Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Simulation study on multilayer limited angle scanned electron beam X-ray CT arrangements for two-phase flow measurements

Bieberle, M.; Hampel, U.; Prasser, H.-M.; Schleicher, E.

Recently, we presented a limited angle computed tomography approach that utilises a scanned electron beam X-ray source to produce multiple projections of an object. From these projections cross sectional images of the object are reconstructed by using iterative reconstruction algorithms. Tests with static as well as dynamic objects proved that the scan rate of the electron beam allows tomographic imaging with 1000 frames per second at an in-plane resolution of 1 mm. In a simulation study on three-dimensional flow data sets obtained with a fast and high-resolution conductivity wire-mesh sensor under real two-phase flow conditions we have shown, that this approach is capable to recover the in-plane phase structure of the flow. However, two problems arise when this measuring method is utilized for quantitative analysis of two-phase flows. Firstly, by acquiring a time sequence of cross sectional images of one plane in the flow no information about the volumetric structure of the flow can be obtained without knowing the different phase velocities. Secondly, the static arrangement of the X-ray focal spot path and the detector arc in one plane allows only a limited angular range from which projections are available. The missing data leads to artefacts in the reconstructed images which increase with the size and complexity of the imaged structures. For these reasons, simulation studies on different extended measurement arrangements with a two-dimensional beam deflection unit including multilayer imaging have been performed. The presentation will be focused on these different arrangements and their influence on the phase structure recovery of two-phase flows.

Keywords: limited angle X-ray CT; two-phase flow measurements

  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography (WCIPT5), 03.-06.09.2007, Bergen, Norway
    Proceedings of the 5th World Congress on Industrial Process Tomography, 259-264
  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography (WCIPT5), 03.09.2007, Bergen, Norway

Publ.-Id: 8986

Interactions of microbes found at Äspö underground lab with actinides such as curium, plutonium and uranium

Moll, H.

Sulfate-reducing bacteria (SRB) frequently occur in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden. The new SRB strain Desulfovibrio äspöensis could be isolated. Results describing the basic interaction mechanisms of uranium, curium, and plutonium with cells of D. äspöensis DSM 10631T will be presented. The interaction experiments with the actinides showed that the cells are able to remove all three actinides from the surrounding solution. The amount of removed actinide and the interaction mechanism varied among the different actinides.
The main U(VI) removal occurred after the first 24 h. The contact time, pH and [U(VI)]initial influence the U removal efficiency. The presence of uranium caused a damaging of the cell membranes. TEM revealed an accumulation of U inside the bacterial cell. D. äspöensis are able to form U(IV). A complex interaction mechanism takes place consisting of biosorption, bioreduction and bioaccumulation.
In the case of 242Pu, solvent extractions, UV-vis- and XANES spectroscopy were used to determine the speciation of the Pu oxidation states. In the first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. Solvent extractions showed that 97 % of the initially present Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 24 h of contact time. Most of the formed Pu(V) dissolves from the cell envelope back to the aqueous solution due to the weak complexing properties of this plutonium oxidation state. Indications were found for a penetration of Pu species inside the bacterial cells.
In the case of curium at a much lower metal concentration of 3x10-7 M, a pure biosorption of Cm(III) on the cell envelope forming an inner-sphere surface complex most likely with organic phosphate groups was detected.
To summarize, the strength of the interaction of D. äspöensis with the selected actinides at pH 5 and actinide concentrations ≥ 10 mg/L ([Cm] 0.07 mg/L) follows the pattern: Cm > U > Pu.

Keywords: microbial interactions; Desulfovibrio äspöensis; actinides

  • Lecture (Conference)
    2nd Annual Workshop of the IP FUNMIG, 21.-23.11.2006, Stockholm, Sweden
  • Contribution to proceedings
    2nd Annual Workshop of the IP FUNMIG, 21.-23.11.2006, Stockholm, Schweden
    Interactions of microbes found at Äspö underground lab with actinides such as Curium, Plutonium and Uranium, Bromma: CM Digitaltryck AB,, 1404-0344, 131-137

Publ.-Id: 8985

A novel approach for 99mTc labelling of peptides organometallic Tc(III) complexes for conjugation of bombesin derivatives

Künstler, J.-U.; Veerendra, B.; Sieckman, G. L.; Smith, C. J.; Pietzsch, H.-J.

Among peptides for tumour targeting bombesin (BBS), binding to gastrin releasing peptide receptors (GRPR) and overexpressed by e.g. prostate and breast carcinomas has a great potential. Thus, various labelled bombesins were described in the literature showing a varying pharmacokinetic behaviour depending on the labelling approach, the spacer between the radiometal moiety and the N-terminus as well as modifications in the peptide sequence.
In this study, the bioactive minimal sequence BBS(7-14) was labelled by the Tc-“4+1” mixed-ligand system, where Tc(III) is coordinated by a monodentate isocyanide bearing the peptide and the tetradentate tripodal chelator tris(2-mercaptoethyl)-amine (NS3).
BBS(7-14) was N-terminally modified with Gly-Gly-Gly, β-Ala and Ser-Ser-Ser as spacer groups and functionalized with 4-isocyanomethyl benzoic acid or 4-isocyanobutyric acid. 99mTc labelling was performed in a two-step ligand exchange procedure starting from 99mTc-EDTA/mannitol. The Re analogues were used as references for chemical characterization and in receptor-binding studies. Complex bearing β-Ala-BBN(7-14) exhibited a GRPR-affinity in the subnanomolar range and high uptake in human prostate (PC-3) cancer cells, whereas pancreatic uptake in biodistribution studies using normal mice was low.

Keywords: Technetium; '4+1' Mixed-ligand Complexes; Organometallic; Bombesin; Peptide Labelling

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGE Editoriali, 2006, 88-89884-04-5, 317-318

Publ.-Id: 8984

99mTc-labelled RGD-Peptide using the "4+1" mixed-ligand approach

Giglio, J.; León, E.; Rey, A.; Künstler, J.-U.; Gniazdowska, E.; Pietzsch, H.-J.

This paper presents the 99mTc-labelling and evaluation of two isocyanide (4-isocyanomethylbenzoic acid = L1, 4-isocyanobutanoic acid= L2) derivatives of the peptide c(RGDyK) using the "4+1" mixed-ligand chelate system. Starting from the precursor 99mTc-EDTA labelling was achieved by reaction of the isocyanide-bearing peptide and the tetradentate ligand containing three non-coordinating carboxyl groups (NS3(COOH)3) resulting in 99mTc(NS3(COOH)3)(L1-c(RGDyK)), 1 and 99mTc(NS3(COOH)3)(L2-c(RGDyK)), 2. A radiochemical purity (RP) of 60% was obtained for both peptides and HPLC purification resulted in RP>95% and stability was >90% after 24h. Plasma protein binding was 27% for 1 and 15% for 2. Both complexes showed preferential renal excretion. Uptake in induced B16F1 murine melanoma was moderate for both compounds but higher tumour/muscle ratios were achieved for 1 at all time points.

Keywords: Tc "4+1" mixed-ligand complexes; 99mTc labelled peptides; RGD peptides

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGE Editoriali, 2006, 88-89884-04-5, 331-332

Publ.-Id: 8983

86Y-labelled L RNA oligonucleotides as Molecular Probes for Positron Emission Tomography (PET)

Schlesinger, J.; Bergmann, R.; Klußmann, S.; Wüst, F.; Pietzsch, H.-J.

A short 5’-aminohexyl-functionalised L RNA oligonucleotide 1 (sequence: UGA CUG ACU GAC 3’, MW 3975) was used to study the influence of two different 86Y DOTA chelates on the biodistribution in Wistar rats. The L-oligonucleotide 1 was conjugated with 1,4,7,10 tetraazacyclododecane-N,N’,N’’,N’’’-tetraacetic acid (DOTA) using N-succinimide ester (DOTA-NHS) 2 and isothiocyanate derivative (p SCN bz DOTA) 4 to afford the corresponding amide 3 and thiourea 5, respectively. Both DOTA-functionalised L RNA oligonucleotides 3 and 5 were labelled with the medium half-life positron-emitting radiometal 86Y (t1/2 = 14.7 h) in 76 % and 85 % radiochemical yield. 86Y-Complexes 3a and 5a represent the first examples of L-oligonucleotides labelled with the positron emitter 86Y.
The in vivo biodistribution of 86Y-complex 3a showed a faster elimination from the body via the kidneys compared to thiourea-containing 86Y-complex 5a. Transient accumulation of radioactivity in the kidneys and the adrenals was found for both 86Y-complexes 3a and 5a. After incubation of 86Y-complex 5a in whole rat blood at 37°C no noticeable decomposition could be observed over 12 h as confirmed by HPLC-analysis

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U.Mazzi: Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGEditoriali, 2006, 88-89884-04-5, 211-214

Publ.-Id: 8982

Positron Emission Tomography

van den Hoff, J.

kein Abstract verfügbar

  • Contribution to external collection
    D. Ganten and K. Ruckpaul: Encyclopedic Reference of Genomics and Proteomics in Molecular Medicine, ed., Heidelberg, New York: Springer Verlag, 2006, 3-540-44244-8, 1446-1449

Publ.-Id: 8981

Reversals made simple: some new results

Stefani, F.; Gerbeth, G.; Günther, U.; Xu, M.; Sorriso-Valvo, L.

We present new results of a very simple model of Earth's magnetic field reversals which is based on an alpha^2 dynamo under the influence of noise. This reversal model relies on the existence of exceptional points of the spectrum of the non-selfadjoint dynamo operator. As new aspects of this model, we delineate its connection with the van der Pol oscillator, we demonstrate a remarkable agreement with the characteristic time scales and the well-known asymmetry of real reversals, and we discuss the deviation from Poissonian statistics in real reversal sequences and in our model. Finally, we present some speculations on the influence of the size of the inner core on the spectral properties of the dynamo operator and on the reversal rate.

  • Lecture (Conference)
    9th MHD Days 2006, 04.-05.12.2006, Heidelberg, Germany

Publ.-Id: 8980

Observation of magnetorotational instability in a liquid metal Taylor-Couette experiment

Gundrum, T.; Gerbeth, G.; Stefani, F.; Rüdiger, G.; Hollerbach, R.

Magnetic fields can play an active role in the formation of stars and black holes by virtue of the Magnetorotational Instability (MRI) which enables outward transport of angular momentum in accretion discs. Using a combination of axial and azimuthal magnetic fields, we provide experimental evidence of the MRI in a liquid metal Taylor-Couette experiment with Reynolds numbers of the order 1000 and Hartmann nubers of the order 10. The MRI mode in the liquid metal alloy GaInSn is measured by Ultrasonic Doppler Velocimetry.

  • Lecture (Conference)
    9th MHD Days 2006, 04.-05.12.2006, Heidelberg, Germany

Publ.-Id: 8979

Proton single voxel spectroscopy of different adipose tissue deposits in mice

Strobel, K.; van den Hoff, J.; Pietzsch, J.

Accumulation of excess abdominal visceral fat has been shown to play crucial roles in the development of cardiovascular disease as well as the development of obesity-related disorders like Diabetes mellitus, hyperlipidemia, and hypertension.
In the last years, rodent models have gained an important role in the investigation of adipose tissue (AT) biology and disorder. In this line, non-invasive differentiation and characterization of various AT deposits in the living animal is a current challenge. Magnetic resonance spectroscopy (MRS) at high magnetic field strength can help us to learn more about lipids in vivo. MRS is applied for brown adipose tissue (BAT), as well as intra-abdominal white adipose tissue (WAT) deposits in mice.
All experiments were carried out in NMRI mice and nude mice. Morphological differentiation between various BAT and WAT deposits was obtained by 1H-MRI at 7 Tesla using a Biospec 70/30 (Bruker, Germany). 1H-MRS has been performed to quantify in vivo the different lipid patterns in BAT and WAT deposits using a volume selective PRESS sequence on 1 to 8 mm3 voxels.
In both nude mice and NMRI mice the various BAT and WAT deposits were clearly distinguished from the non-AT tissue with excellent contrast by T1-weighted MSME MRI sequences. The high resolution spectra obtained at 7 T allow identification of at least 9 different proton resonances specific for lipids, and, thus, for calculation of mono- to polyunsaturated fatty acid ratio in vivo. In this study, nude mice showed a 3-fold higher degree of polyunsaturation of triglyceride fatty acid acyl chains in BAT when compared to NMRI mice. No significant differences were observed in WAT deposits.
High-resolution MRS is a potentially useful tool for studying the biology of different BAT and WAT deposits non-invasively in small experimental animals in vivo.

  • Lecture (others)
    User Meeting 2006 der Fa. Bruker Biospin MRI GmbH, 09.-12.10.2006, Ettlingen, Germany

Publ.-Id: 8978

Impact of tumour hypoxia on the FDG uptake in two human tumour models on nude mice investigated with PET, autoradiography and functional histology

Beuthien-Baumann, B.; Gabrys, D.; Wüllrich, K.; Hofheinz, F.; Krause, M.; Bergmann, R.; Hessel, F.; Yaromina, A.; Eicheler, W.; Baumann, M.

kein Abstract verfügbar

  • Abstract in refereed journal
    Radiotherapy and Oncology Suppl. 1(2006), S142
  • Lecture (Conference)
    ESTRO-Conference, 09.-12.10.2006, Leipzig, Germany

Publ.-Id: 8977

PET-based investigation of cerebral activation following intransal trigeminal stimulation

Hummel, T.; Beuthien-Baumann, B.; Heinke, M.; Oehme, L.; van den Hoff, J.; Gerber, J. C.

kein Abstract verfügbar

  • Abstract in refereed journal
    Chemical Senses 31(2006), A60-A61
  • Lecture (Conference)
    AChems 28th Annual Meeting, 26.-30.04.2006, Sarasota/Florida, USA

Publ.-Id: 8976

Labeling of low-density lipoproteins using the 18F-labeled thiol-reactive reagent N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]maleimide [18F]FBAM

Berndt, M.; Pietzsch, J.; Wüst, F.

The novel thiol group-selective bifunctional 18F-labeling agent N-[6-(4-[18F]fluoro-benzylidene)aminooxyhexyl]maleimide ([18F]FBAM) has been developed. The bifunctional labeling precursor 4 containing a thiol-reactive maleimide group and a carbonyl group-reactive aminooxy group was prepared in only three steps in a total chemical yield of 59%.
Subsequent radiolabeling with 4-[18F]fluorobenzaldehyde gave the bifunctional 18F-labeling agent [18F]FBAM in 29% radiochemical yield. In a typical experiment 3.88 GBq of [18F]fluoride could be converted into 723 MBq of [18F]FBAM within 69 min. Conjugation of [18F]FBAM with thiol groups was exemplified with the cystein-containing tripeptide glutathione and with various apolipoproteins of human low density lipoproteins (LDL) subfractions. The latter one was evaluated with respect to uptake of [18F]FBAM-LDL subfractions in human hepatoma cells (HepG2) in vitro. In vivo biodistribution studies in rats revealed high stability for the [18F]FBAM-LDL subfractions. Moreover, the metabolic fate of the [18F]FBAM-LDL subfractions in vivo was delineated by dynamic PET studies using a dedicated small animal tomograph. Data were compared to former studies using the NH2-reactive 18F-labeling agent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). Compound [18F]FBAM can be considered to be an excellent prosthetic group for the selective and mild 18F-labeling of thiol group-containing biomolecules suitable for subsequent investigations in vitro and in vivo.

Publ.-Id: 8975

Advances in the Production, Processing and MicroPET Image Quality of Technetium-94m

Bigott, H. M.; Laforest, R.; Liu, X.; Ruangma, A.; Wüst, F.; Welch, M.

This work involves the production, processing and imaging of the short-lived, rarely used positron emission tomography (PET) radionuclide technetium-94m (94mTc). Our procedures are an extension of methods reported in the literature and are detailed within. A key modification was the development of a single step that combines purification and concentration of an aqueous 94mTc-pertechnetate solution, which both reduces processing time and increases the final concentration of the solution. Additionally, a convenient method for the direct recovery of 94mTc into an organic solvent was developed, eliminating the solvent transfer step needed for organic syntheses using 94mTc.
Each of these advances potentially extends the scope of syntheses possible with this short-lived radionuclide. To explore the imaging potential of 94mTc, we carried out phantom imaging studies on small-scale high-resolution PET scanners to estimate the limitations of detection associated with 94mTc and PET. Preliminary studies demonstrate that useful images can be obtained with modern image reconstruction algorithms when using a correction for the cascade gamma ray contamination.

  • Nuclear Medicine and Biology 33(2006)7, 923-933

Publ.-Id: 8974

Excitation dynamics in La0.875Sr0.125MnO3 measured by resonant Auger electron and resonant x-ray emission spectroscopies

Mentes, T. O.; Bondino, F.; Magnano, E.; Zangrando, M.; Kuepper, K.; Galakhov, V. R.; Mukovskii, Y. M.; Neumann, M.; Parmigiani, F.

The charge transfer dynamics of an underdoped manganite is probed by resonant x-ray emission and Auger electron spectroscopies at the Mn L3 edge. The dispersion of peak positions, as the incident photon energy is tuned through the absorption threshold, gives direct information on the relaxation rate in terms of the core-hole lifetime and the localization behavior of the states involved. The charge transfer time is found to be around 0.45 fs, with a dependency on the final state d-band occupancy.

Keywords: PACS: 79.60.-i; 72.15.Lh; 71.70.Ch; 78.70.En

Publ.-Id: 8973

CFD-Analysen der Kühlmittelvermischung in Druckwasserreaktoren

Höhne, T.

Buoyancy driven mixing was investigated under simulated natural circulation conditions at the test facility ROCOM.
Experiments with density differences between the ECC water (higher density) resp. the de-borated slugs (lower density) and the ambient coolant was used to validate the CFD software CFX.
A Reynolds stress turbulence model was employed to model the effects of turbulence on the mean flow.
Hybrid meshes consisting at least of 2 million nodes and 4 million elements were used.
The experiment and CFD calculations show in both cases significant mixing effects due to the density differences.
The CFX-5 calculations show a good qualitative agreement with the data. At some local positions differences in the predicted and measured concentration fields occur. The obtained experimental and numerical results can be used for further studies of the core behavior using coupled thermo-hydraulic and neutron-kinetic code systems.
Next Steps: Improvement of turbulence models, calculation with different Reynolds Stress models or DES

Keywords: CFD; Coolant Mixing

  • Lecture (others)
    DECHEMA/GVC-Arbeitsausschuß “Sicherheitsgerechtes Auslegen von Chemieapparaten“, 22.11.2006, Lampertheim, Deutschland

Publ.-Id: 8972

Strahlentherapieplanung bei Hirntumoren mit 18F-3-O-methyl-fluordopa (18F-OMFD) und Positronen-Emissions-Tomographie (PET)

Ahlheit, H.; Oehme, L.; Winkler, C.; Blank, H.; Grabowski, J.; Füchtner, F.; Hoepping, A.; Kotzerke, J.; Beuthien-Baumann, B.

kein Abstract verfügbar

  • Abstract in refereed journal
    Strahlentherapie und Onkologie 182(2006)1, V11-3
  • Lecture (Conference)
    12. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 25.-28.05.2006, Dresden, Germany

Publ.-Id: 8971

Structure and Stability of Molybdenum Sulfide Fullerenes

Bar-Sadan, M.; Enyashin, A. N.; Gemming, S.; Popovits-Biro, R.; Hong, S. Y.; Prior, Y.; Tenne, R.; Seifert, G.

MoS2 nanooctahedra are the smallest stable close-cage structures of MoS2, i.e. the genuine inorganic fullerenes. Here, a combination of experiments and density-functional tight-binding calculations with molecular dynamics annealing are used to elucidate the structures and electronic properties of octahedral MoS2 fullerenes. The calculations show that the octahedra are stable beyond n(Mo)>100, but with the loss of 12 S atoms at the six corners. In contrast to the semi-conducting bulk and nanotubular structures, the Fermi level of the octahedra is situated within a band, hence the nano-octahedra are metalloid. A model derived from these calculations for the treatment of larger structures shows that, in agreement with experiment, multiwall nanooctahedra are stable over a limited size range of about 10^4 to 10^5 atoms; beyond that size, the clusters are converted into spherical nanoparticles. These theoretical findings concerning the critical size for the structural transition, the under-stoichiometry in S, and the electronic nature of the nanooctahedra are confirmed by TEM experiments on particles synthesized by laser ablation.

Keywords: inorganic fullerenes; molybdenum sulfide; density-functional

Publ.-Id: 8969

Quasi-Particle Perspective on Equation of State

Bluhm, M.; Schulze, R.; Seipt, D.; Kämpfer, B.

We propose a procedure for determining the equation of state of strongly interacting matter needed in a
hydrodynamical description of relativistic heavy-ion collisions.

Keywords: QCD equation of state; elliptic flow; quasi-particle model

  • Contribution to proceedings
    Quark Confinement and Hadron Spectrum VII, 02.-07.09.2006, Ponta Delgada Acores, Portugal, 387-390
  • AIP Conference Proceedings 892(2007), 387-390

Publ.-Id: 8968

Quasi-particle perspective on critical end-point

Bluhm, M.; Kämpfer, B.

Within a quasi-particle model for the equation of state of strongly interacting matter for two quark flavors we include phenomenologically features of the QCD critical point and discuss its impact on the equation of state. In particular, we investigate the influence on the quark number susceptibility and the pattern of isentropic trajectories which describe the evolutionary paths of matter during the hydrodynamical expansion of a heavy-ion collision.

  • Contribution to proceedings
    Critical Point and Onset of Deconfinement, 03.-06.07.2006, Florence, Italy
    Proceedings of Science CPOD 2006, 004

Publ.-Id: 8967

Orbitofrontal Dysfunction Related to Both Apathy and Disinhibition in Frontotemporal Dementia

Peters, F.; Perani, D.; Herholz, K.; Holthoff, V.; Beuthien-Baumann, B.; Sorbi, S.; Pupi, A.; Degueldre, C.; Lemaire, C.; Collette, F.; Salmon, E.

Orbitofrontal metabolic impairment is characteristic of the frontal variant of frontotemporal dementia (fv-FTD), as are early changes in emotional and social conduct. Two main types of behavioral disturbances have been distinguished in fv-FTD patients: apathetic and disinhibited manifestations. In this study, we searched for relationships between brain metabolism and presence of apathetic or disinhibited behavior. Metabolic activity and behavioral data were collected in 41 fv-FTD patients from European PET centers. A conjunction analysis of the PET data showed an expected impairment of metabolic activity in the anterior cingulate, ventromedial and orbital prefrontal cortex, the dorsolateral prefrontal cortex and the left anterior insula in fv-FTD subjects compared to matched controls. A correlation was observed between disinhibition scores on the Neuropsychiatric Inventory scale and a cluster of voxels located in the posterior orbitofrontal cortex (6, 28, -24). Comparison of brain activity between apathetic and nonapathetic fv-FTD patients from two centers also revealed a specific involvement of the posterior orbitofrontal cortex in apathetic subjects (4, 22, -22). The results confirm that the main cerebral metabolic impairment in fv-FTD patients affects areas specializing in emotional evaluation and demonstrate that decreased orbitofrontal activity is related to both disinhibited and apathetic syndromes in fv-FTD.

Keywords: Frontotemporal dementia; Positron emission tomography; Apathy; Disinhibition; Social conduct

  • Dementia and Geriatric Cognitive Disorders 21(2006), 373-379
    DOI: 10.1159/000091898

Publ.-Id: 8966

11C-Acetat positron-emission-tomography for occult prostate cancer

Froehner, M.; Beuthien-Baumann, B.; Wirth, M. P.

We report, to our knowledge previously not described, a case of occult prostate cancer, in which 11C-acetate positron emission tomography disclosed tumor manifestation after failure of conventional diagnostic procedures.

Keywords: Prostate cancer; Occult; Positron emission tomography; Bone scan; Metastases

  • Urologic Oncology 24(2006), 410-411

Publ.-Id: 8965

Decomposition of metabolic brain clusters in the frontal variant of frontotemporal dementia

Salmon, E.; Kerrouche, N.; Herholz, K.; Perani, D.; Holthoff, V.; Beuthien-Baumann, B.; Degueldre, C.; Lemaire, C.; Luxen, A.; Baron, J.-C.; Collette, F.; Garraux, G.

Previous studies that measured brain activity in frontotemporal dementia (FTD) used univariate analyses, examining each region of interest separately. We explored in a multicenter European research program the principal brain clusters characterized by a common variability in cerebral metabolism in FTD. Seventy patients with frontal variant (fv) FTD were selected according to international clinical recommendations; principal component analysis (PCA) was performed on FDG-PET metabolic images, looking for covariance clusters in this large population. A first metabolic cluster included most of the lateral and medial prefrontal cortex, bilaterally; PC1 scores correlated with performances on memory and executive neuropsychological tasks. Moreover, FDG-PET images in fv-FTD were further characterized by a metabolic covariance in two clusters comprising the subcallosal medial frontal region, the temporal pole, medial temporal structures and the striatum, separately in the left and in the right hemisphere. The study provides original data-driven arguments for metabolic involvement of separate brain clusters in the rostral limbic system, corresponding to pathological poles differentially affected in each FTD patient.

Publ.-Id: 8964

Experimental and numerical results on the fluid flow driven by a traveling magnetic field

Lantzsch, R.; Galindo, V.; Grants, I.; Zhang, C.; Pätzold, O.; Gerbeth, G.; Stelter, M.

A traveling magnetic field (TMF) driven convection and its transition from a laminar to a time-dependent flow is studied by means of ultrasonic Doppler velocimetry and numerical simulations. The experimental setup comprises a cylindrical cavity containing the electrically conducting model fluid GaInSn and a system of six equidistant coils, which are fed by an out-of-phase current to create an up- or downward directed TMF. Hence, a Lorentz force is induced in the melt which leads to meridional flow patterns. For numerical simulations commercial codes (Opera/Fidap) and a spectral code are used. The characteristic parameters of the magnetohydrodynamic model system are chosen close to the conditions used for Vertical Gradient Freeze (VGF) crystal growth. The axisymmetric basic flow and its dependence on the dimensionless shielding parameter S are examined. It is shown that, for S>10, the flow velocity decreases significantly, whereas almost no influence is found for a smaller shielding parameter. The critical Reynolds number for the onset of instability is found in the range of 300-450. Good agreement between experimental results and the numerical simulations is achieved.

Keywords: Fluid Flows; Magnetic Fields; Stirring; Growth from melt

Publ.-Id: 8963

Effect of pseudophosphorylation and cross-linking by lipid peroxidation and advanced glycation end product precursors on tau aggregation and filament formation

Kuhla, B.; Haase, C.; Flach, K.; Lüth, H.-J.; Arendt, T.; Münch, G.

Accumulation of hyperphosphorylated tau protein as paired helical filaments (PHFs) in pyramidal neurons is a major hallmark of Alzheimer’s disease. Besides hyperphosphorylation, other modifications of the tau protein such as crosslinking are likely to contribute to the characteristic features of PHFs, including their insolubility and resistance against proteolytic degradation. In this study, we have investigated if the four reactive carbonyl compounds acrolein, malondialdehyde, glyoxal and methylglyoxal accelerate the formation of tau oligomers, thioflavin T positive aggregates and fibrils using wild-type and seven pseudophosphorylated mutant tau proteins. Acrolein and methylglyoxal were the most reactive compounds, followed by glyoxal and malondialdehyde in terms of formation of tau dimers and higher molecular weight oligomers. Furthermore, acrolein and methylglyoxal induced the formation of thioflavin T fluorescent aggregates in a triple pseudophosphorylation mimicking mutant to a slightly higher degree than wild type tau. Analysis of the tau aggregates by electron microscopy study showed that formation of fibrils using wild type tau and several tau mutants could be observed with acrolein and methylglyoxal but not with glyoxal and malondialdehyde. Our results suggest that reactive carbonyl compounds, particularly methylglyoxal and acrolein, could accelerate tangle formation in vivo, and that this process could be slightly accelerated, at least in the case of methylglyoxal and acrolein, by hyperphosphorylation. Interference with the formation or the reaction of these reactive carbonyl compounds could be a promising way of inhibiting tangle formation and neuronal dysfunction in Alzheimer’s disease and other tauopathies.

Publ.-Id: 8962

Ion implantation-induced damage depth profile determination in SiC by means of RBS/C and bevelling technique

Romanek, J.; Grambole, D.; Herrmann, F.; Voelskow, M.; Posselt, M.; Skorupa, W.; Zuk, J.

Ion implantation-induced damage depth profiles of 450 keV Al+ ion-implanted 6H-SiC were studied using RBS/C technique for implantations along channeling direction and non-channeling direction with fluence of 3.4 1015 cm2. Bevelling method of sample preparation was used to get access to the deeper situated layers over the whole damaged region and below. To determine damage degree at the specific depth of the bevelled sample, RBS/C technique combined with a 3 MeV Li2+ ion beam of size of about 30 micrometer x 30 micrometer was utilized (micro-RBS/C). The micro-RBS/C method combined with the bevelling technique gave us a possibility to probe deeper reaching damage regions than in the case of conventional RBS/C investigations. It also utilizes a near-surface part of backscattered spectra, which is slightly influenced by damage created by probing ions and a random fraction of probing beam. Additionally, there is no need to perform energy calibration of detector for backscattered particles. Due to much smaller sample area hit by probing ions of micro-beam, the required fluence, comparable to that at conventional RBS/C measurements is obtained at much lower charge. Negligibly small effect of bevelling-induced mechanical damage has been observed in this study. The obtained results by micro-RBS/C method validate the results of computer simulations (Crystal-TRIM software).

Keywords: Ion implantation damage; SiC; micro-RBS

  • Nuclear Instruments and Methods in Physics Research B 251(2006), 148-156

Publ.-Id: 8960

Uranmunition im Boden: - Spektroskopische Untersuchungen zur Sekundärphasenbildung auf abgereichertem Uran

Baumann, N.

Zusammenfassung und Interpretation der Ergebnisse von TRLFS-Messungen an einer Probe von abgereichertem Uran (DU), welches zuvor 182 Tage bei Raumtemperatur einer Calziumphosphatlösung ausgesetzt war. Durch diese Messung konnte die Bildung der Sekundärphase Meta-Autunit und damit eine Reaktion von DU mit der Lösung spektroskopisch nachgewiesen werden.

  • Invited lecture (Conferences)
    Vortragsreihe des Schwerpunktes Bio-Geo der Friedrich-Schiller-Universität Jena, 07.11.2006, Jena, Germany

Publ.-Id: 8959

Quantification of beta+ activity generated by hard photons by means of PET

Möckel, D.; Müller, H.; Pawelke, J.; Sommer, M.; Will, E.; Enghardt, W.

Positron emission tomography (PET) as a method for quality assurance in radiotherapy is well-investigated in the case of therapy with carbon ion beams and successfully applied at the Heavy Ion Medical Accelerator at Chiba (HIMAC), Japan, and the Gesellschaft für Schwerionenforschung (GSI), Germany. By measuring the beta{}^+ activity distribution during the irradiation (in-beam PET) valuable information on the precision of the dose deposition can be obtained. To extend this efficient technique to other radiation treatment modalities may be worthwhile. For example, since positron emitters are generated by high energy photons with energies above 20~MeV due to (gamma{},~n) reactions (predominantly {11}C and {15}O in tissue) in-beam PET seems to be feasible for the radiation therapy with high-energy photons as also shown in Geant4 simulations. Quantitative results on the activation of tissue-equivalent materials at hard photon beams were obtained by performing off-beam PET experiments. Homogeneous PMMA phantoms as well as inhomogeneous phantoms were irradiated with high energy bremsstrahlung. After the irradiation the distributions of the generated positron emitters in the phantoms were measured using a conventional PET scanner. Furthermore, the depth-dose-distributions were determined by means of optically stimulated luminescence detectors. In the experiments an activity per dose comparable to that produced in a typical patient irradiation with carbon ions could be achieved for 34~MV bremsstrahlung. In addition, a high contrast in the PET images for materials with different density and stoichiometry could be detected. Thus, further research concerning the development of in-beam PET seems to be worthwhile.

Publ.-Id: 8958

RBE of 10 kV X-rays determined for the Human Mammary Epithelial Cell Line MCF-12A

Lehnert, A.; Lessmann, E.; Pawelke, J.; Dörr, W.

Presently, an extended discussion about the dependence of the relative biological effectiveness (RBE) on photon energy takes place. The increasing amount of in vitro data in the low-energy region indicates this is a complex dependence which is influenced by the endpoint and cell line studied. In the present investigation, the RBE of 10 kV rays (W anode) was determined relative to 200 kV X-rays (W anode, 0.5 mm Cu filter) for cell survival in the dose range 1 - 10 Gy and induction of micronuclei in the range 0.5 - 3.6 Gy for the human mammary epithelial cells MCF-12A. The RBE for cell survival was found to increase with decreasing dose, being 1.21 ± 0.03 at the 10 % survival rate. Considerably higher values were obtained for the micronucleus induction, where RBEM obtained from the ratio of the linear coefficients of the dose-effect curves was equal to 2.6 ± 0.4 for the fraction of binucleated cells (BNC) with micronuclei (MN) and 4.1 ± 1.0 for the number of MN per BNC. These values, together with our previous data, support a monotonic increase in RBE with decreasing photon energy down to the mean energy of 7.3 keV used in the present study.

Keywords: soft X-rays; RBE; X-ray tube; clonogenic survival; micronucleus test; human mammary epithelial cells; MCF-12A

Publ.-Id: 8957

Radiolabelling of multimeric neurotensin(8-13) analogues with the short-lived positron emitter fluorine-18

Hultsch, C.; Berndt, M.; Bergmann, R.; Wüst, F.

Neurotensin receptors are expressed with high incidence in several human tumour entities. Thus, radiolabelled neurotensin derivatives might be used for tumour targeting. However, its application is limited by insufficient metabolic stability. Metabolic stability might be improved by the synthesis of multivalent peptides.
Three methods for 18F-labelling of dimeric and tetrameric
neurotensin(8-13) derivatives were evaluated with respect to the labelling yield and the required peptide amounts. Labelling using N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) gave low radiochemical yield for the dimeric peptides. Coupling of the tetramer with [18F]SFB was not successful. Furthermore, labelling of aminooxy-functionalized neurotensin(8-13) derivatives using 4-[18F]fluorobenzaldehyde ([18F]FBA) was investigated. High yields were obtained for the dimer whilst coupling of the tetramer only gave low yields.
In contrast to these findings, labelling of sulfhydryl-functionalized
neurotensin(8-13) derivatives using the maleinimide 4-[18F]fluorobenzaldehyde O-[6-(2,5-dioxo-2,5-dihydro-pyrrol-1-yl)-hexyl]-oxime ([18F]FBAM) resulted in high radiochemical yields for both, the dimer and the tetramer. Therefore, [18F]FBAM seems to be the most suitable 18F-labelling agent for multivalent neurotensin(8-13) derivatives.

Publ.-Id: 8956

Synthesis of 18F-labelled stilbenes from 4-[18F]fluorobenzaldehyde using the Horner-Wadsworth-Emmons reaction

Gester, S.; Pietzsch, J.; Wüst, F.

The first application of the Horner-Wadsworth-Emmons reaction in 18F-chemistry is described. This carbonyl-olefination reaction was performed via a “multi-step/one-pot” reaction by the coupling of benzylic phosphonic acid esters (3,5-bis-methoxymethoxybenzyl)-phosphonic acid diethyl ester 2e, (4-methoxymethoxybenzyl)-phosphonic acid diethyl ester 3e and (4-dimethyl-aminobenzyl)phosphonic acid diethyl ester 4d) with 4-[18F]fluorobenzaldehyde to give the corresponding 18F-labelled stilbenes [18F]2g, [18F]3g and [18F]4e exclusively as the expected E-isomers. The radiochemical yields ranged from 9 to 22% (based upon [18F]fluoride, including HPLC purification). The specific activity reached up to 90 GBq/µmol.

Keywords: 18F-labelled stilbenes; [18F]fluorobenzaldehyde; Horner-Wadsworth-Emmons reaction

  • Journal of Labelled Compounds and Radiopharmaceuticals 50(2007)2, 105-113
    DOI: 10.1002/jlcr.1172

Publ.-Id: 8955

Neurotensin Receptors in Adeno- and Squamous Cell Carcinoma

Haase, C.; Bergmann, R.; Oswald, J.; Zips, D.; Pietzsch, J.

Background: Peptide receptors seem to be good markers for receptor targeting because of their overexpression in human cancer. Understanding the role of receptors and their cognate ligands is currently used for both diagnosis and therapy. Candidates playing a key role in tumor biology are the neurotensin receptors (NTR). The expression of NTR in HT-29 cells (human colon adenocarcinoma cell line) and FaDu cells (human squamous cell carcinoma cell line) and in corresponding tumor xenografts on nude mice, was investigated. Materials and Methods: Quantitative RT-PCR of the three receptor subtypes was carried out to study mRNA expression. Receptor protein expression was analyzed by immunohistochemistry with specific antibodies for the three known neurotensin receptors NTR1, NTR2 and NTR3. Results: Analysis of receptor mRNA revealed a strong expression of NTR3 and a weak expression of NTR1 and NTR2 in cultured cells and xenografts. Examining the protein levels, a strong signal for NTR1 was detected in tumor cells and xenografts and only a weak signal was detected for NTR3. Conclusion: Since the receptor protein is targeted in vivo, the enhanced protein expression of NTR1 in xenografts could be a useful tool for molecular targeting with radioligands and for further characterization of carcinogenic processes.

Keywords: Neurotensin; neurotensin receptor; Tumor xenograft model; HT-29; FaDu

  • Open Access Logo Anticancer Research 26(2006), 3527-3534

Publ.-Id: 8954

Synthesis and radiopharmacological characterization of [11C]AL-438 as a nonsteroidal ligand for imaging brain glucocorticoid receptors

Wüst, F.; Knieß, T.; Bergmann, R.; Henry, B.; Pietzsch, J.

The radiosynthesis and the radiopharmacological characterization of [11C]AL-438 as a nonsteroidal ligand for the glucocorticoid receptor (GR) is described. Radiolabelling of the corresponding desmethyl precursor 10 with [11C]MeI gave [11C]AL-438 in decay-corrected radiochemical yields of 30±4% (based upon [11C]CO2) within 35 min at a specific radioactivity of 10-15 GBq/µmol at the end-of-synthesis. The radiopharmacological evaluation of [11C]AL-438 involved biodistribution and small animal PET imaging in rats, and autoradiography studies using rat brain sections.
Biodistribution studies were performed in male Wistar rats and demonstrated high radio-activity uptake in pituitary and brain. However, the inability of high dose corticosterone to block binding would suggest that the radioactivity accumulation in the brain was not receptor-mediated.

  • Bioorganic & Medicinal Chemistry Letters 17(2007), 4035-4039

Publ.-Id: 8953

Bispidine - Ein neues Chelatsystem zur stabilen Bindung von Radiokupfernukliden

Juran, S.; Walther, M.; Stephan, H.; Steinbach, J.

Die Arbeiten zielen auf die Entwicklung von radioaktiven Kupfer(II)-Komplexen mit hoher thermodynamischer Stabilität und schneller Komplexbildungskinetik auf der Basis des 3,7-Diazabicyclo[3.3.1]nonans (Bispidin). Voruntersuchungen haben gezeigt, dass sechszähnige Derivate, die Pyridinfunktionen enthalten, am aussichtsreichsten sind (1). Durch Einführen von Kopplungsstellen am Bispidin soll die Anknüpfung an Biomoleküle ermöglicht werden.
Es wird über die Darstellung von hexadentaten Bispidinderivaten berichtet sowie deren Möglichkeiten zur Kopplung an Biomoleküle diskutiert. Des Weiteren werden Ergebnisse radiopharmakologischer Untersuchungen mit Cu-64 und Cu-67 präsentiert. Schwerpunkt dabei werden in vitro Stabilitätsuntersuchungen und Bioverteilungsstudien sein.

Die Synthese der Bispidinliganden erfolgt durch zwei aufeinanderfolgende Mannich-Kondensationen, wobei Pyridin- und Imidazol-Edukte eingesetzt wurden. An ausgewählten Vertretern wurden Möglichkeiten zur Kopplung an Biomoleküle erprobt. Die entsprechenden Biokonjugate wurden mittels semipräparativer HPLC gereinigt und radioaktiv markiert. Stabilitätstests im Rattenplasma und in Anwesenheit von Konkurrenzliganden (Glutathion, Cyclam) erfolgten.

Es wurden eine Reihe neuer Bispidinliganden dargestellt und die in vitro Stabilität entsprechender Kupfer(II)-Komplexe getestet. Das Bispidingrundgerüst wurde so modifiziert, dass Biomoleküle über eine Carboxylfunktion angekoppelt werden können. Für eine Peptidkopplung erwies sich der Einsatz von HBTU als Reagenz in Anwesenheit von DIPEA am geeignesten. Die dargestellten Konjugate weisen eine günstige Kinetik der Komplexierung sowie eine hohe Stabilität sowohl im Rattenplasma als auch in Anwesenheit von Konkurrenzliganden auf. Es konnte keine Transchelatisierung des Kupfers nachgewiesen werden.

Die dargestellten Kupfer(II)-Komplexe mit sechszähnigen Bispidinliganden weisen eine sehr hohe Stabilität auf und verfügen damit über ein hohes inhärentes Anwendungspotential für radiopharmazeutische Anwendungen in Diagnostik (Cu-64, PET) und Therapie (Cu-67, Endoradionuklidtherapie). Zum Erzielen eines selektiven Anreicherns der radioaktiven Kupferkomplexe im Zielgewebe, sollen sich weitere Untersuchungen insbesondere mit der Kopplung von Antikörpern an das Grundgerüst hexadentater Bispidin-Derivate befassen. Kleintier-PET-Untersuchungen ausgewählter Konjugate sollen sich anschließen.

(1) H. Stephan, S. Juran, M. Walther, J. Steinbach, K. Born, P. Comba
Synthesis, characterization and evaluation of novel chelating agents for copper radionuclides in „Technetium, Rhenium and other Metals in Chemistry and Nuclear Medicine“, U. Mazzi (Ed.), SGE Editoriali, Padova, Italy, 2006, 7, 219-222.

  • Lecture (Conference)
    45. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2007, Hannover, D
  • Abstract in refereed journal
    Nuklearmedizin 46(2007), A42

Publ.-Id: 8952

Validation of CFD models for mono- and polydisperse air-water two-phase flows in pipes

Frank, T.; Zwart, P.; Krepper, E.; Prasser, H.-M.; Lucas, D.

Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, where one of the phases is continuous and the other phase consists of gas or vapor of the liquid phase. The validation of the CFD multiphase flow models against detailed experimental data for simplified flow configurations is a basic requirement for the accurate prediction of more complex flows, like e.g. multiphase flow in fuel rod assemblies with spacer grids under the conditions from ONB to DNB including bulk and wall boiling in a pressurized polydisperse liquid-vapor flow. This paper is therefore aimed on validation of the underlying multiphase flow modeling concepts for gas-liquid monodisperse and polydisperse bubbly flows. CFD predictions using ANSYS CFX and taking into account interphase momentum transfer (drag and non-drag forces) as well as bubble break-up and coalescence are compared to experiments of MT-Loop and TOPFLOW test facilities (FZ Rossendorf, Germany). Best Practice Guidelines have been applied in order to allow for a systematic error quantification and thoroughly assessment of model formulations.

Keywords: CFD; Multiphase flow; experiments; bubble forces; monodispersed flow; polydispersed flow; multiple bubble size classes; model validation; best practice guidelines

  • Lecture (Conference)
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS, 05.-09.09.2006, Garching, Germany
  • Contribution to proceedings
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS, 05.-09.09.2006, Garching, Germany
    Proceedings paper B6-32
  • Nuclear Engineering and Design 238(2008), 647-659
    DOI: doi:10.1016/j.nucengdes.2007.02.056

Publ.-Id: 8951

Capacitance wire-mesh tomograph for multiphase flow applications

Da Silva, M. J.; Schleicher, E.; Hampel, U.

We present a novel wire-mesh tomography system based on electrical capacitance (permittivity) measurements for multiphase flow applications. The system measures with high spatial and high temporal resolution the phase distribution in a flow cross section and can be used to investigate phases having different relative permittivity (dielectric constant) values. A prototype system has been developed and manufactured comprising of a sensor with two layers of 16 wires each and associated electronics. The system achieves 3 mm spatial resolution and can measure up to 625 frames per second. The evaluation of the prototype has shown good accuracy and reproducibility. Initial tests have been performance including an air-oil bubbly flow measurement and the static measurement of a stratified air-oil-water flow.

Keywords: wire-mesh sensor; capacitance; permittivity; non-conducting fluids; multiphase flow

  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography, 03.-06.09.2007, Bergen, Norway
    Proceedings of the 5th World Congress on Industrial Process Tomography: VCIPT, 978 0 85316 265 0, 624-629
  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography, 03.-06.09.2007, Bergen, Norway

Publ.-Id: 8950

Ereignis an der Versuchsanlage TOPFLOW-Heißstrang des Forschungszentrums Dresden - Rossendorf

Kryk, H.; Hessel, G.; Beyer, M.; Carl, H.; Hampel, U.; Strobel, H.

Zur Untersuchung von Zweiphasenströmungen in horizontalen Geometrien wurde am FZD eine neue Versuchsanlage aufgebaut. Sie besteht im Wesentlichen aus einem Druckbehälter mit einem Schnellverschlussdeckel, einer Umluftkühlung sowie einer Kompressorenanlage. Bei einem Test der Wärmeisolierung der Testsektionen kam es zu einem Brand im Druckbehälter. Der damit verbundene Temperatur- und Druckanstieg im Behälter führte zum Abriss der zum Sicherheitsventil führenden Leitung. Personen kamen nicht zu Schaden. Im Zuge der Brand-Ursachenermittlung wurden vom FZD und dem Institut Fresenius u.a. thermische und chemische Analysen des neuen und havarierten Isoliermaterials (Polysiloxan-Schaum) sowie Pyrolyseuntersuchungen mit Gasanalysen durchgeführt. Im Ergebnis der Untersuchungen wurden brennbare Substanzen identifiziert (z.B. niedermolekulare zyklische Siloxane), die bei thermischer Belastung des Isoliermaterials innerhalb der Polysiloxanschaum-Poren entstehen und bei Kontakt mit Luftsauerstoff ein zündfähiges Gemisch bilden können. Ausgegangen wird von einer lokalen Anreicherung brennbarer Substanzen im Isoliermaterial und einer Zündung vorzugsweise am heißesten Anlagenteil. Begünstigt wurde der Zündprozess durch die druckbedingte Herabsetzung der Zündtemperatur, die temperaturbedingte Verringerung von Sauerstoffgrenzkonzentration und UEG sowie der Präsenz eines Platin-Katalysators. Die Brandausbreitung über die gesamte Oberfläche des Isolationsmaterials erfolgte durch Erhitzung umliegender Isolationsmaterial-Bereiche durch Wärmeleitung und Konvektion, Reaktionsbeschleunigung durch Erwärmung unter Bildung weiterer brennbarer Stoffe in den umliegenden Isoliermaterial-Bereichen sowie wärmebedingten Transport der Substanzen an die Oberfläche des Materials. Zur Verhinderung weiterer Störfälle erfolgte ein Austausch des Polysiloxan-Schaumes durch ein anorganisches Isoliermaterial, welches vor dem Einsatz thermischen und chemischen Analysen unterzogen wurde. Da der Einsatz von organischen Substanzen im weiteren Versuchsbetrieb nicht ausgeschlossen werden kann, ist weiterhin eine Anlage zur Inertisierung des Druckbehälters mit Stickstoff geplant.

  • Lecture (others)
    DECHEMA/GVC-Arbeitsausschuss "Sicherheitsgerechtes Auslegen von Chemieanlagen", 22.-23.11.2006, Lampertheim, Germany

Publ.-Id: 8949

Scale-hopping Modelling of Ferroic Functional Elements

Gemming, S.

The modelling concepts of a nanoscale organic field effect transistor on a ferroelectric substrate are presented. The device consists of a ferroelectric substrate with a switchable, macroscopic electric polarisation, an electric-field-sensitive organic molecule, and suitable connectors. The structural and electronic properties of the single components and the major interactions between them are modelled by first-priciples electronic structure calculations. For the influence of the electric field on the optical and the conductivity properties of the larger organic molecules, a related density-functional-based tight-binding scheme was employed, which focusses on the salient features of the electronic system. For the self-assembly of the transistor building blocks, mesoscale approaches based on atomistic pair potentials and on a supramolecular Ising-type modelling have been developped and successfully applied.

Keywords: multi-scale modelling; multifunctional material

  • Invited lecture (Conferences)
    ITF-Seminar, 07.11.2006, Dresden, Deutschland

Publ.-Id: 8948

Intersubband transitions in GaP–AlP heterostructures

Semtsiv, M. P.; Müller, U.; Masselink, W. T.; Georgiev, N.; Dekorsy, T.; Helm, M.

Intersubband optical transitions in doped AlP–GaP multiple quantum wells are investigated using midinfrared absorption. Strong p-polarized absorption corresponding to the transition from the first to the fourth electronic subband in the Xz valley is measured at wavelengths between 5 and 8 microns. Additional absorption peaks related to transitions between confined donor states are also observed. The measured intersubband transition energies are consistent with an X valley conduction band offset between AlP and GaP of 280 meV and a value of 1.1m0 for the longitudinal effective mass for the X valleys of AlP (where m0 is a free electron mass). These values, the role of donors and confined two-dimensional continuum states, and applications of this system for terahertz intersubband devices are discussed.

Keywords: intersubband; infrared GaP; AlP; quantum well

Publ.-Id: 8947

Impact of Four-Quark Condensates on In-Medium Effects of Hadrons

Thomas, R.; Hilger, T.; Zschocke, S.; Kämpfer, B.

Spectral properties of hadrons in nuclear matter are treated in the framework of QCD sum rules. The influence of the ambient strongly interacting medium is encoded in various condensates. Especially, the structure of different four-quark condensates and their density dependencies in light quark systems are exemplified for the omega meson and the nucleon.

Keywords: Medium modifications; Four-quark condensates; QCD sum rules

  • Contribution to proceedings
    Quark Confinement and the Hadron Spectrum VII, 02.-07.09.2006, Ponta Delgada, Portugal: AIP, 978-0-7354-0396-3, 274-277

Publ.-Id: 8946

Stability of 188Re Complexes Prepared with Highly Concentrated [188Re]Perrhenate Eluates from 188W/188Re Generators

Seifert, S.; Schiller, E.; Jentschel, C.; Bergmann, R.; Pietzsch, H.-J.; Wunderlich, G.; Kotzerke, J.; Steinbach, J.

The preparation and stability of a novel 188Re-S4-complex (S4 = bridged DMSA ligand) was studied at therapeutic relevant radioactive concentrations. The results were compared with an 188Re-MAG3 and an 188Re-DMSA preparation which were obtained from 188Re-EDTA by a combined re-oxidation/ligand exchange reaction. The highly concentrated [188Re]perrhenate solution (12-15 GBq/ml) used for preparations was received by successive elution of several 188W/188Re generators connected in series. The preparations were performed under nitrogen, stabilized by adding 15 mg of ascorbic acid and analyzed after 1, 2, and 24 hours by TLC and HPLC. Only about 8 % of perrhenate were detected after 24 h in the 188Re-S4-complex samples. The 188Re-DMSA preparations were only marginally re-oxidized during this time, whereas the stabilized 188Re-MAG3 samples remained nearly stable. Additionally, in vitro and in vivo stability studies at radioactive concentrations of 30-50 MBq/ml were performed with all the complexes. Therefore, the preparations were purified by HPLC and incubated in phosphate buffer as well as rat and human plasma. The in-vivo-stability was determined in rats. Samples of plasma, urine, liver, and intestine were taken off 1 h after application of the 188Re complex solutions. Results from these studies demonstrated that only the 188Re-S4-complex was completely stable in vitro and in all investigated in vivo samples.

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGEditoriali, 2006, 88-89884-04-5, 605-606

Publ.-Id: 8945

Preparation and biological characterization of 188Re(V) oxocomplexes with tetradentate S4-ligands derived from DMSA for labeling of biomolecules

Seifert, S.; Heinrich, T.; Jentschel, C.; Bergmann, R.; Pietzsch, H.-J.

A new type of tetradentate S4-ligands has been synthesized by bridging two molecules of 2,3-dimercaptosuccinic acid for stable binding and easy conjugation of rhenium-188 to biologically interesting structures. The stereoisomeric tetrathiolato S4-ligands form very robust anionic five-coordinated oxorhenium(V) complexes. Two routes for the preparation of the 188Re(V) oxocomplexes I and II with (R)2N(O)C-CH(SH)-CH(SH)-C(O)NH-(CH2)3–NH-(CH2)3–NHC(O)-CH(SH)-CH(SH)-C(O)N(R)2 (ligand 1, R = iBu) and its hydrophilic derivative 2 (R = 1-aza-18-crown-6) were tested and optimized. Several isomers were separated by HPLC from the preparation solutions and characterized in vitro and in vivo. The identity of the species obtained was determined by comparison with the HPLC profiles of reference 185/187Re analogues which were characterized by ESI-MS. All of them were absolutely stable in rat and human plasma solutions. Challenge experiments with cysteine corroborated the high inertness of the isomers towards ligand exchange reactions. Various in vivo samples, taken off at different times from blood, intestine and urine of rats, confirmed the high in vivo stability of the 188Re-S4 complexes. Biodistribution studies using male Wistar rats were performed and resulted in a high uptake and fast clearance from the liver of the more lipophilic cis and trans isomers of complex I (log Po/w between 1.5 and 1.7), whereas the hydrophilic isomers of complex II (log Po/w about -1.75) were preferentially excreted via the renal pathway. The low level of radioactivity in the stomach indicated good in vivo stability.

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGEditoriali, 2006, 88-89884-04-5, 411-414

Publ.-Id: 8944

Dynamics of charged fluids and 1/l perturbation expansions

Znojil, M.; Günther, U.

Some features of the calculation of fluid dynamo systems (spherically symmetric α2-dynamos) in magnetohydrodynamics are studied, the problem connected with the presence of mixed (Robin) boundary conditions is addressed and a new treatment for it is proposed. The perturbation formalism of large l expansions is shown applicable and its main technical steps are outlined.

Keywords: large l expansion; perturbation theory; MHD dynamos; Robin boundary conditions; anharmonic oscillator

Publ.-Id: 8943

Absence of ferromagnetism in V-implanted ZnO single crystals

Zhou, S.; Potzger, K.; Reuther, H.; Skorupa, W.; Helm, M.; Fassbender, J.

The structural and magnetic properties of V doped ZnO are presented. V ions were introduced into hydrothermal ZnO single crystals by ion implantation with fluences of 1.2×10^16 to 6×10^16 cm^-2. Post-implantation annealing was performed in high vacuum from 823 K to 1023 K. The ZnO host material still partly remains in a crystalline state after irradiation, and is partly recovered by annealing. The V ions show a thermal mobility as revealed by depth profile Auger electron spectroscopy. Synchrotron radiation x-ray diffraction revealed no secondary phase formation which indicates the substitution of V onto Zn site. However in all samples no ferromagnetism was observed down to 5 K by a superconducting quantum interference device magnetometer.

Keywords: ZnO; magnetic semiconductor

  • Contribution to proceedings
    10th Joint MMM/Intermag Conference, 07.-11.01.2007, Baltimore, Maryland, United States
  • Journal of Applied Physics 101(2007), 09H109
    DOI: 10.1063/1.2710802
  • Poster
    71. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.03.2007, Regensburg, Germany


Publ.-Id: 8942

Spectroscopic study of defects and inclusions in bulk poly- and nanocrystalline diamond aggregates

Shiryaev, A. A.; Iakoubovskii, K.; Grambole, D.; Dubrovinskaia, N.

Recently, a novel form of nanodiamond exhibiting unusual mechanical properties has been synthesized by high-pressure high-temperature (HPHT) treatment of C60 fullerene, amorphous carbon and diamond powder. In this study, we have characterized the dominant defects in this nanodiamond by a combination of optical absorption, luminescence, Raman, electron spin resonance and elastic recoil detection techniques. Unusually high concentrations (~0.4 at.%) of hydrogen and very low concentrations of nitrogen (~1E-5 at.%) have been detected in diamond grown from C60. Although most of hydrogen is shown to originate from inclusions of foreign phases, such as water, significant concentrations (~0.01 at.%) of hydrogen were also detected as a point defect in the nanodiamond grains. Observed structural differences between the samples made from various carbonaceous materials are attributed to different behaviour of the starting compounds during HPHT treatment.

  • Journal of Physics: Condensed Matter 18(2006), L493-L501

Publ.-Id: 8940

Femtosecond pump-probe spectroscopy of intersubband relaxation dynamics in narrow InGaAs/AlAsSb quantum well structures

Tribuzy, C. V.-B.; Ohser, S.; Winnerl, S.; Grenzer, J.; Schneider, H.; Helm, M.; Neuhaus, J.; Dekorsy, T.; Biermann, K.; Künzel, H.

Intersubband relaxation dynamics in InGaAs/AlAsSb multiquantum wells (QWs) is studied by single-color femtosecond pump-probe measurements. At early delay times, all samples show an exponential decay of the transient transmission occurring with time constants of the order of a picosecond. The relaxation dynamics at later delay times strongly depend on both QW thickness and doping location. A non-single-exponential decay behavior indicates extra competing relaxation channels, as further confirmed by solving three-level rate equations. It is shown that slowly decaying components are due to electron transfer to states related to indirect valleys in the wells or in the barriers.

Keywords: Intersubband relaxation; InGaAs/AlAsSb quantum wells

  • Applied Physics Letters 89(2006), 171104-1-171104-3

Publ.-Id: 8939

Modellierung der Wechselwirkung zwischen Corium und RDB-Stahl im Rahmen von Schmelzerückhaltungsszenarien

Altstadt, E.; Willschütz, H.-G.

Bei einem schweren Störfall mit anschließender Schmelzeverlagerung in das untere Plenum stellt der Reaktordruckbehälter die letzte Sicherheitsbarriere vor einer direkten Belastung des Containments dar. Für eine genauere Einordnung der Vorgänge und Phänomene in diesem Szenario wurden von der EU bzw. der OECD finanzierte Experimente zum Behälterversagen durch Kriechbruch durchgeführt.
Am FZR wurden Modelle entwickelt, die sowohl die Temperaturfeldberechnung als auch die viskoplastische Mechanik des RDB umfassen und geeignet sind, den Versagensmodus und die Versagenszeit des Behälters zu ermitteln. Die Validierung der Modelle erfolgte an Hand von Voraus- und Nachrechnungen zu den Experimenten. Ein Schwerpunkt der Modellierung von prototypischen LWR-Szenarien ist die Berücksichtigung der thermo-chemischen Wechselwirkung der Coriumschmelze mit der RDB-Wand.
Im Rahmen der METCOR-Experimente am Alexandrov-Research Institute (NITI) in Sosnovy Bor wird die Schmelze-Metall-Wechselwirkung im kleinen Maßstab untersucht. Die Ergebnisse zeigen, dass die Ablation des Stahls je nach Zusammensetzung der Schmelze durch Bildung von Eutektika schon deutlich unterhalb der Schmelztemperatur des Stahls einsetzt. Entsprechende Abschmelzmodelle sind in die Finite-Elemente-Modelle zur Simulation der Schmelzerückhaltungsszenarien integriert worden. Die Anwendung dieser Modelle führt zu deutlich reduzierten Restwanddicken.

Keywords: In-vessel melt retention; corrosion damage; finite element analysis; reactor pressure vessel

  • Contribution to proceedings
    MPA Seminar, 05.-06.10.2006, Stuttgart, Germany
    Proceedings on CD-ROM, paper 16.1
  • Lecture (Conference)
    MPA Seminar, 05.-06.10.2006, Stuttgart, Germany

Publ.-Id: 8938

Nachrechnung der Leistungsparameter eines Vollhub-Feder –Sicherheitsventils mit ANSYS CFX

Höhne, T.; Friedel, L.

Mit dem CFX-Code wurden Nachrechnungen von Durchsatzparametern eines Leser Sicherheitsventils mit einem Gitter von 1 Million Hexaeder Zellen vorgestellt. Sehr gute Übereinstimmung wurde bei den Durchsatzkennlinien der vom Hersteller angegebenen Charakteristiken für Luft und Wasser erzielt, es existierte jedoch eine systematische Abweichung bei Luft im Falle hoher Ansprechdrücke durch Realgasverhalten und das Auftreten hohe Ma-Zahlen. Eine CFX-Rechnung mit einem Zweiphasengemisch bei 2 bar Überdruck, 1 mm Blasendurchmesser und 4% Gasanteil ergab eine realistische Erhöhung des Volumenanteils der Gasphase in Abhängigkeit von der Druckabsenkung. Weitere Untersuchungen, insbesondere das Verhalten bei Sattdampf und bei Stoffgemischen im Vergleich mit Experimenten sind geplant.

Keywords: Sicherheitsventil; CFD

  • Invited lecture (Conferences)
    24th CADFEM & ANSYS Germany Users Meeting, 26.10.2006, Stuttgart/Fellbach, Germany

Publ.-Id: 8937

The origin of ferromagnetism in 57Fe ion-implanted semiconducting 6H-polytype silicon carbide

Stromberg, F.; Keune, W.; Chen, X.; Bedanta, S.; Reuther, H.; Mücklich, A.

Semiconducting (mostly p-doped) single crystals of the 6H-polytype of α-SiC(0001) were implanted with 57Fe ions with a nominal dose of 1.0 × 1016, 2.0 × 1016, 3.0 × 1016 or 2.0 × 1017 cm−2 (high-dose sample phd) at 100 or 200 keV ion energy in order to produce diluted magnetic semiconductors (DMSs). After implantation all samples (except p-hd) were subject to rapid thermal annealing at 1000 ◦C for 2 min. The structure was investigated by x-ray diffraction, high-resolution cross-sectional transmission electron microscopy and sputter-Auger depth profiling. The magnetic properties were obtained from superconducting quantum interference device (SQUID) magnetometry and 57Fe conversion electron M¨ossbauer spectroscopy (CEMS) at room temperature (RT) and 4.2 K. Our combined results obtained by several techniques prove unambiguously that ferromagnetism in 57Fe-implanted SiC for Fe concentrations above 3%originatesmostly from epitaxial superparamagnetic Fe3Si (and possibly a small fraction of Fe nanoparticles) in the SiC matrix. We find a wide range of blocking temperatures, TB, which start from 400 K for a dose of 2.0 ×1016 cm−2, and shift downwards to ∼220 K for 3.0× 1016 cm−2. For the lowest dose of 1.0 × 1016 cm−2 at 200 keV, we find evidence of ferromagnetism below 20 K via weak magnetic hyperfine interaction. Our measurements suggest that for a maximum Fe concentration in the range of 1–3%, which corresponds to this lowest Fe dose, the possibility exists to obtain a DMS in Fe-implanted SiC, prepared at lower or equal implantation doses.

Publ.-Id: 8936

FELBE Free-Electron Laser: Status and Application for Time Resolved Spectroscopy Experiments

Winnerl, S.; Stehr, D.; Drachenko, O.; Schneider, H.; Helm, M.; Seidel, W.; Michel, P.; Schneider, S.; Seidel, J.; Grafström, S.; Eng, L.-M.; Roch, T.; Strasser, G.; Maier, T.; Walther, M.

This paper reviews the basic properties of the infrared free-electron laser FELBE at the Forschungszentrum Rossendorf. At present FELBE delivers pulses with typical durations of 0.9–5 ps in the wavelength range 4–22 µm, which soon will be extended to 150 µm. Furthermore we report on recent experiments using FELBE, namely the study of phonon resonances in ferroelectric domains using a newly designed scattering scanning near-field optical microscope (s-SNOM), as well as pump-probe spectroscopy on doped semiconductor superlattices. The pump-probe signal reflects, apart from a component due to the bleaching of the interminiband transition, the temperature of the miniband electrons on a picosecond timescale.

  • Invited lecture (Conferences)
    Joint 31st International Conference on Infrared and Millimter Waves and 14th International Conference on Terahertz Electronics, 18.-22.09.2006, Shanghai, China
  • Contribution to proceedings
    Joint 31st International Conference on Infrared and Millimeter Waves and 14th International Conference on Terahertz Electronics, 18.-22.09.2006, Shanghai, China
    Conference digest of the 2006 IRMMW-THz 2006: Piscataway, NJ : IEEE Operations Center, 1-4244-0399-5, 159-159

Publ.-Id: 8935

RPV material investigations of the former VVER-440 Greifswald NPP

Rindelhardt, U.; Viehrig, H.-W.; Konheiser, J.; Noack, K.; Gleisberg, B.

The Greifswald NPP was operated between 1973 and 1990. The units are of Russian WWER-440-230 type. Now trepans from the RPV were gained to investigate the post mortem properties of the material.
The paper describes the results of weld metal originating from the critical weld of the RPV of unit 1. The RPV of this unit was annealed after 14 years of operation, followed by two additional years of operation.
The neutron dosimetry was based on fluence calculations as well as retrospective Nb dosimetry. Both approaches are shortly described. A decrease of 60% through the thickness of the RPV was found by both methods.
The material test results comprise Charpy-V, tensile and fracture toughness parameters. The main interest is focussed on the comparison of assessment codes applied in Russia and other European countries where WWER-440 reactors are operated. An additional aspect is the comparison of results determined on sub-size Charpy specimens immediately after the annealing procedure.
The first results show, that the material properties are near the predicted values.

Keywords: RPV; neutron dosimetry; neutron embrittlement; material properties

  • Contribution to proceedings
    15th International Conference on Nuclear Energy (ICONE15), 22.-26.04.2006, Nagoya, Japan
    Proceedings of ICONE-15, JSME No 07-202, Contribution 15-1035
  • Lecture (Conference)
    15th International Conference on Nuclear Energy (ICONE15), 22.-26.04.2006, Nagoya, Japan

Publ.-Id: 8934

Radiochemische Analysen von 93mNb in Druckkesselstahl und Vergleiche mit Fluenzberechnungen

Gleisberg, B.; Rindelhardt, U.; Konheiser, J.

Zur Untersuchung der Materialeigenschaften wurden aus dem Reaktordruckbehälter des Blockes 1 des ehemaligen KKW Greifswald Materialproben entnommen. Die interessierenden Eigenschaften werden durch die während des Betriebes auftretende Neutronenstrahlung bestimmt.
Im Beitrag wird dargestellt, wie durch Messungen der Nb-Aktivität die Neutronenfluenz bestimmt wurde. Niob ist im im untersuchten Material nur als Spurenmetall erhalten. Die vorgenommenen Trennverfahren zur Isolation von Nb werden dargestellt.Die Messergebnisse werden mit Rechenergebnissen verglichen.

Keywords: Neutron fluence; reactor pressure vessel material; neutron embrittlement

  • Lecture (Conference)
    Radiochemische Analytik bei Betrieb und Rückbau kerntechnischer Anlagen, der Deklaration von Abfällen und im Strahlenschutz, 19.-20.06.2006, Dresden, Germany

Publ.-Id: 8933

High resolution gamma ray tomography of a rotating hydrodynamic coupling

Hampel, U.; Bieberle, A.; Schleicher, E.; Zippe, C.; Hoppe, D.

Hydrodynamic couplings are being used for torque transfer in heavy duty systems, such as naval vessels, power plants, locomotives or other transport vehicles. A hydrodynamic coupling essentially consists of two rotating bladed wheels, the pump and the turbine wheel, which are placed inside a metal enclosure. In operation the coupling is partially filled with a fluid and this fluid realises the momentum transfer from the driving side (pump) to the load side (turbine). The flow conditions in the coupling determine its operational behaviour. A known problem of such devices is the sudden change of slip during a continuous increase or decrease of either load or angular velocity of the pump. To investigate the behaviour of a hydrodynamic coupling the flow structure inside the coupling must be disclosed. But there only few measurement techniques which are applicable. Thus, the flow inside the pump is a heavily turbulent two-phase flow that is hardly accessible to optical or other measurement techniques. Gamma ray tomography provides a convenient method to measure the time integrated phase distribution within such a coupling. We performed such measurements in the past with the help of a low resolution gamma ray tomography system. Now we continued to use a high resolution gamma ray tomograph for that purpose. The measurements were carried out using a Cs-137 isotopic source and a detector arc with 2 mm spatial resolution. The test coupling mostly consists of aluminium and has an outer diameter of approximately 500 mm. For the measurement we employed the angle resolved data acquisition scheme that allows us to image rotating distributions with a fixed tomography setup. In the paper we will discuss the application of gamma ray tomography to this particular industrial problem.

Keywords: gamma ray tomography; hydrodynamic coupling; flow measurement

  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography (WCIPT5), 03.-06.09.2007, Bergen, Norway
    Proceedings of the 5th World Congress on Industrial Process Tomography, 978 0 85316 265 0, 683-689
  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography (WCIPT5), 03.-06.09.2007, Bergen, Norway

Publ.-Id: 8932

High resolution gamma ray tomography and its application to the measurement of phase fractions in chemical reactors

Hampel, U.; Bieberle, A.; Schleicher, E.; Hessel, G.; Zippe, C.; Friedrich, H.-J.

We applied gamma ray tomography to the problem of phase fraction measurement in chemical reactors. Therefore, we used a new tomography device that is operated with a Cs-137 source and a high resolution gamma ray detector. One application example is the reconstruction of the fluid distribution and the measurement of radial gas fraction profiles in a laboratory scale stirred vessel. The tomograph was used to obtain radiographic projections of the averaged gamma ray attenuation for different stirrer speeds along the height of the vessel. With tomographic reconstruction techniques we calculated the angularly averaged radial distribution of the attenuation coefficient for as many as 150 single cross-sectional planes and synthesised from this data set the axial and radial fluid distribution pattern. Further, we exemplarily reconstructed the radial gas fraction distributions induced by the stirrer in the area of the stirrer blades. In a second application the gamma ray measurement system was used to visualise gas inclusions in a water cleaning column that is used to remove hazardous heavy metal species from water.

Keywords: gamma ray tomography; chemical reactor; flow measurement; gas hold-up; liquid hold-up

  • Lecture (Conference)
    The 5th International Symposium on Measurement Techniques for Multiphase Flows, 10.-13.12.2006, Macao, China
  • Contribution to proceedings
    The 5th International Symposium on Measurement Techniques for Multiphase Flows, 10.-13.12.2006, Macao, China
    Multiphase Flow: The Ultimate Measurement Challange, 942-948
  • Contribution to proceedings
    Multiphase Flow - the Ultimate Measurement Challenge, 10.-13.12.2006, Macao, China
    Proceedings of the 5th International Symposium on Measurement Techniques for Multiphase Flows and 2nd International Workshop on Process Tomography: American Institute of Physics, 753-759

Publ.-Id: 8931

Wasserkraftnutzung in Ostdeutschland

Rindelhardt, U.

Im Beitrag werden der aktuelle Stand und die Potenziale der Wasserkraftnutzung in Ostdeutschland beschrieben. Ausgehend von der historischen Entwicklung im letzten Jahrhundert wird insbesondere die Reaktivierung von Wasserkraftanlagen nach der Wiedervereinigung diskutiert. Die bestehenden Wasserkraftanlagen und die ausbauwürdigen Potenziale liegen vor allem an den Nebenflüssen der Elbe, die Leistung übersteigt nur bei wenigen Anlagen 1 MW. Das bis zum Jahr 2010 nutzbare Potenzial liegt bei 650 GWh/a, eine Nutzung des größeren Potenzials der Elbe (1 TWh/a) ist gegenwärtig nicht absehbar.

Keywords: Wasserkraft; Erneuerbare Energien

  • Wasserwirtschaft 97(2007)6, 33-36

Publ.-Id: 8930

Einsatz spektroskopischer Methoden zur Abschätzung der Stabilität dentritischer Metallkomplexe

Röhrich, A.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    SFB-624 Workshop "Affinität zu supramolekularen Templaten", 13.10.2006, Bonn, Germany

Publ.-Id: 8929

Untersuchungen zur in vitro Stabilität von Kupfer(II)-Komplexen sechszähniger Bispidinderivate

Juran, S.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    SFB-624 Workshop "Affinität zu supramolekularen Templaten", 13.10.2006, Bonn, Germany

Publ.-Id: 8928

Charakterisierung supramolekularer Rezeptoren mittels der Radiotracertechnik

Stephan, H.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    SFB-624 Workshop "Affinität zu supramolekularen Templaten", 13.10.2006, Bonn, Germany

Publ.-Id: 8927

Dissociation of Si+ ion implanted and as-grown thin SiO2 layers during annealing in ultra-pure neutral ambient by emanation of SiO

Beyer, V.; von Borany, J.; Heinig, K.-H.

We have observed a very inhomogeneous dissociation of stoichiometric and non-stoichiometric thin SiO2 layers (thermally grown on Si substrates) during high temperature annealing at a low partial pressure of oxygen. During this process some silicon of the (100)Si substrate and, in case of Si ion implantation, additionally excess Si is consumed. The SiO2 dissociation has been studied by electron microscopy and Rutherford backscattering spectrometry. Large holes (>1µm) in non-implanted oxide layers have been observed which evolve probably from defects located at the Si/SiO2 interface. For Si implanted SiO2 additionally the formation of voids within the oxide during annealing has been observed preferably at the position of the implanted Si excess. Oxygen vacancies are possibly emitted from Si/SiO2 interfaces into the oxide and migrate through SiO2 with long-range distortions of the oxide network. In that way the hole and void formation in the oxide can be explained by oxygen-vacancy formation, migration and silicon-monoxide (SiO) emanation. As a driving force for growth of the large holes we identified oxygen diffusion from the Si/SiO2 interface to the bare Si surface. This surface is a sink of oxygen diffusion due to the emanation of volatile SiO, whereas the Si/SiO2 interface serves as an oxygen source. The predicted mechanism is consistent with the geometry of the holes in the SiO2 layer.

Keywords: oxygen-vacancy; Si self-diffusion; SiO; dissociation; SiO2

  • Journal of Applied Physics 101(2007), 053516

Publ.-Id: 8926

Identification of actinide molecule complexes: A new vibrational spectroscopic approach at the free electron laser facility FELBE

Foerstendorf, H.; Seidel, W.; Heim, K.; Bernhard, G.

The free electron laser (FEL) facility at the electron linear accelerator ELBE of the Forschungszentrum Rossendorf, Dresden, Germany, provides an optical laboratory which is suitable for spectroscopic investigations in actinide research. For the first time a great number of actinide elements which are currently in the focus of scientific work in the field of radioecology can now be investigated with laser spectroscopic techniques using infrared FEL radiation. The facility is also open for external users. In this work we present our first results of vibrational spectroscopic experiments for the identification of actinide molecule complexes by Photothermal Beam Deflection (PTBD) spectroscopy using an FEL as a coherent pulsed pump source which can be tuned throughout a broad wavelength range of interest. We demonstrate that reliable absorption spectra of test samples containing uranyl and neptunyl compounds can be obtained which was verified by conventional FT-IR spectroscopy. A prominent feature of photothermal techniques is the capability of detection of low absorptions. Therefore we tried to evaluate the minimum content of actinide ions which can still be detected by our setup of the vibrational PTBD spectroscopic experiment. It was found that the limit is obviously given by the background absorption of the hygroscopic KBr matrix of the samples which is originated by residual water. Furthermore, we present an overview about the technical equipment of the laboratory.

Publ.-Id: 8923

Identification of fluorescent U(V) and U(VI) microparticles in a multispecies biofilm by confocal laser scanning microscopy and fluorescence spectroscopy

Großmann, K.; Arnold, T.; Krawczyk-Bärsch, E.; Diessner, S.; Wobus, A.; Bernhard, G.; Krawitz, R.

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 43 µm thick living multispecies biofilm grown on biotite plates. These particles differ between 1-7 µm in diameter and were located at the bottom of the biofilm in the boundary region of high and low bacterial density. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415 to 475 nm, indicative for uranium(V), or in the range of 480 to 560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilm. 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 was involved.

  • Environmental Science & Technology 41(2007)18, 6498-6504

Publ.-Id: 8922

Materials for Tomorrow

Gemming, S.; Schreiber, M.; Suck, J.-B.; (Editors)

Material science has taken a key position for new technical developments, and is therefore strongly supported by industry and governments. It has nowadays a position between physics, chemistry and engineering and extends from basic science in physics and chemistry on atomic scale to large scale applications in industry. An increasing number of material science study courses at
universities underlines the present and future importance of understanding and developing materials for the future. Looking at
the industry with one of the fastest development at present, the communication industry, it is obvious that a large part of the actual research for future materials is devoted to the understanding of materials to be used in devises developed on the nanometer (nm) scale.

The contributions to this book grew out of the lectures given at the Heraeus Ferien Kurs on materials for today, tomorrow and beyond, held at the University of Technology Chemnitz in October 2004. As the lectures were given to students of different origin (physics, chemistry, material science), the articles not only contain our todays knowledge in each of the fields, but make reference also to basic facts needed for their understanding. Thus the articles combine a presentation of the present research in the field with some basis information on a text book level; they bridge the gap between specialized reviews and study books. In addition, lectures on material simulation, a very fast advancing discipline, are combined with lectures on experimental research in material science, and the techniques used in both of these disciplines.

Keywords: materials design; materials modelling; measuring materials properties

  • Book (Editorship)
    Berlin - Heidelberg - New York: Springer, 2007
    212 Seiten
    ISBN: 978-3-540-47970-3

Publ.-Id: 8921

Simulation of Inorganic Nanotubes

Enyashin, A. N.; Gemming, S.; Seifert, G.

Motivated by the high application potential of carbon nanotubes, the search for other quasi one-dimensional nanostructures has been pursued both by theoretical and experimental approaches. The investigations soon concentrated on layered inorganic materials, which may be exfoliated and rolled up to tubular and scroll-type forms. The present chapter reviews the basic design principles, which govern the search for novel inorganic nanostructures on the basis of energy- and strain-related stability criteria.
These principles are then applied to the prediction and characterisation of the properties of non-carbon, elemental and binary nanotubes derived from layered boride, nitride, and sulfide bulk phases. Finally, the present chapter introduces examples, where one-dimensional nanostructures such as tubes and scrolls have successfully been constructed from non-layered materials, especially from oxides. Examples for the experimental verification of the predicted structures are given throughout the discussion and impressively underline the predictive power of today's materials modelling.

Keywords: nanostructures; quantum-mechanical methods; materials design; nanotubes

  • Contribution to external collection
    Sibylle Gemming, Michael Schreiber, Jens-Boie Suck: Materials for Tomorrow, Berlin - Heidelberg - New York: Springer, 2007, 978-3-540-47970-3, 33-57

Publ.-Id: 8920

Theoretical Investigation of Interfaces

Gemming, S.; Schreiber, M.

The proper treatment of defects is one of the major tasks in materials design, because defects are responsible for the either desirable or detrimental deviations between the characteristics of the material to be tuned and the well-known properties of an ideal crystal. Microelectronic devices work because of clever point defect engineering, line defects govern plastic deformation processes, and interfaces determine the mechanical stability of composite materials. Especially interfaces gain importance with the current trend towards nanoscale materials; first, the surface-to-volume ratio is strongly increased in nanocrystalline material, and, second, stable arrangements of point or line defects require a minimum crystallite size, which can be larger than the actual nanocrystallites. Thus, the present chapter gives an introduction into the most common approaches for modeling interface properties. We introduce the basic concepts of interface symmetry, structure and analysis with a strong focus on the theoretical methods and give an overview of currently available techniques for the modeling and simulation of the interface properties at an atomic-scale level. Two fundamentally different interface types are distinguished: The discussion of the homophase boundary properties is focussed on oxide grain boundaries, which we studied extensively in comparison with amply available experimental observations. For the heterophase boundaries examples of non-reactive, reactively doped, and inherently reactive boundaries are presented. A special focus lies on the interfaces between metals and oxides where the discrepancy of the material properties across the interface is most prominent and all three bonding situations can occur: weak adhesion between inert fragments, activated adhesion upon doping, and strong adhesion.

Keywords: interface; grain boundary; numerical methods; materials desgin

  • Contribution to external collection
    Sibylle Gemming, Michael Schreiber, Jens-Boie Suck: Materials for Tomorrow, Berlin - Heidelberg - New York: Springer, 2007, 978-3-540-47970-3, 91-122

Publ.-Id: 8919

Structural and Electronic Properties of a Mo6S8 Cluster deposited on a Au(111) Surface

Popov, I.; Gemming, S.; Seifert, G.

Atomic and electronic properties of the Mo6S8 cluster are investigated using DFT band structure calculations with pseudopotentials and a plane-wave basis set. The calculations showed that these clusters can be well bound on the surface in a potential well with degenerate local energy minima, despite a negligible net electron transfer between the two subsystems. The cluster may move freely inside this well on the surface. The cluster-surface binding is via S-Au bonds, with additional contributions of the Mo atom in the vicinity of the surface.

Keywords: adsorption; DFT; density-functional theory; cluster; metal surface

  • Physical Review B 75(2007), 245436

Publ.-Id: 8918

Biodistribution and catabolism of 18F-labeled N-epsilon-fructoselysine as a model of Amadori products

Hultsch, C.; Hellwig, M.; Pawelke, B.; Bergmann, R.; Rode, K.; Pietzsch, J.; Krause, R.; Henle, T.

Amadori products are formed in the early stage of the so-called Maillard reaction between reducing sugars and amino acids or proteins. Such nonenzymatic glycosylation may occur during the heating or storage of foods, but also under physiological conditions. N-epslion-fructoselysine is formed via this reaction between the epsilon-amino group of peptide-bound lysine and glucose. Despite the fact that, in certain heated foods, up to 50% of lysyl moieties may be modified to such lysine derivatives, up to now, very little is known about the metabolic fate of alimentary administered Amadori compounds. In the present study, N-succinimidyl-4-[18F]fluorobenzoate was used to modify N-epsilon-fructoselysine at the a-amino group of the lysyl moiety. The in vitro stability of the resulting 4-[18F]fluorobenzoylated derivative was tested in different tissue homogenates. Furthermore, the 4-[18F]fluorobenzoylated N-epsilon-fructoselysine was used in positron emission tomography studies, as well as in studies concerning biodistribution and catabolism. The results show that the 4-[18F]fluorobenzoylated N-epsilon-fructoselysine is phosphorylated in vitro, as well as in vivo. This phosphorylation is caused by fructosamine 3-kinases and occurs in vivo, particularly in the kidneys. Despite the action of these enzymes, it was shown that a large part of the intravenously applied radiolabeled N-epsilon-fructoselysine was excreted nearly unchanged in the urine. Therefore, it was concluded that the predominant part of peptide-bound lysine that was fructosylated during food processing is not available for nutrition.

Keywords: N-epsilon-fructoselysine; Maillard reaction; Amadori products; Fructosamine 3-kinase; Positron emission tomography

Publ.-Id: 8917

The Rossendorf Beamline at ESRF: An XAS Experimental Station for Actinide Research

Scheinost, A.; Hennig, C.; Funke, H.; Rossberg, A.; Bernhard, G.

The Rossendorf Beamline with its X-ray absorption spectroscopy (XAS) station dedicated to actinide research was the first of its kind at a European synchrotron. Since its opening in 1999, it serves for about 30 experiments each year. An overview on the current status of operation modes, the technical details and on access conditions is presented.

  • Contribution to proceedings
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
    Speciation Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources: OECD, 978-92-64-99006-7, 141-149

Publ.-Id: 8916

SANS investigation of neutron-irradiated pressure vessel steels and model alloys

Bergner, F.; Ulbricht, A.

Application of small angle neutron scattering to RPV steels had to be reconsidered, when it was discovered by Atom Probe investigations that irradiation-induced clusters in RPV steels do contain Fe. It was no longer justified in general to determine the total volume fraction of clusters, as long as the magnetic moment of the Fe atoms inside the clusters is not known for sure. The aim of the talk is to compile ways out from this dilemma. The first part is devoted to selected SANS results obtained assuming non-magnetic clusters. The second part is a compilation of 5 ways to solve the questions that arise, if this assumption is not justified. In the third part it will be analyzed, which conclusions remain valid and which have to be modified. If the magnetic character of scatterers is not known in advance, SANS and 3DAP can be combined synergistically: 3DAP yields cluster composition, but sensitivity to vacancies is low. SANS (A-ratio) is particularly sensitive to the vacancy fraction.

Keywords: SANS; RPV steel

  • Invited lecture (Conferences)
    13th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM 13), 16.-20.10.2006, Tsukuba, Japan
  • Contribution to proceedings
    13th Meeting of the International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM 13), 16.-20.10.2006, Tsukuba, Japan
    Proceedings of IGRDM 13

Publ.-Id: 8915

Proteomic Insights into Metabolic Adaptations in Alcanivorax borkumensis Induced by Alkane Utilization

Sabirova, J.; Ferrer, M.; Regenhardt, D.; Timmis, K.; Golyshin, P.

Alcanivorax borkumensis is a ubiquitous marine petroleum oil-degrading bacterium with an unusual physiology specialized for alkane metabolism. This “hydrocarbonoclastic” bacterium degrades an exceptionally broad range of alkane hydrocarbons but few other substrates. The proteomic analysis presented here reveals metabolic features of the hydrocarbonoclastic lifestyle. Specifically, hexadecane-grown and pyruvate-grown cells differed in the expression of 97 cytoplasmic and membrane-associated proteins whose genes appeared to be components of 46 putative operon structures. Membrane proteins up-regulated in alkane-grown cells included three enzyme systems able to convert alkanes via terminal oxidation to fatty acids, namely, enzymes encoded by the well-known alkB1 gene cluster and two new alkane hydroxylating systems, a P450 cytochrome monooxygenase and a putative flavin-binding monooxygenase, and enzymes mediating -oxidation of fatty acids. Cytoplasmic proteins up-regulated in hexadecane-grown cells reflect a central metabolism based on a fatty acid diet, namely, enzymes of the glyoxylate bypass and of the gluconeogenesis pathway, able to provide key metabolic intermediates, like phosphoenolpyruvate, from fatty acids. They also include enzymes for synthesis of riboflavin and of unsaturated fatty acids and cardiolipin, which presumably reflect membrane restructuring required for membranes to adapt to perturbations induced by the massive influx of alkane oxidation enzymes. Ancillary functions up-regulated included the lipoprotein releasing system (Lol), presumably associated with biosurfactant release, and polyhydroxyalkanoate synthesis enzymes associated with carbon storage under conditions of carbon surfeit. The existence of three different alkane-oxidizing systems is consistent with the broad range of oil hydrocarbons degraded by A. borkumensis and its ecological success in oil-contaminated marine habitats.

Publ.-Id: 8914

Genome sequence of the ubiquitous hydrocarbon-degrading marine bacterium Alcanivorax borkumensis

Schneiker, S.; Martins Dos Santos, V.; Bartels, D.; Bekel, T.; Brecht, M.; Buhrmester, J.; Chernikova, T.; Denaro, R.; Ferrer, M.; Gertler, C.; Regenhardt, D.

AAlcanivorax borkumensis is a cosmopolitan marine bacterium that uses oil hydrocarbons as its exclusive source of carbon and energy. Although barely detectable in unpolluted environments, A. borkumensis becomes the dominant microbe in oil-polluted waters. A. borkumensis SK2 has a streamlined genome with a paucity of mobile genetic elements and energy generation–related genes, but with a plethora of genes accounting for its wide hydrocarbon substrate range and efficient oil-degradation capabilities. The genome further specifies systems for scavenging of nutrients, particularly organic and inorganic nitrogen and oligo-elements, biofilm formation at the oil-water interface, biosurfactant production and niche-specific stress responses. The unique combination of these features provides A. borkumensis SK2 with a competitive edge in oil-polluted environments. This genome sequence provides the basis for the future design of strategies to mitigate the ecological damage caused by oil spills.

Publ.-Id: 8913

The partial waveguide resonator of the U100-FEL at FZ Rossendorf

Freitag, M.; Schlenck, R.; Seidel, W.; Willkommen, U.; Wünsch, R.; Wustmann, B.

The partial waveguide resonator of the U100-FEL at FZ-Rossendorf and its peculiarities are ilustrated.

Keywords: free-electron laser; waveguide; resonator; beam diagnostics

  • Contribution to proceedings
    28th International Free Electron Laser Conference, 27.08.-01.09.2006, Berlin, Germany
    The partial-waveguide resonator of the U100-FEL at FZ Rossendorf
  • Poster
    28th Int. Free Electron Laser Conference, 27.08.-01.09.2006, Berlin, Germany

Publ.-Id: 8912

Development of a neutron time-of-flight source at the ELBE accelerator

Klug, J.; Altstadt, E.; Beckert, C.; Beyer, R.; Freiesleben, H.; Galindo, V.; Greschner, M.; Grosse, E.; Junghans, A. R.; Légrády, D.; Naumann, B.; Noack, K.; Schilling, K. D.; Schlenk, R.; Schneider, S.; Seidel, K.; Wagner, A.; Weiss, F.-P.

The ELBE electron beam at Forschungszentrum Rossendorf, Dresden, with energies up to 40 MeV, will be used to produce intense neutron beams. The neutron radiator consists of a liquid lead circuit where bremsstrahlung photons created by the electrons produce neutrons in (gamma,n) reactions. The short beam pulses (5 ps) provide the basis for an excellent time resolution for neutron time-of-flight experiments, giving an energy resolution of about 1 % with a flight path of 4 m. The neutron beam is shaped by a 2.4 m long collimator. The usable energy range is from 50 keV up to 10 MeV when ELBE delivers a beam repetition rate of 0.5 MHz. In this energy interval, there is a need for neutron cross section measurements relevant for the transmutation of minor actinides in nuclear waste, as well as for applications to fission and fusion reactors. The neutron flux at the sample position is 10^7 cm^-2 s^-1. Different detector types are being developed. For neutron capture gamma rays, a BaF2 scintillation detector array of 42 crystals is being constructed, whereas for neutron detection, an up to 1 m^2 large plastic scintillator wall consisting of 1 cm thick scintillation panels is being built.

  • Contribution to proceedings
    International Workshop on Fast Neutron Detectors and Applications, 03.-06.04.2006, Cape Town, South Africa
    Proceedings of Science, (FNDA2006) 015, Italy
  • Lecture (Conference)
    International Workshop on Fast Neutron Detectors and Applications, 03.-06.04.2006, Cape Town, South Africa

Publ.-Id: 8911

Study of Partial Waveguide rf-Linac FELs for Intense THz-Pulse Generation

Tecimer, M.; Oepts, D.; Wünsch, R.; Gover, A.

In this paper we present a time domain analysis of a short pulse partial-waveguide FEL oscillator employing toroidal mirrors and a hole outcoupling. The use of toroidal mirrors with optimized radius of curvature helps to reduce cavity losses arising from the mismatch of the free space propagating optical field into a waveguided one. We introduce semi-analytical expressions for the calculation of the scattering matrix elements describing the loss and mode coupling mechanism as well as the amount of the extracted power from the cavity. The formulation is implemented in a time domain FEL code based on modal expansion approach. The described model is applied to a partial waveguide FEL system and simulation results are compared with measurements.

Keywords: free-electron laser; partial waveguide FEL; THz-pulse generation

  • Nuclear Instruments and Methods in Physics Research A 528(2004), 139-145

Publ.-Id: 8910

Metastable, epitaxial PrCo7 films with high energy product

Patra, A. K.; Neu, V.; Fähler, S.; Grötzschel, R.; Schultz, L.

Epitaxial Pr–Co films with a nominal composition of Pr2Co17 have been prepared on a Cr buffered MgO (110) substrate. Pole figures and magnetic measurements reveal that these Pr–Co films crystallize in a metastable disordered hexagonal PrCo7 phase (TbCu7 type) rather than an ordered rhombohedral Pr2Co17 phase (Th2Zn17 type). Consequently high uniaxial anisotropy at room temperature is observed instead of the planar anisotropy expected for the rhombohedral phase. The energy density obtained in the nonequilibrium Pr–Co films is (BH)max=277 kJ/m3, which exceeds the (BH)max values of single phase Sm–Co films and Sm–Co/Fe and Pr–Co/Co multilayers.

  • Applied Physics Letters 89(2006), 142512

Publ.-Id: 8908

Protein Oxidation and Disease 2006. In: Protein Oxidation and Disease, Recent Research Developments in Pathological Biochemistry 1

Pietzsch, J.; (Editor)

Since the pioneering studies on oxidative modification of proteins exposed to ionizing radiation by swallow, Garrison, Schuessler, and colleagues and on oxidative inactivation of enzymes by metal-catalyzed oxidation systems by Earl Stadtman's group and colleagues, recent progresses in life sciences have led to the development of a range of excellent methods and experimental approaches and procedures that enable an always more detailed investigation and evaluation of the phenomenon of Protein Oxidation at both the micro- and macrostructural level under physiological and pathophysiological conditions, respectively. In this line, this volume "Protein Oxidation and Disease" assesses critically recent evidence that underpins the argument that oxidative damage to proteins is a significant causative or associated factor in aging as well as the etiology, progression, and manifestation of various human diseases.

  • Book (Editorship)
    Trivandrum, India: Research Signpost, 2006
    389 Seiten
    ISBN: 81-308-0028-4

Publ.-Id: 8907

Assessment of Lung Cancer Perfusion by Using Patlak Analysis: What Do We Measure?

van den Hoff, J.

kein Abstract verfügbar

  • Radiology 243(2007)3, 907-908

Publ.-Id: 8906

Blood Flow Quantification with Permeable Contrast Agents: A Valid Technique?

van den Hoff, J.

kein Abstract verfügbar

  • Radiology 243(2007)3, 909-910

Publ.-Id: 8905

Modeling of Focused-Ion-Beam-based Synthesis of Nanowire Structures

Röntzsch, L.; Heinig, K.-H.

Reaction pathways of a novel method to fabricate nanowires (NWs) using focused ion beams (FIBs) are presented. This investigation is based on an extension of TRIM simulations to realistic FIB profiles and on kinetic Monte Carlo simulations by which post-implantation phase separation is described. A focused ion implantation along a straight line leads to local supersaturation of the implanted species in the substrate. During post-implantation annealing, NWs embedded in the substrate form along the implantation trace if the ion fluence was sufficiently high. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. During long-term thermal annealing, NWs disintegrate into regular chains of nanoparticles (Rayleigh instability). Thus, regular chains of metallic nanoparticles can be fabricated which are applicable as surface-plasmon-polariton (SPP) waveguides. Even complex structures involving several NWs, e.g. T- or X-junctions, may be obtained. Crossing points, corners and ends of NWs are subject to a preferential disintegration. Thus, structures suitable for single-electron-transistors may be realized where an isolated nanocluster is located in a tunnel distance from several NW contacts. Moreover, multi-gate NW field effect transistors are predicted to form by crossing FIB traces of different ion fluences.

Keywords: ion beam synthesis; nanowire; kinetic Monte Carlo; phase separation

  • Lecture (Conference)
    15th International Conference on Ion Beam Modification of Materials, 17.-22.09.2006, Taormina, Italien

Publ.-Id: 8904

Synthesis of biologically active substances in Medicinal Chemistry and the development of a new rhenium chelating system for application in radiopharmaceutical science

Heinrich, T.

kein Abstract verfügbar

  • Lecture (others)
    Nuclear Medicine Rounds, 19.06.2006, Boston, USA

Publ.-Id: 8903

Investigation of single-crystals of chromium implanted with 119Sn – ions of various energies

Cieslak, J.; Dubiel, S. M.; Eichhorn, F.; Menzel, M.; Reuther, H.

Single-crystals of chromium doped with 10E16 119Sn ions per cm2 and energies ranging between 45 keV and 190 keV were investigated with conversion electron Mössbauer spectroscopy (CEMS), Auger electron spectroscopy (AES), grazing angle X-ray diffraction (GAXRD), and scanning electron microscopy (SEM). The Mössbauer spectra were found to be significantly different than those of the bulk. Both the maximum and the average hf. field values were higher by a factor of ~ 3 than the corresponding quantities for the bulk. The overall shape of the spectra is also different. GAXRD study has revealed that the near-surface zone of the investigated samples has a nanocrystalline structure with the average size of grains ranging between ~ 20 nm and ~ 40 nm. The latter seems to be the main reason for the observed enhancement of the spin-density and its distortion.

  • Poster
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy
  • Lecture (Conference)
    15th International Conference on Solid Compounds of Transition Elements, 15.-20.07.2006, Krakow, Poland

Publ.-Id: 8902

Ion induced nanopatterns on semiconductors: formation and application

Keller, A.; Roßbach, S.; Facsko, S.; Möller, W.

It is well known that under certain conditions, low and medium energy (typically 0.1 – 100 keV) ion sputtering can induce the formation of self-organized patterns on the irradiated surface [1]. Periodic ripple patterns and hexagonally ordered dot arrays form for oblique and normal ion incidence, respectively. The periodicity of the patterns depends on the sputtering conditions and ranges from some ten nanometres up to several microns. These structures were found on a large variety of materials, such as semiconductors, metals, and insulating surfaces [2]. The first attempt to describe the formation process was made by Bradley and Harper and led to a continuum model based on sputter theory [3].
In this framework, the patterns result from the interplay between curvature dependent sputter yield and diffusion.
To investigate the process of pattern formation, semiconductor surfaces are eroded by sub-keV Ar ions. The topography of the sputtered surfaces is studied by ex-situ atomic force microscopy (AFM).
Off-normal ion erosion of Si creates ripple patterns with a wavelength ranging from 20 nm to 60 nm and amplitude of approximately 2 nm. By means of normal incidence bombardment, well ordered dot arrays are fabricated on GaSb. These arrays exhibit hexagonal symmetry and a periodicity of the order of 40 nm. The amplitude is of the same magnitude as the periodicity. The formation process will be discussed in detail and recent results of our studies on pattern evolution and the influence of boundary conditions are presented.
As a promising application, erosion induced surface patterns can be used as templates in further processes such as molecular beam epitaxy or sputter deposition. The morphological anisotropy of the surface can influence the process significantly. Recent findings of investigations on ripple induced anisotropies in metallic thin films are presented.

[1]M. Navez, D. Chaperot and C. Sella, C. R. Acad. Sci. 254, 240 (1962)
[2]U. Valbusa, C. Boragno and F. Buatier de Mongeot, J. Phys.: Condens. Matter 14, 8153 (2002)
[3]R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)

  • Lecture (Conference)
    16th International Workshop on Inelastic Ion-Surface Collisions, 17.-22.09.2006, Hernstein, Österreich

Publ.-Id: 8901

Simultanbestimmung von Nuklidgemischen durch Auswertung von Multielement LS-Spektren am Beispiel von Pb-210, Bi-210, Po-210 und Ra-226, U-233, Np-237

Nebelung, C.

Es wurde eine Methode entwickelt, Multinuklidproben, wie Pb-210 / Bi-210 / Po-210 oder Ra-226 / U-233 / Np-237, in nur einem Flüssigszintillations (LS)-Spektrum zu bestimmen. Zunächst werden durch a/b-Diskriminierung die a- und b-Spektren getrennt. Im Anschluss daran werden die a- bzw. b-strahlenden Nuklide mittels Pekfitting entfaltet. Die a-Peaks lassen sich am besten mit einer speziellen Peakfittingfunktion beschreiben, die auf der niederenergetischen Seite von der reinen Gaussform abweicht und durch einen exponentiellen Term ersetzt wird. b-Peaks mit geringer Halbwertsbreite werden auch mit dieser Peakfittingfunktion entfaltet, Peaks mit großer Halbwertsbreite durch eine Bi-Gauss-Funktion.
Im System Pb-210 / Bi-210 / Po-210 ist der Spektrenauswertung mit einem a-Strahler Po-210, und zwei b-Strahlern Pb-210 und Bi-210, deren Spektren sich nur geringfügig überlappen recht einfach. Schwieriger ist das im System Ra-226 / U-233 / Np-237, deren Peaks so nah beieinander liegen (4,8 MeV), dass sie durch Peakfitting nicht separiert werden können. Die Bestimmung erfolgt über die b-Tochter von Np-237: Pa-233 und die a-Töchter von Ra-226: Rn-222, Po-218 and Po-214. Als erstes wird Np-237 über Pa-233 bestimmt (Aktivitäten im Gleichgewicht: 1 zu 1, allerdings müssen die b-Töchter von Ra-226 berücksichtigt werden). 5-6 Wochen nach der Probenpräparation, wenn Ra-226 im Gleichgewicht mit den kurzlebigen a-Töchtern ist, wird die Probe erneut gemessen. Aus dem einzeln stehenden Po-214 Peak bei 7.7 MeV wird der Ra-226-Gehalt bestimmt. Zuletzt wird U-233 aus der Differenz Gesamtpeak (bei 4.8 MeV) minus Np-237 und Ra-226 ermittelt.

Keywords: Pb-210; Bi-210; Po-210; Ra-226; U-233; Np-237; liquid-scintillation spectrometry; alpha-beta separation; multi-element spectra; deconvolution; mother-daughter relation

  • Lecture (Conference)
    222. PTB-Seminar, 21.11.2006, Braunschweig, Germany

Publ.-Id: 8900

Correlation between phase formation and magnetic properties of heavy ion irradiated Co/Pt bilayers

Ghosh, S.; Mäder, M.; Groetzschel, R.; Gupta, A.; Som, T.

In this letter, the authors report the correlation between the magnetic and the structural properties of 200 keV Kr and 50 keV Ar ion irradiated Co/Pt bilayer samples at different temperatures and fluences. They observe irradiation induced formation of stable Co–Pt phases, which appears to be more prominent at higher irradiation temperatures. A large shape anisotropy in the hysteresis loop is also observed when irradiated at higher temperatures, which could be indicative of a magnetization reversal. A CoPt ordered/disordered phase formation leads to the enhancement in the coercivity. The sequence of phase formations is predicted by the heat of formation rule.

Publ.-Id: 8898

Phase formation within Au and Ge nanoislands by room temperature ion irradiation

Som, T.; Satpati, B.; Prokert, F.; Cantelli, V.; Kabiraj, D.

We investigate the effects of room-temperature irradiation of Au and Ge nanoislands grown on Si. Our studies show the formation of Au-Ge alloy phase within the islands and wetting of the substrate. High-resolution transmission electron microscopy along with synchrotron radiation-based x-ray reflectivity and grazing incidence x-ray diffraction measurements were performed to characterize the irradiation-induced changes brought into the sequentially deposited Au and Ge island thin films. The results are attributed to the recoil implantation and the transient melting of the nanoislands followed by the formation of crystalline alloy phase.

  • Nanotechnology 17(2006)20, 5248-5253

Publ.-Id: 8897

Atomic-level simulations of epitaxial recrystallization and amorphous-to-crystalline transition in 4H-SiC

Gao, F.; Zhang, Y.; Posselt, M.; Weber, W. J.

The amorphous-to-crystalline transition in 4H-SiC has been studied using molecular dynamics (MD) methods, with simulation times of up to a few hundred ns and at temperatures ranging from 1000 to 2000 K. Two nanosized amorphous layers, one with the normal of the a-c interfaces along the [-12-10] direction and the other along the [-1010] direction, were created within a crystalline cell to study epitaxial recrystallization and the formation of secondary phases. The recovery of bond defects at the interfaces is an important process driving the epitaxial recrystallization of the amorphous layers. The amorphous layer with the a-c interface normal along the [-12-10] direction can be completely recrystallized at temperatures of 1500 and 2000 K, but the recrystallized region is defected with dislocations and stacking faults. On the other hand, the recrystallization process for the a-c interface normal along the [-1010] direction is hindered by the nucleation of polycrystalline phases, and these secondary phases are stable for longer simulation times. A general method to calculate activation energy spectra is employed to analyze the MD annealing simulations, and the recrystallization mechanism in SiC consists of multiple stages with activation energies ranging from 0.8 to 1.7 eV.

Keywords: SiC; recrystallization; computer simulation

  • Physical Review B 74(2006), 104108

Publ.-Id: 8896

Application of rate theory modelling to neutron-irradiated low-Cu and Cu-enriched Fe-based model alloys

Bergner, F.

Rate theory (RT) is a mean-field approach focussed on the long-term evolution of precipitates or clusters of defects and/or solute atoms in the present case. Interactions between any one particular cluster and particular cluster-forming species are replaced by average interactions. Therefore, any space variables drop out and the temporal evolution of the size distribution is at the centre of interest. On the one hand, the assumptions may not be completely valid in the case of displacement cascades and special attention has to be paid to the initial conditions and to the source term. On the other hand, RT allows the evolution of the cluster size distribution to be followed over time intervals corresponding to the operation of a reactor pressure vessel up to end-of-life within reasonable computation time. As a second advantage, cluster size distributions measured by means of small-angle neutron scattering (SANS) are well suited for the experimental validation of RT models.

Application of RT to three particular systems exposed to neutron irradiation will be considered in the presentation:
• the coupled evolution of the concentrations of single vacancies and single self-interstitial atoms (SIAs) in Fe,
• the evolution of the size distribution of vacancy clusters in Fe,
• and the evolution of pure coherent Cu clusters in dilute Fe-Cu.
Special emphasis will be placed on the aspect of experimental validation using SANS results obtained for low-Cu and Cu-enriched Fe-based model alloys. The problem of multi-component clusters will be touched in the outlook.

The first maximum at cluster sizes of about 0.3 nm is caused by the direct generation of small clusters due to neutron irradiation. After some ten days of irradiation a second peak appears, which becomes more and more dominant. It is observed that:

• the shape of the size distribution is rather independent of the model parameters,
• the rate of cluster growth is essentially influenced by sink strength for vacancies and interstitials only,
• and the volume fraction at a given instant of time is influenced by both sink strength and surface tension of Fe.

From these findings a strategy that allows for fitting the calculated size distribution to SANS data is worked out. However, it turns out that even in low-Cu Fe-based alloys except pure Fe the average cluster detected by means of SANS is not a pure vacancy cluster. Comparability is therefore limited and a concept to deal with two- or multi-component clusters is required.

  • Invited lecture (Conferences)
    International School on Experimental Quantification of Irradiation Damage (ISQUID), 25.-29.09.2006, Rochehaut sur Semois, Belgium
  • Contribution to proceedings
    International School on Experimental Quantification of Irradiation Damage (ISQUID), 25.-29.09.2006, Rochehaut sur Semois, Belgium
    Proceedings on CD, Mol: SCK-CEN, 1-47

Publ.-Id: 8895

Application of small-angle neutron scattering (SANS) to irradiated pressure vessel steels and iron based model alloys

Ulbricht, A.

It is known that fast neutron irradiation induces nanometre-sized defects in reactor pressure vessel (RPV) steels. SANS can detect changes of microstructure on such a small size scale and operates as volume integrating measuring method, i.e. statistically reliable mean values can be determined.

Purpose of the talk is to describe preparation, measuring procedure and raw-data treatment of a SANS experiment as well as data interpretation considering as example the analysis of irradiation-induced defect/solute clusters in RPV steels and iron alloys. Preparation covers not only preparation and transport of radioactive specimen but also to submit a scientific proposal to get access to a SANS facility. Part of the measuring procedure and data treatment are absolute calibration, background correction etc.

A particular example for the application of SANS in the field of RPV steels is sketched below. More examples will be outlined in the presentation. Fig. 1 shows a SANS image recorded by an two-dimensional position-sensitive detector consisting of 64x64 cells with a size of 1x1 cm^2. It was obtained for a Fe-based alloy placed in a saturation magnetic field. The scattering vector, Q, is proportional to the scattering angle. The anisotropic scattering pattern is caused by the magnetic field and can be used to separate magnetic and nuclear scattering contributions.

The measured dependence of the scattered intensity on scattering vector (also called scattering curve) is presented in Fig. 2 for an RPV steel in two different irradiation conditions and the unirradiated reference state. An increase of the scattered intensity is observed in the range Q > 0.5 nm^-1. This increase is caused by irradiation-induced defect/solute clusters. The size distribution of these clusters is obtained by Fourier transformation of the scattering curve. The underlying assumptions will be discussed in the talk. The calculated size distribution of the irradiation-induced clusters is shown in Fig. 3.

The basic findings of this experiment are a volume fraction of clusters, which increases with neutron fluence and a mean cluster radius of about 1 nm independent of neutron fluence.

Keywords: small-angle neutron scattering; reactor pressure vessel steel; iron alloy; irradiation damage

  • Invited lecture (Conferences)
    International School on Experimental Quantification of Irradiation Damage (ISQUID), 25.-29.09.2006, Rochehaut sur Semois, Belgium
  • Contribution to proceedings
    International School on Experimental Quantification of Irradiation Damage (ISQUID), 25.-29.09.2006, Rochehaut sur Semois, Belgium

Publ.-Id: 8894

The synthesized hot ion plasmoid experiment at GDT

Anikeev, A. V.; Bagryansky, P. A.; Deichuli, P. P.; Ivanov, A. A.; Kireenko, A. V.; Lizunov, A. A.; Murakhtin, S. V.; Prikhodko, V. V.; Solomakhin, A. L.; Sorokhin, A. V.; Stupishin, N. V.; Collatz, S.; Noack, K.

At present, the GDT experimental facility of the Budker Institute Novosibirsk is upgraded. The construction of the hot ion plasmoid experiment is one part of the upgrade. First experiments with low parameters were carried out and compared with the results of pre-calculations. The paper gives an overview on the present stage of the experiment and on next research activities. The main results are: - The maximal fast ion density was three times greater than the warm ion density. - No evidence of MHD or micro-instabilities was observed, therefore, it can be concluded that the fast ion confinement is fully controlled by Coulomb collisions and charge-exchange. - The feasibility of ambipolar plugging in gas dynamic traps was demonstrated.

Keywords: mirror plasma confinement; gas dynamic trap; GDT experiment; hot ion plasmoid; neutral beam injection

  • Lecture (Conference)
    6th International Conference on Open Magnetic Systems for Plasma Confinement, 17.-21.07.2006, Tsukuba, Japan
  • Fusion Science and Technology 51(2007), 79-81

Publ.-Id: 8893

Induced anisotropies in exchange coupled systems on rippled substrates

Liedke, M. O.; Liedke, B.; Keller, A.; Hillebrands, B.; Mücklich, A.; Facsko, S.; Fassbender, J.

The role of monoatomic steps at the mutual interface between a ferromagnetic and an antiferromagnetic layer in a Ni81Fe19/Fe50Mn50 exchange bias system is enlightened. As a result of the reduced coordination at the step edges a strong uniaxial anisotropy is induced in the polycrystalline Ni81Fe19 layer, which is fixed in its orientation. By means of different field annealing cycles the direction of the induced unidirectional anisotropy can be chosen. For all mutual orientations both anisotropy contributions are superimposed independently and the angular dependence of the magnetization reversal behavior can be described perfectly by a coherent rotation model with one parameter set. In addition it is demonstrated that not only the magnitude of the uniaxial anisotropy contribution but also that of the unidirectional one scales with the step density of the substrate, which is in full agreement with theoretical predictions.

Keywords: magnetism; magnetic anisotropy; exchange bias; ripples; ion erosion; templates

  • Physical Review B 75(2007), 220407(R)

Publ.-Id: 8892

High-temperature induced nano-crystal formation in ion beam-induced amorphous sili-con ripples

Grenzer, J.; Mücklich, A.; Grigorian, S.; Pietsch, U.; Datta, D.; Chini, T. K.; Hazra, S.; Sanyal, M. K.

We report on in-situ investigations of a recrystallization process of an ion beam-induced rip-pled silicon. The one dimensional ripple structure was created by 40Ar+ ion irradiation with dose of ~5x1017 ions/cm2 under an angle 60° with respect to the surface normal at an energy of 60 keV. At the surface the induced ripples have a period and an amplitude of about 915nm and 80nm, respectively. Structure and morphology of ripples were studied by two x-ray grazing in-cidence scattering methods, transmission electron microscopy and atomic force microscopy. X-ray grazing-incidence amorphous scattering pattern were recorded in-situ in a range from 250°C to 750°C. Up to about 500°C mainly we found a single broad scattering maximum cor-responding to the Si(111) inter-planar distances. At higher temperature these peaks becomes sharp and intense indicating the onset of a re-crystallization process in the amorphous top layer.
Two processes were found, a formation of crystalline islands at the top of amorphous surface ripples and a growth of polycrystalline twins close to the former amorphous-crystalline inter-face.

Keywords: grazing incidence amorphous scattering and diffraction; ion beam irradiation; self organized ripples

Publ.-Id: 8891

Bruchmechanische Charakterisierung von WWER-440 Reaktordruckbehälterstählen des Blockes 8 KKW Greifswald

Viehrig, H.-W.; Murasov, M.

Der Block 8 des Kernkraftwerkes Greifswald ist ein Druckwasserreaktor russischer Bauart vom Typ WWER-440-213, dessen Reaktordruckbehälter (RDB) vom SKODA-Konzern in der früheren Tschechoslowakischen Republik Ende der 70er Jahre hergestellt worden ist. Dieser Reaktorblock wurde nicht in Betrieb genommen und der RDB beim Rückbau zerlegt. Im Forschungszentrum Rossendorf sind Grundwerkstoff 15Kh2MFA und Schweißgut 10KhMFT dieses RDB untersucht worden. An Proben aus unterschiedlichen Schmiederingen und Schweißnähten sind Charpy-V-, Bruchzähigkeits- und Zugversuche durchgeführt worden, wobei der Schwerpunkt auf der Ermittlung von Bruchzähigkeiten nach ASTM E1921 und E1820 lag.
Die auf dem “Master-Curve” (MC)-Konzept basierende ASTM-Prüfvorschrift E1921 ist für die Ermittlung einer Referenztemperatur T0 homogener Stähle mit einer kubisch-raumzentrierten Grundstruktur konzipiert. Die Referenztemperatur T0 wird aus einem Datensatz von Bruchzähigkeiten KJc berechnet, die im unteren spröd-duktilen-Übergangsbereich beim Einsatz von Spaltbruch gemessen werden. Insbesondere große und dickwandige Schmiederinge für RDB sind makroskopisch oft nicht homogen. Aus diesem Grund wurden auf dem MC-Konzept basierende Verfahren entwickelt, mit denen sich Referenztemperaturen von Stähle ermitteln lassen, die makroskopisch inhomogen sind. Die SINTAP-Prozedur enthält eine solche Modifikation, die es erlaubt, eine konservative untere Grenzkurve der MC zu bestimmen, welche den spröden Bestandteil widerspiegelt. Mit zwei neuen Erweiterungen des Master-Curve-Ansatzes können Datensätze ausgewertet werden, welche zwei unterschiedliche Bestandteile (bimodal) und zufällig verteilte (random) Inhomogenitäten enthalten.
Mit Proben aus RDB-Grundwerkstoff 15Kh2MFA und Schweißgut 10KhMFT gemessene KJc-Werte sind nach der Standard MC-Methode und den modifizierten MC-Ansätzen ausgewertet worden. Während die KJc- Werte des Schweißgutes nahezu vollständig von der 5%-Fractilen eingehüllt werden, zeigen die KJc-Werte der Grundwerkstoffe ein große Streuung. Dabei liegen deutlich mehr als 5% der KJc-Werte unterhalb der 5%-Fraktilen. Metallographische und fraktographische Untersuchungen zeigen, dass der untersuchte RDB-Grundwerkstoff makroskopisch inhomogen ist und ca. 15 bis 20% interkristalline Spaltflächen in der Bruchfläche zeigt. Die Datensätze der Grundwerkstoffe wurden mit dem Random-MC-Ansatz ausgewertet. Mit diesem Ansatz konnte eine Referenztemperatur T0 und 5%-und 95%-Fraktile berechnet werden, welche die KJc-Datensätze dieser inhomogenen Grundwerkstoffe gut wiedergeben.
Mit dem hier vorgestellten Beispiel wird gezeigt, dass eine kritische Bewertung von nach ASTM E1921 ermittelten Referenztemperaturen notwendig ist. Insbesondere bei kleinen Datensätzen wird eine fraktographische Validierung der Prüfergebnisse für notwendig erachtet.
The Master Curve (MC) approach used to measure the transition temperature, T0, was standardized first-time in the ASTM Standard Test Method E1921 in 1997. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centred cubic (ferritic) structure only. In reality, due to the manufacturing process, the steels in question are seldom fully macroscopically homogeneous.
Charpy size SE(B) specimens of base and weld metal from the WWER-440 Greifswald Unit 8 RPV were tested according to the ASTM test standard E1921-05. The measured fracture toughness values at brittle failure (KJc) of the specimens show a large scatter. In general the KJc values of the RPV weld and base metal follow the trend of the MC. For two base metals more than 5% of the KJc values lie below the 5% fracture probability line. It is therefore suspected that the investigated WWER-440 RPV base material is macroscopically inhomogeneous. In this paper, two recent extensions of the MC for inhomogeneous material are applied on these fracture toughness data and the nature of inhomogeneity was investigated.

Keywords: reactor pressure vessel steel; fracture toughness; Master Curve approach; inhomogeneous material; random inhomogeneity; maximum likelihood procedure; SINTAP procedure

  • Lecture (Conference)
    32. MPA-Seminar “Werkstoff- & Bauteilverhalten in der Energie- & Anlagentechnik” 5. und 6. Oktober 2006, Stuttgart, 05.-06.10.2006, Stuttgart, Germany

Publ.-Id: 8890

Review on gamma and X-ray tomography in process engineering - major groups and technical drivers -

Hampel, U.

Computed tomography is for a long time no being a valuable tool for human medical diagnostics. It has also found applications in non-destructive testing and process diagnostics. Whereas for NDT applications systems with high spatial resolution, three dimensional imaging capability and a high dynamic range of photon energies are required, the challenging parameters for process diagnostics are temporal resolution, costs and flexibility. Many groups have dedicated past and current research to the establishment of tomography imaging modilities which fullfil such requirements. However, the search has not yet been finished. The presentation gives an overview on the past and recent developments in gamma ray and X-ray tomography and discusses their potentials and drawbacks in process diagnostics.

Keywords: gamma ray tomography; X-ray tomography

  • Invited lecture (Conferences)
    Annual Meeting of the Virtual Center of Process Tomography, 05.04.2006, Hudderfield, Great Britain

Publ.-Id: 8889

Wie sicher sind Kernkraftwerke? - Stand der Sicherheitsforschung

Weiß, F.-P.; Willschütz, H.-G.

Zur Zeit werden weltweit über 440 Kernkraftwerke im kommerziellen Leistungsbetrieb eingesetzt. Die überwiegende Mehrheit sind sogenannte Leichtwasserreaktoren (LWR). Das Risiko, dass es beim Betrieb von LWR der heutigen Generation zu einem schweren Unfall (engl. Severe Accident, SA) mit partiellem oder vollständigem Abschmelzen des Reaktorkerns kommt, ist gering. Es lässt sich aber trotz umfangreicher Sicherheitsvorkehrungen nicht vollständig ausschließen.
Bei der Entwicklung und Auslegung von Kernkraftwerken wurde von Beginn an ein erhöhtes Sicherheits- beziehungsweise Schutzkonzept verfolgt, weil bekannt war, dass das radioaktive Inventar, das aus den während des Betriebs entstehenden Spalt- und Aktivierungsprodukten besteht, nicht unkontrolliert freigesetzt werden darf. Es wurde daher von vornherein ein sogenanntes Mehrstufenkonzept („defence-in-depth“) eingeführt, um die in jeder technischen Anlage auftretenden Störungen innerhalb des Kraftwerks zu beherrschen und Unfälle auszuschließen.
Das Mehrstufenkonzept besteht heute aus 4 Ebenen. Die Ebenen 1 bis 3 – Normalbetrieb, Betriebsstörungen und Auslegungsstörfälle – wurden bereits bei der Reaktorauslegung berücksichtigt und dienen der Störfallverhinderung beziehungsweise der Störfallvermeidung. Zur Vermeidung und Begrenzung von schweren Unfällen ist mit dem sogenannten „anlageninternen Notfallschutz“ nachträglich die 4. Ebene eingeführt worden.
Die Wirksamkeit des Defence-in-Depth wird zum einen durch die technische Auslegung sichergestellt. Zum anderen durch die Umsetzung der sogenannten Sicherheitskultur. Die Sicherheitskultur stellt die Gesamtheit der Eigenschaften und Einstellungen von Personen und Organisationen dar, die dafür sorgt, dass dem sicheren Anlagenbetrieb die höchste Priorität zukommt.
Ein Pfeiler der Sicherheitskultur ist die Sicherheitsforschung. In diesem Vortrag werden zwei Beispiele der aktuellen Arbeiten im Forschungszentrum Rossendorf zu sicherheitsrelevanten Fragestellungen behandelt: die sogenannten Borverdünnungstransienten und die Kernschmelzerückhaltung im Reaktordruckbehälter.
Ein kurzer Überblick über die Historie der verschiedenen Kernkraftwerksgenerationen und die Erläuterung der wesentlichen Eigenschaften der aktuell in Bau befindlichen dritten Generation sowie der heute in der internationalen Forschung betrachteten zukünftigen Reaktortypen (Generation IV) schließen den Vortrag ab.

Keywords: Safety of Nuclear Power Plants; Defence in Depth; Saftey Research; Boron Dilution Transients; In Vessel Retention; Generation III; Generation IV

  • Invited lecture (Conferences)
    Ganztagskolloquium am 28. September 2006 "50 Jahre Forschung für die friedliche Nutzung der Kernenergie", 28.09.2006, Dresden, Germany
  • Contribution to proceedings
    50 Jahre Forschung für die friedliche Nutzung der Kernenergie, 28.09.2006, Dresden, Deutschland
    Sitzungsberichte der Leibniz-Sozietät, Berlin: Leibniz-Sozietät e.V., 978-3-89626-689-7, 91-114

Publ.-Id: 8888

Zweiphasige Strömung in Kapillaren und strukturierten Packungen

Bauer, T.; Schubert, M.; Hampel, U.; Lange, R.

The presenation gives an overview on flow models for capillary flow with emphasize on reactive two-phase flows in chemical engineering problems and describes measurement methods that can be used to visualize the flow and measure certain parameters, such as void fraction, film thickness and flow velocity.

Keywords: capillary flow; two phase flow

  • Lecture (Conference)
    Multi-Phase Flow: Simulation, Experiment and Application, 26.-29.06.2006, Dresden, Germany
  • Contribution to proceedings
    Multi-Phase Flow: Simulation, Experiment and Application, 26.-29.06.2006, Dresden, Germany
    Proceedings of "Multi-Phase Flow: Simulation, Experiment and Application"

Publ.-Id: 8887

Dynamic vortex − antivortex interaction and magnetization dynamics of a single cross-tie wall

Kuepper, K.; Buess, M.; Raabe, J.; Quitmann, C.; Fassbender, J.

We report the direct investigation of the vortex-antivortex interaction by imaging the magnetic excitation spectrum of a single cross-tie wall by means of x-ray magnetic circular dichroism - photoemission electron microscopy (XMCD-PEEM). The 10 × 6 μm2 Permalloy rectangle of 20 nm thickness was excited by a short magnetic in plane pulse with a maximum field value of about 20 Oe. The high temporal and lateral resolution allows a detailed quantitative analysis of the magnetodynamic excitations. We find new eigenmodes in the frequency domain which are characteristic for the vortex-antivortex interaction in a single cross-tie wall. We discuss our experiment in the light of micromagnetic simulations.

Keywords: PACS numbers: 75.40.Gb; 75.60.-d; 75.60.Ch; 75.75.+a

  • Lecture (Conference)
    4th International Workshop on Nanoscale Spectroscopy and Nanotechnology, 17.-21.09.2006, Rathen, Germany

Publ.-Id: 8886

Electrical impedance sensors for multiphase flow measurement

Da Silva, M. J.; Schleicher, E.; Hampel, U.

For the investigation of multiphase or multicomponent flows, which are of interest for instance in the oil extraction and processing or in the chemical engineering, there are only few suitable measuring techniques. This presentation gives an overview about the recent efforts of your group in applying high-speed complex impedance measurements for the investigation of dynamic fluid flow. We present a new developed high-speed complex permittivity needle probe as well as a feasibility study for the development of a complex impedance wire-mesh sensor.

Keywords: complex permittivity measurement; heterogeneous mixture; multiphase flow; multicomponent flow; needle probe

  • Lecture (Conference)
    4th Joint FZR & ANSYS Workshop "Multiphase Flows - Simulation, Experiment and Application", 27.-29.06.2006, Dresden, Germany
  • Contribution to proceedings
    FZR & ANSYS Workshop "Multiphase Flows - Simulation, Experiment and Application", 27.-29.06.2006, Dresden, Germany

Publ.-Id: 8885

Measurement of void fraction distributions in full scale fuel element bundles using gamma ray tomography

Bieberle, A.; Schleicher, E.; Hoppe, D.; Kronenberg, J.; Hampel, U.

We introduce first results of a void fraction distribution measurement in boiling water reactor fuel element bundles. We employed a recently developed high resolution gamma ray tomography system with a collimated Cs137 isotopic source and a 320 element detector arc. The average spatial resolution of the system is 3 mm in plane and 8 mm axial. We performed transversal scans in six axial planes, with approximately 25 minutes recording time for each scan. To determine void fraction calibration measurements have been recorded at zero and one hundred percent void fraction respectively. Image reconstruction was performed with standard filtered back projection algorithms.

Keywords: gamma ray tomography; void fraction measurement

  • Contribution to proceedings
    4th International Symposium on Process Tomography, 14.-15.09.06, Warschau, Poland, 95-97
  • Lecture (Conference)
    4th International Symposium on Process Tomography, 14.-15.09.06, Warschau, Poland

Publ.-Id: 8884

Single-crystalline MgAl2O4 spinel nanotubes using a reactive and removable MgO nanowire template

Fan, H.; Knet, M.; Scholz, R.; Nielsch, K.; Pippel, E.; Hesse, D.; Gösele, U.; Zacharias, M.

Using MgO nanowires as a reactive template, we fabricated for the first time single-crystal MgAl2O4 spinel nanotubes through an interfacial solid-state reaction of MgO–Al2O3 core–shell nanowires. Single-crystal MgO nanowires are coated with a conformal thin layer of amorphous Al2O3 via atomic layer deposition. Subsequent annealing at 700 °C activates the interfacial reaction between MgO and Al2O3, transforming the alumina shell into a spinel shell. Finally, after etching away the remaining MgO core in ammonia sulfuric solution, MgAl2O4 spinel nanotubes are obtained. As a transition from conventional planar spinel layers via thin-film interface reactions, our result might open a window for the fabrication of a wide variety of MgO-based spinel one-dimensional nanostructures.

Publ.-Id: 8883

Algorithmic treatment of structure deviations in gamma ray tomography data sets

Hoppe, D.; Hampel, U.; Kronenberg, J.

The measurement of void fraction distribution in electrically heated fuel element bundles suffers from the problem of structure shifts due to thermal expansion and magnetic pinching of the constructive elements during heating. To cope with such displacement problems for subchannel void fraction determination we developed special image processing algorithms. The core feature of these algorithms is a precise tracking of the rods in the images by means of a pattern recognition algorithm. In this way rod displacements can be determined automatically. This allows us to automatically generate a sub-channel integration mask that is subsequently used to determine the void fraction values in the unaffected sub-channel areas.

Keywords: Gammy ray tomography; void measurement

  • Poster
    4th International Symposium on Process Tomography, 14.-15.09.2006, Warsaw, Poland
  • Contribution to proceedings
    4th International Symposium on Process Tomography, 14.-15.09.2006, Warsaw, Poland
    Proceedings, 83-60660-01-8, 163-164

Publ.-Id: 8882

Ultraschnelle Elektronenstrahl-Röntgentomographie

Hampel, U.

The electron beam is commonly used as a unique tool for welding of metal parts, curing and polishing of product surfaces, or sterilisation of goods. In such cases the energy of the beam is used to modify a material. A sideproduct of is X-ray radiation which is considered a hazardous side effect of the processing. However, the X-ray radiation generated by an electromagnetically steered electron beam can also be used for X-ray imaging. Thus, a sophisticated imaging technique is electron beam X-ray computed tomography that has now for more than 20 years been used in cardiac diagnostics. Our group at Institute of Safety Research at FZ Rossendorf uses this technique to perform tomography on multi phase flows. The presentation will introduce the concept that is behind this technique and demonstrate its application on industrially relevant applications.

Keywords: electron beam tomography

  • Lecture (others)
    Ehrenkolloquium des FEP Dresden für Herrn Dr. Panzer, 01.06.2006, Dresden, Germany

Publ.-Id: 8881

Gamma and X-ray tomography

Hampel, U.

The presentation gives an overview on the methods and applications of X-ray and gamma ray tomography in industrial flow measurement problems. Special emphasize will be given on recent results of system development and industrial applications at the Institute of Safety Research at FZ Rossendorf.

Keywords: gamma ray tomography; X-ray tomography

  • Invited lecture (Conferences)
    Annual Meeting of the Virtual Center of Process Tomography, 05.04.2006, Hudderfield, Great Britain

Publ.-Id: 8880

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