Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Coexisting stochastic and coherence resonance in a mean-field dynamo model for Earth's magnetic field reversals
Fischer, M.; Stefani, F.; Gerbeth, G.;
Using a spherical symmetric mean-field alpha^2-dynamo model for Earth's magnetic field reversals, we show the coexistence of the noise-induced phenomena coherence resonance and stochastic resonance. Stochastic resonance was recently invoked to explain the 100 kyr periodicity in the distribution of residence times between reversals. The comparison of the resulting residence time distribution with the paleomagnetic one allows for some estimate of the effective diffusion time of the Earth's core which may be 100 kyr or slightly below rather than 200 kyr as it would result from the molecular resistivity.

Publ.-Id: 11863 - Permalink


Excitation hierarchy in the BEC candidate DTN
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Batista, C. D.; Kawashima, N.; Tsukamoto, M.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.; Krzystek, J.; Glazkov, V. N.; Sosin, S. S.; Smirnov, A. I.;
NiCl2-4SC(NH2)2 (known as DTN) is a quantum S = 1 chain system with strong easyplane anisotropy that is regarded as a new candidate for the Bose-Einstein condensation (BEC) of spin degrees of freedom, with critical fields Bc1 = 2.1 T and Bc2 = 12.6 T. Tuneable-frequency Electron Spin Resonance (ESR) studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode observed in the high-field spin-polarized phase1 and previous experimental results2, a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8.9 K, Jc = 2.2 K, and Ja,b = 0.18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory3 and observed in DTN for the first time. Furthermore, we present a systematic study of the low-energy excitation spectrum of DTN in the fieldinduced magnetically ordered phase (which is regarded as the magnon BEC phase) at temperatures down to 0.45 K. We argue that two gapped modes observed in the experiment4 can be consistently interpreted within a four-sublattice antiferromagnet model with a weak isotropic corner-center interaction of magnetic ions in the body-centered tetragonal lattice with unbroken axial symmetry. The latter is of particular importance, being a necessary prerequisite for the interpreting of the antiferromagnetic ordering in DTN in terms of the BEC scenario. The physically simplest scenario would correspond to the isotropic "corner-center" exchange. Since the exchange interaction within each sublattice is antiferromagnetic, the ground state in DTN in the ordered state (Bc1 < B < Bc2) is predicted to be frustrated and thus infinitely degenerated.
  • Invited lecture (Conferences)
    Highly Frustrated Magnetism (HFM) 2008, 07.-12.09.2008, Braunschweig, Germany

Publ.-Id: 11862 - Permalink


Kleintier Positronen-Emissions-Tomographie zur in vivo Charakterisierung von Tumoren
Bergmann, R.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Wissenschaftliches Kolloquium Leibniz-Institut für Naturstoff-Forschung und Infektionsbiologie e.V. (HKI), 02.12.2008, Jena, Deutschland

Publ.-Id: 11861 - Permalink


Photoactivation experiment on 197Au and its implications on the dipole strength in heavy nuclei
Nair, C.; Junghans, A. R.; Erhard, M.; Bemmerer, D.; Beyer, R.; Grosse, E.; Klug, J.; Kosev, K.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.;
The 197Au(gamma, n) reaction is used as an activation standard for the photodisintegration studies on astrophysically relevant nuclei. At the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf, photoactivation measurements on 197Au have been performed with bremsstrahlung endpoint energies from 8.0 to 15.5 MeV. The measured activation yield is compared with previous experiments as well as calculations using Hauser-Feshbach statistical models. It is shown that the experimental data are best described by a two-lorentzian parametrization with taking the axial deformation of 197Au into account. The experimental 197Au(gamma, n) reaction yield measured at ELBE via the photoactivation method is found to be consistent with previous experimental data using photon scattering or neutron detection methods.
Keywords: bremsstrahlung, photoactivation
  • Physical Review C 78(2008)5, 055802

Publ.-Id: 11860 - Permalink


Influence of irradiation on the metabolism of melanoma cells and development of corresponding in vitro and in vivo models for the characterization of radiopharmaceuticals
Mosch, B.; Müller, K.; Pietzsch, J.;
Aim:
Irradiation is an effective implement for the therapy of solid tumors. But often single cells elude this treatment and constitute a basis for recurrence of the primary tumor and formation of metastases. One possible explanation for this observation could be predicted on irradiationdependent metabolic changes which lead to a predisposition of certain cells to show enhanced survival and migratory activity. The aim of our study was to investigate metabolic properties of irradiated melanoma cells which should further enable us to develop and validate appropriate in vitro and in vivo models for the characterization of new radiopharmaceuticals for diagnosis and therapy of metastases and solid tumors.

Materials and methods:
We applied different singledose X‐ray irradiation (1, 2, 5, 7, 10, and 20 Gy) to murine B16‐F10 melanoma cells. At several timepoints we analyzed cell viability, growth properties, clonogenic regrowth capability, cellular proliferation, and expression of cell cycle markers. Furthermore, we analyzed the cellular uptake of the radiotracers 2‐[18F]Fluor‐2‐desoxy‐D‐glucose and 3‐O‐Methyl‐[18F]fluor‐L‐DOPA, providing information about the glucose and amino acid metabolism before and after irradiation. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of untreated and irradiated melanoma cells to form lung metastases. Results: In a dosedependent manner we detected a decrease in the growth properties, viability and tracer uptake of the melanoma cells, particularly, in the period 3 to 6 days after irradiation. In contrast, already one day after irradiation cell cycle analyses showed an increase in the number of G2/M phase cells and the expression of G2‐phase markers in irradiated compared to untreated cells. Additionally, in vitro analyses showed an influence of irradiation concerning the extent to form lung metastases in the mouse.

Conclusion:
Our results indicate that metabolic changes in melanoma cells after irradiation can be analyzed by a set of different in vitro and in vivo approaches, even in a dose‐dependent manner. Using this experimental approach, we are able to characterize new radiotracers and, furthermore, to investigate metabolic effects of applied radiopharmaceuticals in combination with experimental radiation therapy.
  • Poster
    Annual Congress of the European Association of Nuclear Medicine (EANM), 11.-15.10.2008, München, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 35(2008), S316
    DOI: 10.1007/s00259-008-0896-9

Publ.-Id: 11859 - Permalink


Irradiation of melanoma cells induced changes in the S100A4-RAGE interaction toward a promigratory phenotype
Haase, C.; Wolf, S.; Pietzsch, J.;
Aim:
Tumor metastasis is responsible for most cancer deaths, and can occur after long periods of tumor dormancy. The treatment of metastases would be either radiation only or surgery combined with adjunctive postoperative radiation therapy. Multiple reports have focused on the role of S100A4 in cancer progression, specifically its ability to enhance metastasis. We suggest that RAGE (receptor for advanced glycation endproducts) is a putative receptor for S100A4.
However, the role of S100A4‐RAGE interaction in melanoma metastasis is still unclear. The aim of this study was to characterize molecular and cellular mechanism of irradiated B16‐F10 melanoma cells, thereby, examining changes in the S100A4‐RAGE interaction and the ability for migration of irradiated melanoma cells in the presence of tumor associated macrophages.

Material and Methods:
B16‐F10 cells were exposed to single dose irradiation (5 Gy, 20 Gy) and mouse RAW 264.7 cells were used as a model for tumor‐associated macrophages. The expression of S100A4 and RAGE was quantified via real‐time RT‐PCR and Western‐blot analysis. Furthermore, cell migration was investigated with irradiated B16‐F10 cells in a 24‐transwell chamber for 16 h and 24 h. Migration was influenced by seeding RAW cells as a chemoattractant into the lower
compartments and recombinant S100A4 as a stimulus to the upper compartments. Migratory cells were labeled with Calcein‐AM and quantified in a standard fluorescence microplate reader.

Results:
The total number of vital irradiated B16‐F10 cells is significantly decreased with increasing dose up to 20 Gy and up to six days, thereby altering their morphological appearance. Expression of S100A4 and RAGE is significantly increased in surviving B16‐F10 cells three and six days after 20 Gy (p[[Unsupported Character ‐ ]]0.05). Furthermore, irradiated B16‐F10 cells have a higher migratory activity supposed due to an enhanced expression of S100A4 and RAGE. RAW cells and/or recombinant S100A4 caused a further increasing migration activity of irradiated cells (20 Gy).

Conclusions:
There is a close association of melanoma cells and macrophages with alterations of their migratory and invasive activity after irradiation. We suppose a perpetual para‐/autocrine expression mechanism of extracellular S100A4 and RAGE,
and thereby changing functional properties of melanoma cells towards a promigratory phenotype. This study was supported in part by the Deutsche Forschungsgemeinschaft (grant Pi 304/1‐1).
  • Poster
    Annual Congress of the European Association of Nuclear Medicine (EANM, 11.-15.10.2008, München, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 35(2008), S316
    DOI: 10.1007/s00259-008-0896-9

Publ.-Id: 11858 - Permalink


In vitro investigation of Yttrium-90-citrate-, Erbium-169-citrateand Rhenium-186-sulfur-colloid stability
Bergmann, R.; Pinckert, J.;
Aim:
Yttrium‐90‐citrate‐ (YMM‐1), Erbium‐169‐citrate‐ (ERMM‐1), and Rhenium‐186‐sulfurcolloid (Re‐186‐MM1) were applied in radiosynovectomy (RSO), a local intraarticular injection of radionuclides in colloidal form for radiotherapy. The local metabolism of the colloidal particles is not fully understood; however, knowledge about the leakage is important for risk assessment. Therefore we investigated diffusion of the radionuclides by equilibrium dialysis, which provided
information about interaction of the colloids with synovia, stability and size in controlled equilibrium conditions.

Materials & Methods:
Carrier added YMM‐1, ERMM‐1, Re‐186‐MM1 colloids were dispersed and dialyzed against synovia, different electrolytes and buffers separated by dialysis membranes with a molecular weight cut off (MWCO) of 10,000 Dalton. The activity
concentration in the dialysis compartment was studied up to 24 hours. Tl‐201‐chloride, F‐18‐FDG, and Er‐169‐chloride were used as reference tracers.

Results:
The equilibria were reached at the latest 10 hours after start of dialysis. The ionic Er‐169‐chloride (as negative control) and Re‐186‐perrhenate showed very similar diffusion kinetics compared with reference radiotracers. The colloidal radionuclides, incubated and dialyzed against electrolytes comparable with plasma (MEM Dulbeco medium), human synovia, or phosphate containing buffers were not detected in the dialysis solution (lower 0.5% of applied dose(%ID)), except Re‐186‐MM1. Significant amounts of this compound were found in the dialysis compartment. Incubation of the colloids with isotonic sodium chloride or 0.1 M hydrochloric acid was followed by an activity release into the dialysis solution YMM‐1 (67%ID) and ERMM‐1 (62%ID). Conclusion: The different stabilities of the carrier added radiocolloids studied in different electrolyte solutions was mainly a result of the presence of phosphate ions. The low solubility of the phosphates of rare earth elements, the binding to synovia proteins, and hydroxylation were the main mechanisms of colloidal particle stabilization or reformation of free or secondary formed Erbium or Yttrium ions. This generally results in formation of particles of low diffusibility, increasing the retention of the radiocolloids inside the joint before the radionuclide‐loaded colloidal particles are phagocytozed by macrophages in the inflamed synovial membrane.
  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine (EANM), 11.-15.10.2008, München, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 35(2008), S204
    DOI: 10.1007/s00259-008-0896-9

Publ.-Id: 11857 - Permalink


Biodistribution and metabolism of stabilized bombesin labeled with new Cu-64-chelating ligands
Bergmann, R.; Walther, M.; Juran, S.; Gasser, G.; Pietzsch, J.; Stephan, H.;
Aim:
Gastrin releasing peptide receptors (GRPR) are overexpressed in different human tumors like prostate, breast and squamous cell carcinomas. The goal of this study was to compare the biodistribution and metabolism of a stabilized bombesin analogue radiolabeled with two new Cu‐64‐complexes for PET imaging of GRPR expression in xenografted mice.

Method:
Cu‐64 was complexed with a bis(2‐pyridylmethyl) derivative of 1,4,7‐triazacyclononane (TAC) and a bispidine 1,5‐dicarboxylic acid derivative (Cu‐64‐N2Py4‐OH(COOH)2) conjugated to a stabilized bombesin (BBN) derivative βhomoGlu‐βAla‐βAla‐[Cha13, Nle14]BN(7‐14) (Garcia Garoya et al. 2007). Biodistribution, elimination, and metabolism were studied in rats. Tumor accumulation was exemplarily evaluated with small animal PET in xenografted mice bearing prostate (PC3), squamous cell carcinoma (FaDu), and colorectal (HT‐29) human tumors. Cu‐64 chloride was studied for comparison. Results: PET imaging of Cu‐64‐N2Py4‐OH(COOH)2‐BBN in mice 1 h after injection revealed tumor‐to‐background ratios of 2.1 (PC3), 2.4 (FaDu control), 1.0 (FaDu blocked), and 1.5 (HT‐29). The uptake found in PC3 tumors with tissue sampling was significantly higher (5.3 control; 2.6 blocked). In comparison to the Cu‐64‐TAC‐BBN, the uptake of Cu‐64‐N2Py4‐OH(COOH)2‐BBN in rat pancreas and intestine was lower but the accumulation in kidney, liver, and stomach was higher. The metabolic stabilities of the Cu‐64‐labeled BBN‘s studied were comparable. More than 85% of the original substances were remained after 1 hour in vitro incubation with rat blood or blood plasma. In vivo all compounds were fast metabolized in rats, and lower than 5% of the original compounds were recovered in arterial blood plasma 1 hour after injection. However, the metabolism in xenografted nude mice was slower, after 1 hour 12% of blood plasma activity correspond to the original compound.

Conclusion:
Both investigated new Cu‐64 chelating agents conjugated to a stabilized BBN analogue showed typical BBN biodistribution and GRPR specific accumulation in vivo. The differences in biodistribution and metabolism between Cu‐64‐TAC‐ and Cu‐64‐N2Py4‐OH(COOH)2) labeled BBN demonstrate the influence of the Cu‐64 chelating units on these processes, especially on the nonspecific activity biodistribution. Comparison of biodistribution data of the BBN analogues and Cu‐64 chloride indicate only marginal, if any, in vivo copper demetalation, revealing high in vivo stability of the copper complex units. With further optimization of the radiolabeling in particular of specific activity the low specific uptake should increase. The studied chelating agents appear to be promising candidates for copper labeling of peptides under mild conditions. Partly supported by the 6th framework EU‐project “BioCare”, proposal # 505785.
  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine (EANM), 11.-15.10.2008, München, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 35(2008), S153
    DOI: 10.1007/s00259-008-0896-9

Publ.-Id: 11856 - Permalink


The use of nanocavities for the fabrication of ultrathin buried oxide layers
Ou, X.; Kögler, R.; Skorupa, W.; Möller, W.; Wang, X.; Vines, L.;
A continuous buried oxide (BOX) layer with a thickness of only 58 nm is formed in silicon by oxygen implantation at 185 keV with a very low ion dose of 1×1017 cm-2 and subsequent He implantation. Due to the implanted He efficient oxygen gettering occurs at the implantation induced damage and results in the accumulation of the implanted oxygen as well as of oxygen in-diffused from the annealing atmosphere. The morphology and the resistivity of the resulting silicon-on-insulator (SOI) structure are analyzed by cross section transmission electron microscopy and by cross section scanning spreading resistance microscopy, which is demonstrated to be a promising tool for the characterisation of a thin BOX layer.
Keywords: Ion Implantation, Silicon, Oxygen, SIMOX, BOX

Publ.-Id: 11855 - Permalink


Grafting of Poly(3-hexylthiophene) from Poly(4-bromostyrene) Films by Kumada Catalyst-Transfer Polycondensation: Revealing of the Composite Films Structure
Khanduyeva, N.; Senkovskyy, V.; Beryozkina, T.; Bocharova, V.; Simon, F.; Nitschke, M.; Stamm, M.; Grötzschel, R.; Kiriy, A.;
In order to achieve a stable, long-term operation of flexible electronic devices, it is necessary to firmly fix semiconductive conjugated polymers to plastic substrates, thus preventing their damage against delamination or chemical treatments. Surface-initiated Kumada catalyst-transfer polycondensation of 2-bromo-5-chloromagnesio-3-alkylthiophene from photo-cross-linked poly(4-bromostyrene), PS(Br), films leads to covalent grafting of regioregular head-to-tail poly(3-hexylthiophenes), P3HT. Herein, we investigate the grafting process in detail and elucidate the structure of the resulting composite films using ellipsometry, X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, and conductive mode atomic force microscopy techniques. In particular, we found that the grafting process is much more efficient if thick PS(Br) supporting layers are used. The maximal reachable thickness of the P3HT deposits is directly proportional to the thickness of the supporting PS(Br) layers. The obtained data suggest that the grafting process occurs not only at the PS(Br)/polymerization solution interface but also deeply inside the swollen PS(Br) films, penetrable for the catalyst and for the monomer. The process results into a kind of interpenetrated PS(Br)/P3HT network in which relatively short (∼10 nm) P3HT grafts emanate from long cross-linked PS(Br) chains. The films show good stability against delamination, high electrical conductivity in the doped state, and high swellability that might be exploited for construction of fully “plastic” electronic devices and sensors.
  • Macromolecules 41(2008)20, 7383-7389

Publ.-Id: 11854 - Permalink


Quark mass dependence of thermal excitations in QCD in one-loop approximation
Seipt, D.; Bluhm, M.; Kämpfer, B.;
A comprehensive determination of the quark mass dependence in the dispersion relations of thermal excitations of gluons and quarks in non-Abelian gauge theory (QCD) is presented for the one-loop approximation in Feynman gauge. Larger values of the coupling are admitted, and the gauge dependence is discussed. In a Dyson-Schwinger type approach, the effect of higher orders is estimated for asymptotic thermal masses.

Publ.-Id: 11853 - Permalink


Reactive magnetron sputtering of CuInS2 adsorbers for thin film photovoltaic: relation between deposition parameters and film morphoöogy
Seeger, S.; Grötzschel, R.; Ellmer, K.;
For the preparation of high-quality CuInS2 absorber films, two film properties are decisive: large crystallites and compact film morphologies. In this work we investigate the influence of the deposition parameters discharge power and substrate bias, on the morphology and chemical composition of CuInS2 films, which were prepared by reactive magnetron sputtering (radio frequency) in H2S/Ar atmosphere. A lateral concentration distribution along the substrate axis, which is caused by the arrangement the copper and indium cathodes in our sputtering equipment, was used to study the influence of the Cu-to-In ratio on the film growth. At a Cu-to-In ratio of one, which can be adjusted by the discharge powers at the copper and indium target to be positioned at the middle of the substrate, the crystallites in the film are small in size and separated by crevices from each other. In order to achieve compact CuInS2 films, the negative substrate bias was varied systematically (-15V to -150 V). The influence of the ion assistance, i.e. the impact of positive argon ions onto the growing film, was investigated with respect to the chemical composition and the morphology of the films.
Keywords: magnetron sputtering, CuInS2
  • Lecture (Conference)
    23rd European Photovoltaic Solar Energy Conference, 01.-4.9.2008, Feria Valencia, Spain

Publ.-Id: 11852 - Permalink


Dynamical scaling at the metal-insulator transition in YHx
Pronin, A. V.; Romijn, I. G.; Brom, H. B.; Hoekstra, A. F. T.; Gorshunov, B. P.; Wosnitza, J.;
There are strong indications that the light-induced metal-insulator transition in YHx is a quantum phase transition. If true, the conductivity should develop not only a characteristic scaling behavior with regard to doping and temperature, but also to frequency. Here we present our results on the frequency-temperature scaling of the conductivity in YHx at sub-terahertz frequencies on the insulating and metallic sides of the metal-insulator transition. In the insulating state, the data suggest the expected ω/T-scaling to hold. In the metallic phase, however, this scaling breaks down, and the sub-terahertz conductivity demonstrates frequencyindependent behavior. These results do not agree with the simplest picture of a quantum phase transition.
  • Invited lecture (Conferences)
    3rd International Conference "Fundamental Problems of High Temperature Superconductivity" (FPS'08), 13.-17.10.2008, Moscow-Zvenigorod, Russia

Publ.-Id: 11851 - Permalink


Bacterial Uranium Binding - Basis for the Development of Innovative Materials
Raff, J.;
Within the radio-ecological research on bacteria, living in uranium mining waste piles, it was demonstrated that the microorganisms developed an intelligent detoxification strategy to survive in such an extreme habitat. They possess a special kind of surface layer (S-layer) to protect themselves from uranium. Beside fundamental research on the protein-radionuclide interaction, the S-layers were used for the development of new and innovativ materials. Immobilized on carrier materials, these proteins keep their high and selective metal binding properties and can thusly be used for (multi)functional coatings. For example, the basic technology allows the production of metal selective filter materials for the removal and recovery of metals and the production of photocatalytical active nanoclusters immobilized on different carriers or surfaces. The latter can be used for new and innovative water treatment, whereby pharmaceutical remnants and hormones will be eliminated.
  • Lecture (others)
    INE-FZD Workshop, 22.-23.10.2008, Karlsruhe, Deutschland

Publ.-Id: 11849 - Permalink


Fe nanoparticles embedded in MgO crystals
Shalimov, A.; Potzger, K.; Geiger, D.; Lichte, H.; Talut, G.; Misiuk, A.; Reuther, H.; Stromberg, F.; Zhou, S.; Baehtz, C.; Fassbender, J.ORC
Iron nanoparticles embedded in MgO crystals were synthesized by Fe+ ion implantation at an energy of 100 keV and varying fluences from 3×10e16 to 3×10e17 cm-2. Investigations of structural and magnetic properties of Fe nanoparticles have been performed using magnetometry, x-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy, as well as by theoretical Preisach modeling of bistable magnetic systems. It has been found that alpha- and gamma-Fe nanoparticles are formed for all fluences. The content of the alpha- Fe phase increases at higher fluences and after annealing. The influence of post implantation annealing at 800 ºC in vacuum and under enhanced up to 10 kbar hydrostatic pressure in argon atmosphere on the formation of nanoparticles has been analyzed.
Keywords: iron, ferromagnetic materials, nanoparticles, ion implantation
  • Journal of Applied Physics 105(2009), 064906
  • Virtual Journal of Nanoscale Science & Technology 19(2009)13

Publ.-Id: 11848 - Permalink


Visualizing different uranium oxidation states during the surface alteration of uraninite and uranium tetrachloride
Grossmann, K.; Arnold, T.; Steudtner, R.; Weiss, S.; Bernhard, G.;
The surface alteration of uraninite (U(IV)O2) and uranium tetrachloride UCl4 in air atmosphere was studied by confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy (LIFS) using an excitation wavelength of 408 nm. It was found that within minutes the oxidations state on the surface of the uraninite and the uranium tetrachloride changed. During the surface alteration process U(IV) atoms on the uraninite and uranium tetrachloride surface became stepwise oxidized by a one-electron step at first to U(V) and than further to U(VI). These observed changes in the oxidation states of the uraninite surface were microscopically visualized and spectroscopically identified on basis of their fluorescence emission signal. A fluorescence signal in the wavelength range of 415-475 nm was indicative for metastable uranium(V) and a fluorescence signal in the range of 480-560 nm was identified as uranium(VI). In addition, the oxidation process of tetravalent uranium in aqueous solution at pH 0.3 was visualized by CLSM and U(V) was fluorescence spectroscopically identified.
Keywords: uraninite UO2, uranium, uranium tetrachloride UCl4, CLSM, oxidation states, fluorescence spectroscopy
  • Naturwissenschaften 96(2009)8, 963-974

Publ.-Id: 11847 - Permalink


Exceptionally Long Exciton Photoluminescence Lifetime in ZnO Tetrapods
Zhong, Y.; DjurišIc´, A. B.; Hsu, Y. F.; Wong, K. S.; Brauer, G.; Ling, C. C.; Chan, W. K.;
The fabrication of ZnO tetrapods of an exceptional optical quality, based on a photoluminescence (PL) lifetime in the range of tens of nanoseconds and the absence of defect emission, is found to be possible in a very narrow temperature range only. A reduction in the PL lifetime and an increase in the defect emission are observed for both higher and lower growth temperatures. The obtained PL lifetime for the optimal growth temperature is an order of magnitude higher than the best results achieved in epilayers and single crystals. Temperature dependence of the PL lifetime of high-quality tetrapod samples indicates that the dominant recombination processes are radiative.
  • Journal of Physical Chemistry C 112(2008)42, 16286-16295

Publ.-Id: 11846 - Permalink


Magnetic excitations in the BEC candidate DTN: high-field ESR studies
Zvyagin, S.;
NiCl2-4SC(NH2)2 (known as DTN) is a quantum S = 1 chain system with strong easy-plane anisotropy that is regarded as a new candidate for the Bose-Einstein condensation (BEC) of magnons, with critical fields Bc1 = 2.1 T, Bc2 = 12.6 T (defined at T = 0). Electron Spin Resonance (ESR) studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode observed in the high-field spin-polarized phase at temperatures above Tc (Tc ≤ 1.2 K), a revised set of spin-Hamiltonian parameters is obtained. Our results yield D = 8.9 K, Jc = 2.2 K, and Ja,b = 0.18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Furthermore, we present a systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase at temperatures down to 0.45 K. We argue that two gapped modes observed in the experiment can be consistently interpreted within a four-sublattice antiferromagnet model with a finite interaction between two tetragonal subsystems and unbroken axial symmetry. The latter is of crucial importance for the interpretation of the field-induced ordering in DTN in terms of the BEC of magnons.
  • Invited lecture (Conferences)
    Correlated Electron Systems in High Magnetic Fields, 13.-17.10.2008, Dresden, Deutschland

Publ.-Id: 11845 - Permalink


Spectroscopic studies of the uranium(VI) interaction with nitrogen and sulfur containing model ligands
Raditzky, B.; Joseph, C.;
The migration and interaction behavior of actinides can be effectively influenced by humic substances, biopolymers ubiquitous in natural environments, due to their ability for complex and colloid formation and their redox properties. In addition to oxygen containing functional groups, humic substances also offer sulfur and nitrogen containing functionalities.
The aim of this work is to determine the influence of various nitrogen and sulfur containing functional groups on the uranium(VI) complexation and to evaluate their contribution in comparison to oxygen containing functional groups. For this, simple organic model ligands that can occur as building blocks for humic substances are used. In this study, results are presented for the uranium(VI) complexation by the organic ligands benzenesulfonic acid and 4-hydroxybenzenesulfonic acid as well as anthranilic and nicotinic acid. The complex formation constants for the uranium(VI) complexation were determined applying time-resolved laser-induced fluorescence spectroscopy (TRLFS).
Keywords: uranium(VI), fs-TRLFS, TRLFS, benzenesulfonic acid, 4-hydroxybenzenesulfonic acid, anthranilic acid, nicotinic acid, complexation
  • Lecture (others)
    ACTINET 05-08 Project Meeting, 27.-31.10.2008, Larnaca, Cyprus

Publ.-Id: 11844 - Permalink


Synthetic Humic Acids for Basic Studies of Humic Acid Complexation Properties and Migration Processes
Sachs, S.;
In order to improve the knowledge about the interaction processes between humic acids and metal ions, e.g., actinide ions, various humic acid model substances with different functional properties were developed at the Institute of Radiochemistry. These includes synthetic humic acids with different functional group contents and various structural elements, chemically modified humic acids, humic acids with pronounced redox functionalities, and isotopically labeled humic acids. The presentation gives an overview about the synthesis, characterization and application of the different types of designed humic acid model substances.
Keywords: Humic acid, humic acid model substances, synthesis, characterization, modification, labeling, application
  • Lecture (others)
    ACTINET 05-08 Project Meeting, 27.-31.10.2008, Larnaca, Cyprus

Publ.-Id: 11842 - Permalink


Redox Properties of Humic Substances in the Systems Np(V)/(IV) and U(VI)/(IV)
Schmeide, K.;
The Np(V) and U(VI) reducing capacities of humic substances of varying functionality are discussed.
Keywords: Neptunium, Uranium, Reduction, Tetravalent, Humic acid, Redox processes
  • Lecture (others)
    ACTINET 05-08 Project Meeting, 27.-31.10.2008, Larnaca, Cyprus

Publ.-Id: 11841 - Permalink


Formation of UO2(OH)HA(I) Studied by TRLFS
Sachs, S.;
The complexation of U(VI) with purified Aldrich humic acid was studied at pH 7 under nitrogen atmosphere. Using two independent laser-induced spectroscopic methods, the formation of the ternary uranium(VI) mono hydroxo humate complex (UO2(OH)HA(I)) was studied and complexation data were derived. The results of this study are discussed in comparison to literature data.
Keywords: Humic acid, complexation, uranium, U(VI), ternary complexes, TRLFS
  • Lecture (others)
    ACTINET 05-08 Project Meeting, 27.-31.10.2008, Larnaca, Cyprus

Publ.-Id: 11840 - Permalink


A critical review on atomistic simulations of solid-phase epitaxial regrowth of amorphous Si and Ge layers
Posselt, M.; Gabriel, A.-A.;
In semiconductor technology ultra-shallow junctions are produced by ion implantation and subsequent annealing. The relatively high fluence applied in dopant implantation and the use of pre-amorphization implantation may lead to the formation of an amorphous (a-)layer. In the first stage of annealing the solid phase epitaxial regrowth (SPER) of the a-layer takes place. SPER leads to redistribution of dopants, and they are incorporated into the crystal either substitutionally or within clusters containing self-interstitials (Is) or vacancies. In Si the SPER process leaves beyond the original a/c interface the end-of-range (EOR) damage which contains an excess of Is. During further annealing, free Is are emitted from the EOR damage and may cause an enhanced diffusion of the dopants. It is highly desirable to understand the processes occurring during SPER on the atomic level. This work presents results of classical molecular dynamics simulations of SPER in pure Si and Ge. While in the last decade several authors investigated SPER in Si, the regrowth of a-Ge layers has not been considered yet. The critical review of SPER simulations using different interatomic potentials shows that the experimental regrowth rates cannot be reproduced reasonably well. Moreover, it is found that the results obtained by different groups under virtually equal conditions do not agree. Possible reasons for these differences are outlined. The main cause for the disagreement with experimental data is the inaccuracy of the interatomic potentials used. Proposals for physically-based improvements are discussed. They are based on a better description of the amorphous phase using a modified potential, without changing the established potential for the single-crystalline material. It is shown that a-Si and a-Ge with realistic structural and thermodynamic propertied can be obtained by various modifications of known interatomic potentials, whereas it is very difficult to find a modification which also yields the correct SPER rate.
Keywords: computer simulation, Si, Ge, solid-phase epitaxial regrowth
  • Lecture (Conference)
    The 9th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES2008), 12.-17.10.2008, Beijing, China

Publ.-Id: 11839 - Permalink


Terahertz wave emission from an InGaAsN large area emitter
Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.; Köhler, K.;
We present large-area emitters based on InGaAsN which show efficient THz emission for excitation wavelengths up to 1.35 μm.
The substrate material consists of a 1000 nm GayIn1-yAs1-xNx (y=0.11 and x=0.04) layer grown by molecular-beam epitaxy on semi-insulating GaAs. On top there is an additional GaAs/Al0.3Ga0.7As heterostructure with thicknesses of 5 nm for the GaAs and 60 nm for the AlGaAs layer, respectively. Transmission measurements with a Fourier spectrometer reveal a bandgap corresponding to a wavelength of 1.5 μm. The resistance of a complete device with an active area of 1 mm2 is 0.3 MΩ. This allows operation with high bias fields (30 kV/cm) without being limited by heating. For excitation an optical parametric oscillator (OPO), tunable between 1.1 μm and 1.5 μm, is used. The pulse duration is 280 fs (FWHM). The THz signal is detected using electro-optical sampling with a 1 mm thick ZnTe crystal. The gating beam (λ = 820 nm) for detection is split off from a Ti:sapphire oscillator which drives the OPO.
  • Poster
    GDR-E-2008 THz Workshop, 25.-26.09.2008, Paris, France

Publ.-Id: 11838 - Permalink


Influence of the neutron-kinetic feedback parameter variation on an anticipated transient without SCRAM in a PWR
Kliem, S.; Mittag, S.; Rohde, U.; Weiß, F.-P.;
The complete failure of the reactor scram system upon request during an operational transient is called anticipated transient without scram (ATWS). According to the German regulatory guidelines, postulated ATWS events have to be analyzed with regard to their consequences on the safety of nuclear power plants.

Since the course of ATWS transients is determined by a strong interaction of the neutron kinetics with the thermal hydraulics of the system, coupled 3D neutron kinetic/thermal hydraulic code systems are adequate tools for the analysis of such transients. In the following, the coupled code system DYN3D/ATHLET is applied to the analysis of an ATWS transient. The objective of the present work is to perform a best-estimate analysis with consequent use of a 3D neutron kinetic code (DYN3D) in combination with an advanced thermal hydraulic system code (ATHLET) together with a quantification of differences in the course and the results of transients, which arise from the uncertainties of neutron-physical conditions.

Typically, the complete failure of the main feed water supply is assumed to be the bounding ATWS event with regard to the maximum primary coolant pressure, which can be reached during the transient. The situation is aggravated if the main coolant pumps remain in operation.

For this particular transient, the influence of different neutron-physical conditions on the course of the transient was analyzed. Variations of the reactivity coefficients of the moderator density, the moderator temperature (spectral coefficient) and the fuel temperature were assumed.

One of the most relevant safety parameters in this ATWS event is the primary circuit pressure. It has been found that the spreading of the first pressure maximum is influenced only by the variation of the moderator density coefficient. A variation of the Doppler coefficient contributes only to the second pressure peak. For that reason the spreading of the tolerance limits during the second pressure peak is higher.
  • Contribution to proceedings
    2009 International Conference on Advances in Mathematics, Computational Methods, and Reactor Physics, 03.-07.05.2009, Saratoga Springs, USA
    Proceedings of the 2009 International Conference on Advances in Mathematics, Computational Methods, and Reactor Physics, CDROM paper 201661, La Grange Park: ANS, 9780894480690
  • Lecture (Conference)
    2009 International Conference on Advances in Mathematics, Computational Methods, and Reactor Physics, 03.-07.05.2009, Saratoga Springs, USA

Publ.-Id: 11837 - Permalink


Achieving high free electron mobility in ZnO:Al thin films grown by reactive pulsed magnetron sputtering
Cornelius, S.; Vinnichenko, M.; Shevchenko, N.; Rogozin, A.; Kolitsch, A.; Möller, W.;
The study is focused on improvement of the free electron mobility in Al-doped ZnO films grown by cost-effective deposition method of reactive pulsed magnetron sputtering. At optimum growth conditions it yields low absorbing films with Hall effect mobility of 46 cm2V-1s-1, free electron density of 6x1020 cm-3 and electrical resistivity of 2.26x10-4 Ohm cm. The relation between the mobility and free electron density for the films grown at different conditions is discussed in terms of ionized impurity scattering and impurity clustering mechanism or grain boundary limited transport.
Keywords: transparent conductive oxides, ZnO:Al, reactive magnetron sputtering, electrical properties

Publ.-Id: 11836 - Permalink


Jahrestagung Kerntechnik 2008 - Sektionsbericht Sektion: Thermo- und Fluiddynamik
Schaffrath, A.; Kliem, S.;
Der Beitrag gibt einen Überblick über die in den Sitzungen der Sektion Thermo- und Fluiddynamik gehaltenen Vorträge.
  • atw - International Journal for Nuclear Power 53(2008)8/9, 559-561

Publ.-Id: 11835 - Permalink


Radiation treatment planning in brain tumours Potential impact of 3-O-methyl-6-[18F]fluoro-L-DOPA and PET
Alheit, H.; Oehme, L.; Winkler, C.; Füchtner, F.; Hoepping, A.; Grabowski, J.; Kotzerke, J.; Beuthien-Baumann, B.;
Aim:
Amino acid PET has become an important diagnostic tool for brain tumour imaging. In this data analysis, the potential impact of amino acid PET with 3-O-methyl-6-[18F]fluoro-L-DOPA ([18F]OMFD) on radiation treatment planning is addressed by the following questions: 1. Was tumour tissue identified with OMFD-PET which was not covered by the conventionally derived planning target volume (PTV)? 2. Would the PTV have been changed incorporating OMFD-PET?

Patients, methods:
OMFD-PET of 25 patients after subtotal resection of malignant glioma was evaluated. The region of elevated tracer uptake of PET and of contrast enhancing masses on MRI were outlined as separate gross tumour volumes (GTVMRI and GTVOMFD) and reconstructed in the planning CT for comparison with the conventionally drawn GTVconv. A PTVnew based on GTVconv+MRI was calculated. Pairwise differential volumes were calculated to estimate overlap and differential volumes delineation by each image modality and the PTVconv and PTVnew respectively.

Results:
Differential volume analysis showed > 10 cm3 of GTVOMFD outside GTVconv and GTVMRI in 5/25 patients respectively. From GTVMRI >10 cm3 were found outside GTVOMFD in 8/25 patients. Although all tumour areas indicated by
[18F]OMFD were covered by the conventionally derived PTV, based on a GTVOMFD+MRI, the PTVnew would have been enlarged >20% in seven patients. In seven patients the PTVnew would have been reduced.

Conclusion:
OMFD-PET indicated tumour tissue outside the tumour region identified with MRI, adding valuable information for the delineation of the GTV in radiation treatment planning. OMFD-PET contains the potential to tailor the high dose radiation to the appropriate tumour volume, especially if dose escalation is desired.
Keywords: Brain tumour, positron emission tomography, radiation treatment planning, multimodal imaging, 3-O-methyl-6-[18F]fluoro-L-DOPA

Publ.-Id: 11834 - Permalink


Ultrasound at high magnetic fields: first scientific results at the HLD
Zherlitsyn, S.;
Ultrasound investigations are a powerful experimental tool to study various phase transitions and critical phenomena. This technique is now available at the Dresden High Magnetic Field Laboratory (HLD) as part of the pulsed field user program. The possible application of the infrared radiation produced by next-door free electron lasers for photoacoustic spectroscopy will be discussed. Here I will present two results recently obtained at the HLD by use of ultrasound technique. First, I report results of magnetoacoustic studies of the quantum spin-chain magnet NiCl2-4SC(NH2)2 (DTN) having a field-induced ordered antiferromagnetic (AF) phase. The longitudinal acoustic c33 mode, which propagates along the spin chains, modulates the in-chain exchange interaction and shows a softening, accompanied by energy dissipation in the acoustic wave in the vicinity of the quantum critical points. Another example is CdCr2O4, a geometrically frustrated magnet with a metamagnetic phase transition at 28 T followed by a very wide magnetization plateau with one half of the full moment of S = 3/2 Cr3+. We have performed an ultrasonic investigation of a high quality CdCr2O4 single crystal in pulsed magnetic fields up to 64 T. A minimum in the sound velocity and a peak in the attenuation have been observed at 28 T for temperatures below the temperature of the AF phase transition TN = 7.8 K. Another anomaly in the sound velocity has been observed at 60 T, where the magnetization plateau is terminated. The observed anomalies become smoother at higher temperatures. The experimental data are analyzed by use of a model where the main contribution to the spin-lattice interaction arises from the exchangestriction coupling.
  • Invited lecture (Conferences)
    Physical Phenomena at High Magnetic Fields (PPHMF), 01.-06.08.2008, Laulasmaa Resort, Estonia

Publ.-Id: 11833 - Permalink


Spin dynamics in the BEC candidate DTN studied by high-field ESR
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Batista, C. D.; Krzystek, J.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.; Glazkov, V. N.; Sosin, S. S.; Smirnov, A. I.;
NiCl2-4SC(NH2)2 (DTN) is a quantum S=1 chain system with strong easy-pane anisotropy and a new candidate for the Bose-Einstein condensation of the spin degrees of freedom. Employing high-field electron spin resonance technique, we were able to study frequency-field dependence of magnetic excitations in DTN in fields up to 25 T [1] and at temperatures down to 0.45 K [2]. As a result of our studies, we were able to accurately estimate parameters of the spin-Hamiltonian for this compound. The values were used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement with experimental data has been obtained. In addition, the excitation spectrum in DTN in the field-induced ordered phase has been studied. Two gapped modes have been observed and their frequency-field dependencies. We show that our observations can be consistently interpreted within the four-sublattice antiferromagnet model, involving a finite interaction between two tetragonal sublattices and leaving the axial symmetry intact, which is crucial for the interpretation of the field-induced ordering in DTN in terms of the BEC of magnons. Supported in part by NHMFL (through NSF and DOE) and DFG.
  • Invited lecture (Conferences)
    Physical Phenomena at High Magnetic Fields (PPHMF), 01.-06.08.2008, Laulasmaa Resort, Estonia

Publ.-Id: 11832 - Permalink


Force-induced structural transitions in cross-linked DNA films
André, A.; Fontaine-Vive, F.; Möller, H. M.; Fischer, T.; Maret, G.; Forsyth, V. T.; Gisler, T.;
We report on the preparation and characterization of wet-spun films of sodium DNA in which intermolecular cross-links were introduced following formaldehyde treatment. Raman scattering shows that the DNA in moderately cross-linked films is mainly in th B conformation. Stretching experiments show a transition from plastic to elastomeric behavior with increasing exposure to the cross-linking agent. Elastomeric DNA films are strongly disordered.X-ray diffraction shows that stretching of moderately cross-linked film under controlled high humidity conditions results in increased molecular orientation as well as the appearance of meridional reflections at 7.4-7.8 and 8.2 A. These reflections are not observed for any of the calssical conformations associated with mixed sequence DNA, and may arise from extended base-pair stacking in a stretched DNA structure.

Publ.-Id: 11831 - Permalink


Ultrasonic Investigation of NiCl2-4SC(NH2)2 in the vicinity of the quantum critical points
Zherlitsyn, S.; Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Zvyagin, A. A.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.;
es hat kein Abstract vorgelegen!
  • Poster
    High Frustrated Magnetism (HFM) 2008, 07.-12.09.2008, Braunschweig, Deutschland

Publ.-Id: 11830 - Permalink


Evolution of ferromagnetic order in URhGe alloyed with Ru, Co and Si
Sakarya, S.; Huy, N. T.; van Dijk, N. H.; de Visser, A.; Wagemaker, M.; Moleman, A. C.; Gortenmulder, T. J.; Klaasse, J. C. P.; Uhlarz, M.; von Löhneysen, H.;
We have investigated the evolution of ferromagnetic order in the correlated metal URhGe (Curie temperature TC = 9.5K) by chemical substitutionof Ru, Co and Si. Polycrystalline samples URh1−xRuxGe (x ≤ 0.6), URh1−xCoxGe (x ≤ 0.9) and URhGe1−xSix (x ≤ 0.2) have been prepared and the magnetic properties have been investigated by magnetization and transport experiments. In the case of Ru doping, TC initially increases, but then decreases linearly as a function of x and is completely suppressed for xcr ≈ 0.38. The Curie temperature in the URh1−xCoxGe series has a broad maximum TC = 20K near x = 0.6 and then drops to 8K for x = 0.9. In the case of Si doping TC stays roughly constant. We conclude that the alloy systems URh1−xRuxGe and URh1−xCoxGe are interesting candidates to study the ferromagnetic instability.
  • Journal of Alloys and Compounds 457(2008), 51-56

Publ.-Id: 11829 - Permalink


Flow imaging by high speed transmission tomography
Johansen, G. A.; Hampel, U.; Hjertaker, B. T.;
Fourth generation medical x-ray scanners using a gantry with a rotating X-ray source and a fixed circular detector array as sensor head, are too slow for imaging of the process dynamics for instance in multiphase flows. To avoid inconsistent measurements and motion blurring, all measurements need to be carried out in a short time compared to the process time constants of the process dynamics. Two different high speed tomographic imaging systems are presented here demonstrating that image rates of several thousand images per second is possible.
Keywords: High speed tomographic imaging, Gamma-ray tomography, X-ray tomography, Electron beam scanning tomography, Flow imaging.
  • Contribution to proceedings
    7th International Topical Meeting on Industrial Radiation and Radioisotope Measurement (IRRMA 7), 22.-27.06.2008, Prague, Czech Republic
    Proceedings
  • Applied Radiation and Isotopes 68(2010), 518-524
    DOI: 10.1016/j.apradiso.2009.09.004

Publ.-Id: 11828 - Permalink


Si-based light emitters as a key element for smart biosensors
Rebohle, L.; Cherkouk, C.; Skorupa, W.; Prucnal, S.; Helm, M.;
In this work we will present our concept of direct fluorescence analysis using Ge- or rare earth-implanted Si based light emitters for the detection of estrogen in waterish solutions. We will discuss the performance of these light emitters in terms of efficiency, operation lifetime, stability, and operation voltage and show that they are generally suitable for lab-on-chip applications. In addition we report about the composition and fabrication of a bioactive layer on top of the light emitters which has the task to immobilize estrogen selectively from a waterish sample. Finally, the interaction of a Tb-implanted light emitter with a quantum dot dye is investigated.
Keywords: Smart biosensing, Estrogen detection, Si-based light emission, Electroluminescence, Rare earth ion implantation
  • Lecture (Conference)
    Eurosensors XXII, 07.-10.09.2008, Dresden, Deutschland

Publ.-Id: 11827 - Permalink


The correlation between electroluminescence properties and the microstructure of Eu-implanted MOS light emitting devices
Rebohle, L.; Lehmann, J.; Kanjilal, A.; Prucnal, S.; Nazarov, A.; Tyagulskii, I.; Skorupa, W.; Helm, M.;
In this work we investigated the correlation between the EL, the electrical properties and the microstructure of Eu-implanted MOS light emitting devices. The EL spectrum shows a red EL line centered at 618 nm which is usually assigned to Eu3+ and a broad blue-green EL band attributed to Eu2+. It was found that the red EL is favored by low injection currents, low Eu concentrations, lower anneal temperatures and shorter anneal times, especially for FLA. These properties are correlated with microstructural changes triggered by ion implantation and annealing, especially with the formation and ripening of Eu or Eu oxide clusters which strongly quench the red EL. Finally, the influence of Eu agglomerations at the injecting interface on the electrical properties of the light emitter is discussed.
Keywords: Europium Electroluminescence Si-based light emission MOS
  • Poster
    IBMM 2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland
  • Nuclear Instruments and Methods in Physics Research B 267(2009)8-9, 1324-1327

Publ.-Id: 11826 - Permalink


Rare earth implanted Si-based light emitters and their use for smart biosensor applications
Rebohle, L.; Cherkouk, C.; Prucnal, S.; Helm, M.; Skorupa, W.;
In this presentation we will review our recent progresses in the development of Si-based light emitters consisting of a MOS structure with a rare earth implanted SiO2 layer. Depending on the implanted element, namely Gd, Tb and Eu, the devices exhibit strong electroluminescence in the UV, the green and in the red spectral region. It will be shown that the implantation and annealing conditions during the fabrication strongly influence the microstructural, electrical and electro¬luminescence device properties and are of special importance for the efficiency and life time of future devices. In order to improve the stability of the devices, both LOCOS (local oxidation of Si) processing and additional protection layers made of SiON were applied to the devices. The advantages and the shortcomings of these light emitters regarding their efficiency, life time, electrical excitation conditions, cut-off frequencies and miniaturization potential are compared with the needs of smart photonic and biosensor applications. A special approach for utilizing the light emitters for the detection of organic pollutants in fluid media by fluorescence analysis is discussed in more detail. In this approach the light emitter is directly placed beneath the dye-labelled sample exciting the dye whose light emission can be recorded by a suitable external detector.
Keywords: Smart biosensing, Estrogen detection, Si-based light emission, Electroluminescence, Rare earth ion implantation
  • Invited lecture (Conferences)
    VII-th International Conference on Ion Implantation and other Applications of Ions and Electrons – ION 2008, 16.-19.06.2008, Kazimierz Dolny, Polen
  • Vacuum 83(2009)SI Suppl., S24-S28

Publ.-Id: 11825 - Permalink


Blue and red electroluminescence of Europium-implanted MOS structures as a probe for the dynamics of microstructure
Rebohle, L.; Lehmann, J.; Prucnal, S.; Kanjilal, A.; Nazarov, A.; Tyagulskii, I.; Skorupa, W.; Helm, M.;
The strong blue and red electroluminescence from Eu-implanted SiO2 layers were investigated as a function of implantation and annealing conditions. It is shown that the red electroluminescence assigned to Eu3+ ions is favored by low Eu concentrations, low anneal temperatures and short anneal times. Based on a more quantitative analysis of the electroluminescence spectra this preference is explained by a shorter supply of oxygen for higher Eu concentrations and the growth of Europium oxide clusters with increasing anneal temperatures and anneal times. The correlation between electroluminescence and microstructure is supported by transmission electron microscopy investigations and demonstrates that the electroluminescence of Eu-implanted SiO2 layers can serve as a probe for the microstructural development in the active layer of the light emitter.
Keywords: Europium Electroluminescence Si-based light emission MOS
  • Applied Physics Letters 93(2008), 071908

Publ.-Id: 11824 - Permalink


Si-based light emitters and their use for smart biosensor applications
Rebohle, L.; Cherkouk, C.; Prucnal, S.; Skorupa, W.; Helm, M.;
In this presentation we will give a review about our recent progress in the development of rare earth-implanted Si-based light emitters. The devices consist of a MOS structure with a transparent front electrode made of indium tin oxide (ITO) and a SiON protection layer between the oxide and the ITO layer for a strong life time improvement. Gd, Tb and Eu are implanted in the middle of the oxide layer, and depending on the element the devices show strong electroluminescence in the UV, the green and in the red spectral region. The electrical and electroluminescence properties of these devices are discussed and evaluated in respect of possible applications on the field of biosensor technology. Based on the advantages and the shortcomings of these light emitters an approach for their use in biosensor applications is developed. In this approach the light emitters are utilized for the detection of biological substances by fluorescence analysis. There the emitter is directly placed beneath the dye-labelled sample exciting the dye whose light emission can be recorded by a suitable external detector. A very promising application is the detection of organic pollutants, e.g. estrogen, in drinking water.
Keywords: Smart biosensing, Estrogen detection, Si-based light emission, Electroluminescence, Rare earth ion implantation
  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, 26.-30.05.2008, Strasbourg, Frankreich

Publ.-Id: 11823 - Permalink


Multifunctional Cyclam Derivatives with Carbohydrates and Peptides
Röhrich, A.; Stephan, H.; Kretzschmann, A.; Noll, S.; Bergmann, R.; Steinbach, J.;
Multifunctional chelating systems with linked biomolecules provide the possibility to develop novel diagnostic and therapeutic agents with enhanced stability and improved bio-availability. In this perspective, cyclam derivatives 1 are attractive candidates for developing new metalloradiopharmaceuticals. Biomolecules like sugars and peptides direct the solubility behavior and the targeting efficiency.

Michael addition on cyclam with methyl acrylate and subsequent aminolysis with ethylene diamine delivered the tetraamino product 2.1 Ligands with four sugar units 3 were obtained by thiourea-bridging of sugar isothiocyanates with 2.2 Peptide coupling led to conjugates 4 with the hexapeptide neurotensin(8-13) which is interesting for the targeting of ductal pancreatic carcinomas.

Isothermal titration calorimetry (ITC) was used in order to characterize the interaction between glycoclusters 3 and the lectin Concanavalin A. In vitro binding studies between ligand 4 and the neurotensin receptor 1 (NTR1) were performed using the human colon adenocarcinoma cell line HT-29.

The glycoclusters 3 showed a distinct glycoside clustering effect which can be explained by an entropy advantage for the tetramer compared to the sugar monomer. Thiourea-containing compounds 3 form very stable Cu(II) complexes with slow kinetics.3 On the other hand, a rapid attainment of Cu(II) complexation equilibria was observed in the case of the peptide conjugate 4.

Multifunctional sugar and peptide conjugates of branched cyclam derivatives possess interesting complexation and targeting properties. Peripheral modifications provide the opportunity of tailoring the bio-distribution.

1. Stephan, H.; Geipel, G.; Appelhans, D.; Bernhard, G.; Tabuani, D.; Komber, H.; Voit, B. Tetrahedron Lett. 2005, 46, 3209.
2. Stephan, H.; Röhrich, A.; Noll, S.; Steinbach, J.; Kirchner, R.; Seidel, J. Tetrahedron Lett. 2007, 48, 8834.
3. Röhrich, A.; Noll, S.; Stephan, H.; Steinbach, J.; Bergamini, G.; Balzani, V. in „Technetium, Rhenium and other Metals in Chemistry and Nuclear Medicine“ U. Mazzi (Ed.), SGE Editoriali, Padova, Italy, 2006, 7, 233.
  • Poster
    2nd EUCHEMS Chemistry Congress, Chemistry: The Global Science, 16.-20.09.2008, Torino, Italy

Publ.-Id: 11822 - Permalink


The complex dynamics between the Eu2+ and Eu3+ electroluminescence of Eu-implanted MOS light emitting devices
Rebohle, L.; Lehmann, J.; Prucnal, S.; Nazarov, A.; Tyagulskii, I.; Skorupa, W.; Helm, M.; Biskupek, J.; Kaiser, U.;
Si-based light emitters were fabricated by ion implantation of Eu into a thermally grown oxide layer on Si followed by a thermal treatment and the deposition of a SiON and an indium tin oxide layer. The Eu ions were implanted in such a way that the maximum Eu concentration varies between 0.1 and 6 %. Flash lamp annealing, rapid thermal annealing and furnace annealing at temperatures between 900 and 1100°C were applied in order to activate the Eu-related luminescence centres. The electroluminescence (EL) spectrum of the Eu-implanted SiO2 layers shows a relatively sharp red EL line centered at 618 nm and a broad EL band in the blue-green spectral region which is usually assigned to the light emission of Eu3+ and Eu2+ ions, respectively. In this work we will show that the ratio between blue and red EL shows a complex dependence on the Eu concentration, the annealing time and the annealing temperature, but that some general tendencies can be identified, too. So the blue EL assigned to Eu2+ ions will dominate for high concentrations and high annealing temperatures. The dynamics of Eu2+ and Eu3+ is discussed in the framework of charge injection, charge transport and the EL mechanism which is based on the direct excitation of Eu ions by hot ballistic electrons.
Keywords: Europium Electroluminescence Si-based light emission MOS
  • Lecture (Conference)
    E-MRS 2008 Spring Meeting, 26.-30.05.2008, Strasbourg, Frankreich

Publ.-Id: 11821 - Permalink


Dendritic Ligands with Fluorescent Labels
Röhrich, A.;
Overview on known fluorescent labeled dendrimers and their cellular uptake behavior. New synthetic route using MMTr and boc protecting groups. UV-vis and time-resolved laser fluorescence spectra.
  • Lecture (others)
    5th Supraphone Meeting, 29.-31.05.2008, Prague, Czech Republic

Publ.-Id: 11820 - Permalink


Complexation of uranium(VI) with peptidoglycan
Barkleit, A.; Moll, H.; Bernhard, G.;
We investigated the interaction of UO22+ with peptidoglycan (PG), the main part of the outer membrane of gram-positive bacteria, by potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH (2.0 to 9.0) and concentration range (10-5 to 10-4 M U(VI), 0.01 to 0.2 g/L PG). With potentiometry two different dissociation constants for the carboxyl sites of glutamic acid and diaminopimelic acid (pKa = 4.55 ± 0.02 and 6.31 ± 0.01), and one averaged pKa for hydroxyl and amino groups (which are not distinguishable) (9.56 ± 0.03) and the site densities could be identified. With potentiometry three different uranyl PG complexes were ascertained: two 1 : 1 uranyl carboxyl complexes R-COO-UO2+, one with the glutamic acid carboxyl group (log β110 = 4.02 ± 0.03), which has a very small formation ratio, and one with the diaminopimelic acid carboxyl group (log β110 = 7.28 ± 0.03), and a mixed 1 : 1 : 1 complex with additional hydroxyl or amino coordination, R-COO-UO2(+)-Ai-R (Ai = NH2 or O-) (log β1110 = 14.95 ± 0.02). With TRLFS, also three, but different species could be identified: a 1 : 1 uranyl carboxyl complex R-COO-UO2+ (log β110 = 6.9 ± 0.2), additionally a 1 : 2 uranyl carboxyl complex (R-COO)2-UO2 (log β120 = 12.1 ± 0.2), both with diaminopimelic acid carboxyl groups, and the mixed species R-COO-UO2(+)-Ai-R (Ai = NH2 or O-) (log β1110 = 14.5 ± 0.1). The results are in accordance within the errors of determination.

Publ.-Id: 11819 - Permalink


Cell cycle regulating kinase Cdk4 as a potential target for tumor cell treatment and tumor imaging
Graf, F.; Köhler, L.; Knieß, T.; Wüst, F.; Mosch, B.; Pietzsch, J.;
The cyclin-dependent kinase (Cdk)-cyclin D/INK4/retinoblastoma (pRb)/E2F cascade, which controls the G1/S transition of the cell cycle, has found to be altered in many neoplasias. Inhibition of this pathway by using, e.g., selective Cdk4 inhibitors has been suggested to be a promising approach for cancer therapy. We hypothesized that appropriately radiolabeled Cdk4 inhibitors are suitable probes for tumor imaging and may be helpful studying cell proliferation processes in vivo by positron emission tomography. Herein, we report the synthesis and biological, biochemical, and radiopharmacological characterization of two 124I-labeled small molecule Cdk4 inhibitors (8-cyclopentyl-6-iodo-5-methyl-2-(4-piperazin-1-yl-phenylamino)-8H-pyrido[2,3-d]-pyrimidin-7-one (CKIA) and 8-cyclopentyl-6-iodo-5-methyl-2-(5-(piperazin-1-yl)-pyridin-2-yl-amino)-8H-pyrido[2,3-d]pyrimidin-7-one (CKIB)). Our data demonstrate a defined and specific inhibition of tumor cell proliferation through CKIA and CKIB by inhibition of the Cdk4/pRb/E2F pathway emphasizing potential therapeutic benefit of CKIA and CKIB. Furthermore, radiopharmacological properties of [124I]CKIA and [124I]CKIB observed in human tumor cells are promising prerequisites for in vivo biodistribution and imaging studies.

Publ.-Id: 11818 - Permalink


Microscopic and spectroscopic investigation of U(VI) interaction with the monocellular green alga Chlorella vulgaris
Vogel, M.; Günther, A.; Raff, J.; Bernhard, G.;
The green alga Chlorella vulgaris has the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6 and to a lesser extend at higher pH values. The uranium removal is almost complete at pH 4.4 and 6 by metabolic active and inactive cells under the given experimental conditions. Laser-induced fluorescence spectroscopy was used for the characterization of uranyl species formed in solutions and biomass. Fluorescence spectroscopic investigations indicate differences of the formed algal uranyl complexes in dependence of the metabolic activity of cells and the uranyl speciation. Scanning electron microscopy demonstrates that the algal cell wall is involved in the binding of U(VI).
Keywords: Chlorella vulgaris, algae, uranium(VI), biosorption, TRLFS, SEM
  • Lecture (others)
    Meeting INE-FWR, 22.-23.10.2008, Karlsruhe, Deutschland

Publ.-Id: 11817 - Permalink


PET-CT Co-Registration for In-Beam PET
Fiedler, F.; Sobiella, M.; Enghardt, W.;
In-beam PET is based on the β+-activation of the irradiated volume and of the beam itself by interactions between the incoming ions and the nuclei of the tissue. Due to the special situation of in-beam PET, i.e. space for the rotating patient table and for the beam delivery has to be provided, the unique in-beam PET scanner cannot be a full ring device as in conventional PET imaging. It is necessary for patient evaluation to establish a relationship between the β+-activity created during therapeutic treatment and the anatomy of the patient. Therefore, the PET images have to be superimposed onto the planning X-ray computed tomogram (CT) with sub-millimeter precision. Since in-beam PET images and planning CT are acquired at completely different devices, their coordinates are matched by means of stereotactic coordinates. To enable a high flexibility of the measurement the double head PET scanner is rotatable around the central beam. Due to the weight of the detectors, the PET gantry is deformed under rotation, resulting in a displacement of the crystal positions in comparison to those, which are expected when assuming a rigid body rotation. Therefore, a technical solution to define the exact detector positions at any rotation angles has been developed. An exemplary embodiment will be illustrated by means of the in-beam PET installation at GSI.
Keywords: in-beam PET, PET-CT Coregistration
  • Poster
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Germany
    PET-CT Co-Registration for In-Beam PET

Publ.-Id: 11816 - Permalink


Ion Beam Therapy: Principles and Quality Assurance - Short Course
Kraft, G.; Fiedler, F.; Weyrather, K. W.; (Editors)
Gerhard Kraft studied Physics at Heidelberg and Cologne where he received his Ph.D. in nuclear physics. He founded the biophysics department at GSI where he developed the heavy ion tumor therapy together with Wilma K. Weyrather. She studied Physics at the University of Cologne and received her Ph.D. at the University of Giessen in Radiobiology in 1978. They both together initiated the Radiobiology program at GSI and later on the tumor therapy.

The novel features of the GSI tumor therapy are the extreme target conform beam delivery using an intensity modulated scanning method, the biology based treatment planning and the in vivo control of the patient using online-PET. In order to cover the target with a dose having a homogenous biological effect and a steep gradient at the borders the Target volume is dissected in slices of equal particle energy which are covered by a grid of 20,000 to 50,000 pixels of different beam positions. For all these pixels the individual covering of particles has to be calculated according to the wanted dose level and the actual value of the Relative Biological Effectiveness, RBE, at the specific pixel. These RBE values depend on the physical composition of the beam at each location and the biological properties of the affected tissue mainly on its repair capacity of complex DNA damage.

For the clinical success of the up to now more than 400 patients treated with this technique, the quality assurance of the technical equipment, the biological modelling for the treatment planning and the physical dose delivery are extremely important.

The biological corrections of the treatment planning are based on the Local Effect Model LEM verified in many experiments. It is also confirmed by the follow up of the treated patients that did not show large side and late effects. For the quality assurance of the beam delivery an online measurement of the emission of gamma quants have been developed and used during patient irradiation. When penetrating through the patient a significant fraction of the primary beam such as carbon or other ions under go nuclear reaction with the tissue resulting in radioactive positron emitting isotopes either from the beam such as 11C and 10C or from the target atoms such as 15O. Their positron decay can be monitored from outside and can be used to track the beam stopping inside the patient.

Fine Fiedler did her Ph.D. in 2008 at the Technical University of Dresden and studied the feasibility to monitor the stopping points of the beam inside the patients. She is working in the In-beam-PET group of the Oncoray Dresden. She will report that the PET techniques are capable assessing the relevant parameters for quality assurance in respect to anatomical landmarks. But it has been also shown that it is possible to extend this technique to other ion than carbon such as Protons, 3He, 7Li and 16O.

In general, the short course will introduce in the physical and biological rational of ion beam therapy. It will explain the critical feature in planning and beam delivery and will give the principles for quality assurance.
Keywords: ion therapy
  • Invited lecture (Conferences)
    2008 Nuclear Science Symposium, Medical Imaging Conference and 16th Room Temperature Semiconductor Detector Workshop, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 11815 - Permalink


Atomic-scale structure of Mo6S6 nanowires
Kibsgaard, J.; Tuxen, A.; Levisen, M.; Lægsgaard, E.; Gemming, S.; Seifert, G.; Lauritsen, J.; Besenbacher, F.;
We have studied atomic-scale structure of the Mo6S6 nanowires using Scanning Tunneling Microscopy and Spectroscopy (STM and STS) and Density Functional Theory (DFT). A novel synthesis route based on metallic Mo precursors is presented for the selective formation of elementary pure Mo6S6 nanowires. The Mo6S6 nanowires selectively organize as trimer bundles, and each of the Mo6S6 nanowires consists of an electrically conducting Mo backbone dressed with a sulfur exterior cap. The Mo6S6 nanowires may thus be of interest as novel building blocks in nanoelectronics since the Mo6S6 nanowires exist in a robust, singular structural conformation with uniquely defined electrical (metallic) properties.
Keywords: nanowires, molybedenum sulfide, DFT, DF-TB, density-functional, STM, STS, scanning-tunneling microscopy, scanning tunneling spectroscopy

Publ.-Id: 11814 - Permalink


Electromechanical switch based on Mo6S6 nanowires
Popov, I.; Gemming, S.; Okano, S.; Ranjan, N.; Seifert, G.;
We investigate the structural, electronic, and transport properties of mechanically deformed Mo6S6 nanowires using a density-functional based tight binding method extended with a Green's functions formalism. We present two interesting results: first, the properties of the wire are not affected by bending, and second, a metal-insulator transition occurs when the wire is twisted. This indicates that molybdenum sulfide nanowires can be used as a nanocable to flexibly transfer information between electromechanical switches, which can be also constructed from the same wires. Hence, our results suggest the Mo6S6 nanowires as unique building blocks for future nanodevices.
Keywords: nanowires, molybdenum sulfide, density-functional, DFT, DFTB, conductivity
  • Nano Letters 8(2008)12, 4093-4097
    DOI: 10.1021/nl801456f
  • Abstract in refereed journal
    Physica Status Solidi (A) 3(2009)4, 53

Publ.-Id: 11813 - Permalink


Cell irradiation setup and dosimetry for radiobiological studies at ELBE
Zeil, K.; Beyreuther, E.; Lessmann, E.; Wagner, W.; Pawelke, J.;
The radiation source ELBE delivers different types of secondary radiation, which is used for cell irradiation studies in radiobiological research. Thereby an important issue is the determination of the biological effectiveness of photon radiation as a function of photon energy by using low energetic, monochromatic channeling radiation (10-100 keV) and high energetic bremsstrahlung (up to 40 MV). Radiobiological studies at the research facility ELBE demand special technical and dosimetric prerequisites. Therefore, a cell irradiation system (CIS) has been designed, constructed and installed at the beam line. The CIS allows automatic irradiation of a larger cell sample number and the compensation of spatial inhomogeneity of the dose distribution within the beam spot. The recently introduced GafChromic EBT radiochromic film model has been used to verify the cell irradiation dose deposition achieving a dose uncertainty of <5 %. Both, the installed cell irradiation system and the developed dosimetric procedure based on the use of the EBT film have been experimentally tested at ELBE. The biological effectiveness of 34 MV bremsstrahlung with respect to 200 kV X-rays from a conventional X-ray tube has been determined. An RBE value of 0.75 has been measured in good agreement with literature.
  • Nuclear Instruments and Methods in Physics Research B 267(2008)14, 2403-2410

Publ.-Id: 11812 - Permalink


Elektromagnetisch getriebene Strömungen in elektrochemischen Systemen
Weier, T.; Cierpka, C.; Gerbeth, G.;
Der in elektrochemischen Systemen in der Regel vorhandene Stromfluss führt zusammen mit einem magnetischen Feld zu Lorentzkraftverteilungen im Elektrolyten, die dessen Bewegungszustand modifizieren können. Dieser an sich einfache Effekt kann sich abhängig vom Aufbau der elektrochemischen Zellen in überraschend vielseitigen Strömungsformen äußern. Dies wird anhand von Beispielen demonstriert und im Hinblick auf aktuelle theoretische Vorstellungen diskutiert.
Keywords: Lorentz force, magneto-electrochemistry
  • Lecture (others)
    Lehrstuhlkolloquium Professur für Magnetofluiddynamik, 15.10.2008, Dresden, Germany

Publ.-Id: 11811 - Permalink


Magnetic quantum oscillations in strongly correlated metals – experimental data meets theoretical predictions
Wosnitza, J.;
One of the most powerful methods to determine bulk band-structure parame-ters in metals is the measurement of magnetic quantum oscillations. This can be done e.g. by measuring the field-dependent magnetization, i.e., the de Haas-van Alphen (dHvA) effect, or by resolving Shubnikov-de Haas (SdH) oscillations in the field-dependent resistivity. It is, however, only the comparison with sophisticated band-structure calculation that a deeper understanding of the electronic properties of metals can be gained. Besides the user-lab activities a strong in-house research program is pursued at the HLD. Thereby, the focus is laid on the investigation of correlated electron systems at high magnetic fields. This covers e.g. the recently found clear thermodynamic evi-dence for the existence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a layered organic superconductor [1] and the determination of the band- and angle-resolved superconducting coupling strength in the borocarbide superconductor LuNi2B2C [2].
  • Invited lecture (Conferences)
    DFT Meets Experiment & 7th Tutorial Hands-on-FPLO, 25.-28.08.2008, Dresden, Germany

Publ.-Id: 11809 - Permalink


Science and Infrastructure at the New Dresden High Magnetic Field Laboratory
Wosnitza, J.;
At the Forschungszentrum Dresden-Rossendorf the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden), HLD, has opened his doors for users since the beginning of 2007. Pulsed magnetic fields up to 70 T (with 150 ms pulse length in a 24 mm bore) as well as smaller ones (60-65 T, with 25-50 ms pulse lengths) are available for users. Further pulsed magnets with ever increasing performances are being continuously developed, having set the ambitious goal of reaching 100 T on a 10 ms time scale. A 60 T magnet with a 1 second pulse length is ready to be tested allowing thermodynamic experiments to be performed. At the HLD a world-unique experimental infrastructure is at hand with next-door free electron lasers making possible unique high-field magneto-optical and ESR experiments in the range 4-230 µm. Besides the user-lab activities a strong in-house research program is persued at the HLD. Thereby, the focus is laid on the investigation of correlated electron systems at high magnetic fields. This covers e.g. the recently found clear thermodynamic evidence for the existence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a layered organic superconductor [1] and the determination of the band- and angle-resolved superconducting coupling strength in the borocarbide superconductor LuNi2B2C [2].
  • Invited lecture (Conferences)
    Physical Phenomena at High Magnetic Fields, 01.-06.08.2008, Laulasmaa Resort, Estonia

Publ.-Id: 11808 - Permalink


High magnetic field properties of quasi-two-dimensional organic superconductors
Wosnitza, J.;
Investigations of quasi-two-dimensional (2D) organic charge-transfer salts in high magnetic fields have deepened our understanding of these materials. Comprehensive studies of e.g. magnetic quantum oscillations or angular-dependent transport properties allowed to unravel details of the electronic band-structure. In some cases, deviations from the usually adopted Fermi-liquid picture for metals were observed. For β´´-(BEDT-TTF)2SF5CH2CF2SO3 e.g., strong indications for an incoherent electronic transport across the layers and a field-induced insulating state were found. Strong magnetic fields as well influence the superconducting state, usually by driving the super¬conductor from the Shubnikov into the normal state and thereby suppressing the critical temperature in a well-known monotonous fashion. The 2D organic superconductors are, however, good candidates for exhibiting in addition to the Meissner and Shubnikov phase the so-called FFLO state, named after Fulde, Ferrell, Larkin, and Ovchinnikov, when applying the magnetic field exactly parallel to the conducting layers. In this case, the orbital critical field is much larger than the Pauli-limiting field for these singlet superconductors. In the FFLO state, superconductivity can survive even at magnetic fields above the Pauli limit by sacrificing parts of the superconducting volume with a spatially oscillating order parameter. Our recent high-resolution specific-heat experiments in parallel fields up to 28 T for κ-(BEDT-TTF)2Cu(NCS)2 gave strong evidence for the existence of the FFLO state. For fields above 21 T, the superconducting transition becomes first order signalling that the Pauli limit is reached. Below about 3 K, the upper critical field increases sharply and a second first-order transition appears within the superconducting phase. With additional magnetic-torque measurements up to 32 T we were able to follow the phase diagram down to 50 mK. The well-known electronic band-structure parameters allow a thorough theoretical estimate of the Pauli-limited superconducting phase diagram.
  • Invited lecture (Conferences)
    International Symposium on Molecular Conductors 2008, 22.-25.07.2008, Okazaki, Japan

Publ.-Id: 11807 - Permalink


Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern
Wosnitza, J.;
Was sind Magnetfelder? Wo findet man sie? Wie erzeugt man sie und zu was sind sie nutze? Antworten auf diese Fragen sollen in dem Vortrag durch Vorstellung der weltweiten Bestrebungen, immer höhere Magnetfelder zu erreichen, gegeben werden. Ähnlich wie z. B. Druck und Temperatur haben magnetische Felder einen tief greifenden Einfluss auf den Zustand und Zustandsänderungen der Materie. Untersuchungen von Materialien in hohen Magnetfeldern sind daher mittlerweile Standard und eine Vielzahl von Anwendungen in unserem täglichen Leben sind ohne Magnetfeldeffekte undenkbar. In der Forschung wird der stetig wachsende Bedarf an möglichst großen Magnetfeldstärken durch Hochfeldlaboratorien abgedeckt. In dem neu aufgebauten Hochfeld-Magnetlabor Dresden sollen demnächst gepulste Magnetfelder bis zu 100 Tesla, dem 2,5-millionenfachen des Erdmagnetfelds, erzeugt werden. Erste Hochfeldmagnete sind in Betrieb und seit 2007 hat neben der Eigenforschung der Nutzerbetrieb begonnen. Der momentane Status des Labors, die Schwierigkeiten, die zur Erzeugung so hoher Magnetfelder überwunden werden müssen, und exemplarische wissenschaftliche Ergebnisse aus Hochfeldstudien sollen vorgestellt werden.
  • Invited lecture (Conferences)
    Festkolloquium zum Tag der Physik an der Universität Regensburg, 18.07.2008, Regensburg, Germany

Publ.-Id: 11806 - Permalink


Science at the New Dresden High Magnetic Field Laboratory
Wosnitza, J.;
Since the beginning of 2007, the new Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD) at the Forschungszentrum Dresden-Rossendorf, is accepting proposals for magnet time and has hosted the first user groups. The available user coils at the HLD produce magnetic fields up to about 70 T, with 150 ms pulse length. Besides the ulti-mate goal of a pulsed magnet reaching 100 T for a timescale of 10 ms in a bore of 20 mm, further large-scale magnets (e.g. 60 T, 1 s, 40 mm) are planned. The necessary energy for the pulsed coils is provided by a world-unique 50 MJ capacitor bank. A free-electron-laser facil-ity next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible unique high-field magneto-optical experiments in the range 3-200 µm. Cryotechniques and different sample probes for a broad range of experimental techniques custom designed for the pulsed magnets are readily available for users. In-house research of the HLD focuses on electronic properties of strongly correlated materials at high magnetic fields. Some examples of the scientific work being carried out will be highlighted.
  • Lecture (others)
    Seminar am Max-Planck-Institut Physik komplexer Systeme, 22.05.2008, Dresden, Deutschland

Publ.-Id: 11805 - Permalink


On the influence of spatial discretization in LWR-burnup calculations with HELIOS 1.9
Merk, B.;
Cell- and burnup calculations are the fundament for all deterministic static and transient 3D full core calculations for different operational states of the reactor. The spatial discretization used for the c burnup calculations influences the results for the used integral transport solutions significantly. The arising differences in the neutron flux distribution are demonstrated for different discretization strategies . These differences in the flux distribution cause significant changes in the infinite multiplication factor and in the localized burnup ditribution in the fuel rod for identical averaged burnup. The influence of different discretization strategies on the calculation of homogenized two group cross sections which are forwarded to the 3D full core calculations is investigated and the different calculation times are analyzed.
Keywords: Cell- and Lattice calculation, cross section preparation, HELIOS, Discretization, Burnup calculation
  • Contribution to proceedings
    2009 International Conference on Advances in Mathematics, Computational Methods, and Reactor Physics, 03.-07.05.2009, Saratoga Springs, United States
  • Lecture (Conference)
    2009 International Conference on Advances in Mathematics, Computational Methods, and Reactor Physics, 03.-07.05.2009, Saratoga Springs, United States

Publ.-Id: 11804 - Permalink


An analytical solution for an external source problem with delayed neutron using the Telegrapher's equation
Merk, B.;
This work presents the development of an analytical solution for a space-time dependent neutron transport problem in a one dimensional system consisting of homogenized medium with a central, time dependent external source by Green's functions. The delayed neutron production is implemented with the multiple scale expansion method. Qualitative results are analyzed for a deeper understanding of the effects of space-time dependent neutron transport. An example for the use of the developed solution for the study of the effect of different levels of subcriticality in accelerator driven systems is given.
Keywords: Time Dependent Neutron Transport, Multiple Scale Expansion, Green's Functions, Accelerator Driven Systems
  • Contribution to proceedings
    2009 International Conference on Advances in Mathematics, Computational Methods, and Reactor Physics, 03.-07.05.2009, Saratoga Springs, United States
  • Lecture (Conference)
    2009 International Conference on Advances in Mathematics, Computational Methods, and Reactor Physics, 03.-07.05.2009, Saratoga Springs, United States

Publ.-Id: 11803 - Permalink


Magnetization of Polycrystalline BiFeO3 in High Magnetic Fields
Wardecki, D.; Przenioslo, R.; Sosnowska, I.; Skourski, Y.; Loewenhaupt, M.;
The magnetization of polycrystalline ceramic BiFeO3 has been studied with pulsed magnetic fields up to 58 T. We observe a magnetic transition in both, increasing and decreasing magnetic fields. The critical field of the transition decreases with temperature. It is observed at 18.1 T at 80K and 16.1 T at 235K for increasing fields, whereas with decreasing fields the transition is observed at about 1.5 T below these values. The observed transition is the same as that reported in BiFeO3 single crystals at 10K [Kadomtseva et al.: JETP Lett. 79 (2004) 571]. It was attributed to the destruction of the modulated magnetic ordering in BiFeO3.
  • Journal of the Physical Society of Japan 77(2008)10, 103709

Publ.-Id: 11802 - Permalink


VGF-Kristallzüchtung mit kombinierten AC/DC-Magnetfeldern
Pätzold, O.; Lantzsch, R.; Grants, I.; Gerbeth, G.; Stelter, M.;
s werden Ergebnisse von VGF-Kristallzüchtungen von GaAs und Ge-Si Kristallen unter dem Einfluss eines wandernden Magnetfeldes vorgestellt. Das Magnetfeld erzeugt eine Strömung in der Schmelze, die wiederum deutlichen Einfluss auf die Form der Phasengrenze und die Dotierstoffverteilung in der Nähe der Phasengrenze hat.
  • Lecture (Conference)
    DGKK-Workshop „Herstellung und Charakterisierung von massiven Verbindungshalbleitern“, 09.-10.10.2008, Erlangen, Germany

Publ.-Id: 11801 - Permalink


Sektionsberichte Jahrestagung Kerntechnik 2008 - Teil 1
Dagan, R.; Rohde, U.; Faber, W.;
Von Berichterstattern werden die Präsentationen des fachlichen Teils der Jahrestagung Kerntechnik mit den Technischen Sitzungen und Fachsitzungen zusammengefasst. Der Beitrag beinhaltet Berichte über die Sektion "Reaktorphysik und Berechnungsmethoden".
Keywords: reactor physics, methods of calculations
  • atw - International Journal for Nuclear Power 53(2008)8/9, 556-567

Publ.-Id: 11800 - Permalink


Absolute versus convective helical magnetorotational instability in a Taylor-Couette flow
Priede, J.; Gerbeth, G.;
We analyze numerically the magnetorotational instability of a Taylor-Couette flow in a helical magnetic field (HMRI) using the inductionless approximation defined by a zero magnetic Prandtl number (Pm=0). The Chebyshev collocation method is used to calculate the eigenvalue spectrum for small amplitude perturbations. First, we carry out a detailed conventional linear stability analysis with respect to perturbations in the form of Fourier modes that corresponds to the convective instability which is not in general self-sustained. The helical magnetic field is found to extend the instability to a relatively narrow range beyond its purely hydrodynamic limit defined by the Rayleigh line. There is not only a lower critical threshold at which HMRI appears but also an upper one at which it disappears again. The latter distinguishes the HMRI from a magnetically-modified Taylor vortex flow. Second, we find an absolute instability threshold as well. In the hydrodynamically unstable regime before the Rayleigh line, the threshold of absolute instability is just slightly above the convective one although the critical wave length of the former is noticeably shorter than that of the latter. Beyond the Rayleigh line the lower threshold of absolute instability rises significantly above the corresponding convective one while the upper one descends significantly below its convective counterpart. As a result, the extension of the absolute HMRI beyond the Rayleigh line is considerably shorter than that of the convective instability. The absolute HMRI is supposed to be self-sustained and, thus, experimentally observable without any external excitation in a system of sufficiently large axial extension.
  • Physical Review E 79(2009), 046310

Publ.-Id: 11799 - Permalink


Analyzing of uranium species by fluorescence spectroscopy: A contribution for handling ecological problems caused by uranium mining activities in former Eastern Germany
Baumann, N.; Arnold, T.;
As a consequence of extensive and reckless uranium mining in Eastern Germany by the Soviet mining company WISMUT between 1945 and 1990, numerous mining residues exist including important ecological problems in Saxony and Thuringia today. A main topic is washing out mobile uranium species from the rock piles and for-mer mines by surface water. It is necessary to control the pathway, the species, and the amount of migrating ura-nium compounds, and to investigate the interactions between solid mineral phases and mobile uranium species such as sorption, precipitation and forming secondary uranium minerals.
One tool for analyzing tiny amounts of U(VI) species (but also in a minor way U(IV) and U(V) species) is time-resolved laser-induced fluorescence spectroscopy (TRLFS). This method is well established in the Institute of Radiochemistry (IRC) from the Forschungszentrum Dresden-Rossendorf (FZD), especially in case of problems connected with uranium. TRLFS delivers a fluorescence signal with characteristic features in dependence of concentration and speciation of the fluorescent species in the sample. These features are the positions of the peak maxima, and, secondary, characteristic lifetimes of the signals. This technique is applicable in case of U(VI) spe-cies in water solutions, but also in case of thin U(VI) mineral coatings on solid phases.
In that lecture results of investigations of adsorbed uranium species onto mineral surfaces like from gibbsite and from muscovite are presented. Spectroscopic characterisation of several secondary uranium minerals (e.g. bolt-woodite and compreignacite) by determination of the positions of the peak maxima and the lifetimes from the TRLFS signals are presented. The spectroscopic signatures of these uranium (VI) minerals are useful for identi-fying U(VI) mineral species as colloids, as thin coatings on rocks, as minor components in soils, or as alteration products of nuclear waste. Additionally the interaction between an aqueous solution and metallic uranium was investigated by TRLFS: The identification of an ultra-thin secondary mineral film on a disk of metallic depleted uranium (DU) originated from a British tank shell, which was in contact with a phosphate containing solution, will be showed. This example demonstrates the high sensitivity of TRLFS regarding solid U(VI) phases.
Keywords: Uranium mining, U(VI), TRLFS
  • Lecture (others)
    Seminar, 03.11.2008, Bangkok, Thailand

Publ.-Id: 11797 - Permalink


Povedenie germanii, implantirovannovo v SiO2 vblisi granizui sraschivania kremnii na isolatore Behavior of Germanium Ion-implanted into SiO2 Near the Bonding Interface of a Silicon-on-Insulator Structure
in Russian
Popov, V. P.; Tyschenko, E.; Voelskow, M.; Cherkov, A. G.;
issledovanui svoistva germanii, implantirovannovo v sloi SiO2
The properties of germanium implanted into the SiO2 layers in the vicinity of the bonding interface of silicon-on-insulator structures are studied. It is shown that, under conditions of high-temperature (1100 °C) annealing, germanium nanocrystals are not formed, while the implanted Ge atoms segregate at the Si/SiO2 bonding interface. It is established that, in this case, Ge atoms are found at sites that are coherent with the lattice of the top silicon layer. In this situation, the main type of traps is the positive-charge traps; their effect is interpreted in the context of an increase in the surface-state density due to the formation of weaker Ge–O bonds. It is found that the slope of the drain–gate characteristics of the back MIS transistors increases; this increase is attributed to an increased mobility of holes due to the contribution of an intermediate germanium layer formed at the Si/SiO2 interface.
Keywords: ion implantation germanium SiO2
  • Fizika i Tekhnika Poluprovodnikov 41(2007)3, 301-303
  • Semiconductors 41(2007)3, 291-296

Publ.-Id: 11796 - Permalink


Transport and noise in organic field effect devices
Morawetz, K.; Gemming, S.; Luschtinetz, R.; Kunze, T.; Lipavský, P.; Eng, L. M.; Seifert, G.; Milde, P.; Pankoke, V.;
The transport and fluctuation properties of organic molecules ordered parallel between two Au contact leads are investigated by the method of surface Green function. From first-principles simulation the relevant hopping parameters are extracted and used to calculate nonlinear transport coefficients with respect to an external bias voltage. A staggering of conductance is found in dependence on the number of molecules squeezed in-between the contacts. The thermal properties show an anomalous behavior whenever the voltage reaches the values of the molecular energy levels active for transport. The thermoelectric figure of merit shows a resonance allowing to reach values even larger than one.
  • Physical Review B 79(2009)085405, 1-12

Publ.-Id: 11795 - Permalink


Pattern competition in homogeneously heated fluid layers
Cartland Glover, G. M.; Generalis, S. C.;
Simulations examining pattern competition have been performed on a horizontal homogeneously heated layer that is bounded by an isothermal plane above an adiabatic plane. Several different circulation patterns arose as the heating regime applied to the horizontal layer was modified. The sequence of the patterns formed as the Grashof number was increased had the following order: laminar, rolls, squares, hexagons and pentagons, pentagons and then two square modes of differing orientations. Fourier analysis was used to determine how the key modes interact with each pattern.
Keywords: Convection, Horizontal Layer, Heat Transfer, Stability
  • Open Access LogoEngineering Application of Computational Fluid Mechanics 3(2009)2, 164-174

Publ.-Id: 11794 - Permalink


Ultra fast electron beam x-ray CT scanner for industrial process tomography
Fischer, F.; Hampel, U.; Mattausch, G.;
In many industrial fields, there is a strong interest in the understanding of inner structure and transient behaviour of multi-phase flows. This is relevant for process control and optimisation in chemical industry or has influence on design of safety components in nuclear engineering, for example. The qualification of computational fluid dynamics codes dedicated to simulation of the stationary and transient flows in complex three dimensional geometries requires in-depth knowledge of the details of the real flow structure under various conditions. To extend our measurement capabilities beyond the wire mesh sensor and needle probes used so far [1], we have developed a high-speed x-ray tomography system recently [2]. This new technique offers the opportunity to perform non-intrusive flow measurements with a high frame rate and also at high temperatures and pressures. The basic principle of the system is similar to the EB CT being used in cardiac diagnostics [3]. The scanner consists of an electron beam gun with triode-type cathode system delivering up to 65 mA beam current at 150 kV acceleration voltage. Using fast electron-optical units, the electron beam is focussed onto a semicircular metal target and swept at a frequency of up to 10 kHz along the target thus producing a rapidly moving x-ray spot. A circular x-ray detector comprising 240 CZT pixels measures the x-ray power transmitted through the object which is placed in the center of the scanner head. The detector readings are recorded at a data acquisition rate of 1 MS/s and subsequently used for image reconstruction. Frame rates of up to 7.000 2D slices per second can be achieved in this way. Typical object diameters are up to 120 mm. Spatial resolution is currently in the range of 1 mm feature size but will be improved in the future.
  • Lecture (Conference)
    1st ITG International Vacuum Electronics Workshop, 10.-11.11.2008, Bad Honnef, Deutschland

Publ.-Id: 11793 - Permalink


Air-water experiments in a vertical DN200-pipe
Beyer, M.; Lucas, D.; Kussin, J.; Schütz, P.;
The extensive experimental results presented in this report provide a high-quality database for air-/water flows in a vertical pipe with a nominal diameter of 200 mm. This database can be used for the development and validation of CFD-like models for two-phase flows, e.g. for bubble coalescence and fragmentation. In particular, the investigations aim on the evolution of the two-phase flow along the pipe height. Therefore, up to 18 single measurements with varying distances between the gas injection and measurement plane were realised for each of the 92 combinations of gas and water flow rates. The pressure at the position of the activated gas injection was kept constant at 0.25 MPa(a). This boundary condition has the advantage that the measured data represent exactly the evolution of the flow along the pipe, i.e. they reflect a configuration at which the gas injection is at a fixed height position, while the measurement plane varies. Important results of this test series are time averaged radial profiles of the gas fraction, and the gas velocity, as well as the time and cross-section averaged bubble size distributions. Furthermore, gas fraction data resolved regarding the bubble size and spatial distribution are presented. As in previous test series, flow patterns were analysed, whereby the classification results from the bubble size. A substantial part of these new air/water experiments were quality and plausibility checks of the measured data. In the result, a clear and consistent trend regarding their evolution with increasing distance from the position of the gas injection was found. Comparisons of the trend of time and cross section averaged gas volume fraction along the pipe height with the theoretically expected values were carried out. The influence of the orifice diameter of the gas injection on flow patterns is also discussed in the report.
Freigabe ab 2011
Keywords: Two-phase flow, Gas bubbles, Gas volume fraction distribution, Gas velocity
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-505 2008

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Publ.-Id: 11792 - Permalink


Luft-Wasser Experimente im vertikalen DN200-Rohr
Beyer, M.; Lucas, D.; Kussin, J.; Schütz, P.;
Die im Rahmen dieser Versuchsserie erzielten umfangreichen experimentellen Ergebnisse bilden eine hochwertige Datenbasis für Luft-Wasser-Strömungen in einem vertikalen DN200-Rohr, die für die Entwicklung und Validierung von CFD-Modellen, beispielweise bzgl. Blasenkoaleszenz und -fragmentierung, genutzt werden können. Besonderes interessant ist die Untersuchung der Entwicklung der Zweiphasenströmung über der Rohrhöhe. Aus diesem Grund wurden für jede der 92 betrachteten Kombinationen aus Gas- und Wasser-Volumenstromdichten bis zu 18 Messungen mit variablen Abständen zwischen Gaseinspeisung und Messebene durchgeführt. Dabei wurde der Druck an der Gaseinspeisestelle konstant auf 0,25 MPa(a) gehalten. Diese Randbedingung bietet den Vorteil, dass die so gemessenen Daten die Entwicklung der Strömung über der Rohrhöhe widerspiegeln, d.h. eine Konfiguration beschreiben, bei der das Gas an einer festen Höhenposition eingespeist wird und die Messungen in verschiedenen darüberliegenden Ebenen erfolgen. Wesentliche Ergebnisse dieser Messserie sind radiale zeitgemittelte Profile für den Gasgehalt und die Gasgeschwindigkeit sowie zeit- und querschnittsgemittelte Blasengrößenverteilungen. Außerdem liegen blasengrößen- und ortsaufgelöste Gasgehaltsdaten vor. Wie bereits bei früheren Versuchsserien wurden auch in diesem Fall die Strömungsformen analysiert, wobei die Klassifizierung anhand der Blasengröße erfolgte. Ein wesentlicher Bestandteil dieser neuen Luft/Wasser-Versuche war die Qualitäts- und Plausibilitätsprüfung der Messdaten. Es konnte festgestellt werden, dass die Daten einen eindeutigen, widerspruchsfreien Trend bzgl. ihrer Entwicklung mit zunehmendem Abstand von der Gaseinspeisung aufweisen. Zur Plausibilitätsprüfung wurden Vergleiche des Gasgehaltsverlaufes über der Rohrhöhe mit theoretisch zu erwartenden Kurven durchgeführt. Zusätzlich zu diesen Ergebnissen enthält der Bericht eine Einschätzung des Einflusses des Bohrungsdurchmessers an der Gaseinspeisung auf die sich einstellende Strömung.
Freigabe ab 2011
Keywords: Two-phase flow, Gas bubbles, Gas volume fraction distribution, Gas velocity
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-504 2008

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Publ.-Id: 11791 - Permalink


Miniature conductivity wire mesh sensor for gas-liquid two-phase flow measurement
Hampel, U.; Otahal, J.; Boden, S.; Beyer, M.; Schleicher, E.; Zimmermann, W.; Jícha, M.;
A miniature conductivity wire mesh sensor for gas-liquid two-phase flow measurement in small channels is introduced. The sensor design is similar to the conventional wire mesh sensor for larger flow cross sections with wire electrodes stretched across the flow channel in two adjacent planes and with perpendicular wire orientation between planes. Conductivity measurement is performed by special electronics which consecutively applies bipolar voltage pulse excitation to the sender wires and measures electrical current flow in the wire crossings at the receiver wires. The new design is based on printed circuit board technology. A prototypical sensor made of 2 x 16 stainless steel wires each of 50 µm diameter was manufactured and applied to two-phase flow measurement inside the mixing chamber of an effervescent atomizer. Accuracy of the sensor was studied for static liquid distributions using microscope photography and for dynamic two-phase flow by comparison of wire mesh data with radial gas fraction profiles obtained from X-ray microtomography measurements.
Keywords: wire-mesh sensor, atomizer, two-phase flow, X-ray microtomography

Publ.-Id: 11790 - Permalink


Vacancy-type defects in 6H–silicon carbide induced by He-implantation: a positron annihilation spectroscopy approach
Zhu, C. Y.; Ling, C. C.; Brauer, G.; Anwand, W.; Skorupa, W.;
Six-fold helium ion implantation was carried out on nitrogen doped n-type 6H–SiC epi samples. A box-shaped He-implantation profile and damage region was thus introduced. Vacancy-type defects in the implanted region were studied by positron annihilation spectroscopy using a monoenergetic positron beam. The average size of the vacancy-type defect detected in the as-He-implanted sample was the divacancy (V2). Thermal annealing had the effect of shrinking the defective region. Annealing at temperatures lower than 900 ◦C had the effect of removing vacancy-type defects in the defective region. While the annealing temperature is above 900 ◦C, the size of the vacancy-type defects in the defective region increased with annealing temperature. At the annealing temperature of 1600 ◦C, the defectiveregion reduced to ∼100 nm and the vacancy-type defects within the region agglomerated to clusters having an average size of 14 V2.
  • Journal of Physics D: Applied Physics 41(2008), 195304

Publ.-Id: 11789 - Permalink


Ionenstrahlen – ein Werkzeug zur Herstellung von Nanostrukturen
Schmidt, B.;
Es wird ein Überblich über die Möglichkeiten des Einsatzes von Ionenstrahltechniken zur Erzeugung von Nanostrukturen sowohl auf Festkörperoberflächen als auch vergraben im Festkörper gegeben. Besonders wird dabei auf die Ionenstrahlsynthese von Nanoclustern in SiO2 und die Synthese von Nanodrähten mittels feinfokussierten Ionenstrahlen eingegangen. Zum Schluss wird die Herstellung von Si-Nanodrähten und Nano-Elektro-Mechanischen Systemen (NEMS) beschrieben, die auf der Kombination von lakaler Ga+ FIB-Implantation mit einer selektiven Ätztechnik beruht.
Keywords: ion implantation, ion beam synthesis, nanocluster, nanowire, NEMS
  • Invited lecture (Conferences)
    Internationale Fachmesse für Feinwerktechnik, Ultrapräzision, Micro- und Nanotechnologien -MiNat, MiNat Hot Spot WGL - Nanotechnologie in der Leibnizgesellschaft (WGL), 07.-08.10.2008, Stuttgart, Germany

Publ.-Id: 11788 - Permalink


Cluster growth and luminescence in ion-implanted silica
Fitting, H.-J.; Salh, R.; Kourkoutis, L.; Schmidt, B.;
Scanning electron microscopy (SEM) and cathodoluminescence (CL) in
combination with scanning transmission electron microscopy (STEM) have been used
to investigate thermally grown amorphous silicon dioxide layers implanted
isoelectronically with group IV ions (C+, Si+, Ge+, Sn+, Pb+) as well as with group VI
ions (O+, S+, Se+).
Keywords: Cathodoluminescence, Silica layers, Ion implantation
  • Lecture (Conference)
    14th European Microscopy Congress, 01.-05.09.2008, Aachen, Germany
  • Contribution to proceedings
    14th European Microscopy Congress, 01.-05.09.2008, Aachen, Germany
    S. Richter, A. Schwedt (Eds.):EMC 2008, Vol. 2: Materials Science, Berlin Heidelberg: Springer-Verlag, 17-18

Publ.-Id: 11787 - Permalink


Ecological problems in Saxony related to the former uranium mining activities – fluorescence spectroscopy, a tool for analyzing the uranium binding form
Baumann, N.; Arnold, T.;
As a consequence of extensive and reckless uranium mining in Eastern Germany by the Soviet mining company WISMUT between 1945 and 1990, numerous mining residues exist including important ecological problems in Saxony and Thuringia today. A main topic is washing out mobile uranium species from the rock piles and for-mer mines by surface water. It is necessary to control the pathway, the species, and the amount of migrating ura-nium compounds, and to investigate the interactions between solid mineral phases and mobile uranium species such as sorption, precipitation and forming secondary uranium minerals.
One tool for analyzing tiny amounts of U(VI) species (but also in a minor way U(IV) and U(V) species) is time-resolved laser-induced fluorescence spectroscopy (TRLFS). This method is well established in the Institute of Radiochemistry (IRC) from the Forschungszentrum Dresden-Rossendorf (FZD), especially in case of problems connected with uranium. TRLFS delivers a fluorescence signal with characteristic features in dependence of concentration and speciation of the fluorescent species in the sample. These features are the positions of the peak maxima, and, secondary, characteristic lifetimes of the signals. This technique is applicable in case of U(VI) spe-cies in water solutions, but also in case of thin U(VI) mineral coatings on solid phases.
In that lecture results of investigations of adsorbed uranium species onto mineral surfaces like from gibbsite and from muscovite are presented. Spectroscopic characterisation of several secondary uranium minerals (e.g. bolt-woodite and compreignacite) by determination of the positions of the peak maxima and the lifetimes from the TRLFS signals are presented. The spectroscopic signatures of these uranium (VI) minerals are useful for identi-fying U(VI) mineral species as colloids, as thin coatings on rocks, as minor components in soils, or as alteration products of nuclear waste. Additionally the interaction between an aqueous solution and metallic uranium was investigated by TRLFS: The identification of an ultra-thin secondary mineral film on a disk of metallic depleted uranium (DU) originated from a British tank shell, which was in contact with a phosphate containing solution, will be showed. This example demonstrates the high sensitivity of TRLFS regarding solid U(VI) phases.
Keywords: Uranium mining, U(VI), TRLFS
  • Lecture (others)
    Seminar, 27.10.2008, Hiroshima, Japan

Publ.-Id: 11786 - Permalink


Thermo-mechanische Finite-Elemente-Modellierung zur Schmelzerückhaltung im RDB nach Verlagerung von Corium in das untere Plenum Thermo-mechanical finite element modelling of in-vessel melt retention after corium relocation into the lower plenum
Altstadt, E.; Abendroth, M.; Willschütz, H.-G.;
Bezüglich eines hypothetischen Kernschmelzeszenarios in einem Leichtwasserreaktor ist es notwendig, mögliche Versagensformen des Reaktordruckbehälters sowie Versagenszeiträume zu untersuchen, um die Belastung für das Containment bestimmen zu können.
Vom Institut für Sicherheitsforschung des FZD wurden Finite-Elemente-Modelle erstellt, die sowohl die Temperaturfeldberechnung für die Wand als auch die elastoplastische Mechanik der Behälterwand beschreibt. Die thermischen und mechanischen Berechnungen sind gekoppelt. Das Modell ist in der Lage, Versagenszeit und Versagensposition eines Behälters mit beheiztem Schmelzepool zu berechnen. Es existieren Modelle für die Druckwasserreaktortypen KONVOI und WWER-1000. Es wurden prototypische Szenarien mit und ohne externe Flutung des RDB untersucht, wobei die homogen und die segregierte Schmelzepoolkonfiguration betrachtet wurden. Zusätzlich wurde eine bruchmechanische Bewertung des Thermoschocks, der durch die externe Flutung entsteht, vorgenommen. Auf Grundlage der Experimente im Rahmen des ISTC-Projekts METCOR wurde außerdem die Auswirkung der thermochemischen Wechselwirkung zwischen Corium-Schmelze und RDB-Wand auf das Versagensverhalten des RDB untersucht. Das wichtigste Ergebnis ist, dass eine erfolgreiche Schmelzerückhaltung im RDB auch bei größeren Reaktoren möglich erscheint, wenn eine rechtzeitige Flutung der Reaktorgrube gelingt. Mittels einer statistischen Analyse wurden die Empfindlichkeiten von Ergebnissen gegenüber den Eingangsparametern
und die Unsicherheiten der Ergebnisse quantifiziert.

Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Several experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work. At the Institute of Safety Research of the FZD finite element models have been developed simulating the thermal processes and the viscoplastic behaviour of the vessel wall. The thermal hydraulic and the mechanical calculations are coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool. Models exist for the pressurised water reactor types KONVOI and VVER-1000. Prototypic scenarios with and without external flooding were investigated with consideration of homogeneous and segregated melt pool configurations. Additionally a fracture mechanic evaluation of the thermal shock, originating from the external flooding, was performed. Based on the experimental results of the ISTC project METCOR, the effects of the thermal chemical interaction between corium melt and vessel steel were investigated in the IVR scenarios. An important result of the project is that a successful in-vessel melt retention seems to be possible even for large reactors if the reactor pit can be filled with water before the corium melt is relocated to the lower plenum. By means of statistical analysis the sensitivity of results against input parameter variations was studied. The uncertainty of results was quantified.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-503 2008

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Publ.-Id: 11785 - Permalink


The immobilization of uranium in multispecies biofilms studied by microsensors and confocal microscopy
Krawczyk-Baersch, E.; Arnold, T.;
Multispecies biofilms were cultured in standard culture media (Sifin; TN 1171) with a pH of approximately 7.2, and in air atmosphere condition at room temperature (20 °C). The culture media were pumped through three annular reactors for two months with a flow-rate of 15.2 ml/min, and an inner cylinder rotation speed of 14 rpm. Inside the reactors biofilms were grown on glass slides to a thickness of approximately 600 µm. Two reactors were fed with UO2(ClO4)2 to adjust the total uranium concentration in the culture medium in ecological relevant concentration (5×10-5 M and 5×10-6 M). After three weeks the cultured multispecies biofilms were used for microscopical and spectroscopical studies (CLSM) as well as for O2 microsensor studies.
Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in a living multispecies biofilm grown on biotite plates. These particles ranged between 1 and 7 µm in width and up to 20 µm in length and were located at the bottom and at the edges of biofilms colonies. Anaysis of amplified 16S rRNA fragments and fluorescence in situ hybridization were used to characterize the biofilm communities. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilms. The detection of uranium(V) in a multispecies biofilm was interpreted as a short-lived intermediate of the uranium(VI) to uranium(IV) redox reaction. Its presence clearly documents that the uranium(VI) reduction is not a two electron step but that only one electron is involved.
Concentration profiles of oxygen versus biofilm depths were measured in the biofilms by electrochemical microsensors with a tip diameter of 10µm. A motor-driven micromanipulator was used for moving downwards through the biofilm in 20 or 50µm steps. The microsensor results clearly showed that the vertical profiles of the O2 concentration within the biofilms are affected by the presence as well as by the concentration of U(VI) in the culture media. In the absence of uranium the O2 concentration in the well aerated biofilm decreased slightly. In contrast, O2 concentrations in the biofilms, which were exposed to different concentrations of uranium, decreased with increasing uranium concentration.
  • Lecture (Conference)
    4th Semi-Annual RTDC-2 Meeting of FUNMIG, 29.-30.04.2008, Larnaca, Cyprus

Publ.-Id: 11784 - Permalink


The influence of microbes on the mobility and immobilization of radionuclides e.g. U(VI) in surface and subsurface environments: A microscopical and geochemical study
Krawczyk-Baersch, E.;
The effect of uranium added in ecologically relevant concentrations (1×10-5 M and 1×10-6 M) to stable multispecies biofilms was studied by electrochemical oxygen microsensors with tip diameters of 10 µm and by confocal laser scanning microscopy (CLSM). The results show the different influences of microorganisms on the migration of uranium due to redox processes taking place within biofilm. For the first time the reduction of the U(VI) to metastable U(V) by a one-electron transfer was proved by using a combination of confocal laser microscopy (CLSM) and fluorescence spectroscopy. The microsensor profile measurements in the stable multispecies biofilms exposed to uranium indicated that the bacteria in the top region of the biofilms, i.e. the metabolically most active biofilms zone, battle the toxic effects of aqueous uranium with an increased respiratory activity and high consumption rates. As analysis of the amplified 16S rRNA gene fragments showed, the addition of uranium in ecologically relevant concentrations did not change the bacterial diversity in the stable multispecies biofilms. Adaptation and detoxification mechanisms allow them to resist concentrations of toxic elements. The increased respiratory activity and high consumption rates of the microbes results in larger zones of O2 depletion in the biofilms. These zones may trigger redox processes leading to precipitation of U(IV) solids and consequently to an increased removal and immobilization of uranium from the surrounding bulk solution.
  • Invited lecture (Conferences)
    Institute Seminar, Institute of Chemistry, Cyprus University, 02.05.2008, Nicosia, Cyprus

Publ.-Id: 11783 - Permalink


The response of biofilms to uranium impacts
Krawczyk-Baersch, E.; Brockmann, S.; Arnold, T.; Hofmann, S.; Wobus, A.;
The effect of uranium added in ecologically relevant concentrations (1×10-5 M and 1×10-6 M) to stable multispecies biofilms was studied by electrochemical oxygen microsensors with tip diameters of 10 µm and by confocal laser fluorescence microscopy (CLSM). The microsensor profile measurements in the stable multispecies biofilms exposed to uranium showed that the oxygen concentration decreased faster with increasing biofilm depth compared to the uranium free biofilms. In the uranium containing biofilms, the oxygen consumption, calculated from the steady-state microprofiles, showed high consumption rates of up to 61,7 nmol cm-3s-1 in the top layer (0 - 70 µm) and much lower consumption rates in the lower zone of the biofilms. Staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI) confirmed the high respiratory activities of the bacteria in the upper layer. Analysis of the amplified 16S rRNA gene fragments showed that the addition of uranium in ecologically relevant concentrations did not change the bacterial diversity in the stable multispecies biofilms and is therefore not responsible for the different oxygen profiles in the biofilms. The fast decrease in the oxygen concentrations in the biofilm profiles showed that the bacteria in the top region of the biofilms, i.e. the metabolically most active biofilm zone, battle the toxic effects of aqueous uranium with an increased respiratory activity. This increased respiratory activity results in O2 depleted zones closer to the biofilm/air interface which may trigger uranium redox processes, since suitable redox partners, e.g. extracellular polymeric substance (EPS) and other organics (e.g. metabolites), are sufficiently available in the biofilm porewaters. Such redox reactions may lead to precipitation of uranium(IV) solids and consequently to a removal of uranium from the aqueous phase.
  • Lecture (Conference)
    7. Jenaer Sanierungskolloquium, 22.-23.09.08, Jena, Deutschland

Publ.-Id: 11782 - Permalink


The increase of metabolic activity in biofilms caused by uranium
Krawczyk-Baersch, E.; Brockmann, S.; Arnold, T.; Wobus, A.; Diessner, S.;
Most surface and subsurface environments are inhabited by microorganisms, which do not usually occur as single individual cells in nature but rather in multicellular communities called biofilms. Such biofilms attached to mineral surfaces may considerably influence the migration of toxic and/or radioactive heavy metals in contaminated environments. In our studies multispecies biofilms, which were cultured in air atmosphere on glass slides in biofilm reactors were exposed to uranium in ecologically relevant concentrations, i.e. a total U concentration of 1×10-5 mol/l and 5×10-6 M, respectively. The resulting response of the microbial biofilm community to the added uranium was studied by oxygen microsensors in biofilms. In addition staining methods such as CTC and the DNA-binding DAPI were used in combination with confocal laser microscopy (CLSM). The results reveal that the addition of uranium in ecologically relevant concentrations to stable biofilms has a strong effect on the oxygen concentration and consumption rates in biofilms due to a stimulation of the metabolism of the microbes and, consequently, on their respiratory activity and oxygen consumption. The addition of uranium (VI) in ecologically relevant concentrations (1×10-5 M and 1×10-6 M) to stable multispecies biofilms induced a fast decrease of the oxygen concentration with increasing biofilm depth, which is dependent on the uranium concentration. The microbial response to the addition of uranium occurred within two to three hours and resulted in oxygen concentration profiles similar to the profiles measured three weeks after the uranium addition.
  • Lecture (Conference)
    Biofilms III, 3rd International Conference, 06.-08.10.2008, München, Deutschland

Publ.-Id: 11781 - Permalink


In-situ Measurements on Suspended Nanoparticles with Visible Laser Light, Infrared Light and X-rays
Zänker, H.;
The presence of engineered nanoparticles (ENPs) in the water cycle is a subject of discussion amongst scientists, producers of nanomaterials, environmentalists and politicians. At this stage the influence of ENPs on the environment is still minimum and there is also hardly any experience with measuring such artificial nanoparticles within the complex matrices of environmental samples. However, there is experience with measuring natural nanoparticles in environmental waters. An overview is given on measuring methods with the focus on in-situ methods. They are aimed at studying particle size, particle size distribution, electric charge or binding type of environmental contaminants on the nanoparticles. Examples of use are given for methods such as photon correlation spectroscopy, laser-induced breakdown detection, laser Doppler velocimetry, time-resolved laser fluorescence spectroscopy, Fourier transform infrared spectroscopy and X-rax absorption spectroscopy with synchrotron radiation. The examples show the general strategies of such measurements, indicate typical problems and difficulties and demonstrate how such difficulties can be overcome.
Keywords: Nanoparticles, environmental contaminants, photon correlation spectroscopy, laser-induced breakdown detection, laser Doppler velocimetry, time-resolved laser fluorescence spectroscopy, Fourier transform infrared spectroscopy, X-rax absorption spectroscopy
  • Contribution to external collection
    Nießner, R.; Frimmel, F.H.: Nanoparticles in the Water Cycle. Properties, Analysis and Environmental Relevance., Berlin, Heidleberg, New York: Springer, 2010, 3-642-10317-0, 117-138

Publ.-Id: 11780 - Permalink


The effect of spatial discretization in LWR cell calculations with HELIOS 1.9
Merk, B.; Koch, R.;
Cell and lattice calculations are the basis for all deterministic static and transient 3D full core calculations. The spatial discretization used for the cell and lattice calculations influences the results for these transport solutions significantly. The arising differences in the neutron flux distribution due to different spatial discretization are demonstrated. These differences in the flux distribution cause significant changes in the kinf value. An evaluation of the kinf value for the case of infinitely fine discretization is made. The influence of the discretization on the calculation of homogenized few group cross sections which are forwarded to the 3D full core calculations is investigated. Strategies for improving the discretization are developed and their influence on the calculation time is evaluated.
Keywords: Spatial Discretization, Neutron Transport, HELIOS, Collision Probabilities, Flat-Flux-Approximation
  • Contribution to proceedings
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary
    Proceedings of the 18th Symposium of AER, 9789633726389, 257-266
  • Lecture (Conference)
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary

Publ.-Id: 11779 - Permalink


Character of magnetic excitations in a quasi-one-dimensional antiferromagnet near the quantum critical points: Impact on magnetoacoustic properties
Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Zherlitsyn, S.; Zvyagin, A. A.; Zapf, V. S.; Jaime, M.; Paduan-Filho, A.;
We report results of magnetoacoustic studies in the quantum spin-chain magnet NiCl2-4SC(NH2)2 (DTN) having a field-induced ordered antiferromagnetic (AF) phase. In the vicinity of the quantum critical points (QCPs) the acoustic c33 mode manifests a pronounced softening accompanied by energy dissipation of the sound wave. The acoustic anomalies are traced up to T>TN, where the thermodynamic properties are determined by fermionic magnetic excitations, the “hallmark” of one-dimensional (1D) spin chains. On the other hand, as established in earlier studies, the AF phase in DTN is governed by bosonic magnetic excitations. Our results suggest the presence of a crossover from a 1D fermionic to a three-dimensional bosonic character of the magnetic excitations in DTN in the vicinity of the QCPs
  • Physical Review B 78(2008), 094406

Publ.-Id: 11778 - Permalink


Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal
Wosnitza, J.; Gvozdikov, V. M.; Hagel, J.; Ignatchik, O.; Bergk, B.; Meeson, P. J.; Schlueter, J. A.; Davis, H.; Winter, R. W.; Gard, G. L.;
We report on an anomalous behavior of the spin-splitting zeros in the de Haas–van Alphen (dHvA) signal of a quasi-two-dimensional organic superconductor. The zeros as well as the angular dependence of the amplitude of the second harmonic deviate remarkably from the standard Lifshitz–Kosevich (LK) prediction. In contrast, the angular dependence of the fundamental dHvA amplitude as well as the spin-splitting zeros of the Shubnikov–de Haas (SdH) signal follow the LK theory. We can explain this behavior of the dHvA signal by small chemical-potential (CP) oscillations and find a very good agreement between theory and experiment. A detailed wave-shape analysis of the dHvA oscillations corroborates the existence of an oscillating CP. We discuss the absence of the above spin-zero effect in the SdH signal and argue that in k-(BEDT-TTF)2SF5CH2CF2SO3 it can be explained by an incoherent variable range hopping interlayer transport which is insensitive to the small CP oscillations.
  • Open Access LogoNew Journal of Physics 10(2008), 083032

Publ.-Id: 11777 - Permalink


Spectral-history modeling in DYN3D burnup calculations
Bilodid, Y.; Mittag, S.;
Reactor dynamics codes such as DYN3D use two-group cross sections (XS) which depend on local burnup, given in terms of the energy produced per fuel mass (MWd/kgHM). However, a certain burnup value can be reached under different spectral conditions depending on moderator density and other local parameters. Neglecting these spectral effects, i.e. applying the summary-burnup value only, can cause considerable errors in the calculated power density. In some cases with a high burnup the inaccuracy can reach 20%.
This paper describes a way to take into account spectral-history effects. It is shown that the respective XS correction linearly depends on the actual Pu-239 concentration. The applicability of the method was proved not only for usual uranium oxide fuel, but also for mixed uranium/plutonium oxide (MOX) and fuel assemblies with burnable absorber. A test version of an extended data library containing history coefficients was created. The code DYN3D was extended by new subroutines that calculate the actual distribution of Pu-239 in the core and apply a spectral-history correction for the cross sections.
Keywords: DYN3D, spectral-history effects, burnup history effect, burnup, cross sections.
  • Contribution to proceedings
    18th AER Symposium on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary
    Proceedings of 18th AER Symposium on VVER Reactor Physics and Reactor Safety, Budapest, 978-963-372-639-6, 467-481
  • Lecture (Conference)
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary

Publ.-Id: 11776 - Permalink


The importance of the intracellular glutathione pool of rape cells exposed to heavy metal stress
Viehweger, K.; Geipel, G.;
Uranium is a widespread radioactive toxic heavy metal, released into the biosphere mostly by military purposes and nuclear industry. It is taken up by plant root systems and its chemical toxicity is much more dangerous than the radiological. Thus cell suspensions of rape (Brassica napus) revealed similar intracellular defence reactions after uranium exposure like it is described for other heavy metals (1).
Glutathion is one of the key players in this network, because of its ability to complex xenobiotics via the action of glutathione-S-transferase, its redox-capacity, and/or as precursor in the biosynthesis of heavy metal-binding peptides, e.g. phytochelatines.
Rape cells react with a decrease of the cytoplasmic glutathione pool, revealed by HPLC and TLC, respectively. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) measurements gave an insight in interactions between glutathione and uranium. The possible reduction of the soluble uranium(VI) to an insoluble oxidation state of (IV) by glutathione can be excluded, because of lacking uranium(IV) in the cytoplasm, detected by photoacustic measurements. These findings and the time course of dropping the glutathione pool suggest an involvement in the biosynthesis of pytochelatines, which is proven by HPLC. Experiments addressing the physiological relevance of these parts of cellular defence mechanisms are under way, especially to elucidate whose impact on intracellular heavy metal sequestration.

(1) Clemens, S. (2001). "Molecular mechanisms of plant metal tolerance and homeostasis." Planta V212 (4): 475-486.
Keywords: Glutathion, uranium
  • Contribution to proceedings
    The American Society for Cell Biology 48th Annual Meeting, 13.-17.12.2008, San Francisco, USA

Publ.-Id: 11775 - Permalink


Experimental two-phase flow measurement using ultra fast limited-angle-type electron beam X-ray computed tomography
Bieberle, M.; Fischer, F.; Schleicher, E.; Koch, D.; Menz, H.-J.; Mayer, H.-G.; Hampel, U.;
We report on an experimental evaluation of a novel limited-angle-type ultra fast electron beam X-ray computed tomography approach for the visualization and measurement of a gas-liquid two-phase flow. With this method a simple linear electron beam scan is used to produce radiographic views of a live two-phase flow in a pipe segment of a flow loop. Electron beam scanning can be performed very rapidly, thus a frame rate of 5 kHz is achieved. Radiographic projections are recorded by a very fast detector arc made of CZT elements. This detector records the X-ray radiation passing through the object with a sampling rate of 1 MHz. The reconstruction of slice images from the recorded detector data is a limited angle problem since in our scanning geometry the object’s Radon space is only incompletely sampled. We investigated, whether this technology is able to produce accurate gas fraction data from bubbly two-phase flow. Experiments were performed both on a Perspex phantom with known geometry and an experimental flow loop operated under vacuum conditions in an electron beam processing box.
Keywords: flow measurement, two-phase flow, electron beam tomography, X-ray tomography

Publ.-Id: 11774 - Permalink


Uranium sorption onto opalinus clay and uranium complexation with model ligands - New results.
Joseph, C.; Schmeide, K.; Sachs, S.;
An anaerobic opalinus clay sample was characterized (BET, TC, TOC, CEC, XRD, IR). No significant differences between the aerobic and the anaerobic clay could be determined.
The uranium(VI) sorption onto aerobic opalinus clay (S/L = 60 g/l) in opalinus clay pore water in absence and presence of humic acid was investigated and compared with the according uranium(VI)-kaolinite sorption results.
The model ligands mandelic acid and glycolic acid were chosen for the uranium(IV) complexation. The complex formation constants for the uranium(IV) complexation were determined applying UV-Vis absorption spectroscopy. Thereby, the hydrogen ion concentration was varied.
Sulfur-containing humic acid model substances were synthesized and characterized (S-content, PEC, FTIR, XPS). First investigations of the uranium(VI) complexation of humic acid type M1-S1 were performed.
Keywords: anaerobic opalinus clay, characterization, uranium(VI), sorption, humic acid, mandelic acid, glycolic acid, U(IV)-complexation, tetravalent, synthesis
  • Lecture (others)
    5th Workshop of the joint project "Interaction and transport of actinides in natural argillaceous rock considering humic substances and clay organics", 07.-08.10.2008, Speyer, Germany

Publ.-Id: 11773 - Permalink


Mn - implanted, polycrystalline indium tin oxide and indium oxide films
Scarlat, C.; Vinnichenko, M.; Xu, Q.; Bürger, D.; Zhou, S.; Kolitsch, A.; Grenzer, J.; Helm, M.; Schmidt, H.;
Polycrystalline conducting, ca. 250 nm thick indium tin oxide (ITO) and indium oxide (IO) films grown on SiO2/Si substrates using reactive magnetron sputtering, have been implanted with 1 and 5 at% of Mn at 120 keV, 60 keV and 20 keV, followed by annealing in nitrogen for 10 s at 650oC (rapid thermal annealing, RTA) or in vacuum for 2 h at 200oC (vacuum thermal annealing, VTA). The effect of the post-growth treatment on the structural, electrical, magnetic, and optical properties has been studied. The roughness of implanted films ranges between 3 and 15 nm and XRD measurements revealed a polycrystalline structure. A smaller negative magnetoresistance (MR) has been probed on unimplanted ITO and IO films. By magnetotransport measurements at 5 K and 3 T, the positive MR of the IO film implanted with 1 at% Mn, VTA, and an electron concentration of 1.9×1020 cm-3 amounts to 3%. Spectroscopic ellipsometry has been used to prove the existence of midgap electronic states in the Mn implanted ITO and IO films reducing the transmittance below 80%.
Keywords: diluted magnetic semiconductor, ITO, magnetoresistance, optical constants
  • Poster
    IBMM 2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 267(2009)8-9, 1616-1619
    DOI: 10.1016/j.nimb.2009.01.158

Publ.-Id: 11772 - Permalink


AER working group D on VVER safety analysis – report of the 2008 meeting
Kliem, S.;
The AER Working Group D on VVER reactor safety analysis held its 17th meeting in Garching, Germany during the period 31 March-01 April 2008. The meeting was hosted by the GRS Garching. Altogether 19 participants attend the meeting of the working group D, 16 from AER member organizations and 3 guests from non-member organizations. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations. The given presentations and the discussions can be attributed to the following topics:
• Code benchmarking
• Safety analysis methodology and results
• Reactor pressure vessel thermal hydraulics
• Future activities
New solutions for the second and the third AER benchmarks were presented and discussed. The second dynamic AER benchmark considers a control rod ejection at hot zero power with Doppler feedback, only. The third AER benchmark concerns the same transient and includes additionally the modeling of thermal hydraulics in the core. S. Kliem (FZD) presented an overview on available solutions for the second benchmark. Additionally, results were presented by G. Alekhin (EDO Gidropress) obtained with the KAMAZ-code and J. Hádek (NRI Řež) using the DYN3D code. S. Bznumi (Nuclear and Radiation Centre Yerevan) presented results for the third and C. Parisi (UniPisa) for the first dynamic AER benchmarks. Two further benchmarks calculated in the frame of the EU-NURESIM project were presented by J. Hádek. K. Velkov (GRS) showed preliminary results on a new coupled code benchmark based on Kalinin-3 data (VVER-1000). A summary of the results of the OECD VVER-1000 coolant transient benchmark was given by N. Kolev (INRNE Sofia) and S. Kliem presented the results of a PWR boron dilution benchmark.
M. Bykov (EDO Gidropress) gave an overview on the results of coolant mixing experiments performed at a VVER-1000 test facility. A new CFD model of a VVER-440 reactor pressure vessel was presented by B. Kiss (TU Budapest). A. Kotsarev (Kurchatov Institute) presented the outline of a envisaged coolant mixing benchmark.
E. Syrjälahti (VTT Helsinki) gave an overview on the real time 3D core model of the new Loviisa training simulator. RIA analyses for the Generation IV HPLWR using KIKO3D/ATHLET were presented by A. Keresztúri (AEKI Budapest) and I. Panka (also AEKI Budapest) presented different hot channel calculation methodologies.
  • Contribution to proceedings
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary
    Proceedings of the 18th Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest, 9789633726389, 307-314
  • Lecture (Conference)
    18th Symposium of AER on VVER Reactor Physics and Reactor Safety, 06.-10.10.2008, Eger, Hungary

Publ.-Id: 11771 - Permalink


Kernenergieforschung mit schnellen Neutronen
Junghans, A.; Wagner, A.;
Die Kernenergie ist eine Energiequelle, die nur sehr geringe Emissionen von Treibhausengasen verursacht. Auf internationaler Ebene wird die Entwicklung neuer Kernkraftwerkstypen der 4. Generation betrieben, so dass die Kernenergie auch in Zukunft genutzt werden kann. Dabei wird auch das Problem des langlebigen radioaktiven Abfalls betrachtet. An der Neutronenquelle „nELBE" im Forschungszentrum Dresden-Rossendorf soll in Zukunft untersucht werden, wie langlebiger radioaktiver Abfall, der weltweit in Kernkraftwerken entsteht, so umgewandelt werden kann, dass er nur noch für historisch überschaubare Zeiten in ein Endlager eingeschlossen werden muss. Durch Beschuss mit schnellen Neutronen können langlebige schwere Atomkerne wie etwa Curium oder Neptunium umgewandelt werden und in kurzlebige oder sogar stabile Reaktionsprodukte zerfallen. Bei dieser „Transmutation“ werden also langlebige, radioaktive Atomkerne in kurzlebigere umgewandelt. Nach weniger als 1.000 Jahren haben sie dann das natürliche Radioaktivitätsniveau erreicht.
An nELBE können 100 000 mal pro Sekunde kurze Pulse von schnellen Neutronen produziert werden, mit denen die inelastische Streuung, der Neutroneneinfang und Kernspaltung untersucht werden können. Im Vortrag werden die internationalen Entwicklungen auf dem Gebiet der Transmutation
vorgestellt sowie die neue Neutronenquelle „nELBE“ und unsere ersten Experimente dort gezeigt.
  • Lecture (others)
    6. Dresdner Lange Nacht der Wissenschaften, 04.07.2008, Dresden, Deutschland

Publ.-Id: 11770 - Permalink


nELBE - eine Anlage f¨ur die Transmutationsforschung mit schnellen Neutronen
Beyer, R.; Grosse, E.; Junghans, A.; Rouki, C.; Schilling, K.-D.; Schwengner, R.; Wagner, A.;
An der Strahlungsquelle ELBE in Rossendorf wurde eine Flugzeitanlage aufgebaut für Neutronen aus dem von Elektronen induzierten Kern-Photoeffekt in Blei, das in einem Flüssigmetall-Kreislauf auch die bis zu 30 kW Strahlleistung abführt. Durch konsequente Vermeidung wasserstoffhaltiger Materialien und andere Konstruktionsdetails wird ein Neutronenspektrum erzeugt, das nur schnelle Neutronen enthält und das darüber hinaus sehr ähnlich ist dem Spektrum von Neutronen aus der Spaltung von Aktiniden. Ein solches Spektrum ist günstig für die Transmutation von Radionukliden und fast alle der in der internationalen Initiative zur wissenschaftlichen Vorbereitung einer vierten Kernreaktor-Generation untersuchten Konzepte beruhen auf schnellen Neutronen. Für die Reduktion der Radiotoxizität der Abfälle wichtige und oft nur ungenau bekannte Wirkungsquerschnitte zur Transmutation von Spaltfragmenten und von in Reaktoren gebildeten Aktiniden sollen innerhalb der EU-Initiative EFNUDAT bestimmt werden. [Gefördert durch DFG-Gr1674/2 und EU-FP6]
  • Lecture (Conference)
    DPG Frühjahrstagung, 10.-14.03.2008, Darmstadt, Deutschland

Publ.-Id: 11769 - Permalink


Visualization of uranium in living biofilms in relation to biofilm structure and geochemical conditions
Brockmann, S.; Großmann, K.; Krawczyk-Bärsch, E.; Arnold, T.; Wobus, A.;
The speciation of uranium in environmentally relevant concentrations of 1×10-5 mol/l in biofilms was investigated by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach. The microbial communities in the biofilms were determined by analysis of the amplified 16S rRNA gene fragments. No changes of the microbiological diversity were observed in the biofilms in contact with uranium and without. The respiratory activity was microscopically investigated by staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI). It was found that in the presence of uranium (1×10-5 mol/l added as UO2(ClO4)2) the biofilm responded with a higher respiratory activity of the bacteria in the upper layer, leading to changes of geochemical gradients within the biofilms with corresponding effects on the uranium geochemistry. These effects include a change in oxidation state and precipitation of respective uranium phases.
Laser fluorescence spectroscopy was used to identify in-situ and in a non-invasive fashion the speciation of uranium within the biofilms. A fluorescence signal in the wavelength range of 415-475 nm was indicative for metastable uranium- (V) and a fluorescence signal in the range of 480-560 nm was identified as uranium(VI), clearly showing that redox processes take place within the biofilms.
We found that aqueous uranium in environmentally relevant concentrations may trigger higher O2 consumption rates which lead to larger reducing zones within the biofilms. Consequently, such zones may be responsible for an increased immobilization of uranium from the surrounding bulk solution. Our studies indicated that the microbial influence on the migration behavior of uranium in the environment has to be included in performance assessment studies to predict more realistic uranium migration scenarios.
Keywords: Biofilm, uranium, metabolism, staining, CLSM
  • Poster
    Biofilm III, 3rd International Biofilms Conference, 06.-08.10.2008, Garching, Germany

Publ.-Id: 11768 - Permalink


The nELBE time of flight facility
Junghans, A. R.; Altstadt, E.; Beckert, C.; Beyer, R.; Galindo, V.; Grosse, E.; Hannaske, R.; Klug, J.; Legrady, D.; Naumann, B.; Rouki, C.; Schilling, K. D.; Schneider, S.; Schlenk, R.; Schwengner, R.; Wagner, A.; Weiss, F.-P.; Nolte, R.; Röttger, S.;
The nELBE time of flight facility has become operational at the ELBE superconducting linear accelerator at Forschungszentrum Dresden-Rossendorf. The commissioning started with a beamtime in November 2007 and again in February 2008. With a short flight path of approximately 5 m a 100 kHz repetition rate of the electron beam was used to measure neutron time of flight in the energy range of 0.1 – 10 MeV. The electron beam energy was 25, and 33 MeV with 1-5 A of average electron current. The electron beam intensity was kept low to allow in-beam single particle counting.
The beam profile of neutrons and photons was determined with two plastic scintillators mounted on a translation stage. The neutron time of flight spectrum was determined with plastic scintillators with a low detection threshold of ca. 25 keV and with a 235-U fission chamber from PTB, which also allowed to measure the absolute neutron fluence and estimate the background of low energy neutrons. The transmission of the electron beam line was optimized to reduce the bremsstrahlung background not coming from the photo-neutron source. First transmission measurements of total neutron cross sections were made.
Beam time at nELBE is available as of now and all potential users are invited to submit proposals for experiments. TAA funding through EFNUDAT can be provided.
  • Lecture (Conference)
    Workshop on modern methods using fast neutrons for research related to the transmutation of nuclear waste, 13.-15.02.2008, Dresden, Germany

Publ.-Id: 11767 - Permalink


Gamma-ray strength-function measurements at ELBE
Schwengner, R.;
Dipole-strength functions up to the neutron-separation energies S_n of the N=50 isotones 88Sr, 89Y, 90Zr and the even-mass Mo isotopes from 92Mo to 100Mo have been studied in photon-scattering experiments using the bremsstrahlung facility at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf. To estimate the distribution of inelastic transitions from high-lying levels at high level density to low-lying levels, simulations of gamma-ray cascades were performed. On the basis of these simulations intensities of inelastic transitions were subtracted from the experimental intensity distributions, including the resolved peaks as well as a continuous part formed by unresolved transitions, and the intensities of elastic transitions to the ground state were corrected for their branching ratios. The combination of our gamma,gamma data with (gamma,n) data gives novel information about the dipole-strength functions in the whole energy range from about 4 MeV up to the giant dipole resonance (GDR). They show that
(i) there is extra strength in the energy range from about 6 to about 12 MeV with respect to simple Lorentzian-like approximations of the tail of the GDR,
(ii) the accumulated dipole-strength in the energy range from about 6 to 12 MeV grows with increasung neutron number in the chain of Mo isotopes.
Calculations in the framework of a quasiparticle-random-phase approximation (QRPA) in a deformed Woods-Saxon basis describe the increase of strength towards the heavier Mo isotopes as a consequence of growing nuclear deformation.
Keywords: Nuclear structure, photon scattering, gamma-ray strength-functions, random-phase-approximation.
  • Invited lecture (Conferences)
    Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, 08.-11.07.2008, Athens, Ohio, USA

Publ.-Id: 11766 - Permalink


nELBE: A new facility to produce high brilliance pulses of fast neutrons for transmutation research by time of flight.
Junghans, A.; Klug, J.; Wagner, A.; Weiss, F. P.; Grosse, E.;
The Radiation Source ELBE at Forschungszentrum Dresden-Rossendorf (FZD), with electron energies up to 40 MeV, will be used to produce intense pulses of fast neutrons. The neutron radiator consists of a liquid lead circuit where bremsstrahlung photons generated from the electron beam at ELBE produce neutrons in (γ,n) reactions. Monte Carlo simulations with MCNP4C3/MCNP5 were performed to characterise neutron and photon intensities as well as time and energy distributions, and to optimise the neutron beam. The short beam pulses provide the basis for an excellent time resolution for neutron time-of-flight experiments, giving an energy resolution of about < 2 % with a flight path of ~ 5 m.
  • Lecture (Conference)
    NEMEA-4 - Neutron Measurements, Evaluations and Applications, 16.-18.10.2007, Prag, Czech Republic

Publ.-Id: 11765 - Permalink


Die experimentellen Versuchsanlagen des Instituts für Sicherheitsforschung
Lucas, D.;
Im Vortrag werden verschiedene Versuchsanlagen des Instituts für Sicherheitsforschung zur Untersuchung von Strömungen vorgestellt. Ziel der Versuche ist die Bereitstellung von Daten in hoher Orts- und Zeitauflösung, die für die Entwicklung und Validierung von CFD-Modellen geeignet sind. Daher werden in allen vorgestellten Versuchseinrichtungen innovative Messtechniken eingesetzt. Die ROCOM-Anlage dient der Untersuchung einphasiger Vermischungsvorgänge im Primärkreislauf von Kernreaktoren. Am horizontalen Strömungskanal werden geschichtete Luft-Wasser-Strömungen untersucht. Die TOPFLOW (Transient TwO Phase FLOW) dient der Untersuchung von Dampf-Wasser-Strömungen bei Dücken bis 7 MPa. Mit eine 4 MW Dampferzeuger können bei diesem Druck bis zu 1,5 kg Dampf pro Sekunde erzeugt werden. Die Experimente an vertikalen Teststrecken und im TOPFLOW-Drucktank werden diskutiert.
Keywords: mixing, two phase flow, bubbles, stratified flow, CFD, experimental facilities
  • Lecture (Conference)
    3. Workshop "Strömungssimulation" der Technischen Universität Dresden und des Forschungszentrums Dresden-Rossendorf, 25.09.2008, Dresden, Deutschland

Publ.-Id: 11764 - Permalink


Experiment and simulation of the compositional evolution of Ti-B thin films deposited by sputtering of a compound target
Neidhardt, J.; Mrátz, S.; Schneider, J. M.; Strub, E.; Bohne, W.; Liedke, B.; Möller, W.; Mitterer, C.;
The evolution of the coating stoichiometry with pressure, target-substrate distance, and angle was analyzed for dc sputtering of TixB (x=0.5, 1, 1.6) compound targets by elastic recoil detection analysis. For an investigation of the underlying fundamental processes primarily Ar was used as sputter gas. Additionally, the effect of a reactive gas (N2) as well as bias voltage (floating up to −200 V) was briefly cross-checked. For deposition along the target normal (90°) a pronounced Ti-deficiency of up to 20% is detected. Increasing the pressure or distance from 0.5 to 2 Pa and from 5 to 20 cm, respectively, leads to an almost equivalent linear increase in Ti/B ratio surpassing even the target composition. Off-axis depositions at lower angles (30° and 60°) on the other hand result in a higher Ti/B ratio. This is consistent with results obtained from Monte Carlo simulations combining the respective emission characteristics from the sputter process as well as the gas-phase transport. Hence, the pressure, distance, and sample position induced changes in chemical film composition can be understood by considering gas scattering and the angular distribution of the sputtered flux. The theoretically determined transition from a directional flux to thermal diffusion
was experimentally verified by mass-energy analysis of the film-forming atoms.
  • Journal of Applied Physics 104(2008), 063304

Publ.-Id: 11763 - Permalink


P0707 - Anordnung zur zweidimensionalen Messung des Geschwindigkeitsfeldes in Strömungen
Hampel, U.;
Aufgabe der vorliegenden Erfindung ist es, eine Anordnung zur Messung der Geschwindigkeitsverteilung in einem Messquerschnitt anzugeben, mit der vor allem Flüssigkeits- oder Gasströmungen untersucht werden können und die über ein möglichst effizientes elektronisches Anregungs- und Messschema verfügt. Der Kern der Erfindung ist die Verwendung und Modifizierung eines Gittersensors, bei dem
- die Anregungselektroden (2) und die Empfängerelektroden (3) in jedem Kreuzungspunkt des Gitters durch einen Festkörper mit temperaturabhängem ohmschen Widerstand, dem Hitzeelement (4), elektrisch miteinander verbunden sind,
- die zugeordnete Messelektronik, zusätzlich zu der den Anregungselektroden (2) vorgeschalteten Heizspannungsquelle (5), über eine den Anregungselektroden (2) vorgeschaltete Messspannungsquelle (6) verfügt und
- jede Anregungselektrode (2) mit einem dreipoligen Analogschalter (7) verbunden ist, der die Elektrode wahlweise mit der Heizspannungsquelle (5), der Messspannungsquelle (6) oder Massepotenzial verbindet, sowie jede Empfängerelektrode (3) mit einem Analogschalter (7) verbunden ist, der die Empfängerelektrode (3) wahlweise mit einem festen Bezugspotenzial (zum Beispiel Masse-Potenzial) oder einem Strom-Spannungs-Wandler (8) verbindet.
(Fig 1)
  • Patent
    DE 10 2007 019 927 B3 - 2008.09.25

Downloads:

Publ.-Id: 11762 - Permalink


Electrical properties and structure of transparent conductive oxide films deposited by pulsed reactive magnetron sputtering
Vinnichenko, M.; Rogozin, A.; Cornelius, S.; Shevchenko, N.; Munnik, F.; Gago, R.; Mücklich, A.; Kolitsch, A.; Möller, W.;
Sn-doping of InOx and Al-doping of ZnO is extensively used to create transparent thin film electrodes. However, the mechanisms of donor impurity incorporation and its electrical activation, especially in relation to the film structure and phase composition, are not properly understood. In order to have a deeper insight into these processes, InOx, InOx:Sn, ZnO and ZnO:Al films were grown by reactive pulsed magnetron sputtering from In, In:Sn, Zn and Zn:Al targets, respectively, at substrate temperatures ranging from 40 °C to 580 °C, and characterized by spectroscopic ellipsometry, Hall effect measurements, X-ray diffraction (XRD) and, in case of ZnO and ZnO:Al films, by X-ray absorption near edge spectroscopy (XANES). For InOx:Sn, the film crystallinity always improves with increasing substrate temperature or during isothermal annealing, with the electrical resistivity decreasing. This is explained by Sn donor activation during the film amorphous-to-crystalline transition. In contrast, the electrical resistivity of ZnO:Al films shows a clear minimum at a certain substrate temperature, which correlates with a maximum in crystallinity (grain size). Here, the lower resistivity is due to an increased density and free electron mobility. Increasing the Zn/O2 flux ratio decreases this optimum temperature from 350 °C to 250 °C. At higher temperature, the film electrical properties and crystalline quality decrease due to the formation of a new metastable phase, which is identified as homologous (ZnO)3(Al2O3) by XANES and XRD for low and high Zn/O2 ratio, respectively. The optimization of the oxygen partial pressure, the substrate temperature and the Al concentration allows to minimize the ZnO:Al resistivity down to 2.3-2.5x10^-4 Ohm cm at a significantly improved free electron mobility.
Keywords: transparent conductive oxides, tin-doped indium oxide, aluminum doped zinc oxide
  • Invited lecture (Conferences)
    The Eleventh International Conference on Plasma Surface Engineering, 15.-19.09.2008, Garmisch-Partenkirchen, Germany

Publ.-Id: 11761 - Permalink


Uranium in Biofilms
Arnold, T.;
Biofilms show a complex architecture of heterogeneously distributed sessile bacteria embedded in extracellular polymeric substances (EPS), made of polysaccharides, proteins, lipoproteins and glycoproteins, which are interspersed by open water channels. Biofilms are made of 50-95% water and dissolved substances and are thus considered as hydrogels. Through these water channels nutrients and possibly toxic heavy metals from the surrounding bulk solution effectively infuse into the biofilms to the microorganisms and metabolites and exudates of the microorganisms are transported away.
The attachment of microbial cells to surfaces during biofilm formation leads to major changes in metabolism, resistance, and survivability and therefore the retention of radionuclides by biofilms is probably different from the interactions with single cell suspensions of only one type of bacterial species.
In this study particulate uranium in a multi-spezies biofilm grown at the solid/liquid interface was visualized within the biofilm and spectroscopically identified by a combination of confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy as uranium(VI) and metastable uranium(V). The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium-(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilm. The detection of uranium(V) in a multispecies biofilm was interpreted as a short-lived intermediate of the uranium(VI) to uranium-(IV) redox reaction. Its presence clearly documents that the uranium(VI) reduction is not a two electron step but that only one electron is involved.
Keywords: uranium, biofilms
  • Invited lecture (Conferences)
    7th symposium on remediation in Jena Metal stress: biotic and abiotic factors, 22.-23.09.2008, Jena, Deutschland

Publ.-Id: 11760 - Permalink


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