Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

An optimal model for in vivo radiobiological studies with laser driven proton beams?

Beyreuther, E.; Baumann, M.; Brüchner, K.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Oppelt, M.; Schürer, M.; Wetzig, K.; Pawelke, J.

  • Poster
    1. Retreat of the National Center for Radiation Oncology (NCRO), 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21782

In-vivo dosimetry for particle beams - Radiation Physics

Helmbrecht, S.; Iltzsche, M.; Jannusch, P.; Lutz, B.; Priegnitz, M.; Rohling, H.; Römer, K.; Schöne, S.; Schumann, A.; Weinberger, D.; Pausch, G.; Enghardt, W.; Fiedler, F.

no abstract available

  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21781

Transverse Emittance Compensation

Vennekate, H.; Arnold, A.; Kamps, T.; Kneisel, P.; Lu, P.; Murcek, P.; Teichert, J.; Xiang, R.

Superconducting RF injectors are promising candidates for the particle sources of future accelerators. While machines like high power free electron lasers or energy recovery linacs are planned to be operated with large duty factors, or even continuous wave mode, to increase the beam intensity, they also demand high beam quality. As this is already determined at the very start of the generation of each particle bunch, the concept of an SRF gun becomes appealing. Transverse Emittance marks the beam quality which is of tremendous relevance for all beam optics and further more sets the level of angular resolution of any scattering experiment performed with the beam. Several concepts to enhance this quality with the lately comissioned Rossendorf SRF Gun II have been presented in recent year’s conferences. The talk will summarize the expended efforts, discuss some of the reflections on installation and operation of the used tools and present preliminary results of the recent achievements.

Keywords: SRF Gun; Emittance; ELBE

  • Lecture (Conference)
    DPG Frühjahrstagung 2015 Wuppertal, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21780

Experiments in bubble columns for CFD model validation

Ziegenhein, T.; Rzehak, R.; Lucas, D.

Bubble columns are widely used in industrial application and are an actual object of research. The performance of a bubble column strongly depends on the characteristic of the flow, which can be modeled with the methods of computational fluid dynamics (CFD). A widely used CFD approach for modeling such dispersed multiphase flows is the Eulerian two-fluid approach.
With the Eulerian two-fluid approach large apparatuses can be simulated in a short time; however, the interaction between the dispersed and the continuous phases has to be modelled with closure models. The closure models refer to different forces and effects, such as drag, lift, virtual mass, turbulent dispersion, coalescence & break up and bubble induced turbulence. The usage of a proper set of closure models is an actual discussion in the scientific community (Rzehak & Krepper 2013) and proper experiments are needed for model validation.
To validate the above mentioned effects that the closure models have to cover, a wide range of experiments are needed. In addition, such experiments should allow measuring the relevant data for a model validation. The must have relevant data are the bubble size distribution, the local void fraction and the liquid velocity at different positions.
In the present study an airlift air-water bubble column, a partially aerated air-water bubble column and an air-NaCl solution bubble column is investigated. The bubble size distribution, the local void fraction and the liquid velocity will be shown at different positions in the bubble column. In addition, a comparison of the experimental results with simulations using an Euler-Euler unsteady Reynolds averaged Navier Stokes equation approach as described in Ziegenhein et al. 2015 is given.

Keywords: Bubble columns; multiphase flow; bubbly flows; particle tracking velocimetry; bubble size measurement; void fraction measurement; Airlift; break-up; coalescence

  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 21779

Prompt-Gamma-Imaging for range verification in proton therapy: Towards clinical implementation

Barczyk, S.; Golnik, C.; Priegnitz, M.; Vander Stappen, F.; Janssens, G.; Smeets, J.; Clementel, E.; Hotoiu, L.; de Xivry, J. O.; Baumann, M.; Enghardt, W.; Fiedler, F.; Krause, M.; Prieels, D.; Pausch, G.; Richter, C.

No abstract available

  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21778

PGI & PGT Modeling for realistic Patient Treatment Plans

Priegnitz, M.; Rohling, H.; Schumann, A.; Enghardt, W.; Pausch, G.; Fiedler, F.

No abstract available.

  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21777

Neutron Dose During Proton Therapy

Lutz, B.; Enghardt, W.; Pausch, G.; Fiedler, F.

Work in progress report about the measurement of the neutron field during proton therapy at OncoRay.

  • Poster
    National Center for Radiation Oncology -- 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21776

Experimental Characterization of Vertical Gas-Liquid Pipe Flow For Annular and Liquid Loading Conditions Using Dual Wire-Mesh Sensor

Vieira, R. E.; Parsi, M.; Torres, C. F.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.

In gas well production, liquid is produced in two forms, droplets entrained in the gas core and liquid film flowing on the tubing wall. For most of the gas well life cycle, the predominant flow pattern is annular flow. As gas wells mature, the produced gas flow rate reduces decreasing the liquid carrying capability initiating the condition where the liquid film is unstable and flow pattern changes from fully cocurrent annular flow to partially cocurrent annular flow. The measurement and visualization of annular flow and liquid loading characteristics is of great importance from a technical point of view for process control or from a theoretical point of view for the improvement and validation of current modeling approaches. In this experimental investigation, a Wire-Mesh technique based on conductance measurements was applied to enhance the understanding of the air-water flow in vertical pipes. The flow test section consisting of a 76 mm ID pipe, 18 m long was employed to generate annular flow and liquid loading at low pressure conditions. A 16×16 wire configuration sensor is used to determine the void fraction within the cross-section of the pipe. Data sets were collected with a sampling frequency of 10,000 Hz. Physical flow parameters were extracted based on processed raw measured data obtained by the sensors using signal processing. In this work, the principle of Wire-Mesh Sensors and the methodology of flow parameter extraction are described. From the obtained raw data, time series of void fraction, mean local void fraction distribution, characteristic frequencies and structure velocities are determined for different superficial liquid and gas velocities that ranged from 0.005 to 0.1 m/s and from 10 to 40 m/s, respectively. In order to investigate dependence of liquid loading phenomenon on viscosity, three different liquid viscosities were used. Results from the Wire-Mesh Sensors are compared with results obtained from previous experimental work using Quick Closing Valves and existing modeling approaches available in the literature.

Keywords: Wire-mesh sensor; gas-liquid flow; void fraction; phase distribution; flow visualization

Publ.-Id: 21775

Exploring photochemistry of uranyl(VI)

Tsushima, S.

Photoexcited uranyl(VI) is a mild oxidant and can decompose various biological substances including large molecule like DNA. This reaction constitutes another environmental risk of uranium in addition to its radiotoxicity and chemotoxicity. There are several different mechanisms which may lead to decomposition of organic substances by photoexcited uranyl(VI). This includes hydrogen abstraction by “yl”-oxygen, decarboxylation of uranyl-bound carboxylic group, and ligand-to-metal charge transfer. These mechanisms may also compete with each other and makes mechanistic understanding far from being straightforward. In my talk, I will focus on our recent experimental and theoretical development on DNA photocleavage study. Although hydrogen abstraction is widely believed to be the key reaction in uranyl(VI)–mediated photocleavage of DNA, density functional theory calculations show that direct charge transfer from DNA to photoexcited uranyl(VI) can be an alternative pathway that leads to DNA strand break. In the oxidized state of DNA, electron deficiency is centered mainly on guanine as well as on uranyl–free phosphate, and lesser extent is distributed on adenine and thymine. Presumably there is no unique “hot spot” in DNA and upon irradiation local oxidation occurs in nucleobase or in uranyl–free phosphate in the vicinity of uranium. Oxidation of phosphate eventually leads to DNA strand break. Experiments using circular dichroism (CD) and X-ray absorption spectroscopy (XAS) are in progress.

  • Invited lecture (Conferences)
    The International Chemical Congress of Pacific Basin Societies (PACIFICHEM 2015), Symposium on Experimental and Theoretical Actinide Chemistry: From Fundamental Systems to Practical Applications, 15.-20.12.2015, Honolulu, Hawaii, USA

Publ.-Id: 21774

Polymer and cluster chemistry of f-elements in aqueous solutions

Ikeda-Ohno, A.

Because of their high charge density, the aqueous chemistry of f-elements with lower valences (i.e. tri- and tetravalent) is predominantly controlled by strong hydrolysis producing a variety of hydroxide species. Interestingly enough, this strong hydrolysis often induces the intrinsic formation of polymer and nano-sized cluster complexes which are stable even in aqueous solutions. This seminar will provide a recent overview of the hydrolysis-induced polymer/cluster formation of tetravalent f-elements particularly from the viewpoint of structural chemistry, as well as the associated characterisation techniques (e.g. X-ray absorption spectroscopy or X-ray scattering).

Keywords: actinides; lanthanides; f-elements; hydrolysis; aqueous solution; polymers; clusters; characterisation

  • Invited lecture (Conferences)
    Internal seminar, Institut für Radioökologie und Strahlenschutz, Leibnitz Universität Hannover, 30.04.2015, Hannover, Germany

Publ.-Id: 21773

The effect of magnetic annealing on crystallographic texture and magnetic properties of Fe-2.6%Si

Salih, M. Z.; Uhlarz, M.; Pyczak, F.; Brokmeier, H.-G.; Weidenfeller, B.; Al-Hamdany, N.; Gan, W. M.; Zhong, Z. Y.; Schell, N.

The effect of magnetic annealing on crystallographic texture ,microstructure, defects density and magnetic properties of a Fe-2.6%Si steel has been analyzed. After two stage cold rolling (75% and 60% cold rolled) with intermediate annealing process at (600 °C/1 h) the sample annealed at 600 °C for one hour during which different magnetic field of 0,7 and 14 T were applied has been investigated. The effect of defects density after cold rolling process on the recrystallization texture and magnetic properties was characterized. Heat treatments under a high external field of14 T show a drastic improvement of the magnetic properties such as significantly increased permeability. Neutron diffraction measurements were preferred for measurement of the bulk sample texture so that sufficient grain statistics were obtained. Because of its small wavelength (0.05–0.2 Å) synchrotron diffraction with high photon energy was used to evaluate the defects density by a modified Williamson–Hall plot.

Publ.-Id: 21772

Inference of phase properties from sorting experiments and MLA data

Matos Camacho, S.; Leißner, T.; Bachmann, K.; van den Boogaart, K. G.

In the last 20 years the development of new analytical methods and devices provided the possibility of high-resolution data in almost every field of science. Information is much easier to retrieve and in a depth never known before. But often these methods are expensive and a lot of time is needed for proper data acquisition and analysis. For example, in geosciences the Mineral Liberation Analyser (MLA) provides quantitative mineralogical microstructural information. This is a scanning electron microscope with automated software for high resolution images of rock specimen and sample compounds from mineral processing. The information can be used for evaluating the effect of mineral processing on a given ore sample in order to find the optimal processing parameters of each step and predict the overall recovery and grade the requested value minerals.

For example, the magnetic susceptibility of a mineral phase determines its behaviour during magnetic separation. It can be modelled as a linear combination of the susceptibilities of each occurring mineral phase with respect to its mass fraction:
\begin{equation} \label{equ} \overline{\chi_s} = \sum_{i=1}^{n} \frac{m_i}{m_s}\chi_i. \end{equation} (chi_s: susceptibility of the whole sample, chi_i: susceptibility of the i-th mineral phase, m_s: mass of the whole sample, m_i mass of the i-th mineral phase)

Unfortunately, quite often only the susceptibility of the composition can be measured in an experiment due to several reasons, e.g. if the composition consists of too many distinct components and the contained mineral particles consist of several mineral phases. During the separation the sample is split into several classes. The susceptibility can only be measured for such a class.
But we would like to infer the susceptibility for every single mineral phase. The common approach is a linear model, which fails if we have more mineral phases than susceptibility classes found in the experiment.

Our approach uses bootstrapping for constructing new subsamples out of the measured ones. Since every particle has the given mean property, taking such subsamples is like repeating the experiment. This provides a broader base with subsamples having a much higher variability of phase compositions. We repeat this procedure for every susceptibility class.

Furthermore we often do not only have one single value for each class found in the experiment, but a set of them within a certain bounded range. Instead of using the average we arbitrarily assign one of them to each new sample. This additionally prevents us from too many linear dependent equations using (\ref{equ}). We end up in an over-determined system of linear equations. For the solution we use the Moore-Penrose inverse, giving us the possibility to compute an estimation error for every mineral phase relying on the corresponding eigenvalue.

We will discuss simulation results and apply the method to actual experimental data.

Keywords: Geometallurgy; Statistic; MLA; Linear Model

  • Lecture (Conference)
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 07.-10.09.2015, Freiberg, Deutschland
    Proceedings of the 17th annual conference of the International Association for Mathematical Geosciences

Publ.-Id: 21771

Experimental benchmark of an analytical model for prompt gamma imaging

Sterpin, E.; Janssens, G.; Smeets, J.; Vander Stappen, F.; Prieels, D.; Priegnitz, M.; Perali, I.; Vynckier, S.

A prompt gamma (PG) slit camera prototype recently demonstrated a 1-2 mm accuracy to detect proton range shifts at clinical beam currents by comparing an expected PG detection profile to a measured one. An analytical model has been recently developed to compute the expected profile at practical speed (< 1 s). We present here its benchmark against measurements in heterogeneous phantoms.

  • Lecture (Conference)
    AAPM 2015, 57th Annual Meeting, 12.-16.07.2015, Anaheim, USA
  • Abstract in refereed journal
    Medical Physics 42(2015)6, 3726

Publ.-Id: 21770

Spectroscopic studies on monazite-type ceramics for the conditioning of radioactive waste: Infrared, Raman, X-ray Absorption and Site-Selective Time Resolved Laser Fluorescence Spectroscopy

Neumeier, S.; Arinicheva, Y.; Huittinen, N.; Lozano-Rodriguez, M. J.; Holthausen, J.; Modolo, G.; Scheinost, A. C.; Stumpf, T.; Bosbach, D.

Monazite ceramics are being considered as potential waste forms for immobilization of minor actinides since they exhibit advantageous properties such as high chemical durability and radiation tolerance.
The overall objective of our study is to reveal the mechanisms of solid solution formation as well as the incorporation of the actinides into the crystal structure of the waste matrix. A fundamental understanding of these mechanisms is of great importance with regard to the long-term stability of monazites for safe nuclear waste disposal.
(La,Eu)PO4 and due to quenching effects of high Eu-contents in TRLFS measurements Eu doped (La,Gd)PO4 monazite solid solutions were synthesized by wet chemical methods. Eu serves as surrogate for trivalent actinides. Samples were characterized by XRD, Raman, IR, EXAFS and TRLFS spectroscopies. Structural refinement of XRD data as well as a linear shift of Raman and IR bands towards higher wave numbers shows a linear dependency of lattice parameters on the Eu content according to Vegard’s law. In contrast, EXAFS analysis reveals a decrease only for the La-O distances in the first coordination shell and the first metal-metal distance, while the Eu-O local coordination remains unchanged. TRLFS investigations show that the host cation size in the monazites has very little influence on the Eu3+ incorporation into these materials, but a broadening of the excitation spectra indicate a local disordering of the crystal structure around the dopant

Keywords: Monazite; XRD; EXAFS; IR; TRLFS; Europium

  • Invited lecture (Conferences)
    E-MRS Spring Meeting 2015, 11.-15.05.2015, Lille, France

Publ.-Id: 21769

Investigating Spinodal Decomposition and Coarsening using Massively Parallel Kinetic Metropolis Lattice Monte-Carlo Simulations

Kelling, J.; Heinig, K. H.; Gemming, S.

Nano-structured materials are important for many applications, including energy technologies. The desired structures can be created using bottom-up processes, which utilize self-assembling. By way of spinodal decomposition of a metastable phase, like SiOx into Si and SiO2, sponge-like networks of nanowires can be obtained. Understanding the coarsening kinetics of spinodal structures is crucial not only for bottom-up production, but also helps to increase the life-time of components like porous matrices in fuel cells, where suppression of coarsening has a huge economic impact.

Two theories on coarsening of spinodal structures exist: one assuming diffusion through the bulk [1], the other along interfaces [2]. Since orders of magnitude in both space and time have to be covered by simulations, numerical studies are quite demanding. Nevertheless, simulations are essential in studying systems containing size-inhomogeneities in initial nano-structures, where strongly accelerated coarsening is observed.

Here, a multi-GPU Kinetic Metropolis Lattice Monte-Carlo implementation, capable of atomistic simulations of phase-separation and coarsening at spatio-temporal experimental scales (billions of particles over millions of time-steps) is presented while laying focus on the above-mentioned applications.

[1] A. Chakrabarti, R. Toral, J.D. Gunton, Phys. Rev. B 39(7) 4386 (1989) suggesting a modified Lifschitz-Slyozov law: I.M. Lifshitz, V.V. Slyozov, J. Phys. Chem. Solids 19(1-2), 35-50 (1961)
[2] W.W. Mullins, J. Appl. Phys. 28(3), 333-339 (1957)

Keywords: Nano Structures; GPGPU; Supercomputing; Statistical Physics

  • Lecture (Conference)
    Conference of the Middle European Cooperation in Statistical Physics, 23.-25.03.2015, Esztergom, Hungary

Publ.-Id: 21768

Simulation of Surface Growth and Lattices Gases Using GPUs

Schulz, H.; Kelling, J.; Ódor, G.; Ódor, G.; Ferenc Nagy, M.

Restricted solid on solid surface growth models can be mapped onto binary lattice gases. We show that efficient simulation algorithms can be realized on GPUs either by CUDA or by OpenCL programming. We consider a deposition/evaporation model following Kardar–Parisi–Zhang growth in d+1 dimensions, related to the Asymmetric Simple Exclusion Process. Up to 100 - 400 x speedup can be achieved with respect to the serial code running on a I5 core. This permits studying disorder and aging behavior in these system.

Keywords: Computational Physics; Supercomputing

Publ.-Id: 21767

Radiobiologial response to ultra-short pulsed MeV electron beams of ultra-high pulse dose rate

Beyreuther, E.; Gotz, M.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Oppelt, M.; Schürer, M.; Pawelke, J.

  • Poster
    1. Retreat of the National Center for Radiation Oncology (NCRO), 19.-21.03.2015, Heidelberg, Deutschland
  • Poster
    15th International Congress of Radiation Research, 25.-29.05.2015, Kyoto, Japan

Publ.-Id: 21766

GPGPU Powered 3D Simulations of Micro Droplets in Laser-Ion Acceleration

Huebl, A.; Kluge, T.; Hilz, P.; Bussmann, M.

We present current large scale, full 3D particle-in-cell simulations and studies of laser-ion acceleration utilizing highly over-dense, mass and volume limited micro targets with PIConGPU. Powered by thousands of GPGPUs on Oak Ridge's supercomputer Titan, we show early results such as the influence of the target to laser spot size and the arising acceleration regimes thereof.

The simulations show the capability of PIConGPU, a highly scalable particle-in-cell code for many-core compute architectures that allows for in-situ, real time visualization and ultra-fast computation of large systems.

Keywords: mass-limited targets; PBA; GPGPU; simulation; HPC; laser-ion acceleration

  • Lecture (Conference)
    DPG-Frühjahrstagung: FV Teilchen-, Strahlen- und Medizinphysik, Arbeitskreis Beschleunigerphysik, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21765

Low-energy enhancement of M1 strength

Schwengner, R.; Frauendorf, S.; Larsen, A. C.

Magnetic dipole strength functions have been deduced from averages of a large number of M 1 transition strengths calculated within the shell model for the nuclides 90 Zr, 94Mo, 95 Mo, and 96 Mo. An enhancement of M1 strength toward low transition energy has been found for all nuclides considered. Large M1 strengths appear for transitions between close-lying states with configurations including proton as well as neutron high-j orbits that re-couple their spins and add up their magnetic moments coherently. The M 1 strength function deduced from the calculated M 1 transition strengths is compatible with the low-energy enhancement found in (3He,3He') and (d,p) experiments. The present work presents an explanation of the experimental findings.

Keywords: Strength functions; magnetic dipole strength; shell model

  • Open Access Logo Journal of Physics: Conference Series 580(2015), 012020
    DOI: 10.1088/1742-6596/580/1/012020
  • Invited lecture (Conferences)
    11th International Spring Seminar on Nuclear Physics: Shell Model and Nuclear Structure - achievements of the past two decades, 12.-16.05.2014, Ischia, Italia

Publ.-Id: 21763

Annual Report 2014 - Institute of Resource Ecology

Stumpf, T.; Foerstendorf, H.; Bok, F.; Richter, A.; (Editors)

The Institute of Resource Ecology (IRE) is one of the eight institutes of the Helmholtz-Zentrum Dresden – Rossendorf (HZDR).
The research activities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and focused on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”.
Additionally, various activities have been started investigating chemical and environmental aspects of processing and recycling of strategic metals, namely rare earth elements. These activities are located in the HGF program “Energy Efficiency, Materials and Resources (EMR)”. Both programs, and therefore all work which is done at IRE, belong to the research sector “Energy” of the HGF.
The research objectives are the protection of humans and the environment from hazards caused by pollutants resulting from technical processes that produce energy and raw materials. Treating technology and ecology as a unity is the major scientific challenge in assuring the safety of technical processes and gaining their public acceptance. We investigate the ecological risks exerted by radioactive and nonradioactive metals in the context of nuclear waste disposal, the production of energy in nuclear power plants, and in processes along the value chain of metalliferous raw materials. A common goal is to generate better understanding about the dominating processes essential for metal mobilization and immobilization on the molecular level by using advanced spectroscopic methods. This in turn enables us to assess the macroscopic phenomena, including models, codes, and data for predictive calculations, which determine the transport and distribution of contaminants in the environment.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-059 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 21762

Einfluss von Biofilmen auf das Migrationsverhalten von Uran, Americium und Europium in der Umwelt

Baumann, N.; Zirnstein, I.; Arnold, T.

Die Mechanismen von Immobilisierungsprozessen radioaktiver Schwermetall-Ionen innerhalb von Biofilmen sind noch weitgehend unerforscht. Das liegt an der Komplexität der Biofilme, welche häufig diskrete geochemische Mikromilieus bilden, die sich vom umgebenden Milieu („Bulk Solution“) in Bezug auf dessen Biozönose (der mikrobiellen Diversität), den darin herrschenden geochemischen Bedingung (z.B. Red/Ox-Potential u./o. gelöster Sauerstoffmenge), aber auch in der Konzentration möglicher Komplexbildner (z.B. Metaboliten u./o. EPS-Komponenten) deutlich unterscheiden. Alle diese Faktoren können die Speziation der Radionuklide verändern und damit auch deren Transportverhalten. Für ein besseres Prozessverständnis zu den Wechselwirkungen von Radionukliden mit natürlichen, in Uran-kontaminierten Milieus lebende Mikroorganismen und den damit verbunden Stoffen wurde die Biozönose in Biofilmen und im Grubenwasser des ehem. WISMUT-Uranbergwerkes Königstein nach klassischen mikrobiologischen- und molekularbiologischen Methoden bestimmt. Aus einem Vergleich der Chemie im Biofilm mit der Chemie der umgebenden Lösung wird der Einfluss der Biofilme auf das Migrationsverhalten von Radionukliden in der Natur beurteilt. Die Identifizierung und Quantifizierung von Prokaryoten erfolgte u.a. mit der CARD FISH Methode. Die selektive Visualisierung der EPS-Komponenten in der Matrix der Biofilme wurde mit Hilfe der Konfokalen Laser Scanning Mikroskopie (CLSM) bewerkstelligt.
Zur Untersuchung der Speziation von fluoreszierenden Schwermetall-Ionen wie U(VI) kam die zeitaufgelöste, laser-induzierte Fluoreszenzspektroskopie (TRLFS) zum Einsatz. Um diese Methode auch im mikroskopischen Bereich anwenden zu können, wurde sie weiter zum CLSM hin entwickelt: Da ein 80-MHz-MaiTai-Laser zur Verfügung stand, wurde durch im kHz-Bereich alternierendes Beugen des Anregungslaserstrahls von der Probe weg (und wieder zu ihr hin) mittels akusto-optischem Modulator (AOM) eine quasi-gepulste Laseranregung im kHz-Bereich erreicht. Durch Einbindung von Frequenzvervielfachern („Harmonixx“ von APE Berlin und „Inspire“ von Spectra-Physics) konnte so eine gepulste Anregung innerhalb eines breiten Wellenlängenbereiches (ca. 230-1090 nm) ermöglicht werden. Für die Auswertung des als äußerst schwach zu erwartenden Fluoreszenzsignales (entsprechend des mikroskopisch kleinen Anregungsraumes) wurde die Time-Correlated Single-Photon Counting Methode (TCSPC) – auch „zeitbezügliche Einzelphotonenzählungs-Methode“ – an das Laser-Anregungssystem angepasst. Die Fluoreszenzlebenszeitkurve des Fluoreszenzsignals von U(VI) Species, die sich an der Oberfläche von den Protozoen Euglena Mutabilis befanden, konnte z.B. auf diese Art mit Hilfe der TCSPC ermittelt werden.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-061 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 21761

Carrier relaxation dynamics in graphene

Mittendorff, M.

Graphene, the two-dimensional lattice of sp2-hybridized carbon atoms, has a great potential for future electronics, in particular for opto-electronic devices. The carrier relaxation dynamics, which is of key importance for such applications, is in the main focus of this thesis. Besides a short introduction into the most prominent material properties of graphene and the experimental techniques, this thesis is divided into three main parts.
The investigation of the carrier relaxation dynamics in the absence of a magnetic field is presented in Chapter 3. In the first experiment, the anisotropy of the carrier excitation and relaxation in momentum space was investigated by pump-probe measurements in the near-infrared range. While this anisotropy was not considered in all previous experiments, our measurements with a temporal resolution of less than 50 fs revealed the polarization dependence of the carrier excitation and the subsequent relaxation. About 150 fs after the electrons are excited, the carrier distribution in momentum space gets isotropic, caused by electron-phonon scattering. In a second set of two-color pump-probe experiments, the temperature of the hot carrier distribution, which was obtained within the duration of the pump pulse (about 200 fs), could be estimated. Furthermore, a change in sign of the pump-probe signal can be used as an indicator for the Fermi energy of different graphene layers. Pump-probe experiments in the far-infrared range in reflection and transmission geometry were performed at high pump power. A strong saturation of the pump-induced transmission was found in previous experiments, which was attributed to the pump-induced change in absorption. Our investigation shows the strong influence of pump-induced reflection at long wavelengths, as well as a lot smaller influence of the saturation of the pump-induced change in absorption. At a high pump power, the increase of the reflection exceeds the change in absorption strongly, which leads to negative pump-probe signals in transmission geometry.
In Chapter 4, investigations of the carrier dynamics of graphene in magnetic fields of up to 7T are presented. Even though the optical properties of Landau-quantized graphene are very interesting, the carrier dynamics were nearly unexplored. A low photon energy of 14meV allows the investigation of the intraband Landau-level (LL) transitions. These experiments revealed two main findings: Firstly, the Landau quantization strongly suppresses the carrier relaxation via optical-phonon scattering, resulting in an increased relaxation time. Secondly, a change in sign of the pumpprobe signal can be observed when the magnetic field is varied. This change in sign indicates a hot carrier distribution shortly after the pump pulse, which means that carrier-carrier scattering remains very strong in magnetic fields. In a second set of pump-probe measurements, carried out at a photon energy of 75meV, the relaxation dynamics of interband LL transitions was investigated. In particular, experiments on the two energetically degenerate LL transitions LL−1 ) LL0 and LL0 ) LL1 showed the influence of extremely strong Auger processes.
An ultrafast and extremely broadband terahertz detector, based on a graphene flake, is presented in the last chapter of this thesis. To couple the radiation efficiently to the small flake, the inner part of a logarithmic periodic antenna is connected to it. With a rise time of about 50 ps in a wavelength range of 9 μm to 500 μm, this detector is very interesting to obtain the temporal overlap in two-color pump-probe experiments with the free-electron laser FELBE. Furthermore, the importance of the substrate material, in particular for the high-speed performance, is discussed.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-057 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 21760

Magnetic, thermal and transport properties of Tb3Ru4Al12 with a distorted kagome lattice

Gorbunov, D. I.; Henriques, M. S.; Andreev, A. V.; Skourski, Y.; Dusek, M.

The Tb3Ru4Al12 compound (hexagonal crystal structure) having a distorted kagome net of the Tb atoms is studied on a single crystal by measurements of magnetization, specific heat and electrical resistivity. The system is an antiferromagnet with the Néel temperature TN = 22 K. A substantial magnetic anisotropy is observed that persists at least up to 60 T. Tb3Ru4Al12 displays field-induced magnetic phase transitions: one along [100] and [120] and two along the [001] axis. The transitions are accompanied by sharp peaks in magnetoresistance and subsequently lead to a large negative effect in it, −20% in the longitudinal and −40% in the transverse geometry. The peaks are explained by changes in conduction electron spectra at the transitions due to the interaction between the conduction electrons and localized magnetic moments. The large negative effect suggests field-induced magnetic phases with a reduced period as compared to zero field.

Publ.-Id: 21759

Fast-neutron Induced Reactions at the nELBE Time-of-flight Facility

Junghans, A. R.; Beyer, R.; Elekes, Z.; Grosse, E.; Hannaske, R.; Koegler, T.; Massarczyk, R.; Schwengner, R.; Wagner, A.

The compact neutron-time-of-flight facility nELBE at the superconducting electron accelerator ELBE of Helmholtz-Zentrum Dresden-Rossendorf is being rebuilt and extended with a low-background experimental hall. The neutron radiator consists of a liquid lead circuit without additional neutron moderators. The useful neutron spectrum extends from some tens of keV to about 10 MeV. nELBE is intended to deliver cross section data of fast-neutron nuclear interactions e.g. for the transmutation of nuclear waste and improvement of neutron physical simulations of innovative nuclear systems. Before the extension of the facility, the photon production cross section of 56 Fe was measured with an HPGe detector and the inelastic neutron scattering cross section to the first few excited states in Fe-56 was determined. The neutron total cross sections of Au and Ta were determined in the energy from 200 keV to 7 MeV in a transmission experiment.

Keywords: neutron time-of-flight; neutron induced reactions


Publ.-Id: 21758

Enhanced reactive transport process understanding by means of experiments and modelling at HZDR/IRE

Lippmann-Pipke, J.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    Helmholtz-Koordinierungstreffen, Forschung zu Endlagersystemen FZJ/IEK-6, KIT/INE, HZDR/IRE, 04.-05.03.2015, Jülich, Deutschland

Publ.-Id: 21757

A simple method for deadtime corrections in microbeam measurements.

Munnik, F.

In microbeam measurements on inhomogeneous samples large variations in count-rate can occur. These variations result in variations in deadtime that have to be used to correct elemental distribution maps. However, the deadtime is usually not available on a pixel by pixel basis. In this work, a simple model is proposed to calculate the deadtime for each pixel. Measurements to determine the deadtime per event, needed in the model, are presented and the deadtime corrections are presented for real samples.

Keywords: dead time; PIXE

  • Poster
    14th International Conference on Particle Induced X-ray Emission (PIXE 2015), 26.02.-03.03.2015, Somerset West, South Africa

Publ.-Id: 21756

Eliashberg analysis of the optical conductivity in superconducting Pr2CuOx with x similar or equal to 4

Schachinger, E.; Chanda, G.; Lobo, R. P. S. M.; Naito, M.; Pronin, A. V.

Superconducting Pr2CuOx, x similar or equal to 4 films with T' structure and a Tc of 27 K have been investigated by millimeter-wave transmission and broadband (infrared-to-ultraviolet) reflectivity measurements in the normal and superconducting state. The results obtained by both experimental methods show a consistent picture of the superconducting condensate formation below Tc. An Eliashberg analysis of the data proves d-wave superconductivity and unitary-limit impurity scattering of the charge carriers below Tc. The derived electron-exchange boson interaction spectral function I2chi(omega) shows only marginal changes at the superconducting transition with the mass enhancement factor lambda, the first inverse moment of I2chi(omega), being equal to 4.16 at 30 K and to 4.25 at 4 K.

Publ.-Id: 21755

Comparability and accuracy of nitrogen depth profiling in nitrided austenitic stainless steel

Manova, D.; Díaz, C.; Pichon, L.; Abrasonis, G.; Mändl, S.

A comparative study of nitrogen depth profiles in low energy ion implantation nitrided austenitic stainless steel 1.4301 by glow discharge optical emission spectroscopy (GDOES), secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA) is presented. All methods require calibration either from reference samples or known scattering or reaction cross sections for the nitrogen concentration, while the methods producing a sputter crater – SIMS and GDOES – need additional conversion from sputter time to depth. NRA requires an assumption of material density for a correct conversion from the ‘natural’ units inherent to all ion beam analysis methods into ‘conventional’ depth units. It is shown that a reasonable agreement of the absolute concentrations and very good agreement of the layer thickness is obtained. The observed differences in broadening between the nitrogen distribution near the surface and the deeper region of the nitrided layer–steel interface are discussed on the basis of surface contaminations, surface roughening and energy straggling effects.

Keywords: GDOES; SIMS; NRA; Austenitic stainless steel; Expanded austenite

Publ.-Id: 21754

Towards Atomic Physics in PIConGPU

Huebl, A.; Garten, M.; Widera, R.; Huang, L.; Kluge, T.; Bussmann, M.

Particle-in-Cell (PIC) codes are a ubiquitous tool to study laser-plasma physics in a fully relativistic environment. Theoretical models for plasma based accelerators and corresponding experiments, as planned by the HIBEF collaboration (XFEL), depend dramatically on the ability to precisely predict the complex processes inside of targets.

Unfortunately, basic atomic processes like the ionization dynamics of solid foil target in ultra-high fields of modern short-pulse laser systems in the PW class are not covered by the basic PIC algorithm. This talk shows ways to introduce the microscopic ionization dynamics inside the targets in a self-consistent and rigorous way. Combined with modern compute hardware such as GPUs and manycore systems in general, this paves the road to a new quality of multi-physics simulations with ab-initio modeling of atomic processes in strong laser fields.

Keywords: PIC; GPU; Ionization; CUDA; PIConGPU; HPC; HIBEF

  • Lecture (Conference)
    DPG-Frühjahrstagung: FV Kurzzeitphysik und Plasmaphysik, 02.-05.03.2015, Bochum, Deutschland

Publ.-Id: 21753

Heating and Ionization Dynamics in Solid Density Plasmas Driven by Ultra-short Relativistic Lasers

Huang, L. G.; Kluge, T.; Bussmann, M.; Cowan, T. E.

The dynamics of heating and ionization, which determines the crucial plasma parameters such as temperature, free electron density and so on, is one of the fundamental issues in the realm of ultra-short relativistic laser-solid target interactions. We present our work on investigation of heating and ionization dynamics in solid copper target irradiated by ultra-short intense laser using two dimensional particle-in-cell simulations. The simulation results show that the bulk electron temperature is very sensitive to the initial preplasma scale length. By varying the preplasma scale length from 0 to 0.1 λ_0, the bulk electron temperatures in the interest of region increase from ~26 eV to ~109 eV, which agrees very well with the theory based on Ohmic heating mechanism by treating the return current correctly. The bulk electron heating is finally translated into bulk ionization, which leads to the average Cu ion charge state increasing from ~4.3 to ~10.7.

Keywords: Heating; Ionization; Return Current

  • Lecture (Conference)
    DPG-Frühjahrstagung, 02.-05.03.2015, Bochum, Deutschland

Publ.-Id: 21752

Spectroscopic identification of Np(V) sorption complexes at the mineral oxide-water interface

Müller, K.; Steudtner, R.; Huittinen, N.; Bok, F.; Rossberg, A.

Neptunium (Np) is one of the most important components of nuclear waste to consider for the long-term safety assessment of nuclear waste repositories, due to the increasing enrichment through decay of Am-241, the long half-life and the high toxicity of Np-237. Hence, great attention is attracted to its geochemistry [1]. The molecular processes occurring at the solid-water interfaces present in the biogeosphere, strongly affect its migration [2]. Components of geological materials, such as metal oxides and hydroxides with a widespread environmental presence, high sorption capacity and tendency to form coatings on mineral surfaces, play an important role in regulating the Np mobility [3].
For a better understanding of the molecular events occurring at the mineral surfaces, x-ray absorption and vibrational spectroscopies are useful tools for the in-situ identification of actinyl surface species. In addition, time-resolved measurements provide kinetic information on the surface reactions [4].
In this work, Np(V) sorption on the oxyhydroxides of Fe, Mn, and Al is investigated by a combination of in-situ ATR FT-IR and EXAFS spectroscopies under a variety of environmentally relevant sorption conditions. By comparing Np(V) surface complexation reactions on hematite, magnetite, birnessite, and corrundum a very similar sorption behavior, namely the formation of one single inner-sphere complex can be elucidated. The spectroscopic results improve the geochemical transport modeling of Np(V) macroscopic data [4].

[1] Kaszuba, J.P. et al. (1999) Environ. Sci. Technol. 33, 4427-4433.
[2] O'Day, P.A. (1999) Rev. Geophys. 37, 249-274.
[3] Tochiyama, O. et al. (1996) Radiochim. Acta 73, 191-198.
[4] Müller, K. et al. (2015) Environ. Sci. Technol. 49, 2560-2567.

  • Lecture (Conference)
    Goldschmidt 2015, 16.-21.08.2015, Prague, Czech Republic

Publ.-Id: 21751

Use of spectroscopic and microscopic methods to reveal the evidence of U(VI) sorption on Acidovorax facilis isolated from subsurface environments

Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Arnold, T.

U(VI) biosorption experiments were performed using isolated Acidovorax facilis cell. From TRLFS measurements it can be concluded that phosphoryl groups are the main binding sites for uranyl, located in the lipopolysaccharide (LPS) unit in the outer membrane by Gram-negative Acidovorax facilis cells. In addition, EF-TEM/EELS studies provide microscopically and spectroscopically evidence of U sorbed at the outer membrane of Acidovorax facilis cells by showing high electron density and U ionization intensity peaks. The results support the TRLFS measurements and contribute to a better understanding of the binding mechanisms of U(VI) on Acidovorax facilis cells.

Keywords: Acidovorax facilis; Uranium; sorption; EF-TEM/EELS; TRLFS

  • Lecture (Conference)
    Environmental Radioactivity 2015 Conference, 21.-25.09.2015, Thessaloniki, Greece

Publ.-Id: 21750

Kompromissbereite Supraleitung

Zwicknagl, G.; Wosnitza, J.

Hohe Magnetfelder und Supraleitung vertragen sich üblicherweise nicht: Das Magnetfeld favorisiert parallel ausgerichtete Elektronenspins, während die Supraleitung Cooper-Paare mit antiparallelen Spins voraussetzt. Daher sollte bei ausreichend großen Feldern die Supraleitung zusammenbrechen. Wie Fulde und Ferrell sowie Larkin und Ovchinnikov bereits 1964 vorhergesagt haben, können räumlich getrennte supraleitende sowie magnetisch geordnete Bereiche aber auch bei noch höheren Magnetfeldern koexistieren.

  • Physik Journal 14(2015)3, 31-36

Publ.-Id: 21748

Novel phase transition and metastable regions in the frustrated magnet CdCr2O4

Zherlitsyn, S.; Tsurkan, V.; Zvyagin, A. A.; Yasin, S.; Erfanifam, S.; Beyer, R.; Naumann, M.; Green, E.; Wosnitza, J.; Loidl, A.

A new magnetic phase transition, which we assign to the separation of two different spiral phases, has been observed by ultrasound studies below the Néel temperature (TN = 7.8 K) in the frustrated antiferromagnet CdCr2O4. This transition renormalizes the velocity and amplitude of the transverse acoustic mode cT whereas the longitudinal mode cL is not affected. The specific heat does not show any significant change in the entropy at this transition. Furthermore, in an applied magnetic field, the mode cT exhibits extended metastable magnetostructural states neighboring the one-half magnetization plateau in CdCr2O4. By applying an exchange-striction model we can quantitatively describe the field dependence of the sound velocity below and above the one-half magnetization plateau.

Publ.-Id: 21747

Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy Ni50Mn35In15

Ghorbani Zavareh, M.; Salazar Mejia, C.; Najak, A. K.; Skourski, Y.; Wosnitza, J.; Felser, C.; Nicklas, M.

We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler alloy Ni50Mn35In15 by direct measurements in pulsed magnetic fields up to 6 and 20 T. The results in 6 T are compared with data obtained from heat-capacity experiments. We find a saturation of the inverse MCE, related to the first-order martensitic transition, with a maximum adiabatic temperature change of ΔTad= - 7 at 250 K and a conventional field-dependent MCE near the second-order ferromagnetic transition in the austenitic phase. The pulsed magnetic field data allow for an analysis of the temperature response of the sample to the magnetic field on a time scale of 10 to 100 ms, which is on the order of typical operation frequencies (10–100 Hz) of magnetocaloric cooling devices. Our results disclose that in shape-memory alloys, the different contributions to the MCE and Hysteresis effects around the martensitic transition have to be carefully considered for future cooling applications.

Publ.-Id: 21746

Ultrasmall Nanomaterials for Multimodal Imaging

Stephan, H.

kein Abstract verfügbar

  • Lecture (Conference)
    Gründungsveranstaltung der Deutschen Plattform NanoBioMedizin, DECHEMA, 04.03.2015, Frankfurt/Main, Deutschland

Publ.-Id: 21745

New Approaches for Prediction of Gas Holdups and Validation of the Mixing Length Concept in Gas-Liquid and Slurry Bubble Columns

Nedeltchev, S.; Schubert, M.

The successful prediction of gas holdups in (slurry) bubble columns is very important for both the design and scale-up of these reactors. In the literature hitherto there are only few reliable empirical gas holdup correlations (mainly for gas-liquid bubble columns). In this work, a new approach has been developed for predicting the gas holdups at ambient conditions in gas-liquid bubble columns (0.095 and 0.102 m in ID) operated with 21 pure organic liquids, 17 liquid mixtures and tap water. The same approach was also applied for prediction of gas holdups in a slurry bubble column (0.095 m in ID) operated with 7 three-phase systems under ambient conditions.
The new model for gas holdup prediction in (slurry) bubble columns is based on the theoretical calculation of the gas-liquid interfacial area: a=6ɛg/ds. This correlation is explicitly valid for rigid spherical bubbles. In the case of slurry bubble columns, an empirical correlation developed by Schumpe et al. (1987) for the interfacial area prediction is frequently used. When both correlations are set equal, then the theoretical gas holdup can be calculated provided that one knows how to estimate the Sauter-mean bubble diameter ds and the effective viscosity μeff. The same approach was also applied to gas-liquid bubble columns. However, the interfacial areas were estimated by the empirical correlation of Akita and Yoshida (1974).
In the above-mentioned approaches the estimation of the Sauter-mean bubble diameters ds was based on empirical correlations (Wilkinson et al. (1994) for bubble columns and Lemoine et al. (2008) for slurry bubble columns).
For given gas-liquid-solid system, gas distributor layout and column diameter, the ds value is a function of both the superficial gas velocity and gas holdup (1-ɛg)^1.56 (Lemoine et al., 2008). Following the above-described approach, the ɛg value was calculated (based on a trial and error method) from the ratio ɛg/(1-ɛg)^1.56. The obtained ɛg value in this way was multiplied by a correction factor (a function of Eӧtvӧs number Eo) since the formed bubbles under the tested experimental conditions were oblate ellipsoidal (i.e. non-spherical). In the case of slurry bubble columns, the Eo number was based on the slurry density ρSL.
Following the above-described approach in two-phase bubble columns, it was found that for given gas-liquid system, column diameter and Ug value the theoretical gas holdup could be estimated from the simplified correlation: ɛg^0.13=const. Then the obtained ɛg value was also multiplied by a correction factor (a function of Eo). So, the objective of this part of the research work was to find the best expressions for the correction factors in two-phase and three-phase bubble columns, which fit successfully the experimental gas holdups ɛg.
The determination of the scale of liquid mixing in the main hydrodynamic regimes of bubble column operation is also of essential importance for their design and scale-up. In this context, a new method (and correlation) has been proposed by Kawase and Tokunaga (1991) for the determination of the mixing length (L). The parameter L characterizes the degree and scale of mixing. It can be also associated with the distance over which a turbulent eddy retains its identity.
In this work, a new definition of entropy (E) has been developed on the basis of gas holdup time series data measured by a conductivity wire-mesh sensor in an air-water bubble column (0.15 m in ID). The new entropy has been estimated by means of multiple reconstructions of the signal. It was found that in the Ug range from 0.034 to 0.101 m/s (see Fig. 2), the entropy (E) decreased monotonously and it was correlated to the mixing length L (a function of both column diameter Dc and Ug^−0.38). Secondly, a newly defined information entropy (IE) has been also extracted from the gas holdup fluctuations and correlated to the mixing length in almost the same Ug range (0.022−0.101 m/s).
In a previous publication (Nedeltchev et al., 2014), it was shown that the Kolmogorov entropy (KE) and a new statistical parameter (called “maximum number of signal’s visits in a region” Nvmax) were capable of identifying the range of applicability (0.034≤ Ug≤0.112 m/s) of the mixing length concept. Another statistical parameter F (average/(3×average absolute deviation)) was also introduced by Nedeltchev and Schubert (2015) for validating the range of applicability of the mixing length concept. It was also found that the F index is a function of the mixing length L in the Ug range from 0.034 to 0.112 m/s.
In this work, a comparison of the results obtained by the five different parameters (E, IE, KE, Nvmax and F) is performed. Most of them (except for KE) are new and such a comparison has not been reported in the literature hitherto. It revealed that the determination of the boundaries of the transition flow regime and the range of applicability of the mixing length concept depends to some extent on the parameter used. Based on the above-mentioned parameters it was found that the mixing length concept was applicable only in the transition flow regime. Such a result has not been reported in the previous papers (for instance, in Kawase and Tokunaga, 1991).

Keywords: Gas-liquid bubble columns; Slurry bubble columns; Gas holdup modelling; Mixing length; Applicability range

  • Lecture (Conference)
    12th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering (GLS12), 28.06.-01.07.2015, New York, USA

Publ.-Id: 21744

Radiolabelling of colloids for highly sensitive detection in complex systems

Hildebrand, H.; Schymura, S.; Barthen, R.; Bellido, E.; Ojea-Jiménez, I.; Cydzik-Giacchin, I.; Kozempel, J.; Dalmiglio, M.; Bulgheroni, A.; Cotogno, G.; Simonelli, F.; Gründig, M.; Kulenkampff, J.; Holzwarth, U.; Gibson, N.; Lippmann-Pipke, J. K. F.

Colloids and nanoparticulate matter play an important role in the environment since they can act as carriers for (toxic) compounds and thereby enhance migration of substances that might normally be immobile under the given environmental conditions. The carrier properties of colloidal clay particles, humic substances and silica actinide colloids may play an important role in nuclear waste repositories. However, monitoring of these colloids in complex systems such as geological formations or groundwater is nearly impossible using conventional methods, especially at environmentally relevant concentrations and the high background load of other colloids or dissolved species of the same element. This obstacle can be overcome by the use of radiolabelling, which may be of crucial value in enabling such research.
We have developed various methods of introducing radiotracers into natural organic colloids such as humic or fulvic acids [1] and some of the most common technical nanoparticles, such as Ag0 [2], carbon and TiO2 nanoparticles [3]. Current studies are dealing with radiolabelling of CeO2 and quantum dots.
Five different approaches can be pursued in the radiolabelling of colloids or nanoparticles:
(1) Radiosynthesis – the synthesis of a compound using radioactive material
(2) Radiochemistry – the binding of a radioactive tracer to an existing compound
(3) In-diffusion – the in-diffusion of radioisotopes into existing particles
(4) Direct Activation – the activation of existing particles by proton irradiation
(5) Recoil labelling – the implantation of radionuclides into an existing particles using the recoil of a nuclear reaction

Radiosynthesis can be used to produce custom-made radiolabelled nanoparticles provided a suitable radiotracer is available. If the labelling is isotopic no difference in properties compared to non-radioactive particles are expected. We used this method to produce radiolabelled [105/110mAg]Ag nanoparticles.
Binding a radiotracer to a compound is a way of radiolabelling existing commercial or natural materials by a suitable radiochemical protocol. Carbon nanotubes and humic acids were successfully labelled with radioactive Iodine following the one-pot Iodogen method to yield [124/125/131I]CNTs and [125I]humic acid. No significant change in properties was detected compared to the original compounds.
Commercial TiO2 and Ag0 nanoparticles were labelled by the in-diffusion of isotopic radionuclides into surface defects and lattice structure at elevated temperatures. The resulting [110mAg]Ag0 and [44/45Ti]TiO2 nanoparticles showed no change in properties and the radiolabel proved to be stable under various conditions.
If a cyclotron is available, nanoparticles can be radiolabelled by activation via proton irradiation. The proton irradiation causes a nuclear reaction in the nanopowder producing the radiolabel inside the particles. Commercial TiO2 particles were labelled with 48V via a 48Ti(p,n)48V reaction.
If no suitable radiotracers/nuclear reactions are available for the above described methods, nanoparticles can be labelled utilising the recoil of a nuclear reaction to implant a radiotracer. Typically a mixture of a lithium compound and the to-be-labelled particles is irradiated with protons. The nuclear reaction 7Li(p,n)7Be produces 7Be which is implanted in the nanoparticles due to the recoil of the nuclear reaction. [7Be]MWCNT were produced successfully.
Table 1 shows the results for radiolabelling of particles. The described methods are adaptable for a wide range of other nanoparticles or colloids. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. In the research area of radioactive waste repositories the radiolabelling of humic substances, clay colloids and actinide silica colloids may be of particular interest.

Table 1: Comparison of the radiolabelling procedures and the resulting radiolabelled NP analysis.
Radiolabeling procedure Resulting NP Half-life of the radionuclide Activity concentration [MBq/mg] Detection limit [ng/L]
Radiosynthesis [110mAg]Ag0 250 d 1.5 33
[105Ag]Ag0 41.3 d 0.65 77

Radiochemistry [124I]CNT 4.2 d 8.0 6
[125I]CNT 59.4 d 19.9 2
[131I]CNT 8.0 d 3.7 14

In-Diffusion [110mAg]Ag 250 d 1 50
[44Ti]TiO2 60.4 a 0.01 5000
[45Ti]TiO2 3.08 h 135 0.5

Direct Activation [48V]TiO2 15.97 d 3.7 14
[7Be]MWCNT 53.29 d 0.041 1000

Recoil Labelling [7Be]TiO2 0.3 170
[7Be]SiO2 [4] 53.29 d 1.4 36
[7Be]MWCNT 0.055 1000
[1] Franke, K., Patt, J.T., Kupsch, H., Warwick, P.: Radioiodination of Humic Substances via Azocoupling with 3-[125I]Iodoaniline. Environ Sci Technol 42(11) (2008) 4083 - 4087.
[2] Hildebrand, H., Franke, K.: A new radiolabeling method for commercial Ag0 nanopowder with 110mAg for sensitive nanoparticle detection in complex media. J Nanopart Res 14 (2012) 1142.
[3] Hildebrand, H., Schymura, S., Holzwarth, U., Gibson, N., Dalmiglio, M., Franke, K.: Strategies for radiolabeling of commercial TiO2 nanopowder as a tool for sensitive nanoparticle detection. J Nanopart Res, submitted.
[4] Holzwarth, U., Bellido, E., Dalmiglio, M., Kozempel, J., Cotogno, G., Gibson, N.: 7Be-recoil radiolabelling of industrially manufactured silica nanoparticles. J Nanopart Res 16 (2014) 2574.

  • Poster
    3nd BELBaR Annual Meeting, 05.-06.03.2015, Madrid, Spain

Publ.-Id: 21743

Frequency dependence of an alternating magnetic field driven flow

Cramer, A.; Galindo, V.; Zennaro, M.

The flow induced by a single-phase alternating magnetic field (AMF) is studied mainly numerically, and by two preliminary experiments of quite different size. For validation, the well known dependence of the characteristic velocity on magnetic induction is reproduced experimentally and in the simulations. It is shown that the flow structure depends drastically on the frequency of the AMF. An investigation of the change of the characteristic velocity with frequency results in a quantitative difference of flows in an AMF compared to rotating and travelling magnetic fields.

Keywords: PACS:; 47.15.Rq; 47.85.M-

  • Magnetohydrodynamics 51(2015)1, 133-147

Publ.-Id: 21741

Comparison of New Entropy Profiles in Bubble Columns Operated with Air-Water and Air-Therminol Systems

Nedeltchev, S.; Hampel, U.; Schubert, M.

In a bubble column (0.15 m in ID) operated with an air-water system, a new entropy was extracted from gas holdup fluctuations measured by conductivity wire-mesh sensor. It was capable of identifying three transition velocities Utrans at 0.045, 0.089 and 0.112 m/s. In a different bubble column (0.162 m in ID) operated with an air-therminol LT system at ambient conditions, the new entropy was extracted from photon count time series measured by computed tomography. Three Utrans values were also identified at 0.03, 0.08 and 0.1 m/s. The information entropies yielded similar results.
Based on the new entropy results it can be concluded that the type of fluid and gas sparger used do not affect significantly the second and third Utrans values. There is an effect on the first Utrans value which can be explained with the strong gas maldistribution in the case of the bubble column operated with an air-water system.

Keywords: Bubble column; Flow Regime Identification; Entropy; Wire-Mesh Sensor; Computed Tomography

  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 21740

Performance of timing resistive plate chambers with relativistic neutrons from 300 to 1500MeV

Blanco, A.; Adamczewski-Musch, J.; Boretzky, K.; Cabanelas, P.; Cartegni, L.; Ferreira Marques, R.; Fonte, P.; Fruehauf, J.; Galaviz, D.; Heil, M.; Henriques, A.; Ickert, G.; Körper, D.; Lopes, L.; Palka, M.; Pereira, A.; Rossi, D.; Simon, H.; Teubig, P.; Traxler, M.; Velho, P.; Altstadt, S.; Atar, L.; Aumann, T.; Bemmerer, D.; Caesar, C.; Charpy, A.; Elekes, Z.; Fiori, E.; Gasparic, I.; Gerbig, J.; Göbel, K.; Heftrich, T.; Heine, M.; Heinz, A.; Holl, M.; Ignatov, A.; Isaak, J.; Johansson, H.; Kelic-Heil, A.; Lederer, C.; Lindberg, S.; Löher, B.; Machado, J.; Marganiec, J.; Martensson, M.; Nilsson, T.; Panin, V.; Paschalis, S.; Petri, M.; Plag, R.; Pohl, M.; Rastrepina, G.; Reifarth, R.; Reinhardt, T. P.; Röder, M.; Savran, D.; Scheit, H.; Schrock, P.; Silva, J.; Stach, D.; Strannerdahl, F.; Thies, R.; Wagner, A.; Weigand, F. W. M.

A prototype composed of four resistive plate chamber layers has been exposed to quasi-monoenergetic neutrons produced from a deuteron beam of varying energy (300 to 1500 AMeV) in experiment S406 at GSI, Darmstad, Germany. Each layer, with an active area of about 2000 × 500 mm2, is made of modules containing the active gaps, all in multigap construction. Each gap is defined by 0.3 mm nylon mono-filaments positioned between 2.85 mm thick float glass electrodes. The modules are operated in avalanche mode with a non-flammable gas mixture composed of 90% C2H2F4 and 10% SF6. The signals are readout by a pick-up electrode formed by 15 copper strips (per layer), spaced at a pitch of 30 mm, connected at both sides to timing front end electronics. Measurements of the time of flight jitter of neutrons, in the mentioned energy range, point to a contribution of the resistive plate chamber in the order of 150 ps, independent of the neutron energy.

Keywords: Instrumentation and methods for time-of-flight (TOF) spectroscopy; Resistive-plate chambers; Particle detectors; Neutron detectors (cold, thermal, fast neutrons)

Publ.-Id: 21738

Effect of deposition conditions and annealing temperature on tunnel magnetoresistance and structure of MgO-based double-barrier magnetic tunnel junctions

Feng, W.; Fowley, C.; Bernert, K.; Sluka, V.; Kowalska, E.; Aleksandrov, Y.; Lindner, J.; Fassbender, J.; Gan, H.; Kunz, A.; Hübner, R.; Coey, J. M. D.; Deac, A. M.

Tunnel magnetoresistance was measured in CoFeB-MgO-based double-barrier magnetic tunnel junctions. Variation of the sputtering power density is used to control the relative B content of the middle electrode. Magnetoresistance ratios in both upper and lower junctions are suppressed with respect to the single-barrier case. While the lower junction shows a saturation of the magnetoresistance as a function of high temperature annealing for all sputtering power densities, the upper junction exhibits an increase in magnetoresistance as a function of annealing temperature with higher values for higher sputtering power density. The suppression of high magnetoresistance is attributed to a lack of strong crystallisation in the middle electrode, which is confirmed by cross-section transmission electron microscopy. Slight crystallisation of the middle electrode is achieved at the highest sputtering power density despite that fact that boron diffusion is suppressed due to the adjacent MgO tunnel barriers. Optimal deposition and post annealing conditions resulted in magnetoresistance values of 140 % and 80 % for the upper and lower junctions, respectively.

Keywords: boron diffusion; double-barrier magnetic tunnel junction; sputtering; tunnel magnetoresistance

  • IEEE Transactions on Magnetics 51(2015)11, 4400704
    DOI: 10.1109/TMAG.2015.2435260
  • Poster
    Intermag Conference 2015, 11.-15.05.2015, Beijing, China

Publ.-Id: 21737

Performance of timing Resistive Plate Chambers with protons from 200 to 800 MeV

Machado, J.; Adamczewski-Musch, J.; Blanco, A.; Boretzky, K.; Cabanelas, P.; Cartegni, L.; Ferreira Marques, R.; Fonte, P.; Fruehauf, J.; Galaviz, D.; Heil, M.; Henriques, A.; Ickert, G.; Körper, D.; Lopes, L.; Palka, M.; Pereira, A.; Rossi, D.; Simon, H.; Teubig, P.; Traxler, M.; Velho, P.; Altstadt, S.; Atar, L.; Aumann, T.; Bemmerer, D.; Caesar, C.; Charpy, A.; Elekes, Z.; Fiori, E.; Gasparic, I.; Gerbig, J.; Göbel, K.; Heftrich, T.; Heine, M.; Heinz, A.; Holl, M.; Ignatov, A.; Isaak, J.; Johansson, H.; Kelic-Heil, A.; Lederer, C.; Lindberg, S.; Löher, B.; Marganiec, J.; Martensson, M.; Nilsson, T.; Panin, V.; Paschalis, S.; Petri, M.; Plag, R.; Pohl, M.; Rastrepina, G.; Reifarth, R.; Reinhardt, T. P.; Röder, M.; Savran, D.; Scheit, H.; Schrock, P.; Silva, J.; Stach, D.; Strannerdahl, F.; Thies, R.; Wagner, A.; Wamers, F.; Weigand, M.

A prototype composed of four resistive plate chamber layers has been exposed to quasi-monoenergetic protons produced from a deuteron beam of varying energy (200 to 800 AMeV) in experiment S406 at GSI, Darmstadt, Germany. The aim of the experiment is to characterize the response of the prototype to protons in this energy range, which deposit from 1.75 to 6 times more energy than minimum ionizing particles. Each layer, with an active area of about 2000 × 500 mm2, is made of modules containing the active gaps, all in multigap construction. Each gap is defined by 0.3 mm nylon mono-filaments positioned between 2.85 mm thick float glass electrodes. The modules are operated in avalanche mode with a non-flammable gas mixture composed of 90% C2H2F4 and 10% SF6. The signals are readout by a pick-up electrode formed by 15 copper strips (per layer), spaced at a pitch of 30 mm, connected at both sides to timing front end electronics. Results show an uniform efficiency close to 100% along with a timing resolution of around 60 ps on the entire 2000 × 500 mm2 area.

Publ.-Id: 21736

Development of selective ligands for f-elements separation

Ikeda-Ohno, A.

In order to elucidate the separation mechanism of metals in chemical processes, understanding of the chemical species formed in the processes is fundamental particularly on a molecular level. Structural characterisation is of particular importance to understand the interaction between the metal of interest and separating reagents (i.e. ligands), which would be also beneficial to further improve the efficiency of separation processes and/or to develop new separation ligands. This talk will focus on the development of selective ligands for the separation of f-elements, as well as the coordination chemistry of f-elements with the developed ligands based on several X-ray spectroscopic techniques.

Keywords: f-elements; actinides; lanthanides; coordination chemistry; characterisation; separation

  • Invited lecture (Conferences)
    Microsymposium on Coordination Chemistry, 26.03.2015, TU Dresden, Dresden, Germany

Publ.-Id: 21735

The local environment of cobalt in amorphous, polycrystalline and epitaxial anatase TiO2:Co films produced by cobalt ion implantation

Yildirim, O.; Cornelius, S.; Smekhova, A.; Zykov, G.; Ganshina, E.; Granovsky, A.; Hübner, R.; Bähtz, C.; Potzger, K.

Amorphous, polycrystalline anatase and epitaxial anatase TiO2 films have been implanted with 5 at. % Co+. The magnetic and structural properties of different microstructures of TiO2:Co, along with the local coordination of the implanted Co atoms within the host lattice are investigated. In amorphous TiO2:Co film, Co atoms are in the (II) oxidation state with a complex coordination and exhibit a paramagnetic response. However, for the TiO2:Co epitaxial and polycrystalline anatase films, Co atoms have a distorted octahedral (II) oxygen coordination assigned to a substitutional environment with traces of metallic Co clusters, which gives a rise to a superparamagnetic behavior. Despite the incorporation of the implanted atoms into the host lattice, high temperature ferromagnetism is absent in the films. On the other hand, it is found that the concentration and size of the implantation-induced nanoclusters and the magnetic properties of TiO2:Co films have a strong dependency on the initial microstructure of TiO2. Consequently, metallic nanocluster formation within ion implantation prepared transition metal doped TiO2 can be suppressed by tuning the film microstructure.

Keywords: Dilute magnetic oxides; nano-cluster; Co:TiO2; microstructure

  • Journal of Applied Physics 117(2015)18
    DOI: 10.1063/1.4919702
  • Poster
    DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Germany


Publ.-Id: 21734

Tuning the antiferromagnetic to ferromagnetic phase transition in FeRh thin films by means of low-energy/low fluence ion irradiation

Heidarian, A.; Bali, R.; Grenzer, J.; Wilhelm, R. A.; Heller, R.; Yildirim, O.; Lindner, J.; Potzger, K.

Ion irradiation induced modifications of the thermomagnetic properties of equiatomic FeRh thin films have been investigated. The application of 20 keV Ne+ ions at different fluencies leads to broadening of the antiferromagnetic to ferromagnetic phase transition as well as a shift towards lower temperatures with increasing ion fluence. Moreover, the ferromagnetic background at low temperatures generated by the ion irradiation leads to pronounced saturation magnetization at 5 K. Complete erasure of the transition, i.e. ferromagnetic ordering through the whole temperature regime was achieved at a Ne+ fluence of 3E14 cm-2. It does not coincide with the complete randomization of the chemical ordering of the crystal lattice.

Keywords: Ion irradiation; FeRh

Publ.-Id: 21733

Visualization of steps and surface reconstructions in Helium Ion Microscopy with atomic precision

Hlawacek, G.; Jankovski, M.; Wormeester, H.; van Gastel, R.; Zandvliet, H. J. W.; Poelsema, B.

Helium Ion Microscopy is known for its surface sensitivity and high lateral resolution. Here, we present results of a Helium Ion Microscopy based investigation of a surface confined alloy of Ag on Pt(111). Based on a change of the work function of 25 meV across the atomically flat terraces we can distinguish Pt rich from Pt poor areas and visualize the single atomic layer high steps between the terraces. Furthermore, dechanneling contrast has been utilized to measure the periodicity of the hcp/fcc pattern formed in the 2 ML thick Ag alloy layer. A periodicity of 6.65 nm along the $\langle\overline{11}2\rangle$ surface direction has been measured. In terms of crystallography a hcp domain is obtained through a lateral displacement of a part of the outermost layer by $1/\sqrt{3}$ of a nearest neighbour spacing along $\langle\overline{11}2\rangle$. The findings are perfectly in line with results obtained with Low Energy Electron Microscopy and Phase Contrast Atomic Force Microscopy.

Keywords: Helium Ion Microscopy; Channeling; Surface alloy; Step contrast; Low Energy Electron Microscopy


Publ.-Id: 21732

The development of the market for rare earth elements: insights from economic theory

Schlinkert, D.; van den Boogaart, K. G.

In this paper, a clear and structured economic model is introduced to illustrate complex past and future developments of the market for rare earth elements (REE). The model consists of a sequence of four supply and demand models that give explanations how the mining and separation step of the REE value chain could concentrate in China. Furthermore, the sequence allows giving a coherent scenario for the future developments of the REE market. According to this scenario, the market could transform into an at least oligopoly due to a growing market demand. The validity of this scenario is discussed and evaluated from the perspective of western countries, investors and China. Additionally, a scenario, based on the models, of a propagating monopoly along the value chain will be discussed. Finally, suggestions are made for western governments to promote the transformation and lead it to a positive outcome.

Keywords: rare earth elements; economic model; monopoly; value chain

Publ.-Id: 21731

Crystalline nanostructures on Ge surfaces induced by ion irradiation

Ou, X.; Facsko, S.

Besides conventional low efficiency lithographic techniques broad ion beam irradiation is a simple and potentially mass productive technique to fabricate nanoscale patterns on various semiconductor surfaces. The main drawback of this method is that the irradiated semiconductor surfaces are amorphized, which strongly limits the potential application of these nanostructures in electronic and optoelectronic devices. In this work we report that high-quality crystalline nanostructure patterns are formed on Ge surfaces via Ar+ irradiation at elevated temperatures.
This pattern formation process resembles the pattern formation in homoepitaxy. Therefore, the process is discussed based on a "reverse epitaxy" mechanism.

Keywords: ion induced patterning; nanostructures; reverse epitaxy

Publ.-Id: 21730

Influence of a halophilic archaeum to uranium migration under highly saline conditions

Bader, M.; Drobot, B.; Müller, K.; Stumpf, T.; Cherkouk, A.

In Germany salt rock and clay are considered as potential host rock for the final repository of radioactive waste in deep geological formations. Both possibilities have in common that high saline conditions can occur. In clay deposits of Northern Germany pore water salt concentrations of 4.3 M were measured [1] and in salt rock the salt concentration is up to saturation. Despite these extreme environments some microbes are able to survive. To date little is known about the interactions of halophilic microorganisms with actinides and hence to the migration behavior. But for the safety assessment of the final repository it is important to know the impact of indigenous microorganisms. Microbes can interact with actinides in different ways [2]. Within this study, the sorption of uranium on the cell surface (so called biosorption) of Halobacterium noricense DSM 15987 cells was studied. This halophilic archaeum was chosen due to its worldwide occurrence in salt rock [3]. The reference strain was isolated in an Austrian salt mine [4] and similar species occurred also in the Waste Isolation Pilot Plant (WIPP, Carlsbad, New Mexico, USA) [3].
Biosorption studies were undertaken at pH 6.0 and a NaCl concentration of 3.0 M in dependence of uranium concentration, time and temperature. The uranium content in the supernatant after sorption was measured with ICP-MS (Inductively Coupled Plasma Mass Spectrometry). Both, supernatant and cell pellet, were analyzed with TRLFS (Time-resolved Laser-induced Fluorescence Spectroscopy) to get information about the formed complexes. Furthermore the cells were analyzed with Infrared Spectroscopy.
The results demonstrated that independent of the uranium concentration (10 – 120 µM) around 90 % of the added uranium was sorbed by the cells at room temperature. A time-dependent sorption study showed that this maximal sorption was reached after an incubation time of 42 h. A slightly faster sorption of added uranium could be seen at higher temperatures. Particularly at 50 °C, the maximal sorption was already reached after 24 h. In general, the obtained sorption curve indicated a two-step binding process of added uranium with a fast step within the first hours and a second slower one. For a uranium concentration of 100 µM the metal sorption rate of 37.5 ± 0.7 mg U(VI) per 1 g dry biomass of Halobacterium noricense DSM 15987 was determined .
Interestingly, with increasing time, uranium concentration and temperature the cells began to form agglomerates. Live/Dead staining (LIVE/DEAD® Bac LightTM Bacterial Viability Kit L7012, Molecular Probes) of cells after the biosorption with uranium showed that nearly all single cells were dead whereas agglomerated cells were alive. One conclusion is that this process is a kind of stress response to protect the cells themselves from environmental challenges.
The characterization of the formed cell-uranium-complexes with TRLFS indicated that uranium was bound to cellular carboxylic groups. This can be seen by comparing with literature spectra [5]. The obtained lifetimes of the uranyl complexes differed from those due to the quenching effect of the high chloride concentration to uranium luminescence. The binding of uranium to the carboxylic groups of the cell could be also verified with Infrared Spectroscopy.

[1] J. Larue, VerSi Endlagerung im Tonstein, Abschlussbericht 3607R02538 (2010).
[2] K. Morris, et al., Interactions of microorganisms with radionuclides 2, 101 (2002).
[3] J. S. Swanson, et al., Status report Los Alamos National Laboratory (2012).
[4] C. Gruber, et al., Extremophiles 8, 431 (2004).
[5] M. Vogel, et al., Sci. Total Environ. 409, 384 (2010).

  • Poster
    15th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 21729

Terahertz-driven ultrafast magnetization dynamics in canted antiferromagnetic YFeO3

Lee, J. S.; Kim, T.; Kovalev, S.; Tokunaga, Y.; Tokura, Y.; Gensch, M.

We investigate the coherent precessional motion of the magnetic moment in the canted antiferromagnetic YFeO3 single crystal after excitation by the transient magnetic field of an ultra-short THz pulse. Time-resolved measurements of the magneto-optical response in the presence of external magnetic fields confirm the exclusive magnetic origin of the interaction between THz pulse and the spin system.. By tuning the spectral component of the input THz pulse around the quasi-ferromagnetic mode located near 0.3 THz, we have experimentally verified that the THz control of the spin state requires resonant excitation. We could confirm these results from the simulation based on the Landau-Lifshitz-Gilbert equation with two sub-lattice model for the canted antiferromagnet. Furthermore, we demonstrate that the spin state can be switched all-optically on a picosecond timescale using THz pulses of square and oscillating shapes. Whereas the oscillating THz pulse with a spectral component resonant with the magnetic excitations is necessary for an efficient magnetization switching, we study the possibility for a further reduction of the necessary THz field strength by examining influences of variations in the anisotropy energy and Dzyaloshinskii-Moriya interaction upon the switching behaviors.

Keywords: High-field THz; magnetization Dynamics; spin Dynamics; THz control; ultra-fast

  • Lecture (Conference)
    20th International Conference on Magnetism - ICM2015, 05.-10.07.2015, Barcelona, Spain

Publ.-Id: 21728

Modelling of Free Surface Flow Within the Two-Fluid Euler-Euler Framework

Porombka, P.

Two-phase flows are regularly involved in the heat and mass transfer of industrial processes. To ensure the safety and efficiency of such processes, accurate predictions of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) are required. Direct Numerical Simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore the Euler-Euler framework is often employed for large-scale simulations which involves macro-scale modelling of the turbulent shear stress and the interphase momentum transfer.
As a long term objective, the research activities at Helmholtz-Zentrum Dresden - Rossendorf (HZDR) pursue the development of general models for two-phase flows which are based on first principles and include less empiricism. Part of this effort is focused on the development of an algebraic interfacial area density model (AIAD) [1,2] which enables the simulation of two-phase flows with general morphologies including bubble, droplet and stratified flow regimes with the two-fluid approach.
In this work a short overview of the AIAD model is given and recent developments are presented.
The modelling of the interfacial drag in free surface flows is of particular interest and subject to ongoing research. Apart from empirical correlations which are limited to certain flow regimes, different models have been developed for the local computation of the interfacial drag coefficient [3,4]. In the AIAD model the drag model given by Höhne et al. [3] is used. It has recently been subject to modifications which are presented and validated as a part of this study.
Furthermore, special attention is paid to the turbulence treatment at the phase boundary of free surface flows. A model for the damping effect on the turbulent fluctuations in the near interface region as proposed in [1] is validated in this work.
Model validation is performed by means of simulations of horizontal stratified two-phase flow with the Euler-Euler two-fluid approach and the results are compared to experimental data given by Stäbler [5].

  • Contribution to proceedings
    Joint Fluids Engineering Conference 2015, 26.-31.07.2015, Seoul, Korea
    Proceedings of the Joint Fluids Engineering Conference 2015

Publ.-Id: 21727

Tomography of the ionosphere with geostatistical inversion

Minkwitz, D.; van den Boogaart, K. G.; Hoque, M.; Gerzen, T.

The ionosphere is the upper part of the atmosphere where sufficient free electrons exist to affect the propagation of radio waves. Typically, the ionosphere extends from about 50 -1000 km and its morphology is mainly driven by solar radiation, particle precipitation and charge exchange. In the last decade Global Navigation Satellite Systems (GNSS, e.g. GPS and GLONASS) measurements have become one of the major tools for ionospheric sounding enabling the derivation of the total electron content (TEC) along a satellite to receiver ray path.

Our interest is the reconstruction of the ionosphere's electron density in order to mitigate the ionospheric delay in applications such as GNSS positioning and satellite-based radar imaging. Following the ionosphere's behaviour we establish a non-stationary spatial covariance model of the electron density, where its parameters are estimated in a maximum likelihood approach. Henceforth the integral GNSS TEC measurements and a non-stationary trend model are incorporated. Based on the derived spatial covariance the electron density is estimated by kriging with linear functionals.

Keywords: Bayes inversion; geostatistics of linear functionals

  • Lecture (Conference)
    IAMG 2015 The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    IAMG 2015 - The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
    Proceedings of IAMG 2015, Freiberg: IAMG office, 978-3-00-050337-5

Publ.-Id: 21726

The Effect of Problem Formulation on Adaptive Processing Decisions

van den Boogaart, K. G.; Tolosana Delgado, R.; Matos Camacho, S.

Geometallurgy is concerned with optimal mining and processing decisions based on a quantitative modeling of the ore micro fabric and the processes. The optimal choice is then inferred from a geostatistical model and a processing model (), typically by applying an optimization algorithm to select the best processing within a model formulation. The aim of our contribution is to discuss and show the effect of the problem formulation and on the performance of the optimal solution.

This analysis contains the effect limit input (e.g. grade vs. microfabric, joint distributions vs. correlation, ...), the scope of the decision (e.g. processing path, processing parameters, block decisions vs. shape decisions, decisions on sampling, blending, invest into capacity, sequencing) and of model accuracy (e.g. concerning unmodelled details).

The effects will be demonstrated with simulation examples in perfectly controlled stochastic settings. It can be shown, that problem formulation can have a major impact on the economic result, and that the effect of problem formulation depends on the actual setting.

Keywords: geometallurgy; geostatistics; decission theory

  • Lecture (Conference)
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
    Proceedings of IAMG 2015, Freiberg: IAMG office, 978-3-00-050337-5, 217-226

Publ.-Id: 21725

Influence of carbonate solubilisation on copper leaching from Kupferschiefer with organic acids

Kostudis, S.; Bachmann, K.; Kutschke, S.; Pollmann, K.; Gutzmer, J.

European Kupferschiefer deposits are one of the most important regional copper sources. Its complex structure and fine granularity demand smelting processes which require much energy and release environmentally unfriendly gases like sulphur dioxide. Thus alternative beneficiation strategies like biomining are worthwhile. Furthermore the Kupferschiefer challenges common acidophilic bioleaching approaches due to its high carbonate load consuming acid during decomposition. Therefore leaching in neutral pH ranges seems attractive. However, as decomposition of carbonates may also expose further copper minerals we investigated the influence of carbonate solubilisation on the leaching performance of organic acids. Leaching of copper from Kupferschiefer using biologically produced organic acids was proven to be feasible. Different parameters like pH, particle size and leaching temperature were evaluated. Copper solubilisation was monitored using mass spectrometry and scanning electron microscopy. The paper presents results and provides leaching strategies.

  • Contribution to proceedings
    21st International Biohydrometallurgy Symposium 2015, 05.-08.10.2015, Sanur, Bali, Indonesia
    Proceedings of the 21st International Biohydrometallurgy Symposium 2015
  • Advanced Materials Research 1130(2015), 278-281
    DOI: 10.4028/

Publ.-Id: 21724

Microbial diversity studies of Spanish bentonites: Comparison of clone libraries and Illumina-sequencing based methods

Merroun, M. L.; López-Fernández, M.; Sánchez-Castro, I.; Vargas-Vílchez, R.; Cherkouk, A.

The long-term disposal of radioactive wastes in a deep geological repository (DGR) is the accepted international solution for the treatment and management of these special residues, mainly produced by the nuclear energy industry. The present work describes the structure and composition of microbial communities in Spanish bentonites, considered as natural analogue of the bentonite-engineered barrier, by two different culture- independent approaches based on the 16S ribosomal RNA gene analysis: clone libraries and Illumina sequencing platform. These two techniques showed a high microbial diversity of the bentonite samples studied. The microbial community was dominated by Proteobacteria and Bacteroidetes, and contained bacteria potentially involved in the possible microbial deterioration processes of DGR safety case including transformations of clay minerals, mobilization/immobilization of radionuclides, etc. When analysing all of the datasets from the samples en masse we observed high similarity between the clone libraries and Illumina datasets in terms of dominant groups and the community profiles at the phylum level, while significant differences in the proportion of some phyla and class between the samples were observed. Illumina-sequencing was more sensitive to Bacteroidetes, while in the case of Gammaproteobacteria class, the traditional clone library was much more efficient. The structure and composition of the microbial communities present in the bentonites samples will be discussed in term of geochemistry and mineralogy of the clays, and also on their impact in the safety case of DGR. The results obtained indicate that the combination of both molecular techniques provide an accurate and boarder view of the microbial communities present in complex environmental samples.

  • Poster
    Clays in natural and engineered barriers for radioactive waste confinement, 23.-26.03.2015, Bruessels, Belgium

Publ.-Id: 21723

In situ spectroscopic identification of neptunium(V) inner-sphere complexes on the hematite-water interface

Müller, K.; Gröschel, A.; Rossberg, A.; Bok, F.; Franzen, C.; Brendler, V.; Foerstendorf, H.

Hematite plays a decisive role in regulating the mobility of contaminants in rocks and soils. The Np(V) reactions at the hematite−water interface were comprehensively investigated by a combined approach of in situ vibrational spectroscopy, X-ray absorption spectroscopy and surface complexation modeling. A variety of sorption parameters such as Np(V) concentration, pH, ionic strength, and the presence of bicarbonate was considered. Time-resolved IR spectroscopic sorption experiments at the iron oxide−water interface evidenced the formation of a single monomer Np(V) inner-sphere sorption complex. EXAFS provided complementary information on bidentate edge-sharing coordination. In the presence of atmospherically derived bicarbonate the formation of the bis-carbonato inner-sphere complex was confirmed supporting previous EXAFS findings.1 The obtained molecular structure allows more reliable surface complexation modeling of recent and future macroscopic data. Such confident modeling is mandatory for evaluating water contamination and for predicting the fate and migration of radioactive contaminants in the subsurface environment as it might occur in the vicinity of a radioactive waste repository or a reprocessing plant.

Keywords: iron oxides; Fe2O3; neptunyl; actinides; ATR FT-IR spectroscopy; x-ray absorption; EXAFS; surface complexation

Publ.-Id: 21722

Numerical simulations of a precession driven flow in a cylinder.

Giesecke, A.; Gundrum, T.; Herault, J.; Stefani, F.

Precession has long been discussed as a complementary energy source for driving the geodynamo. A fluid flow of liquid sodium in a cylindrical container, solely driven by precession, is considered as a source for magnetic field generation in the next generation dynamo experiment currently under development in the framework of DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies).
We present results from three-dimensional non-linear hydrodynamic simulations of a precession driven flow in cylindrical geometry. The main focus will be on non-axisymmetric time-dependent flow structures that could be responsible for dynamo action. Promising candidates may be triadic resonances that are caused by non-linear interaction of three distinct inertial modes. These modes have a comparable structure as the columnar convection cells that are responsible for dynamo action in geodynamo simulations, and it seems reasonable to expect similar properties in case of precessional forcing.
Our simulations reveal clear triads at aspect ratios close to predictions from the linear theory. However, the emergence of these structures requires a remarkable long time-span of the order of a few hundred rotation periods till a (quasi-)steady state is reached. Furthermore, the amplitude of the waves with higher azimuthal wavenumbers remains well below the forced m=1 mode. Their ability for dynamo action will have to be verified in future simulations of the magnetic induction equation.

Keywords: DRESDYN; Dynamo; Precession flow

  • Lecture (Conference)
    EGU General Assembly 2015, 13.-17.04.2015, Wien, Oesterreich
  • Open Access Logo Abstract in refereed journal
    Geophysical Research Abstracts 17(2015), EGU2015-5714

Publ.-Id: 21721

Advanced identification and discrimination of Indium-bearing minerals by automated mineralogy

Bachmann, K.; Frenzel, M.; Gutzmer, J.

Studies of the mineralogical deportment of indium generally focus on the measurement of trace concentrations in major ore minerals. The importance of actual In-minerals such as indite, roquesite and sakuraiite is not usually assessed. This is due to their low abundance and optical similarity to other, more common, sulphide minerals (e.g. sphalerite) rendering the reliable assessment of their concentration by traditional methods (point-counting) difficult at best. Their low abundance also means that reference materials for many of the relevant minerals are not readily available.
This contribution presents a general method developed to overcome these problems with SEM-based automated mineralogy. Using five carefully selected ore samples from the Neves-Corvo deposit it is shown that this approach not only allows for the reliable identification of trace indium minerals (roquesite) present within the ores, but it also enables the quantification of their respective concentrations and thus their contribution to the overall indium budget. Furthermore, additional information on other geologically and/or technologically relevant parameters like mineral association, grain shape and grain size are readily available.

Keywords: MLA; Neves Corvo; Indium; roquesite; automated mineralogy

  • Poster
    13th SGA Biennal Meeting, 24.-27.08.2015, Nancy, France

Publ.-Id: 21720

Hydrodynamics analysis in micro-channels of a viscous coupling using gamma-ray computed tomography

Bieberle, A.; Schlottke, J.; Spies, A.; Schultheiss, G.; Banzhaf, M.; Kuehnel, W.; Hampel, U.

In this work, high-resolution gamma-ray computed tomography (HireCT) was applied for the first time on a viscous coupling to visualize the internal operating fluid distribution. The HireCT measurement system comprises a 137Cs isotopic source and a gamma-ray detector arc operated in single photon counting mode and is able to produce cross-sectional images of dense objects with a spatial resolution of about 2 mm. To scan fast rotating parts rotation-synchronized CT scanning mode was employed in these experiments. The analyzed viscous coupling (Visco® clutch of MAHLE Behr) mainly consists of a driven primary disc and a secondary housing with an engine cooling fan mounted on it and is assembled within an experimental rig. The viscous coupling’s primary and secondary parts are axially assembled and a coupling liquid is pumped into engaged radial ring profiles to provide a defined torque transfer. The internal ring channel width, where the coupling liquid is to be observed, is considerably lower than one millimeter. Although the HireCT measurement system is not able to resolve these micro-channels, the coupling liquid can be successfully visualized via its contrast. Investigations have been performed at different filling levels corresponding to different transmission slips of the test coupling. Moreover, both radial and tangential liquid distributions for different operational steady states could be determined. The obtained experimental data were compared to results from computational fluid dynamics (CFD) simulations in some operating points and are in good agreement.

Keywords: viscous coupling; gamma-ray computed tomography; design optimization; CFD

Publ.-Id: 21719

A new methodology for utilizing multidimensional smart Kd-matrices in transport programs for long-term safety assessment

Stockmann, M.; Brendler, V.; Schikora, J.; Flügge, J.; Noseck, U.

Sorption on mineral surfaces is one important retardation process to be considered in long-term safety assessments for radioactive waste repositories. So far a conservative concept with temporally and spatially constant distribution coefficients (Kd values) for each model unit is applied in the respective transport simulations.
In this work we describe a new methodology for integrating temporally and spatially variable distribution coefficients, so-called smart Kd values, into the transport code r³t [1]. These smart Kd values are pre-calculated with a bottom-up approach from mechanistic sorption models (namely surface complexation and ion exchange) and stored in a multidimensional matrix by coupling of three computer codes: PHREEQC [2], UCODE [3] and SimLab [4]. This strategy has numerous advantages over reactive transport codes: (1) One can calculate smart Kd values for a reasonable number of environmental parameter combinations; (2) It is possible to perform uncertainty analysis based on such smart Kd matrices; (3) In contrast to UCODE, SimLab also provides methods for global sensitivity analysis; (4) The overall methodology is much more efficient in computing time than a direct coupling of the geochemical speciation code with the transport code r3t.
The capability of this new methodology is demonstrated exemplarily for the sorption of uranium UVI on a natural sandy aquifer [5] and is able to describe the sorption behavior in dependence of changing geochemical conditions quite well. Complex proof-of-concept scenarios were simulated for the sedimentary overburden of the Gorleben salt formation. Here, results for the upper aquifer are presented and discussed. As a prerequisite, the data processing of the field data [6, 7] is explained, including approximate correlations of environmental input parameters. Eventually, five environmental factors span the multidimensional parameter space for the Kd matrices.
Smart Kd distributions based on Latin-Hypercube samplings are given for different radionuclides covering the elements Am, Cs, Ni, NpV, Ra, SeVI, Th and UVI; with Am and Th also used as chemical analogues for Cm and Pu, respectively. They are then compared to constant values, determined in laboratory experiments [8], which have been used so far in transport calculations for long-term safety assessment. In a last step, ranked sensitivity indices are provided for all the investigated radionuclides to identify the most relevant environmental factors, which should be investigated in more detail in the future to improve both the data base and process understanding.

  • Lecture (Conference)
    MIGRATION 2015, 13.-18.09.2015, Santa Fe, NM, USA

Publ.-Id: 21718

Pygmy resonances and radiative nucleon captures for stellar nucleosynthesis

Tsoneva, N.; Goriely, S.; Lenske, H.; Schwengner, R.

The impact of low-energy multipole excitations and pygmy resonances on radiative neutron and proton capture cross sections in nuclei close to the -stability line is investigated. For this purpose, a microscopic theoretical approach based on self-consistent density functional theory and QRPA formalism extended with multi-phonon degrees of freedom, is implemented in a statistical reaction model. The advantage of the method is the fully microscopic nuclear structure input for unified description of low-energy multi-phonon excitations, pygmy and giant resonances. This is found important for the understanding of the fine structure and dynamics of nuclear response functions at low energies which strongly influence nuclear reaction rates of astrophysical significance. Calculations of the radiative capture cross sections of the reactions 85Kr(n,)86Kr, 87Sr(n,)88Sr and 89Y(p,)90Zr are discussed in comparison with the experiment. For the reactions 89Zr(n,)90Zr and 91Mo(n,)92Mo theoretical predictions of the reaction cross sections are made.

Keywords: Photonuclear reactions; radiative capture reactions; stellar nucleosynthesis; quasiparticle-phonon model

Publ.-Id: 21716

Tregs activated by bispecific antibodies: Killers or suppressors?

Koristka, S.; Cartellieri, M.; Arndt, C.; Feldmann, A.; Seliger, B.; Ehninger, G.; Bachmann, M. P.

In recent years, bispecific antibodies (bsAb) have emerged as promising tools for a target-specific redirection of T cells in order to eliminate malignant cells. However, CD3-engaging constructs might also activate T regulatory cells (Tregs) present in the tumor microenvironment. Whether this has detrimental or beneficial effects for tumor therapy is still controversially discussed.

Keywords: cytotoxicity; immunotherapy; immunsuppression; single-chain bispecific antibodies; T cell retargeting; T regulatory cells

Publ.-Id: 21715

Response of geological resident microbial communities to additions of nitrates and/or acetate, mimicking leachates of bituminized intermediate-level radioactive waste

Moors, H.; Mysara, M.; Cherkouk, A.; Bleyen, N.; Smets, S.; Schwyn, B.; Achim, A.; Wittebroodt, C.; Small, J.; de Cannière, P.; Stroes-Gascoyne, S.; Valcke, E.; Leys, N.

Clay deposits such as the Opalinus Clay formation are studied as host rocks for geological disposal of high- and intermediate-level long-lived radioactive waste in several European countries. Bituminized intermediate-level long-lived radioactive waste contains, besides bitumen and radionuclides, also large amounts of organics, nitrates and sulphates. Over time, these salts will dissolve, leach and diffuse into the surrounding clay host rock, together with water soluble organic substances. To mimic the potential effect of such inorganic– and organic leachates, pulses of nitrate and/or acetate have been injected in intervals of an in situ experiment, called Bitumen-Nitrate-Clay interaction (BN) experiment, running at the Mont Terri geological laboratory (St. Ursanne, Switzerland).
To elucidate whether the microbial communities, present in the BN experiment, are affected or involved in the observed biogeochemical changes.
Beside classical microbial analyses, at pivotal moments (i.e. before, during and after these pulse injection tests), priority was given to DNA-based molecular biology analysis methods, as these methods provide very accurate information on the composition, the metabolic capacity and possible evolution of bacterial communities in response to the nitrate and/or acetate injections.
The changes observed in the bacterial populations appeared to correlate well with the imposed physico-chemical changes. As soon as nitrate was added an overwhelming community shift appeared to nitrate reducing bacteria. If in parallel acetate was offered, the community composition did not alter that much, but the speed of nitrate reduction was increased twentyfold. This high nitrate removal speed was maintained as long as the easily consumable carbon source was abundant.

  • Poster
    FEMS - 6th Congress of European Microbiologists, 07.-11.06.2015, Masstrich, The Netherlands

Publ.-Id: 21714

The Bitumen-Nitrate-Clay Interaction Experiment at the Mont Terri Rock Laboratory, Switzerland: Response of Microbial Communities to Additions of Nitrate and Acetate

Moors, H.; Cherkouk, A.; Mysara, M.; Bleyen, N.; Smets, S.; Schwyn, B.; Albrecht, A.; Wittebroodt, C.; Small, J.; de Cannière, P.; Stroes-Gascoyne, S.; Valcke, E.; Leys, N.

Clay deposits such as the Opalinus Clay formation are studied as host rocks for geological disposal of high- and intermediate-level long-lived radioactive waste in several European countries. Bituminized intermediate-level long-lived radioactive waste contains, besides bitumen and radionuclides, also large amounts of nitrates and sulphates. Over time, these salts will dissolve, leach and diffuse into the surrounding clay host rock, together with water soluble organic substances. The presence of these compounds will induce several processes (e.g. ionic strength changes, ion exchange reactions with Na+, redox reactions with NO3-) that may affect the barrier properties of the clay host rock.
To study the fate of such inorganic– and organic leachates, an in situ experiment, called Bitumen-Nitrate-Clay interaction (BN) experiment, was installed in the Opalinus Clay at the Mont Terri underground research laboratory (St. Ursanne, Switzerland). The BN experiment aims to investigate the impact of a nitrate plume, with or without acetate, on the biogeochemistry of the near-field host rock. Acetate is used as representative of the organic water soluble fraction of bitumen degradation products. At a later stage, the BN experiment also aims to investigate the impact of nitrate and acetate on radionuclide reactivity and transport, especially for the redox sensitive radionuclides (e.g. 79Se, 99Tc, 23xU, …). The microbial analyses of the BN experiment intend to elucidate if and how currently present microbial communities are affected, and if and how microbes are involved in the observed biogeochemical processes. In this respect it is noteworthy to mention that the current BN set-up does not take into account any cement matrix or backfill, and offers the microbes only a pure aquatic environment, at almost neutral pH, in the form of a water-filled borehole. Such set-up allows free movement of nutrients, energy sources and dissolved electron donors and – acceptors, and does not impose any physical and/or chemical restriction on the microorganisms. In a real radioactive waste repository, the conditions will mostly deviate from the ones present in the BN experiment. Therefore, the in situ BN experiment can only be considered as a well engineered disposal 'test case'...

  • Lecture (Conference)
    Clays in natural and engineered barriers for radioactive waste confinement, 23.-26.03.2015, Bruessels, Belgium

Publ.-Id: 21713

Application of HERFD and in-situ XAS to study oxide nuclear fuel and fission product behavior

Martin, P. M.; Bes, R.; Prieur, D.; Vathonne, E.; Carlot, G.; Delorme, R.; Sabathier, C.; Freyss, M.; Garcia, P.; Bertolus, M.; Lebreton, F.; Caisso, M.; Delahaye, T.; Strach, M.; Belin, R.; Martel, L.; Vigier, J.-F.; Somers, J.; Prussmanns, T.; Vitova, T.; Rothe, J.; Dardenne, K.; Solari, P.-L.; Kvashnina, K.; Glatzel, P.; Scheinost, A. C.; Proux, O.

Over the last decades, XAS has evolved as a very useful tool to investigate nuclear materials with applications for fuel manufacturing of for the behavior for fission products. Nowadays, the possibility of applying HERFD measurements to radioactive compounds offers even more possibilities. Two recent studies dealing with the behavior of fission gases in UO2 nuclear fuel and investigating both the electronic and structural properties of uranium based mixed oxide fuels will be presented to illustrate the use of HERFD. Furthermore, recent experimental developments allowing to perform in-situ XAS measurements on actinide-based materials at high temperature and under controlled atmosphere, will be illustrated by the first results obtained on UO2±x and (U,La)O2±x samples.

Keywords: 4th generation nuclear fuels; transmutation

  • Lecture (Conference)
    16th International Conference on X-ray Absorption Fine Structure - XAFS16, 23.-28.08.2015, Karlsruhe, Germany

Publ.-Id: 21712

Electronic and structural changes induced by the incorporation of aliovalent cation in UO2

Prieur, D.; Martin, P.; Bes, R.; Lebreton, F.; Caisso, M.; Delahaye, T.; Strach, M.; Belin, R.; Martel, L.; Vigier, J.-F.; Prussmann, T.; Vitova, T.; Solari, P.; Kvashnina, K.; Scheinost, A. C.; Somers, J.

The incorporation of aliovalent cations into the UO2 structure leads to a change of the U oxidation state and can ultimately affects the physical propertiesy of these U1-yMyO2±x compounds. U1-yLayO2±x, U1-yPuyO2±x and U1-yAmyO2±xhave been investigated in the present work, as these materials are particularly relevant for the nuclear fuel cycle. LIII XANES, LIII HERFD-XANES and MIV HERFD-XANES measurements have been performed to study both electronic and structural environments of these fluorite-type solid solutions.

Keywords: 4th generation nuclear fuel; transmutation; ROBL

  • Lecture (Conference)
    XAFS16 - 16th International Conference on X-ray Absorption Fine Structure, 23.-28.08.2015, Karlsruhe, Germany

Publ.-Id: 21711

Topological spin textures as emitters for multidimensional spin wave modes

Sluka, V.; Weigand, M.; Kakay, A.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.; Raabe, J.; Wintz, S.

In the present contribution we will show that in a stacked vortex pair system with uniaxial magnetic anisotropy, spin waves of different symmetries and dimensionalities can be excited.

Keywords: vortex spin-wave

  • Lecture (Conference)
    20th International Conference on Magnetism, 05.-10.07.2015, Barcelona, Spanien

Publ.-Id: 21710

Electromagnetic Dipole Strength in 124,128,134Xe

Massarczyk, R.; Schwengner, R.; Junghans, A. R.

The electromagnetic dipole strength in several even nuclei in the chain of Xenon isotopes has been investigated at the bremsstrahlung facility of the ELBE accelerator in Dresden, Germany and at the HIγS facility in Durham, USA. The goal of these measurements is to extend the knowledge about the general behavior of the dipole strength in the energy region below the neutron separation energy under the aspect of neutron excess and nuclear deformation.

Publ.-Id: 21709

Staining on heritage building stone identified by NMR spectroscopy

Franzen, C.; Kretzschmar, J.; Franzen, C.; Weiss, S.

Brown staining on both pristine and painted sandstone surfaces is a regular problem reported from new building construction and restoration actions. During the recent restoration of the Großer Wendelstein, an impressive airy stone staircase in the castle Hartenfels in Torgau, Germany, extensive brown staining appeared in distinctive places. Due to the fact that such an incidence occurred while desalination with poultice compresses the usually extreme rare chance of sampling was possible and executed. Several chemical tests combined with Nuclear Magnetic Resonance (NMR) and Infrared (IR) spectroscopy proved humic substances as causation of the intensive staining. In the consequence restorative recommendations are drawn.

Keywords: NMR; IR-spectroscopy; staining; stone restoration; humic fulvic acid

Publ.-Id: 21708

Uptake of Selenium by delta-alumina at elevated temperatures

Franzen, C.; Bok, F.; Jordan, N.

The temperature impact on sorption processes of selenium oxyanions onto alumina was investigated.

Keywords: sorption oxyanions selenate selenite

  • Poster
    HiTAC-II Workshop; High Temperature Aqueous Chemistry, 16.04.2015, Heidelberg, Deutschland

Publ.-Id: 21706

Noise reduction of ultrasonic Doppler velocimetry in liquid metal experiments with high magnetic fields

Seilmayer, M.; Stefani, F.; Gundrum, T.

The last decades have seen a number of liquid metal experiments on the interaction of magnetic fields with the flow of electrically conducting fluids. The opaqueness of liquid metals requires non-optical methods for inferring the velocity structure of the flow. Quite often, such experiments are carried out in the presence of high electrical currents to generate the necessary magnetic fields. Depending on the specific purpose, these currents can reach several kiloamperes. The utilized switching mode power supply can then influence seriously the measurement system by electromagnetic interference. A recent experiment on the azimuthal magnetorotational instability (AMRI) has shown that a hydrodynamically stable Taylor-Couette flow becomes unstable under the influence of a high azimuthal magnetic field. Therefor an electrical current along the axis of the experiment with up to 20 kA generates the necessary field to destabilize the flow. We present experimental results on this AMRI experiment carried out at the PROMISE facility with an enhanced power supply. For this setup, we discuss the elaborate measures that were needed to obtain a reasonable signal-to-noise ratio of the ultrasonic Doppler velocimetrie (UDV) system. In dependence on various parameter variations, some typical features of the observed instability, such as the energy content, the wavelength, and the frequency are analyzed and compared with theoretical predictions.

Keywords: Taylor-Couette flow; magnetorotational instability; noise reduction; Ultrasonic Doppler velocimetry; electromagnetic interference

Publ.-Id: 21705

Validation and verification of the coupled neutron kinetic/thermalhydraulic system code DYN3D/ATHLET

Kozmenkov, Y.; Kliem, S.; Rohde, U.

One of the most intensively developing areas in the LWR multi-physics is a coupling of different best estimate 3-D neutron kinetic (BIPR, DYN3D, KIKO3D, NEM, PARCS, etc.) and thermal hydraulic (ATHLET, CATHARE, RELAP5, etc.) codes. Resulting coupled code systems have advanced capabilities of modeling both steady-state spatial distributions of the core power and their evolutions during different kinds of reactor transients. They are also highly useful in the analyses of possible reactor instabilities. Initial steady-state core power distributions can be disturbed by changes in the reactor loop mass flow rates and/or temperatures, by relocations of the low-temperature/diluted-boron water slugs within the primary system or by movements of control rods.
The coupled code used for LWR simulations in HZDR is DYN3D/ATHLET, which includes the 3-D core neutron kinetic and thermal hydraulic model of own development – DYN3D. The paper reports major capabilities of DYN3D as well as different ways of its coupling with the thermal hydraulic code ATHLET (external, internal and parallel), but mainly focuses on the validation and verification of the coupled code DYN3D/ATHLET. In the course of DYN3D/ATHLET validation/verification nearly 20 real plant transients and dynamic benchmarks have been simulated and analysed. The LWR types covered by these tasks are: VVER-440 (Bohunice-3, Greifswald-5 and Loviisa-1 units), VVER-1000 (Balakovo-1, Balakovo-4, Kalinin-3, Kozloduy-6, Saporozhye-6 and Temelin-2 units), B&W PWR (TMI-1) and BWR/4 MK-1 (Peach Bottom-2). For each reactor unit a computational model was developed according with the benchmark specifications. The simulated tasks describe different scenarios of increasing complexity, including the transients initiated by the main steam header or main steam line breaks, switching off/on of main circulation pumps, turbine trip and generator load drop. Some of the transients are characterized by a strongly asymmetric behavior of the primary system (e.g. caused by a steam line break), and the processes of coolant mixing in the lower and upper reactor plenums as well as in the downcomer are important for these cases. The coupled code DYN3D/ATHLET models the primary coolant mixing in two ways – whether by an appropriate nodalization of the mixing area or by using two specific models for mixing in the lower plenum. The first of the lower plenum mixing models is a part of the coupling interface at the core inlet plane, while the second one is the analytical coolant mixing model developed for the downcomer and the lower plenum regions of VVER-440.
The results of DYN3D/ATHLET simulations were assessed both against available measured data and calculations performed with similar multi-physics codes. The paper includes an overview of the simulated problems and the most representative results of DYN3D/ATHLET validation/verification for all coupling modes. The obtained experience of code validation provides a better understanding of reactor transients with a strong interaction between neutron kinetics and thermal hydraulics, helping to improve computation models. This experience is also useful for the present and further activities in coupling of DYN3D with other best estimate codes, like CFX, TRANSURANUS, etc.

Publ.-Id: 21704

Experimental investigation of irregular motion impact on 4D PET based particle therapy monitoring

Tian, Y.; Stützer, K.; Enghardt, W.; Priegnitz, M.; Helmbrecht, S.; Bert, C.; Fiedler, F.

Particle therapy positron emission tomography (PT-PET) is an in vivo and non-invasive imaging technique to monitor treatment delivery in particle therapy. The inevitable patient respiratory motion during irradiation causes artefacts and inaccurate activity distribution in PET images. 4D maximum likelihood expectation maximization (4D MLEM) allows for a compensation of these effects, but has up to now been restricted to regular motion for PT-PET investigations. However, intra-fractional motion during treatment might differ from that during acquisition of the 4D-planning CT (e.g. amplitude variation, baseline drift) and, therefore, might induce inaccurate 4D PET reconstruction results. This study investigates the impact of different irregular analytical motion patterns on PT-PET imaging by means of experiments with radioactive source and irradiated moving phantoms. Three sorting methods, namely phase sorting, equal amplitude sorting and event-based amplitude sorting, were applied to manage PET list-mode data. The inuence of these sorting methods on the motion compensating algorithm has analysed. The event-based amplitude sorting presented superior performance, although the 4D PT-PET reconstructions still suffered partly from the inexact deformation specifications due to the irregular motion.

Keywords: irregular target motion; 4D PET; particle therapy; dose monitoring

Publ.-Id: 21703

Open volume defects and magnetic phase transition in Fe60Al40 transition metal aluminide

Liedke, M. O.; Anwand, W.; Bali, R.; Cornelius, S.; Butterling, M.; Trinh, T. T.; Wagner, A.; Salamon, S.; Walecki, D.; Smekhova, A.; Wende, H.; Potzger, K.

Magnetic phase transition in the Fe60Al40 transition metal aluminide from the ferromagnetic disordered A2-phase to the paramagnetic ordered B2-phase as a function of annealing up to 1000°C has been investigated by means of magneto-optical and spectroscopy techniques, i.e., Kerr effect, positron annihilation and Mössbauer spectroscopy. The positron annihilation spectroscopy (PAS) has been performed in-situ sequentially after each annealing step at the Apparatus for In-situ Defect Analysis (AIDA) that is a unique tool combining positron annihilation spectroscopy with temperature treatment, material evaporation, ion irradiation, and sheet resistance measurement techniques. The overall goal was to investigate importance of the open volume defects onto the magnetic phase transition. No evidence of variation in the vacancy concentration in matching the magnetic phase transition temperature range (400-600°C) has been found, whereas higher temperatures showed an increase in the vacancy concentration.

Keywords: FeAl; transition metal aluminides; open volume defects; AIDA; SPONSOR; phase transition; annealing; XRD; CEMS; MOKE; PAS

Publ.-Id: 21702

Charged defects and defect-induced processes in nitrogen films

Savchenko, E.; Khyzhniy, I.; Uyutnov, S.; Barabashov, A.; Gumenchuk, G.; Ponomaryov, A.; Bondybey, V.

Radiation effects in solid nitrogen irradiated with an electron beam were studied with emphasis on the role of charged centers in radiation-induced phenomena. The experiments were performed employing luminescence method and activation spectroscopy techniques - spectrally resolved thermally stimulated luminescence TSL and thermally stimulated exoelectron emission. Samples were probed in depth by varying electron energy, thus discriminating radiation-induced processes in the bulk and at the surface. Spectroscopic evidence of the excited N2 * (C3Πu) molecule desorption was obtained for the first time and mechanism of the phenomenon based on recombination of electron with intrinsic charged center N4 + was proposed. The key role of N3 + center dissociative recombination in generation of N radicals is suggested.

Publ.-Id: 21701

Prompt-Gamma-Imaging für die Echtzeit-Reichweiten-Verifikation in der Protonentherapie: Auf dem Weg zur klinischen Implementierung

Barczyk, S.; Golnik, C.; Priegnitz, M.; Vander Stappen, F.; Janssens, G.; Smeets, J.; Clementel, E.; Hotoiu, L.; de Xivry, J. O.; Baumann, M.; Enghardt, W.; Fiedler, F.; Krause, M.; Prieels, D.; Pausch, G.; Richter, C.

Eine besondere Herausforderung der Protonentherapie besteht in der Unsicherheit der Protonenreichweite im Patienten und den resultierenden Unsicherheiten der Dosisverteilung. Hier bietet die Methode der Reichweiten-Verifikation anhand der protoneninduzierten Prompt-Gamma-Emission einen vielversprechenden Ansatz zur Verringerung der Unsicherheiten. Hierfür wurde ein Prototyp einer Prompt-Gamma-Kamera von der Firma IBA entwickelt und für die zukünftige klinische Anwendung an der Dresdner Protonentherapieanlage installiert. In Zusammenarbeit mit IBA erfolgte die umfangreiche Charakterisierung und Vorbereitung der Kamera für die klinische Anwendung. Dies beinhaltete die Hardware- und Softwareentwicklung, Kalibrierung und Qualitätssicherung sowie die Erprobung am Phantom für unterschiedliche Bestrahlungsmodalitäten.

  • Lecture (Conference)
    21. Jahrestagung der DEGRO, 25.-28.06.2015, Hamburg, Deutschland
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 191(2015)1, S35-S36
    DOI: 10.1007/s00066-015-0847-x

Publ.-Id: 21700

Micro-focused Brillouin light scattering: imaging spin waves at the nanoscale

Sebastian, T.; Schultheiss, K.; Obry, B.; Hillebrands, B.; Schultheiss, H.

Spin waves constitute an important part of research in the field of magnetization dynamics. Spin waves are the elementary excitations of the spin system in a magnetically ordered material state and magnons are their quasi particles. In the following article, we will discuss the optical method of Brillouin light scattering (BLS) spectroscopy which is a now a well established tool for the characterization of spin waves. BLS is the inelastic scattering of light from spin waves and confers several benefits: the ability to map the spin wave intensity distribution with spatial resolution and high sensitivity as well as the potential to simultaneously measure the frequency and the wave vector and, therefore, the dispersion properties.

For several decades, the field of spin waves gained huge interest by the scientific community due to its relevance regarding fundamental issues of spindynamics in the field of solid states physics. The ongoing research in recent years has put emphasis on the high potential of spin waves regarding information technology. In the emerging field of \textit{magnonics}, several concepts for a spin-wave based logic have been proposed and realized. Opposed to charge-based schemes in conventional electronics and spintronics, magnons are charge-free currents of angular momentum, and, therefore, less subject to scattering processes that lead to heating and dissipation. This fact is highlighted by the possibility to utilize spin waves as information carriers in electrically insulating materials. These developments have propelled the quest for ways and mechanisms to guide and manipulate spin-wave transport. In particular, a lot of effort is put into the miniaturization of spin-wave waveguides and the excitation of spin waves in structures with sub-micrometer dimensions.

For the further development of potential spin-wave-based devices, the ability to directly observe spin-wave propagation with spatial resolution is crucial. As an optical technique BLS does not only allow to map the spin-wave intensity in general, but it, in particular, enables the realization of sub-micron space resolution. Focusing of the laser beam to a sub-micrometer spot size can be realized by implementing a microscope objective into the optical setup. Over the last decade, this micro-focus BLS technique has become an established method for the investigation of spin waves in microstructured magnetic elements and proved its value in particular regarding magnonics.

In this article, we will discuss the basic principles of the BLS process and illustrate the experimental optical setup. Particular emphasis will be put on the implementation of the high spatial resolution of the BLS microscope and the consequences this has for the experimental realization. In addition, the outline of a computer based operation principle and automated sample positioning will be given. Owing to these improvements in ease of use as well as experimental applicability, the BLS technique has maintained its relevance for investigations of today's research on spin waves in miniaturized magnetic structures. A selection of experiments in this field will be described.

Keywords: Brillouin light scattering; microscopy; spin waves; magnons; magnonics

Publ.-Id: 21698

The Tayler instability in liquid metal batteries and dynamo theory

Weber, N.; Galindo, V.; Kasprzyk, C.; Landgraf, S.; Stefani, F.; Weier, T.

The Tayler instability (TI), a kink-type current-driven instability, is discussed as a crucial ingredient of an alternative α-Ω stellar dynamo model. In the framework of the Tayler-Spruit dynamo, a finite current helicity generated by the TI may produce an α-effect, transforming an azimuthal into a poloidal magnetic field. Going from astrophysics to engineering, the TI may be relevant for Liquid Metal Batteries, too. In the context of renewable energies, such batteries have recently received considerable interest for large scale energy storage. Their main advantages (cheap raw materials, long life-time, low cost) result from their simple construction. Built as a stable density stratification of two liquid metals separated by a molten salt layer, such batteries can be easily scaled up. In that case, currents in the order of a few kA will appear and possibly trigger the TI. If the resulting fluid flow becomes too strong, it may disrupt the electrolyte layer, leading to a battery failure.
A quasi-static numerical model, using an integro-differential approach for the coupling of velocity and magnetic field, is presented and used to simulate the TI in the medium to low magnetic Prandtl number range (1e−3 to 1e−6 ). The properties of the instability (growth rate, velocities in saturation), the influence of the geometric aspect ratio and scaling laws are explored. The relevance of the TI for Liquid Metal Batteries as well as several possible ountermeasures are discussed. Further, the influence of different axial boundary conditions and the interaction of TI and electro-vortex flow is analysed.
The saturation mechanism of the TI at high magnetic Prandtl numbers is commonly explained by the β-effect. We propose a second, hydrodynamic saturation mechanism for the TI at low magnetic Prandtl numbers. This allows us to explain the moderate fluid velocities, observed by Seilmayer et al. in a liquid metal TI experiment. Finally, we analyse the occurence of kinetic and current helicity at magnetic Prandtl numbers between 1e−3 and 1e−6 and show the limit of the quasi-static approximation. We finish with a description of helicity waves of the saturated TI. It’s occurence, frequency and amplitude are characterised in the astrophysical context.

Keywords: Tayler instability; Liquid Metal Battery; stellar dynamo

  • Lecture (Conference)
    Bifurcations and Instabilities in Fluid Dynamics, 15.-17.07.2015, Paris, Frankreich

Publ.-Id: 21697

Low-dimensional compounds containing cyanido groups. XXVIII. Crystal structure, spectroscopic and magnetic properties of two copper(II) tetracyanidoplatinate complexes with 1,2-diaminopropane

Vavra, M.; Potočňák, I.; Dušek, M.; Čižmár, E.; Ozerov, M.; Zvyagin, S. A.

Violet crystals of {[Cu(pn)2]2[Pt(CN)4]}[Pt(CN)4]·2H2O (1, pn=1,2-diaminopropane) and blue crystals of [Cu(pn)Pt(CN)4]n·nH2O (2) were prepared under hydrothermal conditions and characterized using elemental analysis, IR and UV–vis spectroscopy and by X-ray crystal structure analysis. Different number of ν(C≡N) absorption bands of these two compounds reflects their different structures. An X-ray crystal structure analysis has shown that complex 1 is of ionic character and is formed from trinuclear [Cu(pn)2–Pt(CN)4–Cu(pn)2]2+ complex cation and discrete [Pt(CN)4]2– anion together with two molecules of crystal water. On the other hand, complex 2 is of polymeric character and is formed by 2D networks of [Cu(pn)Pt(CN)4]n composition and completed by n molecules of crystal water. Magnetic measurements show the presence of a weak antiferromagnetic exchange interaction in complex 1 (Θ = –0.2 K), while the magnetic susceptibility of complex 2 is well described by the model of uniform S = 1/2 spin chain with exchange interaction J/kB = –1.64 K.

Publ.-Id: 21696

Laser Fluoride Nanoceramic And Method For Production Thereof / Lasertechnische, fluoridische Nanokeramika und Methode zur Herstellung

in Russian

Siebold, M.; Schramm, U.; Garibin, E. A.; Gusev, P. E.; Krutov, M. A.; Mironov, I. A.; Osiko, V. V.; Smirnov, A. N.; Tchernova, Y. V.; Hein, J.; Nietzold, D.; Pohl, H.-J.

(EN) FIELD: chemistry. SUBSTANCE: fluoride nanoceramic is obtained by thermomechanical treatment of the starting crystalline material made from CaF2-YbF3, at plastic deformation temperature to obtain a workpiece in form of a polycrystalline microstructured substance, which is characterised by crystal grain size of 3-100 mcm and a nanostructure inside the grains, by annealing on air at temperature of not less than 0.5 of the melting point with compaction of the obtained workpiece in a vacuum at pressure of 1-3 tf/cm2 until the end of the deformation process, followed by annealing in an active medium of carbon tetrafluoride at pressure of 800-1200 mmHg. The starting crystalline material used can be a fine powder which has been subjected to heat treatment in carbon tetrafluoride, or a moulded workpiece of crystalline material made from the powder and heat treated in carbon tetrafluoride. EFFECT: invention enables to obtain a fluoride nanoceramic with high degree of purity and high uniformity of the structure of said optical material. 4 cl, 3 ex

(RU) Изобретение относится к технологии получения оптических поликристаллических материалов, а именно фторидной керамики, имеющей наноразмерную структуру и усовершенствованные оптические, лазерные и генерационные характеристики. Фторидную нанокерамику получают термомеханической обработкой исходного кристаллического материала, выполненного из CaF2-YbF3, при температуре пластической деформации до получения заготовки в виде поликристаллического микроструктурированного вещества, характеризующегося размером зерен кристаллов 3-100 мкм и наноструктурой внутри зерен, путем отжига на воздухе при температуре не менее 0,5 от температуры плавления с уплотнением полученной заготовки в вакууме при давлении 1-3 тс/см2 до окончания процесса деформации, после чего отжигают в активной среде тетрафторида углерода при давлении 800-1200 мм рт.ст. В качестве исходного кристаллического материала могут быть использованы мелкодисперсный порошок, прошедший термообработку в тетрафториде углерода, или отформованная заготовку кристаллического материала, полученная из порошка и термообработанная в тетрафториде углерода. Изобретение позволяет получать фторидную нанокерамику высокой степени чистоты с повышенной однородностью структуры данного оптического материала. 2 н. и 2 з.п. ф-лы, 3 пр., 1 табл.

  • Patent
    RU2484187 - Erteilung 08.12.2013

Publ.-Id: 21695

Structural investigation of (U0.7Pu0.3)O2-x mixed oxides

Vigier, J.-F.; Martin, P. M.; Martel, L.; Prieur, D.; Scheinost, A. C.; Somers, J.

Uranium-plutonium mixed oxide containing 30% of PuO2 is a candidate fuel for several fast neutron and accelerator driven reactor systems. In this work, a detailed structural investigation on sol-gel synthesized stoichiometric U0.7Pu0.3O2.00 and substoichiometric U0.7Pu0.3O2-x, using X-ray diffraction (XRD), oxygen 17 magic angle spinning nuclear magnetic resonance (17O MAS-NMR) and X-ray absorption spectroscopy is described. As observed by XRD, the stoichiometric U0.7Pu0.3O2.00 is monophasic with a lattice parameter in good agreement with Vegard’s law, while the substoichiometric U0.7Pu0.3O2-x material is biphasic. 17O MAS-NMR confirmed a random distribution of metal atoms and hence an ideal solid solution behaviour for U0.7Pu0.3O2.00. X-ray absorption near-edge structure (XANES) spectroscopy showed the prevalence of plutonium (III) in U0.7Pu0.3O2-x. Extended X-ray absorption fine-structure (EXAFS) spectroscopy indicated a similar local structure around U and Pu, in agreement with the long-range order determined by XRD.

Keywords: MOX; 17O MAS-NMR; XAS; XRD; uranium; plutonium

Publ.-Id: 21694

Partikeltherapie-PET – Optimierung der Datenverarbeitung für die klinische Anwendung

Helmbrecht, S.

Die Strahlentherapie ist einer der drei Partner im interdisziplinären Feld der Onkologie. In Europa, Asien und den USA besteht zunehmend die Möglichkeit einer Therapie mit Strahlen aus geladenen Ionen anstelle von Photonen. Eine Anlage in Dresden befindet sich in der Kommissionierungsphase.
Die Ionenstrahltherapie bietet den Vorteil einer sehr konformalen Behandlung des Tumorvolumens durch die endliche Reichweite der Strahlen und ein ausgeprägtes Dosismaximum kurz vor dem Ende des Strahlpfades. Da eine Therapie in der Regel über bis zu 30 Sitzungen an verschiedenen Tagen durchgeführt wird und der Strahlweg stark von dem durchdrungenen Gewebe beeinflusst wird, sind Verfahren für eine in vivo Verifikation der Strahlapplikation wünschenswert. Eine dieser Methoden ist die Partikeltherapie–Positronen-Emissions-Tomografie (PT-PET). Sie beruht auf der Messung der vom Therapiestrahl erzeugten β+-Aktivitätsverteilung. Da eine direkte Berechnung der Dosis aus der Aktivität in lebendem Gewebe nicht möglich ist, wird die gemessene Aktivitätsverteilung mit einer berechneten Vorhersage verglichen und anschließend entschieden, ob die nächste Therapiesitzung wie geplant erfolgen kann oder Anpassungen notwendig sind. Die vorliegende Arbeit beschäftigt sich mit drei Themen aus dem Bereich der Datenverarbeitung für die PT-PET.
Im ersten Teil wird ein Algorithmus zur Bestimmung von Reichweitendifferenzen aus zwei β+- Aktivitätsverteilungen adaptiert und evaluiert. Dies geschieht zunächst anhand einer Simulationsstudie mit realen Patientendaten. Ein Ansatz für eine automatisierte Analyse der Daten lieferte keine zufriedenstellenden Ergebnisse. Daher wird ein Software-Prototyp für eine semiautomatische, assistierte Datenanalyse entwickelt. Die Evaluierung erfolgt durch Experimente mit Phantomen am 12C-Strahl.
Die erzeugte Aktivitätsverteilung wird von physiologischen Prozessen im Organismus beeinflusst.
Dies führt zu einer Entfernung von Emittern vom Ort ihrer Erzeugung und damit zu einer Verringerung der diagnostischen Wertigkeit der erfassten Verteilung. Zur Quantifizierung dieses als Washout bezeichneten Effektes existiert ein am Tierexperiment gewonnenes Modell. Dieses Modell wird im zweiten Teil der Arbeit auf reale Patientendaten angewendet. Es konnte gezeigt werden, dass das Modell grundsätzlich anwendbar ist und für die betrachtete Tumorlokalisation Schädelbasis ein Washout mit einer Halbwertszeit von (155,7±4,6) s existiert.
Die Berechnung der Vorhersage der β+-Aktivitätsverteilung kann durch übliche Monte-Carlo-Verfahren erfolgen. Dabei werden die Wechselwirkungsquerschnitte zahlreicher Reaktionskanäle benötigt. Als alternatives Verfahren wurde die Verwendung gemessener Ausbeuten (Yields) radioaktiver Nuklide in verschiedenen Referenzmaterialien vorgeschlagen. Auf Basis einer vorhandenen Datenbank dieser Yields und einer existierenden Condensed-History-Monte-Carlo-Simulation wird ein Programm zur Berechnung von Aktivitätsverteilungen auf Yieldbasis entwickelt. Mit der Methode kann die β+-Aktivitätsverteilung in Phantomen und Patienten zufriedenstellend vorhergesagt werden.
Die entwickelten Verfahren sollen einen Einsatz der PT-PET im klinischen Umfeld erleichtern und damit einen breiten Einsatz ermöglichen, um das volle Potential der Ionenstrahltherapie nutzbar zu machen.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-058 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 21693

Field-dependent de Haas-van Alphen frequencies in the non-centrosymmetric compound CrGe

Klotz, J.; Goetze, K.; Bruin, J.; Geibel, C.; Rosner, H.; Weber, K.; Schmidt, M.; Wosnitza, J.

  • Poster
    DPG Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21692

Improving material properties and performance of nuclear targets for transmutation-relevant experiments

Vascon, A.; Wiehl, N.; Runke, J.; Drebert, J.; Reich, T.; Trautmann, N.; Cremer, B.; Kögler, T.; Beyer, R.; Junghans, A. R.; Eberhardt, K.; Düllmann, C. E.

To improve the properties and performance of thin layers produced by molecular plating as targets for nuclear experiments investigations with lanthanide elements (i.e., natural Nd and 147Sm-enriched Sm) were carried out. Plating parameters like roughness of the deposition substrate, plating solvent, electrolyte concentration, and applied current density were varied. The influence of each parameter on the properties of the layers was studied by characterizing the deposits. The characterizations showed that nuclear targets perform differently depending on their layer properties. The results obtained from the investigations were applied for the quantitative preparation of homogeneous large-area (i.e., 42 cm2) 242Pu targets to be used for transmutation-relevant experiments.

Keywords: Molecular plating Improved layer properties α-Particle spectroscopy 242Pu Transmutation

Publ.-Id: 21691

Magnetfelder für die Forschung

Wosnitza, J.

Magnetfelder wirken auf bewegliche Ladungsträger und die magnetischen Freiheitsgrade eines Materials. Sie können somit das Verhalten von Materialien ebenso vielfältig beeinflussen wie z. B. Temperatur und Druck. Hohe Magnetfelder erlauben deshalb in der Physik und vielen anderen Forschungsdisziplinen grundlegende Untersuchungen der elektronischen und magnetischen Eigenschaften der Materie. So sind mehr als 15 Nobelpreise in Physik, Chemie und Medizin eng mit der Forschung in Magnetfeldern verknüpft. Nicht nur deshalb wächst die wissenschaftliche Nachfrage nach Forschungsanlagen, in denen Experimente in hohen Magnetfeldern möglich sind.

  • Book chapter
    in: Physik für Wissenschaftler und Ingenieure 7. deutsche Auflage, Berlin Heidelberg: Springer-Verlag, 2015, 978-3-642-54165-0, 904
    DOI: 10.1007/978-3-642-54166-7

Publ.-Id: 21690

Selenium uptake by cementitious materials: Effect of the redox state

Tits, J.; Rojo, H.; Scheinost, A. C.; Lothenbach, B.; Wieland, E.

Safety assessment studies for low- and intermediate level nuclear waste (L/ILW) repositories predict selenium-75 to be an important dose-determining radionuclide due to its long half-live and its presence in the anionic form resulting in weak retention by common near- and far field minerals. However, such predictions ignore the potential uptake by positively charged anion exchangers present in the cementitious near-field of a L/ILW repository, such as ettringite and hydrocalumite (AFm phases), a group of Ca, Al–layered double hydroxides.
The objective of this work is to investigate the immobilisation of Se under the alkaline and reducing conditions existing in a cement-based repository (-230mV < Eh < -750 mV, 10.0 < pH < 13.5). Under these conditions, Se(IV) and Se(-II) are the dominating redox states and the aqueous Se speciation is dominated by anionic species SeO32-, HSe2- and a series of polyselenides, mainly Se22-, Se32- and Se42-.

Keywords: Selenium; Nuclear waste; Redox; cement

  • Lecture (Conference)
    Migration 2015, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 21689

Influence of Growth Temperature on Structural, Optical, Electrical Properties and the Material Composition of RF Sputtered Zn1-xMgxO:Al Thin Films

Schurig, P.; Kramm, B.; Zhou, S.; Polity, A.; Meyer, B.

Zn1-xMgxO:Al (0.32 ≤ x ≤ 0.43) films were prepared by RF sputter deposition on c-sapphire and soda lime glass substrates with increasing growth temperatures from 298 up to 673 K. A ceramic ZnMgO:Al target was used as deposition material. The influence of the growth temperature on the structural, optical and electrical properties as well as the surface morphology and thin film composition was investigated. The grown films were all poly crystalline with a preferred out of plane orientation associated with the (002) XRD-reflection of ZnO but with a rising (111) MgO peak for higher temperatures. An increase in growth temperature results in a phase evolution from hexagonal to a mixed wurzite/rocksalt phase, a shift of the band gap to higher values as well as a rise in Mg concentration. A direct influence on surface

  • Lecture (Conference)
    2015 MRS Spring Meeting, 06.-10.04.2015, San Francisco, USA

Publ.-Id: 21688

Iron and phosphorus speciation in Fe-conditioned membrane bioreactor activated sludge

Wu, H.; Ikeda-Ohno, A.; Wang, Y.; Waite, T. D.

Iron dosing of membrane bioreactors (MBRs) is widely used as a means of meeting effluent phosphorus targets but there is limited understanding of the nature of iron and phosphorus-containing solids that are formed within the bioreactor (an important issue in view of the increasing interest in recovering phosphorus from wastewaters). In this study, bench scale MBRs were dosed with either ferrous or ferric salts and the Fe and P-containing mineral distributions in the Fe-conditioned sludges determined using X-ray absorption spectroscopy (XAS). Regardless of whether iron was dosed to the anoxic or aerobic chambers and regardless of whether ferrous (Fe(II)) or ferric (Fe(III)) iron was dosed, iron present in the minerals in the conditioned sludges was consistently in the +III oxidation state. Significant proportions of an Fe(III) mineral exhibiting very similar EXAFS spectra to strengite were present in all cases with the remaining fraction dominated by lepidocrocite in the Fe(II)-dosed case and ferrihydrite in the Fe(III)-dosed case. Approximately half the phosphorus in the activated sludge samples was present as a distinct Fe-PO4 mineral (such as strengite or an amorphous ferric hydroxyl phosphate analog) and half as phosphorus adsorbed to an iron oxyhydroxide mineral phase indicating that both co-precipitation and adsorption of phosphorus with iron contribute to removal of phosphorus from the MBR supernatant.

Keywords: Iron; Phosphor; Sulfur; Waste water treatment; Membrane Bioreactors; XAS; Speciation

Publ.-Id: 21687

Positron studies of interaction between yttrium atoms and vacancies in bcc iron with relevance for ODS nanoparticles formation

He, C. W.; Barthe, M. F.; Desgardin, P.; Akhmadaliev, S.; Behar, M.; Jomard, F.

The very high calculated binding energy of vacancy (V)-Y-sub (1.45 eV) in Fe makes it be one possible earliest formation stage of (Y, Ti, O) nanoclusters in ODS alloy. Our direct slow positrons annihilation observations are used to valid the interaction between V and Y. The pure bcc iron samples have been implanted by 1.2 MeV Y ions at three fluences from 1 x 10(14) to 3 x 10(15) cm(-2). Vacancy clusters are observed for all these three fluences. Their size and concentration decrease with Y concentration measured by using SIMS. Two hypotheses are proposed to explain the results, including the formation of complexes V-m-Y-n, and/or of precipitates Y-m-X-n (X = Y, O, etc.). In addition, vacancy clusters are detected deeper than predicted by SRIM calculation due to, at least for a part, channelling which is confirmed by Marlowe calculation and SIMS measurements.

Keywords: Nanostructured ferritic alloys; Dispersion; Metals; FE

Publ.-Id: 21686

New RP-CVD grown ultra-high performance selectively B-doped pure-Ge 20 nm QWs on (100)Si as basis material for post-Si CMOS technology

Mironov, O. A.; Hassan, A. H. A.; Uhlarz, M.; Kiatgamolchai, S.; Dobbie, A.; Morris, R. J. H.; Halpin, J. E.; Rhead, S. D.; Allred, P.; Myronov, M.; Gabani, S.; Berkutov, I. B.; Leadley, D. R.

Magnetotransport studies at low and room temperature are presented for two-dimensional hole gases (2DHG) formed in fully strained germanium (sGe) quantum wells (QW). Two designs of modulation doped heterostructure grown by reduced pressure chemical vapour deposition (RP-CVD) were used and included a normal structure (doping above the Ge channel and inverted structure (doping beneath the Ge channel). The mobility (μH) for the normal structure was measured to be 1.34×106 cm2/Vs with a sheet density (ps) of 2.9×1011 cm-2 at 1.5 K, and μH = 3970 cm2/Vs and ps ~1×1011 cm-2 for room temperature, determined from simulation using the Maximum Entropy- Mobility Spectrum Analysis (ME-MSA) method.
For the inverted structure a μH of 4.96×105 cm2/Vs and ps of 5.25×1011 cm-2 was measured at 90 mK. From the temperature dependent amplitude of Shubnikov de Haas oscillations, the normal structure was found to have a very low effective mass (m*) value of 0.063 m0 and a ratio of transport to quantum lifetime (α) of ~78. This extremely high α is indicative of the carrier transport being dominated by small angle scattering from remote impurities i.e. a sample having an extremely low background impurity level and very smooth hetero-interfaces. The inverted structure had an m* of 0.069 m0 and α ~29, which also indicates exceedingly high quality material.

Keywords: pure strained Ge channel; ultra-high mobility; SdH oscillation; impurity scattering

Publ.-Id: 21685

Bi2Se3Q-switched Nd:YAG ceramic waveguide laser

Tan, Y.; Zhang, H.; Zhao, C.; Akhmadaliev, S.; Zhou, S.; Chen, F.

Using a topological insulator (TI) Bi2Se3 as a saturable absorber, highly stable Q-switched laser pulses were realized in an Nd:YAG ceramic waveguide fabricated by carbon ion irradiation. The laser operation was at a wavelength of 1064 nm, with a repetition rate ranging from 2.7 to 4.7 MHz. The minimum pulsed duration was 46 ns. The maximum output power was up to 168.6 mW corresponding to the pulse energy of 31.3 nJ. This work opens up a practical way for implementation of TI modulated pulsed laser devices in dielectric waveguide platforms.

Keywords: Integrated optics; Lasers; Q-switched; Waveguides; Ion irradiation

Publ.-Id: 21684

Visualization of Heterogeneous Diffusion Processes with PET aligned with 3D FE simulation results

Kulenkampff, J.; Gründig, M.; Zakhnini, A.; Schikora, J.; Gerasch, R.; Lippmann-Pipke, J.

Positron-Emission-Tomography (PET) provides directly the spatial distribution of tracer concentrations with ultimate sensitivity and thus is particularly suited for visualizing the propagation of chemical species in opaque media (Kulenkampff et al. 2013). The method of sequential PET-imaging of the tracer distribution for quantifying diffusion parameters of heterogeneous opaque materials overcomes fundamental problems of common analytical methods, which either are destructive or without spatial resolution. However, these parameters are crucial for the safety analysis of geologic waste repositories in clay (Van Loon et al. 2004), for instance.
We apply longer-living nuclides than in common clinical PET-applications, like 58Co (T1/2=70.86 d) and 22Na (T1/2=2.603 a), and we have to consider the higher density of our specimens, which causes significant attenuation and scattering of photon radiation. These attenuation and scattering effects of the material, as well as the effects of parasitic gamma-radiation of the non-standard PET-nuclides have been quantified with Monte-Carlo-Simulations and are corrected (Zakhnini et al. 2013).
For instance, Opalinus clay rock cores were charged with solutions labelled with the PET-nuclide, and then the tracer distribution was sequentially imaged with PET (Kulenkampff et al. 2015). We aligned the 4D data set with FE simulation results (Comsol Multiphyiscs) and obtained the anisotropic diffusion coefficients. The residuals from the optimized model are attributed to structural inhomogeneities and heterogeneous composition.

Keywords: Diffusion; positron-emission-tomography; tracer

  • Lecture (Conference)
    7th International Symposium on Prcess Tomography, 01.-03.09.2015, Dresden, Deutschland

Publ.-Id: 21683

The Rossendorf Beamline at ESRF – dedicated to investigate radionuclides with X-ray absorption spectroscopy

Hennig, C.

Overwiew about research activities at the Rossendorf Beamline/Grenoble.

Keywords: EXAFS; XRD; Actinides

  • Lecture (others)
    Laboratoire d'Electrochimie et de Physicochimie des Matériaux et des Interfaces, CNRS, Grenoble, 13.02.2015, Grenoble, France

Publ.-Id: 21682

Uranium and uranyl luminescence in agate/chalcedony

Götze, J.; Gaft, M.; Möckel, R.

A systematic investigation of agates from occurrences around the world revealed that macrocrystalline quartz and chalcedony of these samples have unusual high U content. The content of U in agates may reach more than 70 ppm and is in contrast to crystalline quartz from magmatic and metamorphic rocks as well as pegmatite quartz which have U concentrations in the sub-ppm level. Spatially resolved trace-element analyses by LA-ICP-MS illustrate that the distribution of U within the agate samples is heterogeneous and is related to the structural banding. The results indicate that U is incorporated as uranyl ion which is bound to the silica surface and originates from the parallel accumulation of Si and U by alteration processes of surrounding host rocks during agate formation.
The uranyl ion is the cause for the greenish photoluminescence (PL) in agate, which can only be excited by short wavelengths (< 300 nm). The green PL is due to the electron transition from an excited level 1φ1u(1δ1u) back to the 1π3g level and is shown by a typical emission line at ca. 500 nm accompanied by several equidistant lines. These are due to the harmonic vibration of oxygen atoms along the uranyl axis. Luminescence can be detected in samples with U content down to the 1 ppm level.

Keywords: Luminescence; green PL; uranium; uranyl; agate; chalcedony; quartz

Publ.-Id: 21681

Analysis of mineral grades for geometallurgy: combined element to mineral conversion and quantitative X-ray diffraction

Parian, M.; Lamberg, P.; Möckel, R.; Rosenkranz, J.

Knowledge of the grades of valuable elements and their variation is rarely sufficient for geometallurgy. Minerals define not only the value of the deposit, but also the method of extraction and concentration. A number of methods for obtaining mineral grades were evaluated with a focus on geometallurgical applicability, precision and trueness. For geometallurgical program, the number of samples to be analyzed is huge, therefore a method for obtaining mineral grades needs to be cost-efficient, relatively fast, and reliable. Scanning electron microscopy based automated mineralogy is generally regarded as the most reliable method for analyzing mineral grades. However, the method is time demanding and expensive. Quantitative X-ray diffraction has a relatively high detection limit, 0.5%, while the method is not suitable for some base and precious metal ores, but still provides significant details on gangue mineral grades. The usage of the element to mineral conversion has been limited to simple mineralogy because the number of minerals is limited by the number of elements analyzed. This study investigates a new method for the estimation of mineral grades applicable for geometallurgy by combining both quantitative X-ray diffraction with Rietveld refinement and the element to mineral conversion method. The proposed method not only delivers the required turnover for geometallurgy, but also overcomes the shortcomings if XRD or EMC is used alone.

Publ.-Id: 21680

On the Feasibility of using Ex-core Neutron Instrumentation for Reactor State Diagnosis during Accidents

Brachem, C.; Konheiser, J.; Hampel, U.

In the case of a severe reactor accident, knowledge of the coolant level and the state of the core, including the progress of a possible core melt, would be of crucial interest. In such a scenario, the in-core instrumentation will most likely not be available. In this work, we explore the possibility of using the ex-core neutron detectors to gain information about the state of the reactor pressure vessel (RPV) inventory for a light water reactor. These detectors, which are typically implemented as ionization chambers, are located inside the biological shield and might still be operational during a severe accident. Stationary Monte Carlo calculations using the radiation transport code MCNP were performed to simulate the transport of neutrons outside the RPV and the reactions of the ionization chambers. These detector signals are computed for different model reactor states which might occur during a severe accident with core meltdown. The reactor model is based on data from a typical German Pressurized Water Reactor.
The results indicate that a change in coolant level should be detectable. Due to the core’s neutron self-shielding, deformations in the inner core region, such as the formation of a cavity, do not yield different signal rates in the ex-core neutron chambers. Changes not confined to the centre of the core, such as the relocation of corium into the lower head, re detectable by their change in the ionization chambers’ reaction rates.

Keywords: reactor accident; ex-core neutron detectors; MCNP; Pressurized Water Reactor

  • Lecture (Conference)
    23rd International Conference on Nuclear Engineering (ICONE), 17.-21.05.2015, Chiba, Japan
  • Contribution to proceedings
    23rd International Conference on Nuclear Engineering (ICONE), 17.-21.05.2015, Chiba, Japan

Publ.-Id: 21679

SRF Gun – A Candidate for Future CW Linear Accelerators

Arnold, A.

The success future continuous wave (CW) linear accelerators (LINAC) depend strongly on the development of appropriate sources. Thus, high brightness electron injectors for CW operation with megahertz pulse repetition rates and high bunch charges up to 1 nC are a hot topic of contemporary accelerator research and development. Present state-of-the-art CW photo electron sources are limited to a medium acceleration field; DC guns because of high-voltage discharge and normal conducting RF (NCRF) guns because of the dissipated power that scales with the square of the surface magnetic field (P~H²). Thus, in both cases the beam quality as well as the maximum extractable bunch charge is limited.
To get rid of these limitations the SRF gun concept is merging the well-established NCRF gun technology with the superconductivity. The resulting saving on dissipated power allows comparable high acceleration fields in continuous wave operation and thus high brightness and high average current at the same time. The talk will concentrate on the most advance electron source of this kind, the ELBE 3.5 cell SRF gun of Helmholtz-Zentrum Dresden-Rossendorf. Beside a historical classification and an overview on different design concepts, recent results as well as future challenges are discussed.

  • Lecture (others)
    Beschleunigerseminar am Institut für Kernphysik, 28.01.2015, Mainz, Deutschland

Publ.-Id: 21678

Study of the uncertainties due to position change of the PWR aeroball measurement system (AMS)

Konheiser, J.; Seidl, M.; Brachem, C.; Mueller, S.

The Aeroball measurement system (AMS) is an important in-core instrumentation in German pressurized water reactors. Therefore it is essential to know the possible uncertainties of this system. One is the lack of knowledge of the positions of balls in the guide tubes. The position changes can be up to 7 mm. Since the neutron flux distribution is not constant across the guide tubes, different reaction rates can result from the displacements. Both fuel assembly and full core calculations were carried out with the Monte Carlo code MCNP5. Differences in the reaction rates of up to 2% could be determined. In the most cases, differences are only up to 0.5%. The results were hardly influenced by burnup and boron concentration in the water moderator. For fuel assemblies containing gadolinium as a burnable poison a more pronounced reduction could be observed in the direction towards the gadolinium fuel rods. Overall it was found that the AMS measurement values are very robust with regard to possible variations of ball positions.

Keywords: PWR; Aeroball measurement system (AMS); uncertainty; Monte Carlo caculation

Publ.-Id: 21677

U(VI) retention by montmorillonite at high salinities: Surface complexation modeling

Fritsch, K.; Schmeide, K.

Argillaceous rock is one option for hosting radioactive waste repositories in deep geological formations in Germany. Furthermore, clays are considered as backfill material in a variety of nuclear repository types. While South German clay deposits have ionic strengths below 0.5 mol kg-1, the ionic strengths found in North German clay deposits can be as high as 4.5 mol kg-1. Radionuclide retention by clays at such high ionic strengths is rarely investigated and therefore dealt with in the present work.
Montmorillonite serves as model clay in uranium sorption experiments. NaCl is used as background electrolyte. The sorption data generated in the experiments are then processed with surface complexation models to generate thermodynamic formation constants.

Keywords: uranium sorption; argillaceous rock; clay; uranium; montmorillonite; high ionic strength; surface complexation modelling

  • Contribution to proceedings
    International Workshop ABC-Salt (IV) - Actinide Brine Chemistry in a Salt-Based Repository, 14.-15.04.2015, Heidelberg, Deutschland
  • Lecture (Conference)
    International Workshop ABC-Salt (IV) - Actinide Brine Chemistry in a Salt-Based Repository., 14.-15.04.2015, Heidelberg, Germany

Publ.-Id: 21675

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