Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
Uncertainty Analysis of an Interfacial Area Reconstruction Algorithm
Dave, A.; Manera, A.; Beyer, M.; Lucas, D.; Prasser, H.-M.;
Wire mesh sensors (WMS) are state of the art devices that allow high resolution (in space and time) measurement of 2D void fraction distribution in any two-phase flow regime. Data using WMS have been recorded at the Helmholtz Zentrum Dresden Rossendorf (HZDR) [1] for a wide combination of superficial gas and liquid velocities, providing an excellent database for advances in two-phase flow modeling. In two-phase flow, the interfacial area plays an integral role in coupling the mass, momentum and energy transport equations of the liquid and gas phase. While current models used in best-estimate thermal-hydraulic codes (e.g. RELAP5, TRACE, TRACG, etc.) are still based on algebraic correlations for the estimation of the interfacial area in different flow regimes, interfacial area transport equations (IATE) have been proposed to predict the dynamic propagation in space and time of interfacial area [2]. IATE models are still under development and the HZDR WMS experiments would provide an excellent basis for the validation and further advance of these models. The current paper is focused on the algorithms used to reconstruct interfacial area densities from the void-fraction voxel data measured using WMS.
Keywords: wire mesh sensor, two-phase flow, interfacial area transport equation, uncertainty analysis
  • Invited lecture (Conferences)
    16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
    Proceedings of NURETH-16

Publ.-Id: 21840 - Permalink

Direct Condensation and Entrainment steam experiments at the TOPFLOW-DENISE facility
Seidel, T.;
In a hypothetical Small Break Loss of Coolant Accident (SB-LOCA) in a Pressurized Water Reactor (PWR), the Reactor Pressure Vessel wall (RPV) may be exposed to thermal stress, since the Emergency Core Cooling System (ECCS) injects cold water. The loads on the primary loop and RPV walls are determined by mixing processes with the surrounding hot water and by the condensation of steam on the surface.
Computational Fluid Dynamics models are not reliable enough to contribute to reliable safety analysis. For the development and validation of CFD-models, experiments have to meet a high standard of reproducibility, measurement certainty and temporal and local resolution. The pressure tank technology of the TOPFLOW facility allows conducting such experiments at reasonable effort.
The Direct Condensation and Entrainment Installation for Steam Experiments (DENISE) is made for CFD-grade condensation experiments at up to 50 bars pressure. Subcooled water is injected into the DENISE-basin in three different configurations to generate stratified flow, jet and plunging jet (steam entrainment with a jet) experiments with condensation.
The experimental facility is presented along with the high degree of instrumentation. High speed camera, micro thermocouples, coriolis flow meters and movable thermal lances were used.
  • Contribution to proceedings
    46th Annual Meeting on Nuclear Technology, 05.-7.5.2015, Berlin, Deutschland
    Proceedings of the 46th Annual Meeting on Nuclear Technology
  • Lecture (Conference)
    46th Annual Meeting on Nuclear Technology, 05.-7.5.2015, Berlin, Deutschland

Publ.-Id: 21839 - Permalink

Near-wall measurements of the bubble- and Lorentz-force-driven convection at gas-evolving electrodes
Baczyzmalski, D.; Weier, T.; Cierpka, C.; Kähler, C. J.;
Chemical energy storage systems, e.g. in the form of hydrogen or methanol, have a great potential for the establishment of volatile renewable energy sources due to the large energy density. The efficiency of hydrogen production through water electrolysis is, however, limited by gas bubbles evolving at the electrode’s surface and can be enhanced by an accelerated bubble detachment. In order to characterize the complex multi-phase flow near the electrode, simultaneous measurements of the fluid velocities and the size and trajectories of hydrogen bubbles were performed in a water electrolyzer. The liquid phase velocity was measured by PIV/PTV, while shadowgraphy was used to determine the bubble trajectories. Special measurement and evaluation techniques had to be applied as the measurement uncertainty is strongly effected by the high void fraction close to the wall. In particular, the application of an advanced PTV scheme allowed for more precise fluid velocity measurements closer to electrode. This way, the effect of Lorentz forces on the near-wall fluid velocities was investigated. The results show a significantly increased wall parallel liquid phase velocity with increasing Lorentz forces. It is presumed that this enhances the detachment of hydrogen bubbles from the electrode surface and, consequently, decreases the fractional bubble coverage and improves the efficiency. In addition, the effect of large rising bubbles with path oscillations on the near-wall flow was investigated. These bubbles can have a strong impact on the mass transfer near the electrode and thus affect the performance of the process.
Keywords: two-phase flow, gas bubbles, water electrolysis, particle tracking, Lorentz force, MHD effect

Publ.-Id: 21838 - Permalink

18F-JHU94620, a high affinity PET radioligand for imaging of cannabinoid subtype 2 receptors (CB2R)
Moldovan, R.-P.; Deuther-Conrad, W.; Teodoro, R.; Wang, Y.; Fischer, S.; Pomper, M.; Wong, D. F.; Dannals, R. F.; Brust, P.; Horti, A. G.;
CB2R represents a target with increasing importance for neuroimaging due to its upregulation in various pathological conditions. Encouraged by preliminary results obtained with 11C-A-836339 (Ki = 1.2 nM) in a mouse model of acute neuroinflammation (induced by lipopolysaccharide, LPS), we designed a library of fluorinated analogs to develop a radioligand with improved CB2R binding affinity and selectivity.
A series of fifteen analogs of A836339 was synthesized and JHU94620, selected as ligand with the highest CB2R affinity (Ki = 0.38 nM) and selectivity over CB1R (factor 1000). It was labelled from the bromo precursor by standard nucleophilic radiofluorination. For in vivo experiments, control and LPS-treated CD1 mice have been used. Metabolic stability was investigated in plasma samples (30 min p.i) by radio-HPLC. In vitro autoradiography was performed on rat spleen and pig brain using CB1, CB2, and CB1/CB2 specific ligands as competitors.
18F-JHU94620 was prepared in ~10% radiochemical yield, >98% radiochemical purity and specific activity of >150 GBq/μmol. Animal PET revealed a brain uptake comparable to 11C-A-836339. 20-30% higher uptake in LPS-treated mice was found (n=3, p<0.05). In plasma, ~10% of total radioactivity accounted for intact tracer at 30 min p.i. Binding of 18F-JHU94620 on spleen could be displaced by CB2- and CB1/CB2-specific but not by CB1-specific compounds (61%, 44%, and 107% of total binding, respectively, at 1 μM). As expected, in brain slices from healthy pig no specific binding was observed.
18F-JHU94620 is a potential candidate for further studies with PET in neuroinflamation and related disorders.
  • Poster
    SNMMI2015, 05.-10.06.2015, Baltimore, Maryland, USA
  • Open Access LogoAbstract in refereed journal
    Journal of Nuclear Medicine 56(2015)3, 1048

Publ.-Id: 21837 - Permalink

Influence of thyroid hormones on brown adipose tissue activity and browning of white adipose tissues in mice
Krause, K.; Kranz, M.; Weiner, J.; Klöting, N.; Rijntjes, E.; Köhrle, J.; Zeisig, V.; Steinhoff, K.; Deuther-Conrad, W.; Fasshauer, M.; Stumvoll, M.; Sabri, O.; Blüher, M.; Hesse, V.; Brust, P.; Tönjes, A.;
Administration of thyroid hormones (TH) to mammals leads to an increase in basal metabolic rate and thermogenesis. These effects have been attributed to direct actions of TH on metabolically active tissues, such as brown adipose tissue (BAT). Furthermore, TH might stimulate “browning”, i.e. conversion of existing white fat cells to ''brite'' or ''beige'' adipocytes with features of brown adipocytes. However, the impact of TH on BAT activity and “browning” of white adipocytes has not been analyzed under well-controlled conditions in the same experimental setting.
Therefore, it was assessed how thyroid dysfunction, i.e. hyper- and hypothyroidism, affects 1) activity of BAT by 18F-FDG PET/MRI, and 2) affects gene expression of brown and beige adipose tissue differentiation markers in white adipose tissues (inguinal and epididymal, iWAT and eWAT, respectively) and interscapular BAT (iBAT) in mice. We randomized female C57BL/6NTac mice and rendered them hyper- or hyperthyroid (n = 20 per group) according to ATA guidelines (Bianco et al. Thyroid 2014). After 4 weeks of treatment, small animal PET/MR analysis revealed that hypothyroid mice had significantly decreased and hyperthyroid mice had significantly increased interscapular BAT (iBAT) 18F-FDG uptake as compared to euthyroid controls (SUV 3.5 ± 0.7 vs. 6.2 ± 0.6 and SUV 78.0 ± 2.1 vs. 6.16 ± 0.6, respectively). In addition to the findings in iBAT, hypothyroid mice also had significantly diminished glucose disposal in skeletal muscle as compared to both other groups. However, despite the iBAT of hypothyroid mice showing low metabolic activity, significantly higher levels of Ucp1 mRNA was found in iBAT when compared with hyper- and euthyroid animals (p < 0.05 for both). In accordance with these findings, other thermogenic markers including Prdm16, Fgf21, Cidea, Elovl3 and Cox7a1 were all overexpressed in the hypothyroid iBAT. In contrast, the thermogenic genes Ucp1, Prdm16, Fgf21, Cidea, Pgc1α were upregulated in eWAT in hyperthyroid mice as compared to hypothyroid and euthyroid mice. In addition, also markers for beige adipocytes (Cd137, Tmem26), and adipocyte recruitment (Zfp423) were significantly increased in the eWAT of hyperthyroid mice as compared hypo-and euthyroid mice.
In conclusion, these data suggest that TH induce both BAT activity and the thermogenic program in white adipose tissues possibly leading to the browning of white fat depots.
  • Abstract in refereed journal
    Experimental and Clinical Endocrinology & Diabetes 2(2015)123
  • Poster
    58th Symposium of the German Society of Endocrinology, 18.-21.03.2015, Lübeck, Deutschland

Publ.-Id: 21836 - Permalink

Feasibility and Importance of the alpha 7 Nicotinic Acetylcholine Receptor (alpha 7nAChR) as Target for PET Imaging
Deuther-Conrad, W.; Teodoro, R.; Scheunemann, M.; Rötering, S.; Patt, M.; Kranz, M.; Donat, C. K.; Xiong, G.; Fischer, S.; Bucerius, J.; Peters, D.; Cumming, P.; Steinbach, J.; Sabri, O.; Brust, P.;
The α7nAChR is regarded of importance for neurodegeneration, inflammatory processes, certain types of cancer, and in the pathophysiology of atherosclerosis. Our recently developed PET radioligands [18F]NS14490 and [18F]DBT-10 showed high in vitro affinity and selectivity towards α7nAChR. We present the automated syntheses and the preclinical evaluation of both radiotracers by PET in pigs and provide evidence on their suitability for imaging of α7nAChRs in the mentioned diseases.
Materials and Methods:
[18F]NS14490 and [18F]DBT-10 were synthesized using a Tracerlab FX F-N module by direct radiofluorination using the corresponding tosylate and nitro precursors. Dynamic PET studies (~300-400 MBq) were performed in anaesthetized female piglets under control (n=3 each) and blocking conditions (n=3 each; continuous infusion of the highly selective antagonist ligand NS6740). By compartmental modeling using metabolite-corrected plasma input functions the binding parameters in 24 brain regions and on brain blood vessels were estimated. Parametric maps of the distribution volumes (VT) of [18F]NS14490 were calculated. In anticipation of human studies, for [18F]DBT-10 preclinical dose assessment and toxicity studies were performed.
[18F]NS14490 and [18F]DBT-10 were obtained with comparably high RCY (~30-40%), radiochemical purities (~92-95%) and specific activities (>150 GBq/µmol). Maximum brain uptake was reached at 3 min ([18F]NS14490 SUVmax:0.54) and 11.5 min p.i. ([18F]DBT-10 SUVmax:1.89). Comparable metabolism was observed, with 25-30% of both parent compounds in plasma at 60 min p.i. Compartmental modeling allowed reliable estimates of k3’ and binding potential, BPND. NS6740 infusion significantly reduced mean k3’ of [18F]NS14490 by 46% and mean BPND of [18F]DBT-10 by 75%. Reduction of VT on brain blood vessels by NS6740 was clearly visible in parametric maps of [18F]NS14490. SUVmax in blood vessels of 1.3-1.4 was reached at 2-4 min p.i. NS6740 reduced the SUV by 25-35% at 4 h p.i. The estimated effective dose of [18F]DBT-10 administration to humans is 12-14 μSv/MBq. DBT-10 toxicity tests did not predict harmfulness for human tracer studies.
[18F]NS14490 and [18F]DBT-10 are promising PET tracers for imaging of α7nAChR. Our preclinical studies provide evidence for the detection of α7nAChRs by PET in the parenchyma and vasculature of pig brain. This further elucidates the feasibility of PET to visualize vascular α7nAChRs, which may present a tool for investigating involvement of α7nAChRs in the pathophysiology of atherosclerosis. [18F]DBT-10 is selected for further evaluation to obtain approval for translational clinical validation in humans due to its higher affinity, brain uptake, and specific binding.
  • Lecture (Conference)
    EANM 2014, 17.-22.10.2014, Göteborg, Sweden
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 41(2014), 209-210

Publ.-Id: 21835 - Permalink

(Bio)Leaching of copper from Kupferschiefer with citric acid
Kostudis, S.; Bachmann, K.; Kutschke, S.; Pollmann, K.; Gutzmer, J.;
The Central European Kupferschiefer deposit bearing copper up to five percent is the most important natural copper resource in Europe, and thus raised again interest of both industry and science. Due to the complex composition of the shale including copper and sulfide rich ores, carbonates and organic compounds there is no efficient biotechnological approach applied yet. Although promising approaches using acidophilic micoorganisms were presented [1] issues such as acid pretreatment and resulting gypsum waste remain. Thus leaching at neutral and alkalic pH ranges has been investigated using both foreign and indigenous species including yeasts [2-4]. Especially usage of microbially produced organic acids [5] has shown good results regarding copper recovery. In previous studies [4] the impact of glutamic (see figure) and citric acid on copper minerals in Kupferschiefer ore has been examined using bulk chemicals. The presentation compares those results to copper leaching with citric acid as biotechnologically produced product in fermentation broth produced by the yeast Yarrowia lipolytica.
  • Poster
    Goldschmidt2015, 16.-21.08.2015, Prag, Tschechische Republik

Publ.-Id: 21834 - Permalink

P1403 - Kapazitätsdiode, Verfahren zum Herstellen einer Kapazitätsdiode, sowie Speicher und Detektor mit einer solchen Kapazitätsdiode
Schmidt, H.; Selvaraj, L.; Bogusz, A.; Bürger, D.; Prucnal, S.; Skorupa, I.;
Die Erfindung betrifft eine Kapazitätsdiode, ein Verfahren zum Herstellen derselben, sowie einen Speicher und Detektor mit einer solchen Kapazitätsdiode, wobei die Kapazitätsdiode eine erste und eine zweite Elektrode sowie eine kontaktierend zwischen den beiden Elektroden angeordnete Schichtanordnung aufweist, und wobei die Schichtanordnung in Richtung von der ersten zu der zweiten Elektrode hin nacheinander eine Schicht aus einem ferroelektrischen Material und eine Schicht aus einem dielektrischen Material mit elektrisch geladenen Störstellen aufweist.
  • Patent
    DE102014105639 - Erteilung 05.03.2015; Nachanmeldung: WO, CN, EP, US

Publ.-Id: 21833 - Permalink

P1324 - Verfahren und Einrichtung zur Kontrolle der Reichweite von Partikelstrahlung einer Bestrahlungseinrichtung zur Strahlentherapie
Enghardt, W.; Golnik, C.; Pausch, G.; Hueso-Gonzalez, F.;
Die Erfindung betrifft Verfahren und Einrichtungen zur Kontrolle der Reichweite einer Partikelstrahlung in der Strahlentherapie über die Messung prompter Gammastrahlung mit wenigstens einem einzelne Gammaquanten nachweisenden Detektor und mindestens einem Analysator, die sich insbesondere durch ihre einfache und robuste Realisierung sowie eine durch stark reduzierte Messzeit auszeichnen, die eine Reichweitekontrolle in Echtzeit erlaubt. Dazu werden mit Hilfe des Detektors und des Analysators unter Verwendung eines Referenzsignals der Bestrahlungseinrichtung oder eines separaten Partikeldetektors Zeitverteilungen gemessen, die statistische Verteilungen der Flugzeiten von Therapiepartikeln bis zur Emission eines prompten Gammaquants, ergänzt um die Flugzeit des entsprechenden Gammaquants zum Detektor, widerspiegeln. Informationen über die Reichweite der Therapiepartikel werden im Wesentlichen aus diesen Zeitverteilungen abgeleitet.
  • Patent
    DE102013218982 - Offenlegung 26.03.2015, Nachanmeldung: WO, US, EP, JP

Publ.-Id: 21832 - Permalink

SRF Photo Injector for Electron-Laser Interaction
Lu, P.;
simulation and first results
Keywords: 1 nC simulation
  • Lecture (Conference)
    LA3NET conference: Laser applications at accelerators, 25.-27.03.2015, Mallorca, Spain

Publ.-Id: 21831 - Permalink

Beam Diagnostics of the SRF Photoinjector at HZDR, LA³NET Topical Workshop
Lu, P.;
Beam Diagnostics of the ELBE SRF Gun II
Keywords: energy spread, emittance, bunch length
  • Lecture (others)
    LA³NET Topical Workshop: Beam Diagnostics, 23.-24.03.2015, Mallorca, Spain

Publ.-Id: 21830 - Permalink

Application of Layered Double Hydroxides for 99-Tc immobilization
Shcherbina, N.; Franzen, C.; Foerstendorf, H.; Walther, C.;
99Tc is a long-lived (T1/2=2.13·105 y) fission product (FP) of the nuclear fuel cycle (NFC). As a component of nuclear wastes it remains a FP of concern for the safety assessment of a final disposal site. In the heptavalent form Tc(VII)O4-, it is well soluble, poorly sorbed and hence, a highly mobile anion in the environment. A number of strategies have been proposed to reduce 99Tc mobility by irreversible incorporation into the structure of ubiquitous mineral phases . We have recently demonstrated the incorporation of TcO4- in layered double hydroxides (LDH) that were earlier proposed for 79Se and 129I remediation in water treatment technology.
This work is focused on the interaction of 99Tc(VII) with Pyroaurite (PyA) and Hydrotalcite (HTC) - Mg-Fe and Mg-Al LDHs respectively, on simplified CO2- and O2-free conditions. Earlier experiments with Re(VII), considered to be a chemical analogue for 99Tc(VII), have demonstrated little to no uptake of Re(VII). Similar experiments with 99Tc(VII) however have shown a significant increase in 99Tc uptake on LDHs even in the concurrency with CO32- ions. Subsequent leaching experiments have revealed the irreversible character of the 99Tc(VII)-LDH compound. Modern spectroscopic methods are applied in order to understand how 99Tc is accommodated in between the brucite layers of LDHs and whether 99Tc(VII) is reduced to Tc(IV). This information will help to verify, whether LDHs can be used as a host phase for 99Tc long-term and safe storage. Additionally, these data aquired on controlled conditions can be used for modelling of 99Tc geochemical behavior in more complex repository relevant systems.
Keywords: technetium, sorption, retention
  • Poster
    Goldschmidt 2015, 16.-21.08.2015, Praha, Česká republika

Publ.-Id: 21829 - Permalink

The surface complexes of the oxoanions of Se(VI) and Tc(VII) at mineral-water interfaces
Foerstendorf, H.; Heim, K.; Franzen, C.; Jordan, N.;
79Se and 99Tc are fission products of the nuclear fuel cycle and, thus, are of concern during the safety assessment of a nuclear waste disposal site. For a comprehensive description of their mobility in the near and far field of a deep geological repository, the interactions of respective dissolved species with mineral surfaces are of special interest. In particular, the oxoanions Se(VI)O42− and Tc(VII)O4 are considered as mobile species in aquifer due to their high solubility and negative charge.
In this study, the surface reactions of these anions were studied by in situ vibrational spectroscopy which is a dedicated technique for the real time monitoring of the surface processes at the water-mineral interface [1, 2]. For the selenate anion, the formation of two different types of outer-sphere complexes was observed depending on the mineral’s surface. Although both types of sorption complexes behave like typical outer-sphere complexes in terms of macroscopic properties, the different spectral signatures clearly reflect two different molecule symmetries. From the spectra, a slightly distorted tetrahedral geometry, which is close to the aqueous species, and a bidendately coordinated species showing a C2v symmetry were derived. These surface species are denoted as “extended” and “classical” outer sphere complexes, respectively [3, 4].
In homology, spectroscopic sorption experiments with Tc(VII) were performed. The aqueous species should share the same symmetry as for Se(VI), that is a tetrahedral TcO4 ion. From preliminary results of the vibrational spectroscopic sorption experiments, mainly outer-sphere complexes were found which are obviously less specific as it was found for Se(VI).

[1] Foerstendorf, H. et al. (2012) J. Colloid Interface Sci. 377, 299–306. [2] Müller, K. et al. (2015) Environ. Sci. Technol. 49, 2560–2567. [3] Jordan, N. et al. (2011) Geochim. Cosmochim. Acta 75, 1519–1530. [4] Jordan, N. et al. (2013) Geochim. Cosmochim. Acta 103, 63–75.
  • Lecture (Conference)
    Goldschmidt 2015, 16.-21.08.2015, Prague, Czech Republic

Publ.-Id: 21828 - Permalink

Über die zeitlich aufgelöste Messung von Geschwindigkeiten mittels schneller Röntgentomographie
Hoppe, D.;
Für die Bestimmung von Geschwindigkeiten am schnellen Röntgentomographen Rofex eignet sich die Methode der Kreuzkorrelation. Weil dabei manchmal relativ große Integrationsintervalle notwendig sind, kann es zur entsprechend schlechten zeitlichen Auflösung der Geschwindigkeiten kommen. Gezeigt wird, dass mit geeignetem Vorwissen über das sich bewegende Medium oder Objekt trotzdem zumindest regional relativ hohe zeitliche Auflösungen erreichbar sind.
Keywords: Kurzzeit-Kreuzkorrelation, Messebenen, Blasenströmung, Rofex

Publ.-Id: 21827 - Permalink

3D-Röntgentomographie-gestützte Verfolgung von Blasen in flüssigemSchaum
Hoppe, D.;
Durch schnelle Röntgentomographie auf der Grundlage eines magnetisch abgelenkten Elektronenstrahls ist es möglich, 2D-Abbildungen von fluiden Medien zu erzeugen. 3D-Abbildungen wären zwar wünschenswert, sind aber vorerst noch nicht mit vertretbarem Aufwand realisierbar. Trotzdem soll bereits jetzt versucht werden, methodische Studien zur Bestimmung von Geschwindigkeiten in röntgentomographischen 3D-Abbildungen durchzuführen. Speziell werden dynamische Vorgänge in flüssigem Schaum betrachtet.
Keywords: Schaum, Tomographie, Geschwindigkeit, Korrelation

Publ.-Id: 21826 - Permalink

Gutzmer, J.; Klossek, A.; Schulz, T.;
Der effiziente und sorgsame Umgang mit natürlichen Ressourcen bleibt ein Thema von globaler Tragweite. Unabhängig vom Tagespreis steigt der Rohstoffhunger der Welt ungebremst; die Qualität, der für eine Nutzung verfügbaren, primären und sekundären Rohstoffe nimmt dagegen stetig ab. Deshalb ist es wichtig, die Gesellschaft nicht nur für eine Energie-, sondern auch für eine Rohstoffwende mit allen daraus resultierenden Folgen zu sensibilisieren. Vier Jahre nach der Gründung der ersten Knowledge & Innovation Communities (KICs) in den Bereichen Klimaschutz, erneuerbare Energien sowie Informations- und Kommunikationstechnologien rief das Europäische Institut für Innovation und Technologie (EIT) nun ein neues KIC für die mineralischen und metallischen Rohstoffe ins Leben. „EIT Raw Materials“, das weltweit größte Ressourcenkonsortium umfasst mehr als 100 führende Unternehmen, Universitäten und Forschungsinstitute aus 22 europäischen Ländern. Sein Ziel wird es in den kommenden Jahren sein, ein pan-europäisches Netzwerk für die langfristige Zusammenarbeit von Bildung, Forschung und Wirtschaft entlang der gesamten Rohstoff-Wertschöpfungskette zu erschaffen.
Keywords: KIC Knowledge and Innovatione Community, EIT Raw Materials, Rohstoff-Wertschöpfungskette, Netzwerk, Rohstoffsektor, Rohstoffwende, Europa
  • Open Access LogoReSource (2015)28, 1

Publ.-Id: 21825 - Permalink

Kooperationspartnerschaft: Die Helmholtz-Gemeinschaft und die TU Bergakademie; Zeitschrift ACAMONTA 2014
Meyer, B.; Sauerbrey, R.; Gutzmer, J.;
Das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) wurde als nationales Rohstoff-Institut im Jahr 2011 durch das Bundesministerium für Bildung und Forschung (BMBF) gegründet. Es erforscht und entwickelt Technologien für die nachhaltige Versorgung der deutschen Volkswirtschaft mit dringend benötigten mineralischen, insbesondere metallhaltigen Rohstoffen. Das HIF war von Anfang an als ein an das Helmholtz-Zentrum Dresden-Rossendorf (HZDR) angegliedertes Helmholtz-Institut mit Standort Freiberg geplant. Denn so profitiert das HIF sowohl von den Ressourcenkompetenzen der TU Bergakademie Freiberg als auch von der strukturellen Kompetenz des HZDR. Im Folgenden wird die Einbindung des HIF in die Helmholtz-Gemeinschaft Deutscher Forschungszentren und in die Bergakademie dargestellt sowie einige Beispiele aus der gemeinsame Zusammenarbeit beschrieben.
Keywords: ACAMONTA, Freunde und Förderer der TU Bergakademie Freiberg, Helmholtz-Institut Freiberg für Ressourcentechnologie, Kooperation, Rohstoffstrategie, Rohstoffversorgung
  • ACAMONTA Zeitschrift für Freunde und Förderer der Technischen Universität Bergakademie Freiberg 21(2015), 20-23

Publ.-Id: 21824 - Permalink

Reduced pulmonary blood flow in regions of injury 2 hours after acid aspiration in rats
Richter, T.; Bergmann, R.; Musch, G.; Pietzsch, G.; Koch, T.;
Aspiration-induced lung injury can decrease gas exchange and increase mortality. Acute lung injury following acid aspiration is characterized by elevated pulmonary blood flow (PBF) in damaged lung areas in the early inflammation stage. Knowledge of PBF patterns after acid aspiration is important for targeting intravenous treatments. We examined PBF in an experimental model at a later stage (2 hours after injury).

Anesthetized Wistar-Unilever rats (n = 5) underwent unilateral endobronchial instillation of hydrochloric acid. The PBF distribution was compared between injured and uninjured sides and with that of untreated control animals (n = 6). Changes in lung density after injury were measured using computed tomography (CT). Regional PBF distribution was determined quantitatively in vivo 2 hours after acid instillation by measuring the concentration of [68Ga]-radiolabeled microspheres using positron emission tomography.

CT scans revealed increased lung density in areas of acid aspiration. Lung injury was accompanied by impaired gas exchange. Acid aspiration decreased the arterial pressure of oxygen from 157 mmHg [139;165] to 74 mmHg [67;86] at 20 minutes and tended toward restoration to 109 mmHg [69;114] at 110 minutes (P < 0.001). The PBF ratio of the middle region of the injured versus uninjured lungs of the aspiration group (0.86 [0.7;0.9], median [25%;75%]) was significantly lower than the PBF ratio in the left versus right lung of the control group (1.02 [1.0;1.05]; P = 0.016).

The PBF pattern 2 hours after aspiration-induced lung injury showed a redistribution of PBF away from injured regions that was likely responsible for the partial recovery from hypoxemia over time. Treatments given intravenously 2 hours after acid-induced lung injury may not preferentially reach the injured lung regions, contrary to what occurs during the first hour of inflammation.
Keywords: Acute lung injury; Respiratory aspiration; Positron emission tomography; Pulmonary circulation; Pulmonary perfusion; Adult respiratory distress syndrome

Publ.-Id: 21823 - Permalink

Determination of gamma-ray widths in 15N using nuclear resonance fluorescence
Szücs, T.; Bemmerer, D.; Caciolli, A.; Fülöp, Z.; Massarczyk, R.; Michelagnoli, C.; Reinhardt, T. P.; Schwengner, R.; Takács, M. P.; Ur, C. A.; Wagner, A.; Wagner, L.;
Background: The stable nucleus 15N is the mirror of 15O, the bottleneck in the hydrogen burning CNO cycle. Most of the 15N level widths below the proton emission threshold are known from just one nuclear resonance fluorescence (NRF) measurement, with limited precision in some cases. A recent experiment with the AGATA demonstrator array determined level lifetimes using the Doppler Shift Attenuation Method (DSAM) in 15O. As a reference and for testing the method, level lifetimes in 15N have also been determined in the same experiment.
Purpose: The latest compilation of 15N level properties dates back to 1991. The limited precision in some cases in the compilation calls for a new measurement in order to enable a comparison to the AGATA demonstrator data. The widths of several 15N levels have been studied with the NRF method.
Method: The solid nitrogen compounds enriched in 15N have been irradiated with bremsstrahlung. The g-rays following the deexcitation of the excited nuclear levels were detected with four HPGe detectors.
Results: Integrated photon-scattering cross sections of ten levels below the proton emission threshold have been measured. Partial gamma-ray widths of ground-state transitions were deduced and compared to the literature. The photon scattering cross sections of two levels above the proton emission threshold, but still below other particle emission energies have also been measured, and proton resonance strengths and proton widths were deduced.
Conclusions: Gamma and proton widths consistent with the literature values were obtained, but with greatly improved precision.
Keywords: 15N, gamma-ray widths, proton widths, NRF

Publ.-Id: 21822 - Permalink

Long-lived cosmogenic radionuclides: Determination by accelerator mass spectrometry and model applications
Merchel, S.; Enamorado Baez, S. M.; Pavetich, S.; Rugel, G.; DREAMS-Users; DREAMS-Friends;
Introduction: Long-lived radionuclides with half-lives of 0.1-16 Ma (Tab. 1) have nowadays thousands of exciting applications, especially within environmental and geosciences. In nature, the so-called cosmogenic nuclides (CNs) are products of nuclear reactions induced by primary and secondary cosmic rays. Hence, they can be found in extraterrestrial material such as meteorites - originating from the asteroid belt, the Moon or Mars - and lunar samples in higher concentrations (e.g. ~1010 10Be atoms/g or < 0.5 mBq/g). A combination of several CNs is used to reconstruct the exposure history of this unique material while in space (irradiation age) and on Earth (terrestrial age).
Though, in terrestrial material the concentrations are typically only on the order of 104-109 atoms/g (i.e. μBq/g - nBq/g) for 10Be produced in the Earth’s atmosphere, so-called atmospheric or meteoric 10Be, transported to the surface and further absorbed and incorporated at and in, e.g. sediments or ice. Some of the lowest 10Be concentrations (~103 atoms/g), produced in-situ by neutron- and muon-induced nuclear reactions from e.g. oxygen and silicon in quartz, can be found in samples taken from the Earth’s surface. The concentrations of atmospheric or in-situ produced CNs record information to reconstruct sudden geomorphological events such as volcanic eruptions, rock avalanches, tsunamis, meteor impacts, earthquakes and glacier movements. Additionally, glacier movements and data from ice cores give hints for the reconstruction of historic climate changes and providing information for the validation of climate model predicting future changes. Slower processes such as sedimentation, river incision and erosion rates can also be investigated and last but not least, indirect dating of bones as old as several Ma’s is possible.
Anthropogenic production by release from nuclear reprocessing, accidents and weapons testing led to increased levels of CNs in surface water and soil (129I,…), ice (36Cl,…) and of course, material from nuclear installations themselves (41Ca,…).
Some of the CNs can be further used as natural or artificial tracers to follow pathways in oceanography, to date and identify sources of groundwater, to perform retrospective dosimetry and to study aspects in radioecology, phytology, nutrition, toxicology and pharmacology.
Method: Today, the analytical method of choice for long-lived cosmogenic radionuclides – especially non-gamma-active ones - is accelerator mass spectrometry (AMS). In contrast to decay counting, AMS scientists do not wait for the disintegration of the radioactive nucleus. In fact, the not-yet-decayed radionuclides are identified more efficiently by mass spectrometry. The main advantage of using a high-energy accelerator for mass spectrometry is the nearly complete elimination of background and interfering signals, resulting from molecular ions and ions with similar masses e.g. isobars. Thus, AMS generally provides much lower detection limits in comparison to conventional mass spectrometry. Our DREAMS (DREsden AMS) system (Akhmadaliev et al., 2013) offers excellent measurement capabilities also for external users.

Table 1. Radionuclides measured by AMS at DREAMS.
Nuclide t1/2 [Ma] Nuclide ratios of samples [10-12]
(machine blank level)
10Be 1.387 0.01-300 (5x10-16) 10Be/9Be
26Al 0.705 0.001-60 (8x10-16) 26Al/27Al
36Cl 0.301 0.007-700 (2x10-16) 36Cl/35Cl
41Ca 0.104 0.02-9000 (8x10-15) 41Ca/40Ca
129I 15.7 artificial samples (3x10-14) 129I/127I
actinides under development

The benefits from using AMS are obvious and manifold: Smaller sample sizes, easier and faster sample preparation, higher sample throughput and the redundancy for radiochemistry laboratories are largely reducing costs. Lower detection limits widen applications to shorter and longer time-scales and to sample types that could never be investigated before. Nevertheless, basic but accurate radiochemical sample separation is an essential prerequisite for AMS measurements.
Model applications: Some of the first successful CN-projects performed at DREAMS had been:
• Dating of marine sediments (with ANU, ETH, TANDAR, TUM & VERA) by 10Be & 26Al and search for supernova-origin 60Fe (by AMS at ANU & TUM)
• Growth rates of deep-sea manganese nodules by 10Be and 26Al (with Senckenberg)
41Ca-determination in water and concrete from a nuclear power plant by LSC and AMS (with VKTA)
• Reconstruction of meteorites’ history by 10Be, 26Al, 36Cl, 41Ca (with U Poznan & Bern, MPI Mainz,…).

Thanks to all brave DREAMS-users working with a newly installed AMS-facility and for help from colleagues at other AMS-facilities (ANSTO, ANU, ASTER, ETH, VERA…) with cross-measurements and setting-up the time-of-flight-system for future actinide measurements.

Akhmadaliev et al. (2013) Nucl. Instr. Meth. Phys. Res. B 294, 5-10.
Keywords: accelerator mass spectrometry, cosmogenic radionuclides, tracer
  • Lecture (Conference)
    ENVIRA2015 International Conference on Environmental Radioactivity: New Challenges with New Technologies, 21.-25.09.2015, Thessaloniki, Greece

Publ.-Id: 21821 - Permalink

Sponge-like Si-SiO2 nanocomposite as photovoltaic absorber: Synthesis by solid vs. liquid state decomposition of SiOx
Schumann, E.; Heinig, K.-H.; Hübner, R.; Carcelen, V.; Krause, M.; Gemming, S.;
Absorber layers consisting of nanostructured Si are candidates to improve the efficiency of thin film Si solar cells. Si-SiO2 nanocomposites with sponge-like Si embedded in SiO2 are promising materials due to a widened band gap and a maintained electrical interconnectivity. These structures can be formed upon isothermal or rapid thermal annealing of SiOx films (x<1), which leads to phase separation into a percolated network of Si nanowires embedded in SiO2, tentatively accompanied by crystallization of the Si. SiOx layers have been grown by ion beam sputter deposition as well as by reactive magnetron sputtering. Phase separation into Si-SiO2 nanocomposites has been achieved by classical thermal oven treatment, which has been compared to a very rapid thermal processing by scanning a diode laser line source. Compositional and structural characterization has been performed by Rutherford backscattering spectroscopy, energy filtered transmission electron microscopy, and Raman spectroscopy. The two sputter techniques of SiOx lead to distinct nanostructures during the classical thermal treatment throughout a phase separation in the solid state. In contrast, the decomposition with laser treatment occurs in the liquid state.
Keywords: sponge-like, nanostructure, nanocomposite, silicon, siliconoxide, photovoltaic
  • Poster
    79. DPG-Jahrestagung und DPG-Frühjahrstagung der Sektion Kondensierte Materie, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21820 - Permalink

Tailoring the electrical properties of a TiO2 layer by ion-beam irradiation for memristive applications
Blaschke, D.; Bogusz, A.; Huebner, R.; Nierobisch, F.; Rana, V.; Zahn, P.; Gemming, S.;
Reactively sputtered TiO2 thin films on Pt/Ti/SiO2/Si substrates were irradiated with low energy Ar+ ions of different energies to create surface or bulk modifications in the material. Furthermore, the fluence was varied to optimize the level of the modifications, which are e.g. amorphization, surface smoothing, and preferential sputtering of oxygen. These effects were detected by TEM, AFM and supported by TRIDYN simulations, respectively.
The impact of these changes on the electrical properties of the TiO2 layers was monitored by I-V and C-V measurements in top-bottom geometry with Pt, as well as Ti/Pt top contacts. The results indicate a transition from a Schottky-like behavior of the Pt/TiO2 interface to an ohmic one with increasing fluence, which is very similar to the behavior of a Ti/TiO2 interface. Furthermore, the capacity of the complete MIM stack increases with fluence, which points to a reduced effective thickness of the dielectric TiO2 layer after irradiation.

The project is funded by the Initiative and Networking Fund of the Helmholtz Association (Virtual Institute Memriox, VH-VI-422).
Keywords: TiO2, resistive switching, Ar+ irradiation
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21819 - Permalink

Structural and electrical characterization of Ar+ irradiated TiO2 thin films
Blaschke, D.; Agnieszka, B.; Huebner, R.; Munnik, F.; Heller, R.; Scholz, A.; Nierobisch, F.; Rana, V.; Zahn, P.; Gemming, S.;
Transition metal oxide thin films, like TiO2, which show a redox-based switching process between two or more resistance levels, are promising candidates for future memory storage devices.
They are extensively studied to get a better understanding of the role of mobile oxygen ions and/or oxygen vacancies for structural changes and electronic transport inside the films.
A defective, nonstoichiometric TiO2-x layer can act as a reservoir for oxygen vacancies and improves the switching characteristics. Such a layer was introduced into the virgin TiO2 film by low energy Ar+ irradiation with different energies and fluencies to modulate the depths and level of the defective region. The impact of the irradiation to the surface morphology and crystal structure was monitored by AFM and TEM measurements and was found to be surface smoothing and amorphization. The role of the preferential sputtering of oxygen to the stoichiometry of the film was investigated with TRIDYN simulations. Electrical properties of the irradiated films were characterized by I-V and C-V measurements and are related to the structural changes caused by the Ar+ irradiation.

The project is funded by the Initiative and Networking Fund of the Helmholtz Association (Virtual Institute Memriox, VH-VI-422).
Keywords: TiO2, resistive switching, Ar irradiation
  • Poster
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21818 - Permalink

Simultaneous measurement of AMR and observation of magnetic domains with dual Kerr microscopy
Osten, J.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
Anisotropic magneto resistance (AMR) sensors are widely used in daily life. But the influence of magnetic domains on the AMR is still not fully understood. AMR depends on the direction of the magnetization. For the understanding of the AMR it is therefore important to know about the domain structure. Dual Kerr microscopy is used for the observation of the magnetic domains while at the same time the AMR is measured. Dual Kerr microscopy means that it is possible to measure two magnetization directions at the same time. These two sensitivity directions make it possible to calculate quantitative Kerr images for a complete loop. The investigated samples were magnetic stripe patterned permalloy. The patterning was archived with Cr-Implantation. In addition to the measured resistance the AMR is calculated from the quantitative Kerr images. We also compare the field dependence of the AMR by variation of the magnetic field angle.Our measurements show a clear dependence of the AMR on the magnetic domain types. This work is supported by DFG grant FA316/3-2.
Keywords: Kerr microscopy, AMR
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21817 - Permalink

Magnetic Anisotropy in (Cr0.5Mn0.5)2GaC MAX Phase
Salikhov, R.; Semisalova, A. S.; Petruhins, A.; Ingason, A. S.; Rosen, J.; Wiedwald, U.; Farle, M.;
Magnetic MAX phase (Cr0.5Mn0.5)2GaC thin films grown epitaxially on a MgO(111) substrates were studied by ferromagnetic resonance (FMR) at temperatures between 110 K and 300 K. The spectroscopic splitting factor g = 2.00 ± 0.01 measured at all temperatures indicates pure spin magnetism in the sample. At all temperatures we find the magnetocrystalline anisotropy energy to be negligible which is in agreement with the identified pure spin magnetism.
Keywords: Magnetic MAX Phase, Ferromagnetic Resonance, g-factor, Magnetic Anisotropy

Publ.-Id: 21816 - Permalink

Accuracy of parenchymal cerebral blood flow measurements using pseudo-continuous arterial spin labeling in healthy volunteers
Ambarki, K.; Wåhlin, A.; Zarrinkoob, L.; Wirestam, R.; Petr, J.; Malm, J.; Eklund, A.;
Background and Purpose: Arterial spin-labeling method for CBF assessment is widely available but its accuracy is not fully established. We investigated the accuracy of a whole brain arterial spin-labeling technique for assessment of the mean parenchymal CBF (pCBF) and the effect of ageing in healthy volunteers. Phase-contrast MRI was used as the reference method.
Materials and Methods: Ninety-two healthy volunteers were included: 49 young (age range 20-30y) and 43 elderly (65-80y). Arterial spin-labeling pCBF values were averaged over the whole brain to quantify mean pCBFASL.
Total CBF was assessed with phase-contrast MRI as the sum of flow in the internal carotids and vertebral arteries, and subsequent division by brain volume returned the pCBFPCMRI. Accuracy was considered as good if there was less than 5 mL/min/100g in systematic difference against the reference method and if the 95% limits of agreement interval are equal or better than ±10 mL/min/100g
Results: pCBFASL was correlated with pCBFPCMRI (r=0.73, P<0.001).
Significant differences were observed between pCBFASL and pCBFPCMRI in young (P=0.001) as well as in elderly (P<0.001), and the systematic differences were -4±14 mL/min/100g (mean ± 2SD) in young and +6±12 mL/min/100g in elderly. Young subjects showed higher pCBF than elderly for both pCBFPCMRI (Young:57±8, Elderly:54±7 mL/min/100g, P=0.05) and pCBFASL (Young:60±10, Elderly:48±10 mL/min/100g, P<0.001).
Conclusion: Regarding accuracy of the arterial spin-labeling, limits of agreements were too wide while the systematic overestimation in young and underestimation in elderly was close to acceptable. Age-related decrease in pCBF was augmented in arterial spin-labeling compared to phase contrast MRI.
Keywords: ASL-arterial spin-labeling; HE-healthy elderly; HY-healthy young; PCASL-pseudocontinuous ASL; PCBF-parenchymal CBF; PCMRI-phase-contrast MRI; VA-vertebral artery

Publ.-Id: 21815 - Permalink

Partial Volume Correction of Cerebral Perfusion Estimates Obtained by Arterial Spin Labeling
Ambarki, K.; Petr, J.; Wåhlin, A.; Wirestam, R.; Zarrinkoob, L.; Malm, J.; Eklund, A.;
Arterial Spin labeling (ASL) is a fully noninvasive MRI method capable to quantify cerebral perfusion. However, gray (GM) and white matter (WM) ASL perfusions are difficult to assess separately due to limited spatial resolution increasing the partial volume effects (PVE). In the present study, ASL PVE correction was implemented based on a regression algorithm in 22 healthy young men. PVE corrected perfusion of GM and WM were compared to previous studies. PVE-corrected GM perfusion was in agreement with literature values. In general, WM perfusion was higher despite the use of PVE correction.
Keywords: MRI; cerebral perfusion; gray and white matter; arterial spin labeling and healthy
  • Contribution to proceedings
    16. NBC & 10. MTD 2014 joint conferences, 14.-16.10.2014, Gothenburg, Sweden
    16th Nordic-Baltic Conference on Biomedical Engineering, IFMBE Proceedings: Springer International Publishing, 978-3-319-12966-2, 17-19
    DOI: 10.1007/978-3-319-12967-9_5
  • Lecture (Conference)
    16th Nordic-Baltic Conference on Biomedical Engineering, 14.-16.10.2014, Gothenburg, Sweden

Publ.-Id: 21814 - Permalink

Evidence of U(VI) sorption on Acidovorax facilis by TRLFS and EF-TEM/EELS
Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Lünsdorf, H.; Arnold, T.;
Acidovorax facilis, an aerobic Gram-negative Betaproteobacteria which is commonly found in soil, was used for U(VI) sorption experiments. Experiments were performed in batch cultures under aerobic conditions at 25 °C using nutrient broth. For U(VI) sorption experiments UO2(NO3)2 was added to the culture to achieve an initial U concentration of 0.05 and 0.1 M, respectively, at a neutral pH range. The duration of the sorption experiments were limited to 8 h and 48 h, respectively. By time-resolved laser fluorescence spectroscopy (TRLFS) the measured emission spectrum of the cells is characterized by four emission bands with peak maxima at 497.8, 519.5, 544.1 and 568.6 nm ± 0.5 nm. In addition, the spectra of the Uranyl-lipopolysaccharide-complexes R-O-PO3-UO2 and [R-O-PO3]2-UO22-, reported by Barkleit et al. (2008), were used for comparison. They show only a small deviation from those observed in our studies. Hence, it can be concluded that phosphoryl groups are the main binding sites for uranyl, located in the lipopolysaccharide (LPS) unit in the outer membrane by Gram-negative Acidovorax facilis cells. After the U(VI) biosorption experiments, Acidovorax facilis cells were prepared for Energy-filtered transmission electron microscopy (EF-TEM) and electron energy-loss spectroscopy (EELS). The results provide microscopically and spectroscopically evidence of U(VI) sorbed at the outer membrane of Acidovorax facilis cells by showing high electron density and U ionization intensity peaks.
Keywords: Acidovorax facilis, uranium, sorption, TRLFS, EF-TEM
  • Lecture (Conference)
    Goldschmidt Conference, 16.-21.03.2015, Prague, Czech

Publ.-Id: 21813 - Permalink

Estimating the influence of magnetization transfer effects on cerebral blood flow quantification in pseudo-continuous arterial spin labeling
Petr, J.; Schramm, G.; Hofheinz, F.; Maus, J.; van den Hoff, J.;
The magnetization transfer (MT) effects were studied in pseudo-continuous ASL (pCASL). The MT exchange rate was obtained from two pCASL sequences with and without labeling acquired at multiple delays. A mean white-matter MT exchange rate was obtained and the exchange rate in blood was derived from it. Effect on CBF quantification was then calculated using the standard pCASL quantification model for different distances from the labeling plane and different blood velocities in the arteries. CBF underestimation of up to 6% was shown in the slices closest to the labeling plane if the MT effects were ignored
  • Contribution to proceedings
    Annual Meeting of the International Society for Magnetic Resonance in Medicine, ISMRM 2014, 10.-16.05.2014, Milano, Italy
    Proceedings of the International Society for Magnetic Resonance in Medicine, 2677
  • Lecture (Conference)
    Annual Meeting of the International Society for Magnetic Resonance in Medicine, ISMRM 2014, 10.-16.05.2014, Milano, Italy

Publ.-Id: 21812 - Permalink

Linear Instability Analysis of 3D Magnetohydrodynamic Flow by Direct Numerical Simulation
Grants, I.; Gerbeth, G.;
Direct numerical simulation (DNS) is normally used to study turbulent flows. Though, it may be also very useful for linear instability analysis of complex laminar flows. given an essentially three-dimensional basic flow the number of coupled active degrees of freedom may easily exceed 105. Calculation of the full spectrum is hardly possible if meaningful in such cases. Only a few leading modes are needed for the linear instability anaxix. Iteration techniques such as Arnold iteration may be used to find an isolated eigenvalue. A separate effort, however, is then needed to verify that this eigenvalue really has the maximum real part.
Our study demonstrates that the linear instabiolity problem can be effectively solved by means of DNS. The most straight-forward approach would be to calculate the transient equations long enough to ensure that only the leading eigenmode survives. There is, however, a more efficient way to find few leading eigenvalues and eigenmodes. this method approximates n+1 equidistant flow "snapshot" by n modes that vary exponentially in thime. We describe the numberical implementation of this method coupled with DNS and demonstrate it on an example of three-dimensional magnetohydrodynamic flow. This flow models meld motion in the Cxochralski crystal growth process with a horizontal magnetic field (HMF).
  • Contribution to proceedings
    ERCOFTAC WORKSHOP Direct and Large-Eddy Simulation 9 (DLES 9), 03.-05.04.2013, Dresden, Deutschland
    ERCOFTAC Series Volume 20: Springer, 978-3-319-14447-4, 561-567
    DOI: 10.1007/978-3-319-14448-1_71

Publ.-Id: 21811 - Permalink

Topological spin textures as emitters for multidimensional spin wave modes

Sluka, V.; Weigand, M.; Kakay, A.; Schultheiss, K.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.ORC; Raabe, J.; Wintz, S.
In the present contribution we will show that in a stacked vortex pair system with uniaxial magnetic anisotropy, spin waves of different symmetries and dimensionalities can be excited.
  • Lecture (Conference)
    International Colloquium on Magnetic Films and Surfaces, 12.-17.07.2015, Krakow, Poland

Publ.-Id: 21810 - Permalink

Radiative particle-in-cell simulations -from plasma dynamics to electromagnetic spectra
Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.;
We present PIConGPU a fully-relativistic, 3D3V particle-in-cell code running on multiple GPGPUs. Its parallelization and its application in predicting far field radiation during laser-plasma interactions are discussed during the talk.
Keywords: PIConGPU, radiation, GPU
  • Lecture (Conference)
    First MT Student Retreat, 23.-24.02.2015, Hamburg, Deutschland

Publ.-Id: 21809 - Permalink

Characterizing the Kelvin-Helmholtz instability in interstellar jets using radiation
Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.; Schramm, U.;
We present a new diagnostic method to determine the presence of the Kelvin-Helmholtz instability (KHI) in interstellar jets and measuring its main property, the exponential growth rate, using radiation observable on Earth.

Our findings are based on simulations of the relativistic KHI using the 3D3V particle-in-cell code PIConGPU. With its in-situ computation of the emitted far field radiation, we determined angularly resolved radiation spectra for all billions of particles simulated.

We will explain how measuring the electromagnetic radiation from particle jet allows for identifying the stages of the instability and provides a method to settle the question whether the KHI occurs in astro-physical particle jets or not. By identifying these stages, determining the characteristic growth rate of the KHI becomes possible thus providing quantitative insides to the jet dynamics using only the radiation observed on Earth.
Keywords: PIConGPU, KHI, radiation
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21808 - Permalink

Evolution of Spin Wave Modes in Periodically Perturbed Thin Films
Langer, M.; Gallardo, R.; Banholzer, A.; Schneider, T.; Wagner, K.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
The transition from a continuous thin film to a magnonic crystal is studied by ferromagnetic resonance (FMR). Ion irradiation as well as reactive ion beam etching were used to realize a periodic modulation of the sample surface after patterning by electron beam lithography. Mode-splitting in the FMR spectra has been investigated dependent on the size of the perturbations and compared to available analytical perturbation theory. Numerical simulations have been carried out to identify the spin waves corresponding to the mode spectra as well as to understand deviations between measurement and analytical theory for large perturbations. This work is supported by DFG grant LE2443/5-1.
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21807 - Permalink

Radiation as synthetic spectral diagnostics in the particle- in-cell code PIConGPU
Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.; Schramm, U.;
We present in-situ computation of relativistic radiation in the particle- in-cell code PIConGPU that can give both qualitative and quantitative agreement with analytical models and thus has predictive capabilities. This new kind of synthetic spectral diagnostics can be used to infer plasma dynamics with high spatial and temporal resolution.

Our method is based on the far field approximation of Liénard-Wiechert potential. Its direct integration with the highly-scalable GPU framework of PIConGPU allows computing the spectrally and angu- larly resolved radiation for thousands of frequencies, ranging from infrared to x-rays, hundreds of detector positions and billions of particles efficiently. Recent updates allow studying polarization and improve time resolution thus extending the range of applications.

These capabilities are demonstrated using recent simulations of laser wakefield acceleration (LWFA), high harmonics generation during target normal sheath acceleration (TNSA) and the Kelvin-Helmholtz in- stability (KHI).
Keywords: Radiation, Laser Plasma, PIConGPU, GPU, TNSA, KHI, HHG
  • Lecture (Conference)
    DPG-Frühjahrstagung, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21806 - Permalink

Plasmonic Superlensing in Doped GaAs
Fehrenbacher, M.; Winnerl, S.; Schneider, H.; Doring, J.; Kehr, S.; Eng, L.; Huo, Y.; Schmidt, O.; Yao, K.; Liu, Y.; Helm, M.;
We demonstrate a semiconductor based broadband near-field superlens in the mid-infrared regime. Here, the Drude response of a highly doped n-GaAs layer induces a resonant enhancement of evanescent waves accompanied by a significantly improved spatial resolution at radiation wavelengths around lambda = 20 mu m, adjustable by changing the doping concentration. In our experiments, gold stripes below the GaAs superlens are imaged with a lambda/6 subwavelength resolution by an apertureless near-field optical microscope utilizing infrared radiation from a free-electron laser. The resonant behavior of the observed superlensing effect is in excellent agreement with simulations based on the Drude-Lorentz model. Our results demonstrate a rather simple superlens implementation for infrared nanospectroscopy.
Keywords: Superlens, diffraction limit, surface plasmons, near-field microscopy, semiconductor

Publ.-Id: 21805 - Permalink

Determination of the Exchange Stiffness Constant in Ultrathin Magnetic Films by Ferromagnetic Resonance
Langer, M.; Wagner, K.; Sebastian, T.; Schultheiss, H.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
In ultrathin magnetic films of 10 — 20 nm thickness, it is hardly possible to determine the exchange constant A using conventional techniques, such as Brillouin light scattering. In this work, a method is presented allowing for analytical determination of the exchange constant A in ultrathin magnetic films. Periodical surface modulations are introduced by electron beam lithography with subsequent sub-nanometer etching. The periodical stray field induces two-magnon scattering leading to a coupling of the uniform excitation with higher in-plane spin waves. An analytical model is presented, that can be used to precisely calculate the exchange constant A under usage of the measured ferromagnetic
resonance spectra (frequency versus field dependence). This work is supported by DFG grant LE2443/5-1.
  • Poster
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21804 - Permalink

Study of the quasi-free np→npπ+π− reaction with a deuterium beam at 1.25 GeV/nucleon
Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Göbel, K.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Vasiliev, T.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.;
The tagged quasi-free np→npπ+π− reaction has been studied experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI at a deuteron incident beam energy of 1.25 GeV/nucleon (s√∼ 2.42 GeV/c for the quasi-free collision). For the first time, differential distributions for π+π− production in np collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the np→npπ+π− reaction are compared with different models. This comparison confirms the dominance of the t-channel with ΔΔ contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the π+π− invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M∼ 2.38 GeV and with width Γ∼ 70 MeV.

Publ.-Id: 21803 - Permalink

Pulsed magnetic field spectroscopy up to 70 T on the dilute nitride GaAsN
Eßer, F.; Schneider, H.; Winnerl, S.; Drachenko, O.; Patanè, A.; Helm, M.;
Magnetic fields above 45 T offer great opportunities as a tool for materials research but can only be realized in the pulsed regime. We use pulsed magnetic fields up to 70 T for spectroscopic investigations of the dilute nitride GaAsN. This material is a promising candidate for optical applications because of the possibility for tuning its band gap by the nitrogen content. Our studies focus on the exploration of the band structure and in particular on the determination of the effective mass. Cyclotron-resonance spectroscopy indicates that the effective mass is not strongly affected by nitrogen in comparison to previous publications. Our magneto-photoluminescence investigations reveal the formation of localized and delocalized states as a result of the nitrogen incorporation. Delocalized states undergo transitions to localized ones in very high magnetic fields. This result is in good agreement with a pressure dependent study [1].

[1] J. Endicott, A. Patanè, D. Maude, L. Eaves, M. Hopkinson, and G. Hill, Phys. Rev. B 72, 041306(R) (2005)
Keywords: GaAsN, dilute nitride, effective mass, cyclotron-resonance, pulsed magnetic field
  • Lecture (Conference)
    79. DPG-Jahrestagung und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21802 - Permalink

THz spectroscopy of solids using a free-electron laser
Helm, M.;
I will start describing the Dresden free-electron laser FELBE as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in solids. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will present some recent results and will conclude with an outlook on further developments, including the superradiant THz radiation source TELBE.
Keywords: free electron laser, pump probe, spectroscopy
  • Lecture (others)
    Vortrag am Shanghai Institute for Applied Physics (SINAP), 10.03.2015, Shanghai, China

Publ.-Id: 21801 - Permalink

Topological Spin Textures in Magnetic Multilayers
Wintz, S.;
Topological spin textures, such as vortices or skyrmions, are attracting significant attention because of their intriguing fundamental properties as well as their promising applicability in memory devices or spin torque oscillators. A particular topological texture that was theoretically predicted is the two-dimensional hedgehog state, also known as ’spin meron’. It had been unclear, however, whether this kind of highly divergent magnetization structure may occur in real systems. Only recently, evidence for the existence of meron-like pair states was reported for the case of trilayer elements consisting of two ferromagnetic layers and a non-ferromagnetic interlayer [1]. On this background, a direct proof for the existence of meron-like states in trilayer elements via direct magnetic imaging will be presented. It will also be shown that in the presence of biquadratic interlayer exchange coupling, such meron-like pair states may even represent the magnetic ground state of the system. Interestingly, the highly divergent magnetization distribution induces an additional, three-dimensional torus vortex that in-turn causes a symmetry break for the possible topological pair configurations [2]. In addition the dynamic properties of vertically coupled topological spin textures will be addressed, where the focus will be set on spin wave emission processes in such systems.
References: [1] C. Phatak et al., Phys. Rev. Lett. 108, 067205 (2012). [2] S. Wintz et al., Phys. Rev. Lett. 110, 177201 (2013).
Keywords: vortex multilayer
  • Invited lecture (Conferences)
    DPG Frühjahrstagung der Sektion kondensierte Materie, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21800 - Permalink

Magnetic interactions in BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices
Xu, Q.; Sheng, Y.; Khalid, M.; Cao, Y.; Wang, Y.; Qiu, X.; Zhang, W.; He, M.; Wang, S.; Zhou, S.; Li, Q.; Wu, D.; Zhai, Y.; Liu, W.; Wang, P.; Xu, Y.; Du, J.;
The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties. BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices have been fabricated by pulsed laser deposition on (001) SrTiO3 substrates. Using piezoresponse force microscopy (PFM), the ferroelectricity at room temperature has been inferred from the observation of PFM hysteresis loops and electrical writing of ferroelectric domains for both samples. Spin glass behavior has been observed in both samples by temperature dependent magnetization curves and decay of thermo-remnant magnetization with time. The magnetic ordering has been studied by X-ray magnetic circular dichroism measurements, and Fe-O-Mn interaction has been confirmed to be antiferromagnetic (AF). The observed spin glass in BiFe0.5Mn0.5O3 films has been attributed to cluster spin glass due to Mn-rich ferromagnetic (FM) clusters in AF matrix, while spin glass in BiFeO3/BiMnO3 superlattices is due to competition between AF Fe-O-Fe, AF Fe-O-Mn and FM Mn-O-Mn interactions in the well ordered square lattice with two Fe ions in BiFeO3 layer and two Mn ions in BiMnO3 layer at interfaces.

Publ.-Id: 21799 - Permalink

Evaluation of Resistive-Plate-Chamber-based TOF-PET applied to in-beam Particle Therapy Monitoring
Torres-Espellardo, I.; Diblen, F.; Rohling, H.; Solevi, P.; Gillam, J.; Watts, D.; España, S.; Vandenberghe, S.; Fiedler, F.; Rafecas, M.;
Particle therapy is a highly conformal radiotherapy technique which reduces the dose deposited to the surrounding normal tissues. In order to fully exploit its advantages, treatment monitoring is necessary to minimize uncertainties related to the dose delivery. Up to now, the only clinically feasible technique for the monitoring of therapeutic irradiation with particle beams is Positron Emission Tomography (PET).
In this work we have compared a Resistive Plate Chamber (RPC)-based PET scanner with a scintillation-crystal-based PET scanner for this application. In general, the main advantages of the RPC-PET system are its excellent timing resolution, low cost, and the possibility of building large area systems. We simulated a partial-ring scanner based on an RPC prototype under construction within the Fondazione per Adroterapia Oncologica (TERA). For comparison with the crystal-based PET scanner we have chosen the geometry of a commercially available PET scanner, the Philips Gemini TF.
The coincidence time resolution used in the simulations takes into account the current achievable values as well as expected improvements of both technologies. Several scenarios (including patient data) have been simulated to evaluate the performance of different scanners. Initial results have shown that the low sensitivity of the RPC hampers its application to hadron-beam monitoring, which has an intrinsically low positron yield compared to diagnostic PET. In addition, for in-beam PET there is a further data loss due to the partial ring configuration. In order to improve the performance of the RPC-based scanner, an improved version of the RPC detector (modifying the thickness of the gas and glass layers), providing a larger sensitivity, has been simulated and compared with an axially extended version of the crystalbased device. The improved version of the RPC shows better performance than the prototype, but the extended version of the crystal-based PET outperforms all other options.
Keywords: PET, In-beam, RPC, Particle therapy, TOF, Range deviation, Partial-ring

Publ.-Id: 21798 - Permalink

(Bio)Leaching of copper shale with organic acids
Kostudis, S.; Bachmann, K.; Babel, B. M.; Rudolph, M.; Kutschke, S.; Pollmann, K.; Gutzmer, J.;
The talk summarises PhD research activities and results with respect to (bio)leaching of copper from copper shale.
  • Invited lecture (Conferences)
    Freiberger Forschungsforum, 66. Berg-und Hüttenmännischer Tag (BHT), 17.-19.06.2015, Freiberg, Deutschland

Publ.-Id: 21797 - Permalink

Redox transformations and the disposal of radioactive waste: Influence on Se immobilization
Wieland, E.; Rojo, H.; Scheinost, A. C.; Lothenbach, B.; Tits, J.;
Safety analysis of a cement-based repository for low- and intermediate level nuclear waste (L/ILW) has shown that 79Se is an important redox-sensitive, dose-determining radio-nuclide due to its long half-life and weak retardation by common near- and far field minerals. In the sorption data bases currently used for safety analysis it is considered that 79Se is predominantly present as SeO32- in the cementitious near field because oxidizing conditions prevail during waste conditioning. With time, however, reducing conditions will establish in the near field caused by oxygen consumption in the course of metal corrosion. In these conditions Se(-II) is expected to be the dominant redox state of Se. Hence, investigations into the interaction of Se(IV) and Se(-II) with cementitious materials and the reduction of Se(IV) to Se(-II) enable us to assess the long-term fate of Se in conditions relevant to a cement-based repository.
Sorption studies with Se on cementitious materials indicate that Se(IV) and Se(-II) uptake by hydrated calcium aluminates (AFm) and calcium silicate hydrates (C-S-H) phases, the principal host phases for radionuclides in cement paste, is significant and comparable to the uptake by cement paste. The uptake mechanisms of the Se species, however, are only poorly understood. EXAFS studies on Se(IV)-loaded cement phase and wet chemistry experiments suggest that Se(IV) could be taken up into the structure of the cement phases. In the case of AFm phases, for example, anions bound in the interlayer can be replaced, at least partially, by Se(IV) and Se(-II). This explains why AFm phases are more effective in removing Se(IV) and Se(-II) from solution than C-S-H phases.
Investigations into redox transformation are ongoing and the first results already suggest that the uptake mechanism of the Se species plays an important role in the reduction of Se(IV) to Se(-II) in cementitious materials.
Keywords: nuclear waste cement selenium xas
  • Invited lecture (Conferences)
    Goldschmidt 2015, 16.-21.08.2015, Prague, Czech Republic

Publ.-Id: 21796 - Permalink

Leaching of copper from Kupferschiefer by glutamic acid and heterotrophic bacteria
Kostudis, S.; Bachmann, K.; Kutschke, S.; Pollmann, K.; Gutzmer, J.;
Polymetallic Cu–Ag ores of the Central European Kupferschiefer deposits are one of the most important sources of copper in Europe. Because the ores are typically complex and often exceptionally fine-grained the development of efficient alternatives to conventional beneficiation strategies are an important target of current research. Biomining – the use of biological components for metal extraction – may offer solutions that are both efficient and environmentally benign. As conventional bioleaching with acidophilic microorganisms is impeded by the high carbonate content of the Kupferschiefer ores, heterotrophic microorganisms and glutamic acid are investigated as a possible alternative in the present study. The focus of this investigation is solely on the recovery of copper from the Kupferschiefer sensu strictu. Bioleaching experiments were carried out using such material from the Polkowice Mine in Poland. This material is marked by high grade (3.8 wt.% Cu), complex ore mineralogy (chalcocite, bornite, chalcopyrite and covellite in significant quantity) and a gangue mineralogy that is rich in carbonate, organic carbon and clay minerals that together form a very fine-grained matrix. (Bio)leaching experiments yield best results when glutamic acid alone is used – reaching copper recoveries up to 44%. Recoveries are consistently lower in experiments in which glutamic acid and microbiological metabolites are both present. The leaching of chalcocite renders the greatest contribution to the copper recovered to the leach solution in all experiments. It can be concluded that glutamic acid solubilises copper efficiently from Kupferschiefer, mainly from chalcocite.
Keywords: sulphide ores, bacteria, bioleaching, liberation analysis, ore mineralogy

Publ.-Id: 21795 - Permalink

Biologie meets Bergbau: Biotechnologie für die Gewinnung von Kupfer
Kostudis, S.;
Der Vortrag stellt das Helmholtz-Zentrum Dresden-Rossendorf sowie das Helmholtz-Institut Freiberg für Ressourcentechnologie vor und liefert allgemeine Informationen zu biotechnologischen Prozessen in der Kupfergewinnung sowie Einlick in Arbeiten der Arbeitsgruppe Biotechnologie.
  • Lecture (others)
    Nacht der Wissenschaft und Wirtschaft zum Jubiläum, 20.06.2015, Freiberg, Deutschland

Publ.-Id: 21794 - Permalink

Identification of vancomycin interaction with Enterococcus faecalis within 30 minutes using Raman spectroscopy
Assmann, C.; Kirchhoff, J.; Beleites, C.; Hey, J.; Kostudis, S.; Pfister, W.; Schlattmann, P.; Bauer, M.; Popp, J.; Neugebauer, U.;
Vancomycin is an important glycopeptide antibiotic which is used to treat serious infections caused by Gram positive bacteria. However, during the last years a tremendous rise in vancomycin resistances, especially among enterococci, was reported, making fast diagnostic methods inevitable.
In this contribution, we apply Raman spectroscopy to systematically characterize vancomycin-enterococci interactions over a time span of 90 minutes using a sensitive E. faecalis strain and two different vancomycin concentrations above the minimal inhibitory concentration (MIC). Successful action of the drug on the pathogen could be observed already after 30 minutes of interaction time. Characteristic spectral changes are visualized with the help of multivariate statistical analysis (linear discriminant analysis and partial least squares regressions). Those changes were employed to train a statistical model to predict vancomycin treatment based on the Raman spectra. The robustness of the model was tested using data recorded by an independent operator. Classification accuracies of >90% were obtained for vancomycin concentrations in the lower range of a typical trough serum concentration recommended for most patients during appropriate vancomycin therapy.
Characterization of drug-pathogen interactions by means of label-free spectroscopic methods, such as Raman spectroscopy, can provide the knowledge base for innovative and fast susceptibility assays which could speed up microbiological analysis as well as could find applications in novel antibiotic screenings assays.
Keywords: Raman spectroscopy vancomycin, Enterococcus faecalis, bacteria-antibiotic-interaction

Publ.-Id: 21793 - Permalink

Monitoring gravitational and particle shape settling effects on MLA sampling preparation
Heinig, T.; Bachmann, K.; Tolosana-Delgado, R.; van den Boogaart, K. G.; Gutzmer, J.;
Epoxy blocks for automated mineralogy typically contain unsorted material from feeds, concentrates or tailings of the processing chain. In these cases, accuracy and precision of SEM-based analytics not only depend on stable measurement parameters and conditions but also on sample preparation. The major aim of sample preparation is the production of representative specimen mounts to generate valid information about the given samples. However, experiences in preparation indicate an influence on the analytic results of many factors such as resin type, resin viscosity, mineral grain density, grain shape and sample material/resin ratio.
This study aims at evaluating the influence of different material/resin ratios on the representativity of a mineral sample. In order to investigate possible gravitational and shape related settling effects during sample preparation, the use of homogenized Zinnwaldite ore is suitable as it provides sample material with a heterogeneous mineral composition, mineral density (Quartz – Topaz), grain shape (Mica – Quartz) and grain size. Eight specimens were prepared with equal weight aliquots of the same ore material, with increasing resin amount. These polished epoxy mounts were analyzed three times with the Mineral Liberation Analyzer (MLA) at Helmholtz Institute Freiberg for Resource Technology (HIF) to evaluate their difference in modal mineralogy, grain sizes and grain shapes. Each sample was analysed as usual on the XY plane, then polished a bit and measured again on a deeper XY plane; and finally the samples were cut along the YZ plane, remounted and measured again, thus capturing a plane orthogonal to the classical measurement plane.
First visual inspection indicates a connection between the amount of resin and the appearance of gravitational and shape related settling effects. The effects such as fractionating of grains by size and density or specific orientation of elongated grains became stronger the more resin was used. These aspects are statistically tested by comparing the frequency distributions of intersection segments between grains and families of lines (random in the XY planes, 9 equally spaced lines in the case of YZ plane observations), a way to circumvent Stereological degeneration effects. Results suggest a range of material/resin ratio that is suited for sample preparation of this particular ore type, by showing no statistical deviations between the distributions on the XY and YZ planes, hence no or very small gravitational or shape related settling effects.
  • Contribution to proceedings
    Annual Conference of the International Association of Mathematical Geosciences, 07.-10.09.2015, Freiberg, Deutschland
    Proceedings of the Annual Conference of the International Association of Mathematical Geosciences, 978-3-00-050337-5

Publ.-Id: 21792 - Permalink

Peculiar behavior of (U,Am)O2−δ compounds for high americium contents evidenced by XRD, XAS, and Raman spectroscopy
Lebreton, F.; Horlait, D.; Caraballo, R.; Martin, P.; Scheinost, A. C.; Rossberg, A.; Jégou, C.; Delahaye, T.;
In U1 xAmxO2±δ compounds with low americium content (x ≤ 20 at.%) and O/M (oxygen to metal) ratios close to 2.0, trivalent Am is charge-balanced by an equivalent amount of pentavalent U while maintaining the fluorite structure of pure U+IVO2. Up to now, it is unknown, whether this observation holds also for higher americium contents. In this study, we combined therefore X-ray diffraction with Raman and X-ray absorption spectroscopies to investigate U0.5Am0.5O2±δ. Our results indicate that americium is again only present as Am+III, while U+V remains below the amount required for charge balance. Contrary to lower americium contents, this leads to an overall oxygen hypo-stoichiometry with an average O/M ratio of 1.92(2). The cationic sublattice is only slightly affected by the coexistence of large amounts of reduced (Am+III) and oxidized (U+V) cations. Significant deviations from the fluorite structure are, however, evidenced by both EXAFS and Raman spectroscopy in the oxygen sublattice, with the coexistence of vacancies and interstitials consistent with the insertion of U6O12 cuboctahedral-type clusters (as observed in the U4O9 or U3O7 phases). These results thus highlight the specificities of uranium-americium mixed oxides, their behavior being closer to that of trivalent-lanthanide-doped UO2 than to that of U1 xPuxO2±δ MOX fuels.
Keywords: MOX fuel 4th generation nuclear reactors transmutation americium

Publ.-Id: 21791 - Permalink

Morphology and Microstructure of Si-SiO2 Nanocomposite Layers
Hübner, R.;
  • Invited lecture (Conferences)
    EFDS-Workshop "Morphologie und Mikrostruktur dünner Schichten und deren Beeinflussung", 12.03.2015, Dresden, Deutschland

Publ.-Id: 21790 - Permalink

Experimental Characterization of Vertical Downward Two-Phase Annular Flows Using Wire-Mesh Sensor
Vieira, R. E.; Parsi, M.; Mclaury, B. S.; Shirazi, S. A.; Torres, C. F.; Schleicher, E.; Hampel, U.;
Annular two-phase flow has been vastly investigated because of its large and deep involvement in industrial processes, particularly in nuclear engineering and petroleum production facilities. Much effort has been devoted to investigating upward flows involving the flow patterns, void fraction, as well as local interfacial characteristics. However, research for vertical downward two-phase flow, especially of the interfacial characteristics, are comparatively scarce. In order to gain insight on void fraction, interfacial structures and characteristics frequencies, experimental work was performed in downward annular two-phase flow with water and air as process fluids at low pressure conditions. A flow loop, including a 76 mm ID, 16.5 m long vertical pipe, has been instrumented. A state2 of-the-art instrument for two-phase flow measurements based on the fluid conductivity, namely dual Wire-Mesh Sensor (WMS) has been utilized to acquire the experimental data. A total of 43 data points have been acquired at superficial liquid velocities that ranged from 0.005 m/s to 0.10 m/s and superficial gas velocities that varied from 10 m/s to 31 m/s. The effects of liquid viscosity on the measured parameters are also investigated using two different viscosities of 1 and 10 cP. Analysis of time series void fraction data from the dual Wire-Mesh sensors allows the determination of cross-sectional averaged void fraction, local time averaged void fraction distribution, liquid phase distribution around the tube periphery, interfacial structure frequencies, pseudo 3D reconstruction as well as Probability Density Function (PDF) and Power Spectral Density (PSD). The experimental results indicate that the interfacial shape and frequencies are significantly altered by the superficial gas velocity. Comparisons between mechanistic model predictions and the acquired experimental data show a maximum absolute average relative error of approximately 7% for the cross-section void fraction.

Publ.-Id: 21789 - Permalink

On the effect of liquid viscosity on interfacial structures within churn flow: experimental study using Wire Mesh Sensor
Parsi, M.; Vieira, R. E.; Torres, C. F.; Kesana, N. R.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.;
In the churn flow regime, periodical interfacial structures such as liquid slugs and huge waves can coexist and undoubtedly, a phase property such as liquid viscosity can dominate the behavior of these structures. Regrettably, neither are the characteristics of churn flow widely understood nor have the effects of liquid viscosity on gas-liquid flow received enough attention. A Wire Mesh Sensor (WMS) with a 16×16 spatial resolution was employed to discover the effects of liquid viscosity on the behavior of churn flow in a vertical 76.2 mm pipe. Three liquid viscosities of 1, 10, and 40 cP, and superficial liquid velocities of 0.46, 0.61, and 0.76 m/s were employed; whereas, superficial gas velocity ranged from 10 to 27 m/s. Different techniques such as Probability Density Function (PDF), and 2-D and 3-D image reconstruction methods were applied to study the flow. It was noticed that increasing liquid viscosity not only affected the flow pattern but also the appearance frequencies of interfacial structures.
Keywords: Churn Flow; Huge Wave; Wire Mesh Sensor; Multiphase Flow; Liquid Viscosity

Publ.-Id: 21788 - Permalink

Primary and Secondary Beam Stabilization at the ELBE Accelerator Facility
Justus, M.; Jainsch, R.; Kirschke, T.; Lehnert, U.; Michel, P.; Seidel, W.;
Since 2003, ELBE operates as a user facility for fundamental research and life sciences, providing highly brilliant electromagnetic radiation in a broad spectral range, as well as particle beams. The driving source is a 40 MeV, 1 mA electron LINAC in cw mode, utilizing a 13 MHz pulsed thermionic gun and Tesla acceleration technology. Infrared light from two FELs between 3 and 280μm [1] is the foremost secondary radiation used at ELBE. For its applications, different demands in beam stability are put for successful experiments. Therefore, a feedback system for the electron beam position and energy in combination with IR beam intensity feedback using FPGA technology is under development. It is aimed at suppressing beam instabilities caused by thermal behaviour, microphonics and the 50 Hz mains frequency with upper harmonics. This article depicts hardware and software details of the measurement and feedback system and provides first performance results.
Keywords: ELBE, feedback, FEL, stability
  • Open Access LogoContribution to proceedings
    ICALEPCS 2009, 12.-16.10.2009, Kobe, Japan
    Proceedings of ICALEPCS 2009, Geneva: Jacow, 978-4-9905391-0-8
  • Lecture (others)
    ICALEPCS 2009, 12.-16.10.2009, Kobe, Japan

Publ.-Id: 21787 - Permalink

A methodology to quantify the systematic uncertainty in the liquid holdup measurements with Wire Mesh Sensor
Vuong, D.; Aydin, T. B.; Torres, C. F.; Schleicher, E.; Pereyra, E.; Sarica, C.;
The systematic uncertainty in the holdup measurements of a capacitance based WMS has been experimentally evaluated, and a methodology for its quantification is proposed. Tests are conducted in laboratory and in-situ conditions for different mesh grid and pipe inclination angles, and different flow conditions in a high pressure (1.37 MPa) facility with a range of gas and liquid velocity ranges of 2.8 m/s ≤ νSg ≤ 6.9 m/s and 1 cm/s ≤ vSL ≤ 5 cm/s, respectively.
The angle between the phase interface and the sensor wires is ineffective while the pipe inclination angle plays a major role in the deviations of the holdup measurements. Using the proposed methodology, the systematic uncertainty is shown to follow a logarithmic increase as a function of the measured holdup for smaller holdup values (HL ≤ 15%) and to be lower than 1.5% for HL > 15%. This behavior is representative of the systematic uncertainty in the actual flow loop installation.
Under actual flow conditions, the holdup measurements of the trapped liquid by WMS show an Offset compared to the Canty measurements which can be corrected by using the quantified uncertainty in the laboratory tests. Furthermore, the dynamic measurements with WMS show a good agreement with the holdup of the trapped liquid volume within the quantified uncertainty bounds.
Keywords: wire mesh; systematic uncertainty; calibration; two-phase flow

Publ.-Id: 21786 - Permalink

S-layer based nanocomposites for industrial applications
Raff, J.; Matys, S.; Suhr, M.; Vogel, M.; Günther, T.; Pollmann, K.;
This book chapter gives an overview of fundamentals of bacterial S-layers and their use for the production of nano-materials subdivided in the following sections
- What are S-layer?,
- Molecular biology of S-layer proteins,
- General application potential of bacterial S-layers,
- S-layer based coatings and their production,
- New S-layer based nano-materials.
Keywords: S-layers, coatings, nano-materials
  • Book chapter
    Tijana Z. Grove, Aitziber L. Cortajarena: Protein-based Engineered Nanostructures, Heidelberg: Springer-Verlag, 2016, 978-3-319-39194-6, 245-279
    DOI: 10.1007/978-3-319-39196-0

Publ.-Id: 21785 - Permalink

Wechselwirkung von Radiometallen mit biologischen Systemen
Raff, J.; Günther, A.; Moll, H.; Vogel, M.; Drobot, B.; Stumpf, T.;
Metalle interagieren auf vielfältige Art und Weise mit lebenden Organismen. Dies wirkt sich zunächst auf die Metalle selbst aus. Eine veränderte Speziation kann beispielsweise zu einer veränderten Mobilität wie auch zu einer veränderten Bioverfügbarkeit der Metalle in der Umwelt führen. Umgekehrt haben Metalle einen direkten Einfluss auf die Vitalität von Zellen. Neben essentiellen Metallen, die grundlegende Funktionen für den Stoffwechsel erfüllen und damit lebenswichtig sind, gibt es auch toxische Metalle, die den Organismus in höherer Konzentration nachhaltig schädigen können. Radioaktive Metalle, die im Einzelfall nicht nur eine chemische sondern zusätzlich ein radiologische Toxizität aufweisen, können auf Grund der ionisierenden Strahlung Zellbestandteile schädigen oder gar zerstören. Radiometalle können hierbei natürlichen Ursprungs sein oder durch anthropogene Aktivitäten in die Umwelt gelangen. Letzteres umfasst zum Beispiel den Bergbau, die Zementproduktion, die Ausbringung von Phosphatdünger wie auch die störfallbedingte Freisetzung von Radionukliden, Atomwaffentests und die Aufbereitung und Lagerung von radioaktiven Abfällen. Eine Zusammenstellung der wichtigsten Wechselwirkungsmechanismen von Mikroorganismen mit Radiometallen in der Umwelt zeigt nebenstehende Abbildung.
Im Rahmen des Vortrags sollen unterschiedliche Mechanismen auf molekularer Ebene und an Hand von Beispielen ausführlich diskutiert werden. Des Weiteren sollen neben den verschiedenen Varianten einer chemischen Wechselwirkung auch biochemische Effekte in der Zelle berücksichtigt werden. Ziel ist es, auf Basis der unterschiedlichen Wirkungsmechanismen von Radiometallen mit biologischen Systemen, den wechselseitigen Einfluss zum einen auf das Verhalten von Radiometallen in der Umwelt und zum anderen auf den Stoffwechsel von Zellen aufzuzeigen. Die genannten Aspekte sind nicht nur für die Abschätzung der Langzeitsicherheit eines Endlagers für radioaktive Abfälle von Bedeutung, sondern auch für die generelle Abschätzung des Gefährdungspotenzials von Radiometallen für Mensch und Umwelt.
Keywords: Radiometalle, Bioliganden
  • Invited lecture (Conferences)
    GDCh-Wissenschaftsforum Chemie 2015, 30.08.-02.09.2015, Dresden, Deutschland

Publ.-Id: 21784 - Permalink

Dual-modality wire-mesh sensor for visualization of multiphase flows
Dos Santos, E. N.; Vendruscolo, T. P.; Morales, R. E. M.; Schleicher, E.; Hampel, U.; Da Silva, M. J.;
Three-phase gas-liquid-liquid flows are very common in petroleum extraction, production and transport. In this work a dual-modality measuring technique is introduced which may be well applied for gas-liquid-liquid flow visualization. Measuring principle is based on simultaneous excitation with two distinct frequencies to interrogate each crossing point of a mesh sensor which in turn are linked to conductive and capacitive parts of impedance. The developed system can operate 8 transmitter and 8 receiver electrodes at a frame repetition frequency up to 781 Hz. The system has been evaluated by measuring reference components. Deviations to references values are below 10% which considering the fast repetition frequency of measurements is suitable for flow investigation. Furthermore, the developed system was applied to visualize three-phase air-oil-water mixtures in static and dynamic (flowing) conditions, showing that the sensor is a valuable tool to investigate such flows.
Keywords: electrical permittivity; electrical conductivity, dual modality, flow measurement, multiphase flow, petroleum industry

Publ.-Id: 21783 - Permalink

An optimal model for in vivo radiobiological studies with laser driven proton beams?
Beyreuther, E.; Baumann, M.; Brüchner, K.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Oppelt, M.; Schürer, M.; Wetzig, K.; Pawelke, J.;
  • Poster
    1. Retreat of the National Center for Radiation Oncology (NCRO), 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21782 - Permalink

In-vivo dosimetry for particle beams - Radiation Physics
Helmbrecht, S.; Iltzsche, M.; Jannusch, P.; Lutz, B.; Priegnitz, M.; Rohling, H.; Römer, K.; Schöne, S.; Schumann, A.; Weinberger, D.; Pausch, G.; Enghardt, W.; Fiedler, F.;
no abstract available
  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21781 - Permalink

Transverse Emittance Compensation
Vennekate, H.; Arnold, A.; Kamps, T.; Kneisel, P.; Lu, P.; Murcek, P.; Teichert, J.; Xiang, R.;
Superconducting RF injectors are promising candidates for the particle sources of future accelerators. While machines like high power free electron lasers or energy recovery linacs are planned to be operated with large duty factors, or even continuous wave mode, to increase the beam intensity, they also demand high beam quality. As this is already determined at the very start of the generation of each particle bunch, the concept of an SRF gun becomes appealing. Transverse Emittance marks the beam quality which is of tremendous relevance for all beam optics and further more sets the level of angular resolution of any scattering experiment performed with the beam. Several concepts to enhance this quality with the lately comissioned Rossendorf SRF Gun II have been presented in recent year’s conferences. The talk will summarize the expended efforts, discuss some of the reflections on installation and operation of the used tools and present preliminary results of the recent achievements.
Keywords: SRF Gun, Emittance, ELBE
  • Lecture (Conference)
    DPG Frühjahrstagung 2015 Wuppertal, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21780 - Permalink

Experiments in bubble columns for CFD model validation
Ziegenhein, T.; Rzehak, R.; Lucas, D.;
Bubble columns are widely used in industrial application and are an actual object of research. The performance of a bubble column strongly depends on the characteristic of the flow, which can be modeled with the methods of computational fluid dynamics (CFD). A widely used CFD approach for modeling such dispersed multiphase flows is the Eulerian two-fluid approach.
With the Eulerian two-fluid approach large apparatuses can be simulated in a short time; however, the interaction between the dispersed and the continuous phases has to be modelled with closure models. The closure models refer to different forces and effects, such as drag, lift, virtual mass, turbulent dispersion, coalescence & break up and bubble induced turbulence. The usage of a proper set of closure models is an actual discussion in the scientific community (Rzehak & Krepper 2013) and proper experiments are needed for model validation.
To validate the above mentioned effects that the closure models have to cover, a wide range of experiments are needed. In addition, such experiments should allow measuring the relevant data for a model validation. The must have relevant data are the bubble size distribution, the local void fraction and the liquid velocity at different positions.
In the present study an airlift air-water bubble column, a partially aerated air-water bubble column and an air-NaCl solution bubble column is investigated. The bubble size distribution, the local void fraction and the liquid velocity will be shown at different positions in the bubble column. In addition, a comparison of the experimental results with simulations using an Euler-Euler unsteady Reynolds averaged Navier Stokes equation approach as described in Ziegenhein et al. 2015 is given.
Keywords: Bubble columns, multiphase flow, bubbly flows, particle tracking velocimetry, bubble size measurement, void fraction measurement, Airlift, break-up, coalescence
  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 21779 - Permalink

Prompt-Gamma-Imaging for range verification in proton therapy: Towards clinical implementation
Barczyk, S.; Golnik, C.; Priegnitz, M.; Vander Stappen, F.; Janssens, G.; Smeets, J.; Clementel, E.; Hotoiu, L.; de Xivry, J. O.; Baumann, M.; Enghardt, W.; Fiedler, F.; Krause, M.; Prieels, D.; Pausch, G.; Richter, C.;
No abstract available
  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21778 - Permalink

PGI & PGT Modeling for realistic Patient Treatment Plans
Priegnitz, M.; Rohling, H.; Schumann, A.; Enghardt, W.; Pausch, G.; Fiedler, F.;
No abstract available.
  • Poster
    National Center for Radiation Oncology - 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21777 - Permalink

Neutron Dose During Proton Therapy
Lutz, B.; Enghardt, W.; Pausch, G.; Fiedler, F.;
Work in progress report about the measurement of the neutron field during proton therapy at OncoRay.
  • Poster
    National Center for Radiation Oncology -- 1st Scientific Retreat, 19.-21.03.2015, Heidelberg, Deutschland

Publ.-Id: 21776 - Permalink

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

Publ.-Id: 21775 - Permalink

Exploring photochemistry of uranyl(VI)
Tsushima, S.;
Photoexcited uranyl(VI) is a mild oxidant and can decompose various biological substances including large molecule like DNA. This reaction constitutes another environmental risk of uranium in addition to its radiotoxicity and chemotoxicity. There are several different mechanisms which may lead to decomposition of organic substances by photoexcited uranyl(VI). This includes hydrogen abstraction by “yl”-oxygen, decarboxylation of uranyl-bound carboxylic group, and ligand-to-metal charge transfer. These mechanisms may also compete with each other and makes mechanistic understanding far from being straightforward. In my talk, I will focus on our recent experimental and theoretical development on DNA photocleavage study. Although hydrogen abstraction is widely believed to be the key reaction in uranyl(VI)–mediated photocleavage of DNA, density functional theory calculations show that direct charge transfer from DNA to photoexcited uranyl(VI) can be an alternative pathway that leads to DNA strand break. In the oxidized state of DNA, electron deficiency is centered mainly on guanine as well as on uranyl–free phosphate, and lesser extent is distributed on adenine and thymine. Presumably there is no unique “hot spot” in DNA and upon irradiation local oxidation occurs in nucleobase or in uranyl–free phosphate in the vicinity of uranium. Oxidation of phosphate eventually leads to DNA strand break. Experiments using circular dichroism (CD) and X-ray absorption spectroscopy (XAS) are in progress.
  • Invited lecture (Conferences)
    The International Chemical Congress of Pacific Basin Societies (PACIFICHEM 2015), Symposium on Experimental and Theoretical Actinide Chemistry: From Fundamental Systems to Practical Applications, 15.-20.12.2015, Honolulu, Hawaii, USA

Publ.-Id: 21774 - Permalink

Polymer and cluster chemistry of f-elements in aqueous solutions
Ikeda-Ohno, A.;
Because of their high charge density, the aqueous chemistry of f-elements with lower valences (i.e. tri- and tetravalent) is predominantly controlled by strong hydrolysis producing a variety of hydroxide species. Interestingly enough, this strong hydrolysis often induces the intrinsic formation of polymer and nano-sized cluster complexes which are stable even in aqueous solutions. This seminar will provide a recent overview of the hydrolysis-induced polymer/cluster formation of tetravalent f-elements particularly from the viewpoint of structural chemistry, as well as the associated characterisation techniques (e.g. X-ray absorption spectroscopy or X-ray scattering).
Keywords: actinides, lanthanides, f-elements, hydrolysis, aqueous solution, polymers, clusters, characterisation
  • Invited lecture (Conferences)
    Internal seminar, Institut für Radioökologie und Strahlenschutz, Leibnitz Universität Hannover, 30.04.2015, Hannover, Germany

Publ.-Id: 21773 - Permalink

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

Publ.-Id: 21772 - Permalink

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

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

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

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

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

We will discuss simulation results and apply the method to actual experimental data.
Keywords: Geometallurgy, Statistic, MLA, Linear Model
  • Lecture (Conference)
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 07.-10.09.2015, Freiberg, Deutschland
    Proceedings of the 17th annual conference of the International Association for Mathematical Geosciences

Publ.-Id: 21771 - Permalink

Experimental benchmark of an analytical model for prompt gamma imaging
Sterpin, E.; Janssens, G.; Smeets, J.; Vander Stappen, F.; Prieels, D.; Priegnitz, M.; Perali, I.; Vynckier, S.;
A prompt gamma (PG) slit camera prototype recently demonstrated a 1-2 mm accuracy to detect proton range shifts at clinical beam currents by comparing an expected PG detection profile to a measured one. An analytical model has been recently developed to compute the expected profile at practical speed (< 1 s). We present here its benchmark against measurements in heterogeneous phantoms.
  • Lecture (Conference)
    AAPM 2015, 57th Annual Meeting, 12.-16.07.2015, Anaheim, USA
  • Abstract in refereed journal
    Medical Physics 42(2015)6, 3726

Publ.-Id: 21770 - Permalink

Spectroscopic studies on monazite-type ceramics for the conditioning of radioactive waste: Infrared, Raman, X-ray Absorption and Site-Selective Time Resolved Laser Fluorescence Spectroscopy
Neumeier, S.; Arinicheva, Y.; Huittinen, N.; Lozano-Rodriguez, M. J.; Holthausen, J.; Modolo, G.; Scheinost, A. C.; Stumpf, T.; Bosbach, D.;
Monazite ceramics are being considered as potential waste forms for immobilization of minor actinides since they exhibit advantageous properties such as high chemical durability and radiation tolerance.
The overall objective of our study is to reveal the mechanisms of solid solution formation as well as the incorporation of the actinides into the crystal structure of the waste matrix. A fundamental understanding of these mechanisms is of great importance with regard to the long-term stability of monazites for safe nuclear waste disposal.
(La,Eu)PO4 and due to quenching effects of high Eu-contents in TRLFS measurements Eu doped (La,Gd)PO4 monazite solid solutions were synthesized by wet chemical methods. Eu serves as surrogate for trivalent actinides. Samples were characterized by XRD, Raman, IR, EXAFS and TRLFS spectroscopies. Structural refinement of XRD data as well as a linear shift of Raman and IR bands towards higher wave numbers shows a linear dependency of lattice parameters on the Eu content according to Vegard’s law. In contrast, EXAFS analysis reveals a decrease only for the La-O distances in the first coordination shell and the first metal-metal distance, while the Eu-O local coordination remains unchanged. TRLFS investigations show that the host cation size in the monazites has very little influence on the Eu3+ incorporation into these materials, but a broadening of the excitation spectra indicate a local disordering of the crystal structure around the dopant
Keywords: Monazite XRD EXAFS IR TRLFS Europium
  • Invited lecture (Conferences)
    E-MRS Spring Meeting 2015, 11.-15.05.2015, Lille, France

Publ.-Id: 21769 - Permalink

Investigating Spinodal Decomposition and Coarsening using Massively Parallel Kinetic Metropolis Lattice Monte-Carlo Simulations
Kelling, J.; Heinig, K. H.; Gemming, S.;
Nano-structured materials are important for many applications, including energy technologies. The desired structures can be created using bottom-up processes, which utilize self-assembling. By way of spinodal decomposition of a metastable phase, like SiOx into Si and SiO2, sponge-like networks of nanowires can be obtained. Understanding the coarsening kinetics of spinodal structures is crucial not only for bottom-up production, but also helps to increase the life-time of components like porous matrices in fuel cells, where suppression of coarsening has a huge economic impact.

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

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

[1] A. Chakrabarti, R. Toral, J.D. Gunton, Phys. Rev. B 39(7) 4386 (1989) suggesting a modified Lifschitz-Slyozov law: I.M. Lifshitz, V.V. Slyozov, J. Phys. Chem. Solids 19(1-2), 35-50 (1961)
[2] W.W. Mullins, J. Appl. Phys. 28(3), 333-339 (1957)
Keywords: Nano Structures, GPGPU, Supercomputing, Statistical Physics
  • Lecture (Conference)
    Conference of the Middle European Cooperation in Statistical Physics, 23.-25.03.2015, Esztergom, Hungary

Publ.-Id: 21768 - Permalink

Simulation of Surface Growth and Lattices Gases Using GPUs
Schulz, H.; Kelling, J.; Ódor, G.; Ódor, G.; Ferenc Nagy, M.;
Restricted solid on solid surface growth models can be mapped onto binary lattice gases. We show that efficient simulation algorithms can be realized on GPUs either by CUDA or by OpenCL programming. We consider a deposition/evaporation model following Kardar–Parisi–Zhang growth in d+1 dimensions, related to the Asymmetric Simple Exclusion Process. Up to 100 - 400 x speedup can be achieved with respect to the serial code running on a I5 core. This permits studying disorder and aging behavior in these system.
Keywords: Computational Physics, Supercomputing

Publ.-Id: 21767 - Permalink

Radiobiologial response to ultra-short pulsed MeV electron beams of ultra-high pulse dose rate
Beyreuther, E.; Gotz, M.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Oppelt, M.; Schürer, M.; Pawelke, J.;
  • Poster
    1. Retreat of the National Center for Radiation Oncology (NCRO), 19.-21.03.2015, Heidelberg, Deutschland
  • Poster
    15th International Congress of Radiation Research, 25.-29.05.2015, Kyoto, Japan

Publ.-Id: 21766 - Permalink

GPGPU Powered 3D Simulations of Micro Droplets in Laser-Ion Acceleration
Huebl, A.; Kluge, T.; Hilz, P.; Bussmann, M.;
We present current large scale, full 3D particle-in-cell simulations and studies of laser-ion acceleration utilizing highly over-dense, mass and volume limited micro targets with PIConGPU. Powered by thousands of GPGPUs on Oak Ridge's supercomputer Titan, we show early results such as the influence of the target to laser spot size and the arising acceleration regimes thereof.

The simulations show the capability of PIConGPU, a highly scalable particle-in-cell code for many-core compute architectures that allows for in-situ, real time visualization and ultra-fast computation of large systems.
Keywords: mass-limited targets, PBA, GPGPU, simulation, HPC, laser-ion acceleration
  • Lecture (Conference)
    DPG-Frühjahrstagung: FV Teilchen-, Strahlen- und Medizinphysik, Arbeitskreis Beschleunigerphysik, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 21765 - Permalink

Low-energy enhancement of M1 strength
Schwengner, R.; Frauendorf, S.; Larsen, A. C.;
Magnetic dipole strength functions have been deduced from averages of a large number of M 1 transition strengths calculated within the shell model for the nuclides 90 Zr, 94Mo, 95 Mo, and 96 Mo. An enhancement of M1 strength toward low transition energy has been found for all nuclides considered. Large M1 strengths appear for transitions between close-lying states with configurations including proton as well as neutron high-j orbits that re-couple their spins and add up their magnetic moments coherently. The M 1 strength function deduced from the calculated M 1 transition strengths is compatible with the low-energy enhancement found in (3He,3He') and (d,p) experiments. The present work presents an explanation of the experimental findings.
Keywords: Strength functions, magnetic dipole strength, shell model.
  • Open Access LogoJournal of Physics: Conference Series 580(2015), 012020
    DOI: 10.1088/1742-6596/580/1/012020
  • Invited lecture (Conferences)
    11th International Spring Seminar on Nuclear Physics: Shell Model and Nuclear Structure - achievements of the past two decades, 12.-16.05.2014, Ischia, Italia

Publ.-Id: 21763 - Permalink

Annual Report 2014 - Institute of Resource Ecology
Stumpf, T.; Foerstendorf, H.; Bok, F.; Richter, A.; (Editors)
The Institute of Resource Ecology (IRE) is one of the eight institutes of the Helmholtz-Zentrum Dresden – Rossendorf (HZDR).
The research activities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and focused on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”.
Additionally, various activities have been started investigating chemical and environmental aspects of processing and recycling of strategic metals, namely rare earth elements. These activities are located in the HGF program “Energy Efficiency, Materials and Resources (EMR)”. Both programs, and therefore all work which is done at IRE, belong to the research sector “Energy” of the HGF.
The research objectives are the protection of humans and the environment from hazards caused by pollutants resulting from technical processes that produce energy and raw materials. Treating technology and ecology as a unity is the major scientific challenge in assuring the safety of technical processes and gaining their public acceptance. We investigate the ecological risks exerted by radioactive and nonradioactive metals in the context of nuclear waste disposal, the production of energy in nuclear power plants, and in processes along the value chain of metalliferous raw materials. A common goal is to generate better understanding about the dominating processes essential for metal mobilization and immobilization on the molecular level by using advanced spectroscopic methods. This in turn enables us to assess the macroscopic phenomena, including models, codes, and data for predictive calculations, which determine the transport and distribution of contaminants in the environment.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-059 2015


Publ.-Id: 21762 - Permalink

Einfluss von Biofilmen auf das Migrationsverhalten von Uran, Americium und Europium in der Umwelt
Baumann, N.; Zirnstein, I.; Arnold, T.;
Die Mechanismen von Immobilisierungsprozessen radioaktiver Schwermetall-Ionen innerhalb von Biofilmen sind noch weitgehend unerforscht. Das liegt an der Komplexität der Biofilme, welche häufig diskrete geochemische Mikromilieus bilden, die sich vom umgebenden Milieu („Bulk Solution“) in Bezug auf dessen Biozönose (der mikrobiellen Diversität), den darin herrschenden geochemischen Bedingung (z.B. Red/Ox-Potential u./o. gelöster Sauerstoffmenge), aber auch in der Konzentration möglicher Komplexbildner (z.B. Metaboliten u./o. EPS-Komponenten) deutlich unterscheiden. Alle diese Faktoren können die Speziation der Radionuklide verändern und damit auch deren Transportverhalten. Für ein besseres Prozessverständnis zu den Wechselwirkungen von Radionukliden mit natürlichen, in Uran-kontaminierten Milieus lebende Mikroorganismen und den damit verbunden Stoffen wurde die Biozönose in Biofilmen und im Grubenwasser des ehem. WISMUT-Uranbergwerkes Königstein nach klassischen mikrobiologischen- und molekularbiologischen Methoden bestimmt. Aus einem Vergleich der Chemie im Biofilm mit der Chemie der umgebenden Lösung wird der Einfluss der Biofilme auf das Migrationsverhalten von Radionukliden in der Natur beurteilt. Die Identifizierung und Quantifizierung von Prokaryoten erfolgte u.a. mit der CARD FISH Methode. Die selektive Visualisierung der EPS-Komponenten in der Matrix der Biofilme wurde mit Hilfe der Konfokalen Laser Scanning Mikroskopie (CLSM) bewerkstelligt.
Zur Untersuchung der Speziation von fluoreszierenden Schwermetall-Ionen wie U(VI) kam die zeitaufgelöste, laser-induzierte Fluoreszenzspektroskopie (TRLFS) zum Einsatz. Um diese Methode auch im mikroskopischen Bereich anwenden zu können, wurde sie weiter zum CLSM hin entwickelt: Da ein 80-MHz-MaiTai-Laser zur Verfügung stand, wurde durch im kHz-Bereich alternierendes Beugen des Anregungslaserstrahls von der Probe weg (und wieder zu ihr hin) mittels akusto-optischem Modulator (AOM) eine quasi-gepulste Laseranregung im kHz-Bereich erreicht. Durch Einbindung von Frequenzvervielfachern („Harmonixx“ von APE Berlin und „Inspire“ von Spectra-Physics) konnte so eine gepulste Anregung innerhalb eines breiten Wellenlängenbereiches (ca. 230-1090 nm) ermöglicht werden. Für die Auswertung des als äußerst schwach zu erwartenden Fluoreszenzsignales (entsprechend des mikroskopisch kleinen Anregungsraumes) wurde die Time-Correlated Single-Photon Counting Methode (TCSPC) – auch „zeitbezügliche Einzelphotonenzählungs-Methode“ – an das Laser-Anregungssystem angepasst. Die Fluoreszenzlebenszeitkurve des Fluoreszenzsignals von U(VI) Species, die sich an der Oberfläche von den Protozoen Euglena Mutabilis befanden, konnte z.B. auf diese Art mit Hilfe der TCSPC ermittelt werden.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-061 2015


Publ.-Id: 21761 - Permalink

Carrier relaxation dynamics in graphene
Mittendorff, M.;
Graphene, the two-dimensional lattice of sp2-hybridized carbon atoms, has a great potential for future electronics, in particular for opto-electronic devices. The carrier relaxation dynamics, which is of key importance for such applications, is in the main focus of this thesis. Besides a short introduction into the most prominent material properties of graphene and the experimental techniques, this thesis is divided into three main parts.
The investigation of the carrier relaxation dynamics in the absence of a magnetic field is presented in Chapter 3. In the first experiment, the anisotropy of the carrier excitation and relaxation in momentum space was investigated by pump-probe measurements in the near-infrared range. While this anisotropy was not considered in all previous experiments, our measurements with a temporal resolution of less than 50 fs revealed the polarization dependence of the carrier excitation and the subsequent relaxation. About 150 fs after the electrons are excited, the carrier distribution in momentum space gets isotropic, caused by electron-phonon scattering. In a second set of two-color pump-probe experiments, the temperature of the hot carrier distribution, which was obtained within the duration of the pump pulse (about 200 fs), could be estimated. Furthermore, a change in sign of the pump-probe signal can be used as an indicator for the Fermi energy of different graphene layers. Pump-probe experiments in the far-infrared range in reflection and transmission geometry were performed at high pump power. A strong saturation of the pump-induced transmission was found in previous experiments, which was attributed to the pump-induced change in absorption. Our investigation shows the strong influence of pump-induced reflection at long wavelengths, as well as a lot smaller influence of the saturation of the pump-induced change in absorption. At a high pump power, the increase of the reflection exceeds the change in absorption strongly, which leads to negative pump-probe signals in transmission geometry.
In Chapter 4, investigations of the carrier dynamics of graphene in magnetic fields of up to 7T are presented. Even though the optical properties of Landau-quantized graphene are very interesting, the carrier dynamics were nearly unexplored. A low photon energy of 14meV allows the investigation of the intraband Landau-level (LL) transitions. These experiments revealed two main findings: Firstly, the Landau quantization strongly suppresses the carrier relaxation via optical-phonon scattering, resulting in an increased relaxation time. Secondly, a change in sign of the pumpprobe signal can be observed when the magnetic field is varied. This change in sign indicates a hot carrier distribution shortly after the pump pulse, which means that carrier-carrier scattering remains very strong in magnetic fields. In a second set of pump-probe measurements, carried out at a photon energy of 75meV, the relaxation dynamics of interband LL transitions was investigated. In particular, experiments on the two energetically degenerate LL transitions LL−1 ) LL0 and LL0 ) LL1 showed the influence of extremely strong Auger processes.
An ultrafast and extremely broadband terahertz detector, based on a graphene flake, is presented in the last chapter of this thesis. To couple the radiation efficiently to the small flake, the inner part of a logarithmic periodic antenna is connected to it. With a rise time of about 50 ps in a wavelength range of 9 μm to 500 μm, this detector is very interesting to obtain the temporal overlap in two-color pump-probe experiments with the free-electron laser FELBE. Furthermore, the importance of the substrate material, in particular for the high-speed performance, is discussed.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-057 2015


Publ.-Id: 21760 - Permalink

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

Publ.-Id: 21759 - Permalink

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


Publ.-Id: 21758 - Permalink

Enhanced reactive transport process understanding by means of experiments and modelling at HZDR/IRE
Lippmann-Pipke, J.;
Es ist kein Abstract vorhanden.
  • Lecture (others)
    Helmholtz-Koordinierungstreffen, Forschung zu Endlagersystemen FZJ/IEK-6, KIT/INE, HZDR/IRE, 04.-05.03.2015, Jülich, Deutschland

Publ.-Id: 21757 - Permalink

A simple method for deadtime corrections in microbeam measurements.
Munnik, F.;
In microbeam measurements on inhomogeneous samples large variations in count-rate can occur. These variations result in variations in deadtime that have to be used to correct elemental distribution maps. However, the deadtime is usually not available on a pixel by pixel basis. In this work, a simple model is proposed to calculate the deadtime for each pixel. Measurements to determine the deadtime per event, needed in the model, are presented and the deadtime corrections are presented for real samples.
Keywords: dead time, PIXE
  • Poster
    14th International Conference on Particle Induced X-ray Emission (PIXE 2015), 26.02.-03.03.2015, Somerset West, South Africa

Publ.-Id: 21756 - Permalink

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

Publ.-Id: 21755 - Permalink

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

Publ.-Id: 21754 - Permalink

Towards Atomic Physics in PIConGPU
Huebl, A.; Garten, M.; Widera, R.; Huang, L.; Kluge, T.; Bussmann, M.;
Particle-in-Cell (PIC) codes are a ubiquitous tool to study laser-plasma physics in a fully relativistic environment. Theoretical models for plasma based accelerators and corresponding experiments, as planned by the HIBEF collaboration (XFEL), depend dramatically on the ability to precisely predict the complex processes inside of targets.

Unfortunately, basic atomic processes like the ionization dynamics of solid foil target in ultra-high fields of modern short-pulse laser systems in the PW class are not covered by the basic PIC algorithm. This talk shows ways to introduce the microscopic ionization dynamics inside the targets in a self-consistent and rigorous way. Combined with modern compute hardware such as GPUs and manycore systems in general, this paves the road to a new quality of multi-physics simulations with ab-initio modeling of atomic processes in strong laser fields.
Keywords: PIC, GPU, Ionization, CUDA, PIConGPU, HPC, HIBEF
  • Lecture (Conference)
    DPG-Frühjahrstagung: FV Kurzzeitphysik und Plasmaphysik, 02.-05.03.2015, Bochum, Deutschland

Publ.-Id: 21753 - Permalink

Heating and Ionization Dynamics in Solid Density Plasmas Driven by Ultra-short Relativistic Lasers
Huang, L. G.; Kluge, T.; Bussmann, M.; Cowan, T. E.;
The dynamics of heating and ionization, which determines the crucial plasma parameters such as temperature, free electron density and so on, is one of the fundamental issues in the realm of ultra-short relativistic laser-solid target interactions. We present our work on investigation of heating and ionization dynamics in solid copper target irradiated by ultra-short intense laser using two dimensional particle-in-cell simulations. The simulation results show that the bulk electron temperature is very sensitive to the initial preplasma scale length. By varying the preplasma scale length from 0 to 0.1 λ_0, the bulk electron temperatures in the interest of region increase from ~26 eV to ~109 eV, which agrees very well with the theory based on Ohmic heating mechanism by treating the return current correctly. The bulk electron heating is finally translated into bulk ionization, which leads to the average Cu ion charge state increasing from ~4.3 to ~10.7.
Keywords: Heating,Ionization,Return Current
  • Lecture (Conference)
    DPG-Frühjahrstagung, 02.-05.03.2015, Bochum, Deutschland

Publ.-Id: 21752 - Permalink

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

[1] Kaszuba, J.P. et al. (1999) Environ. Sci. Technol. 33, 4427-4433.
[2] O'Day, P.A. (1999) Rev. Geophys. 37, 249-274.
[3] Tochiyama, O. et al. (1996) Radiochim. Acta 73, 191-198.
[4] Müller, K. et al. (2015) Environ. Sci. Technol. 49, 2560-2567.
  • Lecture (Conference)
    Goldschmidt 2015, 16.-21.08.2015, Prague, Czech Republic

Publ.-Id: 21751 - Permalink

Use of spectroscopic and microscopic methods to reveal the evidence of U(VI) sorption on Acidovorax facilis isolated from subsurface environments
Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Arnold, T.;
U(VI) biosorption experiments were performed using isolated Acidovorax facilis cell. From TRLFS measurements it can be concluded that phosphoryl groups are the main binding sites for uranyl, located in the lipopolysaccharide (LPS) unit in the outer membrane by Gram-negative Acidovorax facilis cells. In addition, EF-TEM/EELS studies provide microscopically and spectroscopically evidence of U sorbed at the outer membrane of Acidovorax facilis cells by showing high electron density and U ionization intensity peaks. The results support the TRLFS measurements and contribute to a better understanding of the binding mechanisms of U(VI) on Acidovorax facilis cells.
Keywords: Acidovorax facilis, Uranium, sorption, EF-TEM/EELS, TRLFS
  • Lecture (Conference)
    Environmental Radioactivity 2015 Conference, 21.-25.09.2015, Thessaloniki, Greece

Publ.-Id: 21750 - Permalink

Kompromissbereite Supraleitung
Zwicknagl, G.; Wosnitza, J.;
Hohe Magnetfelder und Supraleitung vertragen sich üblicherweise nicht: Das Magnetfeld favorisiert parallel ausgerichtete Elektronenspins, während die Supraleitung Cooper-Paare mit antiparallelen Spins voraussetzt. Daher sollte bei ausreichend großen Feldern die Supraleitung zusammenbrechen. Wie Fulde und Ferrell sowie Larkin und Ovchinnikov bereits 1964 vorhergesagt haben, können räumlich getrennte supraleitende sowie magnetisch geordnete Bereiche aber auch bei noch höheren Magnetfeldern koexistieren.
  • Physik Journal 14(2015)3, 31-36

Publ.-Id: 21748 - Permalink

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

Publ.-Id: 21747 - Permalink

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

Publ.-Id: 21746 - Permalink

Ultrasmall Nanomaterials for Multimodal Imaging
Stephan, H.;
kein Abstract verfügbar
  • Lecture (Conference)
    Gründungsveranstaltung der Deutschen Plattform NanoBioMedizin, DECHEMA, 04.03.2015, Frankfurt/Main, Deutschland

Publ.-Id: 21745 - Permalink

New Approaches for Prediction of Gas Holdups and Validation of the Mixing Length Concept in Gas-Liquid and Slurry Bubble Columns
Nedeltchev, S.; Schubert, M.;
The successful prediction of gas holdups in (slurry) bubble columns is very important for both the design and scale-up of these reactors. In the literature hitherto there are only few reliable empirical gas holdup correlations (mainly for gas-liquid bubble columns). In this work, a new approach has been developed for predicting the gas holdups at ambient conditions in gas-liquid bubble columns (0.095 and 0.102 m in ID) operated with 21 pure organic liquids, 17 liquid mixtures and tap water. The same approach was also applied for prediction of gas holdups in a slurry bubble column (0.095 m in ID) operated with 7 three-phase systems under ambient conditions.
The new model for gas holdup prediction in (slurry) bubble columns is based on the theoretical calculation of the gas-liquid interfacial area: a=6ɛg/ds. This correlation is explicitly valid for rigid spherical bubbles. In the case of slurry bubble columns, an empirical correlation developed by Schumpe et al. (1987) for the interfacial area prediction is frequently used. When both correlations are set equal, then the theoretical gas holdup can be calculated provided that one knows how to estimate the Sauter-mean bubble diameter ds and the effective viscosity μeff. The same approach was also applied to gas-liquid bubble columns. However, the interfacial areas were estimated by the empirical correlation of Akita and Yoshida (1974).
In the above-mentioned approaches the estimation of the Sauter-mean bubble diameters ds was based on empirical correlations (Wilkinson et al. (1994) for bubble columns and Lemoine et al. (2008) for slurry bubble columns).
For given gas-liquid-solid system, gas distributor layout and column diameter, the ds value is a function of both the superficial gas velocity and gas holdup (1-ɛg)^1.56 (Lemoine et al., 2008). Following the above-described approach, the ɛg value was calculated (based on a trial and error method) from the ratio ɛg/(1-ɛg)^1.56. The obtained ɛg value in this way was multiplied by a correction factor (a function of Eӧtvӧs number Eo) since the formed bubbles under the tested experimental conditions were oblate ellipsoidal (i.e. non-spherical). In the case of slurry bubble columns, the Eo number was based on the slurry density ρSL.
Following the above-described approach in two-phase bubble columns, it was found that for given gas-liquid system, column diameter and Ug value the theoretical gas holdup could be estimated from the simplified correlation: ɛg^0.13=const. Then the obtained ɛg value was also multiplied by a correction factor (a function of Eo). So, the objective of this part of the research work was to find the best expressions for the correction factors in two-phase and three-phase bubble columns, which fit successfully the experimental gas holdups ɛg.
The determination of the scale of liquid mixing in the main hydrodynamic regimes of bubble column operation is also of essential importance for their design and scale-up. In this context, a new method (and correlation) has been proposed by Kawase and Tokunaga (1991) for the determination of the mixing length (L). The parameter L characterizes the degree and scale of mixing. It can be also associated with the distance over which a turbulent eddy retains its identity.
In this work, a new definition of entropy (E) has been developed on the basis of gas holdup time series data measured by a conductivity wire-mesh sensor in an air-water bubble column (0.15 m in ID). The new entropy has been estimated by means of multiple reconstructions of the signal. It was found that in the Ug range from 0.034 to 0.101 m/s (see Fig. 2), the entropy (E) decreased monotonously and it was correlated to the mixing length L (a function of both column diameter Dc and Ug^−0.38). Secondly, a newly defined information entropy (IE) has been also extracted from the gas holdup fluctuations and correlated to the mixing length in almost the same Ug range (0.022−0.101 m/s).
In a previous publication (Nedeltchev et al., 2014), it was shown that the Kolmogorov entropy (KE) and a new statistical parameter (called “maximum number of signal’s visits in a region” Nvmax) were capable of identifying the range of applicability (0.034≤ Ug≤0.112 m/s) of the mixing length concept. Another statistical parameter F (average/(3×average absolute deviation)) was also introduced by Nedeltchev and Schubert (2015) for validating the range of applicability of the mixing length concept. It was also found that the F index is a function of the mixing length L in the Ug range from 0.034 to 0.112 m/s.
In this work, a comparison of the results obtained by the five different parameters (E, IE, KE, Nvmax and F) is performed. Most of them (except for KE) are new and such a comparison has not been reported in the literature hitherto. It revealed that the determination of the boundaries of the transition flow regime and the range of applicability of the mixing length concept depends to some extent on the parameter used. Based on the above-mentioned parameters it was found that the mixing length concept was applicable only in the transition flow regime. Such a result has not been reported in the previous papers (for instance, in Kawase and Tokunaga, 1991).
Keywords: Gas-liquid bubble columns, Slurry bubble columns, Gas holdup modelling, Mixing length, Applicability range
  • Lecture (Conference)
    12th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering (GLS12), 28.06.-01.07.2015, New York, USA

Publ.-Id: 21744 - Permalink

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

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

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

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

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

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

Recoil Labelling [7Be]TiO2 0.3 170
[7Be]SiO2 [4] 53.29 d 1.4 36
[7Be]MWCNT 0.055 1000
[1] Franke, K., Patt, J.T., Kupsch, H., Warwick, P.: Radioiodination of Humic Substances via Azocoupling with 3-[125I]Iodoaniline. Environ Sci Technol 42(11) (2008) 4083 - 4087.
[2] Hildebrand, H., Franke, K.: A new radiolabeling method for commercial Ag0 nanopowder with 110mAg for sensitive nanoparticle detection in complex media. J Nanopart Res 14 (2012) 1142.
[3] Hildebrand, H., Schymura, S., Holzwarth, U., Gibson, N., Dalmiglio, M., Franke, K.: Strategies for radiolabeling of commercial TiO2 nanopowder as a tool for sensitive nanoparticle detection. J Nanopart Res, submitted.
[4] Holzwarth, U., Bellido, E., Dalmiglio, M., Kozempel, J., Cotogno, G., Gibson, N.: 7Be-recoil radiolabelling of industrially manufactured silica nanoparticles. J Nanopart Res 16 (2014) 2574.
  • Poster
    3nd BELBaR Annual Meeting, 05.-06.03.2015, Madrid, Spain

Publ.-Id: 21743 - Permalink

Frequency dependence of an alternating magnetic field driven flow
Cramer, A.; Galindo, V.; Zennaro, M.;
The flow induced by a single-phase alternating magnetic field (AMF) is studied mainly numerically, and by two preliminary experiments of quite different size. For validation, the well known dependence of the characteristic velocity on magnetic induction is reproduced experimentally and in the simulations. It is shown that the flow structure depends drastically on the frequency of the AMF. An investigation of the change of the characteristic velocity with frequency results in a quantitative difference of flows in an AMF compared to rotating and travelling magnetic fields.
Keywords: PACS:, 47.15.Rq, 47.85.M-
  • Magnetohydrodynamics 51(2015)1, 133-147

Publ.-Id: 21741 - Permalink

Comparison of New Entropy Profiles in Bubble Columns Operated with Air-Water and Air-Therminol Systems
Nedeltchev, S.; Hampel, U.; Schubert, M.;
In a bubble column (0.15 m in ID) operated with an air-water system, a new entropy was extracted from gas holdup fluctuations measured by conductivity wire-mesh sensor. It was capable of identifying three transition velocities Utrans at 0.045, 0.089 and 0.112 m/s. In a different bubble column (0.162 m in ID) operated with an air-therminol LT system at ambient conditions, the new entropy was extracted from photon count time series measured by computed tomography. Three Utrans values were also identified at 0.03, 0.08 and 0.1 m/s. The information entropies yielded similar results.
Based on the new entropy results it can be concluded that the type of fluid and gas sparger used do not affect significantly the second and third Utrans values. There is an effect on the first Utrans value which can be explained with the strong gas maldistribution in the case of the bubble column operated with an air-water system.
Keywords: Bubble column, Flow Regime Identification, Entropy, Wire-Mesh Sensor, Computed Tomography
  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 21740 - Permalink

Performance of timing resistive plate chambers with relativistic neutrons from 300 to 1500MeV
Blanco, A.; Adamczewski-Musch, J.; Boretzky, K.; Cabanelas, P.; Cartegni, L.; Ferreira Marques, R.; Fonte, P.; Fruehauf, J.; Galaviz, D.; Heil, M.; Henriques, A.; Ickert, G.; Körper, D.; Lopes, L.; Palka, M.; Pereira, A.; Rossi, D.; Simon, H.; Teubig, P.; Traxler, M.; Velho, P.; Altstadt, S.; Atar, L.; Aumann, T.; Bemmerer, D.; Caesar, C.; Charpy, A.; Elekes, Z.; Fiori, E.; Gasparic, I.; Gerbig, J.; Göbel, K.; Heftrich, T.; Heine, M.; Heinz, A.; Holl, M.; Ignatov, A.; Isaak, J.; Johansson, H.; Kelic-Heil, A.; Lederer, C.; Lindberg, S.; Löher, B.; Machado, J.; Marganiec, J.; Martensson, M.; Nilsson, T.; Panin, V.; Paschalis, S.; Petri, M.; Plag, R.; Pohl, M.; Rastrepina, G.; Reifarth, R.; Reinhardt, T. P.; Röder, M.; Savran, D.; Scheit, H.; Schrock, P.; Silva, J.; Stach, D.; Strannerdahl, F.; Thies, R.; Wagner, A.; Weigand, F. W. M.;
A prototype composed of four resistive plate chamber layers has been exposed to quasi-monoenergetic neutrons produced from a deuteron beam of varying energy (300 to 1500 AMeV) in experiment S406 at GSI, Darmstad, Germany. Each layer, with an active area of about 2000 × 500 mm2, is made of modules containing the active gaps, all in multigap construction. Each gap is defined by 0.3 mm nylon mono-filaments positioned between 2.85 mm thick float glass electrodes. The modules are operated in avalanche mode with a non-flammable gas mixture composed of 90% C2H2F4 and 10% SF6. The signals are readout by a pick-up electrode formed by 15 copper strips (per layer), spaced at a pitch of 30 mm, connected at both sides to timing front end electronics. Measurements of the time of flight jitter of neutrons, in the mentioned energy range, point to a contribution of the resistive plate chamber in the order of 150 ps, independent of the neutron energy.
Keywords: Instrumentation and methods for time-of-flight (TOF) spectroscopy Resistive-plate chambers Particle detectors Neutron detectors (cold, thermal, fast neutrons)

Publ.-Id: 21738 - Permalink

Effect of deposition conditions and annealing temperature on tunnel magnetoresistance and structure of MgO-based double-barrier magnetic tunnel junctions
Feng, W.; Fowley, C.; Bernert, K.; Sluka, V.; Kowalska, E.; Aleksandrov, Y.; Lindner, J.; Fassbender, J.ORC; Gan, H.; Kunz, A.; Hübner, R.; Coey, J. M. D.; Deac, A. M.
Tunnel magnetoresistance was measured in CoFeB-MgO-based double-barrier magnetic tunnel junctions. Variation of the sputtering power density is used to control the relative B content of the middle electrode. Magnetoresistance ratios in both upper and lower junctions are suppressed with respect to the single-barrier case. While the lower junction shows a saturation of the magnetoresistance as a function of high temperature annealing for all sputtering power densities, the upper junction exhibits an increase in magnetoresistance as a function of annealing temperature with higher values for higher sputtering power density. The suppression of high magnetoresistance is attributed to a lack of strong crystallisation in the middle electrode, which is confirmed by cross-section transmission electron microscopy. Slight crystallisation of the middle electrode is achieved at the highest sputtering power density despite that fact that boron diffusion is suppressed due to the adjacent MgO tunnel barriers. Optimal deposition and post annealing conditions resulted in magnetoresistance values of 140 % and 80 % for the upper and lower junctions, respectively.
Keywords: boron diffusion, double-barrier magnetic tunnel junction, sputtering, tunnel magnetoresistance
  • IEEE Transactions on Magnetics 51(2015)11, 4400704
    DOI: 10.1109/TMAG.2015.2435260
  • Poster
    Intermag Conference 2015, 11.-15.05.2015, Beijing, China

Publ.-Id: 21737 - Permalink

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