Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39109 Publications

Cyclotron Resonance of Extremely Conductive 2D Holes in High Ge Content Strained Heterostructures

Mironov, O. A.; Goiran, M.; Galibert, J.; Kozlov, D. V.; Ikonnikov, A. V.; Spirin, K. E.; Gavrilenko, V. I.; Isella, G.; Kummer, M.; von Känel, H.; Drachenko, O.; Helm, M.; Wosnitza, J.; Morris, R. J. H.; Leadley, D. R.

Cyclotron resonance has been observed in steady and pulsed magnetic fields from high conductivity holes in Ge quantum wells. The resonance positions, splittings and linewidths are compared to calculations of the hole Landau levels.

Keywords: Cyclotron resonance; Ge; SiGe; Landau Levels

Publ.-Id: 13931

Treasures as seen under proton irradiation

Neelmeijer, C.

Silicate materials such as glass, porcelain and ceramics, but also geological findings are characterized by their chemical composition. Corresponding fingerprints of unique pieces - e.g. precious objects of art - have to be studied stringently in a non-destructive manner. Elements along the whole periodic system are of analytical interest. These requirements are met by ion beam analysis (IBA) using protons of 4 MeV energy extracted from vacuum into atmospheric pressure. Atoms of the object of investigation, struck by protons, emit characteristic γ-radiation due to nuclear reactions as well as X-rays via proton-electron interactions. Simultaneous detection of PIGE (Particle Induced Gamma-ray Emission) and PIXE (Particle Induced X-ray Emission) signals allows determination of all chemical constituents. PIGE measures the concentration of the main element Si, consequently the SiO2 content. Moreover, PIGE gives the concentrations of accompanying light elements like Li, B, Na, Mg and Al and their natural oxides; also F can be examined.
Maximum information depths in glass are in the order of 40 µm. Hence, the PIGE results represent the silicate material bulk. PIXE provides concentrations of the elements heavier than Al (Z > 13). Maximum PIXE information depths in glass are only 10 µm, which is due to much higher attenuation of X-rays (E~keV) compared to that of γ-rays (E~MeV). Therefore, the PIXE results stand for the bulk material only if the object surface was not attacked by strong deterioration. PIGE-PIXE analysis of silicate materials must be executed in an interactive manner in order to account for radiation absorption effects. Protons reflected from atoms situated in depth regions near the material surface, i.e. Rutherford Backscattering Spectrometry (RBS), inform of environmental degradation. Thus, IBA is best-suited to calculate both the state of preservation as well as the possible danger of progressive deterioration regarding cultural heritage, especially which made from glass [1].
As is known, K-Ca-silica glass gets decomposed by leaching when being exposed to humid surroundings, even under air conditioning in museum collections. Both, protective storage and preventive conservation have become one of the primary tasks in museum science. The performance of IBA is figuring out glass objects of endangered composition as long as indications of alteration are still not visible. Exhibits sui generis dated from baroque era and treasured inside the museum of applied arts in Dresden were already exposed to the proton beam in air. Several exhibits show visually opacity, some of them a network of fine cracks. The final evaluation of measured data is in the offing. Composition analysis of single obsidian pieces has been a topic of international interest. For their characterization questions have concentrated on fingerprints regarding elements heavier than Fe, being enclosed with low concentrations.
For the bulk materials of interest IBA detection limits are in the order of 5 - 300 µg/g, thus falling for light elements Z < 22 (Ti) below that of X-ray fluorescence spectrometry.

Reference: [1] M. Mäder, C. Neelmeijer, Nucl. Instr. and Meth. B 226 (2004) 110 - 118

Keywords: analysis; non-destructive; ion beam analysis; PIGE; PIXE; RBS; art; preventive conservation; obsidian; detection limits

  • Lecture (Conference)
    Analytica2010, 23.-25.03.2010, München, Germany

Publ.-Id: 13930

Countercurrent gas-liquid flow in a hot leg under reflux cooling - numerical calculations for steam-water tests at FZD

Kinoshita, I.; Murase, M.; Utanohara, Y.; Lucas, D.; Vallée, C.; Tomiyama, A.

Numerical calculations using FLUENT6.3.26 were conducted for steam-water CCFL tests using the 1/3rd scale rectangular channel simulating a PWR hot leg at FZD, and the results were compared with the FZD data.

Keywords: PWR; reflux cooling; hot leg; countercurrent gas-liquid flow; numerical calculations

  • Contribution to proceedings
    Annual meeting of the Atomic Energy Society of Japan, 26.-28.03.2010, Ibaraki, Japan, 237

Publ.-Id: 13929

Countercurrent gas-liquid flow in a hot leg under reflux cooling - numerical calculations for air-water tests at FZD

Murase, M.; Kinoshita, I.; Utanohara, Y.; Lucas, D.; Vallée, C.; Tomiyama, A.

Numerical calculations using FLUENT6.3.26 were conducted for air-water CCFL tests using the 1/3rd scale rectangular channel simulating a PWR hot leg at FZD, and the results were compared with CCFL characteristics in circular tubes.

Keywords: PWR; reflux cooling; hot leg; countercurrent gas-liquid flow; numerical calculations

  • Contribution to proceedings
    Annual meeting of the Atomic Energy Society of Japan, 26.-28.03.2010, Ibaraki, Japan, 236

Publ.-Id: 13928

High field cyclotron resonance spectroscopy using quantum cascade lasers

Drachenko, O.

Author reviews practical aspects of application of quantum cascade lasers (QCL) to high field laser magneto-spectroscopy of semiconductors. The universal QCL based experimental set-up, covering wide spectral region from 5 up to 120mm is presented. The performance of the setup is illustrated with cyclotron resonance measurements of InGaAs/GaAs and InAs/AlSb quantum wells.

Keywords: cyclotron resonance; high magnetic field; semiconductors; effective mass; quantum cascade laser

  • Invited lecture (Conferences)
    The XIV Nanophysics and Nanoelectronics Symposium, 15.-19.03.2010, Nizhny Novgorod, Russia

Publ.-Id: 13927

The Transformation Pathways of Mo6S2I8 Nanowires into Morphology-Selective MoS2 Nanostructures

Virsek, M.; Krause, M.; Kolitsch, A.; Mrzel, A.; Iskra, I.; Skapin, S. D.; Remskar, M.

Nanomaterials prepared by the sulfurization of Mo6S2I8 nanowires and the time and temperature dependence of the transformation process are investigated by high-resolution transmission electron microscopy, X-ray powder diffraction, and wavelength-dependent Raman spectroscopy. Depending on the temperature, coaxial MoS2 nanotubes or MoS2 “mama”-tubes are formed after 2 h of sulfurization. Using a few minutes of sulfurization time, core-shell nanowires composed of well-ordered MoS2 layers covering a Mo6S2I8 core are formed, proving an outside-to-inside transformation process. The crystallinity of the three MoS2 nanostructures increases with increasing transformation temperature, i.e., in the sequence from MoS2/Mo6S2I8 core-shell structures via coaxial MoS2 tubes to the MoS2 “mama”-tubes. The analysis indicates a different nature of the defects in the MoS2-based nanomaterials, originating from the sulfurization of the Mo6S2I8 than in the conventional MoS2 platelike crystals. A correlation between the Raman spectroscopic parameters and the defect density in MoS2 is identified.

Publ.-Id: 13926

Helium irradiation study on zircon

Nasdala, L.; Grambole, D.; Götze, J.; Kempe, U.; Váczi, T.

Synthetic ZrSiO4 and (mildly to strongly radiation-damaged) natural zircon samples were irradiated with 8.8 MeV 4He2+ ions (fluences in the range 1 x 1013 – 5 x 1016 ions/cm²). For comparison, an additional irradiation experiment was done with 30 MeV 16O6+ ions (fluence 1 x 1015 ions/cm²). The light-ion irradiation resulted in the generation of new (synthetic ZrSiO4) or additional (mildly to strongly metamict natural samples) damage, respectively. The maximum extent of the damage is observed in a shallow depth range approximately 32–33 µm (8.8 MeV He) and ≤ 12 µm (30 MeV O) below the sample surface, respectively, i.e., near the end of the ion trajectories. These depth values, and the observed damage distribution, correspond well to defect distribution patters as predicted by Monte Carlo simulations. The irradiation damage is recognised from the notable broadening of Raman-active vibrational modes, lowered interference colours (i.e., decreased birefringence), and changes in the optical activity (i.e., luminescence emission). At very low damage levels, a broad-band yellow emission centre is generated whereas at elevated damage levels, this centre becomes re-suppressed and samples experience a general decrease of their emission intensity. Most remarkably, there is no indication of any structural recovery process in pre-damaged natural zircon as induced by the light-ion irradiation, which questions the relevance of alpha-assisted annealing of radiation damage in natural zircon.

Keywords: Zircon; Ion irradiation; Radiation damage; Raman spectroscopy; Luminescence

Publ.-Id: 13923

Visualization and holdup measurement of viscous oil-water dispersed pipe flow by capacitance wire-mesh sensor

Da Silva, M. J.; Hampel, U.; Rodriguez, I. H.; H. Rodriguez, O. M.

Experiments were performed in a test facility at NETeF (Thermal-Fluids Engineering Laboratory) of the Engineering School of São Carlos. The facility consists basically of a horizontal glass pipe of 26 mm of inner diameter and 12 m length. Mineral oil (860 kg/m3 density and 100 mPa∙s viscosity) and tap water stored in separated tanks are circulated under controlled conditions through the test pipe. The flow rates of each liquid are individually controlled and measured. After passing the horizontal test section, the mixture flows to a coalescent-plate separator tank. The liquids once separated are returned to their respective storage tanks by gravity. A wire-mesh sensor with 8 x 8 wire configuration was installed close to end of the horizontal pipe at 10.3 m from the entrance. To assemble the wire-mesh sensor in the test pipe, a flange of transparent Perspex was manufactured which allows for optical observations (Fig 1a). A high-speed camera (Optronis, Camrecord 600) was applied to monitor the flow patterns and investigate the influence of wire-mesh sensor in the flow.
Experiments were performed at oil superficial velocity between 0.2 m/s to 1 m/s and water superficial velocity between 1 m/s to 3 m/s. The recording speed was 2000 fps for the high-speed camera and 500 fps for the wire-mesh sensor, whereby data acquisition of both systems was synchronized by a common trigger signal. Figure 1b and 1c show exemplary images of the flow obtained by the both imaging devices. Note that the high-speed camera depicts a lateral view of the flow, while the wire-mesh sensor images show holdup distributions over the cross section of the pipe. From the two-dimensional holdup distribution measured by the wire-mesh sensor we have further determined liquid holdup integrated over different domains thus obtaining time and/or spatially averaged holdup values, e.g. radial profiles or mean holdup. Furthermore, for comparison purposes of holdup measurements, the quick-closing valves (QCV) technique was employed. Good agreement was found between QCV and WMS techniques. In the full paper, a complete description of the measurements will be presented along with a discussion of the accuracy in the measurements.

Keywords: wire mesh sensor; oil-water two-phase flow

  • Contribution to proceedings
    6th World Congress On Industrial Process Tomography (WCIPT6), 06.-09.09.2010, Bejing, China
    Proceedings of the 6th World Congress On Industrial Process Tomography, 1334-1440

Publ.-Id: 13922

Secondary Radiation during 7Li Irradiation of a PMMA Phantom

Kormoll, T.; Fiedler, F.; Müller, A.; Enghardt, W.

no abstract available

Keywords: prompt gamma emission; in-vivo dosimetry

  • Contribution to external collection
    in: GSI Scientific Report, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung, 2010

Publ.-Id: 13921

Fluorine-18 labeling of phosphopeptides: a potential approach for the evaluation of phosphopeptide metabolism in vivo.

Richter, S.; Bergmann, R.; Pietzsch, J.; Ramenda, T.; Steinbach, J.; Wuest, F.

Phosphopeptides are very useful reagents to study signal transduction pathways related with cellular protein phosphorylation/dephosphorylation. Phosphopeptides have also been identified as important drug candidates to modulate intracellular signaling mechanisms through targeting phosphotyrosine, phosphoserine, or phosphothreonine residue-binding protein domains. In this report, we describe the development of a convenient method for the mild and sufficient radiolabeling of phosphopeptides with the short-lived positron emitter fluorine-18 (18F) to allow radiopharmacological studies on phosphopeptide metabolism in vivo by means of positron emission tomography (PET). Radiolabeling was accomplished via conjugation of the N-terminus of polo-box domain (PBD)-binding phosphopeptide H-Met-Gln-Ser-pThr-Pro-Leu-OH with the bifunctional labeling agent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) in reproducible isolated radiochemical yields of 25-28%. Radiopharmacological evaluation in vitro and in vivo of radiolabeled phosphopeptide [18F]FB-Met-Gln-Ser-pThr-Pro-Leu-OH [18F]-3 and its non-phosphorylated analog [18F]FB-Met-Gln-Ser-Thr-Pro-Leu-OH [18F]-4 involved metabolic stability, cell uptake studies, and small animal PET experiments. Radiolabeled phosphopeptide [18F]-3 showed a remarkable high metabolic stability in vivo compared to the corresponding non-phosphorylated peptide [18F]-4. The presented method indicates that radiolabeling of phosphopeptides with [18F]SFB is a promising approach for studying phosphopeptide metabolism in vivo.

Keywords: phosphopeptides; fluorine-18; positron emission tomography (PET)

Publ.-Id: 13920

Formation of uranium(IV)-silica colloids at near-neutral pH

Dreissig, I.; Weiss, S.; Hennig, C.; Bernhard, G.; Zänker, H.

Evidence is provided by photon correlation spectroscopy, ultrafiltration and ultracentrifugation that uranium(IV) can form silicate-containing colloids of a size of 620 nm. A concentration of up to 103 M of colloid-borne U(IV) was observed. The particles are generated in near-neutral to slightly alkaline solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). They remain stable in aqueous suspension over years. Electrostatic repulsion due to a negative zeta potential in the near-neutral to alkaline pH range caused by the silicate stabilizes the U(IV) colloids. The isoelectric point of the nanoparticles is shifted toward lower pH values by the silicate. The mechanism of the colloidal stabilization can be regarded as “sequestration” by silicate, a phenomenon well known from heavy metal ions of high ion potential such as iron(III) or manganese(III,IV), but never reported for uranium(IV) so far. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that U–O–Si bonds, which increasingly replace the U–O–U bonds of the amorphous uranium(IV) xyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids. The next-neighbor coordination of U(IV) in the U(IV)-silica colloids is comparable with that of coffinite, USiO4. The assessment of uranium behavior in the aquatic environment should take the possible existence of U(IV)-silica colloids into consideration. Their occurrence might influence uranium migration in anoxic waters.

Keywords: colloid; uranium(IV); silicic acid; EXAFS; coffinite; carbonate; reduction

Related publications

Publ.-Id: 13918

Monitoring of multi-phase distribution in packing columns using wire-mesh sensor

Zheng, G.; Schubert, M.; Hampel, U.; Grünewald, M.

Absorption packing columns employing gas-liquid counter-current flow are widely used across a wide range of industries. Maldistribution of liquid phase could reduce the contact area of both phases, thus lowering column efficiency. Liquid holdup is an essential parameter that influence pressure drop and load capacity of the packing column. Traditional measurements of local liquid holdups using liquid collector strongly disturb the original conditions which make the results less reliable. In this study the local liquid holdup and their distribution was measured with the state-of-the-art technology using wire-mesh sensor installed below the packing.
Wire-mesh sensor contains 16x16 orthogonally arranged wires (up to 32x32), measuring the complex impedance at every sensing point which is related to the local permittivity over the whole cross section. Matrices which denote the local permittivity are obtained with a frequency up to 1000 frames per second. Knowing pure gas and liquid phase permittivity allows calculation of local phase fractions. Unlike ECT or ERT measurement, grid sensor excellently locates the liquid phase position and the area obstruction is lower than 1 percent.
Stochastic behavior of liquid flow at different time was found. It is shown that large scale of maldistribution near the wall was observed and most of liquid phase flows preferentially in the same zones.
The amount of liquid flowing along the column wall was characterized by analyzing liquid holdups of the annular grid points. It is shown that more than 27% of the liquid phase flows improperly and its amount varies dynamically.
Mesurements with wire-mesh sensor could be employed to correct essential parameters such as effective phase contact area, local liquid holdup and etc. Therefore, mass transfer laws suggested by Billet (1995) and hydraulic model by Mackowiak (2009) could be modified.

Keywords: grid sensor; packing column; distribution; multi-phase

  • Contribution to proceedings
    6th World Congress on Industrial Process Tomography (WCIPT6), 06.-09.09.2010, Bejing, China
    Proceedings of the 6th World Congress on Industrial Process Tomography, pp. 1473-1487

Publ.-Id: 13917

Independent assessment of MARS 3D features: use of experimental data and CFD support

Cherubini, M.; Moretti, F.; D’Auria, F.; Ahn, S. H.; Cho, Y. J.; Höhne, T.

Recent developments of special models and correlations extended the system TH codes capabilities to simulate 3D phenomena. A code assessment process is always needed whenever the new code features are intended for nuclear reactor design and/or licensing applications. The Korean Thermal-Hydraulic code MARS (developed by Korea Atomic Energy Research Institute) experiences such an improvement, extending the 1D flow field formulation.
In this respect the present paper describes the activity conducted to assess the 3D features of the MARS code by independent users. The adopted experimental data are gathered in a test conducted at the ROCOM (Rossendorf Coolant Mixing Model) experimental facility, which reproduced a pump start-up scenario. In addition, to support the interpretation of experimental data and system code results, a CFD analysis has been also performed.
The assessment activity includes a comparison with RELAP5-3D© code, a set of sensitivity calculations and the use of the FFTBM package.

Keywords: RELAP5; CFD; ROCOM

  • Contribution to proceedings
    8th International Conference on Nuclear Option in Countries with Small and Medium Electricity Grids, 16.-20.05.2010, Dubrovnik, Croatia
    Proceedings of the 8th International Conference on Nuclear Option in Countries with Small and Medium Electricity Grids Dubrovnik, Croatia, 16-20 May 2010, CD-ROM
  • Lecture (Conference)
    8th International Conference on Nuclear Option in Countries with Small and Medium Electrical Grids, 16.-20.05.2010, Dubrovnik, Croatia

Publ.-Id: 13916

Detection of gas-liquid dynamics in monolithic channels using ultra-fast x-ray tomography

Schubert, M.; Fischer, F.; Hampel, U.

Monolith structures are a promising catalyst carrier to replace conventional catalyst particle packings in many gas-liquid-solid applications, such as hydrogenation, oxidation and enzymatic reactions. Enhanced reactor performance with respect to mass transfer, selectivity and conversion is mainly attributed to the more intense gas-liquid-solid contact within the regular structure and short diffusion distance due to thin liquid film layer. It is obvious that different flow regimes appear within the channels depending on superficial gas and liquid velocities and monolith channel geometry, e.g. bubble and Taylor flow regimes that feature especially high mass transfer rates and complete wetting of the monolith bed. Furthermore, bubble and slug lengths as well as their frequency and velocity can be tuned by operating conditions for optimization of reactor performance depending on the chemical reaction.
Therefore, gas-liquid dynamics in the channels of a monolith block need to be monitored. However, it was shown that design of gas-liquid distributor is the most crucial issue for uniform utilization of all monolithic channels and the hydrodynamic behavior in the monolith can drastically differ from single channel flow.
CREL laboratory applied gamma-ray tomography to study cross-sectional gas-liquid distribution but gives only time-averaged and blurred data while any temporal gas-liquid in-channel formation remains hidden (Roy and Al-Dahhan, 2005). On the other hand, magnetic resonance tomography from Cambridge University (Professor Gladden) drastically improved chemical engineering imaging, e.g. allowing access inside monolithic channels but exclusively for small diameters and non-metallic reactors (Mantle et al., 2002).
In the present work, a novel ultra-fast X-ray tomograph (Fischer et al., 2008) was applied to study gas-liquid distribution in monolithic structures operated in co-current up-flow. Different monolith configurations were installed and the system was operated at different gas and liquid superficial velocities. Normalized bubbles and slug length frequency distributions, gas and liquid fractions and cross-sectional distribution quality were calculated from image sequences. Furthermore, effect of the monolith in the cross-section on gas-liquid flow pattern was studied with respect to the gas-liquid flow in the pipe without structured internals.

Keywords: monolith reactor; gas-liquid distribution; ultra-fast x-ray tomography

  • Contribution to proceedings
    6th World Congress On Industrial Process Tomography (WCIPT6), 06.-09.09.2010, Bejing, China
    Proceedings of the 6th World Congress on Industrial Process Tomography, pp. 91-102

Publ.-Id: 13915

Experiments on air entrainment due to free falling- and wall-jets

Lopez, J. M.; Danciu, D. V.; Da Silva, M. J.; Hampel, U.; Mohan, R.

In this article, air entrainment as a result of an impinging round water jet and a wall-jet was experimentally studied by means of videometry and image processing methods and also by means of a measuring technique based on a wire-mesh sensor. Therefore, two different experimental setups were utilized. For the first setup, a series of experiments at different conditions was performed and evaluated for both round jets and wall-jets. Jet lengths ranged between 0.01m and 0.2m and jet exit velocities between 0.9 m/s and 3.5 m/s. Image processing algorithms were applied to extract information about jet penetration depth, width of the bubble plume and bubble size distribution. The second facility was used to create a falling film in a square pipe (5 cm x 5 cm). Downstream of the impact point, a wire-mesh sensor was used to measure the gas entrainment characteristics at one axial location. Video image processing was also used in this experiment to gather more qualitative information about the gas entrainment process. Video images were compared with the images obtained by the wire-mesh sensor showing good agreement. The induction trumpet and a thin sheet of gas that is formed around the jet and penetrates into the pool causing the entrainment were clearly identified. Results indicate that the gas void fraction increases and the bubble size decreases as the superficial liquid velocity increases.

Keywords: air entrainment; round jet; wall-jet; falling film; wire-mesh sensor; induction trumpet; gas void fraction

  • Lecture (Conference)
    ASME 2010 Fluids Engineering Summer Meeting FEDSM2010, 01.-05.08.2010, Montreal, Canada
  • Contribution to proceedings
    ASME 2010 Fluids Engineering Summer Meeting FEDSM 2010, 01.-05.08.2010, Montreal, Canada

Publ.-Id: 13914

Marginal turbulent MHD flow in a square duct

Shatrov, V.; Gerbeth, G.

Direct numerical simulations were performed of the turbulent flow in a straight square duct in a transverse magnetic field. Without magnetic field the turbulence can be maintained for values of the bulk Reynolds number above approximately Re=1077 [1]. In the magnetohydrodynamic case this minimal value of the bulk Reynolds number increases with the Hartmann number. The flow is laminar at Re=3000 when the Hartmann number is larger than Ha=12.5 and the flow is turbulent for Ha < 12.0. The secondary mean flow structure is analyzed.

  • Physics of Fluids 22(2010), 084101

Publ.-Id: 13913

Experimental study of gas entrainment by liquid falling film around a stationary Taylor bubble in vertical downward flow

Lopez, J. M.; Danciu, D. V.; Da Silva, M. J.; Hampel, U.; Mohan, R.

Air entrainment by a liquid falling film was experimentally studied by means of videometry, image processing methods, and also by a measuring technique based on wire-mesh sensor. Air was entrained by a plunging liquid film around a stagnant Taylor bubble. Downstream of the impact point, a wire-mesh sensor was used to measure the total gas void fraction, gas void fraction distribution, and bubble size distribution. Results indicate that the gas void fraction increases and the bubble size decreases as the superficial liquid velocity increases. Good agreement was found by comparing video images with the images obtained by the wire-mesh sensor.

Keywords: air entrainment; wire-mesh sensor; Taylor bubble; falling film

  • Lecture (Conference)
    2010 ECTC Proceedings ASME Early Career Technical Conference, 25.-27.03.2010, Tulsa, USA
  • Contribution to proceedings
    2010 ECTC Proceedings ASME Early Career Technical Conference, 25.-27.03.2010, Tulsa, USA

Publ.-Id: 13912

Experimental study and flow visualization of gas entrainment in downward flow

Lopez, J. M.; Danciu, D. V.; Da Silva, M. J.; Hampel, U.; Mohan, R.

Downward bubble flow due to the gas entrainment under a falling film was experimentally investigated using the Wire-Mesh Sensor (WMS) and high speed video camera. The flow pattern was identified using the flow visualization analysis of the WMS. The flow visualization analysis was done in a 2-D (x, y), pseudo 2-D (x, t and y, t), and pseudo 3-D (x, y, t) dimension. The flow pattern observed during the experiments was bubble flow. Good agreement was found by comparing video images with the images obtained by the wire-mesh sensor. Additionally, gas void fraction time series and bubble size distribution are presented. Results show that images obtained from the high speed camera, WMS and experimental observations are in good agreement. Also, it is showed that different approaches for flow pattern recognition can be used. Moreover, results show the influence of the superficial liquid velocity on the gas void fraction and bubble size.

Keywords: air entrainment; flow visualization; flow pattern; wire-mesh sensor; gas void fraction

  • Contribution to proceedings
    7th International Conference on Multiphase Flow,ICMF 2010, 30.05.-04.06.2010, Tampa, Florida, USA

Publ.-Id: 13911

Optimierung des Refinerprozesses hinsichtlich Energieeffizienz und Faserqualität

Mäbert, M.; Bieberle, A.

Die industrielle Herstellung von Faserstoffen beinhaltet eine Vielzahl physikalisch-technologischer Prozesse, deren Komplexität vom Holzplatz bis zur Zerfaserung deutlich zunimmt. Die Zerfaserung im Refiner stellt einen hoch komplexen Prozess dar, dessen Wirkungsweise und physikalische Zusammenhänge zum gegenwärtigen Zeitpunkt nur in geringem Maße beschrieben werden können. Das vorhandene Wissen beruht auf Erfahrungen und empirisch gefundenen Zusammenhängen. Das Potential, dass die umfassende theoretische Durchdringung des Zerfaserungsprozesses und die sich daraus ergebenden Optimierungsmöglichkeiten hinsichtlich Einstellung einer definierten Faserqualität und Energieeinsparung bietet, wird nicht ausgeschöpft. Sichere Erkenntnisse zum Einfluss der Faserqualität auf die einzusetzende Bindemittelmenge und die späteren Eigenschaften der Faserplatten sind gleichfalls nicht vorhanden. Angesichts der getroffenen Feststellungen befasst sich das IHD in einem Projekt mit Untersuchungen zur Optimierung des Refinerprozesses hinsichtlich Energieeffizienz und Faserqualität.

Keywords: Gamma-ray computed tomography; process optimisation; wood refiner

  • Contribution to proceedings
    8. Holzwerkstoffkolloquium, 10.-11.12.2009, Dresden, Deutschland
    Optimierung des Refinerprozesses hinsichtlich Energieeffizienz und Faserqualität
  • Lecture (Conference)
    8. Holzwerkstoffkolloquium, 10.-11.12.2009, Dresden, Deutschland

Publ.-Id: 13910

Process diagnostics and non-destructive testing using high-resolution gamma-ray tomography

Bieberle, A.; Hoppe, D.; Hampel, U.

In this paper, a high-resolution gamma-ray computed tomography (CT) measurement system is presented that was developed to determine phase fractions and other flow parameters in industrial devices operated under real industrial conditions. From CT scans non-superimposed cross-sectional images are reconstructed, which show the local gamma-ray attenuation coefficients within the scanned object slice. An advanced fast read-out electronics facilitates 2-D visualization of rapidly rotating multiphase distributions, such as in stirred chemical reactors or hydrodynamic machines. Furthermore, the CT measurement system can be applied to non-destructive testing of high-density devices to achieve information about the structure of material, i.e. when exposed to mechanical stress.

Keywords: Gamma-ray computed tomography

  • Contribution to proceedings
    IEEE International Conference on Imaging Systems and Techniques (IST 2010), 01.-02.07.2010, Thessaloniki, Griechenland
    Process diagnostics and non-destructive testing using high-resolution gamma-ray tomography
  • Lecture (Conference)
    IEEE International Conference on Imaging Systems and Techniques (IST 2010), 01.-02.07.2010, Thessaloniki, Griechenland

Publ.-Id: 13909

Counter-current flow limitation in a scale-down model of a PWR hot leg

Nariai, T.; Tomiyama, A.; Vallée, C.; Lucas, D.; Kinoshita, I.; Murase, M.

In the case of a hypothetical failure of a residual heat removal system under mid-loop operation during shutdown of a pressurized water reactor (PWR), steam generated in a reactor core and water condensed in a steam generator (SG) form a counter-current flow in a hot leg. Though several studies have been carried out to understand counter-current flow limitation (CCFL) in the hot leg, our knowledge on CCFL is still rudimentary. In this study, a scale-down model of the hot leg (one-fifteenth of the actual plant) is used to investigate the effects of fluid viscosity on CCFL in the hot leg. Air and water or air and glycerol-water solutions are used for the gas and liquid phases, respectively. Water levels in the hot leg are also measured using conductivity probes. The gas and liquid flow rates at CCFL are estimated by applying a one-dimensional momentum equation to the flow in the hot leg. As a result, the following conclusions are obtained. (1) CCFL causes a drastic change in the distribution of water level in the hot leg. (2) The liquid viscosity scarcely affects the interfacial force. The interfacial force is mainly due to form drag caused by the presence of large-amplitude waves.

Keywords: hot leg; counter-current flow; CCFL; PWR

  • Contribution to proceedings
    The 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8), 10.-14.10.2010, Shanghai, China, # N8P0109
  • Lecture (Conference)
    The 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8), 10.-14.10.2010, Shanghai, China

Publ.-Id: 13908

Measurement of wood fibre slurry distributions in a laboratory wood refiner using high-resolution gamma-ray tomography

Bieberle, A.; Mäbert, M.; Hampel, U.

At present, wood fibres for the production of medium density fibreboards (MDF) are produced in acceptable quality, but with high energy consumption. The adjustment of defined fibre properties is quite difficult, because the defibration process in refiners is a very complex one. Currently, its effectiveness as well as physical correlations can only be described to a minor degree. Existing knowledge is based on experiences and empirically retrieved coherences. For this reason, there is still a great demand for optimisation regarding efficiency and defined wood fibre quality. Recently our research group developed a high-resolution gamma-ray computed tomography (CT) measurement system for industrial applications, which has been successfully used in many foregoing projects. It consists of a collimated 137Cs isotopic source, a detector arc, a signal processing unit and a cooling unit. The detector arc contains 320 single detectors based on scintillation technology and the complete measurement system is non-sensitive to electromagnetic fields as well as ambient temperature changes. In a joined project, the CT measurement system of the FZD (Forschungszentrum Dresden - Rossendorf) was applied onto the downscaled refiner of the IHD gemeinnützige GmbH (Institut für Holztechnologie Dresden, Germany). The main objective is to measure wood fibre slurry density differences in the so called ring slit as well as in the refiner gap for the fully working machine. Therefore, classical radiation tomography as well as angular resolved tomography is applied. Results of first experiments will be presented, which were carried out in 2010.

Keywords: Gamma-ray computed tomography; refiner; and wood fibres

  • Contribution to proceedings
    6th World Congress on Industrial Process Tomography, 06.-09.09.2010, Peking, China
    Measurement of wood fibre slurry distributions in a laboratory wood refiner using high-resolution gamma-ray tomography
  • Lecture (Conference)
    6th World Congress on Industrial Process Tomography, 06.-09.09.2010, Peking, China

Publ.-Id: 13907

Four-dimensional flow imaging by ultrafast X-ray computed tomography

Bieberle, M.; Fischer, F.; Menz, H.-J.; Mayer, H.-G.; Hampel, U.

Ultrafast X-ray computed tomography has been developed as a flow imaging technique [1][2] that is able to visualize the phase distribution inside a cross-section of a flow vessel with a spatial resolution of about 1 mm and frame rates of up to 10,000 s-1. The temporal resolution is achieved by fast deflection of an electron beam across an elongated target to produce a moving X-ray source spot. The performance and applicability of this technique has been demonstrated in different two-phase flow experiments such as water-air pipe flows [3], mixing processes or fluidized beds [4] which are of great relevance for the understanding and controlling of various industrial processes. Especially in applications with dense phases, which are opaque to common imaging techniques, ultrafast X-ray tomography can provide important additional information.
Recently, this technique has been advanced towards time-resolved imaging of three-dimensional flow structures. This is achieved by repeated consecutive scanning of a number of tomography planes, which are realised using a stepped target. Thus, several vertically distributed X-ray source paths can be generated. With the reconstructed time-resolved volume data it is possible not only to determine phase distributions but also phase velocities and bubble volumes which are characteristic parameters of the flow. This extended data basis provides the opportunity for an improved validation of computational fluid dynamics codes. The method and first experimental results will be presented.

Keywords: X-ray; computed tomography; ultrafast imaging; two-phase flow

  • Contribution to proceedings
    6th World Congress on Industrial Process Tomography, 06.-09.09.2010, Bejing, China
    Proc. of 6th World Congress on Industrial Process Tomography, 457-462
  • Lecture (Conference)
    6th World Congress on Industrial Process Tomography, 06.-09.09.2010, Bejing, China

Publ.-Id: 13906

Ultrafast Multiphase Flow Imaging by Electron Beam X-ray Computed Tomography

Bieberle, M.; Fischer, F.; Schleicher, E.; Franke, M.; Menz, H.-J.; Mayer, H.-G.; Laurien, E.; Hampel, U.

Ultrafast electron beam X-ray computed tomography (CT) is an imaging technique (Bieberle & Hampel., 2006), which is able to recover the cross-sectional density distribution of multiphase flows with a frame rate of up to 10,000 fps and a spatial resolution of about 1 mm. Originally, electron beam CT was developed for cardiac imaging by Boyd (1983) and modern medical systems reach frame rates of about 20 fps. During the last years, this measurement technique has been advanced and qualified for flow imaging by the Forschungszentrum Dresden-Rossendorf and the University of Stuttgart. Its applicability to different two-phase flows has been demonstrated in a number of experiments (Bieberle et al., 2007, Bieberle et al., 2009). Specifically adapted image reconstruction methods allow to extract the phase boundaries and thus to determine the phase fractions within the tomography plane. The latest developments in ultrafast electron beam X-ray CT include the extension towards two or more tomography planes which enable furthermore to measure phase velocities by using cross correlation techniques. This in turn is essential for determining bubble volumes and volumetric flow rates, which are important parameters for the validation of CFD codes.

Keywords: X-ray; computed tomography; ultrafast multiphase flow imaging

  • Contribution to proceedings
    7th International Conference on Multiphase Flow, 30.05.-04.06.2010, Tampa, FL, USA
    Proceeding of 7th International Conference on Multiphase Flow, 9.3.2
  • Lecture (Conference)
    7th International Conference on Multiphase Flow, 30.04.-04.06.2010, Tampa, FL, USA

Publ.-Id: 13904

Comparison of ultrafast x-ray electron beam tomography and capacitance wire-mesh sensor imaging applied to multiphase flow measurement

Da Silva, M. J.; Fischer, F.; Hampel, U.

In this paper we compare ultrafast electron beam x-ray tomography and wire-mesh sensor imaging for a gas-water two phase flow in a vertical Perspex pipe. A 16 x 16 wire-mesh sensor was applied to measure the flow under controlled conditions in an experimental two-phase flow loop. Part of the flow loop is a two metre tall round pipe of XX mm inner diameter operated with water and air under controlled conditions. A special injector device at the bottom of teh vertical test section provides controlled gasification of the water. This way, different flow patterns and a broad range of void fraction value values can be generated. The ROFEX scanner was installed to visualize the flow just underneath the wire-mesh sensor which is located at a sufficient distance upward the injector to secure a well developed flow.

Experiments were run with flow patterns of bubbly, slug and churn turbulent flow at different liquid and gas superficial velocities. Both sensors produced synchronized data sequences of 10 s at 2,500 frames per second rate. Measured and reconstructed image data was analyzed and compared with respect to cross-sectionally averaged gas fractions, radial as fraction profiles and bubble size distributions. Fairly good agreement between ROFEX scanner and wire-mesh outputs was found for higher mixture superficial velocity while in the lower range some discrepancies were found. Detailed description will be given in the full paper.

Keywords: x-ray tomography; wire-mesh sensor; flow visualization; multiphase flow; comparison of techniques

  • Contribution to proceedings
    6th World Congress On Industrial Process Tomography (WCIPT6), 06.-09.09.2010, Bejing, China
    Proceedings of the 6th World Congress On Industrial Process Tomography, 421-429

Publ.-Id: 13902

Comparison between wire mesh sensor technology and gamma densitometry

Sharaf, S.; Azzopardi, B.; Hampel, U.; Zippe, C.; Beyer, M.; Da Silva, M. J.

Experimental tests were conducted recently to test both the capacitance and conductance wire mesh sensors against gamma densitometry. Similar techniques were utilised in the past at FZD to test the accuracy of the wire mesh sensor (Prasser et al 1998). It is interesting to note that comparisons of the wire mesh sensor have also been done with other measurement devices e.g. ECT (Azzopardi et al, 2009). A small closed loop test facility was utilised. This consisted of a vertical round pipe approximately 1 metre in length, and around 50mm in diameter. A 16 x 16 wire mesh sensor was used, giving a spatial resolution of 3.1mm. This sensor was placed approximately 1 metre above the injector. Temporal resolution or sampling frequency of the sensor was set at 1000 Hz throughout the experiments. Deionised water was used and hence both types of WMS could be utilised. There was a small gas injector at the inlet of the vertical pipe, this allowed compressed air to be injected, and two-phase gas-liquid mixture was generated. The gas superficial velocity was varied between 0.05m/s to 1.4m/s at two liquid velocities of 0.2 and 0.7m/s. The gamma densitometer consisted of collimated source and also a collimated detector to minimise scattering. The source was Cs 137; this generated a gamma beam of 5mm in diameter. The detector used was a NaI scintillation crystal with photomultiplier read-out. The measuring period was 120s (similar methodology was used previously by Prasser et al 1998). The gamma densitometer was placed on a moving platform approximately 1cm below the plane of wires of the sensor, in order to align it accurately using a counter mechanism, with each of the wires of the WMS, and the platform could scan the full section of the pipe. One half of the pipe i.e. 8 wires of the sensor were measured with capacitance WMS and gamma densitometer, and the other half of the pipe was measured with conductance WMS and gamma densitometer. Calibration was carried out for each position i.e. 16 points and data collected for each of the 16 wires at the stated gas and liquid flow rates. In total there were 224 runs. Different flow regimes were observed e.g. bubbly and slug. The count rate from the gamma densitometer detector was converted to void fraction (Stahl et al, 2004). For the cross-sectional void, along each wire, there was good agreement between sensors and the gamma densitometer near the centre of the pipe, however there wasn’t a good agreement near the circumference or edge of the pipe. There was consistent agreement between the capacitance and conductance wire mesh sensors throughout the experiment. This experiment also demonstrated how limited gamma densitometry actually is, i.e. it provides no visualisation. The wire mesh sensor in return gave void fractions at each crossing point i.e. a 16x 16 matrix, at a very high sampling rate, together with visualisation of flow. It also gave bubble identification and size distribution of the bubbles.

Keywords: Gas-Liquid Flow; Wire Mesh Sensor (WMS); Capacitance; Conductance; Gamma Densitometry

  • Contribution to proceedings
    6th World Congress On Industrial Process Tomography (WCIPT6), 06.-09.09.2010, Bejing, China
    Proceedings of the 6th World Congress On Industrial Process Tomography, 1464-1472
  • Open Access Logo Measurement Science and Technology 22(2011), 104019
    DOI: 10.1088/0957-0233/22/10/104019
    Cited 45 times in Scopus

Publ.-Id: 13901

Thermodynamical and Structural Study of Protactinium(V) Oxalate Complexes in Solution

Mendes, M.; Hamadi, S.; Le Naour, C.; Roques, J.; Jeanson, A.; Den Auwer, C.; Moisy, P.; Topin, S.; Aupiais, J.; Hennig, C.; Di Giandomenico, M. V.

The complexation of protactinium(V) by oxalate is studied by X-ray absorption spectroscopy (XAS), capillary electrophoresis coupled with ICP-MS (CE-ICP-MS ) and solvent extraction. XAS measurements show unambiguously the presence of a short single oxo-bond. CE-ICP-MS results indicate the formation of a highly charged anionic complex. The formation constant of PaO(C2O4)+, PaO(C2O4)2– and PaO(C2O4)33– are determined from solvent extraction data by using protactinium at tracer scale (CPa < 10–10M) and different temperatures. Complexation reactions of Pa(V) with oxalate are found to be exothermic with relatively high positive entropic variation.

Keywords: Pa(V) oxalate; Thermodynamics; EXAFS

Related publications

  • Inorganic Chemistry 49(2010), 9962-9971

Publ.-Id: 13900

Competitive Complexation of Nitrates and Chlorides to Uranyl in a Room Temperature Ionic Liquid

Gaillard, C.; Chaumont, A.; Billard, I.; Hennig, C.; Ouadi, A.; Georg, S.; Wipff, G.

By coupling EXAFS, UV-vis spectroscopy and molecular dynamics and quantum mechanical calculations, we studied the complexation of uranyl cations with nitrate and chloride ions in a water immiscible ionic liquid, C4mimTf2N. Both anions are shown to be stronger uranyl ligands than the ionic liquid Tf2N- or triflate anions. Structural parameters of the trinitrate-complex of uranyl are similar to those obtained in organic solvents like acetonitrile. When chloride and nitrate anions are simultaneously present, one never observes “limit” complexes like UO2(NO3)3- or UO2Cl42- alone. At a U/ NO3 /Cl ratio of 1 /2 /2, the dominant species is likely UO2Cl(NO3)2-. When chlorides are in excess over uranyl with different nitrate concentations (U/ NO3 /Cl ratio of 1/2/6, 1/4/4, 1/12/4) the solution contains a mixture of UO2Cl42- and UO2Cl3(NO3)2- species. Furthermore, it is shown that the experimental protocol for introducing these anions (either as uranyl counterion, as added salt, or as ionic liquid component) influences the UV-vis spectra, pointing to kinetic equilibration issues in the ionic liquid.

Keywords: Uranium(VI); ionic liquid; EXAFS

Related publications

  • Inorganic Chemistry 49(2010)14, 6484-6494

Publ.-Id: 13899

Two-phase flow experiments in a model of the hot leg of a pressurised water reactor

Seidel, T.; Vallée, C.; Lucas, D.; Beyer, M.; Deendarlianto

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section.
Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264°C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments.
This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison.
Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes the effect of viscosity into account.

Keywords: two-phase flow; hot leg; counter-current flow limitation (CCFL); Wallis correlation

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-531 2010
    ISSN: 1437-322X
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-010 2011
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 13898

Lysine adsorption on the silanized SiO2-surface for immobilization of the estrogen receptor hER(alpha)

Cherkouk, C.; Rebohle, L.; Skorupa, W.

We investigated the adsorption of the L-Lysine (200 mmol) molecule to a silanized SiO2 surface as a function of the pH value. The SSC (spraying spin coating)-method [Cherkouk et al, J. of Col. and Int. Sci., 337(2009)] was applied to functionalize the SiO2 surface by using the (3-Aminopropyl)trimethoxysilane (APMS) as coupling agent with a NH2 functional group. We adsorbed lysine molecules for the pH-values of 2.5, 7.5, 8.7, 9.5 and 13 to the silane film. The infrared spectroscopy is not suitable to investigate the system because the NH3+ signal at 1600 cm-1 originating from the silane film overlaps with the infrared signal of the deprotonated carboxyl group of the lysine molecule. X-ray photoelectron spectroscopy (XPS) was used to measure the binding energies C1s and N1s as function of the pH value. This pH change affects the charge state which was fitted in the XPS spectra to obtain the optimal adsorption conditions at pH= 7.5 via carboxyl groups of the lysine to the functionalized SiO2 surface.

Keywords: Lysine; adsorption; SiO2; Si-based light emitter; estrogen receptor; silanization

Publ.-Id: 13897

Modelling of turbulence in bubbly flows

Krepper, E.; Lucas, D.; Schmidtke, M.

In the Euler/Eulerian approach simulating bubbly flow, the influence of the bubbles on the turbulence of the liquid has to be modelled. Vice versa, the structures of the turbulent liquid flow influence the gas void fraction distribution, which is expressed as a turbulent dispersion force. Reliable models for turbulence are an urgent precondition for the improvement of models describing bubble coalescence and bubble breakup in any population balance model. In the present work the different approaches simulating the influence of bubbles on the turbulence are revised and compared to measurements using ANSYS-CFX. Models for the turbulent dispersion force are validated.

Keywords: CFD; turbulence; bubbly flow; model validation

  • Contribution to proceedings
    7th International Conference on Multiphase Flow, ICMF 2010, 30.05.-04.06.2010, Tampa, USA
  • Poster
    7th International Conference on Multiphase Flow, ICMF 2010, 30.05.-04.06.2010, Tampa, USA

Publ.-Id: 13896


Takao, K.; Ikeda, Y.

In crystal structure of the title compound, {[UO2NO3(C4H7NO)2]2O2}, two UO22+ ions are connected by mu-ita2:ita2-O22–. An inversion center is located at the middle point of a O—O bond in the O2 moiety. As a result, the centrosymmetrically expanded dimeric structure is afforded. The O2 unit shows "side-on" coordination and connects two U, i.e., mu-ita2:ita2-O2. The bond lengths between U and the axial O are 1.78 Å (mean), indicating that oxidation state of U is exclusively 6+, i.e., UO22+. Furthermore, the O—O distance in the dioxy­gen moiety is 1.491 Å, which is typical of the peroxide, O22–. Each U atom is eight-coordinate in a hexagonal-bipyramidal geometry. The coordinating atoms of nitrate, pyrrolidine-2-one and mu-ita2:ita2-O22– are located on the equatorial plane, and form an irregular hexagon. The inter­molecular hydrogen bonds are found between N—H of 2-pyrrolidone and the coordinating O of the same ligand in the neighboring complex.

Keywords: uranyl; peroxo; pyrrolidone; nitrate; dimer; single crystal X-ray diffraction

  • Open Access Logo Acta Crystallographica Section E 66(2010), m539-m540
    ISSN: 1600-5368

Publ.-Id: 13895

Application of Computational Chemistry and Experimental Spectroscopy to Nuclear Waste Problem

Tsushima, S.

no abstract for this presentation

  • Invited lecture (Conferences)
    Ulsan National Institute of Science and Technology, 09.03.2010, Ulsan, South Korea

Publ.-Id: 13894

Di-Elektronen in relativistischen Schwerionenkollisionen

Kämpfer, B.

Di-Elektronen in relativistischen Schwerionenkollisionen

  • Invited lecture (Conferences)
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände, 15.-19.03.2010, Bonn, Deutschland

Publ.-Id: 13893

Investigations on in-vessel melt retention for VVER-1000 reactors

Tusheva, P.; Altstadt, E.; Weiss, F.-P.

In recent years, many NPPs have developed and implemented severe accident management guidelines (SAMG). A primary objective of SAMG is prevention or mitigation of the consequences of severe accidents by keeping the reactor pressure vessel (RPV) integrity and reducing the load to the containment.

In-vessel melt retention (IVR) by ex-vessel reactor cooling (EVC) is one of the possible strategies for mitigation of a severe accident. This concept has already been approved by the Finnish Regulatory Agency (STUK) to be a part of the severe accident management procedures for the Loviisa NPP, Finland, with a VVER-440 reactor [1]. Besides its feasibility for such smaller power reactors, the concept is also investigated for some GEN III+ advanced light water reactors with higher core powers, such as the Westinghouse AP-1000. By applying the strategy of in-vessel retention of corium, the possible fuel-coolant interaction in the reactor cavity and thus the pressure loads in the cavity could be avoided.

The late in-vessel phase of a VVER-1000 reactor, applying external cooling of the RPV wall as mitigative severe accident management measure (SAMM), is investigated. The study is based on the FEM computer code ANSYS. Without flooding, the vessel wall would fail, as the necessary temperature for a balanced heat release from the external surface via radiation is near to or above the melting point of the steel. A crucial question regarding the feasibility of the IVR is whether all the decay heat could be transferred through the vessel wall into the water in the reactor cavity. The heat flux distribution from the molten corium to the RPV wall is therefore of high importance.

Keywords: severe accidents; in-vessel melt retention; external vessel cooling; VVER-1000; ANSYS

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Germany
    Tagungsband JTKT2010, CD-ROM
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Germany

Publ.-Id: 13892

A versatile method for simulating pp -> ppe+e- and dp -> pne+e-p_spec reactions

Dohrmann, F.; Froehlich, I.; Galatyuk, T.; Holzmann, R.; Kaehlitz, P. K.; Kaempfer, B.; Moriniere, E.; Pachmayer, Y. C.; Ramstein, B.; Salabura, P.; Stroth, J.; Trebacz, R.; van de Wiele, J.; Wuestenfeld, J.

We have developed a versatile software package for the simulation of di-electron production in pp and dp collisions at SIS energies. Particular attention has been paid to incorporate different descriptions of the Dalitz decay \Delta \to N e+e- via a common interface. In addition, suitable parameterizations for the virtual bremsstrahlung process NN \to NN e+e- based on one-boson exchange models have been implemented. Such simulation tools with high flexibility of the framework are important for the interpretation of the di-electron data taken with the HADES spectrometer and the design of forthcoming experiments.

Publ.-Id: 13891

Passively mode-locked Tm,Ho:YAG laser at 2 µm based on saturable absorption of intersubband transitions in quantum wells

Yang, K.; Bromberger, H.; Ruf, H.; Schäfer, H.; Neuhaus, J.; Dekorsy, T.; Villas-Boas Grimm, C.; Helm, M.; Biermann, K.; Künzel, H.

We report the first demonstration of a solid state laser passively mode-locked through the saturable absorption of short-wavelength intersubband transitions in doped quantum wells: a continuous wave Ti:sapphire laser end-pumped Tm,Ho:YAG laser at the center wavelength of 2.091 μm utilizing intersubband transitions in narrow In0.53Ga0.47As/Al0.53As0.47Sb quantum wells. Stable passive mode-locking operation with maximum average output power of up to 160 mW for 2.9 W of the absorbed pump power could last for hours without external interruption and a mode-locked pulse with duration of 60 ps at repetition rate of 106.5 MHz was generated.

Keywords: mode locking; intersubband transition; saturable absorber; quantum well; solid state laser

Publ.-Id: 13890

Reduction of Se(IV) with Boom Clay: XAS solid phase speciation

Breynaert, E.; Scheinost, A. C.; Dom, D.; Rossberg, A.; Vancluysen, J.; Gobechiya, E.; Kirschhock, C. E. A.; Maes, A.

The geochemical fate of selenium is of key importance for today’s society due to its role as a highly toxic essential micronutrient and as a significant component of High Level Radioactive Waste (HLRW) originating from the operation of nuclear reactors. Understanding and prediction of the long-term behavior of Se in natural environments requires identification of the in situ speciation of selenium. This article describes an XAS-based investigation into the solid phase speciation of Se upon interaction of Se(IV) with Boom Clay, a reducing, complex sediment selected as model host rock for clay-based deep geological disposal of HLRW in Belgium and Europe. Using a combination of long-term batch sorption experiments, linear combination XANES analysis and ITFA-based EXAFS analysis allowed for the first time to identify Se0 as the dominant solid phase speciation of Se in Boom Clay systems equilibrated with Se(IV).

Keywords: selenium; XAFS

Related publications

  • Environmental Science & Technology 44(2010), 6649-6655

Publ.-Id: 13889

Local structure in americium and californium hexacyanoferrates. Comparison with their lanthanide analogues

Dupouy, G.; Bonhoure, I.; Conradson, S. D.; Dumas, T.; Hennig, C.; Le Naour, C.; Moisy, P.; Scheinost, A. C.; Simoni, E.; Den Auwer, C.

Metal hexacyanoferrates are well known molecular solids for a large variety of cations, although very little has been described for actinide adducts. Two new members of actinide(III) hexacyanoferrates have been synthesized with americium and californium cations. They have been structurally characterized by infrared spectroscopy, X-ray diffraction and X-Ray absorption spectroscopy. Combined EXAFS data at the iron K edge and actinide LIII edge lead to propose a three-dimensional model for these two new compounds. Structural data in terms of bond distances have been compared to those reported for the lanthanide(III) hexacyanoferrates. A comparison between the actinide and lanthanide homologues has been carried out, based on ionic radii considerations. Consequently, Am(III)/Nd(III) and Cf(III)/Gd(III) complexes have been compared : the americium adduct with KNdFeII(CN)6.4H2O and the californium adduct with KGdFeII(CN)6.3H2O. Comparison between the present EXAFS data and reported X-ray diffraction data suggests that the americium and neodymium environments are very similar, resulting in a tri-capped trigonal prism polyhedron (CN = 9) where the americium is bonded to six nitrogen atoms and to three water molecules. For the californium adduct, EXAFS derived bond length and angle suggest that the californium cation sits in a bi-capped trigonal prism (CN = 8) as in the gadolinium homologue of known structure. Using EXAFS spectroscopy, this is one of the rare evidences of californium/lanthanide similarities in a molecular compounds. A discussion about actinide(III)/lanthanide(III) comparison and coordination number decrease from Am to Cf is also provided, based on previous crystallographic results reported for the actinide(III) hydrate series

Keywords: XAFS; hexacyanoferrate; actinide; americium; californium

Related publications

Publ.-Id: 13888

Application of the Ultrasound Doppler Velocimetry in a Czochralski crystal growth model experiment

Cramer, A.; Pal, J.; Gerbeth, G.

The present work is concerned with ultrasound and temperature measurements in a Czochralski crystal growth model experiment. In the Czochralski growth, primary strong horizontal temperature gradients are present at the solidification front, which should lead to an axisymmetric flow pattern in the melt volume. To study the flow structure a modified Rayleigh-Bénard configuration was built up in which the upper thermal boundary condition in a Czochralski system is accounted for by a partially cooled surface. The measurements show, that rather a large scale flow pattern develops known as wind in real Rayleigh–Bénard configurations. The wind was always found as the only stable flow pattern for all performed Grashof numbers. Applying a rotating magnetic field (RMF) to the melt volume, the wind starts to co-rotate with the RMF. By analogue with the superposition of the primary and the secondary flow in an RMF, the swirl evoked by the RMF is also superimposed to the wind without any remarkable interaction. Not until the weaker secondary flow produced by the RMF becomes similar in vigour to the buoyant wind does the flow structure in the modified Rayleigh-Bénard system change basically. The results show the applicability of the Ultrasound Doppler Velocimetry (UDV) in the detection and identification of complex flow patterns.

Keywords: Ultrasound Doppler Velocimetry; Temperature gradients; Czochralski crystal growth; Fluid flow

  • Contribution to proceedings
    The 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 07.-09.04.2010, Göteborg, Sweden
    Proceedings of the 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 978-91-7290-292-3, 57-60
  • Lecture (Conference)
    The 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 07.-09.04.2010, Göteborg, Sweden

Publ.-Id: 13887

The sensitivity of the flow driven by a travelling magnetic field to axial alignment

Pal, J.; Cramer, A.; Gerbeth, G.

The present experimental study is concerned with the sensitivity of the flow driven by a travelling magnetic field (TMF) to axial alignment. Referring to the center axis of the TMF generating coil system the fluid volume was stepwise dealigned. Because the flow induced in a TMF is, basically, of a torus type, vertical velocity components are representative for the motion in the meridional plane. To acquire velocity profiles the Ultrasound Doppler velocimetry (UDV) was used which allows gathering the whole profile along the ultrasonic beam. Several transducers were mounted at the bottom of the fluid covering vessel and connected to the multiplexer channels of the UDV device. Eutectic GaInSn was used as working fluid. Analysing mean velocity profiles and the spatiotemporal properties of the flow, the study shows, that already for small deviations from coaxial conditions the flow topology changes.

Keywords: Ultrasound Doppler Velocimetry; Fluid flow; Travelling magnetic field; Stirring

  • Lecture (Conference)
    The 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 07.-09.04.2010, Göteborg, Sweden
  • Contribution to proceedings
    The 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 07.-09.04.2010, Göteborg, Sweden
    Proceedings of the 7th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 978-91-7290-292-3, 85-88

Publ.-Id: 13886

PIConGPU - A scalable particle-in-cell algorithm for graphic cards

Bussmann, M.; Burau, H.; Widera, R.; Hönig, W.; Juckeland, G.; Debus, A.; Kluge, T.; Schramm, U.; Cowan, T.; Sauerbrey, R.

We present the main features of PIConGPU, the - to our knowledge - first scalable particle-in-cell (PIC) code for relativistic laser plasma interactions written for graphical processing units (GPUs). We show that it is possible to use PIConGPU on standard compute clusters equipped with GPUs and introduce the main features that are important to reach good weak scaling when increasing both the size of the system simulated and the number of GPUs.

Keywords: gpu; particle-in-cell; pic; laser; plasma; relativistic; pic; graphic card; simulation; algorithm

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP, 08.-12.03.2010, Hannover, Deutschland

Publ.-Id: 13885

Optimization of flat-cone targets for enhanced laser-acceleration of protons

Antici, P.; Gaillard, S.; Gremillet, L.; Amin, M.; Nakatsutsumi, M.; Romagnani, L.; Tampo, M.; Toncian, T.; Kodama, R.; Audebert, P.; Pépin, H.; Willi, O.; Borghesi, M.; Cowan, T.; Fuchs, J.

We have analyzed the acceleration of laser-generated protons, produced at the rear surface of flat-cone targets irradiated by anultra-intense (I~5 x 1019 W/cm²) short (400fs) laser pulse. We used different target sizes and shapes in order to find the optimum target layout. We find that for targets with a too narrow cone structure, the production of the hot electrons, driving the proton acceleration, islocated prior to the accelerating rear surface of the target, resulting in a reduced maximum proton energy.

Publ.-Id: 13884

Proton, Electron and K-Alpha Emission from Micro-Scale Copper Cone Targets

Kluge, T.; Gaillard, S.; Gall, B.; Lockard, T.; Gautier, C.; Geissel, M.; Offermann, D.; Kraft, S. D.; Schollmeier, M.; Schramm, U.; Sentoku, Y.; Zeil, K.; Cowan, T. E.; Flippo, K. A.; Bussmann, M.

We have conducted two sets of laser-ion acceleration experiments at the LANL 200 TW Trident short-pulse laser comparing regular size flat foils, reduced mass targets and new Cu micro-cone targets to elucidate the production of hot electrons and ions in these targets. Results from the latest experiment show proton energies in excess of ~65 MeV for the cones, compared to ~55 MeV for reduced mass targets and ~45 MeV for regular flat foils for high contrast. Data from Cu K-alpha 2D imaging crystal, an X-Ray single hit CCD, proton beam images on RCF film stacks, and an electron spectrometer are presented.

Keywords: proton; acceleration; laser; high power; ultra intense; cone; pizza-top; direct laser acceleration of surface confined electrons; TNSA

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP, 10.3.2010, Hannover, Deutschland

Publ.-Id: 13883

Radiation effects in nanoparticles

Järvi, T. T.; Pohl, D.; Rellinghaus, B.; Schultz, L.; Albe, K.; Kuronen, A.; Nordlund, K.; Fassbender, J.

Ion irradiation is turning out as a very useful tool for producing nanoparticles in phases that are hard or impossible to obtain otherwise. In addition to promoting chemical ordering in, for instance, FePt particles [1], irradiation has recently been shown to provide a means to remove grain boundaries from alloyed (CuAu, FePt) multiply twinned particles, turning them single-crystalline [2,3]. Irradiation can also be used to densify porous cluster-assembled films without dramatically increasing the grain size [4]. Thus, irradiation provides a versatile tool for controlled engineering of nanoscale systems. We will give an overview of our recent work on radiation effects in nanoparticles. Specifically, the multiply-twinned to single-crystalline transformation, which has been shown to occur via transient amorphization of the alloyed particles, is discussed [3]. The transformation is surprising, as it occurs in alloys, which are known not to amorphize in bulk. In addition to phase transitions, we will review defect production by, on one hand, cascade-producing irradiation [5] (e.g., 25 keV Ga on Au) and, on the other, irradiation in the single knock-on regime [6,7] (e.g., 3 keV He on Pt). The defect production mechanisms and the differences between irradiation response of nanosized and bulk systems are discussed.

[1] U. Wiedwald et al., Appl. Phys. Lett. 90, 062508 (2007).
[2] O. Dmitrieva et al., J. Appl. Phys. 97, 10N112 (2005).
[3] T. T. Järvi et al., EPL 85, 26001 (2009).
[4] K. Meinander and K. Nordlund, Phys. Rev. B 79, 045411 (2009).
[5] T. T. Järvi et al., EPL 82, 26002 (2008).
[6] T. T. Järvi et al., Phys. Rev. B 80, 132101 (2009).
[7] T. T. Järvi et al., J. Appl. Phys. 102, 124304 (2007).

Keywords: nanoparticles; ion irradiation; phase transformation; binary alloys

  • Lecture (Conference)
    Multiscale Materials Modelling, 04.-08.10.2010, Freiburg, Deutschland

Publ.-Id: 13882

Study of the pp \to np\pi+ reaction at 1.25 GeV with HADES

Liu, T.

In pp collisions at 1.25 GeV kinetic energy, the HADES collaboration aimed at investigating the di-electron production related to $\Delta$ (1232) Dalitz decay ($\Delta+ \to pe+e-$). In order to constrain the models predicting the cross section and the production mechanisms of $\Delta$ resonance, the hadronic channels have been measured and studied in parallel to the leptonic channels. The analyses of $pp\to np\pi+$ and $pp\to pp\pi0$ channels and the comparison to simulations are presented in this contribution, in particular the angular distributions being sensitive to $\Delta$ production and decay. The accurate acceptance corrections have been performed as well, which could be tested in all the phase space region thanks to the high statistic data. These analyses result in an overall agreement with the one-$\pi$ exchange model and previous data.

  • Lecture (Conference)
    12th International Conference on Nuclear Reaction Mechanisms, 15.-19.06.2009, Varenna, Italy
  • Contribution to WWW
    arXiv:0909.3399v1 [nucl-ex]:

Publ.-Id: 13881

All-Optical Cooling and Diagnostics for Relativistic Ion Beams

Bussmann, M.; Schramm, U.; Winters, D. F. A.; Walther, T.; Birkl, G.; Dimopoulou, C.; Nolden, F.; Steck, M.; Franzke, B.; Novotny, C.; Geppert, C.; Nörtershäuser, W.; Kozhuharov, C.; Kühl, T.; Stöhlker, T.

Laser cooling of ion beams at relativistic energies at the Experimental Storage Ring (ESR) at GSI has shown that in order to address the complete phase space of an initially hot ion beam, laser systems have to deliver light at a wide range of frequencies. If all ions are cooled by the laser force, the beam momentum spread can be reduced to a level that cannot be resolved by standard accelerator diagnostics. In our talk we introduce new laser systems and optical diagnostics that are currently set up for an upcoming laser cooling experiment at ESR. We discuss the impact of these new developments on the detection of beam ordering referring to laser cooling experiments previously performed at the ESR.

Keywords: laser cooling; esr; ion beam; relativistic energies; gsi; optical; diagnostics

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP, 08.-12.03.2010, Hannover, Deutschland

Publ.-Id: 13880

Origin of the low-mass electron pair excess in light nucleus-nucleus collisions

Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Guber, F.; Hennino, T.; Holzmann, R.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.

We report measurements of electron pair production in elementary p+p and d+p reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n+p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass Me+e- > 0.15 GeV/c2 is about an order of magnitude larger in n+p reactions as compared to p+p. A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C+C reactions are compatible with a superposition of elementary n+p and p+p collisions, leaving little room for additional electron pair sources in such light collision systems.

  • Physics Letters B 690(2010), 118-122

Publ.-Id: 13879

Propagation of vector-meson spectral-functions in a BUU type transport model: Application to di-electron production

Barz, H. W.; Kampfer, B.; Wolf, G.; Zetenyi, M.

The time evolution of vector-meson spectral-functions is studied within a kinetic theory approach. We implement this formalism in a BUU type transport model. Applications focus on rho and omega mesons being important pieces for the interpretation of the di-electron invariant mass spectrum measured by the HADES collaboration for the reaction C + C at 2 AGeV bombarding energy. Since the evolution of the spectral functions is driven by the local density, the in-medium modifications are tiny for small collision systems within this approach.

Publ.-Id: 13878

Role of phi decays for K- yields in relativistic heavy-ion collisions

Schade, H.; Wolf, G.; Kaempfer, B.

The production of strange mesons in collisions of Ar+KCl at a kinetic beam energy of 1.756 AGeV is studied within a transport model of Boltzmann-\"Uhling-Uhlenbeck (BUU) type. In particular, phi, K+ and K- yields and spectra are compared to the data mesured recently by the HADES collaboration and the phi yield measured previously by the FOPI collaboration. Our results are in agreement with these data thus presenting an interpretation of the subleading role of phi decays into K-'s and confirming the importance of the strangeness-exchange channels for K- production.

Publ.-Id: 13877

Charged pion production in C+C and Ar+KCl collisions measured with HADES

Tlusty, P.; Agakishiev, G.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A.; Blanco, A.; Boehmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Dybczak, A.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kaempfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krasa, A.; Krizek, F.; Kruecken, R.; Kuehn, W.; Kugler, A.; Kurepin, A.; Lamas-Valverde, J.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.

Results of a study of charged pion production in 12C+12C collisions at incident beam energies of 1A GeV and 2A GeV, and 40Ar+natKCl at 1.76AGeV, using the spectrometer HADES at GSI, are presented. We have performed a measurement of the transverse momentum distributions of pi+- mesons covering a fairly large rapidity interval, in case of the C+C collision system for the first time. The yields, transverse mass and angular distributions are compared with a transport model as well as with existing data from other experiments.

Publ.-Id: 13876

Dielectron production in pp and dp collisions at 1.25 GeV/u with HADES

Lapidus, K.

Inclusive production of e+e--pairs in pp and dp collisions at a kinetic beam energy of 1.25 GeV/u has been studied with the HADES spectrometer. In the latter case, the main goal was to obtain data on pair emission in quasi-free np collisions. To select this particular reaction channel the HADES experimental setup was extended with a Forward Wall hodoscope, which allowed to register spectator protons. Here, the measured invariant mass distributions demonstrate a strong enhancement of the pair yield for M > 140 MeV/c2 in comparison to pp data.

  • Lecture (Conference)
    19th International Baldin Seminar on High Energy Physics Problems: Relativistic Nuclear Physics and Quantum Chromodynamics (ISHEPP 2008), 29.09.-04.10.2008, Dubna, Russia
  • Contribution to WWW
    arXiv:0904.1128v1 [nucl-ex]:

Publ.-Id: 13875

Measurement of the Spin-Dependence of the pbar-p Interaction at the AD-Ring

Barschel, C.; Bechstedt, U.; Dietrich, J.; Dolfus, N.; Engels, R.; Gebel, R.; Hadamek, H.; Haidenbauer, J.; Hanhart, C.; Kacharava, A.; Krol, G.; Kueven, M.; Langenberg, G.; Lehrach, A.; Lorentz, B.; Maier, R.; Martin, S.; Meissner, U.-G.; Nekipelov, M.; Nikolaev, N. N.; Oellers, D.; D'Orsaneo, G.; Prasuhn, D.; Rathmann, F.; Retzlaff, M.; Sarkadi, J.; Schleichert, R.; Seyfarth, H.; Sibirtsev, A.; Spoelgen, D.; Stein, H. J.; Stockhorst, H.; Stroeher, H.; Weidemann, C.; Welsch, D.; Wieder, P.; Barion, L.; Bertelli, S.; Carassiti, V.; Ciullo, G.; Contalbrigo, M.; Cotta-Ramusino, A.; Dalpiaz, P. F.; Drago, A.; Guidoboni, G.; Lenisa, P.; Pappalardo, L.; Stancari, G.; Stancari, M.; Statera, M.; Azarian, T.; Kulikov, A.; Kurbatov, V.; Macharashvili, G.; Merzliakov, S.; Meshkov, I. N.; Smirnov, A.; Tsirkov, D.; Uzikov, Y.; Barsov, S.; Belostotski, S.; Grigoryev, K.; Kravtsov, P.; Mikirtychiants, M.; Mikirtychiants, S.; Vasilyev, A.; Esser, F. M.; Greven, R.; Hansen, G.; Jadgfeld, F.; Klehr, F.; Soltner, H.; Straatmann, H.; Chiladze, D.; Garishvili, A.; Lomidze, N.; Mchedlishvili, D.; Nioradze, M.; Tabidze, M.; Akopov, N.; Avetisyan, A.; Elbakyan, G.; Marukyan, H.; Taroian, S.; Benati, P.; Erven, W.; Kayser, F. J.; Kleines, H.; Wuestner, P.; Bruncko, D.; Ferencei, J.; Musinsky, J.; Urban, J.; Augustyniak, W.; Marianski, B.; Trzcinski, A.; Zupranski, P.; Dymov, S.; Nass, A.; Steffens, E.; Rathsman, K.; Tegner, P. E.; Thoerngren Engblom, P.; de Leo, R.; Tagliente, G.; Kaempfer, B.; Trusov, S.; Buttimore, N.; Meyer, H. O.

We propose to use an internal polarized hydrogen storage cell gas target in the AD ring to determine for the first time the two total spin-dependent pbar-p cross sections sigma_1 and sigma_2 at antiproton beam energies in the range from 50 to 450 MeV. The data obtained are of interest by themselves for the general theory of pbar-p interactions since they will provide a first experimental constraint of the spin-spin dependence of the nucleon-antinucleon potential in the energy range of interest. In addition, measurements of the polarization buildup of stored antiprotons are required to define the optimum parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to feed a double-polarized asymmetric pbar-p collider with polarized antiprotons. Such a machine has recently been proposed by the PAX collaboration for the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The availability of an intense stored beam of polarized antiprotons will provide access to a wealth of single- and double-spin observables, thereby opening a new window on QCD spin physics.

Publ.-Id: 13874

First fluorescence spectroscopic investigation of Am(III) complexation with an organic carboxylic ligand, pyromellitic acid

Barkleit, A.; Geipel, G.; Acker, M.; Taut, S.; Bernhard, G.

For the first time Am(III) complexation with a small organic ligand could be identified and characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature and trace metal concentration. With pyromellitic acid (1,2,4,5-benzene-tetracarboxylic acid, BTC) as ligand spectroscopic characteristics for the Am BTC complex system as well as for the Am3+(aq) ion were determined at pH 5.0, an ionic strength of 0.1 M (NaClO4) and room temperature. The fluorescence lifetimes were determined to be 20.8 ± 3.4 ns for Am3+(aq) and 27.3 ± 2.3 ns for the Am BTC 1 : 1 complex; the emission maximum for the 5D1 7F1 transition is 691 nm for both species. The complex stability constant for the Am BTC 1 : 1 complex was calculated to be log β110 = 5.42 ± 0.09.

Keywords: TRLFS; time-resolved laser-induced fluorescence spectroscopy; americium; benzenepolycarboxylate

Publ.-Id: 13873

Rare silverpoint drawings by Rembrandt in the focus of SR-XRF

Reiche, I.; Merchel, S.; Radtke, M.; Riesemeier, H.; Bevers, H.

The silverpoint drawing technique had its cumulating period in the late Middle Ages and the Renaissance. However, some undoubtful Rembrandt drawings were made on prepared vellum by the master with this already obsolete technique in the Golden Age. Among these drawings is the best-known portrait of his wife Saskia, 1633 (KdZ1152, Berlin). It is, thus, especially interesting to investigate these drawings. In addition to art historical studies, it was also important to get new insights into the graphical material employed in order to know whether it was different from that one used in former periods, which in turn can give information on the genesis and dating of the drawings.
Silverpoint drawings belong to the most valuable treasures of graphical art collections. They are generally very precise drawings of excellent quality. Therefore, only completely non-destructive analytical methods are applicable. Moreover, they need to be very sensitive because of the low quantity of matter present in the strokes (less than some hundreds of μg/cm2). Several preliminary tests showed that only Particle induced X-ray Emission (PIXE) spectrometry and Synchrotron radiation induced X-ray fluorescence analysis (SR-XRF) fulfil the analytical requirements for the investigations of these drawings meaning that they are sensitive enough, feasible in air and require no sampling.
Synchrotron radiation induced X-ray fluorescence results obtained at the BAMline, BESSY II, HZB, Berlin on three Rembrandt silverpoint drawings of the collection of the Kupferstichkabinett Staatliche Museen zu Berlin will be presented (Reiche et al. 2006).
The chosen method will be explained as well as the requirements for studying non-destructively valuable works of art such as these silver point drawings. The main part of the presentation focusses on the meaning of the results and illustrates how SR-XRF analysis can reinforce art historical assumptions on the genesis, the dating of the drawings and their connection. Additional information can be gained from such analytical studies on the conservation state of the drawings.
The results will also be compared to those available on other silverpoint drawings by Van Eyck, Dürer and the Holbein family (Reiche and Roth, 2008, Ketelsen et al. 2005, Reiche et al. 2004).

References :

I. Reiche and M. Roth, Berliner Beiträge zur Acrhäometrie 21 (2008) 81.
I. Reiche et al., Appl Phys. A 83 (2006) 169.
T. Ketelsen et al., The Burlington Magazine CXLVII, #1224 (2005) 170.
I. Reiche et al., NIMB 226 (2004) 83.

Keywords: SR-XRF; X-Ray Fluorescence; synchrotron; archaeometry

  • Lecture (Conference)
    X-ray techniques in the investigations of the objects of cultural heritage: around Rembrandt and his workshop Research Conference, 13.-16.05.2010, Krakow, Poland

Publ.-Id: 13872

Self-assembled ordered nanostructures on Ge by cluster irradiation

Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Facsko, S.; Pilz, P.

Surface modification with ion beams is a well established technique to create self-organized regular patterns like ripples and dots [1,2]. The pattern can be controlled by the kind of ion species as well as by their energy, fluence and angle of incidence. Future applications in electronic or optoelectronic nanodevices are under discussion [3]. In this contribution we present a novel approach, the irradiation with focused dimer and trimer beams of heavy ions, in particular Bi2 + and Bi3 ++. These clusters from a liquid metal ion source were mass separated in a CANION 31Mplus FIB system from Orsay Physics and focused onto a Ge surface. The acceleration voltage of 30 kV corresponds to energies of 10-15 keV/atom, fluences from 1015 to 1017 cluster/cm2 were applied.
For normal incidence up to an angle of ~30° dot patterns with a pronounced short-range order have been found. The dots are crystalline (as confirmed by Raman measurements), enriched with Bi and have a diameter of 30 nm. The inter-dot distance is about 50 nm. A new quality of the dots is their large aspect ratio of ~1. Using the same fluence and energy/atom, irradiation with single Bi+ ions resulted in the well-known porous Ge surface. Therefore, this new kind of pattern should be caused by cluster effects, not by single ion impacts. The Bradley-Harper model is obviously not valid, in contrast to the fabrication of regular 3-4 nm deep holes in Ge by a 5 keV FIB irradiation with monomer Ga-ions [4]. According to a first analysis, the energy density deposited per volume by the cluster impact cascade must exceed a threshold value to form this new kind of surface pattern. The threshold energy deposited per Ge atom coincides with the heat per atom required for Ge melting. Thus, each cluster impact yields to a small melting pool of <1000nm³ volume. A model based on such pools explains the segregation of Bi into the dots. The Ge surface undulation is caused by a decrease of the Ge volume of 5% during melting. A Ge flux into the Bi rich region occurs due to the Bi concentration dependent Ge melt temperature.
In the range from 30° to 60° no structures occur. The surface becomes very smooth by the heavy cluster beam. Increasing the angle further leads to the formation of ripples perpendicular to the beam direction with a wavelength of about 100 nm and a height of 30 nm. Measurements with back scattered electrons reveal that the top of the ripples is Bi enriched. At still higher angles a transition from ripples to a shingle structure has been found, which are also perpendicular to the beam direction. A rotation into ripple pattern parallel to the beam has been not observed.
References: [1] R.M. Bradley and J.M.E. Harper, J. Vac. Sci Technol. A 6 (1988) 2390-2395. [2] S. Facsko, T. Dekorsy, C. Koerndt, C. Trappe, H. Kurz, A. Vogt, H.L. Hartnagel, Science 285 (1999) 1551-1553. [3] R. Gago et al. Phys. Rev. B 73 (2006) 155414-1-9. [4] Q. Wei et al., Adv. Mat. 21 (2009) 2865-2869.

Keywords: Bi-Liquid Metal Ion Source; FIB; Cluster beam; surface nano-structrues

  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 29.-31.03.2010, Dresden, Deutschland

Publ.-Id: 13871

Crystalline Ge surface nanopatterns by erosion with heavy Bi-dimer and trimer ions

Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Facsko, S.; Pilz, W.

Two features of our heavy-ion-irradiation-induced surface patterns differ drastically from patterns formed on Ge with ions so far: The surface remains crystalline as proven by Raman measurements, and the dots and ripples heights equal their wavelengths (aspect ratio ~1).
The self-organisation of these very regular, high-amplitude dot and ripple patterns on (001)Ge has been found under bombardment with heavy ions of bismuth dimers and trimers. The Bi2 +, Bi3 + and Bi3 ++ ions are formed in a Liquid Metal Ion Source, they were accelerated, focused and scanned by a Focused Ion Beam system. 30 kV acceleration voltage and up to 1017 ions/cm2 have been used.
In the ion impact angle range from normal to ~30° incidence, hexagonal patterns of dots with ~30 nm diameter and ~40 nm height are found. Using a Bi monomer ion beam having the same atomic energy and fluence like the dimer and trimer beams, an amorphous Ge nanosponge is found. In the incidence range from 30° to 60° Bi3 ++ ions smoothen the Ge surface, whereas we found for 60° to 80° and more grazing incidence ripples and shingles perpendicular to the beam, respectively.
The Bi3 ++ ions are 16 times heavier than Ar+ ions, and still 5 times heavier than Xe+ ions. This high ion mass leads to a patterning mechanism different from the Bradley-Harper model, which becomes strikingly apparent by the crystalline Ge surface. An identified threshold of this new patterning mode could help to understand the mechanism: The ion-impact-induced deposition of energy per volume (as estimated by SRIM) must exceed a value which coincides with the energy needed for melting. Thus, Bi segregation during melt pool resolidification and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.

Keywords: Bi- LMIS; FIB; cluster beam; surface structures

  • Invited lecture (Conferences)
    21th International Conference on the Application of Accelerators in Research and Industry CAARI 2010, 08.-13.08.2010, Fort Worth, USA

Publ.-Id: 13870

ESTRAL - Realistic Integration of Sorption Processes in Transport Programs for Long-term Safety Analysis

Stockmann, M.; Brendler, V.; Klemm, K.; Noseck, U.

In safety assessments for radioactive waste repositories in deep geological formations the host formation and/or the sedimentary overburden might act as a barrier, since sorption on mineral surfaces of the sediments can retard the transport of many radionuclides. So far, the retention of radionuclides has been described in respective computer programs by temporally constant distribution coefficients.
A coupling of reactive transport programs with a full geochemistry code is currently not practical due to the high computing costs for the calculation of large model areas and very long time scales as required in long-term safety analysis. Therefore, the present study develops and implements a different methodology to extend the existing 3D transport program r3t [FEI 04] towards a more realistic description of the radionuclide migration under temporal variable geochemical conditions. Such changes might be caused in a sedimentary overburden by a marine transgression or the thawing of permafrost.

Keywords: Safety assessment; repository; radionuclide sorption; "smart Kd"-values

  • Lecture (Conference)
    Jahrestagung Kerntechnik, Workshop "Kompetenzerhaltung in der Kerntechnik", 04.-06.05.2010, Berlin, Deutschland

Publ.-Id: 13869

Role of the soft-iron impellers in the french von-Karman-Sodium (VKS) dynamo experiment

Giesecke, A.; Stefani, F.; Gerbeth, G.

not available
not available

Keywords: dynamo; mhd; vks

  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-541 November 2010, 59-64
    ISSN: 1437-322X

Publ.-Id: 13868

Experimentelle Untersuchungen zur Korrosionschemie und zum Anlagerungsverhalten von Korrosionsprodukten

Kryk, H.; Hoffmann, W.; Hessel, G.

Zur Aufrechterhaltung der Kernkühlung bei Kühlmittelverluststörfällen (KMV) in Leichtwasserreaktoren wird das aus dem Leck im Primärkreislauf austretende Kühlwasser im Reaktorsumpf gesammelt und über Notkühlpumpen in den Kühlkreislauf zurückgeführt. Auf der Saugseite der Notkühlpumpen befinden sich Sumpfsiebe zur Rückhaltung von im Kühlwasser suspendierten Fremdstoffen. Im Fokus von Arbeiten zur Gewährleistung einer gesicherten Kernkühlung bei KMV-Störfällen steht seit Jahren die Erforschung von Transport- und Verblockungsprozessen von Isoliermaterialfasern im Reaktorsumpf bzw. an entsprechenden Rückhaltevorrichtungen. Im Verlauf eines KMV-Störfalles können neben dem Isoliermaterial weitere Feststoffe im Kühlwasser sowohl das Verblockungsverhalten an den Sumpfsieben als auch die Wasserchemie beeinflussen. Speziell der Langzeitkontakt des Leckwasserstrahls mit feuerverzinkten Lichtgitterrosten kann zur Bildung löslicher und partikelförmiger Korrosionsprodukte führen. Im Rahmen eines vom BMWi geförderten Forschungsvorhabens soll der Einfluss derartiger Korrosionsprozesse auf die chemische Zusammensetzung des Kühlwassers und auf das Sumpfsieb-Verstopfungsverhalten untersucht werden. Ziel ist die Unterstützung der Modellierung für eine konsistente Strömungssimulation von KMV-Störfällen unter Einbeziehung von chemischen Langzeiteffekten.
Neben grundlegenden Aussagen zur Korrosionschemie verzinkter Stahloberflächen und Einflussfaktoren auf die Korrosionsprozesse beinhaltet der Vortrag die geplanten Versuchsstrategien und die darauf aufbauenden Auslegungskriterien für die am FZD zu errichtenden Versuchsanlagen für korrosionschemische Experimente unter störfallspezifischen Bedingungen. Weiterhin wird die Mess- und Analysentechnik für die Untersuchung der Korrosionsvorgänge vorgestellt und diskutiert.

Keywords: loss-of-coolant accident; light water reactor; sump strainer; corrosion; hot-dip galvanized steel

  • Lecture (Conference)
    BMWi-Fachkolloquium „Isolationsmaterialbelastete Kühlmittelströmung“, 03.-04.03.2009, Dresden, Deutschland

Publ.-Id: 13867

Radiosynthesis and radiopharmacological evaluation of cyclin-dependent kinase 4 (Cdk4) inhibitors

Koehler, L.; Graf, F.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Wuest, F.

Tumor cells are characterized by their loss of growth control resulting from alterations in regulating pathways of the cell cycle, such as a deregulated cyclin-dependent kinase (Cdk) activity and/or Cdk expression. Appropriately radiolabeled Cdk4 inhibitors are discussed as promising molecular probes for imaging cell proliferation processes and tumor visualization by PET. This work describes the design, synthesis and radiopharmacological evaluation of two 124I-labeled Cdk4 inhibitors as potential radiotracers for imaging of Cdk4 in vivo. Treatment of a solution containing labeling precursors with [124I]NaI gave radiolabeled Cdk4 inhibitors [124I]CKIA and [124I]CKIB in radiochemical yields of up to 35%. 124I-labeled radiotracers [124I]CKIA and [124I]CKIB were used in cell uptake studies as well as biodistribution studies in Wistar rats and small-animal PET in tumor-bearing mice. In vitro radiotracer uptake studies in adherent tumor cells using [124I]CKIA showed substantial uptake in HT-29 and FaDu cells (750–850 %ID/mg protein [124I]CKIA and 900–1000 %ID/mg protein [124I]CKIB) after 1 h at 37 °C. Biodistribution of [124I]CKIA and [124I]CKIB showed rapid blood clearance of radioactivity and an accumulation as well as metabolization in the liver. Both radiotracers were administered intravenously to mouse FaDu xenograft tumor model and imaging studies were performed on a small-animal PET scanner. Both imaging techniques showed only little uptake of both radiotracers in the FaDu tumor xenografts.

Keywords: Iodine-124; Cell cycle; Cyclin-dependent kinase 4 inhibitor; Positron emission tomography (PET)

Publ.-Id: 13866

Proceedings of the 6th International Conference on Electromagnetic Processing of Materials (EPM 2009)

Gerbeth, G.; Eckert, S.; Fautrelle, Y.; (Editors)

Electromagnetic Processing of Materials (EPM) relates to all branches of materials processing where some benefit could be attained from an electromagnetic influence on the process. This covers traditional areas such as liquid metal processing, metal casting and solidification, induction heating, but also crystal growth from the melt, plasma processes, etc. The series of EPM conferences was initiated in 1994 by S. Asai (Japan) and M. Garnier (France).

  • Book (Editorship)
    Dresden: Eigenverlag Forschungszentrum Dresden-Rossendorf, 2009
    903 Seiten
    ISBN: 978-3-936104-65-3

Publ.-Id: 13865

Superconductivity in thin-film germanium in the temperature regime around 1 K

Herrmannsdörfer, T.; Skrotzki, R.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Helm, M.; Wosnitza, J.

We report recent discoveries of superconductivity in p-type-doped germanium which has been fabricated by implantation of gallium ions into near-intrinsic cubic Ge. Depending on the detailed preparation and annealing conditions, we demonstrate that superconductivity can be generated and tailored in thin p-doped layers of the Ge host. By carefully adjusting the annealing parameters, we have been able to raise the onset temperature of superconductivity to about 1.4 K at a Ga peak concentration of ∼10 at.%. This progress and the large in-plane critical magnetic field of about the size of the Chandrasekhar–Clogston limit makes thin-film Ga-doped Ge (Ge:Ga) even more attractive for technological applications. There might be particular interest to utilize on-chip thin-film superconductivity in a semiconducting environment as our preparation method of Ge:Ga is fully compatible with state-of-the-art semiconductor processing used nowadays for the mass production of logic circuits. After its finding in Si and diamond, our work adds another unexpected observation of superconductivity in doped elemental semiconductors and in one of the few remaining ‘islands of the periodic table of elements’ on which superconductivity has not been found so far.

Related publications

  • Superconductor Science and Technology 23(2010), 034007

Publ.-Id: 13864

Scavenger receptors are associated with cellular interactions of S100A12 in vitro and in vivo

Hoppmann, S.; Steinbach, J.; Pietzsch, J.

Increased plasma levels of S100 proteins and interaction of S100 proteins with receptor for advanced glycation end products (RAGE) have been associated with a number of disease states, including chronic inflammatory processes and atherosclerosis. However, data concerning the role of circulating S100 proteins in these pathologies in vivo are scarce and, furthermore, it is currently not known whether RAGE is the sole receptor for extracellular S100 proteins in vivo. We report a novel methodology using recombinant human S100 proteins radiolabelled with fluorine-18, particularly, 18F-S100A12, in receptor binding studies and cellular association studies in vitro, and in dynamic small animal positron emission tomography (PET) studies in rats in vivo. Association to both human aortic endothelial cells and macrophages revealed specific binding of 18F-S100A12 to RAGE, but, furthermore, provides evidence for interaction of 18F-S100A12 to various scavenger receptors (SR). PET data showed temporary association of 18F-S100A12 with tissues overexpressing RAGE (e.g., lung), and, moreover, accumulation of 18F-S100A12 in tissues enriched in cells overexpressing SR (e.g., liver and spleen). Blockade of overall SR interaction by maleylated BSA (malBSA) clearly shows diminished in vivo association of 18F-S100A12 to these tissues as well as a significant increment of the mean plasma residence time of 18F-S100A12 (4.8 ± 0.4 h vs. 2.3 ± 0.3 h). The present approach first demonstrates that besides RAGE also scavenger receptors contribute to distribution, tissue association and elimination of circulating proinflammatory S100A12.

Keywords: Maleylated bovine serum albumin; Receptor for advanced glycation endproducts (RAGE); S100 proteins/calgranulins; Scavenger receptors; Small animal positron emission tomography (PET)

Publ.-Id: 13863

Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6

Cizmar, E.; Zvyagin, S. A.; Beyer, R.; Uhlarz, M.; Ozerov, M.; Skourski, Y.; Manson, J. L.; Schlueter, J. A.; Wosnitza, J.

We report on high-field magnetization, specific heat, and electron-spin-resonance (ESR) studies of the quasi-two-dimensional spin- 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes below TN = 4.38 K is described in the frame of the mean-field theory, confirming a collinear magnetic structure with an easy-plane anisotropy. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the interplane/intraplane exchange interaction ratio, J´ /J = 1/ 16. It is argued that despite the onset of three-dimensional long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and nonmonotonic field dependence of the Néel temperature) are strongly affected by two-dimensional spin correlations.

  • Physical Review B 81(2010), 064422

Publ.-Id: 13862

A Star-Shaped Heteronuclear CrIIIMnII3 Species and Its Precise Electronic and Magnetic Structure: Spin Frustration Studied by X-Ray Spectroscopic, Magnetic, and Theoretical Methods

Prinz, M.; Kuepper, K.; Taubitz, C.; Raekers, M.; Khanra, S.; Biswas, B.; Weyhermüller, T.; Uhlarz, M.; Wosnitza, J.; Schnack, J.; Postnikov, A. V.; Schröder, C.; George, S. J.; Neumann, M.; Chaudhuri, P.

Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to mediate magnetic exchange interactions between the ions. Among them are star-shaped molecules in which antiferromagnetic couplings between the central and peripheral atoms are predominantly present. Those configurations lead to an appreciable spin moment in the nonfrustrated ground state. In spite of its topologically simple magnetic structure, the [CrIIIMnII 3(PyA)6Cl3] (CrMn3) molecule, in which PyA represents the monoanion of syn-pyridine-2-aldoxime, exhibits nontrivial magnetic properties, which emerge from the combined action of single-ion anisotropy and frustration. In the present work, we elucidate the underlying electronic and magnetic properties of the heteronuclear, spin-frustrated CrMn3 molecule by applying X-ray magnetic circular dichroism (XMCD), as well as magnetization measurements in high magnetic fields, density functional theory, and ligand-field multiplet calculations. Quantum-model calculations based on a Heisenberg Hamiltonian augmented with local anisotropic terms enable us not only to improve the accuracy of the exchange interactions but also to determine the dominant local anisotropies. A discussion of the various spin Hamiltonian parameters not only leads to a validation of our element selective transition metal L edge XMCD spin moments at a magnetic field of 5 T and a temperature of 5 K but also allows us to monitor an interesting effect of anisotropy and frustration of the manganese and chromium ions.

  • Inorganic Chemistry 49(2010), 2093-2102

Publ.-Id: 13861

Magnetic excitations of the gapped quantum spin dimer antiferromagnet Sr3Cr2O8

Quintero-Castro, D. L.; Lake, B.; Wheeler, E. M.; Islam, A. T. M. N.; Guidi, T.; Rule, K. C.; Izaola, Z.; Russina, M.; Kiefer, K.; Skourski, Y.

dimers by the dominant antiferromagnetic intrabilayer coupling. The dimers are coupled three dimensionally by frustrated interdimer interactions. A structural distortion from hexagonal to monoclinic leads to orbital order and lifts the frustration giving rise to spatially anisotropic exchange interactions. We have grown large single crystals of Sr3Cr2O8 and have performed DC susceptibility, high-field magnetization and inelastic neutron scattering measurements. The neutron scattering experiments reveal three gapped and dispersive singlet to triplet modes arising from the three twinned domains that form below the transition thus confirming the picture of orbital ordering. The exchange interactions are extracted by comparing the data to a random phase approximation model and the dimer coupling is found to be J0 = 5.551(9) meV, while the ratio of interdimer to intradimer exchange constants is J´/J0 = 0.64(2). The results are compared to those for other gapped magnets.

  • Physical Review B 81(2010), 014415

Publ.-Id: 13860

High-Field ESR in Spin Systems with Competing Magnetic Interactions

Zvyagin, S.

In my talk I will present a short review of our recent high-field Electron Spin Resonance (ESR) studies of spin systems with competing magnetic interactions. This topic will cover Antiferromagnetic Resonance in the multiferroic hexagonal antiferro-magnet YMnO3, ESR in the anisotropic triangular antiferromagnet Cs2CuBr4, and organic spin-1/2 chain systems [Cu(C4H4N2)(NO3)2 and (C6H9N2)CuCl3], in which an additional frustration term originates either from interchain or next-nearest-neighbor exchange interactions. A brief introduction into the recent development of the high-field ESR program at the High Magnetic Field Laboratory in Dresden will be also given.

  • Invited lecture (Conferences)
    HFM R, Magnetic Resonance in highly frustrated magnetic systems, 01.-04.02.2010, Kranjska Gora, Slovenia

Publ.-Id: 13859

Räumlich hochauflösende Computertomografie mit Gammastrahlung zur Untersuchung von Mehrphasenströmungen

Bieberle, A.

Multiphase flows denote flowing mixtures of different fluids, solids and gases, such as oil, water and air. A phase is defined in a thermo dynamical sense as a physically homo-geneous portion of a material. Multiphase flows are to be found in many industrial proc-esses and plants, for instance in oil production, chemical reactors, energy production or driving systems. In many cases, process efficiency as well as safety is directly coupled with the flow behaviour inside industrial facilities. Therefore, there was and is a strong development of invasive and non-invasive measuring and imaging techniques with the aim to improve our understanding of physical flow phenomena and achieve flow optimi-sation and control wherever necessary. Furthermore, flow measurement technology plays an important role in the derivation of physical models for flow simulation with so called CFD (computational fluid dynamics) codes.
Computed tomography (CT) is a non invasive imaging technique that produces non superimposed cross sectional images using analytical, algebraic or statistical reconstruc-tion algorithms. Radiation based transmission tomography therefore employs a radiation source, such as a nuclide or an X-ray source, and a spatially resolving radiation detec-tor. Such as measurement system must acquire radioscopic projections from different angular positions, which can be accomplished either by rotating it around the object of investigation or by rotation of the object itself. In industrial applications nuclide sources with photon energies higher than 500 keV are often used. Such radiation can penetrate metal housings and still gives sufficient contrast between the phases that have to be analysed.
In this work, a new high resolution gamma radiation computed tomography system that uses a 137Cs source was developed. The design and the electronic parts were carefully developed for the application in harsh industrial environments (e.g. temperature and humidity variation as well as electrical and magnetic fields respectively) and high meas-urement accuracy. The spatial resolution of the detector arc is about 2 mm, the stop-ping efficiency for gamma photons with 662 keV energy is about 75% and the deviation of measuring repetition is lower than 1%. The detector arc operates in pulse mode al-lowing excluding scattered gamma photons to a certain degree from the measurement by a pulse height discriminator stage. The developed measurement system was success-fully applied in industrial and laboratory measurement campaigns, for instance meas-urements on an electrically heated rod bundle, a fluid coupling and a chemical reactor. Due to the quantum limitations of the radiation source and slow rotation of the heavy scanner elements the developed gamma radiation computed tomography system can only be used for time-averaged flow measurement with integration times in the range of one minute or more. However, within the frame of this work an extension of the system to the measurement of rapidly rotating fluid distributions is shown. Here, the principle of angle-resolved data acquisition has been implemented which was highly challenging for this type of high resolution radiation detector from an electronic point of view. The developed gamma ray tomography system is not only valuable for flow measurement but has a much wider application range, such as high-energy non-destructive testing of materials and components, such as castings, vehicle constructions or palaeontological objects.

Keywords: Hochauflösende Computertomographie; Gammastrahlung

  • Book (Authorship)
    Dresden: TUDPress, 2009
    122 Seiten

Publ.-Id: 13858

Nanoindentation and transmission electron microscopy of ion-irradiated iron-chromium alloys

Heintze, C.

Ion irradiations combined with nanoindentation provide a means to characterize irradiation damage in a wide range of irradiation temperature and fluence. Nanoindentation results are reported for Fe-2.5at%Cr, Fe9at%Cr and Fe-12.5at%Cr irradiated at 300°C up to 1 and 10 dpa. The effect of Cr content and fluence are discussed. Hardening features were characterized by means of transmission electron microscopy. The ion-induced damage is compared with the damage created by neutron irradiation for the same alloys.

Keywords: ion-irradiation; nanoindentation; TEM; irradiation hardening; iron base alloys

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland
  • atw - International Journal for Nuclear Power 7(2010), 479-481

Publ.-Id: 13857

Bildrekonstruktion für die ultraschnelle Limited-Angle-Röntgen-Computertomographie von Zweiphasenströmungen

Bieberle, M.

Messtechnik für Mehrphasenströmungen steht heutzutage verstärkt im Fokus der Forschung, da Mehrphasenströmungen einerseits maßgeblich die Sicherheit und Effizienz vieler industrieller Prozesse beeinflussen und andererseits - aufgrund der erhöhten Rechenleistung heutiger Computer - zentrales Thema bei der Entwicklung verbesserter Strömungsmodelle für Simulationscodes sind. Die ultraschnelle Röntgen-Computertomographie ist ein neuartiges Messverfahren, das erstmalig eine nicht-invasive sowie zeitlich und räumlich hochauflösende Abbildung von transienten Mehrphasenströmungen erlaubt. Die zu Grunde liegende Limited-Angle-Anordnung stellt dabei besondere Anforderungen an die Bildrekonstruktion, da ein Teil der hierfür benötigten Projektionsinformationen fehlt.
Kernthema dieser Ausgabe der Reihe "Dresdner Beiträge zur zerstörungsfreien Prüftechnik" ist die Entwicklung eines Bildrekonstruktionsalgorithmus', der in der Lage ist, fehlende Projektionsinformationen durch a-priori-Informationen über das Untersuchungsobjekt auszugleichen und somit die Ausprägung von Bildartefakten stark zu reduzieren. Der auf Basis der Level-Set-Methode entwickelte Algorithmus erreicht dieses Ziel durch die Rekonstruktion von Phasengrenzflächen anstelle von Dichteverteilungen. Gleichzeitig umfasst er einen Glättungseffekt, der eine Minimierung des durch die kurzen Messintervalle hervorgerufenen Rauschens bewirkt. Die ultraschnelle Röntgen-Computertomographie sowie der neu entwickelte Level-Set-Rekonstruktionsalgorithmus wurden an diversen Zweiphasenströmungsexperimenten erprobt. Zudem wurde das Messsystems erfolgreich für die Zweiebenen- und Volumentomographie erweitert.

Keywords: X-ray; tomography; ultrafast; image reconstruction; level-set method

  • Book (Authorship)
    Dresden: TUDpress, 2010
    142 Seiten

Publ.-Id: 13856

Nanocrystalline Electroplated Cu-Ni: Metallic Thin Films with Enhanced Mechanical Properties and Tunable Magnetic Behavior

Pellicer, E.; Varea, A.; Pane, S.; Nelson, B. J.; Menendez, E.; Estrader, M.; Surinach, S.; Baro, M. D.; Nogues, J.; Sort, J.

Nanocrystalline 3mm thick Cu1–xNix (0.45 < x < 0.87) films are electrodeposited galvanostatically onto Cu/Ti/Si (100) substrates, from a citrate- and sulphate-based bath containing sodium lauryl sulphate and saccharine as additives. The films exhibit large values of reduced Young’s modulus (173 < Er < 192 GPa) and hardness (6.4 < H < 8.2 GPa), both of which can be tailored by varying the alloy composition. The outstanding mechanical properties of these metallic films can be ascribed to their nanocrystalline nature - as evidenced by X-ray diffraction, transmission electron microscopy, and atomic force microscopy - along with the occurrence of stacking faults and the concomitant formation of intragranular nanotwins during film growth. Due to their nanocrystalline character, these films also show very low surface roughness (root mean square deviation of around 2 nm). Furthermore, tunable magnetic properties, including a transition from paramagnetic to ferromagnetic behavior, are observed when the Ni percentage is increased. This combination of properties, together with the simplicity of the fabrication method, makes this system attractive for widespread technological applications, including hard metallic coatings or magnetic micro/nano-electromechanical devices.

Keywords: magnetism; Ni; magnetic properties; mechanical properties; nanocrystalline

Publ.-Id: 13855

Experimental investigation of the flow in a continuous casting mould under the influence of a transverse DC magnetic field

Timmel, K.; Eckert, S.; Gerbeth, G.

This paper describes laboratory experiments aimed at investigations of flow structures and related transport processes in the continuous casting mould under the influence of an external DC magnetic field. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. Experimental results will be presented which have been obtained using a physical model operating with the room temperature alloy GaInSn. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied up to Hartmann numbers of about 400. The effect of the magnetic field on the flow structure turned out to be rather complex. The flow measurements do not manifest a smooth braking effect which would be expected as an overall damping of the flow velocity and the related fluctuations all-over the mould volume. Variations of the wall conductivity showed a striking impact on the resulting flow structures. The experiments provide a substantial data base for the validation of respective numerical simulations.

Keywords: continuous casting; mould flow; electromagnetic brake; flow measurements; ultrasonic Doppler velocimetry

Publ.-Id: 13854

Evidence for a novel high-field superconductry state in layered organic superconductors

Wosnitza, J.

In the so-called FFLO state, named after Fulde, Ferrell, Larkin, and Ovchinnikov, the super-conducting state can survive even at high magnetic fields above the Pauli paramagnetic limit. The quasi-two-dimensional (2D) organic superconductors have been suggested as good can-didates for exhibiting the FFLO state. When applying the magnetic field exactly parallel to the conducting layers the orbital pair breaking is greatly suppressed and the Pauli limit is reached. We performed high-resolution specific-heat and torque-magnetization experiments in magnetic fields up to 32 T for such 2D organic superconductors. In a very narrow angular region close to parallel-field orientation we observe additional anomalies below the upper critical field sig-naling the existence of an additional superconducting phase. The specific-heat data for kappa-(BEDT-TTF)2Cu(NCS)2 with Tc = 9.1 K show that the superconducting transition becomes first order for fields above 21 T indicating that the Pauli limit is reached. Below about 3 K, the upper critical field increases sharply and a second first-order transition appears within the superconducting phase. These results are corroborated by magnetic-torque data which allowed to follow the phase diagram to lower temperatures and higher fields. Our results give strong evidence for the realization of the FFLO state in organic superconductors.
Work done in cooperation with R. Lortz, B. Bergk, Y. Wang, A. Demuer, I. Sheikin, G. Zwicknagl, and Y. Nakazawa.

  • Invited lecture (Conferences)
    International Symposium on "Novel states in correlated condensed matter - from model systems to real materials", 02.-04.03.2010, Berlin, Deutschland

Publ.-Id: 13853

Ceramics high rate timing RPC

Naumann, L.; Stach, D.; Kotte, R.; Wüstenfeld, J.

A resistive plate counter for timing purposes in the high rate environment of the Compressed Baryonic Matter Experiment has been developed at the Forschungszentrum Dresden-Rossendorf. The detector electrodes are made of a ceramics composite, whose volume resitivity can be tuned in the production process over five orders of magnitude. The detector prototype has been tested with single electrons of 32MeV. It shows an all-time high rate capability for electron fluxes up to 5·10 5s−1cm−2.

Keywords: RPC; Rate capability; Ceramics composite; Bulk resistivity; Detection efficiency; Time resolution

Related publications

Publ.-Id: 13852

The 14N(p,gamma )15O reaction studied at high energy

Marta, M.

The 14N(p,gamma)15O reaction is the bottleneck of the carbon-nitrogen-oxygen (CNO) cycle. Recent studies of this reaction have been performed in the low energy range E < 500 keV. However, also data at higher energy are necessary to extrapolate the S-factor down to the energy range of astrophysical interest. Up to now, only one set of data froman experiment performed in 1987 extends up to 2.5MeV. A new study has been carried out at the high-current FZD Tandetron in Dresden, in the energy region from 0.6 to 2.5MeV. The astrophysics motivations, setup and on-going analysis are presented.

Keywords: CNO cycle; solar neutrinos; capture reaction; gamma-ray spectroscopy

  • Contribution to proceedings
    Fifth European Summer School on Experimental Nuclear Astrophysics, 20.-27.09.2009, Santa Tecla, Sicilia, Italy
    AIP Conference Proceedings, Vol. 1213: American Institute of Physics, 978-0-7354-0756-5, 222-224

Publ.-Id: 13851

Capture of planktonic microbial diversity in fractures by long-term monitoring of flowing boreholes, Evander Basin, South Africa

Davidson, M. M.; Silver, B. J.; Onstott, T. C.; Moser, D. P.; Gihring, T. M.; Pratt, L. M.; Boice, E. A.; Sherwood Lollar, B.; Lippmann-Pipke, J.; Pfiffner, S. M.; Kieft, T. L.; Seymore, W.; Ralston, C.

The diversity of planktonic microorganisms in fluids from a group of flowing subterranean boreholes was monitored from the day they were drilled to as long as three and a half months after drilling as they drained into Evander Au mine. Geochemical analyses of the water, characterization of microbial communities by phospholipids fatty acid (PLFA) and DNA sequence analyses, and calculations of free energy flux indicated thatmine-introduced microbial contaminants, dominated by β and γ Proteobacteria, Cenarchaeaceae and Candidatus Nitrososphaera, were flushed from the boreholes and replaced by fracture water derived microbial communities dominated by Firmicutes, Methanosarcinalesand Thermoproteaceaea. The fracture water was a mixture of paleometeoric water and 2.0 Ga old, diagenetically altered, hydrothermal fluid. The C and H isotopic data for C1−4 indicated that the CH4 was primarily abiogenic in origin although ∼35–50% of it might have originated from microbial methanogenesis. Noble gas analyses yielded estimated residence times of some 10 million years for the fracture water, which is estimated to represent a capture cross-section of 0.25–0.50 km2. The 16S rRNA and dsrAB gene sequences indicated that the indigenous bacterial communities were predominantly comprised of sulfate reducers belonging to the genera Desulfotomaculum, Candiditus Desulforudis and Desulfofustis. The sulfur isotopic analyses of sulfate and sulfide yielded fractionation delta-34S values ranging from 16 to 22% consistent with microbial sulfate reduction.Thermodynamic analyses indicate that methanogenic reactions are inhibited by the high partial pressure of abiogenic CH4 and that sulfate-reducing reactions are more favorable, which is consistent with the abundance of 16S rRNA genes belonging to known sulfate reducing bacteria. Supplemental materials are available for this article. Go to the publisher’s online edition of Geomicrobiology Journal to view the free supplemental files.

Keywords: 16S rRNAphylogeny; dsrAB; sulfate reduction; methanogenesis; isotope geochemistry

Publ.-Id: 13850

Evidence for reduced collectivity around the neutron mid-shell in the stable even-mass Sn isotopes from new lifetime measurements

Jungclaus, A.; Walker, J.; Leske, J.; Speidel, K.-H.; Stuchbery, A. E.; East, M.; Boutachkov, P.; Cederkäll, J.; Doornenbal, P.; Egido, J. L.; Ekström, A.; Gerl, J.; Gernhäuser, R.; Goel, N.; Gorska, M.; Kojouharov, I.; Maier-Komor, P.; Modamio, V.; Naqvi, F.; Pietralla, N.; Pietri, S.; Prokopowicz, W.; Schaffner, H.; Schwengner, R.; Wollersheim, H.-J.

Precise measurements of the lifetimes of the first excited 2+ states in the stable even Sn isotopes 112-124Sn have been performed using the Doppler shift attenuation (DSA) technique. For the isotopes 112Sn, 114Sn and 116Sn the B(E2) transition strengths deduced from the measured lifetimes are in severe disagreement with the previously reported values and indicate a minimum at N = 66. The observed deviation from a maximum at mid-shell is attributed to the obstructive effect of the s1/2 neutron orbital in generating collectivity when being close to the Fermi level.

Keywords: Nuclear structure; gamma-ray spectroscopy; level lifeftimes

Publ.-Id: 13849

Dilepton Production at SIS Energies with HADES

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

One of the main goals of the HADES experiment is to achieve a detailed understanding of dielectron emission from hadronic systems at moderate bombarding energies. Results obtained on electron pair production in elementary N+N collisions pave the way to a better understanding of the origin of the pair excess seen in heavy-ion collisions. This puzzling excess, reported first by the former DLS experiment, is now being investigated systematically by HADES.

Publ.-Id: 13848

High depth resolution analysis of elemental depth distributions in nanocoatings

Neelmeijer, C.; Vieluf, M.; Kosmata, M.; Munnik, F.

Elemental depth distributions in thin films and near surface regions can be obtained with Ion Beam Analysis (IBA) techniques using MeV ions. Depth profiling of films of a few nanometres thickness as well as multilayer arrangements in the nanometre scale is possible with high resolution (HR) spectrometers. At the research centre in Dresden-Rossendorf, two systems are available for high depth resolution analysis, one for medium to heavy elements (Z > 13) using elastic scattering of ions at the target atoms and one for light elements (Z < 14) detecting atoms ejected from the sample (recoils). In both cases, an energy resolution of about 1‰ is obtained using magnetic spectrometers which allow sub-nanometre depth resolution and, thus, the characteristics of thin film interfaces. Advantages and limits of HR-depth profiling are presented. As an example, atomic layer deposition (ALD) of the high-k material ZrO2 has been examined on two different underlayers, i.e. SiO2 or TiN. From the HR-spectrum it is deduced that fifteen ALD cycles result in 1.5 nm ZrO2 (3.8 ● 1015 Zr/cm²) on the SiO2 surface. In more detail simulation and measured energy distribution of C-ions, scattered on the Zr atoms, are in excellent agreement if ZrO2 layer thickness fluctuation is taken into account. The latter can be obtained by considering surface roughness obtained from AFM measurements. The mentioned agreement of measured and simulated HR-spectra proves that there is no diffusion of Zr atoms into the SiO2. In a second example ten ALD cycles of ZrO2 on TiN were studied. Obviously, the TiN underlay causes two effects as visible in the corresponding HR-spectrum: First, the broad low energy tail of the Zr energy distribution can not be verified by ZrO2 layer thickness variations. Thus, TiN certainly induces Zr diffusion which takes place probably preferentially along grain boundaries of the titanium nitride. Estimated diffusion depths extend up to 3 nm. Secondly, only ten ALD cycles are enough to deposit 4.1 ● 1015 Zr/cm2 on this backing. This finding supports the interpretation of stimulated Zr grain boundary diffusion into TiN. The last example presents a nanometre multilayer arrangement of Al/Cu/FePt on SiO2. HR measurements are demonstrated for various elements and their corresponding interfaces in different depths.

  • Poster
    2nd International Conference on Functional Nanocoatings, 28.-31.03.2010, Dresden, Germany

Publ.-Id: 13847

Convectional controlled crystal-melt interface using two-phase radio-frequency electromagnetic heating

Hermann, R.; Gerbeth, G.; Priede, J.; Krauze, A.; Behr, G.; Buchner, B.

The radio frequency floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. This interface depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt flow ranging from intense inwards to outwards flows. Depending on the phase shift between the two induction coils, a transition from a double vortex structure to a single vortex structure to a single vortex structure is created at a preferable phase shift of 90° this change in the flow field has a significant influence on the shape of the solid-liquid interface. Due to their attractive properties for high temperature applications such as high melting temperature, low density, high modulus and good oxidation resistance, the magnetic system was applied to the crystal growth of TiAl alloys.

Publ.-Id: 13846

Improving proton acceleration with circularly polarized intense laser pulse by radial confinement with heavy ions

Huang, L. G.; Lei, A. L.; Bin, J. H.; Bai, Y.; Yu, W.; Yu, M. Y.; Cowan, T. E.

Energetic proton acceleration from interaction of intense short circularly polarized laser pulse with a sandwich target is investigated using two-dimensional particle-in-cell simulation. The sandwich target consists of a hydrogen-plasma layer surrounded by carbon-plasma layers. It is found that the transverse electric fields generated at the plasma layer interfaces efficiently confine the longitudinally accelerated protons to within the hydrogen-plasma layer such that they are collimated and have smaller energy spread compared with a pure proton layer target. The proton energy spectrum can be controlled by adjusting the target parameters, in particular the width of the hydrogen-plasma layer and the density of the carbon-plasma layer.

Publ.-Id: 13845

Enhanced Isochoric Heating from Fast Electrons Produced by High-Contrast, Relativistic-Intensity Laser Pulses

Perez, F.; Gremillet, L.; Koenig, M.; Baton, S. D.; Audebert, P.; Chahid, M.; Rousseaux, C.; Drouin, M.; Lefebvre, E.; Vinci, T.; Rassuchine, J.; Cowan, T.; Gaillard, S. A.; Flippo, K. A.; Shepherd, R.

Thin, mass-limited targets composed of V/Cu/Al layers with diameters ranging from 50 to 300  μm have been isochorically heated by a 300 fs laser pulse delivering up to 10 J at 2×1019  W/cm2 irradiance. Detailed spectral analysis of the Cu x-ray emission indicates that the highest temperatures, of the order of 100 eV, have been reached when irradiating the smallest targets with a high-contrast, frequency-doubled pulse despite a reduced laser energy. Collisional particle-in-cell simulations confirm the detrimental influence of the preformed plasma on the bulk target heating.

Publ.-Id: 13844

Cold quarks stars from hot lattice QCD

Schulze, R.; Kämpfer, B.

At small net baryon densities ab initio lattice QCD provides valuable information on the finite-temperature equation of state of strongly interacting matter. Our phenomenological quasiparticle model provides a means to map such lattice results to regions relevant for future heavy-ion experiments at large baryon density; even the cool equation of state can be inferred to address the issue of quark stars. We report on (i) the side conditions (charge neutrality, beta equilibrium) in mapping latest lattice QCD results to large baryon density and (ii) scaling properties of emerging strange quark stars.

Keywords: lattice qcd htl quasiparticle model quark stars

  • Lecture (Conference)
    Strongly Interacting Matter under Extreme Conditions, 17.-23.01.2010, Hirschegg, Österreich

Publ.-Id: 13843

Temporal pulse control of a multi-10TW diode-pumped Yb:Glass laser

Hornung, M.; Boedefeld, R.; Siebold, M.; Kessler, A.; Schnepp, M.; Wachs, R.; Saevert, A.; Podleska, S.; Keppler, S.; Hein, J.; Kaluza, M.

At the Institute of Optics and Quantum Electronics in Jena, Germany, the currently most powerful diodepumped solid-state laser system with 25-TW peak power POLARIS is in operation. In this paper we give an overview about the dispersion management of the chirped pulse amplification in order to minimize the pulse duration and thus to maximize the intensity available for experiments. A detailed description of the stretcher and compressor design with a novel alignment routine is given as well as measurements for the pulse duration and the temporal contrast. The far field measurement of the beam focussed by an off-axis parabola yields a nearly diffraction limited focal spot.

Publ.-Id: 13842

Original version or not: PIXE-RBS testing of a Meissen porcelain box

Neelmeijer, C.; Roscher, R.

Introduction: The valuation of an artistic object depends decisively on its complete originality. Regarding the 18th century snuffbox, made from Meissen Porcelain, restorers ask the following question: Are both the base body but also the hinged cover originals?

Visual discrepancies concerning especially the shade of porcelain glazing raised doubts. In addition, the onglaze decorations show slight differences in colour and flow. Assured non-destructive materials analysis was in demand to clarify the problem.
External Ion Beam Analysis: The 4-MeV proton beam used in atmosphere and PIXE (Particle Induced X-Ray Emission) simultaneously with RBS (Rutherford Backscattering Spectrometry) for analysis [1,2] proved ideal to get convincing answers. Visible marks due to the beam spot (1 mm2) on the highly sensitive porcelain were avoided by using only 200 pA beam intensity and 30 s irradiation time.
Similarities and differences:
Ornamental painting. The ancient Meissen onglaze colour palette is well-known since decades [3]. In conformity with [3] the artist used the pigment copper green for leaves of trees painted on both bottom and cover (point a). However, the green colourant of the cover contains Co and Zn, not obtained in the X-ray spectrum from the bottom. According to [3] Meissen copper green was made from Cu or brass, an alloy of Cu and Zn, which are both reduced to ashes. The addition of Co is mentioned [3] for getting special shaded green paint. Whether or not such characteristic differences are also present in the case of the crimson clothes can not be revealed. Indeed, the PIXE spec-trum taken from the pink gown on the cover (b) shows signals from Au, to be characteristic for purple [3]. Corresponding low-intensity Au-peaks cannot be identified for the pink skirt painted on the bottom. This is because of the superimposed high-intensity Pb L lines due to another type of glazing.
Porcelain glazing. The bottom comprises comparatively thick lead containing glazing, hence intense Pb-L signals are found in the PIXE spectrum.

The number of lead atoms inside the glazing of the cover (c) is much lower. The latter gets reflected also by comparing Pb-Lγ in the presented PIXE spectra taken from the green leaves painted on glazing. Moreover, RBS taken from pure glazing of the cover makes clear that the few Pb atoms are situated on the glazing surface. This is understandable when supposing Pb to originate from a surface polishing process using Pb containing polish agent. The discussed difference in glazing of cover and bottom and especially the considerable Pb-content of the latter, assumable to be bond as lead oxide, clarifies the apparent discrepancies of shades.
Unfortunately, unglazed positions had not been avail-able for getting compositions of the porcelain body.
Conclusions: Cover and base body of the porcelain box can not be related to one and the same workmanship. The cover was certainly later on replaced or it represents completely a later additive. Despite of differences regarding the green pigments of porcelain paints used on bottom and cover, the box fit the typical Meissen onglaze colour technology. Therefore, the question - original version or not - must be answered by the statement: Certainly not, but there is no doubt concerning original Meissen handcraft.
References: [1] Neelmeijer C. et al. NIMB 118 (1996) 338-345. [2] Neelmeijer C. and Mäder M. NIMB 189 (2002) 293-302. [3] Mields M., Kerami-sche Zeitschrift 8 (1963) 453-459.

  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 29.-31.03.2010, FZD, Germany

Publ.-Id: 13841

Effect of temperature on the retention of 2 keV Cs+ ions in Si

Wilde, C.; Möller, W.; Neidhardt, J.

Introduction: Cesium is a commonly used species for SIMS, because it provides a high negative secondary ion yield. For more quantitative modeling of the secondary ion yield during SIMS the precise knowledge of the amount of Cs retained in the near surface region is vital. Its equilibrium concentration can be theoretically described by the implantation process and the material removal by (self) sputtering. However, the experimentally determined concentrations of Cs ions retained in Si [1] are lower than that predicted by TRIDYN or by the model of Schulz and Wittmaack [2]. This indicates more complex interaction of chemical (compound formation) or physical nature (texture), which is not described by the given models. The chemical incorporation of residual gas is thought to be a possible reason (e. g. [3]). Therefore, an IBA set-up including RBS and ERD for simultaneous in-vacuo detection of Cs and O in Si was developed to analyze the incorporation of oxygen during Cs sputtering as a function of sample temperature in order to draw conclusion of their activation threshold.
Results: Fig. 1 shows the saturation of Cs in Si at room temperature. The temporal development is consistent with the model of implantation and self sputter-ing. Regardless the low partial pressure of oxygen, there is also a strong correlation between Cs and O indicating ion induced incorporation pathways on top of the natural oxide on the untreated Si surface.
Fig. 2 shows the steady state areal densities for Cs and O as a function of temperature. Two discrete steady state regimes for Cs are observed at high (> 500°C) and low (< 250°C) temperatures with an transition, where the steady state areal density de-creases almost linearly by a factor of four. The O concentration behaves congruently, while the deviation at temperatures > 600°C might be attributed to thermal oxidation.
Conclusion: Even though no significant influence on the physical conditions of the sputtering processes are expected within the temperature range, the Cs areal density shows two discrete regimes, which, interestingly, correlate closely to the amount of O incorporated from residual gas even at base pressures below 10-7 mbar. The reported recrystallisation by rapid thermal annealing with an app. 10% increase of sputter yield shown by Anderson [4] for Ar in Ge seems to be much to small to explain this strong de-crease of steady state Cs concentration. Instead overlying chemical processes are thought to play a major role, e. g. the Cs enhanced formation of mixed oxides (e. g. Cs2O shown by Michel et al. [5]) can impact sputtering yields and/or thermally desorb in the ob-served temperature range under UHV conditions. The precise nature remains unclear up to now and follow-up experiments at different O partial pressures might provide further insights.
References: [1] Gnaser H. NIMB 267 (2009) 2808–2816. [2] Schulz F. and Wittmaack K. Ra-diat. Eff. 29 (1976) 31-40. [3] Berghmans B. and Van-dervorst W. J. Appl. Phys. 106 (2009), 033509. [4] Anderson G. S. J. Appl. Phys. 38 (1967) 1607-1611. [5] Michel E. G. et al. Phys. Rev. B 38 (1988) 13999-13406.

  • Poster
    Workshop Ionenstrahlphysik, 29.-31.03.2010, FZD, Germany

Publ.-Id: 13840

Bacterial diversity in opalinus clay samples collected from the Mont Terri Laboratory in April 2009 as estimated by cultivation and direct molecular approaches

Buchvarova, V.; Geissler, A.; Selenska, S.

Bacterial diversity in unperturbed opalinus clay samples was studied by using a molecular approach based on DNA recovery via direct cell lysis, PCR amplification of 16S rRNA gene fragments, cloning, RFLP typing and consequent sequence analyses. Two highly predominant bacterial groups, each including almost one third of the analysed clones, were found. The first group was represented by proteobacterial clones; 70 % of them were affiliated with Acidovorax (Betaproteobacteria). The second numerically predominant group consisted of representatives of several various Clostridium subgroups (Firmicutes). One additional, third predominant group included about 14 % of the studied clones and was affiliated with Bacteroidetes. About one quarter of the analysed 16S rDNA clones possessed individual RFLP types, which indicated the presence in the studied bacterial community of highly diverse bacterial groups in low numbers.
The amount of total DNA, recovered from a parallel opalinus clay sample supplemented with R2A medium and incubated under sterile and anaerobic conditions, was significantly higher. This is an indication of microbial growth. By using the above described 16S rRNA gene retrieval we were able to demonstrate that the stimulated bacterial community in the R2A treated samples was strongly shifted and predominated by two main groups of Firmicutes: Paenibacillus sp. (about the half of the studied clones) and Sporomusa sp. belonging to one non-pathogenic sub-group of Clostridiales (about 42 % of the clones). Interestingly, none of these two bacterial populations was dominant in the unperturbed opalinus clay samples. Moreover, the three times lower number of individual 16S rRNA gene fragments in the clone library of the R2A treated sample then in the untreated one indicates that natural bacterial diversity in the opalinus clay was masked by the selectively induced by the medium two groups of heterotrophic bacteria. The latter was confirmed by the results of our cultivation experiments: up to date three groups of bacterial isolates were cultivated from the R2A treated samples. The first and most predominant group was affiliated with the non-pathogenic Clostridium species, Sporomusa silvacetica, the second - with Paenibacillus wynnii, and the third - with another non-pathogenic Clostridium, namely Clostridium bowmanii. The interactions of some of these isolates with uranium and other radionuclides are planed to be studied.
Additionally, we will analyse the influence of U(VI) on natural bacterial diversity in the opalinus clay samples. Efforts to stimulate the growth of other specific bacterial groups such as sulphate reducers and metal reducers in the opalinus clay samples are in progress.

  • Lecture (others)
    Mont Terri Meeting, 08.-09.03.2010, Paris, France

Publ.-Id: 13838

Factor analysis and sequential extraction unveil geochemical processes relevant for trace metal distributions in fluvial sediments of a pyrite mining area, China

Liu, J.; Chen, Y.; Wang, J.; Qi, J.; Wang, C.; Lippold, H.; Lippmann-Pipke, J.

Four fluvial sediment cores were geochemically analysed for their major elements and for their trace metal contents and represent a sensitive environmental record for heavy metal contamination in a pyrite mining area, Pearl River Basin, South China. While an identification of depositional and post-depositional processes is not possible by means of the vertical profiles of the trace metal contents alone, factor analysis uncovers four main factors that control trace metal distributions in the sediment cores. After analysing the geochemical fractions of heavy metals by a sequential extraction procedure, these four factors could be explained as (i) complexation with organic matter in the sediment (As, Cu, Ni and Zn), (ii) weathering processes by iron reduction and oxidation (Pb, Mo and Cr), (iii) weathering by Mn reduction and oxidation (Tl and Co) and (iv) binding effects of sulphur in the sediment or physical transport of pyrite tailings (Zn). The environmental evaluation by geoaccumulation indices and enrichment factors reveals that the studied sediment cores are significantly contaminated and enriched with As, Tl, Pb and Zn. The risk assessment code additionally suggests low to medium risk of these studied heavy metals on the whole.

Keywords: Trace metal contamination; Factor analysis; Geoaccumulation index; Fluvial sediment; Mining area

Publ.-Id: 13837

Mid-frequency deposition of a-C:H films using five different precursors

Peter, S.; Günther, M.; Hauschild, D.; Grambole, D.; Richter, F.

The plasma-enhanced chemical vapour deposition (PECVD) of amorphous hydrogenated carbon films from pulsed discharges with frequencies in the range from 50 kHz to 250 kHz was investigated. Five different hydrocarbons (acetylene C2H2, isobutene C4H8, cyclopentene C5H8, toluene C7H8 and cycloheptatriene C7H8) were probed as film growth precursors. In addition, two types of pulse-generators with somewhat different waveforms were used to power the discharges in the so called mid-frequency range. The a-C:H films deposited in a parallel-plate reactor were characterised for their thickness/deposition rate, hardness and hydrogen content. The hydrogen concentration in the films varied between 19 at.-% and 37 at.-%. With the substrate temperature held constant, it is roughly in inverse proportion to the hardness. The film with the highest hardness of 25 GPa was formed at a deposition rate of 0.8 μm/h in the C2H2 discharge at the lowest investigated pressure of 2 Pa. With increasing molecular mass of the precursor mostly weaker films were deposited. Relatively high values of both deposition rate and hardness were achieved using the precursor isobutene: a hardness of 21 GPa combined with a deposition rate of 4.1 μm/h. From the probed precursors, isobutene is also most advantageous for a-C:H deposition at higher pressures (up to 50 Pa investigated). But, as an over-all trend, the a-C:H hardness decreases with increasing deposition rate.

Keywords: Diamond-like carbon; a-C:H; PECVD; Pulsed discharge; Precursor

  • Vacuum 84(2010), 958-961


Publ.-Id: 13836

Analyse ultradünner Schichten und deren Grenzflächen mit Nanometertiefenauflösung

Kosmata, M.; Munnik, F.; Neelmeijer, C.; Heller, R.; Vieluf, M.; Merchel, S.; Möller, W.

Die quantitative Elementanalytik von Schichten und Schichtabfolgen im Dickenbereich weniger Nanometer ist in den letzten Jahren von steigender technologischer Relevanz geworden und somit im Fokus der aktuellen Forschung. Im Mittelpunkt dieser materialwissenschaftlichen Fragestellungen steht die Bestimmung von Tiefenverteilungen von Elementen in dünnen Schichten, die durch sequentielle Abscheideverfahren oder nachfolgende Prozessschritte wie Temperung erzielt werden, aber auch der Nachweis unbeabsichtigter Kontamination. Daraus können Informationen im Hinblick auf gezielte Materialentwicklung gewonnen werden und die Qualität bestehender Prozessführungen lässt sich bewerten.
Die meisten konventionellen Analyseverfahren wie z. B. Sekundärionenmassen-spektrometrie (SIMS) sind zur Quantifizierung ihrer Ergebnisse in der Regel auf Referenzmaterialien (gleicher Matrix) angewiesen. Im Gegensatz dazu kann die Ionenstrahlanalyse (ion beam analysis, IBA) standardfrei betrieben werden. Der physikalische Prozess, auf der fast alle Methoden der IBA beruhen, ist die binäre Wechselwirkung von MeV-Ionen mit den Atomkernen in den Schichten. Diese Wechselwirkung, elastische Streuung oder Kernreaktion, ist einfach und genau beschreibbar; kollektive Matrixeffekte treten dabei nicht auf.
Am Ionenstrahlzentrum des FZD kommen hauptsächlich drei Analysemethoden zur Anwendung:
• Kernreaktionsanalyse (Nuclear Reaction Analysis, NRA) zum tiefenabhängigen Nachweis von Wasserstoff über die resonante Kernreaktion 1H(15N,αγ)12C
• Rutherford-Rückstreuspektrometrie (Rutherford Backscattering Spectrometry, RBS) insbesondere zur Detektion von Elementen mit Ordnungszahlen Z > 14
• Elastische Rückstreuanalyse (Elastic Recoil Detection, ERD) zum Nachweis leichter Elemente mit Z = 2-14 (He-Si)
Die zur Messung ultradünner Schichten mit RBS und ERD erforderliche Tiefenauflösung (< 1 nm) kann mit Teilchenspektrometern mit höchster Energieauflösung erreicht werden.

  • Lecture (others)
    seminar an der TU Dresden, 25,02,2010, TU Dresden Institut für Halbleiter - und Mikrosyst, Germany

Publ.-Id: 13835

Novel U(VI) Complexes of Bis(2-hydroxyaryl)imine Ligands: Synthesis, Structural Characterization, and Extraction Studies.

Tanh Jeazet, H. B.; Doert, T.; Gloe, K.; Tsushima, S.; Geipel, G.; Gloe, K.; Bernhard, G.

The coordination chemistry of uranium in different oxidation states has recently generated much attention due to several reasons. The most important reason is the separation of U(VI) present in radioactive waste, but also the effects of U(VI) on our environment are of great interest.[1] The extraction and separation of U(VI) and other actinides, especially the separation from lanthanides, is most difficult due to their similar chemical behavior.[2] However, the introduction of soft heteroatoms, as imine nitrogen, in the ligand systems could be used as a tool for more selective and effective binding and extraction. We have synthesized and characterized some novel U(VI) complexes using multidentate Schiff base ligands. Structures of these complexes were characterized by X-ray crystallography and DFT calculations. It is the intention of this work to determine not only the structure of these complexes but also the extraction ability of the ligands towards U(VI) and Eu(III).

Keywords: Extraction study; radioactive waste; schiff base; uranium

  • Poster
    GDCh-Wissenschaftsforum Chemie, 30.08.-02.09.2009, Frankfurt am Main, Germany

Publ.-Id: 13834

Geochemical study of different-aged mining dump materials in the Freiberg mining district, Germany

Stockmann, M.; Hirsch, D.; Lippmann-Pipke, J.; Kupsch, H.

Historical mining dumps are useful archives for the investigation of weathering processes. The objective of this study was to investigate the weathering behavior of waste-rock material derived from the 800 years old silver ore mining in Freiberg, Germany. For identify time-dependent weathering indices, dumped material of four dumps of different ages and corresponding rock was examined regarding the geochemical composition. The dumped material is characterized by high contents of heavy metal containing sulfidic ores, such as pyrite, arsenopyrite, sphalerite and galena. Acid mine drainage (AMD) is produced by the oxidative weathering of the sulfide minerals and causes the increased dissolving of soluble metals with increasing age of dumps. As a result of these weathering processes, a clear depletion of chalcophile elements in the older dump material (800 years) compared to the youngest dump (100 years) was observed. In the soil horizons downstream the dumps, high quantities of heavy metals (e.g., up to 12000 ppm As, 3300 ppm Pb, 640 ppm Zn), mainly adsorbed on organic matter, were determined and indicate a time-dependent element transfer from the dumps into their surrounding soils.

Keywords: Waste-rock dumps; Heavy metals; Weathering; Mobilization; Adsorption

Publ.-Id: 13833

Scaling of proton energies in ultrashort pulse laser plasma acceleration

Zeil, K.; Kraft, S.; Bock, S.; Bussmann, M.; Cowan, T.; Kluge, T.; Metzkes, J.; Richter, T.; Sauerbrey, R.; Schramm, U.

This paper presents a systematic investigation of an ultrashort pulse laser acceleration of protons that yields unprecedented maximum proton energies of 17MeV at a table-top Ti:sapphire laser power level of 100TW. For plain fewmicron- thick foil targets, a linear scaling of the maximum proton energy with laser power is observed and this is attributed to the short acceleration period close to the target rear surface. Although excellent laser pulse contrast was available, slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from the target normal that could be used for better discrimination of the low-energy part of the spectrum.

Publ.-Id: 13832

Magnetization Dynamics of Coupled Vortices

Wintz, S.; Puzic, A.; Strache, T.; Koerner, M.; Bunce, C.; Marko, D.; Grebing, J.; Fritzsche, M.; Moench, I.; Mattheis, R.; Erbe, A.; Raabe, J.; Quitmann, C.; Fassbender, J.

We report on the layer-resolved imaging of the magnetization dynamics of vortices in different coupling states. The study is performed using time-resolved magnetic soft x-ray microscopy. Magnetic vortices confined into micron-sized trilayer stacks offer a unique opportunity to study the coupling of magnetic moments on the nanoscopic scale. Antiferromagnetically (AFM) coupled vortices can be created within cobalt-IL-permalloy stacks, if the material of the nonmagnetic interlayer (IL) is chosen properly, with the thickness corresponding to the first antiferromagnetic maximum of the interlayer-exchange-coupling (IEC). It is known that the strength, as well as the orientation of the IEC can be modified by noble gas ion irradiation. A controlled neon irradiation of such structures leads to a successive reorientation of the IEC and eventually AFM coupled vortices can be transformed into ferromagnetically (FM) coupled ones. The response of a vortex to an alternating magnetic field depends crucially on the specific orientation of its in-plane magnetization curling (circulation) and the direction of the out-of- plane vortex core (polarization). This holds true especially for the gyrotropic mode, which corresponds to an orbiting of the core around its equilibrium position. The cores in the individual layers of a strictly FM coupled vortex pair show an in-phase motion that is similar to that of a single layer vortex. However, in the case of a vortex pair with AFM coupled in-plane magnetization an inverse sense of gyration can be detected, with highly elliptical trajectories of the individual cores. Furthermore, independent vortex core switching processes were observed in the individual layers of a vortex pair with FM coupled circulation.

Keywords: magnetism; dynamics; vortex; coupling; interlayer-exchange; x-ray microscopy; XMCD

  • Poster
    MML 2010 - IEEE 7th International Symposium on Magnetic Multilayers, 19.-24.09.2010, Berkeley, USA

Publ.-Id: 13831

Determining the radial pair distribution function from X-ray absorption spectra by use of the Landweber iteration method

Rossberg, A.; Funke, H.

The Landweber iteration approach is used to construct the radial pair distribution function (RPDF) from an X-ray absorption (EXAFS) spectrum. The physical motivation for the presented investigation is the possibility to also reconstruct asymmetric RPDFs from the EXAFS spectra. From the methodical point of view the shell fit analysis in the case of complicated spectra would be much more eased if the RPDF for the first shell(s) are computed precisely and independently. The RPDF, as a solution of the fundamental EXAFS integral equation, is examined for theoretical examples, and a detailed noise analysis is performed. As a real example the EXAFS spectrum of curium(III) hydrate is evaluated in a stable way without supplementary conditions by the proposed iteration, i.e. by a recursive application of the EXAFS kernel.

Keywords: EXAFS; pair distribution function; Fredholm integral equation; Landweber iteration

  • Journal of Synchrotron Radiation 17(2010), 280-288
  • Invited lecture (Conferences)
    ACTINET-I3 workshop, Coupling XAS and theoretical chemistry for heavy atoms, 23.-24.07.2010, Avignon, France

Publ.-Id: 13830

Obsidian homogeneity study for provenancing using Ion Beam- and Neutron Activation Analysis

Eder, F.; Neelmeijer, C.; Bichler, M.; Merchel, S.

Obsidian is a natural volcanic glass, which was one of the most appreciated materials of ancient man for cutting tools and has been found in many locations far away from any natural source. Reliable provenancing can provide evidence of contacts over certain distances and information about exchange patterns and mobility of prehistoric people.
The application of analytical methods can assist to solve the problem of obsidian provenancing by means of its highly specific chemical composition, the “chemical fingerprint”. Ion Beam Analysis (IBA) measurements, combining Particle Induced X-ray Emission (PIXE), Particle Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), are frequently used because of their high sensitivity and the non-destructive external beam mode [1-5]. Our studies have been carried out using the 4 MeV proton beam in-air of the 5 MV Tandem accelerator of the FZD. For comparative reasons and in order to obtain additional information, all obsidian samples were analysed by Neutron Activation Analysis (NAA) at the Atominstitut in Vienna, where previous investigations of volcanic rocks and glasses have been performed successfully [6-8].
Obsidian is generally described as a relatively homogeneous material [9]. Therefore, samples from the obsidian source Demenegakion (Milos, Greece) have been analysed in order to check the actual variation range of their chemical compositions. Special attention was paid to banded obsidians to clarify, if these bands show differences in the chemical composition or if these changes in the optical properties are related to inclusions of gas bubbles, microphenocrysts or similar features without significant compositional influence. Furthermore, both the influence of the surface quality and alteration by weathering has been studied.
This study is part of a joint project to apply selected analytical methods, in particular IBA, NAA and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), to reveal a maximum of compositional differences between (geological) samples of obsidian sources available in Europe. This knowledge is essential to decide, which least invasive analytical method should be chosen for the analysis of a specific archaeological artefact, on a case by case basis.

References: [1] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136-146. [2] Mäder M. et al. NIMB 239 (2005) 107-113. [3] Mäder M. and Neelmeijer C. NIMB 226 (2204) 110-118. [4] Jembrih D. et al. NIMB 181 (2001) 698-702. [5] Mäder M. et al. NIMB 136-138 (1998) 863-868. [6] Steinhauser G. et al. Appl. Geochem. 21 (2006) 1362-1375. [7] Steinhauser G. et al. Appl. Radiat. Isot. 65 (2007) 488-503. [8] Saminger S. et al. J. Radioanal. Nucl. Chem. 245 (2000) 375-383. [9] Pollard A.M. and Heron C. (2008) Archaeological chemistry Royal Society of Chemistry, Cambridge 80–81 [2nd edition].

Keywords: archaeometry; RBS; PIXE; PIGE

  • Poster
    12th International Conference on Particle Induced X-ray Emission and its Analytical Applications (PIXE), University of Surrey, 27.06.-02.07.2010, Surrey, GB

Publ.-Id: 13829

Electromagnetic control of local temperature gradients in a Czochralski crystal growth model

Pal, J.; Cramer, A.; Gerbeth, G.

This experimental work is concerned with optimisation of the Czochralski crystal growth process. With respect to the shape of the solidication front and the related mono-crystalline growth, the ratio of the horizontal and the vertical temperature gradient at the triple point liquid-solid atmosphere is thought of being a crucial magnitude, which desirably should be in the order of unity. A liquid metal model experiment was therefore build that allows studying this ratio under the influence of magnetic elds applied to the melt.

Keywords: Czochralski crystal growth; Stirring; Convection

  • Lecture (Conference)
    81st Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), 22.-26.03.2010, Karlsruhe, Deutschland

Publ.-Id: 13828

Kunstwerke - zerstörungsfreie Materialanalyse

Neelmeijer, C.

Kunstwerke sind Unikate, unwiederbringliche Zeugen vergangener Zeit. Ähnlich wie Patienten können sie erkranken, unterliegen der Alterung und bedürfen der Pflege. Das Material, woraus sie bestehen und das Klima, in dem sie aufbewahrt werden, bestimmen ihr Wohlbefinden. Die Oberfläche von Kunstwerken aus Glas, zum Beispiel, kann „rosten“ wie Metall. Wenn das Glasobjekt matt und rissig erscheint, kommt Abhilfe schon sehr spät. Präventive Konservierung heißt das Zauberwort, Vorsorge also. Entscheidend dafür ist die Früherkennung von Veränderungen besser noch die Einschätzung möglicher Schädigungen. Dazu dient die zerstörungsfreie Materialanalyse. Das kann der Protonenstrahl an Luft im Zusammenspiel mit empfindlicher Messtechnik. Am Beispiel Glas, aber auch an Gemälden, Zeichnungen, Tinten auf Urkunden gibt die Präsentation Antworten auf die typischen Fragen von Restauratoren und Kunstwissenschaftlern: Wie gefährdet ist das Kunstwerk, welche Technologien hat der Künstler verwandt um bestimmte ästhetische Eindrücke zu erlangen, gibt es Anzeichen für eine Kopie anstelle des Originals?

Keywords: art objects; non-destructive analysis; ion-beam analysis; glass; porcelain; metal; painting

Related publications

  • Lecture (others)
    Vorlesung, 24.02.2010, Dresden, BRD

Publ.-Id: 13827


Bussmann, M.; Kluge, T.; Gaillard, S.; Flippo, K.; Schramm, U.; Cowan, T. E.

Weltrekord in Protonenbeschleunigung mit Licht: Schnelle Protonen sind zum Beispiel für die Krebstherapie notwendig. Nicht immer kann man dabei an große Beschleunigeranlagen gehen. Forschern gelingt nun neue Bestmarke bei der Laser-Beschleunigung dieser Teilchen.

In der Bestrahlungstherapie von Tumoren spielen schnelle Teilchen eine wichtige Rolle. So können Strahlen schneller Protonen genutzt werden um Augenkrebs zu bekämpfen. Die Erzeugung solcher hochenergetischer Partikelstrahlen ist jedoch nicht nur in großen Beschleunigeranlagen möglich.

Man kann auch Laserlicht nutzen um Protonen und andere geladene Teilchen extrem zu beschleunigen. Dazu wird die Wechselwirkung des Lasers mit einem Materietarget, also einem materiellen Zielobjekt, genutzt. Dabei werden mikroskopischen Längenskalen sehr große Feldstärken erzeugt.

In einem kürzlich vorgestellten Versuch wurde ein neuer Rekordwert für diese Art von Teilchenbeschleunigung erzielt. Einem Forscherteam, an dem mehrere US-amerikanische Universitäten und Forschungseinrichtungen und das Forschungszentrum Dresden-Rossendorf (FZD) beteiligt sind, gelang es, einen Protonenstrahl mit einer Energie von 67 MeV (Megaelektronvolt) zu erzeugen.

Das entspricht der Energie, die ein Elektron oder ein Proton aufnähme, würde es mit einer Spannung von 67 Millionen Volt beschleunigt. Zum Vergleich: An Synchrotron-Beschleunigern wie etwa dam BESSY in Berlin oder PETRA III in Hamburg werden Energien erreicht, die etwa hundert bis tausend mal so groß sind.

Möglich wird die Teilchenbeschleunigung mit Licht durch die hohe Energiedichte moderner Hochleistungs-Kurzpuls-Laser. Trifft ein Puls aus einer solchen Quelle auf Materie, werden die Elektronen derartig stark beschleunigt, dass sie sich von ihren Atomrümpfen lösen.

Ein Plasma entsteht. Die endliche Ausdehnung des Lichtpulses sorgt nun dafür, dass die Elektronen nicht nur quer zur Ausbreitungsrichtung des Lasers beschleunigt werden, wie man das auch bei weniger intensivem Licht beobachtet.

Statt dessen tritt, nach dem der Puls durch die Materie gewandert ist, eine Plasmawelle aus zurückschwingenden Elektronen auf, die auch eine Komponente in Laserausbreitungsrichtung enthält.

Keywords: laser acceleration; cone target; particle-in-cell; pic; simulation; proton energy; high-energy; laser; plasma; record

Publ.-Id: 13826

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