Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34877 Publications

Comparative investigation of the novel radiotracers (R)- and (S)-[18F]fluspidine for imaging of σ1 receptors by PET

Deuther-Conrad, W.; Becker, G.; Patt, M.; Donat, C. K.; Kranz, M.; Stittsworth, S.; Holl, K.; Habermann, B.; Fischer, S.; Wenzel, B.; Mishchenko, L.; Hesse, S.; Steinbach, J.; Wünsch, B.; Lever, S. Z.; Sabri, O.; Brust, P.

Sigma1 receptor (σ1), found in plasma, mitochondrial and endoplasmic reticular membranes and involved in many cellular functions of the endocrine, immune, and nervous systems, is a promising target for novel concepts in diagnostics and therapy of cancer and brain diseases. To support such research by molecular imaging of σ1, we have comparatively evaluated the 18F-labelled (R)- and (S)-enantiomers of the σ1 ligand fluspidine in pigs.

(R)- and (S)-[18F]fluspidine were synthesized from enantiopure tosylate precursors with high specific activities (650-870 GBq/µmol) and radiochemical purity (>99%). Brain pharmacokinetics were investigated by dynamic PET studies in anaesthetized pigs under baseline (n=3 per enantiomer) and blocking conditions (n=3 per enantiomer) using σ1 selective SA4503. SUVs were calculated for 24 MR-defined brain regions. One- and two-tissue compartment modeling was applied to calculate individual rate constants, total distribution volumes (VT) and binding potentials of (R)- and (S)-[18F]fluspidine. Furthermore, VT was estimated from graphical Logan plot analyses. Organ doses (ODs) and effective doses (ED) of both radiotracers were determined in CD-1 mice and an extended single dose toxicity study of (S)-fluspidine was performed in SPRD rats.

(R)- and (S)-[18F]fluspidine displayed significantly different brain uptake kinetics. Although initial SUVs were similar (R)-[18F]fluspidine showed higher values (60-150%) at 120 min p.i. Brain distribution in pigs correlated with brain distribution in CD-1 mice (Fig. 1). SA4503 reduced SUVs and k3 of both radiotracers by ~65% and 70-95%, respectively, in almost all brain regions (Fig. 1B, C), while effects on k4 differed region-specific. VT values estimated by full nonlinear kinetic and Logan analyses correlated highly and revealed also a significant decrease in all brain regions for both radiotracers by SA4503. The expected EDs of (R)- and (S)-[18F]fluspidine to humans are 31 and 28 µSv/MBq, respectively, and up to 620 µg (S)-fluspidine/kg no test item related effects were observed in the toxicity study.

Both [18F]fluspidine enantiomers appear to be suitable for σ1 imaging in human brain. The different pharmacokinetics of (R)-[18F]fluspidine and (S)-[18F]fluspidine may be translated into diagnostic imaging of different pathological conditions such as degenerative as well as cancerous processes.

Fig. 1: Distribution of [18F]fluspidine binding sites in brain. (A) Ex vivo autoradiography of a sagittal rat brain slice obtained at 45 min after intravenous injection of [18F]fluspidine. (B, C) Sagittal brain PET images acquired as summed data from 0-20 min after intravenous injection of piglet with (S)-[18F]fluspidine under baseline conditions (B) or under blocking with SA4503 (C).

  • Poster
    The 10th International Symposium on Funktional NeuroReceptor Mapping of the Living Brain, 21.-24.05.2014, Amsterdam, The Netherlands

Publ.-Id: 20199

Implementation of a fast running full core pin power reconstruction method in DYN3D

Gomez, A.; Sanchez Espinosa, V. H.; Kliem, S.; Gommlich, A.

This paper presents a substantial extension of the pin power reconstruction (PPR) method used in the reactor dynamics code DYN3D with the aim to better describe the heterogeneity within the fuel assembly during reactor simulations. The flexibility of the new implemented PPR permits the local spatial refinement of one fuel assembly, of a cluster of fuel assemblies, of a quarter or eight of a core or even of a whole core. The application of PPR in core regions of interest will pave the way for the coupling with sub-channel codes enabling the prediction of local safety parameters. One of the main advantages of considering regions and not only a hot fuel assembly (FA) is the fact that the cross flow within this region can be taken into account by the subchannel code. The implementation of the new PPR method has been tested analysing a rod ejection accident (REA) in a PWR minicore consisting of 3x3 FA. Finally, the new capabilities of DNY3D are demonstrated by the analysing a boron dilution transient in a PWR MOX core and the pin power of a VVER-1000 reactor at stationary conditions.

Keywords: pin power reconstruction; DYN3D; VVER; whole core pin power predictions; boron dilution; REA; PWR

Publ.-Id: 20198

Application of Sub-second Annealing for Diluted Ferromagnetic Semiconductors

Zhou, S.; Bürger, D.; Schmidt, H.

The dilute ferromagnetic semiconductor GaMnAs provides a great promise for its application in spintronics, which combines two degrees of freedom: charge and spin. Mn ions which substitute Ga sublattice sites provide both local magnetic moments and itinerant holes. The magnetic properties of GaMnAs can be controlled by manipulating free carriers via electrical gating. However, the preparation of ferromagnetic GaMnAs presents a big challenge due to the low solubility of Mn in GaAs. To overcome the low solid solubility limit of transition metal dopants in semiconductors, one needs highly nonequilibrium methods to introduce enough dopants and a short-time annealing to activate them. Both ion implantation and pulsed-laser (or flash-lamp) annealing occur far enough from thermodynamic equilibrium conditions. Ion implantation introduces enough dopants. The subsequent short-time annealing deposits energy in the near-surface region to drive a rapid liquid-phase epitaxial growth. Such a nonequilibrium process maintains the supersaturation induced by ion implantation. In this chapter, we review the application of sub-second annealing in the activation of Mn implanted GaAs as well as GaP.

  • Book chapter
    Wolfgang Skorupa, Heidemarie Schmidt: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 297-314
    DOI: 10.1007/978-3-319-03131-6_15

Publ.-Id: 20196

Sub-nanosecond Thermal Spike Induced Nanostructuring of Thin Solid Films Under Swift Heavy Ion (SHI) Irradiation

Ghosh, S.; Kumar, H.; Singh, S. P.; Srivastava, P.; Kabiraj, D.; Avasthi, D. K.; Bürger, D.; Zhou, S.; Mücklich, A.; Schmidt, H.; Stouquert, J. P.

The interaction between swift heavy ions (SHI) and a solid has been identified as one of the important physical processes to generate or modify nanostructures in thin solid films. The large part of the energy which is deposited in the electronic subsystem of a material by SHI is known as electronic energy loss and gets coupled to the lattice subsystem in a complex way resulting in a transient (picoseconds to sub-nanosecond) thermal spike within a few nanometer diameter region of the thin solid film along the ion path. The temperature of this narrow zone may raise up to 1000 K or more during this time. This transient heating process is known as lattice thermal spike and can be used as a tool to engineer materials down to the nanoscale. Here we address two important consequences of lattice thermal spike; (i) elongation of metal nanoparticles embedded in dielectric thin films and (ii) generation of a-Si/c-Si nanostructures in a silicon nitride matrix.

(i) Metal nanoparticles embedded in a thin film matrix belong to a class of materials that has potential applications as optical and magnetic sensors, storage, memory devices, field emission display etc. The nanoparticle size and shape, orientation, inter-particle separation and dielectric constant of the surrounding matrix are the crucial parameters which control their properties. Thermal spike generated by SHI in these nanoparticles and surrounding matrix can be used as a unique tool to tailor the shape of the embedded nanoparticles, eventually modifying the physical properties of these materials. Metal nanoparticles, which are mostly spherical in shape in as grown films, get elongated along the direction of SHI due to thermal spike induced melting and stress. After a brief introduction of some fundamental aspects and synthesis of these films, a detailed discussion on elongation of nearly spherical Ni nanoparticles embedded in SiO2 thin film matrix under 120 MeV Au ion irradiation is made. Various physical parameters influencing the shape modification of nanoparticles under the framework of thermal spike model are discussed.

(ii) a-Si/c-Si nanostructures embedded in different Si-based dielectric matrix have attracted researchers because of their potential application in low-cost Si-based optoelectronic devices. We report here the response of in-situ formed Si-nanostructures embedded in a Si-rich hydrogenated amorphous silicon nitride matrix to 100 MeV Ni8+ ions irradiation. Si-rich a-SiN x :H films have been prepared by Hg-sensitized Photo Chemical Vapor Deposition. Presence of elemental Si was confirmed from X-ray photoelectron spectroscopy. Irradiation with a fluence of 5×1012 ions/cm2 under normal incidence at room temperature leads to dissolution of these Si-nanostructures. However, irradiation with a relatively higher fluence of 1×1014 ions/cm2 enhances the nucleation and leads to the formation of amorphous Si-nanostructures in the film. In addition, at the surface a novel effect i.e. partial crystallization of Si-nanostructures along the beam direction is observed. The results are explained on the basis of thermal spike model.

  • Book chapter
    Wolfgang Skorupa, Heidemarie Schmidt: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 107-121
    DOI: 10.1007/978-3-319-03131-6_6

Publ.-Id: 20195

Nanonet Formation by Constitutional Supercooling of Pulsed Laser Annealed, Mn-Implanted Germanium

Bürger, D.; Zhou, S.; Höwler, M.; Ou, X.; Kovacs, G. J.; Reuther, H.; Mücklich, A.; Skorupa, W.; Schmidt, H.

This subchapter presents interesting aspects of pulsed laser annealing. During this process, a laser pulse incorporates heat in the near surface region of a semiconductor or a metal. If the energy density is high enough, the system may melt near the surface. Because of the large temperature gradient, a very fast recrystallization may lead to novel physical material properties. Here we present interesting aspects of the formation of a Mn-rich nanonet in germanium. Important physical phenomena are explained in detail. The material has been fabricated by pulsed laser annealing of Mn implanted Ge wafers with a pulse duration of 300 ns. Due to a segregation instability during recrystallization, Mn segregates at the liquid-solid interface and an approximately 40 nm thick Ge:Mn surface layer is strongly enriched with Mn. Transmission electron microscopy plan-view images reveal a percolating Mn-rich nanonet after etching the top 10 nm surface layer. Hysteretic anomalous Hall effect has been observed up to 30 K, but it vanishes after etching away the 40 nm thick Mn-rich Ge:Mn layer. The nanonet seems to support the correlation between magnetization and hysteretic Hall resistance. Intrinsic charge carrier scattering in the threads or vertices of the Ge:Mn nanonet may lead to the observed anomalous Hall effect. In the outlook the nanonet formation is revealed for supercooled Mn-implanted Si.

  • Book chapter
    Wolfgang Skorupa, Heidemarie Schmidt: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 15-33
    DOI: 10.1007/978-3-319-03131-6_2

Publ.-Id: 20194

Protein Conformational Rearrangement induced by the modulation of vibrational modes

Lorincz, I. Z.; Schay, G.; Rauscher, A. A.; Kellermayer, M. S. Z.; Gensch, M.; Malnasi-Csizmadia, A.

We succeeded to induce a specific conformational change in a protein by infrared laser excitation and proved that the reaction was a non-thermal effect. An alpha helical – beta sheet structural rearrangement of an intrinsically fluorescent protein, LSSmOrange was monitored through its fluorescence intensity change upon irradiation with a free electron IR laser. The picosecond timescale IR pulse caused a reversible structural rearrangement of LSSmOrange on the second timescale. We found that the structural rearrangement was induced by a single IR photon with a very low, less than 10-6 photon efficiency and the maximum effect was detected at 1033 cm-1 IR irradiation. The IR induced reaction is not a trivial thermal effect because 1. the IR pulse increases the fluorescence of LSSmOrange whereas temperature jump decreases it, 2. its magnitude depends on the wavelength of the IR pulse. Based on the Arrhenius plots of the IR induced conformational change and its relaxation, we found that the IR excitation increases the free energy of the alpha-helical structure dominated state by 12 kJ/mol. Since this energy shift is exactly equal to the energy of the IR photon, we concluded that there are highly efficient energy flow pathways between the vibrational modes in the protein as it is indicated by recent theoretical calculations. These results may open a new horizon towards the direct investigation of the functional role of vibrational modes in proteins.

  • Lecture (Conference)
    PepCon 2014 - BIT's 7th Annual Protein and Peptide Conference, 25.-28.04.2014, Dalian, China

Publ.-Id: 20193

64Cu-markierte Upconversion-Nanopartikel und ihr Potenzial für die multimodale Bildgebung von Tumoren

Hesse, J.; Barreto, J. A.; Graham, B.; Geipel, G.; Spiccia, L.; Steinbach, J.; Stephan, H.

Das Interesse an der medizinischen Nutzung von Nanomaterialien ist insbesondere auf deren einzigartigen, strukturbedingten Eigenschaften zurückzuführen. Basierend auf unterschiedlichen Materialien, wie Polymeren, anorganische oder organisch-anorganische Hybridsubstanzen, werden Nanoteilchen auf ihre Anwendbarkeit in komplexen biologischen Systemen untersucht. Upconversion(UC)-Nanopartikel zeigen hierbei ein vielversprechendes Potenzial und besitzen bei einer gut abgestimmten Dotierung des anorganisch, kristallinen Wirtsgitters mit ausgewählten Seltenerd-Metallen eine sehr effiziente Lumineszenz[1]. Damit eröffnet sich speziell deren Nutzung für die optische Bildgebung, welche die Aufklärung von Prozessen auf zellulärer Ebene gestattet. Gleichzeitig erlaubt die Oberflächenstruktur der Partikel eine Mehrfachfunktionalisierung mit Chelatoren für die Bindung von Radiometallnukliden für PET und SPECT und tumoraffinen Einheiten wie beispielsweise Peptiden.
Wir berichten über die Synthese und Fluoreszenz-eigenschaften von ultrakleinen (< 10 nm) UC-Nanopartikeln auf der Basis von NaYF4: Yb3+, Er3+ und deren Umhüllung mit verschiedenen Polymeren zur Erzeugung wasserlöslicher und biokompatibler Materialien. Diese Partikel wurden mit einem Picolyl-Derivat des makrocyclischen Liganden 1,4,7-Triazacyclononan funktionalisiert. Der Chelator dient zur Radiomarkierung der Partikel mit 64Cu2+, was die Anwendung eines zusätzlichen bildgebenden Verfahrens, der Positronen-Emissions-Tomographie (PET), er-möglicht. Es werden weiterhin Synthesestragien zur Einführung von tumoraffinen Einheiten auf der Oberfläche der UC-Nanopartikel vorgestellt, die eine Adressierung des auf vielen Tumoren überexprimierten Epidermal Growth Factor Receptors (EGFR) gestatten.
[1] Mader, H. S., Kele, P., Saleh, S. M., Wolfbeis, O. S., Curr. Opin. Chem. Biol. 2010, 14, 582-596

  • Lecture (Conference)
    GDCh-Wissenschaftsforum Chemie 2013, 01.-04.09.2013, Darmstadt, Deutschland

Publ.-Id: 20192

High-Speed PIXE: A spatially resolved PIXE setup at the 6 MV Tandem accelerator

Buchriegler, J.; von Borany, J.; Hanf, D.; Munnik, F.; Nowak, S. H.; Renno, A. D.; Scharf, O.; Ziegenrücker, R.

kein Abstract eingereicht

Keywords: High-Speed PIXE; SLcam; Colour X-Ray Camera

  • Invited lecture (Conferences)
    SLcam(R) User Workshop, 16.01.2014, Berlin, Deutschland

Publ.-Id: 20191

Cryo-Fluoreszenzspektroskopie – Eine innovative Technik für die Wissenschaft

Steudtner, R.; Großmann, K.

Fluoreszenzmikroskopische und fluoreszenzspektroskopische Untersuchungen finden in der Biologie, Medizin, Materialprüfung sowie Geowissenschaften eine breite Anwendung. Dabei spielt die chemische Charakterisierung und die Lokalisierung der verschiedensten Analyte mittels analytischer und bildgebender Verfahren eine wichtige Rolle. Die Analyse von Schwermetallen insbesondere von Radionukliden und seltenen Erden in natürlichen Systemen soll an Hand einer verbesserten Fluoreszenzanalytik bei tiefen Temperaturen erweitert werden. Durch die Weiterentwicklung der Fluoreszenzspektroskopie bei tiefen Temperaturen werden am Helmholz-Zentrum Dresden-Rossendorf nicht nur umweltanalytisch relevante Fragestellung im Bereich der Ressourcenökologie sondern auch verschiedenste Aufgaben aus dem Bereich der medizinischen Forschung bearbeitet.
Durch die Unterstützung der Max-Buchner-Forschungsstiftung konnten wir drei entscheidende Ergebnisse erzielen, welche für zukünftige Projekte die nötige wissenschaftliche Grundlage bieten.
1. Aufbau eines dauerhaften spektroskopischen Tieftemperaturmessplatzes zum schnellen und sensitiven Nachweis von Uran in diversen Umweltproben (Wasser- und Bodenproben)
2. Unterstützung beim Aufbau eines mikroskopischen Tieftemperaturmess-platzes, der mikroskopische Untersuchungen bei -253°C mit bis zu 630 facher Vergrößerung erlaubt.
3. Erste erfolgreiche Messungen mit dem spektroskopischen und mikroskopischen Aufbau im Bereich der Umweltanalytik sowie an verschiedenen medizinisch relevanten Anwendungen.
Langfristig zielen die Arbeiten auf die direkte Visualisierung der Analyten bei tiefen Temperaturen in biologischen und medizinischen Medien in Kombination mit fluoreszenzspektroskopischen Daten, welche zusätzliche molekulare Informationen über die der Mikroumgebung der Chromophore liefern, ab.

  • Open Access Logo CITplus 10(2014), 60-62
  • Lecture (Conference)
    ProcessNet-Jahrestagung, 30.09.-02.10.2014, Aachen, Deutschland

Publ.-Id: 20190

New insight into self-irradiation effects on local and long-range structure of uranium-americium mixed oxides (through XAS and XRD)

Lebreton, F.; Martin, P. M.; Horlait, D.; Bes, R.; Scheinost, A. C.; Rossberg, A.; Delahaye, T.; Blanchart, P.

Uranium-americium mixed oxides could be used as transmutation targets to lower Am inventory in spent nuclear fuels. Due to 241Am activity, these materials are subjected to α-self-irradiation which provokes structural damages. Previous studies on U-Am mixed oxides gave first insight into α-radiation tolerance of these compounds, but have never been carried out for more than a year, whereas Am-bearing targets might be stored up to a few years between fabrication and irradiation. In this work, we study effects of self-irradiation on the structure of U1-xAmxO2± solid solutions (x = 0.15 and 0.2) aged of 3 to 4 years. Especially, X-ray diffraction and X-ray absorption spectroscopy are combined to observe these effects from both long-range and local perspectives. Obtained results show that the fluorite-type structure of U-Am mixed oxides withstands 241Am α-irradiation without major damage. Even though an increase of interatomic distance and structural disorder was observed during the first year of storage, the present results show that no further evolution occurs. Furthermore, comparison between long-range and local evolution suggests that α-self-irradiation-induced defects are mainly located in low-ordered domains. The major difference between samples was even found to be related to differences in fabrication conditions. Based on these results, no detrimental factors have been identified for several-year storage of U-Am transmutation targets before irradiation.

Keywords: nuclear fuel; transmutation; uranium; americium; EXAFS; XRD

Publ.-Id: 20189

Sorption data: Ways from a plain collection to recommended values

Bok, F.; Richter, A.; Brendler, V.

For geochemical modeling of scenarios for the disposal of hazardous radioactive and (chemo)toxic waste, comprehensive and consistent thermodynamic data are required as well as sorption data for the surrounding host rocks. Whereas there are several projects running world-wide to arrive at the comprehensive and consistent thermodynamic data base for the aqueous phase and forming solids, the situation is much worse concerning the reactions on the mineral-water interface. For important processes such as sorption, ion exchange or surface precipitation incompleteness and inconsistencies, restricted ranges of variation (temperature, density, pressure, ionic strength) are abundant leading to hardly comparable results in geochemical modeling.
RES³T – the Rossendorf Expert System for Surface and Sorption Thermodynamics ( – is a free-for-use digitized thermodynamic sorption database utilizing surface complexation models (SCM). It is mineral-specific and can therefore also be used for complex real systems such as rocks or soils. Data records comprise of mineral properties, specific surface area values, characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions. An extensive bibliography is included, providing links not only to the above listed data items, but also to the primary reference. Currently efforts started to combine RES³T with the thermodynamic database THEREDA ( to provide a comprehensive and consistent database for a holistic geochemical modeling.
Sorption speciation calculations of radionuclides on mineral surfaces will be presented, showing the actual consequences of inconsistent and scattered sorption data that can be found in literature, as well as the possibilities of the RES³T database for calculating radionuclide sorption onto complex geologic formations, e.g. the overburden of a nuclear waste disposal. Generally, RES³T proved to be a powerful tool for identifying data gaps for combinations of minerals and sorbing radionuclide essential for the risk assessment of waste disposals or in accident analysis.

Keywords: RES³T; Rossendorf Expert System for Surface and Sorption Thermodynamics; database; THEREDA

  • Invited lecture (Conferences)
    248th ACS National Meeting, 10.-14.08.2014, San Francisco, USA

Publ.-Id: 20188

Search for a live supernova signature of 60Fe in deep-sea sediments and a new half-life measurements of 60Fe

Wallner, A.; Feige, J.; Fifield, L. K.; Golser, R.; Kutschera, W.; Merchel, S.; Rugel, G.; Schumann, D.; Tims, S.; Winkler, S.; Sterba, J.; Bichler, M.

60Fe (2.6 My) is one of the most versatile nuclides in astrophysics. Live 60Fe was identified in the Galaxy. Its stellar production requires neutron densities available only in explosive Supernovae (SNe) or SuperAGB stars. 60Fe is also found in meteorites and indirectly via 60Ni anomalies. Fresh nucleosynthetic products may enter the Solar System (SS) trapped in cosmic dust. Hence, nearby SNe might deposit traces on Earth and since it has negligible terrestrial production, 60Fe is an ideal candidate to search for recent SNe. However, detection requires sensitivities of 60Fe/Fe~10-15 and 60Fe-AMS faces interference from stable 60Ni. So far only TU Munich, combining a MP tandem with a gas-filled magnet, measures 60Fe routinely as los as ~10-16. This group discovered live 60Fe in a deep-sea crust indicating that SNe-isotopes found their way to Earth 2-3 My ago [1]. Work is ongoing at TUM to validate this finding in other archives [2,3]. Further, Rugel et al. [4] measured a half-life substantially longer than previously recommended. We have started a similiar program at the ANU using the 14UD accelerator and a split-pole magnetic spectrograph converted into a gas-filled magnet. A substantial beamtime devoted to 60Fe has resulted in an exceptional sensitivity below 10-16. We have searched for a SN-signal in 3 deep-sea sediment cores (indian Ocean) [5]. We will present exciting new data for 60Fe with high time resolution and will relate it to potantial exposure of the SS to recent SNe. In addition, we re-measured in an independent approach the 60Fe half-life via AMS measurements of the 60 Fe/55Fe ratio.
[1] Knie et al. PRL93 (2004)
[2] Ludwig et al. this conf.
[3] Fimiani et al. LPSC 1659 (2012)
[4] Rugel et al. PRL103 (2009)
[5] Feige et al. this conf.

Keywords: accelerator mass spectrometry; supernova; radionuclide

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20187

Paramagnetic Decoration of DNA origami Nanostructures by Eu3+ Coordination

Opherden, L.; Oertel, J.; Barkleit, A.; Fahmy, K.; Keller, K.

The folding of DNA into arbitrary two- and three-dimensional shapes, called DNA origami, represents a powerful tool for the synthesis of functional nanostructures. Here, we present the first approach toward the paramagnetic functionalization of DNA origami nanostructures by utilizing post-assembly coordination with Eu3+ ions. In contrast to the usual formation of toroidal dsDNA condensates in the presence of trivalent cations, planar as well as rod-like DNA origami maintain their shape and monomeric state even under high loading with the trivalent lanthanide. Europium-coordination was demonstrated by the change in Eu3+ luminescence upon binding to the two DNA origami. Their natural circular dichroism in the Mg2+- and Eu3+-bound state was found to be very similar to that of genomic DNA, evidencing little influence of the DNA origami superstructure on the local chirality of the stacked base pairs. In contrast, the magnetic circular dichroism of the Mg2+-bound DNA origami deviates from that of genomic DNA. Furthermore, the lanthanide affects the magnetic properties of DNA in a superstructure-dependent fashion, indicative of the existence of superstructure-specific geometry of Eu3+ binding sites in the DNA origami that are not formed in genomic DNA. This simple approach lays the foundation for the generation of DNA origami with taylored lanthanide-specificity. Such systems do not require covalent modifications and can be used for the magnetic manipulation of DNA nanostructures or for the paramagnetic alignment of molecules in NMR spectroscopy.

Keywords: magnetic circular dichroism; molecular alignment; lanthanide; NMR spectroscopy

Publ.-Id: 20186

CFD based approach for modeling direct contact condensation heat transfer in two-phase turbulent stratified flows

Apanasevich, P.; Lucas, D.; Beyer, M.; Szalinski, L.

This paper describes a CFD based strategy for the modeling of stratified two-phase flows with heat and mass transfer across a moving steam-water interface due to direct contact condensation. Such flows have been of major importance for example in connection with the analysis of nuclear reactor safety systems, in particular during two-phase Pressurized Thermal Shock (PTS) scenarios. The approach is based on the two-fluid phase-average model. The interfacial friction was modeled by using an Algebraic Interfacial Area Density (AIAD) framework where the drag coefficient is a function of the local flow characteristics. To show the impact of the modeling of interfacial friction the simulation with the AIAD model was compared with a simulation where a constant drag coefficient of 0.44 was used in the whole domain. For the modeling of interfacial heat and mass transfer two correlations for the water heat transfer coefficient based on the penetration theory were utilized. The CFD simulations were validated against a steady-state TOPFLOW-PTS steam-water experiment. In the experiment, very detailed temperature measurements were conducted using special thermocouple lances and infrared thermography. Total condensation rate was determined indirectly by using three different methods. The simulations have depicted that the results obtained with the AIAD model are considerably closer to the experimental observations than the results obtained with the constant drag coefficient. It was also shown that a correct prediction of condensation rates is very important for prediction of the temperature field. In general, the simulations of the TOPFLOW-PTS steam/water experiment with condensation have revealed that Reynolds Averaged Navier-Stokes method can be applied for the simulation of two-phase stratified flows with rather large free surfaces and interfacial heat transfer. However, the modeling of turbulent interfacial heat transfer should be improved.

Keywords: computational fluid dynamics; stratified two-phase flow; pressurized thermal shock; interfacial heat and mass transfer; direct contact condensation; TOPFLOW-PTS experiments

Publ.-Id: 20185

Investigation of vertical gas-liquid pipe flows using ultrafast X-ray tomography – An overview of methods, measurement series and previous results

Banowski, M.; Lucas, D.; Beyer, M.; Szalinski, L.; Hoppe, D.; Hampel, U.

In this presentation, methods, measurement series and previous results of upward, counter-current as well as downward gas-liquid flows at the vertical titanium pipe of the TOPFLOW test facility are shown.

  • Lecture (Conference)
    German CFD Network of Competence, Workshop, 19.-20.03.2014, München-Garching, Deutschland

Publ.-Id: 20184

Systematic investigation of terahertz-induced excitonic Rabi splitting

Teich, M.; Wagner, M.; Stehr, D.; Schneider, H.; Helm, M.; Böttge, C. N.; Klettke, A. C.; Chatterjee, S.; Kira, M.; Koch, S. W.; Khitrova, G.; Gibbs, H. M.

Weak near-infrared and strong terahertz excitation are applied to study excitonic Rabi splitting in (GaIn)As/GaAs quantum wells. Pronounced anticrossing behavior of the split peaks is observed for different terahertz intensities and detunings relative to the intra-excitonic heavy-hole 1s–2p transition. At intermediate to high electric fields the splitting becomes highly asymmetric and exhibits significant broadening. A fully microscopic theory is needed to explain the experimental results. Comparisons with a two-level model reveal the increasing importance of higher excitonic states at elevated excitation levels.

Keywords: QW; FEL; Autler-Townes; THz

Publ.-Id: 20183

One-Group Cross-Section Generation for Monte Carlo Burnup Codes: Multigroup Method Extension and Verification

Kotlyar, D.; Fridman, E.; Shwageraus, E.

Allowing Monte Carlo (MC) codes to perform fuel cycle calculations requires coupling to a point depletion solver. In order to perform depletion calculations, one-group (1-g) cross sections must be provided in advance. This paper focuses on generating accurate 1-g cross section values using Monte Carlo transport codes.
The proposed method is an alternative to the conventional direct reaction rate tally approach, which requires substantial computational effort. The method presented here is based on the multi-group (MG) approach, in which pre-generated MG sets are collapsed with MC calculated flux. In our previous studies, we showed that generating accurate 1-g cross sections requires their tabulation against the background cross section (σ0) to account for the self-shielding effect in unresolved resonance energy range. However, in previous studies, the model used for calculation of σ0 was simplified by relying on user specified Bell and Dancoff factors.
This work demonstrates that 1-g values calculated under the previous simplified model assumptions may not always agree with the directly tallied values. More specifically, the assumption is not universally applicable to the analysis of wide spectrum of reactor systems and may be inaccurate when the number of energy groups is reduced (i.e. from tens of thousands to hundreds of groups). Therefore, the original background cross section model was extended by implicitly accounting for the Dancoff and Bell factors. The method developed here reconstructs the correct value of σ0 by utilizing statistical data generated within the MC transport calculation by default. The proposed method was implemented in BGCore code system. The 1-g cross section values generated by BGCore were compared with those tallied directly from the MCNP code. Very good agreement in the 1-g cross values was observed. The method does not carry any additional computational burden and it is universally applicable to the analysis of thermal as well as fast reactor systems. Adopting this MG methodology, which accounts for self-shielding, allows generating highly accurate cross sections even for significantly reduced number of energy groups (hundreds vs. tens of thousands). This reduction considerably improves the computational efficiency which makes feasible the analysis of large scale reactor problems.

Keywords: Coupled Monte Carlo codes; BGCore; Multi group; One-group cross sections; Background cross section

Publ.-Id: 20182

Experimente zu vertikalen Dampf-Wasser-Rohrströmungen mit ultraschneller Röntgentomographie

Banowski, M.; Lucas, D.; Beyer, M.; Hampel, U.

Gas-Flüssigkeits-Zweiphasenströmungen in Rohrleitungen sind für die Entwicklung und Validierung neuer zweiphasiger CFD-Modelle ein geeigneter generischer Untersuchungsgegenstand. Der Grad an strömungsmorphologischer Komplexität ist relativ hoch, was sich insbesondere in der Ausprägung charakteristischer Strömungsregime mit ihren jeweils spezifischen Impulstransferbeziehungen an der Phasengrenze in Abhängigkeit von Leerrohrgeschwindigkeiten und Stoffwerten äußert. An der TOPFLOW-Versuchsanlage des HZDR werden gegenwärtig umfangreiche experimentelle Studien zu Zweiphasenströmungen in senkrechten Testsektionen für Wasser/Luft- und Wasser/Dampf-Strömungen bis 65 bar Druck durchgeführt. Diese Experimente dienen vordergründig der Erhebung von Messdaten für die CFD-Codeentwicklung. Als Messverfahren kommt in aktuellen Versuchen an einer vertikalen DN50 Testsektion die ultraschnelle Röntgentomographie zum Einsatz. Diese ermöglicht es, den Strömungsquerschnitt mit Bildraten von 2500 Bildern/Sekunde und einer räumlichen Auflösung von etwa 1 mm in zwei jeweils 10 mm entfernten Ebenen abzubilden. Verschiedene Strömungsregime werden durch Wahl der Leerohrgeschwindigkeiten für die Gas- und die Flüssigphase am Versuchsstand eingestellt. Neben der Aufklärung des Strömungsregimes und der Erfassung interessanter Detailstrukturen der Strömung können radiale Gasgehaltsprofile ebenso wie Gasphasengeschwindigkeiten durch automatisierte Auswerteroutinen extrahiert werden. Im Beitrag werden Ergebnisse von Dampf-Wasser-Experimenten zu auf- und abwärtsgerichteten Gleichströmungen bei verschiedenen Druckstufen vorgestellt.
Diese Arbeit wird im Rahmen eines aktuellen Forschungsprojekts, welches vom Bundesministerium für Wirtschaft und Technologie unter der Projektnummer 150 1411 gefördert wird, durchgeführt.

  • Poster
    ProcessNet Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme- und Stoffübertragung, 24.-25.03.2014, Fulda, Deutschland

Publ.-Id: 20181

Investigation of Scintillation Detectors for Prompt Gamma Imaging

Römer, K.; Petzoldt, J.; Berthel, M.; Dreyer, A.; Enghardt, W.; Golnik, C.; Hueso-González, F.; Kormoll, T.; Müller, A.; Pausch, G.; Rohling, H.; Schöne, S.; Weinberger, D.; Fiedler, F.

Characterization of Scintillators with respect to their Application in Prompt Gamma Imaging Systems.

Keywords: Prompt Gamma Imaging; Scintillation Detectors

  • Poster
    OncoRay Retreat 2014, 27.-28.03.2014, Dresden, Deutschland

Publ.-Id: 20180

Experimentelle Untersuchung von aufwärtsgerichteten zweiphasigen Rohrströmungen mit ultraschneller Röntgentomographie

Banowski, M.; Lucas, D.; Beyer, M.; Hampel, U.

Die Entwicklung von CFD-Modellen zur Berechnung von Zweiphasenströmungen für industrielle Anwendungen in der Prozessindustrie stellt eine große Herausforderung dar. Zweiphasenströmungen in Reaktions- oder Trennapparaten sind infolge der auf mehreren Skalen ablaufenden Transportprozesse für Impuls, Stoff und Wärme inhärent hoch komplex. Zur Validierung von CFD-Codes sind daher experimentelle quantitative Daten solcher Strömungen mit hoher zeitlicher und räumlicher Auflösung erforderlich.
An der TOPFLOW-Versuchsanlage des HZDR werden auf diesem Gebiet umfangreiche Versuche an einer vertikalen DN50-Testsektion mit Luft-Wasser und Dampf-Wasser-Strömungen bis zu p = 65 bar und einer weiten Variation der Leerrohrgeschwindigkeiten für Wasser- und Gasphase durchgeführt. Unter Verwendung der am HZDR entwickelten ultraschnellen Röntgentomographie können Strömungsquerschnitte mit Bildraten von bis zu 2500 frames/s und einer räumlichen Auflösung von etwa 1 mm rückwirkungsfrei erfasst und visualisiert werden. Neben der Ermittlung von Strömungsregimen und weiterer charakteristischer Strömunsgkenngrößen dienen diese Untersuchungen dem Erkenntnisgewinn über Strömungsdetails, wie etwa Blasenkoaleszenz und –zerfall, radiale Gasgehaltsprofile, Strömungsverhalten von Kleinblasen in Abhängigkeit benachbarter Blasen sowie Geschwindigkeitsinformationen, in hochturbulenten Zweiphasenströmungen bei industriell relevanten Gasgehalten. Mit Hilfe von speziell entwickelten Bildauswertungsroutinen können diese Daten analysiert und für die Zweiphasen-CFD-Modellvalidierung aufbereitet werden. In diesem Beitrag wird ein Überblick über bisherige Versuche und deren Ergebnisse gegeben.
Diese Arbeit wird im Rahmen eines aktuellen Forschungsprojekts, welches vom Bundesministerium für Wirtschaft und Technologie unter der Projektnummer 150 1411 gefördert wird, durchgeführt.

  • Poster
    ProcessNet Jahrestreffen der Fachgruppen Extraktion und Fluidverfahrenstechnik, 27.-28.03.2014, Fulda, Deutschland

Publ.-Id: 20179

Design, synthesis, characterisation and in vitro studies of hydrophilic, colloidally-stable, 64Cu(II)-labelled, ultra-small iron oxide nanoparticles in a range of human cell lines

Pombo Garcia, K.; Zarschler, K.; Barreto, J. A.; Spiccia, L.; Graham, B.; Stephan, H.

The application of ultra-small super-paramagnetic iron oxide nanoparticles (USPIONs) as versatile diagnostic probes for multimodal imaging in biomedicine, including via magnetic resonance imaging (MRI) and positron emission tomography (PET), requires hydrophilic and biocompatible surface coatings. Herein, we describe the development of USPIONs stabilised by octylamine-modified polyacrylic acid (OPA) and the subsequent
conjugation of a 64Cu(II) chelator, N-(4-aminophenyl)-2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]- acetamide (amino-dmptacn), for radioactivity-based detection. Transmission electron microscopic analysis and dynamic light scattering measurements confirmed the monodispersity and stability of the OPA-USPIONs in aqueous media and revealed a hydrodynamic size of ca. 15 nm. Furthermore, the biocompatibility and cellular uptake efficiency of the functionalised USPIONs was investigated in a range of normal and tumour cell lines. The results clearly show a cell type- as well as time-dependent internalisation of the OPA-USPIONs via active energy-dependent pathways. Biocompatibility of OPA- USPIONs in the concentration range of 10–50 mg mL-1 was demonstrated, while impairment of cellular viability was observed for human umbilical vein endothelial cells at 100 mg mL-1. Upon exposure to human serum, several biomolecules cover the negatively-charged surface of the nanoparticles and a biomolecular corona is formed. Nonetheless, the nanoparticles represent a promising platform for the future development of a bimodal PET-MRI tumour-imaging agent.

1. K. Pombo-Garcia, K. Zarschler, J. A. Barreto, J. Hesse, L. Spiccia, B. Graham, H. Stephan, RSC Advances 2013, 3, 22443.
2. M. P. Monopoli, D. Walczyk, A. Campbell, G. Elia, I. Lynch, F. B. Bombelli and K. A. Dawson, J Am Chem Soc, 2011, 133, 2525-2534.

Acknowledgements: Helmholtz Initiative and Networking Fund (Functional nanomaterials for multimodality cancer imaging (NanoTracking), project ID: VH-VI-421). Australian Research Council Discovery Grant and a Discovery Outstanding Researcher Award and a Senior Research Award by the Humboldt Foundation are gratefully acknowledged by L.S.

  • Poster
    e-WISPOC: European-Winter School on Physical Organic Chemistry, 02.-07.02.2014, Bressanone, Italy

Publ.-Id: 20177

Ultrasmall and radiolabelled upconverting nanophosphors – ready for challenge of multimodal cancer imaging

Hesse, J.; Graham, B.; Geipel, G.; Grenzer, J.; Spiccia, L.; Steinbach, J.; Stephan, H.

The increasing interest in nanomaterials for medical applications is mainly attributed to their unique and structural properties. Based on different materials like polymers, inorganic or organic-inorganic hybrid substances such nanomaterials are investigated for applications in biological systems. Regarding this upconverting nanophosphors exhibit a high potential because of their bright luminescence. With their exceptional characteristic to convert near infrared to visible light (upconversion) these inorganic lanthanide-doped nanoparticles are very attractive as probes for optical imaging with the possibiliy for elucidation of even cellular processes[1]. In addition the surface of the nanoparticles offer the chance for rather multiple functionalisation such as radiometall chelates for PET and SPECT as well as for tumor affine units (peptides, aptamers, antibodies).
We want to present the synthesis and photophysical properties of ultrasmall (<10 nm) upconverting nanophosphors based on a host lattice of NaYF4: (Nd3+),Yb3+, Er3+/Tm3+ which are excited at 800 nm or 980 nm. To generate watersoluble biocompatible nanoparticles the material was coated with different polymers and afterwards functionalized with DMPTACN, a picolyl derivative of the macrocyclic ligand 1,4,7-triazacyclononane. An initial point for further investigations in vitro and in vivo was achieved by radiolabelling with the positron emitter Cu-64.

1. Cheng, L. , Wang, C. , Liu, Z. Nanoscale. 2013, 5, 23-37.

Acknowledgements: This work was funded by the Helmholtz Initiative and Networking Fund „Functional nanomaterials for multimodality cancer imaging“ (NanoTracking, project ID: VH-VI-421).

  • Poster
    e-WISPOC: European-Winter School on Physical Organic Chemistry, 02.-07.02.2014, Bressanone, Italy

Publ.-Id: 20176

Emittance minimization at the ELBE superconducting electron gun

Möller, K.; Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.

The transverse emittance is one of the most important quantities which characterize the quality of an electron source. For high quality experiments low beam emittance is required. By means of theoretical considerations and simulation calculations we have studied how the emittance of the Rossendorf superconducting radio-frequency photoelectron source (SRF gun) can be minimized. It turned out that neither a solenoid magnet nor the effect of space charge forces is needed to create a pronounced emittance minimum. The minimum appears by just adjusting the starting phase of the electron bunch with respect to the RF phase of the gun in a suitable way. Investigation of various correlations between the properties of the beam particles led to an explanation on how the minimum comes about. It is shown that the basic mechanism of minimization is the fact that the longitudinal properties of the particles (energy) are strongly influenced by the starting phase. Due to the coupling of the longitudinal and transverse degrees of freedom by the relativistic equation of motion the transverse degrees of freedom and thereby the emittance can be strongly influenced by the starting phase as well. The results obtained in this study will be applied to minimize the emittance in the commissioning phase of the SRF gun.

Keywords: electron gun; SRF gun; superconducting radio frequency; electron injector; transverse emittance

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-050 2014
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 20175

Metastatic potential of B16-F10 melanoma cells is enhanced by extracellular S100A4 derived from RAW264.7 macrophages

Haase-Kohn, C.; Wolf, S.; Herwig, N.; Mosch, B.; Pietzsch, J.

S100A4, synthesized and secreted from both tumor and stroma cells, modulates an aggressive tumor phenotype in various cancers by intracellular and extracellular interactions which are not completely understood. Because of the high content of tumor-associated macrophages in melanoma, here, a syngeneic model (coculture of mouse B16-F10 melanoma cells (Mel) and RAW264.7 macrophages (Mϕ); administration (i.v.) of Mel and Mϕ/Mel in NMRI nu/nu mice) was used to investigate synthesis and secretion of a) S100A4, b) S100A4-mediated signaling and activation of NFκB, and c) S100A4-mediated modulation of Mel invasiveness in vitro (transwell assay, transwell matrigel assay) and in vivo (metastatic lung colonization), respectively. In this model substantial S100A4 synthesis and secretion is demonstrated in Mϕ. Macrophage-derived S100A4 promotes Mel invasiveness in a paracrine manner in vitro, which is further substantiated in control experiments using recombinant human S100A4 and Mel stably transfected with mouse S100A4. Moreover, the participation of S100A4-mediated signaling, e.g., via the receptor for advanced glycation endproducts (RAGE), resulting in activation of NFκB was demonstrated in all experimental settings. Finally, we demonstrated that interaction of macrophage-derived S100A4 with Mel results in increased metastatic lung colonization in vivo.

Keywords: Melanoma metastasis; Receptor for advanced glycation; endproducts (RAGE); S100 proteins; Tumor-associated macrophages (TAM)

Publ.-Id: 20174

Simultaneous Targeting of Prostate Stem Cell Antigen and Prostate-Specific Membrane Antigen Improves the Killing of Prostate Cancer Cells Using a Novel Modular T Cell-Retargeting System

Arndt, C.; Feldmann, A.; Koristka, S.; Cartellieri, M.; Dimmel, M.; Ehninger, A.; Ehninger, G.; Bachmann, M.

Recently, we described a novel modular platform technology in which T cell-recruitment and tumor-targeting domains of conventional bispecific antibodies are split to independent components, a universal effector module (EM) and replaceable monospecific/monovalent target modules (TMs) that form highly efficient T cell-retargeting complexes. Theoretically, our unique strategy should allow us to simultaneously retarget T cells to different tumor antigens by combining the EM with two or more different monovalent/monospecific TMs or even with bivalent/bispecific TMs, thereby overcoming limitations of a monospecific treatment such as the selection of target-negative tumor escape variants.
In order to advance our recently introduced prostate stem cell antigen (PSCA)-specific modular system for a dual-targeting of prostate cancer cells, two additional TMs were constructed: a monovalent/monospecific TM directed against the prostate-specific membrane antigen (PSMA) and a bivalent/bispecific TM (bsTM) with specificity for PSMA and PSCA. The functionality of the novel dual-targeting strategies was analyzed by performing T cell activation and chromium release assays.
Similar to the PSCA-specific modular system, the novel PSMA-specific modular system mediates an efficient target-dependent and -specific tumor cell lysis at low E:T ratios and picomolar Ab concentrations. Moreover, by combination of the EM with either the bispecific TM directed to PSMA and PSCA or both monospecifc TMs directed to either PSCA or PSMA, dual-specific targeting complexes were formed which allowed us to kill potential escape variants expressing only one or the other target antigen.
Overall, the novel modular system represents a promising tool for multiple tumor targeting.

Keywords: T cell redirection; dual-targeting; recombinant antibody; immunotherapy

Publ.-Id: 20173

A novel ex vivo Isolation and Expansion Procedure for Chimeric Antigen Receptor Engrafted Human T Cells

Cartellieri, M.; Koristka, S.; Arndt, C.; Feldmann, A.; Stamova, S.; von Bonin, M.; Töpfer, K.; Krüger, T.; Geib, M.; Michalk, I.; Temme, A.; Bornhäuser, M.; Lindemann, D.; Ehninger, G.; Bachmann, M. P.

Genetically engineered T lymphocytes are a promising option for cancer therapy. Prior to adoptive transfer they have to be expanded in vitro to reach therapeutically sufficient numbers. So far, no universal method exists for selective in vitro expansion of engineered T lymphocytes. In order to overcome this problem and for proof of concept we incorporated a novel unique peptide sequence of ten amino acids as epitope (ETag) into the binding domains of two novel chimeric antigen receptors (ECARs) directed against either prostate stem cell antigen (PSCA) for the treatment of prostate cancer (PCa) or CD33 for the treatment of acute myeloide leukemia (AML). The epitope tag then was utilized for expanding ECAR engrafted T cells by triggering the modified T cells via a monoclonal antibody directed against the E-Tag (Emab). Moreover, the E-Tag served as an efficient selection epitope for immunomagnetic isolation of modified T cells to high purity. ECAR engrafted T cells were fully functional and mediated profound anti-tumor effects in the respective models of PCa or AML both in vitro and in vivo. The method can be integrated straightforward into clinical protocols to improve therapeutic efficiency of tumor treatment with CAR modified T lymphocytes.

Keywords: adoptive transfer; genetically engineered T cells; chimeric antigen receptor; in vitro cultivation; tumor immunotherapy; Tumor; cancer; T cell; Genetic engineering

Publ.-Id: 20172

Oxygen depth profiling with subnanometre depth resolution

Kosmata, M.; Munnik, F.; Hanf, D.; Grötzschel, R.; Richter, S.; Möller, W.

An High-depth Resolution Elastic Recoil Detection (HR-ERD) set-up using a magnetic spectrometer has been taken into operation at the Helmholtz-Zentrum Dresden-Rossendorf for the first time. This instrument allows the investigation of light elements in ultra thin layers and their interfaces with a depth resolution of less than 1 nm near the surface. As the depth resolution is highly influenced by the experimental measurement parameters, sophisticated optimisation procedures have been implemented. Effects of surface roughness and sample damage caused by high fluences need to be quantified for each kind of material. Also corrections are essential for non-equilibrium charge state distributions that exist very close to the surface. Using the example of an high-k multilayer SiO2/Si3N4Ox/SiO2/Si it is demonstrated that oxygen in ultra-thin films of a few nanometres thickness can be investigated by HR-ERD.

Keywords: high resolution depth profiling; ERD; high-k materials

Publ.-Id: 20171

Characterization of a novel single-chain bispecific antibody for retargeting of T cells to tumor cells via the TCR co-receptor CD8

Michalk, I.; Feldmann, A.; Koristka, S.; Arndt, C.; Cartellieri, M.; Ehninger, A.; Ehninger, G.; Bachmann, M. P.

There is currently growing interest in retargeting of effector T cells to tumor cells via bispecific antibodies (bsAbs). Usually, bsAbs are directed on the one hand to the CD3 complex of T cells and on the other hand to a molecule expressed on the surface of the target cell. A bsAb mediating cross-linkage via CD3 leads to an activation of CD8+ T cells and as a consequence to the killing of the target cells. In parallel, CD4+ T cells including TH1, Th2, TH17 cells and even regulatory T cells (Tregs) will also be activated. Cytokines produced by CD4+ T cells can contribute to severe side effects e. g. life-threatening cytokine storms and, thinking of the immunosupressive function of Tregs, can even be counterproductive. Therefore, we asked whether or not it is feasible to limit the retargeting to CD8+ T cells e. g. via targeting of the co-receptor CD8 instead of CD3. In order to test for proof of concept, a novel bsAb with specificity for CD8 and a tumor-associated surface antigen was constructed. Interestingly, we found that pre-activated (but not freshly isolated) T cells can be retargeted via CD8 leading to an efficient lysis of the target cells.

Keywords: tumor immunotherapy; tumor; cancer; T cell; bispecific antibodies

Publ.-Id: 20170

Letter to the editor: Cytotoxic response of human regulatory 1 T cells upon T cell receptor-mediated activation – a 2 matter of purity

Koristka, S.; Cartellieri, M.; Arndt, C.; Feldmann, A.; Töpfer, K.; Michalk, I.; Temme, A.; Ehninger, G.; Bachmann, M.

kein Abstract verfügbar

Publ.-Id: 20169

Concept for individualized patient allocation: ReCompare-remote comparison of particle and photon treatment plans

Lühr, A.; Löck, S.; Roth, K.; Helmbrecht, S.; Jakobi, A.; Petersen, J. B.; Just, U.; Krause, M.; Enghardt, W.; Baumann, M.

Background: Identifying those patients who have a higher chance to be cured with fewer side effects by particle beam therapy than by state-of-the-art photon therapy is essential to guarantee a fair and sufficient access to specialized radiotherapy. The individualized identification requires initiatives by particle as well as non-particle radiotherapy centers to form networks, to establish procedures for the decision process, and to implement means for the remote exchange of relevant patient information. In this work, we want to contribute a practical concept that addresses these requirements.Methods: We proposed a concept for individualized patient allocation to photon or particle beam therapy at a non-particle radiotherapy institution that bases on remote treatment plan comparison. We translated this concept into the web-based software tool ReCompare (REmote COMparison of PARticlE and photon treatment plans).Results: We substantiated the feasibility of the proposed concept by demonstrating remote exchange of treatment plans between radiotherapy institutions and the direct comparison of photon and particle treatment plans in photon treatment planning systems. ReCompare worked with several tested standard treatment planning systems, ensured patient data protection, and integrated in the clinical workflow.Conclusions: Our concept supports non-particle radiotherapy institutions with the patient-specific treatment decision on the optimal irradiation modality by providing expertise from a particle therapy center. The software tool ReCompare may help to improve and standardize this personalized treatment decision. It will be available from our website when proton therapy is operational at our facility. © 2014 Lühr et al.; licensee BioMed Central Ltd.

Keywords: Particle therapy, Patient selection; Proton therapy; Treatment plan comparison

Publ.-Id: 20168

Visualizing inflammation activity in rheumatoid arthritis with Tc-99 m Anti-CD4-mAb fragment scintigraphy

Steinhoff, K.; Pierer, M.; Siegert, J.; Pigla, U.; Laub, R.; Hesse, S.; Seidel, W.; Sorger, D.; Seese, A.; Künstler, J.-U.; Pietzsch, H.-J.; Lincke, T.; Rullmann, M.; Emmrich, F.; Sabri, O.

T-cell-located CD4 antigen represents one of the therapeutic targets in rheumatoid arthritis (RA). However, up to now there is no established imaging tool to visualize this target in vivo. The aim of our study was to assess the safety and tolerability of a technetium-99 m labelled murine anti-human CD4 IgG1-Fab fragment ([99mTc]-anti-CD4-Fab, [99mTc]-EP1645) in patients with active synovitis due to RA, and to evaluate its potential as a marker of disease activity.
In the present phase I proof of principle study five patients with RA were examined. Planar scans of the whole body, hands, and feet were taken 30 min up to 24 h after application of 550 ± 150 MBq [99mTc]-anti-CD4-Fab, followed by visual analyses, comparison with clinical data in 68 joints per patient and semiquantitative analysis of hand and wrist joints.
Neither infusion related adverse events nor adverse events during follow up were observed. No increase in human anti-murine antibody titres was seen. All patients had positive scans in almost 70% of clinically affected joints. Positive scans were also found in 8% of joints without evidence of swelling or tenderness.
Scintigraphy with [99mTc]-anti-CD4-Fab is a promising technique for evaluation of inflammatory activity in patients with RA, pre-therapeutical evaluation of CD4 status and therapy control. Tracer uptake in clinically inconspicuous joints strongly indicates diagnostic potential of [99mTc]-anti-CD4-Fab. Whether this technique is eligible as a prognostic factor in RA needs to be analysed in further studies as well as the pathophysiological background of clinically affected joints lacking tracer uptake.

Keywords: CD4; Monoclonal antibodies; Technetium-99 m scintigraphy; Rheumatoid arthritis; Molecular imaging

Publ.-Id: 20166

Influence of different chelators on the radiochemical properties of a 68-Gallium labelled bombesin analogue.

Asti, M.; Iori, M.; Capponi, P. C.; Atti, G.; Rubagotti, S.; Martin, R.; Brennauer, A.; Müller, M.; Bergmann, R.; Erba, P. A.; Versari, A.

The radiolabelled bombesin analogue AMBA shows high potential for diagnosis and treatment of prostate and breast cancer, but the influence of different chelators, which differ in terms of radiochemical reactivity and stability, have not been explored so far. In order to find the best suitable chelator for labelling of AMBA, we synthesized AMBA analogues linked to the most commonly used chelators DOTA, NOTA and NODAGA and compared their reactivity and stability after labelling with 68-Gallium.

Keywords: 68Ga-labelling; AMBA-chelators; Bombesin analogues; 68Ga-NODAGA-AMBA; Gallium radionuclides

Publ.-Id: 20165

Radiolabeled anti-EGFR-antibody improves local tumor control after external beam radiotherapy and offers theragnostic potential

Koi, L.; Bergmann, R.; Brüchner, K.; Pietzsch, J.; Pietzsch, H.-J.; Krause, M.; Steinbach, J.; Zips, D.; Baumann, M.

The effect of radioimmunotherapy (RIT) using the therapeutic radionuclide Y-90 bound to the anti-EGFR antibody cetuximab combined with external beam irradiation (EBRT) (EBRIT) on permanent local tumor control in vivo was examined.
Growth delay was evaluated in three human squamous cell carcinoma models after RIT with [(90)Y]Y-(CHX-A''-DTPA)4-cetuximab (Y-90-cetuximab). The EBRT dose required to cure 50% of the tumors (TCD50) for EBRT alone or EBRIT was evaluated in one RIT-responder (FaDu) and one RIT-non-responder (UT-SCC-5). EGFR expression and microenvironmental parameters were evaluated in untreated tumors, bioavailability was visualized by PET using ([(86)Y]Y-(CHX-A''-DTPA)4-cetuximab (Y-86-cetuximab) and biodistribution using Y-90-cetuximab.
In UT-SCC-8 and FaDu but not in UT-SCC-5 radiolabeled cetuximab led to significant tumor growth delay. TCD50 after EBRT was significantly decreased by EGFR-targeted RIT in FaDu but not in UT-SCC-5. In contrast to EGFR expression, parameters of the tumor micromilieu and in particular the Y-90-cetuximab biodistribution or Y-86-cetuximab visualization in PET correlated with the responsiveness to RIT or EBRIT.
EGFR-targeted EBRIT can improve permanent local tumor control compared to EBRT alone. PET imaging of bioavailability of labeled cetuximab appears to be a suitable predictor for response to EBRIT. This theragnostic approach should be further explored for clinical translation.

Keywords: Cetuximab; Combined treatment; Epidermal growth factor receptor (EGFR) inhibition; Radioimmunotherapy; Radiotherapy

Publ.-Id: 20164

Investigations on multi phase flow in inline separators using ultra fast X-ray tomography and wire mesh sensors

Schäfer, T.; Schleicher, E.; Hampel, U.

The optimization of separation processes with respect to the capacity and efficiency and the decreasing of the required residence time for the separation is significant for production of raw materials for petrochemical industries and in numerous operations of process engineering. Compact inline separators with swirl elements provide a smart technology for fast and robust mechanical separation of gases and liquids. A significant advantage of these separators is their small size and their applicability directly in pipes. However, unfavorable operating states in terms of separation quality (selectivity) appearing under specific conditions, caused by flow instabilities. They are leading to gas and liquid carry over effects. For the here presented tomographic investigations, it was a main objective to analyze the fluid dynamics inside and in the surrounding area of these separators, to improve the quality and efficiency of these separators. Therefore, ultrafast X-ray tomography and wire mesh sensor technology were used. Applying these tomographic measurement techniques, hydrodynamic characteristics, like the local distribution of the phase fractions, can be captured with very high spatial and temporal resolution. Thus it was possible, to evaluate the separation quality as well as critical flow regimes. Additionally, the obtained data are a basis for the modeling of the separation processes and the effects occurring thereby. Based on this, CFD simulations of the processes can be executed more accurately and design modifications and optimizations of the inline separators can be derived.

Die Optimierung von Separationsverfahren hinsichtlich Leistungsstärke und Effizienz bei Verringerung der notwendigen Verweilzeiten für die Separation hat eine hohe Bedeutung für die Gewinnung von Rohstoffen für die petrochemische Industrie und in einer Vielzahl verfahrenstechnischer Prozesse. Kompakte Inline-Separatoren mit Drallelementen bieten dabei eine elegante Möglichkeit für eine schnelle und robuste mechanische Separation von Gasen und Flüssigkeiten. Ein wesentlicher Vorteil dieser Separatoren ist ihre geringe Größe und die Möglichkeit des direkten Einsatzes in Rohrleitungen. Dabei treten unter bestimmten Umständen jedoch auch ungünstige Zustände hinsichtlich der Qualität der Separation (Trennschärfe), verursacht durch Strömungsinstabilitäten, auf. Diese führen zu Gas- und Liquid-carry-over Effekten. Ein wesentliches Ziel der hier vorgestellten tomographischen Untersuchungen war es, die Strömungsdynamik in der Umgebung und innerhalb solcher Separatoren aufzuklären, um damit Qualität und Effizienz der Separation weiter zu verbessern. Für diese Untersuchungen wurde neben der ultraschnellen Röntgentomographie auch die Gittersensormesstechnik eingesetzt. Mit diesen beiden tomographischen Messtechniken können hydrodynamische Größen, wie die lokale Verteilung der einzelnen Phasenanteile, mit sehr hoher örtlicher und zeitlicher Auflösung gemessen werden. Mit diesen Messdaten war es möglich, die Separationsqualität zu beurteilen und kritische Strömungsregime zu erkennen. Die gewonnenen Daten bilden zudem die Grundlage für eine Modellierung des Separationsprozesses und dabei auftretender Effekte. Darauf aufbauend können genauere CFD-Simulationen der Prozesse durchgeführt werden und konstruktive Optimierungen für die Inline-Separatoren abgeleitet werden.

Keywords: multi phase flow; inline cyclonic separator; swirl element; x-ray tomography; wire mesh sensor

  • Poster
    Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme- und Stoffübertragung, 24.-25.03.2014, Fulda, Deutschland
  • Open Access Logo Contribution to proceedings
    Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme- und Stoffübertragung, 24.-25.03.2014, Fulda, Deutschland
    KURZFASSUNGEN - Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme– und Stoffübertragung: DECHEMA / VDI, 70-70


Publ.-Id: 20163

Mean-field coefficients for helical flow fields

Giesecke, A.; Stefani, F.

We have performed kinematic simulations of dynamo action driven by a small scale helical flow of a conducting fluid. We considered different Roberts-flow like configurations with and without a vertical mean flow in a periodic Cartesian domain. Mean field coefficients that allow a parameterization of induction effects of the small scale flow in terms of an alpha- and beta-effect are computed with the so-called test-field method. The validity of the test-field method is checked by comparing the numerical solutions obtained with a fully resolved velocity field and the solutions from a low resolution mean field model based on the corresponding alpha- and beta coefficients.

Below and slightly above the dynamo threshold our results show a good agreement in terms of growth-rates and vertical field wavenumber. In the strongly overcritical regime, however, field modes with a larger vertical wave number emerge and require a careful consideration of the scale dependence of the alpha-effect. As expected, the agreement between fully resolved models and mean field models is better for increasing scale separation, i.e., for smaller horizontal flow scales.

The behavior of the beta-effect, that essentially describes an enhancement of the magnetic diffusivity by the action of the small scale flow, is determined by the ratio of horizontal to vertical velocity components. For a small vertical flow amplitude, beta scales proportional to the square of the local magnetic Reynolds number whereas for a large relation between vertical and horizontal flow component, beta becomes proportional to the cube root of Rm. This behavior is in rough agreement with measurements of the turbulent beta-effect from Frick et al. (PRL 2010, 105 (18), 184502).

In models with mean flow we have also taken into account internal rods and/or walls that lie in the center of individual eddies and/or provide a separation of the eddies from each other. These flow guiding fixtures can be made of soft iron with a relative permeability much larger than one. The associated inhomogeneity significantly reduces the critical magnetic Reynolds number. However, the problem of modelling the induction effects caused by the non-uniform permeability distribution within the framework of mean field coefficients is yet to be solved.

Without additional effects of permeability, our results allow an easy extrapolation to arbitraryly large systems that consist of an extremely large number of individual helical eddies. Such flows cannot be resolved in direct simulations, but the corresponding mean field models allow to assess whether a certain configuration provides for dynamo action. Such estimations are indeed useful because the typical flow in the cores of fast reactors consists of a forced helical Motion around each individual fuel rod. The occurrence of dynamo action may cause a significant pressure drop in the system with unpredictable consequences for the cooling of the core.

Keywords: Dynamo; permeability; Mean-Field Dynamo Theory

  • Poster
    9th Pamir International Conference, 16.-20.06.2014, Riga, Latvia
  • Contribution to proceedings
    9th Pamir International Conference, 16.-20.06.2014, Riga, Latvia

Publ.-Id: 20162

Numerical simulations for the DRESDYN precession dynamo

Giesecke, A.; Albrecht, T.; Gerbeth, G.; Gundrum, T.; Stefani, F.

A fluid flow of liquid sodium in a cylindrical container, solely driven by precession, is considered as a source for magnetic field generation in the next generation dynamo experiment. The device is currently under development in the framework of the project DRESDYN at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR).

A preparatory small scale water experiment is already in operation in order to provide the hydrodynamic flow properties. First results show that the precessional forcing converts a rather large amount of kinetic energy from the exterior rotation into internal fluid flow. A further striking feature is the abrupt transition from a large scale, quasi-laminar flow to a more disordered turbulent state. In this state the dynamical pressure is reduced while the power required to maintain the rotation of the container is increased.

For slow precession rates, both the amplitude and the shape of the elementary inertial mode obtained from ultrasonic measurements could be well reproduced in hydrodynamic simulations. The simulations also show the presence of the second state at larger precession rates, however, the transition is less abrupt and the degree of turbulence remains much smaller than in the water experiment.

We have used the time-dependent velocity fields obtained from the numerical simulations as input data for kinematic simulations of the magnetic induction equation. So far, the resulting magnetic field growth rates remain below the dynamo threshold for magnetic Reynolds numbers up to Rm=2000 which is in contradiction with results presented by Nore et al (PRE, 84 (1), 016317). Further simulations are necessary in order to restrict the expedient parameter regime and to allow for an optimization of the experimental configuration.

Another possibility for dynamo action may result from the cyclonic vortices aligned parallel to the symmetry axis of the cylinder that have been observed by Mouhali et al (Exp. Fluids 2012, 53 (6), 1693). These vortices provide a efficient source for helicity but, so far, they have not been found in numerical simulations of precession driven flows. Future simulations of magnetic induction caused by precession driven flows will have to be based on analytical models of These vortices and their temporal behavior. This requires more detailed experimental measurements that are expected from the forthcoming upgrade of the water experiment with a 3d-PIV (Particle Image Velocimetry) system.

Keywords: Dynamo; Precession

  • Poster
    9th Pamir International Conference, 16.-20.06.2014, Riga, Latvia
  • Contribution to proceedings
    9th Pamir International Conference, 16.-20.06.2014, Riga, Latvia
  • Magnetohydrodynamics 51(2015)2, 293-302

Publ.-Id: 20161

Ion beam shaping of embedded metal nanoparticles by Si+ ion irradiation

Balaji, S.; Panigrahi, B. K.; Saravanan, K.; David, C.; Amirthapandian, S.; Kalavathi, S.; Nair, K. G. M.; Hübner, R.

Fine Co and Pt nanoparticles are nucleated when a silica sample is implanted with 400 keV Co+ and 1370 keV Pt+ ions. At the implanted range, Co and Pt react to form small CoxPt(1-x) nanoparticles during Si+ ion irradiation at 300 °С. Thermal annealing of the pre-implanted silica substrate at 1000 °С results in the formation of spherical nanoparticles of various sizes. When irradiated with Si+ ions at 300 °С, particles in the size range of 5 - 17 nm undergo rod-like shape transformation with an elongation in the direction of the incident ion beam, while those particles in the size range of 17 - 26 nm turn into elliptical shape. Moreover, it is suspected that very big nanoparticles (size > 26 nm) decrease in size, while small nanoparticles (size < 5 nm) do not undergo any transformation. During Si+ ion irradiation, the crystalline nature of the nanoparticles is preserved. The results are discussed in the light of the thermal spike model.

Keywords: Ion beam shaping; CoxPt(1-x); Ion tracks; TEM

Publ.-Id: 20160

High-field magnetization and magnetic phase diagrams in Nd2RhIn8 and Tb2RhIn8

Javorský, P.; Pajskr, K.; Klicpera, M.; Cermák, P.; Skourski, Y.; Andreev, A. V.

We present magnetic phase diagrams of Nd2RhIn8 and Tb2RhIn8 determined by magnetization and magnetoresistivity measurements on single crystals, including high-field magnetization up to 60 T. Both compounds order antiferromagnetically with the c-axis as the easy magnetization axis. Their magnetic Phase diagrams are qualitatively rather similar. At low temperatures up to 1/2TN, when applying the field along the tetragonal c-axis, we observe first-order transition to another magnetic phase prior to transition to the ferromagnetic order. The magnetic phase diagrams resemble those of other R2RhIn8 or RRhIn5 compounds.

Publ.-Id: 20159

Experimental investigations on heat transfer and flow structure during high pressure steam condensation in a single near-horizontal pipe of a passive heat removal system

Geißler, T.

Passive safety systems are a feature for improved accident control and mitigation in future nuclear power plants. One example of an advanced boiling water reactor with passive safety systems is the KERENA concept (Wagner u. a., 2011). In this concept a two-stage passive heat transfer chain between the reactor and a large water pool outside the containment is foreseen, which is passively activated in case of an accident. The first stage is an emergency condenser, which transfers the heat from the primary circuit to a core flooding pool in the containment. High-pressure steam condensation in the emergency condenser tubes leads to various complicated flow patterns with strong axial and azimuthal inhomogeneity of the flow. This has feed-back on the local heat transfer and is therefore a challenge for accurate prediction, e. g. by system codes. To investigate the details of flow and heat transfer in emergency condenser pipes the experimental facility COSMEA (Condensation teSt rig for flow Morphology and hEAt transfer studies) with extensive special instrumentation has been setup at HZDR’s TOPFLOW facility. Special attention was paid to obtain wall and fluid temperatures and resolve the local flow patterns during the condensation process. Special measurement techniques are a heat flux probe operated at high wall-differential pressure and X-ray tomography for flow scanning.

Keywords: high pressure condensation; COSMEA; TOPFLOW; passive safety system; heat transfer measurement; x-ray tomography; multiphase flow

  • Lecture (Conference)
    45th Annual Meeting on Nuclear Technology - Preserving Competence in Nuclear Technology, 06.-08.05.2014, Frankfurt am Main, Deutschland
  • Contribution to proceedings
    45th Annual Meeting on Nuclear Technology - Preserving Competence in Nuclear Technology, 06.-08.05.14, Frankfurt am Main, Deutschland
    Proceeding of 45th Annual Meeting on Nuclear Technology

Publ.-Id: 20158

High-field magnetization and magnetoelasticity of single crystalline HoFe5Al7

Gorbunov, D. I.; Yasin, S.; Andreev, A. V.; Skourski, Y.; Arnold, Z.; Zherlitsyn, S.; Wosnitza, J.

Magnetization and ultrasound measurements have been performed in pulsed magnetic fields up to 60 T on a ferrimagnetic HoFe5Al7 single crystal (Curie temperature TC = 216 K, compensation point Tcomp = 65 K) with a tetragonal crystal structure of the ThMn12-type. The compound exhibits a high magnetic anisotropy of the easy-plane type. A large anisotropy is also observed within the basal plane having an easy-magnetization direction along the [110] axis with the spontaneous magnetic moment Ms = 2 μB/f.u. at T = 2 K. Along the easy axis, two first-order field-induced magnetic transitions are observed. At both transitions sharp anomalies in the acoustic properties are found. The critical fields of the transitions depend on temperature in a different manner. Within molecular-field theory and using the high-field magnetization data the Ho-Fe inter-sublattice exchange parameter has been determined to be nHoFe ≈ 4 T/μB. The magnetoelasticity has also been probed by magnetization measurements under hydrostatic pressure. TC decreases with a rate dTC/dp = −10 K/GPa, whereas Tcomp increases with dTcomp/dp = 3.5 K/GPa.

Publ.-Id: 20157

Strongly correlated one-dimensional magnetic behavior of NiTa 2O6

Law, J. M.; Koo, H.-J.; Whangbo, M.-H.; Brücher, E.; Pomjakushin, V.; Kremer, R. K.

The magnetic properties of NiTa2O6 were investigated by magnetic susceptibility, specific heat, electron paramagnetic resonance, neutron powder diffraction, and pulse field magnetization measurements. Accompanying ab initio DFT calculations of the spin-exchange constants complemented and supported our experimental findings that NiTa2O6 must be described as a quasi-1D Heisenberg S=1 spin chain system with a nearest-neighbor only antiferromagnetic spin-exchange interaction of 18.92(2) K. Interchain coupling is by about two orders of magnitude smaller. Electron paramagnetic resonance measurements on Mg1-xNixTa2O6 (x≈1%) polycrystalline samples enabled us to estimate the single-ion zero-field splitting of the S=1 states which amounts to less than 4% of the nearest-neighbor spin-exchange interaction. At 0 T NiTa2O6 undergoes long-range antiferromagnetic ordering at 10.3(1) K evidenced by a λ-type anomaly in the specific heat capacity. On application of a magnetic field the specific heat anomaly is smeared out. We confirmed the magnetic structure by neutron powder diffraction measurements and at 2.00(1) K refined a magnetic moment of 1.93(5) μB per Ni2+ ion. Additionally, we followed the magnetic order parameter as a function of temperature. Last, we found saturation of the magnetic moment at 55.5(5) T with a g factor of 2.14(1), with an additional high field phase above 12.8(1) T. The onset of the new high field phase is not greatly affected by temperature, but rather smears out as one approaches the long-range ordering temperature.

Publ.-Id: 20156

Signature of the topological surface state in the thermoelectric properties of Bi2Te3

Rittweger, F.; Hinsche, N. F.; Zahn, P.; Mertig, I.

We present electronic structure calculations based on density functional theory for the thermoelectric properties of Bi2Te3 films. Conductivity and thermopower are computed in the diffusive limit of transport based on the Boltzmann equation. Bulk and surface contributions to the transport coefficients are separated by a special projection technique. As a result we show clear signatures of the topological surface state in the thermoelectric properties.

Keywords: PACS: 71.15.Mb; 73.50.Lw; 72.20.−i; 03.65.Vf

Publ.-Id: 20154

Building bridges from research to industry: Innovative resource technologies "Made in Germany"

Birtel, S.

Tasks and structure of the Helmholtz Instiute Freiberg, Network, Options for colaboration, introduction of the opti-moly Project in Chile

Keywords: raw materials; strategic metals; Mo recovery

  • Invited lecture (Conferences)
    Länderworkshop und NEtworking Chile- Bergbauigant in der Andenregion, 19.-20.03.2014, Berlin, Germany

Publ.-Id: 20153

Local Ion Irradiation Induced Resistive Threshold and Memory Switching in Nb2O5/NbOx Films

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

Summarizing, metal-insulator-metal devices consisting of one insulating Nb2O5 layer were irradiated with krypton ions to form a metallic NbOx sublayer in order to introduce threshold switching. Two effects were identified that induce this metallic NbOx layer: preferential sputtering at the sample surface and interface mixing at the bottom electrode. These krypton irradiated devices can be operated either as a pure threshold switch or as a combination of both, threshold switch and memory element. The presented fabrication method enables costefficient device manufacturing, since ion irradiation could be structured easily using well established lithography methods. Thus, the threshold switch can be formed in defined areas, e.g. the intersection of top and bottom electrode in cross bar arrays.

Keywords: resistive switching; threshold switching; niobium oxide; ion irradiation

Publ.-Id: 20152

Search for supernova-produced 60Fe in Earth’s microfossil record

Ludwig, P.; Bishop, S.; Egli, R.; Chernenko, V.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gomez-Guzman, J. M.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.; Frederichs, T.

The radioisotope 60Fe (T1/2 = (2.62+0.04) Ma [1]) can be produced in copious amounts during different phases of evolution of massive stars. It is possible that 60Fe-rich supernova debris is deposited into solar system reservoirs [2]. Samples from Pacific Ocean sediment were chosen as sample material for this work. Considering an enrichment of the ocean water with 60Fe after deposition of SN material on Earth, all minerals being formed during that time in the sediment will incorporate 60Fe and preserve the original concentration of 60Fe/Fe, except for natural radioactive decay. One particularly interesting reservoir of in situ formed iron-bearing minerals are magnetosomes. Chains of these magnetite crystals are built up by magnetotactic bacteria, who use it similar to a compass needle for magnetotaxis. After cell death, the magnetosome chains can be preserved over geologically significant timescales and represent a very interesting sample material to look for a 60Fe isotope anomaly.
As sample material for this project, two sediment cores from the Eastern Equatorial Pacific (ODP Leg 138, Sites 848 and 851) were chosen. In order to extract iron from 60Fe rich minerals, the chemical CBD extraction procedure was employed. It was carefully calibrated to only dissolve particles of 200 nm diameter. In this way, dilution of 60Fe from iron-bearing grains from other sources (wind, water), which are typically larger, is reduced. A thorough study of the magnetic properties of the samples was also performed [3]. The concentration of 60Fe/Fe was then measured using accelerator mass spectrometry (AMS) at the GAMS setup at the MLL. Its unique ability to separate isobaric background in a gas-filled magnet allows for sensitivities reaching down to 60Fe/Fe ~10-16 and even lower.
At this point, AMS measurements on the smaller one of the two cores have been completed. Measurements of the larger core are underway and are expected to be completed in mid 2014. The 60Fe/Fe concentration determined in core 848 (smaller core) can be seen in Fig. 2. A total of 7 counts of 60Fe have been observed in a depth range corresponding to an age of 2.0 to 2.6 Ma. The signal is above the expected background. Both, this age and the observed average concentration in this range (60Fe/Fe ~1x10-15) agree well with earlier results from a ferromanganese crust [2]. In order to improve statistics and time resolution, the larger core has to be examined as well. In this larger core 851, a total of 12 counts of 60Fe have been detected so far, but measurements have not been completed yet. In addition to measurements of 60Fe, 10Be and 26Al are also currently being measured in the smaller core, to obtain an independent dating, at the DREAMS facility in Dresden.
[1] G. Rugel et al., Phys. Rev. Lett., 103(2009) 072502
[2] K. Knie et al., Phys. Rev. Lett., 93(2004) 171103
[3] P. Ludwig et al., Global Planet. Change 110(2013) 321-339

Keywords: accelerator mass spectrometry; supernova; cosmogenic radionuclide

Publ.-Id: 20151

Search for supernova produced 60Fe in Earth's microfossil record

Ludwig, P.; Bishop, S.; Egli, R.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gómez Guzmán, J. M.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.

Nucleosynthesis in massive stars can produce copious amounts of the radioisotope 60Fe (T(1/2)= 2.62 Ma). When those stars end their lives in a supernova, material enriched with nucleosynthesis products can be ejected into the interstellar medium. If such supernova debris is picked up by Earth, it can be incorporated into terrestrial reservoirs. After the discovery of live 60Fe atoms in 2-3 Myr old layers of a Pacific Ocean ferromanganese crust (K. Knie et al., Phys. Rev. Lett., 93(2004) 171103), a confirmation of this signal, as well as a mapping of the signal with high time-resolution is desirable. Another reservoir in which the 60Fe signature should have been incorporated in are the fossils of magnetotactic bacteria in ocean sediment. These bacteria form chains of small magnetite crystals for magnetotaxis. After cell death and sedimentation, these magnetic chains can be preserved even over geologically significant timescales. In order to extract iron from secondary, 60Fe bearing minerals only, a carefully tuned chemical leaching technique was employed. A novel technique to characterize this procedure using magnetic measurements was also developed applied to quantify secondary magnetite in our samples. As sample materials, two sediment cores from the Eastern Equatorial Pacific were obtained and processed. The concentration 60Fe/Fe was then measured with accelerator mass spectrometry at the GAMS setup in Garching. It features a gas-filled magnet, allowing for complete isobar suppression in the case of 60Fe and 60Ni, leading to a sensitivity which can reach even below 60Fe/Fe = 1E-16. Additionally, one of the sediment cores was also analyzed for 10Be and 26Al for independent dating of the samples at the DREAMS facility in Dresden.

Keywords: accelerator mass spectrometry; supernova; cosmogenic radionuclide

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20150

Formation of a Eu(III) borate solid species from a weak Eu(III) borate complex in aqueous solution

Schott, J.; Kretzschmar, J.; Acker, M.; Eidner, S.; Kumke, M. U.; Drobot, B.; Barkleit, A.; Taut, S.; Brendler, V.; Stumpf, T.

In the presence of polyborates (detected by 11B-NMR) a weak Eu(III) borate complex formation (lg beta ~ 2, estimated) was observed with time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation progress of this solid was investigated by TRLFS in dependence on the total boron concentration: The lower the total boron concentration the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD, solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.

Keywords: europium; borate; complexation; solid; TRLFS; NMR; IR; PARAFAC

Publ.-Id: 20149

Magnetization dynamics of magnetic domain wall imprinted magnetic films

Hamann, C.; Mattheis, R.; Mönch, I.; Fassbender, J.; Schultz, L.; McCord, J.

The influence of micromagnetic objects on the dynamic magnetic excitation in magnetic thin films is studied by imprinting periodic domain wall patterns through selective ion irradiation in exchange biased Ni81Fe 19/IrMn structures. For high domain wall densities an increased precessional frequency is achieved. The zero field resonance of the domain wall state hereby depends directly on the stripe period, showing a pronounced increase with decrease of domain wall spacing. With the abrupt annihilation of magnetic domain walls with an applied bias field a jump-like decrease in precessional frequency takes place. The experimental data and micromagnetic simulations prove that the characteristic collective dynamic mode for the domain wall configurations is attributed to strongly coupled tilted magnetization structure. This is evidenced by an overlapping Néel wall structure for the narrowly spaced imprinted antiparallel unidirectional anisotropy state. The controlled introduction of high density frozen-in micromagnetic objects is a novel way to control the dynamic magnetic properties of continuous magnetic thin films.

Keywords: magnetism; dynamics; domain wall; ion irradiation

Publ.-Id: 20148

3D microstructural model of freckle formation validated using in situ experiments

Karagadde, S.; Yuan, L.; Shevchenko, N.; Eckert, S.; Lee, P. D.

A 3D model of freckle (solute channel) formation at a microstructural level was coupled with in situ x-ray radiography to investigate the mechanisms of freckle initiation and growth. The model predictions for solute partitioning, diffusion and convection were validated via in situ x-ray radiographic measurements in a Ga-25wt%In alloy, showing good agreement. Other key features, such as freckle channel width and critical Rayleigh number, also correlated well.
This validated model was used to investigate freckle formation under a range of solidification conditions. Two distinct stages of freckle onset were observed, identified via the dendrite tip growth and solute profiles. The first stage corresponds to lower flow velocities with large fluctuations; in the second state the velocities stabilize, with established recirculating flows forming solute channels. The influence of imperfections in dendritic morphology, such as grain boundaries and primary spacing variations, upon the critical Rayleigh number were simulated. It was found that that these features initiate freckles. Non-intuitively, converging grain boundaries were observed to have the greatest propensity for freckle formation.

Keywords: Freckle formation; microstructure; solidification defects; solute transport; chimney formation

Publ.-Id: 20147

Forced convection effects on dendritic growth and freckle formation

Shevchenko, N.; Roshchupkina, O.; Sokolova, O.; Eckert, S.

A directional solidification of Ga–25wt%In alloy within a Hele-Shaw cell under the influence of electromagnetically forced melt convection was studied by X-ray radioscopy. The forced convection was produced by a rotating wheel with two parallel disks containing at their inner sides a set of permanent NdFeB magnets with alternating polarisation [1, 2]. The top part of the solidification cell was positioned in the gap between the disks. Rotation speeds of the magnetic wheel were chosen in the range of 30 – 80 revolutions per minute. The melt flows are almost perpendicular with respect to the growth direction of the dendrites (local flow velocities 0.5 - 1.5 mm/s).
The forced convection provoked a preferential growth of the secondary arms at the upstream side of the primary dendrite arms, whereas the high solute concentration at the downstream side of the dendrites inhibited the formation of secondary branches completely. The changes of secondary arm spacing depended on the melt flow conditions. The accelerated growth of the secondary arms towards the incoming flow blocked the growth of neighboring primary dendrites leading to a considerable increase in the spacing between the primary trunks. Moreover, the primary trunks show a slight inclination towards the inflow. The flow-induced redistribution of the solute concentration leads to the formation of spacious segregation pattern.

Keywords: forced convection; dendrites; melt flow; microstructure

  • Poster
    E-MRS 2014 Spring Meeting, Symposium V : Effect of natural and forced convection in materials crystallization, 26.-30.05.2014, Lille, France

Publ.-Id: 20146

In situ observation of freckle formation in Ga - In alloys under the influence of melt convection

Shevchenko, N.; Gerbeth, G.; Eckert, S.

The directional bottom-up solidification experiments were carried out using a Ga–25wt%In alloy. A visualization of the solidification process and the main convection pattern in solidifying alloys was obtained by using the X-ray imaging technique [1, 2]. Variations of the temperature gradients applied over the solidification cell induce modifications of the melt flow pattern, which lead to different segregation structures.
Solidifications carried out at low temperature gradients (up to 1 K/mm) revealed a considerable number of perturbations of the growing dendritic network. Stable chimneys occur mainly at positions with initial growth defects or grain boundaries; however, not every initial segregation channel evolves into a stable chimney. The long-term stability of these segregation channels is strongly influenced by the transient nature of the melt convection.
The situation at higher temperature gradients up to 2 K/mm is characterized by a converging flow ahead of the mushy zone coming from the side walls. This leads to a continuous accumulation of solute in the central part of the mushy zone followed by a remelting of the solid fraction and the occurrence of a sustaining chimney. This mechanism of chimney formation is different as compared to the case where the development of the segregation channel is linked with any initial growth defect.

Keywords: X-ray imaging; bottom-up solidification; segregation channels; melt convection

  • Invited lecture (Conferences)
    E-MRS 2014 Spring Meeting, Symposium V : Effect of natural and forced convection in materials crystallization, 26.-30.05.2014, Lille, France

Publ.-Id: 20145

Neuroimaging of sigma-1 receptors with positron emission tomography.

Brust, P.

In view of the involvement of sigma-1 receptors in different pathways related to the pathogenesis of various neuropsychiatric diseases and considering the neuroprotective potential of drugs targeting sigma-1 receptors quantitative neuroimaging by positron emission tomography (PET) is regarded as an unique method to investigate sigma-1 receptors in the progress of disease and under therapy. Alterations of sigma-1 receptor densities have been found in psychiatric disorders, neurodegeneration and cancer. Molecular receptor imaging with PET may provide a significant contribution to the understanding of the cross-talk between these receptors and inter- and intracellular signalling systems in these diseases. However the applicability of this imaging approach is still hampered due to lack of suitable radiopharmaceuticals for routine use. Although [11C]SA4503 has been used in human studies for already 10 years its broad clinical applicability is limited. Recent efforts made to develop 18F-labelled PET radiotracers for targeting the sigma-1 receptors in the human brain are presented. The current status of the evaluation of the most favourable radiolabelled compounds, including [18F]fluspidine, in animal models and humans will be discussed. New insights into the function of sigma-1 receptors in human brain will allow a better diagnosis of brain and cancerous diseases and direct a rational development of new therapeutic concepts.

  • Abstract in refereed journal
    Journal of Neurochemistry 130(2014), 13
  • Invited lecture (Conferences)
    12th Meeting of The Asian-Pacific Society for Neurochemistry, 23.-26.08.2014, Kaohsiung, China-Taiwan

Publ.-Id: 20144

Multiple radionuclide study of a recent supernova event in deep-sea sediments with AMS

Feige, J.; Wallner, A.; Bourlès, D.; Fifield, K. L.; Korschinek, G.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.

Long-lived radionuclides such as 26Al, 53Mn, and 60Fe are generated in massive stars and ejected into space by stellar winds and explosions. If a star ends its life in a supernova (SN) explosion close to the solar system, a fraction of these elements might be deposited in terrestrial archives. Recent analysis of a ferromanganese crust [1], fossilized bacteria in deep-sea sediments [2] and lunar samples [3] evidence a 60Fe concentration enhancement ~2-3 Myr ago, suggesting to originate from one or more SNe [1].
We expanded this work to a comprehensive and detailed study of a full set of SN-related radionuclides. Detailed depth profiles of 10Be, 26Al, 53Mn and 60Fe concentrations were measured at three different AMS laboratories for ~100 individual samples from four deep-sea sediment cores from the Indian Ocean. In contrast to our 60Fe data, which shows a clear signal without terrestrial background, a possible 26Al signal from a SN event is hidden within a non-negligible terrestrial background production. The major source of 26Al is spallogenic production by cosmic-rays in the Earth's atmosphere.
We obtained isotope ratios 26Al/27Al of ~10-14 with regularly <10% statistical uncertainty [4]. This allowed us to generate for the first time a full history of precise 26Al data over a time period of 2 Myr for two sediment cores revealing an unexpected smooth depth dependence. We took advantage of it and applied the 26Al/27Al ratio as an independent and enhanced dating tool, comparable to 10Be/9Be but without needing stable isotope measurements. Comparative measurements of 10Be/9Be at the DREAMS and VERA facilities show a very good agreement (~5 %).
[1] Knie et al., Phys. Rev. Lett 93, 2004, [2] Ludwig et al., AMS-13, [3] Fimiani et al., LPSC 1659, 2012, [4] Feige et al., EPJWC,63 2013

Keywords: accelerator mass spectrometry; AMS; supernova; radionuclide

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20143

The first three years of DREAMS: Routine operation and developments

Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.; Ziegenrücker, R.

The DREAMS (DREsden AMS) facility is based on a state-of-the-art 6 MV accelerator AMS-system [1]. Located at the ion beam centre, the accelerator is also used for ion beam analysis (IBA), material modifications and high-energy ion implantation. Though having no 24/7 availability for AMS, the advantage of a multi-purpose accelerator is the synergy effect with respect to joint technology development and µ-beam IBA for the in-situ identification of elements in problematic cathodes.
Most often measured nuclides are 10Be, 26Al and 36Cl. The majority of samples is prepared on-site [2], 36Cl in a dedicated laboratory for halide targets. About 600 10Be unknowns have been measured for different applications [3]. The mean ratio of processing blanks is as low as 3x10-15 10Be/9Be, even when measuring samples with ratios as high as 10-10–10-11. However, the mean machine blank is generally a factor of four lower. While analysing 150 26Al unknowns, machine blanks are as low as 3x10-15 26Al/27Al. Typical high-energy currents (Al3+) e.g. for the in-house standard are about 300 nA (mean / 1 h).
One of the original ion sources has been modified for reducing long-term memory for volatiles [4] and yet applied to ~100 unknowns of 36Cl [e.g. 5]. Measurements of 41Ca are mainly for nuclear decommissioning [6] and cosmochemistry [5] applications.
The high-energy setup is upgraded with a time-of-flight and energy detector system to perform actinide AMS and Super-SIMS [7].
[1] Akhmadaliev et al., NIMB 294 (2013) 5. [2] Merchel et al., AMS-13. [3] Feige et al., Ludwig et al., Ott et al., Rodrigues et al. & Smith et al., AMS-13. [4] Pavetich et al., NIMB, (2014) 10.1016/j.nimb.2014.02.130 & AMS-13. [5] Ott et al., MAPS, subm. [6] Hampe et al., JRNC 296 (2013) 617. [7] Rugel et al., AMS-13.

Keywords: accelerator mass spectrometry; AMS; radionuclide; SIMS; nuclear decommissioning

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20142

DREAMS come true: Dresden SIMS becomes Super-SIMS

Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.; Renno, A. D.; Wiedenbeck, M.; Ziegenrücker, R.

The DREAMS (DREsden AMS) facility [1,2] has been proven to be very suitable for several kinds of applications [3] based on lighter radionuclides. However, the range of applications shall be broaden by upgrading to a so-called Super-SIMS (SIMS = Secondary Ion Mass Spectrometry). Super-SIMS is a combination of trace element AMS (TEAMS) for the determination of stable elements and isotopes using the spatial-resolution - greater than 3 µm (x,y) and 5 nm (z) - of SIMS. Thus, this ultrasensitive analytical method is best-suited for analysing geological samples within our focus of resource technology.
To realize the DREAMS Super-SIMS, a commercial SIMS (CAMECA IMS 7f-Auto) is used as an ion source and connected to a 6 MV accelerator of highest energy stability. Additionally, the high-energy setup of DREAMS will be equipped with a time-of-flight detector and an energy detection system. By the complete destruction of molecules detection limits some orders of magnitude better than for traditional dynamic SIMS are expected, i.e. ~ 10-9 - 10-12 (see e.g. [4]). A dedicated housing around the source guarantees the requirements for stable ion source operation, i.e. stability of temperature (<1°C/h) and humidity (<10%/h). For reducing vibrations the ion source is installed on a cube shaped block made of gabbro (6.4 t weight; 1.4 m x 1.8 m x 0.86 m size). The whole ion source setup can be set on a negative potential of up to -30 kV to allow for higher transmission.
[1] Akhmadaliev et al., NIMB 294 (2013) 5. [2] Rugel et al. & Pavetich et al., AMS-13. [3] Feige et al., Ludwig et al., Ott et al., Rodrigues et al., Smith et al., AMS-13. [4] Maden, PhD thesis, ETH Zurich 2003.

Keywords: accelerator mass spectrometry; SIMS

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20141

Experimental investigation of high pressure condensation and heat transfer in a single near-horizontal pipe

Geißler, T.; Beyer, M.; Hampel, U.

Wärmeübertragungsvorgänge mit Phasenübergang können genutzt werden, um effizient große Energiemengen zu übertragen. Einen Spezialfall stellt die Kondensation in einem leicht geneigten Rohr dar. Bedingt durch den Einfluss der Gravitation stellt sich eine ausgeprägte azimutale Struktur der Strömung mit dem einhergehenden Wärmeübergang ein. Im Gegensatz zu Kondensationsvorgängen in vertikalen Strukturen existieren für den horizontalen Fall nur integrale Beschreibungsmodelle. Mittels hochaufgelösten Kondensationsexperimenten soll ein Beitrag zur Entwicklung von dreidimensionalen Kondensationsmodellen geleistet werden.

Heat-transfer processes with phase change can be used to efficiently transfer large amounts of energy. A special case is the condensation in a nearly-horizontal pipe. Due to the influence of gravity a pronounced azimuthal structure of the flow with the associated heat transfer occurs. In contrast to condensation processes in vertical structures exist for the horizontal case only integral models. The conducted high-resolution condensation experiments will contribute to the development of three-dimensional condensation models.

Keywords: heat transfer; TOPFLOW; condensation; NOKO; KERENA; x-ray tomography; experiment; high pressure

  • Poster
    Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme- und Stoffübertragung, 24.-25.03.2014, Fulda, Deutschland

Publ.-Id: 20140

Studying the constancy of galactic cosmic rays using cosmogenic radionuclides and noble gases in iron meteorites

Smith, T.; Leya, I.; Merchel, S.; Rugel, G.; Pavetich, S.; Wallner, A.; Fifield, K.; Tims, S.; Korschinek, G.

During their orbit in space, extraterrestrial bodies are exposed to cosmic rays. The interaction between these energetic particles and the meteoroides produce both stable and radioactive cosmogenic nuclides that can be used to study, e.g., the size of the meteorite before ablation in the Earth’s atmosphere and the time the object traveled before falling on Earth (exposure age). For a proper interpretation of such data, especially the ages, the temporal constancy of the cosmic ray intensity has to be proven. Doing so and being interested in timescales in the range of a few hundred million years, we have to rely on iron meteorites because their exposure ages range from a few million to a few billion years.
In this study, we systematically investigate the exposure ages of iron meteorites and search for periodic structures in the age distribution. So far, we have studied 28 iron meteorites for 10Be, 26Al, and 36Cl at the DREsden Accelerator Mass Spectrometry (DREAMS) facility [1] and for the noble gas isotopes of He, Ne, and Ar at the University of Bern. The first 53Mn and 60Fe measurements have already been performed at the Australian National University (ANU) and at the TUM (Munich). Finally, 41Ca measurements at DREAMS to identify long terrestrial residence times influencing the radionuclide concentrations are foreseen for the very near future.
The measurements of additional iron meteorites, which will help improving the statistics of the age distribution as well as extending the list of radionuclides and also extending the study to mineral separates from iron meteorites, are currently ongoing.
[1] Akhmadaliev, S. et al. (2013) NIMB 294, 5.

Keywords: accelerator mass spectrometry; cosmic radiation; meteorite

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20139

Packaging for radiation resistant X-ray detectors

Lohse, T.; Oppermann, M.; Metasch, R.; Zerna, T.; Seilmayer, M.; Wolter, K.-J.

Today non-destructive evaluation techniques become more and more important. Consequently, X-ray detectors are suitable tools to get information about specimens. In comparison to the already established scintillation principle, the direct converting method on the basis of semiconductor materials delivers several advantages. Hence, it is necessary to speed this measurement method and develop appropriate packages for these assemblies. In this paper the method of direct converting X-ray line detectors as well as their packaging and relevant aspects are introduced.

Keywords: X-ray detection; electronics packaging; silicon radiation detectors; measurement method; nondestructive evaluation techniques; radiation resistant X-ray detectors; scintillation principle; semiconductor materials; Absorption; Anodes; Detectors; Integrated circuits; Materials; Packaging; X-ray detectors

  • Contribution to proceedings
    33rd International Spring Seminar on Electronics Technology (ISSE 2010), 12.-16.05.2010, Odrębna 4 04-867 Warsaw, Poland
    33rd International Spring Seminar on Electronics Technology (ISSE 2010): Institute of Electrical and Electronics Engineers, 9781424478491, 138-142

Publ.-Id: 20138

Grundlagenuntersuchungen zur selektiven Trennung sehr feiner Partikelsysteme mittels Flüssig-Flüssig Flotation am System Magnetit-Quarz

Leistner, T.; Müller, M.; Rudolph, M.; Peuker, U. A.

Die Vergrößerung des effizienten Anwendungsbereiches von Sortierprozessen in den Bereich feinster Partikelsysteme (0,1 bis 10 µm) stellt aufgrund der Bedeutung komplexer Partikel-Partikel Wechselwirkungen eine erhebliche Herausforderung für die Forschung dar. Einen möglichen Ansatz in diese Richtung stellt die Flüssig-Flüssig Flotation dar. Bei diesem Heterokoagulationsprozess (ähnlich der Flotation) werden anstelle von Luftblasen feine Tröpfchen einer mit Wasser nicht-mischbaren unpolaren Flüssigkeit zum selektiven Austrag von Feststoffpartikeln eingesetzt. In diesem Beitrag werden erste Ergebnisse einer Grundlagenforschungsstudie zur Anwendbarkeit der Flüssig-Flüssig Flotation für die selektive Trennung im Feinstbereich am Beispiel von Magnetit- und Quarzpartikel (< 10 µm) vorgestellt. Als unpolare Flüssigkeit wird Isooktan eingesetzt. Die selektive Anreicherung der Feststoffpartikel an der Isooktan/Wasser-Grenzfläche bzw. der Transfer in die Isooktan-Phase wird in Abhängigkeit von ausgewählten Prozessparametern, wie dem pH-Wert der wässrigen Suspension sowie der Zugabe von grenzflächenaktiven Substanzen, untersucht und quantitativ dargestellt.

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

Publ.-Id: 20137

Photo-neutron reaction cross section for nat-Zr in the end-point bremsstrahlung energies of 12 - 16 and 45 - 70 MeV

Naik, H.; Kim, G. N.; Schwengner, R.; Kim, K.; Zaman, M.; Yang, S. C.; Lee, M. W.; Shin, S. G.; Gey, Y.; Massarczyk, R.; John, R.; Junghans, A.; Wagner, A.; Goswamia, A.; Cho, M.-H.

The natZr(γ, xn)89-86Zr reaction cross-sections were experimentally determined at the end-point bremsstrahlung energies of 12, 14, 16, 45, 50, 55, 60 and 70 MeV by activation and off-line γ-ray spectrometric technique using the 20 MeV electron linac (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany and 100 MeV electron linac at Pohang Accelerator Laboratory (PAL), Pohang, Korea. The natZr(γ, xn)89-86Zr reaction cross-sections as a function of photon energy were also calculated theoretically using TALYS 1.4 computer code. The flux-weighted average values at the end-point energies of 12-16 and 45-70 MeV were obtained from the literature and the TALYS data based on mono-energetic photon and are found to be in good agreement with the present dat. It was also found that the present data and the flux-weighted literature and theoretical values for the natZr (γ, xn)89-86Zr reaction cross-sections increase from the threshold values to a certain energy, where other reaction channels opens. This indicates the role of excitation energy. However, the increase trend of natZr(γ, xn)89,88Zr reaction cross-sections are sharper from the threshold value up to end-point bremsstrahlung energies of 17-22 MeV compared to the same for natZr(γ, xn)87,86Zr reactions. This is due to the Giant Dipole Resonance (GDR) effect besides the role of excitation energy. After a certain values, the individual natZr (γ, xn) reaction cross sections decrease with increase of bremsstrahlung energy due to opening of other reactions, which indicates portioning of energy in different channels.

Keywords: Photonuclear reactions; photoactivation; electron accelerators; bremsstrahlung; cross sections; statistical-model calculations

Publ.-Id: 20136

From tip to toe – Improvements of the DREAMS facility for the determination of volatile and heavy radionuclides

Pavetich, S.; Akhmadaliev, S.; Arnold, M.; Aumaître, G.; Bourlès, D.; Buchriegler, J.; Fifield, K.; Golser, R.; Keddadouche, K.; Martschini, M.; Merchel, S.; Rugel, G.; Srncik, M.; Steier, P.; Wallner, A.; Ziegenrücker, R.

Since the DREAMS (DREsden Accelerator Mass Spectrometry) facility [1] based on a HVE 6 MV Tandetron went operational in 2011, special effort was immediately devoted to upgrading the system for measurements of volatile elements e.g. Cl, I, and heavy elements e.g. actinides.
In the case of volatile elements, understanding and minimizing the ion source memory effect is a key issue for precise AMS-measurements [2,3]. For this purpose, one of the two original HVE sources was mechanically optimised. The new design has a more open geometry to improve the vacuum level and a modified target loading and positioning system, which allows exchanging the cathode aperture together with each target. To evaluate improvements of these modifications in comparison to other up-to-date AMS facilities [4], the long-term memory effect in the ion sources of VERA [5], ASTER [3] (Accélérateur pour les Sciences de la Terre, Environnement, Risques) and DREAMS [1] have been investigated by measuring samples of natural 35Cl/37Cl-ratio and samples containing highly enriched 35Cl (35Cl/37Cl ~1000). In these measurements the modified DREAMS ion source showed the lowest level of ion source memory effect and typically the fastest recovery [4].
To extend the measurement capabilities to actinides a time-of-flight system based on thin carbon foils and Micro Channel Plates was designed and constructed at DREAMS. For an optimal tuning of the system with low currents special beam diagnostic elements were manufactured. In cooperation with ANU first actinide samples were measured at DREAMS.

[1] S. Akhmadaliev et al., NIMB 294 (2013) 5.
[2] R. Finkel et al., NIMB 294 (2013) 121.
[3] M. Arnold et al., NIMB 294 (2013) 24.
[4] S. Pavetich et al., NIMB, accepted.
[5] M. Martschini et al., NIMB 269 (2011) 3188.

Keywords: Accelerator Mass Spectrometry; Cl-AMS; long-term memory effect; actinide AMS; Time-of-Flight; DREAMS

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France

Publ.-Id: 20135

Development of MMRPC prototype for the NeuLAND detector of the R3B collaboration

Datta Pramanik, U.; Chakraborty, S.; Basu, P.; Basu, J.; Banerjee, P.; Bemmerer, D.; Bose, S.; Chatterjee, S.; Elekes, Z.; Kempe, M.; Leifels, Y.; Panja, J.; Mukherjee, A.; Rahaman, A.; Roy, S.; Simon, H.; Sobiella, M.; Stach, D.; Wagner, A.; Yakorev, D.

A prototype of Multi-strip Multi-gap Resistive Plate chamber (MMRPC) with active area 40 cm×20 cm has been developed at SINP, Kolkata as a new Time-Of-Flight (TOF) system with timing resolution σt<120ps and position resolution σx∼0.58cm. The intention is to use multilayers of this type together with converter materials as a high energy neutron (1GeV>En>200MeV) TOF system for the R3B collaboration at the FAIR facility. The design of the detector elements is as follows: a double stack MMRPC with float glass plates and two gas gaps of 0.3 mm per stack. The response of this MMRPC has been studied with cosmic muons and γ-raysγ-rays from a standard radioactive source (60Co) in coincidence with fast inorganic scintillators at SINP laboratory. Recently, response of developed MMRPC has been studied using pulsed electron beam at ELBE, FZD. The details of the MMRPC construction , experimental set-up for investigation of its response and first results are presented.

Keywords: Multi-strip Multi-gap Resistive Plate chamber high energy neutron R3B FAIR

Publ.-Id: 20134

Establishment of two complementary in vitro assays for radiocopper complexes achieving reliable and comparable evaluation of in vivo stability

Zarschler, K.; Kubeil, M.; Stephan, H.

The development of novel radiopharmaceuticals for imaging and therapy requires rapid and reproducible in vitro assays to estimate their in vivo stability and dissociation behaviour. In general, these assays should allow an assessment of dissociation of the radiometal from the radiopharmaceuticals. In the past, a series of chemical challenges has been widely used to estimate complex stability under non-physiological and non-radiotracer conditions providing limited information on the potential in vivo stability. In contrast, we herein present two independent in vitro methods to measure the stability of radiocopper complexes under physiologically relevant conditions. To quantify and compare the dissociation behaviour of six well-established 64Cu chelates (TETA, DOTA, NOTA, Cyclam, diamSar and EDTA), we combine a protein challenge experiment considering the stability of the chelates in the presence of human superoxide dismutase with a serum assay measuring the stability of the radiometal complexes against human serum. Unlike HPLC- and TLC-based analytical techniques, we describe the stability assessments by standard gel electrophoretic procedures, which allow a timesaving workflow as well as simultaneous processing and comparative analysis of a variety of copper-containing chelates and conjugates thereof. [64Cu]Cu-diamSar is the most kinetically stable ligand, whereas the acyclic chelate [64Cu]Cu-EDTA underwent an almost complete complex dissociation. Furthermore, kinetic stability studies in human serum carried out for [64Cu]Cu-diamSar revealed no substantial time-dependent influence under commonly used labelling conditions. Both described assays, the protein challenge experiment as well as the serum stability assay, are not restricted to radiocopper, but may be adopted for other radiometal containing chelates. © 2014 The Royal Society of Chemistry.

Publ.-Id: 20133

Transverse wobbling: A collective mode in odd- A triaxial nuclei

Frauendorf, S.; Dönau, F.

The wobbling motion of a triaxial rotor coupled to a high-j quasiparticle is treated semiclassically. Longitudinal and transverse coupling regimes can be distinguished depending on, respectively, whether the quasiparticle angular momentum is oriented parallel or perpendicular to the rotor axis with the largest moment of inertia.
Simple analytical expressions for the wobbling frequency and the electromagnetic E2 and M1 transition probabilities are derived assuming rigid alignment of the quasiparticle with one of the rotor axes and harmonic oscillations (HFA). Transverse wobbling is characterized by a decrease of the wobbling frequency with increasing angular momentum. Two examples for transverse wobbling, 163 Lu and 135 Pr, are studied in the framework of the full triaxial particle-rotor model and the HFA. The signature of transverse wobbling, decreasing wobbling frequency, and enhanced E2 interband transitions, is found in agreement with experiment.

Keywords: Nuclear structure; triaxial particle-rotor model; E2 transitions

Publ.-Id: 20132

Improving AMS-chemistry: Two steps forward, one step back

Merchel, S.; Bourlès, D. L.; Feige, J.; Ludwig, P.; Pavetich, S.; Ritter, A.; Rodrigues, D.; Rugel, G.; Smith, T.; Ziegenrücker, R.

The DREAMS (DREsden AMS) facility consists of a sophisticated 6 MV accelerator system [1], but also provides two chemistry laboratories for external users. One lab is used for preparation of 10Be, 26Al, 41Ca, 53Mn and 60Fe targets. The other one is dedicated to halide targets (36Cl, 129I), thus, any use of Cl- or S-compounds such as HCl or H2SO4 is strictly prohibited.
Separation protocols are applied to calcite- and quartz-rich samples for in-situ projects [2-4]. Atmospheric 10Be has been leached from marine sediments and Mn-nodules for dating purposes [5] and chemistry refined for bigger samples and heavier nuclides (26Al, 53Mn, 60Fe) [6]. After adapting standard protocols [7] introducing simple Mn-separation by delayed hydroxide separation, higher isobar concentrations (53Cr) have been found asking for further cleaning by ion exchange. With intent to speed-up and simplify the separation procedures for ice and meteorite samples [8], difficulties have been arisen e.g. carryover of Ag+-ions into MnO2, and shortly after overcome. Another chemistry challenge probably mastered is the dissolution of meteoritic troilite (FeS) without losing natCl-carrier before equilibrium with 36Cl, plus suppression of massive isobar amounts. Remaining issues also influencing the quality of AMS-data, such as incorrectly measured stable isotope concentrations (9Be, 27Al), are usually underestimated and harder to tackle.
[1] Akhmadaliev et al., NIMB 294 (2013) 5. [2] Merchel et al., Quat. Geo. 22 (2014) 33. [3] Zech et al., Paleo3 369 (2013) 253. [4] Yildirim et al., Tectonics 32 (2013) 1107. [5] Feige et al., Ludwig et al. & Rodrigues et al., AMS-13. [6] Feige et al., EPJ Web Conf. 63 (2013) 03003. [7] Merchel & Herpers, RCA 84 (1999) 215. [8] Smith et al., AMS-13.

Keywords: accelerator mass spectrometry; cosmogenic radionuclides

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20131

Detectability of proton range shifts in heterogeneous targets with prompt gamma based range monitoring

Priegnitz, M.; Fiedler, F.; Helmbrecht, S.; Janssens, G.; Smeets, J.; Vander Stappen, F.; Enghardt, W.

To make optimal use of the advantages of proton beams in tumor therapy a precise knowledge on their range is required. Recently, a slit camera has been developed using prompt gamma rays emitted during irradiation. First investigations in homogeneous media have shown that the position of the distal falloff of the prompt gamma ray profiles is closely correlated with the Bragg-peak position. Now, heterogeneous targets are under investigation and first results on detectability of range shift as well as range retrieval precision will be presented.

  • Lecture (Conference)
    Dreiländertagung Medizinische Physik - Joint Conference of the SGSMP, DGMP, ÖGMP, 07.-10.09.2014, Zürich, Schweiz
  • Contribution to proceedings
    Dreiländertagung Medizinische Physik - Joint Conference of the SSRMP, DGMP, ÖGMP, 07.-10.09.2014, Zürich, Schweiz
    Abstractbook, 987-3-9816508-5-3, 136-137

Publ.-Id: 20130

Surface speciation of dissolved radionuclides on mineral phases derived from vibrational spectroscopic data

Foerstendorf, H.; Jordan, N.; Heim, K.

A detailed knowledge of the molecular reactions of radionuclides at the aqueous-mineral interface is required for a reliable assessment of their dissemination in the environment. Among numerous spectro-scopic approaches, in situ vibrational spectroscopy has been developed to a powerful tool for the study of surface complexes of heavy metal ions on solid phases. In particular from vibrational data, molecular in-formation can be derived which might be complementary to those obtained from other widely applied techniques, such as X-ray absorption spectroscopy. In this study, a survey of very recent results obtained from sorption reactions of radionuclides, namely U(VI) on iron(hydr)oxides and Se(VI) on metal oxides is given.
A significantly different surface complexation of U(VI) was found for two different iron bearing min-eral phases, that is ferrihydrite and maghemite. As in situ IR spectroscopy allows the investigation of sorption and desorption processes in real time under environmentally relevant conditions, the type of sur-face complexation can be identified by the extent of reversibility of the sorption reactions. Moreover, the evaluation of the formation of ternary U(VI)carbonato surface complexes provides further details of the sorption processes.
The selenate anion (SeVIO42−) preferentially shows relatively weak interactions (physisorption) with mineral phases in the circumneutral pH range. However, the electrostatic interactions of this ion with the mineral surfaces, referred to as outer-sphere complexation, might base on different types of surface com-plexes as shown by vibrational data from surface complexes on different minerals. With respect to the high selectivity of vibrational spectra to molecule symmetry, the results from Se(VI) sorption experiments on different mineral phases clearly demonstrate two different types of outer sphere complexes.

  • Invited lecture (Conferences)
    248th ACS National Meeting & Exposition, 10.-14.08.2014, San Francisco, U.S.A.

Publ.-Id: 20129

Post-irradiation annealing behaviour of neutron-irradiated FeCu, FeMnNi and FeMnNiCu model alloys investigated by means of small-angle neutron scattering

Bergner, F.; Ulbricht, A.; Lindner, P.; Keiderling, U.; Malerba, L.

Neutron irradiation of reactor pressure vessel steels gives rise to the formation of thermodynamically stable and unstable nano-features. The present work is focused on the stability of Cu-, Mn- and Ni-containing solute clusters in model alloys exposed to post-irradiation annealing. Fe0.1Cu, Fe1.2Mn0.7Ni and Fe1.2Mn0.7Ni0.1Cu (wt%) model alloys irradiated up to neutron exposures of 0.1 and 0.19 dpa (displacements per atom) were annealed at stepwise increasing temperatures in the range from 300 °C (i.e. near irradiation temperature) to 500 °C and characterized by means of small-angle neutron scattering (SANS). We have found characteristic differences in the annealing behavior of the alloys. In particular, there is a non-trivial (synergistic-antagonistic) interplay of Mn/Ni and Cu.

Keywords: radiation effects; Fe-based model alloys; SANS; thermal treatment

Publ.-Id: 20128

SiΛvio: A trigger for Λ-hyperons

Münzer, R.; Berger, M.; Fabbietti, L.; Averbeck, R.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Buehler, P.; Cargnelli, M.; Čaplar, R.; Carevic, I.; Charviakova, V.; Crochet, P.; Deppner, I.; Dupieux, P.; Dželalija, M.; Fodor, Z.; Gasik, P.; Gašparić, I.; Grishkin, Y.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kiš, M.; Kienle, P.; Koczon, P.; Kotte, R.; Lebedev, A.; Leifels, Y.; Liu, J. L.; Lopez, X.; Manko, V.; Marton, J.; Matulewicz, T.; Petrovici, M.; Piasecki, K.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczyńska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Widmann, E.; Wiśniewski, K.; Xiao, Z. G.; Yamazaki, T.; Yushmanov, I.; Zhang, X. Y.; Zhilin, A.; Zinyuk, V.; Zmeskal, J.

As online trigger for events containing Λ hyperons in p+p collisions at 3.1 GeV a silicon-based device has been designed and built. This system has been integrated close to the target region within the FOPI spectrometer at GSI and was also employed as a tracking device to improve the vertex reconstruction of secondary decays. The design of the detector components, read-out, the trigger capability as well as the tracking performance are presented. An enrichment factor of about 14 was achieved for events containing a Λ-hyperon candidate.

Keywords: Si Lambda vio; Lambda-hyperons

Publ.-Id: 20127

Amorphization and recrystallization of single-crystalline hydrogen titanate nanowires by N+ ion irradiation

Behera, A. K.; Facsko, S.; Bandyopadyay, M. K.; Das, S.; Chatterjee, S.

We report the phase transformation of hydrogen titanate (H2Ti3O7) nanowires induced by 50 keV N+ ion irradiation at room temperature with fluencies of 1×1015 ions/cm2 and 1×1016 ions/cm2. By high resolution transmission electron microscopy the internal structure of the ion irradiated nanowires is analyzed. While at lower fluence a transformation from crystalline H2Ti3O7 to amorphous TiO2 is observed, at higher fluence a remarkable crystalline-amorphous TiO2 core-shell structure is formed. At this higher fluence the recrystallization occurs in the core of the nanowire and the outer layer remains amorphized. The phase transformation and formation of core-shell structure is explained using the thermal spike model and non-equilibrium thermodynamics. X-ray Photoelectron Spectroscopy and Raman Scattering reveale further insight into the structure of the nanowires before and after ion irradiation.

Keywords: Nanowires; core-shell structure; ion induced phase transformation

Publ.-Id: 20126

Brain Tumor Imaging with Positron Emission Tomography: Potential Alternatives with New 18F-labelled Radiotracers?

Brust, P.

  • Poster
    20th Annual Blood-Brain Barrier Consortium Meeting in collaboration with the International Brain Barriers Society, 20.-22.03.2014, Sunriver, Oregon, USA

Publ.-Id: 20125

Azimuthal Emission Patterns of K+ and of K- Mesons in Ni+Ni Collisions near the Strangeness Production Threshold

Zinyuk, V.; Kang, T. I.; Leifels, Y.; Herrmann, N.; Hong, B.; Averbeck, R.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Berger, M.; Buehler, P.; Cargnelli, M.; Čaplar, R.; Carevic, I.; Crochet, P.; Deppner, I.; Dupieux, P.; Dželalija, M.; Fabbietti, L.; Fodor, Z.; Gasik, P.; Gašparić, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kiš, M.; Koczon, P.; Kotte, R.; Lebedev, A.; Le Fèvre, A.; Liu, J. L.; Lopez, X.; Manko, V.; Marton, J.; Matulewicz, T.; Münzer, R.; Petrovici, M.; Piasecki, K.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczyńska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Widmann, E.; Wiśniewski, K.; Xiao, Z. G.; Yushmanov, I.; Zhang, Y.; Zhilin, A.; Zmeskal, J.; Bratkovskaya, E.; Hartnack, C.

Azimuthal emission patterns of K ± mesons have been measured in Ni + Ni collisions with the FOPI spectrometer at a beam kinetic energy of 1.91 A GeV. The transverse momentum p T integrated directed and elliptic flow of K + and K − mesons as well as the centrality dependence of p T - differential directed flow of K + mesons are compared to the predictions of hadron string dynamics and isospin quantum molecular dynamics transport models. The data exhibits different propagation patterns of K + and K − mesons in the compressed and heated nuclear medium and favor the existence of a kaon-nucleon in-medium potential, repulsive for K + mesons and attractive for K − mesons.

Publ.-Id: 20124

Ancient and recent exposure history of chondrules from two highly primitive meteorites,

Ott, U.; Merchel, S.; Beyersdorf-Kuis, U.; Akhmadaliev, S.; Pavetich, S.; Rugel, G.; Ziegenrücker, R.

Chondrules may have spent several million years as free-floating particles in the solar nebula [1], and if so, been exposed to an early cosmic ray irradiation. The search for “pre-irradiation” in noble gas isotopic signatures has, thus, been actively pursued recently [2-4]. Results for two highly primitive CR3 chondrites (MET00426 & QUE99177) [5] are intriguing: 1) They are among the most unmetamorphosed meteorites, most likely to have retained any pre-irradiation record. 2) Target elements were determined by Instrumental Neutron Activation Analysis on the same material used for noble gas analysis. 3) QUE99177 shows no hint for having been part of an asteroidal regolith. 4) Chondrules show both higher and lower cosmic ray exposure than identically-shielded matrix samples.
The shortest cosmic ray exposure determined via stable noble gases is an upper limit to the recent cosmic ray exposure age. Further constraints can be obtained via radionuclides such as 10Be, 26Al, 36Cl, which have been analyzed at DREAMS [6,7]. Despite sample masses of only 1.6-1.8 mg for single chondrules, ratios are as high as 1-3x10-12 for 10Be/9Be and 26Al/27Al, and 1x10-13 for 36Cl/35Cl, clearly distinguishable from blanks. Preliminary evaluation shows that the radionuclides are not in saturation. However, since the meteorites are finds from Antarctica, one also has to consider decay during terrestrial residence. To better constrain this, AMS of 41Ca and 53Mn is scheduled at DREAMS and ANU, respectively.
Ref.: [1] Cuzzi, Nat. Geosci. 4 (2011) 219. [2] Eugster et al., MAPS 42 (2007) 1351. [3] Das & Murty, MAPS 44 (2009) 1797. [4] Roth et al., MAPS 46 (2011) 989. [5] Beyersdorf-Kuis et al., 44th LPSC (2013) 1999. [6] Akhmadaliev et al., NIMB 294 (2013) 5. [7] Rugel et al., AMS-13.

Keywords: accelerator mass spectrometry; meteorites; solar system

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20123

Retention of selenium oxyanions at the water-mineral interface in the context of nuclear waste repositories

Franzen, C.; Hering, D.; Jordan, N.; Weiss, S.

The radioactive isotope Selenium-79 is a fission product found in nuclear waste. Due to its long half-life of 3.27 ∙ 105 years and its high mobility, it is expected to be one of the isotopes contributing significantly to the potential radiation dose according to safety assessments of nuclear waste underground repositories. A detailed knowledge of the mobility and bioavailability of selenium in its different oxidation states is therefore of great importance for a safe disposal of radioactive waste.
Adsorption onto mineral surfaces of both the engineered and geological barrier is a major process controlling the retention of the water-soluble selenium oxyanions, selenate (SeVIO42 ) and selenite (SeIVO32 ). In this context, it is important to understand to what extent this sorption is influenced particularly by characteristic parameters as expected in deep underground repositories for high level radioactive waste. These parameters include inter alia the presence of different background salts and elevated temperatures.
In this study, a combination of macroscopic sorption experiments, electrophoretic mobility measurements and in-situ ATR FT-IR spectroscopy was used to study the interaction of SeVIO42 and SeIVO32 with aged γ-Al2O3 in the presence of NaCl and MgCl2 and at elevated temperatures up to 60 °C. In this context, γ-Al2O3 can be considered as model mineral phase for more complex rock and backfill materials associated with a nuclear waste repository.
It could be shown that the retention of both Se(VI) and Se(IV) is affected by all three investigated factors pH, ionic strengths of the solution, and temperature. The increase of each parameter results in a decrease of sorption, with the retention of Se(IV) generally being higher than the one of Se(VI). In-situ ATR FT-IR spectroscopy and electrophoretic mobility measurements evidenced the formation of an outer-sphere surface complex of Se(VI) on γ-Al2O3. Concerning Se(IV), a mixture of inner-sphere and outer-sphere surface complexes could be derived.
Any sorption on mineral surfaces is dominated by the surface charge of the mineral. The impact of salinity and temperature on the variable surface charge of γ−Al2O3 was evaluated by zeta potential measurements using laser Doppler electrophoresis. The isoelectric point (pHIEP) of γ-Al2O3 is located at pH 9.6 with a positively charged surface at lower pH values and a negatively charged surface for higher pH values. Increasing the amount of NaCl in the solution (up to I = 1 M) reduces the zeta potential for both the acidic and alkaline pH range. However, in the alkaline range the decrease of the zeta potential is more pronounced. In the presence of 0.1 M MgCl2, the surface charge of γ-Al2O3 becomes positive throughout the studied pH range (3-11). Above pH 10, a sharp potential decrease occurs due to Mg(OH)2 precipitation. The increase of temperature shifts the pHIEP to lower values and decreases the zeta potential in the acidic range.
These changes in the surface properties of the γ-Al2O3 are consistent to the changes in the sorption behaviour of selenate and selenite.
These results indicate that for geochemical modeling and long-term safety assessments concerning selenium-containing waste it is crucial to include the impact of temperature and ionic strengths effects.

  • Lecture (Conference)
    21st General Meeting of the International Mineralogical Association, 01.-05.09.2014, Johannesburg, South Africa

Publ.-Id: 20122

The German P&T study – results and conclusions in the view of the contributing Helmholtz research centers

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

The governmental decision to phase out electric energy production in nuclear power plants in Germany has put some questions on the future of the P&T research. The Bundesministerium für Wirtschaft (ministry of economics) and the Bundesministerium für Bildung und Forschung (ministry of education and research) have launched a study managed by acatech (national academy of science and engineering) in 2012 to answer these questions on a broad scientific basis. The major mandate was to evaluate scientific and technological as well as socio-economic challenges and opportunities of the P&T technology in the view of the phase out decision. The scientific and technological aspects of P&T are analyzed with respect to a possible contribution to the nuclear waste management using the following structure:

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

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

  • Open Access Logo Contribution to proceedings
    Actinide and Fission Product Partitioning and Transmutation 13th Information Exchange Meeting, 23.-26.09.2014, Seoul, Republic of Korea
  • Lecture (Conference)
    Actinide and Fission Product Partitioning and Transmutation 13th Information Exchange Meeting, 23.-26.09.2014, Seoul, Republic of Korea

Publ.-Id: 20121

Evaluation of the application of a molten salt fast reactor for transmutation in the frame of the nuclear phase out

Merk, B.; Rohde, R.

The governmental decision to phase out electric energy production in nuclear power plants in Germany has put some questions on the future of the P&T research. The Bundesministerium für Wirtschaft (ministry of economics) and the Bundesministerium für Bildung und Forschung (ministry of education and research) have launched a study managed by acatech (national academy of science and engineering) in 2012 to answer these questions on a broad scientific basis. One major discussion point was the so-called last transmuter problem which requires much more attention in the case of the nuclear phase out. Transmutation of long lived transuranium isotopes is under the phase out condition only attractive when the last transmuter problem can be solved. A solution for this problem has been proposed in a generic study based on the EVOL molten salt reactor configuration using a twofold operation cycle. It is proposed to operate the fast molten salt reactor for a given time in the transmuter mode feeding the transuranium elements. This operational mode is followed by the deep burn phase where the bred U-233 from the blanket is used as fissile material to burn the last TRU load by more than 90%. The reactor is operated on uranium as fissile material at the end of the deep burn phase which can be forwarded to reactor operation in another country without proliferation concerns as long as it is diluted with U-238 to the required fissile content defined in the non-proliferation guidelines.
Based on this proposal a detailed investigation is presented using the specific German nuclear waste amount and composition in a fertile free salt configuration in the core. A salt configuration based on the MOSART composition is used which is able to carry the required amount of TRUs for the fertile free operation. The transmutation efficiency is evaluated and it is demonstrated that the optimal efficiency of the fertile free configuration can be achieved in the transmuter mode. Following the transmuter mode the nuclide densities are evaluated in the deep burn mode using bred U-233 as fissile material. The remaining TRU amounts are compared during the deep burn mode and evaluated in comparison with the required operation time. The remaining uranium based fissile material configuration is discussed and an estimation is given how many reactors of the EVOL design have to be operated for how many years to burn the remaining German nuclear waste.

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

  • Open Access Logo Contribution to proceedings
    Actinide and Fission Product Partitioning and Transmutation 13th Information Exchange Meeting, 23.-26.09.2014, Seoul, Republic of Korea
  • Poster
    Actinide and Fission Product Partitioning and Transmutation 13th Information Exchange Meeting, 23.-26.09.2014, Seoul, Republic of Korea

Publ.-Id: 20120

Experimental investigation of liquid metal two-phase flows in a continuous casting model

Eckert, S.; Timmel, K.; Shevchenko, N.; Röder, M.; Anderhuber, M.; Gardin, P.

We present an experimental study concerned with the two-phase flow in a mockup of the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing two-phase flows in the mould and the SEN by means of X-ray radioscopy. This setup utilizes the low melting, eutectic alloy GaInSn as model liquid. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously under isothermal conditions. First results about the two-phase flow will be presented here accompanied by a discussion of the advantages and limitations of the X-ray method.
The position of the X-ray observation window can be changed, which allows the inspection of regions around the gas injection point at the tip of the stopper rod or the development of the bubbly flow in the mould. The X-ray images reveal complex flow situations, for instance, argon bubbles might be attracted by the wall of the SEN near the inlet forming huge bubbles there. Smaller bubbles are generated at the bottom of the SEN, where high shear flows exist. The bubbles in the mould are entrapped by the liquid metal jet. The tendency to rise towards the mould level increases with growing bubble size.

Keywords: Liquid metal model; two-phase flow; X-ray imaging

  • Lecture (Conference)
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich
  • Contribution to proceedings
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich

Publ.-Id: 20119

Recent activities for experimental modelling and investigation of the steel flow within the limmcast program at HZDR

Eckert, S.; Gerbeth, G.; Shevchenko, N.; Stefani, F.; Timmel, K.; Wondrak, T.

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present the experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-ups mini-LIMMCAST and X-LIMMCAST will be presented, which work with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. A selection of results will be presented in this paper covering various phenomena occurring in single-phase and two-phase flows.

Keywords: Continuous casting; physical modelling; flow measurements; magnetic field; flow control; electromagnetic brake

  • Lecture (Conference)
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich
  • Contribution to proceedings
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich

Publ.-Id: 20118

A compact solution for ion beam therapy with laser accelerated protons

Masood, U.; Bussmann, M.; Cowan, T. E.; Enghardt, W.; Karsch, L.; Kroll, F.; Schramm, U.; Pawelke, J.

The recent advancements in the eld of laser-driven particle acceleration have made Laser driven Ion Beam Therapy (L-IBT) an attractive alternative to the conventional particle therapy facilities. To bring this emerging technology to clinical application we introduce the Broad Energy Assorted depth-Dose deposition (BEAD) scheme which makes ecient use of the large energy spread and high dose-per-pulse of Laser Accelerated Protons (LAP) and is capable of delivering homogeneous doses to tumors. Furthermore, as a key component of L-IBT solution we present a compact, iso-centric gantry design with 360° rotation capability with an Integrated Shot-to-shot Energy Selection System (ISESS), for efficient transport of LAP with large energy spread to the patient. We show that gantry size could be reduced by a factor of 2-3 compared to conventional gantry systems by utilizing pulsed, air-core magnets.

Keywords: Radiationtherapy; ion beam therapy; laser particle acceleration; beamline; compact gantry; dose distribution

Publ.-Id: 20117

Laborexperimente zur Entstehung und Wirkung kosmischer Magnetfelder

Stefani, F.

Bekanntermaßen entstehen planetare, stellare und galaktische Magnetfelder durch den hydromagnetischen Dynamoeffekt, d.h. durch Selbsterregung in strömenden elektrisch leitfähigen Fluiden. Weniger bekannt ist, dass Magnetfelder auch eine aktive Rolle in der kosmischen Strukturbildung spielen, indem sie Akkretionsscheiben in der Umgebung von Protosternen und Schwarzen Löchern destabilisieren. Der Artikel gibt einen Überblick über die Flüssigmetallexperimente der letzten 15 Jahre, in denen sowohl der Dynamoeffekt als auch die destabilisierende Wirkung von Magnetfeldern auf rotierende Strömungen nachgewiesen worden ist.

  • Praxis der Naturwissenschaften - Physik in der Schule 63(2014)2, 31-37

Publ.-Id: 20116

Terahertz spectroscopy of nanostructures with a free electron laser

Helm, M.

I will start describing the Dresden free-electron laser (FEL) as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in nanostructures. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will mainly discuss experiments studying electronic relaxation processes in semiconductor quantum dots with their totally quantized energy levels, and in graphene with its zero energy gap and linear band dispersion.

Keywords: free electron laser; terahertz; nanostructures; quantum dots; graphene

  • Invited lecture (Conferences)
    Annual BuildMoNa Conference, 04.03.2014, Leipzig, Germany

Publ.-Id: 20115

Ultra-smooth diamond-like carbon coatings with high elasticity deposited at low temperature by direct ion beam deposition

Markwitz, A.; Mohr, B.; Carpeño, D. F.; Hübner, R.

Diamond-like carbon coatings were fabricated under high vacuum at room temperature using a direct ion beam deposition technique based on a penning ion source. Post acceleration and electrostatic scanning were applied to form adhesive and laterally homogenous coatings across 50 mm using ion energies from 3.0 to 10.5 kV. The deposition rate was set to 0.4 nm s-1 to prevent heating of the coating and substrate. Structural, physical and chemical analyses revealed the formation of amorphous atomically flat hydrogenated amorphous carbon (a-C:H) coatings with a sp3 content of typically 20 %. Nanoindentation measurements provided hardness figures of up to 18 GPa combined with high elasticity values of 90 %. Hardness and elasticity values and the sp3 content were measured to be proportional to the ion energy. Furthermore, a growing interface layer was observed with transmission electron microscopy images indicating atomic interlocking between the carbon coating and the silicon substrate. The result highlight the opportunity to produce a-C:H coatings with high elasticity with direct ion deposition at room temperature.

Keywords: diamond-like carbon; amorphous hydrogenated carbon; direct ion beam deposition; room temperature

Publ.-Id: 20114

Optical waveguides in LiTaO3 crystals fabricated by swift C5+ ion irradiation

Liu, G.; He, R.; Akhmadaliev, S.; de Aldana, J.; Zhou, S.; Chen, F.

We report on the optical waveguides, in both planar and ridge configurations, fabricated in LiTaO3 crystal by using carbon (C5+) ions irradiation at energy of 15 MeV. The planar waveguide was produced by direct irradiation of swift C5+ ions, whilst the ridge waveguides were manufactured by using femtosecond laser ablation of the planar layer. The reconstructed refractive index profile of the planar waveguide has showed a barrier-shaped distribution, and the near-field waveguide mode intensity distribution was in good agreement with the calculated modal profile. After thermal annealing at 260 °C in air, the propagation losses of both the planar and ridge waveguides were reduced to 10 dB/cm.

Keywords: Ion irradiation; LiTaO3 crystal; Optical waveguide

Publ.-Id: 20113

Dynamics of marine sediments studied through 10Be

Rodrigues, D.; Arazi, A.; Korschinek, G.; Martí, G. V.; Merchel, S.; Rugel, G.

Marine sediments may originate from the erosion of continental material (containing both cosmogenic 10Be, and 9Be with a ratio around 10-8) that has been carried by rivers to the sea. If the sediments are deposited in zones where a tectonic plate subducts beneath another one, they might follow complex processes, in which part of the sediments are dragged under the plate and the other part is accreted above.

In this work, depth profiles of the 10Be/9Be ratios in marine sediments are being studied near the spot where Nazca, Antarctica and South American tectonic plates join each other.
A preliminary set of seven samples, provided by the Ocean Drill Project [1], were measured at the DREAMS facility [2]; this represents the first measurement of a depth profile near this zone. The isotopic ratios, based on AMS-measurements of 10Be/9Be and determinations of 9Be concentration performed by ICP-MS at HZDR are ranging from 4.9 to 53 x 10-9. Contrary to the expectation they do not decrease with depth, but rise into the interval corresponding to 102 to 145 meters of depth, and from 197 to 256 meters of depth. We show that this result is consistent with a reverse (thrust) fault in the sediments due to the compression pressure exerted by the subduction of the Nazca tectonic plate.

[1] Behrmann et al. Proceedings of the Ocean Drilling Program, Initial Reports, 141, (1992).
[2] Akhmadaliev et al. Nucl. Instr. and Meth. in Physics Research B, 294, 5-10 (2013).

Keywords: accelerator mass spectrometry; cosmogenic nuclide; tectonics

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20112

Hochauflösende Positronen Emissions Tomographie für quantitative, raumzeitliche Prozessvisualisierung in geologischem Material (GeoPET)

Kulenkampff, J.; Lippmann-Pipke, J.

Positronen-Emissions-Tomographie (PET) ist das empfindlichste bildgebende Verfahren der Medizin, um Körperfunktionen in ihrem räumlich-zeitlichen Verlauf sichtbar zu machen. Seit der klinischen Einführung der PET vor etwa 40 Jahren gibt es auch einige Beispiele für den erfolgreichen Einsatz klinischer PET-Scanner in den Geowissenschaften. Explizit wird seit über 10 Jahren die Entwicklung der „GeoPET“-Methode n in der Forschungsstelle Leipzig des HZDR vorangetrieben (Gründig et al., 2007; Kulenkampff et al., 2008; Richter et al., 2000; Richter et al., 2005). Mittels eines kommerziellen hochauflösenden biomedizinischen PET-Scanners (ClearPET) einerseits und ausgereifter Korrektur- und Rekonstruktionsverfahren andererseits haben wir unsere GeoPET-Methode Alleinstellungsmerkmal zur (Transport-)Prozesstomographie in dichtem Medium (z.B. Gesteinen) entwickelt.

PET nutzt die räumliche Detektion der Annihilationsstrahlung (zwei antiparallele Gammas mit jeweils 511 keV), die durch den β+-Zerfall geeigneter Radiotracer entsteht. Beim ClearPET wird die physikalisch maximal mögliche räumliche Auflösung von etwa 1 mm erreicht. Dieser – verglichen mit den Möglichkeiten der Röntgen-CT – geringen räumlichen Auflösung steht die der PET immanente, überragende Empfindlich-keit gegenüber: Die Detektion und Quantifizierung von Tracerkonzentrationen ist auf atomarer Skala möglich: Transport-vorgänge, die sich auf der Nanometerskala abspielen (z.B. gelöste oder nanopartikulär getragene Stoffe) können detektiert und räumlich verortet werden, wenn der Stofftransport eine hinreichende Aktivitäts-konzentration von ca. 0,1 kBq pro Voxel bewirkt (etwa 109 Atome/1 mm³, pikomolar). Diese außergewöhnliche Sensitivität (und Selektivität) ist mit keiner anderen Bildgebungsmodalität erreichbar, insbe-sondere, da wir in repräsentativen Volumen von um 1 L arbeiten, also 106 Voxel. Der Einfluss des Materials – Schwächung und Streuung – ist dabei von zweitrangiger Bedeutung bzw. wird mittels systematischer Verfahren reduziert (Zakhnini et al., 2013).
Sinnvolle Anwendungen liegen in der direkten Visualisierung und Quantifizierung realer chemisch-physikalischer Prozesse (Abb.2a und b). Solche Prozesse können sonst nur über modellhafte Prozess-Simulationen dargestellt werden, indem etwa statistische a-priori-Strukturmodelle oder strukturelle Information aus CT-Bildern oder als Grundlage für LBM- oder FEM-Simulationen genutzt werden (zu letzteren zwei Beispiele in Abb. 3). Bei der direkten Beobachtung chemisch-physikalischer Prozesse in Gesteinen mittels GeoPET zeigen sich regelmäßig Abweichungen von den für Simulationen angenommene Versuchsbedingungen, etwa bezüglich der Homogenität des Probekörpers, der Topologie des Fließpfades oder der Auswirkungen geringster – aber wirkungsvoller – Abweichungen von Idealbedingungen (nicht-Dirac-Injektionsimpulsen, nicht-Punkt-/Linien- oder Flächenhaft homogener Zufuhr von Tracern). Zielparameter sind prozessabhängige, effektive Größen (effektives Transportvolumen, wirksame innere Oberfläche, Geschwindigkeitsverteilung, lokale Retardation), sowie räumlich und tensoriell aufgelöste Dispersions- und Diffusionskoeffizienten.

Die mittels der GeoPET-Methode beobachteten Prozesse können mit Alteration der Struktur durch Auflösung oder Ausfällung einhergehen, welche mit CT oder MRT mit höherer Auflösung, eventuell auch prozessbegleitend-zeitaufgelöst, sichtbar gemacht werden können. Dies entspricht der üblichen Vorgehensweise bei der nuklearmedizinischen PET-CT. Direkte und rückwirkungsfreie ortsaufgelöste Information über das chemische Milieu als Ursache der Alteration kann dagegen nur die PET liefern. Nur hierdurch werden viele bisher deduzierte Parameter direkt messbar und die Ergebnisse von Modellsimulationen verifizierbar.
Begleitend zur Prozessbeobachtung mit der GeoPET wird der Kontrollbereich und das Zyklotron des HZDR in Leipzig zur Produktion von Radiotracern genutzt (siehe z.B. (Mansel et al.)). Hier werden grundlegende geochemische Transport- und Wechselwirkungsstudien durchgeführt, die ebenfalls durch die Anwendung von Radiomarkierungen besonders empfindlich sind, wodurch die geochemische Parametrisierung von Modellen für reaktive Transportvorgänge ermöglicht wird.


Bittner, L., Kulenkampff, J., Gründig, M., Lippmann-Pipke, J. and Enzmann, F., 2014. Direct Observation of Waterglass Impregnation of Fractured Salt Rock with Positron Emission Tomography, International Conference on the Performance of Engineered Barriers: Backfill, Plugs & Seals, BGR, Hannover, Germany.
Gründig, M., Richter, M., Seese, A. and Sabri, O., 2007. Tomographic radiotracer studies of the spatial distribution of heterogeneous geochemical transport processes. Applied Geochemistry, 22: 2334-2343.
Kulenkampff, J., Gründig, M., Richter, M. and Enzmann, F., 2008. Evaluation of positron emission tomography for visualisation of migration processes in geomaterials. Physics and Chemistry of the Earth, 33: 937-942.
Lippmann-Pipke, J., Kulenkampff, J., Gründig, M. and Richter, M., 2011. Matching PET data with COSMOL Multiphysics simulation results, COMSOL Conference, 26.-28.10.2011, Ludwigsburg, Germany.
Mansel, A., Gruhne, S., Franke, K. and Fischer, S., Production of 85Sr at a 18 MeV-cyclotron and purification for geochemical investigations. Submitted to Applied Radiation and Isotopes, submitted.
Richter, M., Gründig, M. and Butz, T., 2000. Tomographische Radiotracerverfahren zur Untersuchung von Transport- und Sorptionsprozessen in geologischen Schichten. Zeitschrift für Angewandte Geologie, 46(2): 101.
Richter, M., Gründig, M., Zieger, K., Seese, A. and Sabri, O., 2005. Positron Emission Tomography for modelling of geochmical transport processes in clay. Radiochimica Acta, 93: 643-651.
Schikora, J., 2012. Simulation of diffusion-adsorption processes in natural geological media by means of COMSOL Multiphysics, Dresden Technical University, Diploma thesis, Dresden, Germany, 95 pp.
Zakhnini, A., Kulenkampff, J., Sauerzapf, S., Pietrzyk, U. and Lippmann-Pipke, J., 2013. Monte Carlo simulations of GeoPET experiments: 3D images of tracer distributions (18F, 124I and 58Co) in Opalinus Clay, anhydrite and quartz. Computers and Geosciences, 57 183-196.

  • Lecture (Conference)
    International Conference on the Performance of Engineered Barriers: Backfill, Plugs & Seals, 06.-07.02.2014, Hannover, Deutschland

Publ.-Id: 20111

Verification of coupled 3D fuel cycle analysis with stable Monte Carlo based code, BGCore, against the nodal diffusion DYN3D code

Kotlyar, D.; Shwageraus, E.; Margulis, M.; Bilodid, Y.; Fridman, E.

Previous studies suggested that different schemes for coupling Monte Carlo (MC) neutron transport with burnup and thermal hydraulic feedbacks may potentially be numerically unstable. This issue can be resolved by application of new Stochastic Implicit Mid-Point (SIMP) methods. In order to assure numerical stability, the new methods do require additional computational effort. The instability issue however, is problem-dependent and does not necessarily occur in all cases. Therefore, blind application of the unconditionally stable coupling schemes, and thus incurring extra computational costs, may not always be necessary. In this paper, we attempt to develop an intelligent diagnostic mechanism, which will monitor numerical stability of the calculations and, if necessary, switch from simple and fast explicit coupling scheme to more computationally expensive but unconditionally stable one. To illustrate this diagnostic mechanism, we performed a coupled burnup and TH analysis of a single BWR fuel assembly. The reference solution was obtained by the state of the art nodal diffusion code – DYN3D. Very good agreement was observed in all neutronic and TH parameters. The results indicate that the developed algorithm can be easily implemented in any MC based code for monitoring of numerical instabilities. The proposed monitoring method has negligible impact on the calculation time even for realistic 3D multi-region full core calculations.

Keywords: Monte Carlo; BGCore; neutronic-burnup-thermal hydraulic coupling; SIMP; stability analysis

  • Contribution to proceedings
    PHYSOR2014, 28.09.-03.10.2014, Kyoto, Japan
    Proceedings of PHYSOR2014

Publ.-Id: 20110

Preclinical Aspects of Nicotinic Acetylcholine Receptor Imaging

Brust, P.; Deuther-Conrad, W.; Donat, C. K.; Barthel, H.; Riss, P.; Paterson, L.; Höpping, A.; Sabri, O.; Cumming, P.

Recent developments in radiochemistry have opened new vistas for investigations of nicotinergic acetylcholine receptors (nAChRs) in living brain by positron emission tomography (PET) and by single photon emission computed tomography (SPECT). In parallel, dedicated instrumentation for molecular imaging in small animals has facilitated preclinical investigations in a number of models in which perturbations in nAChR signalling are implicated, notably Alzheimer’s disease and other neurodegenerative conditions, schizophrenia and other neuropsychiatric disorders, substance abuse and traumatic brain injury. The nAChRs are members of a family of ligand-gated ion channels composed of five subunits, most commonly occurring in the central nervous system as heteropentamers designated α4β2, with lesser amounts of the α7 homopentamer. We present a systematic review of preclinical findings with the diverse nAChR ligands which have been investigated to date. Molecular imaging of the α4β2 nAChR subtype by PET has been successfully achieved by 2-[18F]fluoro-A-85380. Newer agents such as (−)-[18F]flubatine permit quantitation of α4β2 receptors with PET recordings not exceeding 90 min, without the toxicity characteristic of earlier epibatidine derivatives. Imaging studies of α7 nAChRs have been hampered by inadequate pharmacological specificity of available ligands and by the low natural abundance of this receptor subtype in the brain. However, a continued search for optimal ligands is justified by the particular association of α7 nAChRs with aspects of cognitive function. We note that no molecular imaging ligands have been developed for α6-containing nAChRs, despite their importance for the psychopharmacology of nicotine actions in the basal ganglia. Finally, we review the competitive binding model, in which the availability of α4β2 binding sites is altered by competition from endogenous acetylcholine, noting that this approach has yet to be applied for monitoring acetylcholine release in disease models.

  • Book chapter
    Rudi, A.J.O.; Dierckx, A.; Otte, E. F.J.; de Vries, A.; van Waarde: PET and SPECT of Neurobiological Systems, Heidelberg: Springer, 2014, 978-3-642-42013-9, 465-512
    DOI: 10.1007/978-3-642-42014-6

Publ.-Id: 20109

Overview and current status of the PENELOPE project

Siebold, M.

PENELOPE (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) is designed for a pulse energy of 150 J, a repetition rate of 1Hz and a pulse duration of 120 fs after compression. Yb:CaF2 is chosen as gain medium, while each amplifier head consists four He-cooled slabs having a thickness of 5mm and a doping concentration of 1.4mol% Yb3+. The slab diameter of the final 150 J amplifier and its 10 J pre-amplifier is 110 and 55 mm, respectively. A total laser diode peak-power of 1.2 MW is installed for pumping at 980 nm. As front-end a 60 fs Yb:KGW oscillator, a regenerative Yb:CaF2 amplifier and two active mirror Yb:CaF2 multi-pass amplifiers with a pulse energy of 300µJ, 100mJ and 1J are used. The compressor is based on multilayer dielectric (MLD) gratings with a dimension of 94×42cm2, a groove density of 1760 l/mm, a grating distance of 220cm, a hard-clip bandwidth of 50nm, and a output beam diameter of 25cm.

  • Lecture (others)
    Science Palaver talk, 12.02.2014, Jena, Deutschland

Publ.-Id: 20108

High-energy diode-pumped D2O-cooled multi-slab Yb:YAG and Yb:QX-glass lasers

Siebold, M.; Loeser, M.; Harzendorf, G.; Nehring, H.; Tsybin, I.; Röser, F.; Albach, D.; Schramm, U.

We investigated lasing performance of a two-slab Yb:QX glass, a two and a four-slab Yb:YAG laser amplifier which were facet-cooled. As coolant di-Deuterium Oxyde (D2O) flowed between the active slabs while the pump and the laser light were passing through the very low absorbing heavy-water films. A square pump profile with a maximum intensity of 40 kW/cm2 drove the amplifier with a peak fluence of 5.5 J/cm2 at a pulse duration of 6 ns. We demonstrated a maximum pulse energy of 1 J for each gain medium as well as a repetition rate of 10 Hz for Yb:YAG and 1Hz for Yb:QX glass.

Keywords: Laser Amplifiers; Laser cooling; Lasers diode-pumped; Lasers Ytterbium

Publ.-Id: 20107

Towards compositional geochemical potential mapping

Tolosana-Delgado, R.; van den Boogaart, K. G.

Mineral potential mapping aims at defining target zones of future local mineral exploration efforts on the basis of regional geochemical and geological surveys. Geochemical potential mapping typically involves using a small set of elements to predict an anomalous presence of a mineral commodity related with them. In this context it is common to work with logarithmically transformed concentrations of elements. This contribution explores a compositionally compliant approach to potential mapping using geochemical evidences, in which the whole set of components is applied a log-ratio transformation before any potential mapping technique is used. In this way, candidate zones can be identified by its high value in a certain ratio of elements, implying that the important information is a contrast betweeen two or more elements, and not an absolute concentration of one of them. Two different potential mapping techniques are used (a method equivalent to the Fisher rule, and a hierarchical binary logistic regression, both accounting for spatial dependence), with equivalent results.

Keywords: Geostatistics; clr; variation-variograms; centered log-ratio transformation; balance

Publ.-Id: 20106

Astrophysical and experimental implications from the magnetorotational instability of toroidal fields

Rüdiger, G.; Gellert, M.; Schultz, M.; Hollerbach, R.; Stefani, F.

The interaction of differential rotation and toroidal fields that are current-free in the gap between two corotating axially unbounded cylinders is considered. It is shown that non-axisymmetric perturbations are unstable if the rotation rate and Alfven frequency of the field are of the same order, almost independent of the magnetic Prandtl number Pm. For the very steep rotation law Omega proportional to R^2 (the Rayleigh limit) and for small Pm, the threshold values of rotation and field for this azimuthal magnetorotational instability (AMRI) scale with the ordinary Reynolds number and the Hartmann number, respectively. A laboratory experiment with liquid metals like sodium or gallium in a Taylor-Couette container has been designed on the basis of this finding. For fluids with more flat rotation laws, the Reynolds number and the Hartmann number are no longer typical quantities for the instability. For the weakly non-linear system, the numerical values of the kinetic energy and the magnetic energy are derived for magnetic Prandtl numbers <= 1. We find that the magnetic energy grows monotonically with the magnetic Reynolds number Rm, while the kinetic energy grows with Rm/root Pm. The resulting turbulent Schmidt number, as the ratio of the 'eddy' viscosity and the diffusion coefficient of a passive scalar (such as lithium), is of the order of 20 for Pm = 1, but for small Pm it drops to the order of unity. Hence, in a stellar core with fossil fields and steep rotation law, the transport of angular momentum by AMRI is always accompanied by an intense mixing of the plasma, until the rotation becomes rigid.

Publ.-Id: 20105

Numerical Modeling of Bubble Columns Using Experimental Breakup and Coalescence Rates of Bubbles

Azizi, S.; Schubert, M.

The prediction of bubbles size distributions in bubble columns reactors is a great challenge in design and optimization of operating conditions. The implementation of Population Balance Equations (PBE) for bubbly flows into CFD codes allowed better understanding of the hydrodynamic behavior of bubble columns and better quantification of the interfacial area for the estimation of interphase transport phenomena. On the other hand, the complexity of numerical models increased with the introduction of new sub-models for the determination of Bubble Size Distributions (BSD). The formulation of sink and source terms of such PBE is a very controversial issue. These terms depend on assumption on the dominating mechanisms due to turbulence, buoyancy, wake, shear, etc.. However, the unknown physical effects, the variety of constants of Breakup and Coalescence (B&C) kernels as well as their complex coupling with the hydrodynamics of the flow prevent to generalize existing models.
In this work, a new approach will be presented to determine B&C rates in bubble columns using experimental BSD data and hydrodynamic characteristics such as phase fractions at several column heights e.g. obtained by ultrafast X-ray tomography. To calculate the experimental B&C rates, a set of non-linear PBE is solved at each scanning height with the measured hydrodynamic data and statistical equations to consider diameter effect of coalescing bubbles.
The approach was applied to own experimental data and data from literature. Good agreement was found for the numerical simulated BSD and hydrodynamics based on the derived B&C rates compared to experimental data.
For future work, this approach allows to directly validate existing B&C models with different gas and liquid physical properties and operating conditions in order to formulate more generalized B&C models for their implementation in CFD models.

Keywords: Bubble Column; Breakup and Coalescence; Experimental Rates

  • Lecture (Conference)
    Annual Meeting of Computational Fluid Dynamics, Mixing processes and rheology, 24.-25.02.2014, Festung Marienberg Würzburg, Germany

Publ.-Id: 20104

An analytic approach to modeling the optical response of anisotropic nanoparticle arrays at surfaces and interfaces

Persechini, L.; Verre, R.; Mcalinden, N.; Wang, J.; Ranjan, M.; Facsko, S.; Shvets, I.; Mcgilp, J.

Anisotropic nanoparticle (NP) arrays with useful optical properties, such as localized plasmon resonances (LPRs), can be grown by self-assembly on substrates, but these systems often have significant dispersion in NP dimensions and distribution, which makes a numerical approach to modeling the LPRs very difficult. An improved analytic approach to this problem is discussed in detail and applied successfully to NP arrays from three systems that differ in NP metal, shape and distribution, and in substrate and capping layer. The materials and anisotropic NP structures that will produce LPRs in desired spectral regions can be determined using this approach.

Keywords: metallic nanoparticles; plasmonics

Publ.-Id: 20102

Speciation of actinides after plant uptake

Geipel, G.; Viehweger, K.

Besides natural the occurring actinides uranium and thorium the most impact of higher actinides in biological systems is connected to the release of transuranium elements in nuclear accidents as Chernobyl and Fukushima and from scenarios which are seen in the discussion of radioactive waste storage.
In radioactive waste storage sites in the deep underground, however, the first organism which may have contact to actinides are microorganism. In later transport to the earth surface these radionuclides may also access the food chain via several ways of uptake. One of these ways may occur by uptake of actinides by plants.
Nevertheless, the uptake depends on the bioavailability of these elements and therefore also on the speciation or binding form before and after uptake.

It can be stated already here, that some of these radionuclides are much less studied than others. This may be caused by the difficult handling of the radioelements, as they are α-emitting radionuclides and therefore special equipment in the laboratories is necessary as well as regulations of radiation protection have to be considered.

An introduction in the uptake of radionuclides by plants has been given by M. Greger. Besides the description of common uptake mechanisms only few information about actinides is given.
An overview about soil to plant transfer is given by D. Robertson et al. The factors vary very strong depending on plant species, soil and experimental conditions, but compared to Sr isotopes the values for actinides are smaller.

Keywords: Actinides; Speciation; Plants

  • Book chapter
    C. Walther, D.K. Gupta: Radionuclide Contamination and Remediation through Plants, Berlin, Heidelberg: Springer, 2014, 978-3-319-07665-2, 197-214

Publ.-Id: 20101

LC-MS Supported Investigation Of The In Vitro And In Vivo Metabolism Of [18F]Flubatine – A New Radiotracer For Imaging Of α4β2 Nicotinic Acetylcholine Receptors

Ludwig, F.-A.; Fischer, A.; Deuther-Conrad, W.; Donat, C. K.; Smits, B.; Hoepping, A.; Brust, P.; Steinbach, J.

Imaging of brain α4β2 nicotinic acetylcholine receptors (nAChRs), a subtype involved in learning and memory processes, can potentially help to predict prognosis of dementia in neurodegenerative disorders like Alzheimer´s disease (AD). Two [18F]flubatine enantiomers [18F]-1 (derivatives of homoepibatidine) are promising radiotracers for neuroimaging of α4β2-nAChRs [1] and are currently investigated in clinical studies. Therefore, their metabolism was investigated by two different approaches. Initially, (+)- and (−)-1, were incubated with liver microsomes from mouse or human to produce phase I metabolites. After precipitation with acetonitrile, LC-MS/MS studies of the supernatants were performed to compare metabolic stabilities and for structural elucidation of metabolites. Thereafter, (+)-[18F]-1 (~280 MBq) was injected into mice. Liver, plasma and urine samples were taken, precipitated and investigated by radio-HPLC. In order to conclude about chemical identities of the radiometabolites of (+)-[18F]-1, we applied identical chromatographic conditions to both LC-MS and radio-HPLC. LC-MS revealed that both flubatine enantiomers retained a high level of metabolic stability. Furthermore, they were metabolized to higher extent by mouse than by human microsomes. In direct comparison, (+)-1 proved to be more stable than (−)-1. A series of metabolites resulting from oxidation was detected (M0-M6). Presence of each metabolite was species and enantiomer dependent. MS/MS examinations revealed the azabicyclic ring system being exclusively affected by oxidation, namely C- and N-hydroxylation. Using 3-hydroxy flubatine as reference, we identified the radiolabelled derivative (Mc) as one of the metabolites. Correlation with radio-HPLC supports the existence of further radiometabolites resulting from oxidation beside others (Fig. 1). We conclude, that our combined approach offers a useful tool for assignment and finally identification of radiotracer metabolites.

[1] Brust, P. et al. Preclinical Aspects of Nicotinic Acetylcholine Receptor Imaging. In PET and SPECT of Neurobiological Systems; Dierckx, R. A.; Otte, A.; Vries, E. F. de; van Waarde, A.; Luiten, P. G., Eds.; Springer Berlin Heidelberg, 2014; pp 465-512.

  • Poster
    XIII Turku PET Symposium, 24.-27.05.2014, Turku, Finland

Publ.-Id: 20100

Purification Of Used Oxygen-18 Water: Quality Assessment And Re-use

Rötering, S.; Franke, K.; Zessin, J.; Brust, P.; Füchtner, F.; Steinbach, J.; Fischer, S.

Rapid development of PET and the design of larger targets cause a greater need of oxygen-18 enriched water as target material for fluorine-18 production and entail increased costs for oxygen-18 enriched water. This forced us to consider its re-use for research purposes. Used O-18 water is mainly contaminated with metal radionuclides, non-radioactive salts and organic solvents. Here, we present (i) two methods for the removal of organic contaminants, (ii) analytical methods for quality assessment and (iii) findings for irradiation and radiosyntheses using activity produced from re-cycled water. Samples of used target water (1 L containing 44 mg L>sup-1 acetone and 396 mg L>sup-1 ethanol) were treated with UV irradiation (254 nm) [1] or with KMnO4/NaOH at 50°C to reduce the concentration of these contaminants below 50 mg L>sup-1, respectively. Both methods allowed close-to-zero decrease of acetone and decrease of ethanol to 23 ± 20 mg L>sup-1 (n = 8). After vacuum distillation pure re-cycled water was obtained as proven by gamma spectrometry, gas chromatography, ICP-OES, and ion chromatography. Loss of O-18 enrichment (83%, pycnometry) was not observed. A reference study on O-16 water, contaminated by addition of 150 to 200 mg L>sup-1 methanol, ethanol, acetone and acetonitrile, showed a comparable oxidation potential of both methods for methanol, ethanol and acetone (decrease within 48 h below 50 mg L>sup-1). Oxidation of acetonitrile was only achieved with the UV-lamp within 7 days. Re-cycled water and virgin water (Hyox 18 Enriched Water), partly diluted to 83% O-18 enrichment, were irradiated in the Nirtra® Fluor L-target at a CYCLONE 18/9 (iba) with 35 µA and 11.7 µAh. Comparison of produced activities of F-18, N-13 and metal radionuclides confirmed the high quality of the re-cycled water. Compared to undiluted virgin water a loss of the production yield of ~19% was observed. No significant influence on the radionuclide purity or radiochemical reactivity was detected. F-18 obtained from virgin water or re-cycled water irradiation was comparably used for radiosyntheses. Results of automated radiosyntheses (TRACERLAB™ FX-FN) of our new α4β2 nicotinic receptor ligand [18F]flubatine (n=5) and σ1 receptor ligand [18F]fluspidine (n=8) as well as radiosyntheses for development of the α7 nicotinic receptor ligand [18F]NS14490 and 18F-labelled CB2-selective N-aryl-oxdiazolyl-propionamides revealed equivalent yields and unchanged product qualities. The described purification procedures enable a multiple re-cycling of target water for successful F-18 production and application for research purposes with reasonable production yields and efficient economical use of the target water.

[1] DE 29504388 U1, 1995

  • Poster
    XIII Turku PET Symposium, 24.-27.05.2014, Turku, Finland

Publ.-Id: 20099

Uranium(VI) and neptunium(V) retention by clay minerals and natural clay rock – Influence of clay organics, temperature and pore water salinity

Schmeide, K.; Joseph, C.; Fritsch, K.

The long-term disposal of high-level nuclear waste in deep geological formations is discussed worldwide as main strategy for nuclear waste management. In addition to salt and crystalline rock, argillaceous rock has been proposed as potential host rock and backfill material for nuclear waste repositories. This is due to favorable characteristics of clay minerals such as their swelling properties and their large surface areas leading to a low permeability and high retention efficiency toward radionuclides. Sorption and diffusion of safety relevant radionuclides on/in clay rock are important physicochemical processes that have to be studied to contribute to a reliable long-term safety assessment for future nuclear waste repositories.

Clay rock is closely associated with natural organic matter. Low molecular weight organic acids such as acetate, lactate, propionate and formate as well as fulvic and humic acid-like substances can be released from the clay under certain conditions [1]. These organics can influence the migration of radionuclides in the environment by forming soluble complexes or stable colloids. In addition, for the disposal of high-level nuclear waste in clay formations, elevated temperatures of up to 100 °C are expected close to the waste containers resulting from the radioactive decay of the stored radionuclides. Besides that, pore waters of North German clay deposits, considered for underground nuclear waste repositories, show relatively high salinities (2 to 3.5 M). Thus, effects of organic matter, temperature and salinity have to be taken into account for a reliable prediction of radionuclide migration in the geosphere.

Batch sorption studies with clay minerals revealed that the U(VI) sorption onto kaolinite [2] is much higher than the Np(V) sorption [3] in 0.1 M NaClO4. In the presence of humic acid, the actinide sorption is increased in the acidic pH range and decreased in the near-neutral pH range. The influence of ionic strength was studied for U(VI) sorption onto montmorillonite by applying 0.1 to 3 M NaCl and CaCl2 as background electrolytes. It was observed that the ionic strength effect on U(VI) sorption on montmorillonite is very small. In NaCl, a decrease of U(VI) sorption with ionic strength is only observed below pH 6 and up to an ionic strength of 2 M. In CaCl2, U(VI) sorption is at least partly governed by secondary phase formation.

The retention behavior of the natural clay rock Opalinus Clay (Mont Terri, Switzerland) toward U(VI) was studied by means of batch sorption and diffusion experiments. Opalinus Clay is considered as representative host rock of a potential nuclear waste repository in argillaceous rock. For the U(VI) sorption onto Opalinus Clay in synthetic Opalinus Clay pore water (pH = 7.6, I = 0.36 M) at 25 °C, the distribution coefficient, Kd, was determined with 22.2 ± 0.4 L/kg [4]. This shows that the U(VI) sorption is relatively weak under pore water conditions. It is comparable to the Np(V) sorption onto Opalinus Clay (25 ± 5 L/kg [5]). This can be attributed to the predominance of the weakly sorbing Ca2UO2(CO3)3(aq) complex in the Opalinus Clay pore water.

The U(VI) sorption onto Opalinus Clay was also studied in 0.1 M NaClO4 in the pH range 3 to 10. Results of surface complexation modelling [6], applied for blind prediction of pH-dependent U(VI) sorption onto Opalinus Clay, showed that U(VI) may predominantly sorb onto illite and montmorillonite. In addition, U(VI) sorption onto Fe(III) minerals was predicted. U(VI) sorption onto further minerals of the clay (kaolinite, chlorite, quartz, feldspars) is negligible.

With increasing concentration of low molecular weight organic acids (10-5 to 10-2 M), the U(VI) sorption onto Opalinus Clay in pore water decreases due to complex formation in solution. The mobilizing effect of the organics on U(VI) increases in the following sequence: formate < lactate ~ acetate ≤ propionate < tartrate < citrate. In the presence of 1×10-2 M citrate, which has been identified as important ligand in radioactive waste problems, the Kd value for U(VI) amounts to only (1.1 ± 0.3) L/kg. The influence of the organic ligands on the U(VI) sorption onto Opalinus Clay correlates with the stability of the respective U(VI) complexes. In contrast, humic acid (≤ 50 mg/L) does not affect U(VI) sorption [4]. With increasing temperature up to 60 °C, the U(VI) sorption increases both in the absence and in the presence of clay organics.

The U(VI) diffusion in compacted Opalinus Clay was studied in the absence and presence of humic acid at 25 and 60 °C under anaerobic conditions using Opalinus Clay pore water [7]. The effective diffusion and distribution coefficients (De and Kd) determined for U(VI) and humic acid at 25 and 60 °C show that humic acid has no significant influence on the U(VI) diffusion. The diffusion profiles obtained for humic acid in Opalinus Clay at 25 and 60 °C show contributions of at least two different humic acid particle size fractions (< 1 kDa and 10−100 kDa). The smaller humic acid fraction diffused through the whole clay samples at both temperatures within three months whereas the larger humic acid fraction diffused only about 500 µm into the clay. This shows the filtration effect of the compacted clay and also a different sorption affinity of the humic acid size fractions toward Opalinus Clay. At 60 °C, the diffusion profiles of two U(VI) species were observed, which were attributed to a colloidal and an aquatic U(VI) species. The De and Kd value of the aquatic U(VI) species increased with increasing temperature. However, these changes compensated each other, thus, an increase of the temperature to 60 °C did not accelerate the migration of U(VI) through Opalinus Clay.

Under environmentally relevant conditions (pH > 7), U(VI) is only weakly sorbed by the natural clay rock Opalinus Clay. However, since molecular diffusion is the decisive retardation process in clay rock, Opalinus Clay has a good retention potential toward U(VI).

[1] Courdouan, A. et al. (2007) Appl. Geochem. 22, 2926-2939.
[2] Křepelová, A. et al. (2006) Radiochim. Acta 94, 825-833.
[3] Schmeide, K. and Bernhard, G. (2010) Appl. Geochem. 25, 1238-1247.
[4] Joseph, C. et al. (2011) Chem. Geology 284, 240-250.
[5] Wu, T. et al. (2009) Environ. Sci. Technol. 43, 6567-6571.
[6] Joseph, C. et al. (2013) Appl. Geochem. 36, 104-117.
[7] Joseph, C. et al. (2013) Geochim. Cosmochim. Acta 109, 74-89.

Keywords: U(VI); Np(V); Opalinus Clay; clay minerals; adsorption; diffusion; clay organics; humic acid; fulvic acid; temperature

  • Invited lecture (Conferences)
    51st Annual Meeting of the Clay Minerals Society, Texas A&M University, 17.-21.05.2014, College Station, Texas, USA
  • Contribution to proceedings
    51st Annual Meeting of the Clay Minerals Society, Texas A&M University, 17.-21.05.2014, College Station, Texas, USA

Publ.-Id: 20098

Electrical Characterization of Single Molecules via Mechanically Controllable Break Junctions

Wieser, M.; Sendler, T.; Weisbrod, S.; Tang, Z.; Marx, A.; Wolf, J.; Huhn, T.; Scheer, E.; Moresco, F.; Grebing, J.; Erbe, A.

Molecular electronics has been a field of big interest for the last years. Using the technique of mechanically controllable break junctions we characterize different organic molecules, e.g. 1,4-Diethoxy-2,5-bis(4-sulfanyl-phenylethynyl)-benzene (PEEB) and switchable molecular wires, dissolved in an organic non-polar solvent. IV-curves taken from the molecules connected to single gold atom contacts show the expected tunneling behavior described by the single-level model: weak coupling of the molecules to the gold atoms implies an off-resonant tunneling process and a transport through a single channel. Varying the end-groups of the molecules leads to a different transport behavior. Figure 1 shows a 2D histogram of IV-curves of PEEB with amino end-groups. Based on the single-level transport model the analysis of the current-voltage characteristics delivers the energy of the molecular level and the coupling between electrode and molecule. It also indicates a reliable contact of the molecules to the gold atoms. A further goal is the investigation of an electric gate effect on the transport behavior through the molecules.

Keywords: Molecular Electronics; Electronic Transport

  • Poster
    IHRS NANONET Annual Workshop 2013, 10.10.2013, Dresden, Deutschland

Publ.-Id: 20097

Electrical Characterization of Single Organic Molecules via Mechanically Controllable Break Junctions

Sendler, T.; Wieser, M.; Liu, S.-P.; Weisbrod, S.; Tang, Z.; Marx, A.; Wolf, J.; Huhn, T.; Scheer, E.; Moresco, F.; Grebing, J.; Erbe, A.

Molecular electronics has been of big interest for the last years. To allow an electrical characterization of single molecules a reliable contact to gold atoms is required. We ensure this by using single organic molecules with a plain structure, in particular 1,4-Diethoxy-2,5-bis (4-sulfanyl-phenylethynyl)-benzene and single stranded DNA fragments, dissolved in an organic non-polar solvent. For measurements we use the technique of mechanically controllable break junctions. IV-curves taken from single molecules connected to single gold atom contacts show the expected tunneling behavior, from which we gain the energy of the molecular level and the coupling between electrode and molecule.

Keywords: Molecular Electronics; Electronic Transport

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 20096

Direct Determination of Exchange Parameters in Cs2CuBr4 and Cs2CuCl4: High-Field Electron-Spin-Resonance Studies

Zvyagin, S. A.; Kamenskyi, D.; Ozerov, M.; Wosnitza, J.; Ikeda, M.; Fujita, T.; Hagiwara, M.; Smirnov, A. I.; Soldatov, T. A.; Shapiro, A. Y.; Krzystek, J.; Hu, R.; Ryu, H.; Petrovic, C.; Zhitomirsky, M. E.

Spin-1/2 Heisenberg antiferromagnets Cs2CuCl4 and Cs2CuBr4 with distorted triangular-lattice structures are studied by means of electron spin resonance spectroscopy in magnetic fields up to the saturation field and above. In the magnetically saturated phase, quantum fluctuations are fully suppressed, and the spin dynamics is defined by ordinary magnons. This allows us to accurately describe the magnetic excitation spectra in both materials and, using the harmonic spin-wave theory, to determine their Exchange parameters. The viability of the proposed method was proven by applying it to Cs2CuCl4, yielding J/kB = 4.7(2) K, J'/kB = 1.42(7) K, [J'/J ≃ 0.30] and revealing good agreement with inelastic neutronscattering results. For the isostructural Cs2CuBr4, we obtain J/kB = 14.9(7) K, J'/kB = 6.1(3) K, [J'/J ≃ 0.41], providing exact and conclusive information on the exchange couplings in this frustrated spin system.

Publ.-Id: 20095

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