Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Liquid metal experiments with strong magnetic fields and high electrical currents
Seilmayer, M.;
To measure the fluid motion in liquid metal experiments Ultrasound Doppler Velocimetry (UDV) is used very often. The very small UDV signals can be disturbed by high direct current sources due to electromagnetic noise coming from these devices. The presentation will give some ideas and work around to common problems arising with magnetic field generation. All this will be explained on an ongoing experiment to the magneto rotatorical instability (MRI) in our laboratory. Finally some concepts and results will be given to rise measurement quality.
Keywords: EMV, magnetic field, Switching mode power supply, UDV, ultrasound doppler
  • Invited lecture (Conferences)
    Mitarbeiter Seminar, 10.04.-10.09.2013, Illmenau, Thüringen

Publ.-Id: 19833 - Permalink


Electromagnetic method for gas bubble detection in liquid metal flows
Andreew, O.; Gundrum, T.; Wondrak, T.; Eckert, S.; Gerbeth, G.; Dekdouk, B.; Peyton, A.;
We present a combined numerical and experimental investigation of an electromagnetic system dedicated for an operative detection of non-metallic enclosures (gas bubbles) into the liquid metal flows. The method is based on generation of eddy currents in the electrically conducting medium by applying of ac magnetic field and detection of the electromagnetic distortions caused by inhomogeneity of electrical conductivity of the medium. We defined an optimal position and configuration of detector in order to get maximal sensitivity of the system to the spatial distribution of admixture.
Keywords: Electromagnetic Thomogpaphy, Gas Bubbles, Liquid Metal
  • Lecture (Conference)
    2013 International Congress on Advances in Nuclear Power Plants & 28th KAIF/KNS Annual conference - ICAPP 2013, 14.-18.04.2013, Jeju Island, South Korea

Publ.-Id: 19832 - Permalink


Development and application of digital image analysis technique to gas-liquid flows in a pseudo-2D bubble
Thiruvalluvan Sujatha, K.; Lau, Y. M.; Deen, N. G.; Kuipers, J. A. M.;
Bubble columns are widely used in the chemical industry for gas-liquid operations. In-spite of the wide spread use of bubble column reactors, fundamental understanding of interactions between hydrodynamics, mass transfer and chemical reaction in dense systems is still lacking. Several experimental techniques are available to study gas-liquid flows: photographic imaging, particle image velocimetry, X-ray tomography, wire mesh sensors, etc. We developed a digital image analysis technique (DIA) to study the gas-liquid flows in bubble column reactor.
  • Lecture (Conference)
    Joint HZDR & ANSYS Conference - 11th Multiphase Flow Conference & Short Course, 26.-28.11.2013, Dresden, Deutschland

Publ.-Id: 19831 - Permalink


New possibilities for investigation of the technological texture based on electric Parameters: theoretical Analysis and experimental verification
Kozik, T.; Minarik, S.;
Texture is preferred orientation of crystallites in some polycrystalline materials. Different methods are applied to characterize the orientation patterns and determine the orientation distribution. Most of these methods rely on diffraction. This paper introduces the principle of a method used for characterization of ceramics texture based on anisotropy of electrical properties of crystallites in ceramics. The mathematical framework of this method is presented in theoretical part of our work. In experimental section we demonstrate how the theoretical result could be used to evaluate technology texture of ceramic material intended for the production of electronic insulators.
Keywords: ceramics texture, scalar potential, Laplace equation, Bessel function, Bessel differential equation

Publ.-Id: 19830 - Permalink


Structural modifications of thin magnetic Permalloy films induced by ion implantation and thermal annealing, a comparison
Roshchupkina, O. D.; Strache, T.; McCord, J.; Muecklich, A.; Baehtz, C.; Grenzer, J.;
We report the structural properties of thin magnetic Permalloy films treated by two different methods: broad-beam Ga+ ion implantation at an energy of 30keV as well as annealing at different temperatures under ultra-high vacuum. Transmission electron microscope imaging and X-ray diffraction measurements have demonstrated that both ion implantation and annealing (above 300°C) lead to further material crystallization and crystallite growth. Whereas, annealing (above 400°C) leads to a strain-free state with an almost constant lattice parameter and to a further enhancement of the initial (111) texture, ion beam implantation boosts the growth of small arbitrary oriented crystallites and leads to an linear increase of the lattice parameter introducing mirco-strain to the sample. The observed decrease of the saturation magnetization for the implanted samples is mainly attributed to the presence of the non-magnetic Ga atoms incorporated in the Permalloy film itself. The rise of the saturation magnetization for the samples annealed at temperatures above 500°C is explained by an arising de-wetting effect since no ordered FeNi3 phase was detected with anomalous X-ray diffraction.
Keywords: ion beam implantation, microstructure, XRD

Publ.-Id: 19829 - Permalink


Flow measurements in a continuous steel casting model using low temperature liquid metal
Willers, B.; Timmel, K.; Eckert, S.; Gerbeth, G.;
Model experiments with low melting point liquid metals are used to evaluate the flow structure and its related transport processes in metallurgical applications in melt flows. Water model experiments are less important, in particular, in case of strong temperature gradients, two-phase flows or flows exposed to electromagnetic fields. Here we present the Mini-LIMMCAST experimental facility to illustrate the continuous steel casting process using a GalnSn room-temperature liquid metal alloy. The parameters of the facility and the dimensions of the test sections will be given and possibilities to evaluate the flow in the mold will be discussed.
The effect which the magnetic field has on the flow structure turned out to be complex. The flow measurements do not show a general braking effect which would be expected as an overall damping of the flow velocity and its resulting fluctuations in the mold. Not only different magnetic field intensities had a big influence on the flow field, but also the variation of the electromagnetic field position had a striking impact on the resulting flow structures. The flow intensity in the upper part of the mold is also significantly influenced by the movement on the free surface of the metal. During continuous casting, this movement of the free surface is an important parameter to indicate the quality of steel. The experiments provide a substantial database for the validation of respective numerical simulations.
Keywords: magnetic field, liquid metal, flow, flow structure, flow measurement, flow velocity, flow control, continuous casting, magnetic brake, Ruler EMBr, GaInSn
  • Lecture (Conference)
    The 5th International Conference STEELSIM 2013, 10.-12.09.2013, Ostrava, Czech Republic

Publ.-Id: 19828 - Permalink


Simulation of positron energy spectra generated by channeling radiation of GeV electrons in a tungsten single crystal
Azadegan, B.; Mahdipour, S. A.; Wagner, W.;
Positron production based on the generation of channeling radiation by relativistic electrons channeled along the (110) crystallographic plane of a W crystal and the subsequent conversion of radiation into e+e−-pairs in an amorphous tungsten target is described. Electron dechanneling is considered by solving of the Fokker-Planck equation. The continuous potential of the channeling plane is calculated using the Doyle–Turner approximation to the atomic scattering factor taking into account thermal vibrations of the crystal atoms. The trajectories, velocities and accelerations of planar channeled electrons are obtained by solving the classical equation of motion. In the framework of classical electrodynamics, the spectral-energy distribution of radiation is obtained from the Fourier transforms of realistic electron trajectories, velocities and accelerations within the W crystal. The calculations of channeling radiation and dechanneling are carried out by means of our Mathematica codes. The conversion of radiation into e+e− -pairs and the energy distributions of produced positrons are simulated using the GEANT4 package.
Keywords: channeling radiation, dechanneling, positrons, positron source
  • Open Access LogoContribution to proceedings
    RREPS-13 and Meghri-13, 22.-28.09.2013, Yerevan, Lake Sevan, Armenia
    Proceedings of RREPS-13 and Meghri-13, Bristol: IOP Publishing
  • Open Access LogoJournal of Physics: Conference Series 517(2014), 012039
    DOI: 10.1088/1742-6596/517/1/012039

Publ.-Id: 19827 - Permalink


Contact-less Magneto-Elastic Torsional Sensor based on Phase-Shift Measurements
Buchenau, D.; Schmidt, G.; Eckert, S.;
We report on the development of a contactless measurement technique for torsional shear stress τ in ferromagnetic axles or hollow shafts, based on the magneto-elastic effect. In general two different measuring principles for ferromagnetic materials can be realised, based on: the evaluation of the change of magnetic polarisation influenced by mechanical stress ΔJ(τ ) or, the change of the magnetic susceptibility ΔχA(τ). The comprehension of the magnetic polarisation or the magnetic susceptibility in a sensor concept requires an external magnetic field. Preferably alternating magnetic fields were used as mechanical stress can disturb the amplitude but also the phase distribution of the applied magnetic field. As a result of a torsional moment acting on an axle or hollow shaft an angle of twist η appears, which is constant over the length of the twisted object. This angle of twist can be understood as a shift of infinitesimal thin cross-sections in which the whole length of the axle is separated. Beside the macroscopic deformation effect, shear forces taking also effect on the Weiss domains in the microscale of the ferromagnetic material. The effects in the microscale are the base of the magneto-eleastic effect. The combination of the deformation effect in the macro-scale with the deformation of the Weiss domains in the microscale leading to a sophisticated measurement principle for torsional stress in axles or hollow shafts. Magneto-sensitive detectors along or around the measurement object open the possibility for a contactless detection of torsional stress in ferromagnetic materials. Beside a strong measuring signal, free from electromagnetic interference, the introduced contactless measurement principle offers different advantages, like an independence from compression strength, nominal tensile stress, impact load, ferromagnetic hysteresis effects and an independence from the temperature dependent electrical conductivity of the axle or hollow shaft. The characteristics of such a type of sensor are analysed by an electrotechnical model based on Maxwells equations. Beside the chosen design of a contactless torsion sensor and an experimental set-up, the obtained test results are illustrated and reported in the present paper.
Keywords: Magneto-elasticity, magnetic susceptibility and anisotropy, torsional stress, phase-shift

Publ.-Id: 19826 - Permalink


Invasion as target for therapy of glioblastoma multiforme
Vehlow, A.; Cordes, N.;
The survival of cancer patients suffering from glioblastoma multiforme is limited to just a few months even after treatment with the most advanced techniques. The indefinable borders of glioblastoma cell infiltration into the surrounding healthy tissue prevent complete surgical removal. In addition, genetic mutations, epigenetic modifications and microenvironmental heterogeneity cause resistance to radio- and chemotherapy altogether resulting in a hardly to overcome therapeutic scenario. Therefore, the development of efficient therapeutic strategies to combat these tumors requires a better knowledge of genetic and proteomic alterations as well as the infiltrative behavior of glioblastoma cells and how this can be targeted. Among many cell surface receptors, members of the integrin family are known to regulate glioblastoma cell invasion in concert with extracellular matrix degrading proteases. While preclinical and early clinical trials suggested specific integrin targeting as a promising therapeutic approach, clinical trials failed to deliver improved cure rates up to now. Little is known about glioblastoma cell motility, but switches in invasion modes and adaption to specific microenvironmental cues as a consequence of treatment may maintain tumor cell resistance to therapy. Thus, understanding the molecular basis of integrin and protease function for glioblastoma cell invasion in the context of radiochemotherapy is a pressing issue and may be beneficial for the design of efficient therapeutic approaches. This review article summarizes the latest findings on integrins and extracellular matrix in glioblastoma and adds some perspective thoughts on how this knowledge might be exploited for optimized multimodal therapy approaches.

Publ.-Id: 19825 - Permalink


Contactless flow rate measurements in metallic melts
Kontaktlose Durchflussmessung in Metallschmelzen

Buchenau, D.; Eckert, S.; Lenk, S.;
Control of the flow rate of liquid metals is required in a number of technological processes such as the cooling of nuclear reactors, transmutation systems and the dosing and casting of liquid metals. Electromagnetic flow meters play an important role in the diagnostics and automatic control of such processes. For example, the electromagnetic control of casting processes can be used to improve the quality of products by reducing their brittleness and increasing durability at high production efficiency, especially for complex shape components. A number of different electromagnetic flow meter designs have been developed starting from the end of the forties of the last century. One such flowmeter - themagnetic flywheel,which is described in the textbook of Shercliff uses the electromagnetic force exerted by the flow on a close magnet. Commercial electromagnetic flow meters are typically based on the flow-induced electrical voltage measurements by electrodes in direct contact to the melt in a steady magnetic field. In view of the typical problems coming along with applications at liquid metal flows such as high temperatures, interfacial effects and corrosion, the main disadvantage of this type of flow meter is the electrical contact to the liquidmetal, which is necessary to measure the electric potential difference. Therefore, contactless operating measurement techniques are very attractive for liquid metal applications.
Keywords: Contactless electromagnetic flow meter, liquid metal, phase-shift, EMD.ps, rotational frequency.

Publ.-Id: 19824 - Permalink


Visualisation of the Ludford column
Andreew, O.; Kolesnikov, Y.; Thess, A.;
When a liquid metal flows around a truncated cylinder in the presence of a magnetic field which is parallel to the axis of the cylinder, a stagnant region develops above the cylinder. This region is called Ludford column. The Ludford column represents the magnetohydrodynamic (MHD) analogue to the well-known Taylor columns in rotating flows. Whereas Taylor columns can be easily visualised using dye, the visualisation of Ludford columns remained elusive up to now because liquid metals are opaque. We demonstrate that this fundamental limitation of experimental MHD can be overcome by using a superconducting 5-Tesla magnet. This facility permits us to perform MHD experiments in which the opaque liquid metals are replaced with a transparent electrolyte while maintaining the key MHD-effects. We report results of a series of flow experiments in which an aqueous solution of sulphuric acid flows around a bar with square cross section. We vary the Reynolds number in the range 5 < Re < 100 and the Hartmann number in the range 0 < Ha < 14. The experimental procedure involves flow visualisations using tracer particles as well as velocity measurements using particle image velocimetry (PIV). Our experiments provide direct access to the Ludford columns for the first time and reveal the spatial structure of this basic feature of MHD flows.
Keywords: Magneto hydrodynamics, truncated cylinder, PIV, optical visualisation of flow patterns

Publ.-Id: 19823 - Permalink


Nutzung der intrinsischen Eigenschaften bakterieller S-Layer zur Herstellung funktioneller Beschichtungen
Döge, S.;
The intention of this work was to get a distinct conformation of the s-layer Lysinibacillus sphaericus JG-A12. S-layers are interesting for e.g. functional surfaces and filtration media. A distinct conformation of the proteins is important to optimize processes and the range of applications.
The conformation is influenced by different solution compositions for e.g. the pH-value, the buffer concentration and different concentrations of salt. This work summarizes some strategies to achieve a solution of s-layer monomers.
  • Study thesis
    HTW Dresden, 2013
    98 Seiten

Publ.-Id: 19822 - Permalink


Actinide/Lanthanide interaction studies with a typical bacterial isolate from Mont Terri Opalinus Clay a potential host rock for nuclear waste disposal
Moll, H.; Lütke, L.; Cherkouk, A.; Bernhard, G.;
The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock tested for nuclear waste disposal [1]. It is well known that bacteria indigenous to such subterranean environments can affect the speciation and hence the mobility of actinides [2]. The unknown interactions between U(VI), Cm(III)/Eu(III) and Pu with Sporomusa sp. MT-2.99 cells was explored. This bacterium was recently isolated from Mont Terri Opalinus clay core samples by our group. Strong An/Ln interactions of this clay isolate within a broad pH range (2-8) were detected. Thermodynamic stability constants of bacterial U(VI)/Cm(III)/Eu(III) surface species were determined and will be discussed. The biosorption process of U(VI)/Cm(III)/Eu(III) can be described as a pH-dependent binding on phosphoryl and carboxyl sites of the cell membrane. For Pu a complex interaction mechanism was identified. Besides biosorption strong abiotic and biotic plutonium reduction processes were observed. The information obtained in our study is of great importance for predicting the safety of a planned nuclear waste repository.

Acknowledgements. The authors thank the BMWi for financial support (contract no.: 02E10618 and 02E10971) and the BGR for providing the clay samples.

References
[1] M. Thury, P. Bossart (1999). The Mont Terri Rock Laboratory, a new international research project in a Mesozoic shale formation, in Switzerland. Eng. Geol. 52,347-359.
[2] J.R. Lloyd, G.M. Gadd (2011). The Geomicrobiology of Radionuclides. Geomicrobiol. J. 28, 383-386.
Keywords: uranium, curium, europium, plutonium, bacteria, clay rock, biosorption, bioreduction
  • Contribution to proceedings
    IGD-TP Geodisposal 2014 Conference, 24.-26.06.2014, Manchester, United Kingdom
  • Lecture (Conference)
    IGD-TP Geodisposal 2014 Conference, 24.-26.06.2014, Manchester, United Kingdom

Publ.-Id: 19821 - Permalink


Hydrodynamics and transport processes in structured reactor devices
Schubert, M.; Zalucky, J.; Rabha, S.; Hampel, U.;
In the contribution, the recent activites on mass transfer and hydrodynamics in structured packings are presented
  • Lecture (others)
    Half-year-meeting: Helmholtz Energy-Alliance „Energy efficient chemical multiphase processes“, 21.-23.03.2013, Karlsruhe, Deutschland

Publ.-Id: 19820 - Permalink


Silicide induced ion beam patterning of Si(001)
Engler, M.; Frost, F.; Müller, S.; Macko, S.; Will, M.; Feder, R.; Spemann, D.; Hübner, R.; Facsko, S.; Michely, T.;
Low energy ion beam pattern formation on Si with simultaneous co- deposition of Ag, Pd, Pb, Ir, Fe or C impurities was investigated by in-situ scanning tunneling microscopy as well as ex-situ atomic force microscopy, scanning electron microscopy, transmission electron microscopy and Rutherford backscattering spectrometry. The impurities were supplied by sputter deposition. Additional insight into the mechanism of pattern formation was obtained by more controlled supply through e-beam evaporation. For the situations investigated, the ability of the impurity to react with Si, i.e. to form a silicide, appears to be a necessary, but not a sufficient condition for pattern formation. Comparing the effects of impurities with similar mass and nuclear charge the collision kinetics is shown to be not of primary importance for pattern formation. To understand the observed phenomena, it is necessary to assume a bi-directional coupling of composition and height fluctuations. This coupling gives rise to a sensitive dependence of the final morphology on the conditions of impurity supply. Because of this history dependence the final morphology cannot be uniquely characterized by a steady state impurity concentration.
Keywords: ion irradiation, pattern formation, silides

Publ.-Id: 19819 - Permalink


Hydrodynamische Charakterisierung von Blasensäulen
Schubert, M.;
Mehrphasenreaktoren wie Blasensäulen, Festbetten und Wirbelschichten sind das Herzstück der chemischen und biochemischen Industrie. Trotz der weitgefächerten Anwendungsgebiete, stellen Auslegung und Skalierung von Mehrphasenreaktoren immer noch große Herausforderungen dar, insbesondere aufgrund fehlender Messdaten unter industriell relevanten Betriebsbedingungen. Darüber hinaus liegen in industriellen Prozessen meist lichtundurchlässige Strömungen vor – beispielsweise bei hohen Gas- und Flüssigkeitsleerrohrgeschwindigkeiten – die mit bloßem Auge aber auch mit herkömmlicher optischer Messtechnik nicht erfasst werden können. Der Beitrag fast Ergebnisse hydrodynamischer Studien in Blasensäulen mittels gering-invasiver Gittersensorik zusammen. Insbesondere werden Übergänge von Strömungsregimen, Blasengrößenverteilungen und Gasgehalte in Abhängigkeit vom Blasensäulendurchmesser als wesentliche Auslegungsparameter analysiert.
  • Contribution to proceedings
    Proceedings-Paper zur Festschrift zum Kolloquium 60 Jahre Verfahrenstechnikausbildung an der TU Dresden, 24.05.2013, Dresden, Deutschland

Publ.-Id: 19818 - Permalink


Wetting Efficiency in Tubular Reactors with Solid Foam Packings
Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.;
In the recent years, the performance of gas-liquid-solid fixed bed reactors with structured catalysts instead of catalyst particles has been intensively discussed. Structured catalysts based on solid foams with an open cell structure are in particular very promising. Such porous structures combine high specific surface area up to 2000 m²/m³, low single-phase and two-phase pressure drop due to bed porosities between 75 and 95 %, and interconnected pores for enhanced heat and mass transfer (Stemmet et al., 2005; Grosse and Kind, 2011). The performance of fixed bed reactors with structured catalysts depends heavily on the gas-liquid-solid contacting pattern. For a broad range of flow conditions, the liquid phase does not cover the solid surface homogeneously, which is known as partial wetting. The externally wetted fraction, which is defined as fraction of the external solid foam area covered by the liquid phase to the total external solid foam area, is directly linked to the liquid-solid and gas-solid mass transfer and thus, to the overall rate of reaction. The wetting fraction is a function of the superficial gas and liquid velocity and depends also on the physical properties of the liquid phase as well as catalyst shape, surface, porosity, etc. (Nigam and Larachi, 2005). However, studies on the wetting efficiency in trickle bed reactors also indicated the impact of the pre-wetting mode (Joubert and Nicol, 2012).
The aim of this work was to adopt an electrochemical method for: (a) measuring the wetting fraction in tubular reactors with solid foam packings and (b) to study the effect of pre-wetting.
  • Lecture (Conference)
    AIChE Annual Meeting, 03.-08.11.2013, San Francisco, USA

Publ.-Id: 19817 - Permalink


Gas-Liquid Distribution in Tubular Reactors with Solid Foam Packing
Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.;
Solid foam catalysts are a potential replacement for conventional catalyst particles such as extrudates, tablets, hollow cylinders and spheres. They improve the fixed-bed reactor performance in gas-liquid-solid reactions due to their high specific surface area and low pressure drop. Furthermore foam has very narrow residence time distribution which enhances the selectivity. However, there is still a lack of knowledge on the evolving flow patterns in solid foams and the proper design of liquid-phase distributors for industrial applications and conditions. In our contribution, gas-liquid distribution of downward two-phase flow with solid foam packings was studied experimentally. The packings varied in solid foam pore density.
The measurements in a column with 0.1 m inner diameter are based on a combination of a segmented collector (25 compartments of same size) and imaging wire-mesh sensors with 16×16 wires and a pixel resolution of 6.25 mm. Both techniques provided the same results regarding the quality assessment of the flow distribution. The setup was applied to investigate the effect of: different liquid distributors, gas and liquid flow rates, and pre-wetting conditions. The experiments revealed information on liquid spreading along the reactor axis. The flow patterns inside the column are quantified by a maldistribution factor. The results indicate that foam packings cannot effectively counterbalance initial liquid maldistribution. Based on this study results, the design of packed-bed reactors can be improved towards much higher productivity and energy efficiency.
  • Poster
    9th World Congress of Chemical Engineering, 19.-22.08.2013, Seoul, South Korea

Publ.-Id: 19815 - Permalink


Charakterisierung der Siebboden-Fluiddynamik mittels Gittersensor
Schubert, M.; Hampel, U.;
Kolonnen mit Siebböden als trennwirksame Einbauten werden vielfältig zur intensiven Phasenkontaktierung und Stofftrennung eingesetzt. Eine verlässliche Beschreibung der Fluiddynamik auf Kolonnenböden ist die Grundlage für eine effiziente Gestaltung der Trennprozesse, erfolgt jedoch gegenwärtig hauptsächlich erfahrungsbasiert. Voraussetzung zur modellunterstützten Auslegung von Siebböden, vor allem im Hinblick auf die Optimierung von Strömungsmustern, sind Bodenprüfstände mit hochauflösender Spezialmesstechnik. Zur Charakterisierung der Strömungsverhältnisse (z.B. Totzonen, Wirbeln, Kurzschluss- und Rückströmungen) und zur Extraktion fluiddynamischer Kenngrößen (z.B. Verweilzeit) in einem 800 mm Kolonnenprüfstand mit Siebböden (4 % Öffnungsverhältnis, 5 mm Lochdurchmesser) wurde u.a. ein leitfähigkeitsbasierter Gittersensor implementiert. Der Gittersensor besteht aus zwei um 90° versetzt angeordneten Drahtebenen aus 64×51 Drähten mit einem Ebenenabstand von 10 mm. In den Kreuzungspunkten wird in Abhängigkeit der lokalen Leifähigkeit ein Strom mit hoher Abtastfrequenz gemessen, der Aussagen über die transienten Strömungszustände (z.B. Tracermenge, Gas-/Flüssigkeitsanteil) erlaubt. Im Beitrag werden Tracerstudien zur Bestimmung der Flüssigphasenverweilzeit und der Strömungsmuster in Abhängigkeit der hydraulischen Belastungen und der Wehrhöhen vorgestellt.
  • Poster
    Jahrestreffen der Fachgruppen Fluidverfahrenstechnik und Wärme- und Stoffübertragung, 20.-21.03.2013, Baden Baden, Deutschland

Publ.-Id: 19814 - Permalink


Low temperature and decay lifetime photoluminescence of Eu and Tb nanoparticles embedded into SiO2
Lipp Bregolin, F.; Franzen, P.; Boudinov, H.; Sias, U. S.; Behar, M.;
In the present work, we have studied the photoluminescence (PL) and decay lifetime of Tb and Eu nanoparticles (NPs) at low temperatures. The NPs were obtained by ion implantation into a SiO2 matrix. Concerning the PL yield of Tb, it has a maximum at 12 K and decreases with increasing temperatures reaching a minimum at 300 K. On the other hand, the PL lifetime of the PL band centered at 542 nm remains almost constant at a value of 1.6 ms. Concerning Eu, two bands are observed, one narrow centered around 618 nm and the other in the blue-green region (from 400 up to 550 nm). Both PL bands show a minimum yield at 12 K, and then they start to increase with increasing temperatures, reaching their maximum at around 100 K. Then, they start to decrease their yield reaching a minimum at 300 K, being this yield similar to the one obtained at 12 K. For the Eu PL lifetime, two different results were obtained. The narrow PL band centered at 618 nm shows a lifetime of the order of 1.6 ms independent of the temperature. Conversely, the blue-green PL band is strongly temperature dependent, being of the order of several ms for temperatures lower than 100 K down to 500 µs at 300 K.
Keywords: rare-earth photoluminescence Tb nanoparticles Eu nanoparticles Ion implantation Decay lifetime

Publ.-Id: 19813 - Permalink


Hydrogen engineering via plasma immersion ion implantation and flash lamp annealing in silicon-based solar cell substrates
Lipp Bregolin, F.; Krockert, K.; Prucnal, S.; Vines, L.; Hübner, R.; Svensson, B. G.; Wiesenhütter, K.; Möller, H.-J.; Skorupa, W.;
Higher conversion efficiencies while reducing costs at the same time is the ultimate goal driving the advancement of solar cell development. In this work, solar cell emitters are formed in Si substrates by plasma immersion ion implantation (PIII) of phosphine and posterior millisecond-range flash lamp annealing (FLA). In Si-based solar cells, hydrogen plays a fundamental role due to its excellent passivation properties and the optical and electrical properties of the fabricated emitters will be studied, with particular interest in their dependence on the hydrogen content present in the samples. The influence of different FLA annealing parameters and a comparison with traditional thermal treatments such as rapid thermal annealing (RTA) and furnace annealing (FA) will be presented. The samples treated by FLA at 1200 °C for 20 ms in forming gas shows sheet resistance values of the order of 60 Ω/□, and minority carrier diffusion lengths in the range of ~ 200 µm without the use of a capping layer for surface passivation. Those results are significantly better than the ones observed from RTA or FA annealed samples. The simultaneous implantation of hydrogen during the doping process combined with optimal FLA annealing parameters gave promising results for the application of this technology in replacing the conventional POCl3 deposition and diffusion.
Keywords: plasma immersion ion implantation hydrogen engineering emmiter formation flash lamp annealing photovoltaics solar cell

Publ.-Id: 19812 - Permalink


Liquid-solid mass transfer in solid foam packed tubular reactors
Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.;
Solid foams were found to be promising replacements of conventional fixed bed reactor catalysts due to their high specific surface area, high porosity and low pressure drop. Especially, high gas-liquid mass transfer rates were observed in solid foams (Stemmet et al., 2008). However, for liquid limited reactions, high liquid-solid mass transfer rates are required. The liquid-solid mass transfer is strongly affected by the wetting of the packing surface and thus, depends also on the pre-wetting mode. For example Joubert and Nicol (2012) found that solid-liquid mass transfer coefficients in trickle bed reactors exhibit significant multiplicity behavior due to different flow textures. However, to the best of our knowledge, studies on the liquid-solid mass transfer in down flow solid foam tubular reactors are not yet available. To determine liquid-solid mass transfer coefficient we applied the electrochemical diffusion current method (ferricyanide system with excess of NaOH) The method is based on the measurement of current (i.e. electron transfer from cathode to anode) at mass transfer diffusion limited condition, pure nickel foam (Alantum Europe) of same foam density was applied as cathode.
The aim of this study is to determine the effective liquid-solid mass transfer coefficient in tubular solid foam reactors at different axial positions in down-flow trickle mode taking “LEVEC” and “KAN-LIQUID” pre-wetting mode into account.
  • Poster
    9th European Congress of Chemical Engineering (ECCE), 21.-25.04.2013, Den Haag, Netherland

Publ.-Id: 19811 - Permalink


Tomographic and numerical distributor studies in bubble column reactors
Bieberle, A.; Rabha, S.; Schubert, M.; Hampel, U.;
Bubble column reactors are widely preferred in the petro/chemical industries due to flexible residence time, excellent heat and mass transfer characteristics and the absence of moving parts. Here, proper sparger design is essential to tune bubble size and bubble rise velocity and to provide optimal holdup and mixing behavior (Kulkarni and Joshi, 2011). Information pertaining to bubble size distribution, pressure distribution in various distributor is scantily available. Therefore, we provide a comparative study on different gas distributors in terms of gas hold-up and bubble size distribution using gamma-ray computed tomography and wire-mesh sensor techniques. Four different types of gas distributor were used, e.g. sieve plate, ring sparger, spider and radial sparger. In addition, the influence of the gas distributor on the above mentioned parameters is also predicted using Euler-Euler approached and validated with the experimental results.
Keywords: Bubble colums reactors, gamma-ray CT, wire-mesh sensor
  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Extraktion und Mehrphasenströmungen, 19.-20.03.2013, Baden Baden, Deutschland

Publ.-Id: 19810 - Permalink


Experimental observation of transverse modulations in laser-driven proton beams
Metzkes, J.; Kluge, T.; Zeil, K.; Bussmann, M.; Kraft, S. D.; Cowan, T. E.; Schramm, U.;
We report on the experimental observation of transverse modulations in proton beams accelerated from micrometer thick targets which were irradiated with ultra-short (30 fs) laser pulses of a peak intensity of 5·10^20 W/cm^2. The net-like proton beam modulations were recorded using radiochromic film and the data suggest a dependence on laser energy and target thickness for their onset and strength. Numerical simulations suggest that intensity-dependent instabilities in the laser-produced plasma at the target front side lead to electron beam break-up or filamentation, then serving as the source of the observed proton beam modulations.
  • Open Access LogoNew Journal of Physics 16(2014), 023008-1-023008-12
    DOI: 10.1088/1367-2630/16/2/023008
  • Poster
    41st EPS Conference on Plasma Physics, 23.-27.06.2014, Berlin, Deutschland

Publ.-Id: 19809 - Permalink


A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction
Lougovski, A.; Hofheinz, F.; Langner, J.; Schramm, G.; Will, E.; van den Hoff, J.;
The aim of this study is the evaluation of on-the-fly volume of intersection computation for system’s geometry modelling in 3D PET image reconstruction. For this purpose we propose a simple geometrical model in which the cubic image voxels on the given Cartesian grid are approximated with spheres and the rectangular tubes of response (ToRs) are approximated with cylinders. The model was integrated into a fully 3D list-mode PET reconstruction for performance evaluation. In our model the volume of intersection between a voxel and the ToR is only a function of the impact parameter (the distance between voxel centre to ToR axis) but is independent of the relative orientation of voxel and ToR. This substantially reduces the computational complexity of the system matrix calculation. Based on phantom measurements it was determined that adjusting the diameters of the spherical voxel size and the ToR in such a way that the actual voxel and ToR volumes are conserved leads to the best compromise between high spatial resolution, low noise, and suppression of Gibbs artefacts in the reconstructed images. Phantom as well as clinical datasets from two different PET systems (Siemens ECAT HR+ and Philips Ingenuity-TF PET/MR) were processed using the developed and the respective vendor-provided (line of intersection related) reconstruction algorithms. A comparison of the reconstructed images demonstrated very good performance of the new approach. The evaluation showed the respective vendor-provided reconstruction algorithms to possess 34–41% lower resolution compared to the developed one while exhibiting comparable noise levels.
Contrary to explicit point spread function modelling our model has a simple straight-forward implementation and it should be easy to integrate into existing reconstruction software, making it competitive to other existing resolution recovery techniques.

Publ.-Id: 19808 - Permalink


Entwicklung eines Stoffsystems zur Durchführung elektrochemischer Stofftransportmessungen in organischen Medien
Rüdiger, K.;
Die Bestimmung von Stofftransportraten mittels der Grenzstrommethode hat in der Vergangenheit bereits häufig Anwendung in der Untersuchung von Mehrphasenströmungen durch strukturierte Packungen und regellose Schüttungen gefunden. Bis auf eine Ausnahme beschränkten sich bisherige Untersuchungen aber auf wässrige Stoffsysteme, die hinsichtlich ihrer physikalischen Eigenschaften (Dichte, Oberflächenspannung und Viskosität) eher einen Spezialfall in der Durchströmung von Packungen darstellen und sich kaum auf industriell relevante, organische Systeme übertragen lassen. Zur Adaption der Grenzstrommethode auf organische Systeme befasst sich die vorliegende Belegarbeit mit der Suche, Synthese und Langzeitbeständigkeit verschiedener organischer Redoxsysteme und Lösungsmittel sowie potenziell geeigneter Leitelektrolyte für die organische Grenzstrommethode. Untersucht werden hierbei die organometallischen Metallkomplex-Systeme des Eisens mit Bipyridin sowie des Ferrocens in verschiedenen Oxidationsstufen. Weiterhin kommt ein Tetraalkylammoniumsalz als Leitfähigkeitverbesserer in verschiedenen organischen Lösungsmitteln zum Einsatz. In Langzeittests zeigten UV-VIS-Messungen, dass lediglich das Ferrocen-System unter Argonatmosphäre über längere Zeit hinweg seine Zusammensetzung nicht ändert. Lichteinfluss zeigte dabei eine stabilisierende Wirkung. In ersten Vortests wird die Einsetzbarkeit des Systems für die organische Grenzstrommethode unter bestimmten Bedingungen bewiesen.
Betreuer: Johannes Zalucky
Keywords: organo-electrochemical method, mass transfer, ferrocen, organo-metallic complexes, tetraalkyl ammonium salt, stabilizing light, UV-VIS
  • Study thesis
    TU-Dresden, 2013
    63 Seiten

Publ.-Id: 19807 - Permalink


PET/MRI Imaging in High-Risk Sarcoma: First Findings and Solving Clinical Problems
Schuler, M. K.; Richter, S.; Beuthien-Baumann, B.; Platzek, I.; Kotzerke, J.; van den Hoff, J.; Ehninger, G.; Reichardt, P.;
Simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) is a new whole-body hybrid PET/MR imaging technique that combines metabolic and cross-sectional diagnostic imaging. Since the use of MRI in imaging of soft-tissue sarcoma is extremely beneficial, investigation of the combined PET/MRI is of great interest. In this paper, we present three cases and first data. Combined PET/MRI technique can support the process of clinical decision-making and give answers to some meaningful questions when treating patients with STS. Therefore, the combined modality of simultaneous PET/MRI offers new pieces to the puzzle of sarcoma treatment.

Publ.-Id: 19806 - Permalink


Hydrodynamics and transport processes in structured reactor devices: Project status report
Zalucky, J.; Rabha, S.; Schubert, M.; Hampel, U.;
On the occasion of annual project status report, work package progress is presented. The first part includes demarcation of work topics of hydrodynamic groups, status of setup construction and preliminary experimental matrix for CT measurements. The second part is related to actions in mass transfer investigations and reports progress and upcoming investigations with the electrochemical method as well as first successes in zeolite coating of SiSiC foams.
Keywords: annual project status report, energy efficient chemical multiphase processes, hydrodynamic CT investigations, mass transfer
  • Lecture (others)
    Jahrestreffen Helmholtz-Energie-Allianz "Energieeffiziente chemische Mehrphasenprozesse", 30.09.-02.10.2013, Bochum, Deutschland

Publ.-Id: 19805 - Permalink


Chemical reaction related mass transfer measurements in organic environments under industrial relevant conditions
Zalucky, J.;
Within HZDR annual PhD seminar, the PhD motivation, conception, approaches and first results are presented.
Keywords: mass transfer, organo-electrochemical method, zeolite coating, dynamic oxygen sorption technique
  • Poster
    HZDR Doktoranden-Seminar, 07.-09.10.2013, Bautzen, Deutschland

Publ.-Id: 19804 - Permalink


Hydrodynamics and transport processes in structured reactor devices - PhD meeting status report TU Hamburg-Harburg
Zalucky, J.;
On the occasion of half-annual PhD meeting of projekt group at TU Hamburg-Harburg, the status of hydrodynamic setup and current research subproject SiSiC zeolite coating which were investigated under SEM are orally presented.
Keywords: Hydrodynamic setup, SiSiC zeolite coating
  • Lecture (others)
    Half-annual meeting of PhD students within Helmholtz Energy Alliance "Energy Efficient Chemical Multiphase Processes", 26.07.2013, Hamburg, Deutschland

Publ.-Id: 19803 - Permalink


Formation of regularly arranged large grain silicon islands by using embedded micro mirrors in the flash crystallization of amorphous silicon
Henke, T.; Bartha, J. W.; Rebohle, L.; Merkel, U.; Hübner, R.; Albert, M.; Skorupa, W.;
The well-controlled formation of large silicon grains on predetermined positions is a key issue in order to produce single-grain thin film transistors on insulating substrates and thus to enable monolithic 3D integration. One way to achieve this is to artificially control the solidification of molten silicon during the flash crystallization of amorphous silicon. In this work, we present such an approach in which we used patterned metal layers below the amorphous silicon. The metal spots act as embedded micro mirrors and consequently introduce a lateral temperature gradient into the silicon film during flash crystallization. As a result, the grain growth from molten silicon is seeded from the predefined regions with the lowest temperature and thus the formation of large crystal silicon islands proceeds in a controlled manner. In the scope of this study, we evaluated a variety of different mirror patterns with respect to their suitability for this approach and observed that patterns of both circular and line-shaped mirrors are the most promising variants. The resulting silicon islands have pillow-like shapes and are located exclusively in regions between neighboring mirrors. They exhibit dimensions of a few tens of micrometers and consist of grains with sizes up to 28 µm. The formation of single-grain silicon pillow-like structures was observed for particular mirror patterns having circular mirrors. On the other hand, the application of mirror patterns with line-shaped mirrors resulted in the formation of elongated silicon grains which we explained in terms of lateral solidification starting from one edge. Furthermore, this approach exhibits grain filter characteristics leading to the controlled growth of large single grains at predetermined positions.
Keywords: flash lamp annealing, crystallization, liquid phase epitaxy

Publ.-Id: 19802 - Permalink


Inclined rotating fixed bed reactors for process intensification
Härting, H.-U.; Schubert, M.;
After an introduction of the research activities at the Institue of Fluid Dynamics, especially of the Experimental Thermal Fluid Dynamics Department, process intensification is illustrated by working examles from science and industry.
The new reactor concept "inclined rotating fixed bed reactor" is introduced with detailed explanations of the idea, the benefits as well as aspects of the design.
Selected results from hydrodynamic experiments coupled with tomographic imaging are presented.
Keywords: Process intensification, fixed bed reactor, tomographic imaging, rotation, inclination
  • Lecture (Conference)
    HZDR PhD-Seminar 2013, 07.-09.10.2013, Bautzen, Deutschland

Publ.-Id: 19801 - Permalink


Hindered magnetic order from mixed dimensionalities in CuP2O6
Nath, R.; Ranjith, K. M.; Sichelschmidt, J.; Baenitz, M.; Skourski, Y.; Alet, F.; Rousochatzakis, I.; Tsirlin, A. A.;
We present a combined experimental and theoretical study of the spin-½ compound CuP2O6 that features a network of two-dimensional (2D) antiferromagnetic (AFM) square planes, interconnected via one-dimensional (1D) AFM spin chains. Magnetic susceptibility, high-field magnetization, and electron spin resonance (ESR) data, as well as microscopic density-functional band-structure calculations and subsequent quantum Monte Carlo simulations, show that the coupling J2D ≃ 40 K in the layers is an order of magnitude larger than J1D ≃ 3 K in the chains. Below TN ≃ 8 K, CuP2O6 develops long-range order, as evidenced by a weak net moment on the 2D planes induced by anisotropic magnetic interactions of Dzyaloshinsky-Moriya type. A striking feature of this 3D ordering transition is that the 1D moments grow significantly slower than the ones on the 2D units, which is evidenced by the persistent paramagnetic ESR signal below TN. Compared to typical quasi-2D magnets, the ordering temperature of CuP2O6 TN/J2D ≃ 0.2 is unusually low, showing that weakly coupled spins sandwiched between 2D magnetic units effectively decouple these units and impede the long-range ordering.

Publ.-Id: 19800 - Permalink


Size-effects in 2D Transition Metal Chalcogenides
Gemming, S.; Seifert, G.;
Nanoscale Mo_mS_n compounds exist in a large variety of compositions with many different characteristic structural elements and related electronic properties. The structural wealth of Mo_mS_n compounds comprises finite structures such as small clusters and hollow inorganic fullerenes, one-dimensionally extended wires and stripes, or two-dimensional platelets. The structural elements are based either on a three-dimensional Mo_m framework or on platelet-shaped elements derived from the layered MoS_2 bulk structure. The electronic features range from large energy gaps in closed-shell systems over the semiconducting two-dimensional MoS_2 sheet to the metallic conductivity of the brim state in platelets or along the Mo core of wires.
With the help of density-functional calculations the preferred structural elements and the relative stabilities could be correlated with the chemical potentials of sulfur and molybdenum in the system. As structural elements and electronic features are related, this result is the basis for a further tailoring of electronic properties via the preparation conditions. For very small systems Mo_mS_n, with m <= 4, n <= 14 the cluster-platelet transition depends on a sulfur excess of the system of at least one additional S atom per MoS_2 formula unit, i.e. to MoS_3. In the small size regime the most important species are the extremely stable large-gap Mo_4S_6 cluster, Mo_3S_6 as smallest member of (MoS_2)_n platelet family and Mo_3S_3 and Mo_3S_5 as stable building blocks of wires. For one-dimensionally extended conducting structures the termination exhibits a length-dependent crossover of the termination group from (Mo_3S_3)_nS_2 to (Mo_3S_3)_n-1(MoS_4)_2 provided that the chemical potential of sulfur is low and constant. Sulfur-terminated two-dimensional (MoS_2)_nS_m platelets are stable only at the enhanced sulfur chemical potential required to saturate the platelet edges with sulfur up to a stoichiometry of Mo:S = 1:3 in the smallest clusters. In even more sulfur-rich conditions all systems tend to form chemically active, but electronically inert S_2^2- ions.
Keywords: density-functional, molybdenum sulfide, 2D electronics, molecular electronics, inorganic nanotubes, nanotubes, platelet
  • Invited lecture (Conferences)
    Flatlands Beyond Graphene, 17.-21.06.2013, Bremen, Deutschland

Publ.-Id: 19799 - Permalink


Microscopic Processes in Energy and Data Storage
Gemming, S.;
DGK Symposium MS17 - Materials for Electronics:
Energy and Data Storage through the Eyes of Crystallographers
Keywords: multiscale modeling, density-functional, Heisenberg, Ising, multiferroic
  • Invited lecture (Conferences)
    21st Annual Conference of the German Crystallographic Society, 19.-22.03.2013, Freiberg (S), Deutschland

Publ.-Id: 19798 - Permalink


The nELBE (n,fis) experiment
Kögler, T.; Beyer, R.; Hannaske, R.; Junghans, A.; Massarczyk, R.; Schwengner, R.; Wagner, A.;
At the Center for High-Power Radiation Sources at Helmholtz-Zentrum Dresden-Rossendorf fast neutron-induced fission cross section experiments on U(235) and Pu(242) will be investigated by a parallel plate fission ionization chamber. An optimization of chamber parameters was performed using extensive Geant4 simulations with GEF code generated fission observable inputs. Pile-up effects due to the high alpha activity of the plutonium targets have been considered in a realistic geometry. Beyond that, a setup for the determination of the areal density and homogeneity of targets will be presented with a focus on current simulation work.
Keywords: nELBE, parallel plate fission ionization chamber, Geant 4 simulations
  • Lecture (Conference)
    Final ERINDA User Meeting and Scientific Workshop, 01.-03.10.2013, Geneva, Switzerland
  • Open Access LogoContribution to proceedings
    Final ERINDA User Meeting and Scientific Workshop, 01.-03.10.2013, Geneva, Switzerland
    Proceedings of the ERINDA Workshop, CERN, edited by Enrico Chiaveri CERN Proceedings 2014-002: CERN, 978-92-9083-403-8, 25-30

Publ.-Id: 19797 - Permalink


Nanomaterials for Biomedical Applications
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Seminar, Jacobs University Bremen, 08.01.2014, Bremen, Deutschland

Publ.-Id: 19796 - Permalink


Synthesis and biological evaluation of both enantiomers of [18F]flubatine, promising radiotracers with fas kinetics for the imaging of α4β2-nicotinic acetylcholine receptors
Smits, R.; Fischer, S.; Hiller, A.; Deuther-Conrad, W.; Wenzel, B.; Patt, M.; Cumming, P.; Steinbach, J.; Sabri, O.; Brust, P.; Hoepping, A.;
Both enantiomers of the epibatidine analogue flubatine display high affinity towards the α4β2 nicotinic acetylcholine receptor (nAChR) in vitro, accompanied by negligible interactions with diverse off-target proteins. Extended single dose toxicity studies in rodent indicated a NOEL (No Observed Effect Level) of 6.2μg/kg for (-)-flubatine and 1.55μg/kg for (+)-flubatine. We developed syntheses for both flubatine enantiomers and their corresponding precursors for radiolabeling. The newly synthesized trimethylammonium precursors allowed for highly efficient (18)F-radiolabelling in radiochemical yields >60% and specific activities >750GBq/μmol, thus making the radioligands practical for clinical investigation.
Keywords: Alzheimers’s disease (AD), Nicotinic acetylcholine receptor (nAChR), Flubatine, PET, Fluorine-18

Publ.-Id: 19795 - Permalink


Development of 18F-labeled radiotracers for neuroreceptor imaging with positron emission tomography
Brust, P.; van den Hoff, J.; Steinbach, J.;
Positron emission tomography (PET) is an in vivo molecular imaging tool which is widely used in nuclear medicine for early diagnosis and treatment follow-up of many brain diseases. PET uses biomolecules as probes which are labeled with radionuclides of short half-lives, synthesized prior to the imaging studies. These probes are called radiotracers. Fluorine-18 is a radionuclide routinely used in the radiolabeling of neuroreceptor ligands for PET because of its favorable half-life of 109.8 min. The delivery of such radiotracers into the brain provides images of transport, metabolic, and neutotransmission processes on the molecular level.
After a short introduction into the principles of PET, the review mainly focuses on the strategy of radiotracer development bridging from basic science to biomedical application. Successful radiotracer design as described here provides molecular probes which not only are useful for imaging of huma brain diseases, but also allow molecular neuroreceptor imaging studies in various small-animal models of diseases, including genetically-engineered animals. Furthermore, they provide a powerful tool for in vivo pharmacology during the process of pre-clinical drug development to identify new drug targets, to investigate phathophysiology, to discover potential drug candidates, and to evaluate the pharmacokinetics and pharmacodynamics of drugs in vivo.
Keywords: Alzheimer's disease; autoradiography; blood-brain barrier; brain tumor; cholinergic system; kinetic modeling; metabolism; molecular imaging; neurodegeneration; positron emission tomography; precursor; psychiatric disorder; radiotracer; sigma receptor

Publ.-Id: 19794 - Permalink


Brief review on high-field ESR at the EMFL: facilities and applications
Zvyagin, S.;
  • Invited lecture (Conferences)
    Round table on NMR and EPR in ultra-high magnetic fiels (Satellite workshop to EUROMAR 2013), 02.07.2013, Herssonisos, Greece

Publ.-Id: 19793 - Permalink


Analysen zum Neutronenflussrauschen mit Hilfe des Rechenprogramms DYN3D - Abschlußbericht -
Rohde, U.; Bilodid, Y.;
In Computersimulationen wurden Schwankungen der Kühlmitteltemperatur (KMT) am Kerneintritt und des Kühlmittelmassenstromes als mögliche Ursache für erhöhtes Neutronenflussrauschen in Druckwasserreaktoren untersucht. Das Ziel ist die Vermeidung von Neutronenflußschwankungen in einer Größenordnung, die zu einer unbeabsichtigten Auslösung von Signalen zur Reaktorschnellabschaltungführen können.
Als Simulationstool wurde dafür der Rossendorfer Reaktordynamikcode DYN3D eingesetzt. Es wurden transiente Rechnungen mit verschiedenen aufgeprägten Randbedingungen für die Kühlmitteleintrittstemperatur oder den Kühlmittelmassenstrom durchgeführt, in denen dreidimensional die zeitlich variierenden lokalen linearen Stableistungen berechnet wurden. Diese lokalen linearen Stableistungen werden als In-Core-Detektorsignale interpretiert. Dabei wurden zunächst harmonische Oszillationen, dann auch stochastische Fluktuationen der lokalen Kühlmitteleintrittstemperatur oder des Massenstroms betrachtet, die zwischen den einzelnen Brennelementen oder Bereichen des Reaktorkerns auf unterschiedliche Weise korreliert sein können. Mittels Fast Fourier Transformation (FFT) wurden Übertragungsfunktionen zwischen Temperaturstörung und Responsesignal (lokale lineare Stableistung) ermittelt und ausgewertet.
Um den Einfluss von unterkühltem Sieden des Kühlmittels und der Wärmeleitung im Brennstab zu klären, wurden Variantenrechnungen mit verstärktem unterkühltem Sieden sowie mit verändertem Wärmedurchgangskoeffizienten im Gasspalt zwischen Brennstoff und Hülle durchgeführt. Unterkühltes Sieden wurde durch eine Reduzierung des Massenstroms bzw. Erhöhung der Eintrittstemperatur generiert. Weiterhin wurden für einen Referenzfall Untersuchungen zum Einfluss der numerischen Diffusion durchgeführt.
Der größte Teil der Rechnungen wurde für eine generische Kernbeladung eines DWR vom Typ Konvoi durchgeführt. Teilweise wurden auch konkrete, reaktor- und zyklusspezifische thermohydraulische Randbedingungen sowie neutronenphysikalische Wirkungsquerschnitte (WQS) benutzt, um quantitativ belastbare Aussagen zu erhalten.
Die Ergebnisse der DYN3D-Simulationen zum können wie folgt zusammengefasst werden:
• Stochastische, unkorrelierte Schwankungen der KMT am Eintritt in die einzelnen Brennelemente (BE) führen bei realistischer Amplitude nur zu sehr kleinen Schwankungen in der Leistungsdichte, die für eie eventuelle unbeabsichtigte Auslösung eines Signals zur Reaktorschnellabschaltung nicht relevant sind.
• Stochastische Temperaturschwankungen mit Korrelationen zwischen den BE (z.B. bedingt durch Schwankungen der Kaltstrangtemperaturen) können Leistungsdichteschwankungen mit relevanten Amplituden generieren (je nach Grad der Korrelation).
• Schwankungen der Leistungsdichte, die durch Schwankungen der Eintrittstemperatur oder durch Massenstromschwankungen hervorgerufen werden, zeigen ein deutlich unterschiedliches Signalverhalten.
• Unterkühltes Sieden und Variation des WÜ im Gasspalt Brennstoff-Hülle haben nur geringen Einfluss auf das Neutronenflussrauschen.
Aufgrund dieser Ergebnisse können Temperaturschwankungen als Ursache für überhöhtes Neutronenrauschen praktisch ausgeschlossen werden.
Keywords: neutronic noise, temperature fluctuations, statistical analysis, transfer functions, reactor dynamics simulations
  • Article, self-published (no contribution to HZDR-Annual report)
    Helmholtz-Zentrum Rossendorf 2014
    HZDR\FWO\2014\02
    46 Seiten

Publ.-Id: 19792 - Permalink


Optimization of magneto-resistive response of ion-irradiated Exchange biased films through zigzag arrangement of magnetization
Trützschler, J.; Sentosun, K.; Langer, M.; Mönch, I.; Mattheis, R.; Fassbender, J.ORC; McCord, J.
Exchange coupled ferromagnetic-antiferromagnetic Ni81Fe19/Ir23Mn77 films with a zigzag alignment of magnetization are prepared by local ion irradiation in order to shape the anisotropic magneto-resistive behavior of the magnetic thin film structures. A unique uniaxial field sensitivity along the net magnetization alignment is obtained through the orthogonally modulated and magnetic domain wall stabilized magnetic ground state. Controlling local thin film magnetization distributions and thus the overall magnetization response opens unique ways to tailor the magneto-resistive sensitivity of functional magnetic thin film devices.
Keywords: exchange bias, field sensor, ion irradiation, anisotropic magneto-resistance

Publ.-Id: 19791 - Permalink


Design of Radioligands for PET Imaging of Brain Diseases
Brust, P.;
Es ist kein Abstract vorhanden.
  • Invited lecture (Conferences)
    Partnership: Vanderbilt University - Leipzig University - Leipzig University: 5th Scientific Symposium, 30.10.-03.11.2013, Nashville, USA

Publ.-Id: 19790 - Permalink


Synthesis and development of metabolic PSY receptor ligands for imaging
Brust, P.;
  • Invited lecture (Conferences)
    Partnership Vanderbilt University - Leipzig University: 4th Scientific Symposium and Kick-off Meeting, 06.-12.07.2013, Leipzig, Deutschland

Publ.-Id: 19789 - Permalink


Development of Radioligands for Imaging of nAChR
Brust, P.;
  • Invited lecture (Conferences)
    COGNITO Meeting, 27.09.2013, Kopenhagen, Dänemark

Publ.-Id: 19788 - Permalink


Development of 18F-labelled radiopharmaceuticals for brain and tumor imaging
Brust, P.;
  • Invited lecture (Conferences)
    Colloquium series Zhenjiang University, 27.05.2013, Hangzhou, Zhejiang, China

Publ.-Id: 19787 - Permalink


Spin dynamics in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4
Zvyagin, S.;
  • Invited lecture (Conferences)
    EUROMAR 2013, 30.06.-05.07.2013, Hersonissos, Greece

Publ.-Id: 19786 - Permalink


Recent development of the High Field ESR facility at HLD Dresden
Zvyagin, S.;
  • Invited lecture (Conferences)
    Evaluation of research finding applications ETAG (The Estonian Research Council), 21.09.2013, Tallinn, Estonia

Publ.-Id: 19785 - Permalink


Recent development of the high-field ESR facility at the Dresden High Magnetic Field Laboratory
Zvyagin, S.;
  • Invited lecture (Conferences)
    Annual Meeting SPP1601, 12.-14.09.2013, Frauenchiemsee, Deutschland

Publ.-Id: 19784 - Permalink


Unconventional spin dynamics in Cs2CuBr4
Zvyagin, S.;
  • Invited lecture (Conferences)
    ETH Zürich, 26.09.2013, Zürich, Switzerland

Publ.-Id: 19783 - Permalink


Spin dynamics in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4
Zvyagin, S.;
  • Lecture (Conference)
    JEMS2013 - Joint European Magnetic Symposia, 25.-30.08.2013, Rhodos, Greece

Publ.-Id: 19782 - Permalink


Superconductivity in highly Ga-doped germanium and silicon
Skrotzki, R.;
  • Lecture (others)
    Institutsseminar TU Dresden, 08.01.2013, Dresden, Deutschland

Publ.-Id: 19781 - Permalink


Evidence of Field-Induced Ordering in the Dynamic Spin Ice Compund Pr2Sn2O7
Green, E.;
  • Invited lecture (Conferences)
    Ss. Cyril and Methodius University, 27.04.2013, Skopje, Macedonia

Publ.-Id: 19780 - Permalink


Magnetoelastic properties of some uranium intermetallic antiferromagnets as studied by high-field ultrasound measurements
Zherlitsyn, S.;
  • Poster
    2013 Joint UFFC, EFTF, and PFM Symposium, 21.-23.07.2013, Prague, Czech Republic

Publ.-Id: 19779 - Permalink


Pulsed-magnet upgrades at the Dresden High Magnetic Field Laboratory
Zherlitsyn, S.;
  • Lecture (Conference)
    MT 23 - International Conference on Magnet Technology, 14.-19.07.2013, Boston, USA

Publ.-Id: 19778 - Permalink


Strongly correlated electron physics at high magnetic fields: recent science highlights at the HLD
Herrmannsdörfer, T.;
  • Invited lecture (Conferences)
    Institutsseminar Hochfeld Magnetlabor Wroclaw, 16.-17.05.2013, Wroclaw, Poland

Publ.-Id: 19777 - Permalink


Hydrogenation of α-methylstyrene in an inclined rotating fixed bed reactor
Härting, H.-U.; Schubert, M.;
Trickle bed reactors are widespread in the chemical industry for the implementation of heterogeneous catalytic processes, especially for the production of bulk chemicals. Nevertheless, the reactor performance may be limited by liquid maldistribution as well as by poor mass and heat transfer rates. Furthermore, the rather simple reactor design and operation is accompanied by limited degrees of freedom for manipulation of local conditions to enhance the reactor performance.
Dynamic operation strategies, like the periodic inlet flow rate modulation, have been proposed for process intensification of trickle bed reactors [1]. These strategies have been proven to result in increased space-time-yields at lab-scale, however, their positive effects are strongly dampened with increasing reactor length.
The inclined rotating fixed bed reactor is an alternative reactor concept, that aims to transform the temporal periodic operation into a spatial periodic one, which holds for the whole length of the reactor. The inclination of the reactor, with the catalyst fixed between two retaining grates, results in a phase separation, whereas the superimposed slow rotation ensures a periodic wetting and draining of the catalyst and will therefore enhance the access of the gas phase to the active sites (see Figure 1).
By adjustment of the reactor inclination and rotation, the performance of the reactor can be adapted to a given reaction system (e. g. fast or slow kinetics, high or low viscous liquid etc.) to optimize the local conditions with respect to flow regime and subsequently to mass and heat transfer performance for a specific process.
For the evaluation of the new reactor concept, the space-time-yield of the hydrogenation of α-methylstyrene to cumene (C9H10 + H2  C9H12) is investigated in the trickle bed reactor as well as in the inclined rotating fixed bed reactor. The reaction already exhibits mass transfer limititations of the gas phase at moderate conditions, which allows for attributing changes in the space-time-yield directly to the operational conditions [2].
The reactor (dR = 0.1 m, LR = 1.6 m) is operated like a differential loop reactor with a layer of the palladium egg-shell catalyst (Pd/γ-Al2O3, dP = 4 mm, w = 0,1 wt-% Pd) placed in the middle of the otherwise inert fixed bed. The reaction studies are performed at varying pressure (p = 1 and 6 bar) and temperature (θ = 25°C and 40°C) at isothermal conditions. The rotational speed and the inclination angle are adjusted to identify optimal hydrodynamic conditions regarding the space-time-yield.
The results of the reaction studies are discussed with respect to the prevailing flow regimes obtained by additional tomographic imaging studies for the same setup and operating conditions.
Keywords: Hydrogenation, process intensification, fixed bed reactor, inclination, rotation
  • Lecture (Conference)
    "CHEMREACTOR-21" XXI International Conference on Chemical Reactors, 22.-25.09.2014, Delft, The Netherlands

Publ.-Id: 19776 - Permalink


Hydrierung von alpha-Methylstyrol in einem geneigt rotierenden Festbettreaktor
Härting, H.-U.; Lange, R.; Schubert, M.;
Rieselbettreaktoren finden in der chemischen Industrie breite Anwendung zur Realisierung heterogen-katalysierter Reaktionen insbesondere bei hohen Eduktdurchsätzen. Allerding ist die Reaktorleistung durch geringe Stoff- und Wärmeübertragungsraten begrenzt. Zusätzlich können sich Fehlverteilungen der Flüssigphase nachteilig auf Transportprozesse, Katalysatorausnutzungsgrad und -aktivität auswirken. Konzepte mit dynamischer Betriebsweise, wie beispielsweise die periodische Variation des Flüssigphasendurchsatzes am Reaktoreingang, wurden vorgeschlagen, bei denen die zeitgemittelten Raum-Zeit-Ausbeuten gesteigert werden konnten. Dispersionsvorgänge schwächen die positiven Effekte jedoch mit zunehmender Länge des Festbetts ab.
Ein alternatives quasi-periodisches Reaktorkonzept ist der geneigt rotierende Festbettreaktor, bei dem die zeitliche in eine örtliche periodische Betriebsweise überführt wird. Die Reaktorneigung führt zur Separation der Gas- und Flüssigphase; die überlagerte Reaktorrotation resultiert in einer periodischen Be- und Entnetzung der im Reaktor fixierten Katalysatorschüttung, wodurch die Zugänglichkeit der aktiven Zentren für die Edukte, insbesondere der Gasphase, über die gesamte Reaktorlänge verbessert wird. Beim neuen Reaktorkonzept können sowohl die Drehzahl als auch die Neigung in Abhängigkeit vom Reaktionssystem (Reaktionsrate, Flüssigkeitseigenschaften, Katalysator etc.) angepasst werden, um die Strömung (siehe Abbildung 1) für den jeweiligen Prozess zu optimieren.
Zur Leistungsbewertung des neuen Reaktorkonzepts wurde zusätzlich zur hydrodynamischen Charakterisierung die jeweilige Strömung hinsichtlich der Raum-Zeit-Ausbeute einer Modellreaktion vergleichend zum Rieselbettreaktor untersucht. Als Modellreaktion wurde die irreversible unselektive Hydrierung von α-Methystyrol zu Cumol (C9H10+H2 --> C9H12) verwendet, bei der bereits bei moderaten Prozessbedingungen Stoffübertragungs¬limitierungen der Gasphase auftreten (Khadilkar et al., 1999). Die Veränderungen beim Reaktionsumsatz in Abhängigkeit von den Betriebsbedingungen (p = 1 bar und 6 bar, T = 25 °C und 40 °C, isotherm) können damit direkt der Stoffübertragung zugeordnet werden. Für die reaktionstechnischen Studien wurde der Reaktor mit einer dünnen Schicht Palladium-Katalysator (kugelförmiges γ-Al2O3-Trägermaterial, Ø 4 mm, egg-shell, 0,1 Ma.-% Pd) in der Mittelebene des Reaktors (L = 1,6 m, D = 0,1 m) zwischen Inertmaterial befüllt.
Keywords: Hydrogenation, process intensification, fixed bed reactor, alpha-methylstyrene, inclination, rotation
  • Poster
    Jahrestreffen Reaktionstechnik 2014, 28.-30.04.2014, Würzburg, Deutschland

Publ.-Id: 19775 - Permalink


Residence time distribution in an inclined rotating fixed-bed reactor
Härting, H.-U.; Lange, R.; Schubert, M.;
Trickle bed reactors (TBR) are widely applied in the chemical industry for heterogeneous catalytic reactions. Besides their wide application, their performance often suffers from inherent drawbacks, like liquid maldistribution and poor mass and heat transfer rates; and are therefore a promising target for process intensification (PI). PI in such reactors can be realised by a periodic operation of the reactor, which is usually implemented by the modulation of liquid flow rate or liquid inlet concentration. Flow rate modulation is known to increase the mass and heat transfer rates and to significantly increase the time-averaged reaction rates compared to steady state results. On the other hand, the positive effects of the flow rate modulation vanish rapidly along the reactor length due to the fading pulse shape.
An alternative reactor concept for PI is the inclined rotating fixed-bed reactor, which retains the positive effects of flow rate modulation but eludes the deficiencies. The reactor inclination results in phase segregation, whereas the superimposed reactor rotation generates a periodic wetting and draining of the particles in the co-rotating fixed-bed (see Figure 1), thus, transforming the temporal periodic operation into a spatial periodic operation, which is present along the whole reactor length.
To optimize the reactor performance for a given chemical reaction, a reactor model is required, which considers the macro-mixing behaviour. Thus, the aim of this study is the systematic investigation of the influence of reactor inclination and rotation on the residence time distribution (RTD) for selected combinations of gas and liquid superficial velocities. The RTD is examined by the imperfect pulse method, whereat inhouse developed wire-mesh sensors are applied to measure the tracer concentration as well as the in-plane spatial phase distribution at two axial positions in the reactor. The experimental data are fitted to the axial dispersion model with open-open boundary conditions, from which the mean residence time and the Péclet number are extracted.
The results will be discussed with respect to flow regime maps that are based on tomographic imaging. Furthermore, the mean residence time and the Péclet number will be compared with data for the vertical reactor configuration (TBR) and with correlations from the literature.
Keywords: Residence time distribution, process intensification, fixed bed reactor, inclination, rotation
  • Lecture (Conference)
    21st International Congress of Chemical and Process Engineering (CHISA 2014), 23.-27.08.2014, Praha, Česká republika

Publ.-Id: 19774 - Permalink


Analyse des hydrodynamischen und reaktionstechnischen Verhaltens geneigt rotierender Festbettreaktoren für heterogene Mehrphasenreaktionen
Härting, H.-U.;
Der geneigt rotierende Festbettreaktor stellt ein neuartiges Reaktorkonzept mit dem Ziel der Prozessintensivierung dar. Anders als bei bisherigen Ansätzen zur Prozessintensivierung, bei denen dem Reaktor üblicherweise durch Strömungsmodulation eine zeitliche Periodizität aufgeprägt wird, erfolgt hier durch die geneigte Rotation die Aufprägung einer örtlichen Periodizität unter gleichzeitiger quasistationärer Durchströmung des Reaktors.
In der Forschungsarbeit wird die Hydrodynamik des neuen Reaktorkonzepts mittels nichtinvasiver bildgebender Verfahren (Gammastrahlen-Computertomographie) aufgeklärt. Zur Leistungsbewertung wird weiterhin der Einfluss der neuen Betriebsparameter Reaktorneigung und –rotation auf die Raum-Zeit-Ausbeute der Hydrierung von alpha-Methylstyrol zu Cumol untersucht. Klassische Methoden der Verfahrenstechnik, wie die Ermittlung der Verweilzeitverteilung durch Aufgabe von Stoßmarkierungen sowie die Bestimmung von Stoffüber-tragungskoeffizienten werden ebenfalls angewandt. Erste Ergebnisse belegen die Eignung des neuen Reaktorkonzepts zur Einstellung definierter Strömungsformen, z. B. einer stratifizierten Strömung, bei konstanten Durchsätzen.
Keywords: Process intensification, inclined rotating fixed bed reactor
  • Contribution to external collection
    in: Jubiläumsband 60 Jahre Dresdner Verfahrenstechnik, Dresden: Inst. für VT und UT, TU Dresden, 2014, 140-140

Publ.-Id: 19773 - Permalink


Experimental observation of spatially modulated laser-driven proton beams from micrometer thick targets
Metzkes, J.; Kluge, T.; Zeil, K.; Bussmann, M.; Kraft, S. D.; Cowan, T. E.; Schramm, U.;
  • Lecture (Conference)
    Laser and Plasma Accelerator Workshop 2013, 02.-06.09.2013, Goa, India

Publ.-Id: 19772 - Permalink


ISR precision measurements of the 2 pi cross section below 1 GeV with the KLOE experiment and their impact on (g-2)_mu
Müller, S. E.;
During the last 10 years, the use of initial state radiation (ISR) has changed from being a novel method to an established technique for precision measurements of hadronic cross sections at e+e- -colliders. By means of a dispersion integral, these measurements enter the hadronic contribution to the theoretical value of the anomalous magnetic moment of the muon, which still shows a 2-3sigma discrepancy with the experimental value measured at the Brookhaven National Laboratory.

The KLOE collaboration, operating the KLOE experiment at the DAPHNE e+e- -collider in Frascati, has published 4 measurements of the cross section for the process e+e- ->pi+pi- in the energy region below 1 GeV, covering ~70% of the total hadronic contribution to the muon anomaly.

I will present the ISR method in detail using the KLOE measurements as examples, and show how these measurements contribute to the current status of the theoretical evaluation of (g-2)mu.
Keywords: (g-2)_mu, ISR, 2pi cross section, KLOE
  • Lecture (others)
    Institutskolloquium, 09.01.2014, Dresden, Deutschland

Publ.-Id: 19771 - Permalink


Mini-Proceedings of the 14th Meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies
Czyż, H.; Eidelman, S.; Fedotovich, G. V.; Korobov, A.; Müller, S. E.; Nyffeler, A.; Roig, P.; Shekhovtsova, O.; Teubner, T.; Venanzoni, G.; (Editors)
The mini-proceedings of the 14th Meeting of the "Working Group on Rad. Corrections and MC Generators for Low Energies" held in Frascati on September 13, 2013, as a satellite meeting of the PHIPSI13 conference in Rome, are presented. These meetings, started in 2006, have as aim to bring together experimentalists and theorists working in the fields of meson transition form factors, hadronic contributions to (g-2)_\mu and the effective fine structure constant, and development of MonteCarlo generators and Radiative Corrections for precision e+e- and tau physics.
Keywords: | energy: low | electron: energy: low | form factor: transition | fundamental constant: fine structure | radiative correction | magnetic moment | meson
  • Open Access LogoContribution to proceedings
    14th Meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies, 13.09.2013, Frascati, Italy
    Mini-Proceedings of the 14th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies arXiv:1312.0454 [hep-ph]

Publ.-Id: 19770 - Permalink


Constraining the Hadronic Contributions to the Muon Anomalous Magnetic Moment
Masjuan, P.; Venanzoni, G.; Czyż, H.; Denig, A.; Vanderhaeghen, M.; Eidelman, S.; Hu, H.; Kloss, B.; Kupsc, A.; Pettersson, J.; Ahmadov, A. I.; Kuraev, E. A.; Volkov, M. K.; Voskresenskaja, O. O.; Zemlyanaya, E. V.; Müller, S. E.; Ping, R. G.; Redmer, C. F.; Sanchez-Puertas, P.; Nugent, I.; Przedzinski, T.; Roig, P.; Shekhovtsova, O.; Was, Z.; Spiesberger, H.; Tomasi-Gustafsson, E.; Wang, Y.;
The mini-proceedings of the Workshop on "Constraining the hadronic contributions to the muon anomalous magnetic moment" which included the "13th meeting of the Radio MonteCarLow WG" and the "Satellite meeting R-Measurements at BES-III" held in Trento from April 10th to 12th, 2013, are presented. This collaboration meeting aims to bring together the experimental e+e- collider communities from BaBar, Belle, BESIII, CMD2, KLOE, and SND, with theorists working in the fields of meson transitions form factors, hadronic contributions to (g-2)_\mu and effective fine structure constant, and development of Monte Carlo generator and Radiative Corrections for precision e+e- and tau physics.
Keywords: muon: magnetic moment | form factor: transition | fundamental constant: fine structure | electron: pair production | BES | radiative correction | Monte Carlo | BaBar | CMD-2 | BELLE | KLOE | SND | t | eta | pi0 | radiation: initial-state interaction | electron positron: annihilation | photon photon: scattering | tau-: semileptonic decay | eta(958) | effective Lagrangian: chiral | quantum chromodynamics: sum rule | anti-p p: annihilation
  • Open Access LogoContribution to proceedings
    Workshop on "Constraining the hadronic contributions to the muon anomalous magnetic moment" which included the "13th meeting of the Radio MonteCarLow WG" and the "Satellite meeting R-Measurements at BES-III", 10.-12.04.2013, Trento, Italy
    Constraining the Hadronic Contributions to the Muon Anomalous Magnetic Moment arXiv:1306.2045 [hep-ph]

Publ.-Id: 19769 - Permalink


First Test of Lorentz Invariance in the Weak Decay of Polarized Nuclei
Dijck, E. A.; Bekker, H.; van den Berg, J. E.; Böll, O.; Hoekstra, S.; Jungmann, K.; Meinema, C.; Noordmans, J. P.; Nunez Portela, M.; Onderwater, C. J. G.; Pijpker, C.; van der Poel, A. P. P.; Santra, B.; Sytema, A.; Timmermans, R. G. E.; Versolato, O. O.; Willmann, L.; Wilschut, H. W.; Yai, K.; Müller, S. E.;
A new test of Lorentz invariance in the weak interactions has been made by searching for variations in the decay rate of spin-polarized 20Na nuclei. This test is unique to Gamow-Teller transitions, as was shown in the framework of a recently developed theory that assumes a Lorentz symmetry breaking background field of tensor nature. The nuclear spins were polarized in the up and down direction, putting a limit on the amplitude of sidereal variations of the form |(Γup − Γdown)|/(Γup + Γdown) < 3 × 10−3. This measurement shows a possible route toward a more detailed testing of Lorentz symmetry in weak interactions.
Keywords: PACS numbers: 11.30.Cp, 24.80.+y, 23.40.Bw

Publ.-Id: 19768 - Permalink


Thermophysical properties of the liquid GaInSn eutectic alloys
Plevachuk, Y.; Sklyarchuk, V.; Eckert, S.; Gerbeth, G.; Novakovic, R.;
Among different Ga-based alloys the overall properties of the Ga In Sn eutectic alloy make it particularly suitable for many applications. However, the experimental data on its thermophysical properties are rather discrepant. In this work, the electrical and thermal conductivity, thermoelectric power, viscosity, surface tension and density of the Ga In Sn eutectic have been investigated in the temperature range between the melting temperature and 700 K. The experimental results obtained were compared with the data available in the literature. New information from scaling properties of the Ga In Sn eutectic liquid alloy can be used as input for thermodynamic simulations or for the modeling of casting processes.
Keywords: thermophysical properties, liquid metals, GaInSn alloy

Publ.-Id: 19767 - Permalink


U(VI) retention by potential host rocks: Comparison of clay and crystalline rock
Schmeide, K.; Joseph, C.; Brendler, V.;
The long-term disposal of high-level nuclear waste in deep geological formations is discussed worldwide as main strategy for nuclear waste management. This approach requires the use of a multiple barrier system consisting of engineered, geo-engineered, and geological barriers to prevent any release of radionuclides into the geo- and biosphere. Sorption of radionuclides on the host rock of a repository is one important process for retarding their migration. Potential host rocks for nuclear waste repositories that are investigated internationally are salt domes, clay rock, and crystalline rock.
In the present work, the retention behavior of clay and crystalline rock towards U(VI) is compared. For this, sorption of U(VI) onto Opalinus clay from the Mont Terri rock laboratory (Switzerland) was studied in the presence of Opalinus clay pore water (pH = 7.6; I = 0.36 M) [1]. This is compared to U(VI) sorption onto anoxic diorite from Äspö Hard Rock Laboratory (Sweden) that was studied in the presence of Äspö groundwater (pH = 7.8; I = 0.18 M) [2]. The impact of various parameters, such as solid-to-liquid ratio, initial U(VI) concentration, temperature and atmosphere, on U(VI) sorption was studied.
Distribution coefficients, Kd values, determined for the U(VI) sorption onto Opalinus clay and diorite at 25 °C, amount to 22.2 ± 0.4 L/kg [1] and 3.8 ± 0.6 L/kg [2], respectively. This shows that U(VI) sorption onto Opalinus clay is stronger than onto diorite, which can be attributed to its larger surface area. TRLFS and ATR FT-IR spectroscopic measurements showed that the U(VI) speciation in Opalinus clay pore water as well as in diorite groundwater is predominated by the weakly sorbing Ca2UO2(CO3)3(aq) complex. Reduction processes of U play only a subordinate role. The U(VI) sorption increases with increasing temperature.
U(VI) diffusion experiments with intact Opalinus clay bore cores [3] also showed that Opalinus clay has a good retardation potential for U(VI) since the molecular diffusion process through Opalinus clay retards the migration of Ca2UO2(CO3)3(aq).
Generally, it can be concluded that U(VI) retention by clay rock is stronger than that by crystalline rock. This supports decisions to use clay rock not only as host rock but also as backfill material. In case of crystalline rock the natural retention capacity for U is insufficient and has to be strengthened by additional geo-technical and technical barriers that preserve their enclosing capabilities over very long time scales.

[1] Joseph, C., Schmeide, K., Sachs, S., Brendler, V., Geipel, G., Bernhard, G.: Sorption of uranium(VI) onto Opalinus clay in the absence and presence of humic acid in Opalinus clay pore water. Chem. Geology 284, 240-250 (2011).
[2] Schmeide, K., Gürtler, S., Müller, K., Steudtner, R., Bok, F., Joseph, C., Brendler, V.: Interaction of U(VI) with Äspö diorite: A batch and in situ ATR FT-IR sorption study. Appl. Geochem., under review (2014).
[3] Joseph, C., Van Loon, L.R., Jakob, A., Steudtner, R., Schmeide, K., Sachs, S., Bernhard, G.: Diffusion of U(VI) in Opalinus clay: Influence of temperature and humic acid. Geochim. Cosmochim. Acta 109, 74-89 (2013).
Keywords: Uranium, sorption, retention, clay rock, crystalline rock
  • Contribution to proceedings
    RadChem 2014 - 17th Radiochemical Conference, 11.-16.05.2014, Mariánské Lázně, Czech Republic
  • Invited lecture (Conferences)
    RadChem 2014 - 17th Radiochemical Conference, 11.-16.05.2014, Mariánské Lázně, Czech Republic

Publ.-Id: 19766 - Permalink


Nanostructuring Ge Surfaces by Ion Irradiation
Facsko, S.; Fritzsche, M.; Ou, X.; Keller, A.;
Low energy ion irradiation induces the formation of periodic surface patterns. These struc-tured surfaces exhibit periodicities in the range of a few tens to hundreds of nanometers and are promising templates for producing nanostructured thin films. Periodic ripple patterns with wave vector parallel to the ion beam direction are observed frequently for ion irradiation at incidence angles between 50° and 70° to the surface normal. At normal incidence dot or hole patterns with hexagonal symmetry are observed only under special irradiation conditions.
The formation of hexagonally arranged hole patterns on Ge(001) surfaces induced by irradia-tion at normal incidence was studied with a scanned focused Ga+ ion beam (FIB). Hole pat-terns with characteristic length of about 50 nm are observed in a narrow energy range of 4 - 6 keV. Hole patterns induced by FIB irradiations were compared to broad beam Ga+ and Ge+ irradiations with the same ion energy. No differences were found demonstrating that FIB irra-diations with a large overlap of the scanned beam are identical to conventional broad beam irradiations.
Furthermore, ion the formation of checkerboard patterns on Ge surfaces was observed dur-ing 1 keV Ar+ irradiation at normal incidence and higher substrate temperature. Similar to the case of ion irradiated crystalline metal surfaces on the crystalline Ge surface a new instability appears at temperatures above the recrystallization temperature due to the Ehrlich-Schwoebel barrier. In this case, we observe regular checkerboard or hole patterns with the symmetry of the patterns reflecting the crystal structure of the irradiated surface.
Keywords: ion irradiation, surface patterning, Ge, nanostructures
  • Lecture (Conference)
    18th International Conference on Surface Modification of Materials by Ion Beams (SMMIB 2013), 15.-20.09.2013, Kusadasi, Türkiye

Publ.-Id: 19765 - Permalink


Reverse epitaxy: patterns on crystalline Ge surfaces
Facsko, S.; Ou, X.; Keller, A.;
Low energy ion irradiation induces the formation of periodic surface patterns. These structured surfaces exhibit periodicities in the range of a few tens to hundreds of nanometers and are promising templates for producing nanostructured thin films. Periodic ripple patterns with wave vector parallel to the ion beam direction are observed frequently for ion irradiation at incidence angles between 50° and 70° to the surface normal. At normal incidence dot or hole patterns with hexagonal symmetry are observed only under special irradiation conditions.
At room temperature semiconductor surfaces are amorphized by ion irradiation. However, at temperatures higher than the recrystallization temperature the surface remains crystalline and novel ion induced patterns appear with the symmetry of the crystal structure of the material. We present pattern formation on Ge surfaces during 1 keV Ar+ ion irradiation under normal incidence at temperature above the recrystallization temperature of Ge. Similar to the case of ion irradiated crystalline metal surfaces on the crystalline Ge surface a new instability appears at higher temperature due to the Ehrlich-Schwoebel barrier. In this case, regular checkerboard or hole patterns with the symmetry of the patterns reflecting the crystal structure of the irradiated surface are observed.
Keywords: ion irradiation, surface patterning, homoepitaxy
  • Lecture (Conference)
    Symposium on „Nanoscale Pattern Formation at Surfaces“, 26.-30.05.2013, Copenhagen, Danmark

Publ.-Id: 19764 - Permalink


Ion Irradiation of Ge: From Sponge-Like Structures to Periodic Patterns
Böttger, R.; Ou, X.; Fritzsche, M.; Keller, A.; Heinig, K. H.; Bischoff, L.; Liedke, B.; Facsko, S.;
Ion irradiation of Ge surfaces leads to a variety of different morphologies depending on the irradiation conditions. In the energy range of few MeV down to a few tens of keV swelling and the formation of sponge like structures are observed. When lowering the energy these porous structures turn into self-organized periodic surface patterns: at off-normal incidence angles well-known ripple patterns with wave vector parallel or perpendicular to the ion beam direction appear, whereas at normal incidence angles hexagonally ordered dot or hole patterns can be formed. The structure size of the patterns is in the range of 10 to 100 nm and, occa-sionally, a high degree of ordering is achieved.
On materials which turn amorphous during ion irradiation the formation of periodic patterns relies on at least two inter-playing processes: surface roughening due to local variation of ero-sion rate and smoothing via diffusional processes. In addition, atomic relocations on the sur-face and in the bulk resulting from the collision cascade have been identified as equally im-portant or even dominating. At the atomic level the creation of surface and bulk defects, sput-tering, and the influence of the ion beam on surface diffusion processes play a decisive role in the morphology evolution.
At high temperature, when amorphization of the Ge surface is prevented by recrystallization, novel surface patterns are developing during ion irradiation. Similar to the case of ion irradia-tions of crystalline metal surfaces a new instability appears on the crystalline Ge surface due to a Ehrlich-Schwoebel barrier for ascending ion induced vacancies. In this case, regular checkerboard patterns are evolving on the Ge (001) surface with structures oriented along the <100> direction.
Moreover, a new mechanism for pattern formation on Ge has been discovered recently: by polyatomic Bi ion irradiation or monoatomic Bi ion irradiation of hot Ge melt pools are in-duced at the Ge surface by the incident ions. These melt pools can also lead to a surface insta-bility and thus to the formation of periodic dot patterns at normal incidence.
We will present an overview of the different morphologies induced by ion irradiation on Ge surfaces and analyze the dominant formation mechanism.
Keywords: ion irradiation, surface patterning, vacancy diffusion
  • Lecture (Conference)
    Workshop on "Particle - surface interactions: from surface analysis to materials processing" (PASI 2013), 03.-5.05.2013, Luxembourg, Luxembourg

Publ.-Id: 19763 - Permalink


Interaction of highly charged ions with surfaces
Facsko, S.;
Highly charged ions (HCI) release a large amount of potential energy during their neutralization when interacting with solid surfaces. This energy is mostly retained in the solid leading to local phase transformations on a nanometer scale. The study of modifications on surfaces and thin foils as a function of potential and kinetic energy gives insight into the interaction of HCIs with surfaces as well as into phase transformations under these non-equilibrium conditions.
Keywords: Highly charge ions, surfaces, nanostructures
  • Invited lecture (Conferences)
    11th European Conference on Atoms, Molecules and Photons, 24.-28.06.2013, Aarhus, Danmark

Publ.-Id: 19762 - Permalink


Spin Nernst Angle: Definition and qualitative Estimation for Cu Alloys
Zahn, P.; Gemming, S.;
The spin Nernst effect describes the occurrence of a spin current perpendicular to an applied thermal gradient and the spin quantization axis in a non-magnetic material. To quantify the effect, the spin Nernst angle will be defined in a more general way than in ref. [1]. This allows for a clear separation of the transverse spin current into two opposite contributions proportional to the spin Hall angle and the spin Nernst angle, respectively. Qualitative trends for Cu alloys with 3d, 4d and 5d defects extending a resonant scattering model by Fert and Levy [2] will be presented.
The work was partially supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz Virtual Institute MEMRIOX (VH-VI-442) and the DFG Priority Program 'Nanostructured Thermoelectrics' (ZA264/3-2).
[1] K. Tauber et al., Phys. Rev. Lett. 109, 026601 (2012)
[2] A. Fert and P.M. Levy, Phys. Rev. Lett. 106, 157208 (2011)
  • Poster
    550. WE-Heraeus-Seminar 'Spin Transport beyond Boltzmann', 08.-10.01.2014, Bad Honnef, Deutschland

Publ.-Id: 19761 - Permalink


Memory Effects in Resistive Ion-beam Modified Oxides
Zahn, P.; Gemming, S.; Potzger, K.; Schmidt, H.; Mikolajick, T.; Slesazeck, S.; Stöcker, H.; Abendroth, B.; Meyer, D. C.; Dittmann, R.; Rana, V.; Waser, R.; Ronning, C.; Spaldin, N. A.; Basov, D.;
The Virtual Institute MEMRIOX establishes a joint research initiative in the field of ion-tailored oxide-based memristive elements, to be pursued within a novel and unique combination of core competences from the Helmholtz centers Dresden-Rossendorf and Jülich and their university partners in Dresden, Freiberg, Jena, San Diego, and Zürich.
A nanoscale memristive element may prove the concept of the ultimate future non-volatile memory cell with a resistance set directly by electric currents. The Virtual Institute aims at stepping beyond the established layer-by-layer control of intrinsic defects during the synthesis of memristive elements. The project is financed by the Initiative and Networking Funds of the Helmholtz Association (VH-VI-442).
  • Poster
    E-MRS Spring Meeting, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 19760 - Permalink


Gelatin-based biomaterials with tailorable mechanical properties as promising matrices for soft-tissue replacement
Ullm, S.; Tondera, C.; Gebauer, T.; Neffe, A. T.; Lendlein, A.; Pietzsch, J.;
Objectives
Gelatin-based hydrogels are promising degradable materials for soft tissue regeneration. Our approach aims at biopolymer-based polymer networks with tailorable elastic properties and degradation behavior due to different degrees of crosslinking with lysine diisocyanate ethyl ester. Two gelatin-based hydrogel films were compared regarding their influence on vitality, adhesion and proinflammatory activation of both endothelial cells and human macrophages, to investigate representative cells being responsible for tissue integration and degradation of the material.
Materials & methods
10 wt% gelatin solutions were crosslinked with three- (G10LNCO3) or eight-fold (G10LNCO8) excess of isocyanate groups, resulting in hydrogels with tailored Young’s moduli (13 and 55 kPa), swelling (1200 and 350 vol%) and degradation time [1]. For experiments on cell vitality, human leukemia HL-60 cells differentiated to macrophages (MΦ), and primary human aortic endothelial cells (HAEC) were incubated with material eluates for 24 and 48 h. Furthermore, these cells were seeded directly on swollen hydrogels for adhesion assays at 2 or 4 h, as well as for microscopic studies on their infiltration ability into the hydrogels after 48 h and 7 days. In order to characterize the ability of hydrogels to induce proinflammatory effects in cells, expression of COX-2 and the receptor for advanced glycation endproducts was quantified by western blotting after 48 h.
Results
MΦ showed a higher vitality and HAEC showed a lower vitality after incubation with material eluates, which can only be related to fragments formed by partial degradation. Interestingly, the strong difference in degradation rate, with G10LNCO3 showing a mass loss of 60 wt% within 6 days, while G10LNCO8 showed only 5–10 wt% mass loss, did not have an influence on the vitality. The adhesion ability of MΦ to swollen hydrogels was significantly decreased to 30% (p<0.05, ANOVA) for G10LNCO3 and to 38% for G10LNCO8, respectively, when compared with adhesion on normal cell culture plastic. By contrast, HAEC in part showed enhanced adhesion to the materials (116% for G10LNCO3, n.s.; 145% for G10LNCO8, p<0.05). This suggests that gelatin offers adhesion sequences for HAEC, but not for MΦ. A higher degree of crosslinking resulted in higher adhesion of both cell types. Additionally, both cell types infiltrated the materials within 4 days, which highlights the degradability of the material, putatively supported by cell-mediated mechanisms. Direct contact with the materials resulted in an increment of COX-2 expression in both cell lines, with a higher degree of hydrogel crosslinking leading to elevated COX-2 expression. Receptor for advanced glycation endproducts synthesis remained unaffected in both MΦ and HAEC.
Conclusion
The hydrogels provide both a surface preventing adhesion of macrophages and supporting adhesion of endothelial cells, which might lead to good tissue integration. However, the materials or their degradation products induced proinflammatory effects on MΦ depending on the degree of crosslinking. In further studies, these hydrogel films will be studied in animal models concerning their initial interaction with the organism after implantation and their degradation.
Financial & competing interests disclosure
This work is part of a research initiative within the Helmholtz-Portfoliotheme “Technologie und Medizin - Multimodale Bildgebung zur Aufklaerung des In vivo -Verhaltens von polymeren Biomaterialien”.
Reference
1 Tronci G, Neffe AT, Piercea BF, Lendlein A. An entropy–elastic gelatin-based hydrogel system. J. Mater. Chem. 20, 8875–8884
  • Abstract in refereed journal
    Regenerative Medicine 8(2013), S201
  • Poster
    World Conference on Regenerative Medicine, 23.-25.10.2013, Leipzig, Deutschland

Publ.-Id: 19759 - Permalink


Radiosynthesis of 5-(2-[18[F]fluoroethyl)-sunitinib as inhibitor of VEGFR-2 – first results
Kniess, T.; Kuchar, M.; Bergmann, R.; Steinbach, J.; Pietzsch, J.;
Aim:
Radiolabeled inhibitors of receptor tyrosine kinases (RTK) might be suitable probes for monitoring pathophysiological situations related to enhanced expression of the vascular endothelial growth factor receptor (VEGFR). Imaging of
angiogenesis with PET could facilitate for the individual patient the evaluation of e.g. the success of corresponding anti-angiogenic chemotherapy or monitoring the stimulation of the endogenous adaptive vessel growth after implantation of
bioMaterials. For this purpose we developed an 18F-radiolabeled probe, 5-(2-[18F]fluoroethyl)-sunitinib basing on the lead structure of sunitinib®, a multi-kinase inhibitor selective to VEGFR-2.

Materials and Methods:
The non-radioactive reference compound 5-(2-fluoroethyl)-sunitinib was synthesized by Knoevenagel condensation of 5-(2-fluoroethyl)-indoline-2-one with N-[2-(diethylamino)ethyl]-2,4-dimethyl-5-formyl-1H-pyrrole-3-carboxamide. Two suitable precursors for radiolabeling, A and B were obtained by reacting a 5-(2-bromoethyl)-substituted sunitinib derivative with silver 4-toluenesulfonate and silver methanesulfonate, respectively. [18F]Fluoride was produced by the 18O(p,n)18F reaction from [18O]H2O in a 18/9 cyclotron (IBA), separated by an anion exchange cartridge (QMA, Waters) and activated by azeotropic drying with acetonitrile in a stream of nitrogen before use. In a set of radiolabeling experiments 4 mg of precursor A or B were reacted with [18F]fluoride in 500μL of solvent at a scheduled temperature regime for 20 min. The yield of 5-(2-[18F]fluoroethyl)-sunitinib was determined by radio-TLC (silicagel, THF/TEA=9/1).

Results:
The non-radioactive 5-(2-fluoroethyl)-sunitinib was investigated in a competition binding assay against VEGFR-2; a Kd value of 9 nM is justifying its classification as specific inhibitor. The radiolabeling reaction of the precursors A and B was performed at temperatures varying from 60, 90, and 120°C in one of the following solvents: acetonitrile, DMF, and DMSO. As result it turned out that for both precursors in DMF and DMSO only poor labeling yields about 2% could be achieved, whereas by using acetonitrile at 90°C the yield of 5-(2-[18F]fluoroethyl)-sunitinib increased to 7-9%. Reaction temperatures higher than 90°C lead to fast and complete decomposition of the precursors as monitored by several non-radioactive by-products on TLC. Notably no difference in yield was observed by using the methanesulfonyl- or the 4-toluenesulfonyl-precursor.

Conclusions:
The new VEGFR-2 targeted radiolabeled probe 5-(2-[18F]fluoroethyl)-sunitinib was successfully synthesized by radiofluorination of the corresponding methanesulfonyl- or 4-toluenesulfonyl-substituted precursor with [18F]fluoride. First attempts to transfer the labeling method to a remote-controlled system were successful. By now a procedure for the purification of the radiotracer by semi-preparative HPLC and SPE is under development to enable the radiopharmacological evaluation.
  • Poster
    Annual Congress of the European Association of Nuclear Medicine, 19.-23.10.2013, Lyon, France
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 40(2013)Suppl. 2, S316
    DOI: 10.1007/s00259-013-2535-3

Publ.-Id: 19758 - Permalink


Pulmonary Blood Flow Increases in Damaged Regions Directly after Acid Aspiration in Rats
Richter, T.; Bergmann, R.; Knels, L.; Hofheinz, F.; Kasper, M.; Deile, M.; Pietzsch, J.; Ragaller, M.; Koch, T.;
Background: After gastric aspiration events, patients are at risk of pulmonary dysfunction and the development of severe acute lung injury and acute respiratory distress syndrome, which may contribute to the development of an inflammatory reaction. The authors' aim in the current study was to investigate the role of the spatial distribution of pulmonary blood flow in the pathogenesis of pulmonary dysfunction during the early stages after acid aspiration.
Methods: The authors analyzed the pulmonary distribution of radiolabeled microspheres in normal (n = 6) and injured (n = 12) anesthetized rat lungs using positron emission tomography, computed tomography, and histological examination.
Results: Injured regions demonstrate increased pulmonary blood flow in association with reduced arterial pressure and the deterioration of arterial oxygenation. After acid aspiration, computed tomography scans revealed that lung density had increased in the injured regions and that these regions colocalized with areas of increased blood flow. The acid was instilled into the middle and basal regions of the lungs. The blood flow was significantly increased to these regions compared with the blood flow to uninjured lungs in the control animals (middle region: 1.23 [1.1; 1.4] (median [25%; 75%]) vs. 1.04 [1.0; 1.1] and basal region: 1.25 [1.2; 1.3] vs. 1.02 [1.0; 1.05], respectively). The increase in blood flow did not seem to be due to vascular leakage into these injured areas.
Conclusions: The data suggest that 10 min after acid aspiration, damaged areas are characterized by increased pulmonary blood flow. The results may impact further treatment strategies, such as drug targeting.

Publ.-Id: 19757 - Permalink


Neutronics diagnostics for European ITER TBMs: Activation foil spectrometer for short measurement cycles
Klix, A.; Domula, A.; Fischer, U.; Gehre, D.; Pereslavtsev, P.; Rovni, I.;
An important aim of neutronics Test Blanket Module (TBM) experiments in ITER will be to check the prediction accuracy of nuclear responses in an environment closer to a future fusion power reactor than so far provided by existing facilities. The development of measurement methods suitable for the harsh environment in an ITER TBM has been addressed in several recent R&D programs supported by Euratom. Within this framework, KIT is developing an activation foil spectrometer for the measurement of local neutron flux densities in the TBM. We intend to establish a measurement method which allows to record the induced activities in small packages of activation foils simultaneously and to calculate the corre- sponding spectral neutron flux densities with moderate time resolution of tens of seconds immediately after extraction from the TBM. In the present work we propose a candidate set of activation foil materials which cover the neutron energy range from thermal to 14 MeV. In order to assess their basic suitability for such measurements, we have computed induced gamma-ray activities in the foils using a calculated neutron spectrum in a representative position in the European HCPB TBM assuming a short irradiation time of 30 s. In a further step we have investigated pulse height spectra which would be obtained in a typical gamma-ray measurement arrangement in a HPGe detector and concluded that the proposed set of activation foils should be basically suitable for such a measurement system but require improvement of relevant cross sections uncertainties.
Keywords: Neutron flux density, Activation foil, Neutron flux spectrometer, Test Blanket Module

Publ.-Id: 19756 - Permalink


Intersublevel dephasing in InAs/GaAs quantum dots below the Reststrahlen band
Teich, M.; Stephan, D. R.; Winnerl, S.; Schneider, H.; Wilson, L. R.; Helm, M.;
Using transient four-wave mixing in the terahertz range, we have measured the s-p inter-sublevel dephasing time in self-assembled InAs/GaAs quantum dots for transition energies below the Reststrahlen band. Dephasing times of up to 600 ps at a photon energy of 18 meV have been determined. By comparing pump-probe and four-wave mixing measurements, we show that there is no significant influence of any pure dephasing process at low temperature. The linear temperature dependence is consistent with acoustic phonon scattering.
Keywords: quantum dots, THz, FEL, dephasing

Publ.-Id: 19755 - Permalink


Status of Development of the Reactor Dynamics Code DYN3D
Rohde, U.; Kliem, S.; Duerigen, S.; Bilodid, Y.;
The reactor dynamics code DYN3D has been developed in HZDR and its predecessor organizations over more than 20 years. Originally, the code was developed for the analysis of reactivity-initiated transients and accidents in Russian VVER type reactors and recommended by the IAEA as a reference code for the VVER-440/V213 reactor. In the meantime, the code became an advanced simulation tool for transients in Light Water Reactors with 16 users in 7 countries.
The DYN3D code comprises neutron statics and kinetics calculations, thermal hydraulics of the reactor core and modeling of transient fuel rod behavior. In the paper, an outline on the basic models is given.
3D neutronics is based on nodal expansion methods for hexagonal, square and trigonal geometry of the fuel assemblies. With respect to neutron energy resolution, two-group and multi-group versions are available. Besides of standard diffusion approximation, simplified P3 (SP3) transport approach for square and trigonal lattices is implemented. Neutronic calculations can be performed with resolution on fuel assembly or pin-wise level.
Neutronics is coupled to thermal hydraulics, where the reactor core is modeled by parallel coolant channels. One- and two-phase flow in the channels is described based on a four-equations model. The code comprises a simplified thermo-mechanical model of the transient fuel behavior.
Macroscopic neutronic cross section libraries containing the dependence of cross sections from fuel burn-up and thermal hydraulics feedback parameters like fuel temperature, moderator density and temperature or boron concentration can be linked to the code through various data interfaces.
Besides of the basic models, the code disposes of various special features like:
• Zone-wise inner-nodal neutron flux reconstruction at pin level
• Reactor poisson dynamics
• Consideration of history effects in burn-up
• Decay heat model with consideration of the power history before shut down
• Calculation of steady states with external source
Comprehensive efforts have been made on verification and validation of DYN3D against numerical benchmarks, dedicated experiments on neutron kinetics and thermal hydraulics as well as real plant data. Some examples for verification of new models like history effects and SP3 method on trigonal lattice will be given.
Last but not least, examples on the application of DYN3D for the simulation of reactivity initiated accidents like control rod ejection will be shown. An advanced graphical tools for the visualization of the results of calculations will be demonstrated.
Keywords: reactor dynamics, transient simulation, neutron kinetics, thermo-hydraulics model, reactivity initiated accidents, computer code, VVER type reactors
  • Lecture (Conference)
    The 8th International Scientific and Technical Conference “Safety Assurance of NPP with WWER”, 28.-31.05.2013, Podolsk, Russia

Publ.-Id: 19754 - Permalink


Sensitivity Analysis o the Ranking of Input Uncertainties withe Respect to Peak Cladding temperature Uncertainty in a PWR LBLOCA Analysis
Rohde, U.; Kozmenkov, Y.;
An uncertainty analysis of a large break loss-of-coolant accident (LBLOCA) for a German PWR Konvoi was performed using a statistical method, which is based on the Wilks’ theory. The evaluated output parameter is the peak cladding temperature (PCT). The primary goal of this paper is a ranking of the input uncertainties, according to their contributions to the PCT uncertainty in the ATHLET simulation of PWR LBLOCA, by performing a sensitivity analysis. It was shown, that the starting (extended) set of varied parameters can be considerably reduced without any statistically significant influence on the uncertainty analysis results.
The statistical t-test was used to minimize the number of varied parameters. A set of uncertainty parameters with significant impact on the uncertainty of the PCT was identified. The main contribution to the uncertainty of the first cladding temperature maximum during the blowdown phase of the accident is produced by the core parameters that affect the fuel’s stored energy at the beginning of the accident. However, the major contributors to the uncertainty of the second PCT maximum are the uncertainties in the code models, and first of all the uncertainties in the heat transfer coefficients for dispersed and pure steam flows.
Keywords: statistical uncertainty analysis, sensitivity analysis, Large Break LOCA, peak cladding temperature
  • Lecture (Conference)
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Strbske Pleso, Slovakia
  • Contribution to proceedings
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Strbske Pleso, Slovakia
    Proceedings of the 23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest: MTA Energoatom, 978-963-7351-21-1, 501-512

Publ.-Id: 19753 - Permalink


Current status and future perspectives of the COBRA experiment
Ebert, J.; Fritts, M.; Gößling, C.; Goepfert, T.; Gehre, D.; Hagner, C.; Heidrich, N.; Koettig, T.; Neddermann, T.; Oldorf, C.; Quante, T.; Rajek, S.; Reinicke, O.; Schulz, O.; Tebruegge, J.; Timm, J.; Wonsak, B.; Zuber, K.;
The aim of the COBRA experiment is to prove the existence of neutrinoless double-beta-decay (0v𝛽𝛽-decay) and to measure its half-life. For this purpose a detector array made of cadmium-zinc-telluride (CdZnTe) semiconductor detectors is operated at the Gran Sasso Underground Laboratory (LNGS) in Italy. This setup is used to investigate the experimental issues of operating CdZnTe detectors in low-background mode and to identify potential background components, whilst additional studies are proceeding in surface laboratories. The experiment currently consists of monolithic, calorimetric detectors of coplanar grid design (CPG detectors). These detectors are 1 × 1 × 1 cm3 and are arranged in 4 × 4 detector layers. Ultimately four layers will be installed by the end of 2013, of which two are currently operating. To date 82.3 kg⋅days of data have been collected. In the region of interest for 116 Cd around 2.8 MeV, the median energy resolution is 1.5% FWHM, and a background level near 1 counts/keV/kg/y has been reached. This paper gives an overview of the current status of the experiment and future perspectives.
Keywords: CZT COBRA double beta decay neutrino

Publ.-Id: 19752 - Permalink


First Experimental Results on the Azimuthal Magnetorotational Instability
Seilmayer, M.;
More than 50 years ago, Velikhov and Chandrasekhar discovered a hydromagnetic instability which was later coined magnetorotational instability (MRI). For an ideal fluid it implies that a Couette flow between two corotating cylinders in the presence of a magnetic field is only stable as long the angular velocity increases outwards, quite in contrast to Rayleigh's hydrodynamic stability condition which demands the angular momentum to increase outwards.
The experimental verification of the standard version of MRI, with only an axial field being applied, is difficult since it requires both the magnetic Reynolds and the Lundquist number to be in the order of 1. The helical version of MRI, with an azimuthal field applied in addition to the axial one, is much easier to investigate since it requires only a Reynolds number in the order of 1000 and a Hartmann number in the order of 10. Very similar requirements apply to the so-called azimuthal MRI (AMRI), a non-axisymmetric (m=1) version that occurs for purely or strongly dominant azimuthal magnetic fields.
We present first experimental results on the AMRI obtained at the PROMISE facility with an enhanced power supply which can deliver currents up to 20 kA. For this system, we discuss the elaborate measures that were needed to obtaine a reasonable signal-to-noise ratio of the ultrasonic measurement system. In dependence on various parameter variations, some typical features of the observed instability, such as the energy content, the wavelength, and the frequency are analysed and compared with theoretical predictions.
Keywords: AMRI, magnetorotational instability
  • Lecture (Conference)
    eGdR Symposium, 08.-12.07.2013, Ascona, Schweiz

Publ.-Id: 19751 - Permalink


Detecting Supernova Dust on the Earth's Sea Floor with AMS
Feige, J.; Wallner, A.; Breitschwerdt, D.; Fifield, L. K.; Korschinek, G.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.;
An 60Fe anomaly was detected with accelerator mass spectrometry (AMS) - a very sensitive method to measure extremely low isotopic ratios - in a 2 Myr old layer of a ferromanganese crust (Knie et al., 2004). This signal is assumed to be of supernova origin and might be linked to the observation of our solar system being located in a Region of thin, hot interstellar medium. This region, called the Local Bubble, was presumably formed by multiple supernova explosions starting 14 Myr ago. Calculations suggest that at least one of these supernovae occured close enough to the solar system to leave a detectable 60Fe trace on Earth.
New AMS measurements are performed in deep-sea sediments from the Pacific Ocean. An international collaboration of different AMS facilities searches for signatures of the long-lived radionuclides 26Al, 53Mn, and 60Fe in a time range from 1.7 to 3.1 Myr. Magnetostratigraphic dating of the samples is confirmed by measurements of the cosmogenic radionuclide 10Be. All 10Be and 26Al measurements are finished, 53Mn and 60Fe is in progress. First results will be presented and discussed.
Keywords: accelerator mass spectrometry, AMS, supernova, cosmogenic radionuclide
  • Lecture (Conference)
    Symposium "Fathoming Stellar Evolution with Laboratory Precision", DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 19750 - Permalink


Evaluation of the Survey 2011/12 amongest doctoral student within the Helmholtz Association
Seilmayer, M.; Jose, D.; Thonicker, I.; Schmidt, L.;
The Helmholtz Juniors are the PhD students Network of the German Helmholtz-Association (Helmholtz-Gemeinschaft Deutscher Forschungszentren, HGF). Their main effort is an intensive collaboration between the PhD students of the different Helmholtz research centers and an improvement of the PhD education. They consist of elected or delegated members of the PhD representative teams of each center.
In order to represent the interest of the PhD 1 students to the Helmholtz Association, we need to have precise and up-to-date knowledge about the working conditions, problems and wishes of PhDs. This survey is a crucial basis therefore. After 2008 and 2010, this report refers to the third wave of the Helmholtz wide phd survey. Its results technically enable us to even describe developments over the last 4 years, which should be the aim of a separate, comprehensive report in the near future.
Within the Helmholtz-Juniors, the working group PhD-Survey developed, conducted, analyzed, and reported the survey and its data. The raw data is hold by the working group. The report is free to be used by the Helmholtz Centers as well as its PhDs. In the report, the centers are coded by a random number, while each center is told its own number only.
In the report, firstly we provide information about the background of the participants. Secondly we address four main topics of interest, namely PhD project planning, the income situation of PhD students, conditions for starting a family during the time as PhD student and the situation of students of foreign nationalities within the HGF. And thirdly we report results regarding the Helmholtz graduate schools. We do neither refer to every question in the survey nor do we present cross tables or indepth information. If one is interested in further analysis, she may contact the members of this working group. The complete questionnaire is appended.
Keywords: PhD Representation, Helmholtz Juniors, Survey, HeJu
  • Article, self-published (no contribution to HZDR-Annual report)
    Helmholtz-Zentrum Rossendorf 2013
    2011/12
    33 Seiten

Publ.-Id: 19749 - Permalink


Historical Aspects of Subsecond Thermal Processing
Voelskow, M.; Yankov, R. A.; Skorupa, W.;
From atom bomb simulation to advanced semiconductor processing - what a bellicose - to peaceful bottom - up approach this research field experienced
Keywords: historical aspects, subsecond thermal processing
  • Book chapter
    Wolfgang Skorupa, Heidemarie Schmidt: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 1-13
    DOI: 10.1007/978-3-319-03131-6_1

Publ.-Id: 19748 - Permalink


Entwicklung szintillatorbasierter Echtzeit-Detektoren für laserbeschleunigte Protonen
Metzkes, J.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Richter, C.; Schürer, M.; Sobiella, M.; Stiller, N.; Zeil, K.; Schramm, U.;
  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 18.-21.09.2013, Köln, Deutschland

Publ.-Id: 19747 - Permalink


Reflective Optical Probing of the Critical Density Surface in Laser-Produced Plasmas
Metzkes, J.; Zeil, K.; Kraft, S. D.; Kluge, T.; Schramm, U.; Mondal, S.; Ravindra Kumar, G.;
  • Lecture (Conference)
    Meeting Prof. G. Ravindra Kumar Tata Institute of Fundamental Research 2013, 30.08.2013, Mumbai, India

Publ.-Id: 19746 - Permalink


III-V Quantum Dots in Dielectrics Made by Ion Implantation and Flash Lamp Annealing
Prucnal, S.; Turek, M.; Gao, K.; Zhou, S.; Pyszniak, K.; Drozdziel, A.; Zuk, J.; Skorupa, W.;
Different semiconductor nanocrystals synthesized in dielectrics on silicon are very interesting for applications in non-volatile memories and photovoltaics. In this paper we present an overview of microstructural and opto-electronic properties of different III-V quantum dots embedded in SiO2 and Si3N4 made by sequential ion implantation and millisecond range flash lamp annealing. It is shown that within 20 ms post-implantation annealing high quality crystalline III-V quantum dots can be formed in different matrices. Formation of crystalline III-V quantum dots was confirmed by cross-section transmission electron microscopy, photoluminescence and mu-Raman spectroscopy. Flash lamp annealing is essentially a single-flash-single-wafer technique whose main attributes are the ease and control of processing over large wafer batches.
Keywords: III-V, quantum dots, silicon, FLA, ion implantation

Publ.-Id: 19745 - Permalink


Conductivity type and crystal orientation of GaAs nanocrystals fabricated in silicon by ion implantation and flash lamp annealing
Prucnal, S.; Liedke, M. O.; Zhou, S.; Voelskow, M.; Mucklich, A.; Turek, M.; Zuk, J.; Skorupa, W.;
The integration of III-V semiconductor material within silicon technology is crucial for performance of advanced electronic devices. This paper presents the investigations of microstructural and opto-electronic properties of GaAs quantum dots (QDs) formed in silicon by means of sequential ion implantation and flash lamp annealing (FLA). Formation of crystalline GaAs QDs with well-defined crystal orientation and conductivity type was confirmed by high resolution transmission electron microscopy and mu-Raman spectroscopy. The influence of the post implantation millisecond-range annealing on the evolution of the nanoparticles size, shape, crystallographic orientation and doping type of GaAs QDs is discussed.
Keywords: GaAs; Quantum dots; Ion implantation; Flash lamp annealing; Silicon

Publ.-Id: 19744 - Permalink


Short time thermal processing and defects: history and ideology
Skorupa, W.;
In this talk I will treat the fascinating world of defect engineering from the viewpoint of short time thermal processing in the millisecond range. Special focus will be devoted to ion implantation-related issues.
Keywords: millisecond range thermal processing, flash lamp annealing
  • Invited lecture (Conferences)
    International Symposium on Semiconductors: Defects, Doping and Diffusion (IS2D3), 24.-25.10.2013, Oslo, Norway

Publ.-Id: 19743 - Permalink


Nanocrystalline approaches to electronic materials using subsecond thermal processing
Skorupa, W.;
This talk reviews the advances that subsecond thermal processing in the millisecond range using xenon-filled flash lamps brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. An important issue of our work was the formation and characterization of Si-based light electroluminescence from MOS structures with group-IV- and rare earth-containing dielectric layers. Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Regarding photovoltaic applications, we dealt with the ion beam doping and thermal processing of PV silicon demonstrating a distinct improvement of the minority carrier diffusion length compared to RTP and furnace treatments. Whereas these examples base on solid phase processing the more sophisticated approach regards on working with the liquid phase at the surface of solid substrates. A recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (NanoLett. 11, 2814 (2011)).
Moreover, a new approach of forming compound semiconductor nanocrystals inside a silicon nanowire will be demonstrated.
Keywords: Milliscond range annealing, flash lamp annealing, photovoltaics, electroluminescence, III-V nanocrystals, liquid phase processing, silicon nanowire
  • Invited lecture (Conferences)
    223rd ECS Meeting, Symposium E3: Nanocrystal Embedded Dielectrics for Electronic and Photonic Devices, 12.-17.05.2013, Toronto, Canada

Publ.-Id: 19742 - Permalink


Single particle resuspension experiments in turbulent channel flows
Barth, T.; Preuß, J.; Müller, G.; Hampel, U.;
The resuspension of a monolayer of spherical glass and polypropylene particles from a channel floor by a dry and turbulent airflow was investigated. Special attention was given to the influence of the particle size, the particle and wall material, the wall surface roughness and the critical friction velocity. The experiments were performed in an air-driven small-scale test facility and the channel floor was made of interchangeable glass and steel wall segments. The turbulent channel flow was recorded using a planar Particle Image Velocimetry system. Prior to the experiments the spherical particles were classified using Scanning Electron Microscopy techniques. The particles on the channel floor were detected and classified by means of an optical microscope combined with a digital camera. A statistically sufficient particle monolayer was generated on the channel floor by dispersing the particles into the flow during a pure deposition regime. Afterwards, particle resuspension was induced by stepwise increase of the fluid velocity. The resuspension was quantified by the fraction of remaining particles against the friction velocity for a particle diameter range between 3 µm and 45 µm. It was found that particles instantly resuspend once a critical friction velocity is exceeded. Larger particles require lower fluid velocities for the removal than smaller particles. The wall surface roughness seems to scatter the resuspension process with respect to the friction velocity.
Keywords: aerosol particle, turbulent flow, resuspension

Publ.-Id: 19741 - Permalink


Enhanced feedback effects in sodium cooled fast reactors using moderating material – the effect of the plutonium content in the fuel
Merk, B.;
The use of fine distributed moderating material to enhance the negative feedback effects and to reduce the sodium void effecting sodium cooled fast reactor cores is described. The influence of the moderating material on the neutron spectrum is given and evaluated in comparison with the capture cross sections of major materials (U-238, Pu-239, and Pu-240). The influence of the variation of the Pu content on the efficiency of the enhancement of the Doppler effect and on the reduction of the positive coolant and sodium void effect in a representative SFR fuel assembly configuration is analyzed. Additionally the influence of the moderating material combined with the variation of the Pu content on the infinite multiplication factor is studied.
Keywords: Enhanced feedback effects, Fast reactor, SFR, Sodium void effect, Yttrium hydride, Varying PU content
  • Contribution to proceedings
    PHYSOR 2014, 28.09.-03.10.2014, Kyoto, Japan
    PHYSOR 2014 – The Role of Reactor Physics Toward a Sustainable Future
  • Lecture (Conference)
    PHYSOR 2014, 28.09.-03.10.2014, Kyoto, Japan

Publ.-Id: 19740 - Permalink


Phosphorus in-diffusion from a surface source by millisecond flash lamp annealing for shallow emitter solar cells
Normann, H. B.; Vines, L.; Privitera, V.; Skorupa, W.; Schumann, T.; Svensson, B. G.; Monakhov, E. V.;
We have investigated in-diffusion of phosphorus into monocrystalline silicon by depositing a phosphorus source on the surface followed by millisecond flash lamp annealing (FLA) to form shallow emitters for solar cells. By varying both the energy density of a 20 ms flash in the range from 62 to 132 J/cm(2) and the sample preheating, it is observed that FLA treatments can in-diffuse a high concentration of phosphorus atoms becoming electrically active. The most promising emitters are obtained after FLA in the energy range from 110 to 128 J/cm(2) including preheating at 300 degrees C with a peak concentration of 4 - 6 x 10(20) cm(-3). The emitter junction depth for these treatments is in the range of 100 nm to 200 nm, respectively.
Keywords: photovoltaics, solar cell, flash lamp annealing, millisecond annealing, doping, phosphorus, electrical activation

Publ.-Id: 19738 - Permalink


New insights into the nuclear structure in neutron-rich 112,114,115,116,117,118Pd
Luo, Y.; Rasmussen, J.; Hamilton, J.; Ramayya, A.; Frauendorf, S.; Hwang, J.; Stone, N.; Zhu, S.; Brewer, N.; Wang, E.; Lee, I.; Liu, S.; Terakopian, G.; Daniel, A.; Oganessian, Y.; Stoyer, M.; Donangelo, R.; Ma, W.; Cole, J.; Shi, Y.; Xu, F.;
New level schemes of Pd-112,Pd-114,Pd-115,Pd-116,Pd-117,Pd-118 are established by means of gamma-gamma-gamma, gamma-gamma-gamma-gamma and gamma-gamma(theta) measurements of prompt fission gamma rays from Cf-252 using the Gammasphere multi-detector array. Spins/parities were assigned to levels based on gamma-gamma angular correlation measurements, level systematics and decay patterns. In the even-N isotopes Pd-112,Pd-114,Pd-116, two sets of odd-parity bands were identified and extended with spins measured in each band. The odd-parity bands with large level staggerings were interpreted as disturbed chirality with less pronounced triaxial deformations in the Pd isotopes than observed in the chiral symmetry breaking Ru-110,Ru-112 with maximum triaxiality.
Onset of wobbling motion was identified from the sign of the signature splitting in the gamma band of even-even Pd-114, and probably also in Pd-116, as first seen in the N = 68 isotone Ru-112. Maximal triaxiality in Ru and Pd isotopes is found to be reached for N = 68, Ru-112 and Pd-114, 4 neutrons more than predicted in the theoretical calculations.
The new data and TRS calculations allowed a systematic study of the band crossings in the even-N Pd-112,Pd-114,Pd-116 and odd-N Pd-115,Pd-117 isotopes. Now we find a new overall, more complex shape evolution than previously proposed from triaxial prolate in Pd-110 via triaxial oblate in Pd-112 to nearly oblate in Pd-114,Pd-116 with a large change of the triaxial deformation parameter gamma toward nearly oblate in the (pi
g(9/2))(2) alignment in Pd-114,Pd-115,Pd-116,Pd-117,Pd-118, and triaxial-prolate-triaxial-oblate shape coexisting bands in Pd-115.

Publ.-Id: 19737 - Permalink


Hot electron effect on charge formation in SiO2 layer enriched by rare-earth based nanoclusters
Nazarov, A. N.; Tiagulskyi, S. I.; Tygulskyy, I. P.; Lysenko, V. S.; Rebohle, L.; Skorupa, W.;
Fowler-Nordheim (FN) hot electron injection in dielectгics is often used as a method which is alternative to x-ray irradiation. In this work charge trapping during FN еlесtrоп injection in SiO2 implanted bу various rаre-еаrth (RE) impurities (Се, Еu, Gd, Тb, Еr, Тm) with following high tеmреrаturе annealing is considered. Implanted doses correspond to a RE atomic concentration from 0.1 to 1.5 at. %. The charge trapping in Al-SiO2(RE)-n-Si struсturеs is mеаsurеd bу high-frequency (100 kHz) capacitance-voltage (C-V) characteristics and changing of the voltage applied to the structure during еlесtгоп injection at constant current regime. The RE impurity distribution and nanocluster formation in the Sio2 layer after high-temperature annealing (from 900 to 1100°C) are studied bу Rutherford buck sсаttеring (RBS) method and high-resolution transmission electron microscopy (HRTEM) correspondingly. Сhаrgе trаррing раrаmеtеrs (type of charge, capture cross-section, trapped charge concentration) аrе determined at hot electron injection frоm 10E14 to 10E21 e/cm2.

It was shown that at medium electron injection (from 10E15 to 10E18 е/сm2) for аll types of RE impurities negative charge trapping was observed. It was found that mахimum negative сhаrge trapping took place iп Eu implanted dielectrics which demonstrated mахimum size of the formed nanoclusters. A shell model of the defect generation and negative charge trapping around the nanoclusters was proposed. Qualitative calculations of dangling bonds, arоund the RE oxide nanoclusters were performed which confirmеd the obtained ехрегimепtаl results.
Keywords: rare earth, ion implantation, charge trapping MOS structure, electroluminescence
  • Poster
    17th International conference on radiation effects in insulators, 30.06.-05.07.2013, Helsinki, Finland

Publ.-Id: 19736 - Permalink


Dipole strength of 181Ta for the evaluation of the 180Ta stellar neutron capture rate
Makinaga, A.; Massarczyk, R.; Schwengner, R.; Beard, M.; Dönau, F.; Anders, M.; Bemmerer, D.; Beyer, R.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kögler, T.; Röder, M.; Schmidt, K.; Wagner, A.;
The photoabsorption cross section of 181Ta up to the neutron-separation energy is deduced using bremsstrahlung produced with an electron beam of 9.6 MeV energy. The analysis of the measured gamma-ray spectra includes the quasicontinuum of levels at high energy. Simulations of gamma-ray cascades are performed to estimate intensities of inelastic transitions and branching ratios of the ground-state transitions. The resulting photoabsorption cross section shows enhanced dipole strength in the energy range from 5 to 8 MeV, which may be related to a pygmy dipole resonance. The results of the present experiment are compared with predictions of a quasiparticle-random phase approximation in a deformed basis. A combination of the present experimental data and (gamma,n) data is used as an input to the statistical code TALYS applied to calculate cross sections and reaction rates of
photonuclear reactions that are important for the nucleosynthesis of 180mTa.
Keywords: Nuclear resonance fluorescence, photon scattering, photoabsorption cross section, dipole strength function, astrophysical reaction rates, statistical reaction model, quasiparticle random phase approximation, nuclear deformation.

Publ.-Id: 19735 - Permalink


Development and first experimental tests of Faraday cup array
Prokůpek, J.; Kaufman, J.; Margarone, D.; Krůs, M.; Velyhan, A.; Krása, J.; Burris-Mog, T.; Busold, S.; Deppert, O.; Cowan, T. E.; Korn, G.;
A new type of Faraday cup, capable of detecting high energy charged particles produced in a high intensity laser-matter interaction environment, has recently been developed and demonstrated as a real-time detector based on the time-of-flight technique. An array of these Faraday cups was designed and constructed to cover different observation angles with respect to the target normal direction. Thus, it allows reconstruction of the spatial distribution of ion current density in the subcritical plasma region and the ability to visualise its time evolution through time-of-flight measurements, which cannot be achieved with standard laser optical interferometry. This is a unique method for two-dimensional visualisation of ion currents from laser-generated plasmas. A technical description of the new type of Faraday cup is introduced along with an ad hoc data analysis procedure. Experimental results obtained during campaigns at the Petawatt High-Energy Laser forHeavy Ion Experiments (GSI, Darmstadt) and at the Prague Asterix Laser System (AS CR) are presented. Advantages and limitations of the used diagnostic system are discussed.

Publ.-Id: 19734 - Permalink


Internal characterisation of fresh agricultural products using traditional and ultrafast electron beam X-ray computed tomography imaging
Donis Gonzalez, I. R.; Guyer, D. E.; Pease, A.; Barthel, F.;
Currently, destructive techniques can be employed to evaluate the internal attributes of fresh fruits, vegetables and nuts. However, clearly not all produce can be evaluated. Thus, there is a need to develop an in vivo non-destructive technique able to assess fresh agricultural commodity internal components, especially disorders. In this study, medical grade computed tomography (CT) was used to obtain transversal two-dimensional (2D) Images from several fresh agricultural product phenomena. CT scanning was performed by placing and securing numbered samples onto a whole polyethylene sheet, placed on the CT scanner table. Phenomena included the internal decay of chestnuts (Castanea spp.), internal defects in pickling cucumbers (Cucumis sativus), translucency disorder in pineapples (Ananas comosus), pit presence in tart cherries (Prunus cerasus var. Montmorency) and plum curculio (Conotrachelus nenuphar ) infestation of tart cherries.
In addition, an ultrafast X-ray CT scanner was also used to visualise internal characteristics of fresh chestnuts. Chestnuts were labelled and packed in a thin plastic hose, which was pulled through the scanning plane. The 2D CT X-ray images and post-processing three-dimensional CT image recon-struction indicate that CT can be used as an accurate in vivo insight of fresh intact agri-cultural products. Results suggest that there is a potential for non-destructive inline sorting of the internal quality of several agricultural products.
The long-term objective is that the fresh and processing product industries will then be able to detect internal quality attributes of fresh agricultural commodities, at a relatively early stage, after validation under commercial conditions.
Keywords: --

Publ.-Id: 19733 - Permalink


Temperature dependence of ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures
Radek, M.; Bracht, H.; Posselt, M.; Liedke, B.; Schmidt, B.; Bougeard, D.;
Self-atom mixing induced by 310 keV gallium (Ga) ion implantation in crystalline and preamorphized germanium (Ge) at temperatures between 164 K and 623 K and a dose of 1x1015 cm-2 is investigated using isotopic multilayer structures of alternating 70Ge and natGe layers grown by molecular beam epitaxy. The distribution of the implanted Ga atoms and the ion-beam induced depth-dependent self-atom mixing was determined by means of secondary ion mass spectrometry. Three different temperature regimes of self-atom mixing, i.e., low-, intermediate-, and high-temperature regimes are observed. At temperatures up to 423 K, the mixing is independent of the initial structure, whereas at 523 K, the intermixing of the preamorphized Ge structure is about twice as high as that of crystalline Ge. At 623 K, the intermixing of the initially amorphous Ge structure is strongly reduced and approaches the mixing of the crystalline material. The temperature dependence of ion-beam mixing is described by competitive amorphization and recrystallization processes.
Keywords: germanium, isotope multilayer, ion-beam mixing, thermal spike model

Publ.-Id: 19732 - Permalink


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