Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Novel Phase Transition Probed by Sound Velocity in Quasi-One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8
Yamaguchi, H.; Yasin, S.; Zherlitsyn, S.; Omura, K.; Kimura, S.; Yoshii, S.; Okunishi, K.; He, Z.; Taniyama, T.; Itoh, M.; Hagiwara, M.;
We have performed magnetostriction and ultrasound measurements on the quasi-one-dimensional S ¼ 1=2 Ising-like antiferromagnet BaCo2V2O8 in high magnetic fields of up to 51 T. The magnetostriction shows lattice shrinking along the c-axis, and we interpret it as the lattice distortion caused by exchange striction and Van-Vleck paramagnetism. It is clarified that the field dependence of sound velocity is correlated to the magnetostriction. We observed a pronounced softening in the sound velocity of the longitudinal-acoustic c33 mode and found a novel phase transition.
  • Journal of the Physical Society of Japan 80(2011), 033701

Publ.-Id: 15527 - Permalink


Microstructure of superconducting films fabricated by high-fluence Ga implantation in Si
Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.;
The feasibility of embedding extrinsic superconducting nanolayers in commercial (100) silicon due to Ga precipitation is presented. To be far beyond the solid solubility limit of 0.1 at.% a high Ga fluence of 4x1016cm-2 is introduced in silicon by the ion-implantation technique. This leads to 100 nm thick amorphous silicon layers with a Ga peak concentration of 16 at.%. Subsequent recrystallization and Ga precipitation is initiated via rapid thermal annealing (RTA) for 60 seconds at temperatures of 500 – 800°C. A 30 nm sputter deposited SiO2 cover layer is used to protect the silicon surface during implantation and prevent Ga out-diffusion during annealing. It was shown that optimized annealing conditions (600 – 700°C) lead to superconducting layers with critical temperatures of 7 K and in plane critical fields up to 14 T [1]. Details of the layer microstructure investigations using of RBS/C and TEM as well as depth dependent XPS will be presented. The presented structural investigations reveal poly-crystalline silicon layers and show a strong Ga enrichment at the Si/SiO2 interface. Even if no crystalline Ga clusters were detected it is shown that the superconductivity arises due to a high density of amorphous Ga-rich precipitates at the Si/SiO2 interface. Since all involved processing steps are fully compatible with standard microelectronic technology and high criti-cal current densities of more than 2 kA/cm2 are reached, the proposed material system may implicate a high potential for future microelectronic applications.
[1] Skrotzki R. et al., Appl. Phys. Lett. 97 (2010) 192505
  • Lecture (Conference)
    Workshop Ionen- und Positronenstrahlen, 04.-05.07.2011, Neubiberg, Deutschland

Publ.-Id: 15526 - Permalink


Uranium(VI) Complexation with Lactate and Citrate in Dependence on Temperature (7-65°C)
Steudtner, R.; Schmeide, K.; Bernhard, G.;
After disposal in nuclear waste repositories the chemical and migration behavior of actinides depends on many factors. It is estimated that maximum temperatures in the near field of a repository could reach 300°C in dependence on the waste forms [1] and the host rock [2]. Thus, for the long-term safety assessment, knowledge of the interaction of actinides such as uranium with inorganic and organic ligands at elevated temperatures is required. The amount of organic matter in a repository can be separated in humic substances and in low molecular weight organic substances. A not negligible component of low molecular weight organic substances is the group of carboxylic acid. For example, citric acid is used in nuclear reprocessing [3] and acetic, lactic and formic acid were identified in rock extracts and pore water of Opalinus Clay [4]. Reliable experimental data on the complexation of U(VI) in solution at elevated temperatures are still needed.
Therefore, we studied the U(VI) complexation by lactic acid (pH 3) and citric acid (pH 0-10) in the temperature range from 7 to 65°C. Species distribution and complex formation constants were determined by means of UV-Vis and time-resolved laser-induced fluorescence spectroscopy. In the U(VI) lactate system, we identified the formation of 1:1- and 1:2-complexes. In the presence of citrate, we could characterize five U(VI) complexes in dependence on pH value. The complex formation between U(VI) and these both ligands was found to be endothermic and entropy-driven. The complex stability constants of the U(VI) complexes increase with increasing temperature. This could lead to an increased mobility of U(VI) at higher temperatures.
Keywords: Uranium(VI), Lactate, Citrate, Complexation, higher Temperatures
  • Contribution to proceedings
    Goldschmidt 2011, 14.-19.08.2011, Prag, Czech Republic
    Mineralogical Magazine 75, 1940
  • Poster
    Goldschmidt 2011, 14.-19.08.2011, Prag, Czech Republic

Publ.-Id: 15525 - Permalink


High Efficiency Nanosecond Pulse Amplication Based on Diode-Pumped Cryogenic-Cooled Yb:YAG
Koerner, J.; Hein, J.; Kahle, M.; Liebtrau, H.; Kaluza, M.; Siebold, M.;
An output energy of 1.1 J of amplified nanosecond pulses was obtained by utilizing a diode-pumped Yb:YAG laser amplifier with the crystal cooled to 125 K. An all-mirror relay imaging was implemented to accomplish a low loss multi-pass scheme, where a three dimensional folding compensates the astigmatism of spherical mirrors at non-normal incidence. Without the need of diode-wavelength stabilization a for this type of amplifier record high total diode output to amplifier efficiency of 45 % was achieved.
Keywords: Lasers and laser optics
  • Lecture (Conference)
    Advanced Solid-State Photonics (ASSP), 13.-16.02.2011, Istanbul, Turkey

Publ.-Id: 15524 - Permalink


Broadband, diode-pumped Yb:SiO2 multicomponent glass laser
Roeser, F.; Reichelt, A.; Kroll, F.; Siebold, M.; Schramm, U.; Grimm, S.; Kirchhof, J.; Litzkendorf, D.;
We successfully demonstrated cw lasing of ytterbium-doped silica multicomponent glass bulk material. A slope efficiency of 43% and a tuning range from 1010-1080 nm have been achieved.
Keywords: Lasers, diode-pumped; Lasers, ytterbium; Lasers, tunable; Lasers, solid-state; Laser materials; Rare earth and transition metal solid-state lasers
  • Lecture (Conference)
    Advanced Solid-State Photonics (ASSP), 13.-16.02.2011, Istanbul, Turkey

Publ.-Id: 15523 - Permalink


Analysis of a high-energy, diode-pumped Yb:CaF2 disk laser
Loeser, M.; Siebold, M.; Kroll, F.; Roeser, F.; Koerner, J.; Hein, J.; Schramm, U.;
We present gain measurements and a time-resolved thermal lens analysis of a diode pumped, joule-class Yb:CaF2 disk laser. A thermal lens power of 0.05dpt at a single disk and small-signal gain of 5.2 in a two-disk amplifier were achieved at full pump power.
Keywords: Lasers, diode-pumped; Lasers Ytterbium; Laser amplifiers
  • Lecture (Conference)
    Advanced Solid-State Photonics ASSP, 13.-16.02.2011, Istanbul, Turkey

Publ.-Id: 15522 - Permalink


Adsorption of thallium(I) onto geological materials: Effect of pH and humic matter
Liu, J.; Lippold, H.; Wang, J.; Lippmann-Pipke, J.; Chen, Y. H.;
Thallium (Tl) is a typical toxic heavy metal, with higher toxicity than Hg, Cd, Pb. Anthropogenic sources such as coal combustion or mining/smelting activities generated high enrichments of Tl in some areas. For long-term risk assessments, the mobility in geochemical systems is a topic of major interest. Adsorption onto mineral surfaces can be considerably affected by dissolved humic acids (HAs), which are ubiquitous in natural waters. By using radioactive tracers, we were able to investigate co-adsorption of Tl and HAs at low concentration levels to be considered in real scenarios.
Two natural HAs were extracted from river sediments collected in a contaminated mining area in South China (regions of Guangzhou and Yunfu City). They were radiolabeled by an azo-coupling reaction with 14C-aniline. 204Tl(I) was employed as a radiotracer for Tl(I). The geological materials used in this study were goethite, pyrolusite and a natural sediment sample taken from Yunfu City.
For all these substrates, metal adsorption was found to be promoted with increasing pH since more binding sites are provided by deprotonation of surface hydroxyl groups. In contrast, adsorption of HAs was counteracted with increasing pH, which is explained by increasing electrostatic repulsion as a consequence of deprotonation. As expected, the extent of Tl(I)-HA complexation turned out to be very low, with a slight increase at higher pH.
Based on these data, a combined distribution model (Linear Additive Model) was tested for suitability in predicting the pH-dependent influence of HAs on Tl(I) adsorption. Our experimental results could not be reproduced in this way. In view of the fact that the approach worked well in other studies, criteria for its applicability need to be identified. Selectivities within the multicomponent system of humic material, regarding adsorption as well as complexation, are one possible reason for a failure of the model.
  • Lecture (Conference)
    Goldschmidt 2011, 14.-19.08.2011, Praha, Ceska Republika

Publ.-Id: 15521 - Permalink


Time-of-flight detection of fast neutrons
Bemmerer, D.;
The methods of time of flight detection of fast neutrons are reviewed, with an emphasis on the planned NeuLAND detector at FAIR.
  • Invited lecture (Conferences)
    XLII. Arbeitstreffen "Kernphysik" in Schleching/Obb., 24.02.-03.03.2011, Schleching, Deutschland

Publ.-Id: 15520 - Permalink


Prototyping and design for a time-of-flight detector for 1 GeV neutrons at R3B/FAIR
Bemmerer, D.;
At the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, uniquely intensive beams of radioactive ions will become available, enabling many experiments of astrophysical relevance. The Reactions with Relativistic Radioactive Beams (R3B) setup at FAIR will study reactions of such projectiles at energies up to 1 GeV/A. As part of R3B, the planned NeuLAND (New Large Area Neutron Detector) time-of-flight detector shall detect emitted neutrons with a time resolution of sigma < 100 ps and efficiency >90%. Two possible solutions are currently under study for NeuLAND: a pure scintillator concept and a design based on passive converters and multigap resistive plate chambers (MRPC's). The poster will outline the design work on the MRPC-based solution. The measured properties of a 200 cm * 50 cm large MRPC-based neutron detector prototype will be shown, the first device of such a size with thick passive converters inside the MRPC structure.
  • Poster
    European Physical Society 24th Nuclear Physics Divisional Conference: Nuclear Physics in Astrophysics – V, 04.-08.04.2011, Eilat, Israel

Publ.-Id: 15519 - Permalink


A possible underground accelerator in the Dresden Felsenkeller
Bemmerer, D.; Cowan, T.; Szücs, T.; Zuber, K.;
Due to the suppression by the Coulomb barrier, the cross sections of astrophysically relevant nuclear reactions are very low at the stellar energy. Therefore they can only be directly measured in a low-background environment. For more than a decade, the LUNA collaboration has pursued this approach with a 0.4\,MV accelerator in the Gran Sasso underground laboratory in Italy. It was highly successful in studying the nuclear physics of the Sun and of the Big Bang. However, the energy range of LUNA is not sufficient to address the nuclear reactions of stellar helium burning and the neutron source reactions for the astrophysical s-process. Therefore, in the NuPECC 2010 long range plan it is recommended to install one or more accelerators with higher energy underground. A comparison of the background at LUNA (1400\,m rock cover) and the Dresden Felsenkeller (45\,m) has shown that with an anti-muon veto the background counting rates in a $\gamma$-detector differ only by a factor of three. The feasibility of installing a 2-3\,MV accelerator for intense $\alpha$-beams in Felsenkeller will be discussed.
  • Poster
    European Physical Society 24th Nuclear Physics Divisional Conference: Nuclear Physics in Astrophysics V., 04.-08.04.2011, Eilat, Israel
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft, Frühjahrstagung 2011, 21.-25.03.2011, Münster, Deutschland
  • Open Access LogoJournal of Physics: Conference Series 337(2012), 012032
    DOI: 10.1088/1742-6596/337/1/012032

Publ.-Id: 15518 - Permalink


Characterisation and calibration of weak 44Ti sources for astrophysical applications
Schumann, D.; Schmidt, K.; Bemmerer, D.;
Five Ti-44 calibration sources supplied by Paul-Scherrer-Institute have been characterized concerning their activity distribution as well as the absolute activities. Now, calibration sources for nuclear astrophysics experiments with an uncertainty of +/-1.2% are available
Keywords: Ti-44, supernova, alpha-rich freezeout, nuclear astrophysics, activation, low-level counting
  • Contribution to external collection
    A. Türler, M. Schwikowski, and A. Blattmann: Annual Report 2010, Labor für Radio- und Umweltchemie der Universität Bern und des Paul-Scherrer-Instituts, Villigen/Schweiz: Paul-Scherrer-Institut, 2011, 52

Publ.-Id: 15517 - Permalink


Realitätsnahe Einbindung von Sorptionsprozessen in Sicherheitsanalysen
Stockmann, M.; Brendler, V.; Schikora, J.; Noseck, U.; Flügge, J.;
Als Teil eines Langzeitsicherheitsnachweises für Endlager mit radioaktiven Abfällen sind auch Szenarien zu betrachten, bei denen es zu einer Mobilisierung von Radionukliden aus den Abfällen und damit zu deren Transport durch das Endlagersystem kommen kann. Eine wichtige Barriere im System eines Endlagers stellt neben dem Wirtsgestein auch das darüberliegende Deckgebirge dar. Der Transport durch die Geosphäre wird für viele Radionuklide durch Sorption an Oberflächen vorhandener Mineralphasen verlangsamt. In bisher verwendeten Transportprogrammen wird die Rückhaltung der Radionuklide über zeitlich und räumlich konstante Verteilungskoeffizienten (Kd Werte) beschrieben.
Im Rahmen des Vortrages wird das Verbundprojekt ESTRAL (Realitätsnahe Einbindung von Sorptionsprozessen in Transportprogramme für die Langzeitsicherheitsanalyse) (Kooperations-partner: HZDR Dresden-Rossendorf und GRS Braunschweig) vorgestellt. Ziel des Projektes ist es, eine neue Methodik zur Berücksichtigung der Sorption im bestehenden reaktiven Transportcode r³t (radionuclide, reaction, retardation, and transport, GRS) zu entwickeln und zu erproben. Dabei werden die bisher konditionellen Kd-Werte durch so genannte smart Kd-Werte ersetzt, welche auf Basis mechanistischer Modelle (Oberflächenkomplexierungsmodelle) als Funktion wichtiger Einflussgrößen Ei (z.B. pH, Ionenstärke, pCO2, Konzentration Ca2+ und Al3+) im geochemischen Speziationscode PHREEQC berechnet werden. Mit dieser Weiterentwicklung von r3t wird ein Instrumentarium zur Verfügung gestellt, mit dem der Radionuklidtransport unter sich verändernden geochemischen Bedingungen (z.B. infolge Klimaänderungen) realitätsnäher beschrieben werden kann. Eine solche Vorgehensweise wird exemplarisch für den Radionuklidtransport im Deckgebirge des möglichen Endlagers im Salzstock Gorleben entwickelt. Einzelne Einflussgrößen Ei sind bislang im Transportcode r³t nicht verfügbar. Hierzu werden geeignete Methoden zum Transport dieser Parameter sowie Gleichungen zur Beschreibung des pH-Wertes und der Ionenkonzentrationen als Funktion der verfügbaren Mineralphasen in r³t implementiert. Anschließend kann r³t für jeden Raum-Zeit-Punkt vorberechnete Verteilungs-koeffizienten aus einer mehrdimensionalen Matrix in Abhängigkeit von den jeweiligen geochemischen Bedingungen abrufen.
Anhand von Anwendungsrechnungen wird das weiterentwickelte Programm erprobt. Dafür werden zwei verschiedene Prozesse, die als Folge klimatischer Veränderungen auftreten können, untersucht: (1) Der Eintrag von Nordseewasser in das Deckgebirge für den Fall einer Meerestransgression während eines Klimaoptimums, und (2) Die Entwicklung des Deckgebirges in einer Warmzeit nach einer Kaltzeit mit lang andauerndem Permafrost. Bei beiden Prozessen werden sich die geochemischen Bedingungen erheblich verändern, was zu einer gravierenden Veränderung des Sorptionsverhaltens vieler Radionuklide führen wird.
  • Invited lecture (Conferences)
    Jahrestagung Kerntechnik, 17.-19.05.2011, Berlin, Deutschland

Publ.-Id: 15516 - Permalink


The special case of Actinide(IV) complexation by the carboxylic function of small and large organic ligands
Hennig, C.; Takao, K.; Takao, S.; Meyer, M.; Jeanson, A.; Dahou, S.; Den Auwer, C.;
Accidental release of radionuclides from mining activities, nuclear energy production, and radioactive waste storage sites requires research to predict the fate and mobility of these contaminants in the environment and more specific in organisms. To date, the interaction of actinides with biological systems is widely unkown, due to the lack of structural information on the molecular level. The aim of this presentation is to summarize recently explored coordination principles of tetravalent actinides with small carboxylic and aminocarboxylic ligands as well as the interaction with proteins.
Tetravalent actinides form with carboxylate ligands in aqueous solutions at low pH values usually monomeric complexes. They show at the other hand a strong tendency toward hydrolysis already at low pH. As the pH reaches the onset of An(IV) hydrolysis, olation and oxolation occur as competing reactions to the carboxylate complexation. We observed under these circumstances the formation of several well-defined polynuclear species. The carboxylic group acts in such systems as a terminating ligand and stabilizes nanosized polynuclear clusters in solution and in the solid state. It is important to note that this reaction prevents widely the formation of polynuclear hydrolysis species as well as the formation of An(IV) hydrous oxide colloids.
Keywords: tetravalent actinides, carboxylic ligands, proteins, EXAFS, XRD
  • Invited lecture (Conferences)
    Goldschmidt 2011, 14.-19.08.2011, Prague, Czech Republic
  • Abstract in refereed journal
    Mineralogical Magazine (2011), 1010-1010

Publ.-Id: 15515 - Permalink


Comparative study of the U(VI) complexation onto γ-Al2O3 by ATR FT-IR and EXAFS spectroscopy
Müller, K.; Foerstendorf, H.; Rossberg, A.; Stolze, K.; Gückel, K.;
Aluminates, representing an essential component of clay minerals, play a decisive role in regulating the mobility of contaminants in rock and soil formations, in particular due to their tendency to form coatings on mineral surfaces [1].
In this work, U(VI) sorption on γ-Al2O3 is comparatively investigated using in situ vibrational and X-ray absorption spectroscopy. The focus was set to micromolar U(VI) concentrations and a variety of environmentally relevant sorption parameters in order to resolve discrepancies reported earlier [2-4].
Time-resolved (TR) IR spectroscopic sorption experiments at the alumina-water interface evidence the formation of three different species as a function of surface loading (c.f. Fig.): a monomeric carbonate complex, an oligomeric surface complex and a surface precipitate. These results are confirmed by IR experiments performed at different flow rates, pH values, ionic strengths, U(VI) concentrations, and in inert gas atmosphere. Results of EXAFS experiments of batch samples are consistent to these findings.
[1] Guillaumont, R. (1994) Radiochimica Acta 66-7, 231-242. [2] Catalano, J. G. et al. (2005) Geochim. Cosmochim. Acta 69, 3555-3572. [3] Moskaleva, L.V. et al. (2006) Langmuir 22, 2141-2145. [4] Sylwester, E. R. et al. (2000) Geochim. Cosmochim. Acta 64, 2431-2438.
  • Contribution to proceedings
    Goldschmidt conference 2011, 14.-19.08.2011, Prague, Czech Republic
    Mineralogical Magazine, Vol. 75 (3), 1513
  • Poster
    Goldschmidt conference 2011, 14.-19.08.2011, Prague, Czech Republic
  • Lecture (Conference)
    Goldschmidt conference 2011, 14.-19.08.2011, Prague, Czech Republic

Publ.-Id: 15514 - Permalink


Scaling law for the photon spectral density in the nonlinear Thomson-Compton scattering
Seipt, D.; Kämpfer, B.;
We derive a new scaling law for the photon spectral density in nonlinear Thomson/Compton scattering, extending the findings of Heinzl, Seipt, and Kämpfer [Phys. Rev. A 81, 022125 (2010)]. This allows one to easily include the effects of general scattering geometries, e.g., side injection, and of a finite-size detector on the photon spectrum. The scaling law is employed to study substructures emerging in the nonlinear Thomson/Compton spectra due to temporally shaped laser pulses scattering off relativistic electrons. We determine optimum scattering geometries for an experimental verification of these substructures.
Keywords: Thomson scattering, scaling law, electron phase space, photon spectrum
  • Open Access LogoPhysical Review Special Topics - Accelerators and Beams 14(2011)4, 040704

Publ.-Id: 15513 - Permalink


Dosimetry of laser-accelerated electron beams used for in vitro cell irradiation experiments
Richter, C.; Kaluza, M.; Karsch, L.; Schlenvoigt, H.-P.; Schürer, M.; Sobiella, M.; Woithe, J.; Pawelke, J.;
The dosimetric characterization of laser-accelerated electrons applied for the worldwide first systematic radiobiological in vitro cell irradiations will be presented. The laser-accelerated electron beam at the JeTi laser system has been optimized, monitored and controlled in terms of dose homogeneity, stability and absolute dose delivery. A combination of different dosimetric components were used to provide both an online beam as well as dose monitoring and a precise absolute dosimetry. In detail, the electron beam was controlled and monitored by means of an ionization chamber and an in-house produced Faraday Cup for a defined delivery of the prescribed dose. Moreover, the precise absolute dose delivered to each cell sample was determined by an radiochromic EBT film positioned in front of the cell sample. Furthermore, the energy spectrum of the laser-accelerated electron beam was determined. As presented in a previous work of the authors, also for laser-accelerated protons a precise dosimetric characterization was performed that enabled initial radiobiological cell irradiation experiments with laser- accelerated protons. Therefore, a precise dosimetric characterization, optimization and control of laseraccelerated and therefore ultra-short pulsed, intense particle beams for both electrons and protons is possible, allowing radiobiological experiments and meeting all necessary requirements like homogeneity, stability and precise dose delivery. In order to fulfil the much higher dosimetric requirements for clinical application, several improvements concerning, i.e., particle energy and spectral shaping as well as patient safety are necessary.
Keywords: laser particle acceleration, laser-accelerated electrons, dosimetry, radiobiology, radiochromic films, faraday cup, ionization chamber, EBT films

Publ.-Id: 15512 - Permalink


Terahertz nonlinear optics of exciton states
Helm, M.;
Excitons in semiconductor exhibit a hydrogenic energy spectrum, scaled down into the THz range. By pumping the 1s-2p intra-excitonic transition in GaAs/AlGaAs quantum wells with the Dresden free-electron laser, we induce an AC Stark effect, namely the famous Autler-Townes splitting reflecting exciton states dressed by THz photons [1]. The spectrum is probed via band-gap absorption. Under similar conditions, we also observe resonantly enhanced THz sideband generation by mixing the THz and band gap radiation [2].
[1] M. Wagner et al., Phys. Rev. Lett. 105, 167401 (2010)
[2] M. Wagner et al., Appl. Phys. Lett. 94, 241105 (2009)
Keywords: terahertz, exciton, free-electron laser
  • Invited lecture (Conferences)
    Workshop of the GDRI-CNRS: Semiconductors Sources and Detectors of THz Radiation, 29.03.-01.04.2011, Tignes, France

Publ.-Id: 15511 - Permalink


THz spectroscopy of semiconductors at high electric and magnetic fields
Helm, M.;
THz spectroscopy of semiconductors at high electric and magnetic fields
Keywords: terahertz, semiconductors
  • Invited lecture (Conferences)
    4th Annual Meeting of the German Terahertz Center, 28.03.2011, Regensburg, Deutschland

Publ.-Id: 15510 - Permalink


High resolution RBS investigations of ZrO2 layer growth in the initial stage on native silicon oxide and titanium nitride
Vieluf, M.; Munnik, F.; Neelmeijer, C.; Kosmata, M.; Teichert, S.;
High Resolution Rutherford Backscattering Spectrometry (HR-RBS) with a depth resolution of about 0.3 nm near the surface was used to analyse the interface between ultrathin high-k ZrO2-layers and the substrate. In order to improve the quality of the analysis, a method was developed that takes local thickness variations, obtained by atomic force microscopy (AFM), into account during simulation of the HR-RBS spectra. The aim was to study atomic layer deposition (ALD) growth processes on Si(100) covered with native silicon oxide (SiO2) or with TiN. In the first case the interface is sharp, except for a small intermediate ZrSiO4-layer, and no diffusion of Zr-atoms in SiO2 could be detected. A quite different behaviour could be derived from high resolution spectra for the growth of ZrO2 on TiN. In addition, measurements of the surface topography of the TiN-layer revealed non-negligible surface roughness. Diffusion of Zr into polycrystalline TiN was demonstrated for the first time after correction for surface roughness. This observation indicates that already during the first ALD reaction cycle a small proportion of the deposited Zr-atoms diffuses – probably along grain boundaries – into the TiN-layer up to a depth of 3 nm.
Keywords: High Resolution Rutherford Backscattering Spectrometry (HR-RBS); High-k dielectric; Atomic Layer Deposition (ALD)

Publ.-Id: 15509 - Permalink


CFD modelling of adiabatic bubbly flow
Krepper, E.; Morel, C.; Niceno, B.; Ruyer, P.;
The paper describes the simulation of adiabatic gas-liquid flow based on the Euler/Eulerian approach. An adequate characterisation of the momentum exchange between the phases is necessary. The basic experiment investigating the momentum exchange is the vertical upward flow in a pipe. This report describes the main CFD approaches for momentum exchange and the comparison to experimental results for several test conditions. For large gas injection rates, a bubble size distribution including bubble coalescence and fragmentation has to be considered. The paper describes the concept of the inhomogeneous MUSIG model, developed by ANSYS/CFX and HZDR which is implemented in CFX and a comparable concept of a population balance model implemented in NEPTUNE_CFD (CEA, EDF, IRSN and AREVA). Measurements performed in HZDR are used for model validation. Crucial for the quality of the described models are the base approaches for bubble coalescence and fragmentation. Among other influences these phenomena depend on the liquid turbulence. Therefore special attention was devoted on CFD simulation of bubbly turbulent flow based on different model concepts. Concepts based on Reynolds averaged turbulence models are described. In PSI Large Eddy based studies were performed and compared to DEDALE experiments. The work was performed within the NURESIM and the NURISP projects in the frame of sixth and the seventh European Framework Program.
Keywords: CFD, multiphase-flow, adiabatic flow, polydispersed flow, turbulence, experiments, simulations

Publ.-Id: 15508 - Permalink


Weiterentwicklung des Siebmodells und Experimente zum Anlagerungs- und Penetrationsverhalten
Grahn, A.;
Im Vortrag wird der aktuelle Bearbeitungsstand zur Modellierung von Rückhaltevorrichtungen im Notkühlkreislauf von Kernreaktoren berichtet. Die Modellierung unterteilt sich in ein Basismodell zur Berechnung der im Verlauf des Prozesses akkumulierten Isoliermaterialmasse und des daraus resultierenden Druckverlusts über der kompressiblen Packung, sowie in ein erweitertes Modell, das den weiteren Anstieg des Druckverlusts durch Einlagerung von Korrosionspartikeln infolge der Tiefenfiltrationswirkung der Packung in der Spätphase des Kühlmittelverluststörfalls beschreibt. Im Vortrag werden experimentelle und theoretische Arbeiten zur Parametrierung der Modellgleichungen sowie Beispielrechnungen vorgestellt.
Keywords: loss of coolant accident, nuclear reactor safety, pressure loss
  • Lecture (others)
    Fachkolloquium zum BMWi-Projekt 150 1360/150 1363, 17.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15507 - Permalink


Bildgestützte in-vivo Dosimetrie: Von PET zu in-beam SPECT
Fiedler, F.;
No abstract availabe
  • Invited lecture (Conferences)
    23. Weiterbildungsveranstaltung Mitteldeutscher Medizinphysiker in Dresden, 08.-09.04.2011, Dresden, Deutschland

Publ.-Id: 15506 - Permalink


Electron transport and anisotropy of the upper critical magnetic field in a Ba0.68K0.32Fe2As2 single crystals
Gasparov, V. A.; Wolff-Fabris, F.; Sun, D. L.; Lin, C. T.; Wosnita, J.;
Early work on the iron-arsenide compounds supported the view, that a reduced dimensionality might be a necessary prerequisite for high–Tc superconductivity. Later, however, it was found that the zero-temperature upper critical magnetic field, Hc2(0), for the 122 iron pnictides is in fact rather isotropic. Here, we report measurements of the temperature dependence of the electrical resistivity, rho(T), in Ba0.5K0.32Fe2As2 and Ba0.68K0.32Fe2As2 single crystals in zero magnetic field and for Ba0.68K0.32Fe2As2 as well in static and pulsed magnetic fields up to 60 T. We find that the resistivity of both compounds in zero field is well described by an exponential term due to inter-sheet umklapp electron-phonon scattering between light electrons around the M point to heavy hole sheets at the Г point in reciprocal space. From our data, we construct an H–T phase diagram for the inter-plane (H || c) and in-plane (H || ab) directions for Ba0.68K0.32Fe2As2. Contrary to published data for underdoped 122 FeAs compounds, we find that Hc2(T) is in fact anisotropic in optimally doped samples down to low temperatures. The anisotropy parameter, γ = Habc2/Hcc2, is about 2.2 at Tc. For both field orientations we find a concave curvature of the Hc2 lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism we perfectly can describe Hc2(T) and its anisotropy.
  • JETP Letters 93(2011), 26-30

Publ.-Id: 15505 - Permalink


Magneto-acoustic study of single crystalline UCu0.95Ge
Yasin, S.; Andreev, A. V.; Skourski, Y.; Wosnitza, J.; Zherlitsyn, S.; Zvyagin, A. A.;
We present results of a magneto-acoustic study on a UCu0.95Ge single crystal. This compound exhibits antiferromagnetic ordering at 48 K and shows a first-order metamagnetic phase transition at 38 T to a spin-polarized state, i.e., when the magnetic field is applied along the c direction a sharp jump in the magnetization appears. The sound velocity and sound attenuation demonstrate pronounced anomalies in the vicinity of both magnetic phase transitions proving the important role of magneto-elastic interactions in the physics of this actinide compound. Above TN, the acoustic characteristics show some unusual frequency-dependent features which presumably can be related to the dynamics of Cu vacancies in UCu0.95Ge. Our results are discussed in frame of a phenomenological model, which describes qualitatively the main experimental observations.
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15504 - Permalink


Fermi-surface topology of Ce1−xYbxCoIn5
Polyakov, A.; Ignatchik, O.; Bianchi, A. D.; Prevost, B.; Seyfarth, G.; Fisk, Z.; Hurt, D.; Goodrich, R. G.; Wosnitza, J.;
The heavy-fermion (HF) metals are very susceptible to chemical substitution. In these compounds the Kondo coupling between a lattice of local moments and the conduction band creates quasiparticle excitations with large effective masses and the dopants disrupt the coherent Kondo coupling. We study the effect of Yb doping on the Pauli-limited, HF superconductor, CeCoIn5 via de Haas-van Alphen (dHvA) measurements. Yb acts as a non-magnetic divalent substitution for Ce, equivalent to hole doping on the rare-earth site. Our main goal consists in the systematic investigation of the dHvA oscillations on Ce1−xYbxCoIn5 in order to elucidate the evolution of the Fermi surface as a function of Yb. The dHvA data were obtained on high-quality single crystals with different concentrations of Yb atoms. The experiment was performed in a top-loading dilution refrigerator by use of a capacitive torque cantilever technique at temperatures down to 20 mK in magnetic fields up to 18 T.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15503 - Permalink


Gallium nanolayers featuring on-chip superconductivity in silicon
Skrotzki, R.; Herrmannsdörfer, T.; Fiedler, J.; Heera, V.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.;
We demonstrate the feasibility of embedding superconducting Ga nanolayers in commercial (100) oriented silicon wafers and discuss the possibility of potential device applications [1]. Ion implantation and rapid thermal annealing, known as versatile tools of microelectronic technology, have been used for inserting and distributing a gallium dose of up to 4 × 1016 cm2. As proven by structural analysis, a 10 nm thin layer of amorphous Ga-rich precipitates forms during annealing at 600 - 700°C. These structures exhibit a superconducting transition at 7 K. Extended resistivity and magnetization measurements reveal in-plane critical fields around 14 T and critical current densities exceeding 2 kA/cm2. In summary, we proceed with an optimistic outlook concerning the implementation of prospective microstructuring. After all, this would be the next step towards the development of novel semiconductor-based superconducting devices.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15502 - Permalink


Thermodynamic, magnetic and transport properties of Rh17S15
Uhlarz, M.; Ignatchik, O.; Wosnitza, J.; Haase, A.; Doerr, M.; Daou, R.; Rosner, H.; Naren, H. R.; Thamizhavel, A.; Ramakrishnan, S.;
We determined thermodynamic (specific heat), magnetic (magnetization, magnetostriction and susceptibility) and transport (electrical resistivity) properties of the 4d-electron superconductor Rh17S15 (Tc = 5.3 K). The upper critical field is 19.2 T at T = 0.07 K. We investigated both a polycrystal and a single crystal. Specific heat gives (B = 0) = 107 mJ/molK2, meff = 35 m0, and a superconducting energy gap Δ0 = 0.94 meV. The magnetic properties are dominated by flux-line pinning; resistivity likely reveals an amplification of electron-phonon coupling by weak disorder. Additionally, band-structure calculations are presented and interpreted in the context of our own experiments and other recently published results.We interpret our findings in order to find the origin of the strong electronic correlations in Rh17S15 both in the superconducting and in the normal-conducting state.
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15501 - Permalink


Field-induced gap in a quantum spin-1/2 chain in a strong magnetic field
Ozerov, M.; Wosnitza, J.; Čižmár, E.; Feyerherm, R.; Manmana, S. R.; Mila, F.; Zvyagin, S. A.;
Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interaction, that exhibits a field-induced spin gap, are probed by means of pulsed-field electron spin resonance spectroscopy. In particular, we report on a minimum of the gap in the vicinity of the saturation field Bsat = 48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a fully spin-polarized state (with magnon excitations). This interpretation is fully confirmed by quantitative the agreement with DMRG calculations for a spin-1/2 Heisenberg chain with staggered transverse field
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15500 - Permalink


Ergebnisse von Korrosionsuntersuchungen an der Korrosionsversuchsanlage „KorrVA“ des HZDR
Kryk, H.; Hoffmann, W.;
Inhalt der Arbeiten des HZDR im Rahmen des BMWi-Forschungsvorhabens 150 1363 ist u. A. die Untersuchung des Einflusses von Korrosionsprodukten auf das Differenzdruckverhalten von Mineralwolleablagerungen an den Sumpfansaugsieben der Notkühlsysteme von Leichtwasserreaktoren bei Kühlmittelverluststörfällen.
Zur Aufklärung der Korrosionsprozesse und deren Auswirkungen auf die Verstopfung der Sumpfsiebe wurden zahlreiche Experimente in der Korrosionsversuchsanlage „KorrVA“ unter Nutzung von feuerverzinkten Stahlproben durchgeführt. Die Ergebnisse der Langzeit-Korrosionsexperimente lassen auf einen mehrstufigen Korrosionsmechanismus schließen. Zunächst erfolgt eine Auflösung der Zinkschicht in der Borsäure-Lösung. Die dabei entstehenden Zink-Ionen gehen in Lösung und tragen somit nicht signifikant zur Erhöhung des Druckverlustes an den Sumpfsieben bei. Während der zweiten Stufe erfolgt die Auflösung des Basismaterials, welches in weiterer Folge zu unlöslichen Korrosionspartikeln (Rost) reagiert. Diese lagern sich an den mit Isoliermaterial-Fasern belegten Sumpfsieben ab und führen so zu einem weiteren Differenzdruckaufbau. Als Haupteinflussfaktoren des Gesamtprozesses wurden die Aufprallkraft des Leckstrahls auf die Materialoberfläche, die Kühlwasserchemie sowie das Verhältnis der Korrosions-Oberfläche zum Kühlmittel-Volumen und das Verhältnis von Zink-Oberflächen im Leckstrahl zu unter dem Wasserspiegel liegenden verzinkten Oberflächen identifiziert.
Keywords: LWR, LOCA, corrosion, hot-dip galvanised steel, zinc, boric acid
  • Lecture (Conference)
    Fachkolloquium "Partikelströmung", 17.-18.03.2011, Zittau und Dresden, Deutschland
  • Contribution to proceedings
    Fachkolloquium "Partikelströmung", 17.-18.03.2011, Zittau und Dresden, Deutschland
    CD-ROM

Publ.-Id: 15499 - Permalink


Peculiar high-field quantum magnetism in the frustrated S = 1/2 spin chain cuprate linarite
Schäpers, M.; Wolter, A. U. B.; Drechsler, S.-L.; Nishimoto, S.; Skourski, Y.; Uhlarz, M.; Schmitt, M.; Rosner, H.; Rule, K. C.; Süllow, S.; Heide, G.; Büchner, B.;
We present an experimental and theoretical study of the quasi-onedimensional S = 1/2 Heisenberg magnet linarite PbCuSO4(OH)2, with competing ferromagnetic nearest-neighbor and antiferromagnetic nextnearest- neighbor exchange interactions. It includes magnetization and NMR studies as well as theoretical simulations for the determination of the leading exchange couplings, which are about an order of magnitude higher as determined previously [1]. Furthermore, a manifold of field-induced phases are probed, from which we draw a preliminary phase diagram. Notably, spin-lattice relaxation investigations indicate that linarite might undergo a magnetic quadrupolar spin liquid phase transition as recently predicted for such materials.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15498 - Permalink


Investigation of spin- lattice interactions in Ho2Ti2O7 and Dy2Ti2O7
Erfanifam, S.; Zherlytsin, S.; Wosnitza, J.; Petrenko, O.;
Ho2Ti2O7 and Dy2Ti2O7 belong to the family of rare-earth titanates with pyrochlore structure which have attracted much interest in recent years because of their spin-ice ground state and unusual magnetic excitations. Ultrasound experiments have been carried out on Ho2Ti2O7 and Dy2Ti2O7 at low temperatures down to 0.3 K and applied magnetic fields of up to 17.5 T. The temperature as well as field dependences of the relative change of the sound velocity demonstrate some pronounced anomalies below 2 K for the acoustic modes c11 and cL. In addition we have performed magnetization measurements of these two compounds. The observed anomalies and features in the sound velocity and magnetization provide additional information about the spin-lattice interactions in these spin-ice compounds. The role of the lattice degrees of freedom in connection with the emergent quasiparticles (magnetic monopoles) is discussed.
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15497 - Permalink


Investigatons of modified interlayer coupling in the anisotropic antiferromangnet [Cu(pyz)2(HF2)]SbF6
Beyer, R.; Manson, J. L.; Schlueter, J. A.; Wosnitza, J.;
In recent years, many synthetic strategies have emerged with regard to the crystal engineering of functional magnetic materials. The group of J.L. Manson et al. were able to grow single crystals of a quasi-2D antiferromagnet [Cu(pyz)2(HF2)]SbF6 and a defective polymorphic pendant [Cu2(pyz)4F(HF)(HF2)](SbF6)2 where 50% of the HF2- links are broken, leading to two crystallographically unique Cu2+ sites. The chemical composition remains unchanged, the structural configuration indicates a minor Jahn-Teller distortion. We studied the two branches of this compound by means of magnetization and specific heat measurements, in order to get a better understanding of the importance of H-F hydrogen bonds for establishing long-range magnetic ordering in polymeric quantum magnets.
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15496 - Permalink


Development of a new methodology for realistic describing radionuclide retardation in safety assessment
Stockmann, M.; Brendler, V.; Schikora, J.; Noseck, U.; Flügge, J.;
Conceptual model of the new methodology
In previous safety assessments the Kd concept with temporally constant values was applied to describe the radionuclide retardation in the far field of a repository.
Here, the existing transport program r3t [1] used for large model areas and very long time scales has been improved by a new methodology. Implementing the smart Kd concept based on surface complexation allows to consider varying realistic geochemical conditions.
The methodology is based on a description of the sorption of radionuclides as a function of selected, important environmental parameters Ei such as pH, pCO2, ionic strength, concentration of the cations Ca2+ and Al3+ and presence of mineral phases. Exemplarily for a potential repository site in Germany, the Gorleben site has been selected as application case for a proof-of-concept.
Most of the individual parameters Ei are not available in r³t so far. Thus the transport of these influence factors as well as equations describing pH and concentrations of ions as a function of accessible mineral phases had to be implemented. Then the reactive transport model r³t can call for each time-space point pre-calculated Kd values for selected sediments. They are stored in a multidimensional matrix depending on the respective geochemical conditions. Figure 1 shows the frequency distribution of the pre-calculated Kd-values for Am3+ and U6+ and their classification.

Figure 1: Frequency distribution of the pre-calculated Kd values for Am3+ and U6+.

[1] Fein (2004) Report GRS-192.
  • Contribution to proceedings
    Goldschmidt2011, 14.-19.08.2011, Prague, Czech Republic

Publ.-Id: 15495 - Permalink


Intraexciton terahertz nonlinear optics in semiconductor quantum wells: sideband generation and AC Stark splitting
Wagner, M.; Schneider, H.; Stehr, D.; Winnerl, S.; Andrews, A. M.; Schartner, S.; Strasser, G.; Helm, M.;
We investigate nonlinear optics related to the intraexcitonic 1s-2p heavy-hole transition in GaAs/AlGaAs quantum wells. Tuning intense terahertz (THz) light around this resonance we report (i) efficient second order sideband generation and (ii) first clear evidence of the Autler-Townes effect.
Keywords: intraexciton, exciton, AC Stark, Autler-Townes, terahertz, free-electron laser
  • Lecture (Conference)
    35th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THZ 2010), 05.-10.09.2010, Rom, Italien
  • Contribution to proceedings
    35th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THZ 2010), 05.-10.09.2010, Rom, Italien
    IEEE conference proceedings, 978-1-4244-6657-3

Publ.-Id: 15494 - Permalink


Microstructural Evaluation of Ti-6Al-4V alloy after Plasma Immersion Ion Implantation (PIII)
Oliveira, V.; Silva, M. M.; Ueda, M.; Yogi, L.; Zepka, S.; Reis, D. A. P.; Reuther, H.;
Microstructural Evaluation of Ti-6Al-4V alloy after Plasma Immersion Ion Implantation (PIII)
  • Poster
    IX Encontro da SBPMat 2010, IX Brazilian MRS Meeting 2010, 24.-28.10.2010, Ouro Preto, Brasilien

Publ.-Id: 15493 - Permalink


Surface Modification of Ni-Ti SMA by Nitrogen Plasma Immersion Ion Implantation – Tribology Preliminary Results
Camargo, E. N.; Silva, M. M.; Ueda, M.; Mello, C. B.; Otubo, J.; Rigo, O. D.; Reuther, H.;
Surface Modification of Ni-Ti SMA by Nitrogen Plasma Immersion Ion Implantation – Tribology Preliminary Results
  • Poster
    IX Encontro da SBPMat 2010, IX Brazilian MRS Meeting 2010, 24.-28.10.2010, Ouro Preto, Brasilien

Publ.-Id: 15492 - Permalink


Structure and Tribological Properties of the Aged Inconel 718 Superalloy by Plasma Immersion Ion Implantation
Silva, M. M.; Hirschmann, A. C. O.; Moura Neto, C.; Ueda, M.; Reuther, H.; Mello, C. B.;
Structure and Tribological Properties of the Aged Inconel 718 Superalloy by Plasma Immersion Ion Implantation
  • Poster
    5th Int. Conf. on Surfaces, Coatings and Nanostructured Materials, NANOSMAT-5,, 19.-21.10.2010, Reims, Frankreich

Publ.-Id: 15491 - Permalink


Synthesis and evaluation of 1,5-diaryl-substituted tetrazoles as novel selective cyclooxygenase-2 (COX-2) inhibitors
Al-Hourani, B. J.; Sharma, S. K.; Mane, J. Y.; Tuszynski, J.; Baracos, V.; Kniess, T.; Suresh, M.; Pietzsch, J.; Wuest, F.;
A series of 1,5-diaryl-substituted tetrazole derivatives was synthesized via conversion of readily available diaryl amides into corresponding imidoylchlorides followed by reaction with sodium azide. All compounds were evaluated by cyclooxygenase (COX) assays in vitro to determine COX-1 and COX-2 inhibitory potency and selectivity. Tetrazoles 3a–e showed IC50 values ranging from 0.42 to 8.1 mM for COX-1 and 2.0 to 200 lM for COX-2. Most potent compound 3c (IC50 (COX-2) = 2.0 lM) was further used in molecular modeling docking studies.
Keywords: Cyclooxygenase; COX-2 inhibitors; 1,5-Diaryl-tetrazoles

Publ.-Id: 15490 - Permalink


Thermal hydraulic reactor core calculations based on coupling the CFD code ANSYS CFX with the 3D neutron kinetic core model DYN3D
Grahn, A.; Kliem, S.; Rohde, U.; Schütze, J.; Frank, T.;
In order to get the correct feedback on the core reactivity, analyses of postulated reactivity initiated accidents in nuclear reactors require the coupled solution of the neutron transport equation, the equations of heat conduction in the fuel and the heat and momentum transport in the coolant. The paper gives an overview on the coupling of the neutron kinetics code DYN3D with the general purpose fluid dynamics code ANSYS CFX which was carried out to improve the thermal hydraulic part of reactor dynamics simulations. Two steady state simulations of Convoi and VVER type reactors demonstrate that the coupled code system allows for analyses with more plausible results of coupled thermal hydraulics - neutron kinetics problems because three-dimensional coolant flow and heat transport can now be simulated.
Keywords: neutron kinetics, thermal hydraulics, coupled codes
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2011, 16.-19.05.2011, Berlin, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2011, 16.-19.05.2011, Berlin, Deutschland

Publ.-Id: 15489 - Permalink


Uranium immobilization in biofilms from a granitic nuclear waste repository research tunnel. - A microsensor and spectroscopic study.
Krawczyk-Bärsch, E.; Pedersen, K.; Lehtinen, A.; Arnold, T.;
At the depth of 70 m (tunnel chainage 771) of the nuclear waste repository research tunnel ONKALO (Finland), which will be part of the nuclear waste repository in the future, massive biofilms are growing next to a fracture zone in a granitic rock environment. They were described as a pink and solid slime, consisting of Pseudomonas anguilliseptica, Arthrobacter bergeri, Hydrogenophaga sp., Methylobacter tundripaludum, Rhodoferrax ferrireducens, and Haliscomenobacter hydrossis. The samples were removed from the tunnel wall together with the fracture water for uranium sorption experiments in a flow cell. A uranium concentration of 4×10-5 M was adjusted in the fracture water by adding UO2(ClO4)2. The water was pumped through the flow cell in a closed circuit for 42 hours. Microsensor measurements of the redox potential, pH and oxygen were performed in the several millimeters thick biofilms before and after the addition of uranium in order to record the effect of uranium. The obtained data showed significant changes of redox potential, pH and oxygen. The redox potential decreased after the addition of uranium during the experiment from 70  2 mV to -164 mV  2 mV with an increase of the pH from 5.4  0.1 to 7.3  0.1 at the same time, indicating reducing conditions in the microenvironment of the biofilm. The decrease in the oxygen concentration showed that the bacteria in the top region of the biofilms, i.e. the metabolically most active biofilms zone, battled the toxic effects of aqueous uranium with an increased respiratory activity, which resulted in oxygen depleted zones. Redox processes may have been triggered, leading to a removal of uranium from the aqueous phase. Analysis, which were performed before and after the sorption experiment, clearly showed, that 63 % of the added uranium was immobilized.

The retardation of uranium in the biofilm was determined by Energy-filtered Transmission Electron Microscopy (EF-TEM) and Electron Energy Loss Spectroscopy (EELS). Elongated particles of high electron density were observed in the cytoplasm of some rod shaped gram negative bacteria, which were often found associated with large rod shaped bacteria. Analysis of the elongated particles by EELS provided spectroscopic evidence for the presence of uranium immobilization, showing unequivocally uranium ionization intensity peaks of O4,5- and N6,7-edges. Distribution analysis of uranium, phosphorus and calcium clearly showed, that a solid uranium mineral has formed intracellular, which indicates the presence of a solid U-phosphate mineral similar to Autunite (Ca[UO2]2[PO4]2•10-12H2O).

Acknowledgments:
The European Atomic Energy Community Seventh Framework Programme [FP7/2007-2013] under grant agreement n° 212287, Collaborative Project ReCosy is thanked for funding.
Keywords: retardation, uranium, biofilm, nuclear waste repository
  • Lecture (Conference)
    3rd Annual Workshop of ReCosy, 21.-24.03.2011, Balaruc-les-Bains, Frankreich

Publ.-Id: 15488 - Permalink


A 3D heat conduction model for block-type High Temperature Reactors and its implementation into the Code DYN3D
Baier, S.; Kliem, S.; Rohde, S.;
The code DYN3D, devoloped at the Helmholtzzentrum Dresden-Rossendorf, is extended for application of block-type High Temperature Reactors.
It involves a 3D heat conduction model to deal with higher-(than one)-dimensional effects of heat transfer and heat conduction in a block-type HTR. The heat conduction model is coupled with the existing thermal-hydraulic channel model of DYN3D. Fully-coupled (hexagonal) neutron kinetics and thermal hydraulics calculations are performed. It is shown that the model is appropriate to simulate both stationary states and short-time transients (sudden change of reactivity, sudden increase of the inlet coolant temperature) in a block-type HTR.
Keywords: high temperature gas cooled reactor, heat conduction model, transient analysis, computer code, temperature reactivity feedback
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 17.-19.05.2011, Berlin, BRD
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 17.-19.05.2011, Berlin, BRD

Publ.-Id: 15486 - Permalink


The first candidate for chiral nuclei in the A=80 mass region: 80Br
Wang, S. Y.; Qi, B.; Zhang, S. Q.; Hua, H.; Li, X. Q.; Zhu, L. H.; Meng, J.; Liu, L.; Wyngaardt, S. M.; Papka, P.; Ibrahim, T. T.; Bark, R. A.; Datta, P.; Lawrie, E. A.; Lawrie, J. J.; Majola, S. N. T.; Masiteng, L. P.; Mullins, S. M.; Gal, J.; Kalinka, G.; Molnar, J.; Nyako, B. M.; Timar, J.; Juhasz, K.; Schwengner, R.;
Excited states of 80Br have been investigated via the 76Ge(11B, 3n) and 76Ge(7Li, 3n) reactions and a new I = 1 band has been identified which resides 400 keV above the yrast band. Based on the comparison between the experimental results and the triaxial particle rotor model calculations, a chiral character of the two bands within the pi g9/2 X nu g9/2 configuration is proposed, which provides the first evidence for chirality in the A 80 region.
Keywords: Nuclear structure, in-beam spectroscopy, chiral rotation, particle-rotor model

Publ.-Id: 15485 - Permalink


Magnetic moments of the first excited 2+ states in the semi-magic A=112,114,116,122,124 Sn isotopes
Walker, J.; Jungclaus, A.; Leske, J.; Speidel, K.-H.; Ekström, A.; Boutachkov, P.; Cederkäll, J.; Doornenbal, P.; Gerl, J.; Gernhäuser, R.; Goel, N.; Gorska, M.; Kojouharov, I.; Maier-Komor, P.; Modamio, V.; Naqvi, F.; Pietralla, N.; Pietri, S.; Prokopowicz, W.; Schaffner, H.; Schwengner, R.; Wollersheim, H.-J.;
The g factors of the first excited 2+ states in the A=112,114,116,122,124 Sn isotopes have been measured with high accuracy using the transient field technique in combination with Coulomb excitation in inverse kinematics. The experimental results are discussed in a qualitative way on the basis of empirical single particle g factors of the relevant proton and neutron orbitals and compared to a number of different theoretical calculations. The results are found to be best described by shell-model calculations in an extended configuration space. Clear evidence for the contribution of neutron pair excitations from the 1d3/2 to the 0h11/2 orbital to the wave function of the 2+ state in 122,124Sn has been obtained.
Keywords: Nuclear structure, in-beam spectroscopy, magnetic moments, shell model.

Publ.-Id: 15484 - Permalink


Field- and current-induced domain-wall motion in permalloy nanowires with magnetic soft spots
Vogel, A.; Wintz, S.; Gerhardt, T.; Bocklage, L.; Strache, T.; Im, M.-Y.; Fischer, P.; Fassbender, J.ORC; McCord, J.; Meier, G.
We study field- and current-induced domain-wall motion in permalloy nanowires comprising a square-shaped magnetically softened region. Implantation of chromium ions is used to induce pinning sites via a local reduction of the saturation magnetization. Micromagnetic simulations, magnetic transmission soft X-ray microscopy, and electrical measurements are employed to char- acterize the pinning potential which significantly differs for transverse and vortex walls. Reliable domain-wall depinning from a so-called magnetic soft spot by single current pulses is observed. This demonstrates the suitability of these pinning sites for applications.
Keywords: magnetic nanowires, spin transfer torque, magnetic soft spot, x-ray microscopy

Publ.-Id: 15483 - Permalink


Plutonium redox chemistry under anoxic conditions in the presence of iron(II) bearing minerals
Kirsch, R.; Fellhauer, D.; Altmaier, M.; Charlet, L.; Fanghänel, T.; Scheinost, A. C.;
The environmental fate of plutonium, the major transuranium actinide in nuclear waste, is largely impacted by its sorption onto and redox reactions with iron oxide, carbonate or sulfide minerals that form as corrosion products of steel in the "near field" and occur widely in sediments. To obtain information on oxidation state and local structure of Pu in the presence of Fe(II) bearing minerals, electrolytically prepared Pu(V) or Pu(III) (242Pu, 1-3·10-5 M) were, under anoxic conditions, reacted with magnetite (FeIIFeIII2O4) (pH 6-8.5), chukanovite (Fe2(CO3)(OH)2) (pH 8.5) and mackinawite (FeS) (pH 6-8.5). Pu-LIII-edge X-ray absorption spectra (XAS) were collected after 40 d and 8 months of reaction.
In all 14 samples, more than 98 % of Pu was associated with the solid phase and its redox speciation thus accessible by XAS. With magnetite, only the sample prepared at the highest pH and highest Pu loading contained Pu(IV)O2 while in all others Pu was solely present as a tridentate Pu(III) surface complex [1]. The three chukanovite samples all contained both Pu(III) (15 to 40 %) and PuO2. With mackinawite at pH 6 only Pu(III) was present, while all samples prepared at pH7 and higher contained mostly PuO2 and up to approx. 10 % Pu(III).
Through comparison of the different types of minerals (oxide, carbonate, sulfide), reaction pH and Pu/mineral ratios, it becomes apparent that the type of surface complexation (e.g. inner-sphere on magnetite vs. outer-sphere on mackinawite) and total mineral surface area are key parameters in controlling concentrations of dissolved Pu and in determining whether a PuO2 solid phase precipitates. While PuO2 provides an upper limit for concentrations of dissolved Pu, the available mineral surface area and sorption complex stability control what percentage of Pu is present in surface complexes. Under reducing conditions as established through the Fe(II) bearing minerals used here, this mineral surface associated Pu was found to be trivalent. Surface complexed Pu(III) and PuO2 can be thought of being in equilibrium with each other via two processes: a sorption reaction between dissolved and surface complexed Pu(III) and a heterogeneous redox reaction between dissolved Pu(III) and solid phase Pu(IV)O2. It remains to be investigated if and through what mechanisms the Pu solid phase speciation (sorbed Pu(III) vs. solid phase PuO2) might impact the migration behavior of Pu and how, for risk assessment purposes, Pu(III) surface complexes with iron minerals can be implemented into geochemical models.
Keywords: plutonium, redox, EXAFS, XANES, Fe(II)-bearing minerals, mackinawite, magnetite, chukanovite
  • Lecture (Conference)
    Goldschmidt Conference 2012, 24.-29.06.2012, Montreal, Canada
  • Abstract in refereed journal
    Mineralogical Magazine (2012), 1942-1942

Publ.-Id: 15482 - Permalink


Molecular imaging of α7 nicotinic acetycholine receptors in vivo: current status and perspectives
Brust, P.; Deuther-Conrad, W.;
Es ist kein Abstract vorhanden.
  • Open Access LogoBook chapter
    Peter Bright: Neuroimaging-Clinical Applications, Rijeka, Croatia: InTech - Open Access Publisher, 2012, 978-953-51-0200-7, 533-558

Publ.-Id: 15481 - Permalink


Frequency dependence of spin relaxation in periodic systems
Barsukov, I.; Römer, F. M.; Meckenstock, R.; Lenz, K.; Lindner, J.; Hemken To Krax, S.; Banholzer, A.; Körner, M.; Grebing, J.; Fassbender, J.ORC; Farle, M.
As a common method to separate intrinsic and extrinsic spin relaxation processes in a ferromagnet, their frequency dependence is employed. We show, that this current approach may be insufficient for a large class of ferromagnetic systems, since the extrinsic spin relaxation can exhibit non-monotonous, periodic frequency dependence, as demonstrated by a good agreement of ferromagnetic resonance experiment and phenomenologic theory.
Keywords: ferromagnet, magnetic relaxation, magnon-magnon scattering, magnetic resonance, thin films, ion beam irradiation

Publ.-Id: 15480 - Permalink


High-Field ESR in Spin Systems with Reduced Dimensionality
Zvyagin, S.;
Quantum fluctuations in low-dimensional magnets give rise to a variety of exotic strongly correlated states, making those systems an extremely attractive ground for testing various theoretical concepts. In this presentation I will focus on high-frequency and high-field Electron Spin Resonance (ESR) studies of two low-dimensional quantum magnets: copper pyrimidine dinitrate (Cu-PM), a spin-1/2 antiferromagnetic chain system with alternating g-tensor and Dzyaloshinskii-Moriya interactions, and the spin-ladder system (C5H12N)2CuBr4 (known as BPCB). In Cu-PM, the observation of a minimum of the spin gap in the vicinity of the saturation field, Hsat = 48.5 T, is associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized magnon state. This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG calculations for spin-1/2 Heisenberg chain with a staggered transverse field. In BPCB, the zero-field gap in the excitation spectrum, Δ = 16.5 K, is observed directly. In addition, our studies provide straightforward evidence of a pronounced anisotropy in this compound (~ 5% of the rung interaction), which is in contrast to an isotropic spin-ladder model, employed for this system previously. It is argued that such an anisotropy in BPCB is determined by the substantial spin-orbit coupling, which appears to be very important for describing magnetic properties of BPCB. The talk will give also a brief introduction into the recent development of the high-field ESR program at the Dresden High Magnetic Field Laboratory.
  • Invited lecture (Conferences)
    International School and Symposium on Multifunctional Molecule-based Materials, 13.-18.03.2011, Argonne, Illinois, USA

Publ.-Id: 15479 - Permalink


Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field
Zvyagin, S.; Ozerov, M.; Wosnitza, J.; Cizmar, E.; Feyerherm, R.; Manmana, S. R.; Mila, F.;
Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions that exhibits a field-induced spin gap, are probed by means of pulsedfield electron spin resonance spectroscopy. In particular, we report on a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the sine-Gordon region (with solitonbreather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG investigation of the spin-1/2 Heisenberg chain with a staggered transverse field.
  • Lecture (Conference)
    MAR11 Meeting of The American Physical Society, 21.-25.03.2011, Dallas, Texas, USA

Publ.-Id: 15478 - Permalink


Direct Observation of Band-Gap Closure for a Semiconducting Carbon Nanotube in a Large Parallel Magnetic Field
Jhang, S. H.; Marganska, M.; Skourski, Y.; Preusche, D.; Grifoni, M.; Wosnitza, J.; Strunk, C.;
We have investigated the magnetoconductance of semiconducting carbon nanotubes (CNTs) in pulsed, parallel magnetic fields up to 60 T, and report the direct observation of the predicted band-gap closure and the reopening of the gap under variation of the applied magnetic field. We also highlight the important influence of mechanical strain on the magnetoconductance of the CNTs.
  • Physical Review Letters 106(2011), 096802

Publ.-Id: 15477 - Permalink


Damping of de Haas-van Alphen oscillations and vortex-lattice disorder in the peak-effect region of extreme type-II borocarbide superconductors
Maniv, A.; Maniv, T.; Zhuravlev, V.; Bergk, B.; Wosnitza, J.; Köhler, A.; Behr, G.; Canfield, P. C.; Sonier, J. E.;
The study of magnetic quantum oscillations in the superconducting state is of fundamental importance for understanding the nature of superconductivity under high magnetic fields. However, although studied for more than three decades, this phenomenon poses several basic questions that still defy satisfactory answers. A key controversial issue concerns the additional damping observed in the vortex state of many strong type-II superconductors. Here, we show results of μSR, dHvA, and superconducting quantum interference device magnetization measurements on borocarbide superconductors, initially aimed at investigating the “phase-smearing” effect due to inhomogeneous field broadening. It is found, however, that a sharp drop observed in the dHvA amplitude just below Hc2 is correlated with enhanced disorder of the vortex lattice in the peak-effect region, where the phase-smearing effect is negligible. It is concluded that quasiparticle scattering by the pair potential is significantly enhanced due to vortex-lattice disorder, thus generating additional damping in the dHvA amplitude.
  • Physical Review B 83(2011), 104505

Publ.-Id: 15476 - Permalink


Duration measurement of laser-accelerated electron bunches using single-shot THz time-domain interferometry
Debus, A.; Bussmann, M.; Schramm, U.; Sauerbrey, R.; Karsch, S.;
Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches of unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry from coherent transition radiation. Using a ZnTe-based electro-optical setup and a 0.5J, 45fs, 800nm laser beam, we demonstrate that the duration of quasi-monoenergetic electron bunches from laser-wakefield acceleration is 32fs (FWHM) at a best fit and below 38fs at a 90% confidence level.
Keywords: laser-wakefield acceleration, pulse length measurement, electro-optic sampling, time-domain interferometry
  • Poster
    DPG Frühjahrstagung Münster 2011, 21.-25.03.2011, Münster, Deutschland

Publ.-Id: 15475 - Permalink


Traveling-wave Thomson Scattering towards tunable, high-yield sources in the hard X-ray range
Debus, A.; Steiniger, K.; Siebold, M.; Jochmann, A.; Irman, A.; Bussmann, M.; Schramm, U.; Cowan, T.; Sauerbrey, R.;
Thomson sources are compact in size and can provide ultrashort, hard X-ray pulses of high brilliance. However, the finite Rayleigh length at small interaction diameters, makes it increasingly difficult in head-on (180°) Thomson scenarios to avoid higher laser intensities and thus the onset of the nonlinear regime. Effectively, such a geometry limits the peak brilliance of all future Thomson sources. We present a novel concept, Traveling-wave Thomson scattering (TWTS), which allows to obtain centimeter to meter long optical undulators, where interaction length and diameter are independent of each other. With an ultrashort, high-power laser pulse in an oblique angle scattering geometry using tilted pulse fronts, electrons and laser remain overlapped while both beams travel over distances much longer than the Rayleigh length. TWTS offers per pulse photon yields that are 2-3 orders of magnitudes beyond current designs, a minimum scattered bandwidth independent of the ultrashort laser pulse duration and tunability of photon energy without requiring a change in electron energy.
Keywords: Traveling-Wave Thomson Scattering, X-ray, VLS grating, Thomson source
  • Lecture (Conference)
    DPG Frühjahrstagung Kiel 2011, 28.-31.3.2011, Kiel, Deutschland

Publ.-Id: 15474 - Permalink


Design and scaling considerations of Traveling-wave Thomson sources
Debus, A.; Steiniger, K.; Siebold, M.; Jochmann, A.; Irman, A.; Bussmann, M.; Schramm, U.; Cowan, T.; Sauerbrey, R.;
Thomson sources, driven by small linacs or laser-wakefield accelerated (LWFA) electrons are compact in size and can provide ultrashort, hard X-ray pulses of high brilliance. Traveling-wave Thomson scattering (TWTS) is particularly interesting for “pink beam” experiments at hard X-rays in which high photon yields in a single, ultrashort pulses are needed. Above 100keV photon energy, this approach potentially leads to peak brilliances that are beyond the capabilities of existing synchrotron radiation sources. Towards experimental realization, we show how such a Traveling-wave setup has to be implemented. An emphasis is put on the use of varied-line spacing (VLS) gratings for dispersion precompensation of the laser beam at large interaction angles to achieve the required overlap between laser and electrons within the interaction region.
Keywords: Traveling-Wave Thomson Scattering, X-ray, VLS grating, Thomson source
  • Poster
    DPG Frühjahrstagung Kiel 2011, 28.-31.3.2011, Kiel, Deutschland

Publ.-Id: 15473 - Permalink


Long optical undulators with Traveling-Wave Thomson Scattering
Debus, A.; Steiniger, K.; Siebold, M.; Jochmann, A.; Irman, A.; Bussmann, M.; Schramm, U.; Cowan, T.; Sauerbrey, R.;
We present a novel concept for optical undulators that avoids the restrictions by the Rayleigh limit of the laser, which allows to define interaction length and diameter independent of each other. With an
ultrashort, high-power laser pulse in an oblique angle scattering geometry using tilted pulse fronts, electrons and laser remain overlapped while both beams travel over distances much longer than the Rayleigh length. This allows to realize side-scattering in laser-electron beam interactions, without compromises with regard to luminosity or overlap.
This is of particular interest for linac-driven Thomson sources, where this Traveling-wave Thomson scattering (TWTS) setup could increase per pulse photon yields 2-3 orders of magnitudes beyond current headon (180°) scattering designs. Also, the smallest achievable scattered bandwidth is controlled by the width of a cylindrically focused laser beam and thus is independent of the ultrashort laser bandwidth. Due to the flexibility in side-scattering angle, photon energies become tunable over a large spectral range without requiring a change in electron energy.
Keywords: Traveling-Wave Thomson Scattering, X-ray, VLS grating, Thomson source
  • Lecture (Conference)
    DPG Frühjahrstagung Münster 2011, 21.-25.03.2011, Münster, Deutschland

Publ.-Id: 15472 - Permalink


Experimental challenges of Traveling-wave Thomson Scattering
Debus, A.; Steiniger, K.; Siebold, M.; Jochmann, A.; Irman, A.; Bussmann, M.; Schramm, U.; Cowan, T.; Sauerbrey, R.;
Traveling-wave Thomson scattering is a novel interaction design that allows circumventing the Rayleigh limit in optical undulators, which is interesting for possible realizations of Thomson scattering sources with photon yields per pulse that are 2-3 orders of magnitudes beyond current designs. Here we present details on how a Traveling-wave setup has to be implemented in experiment. An emphasis is put on the use of varied-line spacing (VLS) gratings for spatio-temporal beam shaping at large interaction angles to achieve optimal overlap. At the FZD we are using the high-power laser system DRACO (250TW) to realize a Thomson source with electrons from the linear accelerator ELBE or laser-plasma accelerated electrons. We present the current status and further progress towards a head-on Thomson source and a Traveling-Wave Thomson scattering source aiming for high photon yields per pulse.
Keywords: Traveling-wave Thomson scattering, TWTS, X-ray, VLS gratings, Thomson source
  • Poster
    DPG Frühjahrstagung Münster 2011, 21.-25.03.2011, Münster, Deutschland

Publ.-Id: 15471 - Permalink


Space-time couplings at the DRACO laser
Debus, A.;
The effect of spatio-temporal distortions in the DRACO laser potentially leads to pulse-front tilts in the laser focus on the order of tens of degrees. It is emphasized, that for controlling the focal pulse-front tilt, it is not only necessary to analyze angular dispersion, but additionally spatial and group delay dispersion. A qualitative picture of the space-time couplings is presented and quantitatively discussed at the example of an imperfectly aligned DRACO compressor. The results suggest that the focal pulse front tilt is currently unknown and that more precise measurements of both spatial and group delay are required.
Keywords: spatio-temporal distortions, DRACO, pulse-front tilt
  • Lecture (others)
    Gruppenklausur in Gries, Austria / HZDR retreat, 27.02.-3.3.2011, Gries, Austria

Publ.-Id: 15470 - Permalink


Imidazole Containing Bispidine Ligands: Synthesis, Structure and Cu(II)-Complexation
Walther, M.; Matterna, M.; Juran, S.; Fähnemann, S.; Stephan, H.; Kraus, W.; Emmerling, F.;
The preparation and characterization of tris-pyridyl bispidine (3,7-diazabicyclo[3.3.1]nonane) derivatives with benzimidazole and imidazole donor groups at the N3 position of the bispidine skeleton and their copper(II) complexes are reported. The impact of the hetaryl substituents on the configuration isomerism of piperidones and their corresponding bispidones has been studied by 1H NMR spectroscopy. The di-pyridyl piperidones with benzimidazole, imidazole and the Cu(II) complex of the benzimidazole containing bispidone have been characterized by X-ray single crystal diffraction.
  • Zeitschrift für Naturforschung Section B - A Journal of Chemical Sciences 66b(2011), 721-728

Publ.-Id: 15469 - Permalink


Preparation and Characterization of Magnetic Tunnel Junctions with Spin Transfer Torque
Höwler, M.; Bernert, K.; McCord, J.; Potzger, K.; Fritzsche, M.; Mücklich, A.; Fassbender, J.ORC; Kirsch, K.; Mattheis, R.; Slesazeck, S.
Current-perpendicular-to-plane (CPP) magnetic tunnel junctions (MgO-MTJ) have been prepared using electron beam lithography as well as argon ion beam etching. A tantalum hardmask was utilized for pattern transfer. The size of the elliptical nanopillars could be decreased down to 90nm x 150 nm while preserving a TMR ratio of 92.5 %. TEM images proof the absence of redepositions at the MgO layer edge and give an insight into the interface quality. Magnetization switching was performed using either static magnetic fields and/or dc current (spin torque). The nanopillars could be characterized at temperatures ranging from 5 K to 150 K and room temperature. The analysis of magnetization dynamics included single-shot time-resolved magnetoresistance measurements as well as dc current induced oscillations of the free-layer magnetization.
Keywords: magnetic tunnel junction, MgO, spin transfer torque effect, preparation, electron beam lithography, ion beam etching
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15468 - Permalink


Bestimmung langlebiger Radionuklide mit Beschleunigermassenspektrometrie (AMS) mit DREAMS: Von Bergstürzen über Klimaforschung bis Rückbau
Merchel, S.; Akhmadaliev, S.; Rugel, G.;
Das Helmholtz-Zentrum Dresden-Rossendorf (HZDR) hat sein Spektrum ionenanalytischer Verfahren um eine weitere hochsensitive Methode erweitert: die Beschleunigermassenspektrometrie (accelerator mass spectrometry = AMS). Diese AMS ist prädestiniert zur Bestimmung langlebiger Radionuklide (t1/2 ≥ 100 a), die entgegen der allgemein üblichen Zerfallszählung, nicht durch den eigentlichen Zerfall detektiert werden. Vielmehr werden die noch nicht zerfallenen Nuklide wesentlich effizienter massenspektrometrisch bestimmt. Dabei besitzt die AMS gegenüber der konventionellen Massenspektrometrie den Vorteil, dass sie Störsignale von Molekülionen und Isobaren effektiver unterdrücken kann. Die AMS liefert somit weitaus niedrigere Nachweisgrenzen (20000 Atome/g oder 10-9 Bq) als die konventionellen Methoden.
Im Gegensatz zu den in Europa gängigen niederenergetischen AMS-Anlagen, die sich weitgehend auf die Bestimmung von 14C spezialisiert haben, wird die AMS-Anlage des HZDR - DREAMS (DREsden AMS) - als erste moderne Anlage in der EU mit einer Terminalspannung von 6 MV betrieben. Aufgrund der instrumentellen Weiterentwicklungen der AMS, die die Bestimmung von Isotopenverhältnissen im Bereich von 10-16 nun ermöglichen [1], haben sich die interdisziplinären Applikationsgebiete stark ausgeweitet. Anfänglich bevorzugt untersuchte Proben aus Kosmochemie, Astrophysik und nukleare Daten, werden zunehmend von Proben aus Strahlenschutz, Nuklearsicherheit, Nuklearentsorgung, Radioökologie, Phytologie, Ernährungswissenschaften, Toxikologie und Pharmakologie verdrängt. DREAMS fördert nicht nur die interne Vernetzung der HZDR-Forschungsaktivitäten in der Materialforschung, Strahlenphysik, Radiochemie und Radiopharmazie. Zudem steht DREAMS auch externen Nutzern, insbesondere denen von anderen Helmholtz-Zentren und Universitäten, zur Verfügung. Kommerzielle Proben aus dem Rückbau und der Hydrogeologie runden das DREAMS-Profil ab.
Eine zwingende Voraussetzung für ein erfolgreiches AMS-Labor ist allerdings die Installation radiochemischer Probenpräparationslabore. Die Ansprüche an die chemische bzw. Nuklidreinheit der AMS-Proben sind zwar wesentlich geringer als z.B. die der alpha- oder beta-Spektrometrie und die stark verringerten Probenmengen erleichtern grundsätzlich die Aufbereitung, jedoch muss aufgrund der Nachweisstärke der AMS ein besonderes Augenmerk auf (Kreuz-)Kontaminationen gelegt werden. Erste Projekte aus den Geo- und Umweltwissenschaften mit der TUBA Freiberg, der Uni Rennes, der Uni Bayreuth, der BGR Hannover, dem Alfred-Wegener-Institut, dem GFZ und der Uni Potsdam zeigen, dass der Erfolg etablierter radiochemischer Trennungsgänge u.a. proportional der Laborerfahrung der Probenpräparatoren ist.
Referenzen [1] S. Merchel et al, Nucl. Instr. and Meth. B 266 (2008) 4921.
Keywords: accelerator mass spectrometry
  • Lecture (Conference)
    GDCh-Wissenschaftsforum Chemie 2011, 04.-07.09.2011, Bremen, Deutschland

Publ.-Id: 15467 - Permalink


Entwicklung nanoskaliger funktionaler Schichten auf Basis von bakteriellen Hüllproteinen
Weinert, U.; Günther, T.; Müller, N.; Pollmann, K.; Raff, J.;
Bakterielle Hüllproteine stellen die äußerste Abgrenzung von vielen Bakterien und fast allen Archaeen zu ihrer Umwelt dar. Isoliert sind diese Proteine in der Lage, in wässrigen Systemen oder auf Oberflächen zu rekristallisieren und regelmäßige Gitterstrukturen auszubilden. Ihre Fähigkeit hochstrukturierte Nanoschichten zu bilden und das Vorhandensein von zahlreichen frei zugänglichen funktionellen Gruppen qualifizieren diese Proteine als Matrix für die Herstellung nanoskaliger funktioneller Schichten, wie z.B. sensorischen Schichten. Ziel unserer Arbeit ist die Entwicklung von Sensoren für die Detektion kleinster Mengen an Pharmaka, z. B. Canamycin A und von Metallen in wässrigen Systemen.

Dabei ist es möglich, verschiedene Komponenten wie optische Signalgeber und einen spezifischen Rezeptor für bestimmte Substanzen, sequentiell an das Protein zu koppeln. Für die Signalgebung werden Fluoreszenzfarbstoffe genutzt, die in der Lage sind, einen Fluoreszenz Resonanz Energietransfer (FRET) zu erzeugen. Bei diesem Effekt wird Energie von einem Donor-Farbstoff auf einen Akzeptor-Farbstoff übertragen. Im Resultat wird die Fluoreszenz des Donors vermindert und die des Akzeptors erhöht. Da dieser Energietransfer sehr empfindlich auf äußere Veränderungen reagiert, soll der zu detektierende Analyt diesen durch Quenching stören.
Als spezifische Rezeptoren dienen Aptamere. Aptamere sind kurze Oligonukleotide, die ähnlich wie Antikörper nach dem Schlüssel-Schloss-Prinzip funktionieren, jedoch aufgrund ihrer chemischen Eigenschaften weitaus stabiler sind. Mittels dieser chemischen Antikörper lassen sich eine Vielzahl verschiedener Targetmoleküle spezifisch an die sensorische Schicht binden.

Die Erzeugung eines FRET zwischen zwei S-Layer-gebundenen Fluoreszenzfarbstoffen konnte bereits mittels Bestimmung der Fluoreszenzlebensdauer nachgewiesen werden. Ebenso konnten Anti-Thrombin-Aptamere als Modell erfolgreich gebunden werden und deren Funktionalität mittels Affinitätsmessungen nachgewiesen werden. Somit wurden bereits wichtige Zwischenziele für den Aufbau einer sensorischen Schicht erreicht. In einem nächsten Schritt sollen beide Komponenten auf dem Protein gekoppelt werden und so eine nanoskalige sensorische Schicht erzeugt werden.
Keywords: S-layer proteins, sensory layer, FRET, aptamers
  • Lecture (Conference)
    7. Deutsches BioSensor Symposium, 03.-06.04.2011, Heilbad Heiligenstadt, Deutschland

Publ.-Id: 15466 - Permalink


Magnetic domain structure evolution in NiMnGa magnetic shape memory alloy
Neudert, A.; McCord, J.;
We have investigated the magnetic domain structure evolution due to twin boundary motion in single crystalline NiMnGa (10M) magnetic shape memory samples. Due to the high mobility of the twin boundaries they can be moved by applying a magnetic field or mechanical stress. In general, the equilibrium domain width in magnetic samples depends on the interplay of demagnetization and anisotropy energy. Depending on the orientation of the easy axis within a magnetic sample different equilibrium widths can be found. We investigated the magnetic domain structure using optical polarization microscopy and magnetic indicator film technique. We found that the qualitative domain structure depends on whether the sample was subjected to magnetic fields or mechanical stresses. In both cases the twin boundary is moved and therefore the orientation of the magnetic easy axis is changing. During the field induced motion the variants are partially saturated, whereas during the stress induced motion the net magnetization in the variants is unchanged. This results in a completely different remagnetization process and magnetic domain structure. Using domain theory the equilibrium domain width can be calculated and is compared with the experimental values. We greatly acknowledge support by DFG priority program SPP 1239.
Keywords: magnetic shape memory alloy, magnetic domains
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 15.03.2011, Dresden, Germany

Publ.-Id: 15465 - Permalink


CFD for subcooled flow boiling: Simulation of DEBORA experiments
Krepper, E.; Rzehak, R.;
In this work we investigate the present capabilities of CFD for wall boiling. The computational model used combines the Euler / Euler two-phase flow description with heat flux partitioning. Very similar modelling was previously applied to boiling water under high pressure conditions relevant to nuclear power systems. Similar conditions in terms of the relevant non-dimensional numbers have been realized in the DEBORA tests using Dichlorodifluoromethane (R12) as the working fluid. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size.
After reviewing the theoretical and experimental basis of correlations used in the model, give a careful assessment of the necessary recalibrations to describe the DEBORA tests. It is then shown that within a certain range of conditions different tests can be simulated with a single set of model parameters. As the subcooling is decreased and the amount of generated vapour increases the gas fraction profile changes from wall to core peaking. This is a major effect not captured by the present modelling. Some quantitative deviations are assessed as well and directions for further model improvement are outlined.
Keywords: CFD, two phase flow, boiling, momentum exchange

Publ.-Id: 15464 - Permalink


Rise and fall of defect induced ferromagnetism in SiC single crystals
Li, L.; Prucnal, S.; Yao, S. D.; Potzger, K.; Anwand, W.; Wagner, A.; Zhou, S.;
6H-SiC single crystals containing VSi-VC divacancies are investigated with respect to magnetic and structural properties. We found that an initial increase of structural disorder leads to pronounced ferromagnetic properties at room temperature. Further introduction of disorder lowers the saturation magnetization and is accompanied with the onset of lattice amorphization. Close to the threshold of full amorphization, also divacancy clusters are formed and the saturation magnetization nearly drops to zero.
Keywords: Silicon carbide, defect induced magnetism
  • Applied Physics Letters 98(2011)22, 222508

Publ.-Id: 15463 - Permalink


Corrosion Resistance of NiTi SMA Modified by Nitrogen Plasma Immersion Ion Implantation
Camargo, E. N.; Silva, M. M.; Ueda, M.; Otubo, J.; Baldissera, S. C.; Pichon, L.; Reuther, H.;
Corrosion Resistance of NiTi SMA Modified by Nitrogen Plasma Immersion Ion Implantation
  • Poster
    5th Int. Conf. On Surfaces, Coatings and Nanostructured Materials, NANOSMAT-5, 19.-21.10.2010, Reims, Frankreich

Publ.-Id: 15462 - Permalink


Modification of Surface Properties of Ti-16Si-4B Powder Alloy by Plasma Immersion Ion Implantation
Fernandes, B. B.; Ueda, M.; Mello, C. B.; Fernandes, P. B.; Reuther, H.; Ramos, A. S.;
Results of the surface modification of Tie16Sie4B powder alloy by nitrogen ion implantation are presented, together with the experimental description of the preparation of that powder by high-energy ball milling and hot pressing. The phase structure, chemical composition and morphology of sample surfaces were observed by utilizing X-ray diffractometer (XRD), atomic force microscope (AFM) and scanning electron microscopy (SEM). A tribological characterization was carried out with a ball-on-disc tribometer and an SEM. Friction coefficient is compared with the one obtained for Tie6Ale4V alloy and the wear scars characterized by SEM/EDS (energy dispersive spectroscopy). The concentration profile of the detected elements have been investigated using Auger electron spectroscopy (AES) depth profiling. Our results show that a shallow implanted layer of oxygen and nitrogen ions were obtained at the Tie16Si e4B alloy surface, sufficient to modify slightly its tribological properties.

Publ.-Id: 15461 - Permalink


Magnetic Au Nanoparticles on Archaeal S-layer Ghosts as Templates
Selenska-Pobell, S.; Reitz, T.; Schönemann, R.; Herrmannsdörfer, T.; Merroun, M.; Geißler, A.; Bartolomé, J.; Bartolomé, F.; Garcia, L. M.; Wilhelm, F.; Rogalev, A.;
Gold nanoparticles with a size of 2.5 nm were produced using the SlaA-layer ghosts of the archaeon Sulfolobus acidocaldarius as a template. These archaeal bio-Au nanoparticles differ significantly from those of the bacterial bio-Au nanoparticles produced on the S-layer of Bacillus sphaericus. The archaeal Au nanoparticles consist exclusively of Au(0), while the bacterial ones represent a mixture of Au(0) and Au(III). The most impressive feature of the archaeal Au nanoparticles is that they are paramagnetic, in contrast to the bacterial ones and also to bulk gold. As demonstrated by SQUID magnetometry, the archaeal bio-Au possess an unusually large magnetic moment of about 0.1 µB/Au atom. HR-TEM combined with EDX analysis revealed that the archaeal Au nanoparticles are linked to sulfur atoms. The latter originate from the thiol groups of the cystein amino acid residues which are characteristic for the SlaA-layer of S. acidocaldarius but absent in the S-layer of B. sphaericus.
Keywords: Magnetic gold nanoparticles, Sulfolobus acidocaldarius, surface layer (S-layer)
  • Open Access LogoNanomaterials and Nanotechnology 1(2011)2, 8-16

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Publ.-Id: 15460 - Permalink


Dipole-strength functions in 86Kr and 136Ba
Massarczyk, R.;
This talk was a presentation about my diploma thesis. A overview over the ELBEfacility, photon scattering experiments and GEANT4 simulations was presented.
Keywords: Photon scattering, nuclear spectroscopy, nuclear structure, gamma strength function
  • Lecture (others)
    Mini-Workshop on Applications of Electron Bremsstrahlung, 17.-18.01.2011, Dresden, Deutschland

Publ.-Id: 15459 - Permalink


Bestimmung der elektromagnetischen Dipolstärkeverteilung in mittelschweren Atomkernen mittels Kernresonanzfluoreszenz
Massarczyk, R.;
Im Rahmen der Arbeit wurden Experimente aus den Jahren 2008/09 für die Kerne 86Kr und 136Ba analysiert. Zur Auswertung mussten neben Photonenfluss- und Effizienzbestimmung auch Simulationen durchgeführt werden, welche die experimentellen Bedingungen widerspiegeln. Nicht am Kern gestreute Ereignisse und Detektorantwortfunktionen wurden mit Hilfe des Programmpaketes GEANT4 simuliert, um in den gemessenen Daten berücksichtigt zu werden. Daraus zeigt sich, dass neben diskreten Energiezuständen auch ein beachtlicher Teil des ermittelten Anregungsquerschnitts in einer Art Quasikontinuum aus unauflösbaren Peaks liegt. Die ermittelten Wirkungsquerschnitte werden mit Hilfe eines statistischen Ansatzes auf Verzweigung in mögliche Zerfallskanäle und auf Fütterung durch Zustände höherer Energie korrigiert.
Keywords: Photon scattering, nuclear spectroscopy, nuclear structure, gamma strength function
  • Diploma thesis
    TU Dresden und Helmholtz-Zentrum Dresden-Rossendorf, 2011
    88 Seiten
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-047 2014

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Publ.-Id: 15458 - Permalink


Molecular identification of xenobiotic degrading bacteria via the 16S rDNA approach
Satschanska, G.; Selenska-Pobell, S.;
Molecular identification of five xenobiotic degrading bacteria was performed by using the16S rDNA approach. The strains KCM-R10 and KCM-R11 were isolated from polluted environments near the biggest Pb-Zn smelter on the Balkan Peninsula - KCM. AP9 strain was isolated from activated sludge of the Sofia waste water treatment plant and BT271 - from a phenol-polluted soil in the region of the petrochemical plant near the town of Burgas. The “U”-strain is a bacterial culture of the laboratory microbial collection of Sofia University. All strains are transforming or degrading xenobiotics such as heavy metals, phenol and its derivatives. PCR amplification of their 16S rRNA genes, RFLP analysis of the obtained amplicons with MspI and HaeIII endonucleases and sequencing were conducted. The isolate KCM R10 was affiliated with Pseudomonas sp., the isolates KCM R11 and BT271 – with Bacillus sp., the isolate AP9 - with Pseudomonas putida, and the isolate called “U” - with Bacilluis amyloliquifaciens. The strains are promising for application as mixed cultures in the industrial waste water purification
  • Lecture (Conference)
    Ecology, 28.-29.04.2011, Sofia, Bulgaria

Publ.-Id: 15457 - Permalink


Bestimmung der elektromagnetischen Dipolstärkeverteilung in Atomkernen mittels Kernresonanzfluoreszenz an ELBE
Massarczyk, R.; Cowan, T.; Junghans, A. R.; Grosse, E.; Schramm, G.; Schwengner, R.; Wagner, A.;
Beitrag zum Barkhausenposterpreis 2011
  • Poster
    Dresdner Barkhausen-Poster-Preis 2011 für Studenten und Nachwuchswissenschaftler, 28.01.2011, Dresden, Deutschland

Publ.-Id: 15456 - Permalink


Dipole strength in 86Kr up to the neutron-separation energy
Massarczyk, R.; Schwengner, R.; Junghans, A. R.; Rusev, G.; Schramm, G.; Wagner, A.;
For the firrst time a high-pressure gas target has been investigatetd at the bremsstrahlung facility at the ELBE accelerator of the Forschungszentrum Dresden-Rossendorf. The experiment was carried out at an electron beam energy of 12MeV in order to study the energy region up to the neutron separation. GEANT4 simulations were performed to subtract the atomic background from the measured spectrum and deduce the intensity of the resonantly scattered gamma-rays. Considering also transitions from states in the quasicontinuum, simulations of gamma-ray cascades were carried out with a new code to estimate branching ratios. As a result the photoabsorption cross section obtained from transitions to the ground state is calculated. The data will be presented in the context of further photon-scattering experiments performed in Rossendorf on the stable isotopes at the closed neutron shell N = 50.
Keywords: Photon scattering, nuclear spectroscopy, nuclear structure, gamma strength function
  • Lecture (Conference)
    DPG Frühjahrstagung 2011 Münster, 21.-25.03.2011, Münster, Deutschland

Publ.-Id: 15455 - Permalink


Investigating fluorinated cycloalkyl groups for increased metabolic stability using a Tyrosine model system
Franck, D.; Kniess, T.; Steinbach, J.; Zitzmann-Kolbe, S.; Friebe, M.; Dinkelborg, L. M.; Graham, K.;
Objectives:
The aim was to investigate whether fluorocyclobutyl rings can be introduced into targeting probes to improve metabolic stability, while maintaining its binding affinity, using tyrosine as a model system for the LAT transporters.

Methods:
The precursor, cis-cyclobutane-1,3-diol ditosylate, its corresponding F-19 reference compound trans-3-fluorocyclobutanol (FCB), along with the cis-(3-fluorocyclobutyl)-tyrosine (3FCBT), were synthesized using standard organic chemistry methodologies. The non-radioactive 3FCBT was tested in competition and efflux stimulation cell assays using A549 human lung carcinoma cells with [3H]-D-Tyrosine. The metabolic stability of reference compound 3FCBT was studied in both rat hepatocytes and human plasma. Radiosynthesis methods using standard radiofluorination of the prosthetic group [18F]FCB and its conjugation to tyrosine gave the desired 3[18F]FCBT after chromatographic purification. In vitro studies were performed in A549 cells using 3[18F]FCBT and incubated at 37°C for 10, 20, 30 and 60 minutes with and without inhibitors fluoroethyl-tyrosine (FET) and non-radioactive
3FCBT.

Results:
The syntheses of cis-cyclobutane-1,3-diol ditosylate, trans-3-fluorocyclobutanol (FCB), along with the cis-(3-fluorocyclobutyl)-tyrosine (3FCBT) were established. 3FCBT was shown to block the uptake of [3H]-D-tyrosine in the competition cell assay and could stimulate the release of 3H]-D-Tyrosine from the cell in an efflux stimulation cell assay. 3FCBT showed very high stability in both rat hepatocytes (> 95%) and human plasma (> 95%). The unoptimized radiosynthesis gave the desired 3[18F]FCBT, via the prosthetic group [18F]FCB, in moderate yield (12%) with high radiochemical purity (> 99%). The cell uptake showed an increase of 3[18F]FCBT over time and reached a plateau of 5.87% after 30 minutes.

Conclusions:
The radiosynthesis of the prosthetic group [18F]FCB and its conjugation to tyrosine to give 3[18F]FCBT were successfully established. The introduction of 3[18F]FCBT into the LAT-targeting vector D-Tyr was characterized by a significant in vitro uptake in A549 cells and was actively transported into these cells. The encouraging results warrant further investigations of this tracer in the in vivo setting.
  • Lecture (Conference)
    SNM 58th Annual Meeting, 04.-08.06.2011, San Antonio, USA

Publ.-Id: 15453 - Permalink


Experiments on evaporating pipe flow
Lucas, D.; Beyer, M.; Szalinski, L.;
Evaporating two-phase flows were investigated in an 8 m long vertical pipe with an inner diameter of 195.3 mm. The phase transfer was induced by depressurization of the pipe starting from 1, 2, 4 and 6.5 MPa. The pressure relief was done for an upward liquid flow in the test section as well as for stagnant liquid. These experiments complete the extensive CFD-grade database obtained at the same test section for adiabatic two-phase flows and flows with bubble condensation along the pipe. Detailed information on the structure of the steam-water interface was obtained using a pair of wire-mesh sensors. The established database is suitable for the development and validation of CFD.
Keywords: poly-disperse flow, evaporation, pressure relief, phase transfer, bubble size
  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, paper NURETH14-061, 25.-30.09.2011, Toronto, Ontario, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), paper 061
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Ontario, Canada

Publ.-Id: 15452 - Permalink


Measurement of two-phase flow parameters with multi-channel gamma densitometry and local void probes at the INKA test facility
Schleicher, E.; Bieberle, A.; Tschofen, M.; Hampel, U.; Lineva, N.; Maisberger, F.; Leyer, S.;
In the integral test facility "INKA" at AREVA NP GmbH in Karlstein, Germany, different passive safety systems of the boiling water reactor concept "KERENA" are being tested. One of these systems is the emergency condenser (EC) which starts automatically in case of a loss of coolant accident with the descent of the filling level in the reactor pressure vessel causing fast heat dissipation. For the exact balance and description of the processes in the emergency condenser a more precise understanding of the two-phase flow in the EC pipes is essential. In this paper we describe the instrumentation of the EC bundle itself as well as the condensate line with thermo needle probes to determine the phase distribution and phase temperatures with high temporal resolution of 10 kHz along the EC circuit. The needle probes have been designed for fast local measurement of void fraction and temperature under extreme conditions like water-steam ambience under 310°C and 9 MPa. The phase measurement is realized by use of an electrical conductivity signal measured at the probe tip. A micro-sheath thermocouple serves as the measuring electrode, hence the conductivity and the temperature signal can be measured simultaneously exactly at the same position in the flow. With this technology it is possible to differentiate between steam and non-condensable gases. Additionally, the EC return pipe has been instrumented with a multichannel gamma densitometer to measure the cross-sectional gas fraction in the condensate line. The gamma densitometer measures the ray attenuation of gamma rays from a Cs137 source along 34 single beams through the 200 mm steel pipe at 10 Hz sampling rate. From these attenuation data the cross-sectional void fraction can be calculated with an accuracy of about 3 %. The paper gives a short overview of the passive safety concept of the KERENA system, the development of the special instrumentation and measuring techniques for extreme temperatures and pressure and discusses the first experimental results in the INKA test facility in Karlstein.
Keywords: nuclear thermal hydraulics instrumentation, needle probes, gamma densitometry
  • Contribution to proceedings
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14 , 25.-30.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14)
  • Lecture (Conference)
    NURETH-14, 25.-29.09.2011, Toronto, Canada, 25.-30.09.2011, Toronto, Canada

Publ.-Id: 15451 - Permalink


Radiation exposure by (-)-F18-NCFHEB, a new PET tracer for imaging of cerebral alpha4beta2 nicotinic acetylcholine receptors (nAChRs)
Sattler, B.; Wilke, S.; Starke, A.; Patt, M.; Hoepping, A.; Graef, S.; Schoenknecht, P.; Hegerl, U.; Brust, P.; Sabri, O.;
Objectives : (-)-[F-18]Norchloro-fluoro-homoepibatidine ((-)-NCFHEB) is a new tracer for neuroimaging of alpha4beta2 nAChRs with PET. To assess the radiation risk after application of the radioligand, the biodistribution, organ doses (OD) and the effective dose (ED) were determined in a phase 0/1 trial.
Methods : Whole body dosimetry of (-)-NCFHEB was performed in 3 healthy volunteers (59.6±3.9a; weight 74.3±3.1kg; 2m, 1f). The subjects were sequentially imaged up to 7h post i.v. injection of 353.7±10.2 MBq of (-)-NCFHEB on a SIEMENS Biograph16 PET/CT-system with 9 bed positions (BP) per frame, 1.5-6min/BP, CT-attenuation correction and iterative reconstruction. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activity-data. The ODs were calculated using the adult male model with OLINDA. The ED was calculated using tissue weighing factors as published in the ICRP 103/2007.
Results : The highest OD was received by the urinary bladder (80.2±37.8), followed by liver (44.7±5.4) and kidneys (38.6±5.1). The highest contribution to the ED was by the lungs (3.7±0.6) and the urinary bladder (3.2±1.5). The ED by i.v. application of (-)-NCFHEB is 22.9±0.7 (all in [μSv/MBq]).
Conclusions : The ED after i.v. application of 300 MBq (-)-NCFHEB is 6.8±0.2mSv. This corresponds to values obtained with other [F-18]-labeled compounds. These favorable dosimetry data encourage the further development of (-)-NCFHEB as a clinical tool for imaging of alpha4beta2 nAChRs with PET.
  • Poster
    SNM 58th Annual Meeting, 04.-08.06.2011, San Antonio, Texas, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 52(2011), 1459

Publ.-Id: 15450 - Permalink


Plasma immersion implantation for the corrosion protection of lead in pipe organs
Skorupa, W.; Cherkouk, C.; Prucnal, D.; Henke, S.; Reuter, H.; Hahn, A.; Skorupa, K.; Jehmlich, R.; Werner, H.; Pfeiffer, D.; Eule, A.-C.;
A new technique for the corrosion protection of lead in pipe organs is presented using plasma immersion implantation of nitrogen. A 20 nm surface layer protects against a massive acetic acid impact leading without protection to a strong etching effect which destroys the lead surface quality.
Keywords: plasma immesion implantation, nitrogen acetic acid impact, corrosion protection
  • Invited lecture (Conferences)
    2. Internationale Konferenz des Instituts für Orgel und Orgelbau an der Hochschule für Künste Bremen, 17.-19.03.2011, Lemgo, Deutschland

Publ.-Id: 15449 - Permalink


CFD studies on the phenomena around counter-current flow limitations of gas/liquid two-phase flow in a model of a PWR hot leg
Deendarlianto; Höhne, T.; Lucas, D.; Vallée, C.; Montoya, G.;
In order to improve the understanding of counter-current two-phase flow and to validate new physical models, CFD simulations of a 1/3rd scale model of the hot leg of a German Konvoi pressurized water reactor (PWR) with rectangular cross section were performed. Selected counter-current flow limitation (CCFL) experiments conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) were calculated with ANSYS CFX using the multi-fluid Euler-Euler modelling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model.

In the simulation, the drag law was approached by a newly developed correlation of the drag coefficient (Höhne & Vallée, 2010) in the Algebraic Interfacial Area Density (AIAD) model. The model can distinguish the bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicate also a quantitative agreement between calculations and experimental data for the CCFL characteristics and the water level inside the hot leg channel.
Keywords: Algebraic interfacial area density (AIAD) model, Drag coeficient, Countercurrent flow limitations (CCFL), Pressurized water reactor (PWR), Hot leg

Publ.-Id: 15448 - Permalink


Aptamer modifizierte bakterielle Oberflächenstrukturen für die Entwicklung neuer Sensoren
Pollmann, K.;
Projektvorstellung
  • Poster
    BIONA Statusseminar, Industriekongress, 16.-17.04.11, Berlin, Deutschland

Publ.-Id: 15446 - Permalink


Die zunehmende Bedeutung von biotechnologischen Innovationen für angrenzende Branchen
Pollmann, K.;
Biotechnologie in angrenzenden Branchen
  • Invited lecture (Conferences)
    6. Innovationsbörse Sachsen, 30.03.11, Görlitz, Deutschland

Publ.-Id: 15445 - Permalink


Cholinergic markers are altered in two different models of traumatic brain injury
Donat, C. K.; Hoffmeister, P.-G.; Walter, B.; Deuther-Conrad, W.; Schuhmann, M. U.; Voigt, C.; Bauer, R.; Meixensberger, J.; Brust, P.;
Traumatic brain injury (TBI) is the leading cause of death and disability in childhood, adolescence and early adulthood and often results in cognitive impairments. There is evidence from behavioural animal experiments and patient studies that those cognitive deficits are related to functional alterations within the cholinergic system. The present study was performed to investigate cholinergic markers in two different animal models of TBI with emphasis on the time-course of posttraumatic events and critical brain regions. The identification of sensitive targets within the cholinergic system is a precondition for the development of radioligands for neuroimaging of TBI patients with Positron-Emission-Tomography (PET).

Male Sprague-Dawley rats were randomized into three groups (post-TBI survival time: 2 h, 24 h and 72 h), anaesthetized and subjected to sham injury (control, n = 8) or controlled cortical impact injury (CCI) (n = 8) with 2 mm depth of impact at a velocity of 4 m/sec.
Thirteen newborn piglets (post-TBI survival time: 6 h) underwent fluid percussion (FP) injury (n = 7) or sham operation (n = 6) with an impact pressure of 3.8 ± 0.3 atmospheres.
For both species, cryostat brain sections were cut (rat 12 µm, pig 20 µm) and density of nicotinic (nAChR; α7, α4*/α3*), muscarinic (mAChR; M1-M5) acetylcholine receptors and the vesicular acetylcholine transporter (vAChT) were assessed with in vitro autoradiography. Additionally, histochemical staining of the acetylcholinesterase (AChE) was performed.

A significant decline in the receptor density of the α4*/α3* nAChR up to -33% was found in injured rats within brain regions critical for cognitive processes (thalamus, basal forebrain). In contrast, the brains of injured piglets did not reveal significant changes in receptor density.
The α7 nAChR density was drastically reduced (up to -47%) in injured rats at all time points and in piglets. Rats showed early decline of receptor density in 14 of 15 investigated brain regions (including hippocampus, thalamus, basal forebrain and cortex), while in piglets impairment was found especially in the hippocampus.
The mAChR showed smaller (~-20%), time-dependent reductions in injured rats and in piglets. However, almost identical brain regions were affected as found for α4*/α3* nAChR.
Histochemical staining indicated region-dependent increases and decreases in AChE activity in rats after TBI (~+/-20%) in contrast to injured piglets where only increased AChE-activity (+20%) was found.

In conclusion, cholinergic markers are significantly altered after experimental TBI independently of species, age and model. Even though differences in methodology do not allow direct comparisons between both models, results indicate common mechanisms of cholinergic changes after TBI. Considering the role of cholinergic markers for cognition in the brain, it seems likely that these alterations contribute to attention and memory deficits. Identifying the underlying mechanisms, for instance with PET, could help to ameliorate deficits in TBI-patients.
Keywords: traumatic brain injury, acetylcholine system, rat, pig, newborn, autoradiography
  • Poster
    9th Göttingen Meeting, 23.-27.03.2011, Göttingen, Deutschland

Publ.-Id: 15444 - Permalink


Phase fraction distribution measurement of oil-water flow with capacitance wire-mesh sensor
Da Silva, M. J.; Hampel, U.; Rodriguez, I. H.; Rodriguez, O. M. H.;
In this article, a novel wire-mesh sensor based on permittivity (capacitance) measurements is applied to generate images of phase fraction distribution and investigate the flow of viscous oil and water in a horizontal pipe. Phase fraction values were calculated from the raw data delivered by the wire-mesh sensor using different mixture permittivity models. Furthermore, these data were validated against quick-closing valve measurements. Investigated flow pattern were dispersion of oil in water (Do/w) and dispersion of oil in water and water in oil (Do/w&w/o). Maxwell-Garnett mixing model is better suited for Dw/o and Logarithimc model for Do/w&w/o flow pattern. Images of time-averaged cross-sectional oil fraction distribution along with axial slice images were used to visualize and disclose some details of the flow.
Keywords: wire-mesh sensor, liquid-liquid flow, viscous oil, phase fraction measurement, flow visualization
  • Measurement Science and Technology 22(2011)10, 104020

Publ.-Id: 15443 - Permalink


Compact magnetospectrometer for pulsed magnets based on infrared quantum cascade lasers
Drachenko, O.; Winnerl, S.; Schneider, H.; Helm, M.; Wosnitza, J.; Leotin, J.;
In this paper we present a portable quantum cascade laser (QCL) based infrared magnetospectrometer covering the spectral range from 5 to 120 μm. The variation of the excitation wavelength is enabled by an easy change of the QCL plug-in modules, while the use of any other external source is also possible. The performance of the setup is illustrated via cyclotron–resonance studies under pulsed magnetic fields up to 60 T.
Keywords: cyclotron resonance, infrared spectrometers, lasers
  • Review of Scientific Instruments 82(2011)3, 033108-1-033108-6
    DOI: 10.1063/1.3556441

Publ.-Id: 15442 - Permalink


FISH based analysis of 10 kV and 25 kV soft X-ray induced DNA damage in 184A1 human mammary epithelial cells
Beyreuther, E.; Dörr, W.; Lehnert, A.; Leßmann, E.; Pawelke, J.;
Over the past years, several in vitro studies have been performed on DNA damage induced by soft X-rays, especially in the energy range below 50 keV. Radiation effects originating from such low-energy photons are relevant in the context of medical diagnostics, e.g. mammography, or of accidental exposure to scattered radiation. The present study was initiated to investigate the X-ray energy dependent induction of stable and unstable chromosomal aberrations in the human mammary epithelial cell line 184A1. Three colour fluorescence in situ hybridisation was applied to identify chromosomal damage in chromosomes 1, 8 and 17, induced by 10 kV or 25 kV soft X-rays as well as by 200 kV X-rays as a reference quality.
Based on dose dependencies in the range of 0.5 to 5 Gy, RBE values of 0.84 ± 0.09 and 1.45 ± 0.18 were found for stable translocations induced by 25 kV and 10 kV X-rays, respectively, using 200 kV X-rays as reference. Moreover, the analysis of the minimum number of breaks, as required to form the visible chromosomal damage, resulted in similar RBE values of 0.93 ± 0.07 for 25 kV X-rays and 1.25 ± 0.10 for 10 kV X-rays relative to 200 kV X-rays. In addition, non-DNA-proportional contributions of chromosomes 8 and 17 to the whole DNA damage and deviations from the expected 1:1 ratio of translocations and dicentrics were revealed for the mammary epithelial cell line 184A1.
Keywords: RBE, soft X-rays, chromosomal aberrations, 184A1, FISH, mammary epithelial cells
  • Radiation and Environmental Biophysics 51(2012), 33-42
    DOI: 10.1007/s00411-011-0396-3
  • Poster
    12th International Wolfsberg Meeting on Molecular Radiation Biology / Oncology 2011, 25.-27.06.2011, Wolfsberg Castle/Ermatingen, Schweiz
  • Contribution to proceedings
    12th International Wolfsberg Meeting on Molecular Radiation Biology / Oncology 2011, 25.-27.06.2011, Wolfsberg Castle/Ermatingen, Schweiz
    Proceedings Book Molecular Radiation Biology/Oncology, Vol. 9, 3-9808819-6-2

Publ.-Id: 15441 - Permalink


Overview of laser cooling of relativistic C3+ ion beams at ESR
Bussmann, M.; Kroll, F.; Loeser, M.; Siebold, M.; Schramm, U.; Wen, W.; Winters, D. F. A.; Beck, T.; Rein, B.; Walther, T.; Birkl, G.; Nörtershäuser, W.; Kühl, T.; Novotny, C.; Kozhuharov, C.; Geppert, C.; Steck, M.; Dimopoulou, C.; Nolden, F.; Ma, X.; Stöhlker, T.;
We present an overview of the setup for all-optical cooling and beam diagnostics for relativistic C3+ ion beams at the Experimental Storage Ring (ESR) at GSI. With new optical diagnostics it is foreseen to improve the measurement of the longitudinal momentum spread of the beam by at least an order of magnitude. The new optical diagnostics together with the new Schottky diagnosis and beam profile monitor available at ESR will allow to access the complete phase space evolution of the beam inside the storage ring. With new laser systems developed for cooling beams with an initially large energy spread it will be possible to replace the electron cooler that was used to reduce the initial momentum spread of the ion beam.
Keywords: laser cooling, ion beam, relativistic energy, diagnostics, optical detection, beam parameters, phase space
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15440 - Permalink


PIConGPU - A scalable GPGPU implementation of the particle-in-cell algorithm
Bussmann, M.; Burau, H.; Berninger, F.; Kluge, T.; Debus, A.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Widera, R.; Hönig, W.; Juckeland, G.; Nagel, W.; Kilian, P.; Ganse, U.; Siegel, S.; Spanier, F.; Ragan-Kelley, B.; Verboncoeur, J.;
We present PIConGPU, an efficient and scalable implementation of the particle-in-cell algorithm for GPGPUs. We discuss the main building blocks of PIConGPU, the data access patterns used for both particle and field data and the communication model that allows to hide the large latency of network communication between GPGPU nodes on a cluster. PIConGPU provides a general framework which can be used to study both relativistic and nonrelativistic plasmas. We show first results on relativistic laser wakeeld acceleration of electrons in underdense plasmas and on the progress of integrating new physics models. The fast response time of the code makes it possible to receive results in hours compared to weeks with particle-in-cell codes running on mid-size commodity clusters. With this increase in computational
speed extensive parameter scans become possible even for large physical systems.
Keywords: particle-in-cell, pic, gpu, algorithm, latency, wakefield, acceleration, electron
  • Lecture (Conference)
    DPG Frühjahrstagung Münster, Hadronen und Kerne, 21.-25.03.2011, Münster, Deutschland
  • Lecture (Conference)
    DPG Frühjahrstagung Kiel, Plasmaphysik und Kurzzeitphysik, 28.-31.03.2011, Kiel, Deutschland

Publ.-Id: 15439 - Permalink


Enhanced laser ion acceleration from mass-limited foils
Kluge, T.; Enghardt, W.; Kraft, S. D.; Zeil, K.; Schramm, U.; Cowan, T. E.; Bussmann, M.;
We have performed an analysis of ultra-intense laser interaction with solid mass-limited targets (MLT) via electrodynamic 2D3V particle-in-cell simulations. The interaction with long (300 fs) high intensity (1020W=cm2) laser pulses with targets of diameter down to 1 micron is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. We developed an analytical model which enables us to predict the electron energy distribution of an MLT. Our results suggest that the most signicant ion energy enhancement should be expected for MLT with diameter below the laser focal spot
size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.
Keywords: mass-limited targets, electron recirculation, particle-in-cell, simulation, pic, foil, electron sheath, heating, ion energy, coulomb explosion
  • Lecture (Conference)
    DPG Frühjahrstagung Münster, Hadronen und Kerne, 21.-25.03.2011, Münster, Deutschland

Publ.-Id: 15438 - Permalink


Electron acceleration mechanisms in cone targets - scaling up the energy of laser accelerated ions
Kluge, T.; Gaillard, S.; Flippo, K.; Gall, B.; Lockard, T.; Geissel, M.; Offermann, D.; Schollmeier, M.; Kraft, S. D.; Metzkes, J.; Zeil, K.; Schramm, U.; Sentoku, Y.; Enghardt, W.; Sauerbrey, R.; Bussmann, M.; Cowan, T. E.;
In 2009, at the LANL Trident laser facility a new world record in laser accelerated proton energy has been set, exceeding 65 MeV, using hollow conical targets. We performed 2D collissional PIC simulations and identify two novel electron acceleration mechanisms that have not been considered before to enhance ion acceleration: the direct acceleration of electrons comoving with the driving laser along the the cone-wall inner surface (DASE) and the acceleration of electrons in surface plasma waves (PWA). We nd that they are responsible for a signicant increase in both electron number and energy in the case of a grazing laser incidence onto the inner cone wall surface compared to regular flat foils. We study the scaling of the electron and ion energies for various target and laser parameters.
Keywords: cone target, laser, proton, acceleration, beam, maximum energy, electron dynamics, heating, simulation, particle-in-cell, pic
  • Lecture (Conference)
    DPG Frühjahrstagung Münster, Hadronen und Kerne, 21.-25.03.2011, Münster, Deutschland

Publ.-Id: 15437 - Permalink


Interaction of intersubband transitions and ponderomotive responce in doped GaAs/AlGaAs multiple quantum wells at the THz regime
Baudisch, M.; Wagner, M.; Helm, M.; Stehr, D.;
In the present work we investigate the line shape of the broadband terahertz (THz) response in doped multiple quantum wells by means of field-resolved detection. In an optically excited structure we recently observed a Fano-like shape of the THz response [1]. This results from the superposition of the broad continuous ponderomotive response and the sharp intersubband transition. The first originates from the force that takes effect on carriers in an oscillating electromagnetic field. The applied spectroscopy technique is time-resolved ultrabroadband THz spectroscopy. The THz radiation is generated by phase-matched optical rectification of 10 fs near-infrared pulses in 50 μm thin GaSe crystals. The pulses are tuneable in a range from 15 to 40 THz with a width (FWHM) of up to 15 THz. The field-resolved detection is done by phase-matched electro optic sampling. The applied detection method is crucial for observing the effect since the ponderomotive current can only be seen as a lossless phaseshift of the transmitted THz radiation while the intersubband transition leads to an absorption. Thus we are able to observe directly the superposition of ponderomotive current and intersubband transition in the time-domain.
[1] D. Golde et al., Phys. Rev. Lett. 102, 127403 (2009).
Keywords: Terahertz, intersubband transition, fano, ponderomotive
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15436 - Permalink


Phonon contribution to the thermodynamics of pure and mixed clusters in bcc-Fe
Talati, M.; Posselt, M.; Bonny, G.; Al-Motasem, A. T.; Bergner, F.;
The irradiation-enhanced nanostructural evolution in reactor pressure vessel steels is a multiscale phenomenon. It can be effectively studied by rate theory for which necessary parameters must be obtained through atomistic simulations. The present work focuses on the phonon contribution to the thermodynamics of nanoclusters consisting of vacancy and/or Cu. In all calculations the most recent Fe-Cu interatomic potential developed by Pasianot and Malerba is employed. The vibrational density of states determined by the dynamical matrix method is used to calculate the phonon contribution to free energy of formation and free binding energy of the clusters. Pure bcc-Fe and pure fcc-Cu are used as references in the calculation of the free energy of formation. The vibrational contribution to the total free energy of these metals determined in this work is compared with available CALPHAD data and with literature data obtained by first-principle methods or interatomic potentials. In the case of pure vacancy clusters and for many mixed vacancy-Cu clusters the absolute value of the total free binding energy decreases with increasing temperature. Pure Cu clusters show the opposite behavior.
Keywords: Vibrational Density of States, Total free energy, Free binding energy, bcc-Fe , Thermodynamics, Molecular Dynamics Simulation
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 15435 - Permalink


Tribological Aspects of Carbon-Based Nanocoatings - Theory and Simulation
Kunze, T.; Gemming, S.; Posselt, M.; Seifert, G.;
Nanocoatings have the potential to improve the surface properties of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency. An important example are diamond-like carbon (DLC) films, which exhibit high mechanical stability depending on their deposition process. We present an introduction to this field of tribology by giving a short overview on DLC films, on the influence of lubricants from a theoretical point of view and in a broader sense, on basic principles of modeling tribological processes with molecular dynamic methods.

Publ.-Id: 15434 - Permalink


Direct observation of antiferromagnetically oriented spin vortex states in magnetic multilayer elements
Wintz, S.; Strache, T.; Körner, M.; Fritzsche, M.; Markó, D.; Mönch, I.; Mattheis, R.; Raabe, J.; Quitmann, C.; McCord, J.; Erbe, A.; Fassbender, J.ORC
We report on the coupling of spin vortices in magnetic multilayer elements. The magnetization distribution in thin film disks consisting of two ferromagnetic layers separated by a nonmagnetic spacer is imaged layer- resolved by using x-ray microscopy. We directly observe two fundamentally different vortex coupling states, namely antiferromagnetic and ferromagnetic orientation of the flux directions. It is found that these states are predetermined for systems that involve a sufficiently strong interlayer exchange coupling, whereas for the case of a purely dipolar interaction both states are transformable into each other.
Keywords: magnetic vortex, vortex coupling, magnetic multilayer, magnetic microscopy
  • Applied Physics Letters 98(2011), 232511

Publ.-Id: 15433 - Permalink


Structure and energetics of nanoclusters in bcc-Fe containing vacancies, Cu, and Ni
Al-Motasem, A. T.; Posselt, M.; Bergner, F.; Birkenheuer, U.;
Reactor pressure vessel (RPV) steels consist of polycrystalline bcc-Fe containing Cu, Ni and other foreign atoms. The continuous irradiation by fast neutrons leads to supersaturation of vacancies and self-interstitials and enhances the diffusion of Cu and Ni which occurs via the vacancy mechanism. These processes favor the formation of nanoclusters consisting of vacancies, Cu and Ni. The interaction of dislocations with these precipitates is considered to be the main cause of hardening and embrittlement of the RPV steels. In order to model the evolution of the precipitates under irradiation by rate theory, the energetics and thermodynamics of the clusters must be known. These data are hardly obtainable by experiments, however, they can be provided by atomic-level computer simulations. In the present work a combination of on-lattice Monte Carlo simulations and off-lattice Molecular Dynamics calculations is employed to determine structure and energetics of the nanoclusters. The atomistic simulations show that ternary clusters exhibit a shell structure with a core consisting of vacancies followed by a shell of Cu and an outer shell of Ni. Binary vacancy-Cu and Ni-Cu clusters show a similar shell structure, whereas the atomic configuration of vacancy-Ni agglomerates is completely different.
Keywords: LMMC, MD, binding energy.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Germany

Publ.-Id: 15431 - Permalink


Expression, purification and fluorine-18 radiolabeling of recombinant S100A4: a potential probe for molecular imaging of receptor for advanced glycation endproducts in vivo?
Wolf, S.; Haase-Kohn, C.; Lenk, J.; Hoppmann, S.; Bergmann, R.; Steinbach, J.; Pietzsch, J.;
Data concerning the pathophysiological role of extracellular S100A4, a member of the multigenic family of Ca2+-modulated S100 proteins, and its interaction with the receptor for advanced glycation endproducts (RAGE) or other putative receptors in tumorigenesis, metastasis, and inflammatory processes in vivo are scarce. One reason is the shortage of suitable radiotracer methods. We report a novel methodology using recombinant human S100A4 as potential probe for molecular imaging and functional characterization of this interaction. Therefore, human S100A4 was cloned as GST fusion protein in the bacterial expression vector pGEX-6P-1 and expressed in E. coli strain BL21. Purified recombinant human S100A4 was radiolabeled with the positron emitter fluorine-18 (18F) by conjugation with N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). The radioligand [18F]fluorobenzoyl-S100A4 (18F-S100A4) was used in cell binding experiments in RAGE-bearing human melanoma cells and endothelial cells in vitro, and in both biodistribution experiments and small animal positron emission tomography (PET) studies in normal rats in vivo. The cellular association and tissue-specific distribution of 18F-S100A4 in vitro and in vivo correlated well with the protein expression and anatomical localization of RAGE, e.g., in the vascular system and in lung. Compared to other S100 RAGE radioligands, the overall findings of this study indicate that extracellular S100A4 in vivo shows only a moderate interaction with RAGE and, furthermore, exhibits a substantially faster metabolic degradation. On the other hand, the approach allows the use of quantitative small animal PET and provides a novel probe to both delineate functional expression and differentiate multiligand interaction of RAGE under normal and pathophysiological
conditions in rodent models of disease.
Keywords: Endothelial cells; Melanoma cells; Molecular imaging; Multiligand receptors; Protein radiolabeling; Small animal positron emission tomography (PET); S100 proteins
  • Amino Acids 41(2011), 809-820

Publ.-Id: 15430 - Permalink


Dedicated 3D list-mode reconstruction for whole-body PET
Lougovski, A.; Langner, J.; Hofheinz, F.; Brüning, E. M.; van den Hoff, J.;
Although all currently available PET scanners support 3D acquisition protocols, full 3D image reconstruction is only rarely available in clinical PET. Usually, Fourier rebinning is used to reduce the image reconstruction to a set of independent 2D problems. Nowadays, faster computer systems allow to consider real 3D reconstruction as superior approach even for clincial routine, especially for whole body investigations. We report on our work on a dedicated whole-body image reconstruction using a 3D list-mode-based algorithm.

Methodik/Methods:
We implemented a 3D Ordinary Poisson List-mode Ordered Subsets Expectation Maximization algorithm (3D-LMOSEM) with on-the-fly calculation of the system matrix. Matrix elements are considered to be proportional to the intersection volume of voxels with Lines-of-Response (LORs) having a finite cross section. Two assumptions were used in this calculation:
i) the voxel grid is considered to consist of overlapping spheres, where the sphere volume is taken to be equal to that of the corresponding cubic voxel,
ii) LORs are cylinders whose axes connect the centers of the contributing detectors and the radii are calculated from the initial LOR volume.
This procedure reduces the complexity of system matrix computation considerably. The reconstruction is performed simultaneously for all bed positions. This bears the following advantage:
i) count loss in overlap regions is avoided leading to improved image quality,
ii) simultaneous reconstruction of all bed positions enables improved scatter calculation.
The new reconstruction was evaluated by comparison with the standard sinogram-based attenuation weighted OSEM-reconstruction (AW-OSEM) available with our Siemens EXACT HR+ scanner. The evaluation addressed these parameters: i) quantitative accuracy; ii) spatial resolution (FWHM comparison), iii) artifacts and noise characteristics.

Ergebnisse/Results:
Quantitative analysis yielded differences of mean values in selected regions-of-interest below a few percent. 3D-LMOSEM shows much better resolution (4.05 mm in brain and 4.35 mm in whole-body) compared to AW-OSEM (5.65 mm and 5.98 mm, respectively) with less inhomogeneity artifacts and noise. Typical 3D-LMOSEM reconstruction time for a FDG whole-body scan (7 bedpos; 6 min each) is 220 min using 80x2.3 GHz cores.

Schlussfolgerungen/Conclusions:
Compared to AW-OSEM the 3D-LMOSEM provides improved image resolution while decreasing overall noise level. The possibility to reconstruct all bed positions in one run prevents count loss and allows for a more accurate Out-of-FOV scatter correction. Due to the use of multi-threading and distributed computing techniques reconstruction times are approaching a level which will allow use of 3D-LMOSEM in clinical routine in the near future.
  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A29
  • Lecture (Conference)
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaften für Nuklearmedizin 2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 15429 - Permalink


Locally adaptive image filtering for noise reduction in PET
Langner, J.; Hofheinz, F.; Lougovski, A.; Brüning, E. M.; Oehme, L.; Beuthien-Baumann, B.; van den Hoff, J.;
As well known, the signal-to-noise ratio (SNR) of PET images can be low. This is especially true for whole body examinations of heavy patients, for respiratory-gated studies, and dynamic studies with short frames. In these cases linear smoothing filters (LF) such as a Gaussian filter are usually applied in order to achieve an acceptable SNR. Image resolution is, however, reduced by these LFs. This affects detectability and quantification of small structures. Interesting alternatives to LFs are non-linear, locally adaptive filters (NLF), which enable noise reduction while preserving strong edges in the data. It was the aim of this study to investigate the performance of a special NLF (bi-lateral filter, BF) when applied to low SNR images in PET.

Methodik/Methods:
The BF consists of the product of a spatially dependent part and an intensity dependent part. In one spatial dimension the filter weights are defined as W(n-n0) = S * exp(-(n-n0)2/2/sn2) * exp(-(I(n)-I(n0))2/2/sI2) where n0 is the index of the target voxel, n is the index of neighboring voxels, sn is the spatial standard deviation, I(n), I(n0) are the intensities of n and n0, sI is the intensity standard deviation, and S normalizes the sum over all weights to unity. Due to the intensity dependence this filter is not invariant but adjusted individually for each choice of n0, thus it is locally adaptive. The filter works by penalizing voxels, which are distant from n0 either in the spatial or the intensity domain. The latter property leads to preservation of sharp edges. To quantify the effects of this filter, phantom measurements were performed with F-18 using a cylinder phantom (∅=20 cm, h=18 cm; 6 spheres with 2.7 - 27 ml). Three different sphere-to-background ratios were investigated in list-mode in order to assess different SNR levels. The image data were filtered, both with the BF and a LF. The filtered data were analyzed for changes in noise level, resolution, and signal recovery. Furthermore, clinical respiratory-gated whole body studies were investigated with BF and compared to LF filtered images.

Ergebnisse/Results:
In the phantom studies the BF is able to preserve the spatial resolution of the original data near the edges of the spheres while improving the noise characteristics. Signal recovery even of small spheres is not significantly reduced. Using the LF seriously compromises spatial resolution and leads to unacceptable reduction of signal recovery. The positive properties of the filter were also apparent when applying the BF to single gates of respiratory-gated studies, which otherwise were not suitable for visual inspection.

Schlussfolgerungen/Conclusions:
NLF is a powerful alternative to LF, especially for studies with high noise. Its performance, however, critically depends on a sensible choice of the intensity standard deviation sI. Further work will show whether the filter is suitable for clinical use.
  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A92
  • Poster
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaften für Nuklearmedizin 2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 15428 - Permalink


Accuracy of MR-based attenuation: first experience with a whole-body PET/MR system
Brüning, E. M.; Langner, J.; Hofheinz, F.; Will, E.; Beuthien-Baumann, B.; Oehme, L.; Platzek, I.; Steinbach, J.; Laniado, M.; Kotzerke, J.; van den Hoff, J.;
Combined PET/MR systems for whole body investigations have been developed recently and are now starting to become available. One of the first of these systems (Gemini TF PET/MR, Philips) has been installed at our site. PET/MR is expected to provide new possibilities, notably in the area of quantitative bimodal functional imaging.
Quantitative PET imaging requires attenuation correction (AC), which is straightforward for PET/CT but not for PET/MR. In order to ensure quantitative accuracy of the PET data in the absence of a measured AC, one needs to use MR-based AC (MRAC), which relies on a combination of templates and accurate segmentation and tissue type identification of a suitable MR scan. Here, we report on a first evaluation of MRAC in phantoms as well as in patient investigations with the new system.

Methodik/Methods: A NEMA IEC Body Phantom was used. Data were evaluated regarding quantitative accuracy of background and sphere activity as well as homogeneity of the background. Reconstructed resolution was assessed as well. Evaluation of MRAC in patients is performed by direct comparison of MRAC with a transmission based AC (TMAC) acquired with an ECAT Exact HR+ (Siemens).

Ergebnisse/Results: Background inhomogeneity was found to be < 4% across the whole phantom. The reconstructed activity in the sphere inserts deviates from the known true values by < 5%. No artifacts related to erroneous AC could be observed in these measurements. The reconstructed resolution (FWHM) in these measurements was determined to be (5.01 - 5.48) mm. Patient studies will be performed in the coming months and evaluated as described above. The corresponding results will be reported.

Schlussfolgerungen/Conclusions: The vendor provided MRAC algorithms yielded very good results in our first phantom measurements both with respect to quantitative accuracy as well as regarding general image quality. The upcoming patient investigations will show whether these findings can be confirmed in whole body applications as well.
  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A49
  • Lecture (Conference)
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaften für Nuklearmedizin 2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 15427 - Permalink


Thioantimonates in geothermal waters
Planer-Friedrich, B.; Scheinost, A. C.;
The formation of aqueous antimony sulfide complexes upon dissolution of stibnite (Sb2S3) and their importance for geothermal antimony transport has often been stressed. All the more surprising, up to date only laboratory studies and theoretical calculations support the existence of these thioantimony species1-5. We successfully applied alkaline chromatographic separation and detection by inductively coupled plasma mass spectrometry (AEC-ICP-MS) previously used for thioarsenates6, for the determination of two antimony-sulfur species in synthetic solutions and natural geothermal waters. Based on their S/Sb ratios of 3.08 ± 0.28 and 4.05 ± 0.32 they were provisionally assigned as tri- and tetrathioantimonate. Using X-ray absorption spectroscopy (XAS), the identity of tetrathioantimonate was confirmed based on shell fits by about 4 Sb-S paths (CN 4.2-4.3) and the characteristic pentavalent Sb-S binding length of 2.33-2.34 Å. Aqueous trithioantimonate concentrations were too low for structural characterization.
XAS analyses further confirmed that the initial species formed from antimonite in the presence of excess sulfide under anoxic conditions is not a pentavalent thioantimonate, but the trivalent trithioantimonite (CN 3.4-3.7, binding length 2.40-2.41 Å). However, this species is highly instable and rapidly transforms either to tetrathioantimonate in the presence of oxygen or antimonite at excess OH- versus SH- concentrations. Thioantimonites thus escape chromatographic detection even in complete absence of oxygen.
In natural geothermal waters from Yellowstone National Park, where oxygen concentrations > 0.2 mg/L render the presence of thioantimonites highly unlikely, tri- and tetrathioantimonate were detected. In accordance with our own laboratory studies and previous observations1-5 their share increased at increasingly alkaline pH and with increasing sulfide and decreasing oxygen concentrations to a maximum of 30 and 9% of total antimony, respectively. However, given the large S/Sb ratio (100 to 10,000) almost quantitative transformation of antimony to thioantimonates would have been expected based on results in synthetic pure antimony solutions. We postulate that the presence of arsenic and direct competition for a limited source of sulfide affects thioantimonate formation in natural waters. In the same samples, thioarsenate formation at S/As ratios of 2 to 4 is much higher (> 80% of total arsenic) and corresponds to results from synthetic pure arsenic solutions. Sulfur might therefore be a key species in helping to resolve different results and an ongoing controversy on similar 7, 8 or dissimilar 9, 10 behavior of arsenic and antimony in the environment.


References
[1] Tossell, J.A., 1994: Geochimica et Cosmochimica Acta 58, 5093. [2] Wood, S.A., 1989: Geochimica et Cosmochimica Acta 53, 237. [3] Mosselmans, J. F. W. et al., 2000: Applied Geochemistry 15, 879. [4] Helz, G. R. et al., 2002: Environmental Science and Technology 36, 943. [5] Sherman, D. M. et al., 2000, Chemical Geology 167, 161. [6] Planer-Friedrich, B. et al., 2007: Environmental Science & Technology 41, 5245. [7] Vink, B.W., 1996: Chemical Geology 130, 21. [8] Sakamoto, H. et al., 1988: Bulletin of the Chemical Society of Japan 61, 3471. [9]. Stauffer, R.E.; Thompson, J.M., 1984: Geochimica et Cosmochimica Acta 48, 2547. [10] Landrum, J.T. et al., 2009: Applied Geochemistry 24, 664.
Keywords: Antimony EXAFS thio-S
  • Lecture (Conference)
    Antimony 2011: 2nd International Workshop on Antimony in the Environment, 21.-24.08.2011, Jena, Germany

Publ.-Id: 15426 - Permalink


Zwei oder vier Stunden [18F]FMISO-PET in Kopf-Hals-Karzinomen: Wann ist der Bildkontrast am höchsten?
Abolmaali, N.; Haase, R.; Koch, A.; Zips, D.; Steinbach, J.; Baumann, M.; Kotzerke, J.; Zöphel, K.;
Die [18F]Fluormisonidazol-Positronenemissionstomographie (FMISO-PET) ist ein nicht invasives Bildgebungsverfahren, das hypoxische Subvolumina in Tumoren detektieren kann. Die FMISO-PET kann dynamisch oder statisch nach unterschiedlichen Uptakezeiten post injectionem (p.i.) akquiriert werden, hat aber ein vergleichsweise niedriges Signal zu Rausch Verhältnis (SNR). Ziel dieser Studie war es für spätere Analysen zu klären, ob der Bildkontrast in statisch aufgenommenen Untersuchungen nach einer Uptakezeit von zwei Stunden (MISO2) oder vier Stunden (MISO4) p.i. höher ist. Patienten, Methoden: Bei einer Subgruppe von 23 Patienten einer prospektiven Studie zur kurativen Radiochemotherapie (RCT) von Plattenepithelkarzinomen des Hals-Nasen-Rachen-Raumes (HNSCC) wurden vor und während der Therapie [18F]Fluordeoxyglukose (FDG-)PET-Untersuchungen durchgeführt. Zusätzlich wurden bei diesen Patienten FMISO-PET-Aufnahmen zwei und vier Stunden p.i. nach Strahlentherapiedosen von im Mittel 11Gy, 23Gy und 57Gy während der RCT akquiriert. Nach Koregistrierung aller PET- und CT-Datensätze wurde die Rover-Software (ABX, Radeberg) verwendet, um das aus der FDG-PET abgeleitete „gross tumour volume“ der Primärtumoren festzulegen. Diese Volumina wurden in die FMISO-Datensätze kopiert um Hypoxie innerhalb des Primärtumors zu definieren. Der Kontrast zwischen hypoxischen Regionen in den Aufnahmen MISO2 und MISO4 wurde untersucht und mit dem Wilcoxon-Rangsummen-Test auf signifikante Unterschiede geprüft. Ergebnisse: Der mittlere SUVmax der Primärtumoren aller Untersuchungen war 2.2 (stdev: 0.4, min: 1.3, max: 3.4) nach 2 h p.i. und 2.4 (stdev: 0.7, min: 1.1, max: 4.4) nach 4 h p.i.. Der mittlere SUVmax in der Nackenmuskulatur war zwei und vier Stunden p.i. 1.5 und der mittlere SUVmean fiel von 1.2 nach 2 h auf 1.1 nach 4 h ab. Diese geringen Veränderungen bedingten aber einen steigenden Kontrast von MISO2 nach MISO4. Für die unterschiedlich definierten Kontraste ergab der Wilcoxon-Rangsummen-Test signifikant höhere Werte in den Untersuchungen vier Stunden p.i. (p < 0.002). Schlussfolgerung: Die Datenakquisition für die [18F]FMISO-PET sollte vorzugsweise vier Stunden p.i. erfolgen, da der Kontrast zwei Stunden p.i. schlechter ist. Diese Datensätze eignen sich deshalb besser für weitere Analysen, z. B. für die verbesserte Definition hypoxischer Tumorsubvolumina zur Strahlentherapieplanung.
Keywords: FMISO PET, Kopf/Hals-Tumoren, Tumor-zu-Muskel-Signalverhältnis, Kontrast-zu-Rausch-Verhältnis, Bioimaging, Strahlentherapieplanung

Publ.-Id: 15425 - Permalink


Subharmonic Resonant Optical Excitation of Confined Acoustic Modes in a Free-Standing Semiconductor Membrane at GHz Frequencies with a High-Repetition-Rate Femtosecond Laser
Bruchhausen, A.; Gebs, R.; Hudert, F.; Issenmann, D.; Klatt, G.; Bartels, A.; Schecker, O.; Waitz, R.; Erbe, A.; Scheer, E.; Huntzinger, J.; Mlayah, A.; Dekorsy, T.;
We propose subharmonic resonant optical excitation with femtosecond lasers as a new method for the characterization of phononic and nanomechanical systems in the gigahertz to terahertz frequency range. This method is applied for the investigation of confined acoustic modes in a free-standing semiconductor membrane. By tuning the repetition rate of a femtosecond laser through a subharmonic of a mechanical resonance we amplify the mechanical amplitude, directly measure the linewidth with megahertz resolution, infer the lifetime of the coherently excited vibrational states, accurately determine the system's quality factor, and determine the amplitude of the mechanical motion with femtometer resolution.
Keywords: Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects, Time resolved reflection spectroscopy, Mechanical modes of vibration

Publ.-Id: 15424 - Permalink


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