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31745 Publications
Impact of functionalized coligands on the pharmacokinetics of 99mTc(III) ‘4+1’ mixed-ligand complexes conjugated to bombesin
Künstler, J.-U.; Bergmann, R.; Gniazdowska, E.; Kozminski, P.; Walther, M.; Pietzsch, H.-J.;
Bombesins (BN) containing 99mTc ‘4+1’ complexes may be useful to detect tumors expressing the gastrinreleasing peptide receptor (GRPR). Derivatives of the formula [99mTc(NS3R)(L2-BNst)] were synthesized, in which Tc(III) is coordinated by an isocyanide L2-BNst bearing the peptide (BNst=βAla-βAla-Gln-Trp-Ala-Val-Gly-His-Cha-Nle-NH2) and a tetradentate chelator NS3R. NS3R consists of 2,2′,2″-nitrilotriethanethiol (NS3) bearing a crown ether (NS3crown), an aliphatic amine (NS3en) and a tricarboxylic acid (NS3(COOH3). Nonradioactive Re compounds were prepared and analysed by electrospray ionization mass spectrometry. The structural similarity to the 99mTc conjugates was demonstrated by their identical HPLC elution profiles. The lipophilicity of [99mTc(NS3R)(L2-BNst)] decreased depending on the coligands NS3crown (log DO/W, pH=7.4, 0.98±0.11), NS3en (−0.49±0.07) and NS3(COOH)3 (−2.01±0.09). Biodistribution in normal rats was characterized by an increasing kidney uptake and a decreasing uptake into the liver corresponding to the reduced lipophilicity of the conjugates. The pancreatic uptake expressed by the organ/blood ratio of standardized uptake values at 60 min p.i. in rats was 8.6±1.2 for [99mTc(NS3en)(L2-BNst)] and higher compared to the other conjugates. The pancreas/liver ratio of the SUV at 60 min p.i. in rats was highest for [99mTc(NS3(COOH)3)(L2-BNst)] at 8.4±1.3. [99mTc(NS3en)(L2-BNst)] was further studied in tumor-bearing mice and its pancreas/blood and pancreas/liver ratios were lower, however the pancreas/kidney ratios were higher in mice compared to rats. The activity uptake of [99mTc(NS3en)(L2-BNst)] into the PC-3 tumor xenografts was low (%ID/g: 0.83±0.18 at 60 min; SUV: 0.21±0.05 at 60 min) but specific.
Keywords: Technetium; ‘4+1’ mixed-ligand complex; Peptide; Bombesin; Metabolism

Publ.-Id: 16070 - Permalink


Interaction of an edge dislocation with Cu–Ni-vacancy clusters in bcc iron
Terentyev, D.; Malerba, L.; Bonny, G.; Al-Motasem, A. T.; Posselt, M.;
In this work we studied the interaction of a ½<111>{110} edge dislocation with Cu-rich precipitates, mimicking those that are known to form in RPV steels. We have applied a combination of Monte Carlo and molecular dynamics techniques to explore the structure and obstacle strength of Cu–Ni-vacancy clusters of nanometric size below the resolution limit of transmission electron microscopy. The results show that the strength of Cu-vacancy, Cu–Ni and Cu–Ni-vacancy clusters is comparable or even smaller than that of pure Cu clusters, but considerably smaller than the strength of pure vacancy clusters or nanovoids. Thus, the enrichment of small Cu precipitates by Ni atoms and/or a small amount of vacancies does not increase their obstacle strength, at least in the case of edge dislocations.
Keywords: We studied the interaction of a an edge dislocation with Cu–Ni-vacancy precipitates, known to form in RPV steels. "Combination of Monte Carlo and MD techniques was used to explore structure and obstacle strength of these clusters. "The strength of Cu-vacancy, Cu–Ni and Cu–Ni-vacancy clusters is comparable or even smaller than that of pure Cu clusters."The enrichment of Cu precipitates by Ni atoms and/or by vacancies does not increase their obstacle strength.

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Publ.-Id: 16069 - Permalink


Radiobiological applications of ultrashort pulse laser-accelerated proton beams
Zeil, K.; Kraft, S.; Bussmann, M.; Cowan, T. E.; Kluge, T.; Metzkes, J.; Richter, T.; Sauerbrey, R.; Schramm, U.; Richter, C.; Beyreuther, E.; Enghardt, W.; Karsch, L.; Laschinsky, L.; Naumburger, D.; Pawelke, J.;
Ultrashort pulse laser proton acceleration is demonstrated to yield energies hitherto only accessible with high energy lasers. Up to 20 MeV protons are observed with the FZD Draco Ti:Sa laser with ~30 fs pulses and only 2 J. This proton energy range allows for first well controlled applications. The radiation dose per shot observed for energies above 10 amounts to few Gy and thus provides excellent starting conditions for the irradiation of in vitro tumour cells with the aim of determining dose dependent biological damage. A first experiment demonstrates the availability of all components indispensable for systematic radiobiological studies: A laser-plasma accelerator providing stable proton spectra with maximum energy exceeding 15MeV over hundreds of pulses and applicable doses of a few Gy within few minutes, a beam transport and filtering system, an in-air irradiation site, a dedicated dosimetry system providing both online dose monitoring and a precise absolute dose information applied to the cell sample, and the full infrastructure for analysing radiation induced damage in cells.

[1] S.D. Kraft, K. Zeil, et al., New J. Phys. 12, 085003 (2010).
  • Poster
    52nd Annual Meeting of the APS Division of Plasma Physics, 08.-12.11.2010, Chicago, USA

Publ.-Id: 16068 - Permalink


Progress towards laser-driven Particle Therapy accelerators
Cowan, T. E.; Schramm, U.; Bussmann, M.; Burris, T.; Fiedler, F.; Gaillard, S.; Herrmannsdoerfer, T.; Kluge, T.; Kraft, S. D.; Metzkes, J.; Sauerbrey, R.; Zeil, K.; Baumann, M.; Enghardt, W.; Pawelke, J.;
Recent successes in laser-ion acceleration have motivated research towards laser-driven compact accelerators for medical therapy. Realizing laser-ion acceleration for medical therapy will require adapting both the laser-ion acceleration to the medical requirements, as well as the treatment methodology to the foreseeable laser constraints. Three key scientific and technological challenges are identified: increasing laser-accelerated proton energies to 250 MeV; developing compact, strong field magnetic beam manipulation systems; and development of real-time in-vivo dosimetry to enable pulse-by-pulse active feedback and control. Progress in each of these key areas are reviewed, with special emphasis on the prospect of increasing the energy of laser accelerated protons by modifications of the Target Normal Sheath Acceleration process.
  • Poster
    52nd Annual Meeting of the APS Division of Plasma Physics, 08.-12.11.2010, Chicago, USA

Publ.-Id: 16067 - Permalink


Energy scaling of laser accelerated protons, and performance of reduced mass targets
Metzkes, J.; Zeil, K.; Kraft, S. D.; Bock, S.; Bussmann, M.; Helbig, U.; Kluge, T.; Cowan, T. E.; Sauerbrey, R.; Schramm, U.;
Proton acceleration from thin foils and reduced mass targets is studied with the 150 TW Ti:Sa DRACO Laser at FZD. DRACO has ~30 fs pulses, with up to 5 J at 10 Hz, and a contrast of 1e-10 in the ps regime, and 1e-9 to 1e-10 in the ns regime. Proton spectra are measured in radiochromic film stacks and magnetic spectrometers. Flat metallic foils exhibit a near-linear scaling of the maximum proton energy with laser power, consistent with [1] in the limiting case of ultrashort laser pulses [2]. Despite the high laser contrast, a slight deformation of the target rear surface results in a reproducible deflection of the emission of energetic protons away from the target normal direction [2]. The mass limited targets of 2 μm thick Si, were fabricated by MEMS techniques and ranged from 20x20 µm2 to 100x100 µm2 lateral size. Significant influence of the target edge and supporting stalks is observed, which depending on size can both both increase or decrease the maximum proton energy in comparison to a flat foil.

[1] J. Schreiber et al., PRL 97, 045005 (2006).
[2] K. Zeil et al., NJP 12, 045015 (2010)
  • Poster
    52nd Annual Meeting of the APS Division of Plasma Physics, 08.-12.11.2010, Chicago, USA

Publ.-Id: 16066 - Permalink


Theoretical understanding of record proton energies from laser acceleration with cone targets and future prospects
Kluge, T.; Gaillard, S. A.; Flippo, K.; Bussmann, M.; Burris, T.; Gall, B.; Geissel, M.; Lockard, T.; Metzkes, J.; Offermann, D. T.; Rassuchine, J.; Schollmeier, M.; Schramm, U.; Sentoku, Y.; Zeil, K.; Cowan, T. E.;
The laser-acceleration of protons to 67.5 MeV has recently been observed at the LANL Trident laser using novel cone targets [1]. The measured enhancement in proton energy is understood from collisional Particle in Cell simulations, which show that the hot electron temperature, responsible for the Target Normal Sheath Acceleration at the cone-top, is significantly increased when the laser grazes the cone wall. This is due to the extraction of electrons from the cone wall by the laser electric field, and their boost in the forward direction by the vxB term of the Lorentz force. This is in contrast to previous predictions of optical collection and wall-guiding of electrons in angled cones [2]. This new mechanism should enable new and more robust target designs for reaching high laser-accelerated proton energies.

[1] S.A. Gaillard, invited talk NI3.00004.
[2] Y. Sentoku et al, Phys. Plasmas 11, 3083 (2004).
  • Poster
    52nd Annual Meeting of the APS Division of Plasma Physics, 08.-12.11.2010, Chicago, USA
  • Invited lecture (Conferences)
    52nd Annual Meeting of the APS Division of Plasma Physics, 10.11.2010, Chicago, USA

Publ.-Id: 16065 - Permalink


The electrical and electroluminescence properties of rare earth implanted MOS light emitting devices in the near infrared
Rebohle, L.; Lehmann, J.; Prucnal, S.; Helm, M.; Skorupa, W.;
In the past, the suitability of Er for Si-based light emission was already investigated in detail. However, much less attention has been paid to Nd and Ho which exhibit several emission lines in the near infrared according to their 4f energy level scheme. In this work we measure the electrical and electroluminescence properties of Nd- and Ho-implanted MOS structures and compare them with the corresponding properties of Er-implanted devices. Based on these results their suitability for integrated photonic devices is discussed.
Keywords: Electroluminescence, Erbium, Neodymium, Holmium, Rare Earth, Optoelectronic Device, Si-based light emission
  • Lecture (Conference)
    EMRS Fall Meeting, 19.-23.09.2011, Warsaw, Poland
  • Journal of Luminescence 132(2012), 3151-3153
    DOI: 10.1016/j.jlumin.2011.11.024

Publ.-Id: 16064 - Permalink


Inclusive e+e pair production in p+p and p+Nb collisions at Ekin = 3.5 GeV
Weber, M.; Agakishiev, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kozuch, A.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; 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.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
We report on recent data of e+e- pair emission in proton nucleus collisions at energies above the light vector meson production thresholds. Invariant mass distributions for the p+Nb system at Ekin = 3.5 GeV are compared to data from elementary p+p reactions at the same beam energy. We observe a constant π0/ω yield ratio for both systems but an excess in the mass region above the π0 mass. Furthermore we present here the normalization procedure that was applied to p+Nb collisions by measuring the production of negative pions in the HADES acceptance.

Publ.-Id: 16063 - Permalink


Locally Adaptive Filtering for Edge Preserving Noise Reduction on Images with low SNR in PET
Langner, J.; Hofheinz, F.; Beuthien-Baumann, B.; van den Hoff, J.;
As well known, the signal-to-noise ratio (SNR) of PET images can be considerably low. This is especially true for whole-body examinations of heavy patients, for respiratorygated studies, and dynamic studies with short frames. In these cases linear smoothing filters (LF) such as a Gaussian filter are applied in order to achieve an acceptable SNR. Image resolution is, however, considerably reduced by these LFs. This affects detectability and quantification of small structures. Interesting
alternatives to LFs are non-linear, locally adaptive filters (NLF), which enable noise reduction while preserving sharp edges.
It was the aim of this study to investigate the performance of a special NLF (bilateral filter, BF) when applied to images with a low SNR. In three phantom studies using a cylinder phantom with sphere inserts different signal-to-background ratios have been investigated. In addition, images with different noise levels were generated. Finally, respiratory-gated whole-body studies were analyzed. All data were filtered, both with BF and LF. The results were analyzed regarding noise level, image resolution and relative signal recovery.
In the phantom studies BF is able to preserve the spatial resolution near the edges of the spheres while improving the noise characteristics. Signal recovery even of small spheres is not significantly reduced. Using LF compromises the spatial
resolution and leads to unacceptable reduction of signal recovery. The positive properties of BF were also apparent when applying it to single gates of respiratory-gated studies, which otherwise were not suitable for visual inspection.
NLF is a powerful alternative to LFs commonly used in PET. For studies with high noise and high signal-to-background ratios using NLFs represents a suitable filter for edge preserving image enhancement. Its performance, however, is critically dependent on a sensible choice of its intensity and spatial dependent part.
  • Poster
    IEEE Nuclear Science Symposium and Medical Imaging Conference, 23.-29.10.2011, Valencia, Spain

Publ.-Id: 16062 - Permalink


Isothiocyanate containing bifunctional chelating ligands for copper(II) based on the 1,4,7-triazacyclononane (TACN) skeleton
Ruffani, A.; Stephan, H.; Steinbach, J.;
Introduction:
The aim of this work is the development of bifunctional chelating agents (BFCAs) for mild and selective labelling of proteins with copper radioisotopes. In this perspective, the triazacyclononane derivative with two pyridyl pendant arms 1
(DMPTACN) seems to be useful. DMPTACN 1 and its bombesin conjugates can readily form very stable radiocopper(II) complexes under physiological conditions.1 The remaining secondary amine group of ligand 1 may be utilized to introduce the isothiocyanate group allowing the conjugation to appropriate biomolecules, e.g. proteins/antibodies by thiourea-bridging.
Results and Discussion:
Compound 1 was synthesized by a eleven-step sequence according to the previously published procedure.1 Treating the secondary amino group of 1 with 2-bromoacetamide reagents gave the appropriate N-Boc protected predecessors 2 (Figure 1). Subsequent cleavage of the Boc protection group with trifluoroacetic acid led smoothly to the 4-aminophenyl and 4-aminobenzyl derivatives of DMPTACN 3. In the last step, the isothiocyanates 4, synthesized by the reaction of
2 with thiophosgen proved to be high yielding. First labelling experiments of DMPTACN isothiocyanates 4 with [64Cu]CuCl2 were performed in 0.1M MES/NaOH buffer at a pH = 6.2 and 251C, resulting in a radiochemical purity of higher than 99% within few minutes. The reactivity of the 64Cu-labeled isothiocyanates with primary amino groups was tested using glycine as model compound. Applying a ten-fold excess of glycine, the reaction was completed after 4 h at room temperature. To prove the potential to label proteins, the monoclonal antibody C225 was investigated. In a first approach, ligands 4 were radiolabelled with 64Cu, and subsequently conjugated to C225. For this pre-labelling strategy, a specific activity of 2.5 GBq/mmol was obtained. The post-labelling approach is more practical. The achievable ligand-toantibody ratios were 5:1, analyzed by Maldi-Tof mass spectrometry. Rapid labelling of the DMPTACN-containing antibody with [64Cu]CuCl2 was achieved to give a specific activity of 304 GBq/mmol.
Conclusion:
DMPTACN isothiocyanates are attractive bifunctional agents for the radiocopper(II)-labelling of proteins featuring very high chemical stabiliy.
Reference
[1] G. Gasser, L. Tjioe, B. Graham, M. J. Belousoff, S. Juran, M. Walther, J.-U. Ku¨ nstler, R. Bergmann, H. Stephan, L. Spiccia, Bioconjugate Chem. 2008, 9, 719–730.
Keywords: TACN; copper-64; isothiocyanate; C225
  • Lecture (Conference)
    17th Workshop of the International Isotope Society – Central European Division. The Synthesis and Applications of Isotopes and Isotopically Labelled Compounds, 23.-24.09.2010, Bad Soden, D
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), 281-282
    DOI: 10.1002/jlcr.1859

Publ.-Id: 16061 - Permalink


New maleimide functionalized NOTA-derivatives: Synthesis and 64Cu/68Ga labelling of thiol modified L-oligonucleotides
Schubert, M.; Förster, C.; Bergmann, R.; Klussmann, S.; Pietzsch, H.-J.; Steinbach, J.;
Introduction:
The macrocyclic chelator 1,4,7–triazacyclononane triacetic acid (NOTA) is very suitable to label molecules with 64Cu or 68Ga due to its fast complex formation resulting in thermodynamically and kinetically stable complexes. Here we describe a convenient synthesis procedure for maleimide-functionalized NOTA derivatives for stable binding thiol groups of carrier molecules such as peptides, oligonucleotides or antibodies. This principle is examplified by coupling of thiol-modified L-oligonucleotides which are of great interest for pre-targeting approaches in radio-immunotherapy 1.
Results and discussion:
NOTA-monomaleimide 3 and NOTA-bismaleimide 4 were synthesized by nucleophilic addition of aminoethyl maleimide 1 or bismaleimide 2 to p–SCN-Bn-NOTA. At the next reaction step the NOTA-maleimides were conjugated
with a 50-mercaptohexyl-modified L-oligonucleotide.
64Cu or 68Ga labelling of conjugates 5 and 6 occurred very fast and with good radiochemical yields in NH4OAc buffer. The specific activities resulted in 13.0 GBq/mmol for [64Cu]Cu5, 6.7 GBq/mmol for [68Ga]Ga5, 5.8 GBq/mmol for [64Cu]Cu6 and 2.6 GBq/mmol for [68Ga]Ga6. Small animal PET imaging in mice with [64Cu]Cu5 showed that after 2 hours most of the injected activity was located in the bladder.
Conclusion:
The new ligand systems show advantages which make them interesting for further biological studies, namely the easy synthesis procedure, the fast labelling with 64Cu or 68Ga and the transferability of the conjugation principle to other carrier molecules such as peptides or antibodies.
Reference
[1] J. Schlesinger et al., Bioconjugate Chem. 2008, 19, 928–939.
  • Lecture (Conference)
    17th Workshop of the International Isotope Society – Central European Division. The Synthesis and Applications of Isotopes and Isotopically Labelled Compounds, 23.-24.09.2010, Bad Soden, D
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), 279-280
    DOI: 10.1002/jlcr.1859

Publ.-Id: 16060 - Permalink


Mono- and bis-maleimido-functionalized NOTA for site-specific modifications
Förster, C.; Schubert, M.; Pietzsch, H.-J.; Steinbach, J.;
Objectives:
The purpose was to develop applicable synthetic strategies for the preparation of new NOTAmaleimides for site-specific introduction into radiopharmaceutically relevant (macro)molecules. This approach should be characterized by low synthetic effort and high grade of flexibility concerning length and chemical nature of spacer units connecting the NOTA to the maleimide entities.
Methods:
To translate the idea and above stated requirements, the commercially available 1 and 2 were used as starting NOTA compounds. For the covalent attachment of maleimide derivatives with different linkers (aliphatic C2 to C6 as well as PEG28), two synthetic pathways were investigated (scheme 1). The first is based on nucleophilic addition reaction of an aromatic isothiocyanate with a primary amino group. Due to the limited availability of amino functionalized maleimides, a second protocol was developed. Therefore, the aromatic amino group of 2 was used for coupling reactions with NHS-ester functionalized maleimide derivatives. After establishment of these two
methods, a selection of products was engaged in coupling reactions with thiol modified L-oligonucleotides (L-DNA) for tumor pretargeting studies.

Results:
The high sensitivity of the starting materials as well as the products 3a-b and 4a-e in terms of hydrolyzation side reactions necessitated optimization of reaction parameters (solvent, pH value, stoichiometry, reaction time, etc.). Yields of 30-40 % and 83-86 % for 3a-b and 4a-d were achieved, respectively. A yield of 50 % was attained for the PEG28 derivative 4e. High specific activities resulted upon labeling different L-DNA-NOTA conjugates with 64Cu and 68Ga for biodistribution studies in Wistar rats.
Conclusions:
As a proof of concept, we demonstrate the practicability of these two methods by engaging various linkers. The broad variety of commercially available NHS-ester modified maleimides in respect to different spacer length, shape, and polarity emphasizes the high flexibility for the design of tailored NOTA-maleimides for diverse applications.
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, The Netherlands
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S324

Publ.-Id: 16059 - Permalink


Synthesis and in vitro characterisation of complementary L-oligonucleotides and their antibody conjugates
Schubert, M.; Förster, C.; Bergmann, R.; Vonhoff, S.; Klussmann, S.; Walther, M.; Pietzsch, J.; Pietzsch, H.-J.; Steinbach, J.;
Objectives:
Complementary L-oligonucleotides (L-ONs) are characterized by high metabolic stability and low immunogenicity, in combination with the absence of natural hybridization targets and therefore represent a potential effector and conjugated with the targeting antibody as binding pairs in pretargeting technologies. PEG modification of the L-DNA will allow the pharmacokinetic tailoring of the effector molecules. Therefore we studied the effect of various sizes of PEG conjugates on the hybridisation of the L-DNA molecules with the complementary L-DNA-Cetuximab conjugates.
Methods:
Cetuximab as targeting probe for the endothelial growth factor receptor was a) modified with 1,4,7 triazacyclononane-1,4,7-triacetic acid (NOTA), b) modified with maleimide moieties by conjugation of the bifunctional cosslinker 4 maleimidobutyric acid N-hydroxysuccinimide ester (GMBS), c) conjugated with the complementary thiol-bearing single strand 17mer-c-L-DNA-SH. The degree of bound NOTA, maleimide and c-L DNA were determined by MALDI-TOF or UV/VIS spectroscopy. HS-PEG-L-DNAs with PEG sizes of 2, 5 and 10 kDa were conjugated with NOTA-maleimide and labelled with 64Cu++. The hybridisation was carried out in vitro with the radiolabeled L-DNA in different stoichiometrical ratios to NOTA-c-L-DNA-Cetuximab and analysed by agarose gel electrophoresis or UV-spectroscopy.
Results:
Four different L-DNA-Cetuximab-conjugates bearing 2.2±0.8, 2.9±1.1, 4.9±1.4 and 9±2 L-DNA chains (mean±SEM, n=3) were synthesized. PEGs with molecular masses of 2, 5 and 10 kDa did not clearly influence the hybridization of the 64Cu-NOTA-PEG-L-DNA-conjugates with the complementary DNA-Cetuximab in vitro. Maximal hybridisation was reached in ratios equal and larger than 1:1 calculated from the DNA amount. The number of bound c-L-DNA on Cetuximab in the radioactive titration experiments were 2, 2.5, 5 and 9.5, which well agreed with 2.2, 2.9, 4.9 and 9, respectively, determined by direct UV/VIS spectroscopy of the c-L-DNA-NOTA-Cetuximab-conjugates.
Conclusion:
The effector 64Cu-NOTA-PEG-L-DNA and the targeting probe NOTA-c-L-DNA-Cetuximab were synthesised, characterized and tested. The number of c-L-DNA on the Cetuximab was sufficient for in vitro hybridisation. The size of the PEG spacer did not clearly influence the in vitro hybridisation of the c-L-DNA-NOTA-Cetuximab-conjugates. This characteristic of the studied L-ON derivatives seems to be suitable for in vivo application. The potential of this L-ON approach in the pretargeting technology is currently under in vitro and in vivo investigation.
  • Poster
    19th International Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, The Netherlands
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S405

Publ.-Id: 16058 - Permalink


Neue Entwicklungen in der PET/CT Hybridbildgebung: Nutzen für die Strahlentherapie?
Hofheinz, F.; Perrin, R.; van den Hoff, J.; Zips, D.;
Die kombinierte PET/CT Bildgebung hat nach ihrer klinischen Einführung im Jahr 2001 in kurzer Zeit große Bedeutung in der Onkologie und Strahlentherapie erlangt (siehe z.B. [1-7]). Die Fähigkeit zur quasi-simultanen akkuraten morphologischen CT- und funktionellen PET-Bildgebung bei methodenbedingt gewährleisteter guter räumlicher Korrespondenz der beiden tomographischen Bilddatensätze ist der wesentliche Grund hierfür.

Die Gerätetechnik hat sich in diesen rund zehn Jahren kontinuierlich fortentwickelt. CT-seitig erfolgte hier ein Übergang von den initial verwendeten Einzeilengeräten zu den heute üblichen 64-128-Zeilengeräten, welche die im Vergleich zur PET ohnehin gute Ortsauflösung der CT weiter verbessern, v.a. aber die Untersuchungszeiten deutlich verkürzen. Auch PET-seitig wurden und werden große Fortschritte in der Gerätetechnik erreicht, die im folgenden noch näher diskutiert werden sollen, da insbesondere die kontinuierliche Verbesserung der PET-Bildgebung für den prospektiven Nutzen der PET/CT für die Belange der Strahlentherapie von entscheidender Bedeutung ist.

Maßgebliches Interesse besteht aus strahlentherapeutischer Sicht daran, die durch die PET gelieferte Information hinsichtlich verschiedener relevanter Parameter wie Tumorstoffwechsel und -hypoxie in eine individualisierte Bestrahlungsplanung optimal einzubringen. Aus messtechnischer Sicht sind die hauptsächlichen Anforderungen an die funktionelle PET/CT-Bildgebung in diesem Zusammenhang: Gewährleistung der bestmöglichen Koregistrierung von CT- und PET-Bilddaten, hohe Genauigkeit der quantitativen funktionellen PET-Parameter (z.B. SUV-Werte und Targetvolumen) und möglichst hohe (praktisch nutzbare) räumliche Auflösung der PET.

Publ.-Id: 16057 - Permalink


Instability types at ion-assisted alloy deposition: from two-dimensional to three-dimensional nanopattern growth
Abrasonis, G.; Morawetz, K.;
Ion irradiation during film growth has a strong impact on structural properties. Linear stability analysis is employed to study surface instabilities during ion-assisted growth of binary alloys. An interplay between curvature-dependent ion-driven and deposition-driven instabilities is investigated. We demonstrate that ion irradiation of growing binary alloys leads to the formation of composition-modulated surface patterns. It is shown that the ion-to-atom arrival ratio R is the pattern control parameter. Close to the instability threshold we identify different regimes of instabilities driven by ion- or deposition-induced surface roughness processes, or roughness-composition feedback interactions. In particular, the synergistic effects of the curvature-dependent displacement and deposition coupling to the preferential sputtering or to the preferential diffusivity are found to induce instabilities and pattern formation. Depending on the film growth and ion-irradiation conditions, the instabilities show stationary or oscillating behavior. The latter one is exclusively connected with ion irradiation. The corresponding phase diagrams are presented in terms of experimentally accessible parameters. This shows an alternative way to control surface patterning and to grow three-dimensional laterally or vertically ordered nanostructures.

Publ.-Id: 16056 - Permalink


Supernovae im Labor
Schmidt, K.; Akhmadaliev, C.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A.; Marta, M.; Schwengner, R.; Szücs, T.; Wagner, A.; Zuber, K.;
Das Nuklid 44Ti (Halbwertszeit 59 Jahre) wird in Supernovae erzeugt. Die Gamma-Strahlung aus seinem Zerfall lässt sich in weltraumgestützten Gamma-Teleskopen nachweisen und kann als Werkzeug zum Test von Supernova-Modellen genutzt werden. Hierfür ist eine genaue Kenntnis der Kernreaktionsraten für die Erzeugung und Zerstörung von 44Ti erforderlich. Die 40Ca(alpha,gamma)44Ti-Reaktion dominiert die Erzeugung von 44Ti. Ihre Rate wird von einer Vielzahl von Resonanzen bestimmt. Um präzise Daten zu gewinnen, wurde die Stärke des Resonanztripletts bei 4.5MeV Gamma-Energie am Dresdner 3MV Tandetron sowohl mittels in-beam Gamma-Spektrometrie als auch durch eine Aktivierungsmessung im Felsenkeller-Niederniveaumesslabor gemessen. Eine Untersuchung der bestrahlten Proben mittels Beschleunigermassenspektrometrie ist geplant. – Gefördert von der EU (FP7-SPIRIT 227012) und der DFG (BE 4100/2-1).
Keywords: 44Ti Supernova 40Ca(alpha,gamma)44Ti 3MV Tandetron Felsenkeller
  • Poster
    9. Dresdner Lange Nacht der Wissenschaften, 01.07.2011, Dresden, Deutschland

Publ.-Id: 16055 - Permalink


Ion-Assisted Physical Vapor Deposition: Principles and Applications
Abrasonis, G.;
Many physical vapor deposition (PVD) methods involve the energetic particle bombardment of growing film surfaces. While the source, energy and flux of such energetic particles strongly depend on the PVD method, the basic processes they induce on the film surface are similar. Such an irradiation has a beneficial effect on different structural properties of coatings or thin films such as densification, grain morphology, adhesion, texture. This has a direct impact on the mechanical, tribological, electrical, optical or chemical performance of such films.

The aim of this talk is to give a brief overview on (i) different PVD techniques involving energetic particles and (ii) basic ion-solid interaction processes and how they influence the thin film growth process. Some recent results of our group on the ion-assisted growth of nanocomposite thin films will be also presented.
  • Invited lecture (Conferences)
    The 13th International Conference - School Advanced Materials and Technologies, 27.-31.08.2011, Palanga, Lithuania

Publ.-Id: 16052 - Permalink


Current driven flow instabilities in large scale liquid metal batteries and their management
Weier, T.; Stefani, F.; Gundrum, T.; Gerbeth, G.;
Liquid metal batteries, i.e. batteries in which both electrodes as well as the electrolyte are in the liquid state, usable for grid-scale energy storage have received considerable attention recently . A current and comprehensive account focusing on their applicability in future large scale storage systems is provided by Bradwell, earlier investigations of the technology were oriented on smaller units and thermally regenerative electrochemical systems.

A battery with fully liquid active inventary has a number of advantages: when densities are chosen properly, the battery is self-assembling due to stable stratification. Liquid-liquid interfaces allow for very fast kinetics and thereby rapid charging and discharging. Structureless (liquid) electrodes are insusceptible to aging providing nearly unlimited cyclability. Liquid metal batteries may be built from abundant and cheap feedstock. NaS and ZEBRA batteries share several of the advantages mentioned above, but require large initial investments due to their complicated construction, which is mainly dictated by the fragile ceramic electrolyte. In any case, scalability is a key enabler for cheap grid storage and ease of scale-up is one of the main underlying assumptions of liquid metal battery development. However, large electrode areas and high current densities imply large total current per cell and here electromagnetics together with fluid mechanics - i.e. magnetohydrodynamics - comes into play.

Aluminium reduction cells - which are often mentioned to have sparked the idea for large scale energy storage using liquid metals, see, e.g., - suffer from an interfacial instability which puts a constraint on the minimum electrolyte thickness. While this limitation has also to be considered, our focus is on another kind of instabilty, which limits the upper size of liquid metal batteries and is known in astrophysics under the label Tayler instability (TI). In our context, the TI is a kink-type (i.e. non-axisymmetric) instability that occurs if the current through a column of liquid metal exceeds some critical value in the order of kA, depending on the material properties. If this current threshold is exceeded, the TI would lead to a stirring of the battery inventory destroying the stable density stratification and short-circuiting the electrodes. Due to its potentially dramatic consequences, the TI should definitely be avoided during liquid metal battery operation.

One possibility to circumvent the instability is to use cells with a central bore. Depending on the ratio of bore to cell diameter, the instability can be shifted to higher total currents. Feeding a current through the bore opposing the current in the cell is a means to suppress the TI totally and would therefore be preferred in practical settings.
Keywords: liquid metal battery, Tayler instability, magnetohydrodynamics, energy storage
  • Poster
    6th International Renewable Energy Storage Conference and Exhibition (IRES 2011), 28.-30.11.2011, Berlin, Deutschland

Publ.-Id: 16051 - Permalink


Photoluminescence dynamics in GaAs/AlGaAs quantum wells under pulsed intersubband excitation
Zybell, S.; Schneider, H.; Winnerl, S.; Köhler, K.; Helm, M.;
The photoluminescence (PL) emission of semiconductor quantum wells (QWs) at low temperatures for low and intermediate excitation densities shows long rise times, as only zero-momentum states can directly couple to the photons. The relaxation of the electron-hole plasma into the k=0 state and the binding of free electron-hole pairs into excitons has been extensively studied and debated in literature. Amo et al. [1] studied the effects of the sudden warming of the relaxing carrier distribution by applying a second, time-delayed interband excitation pulse.
We present a detailed study on time-resolved photoluminescence from an undoped GaAs/AlGaAs multiple QW sample quenched by a time-delayed mid-infrared (MIR) pulse causing an intersubband transition. Our experimental technique is based on the synchronization of a pulsed table-top Ti:sapphire laser with a free-electron laser (FEL) operating in continuous pulsing mode (13 MHz). The user facility FELBE at Helmholtz-Zentrum Dresden-Rossendorf is tunable and covers a wavelength range from 4 to 280 µm. The picosecond Ti:sapphire laser pulses operating at a photon energy of 1.64 eV create a free-carrier density of approximately 5x1010 cm-2 per well in the MQW structure via interband excitation. The PL is detected by a streak camera attached to a grating spectrometer, which allows for spectral and temporal resolution of the signal (see Fig. 1b). PL quenching is induced by a delayed MIR pulse from the FEL tuned to the intersubband energy of the sample of 172 meV (7.2 µm). Since the MIR pulses (~2 ps) are much shorter than the PL recovery time, a clear sharp dip appears in the PL transient at the arrival time of the MIR pulse. The PL recovers to a slightly higher intensity as compared to the unperturbed case due to particle conservation (see Fig. 1b). As no carriers are newly injected, the carrier dynamics can be directly studied from the PL recovery within the time resolution of our experimental setup (~ 25 ps).
The experimental data can be accurately described by a rate-equation model, where possible states in the conduction band are reduced to two effective levels. The PL recovery time was found to be the same as the PL rise time for all studied MIR fluences and temporal positions of the dip. This implies that the PL recovery accounts for the cooling of the carrier distribution rather than the formation of radiative states. The observed cooling time linearly decreases with MIR fluence due to lattice heating induced by the FEL. Performing polarization sensitive measurements, we were able to discriminate the contributions of free-carrier absorption from that of intersubband absorption, where the latter is 20 times more efficient than the free-carrier absorption (see Fig. 2). This approach also provides a new method to investigate the strictness of the polarization selection rules for intersubband absorption.


[1] A. Amo, D. Ballarini, D. Sanvitto, E. Kozhemyakina, L.Vina, A. Lemaitre, D. Bajoni, and J. Bloch, Appl. Phys. Lett 92, 061912 (2008).
Keywords: quantum wells, intersubband transition, time-resolved photoluminescence
  • Lecture (Conference)
    The 11th International Conference on Intersubband Transitions in Quantum Wells (ITQW 2011), 11.-17.09.2011, Le Dune Resort & Spa Badesi, Sardinia, Italia

Publ.-Id: 16050 - Permalink


Reynolds Averaged Navier-Stokes (RANS) und Large Eddy Simulations (LES) of the air-water TOPFLOW-PTS experiment
Niceno, B.; Lumpp, T.; Apanasevich, P.; Lucas, D.;
The occurrence of a PTS in a reactor vessel is an important phenomenon for assessing nuclear reactor safety. New experiment was conducted at HZDR, focused on thermal mixing processes in the cold leg and the downcomer of two-phase PTS case. Present work reports CFD analysis of steady-state air-water case. CFD analysis was conducted with two turbulence-modeling approaches, RANS and LES. Multiphase situation was modeled with VOF approach. Simulations were performed using the ANSYS Fluent 12 package. Comparison of computed temperatures results and measurements along the thermo-couple lines revealed results depend on the turbulence model used.
Keywords: CFD, Pressurized thermal shock, LES, RANS
  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14), 25.-30.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14)
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14), 25.-30.09.2011, Toronto, Canada

Publ.-Id: 16049 - Permalink


The free-electron laser as a tool for time-resolved, nonlinear, and near-field spectroscopy
Helm, M.;
We present three examples of infrared spectroscopic investigations of semiconductors: exciton dressed states in quantum wells, pump-probe measurements on graphene, and near-field spectroscopy of buried quantum dots.
Keywords: free-electron laser, pump-probe, quantum dots, graphene, exciton
  • Invited lecture (Conferences)
    36th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2011), 02.-07.10.2011, Houston, USA
  • Contribution to proceedings
    36th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2011), 02.-07.10.2011, Houston, USA: IEEE, E-ISBN : 978-1-4577-0508-3, 6105078
    DOI: 10.1109/irmmw-THz.2011.6105078

Publ.-Id: 16048 - Permalink


Coherent switching of a THz intersubband polarization in a quantum well
Wagner, M.; Helm, M.; Sherwin, M. S.; Stehr, D.;
Using low-frequency terahertz pulses we present ultrafast optical switching of a coherent intersubband polarization in a semiconductor quantum well.
Keywords: terahertz, intersubband, quantum well, coherent
  • Lecture (Conference)
    11th International Conference on Intersubband Transitions in Quantum Wells (ITQW 2011), 11.-17.09.2011, Badesi, Italy

Publ.-Id: 16047 - Permalink


Numerical simulations of the TOPFLOW-PTS steam-water experiment
Apanasevich, P.; Lucas, D.; Hoehne, T.;
The correct analysis of the Pressurized Thermal Shock requires the simulation of the thermal mixing that occurs when cold Emergency Core Cooling (ECC) water is injected into the cold leg, where it flows to the downcomer and mixes with the hot coolant present in the primary circuit. In the framework of the NURISP (NUclear Reactor Integrated Simulation Project) project attempts are being made to improve the CFD modeling for two-phase PTS scenarios. For this purpose, two steady-state reference cases from the TOPFLOW-PTS experimental program were defined: one for air-water and one for steam-water flow. The current paper focuses only on the steam-water reference case. The pre-test simulations were performed with the commercial CFD code ANSYS CFX 12.0. The simulations of the steam-water reference test predicted a thermal stratification in the cold leg at the entrance into the downcomer and in the downcomer itself.
Keywords: Stratified flow, Direct contact condensation, CFD, Pressurized thermal shock
  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14), 25.-30.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14)
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14), 25.-30.09.2011, Toronto, Canada

Publ.-Id: 16046 - Permalink


Dreams for DREAMS - The DREsden Accelerator Mass Spectrometry facility
Merchel, S.; Akhmadaliev, S.; Pavetich, S.; Rugel, G.;
Eingeladener Vortrag ohne Abstract
Keywords: accelerator mass spectrometry, AMS
  • Invited lecture (Conferences)
    Graduiertenkollegseminar des Graduiertenkolleg "Elementspeziation", 16.-18.10.2011, Bad Münster am Stein, Deutschland

Publ.-Id: 16045 - Permalink


Uranium(VI) speciation in natural occurring water samples at pH 3 – 4, determined by TRLFS
Baumann, N.; Arnold, T.;
Knowledge in speciation is a requirement in investigations about migration paths of heavy metal con-taminations in the natural environment. A very helpful tool with an extremely low detection limit for analyzing speciation of certain radioactive heavy metal ions like uranium (VI) is the Time-resolved Laser-induced Fluores-cence Spectroscopy (TRLFS). This technique is particularly useful for detection of speciation from those ions in very low, but environmental relevant concentrations. So TRLFS can be useful in safety assessment concerning migration behaviour of fluorescent and radioactive elements.
In this study, TRLFS was applied to determine the uranium speciation in natural occurring seepage water sam-ples, and in soil water samples, all samples collected from test site “Gessenwiese” close to Ronneburg in Eastern Thuringia (Germany), were analyzed by TRLFS. This test site was installed as part of a research program of the Friedrich Schiller University Jena for investigations within the area of recultivated former uranium mining heaps.
The TRLFS measurements on water samples collected within test site Gessenwiese revealed that the uranium speciation in these seepage waters and soil waters is dominated by the hydrolyzed and monomer uranium (VI) sulfate species UO2SO4(aq). The analysis were based on the position of the peak maxima from the fluorescence signal, and their mono-exponential decay curve. Despite of the presence of high amounts of well-known fluores-cence quenchers like iron (up to 18.3 ppm) and manganese (up to extend of 97.4 ppm), the obtained uranium (VI) fluorescence signals from the natural surface and soil water samples showed sufficiently high intensity and thus could be analysed.
The here presented results are a convincing example for the suitability of TRFLS in analyzing the speciation of uranium from natural occurring water samples with pH values between 3.2 and 4.0. They were published in [1] and via Open Access.

Reference:
[1] N. Baumann, T. Arnold and M. Longschinski, J Radioanal Nucl Chem, accepted Aug. 2011
  • Contribution to proceedings
    10. Jenaer Sanierungkolloquium, 04.-06.10.2011, Dornburg, Deutschland
    Konferenzband zum 10. Jenaer Sanierungskolloquim

Publ.-Id: 16044 - Permalink


Synergistic Approach of Structure-Based and Ligand-Based Drug Design for the Development of selective Cannabinoid Receptor Ligands
Günther, R.; Brust, P.;
Cannabinoid receptors (CB) are G-protein coupled receptors involved in many physiological processes, like learning, appetite, nociception and others. Two subtypes (termed CB1 and CB2) are involved in slightly different processes [1]. Thus, it is important to gain more insight into the the cannabinoid receptor system and the potential effects of cannabinoid therapeutics.

By combining [2] 3D-QSAR, pharmacophore modeling, comparative modeling and molecular docking we could identify features responsible for receptor subtype specificity. Various pharmacophore models were derived from in-house libraries and data available in the literature. 3D structures of both receptor subtypes were created employing comparative modeling methods. The models were subjected to molecular simulations in solvated lipid bilayers to sample different receptor conformations. The models were used for molecular docking studies with small compound libraries.
Employing the data obtained in the pharmacophore/3D-QSAR studies as additional constraints delivered valuable information on affinity and selectivity of the compounds towards CB1 and CB2. The results from this synergistic modeling approach could improve our understanding of the protein–ligand interactions involved.
[1] Pertwee, RG. Ligands that target cannabinoid receptors in the brain: from THC to anandamide and beyond Addict Biol 2008, 13:147–159.
[2] This synergistic approach has been implemented into the MOE modeling package (MOE: Chemical Computing Group Inc. Montreal. H3A 2R7 Canada. http://www.chemcomp.com)
  • Poster
    7th German Conference on Chemoinformations, 06.-08.11.2011, Goslar, Deutschland

Publ.-Id: 16042 - Permalink


Depth-filtration model for compressible fibrous cakes
Grahn, A.; Kryk, H.; Kästner, W.; Alt, S.; Kratzsch, A.;
Flow through fibrous materials is encountered in a number of industrial applications, such as paper making, air and liquid filtration or manufacture of composite materials. Particle retention and pressure drop in beds of fibrous materials are difficult to predict because such beds easily compact under the action of fluid drag forces and thus exhibit significant variations of hydraulic and filtration properties along the flow direction and with time. This study proposes a semi-empirical model to calculate the time dependent clogging of compressible fibrous cakes due to the capturing of suspended particles as they pass through the cake. An experimental and a data evaluation procedure are suggested for determining the empirical parameters of the model equations.
Keywords: depth filtration, pressure drop, compressible fibre cake

Publ.-Id: 16041 - Permalink


Study on severe accidents and countermeasures for VVER-1000 reactors using the integral code ASTEC
Tusheva, P.; Schäfer, F.; Reinke, N.; Altstadt, E.; Kliem, S.;
The research field focussing on the investigations and the analyses of severe accidents is an important part of the nuclear safety. To maintain the safety barriers as long as possible and to retain the radioactivity within the airtight premises or the containment, to avoid or mitigate the consequences of such events and to assess the risk, thorough studies are needed. On the one side, it is the aim of the severe accident research to understand the complex phenomena during the in- and ex-vessel phase, involving reactor-physics, thermal-hydraulics, physico-chemical and mechanical processes. On the other side the investigations strive for effective severe accident management measures.

This paper is focused on the possibilities for accident management measures in case of severe accidents. The reactor pressure vessel is the last barrier to keep the molten materials inside the reactor, and thus to prevent higher loads to the containment. To assess the behaviour of a nuclear power plant during transient or accident conditions, computer codes are widely used, which have to be validated against experiments or benchmarked against other codes. The analyses performed with the integral code ASTEC cover two accident sequences which could lead to a severe accident: a small break loss of coolant accident and a station blackout. The results have shown that in case of unavailability of major active safety systems the reactor pressure vessel would ultimately fail. The discussed issues concern the main phenomena during the early and late in-vessel phase of the accident, the time to core heat-up, the hydrogen production, the mass of corium in the reactor pressure vessel lower plenum and the failure of the reactor pressure vessel. Additionally, possible operator’s actions and countermeasures in the preventive or mitigative domain are addressed. The presented investigations contribute to the validation of the European integral severe accidents code ASTEC for VVER-1000 type of reactors.
Keywords: Severe accidents, severe accident management, SBLOCA, SBO, primary side depressurization, vessel failure, ASTEC
  • Kerntechnik 77(2012)4, 271-277

Publ.-Id: 16040 - Permalink


Microbial Life in Uranium-contaminated Milieus
Zirnstein, I.; Gagell, C.; Arnold, T.; Krawczyk-Bärsch, E.; Röske, I.;
Microorganisms often form communities, so-called biofilms, in its natural habitats. In every territory of the world they play an important role. Biofilms contain different types of microorganisms e.g. bacteria, fungi, amoebae, algae etc. Together with the self-produced matrix, called EPS (extracellular polymeric substances), they constitute a kind of microenvironment. The supply of nutrients is mediated by open water channels. Just the same way toxic heavy metals could possibly infiltrate the biofilm. In order to understand the migration and transport processes of uranium in nature it is necessary to study the interaction of uranium with biofilms.
Biofilms are located in the former uranium mine Königstein (Saxony) in a depth of 250 m. There are two types of biofilms: stalactite-like biofilms and drainage biofilms. The water is characterized by high concentrations of uranium, protons and sulfate ions. The microscopic and genetic analysis of the Königstein biofilms revealed a rich diversity of microorganisms within the biofilm. Astonishing, we also found fungi and eukaryotes such as amoebae, insects, ciliates among bacteria to live under the extreme conditions of the mine.
Königstein mine was flooded last year (2010). Other mining sites of Saxony were flooded a long time ago. Recent studies compare the microbial diversity after (selected mining sites) and before (Königstein mine) flooding. The aim of the work is to visualize the whole biofilm and to analyze its interaction with uranium.
  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Germany

Publ.-Id: 16039 - Permalink


Intelligente Strömungsfolger zur räumlichen Parametererfassung in großskaligen Behältern
Reinecke, S.; Kryk, H.; Hampel, U.;
Die räumliche Erfassung relevanter Prozessparameter wird bei einer Vielzahl industrieller Anwendungen durch den begrenzten Zugang zum Prozess erschwert. Beispiele sind Reaktoren mit Rührwerken, Bioreaktoren, Fermenter und Schüttgutbehälter. In solchen Behältern ist die Installation von fest angebrachten Sensoren und Kabelverbindungen oft nicht realisierbar oder unerwünscht. Herkömmliche Messsonden werden üblicherweise nur lokal installiert, womit die Erfassung räumlich verteilter Parameter nur eingeschränkt möglich ist. Zudem sind räumlich auflösende Apparate, wie Kameras oder Tomographiemesssysteme, meist nicht anwendbar. Daher bietet die Überwachung der räumlichen Verteilung relevanter Prozessparameter ein hohes Potential für die verbesserte Untersuchung und die Optimierung der Anlagen und Prozesse.
Speziell für Fermenter sind der lokale Vergärungsgrad von Biomasse, Temperaturprofile, pH-Wertverteilungen, Gas- und Flüssigkeitsbestandteile im Substrat sowie lokale Strömungscharakteristiken (Geschwindigkeitsprofile, Totzonen, Kurzschlussströmungen) für die Einschätzung der Prozesseffizienz von Interesse. Dabei kann es oft ausgehend von wenigen physikalischen Basisparametern, wie Temperatur und Druck, Rückschlüsse auf die Effektivität der Heiz- und Rührregime geben. Autonome Sensortechnologien ermöglichen die messtechnische Erfassung verteilter Parameter durch den Einsatz intelligenter Strömungsfolger und gewinnen deshalb zunehmend an Bedeutung für Anwendungen in der Prozessindustrie.
Zur Erfassung räumlich verteilter Parameter in Prozessbehältern wurde ein Schwarm autonomer Sensorkapseln mit einer zugehörigen Basiseinheit entwickelt und getestet. Die Validierung des Messsystemes erfolgte unter realen Strömungsbedingungen in einem Pilotfermenter. Die aufgenommenen Messdaten und die daraus extrahierten Parameterprofile liefern neuwertige und verlässliche Informationen über den Zustand im Prozess und die vorherrschenden Strömungsbedingungen.
  • Lecture (Conference)
    Mess- und Regelungskonzepte in der Lebensmittel- und Umweltbiotechnologie, 18.10.2011, Gerlingen, Deutschland
  • Contribution to proceedings
    Mess- und Regelungskonzepte in der Lebensmittel- und Umweltbiotechnologie, 18.10.2011, Gerlingen, Deutschland, 18.10.2011, Gerlingen, Deutschland
    Fachgruppentagung Mess- und Regelungskonzepte in der Lebensmittel- und Umweltbiotechnologie

Publ.-Id: 16038 - Permalink


Biofilms growing in an underground Uranium mine
Zirnstein, I.; Gagell, C.; Arnold, T.; Krawczyk-Bärsch, E.; Röske, I.;
The eukaryotic diversity of biofilm microorganisms in the underground uranium mine Königstein in Saxony/Germany was studied by molecular methods and microscopy. The Königstein mine is currently in the process of remediation. Due to technical leaching with sulphuric acid, the mine water is characterized by low pH, high concentrations of toxic heavy metals and uranium (up to 3×10-4 M) (Arnold et al. 2010). Biofilms in the Königstein mine grew underground in the mine galleries in a depth of 250 m (50 above sea level) either as stalactite-like slime communities or as acid streamers in the drainage channels. Previously conducted studies on the bacterial diversity in both biofilm communities in the uranium mine Königstein showed that beta-proteobacterium affiliated with Ferrovum myxofaciens, also designated “Ferribacter polymyxa” were identified as dominating bacterial species (Brockmann et al. 2010).
Biofilms are not only composed of bacteria, but may also include archaea and eukaryotic organisms. The eukaryotic diversity of the Königstein biofilms was analysed by molecular methods, i.e. 18S rDNA PCR, cloning and sequencing, which were used to determine the DNA-fragments of the microorganism, and by microscopic investigations. It was found that the eukaryotic biofilm communities of the Königstein environment showed a limited number of different heterotrophic species and consist of a variety of lineages belonging to nine major taxa: Ciliates, Flagellates, Amoebae, Heterolobosea, Fungi, Apicomplexa, Stramenopiles, Rotifers and Arthropoda and in addition a large number of uncultured eukaryotes, denoted as acidophilic eukaryotic cluster (AEC). As dominant eukaryotic species in the underground Königstein environment were identified Vahlkampfia species, Bodo species, and Oxytricha species. Flagellates, e.g. Bodo saltans, Stramenopiles, e.g. Diplophrys archeri and Rotifers were discovered for the first time in acid mine drainage (AMD) milieus characterized by high concentrations of uranium.
These eukaryotes in the studied biofilms are part of a biofilm community and represent a cycle of a food chain. This study shows that not only bacteria and archaea were identified in extreme AMD environments, but also eukaryotic species were found. These observed eukaryotes may influence significantly carbon cycling and metal immobilization within biofilms.
Keywords: Eukaryote, uranium, acid mine drainage, biofilm, microbial diversity, snottite, acid streamer, 18S rDNA PCR, Light microscopy
  • Lecture (Conference)
    10th symposium on remediation, 04.-05.10.2011, Jena, Germany

Publ.-Id: 16037 - Permalink


Carrier relaxation in epitaxial graphene photoexcited near the Dirac point
Winnerl, S.; Orlita, M.; Plochocka, P.; Kossacki, P.; Potemski, M.; Winzer, T.; Malic, E.; Knorr, A.; Sprinkle, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.;
We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 - 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical phonon frequency, however, owing to the presence of hot carriers, optical phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes.

Publ.-Id: 16036 - Permalink


Room-temperature operation of a unipolar nanodiode at terahertz frequencies
Balocco, C.; Kasjoo, S. R.; Lu, X. F.; Zhang, L. Q.; Alimi, Y.; Winnerl, S.; Song, A. M.;
We report on the room-temperature electrical rectification at 1.5 THz of a unipolar nanodiode based on symmetry breaking in a nanochannel. The exploitation of its nonlinear diodelike characteristic and intrinsically low parasitic capacitance enables rectification at ultrahigh speed. The zero-voltage threshold and unique planar layout make the nanodiode suitable for building large arrays. This is the highest speed reported in nanorectifiers to date.
  • Applied Physics Letters 98(2011), 223501

Publ.-Id: 16035 - Permalink


Near-field spectroscopy on semiconductor micro- and nanostructures at FELBE
Winnerl, S.;
The combination of near-field microscopy with spectral resolution in the mid-infrared and terahertz range can address a large number of specific elementary and collective excitations locally. This is of interest for a variety of materials such as semiconductors, strongly correlated materials and biomolecules.
The free-electron laser FELBE provides a quasi-cw beam of radiation tunable in the range from 4 – 230 µm (photon energy 310 – 5 meV) for a scattering near-field microscope (sSNOM) based on a home-built atomic-force microscope. We demonstrate its potential to obtain quantitative information on buried semiconductor structures by determining the carrier concentration of boron-implanted stripes in a silicon matrix [1]. To this end, FELBE is tuned in the region of the plasma resonance of the holes in the implanted regions and the contrast of the sSNIM images is analyzed. Next we present a study of spectroscopy on exciting nanostructures, namely self-assembled InAs quantum dots. Due to their three-dimensional confinement, the dots exhibit atom-like states. However, many of the key features such as extremely sharp optical transition lines (at low temperature) are masked by the variation of energy levels from dot-to-dot due to differences in size and composition. Therefore in recent years many techniques have been developed to study single quantum dots. We address doped InAs quantum dots overgrown with 70 nm of GaAs by tuning the wavelength to intersublevel transitions of conduction band states. In Fig. 1 sSNIM images are shown for the photon energies of 86 meV and 91 meV. While for the first one, which corresponds to the p-d electronic resonance in the dots, individual quantum dots are clearly resolved, the contrast vanishes for the slightly higher photon energy. A similar behavior is observed for photon energies around 122 meV, corresponding to the s-d transition in the dots. The resonances of individual quantum dots measured with the sSNIM exhibit a linewidth of about 5 meV. This is about 4 times smaller than the inhomogeneously broadened linewidth obtained at room temperature from an ensemble of quantum dots.

This work was performed in collaboration with R. Jacob, J. Bhattacharyya, D. Stehr, H. Schneider, M. Helm (HZDR), M. T. Wenzel, H.-G. von Ribbeck, L. M. Eng (TU Dresden), S. C. Kehr (Univ. St. Andrews, St. Andrews, UK) P. Atkinson, A. Rastelli, O. G. Schmidt (IFW Dresden).

References
[1] R. Jacob, S. Winnerl, H. Schneider, M. Helm, M. T. Wenzel, H.-G. von Ribbeck, L. M. Eng, and S. C. Kehr, Opt. Express 18, 26206 (2010).
  • Invited lecture (Conferences)
    6th Workshop on Infrared Specrtoscopy and Microscopy with Accelerator-Based Sources, 04.-08.09.2011, Trieste, Italy

Publ.-Id: 16034 - Permalink


Relaxation dynamics in graphene excited in the mid and far infrared
Winnerl, S.; Orlita, M.; Plochocka, P.; Schneider, H.; Helm, M.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.;
The relaxation dynamics is of key importance for understanding basic properties of graphene as well as for electronic and optoelectronic device applications. Various degenerate and two-color pump-probe studies have been carried out for excitation energies E = 1.6 eV [1-5].
We performed degenerate pump-probe spectroscopy at much lower energies (E = 15 – 250 meV) by applying a free-electron laser as a source of tunable picosecond radiation pulses. We investigated multilayer graphene samples grown by thermal decomposition on the carbon terminated surface of 6H-SiC. For the largest photon energy E = 245 meV the observed pump-probe signals can be characterized by two relaxation times of 0.5 ps and 5 ps at a lattice temperature of 10 K. For the lower photon energies the relaxation times are much longer, namely 15 ps for E = 72 meV and 25 ps for both E = 30 meV and E = 20 meV. The faster relaxation at 245 meV is attributed to the contribution of optical phonons, while at the lower energies only acoustic phonons are involved. This interpretation is corroborated by studying the temperature dependence of the pump-probe signals. While for the highest photon energy both the relaxation times and maximum transmission change depend only weakly on temperature, for lower photon energies the transmission change decreases rapidly and the relaxation times get much faster when the temperature is increased. Furthermore we find that the pump-induced transmission change saturates for moderate intensities (1 – 10 µJ/cm^2, depending on photon energy) and a maximum transmission change of about 10 % can be achieved. This is valuable information for the application of graphene as a saturable absorber in the mid and far infrared range.
While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV. The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy). We discuss the experimental results and a simple model based on rate equations.

References
[1] J.M. Dawlaty et al., Appl. Phys. Lett. 92, 042116 (2008).
[2] D. Song et al., Phys. Rev. Lett. 101, 157402 (2008).
[3] P.A. George et al., Nano Lett. 8 ,4248 (2008).
[4] H. Wang et al., Appl. Phys. Lett., 96, 081917 (2010).
[5] D. Sun et al., Phys. Rev. Lett. 104, 136802 (2010).
  • Poster
    Graphene Week 2011, 24.04.-29.09.2011, Obergurgl, Austria

Publ.-Id: 16033 - Permalink


Enroute to investigating protein dynamics under selective vibrational excitation at the THz FEL FELBE
Bauer, C.; Gensch, M.; Heberle, J.;
We aim at investigating proteins under the irradiation with intense THz radiation tuned in resonance to specific vibrational modes. This approach is much in analogy to recent experiments that showed selective vibrational control in complex materials [01, 02, 03]. To achieve the necessary sensitivity for protein dynamics we combine a novel time-resolved IR difference spectroscopic setup with uniquely intense, tunable narrow bandwidth THz radiation (1.2 – 66 THz) of the THz free electron laser FELBE.

Publ.-Id: 16032 - Permalink


The coherent THz facility at ELBE: Enroute to naturally synchronized THz pump THz probe experiments beyond the 100 J pulse energy limit and single shot electron bunch diagnostics
Gensch, M.;
At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at FLASH [1,2] the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses. The pulse energies are expected to exceed the 100 J limit at scalable repetition rates between 1 and 200 KHz (cw), thereby the coherent THz facility will represent a worldwide unique facility. Besides user experiments the laboratory is also foreseen as a test bed for THz-based electron bunch diagnostics (arrival time, bunch form, …) on cw linear accelerators. The current status of the project and planned experiments are presented.
[1] M. Gensch et. al., The new THz undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[2] U. Fruehling, M. Wieland, M. Gensch et. al., Single-shot Terahertz-field driven Streak camera, Nature Photonics 3 (2009), 523.
[3] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch et. al., Few Femtosecond Timing at 4th Generation X-ray light sources, Nature Photonics 5 (2011), 162.
  • Invited lecture (Conferences)
    Brookhaven National Lab - Ultrafast Meeting, 07.10.2011, New York, USA

Publ.-Id: 16031 - Permalink


The coherent THz facility at ELBE: Enroute to naturally synchronized THz pump THz probe experiments beyond the 100 J pulse energy limit and single shot electron bunch diagnostics
Gensch, M.;
At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at FLASH [1,2] the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses. The pulse energies are expected to exceed the 100 J limit at scalable repetition rates between 1 and 200 KHz (cw), thereby the coherent THz facility will represent a worldwide unique facility. Besides user experiments the laboratory is also foreseen as a test bed for THz-based electron bunch diagnostics (arrival time, bunch form, …) on cw linear accelerators. The current status of the project and planned experiments are presented.
[1] M. Gensch et. al., The new THz undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[2] U. Fruehling, M. Wieland, M. Gensch et. al., Single-shot Terahertz-field driven Streak camera, Nature Photonics 3 (2009), 523.
[3] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch et. al., Few Femtosecond Timing at 4th Generation X-ray light sources, Nature Photonics 5 (2011), 162.
  • Invited lecture (Conferences)
    Kolloquium PTB, 16.08.2011, Berlin, Deutschland

Publ.-Id: 16030 - Permalink


Multijoule scaling of laser-induced condensation in air
Petrarca, M.; Henin, S.; Stelmaszczyk, K.; Bock, S.; Kraft, S.; Schramm, U.; Vaneph, C.; Vogel, A.; Kasparian, J.; Sauerbrey, R.; Weber, K.; Wöste, L.; Wolf, J.-P.;
Using 100 TW laser pulses, we demonstrate that laser-induced nanometric particle generation in air increases much faster than the beam-averaged incident intensity. This increase is due to a contribution from the photon bath, which adds up with the previously identified one from the filaments and becomes dominant above 550 GW/cm2. It appears related to ozone formation via multiphoton dissociation of the oxygen molecules and demonstrates the critical need for further increasing the laser energy in view of macroscopic effects in laser-induced condensation.
Keywords: 42.65.Jx Beam trapping, self-focusing, and thermal blooming; 52.38.-r Laser-plasma interactions; 92.60.Mt Particles and aerosols; 92.60.Nv Cloud physics and chemistry

Publ.-Id: 16026 - Permalink


Dose controlled radiobiological experiments with ultra-short pulse laser accelerated proton beams
Schramm, U.;
Dose controlled radiobiological experiments with ultra-short pulse laser accelerated proton beams
  • Invited lecture (Conferences)
    Laser and Plasma Accelerators Workshop 2011, 20.-24.06.2011, Wuzhen and Shanghai, China

Publ.-Id: 16025 - Permalink


Radiobiological applications of laser accelerated ion beams and visions for future research infrastructure
Schramm, U.;
Radiobiological applications of laser accelerated ion beams and visions for future research infrastructure
  • Invited lecture (Conferences)
    Fourth EMMI workshop on Plasma Physics with Intense Heavy Ion and Laser Beams, 02.-04.05.2011, Darmstadt, Deutschland

Publ.-Id: 16024 - Permalink


Combining real-space data analysis of HEXS and XAS to determine the structure of amorphous colloids
Hennig, C.;
Structure analyses of amorphous colloids suffer from absence of periodic structural order and restrict the analytical techniques to near-order sensitive ones like real-space analysis of high-energy X-ray scattering (HEXS) and X-ray absorption spectroscopy (XAS). High-energy X-ray scattering provides precise distances and quantitative electron densities, but comprise scattering contributions from all scattering pairs in the structure whose separation becomes difficult with increasing number of elements involved. EXAFS, in contrast, is an element selective technique and provides exclusively structural information from the direct neighborhood of the absorbing atom, but suffer often from destructive interference effects as soon as the symmetry of the structure becomes low. A combination of these techniques is widely able to overcome their individual restrictions. Basic principles and examples will be discussed in detail.
Keywords: EXAFS, HEXS
  • Lecture (Conference)
    Workshop on Analysis of Diffraction Data in Real Space, ADD2011, 12.-14.10.2011, Grenoble, France

Publ.-Id: 16023 - Permalink


Numerical and experimental modeling of VGF-type buoyant flow under traveling magnetic field
Galindo, V.; Niemietz, K.; Pätzold, O.; Gerbeth, G.; Stelter, M.;
Experimental and numerical modeling of a Vertical Gradient Freeze-type buoyant flow under a traveling magnetic field is presented. Low-temperature flow experiments were carried out using a GaInSn alloy. Radial heating and cooling of the melt leading to a double vortex buoyant flow like in typical VGF growth was introduced and systematically varied by means of a model furnace. The combined VGF-TMF flow was investigated with focus on the transition from a stationary to a time-dependent flow regime. The stability threshold was found to be significantly influenced by the mutual interaction of electromagnetically driven and buoyant flows.
Keywords: crystal growth, traveling magnetic field, vertical gradient freeze
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Corsica, France
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 193-197
  • Lecture (Conference)
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Corsica, France

Publ.-Id: 16022 - Permalink


Investigations of nano structures on ta-C films made by gallium FIB lithography
Philipp, P.; Bischoff, L.;
Hydrogen free Diamond like carbon films (DLC) with high sp3 content, fabricated by mass filtered vacuum arc deposition and modified by Ga+ FIB irradiation were investigated.

For electrical characterization at room temperature van-der-Pauw structures were written by direct Ga+ FIB lithography. The sheet resistance RS decreases with increasing ion fluence due to the increase of the sp2 content in the irradiated regions, where a minimum of RS = 290 at 1.6 x 1017 cm2 was achieved. Hall measurements were used to study the charge carrier mobility. Therefore 4- and 6-terminal device structures were fabricated by combining FIB and optical lithography on DLC layers. The layers with a thickness in the range between 20 and 110 nm had a sp3 content above 65% and are deposited on a Si substrate. The FIB made structures were partly covered by 400x400 µm² Au contact pads, produced by lift off technique. Hall measurement results are interpreted as a function of the Ga+ fluence, the structure size and the DLC layer thickness. For a second set of samples a SiO2 interface layer between DLC and Si substrate was used to avoid leakage current through the bulk Si. The results for the two sample types are compared and the influence to the leakage current will be discussed. Additionally, conducting graphitic nanowires were investigated (length 10 µm, width 200 nm to 5 µm) delivering a resistance of 130 k for 5 µm width and 300 M for 300 nm width, respectively.

Ga+ irradiation under higher temperatures shows dot formation due to Ga segregation that was observed above 400°C at fluences higher than 1 x 1016 cm2. The Ga-dots were studied by SEM/EDX and AFM. Increasing Ga+ fluence leads to an increase of the dot areal density. Diameter and height of the dots are growing with temperature.

Ion beam induced graphitization of DLC films by FIB in the nanoscale offers prospective applications of conductive nanostructures in an insulating matrix.
Keywords: tetrahedral amorphous carbon; focused ion beam; graphitization; nano-structures; van-der-Pauw
  • Poster
    Diamond 2011 - 22nd European Conference on Diamond, Diamond-like Materials and Nitrides, 04.-08.09.2011, Garmisch-Partenkirchen, Germany
  • Diamond and Related Materials 23(2012), 140-143
    DOI: 10.1016/j.diamond.2012.01.025

Publ.-Id: 16019 - Permalink


Quantitative analysis of the order of Bi ion induced dot patterns on Ge
Böttger, R.; Bischoff, L.; Facsko, S.; Schmidt, B.;
We demonstrate that the temperature dependent focused ion beam irradiation of (100) Ge surfaces with 20 keV Bi+ ions leads to variably ordered hexagonal dot pattern. We show that the average information gain about the spatial order can be signicantly increased by image preprocessing transforming the power spectral density into the pair correlation function. Order parameters are derived from the pair correlation function for the comparison of highly ordered patterns.
Keywords: nanodots, nanoholes, pair correlation function, hexagonal order, image analysis

Publ.-Id: 16018 - Permalink


Experiments with neutrons and photons at ELBE
Schwengner, R.; Keywords: Neutron scattering, fast neutrons, neutron capture, cold neutrons, photon scattering, bremsstrahlung, cross sections, statistical model, strength function, level density, transmutation.
  • Invited lecture (Conferences)
    The Fourteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, 28.08.-02.09.2011, Guelph, Canada
  • Contribution to proceedings
    The Fourteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, 28.08.-02.09.2011, Guelph, Canada
    Proceedings of the Fourteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics

Publ.-Id: 16010 - Permalink


A method for correct averaging in transmission radiometry
Hampel, U.; Wagner, M.;
Transmission radiometry with photon or particle radiation is a common technique for the measurement of thickness, density and composition of materials, e.g. in production lines and in multiphase flow metering. Moreover, radiation transmission measurement is the basis for many imaging techniques, such as x-ray and gamma ray tomography. A common problem associated with transmission measurement is correct temporal averaging for time-varying material properties. Averaging the intensity signal at the detector over time and taking this mean to calculate average ray attenuation leads to incorrect results when attenuation changes within the integration period. This paper discusses the implications of this systematic error and introduces a methodology for correct averaging which is applicable even to very low intensity measurements.
Keywords: transmission radiometry, dynamic error

Publ.-Id: 16009 - Permalink


Novel Ge nanopattern by heavy Bi monomer irradiation
Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.; Pilz, W.; Heinig, K.-H.; Facsko, S.;
Surface pattern on Ge induced by Bi cluster ions doffer drastically from morphology after monomer irradiation. Large aspect ratios of dots and ripples and crystalline surfaces after cluster irradiation have been observed. A novel patterning mechanism explains the dot formation qualitatively by means of local tiny melt pools induced by ion impact . Moreover this model predicts the formation of dot pattern even for monomer irradiation at elevated temperature. The aim of this work is to investigate the pattern formation by heavy Bi monomer bombardment. Surface pattern obtained at room temperature and under normal incidence are investigated in an ion energy range from 4 to 60 keV. A energy driven pattern transition from hole over dot to sponge like structures is observed. Moreover, the pattern formation by Bi monomer ions is investigated at elevated temperatures showing a energy dependent transition from sponge to dot like pattern.
Keywords: Bi ion monomer cluster pattern formation
  • Lecture (Conference)
    Nanoscale pattern formation at surfaces, 18.-22.09.2011, El Escorial, Spain

Publ.-Id: 16008 - Permalink


Engineered Nanoparticles and Their Identification Among Natural Nanoparticles
Zänker, H.; Schierz, A.;
Due to the huge excess of natural nanoparticles, the identification and quantification of engineered nanoparticles is a big challenge to the analyst. Moreover, identification in a qualitative sense and quantification by mass concentration alone is not sufficient since the potential environmental hazard arising from engineered nanoparticles is controlled by a number of further properties of the particles. The most important methods of nanoparticle fractionation and nanoparticle detection are discussed. It is shown that coupled techniques are increasingly applied. Dedicated techniques that are tailored to the search for a certain targeted engineered nanoparticle are more promising than universal approaches that aim at the search for any engineered nanoparticles. Analyses should not rely on only one method but several complementary methods should be used.
Keywords: Engineered nanoparticles, environmental hazard, fractionation, detection, coupled methods

Publ.-Id: 16007 - Permalink


Microfluidic system for endocrine disrupting chemicals detection in waterish solution
Cherkouk, C.; Rebohle, L.; Howitz, S.; Skorupa, W.;
We present a microfluidic cell plate for endocrine disrupting chemicals (EDCs) detection, like estrogenic activity, in waterish solution. This platform technology consists of four independent micro flow units made of polydimethylsiloxane (PDMS) and glass, which enables a selective detection of up to four species of the EDCs per one-way chip containing the corresponding immobilized receptor. The concept of the detection is based on direct fluorescence analysis. In order to found out the electrical parameters of the microfluidic system electroluminescence (EL) measurements as a function of the concentration of the QD800 dye were investigated. Finally, the microfluidic device was attached to the flow control system. Different edge filters were tested in order to attenuate the MOSLED light signal and to maximize the QD800 dye signal at 800 nm which works best for a 780 nm edge filter. Measurements using an integrated photo diode as detector were performed to point out the relationship between the dark and photo current.
Keywords: Si-based light emission, biosensor, microfluidic, fluorescence, estrogen, EDC.
  • Poster
    Eurosensor XXV, 05.-8.9.2011, Athen, Griechenland
  • Contribution to proceedings
    Microfluidics and LoC, 05.-8.9.2011, Athen, Griechenland, Holand: Elsevier

Publ.-Id: 16006 - Permalink


Secondary Electron Emission from Surfaces during Focused Ion Beam Irradiation
Bischoff, L.; Böttger, R.;
Scanning ion microscopy (SIM) based on secondary electron (SE) imaging initiated by focused ion beam (FIB) irradiation of surfaces can yield important information about the topography, the material changes or crystallographic orientations of a specimen. Compared to a scanning electron microscope (SEM) based on a similar principle the information comes from a very near surface region due to the small penetration depth of the ions. A disadvantage of the SIM is the lower spatial resolution and the fact that energetic ions damage the surface during imaging by implantation and sputtering processes.
The aim of this work is to investigate the behavior of a mass-separated FIB working with a bismuth liquid metal ion source which emits a broad spectrum of single and double charged monomers as well as cluster ions in the frame of the examination of the self-organization of nano-pattern on surfaces under heavy ion erosion [3]. The study of all interactions of the primary beam within the surface and the knowledge of the fundamental parameters leads to a more correct interpretation of the secondary electron images.
Keywords: FIB, secondary electron emission, work function
  • Lecture (Conference)
    Nanoscale pattern formation at surfaces, 18.-22.09.2011, El Escorial, Spain

Publ.-Id: 16005 - Permalink


Study of Formation and Thermodynamic Properties of Aqueous U(VI) – Uric Acid System by Time – Resolved Laser – Induced Fluorescence Spectroscopy (TRLFS)
Osman, A. A. A.; Geipel, G.;
Background
Due to the progression of uranium content in the bio-sphere at present, uranium is expected to be increasingly accumulated in the food chain and eventually in the living organisms. To get valuable information and to understand its toxicity, behaviour and distribution in such cellular level; knowledge about uranium (VI) speciation in biosystems will be useful for evaluating toxicity after uranium exposure. Little is known about interaction and behaviour of uranium with some biomolecules (e.g. urea and uric acid) that commonly present in biological fluids or in bio-system. In attempt to provide information in this context, we investigate some important thermodynamic data upon complexation of uranium with some single bioligands, viz., uric acid using TRLFS.
  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Germany

Publ.-Id: 16000 - Permalink


Complexation of An(III)/Ln(III) with Borates
Schott, J.; Barkleit, A.; Acker, M.; Brendler, V.; Bernhard, G.;
Investigations to the mobilisation of radionuclides are essential in the risk assessment of radionuclides in the environment and the safety assessment of nuclear waste repositories. The mobilisation of radionuclides takes place for instance by the formation of water soluble complexes or sorption processes on mineral surfaces. Concerning the required risk and safety assessments a wide knowledge about the chemical and physical behavior of radionuclides, particularly actinides, is needed. Thus, interaction studies of radionuclides are carried out, e.g. complexation studies with components of the environmental compartments (humic acids, bioligands, inorganic ligands, bacteria, …).
Borates (e.g. boric acid B(OH)3 and its salts or esters) are ubiquitous compounds in the environment (rocks, soils, natural waters) and are used in many applications, e.g. glass production, detergents, agriculture and nuclear technology. Thus, there are many sources for the release of borates in the environment. But although there is a relevance of borates in the environment and, perhaps, in nuclear waste repositories, the Ln(III)/An(III)-borate system is investigated insufficiently.
The work concentrates on the complex formation in the An(III)/Ln(III)-borate system. The influence of temperature and ionic strength on the complexation will be investigated.
Keywords: Europium, Americium, borates, complexation studies, temperature, ionic strength
  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Germany

Publ.-Id: 15999 - Permalink


Simulations of RUTA-70 reactor with CERMET fuel using DYN3D/ATHLET and DYN3D/RELAP5 coupled codes
Kozmenkov, Y.; Rohde, U.; Baranaev, Y.; Glebov, A.;
RUTA-70 is a pool type reactor with the rated power of 70 MW designed as a district heat supplying facility. The basic design principles of this reactor are simplicity of the design and a high safety level due to a low pressure and a large coolant inventory in the primary system. The core design with the CERMET fuel rods also contributes to the reactor safety due to a high thermal conductivity of the fuel matrix and its role as the additional barrier to the fission products release.

RUTA-70 model for simulations with the internally coupled code systems DYN3D/ATHLET and DYN3D/RELAP5 was developed. A 3-D power distribution in the core is calculated by DYN3D with thermal-hydraulic feedback from the system codes. The reactor facility model includes reactor pool, two reactor loops, circulation pumps, primary and the secondary heat exchangers and core channels. The core model consists of 16 fuel assemblies in the 60-degree symmetry sector with different burnable absorber (Gd) concentrations.

The steady-state with the rated reactor parameters and a BDB accident scenario were simulated with the DYN3D/ATHLET and DYN3D/RELAP5 coupled code systems to verify these codes. The simulated accident is initiated by the trip of two operating primary circulation pumps. Additionally to the initial event the SCRAM failure is postulated.

The compared codes give close predictions for the initial and final states of the accident but not for the transition between them. The observed deviations are explained by differences in the subcooled boiling models of the system codes ATHLET and RELAP5. Both simulations confirm a high level of the reactor inherent safety. The allowed safety margins were not reached.
Keywords: pool type reactor, low pressure, CERMET fuel, coupled code, accident simulation, subcooled boiling, reactor stability
  • Contribution to proceedings
    21st Symposium of AER on VVER Reactor Physics and Safety, 19.-23.09.2011, Dresden, Deutschland
    Proceedings of the 21st Symposium of AER on VVER Reactor Physics and Safety, 595-613
  • Lecture (Conference)
    21st Symposium of AER on VVER Reactor Physics and Safety, 19.09.-23.11.2011, Dresden, Deutschland

Publ.-Id: 15998 - Permalink


Effect of superimposed magnetic field on hydrogen evolution reaction
Koza, J.; Mühlenhoff, S.; Zabinski, P.; Nikrityuk, P.; Eckert, K.; Uhlemann, M.; Gebert, A.; Weier, T.; Schultz, L.; Odenbach, S.;
The effect of uniform magnetic fields on hydrogen evolution reaction during metal deposition and water electrolysis was investigated by means of electrochemical techniques coupled with in-situ microscopic observation, velocity measurements and numeric simulation. The desorption of hydrogen bubbles is enhanced in applied magnetic fields independent on their orientation relative to electrode surface. The origin of this effect is attributed to Lorentz force driven convection generated by the applied magnetic field.
Keywords: two-phase flow, electrolysis, Lorentz force
  • Lecture (Conference)
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 789-793

Publ.-Id: 15997 - Permalink


On the action of magnetic gradient forces in microstructured copper deposition
Mutschke, G.; Tschulik, K.; Weier, T.; Uhlemann, M.; Bund, A.; Alemany, A.; Fröhlich, J.;
The relative influence of the Lorentz force and the magnetic gradient force on micro-structured copper deposition is studied with simple magnetic elements consisting of cylindrical permanent magnets are placed closely behind the surface of the cathode. Analytical findings and numerical simulations reveal that for magnets of small diameter the magnetic gradient force dominates. Experimental investigations find that the thickness of the deposited copper layer increases in the vicinity of the magnets. The combined analysis of simulations and experiments shows that this enhancement of mass transfer results from a local convection towards the electrode which is forced by the magnetic gradient force.
Keywords: electrodeposition, Lorentz force, magnetic gradient force
  • Lecture (Conference)
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 725-728

Publ.-Id: 15996 - Permalink


The simplified P3 approach on a trigonal geometry in the nodal reactor code DYN3D
Duerigen, S.; Fridman, E.;
DYN3D is a three-dimensional nodal diffusion code for steady-state and transient analyses of Light-Water Reactors (LWRs) with square and hexagonal fuel assembly geometries. Currently, several versions of the DYN3D code are available including a multi-group diffusion and a simplified P3 (SP3) neutron transport option. In this work, the multi-group SP3 method based on trigonal-z geometry was developed. The method is applicable to the analysis of reactor cores with hexagonal fuel assemblies and allows flexible mesh refinement, which is of particular importance for VVER-type Pressurized Water Reactors (PWRs) as well as for innovative reactor concepts including block type High-Temperature Reactors (HTRs) and Sodium Fast Reactors (SFRs). In this paper, the theoretical background for the trigonal SP3 methodology is outlined and the results of a preliminary verification analysis are presented by means of a simplified VVER-440 core test example. The accordant cross sections and reference solutions were produced by the Monte Carlo code SERPENT. The DYN3D results are in good agreement with the reference solutions. The average deviation in the nodal power distribution is about 1%.
Keywords: DYN3D, simplified P3, SP3, trigonal, hexagonal, nodal
  • Contribution to proceedings
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany
  • Lecture (Conference)
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany

Publ.-Id: 15995 - Permalink


Simulation of AER-7 benchmark problem with the coupled code DYN3D/ATHLET
Kozmenkov, Y.; Kliem, S.;
The 7th dynamic benchmark is the most recent problem specified within the AER activities on verification of the coupled neutronic/thermal-hydraulic codes. This is the VVER-440 transient initiated by re-connection of the isolated reactor circulation loop filled with a low-temperature coolant. During the transient a core power excursion with a non-symmetric radial distribution is expected due to incomplete coolant mixing at the core inlet.

The externally coupled code system DYN3D/ATHLET developed in HZDR was used in the benchmark simulation. In the case of external coupling all neutronic and thermal-hydraulic parameters of the core are calculated by the 3D code of neutron kinetics DYN3D.

The computer model of the VVER-440 reactor used in the AER-7 calculations represents a modified version of the earlier developed input deck for the AER-6 benchmark simulation. The model includes 6 reactor loops with the main circulation pumps and steam generators. The secondary system is modelled up to the turbine valves. The 3D core model includes all 349 fuel assemblies (assembly-by-assembly approach).

The main results of the benchmark calculation are presented and discussed.
Keywords: dynamic benchmark, VVER-440, coupled code verification, 3D core model
  • Contribution to proceedings
    21st Symposium of AER on VVER Reactor Physics and Safety, 19.-23.09.2011, Dresden, Deutschland
    Simulation of AER-7 benchmark problem with the coupled code DYN3D/ATHLET, 449-462
  • Lecture (Conference)
    21st Symposium of AER on VVER Reactor Physics and Safety, 19.-23.09.2011, Dresden, Deutschland

Publ.-Id: 15994 - Permalink


Millisecond flash-lamp annealing of LaLuO3
Lehmann, J.; Shevchenko, N.; Mücklich, A.; von Borany, J.; Skorupa, W.; Schubert, J.; Lopes, J. M. J.; Mantl, S.;
Metal-oxide-semiconductor capacitors containing the alternative high-k dielectric LaLuO3 were treated by flash lamp annealing (FLA). Capacitance–voltage (C–V) and current–voltage (J–V) characteristics reveal an increase in the capacitance for the flashed samples while the very low leakage current of the LaLuO3 is retained. Microstructural investigations confirm the thermal stability of the film even after FLA at 1200 °C, 20 ms.
Keywords: High-k dielectrics Alternative high-k dielectrics Higher-k dielectrics Ternary rare earth oxides Ternary high-k oxides Rare-earth based gate oxides Electrical properties
  • Poster
    17th Conference on "Insulating Films on Semiconductors", 21.-24.06.2011, Grenoble, France
  • Microelectronic Engineering 88(2011), 1346-1348
    DOI: 10.1016/j.mee.2011.03.126

Publ.-Id: 15993 - Permalink


DNS and experiments of electromagnetic flow control on an inclined flat plate
Albrecht, T.; Weier, T.; Gerbeth, G.; Metzkes, H.; Stiller, J.;
We investigate the separated flow around an inclined flat plate at a Reynolds number of 104 by Direct Numerical Simulation (DNS) and time-resolved Particle Image Velocity (PIV). Flow separation is suppressed using sinusoidally and rectangularly oscillating Lorentz forces in streamwise direction. An rms momentum coefficient of 2.25% increases the time-averaged lift, deduced from PIV by a global momentum approach, by 20–45%. Whereas sinusoidal forcing increases both lift and drag, rectangular waves create no significant additional drag. Analysis of the DNS flow structures reveals different immediate vortex dynamics induced by the actuation.
Keywords: flow control, Lorentz force, flow separation
  • Poster
    8th International Pamir Conference on Fundamental and Applied MHD, 05.09.2011, Borgo, Frankreich
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 375-379

Publ.-Id: 15992 - Permalink


Image based in-vivo dosimetry: from PET to in-beam SPECT
Fiedler, F.; Dersch, U.; Golnik, C.; Kormoll, T.; Enghard, W.;
Radiation therapy is an important treatment modality in cancer therapy. New radiation species, like protons and light ions have the potential of increasing tumor conformality of irradiation. Because of the way these particles deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the damage of the surrounding healthy tissue. Such high precision radiotherapy treatment requires efficient quality assurance techniques. Small changes in the irradiated volume will lead to a mismatch of the deposited dose maximum and the tumor. This causes missing dose in the tumor volume and potential damage to healthy tissue. Therefore, a dose monitoring system is highly desirable. Between 1997 and 2008, the in-beam Positron Emission Tomography (PET) method was used at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany, for monitoring the dose delivered by 12C beams. Since the positive clinical impact of the method has been shown at the Dresden Proton Therapy facility an in-room PET/CT will be installed for the same purpose.
Due to inherent limitations of this method, a direct quantification of the delivered dose is not feasible. Therefore, another approach based on dose monitoring by detection of prompt gamma rays is currently under investigation. For this purpose a Compton camera design was evaluated with respect to the special requirements and conditions that arise from this application. Different concepts were compared by means of simulation. Now the construction of a first prototype is under way.
Keywords: in vivo dosimetry, in-beam PET, in-beam SPECT
  • Invited lecture (Conferences)
    SCINT 2011 - 11th International Conference on Inorganic Scintillators and their Applications, 12.-16.09.2011, Gießen, Deutschland

Publ.-Id: 15991 - Permalink


Potential Use of Thorium in PWRs
Fridman, E.;
There has been a recent revival of interest in Th-based fuel cycles, particularly for commercial Pressurized Water Reactors (PWR), motivated primarily by their potential to address concerns related to the proliferation potential, saving of natural uranium resources, and waste disposal of the conventional uranium fuel cycle. The objective of this talk is to provide an overview of some of the recent studies examining implementation scenarios, potential benefits and drawbacks associated with the use of Th-based fuels in current generation of PWRs.
  • Invited lecture (Conferences)
    494. Wilhelm und Else Heraeus-Seminar on Innovative Nuclear Power in a Closed Fuel Cycle Scenario, 05.-08.12.2011, Physikzentrum Bad Honnef, Germany

Publ.-Id: 15990 - Permalink


Paradox of Velikhov-Chandrasekhar and the ultimate limit for the onset of helical magnetorotational instability
Oleg N. Kirillov, F. S.;
The magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable accretion discs. By using theWKB approximation and methods of singular function theory, we resolve two different paradoxes of MRI that appear in the limits of infinite and vanishing magnetic Prandtl number. For the latter case we derive a new strict limit of the critical Rossby number. This new limit of Roc = −0.802, which appears for a finite Lundquist number of Lu= 0.618, extends the formerly known inductionless Liu limit of Roc = −0.828 valid at Lu = 0.
Keywords: MHD, Rossby number, Lundquist number, helical magnetorotational instability
  • Lecture (Conference)
    17th International Couette-Taylor Workshop, 25.-27.07.2011, University of leeds, United Kingdom

Publ.-Id: 15988 - Permalink


Standard and helical magnetorotational instability: How singularities create paradoxal phenomena in MHD
Kirillov, O. N.; Stefani, F.;
The magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable rotating shear flows, e.g., in Couette-Taylor cells and in accretion disks. What laws of differential rotation are susceptible to the destabilization by the axial or helical magnetic field? The answer to this vital for astrophysical and experimental applications question inevitably leads to the study of spectral and geometrical singularities on the instability threshold. The singularities provide a connection between seemingly discontinuous stability criteria and thus explain paradoxes in the theory of MRI that were kept poorly understood since 1950s. By using the WKB approximation and methods of singular function theory, we resolve two different paradoxes of magnetorotational instability that appear in the limits of infinite and vanishing magnetic Prandtl number. For the latter case we derive a new strict limit of the critical Rossby number. This new limit of Roc = −0.802, which appears for a finite Lundquist number of Lu = 0.618, extends the formerly known inductionless Liu limit of Roc = −0.828 valid at Lu = 0.
Keywords: Magnetorotaional instability, singularity theory, helical magnetorotational instability, Rayleigh line, Velikhov-Chandrasekhar paradox, inductionless HMRI
  • Invited lecture (Conferences)
    Kolloquium des Instituts für Analysis, Dynamik und Modellierung, 13.-15.07.2011, Universität Stuttgart, Deutschland

Publ.-Id: 15987 - Permalink


Singularities in Structural Optimization of the Ziegler Pendulum
Kirillov, O. N.;
Structural optimization of non-conservative systems with respect to stability criteria is a research area with important applications in fluid-structure interactions, friction-induced instabilities, and civil engineering. In contrast to optimization of conservative systems where rigorously proven optimal solutions in buckling problems have been found, for nonconservative optimization problems only numerically optimized designs have been reported. The proof of optimality in non-conservative optimization problems is a mathematical challenge related to multiple eigenvalues, singularities in the stability domain, and non-convexity of the merit functional. We present here a study of optimal mass distribution in a classical Ziegler pendulum where local and global extrema can be found explicitly. In particular, for the undamped case, the two maxima of the critical flutter load correspond to a vanishing mass either in a joint or at the free end of the pendulum; in the minimum, the ratio of the masses is equal to the ratio of the stiffness coefficients. The role of the singularities on the stability boundary in the optimization is highlighted, and an extension to the damped case as well as to the case of higher degrees of freedom is discussed.
Keywords: Parametric optimization, singularities on the stability boundary, non-conservative system, non-self-adjoint operator, Jordan block
  • Open Access LogoActa Polytechnica 51(2011)4, 32-43

Publ.-Id: 15986 - Permalink


Paradoxes of magnetorotational instability and their geometrical resolution
Kirillov, O. N.; Stefani, F.;
Magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable accretion discs. By using the WKB approximation and methods of singular function theory, we resolve two different paradoxes of MRI that appear in the limits of infinite and vanishing magnetic Prandtl number. For the latter case, we derive a strict limit of the critical Rossby number. This limit of Roc=−0.802, which appears for a finite Lundquist number of S=0.618, extends the formerly known inductionless Liu limit of Roc=−0.828 valid at S=0.
Keywords: Standard magnetorotational instability, helical magnetorotational instability, paradox of Velikhov and Chandrasekhar, paradox of inductionless HMRI, Liu limit, magnetic Prandtl number, WKB, Plucker conoid

Publ.-Id: 15984 - Permalink


Materials research at the Helmholtz-Beamline at European XFEL: Ideas for proposals
Posselt, M.;
not available, please contact the author
Keywords: laser-solid interaction, ion-solid interaction, kinetic processes, X-ray analysis, XFEL
  • Lecture (Conference)
    Workshop on Petawatt-Lasers at Hard X-Ray Light Sources Dresden-Rossendorf, September 5 to 9, 2011, 05.-09.09.2011, Dresden, Germany

Publ.-Id: 15983 - Permalink


TEM investigation contributing to the comprehension of superconductivity in Ga-doped Si
Mücklich, A.; Fiedler, J.; Heera, V.;
TEM investigation contributing to the comprehension of superconductivity in Ga-doped Si
Keywords: Ga ion implantation, rapid thermal annealing, superconductivity
  • Poster
    MC2011, Microscopy Conference 2011, 28.08.-02.09.2011, Kiel, Deutschland

Publ.-Id: 15982 - Permalink


Electrical properties of ZnO nanorods studied by conductive atomic force microscopy
Beinik, I.; Kratzer, M.; Wachauer, A.; Wang, L.; Lechner, R. T.; Teichert, C.; Motz, C.; Anwand, W.; Brauer, G.; Chen, X. Y.; Hsu, X. Y.; Djurisic, A. B.;
ZnO nanostructures are promising candidates for the development of novel electronic devices due to their unique electrical and optical properties. Here, we present a complementary electrical characterization of individual upright standing and lying ZnO nanorods using conductive atomic force microscopy (C-AFM). Initially, the electrical properties of the arrays of upright standing ZnO NRs were characterized using two-dimensional current maps. The current maps were recorded simultaneously with the topography acquired by contact mode AFM. Further, C-AFM was utilized to determine the local current-voltage (I-V) characteristics of the top and side facets of individual upright standing NRs. Current-voltage characterization revealed a characteristic similar to that of a Schottky diode. Detailed discussion of the electrical properties is based on local I-V curves, as well as on the 2D current maps recorded from specific areas.
Keywords: ZnO nanorods, conductive atomic force microscopy, electrical properties

Publ.-Id: 15981 - Permalink


Deep level transient spectroscopic study of oxygen implanted melt grown ZnO single crystal
Ye, Z. R.; Lu, X. H.; Ding, G. W.; Fung, S.; Ling, C. C.; Brauer, G.; Anwand, W.;
Deep level traps in melt grown ZnO single crystal created by oxygen implantation and subsequent annealing in air were studied by deep level transient spectroscopy measurement between 80 and 300 K. The EC–0.29 eV trap (E3) was the dominant peak in the as-grown sample and no new defects were created in the as-O-implanted sample. The single peak feature of the deep level transient spectroscopy (DLTS) spectra did not change with the annealing temperature up to 750 °C, but the activation energy decreased to 0.22 eV. This was explained in terms of a thermally induced defect having a peak close to but inseparable from the original 0.29 eV peak. A systematic study on a wide range of the rate window for the DLTS measurement successfully separated the Arrhenius plot data originated from different traps. It was inferred that the E3 concentration in the samples did not change after the O-implantation. The traps at EC–0.11, EC–0.16 and EC–0.58 eV were created after annealing. The EC–0.16 eV trap was assigned to an intrinsic defect. No DLTS signal was found after the sample was annealed to 1200 °C.
Keywords: deep level transient spectroscopy, ZnO single crystal, oxygen implantation, deep level traps

Publ.-Id: 15980 - Permalink


Risiko und Risikoakzeptanz kerntechnischer Anlagen
Werner, M.;
Ausgehend von geeigneten Definitionen der zentralen Begriffe Zuverlässigkeit, Risiko und Sicherheit im technischen Sinn ergibt sich die grundsätzliche Möglichkeit der Bestimmung des Risikos für technische Systeme. Im Rahmen der Zuverlässigkeits- und Risikoanalyse können diese mathematisch belastbaren Definitionen auch die Stochastik von technischen Ausfällen und dadurch ausgelösten Unfällen berücksichtigen.
In Zusammenhang mit dem Sicherheitskonzept für deutsche Kernkraftwerke werden determinierte und probabilistische Methoden zur Bestimmung des Risikos bei der Nutzung der Kernenergie angewendet. Hierbei werden insbesondere auf das gestaffeltes Sicherheitskonzept, das Schutzzielkonzept sowie bestimmte Auslegungsprinzipien zur Verminderung des kerntechnischen Risikos eingegangen.
In einem weiteren Teil des Vortrages wird auf die Fragestellung im Umgang mit dem Restrisiko der kerntechnischen Nutzung eingegangen. Der Vergleich von wahrgenommenen mit tatsächlichen Risiken im technischen Bereich wie auch im Alltagsleben fällt häufig sehr unterschiedlich aus. Auch hängt die Akzeptanz eines Risikos sehr stark von einem zu erwartenden Nutzen ab.
Die methodische Darstellung von Risikoakzeptanz und Risikowahrnehmung auf der individuellen sowie auf der gesellschaftlichen Ebene ist nur im Rahmen komplexer Zusammenhänge möglich.
Keywords: risk analysis, risk acceptance, nuclear energy
  • Contribution to proceedings
    Zittauer Kraftwerkschemisches Kolloquium, 22.-23.09.2011, Zittau, Deutschland
    Wissenschaftliche Berichte der Hochschule Zittau/Görlitz

Publ.-Id: 15979 - Permalink


Time Efficient Fabrication of Ultra Large Scale Nano Dot Arrays Using Electron Beam Lithography
Grebing, J.; Faßbender, J.ORC; Erbe, A.
Many applications in plasmonics or sensorics require large scale arrays of nano-sized dot structures with rather high surface coverages. Typical dimensions, e.g., 50nm diameter, 200nm center-center distance, 1000µm × 1000µm arrays, quickly lead to extremely high numbers of objects in the design to be handled by both the software and the lithography system. In case of the aforementioned dimensions this would amount to be about 2.5 × 107 objects.

Using regular techniques the dots would be represented by a matrix of circles or dots in the design – or references to those, for that matter. Any changes in the layout of the structures would require a rather large effort since every object or reference would have to be edited. Additionally, with commonly used lithography systems the writing times quickly exceed reasonable values due to the beam settling times normally required for each object in the design. Even with values as low as 1ms the overall sum of the settling times would be roughly 7hrs. This is excluding the actual writing times!

The alternative method for the creation of ultra large scale nano dot arrays presented here is astonishingly simple and does not require any particular efforts: In electron beam lithography, exposure is based on single pixels – or dots – with defined distances (step size). The overlap of the single pixels yields the desired continuous structures. Thus, separating these pixels by the distance required for the lattice of nano dots, i.e., setting the step size to the lattice constant, would result in the desired lattice. This may be achieved by underexposing a regular rectangle by a factor of about 1/10 of the clearing dose, i.e., the result is a lattice of separated dots. The diameter of the dots may be adjusted within certain limits by the dose used for exposure.

As a result not only the writing times are strongly decreased – depending on the parameters many hours of processing time may be saved – but also handling of an array of dots is simplified to the action on rectangles or other shapes in the GDSII editor. No hassle with millions of dots is required.

As a proof of principle, different large lattices have been produced using a Raith 150TWO system in a lift-off process with PMMA or ZEP as resists on silicon. Additionally, a 4000µm × 4000µm lattice with a lattice constant of 500nm has been produced in an etching process with HSQ as the resist and reactive ion beam etching (RIBE) structuring gold on glas as a possible application for plasmonic sensors. Compared to the regular technique the processing times could be greatly reduced. The resulting samples show almost perfect lattices, the shape of the dots is also of good quality. Multiple exposures with shifted write fields also enables fabrication of hexagonal lattices or dipole structures.
Keywords: electron beam lithography, plasmonics, photonic crystal
  • Poster
    37th International Conference on Micro and Nano Engineering, 20.-23.09.2011, Berlin, Deutschland
  • Microelectronic Engineering 97(2012), 55-58
    DOI: 10.1016/j.mee.2012.05.029

Publ.-Id: 15978 - Permalink


Axisymmetric magnetic field modes in heterogeneous domains
Giesecke, A.; Stefani, F.; Gerbeth, G.;
Inspired by the setup of the von-K\'arm\'an-Sodium (VKS) dynamo experiment numerical simulations of the kinematic induction equation have been carried out in a cylindrical domain. A localized internal distribution of large relative permeability is considered that represents soft iron material within a conducting fluid flow.

So called paramagnetic pumping at the interface between fluid and soft iron causes a selective enhancement of the axisymmetric azimuthal field component, ultimately leading to a decoupling between poloidal and toroidal magnetic field. For moderate magnetic Reynolds numbers, the poloidal component decays faster than the toroidal part or the simplest non-axisymmetric mode ($m1$). This effect only concerns the necessarily decaying axisymmetric field and does not occur in case of a larger/smaller electrical conductivity.

The phenomenon requires a particular setup e.g. a thin disk-like permeability distribution and remains restricted to the axisymmetric field modes. However, these properties indeed apply to the VKS dynamo.

The separation of poloidal and toroidal modes might be important with regard to mean field dynamo models of the VKS dynamo since the decoupling effectively disrupts the possibility for a closure of the dynamo cycle. However, the separation of the axisymmetric field modes can be prevented by an non-axisymmetric permeability distribution, which might give a hint why dynamo action is absent in experiments where the fluid flow is driven by an impeller system composed of soft iron disks and stainless steel blades.
Keywords: Dynamo
  • Lecture (Conference)
    iGDR Meeting, Cargesse 2011, 12.-16.09.2011, Cargese, France

Publ.-Id: 15976 - Permalink


Vibrational spectroscopy of actinyl complexes
Gückel, K.;
Vibrational spectroscopy potentially provides structural information of molecule complexes. Actinyl ions can be identified by the frequency of their antisymmetric stretching vibrational mode which generally correlates with the character of the molecular environment of the actinyl ion group.
In this study the sorption behavior and the formed complexes of Uranium(VI) on gibbsite in inert gas and ambient atmosphere were analyzed by means of ATR FT-IR spectroscopy.
  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Deutschland

Publ.-Id: 15975 - Permalink


Temperature Impact on the Sorption of Selenate onto Anatase
Franzen, C.; Jordan, N.; Müller, K.; Meusel, T.; Brendler, V.;
The radioactive isotope Selenium-79 is a long-lived fission product found in nuclear waste. Due to its long half live of 3.27 ∙ 105 years [1] it is expected to be one of the most contributing isotopes concerning safety assessments of nuclear waste underground repositories. The control of the mobility and bioavailability of selenium is therefore of great importance for a safe disposal of radioactive waste.
One major process controlling selenium mobility and bioavailability is the adsorption onto mineral surfaces of both the geological and engineered barrier.
The present study focuses on the impact of temperature on the sorption of selenate (SeO42-) onto anatase (TiO2). The sorption of selenate onto anatase at different temperatures (25°C – 60°C) was investigated both with batch experiments and ATR-FT-IR spectroscopy. In order to explain possible differences in sorption at higher temperatures, the surface of the anatase was investigated.
Keywords: Selenate; Se(VI); Anatase; Sorption; HighTemperatures
  • Poster
    HiTAC Workshop, 09.11.2011, Karlsruhe, Deutschland

Publ.-Id: 15974 - Permalink


Tectonic implications of fluvial incision and pediment deformation at the northern margin of the Central Anatolian Plateau based on multiple cosmogenic nuclides
Yildirim, C.; Schildgen, T.; Echtler, H.; Melnick, D.; Bookhagen, B.; Çiner, A.; Niedermann, S.; Merchel, S.; Martschini, M.; Steier, P.; Strecker, M.;
We document Quaternary fluvial incision driven by fault-controlled surface deformation in the inverted intermontane Gökırmak Basin in the Central Pontide mountains along the northern margin of the Central Anatolian Plateau. In situ-produced 10Be, 21Ne and 36Cl concentrations from gravel-covered fluvial terraces and pediment surfaces along the trunk stream of the basin (the Gökırmak River) yield model exposure ages ranging from 7.0 ± 0.6 ka to 337 ± 43 ka and average fluvial incision rates over the past ~340 ka of 0.28 ± 0.01 mm a-1. Similarities between river incision rates and coastal uplift rates support the inference that regional uplift is responsible for the river incision. Model exposure ages of surfaces on deformed pediments along tributaries of the trunk stream range from 48 ± 4 ka to 96 ± 9 ka, demonstrating that the thrust faults responsible for the pediment deformation were active at least until those times, and possibly remained active afterwards. Together, our data demonstrate cumulative incision that is linked to active internal shortening and uplift of ~0.3 mm a-1 in the Central Pontide orogenic wedge at the northern margin of the Central Anatolian Plateau.
Keywords: Central Anatolian Plateau, Northern Margin, Central Pontides, Orogenic Wedge, Fluvial Incision, Uplift, accelerator mass spectrometry, TCN, terrestrial cosmogenic nuclide, exposure age

Publ.-Id: 15973 - Permalink


Langlebige Radionuklide in Geo-/Biosystemen
Steudtner, R.; Großmann, K.; Joseph, C.; Vogel, M.; Brendler, V.;
Nach der Katastrophe in Fukushima im März 2011 beschloss die Bundesregierung den schrittweisen Ausstieg aus der Atomenergie bis zum Jahre 2022. Innerhalb dieser elf Jahre sollen die neun verbliebenen Atomkraftwerke vom Netz genommen werden. Aber in diesen Zeitraum wird es keine endgültige Lösung zum Thema der Endlagerung in Deutschland geben. Zurzeit werden die in Deutschland anfallenden radioaktiven Abfälle in Zwischenlager gebracht. Für schwach- und mittelradioaktive Stoffe sind es die Landessammelstellen der Bundesländer. Die Kernkraftwerke und Forschungseinrichtungen besitzen standortbezogene Zwischenlager. Die hochradioaktiven Abfälle aus der Wiederaufarbeitung abgebrannter Brennelemente werden nach der erteilten Genehmigung zur Aufbewahrung in den zwei zentralen Zwischenlagern in Ahaus und Gorleben gelagert.
Für die Genehmigung zum Bau eines Endlagers muss der Sicherheitsnachweis zur Endlagersicherheit geführt werden. Der umfassende Sicherheitsnachweis enthält die Aspekte der Errichtungs- und Betriebsphase (Sicherheitsnachweise für die Betriebsphase) und die Aspekte der Nachbetriebsphase im Langzeitsicherheitsnachweis. Im Langzeitsicherheitsnachweis werden alle qualitativen und quantitativen Analysen und Argumente zur Begründung der Sicherheit für die Nachbetriebsphase eines Endlagersystems zusammengeführt [1]. Der Langzeitsicherheitsnachweis unterteilt sich in:
­ - die Langzeitsicherheitsanalyse mit Konsequenzenanalyse,
­ - Aussagen zur Robustheit und Zuverlässigkeit der Sicherheitsbewertung,
­ - Ergänzende Argumente: Indikatoren, Analoga, etc.
Die Langzeitsicherheitsanalyse kann als die standortspezifische Analyse der Funktion des Endlagersystems im Hinblick auf die radiologischen Konsequenzen verstanden werden und beinhaltet die Untersuchung des zukünftigen Verhaltens eines verschlossenen Endlagers mit radioaktiven Abfällen innerhalb eines vorgegebenen Nachweiszeitraums (1 Million Jahre) [1].
Ziel der Langzeitsicherheitsanalyse ist es mögliche Ursachen und Abläufe einer Freisetzung von Radionukliden aus einem verschlossenen Endlager sowie deren zukünftige Auswirkungen auf die Umwelt und die Bevölkerung vorherzusagen.
Die derzeitig sicherste Entsorgung für radioaktive Stoffe ist die Endlagerung in tiefen geologischen Formationen [2]. Diese Lagerung weist ein Multibarrierensystem auf, welches die radioaktiven Abfälle von der Biosphäre isolieren soll. Ein aus mehreren unabhängigen Barrieren bestehendes System soll den Schadstoffaustrag aus dem Endlager wirkungsvoll verhindern [3]. Es setzt sich zusammen aus:
­ - Technische Barriere
o Brennstoffmatrix
o Container
­ - Geotechnische Barriere
o Verfüllung der Bohrlöcher
o Untertägiges Dammsystem
o Verfüllung des Schachtsystems
­ - Geologische Barriere
o Wirtsformation (Salz, Granit, Ton)
o Deckgebirge mit Aquifersystem
In der Langzeitsicherheitsanalyse wird angenommen, dass es im Endlager zum Wassereintritt kommt. Dies hat zur Folge, dass die Behälter korrosiv zersetzt werden und es zur Auflösung der Abfallmatrix kommt. Infolgedessen können die Radionuklide mobilisiert werden und durch die verschiedenen Barrieren in die Biosphäre gelangen. Während des Transportes von der Geo- zur Biosphäre können die freigesetzten Radionuklide eine Vielzahl von Wechselwirkungen eingehen. Dabei spielen neben ihrem Komplexbildung-, Sorption- und Diffusionsverhalten, die Kolloidbildung und die Wechselwirkungen mit Mikroorganismen, Biofilmen, Pflanzen und letztendlich mit dem menschlichen Organismus die wichtigsten Rollen. Wir, das Institut für Radiochemie, wollen mit Hilfe unserer umfangreichen analytischen Möglichkeiten zur Identifizierung und Beschreibung der ablaufenden Prozesse beitragen. An fünf Beispielen sollen die verschiedenen Arbeiten im Institut für Radiochemie (IRC) näher vorgestellt werden.

1. Fein, E., I. Müller-Lyda, and A. Rübel, Endlagerung wärmeentwickelnder radioaktiver Abfälle in Deutschland, in Wissenschaftlich-Technische Berichte GRS-247. 2008, Gesellschaft für Anlagen- und Reaktorsicherheit mbH: Braunschweig / Darmstadt.
2. Auswahlverfahren für Endlagerstandorte, Empfehlungen des AkEnd – Arbeitskreis Auswahlverfahren Endlagerstandorte. 2002: (www.akend.de).
3. Geckeis, H., V. Metz, and B. Kienzler, Geochemisches Verhalten der Radionuklide im Multibarrierensystem nuklearer Endlager. Nachrichten - Forschungszentrum Karlsruhe, 2004. 36(2): p. 110-115.
Keywords: Uran, Endlager, Speziation
  • Invited lecture (Conferences)
    Zittauer Kraftwerkschemisches Kolloquium, 22.09.-23.11.2011, Lückendorf, Deutschland
  • Contribution to proceedings
    Zittauer Kraftwerkschemischen Kolloquium, 22.09.-23.11.2011, Lückendorf, Deutschland

Publ.-Id: 15972 - Permalink


Preliminary multi-method spectroscopic approach for the uranium(VI) hydrolysis at temperatures up to 60°C
Steudtner, R.; Müller, K.; Meusel, T.; Brendler, V.;
For the safety assessment of high-level nuclear waste repositories in deep geologic formations, the understanding of actinide migration behaviour is one of the most important issues. In recent decades, the solution chemistry, e.g. hydrolysis [1], complexation with inorganic ligands [1], but also the interactions of the actinides at interfaces with the geo- and biosphere have been intensely investigated [2]. However, because of the experimental difficulties, only few studies have been performed at temperatures outside the range 20 – 30°C which hampers the prediction of actinide reactive transport in the environment of heat generating high-level nuclear waste repositories.
The speciation of (radioactive) metal ions in solution will be affected by the thermal conditions, since the properties of water, e.g. density, dielectric constant, viscosity, ion product, are altered with temperature and pressure [3,4].
The formation and distribution of U(VI) hydrolysis species is predicted to depend strongly on the temperature. In particular the stability of U(VI) polynuclear hydroxo complexes, which are dominant species at 25°C may change. According to experimental studies of other metal ions, namely Al(III) and La(III), the nuclearity of polynuclear complexes decreases upon increasing temperature [5,6]. At 25°C several spectroscopic techniques, namely UV-vis, TRLFS, EXAFS and vibrational spectroscopy have been applied for identification and structural characterization of U(VI) hydroxo species [7-10]. At elevated temperatures, TRLFS was used for the determination of luminescent characteristics of single hydroxo species as a function of the temperature [11,12]. But, approaches to examine alterations in the thermodynamic data itself are rare.
In this study, we investigate the U(VI) hydrolysis reactions up to 60°C using a multi-methodical approach by application of TRLFS and ATR FT-IR spectroscopy. The spectral data is compared to computed speciation patterns based on state-of-the-art thermodynamic models.

1.Guillaumont, R. et al., Update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technetium. Chemical Thermodynamics Vol. 5, OECD Nuclear Energy Agency, Elsevier (2003).
2.Brendler, V. et al., RES3T-Rossendorf expert system for surface and sorption thermodynamics, Journal of Contaminant Hydrology 281-291 (2003).
3.Marshall, W.L. et al., Io product of water substance, 0 - 1000°C, 1-10,000 bars - New international formulation and its background, Journal of Physical and Chemical Reference Data 2, 295-304 (1981).
4.Fernandez, D.P. et al., A formulation for the static permittivity of water and steam at temperatures from 238 K to 873 K at pressures up to 1200 MPa, including derivatives and Debye-Huckel coefficients, Journal of Physical and Chemical Reference Data 4, 1125-1166 (1997).
5.Mesmer, R.E. et al., Acidity measurements at elevated temperatures. 5. Aluminum ion hydrolysis, Inorg. Chem. 10, 2290-2296 (1971).
6.Ciavatta, L. et al., The hydrolysis of the La(II) ion in aqueous perchlorate solution at 60°C, Polyhedron 6, 1283-1290 (1987).
7.Meinrath, G., Uranium(VI) speciation by spectroscopy, J. Radioanal. Nucl. Chem. 1-2, 119-126 (1997).
8.Moulin, C. et al., Time-resolved laser-induced fluorescence as a unique tool for low-level uranium speciation, Appl. Spectrosc. 4, 528-535 (1998).
9.Müller, K. et al., Aqueous uranium(VI) hydrolysis species characterized by attenuated total reflection Fourier-transform infrared spectroscopy, Inorg. Chem. 21, 10127-10134 (2008).
10.Tsushima, S. et al., Stoichiometry and structure of uranyl(VI) hydroxo dimer and trimer complexes in aqueous solution, Inorg. Chem. 25, 10819-10826 (2007).
11.Eliet, V. et al., Time-resolved laser-induced fluorescence of uranium(VI) hydroxo-complexes at different temperatures, Appl. Spectrosc. 1, 99-105 (2000).
Keywords: U(VI), TRLFS, ATR FT-IR, high temperature
  • Poster
    HiTAC - High Temperature Aqueous Chemistry, 09.11.2011, Karlsruhe, Deutschland

Publ.-Id: 15971 - Permalink


Nano-structure analysis of Fe implanted SnO2 films by 57Fe and 119Sn CEMS
Nomura, K.; Reuther, H.;
SnO2 films were implanted with 57Fe at substrate temperatures of room temperature and 300°C. The chemical states of Fe and Sn were characterized by 57Fe CEMS and 119Sn CEMS, respectively. The implanted Fe species exist as Fe(II) and Fe(III) in SnO2 films, which also are reduced into Sn(II)on the implanted surface. The as prepared and post annealed at 500°C samples did not show Kerr effect, but the sample implanted with 1 × 1017 Fe ions/cm2 at 300°C showed Kerr effect although magnetic sextets were not clearly observed in the 57Fe CEM spectra. The Kerr effect disappeared after annealing. It suggests that the number of magnetic defects decreases by absorption of oxygen. Magnetic relaxation appeared in the case of low implantation of 5 × 1016 Fe ions/cm2, which is considered to be due to antiferromagnetism or paramagnetic relaxation.

Publ.-Id: 15970 - Permalink


Planar optical waveguides in Bi4Ge3O12 crystal fabricated by swift heavy-ion irradiation
Yang, J.; Zhang, C.; Chen, F.; Akhmadaliev, S.; Zhou, S.;
We report on the fabrication of the planar waveguides in the Bi4Ge3O12 crystal by using 17 MeV C5+ or O5+ ions at a fluence of 2×1014 ions/cm2. The reconstructed refractive index profiles of the waveguides produced by either C5+ or O5+ irradiation are the “well” + “barrier” pattern distribution. The two-dimensional modal profiles of the planar waveguides, measured by using the end-coupling arrangement, are in good agreement with the simulated modal distributions. After thermal annealing treatment at 260°C for 30 min, the propagation loss for C5+ and O5+ irradiated waveguides could be reduced down to ~1.1 dB/cm and ~4.8 dB/cm, respectively, which exhibit acceptable guiding qualities for potential applications in integrated optics.
Keywords: Integrated optics devices; Waveguides

Publ.-Id: 15969 - Permalink


Direct observation of preferential transport pathways in salt rocks by means of GeoPET
Kulenkampff, J.; Enzmann, F.; Gründig, M.; Wolf, M.; Lippold, H.; Lippmann-Pipke, J.;
Migration of radionuclides out of a salt-based repository requires transport pathways, where substances propagate by molecular diffusion or even pressure-driven advection. Diffusion coefficients and permeability, being very low in most intact saline rocks, are likely to increase considerably under geomechanical stress, inevitably occurring for instance in the excavation damage zone. Observation and evaluation of transport processes in such heterogeneously structured materials are most demanding, because they likely occur in either extremely localized, macroscopic but rare fractures or in dispersed, mostly indiscernible but still connected microscopic voids.
Applying salt solutions labelled with radionuclides we are able to observe such processes directly and - presumably for the first time with due resolution and sensitivity – with our GeoPET method. The same processes are studied with Lattice-Boltzmann flow simulations on µCT-based images of the same samples. This strategy contrasts the common use of computer simulations based on a priori material parameters, and allows for the matching of flow simulation results in “real structures” with real time flow monitoring in the same samples. Here we report on results obtained from a number of drill cores from the ancient Stassfurt salt mine and its overburden, including aged backfill material, which has been analysed in the framework of our joint research project, funded by the Federal Ministry of Education and Research (BMBF) (Wolf et al., 2010).
Keywords: PET, reactive transport, Lattice Boltzmann, transport experiments
  • Lecture (Conference)
    ABC-Salt Workshop, 07.-08.11.2011, Karlsruhe, Deutschland

Publ.-Id: 15968 - Permalink


16 kW Upgrade of the 1.3 GHz ELBE RF-System with Solid State Amplifiers
Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.;
The superconducting CW- LINAC (1.3 GHz) of the radiation source ELBE is in permanent operation since May 2001/1/. In 2011 an upgrade program of ELBE is in progress to support additional applications. One part of the program is to double the RF-power per cavity to at least 16 kW. Since we started ELBE in May 2001 substantial progress was made in all fields contributing accelerator science. As far as RF-amplifier technology is concerned IOT-based and Solid State Amplifiers compete with klystrons. To prepare for the power upgrade of ELBE we developed a couple of activities, like:
Test of the ELBE RF-couplers and waveguide windows
Test of an available 30 kW IOT amplifier with beam
Test of a 10 kW solid state amplifier (SSPA) with beam
Test of two 10 kW SSPA’ s with beam
Redesign of the Low level RF controller
Redesign of the technical water cooling.
Keywords: LINAC RF ELBE RF 1300 MHz Solid State Power Amplifiers 1,3 GHz SSPA SC LINAC Power RF LINAC RF IOT Paralleling Solid State Power Rf Amplifiers
  • Open Access LogoContribution to proceedings
    IPAC 2011 (Second International Particle Accelerator Conference), 04.-09.09.2011, San Sebastian, Spain
    16 kW Upgrade of the 1.3 GHz ELBE RF-System with Solid State Amplifiers: JACoW, 379-381
  • Poster
    IPAC 2011, 04.-09.09.2011, San Sebastian, Spain

Publ.-Id: 15967 - Permalink


Microspectroscopy on perovskite-based superlenses
Kehr, S. C.; Yu, P.; Liu, Y. M.; Parzefall, M.; Khan, A. I.; Jacob, R.; Wenzel, M. T.; Ribbeck, H.-G.; Helm, M.; Zhang, X.; Eng, L. M.; Ramesh, R.;
Superlenses create sub-diffraction-limit images by reconstructing the evanescent fields arising from an object. We study the lateral, vertical, and spectral field distribution of three different perovskite-based superlenses by means of scattering-type near-field microscopy. Subdiffraction- limit resolution is observed for all samples with an image contrast depending on losses such as scattering and absorption. For the three lenses superlensing is observed at slightly different frequencies resulting in an overall broad frequency range of 3.6 THz around 20 THz.
Keywords: superlens, terahertz, perovskite, oxide, near-field microscopy, free-electron laser
  • Open Access LogoOptical Materials Express 1(2011), 1051-1060

Publ.-Id: 15966 - Permalink


XPS analysis and valence band structure of a low-dimensional SiO2/Si system after Si+ ion implantation
Zatsepin, D. A.; Mack, P.; Wright, A. E.; Schmidt, B.; Fitting, H.-J.;
A X-ray photoelectron spectroscopy (XPS) of valence band (VB) and core levels are performed for a SiO2/p-Si heterostructure containing a thin oxide layer of d = 20 nm thickness and implanted by Siþ ions. With an implantation energy of 12 keV the maximum density of the implanted Si+ profile is located close to the SiO2–Si interface at a depth of 18 nm, but a piling-up of Si is also found immediately beneath the surface up to 2 nm, i.e., within the escape depth of XPS electrons. Thus we may expect a partial phase separation associated with Si aggregation and nanocluster formation imbedded in a nonstoichiometric SiOx matrix. By means of XPS and in comparison to X-ray emission spectroscopy (XES) the related changes of the VB structure are investigated.
Keywords: electronic structure, ion implantation, SiO2, X-ray emission spectra, X-ray photoelectron spectra

Publ.-Id: 15965 - Permalink


Large-eddy simulation of single-phase pressurized thermal shock
Loginov, M. S.; Shams, A.; Komen, E.; Höhne, T.;
Pressurized Thermal Shock (PTS) is identified as one of the safety issues where Computational Fluid Dynamics (CFD) can bring real benefits. Turbulence modeling may impact the overall accuracy of the calculated thermal loads on the Reactor Pressure Vessel (RPV) walls. Therefore advanced methods for turbulent flows are required. In the current paper, we summarize our efforts on large-eddy simulations (LES) of a complex turbulent mixing in the RPV. First, the mesh resolution is investigated, and a comparison procedure is established. The analysis have shown necessity of comparison in both time and frequency domains. Next, a validation against experiment is performed using three cases with different flow rates in the primary loop. The validation results have successfully reproduced the flow patterns and have shown good quantitative agreement for the near-wall temperature drop.
Keywords: CFD, LES, PTS
  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Kanada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), CD-ROM
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Kanada

Publ.-Id: 15964 - Permalink


Multi.Modal Imaging Using Bispidine-Derivatives
Fähnemann, S.;
kein Abstract verfügbar
  • Lecture (Conference)
    8th Supraphone Meeting, 07.-10.09.2011, Funchal, Portugal

Publ.-Id: 15963 - Permalink


Mehrfunktionelle Bispidinderivate für die duale Bildgebung
Fähnemann, S.; Walther, M.; Stephan, H.; Steinbach, J.;
Die Multimodale Bildgebung („Molecular Imaging“) ermöglicht durch die Kombination unterschiedlicher Verfahren eine verbesserte Diagnostik und ist damit Grundlage für eine zielgerichtete personalisierte Therapie von komplexen Krankheiten, wie z.B. Krebs. In diesem Zusammenhang werden insbesondere Computertomographie (CT), Magnetresonanztomographie (MRT), Positronen-Emissions-Tomographie (PET), Single- Photon-Emission-Computed-Tomography (SPECT) und optische Bildgebung eingesetzt [1, 2].
Derivate von 3,7-Diaazabicyclo[3.3.1]nonanen (Bispidine) bieten die Möglichkeit für ein duales Labeling. Sie bilden sehr stabile Komplexe mit radioaktiven Kupferisotopen und gestatten nach entsprechender Funktionalisierung mit Vektormolekülen eine Visualisierung von Tumoren mittels PET [3]. Bispidinliganden verfügen darüber hinaus über weitere funktionelle Gruppen, die die Einführung von Farbstoffen und zielsuchenden Molekülen gestatten.

Die Funktionalisierung der Hydroxygruppe (C9-OH) des Bispidins mit einem Fluoreszenzfarbstoff kann mittels Aktivesterbildung durch Umsetzung mit Chlorameisensäurenitrophenylester und anschießender Urethanbildung mit einem aminofunktionalisierten Farbstoffmolekül realisiert werden.
Es wird über die Synthese derartiger Liganden sowie die Charakterisierung der Fluoreszenzeigenschaften und die Markierung mit dem PET-Radionuklid 64 Cu berichtet.

Literatur:

[1] J.V. Frangioni, J. Clin. Oncol. 2008, 26, 4012-4021.
[2] A. Louie, Chem. Rev. 2010, 110, 3146-3195.
[3] S. Juran, M. Walther, H. Stephan, R. Bergmann, J. Steinbach, W. Kraus, F. Emmerling, P. Comba, Bioconjugate Chem. 2009, 20, 347-359.
  • Poster
    GDCH-Wissenschaftsforum 2011, 04.-07.09.2011, Bremen, D

Publ.-Id: 15962 - Permalink


Multiple Spectroscopic and Microscopic Study on Hydrolysis of Tetravalent Cerium: In-situ Characterization of Ce(IV) Hydrolytic Species in an Aqueous Solution
Ikeda, A.;
Because of its chemical similarity and stable tetravalent oxidation state in solution, cerium (Ce) is often employed as an analogue of tetravalent actinides (An(IV)) in various research fields related with actinides. Besides, its dioxide compound, CeIVO2, has recently attracted considerable attention owing to its wide variety of industrial applications, such as catalysis, oxygen storage, fuel cells, or luminescent materials.
Hydrolysis is one of the most fundamental reactions of metal ions in an aqueous solution. In fact, the hydrolysis behaviour of tetravalent cerium (Ce(IV)) has been studied and often compared with those of An(IV) in order to evaluate its suitability as an analogue of An(IV). Furthermore, the hydrolysis–precipitation process of cerium ions is also of great importance in its industrial applications, since it is one of the most straightforward and simple methods to produce CeO2. However, despite these importance of hydrolysis reaction in the basic- and applied research fields for Ce, most of the precedent studies have focused on its thermodynamical aspects, and still little has been known about the complex structure of Ce(IV) hydrolytic species formed in solution. In this study, multi-spectroscopic (i.e., X-ray absorption spectroscopy (XAS), high energy X-ray scattering (HEXS), dynamic light scattering (DLS)) and microscopic (TEM) techniques have been employed to structurally characterize the hydrolytic Ce(IV) species in an aqueous solution. The results indicate that nanocrystalline CeO2 forms and grows up in an aqueous solution as the hydrolysis proceeds with increasing pH. On the presentation, the results will be also discussed with the corresponding An(IV) hydrolytic species.
Keywords: lanthanides, cerium, Ce(IV), hydrolysis, XAS, HEXS, DLS, TEM
  • Invited lecture (Conferences)
    Lecture (invited), 27.09.2011, Strasbourg, France

Publ.-Id: 15961 - Permalink


Immobilization of uranium in biofilm microorganisms exposed to groundwater seeps over granitic rock tunnel walls in Olkiluoto, Finland
Krawczyk-Bärsch, E.; Lünsdorf, H.; Arnold, T.; Bok, F.; Steudtner, R.; Pedersen, K.; Lehtinen, A.; Brendler, V.;
In the underground rock characterization facility tunnel "ONKALO" in Finland massive biofilms were observed attached to the fractured bedrock at a depth of 70 m. Experiments were performed in the laboratory to study the effect on the behavior of uranium in biofilms by adding uranium to the fracture water with a final uranium concentration (4 x10-5 M) relevant for what can be expected from an injured and leaking waste canister in the far-field during a nuclear event in a HLW repository. The results obtained by analysis, microsensor measurements, TRLFS investigation, EF-TEM/EELS studies and thermodynamic calculations clearly indicate that biofilms have to be considered as microenvironments, which differ significantly from the surrounding medium. Inside the biofilm a pH of 5.37 was recorded, which is about 3.5 units lower than the pH of the surrounding fracture water. Similarly, the redox potential of +73 mV is approximately 420 mV lower than the redox potential measured in the fracture water. The addition of uranium results in an increase of the pH in the biofilm to 7.27 and a decrease of the redox potential to -164 mV mV. The changes of redox potential and pH are influencing the bioavailability of uranium since microbial metabolic processes are sensitive to metals and their speciation. EF-TEM investigations showed that in the biofilm uranium was immobilized intracellular in bacteria by a biologically mediated uranyl phosphate formation similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O). In contrast, TRLFS studies of the contaminated fracture water showed aqueous uranium carbonate species, most likely Ca2UO2(CO3)3, which was formed using the available high amount of carbonate from the water. The results are in agreement with the thermodynamic calculation of the theoretical predominance field of uranium species, formed in the uranium contaminated fracture water at the measured geochemical parameters.
Our studies clearly demonstrate that biological systems have to be considered as a part of natural systems in respect to radionuclide immobilization. They are contributing to an improved understanding on the response mechanisms of biofilms towards radionuclides in respect to safety assessments of the radioactive waste repositories.
Keywords: uranium, biofilms, microsensors, TEM, TRLFS, thermodynamic calculation

Publ.-Id: 15960 - Permalink


Electrochemical behaviour of tetrachloro and tetrabromo uranyl complexes in room temperature ionic liquids
Sornein, M.-O.; Cannes, C.; Le Naour, C.; Mendes, M.; Hennig, C.;
The redox properties of tetrahalo uranyl(VI) complexes ([UVIO2X4]2 with X = Cl or Br) have been investigated in the ionic liquids [BuMeIm][Tf2N] and [MeBu3N][Tf2N], where [BuMeIm]+ and [MeBu3N]+ are respectively the 1-butyl-3-methylimidazolium and the tributylmethylammonium cations, both associated with the bis(trifluoromethylsulfonyl)imide anion [Tf2N]. The results suggest that the reduction of [UVIO2X4]2 occurs via an Electron transfer – Chemical reaction – Electron transfer mechanism (ECE mechanism). We have shown by voltammetry that the first electron transfer is quasi-reversible and involves one electron, leading to the tetrahalo uranium(V) complex. This compound undergoes a chemical reaction and its stability depends both on the halide ligand and on the ionic liquid. The most stable complex is [UVO2Cl4]3 in [BuMeIm][Tf2N]. We have assumed that the [BuMeIm]+ cation interacts more strongly by H-bonding than the [MeBu3N]+ cation with the uranium complex, as it is the case for other anionic uranium species. Moreover, in presence of excess chloride ions, the consecutive chemical reaction is not observed anymore by cyclic voltammetry.
Keywords: Uranium, Ionic liquid, Redox properties, Tetrachloro complex, Tetrabromo complex

Publ.-Id: 15959 - Permalink


Uptake and binding of U(VI) by the green alga Chlorella vulgaris
Vogel, M.; Günther, A.; Raff, J.; Bernhard, G.;
For the risk assessment of radionuclides in the environment a comprehensive elucidation of the migration behavior of U(VI) in biosphere is necessary. Aim of this study was the quantitative and structural characterization of the interaction between U(VI) and the green alga Chlorella vulgaris at U(VI) concentrations from 5 μM to 1 mM, and in the pH range of 4.4 to 7.0 with special focus on metabolic activity. The obtained findings of the sorption experiments demonstrate clearly, the interactions with U(VI) are heavily influenced by the U(VI) concentration and the status of the Chlorella cells. Living cells bind in a 0.1 mM U(VI) solution at pH 4.4 within 5 min 14.3±5.5 mg U/g dry biomass and dead cells 28.3±0.6 mg U/g dry biomass. Furthermore, Chlorella cells die at concentration higher than 0.1 mM within 48 h. Interestingly, at lower U(VI) concentration of 5 μM, living cells firstly bind almost all U(VI) within the first 5 min of incubation. But then algal cells mobilize up to 80% of the bound U(VI) during ongoing incubation. The release of metabolism related substances is suggested to cause this mobilization of U(VI). As potential leachates for algal-bound U(VI) oxalate, citrate and ATP were tested and found to be able to mobilize more than 50% of the algal-bound U(VI).
The formed U(VI)-algae-complexes were structurally characterized by TRLF, EXAFS and ATR-FTIR spectroscopy. Obtained results demonstrate carboxylic and organic/inorganic phosphate groups were involved in the U(VI) complexation with varying contributions dependent on cell status, U(VI) concentration and pH.
With the help of TEM U(VI) was detected in form of 30-70 nm needle-like deposits in the cell wall of living algae.
Keywords: uranium, algae, Chlorella, biosorption, TRLFS, EXAFS, ATR-FTIR, TEM
  • Lecture (Conference)
    10th symposium on remediation/ 10. Sanierungskolloquium, 03.-05.10.2011, Jena, Deutschland

Publ.-Id: 15958 - Permalink


Long term irradiation phenomena in RPV steels - the LONGLIFE project
Altstadt, E.; Bergner, F.; Hein, H.;
The increasing age of European Nuclear Power Plants and envisaged extensions of reactor pressure vessel (RPV) lifetimes up to 80 years require the accurate prediction and management of RPV neutron irradiation embrittlement. LONGLIFE (“Treatment of long term irradiation embrittlement effects in RPV safety assessment”) is a collaborative project of the 7th Framework Programme of EURATOM. This project has been initiated as the next step forward towards obtaining an improved understanding of irradiation effects in RPV steels under conditions representative of long term operation (LTO) of RPVs. Phenomena which might become important at high neutron fluences (such as late-blooming effects and flux effects) must be considered in detail as part of the process of upgrading safety assessments and embrittlement surveillance procedures to underwrite the safety of LTO of RPVs. The work starts with the collection and evaluation of plant-specific information and data such as target neutron fluences for LTO and the chemical compositions of the materials. This includes a survey of available results of RPV materials data from decommissioned plants of validating surveillance data and studying specific irradiation effects relevant for LTO. Microstructural data are obtained from different techniques with the aim of assessing the adequacy of current dose-damage models with respect to their relevance to the mechanisms of irradiation damage associated with LTO of RPVs. Complementary mechanical tests are performed in order to address gaps in existing experimental data. Microstructural data pertaining to the evolution of irradiation damage are correlated with changes in mechanical properties, and the most important influencing factors will be identified. Surveillance guidelines for LTO of RPV base materials and welds will be developed as one of the principal outputs of the project. The scope of work and the project structure are outlined in the paper. Two LTO relevant phenomena – late blooming effect and flux effect – are discussed more detailed.
Keywords: Reactor Pressure Vessel Steel, Irradiation Embrittlement, Long Term Operation
  • Book chapter
    T. Yamamoto: Effects of Radiation on Nuclear Materials: 25th Volume, STP 1547, USA: ASTM International, 2013, 978-0-8031-7533-4, 096205STP
    DOI: 10.1520/STP104113

Publ.-Id: 15957 - Permalink


Single-ion induced surface nanostructures - A comparison between slow highly-charged and swift heavy ions
Aumayr, F.; Facsko, S.; El-Said, A. S.; Trautmann, C.; Schleberger, M.;
The present topical review focuses on recent advances in the understanding of the formation of surface nanostructures, an intriguing phenomenon in ion - surface interaction due to the impact of individual ions. In many solid targets, swift heavy ions produce narrow cylindrical tracks accompanied by the formation of a surface nanostructure. More recently, a similar nanometric surface effect has been revealed for the impact of individual, very slow but highlycharged ions. While swift ions transfer their large kinetic energy to the target via ionization and electronic excitation processes (electronic stopping), slow highly-charged ions produce surface structures due to potential energy deposited at the top surface layers. Despite the differences in primary excitation, the similarity between the nanostructures is striking and strongly points to a common mechanism related to the energy transfer from the electronic to the lattice system of the target. A comparison of surface structures induced by swift heavy ions and slow highly-charged ions provides valuable insight to better understand the formation mechanisms.
Keywords: highly-charged ions, swift heavy ions, ion-surface interaction, nanostructures, AFM, STM, hillocks, craters, pits, tracks, kinetic energy, potential energy, sputtering, electron emission, KBr, LiF, CaF2, BaF2, SrTiO3, TiO2, mica, polymers, PMMA, HOPG, Si, Au

Publ.-Id: 15956 - Permalink


Design of Radioligands for PET Imaging of Neuropsychiatric and Neurodegenerative Diseases
Brust, P.;
Es ist kein Abstract vorhanden.
  • Lecture (others)
    Kolloquium, 03.11.2011, Magdeburg, Deutschland

Publ.-Id: 15955 - Permalink


Numerical study of a bubble plume generated by bubble entrainment from an impinging jet
Zidouni Kendil, F.; Krepper, E.; Bousbia Salah, A.; Lucas, D.; Mataoui, A.;
The current paper presents the prediction results of a bubbly flow under plunging jet conditions using multiphase mono- and poly-dispersed approaches. The models consider interfacial momentum transfer terms arising from drag, lift, and turbulent dispersion force for the different bubble sizes. The turbulence is modeled by an extended k–ε model which accounts for bubble induced turbulence. Furthermore in case of a poly-dispersed air–water flow the bubble size distribution, bubble break-up and coalescence processes as well as different gas velocities in dependency on the bubble diameter are taken into account using the Inhomogeneous MUSIG model. This model is a generalized inhomogeneous multiple size group model based on the Eulerian modeling framework which was developed in the framework of a cooperative work between ANSYS-CFX and Forschungszentrum Dresden-Rossendorf (FZD). The latter is now implemented into the CFD code CFX.
According to the correlation on the lateral lift force obtained by Tomiyama (1998); this force changes its sign in dependence on the bubble size. Consequently the entrained small bubbles are trapped below the jet. They can escape from the bubble plume only by turbulent fluctuations or by coalescence. If the size of the bubbles generated by coalescence exceeds the size at which the lift force changes its sign these large bubbles go out from the plume and rise to the surface.
A turbulent model based on an additional source term for turbulence kinetic energy and turbulence eddy dissipation equation is compared to the common concept for modeling the turbulence quantities proposed by Sato et al. (1981). It has been found that the large bubble distribution is slightly affected by the turbulence modeling which affects particularly the bubble coalescence and break-up process.
Keywords: impinging jet, CFD, experiments, simulations, lift bubble force, population balance model

Publ.-Id: 15954 - Permalink


Structural, Electronic, and Magnetic Properties of Quasi-1D Quantum Magnets [Ni(HF2)(pyz)2]X (pyz = pyrazine; X = PF6-, SbF6-) Exhibiting Ni-FHF-Ni and Ni-pyz-Ni Spin Interactions
Manson, J. L.; Lapidus, S. H.; Stephens, P. W.; Peterson, P. K.; Carreiro, K. E.; Southerland, H. I.; Lancaster, T.; Blundell, S. J.; Steele, A. J.; Goddard, P. A.; Pratt, F. L.; Singleton, J.; Kohama, Y.; Mcdonald, R. D.; Del Sesto, R. E.; Smith, N. A.; Bendix, J.; Zvyagin, S. A.; Kang, J. H.; Lee, C.; Whangbo, M. H.; Zapf, V. S.; Plonczak, A.;
[Ni(HF2)(pyz)2]X {pyz = pyrazine; X = PF6- (1), SbF6- (2)} were structurally characterized by synchrotron X-ray powder diffraction and found to possess axially compressed NiN4F2 octahedra. At 298 K, 1 is monoclinic (C2/c) with unit cell parameters, a = 9.9481(3), b = 9.9421(3), c = 12.5953(4) angstrom, and beta = 81.610(3) degrees while 2 is tetragonal (P4/nmm) with a = b = 9.9359(3) and c = 6.4471(2) angstrom and is isomorphic with the Cu-analogue. Infinite one-dimensional (1D) Ni-FHF-Ni chains propagate along the c-axis which are linked via mu-pyz bridges in the ab-plane to afford three-dimensional polymeric frameworks with PF6- and SbF6- counterions occupying the interior sites. A major difference between 1 and 2 is that the Ni-F-H bonds are bent (similar to 157 degrees) in 1 but are linear in 2. Ligand field calculations (LFT) based on an angular overlap model (AOM), with comparison to the electronic absorption spectra, indicate greater pi-donation of the HF2- ligand in 1 owing to the bent Ni-F-H bonds. Magnetic susceptibility data for 1 and 2 exhibit broad maxima at 7.4 and 15 K, respectively, and lambda-like peaks in d chi T/dT at 6.2 and 12.2 K that are ascribed to transitions to long-range antiferromagnetic order (TN). Muon-spin relaxation and specific heat studies confirm these TN's. A comparative analysis of chi vs T to various 1D Heisenberg/Ising models suggests moderate antiferromagnetic interactions, with the primary interaction strength determined to be 3.05/3.42 K (1) and 5.65/6.37 K (2). However, high critical fields of 19 and 37.4 T obtained from low temperature pulsed-field magnetization data indicate that a single exchange constant (J(1D)) alone is insufficient to explain the data and that residual terms in the spin Hamiltonian, which could include interchain magnetic couplings (J(perpendicular)), as mediated by Ni-pyz-Ni, and single-ion anisotropy (D), must be considered. While it is difficult to draw absolute conclusions regarding the magnitude (and sign) of J(perpendicular) and D based solely on powder data, further support offered by related Ni(II)-pyz compounds and our LFT and density-functional theory (DFT) results lead us to a consistent quasi-1D magnetic description for 1 and 2.
  • Inorganic Chemistry 50(2011), 5990-6009

Publ.-Id: 15953 - Permalink


Frustrated couplings between alternating spin-1/2 chains in AgVOAsO4
Tsirlin, A.; Nath, R.; Sichelschmidt, J.; Skourski, Y.; Geibel, C.; Rosner, H.;
We report on the crystal structure and magnetic behavior of the spin-1/2 compound AgVOAsO4. Magnetic susceptibility, high-field magnetization, and electron spin resonance measurements identify AgVOAsO4 as a gapped quantum magnet with a spin gap Delta similar or equal to 13 K and a saturation field mu0Hs similar or equal to 48.5 T. Extensive band structure calculations establish the microscopic magnetic model of spin chains with alternating exchange couplings J similar or equal to 40 K and J' similar or equal to 26 K. However, the precise evaluation of the spin gap emphasizes the role of interchain couplings which are frustrated due to the peculiar crystal structure of the compound. The unusual spin model and the low energy scale of the exchange couplings make AgVOAsO4 a promising candidate for an experimental investigation of Bose-Einstein condensation in high magnetic fields.
  • Physical Review B 83(2011)14, 144412

Publ.-Id: 15952 - Permalink


Control of Rectifying and Resistive Switching Behavior in BiFeO3 Thin Films
Shuai, Y.; Zhou, S.; Wu, C.; Zhang, W.; Bürger, D.; Slesazeck, S.; Mikolajick, T.; Helm, M.; Schmidt, H.;
BiFeO3 thin films have been grown on Pt/Ti/SiO2/Si substrates with pulsed laser deposition using Au as the top electrode. The resistive switching property of the Au/BiFeO3/Pt stack has been significantly improved by carefully tuning the oxygen pressure during the growth, and a large switching ratio of ∼4500 has been achieved. The deposition pressure modifies the concentration of oxygen vacancies and the rectifying behavior of the Au/BiFeO3 junction, and consequently influences the resistive switching behavior of the whole stack. The switching takes place homogeneously over the entire electrode, and shows a long-term retention.
Keywords: resistive switching, BiFeO3, nonvolatile

Publ.-Id: 15951 - Permalink


Coherent control of a THz intersubband polarization in a voltage controlled single quantum well
Wagner, M.; Helm, M.; Sherwin, M. S.; Stehr, D.;
Ultrashort terahertz pulses in the far-infrared spectral region centered around 2 terahertz are used to coherently control an intersubband polarization in a GaAs/AlGaAs quantum well structure at low temperature. While the first pulse excites a macroscopic polarization, a second, temporally delayed pulse switches the polarization off or refreshes it depending on the relative time delay. The switching is directly demonstrated in the time-domain for the few picosecond long free-induction decay of the induced polarization. Additionally, the absorption line is found to be purely homogeneously broadened. Model calculations based on the optical Bloch equations agree well with the experimental data.
Keywords: coherent control, terahertz, intersubband polarization, ultrafast
  • Applied Physics Letters 99(2011), 131109

Publ.-Id: 15950 - Permalink


Metal Nanoparticles/Nanowires Selfassembly on Ripple Patterned Substrate - Mechanism, Properties and Applications
Ranjan, M.;
Plasmonic properties of self-assembled silver nanoparticles/nanowires array on periodically patterned Si (100) substrate are reported with special attention on the mechanism of nanoparticles self-assembly. The advantage of this bottom up approach over other self-assembling and lithographic methods is the flexibility to tune array periodicity down to 20 nm with interparticle gaps as low as 5 nm along the ripple.
Ripple pattern have shallow modulation (~2 nm) still particles self-assembly was observed in non-shadow deposition. Therefore adatoms diffusion and kinetics is important on ripple surface for the self-assembly. PVD e-beam evaporation method used for deposition has proven to be superior to sputter deposition due to lower incident flux and lower atom energy. It was found that particles self-assembly largely dependent on angle of incidence, substrate temperature, and deposition direction due to ripple asymmetric tilt. Ostwald ripening observed during annealing on ripples substrate has striking dependency on ripple periodicity and was found to be different compared to Ostwald ripening on flat Si surface.
In-situ RBS measurements of deposited silver on flat and rippled substrate confirmed different sticking of atoms on the two surfaces. The difference between maximum and minimum of the calculated local flux show a peak at an incidence angle of 70o with respect to surface normal. This explains the best alignment of particles at this angle of incidence compare to others.
Self-assembled nanoparticles are optically anisotropic, i.e. they exhibit a direction dependent shift in LSPR. The reason of the observed anisotropy is a direction dependent plasmonic coupling. Different in plane and out of the plane dielectric coefficients calculated by modelling Jones matrix elements, confirms that nanoparticle/nanowire array are biaxial anisotropic (ex ¹ ey ¹ ez). The nanoparticles are predominantly insulating while nanowires are both metallic and insulating depending on the dimension.
Silver nanoparticles/nanowires self-aligned on pre-patterned rippled substrate are presented for the first time as an active SERS substrate. Anisotropic SERS response in such arrays is attributed to different field enhancement along and across the ripples. Strong plasmonic coupling in elongated nanoparticles chain results in significantly higher SERS intensity then spherical nanoparticles/nanowires and non-ordered nanoparticles. Higher SERS intensity across the nanowires array in comparison to along the array (bulk silver) confirms electromagnetic field enhancement (hot-junction) is responsible for SERS phenomenon.
Self-assembly of cobalt nanoparticle on ripple pattern substrate is also reported. Due to less adatom mobility and higher sticking cobalt self-assembly is possible only at much higher temperature. A strong uniaxial magnetic anisotropy was observed not observed for non ordered cobalt particles.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-007 2011
    ISSN: 1437-322X

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