Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

Influence of Hot Implantation on Residual Radiation Damage in Silicon Carbide

Rawski, M.; Zuk, J.; Kulik, M.; Drozdziel, A.; Li, L.; Prucnal, S.; Pyszniak, K.; Turek, M.

Remarkable thermomechanical and electrical properties of silicon carbide (SiC) make this material very
attractive for high-temperature, high-power, and high-frequency applications. Because of very low values of
diffusion coefficient of most impurities in SiC, ion implantation is the best method to selectively introduce
dopants over well-defined depths in SiC. Aluminium is commonly used for creating p-type regions in SiC.
However, post-implantation radiation damage, which strongly deteriorates required electric properties of the
implanted layers, is difficult to anneal even at high temperatures because of remaining residual damage. Therefore
implantation at elevated target temperatures (hot implantation) is nowadays an accepted method to decrease the
level of the residual radiation damage by avoiding ion beam-induced amorphization. The main objective of this
study is to compare the results of the Rutherford backscattering spectroscopy with channeling and micro-Raman
spectroscopy investigations of room temperature and 500 ±C Al+ ion implantation-induced damage in 6H-SiC and
its removal by high temperature (up to 1600 ±C) thermal annealing.

Keywords: ion implantation; SiC; Raman spectroscopy

  • Open Access Logo Acta Physica Polonica A 120(2011), 192

Permalink: https://www.hzdr.de/publications/Publ-16316
Publ.-Id: 16316


Inclusive dielectron spectra in p+p collisions at 3.5 GeV

Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chen, J. C.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Lalik, R.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

We present the inclusive invariant-mass, transverse momentum and rapidity distributions of dielectrons (e+e- pairs) in p+p interactions at 3.5 GeV beam kinetic energy. In the vector-meson mass region, a distinct peak corresponding to direct ω decays is reconstructed with 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance of the HADES apparatus for e+e- invariant masses above 0.2 GeV/c2 and for transverse momenta pt < 1 GeV/c, acceptance corrections are to a large extent model independent. This allows us to extract from dielectron data for the first time at this energy the inclusive production cross sections for light vector mesons. Inclusive production cross sections for π0 and η mesons are also reported. The obtained results will serve as an important reference for the study of vector mesons production in proton-nucleus and heavy-ion collisions. Furthermore, using this data, an improved value for the upper bound of the branching ratio for direct η decays into the electron-positron channel is obtained.

Permalink: https://www.hzdr.de/publications/Publ-16315
Publ.-Id: 16315


Terahertz nonlinear and coherent effects in semiconductor nanostructures

Helm, M.

The Autler-Townes effect (Rabi splitting) is observed in semiconductor quantum wells, when pumping the intra-excitonic 1s-2p transition with a THz free-electron laser. In a second experiment using time-domain spectroscopy, it is shown that the THz intersubband polarization in a quantum well can be coherently manipulated using a second, phase-locked THz pulse.

Keywords: terahertz; nonlinear; coherent; semiconductor; nanostructure

  • Invited lecture (Conferences)
    International Symposium on Terahertz Nanoscience (TeraNano 2011), 24.-25.11.2011, Osaka, Japan
  • Contribution to proceedings
    International Symposium on Terahertz Nanoscience (TeraNano 2011), 24.-25.11.2011, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-16314
Publ.-Id: 16314


THz science in semiconductor quantum structures

Helm, M.

THz science in semiconductor quantum structures

Keywords: THz; semiconductors; quantum structures

  • Invited lecture (Conferences)
    Nano-Carbon Terahertz Science, 22.11.2011, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-16313
Publ.-Id: 16313


Pairs of diverging-converging spin vortices in biquadratically interlayer exchange coupled elements

Wintz, S.; Bunce, C.; Banholzer, A.; Strache, T.; Körner, M.; Gemming, S.; Erbe, A.; McCord, J.; Raabe, J.; Quitmann, C.; Fassbender, J.

Spin structures have been a relevant topic of magnetism research for many years. In particular, magnetic vortices have attracted much at- tention, due to their non-trivial topology and the various dynamic modes they exhibit. A magnetic vortex consists of a planar, flux- closing magnetization curl that turns out of the plane in the central nanoscopic core. For a single layer structure, the curl’s radial components typically cancel each other out. Recent investigations show that this holds also true for multilayer vortex systems comprising bilinear interlayer exchange coupling (IEC). In this contribution we report on pairs of diverging-converging spin vortices occurring in biquadratically coupled systems. Using magnetic x-ray microscopy we directly observe that the individual vortices of such pairs possess a residual radial magnetization component. From this ∇M𝑥𝑦 ̸= 0, an additional perpendicular magnetization divergence ∇M𝑧 is analytically deduced. We compare our continuous model with discrete micromagnetic simulations.

Keywords: magnetism; vortex; multilayer; coupling; interlayer; biquadratic; exchange

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2012, 25.-30.03.2012, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-16312
Publ.-Id: 16312


Imaging of the brain serotonin transporters (SERT) with 18F-labelled fluoromethyl-McN5652 and PET in humans

Hesse, S.; Brust, P.; Mäding, P.; Becker, G.-A.; Seese, A.; Patt, M.; Sorger, D.; Zessin, J.; Sacher, J.; Lobsien, D.; Habermann, B.; Meyer, P. M.; Füchtner, F.; Luthardt, J.; Bresch, A.; Steinbach, J.; Sabri, O.

Purpose [1134 C]DASB is currently the most frequently applied highly selective radiotracer for visualisation and quantification of central SERT. Its use, however, is hampered by the short half life of carbon-11, the moderate cortical test retest reliability, and the lack for quantifying endogenous serotonin. Labelling with fluorine-18 allows in principle for longer acquisition times for kinetic analysis in brain tissue and may provide higher sensitivity. The aim of our study was to firstly apply in human the new highly SERT-selective fluorine-18 labelled fluoromethyl analogue of (+)-McN5652 ((+)-[1840 F]FMe-McN5652) and to evaluate its potential for SERT quantification.
Methods
The PET data of five healthy volunteers (3 male, 2 female, age 39 ± 10 years) coregistered with individual MRI were semi-quantitatively assessed by volume-of-interest analysis using the software package PMOD. Rate constants and distribution volume ratios (DVR) were calculated using a 2-tissue compartment model and arterial input function measurement were corrected for metabolites/plasma data. Standardized uptake region-to-cerebellum ratios as measure of specific radiotracer accumulation were compared with those of a [1146 C]DASB-PET data set of healthy subjects (10 male, 11 female, 38 ± 8 years).
Results
The 2-tissue compartment model provided adequate fits to the data. Estimates of total distribution volume (VT) demonstrated good identifiability based on coefficient of variation (COV) for the volumes of interest (VOIs) in SERT-rich and also for cortical areas (COV VT < 10%).
Compared with [11C]DASB-PET, there was a tendency to lower mean values in (+)-[1851 F]FMe-McN5652 PET, however, the standard deviation was also somewhat lower. Altogether, cerebral (+)-[1853 F]FMe-McN5652 uptake corresponds well with the known SERT distribution also in humans.
Conclusion
The results showed also that (+)-[1855 F]FMe-McN5652 is suitable for in vivo quantification of SERT with PET. Because of the long half-life of fluorine-18, a widespread application within a satellite concept seems feasible.

Keywords: Serotonin receptor; Positron emission tomography; PET; 18F

Permalink: https://www.hzdr.de/publications/Publ-16309
Publ.-Id: 16309


Development of radioligands for α7-nAChR imaging with positron emission tomography

Brust, P.; Peters, D.; Deuther-Conrad, W.

Molecular imaging of brain structures by highly sensitive non-invasive techniques offers unique possibilities in the understanding of physiological and pathological processes in the central nervous system. In particular, the quantitative analysis by positron emission tomography (PET) of α7 nicotinic acetylcholine receptors ( α7 nAChR), which are involved in different signalling pathways in the brain, is assumed to provide important information on the relation between receptor dysfunction and the pathogeneses of neuropsychiatric brain diseases, but the applicability of this imaging approach is still hampered due to insufficient imaging agents. This paper presents the recent efforts made to develop PET radiotracers targeting α7 nAChR as well as the current state of the evaluation of the most promising radiolabelled compounds in animal models and humans.

Permalink: https://www.hzdr.de/publications/Publ-16308
Publ.-Id: 16308


Synthesis, radiofluorination and pharmacological evaluation of fluoromethyl substituted spirocyclic PET tracers for labeling of σ1 receptors in the central nervous system and comparison with longer homologues

Maisonial, A.; Grosse Maestrup, E.; Wiese, C.; Hiller, A.; Schepmann, D.; Deuther-Conrad, W.; Fischer, S.; Brust, P.; Wünsch, B.

The spirocyclic s1 receptor ligand 1 (1’-benzyl-3-(fluoromethyl)-3H-spiro[[2]benzofuran-1,4’-piperidine]) was prepared in four steps starting from methoxy derivative 5. Due to its high s1 affinity (Ki = 0.74 nM) and selectivity against several other relevant targets, 1 was investigated as 18F-labeled PET tracer and its biological properties were compared with those of homologous fluoroalkyl derivatives 2-4. The fluoromethyl derivative 1 was faster metabolized in vitro than homologues 2-4. In contrast to the radiosynthesis of [18F]2-4, the nucleophilic substitution of the tosylate 15 using the K[18F]F-K222-carbonate complex required heating to 150 °C in DMSO to achieve high labeling efficiencies. Whereas radiometabolites of [18F]2-4 were not detected in vivo in the brain of mice, two radiometabolites of [18F]1 were found. Analysis of ex vivo autoradiography images provided rather low target-to-nontarget ratio for [18F]1 compared with [18F]2-4. [18F]1 showed a fast uptake in the brain, which decreased continuously over time. The brain-to-plasma ratio of the radiotracer [18F]1 was only exceeded by the fluoroethyl tracer [18F]2.

Permalink: https://www.hzdr.de/publications/Publ-16307
Publ.-Id: 16307


Spektroskopische Untersuchungen zum Verhalten von Neptunium und Uran in der Geosphäre

Müller, K.

The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces.
Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral - water interfaces of oxides of titania, alumina, silica, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
From the infrared spectra, a significant change of the U(VI) speciation is derived upon lowering the U(VI) concentration from the milli- to the micromolar range, strongly suggesting the dominance of monomeric U(VI) hydrolysis products in the micromolar solutions. In contradiction to the predicted speciation, monomeric hydroxo species are already present at pH ≥ 2.5 and become dominant at pH 3. At higher pH levels (> 6), a complex speciation is evidenced including carbonate containing complexes.
For the first time, spectroscopic results of Np(VI) hydrolysis reactions are provided in the submillimolar concentration range and at pH values up to 5.3, and they are comparatively discussed with U(VI). For both actinides, the formation of similar species is suggested at pH ≤ 4, whereas at higher pH, the infrared spectra evidence structurally different species. At pH 5, the formation of a carbonate-containing dimeric complex, that is (NpO2)2CO3(OH)3^-, is strongly suggested, whereas carbonate complexation occurs only under more alkaline conditions in the U(VI) system.
The results from the experiments of the sorption processes clearly demonstrate the formation of stable U(VI) surface complexes at all investigated mineral phases. This includes several metal oxides, namely TiO2, Al2O3, and SiO2, serving as model systems for the elucidation of more complex mineral systems, and several alumosilicates, such as kaolinite, muscovite and biotite. From a multiplicity of in situ experiments, the impact of sorbent characteristics and variations in the aqueous U(VI) system on the sorption processes was considered.
A preferential formation of an inner-sphere complex is derived from the spectra of the TiO2 and SiO2 phases. In addition, since the in situ FT-IR experiments provide an online monitoring of the absorption changes of the sorption processes, the course of the formation of the U(VI) surface complexes can be observed spectroscopically. It is shown that after prolonged sorption time on TiO2, resulting in a highly covered surface, outer-sphere complexation predominates the sorption processes. The prevailing crystallographic modification, namely anatase and rutile, does not significantly contribute to the spectra, whereas surface specific parameters, e.g. surface area or porosity are important.
A significant different surface complexation is observed for Al2O3. The formation of innerspheric species is assumed at low U(VI) surface coverage which is fostered at low pH, high ionic strength and short contact times. At proceeded sorption the surface complexation changes. From the spectra, an outer-spheric coordination followed by surface precipitation or polymerization is deduced. Moreover, in contrast to TiO2, the appearance of ternary U(VI) carbonate complexes on the γ-Al2O3 surface is suggested.
The first results of the surface reactions on more complex, naturally occurring minerals (kaolinite, muscovite and biotite) show the formation of U(VI) inner-sphere sorption complexes. These findings are supported by the spectral information of the metal oxide surfaces.
In this work, first spectroscopic results from sorption of aqueous Np(V) on solid mineral phases are provided. It is shown that stable inner-sphere surface species of NpO2 ^+ are formed on TiO2. Outer-sphere complexation is found to play a minor role due to the pH independence of the sorption species throughout the pH range 4 - 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2, and ZnO indicate structurally similar bidentate surface complexes.
The multiplicity of IR spectroscopic experiments carried out within this study yields a profound collection of spectroscopic data which will be used as references for future investigations of more complex sorption systems in aqueous solution. Furthermore, from a methodological point of view, this study comprehensively extends the application of ATR FT-IR spectroscopic experiments to a wide range in the field of radioecology.
The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V/VI), in the environment. Consequently, more reliable predictions of actinides migration which are essential for the safety assessment of nuclear waste repositories can be performed.

  • Invited lecture (Conferences)
    Jahresveranstaltung "Woman in Nuclear", 24.-25.11.2011, Biblis, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16306
Publ.-Id: 16306


α4β2 nicotinic acetylcholine receptor PET to study the cholinergic function in patients with MCl and Alzheimer’s disease

Sabri, O.; Brust, P.; Barthel, H.

Einleitung
In Alzheimer’s disease (AD), there is growing evidence for the brain nicotinic acetylcholine receptors (nAChRs) being reduced at very early disease stages (in transgenic Tg2576 mice even earlier than beta-amyloid plaque deposition [Int J Devl Neurosci 2003]) and for this reduction being strongly associated with cognitive decline. Our group aims at developing and testing new nAChR positron emission tomography (PET) tracers with the goal to improve early dementia diagnosis.
Methode
We tested A85380, an 18F-labeled PET tracer which binds to the α4β2-subunit of the nAChR, and could show that nAChRs are highly significantly reduced in brain areas affected by AD-pathology in patients with early AD (correlating significantly with impaired cognition), and even in subjects with MCI who later progressed to AD [Eur J Nucl Med Mol Imaging 2011]. Using A85380, however, PET imaging of up to seven hours is required. This limitation encouraged to search for better suited tracers to be used as biomarkers in clinical routine. As a result we developed the 18F-labeled epibatidine derivative NCFHEB [Synapse 2008]. The first-in-man study testing this tracer in AD-patients and healthy controls (HCs) is ongoing. First results show that this tracer might allow imaging of nAChRs in a 20 minutes scan within 90 minutes and a significantly lower tracer binding in AD-patients compared to HCs.
Diskussion/Ergebnisse
Taken together, we were successful in the implementation of PET to image nAChRs in dementia. Our PET results support the concept of the nicotinic system being involved at early AD stages, providing motivation to further develop PET imaging for early AD diagnosis, prognosis, and therapy control.

  • Lecture (Conference)
    DGPPN Kongress 2011, 23.-26.11.2011, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16305
Publ.-Id: 16305


Synthesis of an 18F-labeled cyclin-dependent kinase-2 inhibitor

Svensson, F.; Kniess, T.; Bergmann, R.; Pietzsch, J.; Wuest, F.

The radiosynthesis of N-(5-(((5-(tert-butyl)oxazol-2-yl)methyl)thio)thiazol-2-yl)-4-[18F]fluoro-benzamide [18F]2 as a potential radiotracer for molecular imaging of cyclin-dependent kinase-2 (CDK-2) expression in vivo by positron emission tomography is described. Two different synthesis routes were envisaged. The first approach followed direct radiofluorination of respective nitro- and trimethylammonium substituted benzamides as labeling precursors with no-carrier-added (n.c.a.) [18F]fluoride. A second synthesis route was based on the acylation reaction of 2-aminothiazole derivative with labeling agent [18F] SFB. Direct radiofluorination afforded 18F-labeled CDK-2 inhibitor in very low yields of 1%–3%, whereas acylation reaction with [18F]SFB gave 18 F-labeled CDK-2 inhibitor [18 F]2 in high yields of up to 85% based upon [18 F]SFB during the optimization experiments. Large scale preparation afforded radiotracer [18 F]2 in isolated radiochemical yields of 37%–44% (n=3, decay-corrected) after HPLC purification within 75 min based upon [18 F]SFB. This corresponds to a decay-corrected radiochemical yield of 13%–16% based upon [18F]fluoride. The radiochemical purity exceeded 95% and the specific activity was determined to be 20 GBq/mmol.

Keywords: cyclin-dependent kinase 2; fluorine-18; radiofluorination; [18F]SFB

  • Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), 769-774
    DOI: 10.1002/jlcr.1922

Permalink: https://www.hzdr.de/publications/Publ-16304
Publ.-Id: 16304


Cyclin-Dependent Kinases (Cdk) as Targets for Cancer Therapy and Imaging

Graf, F.; Wuest, F.; Pietzsch, J.

kein Abstract verfügbar

  • Open Access Logo Book chapter
    Gali-Muhtasib H: Advances in Cancer Therapy, Croatia: Rijeka: InTech, 2011, 978-953-307-703-1, 265-288

Permalink: https://www.hzdr.de/publications/Publ-16302
Publ.-Id: 16302


Combined approach of microsensor and EF-TEM/EELS studies to study the speciation of uranium in biofilms and in the surrounding bulk solution

Krawczyk-Bärsch, E.; Lünsdorf, H.; Pedersen, K.; Arnold, T.; Bok, F.; Steudtner, R.; Lehtinen, A.; Brendler, V.

The effects of a microbial habitat (biofilm) on the transport behavior of uranium in a simulated incident in an underground repository were studied by pH and Eh microelectrodes and energy-filtered transmission electron microscopy (EF-TEM), and electron energy-loss spectroscopy (EELS). Biofilm samples were collected in the underground rock characterization facility tunnel ONKALO (Finland) and positioned in a rectangular flow cell for immobilization experiments by adding uranium to the bulk solution to a final uranium concentration of 4.25 × 10–5 M. The bulk solution was pumped through the flow cell in a closed circuit, simulating in situ conditions on the tunnel wall. The use of microelectrode with a tip diameter of 10 µm to measure pH and Eh in the biofilm proved to be essential to indicate that the biofilm has formed its own microenvironment. EF-TEM and EELS studies indicated that uranium in the biofilm was immobilized intracellularly in microorganisms by the formation of metabolically mediated uranyl phosphate, similar to Autunite. In contrast, time resolved laser fluorescence spectroscopy (TRLFS) in the bulk solution identified aqueous uranium carbonate species, likely (Ca2UO2[CO3]3), formed due to the high concentration of carbonate. The results were further confirmed by thermodynamic calculations of the predominant field of uranium species, formed in the bulk solution.
Our combined approach clearly showed that uranium was removed from solution and immobilized exclusively in biofilm microorganisms. In contrast, the aqueous uranyl carbonates species, formed in the bulk solution, may contribute to the migration of U(VI) and consequently to environmental hazard.

Keywords: biofilm; uranium; microelectrodes; EF-TEM

  • Lecture (Conference)
    marc ix - Methods & Application of Radioanalytical Chemistry, 25.-30.03.2012, Kailua-Kona, USA

Permalink: https://www.hzdr.de/publications/Publ-16301
Publ.-Id: 16301


Radiation field characterization and shielding studies for the ELI Beamlines Facility

Ferrari, A.; Amato, E.; Margarone, D.; Cowan, T.; Rus, B.

The ELI (Extreme Light Infrastructure) Beamlines Facility in the Czech Republic, which is planned to complete the installation in 2015, is one of the four pillars of the ELI european project. Several laser beamlines with ultrahigh intensities and ultrashort pulses are foreseen, offering versatile radiation sources in an unprecedented energy range: laser-driven particle beams are expected to range between 1 GeV and 50 GeV for electrons and from 100 MeV up to 3 GeV for protons. The number of particles delivered per laser shot is estimated to be 109-1010 for the electron beams and 1010-1012 for the proton beams.
The high energy and current values of the produced particles, together with the potentiality to operate at 10 Hz laser repetition rate, require an accurate study of the primary and secondary radiation fields to optimize appropriate shielding solutions: this is a key issue to minimize prompt and residual doses in order to protect the personnel, reduce the radiation damage of electronic devices and avoid strong limitations in the operational time.
A general shielding study for the 10 PW (0.016 Hz) and 2 PW (10 Hz) laser beamlines is presented here. Starting from analytical calculations, as well as from dedicated simulations, the main electron and proton fields produced in the laser-matter interaction have been described and used to characterize the "source terms" in full simulations with the Monte Carlo code FLUKA. The secondary radiation fields have been then analyzed to assess a proper shielding. The results of this study and the proposed solutions for the beam dumps of the high energy beamlines are presented, together with a cross-check analysis performed with the Monte Carlo code GEANT4.

Keywords: particle acceleration from laser-matter interaction; shielding; Monte Carlo; radiation protection

Permalink: https://www.hzdr.de/publications/Publ-16300
Publ.-Id: 16300


Layer by Layer investigation on the magneto-transport properties of ferromagnetic Ge:Mn prepared by pulsed laser

Bürger, D.; Zhou, S.; Höwler, M.; Kovacs, G.; Reuther, H.; Skorupa, W.; Helm, M.; Schmidt, H.

The fabrication of ferromagnetic semiconductors is one big step to realize spintronic devices. Beside GaAs:Mn also Ge:Mn is a very interesting material system [1-2].
Moreover, the lattice inversion symmetry of Ge leads to weak spin-orbit interaction and enhanced spin-lifetime and spin-diffusion lengths of more than 100 μ m. This is shown in Ge nanowires at 4.2 K [3].
Also a spin diffusion up to 225 K could be shown in weakly n-doped Ge [4].
In a previous work we investigated ferromagnetism in Ge:Mn thin films. Hysteretic Hall resistance after Mn implantation and short-time pulsed laser annealing (PLA) has been observed [5].
Similar to low temperature molecular beam epitaxy [1], the clustering of Mn inside the material has to be prevented. Especially after PLA, the Mn segregation leads to the formation of a Mn enriched surface layer. In our work, we performed layer by layer magneto-transport measurements after different etching steps. The hysteretic properties are vanishing after removing the segregated Mn-rich phases. In conclusion, we think that the observed hysteretic Hall resistance may have its origin in the scattering of spin-polarized holes on these Mn-rich phases. Such hysteretic transport properties have not yet been reported for Ge with embedded Mn-rich clusters. The vanishing hysteresis at 30 K and above can be interpreted by the increasing decoherence between the individual Mn rich clusters or/and the reduced magnetization of the clusters itself.
[1] M. Jamet et al., Nature Materials 5, 653 (2006) [2] Y.D. Park et al., Science 295, 651 (2002) [3] E. S. Liu et al., Nano Letters 10, 3297 (2010) [4] Y. Zhou et al. arXiv:1103.5095v1 (2011) [5] S. Zhou et al., Phys. Rev. B 81, 165204 (2010)

Keywords: implantation; segregation; pulsed laser annealing; ferromagnetic semiconductor

  • Poster
    56th annual conference on magnetis and magnetic materials, 30.10.-03.11.2011, Scottsdale, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-16299
Publ.-Id: 16299


Depth-resolved magnetotransport properties of ferromagnetic Ge:Mn

Bürger, D.; Zhou, S.; Höwler, M.; Kovacs, G.; Reuther, H.; Skorupa, W.; Helm, M.; Schmidt, H.

The fabrication of ferromagnetic semiconductors is one big step to realize spintronic devices. Beside GaAs:Mn also Ge:Mn is a very interesting material system [1-2]. Moreover, the lattice inversion symmetry of Ge leads to weak spin-orbit interaction and enhanced spin-lifetime and spin-diffusion lengths of more than 100 µm. This is shown in Ge nanowires at 4.2 K [3]. Also a spin diffusion up to 225 K could be shown in weakly n-doped Ge [4]. We investigated ferromagnetism in Ge:Mn thin films [5]. Hysteretic Hall resistance after Mn implantation and short-time pulsed laser annealing (PLA) has been observed. Similar to low temperature molecular beam epitaxy [1], the inhomogenous distribution of Mn inside the material has to be prevented. Especially after PLA, the Mn segregation leads to the formation of a Mn enriched surface layer. In our work, we performed layer-by-layer etching of ferromagnetic Ge:Mn and subsequent depth-resolved magnetotransport measurements. The hysteretic properties are vanishing after removing the segregated Mn-rich phases. In conclusion, we think that the hysteretic Hall resistance may have its origin in the scattering of spin-polarized holes on these Mn-rich phases. The vanishing hysteresis at 30 K can be interpreted by the increasing spin decoherence between the individual Mn rich clusters or/and the reduced magnetization of the clusters itself at increased temperature.

Keywords: implantation; pulsed laser annealing; segregation; manganese; magnetic semiconductor

  • Lecture (Conference)
    Subtherm 2011, 24.-27.10.2011, Dresden, Deutschland
  • Poster
    Subtherm 2011, 24.-27.11.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16298
Publ.-Id: 16298


Dielectric function and magneto-optical Voigt constant of Cu2O: A combined spectroscopic ellipsometry and polar magneto-optical Kerr spectroscopy study

Haidu, F.; Fronk, M.; Gordan, D. O.; Scarlat, C.; Salvan, G.; Zahn, R. T. D.

Cuprous oxide is a highly interesting material for the emerging field of transparent oxide electronics. In this work the energy dispersion of the dielectric function of Cu2O bulk material is revised by spectroscopic ellipsometry measurements in an extended spectral range from 0.73 to 10 eV. For the first time, the magneto-optical Kerr effect was measured in the spectral range from 1.7 to 5.5 eV and the magneto-optical Voigt constant of Cu2O was obtained by numerical calculations from the magneto-optical Kerr effect spectra and the dielectric function.

Permalink: https://www.hzdr.de/publications/Publ-16297
Publ.-Id: 16297


Radiosynthesis and Radiotracer Properties of a 7-(2-[F-18]Fluoroethoxy)-6-methoxy-pyrrolidinylquinazoline for Imaging of Phosphodiesterase 10A with PET

Funke, U.; Deuther-Conrad, W.; Schwan, G.; Maisonial, A.; Scheunemann, M.; Fischer, S.; Hiller, A.; Briel, D.; Brust, P.

Phosphodiesterase 10A (PDE10A) is a key enzyme of intracellular signal transduction which is involved in the regulation of neurotransmission. The molecular imaging of PDE10A by PET is expected to allow a better understanding of physiological and pathological processes related to PDE10A expression and function in brain. The aim of this study was to develop a new 18F-labeled PDE10A ligand based on a 6,7-dimethoxy-4-pyrrolidinylquinazoline and to evaluate its properties in biodistribution studies. Nucleophilic substitution of the 7-tosyloxy-analogue led to the 7-[18F]fluoroethoxy-derivative [18F]IV with high PDE10A affinity (KD,PDE10A=14 nM), radiochemical yields of 25±9% (n=9), high radiochemical purity of ≥99% and specific activities of 110-1100 GBq/mol. [18F]IV entered rapidly into the brain of female CD-1 mice with a peak uptake of 2.3%ID/g in striatum at 5 min p.i.. High metabolic stability in brain was observed. However, blocking studies revealed no target specific accumulation of [18F]IV. Therefore, successful imaging of PDE10A using 18F-labeled 6,7-dialkoxyquinazoline derivatives requires further structural optimization.

Keywords: PDE10A; Quinazoline; Fluorine-18; Positron emission tomography; PET

Permalink: https://www.hzdr.de/publications/Publ-16296
Publ.-Id: 16296


Alpha7 nicotinic acetylcholine receptors as a potential target for imaging of brain disorders with Positron Emission Tomography

Brust, P.; Knudsen, G. M.; Mikkelsen, J. D.; Ettrup, A.; Deuther-Conrad, W.; Peters, D.

Molecular imaging of brain structures by non-invasive techniques offers unique possibilities in the understanding of physiological and pathological processes in the central nervous system. In particular, the quantitative analysis by positron emission tomography (PET) of alpha7 nicotinic acetylcholine receptors (α7nAChR) could provide important information on the relation between receptor dysfunction and the pathogeneses of neurodegenerative brain diseases. However, the applicability of PET for α7nAChR imaging is still hampered by a lack of validated radiotracer for human use.
As radiotracers for imaging α7nAChR, 18F- and 11C-labelled 1,4-diazabicyclo-[3.2.2]nonane derivatives (NS10743 and NS14492) were developed and investigated for in vivo imaging characteristics. Brain autoradiography and organ distribution in mice showed specific accumulation of [18F]NS10743 in α7nAChR expressing brain substructures and peripheral organs. In pigs [18F]NS10743 readily entered the brain (peak SUV ~2.5), with the highest uptake in α7nAChR expressing brain regions such as the colliculi, thalamus, temporal lobe, and hippocampus. Pretreatment followed by constant infusion of NS6740, a selective α7nAChR antagonist, significantly reduced the specific binding of [18F]NS10743 in receptor-dense regions of pigs.
[11C]NS14492, a radioligand of similar high affinity and selectivity in vitro, also showed high uptake in the pig brain (peak SUV ~2.2) with a distribution pattern in accordance with α7nAChR expression. Homologous blocking or pretreatment with the α7nAChR partial agonist SSR180711 both reduced distribution volumes of [11C]NS14492 in all examined regions in a dose-dependent manner.
In conclusion, because of their high brain uptake and regional distribution in accordance with α7nAChR expression pattern in the pig brain, 1,4-diazabicyclo-[3.2.2]nonane derivatives are promising PET radioligands for in vivo mapping and quantitative imaging of α7nAChR. Furthermore, in vivo in pigs the PET radioligand brain binding can be dose-dependently blocked by α7nAChR antagonists.

  • Invited lecture (Conferences)
    28th CINP Congress, 03.-07.06.2012, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-16293
Publ.-Id: 16293


Sublattice-specific ordering of ZnO layers during the heteroepitaxial growth at different temperatures

Redondo-Cubero, A.; Vinnichenko, M.; Krause, M.; Mücklich, A.; Mun˜Oz, E.; Kolitsch, A.; Gago, R.

The effect of the substrate temperature on the sublattice ordering in ZnO layers grown by reactive pulsed magnetron sputtering on sapphire has been investigated by different techniques. The improvement of the crystal quality and heteroepitaxial growth at relatively low temperatures (550 °C) is verified by X-ray diffraction, high-resolution transmission electron microscopy, Rutherford backscattering spectrometry in channeling mode (RBS/C), and Raman spectroscopy. Sublattice-resolved analysis by resonant RBS/C and Raman spectroscopy reveals that the progressive transition to the single crystal phase is accomplished in a faster way for Zn- than for O-sublattice. This behavior is attributed to the preferential annealing of defects in the Zn sublattice at low temperatures when compared to those of the O sublattice.

Keywords: ZnO; reactive pulsed magnetron sputtering; defects; structure

Permalink: https://www.hzdr.de/publications/Publ-16292
Publ.-Id: 16292


Kernkraftwerk Krümmel – Berechnung der Fluidlasten in der Kondensationskammer bei luftarmer Kondensation mit einem Randelemente-Verfahren

Wagner, M.; Estorf, M.

Im Fall eines Frischdampfleitungsbruchs wird Dampf über die Kondensationsrohre in die Kondensationskammer gepresst. Dabei ergeben sich an den in die Wasservorlage eintauchenden Rohrenden Dampfblasen, die sich zyklisch erweitern und wieder kollabieren. Bei geringem Anteil nicht kondensierbaren Gases führt der Kollaps der Blasen zu starken Druckstößen, welche die Wände der Kondensationskammer belasten. Die physikalischen Zusammenhänge des intermittierenden Blasenkollapses sowie die den Vorgang beeinflussenden Parameter sind in umfangreichen Experimenten untersucht. Die auftretenden Drücke auf der Behälterwand wurden in Testbehältern experimentell ermittelt, statistisch ausgewertet und in konservativer Weise für die Spezifikation der entsprechenden Lasten am Sicherheitsbehälter des KKK verwendet. Dazu erfolgte eine potentialtheoretische Skalierung des Druckes aufgrund der berechneten Lösung der Potentialgleichung auf Basis einer vereinfachten abgewickelten, rechteckigen Geometrie der Wasservorlage.
Der vorliegende Bericht bewertet diese mit vereinfachter Geometrie erzeugte Lösung der Potentialgleichung anhand einer genaueren Berechnung des Behälterpotentials für die tatsächliche 3-dimensionale Geometrie. Die Potentialgleichung wird hier mit einer Randelemente-Methode gelöst. Anschließend werden mit Hilfe von Monte-Carlo-Rechnungen die Einflüsse der unterschiedlich stark auftretenden Druckamplituden sowie der Asynchronität der Kondensationsereignisse auf die zu erwartenden Lasten ermittelt.

Keywords: condensation chamber; pressure distribution; potential equation; boundray element method

  • Other report
    Institutsbericht: HZDR\FWS\2011\07, 2011
    28 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16291
Publ.-Id: 16291


Ion-implantation induced nano distortion layer and its influence on nonlinear optical properties of ZnO single crystals

Zheng, C. C.; Xu, S. J.; Ning, J. Q.; Chen, Y. N.; Lu, X. H.; Ling, C.-C.; Che, C. M.; Gao, G. Y.; Hao, J. H.; Brauer, G.; Anwand, W.

Second harmonic generation (SHG) and X-ray diffraction rocking curves of high-quality ZnO single crystals implanted by different ions (He, Cu, and Zn) were investigated. Interestingly, it was found that both He-and Zn-implanted samples show a convinced increment in SHG efficiency while the Cu-implanted one does not. X-ray diffraction rocking curves of the samples show satellite structures, and the simulations firmly reveal the formation of quasi-interfaces inside He-and Zn-implanted crystals. These quasi-interfaces lead to SHG improvement in the two samples. Polarization dependence of SHG of the samples on the excitation light also evidences this conclusion.

  • Journal of Applied Physics 110(2011)8, 083102

Permalink: https://www.hzdr.de/publications/Publ-16290
Publ.-Id: 16290


Mid-infrared pump-related electric-field domains in GaAs/(Al,Ga)As quantum-cascade structures for terahertz lasing without population inversion

Giehler, M.; Wienold, M.; Schrottke, L.; Hey, R.; Grahn, H. T.; Pavlov, S. G.; Hübers, H.-W.; Winnerl, S.; Schneider, H.

We investigate the effect of mid-infrared (MIR) pumping on the transport properties of GaAs/(Al,Ga)As terahertz (THz) quantum lasers (TQLs), which rely on quantum coherence effects of intersubband transitions. Aiming at THz lasing at elevated temperatures, we extend the concept of THz gain with and without population inversion of a single, MIR-pumped, electrically driven THz stage proposed by Waldmueller et al. [Phys. Rev. Lett. 99, 117401 (2007)] to an entire TQL. However, experiments using a CO2 as well as a free-electron laser and numerical simulations show that this resonant MIR pumping causes a negative differential conductivity (NDC) in addition to the NDC caused by sequential tunneling. Lasing of these TQLs is prevented by the formation of electric-field domains below the resonance field strength for gain of each single THz stage.

Keywords: quantum cascade laer; intersubband transition; GaAs/AlGaAs; free-electron laser

Permalink: https://www.hzdr.de/publications/Publ-16289
Publ.-Id: 16289


High-field terahertz investigations on semiconductor quantum structures

Schneider, H.

This seminar reviews our recent experimental studies involving terahertz (THz) and mid-infrared radiation from the free-electron laser facility FELBE in Dresden, Germany. As examples for linear measurements, cyclotron resonance spectroscopy and aperture-less near-field microscopy will be addressed. Applications of nonlinear THz spectroscopy include pump-probe experiments in graphene, and nonlinear THz two-photon intersubband excitation in semiconductor quantum wells. The final part of my talk will concentrate on two-color THz spectroscopy, in particular THz sideband generation and coherent dynamics of excitons dressed by strong THz beams.

Keywords: terahertz THz spectroscopy; free-electron laser; semiconductor quantum well; two-photon transition; excitons

  • Lecture (others)
    Seminar, Hebrew University of Jerusalem, 09.11.2011, Jerusalem, Israel

Permalink: https://www.hzdr.de/publications/Publ-16288
Publ.-Id: 16288


Paradoxical transitions to instabilities in hydromagnetic Couette-Taylor flows

Kirillov, O. N.; Pelinovsky, D. E.; Schneider, G.

By methods of modern spectral analysis, we rigorously find distributions of eigenvalues of linearized operators associated with an ideal hydromagnetic Couette-Taylor flow. Transition to instability in the limit of vanishing magnetic field has a discontinuous change compared to the Rayleigh stability criterion for hydrodynamical flows, which is known as the Velikhov-Chandrasekhar paradox.

Keywords: Magnetorotational instability; boundary eigenvalue problem; eigencurves; Velikhov-Chandrasekhar paradox

Permalink: https://www.hzdr.de/publications/Publ-16287
Publ.-Id: 16287


Enhancements of high-resolution gamma-ray computed tomography

Bieberle, A.; Berger, R.; Nehring, H.; Hampel, U.

Recently, we developed a transportable high-resolution gamma-ray computed tomography (GCT) measurement system for the investigation of phase distributions in multi-phase flows in technical apparatus. The GCT measurement system contains a collimated isotopic source (137Cs), a radiation detector arc and an external signal processing as well as thermal stabilisation unit. For tomographic scans radiographic projections are obtained from different angular positions by rotating either the measuring ensemble or the object of interest. To improve the mechanical and thermal handling of the existing radiation measurement electronics, in a first step a new modular signal processing board was developed. It implements variable gain amplifier stages, gamma photon counters as well as data transfer and communication to a standard PC into the detector arc. Furthermore, the new developed electronics allows various arrangements of multiple detector modules. In a second step the thermal stabilisation system was integrated into the detector arc. Two 30 W (thermal power) Peltier elements directly placed onto the top side of the detector base plate undertake the task of thermal stabilisation. Into the back side of the base plate, a spatially optimised channel is milled in which a fluid, driven by an integrated centrifugal pump, realises a homogeneous temperature distribution. Thus, the heat losses of the active electronics that are connected to the base plate can be efficiently dissipated, which is the key for a good measuring repeat accuracy. The functionality of the thermal stabilisation design was proven by an IR camera.

Keywords: Gamma-ray tomography; multiple detector module

  • Contribution to proceedings
    6th International Symposium on Process Tomography, 26.-28.03.2012, Cape Town, South Africa
    Proceedings of 6th International Symposium on Process Tomography
  • Lecture (Conference)
    6th International Symposium on Process Tomography, 26.-28.03.2012, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-16286
Publ.-Id: 16286


Radio-coloration of Diamond

Nasdala, L.; Grambole, D.; Harris, J. W.; Schulze, D. J.; Hofmeister, W.

This study investigated the green and orangy brown spots that commonly occur on the surface of rough diamonds and which are caused by external irradiation by helium ions in the form of alpha particles. These ions are believed to be generated by the decay of radionudides in radioactive minerals that were located close to a diamond in irs geologic past. Helium ions generated in the U- and Th-decay chains have energies in the 4.0-8.8 MeV range; their travel distances in diamond arc up tO 29 1-1m. Depending on rhe sizes (mostly unknown) of rhe radiation sources and their proximity to the diamond's surface, helium irradiation typically results in blurred round spots with green color. These spots are usually deformed semi-spheres with fuzzy boundaries. With moderate-temperature heating, the green radio-coloration turns orange-brown. Raman measurements revealed that these richly colored green and brown spots represent elevated levels of radiation dan1age. The same observation was made on spots produced by the irradiarion of diamond plates with 8.8 MeV He ions in a tandem accelerator, foUowed by annealing experiments. The transformation from green to brown was accompanied by relatively low degrees of structural reconstitution.
Our experiments showed that irradiation with about l x l 016 He ions per cm2 is needed to produce strong radio-coloration. This in rum leads us to conclude that radio-coloration on the surface of natural stones must be a long-tenn process: A typical spot has a size on the order of 1,000 fU112, requiring about 1 x 1011 helium ions. If the helium irradiation emanated, for instance, from a 5 fUll uraninirecrysral {>80wr.% U), it would rake more than 10 million years to accumulate l x 1011 helium ions in the neighboring diamond In the case of a lO fUll zircon crysra1 containing 1,000 ppm of uraniurn, that same alpha dose would require more than 2 billion years, which seems implausible. Therefore, radio-coloration is likely due to the action of small grains of strongly radioactive phases that lay adjacent to the diamond for at least several million years.

  • Abstract in refereed journal
    Gems & Gemology 47(2011), 105-106

Permalink: https://www.hzdr.de/publications/Publ-16285
Publ.-Id: 16285


ELBE Timing System

Kuntzsch, M.

German-Turkish Workshop on Superconducting Accelerators for FEL and Bremsstrahlung Applications

Keywords: ELBE Timing System

  • Lecture (Conference)
    German-Turkish Workshop on Superconducting Accelerators for FEL and Bremsstrahlung Applications, 31.01.-03.02.2011, Antalya, Turkey

Permalink: https://www.hzdr.de/publications/Publ-16284
Publ.-Id: 16284


Concept of Femtosecond Timing and Synchronization Scheme at ELBE

Kuntzsch, M.; Buechner, A.; Gensch, M.; Jochmann, A.; Kirschke, T.; Lehner, U.; Roeser, F.; Bock, M. K.; Bousonville, M.; Felber, M.; Lamb, T.; Schlarb, H.; Schulz, S.

The Radiation Source ELBE at Helmholtz-Zentrum Dresden-Rossendorf is undergoing an extension to offer capacity for various applications. The extension includes the setup of a THz-beamline with a dedicated laboratory and a beamline for electron-beam - high-power laser interaction. The current synchronization scheme offers stability on the picoseconds level. For pump-probe experiments using optical lasers, the desired synchronization between the pump and the probe pulse should be on the femtosecond scale. In the future there will be an optical synchronization system with a pulsed fiber laser as an optical reference. The laser pulses will be distributed over stabilized fiber links to the remote stations. It is planned to install EOM-based beam arrival time monitors (BAMs) in order to monitor the bunch jitter and to establish a beam-based feedback to reduce the jitter. Besides that, the timing system has to be revised to generate triggers for experiments with low repetition rate, two electron guns (thermionic DC, superconducting RF) and several lasers. The Poster will show the possible layout of the future Timing and Synchronization System at ELBE.

Keywords: Synchronization Timing ELBE

  • Open Access Logo Contribution to proceedings
    International Particle Accelerator Conference, 04.-09.09.2011, San Sebastian, Spain
    Concept of Femtosecond Timing and Synchronization Scheme at ELBE
  • Poster
    International Particle Accelerator Conference, 04.-09.09.2011, San Sebastian, Spain

Permalink: https://www.hzdr.de/publications/Publ-16283
Publ.-Id: 16283


Report on the redesign of the fibre link stabilisation units at FLASH

Bock, M. K.; Lamb, T.; Bousonville, M.; Felber, M.; Gessler, P.; Schlarb, H.; Schmidt, B.; Schulz, S.; Kuntzsch, M.

Recently, the fibre link stabilisation unit of the optical synchronisation system at FLASH has been subject to several design changes involving some major issues. Enhancements of the optical design have led to improvements in the efficiency of the free space optics and a new optical delay line allows for a more than two times longer adjustment range. The amplitude noise, encountered previously at the remote station of the links, was drastically decreased by a new beam splitting configuration. In future, this new link design will not only be used for the planned additional fibre links at FLASH, but it will also replace the already installed ones. In this paper we report on the changes of opto-mechanical design and we present first results from the recently commissioned links.

Keywords: Synchronization Synchronisation FLASH

  • Open Access Logo Contribution to proceedings
    Free Electron Laser Conference, 22.-26.08.2011, Shanghai, China
    Report on the redesign of the fibre link stabilisation units at FLASH

Permalink: https://www.hzdr.de/publications/Publ-16282
Publ.-Id: 16282


Future Timing and Synchronization Scheme at ELBE

Kuntzsch, M.; Buechner, A.; Lehnert, U.; Roeser, F.

The Radiation Source ELBE at Helmholtz-Zentrum Dresden-Rossendorf is currently extended to oer capacity for new experiments. The reconstruction includes the setup of a THz-beamline with a dedicated user laboratory and a beamline for electron-beam - high-power laser experiments. The current synchronization scheme oers stability to the picoseconds level. The newexperiments require a femtosecond synchronization in order to get field-strength resolved THz-probes and to have a stable overlap between the electron-bunches with the laser pulses. In the future there will be a MIT/Desy-like System with a pulsed fiber laser as an optical reference oscillator. The laser pulses will be distributed over stabilized fiber links to the remote stations. Later on it is planned to install EOM-based beamarrival timemonitors (BAMs) in order tomonitor the bunch jitter and to establish a feedback system to reduce the jitter. Besides that, the timing system has to be revised to trigger experiments with lowrepetition rate, two guns (thermionic DC, superconducting RF) and lasers. The Posterwill showthe Layout of the possible future Timing and Synchronization System at ELBE.

Keywords: Timing Synchronization ELBE

  • Open Access Logo Contribution to proceedings
    DIPAC2011 - Beam Diagnostics and Instrumentation for Particle Accelerators, 16.-18.05.2011, Hamburg, Germany
    Future Timing and Synchronization Scheme at ELBE
  • Poster
    DIPAC2011 - Beam Diagnostics and Instrumentation for Particle Accelerators, 16.-18.05.2011, Hamburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-16281
Publ.-Id: 16281


Entwicklung hochspezifischer und sensitiver Biosensoren auf Basis von bakteriellen Hüllproteinen und Aptameren

Weinert, U.; Pollmann, K.; Nikolaus, N.; Strehlitz, B.; Raff, J.

Im Zuge der immer genaueren Kontrollen von Arzneimittelresten in z. B. Lebensmitteln, steigt die Nachfrage nach sensitiveren und spezifischeren Sensoren. Auch in der Trinkwassserqualität steigt die Nachfrage nach Kontrollen von Pharmaka-Reststoffen. Dem entgegen steht, dass die Detektion von derartigen Substanzen häufig mit viel analytischen Aufwand verbunden ist und meist nur offline erfolgen kann.
In dieser Arbeit soll daher ein Biosensor entwickelt werden, der bestehend aus bakteriellen Hüllproteinen, Aptameren und Fluorophoren, in der Lage ist kleinste Mengen an bestimmten Arzneimitteln in wässrigen Systemen zu detektieren.

Keywords: S-layer proteins; sensory layer; biosensor; aptamers

  • Poster
    10. Dresdner Sensor-Symposium, 05.-07.12.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16280
Publ.-Id: 16280


Enhancing the high temperature capability of Ti-alloys

Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.

Titanium and its alloys can not be used at elevated temperatures in oxidizing environment because the rutile layer gets deteriorated. With increasing temperature the passivation vanishes which protects the alloys at low temperatures. Furthermore the enhanced oxygen inward diffusion at elevated temperatures worsens the mechanical properties by -case formation. To overcome this problem a combined Al- plus F-treatment was developed. The combination of Al-enrichment at the surface zone so that intermetallic TiyAlx-layers are formed plus stabilisation of the alumina formation by the fluorine effect led to good results in high temperature exposure tests of several Ti-alloys. In this paper the achieved improvements are described and the results will be discussed for a use of Ti-alloys in several high temperature applications.

  • Lecture (Conference)
    European Congress and Exhibition on on Advanced Materials and Processes (EUROMAT 2011), 12.-15.09.2011, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-16279
Publ.-Id: 16279


New developments concerning the fluorine effect for TiAl-alloys

Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.

The fluorine effect improves the oxidation resistance of TiAl-alloys drastically. The formation of a non protective fast growing mixed oxide scale is suppressed and instead a protective alumina layer is formed after fluorine treatment. Fluorine can be applied by several methods which, however, have to be optimised. An overdoping can lead to enhanced oxidation and worsen the situation. The parameters for an optimised process will be described. An improvement of the already good performance of specimens treated only with fluorine can be achieved e.g. by dipping in inorganic acids containing additional elements to fluorine. The results of high temperature oxidation tests of differently treated TiAl-samples will be presented. Post experimental metallographic investigations reveal the oxide scales formed so that the effect can be rated. Finally the results will be discussed in the view of the models for the fluorine effect.

  • Lecture (Conference)
    European Congress and Exhibition on on Advanced Materials and Processes (EUROMAT 2011), 12.-15.09.2011, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-16278
Publ.-Id: 16278


Development and characterization of advanced coatings for TiAl alloys

Pelic, B.; Bortolotto, L.; Goldberg, S.; Witschel, B.; Rafaja, D.; Masset, P. J.; Donchev, A.; Yankov, R.; Kolitsch, A.; Schütze, M.

Titanium aluminides exhibit quite good mechanical properties even at elevated temperatures for aeronautic and automobile applications. Their low specific density (half of classical nickel based super alloys) makes them attractive for applications where the mass is a critical parameter, i.e. rotating pieces. At elevated temperatures they suffer of environmental embrittlement by hot gases, which deteriorates drastically their mechanical properties and still hampers their use to temperatures above 500°C in industrial applications. In this work, coatings involving reactive elements such Cr, Y combined with the halogen effect (fluorine surface treatment) have been developed using MO-CVD, CVD, PVD and HVOF techniques. The coatings were characterized as produced and after annealing by means of glancing XRD, GDEOS to analyze their structure, homogeneity and composition, respectively. The adhesion properties of the coatings were measured by using impact tests before and after oxidation. The oxidation behavior of the produced coatings was evaluated in the temperature range of the industrial use, e.g. 600-850°C whereas corrosion tests were conducted using Na2SO4-NaCl mixtures in dry and wet environments. After oxidation/corrosion test post-mortem analysis was carried out using SEM-EDX, EPMA analysis to investigate the oxide layer composition, structure and the corrosion products, respectively. Mechanical properties losses of coated specimens after oxidation/corrosion due to embrittlement were evaluated using 4 point bending test combined with acoustic emission. It was shown that some of the developed coatings reduce the embrittlement sensibility of these alloys.

Keywords: TiAl alloys; coatings; CVD; PVD; HVOF; high temperature oxidation/corrosion

  • Poster
    European Congress and Exhibition on Advanced Materials and Processes (EUROMAT 2011), 12.-15.09.2011, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-16277
Publ.-Id: 16277


Surface engineering of Ti and low-Al content Ti-base alloys for high-temperature environmental protection

Yankov, R. A.; Kolitsch, A.; von Borany, J.; Mücklich, A.; Munnik, F.; Steinert, M.; Frenzel, C.; Donchev, A.; Schütze, M.

An oxygen barrier coating has been developed, which is effective in preventing oxidation and oxygen embrittlement of Ti and several low-Al content Ti-base alloys during exposure to oxidizing environments at elevated temperatures. The fabrication process has involved magnetron co-sputtering of titanium and aluminum followed by vacuum annealing and plasma immersion ion implantation of fluorine. The resulting coating consists primarily of γ-TiAl while containing a minor portion of Ti3Al present in the coating/substrate interfacial region. The implantation of fluorine provides the necessary conditions for triggering the halogen effect upon subsequent high-temperature exposure in air. Systematic characterization of the coating material in terms of microstructure, phase formation and element depth distribution has been performed using cross-sectional transmission electron microscopy (XTEM) in conjunction with electron energy loss spectroscopy (EELS), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and elastic recoil detection (ERD). Overall, the coating fabrication process has been found to be independent of the substrate material making the technique universally applicable at least to the alloys studied. Following oxidation in air at 600°C for 100 h, specimens have been prepared for metallographic analysis, and their cross sections have been characterized by scanning electron microscopy (SEM) in combination with EDX, and electron probe microanalysis (EPMA). The results obtained show that during oxidation exposure the γ-TiAl coating is capable of forming a protective alumina-containing scale, which serves as an oxygen barrier, thereby preventing oxygen embrittlement in the substrate material. In addition, since the only constituents of the coating are Ti and Al, it exhibits excellent chemical substrate compatibility.

  • Poster
    Dresdner Werkstoffsymposium "Werkstoffe für die Mobilität", 08.-09.12.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16276
Publ.-Id: 16276


Magneto-optical observation of four-wave scattering in a 15-nm Ni81Fe19 film during large-angle magnetization precession

Nembach, H. T.; Livesey, K. L.; Kostylev, M. P.; Martin-Pimentel, P.; Hermsdoerfer, S. J.; Leven, B.; Fassbender, J.; Hillebrands, B.

Large-angle magnetization precession induced by a short pulsed magnetic field in a 15-nm thick Ni81Fe19 film is observed by use of a time-resolved magneto-optical Kerr effect technique with sensitivity to all three components of the magnetization vector. A reduction of the magnitude of the magnetization vector |M| during large-angle precession is inferred and indicates incoherent dynamics due to excitation of traveling spinwaves with wavelengths smaller than the diameter of the sampling area, that is, the laser spot size for the magneto-optical measurements. The reduction in |M| depends on the magnetic bias field Hbias, which can be qualitatively understood by comparison to the theoretical threshold for observing four-magnon scattering in a small time interval t. We estimate that two-magnon scattering cannot explain the experimental results.

Permalink: https://www.hzdr.de/publications/Publ-16275
Publ.-Id: 16275


Radiolabelling of commercial Ag0 and TiO2 nanoparticles with 110mAg and 44Ti for life-cycle studies

Hildebrand, H.; Franke, K.

Vortrag im Rahmen eines Workshops, kein gesonderter Abstract vorhanden.
Dieser Workshop beschäftigt sich speziell mit der Radiomarkierung von Nanopartikeln. Eigene Ergebnisse sollen mit Fachkollegen aus ganz Europa diskutiert werden. Ziel ist es auch, ggf. neue Kooperationen anzubahnen.

  • Lecture (Conference)
    CYCLEUR Workshop, 28.-29.11.2011, Ispra, Italia

Permalink: https://www.hzdr.de/publications/Publ-16274
Publ.-Id: 16274


Interactive calibration and registration of electromagnetic trackung systems for Virtual Reality

Skripcak, T.; Tanuska, P.; Schmeißer, N.

This article is aimed on the calibration and registration of electromagnetic tracking system for the purpose of immersive virtual reality application. The first part of the article provides a basic introduction into position and orientation tracking subsystems and denotes problems which are occurring while electromagnetic approach is used for tracking purposes. After that two methods for tracking system calibration are presented and also a solution for position registration of tracking systems with projection space is provided. Second part is focused on interactive calibration application, where the process of development and a resulting application structure is described. Finally results obtained by usage of interactive calibration application are compared. The main goal of this article is to present a way of dealing with static errors in virtual reality application in order to obtain proper alignment of the virtual and real world.

Keywords: virtual reality; electromagnetic tracking system; calibration; registration

  • Contribution to proceedings
    IDS - INTERNATIONAL DOCTORAL SEMINAR, 15.-17.5.2011, Smolenice, Slovakia
    International Doctoral Seminar 2011 : Proceeding. Smolenice Castle, SR, Trnava: AlumniPress, 978-80-8096-145-9, 365-375

Permalink: https://www.hzdr.de/publications/Publ-16273
Publ.-Id: 16273


Design and Implementation of Interactive Visualisation Configuration using Interaction Paradigms in Virtual Reality Environment

Skripcak, T.; Tanuska, P.; Schmeißer, N.

This article is aimed on the specific task of interaction with an immerse visualisation application. The first part of the article provides basic introduction into interaction paradigms in 3D space. After that classification and description of standard interaction tasks are presented. We introduce our view of matter on relations between the 3D interaction and standard interaction techniques. The second part describes hardware and software components of our VR system. Furthermore an overview of the architecture and implementation details of system for interactive visualisation configuration is discussed. We describe design specifications of a 3D UI, which helps to make interaction less error prone for inexperienced users. A specific solution for performing numerical input is also provided. The main goal of the article is to describe how 3D user interface paradigms can be implemented in the VR system.

Keywords: VirtualReality visualization; 3d interaction

  • Open Access Logo International Journal of Soft Computing and Engineering (IJSCE) 1(2011)5, 57-65

Permalink: https://www.hzdr.de/publications/Publ-16272
Publ.-Id: 16272


TOPFLOW-Experimente, Modellentwicklung und Validierung von CFD-Codes für Wasser-Dampf-Strömungen mit Phasenübergang

Lucas, D.; Beyer, M.; Krepper, E.; Vallée, C.; Höhne, T.; Seidel, T.; Szalinski, L.; Hampel, U.; Schmidtke, M.; Schleicher, E.; Pietruske, H.; Schütz, P.; Danciu, D.; Zhang, D.; Deendarlianto; Barthel, F.; Zippe, C.; Hänsch, S.; Carl, H.; Weiß, F.-P.

Das Ziel des Vorhabens bestand in der Ertüchtigung von CFD-Codes für Wasser-Dampf-Strömungen mit Phasenübergang. Während CFD-Verfahren für einphasige Strömungen bereits breite Anwendung in der Industrie finden, steht ein entsprechender Einsatz für Zweiphasenströmungen auf Grund der komplexen Phasengrenzfläche und den davon beeinflussten Wechselwirkungen erst am Anfang. Für die Weiterentwicklung und Validierung geeigneter Schließungsmodelle werden experimentelle Daten mit hoher Orts- und Zeitauflösung benötigt. Solche Daten wurden an der TOPFLOW-Versuchsanlage des HZDR durch Kombination von Experimenten bei praxisnahen Parametern für die Reaktorsicherheit (große Skalen, hohe Drücke und Temperaturen) und innovativer Messtechnik gewonnen. Die Gittersensortechnik, mit der detaillierte Informationen über die Phasengrenzfläche gewonnen werden können, wurde in adiabaten Wasser-Luft-Experimenten sowie Kondensations- und Druckentlastungsexperimenten in einem großen DN200-Rohr eingesetzt. Umfangreiche Datenbasen mit hoher Qualität stehen im Ergebnis des Vorhabens zur Verfügung. Die Technologie für die schnelle Röntgentomographie, die Messungen ohne Strömungsbeeinflussung ermöglicht, wurde weiter entwickelt und in einer ersten Messserie erfolgreich eingesetzt. Hochaufgelöste Daten wurden auch in Experimenten zu verschiedenen Strömungssituationen (z.B. Gegenstrombegrenzung) in einem Modell des heißen Strangs eines Druckwasserreaktors gewonnen. Für die Wasser-Dampf-Experimente bei Drücken von bis zu 5 MPa wurde dabei erstmals die neu entwickelte innovative Drucktanktechnologie eingesetzt. Zur Ertüchtigung von CFD-Codes für Zweiphasenströmungen wurde das Inhomogene MUSIG-Modell für Phasenübergänge in Kooperation mit ANSYS erweitert und anhand der o.g. TOPFLOW-Experimente validiert. Außerdem erfolgten Verbesserungen u.a. für die Turbulenzmodellierung in Blasenströmungen sowie Simulationen zur Validierung der Modelle für Blasenkräfte und Blasenkoaleszenz und -zerfall. Ein wesentlicher Fortschritt wurde bei der Modellierung freier Oberflächen durch die Verallgemeinerung des AIAD-Modells erreicht. Die am Heißstrangmodell ermittelten Flut¬kurven können unter Nutzung dieses Modells in guter Übereinstimmung berechnet werden.

Keywords: CFD; two-phase flow; safety research; experiment; model development; validation

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-011 2011
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-16271
Publ.-Id: 16271


Cyclotron resonance and interband optical transitions in HgTe/CdTe(0 1 3) quantum well heterostructures

Ikonnikov, A.; Zholudev, M.; Spirin, K.; Lastovkin, A.; Maremyanin, K.; Aleshkin, V.; Gavrilenko, V.; Drachenko, O.; Helm, M.; Wosnitza, J.; Goiran, M.; Mikhailov, N.; Dvoretskii, S.; Teppe, F.; Diakonova, N.; Consejo, C.; Chenaud, B.; Knap, W.

Cyclotron resonance spectra of 2D electrons in HgTe/CdxHg1−xTe (0 1 3) quantum well (QW) heterostructures with inverted band structure have been thoroughly studied in quasiclassical magnetic fields versus the electron concentration varied using the persistent photoconductivity effect. The cyclotron mass is shown to increase with QW width in contrast to QWs with normal band structure. The measured values of cyclotron mass are shown to be systematically less than those calculated using the 8 × 8 Kane model with conventional set of HgTe and CdTe material parameters. In quantizing pulsed magnetic fields (Landau level filling factor less than unity) up to 45 T, both intraband (CR) and interband magnetoabsorption have been studied at radiation wavelengths 14.8 and 11.4 µm for the first time. The results obtained are compared with the allowed transition energies between Landau levels in the valence and conduction bands calculated within the same model, the calculated energies being again systematically less (by 3–14%) than the observed optical transition energies.

Keywords: Semiconductors; cyclotron resonance; quantum wells; topological isolators

Permalink: https://www.hzdr.de/publications/Publ-16270
Publ.-Id: 16270


Thin film intermetallic compound formation by flash-lamp annealing: an implication of ultra-fast alloying and metallurgy

Yankov, R. A.; Kolitsch, A.; von Borany, J.; Munnik, F.; Voelskow, M.; Schumann, T.; Skorupa, W.; Donchev, A.; Schütze, M.

Experiments have been undertaken to explore the possibility of rapidly melting and alloying thin metal films by flashlamp annealing (FLA). Aluminum layers of a thickness of 100 to 500 nm have been deposited on α-titanium substrates by magnetron sputtering. The structures have then been heat-treated by FLA in air using flash duration of 20 msec, energy density of 60 to 100 J/cm2, and maximal temperature of 800 to 1660°C. X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA) have been used for sample characterization. The as-deposited Al films are amorphous/nanocrystalline (grain size ~ 5 nm) in nature. Heat treatment by FLA has been found to produce an intermetallic TiAl3 phase. For comparison, under conditions of standard furnace annealing, the formation of this compound in the thin film reaction of Al and Ti necessitates anneal temperatures and times typically in excess of 400°C and 1 h, respectively. Furthermore, the intermetallic TiAl3 phase formed by FLA appears to be present in a region extending from the surface to a depth of a few hundred nm. Importantly, no pure Al phase has been detected either at the surface or in the substrate bulk. XRD measurements have also identified negligibly small amounts of Al and Ti oxide phases. It is expected that one may obtain TiAl phases other than TiAl3 by varying both the film composition (i.e. by co-depositing Al and Ti instead of Al only) and the FLA parameters. The results of this study indicate that FLA of thin metal films is a promising technique for rapid surface alloying and compound formation. For the particular case of the Ti/Al system, t he i ntermetal lc if il ms s o f abricated m ay h ave r el evance t o h igh-temperature m icroel ectronics applications (diffusion barriers, conduction lines etc) as well as to the oxidation protection of titanium and titaniumaluminum alloy surfaces by forming suitable intermetallic TiAl phases.

Keywords: rapid melting and alloying; FLA; intermetallic TiAl3 phase

  • Lecture (Conference)
    subtherm; International Topical Workshop on Subsecond Thermal Prosessing of advanced Materials, 25.-27.10.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16269
Publ.-Id: 16269


Interactions between GaO4Al12(OH)24(H2O)127+ and cellulosic materials

Sundman, O.; Persson, P.; Banerjee, D.; Ohman, L.-O.

The adsorption qualities of GaO4Al12(OH)24(H2O)127+, a polycation with ε-Keggin structure, and its stability in contact with anionic cellulosic materials, was investigated under different concentration and ionic strength conditions. The cellulosic materials employed were two different fully bleached fibre materials, carboxyl methyl cellulose (CMC), and a spin coated cellulose model surface. As analytical techniques, pH-measurements, potentiometric titrations, ICP-OES, QCM-D, equilibrium calculations and Extended X-ray Absorption Fine Structure (EXAFS) were used. The adsorption is very strong and the addition of GaO4Al12(OH)24(H2O)127+ to a fibre suspension results in a rapid decrease in pH, followed by a small and slow increase in pH. This behaviour can be explained as due to a rapid and strong adsorption of intact GaO4Al12(OH)24(H2O)127+ ions, followed by a slow, and minor, 3-8 %, decomposition into different monomers. Alternative layer by layer adsorption of this ion, and CMC, on a spin coated cellulose model surface, constitutes further evidence for the strong interactions between the anionic cellulose materials and GaO4Al12(OH)24(H2O)127+. It is shown that the strong adsorption observed could not be described as due to an unspecific Donnan adsorption behaviour, neither of GaO4Al12(OH)24(H2O)127+ nor Ga and Al monomers, and specific surface complex formation is therefore discussed and applied.

Keywords: EXAFS; GaO4Al12(OH)24(H2O)127+; ionic exchange; Donnan equilibrium

Permalink: https://www.hzdr.de/publications/Publ-16268
Publ.-Id: 16268


Erfolgreich gegen Krebs – Präzisionsbestrahlungen mit Ionen

Fiedler, F.; (Editor)

no abstract available

  • Lecture (others)
    Physik am Samstag, 19.11.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16267
Publ.-Id: 16267


The complexation of uranium(VI) and atmospherically derived CO2 at the ferrihydrite-water interface probed by time-resolved vibrational spectroscopy

Foerstendorf, H.; Heim, K.; Rossberg, A.

The sorption reactions of uranium(VI) at the ferrihydrite(Fh)-water interface were investigated in the absence and presence of atmospherically derived CO2 by time-resolved in situ vibrational spectroscopy. The spectra clearly show that a single uranyl surface species, most probably a mononuclear bidentate surface complex, is formed irrespective of the presence of atmospherically derived CO2. The character of the carbonate surface species correlates with the presence of the actinyl ions and changes from a monodentate to a bidentate binding upon sorption of U(VI). From the in situ sorption experiments under mildly acid conditions, the formation of a ternary surface complex is derived where the carbonate ligands coordinate bidentately to the uranyl moiety (≡UO2(O2CO)x). Furthermore, the release reaction of the carbonate ligands from the ternary surface complex is found to be considerably retarded compared to those from the pristine surface suggesting a tighter bonding of the carbonate ions in the ternary complex. Simultaneous sorption of U(VI) and atmospherically derived carbonate onto pristine Fh shows formation of binary monodentate carbonate surface complexes prior to the formation of the ternary complexes.

Keywords: Ternary surface complex; uranyl; carbonate; ferrihydrite; time-resolved spectroscopy; ATR FT-IR spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-16266
Publ.-Id: 16266


High Conversion Th-U233 fuel assembly for current generation of PWRs

Baldova, D.; Fridman, E.

This paper presents a preliminary design of a high conversion Th-U233 fuel assembly applicable for current generation of Pressurized Water Reactor (PWRs). The considered fuel assembly has a typical 17×17 PWR lattice. However in order to increase the conversion of Th232 to U233, the assembly was subdivided into the two regions called seed and blanket. The central seed region has a higher than blanket U233 content and acts as a neutron source for the peripheral blanket region. The latest acts as a U233 breeder. While the seed fuel pins have a standard dimensions the blanket fuel radius was increased in order to reduce the moderation and to facilitate the resonance neutron absorption in blanket Th232. The U233 content in the seed and blanket regions was optimized to achieve maximal initial to discharged fissile inventory ratio (FIR) taking into account the following constrains: 1) target fuel cycle length of 18 months assuming 3-batch reloading scheme, 2) during the fuel cycle the core k-eff should be higher or equal to 1. In this study the neutronic calculations were performed on the fuel assembly level using the Helios deterministic lattice transport code. The fuel cycle length and the core k-eff were estimated with the help of Non Linear Reactivity Model. The applicability of the Helios code for the analysis of the Th-based high conversion designs was confirmed with the help of continuous-energy Monte-Carlo code Serpent. The results of optimization studies show that for the heterogeneous seed and blanket (SB) fuel assembly the FIR of about 0.94 can be achieved.

Keywords: High Conversion Fuel Cycle; Seed-blanket fuel assembly

  • Contribution to proceedings
    PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, 15.-20.04.2012, Knoxville, Tennessee, USA
  • Lecture (Conference)
    PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, 15.-20.04.2012, Knoxville, Tennessee, USA

Permalink: https://www.hzdr.de/publications/Publ-16265
Publ.-Id: 16265


Influence of low uranium concentrations on Peanibacillus sp. JG-TB8 using calorimetric metabolic monitoring

Obeid, M.; Geissler, A.; Fahmy, K.; Oertel, J.

The qualitative and quantitative risk assessment of radiotoxicity in contaminated sites plays a key role in radioecological monitoring and for environmental protection. High doses of radioactivity are physically measurable in the near field of nuclear waste disposals. However, it is a major challenge to develop methods for low dose risk assessments typical for the far field, where transmission of radionuclides into the food chain may lead to health risks that are not detectable by conventional methods. To address this problem, a novel approach using metabolic monitoring of bacterial cell growth was established using the Thermal Activity Monitor (TAMIII; TA intruments, USA) as a multichannel microcalorimeter to identify the minimal dose of radionuclides that generates a measurable change in metabolic heat release. In this approach, the toxicity of a radionuclide was defined as a measurable effect on the metabolic activity of Peanibacillus sp. JG-TB8, a gram-positive bacterium isolated from a soil sample of the uranium mining waste pile “Haberland” (Johanngeorgenstadt, Saxony, Germany). Liquid cultures of this strain were exposed to micromolar concentrations of uranium (VI) salts and the metabolic heat release measured as a function of time and temperature. The non-radioactive "heavy metal stress" exerted by europium (Eu(III)) served as reference under the same conditions. Preliminary results show distinct and reproducible effects of uranium and europium on the time-dependent heat release already at 10 µM concentration. The toxicity of uranium and europium caused a decrease of maximal heat flow compared to control samples. In contrast to europium, for which the inhibitory action scales with concentration, uranium influences bacterial growth in a more complicated manner which strongly depends on temperature and pH, probably as a consequence of its different speciations. The results demonstrate that microcalorimetric monitoring is an extremely sensitive tool to investigate the influence of low heavy metal and radionuclide concentrations on the metabolic activity of microorganisms as shown here for Peanibacillus sp. JG-TB8.

Keywords: radiotoxicity; microcalorimetry; heavy metal

  • Poster
    Uranium biogeochemistry: transformations and applications, 11.-16.03.2012, Monte Verita, Ascona, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-16264
Publ.-Id: 16264


Long intersubband relaxation times in n-type germanium quantum wells

Ortolani, M.; Stehr, D.; Wagner, M.; Helm, M.; Pizzi, G.; Virgilio, M.; Grosso, G.; Capellini, G.; de Seta, M.

We measured the non-radiative intersubband relaxation time in n-type modulation-doped Ge/SiGe multi-quantum wells of different thickness by means of degenerate pump-probe experiments. The photon energy was tuned to be resonant with the lowest conduction band intersubband transitionenergy (14-29 meV), as measured by terahertz absorption spectroscopy and in agreement with bandstructure calculations. Temperature-independent lifetimes in excess of 30 ps were observed.

Keywords: intersubband; germanium; free-electron laser; relaxation time; terahertz

  • Applied Physics Letters 99(2011), 201101

Permalink: https://www.hzdr.de/publications/Publ-16262
Publ.-Id: 16262


Revised Methods for Few-Group Cross Sections Generation in The Serpent Monte Carlo Code

Fridman, E.; Leppänen, J.

This paper presents new calculation methods, recently implemented in the Serpent Monte Carlo code, and related to the production of homogenized few-group constants for deterministic 3D core analysis. The new methods fall under three topics: 1) Improved treatment of neutron-multiplying scattering reactions, 2) Group constant generation in reflectors and other non-fissile regions and 3) Homogenization in leakage-corrected criticality spectrum. The methodology is demonstrated by a numerical example, comparing a deterministic nodal diffusion calculation using Serpent-generated cross sections to a reference full-core Monte Carlo simulation. It is concluded that the new methodology improves the results of the deterministic calculation, and paves the way for Monte Carlo based group constant generation.

Keywords: Serpent; Monte Carlo; lattice physics; few-group cross-section generation; reflector cross sections; criticality spectrum; 3D core analysis

  • Contribution to proceedings
    PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, 15.-20.04.2012, Knoxville, Tennessee, USA
  • Lecture (Conference)
    PHYSOR 2012 – Advances in Reactor Physics – Linking Research, Industry, and Education, 15.-20.04.2012, Knoxville, Tennessee, USA

Permalink: https://www.hzdr.de/publications/Publ-16261
Publ.-Id: 16261


Radio- and fluorescence-labelled Cetuximab for multimodal imaging

Zenker, M.; Bergmann, R.; Walther, M.; Pietzsch, H.-J.; Heldt, J.-M.; Steinbach, J.

Objectives:
Radio (64Cu++) and fluorescence (Alexa Fluor 488) labelled Cetuximab (C225) offers the possibility of multimodal imaging of epidermal growth factor receptor (EGFR). ([64Cu]Cu-NOTA)7-C225-(Alexa Fluor 488)7 was synthesized and the imaging and biodistribution has been proved by small animal PET and ex vivo studies of cryo-sections of xenotransplanted mice.
Methods:
1) Synthesis of (NOTA)x-C225-(Alexa Fluor 488)y (C225-Conjugate). The C225 solution (Erbitux, Merck KGaA, Germany) was buffer-exchanged with a NaHCO3 solution (50 mM, pH 6.0) containing NaCl (150 mM) using a Jumbosep 30 k molecular weight cut-off concentrator (Pall Life Sciences, Germany). NOTA (2-(pisothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid, p-SCN-Bn-NOTA, Macrocyclics, USA) and Alexa Fluor 488 (Alexa Fluor 488 carboxylic acid 2,3,5,6-tetrafluorophenyl ester, Invitrogen, United Kingdom) has been conjugated to C225 lysine amino residues in a single step. Just prior to protein conjugation, NOTA and Alexa Fluor 488 were dissolved in HEPES-buffer (400 μL, 500 mM, pH 7.2) and added to the C225 solution to achieve a molar reaction ratio of 10:1 (NOTA:C225) and gently manually agitated. The reaction mixture was allowed to incubate in the dark at 25°C for 24 h without further stirring. Excess NOTA chelator and dye were removed by passage of the reaction solution through a Jumbosep. The buffer-exchange was performed with an NH4OAc solution (50 mM, pH 6.0) containing NaCl (150 mM). Protein concentration and the number of conjugated dye molecules per mAb were determined by UV/VIS absorption at 280 nm and 495 nm (excitation maxima of Alexa Fluor 488), respectively. The number of NOTA introduced was determined using MALDI-TOFMS. 2) Radiolabeling with 64Cu. A solution of [64Cu]CuCl2 in HCl (0.04 M, 50 MBq) was added to the C225-conjugate (100 μg) plus MES buffer (100 μL, 200 mM, pH 6.1) in 2 mL protein low-binding tubes (Eppendorf, Germany), vortexed immediately and incubated at 30°C for 30 min. Radiochemical yield (RCY) was determined by radio-ITLC. Before ITLC-analyses, free TETA chelator (32 μL; 0.1 μg/μL) was added to the reaction mixture for quenching the labelling reaction and fixing unreacted radionuclide. Therefore a second incubation at 30°C for 30 min was necessary. As stationary ITLC-phase, a 10 cm ITLC-SA strip (Varian GmbH, Germany) and as mobile phase a 0.9% NaCl solution has been used. The radio labelled antibody was purified by spin filtration using Microcon 30 k (Millipore). 3) Biodistribution. Squamous cell carcinoma (FaDu) tumour bearing NMRI nu/nu mice were studied with PET at 24 h p.i. The fine distribution of the probe was then characterized using whole body cryosectioning. The 64Cu-activity was compared with the fluorescence distribution.
Results:
The BFC NOTA and Alexa Fluor 488 were successfully simultaneously conjugated to C225. The resulting conjugate is (NOTA)1-C225-(Alexa Fluor 488)7. Radionuclide labelling was achieved within 30 min with optimization of the molar ratio of NOTA:C225: Alexa Fluor 488 during the conjugation. The radioimmunoconjugate exhibited high accumulation in xenotransplanted FaDu tumours in mice after 24 hours. The 64 Cu-activity concentration correlated well with the fluorescence in most tissues except the liver.
Conclusions:
Dual-labelled immunoconjugates represent a potential probe for translational application in tumour detection, evaluation of long-term distribution and stability studies of the labelled antibody.
Research support: This project was partially supported by “Kompetenzverbund Strahlenforschung” (grant 02NUK006A-E).

  • Poster
    19th International Symposium on Radiopüharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S196

Permalink: https://www.hzdr.de/publications/Publ-16260
Publ.-Id: 16260


Electron Temperature Scaling in Laser Interaction with Solids

Kluge, T.; Cowan, T.; Debus, A.; Schramm, U.; Zeil, K.; Bussmann, M.

A precise knowledge of the temperature and number of hot electrons generated in the interaction of shortpulse high-intensity lasers with solids is crucial for harnessing the energy of a laser pulse in applications such as laser-driven ion acceleration or fast ignition. Nevertheless, present scaling laws tend to overestimate the hot electron temperature when compared to experiment and simulations. We present a novel approach that is based on a weighted average of the kinetic energy of an ensemble of electrons. We find that the scaling of electron energy with laser intensity can be derived from a general Lorentz invariant electron distribution ansatz that does not rely on a specific model of energy absorption. The scaling derived is in perfect agreement with simulation results and clearly follows the trend seen in recent experiments, especially at high laser intensities where other scalings fail to describe the simulations accurately.

Keywords: Laser; Electron; Proton; Ion; Temperature; Energy; Scaling; PIC; Model; Analytic; Acceleration; TNSA

  • Physical Review Letters 107(2011), 205003
    DOI: 10.1103/PhysRevLett.107.205003
  • Lecture (Conference)
    Dresden Enlite, 16.-20.04.2012, Dresden, Deutschland
  • Poster
    Dresden Enlite, 16.-20.04.2012, Dresden, Deutschland
  • Poster
    33rd International Workshop on Physics of High Energy Density in Matter, 13.-18.01.2013, Hirschegg, Österreich
  • Lecture (Conference)
    SPIE Optics+Optoelectronics, 15.-18.04.2013, Prag, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-16259
Publ.-Id: 16259


Radiolabelled cathepsin inhibitors as potential PET tracers for tumour imaging

Löser, R.; Frizler, M.; Bergmann, R.; Dombrowski, L.; Knieß, T.; Gütschow, M.; Steinbach, J.

Objectives:
Thiol-dependent cathepsins are a class of cysteine proteases that have been shown to be linked to the progression of cancer in multiple ways. Particularly crucial is their involvement in proteolytic pathways that are related to tumour invasion and metastasis [1]. The aim of this study was the design of cathepsin inhibitors based on the structure of the azadipeptide nitrile chemotype [2] that permit the labelling with the positron emitters fluorine-18 and carbon-11 and to evaluate the
potential of this inhibitor class for functional tumour imaging by PET. Additionally, a first insight into the pharmacokinetic behaviour of these inhibitors should be gained.
Methods:
The fluorine atom was linked by an ethylene bridge to the inhibitor core structure. Labelling with fluorine-18 was achieved by fluoroethylation of 1 with different substituted [18F]2-fluoroethyl benzenesulfonates [3]. In addition, the introduction of radiofluorine into 2 was attempted by direct fluorination of the corresponding tosyl and nosyl precursors. The stability of the tracer against chemical and enzymatic degradation as well as its metabolic fate in rat blood was investigated and its biodistribution was studied in vivo by small animal PET. To obtain an 11C-based tracer, the fluoroethyl group of 2 was replaced by methyl. Introduction of carbon-11 was done by conversion of the phenolic precursor 1 with [11C]methyl iodide generated by the gas-phase method. The affinities of the compounds 1-3 to their targets were determined in kinetic enzyme assays.
Results:
The azadipeptide nitriles 1-3 exhibited inhibition constants in the single-digit to subnanomolar range against the oncologically relevant cathepsins L, S, and B. Among the various 18F-fluoroethylating agents tested, [18F]2-fluoroethyl nosylate revealed as the most efficient one. This enabled the two-step radiosynthesis of [18F]2 in an average RCY (d.c.) of 27±5% (n = 13). The direct radiofluorination of the corresponding sulfonate precursors could provide [18F]2 in only low labelling yields. PET studies in rats together with in vitro investigations indicated the trapping of the tracer in erythrocytes, which could be attributed to its inherent thiol reactivity. The tracer [11C]3 could be obtained in labelling yields of 35-42% depending on the employed base. Its radiopharmacological behaviour is under current investigation.
Conclusions:
With the azadipeptide nitriles 2 and 3 highly potent cathepsin inhibitors were found and their labelling with fluorine-18 and carbon-11 could be successfully established. The compounds’ suitability as PET tracers for functional tumour imaging seems to be limited due to their thiol reactivity. The radiolabelling of further cathepsin inhibitors is underway.
References:
[1] Mohamed & Sloane (2006) Nat. Rev. Cancer 6, 764-775, [2] Löser et al. (2008) Angew. Chem.
Int. Ed. 47, 4331-4334, [3] Musachio et al. (2005) J. Label. Compd. Radiopharm. 48, 735-747

  • Poster
    19th International Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S190

Permalink: https://www.hzdr.de/publications/Publ-16258
Publ.-Id: 16258


Development and fluorine-18-radiolabeling of benzodioxolylpyrimidine EphB4 receptor inhibitors

Mamat, C.; Neuber, C.; Mosch, B.; Pietzsch, J.; Steinbach, J.

Objectives: Ephrins and Eph receptors were found to be disregulated in several human tumor entities like breast, colon, liver, prostate or melanoma [1]. Concerning Eph/ephrin signalling, the EphB4/ephrinB2 system seems to play a major role in tumor angiogenesis [2]. Several inhibitors were reported based either on peptides which block the extracellular ephrin binding domain [3] or small organic molecules which block the intracellular kinase domain of Eph receptors. For this purpose, promising EphB4 kinase inhibitors based on the dioxolylpyrimidine scaffold were used for the development of a novel radiofluorinated PET tracer candidate [4].
Methods:
Compound 1 (figure 1) represents an advantageous molecule for the development of a fluorine-18 containing radiotracer. It shows an adequate affinity to EphB4 (90 nM) and consists of two structural parts. For the synthesis of the new radiotracer [18F]2, the methylsulfonylphenyl residue in 1 was replaced by a 3-fluoropropylsulfonylphenyl moiety (part B). This part of the molecule was prepared starting from sodium benzenesulfinate and 1-bromopropanol in 5 synthesis steps. Part A of the radiotracer as well as the lead compound containing the benzodioxole moiety was synthesized as described previously [4]. Finally, the non-radioactive reference 2 was obtained after 6 steps, whereas the respective tosylate precursor was prepared within 7 steps. Cellular binding and internalization of [18F]2 was investigated in human A375 melanoma cells as well as A375 cells stably transfected with human EphB4 receptor or mock vector. Furthermore, specific binding and potential transport mechanisms were analyzed by application of different specific inhibitors.
Results:
Starting from a 2 GBq [18F]fluoride batch, 65±5 MBq of [18F]2 were obtained with >95% radiochemical purity within 60 min synthesis time (including HPLC purification tR = 3.9 min, acetonitrile:water, 1:1 + 0.1% TFA). The best conditions for radiolabeling of the tosylate precursor were found to be acetonitrile as solvent at 90 °C for 15 min. Afterwards, water was added and the mixture was filtered prior to the HPLC purification. Cell association studies in melanoma cells showed time dependent increase in binding and internalization of [18F]2. Both inhibition with lead compound 1 and [19F]2 significantly decreased binding and internalization of [18F]2
indicating specific EphB4 binding. However, involvement of other kinases for binding can not be excluded. Moreover, participation of ATP-binding cassette transporters for cellular uptake is indicated.
Conclusions:
A novel potential EphB4 inhibitor based on the dibenzodioxolylpyrimidine scaffold has been synthesized and successfully radiolabeled with fluorine-18. Further biological studies including dynamic small animal PET are currently in progress.
References:
[1] B. Mosch, B. Reissenweber, C. Neuber, J. Pietzsch (2010), J. Oncol., DOI: 10.1155/2010/135285,
[2] E. Pasquale (2010), Nature Rev. Cancer, 10, 165, [3] J. E. Chrencik, A. Brooun, M. I. Recht, G. Nicola, L. K.
Davis, R. Abagyan, H. Widmer, E. B. Pasquale, P. Kuhn, (2007), J. Chem. Biol. 282, 36505, [4] C. Bardelle, T.
Coleman, D. Cross, S. Davenport, J. G. Kettle, E. J. Ko, A. G. Leach, A. Mortlock, J. Read, N. J. Roberts, P.
Robins, E. J. Williams, (2008) Bioorg. Med. Chem. Lett., 18, 2776.

  • Poster
    19th International Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S178

Permalink: https://www.hzdr.de/publications/Publ-16257
Publ.-Id: 16257


McMurry cyclization in 18F-labeling - radiosynthesis of a 2,3-diarylsubstituted COX-2 inhibitor

Laube, M.; Kniess, T.; Bergmann, R.; Steinbach, J.; Pietzsch, J.

Objectives:
Cyclooxygenase-2 (COX-2) is an inducible enzyme overexpressed under inflammatory conditions and is assumed to play a key role in cancerogenesis. Functional imaging of COX-2 expression in vivo by means of COX-2 inhibitors radiolabeled with positron emitters is a challenging approach, e.g., for differentiation of inflammatory processes and cancer1. Despite of different attempts, up to now a suitable radiotracer for COX-2 expression is unavailable. We developed an 18F-labeled COX-2 inhibitor [18F]3 from the type of a 2,3-diarylsubstituted indole via the McMurry cyclization. Thereby, with this labeling approach we got access with [18F]fluoride to the indole system which is, in principle, poorly activated for a nucleophilic substitution.
Methods:
The potent COX-2 inhibitor 3 (IC50=0.02 μmol) was synthesized as reference compound2. The labeling precursor 1 bearing a trimethylammonium leaving group was obtained in a six-step synthesis sequence. The radiolabeling reaction was performed as an one pot-two step procedure starting first by introduction of [18F]fluoride by a nucleophilic substitution at 1 followed by McMurry cyclization to form the indole core structure (Figure 1). The radiosynthesis was carried out with an automated nucleophilic synthesizer TracerLABFXN (GE) and has been optimized with respect of the base, solvent, and temperature. Purification of [18F]3 was performed by semi-preparative HPLC and SPE with C18 cartridges.
Results:
Considering a set of optimization experiments it turned out that for the McMurry cyclization the use of THF is inevitable. Hence, the radiolabeling was performed in acetonitrile at 110-120°C, the solvent was removed under vacuum, and the McMurry reaction was run in pure THF at 90-100°C. Under these conditions the intermediate [18F]2 was formed in 10-15% yield and the cyclization step provided the desired McMurry product [18F]3 in 50-82% yield. A typical module assisted radiosynthesis of [18F]3 starting with 8 GBq of [18F]fluoride and 15 mg precursor 1 yielded 490 MBq of [18F]3 (10% overall yield d.c.) within 80 min synthesis time. The radiochemical purity of [18F]3 after HPLC purification was > 98% and the specific activity was determined to be 74-91 GBq/μmol at end of synthesis.
Conclusions:
A highly potent and selective COX-2 inhibitor from type of a 2,3-diarylsubstituted indole was labeled with fluorine-18 in a two step fully automated radiosynthesis giving a potential PET tracer for functional imaging of COX-2 in vivo. In best to our knowledge, this is the first time that McMurry cyclization was utilized in PET-chemistry as labeling approach to get access to poorly activated compounds by nucleophilic substitutions with [18F]fluoride. In vitro stability studies in rat plasma and blood and in vivo studies in rats showed high stability of [18F]3 over two hours. Cell uptake studies with [18F]3 in THP-1, FaDu, HT29, A2058 and A375 cell lines are under the way as well as small animal PET investigations in HT29 mouse xenograft models.
References:
[1] Kuge et al., (2009), Nucl. Med. Biol., 36, 869-876,
[2] Hu et al., (2003), Bioorg. & Med. Chem.,11, 1153-1160

  • Lecture (Conference)
    19th International Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S73

Permalink: https://www.hzdr.de/publications/Publ-16256
Publ.-Id: 16256


Systematic alteration of PEGylation grade of 68Ga- and 64Cu-labeled L-oligonucleotides for tailored pharmacokinetics as prerequisite for tumor pretargeting technologies

Förster, C.; Schubert, M.; Bergmann, R.; Walther, M.; Pietzsch, J.; Pietzsch, H.-J.; Steinbach, J.

Objectives:
The favorable properties of non-natural, L-configured oligonucleotides (L ON) such as rapid hybridization, the lack of natural hybridization targets in vivo as well as their high metabolic stability [1] award L-ONs as a promising tool for tumor pretargeting technologies. As a result of their oligoanionic nature, 17mer-L-ONs are correlated with very fast blood clearance and high kidney retention [1]. Therefore, improvement of these two parameters was indispensable. To minimize the kidney accumulation and to increase the bioavailability by increasing of the area under the blood curve (AUC), polyethylene glycol (PEG) units of increasing size 2000-20000 Da were conjugated to the 17mer lead structure. Beside effect of PEGylation, the influences of different chelators and labeling ions on the biodistribution behavior of 64Cu- and 68Ga-labeled 17mer-L-ON-PEGs were investigated.
Methods:
17mer-L-DNA (HO-C6H12-S-S-C6H12-5’GCGGCTGTG-CGGTGCGG3’-amino modifier) was 3’-modified with different PEG substituents. By using the mercaptohexyl spacer at 5’-position, new developed NOTA-maleimide derivatives as well as a commercially available DOTA-maleimide were conjugated. After radiolabeling with 64Cu and 68Ga and intravenously administration in healthy Wistar rats, biodistribution data by organ and tissue sampling were determined 5 min p.i. as well as 60 min p.i. Blood clearance half lifes were calculated using of dynamic PET studies. The influence of PEGylation on hybridization was investigated in vitro by gel-electrophoresis.
Results:
The increasing molecular mass of the conjugated PEG units led to significantly decreased kidney retention at 60 min from 56.3±4.1%ID (64Cu; 2 kDa PEG) and 52.4±6.1%ID (68Ga; 2 kDa PEG) to 6.5±0.4%ID (64Cu; 20 kDa PEG) and 6.9±0.6% (68Ga; 20 kDa PEG), respectively. However, the liver uptake was slightly increased at 60 min p.i. from 4.8±0.2%ID (64Cu; 2 kDa PEG) and 2.6±0.4%ID (68Ga; 2 kDa PEG) to 13.3±2.1%ID (64Cu; 20 kDa PEG) and 10.7±2.7%ID (68Ga; 20 kDa PEG). The activity concentrations in all other measured organs, except the blood, were at 60 min p.i. negligible (< 0.5%ID/g or <1 SUV). The biological half-lives in the blood were 10.8 min (2 kDa PEG), 9.6 min (5 kDa PEG), 27.7 min (10 kDa PEG), and 39.4 min (20 kDa PEG) for 68Ga-labeled compounds. Based on gel-electrophoresis investigations, no PEG-induced inhibition of hybridization was found. In vitro hybridization was completed in less than 30 s, whereas the optimal ratio of complementary L DNA single strands was between 1:1 (2-5 kDa) to 1:1,25 (10-20 kDa).
Conclusions:
PEGylation of our 17mer-L-ON resulted in significantly reduced kidney retention, favorable blood circulation half-life, and very low unspecific tissue accumulations. Low kidney and liver accumulations were found for 5 kDa and 10 kDa PEG derivatives. Increasing size of PEG units shifted the hybridization equilibrium to slightly higher DNA ratios without clear hybridization inhibition. The introduction of NOTA or DOTA as chelating moiety enables radiolabeling with various metallic radionuclides for diagnostics and therapy. These results emphasize the high-grade potential of L-ON as a complementary tool for tumor pretargeting technologies.
Reference:
Schlesinger, J. et al., (2008), Lett. Drug Des. Discovery, 3, 330-335

  • Lecture (Conference)
    19th Internatzional Symposium on Radiopharmaceutical Sciences, 28.08.-02.09.2011, Amsterdam, Niederlande
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), S62

Permalink: https://www.hzdr.de/publications/Publ-16255
Publ.-Id: 16255


Effects of very rapid thermal processing on the properties and bonding structure of Al-doped ZnO thin films

Vinnichenko, M.; Hauschild, D.; Lissotschenko, V.; Cornelius, S.; Krause, M.; Gago, R.; Mücklich, A.; Kolitsch, A.

The combination of low-temperature deposition with very rapid thermal processing (vRTP) at air is a promising approach of synthesis of high-quality thin films of transparent conductive oxides (TCOs) at large areas. However, microscopic mechanisms of TCO film properties modification during such treatment are not understood properly which hampers application of the post-deposition vRTP. In order to resolve this problem, Al-doped ZnO (AZO) films grown onto unheated fused silica substrates by reactive pulsed magnetron sputtering were vRTP processed using a laser source with ~1 ms dwell time. The morphology, bonding structure, electrical and optical properties of as-deposited films were systematically compared with those of the vRTP processed ones. The electrical resistivity of the films drops from 1.4x10-3 to 4.6x10-4 Ohm cm with simultaneous substantial decrease of the film optical extinction in the visible at optimum processing conditions. The resistivity decrease is due to simultaneous increase of the free electron density (from 3.8x1020 to 6.2x1020 cm-3) and mobility (from 12 to 22 cm2V-1s-1). It is also observed that vRTP leads to a substantial decrease of the A1(LO) and E1(LO) disorder-enhanced lines in Raman spectra. This is interpreted in terms of decreasing concentration of point defects because both x-ray diffraction and high-resolution TEM show no improvement of the film crystal quality which might have a similar effect on the Raman spectra. Substantial modification of the O K-edge x-ray absorption near edge structures (XANES) spectra of the vRTP processed AZO films (which are dense and void free already in as deposited state) suggests that these might be oxygen-related point defects or defect complexes. Decrease of concentration of these defects may explain increase of the free electron mobility and decrease of the optical extinction in the visible.
The authors gratefully acknowledge financial support of BMBF under the RainbowEnergy Project.

Keywords: transparent conductive oxides; Al-doped ZnO; diode laser processing

  • Poster
    International topical workshop on “Subsecond thermal processing of Advanced Materials 2011" Subtherm-2011, 25.-27.10.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16254
Publ.-Id: 16254


S100A2 in cancerogenesis: a friend or a foe?

Wolf, S.; Haase-Kohn, C.; Pietzsch, J.

Owing to the exceptional intracellular distribution and the heterogeneous expression pattern during transformation and metastasis in various tumors, the EF-hand calcium-binding protein S100A2 attracts increasing attention. Unlike the majority of S100 proteins, S100A2 expression is downregulated in many cancers and the loss in nuclear expression has been associated with poor prognosis. On the other hand, S100A2 is upregulated in some cancers. This mini review highlights the general characteristics of S100A2 and discusses recent findings on its putative functional implication as a suppressor or promoter in cancerogenesis.

Keywords: Calcium-binding protein; EF-hand; p53 Protein family; Receptor for advanced glycation endproducts (RAGE); Tumor promotor; Tumor suppressor Introduction

Permalink: https://www.hzdr.de/publications/Publ-16253
Publ.-Id: 16253


Novel Technology of Laser Driven Proton Beams for a Potential Application in Cancer Therapy: in Vitro Dose Response Studies

Laschinsky, L.; Baumann, M.; Beyreuther, E.; Karsch, L.; Lessmann, E.; Oppelt, M.; Richter, C.; Schramm, U.; Schürer, M.; Pawelke, J.

Background: The development of the new technology of proton and ion acceleration by ultra-high intensity lasers for cancer therapy is the goal of the German joint research project “onCOOPtics”. The laser based acceleration promises compact and economic therapy facilities that are suitable for already existing clinics. In contrast to conventional particle acceleration the laser based method results in beams of very short pulses with ultra-high pulse dose and correspondingly peak dose rate. Within the project multidisciplinary issues like development and optimization of high-intensity laser systems, efficient proton acceleration schemes and proton beam transport are handled. Moreover, the physical and real-time dosimetric characterization as well as the investigation of radiobiological consequences of laser accelerated beams are essential. These imply translational investigations starting from in vitro cell irradiation.

Material and Methods: Systematic in vitro cell experiments were performed at the 150 terawatt laser facility DRACO at HZDR. Proton pulses up to 20MeV were accelerated, whereas the broad proton spectrum was downward limited to 6MeV using an energy-filter-system. An in-house developed integrated dosimetry and cell irradiation system (IDOCIS) was tested and calibrated allowing precise dosimetry as well as the exact positioning of each cell sample. Cell survival and residual DNA double strand breaks were determined after irradiation of the tumour cell line SKX in a dose range from 0.5Gy to 4.3Gy. Additionally, reference irradiation were performed with continuous proton beam at a conventional Tandem accelerator and with a 200 kVp X-ray tube.

Results: A stable and reproducible laser driven proton beam was achieved for experiments over weeks including real-time dose and energy spectrum monitoring as well as precise absolute dosimetry. The comparison of the radiobiological effectiveness of conventional and laser accelerated proton beams show no significant difference for in vitro cell irradiation.

Conclusions: These first systematic in vitro cell response studies with precise dosimetry of laser driven protons represent an important step toward the development of laser accelerated particles for radiotherapeutic application. Further experiments with other human cell lines and in vivo studies are under way.

The work was supported by the BMBF, grant no. 03ZIK445.

  • Open Access Logo Contribution to proceedings
    ECCO 16 - ESMO 36 Stockholm Cancer Conference, 23.-27.09.2011, Stockholm, Sweden
    Novel Technology of Laser Driven Proton Beams for a Potential Application in Cancer Therapy: in Vitro Dose Response Studies, 0959-8049
  • European Journal of Cancer 47(2011), S190
    DOI: 10.1016/S0959-8049(11)70964-9

Permalink: https://www.hzdr.de/publications/Publ-16252
Publ.-Id: 16252


S100 proteins in health and disease

Pietzsch, J.

kein Abstract verfügbar

Permalink: https://www.hzdr.de/publications/Publ-16251
Publ.-Id: 16251


Ultrafast X-ray computed tomography of gas-solid fluidized beds

Bieberle, M.; Barthel, F.; Hampel, U.

Gas-solid fluidized beds find various applications in chemical and process engineering, for instance in fluid catalytic cracking, drying of particulate solids or polyolefin production. The gas-particle flow in fluidized beds is generally complex and difficult to observe, but exact information on voidage distribution and solid transport is urgently needed for assessment, monitoring, modelling and optimization of fluidized bed operation.
Only few of the currently available flow measurement techniques are applicable to dense fluidized beds. Optical imaging and laser-based methods are at the most merely able to capture the peripheral structure of the solids phase or to provide local information by using probes. For tomographic techniques, such as electrical capacitance tomography (ECT), positron emission tomography (PET) or common X-ray CT, it is in general difficult to provide high spatial and high temporal resolution at the same time.
We here introduce a much faster X-ray tomography approach which is based on electron beam scanning. There, an electron beam is rapidly swept along a circular target to produce a moving X-ray source. A static detector ring with 240 detector elements synchronously captures the radiation intensity. From the resulting radiographic projections of the object of interest non-superimposed cross-sectional density distributions are reconstructed. Beside its really fast scanning capability other advantages of this approach are the use of a single electron beam generator and the high versatility of the electron beam with respect to scan patterns and scanning speed. With our approach we have already demonstrated multiphase flow imaging with frame rates of up to 10.000 fps and a spatial resolution in the range of better than 1 mm.
The results presented here include studies at a bubbly fluidized bed with monodisperse spherical particles, in which the capability of the method to visualize the particle dynamics and the internal structure of the fluidized bed in very detail are demonstrated.

Keywords: tomography; ultrafast; fluidized bed; voidage; visualization

  • Lecture (Conference)
    gas-liquid and gas-liquid-solid reactor engineering congress (GLS 10), 26.-29.06.2011, Braga, Portugal

Permalink: https://www.hzdr.de/publications/Publ-16250
Publ.-Id: 16250


Ultrafast X-ray computed tomography for the analysis of gas-solid fluidized beds

Bieberle, M.; Barthel, F.; Hampel, U.

Gas-particle flow in fluidized beds is generally complex and difficult to observe. But exact information on voidage distribution and solid transport is urgently needed for assessment, monitoring, modelling, and optimization of fluidized bed operation. So far, there was a lack of suitable measurement and imaging techniques to disclose the complex flow structures in fluidized beds with high spatial and temporal resolution. The recently developed ultrafast X-ray computed tomography technique is superior for such types of multiphase flows and its performance has been demonstrated in this study. Spatial resolution in the range of one millimetre and temporal resolution of several thousand cross-sectional images per second allows at the same time imaging and analysis of voidage structures as well as single particle movement. In this study, the capability of imaging fluidized bed behaviour at different column diameters and gas flow rates has been analysed.

Keywords: tomography; ultrafast; fluidized bed; voidage; visualization

Permalink: https://www.hzdr.de/publications/Publ-16249
Publ.-Id: 16249


A new radiolabeling method for commercial Ag0 nanopowder with 110mAg for sensitive nanoparticle detection in complex media

Hildebrand, H.; Franke, K.

Nanoparticle (NP) tracking in complex media is still a challenge since NP concentrations are expected to be low compared to elemental background levels as it can be found in environmental matrices. This study presents a new method for radiolabeling of commercial silver nanopowder (Ag0-NPs, dp < 100 nm) with 110mAg radionuclides (t1/2 = 250 d) that provide an adequate time frame for particle detection, localization and tracking under various experimental conditions. The radiolabeling procedure ensures high efficiency, stability and consistency of particle properties. Detection of Ag0-NP in concentrations as low as 125 ng kg-1 could be reached. For the first time, an appropriate tool for life-cycle studies of commercial Ag0-NPs is provided without changing chemical composition of the material. This is of great importance e.g. for research in the field of nanotoxicology.

Keywords: radiolabeling; nanoparticle; silver; nanoparticle detection; nanoparticle tracking

Permalink: https://www.hzdr.de/publications/Publ-16248
Publ.-Id: 16248


Grain alignment in poly-Si films by means of Plasma Immersion Ion Implantation (PIII) in combination with Flash Lamp Annealing (FLA)

Endler, R.; Voelskow, M.; Skorupa, W.

A series of experiments have been performed with the aim to improve the electrical and structural properties of CVD – deposited thin polycrystalline silicon films. Using an advanced ion implantation technique like Plasma-Immersion-Ion- Implantation (PIII) in combination with short time Flash-Lamp-Annealing (FLA) it has been shown that in comparison to the as deposited state a significant enlargement of the mean grain size occurs, accompanied by a more pronounced texturizing. Furthermore, the main crystallographic axes of the grains have been found to be mostly parallel to the direction of the particle stream. Whereas the enlargement of the mean grain size due to ion channelling was already reported by Reif et al. in the 80s, in the present work the SSIC technique (Seed Selection though Ion Channelling) was applied for the first time using the PIII process. This technique ensures a high throughput; additionally the costs for the implantation step can be reduced in comparison to conventional ion implantation. Furthermore, in contrast to the well known existing recrystallization techniques like cw-laser annealing or lateral zone melting recrystallization (ZMR), the proposed method circumvents problems arising from several mass transports characteristics of techniques based on melt processes.

Keywords: Flash Lamp Annealing; Poly-Si; SSIC

  • Poster
    Subtherm2011, 24.-27.10.2011, Dresden, BRD

Permalink: https://www.hzdr.de/publications/Publ-16247
Publ.-Id: 16247


Timing (a) FLASH

Tavella, F.; Stojanovic, N.; Geloni, G.; Gensch, M.

Many fundamental processes in nature like chemical reactions or phase transitions occur on the few femtosecond time and few nanometres to few angstroms length scale. On a way to their understanding, great hope lies on investigations of their dynamic using the bright, coherent X-ray pulses from free electron lasers (FELs) that have a duration and wavelength commensurate with that of these processes.
We developed a method to measure the arrival time of the X-ray pulses at FLASH with respect to the pump-probe laser in the experimental hall on a few femtosecond timescale, making use of the THz beamline [1]. Method is easily transferable to other advanced light source working with ultrashort electron bunches and therefore of high general interest.

  • Open Access Logo Contribution to external collection
    in: DESY Highlights 2011, Hamburg: DESY, 2012

Permalink: https://www.hzdr.de/publications/Publ-16246
Publ.-Id: 16246


The Rossendorf Beamline at ESRF: A multipurpose X-ray absorption spectroscopy and scattering beamline for Environmental and Materials Sciences

Scheinost, A. C.

The Rossendorf Beamlines at ESRF is operated since 1997 by the Helmholtz Center Dresden-Rossendorf. As a multipurpose synchrotron x-ray beamline, it serves both inhouse and collaborative research in Environmental and Materials Science. Its optics provide tunable monochromatic x-rays to two experimental stations, the first specialized in bulk x-ray absorption spectroscopy for environmental radionuclide research, and the second specialized in a variety of scattering techniques to elucidate the structure of thin films and other materials. The first focus of my talk will be on the performance of the optics, which are donated to SESAME. I will then show some research examples, and give an overview on the organization, funding and personnel input, and productivity parameters (publications, projects, and outreach).

Keywords: Environmental Sciences; Materials Sciences; ROBL; Synchrotron

  • Invited lecture (Conferences)
    SESAME User Meeting 2011, 12.11.2011, Amman, Jordan

Permalink: https://www.hzdr.de/publications/Publ-16245
Publ.-Id: 16245


X-ray absorption spectroscopy for environmental sciences: examples and technical challenges

Scheinost, A. C.

Due to its element specificity, low detection limit, and independence on long-range and crystalline order, X-ray absorption spectroscopy (XAS) is one of the most versatile tools to elucidate the electronic and molecular structure of almost any element in environmental samples. It is fundamental to study the speciation and structure of dissolved (aqueous) complexes, from the most simple solvated ion to polyatomic complexes, to colloids, amorphous and crystalline solids. Furthermore, it is extremely useful to study sorption and redox reactions at the water/solid interface. I will demonstrate its application in environmental chemistry to study the fate of metal contaminants in soils, sediments and water bodies.

Keywords: XAS; XAFS; EXAFS; XANES; environmental sciences

  • Invited lecture (Conferences)
    SESAME User Meeting 2011, 12.11.2011, Amman, Jordan

Permalink: https://www.hzdr.de/publications/Publ-16244
Publ.-Id: 16244


The Ksar Ghilane 002 shergottite – the 100th registered Martian meteorite Fragment

Llorca, J.; Roszjar, J.; Cartwright, J. A.; Bischoff, A.; Pack, A.; Ott, U.; Merchel, S.; Rugel, G.; Fimiani, L.; Ludwig, P.; Allepuz, D.; Casado, J. V.

We report on the discovery of a new shergottite from Tunisia, Ksar Ghilane (KG) 002, which is the 100th Martian meteorite fragment registered in the Meteoritical Bulletin. This single stone, weighing 538 g, is a coarse-grained basaltic shergottite, mainly composed of maskelynitized plagioclase (~52 vol.%) and pyroxene (~37 vol.%). It also contains Fe-rich olivine (~4.5 vol.%), large Ca-phosphates, including both merrillites and Cl-apatites (~3.4 vol.%), minor amounts of silica or SiO22-normative K-rich glass, pyrrhotite, Ti-magnetite, ilmenite, and accessory baddeleyite. The largest crystals of pyroxene and plagioclase reach sizes of ~4 mm and ~5 mm. Regarding texture, KG 002 shares some similarities with the evolved NWA 2800 Martian sample. Pyroxene compositions in KG 002 are Fs26-96En5-50Wo2-41 (n=82). They typically range from cores of about Fs29En41Wo30 to rims of about Fs68En14Wo17. Most plagioclases (maskelynites) are Ab41-49An39-58Or1-7 in composition, but some can be as anorthitic as An94. Olivine occurs mainly within symplectitic intergrowths, in paragenesis with ilmenite, or at neighboring areas of symplectites. These minerals are Fa91-96 in composition. Ksar Ghilane 002 is heavily shocked (S5) as indicated by mosaic extinction of pyroxenes, maskelynitized plagioclase, the occurrence of localized shock melt glass pockets and low radiogenic He concentration. Two analyses of oxygen isotopes (delta18O=+5.09 and 5.26‰, delta17O=+3.0 and +3.2‰, and Δ17O=+0.28 and +0.43‰) confirm that this rock is a normal member of the SNC suite of meteorites. Bulk chemical analyses indicate that KG 002 belongs to the main group of basaltic shergottites and it is strikingly similar to the highly-evolved Los Angeles meteorite. According to the K, U, Ba and Sr abundances and fresh appearance of sulfides, KG 002 is not significantly weathered, although a positive Ce anomaly is recognized in the REE pattern. Ksar Ghilane 002 is slightly depleted in LREE and shows a positive Eu anomaly providing evidence for complex magma genesis and mantle processes on Mars. Noble gases with a composition thought to be characteristic for Martian interior may be a dominant component in KG 002. 10Be, 26Al, and 53Mn measurements and comparison with theoretical Monte-Carlo calculations of production rates indicate that KG 002 has been exposed most likely as a single meteoroid body of 35-65 cm radius between 2.8 and 3.7 Ma. Ksar Ghilane 002 strongly resembles Los Angeles and NWA 2800 basaltic shergottites in element composition, petrography and mineral chemistry, suggesting a possible launch-pairing. The CRE ages of KG 002 and Los Angeles may suggest an ejection event at ~3.0 Ma.

Keywords: accelerator mass spectrometry; AMS; cosmogenic radionuclide; Mars; meteorite; noble gases

Permalink: https://www.hzdr.de/publications/Publ-16243
Publ.-Id: 16243


Influence of storage on the position of the germinal disc in the fertilized unincubated chicken egg

Burkhardt, A.; Meister, S.; Bergmann, R.; Koch, E.

The breeding of male layer chickens is currently considered to be highly uneconomical. In Germany alone, 40 to 50 million newly hatched male chickens were killed annually immediately after hatching. Therefore, it is necessary to find a method for sexing chickens early in the embryonic development, preferably before incubation. The genotypic sex of an egg can be determined using information found in the germinal disc, so knowledge of the exact position of the germinal disc is essential for further sexing, or for other actions such as the in ovo injection of agents. Previous studies have shown that the germinal disc is located somewhere on top of the yolk. However, no studies have yet been performed that investigate the influence of time spent in horizontal storage on the position of the germinal disc. Magnetic resonance imaging was chosen to determine this influence on the position of the germinal disc. It was found that eggs placed horizontally for long periods of time befor!
e scanning had significant changes in the positions of their germinal discs compared with those of eggs scanned minutes after positioning. The position of the germinal disc in eggs, minutes after horizontal positioning, deviated 14.7 +/- 0.6 mm from the maximum vertical plane of the egg (zero position) in the z-direction; eggs scanned after 96 h of horizontal positioning showed a deviation of only 4.9 +/- 1.6 mm. The x-axis also exhibited changes in the position of the germinal disc over time. Immediately after horizontal positioning, the eggs showed a deviation of 0.4 +/- 0.4 mm in the x-direction, whereas the deviation after 96 h was 2.9 +/- 0.5 mm. These results show that horizontal positioning of the egg hours before the measurement is necessary.

Permalink: https://www.hzdr.de/publications/Publ-16242
Publ.-Id: 16242


On the effect of different placing ZrH moderator material on the performance of a SFR core

Merk, B.; Weiß, F.-P.

The structure for the development of a fuel assembly design with reduced sodium void achieved by the use of the moderating material ZrH is investigated. In the study the sodium void effect, as well as the major feedback coefficients are analyzed. Besides the feedback coefficients, the influence on the operational parameters like neutron flux distribution, power distribution, and burnup distribution is investigated for the different possibilities of arranging the moderating material in the fuel assembly. Additionally, the fuel cycle parameters – breeding and minor actinide production – are analyzed. For a first evaluation of the behavior during transients the influence of temperature changes in the ZrH is studied.

Keywords: Sodium void effect; SFR; Fast reactor; Zirconium hydride; designable feedback coefficient

  • Contribution to proceedings
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA
  • Lecture (Conference)
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA

Permalink: https://www.hzdr.de/publications/Publ-16241
Publ.-Id: 16241


On the possible gain of the application of the sp3 solution in nodal codes

Merk, B.

The simplified PN method has attracted much attention in reactor physics. The implementation of an increased order expansion has the potential to improve the results. It is investigated if this potential can be released under the specific features of nodal codes with fuel assembly sized calculation cells.
One dimensional analytical solutions for the one and two energy-group diffusion, SP3 and P3 equations are derived. The results are compared with reference solutions calculated with ONEDANT and HELIOS. Tests are performed on the Brantley, Larsen one-group test case and on a pin cell with real reactor materials. For the evaluation of the differences between the diffusion and the SP3 solutions in the nodal code configuration, benchmark configurations are investigated.
A comparison of the diffusion and the SP3 results show improvements for the test case using fuel element size nodes when compared to a reference solution using the identical cross section basis. Comparing with a multi-group reference solution shows that the diffusion solution sometimes behaves better due to error cancellation. To achieve the full gain of the SP3 method in nodal calculations, a new standard for light water reactor calculations has to be defined with a refined energy-group structure.

Keywords: simplified PN; nodal calculations; reactor physics; analytical solutions; neutron transport

  • Contribution to proceedings
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA
  • Lecture (Conference)
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA

Permalink: https://www.hzdr.de/publications/Publ-16240
Publ.-Id: 16240


An analytical solution for the consideration of the effect of adjacent fuel assemblies; comparison of rectangular and hexagonal structures

Merk, B.; Rohde, U.

A new analytical method is described to deal with the Leakage Environmental Effect. The method is based on the analytical solution of the two group diffusion equation for two adjacent fuel assemblies. The quality of the results for this highly efficient method is demonstrated for quadratic fuel assemblies. In additional tests the transferability of the concept to hexagonal VVER-440 type fuel assemblies is shown and a comparison between the results for rectangular and hexagonal assemblies is given.

Keywords: Analytical solution; Homogenization; Cross-section preparation; Leakage assembly environmental effect; Diffusion equation

  • Contribution to proceedings
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA
  • Lecture (Conference)
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, USA

Permalink: https://www.hzdr.de/publications/Publ-16239
Publ.-Id: 16239


An analytical solution for the consideration of the effect of adjacent fuel assemblies; extension to hexagonal fuel assemblies

Merk, B.; Rohde, U.

A new analytical method is described to deal with the Leakage Environmental Effect. The method is based on the analytical solution of the two group diffusion equation for two adjacent fuel assemblies. The quality of the results for this highly efficient method is demonstrated for quadratic fuel assemblies. In additional tests the transferability of the concept to hexagonal VVER-440 type fuel assemblies is shown.

Keywords: VVER; Analytical Solution; Homogenization; Cross Section Preparation; Leakage Assembly Environmental Effect

  • Contribution to proceedings
    AER Symposium, 19.-23.09.2011, Dresden, Deutschland
  • Lecture (Conference)
    AER Symposium, 19.-23.09.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16237
Publ.-Id: 16237


Accuracy of MR-based attenuation correction First experience with a whole-body PET/MR system

Schramm, G.; Brüning, E. M.; Langner, J.; Hofheinz, F.; Will, E.; Beuthien-Baumann, B.; Oehme, L.; Platzek, I.; Steinbach, J.; Laniado, M.; Kotzerke, J.; van den Hoff, J.

Purpose/Introduction: Sequential PET/MR scanners for whole body investigations have been developed only recently and are starting to become commercially available. In 2011, one of the first of these combined systems (Ingenuity TF PET/MR, Philips) was installed at our institute. PET/MR is expected to offer new possibilities, in particular in the field of quantitative bimodal functional imaging [1]. Quantitative PET requires attenuation correction (AC) which is commonly based on a measurement of the photon attenuation using either a radioactive source in standalone PET (RSAC), or CT in PET/CT systems (CTAC). In PET/MR systems such a measurement cannot be performed, therefore AC is based on a dedicated MR measurement (MRAC) plus segmentation and tissue type identification [2]. Here, we report on a first evaluation of MRAC in whole body investigations with the new system.

Subjects and Methods: Evaluation of MRAC is performed by a direct comparison of MRAC maps acquired with the Philips Ingenuity TF PET/MR and RSAC maps acquired with a Siemens ECAT Exact Hr+ PET scanner for 18 patients. Moreover, the quantitative influence of AC on the reconstructed images was investigated.

Results: In most cases the MRAC maps match the RSAC maps very well. Artefacts due to dental implants and sternal cerclages were found. In one case, the algorithm was not able to separate tissue from air in the patients lung. The influence of these artefacts on the reconstructed PET image will be reported.

Discussion/Conclusions: The vendor-provided MRAC algorithms yielded good results in our first patient measurements with respect to soft tissue and air segmentation. However, the algorithm relies on anatomic reference data and thus artefacts arise if the anatomy of the patient does not fit to the reference. In the future, an improved separation between tissue, bone and air without using anatomic reference data might be achieved with ultra short echo time sequences [3,4].

References:

[1] Pichler, B.J. et al., 2008, Sem. Nucl. Med., 199-208
[2] Martinez-Möller, A. et al., 2009, J. Nucl. Med., 520-526
[3] Catana, C. et al., 2010, J. Nucl. Med., 1431-1438
[4] Keereman, V. et al., 2010, J. Nucl. Med., 812-818

  • Lecture (Conference)
    ESMRMB Congress 2011, 06.-08.10.2011, Leipzig, D
  • Abstract in refereed journal
    Magnetic Resonance Materials in Physics, Biology and Medicine 24(2011), 199

Permalink: https://www.hzdr.de/publications/Publ-16236
Publ.-Id: 16236


Synthesis, colloidal stability and 64Cu labeling of iron oxide nanoparticles bearing different macrocyclic ligands

Barreto, J. A.; Matterna, M.; Graham, B.; Stephan, H.; Spiccia, L.

The synthesis, solution stability and 64Cu2+ labeling of magnetite nanoparticles (NPs) coated with different macrocycles is reported, together with the stability of the resulting radioisotope-labeled NPs to transchelation by the competing ligand cyclam, and their stability in blood serum. Three macrocycles, 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane (dmptacn),1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,4,7,10-tetraazacyclododecane (cyclen), and
3-aminopropyltriethoxysilane were used to modify the magnetite NPs. The ligands were covalently linked to the surface of the NPs with high efficiency by reaction of the corresponding
3-(3-(triethoxysiloxy)propoxy)propan-2-ol derivatives with the NPs. According to transmission electron microscopy (TEM), the uncoated magnetite NPs and macrocycle-functionalized congeners have an average diameter of 6 to 7 nm. The NPs form stable colloidal suspensions in 0.05 M aqueous 2-(N-morpholino)ethanesulfonic acid (MES) buffer, which consist of larger aggregates with a mean hydrodynamic size of about 200 nm. The NPs with the appended macrocycles can be efficiently labeled with 64Cu2+ ions and the radioactivity persists in rat plasma for at least 24 h. Challenge experiments with cyclam also indicate that the radiocopper complexes are highly stable, with the dmptacn-functionalized NPs showing the highest resistance to metal ion leakage. Overall, the dmptacn-functionalized iron oxide NPs provide an excellent platform for the development of robust multimodal cancer imaging/therapeutic agents.

  • New Journal of Chemistry 35(2011), 2705-2712

Permalink: https://www.hzdr.de/publications/Publ-16235
Publ.-Id: 16235


Concomitant targeting of cyclooxygenase-2 and oxidant stress pathways for radioprotection of endothelial cells.

Pietzsch, J.; Laube, M.; Pietzsch, F. J.; Bergmann, R.; Knieß, T.

kein Abstract verfügbar

  • Contribution to external collection
    Lewis BS, Flugelman MY, Halon DA (eds.): Coronary Artery Disease: 2011 Update, Bologna: Medimond S. r. l - Monduzzi Editore International, 2011, 978-88-7587-619-7, 107-110

Permalink: https://www.hzdr.de/publications/Publ-16234
Publ.-Id: 16234


Site-selective radiolabeling of peptides by 18F-fluorobenzoylation with [18F]SFB in solution and on solid phase - a comparative study

Kuchar, M.; Pretze, M.; Knieß, T.; Steinbach, J.; Pietzsch, J.; Löser, R.

Peptides labeled with short-lived positron-emitting radionuclides are of outstanding interest as probes for molecular imaging by positron emission tomography (PET). Herein, the site-selective incorporation of fluorine-18 into lysine-containing peptides using the prosthetic labeling agent N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) is described. The reaction of [18F]SFB with four biologically relevant resin-bound peptides was studied and optimized. For comparison, each peptide was 18F-fluorobenzoylated in solution under different conditions and the product distribution was analyzed confirming the advantages of the solid phase approach. The method's feasibility for selective radiolabeling either at the N-terminus or at the lysine side chain was demonstrated. Labeling on solid phase with 18F]SFB resulted in crude 18F-fluorobenzoylpeptides whose radiochemical purities were typically greater than 90 % and that could be prepared in synthesis times from 65 to 76 min.

Permalink: https://www.hzdr.de/publications/Publ-16233
Publ.-Id: 16233


Biosorptive Kompositmaterialien für die Rückgewinnung von Wertstoffen: Neue Konzepte und Anwendungspotenziale

Pollmann, K.; Raff, J.; Kutschke, S.

Es werden Konzepte zur Entwicklung von biosorptiven Materialien für die (Rück-)gewinnung von Metallen vorgestellt.

  • Invited lecture (Conferences)
    Biomining von Sekundärrohstoffen - Workshop 3 des Innovationsforums "Geobiotechnologie - mikrobiologische Verfahren in Bergbau und Umweltschutz", 14.-15.12.2011, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16232
Publ.-Id: 16232


Herstellung von 61Cu mit hoher spezifischer Aktivität über die 64Zn(p,α)61Cu-Reaktion

Thieme, S.; Walther, M.; Rajander, J.; Pietzsch, H.-J.; Solin, O.; Steinbach, J.

Ziel:
Die Herstellung von 61Cu hoher spezifischer Aktivität erfordert besonders aufwändige Maßnahmen, um Metallkontaminationen sowohl durch Cu-Isotope als auch durch andere Metalle zu minimieren. Dementsprechend müssen die herkömmlichen Methoden verfeinert werden, um 61Cu sowohl in hoher Qualität als auch effektiv herstellen zu können. Vergleichswerte über spezifische Aktivitäten von 61Cu sind in der Literatur selten zu finden. McCarthy et al. berichten zu spez. Aktivitäten von 61Cu im Bereich von 47 bis 190 GBq/µmol; erzeugt durch 61Ni(p,n)61Cu und 60Ni(d,n)61Cu-Reaktion. Eine Alternative dazu stellt die 64Zn(p,α)61Cu-Reaktion dar. Das hierfür genutzte Targetmaterial 64Zn (99,3% Isotopenanreicherung) ist im Vergleich zu angereichertem 61Ni weitaus weniger kostenintensiv.
Methoden:
Für die Bestrahlung am Zyklotron wird ein massiver Targetträger aus Gold verwendet, auf dem ca. 100 mg angereichertes 64Zn (99,3% Isotopenanreicherung) abgeschieden sind. Die radiochemische Trennung erfolgt über Ionenaustauschtechniken nach Literaturangaben. Die angewandte Methode nutzt eine Ionenaustauscherkaskade, die aus zwei Kationenaustauscher-Säulen und einer Anionenaustauscher-Säule besteht. Dabei sorgt der doppelte Kationenaustauscherschritt für die effektive Abtrennung von Galliumisotopen (66/67/68Ga) und die Anionenaustauscher-Säule für die Trennung des 61Cu vom Zn-Targetmaterial. Der Gesamtprozess zur Gewinnung des gereinigten 61Cu dauert eine Stunde. Die Methode umfasst die Wiedergewinnung des eingesetzten 64Zn, welches danach zur erneuten Verwendung zur Verfügung steht. Das optimierte Verfahren nutzt kleinere Ionenaustauschersäulen als bisher und ausschließlich wässrige Salzsäure; Details vgl. Thieme et al.. Die Ermittlung der spezifischen Aktivität erfolgt über TETA-Titrationen und ICP-MS-Analysen. Es wurden Bestrahlungen an zwei verschiedenen Zyklotronen durchgeführt: am Cyclone 18/9 (IBA, Belgien) des Instituts für Radiopharmazie, Dresden-Rossendorf und am CC 18/9 (Efremov Institut, St. Petersburg, Russland) des Turku PET Centre in Turku, Finnland.
Ergebnisse:
Die Bestrahlungen mit dem Cyclone 18/9 wurden mit 12 µA und 16 MeV durchgeführt. Dies führte innerhalb von 30 Minuten zu Ausbeuten von ca. 300 MBq 61Cu (EOB). Am CC 18/9 wurde mit 30 µA, 13 MeV, 30 Minuten gearbeitet. Dabei wurden ebenfalls 330-400 MBq 61Cu (EOB) erzeugt, bei einer Bestrahlungszeit von 3 Stunden bis zu 1150 MBq 61Cu (EOB). Am CC 18/9 wurde eine extrem hohe spezifische Aktivität des 61Cu von über 1000 GBq/µmol erreicht. Demgegenüber fielen die spezifischen Aktivitäten am Cyclone 18/9 deutlich ab, es konnte nur eine spezifische Aktivität von ca. 2 GBq/µmol erzielt werden. Wahrscheinlich tritt in diesem Fall eine Kontamination mit stabilem Kupfer schon während der Bestrahlung auf. Möglicherweise geht diese von der Targethalterung am Zyklotron aus, da sie nicht wie beim CC 18/9 komplett aus Aluminium, sondern größtenteils aus Messing besteht. Bisherige Versuche zum Schutz des Targetträgers und des Targetmaterials vor derartigen Kontaminationen bzw. der Versuch, Kontaminationen während des Trennprozesses zu verhindern, blieben erfolglos.
Schlussfolgerungen:
Die Ergebnisse zeigen, dass es prinzipiell möglich ist, 61Cu mit hoher spezifischer Aktivität mit Hilfe der 64Zn(p,α)61Cu-Reaktion herzustellen. Die genutzte radiochemische Trennmethode bietet sich hervorragend für eine routinemäßige Herstellung von 61Cu an.

  • Lecture (Conference)
    19. Jahrestagung der Arbeitsgemeinschft Radiochemie/Radiopharmazie der DGN, 15.-17.09.2011, Ochsenfurt, D

Permalink: https://www.hzdr.de/publications/Publ-16231
Publ.-Id: 16231


Materialcharakterisierungen mit Antimaterie: Atomaren Defekten auf der Spur

Wagner, A.

Materialcharakterisierungen mit Antimaterie: Atomaren Defekten auf der Spur

  • Lecture (others)
    Tagung des Fachausschusses Materialcharakterisierung der Deutschen Gesellschaft für zerstörungsfreie Prüfung e.V., 07.-08.11.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16230
Publ.-Id: 16230


SiC growth modification and stress reduction in FLASiC assisted liquid phase epitaxy

Pezoldt, J.; Stauden, T.; Morales, F.; Polychroniadis, E. K.; Voelskow, M.; Skorupa, W.

The defect density of the epitaxial SiC layers on Si result from the high defect density in the seeding layer formed by carbonization of the Si substrate. A method to reduce the defect density is flash lamp annealing. The recrystallisation can be improved if a three layers stack consisting of 3C-SiC/Si/3C-SiC/Si-substrate is used (iFLASiC-process). To improve the recrystallization C, Ge or both elements were added to Si. Ge and C additions to the Si and subsequent FLASiC processing l ead t o a s ubstantial increase o f t he m ass t ransfer. T he g rowth r ate r eached 1 0.0 μm/s. T he a chieved thickening of the lower layer strongly depends on the Si composition and is caused by the modification of the optical properties and the mass transport properties of the Si. Ge incorporation into Si and therefore into the Si melt enhance the mass transport from the upper SiC layer to the lower one. C incorporation into Si increases the available C contributing to SiC growth. Both elements lower the Si band gap increasing light absorption. Beside the growth modification the in plane strain in the 3C-SiC layer turns from tensile strain with a value of 0.0004 in the non buckling case to an in plane compressive strain with a strain value of - 0.0046. Non annealed layers of comparable thickness deposited under the same conditions exhibit tensile residual strain in the range of 0.002 to 0.006. FLASiC is not only able to improve the layer quality but also reduces the residual stress.

Keywords: Flash Lamp Annealing; SiC; Liquid Phase Epitaxy

  • Poster
    subtherm 2011 - International Topical workshop on Subsecond Thermal Processing of Advanced Materials, 25.-27.10.2011, Dresden, BRD

Permalink: https://www.hzdr.de/publications/Publ-16229
Publ.-Id: 16229


Synchrotron-based X-ray techniques for radioactive materials research: Understanding the chemical behaviour of radionuclides in solution

Ikeda, A.

Treatment of spent nuclear fuels (SNFs) is one of the critical issues in the world’s nuclear power industry. The international consensus thus far is that the SNFs are supposed to be reprocessed to extract reusable nuclides (e.g., Pu or U) by solvent extraction, or buried deep in the ground to permanently isolate them from human contact. The basic- and applied research related with these SNFs treatments always requires fundamental information on the chemical behaviour of radionuclides in solution, since most chemical processes relevant to the treatment of SNFs (e.g., solvent extraction or geological disposal) occur in solution.
As one of the powerful experimental probes for radioactive materials research, synchrotron-based X-ray techniques have been extensively employed for the last few decades. This seminar will focus on the application of synchrotron-based X-ray methods to the study of radionuclides in solution systems, including the following three sub-topics: (1) X-ray absorption spectroscopy (XAS) and high energy X-ray scattering (HEXS) for characterizing the hydrolytic species of tetravalent cerium (Ce(IV)) in aqueous solution, (2) X-ray absorption spectroscopy for understanding the redox behaviour of actinides in aqueous solution, (3) multiple spectroscopic (XAS and UV-visible-NIR) and quantum chemical approach for acquiring structural information of individual chemical species in the mixed system.

Keywords: Synchrotron; XAS; HEXS; Actinides; Lanthanides; Solution; Spectroscopy

  • Invited lecture (Conferences)
    CLS internal seminar, 23.11.2011, Canadian Light Source, Saskatoon, Canada

Permalink: https://www.hzdr.de/publications/Publ-16227
Publ.-Id: 16227


ATHLET models for the Emergency Condenser and the Containment Cooling Condenser of the INKA test facility

Hristov, H. V.; Kozmenkov, Y.; Schäfer, F.

The ATHLET code (GRS®) has been used for the numerical analyses of the EC (Emergency Condenser) and the CCC (Containment Cooling Condenser) performance at the INKA (INtegralversuchsanlage KArlstein) test facility. Three ATHLET 2.2 Cycle A models have been developed: EC, CCC and Integral model.
The EC model predictions for the postulated steady state scenario (EC characteristic curves) were compared with the old simulations (ATHLET 2.1 Cycle A model for of the EC). INKA EC transient run at 45 bar primary pressure was used as second validation step for the assessment of the different ATHLET versions influence on the numerical predictions. The EC ATHLET Cycle 2.2 A model validation was extended further with the transient EC INKA experiment at 80 bar primary pressure.
Technically, the CCC ATHLET model was based on the old CCC ATHLET 2.1 Cycle A one. However, significant improvements have been accomplished in order to make it capable of adequately representing the INKA CCC experimental layout and conditions. Two models have been developed to account for the different sparger designs. Experimental data (information) analyses have been in addition carried out due the initial poor model performance. The CCC ATHLET 2.2 Cycle A model ability to correctly capture the CCC heat transfer and in general the process has been demonstrated. Second CCC ATHLET model has been developed to incorporate the new sparger design. The model has been partly validated against the provided experimental data. While it was able to calculate well the initial stage of the experiment, it failed to represent the final one.
An integral INKA ATHLET model, which includes both the EC and the CCC, has been developed. This model incorporates the CCC one with new sparger design. Two LOCA scenarios have been postulated for the investigation of the EC-CCC performance under the INKA configuration. These scenarios include RPV (Reactor Pressure Vessel) and RSL (Reactor Steam Line) break. The EC – CCC joined operation under the break scenarios has been analysed.

- vertraulich -
Nachfrage bei Dr. S. Kliem

  • Other report
    Dresden: HZDR, 2011
    94 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16226
Publ.-Id: 16226


Synchrotron radiation-based X-ray diffraction during magnetron co-sputtering of Ni-Ti films

Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.

The study of Ni-Ti shape memory alloy films is of great technological interest for applications in the field of microengineering. They can work as sensors and actuators at the same time. However, there are still important issues unresolved like formation of film texture and its control. Films exhibiting the two-way shape memory effect are also required. A better understanding of the underlying growth mechanisms and their microstructural development requires sophisticated in-situ techniques. A two-magnetron sputter deposition chamber mounted into the six-circle diffractometer of the Rossendorf Beamline at the European Synchrotron Radiation Facility has been used for the processing of the Ni-Ti films. The in-situ x-ray diffraction studies enabled us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters (Ti target power) during film growth. It has been found that the type of substrate plays an important role for the preferential orientation of sputtered Ni-Ti films. In some cases they exhibit a pronounced depth dependence of their preferential orientations. Amorphous SiO2 and TiN buffer layers have been used to successfully control their crystallographic orientations. This is an important achievement since the texture has a strong influence on the extent of the strain recovery of the Ni-Ti films. The deposition conditions leading to films mainly containing grains with (100) or (110) planes of the B2 phase parallel to the film surface are presented. The deposition of graded Ni-Ti films by changing deliberately the Ti:Ni ratio, thereby altering microstructure and transformation temperatures across the film thickness, has also been performed. The aim has been the optimization of the deposition parameters in order to fabricate films with a “two-way” actuation (films with a combination of superelasticity and shape memory characteristics). It will lead to the development of smaller devices due to an optimal design of microdevices regarding size and weight (i.e., no consideration has to be paid to a resetting spring).

  • Poster
    EUROMAT 2011 (Symposium A54: Shape Memory Alloys (SMA) - Materials and Devices), 14.-15.09.2011, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-16225
Publ.-Id: 16225


Optimising the efficiency of pulsed diode pumped Yb:YAG laser amplifiers for ns pulse generation

Ertel, K.; Banerjee, S.; Mason, P.; Phillips, P.; Siebold, M.; Hernandez-Gomez, C.; Collier, J.

We present a numerical model of a pulsed, diode-pumped Yb:YAG laser amplifier for the generation of high energy ns-pulses. This model is used to explore how optical-to-optical efficiency depends on factors such as pump duration, pump spectrum, pump intensity, doping concentration, and operating temperature. We put special emphasis on finding ways to achieve high efficiency within the practical limitations imposed by real-world laser systems, such as limited pump brightness and limited damage fluence. We show that a particularly advantageous way of improving efficiency within those constraints is operation at cryogenic temperature. Based on the numerical findings we present a concept for a scalable amplifier based on an end-pumped, cryogenic, gas-cooledmulti-slab architecture.

Keywords: Laser amplifiers; Lasers pulsed; Lasers ytterbium; Pumping

Permalink: https://www.hzdr.de/publications/Publ-16224
Publ.-Id: 16224


Simultaneous time and wavelength resolved spectroscopy under two-colour near infrared and terahertz excitation

Bhattacharyya, J.; Wagner, M.; Zybell, S.; Winnerl, S.; Stehr, D.; Helm, M.; Schneider, H.

Time and wavelength resolved spectroscopy requires optical sources emitting very short pulses and a fast detection mechanism capable of measuring the evolution of the output spectrum as a function of time. We use table-top Ti:sapphire lasers and a free-electron laser (FEL) emitting ps pulses as excitation sources and a streak camera coupled to a spectrometer for detection. One of the major aspects of this setup is the synchronization of pulses from the two lasers which we describe in detail. Optical properties of the FEL pulses are studied by autocorrelation and electro-optic sampling measurements. We discuss the advantages of using this setup to perform photoluminescence quenching in semiconductor quantum wells and quantum dots. Carrier redistribution due to pulsed excitation in these heterostructures can be investigated directly. Sideband generation in quantum wells is also studied where the intense FEL pulses facilitate the detection of the otherwise weak nonlinear effect.

Keywords: Photoluminescence quenching; streak camera; time and wavelength resolved spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-16223
Publ.-Id: 16223


Thickness independent magneto-optical coupling constant of nickel films in the visible spectral range

Mok, K. M.; Scarlat, C.; Kovacs, G. J.; Li, L.; Zviagin, V.; McCord, J.; Helm, M.; Schmidt, H.

Magneto-optical properties of nominally 10, 20, and 30 nm thick ferromagnetic Ni films have been investigated at room temperature by vector-magneto-optical generalized ellipsometry under saturated magnetization conditions in the sample surface plane. The magneto-optical dielectric tensor of Ni has been determined by reflection Mueller matrix ellipsometry in the spectral range from 300 to 1100 nm. Different sets of magnetic field induced Mueller matrix elements enable us to identify the magnetization directions in the sample. The extracted magnetic field and thickness independent magneto-optical coupling constant is useful for modeling the Mueller matrix and complex Kerr angle of magnetized Ni thin films in layered sample systems in dependence of the incident angle of light, wavelength, and magnetization.

Keywords: Mueller matrix; generalized ellipsometry; magneto-optics; nickel

Permalink: https://www.hzdr.de/publications/Publ-16222
Publ.-Id: 16222


Formation of U(VI) lactate and citrate complexes and their sorption onto Opalinus Clay between 10 and 60°C

Schmeide, K.; Steudtner, R.; Bernhard, G.

Results to the U(VI) complexation with lactate and citrate and the influence of these ligands on U(VI) sorption onto Opalinus Clay (OPA) (Mont Terri, Switzerland) between 10°C and 60°C are shown.

Keywords: Complexation; sorption; uranium(VI)

  • Poster
    Workshop "HiTAC – High Temperature Aqueous Chemistry", 09.11.2011, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-16221
Publ.-Id: 16221


Wechselwirkungen von Actiniden mit Biomolekülen

Barkleit, A.

Die Komplexierung von Uran(VI) und Cm(III) mit den Zellwandkompartimenten Lipopolysaccharid und Peptidoglycan, charakterisiert durch TRLFS, EXAFS und FT-IR, wird dargestellt.

Keywords: uranyl; curium; lipopolysaccharide; peptidoglycan; TRLFS; EXAFS; FT-IR

  • Invited lecture (Conferences)
    2. Workshop zum Innovationsforum Geobiotechnologie, 03.-04.11.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16220
Publ.-Id: 16220


Field- and current-induced domain-wall motion in permalloy nanowires with magnetic soft spots

Meier, G.; Vogel, A.; Wintz, S.; Gerhardt, T.; Bocklage, L.; Strache, T.; Im, M.-Y.; Fischer, P.; Fassbender, J.; McCord, J.

New concepts of high-density and ultrafast nonvolatile data storage devices involve the controlled motion of magnetic domain walls (DWs) in nanowires [1]. To realize such a device, reproducible and reliable pinning sites for individual DWs are required. Geometric constrictions are widely used to create local confining potentials acting as pinning sites [2]. As an alternative, pinning sites can be induced via a local modification of magnetic properties by ion irradiation [3]. In this case, a variation in the wire geometry on the nanoscale is not required. Implantation of chromium ions into permalloy is known to cause alloying and structural defects which lead to a reduction in the saturation magnetization MS, and the magnetic anisotropy as well as to a change in the exchange constant and the damping parameter [4]. The strength of the pinning potential can be tuned by the chromium ion fluence applied to induce the so-called magnetic soft spots [3].
Micromagnetic simulations, high resolution magnetic transmission soft X-ray microscopy at beamline 6.1.2 of the Advanced Light Source in Berkeley, CA, USA, and electrical measurements of the anisotropic magnetoresistance are employed to characterize the pinning potential which significantly differs for transverse and vortex walls. We demonstrate field-induced DW pinning and depinning as well as reliable DW depinning by single current pulses in a permalloy nanowire containing a square-shaped magnetic soft spot [5]. Lower requirements on the lithography in comparison to geometric constrictions on the nanoscale, a smaller distribution of properties due to parallel processing during implantation, and fine tunability of the pinning potential via the chromium ion fluence make the magnetic soft spots a promising candidate for applications.
Financial support by the Deutsche Forschungsgemeinschaft via Grant Nos. FA314/3-2 and MC9/7-2, the SFB 668 and the GrK 1286 as well as the Forschungs- und Wissenschaftsstiftung Hamburg via the Exzellenzcluster “Nano- Spintronik” is gratefully acknowledged. Operation of the X-ray microscope is supported by the US Department of Energy under Contract No. DE-AC02-05-CH11231.
References: [1] D. A. Allwood, Gang Xiong, M. D. Cooke, C. C. Faulkner, D. Atkinson, N. Vernier, R. P. Cowburn, Science 296, 2003 (2002); S. S. P. Parkin, U. S. Patent No. US 683 400 5 (2004).
[2] M.-Y. Im, L. Bocklage, P. Fischer, and G. Meier, Phys. Rev. Lett. 102, 147204 (2009).
[3] A. Vogel, S. Wintz, J. Kimling, M. Bolte, T. Strache, M. Fritzsche, M.-Y. Im, P. Fischer, G. Meier, and J. Fassbender, IEEE Trans. Mag. 46, 1708 (2010).
[4] J. Fassbender and J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
[5] A. Vogel, S. Wintz, T. Gerhardt, L. Bocklage, T. Strache, M.-Y. Im, P. Fischer, J. Fassbender, J. McCord, and G. Meier, Appl. Phys. Lett. 98, 202501 (2011).

Keywords: domain wall; soft spot

  • Lecture (Conference)
    56th Annual Conference on Magnetism & Magnetic Materials, 30.10.-03.11.2011, Scottsdale, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-16219
Publ.-Id: 16219


Microorganisms in potential nuclear waste disposal host rocks

Geissler, A.; Moll, H.; Bachvarova, V.; Lütke, L.; Selenska-Pobell, S.; Bernhard, G.

It is known that microorganisms exist in host rocks of potential nuclear waste disposals. In this talk, some results will be presented from the current project about the microbial diversity in clay (Opalinus clay) and the interactions of dominant microorganisms with actinides. Especially the interactions of a Sporomusa sp. clay isolate with Curium(III) will be shown. In the second part of the talk, some information’s will be given about Halophiles in general and future plans to investigate the microbial diversity in salt rocks.

  • Lecture (Conference)
    ABC Salt Workshop, 07.-08.11.2011, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-16218
Publ.-Id: 16218


Kinetics and Thermodynamics of Defects and Nanostructures

Posselt, M.

Computer simulations using classical interatomic potentials are an efficient tool to investigate and understand atomic-level properties and processes in advanced materials. They allow the consideration of length and time scales which are often hardly accessible by experiments. However, the accuracy of the interatomic potentials employed in such type of simulations determines decisively the quality of the obtained results. Therefore, these potentials must be continuously improved and evaluated.
In the talk two applications of atomistic computer simulations are illustrated. The focus is on kinetics and thermodynamics of defects and nanostructures in materials for micro- and nanoelectronics and in structural materials for fission reactors.
The first example deals with the investigation of basic migration mechanisms of mono- and di-(self-)interstitials in Si using molecular dynamics simulations. Both the atomic mobility due to the presence of the defect and the defect mobility itself were determined. The mechanism of di-interstitial migration depends on temperature, in contrast to that of the mono-interstitial.
The subject of the second example is the structure, energetics and thermodynamics of coherent nanoclusters in bcc-Fe containing vacancies, Cu and Ni. For clusters up to a size of 200 monomers (vacancies, Cu and Ni atoms) the most stable configurations at T=0 are determined by Metropolis Monte Carlo simulations and their formation and binding energies are calculated. The temperature-dependent free formation and free binding energies of the nanoclusters are determined by taking into account configurational contributions which are calculated using the Wang-Landau Monte Carlo method.

Keywords: Si; mono-interstitials; di-interstitials; kinetics; Molecular Dynamics; Fe-based alloys; nanoclusters energetics; thermodynamics; Monte-Carlo simulations

  • Lecture (others)
    Seminarvortrag, Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, 24.10.2011, Livermore, USA
  • Lecture (others)
    Seminarvortrag, Materials Science Laboratory, Los Alamos National Laboratory, 27.10.2011, Los Alamos, USA

Permalink: https://www.hzdr.de/publications/Publ-16217
Publ.-Id: 16217


Structure, Energetics and Thermodynamics of Embedded Nanoclusters

Posselt, M.

not available, please contact the author

Keywords: embedded nanoclusters; structure; energetics; thermodynamics

  • Lecture (others)
    Seminarvortrag, Department of Mathematical Sciences, Loughborough University, 20.10.2011, Loughborough, UK

Permalink: https://www.hzdr.de/publications/Publ-16216
Publ.-Id: 16216


Ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures

Bracht, H.; Radek, M.; Kube, R.; Knebel, S.; Posselt, M.; Schmidt, B.; Haller, E.; Bougeard, D.

Gallium (Ga) implantation induced self-atom mixing in crystalline and amorphous germanium (Ge) is investigated utilizing isotopically controlled Ge multilayer structures grown by molecular beam epitaxy. The distribution of the Ga ions and the ion-beam induced depth-dependent mixing of the isotope structure was determined by means of secondary ion mass spectrometry. Whereas the distribution of Ga in the crystalline and amorphous Ge is very similar and accurately reproduced by computer simulations based on binary collision approximation (BCA), the ion-beam induced self-atom mixing is found to depend strongly on the state of the Ge structure. The experiments reveal stronger self-atom mixing in crystalline than in amorphous Ge. Atomistic simulations based on BCA reproduce the experimental results only when unphysically low Ge displacement energies are assumed. Analysis of the self-atom mixing induced by silicon implantation confirms the low displacement energy deduced within the BCA approach. This demonstrates that thermal spike mixing contributes significantly to the overall mixing of the Ge isotope structures. The disparity observed in the ion-beam mixing efficiency of crystalline and amorphous Ge indicates different dominant mixing mechanisms. We propose that self-atom mixing in crystalline Ge is mainly controlled by radiation enhanced diffusion during the early stage of mixing before the crystalline structure turns amorphous, whereas in an already amorphous state self-atom mixing is mediated by cooperative diffusion events.

Keywords: ion-beam mixing; germanium; amorphous germanium

Permalink: https://www.hzdr.de/publications/Publ-16215
Publ.-Id: 16215


A Technology Platform for Translational Research on Laser Driven Particle Accelerators for Radiotherapy

Enghardt, W.; Bussmann, M.; Cowan, T.; Fiedler, F.; Kaluza, M.; Pawelke, J.; Schramm, U.; Sauerbrey, R.; Tünnermann, A.; Baumann, M.

It is widely accepted that proton or light ion beams may have a high potential for improving cancer cure by means of radiation therapy. However, at present the large dimensions of electromagnetic accelerators prevent particle therapy from being clinically introduced on a broad scale. Therefore, several technological approaches among them laser driven particle acceleration are under investigation.
Parallel to the development of suitable high intensity lasers, research is necessary to transfer laser accelerated particle beams to radiotherapy, since the relevant parameters of laser driven particle beams dramatically differ from those of beams delivered by conventional accelerators: The duty cycle is low, whereas the number of particles and thus the dose rate per pulse are high. Laser accelerated particle beams show a broad energy spectrum and substantial intensity fluctuations from pulse to pulse. These properties may influence the biological efficiency and they require completely new techniques of beam delivery and quality assurance.
For this translational research a new facility is currently constructed on the campus of the university hospital Dresden. It will be connected to the department of radiooncology and host a petawatt laser system delivering an experimental proton beam and a conventional therapeutic proton cyclotron. The cyclotron beam will be delivered on the one hand to an iso-centric gantry for patient treatments and on the other hand to an experimental irradiation site. This way the conventional accelerator will deliver a reference beam for all steps of developing the laser based technology towards clinical applicability.

Keywords: Radiotherapy; photons; electrons; protons; ions; cyclotron; synchrotron; laser particle acceleration

  • Contribution to proceedings
    SPIE Optics + Optoelectronics, 18.-21.04.2011, Czech Republic, Prague
    Proceedings of the SPIE, Vol. 8079, 79681

Permalink: https://www.hzdr.de/publications/Publ-16214
Publ.-Id: 16214


CFD-Modellierung von Wandsieden und technische Anwendung

Krepper, E.; Rzehak, R.

Die Verifikation von Auslegungsverbesserungen an Brennelement-Abstandhaltern und ihr Einfluss auf den kritischen Wärmestrom erfordert kostspielige Experimente. Deswegen ist die Ergänzung oder sogar der Ersatz dieser Experimente durch numerische Analysen von großem Interesse. CFD-Modelle haben das Potential der Entwicklung von Modellansätzen unabhängig von der bestimmten Geometrie.
Der Vortrag beschreibt den aktuellen Stand der CFD-Modellierung wan Wandsieden und mögliche Beiträge zur Brennelementauslegung. Mit dem aktuellen Stand ist zumindest die vergleichende qualitative Analyse möglich. Bessere quantitativ zuverlässige Resultate sind mit verbesserten Modellen möglich, die auf CFD-tauglichen Experimenten basieren. Der kürzliche Fortschritt bei der Kopplung des Wandsiedemodells mit einem Populationsbilanzmodell wurde gezeigt. Vieleversprechende Reultate sind mit der in Entwicklung befindlichen schnellen Röntgentomographie zu erwarten.

Keywords: CHF; CFD; mixing vanes; subcooled boiling; fuel assembly design; DEBORA tests; MUSIG model

  • Invited lecture (Conferences)
    Kompaktkurs "Kavitation", 27.-28.10.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16213
Publ.-Id: 16213


CFD-Modelling of subcooled boiling and their technical application

Krepper, E.; Rzehak, R.

The verification of design improvements of a fuel assembly of a nuclear reactor core and their influence on the critical heat flux require expensive experiments. Therefore the supplementation or even the replacements of experiments by numerical analyses are of relevant interest in fuel assembly design. The CFD modeling has the potential of simulation independent on the certain geometry.
The presentation describes the actual state of CFX modeling of subcooled boiling and their possible contribution for rod bundle design. The comparative investigation of different designs is possible at least qualitatively. For more quantitatively reliable results the models have to be improved. In the presentation the demands on the accuracy of measured values are established. Most promising results are expected by tomographic methods like by fast X-ray tomography.

Keywords: CHF; CFD; mixing vanes; subcooled boiling; fuel assembly design; DEBORA tests

  • Invited lecture (Conferences)
    ANSYS Conference & 29. CADFEM Users’ Meeting 2011, 19.-21.10.2011, Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16212
Publ.-Id: 16212


An analytical solution of the time dependent diffusion equation in a composite slab

Glivici-Cotruta, V.; Merk, B.

The time-dependent, one-dimensional diffusion equation is solved for a finite slab of two layers. An external source is supplied to one of the layers. The differential equations are subject to the reflecting boundary conditions at the two outer boundary surfaces. The flux and the current density are continuous across the interface between two media. The exact analytical solution is expressed in terms of a Green's function. The solution is developed by the application of the Laplace transformation.

Keywords: Green's function; diffusion; Laplace transformation; composite slab

Permalink: https://www.hzdr.de/publications/Publ-16211
Publ.-Id: 16211


Terrestrial cosmogenic radionuclides for geomorphology applications

Merchel, S.

ohne Abstract, eingeladener Vortrag

Keywords: cosmogenic radionuclides; TCN; AMS accelerator mass spectrometry

  • Lecture (others)
    Seminar, School of Geography, Politics and Sociology, 02.11.2011, Newcastle upon Tyne, UK

Permalink: https://www.hzdr.de/publications/Publ-16210
Publ.-Id: 16210


The Emerging Opportunities of New Multimeric Cyclam Based Copper Chelators in Multimodal Imaging

Kubeil, M.

kein Abstract verfügbar

  • Lecture (Conference)
    8th Supraphone Meeting, 07.-10.09.2011, Funchal, Portugal

Permalink: https://www.hzdr.de/publications/Publ-16209
Publ.-Id: 16209


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