Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Determination of size and density of embedded Ge nanocrystals in SiO2 by scanning force microscopy using a tomographic approach
Beyer, R.; von Borany, J.;
Germanium nanocrystals in silicondioxide were studied by atomic force microscopy (AFM) in order to reveal their size, density and distribution. The generation of the nanocrystals was accomplished by Ge+ ion implantation into a 100 nm silicondioxide layer and subsequent annealing at high temperatures in an inert atmosphere. Rutherford backscattering spectroscopy was applied in order to reveal the Ge distribution after implantation and annealing, and the formation of the nanocrystals was proven by transmission electron microscopy. The oxide layer was gradually etched in order to uncover the nanocrystals located at different depth positions within the SiO2 layer. Subsequently, the unveiled surfaces were examined by AFM in order to determine the size and density of the exposed nanocrystals. A correlation between the nanocrystal properties and the Ge implantation dose was corroborated.
Keywords: nanocrystals, silicondioxide, scanning force microscopy
  • Lecture (Conference)
    14th European Conference on Applications of Surface and Interface Analysis (ECASIA'11), 06.09.2011, Cardiff, Wales
  • Surface and Interface Analysis 44(2012), 1018-1021
    DOI: 10.1002/sia.5007

Publ.-Id: 16696 - Permalink

Organ culture of rat arteries for experimental studies of radiation-induced vascular dysfunction in vitro / in situ
Ullm, S.;
kein Abstract verfügbar
  • Diploma thesis
    Technische Universität Bergakademie Freiberg, Fakultät Chemie und Physik, 2011
    85 Seiten

Publ.-Id: 16695 - Permalink

SPIRIT- Ion Beam Applications for Europe
Möller, W.;
SPIRIT (Support of Public and Industrial Research using Ion beam Technology) is an Integrating Activities project integrating 11 leading European ion beam facilities. Transnational access is provided by supplying ions in an energy range from ~10 keV to 100 MeV for modification and analysis of solid surfaces, interfaces, thin films and nanostructured systems. The techniques cover materials, biomedical and environmental research and technology. Related R&D activities aim at the improvement of the experimental procedures and the installation of novel equipment. Numerous networking activities address both the interaction between the project partners and information and dissemination towards new users. The present contribution gives a short overview of the project structure and its activities, as well as its performance during the first two years.
Keywords: Ion Technologies Transnational Access

Publ.-Id: 16694 - Permalink

THEREDA – A thermodynamic database for increasing confidence in waste disposal
Richter, A.; Bok, F.; Brendler, V.;
For geochemical modeling of scenarios for the disposal of radioactive and (chemo)toxic waste, comprehensive and internally consistent thermodynamic data are required as well as sorption data for the surrounding host rocks. The use of different databases renders it difficult to compare results of geochemical modeling, due to incompleteness, inconsistencies, resticted ranges of variation (temperature, density, pressure), limitations in solution composition (ionic strength) and last but not least missing sorption data.
THEREDA (THErmodynamic REference DAtabase, – a cooperative project of leading research institutes in Germany – adresses these issues, providing full documentation, transparency of all data and a detailed quality assurance scheme [1,2].
THEREDA contains data for the three ion-ion interaction models: extendend Debye-Hückel, Specific Ion Interaction Theory, and Pitzer model. At present, two datasets has been released: the oceanic salt system (Na+, K+, Mg2+, Ca2+, Cl−, SO42−, H+, and H2O(l) within a temperature range of 273.15–523.15 K) and Am/Nd/Cm (Am(III), Nd(III), Cm(III), Na+, Mg2+, Ca2+, Cl−, H+, H2O(l) at 273.15 K). Tailored parameter files for various geochemical modeling codes are provided (PhreeqC, ChemApp, EQ3/6, Geochemist‘s Workbench). Documented benchmark calculations allow comparisons with other databases as well as between the different geochemical codes. All data, documentation and references are freely accessible via the projects homepage. Additionally, a user forum allows direct contact with the THEREDA members.
A holistic view of geochemical processes in the context of a safety analysis requires the inclusion of sorption calculations. A thermodynamically consistent treatment of these processes is only possible with surface complexation modeling (SCM). Respective data are already compiled in the RES³T database [3] (, providing competing entries for many systems. An integration into THEREDA thus not only requires a synchronisation of data structures but also a rigorous review process, leading to uniform recommended data sets for each sorbent-sorptive system. This data review process is already in progress.

[1] Altmaier et al. (2011), Report GRS-265, 63 p.
[2] Altmaier et al. (2008) ATW 53, 249–253.
[3] Brendler et al. (2003) J. Contam. Hydrol. 61, 281–291.
Keywords: thermodynamic database, THEREDA, sorption database, RES3T, geochemical modeling
  • Abstract in refereed journal
    Mineralogical Magazine 76(2012), 2283
  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada

Publ.-Id: 16693 - Permalink

Neue zellpenetrierende Phosphopeptide für die molekulare Bildgebung
Richter, S.;
kein Abstract verfügbar
  • Doctoral thesis
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, 2011
    150 Seiten

Publ.-Id: 16692 - Permalink

Molekulare Charakterisierung der Rezeptortyrosinkinase EphB4 an humanen Melanomzellen
Hoche, T.;
kein Abstract verfügbar
  • Other
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Biologie, 2011
    39 Seiten

Publ.-Id: 16691 - Permalink

NO-Donoren als potentielle Radioprotektoren bei strahleninduzierter vaskulärer Dysfunktion
Bechmann, N.;
kein Abstract verfügbar
  • Other
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Chemie, 2011
    81 Seiten

Publ.-Id: 16690 - Permalink

Sekretion und funktionelle Bedeutung von extrazellulärem S100A4-Protein im humanen Melanom
Tandler, N.;
kein Abstract verfügbar
  • Other
    Technische Universität Bergakademie Freiberg, Fakultät Chemie und Physik, 2011
    73 Seiten

Publ.-Id: 16689 - Permalink

Magnetismus und Leitfähigkeit - Zwei untypische Supraleiter: 1) Vom Halbleiter zum Supraleiter in Ga-dotiertem Ge ; 2) Supraleitung & Magnetismus in nanostrukturiertem Bi3Ni
Skrotzki, R.;
  • Lecture (others)
    Mitarbeiterseminar, Institut für anorganische Chemie II, Arbeitskreis Prof. Ruck, 27.-27:01:2012, Dresden, Deutschland

Publ.-Id: 16688 - Permalink

Nachweis von Eicosanoiden mittels LC-MS.
Sehn, F.;
kein Abstract verfügbar
  • Other
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Chemie, 2011
    69 Seiten

Publ.-Id: 16687 - Permalink

Relaxation dynamics in graphene excited with low photon energies
Winnerl, S.; Mittendorff, M.; Schneider, H.; Helm, M.; Orlita, M.; Potemski, M.; Winzer, T.; Malic, E.; Knorr, A.; Berger, C.; de Heer, W. A.;
The pump-induced transmission of graphene grown epitaxially on hexagonal SiC was studied in degenerate pump-probe experiments with photon energies in the range from 10 to 250 meV. Different relaxation times ranging from 0.5 ps to 300 ps were found. A strong increase of the relaxation time was observed when the photon energy was below the optical phonon energy (~200 meV). The experiments were complemented by microscopic modelling based on the graphene Bloch equations. This allowed us to identify the physical processes which are responsible for the carrier relaxation channels. We discuss the role of Auger-type processes, optical and acoustic phonons. The modelling, which is in good agreement with the experimental results, reveals that optical phonon scattering becomes significantly less efficient when the energy of the excitation photons is below the optical phonon energy. Surprisingly, however, scattering via optical phonons is still the predominant relaxation channel, even at lower energies. This is attributed to the presence of hot carriers, which can still fulfil energy conservation requirements [1].
For photon energies about twice the value of the Fermi energy Ef, which is about 10 meV for the quasi-intrinsic layers of the epitaxial graphene, an interesting effect is observed. As the photon energy is reduced below 2Ef, a transition from pump-induced transmission to pump-induced absorption occurs. While the induced transmission is associated with Pauli blocking of carriers which underwent interband transition, the induced absorption is caused by a change of the electron temperature due to intraband absorption.
Keywords: Relaxation dynamics, graphene, ultrafast spectroscopy
  • Lecture (Conference)
    Graphene Week, 03.-08.06.2012, Delft, The Netherlands

Publ.-Id: 16686 - Permalink

Relaxation dynamics in Landau-quantized graphene probed in the mid-infrared range
Mittendorff, M.; Winnerl, S.; Schneider, H.; Helm, M.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.;
In contrast to usual semiconductors in graphene the Landau levels (LL) are not equidistant. This provides the unique feature to investigate a single LL transition selectively. By applying magnetic fields of up to 7 T we could investigate three different transitions at a fixed wavelength of 16.5 µm via pump-probe measurements. By varying the magnetic field the photon energies got resonant to the different transitions. For the transition LL0(-1)->LL1(0) we could not only observe an increase of the pump-probe signal by a factor of 2.5 but also a decrease of the relaxation time from 20 ps to 5 ps. Interestingly, the reduced relaxation time is observed in a wider range of magnetic fields then the increase of the signal amplitude. Additionally the minimum of the relaxation time is shifted in respect to the maximum signal. For the transitions LL-1(-2)->LL2(1) and LL-2(-3)->LL3(2) we could only observe an slight increase of the pump-probe signal.
  • Lecture (Conference)
    DPG Frühjahrstagung, 29.03.2012, Berlin, Deutschland

Publ.-Id: 16685 - Permalink

Untersuchung von Molekülinteraktionen mittels Oberflächen-Plasmon-Resonanz
Lenk, J.;
kein Abstract verfügbar
  • Other
    Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Chemie und, 2011
    64 Seiten

Publ.-Id: 16684 - Permalink

Carrier relaxation in Landau-quantized graphene
Mittendorff, M.; Winnerl, S.; Schneider, H.; Helm, M.; Orlita, M.; Potemski, M.; Berger, C.; de Heer, W. A.;
We report on pump-probe measurements on quasi-neutral sheets of multilayer epitaxial graphene in magnetic fields. Using THz radiation, generated by the free electron laser, we directly probe the relaxation of Dirac fermions among well-resolved Landau levels (LLs). In contrast to conventional semiconductors, the Landau level spacing in graphene is not equidistant. Hence it is possible to investigate a single LL transition selectively. To this end we performed pump-probe measurements at a wavelength of 16.5 µm and applied a magnetic field of up to 7T. We varied the magnetic field for resonant measurements at different LL transitions. For the transitions LL-1(-2) -> LL2(1) and LL-2(-3) -> LL3(2) we could observe a slight increase of the pump-probe signal but no change in the relaxation time. For the transition LL-1(0) -> LL0(1) the pump-probe signal increased by a factor of 2.5 while the relaxation time decreased from 20 ps to 5 ps. These measurements were done with linear polarized radiation. To understand the decrease in the relaxation time additional measurements were carried out with circularly polarized radiation. The circularly polarized radiation enables to distinguish between the transition LL-1->LL0 and LL0->LL1. We performed the experiment in all combinations of left and right polarized radiation for the pump and probe beam. This revealed complex dynamics involving positive and negative signals. We suggest this to result from different relaxation channels including Auger processes.
Keywords: Landau quantization relaxation dynamics pump-probe magnetic field epitaxially grown
  • Poster
    Graphene Week 2012, 04.-08.06.2012, Delft, the Netherlands

Publ.-Id: 16683 - Permalink

Interaction of the receptor for advanced glycation endproducts (RAGE) with extracellular S100A4 modulates malignancy and radiation response of melanoma.
Haase-Kohn, C.; Pietzsch, J.;
wird nachgereicht
  • Poster
    Keystone Symposia on Molecular and Cellular Biology, 06.-11.03.2011, Keystone, Colorado, USA

Publ.-Id: 16682 - Permalink

Opredelenie termodinamicheskikh uslovii metamorfizma Kasakhskoj Svity dokembriya armenii po amfibolovomu termobarometru
in Russian
Aghamalyan, V. A.; Schulz, B.; Renno, A. D.; Lange, J.; Lorsabyan, T. K.;
Armenian Precambrian basement rocks metamorphism P and T conditions are defined applying amphibole thermobarometer by means of 104 amphibole microprobe chemical analyses. Measurements have been done on 2 samples of ophiolitic metabasalte amphibolites of the Precambian Kasakh suite. The general trend of metamorphism has been defined in the average amphibolite and green-schist facies in ranges T=420-640°C and P=1,6-5,7 kbar of low geothermal gradient of 12°C/km. Prograde megnesiohornblende-tschermakite and retrograde megnesiohornblende-actinolite zonation has been revealed, and also relics of kaersutite have been found. Relics of kaersutite are preserved from primary magmatic hornblende of the initial basalts
Keywords: Petrology; Armenia; Kasakh Suite; Geothermobarometry
  • Uchenie Zapiski Erevanskogo Gosudarstvennogo Universiteta (2011)3, 3-8

Publ.-Id: 16681 - Permalink

Optical afterburner for a SASE FEL: First results from FLASH
Foerst, M.; Gensch, M.; Riedel, R.; Tavella, F.; Schneidmiller, E. A.; Stojanovic, N.; Yurkov, M. V.;
Radiation pulse from a Self-Amplified Spontaneous Emission Free Electron Laser (SASE FEL) consists out of spikes (wavepackets). Energy loss in the electron beam (averaged over radiation wavelength) also exhibit spiky behavior on a typical scale of coherence length, and follows the radiation pulse envelope. These modulations of the electron beam energy are converted into large density (current) modulations on the same temporal scale with the help of a dispersion section, installed behind the x-ray undulator.
Powerful optical radiation is then generated with the help of a dedicated radiator (afterburner). We have recently demonstrated this principle at the Free Electron Laser in Hamburg (FLASH), and this paper present the first experimental results.
Keywords: X-ray photondiagnostic, THz, SRF accelerator, THz based electron bunch diagnostic
  • Open Access LogoContribution to proceedings
    IPAC 2011, 04.-09.09.2011, San Sebastian, Spain
    Proceedings of IPAC

Publ.-Id: 16680 - Permalink

Control of vortex pair states by post-deposition interlayer exchange coupling modification
Wintz, S.; Strache, T.; Körner, M.; Bunce, C.; Banholzer, A.; Mönch, I.; Mattheis, R.; Raabe, J.; Quitmann, C.; McCord, J.; Erbe, A.; Lenz, K.; Fassbender, J.ORC
We report on both the global and micromagnetic properties of interlayer exchange coupled spin systems. Irradiation with Ne ions is employed to achieve a phase transition from antiferromagnetic to ferromagnetic coupling. For extended trilayer films a full quantitative analysis of the bilinear and biquadratic coupling constants is performed. With increasing ion fluence we observe a steady increase of the bilinear coupling constant at an almost negligible decrease in saturation magnetization. The mixing of atoms at the layer interfaces is identified as the origin for this. The effects of ion modification on the magnetic microstructure are studied for the model system of layered vortex pairs. X-ray microscopy is used to directly image the individual magnetization circulations in trilayer disks. The circulation configuration is found to be determined by the film coupling for both coupling orientations with a homogenous coupling angle throughout the structure. For the vortex cores however, micromagnetic simulations indicate that due to the significant local demagnetization fields the parallel states are always energetically preferred. Nevertheless antiparallel configurations are metastable, having their signature in reduced core diameters. Our study provides new results on spin structures in interlayer exchange coupled trilayers and it demonstrates a promising way to control the local interlayer coupling post-deposition.
Keywords: magnetic vortex, x-ray microscopy, interlayer exchange coupling, ion beam modification

Publ.-Id: 16679 - Permalink

Applications of ion beams in Nanotechnology
Facsko, S.;
Ion beam are used largely in industry for surface treatment and deposition. In the last years low energy ion beam irradiation have shown potential for surface nanostructuring, either by direct writing with a focused ion beam, or by self-organized pattern formation during broad beam irradiations. I will present current activities of the HZDR of surface nanostructuring with oin beams and the application of such patterns in magnetism and plasmonics.
Keywords: ion beams, nanopatterning
  • Lecture (others)
    Dies academicus timisorensis, 26.-27.05.2011, Timisoara, Romania

Publ.-Id: 16678 - Permalink

Strength and limitations of continuum equations for sputter induced pattern formation
Facsko, S.; Keller, A.; Liedke, B.; Heinig, K.-H.;
Erosion of surfaces by ion beam sputtering leads frequently to the formation of periodic patterns, which show up as a ripple pattern under off-normal incidence and as hexagonally ordered dot patterns under normal or close to normal ion incidence.1 A first successful attempt to describe the formation of these patterns theoretically has been given by Bradley and Harper.2 In their model they assumed that ion sputtering is introducing a surface instability which is proportional to the surface curvature and will increase surface roughness. In addition, thermally activated surface self-diffusion has been considered as a smoothing mechanism. Finally, the interplay between these two competing mechanisms leads to a selection of a narrow range of surface modes which grow fastest under ion irradiation. This model has been translated into a linear continuum equation, now well known as the Bradley-Harper equation. The simplified partial differential equation already predicts successfully main experimental observations, like the change in ripple orientation when going to grazing incidence and isotropic patterns under normal incidence. However, it fails to explain the long time behaviour and the detailed dynamics of the pattern evolution.
Based on the Bradley-Harper model many extensions have been proposed since then. Some of them like the damped or undamped Kuramoto-Sivashinsky (KS) equation3 show a good qualitative agreement, however they still fail to predict several important experimental observations. In addition main improvements have been achieved by including the mass rearrangement on the surface induced by the ion impact.4
Recently, new models have been proposed for the description of pattern formation, which go beyond the KS equation. They introduce coupled fields, e.g. for the mobile species or the concentrations of the elements in compound materials.5 However, there is still a gap to be closed between the continuum equations and the microscopic model describing the collision cascade, the energy deposition into the surface, or the crater function induced by the ion impact. Here, theoretical approaches combining binary collision approximation for the ion irradiation and kinetic Monte Carlo simulations for the subsequent relaxation promise a detailed description of the mechanisms involved in the pattern formation process.
In this presentation the strengths and limitations of the existing continuum equations and extended models will be discussed and will be compared to experiments and kMC simulations.
Keywords: pattern formation
  • Invited lecture (Conferences)
    INTERNATIONAL CONFERENCE on Ion-Beam Induced Nanopatterning of Materials, 06.-10.02.2011, Bhubaneswar, Indien

Publ.-Id: 16677 - Permalink

Electrical Characterization of Short DNA Fragments
Wieser, M.; Liu, S.-P.; Weisbrod, S.; Tang, Z.; Marx, A.; Scheer, E.; Erbe, A.;
The electrical transport properties of DNA molecules are important for future molecular electronics applications. We characterized the electrical conductance of single DNA fragments in ambient condition and in buffer solution using a Mechanically Controllable Break Junction (MCBJ) setup which allows us binding molecules between two gold electrodes. We analyzed the electrical conductance of double stranded DNA and G-quadruplex molecules. G-quadruplex molecules consist of four guanine bases arranged in the shape of a square and a cation in the center. The electrical characterization is done by investigating the I-V curves characteristics of the molecules in different conditions.
Keywords: DNA, molecules, molecular electronics, conductance, MCBJ, Mechanically Controllable Break Junction
  • Poster
    DPG Frühjahrstagung 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 16676 - Permalink

Atomistische Simulation der Selbstorganisation bei der Ionenstrahlerosion
Kranz, A.; Heinig, K.-H.; Liedke, B.;

Während Ionenbestrahlung von Festkörpern kann es zur Bildung von Oberflächenstrukturen wie Ripples und Nanodots kommen. Diese Bildung wird mit Computerexperimenten untersucht werden. Dabei wird eine zweistufige Simulationsmethode eingesetzt, die im ersten Schritt die Kollisionskaskade eines Ioneneinschlages mit Binary Collision Approximation berechnet und im zweiten Schritt die Defektkinetik mittels kinetic Monte Carlo simuliert. Diese beiden Stufen werden für jeden Ioneneinschlag wiederholt. Dabei ergeben sich zwei mögliche Ansätze, die Simulationsergebnisse zu untersuchen.
Zum einen kann überprüft werden, inwieweit die simulierte Oberfläche verfügbaren Kontinuumsmodellen für die Musterbildung genügt. Der Vorteil der Simulation gegenüber dem Experiment besteht darin, dass man die volle zeitliche Entwicklung der Oberfläche anstelle einzelner Momentaufnahmen bekommt. Damit können unmittelbar bestehende Theorien bewerten werden.
Zum anderen kann man während der Simulation die Bewegung jedes einzelnen Atoms verfolgen. Dadurch kann man die Wahrscheinlichkeiten registrieren, mit denen die Atome in die unterschiedlichen Richtungen springen. Daraus kann der Massestrom und dessen Divergenz berechnet werden. Da die Divergenz des Massestroms nach dem zweiten Fick'schen Gesetz der Diffusion proportional zur zeitlichen Änderung der Konzentration und damit zur zeitlichen Änderung der Oberflächenhöhe ist, kann man damit Aussagen über die treibenden Mechanismen bei der Musterbildung treffen.
In diesem Vortrag sollen beide Ansätze vorgestellt und anhand eines Beispiels erläutert werden.

During ion beam irradition it is possible to observe the formation of surface structures like ripples and nanodots. This formation is examined by computer experiments. Therefore, a two step simulation method is used which calculates the collision cascade of one ion impact by binary collision approximation in a first step followed by the simulation of the defect kinetic via kinetic Monte Carlo. These two steps are repeated for each ion impact. There are two task possible to analyse the simulation results.
On the one hand, one can examine how good the simulated surface satisfies available continuum models of pattern formation. As an advantage of the simulation over experiments one can get the full temporal evolution of the surface instead of only snapshots. Therefore, existing theories can be evaluated immediately.
On the other hand, the movement of every single atom can be tracked so that one can register the probabilities of jumps of an atom into different directions. With this jump rates, the mass current and its divergences can be calculated. As the divergence of the mass current is proportional to the temporal change of surface height - this is indirectly implied by Fick's law of diffusion - statements about the driving mechanisms of pattern formation are possible.
Here, both tasks are presented and explained with the help of an example.

Keywords: atomistic simulation, BCA, kMC, ripples, mass current
  • Lecture (others)
    Spring meeting of the DFG FOR 845 "Selbstorganisierte Nanostrukturen durch niederenergetische Ionenstrahlerosion", 01.-02.02.2011, Siegen, Deutschland

Publ.-Id: 16675 - Permalink

Lokalanalytische Ressourcenanalytik
Renno, A. D.; Merchel, S.; Munnik, F.; Fassbender, J.ORC
eingeladener Beitrag ohne Abstract
Keywords: resource analytics, ion beam analysis, PIXE, PIGE
  • Contribution to external collection
    in: ACAMONTA – Zeitschrift des VFF und der TU Bergakademie Freiberg 18, Freiberg: Freunde und Förderer der TU Bergakademie Freiberg, 2011, 24-26

Publ.-Id: 16673 - Permalink

Silica-stabilized actinide(IV) colloids at near-neutral pH
Zänker, H.; Weiss, S.; Hennig, C.; Dreissig, I.;
Due to their low solubility, tetravalent actinides, An(IV), are usually assumed to be immobile in natural waters. However, it is also well known that insoluble precipitation products can be mobile if they occur as colloids. For An(IV) oxyhydroxides this phenomenon has thoroughly been studied [1]. Here we describe the formation of a new type of An(IV) colloids [2].
Evidence is provided that uranium(IV) and Th(IV) can form silicate-containing colloids in near-neutral solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). These particles remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne An(IV) was observed which is a concentration significantly higher than the concentrations of truly dissolved or colloidally suspended waterborne An(IV) species hitherto reported for the near-neutral pH range. The prevailing size of the particles is below 20 nm. The higher the silicate concentration and the pH, the smaller (and obviously the more stable) are the particles that are formed (however, silicate at the concentrations tested does not form particles in the absence of the actinides). Electrostatic repulsion due to a negative zeta potential caused by the silicate stabilizes the nanoparticles. The mechanism of colloidal stabilization can be regarded as “sequestration” by silicate, a phenomenon well known from trivalent heavy metal ions such as iron(III) [3] or curium(III) [4], but never reported for tetravalent actinides so far. U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids. The next-neighbor coordination of U(IV) in the U(IV)-silica colloids is comparable with that of coffinite, USiO4.
The assessment of actinide behavior in the aquatic environment should take the possible existence of An(IV)-silica colloids into consideration. Their occurrence might influence actinide migration in anoxic waters.

[1] Altmaier et al. (2004) Radiochim. Acta 92, 537-543. [2] Dreissig et al. (2011) Geochim. Cosmochim. Acta 75, 352-367. [3] Robinson et al. (1992) J. Am. Water Works Assn. 84, 77-82. [4] Panak et al. (2005) Radiochim. Acta 93, 133-139.
Keywords: Colloids, nanoparticles, tetravalent actinides, silica
  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Open Access LogoAbstract in refereed journal
    Mineralogical Magazine 76(2012)6, 2581

Publ.-Id: 16671 - Permalink

Smart Kd-concept based on Surface Complexation Modeling
Stockmann, M.; Brendler, V.; Schikora, J.; Britz, S.; Flügge, J.; Noseck, U.;
Methodology. Sorption on mineral surfaces of sediments is one important retardation process for radionuclides to be considered in long-term safety assessments for radioactive waste repositories. Previously, the Kd-concept with temporally constant values was applied to describe the radionuclide retardation in the far field of a repository.
In this study, pre-calculated distribution coefficients (Kds) based on surface complexation models (SCM) are implemented in the existing 3D transport program r3t [1]. The so-called smart Kd-values are calculated as a function of important environmental parameters to reflect changing geochemical conditions. Respective multi-dimensional Kd-matrices are generated and stored a-priori to any r³t run. The calculations follow a bottom-up approach, i.e. the sorption of an element on each single mineral phase contributes to the distribution coefficient for a sediment.
Results. As an exemplary proof-of-concept, the Gorleben site (a potential repository site in Germany) was selected. Figure 1 shows the 3D plot for the logKd-matrix of UO22+ in the upper aquifer (UAF) at the Gorleben site as a function of pH, [Ca], and [DIC] (logarithmic scale). These pre-calculated logKd-values vary between -6.8 and 0.75. Comparing to the temporally constant conservative logKd of -2.7 from [2], which was previously used in r³t for the retention of UO22+ in fresh water in the upper aquifer at the Gorleben site, the resulting mean logKd of -2.74 shows a good general agreement, but account now for geochemical variations.
  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Abstract in refereed journal
    Mineralogical Magazine 76(2012)6, 2412

Publ.-Id: 16670 - Permalink

Numerical Integrator for Continuum Equations of Surface Growth and Erosion
Keller, A.; Facsko, S.; Cuerno, R.;
Growth of thin films by physical vapour deposition and erosion of solid surfaces by ion beam sputtering have high relevance in the fields of micro- and nanotechnology. Therefore the theoretical modelling of the surface morphology and its evolution during growth and erosion has received considerable attention. Compared to atomistic models, continuum equations are able to cover a much larger spatial and temporal scale accessing the macroscopic scales at which nontrivial features of the morphological dynamics occur. This is especially relevant for surface erosion which can induce a linear instability of the surface, resulting in the formation of periodic nanoscale patterns.
In this chapter, the software package “Ripples and Dots” is presented which is designed for the numerical integration of continuum equations modelling the surface evolution during ion beam erosion in (2+1) dimensions. These equations are based on the Bradley-Harper (BH) model and often feature in addition to the linear instability also nonlinear and noise terms, e.g. the prominent Kuramoto-Sivashinsky (KS) equation. However, due to the similarity with continuum equations for interface growth the software package can be used as well for studying continuum equations describing thin film growth, like the well known Kadar-Parisi-Zhang (KPZ) equation, the Edwards-Wilkinson (EW) equation, and the linear molecular beam epitaxy (MBE) equation.
Numerical data obtained by integrating various continuum equations for surface erosion is presented and compared to analytical predictions and experimental observations. It is demonstrated that the evolution of the surface morphology observed in the numerical integrations is in good qualitative agreement with experimental results both for normal and oblique ion incidence. In addition, also the special cases of erosion at oblique ion incidence with simultaneous sample rotation and erosion with multiple ion beams are presented.
  • Book chapter
    Sarhan M. Musa: Computational Nanotechnology: Modeling and Applications with MATLAB, Boca Raton: CRC Press, 2011, 978-1439841761, 189-215

Publ.-Id: 16669 - Permalink

Temperature Impact on the Sorption of Selenate onto Anatase
Franzen, C.; Jordan, N.; Müller, K.; Meusel, T.; Brendler, V.;
The radioactive isotope Selenium-79 is a long-lived fission product found in nuclear waste. Due to its long half live of 3.27 ∙ 105 years [1] it is expected to be one of the most contributing isotopes concerning safety assessments of nuclear waste underground repositories. The control of the mobility and bioavailability of selenium is therefore of great importance for a safe disposal of radioactive waste.
One major process controlling selenium mobility and bioavailability is the adsorption onto mineral surfaces of both the geological and engineered barrier.
The present study focuses on the impact of temperature on the sorption of selenate (SeO42-) onto anatase (TiO2). The sorption of selenate onto anatase at different temperatures (25°C – 60°C) was investigated both with batch experiments and ATR-FT-IR spectroscopy. In order to explain possible differences in sorption at higher temperatures, the surface of the anatase was investigated.
Keywords: Selenate; Se(VI); Anatase; Sorption; HighTemperatures
  • Open Access LogoContribution to proceedings
    HiTAC - High Temperature Aqueous Chemistry, 09.11.2011, Karlsruhe, Deutschland
    Proceedings of the International Workshops ABC-Salt (II) and HiTAC 2011, Karlsruhe: KIT Scientific Publishing, 978-3-86644-912-1, 163-164

Publ.-Id: 16668 - Permalink

Radiotracer studies on the kinetics and equilibrium characteristics of adsorption of humic matter
Lippold, H.; Lippmann-Pipke, J.;
Humic substances are ubiquitous in near-surface natural waters, and they are known to act as carriers for organic and inorganic contaminants [1, 2]. In order to assess the impact of such humic-bound mobilization, transport models are developed (see [3] for a review). As a prerequisite, reaction rates for adsorption and desorption are commonly assumed to be high enough to ensure a steady local equilibrium under flow conditions. For humic matter as a polydisperse system of highly charged colloids, however, it is unclear whether a dynamic adsorption equilibrium (i.e., a permanent run of adsorption and desorption at equal rates) actually exists. Low recoveries in column experiments with geological materials suggest a limited reversibility.

Using kaolinite as an adsorbent, the kinetics of adsorption and desorption were studied for a humic acid (Aldrich) and a fulvic acid (isolated from bog water). Their radiolabeling with 14C (accomplished by azo coupling with [14C]aniline) allowed sensitive detection and enabled tracer exchange experiments at surface saturation, providing direct insight into the dynamics of the adsorption equilibria for the first time. In these studies, a negligible amount of radiolabeled humic or fulvic acid was contacted with equilibrated systems of kaolinite and non-labeled humic material at different durations ranging from 6 hours to 4 weeks.

The equilibrium state of adsorption was attained within few hours for the fulvic acid, whereas the process took considerably longer for the humic acid (~ 2 days), possibly as a consequence of competition effects within the polydisperse system [4]. In desorption experiments, initiated by diluting the supernatant, not any release was observed within a time frame of 4 weeks, neither for the humic acid nor for the fulvic acid. In view of transport modeling, this finding is rather disturbing since the basic assumptions do not hold if adsorption is irreversible. Our tracer exchange experiments, however, revealed that labeled humic material is adsorbed even though it is confronted with a saturated surface. Consequently, an exchange must take place, indicating a reversible process, albeit an exchange time of ~ 4 weeks was required for both materials until the adsorption equilibrium was quantitatively represented by the tracer. Apparently, the competitive situation in its presence is a stronger driving force for desorption than is a concentration gradient. Models for humic-bound transport are thus applicable under comparable conditions.

[1] MacKay & Gschwend (2001) ES&T 35, 1320-1328. [2] Dearlove et al. (1991) Radiochim. Acta 52/53, 83-89. [3] Lippold & Lippmann-Pipke (2009) J. Contam. Hydrol. 109, 40-48. [4] Van de Weerd et al. (1999) ES&T 33, 1675-1681.
  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Abstract in refereed journal
    Mineralogical Magazine 76(2012), 2015-2015

Publ.-Id: 16667 - Permalink

Fracture mechanics characterisation of forged base metal ring of the decommissioned reactor pressure vessel of NPP Greifswald WWER-440 unit 4
Viehrig, H.-W.; Houska, M.; Altstadt, E.; Kuechler, R.;
The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald NPP representing the first generation of Russian type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs represent different material conditions viz. irradiated, irradiated & annealed and irradiated, annealed and re-irradiated. The paper presents test results measured on the trepan taken from the forged base metal ring 0.3.1. located in the reactor core region of the Unit 4 RPV. This unit was shut down after 11 years of operation and represents the irradiated condition. The key part of the testing is focused on the determination of the reference temperature T0 following the ASTM test standard E1921-10. The T0 of 11 thickness locations from the inner to the outer RPV wall varies between 112°C and 130°C with a mean value of 121°C. These are very low values for WWER RPV steel irradiated with fluences between 5.4 to 1.2•1019n/cm2 (E>0.5 MeV) from the inner to the outer RPV wall.
The fracture toughness values at cleavage failure, KJc, measured on LS oriented pre-cracked and side-grooved Charpy size SE(B) specimens from defined thickness locations of the forged ring strongly scatter. More than allowed 2% of the specimen size adjusted KJc-1T values lie below the fracture toughness curve for 2% fracture probability. The application of modified MC based evaluation methods indicates the material as non-homogeneous. Because of very low KJc values the SINTAP step 3 evaluation gave a maximum T0SINTAP of -40°C. The multimodal MC evaluation of KJc values from all thickness locations gives a T0MM of -118°C and a standard deviation of 25 K. The course of the fracture toughness curves evaluated by multi modal approach also do not represent the measured KJc values since more than 2% lie below the fracture toughness curve for 2% fracture probability. The reason for the occurrence of very low KJc values is seen in intergranular planes detected on the fractured surfaces of the specimens.
Keywords: reactor pressure vessel steel, neutron irradiation, fracture toughness, Master Curve approach, non-homogeneous steel, SINTAP, multimodal approach
  • Lecture (Conference)
    25th Symposium on Effects of Radiation on Nuclear Materials, 15.-17.06.2011, Anaheim, USA
  • Contribution to external collection
    in: ASTM STP1547, West Conshohocken: ASTM International, 2012, 978-0-8031-7533-4, 69-84

Publ.-Id: 16666 - Permalink

Long term irradiation phenomena in RPV steels - the LONGLIFE project
Altstadt, E.; Bergner, F.; Hein, H.;
The increasing age of European Nuclear Power Plants and envisaged extensions of reactor pressure vessel (RPV) lifetimes up to 80 years require the accurate prediction and management of RPV neutron irradiation embrittlement. LONGLIFE (“Treatment of long term irradiation embrittlement effects in RPV safety assessment”) is a collaborative project of the 7th Framework Programme of EURATOM. This project has been initiated as the next step forward towards obtaining an improved understanding of irradiation effects in RPV steels under conditions representative of long term operation (LTO) of RPVs. Phenomena which might become important at high neutron fluences (such as late-blooming effects and flux effects) must be considered in detail as part of the process of upgrading safety assessments and embrittlement surveillance procedures to underwrite the safety of LTO of RPVs. The work starts with the collection and evaluation of plant-specific information and data such as target neutron fluences for LTO and the chemical compositions of the materials. This includes a survey of available results of RPV materials data from decommissioned plants of validating surveillance data and studying specific irradiation effects relevant for LTO. Microstructural data are obtained from different techniques with the aim of assessing the adequacy of current dose-damage models with respect to their relevance to the mechanisms of irradiation damage associated with LTO of RPVs. Complementary mechanical tests are performed in order to address gaps in existing experimental data. Microstructural data pertaining to the evolution of irradiation damage are correlated with changes in mechanical properties, and the most important influencing factors will be identified. Surveillance guidelines for LTO of RPV base materials and welds will be developed as one of the principal outputs of the project. The scope of work and the project structure are outlined in the paper. Two LTO relevant phenomena – late blooming effect and flux effect – are discussed more detailed.
Keywords: Reactor Pressure Vessel Steel, Irradiation Embrittlement, Long Term Operation
  • Invited lecture (Conferences)
    25th Symposium on Effects of Radiation on Nuclear Materials, 15.-17.06.2011, Anaheim, USA

Publ.-Id: 16665 - Permalink

Numerical and experimental modelling of VGF-type buoyant flow under the influence of travelling and rotating magnetic fields
Galindo, V.; Niemietz, K.; Pätzold, O.; Gerbeth, G.;
Numerical and experimental modelling of a VGF-type (VGF - Vertical Gradient Freeze) buoyant flow under the influence of both travelling and rotating magnetic fields (TMF and RMF, respectively) is presented. Low-temperature flow experiments were carried out using a GaInSn alloy as model fluid. Radial heating and cooling of the melt leading to a meridional double vortex flow like in typical VGF growth, was introduced using a double-walled melt container. The flow was found to be significantly influenced by the mutual interaction of buoyant and electromagnetically driven forces. With increasing axial temperature difference, the buoyant flow becomes more concentrated in the upper and lower part of the melt leaving an extended melt zone with low flow velocity around the mid-height. Furthermore, VGF-type buoyancy is found to stabilize TMF- and RMF-induced melt flows. Besides, the time evolution of the flow just above the stability threshold is studied. In the case of combined VGF-type/RMF flow complex fluctuation patterns are observed, which depends sensitively on the applied thermal field.
Keywords: Fluid flows; Magnetic fields; Vertical gradient freeze technique; numerical simulation
  • Lecture (Conference)
    5th International Workshop on Crystal Growth Technology, 26.-30.06.2011, Berlin, Germany

Publ.-Id: 16664 - Permalink

Safety Monitoring of Components and Materials of Nuclear Power Plants
Gokhman, A. R.; Bergner, F.;
Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-9at%Cr and Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 1.5 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. For both alloys a saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC for the doses above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. CD modeling of Cr precipitates has been done with taking into account of deviation of this system from the ideal cluster gas. A specific surface tension of about 0.17 J/m2 between the alpha matrix and the Cr-rich alpha' precipitate and the rate at which Cr monomers are absorbed about 7.94 m-1 were found as best fit values for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS. Taking into account the formation and migration of Fe-Cr interstitial as additional link between the CD master equations for the self-defects and the CD master equations for the Cr precipitates, may lead to improve CD results for irradiated Fe-9at%Cr alloy. The assumption on the constant composition of Fe-Cr precipitates under neutron irradiation has been checked by means of new master equation of CD respect of the distribution function of clusters not only on size but also on composition. The slight dependence of the composition on the size of Fe-Cr precipitates is found.
  • Contribution to proceedings
    NATO Advanced Research Workshop on Nanodevices and Nanomaterials for Ecological Security, 20.-23.06.2011, Riga-Jurmala, Latvia
    Nanodevices and Nanomaterials for Ecological Security (Eds. Y.N. Shunin and A.E. Kiv), NATO Science for Peace and Security Series B: Physics and Biophysics, Dordrecht: Springer, 978-94-007-4118-8, 325-338

Publ.-Id: 16663 - Permalink

Preliminary multi-method spectroscopic approach for the uranium(VI) hydrolysis at temperatures up to 60°C
Steudtner, R.; Müller, K.; Meusel, T.; Brendler, V.;
For the safety assessment of high-level nuclear waste repositories in deep geologic formations, the understanding of actinide migration behaviour is one of the most important issues. In recent decades, the solution chemistry, e.g. hydrolysis [1], complexation with inorganic ligands [1], but also the interactions of the actinides at interfaces with the geo- and biosphere have been intensely investigated [2]. However, because of the experimental difficulties, only few studies have been performed at temperatures outside the range 20 – 30°C which hampers the prediction of actinide reactive transport in the environment of heat generating high-level nuclear waste repositories.
The speciation of (radioactive) metal ions in solution will be affected by the thermal conditions, since the properties of water, e.g. density, dielectric constant, viscosity, ion product, are altered with temperature and pressure [3,4].
The formation and distribution of U(VI) hydrolysis species is predicted to depend strongly on the temperature. In particular the stability of U(VI) polynuclear hydroxo complexes, which are dominant species at 25°C may change. According to experimental studies of other metal ions, namely Al(III) and La(III), the nuclearity of polynuclear complexes decreases upon increasing temperature [5,6]. At 25°C several spectroscopic techniques, namely UV-vis, TRLFS, EXAFS and vibrational spectroscopy have been applied for identification and structural characterization of U(VI) hydroxo species [7-10]. At elevated temperatures, TRLFS was used for the determination of luminescent characteristics of single hydroxo species as a function of the temperature [11,12]. But, approaches to examine alterations in the thermodynamic data itself are rare.
In this study, we investigate the U(VI) hydrolysis reactions up to 60°C using a multi-methodical approach by application of TRLFS and ATR FT-IR spectroscopy. The spectral data is compared to computed speciation patterns based on state-of-the-art thermodynamic models.

1.Guillaumont, R. et al., Update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technetium. Chemical Thermodynamics Vol. 5, OECD Nuclear Energy Agency, Elsevier (2003).
2.Brendler, V. et al., RES3T-Rossendorf expert system for surface and sorption thermodynamics, Journal of Contaminant Hydrology 281-291 (2003).
3.Marshall, W.L. et al., Io product of water substance, 0 - 1000°C, 1-10,000 bars - New international formulation and its background, Journal of Physical and Chemical Reference Data 2, 295-304 (1981).
4.Fernandez, D.P. et al., A formulation for the static permittivity of water and steam at temperatures from 238 K to 873 K at pressures up to 1200 MPa, including derivatives and Debye-Huckel coefficients, Journal of Physical and Chemical Reference Data 4, 1125-1166 (1997).
5.Mesmer, R.E. et al., Acidity measurements at elevated temperatures. 5. Aluminum ion hydrolysis, Inorg. Chem. 10, 2290-2296 (1971).
6.Ciavatta, L. et al., The hydrolysis of the La(II) ion in aqueous perchlorate solution at 60°C, Polyhedron 6, 1283-1290 (1987).
7.Meinrath, G., Uranium(VI) speciation by spectroscopy, J. Radioanal. Nucl. Chem. 1-2, 119-126 (1997).
8.Moulin, C. et al., Time-resolved laser-induced fluorescence as a unique tool for low-level uranium speciation, Appl. Spectrosc. 4, 528-535 (1998).
9.Müller, K. et al., Aqueous uranium(VI) hydrolysis species characterized by attenuated total reflection Fourier-transform infrared spectroscopy, Inorg. Chem. 21, 10127-10134 (2008).
10.Tsushima, S. et al., Stoichiometry and structure of uranyl(VI) hydroxo dimer and trimer complexes in aqueous solution, Inorg. Chem. 25, 10819-10826 (2007).
11.Eliet, V. et al., Time-resolved laser-induced fluorescence of uranium(VI) hydroxo-complexes at different temperatures, Appl. Spectrosc. 1, 99-105 (2000).
Keywords: U(VI), TRLFS, ATR FT-IR, high temperature
  • Contribution to proceedings
    HiTAC - High Temperature Aqueous Chemistry, 09.11.2011, Karlsruhe, Deutschland
    Proceedings of the International Workshops ABC-Salt (II) and HiTAC 2011: KIT Scientific Publishing, 978-3-86644-912-1, 177-178
  • Poster
    DMG-DGK-BMBF-ImmoRad Workshop "From atomistic calculations to thermodynamic modelling, 18.-22.02.2013, Frankfurt, Deutschland

Publ.-Id: 16662 - Permalink

Cluster Dynamics Study of Defect Evolution in Neutron-Irradiated Dilute and Concentrated Fe-Cr Alloys
Gokhman, A. R.; Bergner, F.; Birkenheuer, U.; Ulbricht, A.;
Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-9at%Cr and Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 1.5 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. For both alloys a saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. CD modeling of Cr precipitates has been done with taking into account of deviation of this system from the ideal cluster gas. A specific surface tension of about 0.17 J/m2 between the alpha matrix and the Cr-rich alpha' precipitate and the rate at which Cr monomers are absorbed about 7.94 m-1 were found as best fit values for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS.
Keywords: Cluster dynamics, neutron irradiation, chromium iron alloys, defects
  • Open Access LogoContribution to proceedings
    25th Research Workshop Nucleation Theory and Applications, 16.-23.04.2011, Dubna, Russia
    Nucleation Theory and Applications XIII, Dubna: JINR, 978-5-9530-0301, 259-267

Publ.-Id: 16661 - Permalink

XAS Study of dense U1-YAmYO2-X (Y=0.10; 0.15; 0.20) compounds
Prieur, D.; Martin, P. M.; Jankowiak, A.; Gavilan, E.; Scheinost, A. C.; Leorier, C.; Herlet, N.; Dehaudt, P.; Laval, J.-P.; Blanchart, P.;
U1-yAmyO2-x blankets are promising fuels for the transmutation of Minor Actinides (MA) in Fast Neutron Reactors. The fabrication of dense U1-yAmyO2-x pellet is challenging due to the high oxygen potential of the AmO2-x. As a consequence, a thermodynamical modelling is currently developed to determine optimum sintering conditions for given O/M ratios and MA content. Due to the lack of experimental data in the U-Am-O system [1] to refine the modelling, an experimental determination of the O/M ratio is mandatory as also its eventual consequences on the homogeneity of the solid solution. The present work focuses on the XAS characterization of U1-yAmyO2-x obtained by a conventional powder metallurgy process [2] for different sintering conditions and Am contents (10, 15, 20%). Thanks to XANES measurements, relative content of different U and Am oxidation states (+III, +IV, +V) have been obtained giving access to an experimental determination of O/M ratio as a function oxygen potential fixed during sintering. It was shown that the Am oxidation state remains unchanged at +III while there is a U(IV)/U(V) mixed valence depending on the oxygen potential. As expected, the calculated O/M ratio increase with the oxygen potential is only supported by a partial oxidation of uranium cations to U(+V). EXAFS data collected at Am and U edges showed, as suggested by laboratory XRD measurements, that a solid solution at molecular scale is obtained for all the Am content. From the calculated molar fraction of U4+, U5+ and Am3+ this solid solution can be written as U4+(1-Ay)(1-y)U5+Ay(1-y)Am3+O2-x where A is a constant.

[1] W. Bartscher and C. Sari, J. of Nuc. Mat., 118, 220-223(1983).
[2] D. Prieur and al, Powd. Tech., (2010).
Keywords: Americium, Transmutation, XAS, Oxygen potential
  • Contribution to proceedings
    Actinide XAS 2011, 02.-04.03.2011, Harima Science Garden City, Japan
    Proceedings of the Actinide XAS 2011

Publ.-Id: 16660 - Permalink

Spectroscopic Characterization of Eu(III) and Am(III) Complexes with Small Organic Molecules at Elevated Temperatures
Barkleit, A.; Geipel, G.; Acker, M.; Taut, S.;
Clay minerals which are components of potential host rock formations for nuclear waste repositories can contain small organic molecules like formate, citrate or lactate. Such small organic molecules can like the ubiquitous humic acids influence the migration behavior of radionuclides. Different substituted benzoic acids can mimic the main functionalities and are often used as model compounds for humic substances.
The understanding of the complex behavior of radionuclides with such natural organic matter and the thermodynamic quantification of the interaction especially at elevated temperatures is of great importance to simulate and predict their migration behavior in the environment, particularly in the near field of nuclear waste disposals where higher temperatures are prevailing.
We present the investigation of the complex behavior of Am(III) and Eu(III) with lactate and salicylate at ambient and elevated temperatures with time-resolved laser-induced fluorescence spectroscopy (TRLFS) and the resulting thermodynamic data (reaction enthalpy, reaction entropy). Whereas the complexation with lactate is for both cations nearly temperature independent, is the complexation with salicylate clearly an endothermic reaction.
Keywords: Americium, Europium, Lactate, Salicylate, TRLFS, High Temperatures
  • Poster
    HiTAC Workshop, 09.11.2011, Karlsruhe, Deutschland

Publ.-Id: 16659 - Permalink

Hardening and microstructure of neutron- and ion-irradiated Fe-Cr alloys
Heintze, C.; Altstadt, E.; Bergner, F.; Hernández Mayoral, M.; Xie, M.; Birkenheuer, U.;
Understanding the irradiation behaviour of binary Fe-Cr alloys is basic for the optimization of ferritic/martensitic chromium steels for future applications under conditions of high neutron exposures. In this work self-ion irradiation with the ion beam scanned over the sample was used in order to simulate neutron damage in Fe-12.5at%Cr. The material irradiated at 300°C up to a damage level of 1 dpa was exposed to isochronal annealing treatments in the range from 300 to 550°C and the indentation hardness was measured as a function of annealing temperature. We have found the presence of two recovery steps. The first one takes place at 300°C, i.e. at irradiation temperature, and gives rise to a 45% recovery of the irradiation-induced hardness increase. The second step occurs in the range from 400 to 550°C and gives rise to full recovery. The findings are discussed in terms of the dissolution of hardening features, such as dislocation loops and ’-phase particles. In addition, rate theoretical considerations were used to investigate possible flux effects caused by the pulsed irradiation experienced by the material due to the scanning ion beam. It was found, that no significant additional flux effects arise from the pulsing.
  • Lecture (Conference)
    OECD Nuclear Energy Agency International Workshop on Structural Materials for Innovative Nuclear Systems (SMINS-2), 31.08.-03.09.2010, Daejeon, Republic of Korea

Publ.-Id: 16658 - Permalink

Ion beam processing of surfaces and interfaces – Modeling and atomistic simulations
Liedke, B.;
Self-organization of regular surface pattern under ion beam erosion was described in detail by Navez in 1962. Several years later in 1986 Bradley and Harper (BH) published the first self-consistent theory on this phenomenon based on the competition of surface roughening described by Sigmund’s sputter theory and surface smoothing by Mullins-Herring diffusion. Many papers that followed BH theory introduced other processes responsible for the surface patterning e.g. viscous flow, redeposition, phase separation, preferential sputtering, etc. The present understanding is still not sufficient to specify the dominant driving forces responsible for self-organization. 3D atomistic simulations can improve the understanding by reproducing the pattern formation with the detailed microscopic description of the driving forces. 2D simulations published so far can contribute to this understanding only partially.

A novel program package for 3D atomistic simulations called trider (TRansport of Ions in matter with DEfect Relaxation), which unifies full collision cascade simulation with atomistic relaxation processes, has been developed. The collision cascades are provided by simulations based on the Binary Collision Approximation, and the relaxation processes are simulated with the 3D lattice kinetic Monte-Carlo method. This allows, without any phenomenological model, a full 3D atomistic description on experimental spatiotemporal scales. Recently discussed new mechanisms of surface patterning like ballistic mass drift or the dependence of the local morphology on sputtering yield are inherently included in our atomistic approach.

The atomistic 3D simulations do not depend so much on experimental assumptions like reported 2D simulations or continuum theories. The 3D computer experiments can even be considered as ’cleanest’ possible experiments for checking continuum theories. This work aims mainly at the methodology of a novel atomistic approach, showing that: (i) In general, sputtering is not the dominant driving force responsible for the ripple formation. Processes like bulk and surface defect kinetics dominate the surface morphology evolution. Only at grazing incidence the sputtering has been found to be a direct cause of the ripple formation. Bradley and Harper theory fails in explaining the ripple dynamics because it is based on the second-order-effect ‘sputtering’. However, taking into account the new mechanisms, a ‘Bradley-Harper equation’ with redefined parameters can be derived, which describes pattern formation satisfactorily. (ii) Kinetics of (bulk) defects has been revealed as the dominating driving force of pattern formation. Constantly created defects within the collision cascade, are responsible for local surface topography fluctuation and cause surface mass currents. The mass currents smooth the surface at normal and close to normal ion incidence angles, while ripples appear first at θ ≥ 40°.

The evolution of bimetallic interfaces under ion irradiation is another application of trider described in this thesis. The collisional mixing is in competition with diffusion and phase separation. The irradiation with He+ ions is studied for two extreme cases of bimetals: (i) Irradiation of interfaces formed by immiscible elements, here Al and Pb. Ballistic interface mixing is accompanied by phase separation. Al and Pb nanoclusters show a self-ordering (banding) parallel to the interface. (ii) Irradiation of interfaces by intermetallics forming species, here Pt and Co. Well-ordered layers of phases of intermetallics appear in the sequence Pt/Pt3Co/PtCo/PtCo3/Co. The trider program package has been proven to be an appropriate technique providing a complete picture of mixing mechanisms.
Keywords: kMC, BCA, TRIM, TRIDYN, TRIDER, self-organization, ripples, IBS, interface mixing, bilayers, bimetals, multilayers
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-012 2011
    ISSN: 2191-8716


Publ.-Id: 16657 - Permalink

Numerical simulation of the insulation material transport in a PWR core under loss of coolant conditions
Höhne, T.; Grahn, A.; Kliem, S.; Rohde, U.; Weiss, F.-P.;
In 1992, strainers on the suction side of the ECCS pumps in Barsebäck NPP Unit 2 became partially clogged with mineral wool after a safety valve opened because steam impinged on the thermally-insulated equipment and released mineral wool. This event pointed out that strainer clogging in the course of a loss-of-coolant accident is an issue and induced many investigations to understand and prevent strainer clogging effects.

Modifications of the insulation material, the strainer area and mesh size were carried out in most of the German NPPs. Moreover, back flushing procedures to remove the mineral wool from the strainers and differential pressure measurement were implemented to assure the performance of emergency core cooling during the containment sump recirculation mode.

Nevertheless, it cannot be completely ruled out, that a limited amount of the smaller fractions of insulation material could be transported into the RPV. During a postulated cold leg LOCA with hot leg ECC injection, the fibres enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might affect the ECC flow into the core and could result in degradation of core cooling.

It was the aim of the numerical simulations presented to study where and how many mineral wool fibers are deposited at the upper spacer grid. The 3D, time dependent, multi-phase flow problem was modelled by applying the CFD code ANSYS CFX.

The spacer grids were modeled as a strainer, which completely retains all the insulation material that reaches the uppermost spacer level. There, the accumulation of the insulation material gives rise to the formation of a compressible fibrous layer, the permeability of which to the coolant flow is calculated in terms of the local amount of deposited material and the local value of the superficial liquid velocity.

Before the switch over of the ECC injection from the flooding mode to the sump mode, the coolant circulates in an inner convection loop in the core extending from the lower plenum to the upper plenum. The CFD simulations have shown that after starting the sump mode, the ECC water injected through the hot legs flows down into the core via so-called "brake through channels" located in the outer core region where the downward leg of the convection role had established. The hotter, lighter coolant rises in the center of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the break through zones. This means that the fibres are not uniformly deposited over the core cross section.

When the inner recirculation stops later in the transient, insulation material can also be collected in other regions of the core cross section at the level of the upper spacer grids. Nevertheless, with a total of 2.7 kg fiber material deposited at the uppermost spacer level, the pressure drop over the fiber cake is not higher than 8 kPa and all the ECC water could still enter the core. The CFD calculation does not yet include steam production in the core and also does not include re-suspension of the insulation material during reverse flow. This will certainly further improve the coolability of the core.
Keywords: CFD, Fibre, Core, PWR

Publ.-Id: 16656 - Permalink

Ripples and dots generated by lattice gases
Ódor, G.; Liedke, B.; Heinig, K.-H.; Kelling, J.;
We show that the emergence of different surface patterns (ripples, dots) can be well understood by a suitable mapping onto the simplest nonequilibrium lattice gases and cellular automata. Using this efficient approach difficult, unanswered questions of surface growth and its scaling can be studied. The mapping onto binary variables facilitates effective simulations and enables one to consider very large system sizes. We have confirmed that the fundamental Kardar–Parisi–Zhang (KPZ) universality class is stable against a competing roughening diffusion, while a strong smoothing diffusion leads to logarithmic growth, a mean-field type behavior in two dimensions. The model can also describe anisotropic surface diffusion processes effectively. By analyzing the time-dependent structure factor we give numerical estimates for the wavelength coarsening behavior.
Keywords: Ripple, Dot, KPZ, Kuramoto–Sivashinsky, Mullins–Herring, Lattice gas, Coarsening, Scaling, PSD

Publ.-Id: 16655 - Permalink

Nanoscale characterization of ODS Fe-9%Cr model alloys compacted by spark plasma sintering
Heintze, C.; Hernández-Mayoral, M.; Ulbricht, A.; Bergner, F.; Shariq, A.; Weissgärber, T.; Frielinghaus, H.;
Ferritic/martensitic high-chromium steels are leading candidates for fission and fusion reactor components. Oxide dispersion strengthening is an effective way to improve properties related to thermal and irradiation-induced creep and to extend their elevated temperature applications. An extensive experimental study focusing on the microstructural characterization of oxide-dispersion strengthened Fe-9wt%Cr model alloys is reported. Several material variants were produced by means of high-energy milling of elemental powders of Fe, Cr and commercial yttria powders. Consolidation was based on spark plasma sintering. Special emphasis is placed on the characterization of the nano-particles using transmission electron microscopy, small-angle neutron scattering and atom probe tomography. The microstructure of the investigated alloys and the role of the process parameters are discussed. Implications for the reliability of the applied characterization techniques are also highlighted.
  • Lecture (Conference)
    DIANA I: 1st International workshop on dispersion strengthened steels for advanced nuclear applications, 04.-08.04.2011, Aussois, France

Publ.-Id: 16654 - Permalink

Response of human mesenchymal stem cells to nanopatterned surfaces
Keller, A.; Andersen, O. Z.; Foss, M.; Facsko, S.; Kraft, D. C.; Besenbacher, F.;
Artificial biomaterials play an important role in bioengineering, e.g. in regenerative medicine, biosensing, and orthopedics. The success of orthopedic implants depends on early bone formation and strong binding between bone and implant. The ability of osteogenic cells to adhere, proliferate, and differentiate on the implant surface is thus crucial for the formation of new bone tissue and the subsequent osseointegration of the implant.
Bone is a hierarchically composed biomaterial exhibiting topographical features such as fiber networks, interconnecting pores, and mineral crystallites with dimensions ranging from the macro to the nanoscale [1]. Micro and nanoscale surface topography thus has a strong influence on the proliferation, morphology, and differentiation of various cell types [2]. Therefore, the topographical design of implant surfaces is a promising route toward novel and improved medical implants [1].
Recently, it was demonstrated that even topographical features with a height below 10 nm can affect the adhesion and proliferation of mesenchymal stem cells (MSCs) [3]. However, only few techniques provide reliable control of the nanoscale surface topography over macroscopic areas. Therefore, in this work, we investigate the response of MSCs to well-defined nanorippled surfaces fabricated by ion beam sputtering which enables a precise tuning of the pattern dimensions by adjusting the ion energy [4]. The periodicity and height of the patterns range from 45 to 630 nm and from 3 nm to 70 nm, respectively. A strong influence of the ripple dimensions on MSC proliferation and morphology is observed.
[1] Stevens and George, Science, 310, 1135 (2005).
[2] Lord, Foss, and Besenbacher, Nano Today, 5, 66 (2010).
[3] Dolatshahi-Pirouz et al., ACS Nano, 4, 2874 (2010).
[4] Fassbender et al., New J. Phy., 11, 125002 (2009).
  • Lecture (Conference)
    Nanoscale Pattern Formation at Surfaces, 18.-22.09.2011, El Escorial, Spanien

Publ.-Id: 16653 - Permalink

The contributions of defect kinetics and sputtering to pattern formation
Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.;
The search for the dominating driving force for surface pattern formation under ion irradiation is performed by atomistic 3D computer simulations taking into account the full ion-induced collision cascades as well as the defect relaxation kinetics. For this aim a novel program package called TRIDER (TRansport of Ions in matter with DEfect Relaxation), which unifies full collision cascade simulation with the calculation of atomistic relaxation processes, has been developed. The collision cascades are provided by simulations based on the Binary Collision Approximation, and the relaxation processes are simulated with the 3D lattice kinetic Monte-Carlo method. This allows, without any phenomenological model, a full 3D atomistic description on experimental spatiotemporal scales. The dependence of the local morphology on sputtering yield and recently discussed new mechanism contributing to surface patterning like ballistic mass drift are inherently included in our atomistic approach.
Compared to 2D simulations based on the Solid-On-Solid (SOS) approach or continuum theories, the presented 3D simulations include the contribution of ion-induced subsurface processes to pattern formation, e.g. bulk interstitial and vacancy recombination at the surface. In order to reveal the dominating driving force for pattern formation, collision cascade simulations have been performed for two artificial cases: (i) simulations where sputtering has been suppresses artificially, (ii) simulations where only sputter-induced vacancy creation is taken into account (the original idea for the formulation of the Bradley-Harper equation). In this connection, for checking continuum theories, the 3D computer experiments can be considered as ‘cleanest’ possible experiments.
The computer simulations predict that sputtering is not the dominant driving force of pattern formation. Processes like bulk and surface defect kinetics dominate the surface morphology evolution. Only at grazing incidence the sputtering has been found to dominate the ripple formation. Surface mass currents originating from bulk defect recombination at the surface cause smoothing at ion impact angles <45°.
Keywords: Ripples, TRIDER, TRIM, KMC, Monte-Carlo, atomistic simulation, ion beam irradiation, self organization
  • Lecture (Conference)
    Nanoscale Pattern Formation at Surfaces Congress, 18.-22.09.2011, El Escorial, Madrid

Publ.-Id: 16652 - Permalink

Surface patterning by ion bombardment: predictions of largescale atomistic simulations
Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.;
Despite of intense studies in recent years, atomistic understanding of surface evolution during ion irradiation is still under discussion. Continuum models, like the Bradley and Harper theory, cannot explain microscopic processes during ion irradiation. So far, atomistic simulations could not describe pattern dynamics on spatiotemporal scales of experiments.
We present a novel program package that unifies the simulation of collision cascades with kinetic Monte-Carlo simulations. The 3D atom relocations were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetically unstable atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code. Our studies show that: (i) bulk defects continuously created within the collision cascade are responsible for local surface topography fluctuations and induce surface mass currents. These currents smooth the surface from normal incidence up to 𝜃 = 40°, whereas at 𝜃 > 40° ripple
patterns appear; (ii) sputtering is not the dominant driving force for the ripple formation at non-grazing incidence angles. Surface patterning is caused by processes like bulk and surface defect migration, recombination, bulk and surface diffusion and ion induced diffusion.
Keywords: TRIM, TRIDER, ripples, ion beam irradiation, sputtering, BCA, KMC, Monte-Carlo
  • Lecture (Conference)
    75. Jahrestagung der DPG und DPG Frühjahrstagung, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 16651 - Permalink

Interaction of selenite with iron sulphide minerals: a new perspective
Breynaert, E.; Dom, D.; Scheinost, A. C.; Kirschhock, C. E. A.; Maes, A.;
XAS-based studies of the interaction of selenite with FeS2 and FeS at circum-neutral pH have shown that selenite is reduced to solid state zero-valent Se and FeSex, respectively [1-4]. While these results were initially unexpected, the occurrence of dissolved, low oxidation state selenium species in presence of insoluble elemental Se, resulting from selenite reduction in pyrite containing clay systems, was astonishing. In addition, several authors encountered an identical Se phase solid phase in presence of pyrite, but none of them has been able to relate this phase to a specific mineral.
Correlating selenium redox chemistry with sulphide mineral oxidation pathways allowed to relate these observations to the different oxidation behaviour observed between acid-soluble and acid-insoluble metal sulphides [5].
Acid insoluble metal sulphides such as pyrite, molybdenite or tungstenite exhibit oxidative dissolution only. Upon six consequent one-electron oxidation steps, a thiosulphate anion is liberated (thiosulphate pathway). Acid soluble metal sulphides (troilite, mackinawite, sphalerite, etc.) can exhibit both non-oxidative dissolution, hence liberating sulphide species (H2S, HS-,S2-), and oxidative dissolution in presence of FeIII with the release of sulphide cations (e.g. H2S+), that spontaneously dimerize into disulphide species which can further react to form polysulphide (polysulphide pathway) and finally elemental sulphur.
While the end products resulting from Se(IV) reduction by acid-soluble iron sulphur minerals are fairly well known, both the solid and liquid phase products from the interaction of SeO32- with pyrite are poorly characterized. Although the solid phase reaction product in could not yet be assigned to a specific phase, it was clearly identified as a Se0 compound and trigonal (grey) selenium could be excluded as a canditate species.[4]
The presence of an unexpectedly high concentration of reduced, dissolved species in presence of pyrite, induced the formulation of a new pyrite-based reduction mechanism. Based on this mechanism, hypothesis was put forward about the identity of the unknown dissolved species. In addition, the new mechanism allows explaining all current experimental observations, more specifically the presence of this currently non-identified dissolved species and the unexpected relation between Se(IV) reduction and pH.[6]

[1] Breynaert, E., et al. (2008) ES&T. 42(10): 3595-3601.
[2] Scheinost, A.C. and Charlet, L. (2008) ES&T. 42(6): 1984-1989.
[3] Scheinost, A.C., et al. (2008) J. Contam. Hydrol. 102(3-4): 228-245.
[4] Breynaert, E., et al. (2010) ES&T. 44(17): 6649-6655.
[5] Rohwerder, T. and Sand, W.(2007) in Microbial Processing of Metal Sulfides 35-58.
[6] Kang, M., et al. (2011) ES&T. 45: 2704-2710.
Keywords: selenium exafs xanes redox pyrite
  • Invited lecture (Conferences)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Lecture (Conference)
    Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, 22.-25.10.2012, Montpellier, France

Publ.-Id: 16649 - Permalink

XRD and XAS structural characterization of mixed-valence plutonium(III,IV) oxalate hydrates used to obtain controlled particle shape of plutonium oxide
Tamain, C.; Arab-Chapelet, B.; Martin, P. M.; Rivenet, M.; Scheinost, A. C.; Grandjean, S.; Abraham, F.;
The oxalic conversion of plutonium into oxide is one of the most important steps of the present fuel cycle dealing with the recycling of plutonium contained in the used fuel. This operation, which occurs at the end of the PUREX process, includes two steps, oxalic precipitation followed by calcination in air, and permits to elaborate one of the main starting materials for the MOX fuel fabrication. Coordination chemistry of plutonium with oxalic acid is rich and several plutonium oxalate hydrates, the quite well-known PuIV(C2O4)2.6H2O1 and PuIII2(C2O4)3.10H2O2 and the other novel structures described here, can lead to PuO2. Considering the morphology of the plutonium oxalate particles, it is interesting to notice that there is a strong correlation between the shape of these particles and the crystal structure of the plutonium oxalate.
Keywords: plutonium exafs xanes nuclear fuel mox
  • Contribution to proceedings
    Plutonium Futures - The Science 2012, 15.-20.07.2012, Cambridge, United Kingdom

Publ.-Id: 16648 - Permalink

Oxide Minerals in Soils
Kaempf, N.; Scheinost, A. C.; Schulze, D. G.;
Oxide minerals or oxides comprise the oxides, hydroxides, oxyhydroxides, and hydrated oxides of Fe, Mn, Al, Si, and Ti. They commonly occur in soils, particularly those in advanced stages of weathering where they can sometimes account for as much as 50% of the total soil mass. In the discussion to follow, a polyhedral approach will be used to introduce the mineral species and highlight their major differences and similarities (Figure 22.1). For additional structural details, the reader is referred to the literature cited. Thereafter, their occurrence and formation in soils and their influence on soil properties will be discussed, concluding with the major techniques for identifying these minerals in soils.
Keywords: oxides minerals soil xrd
  • Book chapter
    Pan Ming Huang, Yuncon Li, Malcolm E. Sumner: Handbook of Soil Sciences: Properties and Processes, Part III: Soil Mineralogy, USA: CRC Press, Taylor & Francis Group, 2011, 1439803056, 22

Publ.-Id: 16647 - Permalink

Lasermodifikation von TCOs
Hauschild, D.; Vinnichenko, M.;
No abstract available.
  • Lecture (Conference)
    5. Fachtagung Transparent leitfähige Schichten (TCO), 28.-30.11.2011, Neu-Ulm, Deutschland

Publ.-Id: 16646 - Permalink

Nanohole Pattern Formation on Germanium Induced by Focused Ion Beam and Broad Beam Ga+ Irradiation
Fritzsche, M.; Mücklich, A.; Facsko, S.;
Hexagonally ordered nanohole patterns were produced on Ge(100) surfaces by focused Ga+ ion beam and by broad Ga+ ion beam irradiations with 5 keV energy under normal incidence. Identical patterns were obtained by irradiations with a scanning focussed ion beam under dierent irradiation conditions and with a broad Ga+ beam without scanning and ve orders of magnitude smaller ion flux. Thus we could demonstrate that nanohole pattern formation is independent of ion flux over several orders of magnitude and scanning of a FIB under appropriate conditions is identical to broad ion beam irradiation.

Publ.-Id: 16645 - Permalink

Die Jagd nach dem Weltrekord - Forschung in hohen Magnetfeldern
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Vorlesung in der Reihe "Physik am Samstag" der Fachrichtung Physik der TU Dresden, 03.12.2011, Dresden, Deutschland

Publ.-Id: 16644 - Permalink

World record race - Research at high magnetic fields
Wosnitza, J.;
  • Invited lecture (Conferences)
    SFB/Transregio 21 Workshop 2011 "Common perspectives of mesoscopic systems and quantum gases", 13.-16.11.2011, Günzburg, Deutschland

Publ.-Id: 16643 - Permalink

de Haas-van Alpen investigations of iron pnictides: first results
Wosnitza, J.;
  • Invited lecture (Conferences)
    Kick-off meeting of the SPP 1458 "High-temperature superconductivity in iron pnictides, 24.-25.02.2011, Dresden, Deutschland

Publ.-Id: 16642 - Permalink

Monte-Carlo simulation to optimize SPECT-hardware dedicated to in-beam control of particle therapy
Rohling, H.; Dersch, U.; Fiedler, F.; Golnik, C.; Kormoll, T.; Müller, A.; Schöne, S.; Enghardt, W.;
Therapeutic irradiation with ions and protons is superior to a treatment with gammas with respect to tumour conformity of dose and damage of normal tissue. On the other hand, mispositioning of the patient or density changes in the treated volume may easily compromise the success of treatment.
For this reason, non-invasive, in-situ dose verification is necessary. The only clinically proven method up to now is Positron Emission Tomography [Eng04]. This method does not allow direct dose quantification due to limited angle artefacts and washout in the patient. Another promising approach is in-beam SPECT: the detection of prompt gamma-rays following nuclear interaction between the ions and the atoms of the penetrated tissue. Detection systems based on Compton-scattering and pair-conversion are now under investigation. So far, Compton-cameras have been used for diagnostic imaging in nuclear medicine and astronomy. In telescopes also pair-creation cameras are established [Zog04]. In contrast to this, in-beam dose verification systems have to manage the specific energy range and low count rates due to the patient dose.

A prototype of a Compton-camera is under construction at OncoRay [Kor10, Fie11, Kor11]. It consists of a scatter layer made from CZT and an absorption layer (LSO).
From the energy deposited in the detector planes a cone surface of all possible directions of the incident photon can be reconstructed [Sch11]. The expected energy distribution of the prompt gammas is calculated by means of simulations based on treatment plan data [Fie11].
To optimize the setup simulations are required. Therefore, the Monte-Carlo framework GEANT4 is used for:

(1) Analysis of the efficiency in dependence of the geometry;
(2) Study of background caused by backscattered photons and other secondary particles;
(3) Development of filters for event selection;
(4) Study parameters influencing the spatial resolution of the reconstructed image (multiple Compton-scattering inside a detector layer, escape of energy, intrinsic radioactivity of the detector material, Doppler-broadening);
(5) Creation of test data sets as input for the reconstruction.

For photon energies above 7 MeV the pair production is the dominant electromagnetic process in CZT. To use these events the Compton-camera might be combined with a pair-conversion camera by adding thin silicon layers in between to track the path of the electron and the positron produced during pair conversion. Exploiting this information the direction of the incident photon can be deduced.
Unfortunately, the angular resolution is heavily degraded especially for photons with rather low incident energies by small-angle scattering of the secondary particles and by the recoil of the nuclei when a pair production takes place [Gol11]. Both effects were studied whereas the latter is not included in the GEANT4 code version 9.3. This simulation serves as basis for the development of an iterative reconstruction algorithm dedicated to in-beam SPECT with a pair production camera. Apart from the analysis of efficiency, angular resolution and noise, the combination of a pair production and a Compton-camera is a challenging task.

Results on simulations for optimizing the setup and the refinement of the reconstruction algorithm for a clinical dose verification system will be presented.

[Eng04] W. Enghardt et al., Nucl. Instr. and Meth. A 525 (2004)
[Fie11] F. Fiedler et al., Nucl. Sci. Symp. IEEE (2011), accepted
[Gol11] C. Golnik et al., Nucl. Sci. Symp. IEEE (2011), accepted
[Kor10] T. Kormoll et al., Nucl. Instr. and Meth. A (2010)
[Kor11] T. Kormoll et al., Nucl. Sci. Symp. IEEE (2011), accepted
[Ric10] M.-H. Richard et al., IEEE Transactions on Nuclear Science (2010)
[Sch11] S. Schöne et al., Proc. Fully 3D Meeting (2011)
[Zog04] A. Zoglauer et al., Nucl. Sci. Symp. Conf. Rec. IEEE (2004)
  • Poster
    ICTR-PHE 2012 - International #Conference on Translational Research in Radiation Oncology, 27.02.-02.03.2012, Genf, Schweiz
  • Radiotherapy and Oncology 102(2012), S46

Publ.-Id: 16641 - Permalink

Curium(III) speciation studies with cells of a groundwater strain of Pseudomonas fluorescens
Moll, H.; Lütke, L.; Barkleit, A.; Bernhard, G.;
Ubiquitous Pseudomonads have great potential to influence the speciation and mobility of actinides in the environment. This study explores the unknown interaction between curium(III) and cell-suspensions of Pseudomonas fluorescens (CCUG 32456) isolated from the Äspö site, Sweden.
The interaction between curium(III) and P. fluorescens cells was studied at trace curium(III) concentrations (0.3 µM) using time-resolved laser-induced fluorescence spectroscopy. Extraction studies have shown that the biosorption of curium(III) is a reversible process. Two Cm3+-P. fluorescens (CCUG 32456) species could be identified, R-O-PO3H-Cm2+ and R-COO-Cm2+, having emission maxima at 599.6 and 601.9 nm, respectively. The corresponding surface complexation constants were determined to be log β111 = 12.7 ± 0.6 and log β110 = 6.1 ± 0.5, respectively.
Keywords: curium; Pseudomonas fluorescens; bacteria; fluorescence spectroscopy; TRLFS; complexation

Publ.-Id: 16640 - Permalink

Application of Different Nuclides in Retrospective Dosimetry
Konheiser, J.; Mittag, S.; Viehrig, H.-W.;
Activities of nuclides produced by neutron irradiation of reactor-pressure-vessel (RPV) steel are used to validate respective fluence calculations. Niobium, nickel and technetium isotopes from RPV trepans of the decommissioned NPP Greifswald (VVER-440) have been analyzed. The activities were determined by TRAMO (Monte-Carlo) fluence calculations,,newly applying 640 neutron-energy groups and ENDF/B7 data. Compared to former results, up to 20% higher fluences have been computed, leading to somewhat better agreement of measurement and calculation, particularly in case of Tc-99.
Keywords: fluence calculations; Nonte-Carlo program; retrospective dosimetry; Niobium; Nickel; Technetium
  • Journal of ASTM International 9(2012)3

Publ.-Id: 16639 - Permalink

Das Hochfeld-Magnetlabor Dresden: Rekorde in Rossendorf
Uhlarz, M.;
  • Lecture (Conference)
    Tag der Wissenschaften 2011 am BSZ Radebeul, 08.06.2011, Radebeul, Deutschland

Publ.-Id: 16638 - Permalink

Development of a soft-magnetic shield for magnetic prostheses
Uhlarz, M.;
  • Lecture (Conference)
    MAGISTER M30 Meeting, 16.-17.06.2011, Edingburgh, United Kingdom

Publ.-Id: 16637 - Permalink

Magnetic characterization of implantable magnetic scaffolds and powders: Activities at HZDR
Uhlarz, M.;
  • Lecture (Conference)
    MAGISTER M30 Meeting, 16.-17.06.2011, Edingburgh, United Kingdom

Publ.-Id: 16636 - Permalink

Superposition of ferromagnetic and antiferromagnetic spin chains in the quantum magnet BaAg2Cu[VO4]2
Tsirlin, A. A.; Müller, A.; Lorenz, B.; Skourski, Y.; Rosner, H.;
Based on density functional theory band-structure calculations, quantum Monte Carlo simulations, and highfield magnetization measurements, we address the microscopic magnetic model of BaAg2Cu[VO4]2 that was recently proposed as a spin- 1/2 anisotropic triangular lattice system. We show that the actual physics of this compound is determined by a peculiar superposition of ferromagnetic and antiferromagnetic uniform spin chains with nearest-neighbor exchange couplings of J (1)a ~ −19 K and J (2)a ~ 9.5 K, respectively. The two chains featuring different types of the magnetic exchange perfectly mimic the specific heat of a triangular spin lattice, while leaving a clear imprint on the magnetization curve that is incompatible with the triangular-lattice model. Both ferromagnetic and antiferromagnetic spin chains run along the crystallographic a direction, and slightly differ in the mutual arrangement of the magnetic CuO4 plaquettes and nonmagnetic VO4 tetrahedra. These subtle structural details are, therefore, crucial for the ferromagnetic or antiferromagnetic nature of the exchange couplings, and put forward the importance of comprehensive microscopic modeling for a proper understanding of quantum spin systems in transition-metal compounds.

Publ.-Id: 16635 - Permalink

Magnetic properties and exchange integrals of the frustrated chain cuprate linarite PbCuSO4(OH)2
Wolter, A. U. B.; Lipps, F.; Schäpers, M.; Drechsler, S.-L.; Nishimoto, S.; Vogel, R.; Kataev, V.; Büchner, B.; Rosner, H.; Schmitt, M.; Uhlarz, M.; Skourski, Y.; Wosnitza, J.; Süllow, S.; Rule, K. C.;
We present a detailed study in the paramagnetic regime of the frustrated s = 1/2 spin-compound linarite PbCuSO4(OH)2 with competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions. Our data reveal highly anisotropic values for the saturation field along the crystallographic main directions, with ∼7.6, ∼10.5, and ∼8.5 T for the a, b, and c axes, respectively. In the paramagnetic regime, this behavior is explained mainly by the anisotropy of the g factor, but leaving room for an easy-axis exchange anisotropy. Within the isotropic J1-J2 spin model, our experimental data are described by various theoretical approaches, yielding values for the exchange interactions J1 ∼ −100 K and J2 ∼ 36 K. These main intrachain exchange integrals are significantly larger as compared to the values derived in two previous studies in the literature and shift the frustration ratio α = J2/|J1| ≈ 0.36 of linarite closer to the one-dimensional critical point at 0.25. Electron spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements further prove that the static susceptibility is dominated by the intrinsic spin susceptibility. The Knight shift as well as the broadening of the linewidth in ESR and NMR at elevated temperatures indicate a highly frustrated system with the onset of magnetic correlations far above the magnetic ordering temperature TN = 2.75(5) K, in agreement with the calculated exchange constants.

Publ.-Id: 16634 - Permalink

B-T phase diagram of CoCr2O4 in magnetic fields up to 14 T
Pronin, A. V.; Uhlarz, M.; Beyer, R.; Fischer, T.; Wosnitza, J.; Gorshunov, B. P.; Komandin, G. A.; Prokhorov, A. S.; Dressel, M.; Bush, A. A.; Torgashev, V. I.;
We have measured the magnetization and specific heat of multiferroic CoCr2O4 in magnetic fields up to 14 T. The high-field magnetization measurements indicate a new phase transition at T = 5–6 K. The phase between T and the lock-in transition at 15 K is characterized by magnetic irreversibility. At higher magnetic fields, the irreversibility increases. Specific-heat measurements confirm the transition at T , and also show irreversible behavior. We construct a field-temperature phase diagram of CoCr2O4.

Publ.-Id: 16633 - Permalink

Recent Topics of Organic Superconductors
Ardavan, A.; Brown, S.; Kagoshima, S.; Kanoda, K.; Kuroki, K.; Mori, H.; Ogata, M.; Uji, S.; Wosnitza, J.;
Recent developments in research into superconductivity in organic materials are reviewed. In the epoch-defining quasi-one-dimensional TMTSF superconductors with Tc ~ 1 K, Tc decreases monotonically with increasing pressure, as do signatures of spin fluctuations in the normal state, providing good evidence for magnetically-mediated pairing. Upper critical fields exceed the Zeeman-limiting field by several times, suggesting triplet pairing or a transition to an inhomogeneous superconducting state at high magnetic fields, while triplet pairing is ruled out at low fields by NMR Knight-shift measurements. Evidence for a spatially inhomogeneous superconducting state, Fulde–Ferrel–Larkin–Ovchinnikov state, which has long been sought in various superconducting systems, is now captured by thermodynamic and transport measurements for clean and highly two-dimensional BEDT-TTF and BETS superconductors. Some of the layered superconductors also serve as model systems for Mott physics on anisotropic triangular lattice. For example, the Nernst effect and the pseudo-gap behavior in NMR relaxation are enhanced near to the Mott transition. In the case of increasing spin frustration, the superconducting transition temperature is depressed, and antiferromagnetic ordering is eliminated altogether in the adjacent Mott insulating phase. There is an increasing number of materials exhibiting superconductivity in competition or cooperation with charge order. Theoretical studies shed light on the role of spin and/or charge fluctuations for superconductivity appearing under conditions close to those of correlation-induced insulating phases in the diversity of organic materials.

Publ.-Id: 16632 - Permalink

Temperature dependence of the London penetration depth in Pr2CuO4 from millimeter-wave optical experiments
Pronin, A. V.; Fischer, T.; Wosnitza, J.; Ikeda, A.; Naito, M.;
We have investigated the in-plane penetration depth, λ(T), of nominally undoped superconducting Pr2CuO4 films (Tc = 27.5 K) by measuring the phase-sensitive millimeter-wave transmission at temperatures between 2 and 30 K. The overall temperature dependence of the superfluid density, ns = λ2(0 K)/ λ2(T), resembles the behavior typical for the cuprate superconductors [ns(T) / ~ 1 (T/Tc)2]. However, a closer look on the penetration depth at low temperatures reveals flattening of its temperature dependence. We find λ(T) / Tn with n = 2.8 ± 0.2.

Publ.-Id: 16631 - Permalink

Dinuclear complexes of tetravalent cerium in an aqueous perchloric acid solution
Ikeda-Ohno, A.; Tsushima, S.; Hennig, C.; Yaita, T.; Bernhard, G.;
Primary aquo species of tetravalent cerium (Ce(IV)) in perchloric acid has been identified as a single oxo-bridging dinuclear complex, not a mononuclear one, by extended X-ray absorption fine structure (EXAFS) spectroscopy combined with density functional theory (DFT) calculations.
Keywords: Tetravalent cerium, Dimer, XAS, EXAFS, DFT calculations

Publ.-Id: 16630 - Permalink

Field-induced gap in a quantum spin-1/2 chain in strong magnetic fields
Zvyagin, S.;
Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions that exhibits a field-induced spin gap, are probed by means of high-frequency electron spin resonance spectroscopy in pulsed magnetic fields up to 64 T. In particular, we report on a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations in the magnetic excitation spectrum) to a spin-polarized state with magnon excitations (Fig. 1). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG calculations for spin-1/2 Heisenberg chain with a staggered transverse field [1]. Such a behavior appears to be a general feature of the high-field excitation spectrum of quantum spin-1/2 chain systems with alternating g-tensor and/or Dzyaloshonskii-Moriya interactions. In addition, the development of the high-field Electron Spin Resonance facilities at the Dresden High Magnetic Field Laboratory is reported.
This work was partly supported by DFG and EuroMagNET II.
  • Invited lecture (Conferences)
    International Workshop "Advanced ESR Studies for New Frontiers in Biofunctional Spin Science and Technology" (AEBST 2011), 13.-14.11.2011, Kobe, Japan

Publ.-Id: 16629 - Permalink

Biotechnologie zur Gewinnung von Ressourcen
Pollmann, K.; Kutschke, S.; Raff, J.;
Vorstellung der Forschungsvorhaben Ressourcengewinnung
  • Lecture (others)
    Vorstellung beim Städtebund Silberberg, 27.01.2012, Aue, Deutschland

Publ.-Id: 16628 - Permalink

EduGATE - basic examples for educative purpose using the GATE simulation platform
Pietrzyk, U.; Zakhnini, A.; Axer, M.; Sauerzapf, S.; Benoit, D.; Gaens, M.;
EduGATE is a collection of basic examples to introduce students to the fundamental physical aspects of medical imaging devices. It is based on the GATE platform, which has received a wide acceptance in the field of simulating medical imaging devices including SPECT, PET, CT and also applications in radiation therapy.
GATE can be configured by commands, which are, for the sake of simplicity, listed in a collection of one or more macro files to set up phantoms, multiple types of sources, detection device, and acquisition parameters. The aim of the EduGATE is to use all these helpful features of GATE to provide insights into the physics of medical imaging by means of a collection of very basic and simple GATE macros in connection with analysis programs based on ROOT. A graphical user interface to define a configuration is also included.
Keywords: Monte Carlo Simulation, GATE, PET, SPECT, Education, Imaging

Publ.-Id: 16627 - Permalink

Numerical simulations of CCFL experiments using a morphology detection algorithm
Höhne, T.; Darlianto, D.; Lucas, D.;
In order to improve the understanding of counter-current two-phase flows and to validate new physical models, CFD simulations of 1/3rd scale model of the hot leg of a German Konvoi PWR with rectangular cross section was performed. Selected counter-current flow limitation (CCFL) experiments at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) were calculated with ANSYS CFX 12.1 using the multi-fluid Euler-Euler modeling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a SST turbulence model for each phase. In the simulation, the surface drag was approached by a new correlation inside the Algebraic Interfacial Area Density (AIAD) model. The AIAD model allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. The goal is to provide an easy usable AIAD framework for all ANSYS CFX users, with the possibility of the implementation of their own correlations.
Keywords: Numerical simulation, CFD, CCFL, AIAD model, reflux condensation, PWR hot leg, air-water experiment

Publ.-Id: 16626 - Permalink

Image-Processing-Based Study of the Interfacial Behavior of the Countercurrent Gas-Liquid Two-Phase Flow in a Hot Leg of a PWR
Montoya, G.; Deendarlianto; Lucas, D.; Höhne, T.; Vallee, C.;
The interfacial behavior during counter-current two-phase flow of air-water and steam-water in a model of a PWR hot leg was studied quantitatively using digital image processing of a subsequent recorded video images of the experimental series obtained from the TOPFLOW facility, Helmholtz-Zentrum Dresden-Rossendorf e.V. (HZDR), Dresden, Germany. The developed image processing technique provides the transient data of water level inside the hot leg channel up to flooding condition. In this technique, the filters such as median and Gaussian were used to eliminate the drops and the bubbles from the interface and the wall of the test section. A Statistical treatment (average, standard deviation, and probability distribution function (PDF)) of the obtained water level data was carried-out also to identify the flow behaviors.

The obtained data are characterized by a high resolution in space and time, which makes them suitable for the development and validation of CFD-grade closure models, e.g. for two-fluid model. This information is essential also for the development of mechanistic modeling on the relating phenomenon. It was clarified that the local water level at the crest of the hydraulic jump is strongly affected by the liquid properties.
Keywords: CFD, Hot Leg
  • Open Access LogoScience and Technology of Nuclear Installations 2012(2012), ID 209542
    DOI: 10.1155/2012/209542

Publ.-Id: 16625 - Permalink

Counter-current Flow Limitation of Gas-Liquid Two phase Flow in Nearly Horizontal Pipe
Prayitno, S.; Santoso, R.; Darlianto, D.; Höhne, T.; Lucas, D.;
Experimental on the work counter current two phase flow of air and gas in nearly horizontal flows have been performed. The experiments are conducted with 50 mm inner diameter pipe, in two inclination angle setting (20° and 10° from horizontal) and smooth liquid and air inlet i.e. a porous liquid inlet and a nozzle connected with calm section for gas inlet. The effect of liquid properties are examined by using five different working fluids (Water, two different concentration of butanol and glycerin aqua solutions). As results, (1) CCFL causes a drastic change in the delivered liquid to the lower plenum. (2) The effect of inclination angle is significantly observed. The flooding gas superficial velocity needed decreases with inclination angle. (3) The liquid viscosity affects the flooding phenomena.
Keywords: counter-current flow limitation, flooding, inclined pipe, liquid properties

Publ.-Id: 16624 - Permalink

CFD studies of the insulation material transport inside the reactor pressure vessel under LOCA conditions
Höhne, T.; Grahn, A.; Kliem, S.;
In 1992, strainers on the suction side of the ECCS pumps in Barsebäck NPP Unit 2 became partially clogged with mineral wool because after a safety valve opened the steam impinged on thermally-insulated equipment and released mineral wool. This event pointed out that strainer clogging is an issue in the course of a loss-of-coolant accident (LOCA). In the LOCA event inside the containment, energetic pressure waves and fluid jets would impinge upon components in the vicinity of the break and could release thermal insulation and dust. In addition, debris can be created by chemical reactions between reactive ECC solutions and the materials in the containment. These reactions may result in additional debris such as disbanded coatings and chemical precipitates being generated [1].Through transport mechanisms such as entrainment in steam/water discharge from the break and wash down due to condensate flow in the containment, a fraction of the generated debris and other material in the containment would be transported to the containment sump. Subsequently, if the ECCS is operating in the sump recirculation mode, the debris suspended in the containment sump would begin to accumulate on the sump strainers. A small part could penetrate trough the strainers and could be transported towards the core. The accumulation of this suspended debris on the sump strainers can create an almost uniform covering on the strainer, which would tend to increase the head loss across the strainer. On account of this phenomenon, modifications of the insulation material, the strainer size and the mesh size at the strainers were carried out in most of the German NPPs to assure the emergency core cooling during the sump recirculation mode. Moreover, differential pressure measurements and back flushing procedures were implemented to remove the mineral wool from the strainers, before the differential pressure exceeds a certain level. Nevertheless, it cannot be completely ruled out, that small fractions of the insulation material are transported into the RPV. During hot leg ECC injection, the fibres enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might cause a reduction of the ECC flow into the core and degradation of core cooling.
It was the aim of the numerical simulations to study where and how many mineral wool fibres are deposited at the upper spacer grid. The 3D, time dependent, multi-phase flow problem was modelled applying the CFD code ANSYS CFX. Best practice guidelines were used to specify the grid size, turbulence model and the multiphase model. The spacer grids were modelled as a strainer, which completely retains all the insulation material reaching the uppermost spacer level. In this model, which was validated against experiments at HTWS Zittau, the accumulation of the insulation material gives rise to the formation of a compressible fibrous cake, the permeability of which to the coolant flow is calculated in terms of the local amount of deposited material and the local value of the superficial liquid velocity. The CFD simulations have shown that after starting the sump mode, the ECC water injected through the hot legs flows down into the core at so-called “breakthrough channels” at the outer regions of the core, which were first recognized in UPTF experiments. In contradiction the hotter, lighter coolant rises in the centre of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the breakthrough zones. This means that the fibres are not uniformly deposited over the core cross section.
Further investigations are necessary to determine the accumulation of insulation material for a longer period of time. Also steam production in the core or re-suspension of the insulation material during back flow should be considered.
Keywords: CFD, UPTF, ECC, RPV
  • Lecture (Conference)
    CFD4NRS-4, The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology, 10.-12.09.2012, Daejeon, Korea
  • Contribution to proceedings
    CFD4NRS-4, The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology, 10.-12.09.2012, Daejeon, Korea

Publ.-Id: 16623 - Permalink

CFD-modelling of CCFL phenomena in a PWR hot leg model
Höhne, T.; Darlianto, D.; Lucas, D.;
The detailed three-dimensional (3-D) information on the transient flow behaviour under countercurrent flow limitation (CCFL) in a pressurized water reactor (PWR) hot leg is an important issue in the reactor safety analysis. It relates to a hypothetical scenario of small break Loss of Coolant Accident (LOCA) in a PWR, and leads to the reflux-condensing mode. During this scenario, a part of the condensate flows back towards the reactor pressure vessel (RPV) in counter current to the steam. In this mode, a CCFL could occur, affecting the core cooling. Deendarlianto et al. (2011a) has already reviewed different applications of CFD codes to simulate the phenomena around the CCFL in a PWR hot leg. They indicated that there is still a lack of knowledge regarding suitable closure models for this application. In some cases empirical correlations originally obtained for one-dimensional codes were used for this multidimensional problem.
Keywords: LOCA, PWR, AIAD, CFD
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2012, 22.-24.05.2012, Stuttgart, Deutschland

Publ.-Id: 16622 - Permalink

Multiphase Flows in Industrial Applications – Theory, Experiments and CFD Validation
Höhne, T.;
Strong increase of usage of three-dimensional Computational Fluid Dynamics (CFD) in industrial applications because for instance
pressurized thermal shocks,
coolant mixing,
thermal striping
cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.
Keywords: CFD, slugging, pressurized thermal shocks, coolant mixing, thermal striping
  • Invited lecture (Conferences)
    International Seminar Series 2012, Universitas Gadjah Mada, Faculty of Engineering, 30.01.2012, Yogyakarta, Indonesia

Publ.-Id: 16621 - Permalink

CFD in Safety of Nuclear Industry
Höhne, T.;
Strong increase of usage of three-dimensional Computational Fluid Dynamics (CFD) in industrial applications because for instance
pressurized thermal shocks,
coolant mixing,
thermal striping
cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.
Keywords: CFD, slugging, pressurized thermal shocks, coolant mixing, thermal striping
  • Invited lecture (Conferences)
    International Conference on Computational Modeling Validation, 14.-15.01.2012, Sydney, Australien
  • Open Access LogoContribution to proceedings
    International Conference on Computational Modeling Validation, 14.-15.01.2012, Sydney, Australien

Publ.-Id: 16620 - Permalink

Recent Developments in CFD Modeling of Multiphase Flows
Höhne, T.;
CFD (Computational Fluid Dynamics) is the simulation of fluids engineering systems using modeling (mathematical physical problem formulation) and numerical methods (discretization methods, solvers, numerical parameters, and grid generations, etc.)
CFD made possible by the advent of digital computer and advancing with improvements of computer resources (500 Floating Point Operations per Second (flops), 1947 10 Petaflops, 2011)
Keywords: CFD, AIAD, Multiphase flow
  • Invited lecture (Conferences)
  • Open Access LogoContribution to proceedings

Publ.-Id: 16619 - Permalink

Modelling and Simulation of 4D GeoPET Measurements with COMSOL Multiphysics 4.2a
Schikora, J.; Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.;
Our GeoPET-method allows the 4D monitoring of (reactive) transport processes in geological material on laboratory scale (Gründig et al., 2007; Kulenkampff et al., 2008; Richter et al., 2005) by quantitative imaging of tracer concentrations. Recently we have conducted a long-term 22Na+ in-diffusion experiment in an Opalinus clay drill core over aperiod of 7 months. We modelled this experiment with COMSOL Multiphysics ® 4.2a (3D convection-diffusion equation, PDE mode, PARDISO solver) for reproducing the observed spatiotemporal concentration distribution data with the following underlying equation for this anisotropie diffusion and adsorption:
8Ci ( ) 8q
cßt = \l Dc . \lCi P8t
-c [-] porosity, ci[moVm3] 22Na+concentration, D e [m2/s] tensor of the effective diffusion constant for 22Na+ in Opalinus clay, P [kg/m3 ] bulk density and 8q/8t sink term for considering the sorption. By importing GeoPET images from various time steps and applying the Optirnization Module (least square fit applying the LevenbcrgMarquardt algorithrn) to these images we efficiently deterrnined hest fit values e.g. of the diffusion tensor. Cornbined with the parameter sweep operation the sensitivity analysis is performed in parallel and covers the range of literature values for porosity and Kd values for 22Na+sorption on Opalinus cIay.
The experimental data could be reproduced quite weIl, but the obtained parameter values for diffusion parallel and normal to the bedding are slightly larger than reported in Gimmi and Kosakowski (2011). This is coherent with our observations of an emerging gas bubble in the central borehole tracer reservoir: Soil moisture tension in the partly unsaturated clay must have significantly influenccd thc transport regime by an additional advective component.
We suggest COMSOL Multiphysics ® is a powerful tool for the inverse modelling of timedependent, multidimensional experimental data as obtained by GeoPET.
Gründig, M. et a1., 2007. Tomographie radiotraeer studies ofthe spatial distribution ofheterogeneous geoehemieal transport proeesses. Appl. Geochem., 22: 2334-2343.
Kulenkampff, J. et al., 2008. Evaluation ofpositron emission tomography for visualisation ofmigration proeesses in geomaterials. Phys. Chern. Earth, 33: 937-942.
Richter, M. et al., 2005. Positron Emission Tomography for modelling of geochmical transport processes in clay. Radiochirn. Acta, 93: 643-651.
Gimmi, T. & Kosakowski, G. 2011. How mobile are sorbed eations in clay and clay rocks? Environ. Sei. Techn., 45:1443-1449
  • Poster
    EGU General Assembly 2012, 22.-27.04.2012, Wien, Österreich

Publ.-Id: 16618 - Permalink

Influence of Temperature on the Sorption of Selenate onto Anatase
Franzen, C.; Jordan, N.; Mueller, K.;
The radioactive isotope Selenium-79 is a long-lived fission product found in nuclear waste. Due to its long half life of 3.27 ∙ 105 years, it is expected to be one of the isotopes most contributing to the potential radiation dose according to safety assessments of nuclear waste underground repositories. A detailed knowledge of the mobility and bioavailability of selenium is therefore of great importance for a safe disposal of radioactive waste.
One major process controlling selenium mobility and bioavailability is the adsorption onto mineral surfaces of both the geological and engineered barrier. High level and long-lived radioactive waste increase the temperature in the vicinity of the waste disposal site. Thus, it is important to understand to what extent this temperature increase influences the sorption of selenium.
The present study focuses on the impact of temperature on the sorption of selenate (SeO42-) onto anatase (TiO2). Because of its abundance in rocks and its well-known crystal structure, anatase represents an ideal model system for the study of sorption behaviour of Se onto transition metal oxide phases. The sorption of selenate onto anatase at different temperatures (25 °C – 60 °C) was investigated both with batch experiments and ATR FT-IR spectroscopy. In order to explain possible differences in sorption at higher temperatures, the surface of the anatase was investigated.
The sorption of Se(VI) onto anatase as a function of pH was similar at 25 °C and 60 °C, i.e. sorption decreased with increasing pH. However, the sorption capacity of anatase towards Se(VI) was lowered at a higher temperature. Furthermore, the pH value above which no Se(VI) sorption occurs was shifted to lower pH values (from pH 6.5 at 25 °C to pH 5.5 at 60 °C).
The isoelectric point of anatase (pHIEP) was located at pH 6.3 at 25 °C. At higher temperatures, the pHIEP was shifted towards lower pH with a value of 5.5 at 60 °C. In addition, the absolute values of the zeta potential were lowered at higher temperatures. Both findings were in good agreement with the batch experiments.
The observed decrease in selenate sorption at higher temperatures could be assigned to a change in the surface properties of anatase.
Keywords: Selenium; selenate; sorption; anatase; temperature
  • Lecture (Conference)
    Experimental Mineralogy Petrology and Geochemistry, 04.-07.03.2012, Kiel, Deutschland

Publ.-Id: 16617 - Permalink

THEREDA - One Database for thermodynamic and sorption data
Bok, F.; Brendler, V.; Richter, A.;
For geochemical modeling of scenarios for the disposal of radioactive and (chemo)toxic waste, comprehensive and internally consistent thermodynamic data are required as well as sorption data for the surrounding host rocks. The use of different databases renders it difficult to compare results of geochemical modeling, due to incompleteness, inconsistencies, resticted ranges of variation (temperature, density, pressure), limitations in solution composition (ionic strength) and last but not least missing sorption data.
THEREDA (THErmodynamic REference DAtabase, is a project adressing these issues through high quality standards: full documentation and thus transparency of all data, internal consistency, quality assurance measures, different interaction models, comprehensiveness. It shall imporve geochemical modelling for various environmental applications, namely radiochemical waste disposal assessment.
THEREDA contains data for the three ion-ion interaction models: extendend Debye-Hückel, Specific Ion Interaction Theory, and Pitzer model. Tailored parameter files for various geochemical modeling codes are provided (PhreeqC, ChemApp, EQ3/6, Geochemist‘s Workbench). Documented benchmark calculations allow comparisons with other databases as well as between the different geochemical codes. All data, documentation and references are freely accessible via the projects homepage. Additionally, a user forum allows direct contact with the THEREDA members.
A holistic view of geochemical processes in the context of a safety analysis requires the inclusion of sorption calculations. A thermodynamically consistent treatment of these processes is only possible with surface complexation modelling (SCM). Existing SCM data from the RES³T (Rossendorf expert system for surface and sorption thermodynamics, database is currently subjected to critical evaluation and will be included in THEREDA.
Keywords: THEREDA, RES³T, RES3T, database, thermodynamic, sorption
  • Poster
    Experimental Mineralogy Petrology and Geochemistry 2012, 04.-07.03.2012, Kiel, Deutschland
  • Contribution to proceedings
    Experimental Mineralogy Petrology and Geochemistry 2012, 04.-07.03.2012, Kiel, Deutschland

Publ.-Id: 16616 - Permalink

Different types of outer-sphere complexes of selenate ions on mineral surfaces
Jordan, N.; Ritter, A.; Heim, K.; Foerstendorf, H.;
  • Lecture (others)
    Helmholtz-Koordinierungstreffen, 23.-24.01.2012, Karlsruhe, Deutschland

Publ.-Id: 16615 - Permalink

Manuskriptband für die Berliner Recycling- und Rohstoffkonferenz 2012
Dürkoop, A.; Gutzmer, J.; Faulstich, M.; Klossek, A.;
Auf Basis der Rohstoffstrategie und der High-Tech Strategie 2020 der Bundesregierung (2010a, 2010b) sollen mit der vom Bundesministerium für Bildung und Forschung (BMBF) geförderten Maßnahme „r3 – Innovative Technologien für Ressourceneffizienz – Strategische Metalle und Mineralien“ konkrete Vorschläge für die Erhöhung der Versorgungssicherheit strategisch bedeutender Ressourcen in Deutschland erarbeitet werden. Unter diesen strategisch bedeutenden Ressourcen sind seltene Metalle und Industriemineralien zu verstehen, die mehr und mehr in der High-Tech-Industrie zum Einsatz kommen. Im Rahmen der Fördermaßnahme r³ wird neben zahlreichen Verbundprojekten ein übergeordnetes Begleitforschungsprojekt „INTRA r³+“ angestrebt, welches die Fördermaßnahme koordiniert, entstandenes Wissen bündelt und die Forschungspartner miteinander vernetzt. Ein zentrales Anliegen von INTRA r3+ ist die Aufbereitung und Kommunikation des entstandenen Wissens sowie die Entwicklung von gezielten Transfermaßnahmen für Akteure und Interessengruppen inner- und außerhalb des Forschungsnetzwerkes. Durch diese Maßnahmen soll der Weg zur Übertragung und wirtschaftlichen Nutzung der Projektergebnisse erleichtert werden.
Das Begleitforschungsprojekt startete im November 2011 und wird bis Januar 2016 als Serviceprogramm für r3 die Forschungsaktivitäten zur Optimierung der gesamten Wertschöpfungskette der Bereitstellung von strategischen Metallen und Industriemineralien begleiten. Koordinator des INTRA r3+ ist das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF), (siehe Punkt V). Die geförderten Verbundprojekte innerhalb des r3-Rahmenprogramms werden ab Mitte 2012 mit ihren Forschungsarbeiten für innovative Technologien zur Ressourceneffizienz beginnen.
Durch die Bündelung, Analyse und Bewertung neuer Erkenntnisse sollen im Begleitforschungsprojekt INTRA r3+ Impulse erzeugt werden, die einerseits auf eine erfolgreiche Durchführung der Verbundprojekte abzielen, anderseits die Kooperation und Vernetzung der Verbundprojekte untereinander fördern sollen. Die Verbundprojekte werden dafür in verschiedene Forschungscluster unterteilt, die wiederum von Clusterbetreuern gesteuert werden. Im Rahmen von INTRA r³+ steht den technischen Verbundprojekten auch ein Analyseservice im Gerätepool des Koordinators HIF zur Verfügung.
Keywords: Resource efficieny rare earth elements industrial minerals recycling substitution urban-mining
  • Invited lecture (Conferences)
    Berliner Recycling- und Rohstoffkonferenz 2012, 26.-27.03.2012, Berlin, Deutschland

Publ.-Id: 16614 - Permalink

Specific targeting of hypoxic tumor tissue with nitroimidazole-peptide conjugates
Splith, K.; Bergmann, R.; Pietzsch, J.; Neundorf, I.;
Nitroimidazole–peptide conjugates: Attachment of a nitroimidazole unit to a cell-penetrating peptide was used to create conjugates able to target hypoxic tumor tissue. In vivo studies have demonstrated the successful delivery of these conjugates to even less well-perfused hypoxic regions in solid tumors. This approach provides a targeted delivery system with the option to use it as an imaging agent or to conjugate it with therapeutics.
Keywords: * antitumor agents; * cell-penetrating peptides; * drug delivery; * hypoxia; * tumor targeting

Publ.-Id: 16613 - Permalink

The impact of atmospheric carbonate on the sorption of actinyl (V/VI) ions onto gibbsite studied by in situ ATR FT-IR and EXAFS spectroscopy
Gückel, K.; Foerstendorf, H.; Rossberg, A.;
The talk shows a first comparative insight into the course of the surface complex formation of U(VI) and Np(V) onto gibbsite on a molecular level studied by ATR FT-IR and EXAFS spectroscopy.
  • Lecture (others)
    HELMHOLTZ-KOORDINIERUNGSTREFFEN 2012, 23.-24.01.2012, Karlsruhe, Deutschland

Publ.-Id: 16612 - Permalink

Determination of potential landscapes using video microscopy
Kreuter, C.; Leiderer, P.; Erbe, A.;
Video microscopy can be used for the detection of surface potentials, when colloidal particles are present and act as tracer particles for then surface corrugation. Here we present measurements on colloidal particles, which are confined in narrow channels on a substrate and interact with a barrier, which impedes the motion along the channel. The motion of the particles then contains information on the gravitational potential as well as on the potential defined by the presence of the barrier. Statistical analysis is performed in order to extract the potential shapes which arise from the two interactions. We use brownian dynamics simulations in order to complement the experiments with tests of a large range of scenarios, which cannot be accessed in experiments.
Keywords: video microscopy, colloidal model systems, soft matter

Publ.-Id: 16611 - Permalink

Influence of the residual oxygen in the plasma immersion ion implantation (PI3) processing of materials
Ueda, M.; Silva Jr., A. R.; Mello, C. B.; Silva, G.; Reuther, H.; Oliveira, V. S.;
In this work, we investigated the effects of the contaminants present in the vacuum chamber of the PI3 system, in particular, the residual oxygen, which results in the formation of the oxide compounds on the surface and hence is responsible for the high implantation energies required to achieve reasonably thick treated layers. We used a mass spectrometer (RGA) with a quadruple filter to verify the composition of the residual vacuum and pressure of the elements present in the chamber. Initially we found a high proportion of residual oxygen in a vacuum with a pressure of 1 × 10−3 Pa. Minimizing the residual oxygen percentage in about 80%, by efficient cleaning of the chamber walls and by improving the gas feeding process, we mitigated the formation of oxides during the PI3 process. Therefore we achieved a highly efficient PI3 processing obtaining implanted layers reaching about 50 nm, even in cases such as an aluminum alloy, where is very difficult to nitrogen implant at low energies. We performed nitrogen PI3 treatment of SS304 and Al7075 using pulses of only 3 kV and 15 × 10−6 s at 1 kHz with an operating pressure of 1 Pa.

Publ.-Id: 16610 - Permalink

Ion Beam Modification of Magnetic Materials
Fassbender, J.ORC
Overview of current research on ion beam modification of magnetic materials
Keywords: magentism, ion irradiation, ion implantation
  • Invited lecture (Conferences)
    IMW-Seminar des IFW Dresden, 19.01.2012, Dresden, Deutschland
  • Invited lecture (Conferences)
    Colloquium CIC Nanogune San Sebastian, 16.02.2016, San Sebastian, Spanien
  • Invited lecture (Conferences)
    International Conference on 'Accelerators in Materials and Medical Sciences' 2017, 05.-07.10.2017, Dubai, United Arabic Emirates

Publ.-Id: 16609 - Permalink

Interaction of U(VI) with Bacterial Isolates from Äspö and Mont Terri
Lütke, L.; Moll, H.; Bachvarova, V.; Geißler, A.; Selenska-Pobell, S.; Bernhard, G.;
Microorganisms are ubiquitous in nature, having a significant impact on the sorption and hence the migration behavior of actinides. Thus it is necessity to characterize the actinide-bacteria species formed and to elucidate the involved interaction mechanisms. This talk deals with the interaction of two microbial strains isolated from destined host rocks for future nuclear waste deposition, namely Pseudomonas fluorescens from Äspö, Sweden, and a novel strain of the genus Paenibacillus from Mont Terri, Switzerland. Potentiometric titration, TRLFS and EXAFS results on the U(VI) interaction with these strains are presented. The talk involves a special focus on the effect of the cell wall constitution (Gram-negative vs. Gram-positive) and the oxygen availability on the U(VI) speciation.
Keywords: Uranium, Pseudomonas fluorescens, Paenibacillus sp., Speciation, Potentiometric Titration, TRLFS, EXAFS
  • Lecture (others)
    Helmholtz-Koordinierungstreffen 2012, 23.-24.01.2012, Karlsruhe, Deutschland

Publ.-Id: 16608 - Permalink

Biological characterization of [18F]-radiolabeled anilinopyrimidine: a potential radiotracer for EphB4 receptor imaging
Neuber, C.; Mosch, B.; Mamat, C.; Bergmann, R.; Pietzsch, J.;
The receptor tyrosine kinase EphB4 and its ligand ephrinB2 play a critical role in tumor angiogenesis. Therefore, EphB4/ephrinB2 system is a potential target for tumor diagnosis and therapy, and different approaches including tyrosine kinase inhibitors are under investigation. Our study aimed the development and biological characterization of a novel radiotracer targeted to EphB4.
Material and Methods:
Based on a known EphB4 kinase inhibitor (lead compound 1) containing a bis anilinopyrimidine motif a methylsulfonyl residue was replaced by 3 fluoropropylsulfonyl moiety (2) followed by 18F-radiolabeling ([18F]2). Human melanoma cells A375 transfected with human EphB4 full length protein (A375 EphB4) or mock plasmid (A375 pIRES) were analyzed for cell viability and EphB4 tyrosine phosphorylation after incubation with compounds 1 and 2. Cellular uptake of [18F]2 was investigated using specific inhibitors. [18F]2 was analyzed in biodistribution experiments and dynamic positron emission tomography (PET) studies using nude mice bearing A375 EphB4 or A375 pIRES tumors.
Overexpression of EphB4 in A375 EphB4 cells was confirmed by mRNA and protein expression. Both compound 1 and 2 reduced EphB4 tyrosine phosphorylation and influenced cell morphology and viability. [18F]2 showed internalization by A375 and transfected A375 cells. Partial inhibitory effects of different specific inhibitors provided information on possible uptake mechanisms, which further have to be characterized. Biodistribution and PET studies revealed high stability of [18F]2 in vivo with fast hepatobiliary excretion. No differences between A375 EphB4 and A375 pIRES tumors could be observed in uptake of [18F]2.
The novel compound 2 substantially inhibited EphB4 tyrosine phosphorylation, when radiolabelded with 18F represents a potential PET tracer. Since [18F]2 was internalized by A375 melanoma cells in vitro the use of [18F]2 for imaging of EphB4 in vivo by PET is supported. However, further studies will deal with optimization of its pharmacokinetic properties.
  • Lecture (Conference)
    5th European Workshop on "Apoptosis, Angiogenesis & Hypoxia in Tumor Microenvironment: Biological aspects and Imaging", 05.-08.10.2011, Berder Island, France
  • Contribution to proceedings
    5th Berder Meeting on Apoptosis, Angiogenesis and Hypoxia in Tumor Microenvironment: Biological Aspects and Imaging, 05.-08.10.2011, Berder Island, France
    Proceedings of the 5th Berder Meeting on Apoptosis, Angiogenesis and Hypoxia in Tumor Microenvironment: Biological Aspects and Imaging, 33-34

Publ.-Id: 16607 - Permalink

Influence of external radiation on cellular properties and Eph receptor/ephrin expression in human melanoma cells
Mosch, B.; Pietzsch, D.; Pietzsch, J.;
There is first experimental evidence that progression and metastasis of melanoma is associated with receptor tyrosine kinases (RTK) of the Eph receptor family. However, RTK can be regulated by different factors, but the influence of radiation on Eph receptors and their ligands and, furthermore, on melanoma metastasis is unclear. In this study, we radiated one pre-metastatic and three metastatic human melanoma cells lines, including one self-generated metastatic cell line with X-rays (5 and 10 Gy vs. sham). At day 1 and day 7 post radiation we analyzed cellular viability, proliferation, colony formation, migration, adhesion, and motility. Additionally, selected Eph receptors and ephrin ligands were analyzed regarding radiation-dependent changes in mRNA and protein.
In all cell lines a dose dependent decrease in viability and cell growth for up to 1 week after radiation was demonstrated. Colony formation was unaffected in pre-metastatic and only marginally influenced in metastatic cell lines. Migration and adhesion increased 1 day after radiation, while motility of all cells decreased. In contrast, 7 days after radiation, migration decreased while adhesion remained increased in treated cells. Furthermore, an increase in motility was observed in pre-metastatic cells. For EphA2 we detected an increase in mRNA in 2 of 3 metastatic cell lines, with simultaneously decreased protein level. EphA3 was found to be up-regulated in mRNA and protein in 3 of 4 cell lines. Expression of ephrinA1 and A5 was generally low and seemed unaffected by radiation, with the exception of an increase in ephrinA1 mRNA in 3 of 4 cell lines.
In conclusion, we showed that X-ray radiation strongly decreased viability and proliferation of human melanoma cells. Concerning metastatic properties, it remained ambiguous if X-ray acts pro- or anti-metastatic to melanoma cells, probably depending on cell line and time after radiation. Regarding the present data an involvement of A-type Eph receptors in radiation-mediated effects in melanoma can be hypothesized. Ongoing studies will clarify whether and how over-expression and inhibition of Eph influences metastatic properties of human melanoma cells.
  • Poster
    Keystone Symposium “Stem cells, Cancer and Metastasis”, 06.-11.03.2011, Keystone, Colorado, USA

Publ.-Id: 16606 - Permalink

Development of [90Y]Y-CHX-A´´-DTPA-Cetuximab for combination of radioimmunotherapy and external radiotherapy: Radiochemistry and first in vivo results
Heldt, J.-M.; Koi, L.; Zenker, M.; Brüchner, K.; Dittfeld, C.; Bergmann, R.; Mosch, B.; Pietzsch, H.-J.; Pietzsch, J.; Zips, D.; Kunz-Schughart, L. A.; Baumann, M.; Steinbach, J.;
Radiochemical development, characterisation and preparation of [90Y]Y-CHX-A´´-DTPA-Cetuximab ([90Y]C225). Preclinical evaluation of [90Y]C225 by combination of radioimmunotherapy and external radiotherapy.
CHX-A´´-DTPA was conjugated to C225 via thiourea bond formation in HEPES-buffer at pH 7.2 by reacting 20 equivalents of chelator with C225 for 24 h. Purification of the conjugate was done by ultrafiltration. Chelator to C225 ratio was determined by MALDI-TOF MS and the conjugate’s affinity determined by flow cytometric analysis. Radiolabeling was performed in MES buffer at pH 6.1 at 30°C for 30 min using [90Y]YCl3. Free DTPA chelator (0.1 μg/μL) was added to the reaction mixture for quenching the labeling reaction and fixing unreacted radionuclide. Ex vivo autoradiography ([90Y]C225) was performed, in vivo kinetics were measured with PET using 86Y as radiolabel and biodistribution studies were performed. FaDu tumour bearing nude mice were treated with [90Y]C225 (2.8 MBq 13 g C225 / mouse, i.v.) and external beam irradiation (X-rays, single dose, 1.1 Gy/min). Experimental endpoints are the tumour growth delay and the local tumour control. Some animals are still in follow-up and not all cohorts are completed. The data are preliminary (figure 1B).
MALDI-TOF MS analysis of the purified conjugate showed that approximately 5 CHX-A´´-DTPA moieties have been conjugated to C225. The conjugate has not lost affinity to EGFR on cell surfaces when compared to the unconjugated C225 at 0.33 nM (flow cytometry). CHX-A´´-DTPA-C225 was labelled with [90Y]YCl3 with radiolabelling yields >95% and a reproducible specific activity of 1.2 GBq/mg was achieved. Autoradiography studies revealed high tumour accumulation 48 h p.i., also PET showed an increasing antibody accumulation in the tumour, which was abundant after 24 h p.i. These data validate the conjugate to be suitable for therapeutical studies: The combined treatment (internal and external irradiation) was well tolerated by all mice and no histological alterations in organs could be found. The preliminary data in Figure 1B clearly show a dose-effect of the external irradiation. A significant improvement of the local tumour control after external irradiation with 26 Gy was achieved after application of 13 g of radiolabelled C225 compared to unlabelled C225 or to the treatment by external irradiation solely.
[90Y]C225 has been successfully prepared, characterized and it can be produced in routine with high avidity and specific activity as prerequisite for long-term preclinical therapeutic studies. Our in-vivo preliminary data support the concept that multimodal cancer treatment results in a potentially relevant improvement of local tumour control in an experimental tumour model.
Research Support:
The Bundesministerium für Bildung und Forschung (grant 02NUK006, framework “Kompetenzverbund Strahlenforschung” (KVSF)) is gratefully acknowledged for the financial support.
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences (ISRS), 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S568

Publ.-Id: 16605 - Permalink

Radiosynthesis of 3-[18F]fluoropropanesulfonamides derived from aliphatic and aromatic amines
Löser, R.; Hiller, A.; Fischer, S.; Funke, U.; Maisonial, A.; Brust, P.; Steinbach, J.;
Facing the ample palette of prosthetic groups available for the introduction of radiofluorine into pharmacologically relevant molecules, the careful selection of the appropriate labelling agent often reveals critical for tracer development as it can influence target binding and/or stability in vivo. Labelling based on the formation of carboxylic acid amides often results in metabolic instability due to hydrolytic cleavage. As an alternative to acyl-based prosthetic groups the 3-[18F]fluoropropanesulfonyl group introduced by Li et al. attracted our interest [1]. Therefore, we established and optimised the preparation of 3-[18F]fluoropropanesulfonyl chloride in our lab and studied its reaction with various aliphatic and aromatic amines.
To obtain 3-[18F]fluoropropanesulfonyl chloride ([18F]4) we followed the route described in [1] that includes conversion of intermediary 3-[18F]fluoropropyl thiocyanate ([18F]3) with chlorine leading to the desired sulfonyl chloride (Figure 1). As the preparation of [18F]3 from the corresponding tosyl precursor 1 proceeded with only moderate labelling yields, the nosylate 2 was synthesised by two different pathways both starting from 3-bromopropanol. The syntheses of the non-radioactive sulfonamides as reference compounds resembled those of the radiotracers with the oxidation of 3 to 4 as the key step. This was realised by employing a solution of chlorine in water using acetic acid as organic co-solvent. The resulting sulfonyl chloride 4 was reacted with various aliphatic and aromatic amines. Due to the fact that 3 and 4 show an almost identical chromatographic behaviour on silica gel
as observed by TLC, a radio-HPLC method had to be developed that allowed to prove the identity of [18F]4 but prevented its hydrolysis on the column. The synthesis of the final radioactive sulfonamides was done by reacting
[18F]4 with different primary and secondary aliphatic amines as well as various aniline derivatives in dichloromethane at room temperature both in the absence and presence of triethylamine (TEA) and/or 4-
dimethylaminopyridine (DMAP) as reaction enhancing mediators. The results were evaluated by radio-TLC and radio-HPLC.
The nosyl precursor 2 accounted for high labelling yields of 78-85% (n=11) in the first step of the radiosynthesis. A concentration of 2.5 to 3.0 mg/mL and a reaction time of 10 min in acetonitrile (approx. 0.4 mL) at reflux were found to be optimal for the radiofluorination of 2. For the conversion of [18F]3 into the corresponding sulfonyl chloride the repetitive treatment of this intermediate adsorbed at a C18 matrix with an aqueous solution of chlorine and subsequent desorption with dichloromethane led to [18F]4 of high radiochemical purity ranging from 85 to 95%. The reaction of [18F]4 with primary amines always resulted in high yields of radioactive sulfonamides (75 to 85%) that did not improve upon addition of TEA or DMAP. In contrast, the conversion of [18F]4 with various anilines was low (<10%) but could be significantly increased in the presence of TEA or DMAP resulting in yields of 55 to 65%.
The structural optimisation of the sulfonate precursor together with optimised reaction conditions for the radiosynthesis of 3-[18F]fluoropropanesulfonyl chloride ([18F]4) enabled the preparation of 3-[18F]fluoropropanesulfonamides derived from various aliphatic and aromatic amines. This will allow the preparation of 18F-labelled sulfonamides of pharmacologically interesting amino-functionalised compounds.
[1] Li et al. (2008) J. Label. Compd. Radiopharm. 51, 23-27
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences (ISRS), 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S477

Publ.-Id: 16604 - Permalink

Design and synthesis of novel radiolabelled peptide-based Eph receptor inhibitors for PET
Pretze, M.; Mamat, C.; Steinbach, J.;
Eph receptors and their ephrin ligands belong to the largest receptor tyrosine kinase family of transmembrane proteins. Since Eph receptors are found to be dysregulated in certain tumour species [1, 2] many efforts have been made to inhibit such receptors in order to stop tumourigenesis and tumour growth [3]. To date, several promising candidates of small molecules exist [4, 5], which inhibit Eph receptors at the intracellular domain. Furthermore, peptides with the key amino acid sequence SNEW show the highest affinity for the EphB2 receptor and, in this regard, block the extracellular receptor domain [6]. In this case, the development of a labelling strategy for the radiofluorination of SNEW peptides to design new PET-tracers is promising for specific tumour diagnosis.
Several novel SNEW peptides were synthesized via an automated Fmoc-protecting group strategy. The key sequence at the N-terminus has to be unmodified in order to sustain the affinity to EphB2-receptor. The C-terminus was modified with cysteine, lysine and azidoproline for a radiofluorination with [18F]FBAM, [18F]SFB [7] and by use of bioorthogonal reactions like the Staudinger ligation or the Huisgen cycloaddition.
Since the key sequence of SNEW peptides is essential for the affinity to the EphB2-receptor, the SNEW peptides were modified at the C-terminus for the bioorthogonal labelling. In order to compare the new bioorthogonal reactions with established labelling methods, the cysteine modified SNEW peptide was reacted with [18F]FBAM (60 °C, 60 min, Sørensen-buffer (pH = 7.2)/acetonitrile (vv = 1:1)). Additionally, [18F]BFP as new and
versatile labelling building block for the copper-catalyzed Huisgen-cycloaddition was developed. Therefore, the azidoproline modified SNEW peptide was labelled with this click building block under milder conditions (r.t., 30 min, Sørensen-buffer (pH = 7.2)/ethanol (vv = 1:1)).
New labelling building blocks were synthesized for the bioorthogonal radiofluorination of novel azide-functionalized peptides with a SNEW sequence and compared to standard labelling methods like [18F]FBAM. The SNEW peptides show a high affinity to the EphB2 receptor and represent promising radiotracers for a specific tumour diagnosis.
[1] Surawska, H.; Ma, P. C.; Salgia, R., (2004), Cytokine Growth Factor Rev., 15, 419-433,
[2] Mosch, B.; Reissenweber, B.; Neuber, C.; Pietzsch, J., (2010), J. Oncol., DOI: 10.1155/2010/135285,
[3] Choi, Y.; Syeda, F.; Walker, J. R.; Finerty Jr., P. J.; Cuerrier, D.; Wojciechowski, A.; Liu, Q.; Dhe-Paganon, S.; Gray, N. S., (2009), Bioorg. Med. Chem. Lett., 19, 4467-4470,
[4] Miyazaki, Y.; Nakano, M.; Sato, H.; Truesdale, A. T.; Stuart, J. D.; Nartey, E. N.; Hightower, K. E.; Kane-Carson, L., (2007), Bioorg. Med. Chem. Lett., 17, 250-254,
[5] Caligiuri, M.; Molz, L.; Liu, Q.; Kaplan, F.; Xu, J. P.; Majeti, J. Z.; Ramos-Kelsey, R.; Murthi, K.; Lievens, S.; Tavernier, J.; Kley, N., (2006), Chem. Biol., 13, 711-722.
[6] Chrencik, J. E.; Brooun, A.; Recht, M. I.; Nicola, G.; Davis, L. K.; Abagyan, R.; Widmer, W.; Pasquale, E. B.; Kuhn, P., (2007), J. Biol. Chem., 282, 36505-36513.
[7] Wuest, F.; Köhler, L.; Berndt, M.; Pietzsch, J., (2009), Amino Acids, 36, 283-295
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences (ISRS), 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S460

Publ.-Id: 16603 - Permalink

Site-selective labelling of peptides with fluorine-18 in solution and on solid phase using succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) – a comparative study
Kuchar, M.; Pretze, M.; Mamat, C.; Knieß, T.; Steinbach, J.; Löser, R.;
The growing interest in peptides as probes for the molecular imaging of physiological and pathological processes by positron emissions tomography (PET) is accompanied with the increasing need for generally applicable methods that allow a selective labelling of these biomolecules [1]. The site-selective introduction of the well-established 4-[18F]fluorobenzoyl prosthetic group into peptides containing multiple amino acids with nucleophilic entities located in the side chains is very often challenging. This is especially valid for lysine-containing peptides. Sometimes, a selective labelling can be achieved by taking advantage of the slight difference between the pKa values of the N-terminus and the ε-amino group of lysine [2]. However, the success of this strategy is moderate. Therefore, the potential to label various lysine containing peptides with [18F]SFB at defined sites by solid-phase synthesis was evaluated in this study in comparison to 18F-fluorobenzoylation in solution.
Four different peptides were chosen to comparatively evaluate the solid phase approach and labelling in solution (Figure 1). The selection included the N-terminal telopeptide of collagen α1(I) 1 [3] and its derivative 2 [4] both containing a lysine residue important for collagen crosslinking, the k7 sequence of a cell-penetrating peptide 3 [5] and a derivative of a so-called SNEW peptide 4. The latter is a ligand for the EphB2 receptor whose binding affinity is critically dependent on a free N-terminus [6]. The aim was to label 1-3 at their N-terminus whereas 4 was to be labelled selectively at its C-terminal lysine residue. The precursors as well as the corresponding non-radioactive fluorobenzoylated peptides were synthesised by microwave-assisted solid-phase peptide synthesis employing the Fmoc/tBu strategy. For labelling in solution the fully deprotected peptides were reacted with [18F]SFB at pH 7 and 9. Labelling on solid phase was carried out by suspending the preswollen peptide-loaded resin in a mixture of DMF and phosphate buffer containing [18F]SFB followed by a washing step and final acidic deprotection and cleavage from the resin. For every labelling experiment the labelling yields were determined by radio-HPLC. In addition, peptides 1 and 2 were labelled in solution by using derivatives with Alloc/All-protected side chains followed by Pd-catalysed deprotection and solid phase extraction.

1 *H-Leu-Ser-Tyr-Gly-Tyr-Asp-Glu-Lys-Ser-Thr-Gly-Ile-Ser-Val-Pro-NH2
2 *H-Gly-Gly-Gly-Asp-Pro-Lys-Gly-Gly-Gly-Gly-Gly-NH2
3 *H-Lys-Lys-Arg-Lys-Ala-Pro-Lys-Lys-Lys-Arg-Lys-Phe-Ala-NH2
4 H-Ser-Asn-Glu-Trp-Ile-Leu-Pro-Arg-Leu-Pro-Gln-His-Val-*Lys-NH2

Figure 1. Sequences of the peptides studied in the labelling experiments. The desired labelling position is indicated by an asterisk.

Labelling in solution always resulted in product mixtures independent of the pH that were often difficult to purify. In contrast, labelling on solid-phases yielded 18F-fluorobenzoylated peptides in radiochemical purities of 95-99%. The optimised procedure allowed to prepare the labelled peptides in activities ranging from 30-100 MBq (8-15%, d.c.) with a specific activity of 10-12 GBq/μmol and a reaction time of 135-140 min (without [18F]SFB production). The labelling of the Alloc/All-protected peptides in solution was less successful due to the presence of unreacted [18F]SFB during the deprotection step.
The selective labelling [18F]SFB on solid phase is a useful tool in the development of radiotracers based on peptides, especially if the lysine side chain or the N-terminus is functionally important for target binding.
[1] Tolmachev & Stone-Elander (2010) Biochim. Biophys. Acta 1800, 487-510,
[2] Wester et al. (1995) J. Label. Compd. Radiopharm. 37, S513-S515,
[3] Helseth et al. (1979) Biopolymers 18, 3005-3014,
[4] Nagan & Kagan (1994) J. Biol. Chem. 269, 22366-22371,
[5] Rennert et al. (2008) ChemMedChem 3, 241-253
[6] Chrencik et al. (2007) J. Biol. Chem. 282, 36505-36513
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences (ISRS), 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S449

Publ.-Id: 16602 - Permalink

Fluorinated cyclobutyl group for increased metabolic stability using a tyrosine model system
Franck, D.; Kniess, T.; Steinbach, J.; Zitzmann-Kolbe, S.; Friebe, M.; Dinkelborg, L.; Graham, K.;
Objectives: [18F]Fluoroalkyl chains are known to be potential sites for metabolic instability and can result in suboptimal PET image quality [1]. The aim of this work was to develop the [18F]fluorocyclobutyl substituent as a novel 18F-labeled prosthetic group that should have an increased metabolic stability whilst maintaining its efficacy. The well-characterized tyrosine LAT transporter system was used as a model test system.
The precursors (cis-cyclobutane-1,3-diol ditosylate and tert-butyl N-(tert-butoxycarbonyl)-O-[trans-3-(tosyloxy)cyclobutyl]-L-tyrosinate) and the reference compound, 3-(cis-fluorocyclobutyl)-tyrosine, for the indirect and direct radiosyntheses of 3-(cis-[18F]fluorocyclobutyl)tyrosine (3-[18F]FCBT) were synthesized. The radiosynthesis of the 3-[18F]FCBT via indirect and direct methods were successfully established as outlined in Scheme 1. In vitro studies were performed in A549 cells after incubation with 3-[18F]FCBT at 37°C for up to 60 min with/without inhibitors FET and non-radioactive 3-FCBT. In vivo PET imaging studies were performed on mice bearing human lung cancer xenografts (A549 carcinoma).
3-[18F]FCBT was synthesized via the direct method from precursor 3 in good yield (27-37% d.c.) and excellent radiochemical purity (>99%) in 57-73 minutes. In comparison, the indirect method from the precursor 1 and tyrosine gave only moderate yields (6-12% d.c.) and required longer synthesis times (140-158 minutes). The cell uptake studies showed an increase of 3-[18F]FCBT over time reaching a plateau of 5.87% at 30 min . In animal PET imaging the A549 lung carcinoma xenografts in mice were clearly visualized by the injection of 6 MBq 3-[18F]FCBT. The compound showed fast clearance from the blood and renal as well as hepatobiliary excretion. Preliminary in vitro stability investigations using 3-FCBT indicate excellent stability.
The radiosynthesis of 3-[18F]FCBT via indirect and direct methods were established The introduction of fluorinated cyclobutyl group into the LAT-targeting tyrosine was shown to be tolerated and actively transported in the in vitro and in vivo setting using A549 cells and their xenografts. The principle of this fluorinated cyclobutyl group as stabilizing moiety will be further investigated.
[1] Treble, (1962) Biochemistry, 82, 129-134
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences (ISRS), 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S447

Publ.-Id: 16601 - Permalink

Automated radiosynthesis and purification of the thiol-reactive labeling agent [18F]FBAM
Kniess, T.; Kuchar, M.; Steinbach, J.; Pietzsch, J.;
Objectives: The interest on 18F-radiolabeled peptides and proteins has increased over the last decade. Consequently, prosthetic groups as N-succinimidyl 4-[18Ffluorobenzoate ([18F]SFB) have been designed for labeling peptides at the amino functionality. Due to in some cases unsatisfactory or inconsistent radiolabeling results with [18F]SFB a strategy directed to a single functionality would circumvent these drawbacks. Therefore, prosthetic groups reacting exclusively with thiol groups were designed1, one of them N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl] maleimide [18F]FBAM2 (Figure 1). To make [18F]FBAM more applicable for routine use we developed an automated radiosynthesis of this labeling agent including a solid phase purification3.
The labeling precursor 4-N,N,N-trimethylaminobenzaldehyde triflate, the FBAM precursor N-(6-aminooxyhexyl)maleimide hydrochloride and the non-radioactive FBAM were synthesized according to the literature2. [18F]Fluoride was produced on a CYCLONE 18/9 Cyclotron (IBA) via the 18O(p,n)18F reaction. A commercially available synthesis module TRACERlab FXFDG (GE) was adapted in terms of program and hardware. Results: For the 18F-labeling 10 mg of 4-N,N,N-trimethylaminobenzaldehyde triflate were reacted with the [18F]KF-Kryptofix222 complex in 1.0 mL of acetonitrile for 10 min at 90°C in reactor 1. After addition of 12 mL of water the solution was passed over a Strata C18U cartridge (Phenomenex) to trap the 4-[18F]fluorobenzaldehyde. The cartridge was eluted with 3.5 mL of methanol into reactor 2 and 7 mg of the aminooxy-precursor was added dissolved in 0.5 mL of methanol. The Schiff-base reaction was performed for 6 min at 40°C, 10 mL of water were added and the content of reactor 2 was passed over a LiChrolut RP18 cartridge (Merck). After washing with 6 mL of acetonitrile/water=1:1 the [18F]FBAM was finally eluted with 2mL of acetonitrile into a product vial. A typical radiosynthesis started with 3.1 GBq [18F]fluoride and yielded about 580 MBq [18F]FBAM (29% yield d.c.) within a total synthesis time of 40 min, the radiochemical purity was 94-98% .
An automated procedure for the routine radiosynthesis of [18F]FBAM will help to make the thiolreactive prosthetic group more broadly available for selective 18F radiolabeling of peptides and proteins as
molecular imaging probes.
Research Support:
[1] Toyokuni et al., (2003), Bioconjug. Chem., 14, 1253-159, [2] Berndt et al., (2007), Nucl. Med. Biol., 34, 5-15[3] Kniess et al., (2011), Appl. Radiat. Isot., submitted
  • Poster
    19 International Symposium on Radiopharmaceutical Sciences (ISRS), 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S413

Publ.-Id: 16600 - Permalink

Magnetic solitons in quantum spin chains
Zvyagin, S.;
The first documentary observation of solitons was done in 1834 by John Scott Russell on Union Canal in Scot-land, UK, who found that a heap of water in a canal propagates undistorted over several kilometers. Nowadays, a large number of soliton manifestations is known, including for instance solitons in fiber-optics communication systems, solitons in conducting polymers, low-frequency collective motion in proteins and DNA, etc. Many types of solitons can be described using the famous sine-Gordon equation... The sine-Gordon equation can be solved exactly, with solitons and their bound states, breathers, as solution. In this presentation I will talk about magnetic solitary waves in quantum spin chains, probed in copper pyrimidine dinitrate (Cu-PM, which is a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions) by means of high-frequency and high-field Electron Spin Resonance (ESR) spectroscopy. Signa-tures of three breather branches and a soliton were identified, as predicted by the sine-Gordon quantum-field theory. Having a fully quantum-mechanical nature, the solitary waves in quantum spin chains can be destroyed by thermal fluctuations. This can be nicely illustrated by analyzing the parameters of ESR spectra using a new theoretical concept by Oshikawa and Affleck. Finally, I will show the crucial effect of high magnetic fields sup-pressing the solitary-wave behavior and transforming the soliton-breather excitation spectrum into magnons. These studies were done employing ESR technique in pulsed magnetic fields up to 64 T. Excellent agreement between the theory and experiment in all cases was obtained. In addition, the development of the high-field Elec-tron Spin Resonance facilities at the Dresden High Magnetic Field Laboratory will be presented.
  • Invited lecture (Conferences)
    Seminar University of Kyoto, 30.11.2011, Kyoto, Japan

Publ.-Id: 16599 - Permalink

ESR studies of the quasi-2D frustrated Cs2CuBr4
Zvagin, S. A.; Kamenskyi, D.; Wosnitza, J.; Ikeda, M.; Fujita, T.; Hagiwara, M.; Kyokuen, N. N.; Starykh, O. A.; Hu, R.; Ryu, H.; Petrovic, C.;
We report low-temperature electron spin resonance (ESR) studies of single-crystalline samples of Cs2CuBr4, a spin-1/2 antiferromagnet with a triangular spin-lattice structure. A remarkable angular dependence of the resonance field, including the splitting of the ESR line for some orientations of the magnetic field, and the presence of a gap in the ESR excitation spectrum at temperatures above TN ~1.3 K have been revealed. Our observations suggest that uniform Dzyaloshinskii-Moriya interaction affects the low-energy excitation spectrum in this frustrated compound. The results are compared with that obtained recently for the isostructural material Cs2CuCl4 [Povarov et al., Phys. Rev. Lett. 107, 037204 (2011)]
  • Lecture (Conference)
    APS March Meeting, 27.02.-02.03.2011, Boston, USA
  • Lecture (Conference)
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16598 - Permalink

The Attempt of Using GaN(Cs) Cathodes for Photo Injectors
Teichert, J.; Arnold, A.; Michel, P.; Murcek, P.; Xiang, R.;
There are a lot of opportunities to improve the electron source quality. Especially for the high average power gun producing up to mA level of average current, the searching for the better photo cathodes is a principal challenge. Gallium nitride (GaN) is a novel III-V semiconductor with the wide band gap close to the Cs2Te. As photo emitter material, GaN has a number of interesting characteristics. It has high QE and the negative electron affinity (NEA) on its surface can be achieved only with cesium; GaN (Cs) is more robust against contamination than GaAs and multi-alkali photocathodes. Thus GaN(Cs) has the chance to be a candidate for a high average current source. In this paper, the result of the first activation experiment in HZDR and the next plan will be presented.
Keywords: Photo Cathode, Electron Source, GaN, Gallium Nitride, NEA, Quantum Efficiency
  • Poster
    ERL 2011, The 50th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 16.-21.10.2011, Tsukuba, Japan

Publ.-Id: 16597 - Permalink

NMR signal averaging in 62 T pulsed fields
Meier, B.; Greiser, S.; Haase, J.; Herrmannsdörfer, T.; Wolff-Fabris, F.; Wosnitza, J.;
es hat kein Abstract vorgelegen.
  • Lecture (Conference)
    Gordon Research Seminar Magnetic Resonance, 11.06.2011, Biddeford, USA
  • Poster
    Gordon Research Conference Magnetic Resonance, 12.06.2011, Biddeford, USA

Publ.-Id: 16596 - Permalink

Ultrasound Investigations of Magnetic Monopole in Spin Ice
Erfanifam, S.;
  • Poster
    6th PhD Seminar, 05.-07.10.2011, Rabenberg, Deutschland

Publ.-Id: 16595 - Permalink

Gallium-induced thin-film superconductivity in Ge and Si and its possible applications
Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Fiedler, J.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Helm, M.; Wosnitza, J.;
We present two unconventional routes of embedding superconducting nanolayers in a semiconducting environment. On the one hand, ion implantation and subsequent annealing have been used to prepare intrinsic superconducting thin-films of Ga-doped germanium (Ge:Ga) with Tc of 0.5 to 1.2 K. On the other hand, the same technique has been applied to fabricate thin amorphous Ga-rich layers in silicon (Si:Ga) revealing a Tc of about 7 K. Extended structural investigations by means of XTEM, EDX, RBS/C, and SIMS have been performed in addition to low-temperature electrical transport and magnetization measurements. A narrow window of preparation parameters turns out to be necessary to obtain best sample properties in a reproducible way. While Ge:Ga films scale 60 - 100 nm and reveal a small critical current density Jc ≈ 3 A/cm2, Si:Ga layers exhibit Jc > 1 kA/cm2 and a thickness of 15 nm. Relative high and anisotropic critical fields have been found for both nanostructures proving their quasi-two-dimensionality. The implementation of prospective microstructuring may offer an on-chip combination of super- and semiconducting circuits that could be integrated in novel heterostructured devices.
  • Lecture (Conference)
    EUCAS 2011, 18.-23.09.2011, Den Haag, The Netherlands
  • Poster
    6th PhD Seminar, 05.-07.10.2011, Rabenberg, Deutschland

Publ.-Id: 16594 - Permalink

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