Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

Imprints of a critical point on photon emission

Wunderlich, F.; Kämpfer, B.

The linear sigma model with linearized fluctuations of all involved fields facilitates the onset of a sequence of first-order phase transitions at a critical point. This phase structure has distinctive imprints on the photon emission rates. We argue that analogously a critical point in the QCD phase diagram manifests itself by peculiarities of the photon spectra, in particular when the dynamical expansion path of matter crosses the phase transition curve in the vicinity of the critical point.

Publ.-Id: 22730

Fission product yield distribution in the 12, 14, and 16 MeV bremsstrahlung-induced fission of 232Th

Naik, H.; Kim, G. N.; Schwengner, R.; Kim, K.; John, R.; Massarczyk, R.; Junghans, A.; Wagner, A.; Goswami, A.

The absolute cumulative yields of various fission products in the 12, 14, and 16 MeV bremsstrahlung-induced fission of 232 Th were determined using a recoil catcher and an off-line γ-ray spectrometric technique using the ELBE electron linac of Helmholtz-Zentrum Dresden-Rossendorf in Dresden, Germany. The mass chain yields were obtained from the absolute cumulative yields by correcting the charge distribution. The peak-to-valley ratio, average light mass ( AL ) and heavy mass ( AH ) values, and average number of neutrons ( exp ) in the bremsstrahlung-induced fission of 232 Th at different excitation energies were obtained from the mass chain yield data. The present study and existing literature data for the 232 Th(γ, f) reaction are compared with similar data for the 238 U(γ, f) reaction at various excitation energies, and surprisingly different behavior was found in the two fissioning systems.

Keywords: Photofission; bremsstrahlung; fission product yield

Publ.-Id: 22729

Ecological and industrial aspects of the interaction of radionuclides with bacterial S-layer proteins

Raff, J.; Vogel, M.; Schmoock, C.; Lehmann, F.; Drobot, B.; Moll, H.; Matys, S.; Börnick, H.; Worch, E.; Pollmann, K.

Radionuclides interact with biomass in various ways. In general, the different interaction mechanisms can be assigned to two physiological aspects, first a radiological toxicity and second a chemical toxicity. Bacteria and archaea developed very early in evolution a multifunctional cell envelope called surface-layer (S-layer) which protects bacteria in extreme environments. This layer is a para-crystalline protein lattice formed by the self-assembly of secreted proteins on the cell wall of bacteria and archaea. S-layers are often glycosylated and phosphorylated and their lattice formation depends often on bivalent cations such as calcium. In case of bacteria living in radionuclide and heavy metal contaminated environments, S-layers are able to act first of all as scavenger for reactive oxygen species (ROS) formed by either radiolysis of water or Fenton reaction. The inactivation of the radicals is achieved by intermolecular crosslinking of tyrosine residues of the protein monomers. Secondly, S-layer proteins are able to selectively bind several radionuclides such as uranium and curium but also other toxic elements such as arsenic. By restraining these metals on the surface of the cell a toxication of the organism is prevented. Interestingly, the mechanism and binding behavior is different for different elements and is highly dependent on pH. Whereas the hexavalent uranium is bound by several surface exposed functional groups and is easily released at acidic pH, the trivalent curium substitutes calcium and is only released at pH 2.5 or below. The stable and selective curium complexation is especially interesting as lanthanides are considered as chemical analogous for trivalent actinides. Thusly, S-layers bind also rare earth elements very effectively, being highly interesting for the development of metal selective filter materials for their enrichment and recovery.

Keywords: radionuclides; lanthanides; S-layers; reactive oxygen species

  • Poster
    Annual Conference 2016 of the Association for General and Applied Microbiology (VAAM), 13.-16.03.2016, Jena, Deutschland

Publ.-Id: 22728

Effect of external stress on dislocation bias factor in Fe-based alloy

Bakaev, A.; Terentyev, D.; Chang, Z.; Posselt, M.

not available, please contact the authors

Keywords: ferritic steels; dislocation bias factor; external stress; molecular statics

  • Lecture (Conference)
    Workshop on nuclear Fe alloys: Modelling and Experiments, 21.-22.09.2015, Getafe/Madrid, Spain

Publ.-Id: 22727

Numerical Simulations for the planned precession dynamo experiment at HZDR

Giesecke, A.; Stefani, F.

In a next generation dynamo experiment currently under development at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a fluid flow of liquid sodium, solely driven by precession, will be considered as a possible source for magnetic field generation. The experiment is mainly motivated by alternative concepts for astrophysical dynamos that are based on mechanical flow driving like the geodynamo model by Malkus (Science 1968, 160, 3825, 259-264) or the model for the ancient lunar dynamo from Dwyer (Nature 2011, 479, 7372, 212-214).

I will present results from non-linear hydrodynamic simulations with moderate precessional forcing dedicated to the planned experiment.
The simulations reveal a non-axisymmetric forced mode with an amplitude of up to one fourth of the rotation velocity of the cylindrical container confirming that precession provides a rather efficient flow driving mechanism even at moderate precession rates.

Promising candidates for exciting a dynamo may be triadic resonances in terms of three distinct inertial modes (so called Kelvin modes, the natural flow eigenmodes in a rotating cylinder) which may emerge from first order non-linear interactions when the height of the container matches their axial wave lengths.
The involved free Kelvin modes are characterized by a high azimuthal wave number and an axial structure comparable to the structure of the columnar convection cells that are responsible for dynamo action in geodynamo simulations.
We find triadic resonances at aspect ratios close to those predicted by the quasi-linear theory except around the primary resonance of the forced mode. In that regime the fundamental forced mode becomes unstable at low Ekman number thus inhibiting the triadic resonance.

Our results will enter into the development of flow models that will be used in kinematic simulations of the electromagnetic induction equation in order to determine whether a precession driven flow will be capable to drive a dynamo at all and to limit the parameter space within which the occurrence of dynamo action is most promising.

Keywords: Dynamo; Precession; DRESDYN

  • Lecture (Conference)
    MHD-Days 2015, 07.-09.12.2015, Ilmenau, Deutschland

Publ.-Id: 22726

Self-assembly of Ge quantum dots on periodically corrugated Si surfaces

Buljan, M.; Facsko, S.; Delač Marion, I.; Mikšić Trontl, V.; Kralj, M.; Jerčinović, M.; Baehtz, C.; Muecklich, A.; Holý, V.; Grenzer, J.; Radić, N.

The fabrication of regularly ordered Gequantum dot arrays on Si surfaces usually requires extensive preparation processing, ensuring clean and atomically ordered substrates, while the ordering parameters are quite limited by the surface properties of the substrate. Here, we demonstrate a simple method for fabrication of ordered Gequantum dots with highly tunable ordering parameters on rippled Si surfaces. The ordering is achieved by magnetron sputter deposition, followed by an annealing in high vacuum. We show that the type of ordering and lattice vector parameters of the formed Gequantum dot lattice are determined by the crystallographic properties of the ripples, i.e., by their shape and orientation. Moreover, the ordering is achieved regardless the initial amorphisation of the ripples surface and the presence of a thin oxide layer.

Publ.-Id: 22725

P1409 - Thermisches Anemometer

Barthel, F.; Schleicher, E.

Die Erfindung betrifft ein thermisches Anemometer zum Erfassen der Strömungscharakteristik einer mehrphasigen Fluidströmung mit einer flüssigen Phase und einer gasförmigen Phase, wobei das Anemometer ein elektrisch beheizbares Strömungssensorelement zum Einbringen in die Fluidströmung und eine Impedanzmessvorrichtung zum Erfassen der Impedanz eines an das Strömungssensorelement angrenzenden Volumens der Fluidströmung aufweist, und wobei von dem Anemometer die Heizleistung des Sensorelements in Abhängigkeit von der erfassten Impedanz eingestellt wird.

  • Patent
    DE102014113031 - Erteilung 19.11.2015

Publ.-Id: 22724

Three new low-energy resonances in the 22Ne(p,γ)23Na reaction

Cavanna, F.; Depalo, R.; Aliotta, M.; Anders, M.; Bemmerer, D.; Best, A.; Böltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Corvisiero, P.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Prati, P.; Scott, D. A.; Somorjai, E.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.

The 22Ne(p,γ)23Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle affects the synthesis of the elements between 20Ne and 27Al in asymptotic giant branch stars and novae. The 22Ne(p,γ)23Na reaction rate is very uncertain because of a large number of unobserved resonances lying in the Gamow window. At proton energies below 400\,keV, only upper limits exist in the literature for the resonance strengths. Previous reaction rate evaluations differ by large factors. In the present work, the first direct observations of the 22Ne(p,γ)23Na resonances at 156.2, 189.5, and 259.7\,keV are reported. Their resonance strengths have been derived with 2-7\% uncertainty. In addition, upper limits for three other resonances have been greatly reduced. Data were taken using a windowless 22Ne gas target and high-purity germanium detectors at the Laboratory for Underground Nuclear Astrophysics in the Gran Sasso laboratory of the National Institute for Nuclear Physics, Italy, taking advantage of the ultra-low background observed deep underground. The new reaction rate is a factor of 5 higher than the recent evaluation at temperatures relevant to novae and asymptotic giant branch stars nucleosynthesis.

Keywords: Nuclear Astrophysics; Asymptotic giant branch stars; Hot bottom burning; LUNA; Underground nuclear astrophysics; Hydrogen burning; Nova nucleosynthesis; Supernova nucleosynthesis

Publ.-Id: 22723

A systemic approach to the problems of the rare earth market

Klossek, P.; Kullik, J.; van den Boogaart, K. G.

China’s dominance of the rare earth market created issues of major concern since 2010: Limited export quotas and consecutive price peaks led to fears concerning supply security. Forward integration is shifting the rare earth-dependent high-technology value chain to China. China’s export embargo to Japan showed the world the strategic relevance of its economic dependence on China’s rare earth products. Despite multiple political and industrial efforts outside China, it was not possible to build up an independent rare earth supply chain. We think that this is prevented by systemic problems of the market. This paper examines these distortions of the rare earth market with a systemic approach. Problems are identified and structured qualitatively in order to expose their economic and political connections. They are (1) competing political-economic models, (2) resource nationalism, (3) market opacity, (4) a lack of trust, (5) weak cooperation and (6) short- versus long-term approaches and profit orientation. These problems are interconnected and create vicious circles. In this context, the paper discusses literature solutions and a new proposal, which provides incentives for a higher diversification of the REE market.

Keywords: Systemic approach; rare earth elements; supply security; state involvement; resource markets

Publ.-Id: 22722

Gemeinsames Recycling von Flachbildschirmen und Bleigläsern

Wolf, R.; Stelter, M.

Derzeit werden weder Bleigläser noch Flachbildschirme wirtschaftlich recycelt. Kathodenstrahlröhren von Monitoren und alten Fernsehgeräten enthalten Blei, ein Massenmetall mit moderatem Preis. Flachbildschirme enthalten Indium und Zinn in so geringen Konzentrationen, dass ein Recycling unwirtschaftlich ist. Ein neues Verfahren wird präsentiert, das beide Abfälle in einem Prozess recycelt, um alle enthaltenen Metalle sowie Glas zurück zu gewinnen. Ein zusätzlicher Vorteil ist das Zero-Waste-Konzept des Verfahrens, da die Endprodukte verwertbares Glas sowie eine Metallphase, die alle Wertmetalle enthält, sind.

Neither lead glass nor flat screens are recycled in an economic way today. Glass from the cathode-ray tubes (CRTs) contains lead, a base metal with a moderate price. Flat screens (LCDs) contain indium and tin in low concentrations. These metals are highly valued, but low concentrations in the panels prohibited recycling. Therefore, a new recycling process is presented to recycle both wastes (CRTs and flat screens) in one process to recover all metals and glass. An additional benefit is the zero waste concept of this process because the products are usable glass and a metal phase containing all valuable metals.

Keywords: Blei; Flachbildschirme; Glas; Indium; Recycling Flat screens; Glass; Indium; Lead; Recycling

Publ.-Id: 22721

Focused ion beam optical patterning of ta-C films

Tsvetkova, T.; Berova, M.; Sandulov, M.; Kitova, S.; Avramov, L.; Boettger, R.; Bischoff, L.

Optical contrast formation by Ga+ ion implantation has been made use of for focused ion beam (FIB) writing of nano-scale optical patterns in tetrahedral amorphous carbon (ta-C). Initial UV-VIS optical spectroscopy results with Ga+ broad-beam ion implantation have shown well expressed ion beam induced photo-darkening effect in thin ta-C films. It is manifested by a significant shift of the optical absorption edge to lower photon energies as obtained from optical transmission measurements of ta-C samples, implanted with Ga+ at ion energy E = 20 keV and ion fluences D = 3e14 and 3e15 cm-2. This shift is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). The obtained optical contrast (between implanted and unimplanted film material) could be made use of in the area of high-density optical data storage using focused Ga+ ion beams. The underlying structural modifications, induced by the Ga+ ion bombardment, have been investigated by x-ray photo-electron spectroscopy (XPS), transmission (TEM) and scanning (SEM) electron microscopy measurements. Focused ion beam (FIB) implanted patterns in ta-C samples, obtained with a fluence of 5e15 cm-2, are also presented.

Keywords: Tetrahedral amorphous carbon; Focused ion beams; Optical data storage

  • Lecture (Conference)
    19th International Conference on Surface Modification of Materials by Ion Beams (SMMIB - 2015), 22.-27.11.2015, Chiang Mai, Thailand
  • Open Access Logo Surface & Coatings Technology 306(2016), 341-345
    DOI: 10.1016/j.surfcoat.2016.07.088


Publ.-Id: 22720

Magnetic dipole excitations of 50Cr

Pai, H.; Beck, T.; Beller, J.; Beyer, R.; Bhike, M.; Derya, V.; Gayer, U.; Isaak, J.; Krishichayan, J. K.; Löher, B.; Nesterenko, V. O.; Pietralla, N.; Martinez-Pinedo, G.; Ponomarev, V. Y.; Reinhard, P.-G.; Repko, A.; Ries, P. C.; Romig, C.; Savran, D.; Schwengner, R.; Tornow, W.; Werner, V.; Wilhelmy, J.; Zilges, A.; Zweidinger, M.

The low-lying M 1-strength of the open-shell nucleus 50 Cr has been studied with the method of nuclear resonance fluorescence up to 9.7 MeV, using bremsstrahlung at the superconducting Darmstadt linear electron accelerator S-DALINAC and Compton backscattered photons at the High Intensity γ-ray Source (HIγS) facility between 6 and 9.7 MeV of the initial photon energy. Fifteen 1+ states have been observed between 3.6 and 9.7 MeV. Following our analysis, the lowest 1+ state at 3.6 MeV can be considered as an isovector orbital mode with some spin admixture. The obtained results generally match the estimations and trends typical for the scissors mode. Detailed calculations within the Skyrme Quasiparticle Random-Phase-Approximation method and the Large-Scale Shell Model justify our conclusions. The calculated distributions of the orbital current for the lowest 1+ -state suggest the schematic view of Lipparini and Stringari (isovector rotation-like oscillations inside the rigid surface) rather than the scissors-like picture of Lo Iudice and Palumbo. The spin M1 resonance is shown to be mainly generated by spin-flip transitions between the orbitals of the f p-shell.

Keywords: Photon scattering; nuclear resonance fluorescence; bremsstrahlung; monoenergetic and polarized gamma radiation; magnetic dipole excitations; QRPA; shell model

Publ.-Id: 22719

Study of the Interaction of Eu3+ with Microbiologically Induced Calcium Carbonate Precipitates using TRLFS

Johnstone, E. V.; Hofmann, S.; Cherkouk, A.; Schmidt, M.

The microbial induced biomineralization of calcium carbonate using the ureolytic bacterium Sporosarcina pasteurii in the presence of trivalent europium, a substitute for trivalent actinides, was investigated by time resolved laser-induced fluorescence spectroscopy (TRLFS) and a variety of physicochemical techniques. Results showed that the bacterial-driven hydrolysis of urea provides favorable conditions for CaCO3 precipitation and Eu3+ uptake due to subsequent increases in NH4+ and pH in the local environment. Precipitate morphologies were characteristic of biogenically formed CaCO3 and consistent with the respective mineral phase compositions. The formation of vaterite with some calcite was observed after one day, calcite with some vaterite after one week, and pure calcite after two weeks. The presence of organic material associated with the mineral was also identified and quantified. TRLFS was used to track the interaction and speciation of Eu3+ as a molecular probe with the mineral as a function of time. Initially, Eu3+ is incorporated into the vaterite phase, while during CaCO3 phase transformation Eu3+ speciation changes resulting in several species incorporated in the calcite phase either substituting at the Ca2+ site or in a previously unidentified, low-symmetry site. Comparison of the biogenic precipitates to an abiotic sample shows mineral origin can affect Eu3+ speciation within the mineral.

Keywords: Biomineralization; TRLFS; fluorescence; europium; calcite; CaCO3


Publ.-Id: 22718

Characterization of Smithsonian microbeam standards by micro-PIXE and -PIGE methods.

Le Bras, L.

High quality and certified standards are necessary to perform accurate and reliable measurements. However, it is complicated to find certified mineral reference materials to calibrate analytical devices like electron microprobe. The aim of the study is to characterize with a high accuracy and precision existing mineral standards in order to perform these calibrations. Standards are coming from the Smithsonian Institute collections at Washington D.C. (U.S.A). Last results of analyzes performed of these standards have been published in 1980 and have been achieved by chemical wet analyzes. It is necessary to perform further investigations to characterize these standards from the chemical and mineralogical point of view in order to use them. 10 mineral standards have been selected in the Smithsonian Microbeam Standard collection according to chemical, crystallographic and geologic criteria. The 3 target are, first to find new trace elements which have not been detected yet, then to quantify all the elements in the standards and at last to check the homogeneity of the samples, an important parameter for performing high quality measurements. Therefore, 2 methods have been selected. They are based on an X- and Gamma-ray emission of samples atoms after collision with an incident proton beam. They are called PIXE and PIGE. They are used respectively for heavy (Z>18) and light (Z<18) element analyzes. An ion microprobe has been used with a particle accelerator in order to provide a 3.54 MeV proton beam to perform analyzes. Results are raw PIXE and PIGE spectra. They are processed with different methods to reach the targets of the study. New trace elements have been found and quantified thanks to data processing. Quantification is irrelevant for minerals with high light elements concentrations because they cannot be quantified. Statistics have been performed on elements distribution through the analyzed particles. Further analyses, and in particular X-ray fluorescence, have to be achieved in order to bring more precisions about the obtained data.

Keywords: Standards; Trace element; Quantification; PIXE; PIGE

  • Master thesis
    Institut Polytechnique LaSalle Beauvais, 2015
    Mentor: Dr. Axel Renno; Dr. Mohamed Nasraoui
    174 Seiten

Publ.-Id: 22717

Electron-Phonon Coupling in Aluminium

Vorberger, J.

An experimental-theoretical investigation of the electron-phonon-coupling in aluminium.

Keywords: electron-phonon coupling; aluminium; two-temperature model; non-equilibrium; phonons; DFT; DFT-MD; electron diffraction

  • Invited lecture (Conferences)
    Laser- und Quantenoptikseminar, 13.11.2015, Kaiserslautern, Deutschland

Publ.-Id: 22716

Alignment of Gold Nanoparticle-Decorated DNA Origami Nanotubes: Substrate Prepatterning versus Molecular Combing

Teschome, B.; Facsko, S.; Gothelf, K. V.; Keller, A.

DNA origami has become an established technique for designing well-defined nanostructures with any desired shape and for the controlled arrangement of functional nanostructures with few nanometer resolution. These unique features make DNA origami nanostructures promising candidates for use as scaffolds in nanoelectronics and nanophotonics device fabrication. Consequently, a number of studies have shown the precise organization of metallic nanoparticles on various DNA origami shapes. In this work, we fabricated large arrays of aligned DNA origami decorated with a high density of gold nanoparticles (AuNPs). To this end, we first demonstrate the high-yield assembly of high-density AuNP arrangements on DNA origami adsorbed to Si surfaces with few unbound background nanoparticles by carefully controlling the concentrations of MgCl2 and AuNPs in the hybridization buffer and the hybridization time. Then, we evaluate two methods, i.e., hybridization to prealigned DNA origami and molecular combing in a receding meniscus, with respect to their potential to yield large arrays of aligned AuNP-decorated DNA origami nanotubes. Because of the comparatively low MgCl2 concentration required for the efficient immobilization of the AuNPs, the prealigned DNA origami become mobile and displaced from their original positions, thereby decreasing the alignment yield. This increased mobility, on the other hand, makes the adsorbed origami susceptible to molecular combing, and a total alignment yield of 86% is obtained in this way.

Keywords: DNA origami; gold nanoparticles; alignment; molecular combing; nanopatterning

Publ.-Id: 22715

Covellite (Bio)-Leaching with Amino Acids

Barthen, R.; Karimzadeh, L.; Gründig, M.; Lippold, H.; Franke, K.; Lippmann-Pipke, J.

Covellite is one of the main copper sulfides found in Kupferschiefer [1]. Besides that there are also indications of secondary covellite formation during leaching processes of related sulfides [2]. Therefore, understanding of covellite dissolution in the context of Kupferschiefer bioleaching is of great importance. However, conventional bioleaching employing acidophilic microorganisms is impeded due to its high acid neutralizing capacity. The Use of neutrophilic bacteria secreting metabolites capable of metal interactions may circumvent this problem. Thus, we synthesized an artificial covellite [3] and subjected it to both chemical and biological leaching. Parameters considered important for covellite dissolution involve e.g. type and concentration of leaching agent, pH, and temperature, presence of other metals or solid phases with adsorptive capacities. First results from batch assays revealed that amino acids might be suitable leaching agents. Physicochemical parameters, which determine leaching success, differ between different amino acids. We found that covellite dissolution is strongly pH dependent for glutamic acid, aspartic acid and arginine, whereas for glutamine and asparagine this could not be shown. The different behavior is currently attributed to the differences in stability of the formed copper-amino acid complexes. In addition pH determines chemical speciation of leaching agent which in turn is a key factor in complex formation. Growth of bacteria sometimes is heavily influencing pH and thus leaching success. Knowledge of these crucial parameters and how they interact, allows for optimization of the leaching process. Furthermore, it is planned to produce amino acids in-situ, by e.g. Corynebacterium glutamicum, to ensure an economical feasible process.

1. Kutschke, S., et al., Bioleaching of Kupferschiefer blackshale – A review including perspectives of the Ecometals project. Minerals Engineering, 2015. 75: p. 116-125.
2. Kostudis, S., et al., Leaching of copper from Kupferschiefer by glutamic acid and heterotrophic bacteria. Minerals Engineering, 2015. 75: p. 38-44.
3. Xin, M., K. Li, and H. Wang, Synthesis of CuS thin films by microwave assisted chemical bath deposition. Applied Surface Science, 2009. 256(5): p. 1436-1442.

  • Poster
    Annual Conference 2016 of the Association for General and Applied Microbiology(VAAM) / Jahrestagung 2016 der Vereinigung für Allgemeine und Angewandte Mikrobiologie (VAAM), 13.-16.03.2016, Jena, Deutschland

Publ.-Id: 22714

Glioblastoma multiforme: emerging treatments and stratification markers beyond new drugs.

von Neubeck, C.; Seidlitz, A.; Kitzler, H. H.; Beuthien-Baumann, B.; Krause, M.

Glioblastoma multiforme (GBM) is the most common primary brain tumour in adults. The standard therapy for GBM is maximal surgical resection followed by radiotherapy with concurrent and adjuvant temozolomide (TMZ). In spite of the extensive treatment, the disease is associated with poor clinical outcome. Further intensification of the standard treatment is limited by the infiltrating growth of the GBM in normal brain areas, the expected neurological toxicities with radiation doses >60 Gy and the dose-limiting toxicities induced by systemic therapy. To improve the outcome of patients with GBM, alternative treatment modalities which add low or no additional toxicities to the standard treatment are needed. Many Phase II trials on new chemotherapeutics or targeted drugs have indicated potential efficacy but failed to improve the overall or progression-free survival in Phase III clinical trials. In this review, we will discuss contemporary issues related to recent technical developments and new metabolic strategies for patients with GBM including MR (spectroscopy) imaging, (amino acid) positron emission tomography (PET), amino acid PET, surgery, radiogenomics, particle therapy, radioimmunotherapy and diets.

Publ.-Id: 22713

Radiation therapy and the global health agenda

Jaffray, D. A.; Atun, R.; Barton, M.; Baumann, M.; Gospodarowicz, M.; Hoskin, P.; Knaul, F. M.; Lievens, Y.; Rosenblatt, E.; Torode, J.; van Dyk, J.; Vikram, B.; Union for International Cancer Control'S Global Task Force On Radiotherapy For Cancer Control

There ist no abstract

Publ.-Id: 22711

γH2AX assay in ex vivo irradiated tumour specimens: A novel method to determine tumour radiation sensitivity in patient-derived material.

Menegakis, A.; von Neubeck, C.; Yaromina, A.; Thames, H.; Hering, S.; Hennenlotter, J.; Scharpf, M.; Noell, S.; Krause, M.; Zips, D.; Baumann, M.


To establish a clinically applicable protocol for quantification of residual γH2AX foci in ex vivo irradiated tumour samples and to apply this method in a proof-of-concept feasibility study to patient-derived tumour specimens.

Evaluation of γH2AX foci formation and disappearance in excised FaDu tumour specimens after (a) different incubation times in culture medium, 4Gy irradiation and fixation after 24h (cell recovery), (b) 10h medium incubation, 4Gy irradiation and fixation after various time points (double strand break repair kinetics), and (c) 10h medium incubation, irradiation with graded single radiation doses and fixation after 24h (dose-response). The optimised protocol was applied to patient-derived samples of seminoma, prostate cancer and glioblastoma multiforme.

Post excision or biopsy, tumour tissues showed stable radiation-induced γH2AX foci values in oxic cells after >6h of recovery in medium. Kinetics of foci disappearance indicated a plateau of residual foci after >12h following ex vivo irradiation. Fitting the dose-response of residual γH2AX foci yielded slopes comparable with in situ irradiation of FaDu tumours. Significant differences in the slopes of ex vivo irradiated patient-derived tumour samples were found.

A novel clinically applicable method to quantify residual γH2AX foci in ex vivo irradiated tumour samples was established. The first clinical results suggest that this method allows to distinguish between radiosensitive and radioresistant tumour types. These findings support further translational evaluation of this assay to individualise radiation therapy.

Keywords: Biomarker; DNA repair; Radiotherapy; Tumour biopsy; γH2AX foci

Publ.-Id: 22709

In vivo studies of the PARP inhibitor, AZD-2281, in combination with fractionated radiotherapy: An exploration of the therapeutic ratio

Gani, C.; Coackley, C.; Kumareswaran, R.; Schütze, C.; Krause, M.; Zafarana, G.; Bristow, R. G.


Pre-clinical data have shown that PARP inhibitors (PARPi) may increase the efficacy of radiotherapy in prostate cancer. However, it is uncertain as to whether PARPi lead to clonogenic kill when combined with radiotherapy (RT).

We tested the PARP inhibitor AZD-2281 as a radiosensitizing agent under oxic and hypoxic conditions for clonogenic survival in vitro and in vivo using the human prostate cancer cell line, 22Rv1. In addition, the effects of PARPi+RT on normal tissue were investigated using a crypt clonogenic assay.

AZD-2281 inhibited cellular PARP activity under both oxic and hypoxic conditions. The addition of AZD-2281 radiosensitized 22Rv1 cells under oxia, acute hypoxia and chronic hypoxia in vitro. The combination of AZD-2281 with fractionated radiotherapy resulted in a significant growth delay and clonogenic kill in vivo. No increased gut toxicity was observed using this combined PARPi+radiotherapy regimen.

This is the first preclinical study to demonstrate direct clonogenic kill in vivo by the addition of AZD-2281 to radiotherapy. As we did not observe gut toxicity, the use of PARPi in the context of prostate cancer radiotherapy warrants further investigation in clinical trials.

Keywords: AZD-2281; Clonogenic assay; EF5; Gamma H2AX; Growth delay; Gut toxicity; PARP inhibitors; Prostate cancer

Publ.-Id: 22708

Residual γH2AX foci after ex vivo irradiation of patient samples with known tumour-type specific differences in radio-responsiveness

Menegakis, A.; de Colle, C.; Yaromina, A.; Hennenlotter, J.; Stenzl, A.; Scharpf, M.; Fend, F.; Noell, S.; Tatagiba, M.; Brucker, S.; Wallwiener, D.; Boeke, S.; Ricardi, U.; Baumann, M.; Zips, D.


To apply our previously published residual ex vivo γH2AX foci method to patient-derived tumour specimens covering a spectrum of tumour-types with known differences in radiation response. In addition, the data were used to simulate different experimental scenarios to simplify the method.

Evaluation of residual γH2AX foci in well-oxygenated tumour areas of ex vivo irradiated patient-derived tumour specimens with graded single doses was performed. Immediately after surgical resection, the samples were cultivated for 24h in culture medium prior to irradiation and fixed 24h post-irradiation for γH2AX foci evaluation. Specimens from a total of 25 patients (including 7 previously published) with 10 different tumour types were included.

Linear dose response of residual γH2AX foci was observed in all specimens with highly variable slopes among different tumour types ranging from 0.69 (95% CI: 1.14-0.24) to 3.26 (95% CI: 4.13-2.62) for chondrosarcomas (radioresistant) and classical seminomas (radiosensitive) respectively. Simulations suggest that omitting dose levels might simplify the assay without compromising robustness.

Here we confirm clinical feasibility of the assay. The slopes of the residual foci number are well in line with the expected differences in radio-responsiveness of different tumour types implying that intrinsic radiation sensitivity contributes to tumour radiation response. Thus, this assay has a promising potential for individualized radiation therapy and prospective validation is warranted.

Keywords: DNA repair; Intrinsic radiation sensitivity; Personalized radiation oncology; Radiotherapy; Tumour specimens; γH2AX foci

Publ.-Id: 22707

EGFR and β1-integrin targeting differentially affect colorectal carcinoma cell radiosensitivity and invasion.

Poschau, M.; Dickreuter, E.; Singh-Müller, J.; Zscheppang, K.; Eke, I.; Liersch, T.; Cordes, N.


Simultaneous targeting of β1 integrin receptor and epidermal growth factor receptor (EGFR) showed higher level of radiosensitization in head and neck cancers than monotherapies. As EGFR inhibition is similarly performed in colorectal cancer (CRC), we investigated the radiosensitizing and anti-invasive potential of β1-integrin/EGFR inhibition in CRC cell lines grown in more physiological three-dimensional (3D) matrix-based cell cultures.

DLD-1 and HT-29 cells were used for 3D-colony formation, invasion and proliferation assays and Western blotting. β1 integrin, focal adhesion kinase and EGFR were inhibited by AIIB2, TAE226 and Cetuximab, respectively. KRAS and BRAF knockdown were accomplished using small-interfering RNA technology. Single doses of X-rays ranged from 2Gy to 6Gy and 5-fluorouracil (5-FU) concentration was 10μM.

Neither β1-integrin/EGFR inhibition nor KRAS or BRAF depletion nor 5-FU significantly modified CRC cell radiosensitivity. Cetuximab, AIIB2 and Cetuximab/AIIB2 differentially modulated MAPK, JNK and AKT phosphorylation. AIIB2 and TAE226 significantly decreased cell invasion.

Our data show inefficiency of Cetuximab and AIIB2 on top of radiochemotherapy. The functions of KRAS and BRAF in therapy resistance remain unanswered and warrant further preclinical molecular-driven investigations. One promising approach might be β1 integrin targeting for reducing metastatic CRC cell spread.

Keywords: Colorectal carcinoma; EGFR; Invasion; Ionizing radiation; β1 integrin

Publ.-Id: 22706

Summary of Working Group 2: Ion beams from plasmas

Schramm, U.; Borghesi, M.

Extenive summary of the working group of the 2nd European Advanced Accelerator Workshop held on ELBA 2015 on ion acceleration with lasers including a summary of published maximum proton energies.

Keywords: Plasma ion acceleration

Publ.-Id: 22705

Voronoï analysis of bubbly flows via ultra fast X-ray tomographic imaging

Lau, Y. M.; Müller, K.; Azizi, S.; Schubert, M.

Although clustering of bubbles plays a signifant role in bubble column reactors regarding the heat and mass transfer due to bubble-bubble and flow field interactions, it has yet to be fully understood. Contrary to flows in bubble columns, most literature studies on clustering report numerical and experimental results on dilute or micro-bubbly flows. In this paper, clustering of bubbles in a cylindrical bubble column of 100 mm diameter is experimentally investigated. Ultra fast X-ray tomographic imaging is used to obtain the bubble positions within a hybrid Eulerian framework. By means of Voronoï analysis, the clustering behaviour of bubbles is investigated. Experiments are performed with different superficial gas velocities, where Voronoï diagrams are constructed at several column heights. From the PDFs of the Voronoï diagrams, it is shown that the bubble structuring in terms of hybrid volume dimensions develops slower than the bubble size distribution. The measured PDFs are compared with the PDF of randomly distributed points, which showed that the amount of bubbles as part of clusters (Voronoï cells < V/V_cluster ) as well as bubbles as part of voids (Voronoï cells > V/V_void) increases with the superficial gas velocity. It is found that all experiments have an approximate cluster limit V/V cluster of 0.63, while the void limit V/V void varies between 1.5 and 3.0.

Keywords: Bubble clustering; ultra fast X-ray tomography; bubble column; bubble size distribution; Voronoï diagrams

Publ.-Id: 22703

Modeling 3-D bubble heat transfer in gas-solid fluidized beds using DEM

Patil, A. V.; Peters, E. A. J. F.; Lau, Y. M.; Kuipers, J. A. M.

Computational fluid dynamics discrete element method simulations of a 3D fluidized bed at nonisothermal conditions are presented. Hot gas injection into a colder bed that is slightly above minimum fluidization conditions is modeled in a 3D square bed containing up to 8 million particles. In this study, bubbles formed in monodisperse beds of different glass particle sizes (0.25, 0.5, 0.75, and 1 mm) and using hot-gas-injection temperatures ranging from 700 to 1100 K are analyzed. Bubble heat-transfer coefficients in 3D fluidized beds are reported and compared with theoretical predictions on the basis of the Davidson and Harrison model.

Publ.-Id: 22702

Formation of solution species and nanoparticles of tetravalent metal ions in aqueous solution

Hennig, C.

The presentation summarizes (i) technical configuration and equipment of the Rossendorf Beamline at the European Synchrotron Radiation Facility / Grenoble, (ii) structure - mobility relationship of An(IV) oxyhydroxy nanoparticles in the environment, and (iii) coordination of An(IV) and Zr(IV) with small carboxylate ligands.

Keywords: ROBL; EXAFS; An(IV); Zr(IV)

  • Invited lecture (Conferences)
    Vortrag im Rahmen des Schwerpunktprogramms „Understanding of Metal Oxide/Water Systems at the Molecular Scale: Structural Evolution, Interfaces, and Dissolution“, 15.10.2015, Berlin, Deutschland

Publ.-Id: 22700

Single-shot betatron source size measurement from a laser-wakefield accelerator

Köhler, A.; Couperus, J. P.; Zarini, O.; Jochmann, A.; Irman, A.; Schramm, U.

Betatron radiation emitted by accelerated electrons in laser-wakefield accelerators can be used as a diagnostic tool to investigate electron dynamics during the acceleration process.
We analyse the spectral characteristics of the emitted Betatron pattern utilizing a 2D x-ray imaging spectroscopy technique. Together with simultaneously recorded electron spectra and x-ray images, the betatron source size, thus the electron beam radius, can be deduced at every shot.

Keywords: betatron radiation; LWFA; Laser-wakefield acceleration

  • Contribution to proceedings
    2nd European Advanced Accelerator Concepts Workshop, 13.-19.09.2015, La Biodola, Isola d'Elba, Italia
    Nuclear Instruments and Methods in Physics Research Section A: Elsevier B.V., 265-269
    DOI: 10.1016/j.nima.2016.02.031
  • Lecture (Conference)
    2nd European Advanced Accelerator Concepts Workshop, 13.-19.09.2015, La Biodola, Isola d'Elba, Italia

Publ.-Id: 22699

Interactions of natural occurring eukaryotic microorganisms with uranium(VI)

Gerber, U.; Krawczyk-Bärsch, E.; Arnold, T.; Merroun, M. L.

Despite high uranium concentrations (up to 14 mg/L) and low pH (2.5 – 3.0) a high microbial diversity was detected by culture independent methods in the flooding water of the former uranium mine Königstein (Saxony, Germany). In this study we used culture dependent techniques for the isolation of eukaryotic microorganisms from the flooding water. It was possible to isolate different eukaryotic fungi with a glucose rich medium. The microbial isolates identified by 16S rDNA and 18S rDNA were tested for their uranium tolerance abilities by the determination of the minimal inhibitory concentration (MIC) on solid media. The results showed high tolerances of uranium (up to 6 mM) on solid agar plates. Based on these results isolate KS5 (Rhodosporidium toruloides) and one reference organism DSM 10134 (Rhodosporidium toruloides) were selected for further uranium interaction experiments. Uranium biosorption tests indicated that the cells of the strain KS5 and the reference DSM 10134 are able to remove high amounts of uranium ranging between 120 and 160 mg uranium/g dry biomass. To test the uranium tolerance quantitative in liquid media flow cytometry experiments with KS5 and DSM 10134 were done. These results showed a higher uranium tolerance of the isolate KS5 compared to the reference culture of DSM 10134 like the tolerance test on solid medium. Summarizing the results of this study indicate that eukaryotic microorganisms within a uranium-contaminated environment could play an important role in the bioremediation of radionuclides.

Keywords: Uranium; Bioremediation; Biosorption; Bioaccumulation

  • Poster
    Ecology of Soil Microorganisms, 29.11.-03.12.2015, Prag, Tschechien

Publ.-Id: 22698

Reduction of U(VI) by anaerobic microorganisms within the flooding water of Königstein

Gerber, U.; Röder, G.; Krawczyk-Bärsch, E.; Arnold, T.

The results of culture-independent methods e.g. pyrosequencing of the 16S rDNA revealed in several anaerobic bacteria. The majority were Firmicutes and Deltaproteobacteria. Several sequences of sulfate-reducing bacteria like Desolfosporosinus, Desulfitobacterium, Desulfovibrio and Desulfatirhabdium could be detected. The results of previous studies showed that sulfate-reducing bacteria (SRB) are able to reduce uranium(VI) to uranium(IV) as well. The reduction of uranium could be used for an in situ bioremediation purpose. The experiments with the flooding water in Königstein revealed that anaerobic microorganisms which were enriched with 10 mM Glycerol are able to reduce uranium(VI) to uranium(IV).

Keywords: Uranium; Bioremediation; Biotransformation; SRB

  • Lecture (others)
    2. Workshop TP5 TransAqua, 16.-17.11.2015, Jena, Deutschland

Publ.-Id: 22697

Search for the superconducting gap structure in κ-(BEDT-TTF)2X by use of thermal-conductivity measurements

Green, E. L.; Kühlmorgen, S.; Schönemann, R.; Müller, J.; Wosnitza, J.

κ-ET2X, where ET is bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF), is a family of organic charge transfer salts consisting of conducting ET layers interspersed between insulating X- anions. For almost two decades it has been debated whether these quasi-two-dimensional (Q2D) superconductors are conventional BCS-type or unconventional d-wave similar to the cuprates. A variety of measurements techniques, including NMR, specific heat, and STM, have been employed, but the results do not concur in regards to the pairing symmetry. To investigate this further, thermal conductivity measurements were performed on single crystal X = Cu[N(CN)2]Br and Cu(NCS)2, both of which undergo superconducting transitions at Tc ≈ 11.5 K and 9.5 K, respectively. In both samples, a relatively large peak in the temperature dependence appears just below Tc which is due to the opening of a superconducting gap and is indicative of high-quality samples. Furthermore, at zero magnetic field, the phonon contribution dominates in both samples at low temperatures (down to 150 mK), as evidenced by a T3 behavior, with no significant remnant electronic contribution in X = Cu[N(CN)2]Br and only a small contribution in X = Cu(NCS)2. Interestingly, when a magnetic field of μoH = 14 T is applied parallel to the conducting layers, the thermal conductivity is smaller in X = Cu[N(CN)2]Br compared to the zero field data, but is significantly larger in X = Cu(NCS)2. Our results demonstrate the importance of electron-phonon scattering in these Q2D superconductors.

  • Lecture (Conference)
    ISCOM 2015, 06.-11.09.2015, Bad Goegging, Deutschland

Publ.-Id: 22696

P0601 - Verfahren zur Kontrolle von Bestrahlungen an Bestrahlungseinrichtungen mit in-beam Positronenemissionstomographen

Crespo, R.; Enghardt, W.; Fiedler, F.; Heidel, K.

Verfahren zur Kontrolle von Bestrahlungen an Bestrahlungseinrichtungen mit in-beam Positronenemissionstomographen, wobei die Mikrostruktur des Strahls verwendet wird, dadurch gekennzeichnet, – dass die Flugzeitdifferenz der Annihilationsquanten gemessen wird und – die Korrelation des Annihilationsortes mit den Strahlortskoordinaten in ein Echtzeitdatenerfassungssystem eingespeist wird und – aus der Korrelation des Annihilationsortes und der Strahlortskoordinaten und der Mikro- und Makrostruktur des Strahls eine off-line-Korrektur der Abbildungsfehler auf Grund physiologischer Prozesse durch Abtrennung der lang- und kurzlebigen Positronenemitter erfolgt.

  • Patent
    DE102006004687 - Offenlegung 18.10.2007, Erteilung 05.11.2015, Nachanmeldungen: WO, EP

Publ.-Id: 22695

Material Requirements for Non-destructive Pulsed Magnets

Zherlitsyn, S.

  • Invited lecture (Conferences)
    2015 MRS Fall Meeting & Exhibit, 29.11.-04.12.2015, Boston, USA

Publ.-Id: 22694

Uranium interaction with DNA and protein

Tsushima, S.

there is no abstract for this talk

Keywords: actinide; biophysics; photochemistry

  • Lecture (Conference)
    Workshop on Fragment Molecular Orbital Method (FMO) Application to Actinide Research, 10.-11.12.2015, Ochanomizu University, Tokyo, Japan

Publ.-Id: 22693

Microscopic Study of the Fulde-Ferrell-Larkin-Ovchinnikov State in an All-Organic Superconductor

Koutroulakis, G.; Kühne, H.; Schlueter, J. A.; Wosnitza, J.; Brown, S. E.

Quasi-two-dimensional superconductors with a sufficiently weak interlayer coupling allow magnetic flux to penetrate in the form of Josephson vortices for in-plane applied magnetic fields. A consequence is the dominance of the Zeeman interaction over orbital effects. In the clean limit, the normal state is favored over superconductivity for fields greater than the paramagnetic limiting field, unless an intermediate, inhomogeneous state is stabilized. Presented here are nuclear magnetic resonance (NMR) studies of the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state for β''-(ET)2SF5CH2CF2SO3. The uniform superconductivity-FFLO transition is identified at an applied field value of 9.3(0.1) T at low temperature (T = 130 mK), and evidence for a possible second transition between inhomogeneous states at ∼11 T is presented. The spin polarization distribution inferred from the NMR absorption spectrum compares favorably to a single-Q modulation of the superconducting order parameter.

Publ.-Id: 22692

Radiobiological influence of megavoltage electron pulses of ultra-high pulse dose rate on normal tissue cells

Laschinsky, L.; Karsch, L.; Leßmann, E.; Oppelt, M.; Pawelke, J.; Richter, C.; Schürer, M.; Beyreuther, E.

Regarding the long term goal to develop and establish laser based particle accelerators for a future radiotherapeutic treatment of cancer the radiobiological consequences of the characteristic short intense particle pulses with ultra-high peak dose rate but low repetition rate of laser-driven beams have to be investigated. This work presents in vitro experiments performed at the radiation source ELBE (Electron Linac for beams with high Brilliance and low Emittance). This accelerator delivered 20 MeV electron pulses with ultra-high pulse dose rate of 10^10 Gy/min either at the low pulse frequency analogue to previous cell experiments with laser-driven electrons or at high frequency for minimizing the prolonged dose delivery and to perform comparison irradiation with a quasi-continuous electron beam analogue to a clinically used linear accelerator. The influence of the different electron beam pulse structures on the radiobiological response of the normal tissue cell line 184A1 and two primary fibroblasts were investigated regarding clonogenic survival and the number of DNA double strand breaks that remain 24 hours after irradiation. Thereby, no significant differences in radiation response were revealed for both biological endpoints and for all probed cell cultures. These results provide evidence that the radiobiological effectiveness of the pulsed electron beams is not affected by the ultra-high pulse dose rates alone.

Keywords: Laser-driven radiotherapy; cell response to electron beams; pulsed irradiation; ultra-high pulse dose rate; normal tissue cell culture


Publ.-Id: 22691

Partial cross sections of the 92Mo(p,γ) reaction and the γ-strength in 93Tc

Mayer, J.; Goriely, S.; Netterdon, L.; Peru, S.; Scholz, P.; Schwengner, R.; Zilges, A.

Background: For a p nucleus, 92 Mo has a high natural isotopic abundance of over 14 %. The γ-process nucleosynthesis is believed to produce 92 Mo, but fails to explain its large abundance, especially with respect to the other p nuclei produced in the same stellar environment. Further studies require precise nuclear models for the calculation of reaction cross sections. Purpose: A measurement of the total and partial cross sections of the 92Mo(p,γ)93Tc reaction allows a stringent test of statistical model predictions. Not only different proton+nucleus optical model potentials, but also the γ-ray strength function of 93Tc can be investigated. In addition, high resolution in-beam γ-ray spectroscopy enables determination of new precise nuclear structure data on 93Tc.
Method: Total and partial cross-section values were measured by means of the in-beam method. Prompt γ-rays produced during the irradiation of 92Mo with protons at seven different energies between 3.7 MeV to 5.3 MeV were detected using the high-purity germanium (HPGe) detector array HORUS at the Institute for nuclear Physics, University of Cologne. The γγ-coincidence method was applied to correlate γ-ray cascades in 93Tc with their origin in the 92Mo+p compound state.
Results: The measured cross sections are compared to Hauser-Feshbach calculations using the statistical model code TALYS on the basis of different nuclear physics input models. Using default settings based on standard phenomenological models, the experimental values cannot be reproduced. A shell model calculation was carried out to predict the M1 strength in 93Tc. Together with Gogny- or Skyrme-HFB plus Quasi-Particle Random Phase Approximation (QRPA) for the gamma-ray strength model, the description between experimental data and theoretical predictions could be significantly improved. In addition, deviations from the adopted level scheme were found.
Conclusions: Using Gogny- or Skyrme-HFB+QRPA E1 and shell-model M1 strength, statistical model predictions can be significantly improved. Partial cross sections provide a valuable testing ground for γ-ray strength functions for nuclear astrophysics applications. In addition, they can be used to investigate nuclear-structure properties of the compound nucleus.

Keywords: Proton capture; cross sections; gamma-strength; QRPA; shell model

Publ.-Id: 22690

Porosity, particle velocity, and diffusion coefficient evolution due to kinetic mineral dissolution - application of iCP (interface COMSOL PHREEQC) for reactive transport modelling

Karimzadeh, L.; Lippmann-Pipke, J.

Changes in porosity, pore water velocity, and diffusion coefficient due to physical and geochemical process are of great importance in reactive transport modelling. Here we present first results and planned tasks resulting from our activities in the ongoing EU-project BioMore [1] that focuses on leaching carbonaceous copper shale ore. Processes such as mineral dissolution and precipitation, clay mineral swelling and squeezing and mineral structure deformation can have significant effect on porosity, permeability and diffusion coefficient. Mineral precipitation decreases the porosity inhibiting solute transport in porous media. On the other hand mineral dissolution increases the porosity and may provide preferential pathways for fluids and dissolved solutes. Accordingly, combining methods for predicting dynamic matrix-material properties in the proposed solute transport models is useful. A finite element based reactive transport model, iCP [2], was developed to simulate kinetic dissolution of calcite and porosity evolution under high acidic condition. An acidic solution with a pH of 1.5 is injected into a 0.25 m long, 0.05 m wide axial fracture flanked by porous media containing 1wt.% calcite. The processes considered in the model are advective-dispersive transport in the fracture calculated by COMSOL Multiphysics (COMSOL, 2015) and kinetically controlled calcite dissolution and precipitation in the porous media simulated by means of PHREEQC [3]. Calcite dissolution is monitored by means of pH and Ca+2 concentrations in the pore fluid and fracture solution. The porosity evolution is calculated by considering the mineral volume fraction change and updated over throughout the time steps for each grid cell of the porous media. Induced tortuosity and effective diffusion coefficient are calculated and updated based on Archie’s low and Millington and Quirk equations respectively.
In cooperation with coworkers and partners further tasks will consider more realistic fracture structure geometry, quantified advective distributions obtained from GeoPET imaging [4] and a more complex geochemical porous matrix.
Overall aims of the project are realistic prognosis calculations for acid consumption, copper release and fluid flux rates as a function of time, aperture width and calcite content.

[2] Nardi, A.; Idiart, A. ; Trinchero, P. ; Manuel de Vries, L. ; Molinero, J. (2014): Interface COMSOL-PHREEQC (iCP), an efficient numerical framework for the solution of coupled multiphysics and geochemistry. Computers & Geosciences 69, 10-21.
[3] Parkhurst, L.D. ; Appelo, C.A.J. (1999): User's Guide to PHREEQC (Version 2)-A Computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. U.S. Geological Survey, Denver, Colorado, p. 326.
[4] Kulenkampff, J.; Gründig, M.; Korn, N.; Zakhnini, A.; Barth, T.; Lippmann-Pipke, J. (2014): Application of high-resolution positron-emission-tomography for quantitative spatiotemporal process monitoring in dense

Keywords: Reactive Transport Modelling; Porosity; Pore Water Velocity; Diffusion Coefficient

  • Lecture (Conference)
    6th Workshop of the PhD Network on Reactive Transport - Modeling and Experiments, 30.11.-01.12.2015, Jülich, Deutschland

Publ.-Id: 22689

Charakterisierung von Morphologie und ortsaufgelöster Zusammensetzung von Materialien für neuartige Energiewandlungs- und speichersyteme mittels eines Ionenmikroskops

von Borany, J.; Hlawacek, G.; Fassbender, J.

Im Rahmen des Projektes wurde ein Ionenmikroskop (Version: ORION NanoFab der Firma Carl Zeiss Microscopy GmbH) er-worben, im Helmholtz-Zentrum Dresden – Rossendorf in Betrieb genommen und bereits für eine Reihe von Nutzer-Experimenten eingesetzt. Dies beinhaltete gleichermaßen Anwendungen in den Bereichen hochauflösende Ionenmikroskopie als auch Beispiele zur Materialmodifikation (Implantation und Strukturierung). Alle Leistungsparameter des Gerätes konnten erreicht werden. Die bisher durchgeführten Beispiel-Untersuchungen haben gezeigt, dass die Vorteile des Gerätes bei der Charakterisierung von iso¬lierenden, porösen oder keramischen Proben und die hohe Tiefenschärfe bei der Abbildung von hoher Relevanz bei der Unter¬suchung von Materialien für die Energietechnik sind.
Als darüber hinausgehendes Ergebnis konnte mittels einer eigenständigen Forschung eine Methode zur Bestimmung der Materialzusammensetzung von Probenoberflächen am Ionenmikroskop entwickelt werden. Dafür werden Verfahren der Ionen-analytik (Rückstreutechnik und Sekundärionen-Massenspektrometrie) eingesetzt. Die dabei realisierte technische Lösung (Flugzeit-Spektrometrie) erfordert nur wenige Zusatzkomponenten am Gerät. Die bisher erreichte Ortsauflösung beträgt ca. 50 nm und kann durch geringe Modifikationen am Gerät weiter verringert werden. Damit können am Ionenmikroskop erstmalig auch analytische Fragestellungen zur chemischen Zusammensetzung von Proben-Oberfläche im sub-100 nm Bereich untersucht werden.
Das Gerät steht im Rahmen der Nutzereinrichtung „Ionenstrahlzentrum“ des HZDR und des Nanoanalytik-Zentrums Dresdens für wissenschaftliche Untersuchungen, aber auch für Partner aus der Industrie zur Verfügung. Die technische und wissenschaftliche Betreuung des Gerätes ist langfristig gesichert, wodurch ein hoher Grad an Nutzerunterstützung angeboten werden kann.

Keywords: Materialcharakterisierung; Ionentechnologie; Ionenmikroskopie; Nanoanalytik; Ionenstreuung; SIMS; RBS

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2015
    Abschlußbericht für Bundesministerium
    14 Seiten
    ISSN: 2191-8708, eISSN: 2191-8716

Publ.-Id: 22687

Towards clinical application: Prompt gamma imaging of passively scattered proton fields with a knife-edge slit camera

Priegnitz, M.; Barczyk, S.; Nenoff, L.; Golnik, C.; Keitz, I.; Werner, T.; Mein, S.; Smeets, J.; Vander Stappen, F.; Janssens, G.; Hotoiu, L.; Fiedler, F.; Prieels, D.; Enghardt, W.; Pausch, G.; Richter, C.

Prompt γ-ray imaging with a knife-edge shaped slit camera provides the possibility of verifying proton beam range in tumor therapy. Dedicated experiments regarding the characterization of the camera system have been performed previously. Now, we aim at implementing the prototype into clinical application of monitoring patient treatments. Focused on this goal of translation into clinical operation, we systematically addressed remaining challenges and questions. We developed a robust energy calibration routine and corresponding quality assurance protocols. Furthermore, with dedicated experiments, we determined the positioning precision of the system to 1.1 mm (2σ).
For the first time, we demonstrated the application of the slit camera, which was intentionally developed for pencil beam scanning, to double scattered proton beams. Systematic experiments with increasing complexity were performed. It was possible to visualize proton range shifts of 2 - 5 mm with the camera system in phantom experiments in passive scattered fields. Moreover, prompt γ-ray profiles for single iso-energy layers were acquired by synchronizing time resolved measurements to the rotation of the range modulator wheel of the treatment system. Thus, a mapping of the acquired profiles to different anatomical regions along the beam path is feasible and additional information on the source of potential range shifts can be obtained.
With the work presented here, we show that an application of the slit camera in clinical treatments is possible and of potential benefit.

Keywords: proton therapy; prompt gamma imaging; range verification; slit camera; double scattering; passively scattered proton treatment

Publ.-Id: 22685

Electromagnetic strength functions from photon scattering

Schwengner, R.

Gamma-ray strength functions are an important ingredient for the calculation of reaction cross sections within the statistical model. Photon scattering from nuclei is a specific tool to study dipole strength functions below the neutron-separation energy as predominantly states with spin J = 1 are excited from the ground state in an even-even nucleus. We present photon-scattering experiments using bremsstrahlung at the γELBE facility of Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and using quasi-monoenergetic, polarized γ rays at the HIγS facility of the Triangle Universities Nuclear Laboratory (TUNL) in Durham. To deduce the photoabsorption cross sections at high excitation energy and high level density, unresolved strength in the quasi-continuum of nuclear states and branching ratios of the ground-state transitions have to be taken into account. In the analysis of the spectra measured by using bremsstrahlung at γELBE, we include the continuum and perform simulations of statistical γ-ray cascades using the code γDEX to estimate intensities of inelastic transitions to low-lying excited states. Simulated average branching ratios are compared with model-independent branching ratios obtained from spectra measured by using monoenergetic γ beams at HIγS.
Photoabsorption cross sections deduced in this way are presented for selected nuclides. Strength in the energy region of the so-called pygmy dipole resonance (PDR) is considered in nuclei around mass 80 and in xenon isotopes.

Keywords: Photon scattering; nuclear resonance fluorescence; bremsstrahlung; monoenergetic polarized γ rays; E1 and M1 γ-ray strength functions; statistical γ-ray cascades

  • Invited lecture (Conferences)
    Fall Meeting of the Division of Nuclear Physics of the American Physical Society, 28.-31.10.2015, Santa Fe, NM, USA

Publ.-Id: 22684

Gamma-ray strength functions in 74Ge

Schwengner, R.

The germanium isotopic chain is of interest for a variety of applied nuclear science purposes due to its presence in high-resolution solid state and scintillation detectors and its use as a density-matching diagnostic constituent in plastic ignition capsules at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). In particular, it is essential for use in extracting the neutron capture cross section for astrophysically relevant neutron energies from germanium nuclei seeded into NIF capsules observed using the Gamma Reaction History (GRH) detector system. These Ge(n,γ) experiments will be used to establish the utility of NIF to perform neutron capture cross section measurements for the interpretation of s-process abundance data.
To study the γ-ray spectrum from excited states in germanium isotopes a combination of experiments using neutron capture and alternative reaction techniques is proposed in an international collaboration. These experiments will take place using thermal neutron capture at the Budapest neutron center, the STARS-LIBERACE (LBNL) and AFRODITE (Capetown) spectrometers for discrete spectroscopy measurements, the CACTUS array at the University of Oslo and the bremsstrahlung facility at ELBE of HZDR for statistical γ-ray measurements. The first part of this contribution presents photoabsorption cross sections determined from nuclear-resonance fluorescence (NRF) experiments performed at the bremsstrahlung facility γELBE. Strength functions deduced from the present NRF experiments are compared with the ones obtained from experiments using (3He,3He') reactions at the cyclotron of Oslo University.
The second part considers calculations of strength functions within the shell model that are analogous to the ones earlier discussed for Mo isotopes. The results of calculations of low-energy M1 strength for 74Ge are compared with experimental strength functions deduced from the (3He,3He') experiments. Predictions for the M1 strength in heavier Ge isotopes are shown.

Keywords: Photon scattering; nuclear resonance fluorescence; gamma-ray strength functions; shell-model calculations

  • Invited lecture (Conferences)
    5th Workshop on Nuclear Level Density and Gamma Strength, 18.-22.05.2015, Oslo, Norwegen

Publ.-Id: 22683

Hybrid microscopic depletion model in nodal code DYN3D

Bilodid, Y.; Kotlyar, D.; Shwageraus, E.; Fridman, E.; Kliem, S.

The paper presents a general hybrid method that combines the micro-depletion method with correction of micro- and macro- diffusion parameters to better account for the spectral history effects. The fuel in a core is subjected to time- and space-dependent operational conditions (e.g. coolant density), which cannot be predicted in advance. However, lattice codes assume some average conditions to generate cross sections (XS) for nodal diffusion codes such as DYN3D. Deviation of local operational history from average conditions leads to accumulation of errors in XS, which is referred as spectral history effects. This paper demonstrates gaps that exist in the current methods used to account for the spectral history effects and presents an alternative, more generalized method. The method, which in principal extends the micro-depletion methods, was implemented in DYN3D and verified on multiple test cases. The results obtained with DYN3D were compared to those obtained with Serpent, which was also used to generate the XS. The observed differences are within the statistical uncertainties.

Publ.-Id: 22682

Radiopharmacological characterization of 64Cu-labeled α-MSH analogs for potential use in imaging of malignant melanoma

Gao, F.; Sihver, W.; Jurischka, C.; Bergmann, R.; Haase-Kohn, C.; Belter, B.; Steinbach, J.; Carta, D.; Bolzati, C.; Calderan, A.; Pietzsch, J.; Pietzsch, H.-J.

The melanocortin-1 receptor (MC1R) plays an important role in melanoma growth, angiogenesis and metastasis, and is overexpressed in melanoma cells. α-Melanocyte stimulating hormone (α-MSH) and derivatives are known to bind with high affinity at this receptor that provides the potential for selective targeting of melanoma.
In this study, one linear α-MSH-derived peptide Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH2 (NAP-NS1) without linker and with εAhx-β-Ala linker, and a cyclic α-MSH derivative, [Lys-Glu-His-D-Phe-Arg-Trp-Glu]-Arg-Pro-Val-NH2 (NAP-NS2) with εAhx-β-Ala linker were conjugated with p-SCN-Bn-NOTA and labeled with 64Cu. Radiochemical and radiopharmacological investigations were performed with regard to transchelation, stability, lipophilicity and in vitro binding assays as well as biodistribution in healthy rats.
No transchelation reactions, but high metabolic stability and water solubility were demonstrated. The linear derivatives showed higher affinity than the cyclic one.
[64Cu]Cu-NOTA-εAhx-β-Ala-NAP-NS1 ([64Cu]Cu-2) displayed rapid cellular association and dissociation in murine B16F10 cell homogenate. All [64Cu]Cu-labeled conjugates exhibited affinities in the low nanomolar range in B16F10. [64Cu]Cu-2 showed also high affinity in human MeWo and TXM13 cell homogenate. In vivo studies suggested that [64Cu]Cu-2 was stable, with about 85% of intact peptide in rat plasma at 2 h p.i. Biodistribution confirmed the renal pathway as major elimination route. The uptake of [64Cu]Cu-2 in the kidney was 5.9% ID/g at 5 min p.i. and decreased to 2.0% ID/g at 60 min p.i.
Due to the prospective radiochemical and radiopharmacological properties of the linear α-MSH derivative [64Cu]Cu-2 this conjugate is a promising candidate for tracer development in human melanoma imaging.

Keywords: Melanocortin-1 receptor; α-MSH analogs; 64Cu labeling; malignant melanoma

Publ.-Id: 22681

Experimental study of a bubble-driven liquid metal two-phase flow under the influence of AC magnetic fields

Vogt, T.; Zhang, C.; Eckert, S.; Gerbeth, G.

Bubble-driven flows are used in many industrial facilities. In metallurgical applications, gas bubbles are injected into furnaces, ladles, or similar melt containing transfer vessels in order to homogenize the melt and their physi-cal and chemical properties. The principle is that a bubble plume accelerates the surrounding liquid upward and produces a recirculation zone. This method is used for steelmaking in bottom blown reactors, and the hydrodynamics of such gasstirred melts were studied in depth by Sahai and Guthrie,[1,2] Johansen et al.,[3] and Mazumdar et al.[4]
The efficiency of gas-stirred systems can be discussed in terms of mixing time, input energy rate, mixing vessel shape, or the type and location of the gas injection. The high relevance of liquid metal stirring makes it worth-while to search for possible improvements of such a pro-cess. A mixing enhancement could yield a better material quality, a reduction of the mixing time, and therefore result in lower mixing gas consumption or lower electric power consumption.
In general, the application of AC magnetic fields can be used to force a motion inside conducting liquids such as liquid metal. Therefore, the overall efficiency of gas-stirred liquid metal systems may be improved by the ap-plication of customized AC-magnetic fields. In this paper, an experimental study is presented considering the influ-ence of different AC magnetic fields on a bubble-driven flow of a liquid metal. The investigation is focused on the bubble distribution and the liquid circulation inside a liq-uid metal column driven by a central jet produced by gas injection. The fluid vessel has a circular cross-section and electrically insulating walls. Low gas flow rates were applied, resulting in a plume of separated bubbles rising inside a spot around the cylinder axis.

  • Lecture (Conference)
    9th International Symposium on Measurement Techniques for Multiphase Flow, 23.-25.09.2015, Sapporro, Japan

Publ.-Id: 22679

Spontaneous occurence of inertial waves in a rotating liquid metal flow.

Vogt, T.; Räbiger, D.; Eckert, S.

The dynamics of free inertial waves inside a cylindrical volume was investigated experimentally in this study. The liquid metal GaInSn was chosen as fluid in order to enable a contactless stimulation of the flow inside the cylinder by means of a rotating magnetic field which generates a supercritical rotating motion of the liquid. The experiment demonstrates that inertial waves may be excited spontaneously by turbulent structures in the rotating flow. A prominent feature of our experimental configuration is the interaction between the inertial modes and the secondary flow arising from the Ekman transport. We observed the formation of inertial waves even without any external triggering in form of deliberate disturbances of the rotating flow field. The reason for such a spontaneous excitation of inertial waves can be explained by the existence of Taylor-Görtler vortices at the sidewall of the vessel. These TG-vortices are conveyed by the secondary flow towards the top and bottom of the vessel where they dissipate in the Bödewadt layer. Such a vortex dissipation in the Bödewadt layer leads to a perturbation of the Ekman pumping resulting in the excitation of an inertial wave.

  • Lecture (Conference)
    Bifurcations and Instabilities in Fluid Dynamics, 15.-17.07.2015, Paris, France

Publ.-Id: 22678

The formation of a magnetically driven tornado-like vortex

Vogt, T.; Grants, I.; Eckert, S.; Gerbeth, G.

A tornado-like vortex is driven by magnetic body forces. A continuously applied rotating magnetic field provides the source of the angular momentum. A pulse of about one order of magnitude stronger travelling magnetic field drives a converging flow that temporarily focuses this angular momentum towards the axis of the container. A highly concentrated vortex forms that produces a funnel-shaped surface depression. The considered transient flow may find a practical application for the purpose of contact-less mixing of floating particles into molten metal, for instance, during the production of oxide dispersion strengthened (ODS) alloys. We explore experimentally the duration, the depth and the conditions of formation of this funnel. Additionally, we measure the axial velocity and calculate the axisymmetric flow field of this transient vortex at a lower force magnitude.

Keywords: ODS-alloys; rotating flows; vortex dynamics; magnetohydrodynamics

  • Lecture (Conference)
    Nagy El-Kaddah Memorial Symposium on Magnetohydrodynamics (MHD) in Material Processing, 15.-19.03.2015, Orlando, United States of America

Publ.-Id: 22677

Time of Flight Backscattering and Secondary Ion Mass Spectrometry in a Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; Gnauck, P.; Facsko, S.; von Borany, J.

Helium ion microscopes (HIM) have developed into a frequently used imaging device in several laboratories around the world. Beside a sub nano-meter resolution and a high depth of focus the latest generation of HIM devices (Zeiss Orion NanoFab) offers the ability to make use of Neon ions enabling additional possibilities for surface modifications on the nm scale [1].
While the image generation in a HIM is based on evaluating the amount of secondary electrons (SE) the information carried by the energy of the backscattered He/Ne projectiles (BS) is not taken into consideration at the moment. Thus the HIM offers excellent topographic imaging capabilities but chemical information (in terms of elemental composition) of the surface is barely accessible. Nevertheless back-scattered particles carry that information and may be used to provide additional contrast mechanism(s). First attempts to measure BS energy spectra were carried out by Sijbrandij et al. [2] and gave evidence for the general feasibility but also revealed that a quantitative chemical analysis of thin layers would require the development of more sophisticated detection concepts than those used in their experiments (silicon surface barrier detector).

Since the primary He/Ne energy is rather low (10-35 keV) back-scattering spectrometry is suffering various difficulties like high contribution of multiple scattering, non-Rutherford backscattering cross sections and an energy dependent charge fraction. Further the angular spread in the collision cascade as well as the high sputtering yields in this energy regime define physical limits on the maximum achievable lateral resolution and the detection sensitivity. In this contribution we will address these challenges and present our experimental approach and the corresponding results of performing BS spectrometry in a HIM.

We show that pulsing the primary ion beam and measuring the Time of Flight (ToF) of the BS He/Ne ions presents a promising technique of performing BS spectrometry in a HIM in terms of sensitivity, energy resolution and lateral resolution.
Our approach enables us also to perform Secondary Ion Mass Spectrometry (SIMS) by just biasing the sample to a positive potential (of several 100V). Advantages and limitations of this technique will be discussed and compared to those of BS spectrometry.
[1] [1] G. Hlawacek, V . V eligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B 32(2), 2014, 020801.
[2] [2] S. Sijbrandij, B. Thompson, J. Notte, B. W. Ward and N. P. Economou, J. Vac. Sci. Technol. B, 26(6), 2008, 2103-2106

  • Poster
    21st International Workshop on Inelastic Ion-Surface Collisions (IISC-21), 20.10.2015, Donostia-San Sebastian, Spain

Publ.-Id: 22676

Pulsed TOF-SIMS in a Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.; von Borany, J.

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their enormous lateral resolution of below 0.3 nm and the highest field of depth make them a unique tool in surface imaging [1]. So far the possibilities to identify target materials (elements) are rather limited or need complex detection setups. In the present contribution we will present a new and relatively easy to implement time of flight method for Ion Beam Analysis (IBA) in the HIM. We utilize pulsed time of flight spectrometry to obtain elemental information from the sample. We will show initial results demonstrating the flexibility and applicability of the method to image samples with target mass contrast and analyze the target compositions. Pulsing the primary helium or neon ion beam and measuring the time of flight of secondary particles from the sample allows to obtain the energy of the backscattered particles or the mass of the sputtered target ions. This has been achieved by chopping the primary ion beam down to pulse widths of 5.5 ns by use of the built in beam blanker and a customized plug-on beam blanking electronics. The secondary particles are detected by means of a multi channel plate mounted on a flange of the HIM. The focus of the contribution will be on the TOF-SIMS concept. SIMS complements the RBS in a way that lateral resolved TOF-SIMS would enable fast qualitative elemental identification and contrast where the TOF-RBS serves quantitative sample compositions free from standards. In addition we point out mayor challenges, downsides and physical limitation of IBA in the HIM.
[1] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B 32(2), 2014

  • Poster
    22nd International Conference on Ion Beam Analysis, 16.06.2015, Opatija, Croatia

Publ.-Id: 22675

Feasibility Study on Cardiac Arrhythmia Ablation Using High-Energy Heavy Ion Beams

Lehmann, I. H.; Graeff, C.; Simoniello, P.; Constantinescu, A.; Takami, M.; Lugenbiel, P.; Richter, D.; Eichhorn, A.; Prall, M.; Kaderka, R.; Fiedler, F.; Helmbrecht, S.; Fournier, C.; Erbeldinger, N.; Thomas, D.; Katus, H. A.; Johnson, S. B.; Parker, K. D.; Debus, J.; Asirvatham, S. J.; Bert, C.; Durante, M.; Packer, D. L.

Rationale ─ Accelerated carbon ions (12C) are rigorously accurate and effective in cancer radiation therapy.
Objective ─ To ablate cardiac locations using a scanned 12C beam in an intact chronic sham-controlled large animal model.
Methods and Results ─ Seventeen pigs were randomized to irradiation of atrioventricular junction (AVJ; 25, 40, and 55 Gy), left atrial right superior pulmonary vein junction (40 Gy), freewall LV (40 Gy), and sham-group. Electroanatomical (EA) mapping, fiducial-, and pacemaker implantation were performed. Cardiac gated CTs were obtained during breath-hold at expiration. Targets were contoured and case-specifically expanded for motion coverage. 12C was delivered using rescanned raster pencil-beams. Animals were followed for up to 6 months.
Fourteen pigs (mean weight 33.8 ± 3.5 kg) were irradiated using a horizontal beam line. For AVJ a mean volume of 1.8 ± 0.1 cc was irradiated. For PVI and LV, mean volumes were 14.9 ± 1.8, and 2.4 ± 0.3 cc, respectively. Risk structures were spared. Animals stayed in sinus rhythm during irradiation. In-beam positron-emission-tomography confirmed precise 12C delivery. Complete atrioventricular block developed over the course of 4 months in 40 and 55 Gy animals. EA mapping confirmed an area without electrogram in the His-location. Histology revealed strong target fibrosis. Apoptosis was found as one of the mechanisms of cell death, being present after 3, but not 6 months.
Conclusion ─ Accelerated 12C is a highly focused form of particle therapy that is a new means for precise cardiac arrhythmia elimination without any invasive procedural access to the body.

Keywords: Atrial Fibrillation; Particle Therapy; Carbon Ion Beam; Atrioventricular Node; Ventricular Tachycardia; Ablation; Catheter-free

Publ.-Id: 22674

Characterization of the microbunch time structure of proton pencil beams at a clinical treatment facility

Petzoldt, J.; Römer, K. E.; Enghardt, W.; Fiedler, F.; Golnik, C.; Hueso-González, F.; Helmbrecht, S.; Kormoll, T.; Rohling, H.; Smeets, J.; Werner, T.; Pausch, G.

Proton therapy is an advantageous treatment modality compared to conventional radiotherapy. In contrast to photons, charged particles have a definite range and can thus spare organs at risk. Additionally, the increased ionization density in the so-called Bragg peak close to the particle range can be utilized for maximum dose deposition in the tumour volume. Unfortunately, the accuracy of the therapy can be dected by range uncertainties which have to be covered by additional safety margins around the treatment volume. A real-time range and dose verification is therefore highly desired and would be key to exploit the major advantages of proton therapy.
Prompt gamma rays, produced in nuclear reactions between projectile and target nuclei, can be used to measure the proton's range. The prompt gamma-ray timing (PGT) method aims at obtaining this information by determining the gamma-ray emission time along the proton path using a conventional time-of-ight detector setup.
First tests at a clinical accelerator have shown the feasibility to observe range shifts of about 5mm at clinically relevant doses. However, PGT spectra are smeared out by the bunch time spread. Additionally, accelerator related proton bunch drifts against the radio frequency have been detected, preventing a potential range verification. At OncoRay, First experiments using a proton bunch monitor (PBM) at a clinical pencil beam have been conducted. Elastic proton scattering at a hydrogen-containing foil could be utilized to create a coincident proton-proton signal in two identical PBMs.
The selection of coincident events helped to suppress uncorrelated background. The PBM setup was used as time reference for a PGT detector to correct for potential bunch drifts. Furthermore, the corrected PGT data were used to image an inhomogeneous phantom. In a further systematic measurement campaign, the bunch time spread was measured for several beam energies between 69 and 225MeV as well as for variable momentum limiting slit openings.We conclude that the usage of a PBM increases the robustness of the PGT method in clinical conditions and that the obtained data will help to create reliable range verification procedures in clinical routine.

Keywords: proton therapy; range verification; beam monitoring; prompt gamma imaging; prompt gamma ray timing

Publ.-Id: 22673

The influence of ignoring higher bone attenuation on pelvic and spinal lesions in [18F]NaF PET/MRI examinations.

Schramm, G.; Oehme, L.; Maus, J.; Hofheinz, F.; Petr, J.; Lougovski, A.; Beuthien-Baumann, B.; van den Hoff, J.

Aim: MRI-based attenuation correction (MRAC) in clinical whole-body PET/MRI imaging routinely is based on tissue type segmentation. Due to lack of MRI signal in cortical bone and the varying signal of spongeous bone, standard whole-body segmentation-based MRAC neglects the difference between the attenuation coefficient of soft tissue and the (higher) one of bone (MRAC-nobone). In the present work we have quantified the bias caused by MRAC-nobone in spinal and pelvic lesions in 20 PET/MRI examinations with [18F]NaF using the reconstructed PET standard uptake value (SUV) as the relevant measure. Methods: We reconstructed 20 PET/MRI [18F]NaF patient data sets acquired with a Philips Ingenuity TF PET/MRI. First, we used the vendor-provided MRAC-nobone algorithm to reconstruct PET-nobone. Second, we used a threshold-based algorithm developed in our group to automatically segment bone structures in the [18F]NaF PET images. Subsequently, an attenuation coefficient of 0.11 1/cm was assigned to the segmented bone regions in the MRI-based attenuation image (MRAC-bone) which was used to reconstruct PET-bone. The automatic bone segmentation algorithm was validated in 6 PET/CT [18F]NaF examinations. Finally, relative SUVmean and SUVmax differences between PET-bone and PET-nobone of 8 pelvic and 41 spinal lesions, and of other regions such as lung, liver, and bladder were calculated. Results: The comparison of [18F]NaF-based and CT-based bone segmentation in the 6 PET/CT patients showed a Dice similarity of 0.7 with a true positive fraction of 0.72 and a false positive fraction of 0.35. The [18F]NaF-based bone segmentation worked well in the pelvis and spine. However, it showed artifacts in the skull and in the extremities. The analysis of the 20 [18F]NaF PET/MRI examinations revealed relative SUVmax differences between PET-nobone and PET-bone of (-8.7% ? 2.7%, p = 0.01) and (-8.1% ? 1.9%, p = 2.4e-8) in pelvic and spinal lesions, respectively. A maximum SUVmax underestimation of -13.7% was found in lesion in the third cervical spine. The averaged SUVmean differences in volumes of interests in lung, liver and bladder were below 3%. Conclusion: Neglecting higher bone attenuation in MRAC leads to a systematic moderate SUV underestimation in spinal and pelvic lesions. The developed automatic [18F]NaF PET-based bone segmentation allows to include higher bone attenuation in whole-body MRAC and thus improves quantification accuracy for pelvic and spinal lesions in [18F]NaF PET/MRI examinations enabling direct comparisons to PET/CT examinations.

  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine (EANM), 10.-14.10.2015, Hamburg, D
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 42(2015), S151
    DOI: 10.1007/s00259-015-3198-z

Publ.-Id: 22672

Correlation of SUVand tumor to blood standard uptake ratio (SUR) with the metabolic uptake rate derived from quantitative dual time point measurements.

Hofheinz, F.; van den Hoff, J.; Lougovski, A.; Ego, K.; Amthauer, H.; Apostolova, I.

Aim: Determination of tumor SUV is widely used for quantitative assessment of tumor metabolism in FDG-PET. However, the SUV approach has several well known limitations compromising its ability to act as a surrogate parameter of glucose consumption. Recently, we have shown that SUR overcomes most of these limitations as long as FDG kinetics in the target structure can be considered irreversible [1,2]. Excellent linear correlation of SUR and Km from Patlak analysis was found using dynamic imaging of liver metastases. However, due to the perfectly standardized uptake period used for SUR determination and the comparatively short uptake period these results are not directly applicable to clinical whole body examinations, in which the uptake periods often vary considerably. Therefore, the aim of this work was to investigate the correlation of SUR and Km in clinical whole body scans, where Km was approximated by Ks derived from dual time point (DTP) measurements [3]. Methods: DTP FDG-PET/CT was performed in 76 consecutive patients with histologically proven NSCLC. In the PET images the primary tumor was delineated with an adaptive threshold method. For determination of the blood SUV the aorta was delineated manually in the attenuation CT. The aorta ROI was transferred to the PET image. Blood SUV was computed as the mean value of the aorta ROI. SUR values were computed as ratio of tumor SUV and blood SUV. SUR values were scan-time-corrected to 60 min p.i. as described in [2]. Metabolic uptake rate Ks was computed similar to the procedure in [3]. The correlation of SUV and SUR with Ks was investigated. Results: There was highly significant correlation of SUR and Ks ( R2=0.9). However, the correlation coefficient appeared somewhat lower than previous results obtained from dynamic imaging and standardized uptake times (R2=0.96 [1]). As expected, SUV showed markedly lower correlation with Ks than SUR (R2=0.76). Conclusion: Our results show that in clinical whole body PET the correlation of uptake values with the metabolic trapping rate can be improved notably by blood normalization and scan-time-correction. Furthermore, the high correlation of SUR with Ks indicates that for histologically unambigous tumor lesions DTP do not provide added value in comparison to the SUR approach. Literature: [1] EJNMMI Res 2013,3:77 [2] EJNMMI Res 2014,4:18 [3] EJNMMI Res 2012,3:16

  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine (EANM), 10.-14.10.2015, Hamburg, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 42(2015), S70-S71
    DOI: 10.1007/s00259-015-3198-z

Publ.-Id: 22670

Evaluation of the influence of truncation artifacts using in-vivo based quantification accuracy methods in combined PET/MRI

Maus, J.; Schramm, G.; Hofheinz, F.; Oehme, L.; Lougovski, A.; Petr, J.; Platzek, I.; Beuthien-Baumann, B.; Steinbach, J.; Kotzerke, J.; van den Hoff, J.

Aim: Quantitative accuracy of standardized uptake values (SUV) and tracer kinetic uptake parameters in patient investigations requires determination of regional activity concentrations in PET data. This determination rests on the assumption that the scanner calibration is valid in-vivo. In a recent study we introduced a method to test this assumption. For 3 different PET and PET/CT systems the activity concentration of urine samples measured in a well-counter were compared to those derived from PET images of the bladder. The study demonstrated a low but systematic underestimation of 7-12% of PET relative to a cross-calibrated well-counter for 56 subjects. In the present study we have applied this method to the Philips Ingenuity-TF PET/MR to evalute the impact of MR-based truncation artifcats on the overall quantitative accuracy of this system. Methods: 21 clinical whole-body F18-FDG scans were included in this study. The bladder region was imaged as the last bed position and urine samples were collected afterwards. PET images were reconstructed including MR-based attenuation correction with and without truncation compensation and 3D region-of-interests (ROI) of the bladder were delineated by 3 observers. Activity concentrations were determined in the PET images for the bladder as well as for the urine by measuring the samples in a well-counter. Results: The in-vivo activity concentrations of the bladder were significantly lower in PET/MR than in the well-counter with a ratio of the former to the latter of 0.756?0.060 (mean? and a range of [0.604-0.858]. Linearity scans revealed a systematic error of 8-11 % (avg. 9 %). After correcting for this systematic bias caused by shortcomings of the manufacturer?s calibration procedure the PET to well-counter ratio increased to 0.832?0.064 [0.668-0.941]. After applying compensation for truncation of the upper extremities in the MR-based attenuation maps the ratio further increased to 0.871?0.069 [0.693-0.992]. Conclusions: Our results show, that the Ingenuity-TF PET/MR underestimates activity concentrations in the bladder by 17% which is 7 percentage points larger than in the previously investigated PET/CT systems. This difference in behavior can be attributed to remaining limitations of MR-based attenuation correction as our results on truncation compensation related influences suggest - leaving only a 2 pp. larger underestimation of activity concentrations if corrected. Thus, quantification accuracy of the Ingenuity-TF PET/MR can be considered acceptable for clinical purposes. The comparison of PET images from the bladder region with urine samples has proven a useful method to evaluate quantification accuracy of different PET systems in-vivo.

  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine (EANM), 10.-14.10.2015, Hamburg, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 42(2015), S18-S19
    DOI: 10.1007/s00259-015-3198-z

Publ.-Id: 22669

First-In-Man Biodistribution und Inkorporationsdosimetrie von (S)-(-)-18F-Fluspidine zur Darstellung zerebraler σ1-Rezeptoren mit PET

Sattler, B.; Kranz, M.; Wüst, N.; Patt, M.; Meyer, P. M.; Deuther-Conrad, W.; Fischer, S.; Wünsch, B.; Steinbach, J.; Brust, P.; Sabri, O.

Ziel: Zur Abschätzung des Strahlenrisikos für Menschen nach i.v. Applikation von (S)-(-)-18F-Fluspidine sind die Erhebung der Biodistribution und inkorporationsdosimetrische Messungen an gesunden Probanden erforderlich. Die Organdosen (OD), sowie die effektive Dosis (ED) wurden erhoben und mit präklinischen Ergebnissen (Kleintier PET/MR* sowie Organentnahme**) verglichen.

Methodik: 3 gesunde Probanden (Alter 20,3 ± 3,3 a, Gewicht: 55,7 ± 4,2 kg, 2 w, 1 m) wurden nach i.v. Injektion von 255 ± 9 MBq (S)-(-)-18F-Fluspidine an 10 Zeipunkten bis zu 7 h p.i. an einem PET/CT (SIEMENS Biograph16) untersucht. Das Protokoll umfasste 8 Bettpositionen (BP), 1,5 – 6 min/BP, CT-Schwächungskorrektur, und iterative Rekonstruktion (OSEM, 4 Iterationen, 8 Subsets). In den Untersuchungspausen wurde sämtlicher Urin gesammelt, volumetriert, aktivimetriert und in der Dosisabschätzung berücksichtigt. Die den Tracer anreichernden Quellorgane wurden identifiziert und per VOI-Analyse deren Aktivitätskonzentrationen ermittelt. Die Zeit-Aktivitäts-Daten wurden durch exponentielle Kurven approximiert, die kumulierte Aktivität berechnet und die OD mit OLINDA/EXM (v1.0) abgeschätzt. Zur Berechnung der ED wurden die Gewebewichtungsfaktoren der ICRP 103 verwendet.

Ergebnisse: Die höchste OD (µSv/MBq) erhält im Mittel die Leber (80,3), gefolgt von Gallenblase (61,7), Dünndarm (54,8), Magen (35,2) und Niere (33,1). Die größten Beiträge zur ED (µSv/MBq) entstehen durch Magen (4,2), Lunge (3,6), Leber (3,2) und rotes Knochenmark (2,8). Die ED nach i.v. Applikation von (S)-(-)-18F-Fluspidine ergibt sich zu von 22,2 ± 0,4 µSv/MBq.

Schlussfolgerungen: Nach Injektion von 300 MBq (S)-(-)-18F-Fluspidine ergibt sich die ED zu 6,7 mSv. Sie liegt damit in der Größenordnung anderer 18F-markierter Tracer (z. B. (+)-Flubatine = 6,9 mSv, FDG = 5,7 mSv) und 42%* bzw. 25%** über der abgeschätzten ED aus präklinischen Untersuchungen.

  • Lecture (Conference)
    54. Jahrestagung der DGN 2016, 20.-23.04.2016, Dresden, Deutschland

Publ.-Id: 22668

Reverse Epitaxy on Elemental Semiconductors

Engler, M.; Michely, T.; Facsko, S.

Self-organized pattern formation during ion beam erosion can produce a variety of periodic patterns. Depending on the substrate and the irradiation conditions ripples, dots, holes or checkerboard patterns have been observed [1]. Pattern formation by low energy ion beam irradiation at low temperature, where the semiconductor surface is amorphized has been studied in detail in the last decades.

Low energy ion beam irradiation performed above the dynamic recrystallization temperature prevents the amorphization of the semiconductor surface. Above this transition temperature, the diffusion of adatoms and vacancies across step edges is hindered by an additional potential barrier, the Ehrlich-Schwoebel barrier. This barrier induces an effective destabilizing surface current during ion beam irradiation. This instability induces pattern formation even at conditions leading to a smooth surface below the transition temperature.

This mechanism, termed reverse epitaxy [2], allows the creation of novel types of surface patterns aligned to certain crystallographic directions of the irradiated surface.

In this contribution we will present different types of patterns on elemental semiconductor surfaces and how it can be changeds by choosing the surface orientation and the irradiation conditions. For example, the pattern changes qualitatively on Si(100) under 2 keV Kr ion irradiation (Figures 1 and 2) with the ion fluence. Furthermore the pattern symmetry is determined by the symmetry of the irradiated surface. For Si(100) the ridges in the high fluence case are aligned to the [010] and [001] directions, whereas on Si(110) (Figure 3) the pattern is symmetric to the [110] and [001] directions.

[1] Chan, Wai Lun, and Eric Chason. J. Appl. Phys. 101 (2007): 121301
[2] Ou, Xin, Adrian Keller, Manfred Helm, Jürgen Fassbender, and Stefan Facsko. Phys. Rev. Lett. 111 (2013): 016101

  • Lecture (Conference)
    21st International Workshop on Inelastic Ion-Surface Collisions (IISC-21), 19.10.2015, Donostia-San Sebastián, España
  • Invited lecture (Conferences)
    International Conference on Nanostructuring with Ion Beams (ICNIB2015), 23.-25.11.2015, Agra, India

Publ.-Id: 22667

Data compilation and evaluation for U(IV) and U(VI) for the Thermodynamic Reference Database THEREDA

Richter, A.; Bok, F.; Brendler, V.

THEREDA (Thermodynamic Reference Database) is a collaborative project, which has been addressed this challenge. The partners are Helmholtz-Zentrum Dresden-Rossendorf, Karlsruhe Institute of Technology (KIT-INE), Gesellschaft für Anlagen- und Reaktorsicherheit Braunschweig mbH (GRS), TU Bergakademie Freiberg (TUBAF) and AF-Consult Switzerland AG (Baden, Switzerland). The aim of the project is the establishment of a consistent and quality assured database for all safety relevant elements, temperature and pressure ranges, with its focus on saline systems. This implied the use of the Pitzer approach to compute activity coefficients suitable for such conditions. Data access is possible via commonly available internet browsers under the address
One part of the project - the data collection and evaluation for uranium – was a task of the Helmholtz-Zentrum Dresden-Rossendorf. The aquatic chemistry and thermodynamics of U(VI) and U(IV) is of great importance for geochemical modelling in repository-relevant systems. The OECD/NEA Thermochemical Database (NEA TDB) compilation is the major source for thermodynamic data of the aqueous and solid uranium species, even though this data selection does not utilize the Pitzer model for the ionic strength effect correction. As a result of the very stringent quality demands, the NEA TDB is rather restrictive and therefore incomplete for extensive modelling calculations of real systems. Therefore, the THEREDA compilation includes additional thermodynamic data of solid secondary phases formed in the waste material, the backfill and the host rock, though falling into quality assessment (QA) categories of lower accuracy. The data review process prefers log K values from solubility experiments (if available) to those calculated from thermochemical data.

Keywords: thermodynamic database; THEREDA; geochemical modelling; uranium

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-065 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 22666

In-situ observation of dendritic solidification under the influence of natural and electromagnetically driven convection

Eckert, S.; Shevchenko, N.; Roshchupkina, O.; Sokolova, O.

The directional solidification of Ga–25wt%In alloys within a Hele-Shaw cell was visualized by means of X-ray radioscopy. The experimental investigations are especially focused on the impact of melt convection on the dendritic growth. Natural convection occurs during a bottom up solidification because lighter solute is rejected at the solid-liquid interface leading to an unstable density stratification. Forced convection was produced by a rotating wheel with two parallel disks containing at their inner sides a set of permanent NdFeB magnets with alternating polarization. The direction of forced melt flow is almost horizontal at the solidification front whereas local flow velocities in the range between 0.1 and 1.0 mm/s were achieved by controlling the rotation speed of the magnetic wheel. Melt flow induces various effects on the grain morphology primarily caused by the convective transport of solute. Our observations show a facilitation of the growth of primary trunks or lateral branches, suppression of side branching, dendrite remelting and fragmentation. The manifestation of all phenomena depends on the dendrite orientation, local direction and intensity of the flow. The forced flow eliminates the solutal plumes and damps the local fluctuations of solute concentration. It provokes a preferential growth of the secondary arms at the upstream side of the primary dendrite arms, whereas the high solute concentration at the downstream side of the dendrites can inhibit the formation of secondary branches completely. Moreover, the flow changes the inclination angle of the dendrites and the angle between primary trunks and secondary arms.

Keywords: X-ray radioscopy; solidification; dendrites; segregation; solutal convection; electromagnetic stirring

  • Invited lecture (Conferences)
    8th International Conference on Electromagnetic Processing of Materials, EPM 2015, 12.-16.10.2015, Cannes, France

Publ.-Id: 22665

Flow measurements in a liquid metal model of a bloom caster under the effect of rotary electromagnetic stirring

Willers, B.; Eckert, S.; Barna, M.; Reiter, J.

This paper presents an experimental study of electromagnetically stirred flow in the mold using a 1:3 scale acrylic glass model of the round bloom caster from voestalpine Stahl Donawitz GmbH. An electromagnetic stirrer was installed at the mold producing a rotating magnetic field (RMF). Flow measurements were performed by means of the ultrasound Doppler velocimetry (UDV) at room temperature in the eutectic alloy GaInSn. Up to 10 ultrasonic transducers were employed simultaneously in order to obtain a two-dimensional reconstruction of the flow structure. The experiment provides an extensive and valuable data base for validation of numerical methods.

Keywords: Continuous casting; electromagnetic stirring; rotating magnetic field; flow measurements

  • Lecture (Conference)
    8th International Conference on Electromagnetic Processing of Materials, EPM 2015, 12.-16.10.2015, Cannes, France
  • Contribution to proceedings
    8th International Conference on Electromagnetic Processing of Materials, EPM 2015, 12.-16.10.2015, Cannes, France, 978-2-9553861-0-1, 511-514

Publ.-Id: 22664

Applications of Ultrasonic Doppler Velocimetry to flow measurements in hot liquid metals

Eckert, S.; Franke, S.; Gundrum, T.; Gerbeth, G.; Willemetz, J.-C.

The successful application of the ultrasound Doppler method at hot channel flows by means of commercial high temperature probes is presented. To obtain sufficient Doppler signals, different problems have to be solved: the transmission of the ultrasonic beam through the channel wall made of stainless steel, the acoustic coupling between the transducer and the channel wall, and the wetting of the inner surface of the wall by the liquid metal, respectively. An integrated sensor concept and method are figured out to meet these requirements. The feasibility of this sensor concept is demonstrated at experiments in metallic melts at temperatures up to 230°C. Measurements are performed at a circular channel flow at the LIMMCAST facility at HZDR applying an eutectic bismuth-tin alloy. In addition, a lead-bismuth flow in a rectangular channel profile measured at the METAL:LIC loop at the Institute of Physics Riga (IPUL) is presented in this report.

Keywords: Flow measurements; ultrasound Doppler method; liquid metal; channel flow; high temperature melts

  • Lecture (Conference)
    8th International Conference on Electromagnetic Processing of Materials, EPM 2015, 12.-16.10.2015, Cannes, France
  • Contribution to proceedings
    8th International Conference on Electromagnetic Processing of Materials, EPM 2015, 12.-16.10.2015, Cannes, France, 978-2-9553861-0-1, 495-498

Publ.-Id: 22663

An EXAFS spectroscopic study of Am(III) complexation with lactate

Fröhlich, D. R.; Skerencak-Frech, A.; Kaplan, U.; Koke, C.; Rossberg, A.; Panak, P. J.

The pH dependence (1–7) of Am(III) complexation with lactate in aqueous solution is studied using extended X-ray absorption fine-structure (EXAFS) spectroscopy. Structural data (coordination numbers, Am—O and Am—C distances) of the formed Am(III)–lactate species are determined from the raw k3-weighted Am LIII-edge EXAFS spectra. Between pH 1 and pH 6, Am(III) speciation shifts continuously towards complexed species with increasing pH. At higher pH, the amount of complexed species decreases due to formation of hydroxo species. The coordination numbers and distances (3.41–3.43 Å) of the coordinating carbon atoms clearly point out that lactate is bound `side-on' to Am(III) through both the carboxylic and the α-hydroxy function of lactate. The experimentally determined coordination numbers are compared with speciation calculations on the basis of tabulated thermodynamic stability constants. Both EXAFS data and thermodynamic modelling are in very good agreement. The EXAFS spectra are also analyzed by iterative transformation factor analysis to further verify the determined Am(III) speciation and the used structural model.

Keywords: EXAFS; americium; coordination chemistry; lactate; aqueous speciation

Publ.-Id: 22662

Injection Control for Electrons in Laser-Driven Plasma Wakes on the Femtosecond Time Scale

Huebl, A.

Laser-driven plasma wakefield accelerators provide accelerating electric fields orders of magnitude higher compared to conventional accelerators. Towards the generation of quasi-monoenergetic, multi-gigaelectronvolt electron beams, a precise control in the femtosecond time scale of the injection of electrons is needed.
In this diploma thesis a new computational method to study external injection of electrons in laser-wakefield accelerators was derived. By loading a relativistic, charged particle bunch with arbitrary distribution in energy, space and time new ways to study the properties of wakefield accelerated electrons are possible.
Furthermore, the proposed scheme was implemented together with an advanced field solver to suppress numerical Cherenkov noise in the open source Particle-in-Cell code PIConGPU as they are critical to reduce numerical uncertainties in relativistic simulations.
Powered with modern compute hardware (GPUs) it is now possible to reach a new quality of predictive simulations, running repeated simulations in a few hours compared to weeks as with today’s legacy codes. New parallel algorithms to study the evolution of the acceleration process have been implemented such as the in-situ calculation of a two-dimensional phase space distribution. Providing live feedback from simulations introduces a paradigm change towards interactive numerical studies and dramatically reduces the amount of data for post-processing.
Finally, numerical studies have been carried out benefiting from the new methods and implementations such as an extended down-ramp triggered self-injection scenario suitable for the reproducible generation of tunable electron bunches.

Keywords: LPA; HPC; PIC; simulation; GPU; LWFA

  • Diploma thesis
    TU Dresden, 2014
    Mentor: Prof. Dr. U. Schramm, Dr. Michael Bussmann
    117 Seiten

Publ.-Id: 22661

Synthetic Diagnostics & Atomic-Physics Coupling in PIC Simulations

Huebl, A.; Widera, R.; Pausch, R.; Worpitz, B.; Eckert, C.; Burau, H.; Garten, M.; Debus, A.; Kluge, T.; Bussmann, M.

PhD Seminar talk to a broad audience (chemists, biologists, other physicists from different domains) about my PhD topic.

Keywords: PIC; simulation; LPA; HPC; GPU

  • Lecture (others)
    HZDR PhD Seminar, 02.-04.11.2015, Altenberg, Deutschland

Publ.-Id: 22660

Feasibility study of detecting vacuum birefringence with X-ray free electron lasers and high-power optical lasers

Schlenvoigt, H.-P.; Heinzl, T.; Schramm, U.; Cowan, T.; Sauerbrey, R.

  • Lecture (Conference)
    QED vacuum birefringence workshop, 01.-03.11.2015, Hamburg, Deutschland


Publ.-Id: 22659

Detecting vacuum birefringence with X-ray free electron lasers and high-power optical lasers: A feasibility study

Schlenvoigt, H.-P.; Heinzl, T.; Schramm, U.; Cowan, T.; Sauerbrey, R.

We study the feasibility of measuring vacuum birefringence by probing the focus of a high-intensity optical laser with an X-ray free electron laser (XFEL). This amounts to performing a new type of QED precision experiment, employing only laser pulses, hence space- and time-dependent fields. To set the stage, we briefly review the status of QED precision tests and then focus on the example of vacuum birefringence. Adopting a realistic laser beam model in terms of pulsed Gaussian beams we calculate the induced phase shift and translate it into an experimental signal, counting the number of photons with flipped polarization. We carefully design a detailed experiment at the European XFEL operating in self-seeded mode, supplemented by a petawatt class optical laser via the HIBEF project. Assuming all components to represent the current state of the art, in particular the X-ray polarizers, realistic estimates of signal-to-noise ratios plus ensuing acquisition times are provided. This is accompanied by a statistical analysis of the impact of poor laser focus overlap either due to timing and pointing jitter as well as limited alignment accuracy. A number of parasitic effects are analyzed together with appropriate countermeasures. We conclude that vacuum birefringence can indeed be measured upon combining an XFEL with a high-power optical laser if depolarization effects in the x-ray lenses can be controlled.

Keywords: X-ray; Free-electron laser; High-power laser; QED

Publ.-Id: 22658

Vertical coupling of laser glass microspheres to buried silicon nitride ellipses and waveguides

Navarro-Urrios, D.; Ramírez, J. M.; Capuj, N. E.; Berencén, Y.; Garrido, B.; Tredicucci, A.

We demonstrate the integration of Nd3+ doped barium-titanium-silicate microsphere lasers with a silicon nitride photonic platform. Devices with two different geometrical configurations for extracting the laser light to buried waveguides have been fabricated and characterized. The first configuration relies on a standard coupling scheme, where the microspheres are placed over strip waveguides. The second is based on a buried elliptical geometry whose working principle is that of an elliptical mirror. In the latter case, the input of a strip waveguide is placed on one focus of the ellipse, while a lasing microsphere is placed on top of the other focus. The fabricated elliptical geometry (ellipticity=0.9) presents a light collecting capacity that is 50% greater than that of the standard waveguide coupling configuration and could be further improved by increasing the ellipticity. Moreover, since the dimensions of the spheres are much smaller than those of the ellipses, surface planarization is not required. On the contrary, we show that the absence of a planarization step strongly damages the microsphere lasing performance in the standard configuration.

Keywords: Microspheres; Nitrides; Silicates; Silicon nitride; Titanium nitride; Waveguides; Elliptical mirrors; Geometrical configurations; Lasing performance; Microsphere laser; Surface planarization; Titanium silicate; Vertical coupling; Waveguide coupling

Publ.-Id: 22657

Depencency of Structure, Mechanical and Electrical Properties on Rotating Magnetic Field in the Bi-Sn-Ag Ternary Eutectic Alloy

Kaya, H.; Çadirli, E.; Gündüz, M.; Räbiger, D.; Eckert, S.

A profound understanding of the solidification behavior under the impact of an intense melt flow is important to controll the microstructure and macrostructure of alloys in industry. In the present study, cylindrical samples of a Bi-Sn-Ag ternary eutectic alloy were exposed to a rotating magnetic field (RMF) during directional solidification. The morphology was transformed from a coarser plate-like structure to a fine fibrous eutectic structure with increasing field strength. The dependence of the eutectic spacing, microhardness (HV), ultimate tensile stress, electrical resistivity of the Bi-Sn-Ag eutectic alloy on the RMF-driven flowwas investigated in this study. Reference measurements of electrical resistivity for cast samples without RMF in the temperature range of 20-200 oC were also measured by the four-point probe technique. The enthalpy of fusion and specific heat (Cp) for the same alloy was determined by means of differential scanning calorimeter (DSC) from the heating trace during the transformation from the eutectic liquid to eutectic solid. The results obtained in the present work were compared with published data available in the literature.

Keywords: Bi-Sn-Ag, Structures; Microhardness; Tensile stress; Electrical resistivity; thermal properties

Publ.-Id: 22656

Fermi surface of the superconductor BaIr2P2

Förster, T.; Bergk, B.; Ignatchik, O.; Bartkowiak, M.; Blackburn, S.; Coté, M.; Seyfarth, G.; Berry, N.; Fisk, Z.; Sheikin, I.

We report on de Haas–van Alphen (dHvA) and band-structure studies of the iridium-pnictide superconductor BaIr2P2 (Tc = 2.1 K). The observed dHvA frequencies can be well understood by our band-structure calculations with two bands crossing the Fermi energy leading to a strongly corrugated Fermi-surface cylinder around the X point and a highly evolved, multiconnected Fermi surface extending over the whole Brillouin zone. The experimental effective masses are found to be considerably larger than the calculated band masses suggesting strong many-body interactions. Nevertheless, Tc remains only moderate in BaIr2P2 contrary to isostructural iron pnictides which probably is related to the largely different Fermi-surface topologies in these materials.

Publ.-Id: 22655

Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4

Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; Wosnitza, J.; Krzystek, J.; Yoshizawa, D.; Hagiwara, M.; Hu, R.; Ryu, H.; Petrovic, C.; Zhitomirsky, M. E.

We report on high-field electron spin resonance (ESR) studies of magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4. Frequency-field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero-field energy gap, ∆ ≈ 9:5 K, observed in the low-temperature excitation spectrum of Cs2CuBr4 [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamics in Cs2CuBr4 is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangular-lattice antiferromagnet.

Publ.-Id: 22654

Investigation of a viscous coupling using CFD validated by enhanced tomographics imaging techniques

Schlottke, J.; Bieberle, A.; Kühnel, W.

In this contribution, simulation results and validation measurements of a viscous coupling are presented. The analyzed Visco® clutch of MAHLE Behr is used to control the speed of the cooling fan of heavy duty trucks. It consists of a driven primary disc and a secondary housing with an engine cooling fan mounted on it. High viscous oil is pumped into small channels between these parts. The fan speed therefore depends on the amount of oil and its distribution within the clutch. Challenges for both simulation as well as measurements arise from high rotation rates, the small dimension of the microchannels, and the non newtonian behaviour of the working fluid.

Keywords: CFD; gamma-ray CT; viscous coupling; two phase flow

  • Lecture (Conference)
    13th Multiphase Flow Conference, 24.-26.11.2015, Dresden, Deutschland

Publ.-Id: 22653

Interaction of radionuclides with the biosphere

Raff, J.; Günther, A.; Moll, H.; Vogel, M.; Suhr, M.; Drobot, B.; Li, B.; Foerstendorf, H.; Stumpf, T.

This presentation gives a brief overview about the research being conducted at the Institute of Resource Ecology on the interaction of biosystems with radionuclides.

Keywords: radionuclides; biosystems; interaction

  • Lecture (others)
    Institute seminar School of Chemistry, University of Manchester, 26.10.2015, Manchester, United Kingdom

Publ.-Id: 22652

Beiträge zur röntgenradioskopischen Visualisierung und Charakterisierung von Erstarrungsvorgängen und zweiphasigen Strömungsphänomenen in metallischen Schmelzen

Boden, S.

Röntgenradioskopische Bildgebungsverfahren ermöglichen es, ein besseres Verständnis der zweiphasigen Strömungsphänomene und der Prozesse der Mikrostrukturentstehung während der Erstarrung in Metallschmelzen intuitiv zu gewinnen, da diese Verfahren die innere Gestalt der sonst undurchsichtigen Flüssigkeiten abbilden. In der vorliegenden Arbeit wurden dazu Untersuchungen zu zwei unterschiedlichen Teilaufgaben durchgeführt. Zum einen wurde die Dichteverteilung in dünnen Erstarrungsproben in Echtzeit und in-situ mit räumlichen Auflösungen von wenigen Mikrometern untersucht, um den Einfluss natürlicher und erzwungener Schmelzenströmungen auf die Erstarrung einer binären Gallium-Indium-Metalllegierung experimentell nachzuweisen. Zum anderen wurden Gasblasenströmungen in nichttransparenten Metallschmelzen nicht-invasiv und in-situ visualisiert und charakterisiert, um Kenntnis der Eigenschaften und der Bewegung von Argon-Einzelblasen und Blasenketten in flüssigem Gallium-Indium-Zinn ohne und unter dem Einfluss eines externen magnetischen Feldes zu erlangen. Diese experimentellen Untersuchungen wurden mit einem Mikrofokus-Röntgenbildgebungssystem durchgeführt. Die Implementation angepasster Bildverarbeitungs-algorithmen ermöglichte die präzise quantitative Vermessung der dendritischen Strukturparameter und der Wachstumsgeschwindigkeiten. Die Strömungsgeschwindigkeiten in der Schmelze vor der Erstarrungsfront wurden durch Berechnung des optischen Flusses in den Röntgenbildsequenzen vermessen. Thermosolutale Konvektionsbewegungen und der Einfluss magnetisch angetriebener erzwungener Schmelzenströmung auf die Gefügeentstehung konnten durch die Röntgenvisualisierung nachgewiesen werden. Die lokale Akkumulation angereicherter Schmelze, das Aufschmelzen von Dendritenarmen und das Entstehen von Entmischungskanälen im Zweiphasengebiet hinter der Erstarrungsfront wurden unmittelbar beobachtet. Für die Untersuchung des Verhaltens von Gasblasen in einer schmalen Flüssigmetall-Blasensäule wurde das Röntgenbildgebungssystem modifiziert. Das ermöglichte die Vermessung der Gasblasengrößen, der Trajektorien und der Geschwindigkeiten zur Charakterisierung der Blasenströmungen. Die Abhängigkeit der Gasblasengrößen von der Benetzung der Mündungsöffnung wurde gezeigt. Vergleichsexperimente im Gas-Wasser-System verdeutlichten die signifikanten Unterschiede der zweiphasigen Gas-Flüssigmetall-Strömungen.

  • Doctoral thesis
    TU Dresden, Fakultät Elektrotechnik und Informationstechnik, 2016
    Mentor: Prof. Dr.-Ing. habil. Uwe Hampel
    202 Seiten

Publ.-Id: 22651

Measurement of Taylor bubble shape in square channel by microfocus X-ray computed tomography for investigation of mass transfer

Boden, S.; Haghnegahdar, M.; Hampel, U.

This paper addresses the measurement of the dynamic evolution of Taylor bubble shape during mass transfer. Carbon dioxide (CO2) Taylor bubbles were placed in countercurrent water flow in a square channel. Microfocus X-ray radiography enabled the measurement of volumetric mass transfer rates. The measurements were calibrated by microfocus X-ray computed tomography scans of non-dissolving Taylor bubbles. The reconstruction algorithm was adapted to correct the slight motion of the Taylor bubble during the tomographic scan. The obtained three-dimensional representation of the Taylor bubble’s shape enabled the measurement of Taylor bubble’s true volume and interfacial area. The thin film region of the constricted Taylor bubble’s surface near the planar channel walls was extracted from the data and the ratio to the total Taylor bubble surface was computed. The volumetric dissolution rates were measured in circular and square channels.

Keywords: Taylor bubble; microfocus X-ray computed tomography; mass transfer

Publ.-Id: 22650

LC-MS-unterstützte Untersuchungen zum Metabolismus des Sigma-1-Rezeptorliganden (–)-(S)-[18F]Fluspidine

Ludwig, F. A.; Fischer, S.; Houska, R.; Hoepping, A.; Patt, M.; Holl, K.; Wünsch, B.; Sabri, O.; Steinbach, J.; Brust, P.

Ziel: In einer jüngst begonnenen klinischen Studie (1) wird die Veränderung der Verfügbarkeit von Sigma-1-Rezeptoren bei Patienten mit Depression mittels (–)-(S)-[18F]Fluspidine (2) und PET untersucht. Neben der Bestimmung des Anteils an Radiotracer in Plasma und Urin, war die Strukturaufklärung nachgewiesener Radiometaboliten Gegenstand unserer Arbeiten.

Methodik: Nach Injektion von 255±9 MBq (n=3) (–)-(S)-[18F]Fluspidine, wurden Plasma (15, 30 min p.i.) und Urin (120 min p.i.) der Versuchsteilnehmer per Radio-HPLC untersucht. Für In-vitro-Studien wurden der Radiotracer bzw. unmarkiertes (–)-(S)-Fluspidine jeweils mit Lebermikrosomen des Menschen (HLM) sowie NADPH und /oder aktivierter Glucuronsäure (UDPGA) bei 37°C in PBS-Puffer inkubiert und die Ansätze mittels Radio-HPLC bzw. LC-MS untersucht. Mit Hilfe verschiedener MS-Methoden (z. B. EPI, MS3) wurden Strukturen von Metaboliten identifiziert und im Menschen gebildeten Radiometaboliten zugeordnet.

Ergebnisse: Bei ersten Messungen an Probanden lag der Anteil an (–)-(S)-[18F]Fluspidine im Plasma nach 30 min bei 85%. Die Extraktionsausbeute der Plasmafällung betrug 96-98%. Im Urin wurde ein Radiotracer-Anteil von 0 - 4% (120 min, p.i., n=3) bestimmt. Es wurden 3 Hauptmetaboliten detektiert. Durch Inkubation mit HLM wurden unter oxidativen Bedingungen, Metaboliten in vitro gebildet. Mit UDPGA wurde zudem die Bildung von Glucuroniden beobachtet, von denen eines chromatographisch mit einem im Menschen gefundenen Haupt-Radiometaboliten übereinstimmt. LC-MS-Untersuchungen zeigten, dass dieser durch Glucuronidierung infolge einer Oxidation am nicht-benzylischen Molekülteil entstand.

Schlussfolgerungen: Erste klinische Untersuchungen zeigten eine für die Anwendung geeignete metabolische Stabilität, wobei einer der Hauptmetaboliten bereits identifiziert werden konnte. Über weitere Daten im Studienverlauf sowie über Strukturaufklärung wird berichtet.

(1) DRKS-ID:DRKS00008321
(2) Fischer et al. Eur J Nucl Med Mol Imaging (2011) 38: 540-551

  • Lecture (Conference)
    54. Jahrestagung der DGN, 20.-23.04.2016, Dresden, Deutschland

Publ.-Id: 22649

X-ray tomographic measurement of Taylor bubble shape for investigation of mass transfer coefficients

Boden, S.; Haghnegahdar, M.; Hampel, U.

Several experimental and mathematical modelling studies have been done to quantify the effect of different parameters such as liquid properties, bubble velocity, bubble size and level of contamination of fluid on the liquid side mass transfer from gas bubbles to liquids and various correlations have been proposed. However, little attention has been paid to the influence of the pipe wall on mass transfer coefficient particularly for millimeter sized channels.

In this work, the absorption rate of a single Taylor bubble of carbon dioxide in water is investigated using a new technique in vertical channels. The liquid side mass transfer is studied by measuring the changes in the size of the bubble at constant pressure. The experiments cover a large range of initial Taylor bubble length varying from 6 to 24 mm. The channel is a glass channel with 6 mm hydraulic diameter and circular and square cross section. The bubble is continuously monitored by holding the bubble stationary using a downward flow of liquid. The method which is used to measure the variation of the bubble size is microfocus X-ray radioscopy and tomography.

The results show that by application of the radioscopy and tomography technique the evolution of the bubbles shape during mass transfer reliably can be measured. This technique was suitable for determining the three-dimensional shape of Taylor bubbles in channels and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles. The processed images, which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer between bubble and liquid.

Keywords: Microfocus X-ray tomography; Taylor bubble; Mass transfer

  • Contribution to proceedings
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Germany
    Proceedings of the 7th International Symposium on Process Tomography
  • Poster
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Germany

Publ.-Id: 22648

Dynamics of metal-humate complexation equilibria as revealed by isotope exchange studies – a matter of concentration and time

Lippold, H.; Eidner, S.; Kumke, M. U.; Lippmann-Pipke, J.

Complexation with dissolved humic matter can be crucial in controlling the mobility of contaminant metals. For speciation and transport modeling, a dynamic equilibrium process is commonly assumed, where association and dissociation run permanently. This is, however, questionable in view of reported observations of a growing resistance to dissociation over time. In this study, the isotope exchange principle was employed to gain direct insight into the dynamics of the complexation equilibrium, including kinetic stabilization phenomena. Terbium(III) was used as an analogue of trivalent actinides. Isotherms of binding to humic acid, determined by means of 160Tb as a radiotracer, were found to be identical regardless of whether the radioisotope was introduced together with the bulk of stable 159Tb or subsequently after pre-equilibration for up to 3 months. The existence of a dynamic equilibrium was thus evidenced since all available binding sites are occupied in the plateau region of the isotherm. If the small amount of 160Tb was introduced prior to saturation with 159Tb, the expected partial desorption of 160Tb occurred at much lower rates than those observed for the equilibration process in the reverse procedure. In addition, the rates showed a distinct dependence on the time of pre-equilibration. Obviously, stabilization phenomena are confined to the most reactive sites of humic molecules. Analyzing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 2 years are needed to attain equilibrium.


Publ.-Id: 22647

Irradiation hardening of Fe-9Cr-based alloys and ODS Eurofer: effect of helium implantation and iron-ion irradiation at 300 °C including sequence effects

Heintze, C.; Bergner, F.; Hernandez-Mayoral, M.; Kögler, R.; Müller, G.; Ulbricht, A.

Single-beam, dual-beam and sequential iron- and/or helium-ion irradiations are widely accepted to simulate more application-relevant but hardly accessible irradiation conditions of generation-IV fission and fusion candidate materials for certain purposes such as material pre-selection, identification of basic mechanisms or model calibration. However, systematic investigations of sequence effects capable to critically question individual approaches are largely missing. In the present study, sequence effects of iron-ion irradiations at 300 °C up to 5 dpa and helium implantations up to 100 appm He are investigated by means of post-irradiation nanoindentation of an Fe9%Cr model alloy, ferritic/martensitic 9%Cr steels T91 and Eurofer97 and oxide dispersion strengthened (ODS) Eurofer. Different types of sequence effects, both synergistic and antagonistic, are identified and tentative interpretations of the findings are suggested.

Keywords: Ferritic-martensitic chromium steel; Oxide dispersion strengthened steel; Dual-beam ion irradiation; Nanoindentation

Publ.-Id: 22646

Reflective optical probing of laser-driven plasmas at the rear surface of solid targets

Metzkes, J.; Zeil, K.; Kraft, S. D.; Rehwald, M.; Cowan, T. E.; Schramm, U.

In this paper, a reflective optical pump-probe technique for laser-driven plasmas at solid density target surfaces is presented. The technique is termed high depth-of-field time-resolved microscopy and it exploits the angular redistribution of the probe beam intensity after the probe’s reflection from an expanded and hence non-planar iso-density surface in the plasma. The main application of the robust technique, which uses simple imaging of the probe beam, is the spatio-temporal resolution of the plasma formation and expansion at the target rear surface. Analytic and numerical modeling of the experimental setup are applied for the analysis of the experimental results. The relevance and potential of the optical plasma probing method is highlighted by the application to targets of different geometries, helping to understand the target shape-related differences in the ion acceleration performance.

Keywords: optical probing; reduced-mass targets; laser-driven ion acceleration; laser-driven plasmas

Publ.-Id: 22645

Contactless Inductive Bubble Detection in a Liquid Metal Flow

Gundrum, T.; Büttner, P.; Dekdouk, B.; Peyton, A.; Wondrak, T.; Galindo, V.; Eckert, S.

The detection of bubbles in liquid metals is important for many technical applications.
The opaqueness and the high temperature of liquid metals set high demands on the measurement system. The high electrical conductivity of the liquid metal can be exploited for contactless methods based on electromagnetic induction. We will present a measurement system which consists of one excitation coil and a pickup coil system on the opposite sides of the pipe. With this sensor we were able to detect bubbles in a sodium flow inside a stainless steel pipe and bubbles in a column filled with a liquid Gallium alloy.

Keywords: contactless inductive measurements; two phase flow; liquid metal; bubble detection; void fraction


Publ.-Id: 22644

Interaction of trivalent lanthanides and actinides with calcium binding proteins

Drobot, B.; Raff, J.

Presentation of luminescence spectroscopic results on the interaction of trivalent lanthanides and actinides witch calcium binding proteins.

  • Lecture (others)
    Meeting with the Natrajan Group (The University of Manchester), 26.10.2015, Manchester, Great Britain

Publ.-Id: 22643

Amorphous to crystalline phase transition: onset of pattern formation during ion erosion of Si(001)

Engler, M.; Michely, T.

The morphological evolution of Si(001) is investigated for normal incidence 2 keV Kr+ ion irradiation under ultra high vacuum conditions as a function of temperature and ion fluence through scanning tunneling microscopy and low energy electron diffraction. Under the conditions chosen, the selvage of Si(001) amorphizes below the critical temperature Tc of 670 K, while above it remains crystalline. Below Tc the sample remains flat, irrespective of the ion fluence. Above Tc, the crystalline sample displays for fixed ion fluence and as a function of sample temperature a pronounced roughness maximum at 700 K. Around this temperature, with increasing ion fluence a strong increase of roughness as well as coarsening are observed. Pyramidal pits and mounds develop, with facets formed by Si steps and narrow reconstructed terraces. Most exciting, with increasing ion fluence the pattern reorients from pits and mounds with edges along the ⟨110⟩ directions to ridges and valleys rotated ≈45° to the ⟨110⟩ directions. Pattern formation and the reorientation transition are discussed in terms of a step edge barrier for vacancies, terrace and step edge diffusion.

Keywords: pattern formation; silicon; Si(001); ion beam erosion; scanning tunneling microscopy; STM; low energy electron diffraction; LEED

Publ.-Id: 22642

Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J.; Huang, J.; Facsko, S.

Time of flight Rutherford backscattering spectrometry (ToF–RBS) was successfully implemented in a helium ion microscope (HIM). Its integration introduces the ability to perform laterally resolved elemental analysis as well as elemental depth profiling on the nm scale. A lateral resolution of ≤ 54 nm and a time resolution of ∆t ≤ 17 ns (∆t/t = 5.4%) are achieved. By using the energy of the backscattered particles for contrast generation, we introduce a new imaging method to the HIM allowing direct elemental mapping as well as local spectrometry. In addition laterally resolved time of flight secondary ion mass spectrometry (ToF–SIMS) can be performed with the same setup. Time of flight is implemented by pulsing the primary ion beam. This is achieved in a cost effective and minimal invasive way that does not influence the high resolution capabilities of the microscope when operating in standard secondary electron (SE) imaging mode. This technique can thus be easily adapted to existing devices. The particular implementation of ToF–RBS and ToF–SIMS techniques are described, results are presented and advantages, difficulties and limitations of this new techniques are discussed.

Keywords: heliumionmicroscope; timeofflight; elementalanalysis; Rutherfordbackscatteringspectrometry; neutral impact–collision ion scattering spectroscopy; secondary ion mass spectrometry

  • Ultramicroscopy 162(2016), 91-97
    DOI: 10.1016/j.ultramic.2015.12.005
  • Poster
    10th PhD seminar, 04.11.2015, Altenberg, Deutschland
  • Lecture (others)
    Project Meeting, 27.10.2015, Oberkochen, Deutschland
  • Contribution to WWW
    arXiv: 1510.04594:
  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 09.03.2016, Regensburg, Deutschland

Publ.-Id: 22641

Nanometer TOF-RBS and TOF-SIMS in a Helium / Neon Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Facsko, S.; Notte, J.; Huang, J.

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their excellent lateral resolution down to 0.3 nm and their high field of depth make them a unique tool in surface imaging [1]. So far the possibilities to identify target materials (elements) are rather limited or need complex detection setups. In addition we will discuss major challenges and physical limitations of ion beam analysis in the HIM.

We will present a new and relatively easy to implement method for ion beam analysis in the HIM by means of time of flight spectrometry to obtain elemental information from the sample. We will demonstrate the flexibility and applicability of the method to image samples with target mass contrast, to analyze the target compositions, and to measure depth profiles of films with few tens of nm thickness.

Pulsing the primary helium or neon ion beam and measuring the time of flight of ejected particles allows to obtain the energy of the backscattered particles as well as the mass of the ionized, sputtered target atoms. This has been achieved by chopping the primary ion beam down to pulse widths of 18 ns by use of the built in beam blanker and a customized plug-on beam blanking electronics. The secondary particles are detected by means of a multi channel plate mounted on a flange of the HIM.

We will show TOF-RBS and TOF-SIMS measurements for different materials, which can give complementary information. Lateral resolved TOF-SIMS allows to quickly obtain qualitative elemental mapping while the TOF-RBS gives the standard-free quantitative sample composition of regions of interest. We will also show, that with TOF-RBS depth profiling of nm-thick layers is possible.

[1] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B 32(2), 2014

  • Lecture (Conference)
    AVS 62nd International Symposium & Exhibition (AVS-62), 22.10.2015, San José, United States of America

Publ.-Id: 22640

A novel approach for ion beam analysis with sub-100 nm spatial resolution using an ion microscope

Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.; von Borany, J.

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their excellent lateral resolution down to 0.3 nm and their high field of depth make them a unique tool in surface imaging [1]. So far the possibilities to identify target materials (elements) are rather limited or need complex detection setups. In addition we will discuss major challenges and physical limitations of ion beam analysis in the HIM.

We will present a new and relatively easy to implement method for ion beam analysis in the HIM by means of time of flight spectrometry to obtain elemental information from the sample. We will demonstrate the flexibility and applicability of the method to image samples with target mass contrast, to analyze the target compositions, and to measure depth profiles of films with few tens of nm thickness.

Pulsing the primary helium or neon ion beam and measuring the time of flight of ejected particles allows to obtain the energy of the backscattered particles as well as the mass of the ionized, sputtered target atoms. This has been achieved by chopping the primary ion beam down to pulse widths of 18 ns by use of the built in beam blanker and a customized plug-on beam blanking electronics. The secondary particles are detected by means of a multi channel plate mounted on a flange of the HIM.

We will show TOF-RBS and TOF-SIMS measurements for different materials, which can give complementary information. Lateral resolved TOF-SIMS allows to quickly obtain qualitative elemental mapping while the TOF-RBS gives the standard-free quantitative sample composition of regions of interest. We will also show, that with TOF-RBS depth profiling of nm-thick layers is possible.

[1] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B 32(2), 2014

  • Lecture (others)
    Meeting User Selection Panel, 09.10.2015, Dresden, Deutschland

Publ.-Id: 22639

Nanometer TOF-RBS and TOF-SIMS in a Helium/Neon Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.; von Borany, J.

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their excellent lateral resolution down to 0.3 nm and their high field of depth make them a unique tool in surface imaging [1]. So far the possibilities to identify target materials (elements) are rather limited or need complex detection setups.
We will present a new and relatively easy to implement method for ion beam analysis in the HIM by means of time of flight spectrometry to obtain elemental information from the sample. We will demonstrate the flexibility and applicability of the method to image samples with target mass contrast, to analyze the target compositions, and to measure depth profiles of films with few tens of nm thickness.
Pulsing the primary helium or neon ion beam and measuring the time of flight of secondary particles from the sample allows to obtain the energy of the backscattered particles or the mass of the sputtered target atoms (and ions). This has been achieved by chopping the primary ion beam down to pulse widths of 18 ns by use of the built in beam blanker and a customized plug-on beam blanking electronics. The secondary particles are detected by means of a multi channel plate mounted on a flange of the HIM.
We will show TOF-RBS and TOF-SIMS measurements for different materials which can give complementary information. Lateral resolved TOF-SIMS allows to quickly obtain qualitative elemental mapping while the TOF-RBS gives the standard-free quantitative sample composition of regions of interest. We will also show, that with TOF-RBS depth profiling of nm-thick layers is possible. In addition we will discuss major challenges and physical limitations of ion beam analysis in the HIM.
[1] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B 32(2), 2014

  • Poster
    10. DACH FIB-Workshop, 03.06.2015, Halle, Deutschland
  • Lecture (Conference)
    Workshop für Ionenstrahlen und Nanostrukturen 2015​, 24.07.2015, Heidelberg, Deutschland

Publ.-Id: 22638

Euler-Euler Modeling of Mass-Transfer in Bubbly Flows

Rzehak, R.; Krepper, E.

CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. Concerning the fluid dynamics of bubbly flows a certain degree of predictive capability has been reached recently. However, concerning mass transfer only few studies have been performed to date.
The present contribution gives an overview over the available results on closure relations for physical absorption/desorption, i.e. mass transfer without chemical reactions. Unsolved issues are highlighted, in particular on which parameters a suitable correlation for the mass transfer coefficient should be based.
In addition, a preliminary study on model validation is presented which makes use of experimentally determined mass transfer coefficients. The need for and requirements on suitable data for this purpose are emphasized.

Keywords: mass-transfer; dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; closure relations; CFD simulation; model validation

  • Lecture (Conference)
    14th Workshop on Two-Phase Flow Predictions, 07.-10.09.2015, Halle, Deutschland

Publ.-Id: 22637

Charge-state-dependent energy loss of slow ions. II. Statistical atom model

Wilhelm, R.; Möller, W.

A model for charge-dependent energy loss of slow ions is developed based on the Thomas-Fermi statistical model of atoms. Using a modified electrostatic potential which takes the ionic charge into account, nuclear and electronic energy transfers are calculated, the latter by an extension of the Firsov model. To evaluate the importance of multiple collisions even in nanometer-thick target materials we use the charge-state-dependent potentials in a Monte Carlo simulation in the binary collision approximation and compare the results to experiment. The Monte Carlo results reproduce the incident charge-state dependence of measured data well [see R. A. Wilhelm et al., Phys. Rev. A 93, 052708 (2016)], even though the experimentally observed charge exchange dependence is not included in the model.

Keywords: low energy ions; ion charge state; stopping power; energy loss; highly charged ion; charge exchange

Publ.-Id: 22636

Charge-state-dependent energy loss of slow ions. I. Experimental results on the transmission of highly charged ions

Wilhelm, R.; Gruber, E.; Smejkal, V.; Facsko, S.; Aumayr, F.

We report on energy loss measurements of slow (v≪v0), highly charged (Q>10) ions upon transmission through a 1-nm-thick carbon nanomembrane. We emphasize here the scaling of the energy loss with the velocity and charge exchange or loss. We show that a weak linear velocity dependence exists, whereas charge exchange dominates the kinetic energy loss, especially in the case of a large charge capture. A universal scaling of the energy loss with the charge exchange and velocity is found and discussed in this paper. A model for charge-state-dependent energy loss for slow ions is presented in paper II in this series [R. A. Wilhelm and W. Möller, Phys. Rev. A 93, 052709 (2016)].

Keywords: low energy ions; ion charge state; stopping power; energy loss; highly charged ion; charge exchange

Publ.-Id: 22635

Unified modeling of bubbly flows in pipes, bubble columns, and airlift columns

Rzehak, R.; Ziegenhein, T.; Kriebitzsch, S.; Krepper, E.; Lucas, D.

The purpose of computer-aided process engineering (CAPE) is to assist the development and operation of complex processes involving chemical or physical change. Computational fluid dynamics (CFD) simulations are a means to study in detail unit operations, such as mixing, reaction, separation or combinations thereof, performed in a specific type of equipment. In particular scale-up studies and the evaluation of concepts for process intensification in an early design phase promise high benefits in terms of identifying energy- and resource-efficient solutions that are expensive to assess by conventional semi-empirical methods.
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models describing the physics on the scale of individual bubbles or groups thereof. A large number of works exists, in each of which largely a different set of closure relations is compared to a different set of experimental data. For the limited range of conditions to which each model variant is applied, reasonable agreement with the data is mostly obtained, but due to a lack of comparability between the individual works no complete, reliable, and robust formulation has emerged so far. Moreover, the models usually contain a number of empirical parameters that have been adjusted to match the particular data that were used in the comparison. Predictive simulation, however, requires a model that works without any adjustments within the targeted domain of applicability.
As a step towards this goal, an attempt has been made to collect the best available description for all aspects known to be relevant for adiabatic bubbly flows where only momentum is exchanged between liquid and gas phases. Apart from interest in its own right, results obtained for this restricted problem also provide a good starting point for the investigation of more complex situations including heat and mass transport and possibly phase change or chemical reactions.
Aspects requiring closure for the case under consideration are: (i) the exchange of momentum between liquid and gas phases, (ii) the effects of the dispersed bubbles on the turbulence of the liquid carrier phase, and (iii) processes of bubble coalescence and breakup that determine the distribution of bubble sizes. All of these aspects are coupled and therefore in principle have to be considered as a whole.
At the same time it is highly desirable to separately validate the individual sub-models of this complex coupled problem. To this end we use a step-by-step procedure where we first consider situations where a fixed distribution of bubble sizes may be imposed. In this way the sub-models for bubble forces (i) and bubble-induced turbulence (ii) can be validated independently of bubble coalescence and breakup processes (iii). The latter will be added later on in a second step building on the already established sub-models for the former.
In the present contribution the baseline model referred to above is applied to several different configurations commonly encountered in chemical engineering applications, namely bubbly flows in pipes, bubble columns, and airlift columns. Since in all of these systems the small scales are governed by the same physics it is expected that they can be treated in a unified manner using the same set of closure relations. By comparison of simulation results to experimental data taken from the literature this is shown to be the case within a certain accuracy and the model is validated for all of these configurations.
In this way a starting point for the prediction of flow phenomena is obtained. Expanding the range of applicability as well as the achieved accuracy is a continuously ongoing development effort. From the observed level of agreement between simulation and experiment issues requiring further investigation can be identified. This includes both the need for further model development and the need for CFD-grade experimental investigations.

Keywords: Dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; closure relations; CFD simulation; model validation; pipe flow; bubble column; airlift column

  • Lecture (Conference)
    12th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering, 28.06.-01.07.2015, New York, USA
  • Open Access Logo Chemical Engineering Science 157(2017), 147-158
    DOI: 10.1016/j.ces.2016.04.056


Publ.-Id: 22634

Baseline Model for Simulation of Bubbly Flows

Rzehak, R.; Ziegenhein, T.; Krepper, E.; Lucas, D.

CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. A large body of work using different closure relations of varying degree of sophistication exists, but no complete, reliable, and robust formulation has been achieved so far.
The closure relations describe phenomena on the small spatial scale of individual bubbles. Hence, for all systems where this small scale behavior is governed by the same physics, the same set of closure relations should be applicable. Therefore it is expected that many systems differing on larger scales can be treated in a unified manner. To show this feasibility we presently consider adiabatic bubbly flows where only momentum is exchanged between liquid and gas phases.
The best available descriptions for the forces acting on the bubbles and the bubble-induced turbulence, which are the relevant aspects requiring closure under these circumstances, have been collected into a baseline model. By keeping all correlations and all parameter values fixed, the applicability of this model to a variety of situations is demonstrated. Future improvements of the model should work for the entire domain of applications.
The model has previously been validated against data for steady flows in pipes and bubble columns. Here, further comparison is made for an airlift column and plume oscillations in bubble columns. A crucial parameter in the model is the bubble size for which reliable measurements are often not available. In this case parametric variations are investigated. From the observed level of agreement between simulation and experiment, issues requiring further investigation will be identified.

  • Lecture (Conference)
    ProcessNet Fachgruppertreffen CFD, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 22633

Simple scaling equations for electron spectra, currents and bulk heating in ultra-intense short-pulse laser-solid interaction

Kluge, T.; Bussmann, M.; Cowan, T. E.; Schramm, U.

Intense and energetic electron currents can be generated by ultra-intense lasers interacting with solid density targets.
Especially for ultra-short laser pulses their temporal evolution needs to be taken into account for many non-linear processes as instantaneous currents may differ significantly from the average.
Hence, a dynamic model including the temporal variation of the electron currents which goes beyond a simple bunching with twice the laser frequency but otherwise constant current is needed.
Here we present a new time-dependent model to describe the laser generated currents and obtain simple expressions for the temporal evolution and resulting corrections of averages.
To exemplify the model and its predictive capabilities we show the impact of temporal evolution, spectral distribution and spatial modulations on Ohmic heating of the bulk target material.


Publ.-Id: 22632

Characterisation of irradiation-induced defects in ZnO single crystals

Prochazka, I.; Cizek, J.; Lukac, F.; Melikhova, O.; Valenta, J.; Havranek, V.; Anwand, W.; Skuratov, V. A.; Strukova, T. S.

Positron annihilation spectroscopy (PAS) combined with optical methods was employed for characterisation of defects in the hydrothermally grown ZnO single crystals irradiated by 167 MeV Xe26+ ions to fluences ranged from 3×10^12 to 1×10^14 cm−2. The positron lifetime (LT), Doppler broadening as well as slow-positron implantation spectroscopy (SPIS) techniques were involved. The ab-initio theoretical calculations were utilised for interpretation of LT results. The optical transmission and photoluminescence measurements were conducted, too. The virgin ZnO crystal exhibited a single component LT spectrum with a lifetime of 182 ps which is attributed to saturated positron trapping in Zn vacancies associated with hydrogen atoms unintentionally introduced into the crystal during the crystal growth. The Xe ion irradiated ZnO crystals have shown an additional component with a longer lifetime of ≈ 360 ps which comes from irradiation-induced larger defects equivalent in size to clusters of ≈ 10 to 12 vacancies. The concentrations of these clusters were estimated on the basis of combined LT and SPIS data. The PAS data were correlated with irradiation induced changes seen in the optical spectroscopy experiments.

Keywords: ZnO; Xe irradiation; defects; positron annihilation

Publ.-Id: 22631

Electron beam final focus system for Thomson scattering at ELBE

Krämer, J. M.; Budde, M.; Bødker, F.; Irman, A.; Jochmann, A.; Kristensen, J. P.; Lehnert, U.; Michel, P.; Schramm, U.

The design of an electron beam final focus system (FFS) aiming for high-flux laser-Thomson backscattering X-ray sources at ELBE is presented. A telescope system consisting of four permanent magnet based quadrupoles was found to have significantly less chromatic aberrations than a quadrupole doublet or triplet as commonly used. Focusing properties like the position of the focal plane and the spot size are retained for electron beam energies between 20 and 30 MeV by adjusting the position of the quadrupoles individually on a motorized stage. The desired ultra-short electron bunches require an increased relative energy spread up to a few percent and, thus, second order chromatic effects must be taken into account. We also present the design and test results of the permanent magnet quadrupoles. Adjustable shunts allow for correction of the field strength and compensation of deviations in the permanent magnet material.
For a beam emittance of 13 mm mrad, we predict focal spot sizes of about 40 μm (rms) and divergences of about 10 mrad using the FFS.

Keywords: PMQ; Final focus system; Chromatic aberration; Thomson scattering; ICS

Publ.-Id: 22630

Investigation of nanocrystalline Gd films loaded with hydrogen

Hruska, P.; Cizek, J.; Dobron, P.; Anwand, W.; Mücklich, A.; Gemma, R.; Wagner, S.; Uchida, H.; Pundt, A.

The present work reports on microstructure studies of hydrogen-loaded nanocrystalline Gd films prepared by cold cathode beam sputtering on sapphire (1 1 -2 0) substrates. The Gd films were electrochemically step-by-step charged with hydrogen and the structural development with increasing concentration of absorbed hydrogen was studied by transmission electron microscopy and in-situ X-ray diffraction using synchrotron radiation. The relaxation of hydrogen-induced stresses was examined by acoustic emission measurements. In the low concentration range absorbed hydrogen occupies preferentially vacancy-like defects at GBs typical for nanocrystalline films. With increasing hydrogen concentration hydrogen starts to occupy interstitial sites. At the solid solution limit the grains gradually transform into the beta-phase (GdH2). Finally at high hydrogen concentrations xH > 2:0 H/Gd, the film structure becomes almost completely amorphous. Contrary to bulk Gd specimens, the formation of the gamma-phase (GdH3) was not observed in this work.

Keywords: Gadolinium; hydrogen; defects; thin films

Publ.-Id: 22629

Defect studies of H+ implanted niobium

Prochazka, I.; Cizek, J.; Havranek, V.; Anwand, W.

Defects in Nb specimens implanted with H+ ions were investigated using three complementary techniques of positron annihilation spectroscopy: (i) the positron lifetime (LT) measurements employed for identification of defects in implanted specimens, (ii) the coincidence Doppler broadening (CDB) technique used for investigation of chemical surroundings of defects, and (iii) the variable energy positron annihilation spectroscopy (VEPAS) served for defects depth profiling studies. The virgin Nb sample exhibits a single component spectrum with lifetime of 128 ps which testifies that the sample can be considered as a defect-free material. The sample implanted with H+ ions exhibits two additional positron components with lifetimes of 182 and 204 ps. These components were attributed to the implantation-induced vacancies surrounded by two and one hydrogen atom, respectively. The presence of hydrogen attached to vacancies was confirmed also by CDB investigations.

Keywords: niobium; hydrogen; defects; positron annihilation

Publ.-Id: 22628

Tomographic characterisation of gas-jet targets for laser wakefield acceleration

Couperus, J. P.; Köhler, A.; Wolterink, T. A. W.; Jochmann, A.; Zarini, O.; Bastiaens, H. M. J.; Boller, K. J.; Irman, A.; Schramm, U.

Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. The acceleration medium is provided by a target that creates a local well-defined gas-density profile inside a vacuum vessel. Target development and analysis of the resulting gas-density profiles is an important aspect in the further development of LWFA.
Gas-jet targets are widely used in regimes where relatively high electron densities over short interaction lengths are required (up to several millimetres interaction length, plasma densities down to ~1018 cm-3).
In this paper we report a precise characterisation of such gas-jet targets by a laser interferometry technique. We show that phase shifts down to 4 mrad can be resolved. Tomographic phase reconstruction enables detection of non-axisymmetrical gas-density profiles which indicates defects in cylindrical nozzles, analysis of slit-nozzles and nozzles with an induced shock-wave density step. In a direct comparison between argon and helium jets we show that it cannot automatically be assumed, as is often done, that a nozzle measured with argon will provide the same gas density with helium.

Keywords: Laser wakefield acceleration; LWFA; gas-jet analysis; interferometry; tomography


Publ.-Id: 22627

P1304 - Komplementärer Widerstandsschalter, dessen Herstellung und Verwendung

Schmidt, H.; You, T.; Du, N.; Bürger, D.; Skorupa, I.

Die Erfindung beschreibt die Herstellung eines komplementären Widerstandsschalters mit zwei Terminals T1 und T2, in welchen jede Boolesche Grundfunktion nichtflüchtig durch Anlegen einer Schreibspannung im Zweischritt-Verfahren geschrieben werden kann. Der Zustand des komplementären Widerstandsschalters kann durch Anlegen einer konstanten, von den Eingangsparametern der Booleschen Funktion abhängigen, niedrigen positiven oder negativen Lesespannung ("Level Read") ausgelesen werden. Weiterhin wird die Integration des komplementären Widerstandsschalters an den Kreuzungspunkten einer Gitterstruktur (Array) als Logiktor in einem Logikschaltkreis zur Realisierung nichtflüchtiger Boolescher Funktionen oder als analoger Block mit Logiktor zur Realisierung von Filtern und Verstärkern beschrieben.

  • Patent
    DE102013200615 - Offenlegung 17.04.2014, Nachanmeldungen: WO als P1401

Publ.-Id: 22626

P1401 - Komplementärer Widerstandsschalter, kontaktierte polykristalline piezo- oder ferroelektrische Dünnschicht, Verfahren zum Verschlüsseln einer Bitfolge

Bürger, D.; Du, N.; Kolitsch, A.; Manjunath, N.; Ou, X.; Schmidt, H.; Shuai, Y.; Skorupa, I.; You, T.

Gemäß verschiedenen Ausführungsformen kann ein komplementärer Widerstandsschalter aufweisen: zwei äußere Kontakte (T1, T2 ), zwischen denen zwei piezo- oder ferroelektrische Schichten (11a und 11b) liegen, die durch einen inneren gemeinsamen Kontakt voneinander getrennt sind, dadurch gekennzeichnet, dass mindestens ein Bereich der piezo- oder ferroelektrischen Schicht (11a und 11b) mindestens einmal derart modifiziert ist, dass in der piezo- oder ferroelektrischen Schicht (11a und 11b) jeweils zwischen dem inneren Kontakt und dem zugehörigen äußeren Kontakt ein Bereich (11') der Dicke (d ') entsteht, weicher mindestens zusätzlich in einem Bereich (11") der Dicke (d") modifiziert sein kann, wobei a) die äußeren Kontakte Oberflächenkontakte (Sa) und (Sb) und der innere Kontakt ein gemeinsamer zugehöriger Gegenkontakt (O) oder die äußeren Kontakte Gegenkontakte (Oa) und (Ob) und der innere Kontakt ein gemeinsamer zugehöriger Oberflächenkontakt (S) sind, b) die Oberflächenkontakte (S), (Sa) und (Sb) gleichrichtend und die Gegenkontakte (O) bzw. (Oa) und (Ob) nicht-gleichrichtend sind, c) sich die modifizierten Bereiche in der piezo- oder ferroelektrischen Schicht (11a und 11b) an den Oberflächenkontakten (S) bzw. (Sa) und (Sb) ausbilden, d) die piezo- oder ferroelektrische Schichten (11, 11', 11") verschiedene verspannungsabhängige strukturelle Phasen mit unterschiedlicher Bandlücke und/oder unterschiedlicher Polarisationsladung aufweisen, und e) die elektrische Leitfähigkeit der piezo- oder ferroelektrischen Schichten (11, 11', 11") unterschiedlich ist.

  • Patent
    WO2014111481 - Offenlegung 24.07.2014, Nachanmeldungen: EP, US

Publ.-Id: 22624

Targetry for Laser Wakefield Acceleration

Couperus, J. P.; Irman, A.; Jochmann, A.; Köhler, A.; Messmer, M.; Zarini, O.; Schramm, U.

Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. Target development and analysis is an important aspect in the further development of LWFA.
For short interaction length, high density LWFA schemes (up to several millimetres interaction length, plasma densities down to ~1018 cm3) gas-jet targets are used. These targets are analysed by a laser interferometry setup which can resolve phase shifts down to 4 mrad. Tomographic reconstruction enables detection of non-axisymmetrical defects in cylindrical nozzles and analysis of slit-nozzles and nozzles with an induced shock-wave density step.
For lower density and longer interaction length LWFA schemes, high laser intensity must be maintained over distances much longer than the Rayleigh length. Therefore laser guiding is necessary to counteract the diffraction induced divergence of the beam.
For this, a plasma channel is created inside a capillary via the concept of slow capillary discharge and characterised using an interferometric method. It is shown that the plasma channel has a refractive index profile suitable for laser guiding. As the first step, the pressure range and the time window in which guiding can occur are determined by guidance of a He-Ne laser. With the gained knowledge, laser guiding capabilities of a pulsed Ti:Sa laser are shown. The results show a broad, easy to realise parameter window for pressure and time in which a laser intensity transmission of above 75% is achieved.

Keywords: Laser wakefield acceleration; LWFA; gas-jet analysis; interferometry; tomography

  • Lecture (Conference)
    Laser Applications at Accelerators, 26.03.2015, Palmanova, Spain

Publ.-Id: 22623

Development and characterisation of gas-jet and discharge capillary targets for LWFA

Couperus, J. P.; Irman, A.; Jochmann, A.; Köhler, A.; Messmer, M.; Zarini, O.; Schramm, U.

Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. Target development and analysis is an important aspect in the further development of LWFA.
For short interaction length, high density LWFA schemes (up to several millimetres interaction length, plasma densities down to ~1018 cm3) gas-jet targets are used. These targets are analysed by a laser interferometry setup which can resolve phase shifts down to 4 mrad. Tomographic reconstruction enables detection of non-axisymmetrical defects in cylindrical nozzles and analysis of slit-nozzles and nozzles with an induced shock-wave density step.
For lower density and longer interaction length LWFA schemes, high laser intensity must be maintained over distances much longer than the Rayleigh length. Therefore laser guiding is necessary to counteract the diffraction induced divergence of the beam.
For this, a plasma channel is created inside a capillary via the concept of slow capillary discharge and characterised using an interferometric method. It is shown that the plasma channel has a refractive index profile suitable for laser guiding. As the first step, the pressure range and the time window in which guiding can occur are determined by guidance of a He-Ne laser. With the gained knowledge, laser guiding capabilities of a pulsed Ti:Sa laser are shown. The results show a broad, easy to realise parameter window for pressure and time in which a laser intensity transmission of above 75% is achieved.

Keywords: Laser wakefield acceleration; LWFA; gas-jet analysis; interferometry; tomography

  • Poster
    Laser Plasma Acceleration Workshop 2015, 10.-15.05.2015, Guadeloupe, France

Publ.-Id: 22622

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