Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32619 Publications
Ion beam induced structural modifications in nano-crystalline permalloy thin films
Roshchupkina, O.;
In the last years, there is a rise of interest in investigation and fabrication of nanometer sized magnetic structures due to their various applications (e.g. for data storage or micro sensors). Over the last several decades ion beam implantation became an important tool for the modification of materials and in particular for the manipulation of magnetic properties. Nanopatterning and implantation can be done simultaneously using focused-ion beam (FIB) techniques. FIB implantation and standard ion implantation differ in their beam current densities by 7 orders of magnitude. This difference can strongly influence the structural and magnetic properties, e.g. due to a rise of the local temperature in the sample during ion implantation.

In previous investigations both types of implantation techniques were studied separately. The aim of the current research was to compare both implantation techniques in terms of structural changes and changes in magnetic properties using the same material system. Moreover, to separate any possible annealing effects from implantation ones, the influence of temperature on the structural and magnetic properties were additionally investigated.

For the current study a model material system which is widely used for industrial applications was chosen: a 50 nm thick non-ordered nano-crystalline permalloy (Ni81Fe19) film grown on a SiO2 buffer layer based onto a (100)-oriented Si substrate. The permalloy films were implanted with a 30 keV Ga+ ion beam; and also a series of as-deposited permalloy films were annealed in an ultra-high vacuum (UHV) chamber.

Several investigation techniques were applied to study the film structure and composition, and were mostly based on non-destructive X-ray investigation techniques, which are the primary focus of this work. Besides X-ray diffraction (XRD), providing the long-range order crystal structural information, extended X-ray absorption fine structure (EXAFS) measurements to probe the local structure were performed. Moreover, the film thickness, surface roughness, and interface roughness were obtained from the X-ray reflectivity (XRR) measurements. Additionally cross-sectional transmission electron microscope (XTEM) imaging was used for local structural characterizations. The Ga depth distribution of the samples implanted with a standard ion implanter was measured by the use of Auger electron spectroscopy (AES) and Rutherford backscattering (RBS), and was compared with theoretical TRIDYN calculation. The magnetic properties were characterized via polar magneto-optic Kerr effect (MOKE) measurements at room temperature.

It was shown that both implantation techniques lead to a further material crystallization of the partially amorphous permalloy material (i.e. to an increase of the amount of the crystalline material), to a crystallite growth and to a material texturing towards the (111) direction. For low ion fluences a strong increase of the amount of the crystalline material was observed, while for high ion fluences this rise is much weaker. At low ion fluences XTEM images show small isolated crystallites, while for high ones the crystallites start to grow through the entire film. The EXAFS analysis shows that both Ni and Ga atom surroundings have a perfect near-order coordination corresponding to an fcc symmetry. The lattice parameter for both implantation techniques increases with increasing ion fluence according to the same linear law. The lattice parameters obtained from the EXAFS measurements for both implantation types are in a good agreement with the results obtained from the XRD measurements. Grazing incidence XRD (GIXRD) measurements of the samples implanted with a standard ion implanter show an increasing value of microstrain with increasing ion fluence (i.e. the lattice parameter variation is increasing with fluence). Both types of implantation result in an increase of the surface and the interface roughness and demonstrate a decrease of the saturation polarization with increasing ion fluence.

From the obtained results it follows that FIB and standard ion implantation influence structure and magnetic properties in a similar way: both lead to a material crystallization, crystallite growth, texturing and decrease of the saturation polarization with increasing ion fluence. A further crystallization of the highly defective nano-crystalline material can be simply understood as a result of exchange processes induced by the energy transferred to the system during the ion implantation. The decrease of the saturation polarization of the implanted samples is mainly attributed to the simple presence of the Ga atoms on the lattice sites of the permalloy film itself.

For the annealed samples more complex results were found. The corresponding results can be separated into two temperature regimes: into low (<400 C) and high (>400 C) temperatures. Similar to the implanted samples, annealing results in a material crystallization with large crystallites growing through the entire film and in a material texturing towards the (111) direction. The EXAFS analysis shows a perfect near-order coordination corresponding to an fcc symmetry. The lattice parameter of the annealed samples slightly decreases at low annealing temperatures, reaches its minimum at about ~400 C and slightly rises at higher ones. From the GIXRD measurements it can be observed that the permalloy material at temperatures above >400 C reaches it's strain-free state. On the other hand, the film roughness increases with increasing annealing temperature and a de-wetting of the film is observed at high annealing temperatures. Regardless of the material crystallization and texturing, the samples annealed at low temperatures demonstrate no change in saturation polarization, while at high temperatures a rise by approximately ~15% at 800 C was observed. The rise of the saturation polarization at high annealing temperatures is attributed to the de-wetting effect.
Keywords: permalloy, focused ion beam, broad beam ion implantation, annealing, magneto-optic Kerr effect, extended X-ray absorption fine structure, X-ray diffraction
  • Doctoral thesis
    TU Dresden, 2013
    130 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19903
Publ.-Id: 19903


The novel HDAC inhibitor NDACI054 sensitizes human cancer cells to radiotherapy.
Hehlgans, S.; Storch, K.; Lange, I.; Cordes, N.;
BACKGROUND AND PURPOSE:

Inhibition of histone deacetylases (HDACs) has preclinically and clinically shown promise to overcome radio- and chemoresistance of tumor cells. NDACI054 is a novel HDAC inhibitor, which has been evaluated here for its effects on cell survival and radiosensitization of human tumor cell lines from different origins cultured under more physiological three-dimensional (3D), extracellular matrix (ECM)-based conditions.

MATERIAL AND METHODS:
A549 lung, DLD-1 colorectal, MiaPaCa2 pancreatic and UT-SCC15 head and neck squamous cell carcinoma cells were treated with increasing NDACI054 concentrations (0-50 nM, 24 h) either alone or in combination with X-rays (single dose, 0-6 Gy). Subsequently, 3D clonogenic cell survival, HDAC activity, histone H3 acetylation, apoptosis, residual DNA damage (γH2AX/p53BP1 foci assay 24h post irradiation) and phosphorylation kinetics of Ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), Caspase-3 and Poly(ADP-ribose)-Polymerase 1 (PARP 1) cleavage were analyzed.

RESULTS:
NDACI054 potently decreased HDAC activity with concomitant increase in acetyl-histone H3 levels, mediated significant cytotoxicity and radiosensitization. These effects were accompanied by a significant increase of residual γH2AX/p53BP1-positive foci, slightly elevated levels of Caspase-3 and PARP 1 cleavage but no induction of apoptosis.

CONCLUSIONS:
Our data show potent antisurvival and radiosensitizing effects of the novel HDAC inhibitor NDACI054 encouraging further preclinical examinations on this compound for future clinical use.
Keywords: 3D cell culture, Cancer cell lines, DNA repair, HDAC inhibitor, Ionizing radiation

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Permalink: https://www.hzdr.de/publications/Publ-19902
Publ.-Id: 19902


Contactelss Inductive Flow Tomography
Wondrak, T.; Timmel, K.; Klotsche, K.; Gerbeth, G.; Stefani, F.;
The Contactless Inductive Flow Tomography (CIFT) allows for determining flow structures in conducting liquids which are exposed to one or more external magnetic fields. Measuring the induced fields around the fluid volume for each of the applied fields, it is possible to infer the velocity field by solving an inverse problem with appropriate regularization techniques. We will give an overview of the CIFT method and present the measurement system for the model of a continuous caster at the HZDR. We will conclude with new developments towards a robust measurement of the very small induced magnetic fields.
  • Lecture (Conference)
    The International Symposium on Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry, 25.-27.03.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19901
Publ.-Id: 19901


Nonvolatile resistive switching in multiferroic YMnO3 thin films
Bogusz, A.; Skorupa, I.; Blaschke, D.; Schmidt, O. G.; Schmidt, H.;
Intensive research on multiferroic materials [1] is driven by the possibility of creating novel, miniaturized tunable multifunctional devices [2]. This work investigates resistive switching behavior of YMnO3 thin films, which can be utilized in new generation memory devices. Series of YMnO3 films were grown by pulsed laser deposition on Si substrates with Pt bottom electrode at temperatures varying between 500∘C and 850∘C. Characterization of as-grown samples by X-ray diffraction and scanning electron microscopy was followed by determination of electrical properties of films in metal-insulator-metal (MIM) configuration. Results showed that the YMnO3 films grown at 800∘C exhibit the best resistive switching properties with high resistance ratio (>10000) of high over low resistance state. Switching mechanism is ascribed to the structural transitions within the film upon applied current.
[1] A. Bogusz et al., Defect Diffus. Forum 323-325, 115 (2012)
[2] Y. Shuai, H. Schmidt et al., J. Appl. Phys. 109, 124117 (2011); J. Appl. Phys. 111, 07D906 (2012)
  • Lecture (Conference)
    DPG Spring Meeting, 10.-15.03.2013, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-19900
Publ.-Id: 19900


Current-induced magnetization dynamics in a spin-valve comprising two spin-transfer torque-coupled ferromagnetic layers
Sluka, V.; Fowley, C.; Bernert, K.; Gan, H.; Fassbender, J.ORC; Deac, A. M.
Typical all-metallic spin-torque oscillators are nanopillars comprising two easy-plane ferromagnetic elements separated by a nonmagnetic metal spacer. One of the layer magnetizations is fixed and serves as the polarizer for the current while the second layer is susceptible to spin-transfer torque. Subjected to d.c. currents and external magnetic fields, these devices exhibit wellknown types of magnetization dynamics such as small-/ large-angle or clamshell precession, generating microwave signals at several Gigahertz [1]. Here, we investigate a system that differs from the above in two ways. First, our nanopillar combines an uniaxial in-plane anisotropy-ferromagnet (FM1) with a second layer (FM2) exhibiting a perpendicular anisotropy (PMA). Thus our system resembles the one studied in [2], however, in our case none of the layers is fixed, meaning that both layer magnetizations are coupled by the current and can move freely under the action of the spin-torque. Using the generalization of Slonczewski’s model [3] to asymmetric spin-valves [4,5], the d.c. current-induced magnetization dynamics in perpendicular applied field is studied numerically within the framework of the macrospin model. The resulting current-field phase diagram displays regimes of single and combined layer motion. Within fields below the effective PMA and currents smaller than -2 mA or larger than 4 mA (for the parameters chosen), the magnetization of FM1 basically precesses in-plane for the external field exceeding a threshold value. The latter increases with the current magnitude for both current polarities, climbing up to ±176 mT at +25 mA. The simultaneous excitation of FM1 and FM2 however exhibits a more asymmetric current dependence (Fig. 1). Within the simultaneously excited regime, the complexity of the trajectories is found to vary strongly with applied currents and fields. Fig. 2 shows example spectra taken at the locations indicated in Fig. 1. Viewed from a commoving frame, some trajectories correspond to largeangle precession, while others behave entirely differently from what is found in common fixed-free layer spin-valves. This is reflected in the obtained power spectra which range from near-harmonic to broad noise-like.

[1] S. I. Kiselev et al., Nature 425, 380 (2003).
[2] W. H. Rippard et al., Phys. Rev. B 81, 014426 (2010).
[3] J. C. Slonczewski, J. Magn. Magn. Mater. 247, 324 (2002).
[4] J. Xiao et al., Phys. Rev. B 70, 172405 (2004).
[5] J. Xiao et al., Phys. Rev. B 72, 014446 (2005).
Keywords: spin-transfer torque, magnetization dynamics, spin-valve, spin-torque oscillator
  • Poster
    12th Joint MMM/Intermag Conference, 14.-18.01.2013, Chicago, Illinois, USA

Permalink: https://www.hzdr.de/publications/Publ-19899
Publ.-Id: 19899


Measurement techniques for liquid metal flows
Wondrak, T.;
The measurement of flow properties in liquid metals is usually hampered by the high temperature and the opaqueness of liquid melts.
In this lecture we will give an overview of the available measurement techniques including potential probes, ultrasound Doppler velocimetry, x-ray radioscopy, phase shift flow meters, Lorentz force velocimetry and contactless inductive flow tomography.
Keywords: liquid metal, flow measurement
  • Invited lecture (Conferences)
    549. WE-Heraeus-Seminar on Liquid Metal MHD, 15.-18.10.2013, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19898
Publ.-Id: 19898


Contactless inductive flow tomography and mutual inductance tomography for a model of continuous casting
Wondrak, T.; Timmel, K.; Gundrum, T.; Stefani, F.; Eckert, S.; Gerbeth, G.; Peyton, A. J.; Yin, W.; Terzija, N.;
We present the results of simultaneous measurements of the flow field in a slab casting mould by the Contactless Inductive Flow Tomography (CIFT) and of the gas/liquid distribution in one cross section of the submerged entry nozzle (SEN) by the Mutual Inductance Tomography (MIT) for a physical model consisting of a mould with the cross section of 140 x 35 mm^2. Additionally, we present a new measuring system for CIFT using pickup coils and the first measurement of the flow field in a mould with the cross section of 400 x 100 mm^2.
Keywords: continuous casting, flow measurement, contactless inductive flow tomography, liquid metal, mutual inductance tomography
  • Open Access Logo Contribution to proceedings
    7th World Congress on Industrial Process Tomography - WCIPT7, 02.-05.09.2013, Krakow, Poland
    Procedia Engineering, 650-659
  • Lecture (Conference)
    7th World Congress on Industrial Process Tomography - WCIPT7, 02.-05.09.2013, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-19897
Publ.-Id: 19897


Interaction of electronic excitations of Tm3+ ions with acoustic vibrations in KTm(MoO4)2
Kamenskyi, D.; Poperezhai, S.; Gogoi, P.; Engelkamp, H.; Maan, J. C.; Wosnitza, J.; Kut’Ko, V.;
Electron paramagnetic resonance spectra of KTm(MoO4)2 were measured as a function of magnetic field between 3 and 11.5 cm−1 at T = 2 K. We found that in addition to the absorption line caused by the electronic excitation of Tm3+ ions, the spectra contain sidebands. Far-infrared transmission measured with polarized light from 10 to 75 cm−1 revealed vibration modes at 16.7 and 25.7 cm−1 for polarizations Eω ∥ a and Eω ∥ c, respectively. We show that sidebands in the spectra of paramagnetic resonance result from a parametric resonance between the electronic excitations of the Tm3+ ions and the acoustic vibrations of the crystal lattice.

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Permalink: https://www.hzdr.de/publications/Publ-19896
Publ.-Id: 19896


Visualization of the flow in the mold by contactless inductive flow tomography in the presence of a magnetic brake
Wondrak, T.; Klotsche, K.; Timmel, K.; Gundrum, T.; Stefani, F.; Eckert, S.; Gerbeth, G.;
In order to enhance the productivity and to achieve higher steel cleanliness in continuous casting the application of various magnetic fields is considered an efficient tool for controlling the flow in the mold. For instance, DC magnetic fields perpendicular to the wide faces of the mold are used to dampen the jets emerging from the submerged entry nozzle (SEN). Especially in this case, even a rough knowledge of the flow structure in the mold would be highly desirable.
The Contactless Inductive Flow Tomography (CIFT) allows reconstructing the dominating two-dimensional flow structure in a slab casting mold by applying one external magnetic field and by measuring the flow induced magnetic fields along the narrow faces of the mold.
For a physical model of a continuous caster, consisting of a mold with a cross section of 140 mm x 35 mm, we will present first measurements of the flow induced magnetic field in the presence of a magnetic brake of the ruler type. The first results demonstrate the viability of the CIFT measurement technique in such a configuration.
Keywords: continuous casting, flow measurement, contactless inductive flow tomography, liquid metal
  • Contribution to proceedings
    5th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking - STEELSIM 2013, 10.-12.09.2013, Ostrava, Czech Republic
    Proceedings of STEELSIM 2013, 978-80-260-3912-9
  • Lecture (Conference)
    5th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking - STEELSIM 2013, 10.-12.09.2013, Ostrava, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-19895
Publ.-Id: 19895


Experimental studies of dark current in a superconducting RF photo-injector
Xiang, R.; Arnold, A.; Kamps, T.; Lu, P.; Michel, P.; Murcek, P.; Vennekate, H.; Staats, G.; Teichert, J.;
A superconducting RF photo injector (SRF gun) has been put in operation successfully at the radiation source ELBE. It produces a 13 MHz, low emittance, CW beam with beam current up to 400 μA and energy of 3 MeV. During the gun operation, the field emission from the niobium cavity and the Cs2Te cathodes produces dark current. In this work, we studied the dark current of the SRF gun by using the existing diagnostics beam line. The dependency of the intensity and the energy spectrum on the cavity gradient and the cathode voltage were examined, and the emission sources were analyzed. Furthermore, the new project of installing a strip line kicker to reduce the dark current effect is presented.
Keywords: SRF gun, field emission, dark current, niobium cavity, Cs2Te cathode,energy spectrum

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Permalink: https://www.hzdr.de/publications/Publ-19894
Publ.-Id: 19894


The status of new transport chamber and the problem of cathode-puck
Xiang, R.; Murcek, P.;
We present here the status of the new cathode transport system at HZDR and also discuss the problem of the cathode-puck design
Keywords: photocathode, transport, high vacuum
  • Invited lecture (Conferences)
    Photocathode Research For High Brightness Electron Beams (PCHB)-Meeting, 05.08.2013, Mainz, Germany

Permalink: https://www.hzdr.de/publications/Publ-19893
Publ.-Id: 19893


Konstruktion der Transportkammer und der Kathodenhalterung und Manipulatoren
Xiang, R.; Murcek, P.;
In this talk we present the design of a new cathode transport system.
Keywords: cathode transport, high vacuum
  • Invited lecture (Conferences)
    PCHB kickoff meeting: Photokathoden-Treffen in Dresden-Rossendorf, 06.03.2013, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19892
Publ.-Id: 19892


Photocathode for Rossendorf SRF gun
Xiang, R.;
Rossendorf SRF gun is an electron source for high current electron beams based on superconducting RF technology and laser driven photocathode. Semiconductor Cs2Te photocathodes are the standard electron sources. Up to now eight Cs2Te photocathodes have been operated in the SRF gun. Quantum efficiency (Q.E.) of 1% and life time of months satisfy the gun operation. Besides the present Cs2Te photocathode, GaAs(Cs, O) attracts a lot of attention because of its high QE in the visible light range and the probability to produce high polarization beams. A new preparation system for GaAs is developing, and we will later examine the activation and performance of GaAs photocathodes in SRF gun.
Keywords: electron source, SRF gun, photocathode, QE, Cs2Te, GaAs
  • Lecture (Conference)
    1st Topical Workshop on Laser Based Particle Sources, 20.-22.02.2013, CERN, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-19891
Publ.-Id: 19891


GaAs photocathodes for the high-current SRF gun at Rossendorf
Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.; Kamps, T.; Barday, R.;
The Rossendorf SRF gun has been successfully put into operation at the ELBE accelerator facility with average current up to 250 μA. In order to achieve higher current and better beam quality, new updates are going on. One of the recent activities is to develop a new GaAs(Cs,O) photocathode preparation and transportation system. In this presentation we will show the status of GaAs cathode preparation, and also the XHV transfer vessel which allows for the efficient cathode transport from the preparation chamber into the SRF gun or to the analysis devices.
Keywords: SRF gun, high current, GaAs, photocathode, cathode transport
  • Poster
    The 4th International Particle Accelerator Conference (IPAC13), 12.-17.05.2013, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-19890
Publ.-Id: 19890


Transmission Electron Microscopy @ HZDR
Hübner, R.;
  • Lecture (others)
    Kolloquium des Helmholtz-Instituts Freiberg für Ressourcentechnologie, 04.03.2013, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19889
Publ.-Id: 19889


Scintillator-based detectors for laser-accelerated protons – A survey of developments within the Dresden laser acceleration program
Kroll, F.; Cowan, T. E.; Karsch, L.; Kraft, S. D.; Metzkes, J.; Pawelke, J.; Schramm, U.; Zeil, K.;
Proton beams by their well-confined energy-loss in matter are a promising tool for the improvement of radiotherapy of cancer and are currently under intense medical investigation. Wider clinical use, however, is limited by the complexity and expense of current proton and ion accelerators. Compact laser driven proton therapy accelerators are discussed as a promising alternative, yet require substantial development in reliable beam generation, transport and monitoring.

Therefore, in parallel to the development of laser driven proton therapy accelerators at Helmholtz-Zentrum Dresden-Rossendorf, advancement in instrumentation for laser driven protons is essential. Most importantly, these new diagnostic tools need to speedwise match the repetition rates of state-of-the-art high power laser systems and need to be adapted to the harsh plasma environment of laser based accelerators, not neglecting their fitment to the properties of laser accelerated proton pulses such as the high flux and the broad energy spectrum.

We will present three types of scintillator-based detectors, all being optimized for specific stages of the experimental chain: a one-dimensional space- and energy-resolved detector for online spectral stability control of the acceleration performance [1], a two-dimensional space- and energy-resolved detector for source characterization measurements, and a three-dimensional detector for precise dose verification in a water-equivalent medium with regards to medical quality assurance [2].

[1] J. Metzkes, et al.: A scintillator-based online detector for the angularly resolved measurement of laser-accelerated proton spectra, Review of Scientific Instruments
[2] F. Kroll, et al.: Preliminary investigations on the determination of three-dimensional dose distributions using scintillator blocks and optical tomography
Keywords: scintillator, detector, dosimeter
  • Lecture (others)
    Annual Meeting of the LIGHT collaboration, 29.05.2013, GSI Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19888
Publ.-Id: 19888


Shaping laser accelerated ions for future applications – The LIGHT collaboration
Busold, S.; Almomani, A.; Bagnoud, V.; Barth, W.; Bedacht, S.; Blažević, A.; Boine-Frankenheim, O.; Brabetz, C.; Burris-Mog, T.; Cowan, T. E.; Deppert, O.; Droba, M.; Eickhoff, H.; Eisenbarth, U.; Harres, K.; Hoffmeister, G.; Hofmann, I.; Jaeckel, O.; Jaeger, R.; Joost, M.; Kraft, S.; Kroll, F.; Kaluza, M.; Kester, O.; Lecz, Z.; Merz, T.; Nürnberg, F.; Al-Omari, H.; Orzhekhovskaya, A.; Paulus, G.; Polz, J.; Ratzinger, U.; Roth, M.; Schaumann, G.; Schmidt, P.; Schramm, U.; Schreiber, G.; Schumacher, D.; Stoehlker, T.; Tauschwitz, A.; Vinzenz, W.; Wagner, F.; Yaramyshev, S.; Zielbauer, B.;
The generation of intense ion beams from high-intensity laser-generated plasmas has been the focus of research for the last decade. In the LIGHT collaboration the expertise of heavy ion accelerator scientists and laser and plasma physicists has been combined to investigate the prospect of merging these ion beams with conventional accelerator technology and exploring the possibilities of future applications. We report about the goals and first results of the LIGHT collaboration to generate, handle and transport laser driven ion beams. This effort constitutes an important step in research for next generation accelerator technologies.
Keywords: Laser, Proton, Ion, Acceleration

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Permalink: https://www.hzdr.de/publications/Publ-19887
Publ.-Id: 19887


The world’s first superconducting RF photo injector operated at a LINAC
Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.;
The success of future synchrotron light sources mainly depends on the development of an appropriate electron source. At the moment, the superconducting radio frequency (RF) photo injectors (SRF guns) seem to be the most promising candidate to achieve the required peak brightness and the high average current at the same time. This contribution summarizes the working principle and important results of the most advanced SRF gun project in the world.
Keywords: SRF gun, superconducting RF photoinjector, ELBE, FEL
  • Poster
    Internationaler »Dresden Barkhausen Award 2012«, 08.03.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19886
Publ.-Id: 19886


Selected experiences of 6 years Rossendorf SRF Gun
Arnold, A.;
At the radiation source ELBE an SRF gun has been developed and put into operation in 2007. The gun has a 3 ½ cell niobium cavity for 1.3 GHz and uses normal-conducting photo cathodes. Since 2010 the gun has delivered beam into the ELBE linac. Recently a new driver laser with 13 MHz pulse repetition rate allows us to operate the IR free-electron lasers (FEL) with the SRF gun. The successful operation of the SRF gun confirms the general design with an elliptical cavity, superconducting RF choke filter, and normal-conducting photocathodes as well as the proper design of most of the subsystems like couplers and tuners. This contribution presents important experiences out of 6 years of operating the Rossendorf SRF gun.
Keywords: SRF gun, superconducting RF photoinjector, ELBE, Nb cavity
  • Invited lecture (Conferences)
    TESLA Technology Collaboration - 1st topical meeting on CW SRF, 12.-14.06.2013, Ithaca, NY, USA

Permalink: https://www.hzdr.de/publications/Publ-19885
Publ.-Id: 19885


Coupling Schemes and Measurements for Multiple Eigenmode Application at SRF Guns
Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.;
Superconducting electron sources are a promising candidate to meet the challenges of future electron accelerator, such as high average beam current and high peak brilliance at the same time. Compared to their normal conducting rf equivalent and due to the Meissner-Ochsenfeld effect, the solenoid for emittance compensation has to be placed far in front of the cathode. To solve this problem the use of transverse electric (TE) modes in parallel to the accelerating mode was proposed*. This contribution presents two suitable coupling schemes and first rf measurements at the warm and cold HZDR SRF gun cavity.
Keywords: superconducting RF photoinjector, SRF gun, photo cathode, ELBE, TE mode, emittance compensation
  • Poster
    SRF 2013 - 16th International conference on RF Superconductivity, 23.-27.09.2013, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-19884
Publ.-Id: 19884


Status report of the enhanced ELBE SRF gun
Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Kneisel, P.; Turlington, L.; Stirbet, M.; Eremeev, G.;
Within the last years a superconducting RF photoinjector (SRF gun), equipped with all components, was successfully put into operation at the linear accelerator ELBE. Although world’s first LINAC injection was demonstrated and first user experiments were carried out, higher average current and better beam emittances are required. To fulfil this needs a second and significantly enhanced SRF gun is currently under construction at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The main part of this development is a modified version of our 1.3 GHz 3.5 cell cavity that was fabricated and tested in collaboration with Thomas Jefferson Lab National Accelerator Facility (TJNAF). Moreover, a lot of engineering work was done to fix the problems of our first SRF gun and to integrate a superconducting solenoid into the new cryomodule. In this contribution, we will report on technical challenges, critical assembly steps and first test results of the second version of our superconducting RF photoinjector.
Keywords: superconducting RF photoinjector, SRF gun, photo cathode, ELBE
  • Poster
    4th International Particle Accelerator Conference, IPAC13, 12.-17.05.2013, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-19883
Publ.-Id: 19883


THz based femtosecond level arrivaltime monitor for quasi-cw electron accelerators
Kovalev, S.; Green, B.; Gensch, M.;
In this contribution we present an electro-optic arrival time monitor for coherent THz pulses. The monitor operates robustly at high repetitionrates and extremely low THz pulse energies. It thereby has the potential to provide few femtosecond-level synchronization on next generation large scale X-ray photon sources based on high repetition rate electron accelerators such as X-ray FEL´s or energy recovery linacs.
  • Poster
    DPG Frühjahrstagung, 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19882
Publ.-Id: 19882


Pulsed power technology for laser-accelerated particle experiments – A survey of developments within the Dresden laser acceleration program
Kroll, F.; Cowan, T. E.; Herrmannsdörfer, T.; Masood, U.; Joost, M.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Schramm, U.; Zeil, K.; Zherlitsyn, S.;
Since the mid-1950s, pulsed (iron-free) high-field magnets have become a common, versatile research tool. Applications in solid state physics have promoted the development of sophisticated magnets that nowadays can achieve fields above 90 T repeatedly.

We report here another area of application for pulsed power magnet technology; namely the use of pulsed magnets as effective devices for particle beam optics with application in the fields of radiation and accelerator physics as well as medical physics: Pulsed power solenoids for focusing of laser-accelerated particle beams might allow for the use of these new radiation qualities in medical radiation therapy or could function as a crucial part of a compact, laser-based ion source. The development of pulsed high field multipoles could permit highly compact beam guidance systems.

The presentation gives a survey of pulsed power developments, including various pulsed high field magnets as well as pulsed power sources. The scalability to cancer therapy relevant application will be critically discussed.
Keywords: pulsed magnets, laser acceleration, laser-plasma-physic, high fields
  • Lecture (others)
    Annual Meeting of the LIGHT Collaboration, 29.05.2013, GSI Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19881
Publ.-Id: 19881


Microbial ecology: Characteristics of bacteria from heavy metal contaminated mining waste piles
Eigenschaften von Bakterien aus Schwermetall-kontaminierten Halden: Mikrobielle Ökologie

Lederer, F. L.; Günther, T. J.; Raff, J.; Flemming, K.; Pollmann, K.;
Bacterial isolates from a uranium mining waste pile are adapted in a very special kind of way to their heavy metal contaminated environment. Genome analyses identified many genes that might support the incidence of these strains in their special habitat. Using the Next Generation Sequencing Technology multiple surface (S-) layer genes and different kinds of metal transporter genes were identified. These data give the genetic affirmation that these strains are adapted substantial to their environment.
Keywords: Next Generation Sequencing

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Permalink: https://www.hzdr.de/publications/Publ-19880
Publ.-Id: 19880


Thermally Excited Ferromagnetic Resonance in MgO-based Magnetic Tunnel Junctions
Kowalska, E.; Bernert, K.; Aleksandrov, Y.; Fowley, C.; Sluka, V.; Mangin, S.; Lindner, J.; Fassbender, J.ORC; Deac, A. M.
Spin polarized currents can exert a so-called spin-transfer torque to the magnetic moment of a ferromagnetic layer. One application of this phenomenon is the spin torque nano-oscillator (typically an MgO-based magnetic tunnel junction (MTJ)) which can act as a tunable microwave emission source. However, a more detailed understanding of the spin-torque physics is needed. For example, the spin torque bias dependence of the two spin torque components (in-plane and fieldlike) is still widely discussed in the community [1]. We present results for MgO-MTJs obtained by thermally excited ferromagnetic resonance (TE-FMR). With the help of TE-FMR, the bias dependence of the two spin-transfer torques can be determined from the peak position and linewidth [2]. Microwave measurements were carried out in the frequency range of 1-9 GHz at positive and negative magnetic fields and for different dc current values. Analyzing this data, we could separate the in-plane and field-like spin torque components and determine their bias dependence.
Keywords: Spin-Transfer Torque, Magnetic Tunnel Junction, Thermally Excited Ferromagnetic Resonance
  • Poster
    The IEEE Magnetics Society Summer School, 09.-14.06.2013, Assisi, Italy

Permalink: https://www.hzdr.de/publications/Publ-19879
Publ.-Id: 19879


Trace concentration – Huge impact: Nitrate in the calcite/Eu(III) system
Hofmann, S.; Voitchovsky, K.; Schmidt, M.; Stumpf, T.;
The interactions of trivalent lanthanides and actinides with secondary mineral phases such as calcite is of high importance for the safety assessment of deep geological repositories for high level nuclear waste (HLW). Due to similar ionic radii, calcium-bearing mineral phases are suitable host minerals for Ln(III) and An(III) ions. Especially calcite has been proven to retain these metal ions effectively by both surface complexation and bulk incorporation. Since anionic ligands (e.g., nitrate) are omnipresent in the geological environment and due to their coordinating properties, their influence on retentive processes should not be underestimated. Nitrate is a common contaminant in most HLW forms as a result of using nitric acid in fuel reprocessing. It is also formed by microbial activity under aerobic conditions. In this study, atomic force microscopy investigations revealed a major influence of nitrate upon the surface of calcite crystals. NaNO3 causes serious modifications even in trace amounts (<10-7 M) and forms a soft surface layer of low crystallinity on top of the calcite crystal. Time-resolved laser fluorescence spectroscopy of Eu(III) showed that, within this layer, Eu(III) ions are incorporated, while losing most of their hydration shell. The results show that solid solution modelling for actinides in calcite must take into account the presence of nitrate in pore and ground waters.
Keywords: DISSOLVED ORGANIC-MATTER; LUMINESCENCE SPECTROSCOPY; PORE-WATER; CALCITE; CLAY; TIME; CHEMISTRY; DISSOLUTION; TRANSITION; ADSORPTION

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Permalink: https://www.hzdr.de/publications/Publ-19878
Publ.-Id: 19878


First direct measurement of the 2H(α,γ)6Li cross section at Big Bang energies and the primordial lithium problem
Anders, M.; Trezzi, D.; Menegazzo, R.; Aliotta, M.; Bellini, A.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Davinson, T.; Elekes, Z.; Erhard, M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Junker, M.; Lemut, A.; Marta, M.; Mazzocchi, C.; Prati, P.; Rossi Alvarez, C.; Scott, D. A.; Somorjai, E.; Straniero, O.; Szücs, T.;
Recent observations of 6Li in metal poor stars suggest a large production of this isotope during Big Bang Nucleosynthesis (BBN). In standard BBN calculations, the 2H(α,γ)6Li reaction dominates 6Li production. Unfortunately, this reaction has never been directly measured inside the BBN energy region because its cross section drops exponentially at low energy. Indirect measurements using the Coulomb dissociation of 6Li only give upper limits owing to the dominance of nuclear breakup processes. Here, we report on the results of the first measurement of the 2H(α,γ)6Li cross section directly at Big Bang energies. The experiment was performed deep underground at the LUNA 400kV accelerator in Gran Sasso, Italy. The 6Li/7Li isotopic abundance ratio from standard BBN has been determined to be (1.5±0.3)×10−5, entirely from experimental data. The much higher 6Li/7Li values reported for halo stars will likely require a non-standard physics explanation.
Keywords: Underground nuclear astrophysics Big Bang nucleosynthesis LUNA

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Permalink: https://www.hzdr.de/publications/Publ-19877
Publ.-Id: 19877


Underground nuclear astrophysics for the Sun, and for the Big Bang
Bemmerer, D.;
After the resolution of the solar neutrino problem in 2002, the study of the Sun has now entered a precision era, and an entirely new dilemma has come up: New elemental abundance data from Fraunhofer line analyses are in contradiction with helioseismological observables. Observations of 13N and 15O neutrinos from the Sun may address this so-called solar abundance problem, but their interpretation will require precise nuclear reaction data. Due to the low cross sections involved, such data can only be provided by experiments in an underground low-background setting. Work at the world's only underground accelerator, the 0.4 MV LUNA machine in Gran Sasso (Italy), on solar fusion reactions and on the Big Bang production of lithium-6 and -7 will be reviewed. Higher-energy underground accelerators are planned in Italy and also at the Dresden Felsenkeller in Germany.
Keywords: Underground nuclear astrophysics Hydrogen burning Big Bang nucleosynthesis LUNA Felsenkeller
  • Invited lecture (Conferences)
    VERA-Seminar (Vienna Environmental Research Accelerator), 07.11.2013, Wien, Österreich
  • Invited lecture (Conferences)
    Seminar Institute of Theoretical Physics, 04.04.2014, Wroclaw, Polen

Permalink: https://www.hzdr.de/publications/Publ-19876
Publ.-Id: 19876


Underground nuclear astrophysics
Bemmerer, D.;
I give a brief review of the progress of underground nuclear astrophysics work within EuroGENESIS.
Keywords: Underground nuclear astrophysics LUNA Felsenkeller Hydrogen burning alpha-rich freezeout
  • Lecture (Conference)
    MASCHE annual meeting (Massive Stars as Agents of Chemical Evolution, part of EuroGENESIS), 03.12.2013, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19875
Publ.-Id: 19875


Underground experimental nuclear astrophysics in Germany
Bemmerer, D.;
I review the status of underground nuclear astrophysics work in Germany.
Keywords: Experimental nuclear astrophysics Underground accelerators Felsenkeller LUNA
  • Invited lecture (Conferences)
    Nukleare Astrophysik in Deutschland: Status und Perspektiven, 04.12.2013, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19874
Publ.-Id: 19874


Underground nuclear astrophysics at the Dresden Felsenkeller: status report
Bemmerer, D.;
The status of nuclear astrophysics related work at the Dresden Felsenkeller is reviewed.
Keywords: experimental nuclear astrophysics hydrogen burning alpha-rich freezeout supernova nucleosynthesis Felsenkeller LUNA
  • Invited lecture (Conferences)
    Nuclear Astrophysics Virtual Institute (NAVI) annual meeting, 16.-17.12.2013, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19873
Publ.-Id: 19873


The multiferroic properties of polycrystalline Bi1-xYxFeO3 films
Sheng, Y.; Rui, W.; Qiu, X.; Du, J.; Zhou, S.; Xu, Q.;
Polycrystalline Bi1−xYxFeO3 films with varying x from 0 to 0.30 were prepared by pulsed laser deposition (PLD) on surface oxidized Si (100) substrates with LaNiO3 as buffer layer. The influence of Y doping on the structure, ferroelectric properties and exchange bias have been systematically investigated. X-ray diffraction and Raman spectroscopy studies revealed the structural transition from rhombohedral R3c to orthorhombic Pn21a with increasing x above 0.10. The leakage current density of BiFeO3 has been effectively suppressed by Y doping, and well saturated P-E loops have been observed in Bi1-xYxFeO3 (0.01≤x≤0.07). Exchange bias field with a 3.6 nm thick NiFe layer increases with increasing x to 0.01, then decreases with further increasing x.
Keywords: multiferroics, BiFeO3, exchange bias, ferroelectricity

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Permalink: https://www.hzdr.de/publications/Publ-19872
Publ.-Id: 19872


Carbon based functional coatings for tribological applications
Krause, M.; Abrasonis, G.; Gemming, S.; Faßbender, J.ORC; Makowski, S.; Weihnacht, V.; Leson, A.; Kunze, T.; Posselt, M.; Joswig, J.-O.; Seifert, G.; Götze, A.; Hübner, M.; Zellbeck, H.
The automotive industry is an essential branch for the industrial site Saxony. Within the past 20 years high-tech production centers have been built by the leading German car producers Volkswagen, BMW, and Porsche in Zwickau, Dresden, Chemnitz and Leipzig. According to estimations about 10 % of the jobs in Saxony subjected to social insurance are settled in the car related industry. This industrial sector on the one hand faces strong competitors from Asia and the USA, and on the other hand is challenged by the CO2 emission goals of the European Union for the next decade. These complex circumstances have to be dealt with innovative concepts in general and new approaches in research and development (R & D) in particular. The subproject ECEMP D1 is developing new, nanostructured, wear-resistant tribological coatings for the automotive engineering. These coatings provide a significant reduction of the friction in wear loaded car components and enable the more efficient use of fuel and materials.
Keywords: Energy efficiency, atomistic tribological simulations, nanocomposites, t-aC, engine test bench experiments
  • Contribution to proceedings
    International ECEMP Colloquium 2013, 24.-25.10.2013, Dresden, Deutschland
    Ressourcenschonende Werkstoffe - Technologien - Prozesse: Verlag Wissenschaftliche Scripten, 978-3-95735-006-0, 423-426

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Permalink: https://www.hzdr.de/publications/Publ-19871
Publ.-Id: 19871


Spatio-temporal features of oil-air interface for stratified-wavy two phase flow in horizontal pipes with a 6-inch diameter
Aydin, T. B.; Schleicher, E.; Karami, H.; Torres, C.; Pereyra, E.; Sarica, C.;
Interfacial wave characteristics have been studied experimentally in stratified-wavy configuration for oil-air two-phase flow at Tulsa University Fluid Flow Projects (TUFFP) 6-inch low pressure flow loop. Flow rates of each test fluid are adjusted such that the superficial liquid and gas velocities vary between 0.01m/s ≤ υSL ≤ 0.02m/s and 10m/s ≤ υSG ≤ 16m/s, respectively, in horizontal pipe configuration.
During the course of the investigation, the cross-sectional distributions of void fraction are synchronously obtained at two different streamwise locations of the pipe by using two wire mesh sensors, each with a 32 x 32 grid resolution. The spatial distribution of the phases, obtained by analyzing the measured void fractions, reveal several instantaneous quantities of the flow configuration at each cross-section such as interface geometry, liquid holdup, wetted pipe area and liquid height. The sequential acquisition of the void fractions reveal the temporal evolution of these quantities within the planes of measurement. In addition, the cross-correlation of the data from both of the wire mesh sensors enable the characterization of important surface wave parameters such as wave celerity, and structural frequency.
The instantaneous information on the liquid holdup, wetted pipe area and liquid height are the advantages of the current experimental technique over conventional methods employing quick closing valves, and high-speed flow visualization. In order to understand the effect of sensor grid resolution on these quantities, the results have also been re-arranged using coarser mesh configurations by analyzing the same data also on 24 x 24, and 16 x 16 grid sizes. Furthermore, the analysis on the grid size is enriched by the comparison with the results obtained by using other methods for similar flow conditions in other experiments.
The wave celerity is observed to increase with superficial liquid and gas velocities, which is in good agreement with the previous studies. Spectral analyses performed on each element of the data matrix reveal the distribution of the dominant wave numbers within the pipe cross-section. In addition, a unique void fraction reconstruction technique is employed to quantitatively visualize the phase distributions passing through the wire mesh sensor in a three-dimensional fashion. This type of visualization is shown to be effective on the identification of the important wave structures and their spatial distributions within the pipe cross-section. This is a strong advantage over the window crossing method, due to the accuracy in spectral analysis, and over the capacitance sensors due to the global cross-sectional information.
Keywords: two-phase flow, liquid holdup, liquid gas Interface, wire-mesh sensors
  • Contribution to proceedings
    9th North American Conference on Multiphase Technology, 11.-13.06.2014, Banff, Canada
    Proceedings of 9th North American Conference on Multiphase Technology

Permalink: https://www.hzdr.de/publications/Publ-19870
Publ.-Id: 19870


GTV differentially impacts locoregional control of non-small cell lung cancer (NSCLC) after different fractionation schedules: Subgroup analysis of the prospective randomized CHARTWEL trial
Soliman, M.; Yaromina, A.; Appold, S.; Zips, D.; Reiffenstuhl, C.; Schreiber, A.; Thames, H.; Krause, M.; Baumann, M.;
Purpose: To evaluate the impact of fractionation schedule on the size of the gross tumour volume (GTV) effect on tumour control after radiotherapy of NSCLC.
Material and methods: A subgroup analysis on 163 patients treated in a randomized phase III trial of CHARTWEL (continuous hyperfractionated accelerated radiotherapy-weekend less) vs conventional radiotherapy was performed. The influence of GTV and other baseline factors on local failure (LF), disease-free survival (DFS), distant metastases (DM), and overall survival (OS) was estimated using the Cox Proportional Hazards model.
Results: Superior local control was achieved by CHARTWEL compared to conventional radiotherapy (HR 0.54, p = 0.015). The hazard of LF increased with increasing GTV for both conventional fractionation and CHARTWEL, however the increase for the latter was less pronounced and not significant.
Conclusion: Highly accelerated CHARTWEL treatment was significantly more effective than conventional radiotherapy for locoregional control of NSCLC. GTV had a significant effect on locoregional control after conventional fractionation, an effect that was not significant with CHARTWEL. This is the first study to demonstrate that the magnitude of the time factor of fractionated radiotherapy increases with tumour volume. (C) 2012 Elsevier Ireland Ltd. All rights reserved.
Keywords: Gross tumour volume; Non-small-cell lung cancer; CHARTWEL; Accelerated radiotherapy; Randomized trial KeyWords Plus: GROSS TUMOR VOLUME; ACCELERATED RADIOTHERAPY CHART; RADIATION-THERAPY; LOCAL-CONTROL; CONVENTIONAL RADIOTHERAPY; CARCINOMA XENOGRAFTS; MULTICENTER TRIAL; PROGNOSTIC-FACTOR; TREATMENT TIME; NUDE-MICE

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Permalink: https://www.hzdr.de/publications/Publ-19869
Publ.-Id: 19869


Time in radiation oncology - Keep it short!
Buetof, R.; Baumann, M.;
there is no abstract
Keywords: CELL LUNG-CANCER; CONVENTIONALLY FRACTIONATED RADIOTHERAPY; RANDOMIZED MULTICENTER TRIAL; LOCALLY ADVANCED HEAD; NECK-CANCER; ACCELERATED RADIOTHERAPY; PROSTATE-CANCER; NUDE-MICE; PHASE-III; DIAGNOSTIC DELAY

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Permalink: https://www.hzdr.de/publications/Publ-19868
Publ.-Id: 19868


Towards clinical evidence in particle therapy: ENLIGHT, PARTNER, ULICE and beyond
Combs, S.; Djosanjh, M.; Poetter, R.; Orrechia, R.; Haberer, T.; Durante, M.; Fossati, P.; Parodi, K.; Balosso, J.; Amaldi, U.; Baumann, M.; Debus, J.;
there is no abstract
Keywords: CARBON-ION RADIOTHERAPY; CALIFORNIA-ONCOLOGY-GROUP; CONFORMAL RADIATION-THERAPY; I-II TRIAL; SKULL BASE; RANDOMIZED-TRIAL; PHASE-I; CHARGED-PARTICLES; PROSTATE-CANCER; PROTON THERAPY

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Permalink: https://www.hzdr.de/publications/Publ-19867
Publ.-Id: 19867


Algorithm to Measure Three-Dimensional Velocity of Individual Bubble Acquired with Wire-Mesh Sensors
Furuya, M.; Kanai, T.; Arai, T.; Shirakawa, K.; Schleicher, E.;
A two-phase flow often exhibits a complicated three-dimensional structure by nature even in a simple vertical pipe. In order to model such a complicated flow structure and to validate multiphase flow CFD, experimental database for three dimensional velocity and void fraction distributions are crucial. The paper addresses an algorithm to measure three-dimensional velocity of individual bubble with a bubble paring scheme. The bubble paring scheme finds a pair of bubble in two sets of wire-mesh sensor data to determine the direction and magnitude of velocity vector for each bubble. The devised scheme was applied to the vertical upward air-water flow (jG=0.64m/s, jL=0.64m/s) in a large diameter pipe (i.d. 224mm). The bubble pairing scheme visualized the developing process of two-phase flow: large bubbles coalesced with each other to move toward the center, while the rest of bubbles broke up into smaller bubbles and decelerated.
Keywords: bubbly flow, bubble identification, bubble tracking velocimetry, void fraction, bubble size, wire-mesh sensor
  • Contribution to proceedings
    The 16th International Symposium on Flow Visualization (ISFV16), 24.-28.06.2014, Okinawa, Japan
    Proceedings of the 16th International Symposium on Flow Visualization

Permalink: https://www.hzdr.de/publications/Publ-19866
Publ.-Id: 19866


Untersuchung der Supernovareaktion 40Ca(α,γ)40Ti durch Aktivierung an der PTB und γ-Zählung im Felsenkeller Dresden
Schmidt, K.; Akhmadaliev, S.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Dietz, M.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Marta, M.; Menzel, M.-L.; Schwengner, R.; Szücs, T.; Wagner, A.; Wagner, L.; Yakorev, D.; Zuber, K.;
Modelle einer Kernkollaps-Supernova sagen vorher, dass 44Ti (Halbwertszeit = 58,9 a) produziert wird. Dementsprechend werden mehrere 44Ti-Gammastrahlungsquellen in unserer Galaxie erwartet. Jedoch konnte 44Ti bisher nur in den Supernovaüberresten Cassiopeia A und SN 1987A nachgewiesen werden. 40Ca(α,γ)44Ti ist die wichtigste Reaktion, die 44Ti erzeugt. Ihre Reaktionsrate wird durch mehrere Resonanzen dominiert. Es ist geplant, die astrophysikalisch wichtige Resonanz bei 2758 keV am 3,7 MV Van-de-Graaff-Beschleuniger der Physikalisch-Technischen Bundesanstalt zu aktivieren und anschließend die Resonanzstärke durch eine Aktivierungsmessung im Niederniveaumesslabor Felsenkeller zu bestimmen.
Keywords: core-collapse supernova, calcium-40, titanium-44, PTB, resonance strength, ultra-low-background facility Felsenkeller Dresden
  • Lecture (others)
    Vortrag an der Physikalisch-Technische Bundesanstalt Braunschweig, 27.11.2013, Braunschweig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19865
Publ.-Id: 19865


Strength of the Ep = 1.842 MeV resonance in the 40Ca(p,γ)41Sc reaction reexamined
Schmidt, K.; Akhmadaliev, S.; Anders, M.; Bemmerer, D.; Caciolli, A.; Dietz, M.; Elekes, Z.; Junghans, A. R.; Menzel, M.-L.; Schwengner, R.; Wagner, A.; Zuber, K.;
The strength of the Ep = 1.842 MeV resonance in the 40Ca(p,γ)41Sc reaction is determined with two different methods: First, by an absolute strength measurement using calcium hydroxide targets, and second, relative to the well-determined strength of the resonance triplet at Eα = 4.5 MeV in the 40Ca(α,γ)44Ti reaction. The present new value of ωγ = (0.192 ± 0.017) eV is 37% (equivalent to 3.5 σ) higher than the evaluated literature value. In addition, the ratio of the strengths of the 1.842 MeV 40Ca(p,γ)41Sc and 4.5 MeV 40Ca(α,γ)44Ti resonances has been determined to be 0.0229 ± 0.0018. The newly corrected strength of the 1.842-MeV resonance can be used in the future as a normalization point for experiments with calcium targets.
Keywords: calcium-40, scandium-41, calcium hydroxide, titanium-44, resonance strength

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Permalink: https://www.hzdr.de/publications/Publ-19864
Publ.-Id: 19864


Underground study of the 17O(p,γ)18F reaction relevant for explosive hydrogen burning
Di Leva, A.; Scott, D. A.; Caciolli, A.; Formicola, A.; Strieder, F.; Aliotta, M.; Anders, M.; Bemmerer, D.; Broggini, C.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; José, J.; Junker, M.; Laubenstein, M.; Menegazzo, R.; Napolitani, E.; Prati, P.; Rigato, V.; Roca, V.; Somorjai, E.; Salvo, C.; Straniero, O.; Szücs, T.; Terrasi, F.; Trezzi, D.;
Background: The O17(p,γ)F18 reaction affects the production of key isotopes (e.g., F18 and O18) in the explosive hydrogen burning that powers classical novae. Under these explosive conditions, the reaction rate is dominated by contributions from a narrow resonance at Ec.m.=183keV and by the combined contributions of direct capture and low-energy tails of broad resonances. At present, the astrophysical reaction rate is not well constrained because of the lack of data in the energy region appropriate to classical novae.
Purpose: This study aims at the measurement of the O17(p,γ)F18 reaction cross section in order to determine its reaction rate in the temperature region appropriate to explosive hydrogen burning in novae.
Method: The O17(p,γ)F18 reaction cross section was measured using both the prompt detection of the emitted γ rays and an activation technique. Measurements were carried out at the Laboratory for Underground Nuclear Astrophysics (Gran Sasso, Italy) where the strongly reduced cosmic-ray-induced background allows for improved sensitivity compared to previous studies.
Results: The O17(p,γ)F18 reaction cross section was measured in the range Ec.m.=160 to 370keV. The strength of the Ec.m.=183keV resonance, ωγ=1.67±0.12μeV, was determined with unprecedented precision. The total S factor was obtained through a combined fit of prompt γ-ray and activation results. An overall global fit including other existing data sets was also carried out and a recommended astrophysical reaction rate is presented.
Conclusions: The reaction rate uncertainty attained in this work is now below the required precision for nova models. We verified, following a full set of hydrodynamic nova models, that the abundances of oxygen and fluorine isotopes obtained with the present reaction rate are determined with 10% precision and put firmer constraints on observational signatures of novae events.
Keywords: Nuclear astrophysics hydrogen burning nova nucleosynthesis underground LUNA

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Permalink: https://www.hzdr.de/publications/Publ-19863
Publ.-Id: 19863


Asymmetric Synthesis of Spirocyclic 2-Benzopyrans for Positron Emission Tomography of σ1 Receptors in the Brain
Holl, K.; Schepmann, D.; Fischer, S.; Ludwig, F. A.; Hiller, A.; Donat, C. K.; Deuther-Conrad, W.; Brust, P.; Wünsch, B.;
Sharpless asymmetric dihydroxylation of styrene derivative 6 afforded chiral triols (R)-7 and (S)-7, which were cyclized with tosyl chloride in the presence of Bu2SnO to provide 2-benzopyrans (R)-4 and (S)-4 with high regioselectivity. The additional hydroxy moiety in the 4-position was exploited for the introduction of various substituents.
Williamson ether synthesis and replacement of the Boc protective group with a benzyl moiety led to potent σ1 ligands with high σ12-selectivity. With exception of the ethoxy derivative 16, the (R)-configured enantiomers represent eutomers with eudismic ratios of up to 29 for the ester (R)-18. The methyl ether (R)-15 represents the most potent σ1 ligand of this series of compounds, with a Ki value of 1.2 nM and an eudismic ratio of 7. Tosylate (R)-21 was used as precursor for the radiosynthesis of [18F]-(R)-20, which was available by nucleophilic substitution with K[18F]F K222 carbonate complex. The radiochemical yield of [18F]-(R)-20 was 18%–20%, the radiochemical purity greater than 97% and the specific radioactivity 175–300 GBq/μmol. Although radiometabolites were detected in plasma, urine and liver samples, radiometabolites were not found in brain samples. After 30 min, the uptake of the radiotracer in the brain was 3.4% of injected dose per gram of tissue and could be reduced by coadministration of the σ1 antagonist haloperidol. [18F]-(R)-20 was able to label those regions of the brain, which were reported to have high density of σ1 receptors.
Keywords: 2-benzopyrans; Sharpless Asymmetric Dihydroxylation; spirocycles; σ affinity; radiochemistry; positron emission tomography; autoradiography; organ distribution

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Permalink: https://www.hzdr.de/publications/Publ-19862
Publ.-Id: 19862


Dose Assessment and Comparison in Mice, Piglets and Humans
Kranz, M.; Sattler, B.; Patt, M.; Fischer, S.; Hiller, A.; Donat, C. K.; Deuther-Conrad, W.; Hoepping, A.; Sattler, T.; Wünsch, B.; Steinbach, J.; Sabri, O.; Brust, P.;
  • Lecture (others)
    3. Dresdner Workshop "Molekulare Bildgebung in den Lebenswissenschaften", 05.06.2013, Rossendorf, Deutschland
  • Invited lecture (Conferences)
    Weiterbildungsveranstaltung für Ärzte am Universitätsklinikum Carl Gustav Carus der Technischen Universität Dresden, 28.01.2014, Dresden, Deutschland
  • Lecture (others)
    Doktoranden-Kolloquium des BBZ, 03.12.2014, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19861
Publ.-Id: 19861


Microorganisms in potential host rocks for geological disposal of nuclear waste and their interactions with uranium
Cherkouk, A.; Lütke, L.; Moll, H.; Bachvarova, V.; Selenska-Pobell, S.; Bernhard, G.;
The long-term safety of nuclear waste in a deep geological repository is an important issue in our society. For the safety assessment of such a repository it is necessary to know what microorganisms are present in the potential host rocks (e.g. clay, salt) and how these microorganisms can influence the performance of a repository to potentially reduce their activity.
In this study, the analysis of bacterial diversity in a sample from the Mont Terri Opalinus clay demonstrated the predominance of representatives of Firmicutes, Betaproteobacteria, and Bacteriodetes. Alpha-, Beta- and Gammaproteobacteria were detected in the porewater samples from the Mont Terri rock laboratory, whereas Gammaproteobacteria especially Pseudomonas sp. dominated the bacterial community.
Among other isolates, a Paenibacillus sp., as a representative of Firmicutes, was isolated from the clay under anaerobic conditions. Accumulation experiments and potentiometric titrations showed a strong interaction of Paenibacillus sp. cells with U(VI) within a broad pH range (3-7) [1].
Additionally, we will present a study on the interactions of the halophilic archaea Halobacterium noricense DSM 15987, an salt rock representative reference strain, with U(VI) at high ionic strength. These results contribute to the safety assessment of a prospective nuclear waste repository.
  • Poster
    IGD-TP Geodisposal 2014, 24.-26.06.2014, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-19860
Publ.-Id: 19860


Efficient laser-driven proton acceleration in the ultra short pulse regime
Zeil, K.;
The work described in this thesis is concerned with the experimental investigation of the acceleration of high energy proton pulses generated by relativistic laser-plasma interaction and their application. Using the high intensity 150TW Ti:sapphire based ultra-short pulse laser Draco, a laser-driven proton source was set up and characterized. Conducting experiments on the basis of the established target-normal sheath acceleration (TNSA) process, proton energies of up to 20MeV were obtained. The reliable performance of the proton source was demonstrated in the first direct and dose controlled comparison of the radiobiological effectiveness of intense proton pulses with that of conventionally generated continuous proton beams for the irradiation of in vitro tumour cells. As potential application radiation therapy calls for proton energies exceeding 200MeV. Therefore the scaling of the maximum proton energy with laser power was investigated and observed to be near-linear for the case of ultra-short laser pulses. This result is attributed to the efficient predominantly quasi-static acceleration in the short acceleration period close to the target rear surface. This assumption is furthermore confirmed by the observation of prominent non-target-normal emission of energetic protons reflecting an asymmetry in the field distribution of promptly accelerated electrons generated by using oblique laser incidence or angularly chirped laser pulses. Supported by numerical simulations, this novel diagnostic reveals the relevance of the initial prethermal phase of the acceleration process preceding the thermal plasma heath expansion of TNSA. During the plasma expansion phase, the efficiency of the proton acceleration can be improved using so called reduced mass targets (RMT). By confining the lateral target size which avoids the dilution of the expanding sheath and thus increases the strength of the accelerating sheath fields a significant increase of the proton energy and the proton yield was observed.
  • Doctoral thesis
    TU Dresden, 2013
    127 Seiten

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Publ.-Id: 19859


Pu interaction studies with a typical bacterial isolate from Mont Terri Opalinus clay
Moll, H.; Lütke, L.; Cherkouk, A.; Bernhard, G.;
Nuclear waste is supposed to be stored in deep geological formations. An example is the Opalinus clay formation located in the North-Western part of Switzerland (Mont Terri URL) which is currently studied in terms of its suitability as host rock for future nuclear waste storage. In this talk, results will be presented and discussed describing the interactions of a specific novel Sporomusa sp. isolate with plutonium. Results from accumulation experiments as well as detailed plutonium oxidation state changes in the presence and absence of an electron donor will be discussed.
Keywords: plutonium, Mont Terri, Opalinus Clay, Sporomusa sp., solvent extractions
  • Lecture (Conference)
    TD-246 Joint BN, GD, HT, MA Mont Terri Meeting, 10.-11.02.2014, St. Ursanne, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-19858
Publ.-Id: 19858


Disentangling defect-induced ferromagnetism in SiC
Wang, Y.; Li, L.; Prucnal, S.; Chen, X.; Tong, W.; Yang, Z.; Munnik, F.; Potzger, K.; Skorupa, W.; Gemming, S.; Helm, M.; Zhou, S.;
We present a detailed investigation of the magnetic properties in SiC single crystals bombarded with neon ions. Through careful measuring of the magnetization of virgin and irradiated SiC, we decompose the magnetization of SiC into paramagnetic, superparamagnetic, and ferromagnetic contributions. The ferromagnetic contribution persists well above room temperature and exhibits a pronounced magnetic anisotropy. We qualitatively explain the magnetic properties as a result of the intrinsic clustering tendency of defects.

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Publ.-Id: 19857


Search for Supernova-produced 60Fe in the Earth's Fossil Record
Bishop, S.; Ludwig, P.; Egli, R.; Chernenko, V.; Faestermann, T.; Famulok, N.; Fimiani, L.; Frederichs, T.; Gomez, J.; Hain, K.; Hazlik, M.; Korschinek, G.; Merchel, S.; Rugel, G.;
Approximately 1.8 to 2.8 Myr before the present our planet was subjected to the debris of a supernova explosion. The terrestrial proxy for this event was the discovery of live atoms of 60Fe in a deep-sea ferromanganese crust [Knie et al., Phys. Rev. Lett. (2004)]. The signature for this supernova event should also reside in magnetite (Fe3O4) magnetofossils produced by magnetotactic bacteria extant at the time of the Earth-supernova interaction; these bacteria were and are ubiquitous in all ocean sediments. We have conducted accelerator mass spectrometry (AMS) measurements, searching for live 60Fe in the magnetofossil component of a Pacific Ocean sediment core (ODP Core 848); additional AMS measurements are now ongoing with a second Sediment core (ODP Core 851) in which we expect to find a higher 60Fe signal. This talk will present the current preliminary status of our 60Fe search results for both sediment cores.
Keywords: accelerator mass spectrometry, supernova, AMS, cosmogenic nuclide
  • Lecture (Conference)
    DPG Frühjahrstagung der Fachverbände Physik der Hadronen und Kerne, Didaktik der Physik, 17.-21.03.2014, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19856
Publ.-Id: 19856


Comparing OSL and CN techniques for dating fluvial terraces and estimating surface process rates in Pamir
Fuchs, M. C.; Gloaguen, R.; Pohl, E.; Sulaymonova, V.; Merchel, S.; Rugel, G.;
The quantification of surface process rates is crucial for understanding the topographic evolution of high mountains. Spatial and temporal variations in fluvial incision and basin-wide erosion enable to decipher the role of tectonic and climatic drivers. The Pamir is peculiar in both aspects because of its location at the western end of the India-Asia collision zone, and its position at the edge of two atmospheric circulation systems, the Westerlies and the Indian Summer Monsoon. The architecture of the Panj river network indicates prominent variations across the main tectonic structures of the Pamir. The trunk stream, deflects from the predominantly westward river orientation and cuts across the southern and central Pamir domes before doubling back to the west and leaving the orogen.
Optically stimulated luminescence (OSL) dating of fluvial terraces reveals short-term sedimentation along the trunk stream during the last ~25 kyr. The agreement of OSL results to new exposure ages based on the cosmogenic nuclide (CN) 10Be confirms accurate terrace age modelling and treatment of incomplete bleaching. The consistent terrace sedimentation and exposure ages suggest also fast terrace abandonment and rapid onset of incision. Considerable differences in terrace heights reflect high spatial variations of fluvial incision, independent of time interval, change in rock type or catchment increase. Highest rates of (5.9 + 1.1) mm/yr to (10.0 + 2.0) mm/yr describe the fluvial dynamic across the Shakhdara Dome and that related to the Darvaz Fault Zone. Lower rates of (3.9 + 0.6) mm/yr to (4.5 + 0.7) mm/yr indicate a transient stage north of the Yazgulom Dome. Fluvial incision decreases to rates ranging from (1.7 + 0.3) mm/yr to (3.9 + 0.7) mm/yr in graded river reaches associated to southern dome boundaries. The pattern agrees to the interpretation of successive upstream river captures across the southern and central Pamir domes inferred from morphometric analyses of river and valley profiles.
Basin-wide erosion rates based on 10Be concentrations in modern fluvial sediments yield relatively consistent rates between (0.61 + 0.1) mm/yr and (0.75 + 0.14) mm/yr along the Panj. The increasing Panj catchment averages variations of tributary basins, but minor variations in erosion rates of along-stream sub-basins resemble the pattern of OSL-based incision rates. In contrast, basin-wide erosion rates of tributary basins clearly differentiate between plateau-related sub-basins of (0.05 + 0.01) mm/yr to (0.17 + 0.03) mm/yr, and plateau margin-related sub-basins of (0.38 + 0.06) mm/yr to (1.43 + 0.26) mm/yr. The differentiation in plateau-related and marginal sub-basins and the northward increase in erosion rates correlate with the 75-percentile of the slope distribution within respective basins and to a minor degree to cumulative annual precipitation.
Keywords: cosmogenic nuclides, erosion
  • Poster
    European Geosciences Union (EGU) General Assembly, 27.04.-02.05.2014, Wien, Österreich

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Publ.-Id: 19855


Silica-stabilised actinide(IV) colloids in neutral and slightly alkaline solutions
Zänker, H.; Hennig, C.; Weiss, S.;
Due to their low solubility, tetravalent actinides, An(IV), are usually assumed to be immobile in natural waters. However, insoluble precipitation products can also be mobile if they occur as colloids. For An(IV) oxyhydroxides this phenomenon has thoroughly been studied. The formation of a further type of An(IV) colloids is described (cf. [1]): Silica-containing U(IV), Th(IV) and Np(IV) colloids formed in near-neutral to slightly alkaline solutions of background chemicals of geogenic nature (carbonate, silicic acid, Na+). Whereas the silica-containig colloids addressed in the BELBaR project are formed by the adsorption of radionuclides onto pre-existing silica particles, the colloids here under discussion result from a reaction of dissolved An(IV) with dissolved silicic acid (co-precipitation). An-O-Si bonds, which increasingly replace the An-O-An bonds of the amorphous actinide(IV) oxyhydroxide with increasing silica concentration, make up the internal structure of these colloids as was elucidated by EXAFS spectroscopy and further spectroscopic methods. A strong shift of the particles’ isoelectric point by silica incorporation is observed. The particles remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne An(IV) was observed. The prevailing size of the particles is below 20 nm (about 10 to 100 kDa). The question if such An(IV) colloids may contribute to the mobility of the actinides in the near-field or the far-field of a nuclear waste repository is discussed.
Keywords: tetravalent actinides, silica, colloids, particle size, isoelectric point, EXAFS
  • Lecture (Conference)
    IGDTP-Geodisposal 2014, 24.-26.6.2014, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-19854
Publ.-Id: 19854


Quantifying ages of river terraces and basin wide denudation rates in Pamir
Sulaymonova, V. A.; Fuchs, M. C.; Gloaguen, R.; Merchel, S.; Rugel, G.;
The Pamir is located at the western edge of the Indian indenter and results from the India-Asia collision. The Pamir also lies at the transition between zones dominated either by the Westerlies or the Indian Summer Monsoon. The ongoing tectonic deformation together with the climatic gradients from the two prevailing atmospheric circulation systems provide a natural laboratory to study surface processes and their rates. To determine and quantify the interaction between tectonics and the drainage system in the Tajik Pamir we use cosmogenic nuclide based techniques.
We measured 10Be and 26Al concentrations of modern fluvial sediments sampled from drainage system of Pamirs. Depth profiles enable to determine exposure ages of fluvial terraces, while the modern river sediments reveal basin-wide erosion rates.
However, accurate measurement results depend on the quality of the sample preparation. The samples from Pamir contain a high amount of various feldspars that are very difficult to separate from quartz using standard procedures such as magnetic or density separation. Unclean samples cause uncertainties in chemical procedures, especially in the case of combined 10Be and 26Al analysis. We developed a feldspar flotation in addition to our sample preparation procedure that allowed an almost complete separation of the quartz, up to 95%. Several depth profiles were analyzed to determine the exposure age of fluvial terraces. The first results of one terrace along the southern Panj River east of Langar, and one along the Shakhdara River are promising. The AMS results demonstrated that the depth profiles are consistent, with 10Be and 26Al concentrations decreasing with depth. The results of both fluvial terraces show similar denudation rates 0.5 mm/yr., while exposure age analysis yields 3.5 ka for the Langar and 19 ka Shakhdara terrace. Further analyses are ongoing. These ages are validated by OSL dates at or nearby the same sites. 10Be denudation rates on modern river samples refine the picture produced by one of us (see Fuchs et al., same session).
Keywords: cosmogenic nuclides, fluvial terraces, erosion rate
  • Poster
    European Geosciences Union (EGU) General Assembly, 27.04.-02.05.2014, Wien, Österreich

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Publ.-Id: 19853


Application of the method for uncertainty and sensitivity evaluation to results of PWR LBLOCA analysis calculated with the code ATHLET. Part 2: Sensitivity analysis
Kozmenkov, Y.; Rohde, U.;
In the previously published part 1 of the paper the uncertainty analysis of the large break loss-of-coolant accident (LBLOCA) for German PWR Konvoi was performed using a statistical method, which is based on the Wilks’ theory. The evaluated output parameter is the peak cladding temperature (PCT). The primary goal of this (second) part of the paper is a ranking of the input uncertainties, according to their contributions to the PCT uncertainty in the ATHLET simulation of PWR LBLOCA, by performing a sensitivity analysis. It was shown, that the first extended set of varied parameters used in part 1 can be considerably reduced without any statistically significant influence on the uncertainty analysis results. Thus, it can be shown that the input uncertainty vector based on the LBLOCA PIRT of AREVA GmbH was complete.
To minimize the number of varied parameters the statistical t-test was used and, thus, a set of uncertainty parameters with significant impact on the uncertainty of the PCT was identified. The main contribution to the uncertainty of the first cladding temperature maximum during the blowdown phase of the accident is produced by the core parameters that affect the fuel’s stored energy at the beginning of the accident. However, the major contributors to the uncertainty of the second PCT maximum are the uncertainties in the code models, and first of all the uncertainties in the heat transfer coefficients for dispersed and pure steam flows.
Keywords: LBLOCA, PWR, blowdown phase, reflood phase, ATHLET code, input uncertainties, peak cladding temperature, sensitivity analysis, t-test, PIRT completeness

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Publ.-Id: 19852


Experimental Investigation of the Effect of 90 Degrees Standard Elbow on Horizontal Gas-Liquid Stratified and Annular Flow Characteristics using Dual Wire Mesh Sensors
Vieira, R. E.; Kesana, N. R.; Torres, C. F.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.;
Fluid flowing through pipelines often encounters fittings such as elbows. Although it is true that two-phase flow patterns observed in elbows are qualitatively the same as those seen in straight pipes, the presence of a pipe elbow can modify relative positions and local velocities of the two phases as they are subjected to forces in addition to those encountered in a straight pipe. That redistribution can affect pressure drop values, chemical inhibitor concentration and distribution to the top of the pipe, as well as the erosion pattern occurring from solid particles such as sand that is entrained in oil and gas transportation pipelines. In this work, a Wire-Mesh Sensor technique based on conductance measurements of void fraction was applied to investigate two-phase pipe flow through a standard elbow. The horizontal flow test section, consisting of a 76 mm ID, 18 m long pipe, was employed to generate stratified-wavy and annular flow conditions. Two 16×16 Wire-Mesh configuration sensors were positioned either 0.9 m upstream or 0.6 m downstream of the bend. The experiments were conducted at different liquid and gas superficial velocities that ranged from 0.03 m/s to 0.2 m/s and from 9 m/s to 34 m/s, respectively. The effects of liquid viscosity on the measured parameters are also investigated using two different viscosities of 1 and 10 cP. Stratified-slug transition, stratified wavy and annular flow patterns were observed visually in the clear section placed upstream of the Wire-Mesh sensors. Analysis of time series void fraction data from the dual Wire-Mesh sensors allows the determination of mean void fraction, local time average void fraction distribution, liquid phase distribution around the tube periphery, interfacial structure velocities, as well as Probability Density Function characteristic signatures within the cross-section of pipe before and after the elbow. The results indicate that the distribution of gas and liquid phases and interfacial velocities are significantly altered even 20 diameters downstream of the elbow.
Keywords: Wire-Mesh Sensor, two-phase flow, flow visualization, void fraction

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Permalink: https://www.hzdr.de/publications/Publ-19850
Publ.-Id: 19850


Experimental Investigation of Slug Characteristics through a Standard Pipe Bend
Kesana, N. R.; Vieira, R. E.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.;
Slug flow is a very common flow pattern encountered during the production of petroleum fluids. Likewise, pipe bends are often used to change the direction of the fluids during transportation. This work focuses on comparing various slug characteristics before and after a pipe bend. For this investigation, a dual Wire Mesh Sensor (WMS) is utilized. Measurements are made by placing the sensor before and after the bend. In order to obtain higher spatial and temporal resolution of the signals, a sampling frequency of 10,000 Hz is used. Experiments were conducted in a 76.2 mm (3-inch) diameter pipe utilizing air and water as fluids. Effect of fluid viscosity is also studied by conducting the experiments using three different liquid viscosities: 1, 10 and 40 cP. The experiments were conducted with superficial gas velocity ranging from 9.1 m/s to 35 m/s, and superficial liquid velocity ranged from 0.45 to 0.76 m/s. The three-dimensional time series void data from the Wire-Mesh sensor before and after the bend are analyzed to obtain averaged void fractions, structure of the slugs, void in liquid slugs, bubble size distributions, and radial profiles of gas velocity. Also, this study presents the differences in the void fraction distributions in slugs and pseudo slugs. Since pseudo slugs occur between slug and annular regimes, this information can further the understanding of the effect of flow characteristics on erosion occurring from solid particles for this flow pattern. Finally, from this comprehensive analysis the influence of the bend on the gas and liquid distributions over the cross-section has been discussed.
Keywords: Solid particle erosion, Multiphase slug flow, Wire Mesh Sensor
  • Contribution to proceedings
    22nd Symposium on Industrial Flows, ASME International Mechanical Engineering Congress & Exposition, 15.-21.11.2013, San Diego, California, USA
    Proceedings of ASME 2013 International Mechanical Engineering Congress & Exposition 2013

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Permalink: https://www.hzdr.de/publications/Publ-19848
Publ.-Id: 19848


Hypoxia-inducible factor pathway inhibition resolves tumor hypoxia and improves local tumor control after single-dose irradiation
Helbig, L.; Koi, L.; Brüchner, K.; Gurtner, K.; Hess-Stumpp, H.; Unterschemmann, K.; Pruschy, M.; Baumann, M.; Yaromina, A.; Zips, D.;
Purpose To study the effects of BAY-84-7296, a novel orally bioavailable inhibitor of mitochondrial complex I and hypoxia-inducible factor 1 (HIF-1) activity, on hypoxia, microenvironment, and radiation response of tumors. Methods and Materials UT-SCC-5 and UT-SCC-14 human squamous cell carcinomas were transplanted subcutaneously in nude mice. When tumors reached 4 mm in diameter BAY-84-7296 (Bayer Pharma AG) or carrier was daily administered to the animals. At 7 mm tumors were either excised for Western blot and immunohistologic investigations or were irradiated with single doses. After irradiation animals were randomized to receive BAY-84-7296 maintenance or carrier. Local tumor control was evaluated 150 days after irradiation, and the dose to control 50% of tumors (TCD50) was calculated. Results BAY-84-7296 decreased nuclear HIF-1α expression. Daily administration of inhibitor for approximately 2 weeks resulted in a marked decrease of pimonidazole hypoxic fraction in UT-SCC-5 (0.5% vs 21%, P<.0001) and in UT-SCC-14 (0.3% vs 19%, P<.0001). This decrease was accompanied by a significant increase in fraction of perfused vessels in UT-SCC-14 but not in UT-SCC-5. Bromodeoxyuridine and Ki67 labeling indices were significantly reduced only in UT-SCC-5. No significant changes were observed in vascular area or necrosis. BAY-84-7296 before single-dose irradiation significantly decreased TCD50, with an enhancement ratio of 1.37 (95% confidence interval [CI] 1.13-1.72) in UT-SCC-5 and of 1.55 (95% CI 1.26-1.94) in UT-SCC-14. BAY-84-7296 maintenance after irradiation did not further decrease TCD50. Conclusions BAY-84-7296 resulted in a marked decrease in tumor hypoxia and substantially reduced radioresistance of tumor cells with the capacity to cause a local recurrence after irradiation. The data suggest that reduction of cellular hypoxia tolerance by BAY-84-7296 may represent the primary biological mechanism underlying the observed enhancement of radiation response. Whether this mechanism contributes to the improved outcome of fractionated chemoradiation therapy warrants further investigation.

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Publ.-Id: 19847


Plasmonic off-axis unidirectional beaming of quantum-well luminescence
Dimaria, J.; Dimakis, E.; Moustakas, T. D.; Paiella, R.;
Plasmonic off-axis unidirectional beaming of luminescence is demonstrated using nitride semiconductor quantum wells. The underlying mechanism involves the near-field excitation of surface plasmon polaritons on an ultrathin metal film, which are then diffractively scattered by an adjacent periodic array of asymmetric metallic nanoparticles. By tailoring the nanoparticles shape, we show that forward scattering can be suppressed in favor of backward diffraction (or vice versa), thereby enabling unidirectional beaming at geometrically tunable oblique angles. These nanostructures can be used to control the output light directionality of arbitrary planar luminescent devices, with a spatial resolution that would be unattainable with bulk optics.

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Publ.-Id: 19846


Application of a three-feature dispersed-barrier hardening model to neutron-irradiated Fe-Cr model alloys
Bergner, F.; Pareige, C.; Hernández-Mayoral, M.; Malerba, L.; Heintze, C.;
An attempt is made to quantify the contributions of different types of defect-solute clusters to the total irradiation-induced yield stress increase in neutron-irradiated (300 °C, 0.6 dpa), commercial-purity Fe-Cr alloys (target Cr contents of 2.5, 5, 9 and 12 at% Cr). Former work based on the application of transmission electron microscopy, atom probe tomography, and small-angle neutron scattering revealed the formation of dislocation loops, NiSiPCr-enriched clusters and alpha’-phase particles, which act as obstacles to dislocation glide. The values of the dimensionless obstacle strength are estimated in the framework of a three-feature dispersed-barrier hardening model. Special attention is paid to the effect of measuring errors, experimental details and model details on the estimates. The three families of obstacles and the hardening model are well capable of reproducing the observed yield stress increase as a function of Cr content, suggesting that the nanostructural features identified experimentally are the main, if not the only, causes of irradiation hardening in these alloys.
Keywords: Radiation hardening, Fe-Cr alloys

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Publ.-Id: 19845


Polynuclear complexes of tetravalent actinides and lanthanides with simple carboxylate ligands
Hennig, C.;
Polyanuclear An(IV) carboxylate complex were identified in aqueous solution. The related complex species were preserved in crystals and their structures were determined. The structural identity of the species in solution and in solid state was tested by EXAFS spectroscopy.
Keywords: actinides, carboxylates, EXAFS, XRD
  • Lecture (others)
    Forschungszentrum Juelich, Institute of Energy and Climate Research, 06.02.2014, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19844
Publ.-Id: 19844


Robust energy enhancement of ultra-short pulse laser accelerated protons from reduced mass targets
Zeil, K.; Bussmann, M.; Cowan, T. E.; Kluge, T.; Kraft, S. D.; Metzkes, J.; Schramm, U.;
We present a systematic study of the ultrashort pulse laser driven acceleration of protons from thin targets of finite lateral size, so-called reduced mass targets (RMTs). Reproducible series of targets, manufactured with lithographic techniques, and varying in size, thickness, and mounting geometry were irradiated at the 150 TW Draco Laser facility of the Helmhotz-Zentrum Dresden-Rossendorf with ultrashort (30 fs) laser pulses of intensities of about 8 • 10^20 W/cm^2. A robust maximum energy enhancement of almost a factor of two was found when compared to reference irradiations of plain foils of the same thickness and material. Furthermore, these targets exhibit a reduced performance dependence on target thickness compared to standard foils, which, based on detailed PIC simulations can be explained by the influence of the RMT geometry on the electron sheath. The performance gain was, however, restricted to lateral target sizes of about 50 μm which was attributed to edge and mounting structure influences. The contribution of the large electric fields at the target edges to the proton acceleration performance was investigated with measurements of the proton beam profile as well as optical pump and probe experiments.
  • Lecture (Conference)
    Laser and Plasma Accelerator Workshop 2013, 04.09.2013, Goa, India

Permalink: https://www.hzdr.de/publications/Publ-19843
Publ.-Id: 19843


CFD simulations of steam-water flow with condensation
Apanasevich, P.; Lucas, D.;
Gas-liquid two-phase flows have become increasingly important in engineering equipment and technology (e.g. in chemical or process industries). Depending on mass flow rates, geometry and the fluid properties, different flow regimes can occur (e.g. bubble flow, stratified flow, droplet flow etc.). The current project focuses on stratified two-phase flows with heat and mass transfer across a moving interface due to direct contact condensation (DCC) in horizontal pipes or channels. In case of direct contact condensation, the resistance to condensation heat transfer considerably lower compared to film-wise condensation. Hence, DCC allows a considerably better heat exchange between the phases. Direct contact condensation is used in a variety of heat transfer devices (such as direct contact condensers), which offer the possibility of increased per-formance. DCC has also been of major importance in connection with the analysis of nuclear reactor safety systems, in particular during two-phase pressurized thermal shock (PTS) scenari-os. PTS occurs when there are large thermal loads on the Reactor Pressure Vessel wall during an accident. Therefore, the modeling of direct contact condensation is a task of considerable im-portance. Condensation phenomena depend on the turbulence in the liquid phase. To consider pronounced 3D effects and local phenomena CFD methods need to be used. Generally, two-phase CFD models are not yet mature and have to be qualified for two-phase flows. The work aims at the development and validation of CFD models for two-phase stratified flows including heat and mass exchange between the phases. A promising model development strategy implies experimental data with high resolution both in space and time for the entire domain of interest. To investigate two-phase PTS scenarios with DCC, the TOPFLOW-PTS experiments were carried out at the TOPFLOW test facility of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) [1]. The goal of the paper is to present the CFD simulations of a TOPFLOW-PTS steam-water experiment and to discuss the limits of the models used.
Keywords: CFD, pressurized thermal shock, direct contact condensation, TOPFLOW-PTS experiments
  • Lecture (Conference)
    International Colloquim 150th Birthday of Richard Mollier Heat transfer phenomena in external fields: Basis research for next generation energy machines, 21.-22.11.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19842
Publ.-Id: 19842


Carbon Cage Vibrations of M@C82 and M2@C2n (M = La, Ce; 2n = 72, 78, 80): The Role of the Metal Atoms
Popov, A. A.; Kästner, C.; Krause, M.; Dunsch, L.;
Infrared spectra of La2@C80 and a series of Ce-based endohedral metallofullerenes (EMFs), including Ce@C82, Ce2@C72, Ce2@C78, and Ce2@C80 are reported. DFT calculations are used for their thorough analysis and assignment. The vibrations of the fullerene cages in all studied EMFs differ from those of their empty, charged cage analogues. Furthermore, EMFs with the same carbon cage but different type of encapsulated species also show significant differences in their cage vibrational patterns. These phenomena are explained by a different coupling of the vibrational modes as well as by the different charge distributions in EMFs and empty, isostructural fullerene anions.
Keywords: Endohedral fullerene, metallofullerene, vibrational spectroscopy, density functional theory

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Publ.-Id: 19841


Development of a transport solver for DYN3D on the basis of CCCP with orthonormal flux expansion
Litskevich, D.; Merk, B.;
DYN3D is a well-known and widely used computer code for reactor physics simulation of nuclear power plants, in particular for reactors with hexagonal fuel assembly structures. It has been developed in Helmholtz-Zentrum Dresden-Rossendorf, Germany. The standard version of the DYN3D code can be used for investigations of transients in light water reactors cores with hexagonal or quadratic fuel assemblies. In order to determine the pin with the maximum power in selected assemblies, a two-dimensional pin power reconstruction can be performed based on the node homogenized neutron flux. A superposition of global diffusion solution of the full core calculation with the assembly pin powers obtained in the cell calculations is used therefore. This method is implemented in DYN3D for reconstruction of power inside selected assemblies. An improved onset would be a hybrid solution, the coupling of the full core diffusion solver with an advanced transport solver on fuel assembly base. This method can be used to directly determine the power distribution for each rod inside fuel assemblies by applying a transport solver using unstructured mesh and boundary conditions extracted from the full core diffusion solution. Nowadays, this mentioned methodology is under development. In the present work an advanced multigroup transport method of current coupling collision probability (CCCP) with orthonormal flux expansion inside the calculation regions is being developed and tested for cylindrical, hexagonal geometries and for assemblies of hexagonal cells. The results of test calculations demonstrate very good agreement with the results obtained from Monte Carlo calculations. Multigroup calculations for hexagonal assemblies with cross-sections prepared using the HELIOS code show good agreement with HELIOS reference solution, too. These convincing results encourage the implementation of this advanced pin power calculation method into DYN3D as future pin-power determination method using currents from nodal solution as boundary conditions.
Keywords: Transport equation, current coupling collision probability method, DYN3D
  • Open Access Logo Contribution to proceedings
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia
    Proceedings of the 23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest: MTA Energoatom, 38-48
  • Lecture (Conference)
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-19840
Publ.-Id: 19840


Sintering and Crystallization during the Production of Strontium-Anortite Glass Ceramic
Sarkisov, P. D.; Orlova, L. A.; Popovich, N. V.; Bruntsch, R.; Chainikova, A. S.; Klinkmueller, K.; Shchegoleva, N. E.;
Crystallization and sintering, which occur during firing, during the production of strontium-anortite glass ceramics by means of powder metallurgy are studied. It is shown that the dispersity of the initial glass powder and the temperature–time firing regimes affect the crystallization temperature and heat, the nature of the precipitating phases and the sintering temperature interval and kinetics of the particles. It is determined that for ceramizing glass compositions there exists a narrow powder dispersity interval in which densely sintered materials with the required composition and high mechanical properties can be obtained using multistep heat-treatment.
Keywords: glass ceramic, sintering, dispersity, strontium anortite, SrO–Al2O3–SiO2

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Permalink: https://www.hzdr.de/publications/Publ-19839
Publ.-Id: 19839


Importance of nuclear triaxiality for electromagnetic strength, level density and neutron capture cross sections in heavy nuclei
Grosse, E.; Massarczyk, R.; Junghans, A. R.;
Cross sections for neutron capture in heavy nuclei in the energy range of unresolved resonances are predicted simultaneously to data on level densities at the neutron threshold and average photon widths from 132 spin-0 target nuclei with 70
  • Open Access Logo Contribution to proceedings
    Final ERINDA User Meeting and Scientific Workshop, 01.-03.10.2013, Geneva, Switzerland
    Proceedings of the ERINDA Workshop, CERN, edited by Enrico Chiaveri CERN Proceedings 2014-002, Geneva: CERN, 978-92-9083-403-8, 135-144
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    Permalink: https://www.hzdr.de/publications/Publ-19838
    Publ.-Id: 19838


    Transmutation of high-level radioactive waste - Perspectives
    Junghans, A.; Beyer, R.; Grosse, E.; Hannaske, R.; Kögler, T.; Massarczyk, R.; Schwengner, R.; Wagner, A.;
    In a fast neutron spectrum essentially all long-lived actinides (e.g. Plutonium) undergo fission and thus can be transmuted into generally short lived fission products. Innovative nuclear reactor concepts e.g. accelerator driven systems (ADS) are currently in development that foresee a closed fuel cycle. The majority of the fissile nuclides (uranium, plutonium) shall be used for power generation and only fission products will be put into final disposal that needs to last for a historical time scale of only 1000 years. For the transmutation of high-level radioactive waste a lot of research and development is still required. One aspect is the precise knowledge of nuclear data for reactions with fast neutrons. Nuclear reactions relevant for transmutation are being investigated in the framework of the european project ERINDA. First results from the new neutron time-of-flight facility nELBE at Helmholtz-Zentrum Dresden-Rossendorf will be presented.
    • Open Access Logo Contribution to proceedings
      Final ERINDA User Meeting and Scientific Workshop, 01.-03.10.2013, Geneva, Switzerland
      Proceedings of the ERINDA Workshop, CERN, edited by Enrico Chiaveri CERN Proceedings 2014-002, Geneva: CERN, 978-92-9083-403-8, 175-181

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    Permalink: https://www.hzdr.de/publications/Publ-19837
    Publ.-Id: 19837


    Kinetics and activation parameters of the reaction of organoarsenic(V) compounds with glutathione
    Kretzschmar, J.; Brendler, E.; Wagler, J.; Schmidt, A.-C.;
    In this work the kinetics of the reaction of glutathione (GSH) with different organoarsenic(V) compounds is investigated. This includes phenylarsonic acid (PAA), 4-hydroxy-3-nitrophenylarsonic acid (HNPAA), p-aminophenylarsonic acid (p-APAA) and o-aminophenylarsonic acid (o-APAA) as well as monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). The reaction progress was monitored in real time by 1H-NMR, which allowed the determination of rate coefficients and half-lives as well as activation energies, enthalpies and entropies of activation and, eventually, Gibbs free energies of activation. The reaction consists of two steps: redox reaction and conjugation. In all investigated systems, the conjugation is fast compared to the redox reaction, which therefore is rate determining. All investigated phenylarsonic acids are subject to the same rate law, showing overall reaction orders of 3 and half-life values between 47.7 ± 0.2 and 71.0 ± 3.6 min, corresponding to reaction rates between 1330 ± 10 L2 mol-2 min-1 and 850 ± 5 L2 mol-2 min-1, respectively. The methylated compounds react slower, showing half-lives of 76.6 ± 0.4 and 444 ± 10 min for DMAA and MMAA, respectively. The obtained enthalpies of activation range from 20 to 36 (± 2) kJ mol-1 and the entropies of activation are within −154 and −97 (± 7) J mol-1 K-1. The results reveal a correlation of the toxicity of the arsenic compound and the reaction rate with GSH. This may pave the way for the estimation of the toxicity of such compounds by simple kinetic studies.
    Keywords: glutathione, roxarsone, phenylarsonic acid, arsanilic acid, arsenic detoxification, kinetics, NMR

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    Permalink: https://www.hzdr.de/publications/Publ-19836
    Publ.-Id: 19836


    All-optical helicity dependent magnetic switching in Tb-Fe thin films with a MHz laser oscillator
    Hassdenteufel, A.; Schubert, C.; Hebler, B.; Schultheiss, H.; Fassbender, J.ORC; Albrecht, M.; Bratschitsch, R.
    We demonstrate all-optical magnetic switching (AOS) in an amorphous Tb30Fe70 thin film, triggered by a 5.1 MHz laser oscillator. The magnetic layer is grown on a SiO2/Si substrate. An identical magnetic film deposited on a microscope glass slide shows no AOS and only exhibits thermally induced demagnetization. This effect is due to heat accumulation by multiple laser pulses because of the low thermal conductivity of the glass substrate. In contrast, the use of a proper heat sink (e.g. SiO2/Si) abolishes need for low repetitive laser amplifier systems to induce AOS and paves the way for a cheap and easy to use technological implementation with conventional laser oscillators.
    Keywords: Ultrafast technology; Ultrafast phenomena; Ultrafast processes in condensed matter, including semiconductors; Optical data storage; Magneto-optical materials; Optical storage-recording materials
    • Open Access Logo Optics Express 22(2014)8, 10017-10025
      DOI: 10.1364/OE.22.010017
    • Lecture (Conference)
      CLEO 2014, 08.-13.06.2014, San Jose, Kalifornien, USA

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    Permalink: https://www.hzdr.de/publications/Publ-19835
    Publ.-Id: 19835


    Electromagnetic method for detection of gas bubbles in two phase liquid metals flows
    Andreew, O.; Gundrum, T.; Wondrak, T.; Eckert, S.; Gerbeth, G.; Dekdouk, B.; Peyton, A.;
    We present a combined numerical and experimental investigation of an electromagnetic system dedicated for an operative detection of non-metallic enclosures (gas bubbles) into the liquid metal flows. The method is based on the generation of eddy currents in the electrically conducting medium by applying AC magnetic field and the detection of the electromagnetic distortions caused by heterogeneity of electrical conductivity of the medium. We defined an optimal position and configuration of detector and excitation coil in order to get maximal sensitivity of the system to the spatial distribution of admixture.
    Keywords: two-phase flow; electromagnetic tomography; gas bubbles.
    • Lecture (Conference)
      7th World Congress on Industrial Process Tomography, WCIPT7, 02.-05.09.2013, Krakow, Poland
    • Lecture (Conference)
      2013 International Congress on Advances in Nuclear Power Plants (ICAPP2013) & The 28th Korea Atomic Industrial Forum Inc., 14.-18.04.2013, Jeju, Korea

    Permalink: https://www.hzdr.de/publications/Publ-19834
    Publ.-Id: 19834


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

    Permalink: https://www.hzdr.de/publications/Publ-19833
    Publ.-Id: 19833


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

    Permalink: https://www.hzdr.de/publications/Publ-19832
    Publ.-Id: 19832


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

    Permalink: https://www.hzdr.de/publications/Publ-19831
    Publ.-Id: 19831


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

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    Permalink: https://www.hzdr.de/publications/Publ-19830
    Publ.-Id: 19830


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

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    Permalink: https://www.hzdr.de/publications/Publ-19829
    Publ.-Id: 19829


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

    Permalink: https://www.hzdr.de/publications/Publ-19828
    Publ.-Id: 19828


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

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    Permalink: https://www.hzdr.de/publications/Publ-19827
    Publ.-Id: 19827


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

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    Permalink: https://www.hzdr.de/publications/Publ-19826
    Publ.-Id: 19826


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

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    Permalink: https://www.hzdr.de/publications/Publ-19825
    Publ.-Id: 19825


    Contactless flow rate measurements in metallic melts
    Kontaktlose Durchflussmessung in Metallschmelzen

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

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    Permalink: https://www.hzdr.de/publications/Publ-19824
    Publ.-Id: 19824


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

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    Permalink: https://www.hzdr.de/publications/Publ-19823
    Publ.-Id: 19823


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

    Permalink: https://www.hzdr.de/publications/Publ-19822
    Publ.-Id: 19822


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

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

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

    Permalink: https://www.hzdr.de/publications/Publ-19821
    Publ.-Id: 19821


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

    Permalink: https://www.hzdr.de/publications/Publ-19820
    Publ.-Id: 19820


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

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    Permalink: https://www.hzdr.de/publications/Publ-19819
    Publ.-Id: 19819


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

    Permalink: https://www.hzdr.de/publications/Publ-19818
    Publ.-Id: 19818


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

    Permalink: https://www.hzdr.de/publications/Publ-19817
    Publ.-Id: 19817


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

    Permalink: https://www.hzdr.de/publications/Publ-19815
    Publ.-Id: 19815


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

    Permalink: https://www.hzdr.de/publications/Publ-19814
    Publ.-Id: 19814


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

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    Permalink: https://www.hzdr.de/publications/Publ-19813
    Publ.-Id: 19813


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

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    Permalink: https://www.hzdr.de/publications/Publ-19812
    Publ.-Id: 19812


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

    Permalink: https://www.hzdr.de/publications/Publ-19811
    Publ.-Id: 19811


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

    Permalink: https://www.hzdr.de/publications/Publ-19810
    Publ.-Id: 19810


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

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    Permalink: https://www.hzdr.de/publications/Publ-19809
    Publ.-Id: 19809


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

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    Permalink: https://www.hzdr.de/publications/Publ-19808
    Publ.-Id: 19808


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

    Permalink: https://www.hzdr.de/publications/Publ-19807
    Publ.-Id: 19807


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

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    Permalink: https://www.hzdr.de/publications/Publ-19806
    Publ.-Id: 19806


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

    Permalink: https://www.hzdr.de/publications/Publ-19805
    Publ.-Id: 19805


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

    Permalink: https://www.hzdr.de/publications/Publ-19804
    Publ.-Id: 19804


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

    Permalink: https://www.hzdr.de/publications/Publ-19803
    Publ.-Id: 19803


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

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    Permalink: https://www.hzdr.de/publications/Publ-19802
    Publ.-Id: 19802


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

    Permalink: https://www.hzdr.de/publications/Publ-19801
    Publ.-Id: 19801


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