Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

Contactless inductive flow tomography

Stefani, F.; Gundrum, T.; Gerbeth, G.

The three-dimensional velocity field of a propeller driven liquid metal flow is reconstructed by a contactless inductive flow tomography (CIFT). The underlying theory is presented within the framework of an integral equation system that governs the magnetic field distribution in a moving electrically conducting fluid. For small magnetic Reynolds numbers this integral equation system can be cast into a linear inverse problem for the determination of the velocity field from externally measured magnetic fields. A robust reconstruction of the large scale velocity field is already achieved by applying the external magnetic field alternately in two orthogonal directions and measuring the corresponding sets of induced magnetic fields. Kelvin's theorem is exploited to regularize the resulting velocity field by using the kinetic energy of the flow as a regularizing functional. The results of the new technique are shown to be in satisfactory agreement with ultrasonic measurements.

Permalink: https://www.hzdr.de/publications/Publ-6477
Publ.-Id: 6477


Correlation between bonding structure and microstructure in fullerene-like carbon nitride thin films

Gago, R.; Jiménez, I.; Neidhardt, J.; Abendroth, B.; Caretti, I.; Hultman, L.; Möller, W.

The bonding structure of highly ordered fullerene-like (FL) carbon nitride (CNx) thin films have been assessed by x-ray absorption near edge spectroscopy (XANES). In particular, samples with different degree of FL character (in terms of graphene plane alignment, extension, and cross-linking) have been analyzed to discern spectral signatures of the microstructure formation. The XANES spectra of FL-CNx films resemble that of graphitic CNx, indicating a sp2 character for C and N atoms. However, the evolution of the FL structure is promoted with the dominance of three-fold N over pyridine-like and cyanide-like bonding environments. In addition, the p*/s* ratio at the C(1s) edge is constant, independent of the change in FL character, while it decreases ~40% at the N(1s) edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of C-sp3 hybrids with the development of FL structures and, additionally, that a different spatial localization of p electrons at C and N sites takes place in curved graphitic structures. The latter has implications for the elastic properties of graphene sheets and could as such explain the outstanding elastic properties of FL-CNx.

  • Physical Review B, 71(2005)12, 5414

Permalink: https://www.hzdr.de/publications/Publ-6476
Publ.-Id: 6476


Breakdown of Burton-Prime-Slichter approach and lateral solute segregation in radially converging flows

Priede, J.; Gerbeth, G.

A theoretical study is presented of the effect of a radially converging melt flow on the radial solute segregation in simple solidification models. We show that the classical Burton-Prim-Slichter (BPS) theory describing the effect of a diverging flow on the solute incorporation into the solidifying material breaks down for converging flows. The breakdown is caused by a divergence of the integral defining the effective boundary layer thickness which is the basic concept of the BPS theory. The divergence can formally be avoided by restricting the axial extension of the melt to a layer of finite height. This allows us to obtain radially uniform solutions for the solute distributions which, however, are valid only for weak melt flows with an axial velocity away from the solidification front comparable to the growth rate. There is a critical melt velocity for each growth rate at which the solution passes through a singularity and becomes physically inconsistent for stronger melt flows. Thus, the radially uniform solute distribution becomes incompatible with a converging flow exceeding the growth rate, and a radial segregation sets in. The solute distribution is analysed in detail for a solidification front presented by a disk of finite radius R0 subject to a converging melt flow. We obtain similarity and matched asymptotic solutions showing that the radial solute concentration depends on the radius r as ln1/3(R0/r) and ln(R0/r) close to the rim and at large distances from it, respectively. The converging flow causes a solute pile-up forming a logarithmic concentration peak at the symmetry axis which might be an undesirable feature for crystal growth processes.

  • Journal of Crystal Growth 285(2005), 261-269

Permalink: https://www.hzdr.de/publications/Publ-6475
Publ.-Id: 6475


Erneuerbare Energien: Das Beispiel Windenergie

Rindelhardt, U.

Die Nutzung der Windenergie zur Stromerzeugung hat in den letzten Jahren ein beachtliches Niveau erreicht. Im Vortrag wird der gegenwärtige technische Entwicklungsstand vorgestellt. Ferner werden die mit der Aufnahme von großen fluktuierenden Mengen Windstromes im Höchstspannungsnetz auftretenden Probleme und Konsequenzen diskutiert.

Keywords: Windenergie

  • Lecture (others)
    Antrittsvorlesung, Technische Universität Chemnitz, 04.05.2004, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-6474
Publ.-Id: 6474


Grid connected PV systems in Saxony: A ten years review

Hiller, W.; Rindelhardt, U.; Voigtländer, I.

Even in former East Germany, photovoltaic has being used increasingly for generating electricity. Through weaker buying power the absolute numbers of pv plants are far lower than in the western federal states, but a series of remarkable results was achieved nonetheless. This paper discusses the developments in the federal state Saxony.
It is based on long term results on selected photo-voltaic plants as well as data recorded by the regional electricity supplier Energieversorgung Ostsachsen (ESAG), Dresden, in 2002 and 2003 [1].

Keywords: photovoltaic plants

  • Contribution to proceedings
    EuroSun 2004, 20.-23.06.2004, Freiburg, Germany
    Procedings Vol. 3, 401-407
  • Lecture (Conference)
    EuroSun 2004, 20.03.-23.06.2004, Freiburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-6472
Publ.-Id: 6472


Regional differences in cerebral blood flow and cerebral ammonia metabolism in patients with cirrhosis

Ahl, B.; Weissenborn, K.; van den Hoff, J.; Fischer-Wasels, D.; Köstler, H.; Hecker, H.; Burchert, W.

Clinical and histopathological findings hint at regional differences in the brain's sensitivity to metabolic changes in cirrhosis. The aim of the present study was to examine regional differences in cerebral ammonia metabolism in patients with cirrhosis and grade 0-to-I hepatic encephalopathy (HE). 13N-ammonia, 15O-water positron emission tomography (PET) and magnetic resonance imaging (MRI) were performed. Quantitative values of cerebral blood flow (CBF) and the initial cerebral ammonia uptake rate (K1) were derived for several regions of interest from images of the desired parameters after interactive coregistration with the patients' MRI-studies. CBF (mL/mL/min), K1 (mL/mL/min), and the ammonia extraction fraction (K1/CBF) showed marked regional variance with the highest levels in the thalamus, the lenticular nucleus, and the cerebellum. In conclusion, the regional differences in cerebral ammonia uptake correspond to the distribution of histopathological changes in the brain of patients with cirrhosis as well as clinical features of HE, characterized by signs of basal ganglia and cerebellar dysfunction with corresponding signs of functional impairment, especially of the frontal cortex and cingulate gyrus.

Permalink: https://www.hzdr.de/publications/Publ-6471
Publ.-Id: 6471


UV Raman Spectroscopy of Boron Nitrides

Ferrari, A. C.; Reich, S.; Casiraghi, C.; Arenal De La Concha, R.; Loiseau, A.; Gago, R.; Abendroth, B.; Zhang, W. J.; Chan, C. Y.; Bello., I.; Robertson, J.

Boron nitride is a remarkable material both for its fundamental properties and for applications [1]. It exists in different polytypes, the sp2 bonded hexagonal and rhombohedral structure and the sp3 cubic and wurzite phases. All phases are high band-gap semiconductors (>5 eV). Cubic boron nitride, c-BN, is of particular interest for its properties similar to diamond [1,2]. Physical or chemical vapor deposition of boron nitride films can often result in the growth of the less dense hexagonal BN (h-BN). BN nanotubes are also very interesting [3]. Their properties, as for carbon nanotubes, can be derived by studying the wrapping of a single layer of h-BN [3]. Boron Carbon Nitrides (BCN) thin films are also useful for hard coating applications and as semiconductors with variable gap [4]. Raman and Infrared spectroscopy are quick and non-destructive tools to assess the properties of materials. Infrared spectroscopy is the most widely used for boron nitrides. It is very sensitive to polar BN bonds. The spectra for c-BN and h-BN show distinct IR features [1]. Raman spectroscopy is rarely used because of its inferior sensitivity, especially in the case of thin films. This is opposite to diamond-like carbons, where Raman spectroscopy is a standard characterization tool [5]. However, Infrared spectroscopy has limitations. The substrate has to be either transparent or not highly reflective. Raman spectroscopy has no requirement on the substrate properties and can simultaneously give informantion on phase composition, crystallinity, size and stress. In order to successfully apply Raman scattering in boron nitrides its low sensitivity has to be overcome. This can be done by measuring the samples with an excitation energy closer to their band gap. Here we measure BN samples by UV Raman spectroscopy at 5.1 and 5.4 eV. This enhances the BN Raman cross-section and paves the way to making UV Raman scattering a standard tool for boron nitrides characterization. We studied the UV Raman spectra of a variety of boron nitride samples ranging from h-BN (bulk and thin film), c-BN (single crystals, thin and thick films), mixed h-BN and c-BN phases and BCN films with varying B, C and N content. The UV Raman spectra of c-BN and h-BN are so intense that a clear measurement of the second order Raman signal is possible. This allows us to probe for the first time non-zone center phonons and validate the predictions of first-principles calculations of BN properties [3,6]. For h-BN, whilst the high-energy optical phonons are in excellent agreement with theory, the ionic interaction was strongly underestimated for lower energies [6]. The first order UV Raman spectra of thin and nano-crystalline films also show the activation of non-zone center phonons and IR modes, such as the 800 cm-1 mode of h-BN. In BCN films the direct signature of BN bonds can be seen, being no more shadowed by the carbon phase.

1. P. B. Mirkarimi, K. F. McCarty, D. L. Mellin, Mat. Sci. Eng. R21, 47 (1997)
2. W. Zhang, S. Matsumoto, Q. Li, I. Bello, S. T. Lee, Adv. Funct. Mat. 12, 250 (2002)
3. L. Wirtz et al. Phys. Rev. B 68, 045425 (2003)
4. R. Gago et al. J. Appl. Phys. 92, 5177 (2002)
5. A.C. Ferrari, J. Robertson, Phys. Rev. B 61, 14095 (2000); 64 075451 (2001)
6. G. Kern, G. Kresse, J. Hafner, Phys. Rev. B 59, 8551 (1999)

  • Lecture (Conference)
    15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides & Silicon Carbide (DIAMOND 2004), 12-17 September 2004, Riva del Garda, Trentino, Italy

Permalink: https://www.hzdr.de/publications/Publ-6470
Publ.-Id: 6470


Efecto del Ar en películas CNxHy depositadas mediante ECR-CVD

Camero, M.; Gago, R.; Gómez-Aleixandre, C.; Albella, J. M.

Carbon nitride films have been deposited by ECR-CVD, from Ar/CH4/N2 gas mixtures with different methane concentrations. Infrared Spectroscopy and Elastic Recoil Detection Analysis have been used for films characterisation and Optical Emission Spectroscopy for plasma analysis. Argon concentration in the gas mixture controls the growth rate as well as the composition of the film. In the proposed model, argon plays a key role in the activation of methane molecules. Also, during the growth of the film, two processes may be considered: i) Film formation and ii) Etching of the growing surface. Changing the gas mixture composition affects both processes, which results in films with different composition and structure as well as different deposition rates.

Keywords: Thin films; hydrogenated carbon nitride; ECR-CVD; Argon

  • Boletín de la Sociedad Española de Cerámica y Vidrio 43(2004), 491-493

Permalink: https://www.hzdr.de/publications/Publ-6469
Publ.-Id: 6469


X-ray diffraction study of stress relaxation in cubic boron nitride films grown with simultaneous medium-energy ion bombardment

Abendroth, B.; Gago, R.; Eichhorn, F.; Möller, W.

Relaxation of the intrinsic stress of cubic boron nitride (cBN) thin films has been studied by x-ray diffraction (XRD) using synchrotron light. The stress relaxation has been attained by simultaneous medium-energy ion bombardment (2-10 keV) during magnetron sputter deposition, and was confirmed macroscopically by substrate curvature measurements. In order to investigate the stress-release mechanisms, XRD measurements were performed in in-plane and out-of-plane geometry. The analysis shows a pronounced biaxial state of compressive stress in the cBN films grown without medium-energy ion bombardment. This stress is partially released during the medium-energy ion bombardment. It is suggested that the main path for stress relaxation is the elimination of strain within the cBN grains due to annealing of interstitials.

  • Applied Physics Letters 85(2004)24, 5905-5907

Permalink: https://www.hzdr.de/publications/Publ-6467
Publ.-Id: 6467


Interaction of nitrogen atoms in expanded austenite formed in pure iron by intense nitrogen plasma pulses

Piekoszewski, J.; Sartowska, B.; Walis, L.; Werner, Z.; Kopcewicz, M.; Prokert, F.; Stanislawski, J.; Kalinowska, J.; Szymczyk, W.

The paper presents the results of experiments on modification of pure iron by high intense nitrogen pulsed-plasma treatment. The duration of nitrogen plasma pulses is approximately 1 µs, and the energy density amounts to about 5 J/cm2. Such pulses are capable to melt the surface layer of the substrate (1-2 µm) and to introduce a significant concentration of nitrogen into the molten layer. Nuclear reaction analysis (NRA), X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS) were used for characterisation of the treated samples. The main results of the data analysis are as follows:it has been stated that such treatment leads to gradual transformation of initial alpha-phase into austenitic gamma structure in which expanded austenite gammaN is present. Treatment with 20 pulses results in almost complete transformation and introduces a retained dose of nitrogen estimated as 5.5 x 1017 N/cm2. The susceptibility for expansion of the lattice transformed to austenite in this way is smaller than in the case when the steel subjected to conventional nitriding is orginally of austenite type. The analysis of the ratio of gamma to gammaN as a function of the nitrogen content provides a firm evidence that strong repulsion forces act between the first and the second nearst-neighbour nitrogen atoms in the fcc austenitic structure as a result of nitriding of pure iron by intense nitrogen plasma pulses.

Keywords: alpha-to-gamma phase transformation in iron; expanded austenite; intense nitrogen plasma pulses

  • Nukleonika 49(2004)2, 57-60

Permalink: https://www.hzdr.de/publications/Publ-6466
Publ.-Id: 6466


Materials analysis in archaeometrical studies - The cases of ceramics pigments and of gold objects

Constantinescu, B.; Bugoi, R.; Cojocaru, V.; Grambole, D.; Herrmann, F.; Popovici, D.

The scientific analysis of archaeological objects ideally requires the availability of methods, which are simultaneously non-destructive, fast, universal, versatile, sensitive and multielemental. Analyses of source materials combined with analyses of the objects could distinguish from pieces produced in different regions. Our purpose is to help archaeologists to identify objects provenance (workshops, technologies, mines) and to explain different commercial, military and political aspects. We used 241Am source based XRF (X-ray Fluorescence), 3 MeV protons induced PIXE (Particle Induced X-ray Emission), 11 MeV proton activation analysis (PAA) and 3 MeV protons micro-PIXE methods. The above mentioned methods are complementary and they work better together. Some results on pigments from Cucuteni Neolithical and Iznik Medieval ceramics, especially the case of black (Manganese) and blue (Cobalt) colours are presented. We also report a study on ancient Dacian gold coins. The method used were XRF and PAA. Three groups of coins with different composition were found, corresponding to simple, complex and no monogram pieces. Possible historical conclusions are discussed. Finally, micro-PIXE results on some ancient gold objects from Romanian Pietrosa hoard are reported.

Keywords: XRF; PIXE; PAA; microPIXE; ceramics; pigments; gold

  • Rom. Journ. Phys. 48 (2003) 347-354

Permalink: https://www.hzdr.de/publications/Publ-6465
Publ.-Id: 6465


Synthesis and biological evaluation of silylated mixed-ligand 99mTc complexes with the [PNS/S] donor atom set

Fernandes, C.; Knieß, T.; Gano, L.; Seifert, S.; Spies, H.; Santos, I.

New oxotechnetium compleses of general formula [99mTc(O)(PNS)(S(CH2)nOSiR3] (4-6) were synthesized by direct reduction of [[99mTcO4]- with stannous chloride, in the presence of the tridentate heterofunctionalized phosphine H2PNS and of the monodentate silylated thiols [HS(CH2)nOSiR3] (n=2, R=Ph (1); n=3, R=Ph (2); n=3, R=Et (3)). The mixed-ligand rhenium and technetium complexes of general formula [M(O)(PNS)(S(CH2)nOH] (n=2: M=99mTc, (7), M=Re, (7a); n=3: M=99m, (8), M=Re, (8a)) were also prepared. All the 99mTc complexes were obtained with high radiochemical purity (> 95 %), after purification by HPCL, and were characterized by comparison of their HPLC profiles with the ones obtained for the corresponding Re compounds. The silylated compounds 4-6 are stable in phosphate saline buffer (PBS) pH 7.4; rat plasma, human serum and whole blood, and do not bind to plasmatic proteins, and also do not challenge with glutathione. The biological behavior of [99mTc(O)(PNS)(S(CH2)nOH] (7, 8) and [99mTc(O)(PNS)(S(CH2)nOSiR3] (4-6) was studied. The effect of the pH on the cleavage of the O-Si bond in complexes 4-6 was also evaluated.

Keywords: Mixed-ligand complexes; 99mTc; Biological evaluation

Permalink: https://www.hzdr.de/publications/Publ-6464
Publ.-Id: 6464


Study of a liquid metal field ion emitter for the production of Si ions

Aidinis, C. J.; Bischoff, L.; Mair, G. L. R.; Londos, C. A.; Ganetsos, T.; Akhmadaliev, C.

The study of AuSi liquid metal alloy ion sources (LMAIs) for the production of Si ions is not new. However, the present work encompasses in a concise form almost all fundamental aspects of source behaviour, in particular of a Au82Si18 source. A key finding, manifested in the behaviour of the ion extraction voltage with temperature, is the abnormal behaviour of the surface tension coefficient of the alloy with temperature. An important deduction, however, concerns the mechanisms responsible for the creation of doubly charged ions: reasons of self-consistency suggest that while Si++ is directly field-evaporated, Au++ must form by the post-ionization of Au+. (C) 2004 Elsevier B.V. All rights reserved.

Keywords: liquid metal alloy ion sources; temperature; doubly charged ions; field-evaporation; post-ionization

Permalink: https://www.hzdr.de/publications/Publ-6463
Publ.-Id: 6463


Calcium dipicolinate induced germination of Bacillus spores embedded in thin silica layers: novel perspectives for the usage of biocers

Matys, S.; Raff, J.; Soltmann, U.; Selenska-Pobell, S.; Böttcher, H.; Pompe, W.

The germination rate of sol-gel immobilized spores of B. sphaericus JG-A12 in thin silica layers is 5-8 fold enhanced after pre-incubation with an 1:1 chelate of calcium and dipicolinic acid. This germination potential is conserved during long-time storage of 2.5 years.

Permalink: https://www.hzdr.de/publications/Publ-6462
Publ.-Id: 6462


Cyclopentadienyl tricarbonyl complexes of 99mTC for the in vivo imaging of the serotonin 5-HT1A receptor in the brain

Saidi, M.; Kretzschmar, M.; Seifert, S.; Bergmann, R.; Pietzsch, H.-J.

The present interest in the 5-HT1A receptor is due to its implicated role in several major neuropsychiatric disorders such as depression, eating disorders and anxiety. For the diagnosis of these pathophysiological processes it is important to have radioligands in hand able to specifically bind on the 5-HT1A receptor in order to allow brain imaging. Due to the optimal radiation properties of 99mTc there is a considerable interest in the development of 99mTc radiopharmaceuticals for imaging serotonergic CNS receptors using single-photon emission tomography (SPET) [1,2].
Here we introduce two cyclopentadienyl technetium tricarbonyl conjugates of piperidine derivatives which show high accumulation of radioactivity in brain areas rich in 5-HT1A receptors. The complexes have been synthesized starting from the ferrocene complexes N-(alkyl)piperidino-4-[bispentahaptocyclopentadenyl)iron]carboxylate (with alkyl = methyl, isopropyl) [3]. Their chemical identity was confirmed by chromato-graphic methods and electrospray mass spectrometry.
The in vivo uptake of the 99mTc ligands in the whole rat brain and into brain regions was investigated. To determine the pharmacological specificity and selectivity, a group of rats was pretreated with several receptor ligands. The evaluation was carried out by quantitative digital ex vivo autoradiography.
Furthermore, we report the in vitro receptor affinity and biodistribution of the two candidates in order to demonstrate the suitability of the concept and to elucidate the influence of the building blocks on the biobehaviour of the complexes.

  • Invited lecture (Conferences)
    2. International Symposium on Bioorganometallic Chemistry (ISBOMC04), 14.-19.07.2004, Zürich, Swizerland
  • Journal of Organometallic Chemistry 689(2004)25, 4739-4744
    DOI: 10.1016/j.jorganchem.2004.09.004

Permalink: https://www.hzdr.de/publications/Publ-6461
Publ.-Id: 6461


Labelling of biomolecules using organometallic Tc(III) and Re(III) mixed-ligand complexes

Schiller, E.; Kraus, W.; Seifert, S.; Pawelke, B.; Bergmann, R.; Spies, H.; Pietzsch, H.-J.

Trigonal-bipyramidal Tc(III) and Re(III) mixed-ligand complexes of the general formula [MIII(L1)(L2)] (M = Tc, Re; L1 = 2,2‘,2“-nitrilotris-(ethanethiol) NS3 or NS3-COOH; L2 = isocyanide or phosphine) are stable against ligand exchange with cysteine or glutathione and in vitro incubations with plasma as well as whole blood of rats. Therefore, such complexes represent an interesting tool concerning the possibilities of designing biologically relevant 99mTc or 188Re labelled compounds. The introduction of a carboxyl group into the tetradentate ligand and/or the monodentate ligand enables the conjugation of biomolecules as well as fine-tuning of lipophilicity. Improved methods for n.c.a. preparations will be presented. To avoid formation of reduced-hydrolysed species of both metals the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand (NS3) or its carboxyl derivative (NS3-COOH) and the monodentate phosphine or isocyanide to the so-called ‘4+1’ complexes. The isocyanides are used in form of their copper(I) complexes, [Cu(CN-R)4]Cl. That facilitates storage stability and allows kit formulations. Moreover, using that stabilized form of isocyanides enables the formation of 188Re isocyanide complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed and that results in high specific activity labelling of interesting molecules. The stability of various 99mTc and 188Re complexes will be discussed. The described approach allows the functionalization of a biomolecule with the tripodal as well as the monodentate ligand. The isocyanides and phosphines offer the possibility to vary the length and type of spacer for coupling the biomolecule.

  • Lecture (Conference)
    European Symposium on Radiopharmacy and Radiopharmaceuticals, 09.-12.09.2004, Danzig, Poland
  • Invited lecture (Conferences)
    Meeting der COST ACTION B12 "Radiotracers for in vivo assessment of biological function", 21.05.2004, Lissabon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-6460
Publ.-Id: 6460


Synthesis and biological evaluation of a new type of technetium-labelled fatty acids for myocardial metabolism imaging

Walther, M.; Jung, C. M.; Bergmann, R.; Pietzsch, J.; Rode, K.; Stehr, S.; Heintz, A.; Wunderlich, G.; Kraus, W.; Pietzsch, H.-J.; Kropp, J.; Deussen, A.; Spies, H.

Introduction: In an effort to develop technetium-labelled fatty acid analogues for myocardial metabolism imaging rhenium model complexes and their 99mTc analogues were synthesized according to the '4+1' mixed-ligand approach and investigated in vitro and in vivo.

Materials and Methods: The rhenium model complexes were completely characterised by NMR, IR, MS, EA and the geometrical impact of the chelate unit on the integrity of the fatty acid head structure was determined by single crystal X-ray analyses. To estimate the diagnostic value of the 99mTc-labelled fatty acids the compounds were investigated using the isolated constant-flow-perfused guinea pig heart model (see presentation A. Heintz et al.), in cell-uptake experiments and in biodistribution studies using male Wistar rats (5 - 6 weeks old, body weight 151 ± 15 g).

Results: The new fatty acid tracers contain the metal core in the oxidation states +3, well-wrapped in a trigonal-bipyramidal coordination moiety which is attached at the omega-position of a fatty acid chain. This structural feature is considered to be a good imitate of the well-established iodinated phenyl fatty acid. The formation of the rhenium models was accomplished by ligand exchange reactions using different pre-formed rhenium precursors. Noticable heart uptake of the 99mTc tracers being in the order of 2 % ID/g 5´p.i. and accompanied by a good heart to blood ratio of 8.6 confirms the remarkably results of the perfused heart experiments. A significant time-dependent cell uptake in HepG2 cells is shown for two representatives.

Conclusion: Further species such as mice and guinea pigs will be involved to characterise in vivo patterns of those derivatives, that show high extraction rates in the isolated constant-flow-perfused guinea pig heart model. While the tracers are superior to other described Tc-fatty acid imitates with regard to good heart to blood ratios, heart to liver ratio has to be improved. For this, chemical modifications will be performed at the chelating part as well as at the alkyl chain.

  • Lecture (Conference)
    European Symposium on Radiopharmacy and Radiopharmaceuticals 2004, 09.-12.09.2004, Danzig, Poland

Permalink: https://www.hzdr.de/publications/Publ-6458
Publ.-Id: 6458


Myocardial extraction of a new type of technetium-labeled fatty acids

Heintz, A.; Stehr, S. N.; Wunderlich, G.; Walther, M.; Jung, C. M.; Bergmann, R.; Pietzsch, J.; Rode, K.; Kraus, W.; Pietzsch, H.-J.; Kropp, J.; Spies, H.; Deussen, A.

Introduction: Newly developed technetium-labeled fatty acid analogues are promising agents for myocardial metabolism imaging. We tested the myocardial extraction of 99mTc analogues of rhenium model complexes synthesized according to the '4+1' mixed-ligand approach (see presentation M. Walther et al.) in a guinea pig heart LANGENDORFF model

Materials and Methods: Firstly 30 min of steady state perfusion with 10 ml/min of normotherm Krebs-Henseleit-Buffer enriched with 0,1 % albumin was performed. Isolated guinea pig heart were then perfused with fatty acid tracers for 180 seconds in a 1:100 ratio. The venous effluate was collected in intervals of 15 s for 225 s following the start of tracer infusion. Perfusion was stopped, the heart was dissected into atria and ventricle compartments and γ-activity was measured. Eight new (C11, C12, C15, C10S, C11S, C12S, C14S, C16S) and for known control substances (123I-IPPA, 123I-BMIPP, 99mTc-MIBI, 99mTc-DTPA) were tested in this model (n=3-5).

Results: All eight substances showed acceptable extractions rates. Especially experiments with the C11 (39.8 %), but also C12 (14.8 %)and C11S (17.1 %) fatty acid analogues showed excellent results.

Conclusion: When compared with extraction rates for IPPA determined with the same set-up, extraction for the C11 and 11S compounds is 3 fold and 1.3 fold, respectively. These results confirm our hypothesis that the "4+1" Tc(III) chelate unit is promising tool for the Tc-labelling of fatty acids. Further experiments with different species are planned to elucidate exact myocardial uptake mechanisms.

  • Poster
    European Symposium on Radiopharmacy and Radiopharmaceutical 2004, Danzig, 09.-12.09.2004

Permalink: https://www.hzdr.de/publications/Publ-6457
Publ.-Id: 6457


Design of a photoneutron source for time-of-flight experiments at the radiation source ELBE

Altstadt, E.; Beckert, C.; Freiesleben, H.; Galindo, V.; Grosse, E.; Junghans, A.; Naumann, B.; Weiss, F.-P.

The new radiation source ELBE at Research Center Rossendorf uses the high brilliance electron beam from a superconducting LINAC to produce various secondary beams. Electron beam intensities of up to 1 mA at energies between 12 MeV and 40 MeV can be delivered with a wide variability in the electron pulse structure. The maximum pulse frequency is 13 MHz with a pulse width less than 10 ps. The small emittance of the electron beam permits the irradiation of very small volumes. These main beam parameters led to the idea to convert the intense picosecond electron pulses into sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator and to produce neutrons by bremsstrahlung photons through (gamma,n)-reactions. In order to enable measurements of energy resolved neutron cross sections like (n,p), (n,alpha) and (n,f) with a time-of-flight arrangement with a short flight path of only a few meters, it is necessary to keep the volume of the radiator for neutron production as small as possible to avoid multiple scattering of the emerging neutrons which would broaden the neutron pulses. It is the primary physics objective of this neutron source to determine neutron cross sections firstly for construction materials of fusion and fission reactors, for which it is important to select radiation hard materials, and secondly for the handling of waste from such reactors, especially in order to find processes which transmute long-lived radioactive nuclides into short-lived and finally stable ones. In addition, the distribution of fragments can be analyzed which are produced by neutron-induced transmutation of long-lived radioactive nuclides. Furthermore experiments can be performed which address problems of nuclear astrophysics.
The energy deposition of the electron beam in the small neutron radiator is that high that any solid material would melt. Therefore, the neutron radiator consists of liquid lead flowing through a channel of 11.2×11.2 mm² cross section. From the thermal and mechanical point of view molybdenum turned out to be the most suited channel wall (thickness 0.5 mm) material. Depending on the electron energy and current up to 20 kW power will be deposited into a radiator volume of 3 cm³. This heating power is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are in the range of 2 m/s in the radiator section. The electrons that are not stopped in the radiator and the secondary radiation are dumped in an aluminum beam dump. To reduce the radiation background in the measuring direction, the neutrons are decoupled from the radiator at an angle of 90° with respect to the impinging electrons. Particle transport calculations were carried out using the Monte Carlo codes MCNP and FLUKA. These calculations predict a neutron source strength of 7.88e+12 and 2.67e+13 n/s for electron energies between 20 and 40 MeV. At the measuring place 362 cm away from the radiator, neutron fluxes of 1.7e+7 n/(cm² s) will be obtained. The mentioned time-of-flight distance allows for an energy resolution better than 1%. The maximum usable neutron energy is about 7 MeV.

Keywords: neutron; source; photoneutron; flux; pulsed; radiator; time-of-flight; cross section

  • Lecture (Conference)
    12th International Conference on Nuclear Engineering ICONE-12, 25.-29.04.2004 Washington D.C., United States
  • Contribution to proceedings
    12th International Conference on Nuclear Engineering ICONE-12, Washington D.C., USA, April 25-29, 2004, Proceedings on CD-ROM paper 49456

Permalink: https://www.hzdr.de/publications/Publ-6456
Publ.-Id: 6456


Evaluation and ranking of restoration strategies for radioactively contaminated sites

Zeevaert, T.; Bousher, A.; Brendler, V.; Hedemann Jensen, P.; Nordlinder, S.

An international project, whose aim was the development of a transparent and robust method for evaluating and ranking restoration strategies for radioactively contaminated sites (RESTRAT), was carried out under the Fourth Framework of the Nuclear Fission Safety Programme of the EU. The evaluation and ranking procedure used was based on the principles of justification and optimisation for radiation protection. A multi-attribute utility analysis was applied to allow for the inclusion of radiological health effects, economic costs and social factors. Values of these attributes were converted into utility values by applying linear utility functions and weighting factors, derived from scaling constants and expert judgement. The uncertainties and variabilities associated with these utility functions and weighting factors were dealt with by a probabilistic approach which utilised a Latin Hypercube Sampling technique. Potentially relevant restoration techniques were identified and their characteristics determined through a literature review. The methodology developed by this project has been illustrated by application to representative examples of different categories of contaminated sites; a waste disposal site, a uranium tailing site and a contaminated freshwater river.

Keywords: Restoration; Radioactivity; Ranking; Evaluation; Optimisation

  • Journal of Environmental Radioactivity 56 (1-2), 33-50 (2001)

Permalink: https://www.hzdr.de/publications/Publ-6455
Publ.-Id: 6455


First attempt to chemically identify element 112

Yakushev, A. B.; Buklanov, G. V.; Chelnokov, M. L.; Chepigin, V. I.; Dmitriev, S. N.; Gorshkov, V. A.; Hübener, S.; Lebedev, V. Y.; Malyshev, O. N.; Oganessian, Y. T.

The first attempt to chemically identify one of the recently discovered long-lived isotopes of superheavy elements, namely 283112 (3 min, SF), made at FLNR, Dubna is reported. The nuclide was produced by fusion of accelerated 48Ca with a target of natural U, which contained some Nd to simultaneously produce also short-lived Hg nuclides. According to test experiments with Hg, the expected lighter homologue of element 112, both elements can be isolated from the products of the bombardment in metallic state, and transported from the target in flowing He gas to a detection system, where spontaneous fission and alpha decays 49-s 185Hg) were registered using PIPS detectors. The surface of the detectors was covered with a thin layer of Au or Pd which ensured the detection of Hg with high efficiency due to its chemisorption on these surfaces. While about three SF events could be expected, not a single one was detected at an upper limit for the production cross section of about one picobarn. This may point to a "Rn-like" rather than "Hg-like" behavior of element 112. A new experiment is planned, in which both a "Rn-like" and a "Hg-like" species could be detected.

  • Radiochimica Acta 89 (11-12), 743 (2001)

Permalink: https://www.hzdr.de/publications/Publ-6454
Publ.-Id: 6454


A theoretical study of uranyl hydroxide monomeric and dimeric complexes

Tsushima, S.; Reich, T.

Structures of uranyl hydroxide monomeric UO2(OH)20, and dimeric (UO2)2(OH)22+ were studied by hybrid density functional theoretical calculations. It was found out that both the monomeric ortho-UO2(OH)20 and dimeric (UO2)2(OH)22+ complexes have bent O=U=O angles (~170°). This is attributed to significant donation from the equatorial OH ligands to the uranyl moiety. It was also found that the ortho- and meta-UO2(OH)2(H2O)30 complexes lie very close in energy, and that both isomers may exist in normal aqueous media.

  • Chemical Physics Letters 347 (1-3), 127-132 (2001)

Permalink: https://www.hzdr.de/publications/Publ-6453
Publ.-Id: 6453


Hydrogen-induced defects in bulk niobium

Cizek, J.; Prochazka, I.; Becvar, F.; Kuzel, R.; Cieslar, R.; Brauer, G.; Anwand, W.; Kirchheim, R.; Pundt, A.

Our aim in the present work was to investigate changes of the defect structure of bulk niobium induced by hydrogen loading. The evolution of the microstructure with increasing hydrogen concentration was studied by x-ray diffraction and two complementary techniques of positron annihilation spectroscopies (PAS), namely positron lifetime spectroscopy and slow positron implantation spectroscopy with the measurement of the Doppler broadening, in defect-free Nb (99.9%) and Nb containing a remarkable number of dislocations. These samples were electrochemically loaded with hydrogen up to xH=0.06 [H/Nb], i.e. in the alpha-phase region, and it was found that the defect density increases with hydrogen concentration in both Nb samples. This means that hydrogen-induced defects are created in the Nb samples. A comparison of PAS results with theoretical calculations revealed that vacancy-hydrogen complexes are introduced into the samples due to hydrogen loading. Most probably these are vacancies surrounded by 4 hydrogen atoms.

Keywords: PACS number(s): 78.70.Bj; 61.72.-y

Permalink: https://www.hzdr.de/publications/Publ-6452
Publ.-Id: 6452


Spectroscopic Study of Cm(III) Sorption onto -Alumina

Stumpf, T.; Rabung, T.; Klenze, R.; Geckeis, H.; Kim, J. I.

The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under an Ar atmosphere at an ionic strength of 0.1 M NaClO4. The pH is varied between 2 and 10 and the metal ion concentration between 2.7×10−8 and 4.5×10−5 mol/L. With increasing pH, two Cm(III)–alumina surface species are identified which are attributed to≡Al–O–Cm2+(H2O)5 and≡Al–O–Cm+(OH)(H2O)4. The two curium–alumina surface complexes are characterized by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110s). In the concentration range investigated, the surface complex formation is not dependent on the metal ion concentration but only on the pH. Additionally, the concentration ratio of the two surface species is found to be independent of the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages.

  • Journal of Colloid and Interface Science 238 (1), 219-224 (2001)

Permalink: https://www.hzdr.de/publications/Publ-6451
Publ.-Id: 6451


EXAFS as a tool for bond-length determination in the environment of heavy atoms

Hennig, C.; Reich, T.; Funke, H.; Rossberg, A.; Rutsch, M.; Bernhard, G.

Single crystal X-ray diffraction measurements are complicated in the presence of heavy atoms. In these cases the structure factors are mainly influenced by the heavy catterers and the error in determination of atomic coordinates increases for light atoms. The difficulties grow if the unit cell dimensions or the space group symmetry remain uncertain. If the structure model is similar to the correct structure, it is difficult to find an independent criterion for the accuracy of the bond-length determination. We demonstrate that extended X-ray absorption fine structure (EXAFS) spectroscopy is a useful tool for the investigation of local bond lengths in the environment of heavy atoms.

Keywords: heavy atoms; uranyl arsenate; EXAFS; XRD

  • Journal of Synchrotron Radiation 8 (2), 695-697 (2001)
  • Zeitschrift für Kristallographie (2000)17, 81

Permalink: https://www.hzdr.de/publications/Publ-6450
Publ.-Id: 6450


A climatology of 7Be at four high-altitude stations at the Alps and the Northern Apennines

Gerasopoulos, E.; Zanis, P.; Stohl, A.; Zerefos, C. S.; Papastefanou, C.; Ringer, W.; Tobler, L.; Hübener, S.; Gäggeler, H. W.; Kanter, H. J.; Tositti, L.; Sandrini, S.

The 7Be activity concentrations measured from 1996 to 1998 at four high-altitude stations, Jungfraujoch—Switzerland, Zugspitze—Germany, Sonnblick—Austria and Mt. Cimone—Italy, were analyzed in combination with a set of, meteorological and atmospheric parameters such as the tropopause height, relative and specific humidity and also in conjunction with 3D back-trajectories in order to investigate the climatological features of 7Be. A frequency distribution analysis on 7Be activity concentrations revealed the existence of two concentration classes around 1.5 and 6 mBq m−3 and a transition class between the two modes of the distribution at 3–4 mBq m−3. Cross-correlation analysis performed between 7Be and a number of meteorological and atmospheric parameters at the first three stations showed a strong negative correlation with relative humidity (−0.56, −0.51, −0.41) indicating the importance of wet scavenging as a controlling mechanism. Also, the positive correlation with the height of 3-days back-trajectories and tropopause height (+0.49/+0.43, +0.59/+0.36, +0.44/+0.38) shows that downward transport from the upper or middle to lower troposphere within anticyclonic conditions plays also an important role. Trajectory statistics showed that low 7Be concentrations typically originate from lower-altitude subtropical ocean areas, while high concentrations arrive from the north and high altitudes, as is characteristic for stratospheric intrusions. Although the 7Be activity concentrations are highly episodic, the monthly means indicate an annual cycle with a late-summer maximum at all stations. The correlation coefficients calculated for monthly means of the 7Be and atmospheric data suggest that the main predictor controlling the seasonality of the 7Be concentrations is tropopause height (+0.76, +0.56, +0.60), reflecting more vertical transport from upper tropospheric levels into the lower troposphere during the warm season than during the cold season.

Keywords: 7Be; Alps; Climatology; Stratospheric intrusions; Surface ozone

  • Atmospheric Environment 35 (36), 6347-6360 (2001)

Permalink: https://www.hzdr.de/publications/Publ-6449
Publ.-Id: 6449


Synthesis of [1,2-14C]trichloroacetic acid

Bubner, M.; Fuksová, K.; Matucha, M.; Heise, K. H.; Bernhard, G.

A growing interest in the phytotoxic effects of trichloroacetic acid (TCA) has led us to develop a small-scale (<1 mmol) one-pot synthesis of [1,2-14C]TCA with >70% yield and specific activity of 3.7 GBq/mmol

Keywords: [1,2-14C]trichloroacetic acid; one-pot synthesis

  • Journal of Labelled Compounds and Radipharmaceuticals 44 (11), 811-814 (2001)

Permalink: https://www.hzdr.de/publications/Publ-6448
Publ.-Id: 6448


Uranyl Surface Speciation on Silica Particles Studied by Time-Resolved Laser-Induced Fluorescence Spectroscopy

Gabriel, U.; Charlet, L.; Schläpfer, C. W.; Vial, J. C.; Brachmann, A.; Geipel, G.

The sorption of uranyl ions onto amorphous silica has been studied in the presence of atmospheric CO2 by laser-induced time-resolved fluorescence spectroscopy at trace concentrations (1.0 and 0.1 M). Two fluorescent uranyl surface complexes have been identified in the pH range 4 to 9. Both complexes could be differentiated by lifetimes (170±25 s at low pH and 360±50 s at high pH) and fluorescence emission spectra. Within the constant capacitance model framework they are described by mononuclear (1 : 1) complexes with release of two and three protons, respectively. When fluorescence data were compared to wet chemistry sorption data, a third “silent” ternary uranyl–silica–carbonate surface complex had to be postulated to account partly for adsorption between pH 8.0 and 9.0. Three independent data sets led therefore to the identification of three surface complexes, postulated as &tbond;SiO2UO2°,&tbond;SiO2UO2OH-, and &tbond;SiO2UO2OHCO33-.

  • Journal of Colloid and Interface Science 239, 358-369 (2001)

Permalink: https://www.hzdr.de/publications/Publ-6447
Publ.-Id: 6447


FTIR Studies of Phytochrome Photoreactions Reveal the C=O Bands of the Chromophore: Consequences for Its Protonation States, Conformation, and Protein Interaction

Foerstendorf, H.; Benda, C.; Gärtner, W.; Storf, M.; Scheer, H.; Siebert, F.

The molecular changes of phytochrome during red far-red and reverse photoreactions have been monitored by static infrared difference spectroscopy using the recombinant 65 kDa N-terminal fragment assembled with a chromophore chemically modified at ring D or with a chromophore isotopically labeled with 18O at the carbonyl group of ring A. This allows the identification of the C=O stretching vibrations of rings D and A. We exclude the formation of an iminoether in Pfr. The positions of both these modes show that the chromophore always remains protonated. The upshift of the C=O stretch of ring D in the first photoproducts is explained by a twisted methine bridge connecting rings C and D. The changes in the vibrational pattern during the red far-red conversion show that the backreaction is not just the reversal of the forward reaction. The infrared difference spectra of the fragment deviate very little from those of the full-length protein. The differences which are related to the lack of the C-terminal half of the protein constituting the signaling domain are possibly important for the understanding of the signaling mechanism.

  • Biochemistry 40, 14952-14959 (2001)

Permalink: https://www.hzdr.de/publications/Publ-6446
Publ.-Id: 6446


Sorption behavior of U(VI) on phyllite: experiments and modeling

Arnold, T.; Zorn, T.; Zänker, H.; Bernhard, G.; Nitsche, H.


The sorption of U(VI) onto low-grade metamorphic rock phyllite was modeled with the diffuse double layer model (DDLM) using the primary mineralogical constituents of phyllite, i.e. quartz, chlorite, muscovite, and albite, as input components, and as additional component, the poorly ordered Fe oxide hydroxide mineral, ferrihydrite. Ferrihydrite forms during the batch sorption experiment as a weathering product of chlorite. In this process, Fe(II), leached from the chlorite, oxidizes to Fe(III), hydrolyses and precipitates as ferrihydrite. The formation of ferrihydrite during the batch sorption experiment was identified by Mössbauer spectroscopy, showing a 2.8% increase of Fe(III) in the phyllite powder. The ferrihydrite was present as Fe nanoparticles or agglomerates with diameters ranging from 6 to 25 nm, with indications for even smaller particles. These Fe colloids were detected in centrifugation experiments of a ground phyllite suspension using various centrifugal forces.

The basis for the successful interpretation of the experimental sorption data of uranyl(VI) on phyllite were: (1) the determination of surface complex formation constants of uranyl with quartz, chlorite, muscovite, albite, and ferrihydrite in individual batch sorption experiments, (2) the determination of surface acidity constants of quartz, chlorite, muscovite, and albite obtained from separate acid–base titration, (3) the determination of surface site densities of quartz, chlorite, muscovite, and albite evaluated independently of each other with adsorption isotherms, and (4) the quantification of the secondary phase ferrihydrite, which formed during the batch sorption experiments with phyllite. The surface complex formation constants and the protolysis constants were optimized by using the experimentally obtained data sets and the computer code FITEQL. Surface site densities were evaluated from adsorption isotherms at pH 6.5.

The uranyl(VI) sorption onto phyllite was accurately modeled with these newly determined constants and parameters of the main mineralogical constituents of phyllite and the secondary mineralization phase ferrihydrite. The modeling indicated that uranyl sorption to ferrihydrite clearly dominates uranyl sorption, showing the great importance of secondary iron phases for sorption studies.

Keywords: Surface complexation modeling; Quartz; Chlorite; Muscovite; Albite; Ferrihydrite

  • Journal of Contaminant Hydrology, Vol: 47, Issue: 2-4, pp. 219-23, February, 2001

Permalink: https://www.hzdr.de/publications/Publ-6444
Publ.-Id: 6444


Ermüdungsrissausbreitung in Aluminiumlegierungen – Datenbasis und Anwendungen im Rahmen des Damage-Toleranz-Konzeptes

Bergner, F.; Thieme, M.; Zouhar, G.; Franke, R.

Aluminiumknetlegierungen haben sich seit langem im Bereich der Außenhaut des Rumpfes und der Tragflächen von Verkehrsflugzeugen bewährt. Klassische Vertreter sind die hochfeste Legierung 7075 T6 sowie die als schädigungstolerant geltende Legierung 2024 T3. In den letzten Jahren hat sich vor dem Hintergrund des Erfordernisses der Gewichtsreduzierung sowie der Einführung neuer Bauweisen und Fertigungsverfahren der Blick auf ein breiteres Spektrum von Aluminiumlegierungen geöffnet. Für eine fundierte Bewertung dieser Legierungen werden zuverlässige Materialdaten benötigt, wobei im Rahmen des Schädigungs-Toleranz-Konzeptes die Ermüdungsrissausbreitung von besonderem Interesse ist. Unglücklicherweise sind zuverlässige Rissaubreitungsdaten nicht ohne weiteres aus der Literatur beschaffbar. Eine diesbezügliche Studie [Sinclair und Pieri, On obtaining fatigue crack growth parameters from the literature, Int. J. Fatigue 12 (1990) 57-62] kam zu dem ernüchternden Urteil, dass für nominell gleiche Werkstoffe die Streubreite der Literaturangaben deren praktischen Nutzen ernsthaft in Frage stellt. Folgerichtig kommt der Angabe der Messbedingungen sowie der Bekanntgabe der Originalmessdaten große Bedeutung zu.

Im vergangenen Jahrzehnt wurde in einem breit angelegten Versuchsprogramm eine neue Datenbasis mit Ergeb-nissen von Ermüdungsrissausbreitungsmessungen aufgestellt. Die Datenbasis beruht weitgehend auf Messungen mit konstanter Spannungsamplitude (Spannungsverhältnis R=0,1) an mittenangerissenen Proben (Probenbreite 160 mm) aus gewalzten dünnen Blechen (Blechdicke 1,5 bis 3 mm) unterschiedlicher Aluminiumknetlegierungen. Der Riss-fortschritt wurde lichtoptisch gemessen, die Auswertung erfolgte im Rahmen der linear-elastischen Bruchmechanik gemäß Norm ASTM E647. Die Datenbasis enthält neben den Originalmesswerten (Risslänge a, Lastspielzahl N) und den berechneten Werten der Rissausbreitungskurve (Rissausbreitungsrate da/dN über der Schwingbreite des Spannungsintensitätsfaktors DK) auch Zugversuchskennwerte und Restfestigkeiten. Sofern die Materialmenge ausreichte, wurden für jeden Werkstoffzustand in den Orientierungen längs bzw. quer zur Walzrichtung mindestens je fünf Zugversuche und fünf Rissausbreitungsversuche durchgeführt. Für ausgewählte Aluminiumlegierungen wurde auch das Spannungsverhältnis (R=0,5) oder das Umgebungsmedium (3,5%ige NaCl-Lösung) variiert. Speziell für die Aluminiumlegierung 6013 T6 erfolgten Messungen in 3,5%iger NaCl-Lösung im Frequenzbereich von 4 mHz bis 40 Hz.

Ziel des Beitrages ist es, die Datenbasis einem breiteren Interessentenkreis bekannt und zugänglich zu machen. Sie enthält unter anderem Ermüdungsrissausbreitungsdaten für jeweils mehrere 2000er (Hauptlegierungselement Cu), 6000er (Hauptlegierungselemente Mg und Si) und 7000er (Hauptlegierungselement Zn) Aluminiumknetlegierungen im kalt- sowie im warmausgelagerten Zustand. An ausgewählten Beispielen soll gezeigt werden, wie die Materialdaten zur vergleichenden Bewertung der einzelnen Werkstoffe herangezogen werden können. Sofern die Belastungsbedingungen (konstante Spannungsamplitude, Spannungsverhältnis) eine Übertragung auf ein Bauteil zulassen, können durch Integration der Ermüdungsrissausbreitungskurven Restlebensdauern für das betreffende Bauteil abgeschätzt und geeignete Inspektionsintervalle festgelegt werden.

  • Lecture (Conference)
    Deutscher Luft- und Raumfahrtkongress, 20.-23.09.2004, Dresden, Germany
  • Contribution to external collection
    Jahrbuch 2004 der Deutschen Gesellschaft für Luft- und Raumfahrt, ISSN 0070-4083, Bonn: DGLR, 2004, S. 81-90.

Permalink: https://www.hzdr.de/publications/Publ-6443
Publ.-Id: 6443


Synthesis of 4-([18F]fluoromethyl)-2-chlorophenylisothiocyanate: A novel bifunctional 18F-labelling agent

Wüst, F.; Müller, M.; Bergmann, R.

The one-step radiosynthesis of 4-([18F]fluoromethyl)-2-chlorophenylisothiocyanate 18F-7 as a novel bifunctional 18F-labelling agent is described. Optimised reaction conditions in a remotely controlled synthesis module gave isothiocyanate 18F-7 in radiochemical yields of 45 % (decay-corrected) within 40 min and high radiochemical purity of > 95 % after solid-phase-extraction. Coupling of compound 18F-7 with the primary amine benzylamine as a model reaction afforded the corresponding ((4-[18F]fluoromethyl)-2-chloro-phenyl)-benzyl thiourea 18F-8 in a high radiochemical yield of > 90 %. Stability studies of thiourea 18F-8 in terms of radiodefluorination showed appreciable buffer stability at pH 7.4, whereas significant radiodefluorination was observed when 18F-8 was incubated in buffers af pH 3.6 and pH 9.4. Preliminary dynamic PET studies with thiourea 18F-8 in male Wistar rats showed high bone accumulation, indicative of high in vivo radiodefluorination.

  • Radiochimica Acta 92(2004)4-6, 349-353

Permalink: https://www.hzdr.de/publications/Publ-6442
Publ.-Id: 6442


EXAFS structural analysis of aqueous uranium(VI) complexes with lignin degradation products

Reich, T.; Roßberg, A.; Baraniak, L.; Hennig, C.; Bernhard, G.; Nitsche, H.

Uranium LIII-edge extended X-ray absorption fine structure (EXAFS) analysis was carried out on aqueous uranium(VI) complexes with monomeric intermediates of the natural wood-degradation process such as protocatechuic acid (3,4-dihydroxybenzoic acid), catechol (2-hydroxyphenol), pyrogallol (1,2,3-trihydroxybenzol), and vanillic acid (4-hydroxy-3-methoxybenzoic acid). The structural parameters of the 1:1 complexes with protocatechuic acid and vanillic acid in weakly acidic solution indicate that the carboxylic group coordinates the uranyl cation in a bidentate mode in the equatorial plane. Based on the identical structural parameters observed for protocatechuic acid, catechol and pyrogallol in alkaline media, we conclude that the coordination with uranium occurs via the neighboring OH groups of the phenols under formation of a five-membered ring.

  • Radiochimica Acta 88, 593-597 (2000)

Permalink: https://www.hzdr.de/publications/Publ-6441
Publ.-Id: 6441


Soluble humic substances from in situ precipitated microcrystalline calcium carbonate, internal sediment, and spar cement in a Cretaceous carbonate mud-mound

Neuweiler, F.; Rutsch, M.; Geipel, G.; Reimer, A.; Heise, K. H.

Albian carbonate mud-mound limestones exposed near Iraneta, northern Spain, show a fabric- and particle-specific fluorescence. Intense fluorescence is restricted to in situ precipitated microcrystalline (automicritic) fabrics, calcified demosponges, and coralline sponges. Intermediate intensity derives from micritized bioclasts, pellets, and a rim of marine bladed cement. Most invertebrate skeletons, late-diagenetic equant cement, and crosscutting zones of dolomitization are weakly to nonfluorescent. Internal microcrystalline sediment (allomicrite) and red algae debris have variable fluorescence. Correlation between rock fluorescence and soluble humic substances was evaluated from 3 g of automicrite, allomicrite, and cement. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) with ultra-short pulses on two extracrystalline fractions (NaOH-soluble) and two intracrystalline fractions (HCl-soluble and NaOH-soluble) showed that most of the soluble humic substances of automicrite are within the crystals; but conversely, are significantly enriched on outer surfaces of allomicrite. Spar cement is close to detection limits. Fluorescence lifetimes are in the range of 0.5–2 ns and 3.5–6 ns. We conclude that precipitation of automicrite took place during oxidative organic matter diagenesis, i.e., during condensation reactions of degradation products of marine biopolymers. By contrast, allomicrite formed by skeletal breakdown followed by ingestion, organic coating, and reingestion during deposit feeding. A humic-substance–based model of marine polymer gels represents a new approach for the understanding of ancient polygenetic carbonate muds, so typical of Phanerozoic mud-mounds in deeper water settings.

  • Geology 28, 851-854 (2000)

Permalink: https://www.hzdr.de/publications/Publ-6440
Publ.-Id: 6440


Solution coordination chemistry of uranium in the binary UO22+}-SO42- and the ternary UO22+-SO42--OH- system

Moll, H.; Reich, T.; Hennig, C.; Roßberg, A.; Szabó, Z.; Grenthe, I.

The structure and reaction dynamics in the systems UO22+-SO42- and UO22+-SO42--OH- were investigated using EXAFS and 17O-NMR spectroscopy. Uranium LIII edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Å. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Å. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO22+ + SO42- ⇔ UO2SO4 (k1), (2) U*O22+ + UO2SO4 ⇔ U*O2SO4 + UO22+ (k2), (3) UO22+ + UO2(SO4)22- ⇔ 2 UO2SO4 (k3), and (4) UO2SO4 + SO42- ⇔ UO2(SO4)22- (k4). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their 17O chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.

  • Radiochimica Acta 88, 559-566 (2000)

Permalink: https://www.hzdr.de/publications/Publ-6439
Publ.-Id: 6439


Spectroscopic properties of uranium(VI) minerals studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

Geipel, G.; Bernhard, G.; Rutsch, M.; Brendler, V.; Nitsche, H.

We studied the fluorescence properties of 120 uranium minerals in order to provide a data base of potential secondary solids that may form in the flooding process of defunct uranium mines. This data base may provide a link of the fluorescence spectra of the minerals to solution spectra containing so far unknown tertiary and quaternary solution complexes in environmental uranium(VI)-containing waters. In our initial effort to establish the data base, we are focusing on phosphate- and arsenate-containing uranium(VI) minerals. Except for chernikovite [(H3O)2(UO2)2(PO4)2 · 6H2O], these minerals show intensive fluorescence emissions bands with a bathochromic shift of up to 18 nm compared to the fluorescence of the uranyl ion in solution. We found hypsochromic shifts of the fluorescence emission for the uranyl phosphates and bathochromic shifts for the uranyl arsenates. The band spacing of the fluorescence emissions from the 20502 cm-1 level are comparable to the vibrational frequency available from IR-data. Using these data we estimated the axial U-O bond lengths. The decrease of the vibration frequency from 813 cm-1 (saleiite, [Mg(UO2)2(PO4)2 · 10(H2O)]) to 794 cm-1 (uranocircite, [Ba(UO2)2(PO4)2 · 12(H2O)]) is related to a slight increase of the U-O bond length by 3 pm. In both series, the fluorescence lifetime decreases with decreasing crystal water. This is different compared to solution spectra where the lifetime increases as water is displaced from the inner coordination shell. Comparing the fluorescence data of the mineral troegerite [H2(UO2)2(AsO4)2 · 8(H2O)] with the fluorescence spectra of uranyl arsenate solutions, we identified one of the three uranyl arsenate complexes in solution as HUO2(AsO4)(aq.).batch experiment at anoxic conditions proved that pyrite can immobilise U(VI).

  • Radiochimica Acta 88, 757-762 (2000)

Permalink: https://www.hzdr.de/publications/Publ-6438
Publ.-Id: 6438


The MHD α²-dynamo, Z2-graded pseudo-Hermiticity, level crossings, and exceptional points of branching type

Günther, U.; Stefani, F.; Gerbeth, G.

The spectral branching behavior of the 2×2 operator matrix of the magneto-hydrodynamic α²-dynamo is analyzed numerically. Some qualitative aspects of level crossings are briefly discussed with the help of a simple toy model which is based on a Z2-graded-pseudo-Hermitian 2×2 matrix. The considered issues comprise: the underlying SU(1,1) symmetry and the Krein space structure of the system, exceptional points of branching type and diabolic points, as well as the algebraic and geometric multiplicity of corresponding degenerate eigenvalues.

  • Czechoslovak Journal of Physics 54(2004), 1075-1089

Permalink: https://www.hzdr.de/publications/Publ-6437
Publ.-Id: 6437


Chemical characterization of bohrium (element 107)

Eichler, R.; Brüchle, W.; Dressler, R.; Düllmann, C. E.; Eichler, B.; Gäggeler, H. W.; Gregorich, K. E.; Hoffmann, D. C.; Hübener, S.; Jost, D. T.; Kirbach, U. W.; Laue, C. A.; Lavanchy, V. M.; Nitsche, H.; Patin, J. B.; Piguet, D.; Schädel, M.; Shaughnessy, D. A.; Strellis, D. A.; Taut, S.; Tobler, L.; Tsyganov, Y. S.; Türler, A.; Vahle, A.; Wilk, P. A.; Yakushev, A. B.

The arrangement of the chemical elements in the periodic table highlights resemblances in chemical properties, which reflect the elements' electronic structure. For the heaviest elements, however, deviations in the periodicity of chemical properties are expected1-3: electrons in orbitals with a high probability density near the nucleus are accelerated by the large nuclear charges to relativistic velocities, which increase their binding energies and cause orbital contraction. This leads to more efficient screening of the nuclear charge and corresponding destabilization of the outer d and f orbitals: it is these changes that can give rise to unexpected chemical properties. The synthesis of increasingly heavy elements4-6, now including that of elements 114, 116 and 118, allows the investigation of this effect, provided sufficiently long-lived isotopes for chemical characterization are available7. In the case of elements 104 and 105, for example, relativistic effects interrupt characteristic trends in the chemical properties of the elements constituting the corresponding columns of the periodic table8, whereas element 106 behaves in accordance with the expected periodicity9-12. Here we report the chemical separation and characterization of six atoms of element 107 (bohrium, Bh), in the form of its oxychloride. We find that this compound is less volatile than the oxychlorides of the lighter elements of group VII, thus confirming relativistic calculations13 that predict the behaviour of bohrium, like that of element 106, to coincide with that expected on the basis of its position in the periodic table.

  • Nature 407, 63-65 (2000)

Permalink: https://www.hzdr.de/publications/Publ-6435
Publ.-Id: 6435


Application of LIBD to the determination of the solubility product of thorium(IV)-colloids

Bundschuh, T.; Knopp, R.; Müller, R.; Kim, J. I.; Neck, V.; Fanghänel, T.

A new experimental method is presented for the determination of solubility data, which is based on the laser-induced breakdown detection (LIBD). The method is capable of monitoring the initial colloid generation when the metal ion concentration reaches or just exceeds the solubility at given pH. The application is made to determine the solubility of Th(IV) in acidic solutions at I = 0.5 M (NaCl) and 25 °C. The initial colloid formation is determined as a function the H+ concentration in a series of 2.8 × 10-2 - 8.9 × 10-5 M thorium solutions. The conditional solubility product (log K'sp = -49.54 ± 0.22) obtained in this study corresponds to an equilibrium between solution and colloidal thorium dioxide particles. The solubility product at I = 0 (log K°sp = -52.8 ± 0.3) is calculated with the SIT coefficients of the NEA-TDB. It corresponds to the known value for crystalline ThO2(cr), in particular if the small particle size of about 20 nm is taken into account. The present results indicate that the high thorium solubilities measured in the previous studies for amorphous Th(IV) hydroxide or hydrous oxide are primarily caused by the inclusion of polynuclear species or Th(IV) colloids of very small size.

  • Radiochimica Acta 88, 625-629 (2000)

Permalink: https://www.hzdr.de/publications/Publ-6427
Publ.-Id: 6427


Spectroscopic characterization of alkaline earth uranyl carbonates

Amayri, S.; Reich, T.; Arnold, T.; Geipel, G.; Bernhard, G.

A series of alkaline uranyl carbonates, M[UO2(CO3)3]•nH2O (M = Mg2, Ca2, Sr2, Ba2, Na2Ca, and CaMg) was synthesized and characterized by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) after nitric acid digestion, X-ray powder diffraction (XRD), and thermal analysis (TGA/DTA). For the first time, the molecular structure of these compounds was characterized by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Crystalline Ba2[UO2(CO3)3]•6H2O was obtained for the first time. The EXAFS analysis showed that this compound consists of (UO2)(CO3)3 clusters similar to the other alkaline earth uranyl carbonates. The average U-Ba distance is 3.90±0.02 Å. Fluorescence wavelengths and life times were measured using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The U-O bond distances determined by EXAFS, TRLFS, and XPS agree within the experimental uncertainties. The spectroscopic signatures observed could be useful for identifying uranyl carbonate species adsorbed on mineral surfaces.

Keywords: uranium; alkaline earth; carbonate; synthesis; structure; spectroscopy; EXAFS; TRLFS; XPS

Permalink: https://www.hzdr.de/publications/Publ-6426
Publ.-Id: 6426


Institute of Radiochemistry - Profile, goals and scientific results -

Bernhard, G.

  • Lecture (others)
    Invited Talk, Group Meeting, 05.04.2004, UC at Berkeley, LBNL, United States

Permalink: https://www.hzdr.de/publications/Publ-6424
Publ.-Id: 6424


Radioecological research at the Institute of Radiochemistry, FZR

Bernhard, G.

Radioecological research at the Institute of Radiochemistry, FZR

  • Lecture (others)
    Shanghai Institute of Applied Physics, 26.04.2004, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-6423
Publ.-Id: 6423


Transfer of Uranium to Plants - Aspects of Chemical Speciation

Bernhard, G.

Transfer of Uranium to Plants - Aspects of Chemical Speciation

  • Lecture (others)
    Invited Talk - American Chemical Society, Symposium 2004, Anaheim, United States

Permalink: https://www.hzdr.de/publications/Publ-6422
Publ.-Id: 6422


Wechselwirkung von Uran mit Biosystemen - Aspekte der chemischen Speziation

Bernhard, G.

Wechselwirkung von Uran mit Biosystemen

  • Lecture (others)
    Freie Universität Berlin 21.06.2004, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-6421
Publ.-Id: 6421


Blind prediction of Cu(II) sorption onto goethite: Current capabilities of surface complexation modeling

Richter, A.; Brendler, V.; Nebelung, C.

The paper presents examples illustrating the current blind predictive capabilities of surface complexation models (SCM) in combination with a respective database RES3T (Rossendorf Expert System for Surface and Sorption Thermodynamics).
The general strategy for the selection of numerical data is discussed. Based on the information about the minerals collected in the sorption database RES3T, first a set of relevant surface species must be formed. Then respective surface complexation parameters are taken from RES3T: the binding site density for the minerals, the surface protolysis constants, and the stability constants for all relevant surface complexes. To be able to compare and average thermodynamic constants originating from different sources a normalization concept is applied.
In a second part the current capabilities of SCM is demonstrated based on a blind prediction exercise. The system covered is the Cu(II) sorption onto goethite, with the predictions compared to raw data from three independent experimental investigations. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected to account for electrostatics. The calculations were performed with the FITEQL code, version 3.2.
In most cases the model prediction represented the experimental values for the sorbed amount of Cu(II), expressed as conventional distribution coefficients KD, within one order of magnitude or better.
We conclude, that the application of SCM can indeed be very valuable for estimating distribution coefficients for contaminants in well defined mineral systems. The SCM database so far assembled within the RES3T project is able to provide the respective parameter sets following the outlined stepwise strategy of species selection, data collection, normalization and averaging.

Keywords: surface complexation; database; blind prediction; adsorption; copper; goethite; distribution coefficient

  • Geochimica et Cosmochimica Acta 69(2005), 2725-2734

Permalink: https://www.hzdr.de/publications/Publ-6419
Publ.-Id: 6419


Comparative investigations to corrosion fatigue of Al-Cu and Al-Mg-Si alloys

Thieme, M.; Bergner, F.; Haase, I.; Worch, H.

One of the serious problems encountered in the use of various materials in technology is the occurrence of fatigue phenomena as an undesirable material damage under cyclic mechanical load. For aluminium alloys this issue is of extremely high importance in case of their utilisation for aircraft purposes, e.g., where a very wide spectrum of frequencies occur. Moreover, the cyclic loading may be joined by the presence of specific electrolyte media. Therefore, the material candidates must be thoroughly examined in view of their sensitivity to fatigue as well as to corrosion fatigue. Usually, the Cu-containing alloy EN-AW 2024 T3 is applied besides 7075 T6 in Airbus aircrafts, but the weldable alloy 6013 T6 is considered to be a potential alternative. Referring to former investigations on the environmental sensitivity in the fatigue behaviour this paper brings up experimental findings as well as expanded considerations about damaging mechanisms and modelling. The situation with the alloy 6013 T6 is emphasized. The propagation of cracks under cyclic load in different environments, such as vacuum, air or aqueous media, is described by means of fracture mechanics. This enables discrimination in view of the influence of environmental factors and, hence, the participation of corrosion processes.

Keywords: Fatigue Crack Growth; Corrosion Fatigue; Aluminium Alloy

  • Lecture (Conference)
    4th Kurt Schwabe Corrosion Symposium 'Mechanisms of Corrosion and Corrosion Prevention', 13.-17.06.2004, Espoo, Finland
  • Contribution to proceedings
    Proceedings 4th Kurt Schwabe Corrosion Symposium 'Mechanisms of Corrosion and Corrosion Prevention', 13.-17.06.2004, Espoo, Finland, pp. 103-111

Permalink: https://www.hzdr.de/publications/Publ-6418
Publ.-Id: 6418


Silicon-based electrically driven microcavity LED

Potfajova, J.; Sun, J. M.; Winnerl, S.; Dekorsy, T.; Skorupa, W.; Schmidt, B.; Helm, M.; Mantl, S.; Breuer, U.

A silicon pn -diode was embedded into a microcavity composed of a buried metal silicide as bottom reflector and a Si/SiO 2 Bragg mirror as top reflector. Spectral narrowing and an increased intensity of the Si bandgap electroluminescence was observed.

Keywords: silicon based light emission; mirocavity; optical interconnects

Permalink: https://www.hzdr.de/publications/Publ-6417
Publ.-Id: 6417


Measurements of the bulk velocity during solidification of metallic alloys

Eckert, S.; Willers, B.; Gerbeth, G.

The melt convection during solidification has a considerable influence on the nucleation process and the grain structure. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow in a Sn-15wt%Pb alloy solidified directionally from a water cooled copper chill. The flow is driven by a rotating magnetic field. We present velocity profiles measured during the solidification process. Moreover, from the UDV measurements the current position of the solidification front can be estimated.

Keywords: solidification; forced convection; velocity measurements; UDV

  • Metallurgical and Materials Transactions A 36(2005), 267-270

Permalink: https://www.hzdr.de/publications/Publ-6416
Publ.-Id: 6416


Excitons in Si nanocrystals: Confinement and migration effects

Heitmann, J.; Muller, F.; Yi, L.; Zacharias, M.; Kovalev, D.; Eichhorn, F.

A detailed analysis of the strong room-temperature photoluminescence (PL) signal of size controlled nc-Si is reported. The size control of nc-Si is realized by evaporation of SiO/SiO2 superlattices and subsequent thermally induced phase separation. By this method the synthesis of completely SiO2 passivated Si nanocrystals with a controlled size is demonstrated. A strong blueshift of the photoluminescence signal from 1.3 to 1.65 eV with decreasing crystal size is observed. Resonant photoluminescence measurements prove the breakdown of the k-conservation rule for nc-Si by showing an increase in the no-phonon transition probability with decreasing crystal size. A no-phonon to phonon assisted transition probability ratio above 1 is detected at 4.5 K. These results confirm quantum confinement as the origin of the investigated luminescence signal. The size dependence of the different luminescence properties and the very high no-phonon transition probability indicate a lower confin!
ement barrier compared to other systems containing nc-Si and additional migration effects of the excitons between the nanocrystals. A separation of quantum confinement and migration effects on the PL signal is possible due to the very narrow size distribution of the nc-Si and detailed time and temperature dependent investigations of the photoluminescence.

  • Physical Review B 6919(2004)19, 5309-5309

Permalink: https://www.hzdr.de/publications/Publ-6415
Publ.-Id: 6415


Virtues and pitfalls in structural analysis of compound semiconductors by the complementary use of RBS/channeling and high resolution X-ray diffraction

Turos, A.; Gaca, J.; Wojcik, M.; Nowicki, L.; Ratajczak, R.; Groetzschel, R.; Eichhorn, F.; Schell, N.

InP single crystals implanted with 1.2 MeV As-ions and InP/InGaAsP superlattices were studied with RBS/c and high resolution X-ray diffraction (HRXRD). The principal advantage of HRXRD is the determination of interplanar spacing with an accuracy of 10(-5). One should be aware of a variety of pitfalls inherently involved with the nature of X-ray diffraction. These are primarily due to the ambiguity of X-ray rocking curves evaluation. Additional peaks appearing in X-ray rocking curves after ion implantation are usually attributed to regions with distinct lattice parameter. Calculations using damage profiles measured by RBS/c indicated that they could result from X-ray interference effects. For quaternary compounds where HRXRD can hardly detect local change of composition RBS was applied for this purpose. The great accuracy of HRXRD is also advantageous for the RBS analysis: determination of lattice spacing allows the layer density determination hence, the depth scale can be expressed in linear units and stopping power data can be adjusted accurately.

Keywords: III-V semiconductors; Heterostructures; RBS/channeling; HRXRD

  • Nuclear Instruments and Methods in Physics Research B 219-20(2004), 618-625

Permalink: https://www.hzdr.de/publications/Publ-6414
Publ.-Id: 6414


On the Hydrodynamics of Bubble Columns: Comparison of Experimental Measurements with Computational Fluid Dynamics Calculations

Vanga, B. N. R.; Krepper, E.; Zaruba, A.; Prasser, H.-M.; de Bertodano, L.

The hydrodynamics of a rectangular bubble column operating in the dispersed bubbly regime has been experimentally and numerically investigated. The bubble column was locally aerated using a sparger located in the center of the bottom plate. The experimental studies involve wire-mesh tomography measurements for void fraction and bubble size distributions and digital image rocessing of high speed camera images for estimation of bubble velocities, size distributions and flow patterns. Experiments were performed for various aspect ratios (height of water column to width ratio) and superficial gas velocities. Computational fluid dynamic calculations of transient flow for the above bubble column were performed using an Eulerian-Eulerian two fluid model. Turbulence in the liquid phase was accounted for, using the k-epsilon turbulence model. The effect of the gas phase on turbulence in the continuous phase was modeled using Sato’s eddy viscosity model for bubble-induced turbulence. A systematic analysis of the interfacial momentum transfer terms has been conducted. It was found that the non-drag bubble forces play a very prominent role in the predicting the correct flow pattern and void fraction distributions. In the calculations, the lift force and the wall force were considered. A ‘wall peak’ in the time averaged void fraction distribution has been experimentally observed and this cannot be predicted without including these non-drag forces in the numerical calculations. In this paper, experimental data are compared with the results of the numerical simulations.

Keywords: bubble columns; two-phase flow; modelling; turbulence; interfacial momentum transfer

  • Lecture (Conference)
    5th International Conference on Multiphase Flow, ICMF 04, 30.05.-04.06.2004, Yokohama, Japan
  • Contribution to proceedings
    5th International Conference on Multiphase Flow, ICMF 04, 30.05.-04.06.2004, Yokohama, Japan, paper 264

Permalink: https://www.hzdr.de/publications/Publ-6413
Publ.-Id: 6413


Angular distributions for H-3,4(Lambda) bound states in the He-3,He-4(e,e ' K+) reaction

Dohrmann, F.; Ahmidouch, A.; Armstrong, C. S.; Arrington, J.; Asaturyan, R.; Avery, S.; Bailey, K.; Baker, O. K.; Bitao, H.; Breuer, H.; Brown, D. S.; Carlini, R.; Cha, J.; Chant, N.; Christy, E.; Cochran, A.; Cole, L.; Crowder, J.; Danagoulian, S.; Elaasar, M.; Ent, R.; Fenker, H.; Fujii, Y.; Gan, L.; Garrow, K.; Geesaman, D. F.; Gueye, P.; Hafidi, K.; Hinton, W.; Juengst, H.; Keppel, C.; Liang, Y.; Liu, J. H.; Lung, A.; Mack, D.; Markowitz, P.; Mitchell, J.; Miyoshi, T.; Mkrtchyan, H.; Mtingwa, S. K.; Mueller, B.; Niculescu, G.; Niculescu, I.; Potterveld, D. H.; Raue, B. A.; Reimer, P. E.; Reinhold, J.; Roche, J.; Sarsour, M.; Sato, Y.; Segel, R. E.; Semenov, A. Y.; Stepanyan, S.; Tadevosian, V.; Tajima, S.; Tang, L.; Uzzle, A.; Wood, S.; Yamaguchi, H.; Yan, C.; Yuan, L.; Zeier, M.; Zeidman, B.; Zihlmann, B.

The H-3,4(Lambda) and H-4(Lambda) hypernuclear bound states have been observed for the first time in kaon electroproduction on He-3,He-4 targets. The production cross sections have been determined at Q(2)=0.35 GeV2 and W=1.91 GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the He-3,He-4(e,e(')K(+))(Lambda)H-3,H-4 processes to the elementary cross section H-1(e,eK(+))Lambda on the free proton, measured during the same experiment.

  • Physical Review Letters 93(2004), 242501

Permalink: https://www.hzdr.de/publications/Publ-6412
Publ.-Id: 6412


Tailoring Magnetism by Light-Ion Irradiation

Fassbender, J.; Ravelosona, D.; Samson, Y.

Due to the reduced dimension, the magnetic properties of ultrathin magnetic films and multilayers, e.g. magnetic anisotropies and exchange coupling, often depend strongly on the surface and interface structure. In addition chemical composition, crystallinity, grain sizes and their distribution govern the magnetic behaviour. All these structural properties can be modified by light-ion irradiation in an energy range from 5 - 150 keV due to the energy loss of the ions in the solid along their trajectory. Consequently the magnetic properties can be tailored by ion irradiation. Similar effects can also be observed using Ga+ ion irradiation, which is the common ion source in focused ion beam lithography.

Examples for ion induced modifications of magnetic anisotropies and exchange coupling are presented. This review is limited to radiation induced structural changes giving rise to a modification of magnetic parameters. Ion implantation is discussed only in special cases.

Due to the local nature of the interaction, magnetic patterning without affecting the surface topography becomes feasible, which may have an applied interest. The main patterning technique is homogeneous ion irradiation through masks. Focused ion beam and ion projection lithography are commonly only relevant for larger ion masses. The creation of magnetic feature sizes below 50 nm is shown. In contrast to topographic nanostructures the surrounding area of these nanostructures can be left ferromagnetic leading to new phenomena at their mutual interface.

Most of the material systems discussed here are important for technological applications. The main areas are magnetic data storage applications, such as, hard magnetic media with a large perpendicular magnetic anisotropy or patterned media with an improved signal to noise ratio, and magnetic sensor elements. It will be shown that light-ion irradiation has many advantages for design of new material properties and the fabrication technology of actual devices.

Keywords: magnetism; light ion irradiation; magnetic patterning; exchange bias; magnetic anisotropy; exchange coupling

Permalink: https://www.hzdr.de/publications/Publ-6411
Publ.-Id: 6411


Ex-vessel Core Melt Stabilization Research (ECOSTAR)

Alsmeyer, H.; Albrecht, G.; Meyer, L.; Häfner, W.; Journeau, C.; Fischer, M.; Hellmann, S.; Eddi, M.; Allelein, H.-J.; Bürger, M.; Sehgal, B. R.; Koch, M. K.; Alkan, Z.; Petrov, J.; Gaune-Escard, M.; Altstadt, E.; Bandini, G.

The Project on Ex-Vessel Core Melt Stabilization Research (ECOSTAR) started in January 2000 and to be concluded by end of 2003. The project is performed by 14 partner institutions from 5 European countries and involves a large number of experiments with low and high temperature simulant melts and real corium at different scales. Model development and scaling analysis allows application of the research results to existing and to future LWRs in the area of reactor design and accident mitigation.
The project is oriented toward the analysis and mitigation of severe accident sequences that could occur in the ex-vessel phase of a postulated core melt accident. The issues are: (1) the release of melt form the pressure vessel, (2) the transfer and spreading of the melt on the basement, (3) the analysis of the physical-chemical processes that are important for corium behavior especially during concrete erosion with onset of solidification, and (4) stabilization of the melt by cooling through direct water contact.
The results achieved so far, resolve a number of important issues: The amount of melt that could be transferred at RPV failure from the RPV into the containment can be substantially reduced by lowering the residual pressure in the primary circuit. It is found that melt dispersion is also strongly depending on the location of the RPV failure, and that lateral failure results in substantially less melt dispersion. During melt release, the impinging melt jet could erode parts of the upper basement surface. Jet experiments and a derived heat transfer relation allow estimation of its contribution to concrete erosion. Spreading of the corium melt on the available basement surface is an important process, which defines the initial conditions for concrete attack or for the efficiency of cooling in case of water contact, respectively. Validation of the spreading codes based on a large-scale benchmark experiment, is underway and will allow determination of the initial conditions, for which a corium melt can be assumed to spread homogeneously over the available surface. Experiments with UO2-based corium melts highlight the role of phase segregation during onset of melt solidification and during concrete erosion. To cool the spread corium melt, the efficacy of top flooding and bottom flooding is investigated in small scale and in large-scale experiments, supported by model developments. Project assessment is continuing to apply the results to present and future reactors.

Keywords: Ex-vessel corium melt stabilization; Molten-corium-concrete interaction; Corium properties; Melt spreading; Melt cooling

  • Nuclear Engineering and Design, 235(2005)2-4, 271-284

Permalink: https://www.hzdr.de/publications/Publ-6410
Publ.-Id: 6410


Untersuchung strahleninduzierter Chromosomenaberrationen

Wolfring, E.

Bestrahlung der Brustdrüsenepithelzellinie MCF-12A mit Röntgenstrahlung aus konventionellen Röntgenröhren und Bestimmung der Dosis-Effekt-Kurve

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-404 2004
    ISSN: 1437-322X

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-6409
Publ.-Id: 6409


Boron-dilution Transients in PWRs

Weiß, F.-P.

Boron 10 is a strong thermal neutron absorber. As boric acid solved in the coolant of PWRs, it is used to compensate the excess reactivity of the reactor especially at the beginning of the fuel cycle. Therefore, an inadvertent or even unavoidable reduction of the boron concentration means an increase of reactivity that might result in a power excursion, a so called boron dilution transient.
The reactivity increase depends on the of mixing of the underborated water with the coolant inventory in the downcomer (DC) and lower plenum (LP) where the boron concentration is still on the normal high level.
After introducing the different boron dilution scenarios, results of the latest PKL (Primärkreislauf test facility at FANP) experiments will be presented aiming at the assessment of the maximum slug volume for the different safety injection cases. Moreover, the ROCOM (Rossendorf Coolant Mixing) tests will be discussed that were performed to study mixing phenomena inside the reactor pressure vessel (RPV) and which provided typical boron concentration profiles at the core entrance for the different flow regimes. These experiments are used to develop and validate calculation models for boron mixing. Such models are needed to get information about realistic time dependent boron concentration profiles over the cross section of the core entrance. The obtained concentration profiles are used as boundary conditions for coupled neutronic / thermal-hydraulic core calculations to show whether recriticality of the shut down reactor is reached and how high the maximum power peak can be. The results of such calculations will be presented proving that these deborated slugs can cause prompt criticality. Nevertheless, due to the fast Doppler feedback no core damage occurs even with the maximum slug volume of 36m³ .

  • Lecture (others)
    29. Fachsitzung der Internationalen Länderkommision Kerntechnkik, 24.05.2004, Stuttgart, Germany

Permalink: https://www.hzdr.de/publications/Publ-6408
Publ.-Id: 6408


Aktuelle Entwicklungen auf dem Gebiet der nuklearen Sicherheitsforschung

Weiß, F.-P.

The presentation starts from sustainability considerations of different energy carries like oil, hoard cool, or nuclear energy.
It is highlighted, that in terms of sustainability nuclear energy suffers from the danger of proliferation of weapons grade material, the maximum damage of a conceivable severe accident, and the extremely long isolation period of the nuclear waste in the final disposal. Discussing the safety analysis of so called boron dilution transients in PWRs, the behaviour of the reactor pressure vessel during a severe core melt accident, and the possibilities of the transmutation of long lived radio-nuclides it is shown how modern nuclear safety research can contribute to improved sustainability performance of nuclear energy.

  • Invited lecture (Conferences)
    Kolloquium: Kompetenz zur Kerntechnik in Lehre und Forschung, 25.-26.06.2004, Zittau, Germany

Permalink: https://www.hzdr.de/publications/Publ-6407
Publ.-Id: 6407


Recents Developments in Nuclear Safety Research

Weiß, F.-P.

The presentation starts from sustainability considerations of different energy carries like oil, hoard cool, or nuclear energy.
It is highlighted, that in terms of sustainability nuclear energy suffers from the danger of proliferation of weapons grade material, the maximum damage of a conceivable severe accident, and the extremely long isolation period of the nuclear waste in the final disposal. Discussing the safety analysis of so called boron dilution transients in PWRs, the behaviour of the reactor pressure vessel during a severe core melt accident, and the possibilities of the transmutation of long lived radio-nuclides it is shown how modern nuclear safety research can contribute to improved sustainability performance of nuclear energy.

  • Invited lecture (Conferences)
    Conference on Multi-Phase Flow: Simulation, Experiment and Application, 28.-30.06.2004, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-6406
Publ.-Id: 6406


Migration of di- and tri-interstitials in silicon

Posselt, M.; Gao, F.; Zwicker, D.

Small self-interstitial clusters play an important role in the evolution of radiation damage in Si during post-implantation annealing. These small clusters can be formed by two different processes: (i) fast relaxation of highly disordered cascade regions immediately after ion impact and (ii) clustering of diffusing self-interstitials in the first stage of the annealing process.
The structure and energetics of the small self-interstitial clusters have been investigated by different theoretical methods. However, there are only few data on their mobility and migration mechanisms. They have been mainly obtained by static potential energy calculations. This work presents results of a systematic molecular dynamics study of the migration of di- and tri-interstitials. A classical potential approach is employed since it allows the investigation of defect migration under relatively realistic conditions, by considering large computational cells, long periods and different initial conditions. The di- and tri-interstitial configurations with the lowest formation energies are determined, and the results are compared with literature data. Then, the migration of di- and tri-interstitials is followed for 10 – 30 ns, at temperatures between 800 and 1600 K. Defect diffusivity and self-diffusion coefficient per defect are obtained by the Wigner-Seitz cell analysis and the Guinan method as well as from the mean square displacements of all atoms. The effective migration energies are determined and compared with the data from literature. The elementary migration mechanisms are discussed in detail by the analysis of movies and snapshots of defect trajectories and atomic rearrangements.

Keywords: defects; diffusion; migration; silicon; computer simulation

  • Lecture (Conference)
    7th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2004), June 28 - July 2, 2004, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-6405
Publ.-Id: 6405


Bacterial mediated formation of Pd-nanoclusters for the development of biocatalysts

Pollmann, K.; Raff, J.; Merroun, M. L.; Fahmy, K.; Mikeehenko, I.; Creamer, N.; Macaskie, L.; Selenska-Pobell, S.

The bacterial strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. The cells of this strain are capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters [1]. Further, they are enveloped by a surface layer (S-layer) which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date [2]. The highly ordered crystalline S-layers are one of the most common cell envelope structures of bacteria and archaea [3]. They are composed of protein monomers which possess the ability to self-assemble into two-dimensional paracrystalline lattices. The highly regular structure of the S-layers with many pores of identical size offers good binding sites for different metals and nucleation sites for the formation of metal nanoclusters or minerals.
EXAFS and IR analyses of the interactions of purified and recrystallised S-layer with Pd(II) demonstrated, that Pd(II) is bound to the carboxyl groups of the protein. In accordance to these results the C-terminal domain of the protein was found to contain aspartate and glutamate rich stretches which we assume to be responsible for the deposition of Pd in the pores of the protein lattices. Interestingly, the Laser Induced Infrared spectroscopic analysis showed that the deposition of the Pd complexes stabilizes the structure of the protein. The bound Pd(II) is reduced to metallic Pd nanoclusters in the presence of reducing agents which is in agreement with previous studies on another S-layer [4]. In addition, Pd nanoclusters are formed on the intact cells of B. sphaericus JG-A12 via a two step process consisting of biosorption (I) and of consequent metal reduction (II) in the presence of molecular H2 as an electron donor. The metallic nature of the clusters was confirmed by EXAFS and their size was estimated to be about 9-10 Ǻ. TEM analysis showed that the clusters are localised at specific sites of the bacterial cell wall, indicating the primary role of the S-layer in their formation.
The Pd nanoclusters formed on S-layer and bacterial cell templates are highly interesting for technical applications, e. g for the development of novel catalysts. Genetic engineering of the S-layer is applied for optimising its capability to form Pd nanoclusters with increased catalytic activity and also in order to extend its binding capacity to other metals of industrial interest.

1. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67.
2. Raff, J. (2002) “Wechselwirkungen der Hüllproteine von Bakterien aus Uranabfallhalden mit Schwermetallen“ PhD Thesis, FZR-Report No. 358.
3. Sleytr, U. et al. (1997) FEMS Microbiol. Rev. 20, 47-97.
4. Wahl et al. (2001) Advanced Materials 13, 736-740.

  • Lecture (Conference)
    Biometals 2004, 03.-05.09.2004, Garmisch-Partenkirchen, Germany
  • Contribution to proceedings
    Biometals 2004, 03.-05.09.2004, Garmisch-Partenkirchen, Germany
    Proceedings

Permalink: https://www.hzdr.de/publications/Publ-6404
Publ.-Id: 6404


Interaction of Uranium with bacterial strains isolated from Uranium contaminated environments: Microscopic and spectroscopic studies

Merroun, M. L.

Uranium is a long-living radionuclide that represents ecological and human health hazards. The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive waste. It is critical that the uranium in these wastes has to be effectively immobilized and removed away in order to prevent ground water contamination. Microbial biosorption of U(VI) was proposed as one of the methods for uranium immobilization. In this paper, we describe the isolation of bacterial strains from water and soil samples collected from different uranium contaminated environments. Phylogenetic analysis of these strains revealed that they are related to Stenotrophomonas maltophilia, Bacillus sphaericus, Microbacterium oxydans, Pseudomonas rhodesiae etc. As estimated by using ICP-MS these natural isolates possess a high ability to accumulate uranium and other heavy metals such as Cd, Pb, Ni and Ag. The bacterial uranium tolerance was studied using flow cytometry techniques. X-ray absorption near-edge structure analysis showed that the cells of these strains precipitate U(VI) as autunite-like phase (inorganic uranyl phosphate phase) at pH 4.5, probably due to the release of the inorganic phosphate from the cells. However, at pH 2 the uranium bonding was consistent with the formation of complexes with organic bound phosphate of the cell surface. These results are in agreement with those found by infrared measurements.Transmission electron microscope and energy dispersive X-ray analysis showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees.

  • Lecture (others)
    Invited Talk at the Institut for Nuclear Chemistry, University Mainz, 06.06.2004, Mainz, Germany

Permalink: https://www.hzdr.de/publications/Publ-6403
Publ.-Id: 6403


Isolation, characterization and U(VI)-Immobilizing potential of bacterial Strains from Uranium contamined environments

Merroun, M. L.; Rossberg, A.; Hennig, C.; Selenska-Pobell, S.

Uranium is a long-living radionuclide that represents ecological and human health hazards. The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive waste. It is critical that the uranium in these wastes has to be effectively immobilized and removed away in order to prevent ground water contamination. Microbial biosorption of U(VI) was proposed as one of the methods for uranium immobilization. In this paper, we describe the isolation of bacterial strains from water and soil samples collected from different uranium contaminated environments. Phylogenetic analysis of these strains revealed that they are related to Stenotrophomonas maltophilia, Bacillus sphaericus, Microbacterium oxydans, Pseudomonas rhodesiae etc. As estimated by using ICP-MS these natural isolates possess a high ability to accumulate uranium and other heavy metals such as Cd, Pb, Ni and Ag. The bacterial uranium tolerance was studied using flow cytometry techniques. X-ray absorption near-edge structure analysis showed that the cells of these strains precipitate U(VI) as autunite-like phase (inorganic uranyl phosphate phase) at pH 4.5, probably due to the release of the inorganic phosphate from the cells. However, at pH 2 the uranium bonding was consistent with the formation of complexes with organic bound phosphate of the cell surface. These results are in agreement with those found by infrared measurements.Transmission electron microscope and energy dispersive X-ray analysis showed strain-specific extracellular and/or intracellular uranium accumulation to varying degrees.

  • Poster
    Biometals 2004 (03.-05.09.2004), Garmisch-Partenkirchen
  • Contribution to proceedings
    Biometals 2004, 03.-05.09.2004, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-6402
Publ.-Id: 6402


Atomistic study of intrinsic defect migration in 3C-SiC

Gao, F.; Weber, W. J.; Posselt, M.; Belko, V.

Atomic-scale computer simulations, both molecular dynamics (MD) and the nudged-elastic band methods, have been applied to investigate long-range migration of point defects in cubic SiC (3C-SiC) over the temperature range from 0.36Tm to 0.95Tm (melting temperature). The point defect diffusivities, activation energies, and defect correlation factors have been obtained. Stable C split interstitials can migrate via the first- or second-nearest-neighbor sites, but the relative probability for the latter mechanism is very low. Si interstitials migrate directly from one tetrahedral position to another neighboring equivalent position by a kick-in/kick-out process via a split-interstitial configuration. Both C and Si vacancies jump to one of their equivalent sites through a direct migration mechanism. The migration barriers obtained for C and Si interstitials are consistent with the activation energies observed experimentally for two distinct recovery stages in irradiated SiC. Also, energy barriers for C interstitial and vacancy diffusion are in reasonable agreement with ab initio data.

Keywords: Defects; diffusion; SiC; computer simulation

Permalink: https://www.hzdr.de/publications/Publ-6401
Publ.-Id: 6401


He Ion Irradiation Induced Phase Transformation of Icosahedral FePt Nanoparticles

Dmitrieva, O.; Acet, M.; Liedke, M. O.; Rellinghaus, B.; Fassbender, J.

One potential material system for high density magnetic recording consists of monodisperse, highly anisotropic FePt nanoparticles. In order to exhibit high magnetic anisotropy the fct-L10 phase is required.
FePt nanoparticles (dP = 6 nm) with concentration close to the stoichiometric composition have been prepared by DC magnetron sputtering in Ar and subsequent thermal annealing in the gas phase [1]. Recently, we have shown that under appropriate preparation conditions (pAr = 0.5 mbar, rAr = 100 sccm, Tanneal = 600 – 1000 °C), the obtained particles are monodisperse but unfortunately of icosahedral structure [1,2]. Strikingly, these icosahedra are very stable and even post-deposition annealing of these FePt icosahedra for 30 min at T = 1000 °C did not result in a structural phase transition of the particles, although L10 phase is known to be the thermodynamic equilibrium structure of (bulk) FePt.
In order to investigate both the stability of the icosahedral structure and the potential of He ion irradiation for inducing a structural phase transformation, likewise prepared FePt nanoparticles were deposited onto amorphous carbon films (TEM grids) and irradiated with He ions (5 keV) at room temperature. The ion fluence was varied in the range between 1•1016 and 3•1017 ions/cm2. HRTEM investigations on the irradiated particles show that with increasing fluence, the icosahedral particles become increasingly destabilized at the expense of fcc polycrystalline and single crystal particles. Adjacent particles are observed to coalesce (sinter) under the impact of the ion beam thereby indicating an enhanced diffusivity due to (temporarily) increased defect concentrations. The influence of the modified particle structure (with lower symmetry) on the result of a subsequent post-deposition annealing of the irradiated FePt nanoparticles is discussed.

Part of this work is supported by the Deutsche Forschungsgemeinschaft within SFB 445.

[1] S. Stappert, B. Rellinghaus, M. Acet, and E.F. Wassermann, J. Cryst. Growth 252 (2003) 440-450.
[2] S. Stappert, B. Rellinghaus, M. Acet, and E.F. Wassermann, Proc. Mat. Res. Soc. Vol. 704, pp. 73-78 (2002).

Keywords: magnetism; nanoparticles; FePt; hard magnetic materials; He ion irradiation; structural phase transformation

  • Poster
    Conference on Magnetism and Magnetic Materials, Jacksonville, USA, 07.-11.11.2004, Abstract DR-5

Permalink: https://www.hzdr.de/publications/Publ-6400
Publ.-Id: 6400


Anisotropy patterning of amorphous CoFeSiB films by He -ion radiation

McCord, J.; Fassbender, J.; Liedke, M. O.; Fromberger, M.; Quandt, E.; Schultz, L.

The alteration of magnetic properties in magnetic thin films by ion radiation has gained increasing attention in recent years. Most of the experiments focus on magnetic multilayers, e.g. Pt/Co [1] or exchange bias [2] systems. Only a few results are obtained from soft magnetic polycrystalline single-layer films [3] using Ga - ions. Here, we present data on the local alteration of the magnetic anisotropy axis in amorphous soft magnetic (Fe9090Fe10)78B10Si12 films by He -ion radiation in an applied magnetic in-plane field. Sputtered CoFeSiB (thickness 30 nm) were irradiated with 5 keV He -ions with a fluence ranging from 5 10^14 ions/cm2 to 5 10^16 ions/cm2. A magnetic field of 600 Oe was applied during irradiation aligned under an angle to the initial easy axis of anisotropy. Above a fluence of 1016 ions/cm2 a rotation of uniaxial anisotropy in the applied field direction in the irradiated areas is observed by MOKE magnetometry and complementary domain observation by Kerr microscopy in the longitudinal mode. No degradation in magnetic properties relative to the as-deposited state is found from the magnetization loops on non-patterned samples. The easy axis coercivity is typically around Hc,ea = 2 Oe and the anisotropy field around Hk = 18 Oe. Using irradiation together with photolithography the films were irradiated locally, thus resulting in "anisotropypatterned" structures. Domain patterns in differently anisotropy-patterned elements with varying angles of anisotropy and edge orientation, separating regions of different anisotropy alignment, are shown. The influence of the patterning on the (still) full film reversal and the resulting border domain structures are discussed in detail.
References:
[1] C. Chappert et al., Science 280, 1919 (1998)
[2] A. Mougin et al., Phys. Rev. B 63, 060409 (2001)
[3] Woods et al., Appl. Phys. Lett. 81(7), 1267-1269 (2002)

Keywords: magnetism; anisotropy patterning; He ion irradiation; soft magnetic materials

  • Lecture (Conference)
    Conference on Magnetism and Magnetic Materials, Jacksonville, USA, 07.-11.11.2004, Abstract HC-1, Jacksonville, USA

Permalink: https://www.hzdr.de/publications/Publ-6399
Publ.-Id: 6399


Modified Gilbert Damping due to Exchange Bias in NiFe/FeMn Bilayers: Abstract DF-12

Weber, M.; Nembach, H.; Hillebrands, B.; Fassbender, J.

An all-optical pump probe technique is used to investigate the magnetization dynamics and the magnetic damping behaviour in the polycrystalline Ni80Fe20/Fe50Mn50 exchange bias system. It is demonstrated that the magnetic damping increases linearly with the exchange bias field magnitude. The results can be understood taking the exchange bias effect as an additional dissipation mechanism into account.
In order to investigate the magnetization dynamics an 8.5 ps laser excitation is used. Within the laser pulse duration the temperature is raised, resulting in a collapse of the exchange bias field. Due to the fast recovery time on the order of 160 ps a magnetization precession is induced and the Gilbert magnetic damping parameter is determined by comparison of the experimental data to macrospin simulations on the basis of the Landau-Lifshitz-Gilbert equation. The exchange bias field dependence is studied employing the antiferromagnetic thickness dependence by preparing a wedge shaped FeMn layer (0 – 10 nm) on top of a 5 nm NiFe layer.

Keywords: magnetism; magnetization dynamics; magnetic damping; exchange bias

  • Lecture (Conference)
    Conference on Magnetism and Magnetic Materials, 07.-11.11.2004, Jacksonville, USA

Permalink: https://www.hzdr.de/publications/Publ-6398
Publ.-Id: 6398


All-Optical Probe of Magnetization Dynamics in exchange coupled NiFe/FeMn Bilayers on the Picosecond Timescale

Weber, M.; Nembach, H.; Hillebrands, B.; Fassbender, J.

A 8.5 ps short laser excitation (pulse energy: 10 nJ, spot size: 30 µm) is used to thermally control the magnetization of a polycrystalline, mesoscopic NiFe/FeMn exchange biased bilayer system on a picosecond time scale. Due to the creation of a hot spin and phonon gas the exchange coupling across the interface between the ferromagnetic and antiferromagnetic layers is reduced upon arrival of the excitation pulse.

Within 10 picoseconds a fast optical unpinning of the exchange bias coupling is observed for the easy axis geometry as well as for the hard axis case by longitudinal Kerr effect of a time-delayed weak probe pulse. This leads to a reduction of the exchange bias field Heb of about 50 percent (shown in Fig. 1) and to a dramatic increase of the zero-field susceptibility, respectively [1]. A similar time dependence is found for the coercive field Hc of the 50µm x 50µm sample structure under investigation. These effects indicate that the lattice temperature at the FM/AFM interface is elevated close to the blocking temperature Tb (155°C for FeMn) of the exchange coupled system. The fast optical unpinning is followed by a slower recovery of the exchange bias field and the zero-field susceptibility governed by a phenomenological spin-lattice time constant of 160 ps. Pump-probe measurements on a sample with different thicknesses of FeMn, thus different exchange bias field values, show that this relaxation time is independent of the bias field strength.

Keywords: magnetism; exchange-bias; pump-probe; time-resolved; MOKE

  • Lecture (Conference)
    International Workshop on Exchange Bias in Magnetic Nanostructures, 16.-18.09.2004, Biarritz, France
  • Contribution to proceedings
    International Workshop on Exchange Bias in Magnetic Nanostructures, Biarritz, France, 16.-18.09.2004, S. 35-36

Permalink: https://www.hzdr.de/publications/Publ-6397
Publ.-Id: 6397


Investigation of the Fe19Ni81/Fe50Mn50 exchange bias system with varying Cu spacer layer for partial decoupling

Liedke, M. O.; Nembach, H.; Hillebrands, B.; Fassbender, J.

The exchange coupling across an interface between a ferromagnetic and an antiferromagnetic layer may result in the so-called exchange bias effect evidenced by a shift of the hysteresis loop along the magnetic field axis. To study the role of the exchange interaction at and near the interface, Ni81Fe19/Fe50Mn50 bilayers have been studied, which have an intervening Cu layer of varying thickness and position in the antiferromagnetic Fe50Mn50 layer. The role of the intervening Cu layer is to generate partial exchange decoupling. The main motivation is to investigate in which way each antiferromagnetic monolayer contributes to the total exchange bias and what governs the AF thickness dependence? In general introducing an intervening layer in the antiferromagnet can be understood as a well defined layer of defects. The interpretation of the results might be easier than for dilution experiments [1] and contribute to a deeper understanding of the correlation between exchange bias field and coercivity.
We have prepared and investigated a polycrystalline Ni81Fe19/Fe50Mn50 bilayer with an intervening wedge-shaped (0 – 7 Å) Cu layer. As a growth template a Si(100) wafer with a 150 Å thick Cu buffer layer was used. The thickness of the ferromagnetic Ni81Fe19 layer is 50 Å. On top a wedge (0 – 100 Å) of the antiferromagnetic Fe50Mn50 was grown. Next, a Cu spacer wedge was grown perpendicular to the wedge direction of the Fe50Mn50 film. Finally, an additional wedge of Fe50Mn50 was grown on top with the opposite direction in order to keep the total Fe50Mn50 thickness at 100 Å throughout the whole sample (see the sketches in Fig. 1). For protection a 20 Å thick Cr layer was deposited. As a result, a sample was obtained, where in one direction the position of the intervening Cu layer varies from the interface to the top surface of the Fe50Mn50 layer at constant Cu thickness, and in the other direction the Cu thickness varies. To initialize the exchange bias effect the sample was annealed above the Néel temperature and cooled in an applied field back to room temperature.
Hysteresis loops were measured as a function of position on the sample using longitudinal magneto-optic Kerr effect magnetometry. From the loops the exchange bias field Heb and the coercive field Hc were extracted as a function of the Cu spacer thickness, tCu, and of the thickness tFeMn of the lower Fe50Mn50 layer, which is directly exchange coupled to the Ni81Fe19 layer. The results are shown in Fig.1.
The obtained two-dimensional maps provide us easily with global information about the influence of the partial decoupling of the antiferromagnet as a function of tCu and tFeMn.
To obtain more quantitative information several line scans along the horizontal and vertical axes in Fig. 1 were evaluated (not shown here).
For the exchange bias field two different behaviors appear with increasing tFeMn. On one hand Heb decreases for a small Cu thickness close to the ferromagnetic/antiferromagnetic interface, on the other hand Heb increases for a small Cu thickness distant to the interface. For larger tFeMn the typical antiferromagnetic thickness dependence can be found. With increasing tCu a shift of the Heb maximum to higher tFeMn is observed. For a line scan along the Cu wedge for tFeMn = 0 a good agreement with previous results is found [2].
The evolution of the coercivity is different. For small Cu thickness tCu no variation of Hc is observed for scans along tFeMn. It can be concluded that there is no direct connection between exchange bias field Heb and coercive field Hc. The position of the Heb maximum depends on Cu thickness and position within the antiferromagnetic layer but the maximum in Hc always stays the same. In addition it is found that the exchange bias field also depends slightly on cap layer thickness.

Keywords: magnetism; exchange bias; exchange coupling

  • Poster
    International Workshop on Exchange Bias in Magnetic Nanostructures, Biarritz, France, 16.-18.09.2004

Permalink: https://www.hzdr.de/publications/Publ-6396
Publ.-Id: 6396


Damping in thin NiFe films

Nembach, H.; Weber, M.; Fassbender, J.; Hillebrands, B.

We investigated the damping and spin wave creation in thin NiFe films with time-resolved magneto-optic Kerr effect magnetometry for small and large angle excitations. To gain further insight in the underlying damping process we employ a special measurement procedure, which allows us to determine all three magnetization vector components and therefore the length of the magnetization vector. A reduction of the magnitude of the magnetization vector indicates the creation of spin waves. These spin waves can be created directly by the stripline or by multi-magnon processes.
The experimentally determined magnetization trajectory is compared with numerical simulations based on the Landau-Lifshitz equation, and the damping constant is extracted from these simulations

Keywords: magnetism; permalloy; magnetization dynamics; magnetic damping

  • Poster
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 08.-12.03.2004

Permalink: https://www.hzdr.de/publications/Publ-6395
Publ.-Id: 6395


Strukturelle Untersuchung ionenbestrahlter Austausch-Verschiebungsschichtsysteme

Blomeier, S.; Fassbender, J.; Hillebrands, B.; Mcgrouther, D.; Mcvitie, S.; Chapman, J. N.

Vor Kurzem konnte gezeigt werden, dass die magnetischen Eigenschaften von Austausch-Verschiebungssystemen durch Ionenbestrahlung gezielt beeinflusst werden können. Ein Modell wurde vorgeschlagen, welches die Änderung der magnetischen Eigenschaften der bestrahlten Systeme einer ioneninduzierten Änderung ihrer Struktur zuschreibt. Insbesondere wird die Erzeugung von Punktdefekten für die beobachteten Veränderungen verantwortlich gemacht. Um dieses Modell zu testen, wurde das ionenbestrahlte System NiFe/FeMn mit Hilfe von Transmissionselektronenmikroskopie untersucht. Es wurden Hellfeld-, Dunkelfeld- und Beugungsbilder von dem System aufgenommen und ausgewertet. Daraus wurden Morphologie, Partikelgrößen und kristallographische Struktur des Systems bestimmt und deren Abhängigkeit von der Bestrahlung durch 5 keV He+-Ionen und 30 keV Ga+-Ionen untersucht. Es konnte gezeigt werden, dass sich weder Partikelgrößen noch kristallographische Struktur mit zunehmender Ionendosis signifikant verändern. Diese Ergebnisse unterstützen die Theorie der defektinduzierten Modifikation der Austausch-Verschiebung.

Keywords: magnetism; exchange-bias; TEM; structural characterization

  • Poster
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 08.-12.03.2004

Permalink: https://www.hzdr.de/publications/Publ-6394
Publ.-Id: 6394


Investigation of the Fe19Ni81/Fe50Mn50 exchange bias system with varying Cu spacer layer for partial decoupling

Liedke, M. O.; Nembach, H.; Fassbender, J.; Hillebrands, B.

In order to modify the exchange interaction in a Fe19Ni81/Fe50Mn50 exchange bias system a Cu interlayer of varying thickness and position with respect to the interface has been introduced. In one direction the position of the intervening Cu layer varies from the interface to the top surface of the Fe50Mn50 layer at a constant Cu thickness, and in the other direction the Cu thickness itself varies. The introduction of the Cu layer leads to a partial exchange decoupling. The samples were grown in a UHV MBE system and investigated by magneto-optic Kerr effect magnetometry. Two-dimensional maps are obtained, which provide global information about the influence of the partial decoupling of the antiferromagnet as a function of Cu thickness tCu and FeMn thickness tFeMn. In order to obtain more quantitative information several line scans along the horizontal and vertical axes were evaluated. The influence of the partial decoupling on the origins of exchange bias will be discussed.

Keywords: magnetism; exchange-bias; exchange coupling

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 08.-12.03.2004, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-6392
Publ.-Id: 6392


Modifikation der magnetischen Eigenschaften austausch-gekoppelter NiFe/FeMn Filme durch Beschuss mit Ga+-Ionen

Blomeier, S.; Fassbender, J.; Hillebrands, B.; Mcgrouther, D.; O'Neill, R.; Mcvitie, S.; Chapman, J. N.

Der Einfluss der Bestrahlung von 30 keV Ga+-Ionen auf die magnetischen Eigenschaften des polykristallinen NiFe/FeMn Austausch-Bias-Systems wurde untersucht. In diesem Zusammenhang wurde ein Modell getestet, welches die Änderung der magnetischen Eigenschaften der bestrahlten Systeme einer ioneninduzierten Änderung ihrer Struktur zuschreibt. Dieses Modell war ursprünglich für die Bestrahlung mit He+-Ionen entwickelt worden und macht die Erzeugung von Punktdefekten für die beobachteten Veränderungen verantwortlich. Diesbezüglich wurde auch eine Simulation durchgeführt, die den Beschuss durch He+- und Ga+-Ionen vergleicht. Es konnte gezeigt werden, dass sich das oben genannte Modell auf die Bestrahlung mit Ga+-Ionen übertragen lässt und durch die Ergebnisse der Simulation unterstützt wird. Überdies wurde getestet, ob sich das untersuchte System durch die Bestrahlung mit Ga+-Ionen magnetisch strukturieren lässt. Es konnte nachgewiesen werden, dass auf einer Skala von 10^2 - 10^3 nm eine magnetische Strukturierung mit bestimmten Einschränkungen möglich ist

Keywords: magnetism; exchange-bias; focused ion beam; Ga irradiation; magnetic patterning

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Regensburg, 08.-12.03.2004

Permalink: https://www.hzdr.de/publications/Publ-6391
Publ.-Id: 6391


Optische Kontrolle der Magnetisierung in austauschgekoppelten NiFe/FeMn Filmen auf der Pikosekundenzeitskala

Weber, M.; Nembach, H.; Fassbender, J.

Eine 9 Pikosekunden kurze Laseranregung (Pulsenergie: 10 nJ, Spotgröße: 25 mm) wird zur thermischen Kontrolle der Magnetisierung eines NiFe/FeMn Bilagensystems auf der Pikosekundenzeitskala eingesetzt. Aufgrund der Erzeugung eines heissen Phononen- /Spingases durch den anregenden Laserpuls wird die Austauschkopplung an der Grenzfläche zwischen Ferro- und Antiferromagnet teilweise unterdrückt. Innerhalb von 20 Pikosekunden wird eine schnelle Reduktion der Austauschkopplung mittels longitudinalem Kerr-Effekt des zeitverzögerten Probepulses sowohl für die magnetisch leichte als auch harte Richtung nachgewiesen. Dies führt zu einer Reduktion des Austausch-Verschiebungsfeldes von ca. 50 Prozent, bzw. zu einem dramatischen Anstieg der Nullfeld-Suszeptibilität. Diese Effekte können durch ein nahe an die sogenannte Blocking-Temperatur Tb (155o C für NiFe/FeMn) erwärmtes Gitter an der FM/AFM-Grenzfläche verstanden werden. Dem schnellen thermischen Unterdrücken der Austauschkopplung folgt eine langsamere Erholung des Austausch-Verschiebungsfeldes bzw. der Nullfeld-Suszeptibilität mit einer Zeitkonstante von ca. 170 ps.

Keywords: magnetism; exchange-bias; pump-probe; time-resolved

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 08.-12.03.2004, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-6390
Publ.-Id: 6390


Structure and interface characterisation of Exchange Bias FeMn-FeNi films

Solina, D.; Liedke, M. O.; Tietze, U.; Fassbender, J.; Schreyer, A.

X-ray and neutron scattering studies have been carried out on thermally evaporated FeMn-FeNi exchange bias systems before and after ion irradiation by helium ions. Helium ion dosages of 10^14 - 1017 ions /cm-2 have been used. The ion irradiation has shown to alter the exchange bias characteristics of the samples with dose and rate. X-ray diffraction measurements on the samples were made to assess the epitaxy of the layers to the substrate. In order to assess the effect of ion irradiation on these films, both neutron and x-ray reflectivity measurements were performed and the data modelled simultaneously. A final model was chosen that approximated both sets of data well. The reflectivity data suggest that the samples are prone to etching of the surface layer by the ions and that ion irradiation encourages interlayer mixing resulting in a smearing of the oscillations. Increased ion dosages result in a complete loss of exchange bias properties which is supported with loss in inter-layer definition by ion irradiation.

Keywords: magnetism; exchange-bias; x-ray scattering; neutron scattering; thin film magnetism

  • Poster
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Regensburg, 08.-12.03.2004

Permalink: https://www.hzdr.de/publications/Publ-6389
Publ.-Id: 6389


Developing Air-Water Flow in a Vertical 200 mm Tube (TOPFLOW)

Prasser, H.-M.

In the lecture, an overview of the experimental work perfromed at the Rossendorf multi-purpose thermal hydaulic test facility TOPFLOW concerning the flow structure in vertical pipes as well as of the function of wire-mesh sensors was given. Experimental results on the evolution of the radial gas fraction profiles, gas velocity profiles and bubble size distributions in a gas-liquid two-phase flow along a large vertical pipe of 194 mm inner diameter are presented. The tests were performed with two wire-mesh sensors. They were used to record sequences of two-dimensional distributions of local instantaneous gas fraction within the complete pipe cross-section with a lateral resolution of 3 mm and a sampling frequency of 2500 Hz. This data is the basis for a fast flow visualization and for the calculation of the mentioned profiles. The gas fraction profiles were obtained by averaging the sequences over time, velocities were measured by cross-correlation of the signals of the two sensors, which were located on a short (63 mm) distance behind each other. The high resolution of the mesh sensors allows to identify regions of connected measuring points in the data array, which are filled with the gas phase. This method was used to obtain the bubble size distributions.
In the experiments, the superficial velocities ranged from 0.04 to 8 m/s for the gas phase and from 0.04 to 1.6 m/s for the liquid. In this way, the experiments cover the range from bubbly to churn turbulent flow regimes. The evolution of the flow structure was studied by varying the distance between the gas injection and the sensor position. This distance was changed by the help of a so-called variable gas injection set-up. It consists of 6 gas injection units, each of them equipped with three rings of orifices in the pipe wall for the gas injection. These rings are fed with the gas phase from ring chambers, which can be individually controlled by valves. The middle ring has orifices of 4 mm diameter, while the upper and the lower rings have nozzles of 1 mm diameter. In this way, 18 different inlet lengths and two different gas injection geometries can be chosen. The latter allows to vary the initial bubble diameter at identical superficial velocities. The test setup is designed for steam-water operation at up to 7 MPa saturation pressure as well, which will be performed later. The paper presents the results of air-water tests.
A special data evaluation technique allows to study the evolution of radial gas fraction profiles that are decomposed according to bubble size classes. In this way, the behavior of bubbles of different
diameter can be observed, which experience different non-drag forces depending on their diameter. A parallel test section of 52.3 mm inner diameter allows the study of scaling effects.

Keywords: air-water flow; two-phase flow; flow structure; radial gas fraction profiles; gas velocity profiles; bubble size distributions; wire-mesh sensors

  • Lecture (Conference)
    Multi-phase Flow: Simulatio, Experiment and Applications, ANSYS-CFX / FZR workshop, 28.-30.06.2004, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-6388
Publ.-Id: 6388


Measurement Techniques for Multiphase Flows

Prasser, H.-M.

The lecture presented an overview of the state of art of instrumentation for transient and staedy state multi-phase flows with a special attention to gas-liquid flows. The methods discussed are: impedance probes, wire-mesh sensors, optical fibre probes, gamma tomography, X-ray tomography, 3D pulsed holography, neutron radiography. Short descriptions of the measuring methods developed in Rossendorf were included. This concerns electrical impedance probes, wire-mesh sensors, gamma-tomography for periodically changing transient gas fraction fiels (e.g. in axial pumps and turbo couplings) and highthe status of the development of a -speed X-ray tomography system on the basis of a scanned electron beam.

Keywords: multi-phase flow; impedance probes; wire-mesh sensors; optical fibre probes; gamma tomography; X-ray tomography; 3D pulsed holography; neutron radiography

  • Lecture (Conference)
    Multiphase Flows in Industrial Applications CFX-Germany, ANSYS-CFX / FZR workshop, Lecture on Short Course on Multiphase Flows, 28.-30.06.2004, Dresden, Germany
  • Lecture (Conference)
    Multi-phase Flow: Simulatio, Experiment and Applications, ANSYS-CFX / FZR workshop, Lecture on Short Course on Multiphase Flows, 28.-30.06.2004, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-6387
Publ.-Id: 6387


Wire-Mesh Sensors - a Useful Tool for Two-phase Flow Model Development

Prasser, H.-M.

Wire-mesh sensors have achieved a high spatial and time resolution and can therefore contribute considerably to the development of models for CFD codes

Keywords: gas-liquid flow; two-phase flow; wire-mesh sensors

  • Lecture (Conference)
    Multiphase Flows in Industrial Applications CFX-Germany, ANSYS-CFX / FZR workshop, FZ-Rossendorf 28.-30.04.2003.

Permalink: https://www.hzdr.de/publications/Publ-6386
Publ.-Id: 6386


Air-Water Flow in a Vertical Pipe with Sudden Changes of the Superficial Water Velocity

Prasser, H.-M.; Krepper, E.

A constant air flow rate was injected into an upwards water flow, while the superficial water velocity was suddenly changed by activating a butterfly valve, the flap of which was perforated. In this way, both a jump-like decrease and increase of the liquid flow rate were studied. Measurements were taken by two wire-mesh sensors mounted at a short distance behind each other. They were placed 3030 mm downstream of the gas injection. Time sequences of the average gas fraction, radial gas fraction and gas velocity profiles as well as bubble size distributions were derived from the wire-mesh sensor data. The velocities were obtained by cross-correlating the signals of the two successive sensors.
Closely after a sudden increase of the liquid superficial velocity, the content of the pipe segment between gas injection and sensor contains still bubbles that were generated before the perturbation. In the first approximation, the cross-section averaged gas fraction should therefore remain the same as before for the duration of the passage of this portion of two-phase mixture. However, the wall peak in the radial gas fraction profile became more pronounced and shifted towards the wall. This was predicted with a CDF code (CFX-4) as well. However, the experimental observations are indicating a significant decrease of the cross-section averaged gas fraction, which can only be explained by an increase of the drift velocity. The latter was supported by gas velocity profiles obtained by cross-correlation of the signals of the two available sensors. We conclude that there is an effect of growing bubble rise velocity with increasing liquid superficial velocity. The nature of this effect is still unclear. In addition, the described effect was observed with inversed tendencies in case of a sudden reduction of the liquid flow rate.

Keywords: pulsed flow; gas-liquid flow; transient two-phase flow; wore-mesh sensor; CFD; drift flux model; vertical pipe flow

  • Lecture (Conference)
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation 22.-24.09.2004, Pisa, Italy
  • Contribution to proceedings
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation 22.-24.09.2004, Pisa, Italy, proceedings on CD-ROM, paper ms14.

Permalink: https://www.hzdr.de/publications/Publ-6384
Publ.-Id: 6384


Measurement of Bubble Velocity Profiles and Turbulent Diffusion Coefficients of the Gaseous Phase in Rectangular Bubble Column using Image Processing

Zaruba, A.; Krepper, E.; Prasser, H.-M.; Schleicher, E.

The flow in a rectangular bubble column with a cross-section of 100x20 mm and a height of 1500 mm was studied using a high-speed video system. Series of the images were taken at a frequency of 500 Hz at different elevations. The images were treated by means of a bubble recognition algorithm. It allows the tracking of most of the individual bubbles in a bubble swarm. Time-averaged velocity profiles and turbulent diffusion coefficients were derived as a function of the superficial gas velocity.
To measure the turbulent diffusion coefficient of the gaseous phase the lateral displacement of bubbles traveling over a certain vertical distance was transformed into a probability density distribution. It was found that the shape of distributions fits well to a Gaussean standard distribution. Dispersion coefficients were found to grow nearly proportionally to the square root of the vertical distance. Diffusion coefficients were calculated from the proportionality factor and were compared to correlations from the literature. Experiments were performed at superficial gas velocities ranging from 0.5 to 4 mm/s. The bubbles were generated either by a porous sparger or a set of capillaries placed at the bottom of the column. Measurements were taken at heights between 1 and 1.5 m, where the bubble cloud was occupying the entire cross section.

Keywords: bubble column; turbulence; high-speed imaging; image processing; turbulent dispersion; bubble size; bubble velocity

  • Lecture (Conference)
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation, 22.-24.09.2004, Pisa, Italy
  • Contribution to proceedings
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation, 22.-24.09.2004, Pisa, Italy, Proceedings on CD-ROM, paper ms19.

Permalink: https://www.hzdr.de/publications/Publ-6383
Publ.-Id: 6383


A study of non-symmetric air water flow using wire-mesh sensor

Wangjiraniran, W.; Aritomi, M.; Kikura, H.; Motegi, Y.; Prasser, H.-M.

This study investigates the characteristics of upward air-water flow for non-symmetric initial condition in the 50 mm vertical tube. Wire Mesh Sensor is utilized to obtain the local properties of the gas phase i.e. void fraction, gas velocity and bubble size. To generate the non-symmetric initial flow condition, air is supplied from a single injecting hole and mixed into the liquid flow inside the pipe through a narrow-ring shaped exit. In this case, large bubble can be generated at the inlet. In this experiment, the characteristics of bubble formation at the inlet and flow evolution along the pipe are emphasized. The results show the capability of the measurement technique to analyze the non-symmetric distribution of the gas phase. The effects of superficial gas and liquid velocity on the bubble distributions and on the local void fraction spreading at the inlet are clarified. The flow evolution dominated by bubble coalescence and break up is discussed in term of the development of Sauter mean diameter over the cross- section of the pipe. The results also show an inconsistency with uniform flow conditions at low gas flux. Hence, the effect of phase distribution spreading is proposed. In addition, the development of rising gas velocity in term of mean bubble size during coalescence and break up is revealed.

Keywords: gas-liquid flows; non-symmetric flows; wire mesh sensor; flow evolution; bubble rising velocity

  • Experimental Thermal and Fluid Science 29(2005)3, 315-322

Permalink: https://www.hzdr.de/publications/Publ-6382
Publ.-Id: 6382


Influence of the Gas Injection on the Void Fraction Profiles and Bubble Size Distributions of a Air-Water Flow in Vertical Pipes

Prasser, H.-M.

The paper reports about air-water tests in two different vertical pipes, one of 52.3 mm inner diameter, the other of 194.1 mm. In both cases, wire-mesh sensors with a measuring frequency of 2500 Hz were applied. They were used to measure radial gas fraction profiles, velocity profiles and bubble size distributions. Scaling effects were found by comparing the results for the two different pipe diameters. A variation of the air injection conditions allowed to study the influence of the primary bubble size. It was found that the kind of gas injection has a deciding influence at the appearance of a wall peak in the gas fraction profile as well as at the establishing gas fraction profiles and bubble size distributions in general.

Keywords: Gas-liquid flow; two-phase flow; wire-mesh sensor; gas fraction profiles; gas velocity profiles; bubble size

  • Lecture (Conference)
    5th International Conference on Multiphase Flow, ICMF’04, 30.05.-04.06.2004, Yokohama, Japan
  • Contribution to proceedings
    5th International Conference on Multiphase Flow, ICMF’04, 30.05.-04.06.2004, Yokohama, Japan, paper 187

Permalink: https://www.hzdr.de/publications/Publ-6381
Publ.-Id: 6381


Leserbriefe

Prasser, H.-M.

Die friedliche Nutzung der Kernenergie hat heute einen besonderen Bedarf an Öffentlichkeitsarbeit. In keiner anderen Technologiesparte ist die Diskrepanz zwischen dem Nutzen und dessen Bewertung durch die Öffentlichkeit, zwischen den tatsächlichen Risiken und den Ängsten in der Bevölkerung, zwischen dem Stand der Technik und veröffentlichter Meinung so gravierend, wie hier. Die Ursache liegt zum großen Teil auch in Versäumnissen in der Vergangenheit. Die Kernenergiebefürworter haben durch ihre zurückhaltende Öffentlichkeitsarbeit den mehrheitlich gegen die Kernenergie eingestellten Umweltverbänden und Bürgerbewegungen in den Medien praktisch vollständig das Feld überlassen. Dies hat über eine Reihe von Rückkopplungen zu Verstärkungseffekten geführt, die es nun schwer machen, die Öffentlichkeit mit sachlichen Argumenten zu erreichen. Nur mühsam gelingt es, den verlorenen Boden zurückzugewinnen. Die Kerntechnische Gesellschaft muß den Part der Argumentation für die Kernenergie als Zukunftsoption übernehmen und stärker die in der wissenschaftlich-technischen Weiterentwicklung liegenden Potenzen für Umwelterhalt, Ressourcensicherung und Sicherheit herausstellen.
Die Kerntechnische Gesellschaft stützt sich als gemeinnütziger Verein naturgemäß in hohem Maß auf das Engagement seiner Mitglieder. Das Verfassen von Leserbriefen kann in diesem Zusammenhang gewissermaßen als dezentrale Form der Öffentlichkeitsarbeit angesehen werden. Leserbriefe können und sollen jedoch die persönliche Meinung des Verfassers zum Ausdruck bringen. Leserbriefaktionen, bei denen zentral vorgefasste Parolen an die Öffentlichkeit gebracht werden sollen, entsprechen meiner Meinung nach nicht dem Niveau unserer Kerntechnischen Gesellschaft und seiner Mitglieder. Wohl aber ist es nötig und zulässig, zu einem stärkeren Engagement auf diesem Gebiet aufzurufen. Der vorliegende Beitrag soll deshalb nicht als starrer Leitfaden für eine inhaltliche Gestaltung von Leserbriefen verstanden werden. Es soll vielmehr die persönlichen Ansichten des Autors zur Diskussion stellen und seine Erfahrungen vermitteln, um damit alle diejenigen, die es noch nicht versucht haben, zum Einbringen ihrer persönlichen Meinung auf dem Weg des Leserbriefes zu ermutigen.

Keywords: Kernenergie; Öffentlichkeitsarbeit; Leserbriefe

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2000, Bonn, 23.-25. Mai, Fachsitzung Kommunikation mit der Öffentlichkeit, Herausgeber: Deutsches Atomforum e.V., Bonn, Juni 2000, S. 39-48.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2000, Bonn, 23.-25. Mai, Fachsitzung Kommunikation mit der Öffentlichkeit, Herausgeber: Deutsches Atomforum e.V., Bonn, Juni 2000, S. 39-48.

Permalink: https://www.hzdr.de/publications/Publ-6380
Publ.-Id: 6380


Evolution of the structure of a gas-liquid two-phase flow in a large vertical pipe

Prasser, H.-M.; Beyer, M.; Carl, H.; Gregor, S.; Lucas, D.; Pietruske, H.; Schütz, P.; Weiss, F.-P.

Experimental results on the evolution of the radial gas fraction profiles, gas velocity profiles and bubble size distributions in a gas-liquid two-phase flow along a large vertical pipe of 194 mm inner diameter are presented. The tests were performed at the TOPFLOW facility in Rossendorf, where two wire-mesh sensors were used to measure sequences of two-dimensional distributions of local instantaneous gas fraction within the complete pipe cross-section with a lateral resolution of 3 mm and a sampling frequency of 2500 Hz. This data is the basis for a fast flow visualization and for the calculation of the mentioned profiles. The gas fraction profiles were obtained by averaging the sequences over time, velocities were measured by cross-correlation of the signals of the two sensors, which were located on a short (63 mm) distance behind each other. The high resolution of the mesh sensors allows to identify regions of connected measuring points in the data array, which are filled with the gas phase. This method was used to obtain the bubble size distributions.
In the experiments, the superficial velocities ranged from 0.04 to 8 m/s for the gas phase and from 0.04 to 1.6 m/s for the liquid. In this way, the experiments cover the range from bubbly to churn turbulent flow regimes. The evolution of the flow structure was studied by varying the distance between the gas injection and the sensor position. This distance was changed by the help of a so-called variable gas injection set-up. It consists of 6 gas injection units, each of them equipped with three rings of orifices in the pipe wall for the gas injection. These rings are fed with the gas phase from ring chambers, which can be individually controlled by valves. The middle ring has orifices of 4 mm diameter, while the upper and the lower rings have nozzles of 1 mm diameter. In this way, 18 different inlet lengths and two different gas injection geometries can be chosen. The latter allows to vary the initial bubble diameter at identical superficial velocities. The test setup is designed for steam-water operation at up to 7 MPa saturation pressure as well, which will be performed later. The paper presents the results of air-water tests.
A special data evaluation technique allows to study the evolution of radial gas fraction profiles that are decomposed according to bubble size classes. In this way, the behavior of bubbles of different diameter can be observed, which experience different non-drag forces depending on their diameter. A parallel test section of 52.3 mm inner diameter allows the study of scaling effects.

Keywords: Gas-liquid flow; two-phase flow; wire-mesh sensor; flow structure; bubble size; gas fraction; vertical pipe flow

  • Lecture (Conference)
    Eleventh International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    Eleventh International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 11), 02.-06.10.2005, Avignon, France, paper 399.
  • Nuclear Engineering and Design 237(2007), 1848-1861

Permalink: https://www.hzdr.de/publications/Publ-6379
Publ.-Id: 6379


Evolution of Interfacial Area Concentration in a Vertical Air-Water Flow Measured by Wire-Mesh Sensors

Prasser, H.-M.; Gregor, S.

Conservation equations for one or more classes of the interfacial area concentration is one of the concepts to take into account the evolution of the flow structure in a gas-liquid two-phase flow in thermal hydraulic or, respectively, CFD modeling. The measurement of the interfacial area concentration is therefore of large importance for the development and validation of those models. The paper presents the results of an application of wire-mesh sensors to obtain the interfacial area concentration in vertical pipes of 52.3 and 194.1 mm inner diameter as an alternative to the widely used multiple-tip optical fiber probes. The measuring data of a mesh sensor is represented by a threedimensional matrix of local instantaneous gas fractions recorded as a time sequence (sampling frequency 2.5 - 10 kHz) at the crossing points of the wires (resolution in x-y direction: 3 mm).
Velocity information necessary to convert the time axis in an Eulerian z-axis was obtained by means of cross-correlation calculated between the signals of two identical mesh sensors located at a small distance behind each other. Three methods are used to deduce the interfacial area concentration from the wire-mesh sensor data:
• Calculation of the sum of the interfacial area represented by bubbles, which are identified as regions of connected gas filled elements in the data array, where the superficial area of an individual bubble is calculated under the assumption of a ellipsoid bubble shape. This method is restricted to low gas fractions, where bubble shapes are still close to the assumed geometry.
• A second method consists in the calculation of the sum of the contribution of the gas fraction in each local control volume of the sensor formed by two crossing wires. This control volume is approximated by a sphere with a volume-equivalent diameter. Furthermore, it is assumed, that the gas-liquid interface is a plane that cuts this sphere in a part filled with gas and another part that is filled with liquid. In this way, a correlation between the local interfacial area and the local instantaneous gas fraction can be found, in which the local interfacial area concentration is at its maximum at 50 % volumetric gas fraction and decreases to zero at both 0 % and 100 % local instantaneous gas fraction. This method can be applied to large bubbles with an arbitrary shape.
• In order to decrease the measuring error arising from the fact that gas fractions in measuring points inside large bubble as well as inside completely liquid-filled regions are not exactly equal to 100 % or, respectively, 0 %, and which therefore may significantly contribute to an overestimation of the interfacial area, a third method was applied, which is based on the identification of points that belong to the surface of the bubbles.
All three methods were applied to a vertical air-water flow. Since the distance between the sensors and the gas injection was varied, it was possible to characterize the change of the interfacial area concentration along the pipe. By combining the method with bubble size measurements, a decomposition of the interfacial area concentration into more then one bubble size classes was performed as well. The obtained results were compared to the findings reported in literature. The use of mesh sensors proved to be very efficient, since a bubble-size decomposed interfacial area concentration measurement in an entire pipe cross-section can be performed in a few seconds, which is very efficient compared to the use of local probes.

Keywords: gas-liquid flow; wire-mesh sensor; interfacial area concentration; vertical flow; two-phase flow

  • Lecture (Conference)
    Eleventh International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    Eleventh International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 11), 02.-06.10.2005, Avignon, France. paper 398.

Permalink: https://www.hzdr.de/publications/Publ-6378
Publ.-Id: 6378


Experiments on Turbulent Diffusion of the Gaseous Phase in Rectangular Bubble Column Using Image Processing

Zaruba, A.; Krepper, E.; Prasser, H.-M.

The paper describes the application of high-speed video observation combined with digital image processing techniques to measure the turbulent diffusion coefficient of the gaseous phase in a bubble column. The test channel is a rectangular bubble column with a cross-section of 100x20 mm and a height of 1500 mm. Sequences of the images were taken at different heights of the column with a high-speed video system. A diffuse illumination from the backside of the column was found to produce bubble images with a characteristic bright spot in the center. This bright spot was used for a bubble tracking that tolerates some overlapping of the bubbles. This allows to enhance the applicability of the bubble tracking to higher gas fractions compared to the tracking of the entire bubble shadows. After the bubble trajectories were extracted from the image sequence, the lateral displacement of bubbles between two virtual horizontal measuring planes was calculated for each bubble that crosses both planes. This lateral displacement is caused by the turbulent fluctuations of the bubble velocity. It is analyzed statistically by constructing probability density functions of the lateral displacement, which can be well described by Gaussean standard distributions. The dispersion coefficient of the standard distributions that were fitted to the experimental data shows a linear dependency from the square-root of the vertical distance between the two control planes, which supports the assumption of a diffusion model for the lateral displacement. Deviations from the linear dependency were identified to be the result of deterministic oscillatory motions of the rising bubbles. This effect is typical for low-viscosity liquids, while the bubble oscillations are damped at higher viscosities. Results are presented for different gas flow rates (superficial gas velocity ranged from 0.5 to 4 mm/s), different primary bubble sizes produced by a variation of the sparger and for liquids with different viscosity (water, ethylene glycol, mixtures of both). All measurements were taken at heights between 1 and 1.5 m, where the bubble cloud was occupying the entire cross section. Beside the turbulent diffusion study, the optical observation was used to obtain bubble sizes, gas fractions and rise velocities. Measured diffusion coefficients were compared to correlations from the literature and CFD simulations of the column using the code CFX.

Keywords: Gas-liquid flow; bubble columns; image processing; turbulence; turbulent diffusion

  • Lecture (Conference)
    Eleventh International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    Eleventh International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 11, 02.-06.10.2005, Avignon, France, Proceedings CD-ROM, paper 388

Permalink: https://www.hzdr.de/publications/Publ-6377
Publ.-Id: 6377


Polymerization Processes of Epoxy Matric Composites under Simulated Free Space Conditions

Kondyurin, A. V.; Lauke, B.; Richter, E.

Permalink: https://www.hzdr.de/publications/Publ-6376
Publ.-Id: 6376


Analysis of the Ni81Fe19/Fe50Mn50 exchange bias system with a varying Cu spacer thickness and position for partial decoupling

Liedke, M. O.; Nembach, H.; Hillebrands, B.; Fassbender, J.

In order to study the role of the exchange interaction at and near the interface, Ni81Fe19/Fe50Mn50 bilayers have been studied, which have an intervening layer of varying thickness and position in the anti ferromagnetic Fe50Mn50 layer. The role of the intervening layer is to generate partial exchange decoupling. As a result, samples were obtained, where in one in-plane direction the position of the intervening layer varies from the interface to the top surface of the Fe50Mn50 layer at a constant intervening layer thickness, and in the other in-plane direction the intervening layer thickness varies. Two-dimensional maps of the resulting exchange bias field and the coercive field were obtained from magneto-optic Kerr effect magnetometry measurements. The role of the position and strength of the partial decoupling within the anti ferromagnetic layer on the exchange bias effect and the coercive field is discussed.

Keywords: magnetism; exchange bias; thin films; exchange coupling

  • Poster
    JEMS'04, Dresden, 06.-10.09.2004
  • Contribution to external collection
    JEMS'04, Dresden, 06.-10.09.2004

Permalink: https://www.hzdr.de/publications/Publ-6375
Publ.-Id: 6375


Modification of the magnetic properties of exchange coupled NiFe/FeMn films by Ga+ ion irradiation

Blomeier, S.; Mcgrouther, D.; Neill, R. O.; Mcvitie, S.; Chapman, J. N.; Weber, M. C.; Hillebrands, B.; Fassbender, J.

The influence of 30 keV Ga+ ion irradiation on the magnetic properties of polycrystalline NiFe/FeMn exchange bias layers were investigated. In this context, it was of particular interest to determine whether a previously observed enhancement of the bias field value for the irradiation with 5 keV He+ ions is a material-specific or an ion-specific effect. Moreover, the capability of magnetic micropatterning using Ga+ ions from a Focused Ion Beam source was tested. It could be demonstrated that magnetic patterning with a lower limit in the range of 100 – 1000 nm is possible.

Keywords: magnetism; exchange-bias; focussed ion beam; magnetic patterning

  • Poster
    JEMS'04, Dresden, 06.-10.09.2004
  • Journal of Magnetism and Magnetic Materials 290(2005)1, 731-734

Permalink: https://www.hzdr.de/publications/Publ-6374
Publ.-Id: 6374


Reflectivity characterization of ion irradiated exchange bias FeMn-FeNi films

Solina, D.; Liedke, M. O.; Tietze, U.; Fassbender, J.; Schreyer, A.

X-ray reflectivity, neutron reflectivity studies and Magneto-Optic Kerr Effect measurements (MOKE) have been carried out on thermally evaporated FeMn-FeNi exchange biased films before and after ion irradiation by helium ions. MOKE shows that ion irradiation reduces the exchange bias characteristics of the samples with increased dose. Modelling of the reflectivity data infers that atoms from the buffer layer are displaced by the ions and imbedded into the substrate material. The correlation between these strong structural modifications by irradiation with the reduction of the exchange bias will be discussed.

Keywords: magnetism; exchange-bias; x-ray reflectivity; neutron scattering

  • Poster
    MML'04, Boulder, USA, 07.-11.06.2004

Permalink: https://www.hzdr.de/publications/Publ-6373
Publ.-Id: 6373


Application of light ion irradiation on the magnetic properties of exchange bias layers

Fassbender, J.

Due to the reduced dimension, the magnetic properties of ultrathin magnetic films and multilayers, e.g. magnetic anisotropies and exchange coupling, often depend strongly on the surface and interface structure. In addition chemical composition, crystallinity, grain sizes and their distribution govern the magnetic behaviour. All these structural properties can be modified by light-ion irradiation in an energy range from 5 – 150 keV due to the energy loss of the ions in the solid along their trajectory. Consequently the magnetic properties can be tailored by ion irradiation. Similar effects can also be observed using Ga+ ion irradiation, which is the common ion source in focused ion beam lithography. Examples for ion induced modifications of magnetic properties in exchange bias systems are presented.

Due to the local nature of the interaction, magnetic patterning without affecting the surface topography becomes feasible, which may have an applied interest. In contrast to topographic nanostructures the surrounding area of these nanostructures can be left ferromagnetic leading to new phenomena at their mutual interface.

Most of the material systems discussed here are important for technological applications. It will be shown that light-ion irradiation has many advantages for design of new material properties and the fabrication technology of actual devices.

Keywords: magnetism; exchange-bias; ion irradiation; thin magnetic films; magnetic patterning

  • Lecture (Conference)
    Sommerschule der EU-RTN Netzwerke "Nexbias" und "Ultraswitch", 13. – 17.09.2004, Biarritz, France

Permalink: https://www.hzdr.de/publications/Publ-6372
Publ.-Id: 6372


Ion beams for magnetic thin film applications

Fassbender, J.

Due to the reduced dimension, the magnetic properties of ultrathin magnetic films and multilayers, e.g. magnetic anisotropies and exchange coupling, often depend strongly on the surface and interface structure. In addition chemical composition, crystallinity, grain sizes and their distribution govern the magnetic behaviour. All these structural properties can be modified by light-ion irradiation in an energy range from 5 - 150 keV due to the energy loss of the ions in the solid along their trajectory. Consequently the magnetic properties can be tailored by ion irradiation. Due to the local nature of the interaction, magnetic patterning without affecting the surface topography becomes feasible, which may have an applied interest. In contrast to topographic nanostructures the surrounding area of these nanostructures can be left ferromagnetic leading to new phenomena at their mutual interface. An overview over the present status will be presented.

Keywords: magnetism; ion irradiation; He; thin magnetic films; magnetic patterning

  • Lecture (Conference)
    14th International Conference on Ion Beam Modification of Materials (IBMM 2004), Abstract VIII A - Applications, 05. – 10.09.2004, Monterey, USA

Permalink: https://www.hzdr.de/publications/Publ-6371
Publ.-Id: 6371


Optical control of the magnetization on the picosecond timescale

Fassbender, J.

A 9 ps long laser pulse (energy: 10 nJ, spot diameter: 25 µm) is used to thermally control the magnetization of a NiFe/FeMn exchange bias bilayer system on the ps-time scale. The short laser pulse creates a hot phonon/spin gas. Consequently the exchange coupling across the interface between the ferro- and antiferromagnetic layer is reduced within 20 ps. This fast reduction of the exchange coupling is sensed by a time delayed probe pulse and analyzed with longitudinal magneto-optic Kerr effect. The time evolution of the exchange bias field in the easy magnetization direction and of the zero field suszeptibility in the hard magnetization direction is investigated. Within the first 20 ps a reduction of the exchange bias field of about 50 percent is observed. In addition a drastic increase of the zero field suszeptibility is found. The results can be understood concerning that the crystal lattice is heated close to the blocking temperature of the FeMn film (150°C). After the fast thermal reduction of the exchange coupling a slow recovery of the exchange bias field and the zero field suszeptibility is observed with a time constant of 170 ps.

Keywords: magnetism; exchange-bias; pump-probe; MOKE

  • Lecture (Conference)
    Academy Colloquium "Ultrafast spin and magnetization dynamics in magnetic nanostructures", 15. – 17.06.2004, Amsterdam, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-6370
Publ.-Id: 6370


Optical control of the magnetization on the picosecond timescale

Fassbender, J.

A 9 ps long laser pulse (energy: 10 nJ, spot diameter: 25 µm) is used to thermally control the magnetization of a NiFe/FeMn exchange bias bilayer system on the ps-time scale. The short laser pulse creates a hot phonon/spin gas. Consequently the exchange coupling across the interface between the ferro- and antiferromagnetic layer is reduced within 20 ps. This fast reduction of the exchange coupling is sensed by a time delayed probe pulse and analyzed with longitudinal magneto-optic Kerr effect. The time evolution of the exchange bias field in the easy magnetization direction and of the zero field suszeptibility in the hard magnetization direction is investigated. Within the first 20 ps a reduction of the exchange bias field of about 50 percent is observed. In addition a drastic increase of the zero field suszeptibility is found. The results can be understood concerning that the crystal lattice is heated close to the blocking temperature of the FeMn film (150°C). After the fast thermal reduction of the exchange coupling a slow recovery of the exchange bias field and the zero field suszeptibility is observed with a time constant of 170 ps.

Keywords: magnetism; exchange-bias; pump-probe; MOKE

  • Lecture (Conference)
    International Workshop on "Magneto-optics of magnetic thin films and multilayers", 29. – 30.04.2004, Duisburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-6369
Publ.-Id: 6369


Betriebshandbuch für die Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW

Beyer, M.; Carl, H.; Schütz, P.; Pietruske, H.; Lenk, S.

Ausgehend von einer ausführlichen Beschreibung der Mehrzweckversuchsanlage TOPFLOW und der zu ihrem Betrieb erforderlichen Bedien- und Sicherheitshinweise enthält dieses Betriebshandbuch Anweisungen zur Inbetriebnahme der Versuchsanlage sowie für die Vorbereitung und Durchführung von Experimenten zur Untersuchung von transienten Zweiphasenströmungen mit den Medien Dampf-Wasser bzw. Luft-Wasser. Erläuterungen über Sonderbetriebsfälle schließen das Betriebshandbuch ab. Eine Auflistung der technologischen Verriegelungen und Visualisierungen der Anlagenschemata aus dem Prozessleitsystem sind als Anlagen angefügt.

Keywords: Thermohydraulik; TOPFLOW; Zweiphasenströmungen; Betriebshandbuch

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-405
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-6368
Publ.-Id: 6368


Intersubband semiconductor light sources: history, status, and future

Helm, M.

After the first theoretical proposal in 1971, it took more than two decades until the first laser based on intersubband transitions in semiconductor quantum structures was demonstrated. The progress since then has indeed been spectacular with lasers now spanning the range from 3.5 to 140 microns. The physics of these devices will be elucidated and some crucial achievements will be highlighted. Finally the perspectives for closing the still existing wavelength gap (25-60 microns) and extending the covered range to even longer as well as shorter wavelength will be discussed.

Keywords: intersubband transitions; quantum cascade laser; semiconductor light emitters; infrared

  • Lecture (Conference)
    Plenary talk at The Joint 29th International Conference on Infrared and Millimeter Waves and 12th International Conference on Terahertz Electronics (IRMMW 2004/THz 2004), Karlsruhe, Germany
  • Contribution to proceedings
    Infrared and Millimeter Waves, 2004 and 12th International Conference on Terahertz Electronics, 2004. Conference Digest of the 2004 Joint 29th International Conference on 27 Sept.-1 Oct. 2004 Page(s): 57 - 58

Permalink: https://www.hzdr.de/publications/Publ-6367
Publ.-Id: 6367


In-depth optical and structural study of silver-based low-emissivity multilayer coatings for energy-saving applications

Martín-Palma, R. J.; Gago, R.; Vinnichenko, M.; Martínez-Duart, J. M.

Low-emissivity coatings on glass, which provide highly efficient heat isolation, are nowadays extensively used in windows in offices and residential buildings for the purpose of saving energy in air conditioning. In this paper, multilayer low-emissivity coatings with the structure glass/SnO2/Ni–Cr/Ag/Ni–Cr/SnO2 were deposited onto large glass substrates in an industrial sputtering system. The extremely low thickness of the layers which compose such structures, as well as the large substrate area, causes the structure and impurity content of the films and interfaces to play an important role in providing efficient energy-saving performance as well as high optical transmittance. Thus, in-depth characterization was performed by spectroscopic ellipsometry, Rutherford backscattering spectroscopy and Auger electron spectroscopy. The use of these characterization techniques provides the great advantage of allowing the investigation of the whole multilayer system, including the interfaces. However, the properties of the individual layers (density, composition and optical behaviour) were also determined independently and compared to the values of corresponding bulk materials. Special attention is devoted to inter-diffusion of species.

Permalink: https://www.hzdr.de/publications/Publ-6366
Publ.-Id: 6366


Structure analysis and speciation of actinide systems using XAFS

Hennig, C.

Invited Lecture

  • Lecture (others)
    16.02.2004, CEA Marcoule, France

Permalink: https://www.hzdr.de/publications/Publ-6363
Publ.-Id: 6363


Combining EXAFS and X-ray powder diffraction to solve structures containing heavy atoms

Hennig, C.; Reich, T.; Kraus, W.; Reck, G.; Prokert, K.; Schell, N.

Determination of structures using X-ray powder diffraction is complicated if the reflection intensities are mainly influenced by the scattering from heavy atoms and the atomic coordinates of light atoms remain uncertain. A method like EXAFS, which is sensitive to short range order, gives reliable atomic distances in the surroundings of heavy atoms with a precision of ± 0.02 Å. The probability for obtaining the complete structure from X-ray powder diffraction increases if one includes parameters derived from EXAFS measurements as restraints during the procedure of structure solving. We demonstrate the potential of combining EXAFS and X-ray powder diffraction by solving the structure UO2[H2AsO4]2×H2O. The procedure starts with the determination of space group and cell parameters from XRD powder data. In a second step the absolute values of the structure factor |F| are separated by iterating a decomposition formula. The heavy atom positions are determined by direct methods. In the third step atomic distances of coordination polyhedra are estimated using EXAFS. Subsequently, the complete coordination geometries around the heavy atoms including reliable distances are used as restraints in the structure solving and refinement procedure.

  • Physica Scripta T115(2005), 352-355

Permalink: https://www.hzdr.de/publications/Publ-6362
Publ.-Id: 6362


Spéciation des complexes du technétium par couplage SAX - Electrochimie

Poineau, F.; Fattahi, M.; Grambow, B.; Den Auwer, C.; Hennig, C.

Le couplage SAZ - Elèctrochimie s'avère être une méthode pour la spéciation des espèces réduites du technetium. Cette méthode pourra être étendue à l'étude des espèces instables des actinides et des produits de fission.

  • Poster
    Journée de Radiochimie, 5.-6.2.2004, Avignon, France

Permalink: https://www.hzdr.de/publications/Publ-6361
Publ.-Id: 6361


Polarized EXAFS of uranium L1 and L3 edges - A comparison

Hennig, C.; Scheinost, A.

Uranium(VI) consists predominantly of two double bonded oxygen atoms in axial direction (Oax) and 4, 5 or 6 oxygen atoms in the equatorial plane (Oeq). This anisotropic coordination leads to a strong polarization dependence of XAFS. Responsible for the polarization dependence are the electron waves with different impulse-momentum at the L1 and L3 edges. We investigated this effect by comparing experimental data with the theory. The Theory and experiment are in good agreement. The polarization dependence of L1 edge is significantly stronger that of L3 edge.

  • Poster
    14th ESRF User Meeting, 10./11.02.2004

Permalink: https://www.hzdr.de/publications/Publ-6360
Publ.-Id: 6360


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