Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Mineralogical Changes within Polish Weissliegend Sandstones During Bioleaching

Heim, J.; Bachmann, K.; Rahfeld, A.; Möckel, R.; Schopf, S.; Gutzmer, J.; Schlömann, M.

The Kupferschiefer is one of the most important sources of copper and silver in Europe, with resources located mainly in Poland and Germany. Mineralization is stratabound and hosted by sedimentary rocks comprising of sandstone, black shale, and carbonate rocks. Because Kupferschiefer-type ores are typically complex and very fine-grained, alternative approaches for metal recovery, such as bioleaching, are becoming an attractive alternative to flotation.
The focus of this study was a detailed monitoring of mineralogical changes through time during bioleaching of sandstone-hosted Cu-mineralization from two Polish Cu-mines. The change of modal mineralogy, mineral associations, microbial activity and copper recovery of a copper bearing sandstone during bioleaching with Acidithiobacillus ferrooxidans DSM 14882 was investigated. A series of 18 batch cultures and 18 abiotic controls in shaking flasks with a solid content of 6 wt.% was prepared and sampled every 3 to 4 days over a period of 18 days. Mineralogical analysis of leaching residues was done by mineral liberation analysis (MLA) and X-Ray powder diffraction (XRD), while chemical analysis of dissolved copper and ferric/ferrous iron was carried out with ion chromatography (IC).
The investigated sandstone ore contained 2.5 wt.% copper, mainly bound to the copper minerals chalcocite (Cu2S, 1.3 wt.%), covellite (CuS, 1.0 wt.%) and bornite (Cu5FeS4, 0.9 wt.%). After 18 days the copper extraction was 84% for biotic samples and therefore significantly higher compared to abiotic controls (52%). MLA data showed that biotic dissolution was faster for all three copper ore minerals. The results of detailed mineralogical analysis indicate a passivation by jarosite during the leaching process, especially caused by ammoniojarosite. It was possible to trace progressive changes of each copper sulphide over the entire bioleaching process and calculate dissolution/formation rates by means of MLA data.

Keywords: Bioleaching; Acidithiobacillus ferrooxidans; Weissliegend sandstone; automated mineral liberation analysis; XRD

  • Contribution to proceedings
    IMWA 2016, Annual Conference, Mining meets Water – Conflicts and Solutions, 11.-15.07.2016, Leipzig, Deutschland

Publ.-Id: 23778

Hydrogen release from irradiated elastomers measured by Nuclear Reaction Analysis

Jagielski, J.; Ostaszewska, U.; Bielinski, D.; Grambole, D.; Romaniec, M.; Jozwik, I.; Kozinski, R.; Kosinska, A.

Ion irradiation appears as an interesting method of modification of elastomers, especially friction and wear properties. Main structural effect caused by heavy ions is a massive loss of hydrogen from the surface layer leading to its smoothening and shrinking. The paper presents the results of hydrogen release from various elastomers upon irradiation with H+, He+ and Ar+ studied by using Nuclear Reaction Analysis (NRA) method. The analysis of the experimental data indicates that the hydrogen release is controlled by inelastic collisions between ions and target electrons. The last part of the study was focused on preliminary analysis of mechanical properties of irradiated rubbers

Keywords: Ion implantation; Elastomers; Ion beam analysis; Hydrogen release

Publ.-Id: 23777

Velocity Measurement For Two-Phase Flows Based On Ultrafast X-ray Tomography

Barthel, F.; Bieberle, M.; Hoppe, D.; Banowski, M.; Hampel, U.

The ultrafast electron beam X-ray tomography scanner ROFEX is used for the investigation of multiphase flows. Its functional principle allows us to obtain sequences of cross-sectional flow images, which shows local attenuation properties of the flow. Hence, the X-ray CT images mainly reveal the shape and interfaces of flow constituents, such as gas, liquid and solids via their X-ray contrast. It is, however, more difficult to obtain velocity information from multi phase flows. In this article we discuss different methods to extract information on the velocities of particles or interfaces as well as for continuous phase. For disperse phase velocity measurement, e.g. ingas–liquidorgas–solids flows, we employ cross-correlation based techniques using two imaging planes. Apart from the standard cross-correlation technique we developed a method and algorithm, which is capable to identify identical bubbles in the two planes giving us a unique Lagrangian particle-related velocity information. Eventually we give an example of velocity measurement in the continuous liquid phase using an X-ray contrast agent.

Keywords: Ultrafast X-raytomography; Velocity measurement; Cross-correlation; ROFEX

Publ.-Id: 23776

Anomalous Hall Effect in Polycrystalline MnxSi1–x (x ≈ 0.5) Films with the Self-Organized Distribution of Crystallites over Their Shapes and Sizes

Chernoglazov, K. Y.; Nikolaev, S. N.; Rylkov, V. V.; Semisalova, A. S.; Zenkevich, A. V.; Tugushev, V. V.; Vasil’Ev, A. L.; Chesnokov, Y. M.; Pashaev, E. M.; Matveev, Y. A.; Granovskii, A. B.; Novodvorskii, O. A.; Vedeneev, A. S.; Bugaev, A. S.; Drachenko, O.; Zhou, S.

The structural, transport, and magnetic characteristics of polycrystalline MnxSi1 – x (x ≈ 0.51–0.52) films grown by pulsed laser deposition onto Al2O3(0001) substrates when the low-energy components are deposited owing to collisions with the atoms of the buffer gas have been studied in the “shadow” geometry. The magnetization of these films is determined by two ferromagnetic phases—the high-temperature phase with the Curie temperature TC ≈ 370 K and the low-temperature one with TC ≈ 46 K. The anomalous Hall effect changes sign from positive to negative with a decrease in temperature. The sign change occurs in the temperature range of 30–50 K; the specific value of this temperature depends on the thickness of the MnxSi1–x film. The results can be interpreted in terms of the structural self-organization related to the formation of two layers in the course of film growth. These layers have nearly the same chemical composition but significantly differ in the shapes and sizes of crystallites. This leads to a drastic difference in the values of TC and in the value and the sign of the anomalous Hall effect for such layers.

Keywords: SiMn alloys; room-temperature ferromagnetism; PLD; anomalous Hall effect


Publ.-Id: 23775

Remote sensing exploration of Nb-Ta-LREE-enriched carbonatite (Epembe/Namibia)

Zimmermann, R.; Brandmeier, M.; Andreani, L.; Mhopjeni, K.; Gloaguen, R.

On the example of the Epembe carbonatite-hosted Nb-Ta-LREE deposit we showcase the use of hyperspectral reflectance data and geomorphic indicators to improve the remote sensing exploration of structurally controlled critical raw material deposits. It further demonstrates how exploration can benefit from a combination of expert knowledge and remotely sensed relief as well as imaging data. In a first stage, multi-source remote sensing data feed lithological mapping based on \textit{kohonen} Self-Organizing maps. We show that morphological indices such as Topographic Position Index, and spatial coordinates are crucial parameters to improve the accuracy of carbonate classification by 10%. The resulting lithological map shows the spatial distribution of the ridge forming carbonatite dyke, the fenitization zone, syenite plugs and mafic intrusions. In a second step, the internal zones of the carbonatite complex were identified using multi-range spectral feature fitting (MRSFF) algorithm and a specific decision tree. This approach allowed detecting potential enrichment zones characterized by an abundance of fluorapatite and pyroxene as well as dolomite-carbonatite (beforsite). Cross validation of the mineral map with field observations and radiometric data confirm the accuracy of the proposed method.

Keywords: Carbonatite; REE; Self-Organizing Maps; Decision Tree; Spectral Feature Fitting; Geomorphology; Namibia; HyMap; SRTM

Publ.-Id: 23774

Direct measurements of the magnetocaloric effect in pulsed magnetic fields

Skourski, Y.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    European Campus Card Conference (ECCA) 2016, 22.-24.05.2016, Wroclaw, Polen

Publ.-Id: 23773

BMBF-Verbundprojekt SAVE: Sicherheitsrelevante Analyse des Verhaltens von Armaturen, Kreiselpumpen und Einlaufgeometrien unter Berücksichtigung störfallbedingter Belastungen

Szeliga, N.; Bezecny, D.; Richter, S.; Hoffmann, M.; Schlüter, M.; Schäfer, T.; Hampel, U.; Blömeling, F.; Lawall, R.; Hamberger, M.; Walberer, A.

In Leichtwasserreaktoren sind Not- und Nachkühlsysteme vorhanden, die auch bei einem Kühlmittelverluststörfall zu jedem Zeitpunkt die im Kern erzeugte Nachzerfallsleistung über einen längeren Zeitraum abführen müssen. Dazu muss die für die Abfuhr der Nachwärme erforderliche Menge Wasser zur Verfügung stehen. Die Not- und Nachkühlsysteme müssen derart betrieben werden, dass ihre Funktion weder durch Einschränkungen des hydraulischen Verhaltens noch durch mechanische Probleme beeinträchtigt wird. Insbesondere Gasmitriss durch luftziehende Hohlwirbel, Dralleintrag sowie Kavitation können zu einer Störung oder sogar zu einem Ausfall des Not- oder Nachkühlsystems führen. Das Ziel des Verbundprojektes SAVE ist die Bereitstellung von verbesserten bzw. neuen Berechnungsgleichungen sowie von Auslegungsempfehlungen zur Vermeidung von Gasmitriss in Pumpenzuläufen. Da sich ein Gasmitriss nicht immer konstruktiv ausschließen lässt, erfolgt darüber hinaus die Beschreibung des Gasmitrisses in Pumpenzuläufen und des hieraus resultierenden Einflusses auf Kreiselpumpen und Armaturen. Hierfür werden experimentelle Messungen an groß- und kleindimensionierten Anlagenkomponenten durchgeführt und durch dreidimensionale Strömungssimulationen (CFD) ergänzt. Die Ergebnisse der Untersuchungen dienen der Aufstellung und Validierung theoretischer Modelle, die durch physikalisch begründete Ansätze an reale Prozesse angepasst werden können. Die experimentelle und theoretische Analyse ist für die Ermittlung von Gültigkeitsbereichen und Skalierungsansätzen sowie für die Gewährleistung der Übertragbarkeit auf andere Stoffsysteme und Betriebsbedingungen unerlässlich. Dies wiederum ermöglicht eine Übertragung der Erkenntnisse über die nukleare Sicherheitsforschung hinaus auf andere Forschungsbereiche.

  • Lecture (Conference)
    48. Kraftwerkstechnisches Kolloquium, 18.-19.10.2016, Dresden, Deutschland
  • Book chapter
    in: Kraftwerkstechnik 2016, Freiberg: Saxonia Standortentwicklungs- und -verwaltungsgese, 2016, ISBN 978-3-934409-69-9

Publ.-Id: 23772

Experimentelle Untersuchung von Armaturen und Kreiselpumpen unter störfallbedingten Belastungen

Schäfer, T.; Szeliga, N.; Bezecny, D.; Richter, S.; Hoffmann, M.; Blömeling, F.; Lawall, R.; Hamberger, M.; Walberer, A.; Schlüter, M.; Hampel, U.

In Kraftwerken ist der zuverlässige Betrieb von Pumpen und Armaturen eine Grundvoraussetzung für einen effizienten und sicheren Betrieb. Beispielsweise sind in Kernkraftwerken mit Leichtwasserreaktoren Not- und Nachkühlsysteme vorhanden, die auch bei einem Kühlmittelverluststörfall zu jedem Zeitpunkt die im Kern erzeugte Nachzerfallsleistung über einen längeren Zeitraum abführen müssen. Im Rahmen des Verbundprojektes SAVE wird das Verhalten von Pumpen und Armaturen in Leichtwasserreaktoranlagen unter kritischen Betriebsbedingungen untersucht. Ein Schwerpunkt bildet dabei die Problematik des Gasmitrisses durch Hohlwirbelbildung in Pumpenzulaufbecken sowie die Auswirkung von Luftmitriss auf das Betriebsverhalten der Komponenten. Dazu wurden umfangreiche experimentelle Studien an Einlaufbeckengeometrien, Kreiselpumpen und Armaturen durchgeführt und durch numerische Simulationen begleitet. Ziel ist die experimentelle Validierung bzw. Weiterentwicklung von Modellen zur Auslegung von Einlaufgeometrien sowie zur Festlegung sicherer Einlaufüberdeckungen. Die Ergebnisse können für die Auslegung, Optimierung, Nachrechnung sowie Prüfung von Zulauf- und Armaturgeometrien genutzt werden. Einer der Schwerpunkte liegt hierbei auf der Erfassung von Maßstabseffekten, wofür Untersuchungen in verschiedenen Größenordnungen durchgeführt wurden. Die Arbeiten umfassen u. a. die experimentelle Untersuchung der Hohlwirbelbildung im Pumpenansaugbecken sowie der Auswirkungen des daraus resultierenden Luftmitrisses auf nachfolgende Systemkomponenten wie Kreiselpumpen und Armaturen, die tomographische Untersuchung und Visualisierung der Gas-Flüssigkeitsverteilungen im Inneren von Kreiselpumpen und Armaturen sowie die experimentelle Untersuchung von nuklearen Armaturen in verschiedenen Stresstests, so zum Beispiel unter erhöhten seismischen Belastungen. Begleitet werden die experimentellen Untersuchungen von numerischen Simulationen, wobei die experimentell erzielten Ergebnisse in eine verbesserte Modellbildung einfließen.

Keywords: Kreiselpumpen; Armaturen; störfallbedingte Belastungen; Hohlwirbelbildung; Gaseintrag

  • Poster
    48. Kraftwerkstechnisches Kolloquium, 18.-19.10.2016, Dresden, Deutschland

Publ.-Id: 23771

Precise image-guided irradiation of small animals: a flexible non-profit platform

Tillner, F.; Thute, P.; Löck, S.; Dietrich, A.; Fursov, A.; Haase, R.; Lukas, M.; Rimarzig, B.; Sobiella, M.; Krause, M.; Baumann, M.; Bütof, R.; Enghardt, W.

Preclinical in-vivo studies using small animals are essential to develop new therapeutic options in radiation oncology. Of particular interest are orthotopic tumour models, which better reflect the clinical situation in terms of growth patterns and microenvironmental parameters of the tumour as well as the interplay of tumours with the surrounding normal tissues. Such orthotopic models increase the technical demands and the complexity of preclinical studies as local irradiation with therapeutically relevant doses requires image-guided target localisation and accurate beam application. Moreover, advanced imaging techniques are needed for monitoring treatment outcome. We present a novel Small Animal Image-Guided Radiation Therapy (SAIGRT) system, which allows for precise and accurate, conformal irradiation and X-ray imaging of small animals. High accuracy is achieved by its robust construction, the precise movement of its components and a fast high-resolution flat-panel detector. Field forming and X-ray imaging is accomplished close to the animal resulting in a small penumbra and a high image quality. Feasibility for irradiating orthotopic models has been proven using lung tumour and glioblastoma models in mice. The SAIGRT system provides a flexible, non-profit academic research platform which can be adapted to specific experimental needs and therefore enables systematic preclinical trials in multicentre research networks.

Keywords: translational cancer research; small animal research platform; image-guided radiotherapy (IGRT); cone beam computed tomography (CBCT); orthotopic tumour models; precision irradiation; X-ray dosimetry

Publ.-Id: 23770

Are established glioblastoma models suitable to mirror the radiobiology of patient tumors?

Dietrich, A.; Jakob, A.; von Neubeck, C.; Fursov, A.; Tillner, F.; Baumann, M.; Krause, M.; Bütof, R.

Introduction: Suitable in vivo modelling of Glioblastoma multiforme (GBM) is essential for developing new radio-oncological treatment strategies. On the translational axis from bench to bedside, it is important to have a model which closely reflects the clinical situation. However, it is also essential to investigate clinically relevant endpoints and use models which are reasonable regarding costs and feasible regarding statistically necessary animal numbers. Established cell lines are comprehensively characterized and can be efficiently engrafted in large cohorts of animals. In this project, a panel of five human GBM cell lines (U 87 MG, U 251 MG, A7, LN 229, HGL21) is characterized after subcutaneous and orthotopic xenograft transplantation (take rate, radiosensitivity, histology, putative stem cell markers (SM)) to investigate their potential as suitable GBM models.

Methods: Limiting dilution assays were performed using subcutaneous injection of decreasing cell numbers. Intrinsic radiosensitivity and effectiveness of combined Radiochemotherapy was studied by irradiation of subcutaneous tumors with different dose levels. Take dose 50% (TD50) and tumor control dose 50% (TCD50) were calculated. For orthotopic transplantation, mCherry- or luciferase-positive cell variants were used. Intracranial transplantation was performed with a stereotactic frame. Tumor growth was assessed weekly via optical imaging and contrast-enhanced magnetic resonance imaging. After excision, tumors were analysed histologically (Haematoxylin/Eosin, SM).

Results: Both, TD50 and TCD50 values are low for the five GBM models. One of four investigated models showed no signs of orthotopic tumor growth. Two models grew within 30-60 days to end size but the histological phenotype showed weak analogy to GBM patients. Stem cell marker heterogeneity was high between the models and also differed between the orthotopic and heterotopic transplantation site (e.g. Nestin positivity in U-87 MG ortho: 100%, hetero: ~80%).

Conclusion: The low TD50 values indicate high amounts of cancer initiating cells. However, the surprisingly low TCD50 values are in contrast to the remarkable radioresistance of GBM in patients. Additionally, no investigated model shows a GBM-like histology after orthotopic transplantation. Although xenograft models from established cell lines of other entities very closely mirror the clinical situation, this remains questionable for GBM.

  • Lecture (Conference)
    19th Annual Meeting of the Society for Biological Radiation Research - GBS, 26.-28.09.2016, Erlangen, Deutschland

Publ.-Id: 23769

Experimental study of centrifugal pumps under gas entrainment conditions

Schäfer, T.; Neumann, M.; Bieberle, A.; Hampel, U.

The effects of gas entrainment in centrifugal pumps have been experimentally investigated. Depending on different gas entrainment conditions, the impact on the hydraulic power of the pump has been analyzed and the influence of the pump installation position has been disclosed. Additionally, high-resolution gamma-ray computed tomography (HireCT), operated in time-averaged rotation-synchronized scanning mode, has been used to resolve and quantify the local gas/liquid phase fraction distribution inside the operating pump impeller. Based on these quantitative tomographic measurements, gas holdup profiles along selected streamlines have been calculated and gas accumulation inside the impeller chambers has been visualized.

Keywords: centrifugal pump; gas entrainment; two-phase flow; gas holdup; gamma-ray computed tomography

  • Lecture (Conference)
    47th Annual Meeting on Nuclear Technology (AMNT47), 10.-12.05.2016, Hamburg, Deutschland
  • Contribution to proceedings
    47th Annual Meeting on Nuclear Technology (AMNT47), 10.-12.05.2016, Hamburg, Deutschland
    Proceedings of 47th Annual Meeting on Nuclear Technology (AMNT47)

Publ.-Id: 23768

Advanced imaging techniques for multiphase flow analysis in industrial and scientific applications

Schäfer, T.

survey lecture on recent imaging techniques developed at HZDR focused on industrial and scientific applications

Keywords: process tomography; gamma-ray CT; ultrafast X-ray Ct; wire mesh sensor; process microscope

  • Lecture (others)
    Strategiegespräch Fa. Bitzer, 24.02.2016, Schkeuditz, Deutschland

Publ.-Id: 23767

Large magnetoresistance of insulating silicon films with superconducting nanoprecipitates

Heera, V.; Fiedler, J.; Skorupa, W.

We report on large negative and positive magnetoresistance in inhomogeneous, insulating Si:Ga films below a critical temperature of about 7 K. The magnetoresistance effect exceeds 300% at temperatures below 3Kand fields of 8T. The comparison of the transport properties of superconducting samples with that of insulating ones reveals that the large magnetoresistance is associated with the appearance of local superconductivity. A simple phenomenological model based on localized Cooper pairs and hopping quasiparticles is able to describe the temperature and magnetic field dependence of the sheet resistance of such films.

Keywords: insulating silicon films; superconducting nanoprecipitates; Ga doping; low temperature magnetoresistance; transport model

Publ.-Id: 23765

Carbon nanotubes in low molar mass liquid crystals

Schymura, S.; Park, J. H.; Dierking, I.; Scalia, G.

Carbon nanotubes constitute a highly anisotropic form of carbon with outstanding mechanical, thermal end electrical properties. Their dispersion and organization are important but challenging issues and this chapter describes the advantages of using thermotropic liquid crystals as host for nanotube dispersion and ordering.

Keywords: Kohlenstoff-Nanoröhrchen/ carbon nanotube; Flüssigkristall/ liquid crystal

  • Book chapter
    Lagerwall, Jan P.F., Scalia, Giusy: Liquid Crystals with Nano and Microparticles, London: World Scientific, 2016, 603-630
    DOI: 10.1142/9789814619264_0017

Publ.-Id: 23764

Bipolar resistive switching in YMnO3/Nb:SrTiO3 pn-heterojunctions

Bogusz, A.; Bürger, D.; Skorupa, I.; Schmidt, O. G.; Schmidt, H.

Resistively switching oxides are promising materials for use in electronic applications such as nonvolatile memories, logic gates, and artificial synapses. This work presents the bipolar resistive switching (BRS) in YMnO3/Nb:SrTiO3 pn-heterojunctions. A thermally driven electroforming process is required prior to the observed BRS. Results indicate that the BRS in YMnO3/Nb:SrTiO3 originates from the combined effects of charge trapping and detrapping processes along with the electro-migration of charged point defects in the depletion layer of the pn-heterojunction. It is shown that the built-in voltage of the pn-heterojunctions can be tuned by the oxygen partial pressure during growth of the YMnO3 thin film and impacts the working parameters of the resistively switching cell. This study provides a guideline for material engineering of bipolar resistive switches based on pn-heterojunctions.

Keywords: YMnO₃; Nb:SrTiO₃; bipolar resistive switching; pn-heterojunction; forward current; reverse current

Publ.-Id: 23763

Thomson scattering measurement of a collimated plasma jet generated by a high-power laser system

Ishikawa, T.; Sakawa, Y.; Morita, T.; Yamaura, Y.; Kuramitsu, Y.; Moritak, T.; Sano, T.; Shimoda, R.; Tomita, K.; Uchino, K.; Matsukiyo, S.; Mizuta, A.; Ohnishi, N.; Crowston, R.; Woolsey, N.; Doyle, H.; Gregori, G.; Koenig, M.; Michaut, C.; Pelka, A.; Yuan, D.; Li, Y.; Zhang, K.; Zhong, J.; Wang, F.; Takabe, H.

We present first measurements of spectrally resolved x-rays scattered from cryogenic hydrogen jets in the single photon counting limit. The 120 Hz capabilities of the LCLS, together with a novel hydrogen jet design, allow for the ability to record a near background free spectrum. Such high-dynamic-range x-ray scattering measurements enable a platform to study ultra-fast, laser-driven, heating dynamics of hydrogen plasmas. This measurement has been achieved using two Highly Annealed Pyrolytic Graphite (HAPG) crystal spectrometers to spectrally resolve 5.5 keV x-rays elastically and inelastically scattered from cryogenic hydrogen and focused on to Cornell-SLAC Pixel Array Detectors (CSPAD).

Keywords: x-ray scattering; x-ray lasers; hydrogen

Publ.-Id: 23762

The peculiar chemistry of the nuclear fuel-sodium coolant interaction

Smith, A. L.; Raison, P. E.; Y. Colle, J.; Colineau, E.; Griveau, J.-C.; Hen, A.; Beneš, O.; Guéneau, C.; Martin, P.; Prieur, D.; Martel, L.; Magnani, N.; Caciuffo, R.; Sanchez, J. P.; Charpentier, T.; Scheinost, A. C.; Hennig, C.; Kvashnina, K.; Suard, E.; Wallez, G.; Cheetham, A. K.; Konings, R. J. M.

In the event of a clad breach in Sodium-cooled Fast Reactors (SFRs), the metallic sodium coolant will enter the pin and react with the (U, Pu, Np)O2 fuel. The reaction products are numerous, but there is still little knowledge of their structural and thermodynamic properties. Under the oxygen potential conditions of the reactor, pentavalent Na3U1-xPuxO4 is expected to form, but its structure was the subject of controversy until now. This compound was shown in the 1980s to be of lower density and lower thermal conductivity than the fuel, leading to local swelling and creation of hot spots. Such a situation can induce further cladding failure and result in a contamination of the primary coolant with highly radioactive fission products.

In this work, we have revisited the crystal structure of the Na3MO4 (M=U,Np,Pu) reaction product. Surprisingly, the structure of the sodium uranate differs from the one observed with neptunium and plutonium. In addition, this phase can accommodate excess sodium on the uranium site, with subsequent charge compensation from U(V) to U(VI), which was not previously foreseen. By contrast, the sodium neptunate and plutonate remain pentavalent.

Temperature and oxygen potential are the two fundamental parameters that control the chemistry of the interaction. Assessing the margin to the safe operation of SFRs requires a thorough knowledge of the actinide cation valence state in the reaction products, and a complete thermodynamic description of the system. The valence state was determined in the Na-M-O (M=U,Np,Pu) ternary phases using XANES and Mössbauer spectroscopy, covering a wide range of oxidation states, namely (IV) to (VII). Coupling experimental thermodynamic investigations with thermodynamic modelling assessments using the CALPHAD method, we have calculated the phase equilibria in the Na-U-O system, and derived the oxygen potential threshold required within the fuel (and sodium coolant) to form the sodium uranate ternary phases.

Keywords: Sodium-cooled nuclear reactor; safety; uranium; sodium uranate; EXAFS; XANES; Moessbauer

  • Invited lecture (Conferences)
    NuMat2016: The Nuclear Materials Conference, 07.-10.11.2016, Montpellier, France

Publ.-Id: 23761

Polymer and cluster chemistry of tetravalent cerium (Ce(IV)) in aqueous solutions

Ikeda-Ohno, A.

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

Keywords: f-elements; hydrolysis; cerium; tetravalent; characterisation; X-ray; polymer; cluster

  • Invited lecture (Conferences)
    UMR Internal Colloquium, 25.07.2016, UMR, Université de Lille, France

Publ.-Id: 23760

Viren als Nützlinge - Biologie hilft beim Recycling

Lederer, F.

Populärwissenschaftlicher Beitrag unter Vorstellung der Phage Surface Display Methode und aktuellen Forschungsergebnissen im MinePep Projekt

Keywords: Phage surface display; Peptide; Seltene Erden; Lanthanphosphat

  • Lecture (others)
    Tag des offenen Labors am HZDR, 28.05.2016, Dresden, Deutschland

Publ.-Id: 23759

Fluid Dynamics in a Bubble Column: New Experiments and Simulations

Rzehak, R.; Krauß, M.; Kováts, P.; Zähringer, K.

Bubble columns are a common type of multiphase reactors used in many chemical engineering applications. Optimization and scale-up of bubble column processes is a complex task that can greatly benefit from multiphase CFD simulations. Calculations on industrial scales become feasible by the Euler-Euler two-fluid model, but suitable closure relations describing interfacial exchange processes are needed for practical application. Concerning pure fluid dynamics of dispersed gas-liquid multiphase flow an ongoing effort has led to a validated set of closures that is applicable under a rather broad range of conditions. The availability of new experimental data with large spatial and temporal resolution and high accuracy for a comprehensive set of observables and a range of different conditions provides the opportunity for further testing of this model. In this way the reliability of the obtained predictions is continually increased.

Keywords: bubble-columns; CFD simulation; Euler Euler two fluid model; shadowgraphy; PIV; model validation


Publ.-Id: 23757

Structural and kinetic considerations for the application of the traceless Staudinger ligation to future 18F radiolabeling using XRD and 19F-NMR

Köckerling, M.; Mamat, C.

A 4-fluorobenzoate-functionalized phosphane was synthesized and reacted with different azides using the traceless Staudinger ligation as a representative sample reaction for future radiolabeling purposes with short-lived radionuclides like fluorine-18. For this purpose, the reaction rate was evaluated at different temperatures. The effect of starting material concentrations and the influence of the steric effect coming from the applied azides were investigated. 19F NMR was used to determine the reaction half-live (τ1/2) and the reaction rate constant (kobs) of this ligation under mild reaction conditions in a water–acetonitrile mixture. Furthermore, the phosphane key compound 1 (orthorhombic, space group Pna21, a = 18.6363(9), b = 8.3589(4), c = 18.5480(9) Å, V = 2889.4(2) Å3, Z = 8, Dobs = 1.277 g/cm3), which acts as starting material for all subsequent syntheses, and the fluorine-containing phosphane 3 (monoclinic, space group P21/c, a = 8.321(2), b = 16.160(4), c = 14.940(4) Å, β = 99.51(1)°, V = 1981.4(8) Å3, Z = 4, Dobs = 1.342 g/cm3) were analyzed by single-crystal XRD.

Keywords: Click; bioorthogonal; building blocks; kinetics


Publ.-Id: 23756

Statistical Analysis of the Early Phase of SBO Accident for PWR

Kozmenkov, Y.; Jobst, M.; Kliem, S.; Schaefer, F.; Wilhelm, P.

A statistical approach is used to analyse the early phase of station blackout accident for generic German PWR with the best estimate system code ATHLET-CD as a computation tool. The analysis is mainly focused on the timescale uncertainties of the accident events which can be detected at the plant. The developed input deck allows variations of all input uncertainty parameters relevant to the case. The list of identified and quantified input uncertainties includes 30 parameters related to the simulated physical phenomena/processes. Time uncertainties of main events as well as the major contributors to these uncertainties are defined. A linear regression analysis is used for predicting times of future events from detected times of occurred/past events. The presented statistical approach could be helpful for assessing and improving existing or elaborating additional emergency operating procedures aimed to prevent severe damage of reactor core.

Keywords: Pressurized water reactor; best estimate simulation; station blackout; accident management measures; statistical approach; timescale uncertainties of events; sensitivity analysis; linear regression; prediction intervals

Publ.-Id: 23754

Uranium contaminated drinking water linked to leukaemia – revisiting a case study from South Africa taking alternative exposure pathways into account

Winde, F.; Erasmus, E.; Geipel, G.

The paper presents results of a follow-up to an earlier study which established a geospatial link between naturally elevated uranium (U) levels in borehole water and haematological abnormalities in local residents serving as a proxy for leukaemia prevalent in the area. While the original study focussed on drinking water only, this paper also explores alternative exposure pathways including the inhalation of dust and the food chain.
U-levels in grass and tissue of sheep generally reflect U-levels in nearby borehole water and exceed background concentrations by 20 to nearly 500 times. U-levels in sheep tissue increase with age of the animal. Wool showed the highest U-concentration followed by other non-consumable tissue such as hooves, teeth and bones. Lower levels occur in edible parts such as meat and inner organs. The U-deposition rate in wool is several orders of magnitudes higher than in bone as a known target organ. Wool is an easy-to-sample noninvasive bioindicator for U-levels in meat. Depending on the original water content, dried samples show up to 5 times higher U-levels than identical fresh material.
Contaminated drinking water is the main exposure pathway for farm residents resulting in U-uptake rates exceeding the WHO’s tolerable daily intake (TDI) limit by up to 900%. This is somewhat mitigated by the fact that U-speciation is dominated by a neutral calcium-uranyl-carbonate complex of relatively low toxicity. Commercially available household filters are able to significantly reduce U-levels in well water and are thus recommended as a short-term intervention. Based on average consumption rates sheep meat, as local staple food, accounts for 34% of the TDI for U. Indoor levels of radon should be monitored, too, since it is linked to both, U and leukaemia. With elevated U-levels being present in other geological formations across South Africa boreholes in these areas should be surveyed.

Keywords: uranium; groundwater; sheep; leukaemia; food chain

Publ.-Id: 23753

Modelling of Oxide Dispersion Strengthened Fe alloys with Kinetic Monte Carlo simulation supported by DFT calculations

Liedke, B.; Posselt, M.; Murali, D.; Claisse, A.; Olsson, P.

Oxide Dispersion Strengthened (ODS) steels are considered as one of the most promising candidates for structural materials in next generation nuclear fusion reactors and future nuclear fission reactors [1]. The ODS materials consist of a ferritic or ferritic/martensitic Fe-Cr matrix filled with yttria-based oxide particles and is fabricated during mechanical alloying and hot consolidation processes. It is well known that their extraordinary properties such as high-temperature creep strength as well as high dose ion/neutron irradiation resistance are due to formation of small Y-Ti-O clusters with a size of few nanometers. Besides their significant effect on reduction of dislocations and grain-boundaries mobility, the nanoclusters also act as traps for point defects like vacancies, interstitials and helium, which may be typically generated in a nuclear reactor. It is still under debate what the formation mechanisms of the nanoclusters are and why they prove such high temperature and radiation damage stability.
Experimental methods typically applied to investigate the issues stated above cannot fully reflect the atomic-scale of the nanoclusters, as well as the mechanisms related to their formation, evolution and destruction upon radiation damage. Therefore, atomistic computer experiments can significantly contribute to a general understanding.
In this work, kinetic Monte Carlo (KMC) technique is applied to study evolution of Y-Ti-O nanoclusters in a bcc-Fe and FeCr matrix. Starting from a uniform distribution of O, Y, Ti atoms in the matrix at first a stationary state is produced by high temperature annealing. Such a state is characterized by a certain population of Y-Ti-O nanoclusters. Then vacancies and interstitials are introduced in order to simulate ion and neutron irradiation taking into account realistic conditions, and the evolution of the nanostructure is studied. The parameters for the atomic interactions used in KMC were obtained recently by first-principle Density-Functional-Theory calculations and applied in Metropolis Monte Carlo simulations on energetics, structure and composition of the Y-Ti-O nanoclusters [2].
1. G. R. Odette, M. J. Alinger, B. D. Wirth, Annu. Rev. Mater. Res. 38, 471 (2008)
2. M. Posselt, D. Murali, B. K. Panigrahi, Modelling Simul. Mater. Sci. Eng. 22, 085003 (2014)

Keywords: ODS alloys; DFT; KMC; atomistic modelling; radiation damage

  • Lecture (Conference)
    3rd ODISSEUS Workshop, 19.-20.04.2016, HZDR, Germany

Publ.-Id: 23752

Investigations on viscous couplings using time-averaged rotation-synchronized gamma-ray computed tomography

Bieberle, A.; Schlottke, J.; Kühnel, W.; Hampel, U.

For controlled transfer of high torques in devices, like engine fans and/or four wheel drives, viscous couplings are frequently used. Torque transfer is realized in viscous couplings by a working fluid, mainly responsible for the transfer quality, i.e. efficiency and operating range as well as stability. Unfortunately, investigations at rapidly rotating couplings is challenging since they consist of dense material, e.g. aluminum, have no optical access and the work area is composed of ring channels being significantly smaller than on millimeter. Thus, the high-resolution computed tomography measurement system (HireCT) is used for contactless liquid investigations in an industrial viscous coupling operated under various authentic operation scenarios. Despite the limited spatial resolution of approximately 2 mm and a measuring interval of approximately 900 s sharp liquid phase distributions could be provided in both primary disc and housing side of the coupling from a single CT scan. Here, the so called time-averaged rotation synchronized CT scanning mode is applied, where the acquired projection data stream are synchronized and averaged corresponding to the rotational position of the couplings’ parts. Therefore, zero crossing signals from the primary and secondary side are simultaneously acquired. The reconstructed data comprises the cross-section of the coupling and liquid distribution correspondingly.

Keywords: gamma-ray computed tomography; viscous coupling

  • Contribution to proceedings
    8th World Congress On Industrial Process Tomography, 26.-29.09.2016, Iguassu Falls, Brasilien
  • Lecture (Conference)
    8th World Congress On Industrial Process Tomography, 26.-29.09.2016, Iguassu Falls, Brasilien

Publ.-Id: 23751

Switching CAR T cells on and off: A novel modular platform for retargeting of T cells to AML blasts

Cartellieri, M.; Feldmann, A.; Koristka, S.; Arndt, C.; Loff, S.; Ehninger, A.; von Bonin, M.; Bejestani, E. P.; Ehninger, G.; Bachmann, M. P.

The adoptive transfer of CD19-specific chimeric antigen receptor engineered T cells (CAR T cells) resulted in encouraging clinical trials in indolent B cell malignancies.
However, they also show the limitations of this fascinating technology: CAR T cells can lead to even life-threatening off-tumor, on-target side effects if CAR T cells cross-react with healthy tissues.
Here, we describe a novel modular universal CAR platform technology termed UniCAR, which reduces the risk of on-target side effects by a rapid and reversible control of CAR T cell reactivity. The UniCAR system consists of two components: (i) a CAR for an inert manipulation of T cells, and (ii) specific targeting modules (TMs) for redirecting UniCAR T cells in an individualized time- and target-dependent manner. UniCAR T cells can be armed against different tumor targets simply by replacement of the respective TM for (i) targeting more than one antigen simultaneously or subsequently to enhance efficacy, and (ii) reducing the risk for development of antigen-loss tumor variants under treatment. Here we provide “proof of concept” for retargeting of UniCAR T cells to CD33 and/or CD123 positive AML Blasts in vitro and in vivo.

Keywords: adoptive T cell therapy; acute myeloid leukemia; CD33; CD123; chimeric antigen receptor; targeted immunotherapy

Publ.-Id: 23750

Recent progress at the LUNA 400 kV underground accelerator

Bemmerer, D.

The experimental study of radiative capture reactions directly at the energies of relevance for astrophysics requires long experiments with low counting rate. This type of study has greatly bene ted in recent years from the ultra-low gamma-ray background level underground, in the INFN Gran Sasso laboratory, Italy. There, the LUNA 400kV accelerator has enabled a rich research program. The 2 H(alpha,gamma)6 Li reaction has been studied for the first time in the Big Bang energy region. Very recently, three resonances have been observed for the first time in the 22 Ne(p,gamma)23 Na reaction, directly at energies relevant for the hot- bottom burning process in asymptotic giant branch stars. Studies on other hydrogen burning reactions on 17,18O and 23Na are ongoing, with promising preliminary results. The group report will show an overview of recent progress and discuss future perspectives, in particular on the future LUNA experiment on the Big Bang 2H(p,gamma)3He reaction.

Keywords: Nuclear Astrophysics underground LUNA Big Bang nucleosynthesis hydrogen burning NeNa cycle

  • Lecture (Conference)
    Frühjahrstagung 2016 der Deutschen Physikalischen Gesellschaft, 14.-18.03.2016, Darmstadt, Deutschland

Publ.-Id: 23749

Felsenkeller shallow-underground 5 MV accelerator for nuclear astrophysics, status and outlook

Bemmerer, D.

Felsenkeller shallow-underground 5 MV accelerator for nuclear astrophysics, status and outlook is discussed as of February 2016, with a view also on potential European collaborations.

Keywords: Nuclear Astrophysics Underground Nuclear Astrophysics Helium burning Solar fusion Felsenkeller

  • Invited lecture (Conferences)
    2nd Workshop on Nuclear Astrophysics at the Canfranc Underground Laboratory, 29.02.-01.03.2016, Canfranc Estacion, Spanien
  • Lecture (Conference)
    German-Japanese minisymposium on hot topics in particle and nuclear physics, 12.05.2016, Dresden, Deutschland

Publ.-Id: 23748

Progress of the Felsenkeller shallow-underground 5 MV accelerator for nuclear astrophysics early 2016

Bemmerer, D.

The progress of the Felsenkeller shallow-underground 5 MV accelerator for nuclear astrophysics is reviewed, as of early 2016

Keywords: Felsenkeller; Nuclear Astrophysics Underground; nuclear astrophysics low-background; measurements solar fusion helium burning

  • Lecture (Conference)
    NAVI Physics Days, 18.01.2016, Darmstadt, Deutschland

Publ.-Id: 23747

Towards SiPM readout for the NeuLAND large plastic scintillator

Bemmerer, D.

Towards SiPM readout for the NeuLAND large plastic scintillator

Keywords: R3B NeuLAND neutron time of flight picosecond timing ELBE scintillator silicon photomultiplier

  • Invited lecture (Conferences)
    Fraunhofer IMS workshop on CMOS SiPM technology, 26.11.2015, Duisburg, Deutschland

Publ.-Id: 23746

The copper spoil heap Knappenberg, Austria, as a model for metal habitats - Vegetation, substrate and contamination

Adlassnig, W.; Weiss, Y. S.; Sassmann, S.; Steinhauser, G.; Hofhansl, F.; Baumann, N.; Lichtscheidl, I. K.; Lang, I.

Historic mining in the Eastern Alps has left us with a legacy of numerous spoil heaps hosting specific, metal tolerant vegetation. Such habitats are characterized by elevated concentrations of toxic elements but also by high irradiation, a poorly developed substrate or extreme pH of the soil. This study investigates the distribution of vascular plants, mosses and lichens on a copper spoil heap on the ore bearing Knappenberg formed by Prebichl Layers and Werfener Schist in Lower Austria. It serves as a model for discriminating between various ecological traits and their effects on vegetation.Five distinct clusters were distinguished: (1) The bare, metal rich Central Spoil Heap was only colonised by highly resistant specialists. (2) The Northern and (3) Southern Peripheries contained less copper; the contrasting vegetation was best explained by the different microclimate. (4) A forest over acidic bedrock hosted a vegetation overlapping with the periphery of the spoil heap. (5) A forest over calcareous bedrock was similar to the spoil heap with regard to pH and humus content but hosted a vegetation differing strongly to all other habitats.Among the multiple toxic elements at the spoil heap, only Cu seems to exert a crucial influence on the vegetation pattern. Besides metal concentrations, irradiation, humidity, humus, pH and grain size distribution are important for the establishment of a metal tolerant vegetation. The difference between the species poor Northern and the diverse Southern Periphery can be explained by the microclimate rather than by the substrate. All plant species penetrating from the forest into the periphery of the spoil heap originate from the acidic but not from the calcareous bedrock.

Keywords: Copper pollution; Metal tolerance; Metallophytes; Mine residues; Ore minerals

Publ.-Id: 23745

Dual β1 integrin and JNK inhibition decreases radiochemoresistance and invasion of Glioblastoma stem-like cells

Vehlow, A.; Klapproth, E.; Storch, K.; Temme, A.; Krause, M.; Cordes, N.

Background: The poor prognosis associated with Glioblastoma multiforme (GBM) largely arises from the radiochemotherapy resistance of GBM cells and their aggressive infiltration and destruction of the healthy brain. β1 integrin and c-Jun N terminal kinase (JNK) are potential therapeutic targets in GBM owing to their regulation of radioprotective pro-survival and pro-invasive signaling hubs in Glioblastoma stem-like cells and the tumor bulk. Here, we evaluate the effect of simultaneous targeting of β1 integrin and JNK in combination with radiochemotherapy on clonogenic survival and invasion of patient-derived GBM stem-like cells and GBM cell lines in vitro and in an orthotopic GBM mouse model.
Methodology: The sphere forming capacity, clonogenic survival and invasion of patient-derived GBM stem-like cells (GS-8, DK41, DK42) and Glioblastoma cell lines (HT7606, T4, U343-MG) was analyzed upon irradiation (0-6 Gy X-ray), chemotherapy (Temozolomide, TMZ, IC10) or a combination of both. Simultaneously, β1 integrin was inhibited by the specific antibody AIIB2 and JNK activation was blocked by pharmacologic inhibition using SP600125 (IC10, IC50). In addition, tumor growth and survival of mice with orthotopic GBM were assessed upon dual β1 integrin/JNK inhibition combined with radiochemotherapy. Changes in signal transduction mechanisms were examined by means of Western blotting and broad-spectrum phosphoproteome analysis. Cell cycle changes were evaluated by FACS and alterations in DNA repair mechanisms were quantified by immunofluorescent staining of DNA double strand breaks.
Results: Co-inhibition of β1 integrin and JNK strikingly induces radiochemosensitization and blocks invasion of patient-derived GBM stem-like cells and GBM cell lines. In line, the combination of radiochemotherapy plus dual targeting significantly delays tumor growth resulting in prolonged median survival of mice bearing orthotopic GBM. Mechanistically, phosphoproteome and functional analysis reveals that the radiochemosensitizing potential of the β1 integrin/JNK co-inhibition is caused by a prolonged G2/M arrest upon irradiation due to a defective repair of DNA double strand breaks.
Conclusion: Here, we suggest co-targeting of β1 integrin and JNK as a promising approach to overcome radiochemoresistance of GBM in-vitro and in-vivo. Intriguingly, sphere forming capacity and invasion of GBM stem-like cell populations as well as clonogenicity and invasion of established GBM cell lines could be substantially reduced upon dual targeting simultaneously to conventional radiochemotherapy. Currently, ongoing studies are aimed at identifying possible bypass mechanisms.

  • Lecture (Conference)
    GBS-Jahrestagung, 26.-28.09.2016, Erlangen, Deutschland

Publ.-Id: 23744

Ultra-sensitive γ-ray spectroscopy set-up for investigating primordial lithium problem

Gervino, G.; Gustavino, C.; Trezzi, D.; Aliotta, M.; Anders, M.; Boeltzig, A.; Bemmerer, D.; Best, A.; Broggini, C.; Bruno, C.; Caciolli, A.; Cavanna, F.; Corvisiero, P.; Davinson, T.; Depalo, R.; Dileva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Guglielmetti, A.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Prati, P.; Scott, D. A.; Straniero, O.; Szücs, T.

To precisely determine BBN 6Li production, the cross-section of the nuclear reaction 2H(α, γ)6Li must be directly measured within the astrophysical energy range of 30–400 keV. This measure requires an ultra- low γ-ray background in the experimental set-up. We have realized the conditions matching these very strict requirements at LUNA, the deep underground accelerator laboratory active in the INFN Gran Sasso National Laboratory (LNGS), Italy: the γ-ray spectrometer background has been reduced down to reach unmatched low levels, comparable to the good ones experienced in dedicated off-line underground ultra low γ counting rate. We present and discuss the γ-ray background reduction reached in the HpGe spectrometer, where most of the remaining γ-ray background seen in the spectra are coming from the energetic deuterons scattered in the gas target by the α beam. Thanks to the low neutron environmental background at LUNA, the effect of this weak flux of 2–3 MeV neutrons on HpGe detectors has been studied in details and the results are presented and discussed.

Keywords: Gamma spectroscopy Underground Physics Lithium problem

Publ.-Id: 23743

Coordination chemistry of tetravalent actinides

März, J.

Against the background of nuclear waste disposal, the interactions between actinides and organic complexation agents were studied. Actinides show a variety of different oxidation states, but in case of a deep disposal, the tetravalent species can be predominant in the environment. We synthesised An(IV) chlorides and iodides as actinide starting materials and studied organic ligand systems ranging from pure oxygen to pure nitrogen donors. Some first isostructural actinide complexes were determined by single crystal X-ray diffraction and spectroscopic techniques showing the typical shortening of the donor-acinide bonds across the actinide series.

Keywords: Tetravalent actinides; Coordination chemistry

  • Invited lecture (Conferences)
    8th International Workshop on „Coordination Chemistry of Metals with Medical Relevance and Supramolecular Building Blocks“, 26.-27.05.2016, Berlin, Deutschland

Publ.-Id: 23742

Cosmic Background Measurements at a Proposed Underground Laboratory by the REGARD Muontomograph

Oláh, L.; Surányi, G.; Barnaföldi, G. G.; Bemmerer, D.; Hamar, G.; Melegh, H. G.; Varga, D.

A portable cosmic particle tracking detector has been developed by the REGARD group with angular resolution of 10 mrad. The Close Cathode Chamber-based tracking system is optimized for environmental and geophysical applications with its weight of 15 kg and size of 51 cm × 43 cm × 32 cm. Our aim was to determine the cosmic background at the site of the proposed accelerator and experimental facilities at an approximate 50 meter depth in Felsenkeller, Dresden, Germany. Here, we present our high-precision muon flux measurements, which have been performed during 44 days in one of the tunnels. Angular acceptance of our mapping covered full 2π solid angle of the upper hemisphere. The maximum flux value is found to be below 2.5 m^{-2}sr^{-1}s^{-1}.

Keywords: Felsenkeller Nuclear Astrophysics Muon flux

Publ.-Id: 23741

Nuclear astrophysics with radioactive ions at FAIR

Reifarth, R.; Altstadt, S.; Göbel, K.; Heftrich, T.; Heil, M.; Koloczek, A.; Langer, C.; Plag, R.; Pohl, M.; Weigand, K. S. M.; Adachi, T.; Aksouh, F.; Al-Khalili, J.; Algarawi, M.; Alghamdi, S.; Alkhazov, G.; Alkhomashi, N.; Alvarez-Pol, H.; Alvarez-Rodriguez, R.; Andreev, V.; Andrei, B.; Atar, L.; Aumann, T.; Avdeichikov, V.; Bacri, C.; Bagchi, S.; Barbieri, C.; Beceiro, S.; Beck, C.; Beinrucker, C.; Belier, G.; Bemmerer, D.; Bendel, M.; Benlliure, J.; Benzoni, G.; Berjillos, R.; Bertini, D.; Bertulani, C.; Bishop, S.; Blasi, N.; Bloch, T.; Blumenfeld, Y.; Bonaccorso, A.; Boretzky, K.; Botvina, A.; Boudard, A.; Boutachkov, P.; Boztosun, I.; Bracco, A.; Brambilla, S.; Briz Monago, J.; Caamano, M.; Caesar, C.; Camera, F.; Casarejos, E.; Catford, W.; Cederkall, J.; Cederwall, B.; Chartier, M.; Chatillon, A.; Cherciu, M.; Chulkov, L.; Coleman-Smith, P.; Cortina-Gil, D.; Crespi, F.; Crespo, R.; Cresswell, J.; Csatlós, M.; Déchery, F.; Davids, B.; Davinson, T.; Derya, V.; Detistov, P.; Diaz Fernandez, P.; Dijulio, D.; Dmitry, S.; Doré, D.; Nas, J. D.; Dupont, E.; Egelhof, P.; Egorova, I.; Elekes, Z.; Enders, J.; Endres, J.; Ershov, S.; Ershova, O.; Fernandez-Dominguez, B.; Fetisov, A.; Fiori, E.; Fomichev, A.; Fonseca, M.; Fraile, L.; Freer, M.; Friese, J.; Borge, M. G.; Galaviz Redondo, D.; Gannon, S.; Garg, U.; Gasparic, I.; Gasques, L.; Gastineau, B.; Geissel, H.; Gernhäuser, R.; Ghosh, T.; Gilbert, M.; Glorius, J.; Golubev, P.; Gorshkov, A.; Gourishetty, A.; Grigorenko, L.; Gulyas, J.; Haiduc, M.; Hammache, F.; Harakeh, M.; Hass, M.; Heine, M.; Hennig, A.; Henriques, A.; Herzberg, R.; Holl, M.; Ignatov, A.; Ignatyuk, A.; Ilieva, S.; Ivanov, M.; Iwasa, N.; Jakobsson, B.; Johansson, H.; Jonson, B.; Joshi, P.; Junghans, A.; Jurado, B.; Körner, G.; Kalantar, N.; Kanungo, R.; Kelic-Heil, A.; Kezzar, K.; Khan, E.; Khanzadeev, A.; Kiselev, O.; Kogimtzis, M.; Körper, D.; Kräckmann, S.; Kröll, T.; Krücken, R.; Krasznahorkay, A.; Kratz, J.; Kresan, D.; Krings, T.; Krumbholz, A.; Krupko, S.; Kulessa, R.; Kumar, S.; Kurz, N.; Kuzmin, E.; Labiche, M.; Langanke, K.; Lazarus, I.; Le Bleis, T.; Lederer, C.; Lemasson, A.; Lemmon, R.; Liberati, V.; Litvinov, Y.; Löher, B.; Lopez Herraiz, J.; Münzenberg, G.; Machado, J.; Maev, E.; Mahata, K.; Mancusi, D.; Marganiec, J.; Martinez Perez, M.; Marusov, V.; Mengoni, D.; Million, B.; Morcelle, V.; Moreno, O.; Movsesyan, A.; Nacher, E.; Najafi, M.; Nakamura, T.; Naqvi, F.; Nikolski, E.; Nilsson, T.; Nociforo, C.; Nolan, P.; Novatsky, B.; Nyman, G.; Ornelas, A.; Palit, R.; Pandit, S.; Panin, V.; Paradela, C.; Parkar, V.; Paschalis, S.; Paw\Lowski, P.; Perea, A.; Pereira, J.; Petrache, C.; Petri, M.; Pickstone, S.; Pietralla, N.; Pietri, S.; Pivovarov, Y.; Potlog, P.; Prokofiev, A.; Rastrepina, G.; Rauscher, T.; Ribeiro, G.; Ricciardi, M.; Richter, A.; Rigollet, C.; Riisager, K.; Rios, A.; Ritter, C.; Rodríguez Frutos, T.; Rodriguez Vignote, J.; Röder, M.; Romig, C.; Rossi, D.; Roussel-Chomaz, P.; Rout, P.; Roy, S.; Söderström, P.; Saha Sarkar, M.; Sakuta, S.; Salsac, M.; Sampson, J.; Sanchez Del Rio Saez, J.; Sanchez Rosado, J.; Sanjari, S.; Sarriguren, P.; Sauerwein, A.; Savran, D.; Scheidenberger, C.; Scheit, H.; Schmidt, S.; Schmitt, C.; Schnorrenberger, L.; Schrock, P.; Schwengner, R.; Seddon, D.; Sherrill, B.; Shrivastava, A.; Sidorchuk, S.; Silva, J.; Simon, H.; Simpson, E.; Singh, P.; Slobodan, D.; Sohler, D.; Spieker, M.; Stach, D.; Stan, E.; Stanoiu, M.; Stepantsov, S.; Stevenson, P.; Strieder, F.; Stuhl, L.; Suda, T.; Sümmerer, K.; Streicher, B.; Taieb, J.; Takechi, M.; Tanihata, I.; Taylor, J.; Tengblad, O.; Ter-Akopian, G.; Terashima, S.; Teubig, P.; Thies, R.; Thoennessen, M.; Thomas, T.; Thornhill, J.; Thungstrom, G.; Timar, J.; Togano, Y.; Tomohiro, U.; Tornyi, T.; Tostevin, J.; Townsley, C.; Trautmann, W.; Trivedi, T.; Typel, S.; Uberseder, E.; Udias, J.; Uesaka, T.; Uvarov, L.; Vajta, Z.; Velho, P.; Vikhrov, V.; Volknandt, M.; Volkov, V.; von Neumann-Cosel, P.; von Schmid, M.; Wagner, A.; Wamers, F.; Weick, H.; Wells, D.; Westerberg, L.; Wieland, O.; Wiescher, M.; Wimmer, C.; Wimmer, K.; Winfield, J. S.; Winkel, M.; Woods, P.; Wyss, R.; Yakorev, D.; Yavor, M.; Zamora Cardona, J.; Zartova, I.; Zerguerras, T.; Zgura, I.; Zhdanov, A.; Zhukov, M.; Zieblinski, M.; Zilges, A.; Zuber, K.

The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.

Keywords: FAIR nuclear astrophysics radioactive ion beams

Publ.-Id: 23740

Primordial nucleosynthesis

Gustavino, C.; Anders, M.; Bemmerer, D.; Elekes, Z.; Trezzi, D.

Big Bang nucleosynthesis (BBN) describes the production of light nuclei in the early phases of the Universe. For this, precise knowledge of the cosmological parameters, such as the baryon density, as well as the cross section of the fusion reactions involved are needed. In general, the energies of interest for BBN are so low (E < 1 MeV) that nuclear cross section measurements are practically unfeasible at the Earth’s surface. As of today, LUNA (Laboratory for Underground Nuclear Astrophysics) has been the only facility in the world available to perform direct measurements of small cross section in a very low background radiation. Owing to the background suppression provided by about 1400 meters of rock at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, and to the high current offered by the LUNA accelerator, it has been possible to investigate cross sections at energies of interest for Big Bang nucleosynthesis using protons, 3He and alpha particles as projectiles. The main reaction studied in the past at LUNA is the 2H(4He,γ)6Li. Its cross section was measured directly, for the first time, in the BBN energy range. Other processes like 2H(p,γ)3He, 3He(2H,p)4He and 3He(4He,γ)7Be were also studied at LUNA, thus enabling to reduce the uncertainty on the overall reaction rate and consequently on the determination of primordial abundances. The improvements on BBN due to the LUNA experimental data will be discussed and a perspective of future measurements will be outlined.

Publ.-Id: 23739

Determination of the Neutron-Capture Rate of 17C for the R-process Nucleosynthesis

Heine, M.; Typel, S.; Wu, M.-R.; Adachi, T.; Aksyutina, Y.; Alcantara, J.; Altstadt, S.; Alvarez-Pol, H.; Ashwood, N.; Avdeichikov, T. A. V.; Barr, M.; Beceiro-Novo, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C. A.; Boretzky, K.; Borge, M. J. G.; Burgunder, G.; Caamano, M.; Caesar, C.; Casarejos, E.; Catford, W.; Cederkäll, J.; Chakraborty, S.; Chartier, M.; Chulkov, L. V.; Cortina-Gil, D.; Crespo, R.; Datta Pramanik, U.; Diaz Fernandez, P.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fraile, L. M.; Freer, M.; Freudenberger, M.; Fynbo, H. O. U.; Galaviz, D.; Geissel, H.; Gernhäuser, R.; Göbel, K.; Golubev, P.; Gonzalez Diaz, D.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heinz, A.; Henriques, A.; Holl, M.; Ickert, G.; Ignatov, A.; Jakobsson, B.; Johansson, H. T.; Jonson, B.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knöbel, R.; Kröll, T.; Krücken, R.; Kurcewicz, J.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lepyoshkina, O.; Lindberg, S.; Machado, J.; Marganiec, J.; Martínez-Pinedo, G.; Maroussov, V.; Mostazo, M.; Movsesyan, A.; Najafi, A.; Neff, T.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Perea, A.; Petri, M.; Pietri, S.; Plag, R.; Prochazka, A.; Rahaman, A.; Rastrepina, G.; Reifarth, R.; Ribeiro, G.; Ricciardi, M. V.; Rigollet, C.; Riisager, K.; Röder, M.; Rossi, D.; Sanchez Del Rio, J.; Savran, D.; Scheit, H.; Simon, H.; Sorlin (Ganil), O.; Stoica, V.; Streicher, B.; Taylor, J. T.; Tengblad, O.; Terashima, S.; Thies, R.; Togano, Y.; Uberseder, E.; van de Walle, J.; Velho, P.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Weigand, M.; Wheldon, C.; Wilson, G.; Wimmer, C.; Winfield, J. S.; Woods, P.; Yakorev, D.; Zhukov, M. V.; Zilges, A.; Zuber, K.

With the R3B-LAND setup at GSI we have measured exclusive relative-energy spectra of the Coulomb dissociation of 18C at a projectile energy around 425~AMeV on a lead target, which are needed to determine the radiative neutron-capture cross sections of 17C into the ground state of 18C. Those data have been used to constrain theoretical calculations for transitions populating excited states in 18C. This allowed to derive the astrophysical cross section σ∗nγ accounting for the thermal population of 17C target states in astrophysical scenarios. The experimentally verified capture rate is significantly lower than those of previously obtained Hauser-Feshbach estimations at temperatures T9≤1~GK. Network simulations with updated neutron-capture rates and hydrodynamics according to the neutrino-driven wind model as well as the neutron-star merger scenario reveal no pronounced influence of neutron capture of 17C on the production of second- and third-peak elements in contrast to earlier sensitivity studies.

Keywords: Coulomb dissociation; radiative neutron capture; nucleosynthesis; r-process


Publ.-Id: 23738

Absolute hydrogen depth profiling using the resonant 1H(15N,αγ)12C nuclear reaction

Reinhardt, T. P.; Akhmadaliev, S.; Bemmerer, D.; Stöckel, K.; Wagner, L.

Resonant nuclear reactions are a powerful tool for the determination of the amount and profile of hydrogen in thin layers of material. Usually, this tool requires the use of a standard of well-known composition. The present work, by contrast, deals with standard-less hydrogen depth profiling. This approach requires precise nuclear data, e.g. on the widely used 1H(15N,αγ)12C reaction, resonant at 6.4\,MeV 15N beam energy. Here, the strongly anisotropic angular distribution of the emitted γ-rays from this resonance has been re-measured, resolving a previous discrepancy. Coefficients of (0.38±0.04) and (0.80±0.04) have been deduced for the second and fourth order Legendre polynomials, respectively. In addition, the resonance strength has been re-evaluated to (25.0±1.5)\,eV, 10\% higher than previously reported. A simple working formula for the hydrogen concentration is given for cases with known γ-ray detection efficiency. Finally, the absolute approach is illustrated using two examples.

Keywords: Hydrogen storage; hydrogen depth profiling; Nuclear resonant reaction analysis


Publ.-Id: 23737

Magnetoresistive detection of single magnetic vortices

Ramasubramanian, L.; Fowley, C.; Kákay, A.; Aleksandrov, Y.; Matthes, P.; Lindner, J.; Fassbender, J.; Gemming, S.; Schulz, S.; Deac, A.

The fundamental oscillation mode of magnetic vortices in thin-film elements has recently been exploited in spin-torque-driven nano-oscillators [A. Wachowiak et al., Science (2002)]. The fundamental frequency is determined by the saturation magnetisation, as well as the geometrical confinement of the magnetisation e.g. the diameter and height of a magnetic disk. The objective of this study is to design magnetic discs, contact them with electrical leads and probe the dynamics of the vortex structures using magnetoresistive detection. By varying the thickness and dimensions of the disk, requirements for the magnetic vortex as a ground state will be determined. The electrical resistance of a single disc is expected to change based on the relative angle between the magnetisation direction and the applied current (the anisotropic magnetoresistance (AMR) effect) [S. Kasai et al, PRL 97, 107204 (2006)]. Using the AMR as a detection technique we will determine if electrical detection of dynamics is feasible in this geometry and its associated limits.

Keywords: magnetic vortex; AMR

  • Poster
    DPG Frühjahrstagung Regensburg 2016, 06.-11.03.2016, Regensburg, Germany

Publ.-Id: 23736

Membrane Lateral Pressure Controls Hydration and Water Mobility at the Copper-Binding Site of the P1B-type Copper ATPase CopA from Legionella Pneumophila

Fahmy, K.; Fischermeier, E.; Sayed, A.

P-type ATPases couple ATP hydrolysis to ion transport. We have reconstituted the copper-transporting P1B-type ATPase LpCopA from Legionella pneumophila into lipid nanodiscs in order to study the influence of membrane lateral pressure on the functionally relevant intra-membrane protein hydration at the ion-binding site. Using site-directed mutagenesis, the solvatochromic fluorophore BADAN was covalently linked to the cysteine residues at the conserved copper-binding CPC motif on transmembrane helix 4. The decomposition of the fluorescence spectra of labeled LpCopA in the micellar and the lipid-inserted state shows that membrane lateral pressure reduces hydration and water mobility in the environment of the more buried Cys-382 with a concomitant change of the local dielectric constant by −9. In contrast, the environment of Cys-384 which is located closer to the putative membrane surface, resembles a “hydrophobic gate” with low water mobility that is little affected by insertion into a bilayer (change of local dielectric constant by −3). The asymmetric hydration and water mobility around the CPC motif provides Cys-382 with a highly dynamic hydration. The data show that membrane lateral pressure may provide a restoring force in hydration / dehydration cycles around Cys-382 in the transmembrane domain during catalytic activity. The lower hydration and mobility in the Cys-384 environment, on the other hand, would favor the dehydration of copper and hinder its re-solvation from the intracellular side.

Keywords: fluorescence; BADAN; nanodisc

  • Poster
    Annual Meeting of the Biophysical Society, 27.02.-03.03.2016, Los Angeles, U S A

Publ.-Id: 23735

Radiative deexcitation of initially slow highly charged ions transmitted through graphene

Wilhelm, R. A.; Gruber, E.; Schwestka, J.; Heller, R.; Kozubek, R.; Hierzenberger, A.; Schleberger, M.; Facsko, S.; Aumayr, F.

The interaction of slow highly charged ions with solid surfaces is associated with many different phenomena. One of them is the formation of a hollow atom or ion already in front of the surface due to resonant electron transfer above the Coulomb barrier between the ion and the surface [1]. A hollow atom is a highly excited neutral particle, which will rapidly de- excite by either radiative or non-radiative processes [2,3].
Here we study the former process when Xenon and Argon ions with charge states up to Q=40 and Q=18, respectively, are transmitted through a freestanding single layer of graphene. Emitted x-rays are detected with a Bruker XFlash detector with an energy resolution of 140eV. Transmitted ions are also detected with an electrostatic analyzer, allowing charge exchange and energy loss measurements. Both ion and x-ray detection can be performed in coincidence in order to clearly distinguish between x-rays emitted from ions transmitted through graphene and ions impinging on the surrounding target holder (see Fig. 1).

  • Poster
    18th International Conference on Physics of Highly Charged Ions, 11.-16.09.2016, Kielce, Polen

Publ.-Id: 23734

Highly charged ion interaction with graphene

Wilhelm, R. A.; Gruber, E.; Smejkal, V.; Schwestka, J.; Kozubek, R.; Hierzenberger, A.; Schleberger, M.; Facsko, S.; Aumayr, F.

Studying ion-solid interaction has a long standing tradition both in fundamental research and for technological applications. The main parameter in this respect is the ion stopping force, i.e. the kinetic energy loss per unit length in a solid. The stopping force depends on the kinetic energy of the ions as well as on the degree of ionization [1]. The latter fact is usually disregarded, because after a few nanometers in a solid the ion accommodates an equilibrium charge state independent of it’s initial charge state. Stopping force in charge equilibrium is very well known.
Here we use slow (v ≪ v0) highly charged ions (Q Z) to study stopping force far from charge equilibrium and the charge equilibration dynamics [2,3]. Using novel two-dimensional materials as target material allows us to limit the ion trajectory in the solid with monolayer precision and thus study non-equilibrium effects.
The left side of fig. 1 shows schematically the experimental conditions with an ion beam transmitted under normal incidence through a freestanding single layer graphene sheet. The ion energy and charge state are measured with an electrostatic analyzer. A typical charge state distribution for Xe30+ ions at 40 keV (310 eV/amu) transmitted through graphene is also shown (right). Ions at this low velocity (0.1v0) are not fully neutralized. Hence, they still capture and stabilize about 20 electrons within the collision time of only 1-3 fs. Especially stabilization of the electrons is surprising, since the classical-over-barrier model for charge exchange [4] predicts the population of highly excited states with principal quantum numbers of n > 10 and a subsequent Auger electron cascade. Such a cascade would lead to the reemission of electrons and thus to a recharging of the ion. Present results show the need for a model beyond classical-over-barrier.
This ultrafast charge exchange process is accompanied by a kinetic energy loss of up to ∆E /E ≈ 10 %, which is about 1 order of magnitude larger than predicted by the SRIM code. In this contribution, recent results on charge exchange and energy loss of highly charged ion at low velocities in graphene will be presented. A qualitative description of the processes involved will be given.

  • Invited lecture (Conferences)
    12th European Conference on Atoms, Molecules and Photons (ECAMP), 05.-09.09.2016, Frankfurt a.M., Deutschland

Publ.-Id: 23733

Charge equilibration and energy loss of slow highly charged ions in single layer graphene

Wilhelm, R. A.; Gruber, E.; Smejkal, V.; Schwestka, J.; Kozubek, R.; Hierzenberger, A.; Schleberger, M.; Facsko, S.; Aumayr, F.

Processes in ion-solid interaction are subject to both fundamental research and technological application. The ion stopping force, i.e. the kinetic energy loss per unit length in a solid is here a key main parameter. The stopping force depends on the kinetic energy of the ions as well as on the ionic charge [1]. Usually the influence of the charge state is neglected, because after a few nanometers in a solid the ion accommodates an equilibrium charge state Qeq independent of it’s initial charge. Stopping force in charge equilibrium is well understood.
In this study we use slow (v≪v0) highly charged ions (Qeq≪Q) to study stopping force far from charge equilibrium [2,3]. Using novel two-dimensional materials as target material allows us to limit the ion interaction in the solid to only a single scattering event.
In our experiment an ion beam is transmitted through a freestanding single layer of graphene. The ion energy and charge state after transmission are measured with an electrostatic analyzer. Ions at low velocity (0.05v0 - 0.25v0) are not fully neutralized. Hence, they still capture and stabilize about 20 electrons within the collision time of less than 3 fs. Especially stabilization of the electrons is surprising, since the classical-over- barrier model for charge exchange [4] predicts the population of highly excited states with principal quantum numbers of n > 10 and a subsequent Auger electron cascade. Such a cascade would lead to the reemission of electrons and thus to a recharging of the ion.
This ultrafast charge exchange process is accompanied by a kinetic energy loss of up to ∆E /E ≈ 10 %, which is about 1 order of magnitude larger than predicted by the SRIM code.

  • Invited lecture (Conferences)
    27th International Conference on Atomic Collisions in Solid (ICACS), 24.-29.07.2016, Lanzhou, China
  • Lecture (Conference)
    Frühjahrestagung der Deutschen Physikalischen Gesellschaft, Sektion Kondensierte Materie, 07.-10.03.2016, Regensburg, Deutschland

Publ.-Id: 23732

Slow highly charged ion induced nanopit formation on the KCl(001) surface

Wilhelm, R. A.; Heller, R.; Facsko, S.

We report on nanostructuring of the KCl(001) surface due to individual impact of slow highly charged ions. Samples were irradiated with Xe ions with charge states of Q = 15 to 40 at kinetic energies from 1.7 to 160 keV. The formation of nanopits at the virgin surface is observed and attributed to a defect mediated desorption process involving the removal of up to 2000 surface atoms per incident ion. The depth of the produced pits is shallow, but not limited to the first monolayer. From the variation of the ion parameters (charge state and kinetic energy) we derive a phase diagram for the structuring of the KCl(001) surface with highly charged ions.


Publ.-Id: 23731

Simulation of ELBE SRF gun II for high-bunch-charge applications

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

The SRF gun at ELBE will benefit most of the local user beamlines for future high-bunch-charge operations. Parallel to its development, simulation-based investigations have been performed to improve the beam quality for THz experiments and Compton backscattering experiments. These two applications have the most challenging requirements: THz experiments benefit significantly from short bunch lengths at the sub-ps level, while Compton backscattering experiments demand small transverse beam sizes of about 30 µm. The beam dynamics of the SRF gun are simulated with ASTRA and the beam transport is optimized using Elegant. Important physical effects included in simulations are introduced first, where the interesting phenomenon of “slice mismatch” is generally quantified and numerically studied. Afterwards, beam transport strategies and optimization methods are proposed which are based on the specific settings of ELBE but also applicable to similar accelerator setups. Finally, optimizations of the SRF gun and the beam transport in ELBE are presented. Results show that the SRF gun is capable of providing 500 pC bunches for both applications with better beam qualities than the currently 100 pC bunches supplied by the existing thermionic DC source.

Keywords: ELBE SRF Gun II; high bunch charge; slice emittance; space charge effect

Publ.-Id: 23730

Time-resolved photoluminescence spectroscopy of Nb4+ and O− polarons in LiNbO3 single crystals

Kämpfe, T.; Haußmann, A.; Eng, L. M.; Reichenbach, P.; Thiessen, A.; Woike, T.; Steudtner, R.

We probe here the optical relaxation properties of Mg-doped wide-band-gap LiNbO3 single crystals with both a high spectral and temporal resolution at cryogenic temperatures. Surprisingly, we observe the photoluminescence to decay in a two-step process: a fast relaxation and a slower one centered around an energy Emax=2.62±0.05 eV. Both decays fit well to the stretched-exponential behavior. Moreover, we are able to associate these energies to the recombination of light-induced Nb4+ and O− small polarons. Also, we checked the stability of our findings by using LiNbO3 single crystals that show on-purpose modified radiative recombination processes, i.e., with a Mg doping both above and below the optical damage resistance threshold, as well as with different poling histories of inverted domains.


Publ.-Id: 23728

Suppressing the cellular breakdown in silicon supersaturated with titanium

Liu, F.; Prucnal, S.; Hübner, R.; Yuan, Y.; Skorupa, W.; Helm, M.; Zhou, S.

Hyper doping Si with up to 6 at.% Ti in solid solution was performed by ion implantation followed by pulsed laser annealing and flash lamp annealing. In both cases, the implanted Si layer can be well recrystallized by liquid phase epitaxy and solid phase epitaxy, respectively.
Cross-sectional transmission electron microscopy of Ti-implanted Si after liquid phase epitaxy shows the so-called growth interface breakdown or cellular breakdown owing to the occurrence of constitutional supercooling in the melt. The appearance of cellular breakdown prevents further recrystallization. However, the out-diffusion and cellular breakdown can be effectively suppressed by solid phase epitaxy during flash lamp annealing due to the high velocity of amorphous-crystalline interface and the low diffusion velocity for Ti in the solid phase.

Keywords: ion implantation; solid phase epitaxy; liquid phase epitaxy; Si; cellular breakdown

Publ.-Id: 23727

A novel Europium (III) nitridoborate Eu3[B3N6]: Synthesis, crystal structure, magnetic properties ,and Raman spectra

Aydemir, U.; Kokal, I.; Prots, Y.; Förster, T.; Sichelschmidt, J.; Schappacher, F. M.; Pöttgen, R.; Ormeci, A.; Somer, M.

A novel europium (III) nitridoborate, Eu3[B3N6], was successfully synthesized by oxidation of Eu3 II[BN2]2 with Br2 at 1073 K. The compound crystallizes in the trigonal space group R3c (No:167) with a=11.9370(4) Å, c=6.8073(4) Å, and Z=6. The crystal structure of Eu3[B3N6] consists of isolated, planar cyclic [B3N6]9- units which are charge-balanced by Eu3+ cations. The oxidation state of Eu was investigated by Mössbauer spectroscopy, electron spin resonance (ESR) spectroscopy, and quantum chemical calculations. The 151Eu Mössbauer spectroscopic measurement at 77 K reveals that the main signal at δ=0.93(7) mm/s is originating from trivalent Europium. Eu3[B3N6] showed no ESR signal in accordance with a non-magnetic (J=0) 7F0 ground state of the 4f6 configuration. Quantum chemical calculations find six electrons in the 4f subshell (4f6) of Eu indicating an oxidation state of +3. We present for the first time the vibrational spectra of a compound with cyclic trimer [B3N6]9- moieties. The Raman spectrum of Eu3[B3N6] is in good agreement with the predicted number of modes for the spectroscopically relevant cyclic [B3N6]9- group with D3h symmetry.

Publ.-Id: 23726

In-Situ Visualisierung und Streaming von Plasmasimulationsdaten

Matthes, A.

Computersimulationen sind heutzutage ein wichtiges, wissenschaftliches Instrument. Visualisierungen dieser helfen dabei die Daten zu verstehen und zu interpretieren. Da auf heutigen Peta- und zukünftigen Exascalesystemen zu viele Daten pro Zeitschritt entstehen, um sie komplett in einem Postprocessingschritt visualisieren zu können, stellt diese Arbeit die In-Situ Visualisierungsbibliothek ISAAC vor, die die Daten direkt nach ihrer Entstehung verteilt visualisieren kann, ohne sie zu speichern oder zu übertragen. Mithilfe von Templates und Template Metaprogrammierung wird ein abstraktes, wiederverwendbares Interface beschrieben, welches trotzdem eine simulationsspezifische Optimierung erlaubt. Die Visualisierung mittels Raytracing erfolgt auf den Originaldaten der Simulation, auch wenn diese auf einem Rechenbeschleuniger wie Nvidia GPUs oder Intel Xeon Phis läuft. In diesem Fall nutzt auch ISAAC die Beschleunigerhardware. Des Weiteren wird die Möglichkeit beschrieben, beliebige Metadaten zwischen Clients und Simulationen auszutauschen, insbesondere um sie live steuern zu können.
Neben der C++ Visualisierungsbibliohtek für Simulationen wird weiterhin ein generischer, zentraler Server zur Videostreamerzeugung motiviert und beschrieben sowie ein einfacher HTML Referenzclient zur Anzeige und Steuerung der Simulation implementiert. Zur Evaluierung der Lösung wird mit ISAAC die verteilte, GPU-beschleunigte Plasmasimulation PIConGPU des HZDR visualisiert. Des Weiteren wird die Rendergeschwindigkeit in Abhängigkeit verschiedener Parameter gemessen und diskutiert.

Computer simulations are important scientific instruments these days. Visualizations help to understand and interpret these data. Since with the classic post processing approach too much data is produced per time step on recent peta scale and future exa scale systems this thesis introduces the in situ visualization library ISAAC, which is able to visualize distributed data right after creation without theneed to store or transmit them. Using templates and template meta programming an abstract and reusable interface is described, which still enables simulation specific optimizations. The visualization over ray tracing works on the original data of the simulation, even if it runs on computation accelerators like Nvidia GPUs or Intel Xeon Phis. In these cases ISAAC is using the accelerators, too. Furthermore a way of sending and receiving meta data from and to simulations is described, especially to be able to steer them.
Besides this C++ library for visualization of simulations, a generic central server for creating video streams is motivated and described and also a simple HTML reference client for showing and steering simulations is implemented. For the evaluation of the solution, ISAAC is used to visualize the distributed gpu-based plasma simulation PIConGPU form the HZDR. Furthermore the speed of rendering dependent on different parameters is measured and discussed.

Keywords: in-situ visualization; simulation steering; in-memory visualization; live visualization; heterogeneous architectures; high performance computing

  • Diploma thesis
    TU Dresden, 2016
    Mentor: Grottel, Sebastian; Bussmann, Michael
    120 Seiten

Publ.-Id: 23725

Live in-Situ Visualisierung und Steuerung von wissenschaftlichen Simulationen auf Hochleistungsrechnern

Matthes, A.; Widera, R.; Hübl, A.; Zenker, E.; Eckert, C.; Gumhold, S.; Grottel, S.; Bussmann, M.

Hochleistungsrechner sind ein wichtiges Instrument für die Forschung. Hochparallele physikalische Simulationen können in Zusammenarbeit mit Experimenten neue Erkenntnisse erschließen oder bestehende hochkomplexe Modelle überprüfen.
Eine solche Simulation stellt die Plasmasimulation PIConGPU des Helmholtz-Zentrums Dresden – Rossendorf (HDZR) dar, die zusätzlich noch Grafikkarten zur weiteren Rechenbeschleunigung nutzen kann. Dabei entstehen jedoch derart viele Daten, dass ein Speichern und nachträgliches Auswerten der wissenschaftlichen Daten nicht mehr möglich ist, weshalb die Simulationsergebnisse live auf dem Hochleistungsrecher visualisiert werden müssen.
Im Rahmen der vorgestellten Diplomarbeit wurde eine abstrakte Bibliothek für die live in-situ Visualisierung und Steuerung von Simulationen beschrieben und implementiert. Der Projektstand zeigt eine live Visualisierung von PIConGPU auf einer stereoskopischen 3D Leinwand während es auf dem Hochleistungscluster Hypnos des HZDR läuft.

Keywords: in-situ visualization; simulation steering; in-memory visualization; live visualization; heterogeneous architectures; high performance computing

  • Lecture (others)
    OUTPUT.DD, 09.06.2016, Dresden, Deutschland

Publ.-Id: 23724

Ultrafast ion heating above 1 keV temperautres in solid density plasmas driven by ultrashort relativistic laser pulses

Huang, L. G.; Cowan, T.

Bulk ion heating driven by high power laser pulses is a fundamental scientific issue and of great interest to the potential applications such as nuclear excitation by electronic processes, inertial confinement fusion and so on. Yet, most theoretical and experimental investigation focus on several hundred picoseconds to nanosecond time scale evolution of ion heating dynamics, relying on radiation-hydrodynamic simulations and high energy laser facilities with the order of nanosecond pulse durations. Both the theoretical and experimental methodologies have constraints. In one hand, the hydrodynamic simulations may smooth out the kinetic effects in solid density plasmas such as species thermal decoupling, spatial mixing and separation. In the other hand, the experimental access using several hundred to kilo-Joule laser facilities is quite limited at present.

We present our recent results on ultrafast ion heating dynamics in solid buried layer targets driven by relativistic laser pulses with tens to hundreds of femtosecond pulse durations and high repetition rates[1]. The kinetic simulations using Particle-in-Cell methodology showing that the light ions within highly compressed solid density plasmas can be heated above 1 keV temperature in several hundred femtosecond time to picosecond time scales. We also found that significant instabilities and ion species mixture showing up which are originated from the interfaces of the solid buried layer targets. The possible heating mechanisms during the internal expansion and compression passage will be discussed and addressed.

In order to connect the ion heating dynamics seen in simulations with experiments, we will discuss the role of in-situ synthetic diagnostics that mimic experimental diagnostics. As one example, analyzing the energy spectrum and angular distribution of generated neutrons is possible to determine the ion temperature and distinguish the beam fusion and thermonuclear fusion, which is a conventional diagnostic method in experiments currently. The other key example we propose to directly probe the buried layer dynamics with coherent scattering techniques using hard X-Ray Free Electron Lasers, which is in principle and feasible to allow for probing fundamental plasma properties in nanosecond and femtosecond resolutions of plasma processes for the first time in the near future[2].


[1] L. G. Huang et al., Phys. Plasmas 20, 093109 (2013)

Keywords: Ion Heating; High power laser; XFEL; solid plasmas

  • Lecture (Conference)
    1st International Conference onMatter and Radiation at Extremes, 08.-12.05.2016, Chengdu, China

Publ.-Id: 23723

Overview on recent research activities related to electrochemical processes in magnetic fields

Mutschke, G.; Yang, X.

The talk will first give a brief introduction of the Helmholtz-Center Dresden-Rossendorf and its Institute of Fluid Mechanics.
It will then give an overview on recent research activities related to electrochemical topics, thereby describing the numerical and the experimental techniques applied and the results obtained. Special focus is drawn on the influence of magnetic fields in electrochemical processes, and recent results are presented in the fields of copper deposition, the evolution of hydrogen during water electrolysis and the enrichment of paramagnetic ions in aqueous electrolytes.

Keywords: electrochemistry; metallurgy; hydrogen production; rare-earth metals; electrolysis; magnetohydrodynamics

  • Lecture (others)
    Eingeladener Vortrag an Department of Physical Chemistry and Metallurgy of Non-Ferrous Metalls, AGH University of Science and Technology, 31.05.2016, Krakau, Polen

Publ.-Id: 23722

Pulse Flow in Solid Foam Packed Reactors: Analysis of Morphology and Key Characteristics

Zalucky, J.; Claußnitzer, T.; Schubert, M.; Lange, R.; Hampel, U.

In this paper, results of an experimental study on pulsing two-phase flow in SiSiC solid foam packed reactors are presented. Thereby, the pulse characteristics in a wide range of water and air fluxes at different axial positions for foams with pore densities of 20, 30, and 45 ppi were investigated using ultrafast X-ray computed tomography. Morphologically, discs, curtains and bowls were encountered as basic pulse shapes, which occurred randomly. The key characteristics, i.e. frequency, velocity and volume of pulses as well as peak and time-averaged liquid holdup, have been extracted by applying a dynamic threshold criterion to time-variant liquid holdup profiles. The key properties strongly depend on axial position, pore density and fluid fluxes and can be distinguished in a local and global mode of pulsing. In the local mode, which evolves close to the regime transition boundary, pulses with small liquid volumes move slowly but frequently through the solid foam packed reactor. In the global mode, significantly faster pulses with large liquid volumes were encountered, which cover most of the reactor cross-section but occur less frequent. Compared to literature data for conventional random packings, the pulse frequency was in a similar range while both pulse velocity and liquid content largely exceeded their counterparts. Phenomenologically, the pore occlusion model was found to be more applicable than the concepts based on flow stability.

Keywords: pulse flow; solid foam packing; pulse properties; ultrafast X-ray computed tomography; pore occlusion model; liquid holdup

Publ.-Id: 23721

Evaluation of flow dynamics and liquid-solid mass transfer in solid foam packed reactors using the limiting current technique

Zalucky, J.; Schubert, M.; Hampel, U.

In heterogeneous catalytic multiphase reactors, such as trickle-bed reactors, the achieved space time yield depends strongly on the individual mass transfer steps between the individual phases. Being a transfer resistance to all reactants, the liquid-solid mass transfer can be considered as the most crucial mass transfer step.
The limiting current technique (also called electrochemical method) is an established method to study liquid-solid mass transfer at any solid surface. By application of an electric potential to Nickel electrodes having a morphology representative for the solid phase of interest, the limiting electric current can be continuously measured and directly related to the liquid-solid mass transfer. Moreover, the method allows to study dynamic shear stress-related phenomena in the liquid film such as flow regime transition or dynamics of pulses.
In recent years, open-cell solid foams have gained lots of interest as catalyst support in multiphase processes. They consist of a highly tortuous continuous solid network with void fractions of approx. 90% and combine large specific surface area with low flow resistance and high thermal conductivity. Moreover, their hydrodynamic behavior in terms of flow regimes under cocurrent downflow, i.e. trickling flow at high gas and liquid flow rates, may open up new modes of operation.
In the present contribution, the limiting current technique is used to evaluate fast flow dynamics at trickling and pulsing flow and corresponding liquid-solid mass transfer in trickle-bed reactors packed with silicon-infiltrated silicon-carbide (SiSiC) foams.

Keywords: Liquid-solid mass transfer; solid foam packed reactors; limiting current technique

  • Lecture (Conference)
    Jahrestreffen der Fachgruppe Wärme- und Stoffübertragung 2016, 29.02.-02.03.2016, Kassel, Deutschland

Publ.-Id: 23720

Alternative FIB Applications using Liquid Metal Alloy Ion Sources

Bischoff, L.; Mazarov, P.; Bruchhaus, L.; Gierak, J.

At this time Focused Ion Beam (FIB) technology is dominated by gallium Liquid Metal Ion Sources (LMIS). But, despite new developments like He/Ne ion microscopes or Xe-FIBs many applications in the µm- or nm range could benefit from ion species other than gallium or noble gases: local ion implantation, ion beam mixing, ion beam synthesis or even Focused Ion Beam Lithography. For this special use cases Liquid Metal Alloy Ion Sources (LMAIS) represent a promising alternative to expand the remarkable application fields for FIB [1]. Switching between the certain species obtained from a chosen alloy using an ExB mass filter in the ion optical column can be applied to change significantly different physical and chemical characteristics of the resulting nanostructures. In other words the electrical, optical, magnetic and/or mechanic properties can be tuned. This offers a large application potential by choosing a well suited LMAIS. Now nearly half of the elements of the Periodic Table are available in FIB technology.
Main properties of a modern LMAIS should be long life-time, high brightness and stable ion current emission. This contribution will involve the physical basics and experimental results of LMAIS, their physical properties and questions of the preparation technology for elementary as well as binary and ternary alloys as source material. Furthermore selected applications of these sources in highly focused beams are given feasible for nano patterning issues as an alternative technology more in research than in industry.

[1] L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Liquid metal alloy ion sources—An alternative for focused ion beam, Appl. Phys. Rev. 3 (2016) 021101.

Keywords: Focused Ion Beam; Liquid Metal Alloy Ion Sources; Nanotechnology

  • Lecture (Conference)
    11th DACH FIB workshop, 27.-28.06.2016, Brno, Czech Republic

Publ.-Id: 23719

Liquid Metal Ion Source driven High Current Ion Beam Injector

Laufer, P.; Bock, D.; Pilz, W.; Bischoff, L.; Tajmar, M.

The capability of Liquid Metal (Alloy) Ion Sources (LMAIS) to emit a broad variety of ions from nearly the half of the periodic table including molecular ions or small clusters, consisting of a few atoms and different charge stages render them unique for special applications. LMAIS are characterized by a high brightness of about 1e6 A/cm² sr, low energy spread of some eV and a compact design which prefer them for focused ion beam (FIB) systems [1] or field emission electric propulsion (FEEP) thrusters in space technology [2].
The main attention is dedicated to the emission of heavy metallic polyatomic ions – a very special of LMAIS. With Bi or Au di- and trimer ions in the energy range of some 10 keV regular self-organized hexagonal dot structures were obtained after room temperature irradiation of Ge at normal incidence using a FIB instrument. The patterning is induced by the enormous energy deposition by the heavy projectiles but due to the low available currents restricted to only small areas [3, 4]. Consequently, an ion injector based on high current LMAIS is the aim of this work to process larger areas adaptable on single-end ion beam systems. Different types of field emitters were tested for a high permanent ion current of much more than 100 µA.
Among classical needle emitters, particularly the application of porous needles from Tungsten and Rhenium and Tantalum capillaries with a 50 µm inner diameter showed an excellent and stable emission behavior. Source materials like Ga for tests, Gold (from Au82Si18 alloy), Lead and Bismuth (Bi or Ga38Bi62 alloy) were investigated. In the developed injector a nearly parallel ion beam of about 2 mm diameter can be obtained by means of an asymmetric ion-optical Einzel lens. Furthermore a mass separation system (Wien filter) selects the desired ions while a quadrupole is used for beam adjustment and astigmatism correction. High cluster ion currents enable the formation of various nanostructures or even smooth surfaces over an area in cm²-range depending on ion species, energy, fluence and angle of incidence. The LMAIS characterization and the performance of the ion beam module for certain experiments will be presented and discussed.

[1] L. Bischoff: “Alloy liquid metal ion sources and their application in mass separated focused ion beams”, Ultramicroscopy 103 (2005), 59. DOI:10.1016/j.ultramic.2004.11.020
[2] M. Tajmar and B. Jang: “New materials and processes for field emission ion and electron emitters”, CEAS Space J. 4 (2013), 47. DOI: 10.1007/s12567-013-0031-z
[3] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko and W. Pilz: “Self-organization of Ge nanopattern under erosion with heavy Bi monomer and cluster ions”, Nucl. Instr. and Meth. B 272 (2012), 198. DOI: 10.1016/j.nimb.2011.01.064
[4] R. Boettger, L. Bischoff, K.-H. Heinig, W. Pilz, and B. Schmidt: “From sponge to dot arrays on (100) Ge by increasing the energy of ion impacts” J. Vac. Sci. Technol. B 30 (2012), 06FFF12. DOI: 10.1116/1.4767269

Keywords: Liquid Metal (Alloy) Ion Sources; polyatomic ions; nanostructures

  • Lecture (Conference)
    1st International Conference on Helium Ion Microscopy and Emerging Focused Ion Beam Technologies (HEFIB 2016), 08.-10.06.2016, Luxembourg City, Luxembourg

Publ.-Id: 23718

Focused Ion Beam Applications using Liquid Metal Alloy Ion Sources

Bischoff, L.; Mazarov, P.; Bruchhaus, L.; Gierak, J.

Presently Focused Ion Beam (FIB) processing is dominated by gallium Liquid Metal Ion Sources (LMIS). But, beside new developments in this field like He/Ne ion microscopes or Xe-FIBs many applications in the µm- or nm range could benefit from ion species other than gallium or noble gases: local ion implantation, ion beam mixing, ion beam synthesis or even Focused Ion Beam Lithography. Therefore Liquid Metal Alloy Ion Sources (LMAIS) represent a promising alternative to expand the remarkable application fields for FIB [1,2]. Simple switching between the certain ion species using an ExB mass filter can be applied to change significantly the physical and chemical nature of the resulting nanostructures -in other words the electrical, optical, magnetic and mechanic properties. This offers a large application potential which can be tuned by choosing a well suited LMAIS. Now nearly half of the elements of the Periodic Table are available in FIB technology. Main properties of a modern LMAIS are long life-time, high brightness and stable ion current. This contribution will cover the physical basics and experimental results of LMAIS, their physical properties (I-V characteristics, energy spread) and questions of the preparation technology using elementary as well as binary and ternary alloys as source material. Furthermore selected applications will be presented to underline the impact of these sources in modern nanotechnology by highly focused ion beams. Recent developments could make these sources feasible for nano patterning issues as an alternative technology more in research than in industry.

[1] L. Bischoff: “Application of mass-separated focused ion beams in nano-technology”, Nucl. Instr. Meth. B 266 (2008), 1846. DOI:10.1016/j.nimb.2007.12.008
[2] L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak: „Liquid Metal Alloy Ion Sources - An Alternative for Focused Ion Beam Technology” , Appl. Phys. Rev. 3 (2016) 021101-1-30
[3] L. Bischoff and Ch. Akhmadaliev: “An alloy liquid metal ion source for lithium”, J. Phys. D: Appl. Phys. 41 (2008) 052001. DOI:10.1088/0022-3727/41/5/052001

Keywords: Focused Ion Beam; Liquid Metal Alloy Ion Sources; Mass spectra

  • Lecture (Conference)
    1st International Conference on Helium Ion Microscopy and Emerging Focused Ion Beam Technologies (HEFIB 2016), 08.-10.06.2016, Luxembourg City, Luxembourg

Publ.-Id: 23717

Incorporation of Eu(III) into Calcite under Recrystallization conditions

Hellebrandt, S. E.; Hofmann, S.; Jordan, N.; Barkleit, A.; Schmidt, M.

The interaction of calcite with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three calcite powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu(III) occurs faster and the speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 µs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk crystal. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different calcites. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na(I). These findings emphasize the different retention potential of calcite as a primary and secondary mineral e.g. in a nuclear waste disposal site.

Keywords: Calcite; recrystallization; incorporation; Europium

Publ.-Id: 23716

Combined use of flow cytometry and microscopy to study the interactions between the gram-negative betaproteobacterium Acidovorax facilis and uranium(VI)

Gerber, U.; Zirnstein, I.; Krawczyk-Bärsch, E.; Lünsdorf, H.; Arnold, T.; Merroun, M. L.

The former uranium mine Königstein (Saxony, Germany) is currently in the process of remediation by means of controlled underground flooding. Nevertheless, the flooding water has to be cleaned up by a conventional wastewater treatment plant. In this study, the uranium(VI) removal and tolerance mechanisms of the gram-negative betaproteobacterium Acidovorax facilis were investigated by a multidisciplinary approach combining wet chemistry, flow cytometry, and microscopy. The kinetics of uranium removal and the corresponding mechanisms were investigated. The results showed a biphasic process of uranium removal characterized by a first phase where 95 % of uranium was removed within the first 8 hours followed by a second phase that reached equilibrium after 24 hours. The bacterial cells displayed a total uranium removal capacity of 130 mg U/g dry biomass. The removal of uranium was also temperature-dependent, indicating that metabolic activity heavily influenced bacterial interactions with uranium. TEM analyses showed biosorption on the cell surface and intracellular accumulation of uranium. Uranium tolerance tests showed that A. facilis was able to withstand concentrations up to 0.1 mM. This work demonstrates that A. facilis is a suitable candidate for in situ bioremediation of flooding water in Königstein as well as for other contaminated waste waters.

Keywords: Acidovorax facilis; AMD; uranium; in situ bioremediation; flow cytometry; metal tolerance


Publ.-Id: 23715

Fundamental investigation of the structure of neodymium-di-(2-ethylhexyl) phosphoric acid combinations using ESI and MALDI spectrometry and NMR spectroscopy

Scharf, C.

Neodymium-DEHPA-species forming in the organic phase during solvent extraction of neodymium with solutions of di-(2-ethylhexyl)phosphoric acid (DEHPA) have been studied. Two samples were prepared, one with a low molar ratio of neodymium to DEHPA which is liquid and clear, and the other with a high molar ratio of neodymium to DEHPA (complete loading) which has the consistency of a gel. Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometric investigations show numerous compounds in addition to the generally assumed species dimeric DEHPA and Nd(DEHP·DEHPA)3, in the liquid sample. NMR spectroscopic investigation of pure DEHPA and of a completely loaded sample confirm the formula of pure DEHPA and of the organic part of Nd(DEHP)3. Furthermore, chemical analysis of a dried completely loaded sample also proves the existence of the species Nd(DEHP)3. Results of X-ray powder diffraction measurement of this sample agree well with literature data.

Keywords: solvent extraction of neodymium; di-(2-ethylhexyl)phosphoric acid; DEHPA; neodymium-DEHPA gel; neodymium-DEHPA species

  • Contribution to proceedings
    International Chemical Congress of Pacific Basin Societies, 15.-20.12.2015, Honolulu, USA
    Proceedings of the International Chemical Congress of Pacific Basin Societies

Publ.-Id: 23714

Ion Beam Injector based on High Current LMIS

Laufer, P.; Bock, D.; Pilz, W.; Bischoff, L.; Tajmar, M.

One of the major advantages of Liquid Metal Alloy Ion Sources (LMAIS) is the capability to emit a broad spectrum of ions from doubly and singly charged ions of nearly the half of the periodic table up to molecular ions or small clusters, consisting of a few atoms and different charge stages. These ion sources, characterized by a high brightness of about 106 A/cm2 sr, low energy spread of some eV and a very compact design are dedicated mostly for focused ion beam (FIB) applications [1] or field emission electric propulsion (FEEP) thrusters in space technology [2]. Normal ions in a wide spectrum of parameters can be provided also by other ion sources. The very special of LM(A)IS are the formation of heavy polyatomic ions from metallic or semiconducting elements, which is of great interest for self-organized surface patterning. So with Bismuth di- and trimer ions regular hexagonal dot structures were obtained after room temperature irradiation of Germanium at normal incidence using a FIB instrument induced by the enormous energy deposition by the heavy projectiles [3, 4]. To employ these heavy ions also for other ion beam systems and especially for larger areas an ion source injector module based on a high current LM(A)IS will be presented. Total emitted ion currents of more than 100 µA can be reached using different types of field emitter in particular porous needles from Tungsten and Rhenium or capillaries, 50 µm inner diameter of Tantalum. Source materials like Ga for tests, Gold (from Au82Si18 alloy), Lead or Bismuth (Bi or Ga38Bi62 alloy) were investigated.
In the injector a nearly parallel ion beam of about 2 mm diameter can be obtained by means of an asymmetric ion-optical Einzel lens. The cluster ion fraction for a certain ion species is in the range of per mil up to a few percent dependent on the emitted elements. A mass separation system (Wien filter) selects the desired ions while a quadrupole is used for beam adjustment and astigmatism correction. High cluster ion currents enable the formation of various nanostructures or even smooth surfaces over an area in cm²-range depending on ion species, energy, fluence and angle of incidence. The LM(A)IS preparation and the performance of the ion beam module at certain experiments will be presented and discussed.

[1] L. Bischoff, Ultramicroscopy 103, 59 (2005).
[2] M. Tajmar and B. Jang, CEAS Space J. 4, 47 (2013).
[3] L. Bischoff, et al., Nucl. Instr. and Meth. B 272,198 (2012).
[4] R. Boettger et al. J. Vac. Sci. Technol. B 30, 06FFF12 (2012).

Keywords: Liquid Metal Alloy Ion Source; Ion Beam Injector; Cluster Ions

  • Lecture (Conference)
    60th International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication (EIPBN), 31.05.-06.06.2016, Pittsburgh, USA

Publ.-Id: 23713

Investigation of thermal spin transfer torque in MgO-based magnetic tunnel junctions using FMR microresonators

Cansever, H.; Kowalska, E.; Fowley, C.; Aleksandrov, Y.; Yildirim, O.; Narkowicz, R.; Lenz, K.; Lindner, J.; Fassbender, J.; Deac, A.

MgO-based magnetic tunnel junctions are commonly used in spintronic device applications, such as recent spin transfer torque random access memory (STT-RAM) because of their non-volatility, fast switching and high storage capacity. Spin transfer torque is defined as a spin polarized current flowing through a ferromagnet exerting a torque on the local magnetization. With thermal spin transfer torque (T-STT), thermally excited electron transport is used instead of spin polarized charge current and provides an interesting way of using thermoelectric effects in magnetic storage applications. Our study focuses on fundamental experimental research aimed at demonstrating that thermal gradients can generate spin-transfer torques in MgO-based magnetic tunnel junctions (MTJs). We use microresonators in order to analyze how the ferromagnetic resonance signal corresponding to the free layer of an in-plane MgO-based tunnel junction device is modified in the presence of a temperature gradient across the barrier.
This work is supported by DFG-SPP1538

  • Poster
    DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Germany

Publ.-Id: 23712

Ultra-doped n-type germanium thin films for sensing in the mid-infrared

Prucnal, S.; Liu, F.; Voelskow, M.; Vines, L.; Rebohle, L.; Lang, D.; Berencén, Y.; Andric, S.; Boettger, R.; Helm, M.; Zhou, S.; Skorupa, W.

A key milestone for the next generation of high-performance multifunctional microelectronic devices is the monolithic integration of high-mobility materials with Si technology. The use of Ge instead of Si as a basic material in nanoelectronics would need homogeneous p- and n-type doping with high carrier densities. Here we use ion implantation followed by rear side flash-lamp annealing (r-FLA) for the fabrication of heavily doped n-type Ge with high mobility. This approach, in contrast to conventional annealing procedures, leads to the full recrystallization of Ge films and high P activation. In this way single crystalline Ge thin films free of defects with maximum attained carrier concentrations of 2.20±0.11E20 cm-3 and carrier mobilities above 260 cm2/(V·s) were obtained. The obtained ultra-doped Ge films display a room-temperature plasma frequency above 1,850 cm-1, which enables to exploit the plasmonic properties of Ge for sensing in the mid-infrared spectral range.

Keywords: Ge; ion implantation; flash lamp annealing; plasmonics

Publ.-Id: 23711

In-situ, steerable, hardware-independent and data-structure agnostic visualization with ISAAC

Matthes, A.; Widera, R.; Hübl, A.; Zenker, E.; Eckert, C.; Gumhold, S.; Grottel, S.; Bussmann, M.

We showcase the C++ template library ISAAC [1,2] for in-situ visualization of simulations or other high rate data sources running distributed on modern HPC systems. As most in-situ visualization solutions suffer from the problem that the simulation data needs to be converted to visualization specific data structures, ISAAC implements a data structure agnostic raycasting algorithm using C++ templates and C++ meta programming. With this ISAAC is not only able to visualize nearly arbitrary simulation data without the need of deep copying or converting it beforehand, but is also capable to use the very same computation device as the simulation itself.

Using the same computation device as the simulation usually limits the scope of usable hardware as modern many-core devices require programming models optimized for the specific hardware, e.g. CUDA for NVIDIA devices, to achieve optimum performance. In order to circumvent this problem ISAAC is based on the abstract kernel interface library Alpaka [3,4], which defines a redundant parallel hierarchy model for many-core architectures that serves as a front end to underlying models such as CUDA, OpenMP or Thread Building Blocks. With this, the ISAAC software renderer can run in-situ on almost every platform currently available.

Not all simulation data is perfectly suited for direct visualization but sometimes requires transformation. ISAAC thus introduces so called Functor Chains, which are very simple precompiled, but at runtime selectable, functions used for local domain transformations of the original simulation data performed before the data is streamed to the raycasting algorithm.

ISAAC is capable of scaling up to Petascale systems using the IceT library. It is not intended for highly specialized visualization but instead renders the classical representation as glowing gas or as iso surfaces. Aside from the obligatory transfer functions for the classification ISAAC also supports an arbitrary amount of random clipping planes useful for a deeper look into the simulated volumes.

ISAAC includes an interface for simulations to send arbitrary live meta data with the live preview and to receive live steering data. The whole communication layer of ISAAC is intentionally based only on open and widely used standards such as Websockets, RTP Streams and especially the open-standard format JSON.

ISAAC provides a server running on the head or login node of the HPC system, which creates the video streams from the visualization and forwards them together with the meta data to a freely selectable number of clients. The video stream created by the server can be received from arbitrary clients such as VLC or even streaming platforms like Twitch. Furthermore, each client can steer the simulations. ISAAC itself introduces a platform-independent HTML5 client, which can be adjusted to the needs of specific simulations easily.

Since every part of ISAAC is open source and makes use of the openly documented JSON communication protocol, it is easily possible to implement new clients or to extend the visualization core itself for simulation-specific features. ISAAC is designed to be as language-, framework-, data-format- and platform-agnostic as possible.

In order to demonstrate the real time capabilities of ISAA we will showcase a live visualization of the GPU-accelerated plasma simulation PIConGPU [5,6]. We show that we can achieve more than ten frames per seconds using 64 GPUs on the Hypnos cluster at Helmholtz-Zentrum Dresden – Rossendorf running both the simulation and visualization simultaneously.

[1] A. Matthes, In-situ Visualisierung und Streaming von Plasmasimulationsdaten, Technical University Dresden (2016)
[3] E. Zenker et al., Alpaka - An Abstraction Library for Parallel Kernel Acceleration, (2016)
[5] M. Bussmann et al., Radiative Signatures of the Relativistic Kelvin-Helmholtz Instability, Proceedings of the International Conference on High Performance Computing, Networking, Storage and Analysis, SC'15, 5, 1 (2013)

Keywords: in-situ visualization; simulation steering; in-memory visualization; live visualization; heterogeneous architectures; high performance computing

  • Lecture (Conference)
    ISC Workshop On In-situ Visualization 2016, 23.06.2016, Frankfurt am Main, Deutschland

Publ.-Id: 23710

Radiation Dose Measurements for high-intensity laser interactions with solid targets at SLAC

Liang, T.; Bauer, J.; Cimeno, M.; Ferrari, A.; Galtier, E.; Granados, E.; Lee, H. J.; Liu, J.; Nagler, B.; Prinz, A.; Rokni, S.; Woods, H. T. M.

A systematic study of photon and neutron radiation doses generated in high-intensity laser–solid interactions is underway at SLAC National Accelerator Laboratory. These laser–solid experiments are being performed using a 25 TW (up to 1 J in 40 fs) femtosecond pulsed Ti:sapphire laser at the Linac Coherent Light Source’s (LCLS) Matter in Extreme Conditions (MEC) facility. Radiation measurements were performed with passive and active detectors deployed at various locations inside and outside the target chamber. Results from radiation dose measurements for laser–solid experiments at SLAC MEC in 2014 with peak intensity between 10^18 and 7.1 10^19 W cm-2 are presented.

Keywords: radiation measurements; laser-induced ionizing radiation


Publ.-Id: 23707

Ionizing Radiation Measurements from Interaction of MEC Laser (0.7 J, 10^19 W/cm2) with Cu and Ni Targets

Liang, T.; Bauer, J.; Blaha, J.; Cimeno, M.; Ferrari, A.; Liu, J.; Rokni, S.; Woods, M.

Laser system upgrades at SLAC Matter in Extreme Conditions (MEC) have increased the potential dose levels generated from laser-matter interactions at LCLS Hutch 6. In July 2014, the 800 nm Ti:sapphire MEC laser operated at 0.7 J with an intensity of 1.0 10^18 W/cm2, and shots were taken on Cu foils and a Ni nanowire target. In August 2014, MEC scientists utilized a deformable mirror improve the laser spot size to achieve an intensity of 1.0 10^19 W/cm2 with 0.7 J, and laser shots were again taken on Cu foil and Ni nanowire. During both experiments, passive (nanoDot, RADOS, 2 mR PIC) and active (Victoreen 451, BF3) detectors were deployed inside and outside the target chamber to measure ionizing radiation from laser shots on Cu and Ni targets, and measurements from active and passive detectors agree. No local cone shielding was in place at MEC during radiation measurements.

Keywords: laser induced ionizing radiation

  • Other report
    SLAC National Accelerator Laboratory, USA: SLAC RADIATION PHYSICS NOTE RP-14-23, 2014
    23 Seiten

Publ.-Id: 23706

Shielding and activation studies for MYRRHA in critical and sub-critical mode

Ferrari, A.; Mueller, S.; Konheiser, J.

This work has been performed in the framework of the FP7 European project MAXSIMA (“Methodology, Analysis and eXperiments for the Safety In MYRRHA Assessment”), which has the goal to support the design of the accelerator-driven system MYRRHA (“Multi-purpose hYbrid Research Reactor for High-Tech Applications”) at SCK-CEN in Mol (Belgium), in view of the licensing of the facility.
The aim of the MAXSIMA Work Package 2 is to provide solid safety analyses for the Belgian safety authorities in view of the licensing process.
The main goal of the Task 2.1 is to support these analyses on one side by providing the needed neutronic parameters as input (see Deliverable D2.1), and on the other side by performing shielding and activation studies using the up-to-date MYRRHA core models.
These studies are the object of the present Deliverable, D2.2.

Keywords: Shielding; accelerator driven systems; MYRRHA; spallation sources

  • Other report
    Report for EU Commission: Deliverable D2.2 of the MAXSIMA EU Project, 2015
    496 Seiten

Publ.-Id: 23705

An activation database for materials used at high-intensity laser acceleration facilities

Ferrari, A.; Fasso, A.; Olsovcova, V.; Versaci, R.

The ELI-Beamlines facility, which is expected to start operation in 2017, will be the high-energy, high repetition-rate laser pillar of the Extreme Light Infrastructure (ELI). The goal of the project is to deliver ultra-short, high-energy laser pulses for generation and applications of high-brightness X-ray sources and accelerated particles. Particle beams are expected to operate in an unprecedented energy range for laser-driven accelerators, going from 1 GeV up to 50 GeV for electrons and from 100 MeV up to 3 GeV for protons. The number of particles per laser shot is estimated to be 10^9-10^10 for electron beams and 10^10-10^12 for proton beams. The high energy and the large current per shot of the produced beams, together with the potentiality to operate at 10 Hz laser repetition rate, require an adequate evaluation of activation in structural materials in order to assess several radiation protection problems, such as minimization of residual dose rates close to and inside the experimental chambers and management of active materials (short and long-term storage and eventual decommissioning).
A large database covering all the energies and materials of interest is being developed using FLUKA, a Monte Carlo code successfully benchmarked for the production of radioactive nuclides. Results for electrons and protons at intermediate energies are presented. These results, although focused on the needs of laser-driven accelerators, are likely to be useful also when designing more conventional facilities.

Keywords: activation; laser induced ionizing radiation

  • Lecture (Conference)
    ARIA 2015 - Workshop on Accelerator Radiation Induced Activation, 15.-17.04.2015, Knoxville, Tennessee, United States

Publ.-Id: 23704

Activation calculations for the MYRRHA accelerator-driven system design

Ferrari, A.; Castelliti, D.; Konheiser, J.; Mueller, S.; Sarotto, M.; Stankovskiy, A.

The MYRRHA facility at SCK-CEN in Mol (Belgium), which is at present in an advanced phase of the design, aims to demonstrate efficient transmutation of high level waste and associated Accelerator-Driven System (ADS) technology. The system is based on a lead-bismuth eutectic (LBE) cooled reactor, working both in critical and in sub-critical operation modes. Neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV, < 4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core. The use of a high energy/high current proton beam, coupled with a nuclear reactor operating in subcritical mode, presents many challenges for various aspects of the design, being minimization of the induced activation a key point. In order to assess the main activation and shielding problems, a method based on the combined use of the two Monte Carlo codes MCNPX and FLUKA has been developed, with the goal to perform detailed analyses of both the radiation fields due to the system in operation, and the coupled residual radiation due to the activated materials. Activation has been then evaluated for typical irradiation patterns and key structural materials, from the spallation target to the structure above the core, the reactor cover and critical points along the proton beamline.
The results of this simulation work are presented, with some implications on the design solutions.

Keywords: Activation; shielding; accelerator driven systems; spallation sources

  • Lecture (Conference)
    ARIA 2015 - Workshop on Accelerator Radiation Induced Activation, 15.-17.04.2015, Knoxville, Tennessee, United States

Publ.-Id: 23703

Source term determination for shielding assessment of high-power laser-plasma experiments

Ferrari, A.; Cowan, T.; Pelka, A.; Nakatsutsumi, M.; Tschentscher, T.; Rokni, S.; Liu, J.; Bauer, J.; Liang, T.; Fasso’, A.; Margarone, D.; Versaci, R.

In an increasing number of experiments, high-power, high-intensity lasers hit targets and create plasma. The laser-plasma interaction will produce hot electrons with a Maxwellian energy spectrum and an electron temperature ranging from about 10 keV to 10 MeV for irradiance between 10^16 and 10^21 W/cm2. The electrons interact in turn with the target, producing bremsstrahlung and possibly photoneutrons, resulting in a radiation field that must be contained by shielding. Since the physics of plasmas is very different from that of the common phases of matter, the shielding design cannot be carried out with only conventional tools.
Different, complementary approaches are possible: to use analytical formulas, to experimentally evaluate source terms to be used as input to established Monte Carlo codes, or to interface those codes with specialized Particle-In-Cell programs, which describe the generation and transport of particles in plasma.
At the Helmholtz-Beamline, which will operate as laser facility at the European XFEL, the shielding design of the High Energy Density (HED) Physics Instrument has been evaluated by using analytical calculations, cross-checked with measurements at the DRACO laser at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). On the other hand an extensive experimental campaign is planned at SLAC, where dedicated radiation measurements will be performed at the Matter in Extreme Conditions (MEC) short-pulse laser facility.

  • Poster
    SATIF-12 Shielding aspects of Accelerators, Targets and Irradiation Facilities, 28.-30.04.2014, Fermilab, Batavia, Illinois, United States

Publ.-Id: 23702

Radiation field calculations around the spallation target and the reactor core for the MYRRHA ADS design

Ferrari, A.; Castelliti, D.; Fernandez, R.; Konheiser, J.; Mueller, S.; Sarotto, M.; Stankovskiy, A.

The MYRRHA facility at SCK·CEN in Mol (Belgium), which should enter the construction phase in 2015, aims to demonstrate efficient transmutation of high level waste and associated Accelerator-Driven Systems (ADS) technology. The system is based on a lead-bismuth eutectic (LBE) cooled reactor, working both in critical and in sub-critical operation modes. The neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV,  4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core. In order to assess the main shielding problems, a method based on the combined use of the two Monte Carlo codes MCNPX and FLUKA has been developed, with the goal to perform detailed analyses of both the radiation fields due to the system in operation, and the coupled residual radiation due to the activated materials. The results of this simulation work are presented, with the implications on the design solutions.

Keywords: Accelerator driven systems; spallation targets; shielding

  • Poster
    SATIF-12 Shielding aspects of Accelerators, Targets and Irradiation Facilities, 28.-30.04.2014, Fermilab, Batavia, Illinois, United States

Publ.-Id: 23701

Shielding and activation studies for the ELI-Beamlines project

Fasso, A.; Ferrari, A.; Korn, G.; Versaci, R.

ELI-beamlines is one of the four pillars of the Extreme Light Infrastructure, a European ESFRI Project, for the next generation of high-energy and high-intensity lasers. It aims at the development of high-brightness sources of X-rays and the acceleration of proton, electron, and ion beams, to be used both for pure research and practical applications.
Aiming at a proper radiation protection assessment, for both shielding and activation, extensive FLUKA simulations have been performed, taking into account the laser high repetition rates. The present work, which is the continuation of the calculations presented at SATIF-10, is the first one based on the design of the facility being constructed and on the updated experimental set-up.

Keywords: Shielding; Monte Carlo calculations; FLUKA

  • Open Access Logo Contribution to proceedings
    SATIF-12 Shielding aspects of Accelerators, Targets and Irradiation Facilities, 28.-30.04.2014, Fermilab, Batavia, Illinois, United States
    Workshop Proceedings: OECD, Nuclear Science NEA/NSC/R(2015)3, 105-111

Publ.-Id: 23700

Measurements of high-intensity laser induced ionising radiation at SLAC

Liang, T.; Bauer, J.; Cimeno, M.; Ferrari, A.; Galtier, E.; Granados, E.; Liu, J.; Nagler, B.; Prinz, A.; Rokni, S.; Tran, H.; Woods, M.

A systematic study of measurements of photon and neutron radiation doses generated in high-intensity laser-target interactions is underway at SLAC National Accelerator Laboratory using a femtosecond pulsed Ti:sapphire laser (800 nm, 40 fs, up to 1 J and 25 TW) at the Linac Coherent Light Source’s (LCLS) Matter in Extreme Conditions (MEC) facility. Preliminary results from recent measurements with the laser-optic-target system (peak intensity 1.8x1018 W/cm2) are presented and compared with results from calculations based on analytical models and FLUKA Monte Carlo simulations.

Keywords: Laser induced ionising radiation; source terms measurements; shielding

  • Open Access Logo Contribution to proceedings
    SATIF-12 Shielding aspects of Accelerators, Targets and Irradiation Facilities, 28.-30.04.2014, Fermilab, Batavia, Illinois, United States
    Workshop Proceedings: OECD, Nuclear Science NEA/NSC/R(2015)3, 40-53

Publ.-Id: 23699

Data-driven model for evaluation of cerebrovascular-reserve measurement with hypercapnia BOLD

Vondráčková, L.; Krukowski, P.; Gerber, J.; Linn, J.; Kybic, J.; Petr, J.

Hypercapnia BOLD with the breath-holding task is a technically easier and more clinically available alternative to cerebrovascular reserve (CVR) mapping than administration of CO enriched air using an air-tight mask. The disadvantage is complicated data evaluation in case the subject does not adhere to the breathing protocol completely. Here, a data-driven approach for evaluation is presented that is more robust to protocol deviations and produces a reasonable CVR map in most cases where the standard model-driven approach fails. This is demonstrated on randomized evaluation of CVR maps of a group of 86 subjects with stenosis or vessel occlusion.

  • Contribution to proceedings
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore
    Proceedings of the 24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
  • Poster
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore

Publ.-Id: 23698

Deformation and resolution issues in partial volume correction of 2D arterial spin labeling data

Petr, J.; Mutsaerts, H. J.; de Vita, E.; Maus, J.; van den Hoff, J.; Asllani, I.

Partial volume (PV) effects are a well-recognized confounder in arterial spin labeling due to its limited spatial resolution. Several algorithms exist to correct for these errors. Nevertheless, PVcorrection is rarely used, mainly because the PV maps obtained from segmented T1-weighted images are regarded as not being suficiently reliable when transformed into ASL space. Here, we show the impact of spatial deformation and resolution in the PV-maps used for PV-correction in the calculation of mean total gray matter (GM) cerebral blood flow (CBF). We also show how the deformations affect the calculation of PV-uncorrected mean GM CBF.

  • Contribution to proceedings
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore
    Proceedings of the 24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
  • Poster
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore

Publ.-Id: 23697

Addressing multi-centre image registration of 3T arterial spin labeling images from the GENetic Frontotemporal dementia Initiative (GENFI)

Mutsaerts, H.; Thomas, D.; Petr, J.; de Vita, E.; Cash, D.; van Osch, M.; Groot, P.; van Swieten, J.; Laforce Jr, R.; Tagliavini, F.; Borroni, B.; Galimberti, D.; Rowe, J.; Graff, C.; Frisoni, G.; Finger, E.; Sorbi, S.; Mendonça, A.; Rossor, M.; Rohrer, J.; Masellis, M.; Macintosh, B.

One obstacle in multi-centre arterial spin labeling (ASL) studies is the variability attributed to differences between vendor- or site-specific ASL implementations. This multi-centre study compares spatial registration methods from ASL to 3D-T1, to reduce the between-subject variability of cerebral blood flow (CBF) maps. Our results demonstrate that choices of image registration have profound effects on ASL data collected using different pulse sequences and/or sites. A rigid-body registration of CBF images to segmented gray matter images produced the most robust similarity outcome as a standard approach across the different ASL implementations.

  • Contribution to proceedings
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore
    Proceedings of the 24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
  • Poster
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore

Publ.-Id: 23696

Perfusion decrease in healthy tissue following radiochemotherapy in glioblastoma patients

Petr, J.; Platzek, I.; Seidlitz, A.; Hofheinz, F.; Maus, J.; Beuthien-Baumann, B.; Krause, M.; van den Hoff, J.

Decrease of perfusion as a side-effect of radio-chemotherapy was observed in several organs (1). However, the relation between the decrease and the radiation dose was not yet extensively studied. Non-invasive measurement of perfusion is now possible with a native MRI sequence called arterial spin labeling (ASL) (2) which offers a semi-quantitative alternative to [O-15]H2O PET measurement. The ASL measurement was used to study the regional perfusion changes in healthy tissue of glioblastoma patients undergoing radiochemotherapy.
Twenty-five patients (age 55.0±14.2 years) with glioblastoma multiforme were scanned in two (n=25) or three (n=13) sessions with interval 4.8 and 8.1 months from the first session, respectively. The ASL scan was co-registered with the treatment-planning CT and the dose plan. Perfusion changes between sessions were calculated in the hemisphere contralateral to the tumor. The perfusion changes were evaluated also in regions created by categorizing the individual dose maps into 10 Gy steps.
The relative perfusion decrease between the first two sessions was not significant (-2.4% and -7.5%) for the low dose regions 0 and 20 Gy. For the high-dose regions, the change was statistically significant and a decrease of -13.3% (20-30 Gy), -18.0% (30-40 Gy), -16.2% (40-50 Gy), and -16.8% (50-60 Gy) was observed. No further decrease of perfusion was observed on the third session. The mean regional changes were between -1.4% and 3.0% and the results were not statistically significant for any dose.
Global decrease of perfusion was observed in healthy tissue 3 months after the radiochemotherapy. The decrease was correlated with the dose received. No further decrease of perfusion was observed 6 months after the therapy.

  • Contribution to proceedings
    54. Jahrestagung der DGN, 20.04.2016, Dresden, Germany
    Proceedings der 54. Jahrestagung der DGN
  • Poster
    54. Jahrestagung der DGN, 20.04.2016, Dresden, Germany

Publ.-Id: 23695

Bestimmung der zerebrovaskulären Reserve mit BOLDMRT unter Atemanhalten bei Patienten mit Stenosen der hirnversorgenden Gefäße

Krukowski, P.; Petr, J.; Puetz, V.; Abramyuk, A.; Linn, J.; Gerber, J.

Die Autoregulation der zerebralen Perfusion ist wichtiger Mechanismus der Homöostase. Hyperkapnie führt im gesunden Gefäßbett zur Dilatation präkapillärer Gefäße und zur Aktivierung der zerebralen Perfusionsreserve (CVR). BOLD (Blood Oxygen Level Dependent)-MRT unter Atemanhalten stellt die Veränderungen dar. Bei Patienten mit Stenosen hirnversorgender Arterien akquirierten wir prospektiv ein BOLD-MRT unter Atemanhalten, evaluierten die Machbarkeit und korrelierten die Zielstenose mit den BOLD-Veränderungen. Wir werteten das BOLD-MRT modell-basiert (Block-Design gefaltet mit der hämodynamischen Antwortfunktion) aus. Die maximale Kreuzkorrelation des Modells mit der durchschnittlichen Signalantwort des Patienten ergab die individuelle Antwort-Verzögerung des BOLD-Signals zum Stimulus Atemanhalten. Least-square fittings des modellierten Signalverlaufs mit den gemessenen Daten ergaben statistische Parameterkarten, die mit einer T1-gewichteten MRT registriert wurden. Wir werteten keine oder negative BOLDAntworten als pathologisch. Wir beurteilten die Parameterkarten im 3-Leser-Konsensus.
Bei 48 von 58 Patienten (82,8 %) waren die Parameterkarten beurteilbar. 36 Patienten hatten eine symptomatische, 12 hatten eine asymptomatische Stenose. 28 Patienten (58 %) hatten Veränderungen der CVR im Stromgebiet der Zielstenose (bei 21 symptomatischen und 7 asymptomatischen). Die Häufigkeit von BOLD-Veränderungen war bei Patienten mit symptomatischen und asymptomatischen Stenosen gleich (58,3 %).
In der Mehrzahl der Patienten sind BOLD-CVR-Veränderungen im Stromgebiet der stenosierten Arterie nachweisbar. Die Lesbarkeit sollte durch alternative Auswerte-Algorithmen verbessert werden.

  • Contribution to proceedings
    50. Jahrestagung der Deutschen Gesellschaft für Neuroradiologie, 15.10.2015, Gürzenich, Köln, Deutschland
    Clinical Neuroradiology: Springer
    DOI: 10.1007/s00062-015-0445-4
  • Poster
    50. Jahrestagung der Deutschen Gesellschaft für Neuroradiologie, 15.10.2015, Gürzenich, Köln, Deutschland

Publ.-Id: 23694

Development of Laser-Driven Proton Beam Therapy

Karsch, L.; Beyreuther, E.; Enghardt, W.; Gotz, M.; Hermannsdörfer, T.; Krause, M.; Masood, U.; Pawelke, J.; Sauerbrey, R.; Schramm, U.; Schürer, M.; Baumann, M.

no abstract available

Publ.-Id: 23692

Design and implementation of a robust and cost-effective double-scattering system at a horizontal proton beamline

Helmbrecht, S.; Baumann, M.; Fiedler, F.; Enghardt, W.; Krause, M.; Lühr, A.

With an increasing number of proton therapy facilities coming into operation, also the interest for research at proton beams increases. Though many centers provide beam at an experimental room, some of these rooms do not feature a device for radiation field shaping, a so called nozzle.
Therefore, a robust, mobile, and cost-effective double-scattering system for horizontal proton beamlines has been designed and implemented.

Materials and methods:
The nozzle is based on the double scattering technique. Two lead scatterers, an aluminum ridge-filter and two brass collimators were optimized in a simulation study to form a laterally homogeneous 10 cm x 10 cm field with a spread-out Bragg-peak (SOBP).
The parts were mainly manufactured using 3D printing techniques and the system was set up at the experimental beamline of the University Proton Therapy Dresden (UPTD).
Measurements of the radiation field were carried out using a water phantom.

High levels of dose homogeneity were found in lateral (dose variation ΔD < ±2%) as well as in beam direction (ΔD < ±3% in the SOBP). The system has already been used for radiobiology and physical experiments.

The presented setup allows for creating clinically realistic extended radiation fields at fixed horizontal proton beamlines and is ready to use for internal and external users.
The excellent performance combined with the simplistic design let it appear as a valuable option for proton therapy centers intending to foster their experimental portfolio.

Keywords: radiation field formation; radiobiology; ion beam therapy; proton therapy; cancer


Publ.-Id: 23691

Reducing in-core zinc borate precipitation after LOCA in pressurized water reactors

Kryk, H.; Harm, U.; Hampel, U.

During the sump recirculation phase after loss-of-coolant accidents (LOCAs) in pressurized water reactors (PWRs), coolant spilling from the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps as part of the emergency core cooling system (ECCS).
Lab-scale studies within previous research projects have shown that the long-term contact of the boric acid containing coolant with hot-dip galvanized steel containment internals may cause corrosion of the corresponding materials influencing the cooling water chemistry due to dissolution of the zinc coat. Generic experimental investigations regarding the solubility of Zn corrosion products in boric acid solutions resulted in a decreasing solubility with increasing temperature. Thus, precipitation of solid corrosion products (zinc borates) cannot be ruled out if zinc containing coolant is heated up due to its recirculation into hot zones.
Consequently, generic corrosion experiments were carried out in a lab-scale corrosion test facility aiming at the development and test of water-chemical measures to prevent zinc corrosion and zinc borate precipitation in boric acid containing coolants.
The experimental results showed a decreasing corrosion rate with increasing pH value of the coolant. Thus, the risk of zinc borate precipitation can be reduced by addition of alkalizing media to the coolant after a LOCA. However, by adding of a moderate amount of alkalizing media to enhance the coolant pH into the neutral region, the zinc borate precipitation rate can be reduced only to about one third but not fully prevented. Extensive suppression of zinc corrosion and zinc borate precipitation is only achievable from a coolant pH of 7.5 resulting in a lithium concentration of 125 ppm if LiOH is used as alkalizing additive. Furthermore, foaming of the coolant cannot be ruled out if the coolant pH is increased into the slightly alkaline region.

Keywords: pressurized water reactor; loss-of-coolant accidents; corrosion; zinc; zinc borate; downstream effects

  • Lecture (Conference)
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Germany
  • Contribution to proceedings
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Germany
    Proceedings 47th Annual Meeting on Nuclear Technology, Berlin: INFORUM Verlags- und Verwaltungsgesellschaft mbH, 978-3-926956-97-2

Publ.-Id: 23690

Bit-Vectorized GPU Implementation of a Stochastic Cellular Automaton Model for Surface Growth

Kelling, J.; Ódor, G.; Gemming, S.

Stochastic surface growth models aid in studying properties of universality classes like the Kardar--Parisi--Zhang class. High precision results obtained from large scale computational studies can be transferred to many physical systems. Many properties, such as roughening and some two-time functions can be studied using stochastic cellular automaton (SCA) variants of stochastic models. Here we present a highly efficient SCA implementation of a surface growth model capable of simulating billions of lattice sites on a single GPU. We also provide insight into cases requiring arbitrary random probabilities which are not accessible through bit-vectorization.

Keywords: Surface Growth; Kardar-Parisi-Zhang; GPU; Monte-Carlo; Stochastic Cellular Automaton

  • Contribution to proceedings
    20th Jubilee IEEE International Conference on Intelligent Engineering Systems 2016, 30.06.-02.07.2016, Budapest, Ungarn
    Proceedings of the 20th Jubilee IEEE International Conference on Intelligent Engineering Systems 2016: IEEE
    DOI: 10.1109/INES.2016.7555127
  • Lecture (Conference)
    20th Jubilee IEEE International Conference on Intelligent Engineering Systems 2016: IEEE, 30.06.-02.07.2016, Budapest, Ungarn
  • Contribution to WWW

Publ.-Id: 23689

The Sorption Processes of U(VI) onto SiO2 in the Presence of Phosphate: from Binary Surface Species to Precipitation

Comarmond, M. J.; Steudtner, R.; Stockmann, M.; Heim, K.; Müller, K.; Brendler, V.; Payne, T. E.; Foerstendorf, H.

The ternary system containing aqueous U(VI), aqueous phosphate and solid SiO2 was comprehensively investigated using a batch sorption technique, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and Surface Complexation Modeling (SCM). The batch sorption studies on silica gel (10 g/L) in the pH range 2.5 to 5 showed no significant increase in U(VI) uptake in the presence of phosphate at equimolar concentration of 20 µM, but significant increase in U(VI) uptake was observed for higher phosphate concentrations. In situ infrared and luminescence spectroscopic studies evidence the formation of two binary U(VI) surface species in the absence of phosphate, whereas after prolonged sorption in the presence of phosphate, the formation of a surface precipitate, most likely an autunite-like phase, is strongly suggested. From SCM, excellent fitting results were obtained exclusively considering two binary uranyl surface species and the formation of a solid uranyl phosphate phase. The results of this study indicate that the sorption of U(VI) on SiO2 in the presence of inorganic phosphate initially involves binary surface-sorption species and evolves towards surface precipitation.


Publ.-Id: 23688

Coordination polymers of tetravalent neptunium with aromatic polycarboxylate ligands

Martin, N.; März, J.; Henry, N.; Volkringer, C.; Ikeda-Ohno, A.; Hennig, C.; Loiseau, T.

Coordination polymers are organic-inorganic complexes built up from the association of metallic centers with O- or N-donor ligands. In the particular case of actinides, previous literatures mainly have reported the synthesis of solid networks bearing U(VI) or Th(IV). Trans-uranium elements have been much less studied due to their high radiotoxicity and limited amount of the material source. Among the possible oxidation states of actinides (An), the tetravalent state has been investigated most actively and large polynuclear oxo-clusters have been isolated for U1,2 or Pu3. In contrast, there is very few data concerning Np(IV) compounds. In 2012, Takao et al.4 reported the presence of a hexanuclear cluster of Np(IV) in an aqueous solution, which is the only polyoxo cluster reported for Np(IV) thus far. The knowledge of the formation of such polynuclear An(IV) species could be of significant importance for the fate of An in contaminated soils containing O-donor ligands, such as humic acids or organic pollutants (e.g. phthalates). In the present work, we studied the crystallization of Np(IV) with various aromatic polycarboxylate ligands in different solvents and analyzed their crystal structures. In water, an infinite chain of Np2O2(H2O)2(1,2-bdc)2 were isolated in the presence of phthalate. This compound crystallizes as aggregates of orange plates, whereas the analogue compound with uranium is obtained as green crystals. With mellitic acid the oxidation of Np(IV) to Np(V) was observed and led to large green plates. Single-crystal XRD analysis revealed layers of {NpO7H2O0-2} units linked to each other via trans-dioxo neptunyl bonds. Similar coordination environments have been observed in the other neptunium(V) compounds5.
The use of other solvents allowed the crystallization of large polynuclear discrete Np(IV) clusters. For example, using DMF, the hexanuclear unit of [Np6O4(OH)4] has been obtained with different dicarboxylic ligands and is the basic building unit to form an open-framework structure. The corresponding structures revealed for the first time the isolation of the hexanuclear cluster An6O8 with Np(IV). These clusters are linked by the ligand creating tetrahedral and octahedral voids in the structure.

Keywords: actinides; neptunium; carboxylates; metal-organic complex; metal-organic framework; polymers; structure characterisation

  • Lecture (Conference)
    Plutonium Futures 2016, 18.-22.09.2016, Baden-Baden, Germany

Publ.-Id: 23687

Tunable Picosecond Laser Pulses via the Contrast of Two Reverse Saturable Absorption Phases in a Waveguide Platform

Tan, Y.; Chen, L.; Wang, D.; Chen, Y.; Akhmadaliev, S.; Zhou, S.; Hong, M.; Chen, F.

How to enhance the optical nonlinearity of saturable absorption materials is an important question to improve the functionality of various applications ranging from the high power laser to photonic computational devices. We demonstrate the saturable absorption (SA) of VO2 film attributed to the large difference of optical nonlinearities between the two states of the phase-transition materials (VO2). Such VO2 film demonstrated significantly improved performance with saturation intensity higher than other existing ultrathin saturable absorbers by 3 orders due to its unique nonlinear optical mechanisms in the ultrafast phase change process. Owing to this feature, a Q-switched pulsed laser was fabricated in a waveguide platform, which is the first time to achieve picosecond pulse duration and maintain high peak power. Furthermore, the emission of this VO2 waveguide laser can be flexibly switched between the continuous-wave (CW) and pulsed operation regimes by tuning the temperature of the VO2 film, which enables VO2-based miniature laser devices with unique and versatile functions.

Publ.-Id: 23686

Zwitterionic polymer-coated ultrasmall superparamagnetic iron oxide nanoparticles with low protein interaction and high biocompatibility

Pombo-García, K.; Weiss, S.; Zarschler, K.; Ang, C.-S.; Hübner, R.; Pufe, J.; Meister, S.; Seidel, J.; Pietzsch, J.; Spiccia, L.; Stephan, H.; Graham, B.

We report the synthesis and detailed in vitro evaluation of zwitterionic ultrasmall superparamagnetic iron oxide NPs (USPIONs) comprised of oleic acid/oleyl alcohol-stabilized magnetite particles (5 nm core diameter) coated with an amphiphilic zwitterionic polymer, poly(maleic anhydride-alt-1-decene) substituted with 3-(dimethylamino)propylamine (PMAL). These particles display a near-neutral zeta potential at pH ≥ 7 and possess high colloidal stability, maintaining a hydrodynamic diameter of ca. 15–20 nm over a wide range of pHs (4–10) and ionic strength (up to 1 M NaCl). They exhibit very low levels of nonspecific protein binding upon exposure to serum, and negligible uptake by phagocytic and non-phagocytic hepatocarcinoma cells, which suggests that they may be able to resist rapid accumulation in the liver and spleen, a common in vivo fate for NPs. The PMAL-USPIONs exhibit very low cytotoxicity and do not elicit an inflammatory response or display hemolytic activity in vitro. Minimal nonspecific uptake by either cancerous or non-cancerous cell lines was observed, an important precondition to achieve highly selective targeting upon further functionalization with an active targeting agent (e.g., antibody or peptide). Overall, this study establishes the considerable potential of PMALUSPIONs as a platform for the future development of “stealth” NP-based imaging and/or therapeutic agents.

Keywords: Iron oxide nanoparticles; zwitterionic coatings; protein corona; macrophages; proteomics


Publ.-Id: 23685

Highlights on metallic photocathodes used in SRF gun

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

For the accelerator-based light sources and the electron colliders, the development of photoinjectors has become a key technology. Especially for the superconducting radio frequency cavity based injector (SRF Gun), the searching for better photocathodes is always a principal technical challenge. To use metallic photocathodes for ELBE SRF Gun is the primary choice to prevent cavity contamination. In this contribution, we will report the investigation of Magnesium (Mg) in ELBE SRF gun, including laser cleaning treatment and the measurement on quantum efficiency, Schottky effect, dark current and damage threshold.

Keywords: SRF gun; photocathode; metallic cathode; magnesium

  • Poster
    the Seventh International Particle Accelerator Conference (IPAC’16), 08.-13.05.2016, Busan, Korea
  • Open Access Logo Contribution to proceedings
    the Seventh International Particle Accelerator Conference (IPAC’16), 08.-13.05.2016, Busan, Korea

Publ.-Id: 23684

Wire-mesh Sensors: Recent Developments and Applications

Schleicher, E.; Tschofen, M.; Kipping, R.; Hampel, U.

Wire-mesh sensors (WMS) are today well established measurement tools to obtain both temporally and spatially highly resolved structural information as well as averaged phase fraction and phase fraction distribution data in air-water and steam-water two-phase flow experiments. Those data, with a spatial resolution of down to 0.5 mm and frame rates up to 10,000 frames per second are suitable to validate CFD code developments. During the last decade, the technology has widely spread in research laboratories all over the world and has been more and more developed towards a turnkey machine for researchers. In this work we summarize the most recent developments in hardware for high temperature and high pressure applications, new electronics with integrated void fraction calculations and flow pattern identification for industrial applications and latest software developments for data analysis and visualization.

A big issue for the application of wire-mesh sensor technology to high pressure high temperature facilities is the complicated pressure-proven and temperature-resistant insulated support and feedthrough of the measuring electrodes. Our new development facilitates a compact metallic body with flanges on both sides with a slot in sensor unit consisting of ceramic insulators and a stainless steel frame. The feedthrough of the wires is realized by commercially available multiple feedthrough fittings.

The most common and proved codes for WMS data analysis have been capsulated in our wire-mesh sensor data processing FrameWork. The tool has got a new, user friendly graphical interface and allows the implementation of new algorithms by the end user. The resulting data and profiles can be visualized within the software and a batch processing tool allows automated “over the weekend” jobs.

The wire-mesh sensor technology so far is a scientific tool for researchers. The huge amount of data, several gigabytes for one measurement of a couple of seconds, has to be stored and processed offline later on. For industrial applications, the users need online data on liquid/gas holdups and flow pattern in the pipelines. An industrial type of wire-mesh sensor electronics has been developed based on an FPGA (field programmable gate array) microcontroller calculating the frame averaged void fraction instantaneously and moreover identifying the flow pattern based on statistical values of the last 10 seconds from the two-phase flow using Fuzzy clustering algorithm.

Keywords: Industrial Process Tomography; Two-Phase Flow Measurement; Wire-Mesh Sensor

  • Contribution to proceedings
    SWINTH-2016, Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics, 15.-17.06.2016, Livorno, Italy
    Proceedings of SWINTH-2016
  • Lecture (Conference)
    SWINTH-2016, Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics, 15.-17.06.2016, Livorno, Italia

Publ.-Id: 23683

X-ray radioscopy as a powerful tool for visualization of liquid metal bubbly flows

Roshchupkina, O.; Shevchenko, N.; Strumpf, E.; Hoppe, D.; Eckert, S.

Many technical applications in metallurgy and the quality of continuous casting rely on liquid metal two-phase flows. Injection of the Argon gas became an integral part of continuous casting since it prevents clogging of the casting nozzle and also separates alumina particles from the melt. On the other hand, injection of gas has many side effects as for example induction of highly turbulent complex two-phase flows. There exist many numerical simulations and water models, but due to large differences in physical properties between water and liquid metals water models and experiments cannot be fully extended to liquid metals. Therefore, direct investigation and understanding of liquid metal two-phase flows became critical. In the present work we demonstrate that X-ray radiography can be used as a powerful tool for the visualization of liquid metal two-phase flows. Here we present an experimental study of ascending bubble chains over a wide range of gas flow rates in GaInSn alloy at room temperature. We report on differences in bubble release frequency, shape, size, velocity etc. and additionally compare with experiments in water. The efficiency of the corresponding measurement technique is primarily validated in water experiments.

* The research is supported by the German Helmholtz Association in form of the Helmholtz-Alliance “LIMTECH”.

Keywords: X-ray radiography; two-phase flows; GaInSn; water

  • Lecture (Conference)
    9th International Conference on Multiphase Flow, 22.-27.05.2016, Firenze, Italy

Publ.-Id: 23682

Topologically stable magnetization states on a spherical shell: curvature stabilized skyrmion

Kravchuk, V. P.; Rößler, U. K.; Volkov, O. M.; Sheka, D. D.; van den Brink, J.; Makarov, D.; Fangohr, H.; Gaididei, Y.

Topologically stable structures, e.g. vortices in a wide variety of matter, skyrmions in ferro- and antiferromagnets, hedgehog point defects in liquid crystals and ferromagnets, are characterized by integer valued topological quantum numbers. In this context the closed surfaces are a prominent subject of study, because they realize a link between fundamental mathematical theorems and real physical systems. Here we perform a topological analysis of equilibrium magnetization states for a thin spherical shell with easy-normal anisotropy. Skyrmion solutions are found for a range of parameters. These magnetic skyrmions on a spherical shell have two principal differences compared to the planar case: (i) they become topologically trivial, and (ii) can be stabilized by curvature effects only, also when Dzyaloshinskii-Moriya interactions are absent. Due to its specific topological nature a skyrmion on a spherical shell can be simply induced by an uniform external magnetic field.

Keywords: Dzyaloshinskii-Moriya interaction; skyrmion; curvature induced effects

Publ.-Id: 23681

Purely Antiferromagnetic Magnetoelectric Random Access Memory

Kosub, T.; Kopte, M.; Hühne, R.; Appel, P.; Shields, B.; Maletinsky, P.; Hübner, R.; Liedke, M. O.; Fassbender, J.; Schmidt, O. G.; Makarov, D.

Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy-efficiency. We propose and realize purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50 times lower writing threshold compared to ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we realize reliable isothermal switching via gate voltage pulses and all-electric read-back at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed and removed for read-out allowing permanent magnets to be used. Based on our prototypes of these novel systems, we construct a comprehensive model of the magnetoelectric selection mechanism in thin films of magnetoelectric antiferromagnets. We identify that growth induced effects lead to emergent ferrimagnetism, which interferes with the linear magnetoelectric effect. After pinpointing lattice misfit as the likely origin, we provide routes to enhance or mitigate this emergent ferrimagnetism as desired. AF-MERAM cells are a general concept for antiferromagnetic spintronics and not limited to memory applications.

Keywords: Magnetoelectric Random Access Memory; Antiferromagnets; anomalous Hall magnetometry; zero-Offset Hall

Publ.-Id: 23680

Synthesis, Morphological, and Electro-optical Characterizations of Metal/Semiconductor Nanowire Heterostructures

Glaser, M.; Kitzler, A.; Johannes, A.; Prucnal, S.; Potts, H.; Conesa-Boj, S.; Filipovic, L.; Kosina, H.; Skorupa, W.; Bertagnolli, E.; Ronning, C.; Fontcuberta I. Morral, A.; Lugstein, A.

In this letter, we demonstrate the formation of unique Ga/GaAs/Si nanowire heterostructures, which were successfully implemented in nanoscale light-emitting devices with visible room temperature electroluminescence. Based on our recent approach for the integration of InAs/Si heterostructures into Si nanowires by ion implantation and flash lamp annealing, we developed a routine that has proven to be suitable for the monolithic integration of GaAs nanocrystallite segments into the core of silicon nanowires. The formation of a Ga segment adjacent to longer GaAs nanocrystallites resulted in Schottky-diode-like I/V characteristics with distinct electroluminescence originating from the GaAs nanocrystallite for the nanowire device operated in the reverse breakdown regime.
The observed electroluminescence was ascribed to radiative band-to-band recombinations resulting in distinct emission peaks and a low contribution due to intraband transition, which were also observed under forward bias. Simulations of the obtained nanowire heterostructure confirmed the proposed impact ionization process responsible for hot carrier luminescence. This approach may enable a new route for on-chip photonic devices used for light emission or detection purposes.

Keywords: Nanowires; flash lamp annealing; ion implantation; GaAs; Si; liquid phase epitaxy

Publ.-Id: 23679

The effect of millisecond flash lamp annealing on electrical and structural properties of ZnO:Al/Si structures

Lindberg, P. F.; Lipp Bregolin, F.; Wiesenhütter, K.; Wiesenhütter, U.; Riise, H. N.; Vines, L.; Prucnal, S.; Skorupa, W.; Svensson, B. G.; Monakhov, E. V.

The effect of millisecond flash lamp annealing (FLA) on aluminum doped ZnO (AZO) films and their interface with Si have been studied. The AZO films were deposited by magnetron sputtering on Si (100) substrates. The electrical and structural properties of the film and AZO/Si structures were characterized by current–voltage, capacitance–voltage, and deep level transient spectroscopy measurements, X-ray diffraction, and secondary ion mass spectrometry. The resistivity of the AZO film is reduced to a close to state-of-the-art value of 2x10-4Ohmcm after FLA for 3ms with an average energy density of 29 J/cm2. In addition, most of the interfacial defects energy levels are simultaneously annealed out, except for one persisting shallow level, tentatively assigned to the vacancy-oxygen complex in Si, which was not affected by FLA. Subsequent to the FLA, the samples were treated in N2 or forming gas (FG) (N2/H2, 90/10%mole) ambient at 200–500 C. The latter samples maintained the low resistivity achieved after the FLA, but not the former ones. The interfacial defect level persisting after the FLA is removed by the FG treatment, concurrently as another level emerges at ~0.18 eV below the conduction band. The electrical data of the AZO films are discussed in term of point defects controlling the resistivity, and it is argued that the FLA promotes formation of electrically neutral clusters of Zink vacancies (VZn’s) rather than passivating/compensating complexes between the Al donors and VZn’s.

Keywords: AZO; flash lamp annealing; magnetron sputtering; doping

  • Journal of Applied Physics 119(2016), 185305
    Online First (2016) DOI: 10.1063/1.4948666

Publ.-Id: 23678

Narrow-band tunable terahertz emission from ferrimagnetic Mn3-xGa thin films

Awari, N.; Kovalev, S.; Fowley, C.; Rode, K.; Gallardo, R. A.; Lau, Y.-C.; Betto, D.; Thiyagarajah, N.; Green, B.; Yildrim, O.; Lindner, J.; Fassbender, J.; Coey, J. M. D.; Deac, A. M.; Gensch, M.

Narrow-band terahertz emission from coherently excited spin precession in metallic Mn3-xGa Heusler alloy nanofilms has been observed. The efficiency of the emission, per nanometer film thickness, is comparable or higher than that of classical laser-driven terahertz sources based on optical rectification. The center frequency of the emission from the films can be tuned precisely via the film composition making this type of metallic films a candidate for efficient on-chip terahertz emitters. Terahertz emission spectroscopy is potentially a sensitive probe of magnetic properties of ultra-thin films.

Keywords: THz emission; ferrimagnets; spin excitations

Publ.-Id: 23677

NeptuniumV retention by siderite under anoxic conditions: Precipitation of NpO2–like nanoparticles and of NpIV pentacarbonate

Scheinost, A. C.; Steudtner, R.; Hübner, R.; Weiss, S.; Bok, F.

The NpV retention by siderite, an FeII carbonate mineral with relevance for the near-field of high-level radioactive waste repositories, was investigated under anoxic conditions. Batch sorption experiments show that siderite has a high affinity for aqueous NpVO2+ across pH 7 to 13 as expressed by solid-water distribution coefficients, log Rd, >5, similar to the log Rd determined for the (solely) tetravalent actinide Th on calcite, suggesting reduction of NpV to NpIV by siderite. Np L3-edge X-ray absorption near edge (XANES) spectroscopy conducted in a pH range typical for siderite-containing host rocks (7 - 8), confirmed the tetravalent Np oxidation state. Extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed a local structure in line with NpO2–like nanoparticles with diameter < 1 nm, a result further corroborated by high-resolution transmission electron microscopy (HRTEM). The low solubility of these NpO2–like nanoparticles (10-9 M), along with their negligible surface charge at neutral pH conditions which favors particle aggregation, suggest an efficient retention of Np in the near-field of radioactive waste repositories. When NpV was added to ferrous carbonate solution, the subsequent precipitation of siderite did not lead to a structural incorporation of NpIV by siderite, but caused precipitation of a NpIV pentacarbonate phase.

Keywords: neptunium; siderite; carbonate; radioactive waste respository; XAFS; XANES


Publ.-Id: 23676

Speciation of tetravalent uranium with inorganic ligands in aqueous solution investigated by UV/vis and time-resolved laser-fluorescence measurements.

Lehmann, S.; Steudtner, R.; Brendler, V.

This work is focused on uranium as the major component of spent nuclear fuel. For safety assessment of a future repository it is important to predict the environmental behavior of uranium in diluted to highly saline aquifer systems. Currently most reports are related to the hexavalent oxidation state which is stable under oxidizing conditions. However, reducing conditions are expected in the near field of high level nuclear waste repository after sealing the repository. Therefore, the major purpose of this study is to improve the knowledge of the physico-chemical properties of the tetravalent uranium and to provide thermodynamic data to enable a better prediction of speciation and solubility limits under reducing conditions.
The aim of this study is to examine the potential of U(IV) fluorescence for speciation studies. Kirishima et al. described in 2004 for the first time the luminescence spectra of the free U(IV) ion [1, 2]. Since then, only a few studies on U(IV) fluorescence properties have been published [3, 4]. However, spectroscopic data of U(IV) are necessary to provide a basic understanding of the U(IV) speciation under environmental conditions. We used in our study a combination of UV/vis spectroscopy with long path flow cell and time-resolved laser-induced fluorescence spectroscopy (TRLFS).
First, a U(IV) stock solution was produced by reduction in an electrochemical cell and was monitored by UV/vis spectroscopy. The residual content of U(VI) was determined by TRLFS to be lower than 1%. After that, we studied the aqueous speciation in presence of various inorganic ligands (ClO4–, Cl–, SO42–, PO43–, CO32–). To perform TRLFS measurements of U(IV) a laser system employing a Nd/YAG driven OPO system as excitation source with λexc = 245 nm were installed including a cryogenic unit for measurements at liquid nitrogen temperature (77 K). We detected the luminescence of the free U(IV) ion in acidic aqueous solution at room temperature (rt) and in frozen state at 77 K. At rt we observe the typical fluorescence properties of U(IV) with the peak maxima at 321, 410 and 523 nm and a fluorescence decay time of 2.6 ± 0.3 ns in perchloric and chloric acid. The detection limit of 10–5 M at rt was determined. By using cryo-TRLFS at 77 K the detection limit was lowered to 5x10–6 M and the fluorescence lifetime increases up to 148.4 ± 6.5 ns. The spectroscopic results are in good agreement with earlier reports for rt [3] and cryo measurements [2]. In contrast to U(VI), which is often quenched by chloride, a well resolved luminescence spectrum of U(IV) was obtained in 0.1 as well as in 1 M HCl.
The potential of U(IV) fluorescence for speciation analysis was assessed in this study. With our setup we could study aqueous U(IV) systems with concentrations lower than 10–5 M and this corresponds to uranium concentrations occurring in the environment [5, 6].

[1] A. Kirishima, Chem. Commun., 2003, (7), 910-911.
[2] A. Kirishima, Radiochim. Acta, 2004, 92, 705-710.
[3] S. Lehmann, J. Radioanal. Nucl. Chem., 2010 283(2), 395-401.
[4] N. Aoyagi, N., J. Radioanal. Nucl. Chem., 2015, 303(2), 1095-1098.
[5] T. Arnold, Geochim. Cosmochim. Acta, 2011, 75(8), 2200-221.
[6] G. Bernhard, J. Alloys Compd., 1998, 271, 201-205.

Keywords: tetravalent uranium; aqueous solution; fluorescence; speciation

  • Lecture (Conference)
    Ninth International Conference on Nuclear and Radiochemistry - NRC9, 29.08.-02.09.2016, Helsinki, Finnland

Publ.-Id: 23675

Redox Stability of Uranium in High Ionic Strength Media: An Electrochemical and Spectroscopic Study

Lehmann, S.; Bok, F.; Ikeda-Ohno, A.; Muñoz, A. G.

Knowledge of redox behavior of uranium in concentrated solutions of the hexary oceanic salt system is essential for the transport modeling of radioactive nuclides in repositories for the long-term disposal of radioactive wastes in rock salt formations. Especially critical is the behavior of the couple U(IV)/U(VI) in the surrounding high ionic strength saline milieu, which regulates the release of mobile U(VI) species at given redox conditions defined by the presence of trace oxygen. The redox potential (Eredox) and the solubility in brines in particular implicate the activity of the different ligand- and hydroxo-complexes (ai): Eredox = f(mi, ai, βj), where βj is the complexation constant. Thus, the prediction of transport behavior of uranium at given chemical environments needs appropriate complexation and thermodynamic models assuming the ionic activities beyond the limited Debye-Hückel theory. This latter is supplied by the Pitzer formulation [1], where deviations from the limit Debye-Hückel behavior are given by specific interaction parameters among the constituting ionic species, which have to be determined experimentally.
The kinetics of the electrochemical reduction and oxidation reactions was studied in a three-electrodes type cell using a Au working electrode, Pt wire counter electrode and a Ag/AgCl in3 M KCl reference electrode. Experiments were performed under an oxygen-free atmosphere in a glove-box. Cyclic voltammetry (CV) and normal pulse voltammetry (NPV) were applied to investigate the influence of chloride concentrations in the kinetics parameters, such as reaction rate, k, and the diffusion coefficient in solutions containing U(VI) or U(IV) in HCl solutions from 0.1 to 1.3 M. The solution speciation of uranium was investigated by UV/vis absorption spectroscopy.
Reference: [1] K.S. Pitzer in Activity coefficients in electrolyte solutions, Ch.3, CRC Press, Boca Raton, Florida, 1991.

Keywords: uranium; saline solutions; electrochemistry; redox behaviour; Pitzer

  • Lecture (Conference)
    PRIME 2016 - Pacific rim meeting on electrochemical and solid-state science, 02.-07.10.2016, Honolulu, Hawaii, USA

Publ.-Id: 23674

Self-Assembled Magnetite Mesocrystalline Films: Towards Structural Evolution from 2D to 3D Superlattices

Brunner, J.; Baburin, I. A.; Sturm, S.; Kvashnina, K.; Rossberg, A.; Pietsch, T.; Andreev, S.; Sturm, E.; Cölfen, H.

This study describes synthesis and detailed characterization of 2D and 3D mesocrystalline films produced by self-assembly of iron oxide (magnetite) truncated nanocubes. The orientational relations between nanocrystals within the superlattice are examined and atomistic models for a detailed description of the structures of the 2D and 3D mesocrystals are introduced. The most efficient space filling within the 3D superstructure is achieved by changing the orientational order of the nanoparticles and following the “bump-tohollow” packing principle. These data provide a fundamental understanding of a mesocrystal formation mechanism and their structural evolution. Structure, composition and magnetic properties of the synthesised nanoparticles are also characterized.

Keywords: magnetite; nanoparticle; self-assembly; mesocrystal; particle films

Publ.-Id: 23673

Complexation studies of modified calix[4]arenes with uranium in non-aqueous solution

Bauer, A.; Schmeide, K.; März, J.; Jäschke, A.; Glasneck, F.; Kersting, B.

The actinide uranium, well known from nuclear power cycle, plays also a role in rare earth production. The rare earth ores contain, apart from various other components, the actinides uranium and thorium occur as undesired constituents. To facilitate the production of rare earth elements, uranium and thorium have to be removed. Due to their modifiable selectivity and solubility calix[n]arenes are interesting compounds for the extraction of actinides and lanthanides. The chalice-like macrocyclic molecules consist of para-substituted phenolic units. The para-substitution determines the solubility of the molecule and the hydroxyl groups serve either directly as complexation site or can be further functionalized to adjust the selectivity of the calix[n]arene.
Several calix[4]arenes with affinity towards actinides or lanthanides are available. These are to be applied to eliminate uranium (IV)/(VI) and thorium from ore concentrates and subsequently, to separate lanthanides. The separation method based on liquid-liquid extraction utilizing the calix[4]arenes. Thereby metal calix[4]arene complexes are formed in the organic phase. For better process understanding we investigated the mechanisms of uranium interaction with the synthesized calix[4]arenes by UV-Vis spectroscopy, TRLFS, isothermal titration calorimetry, single crystal XRD and extraction experiments. The calix[4]arene modified with 8-hydroxychinolin derivatives called L1 is one of the new calix[4]arenes. It achieves a U(VI) extraction yield between 90 to 100 % in the pH range of 4 to 9. It possesses two potential binding sites for U(VI). Stoichiometry determination by the Job´s Plot from UV-Vis data indicates a ligand to metal ratio of 1:2 (Fig. 1). The calix[4]arene-L1 complex absorbs at 280 nm. During spectrophotometric titration of L1 with U(VI) in acetonitrile the absorption maximum decreases and new peaks at 318, 360 and 525 nm occur. Luminescence signals of L1 and uranyl nitrate in acetonitrile are weakened by complex formation. First microcalorimetric measurements confirm the binding of two metal ions by L1. All measurements in solution were carried out at 25°C. In addition to the UV-Vis spectroscopy and isothermal titration calorimetry, the capillary electrophoresis is to be used for determining stability constants.
Whereas in solution a stoichiometry of 1:2 is obviously preferred, the single crystal XRD analysis reveals a formation of a 1:1 U(VI)-L1 complex (Fig. 2). Thereby the hexavalent uranyl ion is coordinated by the singly deprotonated ligand via a N2O2 donor set. The charge is compensated by an additional coordinated nitrate ion. To complete the structure information of the formed U(VI)-L1 complex in solution mass spectrometric and NMR measurements as well as theoretical studies are currently performed. In addition, for better understanding the complexation properties of L1 the interaction with U(IV) and Th(IV) is studied.

Keywords: SE-FLECX; calix[4]arene; uranium; solvent extraction; complexation studies; rare earth production

  • Poster
    The 9th Conference on Nuclear and Radiochemistry – NRC9, 29.08.-02.09.2016, Helsinki, Finnland

Publ.-Id: 23671

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