Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39109 Publications

The two-phase flow at gas-evolving electrodes: bubble-driven and Lorentz-force-driven convection

Weier, T.; Landgraf, S.

We observe electrolysis with gas evolution, a phenomenon occurring in a number of industrial scale electrochemical processes. Here, water electrolysis takes place in a small undivided electrolysis cell consisting of vertical electrodes embedded in a larger glass vessel which contains a dilute NaOH solution. Fluid flow velocities are measured by Particle Image Velocimetry with fluorescent tracers, while size distribution and velocities of the bubbles are determined from bubble shadow images obtained with a high speed camera. Coalescence phenomena are observed in the flow and explain the relatively wide distribution of bubble sizes.
Depending on the gap width and the current density, bubbles ascending near the electrodes form two discernible bubble curtains (low average void fraction, wide gaps) or a flow profile more akin to a channel flow (high average void fraction, small gaps). If the flow consists of separate bubble curtains, instabilities develop not unlike to that of a single phase wall jet.
Finally, the influence of different wall parallel Lorentz force configurations on the velocity distribution in the cell is investigated. These Lorentz forces are generated by permanent magnets mounted behind the electrodes. Depending on gap width, current density, and magnet configuration, liquid phase velocities can be increased by several times compared to the baseline case.

Keywords: water electrolysis; Lorentz force; Particle Image Velocimetry

Publ.-Id: 18089

Numerical simulation of the Tayler instability in liquid metals

Weber, N.; Galindo, V.; Stefani, F.; Weier, T.; Wondrak, T.

The electrical current through an incompressible, viscous and resistive liquid conductor produces an azimuthal magnetic field that becomes unstable when the corresponding Hartmann number exceeds a critical value in the order of 20. This Tayler instability, which is not only discussed as a key ingredient of a non-linear stellar dynamo model (Tayler-Spruit dynamo), but also as a limiting factor for the maximum size of large liquid metal batteries, was recently observed experimentally in a column of a liquid metal.
On the basis of an integro-differential equation approach, we have developed a fully three-dimensional numerical code, and have utilized it for the simulation of the Tayler instability at typical viscosities and resistivities of liquid metals. The resulting growth rates are in good agreement with the experimental data. We illustrate the capabilities of the code for the detailed simulation of liquid metal battery problems in realistic geometries.

Keywords: Tayler instability; Biot-Savart; liquid metal battery

Publ.-Id: 18088

Volcanic glass under fire - A comparison of three complementary analytical methods

Eder, F. M.; Neelmeijer, C.; Pearce, N. J. G.; Bichler, M.; Sterba, J. H.; Ntaflos, T.; Merchel, S.

The two obsidian sources from the island of Melos (Greece), Agia Nychia and Demenegakion, are chemically characterized by three complementary analytical techniques. Ion beam analysis (IBA) comprising of particle induced X-ray emission (PIXE) and particle induced gamma-ray emission (PIGE), neutron activation analysis (NAA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are applied to the same set of geological obsidian samples.
The combination of methods allows a more complete characterisation of obsidian sources and reveals a highly specific chemical composition, the so-called chemical fingerprint. This multi-methodical approach checks also the self-consistency of the analytical results and shows the most reliable and characteristic key elements Co and Sc, but also Fe, Ca and Ti of Melos obsidian deposits. NAA contributes the largest number of reliable elements to the most unambiguous chemical fingerprint comprising in total of 41 elements. Therefore, NAA is the most suitable analytical method for a clear identification of Melos obsidian deposits.
Moreover, the accuracy of methods is demonstrated by the excellent correspondences (calculated correlation coefficient R2=1.00 for IBA and NAA, R2=0.99 for LA-ICP-MS) between determined analytical results obained by IBA, NAA and LA-ICP-MS and certified values of the reference glass BAM-S005B.

Keywords: PIXE; PIGE; neutron activation analysis; LA-ICP-MS

Related publications

Publ.-Id: 18087

Dual-Plane Ultrasound Flow Measurements in Liquid Metals

Büttner, L.; Nauber, R.; Burger, M.; Räbiger, D.; Franke, S.; Eckert, S.; Czarske, J.

An ultrasound measurement system for dual-plane, two-component flow velocity measure-ments especially in opaque liquids is presented.
Present-day techniques for measuring local flow structures in opaque liquids disclose consid-erable drawbacks concerning a line-wise measurement of single ultrasound probes. For study-ing time-varying flow patterns, conventional ultrasound techniques are either limited by a time-consuming mechanical traversing or by the sequential operation of single probes.
The measurement system presented within this paper employs 4 transducer arrays with a total of 100 single elements which allows for a flow-mapping without mechanical traversing. A high frame rate of several 10 Hz has been achieved due to an efficient parallelization scheme using time division multiplex realized by a microcontroller-controlled electronic switching matrix.
The functionality and capability of the measurement system is demonstrated at a liquid metal flow at room temperature inside a cube driven by a rotating magnetic field (RMF). For the first time, the primary and the secondary flow have been studied in detail and simultaneously using a configuration with two crossed measurement planes. The experimental data confirm predictions made by numeric simulation. After a sudden switching on of the RMF inertial oscillations of the secondary flow were observed by means of a time-resolved measurement with a frame rate of 3.4 Hz.
The experiments demonstrate that the presented measurement system is able to investigate complex and transient flow structures in opaque liquids. Due to its ability to study the tem-poral evolution of local flow structures, the measurement system could provide a considerable progress for fluid dynamics research, in particular for applications in the food industry or liq-uid metal technologies.

Keywords: ultrasound Doppler method; ultrasound sensor arrays; flow measurements; liquid metal flow; magnetohydrodynamics

Publ.-Id: 18086

Novel ultrasound array measurement system for flow mapping of complex liquid metal flows

Nauber, R.; Burger, M.; Büttner, L.; Franke, S.; Räbiger, D.; Eckert, S.; Czarske, J.

In magnetohydrodynamics, model experiments are commonly conducted to investigate the interaction between magnetic fields and electrically conductive fluids. The available flow instrumentation for opaque fluids usually lacks the ability to capture and visualize a velocity field in one shot. We present a multidimensional ultrasound array Doppler velocimeter that employs multiple line arrays of transducers and allows to resolve small scale structures in complex flows. The system archives a lateral resolution up to 3mm, an axial resolution of approx. 1:4mm and frame rates up to 30Hz in metal melts at room temperature. A flexible sensor arrangement allows for various measurement configurations, e.g. four planes can be measured simultaneously with one velocity component, two planes with two components or two lines with three components. We present an experiment in a square shaped container driven by a rotating magnetic field and results of a model experiment for continuous steel casting. The measurement system has proven to be a powerful tool for research in magnetohydrodynamics.

Publ.-Id: 18085

Carrier dynamics in graphene near the Dirac point

Helm, M.; Winnerl, S.; Mittendorff, M.; Schneider, H.; Winzer, T.; Malic, E.; Knorr, A.; Orlita, M.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.

We discuss pump-probe experiments on multilayer graphene over a wide range of photon energies (10-250 meV), hereby unveiling the relevant electronic relaxation mechanisms. A slowing down is observed for smaller photon energies and lower temperature, in accord with microscopic calculations. Remarkably we observe a sign change of the probe signal, when the photon energy becomes smaller than twice the Fermi energy. This crossover from induced bleaching to induced absorption is related to the interplay between inter- and intraband absorption. Applying an additional magnetic field we have recently measured the relaxation dynamics between Landau levels, showing a strong dependence on the circular polarization of the light.

Keywords: graphene; infrared; terahertz; free electron laser; relaxation; absorption

Related publications

  • Invited lecture (Conferences)
    Joint Dresden-Japan Workshop on Molecular Scale and Organic Electronic Materials, 11.-13.12.2012, Dresden, Deutschland

Publ.-Id: 18084

Cfd simulation of flashing boiling flow in the containment cooling condenser system of kerena reactor

Liao, Y.; Lucas, D.; Krepper, E.; Rzehak, R.

The KERENA™ reactor is a generation III+ BWR concept, which was originally proposed by AREVA and is currently being developed jointly by AREVA and German utility E.ON (AREVA, 2010). It aims to achieve a cost competitive plant with enhanced safety features and an optimal BWR balance of active and passive safety systems. The containment cooling condensers (CCC) belong to such kind of passive features, which require neither electric power nor switching operations to begin functioning. The CCC unity is connected to a shielding/storage pool, which is located above it, via an inlet to the lower end and a discharge line at the upper end. In case of overpressure or overtemperature, steam in the containment will condense at the outside wall of the condensers. Heat released by steam will be transferred to the cooling water inside the tubes. As it is heated, the cooling water will remove heat from the containment to the water of the shielding/storage pool through a natural circulation.

The performance of the complete CCC system has been investigated experimentally on the full-scale INKA test facility of AREVA in Karlstein (Leyer and Wich, 2012). During the experiment, strong flow instability or water hammer caused by the formation and subsequent destruction of steam bubbles inside the discharge line was observed. In other words, the formation of steam will have a significant influence on the safety operation and heat removal capacity of the system, which requires further investigation. In this case, the mechanism of phase change from water to steam is different from that of the traditional boiling as a result of wall heating. Due to the elevation difference between the CCC and the upper end of the discharge line, which is about 12 m, the drop of hydrostatic pressure along the discharge line exceeds 1bar. The formation of steam is a result of depressurization instead of wall-heating, which is called flashing boiling in contrast to the traditional boiling.

Keywords: KERENA™ reactor; Containment Cooling Condensers (CCC); Flashing boiling; CFD simulation

  • Open Access Logo Contribution to proceedings
    21st International Conference On Nuclear Engineering, 29.07.-02.08.2013, Chengdu, China
    Proceedings of the 21st International Conference On Nuclear Engineering
  • Lecture (Conference)
    21st International Conference On Nuclear Engineering, 29.07.-02.08.2013, Chengdu, China

Publ.-Id: 18083

Cfd simulation of water evaporation under pressure release transients

Liao, Y.; Lucas, D.; Krepper, E.; Rzehak, R.

Water evaporation (flashing) inside a vertical pipe under pressure release transients is investigated by CFD simulations based on the Eulerian two-fluid model. Important assumptions made in the current work are: a) constant bubble diameter; b) no nucleation and c) mass transfer caused only by thermal heat transfer between phases. The predicted evolution of steam volume fraction and water temperature is compared with the measured one, respectively. The results show that the applied model setup in principle can reproduce the flashing process. Whether the evaporation of superheated water can start depends on the initial guess of steam volume fraction and especially the presumed bubble size. A large initial steam volume fraction and a small bubble size will favor the inception of evaporation. Once the flashing is successfully triggered, the maximum evaporated steam is determined by the pressure drop ultimately. Furthermore, the increase of steam volume fraction per unit evaporated mass reduces drastically at high pressure levels due to a large steam to water density ratio. As a result, a relatively small value has to be presumed for bubble size under high pressure conditions in order to launch the evaporation. In addition, the predicted maximum steam volume fraction at a pressure of 65bar is much lower than the measured one. In this case besides the interphase thermal heat transfer consideration of nucleation and bubble growth due to mechanical non-equilibrium across the interface might be helpful.

Keywords: Flashing; Evaporation; CFD; Two-Fluid Model; Mono-dispersed

  • Open Access Logo Contribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH15, 12.-17.05.2013, Pisa, Italy
  • Lecture (Conference)
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH15, 12.-17.05.2013, Pisa, Italy

Publ.-Id: 18082

Few Femtosecond level electron bunch diagnostic at quasi-cw electron accelerators

Green, B.; Kuntzsch, M.; Kovalev, S.; Al-Shemmary, A.; Hauser, J.; Findeisen, S.; Schneider, C.; Kaya, C.; Stojanovic, N.; Michel, P.; Gensch, M.

At the SRF based prototype cw accelerator ELBE a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1-200 KHz regime and with pC bunch charge and repetition rates of 13 MHz, is currently being constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class lasers and the generation of broad and narrow bandwidth coherent THz pulses. Discussed here are ideas for novel online diagnostics of the electron bunch properties (e.g. arrival time and bunch form) based on the time and frequency domain analysis of the emitted coherent THz radiation, but also based on direct measurements by e.g. electro-optic sampling. The suitability of ELBE as a testbed for diagnostic of future cw X-ray photon sources (e.g. energy recovery linacs) will be discussed.

Related publications

  • Poster
    77. Jahrestagung der DPG und DPG Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18081

TELBE - the super-radiant THz test-facility at ELBE

Green, B.; Kovalev, S.; Hauser, J.; Kuntzsch, M.; Al-Shemmary, A.; Schneider, H.; Winnerl, S.; Seidel, W.; Zvyagin, S.; Wall, S.; Radu, I.; Eng, L. M.; Lehnert, U.; Helm, M.; Stojanovic, N.; Heberle, J.; Cavalleri, A.; Michel, P.; Gensch, M.

It has been shown recently that relativistic electron bunches can be utilized for the generation of super-radiant coherent THz radiation by one single pass through an undulator, bending magnet, or CDR/CTR screens. However, the high THz fields have all been achieved at large accelerators that allow for high electron beam energies. A crucially important research topic for the next years at the HZDR is therefore to investigate whether an equally fine control over highly charged electron bunch form can be routinely achieved in a low electron beam energy accelerator like ELBE. If successful this development would allow the generation of high field THz fields by linear accelerators at considerably reduced cost. Given stable operation can be provided, TELBE, could also become a world-wide unique research facility for high field THz science. The current status and an outlook on future developments are presented.

Related publications

  • Poster
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18080

Novel Drift compensation for a femtosecond laser system at a quasi-cw electron accelerator

Green, B.; Kuntzsch, M.; Kovalev, S.; Gensch, M.

A method for electron beam/THz to femtosecond (fs) - laser synchronization drift correction at the quasi-cw linear electron accelerator ELBE is presented, which is utilizing THz radiation generated by a CDR/CTR screen and an undulator respectively. Measurements of these pulses will allow for compensation of slow drifts in the arrival time on millisecond timescales between the THz and the fs-laser pulses. The method requires two electro-optic detection setups which allow for the sampling of a single THz pulse, at two different working points. Given a consistent pulse shape these two data points can provide information on the sign of the arrival time drift relative to the laser. This information can be used both for providing feedback on fs laser arrival time in a potential THz time domain experiment as well as the electron bunch arrival time in the accelerator.

Related publications

  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Germany

Publ.-Id: 18079

Driving magnetization dynamics via mid-infrared phonon excitation

Mährlein, S.; Radu, I.; Gensch, M.; Kimel, A.; Kalashnikova, A.; Kampfratth, T.; Wolf, M.

The fundamental interactions between electrons, spins and the lattice of a solid have always been subject of large scientific interest. Here, we investigate the coupling between phonons and the ordered spin system of ferrimagnetic oxides on ultrashort time scales, an elusive and actively debated issue of modern ultrafast magnetism.
For this purpose, we use intense electromagnetic pulses at terahertz (THz) frequencies, from both table-top and accelerator-based sources, to resonantly excite a specific phonon mode. The impact of this vibrational excitation on the spin system is monitored by detecting the transient Faraday rotation of a subsequently arriving optical probe pulse. As such, we obtain access to the magnetization dynamics with a time resolution of down to 10fs.
These mode-selective pumping experiments show a response of the spin system on a timescale of few picoseconds and thus indicate an (ultra)fast spin-lattice interaction. The possible underlying coupling mechanisms will be discussed.

Related publications

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18078

Analysis and Applications of a Two-Fluid Multi-Field Hydrodynamic Model for Churn-Turbulent Flows

Montoya, G.; Liao, Y.; Lucas, D.; Krepper, E.

Today Computational Fluid Dynamic (CFD) codes are widely used for industrial applications in the case of single phase flows as in automotive or aircraft industries, but multiphase flow modeling had gain an increasing importance in the last years. Safety analyses on nuclear power plants require reliable prediction on steam-water flows in case of different accident scenarios. This is particularly true for passive safety systems as the GEKO component of the KERENA reactor. Here flashing may occur in the riser. In such a case high gas volume fractions and the churn-turbulent flow regime may occur. So far, the codes for the prediction of churn-regime have not shown a very promising behavior in the past. In this paper, a two-fluid multi-field hydrodynamic model has been developed based in the Euler-Euler framework. The main emphasis of this work has been on the modeling and applicability of various interfacial forces between dispersed gaseous phases and the continuous liquid, as well as bubble-bubble interactions, and the evolution of different bubble sizes in an adiabatic vertical pipe inside the churn-turbulent flow regime. All the expected mechanistic models that intervene in this flow pattern have been taken into account including drag force, wall force, lift force, turbulent dispersion, and bubble induced turbulence. Bubble breakup and coalescence has been defined (Liao et al., 2011), and in order to design a polydispersed model related to reality, the inhomogeneous MUSIG approach (Krepper et al., 2008) has been used to defined an adequate number of bubble size fractions, each with their own velocity field. Based on these models, a series of simulations were made on the framework of ANSYS CFX 14.0, and all of the calculations were further validated with experimental data extracted from the TOPFLOW facility at the Helmholtz-Zentrum Dresden-Rossendorf. Different water and gas flow rates were used inside the churn-turbulent flow regime, as well as for the transition from bubbly to churn flow. The calculated cross-section averaged bubble size distributions, gas velocities, and time averaged radial profile for the gas fraction have shown a promising agreement with the experimental data. Nevertheless there are also clear deviations which indicate shortcomings of the present modelling. In order to further improve the modeling of this flow regime, a discussion based on the results will be used to shown a series of limitations of the actual modeling and possible solutions to be implemented in future works.

Best Paper Award

Keywords: Computational; Fluid; Dynamics; CFD; churn-turbulent; flow; GEKO; KERENA; safety; nuclear; Euler-Euler; MUSIG; TOPFLOW; churn

  • Contribution to proceedings
    21st International Conference on Nuclear Engineering - ICONE 21, 29.07.-02.08.2013, Chengdu, China
    Proceedings of the 21st International Conference on Nuclear Engineering (ICONE 21)
  • Poster
    21st International Conference on Nuclear Engineering - ICONE 21, 29.07.-02.08.2013, Chengdu, China
  • Lecture (Conference)
    21st International Conference on Nuclear Engineering - ICONE 21, 29.07.-02.08.2013, Chengdu, China

Publ.-Id: 18077

Free-electron laser spectroscopy of quantum well exciton dynamics

Schneider, H.; Bhattacharyya, J.; Zybell, S.; Winnerl, S.; Helm, M.; Andrews, A. M.; Strasser, G.; Köhler, K.

We report on time-resolved photoluminescence of excitons and electron-hole plasma in GaAs quantum wells under intraband excitation by a free-electron laser in resonance with intersubband and intraexcitonic transitions, respectively, to study relaxation and intraexcitonic scattering.

Keywords: Quantum well excitons; GaAs/AlGaAs; free-electron laser spectroscopy

Related publications

  • Lecture (Conference)
    37th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THZ 2012), 23.-28.09.2012, Wollongong, Australien

Publ.-Id: 18076

Coherent spin wave emission from magnetic vortex cores

Wintz, S.; Erbe, A.; Lindner, J.; Weigand, M.; Stoll, H.; Schütz, G.; Raabe, J.; Quitmann, C.; Tyberkevych, V.; Slavin, A.; Fassbender, J.

Spin wave phenomena are an intensely studied field of magnetism, ranging from fundamental magnonics to possible spin wave applications in logic or oscillator devices. In particular, the propagation of nanoscopic spin waves has come into focus. Typically, micro-striplines or point-contacts are used to excite such spin waves in ferromagnetic media. A real-space observation of nanoscopic spin wave propagation, however, has not been reported yet. On this background we present the direct imaging of spin wave propagation as well as a novel concept for their coherent generation based on the dynamics of interlayer coupled magnetic vortex pairs.

Keywords: spin waves; vortex

  • Lecture (Conference)
    The 8th International Symposium on Magnetic Multilayers (MML) 2013, 19.-24.05.2013, Kyoto, Japan

Publ.-Id: 18075

Theoretical and Practical HOM-Analysis of the Rossendorf SRF-Gun

Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.

In SRF guns, multi-bunch effects of higher order modes (HOM​​) and their influence on beam quality are of particular interest. For this reason a method is presented that considers the accelerated motion of non-relativistic electrons to calculate their coupling impedances. The results are compared with first beam-based measurements and used to discuss a new method for HOM suppression.

Keywords: SRF gun; Higher Order Modes; coupling impedances

Related publications

  • Poster
    26th International Linear Accelerator Conference, LINAC12, 09.-14.09.2012, Tel Aviv, Israel

Publ.-Id: 18074

Simulation of RUTA-70 reactor with CERMET fuel using DYN3D/ATHLET and DYN3D/RELAP5 coupled codes

Kozmenkov, Y.; Rohde, U.; Baranaev, Y.; Glebov, A.

RUTA-70 model for simulations with the internally coupled codes DYN3D/ATHLET and DYN3D/RELAP5 was developed. A 3-D power distribution in the core is calculated by DYN3D with thermal-hydraulic feedback from the system codes. A steady-state corresponding to the full reactor power and an accident scenario initiated by failure of all primary coolant pumps were simulated with the DYN3D/ATHLET and DYN3D/RELAP5 coupled code systems to verify these codes.

The compared coupled codes give close predictions for the initial and final states of the simulated accident but not for the transition between them. The observed deviations are explained by differences in the subcooled boiling models of the employed versions of ATHLET and RELAP5. Nevertheless, both simulations confirm a high level of the reactor inherent safety. The allowed safety margins were not reached.

Keywords: pool type reactor; low pressure; coupled codes; accident analysis; 3D neutron kinetics; subcooled boiling model; reactor safety

  • Kerntechnik 77(2012)4, 249-257

Publ.-Id: 18073

Deliverable navigation for multicriteria step and shoot IMRT treatment planning

Craft, D.; Richter, C.

We consider Pareto surface based multi-criteria optimization for step and shoot IMRT planning. By analyzing two navigation algorithms, we show both theoretically and in practice that the number of plans needed to form convex combinations of plans during navigation can be kept small (much less than the theoretical maximum number needed in general, which is equal to the number of objectives for on-surface Pareto navigation). Therefore a workable approach for directly deliverable navigation in this setting is to segment the underlying Pareto surface plans and then enforce the mild restriction that only a small number of these plans are active at any time during plan navigation, thus limiting the total number of segments used in the final plan.

Publ.-Id: 18071

Study of lifetimes and photoconductivity relaxation in heterostructures with Hg (x) Cd1-x Te/Cd (y) Hg1-y Te quantum wells

Morozov, S.; Joludev, M.; Antonov, A.; Rumyantsev, V.; Gavrilenko, V.; Aleshkin, V.; Dubinov, A.; Mikhailov, N.; Dvoretskiy, S.; Drachenko, O.; Winnerl, S.; Schneider, H.; Helm, M.

Carrier lifetimes in the continuum of the quantum well of a Hg (x) Cd1 - x Te/Cd (y) Hg1 - y Te hetero-structure were studied by terahertz pump-probe spectroscopy. It is found that the relaxation duration of the transmission signal is similar to 65 ps and is independent of the pump power. Such rapid relaxation in these structures is most likely determined by the interaction of holes with acoustic phonons due to a high density of states in the valence band and a larger effective mass compared with electrons. By the obtained data, the times of the interband nonradiative recombination of holes are determined. In this publication, we report the results of numerical calculation of the energy spectrum of the model structure, in which the possibility of obtaining population inversion at specified concentrations of nonequilibrium carriers is analyzed.

Keywords: Relaxation time; HgTe; topological insulator; pump-probe

Related publications

Publ.-Id: 18070

Modelling and analysis of severe accidents for VVER-1000 reactors

Tusheva, P.

Accident conditions involving significant core degradation are termed severe accidents /IAEA:

NS-G-2.15/. Despite the low probability of occurrence of such events, the investigation of severe accident scenarios is an important part of the nuclear safety research. Considering a hypothetical core melt down scenario in a VVER-1000 light water reactor, the early in-vessel phase focusing on the thermal-hydraulic phenomena, and the late in-vessel phase focusing on the melt relocation into the reactor pressure vessel (RPV) lower head, are investigated.

The objective of this work is the assessment of severe accident management procedures for VVER-1000 reactors, i.e. the estimation of the maximum period of time available for taking appropriate measures and particular decisions by the plant personnel. During high pressure severe accident sequences it is of prime importance to depressurize the primary circuit in order to allow for effective injection from the emergency core cooling systems and to avoid reactor pressure vessel failure at high pressure that could cause direct containment heating and subsequent challenge to the containment structure. Therefore different accident management measures were investigated for the in-vessel phase of a hypothetical station blackout accident using the severe accident code ASTEC, the mechanistic code ATHLET and the multi-purpose code system ANSYS.

The analyses performed on the PHEBUS ISP-46 experiment, as well as simulations of small break loss of coolant accident and station blackout scenarios were used to contribute to the validation and improvement of the integral severe accident code ASTEC. Investigations on the applicability and the effectiveness of accident management procedures in the preventive domain, as well as detailed analyses on the thermal-hydraulic phenomena during the early in-vessel phase of a station blackout accident have been performed with the mechanistic code ATHLET. The results of the simulations show, that the effectiveness of the procedures strongly depends on the ability of the passive safety systems to inject as much water as possible into the reactor coolant system.

The results on the early in-vessel phase have shown potentially delayed RPV failure by depressurization of the primary side, as slowing the core damage gives more time and different possibilities for operator interventions to recover systems and to mitigate or terminate the accident. The ANSYS model for the description of the molten pool behaviour in the RPV lower plenum has been extended by a model considering a stratified molten pool configuration. Two different pool configurations were analysed: homogeneous and segregated. The possible failure modes of the RPV and the time to failure were investigated to assess the possible loadings on the containment. The main treated issues are: the temperature field within the corium pool and the RPV and the structure-mechanical behaviour of the vessel wall.

The results of the ASTEC calculations of the melt pool configuration were applied as initial conditions for the ANSYS simulations, allowing a more detailed and more accurate modelling of the thermal and mechanical behaviour of the core melt and the RPV wall.

Moreover, for the late in-vessel phase, retention of the corium in the RPV was investigated presuming external cooling of the vessel wall as mitigative severe accident management measure. The study was based on the finite element computer code ANSYS. The highest thermomechanical loads are observed in the transition zone between the elliptical and the vertical vessel wall for homogeneous pool and in the vertical part of the vessel wall, which is in contact with the molten metal in case of sub-oxidized pool. Assuming external flooding will retain the corium within the RPV. Without flooding, the vessel wall will fail, as the necessary temperature for a balanced heat release from the external surface via radiation is near to or above the melting point of the steel.

Keywords: severe accidents; analysis; VVER-1000; reactors; ASTEC; ATHLET; ANSYS; accident management

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-025 2012
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 18069

Investigation of the Dipole Response in Exotic Nuclei – Experiments at the LAND-R3B Setup

Rossi, D. M.; Adrich, P.; Aksouh, F.; Alvarez-Pol, H.; Aumann, T.; Benlliure, J.; Boehmer, M.; Boretzky, K.; Casarejos, E.; Chartier, M.; Chatillon, A.; Cortina-Gil, D.; Pramanik, U. D.; Emling, H.; Ershova, O.; Fernando-Dominguez, B.; Geissel, H.; Gorska, M.; Heil, M.; Johansson, H.; Junghans, A.; Kiselev, O.; Klimkiewicz, A.; Kratz, J. V.; Kurz, N.; Labiche, M.; Le Bleis, T.; Lemmon, R.; Litvinov, Y. A.; Mahata, K.; Maierbeck, P.; Movsesyan, A.; Nilsson, T.; Nociforo, C.; Palit, R.; Paschalis, S.; Plag, R.; Reifarth, R.; Simon, H.; Suemmerer, K.; Wagner, A.; Walus, W.; Weick, H.; Winkler, M.

We present experimental results on the electromagnetic excitation of neutron-rich nickel isotopes, making use of the R3B-LAND setup at GSI. Exotic beams were produced at approximately 500 MeV/u and their reactions were studied in inverse kinematics. Integral cross sections for 58Ni are discussed and compared to previous data, providing a validation of our experimental method. The E1 excitation-energy distribution of the unstable 68Ni is presented as well, showing an excess in cross section in the 1n decay channel when compared only with a typical Giant Dipole Resonance.

  • Open Access Logo Progress in Theoretical Physics Supplement 196(2012), 465-470
    DOI: 10.1143/PTPS.196.465
    ISSN: 0375-9687

Publ.-Id: 18068

Experimental and numerical modelling of the fluid flow in the continuous casting of steel

Timmel, K.; Miao, X.; Wondrak, T.; Stefani, F.; Lucas, D.; Eckert, S.; Gerbeth, G.

This article gives an overview about the recent research activities with respect to the mould flow in the continuous casting of steel in presence of DC magnetic fields. The magnetic fields appear to be an attractive tool for controlling the melt flow in a contactless way. Various kinds of magnetic systems are already in operation in industrial steel casting, but the actual impact on the melt flow has not been sufficiently verified by experimental studies. The rapid development of innovative diagnostic techniques in low-melting liquid metals over the last two decades enables new possibilities for systematic flow measurements in liquid metal model experiments. A new research program was initiated at HZDR comprising three experimental facilities providing a LIquid Metal Model for continuous CASTing of steel (LIMMCAST). The facilities operate in a temperature range from room temperature up to 400°C using the low-melting alloys GaInSn and SnBi, respectively. The experimental program is focused on quantitative flow measurements in the mould, the submerged entry nozzle and the tundish. Local potential probes, the Ultrasonic Doppler Velocimetry (UDV) and the Contactless Inductive Flow Tomography (CIFT) are employed to measure the melt flow. The behaviour of two-phase flows in case of argon injection is investigated by means of the Mutual Inductance Tomography (MIT) and the X-ray radioscopy. The experimental results provide a substantial data basis for the validation of related numerical simulations. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. First results of the LIMMCAST program reveal important findings such as the peculiar, unexpected phenomenon that the application of a DC magnetic field may excitate non-steady, non-isotropic large-scale flow oscillations in the mould. Another important result of our study is the feature that the electrical boundary conditions, namely the wall conductivity ratio, have a serious influence on the mould flow while it is exposed to an external magnetic field.

Keywords: Mini-Review; continuous steel casting; liquid metal model; electromagnetic brake; turbulence model

  • European Physical Journal - Special Topics 220(2013), 151-166
    DOI: 10.1140/epjst/e2013-01804-5
    ISSN: 1951-6355
    Cited 12 times in Scopus
  • Lecture (Conference)
    The International Symposium on Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry, 25.-27.03.2013, Dresden, Deutschland

Publ.-Id: 18067

Generation and application of channeling X-rays using a novel, low-emittance electron beam - Status and plans

Gabella, W. E.; Brau, C. A.; Choi, B. K.; Ivanov, B.; Jarvis, J. D.; Mendenhall, M. H.; Piot, P.; Mihalcea, D.; Carrigan, R.; Wagner, W.

We plan to use very small emittance electron beams created from our novel, single tip cathodes to make a channeling-radiation X-ray source for X-ray imaging, especially phase contrast imaging. We calculate that we can preserve the electron emittance from the source to the crystal , and focus to a 40 nm spot on the crystal face for 40 MeV electrons.

Keywords: cathode; channeling; channeling radiation; X-rays; phase contrast imaging

Publ.-Id: 18066

Positron energy distributions from a hybrid positron source based on channeling radiation

Azadegan, B.; Mahdipour, A.; Dabagov, S. B.; Wagner, W.

A hybrid positron source which is based on the generation of channeling radiation by relativistic electrons channeled along different crystallographic planes and axes of a tungsten single crystal and subsequent conversion of radiation into e+e- -pairs in an amorphous tungsten target is described. The photon spectra of channeling radiation are calculated using the Doyle-Turner approximation for the continuum potentials and classical equations of motion for channeled particles to obtain their trajectories, velocities and accelerations. The spectral-angular distributions of channeling radiation are found applying classical electrodynamics. Finally, the conversion of radiation into e+e- -pairs and the energy distributions of positrons are simulated using the GEANT4 package.

Keywords: positron; positron source; channeling radiation

Publ.-Id: 18065

Cr segregation on dislocation loops enhances hardening in ferritic Fe–Cr alloys

Terentyev, D.; Bergner, F.; Osetsky, Y.

The effect of chromium on iron hardening via segregation on dislocation loops was studied by atomic scale computer modeling. A combination of Monte Carlo and molecular dynamics techniques together with the recently determined Fe–Cr interatomic potentials fitted to ab initio data was used to investigate Cr segregation on ½<111> interstitial dislocation loops and its impact on the interaction with moving dislocations. The Monte Carlo results reveal that Cr atoms segregate to the loop tensile strain region and dissolve well above the temperature corresponding to the solubility limit. The molecular dynamics results demonstrated that local micro-chemical changes near the loop reduce its mobility and increase the strength. The stress to move a dislocation through the array of Cr "decorated" loops increases due to modification of the dislocation–loop interaction mechanism. A possible explanation for a number of experimental observations being dependent on the radiation dose and for Cr concentration effects on the yield stress is given on the basis of the modeling results.

Keywords: bcc metals; Dislocation loops; Hardening; Segregation

Publ.-Id: 18064

Radiosynthesis and first evaluation in mice of [18F]NS14490 for molecular imaging of α7 nicotinic acetylcholine receptors

Rötering, S.; Scheunemann, M.; Fischer, S.; Hiller, A.; Peters, D.; Deuther-Conrad, W.; Brust, P.

[18F]NS14490, a new potential radiotracer for neuroimaging of α7 nicotinic acetylcholine receptors (α7 nAChRs), was synthesized and evaluated in vitro and in vivo. Radioligand binding studies using [3H]methyllycaconitine and NS14490 as competitor showed a good target affinity (Kiα7= 2.5 nM) and a high selectivity towards other nAChR. Radiosynthesis of [18F]NS14490 was performed by two different labelling procedures: a two-step synthesis using a prosthetic group, which led to 7% labelling yield, and the convenient direct nucleophilic substitution of the corresponding tosylate precursor, which resulted in 70% labelling yield. After optimisation of the isolation, purification and formulation process, biodistribution studies were performed in CD-1 mice. The brain uptake of [18F]NS14490 was comparably low (0.16% ID g-1 wet weight at 5 min p.i.). The radiotracer showed a high metabolic stability in plasma and brain. Also, the target specificity was proven by pre-administration of a highly affine α7 ligand providing a rationale basis for further in vivo evaluation.

Keywords: Radiotracer; 1,4-diazabicyclo[3.2.2]nonane; Alpha 7 nicotinic Acetylcholine Receptors; Positron Emission Tomography; Neuroimaging; Neurodegeneration; Mice

Publ.-Id: 18063

Radiolabelling of engineered nanoparticles – different strategies for Ag0-NP, TiO2-NP and MWCNT

Schymura, S.; Hildebrand, H.; Cydzik, I.; Simonelli, F.; Bulgheroni, A.; Holzwarth, U.; Kozempel, J.; Freyer, A.; Bilz, E.; Gibson, N.; Franke, K.

Here we present different strategies for the radiolaneling of nanoparticles such as Ag(0), TiO2 and carbon nanotubes. In particular we show the diffusion of radionuclides into Ag(0) and TiO2 nanoparticles, the direct activation of nanoparticles by proton irradiation using a cyclotron, the implantation of Be-7 into nanoparticles by the recoil of the nuclear reaction Li-7(p,n)Be-7 and the radioiodination of carbon nanotubes.
All the methods were characterized with repsect to yield, radiolabel stability and possible change of nanoparticle properties.

  • Lecture (Conference)
    Cycleur Meeting 2012, 28.-30.11.2012, Ispra, Italien

Publ.-Id: 18062

Colloidal stability of modified carbon nanotubes

Schymura, S.; Weiß, S.; Zänker, H.; Franke, K.

The implications of a carbon nanotube (CNT) release into the environment are majorly influenced by the colloidal stability of the CNTs in surface or ground waters. A main factor for this stability is the degree of oxidation of the CNTs. Pristine CNTs show very low dispersion stability in water and quickly aggregate and sediment. However, oxidation processes are expected to happen in the environment or are deliberately performed on the CNTs, for better dispersability in technical applications prior to the possible release.
For this study samples of different types of CNTs, multi wall as well as single wall CNTs, were oxidized by a microwave assisted acid treatment with concentrated nitric and sulphuric acid, which allowed a fast reproducible modification of the CNTs. The modification was verified by IR and Raman spectroscopy, thermogravimetric analysis and measurements of the iso-electric point.
The colloidal stability of the so modified CNTs was investigated using dynamic light scattering methods to follow the aggregation and sedimentation of the CNTs as well as establishing the zeta potential of the modified CNTs in waters of different ionic strength.
The colloidal stability of the CNTs in distilled and low ionic strength water exceeds months. This has implications for their transport behaviour upon release into the environment. A transport of CNTs in surface and ground waters can be expected under certain conditions.

  • Poster
    Nanosafe 2012, 13.-15.11.2012, Grenoble, Frankreich

Publ.-Id: 18061

Strategies for the radiolabelling of carbon nanoparticles

Schymura, S.; Cydzik, I.; Bulgheroni, A.; Simonelli, F.; Holzwarth, U.; Kozempel, J.; Franke, K.; Gibson, J.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories a careful risk assessment of their release into the environment becomes mandatory. However the monitoring of nanoparticles in such complex natural systems as geological formations or ground water is nearly impossible using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research. We present here different radiolabelling strategies for carbon nanoparticles, in particular carbon nanotubes (CNTs) whose intriguing physical properties predestine them for widespread application, so that future release into the environment is to be expected.
We have developed three different approaches for the radiolabelling of CNTs. The first is the iodination of carbon nanotubes using radioactive iodine, e.g. I-125 or I-131. Using the Iodogen method known from protein labelling strategies it is possible to radiolabel single- and multi-wall CNTs by binding radioactive iodine on the CNT side wall.
The other strategies involve proton irradiation using a cyclotron and cause the incorporation of radioactive beryllium in between the layers of multi-wall CNTs. The first option is to directly activate carbon by high-energy proton irradiation (> 34 MeV), which causes a (p,3d) nuclear reaction creating Be-7, which intercalates between the graphitic layers of the CNT. The second option is to mix the CNTs with a lithium containing compound like LiH and irradiate at a much lower proton energy to create Be-7 via the (p,n) reaction on Li. The recoil of the Be-7 from the nuclear reaction causes the incorporation of the radiotracer into the structure of multi-wall CNTs.
The methods were tested for labeling yield, achievable activity concentration, pH-dependent stability of the labeling and the influence on NP-properties. Data thus obtained enables the selection of a radiolabeling method appropriate for different experimental conditions.

Keywords: carbon nanoparticles; radiolabelling

  • Lecture (Conference)
    Nanosafe 2012, 13.-15.11.2012, Grenoble, Frankreich

Publ.-Id: 18060

Coulomb excitation of exotic nuclei at the R3B-LAND setup

Rossi, D. M.; Adrich, P.; Aksouh, F.; Alvarez-Pol, H.; Aumann, T.; Benlliure, J.; Böhmer, M.; Boretzky, K.; Casarejos, E.; Chartier, M.; Chatillon, A.; Cortina-Gil, D.; Datta Pramanik, U.; Emling, H.; Ershova, O.; Fernandez-Dominguez, B.; Geissel, H.; Gorska, M.; Heil, M.; Johansson, H.; Junghans, A.; Kiselev, O.; Klimkiewicz, A.; Kratz, J. V.; Kurz, N.; Labiche, M.; Le Bleis, T.; Lemmon, R.; Litvinov, Y. A.; Mahata, K.; Maierbeck, P.; Movsesyan, A.; Nilsson, T.; Nociforo, C.; Palit, R.; Paschalis, S.; Plag, R.; Reifarth, R.; Simon, H.; Sümmerer, K.; Wagner, A.; Walus, W.; Weick, H.; Winkler, M.

Exotic Ni isotopes have been measured at the R3B-LAND setup at GSI in Darmstadt, using Coulomb excitation in inverse kinematics at beam energies around 500 MeV/u. As the experimental setup allows kinematically complete measurements, the excitation energy was reconstructed using the invariant mass method. The GDR and additional low-lying strength have been observed in 68Ni, the latter exhausting 4.1(1.9)% of the E1 energy-weighted sum rule. Also, the branching ratio for the non-statistical decay of the excited 68Ni nuclei was measured and amounts to 24(4)%.

Keywords: Exotic isotopes R3B LAND GSI Coulomb excitation inverse kinematics GDR PDR

Publ.-Id: 18059

Chimney Formation in Solidifying Ga-25wt%In Alloys under the Influence of Thermosolutal Melt Convection

Shevchenko, N.; Boden, S.; Gerbeth, G.; Eckert, S.

The directional solidification of Ga-25wt%In alloys within a Hele-Shaw cell under the influence of thermo-solutal convection was observed by means of X-ray radioscopy. The unstable density stratification at the solidification front causes the formation of rising plumes containing solute-rich liquids. The development of the chimneys and the probability of their surviving depend sensitively on the spatial and temporal properties of the flow field. Variations of the vertical temperature gradient along the solidification cell lead to the observation of different mechanisms for chimney formation. Perturbations of the dendritic structure are the origin of development of segregation freckles in case of low temperature gradients. The long-term stability of these segregation channels is strongly influenced by the transient nature of the melt convection. The situation at higher temperature gradients is characterized by two dominating convection rolls in the liquid phase which are driven by a lateral temperature gradient and the convex shape of the solidification front. The penetration of this flow pattern into the mushy zone results in continuous accumulation of solute in the central part of the mushy zone followed by a remelting of the solid fraction and the occurrence of a stable chimney.

Keywords: directional solidification; X-ray radioscopy; segregation freckles; chimneys; melt convection; plumes

Publ.-Id: 18058

Joint consistent mapping of high-dimensional geochemical surveys

Tolosana-Delgado, R.; van den Boogaart, K. G.

Interpolated maps of compositional variables (in wt\% or ppm) should guarantee that results give a consistent composition: i.e., at any location, all variables must be positive and sum up to 100\%, and should preserve certain geochemical links. (Co)kriging after a normal score transformation is a common choice, though it does not ensure honoring any positivity, constant sum or geochemical constraints. Moreover, it requires a huge effort of consistent modeling of (cross-)variograms. A more suitable way is the application of log-ratio techniques. A D-component system can be univocally expressed with (D-1) log-ratios (e.g., the additive logratio transformation with common denominator TiO2). Any one-to-one logratio transformation can be applied to sampled data; variograms can be estimated for logratio scores; and cokriging can be applied. Back-transformed interpolated scores map the original system components. Consistently modeled cross-variograms provide the same interpolated compositions whatever logratio transformation is used. However, compositional variograms are best modeled through variation-variograms, the set of direct variograms of all possible logratios of two components. They carry the same information, and can be modeled in the same way, as a full set of direct and cross-variograms of any logratio transformation, but they have several advantages for computation and interpretation. First, being positive functions, logarithmic goodness-of-fit criteria can be used, which give more importance to shorter distances (influencing the interpolation itself) than to the sill, prone to larger fluctuations. Second, they can be estimated with a minimum of complete observations; zeros, missing values, values below detection limit and other irregular data have thus much less influence. Third, using ratios of components, systematic differences might be filtered out. This is important in large geochemical surveys, where all samples may have not been treated in the same labs with the same analytical techniques. Fourth and last, the fitted LMC can be rank-deficient. This allows to obtain all component maps just cokriging a few individual factors and combining them together (compositional factorial cokriging). These procedures are illustrated with the horizon C Kola data set, with 25 components and 605 samples covering most of the Kola peninsula (Finland, Norway, Russia).

Keywords: isometric logratio transformation; geostatistics; ilr; clr; BLUE

Publ.-Id: 18057

Prototyping a 2m x 0.5m MRPC-based neutron TOF-wall with steel converter plates

Röder, M.; Aumann, T.; Bemmerer, D.; Boretzky, K.; Caesar, C.; Cowan, T. E.; Hehner, J.; Heil, M.; Elekes, Z.; Kempe, M.; Maroussov, V.; Reinhardt, T. P.; Simon, H.; Sobiella, M.; Stach, D.; Wagner, A.; Wüstenfeld, J.; Yakorev, D.; Zilges, A.; Zuber, K.; for the R3B Collaboration

A 2m x 0.5m large prototype of an MRPC-based (Multi-gap Resistive Plate Chamber) neutron Time-Of-Flight-wall for detecting relativistic neutrons in an energy range from 200MeV to 1 GeV was successfully designed and realized. It consists of steel plates which convert neutrons via hadronic interactions into charged particles, followed by a 2x2 gap MRPC-structure to detect the charged particles. Tests were carried out using 30MeV electrons with an energy close to the minimum of ionization in order to study the properties of the prototype achieving an efficiency larger than 90% and a time resolution better than 100 ps. For units with an active area of 40 cm x 20 cm and otherwise the same design, quasi-monochromatic neutrons with a peak energy of 175MeV were utilized to study their response to relativistic neutrons. Detailed montecarlo simulations were performed both for the small and for the large modules to simulate their properties to both neutrons and electrons and to study the performance of the final neutron detector assembly with an area of 2m x 2m for single-neutron and multi-neutron events.

Keywords: Resistive-plate chambers; Instrumentation and methods for time-of-flight (TOF) spectroscopy; Neutron detectors (cold and thermal and fast neutrons); Detector modelling and simulations I

Related publications

Publ.-Id: 18056

Evidence of formation of AlPO4 tridymite in some municipal sewage sludge ashes

Peplinski, B.; Adam, C.; Adamczyk, B.; Müller, R.; Schadrack, R.; Michaelis, M.; Emmerling, F.; Reuther, H.; Menzel, M.

Sewage sludge ashes (SSAs) are valuable raw materials (high P-content of up to 11 wt%; ca. 600,000 tons per year in the EU). For the conversion of sewage sludge into SSA fluidized bed incinerators are used. The aim of the present study is to test whether that finding is also relevant for a considerably different SSA, which was produced at a differently operated fluidized bed incineration facility in another municipality.

  • Poster
    European Powder Diffraction Conference 13 (EPDIC13), 28.-31.10.2012, Grenoble, France

Publ.-Id: 18055

Charakterisierung von ferromagnetischen Ge:Mn-Nanonetzen nach Synthese mittels Mn-Ionenimplantation und gepulster Laserausheilung

Bürger, D.

Ziel der experimentellen Promotionsarbeit war es, neue Verfahren zur Herstellung von magnetischen Halbleitern für den spinpolarisierten Ladungsträgertransport zu evaluieren. Dazu wurde in der vorliegenden Promotionsarbeit auch ein theoretisches Modell entwickelt, um die Erfolgsaussichten bei der Herstellung verdünnter magnetischer Halbleiter abschätzen zu können.
Zum Einbringen von magnetischen Fremdatomen in Halbleitermaterialien wurde die Ionenimplantation in einem ca. 100 - 200 nm dicken oberflächennahen Bereich, hier z. B. Mangan in Germanium (Ge) und Mangan in Galliumarsenid (GaAs), angewendet. Die durch die Ionenimplantation entstandenen Gitterschäden wurden anschließend mittels laserinduzierter Flüssigphasenepitaxie ausgeheilt. Die Herstellung von magnetischen Halbleitern mittels Implantation und Laserausheilung stellt einen alternativen Ansatz zum konventionellen Wachstum von magnetischen Halbleitern mittles Niedrigtemperatur-Molekularstrahlepitaxie (engl.: Low temperature molecular beam epitaxy, LT-MBE) dar und beruht auf einem anderen thermodynamischen Konzept. Beide Verfahren laufen jedoch unter thermodynamischen Nichtgleichgewichtsbedingungen ab, was eine Voraussetzung für den substitutionellen Einbau von Fremdatomkonzentrationen oberhalb der natürlichen Löslichkeit ist. Dies ist eine notwendige Voraussetzung für die Herstellung von GaAs:Mn oder Ge:Mn mit hohen Mn-Konzentrationen. Die Kopplung zwischen den magnetischen und elektrischen Eigenschaften in magnetischen Halbleitern stellt eine wichtige Voraussetzung z. B. für deren Einsatz in nichtflüchtigen Speicherbauelementen dar, da der magnetische Zustand direkt mit elektrischen Transportmessungen ausgelesen werden kann. Für das in dieser Arbeit hergestellte Materialsystem Ge:Mn konnte die Kopplung von magnetischen und elektrischen Eigenschaften nachgewiesen werden. Der Grund für diese Kopplung ist allerdings nicht der ladungsträgerinduzierte Ferromagnetismus in kristallinem Ge:Mn, sondern der Ferromagnetismus eines perkolierenden manganreichen amorphen Nanonetzes in Ge:Mn. Dabei weist die hergestellte Ge:Mn-Hybridstruktur ähnliche Magnetotransporteigenschaften wie das klassische verdünnte GaAs:Mn auf.
Der Erfolg bei der Herstellung eines amorphen Ge:Mn-Nanonetzes beruht zum großen Teil auf der Verwendung einer relativ langen Laserpulsdauer von 300 ns, welche auf dem Gebiet der Flüssigphasenepitaxie bisher eine untergeordnete Rolle spielte. Durch diese lange Laserpulsdauer kann ein Temperaturgradient in die Probe eingeprägt werden, welcher zu einer konstitutionellen Unterkühlung des Ge:Mn und darauffolgend zu einem instabilen, zellulären Wachstum führt, wobei in den Zellwänden des Ge:Mn-Nanonetzes Mangan angereichert wird.
Nach der Einleitung in Kapitel 1 werden im Kapitel 2 der vorliegenden Arbeit verschiedene Formen des Magnetismus in Festkörpern dargestellt und der Einfluss des Magnetismus auf die Magnetotransport-Eigenschaften von magnetischen Halbleitern diskutiert.
Die Herstellung von ferromagnetischen Halbleitern mittels Ionenimplantation und gepulster Laserausheilung wird im Kapitel 3 detailliert erläutert. Zudem wird ein theoretisches Modell hergeleitet, mit dem eine Abschätzung des zeitabhängigen Temperaturprofils während der Laserausheilung möglich wird.
Der physikalische Zugang, welcher die Formierung des Ge:Mn-Nanonetzes beschreibt, wird anhand von typischen Rekristallisationsphänomenen von Legierungen qualitativ dargestellt.
Im Kapitel 4 werden die zur Untersuchung des Ge:Mn-Nanonetzes verwendeten Charakterisierungsverfahren vorgestellt. Es werden physikalische Ursachen für Messfehler diskutiert, welche bei der Unversuchung von Ge:Mn mittels SQUID- und TEM-Messungen besonders in den Vordergrund treten.
Im Kapitel 5 wird ein im Rahmen dieser Arbeit entwickelter Algorithmus vorgestellt, welcher in eine Monte-Carlo-Simulation implementiert wurde, um Diffusions- und Clustervorgänge von magnetischen Fremdatomen in einem primitiven kubischen Gitter während der Abkühlphase nach einem typischen Laserpuls zu simulieren.
Da sich in den letzten 16 Jahren GaAs:Mn als der Prototyp des verdünnten ferromagnetischen Halbleiters entwickelt hat, werden Teile der im Rahmen dieser Arbeit an GaAs:Mn gewonnenen Erkenntnisse in Kapitel 6 dargestellt. Wie im Kapitel 7 gezeigt wird, weist der Magnetotransport von Ge:Mn ähnliche Eigenschaften wie der Magnetotransport in GaAs:Mn auf. Insbesondere korreliert die Hysterese im anomalen Halleffekt von Ge:Mn mit der Hysterese der Magnetisierung. Die physikalische Ursache für die Hysterese im anomalen Halleffekt in Ge:Mn wird auf die bevorzugte Streuung von spinpolarisierten Ladungsträgern in dem perkolierenden, amorphen, manganreichen Ge:Mn-Nanonetz der Ge:Mn-Hybridstruktur zurückgeführt. Die Morphologie der Ge:Mn-Hybridstruktur wurde mittels TEM ausführlich untersucht.
Im Kapitel 8 werden die gewonnenen Ergebnisse zusammengefasst und es wird ein Ausblick gegeben, welche Anwendungsmöglichkeiten die in dieser Arbeit erlangten Erkenntnisse auch in anderen Forschungsbereichen finden können.
In den Anhängen A.1 - A.8 befinden sich detaillierte Informationen über die Materialparameter von Si, Ge und GaAs, weitere Details über den entwickelten Monte-Carlo Algorithmus, eine Probenübersicht, TEM-Bilder sowie ergänzende Magnetowiderstands- und SQUID-Daten zur weiteren Charakterisierung der hergestellten Ge:Mn-Hybridstruktur.

The aim of this work is the evaluation of the producibility of ferromagnetic semiconductors with spinpolarized charge carrier transport. To reach this aim, in this experimental work also theoretical concepts were developed to estimate the chances of success for the producibility of ferromagnetic semiconductors.
For doping semiconductors with magnetic dopants, ion implantation of manganese in germanium and manganese in GaAs has been used. The damaged surface layer was annealed with laser induced liquidphase-epitaxy. This type of growth is quite different from the conventionally used low temperature molecular beam epitaxy and is based on a different thermodynamical concept. Both growth techniques can be used far from thermodynamical equilibrium conditions and therefore allow dopant concentrations above the natural solubility limit under thermodynamical equilibrium conditions. This is a necessary condition for the fabrication of charge carrier mediated ferromagnetism in GaAs:Mn, Ge:Mn or in transition metal doped silicon. The following coupling between magnetic and electric properties in such systems is a necessary condition for an application in nonvolatile memories, because the magnetic state can be directly read out over the electric response due to the anomalous Hall effect. For our fabricated material system Ge:Mn, a coupling between the electric and magnetic properties, similar to GaAs:Mn, could be reached. The reason for this coupling is not attributed to charge carrier mediated ferromagnetism in crystalline Ge:Mn. The reason is the growth of a percolating Mn-rich amorphous Ge:Mn-nanonet embedded in crystalline Ge:Mn. The successful growth of this Mn-rich nanonet relies on the fact that a laser with a 300 ns long pulse was used that is longer than the typical pulsed excimer or solid state lasers used for liquid-phase-epitaxy. Therefore, a special temperature gradient can be imprinted in the annealed wafer that lead to a constitutional undercooling with an instable, cellular growth and an accumulation of Mn in the nanonet.
The Phd-thesis is structured in the following way: After a short introduction, the different kinds of magnetism are illustrated in the chapter 2. Thereby, also its influence on the Hall effect and further magnetotransport properties are discussed.
Details about sample preparation with ion implantation followed by pulsed laser annealing are explained in chapter 3. Moreover, a model is developed to perform a rough estimation of the temperature profile during PLA. The physical mechanisms, which lead to the formation of the Ge:Mn-nanonet are qualitatively explained by discussing some textbook knowledge for liquid-phase-epitaxy of alloys. In chapter 4 the applied characterization methods of the Ge:Mn-nanonet are presented. Especially, sources of error are presented that have, based on the experience with Ge:Mn, a large influence on the measurement results.
In chapter 5 an algorithm is presented that was implemented in a Monte-Carlo simulation to model diffusion and clustering processes of magnetic dopants in a simple cubic lattice during the cooling process of pulsed laser annealing.
Because of the large experience in the last 16 years with the material system GaAs:Mn as the prototype diluted ferromagnetic semiconductor, in chapter 6 the obtained measurement results from GaAs:Mn are presented. In chapter 7 for the material system Ge:Mn, a similar correlation between the hysteresis in the anomalous Hall effect to its magnetism could be shown. The reason for the hysteretic anomalous Hall effect will be explained on the basis of a preferential scattering of spinpolarized charge carriers in a percolating, Mn-rich, amorphous Ge:Mn-nanonet. The morphology of the nanonet is investigated by TEM.
In chapter 8 the obtained findings are summarized and possible consequences for further research on ferromagnetic semiconductors are discussed. Moreover, suggestions for the use of the developed process in alternative research topics are made.
In the appendix A.1 - A.8 detailed information about the material parameters of Si, Ge, and GaAs, further details about the developed Monte-Carlo algoritm, a sample overview, further TEM pictures, magnetotransport measurements and SQUID-magnetization data for a detailed characterization of the fabricated Ge:Mn-hybridstructure can be found.

Keywords: pulsed laser annealing; magnetic semiconductor; ferromagnetic semiconductor; diluted magnetic semiconductor; secondary phases; nanonet; recrystallization; Mullins-Sekerka instability; constitutional supercooling; Ge-Mn; germanium; manganese; excimer laser; pulse length

Related publications

  • Doctoral thesis
    TU Dresden, Fakultät Mathematik und Naturwissenschaften, 2012
    154 Seiten

Publ.-Id: 18054

Iterative fluid dynamics

Wunderlich, F.; Kämpfer, B.

An iterative scheme is presented to solve analytically the relativistic fluid dynamics equations. The scheme is applied to the longitudinal expansion, the transversal symmetric and the transversal asymmetric (triaxial) expansion as well. Within this scheme it is possible to describe the dynamics of a strongly coupled (i.e. conformal) medium for parameters referring to heavy-ion collisions at LHC.

Publ.-Id: 18053

Uranium at solid/water interfaces: Lessons to be learned from X-ray absorption spectroscopy

Scheinost, A. C.; Rossberg, A.

X-ray absorption spectroscopy is a versatile tool to investigate oxidation state and molecular structure or uranium in aqueous and solid phases and at their common interface. However, the structural analysis is often hampered by limited resolution and range. I will show recent advances to overcome these limitations, including improved XAFS data analysis approaches like Monte-Carlo and Landweber methods; coupling to XAFS-independent methods like DFT and surface complexation modeling as well as to other x-ray methods like HEXS which have a longer detection range.
I will demonstrate the usefulness of these methods by showing recent results on uranyl sorption to mineral surfaces, with a focus on polynuclear and carbonate complexes; Fe(II)-driven interfacial redox processes of uranyl, also in comparison to other actinoides; colloid formation processes of U(IV) and its tetravalent actinoide neighbors.

Keywords: XAFS; XANES; Kohonen maps; DFT

Related publications

  • Invited lecture (Conferences)
    International Workshop on Uranium biogeochemistry:transformations and applications, 11.-16.03.2012, Ascona, Switzerland
  • Lecture (Conference)
    Seminaire de l'Institut de minéralogie et de physique des milieux condensés, 29.11.2012, Paris, France

Publ.-Id: 18052

Measurement of magnetoresistance effects in nanoscale metallic conductors

Warnatz, T.; Wintz, S.; Bali, R.; Wiesenhütter, U.; Grebing, J.; Lindner, J.; Fassbender, J.; Erbe, A.

The magnetic characterization of nanoscale magnetic structures is one of the main prerequisites for the development of magnetoelectric memories and sensors. Here we present magnetoresistance effects of nanostructured metallic films and particles, which can exhibit anisotropic magnetoresistance or giant magnetoresistance effects. The structures are built from a variety of materials and they are measured at low tem- peratures in magnetic fields up to 1.5 T. We correlate the microscopic structure of the materials with the observed magnetic properties. Thus, a deeper understanding of switching and storage of the magnetic state in such nanostructures can be gained.

Related publications

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18051

Broadband THz detection with graphene flakes

Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Schneider, H.; Helm, M.

We demonstrate a broadband THz detector based on graphene flakes, which are produced by scotch-tape method on SiO2/Si, combined with a logarithmic periodic antenna. The antenna is coupled to the graphene flake with an interdigitated comb-like structure in the center. The detectors were characterized at roomtemperature using the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. The responsivity is above 1nA/W for wavelengths from 30µm to 220µm. The rise time of the measured signals is below 100ps and their length is in the range of 200ps, while the pulse duration of the FEL pulses is around 20ps. The effect of the antenna coupling could be confirmed via polarization dependent measurements. Due to the spectral bandwidth combined with high temporal resolution and simple handling these detectors can be very useful for timing purposes of short laser pulses.

Keywords: graphene detector broadband THz

Related publications

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18050

Impact of time-dependent non-axisymmetric velocity perturbations on dynamo action of von-Karman-like flows

Giesecke, A.; Stefani, F.; Burguete, J.

We present numerical simulations of the kinematic induction equation in order to examine the dynamo efficiency of an axisymmetric von-Karman-like flow subject to time-dependent non-axisymmetric velocity perturbations. The numerical model is based on the setup of the French Von-Karman-Sodium dynamo (VKS) and on the flow measurements from a water experiment conducted at the University of Navarra in Pamplona, Spain. The principal experimental observations that are modeled in our simulations are non-axisymmetric vortex-like structures which perform an azimuthal drift motion in the equatorial plane. Our simulations show that the interactions of these periodic flow perturbations with the fundamental drift of the magnetic eigenmode (including the special case of non-drifting fields) essentially determine the temporal behavior of the dynamo state.

We find two distinct regimes of dynamo action that depend on the (prescribed) drift frequency of an (m=2) vortex-like flow perturbation. For comparatively slowly drifting vortices we observe a narrow window with enhanced growth-rates and a drift of the magnetic eigenmode that is synchronized with the perturbation drift. The resonance-like enhancement of the growth-rates takes place when the vortex drift frequency roughly equals the drift frequency of the magnetic eigenmode in the unperturbed system. Outside of this small window, the field generation is hampered compared to the unperturbed case, and the field amplitude of the magnetic eigenmode is modulated with approximately twice the vortex drift frequency. The abrupt transition between the resonant regime and the modulated regime is identified as a spectral exceptional point where eigenvalues (growth-rates and frequencies) and eigenfunctions of two previously independent modes collapse.

In the actual configuration the drift frequencies of the velocity perturbations that are observed in the water experiment are much larger than the fundamental drift frequency of the magnetic eigenmode that is obtained from our numerical simulations. Hence, we conclude that the fulfillment of the resonance condition might be unlikely in present day dynamo experiments.
However, a possibility to increase the dynamo efficiency in the VKS experiment might be realized by an application of holes or fingers on the outer boundary in the equatorial plane. These mechanical distortions provoke an anchorage of the vortices at fixed positions thus allowing an adjustment of the temporal behavior of the non-axisymmetric flow perturbations.

Keywords: Dynamo; Magnetohydrodynamics

Publ.-Id: 18049

Determination of Resonance Parameters and their Covariances from Neutron Induced Reaction Cross Section Data

Schillebeeckx, P.; Becker, B.; Danon, Y.; Guber, K.; Harada, H.; Heyse, J.; Junghans, A. R.; Kopecky, S.; Massimi, C.; Moxon, M. C.; Otuka, N.; Sirakov, I.; Volev, K.

Cross section data in the resolved and unresolved resonance region are represented by nuclear reaction formalisms using parameters which are determined by fitting them to experimental data. Therefore, the quality of evaluated cross sections in the resonance region strongly depends on the experimental data used in the adjustment process and an assessment of the experimental covariance data is of primary importance in determining the accuracy of evaluated cross section data. In this contribution, uncertainty components of experimental observables resulting from total and reaction cross section experiments are quantified by identifying the metrological parameters involved in the measurement, data reduction and analysis process. In addition, different methods that can be applied to propagate the covariance of the experimental observables (i.e. transmission and reaction yields) to the covariance of the resonance parameters are discussed and compared. The methods being discussed are: conventional uncertainty propagation, Monte Carlo sampling and marginalization. It is demonstrated that the final covariance matrix of the resonance parameters not only strongly depends on the type of experimental observables used in the adjustment process, the experimental conditions and the characteristics of the resonance structure, but also on the method that is used to propagate the covariances. Finally, a special data reduction concept and format is presented, which offers the possibility to store the full covariance information of experimental data in the EXFOR library and provides the information required to perform a full covariance evaluation.

Keywords: Nuclear Data measurements; neutron time-of-flight; neutron resonances; parameters and covariances

Related publications


Publ.-Id: 18048

Scientific Capabilities and Technology of the Superconducting Accelerator Based ELBE Facility

Michel, P.

Keywords: 4th Generation Light Source

Related publications

  • Invited lecture (Conferences)
    Workshop on the Science and Technology of 4th Generation Light Source Based on Superconducting Technology AlbaNova, 26.-27.11.2012, Stockholm, Schweden

Publ.-Id: 18047

The U(VI) Speciation Influenced by a Novel Paenibacillus Isolate from Mont Terri Opalinus Clay

Lütke, L.; Moll, H.; Bachvarova, V.; Selenska-Pobell, S.; Bernhard, G.

Bacterial cell walls have a high density of ionizable functional groups available for U(VI) binding, hence have a great potential to affect the speciation of this contaminant in the environment. The studied strain of the genus Paenibacillus is a novel isolate originating from the Mont Terri Opalinus clay formations (Switzerland) which are currently investigated as potential host rock for future nuclear waste storage. The U(VI) binding by the cell surface functional groups was studied by potentiometry combined with time-resolved laser-induced fluorescence spectroscopy (TRLFS). This paper provides stability constants of U(VI) complexed by cell surface functional groups. Additionally the bacteria-mediated liberation of inorganic phosphate in dependence on [U(VI)] at different pH values was studied in order to assess the influence of phosphate release on U(VI) mobilization. It could be shown that in the acidic pH range (pH 3) UO22+ binding onto the cell envelope is governed by coordination to hydrogen phosphoryl sites. Upon increasing pH an increasing coordination of UO22+ to carboxylic and deprotonated phosphoryl sites occurs. At a pH greater than 7 uranyl hydroxides dominate the speciation. In general, UO22+ is bound to the cell envelope with relatively high thermodynamic stability.

Keywords: Uranium; Paenibacillus sp; Opalinus Clay; Mont Terri; Potentiometry; TRLFS

Publ.-Id: 18046

Application of high-resolution positron-emission-tomography for quantitative spatiotemporal process monitoring in dense material

Kulenkampff, J.; Gründig, M.; Korn, N.; Zakhnini, A.; Barth, T.; Lippmann-Pipke, J.

Methods for sensitive quantitative recognition of transport processes in opaque media without retroaction on the process itself are desirable in many scientific and technical fields. Tomographic methods based on the detection of substances labeled with radioisotopes are both most sensitive and without impact on physical or chemical properties.
During the last decade, we developed the “GeoPET-method”, applying positron-emission-tomography (PET) as laboratory method for observing flow and diffusion of reactive and non-reactive chemical species and particles in geomaterials. The substances are labeled with positron-emitting radionuclides, like 18F (decay time T1/2=110 min.), 64Cu (T1/2=12.7 h), 124I (T1/2=4.18 d), 58Co (T1/2=70.9 d), 22Na (T1/2=2.60 y), which are chosen with regard to their chemical properties and the required observation time. We use a pre-clinical PET-scanner (ClearPET by Raytest, Straubenhardt/Germany), taking advantage of its higher resolution (nearly 1 mm in dense material) and higher sensitivity, compared to clinical PET-scanners. The FOV (Field Of View) has a maximum diameter of 160 mm and a length of 100 mm. Process monitoring is accomplished by sequential recording of 3D-images with a minimum frame rate of 1 min and a maximum observation period of about 8*T1/2.
PET clearly outclasses any other tomographic modality with respect to sensitivity and selectivity. However, its application on process observation in dense material is more intricate than the habitual medical application, because substantial adverse effects have to be considered, which are due to attenuation and scattering of the annihilation photons and unfavorable other decay radiation. Applying Monte-Carlo simulations of these effects, we aim at their elimination based on fundamental physical principles.
We successfully applied GeoPET for monitoring of transport of conservative and reactive tracers, particles and humic substances in soil columns and porous or fractured rock cores. Frequently, we observe more strongly localized preferential pathways than anticipated in common transport models, and retention of – even supposedly conservative – tracers during their passage through the material. Recent studies with aerosols in flow loops aim at the verification of CFD-computations of particle deposition and remobilization. As further PET-applications in industrial process tomography we suggest e.g. the characterization of filter processes in catalysts and reactors.
Based on our quantitative images of the spatiotemporal tracer propagation in our column experiments, we parameterize 2D and 3D-numerical reactive transport simulations by inverse modeling. Examples will be demonstrated.

Keywords: pet; reactive transport; tracer

Publ.-Id: 18045

Non-monotonic crossover from single-file to regular diffusion in micro-channels

Siems, U.; Kreuter, C.; Erbe, A.; Schwierz, N.; Sengupta, S.; Leiderer, P.; Nielaba, P.

The diusion behavior of interacting particles determines the behavior of a large number of systems ranging from pedestrians crossing a road to ions passing through channels in living cells. Here we present a system in which the nature of the diusion process varies with changes in the external conditions. We nd this special behavior in a colloidal model system, consisting of micron sized particles which are conned to narrow channels and interact via induced magnetic dipoles. When the density of these particles is changed, diusion alternates between normal Fickian behavior and single-le diusion. This anomalous behavior is induced by the order of the particles in the restricted geometry and does not depend on the exact nature of the inter-particle interactions.

Keywords: Colloidal model systems; statistical physics; transport phenomena in restricted geometries

Publ.-Id: 18044

Work function determination of degenerately Al-doped ZnO by thermionic emission

Wilde, C.; Schmidt, B.; Vinnichenko, M.; Gemming, S.

Degenerately Al-doped ZnO (AZO) is a transparent conductive oxide (TCO) widely used, especially as electrode material in solar cells. The work function of these electrodes is of crucial importance, because it determines the electronic barrier between the TCO and the semiconducting absorber. Therefore, this barrier directly affects the charge collection and thus solar cells efficiency.
In this contribution we report the results of experiments carried out to determine the work function of AZO by using the thermionic emission theory. AZO, as a degenerately doped semiconductor with the Fermi level in the conduction band shows a metal-like behaviour, and, if it is brought into contact with a semiconductor, it forms a Schottky barrier. From measurements of temperature-dependent current-voltage characteristics the work function of AZO can be determined.
We demonstrate that this model of metal/semiconductor contact is applicable to the contact between AZO and a non-degenerately doped substrate (silicon or germanium). The Schottky barrier formation is studied with respect to the substrate conductivity type and surface cleaning. The determined AZO work function variation will be discussed in relation to the film properties and process parameters of reactive and non-reactive DC magnetron sputter deposition.

Keywords: AZO; ZnO; work function; TCO; thermionic emission

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18043

Influence of Laser Pulse Parameters on the Properties of e-e+ Plasmas Created from Vacuum

Blaschke, D.; Kämpfer, B.; Panferov, A. D.; Prozorkevich, A. V.; Smolyansky, S. A.

We use the low density approximation within the kinetic theory approach to vacuum creation of an e-e+ pair plasma (EPPP) in a strong laser field in order to investigate the dependence of the observed EPPP on the form and parameters of a single pulse. The EPPP distribution function is calculated for an abitrary time dependence of the electric field in the multiphoton domain (adiabaticity parameter γ>>1). The dependence on the field strength, the form and spectrum of the field pulse is investigated on the basis of both analytical and numerical methods. The obtained results can be useful for examining some observable secondary processes associated with the dynamical Schwinger effect.

Publ.-Id: 18042

Deep sub-threshold K(892)0 production in collisions of Ar+KCl at 1.76A GeV

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

Results on the deep sub-threshold production of the short-lived hadronic resonance K^{*}(892)^{0} are
reported for collisions of Ar\,+\,KCl at 1.76A~GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The K^{*}(892)^{0} production probability per central collision of P_{K^{*0}}=(4.4 \pm 1.1 \pm 0.5)\times10^{-4} and the K^{*}(892)^{0}/K^{0} ratio of P_{\mbox{K}^{*0}}/P_{\mbox{K}^0}=(1.9 \pm 0.5 \pm 0.3)\times10^{-2} are determined at the lowest energy so far (sqrt{s_{NN}}-sqrt{s_{thr}}=-340~MeV). The K^{*0}/K^{0} ratio is compared with results of other experiments and with the predictions of the UrQMD transport approach and of the statistical hadronization model. The experimental K^{*0}/K^{0} ratio is in fair agreement with the results of the transport model. In a chemically equilibrated medium the ratio corresponds to a temperature of the thermalized system being systematically lower than the value determined by the yields of the stable and long-lived hadrons produced in Ar\,+\,KCl collisions. From the present measurement, we conclude that sub-threshold K^* production either can not be considered to proceed in a system being in thermal equilibrium or these short-lived resonances appear undersaturated, for example as a result of the rescattering of the decay particles in the ambient hadronic medium.

Publ.-Id: 18041

SWCNT growth from C:Ni nanocomposites

Krause, M.; Haluska, M.; Abrasonis, G.; Gemming, S.

Carbon:nickel (C:Ni) nanocomposite thin films deposited by ion beam co-sputtering were used for catalytic chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWCNTs). The SWCNTs were characterized by scanning electron microscopy and Raman spectroscopy. The approach allows a precise and reproducible control of the catalyst diameter, while the embedding carbon matrix prevents the particles from coalescence during catalyst activation and nanotube growth. The SWCNTs obtained from Ni particles with 4 nm diameter have a radial breathing mode frequency distribution of 147.5 +/- 32 cm-1 and a diameter distribution of 1.6 +/- 0.4 nm. Small line widths of the radial breathing mode and ID/IG ratios of 0.05 indicate SWCNTs with a low defect concentration.

Keywords: Nanocomposites; Raman spectroscopy; Single-walled carbon nanotubes; diameter control; growth

Publ.-Id: 18040

Double pion production in np and pp collisions at 1.25 GeV with HADES

Agakishiev, G.; Behnke, C.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Blume, C.; Böhmer, M.; Cabanelas, P.; Chernenko, S.; Dritsa, C.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gill, K.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Holzmann, R.; Huck, P.; Höhne, C.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krebs, E.; Krizek, F.; Kuc, H.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, L.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

The results of double pion production in np and pp collisions at an incident beam energy of 1.25 GeV with the HADES spectrometer at GSI are presented. The np− reactions were studied in dp collisions at 1.25 GeV/u using Forward Wall hodoscope aimed at registering spectator protons. High statistic invariantmass and angular distributions are obtained within the HADES acceptance which are compared with phase-space distributions.

  • Open Access Logo Proceedings of Science (2013), PoS(Baldin ISHEPP XXI)041

Publ.-Id: 18039

Positron Annihilation Spectroscopy at a Superconducting Electron Accelerator

Wagner, A.

-Accelerator-based positron production and annihilation studies at a superconducting electron LINAC
-Development of a pixelated detection system for position-sensitive positron annihilation lifetime measurements
-First experiments with phantom targets
-3D tomographic reconstruction
-Development of a high-energy positron beam for fundamental studies

Keywords: Accelerator-based positron production annihilation superconducting electron LINAC; positron annihilation lifetime measurements

Related publications

  • Lecture (others)
    Institute Seminar, 26.11.2012, Prague, Czech Republic

Publ.-Id: 18038

Shielding and activation studies for the design of the MYRRHA proton beamline

Ferrari, A.; Biarrotte, J.-L.; Perrot, L.; Saugnac, H.; Vandeplassche, D.

Accelerator-driven systems require the use of high energy Mega-Watt proton beams, in combination with a nuclear reactor core operating in sub-critical mode. Between the challenges in the design, key points are the radiation shielding and the minimization of the induced activation.
This study has been done to optimize the design of the MYRRHA facility at SCK•CEN in Mol (Belgium), where a 600 MeV, 4 mA proton beam will be produced and transported through a linear accelerator up to a LBE spallation target, located inside the core of a 100 MW, LBE cooled reactor. To assess the shielding of the proton accelerator, as well as to fix the activation problems that heavily influence the design, an extensive simulation study has been performed with the FLUKA Monte Carlo code. FLUKA has the unique feature to perform via a full Monte Carlo method the transport of both the prompt and the residual radiation, allowing in addition modifications in the geometry and material characterization from the prompt to the residual radiation analysis. The optimization of the elements devoted to the partial or total beam absorption (collimators, beam dump) is also presented: it will be shown how a suitable material configuration will improve the accessibility and the long-term treatment of the irradiated elements

Keywords: Monte Carlo calculations; shielding; activation; ADS systems

  • Lecture (Conference)
    SATIF-11 11th Workshop on Shielding Aspects of accelerators, Targets and Irradiation Facilities, 11.-14.09.2012, Tsukuba, Japan
  • Contribution to proceedings
    SATIF-11 11th Workshop on Shielding Aspects of Accelerators, Targets and Irradiation Facilities, 11.-14.09.2012, Tsukuba, Japan
    Workshop Proceedings NEA No. 7157, Paris: OECD/NEA Publishing, 9789264208544, 13-27
    DOI: 10.1787/9789264208544-en

Publ.-Id: 18037

Shielding assessment of the Helmholtz-Beamline at the european XFEL

Ferrari, A.; Cowan, T.; Schlengvoigt, H.-P.; Schramm, U.

The Helmholtz-Beamline will operate as user facility at the European XFEL, providing a high-power and ultra-intense (PW class) optical laser “end-station”. Unique combination of high-power/high-intensity lasers with high-brilliance X-ray sources, it has the goal to extend the strong scientific potential of the XFEL project.
The laser beams will be transported to the experimental area dedicated to the investigation of matter under high energy density conditions, the HED (High Energy Density) Instrument. Here they will largely be used for the generation of secondary particles for pumping and probing and to create strong field for QED experiments. Aim of this work is the shielding assessment of the HED hutch, including an analysis of the possible activation problems.
As first step the effective radiation source term has been evaluated and verified with the present short-pulse laser operations. The possible radiation source terms, above that of the XFEL beam itself, occur only for the ultra-intense laser beams focused to above 1017 W/cm2. This holds for all of the applications in which the laser is used to accelerate protons or ions for heating or probing, creating additional x-ray backlighters, or generating intense surface harmonics, betatron radiation or electron beams in underdense targets. The hard penetrating radiation comes primarily from energetic electron beams of up to 1 nC charge escaping from underdense targets. At the available laser intensities, energies and target conditions, the effective electron source terms are up to a few-10 nC of bunch charge, in a Mawellian-like distribution with an average up to the relativistic ponderomotive limit of 10 MeV.
This representative radiation field has been then characterized in a full simulation with the Monte Carlo code FLUKA, with the goal to find a reasonable shielding optimization. In addition to the Bremsstrahlung, the most important component of the radiation is given by the neutrons that are produced via photonuclear reactions in the interaction of the electromagnetic shower with the aluminum chamber around the target and the shielding itself. The optimization has been investigated in a standard-condition, high repetition rate experiment (10 Hz) and includes an analysis of both the prompt and the residual radiation, to guarantee safe activities around the chamber after the irradiations and to avoid the eventual accumulation of long-lived radionuclides in the whole hutch area.
All the results of the shielding and activation analysis are here presented and discussed. An excellent solution is obtained with the use of moderate thicknesses of heavy concrete for the shielding walls, in combination with a thin lead layer and a local system of shielding panels of suitable materials. The local shielding is put close to the chamber to suppress the forward directed dose distribution with an efficient structure energy degrader/absorber, with the additional advantage of a large flexibility in case of non standard operation modes, where the use of thicker targets induces intense Bremsstrahlung environments and then more energetic electron beams. These cases will be handled with a case-by-case basis, with additional panels or electron beam transport into dedicated beam dumps.

Keywords: Laser-particle acceleration; Monte Carlo; Shielding Design; Residual Dose Distributions

  • Poster
    ICRS12 - 12th International Conference on Radiation Shielding, 02.-07.09.2012, Nara, Japan

Publ.-Id: 18036

Shielding and activation calculations for the MYRRHA ADS design in the subcritical operation mode

Ferrari, A.; Di Maria, S.; Sarotto, M.; Stankovskiy, A.

Accelerator-driven systems (ADS) are one of the options studied for the transmutation of nuclear waste in the European Community. The design of sub-critical ADS requires high energy and high power proton accelerators, of the order of hundreds MeV and some MW for the proposed demonstration experiments. The use of high energy Mega-Watt proton beams, in combination with a nuclear reactor core operating in sub-critical or critical mode, presents many challenges for various aspects of the design, being radiation shielding and minimization of the induced activation key points.
The present study has been done in the framework of the Central Design Team european project (CDT), which worked with the goal to design the FAst Spectrum Transmutation Experimental Facility (FASTEF) to demonstrate efficient transmutation of high level waste and associated ADS technology. On this design will be based the MYRRHA facility at SCK•CEN in Mol (Belgium), which should start the construction phase in 2015. The heart of the system is a 100 MW lead-bismuth eutectic (LBE) cooled reactor, working both in critical and sub-critical modes. The neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV, 4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core.
With the goal to assess the shielding of the reactor building and to study the activation of the materials in key points around the reactor and in the vertical part of the proton beam-line, an extensive simulation study has been done. Both the Monte Carlo codes MCNPX (version 2.6.0) and FLUKA (version 2011.2) have been used, also with the aim to do a code-to-code comparison and to cross check the results. Starting from the MCNPX model of the reactor core in the sub-critical operation mode, which includes the last part of the vertical proton beamline with the spallation target and the LBE coolant material around the core, until the external vessel, the radiation fields have been fully characterized on suitable surfaces around the core and used as input in a second row of simulations. These calculations have been done with the FLUKA code, which has the unique possibility to compute, in the same simulation, the transport of both the prompt radiation (due to the ADS in operation) and the residual one (due to the activated materials). The neutron fluence behaviour, together with the dose distributions due to the prompt and to the residual radiation, has been then studied. Dose profiles have been evaluated from the core vessel to the external containment and the shielding walls in the horizontal direction, up to the last magnet of the proton beam-line and the final roof in the vertical one. Moreover, the activation of key materials has been characterized for typical irradiation patterns.
The results of the shielding and activation analysis are presented and discussed, together with the main implications on the design solutions.

  • Lecture (Conference)
    ICRS12 - 12th International Conference on Radiation Shielding, 02.-07.09.2012, Nara, Japan

Publ.-Id: 18035

On applicability of the 3D nodal code DYN3D for the analysis of SFR cores

Fridman, E.; Rachamin, R.

DYN3D is an advanced multi-group nodal diffusion code originally developed for the 3D steady-state and transient analysis of the Light Water Reactor (LWR) systems with square and hexagonal fuel assembly geometries. The main objective of this work is to demonstrate the feasibility of using DYN3D for the modeling of Sodium cooled Fast Reactors (SFRs). In this study a prototypic European Sodium Fast Reactor (ESFR) core is simulated by DYN3D using homogenized multi-group cross sections produced with Monte Carlo (MC) reactor physics code Serpent. The results of the full core DYN3D calculations are in a very good agreement with the reference full core Serpent MC solution.

  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13), 04.-07.03.2013, Paris, France
    Proceedings of the International Conference on Fast Reactors and Related Fuel Cycles

Publ.-Id: 18034

Liquid Metal Ion Sources and their application in Nanotechnology

Bischoff, L.

In the last decade focused ion beams (FIB) became an irrecoverable instrument in research and industry. Sample preparation, local ion implantation and ion analysis are the main application topics. Most of the systems are equipped with a gallium liquid metal ion source (LMIS). But, modern trends in nanotechnology require more extended properties like variable ion species, non-contaminating milling at higher rates or higher lateral resolution in the field of ion microscopy.
In this presentation the assembly and the mode of operation as well as the application of alloy LMIS in mass separated FIB systems are introduced. A brief survey about the history of LMIS is given. The ionization principle and the main parameters, like energy spread or brightness of such a source are discussed. The fabrication technology of different types of alloy LMIS will be presented. Finally examples of application of LMIS in the nano-technology are given.

Keywords: Liquid Metal Ion Source; FIB; Indium

Related publications

  • Lecture (others)
    Seminar, 19.11.2012, Mainz, Deutschland

Publ.-Id: 18033

The 40Ca(α,γ)44Ti reaction studied by activation

Schmidt, K.; Akhmadaliev, C.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Dietz, M.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A.; Marta, M.; Menzel, M.-L.; Schwengner, R.; Szücs, T.; Wagner, A.; Yakorev, D.; Zuber, K.

The radioactive nuclide 44Ti is believed to be produced in the alpha-rich freezeout preceding supernova explosions. The γ-lines from its decay have been observed in space-based gamma-observatories for the Cassiopeia A supernova remnant. The rates of the nuclear reactions governing the production and destruction of 44Ti should therefore be known with precision. Using the α-beam of the 3.3 MV Tandetron of Helmholtz-Zentrum Dresden-Rossendorf, the strengths of the 40Ca(α,γ)44Ti resonance triplet at 4.5 MeV α-energy have been restudied by activation. The samples have been analyzed in the Felsenkeller underground γ-counting facility. Preliminary data on lower-lying resonances will be presented, as well.

Keywords: 44Ti; supernova; space-based gamma-observatories; Cassiopeia A; 3.3 MV Tandetron; Felsenkeller; resonance strengths

Related publications

  • Lecture (Conference)
    VIII Tours Symposium on Nuclear Physics and Astrophysics, 02.-07.09.2012, Lenzkirch-Saig, Deutschland

Publ.-Id: 18032

Uranyl(VI) Chemistry in Strong Alkaline Solution: UO2(OH)53- or UO3(OH)33-?

Tsushima, S.; Rossberg, A.; Moll, H.

no abstract for this publication

Related publications

  • Lecture (Conference)
    Status Seminar 2012 "Nuclear Safety Research – From Reactors to Disposal", 11.-12.12.2012, Dresden, Germany

Publ.-Id: 18031

A new database on interfacial area density obtained from wire-mesh sensor measurements

Lucas, D.; Beyer, M.

Interfacial Area Density (IAD) is an important parameter for modeling two-phase flows with mass transfer. Condensation and evaporation rates in dynamic flows are proportional to this parameter. While system codes have to reflect the evolution of the IAD along the flow path, the qualification of CFD-codes requires the detailed information on the three-dimensional distributions. Wire-mesh sensors, which enable the identification of the local phase distribution in gas-liquid flows basing on high frequency conductivity measurements, are widely used for the determination of two-phase flow characteristics in pipes. Basing on the method proposed by Prasser, now an improved algorithm was developed to obtain the interface of the single bubbles and gas structures as well as the local IAD from wire-mesh sensor data. The paper briefly describes the new algorithm, but mainly focusses on the extension of the data-base obtained by the application of this algorithm on a comprehensive experimental test series for adiabatic air-water flows. The experiments were done using a 8 m long pipe with an inner diameter of 195.3 mm. The extended database now besides radial gas volume fraction profiles, radial gas velocity profiles bubble size distributions and differential gas volume fraction in dependence on the bubble size and the radial position includes also detailed data on the space and bubble size dependent IAD.

Keywords: interfacial aera; wire-mesh; database; pipe flow

  • Contribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-15, 12.-15.05.2013, Pisa, Italy
    paper NURETH15-101
  • Lecture (Conference)
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-15, 12.-15.05.2013, Pisa, Italy

Publ.-Id: 18030

4D PT-PET simulation for dose monitoring in moving targets treated with scanned ion beams

Laube, K.; Menkel, S.; Fiedler, F.; Bert, C.; Saito, N.; Enghardt, W.

Ion beams have the advantage of providing steep dose gradients and therefore they allow high tumour conformality and sparing of nearby organs at risk. Precise knowledge of the actual ion range is highly desired since anatomical changes along the beam path could lead to serious misdosage. Especially for intra-fractionally moving targets the continuous density changes and complex dose delivery techniques increase the risk of an inaccurate dose deposition. The applied dose distribution can be monitored by means of particle therapy positron emission tomography (PT-PET), because ion beams generate positron emitters along their path. Since the delivered dose cannot be extracted directly from the PET scan the validation is usually done by means of a comparison between the reconstructed activities from a PT-PET measurement and a PT-PET simulation. Thus, the simulation software for generating predicted PET data from the treatment planning is an essential part of the dose verification routine. For intra-fractionally moving target volumes the PET data simulation has been upgraded by using time-resolved (4D) algorithms to account correctly for the motion dependent displacement of the positron emitters. Moreover, it considers the time dependent relative movement between target volume and scanned beam to simulate the accurate positron emitter distribution generated during irradiation. We will present the revised and extended version of the simulation software which proceeds with motion compensated dose delivery by scanned ion beams to intra-fractionally moving targets. By means of a dedicated preclinical phantom simulation it is demonstrated that even the most ambitious motion-mitigated beam delivery technique of range compensated target tracking can be handled correctly by the simulation code. Results of the 4D PT-PET simulation will be discussed in detail and compared to a reference simulation and a simulation without consideration of relative movement and range compensation.

  • Lecture (Conference)
    4D Treatment Planning Workshop 2012, 12.-13.12.2012, Erlangen, Deutschland

Publ.-Id: 18029

Structure, mechanical, and tribological properties of C:Ni nanocomposite films grown by IBAD

Krause, M.; Kunze, T.; Mücklich, A.; Fritzsche, M.; Wenisch, R.; Posselt, M.; Gemming, S.; Abrasonis, G.

The mechanical and tribological properties of nanostructured carbon:nickel films on silicon substrates are investigated using a multi-scale experimental and theoretical approach. The C:Ni nanostructures comprising either tilted columns or three-dimensionally self-organized nanopatterns are grown by ion-beam assisted deposition (IBAD). Complex layer architectures were obtained by sequential deposition by rotating the substrate in relation to the assisting ion beam after each deposition step. Atomic composition of the films was determined by ion beam analysis. The phase structure of carbon was analyzed by Raman spectroscopy, that of nickel by X-ray diffraction. The microstructure of the films was determined by high resolution transmission electron microscopy. The films show good adhesion as probed by scratch tests. The film hardness is on the order of 20 GPa, and the elastic modulus is at about 200 GPa. Friction coefficients on the order of 0.1 are found for oscillating wear conditions under ambient conditions. Atomistic computer simulations were applied to assist the experimental findings. Dry and liquid contacts are considered. The simulation shows a complex behaviour for the carbon-carbon interaction, e.g. resulting in the formation of a tribo-layer.

Keywords: Ion-beam assisted deposition; Nanocomposites; Microstructure; Tribology; Mechanical Properties

Related publications

  • Poster
    13th International Conference on Plasma Surface Engineering, 10.-14.09.2012, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 18028

Nanostructuring of C:Ni nanocomposite films using ion-beam assisted ion-beam co-sputtering

Krause, M.; Mücklich, A.; Fritzsche, M.; Facsko, S.; Oates, T. W. H.; Buljan, M.; Gemming, S.; Abrasonis, G.

The effect of the assisting low energy ion beam on the structure of nanocomposite thin films is studied for the carbon:nickel system. The parameter range for the ion beam assisted deposition (IBAD) comprised (i) growth temperatures from room temperature to 500°C, (ii) assisting Ar ion energies from 50 eV to 140 eV, and (iii) nickel concentrations from 5 at.% to 40 at.%. Atomic composition of the films was determined by ion beam analysis. The phase structure of the C:Ni thin films was analysed by Raman spectroscopy and X-Ray diffraction. Scanning electron microscopy was applied for surface analysis, and high resolution transmission electron microscopy was used for microstructure determination. The growth of C:Ni nanocomposites without ion assistance is controlled by the phase separation under kinetic constraints of surface and volume diffusion and the film growth rate. In contrast, ordered nanostructures are formed upon utilizing the energy and momentum input of the assisting ion beam. They consist of nanocolumns with varying tilt angles in relation to the film surface, compositionally modulated surface ripples or three-dimensionally ordered nanopatterns throughout the entire thin film thickness. The correlation between IBAD parameters (temperature, ion energy and flux) and nanocomposite morphological and microstructural features (phase structure, tilting angle, and periodicity) will be presented.

Keywords: Ion-beam assisted deposition; nanocomposites; nanostructuring; self-ordering

Related publications

  • Poster
    13th International Conference on Plasma Surface Engineering, 10.-14.09.2012, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 18027

Excitonic resonances in WS2 nanotubes

Staiger, M.; Rafailov, P.; Gartsman, K.; Telg, H.; Krause, M.; Radovsky, G.; Zak, A.; Thomsen, C.

Resonance Raman profiles of WS2 nanotubes of different diameter are presented. We show that the A excitonic transition energy lies below the bulk value and is increasingly redshifted with decreasing diameter of the nanotubes. The findings are attributed to strain effects associated with the curvature of the nanotube walls. A silent Raman mode, the B1u mode, is disorder enhanced in the Raman spectra of WS2 nanomaterials.We discuss the development of the relative intensities of the B1u mode and the nearby A1g mode with nanotube diameter, excitation energy, and hydrostatic pressure in terms of a slight difference in resonance condition.

Keywords: PACS number(s): 78.30.−j; 63.22.Gh; 71.35.Gg

Publ.-Id: 18026

4D particle therapy PET simulation for moving targets irradiated with scanned ion beams

Laube, K.; Menkel, S.; Bert, C.; Enghardt, W.; Helmbrecht, S.; Saito, N.; Fiedler, F.

Particle therapy positron emission tomography (PT-PET) allows for an in vivo and in situ verification of applied dose distributions in ion beam therapy. Since the dose distribution cannot be extracted directly from the beta+-activity distribution gained from the PET scan the validation is done by means of a comparison between the reconstructed beta+-activity distributions from a PT-PET measurement and from a PT-PET simulation. Thus, the simulation software for generating PET data predicted from the treatment planning is an essential part of the dose verification routine. For the dose monitoring of intra-fractionally moving target volumes the PET data simulation needs to be upgraded by using time resolved (4D) algorithms to account correctly for the motion dependent displacement of the positron emitters. Moreover, it has to consider the time dependent relative movement between target volume and scanned beam to simulate the accurate positron emitter distribution generated during irradiation. Such a simulation program is presented which properly proceeds with motion compensated dose delivery by scanned ion beams to intra-fractionally moving targets. By means of a preclinical phantom study it is demonstrated that even the sophisticated motion-mitigated beam delivery technique of range compensated target tracking can be handled correctly by this simulation code. The new program is widely based on the 3D PT-PET simulation program which had been developed at the Helmholtz-Zentrum Dresden-Rossendorf, Germany (HZDR) for application within a pilot project to simulate in-beam PET data for about 440 patients with static tumour entities irradiated at the former treatment facility of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany (GSI). A simulation example for a phantom geometry irradiated with a tracked 12C-beam is presented for demonstrating the proper functionality of the program.

Keywords: 4D particle therapy PET; ion beam therapy; target motion; Monte Carlo; dose monitoring

Publ.-Id: 18025

Large Scale Atomistic Simulations on Nanostructure Evolution

Kelling, J.; Heinig, K.-H.

The Kinetic Metropolis Lattice Monte-Carlo (KMC) method is a means of performing atomistic simulations of self-organization processes in solids at by far larger scales than those accessible via Molecular Dynamics (MD). This method was implemented on modern GPUs, which currently provide the most peek processing performance regarding both cost and energy consumption, achieving up to 70 times higher performance than the sequential reference implementation on a single core of a modern CPU. This enables atomistic simulations at even larger scales, even putting space and time scales comparable to the experiment within range.

  • Poster
    Response Treatment for the Dynamical Properties of Materials with the ABINIT Package, 22.-26.10.2012, ETH Zürich, Schweiz
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Germany

Publ.-Id: 18024

Radiation Dosimetry of (-)-[F-18]-Flubatine - Comparison of animal model data with first-in-man results

Sattler, B.; Kranz, M.; Patt, M.; Donat, C.; Deuther-Conrad, W.; Hiller, A.; Fischer, S.; Smits, R.; Hoepping, A.; Sattler, T.; Brust, P.; Steinbach, J.; Sabri, O.

Aim:(-)-[F-18]-Flubatine (former NCFHEB) is a new tracer for neuroimaging of alpha4beta2 nAChRs with PET. To assess the putative radiation risk after intravenous application of the radioligand, the biodistribution, organ doses (OD) and the effective dose (ED) were determined in pigs and compared to earlier results in mice and humans [SNM2011 No. 1454, 1459]. Method: Whole body dosimetry of (-)-[F-18]-Flubatine was performed in 5 female piglets (age: 44±3.0d, weight: 13.7±1.7kg). The animals were narcotized using 20 mg/kg Ketamine, 2mg/kg Azaperone; 1.5% Isoflurane in 70% N2O/30% O2 and sequentially PET-imaged up to 5h post i. v. injection of 186.6±7.4MBq (-)-[F-18]-Flubatine on a SIEMENS Biograph16 PET/CT-system with 7 bed positions (BP) per frame, 1.5 to 6 min/BP, CT-attenuation correction (AC) and iterative reconstruction (OSEM, 4 iterations, 8 subsets). All relevant organs were defined by volumes of interest using the structural information from the AC-CT. Exponential curves were fitted to the time-activity-data (%ID/g, and %ID/organ). Time and mass scales were adapted to the respective human scale. The ODs were calculated using the adult male model with OLINDA. The ED was calculated using tissue weighting factors as published in the ICRP103. Results: The highest OD was received by the urinary bladder (49.0±19.4µSv/MBq), the kidneys (39.9±6.14µSv/MBq) and the Pancreas (33.8±31.5µSv/MBq). The highest contribution to the ED was by the urinary bladder (2.0±0.8 µSv/MBq), the stomach (1.5±0.3µSv/MBq) and the lungs (1.5±0.2µSv/MBq). The ED to humans following an i. v. injection of (-)-Flubatine according to this data is 13.1±0.9 µSv/MBq. Conclusion: As true for other PET-Tracers too, preclinical incorporation radiation dosimetry underestimates the ED to humans. The ED by (-)-[F-18]-Flubatine yielded from pig- (this study) and mice- (14.2µSv/MBq) studies compared to human dosimetry data (22.6±0.68µSv/MBq) show that animal dosimetry underestimates the potential radiation exposure to humans by 35-37%. This fact needs to be considered in the assessment of the ED to humans in preparation prior to early phase clinical trials. References: The trial is granted by Strahlenschutzseminar in Thüringen e. V.

  • Poster
    EANM'12 - Annual Congress of the European Association of Nuclear Medicine, 27.-31.10.2012, Milan, Italy
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 39(2012), S524

Publ.-Id: 18023

Cerebral Nicotinic Acetylcholine Receptors (nAChRs) In Early Alzheimer’s Disease (AD) Assessed With The New Radioligand [18F]Flubatine and PET

Sabri, O.; Wilke, S.; Graef, S.; Lengler, U.; Schoenknecht, P.; Gertz, H.; Becker, G.; Luthardt, J.; Patt, M.; Hesse, S.; Barthel, H.; Wagenknecht, G.; Hoepping, A.; Hegerl, U.; Brust, P.

Objectives: There is evidence from post-mortem studies that the loss of nAChRs, in particular of the alpha4beta2-nAChR, which is obviously most severely reduced at the onset of AD, is a major contributor to the cognitive deterioration in AD. Accordingly, using 2-[18F]F-A85380 PET we showed significant declines in alpha4beta2-nAChRs in early AD-patients (Sabri et al. 2008; Kendziorra et al. 2010). However, this tracer was not well suited as a biomarker in a routine clinical set-up for early AD-diagnosis because of unfavourable properties (especially long acquisition times up to 7 hours). We, therefore, developed the new radiotracer (-)-[18F]NCFHEB (denominated as [18F]Flubatine) with significantly improved brain uptake and also better nAChR affinity and selectivity (Brust et al. 2008). Here, we present the results of the worldwide first ongoing [18F]Flubatine-PET study in humans.
Methods: 19 mild AD-patients (NINCDS-ADRDA, age 74.5±6.2, MMSE 23.7±2.7) and 20 age-matched healthy controls (HC, age 70.6±4.6, MMSE 28.5±0.8) underwent [18F]Flubatine-PET (370 MBq, 3D-acquisition, ECAT Exact HR+, 4 scans, 0-270 min p. i., motion correction with SPM2). All were nonsmokers and naïve for central acting medication. Kinetic modeling was applied to the VOI-based tissue-activity curves generated for 29 brain regions. Total distribution volume (DV) and binding potential (BP, reference region: corpus callosum) were used to characterize specific binding. Additionally, parametric images of DV were computed (Logan plot).
Results: Image quality of [18F]Flubatine scans was clearly superior to 2-[18F]F-A85380, and a 20 minutes scan already adequate for visual analysis. PET data acquired over only 90 minutes were sufficient to estimate all kinetic parameters of all VOIs with 1-tissue compartment model. Thirty-minute scans were already sufficient for modelling of all cortical VOIs. Tracer distribution was similar to known alpha4beta2-nAChR distribution and DVs in HCs increase as expected with receptor density with the lowest DV in the corpus callosum (5.64±0,87) and highest in the thalamus (24.67±3.91). The AD-patients showed significant BP reductions in distinct cortical regions (p<0.05) compared to HCs.
Conclusions: Due to significant faster kinetics and shorter acquisition time enabling full kinetic modeling within 90 minutes, and superior image quality [18F]Flubatine appears to be a much more suitable tracer than 2-[18F]F-A85380 to image alpha4beta2-nAChRs in humans. In keeping with its diagnostic properties, early AD-patients show declines of alpha4beta2-nAChRs in distinct cortical regions typically affected by AD-pathology. These results indicate that [18F]Flubatine-PET could have a great potential to be tested as a biomarker for early AD-diagnosis.

  • Lecture (Conference)
    EANM'12 - Annual Congress of the European Association of Nuclear Medicine, 27.-31.10.2012, Milan, Italy
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 39(2012), S221
    ISSN: 1619-7070

Publ.-Id: 18022

Preclinical Incorporation Dosimetry of (+)-[F-18]flubatine

Sattler, B.; Kranz, M.; Patt, M.; Donat, C. K.; Deuther-Conrad, W.; Hiller, A.; Fischer, S.; Smits, R.; Hoepping, A.; Sattler, T.; Steinbach, J.; Brust, P.; Sabri, O.


Ziel: (+)-[F-18]flubatine is a new tracer for neuroimaging of alpha4beta2 nAChRs with PET. To assess the radiation risk after intravenous application of the radioligand, the biodistribution, organ doses (OD) and the effective dose (ED) were assessed in pigs and compared to results based on data using the stereoisomere (-)-[F-18]flubatine.

Methodik: Whole body dosimetry was performed in 3 female piglets (age: 43±1.2d, weight: 14±1.0kg) The animals were narcotized and sequentially PET-imaged up to 5h post i.v. injection of 183.5±9.0MBq (+)-[F-18]flubatine on a SIEMENS Biograph16 PET/CT-system with 7 bed positions (BP) per frame, 1.5 to 6 min/BP, CT-attenuation correction (AC) and iterative reconstruction. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activity-data (%ID/g, and %ID/organ). Time- and mass-scales were adapted to the human order of magnitude. The ODs were calculated using the adult male model with OLINDA. The ED was calculated using tissue weighting factors as published in the ICRP103.

Ergebnisse: The highest OD was received by the urinary bladder (71.7±26.3µSv/MBq), the kidneys (45.1±6.5 µSv/MBq) and the brain (32.3±3.24µSv/MBq). The highest contribution to the ED was by the urinary bladder (2.9±1.1 µSv/MBq), the lungs (1.7±0.02µSv/MBq) and the red marrow (1.4±0.1µSv/MBq). According to this data, the ED to humans is 14.3±0.3 µSv/MBq.

Schlussfolgerungen: The effective dose upon i.v. application of about 300 MBq (+)-[F-18]flubatine to humans would be 7.1 mSv, taking into account that preclinical dosimetry underestimates the dose to humans by up to 40%. This is well within the range of what is caused by other F18-labeled compounds to humans. This risk assessment encourages to transfer (+)-[F-18]flubatine from preclinical to clinical study phases and to further develop as a clinical tool for PET imaging of the brain.

  • Lecture (Conference)
    NuklearMedizin2013, 17.-20.04.2013, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 2(2013)52, V74
    ISSN: 0029-5566

Publ.-Id: 18021

Dual-plane Ultrasound Array Doppler Velocimeter for Flow Investigations in Liquid Metals

Nauber, R.; Büttner, L.; Burger, M.; Neumann, M.; Czarske, J.; Franke, S.; Eckert, S.

A dual-plane, dual-component ultrasound array Doppler velocimeter for investigating transient complex flow phenomena in liquid metals is presented. It utilizes four sensor arrays consisting of 25 single element transducers along a line of 67 mm. The system combines a spatial resolution of approx. 3 mm with a temporal resolution of up to 30 Hz using electronic beam traversing and time division multiplex. The modular realization of the measurement system allows flexible sensor configuration, e.g. four planes can be measured with one velocity component, two planes with two components or two lines with three components. Those capabilities are demonstrated by measurements in a magnetically stirred metal melt at room temperature.

Keywords: Ultrasound Doppler Velocimetry; Flow Field Measurements; Ultrasound Sensor Array; Liquid Metals; Magnetohydrodynamics; Rotating Magnetic Field

  • Open Access Logo Contribution to proceedings
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Deutschland
    Proceedings of the 8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 7-10
  • Lecture (Conference)
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Deutschland

Publ.-Id: 18020

Indirekte Bestimmung der photokatalytisch generierten Hydroxylradikale – Anwendungen zur Charakterisierung von erweiterten Oxidationsverfahren

Schmoock, C.; Malkova, M.; Börnick, H.; Gravenhorst, O.; Hartmann, J.; Vogel, M.; Lehmann, F.; Kutschke, S.; Raff, J.; Worch, E.

In den letzten Jahren rückten anthropogene Spurenstoffe im Wasserkreislauf, wie z. B. Pharmakarückstände, global in den Fokus von Wissenschaft und staatlicher Überwachung. Allein in Deutschland sind aktuell etwa 3600 pharmazeutische Wirkstoffe für die Human- und Tiermedizin lizensiert. Es sind derzeit nahezu 150 dieser Spurenstoffe und einige ihrer Metaboliten in Grund- und Oberflächenwässern nachweisbar. Sie gelangen über verschiedene Eintragswege in die aquatische Umwelt. Umweltrelevante Arzneimittel sind häufig biologisch nicht oder nur langsam abbaubar, chemisch stabil und in der wässrigen Phase hoch mobil. Zu den in diesem Zusammenhang am häufigsten angewendeten Wasseraufbereitungsverfahren gehören die sogenannten Advanced Oxidation Processes (AOPs). Diese basieren vornehmlich auf der Bildung und weiteren Reaktion von OH-Radikalen, welche deutlich reaktiver als andere in der Wasser- und Abwasserbehandlung genutzte oxidative Spezies sind. In diesem Zusammenhang stellt die Photokatalyse eine vielversprechende Alternative zu herkömmlichen AOPs dar. Die aktuelle Forschung auf dem Gebiet der Materialentwicklung für photokatalytische Anwendungen beschäftigt sich sowohl mit der Modifizierung der verwendeten Nanopartikel zur Verschiebung ihrer photokatalytischen Aktivität in den Bereich des sichtbaren Lichtes als auch mit deren stabiler Immobilisierung.
Im Rahmen eines BMBF-Verbundprojektes wurde dazu die indirekte Quantifizierung der photokatalytisch generierten Hydroxylradikale unter Anwendung von tertiär-Butanol als Testsubstanz zur Beurteilung der Aktivität neuartig modifizierter Photokatalysatormaterialien etabliert. Das aus dieser Umsetzung entstehende Formaldehyd ist analytisch erfassbar und dient letztendlich als Maß für die Menge an entstandenen Hydroxylradikale. Im Rahmen des Forschungsprojektes wurden verschiedene Strategien für eine effiziente und anhaltende Immobilisierungen der Nanopartikel auf unterschiedlichen Trägermaterialien verfolgt. In diesem Zusammenhang konnten unter Anwendung der indirekten Hydroxylradikalbestimmung die Einflüsse der Immobilisierungstechnik auf die Aktivität der Materialien verfolgt werden. Eine vielversprechende Möglichkeit die photokatalytsich aktiven Nanopartikel strukturiert und definiert zu fixieren ist die Abscheidung dieser unter Nutzung bakterieller Surface(S)-Layer-Proteine. In diesem Zusammenhang sollte unter Nutzung der indirekten Hydroxylradikalbestimmung mittels tertiär-Butanol (tBuOH) sowohl der Einfluss der S-Layer-Proteine auf die photokatalytische Aktivität der Nanopartikel als auch eine möglich Veränderung der S-Layer-Proteine unter Einwirkung von OH-Radikalen untersucht werden.
Neben der Charakterisierung neuartige modifizierter Photokatalysatoren bzw. von Wasserinhaltsstoffen erlaubt die indirekte Bestimmung der generierten OH-Radikale auch den Vergleich verschiedener AOPs, z. B. UV/VUV und Photokatalyse, anhand ihrer Radikalbildung pro Zeiteinheit oder Energieeintrag. Zudem ermöglicht sie die Gegenüberstellung spezieller Vor- und Nachteile der einzelnen Verfahren

  • Lecture (Conference)
    Wasser 2013, 06.-08.05.2013, Goslar, Deutschland

Publ.-Id: 18019

Preclinical dose assessment and comparison of (S)-(-)-[18F]fluspidine and (R)-(+)-[18F]fluspidine, new stereoisomeric PET tracers for imaging of σ1 receptors

Kranz, M.; Sattler, B.; Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Holl, K.; Wünsch, B.; Steinbach, J.; Sabri, O.; Brust, P.

Ziel: [18F]Fluspidine (FPD) is a new radio-ligand for imaging of σ1 receptors, a unique type of chaperone which is connected to cancer and neuropsychiatric diseases. To assess the radiation risk to humans, CD1 mice were injected with (S)-(-)-FPD# and (R)-(+)-FPD##. The biodistribution, the organ doses (OD) and effective dose (ED) were estimated.

Methodik: 28#/22## female CD1 mice (weight: 29.8±2.2g#/29.3±1.9g##) were i.v. injected with 0.35±0.08 MBq#/0.39±0.05 MBq## FPD through the V. caudata lateralis. At 5, 15, 30, 45, 60, 90, 120, 180 and 240 min. p.i. the animals were sacrificed (2-4 per time). The organs were isolated, weighed and counted in a γ-counter to determine mass and radioactivity. The masses of skeleton and muscle were extrapolated. The fractions of activity in the source organs were displayed as %ID and scaled to the human magnitude. Time-activity curves were derived by exponential fitting. The numbers of disintegrations in the source organs were calculated as well the ODs and the ED using OLINDA.

Ergebnisse: For (S)-(-)-FPD# the adrenals receive the highest OD (36.0 µSv/MBq), followed by the kidneys (35.6 µSv/MBq) and upper large intestine (ULI) (33.3 µSv/MBq). The highest contribution to the ED was by lungs (3.7µSv/MBq) and ULI (2.0µSv/MBq). For (R)-(+)-FPD## the lungs receive the highest OD (45.5 µSv/MBq), followed by the kidneys (27.6 µSv/MBq) and ULI (25.6 µSv/MBq). The highest contribution to the ED was by lungs (5.5µSv/MBq) followed by ovaries (2.0µSv/MBq). According to these data, the EDs result in 16.7#/18.4## µSv/MBq.

Schlussfolgerungen: Due to this data, the EDs to humans upon i.v. application of 300 MBq would be 8.4mSv#/9.2mSv##, taking into account that preclinical dosimetry usually underestimates the ED to humans up to 40%. This is within the range of what is caused by other [F18]-labeled compounds. This risk assessment encourages to transfer FPD from preclinical to clinical study phases and to further develop it as a clinical tool for brain and cancer-PET imaging.

  • Lecture (Conference)
    NuklearMedizin2013, 17.-20.04.2013, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 2(2013)52, V75
    ISSN: 0029-5566

Publ.-Id: 18018

Ein Kernastrophysiklabor mit 5 MV Beschleuniger im Felsenkeller

Bemmerer, D.

Motivation und Status des geplanten Beschleunigerlabors im Felsenkeller werden zusammengefasst.

Keywords: Solar fusion; cross section; Felsenkeller; nuclear astrophysics; CNO; cycle proton-proton; chain helium burning

Related publications

  • Invited lecture (Conferences)
    Kolloquium "30 Jahre Felsenkeller", 05.11.2012, Dresden, Deutschland

Publ.-Id: 18017

Experimente zu Kernreaktionsraten in der Sonne und in der Big-Bang Nukleosynthese

Bemmerer, D.

Es wird ein Überblick über Kernreaktionsiwrkungsquerschnitte gegeben, die für solare Neutrinos relevant sind.

Keywords: LUNA solar neutrinos Felsenkeller CNO cycle proton-proton chain Borexino SNO+

Related publications

  • Invited lecture (Conferences)
    Astroteilchenphysik in Deutschland: Status und Perspektiven, 20.-21.09.2012, Zeuthen, Deutschland

Publ.-Id: 18016

Experimental study of the 2H(alpha,gamma)6Li nuclear reaction producing 6Li in standard big bang nucleosynthesis

Bemmerer, D.

The 2H(alpha,gamma)6Li reaction dominates the production of lithium-6 in standard big bang nucleosynthesis. Due to its exceedingly low cross section, this reaction has never been studied experimentally at the relevant energies, and consequently the adopted reaction rate depends on uncertain extrapolations. A direct study of the 2H(alpha,gamma)6Li cross section has recently been performed at the LUNA 400 kV accelerator, located deep underground in the Gran Sasso laboratory, Italy. The expected data lie directly at big-bang energies. It is hoped that they help constrain non-standard lithium-6 production scenarios, by putting the standard Big Bang production on a solid experimental footing.

Keywords: LUNA Big Bang Nucleosynthesis radiative capture nuclear astrophysics

  • Poster
    2nd European Nuclear Physics Conference - EuNPC 2012, 17.-21.09.2012, Bukarest, Rumänien

Publ.-Id: 18015

Shallow-underground study of the supernova reaction 40Ca(α,γ)44Ti and the Dresden Felsenkeller

Bemmerer, D.

The 40Ca(alpha,gamma)44Ti reaction dominates the production of the radionuclide 44Ti (half-life 58.9 years) in the alpha-rich freezeout phase of a supernova. As 44Ti is believed to be produced near the so-called mass cut between ejected and infalling material, its detection may help constrain supernova models. Satellite-based gamma observatories have reported 44Ti detections from one supernova remnant, giving a snapshot of current supernova activity. The main production reaction 40Ca(alpha,gamma)44Ti has been studied in the Felsenkeller shallow-underground laboratory by activation, and at the surface of the Earth by in-beam gamma-spectrometry. New values for the strengths of the resonances near 4.5 and 3.5 MeV have been determined, improving the precision of the astrophysical reaction rate at temperatures of 2.5 GK and above.

Keywords: Supernova titanium-44 resonance strength Felsenkeller Tandetron

Related publications

  • Lecture (Conference)
    2nd European Nuclear Physics Conference - EuNPC 2012, 17.-21.09.2012, Bukarest, Rumänien

Publ.-Id: 18014

Coulomb Dissociation of 27P

Beceiro Novo, S.; Süummerer, K.; Cortina-Gil, D.; Wimmer, C.; Plag, R.; Alvarez-Pol, H.; Aumann, T.; Behr, K.; Boretzky, K.; Casarejos, E.; Chatillon, A.; Datta-Pramanik, U.; Elekes, Z.; Fulop, Z.; Galaviz, D.; Geissel, H.; Giron, S.; Greife, U.; Hammache, F.; Heil, M.; Hoffman, J.; Johansson, H.; Karagiannis, C.; Kiselev, O.; Kurz, N.; Larsson, K.; Le Bleis, T.; Litvinov, Y.; Mahata, K.; Muentz, C.; Nociforo, C.; Ott, W.; Paschalis, S.; Prokopowicz, W.; Rodriguez-Tajez, C.; Rossi, D.; Simon, H.; Stanoiu, M.; Stroth, J.; Typel, S.; Wagner, A.; Wamers, F.; Weick, H.

In this work the astrophysical 26Si(p,gamma)27P reaction is studied using the Coulomb dissociation technique. We performed a 27P Coulomb Dissociation experiment at GSI, Darmstadt (28 May-5 June 2007) using the ALADIN-LAND setup which allows complete kinematic studies. A secondary 27P beam at 498 AMeV impinging a 515mg/cm2 Pb target was used. The relative energy of the outgoing system (26Si+p) is measured obtaining the resonant states of the 27P. Preliminary results show four resonant states measured at 0.360.07, 0.880.09, 1.50.2, 2.30.3 MeV and evidence of a higher state at around 3.1 MeV. The preliminary total cross section obtained for relative energies between 0 and 3 MeV has been measured and yields 55+-7 mb.

Keywords: astrophysical inverse kinematics radioactive beam

Publ.-Id: 18013

44Ti, 26Al and 53Mn samples for nuclear astrophysics: the needs, the possibilities and the sources

Dressler, R.; Ayranov, M.; Bemmerer, D.; Bunka, M.; Dai, Y.; Lederer, C.; Fallis, J.; Murphy, A. S.; Pignatari, M.; Schumann, D.

Exploration of the physics involved in the production of cosmogenic radionuclides requires experiments using the same rare, radioactive nuclei in sufficient quantities. For this work, such exotic radionuclides have been extracted from previously proton-irradiated stainless steel samples using wet chemistry separation techniques. The irradiated construction material has arisen from an extended material research programme at the Paul Scherrer Institute, called STIP (SINQ Target Irradiation Program), where several thousand samples of different materials were irradiated with protons and neutrons of energies up to 570 MeV. In total, 8 × 1017 atoms of 44Ti, ~1016 atoms of 26Al and ~1019 atoms of 53Mn are available from selected samples. These materials may now be used to produce targets or radioactive beams for nuclear reaction studies with protons, neutrons and α-particles. The work is part of the ERAWAST initiative (Exotic Radionuclides from Accelerator Waste for Science and Technology), aimed at facilitating new collaborations between the isotope producers and users from different scientific fields including nuclear astrophysics.

Keywords: Radioactive target nuclear astrophysics supernova titanium-44

Publ.-Id: 18012

Preparation and characterisation of isotopically enriched Ta2O5 targets for nuclear astrophysics studies

Caciolli, A.; Scott, D. A.; Di Leva, A.; Formicola, A.; Aliotta, M.; Anders, M.; Bellini, A.; Bemmerer, D.; Broggini, C.; Campeggio, M.; Corvisiero, P.; Depalo, R.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Marta, M.; Menegazzo, R.; Napolitani, E.; Prati, P.; Rigato, V.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Salvo, C.; Straniero, O.; Strieder, F.; Szücs, T.; Terrasi, F.; Trautvetter, H. P.; Trezzi, D.

The direct measurement of reaction cross-sections at astrophysical energies often requires the use of solid targets of known thickness, isotopic composition, and stoichiometry that are able to withstand high beam currents for extended periods of time. Here, we report on the production and characterisation of isotopically enriched Ta2O5 targets for the study of proton-induced reactions at the Laboratory for Underground Nuclear Astrophysics facility of the Laboratori Nazionali del Gran Sasso. The targets were prepared by anodisation of tantalum backings in enriched water (up to 66% in O-17 and up to 96% in O-18). Special care was devoted to minimising the presence of any contaminants that could induce unwanted background reactions with the beam in the energy region of astrophysical interest. Results from target characterisation measurements are reported, and the conclusions for proton capture measurements with these targets are drawn.

Publ.-Id: 18011

First Direct Measurement of the ^{17}O(p,γ)^{18}F Reaction Cross-Section at Gamow Energies for Classical Novae

Scott, D. A.; Caciolli, A.; Dileva, A.; Formicola, A.; Aliotta, M.; Anders, M.; Bemmerer, D.; Broggini, C.; Campeggio, M.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Laubenstein, M.; Menegazzo, R.; Marta, M.; Napolitani, E.; Prati, P.; Rigato, V.; Roca, V.; Somorjai, E.; Salvo, C.; Straniero, O.; Strieder, F.; Szücs, T.; Terrasi, F.; Trezzi, D.

Classical novae are important contributors to the abundances of key isotopes, such as the radioactive ^{18}F, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The ^{17}O(p,\gamma)^{18}F reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range Ecm = 200 - 370 keV appropriate to hydrogen burning in classical novae. In addition, the E=183 keV resonance strength, \omega \gamma=1.67\pm0.12 \mueV, has been measured with the highest precision to date. The uncertainty on the ^{17}O(p,\gamma)^{18}F reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.

Publ.-Id: 18010

Modelling and validation of turbulence parameters at the interface of horizontal multiphase flows

Höhne, T.

One limitation today in simulating horizontal two phase flow is that there is no special turbulence treatment at the free surface. For self generating waves and slugs, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Without any special treatment of the free surface, the high velocity gradients at the free surface generate too high turbulence when using eddy viscosity models like the k-ε or the k-ω model. In the past turbulence damping (symmetric damping procedures for the solid wall-like damping of turbulence in both gas and liquid phases) were introduced within the Algebraic Interfacial Area Density (AIAD) model into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The AIAD approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered for instance in the interfacial drag formulation.
A further step of improvement of modelling the turbulence is the consideration of small wave turbulence that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. So fare in the present code versions they are neglected. However, the influence on the turbulence kinetic energy of the liquid side can be significantly large. A region of marginal breaking is defined according Brocchini and Peregrine and added as a source term in the turbulent kinetic energy equation.
This paper presents first CFD-simulations on horizontal multiphase flows using the new modelling approach.

Keywords: CFD; AIAD

  • Contribution to proceedings
    8th International Conference on Multiphase Flow 2013 (ICMF), 26.-31.05.2013, Jeju, Korea
  • Lecture (Conference)
    8th International Conference on Multiphase Flow 2013 (ICMF), 26.-31.05.2013, Jeju, Korea

Publ.-Id: 18009

Numerical modeling of stratified two-phase flows in industrial applications

Höhne, T.

In the last decade, applications of Computational Fluid Dynamic (CFD) methods for industrial applications received more and more attention, as they proved to be a valuable complementary tool for design and optimization. The main interest towards CFD consists in fact in the possibility of obtaining detailed 3D complete flow-field information on relevant physical phenomena at lower cost than experiments. Typically free surfaces manifest as stratified and wavy flows in horizontal flow domain where gas and liquid are separated by gravity. Stratified two-phase flows are relevant in many industrial applications, e.g. pipelines, horizontal heat exchangers and storage tanks. This paper presents different CFD-simulations on flows using a new modelling approach for the interfacial drag at free surfaces. The developed drag coefficient model was implemented together with the Algebraic Interfacial Area Density (AIAD) model into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The applications considered include the prediction of counter-current flow limitations (CCFL) in a pressurized water reactor (PWR) hot leg, the development of hydraulic jump during the air-water co-current flow in a horizontal channel, and pressurized thermal shock (PTS) phenomena in a PWR cold leg and downcomer. For the modelling of these tasks, an Euler–Euler approach was used. This approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. To demonstrate the feasibility of the present approach, the computed main parameters of each case were compared with experimental data. It is shown that the CFD calculations agree well with the experimental data. This indicates that the AIAD model combined with new drag force modeling is a promising way to simulate the phenomena in frame of the Euler-Euler approach. Moreover the further validation of the model by including mass transfer effects should be carried out.

Keywords: CCFL; CFD; CFX; AIAD

  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Fluidverfahrenstechnik, 12.-14.03.2013, Weimar, Deutschland

Publ.-Id: 18008

New aspects in the numerical modeling of horizontal two-phase flows in industrial applications

Höhne, T.; Darlianto, D.; Apanasevich, P.

In the last decade, applications of Computational Fluid Dynamic (CFD) methods for industrial applications received more and more attention, as they proved to be a valuable complementary tool for design and optimization. The main interest towards CFD consists in fact in the possibility of obtaining detailed 3D complete flow-field information on relevant physical phenomena at lower cost than experiments.
Typically free surfaces manifest as stratified and wavy flows in horizontal flow domain where gas and liquid are separated by gravity.
Stratified two-phase flows are relevant in many industrial applications, e.g. pipelines, horizontal heat exchangers and storage tanks. This paper presents different CFD-simulations on flows using a new modelling approach for the interfacial drag at free surfaces. The developed drag coefficient model was implemented together with the Algebraic Interfacial Area Density (AIAD) model into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The applications considered include the prediction of counter-current flow limitations (CCFL) in a pressurized water reactor (PWR) hot leg, the development of hydraulic jump during the air-water co-current flow in a horizontal channel, and pressurized thermal shock (PTS) phenomena in a PWR cold leg and downcomer. For the modelling of these tasks, an Euler–Euler approach was used. This approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model.
To demonstrate the feasibility of the present approach, the computed main parameters of each case were compared with experimental data. It is shown that the CFD calculations agree well with the experimental data. This indicates that the AIAD model combined with new drag force modeling is a promising way to simulate the phenomena in frame of the Euler-Euler approach. Moreover the further validation of the model by including mass transfer effects should be carried out.

Keywords: CCFL; AIAD; CFD; PTS

  • Contribution to proceedings
    ASME 2013 Fluids Engineering Division Summer Meeting FEDSM2013, 07.-11.07.2013, Incline Village, USA
    Proceedings of the ASME 2013 Fluids Engineering Division Summer Meeting Vol. 1C
  • Invited lecture (Conferences)
    ASME 2013 Fluids Engineering Division Summer Meeting FEDSM2013, 07.-11.07.2013, Incline Village, USA

Publ.-Id: 18007

Hydrodynamics of inclined rotating fixed bed reactors

Härting, H.-U.; Schubert, M.

Periodic operation of trickle bed reactors is an academically established process intensification concept, especially in cases where the mass transfer of the gas phase to the catalyst surface dominates the overall reactor performance.
Further advantages such as damping hot spots and reducing maldistribution have been mentioned in many studies. However, the positive effect of the cycling feed at the inlet strongly decays along the reactor length. Furthermore, industrial implementation hurdles are caused by the complex transient reactor behavior and its control.

Operating a fixed bed reactor at quasi steady-state conditions while maintaining a periodic operation can be achieved by rotation of an inclined reactor: Inclination promotes the phase separation whereas the superimposed rotation induces a periodic wetting and draining of the fixed bed, resulting in alternating access of the gas and liquid reactants to the catalyst surface. This new reactor concept is illustrated in Figure 1.

To evaluate the new reactor concept, hydrodynamic studies were conducted to reveal the flow regimes and to elucidate the liquid saturation distribution. The latter is visualized by a noninvasive compact γ-ray computer tomography system (CompaCT) with a spatial in-plane resolution of 2 mm.
These hydrodynamic studies cover variations of reactor inclination (α = 15°-90°), rotational speed (up to 60 rpm) and gas and liquid superficial velocities (uL = 0.01 m/s – 0.05 m/s and uG = 0.025 – 0.05 m/s). Results for additional variations of particle size, liquid properties (deionized water, silicone oil, cumene) will be reported as well. Furthermore, the hydrodynamic behavior of the inclined rotating reactor is compared with the vertical non-rotating trickle bed reactor configuration.

The effect of reactor inclination and rotational speed on the liquid saturation distribution is exemplarily shown in Figure 2. The lower area of the depicted tomograms corresponds to the bottommost area of the counterclockwise rotating reactor. These experiments were conducted with deionized water and air at ambient pressure and room temperature (ϑL = 20 °C) in a tubular reactor (ID = 0.1 m, L = 1.2 m) packed with 4 mm glass spheres.

For the lowest rotational speed, the gas phase flows mainly in the upper region of the reactor cross-section (Figure 2 a, d) with a pronounced entrainment of the liquid phase for the lower inclination (Figure 2 a) and a clear phase separation for the higher inclination (Figure 2 d). Increased reactor rotation equalizes the liquid distribution for both inclinations (Figure 2 b, e) and results in a ring-like flow pattern (Figure 2 c, f) for the highest rotational speed.

The new reactor concept provides additional degrees of freedom for flow modulation: Reactor inclination and rotational speed. Their influence on the flow patterns and liquid saturation distribution has been investigated by noninvasive tomographic imaging. In combination with the gas and liquid flow rates, these new degrees of freedom allow for adjusting residence time and periodicity of wetting and draining, respectively.

Keywords: Process intensification; fixed bed reactor; gamma-ray computed tomography; inclination; rotation; phase distribution

  • Lecture (Conference)
    9th European Congress of Chemical Engineering - ECCE 9, 21.-24.04.2013, Den Haag, Niederlande

Publ.-Id: 18006

Scale Resolved Simulations of the OECD/NEA−Vattenfall T-Junction Benchmark using LES methods

Höhne, T.

Mixing of fluids in T-junction geometries is of significant interest for nuclear safety research. The most prominent example is the thermal striping phenomena in piping T-junctions, where hot and cold streams join and turbulently mix, however not completely or not immediately at the T-junction. This results in significant temperature fluctuations near the piping wall, either at the side of the secondary pipe branch or at the opposite side of the main branch pipe. The wall temperature fluctuation can cause cyclical thermal stresses and subsequently fatigue cracking of the wall.

Thermal mixing in a T-junction has been studied for validation of CFD-calculations. A T-junction thermal mixing test was carried out at the Älvkarleby Laboratory of Vattenfall Research and Development (VRD) in Sweden. Data from this test have been reserved specifically for a OECD CFD benchmark exercise. The computational results show that RANS fail to predict a realistic mixing between the fluids. The results were significantly better with scale-resolving methods such as LES, showing fairly good predictions of the velocity field and mean temperatures. The calculation predicts also similar fluctuations and frequencies observed in the model test.

Keywords: T-junction; CFD; mixing; LES; Vattenfall; OECD

Publ.-Id: 18005

Tomographische Untersuchung der Phasenanteile und deren Verteilung in einem geneigt rotierenden Festbettreaktor

Hauswald, T.

Das Institut für Fluiddynamik im Helmholtz-Zentrum Dresden-Rossendorf e. V. (HZDR) beschäftigt sich unter anderem mit der Untersuchung verfahrenstechnischer Prozesse sowie der Entwicklung und Charakterisierung neuer effizienter Mehrphasenkontaktapparate und -reaktoren mittels selbstentwickelter innovativer Messtechnik für Mehrphasenströmungen.
Ein solches neuartiges Reaktorkonzept mit dem Ziel der Prozessintensivierung stellt der geneigt rotierende Festbettreaktor dar. Im Gegensatz zum zeitlich-periodischen Reaktorbetrieb erfolgt die Prozessintensivierung hier durch Aufprägung einer örtlichen Periodizität unter ansonsten stationären Betriebsbedingungen. Aus dieser veränderten Betriebsweise ergeben sich durch die Wahl von Neigung und Drehzahl zusätzliche Freiheitsgrade bei der Strömungsführung und damit zur Beeinflussung der Reaktorleistung.
Im Rahmen der Diplomarbeit ist mittels gamma-tomographischer Messung sowie Druckverlustmessung der Einfluss von Reaktorneigung und -drehzahl auf die Phasenanteile und deren Verteilung bei ausgewählten Gas- und Flüssigkeitsdurchsätzen zu untersuchen und mit dem etablierten Rieselbettreaktor zu vergleichen.

Keywords: Mehrphasenreaktor; Prozessintensivierung; Neigung; Rotation; Computertomographie; Strömungsform

  • Diploma thesis
    TU Dresden, 2012
    118 Seiten

Publ.-Id: 18004

Graphene based broadband THz detector working at room temperature

Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Schneider, H.; Helm, M.

Graphene can serve as an attractive detector material for the whole visible and infrared spectral range. Due to the unique band structure of graphene, with a linear dispersion next to the Dirac point where valence and conduction band touch, the absorption is constant for nearly all photon energies. Furthermore the fast carrier relaxation in graphene allows one to build up fast detectors with an electrical response in the GHz range. We demonstrate a detector based on a graphene flake combined with a logarithmic-periodic antenna structure with an outer diameter of 1mm, which connects the flake via an interdigitated structure. The graphene flake was produced by the scotch-tape method on SiO2/Si. To maximize the photocurrent the two halves of the antenna were made of different metals. The metallization was patterned by electron beam lithography. One arm of the antenna consists of a 60nm thick layer of palladium, the other one of 20nm titanium combined with 40nm of gold. With the free-electron laser FELBE at Dresden-Rossendorf we proved room temperature operation in a wide spectral range (wavelength: 8µm-220µm), the coupling of the antenna was verified by measurements of the polarization dependence of the detector for different wavelengths. Additionally we measured FEL-pulses with pulse durations around 20 ps in the wavelength range of 30µm to 220µm. The rise time of the measured signal was approximately 50 ps, the pulse length was in the range of 200 ps. Even though the responsivity was fairly low (~ 1nA/W), this detector could be very useful for timing purposes in two-color experiments.

Keywords: graphene; detector; broadband

Related publications

  • Lecture (Conference)
    International Workshop on Terahertz Science and Technology, 01.-05.04.2013, Kyoto, Japan

Publ.-Id: 18003

Keine Ahnung von der Strahlung – Unbemerkte alltägliche Radioaktivität

Foerstendorf, H.

  • Lecture (others)
    Kreuz-Uni am Evangelischen Kreuzgymnasium Dresden, 19.11.2012, Dresden, Deutschland

Publ.-Id: 18002

Rayleigh-Benard instability of Czochralski configuration in a transverse magnetic field

Grants, I.; Gerbeth, G.

The linear instability of a rotating conducting liquid cylinder heated from below in a horizontal magnetic field is considered numerically. A condition for the magnetic suppression of the bulk rotation is obtained. If the bulk is rotation dominated then the linear instability is slightly delayed by the field and sets in as a rotating wave. If the bulk is dominated by the magnetic field then the instability has the form of field aligned convection rolls. Outside thin boundary layers the instability then becomes increasingly similar to the onset in a plain channel. The results are discussed in light of previous silicon growth experiments and existing knowledge from related problems.

Keywords: Flow instability; Czochralski method; Semiconducting silicon; Magnetohydrodynamics

Publ.-Id: 18001

Creation of Surface Nanostructures on Al2O3 by Slow Highly Charged Ions

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Akhmadaliev, S.; Facsko, S.

Al2O3 single crystals were irradiated with slow highly charged Xe ions of various charge states from an EBIT (Electron Beam Ion Trap) source. The irradiations were performed at room temperature and under normal incidence. Scanning force microscopy (SFM) was utilized to investigate the topography of the irradiated surfaces. The measurements showed that above a potential energy threshold, each ion creates a nanohillock protruding from the surface. These structures are compared to those created by swift heavy ions (SHI). The results are discussed in terms of potential energy deposition of the highly charged ion and electronic energy loss of SHI.

Related publications

Publ.-Id: 18000

Surface Nanostructuring of LiNbO3 by High-Density Electronic Excitations

El-Said, A. S.; Wilhelm, R. A.; Facsko, S.; Trautmann, C.

Lithium niobate (LiNbO3) single crystals were irradiated with high energy gold ions (0.5-2.2 GeV) at the UNILAC (GSI) and with 150-keV highly charged Xenon ions from an EBIT (Electron Beam Ion Trap, HZDR). The surfaces of the irradiated crystals were analyzed by scanning force microscopy showing very similar topographic changes. Swift heavy ions and slow highly charged ions produce hillock-like surface nanostructures on this surface. In both cases, the energy deposition of the ions is characterized by dense localized electronic excitations and efficient transfer to the lattice. Furthermore, the irradiation results in a shift in the band gap energy as evidenced by UV-Vis absorption spectroscopy. Specific modifications (e.g. hillock size, energy loss threshold) induced by slow highly charged ions are discussed in comparison with effects due to the electronic energy loss by swift heavy ions.

Related publications

Publ.-Id: 17999

Characterisation of nanostructures induced by slow highly charged ion bombardment of HOPG

Ritter, R.; Shen, Q.; Teichert, C.; Wilhelm, R. A.; Facsko, S.; Ginzel, R.; Crespo López-Urrutia, J. R.; Aumayr, F.

Earlier studies, which have identified highly charged ion - induced defects on HOPG surfaces as regions of enhanced friction have been extended by measuring the
microscopic friction coefficient at the impact sites and the surrounding matrix by means of lateral force microsopy. Additional investigations have been performed on samples
irradiated with ions in very high charge states (Xe40+ and Bi62+), and, for the first time, defects have also been found employing the intermittent contact AFM mode (Figure 1), where friction forces are basically eliminated from the measuring process (no pseudotopographic contributions arising from friction). This is a strong indication that there is indeed a true topographic modification (as found for other target surfaces) if the impinging ions exceed a certain potential energy threshold. Furthermore, defects have been imaged in the conductive AFM mode, where strong local changes (imaging at atomic resolution) in the conductivity are apparent.

Related publications

  • Poster
    25th Internation Conference on Atomic Collisions in Solids (ICACS), 21.-25.10.2012, Kyoto, Japan

Publ.-Id: 17998

A Study of the Structural properties of GaN implanted by various rare-earth ions

Mackova, A.; Malinský, P.; Sofer, Z.; Šimek, P.; Sedmidubský, D.; Mikulics, M.; Wilhelm, R. A.

GaN layers with <0001> crystallographic orientation, grown by low-pressure metal-organic vapour-phase epitaxy (MOVPE) on c-plane sapphire substrates, were implanted with 200 and 400 keV Sm+, Tm+, Eu+, Tb+ and Ho+ ions at fluencies of 1×1015– 1×1016 cm−2. The composition of the ion-implanted layers and concentration profiles of the implanted atoms were studied by Rutherford Back-Scattering spectrometry (RBS). The profiles were compared to SRIM 2012 simulations. The structural properties of the ion-implanted layers were characterised by RBS-channelling and Raman spectroscopy. Changes in the surface morphology caused by the ion implantation were examined by Atomic Force Microscopy (AFM). A structural analysis showed a high disorder density of the atoms close to the amorphised structure at the surface layer above an implantation fluence of 5x1015 cm-2 while lower disorder density was observed in the bulk according to the projected range of 400 keV ions. The post-implantation annealing induced significant changes only in the Sm and Eu depth profiles; a diffusion of rare-earths implanted at a fluence of 5x1015 cm-2 to the surface was observed. The annealing caused the reconstruction of the surface layer accompanied by surface-roughness enhancement.

Related publications

Publ.-Id: 17997

Nanopores Milled in Carbon Nanomembranes Due to Impact of Individual Slow Highly Charged Ions

Ritter, R.; Wilhelm, R. A.; Stöger-Pollach, M.; Mücklich, A.; Werner, U.; Beyer, A.; Facsko, S.; Gölzhäuser, A.; Aumayr, F.

Nanostructures produced by slow highly charged ion (HCI) impact on surfaces have been a hot topic recently. In this contribution we present first investigations on the effect of individual slow HCI bombardment of freestanding carbon nano-membranes (CNMs). The CNMs are produced by cross-linking of an aromatic self-assembled monolayer of biphenyl units with lowenergy electrons [5]. The substrate is then subsequently removed and the resulting nanosheet (1 nm thickness) transferred onto a holey carbon TEM grid. CNMs produced in such a way are irradiated by slow Xeq+ ions of various charge states (20 ! q ! 40) and kinetic energies (4 keV ! E ! 180 keV).
After irradiation the CNMs are inspected by high resolution imaging techniques, e.g. TEM, SEM and AFM. On the irradiated CNMs we find nanoscopic pores (3 - 30 nm in diameter, see fig. 1), whose number density corresponds well with the incident ion fluence, indicating that about every HCI produces a nano-hole in the CNM. First evaluations of the size distribution of the created pores indicate that the average diameter of a hole induced by a given ion depends strongly on the potential energy of the projectile ion, but is also influenced by the kinetic energy.

Related publications

  • Poster
    16th International Conference Physics of Highly Charged Ions, 02.07.-07.09.2012, Heidelberg, Deutschland
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 10.-11.07.2012, Augsburg, Deutschland
  • Lecture (Conference)
    1st Bielefeld Workshop on Nanolayers and Artificial Membranes, 04.-06.02.2013, Bielefeld, Deutschland

Publ.-Id: 17996

A New Facility for In-Situ Characterization of Slow Highly Charged Ion Modifications of Various Materials

Wilhelm, R. A.; Facsko, S.; Wagner, J.; Heller, R.

The interaction of highly charged ions (HCI) with materials has been studied intensively in the last years. On various materials local topographic modifications at the ion’s impact site could be identified by means of atomic force microscopy (AFM). The type of the modifications, commonly known as nano-structures, varies from pit-like (KBr, PMMA) to craters (TiO2) and hillock-like structures on CaF2 and others ([1, 2]). Most of the recent studies were performed under ex-situ conditions, meaning the target material was transported under ambient conditions from the place of irradiation to an AFM or scanning tunneling microscope. We present a new experimental set-up for in-situ investigations on HCI induced nano-structures. The set-up is based on an assembly of a Dresden-EBIT (Electron Beam Ion Trap) ion source and an Omicron ultra-high-vacuum-AFM. Samples can be mounted in the AFM and analyzed by means of AFM and STM before, during and after the irradiation with HCI. Samples can be heated in-vacuum to prepare clean surfaces before irradiation. The EBIT delivers highly charged ions with Xe charge states up to q=40+, which can be decelerated to kinetic energies
of only 10 eV·q. Figure 1 shows a drawing of the set-up. The dimensions of the set-up are small compared to other HCI facilities. The EBIT is mounted in a high voltage cave and so a negative potential can be applied, while the AFM chamber is kept on ground potential. The final kinetic energy of the ions is defined by the difference of the extraction potential (respective to ground) and the target potential (ground) by Efinal kin = (Uext − Ubeamline) · q. A lens system focusses the beam onto the target with a beam diameter of less than 1 mm.

Related publications

  • Poster
    16th International Conference Physics of Highly Charged Ions, 02.-07.09.2012, Heidelberg, Deutschland
  • Poster
    25th International Conference on Atomic Collisions in Solids (ICACS), 21.-25.10.2012, Kyoto, Japan

Publ.-Id: 17995

The effect of chemical etching on poly (methyl methacrylate) irradiated with slow highly charged ions

Ritter, R.; Wilhelm, R. A.; Ginzel, R.; Schadauer, P.; Heller, R.; Rupp, W.; López-Urrutia, J. R. C.; Facsko, S.; Aumayr, F.

We have recently demonstrated that individual slow highly charged ions are able to produce nanosized pits on poly (methyl methacrylate) surfaces as a result of direct ablation due to the deposition of their high potential energy, if this energy exceeds a critical minimum value. By exposing irradiated samples to a suitable etchant, such pits can be revealed even below this potential energy threshold as latent damage zones are removed. Existing pits, after contact with the etchant grow both in diameter and depth with different etching dynamics for both dimensions. Systematic studies on the response of irradiated samples to a chemical developer are presented.

Keywords: highly charged ions; PMMA; nano-structuring; atomic force microscopy; chemical etching

Related publications

  • Poster
    16th International Conference Physics of Highly Charged Ions, 02.-07.09.2012, Heidelberg, Deutschland
  • Physica Scripta T156(2013), 014065
    DOI: 10.1088/0031-8949/2013/T156/014065

Publ.-Id: 17994

Phase Diagram for Nanostructuring CaF2 Surfaces by Slow Highly Charged Ions

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Facsko, S.; Lemell, C.; Wachter, G.; Burgdorfer, J.; Ritter, R.; Aumayr, F.

The impact of individual slow highly charged ions (HCI) on alkaline earth halide and alkali halide surfaces creates nano-scale surface modifications. For different materials and impact energies a wide variety of topographic alterations have been observed, ranging from regularly shaped pits to nano-hillocks. We present experimental evidence for the creation of thermodynamically stable defect agglomerations initially hidden after irradiation but becoming visible as pits upon subsequent etching. A well defined threshold separating regions with and without etch-pit formation is found as a function of potential and kinetic energies of the projectile. Combining this novel type of surface defects with the previously identified hillock formation, a phase diagram for HCI induced surface restructuring emerges. The simulation of the energy deposition by the HCI in the crystal provides insight into the early stages of the dynamics of the surface modification and its dependence on the kinetic and potential energies.

Related publications

Publ.-Id: 17993

Synthesis and biological evaluation of 18F labeled fluoro-oligo-ethoxylated 4-benzylpiperazine derivatives for sigma-1 receptor imaging

Wang, X.; Li, Y.; Deuther-Conrad, W.; Xie, F.; Chen, X.; Cui, M.-C.; Zhang, X.-J.; Zhang, J.-M.; Steinbach, J.; Brust, P.; Liu, B.-L.; Jia, H.-M.

We report the synthesis and evaluation of a series of fluoro-oligo-ethoxylated 4-benzylpiperazine derivatives as potential σ1 receptor ligands. In vitro competition binding assays showed that 1-(1,3-benzodioxol-5-ylmethyl)-4-(4-(2-fluoroethoxy)benzyl)piperazine (6) exhibits low nanomolar affinity for σ1 receptors (Ki = 1.85 ± 1.59 nM) and high subtype selectivity (σ2 receptor: Ki = 291 ± 111 nM ; Kiσ2/Kiσ1 = 157). [18F]6 was prepared in 30–50% isolated radiochemical yield, with radiochemical purity of >99% by HPLC analysis after purification, via nucleophilic 18Fˉ substitution of the corresponding tosylated precursor. The log DpH7.4 value of [18F]6 was found to be 2.57 ± 0.10, which is within the range expected to give high brain uptake. Biodistribution studies in mice demonstrated relatively high concentration of radiotracers in organs known to contain σ1 receptors, including the brain, lungs, kidneys, heart, and spleen. Administration ofhaloperidol 5 min prior to injection of [18F]6 significantly reduced the concentration of radiotracer in the above-mentioned organs. The accumulation of radiotracers in the bone was quite low suggesting that [18F]6 is relatively stable to in vivo defluorination.
The ex vivo autoradiography in rat brain showed high accumulation of radiotracer in the brain areas known to possess high expression of σ1 receptors. These findings suggest that [18F]6 is a suitable radiotracer for imaging σ1 receptors with PET in vivo.

Keywords: σ1 receptor; fluoro-oligo-ethoxylated; 4-benzylpiperazine; F-18

Publ.-Id: 17992

Ein neues Konzept zur Modellierung der Positronenemitter-Produktion bei der Partikeltherapie

Priegnitz, M.

Eine der drei Säulen der Krebsbehandlung ist die Strahlentherapie. Einer der neuesten Ansätze hierbei ist die Bestrahlung mit Ionen, zurzeit insbesondere Protonen und Kohlenstoffionen. Diese Hochpräzisionstherapie erfordert ein hohes Maß an Kontrolle, da die applizierte Dosisverteilung sehr empfindlich von Dichteveränderungen im durchstrahlten Gewebe abhängt. Das bisher einzige klinisch eingesetzte Verfahren zur in vivo Überwachung der Dosisapplikation bei Ionenbestrahlungen ist die Positronen-Emissions-Tomographie (PET). Sie ermöglicht eine Verifikation der Teilchenreichweite sowie der Lage des Bestrahlungsfeldes.
Die mit der PET-Methode gemessene Aktivitätsverteilung lässt sich jedoch nicht direkt mit der geplanten Dosisverteilung vergleichen. Daher ist eine Vorherberechnung der erwarteten Aktivitätsverteilung auf der Grundlage des Bestrahlungsplanes notwendig, welche dann mit der Messung verglichen wird und eine qualitative Beurteilung der Bestrahlung ermöglicht. Die Vorherberechnung der erwarteten Aktivitätsverteilung erfordert bislang die Kenntnis einer Vielzahl von Wirkungsquerschnitten. Nur für wenige dieser Wirkungsquerschnitte liegen jedoch Messdaten im benötigten Energiebereich und mit ausreichender Genauigkeit vor. Daher verwenden viele Monte-Carlo-Simulationen intrinsische Kernmodelle oder semi-empirische Modellierungen, die häufig eine unzureichende Genauigkeit aufweisen.

In Fachkreisen ist bisher noch nicht geklärt, welches die optimale Ionensorte für die Tumortherapie ist. Insbesondere Lithiumionen weisen aufgrund ihrer physikalischen und radiobiologischen Eigenschaften ein großes Potenzial auf. Auch für Bestrahlungen mit diesen Ionen ist ein PET-Monitoring der Therapie erstrebenswert. In der vorliegenden Arbeit wird zunächst die Anwendbarkeit der Reichweite-Verifikation mittels PET bei Bestrahlung mit Lithiumionen gezeigt. Des Weiteren wird ein Konzept zur Modellierung der Positronenemitter-Verteilung ohne Kenntnis der Wirkungsquerschnitte entwickelt. Diese Vorhersage beruht auf in Referenzmaterialien (Wasser, Graphit und Polyethylen) gemessenen tiefenabhängigen Positronenemitter-Yields, mit welchen durch geeignete Linearkombination die Verteilung der Positronenemitter in beliebigen Materialien bekannter Stöchiometrie vorausberechnet werden kann. Die Anwendbarkeit des Yield-Konzeptes wird gezeigt für Lithium- und Kohlenstoffbestrahlungen homogener Polymethylmethacrylat (PMMA) Targets sowie verschiedener inhomogener Targets.

Keywords: Positronen-Emissions-Tomographie; PET; in-beam; Strahlentherapie; Ionentherapie; Lithium-Ionen; thick target yield; Yield-Konzept

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-029 2012
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 17991

Synthesis and biological evaluation of a novel Tc-99m cyclopentadienyl tricarbonyl complex ([(Cp-R)Tc-99m(CO)(3)]) for sigma-2 receptor tumor imaging

Chen, X.; Cui, M. C.; Deuther-Conrad, W.; Tu, Y. F.; Ma, T.; Xie, Y.; Jia, B.; Li, Y.; Xie, F.; Wang, X.; Steinbach, J.; Brust, P.; Liu, B. L.; Jia, H. M.

We report the design, synthesis and biological evaluation of a novel (99m)Tc 4-(4-cyclohexylpiperazine-1-yl)-butan-1-one-1-cyclopentadienyltricarbonyl technetium ([(99m)Tc]5) as a potential SPECT tracer for imaging of σ(2) receptors in tumors. [(99m)Tc]5 was prepared in 25±5% isolated radiochemical yield with radiochemical purity of >99% via double-ligand transfer (DLT) reaction from the ferrocene precursor 2b (4-(4-cyclohexylpiperazine-1-yl)-1-ferrocenylbutan-1-one). The corresponding Re-complex 4 and the ferrocenyl complex 2b showed relatively high affinity towards σ(2) receptors in in vitro competition binding assay (K(i) values of 4 and 2b were 64.4±18.5nM and 43.6±21.3nM, respectively) and moderate to high selectivity versus σ(1) receptors (K(i)σ(1)/K(i)σ(2) ratios were 12.5 and 95.5, respectively). The logD value of [(99m)Tc]5 was determined to be 2.52±0.33. Biodistribution studies in mice revealed comparably high initial brain uptake of [(99m)Tc]5 and slow washout. Administration of haloperidol 5min prior to injection of [(99m)Tc]5 significantly reduced the radiotracer uptake in brain, heart, lung, and spleen by 40-50% at 2h p.i.. Moreover, [(99m)Tc]5 showed high uptake in C6 glioma cell lines (8.6%) after incubation for 1h. Blocking with haloperidol to compete with [(99m)Tc]5 significantly reduced the cell uptake. Preliminary blocking study in C6-brain-tumor bearing rats showed that [(99m)Tc]5 binds to σ receptors in the brain-tumor specifically. These results are encouraging for further exploration of (99m)Tc-labeled probes for σ(2) receptor tumor imaging in vivo.

Publ.-Id: 17990

High-temperature oxidation resistance in yttrium implanted stainless steel

Barlak, M.; Piekoszewski, J.; Werner, Z.; Sartowska, B.; Waliś, L.; Starosta, W.; Kierzek, J.; Kowalska, E.; Wilhelm, R. A.; Pochrybniak, C.; Woźnica, M.

Austenitic AISI 304, 316L and ferritic 430 stainless steels were implanted with yttrium to fluences ranging between 1 × 10^15 and 5 × 10^17 ions/cm2. The samples were subjected to oxidation in air at a temperature of 1000°C for a period of 100 h and next examined by stereoscopic optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and Rutherford back scattering spectrometry (RBS). The results obtained with the use of ion implantation are discussed.

Keywords: high-temperature oxidation resistance; ion implantation; yttrium

Related publications

  • Open Access Logo Nukleonika 57(2012), 473-476
    ISSN: 0029-5922

Publ.-Id: 17989

Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.]