Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33407 Publications

Shallow-underground study of the supernova reaction 40Ca(α,γ)44Ti and the Dresden Felsenkeller

Bemmerer, D.
The 40Ca(alpha,gamma)44Ti reaction dominates the production of the radionuclide 44Ti (half-life 58.9 years) in the alpha-rich freezeout phase of a supernova. As 44Ti is believed to be produced near the so-called mass cut between ejected and infalling material, its detection may help constrain supernova models. Satellite-based gamma observatories have reported 44Ti detections from one supernova remnant, giving a snapshot of current supernova activity. The main production reaction 40Ca(alpha,gamma)44Ti has been studied in the Felsenkeller shallow-underground laboratory by activation, and at the surface of the Earth by in-beam gamma-spectrometry. New values for the strengths of the resonances near 4.5 and 3.5 MeV have been determined, improving the precision of the astrophysical reaction rate at temperatures of 2.5 GK and above.
Keywords: Supernova titanium-44 resonance strength Felsenkeller Tandetron
  • Lecture (Conference)
    2nd European Nuclear Physics Conference - EuNPC 2012, 17.-21.09.2012, Bukarest, Rumänien

Permalink: https://www.hzdr.de/publications/Publ-18014
Publ.-Id: 18014


Coulomb Dissociation of 27P

Beceiro Novo, S.; Süummerer, K.; Cortina-Gil, D.; Wimmer, C.; Plag, R.; Alvarez-Pol, H.; Aumann, T.; Behr, K.; Boretzky, K.; Casarejos, E.; Chatillon, A.; Datta-Pramanik, U.; Elekes, Z.; Fulop, Z.; Galaviz, D.; Geissel, H.; Giron, S.; Greife, U.; Hammache, F.; Heil, M.; Hoffman, J.; Johansson, H.; Karagiannis, C.; Kiselev, O.; Kurz, N.; Larsson, K.; Le Bleis, T.; Litvinov, Y.; Mahata, K.; Muentz, C.; Nociforo, C.; Ott, W.; Paschalis, S.; Prokopowicz, W.; Rodriguez-Tajez, C.; Rossi, D.; Simon, H.; Stanoiu, M.; Stroth, J.; Typel, S.; Wagner, A.; Wamers, F.; Weick, H.
In this work the astrophysical 26Si(p,gamma)27P reaction is studied using the Coulomb dissociation technique. We performed a 27P Coulomb Dissociation experiment at GSI, Darmstadt (28 May-5 June 2007) using the ALADIN-LAND setup which allows complete kinematic studies. A secondary 27P beam at 498 AMeV impinging a 515mg/cm2 Pb target was used. The relative energy of the outgoing system (26Si+p) is measured obtaining the resonant states of the 27P. Preliminary results show four resonant states measured at 0.360.07, 0.880.09, 1.50.2, 2.30.3 MeV and evidence of a higher state at around 3.1 MeV. The preliminary total cross section obtained for relative energies between 0 and 3 MeV has been measured and yields 55+-7 mb.
Keywords: astrophysical inverse kinematics radioactive beam

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Permalink: https://www.hzdr.de/publications/Publ-18013
Publ.-Id: 18013


44Ti, 26Al and 53Mn samples for nuclear astrophysics: the needs, the possibilities and the sources

Dressler, R.; Ayranov, M.; Bemmerer, D.; Bunka, M.; Dai, Y.; Lederer, C.; Fallis, J.; Murphy, A. S.; Pignatari, M.; Schumann, D.
Exploration of the physics involved in the production of cosmogenic radionuclides requires experiments using the same rare, radioactive nuclei in sufficient quantities. For this work, such exotic radionuclides have been extracted from previously proton-irradiated stainless steel samples using wet chemistry separation techniques. The irradiated construction material has arisen from an extended material research programme at the Paul Scherrer Institute, called STIP (SINQ Target Irradiation Program), where several thousand samples of different materials were irradiated with protons and neutrons of energies up to 570 MeV. In total, 8 × 1017 atoms of 44Ti, ~1016 atoms of 26Al and ~1019 atoms of 53Mn are available from selected samples. These materials may now be used to produce targets or radioactive beams for nuclear reaction studies with protons, neutrons and α-particles. The work is part of the ERAWAST initiative (Exotic Radionuclides from Accelerator Waste for Science and Technology), aimed at facilitating new collaborations between the isotope producers and users from different scientific fields including nuclear astrophysics.
Keywords: Radioactive target nuclear astrophysics supernova titanium-44

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Permalink: https://www.hzdr.de/publications/Publ-18012
Publ.-Id: 18012


Preparation and characterisation of isotopically enriched Ta2O5 targets for nuclear astrophysics studies

Caciolli, A.; Scott, D. A.; Di Leva, A.; Formicola, A.; Aliotta, M.; Anders, M.; Bellini, A.; Bemmerer, D.; Broggini, C.; Campeggio, M.; Corvisiero, P.; Depalo, R.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Marta, M.; Menegazzo, R.; Napolitani, E.; Prati, P.; Rigato, V.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Salvo, C.; Straniero, O.; Strieder, F.; Szücs, T.; Terrasi, F.; Trautvetter, H. P.; Trezzi, D.
The direct measurement of reaction cross-sections at astrophysical energies often requires the use of solid targets of known thickness, isotopic composition, and stoichiometry that are able to withstand high beam currents for extended periods of time. Here, we report on the production and characterisation of isotopically enriched Ta2O5 targets for the study of proton-induced reactions at the Laboratory for Underground Nuclear Astrophysics facility of the Laboratori Nazionali del Gran Sasso. The targets were prepared by anodisation of tantalum backings in enriched water (up to 66% in O-17 and up to 96% in O-18). Special care was devoted to minimising the presence of any contaminants that could induce unwanted background reactions with the beam in the energy region of astrophysical interest. Results from target characterisation measurements are reported, and the conclusions for proton capture measurements with these targets are drawn.

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Permalink: https://www.hzdr.de/publications/Publ-18011
Publ.-Id: 18011


First Direct Measurement of the ^{17}O(p,γ)^{18}F Reaction Cross-Section at Gamow Energies for Classical Novae

Scott, D. A.; Caciolli, A.; Dileva, A.; Formicola, A.; Aliotta, M.; Anders, M.; Bemmerer, D.; Broggini, C.; Campeggio, M.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Laubenstein, M.; Menegazzo, R.; Marta, M.; Napolitani, E.; Prati, P.; Rigato, V.; Roca, V.; Somorjai, E.; Salvo, C.; Straniero, O.; Strieder, F.; Szücs, T.; Terrasi, F.; Trezzi, D.
Classical novae are important contributors to the abundances of key isotopes, such as the radioactive ^{18}F, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The ^{17}O(p,\gamma)^{18}F reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range Ecm = 200 - 370 keV appropriate to hydrogen burning in classical novae. In addition, the E=183 keV resonance strength, \omega \gamma=1.67\pm0.12 \mueV, has been measured with the highest precision to date. The uncertainty on the ^{17}O(p,\gamma)^{18}F reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.

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Permalink: https://www.hzdr.de/publications/Publ-18010
Publ.-Id: 18010


Modelling and validation of turbulence parameters at the interface of horizontal multiphase flows

Höhne, T.
One limitation today in simulating horizontal two phase flow is that there is no special turbulence treatment at the free surface. For self generating waves and slugs, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Without any special treatment of the free surface, the high velocity gradients at the free surface generate too high turbulence when using eddy viscosity models like the k-ε or the k-ω model. In the past turbulence damping (symmetric damping procedures for the solid wall-like damping of turbulence in both gas and liquid phases) were introduced within the Algebraic Interfacial Area Density (AIAD) model into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The AIAD approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered for instance in the interfacial drag formulation.
A further step of improvement of modelling the turbulence is the consideration of small wave turbulence that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. So fare in the present code versions they are neglected. However, the influence on the turbulence kinetic energy of the liquid side can be significantly large. A region of marginal breaking is defined according Brocchini and Peregrine and added as a source term in the turbulent kinetic energy equation.
This paper presents first CFD-simulations on horizontal multiphase flows using the new modelling approach.
Keywords: CFD, AIAD
  • Contribution to proceedings
    8th International Conference on Multiphase Flow 2013 (ICMF), 26.-31.05.2013, Jeju, Korea
  • Lecture (Conference)
    8th International Conference on Multiphase Flow 2013 (ICMF), 26.-31.05.2013, Jeju, Korea

Permalink: https://www.hzdr.de/publications/Publ-18009
Publ.-Id: 18009


Numerical modeling of stratified two-phase flows in industrial applications

Höhne, T.
In the last decade, applications of Computational Fluid Dynamic (CFD) methods for industrial applications received more and more attention, as they proved to be a valuable complementary tool for design and optimization. The main interest towards CFD consists in fact in the possibility of obtaining detailed 3D complete flow-field information on relevant physical phenomena at lower cost than experiments. Typically free surfaces manifest as stratified and wavy flows in horizontal flow domain where gas and liquid are separated by gravity. Stratified two-phase flows are relevant in many industrial applications, e.g. pipelines, horizontal heat exchangers and storage tanks. This paper presents different CFD-simulations on flows using a new modelling approach for the interfacial drag at free surfaces. The developed drag coefficient model was implemented together with the Algebraic Interfacial Area Density (AIAD) model into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The applications considered include the prediction of counter-current flow limitations (CCFL) in a pressurized water reactor (PWR) hot leg, the development of hydraulic jump during the air-water co-current flow in a horizontal channel, and pressurized thermal shock (PTS) phenomena in a PWR cold leg and downcomer. For the modelling of these tasks, an Euler–Euler approach was used. This approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. To demonstrate the feasibility of the present approach, the computed main parameters of each case were compared with experimental data. It is shown that the CFD calculations agree well with the experimental data. This indicates that the AIAD model combined with new drag force modeling is a promising way to simulate the phenomena in frame of the Euler-Euler approach. Moreover the further validation of the model by including mass transfer effects should be carried out.
Keywords: CCFL, CFD, CFX, AIAD
  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Fluidverfahrenstechnik, 12.-14.03.2013, Weimar, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-18008
Publ.-Id: 18008


New aspects in the numerical modeling of horizontal two-phase flows in industrial applications

Höhne, T.; Darlianto, D.; Apanasevich, P.
In the last decade, applications of Computational Fluid Dynamic (CFD) methods for industrial applications received more and more attention, as they proved to be a valuable complementary tool for design and optimization. The main interest towards CFD consists in fact in the possibility of obtaining detailed 3D complete flow-field information on relevant physical phenomena at lower cost than experiments.
Typically free surfaces manifest as stratified and wavy flows in horizontal flow domain where gas and liquid are separated by gravity.
Stratified two-phase flows are relevant in many industrial applications, e.g. pipelines, horizontal heat exchangers and storage tanks. This paper presents different CFD-simulations on flows using a new modelling approach for the interfacial drag at free surfaces. The developed drag coefficient model was implemented together with the Algebraic Interfacial Area Density (AIAD) model into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The applications considered include the prediction of counter-current flow limitations (CCFL) in a pressurized water reactor (PWR) hot leg, the development of hydraulic jump during the air-water co-current flow in a horizontal channel, and pressurized thermal shock (PTS) phenomena in a PWR cold leg and downcomer. For the modelling of these tasks, an Euler–Euler approach was used. This approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model.
To demonstrate the feasibility of the present approach, the computed main parameters of each case were compared with experimental data. It is shown that the CFD calculations agree well with the experimental data. This indicates that the AIAD model combined with new drag force modeling is a promising way to simulate the phenomena in frame of the Euler-Euler approach. Moreover the further validation of the model by including mass transfer effects should be carried out.
Keywords: CCFL, AIAD, CFD, PTS
  • Contribution to proceedings
    ASME 2013 Fluids Engineering Division Summer Meeting FEDSM2013, 07.-11.07.2013, Incline Village, USA
    Proceedings of the ASME 2013 Fluids Engineering Division Summer Meeting Vol. 1C
  • Invited lecture (Conferences)
    ASME 2013 Fluids Engineering Division Summer Meeting FEDSM2013, 07.-11.07.2013, Incline Village, USA

Permalink: https://www.hzdr.de/publications/Publ-18007
Publ.-Id: 18007


Hydrodynamics of inclined rotating fixed bed reactors

Härting, H.-U.; Schubert, M.
Periodic operation of trickle bed reactors is an academically established process intensification concept, especially in cases where the mass transfer of the gas phase to the catalyst surface dominates the overall reactor performance.
Further advantages such as damping hot spots and reducing maldistribution have been mentioned in many studies. However, the positive effect of the cycling feed at the inlet strongly decays along the reactor length. Furthermore, industrial implementation hurdles are caused by the complex transient reactor behavior and its control.

Operating a fixed bed reactor at quasi steady-state conditions while maintaining a periodic operation can be achieved by rotation of an inclined reactor: Inclination promotes the phase separation whereas the superimposed rotation induces a periodic wetting and draining of the fixed bed, resulting in alternating access of the gas and liquid reactants to the catalyst surface. This new reactor concept is illustrated in Figure 1.

To evaluate the new reactor concept, hydrodynamic studies were conducted to reveal the flow regimes and to elucidate the liquid saturation distribution. The latter is visualized by a noninvasive compact γ-ray computer tomography system (CompaCT) with a spatial in-plane resolution of 2 mm.
These hydrodynamic studies cover variations of reactor inclination (α = 15°-90°), rotational speed (up to 60 rpm) and gas and liquid superficial velocities (uL = 0.01 m/s – 0.05 m/s and uG = 0.025 – 0.05 m/s). Results for additional variations of particle size, liquid properties (deionized water, silicone oil, cumene) will be reported as well. Furthermore, the hydrodynamic behavior of the inclined rotating reactor is compared with the vertical non-rotating trickle bed reactor configuration.

The effect of reactor inclination and rotational speed on the liquid saturation distribution is exemplarily shown in Figure 2. The lower area of the depicted tomograms corresponds to the bottommost area of the counterclockwise rotating reactor. These experiments were conducted with deionized water and air at ambient pressure and room temperature (ϑL = 20 °C) in a tubular reactor (ID = 0.1 m, L = 1.2 m) packed with 4 mm glass spheres.

For the lowest rotational speed, the gas phase flows mainly in the upper region of the reactor cross-section (Figure 2 a, d) with a pronounced entrainment of the liquid phase for the lower inclination (Figure 2 a) and a clear phase separation for the higher inclination (Figure 2 d). Increased reactor rotation equalizes the liquid distribution for both inclinations (Figure 2 b, e) and results in a ring-like flow pattern (Figure 2 c, f) for the highest rotational speed.

The new reactor concept provides additional degrees of freedom for flow modulation: Reactor inclination and rotational speed. Their influence on the flow patterns and liquid saturation distribution has been investigated by noninvasive tomographic imaging. In combination with the gas and liquid flow rates, these new degrees of freedom allow for adjusting residence time and periodicity of wetting and draining, respectively.
Keywords: Process intensification, fixed bed reactor, gamma-ray computed tomography, inclination, rotation, phase distribution
  • Lecture (Conference)
    9th European Congress of Chemical Engineering - ECCE 9, 21.-24.04.2013, Den Haag, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-18006
Publ.-Id: 18006


Scale Resolved Simulations of the OECD/NEA−Vattenfall T-Junction Benchmark using LES methods

Höhne, T.
Mixing of fluids in T-junction geometries is of significant interest for nuclear safety research. The most prominent example is the thermal striping phenomena in piping T-junctions, where hot and cold streams join and turbulently mix, however not completely or not immediately at the T-junction. This results in significant temperature fluctuations near the piping wall, either at the side of the secondary pipe branch or at the opposite side of the main branch pipe. The wall temperature fluctuation can cause cyclical thermal stresses and subsequently fatigue cracking of the wall.

Thermal mixing in a T-junction has been studied for validation of CFD-calculations. A T-junction thermal mixing test was carried out at the Älvkarleby Laboratory of Vattenfall Research and Development (VRD) in Sweden. Data from this test have been reserved specifically for a OECD CFD benchmark exercise. The computational results show that RANS fail to predict a realistic mixing between the fluids. The results were significantly better with scale-resolving methods such as LES, showing fairly good predictions of the velocity field and mean temperatures. The calculation predicts also similar fluctuations and frequencies observed in the model test.
Keywords: T-junction, CFD, mixing, LES, Vattenfall, OECD

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Permalink: https://www.hzdr.de/publications/Publ-18005
Publ.-Id: 18005


Tomographische Untersuchung der Phasenanteile und deren Verteilung in einem geneigt rotierenden Festbettreaktor

Hauswald, T.
Das Institut für Fluiddynamik im Helmholtz-Zentrum Dresden-Rossendorf e. V. (HZDR) beschäftigt sich unter anderem mit der Untersuchung verfahrenstechnischer Prozesse sowie der Entwicklung und Charakterisierung neuer effizienter Mehrphasenkontaktapparate und -reaktoren mittels selbstentwickelter innovativer Messtechnik für Mehrphasenströmungen.
Ein solches neuartiges Reaktorkonzept mit dem Ziel der Prozessintensivierung stellt der geneigt rotierende Festbettreaktor dar. Im Gegensatz zum zeitlich-periodischen Reaktorbetrieb erfolgt die Prozessintensivierung hier durch Aufprägung einer örtlichen Periodizität unter ansonsten stationären Betriebsbedingungen. Aus dieser veränderten Betriebsweise ergeben sich durch die Wahl von Neigung und Drehzahl zusätzliche Freiheitsgrade bei der Strömungsführung und damit zur Beeinflussung der Reaktorleistung.
Im Rahmen der Diplomarbeit ist mittels gamma-tomographischer Messung sowie Druckverlustmessung der Einfluss von Reaktorneigung und -drehzahl auf die Phasenanteile und deren Verteilung bei ausgewählten Gas- und Flüssigkeitsdurchsätzen zu untersuchen und mit dem etablierten Rieselbettreaktor zu vergleichen.
Keywords: Mehrphasenreaktor, Prozessintensivierung, Neigung, Rotation, Computertomographie, Strömungsform
  • Diploma thesis
    TU Dresden, 2012
    118 Seiten

Permalink: https://www.hzdr.de/publications/Publ-18004
Publ.-Id: 18004


Graphene based broadband THz detector working at room temperature

Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Schneider, H.; Helm, M.
Graphene can serve as an attractive detector material for the whole visible and infrared spectral range. Due to the unique band structure of graphene, with a linear dispersion next to the Dirac point where valence and conduction band touch, the absorption is constant for nearly all photon energies. Furthermore the fast carrier relaxation in graphene allows one to build up fast detectors with an electrical response in the GHz range. We demonstrate a detector based on a graphene flake combined with a logarithmic-periodic antenna structure with an outer diameter of 1mm, which connects the flake via an interdigitated structure. The graphene flake was produced by the scotch-tape method on SiO2/Si. To maximize the photocurrent the two halves of the antenna were made of different metals. The metallization was patterned by electron beam lithography. One arm of the antenna consists of a 60nm thick layer of palladium, the other one of 20nm titanium combined with 40nm of gold. With the free-electron laser FELBE at Dresden-Rossendorf we proved room temperature operation in a wide spectral range (wavelength: 8µm-220µm), the coupling of the antenna was verified by measurements of the polarization dependence of the detector for different wavelengths. Additionally we measured FEL-pulses with pulse durations around 20 ps in the wavelength range of 30µm to 220µm. The rise time of the measured signal was approximately 50 ps, the pulse length was in the range of 200 ps. Even though the responsivity was fairly low (~ 1nA/W), this detector could be very useful for timing purposes in two-color experiments.
Keywords: graphene detector broadband
  • Lecture (Conference)
    International Workshop on Terahertz Science and Technology, 01.-05.04.2013, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-18003
Publ.-Id: 18003


Keine Ahnung von der Strahlung – Unbemerkte alltägliche Radioaktivität

Foerstendorf, H.
  • Lecture (others)
    Kreuz-Uni am Evangelischen Kreuzgymnasium Dresden, 19.11.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-18002
Publ.-Id: 18002


Rayleigh-Benard instability of Czochralski configuration in a transverse magnetic field

Grants, I.; Gerbeth, G.
The linear instability of a rotating conducting liquid cylinder heated from below in a horizontal magnetic field is considered numerically. A condition for the magnetic suppression of the bulk rotation is obtained. If the bulk is rotation dominated then the linear instability is slightly delayed by the field and sets in as a rotating wave. If the bulk is dominated by the magnetic field then the instability has the form of field aligned convection rolls. Outside thin boundary layers the instability then becomes increasingly similar to the onset in a plain channel. The results are discussed in light of previous silicon growth experiments and existing knowledge from related problems.
Keywords: Flow instability; Czochralski method; Semiconducting silicon; Magnetohydrodynamics

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Permalink: https://www.hzdr.de/publications/Publ-18001
Publ.-Id: 18001


Creation of Surface Nanostructures on Al2O3 by Slow Highly Charged Ions

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Akhmadaliev, S.; Facsko, S.
Al2O3 single crystals were irradiated with slow highly charged Xe ions of various charge states from an EBIT (Electron Beam Ion Trap) source. The irradiations were performed at room temperature and under normal incidence. Scanning force microscopy (SFM) was utilized to investigate the topography of the irradiated surfaces. The measurements showed that above a potential energy threshold, each ion creates a nanohillock protruding from the surface. These structures are compared to those created by swift heavy ions (SHI). The results are discussed in terms of potential energy deposition of the highly charged ion and electronic energy loss of SHI.

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Permalink: https://www.hzdr.de/publications/Publ-18000
Publ.-Id: 18000


Surface Nanostructuring of LiNbO3 by High-Density Electronic Excitations

El-Said, A. S.; Wilhelm, R. A.; Facsko, S.; Trautmann, C.
Lithium niobate (LiNbO3) single crystals were irradiated with high energy gold ions (0.5-2.2 GeV) at the UNILAC (GSI) and with 150-keV highly charged Xenon ions from an EBIT (Electron Beam Ion Trap, HZDR). The surfaces of the irradiated crystals were analyzed by scanning force microscopy showing very similar topographic changes. Swift heavy ions and slow highly charged ions produce hillock-like surface nanostructures on this surface. In both cases, the energy deposition of the ions is characterized by dense localized electronic excitations and efficient transfer to the lattice. Furthermore, the irradiation results in a shift in the band gap energy as evidenced by UV-Vis absorption spectroscopy. Specific modifications (e.g. hillock size, energy loss threshold) induced by slow highly charged ions are discussed in comparison with effects due to the electronic energy loss by swift heavy ions.
  • Poster
    25th International Conference on Atomic Collisions in Solids (ICACS), 21.-25.10.2012, Kyoto, Japan
  • Nuclear Instruments and Methods in Physics Research B 315(2013), 265-268
    DOI: 10.1016/j.nimb.2013.03.008

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Permalink: https://www.hzdr.de/publications/Publ-17999
Publ.-Id: 17999


Characterisation of nanostructures induced by slow highly charged ion bombardment of HOPG

Ritter, R.; Shen, Q.; Teichert, C.; Wilhelm, R. A.; Facsko, S.; Ginzel, R.; Crespo López-Urrutia, J. R.; Aumayr, F.
Earlier studies, which have identified highly charged ion - induced defects on HOPG surfaces as regions of enhanced friction have been extended by measuring the
microscopic friction coefficient at the impact sites and the surrounding matrix by means of lateral force microsopy. Additional investigations have been performed on samples
irradiated with ions in very high charge states (Xe40+ and Bi62+), and, for the first time, defects have also been found employing the intermittent contact AFM mode (Figure 1), where friction forces are basically eliminated from the measuring process (no pseudotopographic contributions arising from friction). This is a strong indication that there is indeed a true topographic modification (as found for other target surfaces) if the impinging ions exceed a certain potential energy threshold. Furthermore, defects have been imaged in the conductive AFM mode, where strong local changes (imaging at atomic resolution) in the conductivity are apparent.
  • Poster
    25th Internation Conference on Atomic Collisions in Solids (ICACS), 21.-25.10.2012, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-17998
Publ.-Id: 17998


A Study of the Structural properties of GaN implanted by various rare-earth ions

Mackova, A.; Malinský, P.; Sofer, Z.; Šimek, P.; Sedmidubský, D.; Mikulics, M.; Wilhelm, R. A.
GaN layers with <0001> crystallographic orientation, grown by low-pressure metal-organic vapour-phase epitaxy (MOVPE) on c-plane sapphire substrates, were implanted with 200 and 400 keV Sm+, Tm+, Eu+, Tb+ and Ho+ ions at fluencies of 1×1015– 1×1016 cm−2. The composition of the ion-implanted layers and concentration profiles of the implanted atoms were studied by Rutherford Back-Scattering spectrometry (RBS). The profiles were compared to SRIM 2012 simulations. The structural properties of the ion-implanted layers were characterised by RBS-channelling and Raman spectroscopy. Changes in the surface morphology caused by the ion implantation were examined by Atomic Force Microscopy (AFM). A structural analysis showed a high disorder density of the atoms close to the amorphised structure at the surface layer above an implantation fluence of 5x1015 cm-2 while lower disorder density was observed in the bulk according to the projected range of 400 keV ions. The post-implantation annealing induced significant changes only in the Sm and Eu depth profiles; a diffusion of rare-earths implanted at a fluence of 5x1015 cm-2 to the surface was observed. The annealing caused the reconstruction of the surface layer accompanied by surface-roughness enhancement.

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Permalink: https://www.hzdr.de/publications/Publ-17997
Publ.-Id: 17997


Nanopores Milled in Carbon Nanomembranes Due to Impact of Individual Slow Highly Charged Ions

Ritter, R.; Wilhelm, R. A.; Stöger-Pollach, M.; Mücklich, A.; Werner, U.; Beyer, A.; Facsko, S.; Gölzhäuser, A.; Aumayr, F.
Nanostructures produced by slow highly charged ion (HCI) impact on surfaces have been a hot topic recently. In this contribution we present first investigations on the effect of individual slow HCI bombardment of freestanding carbon nano-membranes (CNMs). The CNMs are produced by cross-linking of an aromatic self-assembled monolayer of biphenyl units with lowenergy electrons [5]. The substrate is then subsequently removed and the resulting nanosheet (1 nm thickness) transferred onto a holey carbon TEM grid. CNMs produced in such a way are irradiated by slow Xeq+ ions of various charge states (20 ! q ! 40) and kinetic energies (4 keV ! E ! 180 keV).
After irradiation the CNMs are inspected by high resolution imaging techniques, e.g. TEM, SEM and AFM. On the irradiated CNMs we find nanoscopic pores (3 - 30 nm in diameter, see fig. 1), whose number density corresponds well with the incident ion fluence, indicating that about every HCI produces a nano-hole in the CNM. First evaluations of the size distribution of the created pores indicate that the average diameter of a hole induced by a given ion depends strongly on the potential energy of the projectile ion, but is also influenced by the kinetic energy.
  • Poster
    16th International Conference Physics of Highly Charged Ions, 02.07.-07.09.2012, Heidelberg, Deutschland
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 10.-11.07.2012, Augsburg, Deutschland
  • Lecture (Conference)
    1st Bielefeld Workshop on Nanolayers and Artificial Membranes, 04.-06.02.2013, Bielefeld, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17996
Publ.-Id: 17996


A New Facility for In-Situ Characterization of Slow Highly Charged Ion Modifications of Various Materials

Wilhelm, R. A.; Facsko, S.; Wagner, J.; Heller, R.
The interaction of highly charged ions (HCI) with materials has been studied intensively in the last years. On various materials local topographic modifications at the ion’s impact site could be identified by means of atomic force microscopy (AFM). The type of the modifications, commonly known as nano-structures, varies from pit-like (KBr, PMMA) to craters (TiO2) and hillock-like structures on CaF2 and others ([1, 2]). Most of the recent studies were performed under ex-situ conditions, meaning the target material was transported under ambient conditions from the place of irradiation to an AFM or scanning tunneling microscope. We present a new experimental set-up for in-situ investigations on HCI induced nano-structures. The set-up is based on an assembly of a Dresden-EBIT (Electron Beam Ion Trap) ion source and an Omicron ultra-high-vacuum-AFM. Samples can be mounted in the AFM and analyzed by means of AFM and STM before, during and after the irradiation with HCI. Samples can be heated in-vacuum to prepare clean surfaces before irradiation. The EBIT delivers highly charged ions with Xe charge states up to q=40+, which can be decelerated to kinetic energies
of only 10 eV·q. Figure 1 shows a drawing of the set-up. The dimensions of the set-up are small compared to other HCI facilities. The EBIT is mounted in a high voltage cave and so a negative potential can be applied, while the AFM chamber is kept on ground potential. The final kinetic energy of the ions is defined by the difference of the extraction potential (respective to ground) and the target potential (ground) by Efinal kin = (Uext − Ubeamline) · q. A lens system focusses the beam onto the target with a beam diameter of less than 1 mm.
  • Poster
    16th International Conference Physics of Highly Charged Ions, 02.-07.09.2012, Heidelberg, Deutschland
  • Poster
    25th International Conference on Atomic Collisions in Solids (ICACS), 21.-25.10.2012, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-17995
Publ.-Id: 17995


The effect of chemical etching on poly (methyl methacrylate) irradiated with slow highly charged ions

Ritter, R.; Wilhelm, R. A.; Ginzel, R.; Schadauer, P.; Heller, R.; Rupp, W.; López-Urrutia, J. R. C.; Facsko, S.; Aumayr, F.
We have recently demonstrated that individual slow highly charged ions are able to produce nanosized pits on poly (methyl methacrylate) surfaces as a result of direct ablation due to the deposition of their high potential energy, if this energy exceeds a critical minimum value. By exposing irradiated samples to a suitable etchant, such pits can be revealed even below this potential energy threshold as latent damage zones are removed. Existing pits, after contact with the etchant grow both in diameter and depth with different etching dynamics for both dimensions. Systematic studies on the response of irradiated samples to a chemical developer are presented.
Keywords: highly charged ions, PMMA, nano-structuring, atomic force microscopy, chemical etching
  • Poster
    16th International Conference Physics of Highly Charged Ions, 02.-07.09.2012, Heidelberg, Deutschland
  • Physica Scripta T156(2013), 014065
    DOI: 10.1088/0031-8949/2013/T156/014065

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Publ.-Id: 17994


Phase Diagram for Nanostructuring CaF2 Surfaces by Slow Highly Charged Ions

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Facsko, S.; Lemell, C.; Wachter, G.; Burgdorfer, J.; Ritter, R.; Aumayr, F.
The impact of individual slow highly charged ions (HCI) on alkaline earth halide and alkali halide surfaces creates nano-scale surface modifications. For different materials and impact energies a wide variety of topographic alterations have been observed, ranging from regularly shaped pits to nano-hillocks. We present experimental evidence for the creation of thermodynamically stable defect agglomerations initially hidden after irradiation but becoming visible as pits upon subsequent etching. A well defined threshold separating regions with and without etch-pit formation is found as a function of potential and kinetic energies of the projectile. Combining this novel type of surface defects with the previously identified hillock formation, a phase diagram for HCI induced surface restructuring emerges. The simulation of the energy deposition by the HCI in the crystal provides insight into the early stages of the dynamics of the surface modification and its dependence on the kinetic and potential energies.
  • Physical Review Letters 109(2012), 117602
    DOI: 10.1103/PhysRevLett.109.117602
  • Poster
    25th International Conference on Atomic Collisions in Solids (ICACS), 21.-25.10.2012, Kyoto, Japan

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Publ.-Id: 17993


Synthesis and biological evaluation of 18F labeled fluoro-oligo-ethoxylated 4-benzylpiperazine derivatives for sigma-1 receptor imaging

Wang, X.; Li, Y.; Deuther-Conrad, W.; Xie, F.; Chen, X.; Cui, M.-C.; Zhang, X.-J.; Zhang, J.-M.; Steinbach, J.; Brust, P.; Liu, B.-L.; Jia, H.-M.
We report the synthesis and evaluation of a series of fluoro-oligo-ethoxylated 4-benzylpiperazine derivatives as potential σ1 receptor ligands. In vitro competition binding assays showed that 1-(1,3-benzodioxol-5-ylmethyl)-4-(4-(2-fluoroethoxy)benzyl)piperazine (6) exhibits low nanomolar affinity for σ1 receptors (Ki = 1.85 ± 1.59 nM) and high subtype selectivity (σ2 receptor: Ki = 291 ± 111 nM ; Kiσ2/Kiσ1 = 157). [18F]6 was prepared in 30–50% isolated radiochemical yield, with radiochemical purity of >99% by HPLC analysis after purification, via nucleophilic 18Fˉ substitution of the corresponding tosylated precursor. The log DpH7.4 value of [18F]6 was found to be 2.57 ± 0.10, which is within the range expected to give high brain uptake. Biodistribution studies in mice demonstrated relatively high concentration of radiotracers in organs known to contain σ1 receptors, including the brain, lungs, kidneys, heart, and spleen. Administration ofhaloperidol 5 min prior to injection of [18F]6 significantly reduced the concentration of radiotracer in the above-mentioned organs. The accumulation of radiotracers in the bone was quite low suggesting that [18F]6 is relatively stable to in vivo defluorination.
The ex vivo autoradiography in rat brain showed high accumulation of radiotracer in the brain areas known to possess high expression of σ1 receptors. These findings suggest that [18F]6 is a suitable radiotracer for imaging σ1 receptors with PET in vivo.
Keywords: σ1 receptor; fluoro-oligo-ethoxylated; 4-benzylpiperazine; F-18

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Publ.-Id: 17992


Ein neues Konzept zur Modellierung der Positronenemitter-Produktion bei der Partikeltherapie

Priegnitz, M.
Eine der drei Säulen der Krebsbehandlung ist die Strahlentherapie. Einer der neuesten Ansätze hierbei ist die Bestrahlung mit Ionen, zurzeit insbesondere Protonen und Kohlenstoffionen. Diese Hochpräzisionstherapie erfordert ein hohes Maß an Kontrolle, da die applizierte Dosisverteilung sehr empfindlich von Dichteveränderungen im durchstrahlten Gewebe abhängt. Das bisher einzige klinisch eingesetzte Verfahren zur in vivo Überwachung der Dosisapplikation bei Ionenbestrahlungen ist die Positronen-Emissions-Tomographie (PET). Sie ermöglicht eine Verifikation der Teilchenreichweite sowie der Lage des Bestrahlungsfeldes.
Die mit der PET-Methode gemessene Aktivitätsverteilung lässt sich jedoch nicht direkt mit der geplanten Dosisverteilung vergleichen. Daher ist eine Vorherberechnung der erwarteten Aktivitätsverteilung auf der Grundlage des Bestrahlungsplanes notwendig, welche dann mit der Messung verglichen wird und eine qualitative Beurteilung der Bestrahlung ermöglicht. Die Vorherberechnung der erwarteten Aktivitätsverteilung erfordert bislang die Kenntnis einer Vielzahl von Wirkungsquerschnitten. Nur für wenige dieser Wirkungsquerschnitte liegen jedoch Messdaten im benötigten Energiebereich und mit ausreichender Genauigkeit vor. Daher verwenden viele Monte-Carlo-Simulationen intrinsische Kernmodelle oder semi-empirische Modellierungen, die häufig eine unzureichende Genauigkeit aufweisen.

In Fachkreisen ist bisher noch nicht geklärt, welches die optimale Ionensorte für die Tumortherapie ist. Insbesondere Lithiumionen weisen aufgrund ihrer physikalischen und radiobiologischen Eigenschaften ein großes Potenzial auf. Auch für Bestrahlungen mit diesen Ionen ist ein PET-Monitoring der Therapie erstrebenswert. In der vorliegenden Arbeit wird zunächst die Anwendbarkeit der Reichweite-Verifikation mittels PET bei Bestrahlung mit Lithiumionen gezeigt. Des Weiteren wird ein Konzept zur Modellierung der Positronenemitter-Verteilung ohne Kenntnis der Wirkungsquerschnitte entwickelt. Diese Vorhersage beruht auf in Referenzmaterialien (Wasser, Graphit und Polyethylen) gemessenen tiefenabhängigen Positronenemitter-Yields, mit welchen durch geeignete Linearkombination die Verteilung der Positronenemitter in beliebigen Materialien bekannter Stöchiometrie vorausberechnet werden kann. Die Anwendbarkeit des Yield-Konzeptes wird gezeigt für Lithium- und Kohlenstoffbestrahlungen homogener Polymethylmethacrylat (PMMA) Targets sowie verschiedener inhomogener Targets.
Keywords: Positronen-Emissions-Tomographie, PET, in-beam, Strahlentherapie, Ionentherapie, Lithium-Ionen, thick target yield, Yield-Konzept
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-029 2012

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Publ.-Id: 17991


Synthesis and biological evaluation of a novel Tc-99m cyclopentadienyl tricarbonyl complex ([(Cp-R)Tc-99m(CO)(3)]) for sigma-2 receptor tumor imaging

Chen, X.; Cui, M. C.; Deuther-Conrad, W.; Tu, Y. F.; Ma, T.; Xie, Y.; Jia, B.; Li, Y.; Xie, F.; Wang, X.; Steinbach, J.; Brust, P.; Liu, B. L.; Jia, H. M.
We report the design, synthesis and biological evaluation of a novel (99m)Tc 4-(4-cyclohexylpiperazine-1-yl)-butan-1-one-1-cyclopentadienyltricarbonyl technetium ([(99m)Tc]5) as a potential SPECT tracer for imaging of σ(2) receptors in tumors. [(99m)Tc]5 was prepared in 25±5% isolated radiochemical yield with radiochemical purity of >99% via double-ligand transfer (DLT) reaction from the ferrocene precursor 2b (4-(4-cyclohexylpiperazine-1-yl)-1-ferrocenylbutan-1-one). The corresponding Re-complex 4 and the ferrocenyl complex 2b showed relatively high affinity towards σ(2) receptors in in vitro competition binding assay (K(i) values of 4 and 2b were 64.4±18.5nM and 43.6±21.3nM, respectively) and moderate to high selectivity versus σ(1) receptors (K(i)σ(1)/K(i)σ(2) ratios were 12.5 and 95.5, respectively). The logD value of [(99m)Tc]5 was determined to be 2.52±0.33. Biodistribution studies in mice revealed comparably high initial brain uptake of [(99m)Tc]5 and slow washout. Administration of haloperidol 5min prior to injection of [(99m)Tc]5 significantly reduced the radiotracer uptake in brain, heart, lung, and spleen by 40-50% at 2h p.i.. Moreover, [(99m)Tc]5 showed high uptake in C6 glioma cell lines (8.6%) after incubation for 1h. Blocking with haloperidol to compete with [(99m)Tc]5 significantly reduced the cell uptake. Preliminary blocking study in C6-brain-tumor bearing rats showed that [(99m)Tc]5 binds to σ receptors in the brain-tumor specifically. These results are encouraging for further exploration of (99m)Tc-labeled probes for σ(2) receptor tumor imaging in vivo.

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Publ.-Id: 17990


High-temperature oxidation resistance in yttrium implanted stainless steel

Barlak, M.; Piekoszewski, J.; Werner, Z.; Sartowska, B.; Waliś, L.; Starosta, W.; Kierzek, J.; Kowalska, E.; Wilhelm, R. A.; Pochrybniak, C.; Woźnica, M.
Austenitic AISI 304, 316L and ferritic 430 stainless steels were implanted with yttrium to fluences ranging between 1 × 10^15 and 5 × 10^17 ions/cm2. The samples were subjected to oxidation in air at a temperature of 1000°C for a period of 100 h and next examined by stereoscopic optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and Rutherford back scattering spectrometry (RBS). The results obtained with the use of ion implantation are discussed.
Keywords: high-temperature oxidation resistance, ion implantation, yttrium
  • Open Access Logo Nukleonika 57(2012), 473-476

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Publ.-Id: 17989


International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2012) - Abstract Book

Foerstendorf, H.; Müller, K.; Steudtner, R.; (Editors)
Modern Societies have to consider diverse tasks strongly related to geochemistry sciences. Examples intensively discussed in the public are restoration measures for contaminated industrial fallow grounds, the safe storage of chemical-toxic and radioactive waste, carbon dioxide sequestration to reduce green-house gas emissions, the construction and operation of deep geothermal power plants, the geochemical exploration of natural resources or water and waste water treatments, including desalination efforts. Direct and urgent aspects to be dealt with are analytical and geochemical consequences of the Fukushima Daiichi nuclear disaster. All these cases have one in common – they require reliable thermodynamic data in order to forecast the fate of chemicals in the respective environment.
Whereas a variety of standard methods, such as potentiometry, solubility studies, liquid-liquid extraction or electrochemical titrations, are in widespread use to generate thermodynamic data, it is far less straightforward to assign correct reaction pathways and structural patterns to the underlying chemical transformations. This especially holds for systems with strong tendencies to complexation and oligomerization. Here, it is essential to have proof of evidence for all involved species, which cannot be provided by the aforementioned methods, and is still lacking for various metal-containing systems.
Spectroscopic techniques in combination with approaches from quantum chemistry can be of great benefit for such tasks. However, their application ranges are often restricted with respect to the type of element (and redox state) that can be probed. Further handicaps are imposed by detection limits or other parameters such as pH or salinity. Moreover, the spectroscopic results are often difficult to interpret in an unambiguous way.
To overcome these complications at least partially, this workshop has been initiated. It shall significantly extend the application areas of spectroscopic tools important for lanthanide and actinide chemistry. Emphasis shall be placed on the development of spectroscopic methods towards more challenging environmental conditions – such as very basic pH values, elevated temperatures, pressures, or salinities – extending the range of covered elements and redox states. Furthermore, the exploration of options for lowering detection limits and increasing spatial resolution at sufficiently high signal-to-noise ratios will support future investigations on more complex systems. An approach combining the extension of spectroscopic tools with respect to elements and parameters, improvements of experimental setups, and applications of quantum chemical methods in predictive as well as interpretative ways certainly can be very beneficial.
The workshop hopefully will bundle and strengthen respective research activities and ideally act as a nucleus for an international network, closely collaborating with international partners. I am confident that the workshop will deliver many exciting ideas, promote scientific discussions, stimulate new developments and in such a way be successful.
Keywords: Workshop, Actinide Spectroscopy, Radioactive Waste, Chemical-toxic Waste
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-027 2012
    ISSN: 2191-8708

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Publ.-Id: 17988


Insights into the U(VI) Speciation with Bacterial Isolates from Äspö and Mont Terri

Lütke, L.; Moll, H.; Bachvarova, V.; Selenska-Pobell, S.; Bernhard, G.
In this study we examined the impact of two microbial representatives from actually discussed potential geological formations for nuclear waste storage on the U(VI) speciation. Pseudomonas fluorescens CCUG 32456A isolated from the granitic aquifers at the Äspö Hard Rock Laboratory, Sweden, and a novel strain of the genus Paenibacillus from clay samples of the Mont Terri Rock Laboratory, Switzerland, which we have recently isolated and been able to cultivate, were investigated. To assess the U(VI) interaction with surface functional groups of theses strains, potentiometric titration in combination with time-resolved laser-induced fluorescence spectroscopy (TRLFS) were applied. Based on the stability constants of U(VI) complexes with the bacterial surface functional groups U(VI) species distributions in presence of both strains in dependence on the pH were calculated. The differences in the U(VI) speciation with both strains and the influencing factors will be discussed in detail.
Keywords: P. fluorescens, Paenibacillus sp., Äspö, Mont Terri, TRLFS, potentiometric titration
  • Lecture (others)
    IRS Institutskolloqium, 15.11.2012, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17987
Publ.-Id: 17987


Application of Positron Annihilation Spectroscopy to the Study of Irradiated Fe-Cr alloys

Bergner, F.; Anwand, W.; Butterling, M.; Heintze, C.; Jungmann, M.; Kolitsch, A.; Krause-Rehberg, R.; Ulbricht, A.; Wagner, A.; Wagner, A.
Positron annihilation spectroscopy (PAS) contributes to the investigation of irradiated Fe-based alloys (incl. ODS steels) mainly because of the sensitivity to sub-nm-size open-volume defects. The unique combination of conventional and new PAS techniques, of ion irradiation facilities and hot cell labs available at HZDR are briefly introduced. Gamma-induced PAS (GiPS) is particularly well adapted to neutron-irradiated alloys. Monoenergetic PAS (MePS) is particularly well adapted to ion-irradiated alloys. The comparison and transferability of damage caused by ions and neutrons is an issue. First results on sets of both neutron-irradiated reactor pressure vessel steels and ion-irradiated Fe-Cr alloys addressed in the talk are encouraging.
  • Lecture (Conference)
    21st Workshop on Iron-Chromium Alloys and 3rd Workshop on nuclear Fe alloys: modelling and experiments, 29.-31.10.2012, Alicante, España

Permalink: https://www.hzdr.de/publications/Publ-17986
Publ.-Id: 17986


Small angle neutron scattering

Bergner, F.
Small-angle neutron scattering is capable of detecting nm-sized irradiation-induced features in reactor pressure vessel steels. This method provides the size distribution of nano-features averaged over macroscopic volumes. Both the basics of SANS and technical aspects will be addressed. Selected applications of SANS will be discussed.
  • Invited lecture (Conferences)
    Symposium on irradiation effects in structural materials for nuclear reactors, 17.-21.09.2012, Sevilla, España

Permalink: https://www.hzdr.de/publications/Publ-17985
Publ.-Id: 17985


Bimodal range distributions of low-energy carbon ions in tetrahedral amorphous carbon

Neumaier, P.; Bergmaier, A.; Eckstein, W.; Fischer, R.; Hofsäss, H.; Jäger, H. U.; Kröger, H.; Ronning, C.; Dollinger, G.
Range and mixing distributions of carbon ions deposited onto tetrahedral amorphous carbon films at kinetic energies between 22 eV and 692 eV are measured utilizing high-resolution elastic recoil detection. These data are compared to respective calculations based on binary collision approximation as well as to classical molecular-dynamics simulations. The measured range profiles reveal asymmetric, bimodal structures which are not reproduced from theories. The measured mixing distributions approve the measured range distributions, in particular the observed differences between theory and experiment, which have to be considered in subplantation growth models.
Keywords: Surfaces, interfaces and thin films

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Publ.-Id: 17984


Sources of live 60Fe, 10Be, and 26Al in Lunar core 12025, core 15008, skim sample 69921, scoop sample 69941, and under-boulder sample 69961

Fimiani, L.; Cook, D. L.; Faestermann, T.; Gómez Guzmán, J. M.; Hain, K.; Herzog, G. F.; Korschinek, G.; Ligon, B.; Ludwig, P.; Park, J.; Reedy, R. C.; Rugel, G.
Summary: Relatively high concentrations of live 60Fe (T1/2 = 2.62±0.04 Ma [1]) in lunar surface samples [2 and this study] confirm earlier work [3,4] and suggest the arrival of supernova (SN) debris on the Moon about 2 Ma ago.
Keywords: lunar samples, supernova, 60Fe
  • Poster
    43rd Lunar and Planetary Science Conference, 19.-23.03.2012, The Woodlands, Texas, USA

Permalink: https://www.hzdr.de/publications/Publ-17983
Publ.-Id: 17983


Applications and advantages of laser-induced cryogenic fluorescence microscopy

Grossmann, K.; Tondera, C.; Mosch, B.; Wimmer, C.; Pietzsch, J.
Fluorescence light microscopy has many advantages for the study of cells. Specimen preparation is easy and relatively inexpensive, and the use of appropriate tags gives scientists the ability to visualize specific cells, cell organelles, proteins of interest. However, recent trends in cell analytics tends to use label free methods. In this context it is well known, that the most organic molecules are able to emit fluorescence light after an excitation with light at a characteristic wavelength. At room temperature the fluorescence is frequently minimized by different quenching effects. Some of these quenching effects are strongly influenced by the temperature of the specimen. Normal temperature dependence of fluorescence shows an increasing fluorescence intensity and lifetime when the temperature is lowered.
For label free fluorescence analytics we developed a combined system for laser induced fluorescence spectroscopic and microscopic measurements at temperatures down to 20 K. The system consists of a confocal laser scanning microscope, a very sensitive detector including spectrograph and CCD, and a special cryogenic measuring cell. The cell is characterized by a closed cycle Gifford McMahon-based cryostat and a device for active insulation of cryostat-based vibrations. The design of the measuring cell is constructed for easily adapting on common light microscopes without time consuming reconstructions. Currently microscopic measurements with an up to 630-fold magnification are possible. The use of the novel technique was evaluated in two representative applications. First experiments demonstrate an increment in the intensity of the fluorescence spectrum of different uranium VI species in biological samples by decreasing the temperature down to 20 K. Some of these uranium species show no detectable fluorescence at room temperature (RT), however, at 20 K a characteristic spectrum of uranium was visible. Comparable results show experiments on lactate, citrate, pyruvate and glucose. Second, continuative microscopic experiments in melanoma cell lines demonstrate improved sensitivity in detection of fluorescent dyes at cryogenic conditions. In this regard, DAPI and other fluorescence dyes could be detected in a melanotic mouse melanoma cell line with 100-fold increased sensitivity at 20 K compared to RT. As an additional benefit a lower photobleaching was observed at 20 K compared to RT. Furthermore, the use of laser-induced cryogenic fluorescence microscopy allowed visualization of COX-2 protein expression in amelanotic human melanoma cells using a novel, autofluorescent selective COX-2 inhibitor. The compound did not require additional chemical modification, e.g., by coupling fluorophor substituents. These results show that the new cryogenic measuring chamber represents an interesting and gainful tool for fluorescence based investigations.
Keywords: cryogenic, fluorescence microscopy
  • Invited lecture (Conferences)
    22nd annual conference of the german society for cytometry, 10.-12.10.2012, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17982
Publ.-Id: 17982


Single-shot pulse duration monitor for extreme ultraviolet and X-ray free-electron lasers

Riedel, R.; Shemmary, A. A.; Gensch, M.; Golz, T.; Harmand, M.; Medvedev, N.; Prandolini, M. J.; Sokolowski-Tinten, K.; Toleikis, S.; Wegner, U.; Ziaja, B.; Stojanovic, N.; Tavella, F.
A versatile single-shot temporal diagnostic tool is developed that allows the determination of the extreme ultraviolet (XUV) free-electron laser (FEL) pulse duration and the relative arrival time with respect to an external pump-probe laser pulse. This method is based on optical cross-correlation by time-resolved probing of an optically opaque plasma generated by linear absorption of the FEL XUV pulse within a solid dielectric. In this work we present measurements performed at the FLASH free-electron laser. Using (64±7) fs near infrared (NIR) probe pulses, we determine the FEL pulse duration at two distinct wavelengths, yielding (184±16) fs at 41.5 nm and (21±17) fs at 5.5 nm. We show the possibility to operate the tool as an online diagnostic for pump-probe experiments.

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Publ.-Id: 17981


Accuracy of 9Be-data and its influence on 10Be cosmogenic nuclide data

Merchel, S.; Bremser, W.; Binnie, S.; Bourlès, D. L.; Czeslik, U.; Dunai, T.; Erzinger, J.; Kummer, N.-A.; Leanni, L.; Merkel, B.; Recknagel, S.; Schaefer, U.
The method of choice for the determination of 10Be (t1/2 = 1.378 Ma) is accelerator mass spectrometry (AMS) by measuring 10Be/9Be as low as 10-16. A typical AMS target consists of ~0.5 mg BeO. As most to be radiochemically treated samples are too low in natural Be, a carrier solution containing Be of known concentration is added for sample preparation. The additional amount of 9Be-atoms is taken into account to calculate the number of 10Be-atoms.
Besides, for marine and terrestrial sediments that have absorbed atmospherically-produced 10Be being investigated for dating purposes, and lately also suggested for erosion-rate studies, the determination of 9Be in every individual sample at the ng/g-level is essential.
Thus, for all 10Be-AMS involving 9Be-carrier and/or 9Be measurements, the 10Be-data cannot be more accurate than the 9Be-data of the carrier and/or the samples.
During the recent installation of a new AMS facility [1], special attention has been addressed to the preparation of a 9Be-carrier of low 10Be from Be2SiO4 from a deep mine [2], as earlier studies had shown that commercial solutions contain high amounts of 10Be at the 10-14-level [3]. The 9Be-value is to be determined by a round-robin exercise.
Experimental
The resulting slightly acidic (HCl) Be-solution has been diluted to yield a concentration of ~2000 µg/g checked by three-time repeated gravimetry measurements. Further aliquots of around 1 g each have been sent to seven laboratories experienced with atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES) and/or mass spectrometry (ICP-MS). Two labs still owe results; two labs submitted results by two methods each, i.e. ICP-MS & ICP-MS using standard addition (Lab #4) and AAS & ICP-MS (Lab #6). Alls labs reported results as µg/g or µg/per aliquot to exclude density uncertainties.
Results
All hitherto results are shown with their associated stated uncertainty in ascending order in Fig. 1. Lab #1 is of most distant, but the distance is covered by the large uncertainty stated. Thus, no Grubbs outlier at the significance level of a = 0.01 is identified. Lab #2 is not compatible with four other lab results, which is most probably due to an underestimation of its own uncertainty. Despite this, the weighted mean being metrologically the very best estimate, is also shown with the weighted standard deviation (Fig. 1). These values may change when the last two missing values will be taken into account.
There is no clear dependence on the analytical method. However, it is remarkable that the labs using two methods produced very similar results. So, systematic errors due to handling, e.g. further dilution, of the sample might be more influential than the actual measurement accuracy.
Figure 1: Round-robin 9Be-results.
Conclusion
As the maximum deviation from a single lab result from the weighted mean of this round-robin exercise is ~8%, it seems absolutely necessary for all labs using non-commercial 9Be-carrier to have them analyzed at more than a single lab. Otherwise, their 10Be-results are incorrect at the same order as the used 9Be-carrier.
It seems very likely that the same problem arises if measuring individual samples, thus, constant quality assurance checks by e.g. taking part in round-robin exercises are absolutely necessary. The effect might be even more prominent at the ng/g-level.
References
[1] S. Merchel et al., this meeting.
[2] Kindly provided by C. Varajão, Univ. Federal de Ouro Preto.
[3] S. Merchel et al., Nucl. Instr. Meth. B 266 (2008) 4921-4926.
Keywords: AMS, ICP-MS, ICP-OES, AAS, round-robin, quality assurance
  • Poster
    24th Seminar Activation Analysis and Gamma-Spectroscopy (SAAGAS 24), 26.-28.02.2013, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17980
Publ.-Id: 17980


The (R)-(+)- and (S)-(-)-enantiomers of [18F]fluspidine have different potential for brain imaging of σ1 receptors

Brust, P.; Deuther-Conrad, W.; Patt, M.; Donat, C. K.; Becker, G.; Stittsworth, S.; Maisonial, A.; Habermann, B.; Holl, K.; Funke, U.; Fischer, S.; Hiller, A.; Wenzel, B.; Kranz, M.; Schepmann, D.; Hesse, S.; Lever, S. Z.; Steinbach, J.; Sabri, O.; Wünsch, B.
Objectives: It ist widely accepted that σ1 receptors represent a novel biological target for the pharmacological treatment of various brain diseases, e.g. depression and neurodegeneration. From our series of σ1-specific racemic 18F-fluoroalkylated spirocyclic piperidines we have chosen the superior [18F]fluspidine for detailed investigation of the (R)-(+)- and (S)-(-)-enantiomers with the aim to identify their individual potential for disease-related neuroimaging studies.

Methods: By semi-preparative chiral HPLC on immobilized amylose-tris-(3,5-dimethylphenyl)-carbamate as stationary phase the racemic tosylate precursor of [18F]fluspidine was enantioseparated. Automated radiosynthesis of the two enantiomers was accomplished by nucleophilic substitution and biodistribution studies were performed in CD-1 mice (dose: 240-480 kBq). Furthermore brain pharmacokinetics of the two enantiomers was investigated by dynamic PET studies in pigs (dose: 270-420 MBq). Additionally, the highly selective σ1 receptor agonist SA4503 (5mg/kg) was used in blocking (bolus plus infusion) studies to assess target specificity. SUV values were calculated for 24 MR-defined brain regions. Using a metabolite-corrected plasma input function compartment modelling was applied to estimate kinetic parameters of both enantiomers.

Results: Enantiomerically pure (R)- and (S)-tosylate precursors were obtained with high enantiomeric excess of >98 % and >96 %. (R)- and (S)-[18F]fluspidine were synthetized within ~70 min with RCY of 35-45% (EOS), RCP of >99%, and AS of 550 GBq/μmol and 870 GBq/μmol. In mice, both radiotracers readily passed the blood-brain barrier. However, large differences in brain pharmacokinetics of the two enantiomers were found with continuous increase of brain uptake of (R)-[18F]fluspidine (3.57 %ID/g at 5', 6.01% ID/g at 240' p.i.) in comparison to (S)-[18F]fluspidine with higher initial brain uptake (4.35 %ID/g at 5' p.i.) and rapid clearance (1.04% ID/g at 240' p.i.). Dynamic PET studies in pigs confirmed these enantiomer-related differences (Fig.).
[Fluspidine kinetics in pig brain]
Under baseline conditions, the initial brain uptake of (S)-[18F]fluspidine was higher than that of (R)-[18F]fluspidine (e.g. SUVmax, Cerebellum ~3.4 vs. ~2.9; K1: 0.72 vs. 0.56 ml/g/min). Clearance of (S)-[18F]fluspidine from brain was fast (SUVCerebellum ~1.1 at 95-120' p.i.) whereas the uptake of (R)-[18F]fluspidine remained close to the initial level (SUVCerebellum ~2.5 at 95-120' p.i.). Accordingly the binding potential (k3/k4) of (S)-[18F]fluspidine was much lower (1.7) than that of (R)-[18F]fluspidine (16.3). In comparison to baseline data, application of σ1 specific SA4503 reduced the uptake of (S)- and (R)-[18F]fluspidine in the target region cerebellum by initially 40% and 15% (SUVmax ~2.0 and ~2.5, respectively) and later by ~80% (SUV ~0.2 and ~0.6 at 95-120' p.i., respectively) . Washout kinetics and SUV values determined under blocking conditions indicate both target specificity of the binding as well as minor nonspecific binding of the two radiotracers.

Conclusions: We successfully developed and validated an automated synthesis of the two enantiomers of [18F]fluspidine. The pharmacokinetics of (S)-[18F]fluspidine as investigated in two different animal models suggests that this radiotracer is most suitable for upcoming studies of depression-related changes in receptor expression in human brain. The irreversible-like binding behaviour of (R)-[18F]fluspidine may have advantages for tumor imaging.

Acknowledgements: Supported by DFG (STE 601/10-2, WU 176/7-2) and NIH (T32 EB004822).
Keywords: PET, Sigma receptor, Depression, Neurodegeneration
  • Poster
    XXVIth International Symposium on Cerebral Blood Flow & Metabolism, 20.-23.05.2013, Shanghai, China

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Permalink: https://www.hzdr.de/publications/Publ-17979
Publ.-Id: 17979


Ultrasensitive determination of long-lived radionuclides by accelerator mass spectrometry for applications from the Earth Sciences and cosmochemistry

Merchel, S.; Akhmadaliev, S.; Pavetich, S.; Renno, A. D.; Rugel, G.; Several Dreams-Users
Concentrations of long-lived radionuclides in man-made material e.g. from decommissioning nuclear installations or unintended release are generally high enough to be directly measured by conventional mass spectrometry, decay counting or radiochemical neutron activation analysis. However, often samples need to be radiochemically processed before measurements to enrich radionuclides, eliminate the matrix and disturbing isobars or nuclides of similar decay characteristics.
Though, if the same radionuclides are produced in terrestrial and extraterrestrial matter by cosmic-ray induced nuclear reactions, concentrations are only in very rare cases measurable by other analytical techniques than accelerator mass spectrometry (AMS) after radiochemical separation. Samples from geomorphology applications can contain radionuclides at the level of several ten thousand atoms per gram mineral e.g. quartz or calcite, thus, asking for processing of 100 g starting material.
Experimental - AMS
For accelerator mass spectrometry negative ions (molecules or elements) are extracted from samples containing long-lived radionuclides (t1/2 > 100 a) in a Cs-sputter ion source. By inserting these ions in a tandem accelerator, they gain MeV-energies. Then by passing through matter (gas or foil) at the positively charged terminal in the middle of the accelerator, the negative ions lose outer electrons and convert into multiple-positively charged ions being then further accelerated towards the exit. Effectively all molecules are destroyed by this stripping process.
Generally, AMS is measuring isotope ratios, i.e., stable isotopes are usually detected in Faraday-cups and radionuclides in ionization chambers. Such a set-up of two mass spectrometers in one, namely the first with negative ions of keV-energy, the second with high-energy positive ions of MeV-energy, and combined with several magnetic and electrostatic analyzers (Fig. 1), allows analyzing isotope ratios as low as 10-16, thus, providing the ultimate detection limit of all mass spectrometry methods.
Figure 1: AMS set-up at DREAMS [1-3].
If using isotopically-enriched carrier such as 35Cl, AMS can also be applied to simultaneously measure stable chlorine by isotope dilution, i.e. ID-AMS.
Very recently, a new AMS facility has been installed at the Ion Beam Centre of the Helmholtz-Zentrum Dresden-Rossendorf: DREsden AMS (DREAMS) [1-3], which is capable of measuring 10Be, 26Al, 36Cl, 41Ca, and 129I (t1/2 = 0.1-16 Ma) as low as 10-14-10-16 (radionuclide/stable nuclide).
In 2013, the DREAMS set-up will be extended for measurements of actinides, and in 2014 for stable elements. Expected detection limits for stable isotope ratios are not as good as for radionuclide AMS, but still some orders of magnitude better than for traditional dynamic secondary ion mass spectrometry (SIMS), i.e. 10-9-10-12.
Applications
DREAMS applications are wide-spread e.g. meteoritics, astrophysics, geomorphology, climate research, hydrogeology, resource technology and risk assessment of natural hazards like rock falls.
References
[1] S. Merchel et al., GIT Labor-Fachzeitschrift 56(2) (2012) 88-90.
[2] S. Akhmadaliev et al., Nucl. Instr. Meth. B (2012) in print, doi:10.1016/j.nimb.2012.01.053.
[3] http://www.dresden-ams.de (Nov. 2012).
Keywords: AMS, radionuclide, cosmogenic, cosmochemistry
  • Lecture (Conference)
    24th Seminar Activation Analysis and Gamma-Spectroscopy (SAAGAS 24), 26.-28.02.2013, Garching, Deutschland

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Publ.-Id: 17978


Tuning of the nucleation field in nanowires with perpendicular magnetic anisotropy

Kimling, J.; Gerhardt, T.; Kobs, A.; Vogel, A.; Wintz, S.; Im, M.-Y.; Fischer, P.; Oepen, H. P.; Merkt, U.; Meier, G.
We report on domain nucleation and pinning of domain walls in Co/Pt multilayer nanowires with perpendicular magnetic anisotropy which are patterned using electron-beam lithography, sputter deposition, and lift-off processing. It is found that the nucleation field in these wires can be tuned by changing the geometry of the wire ends. A reduction of the nucleation field by up to 60 percent is achieved when the wire ends are designed as tips. This contrasts with the behavior of soft-magnetic wires for which the domain wall nucleation field increases when they are designed with triangular pointed ends. In order to clarify the origin of the reduced nucleation field observed for Co/Pt nanowires micromagnetic simulations are employed. As result the effect can be attributed to a local reduction of the perpendicular anisotropy caused by shadowing effects of the resist mask during sputter deposition of the multilayer. Related aspects concerning the creation of pinning sites for domain walls are addressed.
Keywords: Co/Pt multilayer, PMA wires, domain wall nucleation, x-ray microscopy

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Publ.-Id: 17977


Time-resolved electronic capture in germanium doped with hydrogen-like impurity centers

Deßmann, N.; Pavlov, S. G.; Shastin, V. N.; Zhukavin, R. K.; Winnerl, S.; Mittendorff, M.; Hübers, H.-W.
The capture of free holes and electrons in germanium (Ge) doped by gallium (Ga) or antimony (Sb) has been studied by a time-resolved pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. For Ga acceptors the relaxation times decrease with increasing pump power from approximately 3 ns to 1 ns (2 ns and 1 ns for Sb donors, respectively). The results support the development of fast photoconductive detectors in the terahertz region of the spectrum.
Keywords: Time resolved spectroscopy, THz, shallow donors in Ge
  • Contribution to proceedings
    37th International Conference on Infrared, Millimeter and Terahertz Waves, 23.-28.09.2012, Wollogon, Australia
    Proceedings of the IEEE 37th International Conference on Infrared, Millimeter and Terahertz Waves, ID:2569425
  • Poster
    37th International Conference on Infrared, Millimeter and Terahertz Waves, 23.-28.09.2012, Wollogon, Australia

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Publ.-Id: 17976


Anomalous Superconductivity in Gallium Nano-Films embedded in Silicon Wafers

Skrotzki, R.
  • Lecture (Conference)
    7th PhD Seminar HZDR, 08.-10.10.2012, Schöneck, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17975
Publ.-Id: 17975


Anomalous Superconductivity in amorphous 10 nm thin Ga films embedded in Si wafers

Skrotzki, R.
  • Lecture (Conference)
    3rd EuroMagNET Summer School, Science in High Magnetic Fields, 30.09.-07.10.2012, Rügen, Deutschland

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Publ.-Id: 17974


Magnetic and acoustic anomalies of UCu0.95Ge in high magnetic fields

Yasin, S.; Andreev, A. V.; Skourski, Y.; Zvyagin, A. A.; Zherlitsyn, S.; Wosnitza, J.
Magnetic and magneto-acoustic properties of the intermetallic compound UCu0.95Ge with antiferromagnetic ground state have been investigated on single crystals in pulsed magnetic fields up to 64 T. A first-order phase transition has been observed for fields applied along the a and c axis at 61 and 38 T, respectively. In both directions, the magnetization trends to saturate at 1.35 μB per formula unit. These field-induced transitions as well as the antiferromagnetic ordering at TN = 48 K are accompanied by pronounced anomalies in the sound velocity and sound attenuation. Additionally, the acoustic characteristics show some unusual frequency-dependent features which presumably can be related to the dynamics of Cu vacancies [1]. The field-temperature phase diagrams are constructed for both magnetic-field directions. The experimental data are analyzed by use of the mean-field approximation and agree qualitatively with the obtained results.
  • Poster
    Quantum Criticality & Novel Phases 2012 (QNCP12), 26.-29.08.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17973
Publ.-Id: 17973


Spin dynamics of the S = 5/2 2D triangular antiferromagnet Ba3NbFe3Si2O14

Choi, K. Y.; Wang, Z.; Ozarowski, A.; van Tol, J.; Zhou, H. D.; Wiebe, C. R.; Skourski, Y.; Dalal, N. S.
We report pulse-field magnetization, ac susceptibility, and 100 GHz electron spin resonance (ESR) measurements on the S = 5/2 two-dimensional triangular compound Ba3NbFe3Si2O14 with the N´eel temperature TN = 26 K . The magnetization curve shows an almost linear increase up to 60 T with no indication of a one-third magnetization plateau. An unusually large frequency dependence of the ac susceptibility in the temperature range of T = 20–100 K reveals a spin-glass behavior or superparamagnetism, signaling the presence of frustration-related slow magnetic fluctuations. The temperature dependence of the ESR linewidth exhibits two distinct critical regimes; (i) ΔHpp(T) α(T-TN)-p with the exponent p = 0.2(1)–0.2(3) for temperatures above 27 K, and (ii) ΔHpp(T) α(T- T)-p with T=12 K and p = 0.8.(1)–0.8(4) for temperatures between 12 and 27 K. This is interpreted as indicating a dimensional crossover of magnetic interactions and the persistence of short-range correlations with a helically ordered state.

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Publ.-Id: 17972


High-field research at the European XFEL

Cowan, T.; Schramm, U.; Herrmannsdörfer, T.; Weckert, E.; Strempfer, J.; von Zimmermann, M.; Stoehlker, T.
We present an initiative to build up a beamline at the European XFEL. This HELMHOLTZBEAMLINE will establish multi-purpose high-power and ultra-intense lasers as well as high-field magnets at the SASE2 end-station of the European XFEL. It will extend the scope of research that can be carried out at the European XFEL beyond the baseline instruments, especially in the areas of strong-field physics, high energy density science, relativistic laserplasma physics, ultra high-pressure astro- and planetary-physics, dynamic-materials research, and magnetic phenomena in condensed matter. At the European XFEL, an x-ray fluence in a single macropulse (600 microseconds, 2700 micropulses, each with 1E12 photons) will be available to, e.g., map out a full field profile for a magnetic absorption spectroscopy experiment, to probe the electronic or ionic structure in a single micropulse, or to investigate magnet-field driven phase transitions. The high photon fluence at the XFEL will allow for using pulsed-field magnets for a wide range of experimental techniques. The HELMHOLTZBEAMLINE will be used to drive matter to extremes of temperature, density, pressure, field strength, and/or particle irradiation, which can be probed with the XFEL beams; or alternatively to probe XFEL-driven samples with laser-generated particles or radiation. The HELMHOLTZ-BEAMLINE is being proposed for funding from the Helmholtz Association research area Matter, by partners HZDR, DESY and HI-Jena. Over 80 research groups from more than 60 institutions in 15 countries have joined this User Consortium as External Partners.
  • Poster
    Workshop on Synchrotron and Neutron Applications of High Magnetic Fields, 17.-19.10.2012, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-17971
Publ.-Id: 17971


On-chip superconductivity above 7 K in microstructured 10 nm thin Ga films embedded in Si wafers

Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Fiedler, J.; Schönemann, R.; Philipp, P.; Bischoff, L.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Helm, M.; Wosnitza, J.
Initiated by the finding of doping-induced ambient-pressure superconductivity in classic group-IV semiconductors, in particular our investigation on Ga-doped Germanium [1], we have succeeded in preparing an even more promising candidate for superconducting onchip application [2]. Ion implantation has been utilized to introduce a high dose of Ga into silicon wafers capped by 30 nm SiO2. Ga segregation underneath the cover was stimulated by subsequent rapid thermal annealing in a narrow time and temperature window. Extended structural investigations by means of XTEM, EDX, RBS/C, and SIMS confirm a reproducible formation of 10 nm thin amorphous Ga-rich layers. In the normal state these layers reveal a sheet resistance with a negative temperature derivative and an absolute value close to the quantum resistance which is about 6 kOhm. The superconducting onset temperature accounts for up to 10 K while a zero-resistance state coincides with diamagnetic screening below 5 K verified by means of resistivity and dc magnetization measurements. Further, superconductivity remains stable up to remarkable high magnetic fields of more than 8 Tesla and exhibits a distinct critical-field anisotropy manifesting its thin-film character. Homogeneity and scale-independent behavior down to 3 micron have been proven by lateral microstructuring via photolithography rendering critical-current densities higher than 50 kA/cm2. Recently, focussed-ion beam technique has been implemented in order to create Josephson junctions - key elements of the prospective first ever built gallium SQUID.
  • Invited lecture (Conferences)
    M2S 2012 - Materials and Mechanisms of Superconductivity, 29.07.-03.08.2012, Washington, USA

Permalink: https://www.hzdr.de/publications/Publ-17970
Publ.-Id: 17970


Semimetallic Paramagnetic Nano-Bi2Ir and Superconducting Ferromagnetic Nano-Bi3Ni by Microwave-Assisted Synthesis and Room Temperature Pseudomorphosis

Boldt, R.; Grigas, A.; Heise, M.; Herrmannsdörfer, T.; Isaeva, A.; Kaskel, S.; Köhler, D.; Ruck, M.; Skrotzki, R.; Wosnitza, J.
Uniform nanocrystals of the intermetallic compounds Bi2Ir (diameter ≥ 50 nm) and Bi3Ni (typical size 200x600 nm) were obtained by a microwave-assisted polyol process at 240 °C. The method was also applied to the spatially confined reaction environment in the microporous exo-template SBA-15 resulting in Bi3Ni particles of about 6 nm. Non-crystalline bundles of parallel Bi3Ni nanofibres that have an individual diameter of less than 1 nm were obtained by reductive pseudomorphosis of the subiodide Bi12Ni4I3 at room temperature. Magnetic susceptibility measurements demonstrate coexistence of ferromagnetism and superconductivity in a single phase for the nanostructured Bi3Ni materials. Curie temperature, coercive field, remnant magnetization, saturation moment, diamagnetic screening, and critical field vary with particle size. The crystal structure of Bi2Ir was determined by Rietveld refinement of powder X-ray diffraction data. Bi2Ir crystallizes in the monoclinic arsenopyrite type (space group P21/c), a superstructure of the markasite type, with a = 690.11(1), b = 678.85(1), c = 696.17(1) pm, and β = 116.454(1)°. In contrast to most of the other phases of this type, the Bi2Ir is not a diamagnetic semiconductor but a weakly paramagnetic semimetal. Conductivity measurements down to 4 K and magnetization measurements in a field of μ0H = 10 mT down to 1.8 K give no evidence for a transition into the superconducting state. Bonding analysis shows prevailing contribution of Bi–Bi interactions to the conduction, whereas Bi–Ir bonding is mostly covalent and localized.

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Permalink: https://www.hzdr.de/publications/Publ-17969
Publ.-Id: 17969


Nuclear magnetic resonance apparatus for pulsed high magnetic fields

Meier, B.; Kohlrautz, J.; Haase, J.; Braun, M.; Wolff-Fabris, F.; Kampert, E.; Herrmannsdörfer, T.; Wosnitza, J.
A nuclear magnetic resonance apparatus for experiments in pulsed high magnetic fields is described. The magnetic field pulses created together with various magnet coils determine the requirements such an apparatus has to fulfill to be operated successfully in pulsed fields. Independent of the chosen coil it is desirable to operate the entire experiment at the highest possible bandwidth such that a correspondingly large temporal fraction of the magnetic field pulse can be used to probe a given sample. Our apparatus offers a bandwidth of up to 20 MHz and has been tested successfully at the Hochfeld-Magnetlabor Dresden, even in a very fast dual coil magnet that has produced a peak field of 94.2 T. Using a medium-sized single coil with a significantly slower dependence, it is possible to perform advanced multi-pulse nuclear magnetic resonance experiments. As an example we discuss a Carr-Purcell spin echo sequence at a field of 62 T.

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Permalink: https://www.hzdr.de/publications/Publ-17968
Publ.-Id: 17968


Spin-lattice coupling in the frustrated antiferromagnet ZnCr2Se4 probed by ultrasound

Felea, V.; Yasin, S.; Günther, A.; Deisenhofer, J.; Krug Von Nidda, H.-A.; Zherlitsyn, S.; Tsurkan, V.; Lemmens, P.; Wosnitza, J.; Loidl, A.
Ultrasound and magnetization studies of the frustrated spinel ZnCr2Se4 are performed as a function of temperature and magnetic field up to 14 T. In zero field, the sound velocity and attenuation reveal significant anomalies at the antiferromagnetic transition at TN ≈ 21 K indicating strong spin-lattice coupling. External magnetic fields shift these anomalies to lower temperatures concomitantly with the reduction of the Neel temperature. At 2 K, the sound velocity as a function of magnetic field manifests three pronounced anomalies: a deep minimum at 5.4 T related to an inflection point of the magnetization followed by two plateaus with distinct stiffness at fields above 7 and 10 T. The first plateau is ascribed to a transformation from a tetragonal to a cubic phase, while the second one corresponds to a state with fully polarized magnetization. The evolution of magnetic and structural states is discussed within a H-T phase diagram and compared with related frustrated magnetic spinels with strong spin-lattice coupling.

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Permalink: https://www.hzdr.de/publications/Publ-17967
Publ.-Id: 17967


Magnetic behaviour of interacting antiferromagnetic nanoparticles

Markovich, V.; Puzniak, R.; Skourski, Y.; Wisniewski, A.; Mogilyanski, D.; Jung, G.; Gorodetsky, G.
Magnetic properties of interacting La0.2Ca0.8MnO3 nanoparticles have been investigated. The field-induced transition from antiferromagnetic (AFM) to ferromagnetic (FM) state in the La0.2Ca0.8MnO3 bulk has been observed at exceptionally high magnetic fields. For large particles, the field-induced transition widens while magnetization progressively decreases. In small particles the transition is almost fully suppressed. The thermoremanence and isothermoremanence curves constitute fingerprints of irreversible magnetization originating from nanoparticle shells. We have ascribed the magnetic behaviour of nanoparticles to a core–shell scenario with two main magnetic contributions; one attributed to the formation of a collective state formed by FM clusters in frustrated coordination at the surfaces of interacting AFM nanoparticles and the other associated with inner core behaviour as a two-dimensional diluted antiferromagnet.

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Permalink: https://www.hzdr.de/publications/Publ-17966
Publ.-Id: 17966


Mineralogical and geochemical investigation of seafloor massive sulfides from Panarea Platform (Aeolian Arc, Tyrrhenian Sea)

Dekov, V. M.; Kamenov, G. D.; Abrasheva, M. D.; Capaccioni, B.; Munnik, F.
Panarea seafloor hydrothermal system is associated with a range of mafic to felsic volcanic rocks. The hydrothermal system is active at present and discharges magmatic-hydrothermal fluids and precipitates massive sulfides. The sulfides exhibit multi-stage deposition, evident in the alternation of several mineral generations that follow a general temporal precipitation sequence: marcasite → alunite → opal. Sr-Nd-Pb isotope data indicate that most of the metals in the sulfides are derived predominantly from the Panarea volcanic rocks with some contribution from ambient seawater and/or local sediments. A remarkable feature of these sulfides is their chondrite-normalized rare earth element (REEN) distribution pattern with a pronounced negative Eu anomaly, which has not been observed previously. Our study demonstrates that this REEN pattern reflects the REE fractionation during sulfide deposition. The ionic radius mismatch between Eu2+ (the main form of Eu in reduced, high-temperature hydrothermal fluids) and the only possible site for REE substitution in the marcasite, that of Fe2+, suggests a crystallographic control on the REEN pattern. Apparently, marcasite precipitation can generate a sulfide deposit with a negative Eu anomaly due to discrimination against Eu2+ relative to REE3+ in the Fe2+ crystallographic site.
Keywords: Eu anomaly, hydrothermal, massive sulfide, rare earth elements, Tyrrhenian Sea

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Publ.-Id: 17965


Contactless inductive flow tomography: A liquid metal flow measuring technique complementary to UDV

Stefani, F.; Gerbeth, G.; Gundrum, T.; Wondrak, T.
The aim of the Contactless Inductive Flow Tomography (CIFT) is the reconstruction of flow structures in metal and semiconductor melts. It relies on the induction of electric currents in moving conductors exposed to magnetic fields. The flow induced deformations of various applied magnetic fields can be measured in the exterior of the melt and utilized for the reconstruction of the velocity field. After a presentation of the principles of CIFT, first applications and possible extensions of the method are discussed and put into the context with traditional measuring techniques such as UDV.
  • Invited lecture (Conferences)
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Germany
  • Contribution to proceedings
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Germany
    Proceedings of the 8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, Dresden: HZDR, 101-104

Permalink: https://www.hzdr.de/publications/Publ-17964
Publ.-Id: 17964


Towards a precession driven dynamo

Stefani, F.; Gundrum, T.; Giesecke, A.; Albrecht, T.; Gerbeth, G.
Precession has been discussed since long as a complementary energy source of planetary dynamos. We present the status of preparations of a large-scale precession-driven dynamo experiment working with liquid sodium. The main focus is laid on the results of a down-scaled water experiment, and on a number of constructional issues of the large machine.
  • Lecture (Conference)
    European GDR Dynamo & MHD Days, 01.-04.10.2012, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-17963
Publ.-Id: 17963


Anisotropic Cascade of Field-Induced Phase Transitions in the Frustrated Spin-Ladder System BiCu2PO6

Kohama, Y.; Wang, S.; Uchida, A.; Prsa, K.; Zvyagin, S.; Skourski, Y.; Mcdonald, R. D.; Balicas, L.; Ronnow, H. M.; Rüegg, C.; Jaime, M.
BiCu2PO6 is a frustrated two-leg spin-ladder compound with a spin gap that can be closed with a magnetic field of approximately 20 T. This quantum phase transition and its related phase diagram as a function of magnetic field and temperature (H, T) are investigated up to 60 T by means of specific heat, magnetocaloric effect, magnetization, and magnetostriction measurements. In contrast to other gapped quantum magnets, BiCu2PO6 undergoes a series of unexpected first- and second-order phase transitions when an external magnetic field is applied along the crystallographic c axis. The application of a magnetic field along the b axis induces two second-order phase transitions. We propose that the anisotropy and complex phase diagram result from the interplay between strong geometrical frustration and spin-orbit interaction necessary for the description of this fascinating magnetic system.

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Permalink: https://www.hzdr.de/publications/Publ-17962
Publ.-Id: 17962


The x-ray magnetic circular dichroism spin sum rule for 3d4 systems: Mn3+ ions in colossal magnetoresistance manganites

Kuepper, K.; Raekers, M.; Taubitz, C.; Uhlarz, M.; Piamonteze, C.; de Groot, F. M. F.; Arenholz, E.; Galakhov, V. R.; Mukovskii, Y. M.; Neumann, M.
The colossal magnetoresistance manganites La0.87±0.02Sr0.12±0.02MnO3+δ, La0.78±0.02Sr0.17±0.02MnO3+δ, and La0.66±0.02Sr0.36±0.02MnO3+ δ (δ close to 0) were investigated by using soft x-ray magnetic circular dichroism (XMCD) and magnetometry. Very good agreement between the values for the average Mn magnetic moments determined with these two methods was achieved by correcting the XMCD spin sum rule results by means of charge transfer multiplet calculations, which also suggest a charge transfer of ~50% for Mn4+ and ~_30% for Mn3+. The magnetic moment was found to be localized at the Mn ions for x = 0.17 and 0.36 at 80 K and for x = 0:12 in the temperature range from 80 to 300 K. We discuss our findings in the light of previously published data, confirming the validity of our approach.

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Permalink: https://www.hzdr.de/publications/Publ-17961
Publ.-Id: 17961


Astrophysical phenomena in the lab: MHD instabilities in liquid metal experiments

Stefani, F.; Gerbeth, G.; Giesecke, A.; Gundrum, T.; Kirillov, O.; Seilmayer, M.
We give an overview about the recent liquid metal experiments on dynamo action and magnetically triggered flow instabilities with relevance to cosmic objetcs like planets, stars, and accretion disks. The prospects for large-scale liquid sodium experiments in the framework of DRESDYN are also discussed.
  • Invited lecture (Conferences)
    Workshop: "Rotation and magnetic fields on the upper main sequence", 05.-06.11.2012, Potsdam, Germany

Permalink: https://www.hzdr.de/publications/Publ-17960
Publ.-Id: 17960


Exciton dynamics in GaAs quantum wells studied with a free-electron laser

Schneider, H.
There is no abstract.
Keywords: GaAs quantum well, terahertz free-electron laser, exciton
  • Invited lecture (Conferences)
    The 6th International Symposium on Ultrafast Phenomena and THz Waves (ISUPTW2012), POEM OSA Topical Meeting, 01.-02.11.2012, Wuhan, China

Permalink: https://www.hzdr.de/publications/Publ-17959
Publ.-Id: 17959


Quantum well infrared photodetectors for dual-band thermal imaging and two-photon detection

Schneider, H.
There is no Abstract.
Keywords: quantum well infrared photodetector, thermal imaging, GaAs/AlGaAs
  • Lecture (others)
    Seminar, University of Electronic Science and Technology of China (UESTC), 18.10.2012, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-17958
Publ.-Id: 17958


Status of the Pulsed-Magnet-Development Program at the Dresden High Magnetic Field Laboratory

Zherlitsyn, S.; Wustmann, B.; Herrmannsdörfer, T.; Wosnitza, J.
The Dresden High Magnetic Field Laboratory (HLD) is a pulsed-field user facility which offers to researches a variety of experimental techniques combined with non-destructive pulsed magnetic fields. Recently a new, 9.5 MJ dual-coil magnet has been commissioned. This magnet has achieved magnetic field of 91.4 T in a 16 mm bore and it is available for users now. In this paper, we report on some key upgrades in the magnet design which have led to breaking the 90 T limit at the HLD. Further possible design improvements are discussed. In addition, we share our operational experience obtained with the pulsed magnets.

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Publ.-Id: 17957


Nanostructured thin manganite films in megagauss magnetic field

Balevicius, S.; Zurauskiene, N.; Stankevic, V.; Kersulis, S.; Plausinaitiene, V.; Abrutis, A.; Zherlitsyn, S.; Herrmannsdörfer, T.; Wosnitza, J.; Wolff-Fabris, F.
We report on the use of the colossal magnetoresistance (CMR) effect in manganites for the measurement of pulsed magnetic fields up to the megagauss limit. To increase the application range in a magnetic field, we fabricated nanostructured La-Sr-Mn-O films consisting of nanocrystallites cummulated into clusters separated by highly amorphous inter-cluster boundaries. We demonstrate that the CMR effect does not saturate in these films at 77K up to 91.4 T. Moreover, the magnetoresistance behavior at 290K shows that nanostructured manganite films are promising candidates for the development of magnetic field scalar sensors operating in wide field and temperature ranges.

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Accommodation of multivalent cations in fluorite-type solid solutions: case of Am-bearing UO2

Prieur, D.; Martin, P.; Lebreton, F.; Delahaye, T.; Banerjee, D.; Scheinost, A. C.; Jankowiak, A.
The radiotoxicity of spent nuclear fuel is mainly due to the content of minor actinides, which could be substantially reduced by Partitioning and Transmutation. A possible transmutation method would be to employ americium-bearing uranium oxide materials as blanket fuels in fast neutron reactors. In order to maintain fuel performance and reactor safety, it is mandatory to control the structural homogeneity and oxygen stoichiometry during the sintering process. In this work, U0.85Am0.15O2±x materials, fabricated by a solid state chemistry process, were sintered at 2023 K under three oxygen potentials, i.e. -375, -350 and -325 kJ.mol-1, thereby significantly extending the range of a previous study. By coupling X-ray diffraction and X-ray absorption spectroscopy measurements, it was shown that fluorite solid solutions are obtained whatever the sintering conditions. The presence of U(+V), pointed out in a previous work for oxygen potentials equal to -520 and -450 kJ.mol-1, was confirmed. This result constitutes the first experimental proof of the existence of U(+V) in An-doped UO2 fluorite materials. Considering the now available extended range, the effect of the oxygen potential is discussed in terms of charge distribution and local structure.
Keywords: XAFS Americium Partitioning Transmutation

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Low electrical resistivity polycrystalline TiO2-based transparent conductive thin films by DC magnetron sputter deposition

Neubert, M.; Vinnichenko, M.; Fiedler, J.; Gebel, T.; Liepack, H.; Kolitsch, A.
Transparent conductive oxides (TCO), mainly In2O3:Sn (ITO), ZnO:Al (AZO) and SnO2:F (FTO) are widely used as transparent electrodes in flat panel displays, thin film solar cells and solid state lighting. The markets for the applications requiring large area electrodes are continuously growing recent years which drives the need for a cost-efficient replacement of conventional TCOs. In addition to a low cost, TiO2 offers unique combination of high refractive index, stability against humidity, the high chemical stability and the non-toxicity. The Nb or Ta doped TiO2 films epitaxially grown on crystalline substrates show electrical and optical properties which are comparable to those of conventional TCOs. However, using expensive crystalline substrates drastically limits applications. It is still a challenge to achieve low electrical resistivity polycrystalline TiO2 films as required for the most applications. Furthermore, it is not possible to get low resistivity in polycrystalline films by direct growth at elevated substrate temperature.
Only a two-step approach containing the deposition of amorphous films followed by annealing in vacuum or hydrogen delivers films with resistivity values in the range of 1·10-3 cm. Even in that case, it is known that electrical, optical and structural properties evolution during crystallization, and crystallization itself, is strongly affected by the Ti/O ratio in the as-deposited films. Achieving required Ti/O ratio remains the main challenge. In order to address this problem, we studied the films formed on glass substrates without heating by DC magnetron sputtering of reduced TiO2-x:Ta ceramic targets followed by vacuum annealing. We achieved oxygen fine-tuning using a MS process in conjunction with a plasma feedback system. The optimum total pressure in combination with O2 fine tuning yielded the films with the best free electron mobility of 8 cm²/Vs. Our approach delivered films with an electrical resistivity in the range of 10-3 W cm, optical transmittance above 80% for 400nm thick films and electrical activation of Ta dopants up to 70% which is substantially higher than that of Al in ZnO. The temperature dependent hall effect measurements show a different behavior of the resistivity vs. temperature with varying film stoichiometry.
Keywords: TCO, TiO2, transparent, conductive, tantalum
  • Lecture (Conference)
    4th International Symposium on Transparent Conductive Materials, 21.-26.10.2012, Hersonnisos, Greece

Permalink: https://www.hzdr.de/publications/Publ-17954
Publ.-Id: 17954


Overview On The Reaction Mechanism And Kinetics Of The Oxidation Of Isobutane And Future Prospects

Willms, T.; Kryk, H.; Hampel, U.
Die Ergebnisse der Literaturrecherche zur Isobutanoxidation werden vorgestellt. Es wird ein ausführlicher Reaktionsmechanismus für die unkatalysierte Oxidation vorgestellt. Außerdem werden einige der ermittelten Reaktionsmodelle vorgestellt und ausgewertet.
Des Weiteren wird die durch Bromwasserstoff katalysierte Variante dieser Reaktion vorgestellt. Sicherheitsaspekte sowie Erkenntnisse zur Stabilität des t-Butylhydroperoxides werden beschrieben und Schlussfolgerungen für das weitere Vorgehen im Rahmen des Projektes gezogen.
  • Lecture (others)
    2. Dresdener Energie-Allianz-Treffen, 07.11.2012, HZDR, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17953
Publ.-Id: 17953


Effect of Ga+ irradiation on the magneto-optic spectra of Pt/Co/Pt sandwiches

Lišková, E.; Veis, M.; Višňovský, Š.; Ferré, J.; Mougin, A.; Mazalski, P.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC
Interfacial changes in rf sputtered Pt/Co(2.6 nm)/Pt sandwiches grown onto sapphire (Al2O3) substrates induced by irradiation of 30 keV Ga+ ions at low dose (1014 ions/cm2) have been investigated by magneto-optic polar Kerr rotation (PKR) spectroscopy between 1 and 5 eV. The irradiation resulted in an increase of PKR over the whole spectral range. The measured PKR spectra were compared with those computed from the transfer matrix formalism using known polar Kerr rotation and ellipticity spectra for Co and five CoxPt1−x alloys. The comparison between measured and computed PKR spectra provided an in-depth profile of Co and Pt ion distributions across the sandwich and confirmed that irradiation favors alloying in the vicinity of the two interfaces. These results are in a good agreement with the profile evaluated independently by TRIDYN simulations. Our results evidence an asymmetry in the irradiation effect due to an excess of Pt–Co alloying at the upper interface. Moreover, the observation of a negative PKR peak around 3.2 eV states definitively the presence of a chemically ordered Co0.75Pt0.25 alloy phase inside the irradiated film structure.
Keywords: Magneto-optical Kerr spectroscopy, Pt/Co thin films, Metal and metal alloys, Ion radiation effect

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Effects of millisecond thermal processing on the properties of ZnO-based transparent conducting materials

Vinnichenko, M.; Hauschild, D.; Krause, M.; Cornelius, S.; Gago, R.; Mücklich, A.; Lissotschenko, V.; Kolitsch, A.
Improvement of the electrical and optical properties of ZnO-based thin films by post-deposition thermal processing at millisecond time scale is an attractive approach to realize low-cost transparent electrodes for different applications. Embedding Ag nanoparticles into ZnO:Al layers can extend functionality of the electrodes by achieving plasmonic light scattering due to spinodal dewetting of the Ag during thermal processing. If applied for preparation of thin film solar cells, both approaches have potential to improve their efficiency without increasing production costs. Nevertheless, this potential remains largely unexplored, partly due to limited understanding of physical mechanisms of the material properties modification during such treatment.
Present study focuses on the investigation of the effects of very rapid thermal processing (vRTP, dwell time of 1 ms) on the ZnO:Al (AZO) and AZO/Ag/AZO film properties using innovative low-cost high power diode laser arrays with microoptically designed line-shaped beam profiles. The method enables treatment of the films on thermally sensitive substrates, because thermal energy is deposited directly in the film, which leads only to partial heating of the substrate. Moreover, it is compatible with in-line growth of the transparent electrodes and is up-scalable to large areas. The properties of the films processed by vRTP and directly grown at elevated substrate temperatures are systematically compared. The AZO films were deposited both by reactive pulsed and non-reactive DC magnetron sputtering (MS). The composite AZO/Ag/AZO films were synthesized using non-reactive DC MS. Only the films grown without substrate heating were subjected to the vRTP.
Even at air ambience, the optimized laser processing of the AZO films results in a decrease of the film electrical resistivity from (1-2)x10-3 to less than 5x10-4 Ω cm. This is accompanied by a substantial increase of the free electron mobility, μe, and density, Ne, and increase of the film transmittance in the visible. Interestingly, the electron mobility values evaluated using Drude term for near-IR spectroscopic ellipsometry data analysis remain higher than the Hall effect values μe both for as deposited and processed films. Both values improve approximately by the same factor due to the laser vRTP. It is known that Hall effect provides information on the electrically connected crystalline grains, while spectroscopic ellipsometry yields intra-grain mobility. Therefore, this result suggests that the AZO film properties improve mainly intra-grain and electrical contact among the grains does not change. This is in agreement with the XRD and X-TEM data showing neither changes in the film morphology nor improvement of the film crystal quality by the vRTP.
The vRTP was observed to cause a substantial decrease of the A1(LO) and E1(LO) disorder-enhanced lines in Raman spectra. Taking into account X-ray absorption near edge structures (XANES) results, annealing of intra-grain oxygen-related point defects is of importance for the AZO electrical properties improvement by vRTP. The as-deposited films having larger amount of defects (according to Raman spectroscopy) improve their optical transmittance to a less extent by laser processing pointing to an importance of the initial state of the film for the results of vRTP.
Using deposition at elevated temperature, the AZO films with better crystal quality but similar electrical and optical properties were achieved only at TS≥250°C. Depositing entire AZO/Ag/AZO stack on heated substrate, the strongest plasmonic resonance was observed in case of TS~450°C. XTEM shows that it is due to the embedded layer of dewetted nano-Ag islands which are ~10 nm thick and have ~60 nm diameter. Achieving similar structures by laser vRTP is in progress.
  • Lecture (Conference)
    4th Symposium on Transparent Conductive Materials 2012, 21.-26.10.2012, Chersonissos, Crete, Greece

Permalink: https://www.hzdr.de/publications/Publ-17951
Publ.-Id: 17951


Crystallization of TiO2:Nb/Ta: effect of the as-deposited film morphology and local order structure

Vinnichenko, M.; Junghähnel, M.; Neubert, M.; Gago, R.; Mücklich, A.; Kolitsch, A.
TiO2-based transparent conductive oxides (TCOs) are of great importance as a cost-efficient, environmentally friendly and chemically inert alternative to conventional TCOs. The two-step process, i.e. growth of amorphous TiO2:Nb (TNO) and TiO2:Ta (TTO) films on glass and their post-deposition annealing provides films with electrical resistivity below 10-3 Ω cm. Further optimization of the growth process and its up-scaling require a deeper understanding of the crystallization process of the TiO2-based amorphous films. Appropriate characterization of the film structure represents a major challenge in this case.
The TNO and TTO films were prepared using two-step process on commercial glass substrates. During the first step, amorphous intermediate material was grown by DC magnetron sputtering of electrically conducting TiO2-x-based ceramic targets. The TNO films were grown using a pilot scale in-line sputtering system with precise adjustment of the O2 flow, fO2, using mass flow controllers. The TTO films were deposited in lab-scale system at higher total pressure and applying a closed-loop feedback system based on plasma emission monitor to tune fO2. The films were subjected to post-deposition thermal annealing in vacuum at TA~450 °C for ~15-60 min. In both cases, it was found that the anatase films with low electrical resistivity (~10-3 Ω cm) and high optical transmittance (>80% in the visible) can be prepared only within very narrow window of fO2 values.
The x-ray amorphous films (those which show no diffraction peaks) upon annealing convert into the films with dramatically different structure and properties depending on the fO2 used during the deposition. In case of fO2fO2*, the as-deposited layers crystallize to high-quality anatase films with high optical transmittance, but higher than optimum electrical resistivity values. The films which form either rutile or anatase phase upon crystallization showed the same signatures characteristic of anatase-like local order in XANES spectra in as-deposited state. This is in apparent contradiction to the crystallization of undoped x-ray amorphous TiO2, when films showing nc-rutile or anatase-like signatures in XANES spectra, crystallize, to rutile and anatase phase, respectively [1]. This discrepancy was resolved by high-resolution cross-sectional TEM measurements. The as-deposited TNO/TTO films grown at fO2fO2* show only homogeneous amorphous morphology. According to TEM, the undoped TiO2 films which converted to rutile after annealing show rutile nanocrystals directly on the film surface [2]. In all cases XANES measurements were performed in total electron yield mode with the electron escape depth in the range of 10 nm, therefore this method is not sensitive to the rutile inclusions situated deeper below the film surface.
These results show that nanocrystallites of rutile present in amorphous TiO2 matrix work as seeds and induce formation of the undesirable rutile phase during annealing. In order to achieve high-quality TiO2-based TCOs, formation of the seeds has to be avoided, which can be realized by careful adjustment of the Ti/O flux ratio during the intermediate film growth.
1. R.Gago, A.Redondo-Cubero, M.Vinnichenko, and L.Vázquez, Chem. Phys. Lett. 511, 367 (2011).
2. R.Gago, M.Vinnichenko, A.Redondo-Cubero, and L.Vázquez, Plasma Process. Polym. 7, 813 (2010).
  • Poster
    4th Symposium on Transparent Conductive Materials 2012, 21.-26.10.2012, Chersonnisos, Crete, Greece

Permalink: https://www.hzdr.de/publications/Publ-17950
Publ.-Id: 17950


Setup and Fabrication of Cost Effective, Robust Fiber Optical Needle Probes for Application in Multiphase Flows

Bloch, G.; Elfner, J.; Finke, K.; Schleicher, E.; Sattelmayer, T.
A fiber optical probe for detection of void fraction in multiphase flows consisting of silica fibers with core diameters of 200 and 400 µm is presented. Using beam splitter optics with a polarizing filter and a diode laser for illumination, a robust and cost-efective sensor was developed and evaluated in two phase flows with and without phase change. The setup and manufacturing process of the components as well as the post processing of the signals are described in detail.
Keywords: Fiber Optics, Fluid Mechanics, Instruments, Optical Methods, Signal Processing
  • Contribution to proceedings
    21. GALA-Fachtagung "Lasermethoden in der Strömungsmesstechnik", 03.-05.09.2013, München, Bundesrepublik Deutschland
    Proceedings der 21. GALA-Fachtagung "Lasermethoden in der Strömungsmesstechnik", Karlsruhe: GALA e.V., 978-3-9805613-9-6, 10-1-10-8

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Experimental investigation of stratified two-phase flows in the hot leg of a PWR for CFD validation

Vallée, C.; Lucas, D.; Tomiyama, A.; Murase, M.
Stratified two-phase flows were investigated in two different models of the hot leg of a pressurised water reactor (PWR) in order to provide experimental data for the development and validation of computational fluid dynamics (CFD) codes. Therefore, the local flow structure was visualised with a high-speed video camera. Moreover, one test section was designed with a rectangular cross-section to achieve optimal observation conditions. The phenomenon of counter-current flow limitation (CCFL) was investigated, which may affect the reflux condenser cooling mode in some accident scenarios.
The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and saturated water at boundary conditions of up to 50 bar and 264°C. The measured CCFL characteristics were compared with similar experimental data and correlations available in the literature. This shows that the channel height is the characteristic length to be used in the Wallis parameter for channels with rectangular cross-sections. Furthermore, the experimental results confirm that the Wallis similarity is appropriate to scale CCFL in the hot leg of a PWR over a wide range of pressure and temperature conditions. Finally, an image processing algorithm was developed to recognise the stratified interface in the camera frames. Subsequently, the interfacial structure along the hot leg was visualised by the representation of the probability distribution of the water level.
Keywords: counter-current flow limitation, CCFL, hot leg, stratified two-phase flow, interfacial structure, image processing
  • VGB PowerTech Journal (2012)12, 40-46
  • atw - International Journal for Nuclear Power 57(2012), 742-750

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Krein space related physics

Günther, U.
Physical models with anti-linear symmetries can often be described by differential operators self-adjoint in suitably chosen Krein spaces.
We briefly comment on the spectral properties of some specific operators self-adjoint in Krein spaces and related effects:
- the operator of the hydrodynamic Squire equation, its scaling behavior and mapping to the operator of the Bender-Boettcher model of PT Quantum Mechanics,
- the cusp-type spectral properties in the vicinity of third-order exceptional points (algebraic branch points),
- the unfolding of higher-order exceptional points of the spectrum of Hamiltonians in PT-symmetric Bose-Hubbard models described with the help of Puiseux series expansions and Newton polygon techniques.
We briefly explain the basic features of the so-called quantum brachistochrone problem for Hamiltonians self-adjoint in Hilbert spaces and in Krein spaces and demonstrate their interrelation geometrically in terms of contraction-dilation maps in projective Hilbert spaces and via positive operator-valued measures (POVMs) and Naimark dilation.
Finally, we briefly comment on recent experimental findings in PT-symmetric (i.e. Krein-space related) physics, especially in optical wave-guide systems and microwave cavities.
Keywords: anti-linear symmetries, Krein spaces, spectral singularities, exceptional points, branch points, PT symmetry, PT quantum mechanics, Squire equation, Bose-Hubbard model, Puiseux series expansion, Newton polygon technique, quantum brachistochrone problem, positive operator-valued measures, Naimark dilation, optical wave guides, microwave cavities
  • Lecture (others)
    Weekly Scientific Seminar of the Department of Applied Functional Analysis, Krakow AGH University of Science and Technology, 21.11.2012, Krakow, Polen

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Publ.-Id: 17946


Ultimate detection limits by accelerator-based mass spectrometry

Merchel, S.; Akhmadaliev, S.; Pavetich, S.; Renno, A. D.; Rugel, G.; Ziegenrücker, R.
Accelerator-based analytical methods, mainly accelerator mass spectrometry (AMS) and ion beam analysis (IBA), have been applied to numerous research projects in recent decades. The key element of both methods is a high-energy particle accelerator running at a terminal voltage of 0.2-14 MV.

For AMS negative ions (molecules or elements) are extracted from samples containing long-lived radionuclides (t1/2 >100 a) in a Cs-sputter ion source. By inserting these ions in a tandem accelerator, they gain MeV-energies, and by passing through matter (gas or foil) at the positively charged terminal in the middle of the accelerator, the negative ions lose outer electrons and convert into multiple-positively charged ions being then further accelerated towards the exit. Effectively all molecules are destroyed by this stripping process. Generally, AMS is measuring isotope ratios, i.e., stable isotopes are usually detected in Faraday-cups and radionuclides in ionization chambers. Such a set-up of two mass spectrometers in one, namely the first with negative ions of keV-energy, the second with high-energy positive ions of MeV-energy, and combined with several magnetic and electrostatic analyzers, allows analyzing isotopic ratios as low as 10-16, thus, providing the ultimate detection limit of all mass spectrometry methods. Very recently, a new AMS facility has been installed at the Ion Beam Centre of the Helmholtz-Zentrum Dresden-Rossendorf: DREsden AMS (DREAMS) [1-3].

Probably in 2014, AMS will be also used for the detection of stable element ratios at DREAMS. The most common terms for this are Trace Element AMS (TEAMS, e.g. [4]) or if the Cs-beam is focused and spatial resolution kept, Accelerator-SIMS or Super-SIMS [5]. However, mainly due to the background e.g. from the ion source, detection limits are expected to be not as low as for “standard” AMS, but still some orders of magnitude better than is the case for traditional dynamic SIMS, i.e. around 10-9-10-12.

References: [1] S. Merchel et al., GIT Labor-Fachzeitschrift 2012, (2) 56, 88. [2] S. Akhmadaliev et al., Nucl. Instr. Meth. B 2012, doi:10.1016/j.nimb.2012.01.053. [3] www.dresden-ams.de. [4] S. Merchel et al., Geochim. Cosmochim. Acta 2003, 67, 4949. [5] S. Matteson, Mass Spectrom. Rev. 2008, 27, 470.
Keywords: AMS, Super-SIMS, TEAMS
  • Lecture (Conference)
    ANAKON 2013, 04.-07.03.2013, Essen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17945
Publ.-Id: 17945


[68Ga]NS3-RGD and [68Ga] Oxo-DO3A-RGD for imaging αvβ3 integrin expression: synthesis, evaluation, and comparison

Knetsch, P. A.; Petrik, M.; Rangger, C.; Seidel, G.; Pietzsch, H.-J.; Virgolini, I.; Decristoforo, C.; Haubner, R.
Introduction:
68Ga-labeled RGD peptides in combination with PET allow non-invasive determination of αvβ3integrin expression which is highly increased during tumor-induced angiogenesis. The aim of this study was to synthesize and evaluate two RGD peptides containing alternative chelating systems, namely [68Ga]NS3-RGD and [68Ga]Oxo-DO3A-RGD and to compare their in vitro and in vivo properties with [68Ga]DOTA- and [68Ga]NODAGA-RGD.

Methods:
Syntheses of both radiotracers followed standard SPPS protocols. For in vitro characterization distribution coefficients, protein binding abilities, serum stabilities, and αvβ3 integrin binding affinities were determined. For in vitro tests as well as for the biodistribution assay αvβ3 positive human melanoma M21 and αvβ3 negative M21-L cells were used.

Results:
68Ga-labeling of NS3-RGD resulted in good radiochemical purity, whereas HPLC analysis showed two peaks with a ratio of 1:6 for [68Ga]Oxo-DO3A-RGD. Distribution coefficients were −3.4 for [68Ga]Oxo-DO3ARGD and −2.9 for [68Ga]NS3-RGD. Both radiotracers were stable in PBS solution at 37°C for 2h but lack stability in human serum. Protein binding was approximately 40% of the total activity for [68Ga]NS3-RGD and 70% for [68Ga]Oxo-DO3A-RGD, respectively, resulting in high blood pool activities. Biodistribution assays confirmed these findings and showed an additional high uptake in liver and kidneys, especially for [68Ga]NS3-RGD. Furthermore, [68Ga]Oxo-DO3A-RGD showed nearly the same activity concentrations in αvβ3 positive and αvβ3 negative tumors.

Conclusions:
[68Ga]Oxo-DO3A-RGD and [68Ga]NS3-RGD have inferior characteristics compared to already existing 68Ga-labeled RGD peptides and thus, both are not suited to image αvβ3 integrin expression. Of all our tested RGD peptides, [68Ga]NODAGA-RGD still possesses the most favorable imaging properties. Moreover this study shows that the use of appropriate chelators to achieve good targeting properties of 68Ga-labeled biomolecules and careful in vitro and in vivo evaluation including comparative studies of different strategies are essential components in designing an effective imaging agent for PET.
Keywords: 68Ga, RGD, αvβ3, Molecular imaging, Angiogenesis

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Publ.-Id: 17943


Target water for F-18 production: Recover – Renew – Reuse

Rötering, S.; Franke, K.; Brust, P.; Fischer, S.; Steinbach, J.
Ziel
Proton irradiation of H2[O-18]O-water is a standard method for F-18 production. Due to the limited availability of O-18 water and increasing costs, its re-use for research purposes gets more and more important. We present two purification methods for the removal of organic contaminants from used target water. The recycled target water is characterized by production yields, radionuclide purity and the use in radiosyntheses.
Methodik
Oxidation of the organic contaminants in the target water was tested with photo-oxidation (254 nm) [1] and a chemical method using KMnO4 as oxidation agent validated by gas chromatography, ICP-OES and pycnometry. Target irradiations were done at similar beam parameters (11.7 DAh) at a CYCLONE 18/9 (IBA, target: 2 mL). Radionuclide purity and yield were determined by a well counter (MED) and gamma spectrometry (ORTEC). Produced F-18 was used in nucleophilic substitution reactions.
Ergebnisse
Both purification methods allow a comparable decrease of organic contaminants from 400 ppm ethanol and 44 ppm acetone to 10 ppm-50 ppm ethanol. The parameters (amount of oxidation agent, temperature, treatment time) for the purification methods were established, allowing comparable irradiation and radiosyntheses as for the original target water. We observed a loss of the production yield (19 %) due to a lower O-18 concentration but no significant influence on the radionuclide purity or radiochemistry.
Schlussfolgerungen
Both methods enable a multiple cycling of target water for the successful production and application of F-18 for research purposes, whereas photo-oxidation is faster. However, the required amount of F-18 limits the cycling process.
For 83 % O-18 enrichment in H2[O-18]O water after one cycle starting from 87 % we achieved reasonable production yields which allow an efficient economical usage of the target water, including the minimization of the target water contamination in the re-collection process.
Literatur
1. Gebrauchsmuster DE 29504388 U1, Forschungszentrum Jülich GmbH, 1995
  • Lecture (Conference)
    NuklearMedizin 2013, 17.-20.04.2013, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 2(2013)52, V29

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Untersuchungen zur Entwicklung eines PET-Tracers für die Phosphodiesterase 10A

Wagner, S.; Scheunemann, M.; Egerland, U.; Fischer, S.; Hoefgen, N.; Brust, P.
Ziel:
Phosphodiesterase 10A (PDE10A) ist ein Schlüsselenzym in der zellulären Signaltransduktion. PDE10A wird hauptsächlich im Striatum exprimiert und spielt vermutlich eine Rolle bei neurologischen Erkrankungen verknüpft mit striataler Hypofunktion wie Schizophrenie. Molekulare Bildgebung mittels PET würde die In-vivo-Untersuchung neurologischer und pathologischer Prozesse in Zusammenhang mit PDE10A und ihrer Expression erlauben. Neuentwickelte Imidazo[1,5-a]chinoxaline zählen als Wirkstoffkandidaten zu einer Gruppe hochpotenter und selektiver PDE10A Inhibitoren (1). Der tricyclische Heterocyclus dient als Leitstruktur für unsere Arbeiten zur Entwicklung eines F-18 markierten Tracers für eine zukünftige PET-Bildgebung der PDE10A.
Methodik:
Zur Darstellung einer Referenzverbindung auf Basis dieser Inhibitoren sollte ein 2-Fluorpyridinbaustein in Position 1 des Imidazo[1,5-a]chinoxalins eingeführt werden. Die 2-Fluorposition, benachbart zum Stickstoff, erlaubt die nukleophile Einführung eines F-18 mit hoher spezifischer Aktivität in der späteren Radiosynthese. Reinheit und Identität der Referenzverbindung wurden mittels NMR, MS und HPLC bestimmt. Die inhibitorische Wirksamkeit auf menschlich rekombinante PDE10A wird zurzeit in Enzym-Assays untersucht.
Ergebnisse:
Der benötigte, bromierte Imidazo[1,5-a]chinoxalinbaustein konnte ausgehend von einem 2,4,6-trisubstituierten Anilin erfolgreich hergestellt werden. In einem konvergenten Syntheseschritt wurde am Ende der Synthesesequenz durch eine Palladium-katalysierte Suzuki-Kupplung ein 2-Fluorpyridinrest eingebaut. Somit konnte eine erste Referenzverbindung erhalten werden.
Schlussfolgerung:
Ein erstes 2-Fluorpyridinderivat konnte als PDE10A Inhibitorkanditat erfolgreich synthetisiert werden. Folglich ermöglicht die Suzuki-Kupplung den Einbau von 2-Fluorpyridinresten und bietet dadurch einen schnellen Zugang zu strukturell divergenten Inhibitoren und möglichen Präkursoren für die spätere Radiosynthese.
Literatur:
(1) Malamas et. al. J. Med. Chem. 2011,54, 7621-7638
  • Poster
    NuklearMedizin2013, 17.-20.04.2013, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 2(2013)52, P24

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Permalink: https://www.hzdr.de/publications/Publ-17941
Publ.-Id: 17941


Y-Ti-O Nanocluster Formation in Bcc Fe Using Dft and Kinetic Monte Carlo Simulations

Murali, D.; Kaur, G.; Jegadeesan, P.; Panigrahi, B. K.; Valsakumar, M. C.; Posselt, M.
Oxide Dispersion Strengthened (ODS) steels are candidate materials for use in nuclear environment as they offer excellent swelling resistance characteristics and enhanced high temperature mechanical properties. ODS steels derive their strength from the dispersion of oxide (Y-Ti-O) nanoclusters in the ferritic matrix. The mechanism of formation, structure, thermal & radiation stability and composition of these nanoclusters are not yet fully understood. We are studying the basic energetic and kinetic properties of solutes and their clusters along with vacancy in bcc Fe using density functional theory and evolution of these nanoclusters using kinetic Monte Carlo simulations. The diffusion coefficients of these solute atoms in bcc Fe have been calculated using Le Claire's nine frequency model. Among these, Y is believed to be rate limiting for the growth of nanoclusters and our calculated diffusion coefficient is found to be three orders of magnitude higher than the experimental one [J. Nucl. Mater. 419, 208 (2011)]. In order to further understand the diffusion behavior of Y in bcc Fe and hence its role in the kinetics of nanocluster formation, we review the Le Claire's diffusion model both in dilute and concentrated limits. Also, in continuation of our previous study of solute atom interaction with vacancy, we discuss our recent results of DFT calculations of solute atom interactions with self-interstitials.
Keywords: ODS, DFT, KMC
  • Lecture (Conference)
    Multiscale Materials Modeling (MMM) 2012, 15.-19.10.2012, Singapore, Singapore

Permalink: https://www.hzdr.de/publications/Publ-17940
Publ.-Id: 17940


On the Role of Cation Interactions in the Reduction Process in Plutonium-Americium Mixed Oxides

Belin, R. C.; Martin, P. M.; Lechelle, J.; Reynaud, M.; Scheinost, A. C.
The oxygen to metal ratio (O/M) is directly related to oxygen potential, which strongly influences the sintering and irradiation performance of nuclear fuels. A better understanding of these two parameters is therefore of major interest. To further ascertain the correlation between O/M ratio and oxygen potential in Am-bearing MOX, several ther-modynamic descriptions are being developed. Despite their differences, they all involve the valence of actinide cations (e.g. U, Pu and Am) as essential parameters. However, as no experimental data on their valence is available, these models rely on assumptions. In the present work, we coupled X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) to follow the behaviour of Pu and Am in three hypo-stoichiometric, U-free Pu1-yAmyO2-x compounds. We provide for the first time a quantitative determination of Pu and Am valences, demonstrating that plutonium reduction from Pu4+ to Pu3+ starts only, once americium reduction from Am4+ to Am3+ is completed. This result fills in an important gap in experimental data, thereby improving the thermodynamic description of nuclear fuels. At last, we suggest that the O/M ratio may still evolve at room temperature for high Am content, which is of main concern for the fabrication of Am-loaded MOX and their storage prior to irradiation.
Keywords: plutonium americium XAFS

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Permalink: https://www.hzdr.de/publications/Publ-17939
Publ.-Id: 17939


Homogeneity testing of natural candidate reference materials for resource technology by three spatially-resolved X-ray methods

Michalak, P. P.; Renno, A. D.; Merchel, S.; Munnik, F.
Quality assurance of natural raw materials (e.g. ores) requires thorough studies on concentration and distribution patterns of technologically relevant trace elements within the mineral matrix at the microscale. Obtaining such a goal is yet only possible with the use of X-ray-based microanalytical methods and a proper set of homogeneous reference materials (RMs).
Three minerals of natural origin: pyrite (FeS2), columbite (FeNb2O6) and sanidine ((K,Na)(Si,Al)4O8) – candidates for RMs for resource technology – have been investigated for their spatial chemical microhomogeneity using three X-ray methods:
• Electron Probe Micro Analysis (EPMA)
• Particle Induced X-ray Emission (PIXE)
• Synchrotron radiation-induced micro-X-ray Fluorescence (Sy-µXRF).

Quantitative (EPMA, PIXE) and qualitative (Sy-µXRF) elemental spatial distribution maps have been obtained for major and trace elements for each mineral. Several trace elements were detected in each of the matrices above the limit of detection (LOD).

EPMA III PIXE III Sy-µXRF
Beam size 2 µm Ø III 3 x 3 µm2 III 5 x 5 µm2
Mapping area 100 µm x 100 µm
Elements-
Pyrite S, Mn, Fe, Co, Ni, Cu, As, Se, Au III Fe, Ni, Cu, As III S, Fe, Ni, Cu, As
LOD range 20 - 350 µg/g III 9 - 28 µg/g III qualitative
Elements-
Sanidine Al, Si, K, Ca, Fe, Ba III K, Ca, Fe, Ga, Ge, Rb, Sr, Ba III Al, Si, K, Ca, Fe, Ga, Ge, Rb, Sr, Ba, Pb
LOD range 90 - 450 µg/g III 1 - 517 µg/g III qualitative
Elements-
Columbite Mg, Al, Ca, Sc, Ti, Mn, Fe, Zr, Nb, Hf, Ta III Ca, Sc, Ti, Mn, Fe, Zr, Nb, Ta, W, U III Sc, Ti, Mn, Fe, Y, Zr, Nb, Ta, W, Th, U
LOD range 40 - 810 µg/g III 24 - 940 µg/g III qualitative

Although all three non-destructive methods are based on X-ray detection, they provide complementary information on chemical composition and microhomogeneity of the tested minerals’ matrices as detection and excitation conditions influencing especially the spectra background and, thus, the LODs.

Most of the elements showed inhomogeneous distribution at the level of 1-3 µm, proving that the selected mineral specimens are not suitable as candidates for RMs. Consequently, artificial minerals are being synthesized and will be investigated by the validated set of X-ray analytical methods to proof their suitability as micro-RMs.
Keywords: reference materials, XRF, PIXE, EPMA
  • Poster
    ANAKON 2013, 04.-07.03.2013, Essen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17938
Publ.-Id: 17938


Quantitative comparison of Taylor Flow simulations based on sharp- and diffuse-interface models

Aland, S.; Boden, S.; Hahn, A.; Klingbeil, F.; Weissmann, M.; Weller, S.
A pressure driven flow of elongated bullet-shaped bubbles in a narrow channel is known as Taylor flow or bubble-train flow. This process is of relevance in various applications of chemical engineering.
In this paper, we describe a typical simplified experimental setting, with surface tension, density and viscosity as prescribed input parameters. We compare a sharp interface model based on a moving grid aligned with the bubble boundary (ALE coordinates) and a diffuse interface model where the bubble shape is implicitly given by a phase-field function.
Four independent implementations based on the two modeling approaches are introduced and described briefly. Besides the simulation of the bubble shapes, we compare some resulting quantities such as pressure difference and film widths within the implementations and to existing analytical and experimental results. The simulations were conducted in 2D and 3D (rotationally symmetric).
Good accordance of the results indicate the applicability and usability of all approaches. Differences between the models and their implementations are visible but in no contradiction to theoretical results.
Keywords: Free surface flow; Multiphase flow; Finite Element Method; Taylor bubbles; Arbitrary Lagrangian Eulerian method; Phase field
  • International Journal for Numerical Methods in Fluids 73(2013)4, 344-361
    DOI: 10.1002/fld.3802

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Permalink: https://www.hzdr.de/publications/Publ-17937
Publ.-Id: 17937


Actinide Computational Study at HZDR: Overview and Outlook

Tsushima, S.
no abstract for this lecture
  • Lecture (Conference)
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-17936
Publ.-Id: 17936


Bakterien sind Bergarbeiter

Raff, J.
Bakterien sind zwar sehr klein, aber ihre Rolle für verschiedene Stoffkreisläufe in der Natur und damit für das Leben auf unserem Planeten ist elementar. Darüber hinaus verfügen sie noch über viele weitere sehr bemerkenswerte Fähigkeiten, die man sich in technischen Prozessen zunutze machen kann. So haben Bakterien verschiedene Entgiftungsstrategien entwickelt, die ihnen zum Beispiel ein Überleben in einer stark metallhaltigen, also eher lebensfeindlichen Umgebung ermöglichen. Die zugrunde liegenden Prozesse lassen sich für die (Rück-) Gewinnung von Spurenmetallen und damit zur Sicherung von Rohstoffen für die Industrie nutzen. Der Vortrag gibt einen Überblick über die Leistungen von Bakterien und stellt dazu aktuelle und geplante Forschungsprojekte am Helmholtz-Institut Freiberg für Ressourcentechnologie vor.
Keywords: Biomining
  • Lecture (others)
    Nacht der Wissenschaft, 08.06.2012, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17935
Publ.-Id: 17935


Abgeschaut aus der Natur: Biobasierte Nanoverbundmaterialien für die Wasserbehandlung

Raff, J.
Bakterielle S-Layer lassen sich aufgrund ihrer strukturellen und biochemsichen Eigenschaften vorteilhaft als Template zur Herstellung hochreaktiver nanostrukturierter Beschichtungen für sehr unterschiedliche technische Anwendungen nutzen. Gerade auch in der Wasserpraxis ergeben sich für derartige Biokompositmaterialien zahlreiche Anwendungen. Aufbauend auf den natürlichen Funktionen bakterieller S-Layer werden am Helmholtz-Zentrum Dresden-Rossendorf verschiedenen S-Layer basierte Materialien entwickelt. Im Fokus stehen gegenwärtig Materialien zur metallselektiven Bindung gelöster Metalle zur Entfernung von Schadstoffen oder zur Rückgewinnugn von Wertstoffen wie auch Materialien zur Detektion und dem Abbau organischer Schadstoffen in Wasser.
Keywords: S-layer, nanotechnology, filter, sensor, catalyst, water treatment
  • Invited lecture (Conferences)
    nANO meets water IV, 08.11.2012, Oberhausen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17934
Publ.-Id: 17934


Importance of configurational contributions to the free energy of nanoclusters

Posselt, M.
An effective simulation method based on the Wang-Landau Monte Carlo algorithm is used in order to demonstrate the significance of the configurational contributions to the free energy of embedded nanoclusters. Starting from the most stable cluster configuration the simulation provides all geometrically different, but simply connected and sufficiently compact configurations of a nanocluster of a given size and the respective formation energies. The knowledge of these data allows the calculation of the free formation and free binding energy of the cluster at . The method is applied to coherent Cu clusters in bcc-Fe. It is shown that even at moderate temperatures the configurational contributions to the free formation and binding energy must not be neglected. The dependence of the monomer free binding energy on clusters size is found to change significantly with increasing temperature which has a considerable effect on the pathway of cluster evolution. Therefore, present investigations provide an essential contribution to the improvement of the input parameters for object kinetic Monte Carlo simulations and rate theory used in multi-scale simulations of the nanostructure evolution. The calculation scheme developed in this work is rather general and applicable to many types of embedded nanoclusters. Compared to the method of overlapping distributions hitherto used in some cases to determine the configurational part of the free energy the new method has major advantages. Various tests are performed in order verify the presented approach and to compare with the results of the other calculation procedure. A roadmap is proposed to include the vibrational contributions to the free energy of the clusters within the framework of the method employed in this work.
Keywords: free energy, nanoclusters, Metropolis Monte Carlo simulations, Wang-Landau Monte Carlo simulations

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Permalink: https://www.hzdr.de/publications/Publ-17933
Publ.-Id: 17933


Control over Janus micromotors by the strength of a magnetic field

Baraban, L.; Makarov, D.; Schmidt, O.; Cuniberti, G.; Leiderer, P.; Erbe, A.
For transportation of molecules or biological cells using artificial motors, the control over their motion, i.e. direction and speed of transfer, is important. Here, we demonstrate that modification of the velocity and orientation of a magnetic Janus particle can be efficiently controlled by tuning the strength of an applied magnetic field. Interestingly, by keeping the same orientation of the magnetic field but changing its magnitude not only velocity of capped particles can be altered but even their direction of motion can be reversed.
Keywords: microparticles, colloidal model systems, micro engines

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Permalink: https://www.hzdr.de/publications/Publ-17932
Publ.-Id: 17932


Contacting metallic nanoparticles on transparent substrates

Erbe, A.; Wiesenhütter, U.; Grebing, J.; Fassbender, J.ORC
We demonstrate reliable contacting of single nanoparticles in metallic junctions. The junctions are prepared using electron beam lithography and investigated by means of transmission electron microscopy and electrical transport measurements. The size, shape and crystalline structure of the particles can be clearly identified in our junctions. These properties are then related to low temperature measurements of the conductance of these devices. Due to the weak coupling of the metallic electrodes to the particles, Coulomb Blockade effects are found in these junctions.
Keywords: Nanoparticles, single electron transistor, transmission electron microscopy

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Permalink: https://www.hzdr.de/publications/Publ-17931
Publ.-Id: 17931


Atomic-level simulations of materials properties and processes

Posselt, M.; Kunze, T.; Al-Motasem, A.
Computer simulations using classical interatomic potentials are an efficient tool to study and understand materials properties and to investigate processes of materials modification on the atomic level. In this manner length and time scales can be considered which are often hardly accessible by experiments. In the talk two applications of atomistic simulations are discussed. The focus is on nanoclusters in structural materials for nuclear fission reactors as well as on friction and wear of nanocoatings.
Subjects of the first example are structure, energetics and thermodynamics of coherent nanoclusters in bcc-Fe containing vacancies, Cu and Ni. These precipitates are formed during neutron irradiation of reactor pressure vessel steel and can cause hardening and embrittlement. For clusters up to a size of 200 monomers (i.e. vacancies, Cu or Ni atoms) the most stable configurations at T=0 and the related formation and binding energies are determined by simulated annealing combined with Metropolis Monte Carlo simulations on a rigid lattice and subsequent off-lattice relaxation. In the case of Cu clusters the temperature-dependent free formation and free binding energies are calculated by the Wang-Landau Monte Carlo method using a rigid lattice model.
The second example concerns the study of basic processes of friction and wear in hydrogen-free tetrahedrally coordinated (or diamond-like) amorphous carbon (ta-C) films. These nanocoatings have a great potential to improve the surface properties of materials and components used in car production. First, the structure and the properties of the films determined by the simulations are compared with experimental data. Second, the atomic-level processes occuring during the friction between two ta-C interfaces are discussed. Particular attention is paid to the formation of the tribolayer and to triboreactions.
Keywords: Atomic-level simulations, materials properties, processes in materials
  • Lecture (others)
    Talk at Department of Physics, Beihang University, 22.10.2012, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-17930
Publ.-Id: 17930


Free energy of embedded nanoclusters: Role of the configurational contributions

Posselt, M.
Diffusion and reaction processes during thermal treatment or particle irradiation can cause the formation of nanoclusters embedded in the host material. This modification often leads to the change of materials properties. Coarse-grained methods such as object kinetic Monte Carlo simulations and rate theory are well suited to simulate the nanocluster evolution on time and length scales easily accessible by experiments. However, these methods need a number of input parameters. One of the most important is the free binding energy of a monomer to a cluster which can be hardly obtained by measurements but can be provided by atomistic simulations. This quantity is calculated using the free formation energy of the clusters which consists not only of the formation energy but also of vibrational and configurational contributions. The present work is focused on the evaluation of the configurational part of the free formation energy. As characteristic examples coherent nanoclusters in bcc-Fe containing Cu and Ni are considered. First-principle data from literature are used to describe the interactions between the atoms. In a first step the most stable cluster configurations at T=0 are determined by Metropolis Monte Carlo simulations and their formation and binding energies are calculated. Second, a modified Wang-Landau Monte Carlo method is employed in order to determine the contribution of all possible geometrical configurations of nanoclusters to the free formation energy. Finally, the total and monomer free binding energies are calculated. It is shown that the configurational contributions to the free energy cannot be neglected if the cluster formation energy is relatively low. The calculation scheme applied in this work can be extended to other types of embedded nanoclusters in solids. Further investigations are required in order to estimate the vibrational contribution to the free energy and to perform a comparison with the configurational part.
Keywords: nanoclusters, free energy, Metropolis Monte Carlo simulations, Wang-Landau Monte Carlo simulations, Cu clusters in bcc-Fe
  • Lecture (Conference)
    MMM 2012 - 6th International Conference on Multiscale Materials Modeling, 15.-19.10.2012, Singapore, Singapore

Permalink: https://www.hzdr.de/publications/Publ-17929
Publ.-Id: 17929


Long-term, on-site borehole monitoring of gases released from an “active” fault system at 3.6km depth, TauTona Gold Mine, South Africa

Lippmann-Pipke, J.; Erzinger, J.; Zimmer, M.; Kujawa, C.; Boettcher, M. S.; van Heerden, E.; Bester, A.; Cason, E.; Reches, Z.
Fluid transport and seismicity are interrelated. Fluids can trigger earthquakes and seismic activity can release fluids from rock formations. The study of this relationship requires direct and near-field observations at focal depth. The international DAFSAM-NELSAM*-projects focus on building the earthquake laboratory in deep gold mines in South Africa. Our DAFGAS-project (Drilling Active Faults - Gas Analytical System) aims to quantify the gases released during seismic events.
One motivation for the project is to investigate the hypothesis that released fluids might be a nutrient supply for microbial ecosystems in active fault zones. Extensive underground activities started in 2004 with establishing a 25 m2 cubby within the Pretorius fault zone at 3.6 km depth for the save installation of comprehensive technical equipment.
For DAFGAS, subsequently two different gas analytical units were installed to measure gases collected in a 40m long borehole crossing the fault. The DAFGAS Team and our collaborators overcame numerous technical problems. Since 2007 a dedicated air-conditioned box protects a mass spectrometer, pumps, a PC, a radon detector and electronics from the harsh underground environment. Since 2009 gas sensitive sensors and a data logger replace the spectrometer and the PC.
In parallel the NELSAM project has installed 9 seismometers in a narrow network surrounding the gas collection system. The accelerometers and geophones record mining activities (e.g. drilling and ore-production blasts) as well as tens of mining-induced earthquakes (magnitude = -4) on and around the Pretorius Fault each day.
Data from three years is presented: Borehole temperature at 40m increased by about 0.8 °C/year to 52.3 °C; different scales of pressure variations on surface (869±5) mbar (three-week mean, maximal and minimal daily mean) and below surface (1130±15) mbar are explained by the barometric formula. The major gas concentrations are constant and air-like with 78 % N2, 21 % O2, 1 % Ar, while the trace gas components CO2, CH4, He and H2 show most interesting trends and variations on weekly, daily, hourly and on the minute-by-minute basis. They are interpreted by means of time series and cross correlation analysis. He, CH4, CO2 and H2 fluxes positively correlate with mining induced seismic activity. The CO2 flux additionally correlates with air pressure. Gas flow rates of H2 and CO2 from the formation into the borehole are calculated for periods with and without mining activity. In passive times they amount to =(1 and 3)*10-7 mol/min and increase to (7.3±0.7)*10-7 and (4.5±0.6)*10-6 mol/min during times of mining induced seismic activity, respectively. The installed gas sensitive electrodes (O2, CO2, CH4 and H2) are clearly more suitable for the underground environment than the mass spectrometer. Their sensitivity is currently only sufficient for H2 and CO2 measurements, however.
*) Drilling Active Faults Laboratory in South African Mines - Natural Earthquake Laboratory in South African Mines
  • Lecture (Conference)
    GeoFuture Workshop, 28.-29.11.2012, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17928
Publ.-Id: 17928


Mikrobielle Diversität im Tongestein (Opalinus-Ton) und Wechselwirkung dominanter Mikroorganismen mit Actiniden – Vorhaben BMWi 0210618

Moll, H.; Lütke, L.; Bachvarova, V.; Geissler, A.; Krawczyk-Bärsch, E.; Selenska-Pobell, S.; Bernhard, G.
Microorganisms exist in host rocks of potential nuclear waste disposals. In this talk, results will be presented from the current project about the microbial diversity in Mont Terri Opalinus clay and the interactions of dominant microorganisms with actinides. Especially the bacterial diversity investigations and the actinide (U, Cm, Pu) interactions with the novel Opalinus clay isolate Sporomusa sp. will be shown and discussed.
Keywords: curium, uranium, plutonium, TRLFS, bacteria, speciation
  • Lecture (others)
    10. Projektstatusgespräch zu BMWi- und BMBF-geförderten FuE-Projekten der Endlagerforschung und der Nuklearen Sicherheitsforschung, 13.-14.11.2012, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17927
Publ.-Id: 17927


Irradiation system for pre-clinical studies with laser accelerated electrons

Schürer, M.; Baumann, M.; Beyreuther, E.; Brüchner, K.; Enghardt, W.; Kaluza, M.; Karsch, L.; Laschinksy, L.; Lessmann, E.; Nicolai, M.; Oppelt, M.; Reuter, M.; Richter, C.; Sävert, A.; Schnell, M.; Woithe, J.; Pawelke, J.
In recent years, the new technology of laser based particle acceleration was developed at such a rate that medical application for cancer therapy could become feasible. Promising more compact and economic proton and ion accelerators the laser technology however results in specific properties, like ultra-short (~ps) and ultra-intensive particle beam pulses. The clinical applicability of such new beam qualities requires comprehensive translational research from basic investigations to cell and animal experiments, finally followed by clinical trials. For the first time, the new laser based irradiation technology was established for animal experiments by the German joint research project “onCOOPtics”. A complete irradiation facility for laser accelerated electrons was developed, set up, commissioned, tested and applied for radiobiological tumour irradiation experiments under usage of a mouse model at the high intensity laser system JETI. The integration of a magnet and a collimator system resulted in an optimized beam transport and efficient electron energy filtration. Moreover, a specific irradiation and dosimetry setup was integrated allowing for the formation of irradiation fields, the real-time control of beam parameters and dose delivery to the tumour. For an accurate and reproducible positioning of the tumour in the irradiation field the mice were fixed in a movable box and the tumour position was online verified by means of a CCD camera system. The combination of both, the advanced laser accelerator system and the newly implemented irradiation and dosimetry setup allowed the successful performance of systematic radiobiological studies over months. Moreover, the practicability and easy handling of the system results in a reasonable duration of about 15 min for the whole procedure of mouse preparation, positioning and irradiation. In conclusion, the successful establishment of all technical requirements for and the performance of systematic animal studies with laser accelerated electrons mark an important step towards the clinical application of laser accelerated particle beams.
  • Biomedical Engineering / Biomedizinische Technik 57(2012), 62-65
    DOI: 10.1515/bmt-2012-4244
  • Lecture (Conference)
    BMT 2012 - Tagung der Biomedizinischen Technik in Jena, 16.-19.09.2012, Jena, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-17926
Publ.-Id: 17926


Hydrolysis of Tetravalent Cerium for a Simple Route to Nanocrystalline Cerium Dioxide: An In Situ Spectroscopic Study of Nanocrystal Evolution

Ikeda-Ohno, A.; Hennig, C.; Weiss, S.; Yaita, T.; Bernhard, G.
Despite the rapid developments in recent nanocrystal research and their expanding applications, the evolution mechanism of nanocrystals remains veiled for the most part due to the lack of appropriate analytical techniques. Here we demonstrate one promising multi-spectroscopic approach for the in situ investigation of nanocrystal evolution. That is, the formation of nanocrystalline cerium dioxide (NC-CeO2) has been probed by dynamic light scattering (DLS), X-ray absorption spectroscopy (XAS) and highenergy X-ray scattering (HEXS). The obtained results indicate that the fine colloidal particles of NC-CeO2 are formed in an acidic aqueous solution simply through the hydrolysis of the initial precursor of small oligomer CeIV species. This information on how NCCeO2 evolves is fundamental to simplifying and alleviating the synthetic strategy for NC-CeO2 production.
Keywords: cerium · hydrolysis ·lanthanides · nanomaterials · X-ray spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-17925
Publ.-Id: 17925


Characterization of a solid Eu-borate species by TRLFS

Schott, J.; Acker, M.; Barkleit, A.; Taut, S.; Brendler, V.
Concerning the safety and risk assessment for a nuclear waste repository the interaction between trivalent lanthanides and actinides and borates is interesting to study. Borates occur in salt deposits (possible host rock for nuclear waste repositories) and can be release due to corrosion of vitrified waste block (borosilicate glass) and storage containers. The investigations concentrate on the reaction between Eu(III) and borates in aqueous solution.
At pH 6 the formation of a Eu borate solid species in presence of polyborates is observed. The formation of the solid Eu borate species depends on the polyborate concentration and ionic strength.
Keywords: lanthanides, actinides, europium, boric acid, borates, polyborates
  • Lecture (Conference)
    BMWi-Verbundprojekttreffen „Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen„, 29.-30.10.2012, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17924
Publ.-Id: 17924


Flüssigmetallbatterien als preiswerte stationäre Speicher - Strömungsmechanische Aspekte

Weier, T.; Stefani, F.; Seilmayer, M.; Weber, N.; Gundrum, T.; Gerbeth, G.
Flüssigmetallbatterien, d.h. elektrochemische Hochtemperaturbatterien mit vollständig flüssigem Inventar, werden derzeit als preiswerte Regelenergiespeicher diskutiert. Das ursprünglich auf kleinere Zellen als Bestandteil thermisch regenerierbarer Systeme gerichtete Konzept soll auf Zellen mit Grundflächen im Quadratmeterbereich übertragen werden.

Eine elektrochemische Zelle mit vollständig flüssigem Inventar hat eine Reihe von Vorteilen: bei gut abgestimmten Dichten von Elektrolyt und aktiven Materialien ist die Batterie selbstassemblierend, eine stabile Dichteschichtung bildet sich aus. Die strukturlosen (flüssigen) Elektroden sind für Alterungserscheinungen unanfällig, versprechen somit gute Zyklierbarkeit, die Kinetik an den flüssig-flüssig Phasengrenzen und die Diffusionsprozesse sind vergleichsweise schnell, was hohe Stromdichten ermöglicht. Als aktive Materialien können breit und ökonomisch verfügbare Ausgangsstoffe eingesetzt werden. Natrium-Schwefel und Natrium-Nickelchlorid Zellen teilen eine Reihe der obengenannten Vorteile, erfordern wegen der komplexen Konstruktion jedoch ein beträchtliches Investitionsvolumen. Die Ausnutzung positiver Skaleneffekte ist ein wichtiges Mittel zur Kostensenkung und die einfache Skalierbarkeit eine der grundlegenden Annahmen bei der Entwicklung von Flüssigmetallbatterien.

Hohe Stromdichten und große Phasengrenzflächen resultieren jedoch in erheblichen Zellströmen. Diese generieren Magnetfelder und mithin beträchtliche elektromagnetische Kräfte. Das flüssige Inventar der Zelle kann auf diese elektromagnetischen Einwirkungen mit Instabilitäten reagieren. Eine dieser Instabilitäten ist die Tayler-Instabilität. Sie führt zu einer starken Strömung im Zellvolumen, die in der Lage ist, die Dichteschichtung zu destabilisieren. In der Folge käme es zu einem Direktkontakt der Elektroden und einem Versagen der Zelle. Der Tayler-Instabilität lässt sich durch konstruktive Maßnahmen begegnen, die in der Lage sind, die gewünschte Skalierbarkeit zu gewährleisten. Sie werden im Vortrag diskutiert.
Keywords: liquid metal batteries, energy storage, Tayler instability
  • Lecture (Conference)
    Sächsisches Forum für Brennstoffzellen und Energiespeicher, 23.10.2012, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17923
Publ.-Id: 17923


OECD PKL2 Project – Final Report on the ROCOM Tests

Kliem, S.; Franz, R.
In the frame of the OECD PKL 2 Project the Test G3.1 was conducted at the PKL test facility. This test was dedicated to the investigation of a fast cool down transient. The transient was initiated by a main steam line break. One of the main objectives of this test was the creation of an experimental data base for the qualification of thermal hydraulic codes against Pressurized Thermal Shock (PTS) and re-criticality aspects. The results of this test are documented in (Dennhardt, 2011). Roughly this test can be divided into two main phases. After opening of the leak on the secondary side of one steam generator, the increased heat transfer leads to an overcooling of the corresponding loop. This overcooling continues till the full evaporation of the steam generator. In the second phase of the transient the emergency core cooling (ECC) system is activated injecting highly borated cold water into the cold legs of two loops.
To investigate in more detail the thermal hydraulic behavior in both phases inside the reactor pressure vessel (RPV) complementary tests on the coolant mixing were conducted at the ROCOM (ROssendorf COolant Mixing) test facility. Experimental results at the RPV inlet derived from the Test G3.1 were used as boundary conditions for the ROCOM tests.
Altogether five ROCOM tests have been conducted within the OECD PKL2 Project. The tests ROCOM 1.1, 2.1 and 2.2 were dedicated to the overcooling phase of the related transient while the tests ROCOM 1.2 and 1.3 are dealing with the ECC injection phase of the transient.
  • Article, self-published (no contribution to HZDR-Annual report)
    Helmholtz-Zentrum Rossendorf 2012
    HZDR\FWO\2012\03
    0086 Seiten

Permalink: https://www.hzdr.de/publications/Publ-17921
Publ.-Id: 17921


Entwicklung einer Version des Reaktordynamikcodes DYN3D für Hochtemperaturreaktoren

Rohde, U.; Apanasevich, P.; Baier, S.; Duerigen, S.; Fridman, E.; Grahn, A.; Kliem, S.; Merk, B.
Basierend auf dem Reaktordynamikcode DYN3D für LWR, wurde die Codeversion DYN3D-HTR für das Blockkonzept eines graphit-moderierten, helium-gekühlten Hochtemperaturreaktors entwickelt. Diese Entwicklung umfasst die:
• methodische Weiterentwicklung der 3D stationären Neutronenflussberechnung für hexagonale Geometrie (HTR-Brennelement-Blöcke),
• Generierung von Wirkungsquerschnittsdaten unter Berücksichtigung der doppelten Heterogenität,
• Modellierung der Wärmeleitung und des Wärmetransports in der Graphitmatrix.
Die nodale SP3-Neutronentransport-Methode in DYN3D wurde auf hexagonale Brennelementgeometrie erweitert. Es wird eine Unterteilung der Hexagone in Dreiecke vorgenommen, so dass die Verfeinerung hexagonaler Strukturen untersucht werden kann. Die Verifikation erfolgte durch Vergleiche mit Monte-Carlo-Referenzlösungen. Für die Behandlung der doppelten Heterogenität der Brennelementstruktur bei Homogenisierung der Wirkungsquerschnitte wurden neue Methoden entwickelt. Zum einen wurde ein zweistufiges Homogenisierungsverfahren basierend auf der Methode der sog. Reactivity Equivalent Transformation (RPT) weiterentwickelt. Zum anderen ermöglichte die Verfügbarkeit des neuen Monte-Carlo-Codes SERPENT die Anwendung eines einstufigen Verfahrens, wobei die 3D heterogenen Strukturen in einem Rechenschritt konsistent erfasst werden können. Weiterhin wur-de in DYN3D ein 3D Wärmeleitungsmodell implementiert, das den radialen und axialen Wärmetransport in der Graphitmatrix beschreiben kann. DYN3D-HTR wurde schließlich anhand der Testfälle für Reaktivitätstransienten erprobt. Die Verifikation erfolgte durch Vergleich zwischen 3D und 1D Berechnung der Wärmeleitung. Schließlich wurde DYN3D mit dem CFD-Code ANSYS-CFX gekoppelt, um auch dreidimensionale Strömungen in Reaktorkernen berechnen zu können. Der Kern wird als poröser Körper modelliert. Die Kopplung wurde an anhand von 2 Testbeispielen, dem Auswurf eines Steuerstabes und einer lokalen Strömungsblockade in einem Brennelement, erprobt.
Keywords: High temperature reactor, neutron transport, cross sections, heat conduction, CFD, transients
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-023 2012
    ISSN: 1437-322X

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Publ.-Id: 17920


Leitlinie für die Hirnperfusions-SPECT mit Tc-99m Radiopharmaka / Hirnperfusions-SPECT with 99mTc-labelled Radiopharmaceuticals DGN-Guidance (S1 Guideline)

Kranert, T.; Menzel, C.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Krause, B. J.; Kuwert, T.; Sabri, O.; Schreckenberger, M.; Tatsch, K.; Grünwald, F.
This paper describes the guideline for perfusion brain imaging with SPECT-technique published by the Association of the Scientific Medical Societies in Germany (AWMF).The purpose of this guideline is to provide practical assistance for indication, examination procedures, findings and their interpretation also reflecting the present state of the art.
Information and instruction are given regarding indication, preparation of the patients and examination procedures of brain perfusion SPECT, including preparation and quality control of the tracer as well as the radiation dosimetry, technical performance of image acquisition with the gamma-camera and image processing. Also advices for interpretation of findings are given. In addition, possible pitfalls are described.

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Publ.-Id: 17919


Experimental database on steam-water flow with phase transfer in a vertical pipe

Lucas, D.; Beyer, M.; Szalinski, L.
The evolution of steam-water flow with an initial sub-cooling along an 8 m long pipe with an inner diameter of about 200 mm was measured to obtain a database suitable for the qualification of CFD-codes on poly-dispersed flows with phase transfer. Phase transfer has to be considered in Nuclear Reactor Safety Research, e.g. in case of sub-cooled boiling or bubble entrainment caused by Emergency Core Cooling (ECC) injection. Bubble size distributions are important, since the phase transfer rate is proportional to the interfacial area density. To develop and validate closure models for CFD codes experimental data with high resolution in space and time are required. The experiments were conducted at the TOPFLOW facility of the Helmholtz-Zentrum Dresden-Rossendorf. Steam was injected into upwards flowing sub-cooled water via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Pressure, steam and water flow rates and the sub-cooling were also varied. Measurements are done using wire-mesh sensors and thermocouples. Data on averaged void fraction, radial gas volume fraction profiles, profiles of the gas velocity and bubble size distributions in dependency of the L/D ratio are available.
Keywords: two-phase flow, pipe flow, bubbles, experiment, phase transfer, condensation, CFD

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Special issue on quantum physics with non-Hermitian operators

Bender, C.; Fring, A.; Günther, U.; Jones, H.; (Editors)
The main motivation behind the call for this special issue was to gather recent results, developments and open problems in quantum physics with non-Hermitian operators. There have been previous special issues in this journal and elsewhere on this subject. The intention of this issue is to reflect the current state of this rapidly-developing field. It has therefore been open to all contributions containing new results on non-Hermitian theories that are explicitly PT-symmetric and/or pseudo-Hermitian or quasi-Hermitian. In the last decade these types of systems have proved to be viable self-consistent physical theories with well defined unitary time-evolution and real spectra. As the large number of responses demonstrates, this is a rapidly evolving field of research.

A consensus has been reached regarding most of the fundamental problems, and the general ideas and techniques are now readily being employed in many areas of physics. Nonetheless, this issue still contains some treatments of a more general nature regarding the spectral analysis of these models, in particular, the physics of the exceptional points, the breaking of the PT-symmetry, an interpretation of negative energies and the consistent implementation of the WKB analysis. This issue also contains a treatment of a scattering theory associated with these types of systems, weak measurements, coherent states, decoherence, unbounded metric operators and the inclusion of domain issues to obtain well defined self-adjoint theories. Contributions in the form of applications of the general ideas include: studies of classical shock-waves and tunnelling, supersymmetric models, spin chain models, models with ring structure, random matrix models, the Pauli equation, the nonlinear Schrödinger equation, quasi-exactly solvable models, integrable models such as the Calogero model, Bose–Einstein condensates, thermodynamics, nonlinear oligomers, quantum catastrophes, the Landau–Zener problem and pseudo-Fermions. Applications close to experimental realization are proposed in optics, including short light pulse models, waveguides and laser systems, and also in electronics.
Keywords: non-Hermitian operators, PT-symmetry, pseudo-Hermiticity, quasi-Hermiticity, exceptional points, Bose-Einstein condensate, shock waves, WKB analysis, Calogero model, spin chains, nonlinear oligomers, pseudo-fermions, waveguides, spectral properties, PT phase transition

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In vivo imaging of lysyl oxidase by fluorine-18 labelled substrate-based radiotracers

Kuchar, M.; Lenk, J.; Bergmann, R.; Wodtke, R.; Mosch, B.; Steinbach, J.; Pietzsch, J.; Löser, R.
The ability of solid tumours to invade surrounding tissues and, in consequence, to metastasise to distant organs is mediated by bidirectional molecular interactions between tumour cells and the extracellular matrix [1,2]. Recently, the copper-dependent amine oxidase lysyl oxidase (LOX, EC 1.4.3.13) could be identified as one of the key players in these processes [3]. Therefore, the development of molecular probes that enable the imaging of this enzyme in vivo by positron emission tomography (PET) was in the focus of this study.
As the enzyme is catalysing the oxidative crosslinking of lysine side chains in collagen and other extracellular proteins, the design of radiotracers based on substrates seemed to be promising. Thus, the N-terminal telopeptide of the alpha1-chain of type I collagen containing the key sequence Asp-Glu-Lys-Ser [4] and peptides derived from this were chosen to be functionalised with fluorine-18 at their N-termini. To achieve this, a method was developed that allows the site-selective 18F-fluorobenzoylation of peptides [5]. The metabolic stability and biodistribution of these potential radiotracers was investigated in male wistar rats.
To estimate the potential of the different lysine-containing peptides for crosslinking with collagen in vivo, their interaction with bovine atelocollagen was investigated by surface plasmon resonance (SPR) experiments.
A panel of tumour cell lines was screened for expression of the enzyme.
The presence of LOX could be confirmed for the human breast cancer cell-lines MDA-MB-231, MCF-7 and the melanoma cell line A375 by RT-PCR as well as western blots. Based on the human A375 cell line, an animal model was established consisting of nude mice bearing tumours derived from these cells. Expression of LOX in the developed tumours was proven by immunohistochemical methods and western blots.
The developed labelling method for site-selective radiolabelling of peptides allowed to obtain the 18F-fluorobenzoylated telopeptide in high radiochemical yields and purities. All peptides show good stability in vivo and even no metabolites could be detected for the cyclopeptide. The biodistribution studies indicate no organ enrichment and fast renal elimination. For the first time, the telopeptide-collagen interaction could be studied quantitatively, indicating dissociation constants in the high micromolar range.
Despite unfavourable pharmokinetics due to fast blood clearance, the compounds show the potential to reflect the LOX acticity in vivo, as concluded from PET imaging experiments with nude mice bearing A375 tumours.
[1] Fidler, I. J. Nat. Rev. Cancer 2003, 3, 453.
[2] Rowe, R. G.; Weiss, S. J. Annu. Rev. Cell Dev. Biol. 2009, 25, 567.
[3] Erler, J. T.; Bennewith, K. L.; Nicolau, M.; Dornhöfer, N.; Kong, C.; Le, Q.-T.; Chi, J.-T. Nature 2006, 440, 1222-1226.
[4] Helseth, D. L.; Lechner, J. H.; Veis, A. Biopolymers 1979, 18, 3005.
[5] Kuchar, M.; Pretze, M.; Kniess, T.; Steinbach, J.; Pietzsch, J.; Löser, R. Amino Acids 2012, 43, 1431-1443.
  • Lecture (Conference)
    3rd Annual Symposium "Physics of Cancer", 01.-03.11.2012, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17914
Publ.-Id: 17914


Validation of the RELAP5 code for the modeling of flashing-induced instabilities under natural circulation conditions using experimental data from the CIRCUS test facility

Rohde, U.; Kozmenkov, Y.
This paper reports on the use of the RELAP5 code for the simulation of flashing-induced instabilities in natural circulation systems. The RELAP 5 code is used for the simulation of transient processes in the Russian RUTA reactor concept operating at atmospheric pressure with forced convection of coolant. However, during transient processes, natural circulation with flashing-induced instabilities might occur. The RELAP5 code is validated against measurement data from natural circulation experiments performed within the framework of a European project (NACUSP) on the CIRCUS facility. The facility, built at the Delft University of Technology in The Netherlands, is a water/steam 1:1 height-scaled loop of a typical natural-circulation-cooled BWR. It was shown that the RELAP5 code is able to model all relevant phenomena related to flashing induced instabilities. The magnitude and frequency of the oscillations were reproduced in a good agreement with the measurement data. The close correspondence to the experiments was reached by detailed modeling of all components of the CIRCUS facility including the heat exchanger, the buffer vessel and the steam dome at the top of the facility.
In the second part of the presentation, the impact of the modeling of subcooled boiling on natural circulation instability is considered. A transient with failure of all primary circulation pumps (initial event) and the failure of reactor SCRAM for the RUTA facility using the coupled neutron kinetics/thermo-hydaulic code systems DYN3D/ATHLET and DYN3D/RELAP5 was simulated. The predictions for initial and final reactor states given by the codes are in good agreement. However, the process of transition between these two states shows a qualitative difference. The DYN3D/RELAP5 code predicts unstable transient behavior of the reactor, while in the DYN3D/ATHLET simulation a smooth change of reactor parameters is observed during the whole accident. It was found that the different stability behavior is due to differences between the subcooled boiling models of the ATHLET and RELAP5 codes.
Despite the different performance of RUTA in the DYN3D/ATHLET and DYN3D/RELAP5 simulations of the accident the obtained results confirm a high intrinsic safety level for this reactor concept. In both compared calculations the allowed safety margins have not been reached. However, further validation of the subcooled boiling models on experiments at low pressure is necessary.
Keywords: boiling water reactor, natural circulation, instability, low pressure, flashing, experimental facility, subcooled boiling
  • Lecture (Conference)
    Scientific Workshop on Reactor Dynamics and Safety 2012, 13.-14.09.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17913
Publ.-Id: 17913


Application of the method of uncertainty and sensitivity evaluation to results of PWR LBLOCA analysis calculated with the code ATHLET

Rohde, U.; Kozmenkov, Y.
Usually, safety analyses are based on the traditional conservative deterministic approach. However, the conservative approach does not allow evaluating the accuracy of results and their deviations from the real values. An alternative approach to reactor safety analyses uses best estimate computer codes together with quantification of uncertainties in model and plant parameters. Uncertainties in the results of safety analysis calculations are related to model uncertainties as well as deficiencies of knowledge of reactor initial conditions.
The German Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) has developed an approach to uncertainty analysis based on the Wilks’ theorem. According to that theorem, the number of calculations to be performed to get a probabilistic estimation of an output parameter with certain coverage at a certain confidence level (e.g., 95%/95%) does not depend on the number of statistically independent input uncertain parameters.
An important part of the analysis is devoted to the selection of the uncertain parameters and definition of the probability distributions and intervals of parameter variation. The variations should cover all parameters which are necessary to describe all phenomena relevant for the considered scenario. The parameter selection is based on a Phenomena Identification and Ranking Table (PIRT) elaborated based on engineering judgment.
In this paper, the results of an uncertainty and sensitivity analysis for a Large Break LOCA scenario for a generic German PWR of the Konvoi design are reported about. The accident was performed using the system code ATHLET Mod 2.2 Cycle A. 47 uncertain parameters were statistically varied, among them 32 model parameters, 7 plant initial state parameters and 7 core parameters. The EXEL-integrated software SUSA developed by GRS is used for generation of the uncertainty parameter vectors, their incorporation into ATHLET input files and for the result analysis. Investigation of the sensitivity of the output parameter (peak cladding temperature) from the uncertain input parameters reveals the most relevant parameters.
Results of this reference uncertainty analysis and a related sensitivity analysis are presented in this report.
Keywords: large break LOCA, uncertainty analysis, sensitivity analysis
  • Lecture (Conference)
    22nd Symposium of Atomic Energy Research (AER) on VVER reactor physics and reactor safety, 01.-05.10.2012, Pruhonice, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17912
Publ.-Id: 17912


Radiolabelling of engineered silver and titania nanoparticles as a tool for sensitive detection of nanoparticle release from surface coatings

Hildebrand, H.; Franke, K.; Gibson, N.; Cydzik, I.; Simonelli, F.; Bulgheroni, A.; Holzwarth, U.; Bilz, E.; Freyer, A.
Engineered nanoparticles (NPs) such as silver and titania are widely used in consumer products e.g. as functional additives in surface coatings. Due to aging or abrasion of these nanocomposites, particle release becomes likely and further transport e.g. in environmental systems could be assumed. Figure 1 shows results from a worst-case scenario study where NP release was enforced due to the use of a quite labile surface coating and photooxidative degradation of the nanocomposite catalysed by TiO2 anatase NPs. For conventional, more stable nanocomposites, accurate and sensitive detection and quantification of NP release is still a challenge due to the fact that released fractions might be small but nevertheless significant. The application of radiotracers provides the excellent option of “visibility”, traceability and quantification of NPs in complex media. Therefore, different radiolabelling strategies for engineered nanopowders (TiO2 P 25, Evonic Industries, dp = 21 nm; Ag0, Sigma Aldrich, dp < 100 nm) were established using a diffusive introduction of 110mAg radionuclides (t1/2 = 250 d) into Ag0-NPs (Hildebrand & Franke, 2012) and 44Ti radionuclides (t1/2 = 63 a) into TiO2-NPs through a low-temperature annealing procedure. Another radiolabelling strategy is the direct activation of Ag0 and TiO2 nanopowders that was done via proton irradiation using a Scanditronix MC40 cyclotron (Abbas et al. 2010, Holzwarth et al. 2012).
Both methods were tested with respect to labelling yield, achievable activity concentration, pH-dependent stability of the labelling and the influence on NP properties. Results obtained show an appropriate selection of radiolabeling methods suitable for different experimental conditions for NP release studies.

Figure 1: Time-dependent degradation of a polyacrylate TiO2 nanocomposite by UV-A-irradiation (intensity ~ 15 mW/cm2) ;A) original, B) after 2 days (50.000x); C) 4 days, D) 8 days, E) 16 days (75.000x); SEM micrographs: Leibniz Institute for Surface Modification.

Abbas K, Cydzik I, Del Torchio R, Farina M, Forti E, Gibson N, Holzwarth U, Simonelli F, Kreyling W (2010) J Nanopart Res 12:2435–2443.
Holzwarth U, Bulgheroni A, Gibson N, Kozempel J, Cotogno G, Abbas K, Simonelli F, Cydzik I (2012) J Nanopart Res 14:880
Hildebrand H and Franke K (2012) J Nanopart Res 14:1142.
Keywords: engineered nanoparticles, radiolabelling, titania, silver
  • Poster
    NanoSAFE'12, 13.-15.11.2012, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-17911
Publ.-Id: 17911


Time-resolved photoluminescence quenching by intra-excitonic transitions in presence of external magnetic field

Bhattacharyya, J.; Zybell, S.; Helm, M.; Schneider, H.; Andrews, A. M.; Strasser, G.; Schneebeli, L.; Böttge, C. N.; Breddermann, B.; Chatterjee, S.; Kira, M.; Koch, S. W.
We present our experimental results on the excitation and manipulation of intra-excitonic transitions in semiconductor quantum wells. We performed time resolved photoluminescence (PL) quenching measurements on a GaAs/AlGaAs multiple QW sample. The excitons were generated by near infrared pulsed laser excitation and intraexcitonic 1s-2p transition was induced by THz laser pulses resonant to the 1s-2p energy separation. We used the free electron laser at Helmholtz-Zentrum Dresden-Rossendorf as the THz source. Due to the population transfer from the 1s to the 2p, the PL intensity at 1s energy decreased abruptly during the incidence of the THz pulse. Such quenching of PL has been reported earlier for intersubband excitations [1].

Interestingly, a simultaneous increase in the PL is observed around the 2p energy. Since radiative recombination is forbidden for the 2p state the enhancement of the PL intensity at higher energy is attributed to emission from the 2s excitonic state, which is nearly degenerate with the 2p state. This implies an appreciable transfer of carriers from 2p to 2s state. This has been predicted in theory [2] and is explained to result from Coulomb scattering. Time resolved measurements allowed us to estimate the time-constants related to the carrier dynamics involved in this 2p-2s transfer. We were also able to control the 2s-2p carrier transfer by an external magnetic field. The energy separations between excitonic levels increase with increasing magnetic field [3]. We employ this effect to reduce the 2p-2s carrier transfer observed as a decrease in the THz induced 2s emission. We can practically switch off this transfer by a magnetic field of about 2.5 T. We will also present a comparison of the experimental data with a microscopic theory which includes Coulomb induced excitonic scattering.

References
1) S. Zybell, et. al., Appl. Phys. Lett. 99, 041103 (2011)
2) M. Kira, et. al. Phys. Rev. Lett. 93, 076402 (2004)
3) H. A. Nickel, et. al. Phys. Rev. B 62, 2773 (2000)
Keywords: Magneto-photoluminescence, free electron laser, intraexcitonic transitions
  • Lecture (Conference)
    11th International Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors, 23.-27.09.2012, Stuttgart, Germany

Permalink: https://www.hzdr.de/publications/Publ-17910
Publ.-Id: 17910


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