Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41709 Publications

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

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

Abstract

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


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

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

Abstract

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


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.

Abstract

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


Damping in thin NiFe films

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

Abstract

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


Strukturelle Untersuchung ionenbestrahlter Austausch-Verschiebungsschichtsysteme

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

Abstract

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


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.

Abstract

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


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.

Abstract

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


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

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

Abstract

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


Structure and interface characterisation of Exchange Bias FeMn-FeNi films

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

Abstract

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


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

Prasser, H.-M.

Abstract

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


Measurement Techniques for Multiphase Flows

Prasser, H.-M.

Abstract

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


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

Prasser, H.-M.

Abstract

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


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

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

Abstract

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


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.

Abstract

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


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

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

Abstract

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


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.

Abstract

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


Leserbriefe

Prasser, H.-M.

Abstract

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


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.

Abstract

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


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

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

Abstract

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


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

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

Abstract

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


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


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.

Abstract

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


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.

Abstract

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


Reflectivity characterization of ion irradiated exchange bias FeMn-FeNi films

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

Abstract

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


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

Fassbender, J.

Abstract

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


Ion beams for magnetic thin film applications

Fassbender, J.

Abstract

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


Optical control of the magnetization on the picosecond timescale

Fassbender, J.

Abstract

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


Optical control of the magnetization on the picosecond timescale

Fassbender, J.

Abstract

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


Betriebshandbuch für die Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW

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

Abstract

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

Downloads

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


Intersubband semiconductor light sources: history, status, and future

Helm, M.

Abstract

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


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.

Abstract

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


Structure analysis and speciation of actinide systems using XAFS

Hennig, C.

Abstract

Invited Lecture

  • Lecture (others)
    16.02.2004, CEA Marcoule, France

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

Abstract

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


Spéciation des complexes du technétium par couplage SAX - Electrochimie

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

Abstract

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


Polarized EXAFS of uranium L1 and L3 edges - A comparison

Hennig, C.; Scheinost, A.

Abstract

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


Pre-irradiation memory effect on the photoluminexcence intensity of Ge-implanted SiO2 layers

Lopes, J. M. J.; Zawislak, F. C.; Fichtner, P. F. P.; Behar, M.; Rebohle, L.; Skorupa, W.

  • Nuclear Instruments and Methods in Physics Research B 218(2004), 438-443

Permalink: https://www.hzdr.de/publications/Publ-6358


Evidence for the Interaction of Technetium colloids with humic substances by X-ray absorption spectroscopy

Maes, A.; Geraedts, K.; Bruggeman, C.; Vancluysen, J.; Rossberg, A.; Hennig, C.

Abstract

Spectroscopic extended X-ray absorption fine structure (EXAFS) evidence was obtained on the chemical environment of 99Tc(IV) atoms formed upon introduction of TcO4 - into four types of laboratory-scale synthetic and natural systems which mimic in situ natural reducing conditions in humicrich geochemical environments: (a) magnetite/pyrite in synthetic groundwater in the absence of humic substances (HSs), (b) magnetite/pyrite in natural Gorleben groundwater in the presence of HSs, (c) Boom clay sediment mixed with synthetic groundwater, and (d) Gorleben sand mixed with natural Gorleben groundwater. The investigated systems obey to pH 8-9 conditions, and all measured samples show similar EXAFS spectra for Tc, which could be fitted by a hydrated TcO2¿ xH2O phase. The results are interpreted as follows: upon introduction of high concentrations (millimolar to micromolar) of TcO4 to chemically reducing environments, small Tc(IV) oxidic polymers are formed, which either may aggregate into larger units (colloids) and finally precipitate or may interact in their polymeric form with (dissolved and immobile) humic substances. This latter type of interactionsTc(IV) colloid sorption onto HSssdiffers significantly from the generally accepted metal-humate complexation and therefore offers new views on the possible reaction pathways of metals and radionuclides in humic-rich environments.

  • Environmental Science & Technology 38(2004), 2044-2051

Permalink: https://www.hzdr.de/publications/Publ-6357


X-ray absorption spectroscopy studies of reactions of technetium, uranium and neptunium with mackinawite

Livens, F.; Jones, M.; Hynes, A.; Charnock, J.; Mosselmans, J.; Hennig, C.; Steele, H.; Collins, D.; Vaughan, D.; Et, A.

Abstract

Technetium, uranium and neptunium may all occur in the environment in more than one oxidation state (IV or VII, IV or VI and IV or V respectively). The surface of mackinawite, the first-formed iron sulfide: phase in anoxic conditions, can promote redox changes so a series of laboratory experiments were carried out to explore the interactions of Tc, U and Np with this mineral. The products of reaction were characterised using X-ray absorption spectroscopy. Technetium, added as TcO4-, is reduced to oxidation state IV and forms a TcS2-like species. On oxidation of the mackinawite in air to form goethite, Tc remains in oxidation state IV but in an oxide, rather than a sulfide environment. At low concentrations, uranium forms uranyl surface complexes on oxidised regions of the-mackinawite surface but at higher concentrations, the uranium promotes surface oxidation and forms a mixed oxidation state oxide phase. Neptunium is reduced to oxidation IV and forms a surface complex with surface sulfide ions. The remainder of the Np coordination sphere is filled with water molecules or hydroxide ions.

  • Journal of Environmental Radioactivity 74(2004), 211-219

Permalink: https://www.hzdr.de/publications/Publ-6356


Structure of uranium sorption complexes at montmorillonite edge sites

Hennig, C.; Reich, T.; Dähn, R.; Scheidegger, A. M.

Abstract

Extended X-ray absorption fine structure (EXAFS) spectroscopy at the uranium LIII-edge was used for determining the structural environment of aqueous uranyl sorbed onto montmorillonite. The study reveals that uranyl uptake at pH ~ 5- ~ 7 and at an initial uranyl concentration of 5×10-5 M takes place at amphoteric surface hydroxyl sites as inner-sphere complex. The measured bond distances between uranium and the equatorial oxygen atoms are in the range of 2.34 Å and 2.37 Å indicating an inner-sphere coordination. At ~ 3.4Å the presence of a U-Al backscattering pair was determined. This backscattering pair indicates that the binding of the uranyl unit to amphoteric surface hydroxyl sites occurs preferred as a bidentate inner-sphere complex on aluminol groups.

Keywords: Montmorillonite; Uranium; Sorption; EXAFS

  • Radiochim. Acta 90, 653-657 (2002)

Permalink: https://www.hzdr.de/publications/Publ-6355


EXAFS and XRD investigations of zeunerite and meta-zeunerite

Hennig, C.; Reck, G.; Reich, T.; Rossberg, A.; Kraus, W.; Sieler, J.

Abstract

In this paper EXAFS was used to determine bond lengths in the structures of zeunerite and meta-zeunerite. The atomic distances between heavy and light scatterers observed using EXAFS in meta-zeunerite deviate approximately 0.1 _A from literature data of single-crystal X-ray diffraction measurements. Because this difference is significant higher than the error limits of EXAFS measurements, the complete crystal structure of meta-zeunerite, Cu[UO2AsO4]2 _ 8 H2O, is revised by X-ray structure analysis. The bond length determinations by EXAFS and the revised XRD data agree within the experimental error limits. In this study EXAFS spectroscopy has proven to be an useful tool for determining precise local bond lengths in the environment of heavy atoms. Moreover, the crystal structure of zeunerite, Cu[UO2AsO4]2 _ 12 H2O, hitherto not been described in the literature, was investigated. Reflex broadening effects and intergrowth relationship between zeunerite and meta-zeunerite show that meta-zeunerite grows in nature due to dehydration of zeunerite. The structural transition from zeunerite to meta-zeunerite is connected with a change in the uranyl arsenate layer arrangement and the crystal water content.

  • Z. Kristallogr. 218 (2003) 37-45

Permalink: https://www.hzdr.de/publications/Publ-6354


An EXAFS and TRLFS study of the sorption of trivalent actinides onto smectite and kaolinite

Stumpf, T.; Hennig, C.; Bauer, A.; Denecke, M. A.; Fanghänel, T.

Abstract

The structure parameters of the Am3+ aquo ion and of Am(III) sorbed onto smectite and kaolinite at varying pH are analyzed using EXAFS. An Am-O distance of 2.47-2.49 Å is found and a coordination number of 8-9 oxygen atoms is observed for the Am3+ and its hydration sphere. Combined TRLFS (Cm(III)) and EXAFS (Am(III)) results show that An(III) sorbs onto smectite at pH 4, forming an outer-sphere complex and retains its complete primary hydration sphere. With increasing pH, inner-sphere sorption onto smectite and kaolinite occurs. The overall number of oxygen atoms coordinating the actinide ion remains about the same at pH 6, with four water molecules being replaced by oxygen atoms from the mineral surface during inner-sphere complex formation. The coordination number of sorbed Am(III) at pH 8 exhibits an apparent decrease, which may be affected by the formation of ternary OH-/Am/clay mineral surface species.

Keywords: Actinides; Clay minerals; EXAFS; Surface complexation; TRLFS

  • Radiochimica Acta 92(2004), 133-138

Permalink: https://www.hzdr.de/publications/Publ-6352


"Programme & Projekte - Beispiele für das Management in einer Forschungseinrichtung"

Joehnk, P.

  • Lecture (others)
    Vortrag Technische Universität, Bergakademie Freiberg, 27.05.2004

Permalink: https://www.hzdr.de/publications/Publ-6351


Grundlagen der Gestaltungslehre als Voraussetzung für gute (wissenschaftliche) Präsentationen

Joehnk, P.

  • Lecture (others)
    Doktorandenklausur, TU Szezcin, TU Lódz, IFW Dresden, Sklarska, Poreba, Polen. - 17.05.2004

Permalink: https://www.hzdr.de/publications/Publ-6350


n-type conductivity in high-fluence Si-implanted diamond

Weishart, H.; Heera, V.; Skorupa, W.

Abstract

Epitaxial SiC nanocrystals are fabricated by high-fluence Si-implantation into natural diamond at elevated temperatures between 760 °C and 1100 °C. Fluences under investigation range from 4.5 to 6.2 x 1017 Si cm-2 . This implantation scheme yields a buried layer rich of epitaxial aligned SiC- nanocrystals within slightly damaged diamond. The generation of a small fraction of graphitic sp2-bonds of up to 15 % in the diamond host matrix can not be avoided. Unintentional coimplantation with nitrogen results in a very high doping level of more than 1021 cm-3 . Resistivity and Hall measurements in van der Pauw geometry reveal a high, thermally stable n-type conductivity with electron concentrations exceeding 1020 cm-3and mobilities higher than 2 cm2/Vs. It is supposed, that both the SiC regions as well as the diamond matrix exhibit n-type conductivity and that the electron transport occurs across the low-resistivity SiC nanograins. In the SiC nanocrystals the electrons originate from nitrogen donors whereas in diamond defects are responsible for the electron conductivity. The formation of disordered graphite, which leads to low electron mobility, is substantially reduced.

Keywords: Ion implantation; thin films; Heterostructures; electronic properties; Ion radiation effects

  • Journal of Applied Physics 97(2005), 103514.

Permalink: https://www.hzdr.de/publications/Publ-6349


Nonlinear Charakteristics of Gas-Liquid Two-phase Flow and Verification of Extended Two-Fluid Model

Misawa, M.; Suzuki, A.; Morikawa, Y.; Minato, A.; Prasser, H.-M.

Abstract

Void fraction distributions of air-water two-phase flow in 3 different diameter vertical tubes (0.042 m, 0.1 m, and 0.2 m) were measured by 16x16 wire-mesh sensors with a sampling frequency of 1 kHz. Also, predictions under the same flow conditions were made by a 3D extended two-fluid model, generating a time-series of cross-section averaged void fraction at the same frequency with the experiment. Fluctuation characteristics from experiments and simulations were analysed in view of the probability density function, frequency spectrum, and Trajectory Parallel Measures (TPM). The analyses of TPM showed that dynamics is well-established for large nunnles whose fiameter is on the order of Taylor wave length in an air-water system, although small bubble void fraction signal is almost random in dynamical point of view. It is shown that the fluctuation component in void fraction time series can be used as one of criteria for validation of numerical models.

Keywords: two-fluid model; gas-liquid flow; wire-mesh sensor; statistical analysis; trajectory parallel measures; code validation

  • 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 213.

Permalink: https://www.hzdr.de/publications/Publ-6348


NuclearReactor - Reaktorphysik populär im Internet - ein Versuch, den Internetauftritt der KTG attraktiver zu machen

Prasser, H.-M.

Abstract

Die Ortssektion Sachsen der Kerntechnischen Gesellschaft bemüht sich kontinuierlich um eine aktuelle und attraktive Präsens im Internet. Mit der eigenen Internetseite "www.ktgsachsen.de", die seit Oktober 2001 besteht, wird versucht, neben der Information für die Mitglieder - in erster Linie Ankündigungen und Auswertungen von Veranstaltungen - mit Diskussionsbeiträgen zur Kernenergie ein breiteres Publikum zu erreichen. Dabei werden unter der Rubrik ARGUMENTE Themen, wie Nachhaltigkeit, CO2-Emissionen und Energieressourcen berührt. Unter der Überschrift NEWS wird über aktuelle Ereignisse informiert. Insgesamt
bleibt die Resonanz auf diese Internetseite jedoch gering. Nur sehr selten trifft Post ein, die auf die publizierten Argumente eingeht oder auch Widerspruch anmeldet. Um die Attraktivität der Internetseite zu erhöhen und dabei gleichzeitig einen Beitrag zum allgemeinen Informationsstand über die physikalischen Grundlagen der Reaktortechnik in der Bevölkerung zu leisten, wurde im November 2003 ein neuer Weg beschritten. Es wurde ein Programm zur On-line Simulation der Kettenreaktion in einem Kernreaktor entwickelt und ins Netz gestellt. Die Ortssektion Sachsen strebt damit die folgenden Ziele an:
(1) Durch eine attraktive Darstellung der physikalischen Prozesse in einem Kernreaktor, die durch interaktive Eingriffe über die Steuerorgane beeinflusst werden können, entsteht eine Art Computerspiel, mit dem es gelingen soll, interessierten Personen - insbesondere Kindern und Jugendlichen - Einblicke in die Reaktorphysik zu ermöglichen. Dabei wird Wert darauf gelegt, die Grundprozesse qualitativ möglichst korrekt und umfassend darzustellen, um einen hohen Bildungseffekt zu erreichen.
(2) Durch die spielerische Erschließung des Stoffes soll die emotionale Barriere, die häufig gegenüber der Kerntechnik besteht, abgebaut werden, um die Besucher der Internetseite an weitergehenden Informationen zu interessieren und die Aufgeschlossenheit für weitere Diskussionen und Argumente zu erhöhen.
(3) Durch ständige Weiterentwicklung sollen in monatlichen Abständen jeweils neue Versionen des Programms mit erweiterten Möglichkeiten angeboten werden, um eine Art Fangemeinde entstehen zu lassen, die der Internetseite ihre Treue hält. Das Programm wurde in der Programmiersprache DELPHI erstellt. Der unter WINDOWS ausführbare Code (EXE) kann zusammen mit einem Manual, welches die physikalischen
Hintergründe in populärwissenschaftlicher Weise beschreibt und dem Anwender numerische Experimente vorschlägt, von der Webseite www.ktg-sachsen.de heruntergeladen werden.

Keywords: Education; Reactor Physics; Public Relation; Monte-Carlo Simulation

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2004, 25. - 27. Mai 2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2004, 25. - 27. Mai 2004, Düsseldorf, Germany, paper 495-500

Permalink: https://www.hzdr.de/publications/Publ-6347


Effect of excess vacancies in ion beam synthesis of SiC nanoclusters

Kögler, R.; Eichhorn, F.; Mücklich, A.; Skorupa, W.; Serre, C.; Perez-Rodriguez, A.

Abstract

SiC nanoclusters are synthesized in Si by simultaneous dual implantation using two ion beams, of C and Si ions. This implantation mode is associated with extra excess vacancy generation. The effect of vacancies on SiC synthesis is investigated in this study. The amount of synthesized SiC is compared for different implantation modes, simultaneous and sequential ones. Sequential pre-deposition of vacancy defects in Si before the C implantation is performed by additional Si and He implantation. The simultaneous dual beam implantation is found to be the only method to improve SiC synthesis. The introduction of vacancies, both excess vacancies and He induced vacancies, by a sequential implantation process is disadvantageous for SiC nanocluster formation. The pre-deposition of vacancy defects is accompanied with higher crystal damage and/or the defects are annealed out during the subsequent C implantation at temperatures above 400oC. Vacancies must be created “in-situ” during C implantation to achieve enhanced output of SiC.

Keywords: Ion implantation; Simultaneous dual implantation; SiC; Si; Ion beam synthesis

  • Vacuum 78(2005)2-4, 177-180

Permalink: https://www.hzdr.de/publications/Publ-6346


Excess vacancies induced by ion beam implantation into silicon

Kögler, R.; Eichhorn, F.; Peeva, A.; Voelskow, M.; Mücklich, A.; Serre, C.; Skorupa, W.

Abstract

The process of formation of excess vacancies by ion implantation is explained. Moreover, the simulation of the process, the experimental detection of excess vacancies and their application for defect engineering is described.

Keywords: Ion implantation; Silicon; Excess vacancies; Electron microscopy; Positron annihilation spectrometry

  • Lecture (Conference)
    V th international conference on ion implantation and other applications of ions and electrons, ION2004, June 14-17, 2004, Kazimierz Dolny, Poland

Permalink: https://www.hzdr.de/publications/Publ-6345


Generation eines Pseudomonas aeruginosa Biofilms auf Biotit und dessen mikroskopische Charakterisierung.

Großmann, K.; Arnold, T.; Bernhard, G.; Garske, B.; Krawietz, R.

Abstract

Zum Studium der Wechselwirkungen von Schwermetallen mit Biofilmen in der Umwelt ist die reproduzierbare Präparation und detaillierte Charakterisierung von Biofilmen auf Mineral- und Gesteinsoberflächen notwendig. Die initialen Aufwachsstadien von auf Biotit erzeugten Pseudomonas aeruginosa Biofilmen wurden mit Rasterelektronenmikroskopie (SEM) und Rasterkraftmikroskopie (AFM) visualisiert. Zum Studium des reifen Biofilms wurden Fluoreszenzmikroskopie und konfokale Fluoreszenzmikroskopie (CLSM) eingesetzt. Die Unterscheidung zwischen lebenden und toten Bakterien erfolgte mit Hilfe eines LIVE/DEAD - Kit. Zur Visualisierung von Polysacchariden innerhalb der EPS wurden Lektine gekoppelt mit Fluoreszenzfarbstoffen verwendet. Hierbei konnten die einzelnen Polysaccharide der EPS unterschieden werden in solche, die direkt an Zellwände der Bakterien gebunden sind und weitere, die eine diffuse Verteilung der EPS im Biofilm aufzeigen. Die Dicke der erzeugten Biofilme auf den Biotitoberflächen wurde mit CLSM bestimmt. Sie schwankte zwischen 5,3 µm für Biofilme, die unter Nährstoffmangel angezogen wurden, und 16,6 µm bei ausgereiften Biofilmen.

Keywords: Biofilm; Pseudomonas aeruginosa; Mikroskopie; Fluoreszenzfarbstoffe; Lectine

  • GWF-Wasser/Abwasser 146(2005) 2, 113-118

Permalink: https://www.hzdr.de/publications/Publ-6344


Validation of models for bubble forces

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

Abstract

Closure laws are needed for the qualification of CFD codes for two-phase flows. In case of bubbly and slug flow, the momentum transfer between the phases is usually modelled by forces acting on the bubbles. These forces depend on the liquid flow field as well as on the size and the shape of the bubbles. To validate models for these forces a detailed database for vertical pipe flow is used. It contains not only the information on the radial distribution of bubbles of different size, but also information on the bubble size distribution. Measurements were done for a large number of combinations of gas and liquid superficial velocities and for two different pipe diameter (DN50 and DN200). An one-dimensional model, which resolves the variables in radial direction and which considers a large number of bubble size classes to account for the size effect, is used for an analysis of models for these forces. The results obtained by this model were compared to 3D results obtained by the commercial code CFX-5.7 for simplified cases with only one bubble class. The effect of the number of bubbles classes as well as the effect of the lateral extension of the bubbles were analysed. For the validation of the bubble forces measured bubble size distributions were taken as an input for the model. On basis of the assumption of an equilibrium of the lateral bubble forces, radial volume fraction profiles were calculated separately for each bubble class. In the result of the validation of different models for the bubble forces, a set of Tomiyama lift and wall force and the Favre averaged turbulent dispersion force was found to reflect the experimental data with best agreement. Some discrepancies remain at high liquid superficial velocities.

Keywords: Two-phase flow; bubble; bubble forces; modelling; CFD

  • Lecture (Conference)
    42nd European Two-Phase Flow Group Meeting, 23.-25.06.2004, Genua, Italy
  • Contribution to proceedings
    42nd European Two-Phase Flow Group Meeting, 23.-25.06.2004, Genua, Italy, paper E1

Permalink: https://www.hzdr.de/publications/Publ-6342


Atomic computer simulations of defect migration in 3C and 4H-SiC

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

Abstract

Knowledge of the migration of intrinsic point defects is crucial to understand defect recovery, various annealing stages and microstructural evolution after irradiation or ion implantation. Molecular dynamics (MD) and the nudged-elastic band method have been applied to investigate long-range migration of point defects in SiC over the temperature range from 0.36 to 0.95 Tm , and the defect diffusion coefficient, activation energy and defect correlation factor have been determined. The results show that the activation energies for C and Si interstitials in 3C-SiC are about 0.74 and 1.53 eV, respectively, while it is about 0.77 eV for a C interstitial in 4H-SiC. The minima energy paths reveal that the activation energies for C and Si vacancies are about 4.1 and 2.35 eV, respectively. Finally, the results are discussed and compared with experimental observations and available ab initio data.

Keywords: Defect diffusion; activation energy; molecular dynamics; nudged-elastic band method

  • Contribution to external collection
    Materials Science Forum, 457-460; Part 1 (2004), 457-460

Permalink: https://www.hzdr.de/publications/Publ-6341


Development of a SAXS-Method to characterize the damage zone around a crack tip in metals

van Ouytsel, K.; Müller, G.

Abstract

The aim was to characterize the damage zone ahead a crack tip in technical aluminium alloys using Small Angle X-ray Scattering. Experiments were conducted at the Austrian beamline at ELETTRA in Trieste from 18th-24th of February 2003. Four specimens of 2024-T351 aluminium alloy, different in shape, deformation condition and grain size, were investigated. Anisotropic grain boundary scattering of the CT-specimen was observed.

Keywords: Small Angle X-ray Scattering (SAXS); damage zone; crack tip

  • Contribution to external collection
    Austrian Small Angle X-ray Scattering (SAXS) Beamline at ELETTRA, Annual Report 2003, published 2004, 51-52

Permalink: https://www.hzdr.de/publications/Publ-6340


Simultaneous Determination of 226Ra, 233U and 237Np by Liquid Scintillation Spectrometry

Nebelung, C.; Baraniak, L.

Abstract

A method has been developed for the simultaneous determination of 226Ra, 233U and 237Np by liquid-scintillation (LS) spectrometry. This method consists in the evaluation of strongly overlapped multi peak spectra by a special peak fit function, considering the deviation of the LS-peak shape from the pure Gaussian distribution. First 237Np is determined using its daughter 233Pa by analyzing the ß-spectrum. 226Ra follows from the α-spectrum recorded 6 weeks after sample preparation. The peak of the three short-lived daughters 222Rn, 218Po and 214Po corresponds to the 226Ra activity under radioactive equilibrium conditions. Finally the 233U activity results from the joint α-peak at 4.8 MeV of the deconvoluted spectrum by subtracting the activity of 226Ra and 237Np. A second option uses the characteristic double peak of 237Np near 4.8 MeV. Due to the fact that the position is accurately known the pure α-spectrum can be analyzed for the determination of the given nuclides.

Keywords: Liquid scintillation; Alpha-Beta- Separation; Deconvolution of Multielement spectra

  • Applied Radiation and Isotopes, 65 (2007) 209-217

Permalink: https://www.hzdr.de/publications/Publ-6337


Molecular Bacterial Diversity in Water at the Deep-Well Monitoring Site Tomsk-7

Nedelkova, M.; Radeva, G.; Selenska-Pobell, S.

Abstract

Bacterial diversity was studied in a water sample collected from a depth of 290-324 m below the land surface from the monitoring site S15 near the city of Tomsk, Siberia, Russia. In order to overcome the problems of culturability of bacteria, we applied a direct molecular approach based on PCR amplification and cloning of the 16S rDNA of the members of the natural bacterial communities. 65% of the cloned sequences were almost identical to the 16S rRNA genes of Dechlorosoma sp. belonging to the Rhodocyclus group of b-subclass of Proteobacteria. Relatively high was the number of the sequences which shared high identities with the 16S rRNA genes of some cultured g-Proteobacteria (6.9%), a-Proteobacteria (4.6%) and with the sequences of mostly uncultured members of Cytophaga/Flavobacterium/Bacteroides (5.4%), Actinobacteria (4.6%) and Planctomycetales (2.3 %). The rest of the retrieved sequences were clustered in small groups, each containing about 1 % of the total number of clones, and they matched with 16S rDNA sequences of Bacillales, Holophaga/Acidobacteria, Nitrospira, and d-Proteobacteria, respectively.

  • Contribution to external collection
    Chin-Fu Tsang and John A. Apps: Developments in Water Science, Underground Injection Science and Technology, Netherlands: Elsevier, 2005, 978-0-444-52068-5, 521-536

Permalink: https://www.hzdr.de/publications/Publ-6336


Time-Dependent Kinematic Dynamos in Finite Cylinders as Treated with the Integral Equation Approach

Xu, M.; Stefani, F.; Gerbeth, G.

Abstract

Dynamo action is generally accepted as the source of cosmic magnetic fields, such as the fields of planets, stars and galaxies. The understanding of dynamos has considerably progressed during the last decades. Recently, the hydromagnetic dynamo effect has been demonstrated experimentally in large liquid sodium facilities in Riga and Karlsruhe.
The electrically conducting fluid is usually confined to a finite domain which is surrounded by an insulator. For only a few cases, such as spheres or cylinders with infinite length, the boundary conditions for the magnetic field are easily implementable. In most cases, including finite cylinders which are relevant for the liquid sodium experiments in Riga, Karlsruhe, Cadarache and New Mexico, the correct handling of the non-local boundary conditions is far from trivial. We have re-formulated Pre-Maxwell's equations to an integral equation system under the assumption that the velocity field is stationary.
The main advantage of this approach is that the numerical solution of the integral equation system does not require any discretization of the exterior region.
In the present work, the integral equation approach is performed on a group of Beltrami flows (and some modifications) with the topologies s2t2, s2t1 and s1t1 in a finite cylinder. Beltrami flows are characterized by maximum helicity for a given magnetic Reynolds number. Due to the axisymmetry of these flows, the integral equation system in the cylindrical system is reduced to a two-dimensional form.
The calculated results show a good agreement with those obtained by a differential equation approach. This integral equation approach exhibits attractive features such as robustness and stability.
The impact of a stagnant conducting layer surrounding the cylinder is also investigated. Such a layer can reduce the critical magnetic Reynolds number significantly, and it can even transform no-dynamos into dynamos. Interestingly, the presence of a layer can also change an oscillatory dynamo to a steady dynamo.

  • Lecture (Conference)
    7th MHD-Days, Technische Universität Ilmenau, 20.-21.09.2004, Ilmenau, Germany

Permalink: https://www.hzdr.de/publications/Publ-6335


Application of gamma tomography to the measurement of fluid distributions in a hydrodynamic coupling

Hampel, U.; Hoppe, D.; Diele, K.-H.; Fietz, J.; Höller, H.; Kernchen, R.; Prasser, H.-M.; Zippe, C.

Abstract

Gamma tomography has been used to investigate the fluid distribution within multiple axial planes of a hydrodynamic test coupling under operating conditions. The tomographic data was obtained by phase correlated averaging of projections from the homogeneously rotating parts of the coupling. By application of the filtered backprojection reconstruction technique to the data we reconstructed average fluid fraction distributions in the transversal planes at different operating points of the coupling.

Keywords: gamma tomography; hydrodynamic coupling; two-phase flow measurement

  • Flow Measurement and Instrumentation 16(2005), 85-90

Permalink: https://www.hzdr.de/publications/Publ-6334


Overview of the present status of the SRF gun design and construction

Teichert, J.; Evtushenko, P.; Janssen, D.; Lehmann, W.-D.; Lehnert, U.; Michel, P.; Schneider, C.; Stephan, J.; Volkov, V.; Will, I.

Abstract

A status report on the SRF photo-injector activities at FZR within the CARE/PHIN project will be given. The new SRF gun has been designed for CW operation at the ELBE linac with an average current of 1 mA, 77 pC bunch charge, and 10 MeV energy. The basic concept of the gun, operating a normal conducting, thermally insolated photo-cathode within a superconducting cavity, have been taken from the first SRF half-cell gun [1] which was successfully tested. In this report the design layout of the SRF photo-injector, the parameters of the superconducting cavity and the expected electron beam parameters are presented. The SRF gun will have a 31/2-cell niobium cavity working at 1.3 MHz and will be operated at 2 K. The cavity consists of three full cells with TESLA-like shapes and a half-cell in which the photocathode is situated.

Keywords: SRF photo-injector; electron source; superconductivity; niobium cavity; electron acceleration

  • Lecture (Conference)
    1st Workshop of ELAN, 04.-06.05. 2004, Frascati, Rom, Italy
  • Contribution to proceedings
    1st Workshop of ELAN, 04.-06.05.2004, Frascati, Italy CARE-Note-2004-010-ELAN

Permalink: https://www.hzdr.de/publications/Publ-6333


Study of e+,e production in elementary and nuclear collisions near the production threshold with HADES

Salabura, P.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bellia, G.; Belvers, D.; Bielcik, J.; Böhmer, M.; Bokemeyer, H.; Boyard, J.; Braun-Munzinger, P.; Chepurnov, V.; Chernenko, S.; Christ, T.; Coniglione, R.; Diaz, J.; Djeridi, R.; Dohrmann, F.; Duran, I.; Eberl, T.; Emeljanov, V.; Fabbietti, L.; Fateev, O.; Fernandez, C.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Fuentes, B.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzalez, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Hoffmann, J.; Holzmann, R.; Ierusalimov, A.; Iorii, J.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanakir, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kotte, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Kurtukian-Nieto, T.; Lang, S.; Lehnert, J.; Maiolino, C.; Marn, J.; Markert, J.; Metag, V.; Montes, N.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Panebratsev, Y.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Przygoda, W.; Rabin, N.; Ramstein, B.; Reshetink, A.; Ritmanh, J.; Rodriguez-Prieto, G.; Roy-Stephan, M.; Rustamov, A.; Sabin-Fernandez, J.; Sadovsky, A.; Sailer, B.; Sanchez, M.; Smolyankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; C., S.; Sudol, M.; Titov, A.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Vazquez, A.; Volkov, Y.; Wagner, V.; Walus, W.; Winkler, S.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.

Abstract

HADES is a second generation experiment designed to study dielectron production in proton, pion, and heavy ion induced reactions at the GSI accelerator facility in Darmstadt. The physics programme of HADES is focused on in-medium properties of the light vector mesons. In this contribution we present status of the HADES experiment, demonstrate its capability to identify rare dielectron signal, show first experimental results obtained from C+C reactions at 2 A GeV and shortly discuss physics programme of up-coming experimental runs.

  • Progress in Particle and Nuclear Physics 53(2004), 49

Permalink: https://www.hzdr.de/publications/Publ-6329


Uranium binding by the natural isolate Bacillus Sphaericus JG-A12 and its application for bioremediation

Raff, J.; Merroun, M.; Rossberg, A.; Foerstendorf, H.; Selenska-Pobell, S.

Abstract

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. Similarly to some other Bacillus isolates from this site, cells and spores of B. sphaericus JG-A12 bind selectively and reversibly large amounts of different toxic metals, such as uranium /1/. The cells of the B. sphaericus strain JG-A12 are covered by a surface layer (S-layer) protein. The latter forms a highly ordered lattice with distinct structural and chemical properties. Because it was shown that S-layers may work as protective coat, matrix for biomineralization, molecular sieve or as ion and molecule trap /2, 3, 4/ their special importance for the interaction of cells with radionuclides and heavy-metals in the surrounding environment is evident. As a consequence of the above mentioned properties, B. sphaericus JG-A12 was investigated with regard to its suitability to work as a binding matrix for bioremediation of uranium mining waste waters. A fundamental requirement for biotechnological application is the complete immobilization of the biomass in a porous structure. In this work, sol-gel techniques were used for embedding B. sphaericus JG-A12 cells, spores and S-layer protein in a SiO2-matrix in order to obtain a novel kind of biological ceramic (biocer) /5/. To select the appropriate filter material, uranium sorption and desorption experiments were carried out with free and immobilized cells, spores and S-layer protein of B. sphaericus JG-A12. Besides quantification of the available binding sites, the formed uranium complexes were investigated also by using infrared and extended X-ray absorption fine structure (EXAFS) spectroscopy. The latter revealed that the binding of uranium by free cells, spores and S-layer occurred via phosphate and carboxyl groups. The presence of phosphate groups was confirmed by different methods not only for cells and spores but also for the S-layer protein. The spectroscopic analysis of the uranium complexes formed by the biocer demonstrates the metal binding via phosphate groups and the formation of a uranium precipitate, what is of special interest for the binding capacity of the biocer. In case of the xerogel uranium was bound to silanol groups. Analyses of the uranium sorption by cells, spores and S-layer protein of B. sphaericus JG-A12 and of the xerogel itself (without biocomponent) showed highest binding capacity for spores followed by cells, S-layer protein and xerogel. In case of embedded biocomponents only the binding capacity of spores is significantly reduced and is lower than for cell- and S-layer-ceramics. Uranium bound to biocers can be completely removed by washing with citric acid.

1. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67
2. Beveridge, T.J. 1979 J. Bacteriol. 139 (3): 1039-1048
3. Schultze-Lam, S. et al. (1992) J. Bacteriol. 174 (24): 7971-7981
4. Sára, M. & Sleytr, U.B. 1987. J. Bacteriol. 169 (6): 2804-2809
5. Raff, J. et al (2003) Chem. Mater 2003; 15(1):240-4

  • 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-6328


Bacterial Diversity in a Soil Sample from a Uranium Mining Waste Pile as estimated via a Culture-Independent 16S rDNA Approach

Satchanska, G.; Golovinski, E.; Selenska-Pobell, S.

Abstract

Bacterial diversity was studied in a soil sample collected from a uranium mining waste pile situated near the town of Johanngeorgenstadt, Germany. As estimated by ICP-MS analysis the studied sample was highly contaminated with Fe, Al, Mn, Zn, As, Pb and U. The 16S rDNA retrieval, applied in this study, demonstrated that more than the half of the clones of the constructed 16S rDNA library were represented by individual RFLP profiles. This indicates that the composition of the bacterial community in the sample was very complex. However, several 16S rDNA RFLP groups were found to be predominant and they were subjected to a sequence analysis. The most predominant group, which represented about 13% of the clones of the 16S rDNA library, was affiliated with the Holophaga/Acidobacterium phyllum. Significant was also the number of the proteobacterial sequences which were distributed in one predominant alpha-proteobacterial cluster representing 11% of the total number of clones and in two equal-sized beta- and gamma-proteobacterial clusters representing each 6% of the clones. Two smaller group representing both 2% of the clones were affiliated with Nitrospira and with the novel division WS3. Three of the analysed sequences were evaluated as a novel, not yet described lineage and one as a putative chimera.

  • Comptes Rendues del Ácademie bulgare des Sciences 57(2004)5, 75-82

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Permalink: https://www.hzdr.de/publications/Publ-6327


Molecular analysis of bacterial populations in water samples from two uranium mill tailings by using a RISA retrieval

Radeva, G.; Selenska-Pobell, S.

Abstract

A ribosomal intergenic spacer amplification (RISA) retrieval was applied to analyze the natural bacterial communities in drain waters of two uranium mill tailings - Gittersee/Coschütz in Germany and Shiprock in the USA. About 35% of the clones from the RISA library constructed for the samples of the German tailings represented a microdiverse population of Planctomycetales. The rest of the clones were affiliated with rather diverse bacterial groups including g- and d- Proteobacteria, Cytophaga/Flavobacterium/Bacteroides (CFB), Nitrospira, Verrucomicrobia and Actinobacteria. 8% of the cloned sequences represented a novel bacterial lineage from the recently described division NC3.
Bacterial diversity in the Shiprock mill tailings was found to be significantly lower. The RISA library constructed for those samples contained only two larger groups of clones, representing b-proteobacterial species and one small group, which was affiliated with d-Proteobacteria.

  • Comptes Rendues de l´Academie bulgare des Sciences 57(2004)6, 111-115

Permalink: https://www.hzdr.de/publications/Publ-6326


Combined Analysis of Threshold-Near Production of ω and φ Mesons in Nucleon-Nucleon Collisions

Kaptari, L. P.; Kämpfer, B.

Abstract

Vector meson (V=ω , φ) production in threshold-near elementary nucleon-nucleon collisions pp to ppV, pn to pnV and pn to dV is studied within an effective meson-nucleon theory.
It is shown that a set of effective parameters can be established to explain fairly well the available experimental data on angular distributions and the energy dependence of the total cross sections without explicit implementation of the Okubo-Zweig-Iisuka rule violation. Isospin effects are considered in details and compared with experimental data whenever available.

Keywords: bector mesons; OZI rule; hadron reactions

  • Eur. Phys. Journal A 23 (2005)291-304

Permalink: https://www.hzdr.de/publications/Publ-6324


Bacterial diversity in water samples from uranium wastes as demonstrated by 16S rDNA and RISA retrievals

Radeva, G.; Selenska-Pobell, S.

Abstract

Bacterial diversity was assessed in water samples collected from several uranium mining wastes in Germany and in the USA by using 16S rDNA and RISA retrievals.
The results obtained using the 16S rDNA retrieval showed that the samples collected from the uranium mill tailings Schlema/Alberoda, Germany, were predominated by Nitrospina-like bacteria, whereas those from the mill tailings Shiprock, New Mexico, USA, were predominated by g-Pseudomonas and Frateuria spp. Additional smaller populations of CFB, a-, and d-proteobacteria were identified in the Shiprock samples as well. Proteobacteria and CFB were also predominant in the third uranium mill tailings studied, Gittersee/Coschütz in Germany, but the groups of the predominant clones were rather small. Most of the clones of the Gittersee/Coschütz samples represented individual sequences that indicated a high level of bacterial diversity. The samples from the fourth uranium waste studied, namely Steinsee Deponie B1 in Germany, were predominantly occupied by Acinetobacter spp.
The RISA retrieval provided results complementary to those obtained by the 16S rDNA analyses. For instance, in the Shiprock samples an additional predominant bacterial group was identified and affiliated to Nitrosomonas sp., whereas in the Gittersee/Coschütz samples Anammox-populations were identified which were not retrieved by the used 16S rDNA approach.

Keywords: bacterial diversity; 16S rDNA; ribosomal intergenic spacer amplification (RISA); uranium wastes

  • Canadian Journal of Microbiology 51(2005)11, 910 - 923

Permalink: https://www.hzdr.de/publications/Publ-6323


Migration of Uranium (IV)/(VI) in the Presence of Humic Acids in Quartz Sand: A Laboratory Column Study

Mibus, J.; Sachs, S.; Nebelung, C.; Bernhard, G.

Abstract

The migration behavior of U(IV)/U(VI) in the presence of humic acids was studied in a laboratory quartz sand system by column experiments. It was found that humic acid influences the transport of U(IV) and U(VI). In presence of humic acid both redox species migrate nearly as fast as the groundwater flow. Retardation factors of 1.11 ± 0.03 and 1.14 ± 0.03 as well as eluate recoveries of 0.83 ± 0.09 and 0.65 ± 0.07 were determined for U(VI) and U(IV), respectively. In case of U(VI) humic acid exhibits a clear mobilizing effect compared to the humic acid-free system. There are also strong indications for a similar effect on the U(IV) transport.
The present study demonstrates that humic acids can play an important role in the migration of tetravalent actinides. Consequently, the humic colloid-borne transport of actinides has to be taken into account in performance assessment.

Keywords: Uranium(IV); Uranium(VI); Humic Acids; Quartz Sand; Migration; Adsorption

  • Journal of Contaminant Hydrology 89 (2007) 199 - 217 DOI 10.1016/j.jconhyd.2006.08.005

Permalink: https://www.hzdr.de/publications/Publ-6322


Biotechnological potential of bacteria from extreme environments

Raff, J.

  • Lecture (Conference)
    Internationales Sales-Meeting, 17.-18.6.2004, Lampertheim, Germany

Permalink: https://www.hzdr.de/publications/Publ-6320


Synthesis of a 11C-labelled Nonsteroisal Glucocorticoid Receptor Ligand as Potential Radiotracer for Imaging Brain Glucocorticoid Receptors with Positron Emission Tomography (PET)

Wüst, F.; Kniess, T.; Bergmann, R.

  • Lecture (Conference)
    12th Workshop of the Central European Division e. V. of the International Isotope Society, 17.-18.06.2004, Bad Soden, Germany
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmceuticals 47(2004), 1051-1052

Permalink: https://www.hzdr.de/publications/Publ-6318


18F-Labelling of a Potent Nonpeptide CCR1 Antagonist for the Diagnosis of the Alz-heimer’s Disease

Mäding, P.; Füchtner, F.; Hilger, C. S.; Halks-Miller, M.; Horuk, R.

Abstract

Objectives: PET imaging of cardiac reporter gene expression holds promise for noninvasive monitoring of gene therapy. Two approaches based on herpesviral thymidine kinase gene(HSV1-tk) habe been applied. Wild-type HSV1-tk was imaged with 2´-fluoro-2´-deoxy-5[124I]-iodo-arabinofuranosyluracil([124I]FIAU), and mutant HSV1-sr39tk was imaged with 9-[4-[18F]-fluoro-3-(hydroxymethylbutyl)guanine([18F]FHBG).
Methods: Adenovirus expressing wild-type HSV1-tk(Adtk), mutant HSV1-sr39tk (Adsr39tk), or control gene (AdLacZ) were directly injected into myocarcardium of 24 rats and 8 pigs. Two days later, dynamic PET imaging was performed for 120 min after injection of [124I]FIAU or [18F]FHBG with a clinical scanner. Imaging with [13N]-ammonia was performed to identify cardiac regions of interest. Pig hearts were sliced into 5 short-axis slices for ex vivo imaging, and regional tracer uptake was analyzed.
Results: For [124I]FIAU, the largest difference of cardiac uptake between Adtk rats and controls was found at 10-30 min after injection (1.7±0.25 vs 0.87±0.22 %dose/ml, p=0.035). No difference was observed at later imaging times due to [124I]FIAU washout. For [18F]FHBG, difference between Adsr39tk rats and controls continuously increased over time and was largest at 105-120 min (1.45±0.45 vs 0.35±0.05 %dose/ml, P=0.0066). Global cardiac reporter probe kinetics in rats was confirmed by regional myocardial analysis in pigs. Transgene expression was specifically visualized by both approaches. Highest target/background ratio of [124I]FIAU in Adtk infected myocardium was 1.50±0.20 vs 2.64±0.49 for [18F]FHBG in Adsr39tk infected areas (P=0.01). In vivo results of rats were confirmed by ex vivo counting and autoradiography. In vivo segmental reporter probe uptake in pigs correlated well with those in ex vivo images.
Conclusions: Both combinations were feasible for PET of cardiac transgene expression in different species. Specific probe kinetics suggests different myocardial handling of pyrimidine ([124I]FIAU) and acycloguanosine ([18F]FHBG) derivatives. Results are in favour of [18F]FHBG because of continuous accumulation over time and higher imaging contrast.

  • Lecture (Conference)
    12th Workshop of the Central European Division e. V. of the International Isotope Society, 17.-18.06.2004, Bad Soden, Germany
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 47(2004), 1053-1054

Permalink: https://www.hzdr.de/publications/Publ-6317


No-carrier added synthesis of 18F-labelled nucleosides using Stille cross-coupling reactions with 4-[18F]fluoroiodobenzene

Wüst, F.; Knieß, T.

Abstract

The radiosyntheses of 5-(4´-[18F]fluorophenyl)-uridine [18F]-11 and 5-(4´-[18F]fluorophenyl)-2´-deoxy-uridine [18F]-12 are described. The 5-(4´-[18F]fluoro-phenyl)-substituted nucleosides were prepared via a Stille cross-coupling reaction with 4-[18F]fluoroiodobenzene followed by basic hydrolysis using 1 M potassium hydroxide. The Stille cross-coupling rreaction was optimized by screening various palladium complexes, additives and solvents. By using optimized labelling conditions (Pd2(dba)3/CuI/AsPh3 in DMF/dioxane (1:1), 20 min at 65 °C), 550 MBq of [4-18F]fluoroiodobenzene could be converted into 120 MBq (33 %, decay-corrected) of 5-(4´-[18F]fluorophenyl)-2´-deoxy-uridine [18F]-12 within 40 min, including HPLC purification.

Keywords: Stille cross-coupling; 4-[18F]fluoroiodobenzene; nucleosides; uridine

Permalink: https://www.hzdr.de/publications/Publ-6316


Migration of di- and tri-interstitials in silicon

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

Abstract

A comprehensive study on the migration of di- and tri-interstitials in silicon is performed using classical molecular
dynamics simulations with the Stillinger–Weber potential. The initial di- and tri-interstitial configurations with the lowest
formation energies are determined, and then, the defect migration is investigated for temperatures between 800 and
1600 K. The defect diffusivity and the self-diffusion coefficient per defect are calculated. Compared to the mono-interstitial,
the di-interstitial migrates faster, whereas the tri-interstitial diffuses slower. The migration mechanism of the diinterstitial
shows a pronounced dependence on the temperature. Like in the case of the mono-interstitial, the mobility of
the di-interstitial is higher than the mobility of the lattice atoms during the defect diffusion. On the other hand, the triinterstitial
mobility is lower than the corresponding atomic mobility. The implications of the present results for the
analysis of experimental data on defect evolution and migration are discussed.

Keywords: Defects; diffusion; silicon; computer simulations

Permalink: https://www.hzdr.de/publications/Publ-6315


Electrochemical behaviour of nickel surface-alloyed with copper and titanium

Pham, M. T.; Maitz, M.; Richter, E.; Reuther, H.; Prokert, F.; Muecklich, A.

Abstract

Ni was surface-alloyed with Cu, Ti or Cu + Ti by ion implantation. This material was examined for its redox and electrocatalytic activity by cyclic voltammetry. The surface was characterized by X-ray photoelectron spectroscopy, X-ray and electron diffraction, and electron and atomic force microscopy. This type of materials exhibited a unique voltammetric response of Ni and was shown to stabilize the ß modification of the Ni oxide/hydroxide. Cu modified the anodic oxidation of glucose and the oxygen evolution to a higher degree than Ti. The morphology and microstructure differed from those of bulk materials.

Keywords: Cu-Ti-Ni alloy electrodes; electrocatalysis; glucose; surface alloying; ion beams

  • Journal of Electroanalytical Chemistry 572 (2004) 185-193

Permalink: https://www.hzdr.de/publications/Publ-6314


On the modelling of bubbly flow in vertical pipes

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

Abstract

To qualify CFD codes for two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. Information on the local structure of the flow is also required by 1D thermal-hydraulic codes. Gas-liquid flow in vertical pipes is a very good object for studying the corresponding phenomena. Here, the bubbles move under clear boundary conditions, resulting in a shear field of nearly constant structure where the bubbles rise for a comparatively long time. The evolution of the flow within the pipe depends on a very complex interaction between bubble forces and bubble coalescence and break-up. E.g. the Lift-force, which strongly influences the radial distribution of the bubbles, changes its sign depending on the bubble diameter. Basing on extensive experimental data with a high resolution in space and time the applicability and the limits for the simulation of bubble flow with current CFD-codes are demonstrated, using the simulation of vertical pipe flow with CFX-4 as an example. Using a simplified model, parametric studies can be conducted. They give an indication for necessary improvements of the codes. Finally a possible way for the improvement of the CFD-codes is shown.

Keywords: two phase flow; bubbly flow; bubble size; vertical pipe flow; computational fluid dynamics

  • Nuclear Engineering and Design 235(2005), 597-611

Permalink: https://www.hzdr.de/publications/Publ-6313


Experimental and Numerical Investigations for Fragmentation and Insulation Particle Transport Phenomena in Water Flow

Hampel, R.; Kästner, W.; Alt, S.; Seeliger, A.; Krepper, E.; Grahn, A.

Abstract

The paper includes the description of separate effect test facilities used for investigations with regard to the fragmentation and the transport behaviour of different insulation materials in multidimensional aqueous flow. The instrumentation of the rigs is specified, in particular modern digital image processing technologies. First experimental results are shown and discussed generated at three acrylic glass test facilities. The experimental data will be use for CFD-modelling and validation. The anticipated modeling concepts are presented and their feasibility is demonstrated. During the ongoing work further results are expected.

Keywords: debris generation; debris transport; debris sedimentation; strainer clogging; experiments; computational fluid dynamics models

  • Poster
    5th International Conference on Multiphase Flow, Yokohama, Japan, May 30–June 4, 2004, Paper No. 555
  • Contribution to proceedings
    5th International Conference on Multiphase Flow, 30.05.-04.06.2004, Yokohama, Japan, Paper No. 555

Permalink: https://www.hzdr.de/publications/Publ-6312


TOPFLOW tests on the structure of the gas-liquid interface in a large vertical pipe

Prasser, H.-M.; Beyer, M.; Böttger, A.; Carl, H.; Lucas, D.; Schaffrath, A.; Schütz, P.; Weiss, F.-P.; Zschau, J.

Abstract

TOPFLOW is a new thermal fluid-dynamic multipurpose test facility designed for generic and applied studies of transient two phase flow phenomena.
The paper presents results obtained in air-water tests which were started in December 2002. The experiments aimed at studying the structure of a gas-liquid two phase flow in pipes of large diameter. The experimental data is used for the visualisation of the two phase flow structure as well as to obtain void fraction profiles and bubble size distributions. Additionally, a new visualisation technique is presented, that consists in the creation of virtual side projection of the flow.

Keywords: TOPFLOW; two phase flow; wire-mesh sensor; void fraction profile; bubble size distribution

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany, CD-ROM 69 - 74

Permalink: https://www.hzdr.de/publications/Publ-6311


Electrochemical activities in the Rossendorf MHD group

Hüller, J.; Weier, T.; Gerbeth, G.

Abstract

Momentum and mass transfer during electrochemical reactions in a small cell can be significantly influenced by Lorentz forces. Depending on the magnetic field configurations, a multitude of flow fields with an accordingly large range of mass transfer conditions can be arranged. The moderate magnetic field of simple permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. The interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.

Our activities were directed to the investigation of some diffusion controled electrochemical reactions like [Fe(CN)6]3+/[Fe(CN)6]4+, Ce4+/Ce3+ and the electrodeposition of Cu2+.

Since Faradaic currents are inherently coupled to electrochemical processes, the mass transfer enhancement attainable by Lorentz force induced convection does not increase the running costs. Therefore it seems attractive to perform further studies in order to determine the underlying scaling laws.

In a second part of the discussion a fluidic microsystem is presented. The silicon-glass wafer system is produced in a micromechanic planar technology and consists of a network of microfluidic channels. The microsystem can be coupled with microsensors and actuators.

  • Lecture (Conference)
    COST F2 Symposium "Electrochemical Flow Measurements and Microfluidics", 01.-03.07.2004, Poitiers, France

Permalink: https://www.hzdr.de/publications/Publ-6310


The Effect of Parameter Uncertainty on Blind Prediction of Np(V) Sorption onto Haematite using Surface Complexation Modelling

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

Abstract

Still, the KD concept of empirical distribution coefficients is the most often utilized approach for description of sorption phenomena. However, as an empirical concept it can not correctly portray the complex processes on the surfaces. A better approach is a Surface Complexation Models (SCM) capable of describing the sorption processes at the mineral-fluid interface on a scientific, quasi-thermodynamic basis. SCM are available in various versions, in which the Diffuse Double Layer Model (DDL), Constant Capacitance Model (CC) and Triple Layer Model (TL) are the most important and applied submodels.
Certainly, during the next decade SCM will replace KD only in some simple systems or systems dominated by one mineral. However, SCM can help to verify measured KD's, to identify the most sensitive experimental parameters, to assign uncertainty limits, to fill gaps difficult to access in sorption experiments, and to help to gain a better process understanding.
RES³T [1]– the Rossendorf Expert System for Surface and Sorption Thermodynamics - is a digitized version of a thermodynamic sorption database as required for the parametrisation of SCM, namely in risk assessment studies.
As an example to illustrate the effect of parameter uncertainty in blind predictions the Np(V) sorption onto haematite was selected.

Keywords: surface complexation modelling; uncertainty analysis; RES3T; blind prediction; Np(V) soerption

  • Lecture (Conference)
    NRC 6 - Sixth International Conference on Nuclear and Radiochemistry, 29.08.-03.09.2004, Aachen, Germany
  • Contribution to external collection
    Advances in Nuclear and Radiochemistry, Schriften des FZ Jülich, 3(2004), 493-495

Permalink: https://www.hzdr.de/publications/Publ-6307


Slow positron annihilation spectroscopy – a tool to characterize vacancy-type damage in ion-implanted 6H-SiC

Brauer, G.; Anwand, W.; Coleman, P. G.; Skorupa, W.

Abstract

Slow Positron Implantation Spectroscopy (SPIS), based on the generation, implantation and subsequent annihilation of mono-energetic positrons in a sample, is used to study depth dependent vacancy-type damage in ion-implanted 6H-SiC. The derivation of physical information from the Doppler-broadened annihilation lineshape is exemplified. It is found that the depth profile of vacancy-type damage formed in SiC co-implanted by Al+ and N+ at 800 °C, and subsequently annealed at 1200 °C and 1650 °C, strongly depends on the sequence of implantations and on annealing conditions. These studies show that annealing at 1650 °C for 10 minutes is not sufficient to remove the vacancy-type damage created by ion implantation.

Keywords: ion implantation; silicon carbide; depth dependent defect profile; positron

  • Vacuum 78(2005), 131-136

Permalink: https://www.hzdr.de/publications/Publ-6305


Annual Report 2003 - Institute of Radiochemistry

Bernhard, G.; Engelmann, H.-J.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-400 2004
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-6302


Annual Report 2003 - Institute of Ion Beam Physics and Materials Research

von Borany, J.; Heera, V.; Helm, M.; Jäger, H. U.; Möller, W.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-396 2004
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-6301


The MHD α2-dynamo: operator pencil, pseudo-Hermiticity, level crossings, spectral phase transitions

Günther, U.; Stefani, F.; Gerbeth, G.

Abstract

The lecture is splitted into three parts. In its first part, a brief introduction is presented into the underlying physics of the dynamo effect of magnetohydrodynamics (MHD), in order to make clear the motivation of the subsequent mathematical considerations. Paleomagnetic evidences for fields reversals of the geomagnetic field are discussed, as well as the results of the Riga dynamo experiment. Special emphasis is laid on the planned next generation dynamo experiments.

In the second part of the lecture, the basic operator-theoretic properties of the 2×2 operator matrix of the spherically symmetric α2-dynamo are discussed: its pseudo-Hermiticity in the case of idealized boundary conditions (with corresponding representation of the operator in a Krein space as indefinite generalization of a Hilbert space), and the general lack of symmetry and Hermiticity for physically realistic boundary conditions. A brief summary is given of the results of Ref. [1] on testing the operator struture on its compatibility with an operator intertwining technique as descriptive tool for possibly existing isospectral classes of dynamo operators. A corresponding no-go theorem is discussed for first-order differential operators as intertwiners.

Subject of the third part of the lecture are recent results on spectral phase transitions. Such phase transtions from non-oscillating dynamo regimes to oscillating regimes occur at two-fold degenerate level-crossing points of the spectrum (exceptional points), where two real-valued branches of the spectrum cross and leave the real axis to develop as pair of complex conjugate branches. Some general properties of the spectrum in the vicinity of the exceptional points are discussed. For this purpose, the linear eigenvalue problem of the 2×2 operator matrix is reformulated as equivalent eigenvalue problem of an associated quadratic operator pencil. Special emphasis is laid on the differences of exceptional points for quantum mechanical operators in Hilbert spaces and for pseudo-Hermitian operators in Krein spaces.

The lecture is completed by a discussion of open operator theoretic problems with relevance for the planned next generation dynamo experiments.

[1] Günther U. and Stefani F., Isospectrality of spherical MHD dynamo operators: pseudo-Hermiticity and a no-go
theorem, J. Math. Phys. 44, 2003, 3097, math-ph/0208012.

Permalink: https://www.hzdr.de/publications/Publ-6300


Machbarkeitstudie für einen industriellen supraleitenden Table Top Elektronenbeschleuniger

Schneider, C.; Büttig, H.; Enghardt, W.; Gabriel, F.; Janssen, D.; Michel, P.; Pobell, F.; Prade, H.; Kudryavtsev, A.; Haberstroh, C.; Sandner, W.; Will, I.

Abstract

At the Forschungszentrum Rossendorf the build-up of the superconducting 1.3 GHz accelerator ELBE is still in progress. Furthermore a new sc photo injector (SRF gun) is under development, which should accelerate electrons up to 10 MeV at 1.3 GHz frequency. The use of electron accelerators is also more and more interesting for applications where the destructive potential of the electrons are used like sterilization of medical waste and medical products, food irradiation or decontamination of sewage. For these processes a high power is required to achieve a high product throughput in a plant. The aim is therefore to use beam powers of around 100 kW or more. Since the applications of electron accelerators in industrial environments are steadily increasing one can speculate about transferring the above named state of the arte technology to industrial electron accelerators. At the FZR a feasibility study of such a table top electron accelerator (TTE) has been performed to investigate its technical limits and marketabilitys.

Keywords: Industrieller Beschleuniger; Fotoemissionskatode; Laser induzierte Emission; Präparationskammer zur Katodenbedampfung; Fotokatode in Beschleunigungskavität; supraleitender Resonator; superconducting cavity; Strahlleistung 50 kW; Strahlenergie 10 MeV; Kryostat; Sterilisation; Entkeimung; Lebensmittelbestrahlung; Lebensmittelpasteurisierung; Beseitigung organischer Schadstoffe; Kunststoffvernetzung

  • Open Access Logo Wissenschaftlich-Technische Berichte FZR-410 2004
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-6299


Performance of differently orientated PV modules - results of a long time measuring program

Rindelhardt, U.; Futterschneider, H.

Abstract

For 10 years an irradiation measuring field has been operated at FZR near Dresden. It consisted of 12 modules with different tilt and azimuth angles. The yearly mean values of the generated DC-energy are presented and directly compared with the predictions of the PEREZ model. The main result of the measurements is the providing of typical module DC power distributions. This distributions can be used to determine the optimal module/inverter power ratio of grid connected PV plants. For nearly optimal orientated generators this ratio should be one. Further a revision of the widely used “European Efficiency” of inverters is suggested, which is based on new weighting factors derived from the measurements. For PV plants a maximum performance ratio of 84% could be estimated. Finally the matching of the daily electricity load with PV plants in Germany is discussed. The load peak in Germany can be covered by an installed PV capacity of 45 GW.

Keywords: PV modules; grid connected; performance

  • Poster
    19th European Photovoltaic Solar Energy Conference and Exhibition, 07.-11.06.2004, Paris, France
  • Contribution to proceedings
    Proceedings on. 19th European Photovoltaic Solar Energy Conference and Exhibition, 07.-11.06.2004, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-6297


Chrombeschichtung von Baustahl mittels Ionenstrahlbehandlung

Reuther, H.; Richter, E.; Prokert, F.; Ueda, M.; Beloto, A. F.; Gomes, G. F.

Abstract

Zur Verbesserung des Korrosionsverhaltens von Baustahl wurde versucht, durch Rückstoßimplantation bzw. Ionenstrahlmischen seine Oberfläche mit einer chromreichen Schicht zu versehen. Dazu wurde polierter Baustahl (SAE 1020) mit Chrom bedampft und anschließend mit Stickstoffionen bestrahlt. Der Ionenbeschuß erfolgte sowohl durch direkte Ionenimplantation als auch durch Plasmaimmersions-Ionenimplantation.

Die so hergestellten Proben wurden mittels Augerelektronenspektroskopie, Konversionselektronen-Mößbauerspektroskopie und Röntgendiffraktometrie untersucht. Die Kombination dieser Verfahren gestattete eine ausreichende Charakterisierung der erzeugten Oberflächenschichten. Während die Schichtung Chrom/Stahl durch die direkte Ionenimplantation kaum verändert wurde, entstand durch die Plasmaimmersions-Ionenimplantation eine (Eisen/Chrom)-Nitridschicht auf der Stahloberfläche.

Nach der Behandlung wurden die Oberflächenhärte und das Korrosionsverhalten bestimmt und mit dem Ausgangszustand verglichen. Während sich bei den direkt implantierten Proben nur die Härte leicht erhöhte, nahm bei den durch Plasmaimmersions-Ionenimplantation behandelten Proben die Korrosionsbeständigkeit zu, so dass für den gewünschten Zweck dieses Verfahren das geeignetere ist.

  • Lecture (Conference)
    13. Arbeitstagung Angewandte Oberflächenanalytik (AOFA 13), 14.-17. September 2004, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-6296


Tomografische Rekonstruktion zweier asynchron rotierender Objekte am Beispiel einer hydrodynamischen Kupplung

Hoppe, D.; Hampel, U.; Zippe, C.; Prasser, H.-M.; Kernchen, R.

Abstract

Zwei asynchron rotierende Objekte sollen gemein-sam tomografisch rekonstruiert werden. Dafür werden tomografische Projektionen immer nur dann vorgenommen, wenn beide Objekte eine bestimmte Relativposition zueinander aufweisen. Die Objekte erscheinen dadurch wie fest miteinander verbunden. Vorhandene radiale Symmetrien der Objekte können ausgenutzt werden. Als praktisches Anwendungsbeispiel dient eine hydrodynamische Kupplung.

Keywords: Tomografie; asynchrone Drehungen; hydro-dynamische Kupplung

  • Technisches Messen 2004(2004)12, 634-639

Permalink: https://www.hzdr.de/publications/Publ-6295


Virtuelle tomografische Rekonstruktionsbilder infolge ungeeigneter Abtastraten

Hoppe, D.

Abstract

Bei tomografischen Bildrekonstruktionen können zu große Detektorabstände oder zu wenige Projektionen Aliasing-Artefakte hervorrufen. Betrachtet werden Objekte, die eine drehsymmetrische Struktur enthalten. Von ihr entsteht neben dem reellen auch ein virtuelles tomografisches Abbild. Gezeigt wird, dass es schwierig sein kann, ein solches virtuelles Abbild als Aliasing-Artefakt zu identifizieren.

Keywords: Tomografie; Drehsymmetrie; Nyquist-Frequenz; Aliasing-Artefakte

  • Technisches Messen 2004(2004)12, 640-642

Permalink: https://www.hzdr.de/publications/Publ-6294


New possibilities for velocity measurements in liquid metals by potential probes

Varshney, K.; Cramer, A.; Gerbeth, G.

Abstract

The improved resolution of potential probe measurements allowed to investigate the turbulent properties of flows driven by various types of alternating magnetic fields. Results will be presented on the turbulent spectra of such flows and the spatio-temporal changes of the mean velocity profiles.

  • Lecture (Conference)
    International. Workshop on "The History of Magnetohydrodynamics", 26.-28.05.2004, Coventry, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-6293


Magnetic field control in aluminum investment casting and the problem of electromagnetic flow rate measurements

Buchenau, D.; Eckert, S.; Witke, W.; Gerbeth, G.

Abstract

The magnetic control of aluminium investment casting is presented as an example of metallurgical applications of external magnetic fields.

  • Lecture (Conference)
    International. Workshop on "The History of Magnetohydrodynamics", 26.-28.05.2004, Coventry, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-6292


Electromagnetic seawater flow control - from old ideas to recent results

Gerbeth, G.; Weier, T.; Shatrov, V.; Mutschke, G.

Abstract

Recent results on separation control with steady and unsteady Lorentz forces will be presented, embedded into the 40 years history of electromagnetic seawater flow control.

  • Lecture (Conference)
    International. Workshop on "The History of Magnetohydrodynamics", 26.-28.05.2004, Coventry, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-6291


Overview of the WWER-440 Benchmark Results

Boehmer, B.

Abstract

The preliminary results of the REDOS project participants for neutron and gamma fluence spectrum integrals obtained for two VVER-440 pressure vessel benchmarks at the LR-0 reactor in Rez have been analyzed. The results of different calculations have been compared with each other and with experiments. The influence of the scintillation detectors on the measurement results was discussed.

  • Lecture (Conference)
    REDOS Progress Meeting, 01.-02.04.2004, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-6290


Hydrogen in a natural Pd-O compound from Gongo Soco, Minas Gerais, Brazil

Cabral, A. R.; Lehmann, B.; Grambole, D.; Herrmann, F.

Abstract

The existence of hydrogen in Pd–O-bearing aggregates, which together with iron oxides form the characteristic dark encrustation of an ouro preto nugget of Gongo Soco, Minas Gerais, Brazil, is confirmed by elastic recoil detection analysis with a heavy-ion microbeam (micro-ERDA). Hydrogen is lost from Pd–O-bearing areas during the micro-analyses, but not from goethite.
The data indicate that the Pd–O–H phase is unstable compared to goethite, giving support to previous observations that it is a transient phase in a transformation to native palladium.

Keywords: : hydrogen; elastic recoil detection analysis; Pd–O-bearing compound; ouro preto nugget; Gongo Soco; Minas Gerais; Brazil

  • Canadian Mineralogist 42(2004), 689-694

Permalink: https://www.hzdr.de/publications/Publ-6289


Summary of the WWER-1000 Benchmark Results

Boehmer, B.

Abstract

The final results of the REDOS project participants for neutron and gamma fluence spectrum integrals obtained for the VVER-1000 pressure vessel benchmark at the LR-0 reactor in Rez had been analyzed. The comparison of different calculations with each other and of calculations with experiments showed in both cases reasonable agreement.

Keywords: Benchmark; LR-0 reactor; neutron and gamma spectrum calculation and measurement; VVER-1000 reactor

  • Lecture (others)
    REDOS Progress Meeting, April 1-2, 2004, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-6288


Results of TRAMO-Calculations of WWER-440 Mock-up Experiments in the LR-0 Reactor

Konheiser, J.

Abstract

Neutron and gamma fluence results for the VVER-440 mock-up at the LR0-reactor in Rez, that were calculated with the Monte Carlo Code TRAMO had been compared with measured data. A reasonable agreement between calculation results and experimental data was reached.

  • Lecture (others)
    REDOS Progress Meeting, April 1-2 2004 Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-6287


Shielding Design of the PANDA Spectrometer at the Munich High-Flux Reactor FRM-II

Noack, K.; Pyka, N.; Rogov, A.; Steichele, E.

Abstract

The start-up of the Munich high-flux reactor FRM-II is going on. At the beam tube SR-2 the spectrometer PANDA has been installed. It is a three-axis neutron spectrometer looking onto a slightly under-moderated cold neutron source. For polarization analysis PANDA is equipped with a vertical cryo-magnet producing fields up to 14.5 Tesla at the sample. To get an appropriate shielding of the high-intensity instrument one had to take into account the large cross-section of the primary beam, several restrictions using magnetic materials, limitations in loading the site and, finally, one had to keep the lateral extent of the shielding small to allow for high scattering angles. The shielding has been designed on the base of results which were achieved by the combined use of both the Monte Carlo code MCNP-4B2 and an analytical method based on one-dimensional dose transmission functions.

Keywords: Shielding Design; Neutron/Gamma Transport; High-Flux Reactor FRM-II; PANDA Spectrometer; Monte Carlo Calculations; MCNP Code

  • Lecture (Conference)
    International Conferences ICRS-10/RPS 2004, 09.-14.05.2004, Funchal, Madeira Island Portugal
  • Radiation Protection Dosimetry 115(2005)1-4, 262-267
    DOI: 10.1093/rpd/nci158

Permalink: https://www.hzdr.de/publications/Publ-6286


Results of TRAMO-Calculations of WWER-1000 Mock-up Experiments in the LR-0 Reactor

Konheiser, J.

Abstract

Neutron and gamma fluence results for the VVER-1000 mock-up at the LR0-reactor in Rez, that were calculated with the Monte Carlo Code TRAMO had been compared with measured data. A reasonable agreement between calculation results and experimental data was reached. Additionally, results obtained with different energy group structures were compared.

Keywords: Monte Carlo calculation TRAMO LR-0; mock-up VVER-1000

  • Lecture (others)
    REDOS Progress Meeting, September 3-6 2003, Elena Bulgaria

Permalink: https://www.hzdr.de/publications/Publ-6285


Creation and evaluation of the VVER-1000 Balakovo-3 ex-vessel dosimetry benchmark for the NEA SINBAD data base

Borodkin, G.; Boehmer, B.; Noack, K.; Khrennikov, N.

Abstract

A new neutron dosimetry benchmark of the NEA SINBAD Data Base is described. This full-scale reactor benchmark, based on VVER-1000 ex-vessel neutron activation measurements performed at the Balakovo NPP, Unit 3 (Balakovo-3), is a result of several years of thorough measurements and calculations. With regard to evaluation of measured and calculated results an international intercomparison study played a key role. This interlaboratory comparison produced the reference measured data expressed as end-of-irradiation activities of reaction products of the reactions: 237Np(n,f), 238U(n,f), 93Nb(n,n'), 58Ni(n,p), 54Fe(n,p), 46Ti(n,p) and 63Cu(n,a). A comprehensive analysis of reactor data used for creating the computational models has been performed. Special attention was paid to the analysis of the reliability of the absolute neutron source distributions. Results of calculations performed by various discrete ordinates and Monte Carlo codes have been used for the benchmark evaluation. It turned out that these calculation results are in agreement within 12 % with the reference measured data. The experience gained by creation and evaluation of the full-scale power reactor benchmark is discussed in the paper.

Keywords: neutron activation measurements; fast neutron benchmark; data base; reactor pressure vessel embrittlement; verification of neutron fluence calculations

  • Lecture (Conference)
    ICRS-10 / RPS 2004 Conferences, 09.-14.05.2004, Funchal, Madeira, Portugal

Permalink: https://www.hzdr.de/publications/Publ-6284


THERMAL EFFECTS DURING CONDENSATION INDUCED WATER HAMMER BEHIND FAST ACTING VALVES IN PIPELINES

Prasser, H.-M.; Böttger, A.; Zschau, J.; Baranyai, G.; Ezsöl, G.

  • Lecture (Conference)
    11th International Conference on Nuclear Engineering Tokyo, JAPAN, April 20-23,2003, Proceedings ICONE11-36310
  • Contribution to proceedings
    11th International Conference on Nuclear Engineering Tokyo, JAPAN, April 20-23,2003, Proceedings ICONE11-36310

Permalink: https://www.hzdr.de/publications/Publ-6282


Range and mixing distributions of low-energy carbon ions as a base for subplantation growth models

Dollinger, G.; Neumaier, P.; Bergmaier, A.; Eckstein, W.; Fischer, R.; Hofsaess, H.; Kroeger, H.; Ronning, C.; Jaeger, H. U.

  • Lecture (Conference)
    European Materials Research Society 2004 Spring Meeting, Symposium J: Synthesis, Characterisation and Advanced Applications of Amorphous Carbon films, contr. J-I.3, 24-28 May 2004, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-6281


In-situ studies of Shape Memory Alloy (SMA) Ni-Ti thin films

Martins, R. M. S.; Schell, N.; Braz Fernandez, F. M.; Silva, R.

Abstract

Ni-Ti thin films (SMA) formed by sputtering have been attracting great interest as powerful actuators in microelectromechanical systems (MEMS) such as microvalves, microfluidic pumps and micromanipulators. Successful implementation of Ni-Ti micro-actuactors requires a good understanding of the relationship among processing, microstructure and proprieties of Ni-Ti thin films. At the ROssendorf BeamLine (ROBL-CRG) at the ESRF, we carried out a series of experiments that clearly illustrate the benefit of in-situ studies, not only during annealing, but also during sputtering. The in-situ annealing experiments, using a Be-dome furnace installed into the six-circle diffractometer of the Materials Research Hutch (MRH) allowed us to determine the kinetics of the phenomena, to identify the sequence of precipitation and to correlate the build-up of the final structure with the processing conditions. The in-situ sputtering experiments during film growth were performed using a magnetron sputter deposition chamber also installed into the six-circle diffractometer [1]. This facility allowed us to follow, almost in “real time”, the structural evolution of the deposited thin film as a consequence of changing deposition parameters.

Keywords: magnetron sputtering; in-situ XRD; real-time structural design; shape memory alloy NiTi

  • Lecture (Conference)
    4th Conference on Synchrotron Radiation in Materials Science (SRMS-4), August 23-25, 2004, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-6280


Real-time and in-situ structural design of functional NiTi SMA thin films

Schell, N.; Martins, R. M. S.; Braz Fernandez, F. M.

Abstract

The real-time structural design of magnetron sputtered NiTi SMA (shape memory alloy) thin films is reported. During deposition the phase content was followed in situ by synchrotron x-ray diffraction and controlled by varying the power of co-sputtering NiTi plus Ti for otherwise fixed deposition parameters. This method allows an optimization of the thin film in respect to its functional properties like phase transition temperature or adhesion as well as an understanding of the actual growth process by revealing temporary intermediate growth states (precipitates) and diffusion processes during film growth. The method is neither restricted to the sputter material (NiTi) nor to the controlling parameter (power) chosen, but immediately applicable to a large class of materials as well as general enough for other deposition parameters.

Keywords: magnetron sputtering; in-situ XRD; real-time structural design; shape memory alloy NiTi

  • Applied Physics A 81(2005)7, 1441-1445; DOI: 10.1007/s00339-004-3201-1

Permalink: https://www.hzdr.de/publications/Publ-6279


Microchanneling Investigation of ß-FeSi2-Structures

Dagkaldiran, Ü.; Grambole, D.; Herrmann, F.; Schreiber, H.-U.; Meijer, J.

Abstract

Semiconducting ß-FeSi2 has currently attracted scientific interest, due to the fact that ß-FeSi2 has a direct band gap of 0.8 eV [1,2]. This property makes it a special candidate for e.g. silicon-based micro-LED’s. Single crystalline ß-FeSi2- layers would even open possibilities for devices like micro-laserdiodes. However, the synthesis of these structures is experimentally extremely delicate.

The temperature during implantation, the energy of the beam, the annealing procedures as well as the fluence and current density of the beam, the structure size of the layer etc. are all key process parameters and have to be optimized with respect to one another.

The first micro channeling analyses of FeSi2-structures, which were produced with an ion energy of 800 keV and sample sizes between 70-190 µm in diameters, were carried out. The combination of the two set-ups, the ion projector at the Ruhr University of Bochum and the micro-channeling set-up at the research centre Rossendorf, allows a fast synthesis as well as the analysis of the samples.

The implantation temperature of the samples was varied between 50 – 350 °C. The results show that bulk formation by Ostwald maturing depends on implantation temperature and structure size. Even if the layers do not show the desired crystalline characteristics, the investigations permit to draw conclusions about the damage of the surface layer with consideration of the bulk formation. This is of enormous interest, in order to optimize and model the embedding into a pn-structure as a step towards the development of a LED.

Additional Raman measurements showed clear fingerprints of ß-FeSi2 [3].

Reference:
[1]: N.E. Christensen;
Electronic structure of ß-FeSi2;
Phys. Rev. B42, 1990, p. 7148-7153

[2]: D. Pankin, F. Eichhorn, E. Wieser, W. Skorupa, W. Henrion, J. Albrecht;
Electrical and optical properties of ß-FeSi2 after Co implantation and annealing;
Nucl. Instrum. Methods Phys. Res. B84, 1994, p. 172-175

[3]: A.G. Birdwell, R. Glosser, D.N. Leong, K.P. Homewood;
Raman investigation of ion beam synthesized ß-FeSi2 ;
J. Appl. Phys., Vol. 89, No. 2, 2001, p. 965- 972

  • Lecture (Conference)
    9th International Conference on Nuclear Microprobe Technology and Applications (ICNMTA-2004), Sept. 13 -17 2004, Cavtat, Dubrovnik, Croatia

Permalink: https://www.hzdr.de/publications/Publ-6278


Porous silicon as an intermediate layer for heterojunction solar cells on p-type Si crystalline substrates

Ulyashin, A.; Bilyalov, R.; Carnel, L.; van Nieuwenhuysen, K.; Grambole, D.; Bruck, A.; Scherff, M.; Monakhov, E.; Kuznetsov, A. Y.; Svensson, B. G.; Beaucarne, G.; Poortmans, J.

Abstract

The study of the influence of ITO deposition process on the defect formation in the interface region of heterojunctions (HJ) is done. The role of intrinsic a-Si:H and as an alternative a thin porous Si buffer layer is analyzed. It is shown that a thin porous Si as a buffer layer in HJ solar cells leads to the improvement of the HJ solar cells efficiency since this layer serves as a protection one of the Si substrate during the ITO deposition process. By DLTS method it is observed that damages created during the deposition of ITO layer can be essentially suppressed by a thin a-Si:H or thin porous Si buffer layers. In case of porous silicon formation by the electrochemical etching the process is “softer” and this thin intermediate layer has similar properties as a-Si:H concerning the hydrogen concentration and the characteristics of Si-H bonds. This conclusion was derived from the Nuclear Reaction Analysis (NRA) and Raman measurements, which are performed on porous-Si/crystalline Si structures. It is concluded that the main role of a thin porous Si layer in a Si based heterojunction structure is the improvement of the interface properties of HJ solar cells due to a protection of the Si substrate during the depositions of a-Si:H and ITO layers.

Keywords: heterojunction; silicon; passivation

  • Lecture (Conference)
    19th European Photovoltaic Solar Energy Conference, 7 - 11 June, 2004, Paris, France
  • Contribution to proceedings
    19th European Photovoltaic Solar Energy Conference, 07.-11.06.2004, Paris, France, 588

Permalink: https://www.hzdr.de/publications/Publ-6277


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