Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Without submitted and only approved publications
Only approved publications

31735 Publications
The nELBE neutron time-of-flight facility
Junghans, A. R.; Altstadt, E.; Beckert, C.; Beyer, R.; Galindo, V.; Grosse, E.; Hannaske, R.; Matic, A.; Mosconi, M.; Naumann, B.; Nolte, R.; Röttger, S.; Schilling, K. D.; Schlenk, R.; Schneider, S.; Schwengner, R.; Wagner, A.; Weiss, F.-P.;
At the superconducting electron linear accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf the neutron time-of-flight facility nELBE has become operational. Fast neutrons in the energy range from 200 keV to 10 MeV are produced by the pulsed electron beam from ELBE impinging on a liquid lead circuit as a radiator. The short beam pulses of 10 ps provide the basis for an excellent time resolution for neutron time-of-flight experiments, giving an energy resolution of about <1% at 1 MeV with a short ight path of 5 m. The neutron intensity on target is ≈ 4*10^4 n/(cm2s) using an electron bunch charge of 77 pC and 100 kHz pulse repetition rate. The energy range of the neutrons produced is well suited for neutron cross section measurements relevant for the development of Generation IV reactor systems and for the transmutation of nuclear waste. First measurements of inelastic neutron scattering cross sections have been performed and will be presented.
  • Contribution to proceedings
    IEEE Nuclear Science Symposium 2008, 19.-25.10.2008, Dresden, Deutschland
    The nELBE neutron time-of-flight facility, 2909
    DOI: 10.1109/NSSMIC.2008.4774974
  • Lecture (Conference)
    IEEE Nuclear Science Symposium, 19.-25.10.2008, Dresden, Deutschland
  • Journal of the Korean Physical Society 59(2011), 1593-1596
    DOI: 10.3938/jkps.59.1593

Publ.-Id: 15303 - Permalink

Electromagnetic strength in heavy nuclei – experiments and a global fit
Beyer, R.; Birgersson, E.; Junghans, A. R.; Massarczyk, R.; Schramm, G.; Schwengner, R.; Grosse, E.;
A global parameterization is presented for the electromagnetic strength in heavy nuclei which gives a rather good fit to respective data in nuclei with mass numbers A between 50 and 240. It relies on a Lorentzian description of the isovector giant dipole resonance and it needs only a very small number of parameters to describe the electric dipole strength down to low excitation energy of importance for radiative capture processes. The resonance energies are chosen to be in accordance to liquid drop model parameters adjusted to ground state masses and to rotation invariant determinations of ground state deformation and triaxiality. By a straightforward use of this information a surprisingly smooth variation of the GDR width with A and Z is found and a full agreement to the predictions of the electromagnetic sum rule is assured. Predictions for radiative neutron capture cross sections compare well to respective data, when the proposed photon strength function is combined with standard prescriptions for the level density in the product nuclei.

Publ.-Id: 15302 - Permalink

The Electron-Ion Scattering experiment ELISe at the International Facility for Antiproton and Ion Research (FAIR) – a conceptual design study
Antonov, A. N.; Gaidarov, M. K.; Ivanov, M. V.; Kadrev, D. N.; Aïche, M.; Barreau, G.; Czajkowski, S.; Jurado, B.; Belier, G.; Chatillon, A.; Granier, T.; Taieb, J.; Dor´C, D.; Letourneaux, A.; Ridikas, D.; Dupont, E.; Berthoumieux, E.; Panebianco, S.; Reymund, F.; Schmitt, C.; Audouin, L.; Khan, E.; Tassan-Got, L.; Aumann, T.; Beller, P.; Boretzky, K.; Dolinskii, A.; Egelhof, P.; Emling, H.; Franzke, B.; Geissel, H.; Kelic-Heil, A.; Kester, O.; Kurz, N.; Litvinov, Y.; Münzenberg, G.; Nolden, F.; Schmidt, K.-H.; Simon, H.; Steck, M.; Weick, H.; Enders, J.; Pietralla, N.; Richter, A.; Schrieder, G.; Zilges, A.; Distler, M. O.; Merkel, H.; Müller, U.; Junghans, A.; Lenske, H.; Fujiwara, M.; Suda, T.; Kato, S.; Adachi, T.; Hamieh, S.; Harakeh, M. N.; Kalantar-Nayestanaki, N.; Wörtche, H.; Berg, G. P. A.; Koop, I. A.; Logatchov, P. V.; Otboev, A. V.; Parkhomchuk, V. V.; Shatilov, D. N.; Shatunov, P. Y.; Shatunov, Y. M.; Shiyankov, S. V.; Shvartz, D. I.; Skrinsky, A. N.; Chulkov, L. V.; Danilin, B. V.; Korsheninnikov, A. A.; Kuzmin, E. A.; Ogloblin, A. A.; Volkov, V. A.; Grishkin, Y.; Lisin, V. P.; Mushkarenkov, A. N.; Nedorezov, V.; Polonski, A. L.; Rudnev, N. V.; Turinge, A. A.; Artukh, A.; Ershov, S. N.; Fomichev, A.; Golovkov, M.; Gorshkov, A. V.; Grigorenko, L.; Klygin, S.; Krupko, S.; Meshkov, I. N.; Rodin, A.; Sereda, Y.; Seleznev, I.; Sidorchuk, S.; Syresin, E.; Stepantsov, S.; Ter-Akopian, G.; Teterev, Y.; Vorontsov, A. N.; Kamerdzhiev, S. P.; Litvinova, E. V.; Karataglidis, S.; Alvarezrodriguez, R.; Borge, M. J. G.; Fernandezramirez, C.; Garrido, E.; Sarriguren, P.; Vignote, J. R.; Fraileprieto, L. M.; Lopezherraiz, J.; Moyadeguera, E.; Udias-Moinelo, J.; Amarosoriano, J. E.; Lallena Rojo, A. M.; Caballero, J. A.; Johansson, H. T.; Jonson, B.; Nilsson, T.; Nyman, G.; Zhukov, M.; Avdeichikov, V.; Hencken, K.; Jourdan, J.; Krusche, B.; Rauscher, T.; Kiselev, D.; Trautmann, D.; Al-Khalili, J.; Catford, W.; Johnson, R.; Stevenson, P.; Barton, C.; Jenkins, D.; Lemmon, R.; Chartier, M.; Cullen, D.; Heinz, A.; Bertulani, C. A.;
The Electron-Ion Scattering experiment ELISe at the International Facility for Antiproton and Ion Research (FAIR) – a conceptual design study

Publ.-Id: 15301 - Permalink

Production of new neutron rich isotopes of heavy elements in fragmentation reactions of 238U projectiles at 1 AGeV
Alvarez Pol, H.; Benlliure, J.; Audouin, L.; Casarejos, E.; Cortina Gil, D.; Enqvist, T.; Fernandez Dominguez, B.; Junghans, A. R.; Jurado, B.; Napolitani, P.; Pereira, J.; Rejmund, F.; Schmidt, K. H.; Yordanov, O.;
The production of heavy neutron-rich nuclei has been investigated using cold-fragmentation reactions of U 238 projectiles at relativistic energies. The experiment performed at the high-resolving-power magnetic spectrometer Fragment Separator at GSI made it possible to identify 40 new heavy neutron-rich nuclei: Pt 205 , Au 207−210 , Hg 211−216 , Tl 214−217 , Pb 215−220 , Bi 219−224 , Po 223−227 , At 225−229 , Rn 230,231 , and Fr 233 . The production cross sections of these nuclei were also determined and used to benchmark reaction codes that predict the production of nuclei far from stability.

Publ.-Id: 15300 - Permalink

Measurement of the inelastic neutron scattering cross section of 56Fe
Beyer, R.; Birgersson, E.; Ferrari, A.; Gehre, D.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Massarczyk, R.; Matic, A.; Nolte, R.; Schilling, K.-D.; Schwengner, R.; Wagner, A.;
Measurement of the inelastic neutron scattering cross section of 56Fe
  • Lecture (Conference)
    EFNUDAT Measurements and Models of Nuclear Reactions, 25.-27.05.2010, Paris, France
  • Open Access LogoContribution to proceedings
    EFNUDAT Measurements and Models of Nuclear Reactions, 25.-27.05.2010, Paris, France
    EPJ web of conferences 8 (2010) 07007
    DOI: 10.1051/epjconf/20100807007

Publ.-Id: 15299 - Permalink

Operation of the liquid lead loop at nELBE
Junghans, A. R.;
Operation of the liquid lead loop at nELBE
  • Lecture (Conference)
    Scientific workshop on Neutron measurements , Theory and Applications Nuclear Data for Sustainable Nuclear Energy, 28.-30.04.2009, Geel, Belgium
  • Contribution to proceedings
    Scientific workshop on Neutron measurements , Theory and Applications Nuclear Data for Sustainable Nuclear Energy, 28.-30.04.2009, Geel, Belgium
    EFNUDAT Fast Neutrons - Proceedings of the Scientific Workshop on Neutron Measurements, 978-92-79-11705-3, 73-77

Publ.-Id: 15298 - Permalink

The nELBE neutron time of flight facility
Junghans, A. R.;
The nELBE neutron time of flight facility
  • Lecture (Conference)
    International Conference on Nuclear Data for Science and Technology 2010, 26.-30.04.2010, Jaju Island, Korea
  • Contribution to proceedings
    International Conference on Nuclear Data for Science and Technology 2010, 26.-30.04.2010, Jeju Island, Korea
    Journal of the Korean Physical Society 59, 1593-1596

Publ.-Id: 15297 - Permalink

Inelastic neutron scattering measurements at the photoneutron source nELBE
Junghans, A. R.;
Inelastic neutron scattering measurements at the photoneutron source nELBE
  • Lecture (Conference)
    Workshop on (in)elastic neutron scattering, 06.-07.12.2010, Strasbourg, France
  • Lecture (Conference)
    Workshop on Gamma Strength and Level Density in Nuclear Physics and Nuclear Technology, 30.08.-03.12.2010, Dresden, Deutschland

Publ.-Id: 15296 - Permalink

Transmutation radioaktiven Abfalls - Grundlagen, Methoden, Perspektiven
Junghans, A. R.;
Transmutation radioaktiven Abfalls - Grundlagen, Methoden, Perspektiven
  • Invited lecture (Conferences)
    Physikalische Kolloquium, 14.01.2011, Darmstadt, Deutschland
  • Invited lecture (Conferences)
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände 2010, 15.-19.03.2010, Bonn, Deutschland
  • Invited lecture (Conferences)
    Jährliches Behördenseminar, 18.11.2010, Berlin, Deutschland

Publ.-Id: 15295 - Permalink

Mechanische Analyse für den Sumpf des SHB des Kernkraftwerks Brunsbüttel (KKB)
Werner, M.; Altstadt, E.;
Es handelt sich um einen vertraulichen Bericht, deshalb kein Abstract.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2011
    7 Seiten

Publ.-Id: 15294 - Permalink

Cross section in deuteron-proton elastic scattering at 1.25 GeV/u
Kurilkin, P. K.; Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Díaz, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gil, A.; Golubeva, M.; González-Díaz, D.; Guber, F.; Hennino, T.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kopp, A.; Korcyl, G.; Kornakov, G. K.; Kotte, R.; Kozuch, A.; Krása, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kählitz, P.; Ladygin, V.; Lamas-Valverde, J.; Lang, S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roskoss, J.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
First results of the differential cross section in dp elastic scattering at 1.25 GeV/u measured with the HADES over a large angular range are reported. The obtained data corresponds to large transverse momenta, where a high sensitivity to the two-nucleon and three-nucleon short-range correlations is expected.
  • Contribution to WWW
    Proc. XXth Int. Baldin Seminar on High Energy Physics Problems "Relativistic Nuclear Physics and Quantum Chromodynamics", JINR, Dubna, Russia, October 4-9, 2010:

Publ.-Id: 15292 - Permalink

Sorption of U(VI) at the TiO2 – water interface: An in situ vibrational spectroscopic study.
Müller, K.; Foerstendorf, H.; Meusel, T.; Brendler, V.; Comarmond, M. J.; Lefèvre, G.; Payne, T. E.;
Molecular-scale knowledge of U(VI) sorption reactions at the water-mineral interface is important for predicting U(VI) transport processes in the environment. In this work, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy was used in a comprehensive investigation of the sorption processes of U(VI) onto TiO2. The high sensitivity of the in situ ATR FT-IR technique allows the study of U(VI) concentrations down to the low micromolar range, which is relevant to most environmental scenarios.
A set of highly purified and well characterized TiO2 phases differing in their origin, the ratio of the most stable polymorphs (anatase and rutile), in specific surface area, isoelectric points and in particle size distribution was investigated. Irrespective of the composition of the mineral phase, it was shown that U(VI) forms similar surface complexes, which was derived from the antisymmetric stretching mode υ3(UO2) showing a characteristic shift to lower wavenumbers compared to the respective aqueous species at a similar low concentration level.
The availability of a fast scanning IR device makes it feasible to perform time-resolved experiments of the sorption processes with a time resolution in the sub-minute range. It is shown that during the early stages of the U(VI) uptake a surface species on the mineral phase is formed characterized by a significantly red-shifted absorption maximum which is interpreted as a bidendate inner-sphere complex. After prolonged sorption, the IR spectra indicate the formation of a second surface species showing a smaller shift compared to the aqueous species. These findings were verified by a series of spectroscopic experiments performed on a U(VI)-saturated surfaces.
Further ATR FT-IR spectroscopic experiments focused on the impact of the U(VI) concentration, the pH value and the exclusion of atmospheric carbonate on the sorption process. The results confirm the presence of two surface species, occurring sequentially as a function of U(VI) surface loading.
This work provides new insights into the sorption processes of U(VI) on titanium dioxide on a molecular level. Basic thermodynamic ideas of surface complexation are substantiated by in situ infrared spectroscopy.

Publ.-Id: 15291 - Permalink

Seidel, W.;
Two free-electron lasers (FELBE; 4-21 μm and 18-250 μm, respectively) have been in routine user operation for a wide range of IR experiments at the radiation source ELBE in the Forschungszentrum Dresden-Rossendorf for several years. The lasers are driven by a superconducting RF linac that permits the generation of a cw-beam with a repetition rate of 13 MHz and a high average beam power. In addition, operation in a macropulse modus (pulse duration >100 µs, repetition rate ≤ 25 Hz) is possible. A few important experiments using the cw-operation are discussed.
  • Lecture (Conference)
    German-Turkish Workshop on Superconducting Accelerators for FEL- and Bremsstrahlung Applications, 31.01.-03.02.2011, Antalya, Turkey

Publ.-Id: 15290 - Permalink

Realization of the Nijmegen THz-FEL
Jongma, R. T.; Engels, A. C. N.; Lof, R. W.; Wijnen, F. J. P.; Wulterkens, G. F. A. J.; Zhaunerchyk, V.; van Dael, P. A. W.; van Roij, A. J. A.; van Vliet, A. P.; van der Zande, W. J.; Dunkel, K.; Piel, C.; Lehnert, U.; Michel, P.; Seidel, W.; Wuensch, R.; van der Meer, A. F. G.;
The Radboud University in Nijmegen received funding to realize a narrow-band THz laser system and a 45 T hybrid magnet system. In this paper we present the technical solutions for realization of the main system components. We present the details of the RI Research Instruments GmbH (a former ACCEL Instruments GmbH activity) LINAC system. Operation of the full system (including the electron source) at 3 GHz is desirable and deemed feasible after first experimental studies. As the Nijmegen FEL will operate at wavelength up to 1.5 mm, the cavity will be fully waveguided, complicating the incorporation of an intra-cavity Fox-Smith interferometer required to induce coherence between micropulses and a Michelson interferometer as most ideal outcoupler. The optical distribution system comprises 150 m of vacuum tubing with 25 cm effective diameter (planar and refocusing) mirrors. A robust yet cost efficient realization taking boundary conditions on optical beam parameters at diagnostics station and user stations into account is foreseen.
  • Poster
    31st International Free Electron Laser Conference 2009, 23.-28.08.2009, Liverpool, UK
  • Contribution to proceedings
    31st International Free Electron Laser Conference 2009, 23.-28.08.2009, Liverpool, UK

Publ.-Id: 15289 - Permalink

In-vivo dosimetry for proton and ion therapy
Fiedler, F.;
no abstract available
Keywords: in-vivo dosimetry
  • Invited lecture (Conferences)
    6th Meeting of the Scientific Advisory Board of OncoRay, 10.02.2011, Dresden, Germany

Publ.-Id: 15288 - Permalink

PM-IRRAS mapping of ultrathin molecular films with high spatial resolution
Steiner, G.; Sablinskas, V.; Seidel, W.; Salzer, R.;
Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) is a very sensitive technique to characterize the degree of molecular ordering in thin films on metallic surfaces. This is the first report of the coupling of a PM-IRRAS microscope to a free electron laser (FEL), a light source of highest brilliance. Some FELs emit in the infrared region and permit the mapping of molecular properties at high lateral resolution. We studied the molecular orientation of octadecanephosphonic acid (OPA) attached to a gold surface with microstructured aluminum oxide islands on the gold. The spatial resolution achieved is 12 μm which corresponds to the diffraction limit of the infrared light used in this study. This is a substantial improvement compared to previous studies using a PM-IRRA accessory together with a commercial Fourier transform infrared spectrometer, where the lateral resolution is noise-limited rather than diffraction-limited. The spectral maps reveal that OPA is preferably attached to the aluminum oxide islands via the bidentate binding mode whereas the tridentate mode is dominating in case of OPA attached to the gold areas.
Keywords: PM-IRRAS - Mapping - Free electron laser - Self-assembly monolayer
  • Analytical and Bioanalytical Chemistry 395(2009), 1641-1650

Publ.-Id: 15287 - Permalink

Interaction of Chlorella vulgaris and Schizophyllum commune with U(VI)
Vogel, M.; Günther, A.; Gube, M.; Raff, J.; Kothe, E.; Bernhard, G.;
For a risk assessment for released radionuclides a comprehensive elucidation of the migration behavior of uranium is necessary. Therefore not only the uranium interactions with the geosphere but also with the biosphere have to be investigated.
The aim of the study was to characterize the sorption of U(VI) by living Chlorella vulgaris and Schizophyllum commune and the molecular structure of formed complexes.
Both organisms bind significant amounts of U(VI) dependent on applied uranium concentration and pH in the range from 4 to 7. At uranium concentration of 0.2 mM Schizophyllum shows binding capacities of around 130 mg U/g dry weight independent of pH value. A higher initial uranium concentration leads to higher binding capacities of 230-280 mg U/g dry weight at pH 5 and 6 for still living Schizophyllum biomass. In contrast to that, Chlorella binds at a uranium concentration of 0.5 mM 75 mg U/g dry weight (pH 4.4). Furthermore, Chlorella cells die at concentration higher than 0.1 mM within 48 h. Therefore further experiments were carried out at a concentration of 5 µM. Under this condition living algae firstly bind almost all uranium within 5 min of incubation, but then again mobilize up to 80% of the bound uranium during ongoing incubation. The release of metabolism related substances is suggested to cause this mobilization of uranium. As potential leachates for algal-bound uranium oxalate, citrate and ATP were tested and found to be able to mobilize 55-87% of the algal-bound uranium within 24 h.
Differences in complexation of uranium by active and inactive algae cells as well as fungal biomass were investigated with a combination of different spectroscopic techniques. Obtained results demonstrated an involvement of carboxylic and organic/inorganic phosphate groups in the uranium complexation with varying contributions dependent on microbial biomass, cell status, uranium concentration and pH.
Keywords: uranium, sorption, Chlorella, Schizophyllum
  • Lecture (Conference)
    6th International Conference Uranium Mining and Hydrogeology, 18.-22.09.2011, Freiberg, Deutschland
  • Contribution to proceedings
    6th International Conference Uranium Mining and Hydrogeology, 18.-22.09.2011, Freiberg, Deutschland

Publ.-Id: 15285 - Permalink

A simple method to prepare microorganisms for AFM analysis
Günther, T.; Raff, J.; Pollmann, K.;
Nowadays AFM becomes a more and more attractive method for microbiologists to investigate Microorganisms. The technique allows imaging over a broad magnitude scale and is not confined by the diffraction limit. Sometimes it is interesting to measure the dimensions of an organism. The other time the question is about surface properties of a cell. The scanning principle makes the AFM technique comparatively slow and the specimen has to be fixed on a flat surface during the scans. It is quite simple to dry the samples on a surface. Drying leads to a good immobilization but also to drying artifacts like denaturation of Proteins and shrinkage of the whole cell due to the loss of water. Therefore it is advantageous for most biological questions to do the imaging in liquids. Immobilization is not trivial as result of the heterogeneous surface properties of different micro organisms. Existing preparation methods are mostly utilizing coated surfaces or lithographicaly prepared surfaces. While lithography is not an option for everyone there is a variety of coatings available for instance poly-L-lysine or gelatine which work quite good with some microorganisms. A new method based on polyelectrolyte coated surfaces combined with centrifugal sedimentation shows promising results regarding the efficiency of immobilization. A variety of micro organisms were tested with the new method showing universality for many organisms. The samples were prepared with and without fixation. Of course fixation simplifies the imaging by enhancing the stability of the samples. But even unfixed Microorganisms can be imaged which opens the field for investigations in respect to cell division or other dynamic processes of living cells.
  • Lecture (Conference)
    Jahrestagung der Vereinigung für allgemeine und angewandte Mikrobiologie, 03.-06.04.2011, Karlsruhe, Deutschland

Publ.-Id: 15284 - Permalink

Effect of temperature and humic acid on the U(VI) diffusion in compacted Opalinus Clay
Joseph, C.; van Loon, L. R.; Jakob, A.; Schmeide, K.; Sachs, S.; Bernhard, G.;
Beside salt dome and granite rock, argillaceous rock is discussed as host rock for a nuclear waste repository. For safety assessment, knowledge about the migration behavior of the actinides is required. In this study, the interaction of U(VI) (110-6 M) with the natural clay rock Opalinus Clay (OPA) from Mont Terri, Switzerland was investigated by diffusion experiments under anaerobic conditions using synthetic OPA pore water [1] as background electrolyte and intact bore cores (diameter: 2.57 cm, thickness: 1.1 cm, density: 2.4 g/cm3).
Due to radioactive decay of the radionuclides, temperatures in the near-field of a nuclear waste repository in argillaceous rock are likely to be increased to ≤ 100°C [2], which can impact the migration behavior of actinides. Thus, the U(VI) diffusion in OPA was investigated in dependence on temperature (25 and 60°C).
Humic acids (HA) occur ubiquitously in nature. They are able to influence the migration of actinides due to their ability for complex and colloid formation and their redox properties. Thus, the influence of HA (10 mg/L) on the U(VI) diffusion was also studied.
At first, HTO diffusion experiments were performed for determination of the diffusion parameters of the OPA samples. The obtained HTO diffusion coefficients and porosities agreed with literature values.
After three months of diffusion time the U(VI) diffusion profiles in the OPA bore core samples were determined. The U(VI) diffusion profiles showed that, compared to the experiment at 25°C, the U(VI) diffusion is increased within the first 1.5 mm at 60°C. After 1.5 mm this effect levels off, which can be attributed to the increased sorption of U(VI) at 60°C. In the presence of HA, at 60°C and diffusion distances ≥ 800 µm, a lower amount of U(VI) was detected in the clay. That means, the U(VI) diffusion was hindered by the presence of HA.
Currently, diffusion and distribution coefficients are determined by fitting of the U(VI) and HA diffusion profiles using the modeling software COMSOL Multiphysics 3.3 [3]. The results will be compared to results of sorption experiments with OPA [4].

[1] F.J. Pearson (1998) PSI Internal report TM-44-98-07, PSI, Villigen, Switzerland.
[2] T. Brasser, et al. (2008), GRS-247, GRS, Braunschweig, Germany.
[3] Finite-element software package.
[4] C. Joseph, et al. (2011), Chem. Geol., accepted.
Keywords: Opalinus Clay, diffusion, uranium(VI), humic acid, temperature
  • Contribution to proceedings
    6th International Conference Uranium Mining Hydrogeology (UMH VI), 18.-22.09.2011, Freiberg, Germany
  • Lecture (Conference)
    6th International Conference Uranium Mining Hydrogeology (UMH VI), 18.-22.09.2011, Freiberg, Germany

Publ.-Id: 15283 - Permalink

Two-dimensional ultrasound Doppler velocimeter for investigations of liquid metal flows
Franke, S.; Lieske, H.; Fischer, A.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.;
In the research area of magnetohydrodynamics (MHD) the pulsed-wave ultrasound Doppler velocimetry (UDV) is a worthwhile measurement technique for flow field investigations of liquid metal flows. Thereto, several UDV instruments are available on the market. However, their capability for two-dimensional mapping of flows is highly limited due to restricted number of scanning elements (max. 20 transducers) and low temporal resolution. Hence, an ultrasound Doppler velocimeter based on ultrasound arrays is developed which allows the measurement of both flow field vectors in the measuring plane of 67 x 67 mm². Thereby, it provides high measurement rates and a high spatial resolution with a significant increased number of scanning lines simultaneously.
The linear ultrasound transducer arrays are arranged orthogonally to each other. There each array measures one flow field component by electronic traversing.
The ultrasound arrays comprise 2x 25 transducer elements each with a centre frequency of 8 MHz and a piezo element size of 2.5 x 5 mm². In operation two adjacent elements are combined to a square transducer pair of 5 x 5 mm² allowing a small lateral scanning step width of 2.5 mm on the one hand and a low divergence of the ultrasound beam and according to this a high lateral resolution up to 2 mm on the other hand.
The requirements for a high temporal resolution and a high number of scanning lines are opponent. To achieve a high measurement rate nevertheless, the measurement is parallelized as much as possible by simultaneous operation of four transducer pairs. Thereby a specific distance between the active transducer pairs avoids spatial crosstalk. For the same reason both arrays are actuated alternatively. This excitation scheme is implemented by a fast multiplex electronics which is a proprietary development. Depending on the averaging time frame rates up to 33 Hz are achieved at pulse repetition rates of 1.5 kHz.
Keywords: ultrasound Doppler velocimetry, array sensor, flow mapping, rotating magnetic field, electromagnetic stirring
  • Lecture (Conference)
    Sensor+Test 2011, 07.-09.06.2011, Nürnberg, Deutschland
  • Contribution to proceedings
    Sensor+Test 2011, 07.-09.06.2011, Nürnberg, Deutschland
    Sensor Proceedings, 165-170

Publ.-Id: 15282 - Permalink

Two-dimensional ultrasound Doppler velocimeter for velocity field measurements of liquid metal flows
Franke, S.; Lieske, H.; Fischer, A.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.;
In the research area of magnetohydrodynamics (MHD) the pulsed-wave ultrasound Doppler velocimetry (UDV) is a worthwhile measurement technique for flow field investigations of liquid metal flows. Thereto, several UDV instruments are available on the market. However, their capability for two-dimensional mapping of flows is highly limited due to restricted number of scanning elements (max. 20 transducers) and low temporal resolution. Hence, an ultrasound Doppler velocimeter based on ultrasound arrays is developed which allows the measurement of both flow field vectors in the measuring plane of 67 x 67 mm². Thereby, it provides high measurement rates and a high spatial resolution with a significant increased number of scanning lines simultaneously.
The linear ultrasound transducer arrays are arranged orthogonally to each other. There each array measures one flow field component by electronic traversing.
The ultrasound arrays comprise 2x 25 transducer elements each with a centre frequency of 8 MHz and a piezo element size of 2.5 x 5 mm². In operation two adjacent elements are combined to a square transducer pair of 5 x 5 mm² allowing a small lateral scanning step width of 2.5 mm on the one hand and a low divergence of the ultrasound beam and according to this a high lateral resolution up to 2 mm on the other hand.
The requirements for a high temporal resolution and a high number of scanning lines are opponent. To achieve a high measurement rate nevertheless, the measurement is parallelized as much as possible by simultaneous operation of four transducer pairs. Thereby a specific distance between the active transducer pairs avoids spatial crosstalk. For the same reason both arrays are actuated alternatively. This excitation scheme is implemented by a fast multiplex electronics which is a proprietary development. Depending on the averaging time frame rates up to 33 Hz are achieved at pulse repetition rates of 1.5 kHz.
Keywords: ultrasound Doppler velocimetry, array sensor, flow mapping, rotating magnetic field, electromagnetic stirring
  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich
  • Contribution to proceedings
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich
    Proceedings in Applied Mathematics and Mechanics (PAMM), 649-650

Publ.-Id: 15281 - Permalink

Efficiency of a DC magnetic field used for braking the flow within a continuous casting mould
Miao, X.; Timmel, K.; Eckert, S.; Lucas, D.; Gerbeth, G.;
The continuous casting technology provides about 90% of the world steel production. The application of DC magnetic fields in form of so-called electromagnetic brakes is considered for an effective flow control with substantial capabilities to improve the product quality or to enhance the productivity of the process. The main effect of the DC field is supposed to result in a uniform reduction of the maximum velocities in the discharging jet from the submerged entry nozzle and to damp violent turbulent fluctuations. However, the electromagnetic braking of such highly turbulent and complex flows is a complicated phenomenon and has not been understood fully until now.
We present numerical and experimental investigations focusing on the fluid flow in the continuous casting mold under the influence of a transverse magnetic field. Numerical calculations were performed using the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model.
Corresponding experimental investigations were carried out at the mockup LIMMCAST at HZDR. The comparison between our numerical calculations and the experimental results display a very well agreement. An important outcome of this study is the feature that the magnetic field does not provide a continuous reduction of the velocity fluctuations at the nozzle port.
Keywords: continuous casting, mould flow, flow measurements, DC magnetic field, electromagnetic brake
  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich

Publ.-Id: 15280 - Permalink

Taylor-Görtler vortex flows driven by a rotating magnetic field inside a liquid metal column
Vogt, T.; Räbiger, D.; Grants, I.; Eckert, S.; Gerbeth, G.;
The spin-up of a fluid in a rotating axisymmetric container is a classical problem in fluiddynamics. Considering a spinning cylinder the viscous forces are responsible to convey the angular momentum from the container walls into the liquid. Therefore, the fluid rotates faster in the boundary layers near the horizontal walls. In those Ekman layers the centrifugal force exceeds the radial pressure gradient and the fluid is driven radial outward. A secondary flow is established which effectively transports the angular momentum to the bulk of the liquid. We consider a circular cylinder filled with a liquid metal which is exposed to a rotating magnetic field (RMF). The magnetic field strength is suddenly increased to B0 and maintained at that value. The magnetic field induces a mainly azimuthal body force, the Lorentz force. This experimental study is concerned with the secondary meridional flow during the time if the fluid spins up from rest. Vertical profiles of the axial velocity have been measured by means of the ultrasound Doppler method. The flow measurements show the existence of two stages during the RMF-driven spin-up, in particular the so-called initial adjustment phase followed by an inertial phase which is dominated by inertial oscillations of the secondary flow. Evolving instabilities in form of Taylor-Görtler vortices have been observed just above the instability threshold.
Keywords: spin-up, rotating magnetic field, Taylor-Görtler vortices, flow measurements, ultrasound Doppler velocimetry
  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich

Publ.-Id: 15279 - Permalink

Curium(III) complexation with surface-layer (S-layer) proteins from a uranium mining waste pile isolate
Moll, H.; Raff, J.; Li, B.; Bernhard, G.;
During the last years the interaction of U(VI) with the isolate Lysinibacillus sphaericus JG-A12, recovered from the uranium mining waste pile “Haberland” near Johanngeorgenstadt (JG), Saxony, Germany, was intensively studied [1, 2]. It could be demonstrated that L. sphaericus JG-A12 shows the ability to form S-layer proteins. This outermost subcellular structure plays an important role for selective binding of heavy metals, for example U(VI) [2]. The interaction of trivalent actinides (e.g., curium) with bacterial S-layer proteins is unknown. This knowledge is essential for the understanding of An(III) interactions at biological solid-water interfaces. Dependent on pH and [Ca] S-layer proteins occur as monomers and polymers in aqueous solution. The main aim of this study is to explore the unknown Cm(III) binding on different S-layers and S-layer protein structures.
The direct speciation technique time-resolved laser-induced fluorescence spectroscopy (TRLFS) has been applied at trace Cm(III) concentrations. Two S-layer suspensions a) Ca-reduced protein containing 195 mmol Ca/mol protein and b) Ca-purified protein were investigated. As a result and illustrated in Figure 1, both S­layers have a high affinity to bind Cm(III) over a broad pH range between 3 and 9. The Ca-reduced S­layer proteins can associate Cm(III) in two coordination environments characterized by individual emission spectra and luminescence lifetimes (e.g., 140 and 300 µs). The results can be interpreted by an intensive Cm(III) interaction with S-layer monomers between pH 3 and 5 with monomer concentrations of 100, 60, and 17 %, respectively; and a dominating interaction with S-layer polymers between pH 6 to 9 with polymer concentrations of 84, 91, 91, and 75 %, respectively. Whereas in the Ca-purified S-layer protein suspension only one Cm(III) coordination environment occurs with a long lifetime of 300 µs. Here the S-layer monomers dominate the whole pH range. The Cm(III)-S-layer species with monomers identified in both protein suspensions is characterized by an intensive and sharp emission band at 602.6 nm. This suggests an incorporation of Cm(III) into the S-layer protein structure. There is high evidence that the main functionality of the S-layer proteins in Cm(III) binding are the carboxyl groups. A Ca titration of the Cm(III) loaded Ca-purified S-layer protein suspension at pH 9 gave evidence for a change of the S­layer speciation probably by forming polymers. This affects the Cm(III) speciation according to the results detected in the Ca-reduced S­layer suspension. In contrast at pH 3 no indications were observed for an coordination change of Cm(III) bound to the Ca-purified S-layer proteins.
This study presents the first speciation results of Cm(III) with S-layer proteins isolated from bacteria recovered from an actinide contaminated environment. This helps to increase our understanding regarding the speciation of Cm(III) at biological solid-water interfaces. The results of the present study are the basis for a detailed investigation of Ca(II) exchange reactions by Cm(III) in proteins in order to understand the important impact of trivalent actinides on the Ca-metabolism in bacterial cells. Also with respect to a possible An(III) transport in living cells.

[1] J. Raff, U. Soltmann, S. Matys, S. Selenska-Pobell, W. Pompe, H. Böttcher (2003). "Biosorption of Uranium and Copper by Biocers." Chem. Mater. 15: 240-244.
[2] M. Merroun, J. Raff, A. Rossberg, C. Hennig, T. Reich, S. Selenska-Pobell (2005). "Complexation of Uranium by Cells and S-layer Sheets of Bacillus sphaericus JG-A12." Appl. Environ. Microbiol. 71: 5532-5543.

The authors are indebted for the use of the 248Cm to the U.S. Department of Energy, Office of Basic Energy Sciences, through the transplutonium element production facilities at Oak Ridge National Laboratory which was made available as part of a collaboration between the HZDR and the Lawrence Berkeley National Laboratory (LBNL).
Keywords: Curium(III), TRLFS, S-layer, Speciation, Lysinibacillus sphaericus JG-A12
  • Contribution to proceedings
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere 2011, 18.-23.09.2011, Beijing, PR China
  • Poster
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products (MIGRATION 2011), 18.-23.09.2011, Beijing, PR China

Publ.-Id: 15278 - Permalink

Speciation of curium(III) bound by bacteria found in rocks considered for nuclear waste disposals
Moll, H.; Bachvarova, V.; Frost, L.; Geissler, A.; Selenska-Pobell, S.; Bernhard, G.;
Bacteria occur ubiquitously in the environment and can significantly affect the migration behavior of actinides released e.g. after an accidental leakage from current and future underground radioactive waste repositories. Curium causes many of the long term radiological and thermal problems associated with nuclear waste disposal. Moreover, Cm(III) is worthwhile to study because it is a representative of the trivalent actinides with excellent luminescence properties and there is limited knowledge of its behavior in biological systems. The aim of our study is to characterize the Cm(III)-bacteria species formed and to elucidate the underlying interaction mechanisms. This knowledge is essential for the prediction of the migration behavior of Cm(III).
This new study is focused on the interaction processes of Cm(III) with bacteria isolated from two geochemical formations considered for nuclear waste disposals a) Pseudomonas fluorescens from granite rocks at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden, and b) Sporomusa sp. from opalinus clay of the Mont Terri Rock Laboratory, Switzerland.
The direct speciation technique time-resolved laser-induced fluorescence spectroscopy (TRLFS) has been applied at trace Cm(III) concentrations. The unknown Cm(III) speciation in the two studied biological systems (P. fluorescens and Sporomusa sp.) was determined in terms of luminescence spectra and lifetimes of: a) original cell suspensions with Cm(III); b) Cm(III) in the supernatants after discarding the cells; c) desorbed Cm(III) from the cell envelopes; and d) irreversibly bound Cm(III) on the biomass. An overview of the emission spectra of Cm(III) in original cell suspensions of P. fluorescens and Sporomusa sp in 0.1 M NaClO4 is presented in Figure 1. Our results demonstrate that both bacteria have a high affinity to bind Cm(III) over a broad pH range between 2 and 8. Moreover, biomass dependent experiments at pH 6 indicate that already at a very low cell concentration of 0.01 mgdry weight/L all Cm(III) is bound by P. fluorescens and Sporomusa sp.. Both strains can associate Cm(III) in two coordination environments characterized by individual emission bands and luminescence lifetimes. Factor analyses of the emission data indicate interactions with carboxyl groups in the acidic pH up to pH 5.5 followed by interactions with phosphoryl groups of the cell surfaces at higher pH values. In the Cm(III)-P. fluorescens system, almost 100 % of the adsorbed Cm(III) was easily desorbed with 0.01 M EDTA solution. This clearly shows that Cm(III) is bound extracellularly on the cell surface via a pure biosorption process. In the Cm(III)-Sporomusa sp. system, however, only 70 % of the bound Cm(III) was easily desorbed by washing with 0.01 M EDTA. Hence, only 70 % of the added Cm(III) was adsorbed in this case in away similar to those of P. fluorescens, i.e. on the cell surface of the Sporomusa sp. isolate. In contrast to the cells of P. fluorescens, the cells of the Sporomusa sp. bind a significant amount of Cm(III), 30 %, irreversibly, that indicates that this part of the added Cm(III) is more strongly bound. Our results demonstrate that there is an evidence for differences between the Cm(III) interaction mechanisms observed in both bacterial systems. In addition, excitation spectra of Cm(III) associated with these bacteria will be discussed to support our conclusions drawn from the luminescence emission measurements.
The results of this study contribute to increase our understanding of the Cm(III) speciation in bacterial systems. This knowledge is necessary for a fundamental understanding of An(III) reactions under natural conditions.

This work was funded by the BMWi under contract number: 02E10618. The authors are indebted for the use of the 248Cm to the U.S. Department of Energy, Office of Basic Energy Sciences, through the transplutonium element production facilities at Oak Ridge National Laboratory which was made available as part of a collaboration between the HZDR and the Lawrence Berkeley National Laboratory (LBNL).
Keywords: Curium(III), Bacteria, Speciation, TRLFS
  • Contribution to proceedings
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere 2011, 18.-23.09.2011, Beijing, PR China
  • Poster
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products (MIGRATION 2011), 18.-23.09.2011, Beijing, PR China

Publ.-Id: 15277 - Permalink

Synthesis, structure determination and (radio-) fluorination of novel functionalized phosphanes suitable for the traceless Staudinger ligation
Mamat, C.; Franke, M.; Peppel, T.; Köckerling, M.; Steinbach, J.;
An elegant and efficient synthesis approach for the preparation of novel benzoate and nicotinate containing phosphanes is presented. This reaction path has a broad substrate scope. Thus, various functionalized phosphanes were obtained in high yields using an esterification procedure under Steglich conditions. A facile blocking of the phosphorus with BH3 as protecting group enables a further derivatization of the benzoate residue. The prepared phosphane derivatives proved to be valuable labeling building blocks for the implementation of a (radio-)fluorination strategy. For this case, these compounds were applied for these labeling purposes using the traceless Staudinger Ligation. In this case, the preparation of a selection of azide-functionalized small organic and bioactive sample molecules and subsequent mild and selective (radio-) fluorination of these derivatives is demonstrated adopting this bioorthogonal ligation method.

Publ.-Id: 15275 - Permalink

Application of quantum chemical calculations to actinide solution chemistry: spectroscopy and photochemistry
Tsushima, S.;
Three examples will be presented at the talk. (1) DFT application to the structural determination of aqueous actinide species. Role of 5f electron to the An-O bond distance and to the selection of monodentate/bidentate will be discussed. (2) Calculation of redox potential of An(VI)/ An(V) for An=U, Np, Pu, Am. (3) Uranyl(VI) luminescence and photochemistry. The mechanisms of uranyl(VI) luminescence quenching and photochemical reduction of uranyl(VI) complexes will be discussed.
  • Invited lecture (Conferences)
    Tokai Research and Development Center of the Japan Atomic Energy Agency (JAEA), 09.03.2011, Tokai, Japan

Publ.-Id: 15274 - Permalink

Retention of uranium in biofilms of a granitic nuclear waste repository research tunnel
Krawczyk-Bärsch, E.; Lünsdorf, H.; Pedersen, K.; Lehtinen, A.; Arnold, T.;
Several mechanisms of interactions of microorganisms with actinides under aerobic conditions are known, e.g. biosorption, interactions with S-layers or bioprecipitation. Some of them have the potential of a substantial retention of actinides, like uranium. However, little is known about the retention processes in a microbial community, such as biofilms. Since bacteria do not usually occur as single individual cells in nature but as multicellular communities, we have to draw our attention on the biofilms. They are characterized by building up their own microenvironment, which can differ significantly from that of the bulk solution with the consequence that biofilms are becoming more important in potential retention processes for actinides.

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 by Pedersen et al. (2008) 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 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).

Pedersen K, Arlinger J, Eriksson S, Hallbeck M, Johansson J, Jägevall S, Karlsson L. Microbiology of Olkiluoto Groundwater. Results and Interpretations 2007. POSIVA Working Report 2008-34. Olkiluoto, Finland.
Keywords: biofilm, uranium, retention, nuclear waste repository
  • Lecture (Conference)
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 18.-23.09.2011, Beijing, China

Publ.-Id: 15273 - Permalink

Uptake of Np(IV) by C-S-H Phases and Cement Paste: An EXAFS Study
Gaona, X.; Dähn, R.; Tits, J.; Scheinost, A. C.; Wieland, E.;
In many nuclear waste disposal concepts cementitious materials are foreseen to be used for the immobilization of long-lived intermediate level wastes (ILW). ILW may contain significant amounts of neptunium-237, which is expected as Np(IV) under the reducing conditions developing after the closure of the repository. Predicting the release of Np(IV) from this environment requires a sufficiently detailed understanding of its interaction with the main sorbing components of cement. In this study, the uptake of Np(IV) by calcium silicate hydrates (C-S-H) and hardened cement paste (HCP) has been investigated using extended X-ray absorption spectroscopy (EXAFS).

Evaluation of EXAFS data from Np(IV)-doped C-S-H and HCP indicates the predominant incorporation of Np in the C-S-H structure throughout the complete sequence of cement degradation. Two species were identified, corresponding to Np(IV) in C-S-H with Ca:Si 1.65 (fresh cement) and 0.75 (highly degraded cement). The coordination environment of Np(IV) was found to depend on the Ca:Si ratio but not on pH, consistently with the aqueous speciation of Np(IV) in the pH range 10 – 13.3 (with predominance of Np(OH)4(aq)). These results unequivocally show that C-S-H are responsible for Np(IV) immobilization in cementitious materials, whilst incorporation in the interlayer of the C-S-H structure is regarded as the predominant uptake mechanism.
Keywords: Neptunium EXAFS cement
  • Poster
    3rd ReCosy Annual Workshop, 21.03.2011, Balaruc-les-Bains, France
  • Environmental Science & Technology 45(2011)20, 8765-8771
    DOI: DOI: 10.1021/es2012897

Publ.-Id: 15272 - Permalink

S-Layer protein from Lysinibacillus sphaericus JG-A12 as matrix for Au-III sorption and Au-nanoparticle formation
Jankowski, U.; Merroun, M.; Selenska-Pobell, S.; Fahmy, K.;
The strain Lysinibacillus sphaericus JG-A12, isolated from the uranium mining site at Haberland. Saxony (Germany) selectively and reversibly accumulates radionuclides and toxic metals. Metal binding occurs to its surface layer (S-layer) surrounding the cells. Here, we have studied by Fourier-transform infrared (FTIR) spectroscopy the protein structure and stability as a function of Au-III binding and the subsequent reductively induced formation of Au-nanoclusters. Similar to previously studied complexes with Pd-II. Au-treated S-layers become resistant to acid denaturation evidenced by little response of their amide I absorption frequency. However, the strong effect of Pd-II on the side chain carboxylate IR absorption intensity is not observed with gold. Particularly after reduction, the carboxyl absorption responds little to acidification and a fraction appears to be protonated already at neutral pH. We ascribe this to a hydrophobic environment of the carboxyl groups after formation of Au-nanoclusters. EXAFS spectra agree with the metallic Au-Au distance but the reduced coordination number indicates that the Au-nanoclusters do not exceed similar to 2 nm. Thus, the S-layer of L. sphaericus JG-A12 provides a biotemplate for efficient Au-nanocluster formation in an acid-resistant matrix and independently of cysteins.

Publ.-Id: 15271 - Permalink

Dismantling of the Cyclotron U-120 at the Research Center Dresden-Rossendorf
Naumann, B.; Friedrich, M.; Matz, W.;
Status report about the dismantling and disposal of the Rossendorf cyclotron U-120.
Keywords: dismantling, disposal, circular accelerator, activation of large-volume components
  • Poster
    10th International Symposium "Conditioning of Radioactive Operational & Decommissioning Wastes", 06.-08.04.2011, Dresden, Deutschland

Publ.-Id: 15270 - Permalink

Uranium(IV)-Silica colloids at near-neutral pH
Zänker, H.; Weiss, S.; Hennig, C.; Dreissig, I.; Bernhard, G.;
Evidence is provided by photon correlation spectroscopy, ultrafiltration and ultracentrifugation that uranium(IV) can form silicate-containing colloids. The particles are generated in near-neutral to slightly alkaline solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). They remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne U(IV) was observed which is a concentration much higher than the concentrations of truly dissolved or colloidally suspended waterborne An(IV) species hitherto reported for the near-neutral pH range. The prevailing size of the particles is below 20 nm. Laser Doppler velocimetry reveals that the nanoparticles are stabilized in solution by electrostatic repulsion due to a negative zeta potential caused by the silicate. The isoelectric point of the nanoparticles is shifted toward lower pH values by the silicate. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids.
Keywords: uranium(IV), silicate, colloids, near-neutral pH
  • Contribution to proceedings
    41ièmes Journees des Actinides, 09.-12.04.2011, Stara Lesna, Slovakia
    Proceedings ot the 41ièmes Journees des Actinides
  • Lecture (Conference)
    Journees des Actinides, 09.-12.04.2011, Stara Lesna, Slovakia

Publ.-Id: 15269 - Permalink

U(VI) sorption on montmorillonite: A macroscopic and microscopic study
Marques Fernandes, M.; Baeyens, B.; Dähn, R.; Scheinost, A. C.; Macé, N.; Bradbury, M. H.;
The mechanism of U(VI) sorption on montmorillonite (Na-SWy-2) in the absence and the presence of carbonate was investigated through a combination of different approaches: macroscopic sorption experiments, modelling with the 2 Site Protolysis Non Electrostatic Surface Complexation and Cation Exchange model and Extended X-ray absorption fine structure (EXAFS) spectroscopy. U(VI) sorption measurements were performed both in the absence and in the presence of carbonate at fixed ionic strength (0.1 M NaClO4) as a function of pH at U(VI) trace concentration (~ 9x10-8 M) and as a function of U(VI) concentration (5x10-8-10-4 M) at pH ~ 8. In the presence of carbonate, experiments were carried out in equilibrium with atmospheric pCO2 and in 1, 3 and 5 mM NaHCO3. The sorption edge data in the absence of carbonate were modelled by considering the formation of the following surface species, ≡SSOUO2+, ≡SSOUO2OH0, ≡SSOUO2(OH)2-, ≡SSOUO2(OH)32-, and ≡SSOUO2(OH)32- on the strong sites. From the isotherm the formation of ≡SW1OUO2+ and ≡SW1OUO2OH0 on the weak sites were derived. Two additional surface complexes on the strong sites, ≡SSOUO2CO3- and ≡SSOUO2(CO3)23- and one surface complex on the weak sites, ºSW1OUO2CO3-, were necessary to reproduce the sorption data in the presence of carbonate. The EXAFS measurements did not allow to verify the formation of ternary uranyl-carbonate complexes on the montmorillonite surface. However the obtained fit parameters, splitting of the equatorial oxygen shell, two Si/Al shells at ~3.09 Å and 3.85 Å and one Fe shell at ~ 3.43 Å clearly indicate that U(VI) forms a mononuclear edge-sharing surface complex, sharing one octahedral Fe, one octahedral Al and one tetrahedral Si/Al. The lack of angular dependence of the Polarized–EXAFS spectra confirms that U(VI) is not sorbed to the montmorillonite surface in the continuity of the octahedral sheet.
Keywords: EXAFS montmorillonite sorption U(VI)

Publ.-Id: 15268 - Permalink

Interaction of U(VI) with Some Bioligands or the Influence of Different Functional Groups on Complex Formation
Frost, L.; Osman, A. A. A.; Geipel, G.; Viehweger, K.; Moll, H.; Bernhard, G.;
U(VI) released anthropogenically, e.g. through mining activities, can be accumulated for instance in plants and consequently can enter further parts of the food chain. Hence it is of crucial importance to study the interaction of U(VI) with cellular ligands, like glutathione, uric acid and benzoic acid. Glutathione, the most abundant thiol compound of a cell, has a well known affinity for heavy metal ions. It is a precursor for phytochelatin synthesis and thus also a model substance for the study on U(VI) phytochelatin interaction. Uric acid (UA) was investigated as a further ligand being potentially capable of chelate formation with U(VI). It is present e.g. in bio-fluids such as urine and sweat. Benzoic acid occurs naturally free and bound as benzoic acid esters in many plant and animal species. Furthermore it is a model ligand to study the interaction with bacterial siderophores and humic acids.
UV-vis and time-resolved laser-induced fluorescence spectroscopy (TRLFS) were applied to investigate complex formation between U(VI) and glutathione, uric acid and benzoic acid. Additionally one of the four major potential binding sites of glutathione, the thiol group, was blocked by derivatization to assess the coordination chemistry more detailed.
In the U(VI)-glutathione system a 1:1 complex with a large stability constant of 39.07 ± 0.15 (at zero ionic strength) could be identified. On the contrary, in the U(VI)-urate and -benzoic acid systems a comparably weak complexation was found.
What are the structure-related reasons for such a considerable discrepancy in complex stability? Investigating the interaction of U(VI) with glutathione-S-conjugates, no decrease in complex stability in comparison to U(VI) complexation by glutathione was found. Thus here a significant involvement of the thiol group in coordination can be excluded. Since benzoic acid offers one carboxyl functionality but exhibits a very weak U(VI) coordination, for U(VI) complexation by glutathione a chelate-like coordination with an involvement of at least one carboxyl functionality can be assumed. Since uric acid coordinates as a bidentate ligand and is suggested to undergo a chelation with U(VI) as well, specifically by its 7-amine and 6-carbonyl group, it follows that chelate formation must not necessarily result in strong complexation.
In general, these results contribute to a better understanding of the intricate U(VI) interactions in biological systems on a molecular level.
Keywords: U(VI), Glutathione, Uric Acid, Benzoic Acid, Complexation, UV-vis spectroscopy, TRLFS
  • Contribution to proceedings
    Uranium Mining and Hydrogeology VI, 18.-22.09.2011, Freiberg, Deutschland
    The New Uranium Mining Boom, Berlin: Springer, 978-3-642-22121-7, 595-606
  • Lecture (Conference)
    Uranium Mining and Hydrogeology VI, 18.-22.09.2011, Freiberg, Deutschland

Publ.-Id: 15267 - Permalink

The geochemical fate of Se(IV) in the Boom Clay system - XAS based solid phase speciation
Breynaert, E.; Scheinost, A.; Dom, D.; Rossberg, A.; Vancluysen, J.; Gobechiya, E.; Kirschhock, C.; Maes, A.;
For more than 30 years the Boom Clay formation is studied as a reference host formation for methodological research concerning clay-based geological disposal of HLRW in Belgium and Europe. Boom Clay provides good sorption capacity, very low permeability and chemically reducing conditions due to the anoxic conditions and the presence of pyrite and siderite. Performance Assessment calculations have indicated Se79 (t1/2 = 2.95×105 y) to be one of the critical radionuclides for the geological disposal of HLRW [1]. Aqueous selenite [Se(+IV)] and selenate [Se(+VI)] are the dominant species in mildly and strongly oxidizing environments. Under reducing conditions the solubility of Se is theoretically controlled by the formation of sparsely soluble selenium phases such as elemental Se or transition metalselenide salts (e.g. FeSe or FeSe2) [2, 3]. Slow kinetic reactions between the different redox states have been observed [4] and proposed to explain different redox phases observed within a single reducing environment. Se oxyanions, such as SeO4 2- and SeO32-, are generally considered as the most mobile forms of Se [5] and their migration through Boom Clay thus is considered as “worst case scenario”. In order to assess their long-term fate it is imperative to understand the influence of different geochemical phases present in the Boom Clay matrix on selenium speciation and mobility. A multidisciplinary approach combining long-term batch sorption experiments with linear combination XANES and ITFA-based EXAFS analysis on different fractions isolated from Boom Clay batch systems equilibrated with Se(IV), identified Se0 as the dominant in situ solid phase speciation of Se in Boom Clay conditions.
[1] SAFIR-2, 2001. Brussels, Belgium. p. 288. [2] Breynaert, E. et al., ES&T. 42 (10): p. 3595. [3] Scheinost, A.C. et al., J. Contam. Hydrol. 102 p. 228. [4] Masscheleyn, P.H. et al., ES&T. 24 (1): p. 91. [5] Elrashidi, M.A. et al., Soil Science 144 (2): p. 141.
Keywords: selenium redox Boom clay
  • Lecture (Conference)
    Goldschmidt Conference, 13.06.2010, Knoxville, Tennessee, USA
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 74(2010)12, A122

Publ.-Id: 15266 - Permalink

Ultraschnelle Elektronenstrahl-Röntgencomputertomographie als Verfahren zur zerstörungsfreien Qualitätskontrolle
Pöpping, U.; Barthel, F.; Tietze, H.; Hampel, U.;
Qualitätskontrollen von Nahrungsmitteln haben eine besondere Bedeutung sowohl zur Sicherstellung eines unbedenklichen Verzehrs als auch zur Feststellung der Güte. Neben der Untersuchung von äußeren Qualitätsmerkmalen sowie chemisch-biologischen Analysen spielt dabei auch die Beschaffenheit im Inneren eine wesentliche Rolle. Die Untersuchung hier kann aber in vielen Fällen nur in Stichproben erfolgen, da das Untersuchungsobjekt dazu zerstört werden muss. Zudem ist die Qualitätsprüfung in der Regel auch nur manuell möglich.

Am Institut für Sicherheitsforschung im Helmholtz-Zentrum Dresden-Rossendorf (HZDR) wurde eine ultraschnelle Elektronenstrahl Röntgencomputertomographie entwickelt. Hierbei handelt es sich um ein bildgebendes Messverfahren, bei dem von einem Untersuchungsobjekt bis zu 7.000 Schnittbilder pro Sekunde bei einer räumlichen Auflösung von ca. 1 mm erzeugt werden können. Dabei wird die für die Rekonstruktion von überlagerungsfreien Schnittbildern benötigte Aufnahme von Durchstrahlungsprojektionen aus unterschiedlichen Blickwinkeln nicht durch die mechanische Drehung von Objekt oder Messsystem erreicht, stattdessen wird ein Elektronenstrahl, der den die Röntgenstrahlung emittierenden Brennfleck auf einem ringförmigen Target erzeugt, elektronisch abgelenkt. Auf diese Weise wird die Untersuchung einer großen Stückzahl von Untersuchungsobjekten innerhalb kurzer Zeit möglich.

Erste Untersuchungen haben die prinzipielle Eignung der - ursprünglich für die Messung in mehrphasigen Strömungen entwickelten - Technologie auch zur zerstörungsfreien Qualitätskontrolle gezeigt. Es konnte für verschiedenste Untersuchungsobjekte wie beispielsweise Wallnüsse, Esskastanien aber auch Paprikaschoten die Rekonstruktion des Inneren in einer prinzipiell für die Qualitätssicherung mehr als ausreichender Güte gezeigt werden.

Die Ergebnisse der ersten Studien lassen auf ein großes Potenzial dieser Technologie für dieses Anwendungsfeld schließen. Allerdings liegt die Expertise am HZDR vor allem in der Entwicklung solcher Messsysteme und nicht in der fachlichen Bewertung von Qualitätsmerkmalen von Nahrungsmitteln. Weitere Forschungs- und Entwicklungsarbeiten, die gemeinsam mit einer Forschungseinrichtung mit notwendiger Expertise auf dem Gebiet der Landwirtschaft bzw. des Gartenbaus angestrebt werden, sind vor allem zur erheblichen Verkürzung der notwendigen Rekonstruktionszeit sowie zur Automatisierung dieser Technologie und des Prozesses selbst notwendig.
Keywords: Ultrafast X-ray computed tomography, quality inspection
  • Poster
    47. Jahrestagung der Deutschen Gartenbauwissenschaftlichen Gesellschaft (DGG) und des Bundesverbandes der Hochschulabsolventen/Ingenieure Gartenbau u. Landschaftsarchitektur (BHGL), 23.-26.02.2011, Hannover, Deutschland
  • Contribution to proceedings
    47. Jahrestagung der Deutschen Gartenbauwissenschaftlichen Gesellschaft (DGG) und des Bundesverbandes der Hochschulabsolventen/Ingenieure Gartenbau u. Landschaftsarchitektur (BHGL), 23.-26.02.2011, Hannover, Deutschland
    Ultraschnelle Elektronenstrahl-Röntgencomputertomographie als Verfahren zur zerstörungsfreien Qualitätskontrolle, Hannover: BHGL & DGG, 1613-088X

Publ.-Id: 15265 - Permalink

Geogases in the Kaapvaal Craton – Origin and modes of transport
Lippmann-Pipke, J.; Sherwood Lollar, B.; Niedermann, S.; Stroncik, N. A.; Naumann, R.; van Heerden, E.; Onstott, T. C.; Erzinger, J.; Zimmer, M.; Kujawa, C.; Boettcher, M.; Bester, A.; Moller, H.; Reches, Z.;
Introduction The deep gold mines of the Witwatersrand Basin, South Africa, have gained recent attention because of reports of deep microbial communities persisting to depths of >3 kilometers - an exotic outpost of the Earth's deep biosphere [1,2]. Prerequisites of such investigations are studies on the age of the deep fracture water [3] and the origin of associated abiogenic CH4- [4] and H2-rich gases [5]. Here we report about insights obtained from two new gas data sets (I, II) with respect to the dynamic of the ultra-deep fluid system [6,7].
Methods (I) The isotopic composition of neon dissolved in deep fracture water and in fluid inclusions of quartz host rock was analyzed, and the results correlated with the isotopic signatures of the biogenic and abiogenic H2- and CH4-rich sample aliquots. (II) In the other project the geogas composition of the free gas was monitored by means of a mass spectrometer and gas sensitive sensors installed just inside the Pretorius Fault Zone at 3.45 km depth in the TauTona Mine. Data from a 4-year observation period are cross-correlated on the minute-by-minute basis with seismic data obtained from a 3-dimensional array of highly sensitive seismometers.
Results (I) Highest ever observed 21Ne/22Ne ratios combined with an anomalous 21Ne/22Ne production ratio imply that the dissolved neon is a 2 Ga metamorphic signal stored in fluid inclusions and accumulating in fracture water since geological times as a result of water rock reaction processes. (II) Geogas concentration variations (4He, H2, CH4, CO2) strongly correlate with seismic signals resulting from mining related blasts and induced earthquakes in the TauTona Mine. The fracture gas permeability of ~ 5*10e-10 m² is estimated on the basis of observed gas flux rates.
Conclusion (I) 21Ne/22Ne ratios may serve as search proxy for regions of the Archean Earth's crust where investigations of the deep biosphere might be focused. (II) Methodological improvements enabled the simultaneous gas geochemical and seismic signal recording in the world deepest operating mine, reflecting the near-field at earthquake focal depths.

[1] Lin et al., Science 2006, 314(5798): 479-482; [2] Chivian et al., Science 2008, 322(5899): 275-278 ; [3] Lippmann et al., GCA 2003, 67(23): 4597-4619; [4] Sherwood Lollar et al., Chem. Geol. 2006, 226(3-4): 328-339; [5] Lin et al., GGG 2005, 6: Q07003; [6] Lippmann-Pipke et al. Chem. Geol., submitted; [7] Lippmann-Pipke et al., Appl. Geol., submitted
  • Invited lecture (Conferences)
    New Horizons for International Investigations into Carbon Cycing in the Deep Crustal Biosphere, 18.-23.01.2011, Bloemfontein, South Africa

Publ.-Id: 15264 - Permalink

Vibrational characteristics of outer-sphere surface complexes: example of sulfate ions adsorbed onto metal (hydr)oxides
Müller, K.; Lefèvre, G.;
The vibrational characteristics of outer-sphere complexes of sulfate at several mineral oxide – water interfaces were investigated by in situ attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. In the IR spectra obtained from surface outer-sphere complexes only one peak of the antisymmetric stretching vibrational mode υ3 similar to the free sulfate ion SO42− in aqueous solution is observed. However, on the investigated (hydr)oxide surfaces of Al3+, Ti4+, Fe2+/3+, Cr3+, Ni2+, Ce4+, Cu2+, Y3+, Zn2+, and Nd3+ a shift of up to 14 cm−1 was found, correlated to the polarizing power of the metal cations. A high polarizing power was found to result in a stronger shift of υ3 compared to the aqueous SO42− ion. Furthermore, the impact of the metal oxide structure on the characteristics of the formed outer-sphere complex was negligible, since different Al and Fe (hydr)oxides did not show any changes in the respective IR spectra. A variation of ionic strength (1 – 10-4 M) and pH (6.8 – 3.1) during the formation of SO42− outer-sphere complexes on g-Al2O3 showed that those changes directly influence the surface potential, without modifying the geometry of the outer-sphere complex.

Publ.-Id: 15263 - Permalink

Synthesis and biological evaluation of new [Tc(N)(PS)]-based mixed-ligand compounds useful in design of target-specific radiopharmaceuticas: the 2-methoxyphenylpiperazine dithiocarbamate derivatives as example
Bolzati, C.; Salvarese, N.; Carta, D.; Refosco, F.; Dolmella, A.; Pietzsch, H.-J.; Bergmann, R.; Bandoli, G.;
This study presents the first application of a general procedure based on the use of the [Tc(N)Cl(PS) (PPh3)] species (PS is an alkyl phosphinothiolate ligand) for the preparation of Tc(N) target-specific compounds. [Tc(N)Cl(PS)(PPh3)] selectively reacts with an appropriate dithiocarbamate ligand (S^Y) to give [Tc(N)(PS)(S^Y)] compounds. 1-(2-Methoxyphenyl)piperazine, which displays a potent and specific affinity for 5HT1A receptors,
was selected as a functional group and conjugated to the dithiocarbamate unit through different spacers (Ln). [99mTc(N)(PS)(Ln)] complexes were prepared in high yield (more than 90%). The chemical identity of 99mTc complexes was determined by high performance liquid chromatography comparison with the corresponding 99gTc complexes. All complexes were found to be inert toward transchelation with an excess of glutathione and cysteine. No notable biotransformation of the native compound into different species by the in vitro action of the serum and liver enzymes was shown. Nanomolar affinity for the 5HT1A receptor was obtained for [99mTc(N)(PSiso)L3] (IC50 = 1.5 nM); a reduction of the affinity was observed for the other complexes as a function of the shortening of the alkyl chain interposed between the dithiocarbamate and the pharmacophore. Negligible brain uptake was found from in vivo distribution data of [99mTc(N)(PSiso)L3]. The key finding of this study is that the complexes maintained good affinity and selectivity for 5HT1A receptors, and the IC50 value for [99gTc(N)(PSiso)L3] being comparable to the IC50 value found for WAY 100635. This result confirmed the possibility of preparing [99mTc(N)(PS)]-based targetspecific compounds without affecting the affinity and selectivity of the bioactive molecules for the corresponding receptors.
Keywords: Technetium, Phosphinothiolate, Dithiocarbamate, 5HT1A receptor, Brain

Publ.-Id: 15262 - Permalink

[18F]1-(3-fluoropropyl)piperazines as model compounds for the radiofluorination of pyrido[2,3-d]pyrimidines
Grosse-Gehling, P.; Wuest, F. R.; Peppel, T.; Köckerling, M.; Mamat, C.;
The visualization of cyclin-dependent kinases (CDKs), which are overexpressed in multiple tumor types, with radiolabeled CDK inhibitors by means of positron emission tomography in vivo is a promising approach for tumor imaging.
Pyrido[2,3-d]pyrimidines belong to a class of inhibitors, which bind with high affinity to CDK4 and CDK6. [18F]1-(3-Fluoropropyl)-4-(4-nitrophenyl)piperazine and [18F]1-(3-fluoropropyl)-4-(4-nitropyridin-3-yl)piperazine represent
structural elements of the appropriate CDK inhibitors and were therefore chosen as model compounds for the incorporation of fluorine-18 into pyrido[2,3-d]pyrimidines. Three methods are known for the preparation of tertiary [18F]3-fluoropropyl-amines:
1) the direct substitution of a good leaving group,
2) the two-step reaction synthesizing a [18F]3-fluoropropyl intermediate,
and 3) the utilization of aziridinium or azetidinium salts. In general, radiofluorinations using azetidinium salts lead to
excellent radiochemical yields in short periods of time. For these reasons we developed a synthesis route to tosylated piperazine precursors and establish a radiolabeling approach based on the incorporation of fluorine-18 into open-chained
tosylates as well as the respective azetidinium spiro compounds to yield the desired radiofluorinated piperazines successfully.
Keywords: Radiofluorination, Spiro compounds, CDK inhibitor, Pyrido[2,3-d]pyrimidines

Publ.-Id: 15261 - Permalink

Radioiodination of humic substances
Franke, K.; Kupsch, H.;
The known IODO-GEN™-method [1] was adapted for radiolabeling of humic and fulvic acids with 131I. The water insoluble oxidizing agent 1,3,4,6tetrachloro-3α,6α-diphenylglycoluril (IODO-GEN™) forms an iodous ion species (I+), which undergoes an electrophilic I/H-substitution on aromatic moieties of the humic and fulvic acids. This method offers mild conditions with a lesser extent of oxidative alterations of the target molecule, accompanied by an easy handling due to the virtual water-insolubility of the oxidizing agent. The method was optimized and different techniques were tested for the purification of the radioiodinated humic material. The yield of the labeling procedure varies between 45 and 75% depending on the provenance of the humic material and the applied purification method. A specific activity up to 40 MBq/mg was achieved. Furthermore, the known inherent photo-susceptibility of the iodinated humic substance and the influence of reducing agents were verified. An additional release of 131I up to 20% and up to 35%, respectively were observed.

Publ.-Id: 15260 - Permalink

Twin boundary motion and magnetic domain distribution investigated by optical polarization microscopy
Neudert, A.; McCord, J.;
An overview of optical studies of magnetic and structural transformation in magnetic shape memory materials is given. The magnetic domain behavior and the motion of twin boundaries in single crystalline bulk samples of the shape memory alloy NiMnGa are investigated by optical polarization microscopy and magnetic indicator film technique. During stress induced twin boundary motion the magnetization reversal takes place by rotation of magnetization, leading to a total rearrangement of the magnetic domain distribution. Time-resolved studies of twin boundary motion induced by pulsed magnetic fields show that the distance traveled by the twin boundary is enhanced with increasing sample temperature. An overview of these and complementary experiments and the obtained results will be given.
Keywords: magnetic shape memory alloy, optical polarization microscopy, time-resolved microscopy
  • Invited lecture (Conferences)
    International Conference on Ferromagnetic Shape Memory Alloys, 18.-22.07.2011, Dresden, Germany

Publ.-Id: 15259 - Permalink

The influence of biofilms on the migration of uranium in acid mine drainage (AMD) waters
Krawczyk-Bärsch, E.; Lünsdorf, H.; Arnold, T.; Brendler, V.; Eisbein, E.; Jenk, U.; Zimmermann, U.;
The uranium mine in Konigstein (Germany) is currently in the process of being flooded. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO2SO4) and UO2++ speciation as well as of the solid uranium species Uranophane [Ca(UO2)(2)(SiO3OH)(2)center dot 5H(2)O] and Coffinite [U(SiO4)(1-x)(OH)(4x)], which are defined in the stability field of pH>4.8 and Eh < 960 mV and pH>0 and Eh<300 mV, respectively. The plotting of the measured redox potential and pH of the AMD water and the biofilm into the calculated pH Eh diagram showed that an aqueous uranium(VI) sulfate complex exists under the ambient conditions. According to thermodynamic calculations a retention of uranium from the AMD water by forming solid uranium(VI) or uranium(IV) species will be inhibited until the pH will increase to >4.8. Even analysis by Energy-filtered Transmission Electron Microscopy (EF-TEM) and electron energy loss spectroscopy (EELS) within the biofilms did not provide any microscopic or spectroscopic evidence for the presence of uranium immobilization. In laboratory experiments the first phase of the flooding process was simulated by increasing the pH of the AMD water. The results of the experiments indicated that the F. myxofaciens dominated biofilms may have a substantial impact on the migration of uranium. The AMD water remained acid although it was permanently neutralized with the consequence that the retention of uranium from the aqueous solution by the formation of solid uranium species will be inhibited.
Keywords: AMD water, Uranium, Biofilm, Ferrovum myxofaciens, microsensor measurement, thermodynamically calculation

Publ.-Id: 15258 - Permalink

Nuclear Astrophysics and Nuclear Transmutation
Wagner, A.;
Albeit their quite disjoint research history, the research areas of nuclear astrophysics and transmutation of nuclear waste show striking similarities resembling the same basics in nuclear physics. In both fields, the electromagnetic response function of nuclei and the nuclear level density play a key role in the explosive stellar burning as in the reduction of long-lived actinides produced in nuclear power plants. In the talk, I will present recent results on the electromagnetic strength function in medium-mass nuclei studied at the superconducting electron linear accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf. Neutron-induced reactions on various nuclei, like neutron capture, neutron inelastic scattering are studied at a new neutron time-of-flight facility, as well.
Keywords: nuclear astrophysics transmutation waste electromagnetic response function nuclei level density long-lived actinides neutron capture inelastic scattering nELBE
  • Invited lecture (Conferences)
    Kernphysikalisches Kolloquium, 27.01.2011, Bonn, Deutschland

Publ.-Id: 15256 - Permalink

Recombinant S-layer production induces disordered cell division in E. coli filaments
Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.;
The rod-shaped bacterium Escherichia coli is one of the best studied microorganism with a size of 1.1-1.5 µm x 2.0-6.0 µm. We used E. coli BL21(DE3), one of the most widely used host in genetic engineering, for heterologous expression of surface layer (S-layer) proteins to enable a fast and efficient protein production.
S-layer are proteins which cover the outermost of many prokaryotes and are probably the basic and oldest forms of bacterial envelopes. These proteins are mostly composed of protein and glycoprotein monomers and have the ability to self-assemble into two-dimensional arrays on interfaces. Several characteristics like their work as molecular sieve, as virulence factor or the protection of the cell from toxic heavy metal ions make S-layer proteins interesting for their usage as filter materials or patterning structures in nanotechnology.
Surprisingly, the heterologous expression of S-layer proteins of the uranium mining waste pile isolate Lysinibacillus sphaericus JG-A12 induced drastic morphological changes of E. coli BL21(DE3) single cells to filaments and tubes enclosing single cells of >100 µm in length. The S-layer expressing E. coli cultures reached a high optical density and cells showed a high viability as well as strong expression of S-layer proteins. The drastically changed cell morphology was investigated by light microscope, AFM and TEM. Analyses with S-layer-GFP expressing cells, which were stained with DAPI and membrane stain, present a disordered cell division process. Our results give a new insight in the morphology and the cell division process in E. coli induced by recombinant proteins.

Lederer et al. (2010) Heterologous expression of the surface-layer-like protein SllB induces the formation of long filaments of Escherichia coli consisting of protein-stabilized outer membrane. Microbiology 156,3584-95.
  • Poster
    FEMS (Federation of European Microbiological Societies), 26.-30.06.2011, Geneva, Switzerland

Publ.-Id: 15255 - Permalink

Recombinant S-layer production induces disordered cell division in E. coli filaments
Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.;
The rod-shaped bacterium Escherichia coli is one of the best studied microorganism with a size of 1.1-1.5 µm x 2.0-6.0 µm. We used E. coli BL21 (DE3), one of the most widely used host in genetic engineering, for heterologous expression of surface layer (S-layer) proteins to enable fast and efficient protein production.
S-layer are proteins which cover the outermost of many prokaryotes and are probably the basic and oldest forms of bacterial envelope. These proteins are mostly composed of protein and glycoprotein monomers and have the ability to self-assemble into two-dimensional arrays on interfaces. Several characteristics like their work as molecular sieve, as virulence factor or the protection of the cell from toxic heavy metal ions make S-layer proteins interesting for their usage as ultrafiltration membranes, drug microcontainers, filter materials or patterning structures in nanotechnology.
Surprisingly, the heterologous expression of S-layer proteins of the uranium mining waste pile isolate Lysinibacillus sphaericus JG-A12 induced drastic morphological changes of E. coli BL21 (DE3) single cells to filaments and single cell enclosing tubes of >100 µm in length. The assumed secretion of tube-stabilizing S-layer proteins was investigated with SDS-PAGE and ß-galactosidase assay. These analyses result in a high S-layer appearance without significant ß-galactosidase activity in the supernatant and the periplasm. The origin and composition of filaments and tubes were analysed by membrane stain studies. We identified that filaments in the exponential growth phase form a continuous intracellular space without partitioning. To investigate the mechanism of filament and tube formation we analyzed GFP/S-layer expressing E. coli with DAPI-stain. The staining showed >50 µm long DNA-fibres that cross the filaments and “DNA-free” areas, the latter exhibiting strong GFP-expression. Our results point to a disordered cell division in E. coli filaments which is effected by recombinant S-layer expression.

[1] Lederer et al. (2010) Heterologous expression of the surface-layer-like protein SllB induces the formation of long filaments of Escherichia coli consisting of protein-stabilized outer membrane. Microbiology 156,3584-95.
  • Poster
    VAAM (Jahrestagung der Vereinigung für Allgemeine und Angewandte Mirkobiologie), 03.-06.04.2011, Karlsruhe, Deutschland

Publ.-Id: 15254 - Permalink

Bulk diffusion induced structural modifications of carbon-transition metal nanocomposite films
Berndt, M.; Abrasonis, G.; Kovacs, G. J.; Krause, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.;
The influence of transition metal (TM=V,Co,Cu) type on the bulk diffusion induced structural changes in carbon:TM nanocomposite films is investigated. The TMs have been incorporated into the carbon matrix via ion beam co-sputtering, and subsequently the films have been vacuum annealed in the temperature range of 300-700°C. The structure of both the dispersed metal rich and the carbon matrix phases has been determined by a combination of elastic recoil detection analysis, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The as-grown films consist of carbidic (V and Co) and metallic (Cu) nanoparticles dispersed in the carbon matrix. Thermal annealing induces surface segregation of Co and Cu starting at >=500°C, preceded by carbide-metal transformation of Co-carbide nanoparticles at ~300°C. No considerable morphological changes occur in C:V films. In contrast to the surface diffusion dominated regime where all the metals enhance the six-fold ring clustering of C, in the bulk diffusion controlled regime only Co acts as a catalyst for the carbon graphitization. The results are consistent with the metal-mediated crystallization mechanism in the C:Co films. The results are discussed on the basis of the metal-carbide phase stability, carbon solubility in metals or their carbides and interface species.

Publ.-Id: 15253 - Permalink

The Dresden High Magnetic Field Laboratory (HLD) - a User Facility for Advanced Pulsed-Field Experiments
Wosnitza, J.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S.;
es liegt kein Abstract vor.
  • Invited lecture (Conferences)
    Physical Phenomena at High Magnetic Fields (PPHMF VII), 04.-08.12.2010, Tallahassee, Florida, USA

Publ.-Id: 15252 - Permalink

The role of water H-bond imbalances in B-DNA substate transitions and peptide recognition revealed by time-resolved FTIR spectroscopy
Khesbak, H.; Savchuk, O.; Tsushima, S.; Fahmy, K.;
The conformational substates BI and BII of the phosphodiester backbone in B-DNA are thought to contribute to DNA flexibility and protein recognition. We have studied by rapid scan FTIR spectroscopy the isothermal BI-BII transition on its intrinsic time scale. Correlation analysis of IR absorption changes occurring within seconds after a reversible incremental growth of the DNA hydration shell identifies water populations w1 (PO2--bound) and w2 (non-PO2--bound) exhibiting weaker and stronger H-bonds, respectively, than those dominating in bulk water. The BII substate is stabilized by w2. The water H-bond imbalance of 3-4 kJ mol-1 is equalized at little enthalpic cost upon formation of a contiguous water network (at 12-14 H2O molecules per DNA phosphate) of reduced n(OH) band width. In this state, hydration water cooperatively stabilizes the BI conformer via the entropically favored replacement of w2-DNA interactions by additional w2-water contacts, rather than binding to BI-specific hydration sites. Such water rearrangements contribute to the recognition of DNA by indolicidin, an antimicrobial 13-mer peptide from bovine neutrophils which, despite little intrinsic structure, preferentially binds to the BI conformer in a water-mediated induced fit. The FTIR spectra resolve sequential steps leading from PO2--solvation to substate transition and eventually to base stacking changes in the complex. In combination with CD-spectral titrations, the data indicate that in the absence of a bulk aqueous phase, as in molecular crowded environments, water relocation within the DNA hydration shell allows for entropic contributions similar to those assigned to water upon DNA ligand recognition in solution.
Keywords: indolicidin netropsin DNA conformation hydration infrared 2D correlation
  • Journal of the American Chemical Society 133(2011), 5834-5842

Publ.-Id: 15251 - Permalink

Fermi surface of the electron-doped cuprate superconductor Nd2−xCexCuO4 probed by high-field magnetotransport
Kartsovnik, M. V.; Helm, T.; Putzke, C.; Wolff-Fabris, F.; Sheikin, I.; Lepault, S.; Proust, C.; Vignolles, D.; Bittner, N.; Biberacher, W.; Erb, A.; Wosnitza, J.; Gross, R.;
We report on the study of the Fermi surface of the electrondoped cuprate superconductor Nd2−xCexCuO4 by measuring the interlayer magnetoresistance as a function of the strength and orientation of the applied magnetic field. We performed experiments in both steady and pulsed magnetic fields on high-quality single crystals with Ce concentrations of x = 0.13–0.17. In the overdoped regime of x > 0.15, we found both semiclassical angledependent magnetoresistance oscillations (AMROs) and Shubnikov–de Haas (SdH) oscillations. The combined AMROs and SdH data clearly show that the appearance of fast SdH oscillations in strongly overdoped samples is caused by magnetic breakdown. This observation provides clear evidence for a reconstructed multiply connected Fermi surface up to the very end of the overdoped regime at x ~ 0.17. The strength of the superlattice potential responsible for the reconstructed Fermi surface is found to decrease with increasing doping level and likely vanishes at the same carrier concentration as superconductivity, suggesting a close relation between translational symmetry breaking and superconducting pairing. A detailed analysis of the high-resolution SdH data allowed us to determine the effective cyclotron mass and Dingle temperature, as well as to estimate the magnetic breakdown field in the overdoped regime.
  • Open Access LogoNew Journal of Physics 13(2011), 015001

Publ.-Id: 15250 - Permalink

High-field ESR in low-dimensional spin systems
Zvyagin, S. A.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Einladung an die University of Heraklion and the FORTH (Institut für Forschung und Technologie), 10.-15.05.2010, Heraklion, Greece
  • Invited lecture (Conferences)
    2016 Hefei Conference on Novel Phenomena in High Magnetic Fields, 29.10.-01.11.2016, Hefei, China

Publ.-Id: 15248 - Permalink

Implementation and workflow for PET monitoring of therapeutic ion irradiation: a comparison of in-beam, in-room, and off-line techniques
Shakirin, G.; Braess, H.; Fiedler, F.; Kunath, D.; Laube, K.; Parodi, K.; Priegnitz, M.; Enghardt, W.;
An independent assessment of the dose delivery in ion therapy can be performed using positron emission tomography (PET). For that a distribution of positron emitters which appear as the result of interaction between ions of the therapeutic beam and the irradiated tissue is measured during or after the irradiation. Three concepts for PET monitoring implemented in various therapy facilities are considered in this paper. The in-beam PET concept relies on the PET measurement performed simultaneously to the irradiation by means of a PET scanner which is completely integrated into the irradiation site. The in-room PET concept allows measurement immediately after irradiation by a standalone PET scanner which is installed very close to the irradiation site. In the off-line PET scenario themeasurement is performed by means of a standalone PET/CT scanner 10–30 min after the irradiation. These three concepts were evaluated according to image quality criteria, integration costs, and their influence onto the workflow of radiotherapy. In-beam PET showed the best performance. However, the integration costs were estimated as very high for this modality. Moreover, the performance of in-beam PET depends heavily on type and duty cycle of the accelerator. The in-room PET is proposed for planned therapy 5 Present address: Philips Research, HTC11, 5656 AE Eindhoven, The Netherlands.
Keywords: in-beam PET, PET monitoring, ion therapy, in-vivo dosimetry

Publ.-Id: 15247 - Permalink

Infrared/terahertz applications in physical sciences
Schneider, H.;
Starting with a brief survey on infrared/THz applications and systems, this talk concentrates on specific research opportunities in physics offered by free-electron lasers (FEL) at infrared/THz wavelengths. Unique properties of FEL radiation are (i) continuous spectral tunability at narrow spectral bandwidth, (ii) high power, (ii) spatial coherence, and (iv) short pulse length. Corresponding experimental techniques include linear, nonlinear/high-field, near-field, and time resolved spectroscopy. After describing the free-electron laser facility FELBE at HZDR, a few recent studies in solid-state physics covering these techniques will be reported.
Keywords: mid-infrared and terahertz (THz) spectroscopy, free-electron laser, semiconductor quantum structures
  • Invited lecture (Conferences)
    Free Electron Laser IR to THz Applications Workshop, 28.01.2011, Bangkok, Thailand

Publ.-Id: 15246 - Permalink

A Markov chain model of classified atomistic transition states for discrete kinetic Monte-Carlo simulations
Numazawa, S.; Smith, R.;
Classical harmonic transition state theory is considered and applied in discrete lattice cells with hierarchical transition levels. The scheme is then used to determine transitions which can be applied in a lattice-based kinetic Monte Carlo (KMC) atomistic simulation model.
The model results in an effective reduction of KMC simulation steps by utilizing a classification scheme of transition levels for thermally activated atomistic diffusion processes. Thermally activated atomistic movements are considered as local transition events constrained in potential energy wells over certain local time periods. These processes are represented by Markov chains of multi-dimensional Boolean valued functions in three dimensional lattice space.
The events inhibited by the barriers under a certain level are regarded as thermal fluctuations of the canonical ensemble and accepted freely.
Consequently, the fluctuating system evolution process is implemented as a Markov chain of equivalence class objects.
It is shown that the process can be characterized by the acceptance of metastable local transitions.
The method is applied to a problem of Au and Ag cluster growth on a rippled surface. The simulation predicts the existence of a morphology dependent transition time limit from a local metastable to stable state for subsequent cluster growth by accretion. Excellent agreement with observed experimental results is obtained.
Keywords: Kinetic Monte-Carlo
  • Physical Review E 84(2011), 046714

Publ.-Id: 15245 - Permalink

A population balance approach considering heat and mass transfer - experiments and CFD simulations
Krepper, E.; Beyer, M.; Lucas, D.; Schmidtke, M.;
Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
Experiments on steam bubble condensation in vertical co-current steam/water flows have been carried out in an 8m long vertical DN200 pipe. Steam is injected into the pipe and the development of the bubbly flow is measured at different distances to the injection using a pair of wire mesh sensors. By varying the steam nozzle diameter the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore condensate slower. Steam pressures between 1-6.5 MPa and sub-cooling temperatures from 2 to 6 K were applied. Due to the drop of hydrostatic pressure along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section. The experimental configurations are simulated with the CFD code CFX using an extended MUSIG approach, which includes the bubble shrinking or growth due to condensation or re-evaporation. The development of the vapour phase along the pipe with respect to vapour void fractions and bubble sizes is qualitatively well reproduced in the simulations. For a better quantitative reproduction, reliable models for the heat transfer at high Reynolds number as well as for bubble breakup and coalescence are needed.
Keywords: two phase flow, experiments, CFD, population balance model, bubble coalescence, bubble breakupo, condensation, evaporation

Publ.-Id: 15244 - Permalink

Biokinetics, metabolism and PET imaging with Cu-64 and Ga-68 labeled ghrelin analogues in rats
Bergmann, R.; Chollet, C.; Pietzsch, J.; Beck-Sickinger, A. G.; Steinbach, J.;
Ghrelin is a gastric peptide involved in food intake control, and growth hormone release. Besides its well-defined orexigenic role, ghrelin is likely involved in tumor development and growth. Therefore, non-invasive imaging agents for determining ghrelin receptors are desirable. However, ghrelin receptors are expressed in low level making detection via imaging difficult. The labeling using activated esters like 4-(F-18-fluoro)benzoyl-succinimide (2) was not possible due to the existence of three primary amino groups per peptide. Therefore, human ghrelin1-28 [Lys16(NODAGA)]-ghrelin1-28 and a short ghrelin inverse agonist NODAGA-KwFwLL-NH2 were synthesised on solid-phase. Subsequently, radiolabeling yielded Cu-64- and Ga-68-NODAGA-peptides in high radiochemical purity (>98%) with a specific activity >10 GBq/Gmol. For basic radiopharmacological characterization biodistribution, small animal PET, and metabolite analysis in arterial blood plasma were carried out in Wistar rats with all 4 radiotracers. The ghrelin analogues were in high amounts taken up by the kidneys. The Cu-64- and Ga-68-NODAGA-KwFwLL-NH2 were for the most part hepathobilliary eliminated. The metabolite analysis showed the well-known des acyl ghrelin as the main metabolite in vivo reaching 90% in blood plasma after one hour. On the other site the NODAGAKwFwLL-NH2 peptides were highly stabile; only 5% metabolites were observed after one hour in rat plasma. Interestingly, the biodistribution and kinetics were similar for the pairs of peptide labeled ether with Cu-64 or Ga-68. This shows the small effect of the different ionization of the Ga-68 (neutral) or Cu-64 (one negative charge) NODAGA complexes on the biodistribution. The blood clearance of these peptides was relative low, with about 50% of starting amount after one hour. The high stability and low blood clearance are important prerequisites for further studies of ghrelin receptor imaging. These results indicate that further in vivo evaluation of radiolabeled ghrelin inverse agonists as potential PET tracers for ghrelin receptors is warranted.

Reference: (1) Holst, B., et al. (2003) High constitutive signaling of the ghrelin receptor--identification of a potent inverse agonist. Mol Endocrinol 17, 2201-10. (2) Bergmann, R., et al. (2002) Biodistribution and catabolism of (18)F-labeled neurotensin(8-13) analogs. Nucl Med Biol 29, 61-72.

Acknowledgement: This project was partially supported by FP7 project “GIPIO”, Project Reference: 223057
  • Poster
    2010 World Molecular Imaging Congress, 08.-11.09.2010, Kyoto, Japan

Publ.-Id: 15243 - Permalink

Dual-labeled Cetuximab-based imaging agent for NIR Fluorescence and PET
Bergmann, R.; Zenker, M.; Walther, M.; Pietzsch, H.-J.; Hofheinz, F.; van den Hoff, J.; Pietzsch, J.; Steinbach, J.;
Cetuximab (C225) as a chimeric monoclonal antibody specifically targets the epidermal growth factor receptor (EGFR) that often is overexpressed in human malignancies. This phenotype is associated with tumor aggressiveness, treatment resistance, and biological heterogeneity with potential to bypass the blockade of the EGFR signaling pathways. The aim of this work was to prepare and characterize the C225 for near infrared fluorescence (NIRF) and PET imaging using a X-SIGHT Large Stokes Shift Dye (X-SIGHT 670 LSS Dye) and [64Cu]Cu-NOTA as a prerequisite for combination of both imaging methods. C225 was conjugated with the bifunctional chelator 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (SCN-Bz-NOTA) and the X-SIGHT 670 Large Stokes Shift Dye, TFP Ester (XS670). The EGFR-affinity of the immunoconjugate resulted in 94% versus 100% of the unmodified C225 measured with specific enzyme-linked immunosorbent assay (ELISA) on EGFR-positive tumor cell line A431. C225-SCNBz-NOTA was labeled with 64Cu within 30 min with high radiolabeling yield and radiochemical purity. The [64Cu]Cu-NOTA-C225-XS670 showed high accumulation in xenotransplanted squamous cell carcinoma tumors in mice after 24 hours imaged with small animal PET and NIRF. The comparison of both methods in living animals showed the high signal intensity and accumulation of the probe in tumors; however only PET allowed the quantitative characterization of the probe distribution in vivo. The subsequent whole body cryosectioning of the animals into 40 µm sections permitted the direct comparison of the autoradiograms and NIRF images of the tissue cuts. The quantitative comparison of the autoradiograms and the NIRF images after coregistration of the corresponding images yielded a good correlation of the pixel intensities, but the different geometric resolution did not allow a pixel vise comparison. The NIRF images showed a higher differentiation than the autoradiograms. The dual-labeled C225 demonstrated the higher resolution and comparable concentration values of the antibody distribution in whole body cryosections of tumor bearing mice using the combination of 64Cu-radioluminography and NIRF imaging. The dual labeling of antibodies is a promising tool for quantitative evaluation of the long time distribution in animals using NIRF of cryosections beyond the decay of the radionuclide used.

Acknowledgement: This project was partially supported by FP7 project “GIPIO”, Project Reference: 223057
  • Poster
    2010 World Molecular Imaging Congress, 08.-11.09.2010, Kyoto, Japan

Publ.-Id: 15242 - Permalink

Multimodality imaging in preclinical cancer research
Bergmann, R.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    4th Bioscan Imaging Users Meeting (European part), 10.10.2010, Vienna, Austria

Publ.-Id: 15241 - Permalink

Identification of transport processes in bioirrigated muddy sediments by [18F]fluoride PET (Positron Emission Tomography)
Roskosch, A.; Lewandowski, J.; Bergmann, R.; Wilke, F.; Brenner, W.; Burchert, R.;
In aquatic environments transport processes across the sediment–water interface are intensified by bioirrigating macrozoobenthos. Transport processes caused by Chironomus plumosus larvae dwelling in U-tubes were investigated by dynamic small animal Positron Emission Tomography (PET) with [18F]fluoride. Significant tracer transport from the burrows into the sediment was detected; penetration was deeper at the outlet branch of the burrow than at the inlet branch. Hence, advection plays a significant role in exchange between water in the burrows and muddy sediment.

Publ.-Id: 15240 - Permalink

Small animal PET for evaluation of tumor therapy
Bergmann, R.;
kein Abstract verfügbar
  • Lecture (others)
    Oncoray Retreat, 28.01.2010, Bautzen, D

Publ.-Id: 15239 - Permalink

Biodistribution, -kinetics, metabolic stability, and imaging with radioactive ghrelin analogues
Bergmann, R.;
kein Abstract verfügbar
  • Lecture (Conference)
    2nd GIPIO meeting, 02.-03.06.2010, Copenhagen, Danmark

Publ.-Id: 15238 - Permalink

Small animal molecular imaging in cancer research
Bergmann, R.;
Quantitative small animal imaging plays a key role in preclinical research and drug development. However, no single imaging modality is perfect and sufficient to gain all the necessary morphologic, physiologic, metabolic or genetic information. For instance, optical fluorescence imaging is difficult to quantify - especially in tissue more than a few millimetres in depth within a subject; magnetic resonance imaging of protons (MRI) has superb resolution but low sensitivity, positron emission tomography (PET) has very high sensitivity but poor resolution, single photon emission tomography (SPECT) has good resolution but low sensitivity and X-ray tomography (CT) has good resolution of bones but cannot good resolve tissues. The combination of multiple molecular imaging techniques can therefore offer synergistic advantages over any modality alone. The multimodal approach by combination of the methods and development of multimodal probes is far from trivial and a challenge for the interdisciplinary work and collaboration of scientists.
In the presentation we provide an overview of the small animal imaging in the Forschungszentrum Dresden-Rossendorf, recent developments of probes and applications in multimodal cancer research. We will show examples of quantitative imaging using low and high molecular weight probes and microspheres labeled for PET, SPECT and optical imaging. The especial developed animal bed system helps us to register the 3D data from different dedicated modalities for combining and comparing the methods. The development of imaging probes is embedded a combination of in vitro and ex vivo evaluation of gene expression, cell uptake and binding studies.
The molecular imaging in mouse and rat models allows us to ‘see’ the biological complexities of tumors for the treatment of this disease. This is one of the most exciting and growing areas in our research.
  • Invited lecture (Conferences)
    International workshop on bio-medical applications of micro-PET, 20.-21.09.2010, Seville, Spain

Publ.-Id: 15237 - Permalink

Small animal imaging in Cancer Research
Bergmann, R.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Budapest, 28.04.2010, Budapest, Hungary
  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Veterinärmedizinische und Pharmazeutische Universität Brno, 27.04.2010, Brno, Czech Republic
  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Karls-University Prague, 26.04.2010, Prague, Czech Republic

Publ.-Id: 15236 - Permalink

Multimodality small animal imaging in tumor biology
Bergmann, R.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Seminar Semmelweis University of Medicine, Faculty of Medicine, Institute of Human Physiology and Clinical Experimental Research, 28.04.2010, Budapest, Hungary

Publ.-Id: 15235 - Permalink

Synthesis and biological evaluation of novel 4-benzylpiperazine ligands for sigma-1 receptor imaging
Li, Z.-J.; Ren, H.-Y.; Cui, M.-C.; Deuther-Conrad, W.; Tang, R.-K.; Steinbach, J.; Brust, P.; Liu, B.-L.; Jia, H.-M.;
We report the synthesis and evaluation of 4-benzylpiperazine ligands (BP-CH3, BP-F, BP-Br, BP-I, and BPNO2) as potential r1 receptor ligands. The X-ray crystal structure of BP-Br, which crystallized with monoclinic space group P21/c, has been determined. In vitro competition binding assays showed that all the five ligands exhibit low nanomolar affinity for r1 receptors (Ki = 0.43–0.91 nM) and high subtype selectivity (r2 receptor: Ki = 40–61 nM; Kir2/Kir1 = 52–94). [125I]BP-I (1-(1,3-benzodioxol-5-ylmethyl)-4-(4-iodobenzyl)piperazine) was prepared in 53 ± 10% isolated radiochemical yield, with radiochemical purity of >99% by HPLC analysis after purification, via iododestannylation of the corresponding tributyltin precursor. The log D value of [125I]BP-I was found to be 2.98 ± 0.17, which is within the range expected to give high brain uptake. Biodistribution studies in mice demonstrated relatively high concentration of radiolabeled substances in organs known to contain r1 receptors, including the brain, lung, kidney, heart, and spleen. Administration of haloperidol 5 min prior to injection of [125I]BP-I significantly reduced the concentration of radioactivity in the above-mentioned organs. The accumulation of radiolabeled substance in the thyroid was quite low suggesting that [125I]BP-I is relatively stable to in vivo deiodination. These findings suggest that the binding of [125I]BP-I to r1 receptors in vivo is specific.

Publ.-Id: 15234 - Permalink

Micro-structured copper electrodeposition in inhomogeneous magnetic fields
Mutschke, G.; Tschulik, K.; Weier, T.; Uhlemann, M.; Bund, A.; Fröhlich, J.;

It is well known that in various electrochemical systems the mass transfer and also the morphology and the structure of the electrodeposits can be influenced by the proper application of magnetic fields. One of the main reasons seems to be the convection induced by the resulting magnetic forces. Lorentz forces have been used to tailor the electrodeposition of metals for quite a while. Only recently, an improved understanding of the convection forced was gained that turned out to be more complex than expected, even in simple geometries [1]. Additionally, the influence of magnetic gradient forces on the preparation of micro-structured metal deposits on field-gradient electrodes has been discussed in the literature [2]. These electrodes consist of magnetic elements such as permanent magnets or magnetized ferromagnetic materials which are arranged beneath the surface of the working electrode. Here, however, besides the magnetic gradient force, also the Lorentz force might influence the deposition process. The presentation will summarize new numerical simulations, analytical findings and experimental results in order to discuss the influence of the different magnetic forces involved and will discuss the prospects towards smaller deposition structures [3,4].

[1] G. Mutschke et al., Electrochim. Acta 55 (2010) 1543.

[2] K. Tschulik et al., Electrochem. Comm. 11 (2009) 2241.

[3] G. Mutschke et al., Electrochim. Acta 55 (2010) 9060.

[4] K. Tschulik et al., Electrochim. Acta 56 (2010) 297.

Keywords: Magnetoelectrochemistry, electrodeposition
  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich

Publ.-Id: 15233 - Permalink

Future aspects of X-ray emission from crystalline undulators at positron channeling
Backe, H.; Krambrich, D.; Lauth, W.; Buonomo, B.; Dabagov, S. B.; Mazzitelli, G.; Quintieri, L.; Lundsgaard Hansen, J.; Uggerhoj, U. I.; Azadegan, B.; Dizdar, A.; Wagner, W.;
In connection with ideas to produce undulator-like radiation in the hundreds of keV up to the MeV region by means of positron and electron channeling, there is renewed interest to study various channeling phenomena also experimentally. With electrons experiments have been performed at the Mainz Microtron MAMI to explore channeling-radiation emission by a 4-period epitaxially grown strained layer SiGe undulator. Unfortunately, high quality positron beams of sufficient intensity are not easily accessible. The only serious candidate in Europe seems to be the Beam Test Facility at INFN LNF Frascati, Italy. Some requirements to extend BTF in a facility which is also well suited for positron channeling-radiation experiments will be outlined.
Keywords: undulator radiation, crystal undulator, positron channeling, channeling radiation
  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Future aspects of X-ray emission from crystalline undulators at positron channeling, Bologna: Societa Italiana di Fisica, 175-180
  • Nuovo Cimento C 34(2011)04, 175-180
    DOI: 10.1393/ncc/i2011-10983-9

Publ.-Id: 15232 - Permalink

Simulation of axial channeling radiation on a thin Ge single crystal
Azadegan, B.; Dabagov, S. B.; Wagner, W.;
Based on classical electrodynamics the radiation emitted by axially channeled electrons has been investigated by means of computer simulations. Using the Doyle-Turner approximation for the atomic scattering factor and taking thermal vibrations of atoms into account, we calculated the two-dimensional continuum potential of the <110> crystallographic axis of a thin Ge single crystal. The trajectories, velocities and accelerations of electrons are obtained by solving the equations of motion in three dimensions, and the spectral-angular distribution of radiation has been calculated in the classical way.
Keywords: axial channeling, channeling radiation, Germanium single crystal
  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Simulation of axial channeling radiation on a thin Ge single crystal, Bologna: Societa Italiana di Fisica, 149-156
  • Nuovo Cimento C 34(2011)04, 149-156
    DOI: 10.1393/ncc/i2011-10919-5

Publ.-Id: 15231 - Permalink

Ion erosion induced surface patterning studied by combined trim and kinetic monte-carlo simulations
Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.;
Understanding of surface morphology evolution induced by ion erosion is still limited. Continuum models cannot explain microscopic processes. On the other hand, so far atomistic simulations could not describe pattern evolution on experimental spatiotemporal scales. Therefore, recently continuum equations were feeded with MD simulation results, which allows the understanding of smoothing mechanisms like an effective mass ‘downhill’ current induced by ballistic drift.

We developed a novel program package which unifies the collision cascade with kinetic Monte-Carlo simulations. This allows a fully atomistic description on experimental spatiotemporal scales. 3D atom relocations were calculated using the binary collision approximation, whereas the thermally activated relaxation as well as diffusive processes were simulated by a bit-coded kinetic 3D Monte Carlo program. Effects like ballistic mass drift or dependence of local morphology on sputtering yield are automatically included by this approach.

The mechanism of ripple formation induced by a local surface currents is studied. The quantitative description of current vectors for different environmental parameters, and initial surface condition of sinusoidal structure, can be analized in time and space, following the local atomic drift. Different driving forces can be distinguished. Without ion irradiation the mass current vectors are always parallel to the surface plane with down-hill direction. Collision-cascade-induced defects change the mass currents significantly. Up-hill currents induce self-organization for certain obligue ion incidence angles. This driving forces causes patterning even without sputtering events.
Keywords: ripples, ion beam sputtering, pattern formation, kinetic Monte-Carlo, TRIM, crater formation, surface mass current
  • Poster
    17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-27.08.2010, Montreal, Canada

Publ.-Id: 15230 - Permalink

Channeling radiation on quartz stimulated by acoustic waves
Wagner, W.; Azadegan, B.; Büttig, H.; Grigoryan, L. S.; Mkrtchyan, A. R.; Pawelke, J.;
The stimulation of channeling radiation by acoustic waves excited in the single crystal has been predicted in early works of the 1980's. Based on quantum calculations, the described experiment aimed at verification of theoretical considerations. Making use of the reverse piezoelectric effect, hypersonic waves of frequency 12 GHz, which corresponds to a dedicated transition between bound states of planar channelled relativistic electrons, were excited in a single-crystal quartz plate. The spectrum of channeling radiation measured under the influence of acoustic waves reveals enhanced radiation intensity. The obtained results are discussed and may be phenomenologically understood assuming electron diffraction on an acoustic superlattice.
Keywords: channeling radiation, quartz single crystal, ultrasound
  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Channeling radiation on quartz stimulated by acoustic waves, Bologna: Societa Italiana di Fisica, 133-140
  • Nuovo Cimento C 34(2011)04, 133-140
    DOI: 10.1393/ncc/i2011-10899-4

Publ.-Id: 15229 - Permalink

Ion-beam-induced interface mixing: unified atomistic simulations of collisional and thermal processes
Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.;
Ion beam processing of materials at elevated temperature, which can be room temperature for metals, is controlled simultaneously by both, collisional and thermally activated processes. So far, large scale process simulations separate these processes, calculating all collision cascades of the complete ion irradiation in the binary collision approximation like the TRIDYN code, and simulating then the defect relaxation/impurity nucleation by kinetic Monte Carlo.

Here we present and apply a unified computer simulation program package which unifies both programs, i.e. after each calculated 3D collisional cascade some kinetic Monte Carlo steps allow relaxation, diffusion, phase separation etc. in the whole volume. Contrary to molecular dynamics simulations, our approach allows studies on experimental spatiotemporal scales. In this presentation we focus on the evolution of interfaces under ion irradiation, where collisional mixing is in competition with thermally activated diffusion and phase separation. He+ irradiations for two extreme cases were studied: (i) Irradiation of interfaces made by immiscible elements, here Al and Pb. Ballistic interface mixing is accompanied by phase separation. Al and Pb nanoclusters form and show self-ordering (banding) parallel to the interface. (ii) Irradiation of interfaces made by intermetallics forming species, here Pt and Co. Well-ordered layers of phases of intermetallics appear in the sequence Pt/Pt3Co/PtCo/PtCo3/Co, resulting in a stepwise changing Pt/Co concentration depth profile. Novel magnetic properties of such sandwiched phases are predicted and can explain the transition between out of plane and in-plane magnetic anisotropy caused by ion irradiation.
Keywords: interface, mixing, bi-layer, kinetic monte-carlo, KMC, TRIM, TRIDYN, phase transition, crystal ordering
  • Lecture (Conference)
    17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-27.08.2010, Montreal, Canada

Publ.-Id: 15228 - Permalink

Quantum uncertainties in the energy of transverse oscillations of planar channeled particle
Mkrtchyan, A. R.; Grigoryan, L. S.; Mkrtchyan, A. H.; Khachatryan, H. F.; Wagner, W.; Azadegan, B.;
It is shown that quantum uncertainties in the energy of transverse oscillations of planar channeled particle become significant at definite values of the crystal period in the direction of channeling. The possibility of producing superlattices with periodical potential is discussed.
Keywords: channeling radiation, quantum uncertainties
  • Contribution to proceedings
    International conference on electrons, positrons, neutrons and X-rays scattering under external influences, 26.-30.10.2009, Yerevan-Meghri, Armenia
    Quantum uncertainties in the energy of transverse oscillations of planar channeled particle, Yerevan, Armenia, 978-99941-2-486-2

Publ.-Id: 15226 - Permalink

Channeling radiation on quartz influenced by acoustic waves
Wagner, W.; Azadegan, B.; Büttig, H.; Mkrtchyan, A. R.; Grigoryan, L. S.; Pawelke, J.;
The influence of acoustic waves excited in a single quartz crystal on the emission of channeling radiation by relativistic electrons has been proved experimentally.
Keywords: channeling radiation, quartz single crystal, ultrasound
  • Contribution to proceedings
    International conference on electrons, positrons, neutrons and X-rays scattering under external influences, 26.-30.10.2009, Yerevan-Meghri, Armenia
    Proceedings of the International conference on electrons, positrons, neutrons and X-rays scattering under external influences, Yerevan, Armenia, 978-99941-2-486-2

Publ.-Id: 15225 - Permalink

Warum Ge und Si durch Ionenimplantation zu Supraleitern werden
Fiedler, J.;
Es konnte gezeigt werden, dass neben Diamant auch die technologisch relevanten Gruppe-IV-Halbleiter Si und Ge im extrem hochdotierten Zustand supraleitend werden. Am Helmholtz – Zentrum Dresden – Rossendorf ist es erstmalig gelungen, supraleitfähige Ge-Schichten in einem zu Fertigungsverfahren der Mikroelektronik kompatiblen Dotierprozess, bestehend aus Ga-Ionenimplantation und Kurzzeitausheilung, herzustellen. Die hochdotierten Ge-Schichten zeigen intrinsische Supraleitung mit kritischen Temperaturen bis zu 1 K. Eine weitere Erhöhung der Dotierkonzentration und damit der kritischen Temperatur ist aufgrund der begrenzten Löslichkeit von Ga in Ge (1 at.%) sehr schwierig. Um dennoch höhere Sprungtemperaturen zu erreichen, wurden die geringe Löslichkeit von Ga in Si (0.1 at.%) sowie die supraleitenden Eigenschaften von Ga ausgenutzt. In Ga implantiertem Si bilden sich Ausscheidungen, wodurch vergrabene, extrinsisch supraleitende Ga reiche Schichten hergestellt werden können. Die kritische Temperatur ist mit 7 K deutlich höher als in dotiertem Ge.
Die Struktur der Proben wurde mit Rutherford Rückstreuspektrometrie (RBS), Transmissionselektronenmikroskopie (TEM) sowie Sekundärionen-Massenspektrometrie (SIMS) untersucht. Für die elektrische Charakterisierung wurden Temperaturen zwischen 100 mK und 400 K sowie Magnetfelder bis 9 T verwendet. Im Vortrag werden die Grundzüge der Dotierung mittels Ionenimplantation sowie die Ergebnisse elektrischer und struktureller Untersuchung beider Materialsysteme vorgestellt.
  • Lecture (others)
    Institutsseminar SS 2011, Institut für Physik, TU Ilmenau, 18.05.2011, Ilmenau, Deutschland

Publ.-Id: 15224 - Permalink

ROBL: The first European actinide XAS beamline in its second decade of operation
Scheinost, A. C.; Hennig, C.; Rossberg, A.; Banerjee, D.;
The Rossendorf Beamline at ESRF (ROBL) in operation since 1998 [1] is together with the INE Beamline at ANKA and the micro-XAS beamline at SLS one of three dedicated radionuclide XAS beamlines in Europe. ROBL is specialized in handling actinide nuclides up to Cf with a total activity to 185 MBq. The wide energy range (5 to 35 keV) permits to run actinide L1, L2 and L3 edges, important for the investigation of mixed actinide systems. Both the high photon flux (6 1011 ph/s on the sample) and the high-performance fluorescence detection makes ROBL suited for very low concentrations (according to XAS standards,  1 ppm XANES,  20 ppm EXAFS). Research at ROBL encompasses basic actinide chemistry, biogeochemistry, environmental chemistry and materials sciences, with applications for the improvement of nuclear waste repositories, remediation of uranium mining areas and other contaminated sites, development of fourth generation nuclear fuels, minor actinide waste forms and transmutation targets. The ROBL team supports users before, during and after the experiments. Own research specializes on the development of new data analysis tools (statistical tools, wavelets, Monte-Carlo simulations, PDF) as well as on actinide redox chemistry (structure of aqueous and non-aqueous complexes, redox mechanisms at water/mineral interfaces). From 2012 on, a major upgrade of the ROBL optics will further increase photon flux, energy range, and spectral resolution; and reduce spot size and data acquisition time; while maintaining reliable and relatively easy operation.

[1] W. Matz et al., Journal of Synchrotron Radiation 6, 1076-1085 (1999).
Keywords: xafs robl xanes xas synchrotron beamline
  • Invited lecture (Conferences)
    Actinide-XAS 2011, 02.02.2011, Harima Science Garden City, Japan

Publ.-Id: 15223 - Permalink

AcXAS, a reference data base for XAS spectra of actinides and other radionuclides
Scheinost, A. C.; Schmeisser, N.; Denecke, M.; Banerjee, D.; Dardenne, K.; Hennig, C.; Rossberg, A.; Rothe, J.; Daehn, R.;
Reference spectra of well characterized samples are crucial for the analysis of x-ray absorption spectra (XAS). In order to avoid that experimentalists have to repeat XAS measurements of standard actinide compounds/species, thereby making more efficient use of costly radionculides, sample preparation, beamtime, radioprotection measures, transport, administration, etc., we are in the process of establishing a public database of actinide XAS reference spectra. The spectra are retrieved from the large data inventory of the three current European radionuclide beamlines, the Rossendorf Beamline at ESRF (France), the INE beamline at ANKA (Germany), and the micro-XAS beamline at SLS (Switzerland), but will also include data from other beamlines. This effort is supported by the European Commission through the ACTINET-I3 project. An overview on data base structure, criteria for data entry and use, as well as on the current status of data will be given.
Keywords: actinides xas xanes exafs data base
  • Poster
    Actinide-XAS 2011, 02.02.2011, Harima Science Garden City, Japan
  • Invited lecture (Conferences)
    ACTINET Plenary Meeting, 01.02.2011, Marcoule, France

Publ.-Id: 15222 - Permalink

Probing redox reactions at the mineral/water interface by X-ray absorption spectroscopy: Reduction of Se, Sn, Sb and Pu by Fe(II)-bearing minerals
Scheinost, A. C.;
Fe(II)-bearing phases are naturally occuring in most anoxic aquifers, and form also at the surface of corroding steel containers under typical nuclear waste repository conditions. Due to their ability to reduce metal and metalloid contaminants, they are expected to play a key role for the migration behaviour of a wide range of radionuclides, including actinides and fission products. Using X-ray absorption spectroscopy as main tool, we have studied reaction end products, mechanisms and kinetics of redox processes at a range of water/mineral interfaces, including magnetite, green rust, mackinawite, siderite and Fe2+-sorbed clays. Our results show that the electron transport within mineral structures and at the surface is controlling the extent and the kinetics of multi-electron redox reactions. Examples that I will show include: (1) The fast reduction of Se(IV) to Se and Se(-II) nanoparticles, a reaction which was previously thought to be extremely slow. (2) The reduction of Pu(V) to Pu(III), which then forms a highly ordered inner-sphere sorption complex at the 111 face of magnetite, instead of the expected precipitation of PuO2 clusters. (3) The oxidation of Sn(II) to Sn(IV), which then forms inner-sphere sorption complexes, instead of the expected precipitation of SnO2. The results highlight the need for direct spectroscopic investigation of such processes, which are difficult to predict by thermodynamic methods, in order to provide reliable risk assessments.
Keywords: Redox interfaces XAFS XANES
  • Lecture (Conference)
    LES Seminar, 15.03.2011, Villigen, Switzerland

Publ.-Id: 15221 - Permalink

Experiments on electromagnetic control of a backward facing step flow
Weier, T.; Wittwer, S.; Albrecht, T.; Gerbeth, G.;

The flow over a backward-facing step is a prototype of a separating and reattaching shear flow and has therefore received a considerable amount of interest. We focus here on the excitation of the separated shear layer since it is often understood as the basic mechanism in active flow control. Forcing frequencies and amplitudes are obviously major parameters of influence, but different signal forms can have a profound impact as well, albeit the physical mechanism behind the latter is still not fully understood.

Electromagnetic body forces offer a simple and direct way to provide excitation by different wave forms. Particle image velocimetry measurements have been performed in a free surface electrolyte channel. We will discuss spatial amplification rates in the unforced shear layer, which show a fair agreement with results obtained by others in free shear layers. Compared to the natural flow, forcing near the optimal excitation frequency St=0.012 leads to a much earlier vortex roll-up and, consequently, the reattachment length is reduced. For the first subharmonic of the optimal excitation frequency, vortex roll up starts later but produces larger vortices. Excitation with the relatively high frequency of St=0.03 has only a very small effect on the flow. Keeping the excitation frequency at St=0.012 and increasing the forcing amplitude leads to earlier vortex roll up, larger vortices, and shorter reattachment lengths.

Keywords: flow control, Lorentz force, backward facing step
  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich

Publ.-Id: 15220 - Permalink

Elektrische Kontaktierung vertikaler Nanostrukturen
Wieser, M.;
Diese Arbeit beschreibt die Herstellung, Kontaktierung und Charakterisierung vertikaler Nanostrukturen in Form von Pfeilern der Höhe 50 nm mit einer elliptischen Querschnittsfläche von 100 × 150 nm. Die hergestellte Gesamtstruktur besteht dabei aus mehreren Metallebenen, so dass der Pfeiler an der Unterseite von einer Grundelektrode und an der Oberseite von einer Deckelektrode kontaktiert wird. Zur Fertigung der Metallebenen wird die Elektronenstrahllithographie mit anschließendem thermischen Bedampfen und Lift-Off genutzt. Die Isolation der Grundelektrode von der obersten Metallebene erfolgt mit einem durch Rotationsbeschichtung aufgetragenen Negativ-Lack aus dem Bereich der Elektronenstrahllithographie, der bei Erwärmung in Siliziumoxid transformiert.
Nach dem Ausarbeiten und Optimieren des Herstellungsprozesses dieser Strukturen sollten erste Nanostrukturen mit integrierter Tunnelbarriere erstellt und charakterisiert werden. Aufgrund von unvorhergesehenen Verzögerungen bei der Herstellung konnten diese Strukturen allerdings nicht fertiggestellt werden, so dass für die Charakterisierungsmessungen auf eine aus einem anderen Projekt bereitgestellte Probe zurückgegriffen werden musste, die einen ähnlichen Strukturaufbau besitzt. Die während der Charakterisierung dieser Probe aufgenommenen Strom-Spannungs-Kennlinien werden mit bekannten quantenmechanischen Tunnelmodellen verglichen.
Keywords: Electrical contacting vertical nanostructures
  • Diploma thesis
    Otto-von-Guericke-Universität Magdeburg, 2010
    79 Seiten

Publ.-Id: 15219 - Permalink

Electrical Contacting of Vertical Nanostructures
Wieser, M.; Grebing, J.; Höwler, M.; Bernert, K.; Schmidt, B.; Fassbender, J.ORC; Erbe, A.
The aim of this new approach is the contacting and characterization of small vertical nanostructures. Therefore, in contrast to conventional lateral contacting a vertical pillar with a height of about 70 nm and an elliptic size of 100 nm × 150 nm is contacted using a bottom electrode, a via with the same height as the pillar and two top electrodes for tipcontacting of measurement devices. The structuring of the different layers is done using electron beam lithography (EBL). A resist layer is used as an insulator between the bottom and the top electrodes. In the center of the pillar an Al2O3 tunnel barrier will be integrated. The current voltage (IV) characteristics of the system will be investigated and compared to the direct tunneling and the Fowler-Nordheim tunneling model. Using this technique we will characterize the electrical properties of oxides with varying thickness.
Keywords: Electrical contacting vertical nanostructures
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 15218 - Permalink

3D vector magnetooptical ellipsometry investigations on magnetic thin film samples at room temperature
Mok, K. M.; Schmidt, H.;
We present the set-up of a vector-magneto-optical generalized ellipsometer (VMOGE) which allows to perform generalized Mueller matrix ellipsometry in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. Using VMOGE measurements, we measured the magneto-optical properties of the elemental ferromagnets Co, Fe, and Ni and extracted the wavelength dependence of the magneto-optical dielectric tensor under saturated magnetization conditions via model analysis.
Keywords: Magnetic semiconductors, spin poalrization, magnetooptical response
  • Lecture (others)
    Halbleiterphysik-Seminar (AG Zahn), TU Chemnitz, 21.01.2011, Chemnitz, Germany

Publ.-Id: 15217 - Permalink

Magnetic characterization of Bi(Fe1 − xMnx)O3
Xu, Q.; Zhou, S.; Wen, Z.; Wu, D.; Qiu, T.; Xu, M.; Potzger, K.; Schmidt, H.;
Bi(Fe1 − xMnx)O3 ceramics (x up to 0.3) were prepared by rapid sintering. Weak ferromagnetism with two magnetic anomalies at low temperatures was observed for Bi(Fe0.95Mn0.05)O3 and Bi(Fe0.9Mn0.1)O3. From temperature-dependent magnetic relaxation measurements, the anomalies at 20 K and 100 K are related to the freezing of cluster spin glass.
Keywords: Multiferroic; Spin glass; Ferromagnetism; Cluster

Publ.-Id: 15216 - Permalink

Synthesis and characterization of nickel cobalt oxide thin films
Calin, G.; Irimia, M.; Scarlat, C.; Purica, M.; Comanescu, F.; Iacomi, F.;
p-Type transparent and conductive cobalt–nickel oxide films of 130 nm thickness, have been deposited by spin coating method on glass substrates. The electrical and optical properties of the oxides have been studied as a function of the x=Co/(Co+Ni) ratio. A combination of x-ray diffraction, x-ray photoelectron spectroscopy and Raman spectroscopy was used in order to investigate thin film structures. Thin films of mixed oxides: NiCo2O4, Ni1.71 Co1.29 O4; NiO were obtained for x>0.60. The electrical conductivity of these films reaches a maximum conductivity at this stoichiometry.
Keywords: p-type TCO, structure, optical properties, electrical properties, Raman spectroscopy.
  • Contribution to proceedings
    International Semiconductor Conference (CAS 2010), 11.-13.10.2010, Sinaia, Romania
    Semiconductor Conference (CAS), 2010 International, Sinaia, 978-1-4244-5783-0, 387-390

Publ.-Id: 15215 - Permalink

Experimental realisation of homogeneous dynamo action
Giesecke, A.; Stefani, F.; Gerbeth, G.;

From the technical point of view the realisation of dynamo action under laboratory conditions is a demanding task because it requires magnetic Reynolds numbers of the order of Rm ~100. So far only three experiments have been able to demonstrate fluid flow driven self-excitation of magnetic fields.

The dynamo experiments in Karlsruhe and Riga, based on an optimized flow geometry, have demonstrated the principal possibility of the magnetic field generation process and its saturation as it occurs e.g. in stars or planets. Both dynamos are characterized by a non-axisymmetric field mode and are theoretically very well understood.

In contrast to this the mechanism responsible for the dynamo process in the von Karman sodium (VKS) experiment is still subject of intense discussion, in particular due to the obscure influence of the flow driving soft iron impellers. Recently, it could be shown numerically that the (localized) high relative permeability of the impellers is responsible for the rather low value of the critical magnetic Reynolds number as well as for the selection of the dominating axisymmetric dynamo mode observed in the experiment (Giesecke et al. 2010, PRL 104). However, to explain a growing axisymmetric field an alpha-effect is required for which the theoretical or experimental justifications remain only vague.

Further progress in the experimental examination of dynamo action is expected from the future dynamo facility that is scheduled at the Helmholtz-Zentrum Dresden-Rossendorf. In order to avoid the influence of internal components or artificial driving mechanisms a precession driven flow of liquid sodium in a cylinder shall provide the necessary energy to exhibit dynamo action. A precession driven dynamo operating in a sphere has been presented by A. Tilgner (2005, Phys. Fl. 17). However, it remains to be shown that precessional flow driving will be possible with sufficient efficiency to overcome the dynamo threshold in a cylindrical geometry as well.

Keywords: Dynamo Simulations Experiments Precession VKS dynamo
  • Lecture (Conference)
    European Geosciences Union General Assembly 2011, 03.-08.04.2011, Wien, Oesterreich
  • Contribution to proceedings
    European Geosciences Union General Assembly 2011, 03.-08.04.2011, Vienna, Austria
    Experimental realisation of homogeneous dynamo action

Publ.-Id: 15214 - Permalink

Oscillating alpha-square dynamos
Giesecke, A.; Stefani, F.; Gerbeth, G.;

A simple way to interpretate the reversal mechanism of the Earth's magnetic field has been achieved in theoretical models based on the interplay between very few magnetic modes.

Motivated by the temporal behavior of elementary multipolar components of the Earth's magnetic field during the last reversal 780ka ago, (Leonhardt & Fabian 2007) the possibility of interacting magnetic modes is examined in a simple mean field model.

Field modes that are suitable canditates to be involved in the reversal process are oscillating eigenfunctions of the linear eigenvalue problem for geodynamo models of alpha2 type.

Regarding the spectrum of the dynamo operator time-dependent solutions arise at so called exceptional points where two stationary modes merge and continue at a single oscillating eigenfunction. In the present model this behavior essentially involves dipolar and octupolar modes. The spectrum exhibits further time-dependent modes of higher order that appear at coupling points of different radial field modes.

In order to couple odd ("dipolar-like") and even ("quadrupolar-like") modes equatorial symmetry breaking is required. However, instead of oscillating eigenfunctions an equatorial asymmetry results in stationary hemispherical dynamos. This behavior can be explained by the approximate dipole-quadrupole degeneration for the unperturbed problem.

More complicated scenarios occur in case of (more realistic) anisotropies of alpha- and beta-effect or through non-linearities caused by the backreaction of the magnetic field (magnetic quenching).

Keywords: Dynamo linear eigenvalue problem alpha-effect reversal geodynamo
  • Lecture (Conference)
    RädlerFest: Alpha Effect and Beyond, 14.-18.02.2011, Stockholm, Sweden

Publ.-Id: 15213 - Permalink

Ga ion irradiation induced spin reorientations in Co films
Mazalski, P.; Maziewski, A.; Tekielak, M.; Ferré, J.; Jaworowicz, J.; Mougin, A.; Liedke, B.; Liedke, M. O.; Fassbender, J.ORC
Some years ago, it has been demonstrated that after submitting Pt/Co/Pt films to increasing ion irradiation dose, one observes a decrease of: (i) perpendicular magnetic anisotropy (up to reach a spin reorientation transition (SRT) towards an in-plane magnetisation state); (ii) coercive field; (iii) Curie temperature (see e.g. [1-3]). In thicker Co films, by increasing the Ga ion dose, two successive inverse SRTs take place [4].
Pt(4.5nm)/Co(2.6nm)/Pt(3.5nm) films were deposited by sputtering on a sapphire substrate. 1mm wide strip regions were irradiated by 30 keV Ga ions under different doses D ranging from 2x1013 to 3x1014 Ga ions/cm2. Samples were studied by polar Kerr PMOKE (out-of-plane magnetization component sensitive), magneto-optical microscopy and local scanning magnetometry using a focused light beam. In-plane magnetized domains were studied using longitudinal magneto-optical Kerr effect, LMOKE. Magnetic Force Microscopy (MFM) was used to image domain patterns at higher spatial resolution. TRIDYN simulations were performed to estimate irradiation driven changes of the in-depth ion distributions. The irradiation driven SRTs are illustrated in Fig.1. Magnetization lies in-plane in the non-irradiated (NI) region. When increasing D, two successive SRTs undergo between planar to perpendicular magnetization states, and again back to a planar state (through a canted magnetization state, as shown from the magnetization curve obtained for D=3x1014 Ga ions/cm2).

This work was partly supported by the EU-“Research Infrastructures Transnational Access” program “Center for Application of Ion Beams in Materials Research” under contract no. 025646 and DAAD.

[1] C. Chappert, H. Bernas, et al., Science 280, 1919 (1998)
[2] J. Ferré and J.-P. Jamet, in Handbook on Magnetism and Advanced Materials. Eds H. Kronmüller and S. Parkin Vol. 3, 1710 (2007).
[3] Fassbender and J. McCord, J. Magn. Magn. Mat. 320 (2008).
[4] J. Jaworowicz, A. Maziewski, P.Mazalski, M.Kisielewski, I. Sveklo, M. Tekielak, V. Zablotski, J. Ferré, N. Vernier, A. Mougin, A. Henschke, J. Fassbender, Appl. Phys. Lett., 95, 022502 (2009).
Keywords: irradiation, SRT, TRIDYN
  • Poster
    IV Euro-Asian Symposium “Trends in MAGnetism”: Nanospintronics. EASTMAG – 2010, 28.06.-02.07.2010, Ekaterinburg, Russia

Publ.-Id: 15212 - Permalink

Magnetooptical Spectroscopy Of Ga+ Irradiated Pt/Co/Pt Sandwiches
Lišková, E.; Veis, M.; Višpovský, Š.; Maziewski, A.; Mazalski, P.; Ferré, J.; Mougin, A.; Liedke, M. O.; Fassbender, J.ORC
The magnetic properties of ultrathin Pt/Co/Pt sandwiches depend on the interface structure and can thus be controlled by ion irradiation [1]. In the present work, we study the magneto-optic properties by polar Kerr rotation upon Ga+ irradiation of Pt(3.5 nm)/Co(2.6 nm) /Pt(4.5 nm) trilayers which have been sputter deposited on (001) Al2O3 substrates. In Figure 1 the MO spectra at saturation before and after irradiation are compared. The enhanced MO amplitude after irradiation results from an increased thickness of the alloyed PtxCo1-x interface layer [2]. The MO spectra were modeled assuming interface PtxCo1-x layers with a monotonous x gradient using the data of ref. [3]. The curves in Fig. 1 were obtained assuming the structure shown in Fig. 2, i.e., Pt(2.8 nm)/ PtxCo1-x(1.1 nm)/Co(2.3 nm) /PtxCo1-x(1.1 nm)/Pt(4.0 nm) and Pt(1.2 nm)/ PtxCo1-x(4.0 nm)/ Co(1.0 nm)/PtxCo1-x(3.0 nm) /Pt(1.5 nm)/Al2O3 for the non-irradiated sample and the sample irradiated with a dose of 1014 Ga+/cm2, respectively. The changes in the MO spectra after irradiation confirm the expected high sensitivity of the coupled 3d levels of Co and 5d levels of Pt (with high spin-orbit interaction) to the interface geometry [2]. Partially supported by NSF (DMR 0605629 and DMR 0907053), Research Corporation (CC6471), CU-NIST Joint Project and by Ministry of Education, Youth and Sport of the Czech Republic (MSM 6198910016, 0021520834 and ME09045), Grant Agency of Charles University (3146/2008), Czech Science Foundation (P204/10/P346), EU-“Research Infra-structures Transnational Access” program “Center for Appli-cation of Ion Beams in Materials Research” (025646) and DAAD.
[1] J. Jaworowicz et al., Appl. Phys. Lett. 95, 022502 (2009)
[2] D. Weller et al. J. Magn. Magn. Mat. 93, 183 (1991)
[3] S. Visnovsky et al., IEEE Trans Magn. 29, 3390 (1993)
Keywords: irradiation, Co, Pt, MOKE
  • Poster
    IEEE 7th International Symposium on Metallic Multilayers (MML2010), 19.-24.09.2010, Berkeley, CA, USA

Publ.-Id: 15211 - Permalink

Influence of Ga+ irradiation on MO spectra of Pt/Co/Pt films
Liskova, E.; Veis, M.; Visnovsky, S.; Mazalski, P.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC; Wawro, A.; Baczewski, L. T.
The magnetic anisotropy of Pt/Co/Pt sandwiches transforms from in-plane to out-of-plane and back as a function of uniform Ga+ ion irradiation fluence [J. Jaworowicz et al., Appl. Phys. Lett. 95 (2009)]. We study the effect of the irradiation on magneto-optical (MO) Kerr spectra between 1 and 5 eV in Pt(5nm)/Co(3.3nm)/Pt(20nm)/Mo(20nm). In the range up to an irradiation fluence of 1e15 ions/cm2 the MO amplitudes gradually increase and at 6e15 ions/cm2 it falls below that of the non-irradiated sample. The results are explained assuming the model system Pt/PtxCo1-x/Co/PtxCo1-x/Pt which accounts for increased PtCo alloy thicknesses at the interfaces. At 6e15 ions/cm2, the reduction in MO amplitudes is explained by the circumstance that a significant part of the sample is ablated and the sandwich reduces to a single alloy layer.
Keywords: irradiation, MOKE
  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15210 - Permalink

Modifications of magnetic properties of Pt/Co/Pt layers induced by Ga irradiations
Gieniusz, R.; Mazalski, P.; Kurant, Z.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC; Wawro, A.; Baczewski, L. T.
The influence of Ga irradiation dose D on the magnetic properties of Pt/Co(d=3.3nm)/Pt trilayers grown by molecular beam epitaxy have been studied by both ferromagnetic resonance (FMR) and magnetooptical magnetometry (PMOKE). A broadening of Co-Pt interfaces induced by irradiation was deduced from X-ray reflectivity. For the nonirradiated sample the magnetisation was in-plane with negligible remanence ThetaR PMOKE hysteresis loops. Increasing D ThetaR(D) displays a maximum in irradiated samples for a dose DM ~ 2,8e14 ions/cm2. FMR study showed a similar behaviour (occurence of a maximum in a function of dose) both effective uniaxial magnetic anisotropy and FMR linewidth. For DM the increase of a uniaxial anisotropy field up to 0.3T was estimated from FMR data. Similar effects have been recently reported for Ga irradiated Co films deposited by sputtering which showed a double spin reorientation [J. Jaworowicz et al., Appl. Phys. Lett., 95 (2009) 022502].
Keywords: SRT, FMR, irradiation
  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15209 - Permalink

X-ray reflectivity investigations of Ga+ ion irradiated Pt/Co/Pt films
Kanak, J.; Stobiecki, T.; Powroznik, W.; Mazalski, P.; Sveklo, I.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC; Wawro, A.; Baczewski, L. T.
The effects of Ga+ ion implantation in MBE grown Mo20nm/Pt20nm/Co3.3nm/Pt5nm films were investigated by low and high angle x-ray diffraction methods. The reflectivity measurements were used for characterization of changes in layer thickness and interface Pt/Co structure upon 30 keV Ga ion irradiation in a fluence range between 0 and 6e15 ions/cm2. The layer stack thickness was found to decrease with increase of Ga+ fluence. Mixing of Pt and Co at interfaces leads to a change of interface roughness of the top layers. The results were compared with high-fluence ion implantation simulations, of the dynamic changes of thickness and composition of layers, obtained using TRIDYN.
Keywords: TRIDYN, irradiation, Co, Pt , SRT
  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15208 - Permalink

Effects of thermal annealing on structural and magnetic properties of thin Pt/Cr/Co multilayers
Tripathia, J. K.; Satpatib, B.; Liedke, M. O.; Guptad, A.; Som, T.;
Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773 K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873 K
Keywords: Pt/Cr/Co multilayer; Structural property; Magnetic property; Thermal annealing

Publ.-Id: 15207 - Permalink

Quenched-in vacancies in Fe-Al alloys
Melikhova, O.; Cizek, J.; Lukac, F.; Procházka, I.; Kuriplach, J.; Anwand, W.; Brauer, G.;
Quenched-in vacancies in Fe-Al alloys with Al content ranging from 24 to 49 at.% were investigated employing two complementary techniques of positron annihilation: slow positron implantation spectroscopy and positron lifetime measurements. It was found that quenched alloys exhibit a very high concentration of vacancies. Although the free positron component cannot be resolved in positron lifetime spectrum in majority of samples, the concentration of quenched-in vacancies can be still determined from the positron diffusion length measured by a variable energy positron beam. The lowest concentration of vacancies was found in a stoichiometric (SM) Fe3Al alloy. The concentration of defects increases with increasing degree of non-stoichiometry with respect to Fe3Al, i.e. in alloys with under-SM and over-SM Al concentration. However, the increase in concentration of quenched-in defects is more pronounced in Al-rich alloys, i.e. alloys containing more than 25 at.% of Al.

Publ.-Id: 15204 - Permalink

Use of superconducting linacs for positron generation: the EPOS system at the Forschungszentrum Dresden-Rossendorf (FZD)
Krause-Rehberg, R.; Jungmann, M.; Krille, A.; Werlich, B.; Pohl, A.; Anwand, W.; Brauer, G.; Butterling, M.; Büttig, H.; Kosev, K. M.; Teichert, J.; Wagner, A.; Cowan, T. E.;
Intense positron sources require the pair production process for the positron generation. In case a pulsed positron source shall be constructed, a superconducting LINACbased accelerator allows generating the required final time structure for the electron beam. This simplifies the positron beam construction. The first such setup, the EPOS system (ELBE Positron Source) at the Forschungszentrum Dresden-Rossendorf (FZD), is described.

Publ.-Id: 15203 - Permalink

Surface nanostructures induced by slow highly charged ions
Facsko, S.; Wilhelm, R. A.; El-Said, A. S.; Heller, R.;
Surface modifications induced by the irradiation with ions have been investigated for long time. Depending on their energy the ions create a crater resulting from nuclear or electronic sputtering or can induce the formation of hillocks at high kinetic energies. For highly charged ions (HCI) the situation is more complex. In addition to their kinetic energy HCI posses also potential energy which is the sum of the ionization energies to create them. This large amount of potential energy is released when interacting with solids and deposited into a small volume close to the surface. The resulting high excitation in the surface can thus induce various modifications [1]. Recently, it has been shown that hillock structures are formed on CaF2 by HCI due to a localized phase transition [2].
In the case of the alkali halide crystal KBr we observed the formation of nanostructures resulting by desorption of surface atoms from a single ion impact site [3]. For high enough charge states each ion produces a mono-atomic deep pit with a diameter of 10-30 nm (depending on the charge state) on the atomically flat surface. The desorption of such a high amount of material can not be induced by kinetic sputtering alone, which dominates in this kinetic energy regime, but is induced by the excitation due to the potential energy. For a kinetic energy of 40 keV a threshold in the potential energy of the HCI is found for the formation of these structures between Xe15+ and Xe20+ around 3 keV. Above this threshold the volume of the pits and therewith the potential sputtering yield exhibits a linear dependence on the potential energy. However, the kinetic energy also plays an important role. For higher kinetic energies the threshold shifts to lower values of the potential energy.
Keywords: highly charged ions, nanostructures, surface modifications
  • Invited lecture (Conferences)
    EMMI Workshop "Physics prospects at the ESR and HITRAP", 27.-30.06.2010, Eisenach, Deutschland

Publ.-Id: 15202 - Permalink

SQUID investigations of Ga+ irradiated epitaxial Pt/Co/Pt trilayers
Liedke, M. O.; Shalimov, A.; Fassbender, J.ORC; Mazalski, P.; Maziewski, A.; Wawro, A.; Baczewski, L. T.
Spin reorientation transition in polycrystalline Pt/Co/Pt trilayers, i.e. rotation of the magnetization from an in-plane to out-of-plane orientation and vice versa can be precisely controlled by ion irradiation fluence [J. Jaworowicz et al., Appl. Phys. Lett., 95 (2009) 022502], similarly to the epitaxial Pt/Co/Pt trilayers exposed to 30 keV Ga+ ions in the fluence range of 1014-1016 ion·cm−2. Magnetic properties of a such irradiated system are studied by means of SQUID magnetometry. Zero field cooling and field cooling dependencies and also magnetization reversal curves are measured and analyzed in the frame of the Preisach model. The model explains structural and magnetic modifications occurring due to ion irradiation. A key magnetic properties, i.e. distribution of coercive and interaction fields, reversible and irreversible magnetic contributions are addressed. The interpretation of the results is also supported by the XRD synchrotron studies.
Keywords: SQUID, spin reorientation transition, Co, Pt, magnetization
  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15201 - Permalink

Magnetic anisotropy engineering: ultrathin Fe films on single crystalline rippled surfaces
Liedke, M. O.; Körner, M.; Lenz, K.; Ranjan, M.; Fassbender, S.; Facsko, J.;
Ultrathin Fe films exhibit an excellent epitaxial relation to MgO(100) substrates because of a very low lattice mismatch (~3.8%). Due to a cubic symmetry of the Fe crystal an in-plane fourfold magnetic anisotropy is induced. By means of ion erosion coherently aligned single crystalline patterns (ripples) are created at the MgO surface, which induce an additional uniaxial magnetic anisotropy in the afterwards deposited Fe film. The uniaxial magnetic anisotropy direction and strength is controlled by an arbitrarily chosen irradiation direction with respect to the sample plane and the ion energy dependent ripple wavelength, respectively. Thus an ensemble of twofold and fourfold anisotropy is created and analyzed by ferromagnetic resonance and magneto-optic Kerr effect techniques. Theoretical analysis reveals both the anisotropy fields and their directions that are in a perfect agreement with the experiment.
Keywords: magnetic anisotropy, ripples, MgO, Fe, single crystalline, ion erosion
  • Lecture (Conference)
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15200 - Permalink

Ions for Nanotechnology
Kolitsch, A.;
The aim of the nanocenter slovakion is its integration into university research (e.g. STU/MtF, materials research), which is highly required by professional public This will enable university to bring its research closer to the needs of industry and shift it to up-to-date topics on one side, and raise funds from private sources in the industry on the other side, which altogether represents a unique chance to train young qualified researchers in the field of contemporary materials research. The activities of the centre will be equally utilised by both in-house and external research and in a wide scale of services oriented on the support in introducing nanostructures using plasma and ion technologies into production processes for external industrial and other users.
The subject of the research, both basic and applied, will be focused on the modification of surface properties, such as hardness, friction, wear, fatigue, adhesion, as well as electrical, magnetic and optical properties, along with corrosion and bio-compatibility using ion beams technologies in the nanometer range. The research will employ the technologies, such as ion implantation (II), ion beam mixing (IBM) and ion beam assisted deposition (IBAD), as well as plasma assisted pulsing, non-pulsing, reactive and non-reactive processes where energetic ions form a decisive component of this process implementation. Highly topical is the research dealing with the development of nanostructures via ion beams.
Typical fields of utilisation are as follows:
• Exposed parts in automotive and mechanical engineering industry (injection nozzles, camshafts, bearings, valves and others);
• Medical and biomedical applications (prosthetics with interesting alloys, even those with the surfaces not sufficiently wear-resistant);
• Surface nitration of stainless steels via ion implantation with the purpose to improve wear resistance of stainless steels while preserving their high corrosion resistance;
• Stents (endoluminal catheter protheses), nano-porous stents for additional controlled administration of drugs, biocompatible and blood-compatible materials, etc. for modern medicine;
• Further possibilities of ion implantation in industry in the fields other than microelectronics, such as precise mechanics, special construction parts of expensive watches;
• High thermal oxidation protection (Ti AL – alloys, turbine construction);
• Mould injection of plastics (improvement of safety in the removing of injection-made plastic parts from the mould, as well as wear protection of highly exposed parts of forming tools);
• Ion implantation of polymers surfaces for the improvement of certain surface properties, such as printability for electric conductivity, biocompatibility, etc.

The important areas of ion beams technology application can be found in the field of ion beam analysis in a nanometer scale as well as in research and industry. Planned procedures are as follows:
• Rutherford Backscattering (RBS)
• Elastic Recoil Detection (ERD)
• Nuclear reaction Analysis (NRA)
• Proton Induced X-ray Emission (PIXE)
• Proton Induced Gamma-ray Emission (PIGE)

They provide a possibility of a non-standard depth profile analysis with high precision of nearly all chemical elements. In special cases, such as hydrogen depth profile analysis or light elements (B, C, N, O) analysis in heavy matrix (steel), they are unequalled when compared to other procedures.
Three groups of devices suggested as basic equipment for various uses of ion implantation are as follows:
• PBII equipment (three machines with various chamber volumes, basic vacuum and pulse voltage);
• Two linear ion implanters in the energetic range up to 500 kV (standard equipment) and 200 kV as a so-called high current implanter;
• 6 MV Tandetron Accelerator with experimental stations for high energy ion implantation and ion beam analysis.

The basic equipment for plasma and ion beam assisted separation processes is as follows:
• IBAD instrumentation with different low energy ion sources;
• Combination of PBII and thin film deposition
• Universal magnetron sputtering application systems with possible reactive middle frequency pulsed dual magnetron sputtering and the possibility of choice for typical plasma diagnostics and thin layers diagnostics.
Along with the implantation processes for micro-electronic development of nano-clusters, nano-wires, and nano-arrays, typical surface processes aiming at nano-scale ordered structures such as surface design created by ion erosion, nano-porosity for bio-medicine usage, blistering, etc., play an important role. Anyway, the magnetic nano-scale order of a structure as an indication of ferro-magnetic phases in non-magnetic materials or magnetic domain configuration using ion beams is of certain interest. Ion-beam-assisted separation process or special reactive processes of magnetron sputtering contributed to a significant achievement in the field of fullerene materials, nano-crystalline highly refracting optical materials or in transparent electrical conductive oxides, which play an important role in solar technology and technology of displays. Coating by super hard substances such as a-C or c-BN is impossible without energetic ions.
Keywords: ion implantation, plasma, ion assisted deposition, plasma based implantation, plasma immersion ion implantation, nanotechnology, hard coatings, doping, accelerator, implanter
  • Invited lecture (Conferences)
    Jahresempfang der Slowakischen Technischen Universität Bratislava, 21.01.2010, Trnava, Slovak Republic
  • Invited lecture (Conferences)
    Jahresempfang der Slowakischen Technischen Universität Bratislava, 21.01.2010, Trnava, Slovak Republic

Publ.-Id: 15199 - Permalink

Exploring uranyl(VI) photochemistry by DFT calculations (in Japanese)
Tsushima, S.;
no abstract for this publication
  • Lecture (Conference)
    Seminar talk at the Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 08.03.2011, Tokyo, Japan

Publ.-Id: 15198 - Permalink

Time-resolved photoluminescence from GaAs/AlGaAs multiquantum wells quenched by pulsed mid-infrared radiation
Zybell, S.; Schneider, H.; Winnerl, S.; Helm, M.;
Several groups have demonstrated the suppression of photoluminescence (PL) from semiconductor quantum wells (QWs) by intense midinfrared radiation (MIR). Since most of the previous studies are done on time-integrated PL the ultrafast changes in the radiative state population are not well understood. We present a detailed study on time-resolved PL from an undoped GaAs/AlGaAs QW sample quenched by MIR pulses from a free-electron laser, which was tuned to the intersubband transition (ISBT) energy. At the arrival time of the MIR pulse a clear sharp dip appears in the PL transient. Free carrier absorption and ISBT are the two processes that take place under MIR excitation and result in an abrupt drop of the radiative state population and consequently in an ultrafast quenching of the PL. Performing polarization sensitive measurements, we were able to discriminate the contributions of free carrier absorption from that of ISBT. A quantitative analysis of the PL dip depth and recovery time as a function of MIR fluence was done using a model based on rate equations.
Keywords: time-resolved photoluminescence, semiconductor quantum wells, intersubband transition
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15197 - Permalink

Voruntersuchungen am HZDR für Filmdickenmessungen an der thermohydraulischen Versuchsanlage KATHY (Karlstein, AREVA NP) mit Gamma-CT
Bieberle, A.; Hoppe, D.; Hampel, U.;
Für die Überprüfung des Strömungsregimes im sogenannten Kaminrohr, das in Kernkraftwerken der AREVA NP zur Anwendung kommen soll, müssen zur Überprüfung des Systems im thermohydraulischen Versuchsstand KATHY in Karlstein (AREVA NP) authentische Betriebsszenarien nachgebildet und getestet werden. Grundlage hierfür sind Simulationen und Berechnungen, die mit direkt am Versuchstand gewonnenen Messwerten überprüft werden müssen. Aus diesem Grund soll der mögliche Einsatz des am HZDR entwickelten hochauflösenden Gamma-Computertomographie-Messsystems (Gamma-CT) zur Bestimmung von Wasserfilmdicken überprüft werden.
Keywords: Gamma-CT, Wasser-Dampf Strömung
  • Other report
    HZDR: HZDR, 2011
    20 Seiten

Publ.-Id: 15196 - Permalink

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