Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

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

  • International Journal of Materials Research 107(2016)4, 362-371
    Online First (2016) DOI: 10.3139/146.111350

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
    Online First (2015) 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

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

European Ion Beam Infrastructures for Materials and Transdisciplinary Research

Fassbender, J.

Ion beam techniques have emerged as key enabling technologies across the international research landscape, vital to innovation in functional materials for special applications, and fields as diverse as cancer treatment, nanomaterials, renewable energy, advanced electronics, and the preservation of cultural heritage. Europe maintains one of the largest groupings of ion beam facilities in the world, and through strategic EU and national support, is poised to become a global leader in ion beam innovation.
Within the HZDR-coordinated EU-FP7 program SPIRIT the leading European ion beam centers have established common standards, best practices and a single point of access for European users to these facilities in the area of materials research which led to an increasing user interest. Now these best practices have to be transferred.
On the one hand to ion beam centers, which could not participate in the previous project, in order to broaden the accessibility of ion beam technology. One current example is the technology transfer of HZDR to the newly established ion beam center SLOVAKION in Trnava in Slovakia in the framework of an EU teaming activity. On the other hand ultra-sensitive technologies like accelerator mass spectrometry, which have not been in the focus of the past integrating activities mainly devoted to materials research, have to be structured at the European level in a similar way in order to significantly widen the potential user community to transdisciplinary research, i.e. in the areas of climate change, efficient and safe use of energy and resources, and healthcare. Last but not least, the industrial use of ion beam technology has to be further promoted. In contrast to rather small industrial use of synchrotron and neutron facilities, the leading ion beam centers in Europe deliver typically around 20% of their beam time to industrial users. However, past experience has shown that industrial use of ion beam technology is predominantly on a national scale basis. Hence, it becomes even more important to foster ion beam technology in European countries that have not yet developed their capabilities to full extent.

Keywords: IBC; SPIRIT; EU

  • Invited lecture (Conferences)
    INARIE - Integrating Access to Pan-European Research Infrastructures in Central and Eastern Europe, 30.11.-02.12.2015, Debrecen, Ungarn

Publ.-Id: 22621

Laser Microstructured Metal Thin Films as Promising Alternative for Indium Based Transparent Electrodes

Eckhardt, S.; Siebold, M.; Lasagni, A. F.

In the search of alternative materials for substituting indium tin-oxide, thin films of copper and aluminum (5 to 40 nm) were structured using direct laser interference patterning with nanosecond and picosecond pulse lasers to improve their optical properties. Using this method, periodic patterns consisting on micro-scaled holes were produced. It was found that the optical transmittance of the structured layers could be increased between 25 to 125% while the electrical resistance was marginally influenced. In addition, improvements in the diffuse transmittance are demonstrated for the processed materials. The laser treatment could enhance the diffuse to total transmission ratio (HAZE) by values ranging from 30 to 82%. The results also show that both of the studied metals succeed to match the frame of properties that is set by typical applications requiring indium thin oxide (ITO) films. For both ns- and ps-based structuring processes, numerical simulations are performed to investigate the ablation mechanisms of the thin films.

Keywords: Laser materials processing; Photovoltaic; Thin films

Publ.-Id: 22620

Application of a Yield Approach for the Prediction of Positron Emitter Distributions Produced During Therapeutic Carbon-Ion Beam Irradiation

Helmbrecht, S.; Priegnitz, M.; Enghardt, W.; Rohling, H.; Fiedler, F.

Positron-Emission-Tomography is a clinically implemented method for in vivo verification of treatment delivery in ion beam therapy. The dose distribution is the relevant measure but PET captures a β+-activity distribution, that is created as a side product during the irradiation.
Therefore, a prediction of the activity distribution is required. We present a simulation code that makes use of measured yields of β+ emitters to perform this task. The yields are available in three reference materials. A conversion from X-ray grey values to a combination of these materials has been set up. The lateral properties of the ion beam are described by means of a formulation of Moliere's scattering theory in thick targets.
A model of the annihilation point density around an emitting nuclide has been implemented in the software to describe the movement of the positrons.
Simulations of phantom experiments as well as of a real patient case were performed. The results are comparable or superior to the results obtained from an established condensed history Monte Carlo code.
We conclude that measured yields can be used as raw data for the calculation of ion beam induced β+-activity distribution instead of nuclear cross sections.

Keywords: PET; simulation; in-beam positron emission tomography; ion beam tumor therapy; hadron therapy; positron emitter distribution; prediction method

Publ.-Id: 22619

Complex formation of tetravalent actindies with small carboxylate ligands

Hennig, C.; Ikeda-Ohno, A.; Takao, S.; Takao, K.; Kraus, W.; Scheinost, A. C.

Tetravalent actinides form strong complexes with the carboxylic acids. Although there is a number of thermodynamic data reported [1-2] there is no information available on the complex structure in aqueous solution.
We used EXAFS spectroscopy to estimate the complex structure of Th4+, U4+, Np4+ and Ce4+ with different carboxylates (RCOO–; R = H, CH3, C2H2NH2) in aqueous solution [3-6]. The structural information from EXAFS data is limited to radial pair distribution functions. To overcome this limitation we forced single crystals to precipitate in different stability ranges of the solution species. Whether or not a species is preserved in a crystal structure was subsequently investigated by EXAFS spectroscopy. The crystal structure, revealed
by single-crystal diffraction, and combined with EXAFS spectroscopy on liquid and solid samples, provides precise information of coordination and structure of the related solution species. These studies show that in all of the investigated aqueous systems hexanuclear complexes [M6O4(OH)4(RCOO)12] appear, which become predominant with increasing ligand concentration as well as increasing pH, and dominate finally the species distribution.
An example is shown in Figure 1. EXAFS spectra were recorded on samples in aqueous solution with 0.05 M Th(IV), 1 M glycine and pH values ranging from 0.5 to 3.2. The spectrum at pH 0.5 shows a single peak representing mononuclear complexes of Th(OH)n (4n)+ with n  2. With increasing pH, the first peak in the Fourier transform becomes more asymmetric and finally splits. A second peak appears at R+ = 3.75 Å, and its intensity rises with increasing pH. This latter feature represents a Th-Th scattering interaction. The data fit indicate the appearance of a hexanuclear complex. This complex is stable until pH 3.2. At higher pH values precipitates a crystalline material. The EXAFS spectrum of this precipitate is identical with that of the solution at pH 3.2, indicating that the structure of the solution species remains preserved in the crystal structure.
Crystals from the precipitate were used for structure analysis by X-ray diffraction. A drawing of the crystal structure is shown in Figure 2, which is in turn representative for the coordination of the predominating solution species at pH 3.2.
The appearance of hexanuclear complexes in aqueous solution corresponds with both, the onset of the metal hydrolysis at the one hand, and the deprotonation of the carboxylic function at the other hand. This results in a competing reaction between hydrolysis and ligation. The hydrolysis results in a polymerization via oxo and hydroxo bonds, whereas the carboxylic function of the ligand results in the formation of 12 terminating chelate rings providing charge neutrality of the hexanuclear core and preventing further polymerization. Most of the thermodynamic data of actinide(IV) carboxylates are estimated assuming mononuclear solution species.
Our studies indicate that future work on tetravalent actinide carboxylates in aqueous solution need consideration of hexanuclear species.
[1] G.M. Sergeev, Radiokhimija 22, 536 (1980).
[2] A. Bismondo, L. Rizzo, G. Tomat, Inorg. Chim. Acta 74, 21 (1983).
[3] S. Takao, K. Takao, W. Kraus, F. Emmerling, A.C. Scheinost, G. Bernhard, C. Hennig, Eur. J. Inorg. Chem. 4771 (2009).
[4] K. Takao, S. Takao, A.C. Scheinost, G. Bernhard, C. Hennig, Inorg. Chem. 51, 1336 (2012).
[5] C. Hennig, S. Takao, K. Takao, S. Weiss, W. Kraus, F. Emmerling, A.C. Scheinost, Dalton Trans. 41, 12818 (2012).
[6] C. Hennig, A. Ikeda-Ohno, W. Kraus, S. Weiss, P. Pattison, H. Emerich, P.M. Abdala, A.C. Scheinost, Inorg. Chem. 52, 11734 (2013).

Keywords: actinides; xafs; thorium; uranium; neptunium; cerium

  • Lecture (Conference)
    Migration 2015: 15th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 22618

Artifical neural networks - another view on actinide chemistry

Rossberg, A.; Scheinost, A. C.

Driven by the enormous increase of computing power in the last few years, several theoretical models for biological neural networks have been developed and new modelling concepts are coming up. Close to their biological counterpart, artificial neural networks (ANNs) have been developed, which can be trained by presenting input data along with the desired output [1]. ANNs are used for example to recognize hand-written text, human faces, natural speech or personal interests, all features now commonly used by web-based social networks like Facebook or by search engines like Google. Another step forward was the development of spiking neural networks, a third generation ANN, which counts at the moment as the closest approximation of biological neural networks [2] and is strongly discussed in the community [3]. In general, ANNs can be considered as a method to infer functional relationships between a cause and the resulting effect. Note that these functional relationships are not inferred from mathematical models; first, the mathematical treatment would be too complex, and second, the required mathematical simplifications by using justified assumptions and constraints would most probably lead to a poor description of the problem. Therefore ANNs are seen as a more efficient and more accurate method to describe complex functional relationships. Here we demonstrate using two examples, that selforganizing maps (SOM) [4,5], a special kind of ANN, are well suited for analysing the complex chemistry of actinides.
The first example shows the relationships between the structure of aliphatic ((di-)hydroxy-)carboxylic acids and their complexation mode towards uranyl (UVI). For this, U LIII-edge EXAFS spectra from 13 aliphatic carboxylic acids (acetic, succinic, tartaric, lactic, 3-hydroxybutyric, citric, formic, malic, maleic, malonic, oxalic, propionic, and tricarballylic acid) at a range of pH, uranium and ligand concentrations were measured, resulting in 60 EXAFS spectra [6]. Based on the known structures of the ligands, SOM was used to determine the dependencies between the structure of the UVI carboxylate complexes and the structure of the interacting ligands, and to derive a predictive classification of the former. SOM revealed, for instance, that acids with an OH-group in α-position cause the formation of monomeric chelates and dimeric and trimeric UVI complexes, while an OH-group in β-position leads only to monomers, where uranyl is bidentately coordinated to the carboxylic group. In the second example, we apply SOM to the U LIII-edge EXAFS spectra of UVI sorption complexes with Al(hydr)oxides in order to determine the dependency of the structure of the formed sorption complexes on relevant physicochemical parameters like pH, pCO2, surface area, and surface loading. SOM here clearly reveals, for example, that polynuclear sorption complexes become predominant the higher the pH and the surface loading, while at low pH mononuclear complexes are present either as binary complexes or – in the presence of carbonate - as ternary complexes.
A properly trained SOM can also be used for the prediction of the spectra and the fractions of the complexes for a given ligand and a set of physicochemical parameters, hence SOM can replace thermodynamic speciation calculations, in case complex formation constants are not available. In turn, for a given spectrum, the corresponding physicochemical parameter can be predicted. SOM is not only restricted to EXAFS, but can use input from any other spectroscopy like NMR, UV-vis, infrared and Raman, or from diffraction/scattering patterns -together with chemical information- in order to derive a reliable multiscale speciation of actinides.

Keywords: Neuronal networks; artifical intelligence

  • Poster
    Migration 2015: 15th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 22617

Nuclear methods for real-time range verification in proton therapy based on prompt gamma-ray imaging

Hueso-González, F.

Accelerated protons are excellent candidates for treating several types of tumours. Such charged particles stop at a defined depth, where their ionisation density is maximum. As the dose deposit beyond this distal edge is very low, proton therapy minimises the damage to normal tissue compared to photon therapy. Nonetheless, inherent range uncertainties cast doubts on the irradiation of tumours close to organs at risk and lead to the application of conservative safety margins. This constrains significantly the potential benefits of proton over photon therapy and limits its ultimate aspirations. Prompt gamma rays, a by-product of the irradiation that is correlated to the dose deposition, are reliable signatures for the detection of range deviations and even for three-dimensional in vivo dosimetry. In this work, two methods for Prompt Gamma-ray Imaging (PGI) are investigated: the Compton camera (Cc) and the Prompt Gamma-ray Timing (PGT). Their applicability in a clinical scenario is discussed and compared. The first method aspires to reconstruct the prompt gamma ray emission density map based on an iterative imaging algorithm and multiple position sensitive gamma ray detectors. These are arranged in scatterer and absorber plane. The second method has been recently proposed as an alternative to collimated PGI systems and relies on timing spectroscopy with a single monolithic detector. The detection times of prompt gamma rays encode essential information about the depth-dose profile as a consequence of the measurable transit time of ions through matter. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and OncoRay, detector components are characterised in realistic radiation environments as a step towards a clinical Cc. Conventional block detectors deployed in commercial Positron Emission Tomography (PET) scanners, made of Cerium-doped lutetium oxyorthosilicate - Lu2SiO5:Ce (LSO) or Bismuth Germanium Oxide - Bi4Ge3O12 (BGO) scintillators, are suitable candidates for the absorber of a Cc due to their high density and absorption efficiency with respect to the prompt gamma ray energy range (several MeV). LSO and BGO block detectors are compared experimentally in clinically relevant radiation fields in terms of energy, spatial and time resolution. On a different note, two BGO block detectors (from PET scanners), arranged as the BGO block Compton camera (BbCc), are deployed for simple imaging tests with high energy prompt gamma rays produced in homogeneous Plexiglas targets by a proton pencil beam. The rationale is to maximise the detection efficiency in the scatterer plane despite a moderate energy resolution. Target shifts, increase of the target thickness and beam energy variation experiments are conducted. Concerning the PGT concept, in a collaboration among OncoRay, HZDR and IBA, the first test at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with several detectors and heterogeneous phantoms is performed. The sensitivity of the method to range shifts is investigated, the robustness against background and stability of the beam bunch time profile is explored, and the bunch time spread is characterised for different proton energies. With respect to the material choice for the absorber of the Cc, the BGO scintillator closes the gap with respect to the brighter LSO. The reason behind is the high energies of prompt gamma rays compared to the PET scenario, which increase significantly the energy, spatial and time resolution of BGO. Regarding the BbCc, shifts of a point-like radioactive source are correctly detected, line sources are reconstructed, and one centimetre proton range deviations are identified based on the evident changes of the back projection images. Concerning the PGT experiments, for clinically relevant doses, range differences of five millimetres in defined heterogeneous targets are identified by numerical comparison of the spectrum shape. For higher statistics, range shifts down to two millimetres are detectable. Experimental data are well reproduced by analytical modelling. The Cc and the PGT are ambitious approaches for range verification in proton therapy based on PGI. Intensive detector characterisation and tests in clinical facilities are mandatory for developing robust prototypes, since the energy range of prompt gamma rays spans over the MeV region, not used traditionally in medical applications. Regarding the material choice for the Cc: notwithstanding the overall superiority of LSO, BGO catches up in the field of PGI. It can be considered as a competitive alternative to LSO for the absorber plane due to its lower price, higher photoabsorption efficiency, and the lack of intrinsic radioactivity. The results concerning the BbCc, obtained with relatively simple means, highlight the potential application of Compton cameras for high energy prompt gamma ray imaging. Nevertheless, technical constraints like the low statistics collected per pencil beam spot (if clinical currents are used) question their applicability as a real-time and in vivo range verification method in proton therapy. The PGT is an alternative approach, which may have faster translation into clinical practice due to its lower price and higher efficiency. A proton bunch monitor, higher detector throughput and quantitative range retrieval are the upcoming steps towards a clinically applicable prototype, that may detect significant range deviations for the strongest beam spots. The experimental results emphasise the prospects of this straightforward verification method at a clinical pencil beam and settle this novel approach as a promising alternative in the field of in vivo dosimetry.

Keywords: proton therapy; range verification; in vivo dosimetry; prompt gamma ray imaging; Compton camera; block detector; scintillation; prompt gamma ray timing

  • Doctoral thesis
    TU Dresden, 2016
    Mentor: Prof. Dr. Wolfgang Enghardt
    141 Seiten


Publ.-Id: 22616

Prompt Gamma Imaging of a Pencil Beam with a High Efficiency Compton Camera at a Clinical Proton Therapy Facility

Hueso-González, F.; Petzoldt, J.; Römer, K. E.; Schöne, S.; Fiedler, F.; Golnik, C.; Kormoll, T.; Pausch, G.; Enghardt, W.

Protons are excellent particles for tumour treatment due to the increased ionization density close to their stopping point. In practice, the uncertainty on the particle range compromises the achievable accuracy. Compton cameras imaging prompt gamma rays, a by-product of the irradiation, have been proposed for indirect range verification years since. At Universitäts Protonen Therapie Dresden, two BGO block detectors (from PET scanners) arranged as Compton camera are deployed for imaging tests with high energy prompt gamma rays produced in PMMA by a proton pencil beam. Target shifts, thickness increase and beam energy variation experiments are conducted. Each measurement lasts about 15 minutes at a low proton beam current. The effect of one centimetre proton range deviations on the backprojected images is analysed. In conclusion, the experimental results highlight the potential application of Compton cameras for high energy prompt gamma ray imaging of pencil beams, as a real-time and in vivo range verification method in proton therapy.

Keywords: proton therapy; prompt gamma ray imaging; range verification; Compton camera; BGO block detector

  • Lecture (Conference)
    2015 IEEE Nuclear Science Symposium and Medical Imaging Conference, 31.10.-07.11.2015, San Diego, USA
  • Contribution to proceedings
    2015 IEEE Nuclear Science Symposium and Medical Imaging Conference, 31.10.-07.11.2015, San Diego, USA
    DOI: 10.1109/NSSMIC.2015.7582136
  • Poster
    NCRO-Retreat, 14.-16.04.2016, Dresden, Deutschland

Publ.-Id: 22615

Bioleaching of covellite - A model system for Kupferschiefer

Barthen, R.; Karimzadeh, L.; Gründig, M.; Grenzer, J.; Scholz, A.; Bischoff, L.; Franke, K.; Lippmann-Pipke, J.

Copper is an important base metal with manifold applications. Rising global demand makes low grade copper deposits increasingly attractive. Kupferschiefer represents Europe´s largest copper deposit. However, economic copper extraction from this calciferous, carbon rich ore with finely dispersed copper minerals is difficult. We aim for a deeper understanding of processes of copper (bio-)leaching at neutral pH. We employ synthetic covellite, microbial strains from Johanngeorgenstadt (Germany), model ligands, and geochemical modelling for elucidation of relevant parameters. We differentiate mineral dissolution, complexation, adsorption, and advection.

Keywords: Bioleaching; synthetic covellite; Kupferschiefer; glutamic acid; complexation

  • Poster
    10. PhD-seminar in Altenberg, 02.-04.11.2015, Altenberg, Deutschland

Publ.-Id: 22614

Joint compositional calibration: a geochronological example

Tolosana-Delgado, R.; van den Boogaart, K. G.; Fiserova, E.; Hron, K.; Dunkl, I.

This contribution explores several issues arising in the measurement of a (geo)chemical composition, specially in the case that the quantities of interest are linear functions of (log)-ratios. This is the case of multi-isotopic geochronological analyses, where an age of a geological material is inferred as a function of several logratios in the isotopic system (Hg202, Pb204, Pb206, Pb207, Pb208, Th232, U235, U238), by using several ratios (e.g., Pb208/Pb206, Pb206/Pb204, Hg202/Pb204, U238/U235), quantities that are scaling invariant and subcompositionally coherent, but which in general cannot be estimated without taking into account additive noise effects incompatible with a purely compositional approach. The proposed ways to a solution heavily build upon the multi- Poisson distribution, higlighting the counting nature of the readings delivered by these measuring machines.

  • Open Access Logo Contribution to proceedings
    6th International Workshop on Compositional Data Analysis, 01.-05.06.2015, L'Escala, Girona, Espana
    Proceedings of the 6th International Workshop on Compositional Data Analysis, 978-84-8458-451-3, 241-257

Publ.-Id: 22613

Biplots for Compositional Regression

Graffelman, J.; Tolosana-Delgado, R.

In the statistical modeling of compositions, the latter can appear as response or explanatory variables, or even in both roles simultaneously. Such modeling is of multivariate nature because compositions consists of vectors of D elements, with potentially large D. Prior to fitting a model, the compositions are typically first transformed by a log-ratio transformation. The transformed compositions remain, however, of multivariate nature. Several techniques from the field of multivariate analysis can be used to analyze the data of which we mention multivariate regression, canonical correlation analysis and redundancy analysis. In multivariate regression the interpretation of the results is complicated by the large number of regression coefficients obtained, and collected in the matrix of regression coefficients B[p,q] with p explanatory and q response variables. Van den Boogaart and Tolosana-Delgado (2013) applied the singular value decomposition of the matrix of regression coefficients in order to find rank two approximations to B so that biplots can be constructed that summarize the relationships between the variables. However, the regression coefficients depend on the scale of the explanatory variables and their variances can be of very different order of magnitude. It is thus more natural to \standardize" the regression coefficient with a Mahanalobis-like transformation prior to biplot construction. Such an approach amounts to a redundancy analysis (also known as reduced-rank regression) of the data, and biplots for this method are discussed in detail by Ter Braak & Looman (1994). In this contribution we develop and apply redundancy analysis in a compositional context, discussing its biplots with empirical geological data and its compositional geometric interpretation.

Keywords: Redundancy analysis; Multivariate regression; Biplot; Conditional biplot; centred log-ratio (clr) transformation

  • Open Access Logo Contribution to proceedings
    6th International Workshop on Compositional Data Analysis, 01.-05.06.2015, L'Escala, Girona, Espana
    Proceedings of the 6th International Workshop on Compositional Data Analysis, 978-84-8458-451-3, 141-147

Publ.-Id: 22612

Linear models for the conditional distribution

van den Boogaart, K. G.; Lehmann, M.; Tolosana Delgado, R.

Our aim is to introduce a regression model for the conditional probablity distributions, of observable random variables as a function of regressors. The approach linear models in Bayes spaces. Bayes spaces are a generalisation of the Aitchison Simplex, which can be seen as the space of all distributions with support 1,...,n to probablity distributions on arbitrary measure spaces. Compositional linear models on the Aitchison simplex turn out to be equivalent to multivariate logistic regression if written in alr representation. Then, likelihood theory for generalized linear models is used to estimate the regression coefficients based on observed realisation of the random variable instead of observed compositions as in compositional regression. This idea is generalized towards Bayes spaces, generating a technique allowing to define and estimate models for the conditional distribution of an observed quantity as a Bayes-space-linear function of regressors.

Keywords: Multinomial Logistic Regression; Bayes Spaces; Compositional Regression

  • Open Access Logo Contribution to proceedings
    6th International Workshop on Compositional Data Analysis, 01.-05.06.2015, L'Escala, Girona, Espana
    Proceedings of the 6th International Workshop on Compositional Data Analysis, 978-84-8458-451-3, 45-53

Publ.-Id: 22611

Baseline Model for Bubbly Flows in OpenFoam: Current Implementation and Future Needs

Kriebitzsch, S.; Rzehak, R.

Many technical processes in industries such as chemical or energy but also numerous natural phenomena involve multiphase flow. Due to the complex physics and the broad range of relevant length scales involved, it is a formidable task to achieve a better understanding of such flows. A detailed insight into the local flow field can be obtained from multiphase computational fluid dynamics, which therefore is a potentially valuable optimization and design tool. Such simulations are feasible within the framework the so-called multi-fluid modelling, in which the different phases are described as interpenetrating continua. Within this framework closure models are necessary to describe the interaction of the phases and 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. Accurate and trustworthy predictions with multiphase CFD are only possible if a fixed set of closures is available that has been validated for a wide range of flow conditions and can therefore reliably be used also for unknown flow problems.
In this work a set of closure relations has been implemented into OpenFOAM, which represents the best available knowledge and is applicable for monodisperse turbulent adiabatic bubbly flow. Specifically we select closures for the exchange of momentum, i.e. drag and non-drag forces, and the effect of the disperse phase on the carrier-phase turbulence, the so-called bubble-induced turbulence. This set of closure models may serve as a baseline for further improvements and extensions to more general situations.
Experimental data for bubbly air-water flows, available from literature and from in-house experiments, are used to validate the model. Overall all three experimental data sets are reasonably well reproduced by the simulation results, in particular in the bulk of the flow. Larger discrepancies show up especially in the near-wall region and for the turbulent quantities. Also for bubble sizes around 4.5 to 5 mm, the reproduction of the experimental data with a monodisperse model becomes challenging. From the validation cases the following needs for further developments are identified:

  • improved modelling of the near-wall region
  • refined description of the bubble-induced turbulence
  • modelling of the bubble-size distribution coupled with multiple momentum equations for the disperse phase.
The authors acknowledge the Helmholtz Association for support of the research within the frame of the Helmholtz Energy Alliance 'Energy Efficient Chemical Multiphase Processes'.

Keywords: OpenFOAM; Bubbly Flow; Modelling; CFD

  • Lecture (Conference)
    The 3rd OpenFOAM User Conference 2015, 19.-20.10.2015, Stuttgart, Deutschland

Publ.-Id: 22610

PET imaging evaluation of [18F]DBT-10, a novel radioligand specific to α7 nicotinic acetylcholine receptors, in nonhuman primates

Hillmer, A. T.; Zheng, M.-Q.; Li, S.; Scheunemann, M.; Lin, S.-F.; Holden, D.; Labaree, D.; Ropchan, J.; Teodoro, R.; Deuther-Conrad, W.; Carson, R. E.; Brust, P.; Huang, Y.

Purpose Positron emission tomography (PET) radioligands specific to α7 nicotinic acetylcholine receptors (nAChRs) afford in vivo imaging of this receptor for neuropathologies such as Alzheimer’s disease, schizophrenia, and substance abuse. This work aims to characterize the kinetic properties of an α7 -nAChR-spe c i f i c radioligand, 7-( 1 ,4-diazabicyclo[3.2.2]nonan-4-yl)-2-[18F]-fluorodibenzo[b,d]thiophene 5,5-dioxide ([18F]DBT-10), in nonhuman primates.
Methods [18F]DBT-10 was produced via nucleophilic substitution of the nitro-precursor. Four Macaca mulatta subjects were imaged with [18F]DBT-10 PET, with measurement of [18F]DBT-10 parent concentrations and metabolism in arterial plasma. Baseline PET scans were acquired for all subjects.
Following one scan, ex vivo analysis of brain tissue was performed to inspect for radiolabeled metabolites in brain. Three blocking scans with 0.69 and 1.24 mg/kg of the α7-nAChRspecific ligand ASEM were also acquired to assess dosedependent blockade of [18F]DBT-10 binding. Kinetic analysis of PET data was performed using the metabolite-corrected input function to calculate the parent fraction corrected total distribution volume (VT/fP).
Results [18F]DBT-10 was produced within 90 min at high specific activities of 428±436 GBq/μmol at end of synthesis.
Metabolism of [18F]DBT-10 varied across subjects, stabilizing by 120 min post-injection at parent fractions of 15–55 %. Uptake of [18F]DBT-10 in brain occurred rapidly, reaching peak standardized uptake values (SUVs) of 2.9–3.7 within 30 min. The plasma-free fraction was 18.8±3.4 %. No evidence for radiolabeled [18F]DBT-10 metabolites was found in ex vivo brain tissue samples. Kinetic analysis of PET data was best described by the two-tissue compartment model. Estimated VT/fP values were 193–376 ml/cm3 across regions, with regional rank order of thalamus>frontal cortex>striatum>hippocampus>occipital cortex>cerebellum>pons. Dosedependent blockade of [18F]DBT-10 binding by structural analog ASEMwas observed throughout the brain, and occupancy plots yielded a VND/fP estimate of 20±16 ml/cm3.
Conclusion These results demonstrate suitable kinetic properties of [18F]DBT-10 for in vivo quantification of α7-nAChR binding in nonhuman primates.

Keywords: Nicotine; Nicotinic acetylcholine receptor; Alpha 7; PET

  • European Journal of Nuclear Medicine and Molecular Imaging 43(2016)3, 537-547
    Online First (2015) DOI: 10.1007/s00259-015-3209-0

Publ.-Id: 22608

Effects of ionic strength and fulvic acid on the adsorption of Tb3+ and Eu3+ onto clay

Poetsch, M.; Lippold, H.

High salinity and natural organic matter are both known to facilitate migration of toxic or radioactive metals in geochemical systems, but little is known on their combined effect.
We investigated complexation of Tb3+ and Eu3+ (as analogues for trivalent actinides) with fulvic acid and their adsorption onto clay in the presence of NaCl, CaCl2 and MgCl2 at ionic strengths up to saturation. 160Tb, 152Eu and 14C were employed as radiotracers, allowing invesitigations at very low concentrations according to probable conditions in far-field scenarios of nuclear waste repositories.
A composite approach (linear additive model) was tested for suitability in the prediction of Kd values for solid-liquid distribution of Tb(III) and Eu(III) in the ternary system of metal ion, clay and fulvic acid based on the constituent binary subsystems. The model was found suitable in reproducing the influence of fulvic acid as a function of ionic strength for bivalent electrolyte cations. In this analysis, it could be shown that high ionic strength does not further enhance the mobilizing potential of humic matter.

Keywords: fulvic acid; metal binding; linear additive model; adsorption; ionic strength


Publ.-Id: 22605

Characterization of scintillator crystals for usage as prompt gamma monitors in particle therapy

Roemer, K.; Pausch, G.; Bemmerer, D.; Berthel, M.; Dreyer, A.; Golnik, C.; Hueso-González, F.; Kormoll, T.; Petzoldt, J.; Rohling, H.; Thirolf, P.; Wagner, A.; Wagner, L.; Weinberger, D.; Fiedler, F.

Particle therapy in oncology is advantageous compared to classical radiotherapy due to its well-defined penetration depth. In the so-called Bragg peak, the highest dose is deposited; the tissue behind the cancerous area is not exposed. Different factors influence the range of the particle and thus the target area, e.g. organ motion, mispositioning of the patient or anatomical changes. In order to avoid over-exposure of healthy tissue and under-dosage of cancerous regions, the penetration depth of the particle has to be monitored, preferably already during the ongoing therapy session. The verification of the ion range can be performed using prompt gamma emissions, which are produced by interactions between projectile and tissue, and originate from the same location and time of the nuclear reaction. The prompt gamma emission profile and the clinically relevant penetration depth are correlated. Various imaging concepts based on the detection of prompt gamma rays are currently discussed: collimated systems with counting detectors, Compton cameras with (at least) two detector planes, or the prompt gamma timing method, utilizing the particle time-of-flight within the body. For each concept, the detection system must meet special requirements regarding energy, time, and spatial resolution. Nonetheless, the prerequisites remain the same: the gamma energy region (2 to 10 MeV), high counting rates and the stability in strong background radiation fields. The aim of this work is the comparison of different scintillation crystals regarding energy and time resolution for optimized prompt gamma detection.

Keywords: Instrumentation for hadron therapy; Scintillators; scintillation and light emission processes (solid and gas and liquid scintillators)

Publ.-Id: 22604

On the hydrodynamics of airlift reactors, Part I: Experiments

Ziegenhein, T.; Zalucky, J.; Rzehak, R.; Lucas, D.

It is more and more possible to design bubbly flow reactors with methods of the computational fluid dynamics (CFD). However, measurements that can be used for model validation are often missing, especially for complex setups like airlift reactors. Such measurements include locally resolved information about the dispersed and continuous phase, particularly the flow field and interface structure. In the present work Reynolds stresses, liquid velocity and gas void fraction profiles as well as bubble size distributions are provided at several positions in the riser and the downcomer in a rectangular airlift reactor for this purpose. In addition, the hydrodynamics inside this airlift reactor are in detail described by the measured values.

Keywords: dispersed gas-liquid multiphase flow; airlift reactor; model validation; particle tracking velocimetry; turbulence; videography; bubble size distribution

Publ.-Id: 22603

Particle tracking using micro bubbles in bubbly flows

Ziegenhein, T.; Garcon, M.; Lucas, D.

Micro bubbles do not contaminate multiphase flows like conventional tracer particles so that the velocity in such can be determined completely non-intrusive by tracking them. Micro bubbles, however, are often larger as conventional tracer particles and have a significantly different density than the surrounding fluid. The ability of micro bubbles to follow the flow is investigated in this work. For this purpose, the particle tracking velocimetry results that are obtained with naturally occurring micro bubbles are compared to particle image velocimetry measurements using PMMA tracer particles. In combination with the used volume illumination, a simple, robust and reliable measuring technique is presented, which is deployable for complex problems from biological to oceanic engineering.
Averaged liquid velocities as well as basic turbulence parameters are determined in a rectangular bubble column for different gas volume flow rates. High flow rats are good manageable due to the volume illumination whereas the PIV measurements using a light sheet are approaching their limits. The general sampling bias in multiphase flows found recently for PIV measurements is also present for particle tracking methods; a hold processor that waits a time depending on the distribution of the particle information over the measuring area gives reasonable results.

Keywords: Velocity measurement; sampling bias; multiphase flow; particle tracking velocimetry; particle image velocimetry; bubble tracking velocimetry; volume illumination


Publ.-Id: 22602

Towards a unified approach for modelling uniform and non‐uniform bubbly flows

Ziegenhein, T.; Rzehak, R.; Ma, T.; Lucas, D.

An important ingredient of closure relations for the Euler-Euler two-fluid model is the description of turbulent fluctuations. Models proposed in the literature disagree concerning the treatment of such on all scales. The large scale fluctuation structures as well as the bubble induced turbulence might be neglected or resolved and/or modeled respectively in different ways. Each treatment has been demonstrated to work for a certain application but a unifying perspective is lacking so far.
To this end a set of closure relations for the fluid dynamics of bubbly flow has been collected that represents the best available knowledge and may serve as a baseline for further improvements and extensions. This model comprises a set of bubble forces as well as a turbulence model including turbulence modification due to the bubbles and has been successfully validated for bubbly flows in pipes and bubble columns. Here it is applied to two sets of data representing non-uniform and uniform flows in bubble columns which are dominated by large scale fluctuations and bubble induced turbulence respectively.

Keywords: dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; CFD simulation; bubble column; bubble-induced turbulence


Publ.-Id: 22601

Visualising the molecular alteration of the calcite (104) – water interface by sodium nitrate

Hofmann, S.; Voitchovsky, K.; Spijker, P.; Schmidt, M.; Stumpf, T.

The reactivity of calcite, one of the most abundant minerals in the earth’s crust, is determined by the molecular details of its interface with the contacting solution. Recently, it has been found that trace concentrations of NaNO3 severely affect calcite’s (104) surface and its reactivity. Here we combine molecular dynamics (MD) simulations, X-ray reflectivity (XR) and in situ atomic force microscopy (AFM) to probe the calcite (104)-water interface in the presence of NaNO3. Simulations reveal density profiles of different ions near calcite’s surface, with NO3- able to reach closer to the surface than CO32- and in higher concentrations. Reflectivity measurements show a structural destabilisation of the (104) surfaces’ topmost atomic layers in NaNO3 bearing solution, with distorted rotation angles of the carbonate groups and substantial displacement of the lattice ions. Nanoscale AFM results confirm the alteration of crystallographic characteristics and the ability of dissolved NaNO3 to alter the structure of interfacial water was observed by AFM force spectroscopy. Our experiments and simulations consistently evidence a dramatic deterioration of the crystals’ surface, with potentially important implications for geological and industrial processes.

Keywords: Calcite; lanthanides; surface; AFM; Molecular dynamics; Surface X-ray Diffraction; nitrate

Publ.-Id: 22599

Defect-induced magnetism in SiC: The new opportunity in spintronics

Liu, Y.

The charge and spin are two intrinsic properties of electron. Electronic devices mainly utilize the charge of electrons, while mass storage devices are based on the spin of electrons. Diluted magnetic semiconductors provide the opportunity to use the charge and spin of electrons simultaneously, which may bring revolutionary changes in the information technology. Progresses have been achieved in the preparation of magnetic wide band-gap semiconductors with Curie temperatures at around room temperature by dopings. However, limited solubility of transition metals often leads to the precipitation of second phases, thwarting the attempts to get the unambiguous experimental results. Recently, there has been increasing evidence that traditional magnetic elements are not the sole source in inducing intrinsic magnetism. The effect of defects on magnetism formation is gradually being realized.
Our work has been focusing on the origin of magnetism in SiC for many years. Early research demonstrated that Mn is not the only source to determine the magnetic ordering in Mn doped SiC. Subsequently, ferromagnetism was induced in SiC by non-TM element Al dopings. Based on the results mentioned above, we carefully investigated the magnetism of neutron irradiated / noble gas ion implanted SiC single crystals in a series of work. The results unambiguously verified that defects can induce magnetism. The intentionally created defects dominated by divacancies (VSiVC) are responsible for the observed magnetism. The long-range ferromagnetic coupling can be attributed to the p electrons of the nearest-neighbor carbon atoms around VSiVC. Besides, the concentration of VSiVC has an optimal value and excess defects will depress the magnetism.

Keywords: Defect-induced magnetism; semiconductor; spintronics; SiC

  • Lecture (others)
    Seminar in the State University of New York at Buffalo, 13.10.2015, Buffalo, United States of America
  • Lecture (others)
    Seminar in Shanghai Institute of Ceramics, Chinese Academy of Sciences, 25.01.2016, Shanghai, China

Publ.-Id: 22598

LIM-only protein FHL2 critically determines survival and radioresistance of pancreatic cancer cells.

Zienert, E.; Eke, I.; Aust, D.; Cordes, N.

Numerous factors determine the current poor prognosis of pancreatic ductal adenocarcinoma (PDAC). One of the greatest challenges to overcome is treatment resistance. Among a large repertoire of intrinsic resistance mechanisms, integrin-mediated cell adhesion to extracellular matrix (ECM) has been identified to be fundamental. Coalesced in focal adhesion complexes, integrins, receptor tyrosine kinases, protein kinases and adapter proteins mediate prosurvival signaling. Four and a half LIM domains protein 2 (FHL2) is one of these adapter proteins, which operates through protein-protein interactions and shows tumor-specific expression. Based on this, we investigated FHL2 expression in PDAC specimens and three-dimensionally grown cell lines and how FHL2 mechanistically contributes to cell survival, cell cycling and radiation resistance. PDAC exhibited a significantly increased and heterogeneous FHL2 expression. Upon FHL2 depletion, pancreatic cancer cell lines showed significantly decreased cell survival, proliferation and radioresistance as well as enhanced apoptosis and MEK/ERK signaling and cyclin D1, E, A and B1 expression were strongly induced. Targeting of FHL2 and MEK1 was similarly effective than FHL2 depletion alone, suggesting MEK1 as a downstream signaling mediator of FHL2. Taken together, our results provide evidence for the importance of the focal adhesion protein FHL2 in pancreatic cancer cell survival, proliferation and radiosensitivity.

Publ.-Id: 22596

DNA Damage Response Assessments in Human Tumor Samples Provide Functional Biomarkers of Radiosensitivity.

Willers, H.; Gheorghiu, L.; Liu, Q.; Efstathiou, J. A.; Wirth, L. J.; Krause, M.; von Neubeck, C.

Predictive biomarkers are urgently needed for individualization of radiation therapy and treatment with radiosensitizing anticancer agents. Genomic profiling of human cancers provides us with unprecedented insight into the mutational landscape of genes directly or indirectly involved in the response to radiation-induced DNA damage. However, to what extent this wealth of structural information about the cancer genome produces biomarkers of sensitivity to radiation remains to be seen. Investigators are increasingly studying the subnuclear accumulation (ie, foci) of proteins in the DNA damage response (DDR), such as gamma-H2AX, 53BP1, or RAD51, as a surrogate of treatment sensitivity. Recent findings from preclinical studies have demonstrated the predictive potential of DDR foci by correlating foci with clinically relevant end points such as tumor control probability. Therefore, preclinical investigations of DDR foci responses are increasingly moving into cells and tissues from patients, which is the major focus of this review. The advantage of using DDR foci as functional biomarkers is that they can detect alterations in DNA repair due to various mechanisms. Moreover, they provide a global measurement of DDR network function without needing to know the identities of all the components, many of which remain unknown. Foci assays are thus expected to yield functional insight that may complement or supersede genomic information, thereby giving radiation oncologists unique opportunities to individualize cancer treatments in the near future.

Publ.-Id: 22595

Implementation of a software for REmote COMparison of PARticlE and photon treatment plans: ReCompare.

Löck, S.; Roth, K.; Skripcak, T.; Worbs, M.; Helmbrecht, S.; Jakobi, A.; Just, U.; Krause, M.; Baumann, M.; Enghardt, W.; Lühr, A.


To guarantee equal access to optimal radiotherapy, a concept of patient assignment to photon or particle radiotherapy using remote treatment plan exchange and comparison - ReCompare - was proposed. We demonstrate the implementation of this concept and present its clinical applicability.

The ReCompare concept was implemented using a client-server based software solution. A clinical workflow for the remote treatment plan exchange and comparison was defined. The steps required by the user and performed by the software for a complete plan transfer were described and an additional module for dose-response modeling was added.

The ReCompare software was successfully tested in cooperation with three external partner clinics and worked meeting all required specifications. It was compatible with several standard treatment planning systems, ensured patient data protection, and integrated in the clinical workflow.

The ReCompare software can be applied to support non-particle radiotherapy institutions with the patient-specific treatment decision on the optimal irradiation modality by remote treatment plan exchange and comparison.

Keywords: Bestrahlungsplanvergleich; Entscheidungsunterstützung; Partikeltherapie; Patientenauswahl; Radiotherapy; Strahlentherapie; decision support; particle therapy; patient selection; treatment plan comparison

Publ.-Id: 22594

Exploring the joint compositional variability of major components and trace elements in the TELLUS soil geochemistry campaign (Northern Ireland)

Tolosana-Delgado, R.; Mckinley, J.

Geochemical datasets are growing in both their number of samples and components, including elements which typical values cover the ranges of magnitude from % to ppm or even ppb. Moreover, the sources of variability increase as well. It is becoming thus increasingly necessary to have appropriate tools to explore this geochemical variability. An example of such framework is provided by any modern regional geochemistry campaign, typically having thousands of samples analysed for several tens of elements covering diverse geological units in non-homogeneous climate-landscape environments. Using the TELLUS soil geochemical survey of Northern Ireland, this paper primarily aims to present one such exploratory case study.

The typical tools to use in this context are all based on principal component analysis (PCA) and variants. Several different alternatives are considered: raw data, standardized data and log-ratio transformed data; classical PCA vs robust PCA; only major components vs. a mixture of major and trace elements. Using the 12 resulting analyses, insights into the nature of the dominant factors of geochemical variability are extracted, and the advantages of a log-ratio approach highlighted.

From a methodological point of view, we show: (i) that raw data should seldom be considered; (ii) standardised data do not show any difference relevant between robust and classical PCA; and (iii) that standardised data and log-ratio data deliver a roughly similar picture, but (iv) logratio data offer much more insights, especially when comparing robust and classical PCA using all variables available.

From the perspective of the case study presented, we conclude that the first two sources of soil geochemical variation are related to the background geology and the presence/absence of blanket peat (a major feature of the landscape of Northern Ireland). Which of the two factors is the dominant one depends on whether robust or classical PCA was used. Besides this (rather expected) result, the analysis showed in addition striking positive correlations between the logratios Se/LOI, MnO/CaO and I/Br; between Br/Ni, Cl/Cr, Sb/TiO2 and Cd/MnO; or between Cs/I, Rb/Zn and Cr/Ni. Also null correlations are detected between the ratios of the second and third groups. Taking into account information on the major lithologies present in Northern Ireland, the third group of ratios appears to describe lithological changes, while the second group of ratios is strongly related. to peat building processes, which not only enrich in LOI (as expected) but in Br, Cl, Cd and Sb as well.

Publ.-Id: 22593

Lorentz TEM Imaging of Stripe Structures Embedded in a Soft Magnetic Matrix

Basith, M.; McVitie, S.; Strache, T.; Fritzsche, M.; Mücklich, A.; Fassbender, J.; McCord, J.

Néel walls in soft magnetic NiFe/NiFeGa hybrid stripe structures surrounded by a NiFe film are investigated by high-resolution Lorentz transmission-electron-microscopic imaging. An antiparallel orientation of magnetization in 1000-nm-wide neighboring unirradiated-irradiated stripes is observed by forming high-angle domain walls during magnetization reversal. Upon downscaling the stripe structure size from 1000 to 200 nm, a transition from a discrete domain pattern to an effective magnetic medium is observed for external magnetic-field reversal. This transition is associated with the vanishing ability of hosting high-angle domain walls between adjacent stripes.

Keywords: magnetism; domains; imaging; ion irradiation

Publ.-Id: 22592

Study of solar wind ions implantation effects in optical coatings in view of Solar Orbiter space mission operation

Bacco, D.; Corso, A. J.; Zuppella, P.; Böttger, R.; Gerlin, F.; Napolitani, E.; Tessarolo, E.; Nardello, M.; Pelizzo, M. G.

Low energy ions coming from the quite solar wind are considered among the causes of potential damage of the optical instrumentation and components on board of ESA Solar Orbiter. Predictions of space radiation parameters are available for instruments on board of such mission. Accelerators are commonly used to reproduce the particle irradiation on a spacecraft during its lifetime at the ground level. By selecting energies and equivalent doses it is possible to replicate the damage induced on space components. Implantation of Helium ions has been carried out on different single layer thin films at LEI facility at Forschungszentrum Dresden-Rossendorf varying the total dose. Profile of the implanted samples has been experimentally recovered by SIMS measurements. The change in reflectance performances of such coatings has been experimentally evaluated and modelled. The outcomes have been used to verify the potential impact on the METIS instrument and to drive the optimization of the M0 mirror coating..

Keywords: Ions; Optical coatings; Equipment and services; Helium; Mirrors; Particles; Radiation; Reflectivity; Thin films; Coating

Publ.-Id: 22590

Ferromagnetism induced by vacancy clusters in Silicon

Liu, Y.; Zhang, X. H.; Yuan, Q.; Han, J. C.; Zhou, S. Q.; Song, B.

Defect-induced ferromagnetism provides an alternative for organic and semiconductor spintronics. Though it is weak, it can be stable above room temperature. Till now it has been confirmed at least in oxides [1, 2] and carbon based materials [3, 4]. Interestingly, the relation between magnetism and defects in Silicon was demonstrated decades ago [5]. Since then, some progresses were made [6-9] and push forward the research of magnetic Mn doped Si a lot but it is drawn little attention itself. Here, with the latest growth purifying technique and sensitive measurements, we investigated the magnetism in Silicon after neutron irradiation and try to correlate the observed magnetism to particular defects in Si.

Keywords: defect-induced ferromagnetism; silicon; neutron irradiation; semiconductors

  • Poster
    ALS User Meeting, 05.-07.10.2015, Berkeley, United States of America

Publ.-Id: 22589

Discrepancy between fluvial incision and denudation rates at the western Pamir margin

Fuchs, M.; Gloaguen, R.; Pohl, E.; Merchel, S.; Andermann, C.; Krbetschek, M.; Rugel, G.

Surface process rates provide keys to unravel controls of tectonics and climate on mountain evolution. In the Pamir, significant discrepancies exist between fluvial incision and denudation rates. Optically stimulated luminescence (OSL)-based fluvial incision outpaces cosmogenic nuclide (Be-10)-based denudation by up to 10 times at the western Pamir margin.
Differences in averaging times of determined rates cannot explain the contrast. The millennial denudation rates are highest (1.0 – 1.5 mm/yr) where long-term (104years) fluvial incision is moderate (2 – 5 mm/yr). In contrast, denudation is lower (~0.8 mm/yr) where incision is highest (7 – 10 mm/yr).

Process rates across the Pamir reveal differing control factors. The longitudinal profile and valley profiles of the Panj highlight links between fluvial incision and tectonic structures. Convex river reaches across the Pamir domes correspond to intense incision, whereas graded river segments coincide with southern dome boundaries. The indicated river captures induce intense incision and base level lowering for basins at the Pamir margins. Both, rapid incision and base level changes, maintain the steep slopes (0.75 quartiles) that are the predominant driver (R2 of ~0.8) for high denudation rates at the Pamir margins (0.5 – 1.5 mm/yr). However, highest denudation and lowest discrepancy to fluvial incision (~2 - 3 times) coincides with the areas receiving the highest annual precipitation. Multiple linear regression of denudation rates with the 0.75 quartiles of basin slopes and precipitation shows an R2 of 0.93. We propose that river captures are responsible for driving the intense incision along the Panj and consequently, provide the conditions for hillslope adjustment that contributes to the high denudation at the Pamir margins. Winter precipitation, and related concentrated discharge during the melting season, may act as limiting factor to hillslope adjustment and consequently, to denudation processes.

Keywords: accelerator mass spectrometry

  • Poster
    AGU Fall Meeting, 14.-18.12.2015, San Francisco, USA


Publ.-Id: 22588

Tailoring dynamic magnetic characteristics of Fe60Al40 films through ion irradiation

Tahir, N.; Bali, R.; Gieniusz, R.; Mamica, S.; Gollwitzer, J.; Schneider, T.; Lenz, K.; Potzger, K.; Lindner, J.; Krawczyk, M.; Fassbender, J.; Maziewski, A.

Magnetization dynamics in Fe60Al40 thin films possessing depth-varying saturation magnetization (Ms) has been studied experimentally and theoretically. Variation in Ms was achieved by irradiation of 40 nm thick, chemically ordered (B2) Fe60Al40 films with Ne+ ions with energies between 0 – 30 keV. The initial B2 phase is paramagnetic and as the penetrating ions cause chemical disordering, the ion-affected region transforms to the ferromagnetic A2 phase. The effective ferromagnetic thickness and the depth of the A2/B2 phase boundary depend on the ion-energy (E); the effective thicknesses are 8.5 and 40 nm respectively for E = 2.5 and 30 keV. Thermally excited spin-waves in films with varying effective ferromagnetic thicknesses were analyzed by employing Brillouin light scattering and vector network analyzer ferromagnetic resonance spectroscopy. The analytical calculations are in good agreement with the experimental values, and show that the observed spin-wave modes are directly related to the effective ferromagnetic thickness; films irradiated with E < 5 keV only show the Damon-Eshbach mode, whereas for 15 < E < 20 keV an additional lower frequency standing spin-wave mode is observed. In films irradiated with E > 20 keV the Damon- Eshbach mode is observed to lie between two standing spin-wave modes. Furthermore, the A2/B2 phase boundary can be shown to act as an asymmetric pinning site. Controlling the depth of the phase boundary by varying the ion-energy can be a path to manipulate spin-wave propagation in materials displaying the phenomenon of disorder induced ferromagnetism.

Publ.-Id: 22587

Evolution of magnetic domain structure formed by ion-irradiation of B2-Fe0.6Al0.4

Tahir, N.; Gieniusz, R.; Maziewski, A.; Bali, R.; Potzger, K.; Lindner, J.; Fassbender, J.

Magnetic domains and magnetization reversal in 40 nm thick films of Fe0.6Al0.4, have been studied by longitudinal magneto-optical Kerr effect. By varying the Ne+ ion-energy E between 2 and 30 keV (keeping a constant fluence), we varied the depth-penetration of the ions, and thereby influenced the homogeneity of the induced saturation magnetization Ms. The dependence of coercivity on ion energy shows maximum for 5 keV Ne+. Considerable differences in the magnetic domain formation and magnetization reversal processes were observed: at low E (≤ 5keV), the reversal process is dominated by domain nucleation mechanism (high density of domain nucleation sites), consistent with the occurrence of an inhomogeneous Ms. Films irradiated with E > 5keV ions exhibit significantly low domain nucleation density, and the reversal is dominated by domain propagation mechanism, suggesting homogeneity in induced Ms. These results demonstrate the tunability of magnetization reversal behavior in materials possessing disorder induced magnetic phase transitions.

Publ.-Id: 22586

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