protective rutile formation to slow growing alumina kinetics, but only for a limited period of time. A subsequent fluorination of the aluminized components gets the fluorine effect to operate. This is away to improve the resistance of technical Ti-alloys against environmental attack, even for longer service times. In this paper the results of high temperature oxidation tests of several untreated and treated Ti-alloys will be presented and their behavior compared.

Keywords: Environmental embrittlement; Fluorine effect; Oxidation

Related publications

  • Contribution to proceedings
    TMS 2014 143rd TMS Annual Meeting 2014, 16.-20.02.2014, San Diego, United States
    TMS 2014 Supplemental Proceedings, 9781118889725, 79-85
    DOI: 10.1002/9781118889879

Publ.-Id: 20987

Potential Impairment of Core Coolability during LOCA due to Precipitation of Zinc Borate

Pointner, W.; Kryk, H.; Kästner, W.; Austregesilo, H.

Within the framework of German nuclear safety research, generic experimental investigations were carried out at HZDR and the Hochschule Zittau/Görlitz aiming at the elucidation of physicochemical and thermo hydraulic mechanism of corrosion product formation, which may occur during the sump circulation operation after loss-of-coolant accidents in pressurized water reactors.
The contact of the boric acid containing coolant with hot-dip galvanized steel containment internals causes corrosion of the corresponding materials resulting in dissolution of the zinc coating. As main result of batch experiments, decreasing solubility of zinc corrosion products in boric acid solutions with increasing temperature was found. Thus, the formation and deposition of solid corrosion products cannot be ruled out if zinc containing coolant is heated up due to its recirculation into hot regions within the cooling circuit. Generic corrosion and deposition experiments at a lab-scale test facility proved that dissolved zinc, formed at low temperatures in boric acid solution by zinc corrosion, may turn into solid deposits of zinc borates when contacting heated zircaloy surfaces during the heating of the coolant. The results obtained at lab-scale were confirmed by generic experiments at semi-technical scale using a 3x3 heating rod configuration including spacer segments as well as a 16x16 (8x8 heated) fuel rod dummy.
Experiments regarding the corrosion kinetics of zinc-coated components were not subject of the study. Therefore, a quantitative transferability of the results to postulated PWR-LOCA is not given so far.

Keywords: pressurized water reactor; loss-off-coolant accident; corrosion; zinc; boric acid; in-vessel effects

  • Lecture (Conference)
    17th WGAMA Meeting, 23.-26.09.2014, Paris, France

Publ.-Id: 20986

Recent developments in surface protection of titanium and titanium-aluminum alloys against environmental degradation at elevated temperatures

Yankov, R.; von Borany, J.; Masset, P. J.; Donchev, A.; Schütze, M.

Titanium and its alloys with aluminum are lightweight structural materials, which find ever-increasing use in a number of advanced aerospace, automotive and power generation applications. These materials, however, are limited in applicability by their inadequate oxidation resistance at elevated temperatures (> 500°C for Ti, and > 750°C for TiAl).
This talk reviews recent advances in using state-of-the-art techniques for surface engineering of Ti, Ti-base alloys and γ-TiAl intermetallics, with a view to rendering them resistant to high-temperature environmental oxidation and oxygen embrittlement.
The first part of the talk covers the surface modification of Ti and low-Al-content Ti-base alloys by using combined techniques involving either aluminization followed by plasma immersion ion implantation (PIII) of fluorine or formation of a surface barrier coating by magnetron sputter co-deposition of Ti and Al followed by vacuum annealing and PIII of F.
The second part focuses on the direct surface treatment of γ-TiAl by PIII of F. Such type of fluorination enables the F-implanted alloy surface to develop a stable, adherent and highly protective alumina scale upon subsequent oxidation in air at temperatures in excess of 1000°C for extended exposure times.
The last part deals with the fabrication of protective TiAl coatings using a two-step coating scheme. First, an Al-rich TiAl layer is formed on the γ-TiAl alloy by either MO-CVD, PVD or thermal spraying. Then the TiAl layer is treated by PIII of F. The resulting coatings are tested for oxidation resistance, oxygen embrittlement, and retention of mechanical properties. A combination of an Al-rich CVD coating and treatment by PIII of F gives the best results. An example is also given of a thermal barrier coating whose structure comprises, instead of a bond coat, a thin alumina layer formed by PIII of F and subsequent high-T oxidation. The results of these studies have been helpful in understanding the oxidation behavior of the surface-engineered alloys from both a scientific and a technological standpoint.

Keywords: titanium; titanium aluminides; high-temperature oxidation; protective coatings

Related publications

  • Invited lecture (Conferences)
    Shechtman International Symposium, 29.06.-04.07.2014, Cancun, Mexico

Publ.-Id: 20985

The Use of Plasma Immersion Ion Implantation in the High-Temperature Oxidation Protection of Low-Al-Content Ti-Base Alloys and TiAl Intermetallics

Yankov, R.; von Borany, J.; Pelic, B.; Donchev, A.; Schütze, M.

Low-Al content Ti-base alloys and TiAl intermetallics are attractive lightweight materials for advanced medium-temperature (500°-750°C) structural applications including components such as jet engine and industrial gas turbine blades, turbocharger rotors and automotive engine valves. However, envisaged service temperatures are in the range of 750° to 1050°C at which these alloys are prone to both destructive oxidation and oxygen embrittlement. Therefore, development of surface-engineering techniques for preventing high-T environmental damage is critical in exploiting the advantages of the TiAl alloys to their fullest extent.
We propose two techniques for protecting candidate Ti-base and TiAl alloys from high-temperature (>750°C) oxidation environments. The first technique involves a single step, namely treating the alloys directly by plasma immersion ion implantation (PIII) of fluorine using a mixture of CH2F2+6.25% Ar as the precursor gas. This technique is applicable to TiAl alloys of an Al content of ~ 45 to 55 at.%. The F implant dose has been found to depend critically on the gas flow rate ratio (GFRR, i.e. CH2F2/Ar) while the resulting F depth profiles show dependence on both the GFRR and the alloy material. Optimum implantation conditions have been established under which the F-implanted alloy surface is able to form a highly protective Al2O3 film upon subsequent oxidation in air. Oxidation resistance has been evaluated by thermal gravimetric analysis (TGA) at temperatures as high as 1050°C for extended exposure times.
The alternative technique is applicable to low-Al-content Ti-base alloys (< 40 at.% Al). It involves the fabrication of a barrier coating in a three-step process, namely formation of a Ti+Al layer by magnetron co-sputtering of Ti and Al followed by vacuum annealing to form a gamma-TiAl coating and, finally, PIII of fluorine. The coating so formed has been shown to prevent further oxidation of the base material at elevated temperatures.

Keywords: Plasma Immersion Ion Implantation; High-Temperature Oxidation; TiAl Intermetallics

Related publications

  • Poster
    19th International Conference on Ion Beam Modification of Materials (IBMM), 14.-19.09.2014, Leuven, Belgium

Publ.-Id: 20984

Internal Dose Assessment of (-)-18F-Flubatine, Comparing Animal Model Datasets of Mice and Piglets with First-in-Human Results

Sattler, B.; Kranz, M.; Starke, A.; Wilke, S.; Donat, C. K.; Deuther-Conrad, W.; Patt, M.; Schildan, A.; Patt, J.; Smits, R.; Hoepping, A.; Schoenknecht, P.; Steinbach, J.; Brust, P.; Sabri, O.

(−)-18F-flubatine is a promising tracer for neuroimaging of nicotinic acetylcholine receptors (nAChRs), subtype α4β2, using PET. Radiation doses after intravenous administration of the tracer in mice and piglets were assessed to determine the organ doses (ODs) and the effective dose (ED) to humans. The results were compared with subsequent clinical investigations in human volunteers.
Twenty-seven female CD1 mice (weight ± SD, 28.2 ± 2.1 g) received intravenous injection of 0.75 ± 0.33 MBq of (−)-18F-flubatine. Up to 240 min after injection, 3 animals per time point were sacrificed and the organs harvested, weighed, and counted in a γ counter to determine mass and activity, respectively. Furthermore, whole-body PET scans of 5 female piglets (age ± SD, 44 ± 3 d; weight ± SD, 13.7 ± 1.7 kg) and 3 humans (2 men and 1 woman; age ± SD, 59.6 ± 3.9 y; weight ± SD, 74.3 ± 3.1 kg) were obtained up to 236 min (piglets) and 355 min (humans) after injection of 186.6 ± 7.4 and 353.7 ± 10.2 MBq of (−)-18F-flubatine, respectively, using a PET/CT scanner. The CT was used for delineation of the organs. Exponential curves were fitted to the time–activity-data, and time and mass scales were adapted to the human anatomy. The ODs were calculated using OLINDA/EXM (version 1.0); EDs were calculated with the tissue-weighting factors of ICRP103.
After the injection of (−)-18F-flubatine, there were no adverse or clinically detectable pharmacologic effects in any of the subjects. The highest activities after injection were found in the kidneys, urinary bladder, and liver. The urinary bladder receives the highest OD in all investigated species, followed by the kidneys and the liver for animals and humans, respectively. On the basis of mouse, piglet, and human kinetic data, the projected human ED of (−)-18F-flubatine was estimated to be 12.5 μSv/MBq in mice, 14.7 ± 0.7 μSv/MBq in piglets, and 23.4 ± 0.4 μSv/MBq in humans.
As has been demonstrated for other PET radiotracers, preclinical (i.e., animal-derived) dosimetry underestimates the ED to humans, in the current case of (−)-18F-flubatine by 34%–44%.

Keywords: radiation dosimetry; positron emission tomography; (−)-18F-flubatine; nicotinic receptors; α4β2

Publ.-Id: 20983

Velocity measurements of heavy liquid metal flows by the Ultrasound Doppler method

Franke, S.; Eckert, S.; Gundrum, T.; Gerbeth, G.

The application of heavy liquid metals as coolant or heat transfer medium in advanced reactor systems demands for a comprehensive knowledge of the flow characteristics. CFD simulations are the main tool to predict the flow behaviour, however, the numerical models have to be validated by experimental data. Flow measurements in hot liquid metals are challenging and the available choice of measuring techniques is rather limited. A great deal of work was done during the last decade to develop suitable measuring principles for applications in metallic melts. The Ultrasound Doppler method can be considered as an attractive technique to obtain real-time velocity profiles in liquid metal flows. Flow measurements in hot metallic melts involve several specific problems, especially the high temperature and the abrasive character of the melt. Furthermore, a sufficient input of acoustic energy into the melt to be measured requires favourable conditions concerning acoustic coupling, transmission and wetting. Moreover, the availability of seeding particles has to be guaranteed to obtain Doppler signals from the fluid. We will present a concept for velocity measurement in a liquid metal channel flow based on high temperature transducer probes in combination with a matched mechanical design of the probe seating. Specific measuring procedure enables us for reliable measurements in a temperature range up to 230°C. The measuring principles are successfully applied at experimental facilities operating with different metal alloys and geometric configurations: At the LIMMCAST (Liquid Metal Model for Continuous Casting) facility of Helmholtz-Zentrum Dresden-Rossendorf we studied the flow profile of a Sn60Bi40 alloy in a circular pipe. Furthermore, the LBE duct flow of the META:LIC loop (Megawatt Target: Lead Bismuth Cooled) at the Institute of Physics in Riga-Salaspils (University of Latvia) was measured. Parametric studies of the velocity profile measurements in the ducts will be presented here. Specific problems arising for the application of the Ultrasound Doppler method in the considered experimental configuration will be discussed.

Keywords: Hot metallic melt flow measurements; Heavy liquid metal coolant; LBE; Ultrasound Doppler velocimetry; LIMMCAST; META:LIC

  • Lecture (Conference)
    SEARCH/MAXSIMA 2014 International Workshop, 07.-10.10.2014, Karlsruhe, Deutschland

Publ.-Id: 20982

Hydrolysis of tetravalent cerium Ce(IV)) - A multi-spectroscopic study on nanocrystalline CeO2 formation

Ikeda-Ohno, A.; Weiss, S.; Tsushima, S.; Hennig, C.

Because of the flexibility between the tri- and tetravalent oxidation states, cerium (Ce) is known to be the only rare earth element (REE) forming a stable pure stoichiometric dioxide compound (CeO2). Owing to this chemical specificity along with the highest natural abundance of Ce among all REEs, the application of CeO2 has spread over a variety of fields. More recently, CeO2 has been employed as nanoparticles with many technological applications, which include the catalysts for harmful gas treat-ment the water gas shift reaction, electrodes for solid oxide fuel cells and a medical use as an artificial superoxide dismutase. These versatile and still emerging applications of CeO2 still require a simpler and more efficient synthetic strategy, particularly for manufacturing CeO2 nanoparticles.
The hydrolysis of tetravalent cerium (Ce(IV)) is a primary step of many wet syntheses for fabricating CeO2 nanoparticles, although all the reported synthetic methods require additional processes, such as heating, adding organic solvents or calcination, subsequent to the initial hydrolysis step to finally yield CeO2 nanoparticles. This means that understanding of the hydrolysis mechanism of Ce(IV) would be beneficial to developing a new concept for the efficient production of CeO2 nanoparticles. Based on this background, this study focuses on the systematic investigation of the hydrolysis behaviour of Ce(IV) using synchrotron-based X-ray techniques (X-ray absorption spectroscopy (XAS) and high en-ergy X-ray scattering (HEXS)), dynamic light scattering (DLS) and transmission electron microscopy (TEM).

Keywords: cerium; Ce(IV); hydrolysis; nanocrystals; XAS; HEXS; DLS; TEM

Related publications

  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, HZDR Dresden, Germany

Publ.-Id: 20980

Liquid backmixing in an inclined rotating tubular fixed bed reactor - Augmenting liquid residence time via flow regime adjustment

Härting, H.-U.; Berger, R.; Lange, R.; Larachi, F.; Schubert, M.

The liquid residence time and backmixing in an inclined rotating tubular fixed bed reactor, operated with gas-liquid co-current downflow, are studied experimentally. This novel reactor concept is introduced to extent the process intensification strategies of chemical multiphase reactors. The intermittent catalyst immersion due to rotation induces a continuous refreshment of the liquid at the catalyst surface and enhances the access of the gas phase to the catalyst in the drained section of the fixed bed. Depending on the inclination angle and rotational velocity, different flow regimes are observed. In particular, the flow regimes with stratified gas-liquid flow can be utilized to enhance the performance of the reactor for heterogeneous catalytic reactions.
The backmixing study is based on the method of the imperfect tracer pulse and the propagation of the tracer is measured by low-intrusive wire-mesh sensors. Compared to conventional trickle bed reactors, the liquid residence time and axial dispersion are increased by the inclination and rotation. The effects of reactor inclination angle and rotational velocity as well as of particle size and liquid superficial velocity on the liquid backmixing in the inclined rotating tubular fixed bed reactor are shown in detail.

Keywords: liquid backmixing; residence time; axial dispersion; flow regimes; gas-liquid flow; process intensification

Publ.-Id: 20979

Formation of zinc corrosion products at water-chemical PWR post-LOCA conditions - Physicochemical effects

Kryk, H.; Hoffmann, W.

During loss-of-coolant accidents (LOCAs) in pressurized water reactors (PWRs), coolant spilling from the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by low pressure injection pumps as part of the emergency core cooling system. The long-term contact of the boric acid containing coolant with hot-dip galvanized steel containment inter-nals (e.g. grating treads, channels, supporting grids of sump strainers) may cause corrosion of the corresponding materials influencing the cooling water chemistry due to dissolution of the zinc coating. Experimental investigations regarding the solubility of Zn corrosion products in boric acid solutions resulted in a decreasing solubility with increasing temperature. Thus, the formation of solid (i.e. particulate) corrosion products cannot be ruled out if the Zn containing coolant is heated up due to its recirculation into hot zones.
During lab-scale experiments, significant amounts of solid corrosion products have been found as deposited layers on hot surfaces as well as in the form of deposits at tubes, fittings and retaining components depending on formation temperature and hydrodynamic conditions. The solid corrosion products were identified as zinc borates. Depending on their forming temperature, different zinc borate compounds may occur having different physicochemical properties.
Although the kinetics of the processes obtained at lab-scale are not transferable to those proceeding during a PWR LOCA due to their dependency on the corroding surface area as well as on the local thermal hydraulics, the results give an insight into physicochemical processes, which might occur in case of zinc corrosion in cooling circuits.

Keywords: loss-of-coolant accident; pressurized water reactor; corrosion; zinc; zinc borate; chemical effects

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2014, 06.-08.05.2014, Frankfurt, Deutschland
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2014, 06.-08.05.2014, Frankfurt, Deutschland

Publ.-Id: 20978

Partikelentstehung und -transport im Kern von Druckwasserreaktoren - Thermo- und fluiddynamische Mechanismen

Renger, S.; Kästner, W.; Alt, S.; Seeliger, A.; Kryk, H.; Hoffmann, W.

Im Rahmen der Reaktorsicherheitsforschung erfolgten an der Hochschule Zittau/Görlitz in Kooperation mit dem Helmholtz-Zentrum Dresden-Rossendorf experimentelle und methodische Untersuchungen für die systematische Klärung physiko-chemischer Mechanismen und deren Auswirkungen auf thermo-fluiddynamische Prozesse, welche während des Sumpfumwälzbetriebs nach Kühlmittelverluststörfällen in einem Kernkraftwerk ablaufen können, falls in boriertem Kühlmittel (KM) gelöstes Zink in Kernbereiche höherer Temperatur (Hot-Spots) gelangt. Das im KM befindliche Zink kann hierbei im Vorfeld durch die Korrosion feuerverzinkter Bauteile freigesetzt werden.
In den Untersuchungen im halbtechnischen Maßstab wurden die physiko-chemischen Mechanismen und der Temperatureinfluss analysiert. Gleichzeitig wurden Auswirkungen dieser Prozesse auf das thermo-fluiddynamische Verhalten in einer Heizstabkonfiguration (3x3-Anordnung mit für Druckwasserreaktoren (DWR) typischen Zirkaloy-Hüllrohren) mit Abstandshaltern erfasst. Im Fokus der Untersuchungen stand dabei das Verhalten derart zusammengesetzter Fluide an beheizten Konfigurationen, die im Kern von DWR auftreten können.
Die durchgeführten Untersuchungen tragen generischen Charakter und liefern Aussagen zum Löslichkeitsverhalten von Zink in borsäurehaltigem KM sowie zur Bildung fester Korrosionsprodukte und den daraus folgenden Auswirkungen.

Keywords: loss-of-coolant accident; pressurized water reactor; corrosion; zinc; chemical effects

  • Poster
    46. Kraftwerkstechnisches Kolloquium 2014, 14.-15.10.2014, Dresden, Deutschland

Publ.-Id: 20977

Light-Induced Switching of Tunable Single-Molecule Junctions

Sendler, T.; Luka-Guth, K.; Wieser, M.; Lokamani, M.; Wolf, J.; Helm, M.; Gemming, S.; Kerbusch, J.; Scheer, E.; Huhn, T.; Erbe, A.

A major goal of molecular electronics is the development and implementation of devices such as single-molecular switches. Here, measurements are presented that show the controlled in situ switching of diarylethene molecules from their nonconductive to conductive state in contact to gold nanoelectrodes via controlled light irradiation. Both the conductance and the quantum yield for switching of these molecules are within a range making the molecules suitable for actual devices. The conductance of the molecular junctions in the opened and closed states is characterized and the molecular level E0 , which dominates the current transport in the closed state, and its level broadening Γ are identified. The obtained results show a clear light-induced ring forming isomerization of the single-molecule junctions. Electron withdrawing side-groups lead to a reduction of conductance, but do not influence the efficiency of the switching mechanism. Quantum chemical calculations of the light-induced switching processes correlate these observations with the fundamentally different low-lying electronic states of the opened and closed forms and their comparably small modification by electron-withdrawing substituents. This full characterization of a molecular switch operated in a molecular junction is an important step toward the development of real molecular electronics devices.

Publ.-Id: 20976

Simulation of gas-liquid flow in a helical static mixer

Zidouni, F.; Krepper, E.; Rzehak, R.; Rabha, S.; Schubert, M.; Hampel, U.

CFD simulations using the Euler-Euler approach are performed to model the gas-liquid bubbly flow in a helical static mixer. The model validation work was based on experiments, which are carried out in a column of diameter 0.08 m packed with helical static mixer elements (length 80 mm / diameter 80 mm). Measurements of gas volume fractions, gas velocities and bubble size distributions by in-house developed ultrafast X-ray electron beam tomography were taken at several planes within the mixer elements (Rabha et al. 2014).
The predicted axial and radial gas phase distribution considering different mono-disperse bubble sizes (3, 5.8 and 8 mm) are studied and validated against the experimental results. The dependency of non-drag forces on the bubble size was considered. Consequently, the bubble size dependent effects of the non-drag forces on the flow and on the cross sectional gas volume fraction distribution are shown.
Despite obvious shortcomings of the models for this application, some conclusions on the suitability of certain mixer designs for gas-liquid dispersion may be drawn already. The swirling flows created by the twist and turn of the helical mixer elements, which in turn pushes the lighter phase towards the center of the pipe is well predicted and validated. Further investigations have to consider the bubble size distribution e.g. by a population balance model to accurately predict the dispersion of the gas phase within and downstream the helical static mixer.

Keywords: helical static mixer; dispersion; gas-liquid multiphase flow; Euler-Euler two fluid model; CFD simulation

Publ.-Id: 20975

„Das sagen unsere Kunden/Partner“ für AHK Chile

Birtel, S.

Das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) fokussiert sich auf interdisziplinäre und technologieorientierte Projekte zur energie- und ressourceneffizienten Nutzung von Hochtechnologierohstoffen aber auch die Nutzung von anderen Metallen und ihren Nebenprodukten. Seit 2011 haben die AHK Chile und das ihr angegliederte Kompetenzzentrum für Bergbau und Rohstoffe gemeinsam mit dem HIF sehr erfolgreich mehrere geeignete chilenische Partner aus Industrie und Forschung identifiziert und erste Projektanbahnung unterstützt. Hierzu zählt unter anderem ein BMBF gefördertes Projekt mit der Codelco Tochter IM2. Besuche bei Projektpartnern und Veranstaltungen wie den Deutsch-Chilenischen Wirtschafstagen, dem Länderworkshop Chile der Vereinigung Rohstoffe und Bergbau e.V. oder den Freiberger Innovationstagen bieten gute Gelegenheiten für persönliche Gespräche. Dies wird komplementiert durch einen regelmäßigen E-Mail-Austausch zu aktuellen Entwicklungen. Dabei profitieren die Wissenschaftler des HIF stark vom großen Engagement des Kompetenzzentrums auch in der Begleitung der Projekte.

Keywords: Zusammenarbeit mit AHK Chile

  • Other report
    Santiago: CHAMCHAL AHK Chile, 2014
    21 Seiten

Publ.-Id: 20974

Variability and lower bound of fracture toughness of welds in the ductile to brittle transition regime

Schindler, H.-J.; Kalkhof, D.; Viehrig, H.-W.

The reference temperature T0 was measured for both T-S and T-L- specimen orientation in 24 layers across the thickness of the beltline weld of a reactor pressure vessel. It turned out to vary in a bandwidth of more than 40K. Because of a high scatter, no clear pattern of T0 as a function of the thickness position could be recognized. A more detailed analysis revealed that the median of KJc was considerably steeper than predicted by the Master-Curve, which leads to a bias of T0 with respect to the testtemperature relative to T0. By a modified evaluation procedure, the scatter of the reference temperature could be significantly reduced, which enabled the global pattern of T0 to be recognized. By comparing the theoretical lower bound to KJc-data of the used specimens with the individual measured KJc a representative T0 that characterizes the overall toughness behaviour of the weld was determined. It turned out to be about 10 K lower than the maximum local T0.

Keywords: reactor pressure vessel; weld metal; fracture toughness; reference temperature

Publ.-Id: 20973

Intra-band dynamics in single InAs/GaAs quantum dots under the influence of strong far-infrared excitation

Stephan, D.; Bhattacharyya, J.; Helm, M.; Huo, Y. H.; Schmidt, O.; Rastelli, A.; Schneider, H.

Inter-band transitions in single quantum dots (QDs) have received a huge amount of scientific interest in the recent past. However, mostly due to technical challenges in dealing with mid- and far-infrared radiation, intra-band transitions have not been explored quite as thoroughly. In this work, we combine micro-photoluminescence (µPL) on low-density annealed InAs/GaAs QDs with additional excitation at intra-band transition energies by pulsed radiation from a free-electron laser (FEL). This scheme enables the probing of the single-dot response in spite of the large diameter of the FEL focus. The investigation of single QDs eliminates undesirable effects such as inhomogeneous broadening which has been observed in previous studies on QD ensembles1–3. In the time domain, the FEL pulse leads to an initial decrease in the PL transient (Fig.1), which we attribute to a temporary redistribution of carriers. The subsequent recovery is significantly larger than would be expected for simple redistribution. By varying the NIR excitation energy, we find that this increase is due to carriers which are initially present close to but not inside the QD (in the wetting layer or in defect states) and which are freed and/or transported to the dot upon incidence of the FEL pulse. When investigating at the PL spectrum of a single dot, we observe a marked difference caused by the FEL pulse (Fig. 2), which implies a change of the excitonic state of the QD.

Related publications

  • Lecture (Conference)
    International Conference on Superlattices, Nanostructures and Nanodevices, 03.-08.08.2014, Savannah, United States of America

Publ.-Id: 20972

Intra-band dynamics in single InAs/GaAs quantum dots probed with a free-electron laser

Stephan, D.; Bhattacharyya, J.; Helm, M.; Huo, Y. H.; Schmidt, O.; Rastelli, A.; Schneider, H.

Compared to the vast amount of research done in the past on inter-band transitions in single quantum dots (QDs), transitions within the bands have received much less attention. The main reasons for this are most likely the largely non-radiative character of intra-band transitions and the technical difficulties associated with the corresponding mid- and far-infrared radiation. In our contribution, we approach this challenge by combining conventional micro-photoluminescence (µPL) on low-density annealed InAs/GaAs self-assembled QDs with additional excitation at intra-band (i.e. inter-sublevel) transition energies by pulsed radiation from a free-electron laser (FEL). In contrast to previous studies on ensembles of QDs1–3, using single dots eliminates undesirable effects such as inhomogeneous broadening. The FEL pulse leads to an initial decrease in the PL transient (Fig.1), which we attribute to a temporary redistribution of carriers. This is followed by a pronounced recovery, such that the integrated PL is larger than for a reference transient without FEL excitation. By varying the NIR excitation energy, we find that this increase is due to carriers which are initially present close to but not inside the QD (in the wetting layer or in defect states) and which are freed and/or transported to the dot upon incidence of the FEL pulse.

Related publications

  • Poster
    8th International Conerence on Quantum Dots, 11.05.-16.10.2014, Pisa, Italia

Publ.-Id: 20971

Optical investigations of GaAsN in high magnetic fields

Eßer, F.; Drachenko, O.; Schneider, H.; Patanè, A.; Hopkinson, M.; Helm, M.

Introducing a few hundredths of a percent of nitrogen into a GaAs-based semiconductor leads to dramatic changes of the electronic and optical properties of the original material system. This can be used in order to intentionally tune the semiconductors characteristics. In particular the bandgap of semiconductors like GaAs and InGaAs, can be strongly reduced by slight nitrogen incorporation, which is attractive for applications, in particular for detectors or light sources.

Even though a lot of effort has been made on the investigation of the effective mass in GaAsN, it is rather challenging to describe the and stucture and in particular the effective mass of this system. We investigate a series of GaAsN samples and make use of high magnetic fields in combination with THz radiation from a free-electron laser, which provides a unique approach in order to find the source of previous inconsistencies. Cyclotron resonance spectroscopy is probably the most direct way to measure the effective mass, but has never been applied before to GaAsN bulk. We compare the results of this method with those of magneto-photoluminescence (PL), which is more commonly applied to dilute nitrides.

Our cyclotron resonance spectroscopy results indicate that the effective mass is not very much affected by the nitrogen doping, in contrast to previous reports (e.g. [1–4]) based on magneto-PL. In our PL investigations in magnetic fields up to 61 T, the observed blueshift of the PL spectrum indicates a similar increase of the effective mass, as reported before in e.g. [1–4]. We will discuss the significance of the particular method and argue that some assumptions have to be reconsidered.

Keywords: GaAsN; ditute nitrides; effective mass; cyclotron-resonance; magneto-photoluminescence; high magnetic field

Related publications

  • Poster
    Optical Properties of Individual Nanowires and Quantum Dots in High Magnetic Field, 24.-26.09.2014, Toulouse, France

Publ.-Id: 20969

5 MeV Proton and 15 MeV Electron Radiation Effects Study on 4H-SiC nMOSFET Electrical Parameters

Alexandru, M.; Florentin, M.; Constant, A.; Schmidt, B.; Michel, P.; Godignon, P.

The impact of proton and electron irradiations on the electrical parameters of 4H-SiC nMOSFETs has been investigated by the time bias stress instability method. This study has allowed observing the effect of holes trapped in the gate oxide together with the generated interface traps. Improvements of important electrical parameters, such as the threshold voltage, the effective mobility and the maximum drain current were observed. These improvements could be connected with the Nitrogen and residual Hydrogen atoms diffusion from the SiO2/SiC interface toward the epilayer during irradiation. These atoms are likely to create other bonds by occupying the Silicon and Carbon’s dangling bond vacancies. This way, the number of passivated Carbon atoms is increased, hence improving the SiO2/SiC interface quality.

Keywords: Charge trapping; electron irradiation; mobility; proton irradiation; SiC MOSFET; SiO2/SiC interface; threshold voltage shift; time bias stress instability

Related publications

Publ.-Id: 20968

Spin Nernst Angle: Definition and qualitative Estimation for Cu Alloys

Zahn, P.; Gemming, S.

The spin Nernst effect describes the occurrence of a spin current perpendicular to an applied thermal gradient and the spin quantization axis in a non-magnetic material. To quantify the effect, the spin Nernst angle will be defined in a more general way than in ref. [1]. This allows for a clear separation of the transverse spin current into two opposite contributions proportional to the spin Hall angle and the spin Nernst angle, respectively. Qualitative trends for Cu alloys with 3d, 4d and 5d defects extending a resonant scattering model by Fert and Levy [2] will be presented.
The work was partially supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz Virtual Institute MEMRIOX (VH-VI-442) and the DFG Priority Program 'Nanostructured Thermoelectrics' (ZA264/3-2).

Keywords: spin Nernst effect; spin caloric; spin orbit coupling; Cu; dilute alloys; thermoelectrics; spin dependent transport

  • Poster
    Material Science and Engineering conference - MSE 2014, 23.-25.09.2014, Darmstadt, Deutschland

Publ.-Id: 20967

Traveling-Wave Thomson-Scattering for brilliant and efficient optical free-electron lasers

Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Schramm, U.

In Traveling-Wave Thomson-Scattering (TWTS) a high-power laser pulse is scattered off a relativistic electron pulse to produce radiation from EUV to Angstrom wavelength. TWTS employs a side-scattering geometry where laser and electron propagation direction enclose an angle to become independent of the Rayleigh length limit for the maximum interaction distance in standard head-on Thomson scattering geometries. For optimum spatial overlap in TWTS geometries the laser pulse features a pulse-front tilt. In this way, the electrons interact with all parts of the laser pulse and brilliances as well as photon scattering efficiencies are by orders of magnitude larger than in standard head-on geometries.
Interaction distances in TWTS are long enough for operation of a free-electron laser.
We show how TWTS experiments can be designed, present experimental parameters for TWTS FELs and discuss experimental challenges in their realization.

Keywords: Traveling-Wave; Thomson Scattering; EUV; X-ray; optical FEL

  • Poster
    3rd annual meeting of the LAOLA collaboration, 06.-07.10.2014, Wismar, Deutschland

Publ.-Id: 20966

Adjusting the Forming Step for Resistive Switching in Nb2O5 by Ion Irradiation

Wylezich, H.; Mähne, H.; Heinrich, A.; Slesazeck, S.; Rensberg, J.; Ronning, C.; Zahn, P.; Mikolajick, T.

Resistive switching devices with Nb2O5 as a switching layer are treated with argon ion irradiation, which generates defects in the oxide layer that support the electroforming step. To distinguish between the effects of layer thinning by sputtering and that of defect generation, devices with different thicknesses of deposited oxide are investigated. It is found that the defect-rich interfaces allow the formation of thick oxides at low forming voltages, and therefore, the effects of the ion irradiation are comparable to the use of reactive electrodes.

Keywords: Resistive switching; Nb2O5; argon; ion irradiation; metal-insulator-metal device; oxide; interfaces; sputtering; electro-forming; forming voltage

Related publications

Publ.-Id: 20965

A high-yield automated radiosynthesis of the alpha-7 nicotinic receptor radioligand [18F]NS10743

Teodoro, R.; Wenzel, B.; Oh-Nishi, A.; Fischer, S.; Peters, D.; Suhara, T.; Deuther-Conrad, W.; Brust, P.

[18F]NS10743, a promising and highly competitive α7 nAChR radioligand has been synthesised so far by microwave irradiation using a manual single-mode device followed by a palladium-catalyzed reduction of remaining nitro-precursor for HPLC separation purposes. For further preclinical and clinical use, regulated production of [18F]NS10743 by fully automated radiosynthesis is a crucial requirement. Therefore, we chose a commercial synthesis module and developed the automated radiosynthesis of [18F]NS10743. Besides evaluation of several radiosynthesis procedures, we performed an extensive HPLC study for quantitative separation of [18F]NS10743 from the corresponding nitro precursor. After implementation of the optimised procedure on a TRACERlabTM FX F-N synthesis module, [18F]NS10743 was obtained in high radiochemical purity (≥ 99%) with an overall radiochemical yield of 32.27% (n=3). The specific activities at the end of the synthesis were 571±17 GBq/µmol (n=3).

Keywords: Alpha-7 nicotinic acetylcholine receptor radioligand; Pet WAVE microwave CEM; radiofluorination; automated radiosynthesis; TRACERlabTM FX F-N

Publ.-Id: 20964

Kurzzeit-Spektroskopie an Halbleiter-Quantenstruktren am Freie-Elektronen-Laser FELBE

Winnerl, S.; Mittendorff, M.; Teich, M.; Jacob, R.; Schneider, H.; Helm, M.

Der mittlere Infrarot- und Terahertz-Bereich bietet Zugang zu einer Vielzahl von faszinierenden Effekten in Halbleiter-Quantenstrukturen, da in diesem Spektralbereich eine Vielzahl von elementaren und kollektiven Anregungen wie z. B. Phononen, Plasmonen und Intersubbandübergängen liegen. Der Freie-Elektronen-Laser FELBE ist durchstimmbar im Bereich von 1 – 80 THz und liefert einen kontinuierlichen Zug von intensiven, schmalbandigen Pikosekundenpulsen, die sich ideal für nichtlineare Spektroskopie und resonante Anregung eignen. Wir zeigen exemplarisch Experimente an zweidimensionalen und nulldimensionalen Systemen und diskutieren sie hinsichtlich spektraler, zeitlicher und räumlicher Auflösung. Insbesondere wird die Ladungsträgerdynamik in selbstorganisierten Halbleiter-Quantenpunkten sowie Spektroskopie an einzelnen Quantenpunkten gezeigt [1-3]. Weiterhin stellen wir Resultate zur Ladungsträgerdynamik in Graphen vor [4,5]. Die Untersuchungen geben wichtige Einblicke in das Verhalten von Ladungsträgern auf kurzen Zeitskalen, insbesondere zu ihrer Phasenkohärenz, ihrer Wechselwirkung untereinander und ihrer Wechselwirkung mit Phononen. Neben der grundlegenden Bedeutung ist die Kenntnis er Kurzzeitdynamik wichtig für die Entwicklung zukünftiger optoelektronischer Bauelemente wie Detektoren, Strahlungsquellen und Elementen zur Informationsspeicherung in Quantencomputern.

[1] E. A. Zibik et al., Nature Mat. 8, 803 (2009).
[2] M. Teich et al., Appl. Phys. Lett. 103, 252110 (2013).
[3] R. Jacob, Nano Lett. 12, 4336 (2012).
[4] S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011).
[5] M. Mittendorff et al., Nature Phys. (under review).

Related publications

  • Invited lecture (Conferences)
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten 2014 (SNI 2014), 21.-23.09.2014, Bonn, Deutschland

Publ.-Id: 20963

Anisotropy of absorption bleaching and carrier relaxation in graphene

Winnerl, S.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.

In the energy region between –1 eV and 1 eV the band structure of graphene is in good approximation described by identical isotropic Dirac cones for electrons and holes, respectively. Therefore, optical properties for interband excitations are typically considered to be isotropic for photon energies below 2 eV. However, our pump-probe experiments at a photon energy of 1.6 eV reveal a pronounced anisotropy in both the excitation characteristics and the subsequent relaxation dynamics. The anisotropy with 2-fold symmetry is induced by the linear polarization of the pump radiation. We compare the experimental results with calculations based on the density matrix formalism and show that optical phonons are mainly responsible for reaching an isotropic carrier distribution.
In the experiments, carried out on multilayer epitaxial graphene, the angle between the polarization of pump and probe beam was varied. Pumping and probing with parallel polarization resulted in two times larger pump-induced transmission as compared to pumping and probing with orthogonal polarization [1]. The initial relaxation after the transmission maximum is faster in the parallel polarization configuration. For time delays larger than 150 fs the induced transmission is similar for the two polarization configurations, indicating that an isotropic carrier distribution is reached. The observed anisotropy in the induced transmission is direct evidence for an anisotropic carrier distribution in k-space. This anisotropy has been predicted by theory [2]. Carriers are preferentially excited in directions perpendicular to the polarization vector of the pump beam. Microscopic modelling, which describes the experimental finding well, allows us to attribute the fast initial relaxation to collinear carrier-carrier scattering. Scattering via optical phonons is mainly responsible for reaching an isotropic distribution.
The results are of fundamental importance as they concern an aspect of the carrier dynamics that has escaped experimental observation so far, despite the large number of publications describing near-infrared pump-probe experiments on graphene. With respect to applications our findings may enable all-optical switches that react differently to pulses of different polarization direction.

[1] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W.A. de Heer, H. Schneider, and M. Helm, Nano Lett. (2014)
[2] M. Malic, T. Winzer, and A. Knorr, Appl. Phys. Lett. 101, 221115 (2012).

Keywords: Carrier dynamics; ultrafast spectroscopy; graphene

Related publications

  • Poster
    Graphene Week, 23.-27.06.2014, Goteborg, Sweden

Publ.-Id: 20962

Time-resolved spectroscopy on Landau-quantized graphene revealing strong Auger scattering

Winnerl, S.; Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.

The carrier dynamics within the system of Landau levels of index n = -1 to n = 0 and n = 1 in graphene is investigated by pump-probe experiments using circularly polarized terahertz radiation. The study, complemented by microscopic modelling, reveals a pronounced carrier redistribution caused by strong Auger scattering.

Keywords: Carrier dyanmics; ultrafast spectroscopy; graphene; Landau quantization; Auger scattering

Related publications

  • Lecture (Conference)
    4th EOS Topical Meeting on Terahertz Science & Technology (TST 2014), 11.-14.05.2014, Camogli, Italia

Publ.-Id: 20961

THz spectroscopy of solids using a free-electron laser

Helm, M.

I will start describing the Dresden free-electron laser FELBE as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in solids. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will mainly discuss nonlinear experiments on excitons in semiconductor quantum wells and pump-probe studies of the relaxation dynamics in graphene. I will conclude with an outlook on further developments, including the superradiant THz radiation source TELBE.

Keywords: free-electron laser; terahertz; quantum wells; graphene

Related publications

  • Lecture (others)
    Seminarvortrag am Fritz-Haber-Institut (FHI), Berlin, 20.10.2014, Berlin, Germany

Publ.-Id: 20960

Development of a labeling system for microorganisms based on antimicrobial peptides

Barthen, R.; Mickein, K.; Kutschke, S.; Pollmann, K.; Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.

Complex biogeochemical processes are essential in various subsurface ecosystems (like in soils and rock formations), and are relevant for e.g. effective bioleaching of metals from various ores. For an improved mechanistic understanding of biogeochemical processes a non-invasive detection method of present microorganisms in a given geological sample is crucial. Ideally, microorganisms from all kingdoms should be determined in a single step (and may be later differentiated from DNA or cell degradation). Furthermore, microbial responses to changes of the physical or chemical conditions of the system such as flow regime, pH, and nutrient concentrations could be addressed non-invasively.
Our strategy for in-situ identification of microorganism in geological samples is to use labeled antimicrobial peptides (AMPs) as selectively binding agents. In the nuclear medical sciences, this strategy is successfully applied for the identification and visualization of bacterial infections in humans [1]. We aim at tagging the AMPs first with fluorescent dyes, in a later step with the radionuclide 18F for imaging with positron emission tomography (PET).
For our study, AMPs are selected based on their ability to bind to the cells of the tested bacterial strains in sub-lethal concentrations while their sorption to matrix compounds is minimal. We show that AMPs readily interact with microorganisms commonly found in soils such as Pseudomonas fluorescence and Lysinibacillus sphaericus. We aim at labeling the AMPs by means of established, commercial crosslinkers.
In combination with our GeoPET method [2-4] 18F-radiolabeled AMPs were an extremely useful agent for the in-situ visualization of microorganisms also in opaque geological environments. Radiolabeled AMPs could be used for the visualization of growth and dispersal of microbial communities in such environments.

  • Lecture (Conference)
    Gemeinsame Jahrestagung der DGHM und der VAAM, 05.-08.10.2014, Dresden, Deutschland

Publ.-Id: 20959

Population dynamics in graphene Landau levels

Helm, M.; Mittendorff, M.; Winnerl, S.; Wendler, F.; Malic, E.; Knorr, A.

Population dynamics in graphene Landau levels

Keywords: graphene; Landau levels; population; pump-probe; free-electron laser; Auger scattering

Related publications

  • Invited lecture (Conferences)
    International Quantum Cascade Lasers School and Workshop 2014, 07.-12.09.2014, Policoro, Italy

Publ.-Id: 20958

A kinetic insight into the formation of neptunium(IV) dioxide NpO2 nanocrystals: a multi-technique study using UV-vis absorption spectroscopy and (high-resolution) transmission electron microscopy

Hübner, R.; Weiss, S.; Hennig, C.; Ikeda-Ohno, A.; Zaenker, H.; Stumpf, T.; Husar, R.

UV-vis absorption spectroscopy proves itself as an convenient method for in-situ monitoring the formation and growth of waterborne An(IV) nanoparticles. Dilution of pure aqueous Np(CO3)56- species in ultrapure water leads to the dynamic self-assembling of NpO2 nanocrystals, monitored among others at absorbance 742 nm.

Nowadays, various state-of-the-art spectroscopic techniques (e.g., X-ray spectroscopies, laser-induced and vibrational spectroscopy, etc.) are available to investigate chemical interactions of actinides (An) on a molecular level. Old-fashioned (or conventional) UV-vis absorption spectroscopy is often underestimated as a powerful tool to investigate the chemistry of An, including An(IV) colloids. The present study spotlights the application of UV-vis absorption spectroscopy to studying the colloid system of An(IV). The chemistry of An(IV) in aqueous solution is typical of a small and highly-charged metal ion with a strong hydrolysis tendency leading low solubility, which often result in the underestimation of the migration behavior of An(IV) on the geological disposal of radioactive wastes. The formation mechanisms of An(IV) colloids?, especially under alkaline and near-neutral conditions relevant to the actual environment, are still unexplored even to date. One important issue to be addressed in An(IV) colloid chemistry is the chemical identification of An(IV) colloids. That is, are the colloids formed ill-defined hydroxide precipitate or hydrous oxides, or highly structured clusters/nanoparticles? In order to characterize An(IV) colloids, we investigated in-situ the aggregation of neptunium(IV) colloids formed under ambient aqueous alkaline conditions. The kinetics of the aggregation of Np(IV) colloids and the formation of Np(IV) nanoparticles were tracked by UV-vis absorption spectroscopy, and their morphology and internal structures were further investigated by transmission electron microscopy (TEM). In this study, we demonstrate that UV-vis absorption spectroscopy is an unique and powerful tool for in-situ monitoring of the hydrolysis reaction of Np(IV) and associated colloid/nanoparticle formation. The obtained results will be further discussed by combining with TEM and X-ray absorption spectroscopy.

Keywords: Neptunium; NpO2; hydrolysis; UV vis; TEM; EXAFS; DLS

Related publications

  • Poster
    ATAS - advanced techniques in actinide spectroscopy, 03.-07.11.2014, Dresden, Deutschland

Publ.-Id: 20957

Intrinsic Formation of Neptunium Nanoparticles in Presence and Absence of Silica: Formation of Np(IV)-silica Colloids and NpO2 Nanocrystals

Husar, R.; Hübner, R.; Hennig, C.; Weiss, S.; Ikeda-Ohno, A.; Zänker, H.; Stumpf, T.

The chemistry of tetravalent actinides An(IV) in aqueous solution is typical of a small highly-charged metal ion with a strong tendency to hydrolize and therefore a low solubility. Disregarding the formation of clusters, nanoparticles and colloids lead to underestimation of the migration behavior. The reaction mechanisms of formation and growth, especially under alkaline and near-neutral environmental conditions are still unexplored. On the way from aqueous species to nanoparticles two fundamental questions in An(IV) chemistry provoke discussion in literature: 1) are hydrolysis and condensation the driving forces toward nano-scaled solids or 2) are formed aggregates ill-defined complex hydroxides, hydrous oxides or highly structured clusters/nanoparticles? Excluding the presence of other oxidation states then An(IV), we performed in situ investigation of the self organised formation of neptunium(IV) aggregates and nanoparticles from aqueous complex precursor under alkaline conditions. The kinetics of the self-assembling of the nanoparticles, their morphology and internal structures were determined. The influence of silica on the formation of highly coordinated NpO2 structure was proved. In particular, former studies confirmed the formation of amorphous silica-containing U(IV) and Th(IV) colloids. Starting from aqueous neptunium(IV) carbonate complexes, we investigated the behavior after dilution in presence and absence of silica by TEM, EXAFS, UV vis spectroscopy, Ultrafiltration and DLS (dynamic light scattering). The formation of nanoparticles was observed. TEM and diffraction pattern show different morphologies and internal structures in dependence of presence or absence of silica.

Keywords: Neptunium; Np(IV); nanoparticles; colloids; An(IV); hydrolysis; neptunium carbonate complex

Related publications

  • Poster
    Plutonium Futures 2014 - the science, 07.-12.09.2014, Las Vegas, USA

Publ.-Id: 20956

Der Salzschmelzenreaktor als Transmutationssystem vor dem Hintergrund des Kernenergieausstiegs

Merk, B.

Salzschmelzenreaktoren besitzen eine lange Historie, zurückgehend auf mehrere Experimente am Oak Ridge Mational Laboratory, die bereits in den 50er und 60er Jahren stattfanden. Das bekannteste hiervon ist das Molten Salt Reactor Experiment (MSRE). Das Konzept des Salzschmelzenreaktors verschwand danach aus dem wissenschaftlichen Fokus. Um die Jahrtausendwende wurde das Konzept dann von russischer und von europäischer Seite wieder aufgegriffen. Zusätzlich wurde das Konzept des Salzschmelzenreaktors im Rahmen des Generation IV International Forums (GIF) als eines der 6 Reaktorkonzepte verankert.
Mit Hinblick auf das Ziel Sustainability des GIF hat sich bereits nach kurzer Zeit eine Verschiebung des Konzeptes für Salzschmelzenreaktoren ergeben. Derzeit untersuchte Reaktoren sind als sogenannte schnelle Systeme ausgelegt und besitzen in im Gegensatz zum MSRE keine Graphitstrukturen innerhalb des Reaktorkerns. Salzschmelzenreaktoren mit schnellem Neutronenspektrum eigenen sich aber nicht nur zur Energieproduktion, sondern sind auch als Transmutationssystem von Interesse und bieten für diesen speziellen Einsatz diverse Vorteile.
Im Vortrag werden die wichtigsten Unterschiede von Reaktoren mit festem Brennstoff (z. B. Sodium Cooled Fast Reactor) und Reaktoren mit flüssigem Brennstoff analysiert und diskutiert. Darauf aufbauend werden die spezifischen Vorteile von Salzschmelzenreaktoren für die Transmutation hergeleitet und die spezifischen Herausforderungen erörtert. Ein besonderer Blick gilt auch den Konsequenzen die sich durch das veränderte Neutronenspektrum, im Vergleich zum MSRE, ergeben.
Abschließend werden ausgewählte neueste wissenschaftliche Ergebnisse zu Salzschmelzenreaktoren vorgestellt. Es wird ein kurzer Einblick in die Ergebnisse der deutschen P&T Studie gegeben und die daraus resultierenden Konsequenzen auf eventuelle zukünftige Forschungsarbeiten zu Salzschmelzenreaktoren beleuchtet.

An overview on the history of molten salt reactors and the projects of the last years is given. The major advantages of molten salt reactors in the view of transmutation are discussed and evaluated in comparison with sodium cooled fast reactors. Finally some scientific highlights are given for the application of molten salt reactors under the bounday conditions of the nuclear ophase out decission in Germany.

Keywords: nuclear; nuclear reactor; molten salt; molten salt reactor; fast reactor; transmutation; nuclear waste management

  • Invited lecture (Conferences)
    Seminar an der RWTH Aachen, 08.07.2014, Aachen, Deutschland

Publ.-Id: 20955

On an optimized neutron shielding for an advanced molten salt fast reactor design

Merk, B.; Konheiser, J.

The molten salt reactor technology has gained renewed interest. In contrast to the historic molten salt reactors, the current projects are based on designing a molten salt fast reactor. Thus the shielding becomes significantly more challenging than in historic concepts. One very interesting and innovative result of the most recent EURATOM project on molten salt reactors – EVOL – is the fluid flow optimized design of the inner core vessel using curved blanket walls. The developed structure leads to a very uniform flow distribution. The design avoids all core internal structures. On the basis of this new geometry a model for neutron physics calculation is presented and applied for a shielding optimization. Based on these results an optimized shielding strategy is developed for the molten salt fast reactor to keep the fluence in the safety related outer vessel below expected limit values. A lifetime of 80 years can be assured, but the size of the core/blanket system has to be significantly increased and will finally be comparable to a sodium cooled fast reac-tor. The HELIOS results are verified against Monte-Carlo calculations with very satisfactory agreement for a deep penetration problem.

Keywords: fast reactor; molten salt reactor; neutron shielding; neutron transport; HELIOS; optimization

  • Contribution to proceedings
    PHYSOR 2014 – The Role of Reactor Physics Toward a Sustainable Future, 28.09.-03.10.2014, Kyoto, Japan
  • Lecture (Conference)
    PHYSOR 2014 – The Role of Reactor Physics Toward a Sustainable Future, 28.09.-03.10.2014, Kyoto, Japan

Publ.-Id: 20954

On the use of a molten salt fast reactor for transmutation fulfilling the requests of the nuclear phase out decision

Merk, B.

The 'Energiewende' in Germany has put some questions on the future of the P&T research. The Bundesministerium für Wirtschaft Energie and the Bundesministerium für Bildung und Forschung have launched a study in 2012 to answer these questions on a broad scientific basis. A major point during the discussions was the so-called last transmuter problem. This requires special attention in the case of the nuclear phase out, since transmutation of transuranium isotopes is only attractive under the phase out condition when this problem can be solved. Recently, a solution has been proposed, the so-called twofold operation cycle using a molten salt fast reactor.
Based on this proposal a simulation for the burning of the 170t TRUs remaining in Germany after the phase out as efficient as possible. A salt configuration based on the MOSART composition is used which is able to carry the required amount of TRUs for the fertile free operation. The requested number of reactors, the required operation time and the expected TRU leftovers are determined. Finally, a general discussion is added which major R&D topics would have to be envisaged for the realization of P&T in a molten salt fast reactor.

Keywords: nuclear; nuclear reactor; molten salt; molten salt reactor; transmutation; nuclear waste management

  • Contribution to proceedings
    Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland

Publ.-Id: 20953

Results and conclusions from the German P&T study – a view of the contributing Helmholtz research centres

Merk, B.; Geist, A.; Modolo, G.; Knebel, J.

The governmental decision for the 'Energiewende' has put some urgent questions on the future of the P&T research. The Bundesministerium für Wirtschaft und Energie and the Bundesministerium für Bildung und Forschung have launched a study managed by acatech in 2012 to answer these questions on a broad scientific basis. The major mandate was to evaluate scientific and technological as well as socio-economic challenges and opportunities of the P&T technology in the view of the phase out decision. The main topics were:

  • Starting point and boundary conditions – waste amounts and final disposal strategies
  • Definition and description of scenarios – possible ways for transmutation in the view of the phase out, European vs. national
  • Technological challenges of P&T – description of the major challenges to be solved on the way to industrial application
  • Current status of R&D – discussion of possible transmutation systems, current R&D status of P&T, development gaps, and future research strategy
  • Safety aspects – special safety aspects including all steps of the P&T cycle
  • International projects & competences in Germany – what is going on around the world and what can be served by the German industry
The socio-scientific, the ecologic, and the economic aspects have been analyzed in parallel using expert interviews, group Delphi, and independent expert opinions on economic, legal, and environmental aspects.
An overview on the results of the study in the view of the contributing Helmholtz research centers (KIT, HZDR, and FZJ) is given. Special focus is put on the political recommendations and the developed research strategy which has been proposed to the ministries. Finally the conclusions of the Helmholtz-Centres regarding their current and future activities are given.

Keywords: nuclear; nuclear waste; nuclear reactors; nuclear waste management; partitioning; transmutation

  • Contribution to proceedings
    Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland

Publ.-Id: 20952

Extraction of valuables from tailings disposals

Leißner, T.; Osbahr, I.; Mütze, T.; Peuker, U. A.

Mining in the Ore Mountains (Germany) has taken place for hundreds of years and in several stages. Each stage produced its typical tailing. According to the former state of the art of the processing much valuables could not be extracted. This was caused by complex interlocking of the minerals, low grades, or by upgrading processes not sensitive enough for small particle sizes. Thus the processing of these fractions was uneconomically. Modern technical possibilities and rising metal prices bring these tailings disposals into focus for the processing of strategic metals.
Mining disposals can be classified in heaps with coarse, low grade rock, which did not undergo a processing, slags and fly ash from smelting, and tailing disposals from mineral processing. The latter is under investigation to integrate them into a geographic information system. The mineral processing of the material will be part of the database besides information about geographic location, structure, amount of valuables, and details of ownership of the heap.
The tailings disposals are composed of coarse, low grade, interlocked particles from density separation processes, medium size particles, which are tailings from flotation, and fines with liberated valuables, which did not undergo flotation. Therefore mineral processing of these disposals comprises the separation of liberated gangue by classification, beneficiation of locked valuables with density separation, liberation of valuables by grinding, and beneficiation of liberated valuables with flotation. The presented work shows the results concerning the composition of one exemplary heap and results of the classification as well as of the preconcentration tests achieved with material from this heap.

  • Contribution to proceedings
    XXVII Internationl Mineral Processing Congress, 20.-24.10.2014, Santiago, Chile: Gecamin

Publ.-Id: 20951

Hydrodynamics of co-current two-phase flow in an inclined rotating tubular fixed bed reactor – Wetting intermittency via periodic catalyst immersion

Härting, H.-U.; Bieberle, A.; Lange, R.; Larachi, F.; Schubert, M.

The hydrodynamics of an inclined rotating tubular fixed bed reactor operated with gas–liquid co-current downflow are studied. Reactor inclination is applied to force phase segregation, while the superimposed rotation of the reactor results in a wetting intermittency via periodic catalyst immersion. The fixed bed is clamped to avoid abrasion of the catalyst. The inclined rotating reactor is presented as a new reactor concept for process intensification of heterogeneous catalytic reactions requiring enhanced mass transfer of the gaseous phase and partial catalyst wetting.
Four different flow regimes with stratified, sickle, annular and dispersed flow patterns are determined experimentally by applying a compact gamma-ray computed tomography system. The effects of (i) gas and liquid superficial velocities, (ii) inclination angle and rotational velocity of the reactor and (iii) physico-chemical properties of the liquid phase on the occurrence of the flow regimes are investigated. The results of these investigations are illustrated with flow maps. In addition, pressure drop and liquid saturation depending on the operating conditions are shown.


  • A new tubular reactor concept for process intensification is introduced.
  • Reactor inclination and rotation allow for wetting intermittency via periodic catalyst immersion.
  • Flow regimes can be adjusted by reactor inclination and rotation independent of liquid saturation.
  • Lower pressure drops can be achieved in comparison to trickle bed reactors.

Keywords: Fixed bed hydrodynamics; Process intensification; Flow regimes; Multiphase flow; Gamma-ray computed tomography

Publ.-Id: 20950

AMNT 2014: Key Topic Reactor Operation, Safety - Report Part 2

Fischer, K. C.; Höhne, T.; Hollands, T.; Schuster, C.; Traichel, A.; Willschütz, H. G.; Wortman, B.

Report on the following sessions of the Annual Conference on Nuclear Technology held in Frankfurt, 6 to 8 May 2014:

Thermo Dynamics and Fluid Dynamics: Experiments and Backfittings for the Improvement of Safety and Efficiency Safety of Nuclear Installations - Methods, Analyses, Results: In-Vessel Phenomena; Ex-Vessel Phenomena; Standards and Regulations; Hazard and Safety Analysis; and Validation and Uncertainty Analysis.
The other Sessions of the Key Topics "Reactor Operation, Safety", "Competence, Innovation, Regulation" and "Fuel, Decommissioning & Disposal" have been covered in atw 10 (2014) and will be covered in further issues of atw. "

Keywords: Numerical Methods; Models; Codes

  • atw - International Journal for Nuclear Power 59(2014)12, 701-702
    ISSN: 1431-5254

Publ.-Id: 20949

Mineral Processing of Lithium-bearing Mica.

Leißner, T.; Rode, S.; Bachmann, K.; Gutzmer, J.; Peuker, U.

This contribution deals with the mineral processing of Li-silicate greisen-type ores comprising of quartz, topaz and zinnwaldite (lithium-rich mica). The origin of the greisen-type ores processed is the Ore Mountains(Germany) where it is explored as a potential resource for the production of lithium carbonate. The goal is to develop a process chain for the enrichment of zinnwaldite using dry techniques only. As basis for the investigation the process chain, which historically was used to process the greisen focused on cassiterite and wolframite, is taken and modified towards the zinnwaldite.
Starting with crushed material with particle sizes smaller than 35 millimeters, investigations on different approaches to grinding to liberate mica from gangue are carried out. Concentrates of zinnwaldite are then produced by magnetic separation of size fractions. To assess the success of grinding, classification and separation, mineral liberation analysis and atomic absorption spectroscopy are used. The amount of lithium measured in the sample with atomic absorption spectroscopy was used to calculate the content of zinnwaldite based on its known mineral chemistry. Combined with the particle size distributions, product qualities are determined. Altogether, this allows the thorough evaluation of the success of comminution with focus on following steps of concentration.

Keywords: lithium; zinnwaldite; magnetic separation; mineral liberation analysis

  • Lecture (Conference)
    International Mineral Processing Congress, 24.-28.09.2012, New Delhi, India

Publ.-Id: 20948

Recent advances in structural geology, lithogeochemistry and exploration for VHMS deposits, Kristineberg area, Skellefte District, Sweden.

Jansson, N.; Hermansson, T.; Persson, M.; Berglund, A.; Kruuna, A.; Skyttä, P.; Bachmann, K.; Gutzmer, J.; Chmielowski, R.; Weihed, P.

Kristineberg is the largest mine and VHMS deposit in the Palaeoproterozoic Skellefte District, Sweden. The deposit was discovered in 1918, and it has been mined since 1941. Besides the Kristineberg deposit, several other VHMS deposits have been mined in the Kristineberg area. Despite the long history of mining, significant advances are still being made in terms of exploration and understanding the geological framework of the ore bodies. A key to this success has been persistence in exploration and a combination of local and regional scale geological, geophysical and geochemical surveys. Holistic industry-university collaborative research projects have furthermore played an important role in bringing together geologists and geophysicists from different disciplines to tackle the large-scale geological framework. Among other things, these projects have resulted in the first structural geological 3D model of the Kristineberg area, better age constraints on the formation of the deposits, a regional alteration map as well as ongoing work to model alteration in 3D. This contribution summarizes the results of these investigations and recent exploration.

Keywords: Kristineberg; Skellefte District; VHMS; 3D modelling; Exploration

  • Poster
    12th Biennial SGA Meeting: Mineral deposit research for a high-tech world, 12.-15.08.2013, Uppsala, Sweden

Publ.-Id: 20947

Alteration in the area of the Kristineberg VHMS deposit, Skellefte district, Sweden.

Bachmann, K.; Gutzmer, J.; Persson, M.; Jansson, N.

The Skellefte district in north-central Sweden is one of the most important mining districts in northern Europe. It contains over 85 pyritic Zn-Cu-Au-Ag massive sulphide deposits of which 21 deposits have been mined since 1924 and 4 are still in operation by Boliden Mineral AB. The most productive deposit, the Kristineberg mine, has been operated by Boliden since 1940 with a current annual production of 670,000 t of polymetallic ore containing 3.0 wt.-% Zn, 0.7 wt.-% Cu, 0.4 wt.-% Pb, 1.9 g/t Au and 47 g/t Ag. Alteration of the volcanic rocks around the Kristineberg deposit is very intense. The main aim of this study has been to describe the alteration intensity and to define alteration trends around the Kristineberg deposit. The success of this approach provides a new exploration tool for future exploration in the Skellefte District where alteration renders the recognition of primary volcanic facies difficult.

Keywords: Kristineberg; Skellefte district; VHMS; alteration

  • Poster
    12th Biennial SGA Meeting: Mineral deposit research for a high-tech world, 12.-15.08.2013, Uppsala, Sweden

Publ.-Id: 20946

Raman spectroscopy – casting (laser) light on microbe – mineral interactions

Kostudis, S.; Kutschke, S.; Pollmann, K.

Highly efficient and sustainable mining strategies gain importance due to the fact that available resources of base metals like copper but strategic elements such as gallium and molybdenum as well face a steadily decreasing grade. This issue is enhanced by the increased demand and production amounts of those metal compounds. Biohydrometallurgy – the use of microorganisms or related substances in metal extraction - provides the potential of processing low grade ores efficiently. Thus it is applied yet in some gold and uranium mining.
Also due to strategic reasons mining of regional resources such as the European Kupferschiefer come to the fore. Its complex composition including sulphide rich ores, carbonates and organic compounds challenges biotechnological approaches. Nevertheless promising approaches have been reported. We examine heterotrophic bioleaching of copper from Kupferschiefer ores. To investigate the interactions between mineral surface and microorganisms Raman spectroscopy offers a versatile applicability: Identification of minerals and differentiation of microorganisms is nicely provided and is accompanied by imaging opportunities in a two or even three dimensional manner. Thus biofilms, for example, can be analysed with respect to microbial diversity or preferences of minerals during the attaching process.

  • Poster
    Microbiology and Infection, 05.-08.10.2014, Dresden, Deutschland

Publ.-Id: 20945

Evaluation of mineral processing by assessment of liberation and upgrading.

Leißner, T.; Mütze, T.; Bachmann, K.; Rode, S.; Gutzmer, J.; Peuker, U.

A model is presented to evaluate mineral processing on basis of gangue recovery and valuables recovery. It combines mineralogical limiting curves with upgrading curves in the Fuerstenau diagram. These curves are used to assess mineral liberation and mineral beneficiation compared with the ideal result. Two new parameters (ratio of separation and ratio of liberation) are calculated based on a comparison of areas enclosed by the mineralogical limiting curve, the upgrading curve, the curve representing a total liberation of valuables, and the curve representing a perfect mixture of valuables and gangue.
An assessment of the success of mineral processing is possible using these parameters. The assessment shows whether the quality of a separation product is influenced by the separation process itself or by the achieved liberation of the feed.
A series of experiments on the magnetic separation of a greisen-type ore proves the applicability of this model to mineral processing. SEM-based image analysis and ICP-OES measurements have been used to obtain the necessary data.

Keywords: liberation; upgrading; separation; mineral liberation analysis

Publ.-Id: 20944

Discrimination of hematite and magnetite in finely intergrown natural iron ores by automated mineralogy.

Bachmann, K.; Bartzsch, A.; Gutzmer, J.

Providing a fast, quantitative characterization of iron ores in terms of liberation, grain sizes and shapes as well as mineral association remains a big challenge. Whilst quantitative mineralogical data are easily attained by QXRD, an automated SEM-EDS based approach is needed for the quantification of relevant microfabric attributes. Two different iron ores were investigated for this study, to illustrate the capabilities and limitations of the latter approach. The first example is a banded-iron formation (BIF) ore from Thabazimbi/RSA, the second ore type studied is a magnetite iron ore from Svappavaaragruvan, c. 50 km east of Kiruna/N-Sweden. The greatest difficulty in the characterization of iron ores is certainly the discrimination between different relevant iron oxides (magnetite, hematite, goethite) that are all of very similar elemental composition – and thus have both very similar backscattered electron (BSE) brightness, as well as almost identical EDS spectra. A principle approach was suggested by Figueroa et al. (2011) by using the Mineral Liberation Analyzer (MLA). The suitability of this method was illustrated on synthetic mixtures. The approach of the present study utilizes the method on thin sections of natural iron ores, which show a fine intergrowth of hematite and magnetite with an unknown composition. For calibration, an in-house magnetite and hematite standard was prepared to further optimize the set-up of the method. A new feature in the MLA suite v.3.1.4 is the capability to define the exact working distance for every single sample separately. Slight variations in the working distance between the different samples and the standard were equalized. The MLA results were compared to bulk chemical data as well as traditional point counting-data by reflected light-microscopy. The results are within a relative error of 5 %. It can be concluded that the method was successfully applied and can be applied to iron ores with complex oxide mineral associations.

  • Poster
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today - Practical Aspects, 22.-24.09.2014, Leoben, Austria

Publ.-Id: 20943

Li isotopes and geochemistry of Li–F–Sn greisen from the Zinnwald deposit.

Bachmann, K.; Seifert, T.; Magna, T.; Neßler, J.

The Sn–W greisen deposits, located in the eastern part of the Variscan metallogenic Erzgebirge province (zinnwaldite Ar–Ar ages between 313 and 315 Ma), are emplaced in highly metamorphosed and/or igneous rocks and typically are associated with post-collisional Li–F-enriched small granitic intrusions. This metallogenic province traditionally belonged to the major source of economic Sn, Ag, U, W, Co and fluorite–barite deposits for central Europe. The Zinnwald/Cínovec Li–Sn greisen deposit is associated with a unique zinnwaldite–quartz–topaz mineralization hosted by an albitized stock-granite.
Li contents and isotope compositions were measured in host albite granites (n=2), greisens (n=3), and a sample from a flat-dipping vein in the Zinnwald deposit, paralleled by individual mineral phases. All investigated bulk rocks have extreme Li contents reaching from 1,600–2,200 ppm in albite-granite, to 3,400–6,200 ppm in greisen-type rocks and to ~8,000 ppm in a vein-type sample, most likely carried by zinnwaldite (15,000–19,200 ppm) and muscovite (9,500–15,700 ppm) whereas albite and quartz, in particular, have significantly lower Li abundances (560–660 and 33–330 ppm, respectively). The high bulk Li contents are very unusual even for chemically evolved granitic systems with the exception of Li-rich pegmatites. Bulk 7Li values are restricted (–1.0 to 0.3 ‰), consistent with late orogenic granites from a larger area of the Erzgebirge Mts.. Zinnwaldite and muscovite carry isotopically heavy Li relative to the corresponding bulk rocks and, at the same time, muscovite always is slightly heavier than zinnwaldite. 7Li values of quartz become progressively heavier from granites through greisens to a vein sample. Zinnwaldite may represent a late-stage ingress of Li-rich fluids/melts rather than indigenous phase of these lithologies because from mass balance considerations and mineral modes, bulk [Li] and 7Li values cannot easily be reconstructed for either sample of the suite.

  • Poster
    Goldschmidt2014, 08.-14.06.2014, Sacramento, USA

Publ.-Id: 20942

Method for evaluation of upgrading by liberation and separation.

Leißner, T.; Mütze, T.; Anatasova, P.; Bachmann, K.; Peuker, U.

A method is presented for the evaluation of mineral processing by liberation and upgrading. The method bases on the plot of recovery of valuables versus the recovery of gangue (Fuerstenau upgrading curve). The locking curve of a feed material was plotted together with the upgrading curve in a Fuerstenau diagram. The assessment of liberation and upgrading is done by a comparison of surfaces formed by the curves and some characteristic lines of the diagram. This plot allows the calculation of two new quantitative measures for liberation and upgrading.
Both parameters can be combined to a third parameter describing the quality of the whole technical setup for mineral processing by subtracting the upgrading parameter from the liberation parameter. The third parameter shows a positive value in cases of upgrading determined processes, a negative value in cases of liberation affected processes and about zero for processes affected equally by liberation and upgrading. Thus it is easily possible to distinguish between poor results in the mineral processing caused by insufficient liberation or poor results caused by insufficient upgrading.
Preliminary results from two case studies, performed on two completely different ore types, are very promising illustrating the practical use of such an approach.

  • Lecture (Conference)
    International Mineral Processing Congress, 20.-24.10.2014, Santiago, Chile

Publ.-Id: 20941

WASA-BOSS: ATHLET-CD model for severe accident analysis for a generic KONVOI reactor

Tusheva, P.; Schäfer, F.; Kozmenkov, Y.; Kliem, S.; Hollands, T.; Trometer, A.; Buck, M.

The work described in this paper is a part of the ongoing joint research project WASA-BOSS, Weiterentwicklung und Anwendung von Severe Accident Codes – Bewertung und Optimierung von Störfallmaßnahmen, aiming at investigation of severe accident scenarios and severe accident management measures in boiling water reactors (BWR) and pressurized water reactors (PWR) [1]. The GRS, IKE and HZDR cooperation is focused on the development of an ATHLET-CD (Analysis of THermal-hydraulics of LEaks and Transients – Core Degradation) code model for a generic PWR of type KONVOI, including investigations of core degradation scenarios and possible accident management. This paper discusses the possible accident management measures (AMM), the ATHLET-CD model as well as the first preliminary simulations for a station blackout (SBO) scenario without and with application of countermeasures.

Keywords: severe accidents; AMM; ATHLET-CD

  • Contribution to proceedings
    Jahrestagung Kerntechnik/Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik/Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Germany
  • atw - International Journal for Nuclear Power 60(2015)7, 442

Publ.-Id: 20940

Multifunctional S-layer proteins as building blocks for hybrid materials

Weinert, U.; Günther, T.; Lehmann, F.; Vogel, M.; Suhr, M.; Matys, S.; Bobeth, C.; Kutschke, S.; Pollmann, K.; Raff, J.

Nanostructured bio-inorganic hybrid materials are very attractive for technical applications, e.g. nanocatalysts, photocatalytic materials, sensors and filter systems. Self-assembling biomolecules like Surface layer (S-layer) proteins represent a promising tool as hybrid material due to their ability to self-assembly in aqueous solutions and on surfaces. In nature S-layer proteins coat the bacterial and archaeal cells with a highly ordered nanostructure and defined symmetry and fulfill various functions, e.g. protection, binding matrix for exoenzymes and molecular sieves. Isolates, which were taken from a uranium mining waste pile in Saxony, produce S layer proteins to protect themselves from heavy metals and radionuclides. If the S layer proteins are saturated with heavy metals or radio nucleotides, the protein will be rejected and a new one will be produced.

We take advantage of the high affinity to heavy metals to produce hybrid filter materials from micro sieves and S-layers. The so called “S-sieves” will be able to bind heavy and noble metals from aqueous solutions even in low concentration ranges economically.

Another aspect will be the synthesis of Pd, Pt and Au nanoparticles on S-layer proteins. Pd and Au nanoparticles were built in the pores of S-layer proteins. Due to that a surface of nanoparticles of a defined size and regularly arrangement can be constructed. Those surfaces will work as nanocatalysts for many technical applications, e.g. the production of CNTs which has already been demonstrated.

Further work deals with the design of a hybrid materials which will work as photocatalysators for drinking water purification. Especially pharmaceuticals can be disintegrated by radicals. The radicals are formed in sunlight and in presence of the catalytic active ZnO- or TiO2-nanoparticles which are coupled and regularly arranged on S-layer protein interface.

These three examples emphasize the use of S-layer proteins their potential in nanotechnology and will give new prospective in the mentioned techniques.

Keywords: hybrid material; s-layer; nanaoparticles; filter material; nanocatalysts

  • Lecture (Conference)
    Multifunctional S-layer proteins as building blocks for hybrid materials, 23.-25.09.2014, Darmstadt, Deutschland

Publ.-Id: 20939

Bioinspired hybrid nanomaterials based on self-assembling proteins

Weinert, U.; Lederer, F.; Günther, T.; Lehmann, F.; Drobot, B.; Vogel, M.; Pollmann, K.; Raff, J.

Many microorganisms like bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins (Fig. 1a) bind toxic metals and metalloids and thusly protect the cells from being damaged by these elements. On other cells, S-layers may act for example as immobilization matrix for exoenzymes, as molecular sieve or as ion and molecule trap.
These properties and their ability to self-assemble in suspension, on surfaces and at interfaces qualify S-layers as interesting building blocks for the construction of new bioinspired nanomaterials for different technical applications. Using the two-dimensional protein arrays, different kinds of surfaces can be nanostructured and novel bio-inorganic hybrid materials with multiple functions can be produced.
Currently three materials are in the focus: metal filters, catalysts and sensors (Fig. 1b). Biocomposites made of microsieves and S-layers are under development to selectively recover strategic metals from aqueous solutions. S-layer proteins with immobilized and regularly arranged metals or metal oxides are useful for diverse catalytic applications. Furthermore, S-layer coatings combining highly specific receptors like aptamers and stable fluorescence dyes are very promising for the construction of new biosensors for organics or pharmaceuticals.
Basis for those materials and their industrial application is an effective production of S-layer proteins. The latter is possible by the extraction of the S-layers from growing cells or by heterologous expression of the proteins. In bacteria or yeasts expressed S-layers can be genetically engineered with molecular modifications to further combine the outstanding S layer protein characteristics with additional expedient features. Native as well as engineered S-layer proteins have an application potential going far beyond above mentioned applications ranging from the chemical industry, water and environmental technologies to medicine.

Keywords: nanoparticles; filter material; S-layer; biosensors; nanocatalysts

  • Lecture (Conference)
    Biomaterials - Made in Bioreactors, 26.-28.05.2014, Radebeul, Deutschland

Publ.-Id: 20938

Correct averaging in transmission radiography: analysis of the inverse problem

Wagner, M.; Hampel, U.; Bieberle, M.

Transmission radiometry is frequently used in industrial measurement processes as a mean to assess the thickness or composition of a material. A common problem encountered in such applications is the so-called dynamic bias error, which results from averaging beam intensities over time while the material distribution changes. We recently reported on a method to overcome the associated measurement error by solving an inverse problem, which in principle restores the exact average attenuation by considering the Poisson statistics of the underlying particle or photon emission process. In this paper we present a detailed analysis of the inverse problem and its optimal regularized numerical solution. As a result we derive an optimal parameter configuration for the inverse problem.

Publ.-Id: 20937

Quantum structure THz photonics and spectroscopy at HZDR

Schneider, H.

Es gibt kein Abstract.

Related publications

  • Lecture (others)
    Seminarvortrag, Centre Suisse d'Electronique et Microtechnique SA (CSEM), 19.09.2014, Neuchâtel, Schweiz

Publ.-Id: 20936

Photoinduzierte Dynamik in der ps Zeit- und THz Frequenz-Domäne

Schneider, H.; Schmidt, J.; Teich, M.; Stephan, D.; Fehrenbacher, M.; Franke, C.; Winnerl, S.; Gensch, M.; Seidel, W.; Helm, M.

Dieser Vortrag stellt die im Rahmen des BmBF-Verbundprojekts PIDID geschaffenen erweiterten Messmöglichkeiten für den Nutzerbetrieb am Freie-Elektronenlaser (FEL) FELBE vor und beschreibt einige exemplarische Experimente. FELBE erlaubt als einziger FEL in Europa einen quasikontinuierlichen Pulsbetrieb, der bei vielen Experimenten zu erheblichen Vorteilen führt im Hinblick auf die Stabilität sowie das Signal-zu-Rauschverhältnis. Aufgrund der Resonatorlänge beträgt die FEL-Pulsrate hierbei 13 MHz (77 ns Pulsabstand). Innerhalb des PIDID-Vorhabens wurden reduzierte Pulsraten (1 kHz bzw. 100 kHz) realisiert, wie sie zur Untersuchung physikalischer Prozesse mit längeren Zeitkonstanten im Bereich µs bis ms benötigt werden. Hierzu wurde ein optischer Schalter aufgebaut, der auf der hohen Reflektivität eines Elektron-Loch-Plasmas beruht, das mittels synchroner optischer Pulse in einem Germaniumkristall angeregt wurde. Des Weiteren wurden ein Fourier-Spektrometer sowie ein Tieftemperatur-Nahfeldmikroskop aufgebaut, die vorwiegend in Teilprojekten der Projektpartner eingesetzt wurden. Im zweiten Teil des Vortrags werden die wichtigsten Messmöglichkeiten an FELBE anhand einiger ausgewählter Experimente dargelegt.

Related publications

  • Lecture (Conference)
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten 2014 (SNI 2014), 21.-23.09.2014, Bonn, Deutschland

Publ.-Id: 20935

Formation of neptunium(IV)-silica colloids at near-neutral and slightly alkaline pH

Husar, R.; Weiss, S.; Hennig, C.; Hübner, R.; Ikeda-Ohno, A.; Zänker, H.

The reducing conditions in a nuclear waste repository render neptunium tetravalent. Thus, Np is often assumed to be immobile in the subsurface. However, tetravalent actinides can also become mobile if they occur as colloidal precipitation products. We show that Np(IV) is able to form silica-rich colloids in solutions containing silicic acid at concentrations of both the regions above and below the “mononuclear wall” of silicic acid at 2∙10-3 M (where silicic acid is expected to start polymerization). These Np(IV)-silica colloids have a size of only very few nanometers and can reach significantly higher concentrations than Np(IV) oxyhydroxide colloids. They can be stable in the waterborne form over longer spans of time. In the Np(IV)-silica colloids the actinide-oxygen-actinide bonds are increasingly replaced by actinide-oxygen-silicon bonds due to structural incorporation of Si. Possible implications of the formation of such colloids for environmental scenarios are discussed.

Keywords: Neptunium; Np(IV)-silica colloids; nanoparticles; EXAFS

Related publications

Publ.-Id: 20934

Low-energy behavior of E2 strength functions

Schwengner, R.

Electric quadrupole strength functions have been deduced from averages of a large number of E2 transition strengths calculated within the shell model for the nuclides 94Mo and 95Mo. These strength functions are compared with phenomenological approximations as provided by the Reference Input Parameter Library (RIPL) for calculations of reaction rates on the basis of the statistical model. The low-energy behavior of the calculated strength functions differs from the one of the phenomenological E2 strength functions and may be used to improve the input for calculations of reaction rates.

Keywords: Photonuclear reactions; photon strength functions; shell model; transition strengths

Publ.-Id: 20933

Monte-Carlo Simulationen zur Untersuchung der Auswirkungen von Quelländerung im Reaktorkern auf die Excore-Instrumentierung

Konheiser, J.

Verschiedene Auswirkungen von möglichen Variationen der Kerngeometrie auf die Signalwerte der Excore-Instrumentierung eines Druckwasserreaktors (DWR) werden in dieser Arbeit gezeigt. Zu diesem Zweck werden Neutronenflüsse für mögliche Brennelementanordnungen mit Hilfe stationären Monte Carlo-Berechnungen außerhalb des Reaktors bestimmt. Typische Daten eines deutschen PWR wurden für die Untersuchungen verwendet.
Unterschiede in den Neutronenflüssen der Excore-Instrumentierung von bis zu 4 % wurden bei Änderungen der Abstände von 1 mm zwischen bestimmten Brennelementen, die im Randbereich des Kerns liegen, berechnet.
Der Grund ist eine verbesserte Moderation von Neutronen, die zu einem höheren Leistung bzw. Neutronenfluss im Randbereich des Kerns führt. Die Folge ist ein höherer Neutronenstrom in Richtung der Excore-Instrumentierung. Dieser Effekt ist Abhängigkeit von Zykluszeitpunkt.
Mögliche Wassertemperaturschwankungen von 1K im Ringspalt, die zu Veränderungen der Wasserdichte und somit des Absorptionsvermögens führen, haben dagegen kaum Auswirkungen auf den Neutronenfluss an der Excore-Instrumentierung.

Effects of possible variations of the core geometry on the signal values of excore instrumentation of a pressure water reactor (PWR) are shown in this work. For this purpose, neutron fluxes outside of the reactor are determined for possible arrangements of fuel assemblies by means of stationary Monte Carlo calculations. Typical data of a German PWR were used for the investigations. Differences in the neutron flux of the excore instrumentation of up to 4% were calculated with changes of the pitch from 1 mm between certain fuel assemblies, which lie in the boundary area of the core. The reason is an improved moderation of neutrons, which results in a higher power and neutron flux in the periphery of the core. The result is a higher neutron flux in the direction of excore instrumentation. This effect is a function of cycle time. Possible water temperature fluctuations of 1 K in the downcomer, which leads to changes in water density and thus in the absorbance, have marginal effect on the neutron flux at the excore instrumentation.

Keywords: excore instrumentation; Monte Carlo calculation; pressure water reactor; neutron flux

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2014
    56 Seiten
    ISSN: 2191-8708, eISSN: 2191-8716

Publ.-Id: 20932

Terahertz spectroscopy of zero- and two-dimensional semiconductor nanostructures with the free-electron laser FELBE

Schneider, H.; Teich, M.; Bhattacharyya, J.; Zybell, S.; Jacob, R.; Winnerl, S.; Helm, M.

The free-electron laser facility FELBE in Dresden, a unique source of intense, quasi-cw, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes, provides unique research opportunities. In high-quality semiconductor quantum wells, we investigate the dynamics of excitons, i.e. two-dimensional, hydrogen-like electron-hole quasi-atoms. Tuning FELBE in resonance with the transition between the excitonic 2s and 2p states (at ca. 2 THz) allows us to study the dynamics of intra-excitonic population transfer. Moreover, strong terahertz pumping results in a characteristic Rabi splitting of the 1s exciton state, which is a manifestation of the intra-excitonic Autler-Townes effect. In semiconductor quantum dots, resonant THz excitation between different sublevels is shown to produce an absorption contrast in aperture-less scattering scanning near-field optical microscopy (s-SNOM). This effect allows us to obtain functional s-SNOM images with deep sub-wavelength resolution, where the contrast originates from far-infrared absorption by single electrons. Quantum dots are also known to have very long electronic relaxation times caused by a reduced phase space for optical phonon scattering. We will report on THz four-wave mixing experiments demonstrating that the associated electronic coherence times approximately equal the population relaxation time at low temperatures. This property makes quantum dots promising for quantum optical applications at THz frequencies.

Keywords: free-electrpn laser

Related publications

  • Lecture (Conference)
    Science@FELs 2014, 15.-17.09.2014, Villigen, Schweiz

Publ.-Id: 20931

QWIP-Based “Ultrafast” Detectors for QCL Research

Schneider, H.

In this talk, I will summarize two approaches for “ultrafast” QWIP-based detection of mid-infrared signals and cover a few examples for practical applications.

Related publications

  • Invited lecture (Conferences)
    International Quantum Cascade Laser School and Workshop 2014 (IQCLSW2014), 07.-12.09.2014, Policoro (Matera), Italien

Publ.-Id: 20930

Intrinsic formation of nanocrystalline neptunium dioxide under neutral aqueous conditions relevant to deep geological repositories

Husar, R.; Hübner, R.; Hennig, C.; Martin, P. M.; Chollet, M.; Weiss, S.; Zänker, H.; Stumpf, T.; Ikeda-Ohno, A.

Nano-sized crystals of neptunium dioxide (NpO2) were prepared successfully based on novel synthetic approach to neutralise a basic Np(IV) carbonate solution. The formation of nanocrystalline NpO2 was monitored by UV/visible absorption and X-ray absorption spectroscopies, and the resultant NpO2 crystals were further characterised by transmission electron microscopy.

Keywords: actinides; neptunium; NpO2; nanocrystals; colloids; formation; UV/visible absorption spectroscopy; X-ray absorption spectroscopy; transmission electron microscopy

Related publications

Publ.-Id: 20928

Selektive Trennung sehr feiner Partikelsysteme mittels Flüssig/Flüssig-Flotation

Leistner, T.; Müller, M.; Erler, J. V.; Rudolph, M.; Peuker, U. A.

Die Vergrößerung des effizienten Anwendungsbereiches von Sortierprozessen in den Bereich feinster Partikelsysteme (0,1 – 10 μm) stellt eine erhebliche Herausforderung für die Forschung dar. Ein möglicher Prozessansatz zur Verbesserung des Sortierergebnisses ist die Flüssig/Flüssig-Flotation. In dieser Studie werden Aussagen bezüglich Anwendbarkeit und Prozessverhalten dieses Ansatzes in Abhängigkeit von ausgewählten Prozessparametern an verschiedenen Modellpartikelsystemen präsentiert.

Keywords: Particle-oil-water emulsions; Phase transfer; Surfactant; Two-liquid flotation; Ultrafine particle separation

Publ.-Id: 20927

Efficient and accurate identification of platinum group minerals by a combination of mineral liberation and electron microprobe analysis

Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.

Identification and accurate characterization of platinum group minerals (PGM) is a very cumbersome procedure due to grain sizes that are mostly below 10 µm and inconspicuous appearance. A novel strategy on finding and quantifying PGM was applied by combining Mineral Liberation Analyzer (MLA) 650F, point logger (JEOL) and a field emission electron probe micro-analyzer (FE-EPMA, JEOL JXA-8530F). Thin sections from a layered intrusion (UG2) in the Bushveld Complex and from two Uralian-Alaskan-type complexes in the Ural Mountains, Russia, were investigated as case studies.
As a first step the PGM are identified, using the Mineral Liberation Analyzer (MLA). The SPL (Sparse Phase Liberation) mode is the best way to find and identify the PGM with high spatial resolution and great accuracy. For this purpose, a series of back-scattered electron images is collected. Within these images, mineral grains are selected that match or exceed a set grey-scale value. These grains are characterized by collecting EDS spectra. Grains identified as PGMs are then marked and coordinates recorded in a format suitable for the EPMA at the point logger. With these coordinates recorded, the sample can be transferred to the microprobe. Despite their small grain sizes the PGM can be retrieved without any difficulties (deviation from the position logged with the point logger is only a few µm). Case studies illustrate that the combination of MLA, point logger and EPMA results in the identification of 4-5 times more PGMs than by careful reflected light microscopy. This is mainly due to the facts that (a) PGM with grain sizes < 5µm are reliably identified and (b) PGM and closely associated base metal sulfides and sulfosalts are well differentiated with the MLA. Furthermore, identification of PGMs remains unaffected by human error and is efficient with respect to the time spent by the mineralogist on a particular sample.
Despite the efficient identification of PGM grains using MLA, the combination with FE-EPMA bears at least one significant advantage. FE-EPMA allows for the accurate determination of mineral chemical composition by WDS, whereas MLA permits only for EDS spot analyses. WDS analyses of PGM by FE-EPMA requires considerable caution, though, due to overlaps of X-rays on both peak and background of almost all PGE and associated elements (e.g. OsMβ on IrMα and AuMβ on HgMα). It is thus necessary to look carefully at every element and to set peak and backgrounds individually for every element. X-ray lines suitable for quantitative analyses (e.g. Mβ instead of Mα) need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction has been developed in order to correct the interferences afterwards. Results obtained in this study attain acceptable totals and atomic proportions, suggesting that the applied corrections are appropriate.

Keywords: Mineral Liberation Analyser; Electron Microprobe; Pointlogger; Platinum Group Minerals; Overlap corrections

  • Contribution to proceedings
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, Practical Aspects, 21.-24.09.2014, Leoben, Österreich
    EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, Antwerp-Wilrijk, Belgien: European Microbeam Analysis Society eV EMAS, 9789082276909, 303-303
  • Poster
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, 21.-24.09.2014, Leoben, Österreich

Publ.-Id: 20926

Abschlussbericht "WTZ Russland - Fluenzberechnungen für Voreilproben beim WWER-440"

Konheiser, J.; Grahn, A.

Reactor pressure vessels (RPV) are non-restorable equipment and their lifetime may restrict the nuclear power plant-life as a whole. Surveillance specimen programs for RPV materials are among the most important measures of in-service inspection pro-grams that are necessary for realistic and reliable assessment of the RPV residual lifetime. In addition to the chemical composition of the RPV steel, the radiation pa-rameters (neutron and gamma fluences and spectra) have the most important impact on the RPV embrittlement characteristics.
In this work, different geometric positions which have influence on the radiation conditions of the samples are investigated. Thus, the uncertainties can be determined in the fluence values of surveillance specimens. The fluence calculations were carried out by the codes TRAMO and DORT. This study was accompanied by ex-vessel neutron dosimetry experiments at Kola NPP, Unit 3 (VVER-440/213), which provide the basis for validation of calculated neutron fluences. The main neutron-activation monitoring reactions were 54Fe(n,p)54Mn and 58Ni(n,p)58Co. The activity measurements were carried out by “Scientific and Engineering Centre for Nuclear and Radiation Safety (SEC NRS).
Good agreement between the deterministic and stochastic calculation results as well as between the calculations and the ex-vessel measurements was found. The aver-age difference between measured and calculated values is 5%. The influence of the channels for surveillance specimens and the shielding effect of a baffle rib on the monitors and on the Monte-Carlo calculated results was studied.
For the surveillance specimens in the maximum of the flux, an average flux of around 2.45 * 1012 neutrons/cm2 was calculated for the neutron flux E> 0.5 MeV. The differences in the surveillance specimens could be up to 20% depending on the direction to the core. Discrepancies up to 10% can be caused by the change of the position of the capsules in the irradiation channel. Based on these calculations the lead factor of specimens was determined. The maximum fluence of RPV may be achieved after two cycles.
The calculated maximum gamma flux is around 3.4 * 1012 g/cm2s for E> 1.0 MeV and around 8.4 * 1012 g/cm2s for E> 0.5 MeV, with the largest part of the flux (around 97%) from the neutron reactions. The gamma fluxes in the surveillance specimens are two to three times bigger than the neutron fluxes. Nevertheless, the material damage by the gamma radiation is very small, because the dpa (displacement per atom) cross sections of gamma rays are about two to three orders of magnitude smaller.
In order to exclude the possibility of healing effects of the samples due to excessive temperatures, the heat release in the surveillance specimens was determined based on the calculated gamma fluences. The analytic treatment of the heat conduction equation and simplified SS geometries were adopted to calculate the range of tem-peratures to be expected. The temperature increase of 20 K above the inlet coolant temperature was estimated using a conservative approach. Under comparatively re-alistic conditions, the heating was reduced to less than 5 K.

Keywords: Reactor pressure vessels; Surveillance specimen; fluence calculation; neutron-activation monitors

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-053 2014
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 20925

Tomographic imaging of gas holdup distribution in pressurized bubble columns

Bieberle, A.; Schubert, M.; Rollbusch, P.; Becker, M.; Schleicher, E.; Hampel, U.

The averaged and radial gas holdup as well as gas phase dynamics and approximate bubble size distribution were studied in a high-pressure bubble column reactor of 4000 mm height and 330 mm diameter. Novel imaging measurement techniques, namely high-resolution gamma-ray computed tomography and wire-mesh sensor, were developed and adapted to the industrial reactor system. The gas phase was nitrogen. Deionized water and cumene were applied as liquid phases. The effect of the superficial gas velocity was studied over a range of 0 to 0.05 m/s at low liquid superficial velocities of 0.008 and 0.018 m/s for operating temperatures and pressures up to 75°C and 18.5 bar, respectively.

Keywords: Bubble column; gas holdup; flow structure; gamma tomography; wire-mesh sensor

  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
    Book of Full-Length Manuscripts, 262-267
  • Poster
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
  • Lecture (Conference)
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland

Publ.-Id: 20924

INTRA r³+ Integration und Transfer der r³ Ergebnisse

Dürkoop, A.

Das Poster präsentiert die Arbeiten im Begleitforschungsprojekt INTRA r³+ zur r³ Fördermaßnahme "Innovative Technologien für Ressourceneffizienz.

  • Poster
    Urban Mining Kongress und r³ Statusseminar 2014, 11.-12.06.2014, Essen, Deutschland

Publ.-Id: 20923

Simultaneous measurement of anisotropic magnetoresistance and observation of magnetic domains by Kerr microscopy

Osten, J.; Lenz, K.; Henschke, A.; Lindner, J.; Fassbender, J.

We report a new instrument, which consists of a Kerr microscope combined with resistance measurements. This setup allows for recording magnetic domains while measuring the anisotropic magnetoresistance (AMR). For this purpose the development of a special sample holder and the extension of the measurement software was needed. The sample holder is equipped with electrical contacts in such a way to apply a current, measure the voltage, and use it in the Kerr microscope. The extension of the measurement software enables one to record resistance and Kerrimages at the same time. This Kerr microscopy combined with the simultaneous measurement of the AMR leads to a better understanding of the AMR behavior.

Keywords: anisotropic magnetoresistance; AMR; magnetic domains; Kerrmicroscope

Related publications

Publ.-Id: 20922

Working with hierarchical databases in R to model geometallurgical data

Matos Camacho, S.; van den Boogaart, K. G.

For the demands of geometallurgy a vast amount of data in multifaceted shape is needed. There are high resolution images from the MLA, data tables with information on the chemistry of some mineral phases, statistics on the distribution of the grain size, and so on. This data needs to be stored in a database, which reflects the often hierarchical structure of it and is flexible enough to be extended with almost any potential occurring information. We provide a MySQL template for such a database. Finding the desired data there can be a tough task, since queries might be highly complex and confusing. Therefore, we developed an easy accessible R interface for accessing this database.

Keywords: R; geometallurgy; MySQL

  • Lecture (Conference)
    16th Annual Conference of the International Association for Mathematical Geosciences, 17.-20.10.2014, New Delhi, India
  • Contribution to proceedings
    16th Annual Conference of the International Association for Mathematical Geosciences, 17.-20.10.2014, New Delhi, India
    Geostatistical and Geospatial Approaches for the Characterization of Natural Resources in the Environment: Challenges,Processes and Strategies Geostatistical, New Delhi: Capital Publishing Company, 978-93-81891-25-4, 341-343

Publ.-Id: 20921

Evidence for Deposition of Interstellar Material on the Lunar Surface

Fimiani, L.; Cook, D. L.; Faestermann, T.; Gómez Guzmán, J. M.; Hain, K.; Herzog, G. F.; Knie, K.; Korschinek, G.; Ligon, B.; Ludwig, P.; Park, J.; Reedy, R. C.; Rugel, G.

Astronomical observations indicate that one or more supernovae (SN) ocurred in the vicinity of our solar system in the recent past (~10Myr) [1,2]. One possible indication of the arrival of SN (or perhaps AGB) debris locally was the detection of 60Fe/Fe (T1/2 = 2.62 Myr [3]) excesses in a ferroman-ganese crust from the Pacific Ocean [4,5]. Another indication came from the Moon. In a previous study [6] we reported a 60Fe/Fe depth profile constructed with 2 samples of the Apollo 12 core 12025, 4 samples of the Apollo 15 core 15008, 2 samples known as ‘skim’, ‘scoop’ and ‘under boulder’ soil collected near the shade of a small boulder in Station 9 during the Apollo 16 mission (shaded samples), and 5 samples of the deep drill core 60007/6, sampled during the same mission. We complete the previous work by reporting new measurements of 53Mn (T1/2 = 3.7 Myr [7]) in the same samples, including deeper samples of the 12025 core, and by using those measurements for a critical assessment of the 60Fe results. We also determined the activities of 60Fe and 53Mn of 7 samples from 4 iron meteorites; these activities were used to establish reference levels for local production due to galactic cosmic rays.

Keywords: supernova; Fe-60; Mn-53

  • Poster
    45th Lunar and Planetary Science Conference, 17.-21.03.2014, Houston, USA

Publ.-Id: 20920

Development of a micro reactor for the isobutane oxidation as a multiphase process

Willms, T.; Kryk, H.; Wiezorek, M.; Hampel, U.

The partial oxidation of liquid isobutane to tertiary butyl hydroperoxide (TBHP) is currently conducted on an industrial scale with bubble columns at a selectivity of 60% and a maximum conversion of 25%. In this process, liquid isobutane is converted with oxygen at high temperatures (130 to 140°C) and pressures (25 to 37 Bar) at high residence times of 10 to 12 hours. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“ a micro reactor has been built and used to investigate this reaction for the first time as a continuous two-phase process in a broad range of flow rates, temperatures (120 to 150°C) and pressures (25 to 100 bar). For the improvement of the selectivity of the industrial process the influence of the residence time, hydrodynamics, initiator, additives and pressure on the reaction is studied. To realize a large range of residence times, flow rates in the range of 15 µl/min to 188 µl/min for isobutane and in the range of 0.1 up to 1.5 ml/min for oxygen were realized, using different capillary lengths which lie between 20 and 100 m. To charac¬terize the isobutane flow, preliminary measurements of the system isobutane – nitrogen were performed in a glass capillary. As the target product and initiator TBHP is sensitive to most metals, the micro reactor and further parts of the lab facility have been coated. To assure reasonable results of the hydrodynamic and kinetic studies, it was also important to realize a flow without pulsation by large pressure fluctuations. Therefore, the pressure is controlled by a gas pressure valve after a gas-liquid separation. The oxidation is followed by taking samples and analysis of the liquid reaction mixture by means of a GC-MS-System. In the frame of the presentation the challenges of the reactor construction and their solutions are discussed.

Keywords: Micro reactor; process intensification; isobutane oxidation

  • Lecture (Conference)
    4th European Conference on Microfluidics, 10.-12.12.2014, Limerick, Ireland

Publ.-Id: 20919

Towards Laser Driven Particle Therapy: from in vitro studies to human tumor irradiation on mice

Beyreuther, E.; Baumann, M.; Brüchner, K.; Hartmann, J.; Kaluza, M.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Oppelt, M.; Reuter, M.; Richter, C.; Sävert, A.; Schürer, M.; Schnell, M.; Woithe, J.; Pawelke, J.

The novel technology of particle acceleration by high intensity lasers promises more compact and cost effective ion sources as well as electron beams of very high energy for radiotherapeutic application. However, compared to conventional beams, laser-driven acceleration results in different beam properties like ultra-short and very intensive pulses, inherent pulse-to-pulse fluctuations, low pulse repetition rate, large beam divergence and broad energy distribution. In consequence, the future medical application of these particle beams requires not only a high power laser system but also new technical solutions for dose delivery and quality assurance as well as comprehensive research on the radiobiological consequences of ultra-short radiation pulses with high pulse dose.
During the last years the laser-driven technology was developed at such a rate that cell samples and small animals can be irradiated. Within the joint research project “onCOOPtics” extensive in vitro dose response studies were already performed comparing the radiobiological effects of laser driven electron and proton beams to their conventional equivalents. As overall result, the obtained dose-effect relationships for human tumor and human normal tissue cells reveal no difference between conventional and laser-driven beams. In a second translational step, in vivo experiments were recently established at the laser system JETI. Although the experiments were motivated by future proton trials, first attempts were performed with laser accelerated electrons, since the homogeneous delivery of prescribed doses to a 3D target volume is easier for electrons than for protons. Tumor irradiation was realized for the murine sarcoma KHT and the human squamous cell carcinoma FaDu grown on nude mice ear. Doses of up to 14 Gy were applied and the radiation induced tumor growth delay was investigated and later on compared to those obtained after similar treatment at a conventional electron Linac. Moreover, the successful performance of such an experiment campaign over a period of several weeks underlines the stability and reproducibility of all implemented methods and setup components. Further experiments with laser accelerated protons are in progress.
The work was supported by the German Federal Ministry of Education and Research
(BMBF), grant nos. 03ZIK445 and 03Z1N511.

  • Lecture (Conference)
    41st Annual Meeting of the European Radiation Research Society, 14.-19.09.2014, Kallithea/Rhodos, Greece
  • Poster
    Space Radiation and Heavy Ions in Therapy Symposium 2015, incl. 15th Workshop on Ion Beams in Biology and Medicine (IBIBAM), 22.-24.05.2015, Osaka, Japan

Publ.-Id: 20918

Ultrafast Terahertz-induced Magnetization Dynamics Studied on a Nanometer Length Scale by Coherent XUV Free-electron Laser Radiation.

Berntsen, M. H.; Müller, L.; Schleitzer, S.; Steinke, I.; Lehmkühler, F.; Schroer, M. A.; Ricci, A.; Al-Shemmary, A.; Stojanovic, N.; Golz, T.; Fischer, B.; Bagschik, K.; Bach, J.; Beyersdorff, B.; Winkler, G.; Frömter, R.; Gensch, M.; Oepen, H. P.; Gutt, C.; Grübel, G.

Free-electron lasers (FELs), with their high photon flux, short pulse lengths, and coherent radiation, are ideal tools for studying complex materials, simultaneously on sub-picosecond time and on nanometer length scales. In particular, by exploiting the magneto-dichroic transitions at the L or M edges of Fe, Co, Ni or Gd, temporal and spatial studies of magnetic systems can be performed.
Infrared-pump–XUV-probe experiments performed at a FEL have revealed that the optically induced demagnetization in magnetic maze-domain structured Co/Pt samples is also accompanied by a spatial response. In this, and other studies using optical (IR) pumping, the magnetization is manipulated by heating of the spin system, i.e. through ultrafast electronic excitations.
Using terahertz (THz) radiation for pumping gives a unique possibility to investigate the influence of ultra-short pulses of strong magnetic fields on the magnetization dynamics since the THz photons do not generate direct electronic heating and because the THz phase can couple directly to the magnetic moments. Hence, the use of THz radiation could bring one a step closer to being able to control magnetism on ultrafast time scales.

  • Poster
    Science at FEL´s, 15.-17.09.2014, Villigen, Schweiz

Publ.-Id: 20917

Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.] [331.] [332.]