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41356 Publications

Morphology induced two-magnon scattering in thin NiFe films

Körner, M.; Lenz, K.; Fritzsche, M.; Facsko, S.; Fassbender, J.

When studying magnetization dynamics of thin magnetic films, intrinsic as well as extrinsic spin relaxation processes have to be taken into account. While intrinsic processes, summarized as Gilbert damping, are well known and studied for the last decades, the focus now has shifted to extrinsic contributions. In this context the two-magnon scattering (TMS) is of particular interest. This type of scattering is induced within thin magnetic films by defects and inhomogeneities. It was shown that periodic magnetic patterns can serve as defect structure, e.g. by periodically varying the magnetization saturation using ion beam irradiation combined with periodic sample patterning by electron beam lithography. Due to irradiation of the material a local variation of the magnetic properties can be achieved [1], where the TMS strength is set by the periodicity of the modification. However, directly patterning the material is time consuming and not suitable for large scale manufacturing. Hence a self-organized nanoscale patterning is more favorable. Broad ion beam erosion is a well-established technique for structuring large surface areas. By varying the irradiation parameters, e.g. ion energy, fluence, and incident angle sinusoidally modulated surfaces (ripples) can be created with a periodicity tuneable over a wide range [2]. Growing magnetic materials on these ripples imprints the corrugation to the material and induces by dipolar effects a wavelength dependent uniaxial magnetic anisotropy (UMA). Furthermore the imprinted corrugation can serve as a spin wave scattering center, modifying the two-magnon damping contribution. Here we present the influence of the substrate surface corrugation on the magnetic damping properties of 30 nm thin Ni80Fe20 (Py) films grown by molecular beam epitaxy at room temperature on rippled Si substrates. Due to ion beam erosion of flat Si as well as natural oxidation of the substrate prior to film deposition, Py films grown on top exhibit a polycrystalline structure that suppresses the intrinsic magneto-crystalline anisotropy almost completely. The in-plane magnetostatic and dynamic properties of these samples were investigated by means of angular and frequency dependent vector network analyzer ferromagnetic resonance (VNA-FMR).
Starting with a planar reference sample the angular together with the frequency dependent linewidth measurements reveal a Gilbert dominated relaxation process, whereby no TMS can be observed. Due to the polycrystalline film structure, only a very weak magnetic anisotropy is observed. This uniaxial magnetic anisotropy (UMA) has a two-fold symmetry and is randomly aligned with respect to the sample edges. Changing to rippled substrates the grown Py film maintains its polycrystalline structure. Depending on the ripple wavelength λ, ranging from 25 nm to 230 nm, an UMA is induced with its easy axis always aligned parallel to the ripple ridges. The strength of the UMA decays with increasing wavelength and is strongest for λ=25 nm. In this case no influence of the corrugation on the damping is observed. This changes drastically for samples with a higher wavelength of λ=230 nm. While the UMA is reduced to the value of the planar reference sample the linewidth measurements now show clear indications for defect induced TMS. This is shown in Fig. 1a, where the peak-to-peak linewidth is plotted as a function of the in-plane magnetic field angle (open circles). Modeling the linewidth results in a Gilbert contribution that is constant for all in-plane field orientations. Additionally an angle dependent TMS contribution is found, which consists of a small four-fold and a dominating two-fold (uniaxial) part. Thereby the direction of minimal linewidth aligns parallel with the ripple ridges, which in turn defines the uniaxial symmetry of the damping. Fig. 1b depicts the frequency dependent measurements parallel (red squares) and perpendicular (green circles) to the ripple ridges. In parallel configuration the damping is purely Gilbert-like, as already observed in the reference measurement. The monotonous increase of the linewidth with applied microwave frequency is instead lost in case of the perpendicular geometry. Here, a preeminent peak is observed with its center at f=10 GHz. Following the description of Barsukov et al. [1] this excessive linewidth increase is a result of defect induced TMS, where the width and frequency position of the peak is determined by the scattering potential, created by the corrugation of the film. The origin and wavelength dependence of these morphology induced linewidth manipulation will be discussed in detail.
We thank I. Barsukov, J. Lindner, and P. Landeros for fruitful discussions. This work is supported
by DFG grant no. FA 314/6-1.
1) I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)
2) J. Fassbender et al., New J. Phys. 11, 125002 (2009)

Related publications

  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012, 24.-28.09.2012, Shanghai, China

Publ.-Id: 17810

Frequency dependence of spin relaxation in periodic systems

Körner, M.; Barsukov, I.; Römer, F. M.; Lenz, K.; Meckenstock, R.; Hemken To Krax, S.; Banholzer, A.; Grebing, J.; Lindner, J.; Farle, M.; Fassbender, J.

In the presence of a periodic scattering potential the spin relaxation in ultrathin ferromagnets is not a monotonous function of the frequency. The spin relaxation rate is found to substantially increase at characteristic frequencies related to the periodicity of the magnon scattering potential (see Fig. 1). This is experimentally confirmed in Ni80Fe20 thin films by artificially introducing different scattering periodicities [1]. The lateral struvturing of the thin film is achieved by Cr+ ion implantation with at an energy of 5 keV and a fluence of 5 × 10E15 ions/cm2 through a 100 nm thick polymethyl methacrylate (PMMA) resist covering the whole sample area. Electron beam lithography was used to fabricate 1 mm long-stripes of width s0 and spacing s1 (i.e., with periodicity l = s0 + s1) within the PMMA resist so that the surface becomes Cr-implanted in a stripewise manner. Frequency dependent Ferromagnetic resonance spectroscopy reveals that the magnetic damping may be increased at specific frequencies by a factor of up to 100%.
This work is supported by the DFG, SFB 491, Grants No. FA 314/6-1 and No. FA 314/3-2.
[1] I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)

Related publications

  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012, 24.-28.09.2012, Shanghai, China

Publ.-Id: 17809

Magnonic Crystals By Means Of Patterned Ion Implantation

Fassbender, J.; Körner, M.; Lenz, K.; Strache, T.; Banholzer, A.; Grebin, J.; Lindner, J.; Barsukov, I.; Römer, F.; Meckenstock, R.; Hemken To Krax, S.; Farle, M.; McCord, J.; Mönch, I.; Mattheis, R.

Ion implantation is a standard process in semiconductor tech¬nology. However, since a doping of metals typically does not have such a tremendous effect as compared to semiconductors ion implantation in metals to achieve a desired electrical, optical or magnetic property is much less explored. A combination of litho-graphy and ion implantation to achieve a lateral ion implantation pattern is a novel route to design and construct artificial materials like photonic or magnonic crystal which rely on the local band gap or spin wave dispersion engineering [1].
The contribution will provide an overview over the different physical mechanisms which allow modifying and tailoring the dynamical magnetic properties, i. e., magnetic damping even in an anisotropic fashion, aiming at the creation of new functional materials. In one example [2] it is demonstrated that the mag¬netic damping parameter in a ferromagnetic/antiferromag¬ne¬tic/ferro¬magnetic trilayer stack can be continuously and spatially varied between two extremal values (see Fig. 1). In a second example [3] the creation of a lateral magnetization pattern by ion implantation gives rise to additional and anisotropic relaxation channels. Potential areas of application are magnonic crystals and band-stop filters in the GHz range.

Acknowledgement: This work was supported by Deutsche Forschungsgemeinschaft SFB491, FA 314/3, FA314/6-1 and MC 9/7.

[1] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
[2] J. McCord, T. Strache, I. Mönch, R. Mattheis, J. Fassbender, Phys. Rev. B 83, 224407 (2011).
[3] I. Barsukov, F. M. Römer, R. Meckenstock, K. Lenz, J. Lindner, S. Hemken to Krax, A. Banholzer, M. Körner, J. Grebing, J. Fassbender, M. Farle, Phys. Rev. B 84, 140410(R) (2011).

Keywords: ion irradiation; ion implantation; magnetic films; modification; magnonics; dynamics

Related publications

  • Lecture (Conference)
    18th International Conference on Ion Beam Modification of Materials (IBMM2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 17808

Tailoring perpendicular anisotropy in Co/Pd multilayers by ion irradiation

Osten, J.; Greene, P.; Ende, T.; Iwata, N.; Lenz, K.; Liu, K.; Fassbender, J.

A major obstacle towards the increase in areal magnetic recording density and the decrease in bit size is the retention of thermal stability while maintaining reasonable write fields. Materials with graded magnetic anisotropy are promising candidates to solve this problem. Here we demonstrate the approach of using post-deposition ion irradiation to tailor the perpendicular anisotropy in Co/Pd multilayer thin films. The films, with uniform as well as graded perpendicular anisotropy, were synthesized by magnetron sputtering. Based on TRIDYN simulations, different primary ion energies are chosen to achieve varying penetration depths of the ions creating a depth dependent anisotropy grading. Before and after ion irradiation, MOKE as well as magnetometry measurements were employed to detect the changes of the magnetic properties. In the irradiated layer of the film domain nucleation is promoted (Fig. 1). Upon ion irradiation, the Co/Pd films exhibit reduced coercivity and remanence with increasing energies. Higher ion energies have a more pronounced effect on reducing the perpendicular anisotropy. The archived anisotropy grading also depends on the original film stack.

Keywords: ion irradiation; magnetism; magnetic recording; thermal stability; graded media

Related publications

  • Poster
    18th International Conference on Ion Beam Modification of Materials (IBMM 2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 17807

Self-consistent isotopic comparative method used to determine dependence of secondary-yields on oxygen concentration in Si-O system up to 33%

Dupuy, J. C.; Prudon, G.; Dubois, C.; Kögler, R.; Akhmadaliev, S.; Perrat-Mabilon, A.

Yields of B+,O+,Si+, B-, O-, and Si- versus oxygen concentration were determined in Si under Ar+ bombardment using the isotopic comparative method (ICM). Samples containing a near-uniform low concentration of 18O and a Gaussian-like profile of 16O with high concentration were fabricated by multi-energy ion implantation. ICM allows to determine the oxygen concentration profile by secondary-ion mass spectrometry. The ion yield can be measured as a function of the oxygen concentration up to 33 at%. Whatever the charge of the secondary ions, all relative ion yields are enhanced with increasing oxygen concentration. Very strong matrix effects due to oxygen are found for B+ (>100), whereas moderate or slight matrix effects are found for Si+ and O- (>10) and for Si-, B-, and O+ (<4). Relative ion yields of B+ and Si+ differ versus oxygen, whereas they are identical for B- and Si-. The relative ionization probability versus oxygen for Si+ agrees very well with the results of William´s group.

Keywords: SIMS; matrix effect; ion yield; silicon-oxygen system; ICM

Related publications

  • Surface and Interface Analysis 45(2013)1, 369-372
    Online First (2012) DOI: 10.1002/sia.5108

Publ.-Id: 17806

Zeitaufgelöste (4D) Rekonstruktion von in-beam PET Daten für das Dosismonitoring bei der Bestrahlung bewegter Zielvolumina in der Ionentherapie

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

no abstract available

Keywords: in-beam PET; moving targets; ion beam therapy

  • Lecture (Conference)
    43. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik e. V. (DGMP), 26.-29.09.2012, Jena, Deutschland

Publ.-Id: 17805

Time resolved (4D) reconstruction of in-beam PET data for the dose monitoring of intra-fractionally moving target volumes in ion beam therapy

Laube, K.; Bert, C.; Fiedler, F.; Helmbrecht, S.; Parodi, K.; Priegnitz, M.; Saito, N.; Enghardt, W.

In-beam positron emission tomography (PET) with a double-head PET scanner has been successfully applied for the in situ dose monitoring of about 440 patients with static tumour entities within a pilot project at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. For future treatment of intra-fractionally moving tumours, mainly located in the lung or liver, a dose monitoring is highly desired since complex beam delivery strategies and continuous respiration-related density changes in the irradiated tissue increase the risk for dose errors. Conventional three-dimensional (3D) in-beam PET measurements taken from moving structures would result in a reproduction of a blurred activity distribution and would, therefore, impede correct dose verification. An implemented motion compensated (4D) reconstruction routine based on the existing 3D Maximum Likelihood Expectation Maximization (MLEM) algorithm has been tested by phantom experiments performed at the GSI facility. Homogeneous polymethyl methacrylate (PMMA) phantoms of dedicated geometries have been irradiated with 12C pencil beams and in-beam PET data acquisition was performed throughout irradiation and additional time beyond to gain better statistics. Motion mitigation techniques of rescanning, gating or tracking have been used for a homogeneous dose deposition in the PMMA targets which performed a one-dimensional cos2- or cos4-shaped motion perpendicular to the beam direction. 4D reconstruction results have been compared to static reference measurements and to reconstruction results without consideration of the
target motion. Evaluation outcome with respect to the conservation of lateral and distal gradients in the reconstructed activity distributions will be shown at the workshop. Furthermore, the acquisition of required input parameters from the accelerator, the motion acquisition and the motion compensation systems and the data handling before reconstruction, like the temporal synchronization of all signals, as well as the necessary improvements for clinical usage of the 4D in-beam PET dose monitoring will be discussed.

Keywords: in-beam PET; moving targets; ion beam therapy; reconstruction

  • Lecture (Conference)
    Tomography, data processing and image reconstruction for medicine and engineering, 10.-12.09.2012, Dresden, Deutschland

Publ.-Id: 17804

Generalizations of Matérn's hard-core point processes

Teichmann, J.; Ballani, F.; van den Boogaart, K. G.

Matérn’s hard-core processes are valuable point process models in spatial statistics. In order to extend their field of application, Matérn’s original models are generalized here, both as point processes and particle processes. The thinning rule uses a distancedependent probability function, which controls deletion of points close together. For this general setting, explicit formulas for first- and second-order characteristics can be given. Two examples from materials science illustrate the application of the models.

Keywords: Point process; marked Poisson process; Matérn hard-core process; dependent thinning; independent thinning; pair correlation function

Publ.-Id: 17803

Entwicklung und Synthese von [18F]Flubatine für die Visualisierung von α4β2 nikotinischen Acetylcholinrezeptoren (nAChRs)

Smits, R.; Hoepping, A.; Fischer, S.; Hiller, A.; Funke, U.; Deuther-Conrad, W.; Steinbach, J.; Sabri, O.; Brust, P.

Ziel: Bei Patienten mit Alzheimer-Demenz (AD) ist die Verfügbarkeit nikotinischer Acetylcholinrezeptoren (nAChR), insbesondere des α4β2 Subtyps im Gehirn reduziert [1]. Die Visualisierung dieser Rezeptoren könnte zu einer frühzeitigen Diagnose der AD beitragen. Die zur Zeit zur Verfügung stehenden Radioliganden haben entweder eine unzureichende Affinität zum Rezeptor oder weisen eine sehr langsame Bindungskinetik auf. Der neue Ligand [18F]Flubatine bietet wesentliche Vorteile. Beide Enantiomere besitzen eine hohe in vitro Affinität [2] und zeigen eine schnelle cerebrale Bindungskinetik in der Maus [3] und im Schwein [4]. Erste humane PET-Studien bestätigen eine hohe Aufnahme im Thalamus, eine geringe unspezifische Bindung und das Erreichen des Bindungsgleichgewichtes in weniger als zwei Stunden. Für die Durchführung von klinischen Studien und für eine potentielle routinemäßige Anwendung war es notwendig, die bestehende Präkursorsynthese zu optimieren. Ein neuer enantiomerenreiner Präkursor soll eine einfache, robuste und effiziente Radiosynthese erlauben, mit dem Ziel der Automatisierung der Tracerproduktion. Zu diesem Zweck wurden eine kleine Bibliothek von Präkursoren mit verschiedenen Schutzgruppen und Abgangsgruppen synthetisiert und getestet.

Methodik: Als Startmaterial für die Synthese der neuen Präkursoren diente das Cbz-geschützte 8-Aza-bicyclo[3.2.1]oct-6-en-3-on, das nach literaturbekannten Verfahren dargestellt wurde. Nach einer reduktiven Heck-Reaktion zur Einführung des Pyridylrestes konnte die C3-Ketofunktion in einer dreistufigen Sequenz deoxygeniert werden. Die Abspaltung der Cbz-Schutzgruppe lieferte den [18F]Flubatine-Standard, dessen Racematspaltung mittels chiraler HPLC gelang. Im Anschluss wurden verschiedene Schutzgruppen und Fluchtgruppen eingeführt, deren [18F]-Markierung untersucht und optimiert wurde. Die Radiomarkierung der verschiedenen Präkursoren erfolgte über ein zweistufiges Verfahren bestehend aus trägerfreier, nucleophiler Radiofluorierung und Abspaltung der Schutzgruppe.

Ergebnisse: Die besten Resultate wurden mit dem Boc-geschützten Trimethylammonium-Präkursor erzielt. Die Ausbeute der unter Phasentransfer-Bedingungen durchgeführten Radiomarkierung betrug 90±5%. Nach Abspaltung der Schutzgruppe mit 1N HCl und Aufreinigung mittels semipräparativer HPLC konnte enantiomerenreines [18F]Flubatine in einer radiochemischen Ausbeute von 70±5% und einer spezifischen Aktivität >750 GBq/µmol erhalten werden.

Schlussfolgerungen: Die Radiosynthese von [18F]Flubatine konnte durch den Einsatz des neuen, enantiomerenreinen Präkursors entscheidend verbessert werden und ermöglicht eine automatisierte Produktion zur klinischen Evaluierung des Radioliganden.

  • Lecture (Conference)
    20. Jahrestagung der AG Radiochemie/Radiopharmazie der DGN, 04.-06.10.2012, Bad Honnef, Deutschland

Publ.-Id: 17802

Severe accident research in the core degradation area: An example of effective international cooperation between the European Union (EU) and the Commonwealth of Independent States (CIS) by the International Science and Technology Center

Bottomleya, D.; Stuckert, J.; Hofmann, P.; Tocheny, L.; Hugon, M.; Journeau, C.; Clément, B.; Weber, S.; Guentay, S.; Hozer, Z.; Herranz, L.; Schumm, A.; Oriolo, F.; Altstadt, E.; Krause, M.; Fischer, M.; Khabensky, V. B.; Bechta, S. V.; Veshchunov, M. S.; Palagin, A. V.; Kiselev, A. E.; Nalivaev, V. I.; Goryachev, A. V.; Zhdanov, V.; Baklanov, V.

The International Science and Technology Center (ISTC) was set up in Moscow to support nonproliferation of sensitive knowledge and technologies in biological, chemical and nuclear domains by engaging scientists in peaceful research programmes with a broad international cooperation. The paper has two following objectives:

1) to describe the organization of complex, international, experimental and analytical research of material processes under extreme conditions similar to those of severe accidents in nuclear reactors and,
2) to inform briefly about some results of these studies.
The main forms of ISTC activity are Research Projects and Supporting Programs. In the Research Projects informal contact expert groups (CEGs) were set up by ISTC to improve coordination between adjacent projects and to encourage international collaboration. The European Commission was the first to use this. The CEG members – experts from the national institutes and industry – evaluated and managed the projects’ scientific results from initial stage of proposal formulation until the final reporting. They were often involved directly in the project’s details by joining the Steering Committees of the project. The Contact Expert Group for Severe Accidents and Management (CEG-SAM) is one of these groups, five project groups from this area from the total of 30 funded projects during 10 years of activity are detailed to demonstrate this: (1) QUENCH-VVER from RIAR, Dimitrovgrad and IBRAE, Moscow, and PARAMETER projects (SF1–SF4) from LUCH, Podolsk and IBRAE, Moscow; these concerned a detailed study of bundle quenching from high temperature; (2) Reactor Core Degradation; a modelling project simulating the fuel
rod degradation and loss of geometry from IBRAE, Moscow; (3) METCOR projects from NITI, St. Petersburg on the interaction of core melt with reactor vessel steel; (4) INVECOR project, NNE Kurchatov City, Kazakhstan; this is a large-scale facility to examine the vessel steel retention of 60 kg corium during the decay heat; and finally, (5) CORPHAD and PRECOS projects, NITI, St. Petersburg undertook a systematic examination of refractory ceramics relevant to in-vessel and ex-vessel coria, particularly examining poorly characterised, limited data or experimentally difficult systems.

Keywords: Severe accident management; core melt down; nuclear reactors; in-vessel melt retention

Publ.-Id: 17801

Impact of 5-lipoxygenase inhibitors on the spatiotemporal distribution of inflammatory cells and neuronal COX-2 expression following experimental traumatic brain injury in rats

Härtig, W.; Michalski, D.; Seeger, G.; Voigt, C.; Donat, C. K.; Dulin, J.; Kacza, J.; Meixensberger, J.; Arendt, T.; Schuhmann, M. U.

Inflammation induced by traumatic brain injury (TBI) is considered as contributor to neuronal death with poor outcome. Although anti-inflammatory strategies were beneficial in experimental TBI, clinical translations mostly failed, probably caused by the complexity of involved cells and mediators. We recently showed in a rat model of controlled cortical impact (CCI) that leukotriene inhibitors (LIs) attenuate contusion growth and improve neuronal survival. This study focuses on spatiotemporal characteristics of macrophages and granulocytes, typically involved in inflammatory processes, and neuronal COX-2 expression. Further, effects of LIs (Boscari/MK-886) were evaluated by quantifying CD68+, CD43+ and COX-2+ cells 24 and 72 h post-CCI in the parietal cortex (PC), CA3 region (CA3r), dentate gyrus (DG) and visual/auditory cortex (v/aC). Correlations were applied to identify inter-cellular relationships. At 24 h, untreated animals showed granulocytes in all regions investigated, decreasing towards 72 h. In contrast, macrophages increased from 24 to 72 h post-CCI in the PC and v/aC. COX-2+ neurones showed no temporal dynamics, except of an increase in the CA3r towards 72 h. Treatment reduced granulocytes at 24 h in the pericontusional penumbra and hippocampus, and reduced macrophages at 72 h in the PC and v/aC. COX-2 expression remained unaffected by LIs, except of time-specific reactions in the DG (increase/decrease at 24/72 h). Interrelations confirmed concomitant cellular reactions beyond initial trauma site. In conclusion, LIs attenuated the cellular inflammatory response following CCI and therefore become attractive as potential treatment strategy. Future studies should clarify region-specific effects and feasible time windows for applying LIs after CCI.

Keywords: Traumatic brain injury; Neuronal death; Macrophage; Granulocyte; COX-2

Publ.-Id: 17800

Reconstruction of Gebel Kamil’s irradiation history

Merchel, S.; Akhmadaliev, S.; Fimiani, L.; Haubold, R.; Herrmann, S.; Korschinek, G.; Ott, U.; Pavetich, S.; Rugel, G.

Data of the lighter cosmogenic radionuclides 10Be, 26Al, 36Cl, and 41Ca are now easily attainable at the accelerator mass spectrometry facility DREAMS [1]. Accompanied by the heavier radionuclides 53Mn and 60Fe, which are measured at the 14 MV tandem at Munich, and stable noble gas nuclides from MPI Mainz, complete and unique exposure histories of extraterrestrial material can be reconstructed.
One of the first meteorites investigated by this team is Gebel Kamil, an ungrouped Ni-rich ataxite that produced an impact crater (Ø: 45 m) in southern Egypt. Two neighboured shrapnel (S) samples and two from the only individual (I) fragment (~83 kg) have been analysed. Comparison with Monte-Carlo calculations of production rates indicate that Gebel Kamil was exposed as a meteoroid body of >120 cm radius. Samples I originate from a moderate shielding of 18-25 cm, whereas samples S are from a deeper position of 53-65 cm. Most reliable 36Cl-36Ar ages of I and S are ~450 Ma calculated after [3].
Ackn.: L. Folco (meteorite) & accelerator crews (support AMS). Ref.: [1] Akhmadaliev et al. (2012) NIMB, in print. [2] Folco et al., Science 329 (2010) 804. [3] Ammon et al., MAPS 44 (2009) 485.

Keywords: cosmogenic; AMS; meteorite

Related publications

  • Lecture (Conference)
    Joint meeting “Paneth Kolloquium”, “The first 10 million years of the solar system” (DFG SPP 1385) & “MEMIN” (DFG FOR 887), 09.-12.10.2012, Nördlingen, Duetschland

Publ.-Id: 17799

Growth mode and texture development in Ni-Ti shape memory alloy (SMA) films during co-sputtering deposition – An in situ synchrotron radiation study

Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.

In-situ X-ray scattering measurements were carried out during Ni-Ti shape memory alloy film processing at the Rossendorf Beamline (BM20-ESRF). The experiments performed with a two-magnetron sputter deposition chamber mounted into the six-circle diffractometer of the beamline enabled us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters (Ti target power) during film growth. The results show that the type of substrate plays an important role for the preferential orientation of sputtered Ni-Ti films. Amorphous SiO2 and TiN buffer layers were used to successfully control their crystallographic orientations. The deposition conditions leading to films mainly containing grains with (100) or (110) planes of the B2 phase parallel to the film surface are presented. The control of texture is an important achievement since it has a strong influence on the extent of the strain recovery of the Ni-Ti films. The deposition of graded Ni-Ti films by deliberately changing the Ti:Ni ratio, thereby altering microstructure and transformation temperatures across the film thickness, provided significant data for the optimisation of the deposition parameters in order to fabricate films with a “two-way” actuation (films with a combination of superelasticity and shape memory characteristics). This is a plus for the miniaturization of Ni–Ti films based devices in the field of micro-electro-mechanical systems since no consideration has to be paid to a resetting spring.

Related publications

  • Poster
    MPA 2012 – 6th International Meeting on Developments in Materials, Processes and Applications of Emerging Technologies, 02.-04.07.2012, Alvor, Portugal

Publ.-Id: 17798

Terahertz nonlinear optics of excitons in quantum wells using a free-electron laser

Helm, M.

Keywords: terahertz; quantum well; free electron laser; exciton

Related publications

  • Invited lecture (Conferences)
    Viennese Symposium on Heterostructures, 07.09.2012, Wien, Österreich

Publ.-Id: 17797

Modification of Ni-Ti surface composition and morphology by plasma immersion ion implantation for biomedical applications

Martins, R. M. S.; Barradas, N.; Alves, E.; Henke, D.; Reuther, H.; Schell, N.; Carmezim, M. J.; Silva, T. M.; Fernandes, J. C. S.

The shape memory effect and superelasticity of Ni-Ti (Nitinol) make it very attractive for biomedical applications. The Ni-Ti alloy (~ 50.4 at.% Ni) selected for this work is austenitic (superelastic) at body temperature. In the frame of the AIM-74 and SPIRIT-77 projects, plasma immersion ion implantation (PIII) has been employed to modify and improve the superficial region of the alloy. The formation of titanium oxynitride (TiNxOy) was achieved by ion implantation of nitrogen. A Ti-rich oxide layer was obtained during the experiments carried out with oxygen. Thus, the parameters to obtain a Ni-depleted surface, which serves as a barrier to out-diffusion of Ni ions from the bulk material, have been successfully established. Furthermore, nanostructured Ni-Ti surfaces have been produced. Synchrotron radiation-based X-ray diffraction data acquired in transmission mode show that the PIII technique only changes the structure of the Ni-Ti alloy top layer preserving superelastic behaviour at body temperature (PIII experiments carried out without intentional heating of the substrate holder). Techniques like thermal oxidation and nitriding also lead to an improved corrosion resistance and Ni-depleted Ni-Ti surface but require high processing temperatures leading to modification of the phase transformation characteristics and loss of specific mechanical properties.

Related publications

  • Lecture (Conference)
    MPA 2012 - 6th International Meeting on Developments in Materials, Processes and Applications of Emering Technologies, 02.-04.07.2012, Alvor, Portugal

Publ.-Id: 17796

Supernova Dust in Terrestrial Deep-Sea Archives

Feige, J.; Wallner, A.; Fifield, L. K.; Korschinek, G.; Merchel, S.; Rugel, G.; Winkler, S. R.

The long-lived radionuclides 26Al, 53Mn and 60Fe are produced in the late burning phases and during a supernova explosion of a massive star. These nuclides are then ejected into space, condensed into dust and, if the supernova occurs in a close distance to the solar system, might be able to reach the Earth. An indication for a close-by supernova in the past, deduced from a signal about 2 Myr ago, has already been identified in a ferromanganese crust [1]. Deep-sea sediments, with higher accumulation rates, provide a higher time resolution and allows therefore a more precise dating of the signal.
Here, samples of two sediment cores originating from the Indian Ocean are analyzed to search for supernova signals. Currently, the only method sensitive enough to detect these signals is accelerator mass spectrometry. Additionally to the supernova-produced nuclides, 10Be, which is constantly produced by cosmic rays in the Earth's atmosphere, is measured to date the sediment cores. First 10Be and 26Al data are presented and discussed.
[1] Knie, K., et al. (2004), Phys. Rev. Lett. 93, 17.

Keywords: supernovae; AMS; radionuclide

Related publications

  • Poster
    Joint meeting “Paneth Kolloquium”, “The first 10 million years of the solar system” (DFG SPP 1385) & “MEMIN” (DFG FOR 887), 09.-12.10.2012, Nördlingen, Deutschland

Publ.-Id: 17795

Radiosynthesis of racemic and enantiomerically pure (–)-[18F]flubatine – A promising PET radiotracer for neuroimaging of α4β2 nicotinic acetylcholine receptors

Fischer, S.; Hiller, A.; Smits, R.; Hoepping, A.; Funke, U.; Wenzel, B.; Cumming, P.; Sabri, O.; Steinbach, J.; Brust, P.

(–)-[18F]flubatine is a promising agent for visualization by PET of cerebral α4β2 nicotinic acetylcholine receptors (nAChRs), which are implicated in psychiatric and neurodegenerative disorders. Here, we describe a substantially improved two-step radiosynthesis strategy for (–)-[18F]flubatine, based on the nucleophilic radiofluorination of an enantiomerically pure precursor followed by deprotection of the intermediate. An extensive leaving group/protecting group library of precursors was tested. Application of a trimethylammonium-iodide precursor with a Boc protecting group provided the best results: Labeling efficiencies of 80-95%, RCY of 60±5%, radiochemical purity of >98%, and a specific activity of >350 GBq/µmol. The radiosynthesis is easily transferable to an automated synthesis module.

Keywords: Fluorine-18; Positron emission tomography; Neuroimaging; α4β2 nicotinic acetylcholine receptors; α4β2 ligands; Radiosynthesis; Leaving groups; Protecting groups

Publ.-Id: 17794

PET/MR for therapy response evaluation in malignant lymphoma: initial experience

Platzek, I.; Beuthien-Baumann, B.; Langner, J.; Popp, M.; Schramm, G.; Ordemann, R.; Laniado, M.; Kotzerke, J.; van den Hoff, J.

Object: To evaluate the feasibility of positron emission tomography/magnetic resonance imaging (PET/MR) with 18fluoro-2-deoxyglucose (FDG) for therapy response evaluation of malignant lymphoma.
Materials and methods: Nine patients with malignant lymphoma who underwent FDG-PET/MR before and after chemotherapy were included in this retrospective study. Average time between the two scans was 70 days. The scans were evaluated independently by two nuclear medicine physicians. The Ann Arbor classification was used to describe lymphoma stage. Furthermore, the readers also rated PET image quality using a five point scale. Weighted kappa was used to calculate interrater agreement.
Results: The initial scan showed foci of increased FDG uptake in all patients, with Ann Arbor stage varying between I and IV. In the follow-up examination, all but one patient showed complete response to chemotherapy. PET image quality was rated as very good or excellent for all scans. Interrater agreement was excellent regarding Ann Arbor stage (kappa = 0.97) and good regarding image quality (kappa = 0.41). Conclusion PET/MR shows promising initial results for therapy response evaluation in lymphoma patients.

Keywords: PET; MRI; Lymphoma

Publ.-Id: 17793

PET/MR in head and neck cancer: initial experience

Platzek, I.; Beuthien-Baumann, B.; Schneider, M.; Gudziol, V.; Langner, J.; Schramm, G.; Laniado, M.; Kotzerke, J.; van den Hoff, J.

Purpose: To evaluate the feasibility of PET/MRI (positron emission tomography/magnetic resonance imaging) with FDG (18F-fluorodeoxyglucose) for initial staging of head and neck cancer.
Methods: The study group comprised 20 patients (16 men, 4 women) aged between 52 and 81 years (median 64 years) with histologically proven squamous cell carcinoma of the head and neck region. The patients underwent a PET scan on a conventional scanner and a subsequent PET/MRI examination on a whole-body hybrid system. FDG was administered intravenously prior to the conventional PET scan (267–395 MBq FDG, 348 MBq on average). The maximum standardized uptake values (SUVmax) of the tumour and of both cerebellar hemispheres were determined for both PET datasets. The numbers of lymph nodes with increased FDG uptake were compared between the two PET datasets.
Results: No MRI-induced artefacts where observed in the PET images. The tumour was detected by PET/MRI in 17 of the 20 patients, by PET in 16 and by MRI in 14. The PET/MRI examination yielded significantly higher SUVmax than the conventional PET scanner for both the tumour (p<0.0001) and the cerebellum (p00.0009). The number of lymph nodes with increased FDG uptake detected using the PET dataset from the PET/MRI system was significantly higher the number detected by the stand-alone PET system (64 vs. 39, p00.001).
Conclusion: The current study demonstrated that PET/MRI of the whole head and neck region is feasible with a wholebody PET/MRI system without impairment of PET or MR image quality.

Keywords: PET/MRI; Head and neck cancer

Publ.-Id: 17792

Intraband carrier dynamics in quantum dots and quantum wells

Bhattacharyya, J.; Zybell, S.; Winnerl, S.; Hopkinson, M.; Wilson, L. R.; Andrews, A. M.; Strasser, G.; Helm, M.; Schneider, H.

Optical properties of self assembled quantum dots (QDs) have dominant inhomogeneous broadening due to the distribution of size and composition of the QDs in the ensemble. The carrier dynamics in such systems is affected by the neighboring dots due to interdot diffusion of carriers. In this work we investigate the intraband relaxation mechanisms in the QDs. We performed time-resolved photoluminescence (PL) quenching measurements on InAs/GaAs self assembled QDs. The samples were excited by near infrared laser pulses and the time and wavelength resolved PL was measured by a streak camera. During the decay of the PL, a THz pulse from a free electron laser, tuned to the intersublevel transition energy of the QDs, was made incident on the sample. This THz pulse induced quenching of the PL, shown by the dip in Fig.1, by re-exciting carriers to higher levels within the QDs. These carriers eventually relaxed back to the ground state (s-state) resulting in the recovery of the s-state PL intensity. Thus, the recovery of the PL was directly related to carrier relaxation dynamics in the QDs. The mechanisms involved were (i) ISL relaxation, where the excited carriers in the QDs directly fell back into the s-state of the same dot and (ii) transfer to adjacent dots via the wetting layer by multiphoton absorption or tunneling. To distinguish these two effects we performed measurements on two samples grown simultaneously but post-growth annealed at different temperatures resulting in different ISL relaxation times of 60 ps and 1.5 ns. From rate equation model fit of the measured data we found that the recovery time of the quenched PL was independent of the ISL relaxation times. This implied that the carrier relaxation within the dots was dominated by mechanisms other than ISL transition. Comparison of the amount of recovered PL signals for different emission energies showed that there was loss of carriers at higher PL energies, as showed in Fig.1(a), and gain of carriers after recovery for lower emission energies [Fig.1(b)]. This indicates carrier transfer among adjacent QDs. Therefore, even for quite low QD densities (4 x 10^10 cm-2 for our samples), interdot carrier transfer plays an important role in intraband carrier relaxation in self assembled QDs.

Keywords: Photoluminescence quenching; FEL; Intraband transition; quantum dots; quantum well

Related publications

  • Lecture (Conference)
    International conference on superlattices, nanostructures and nanodevices, 22.-27.07.2012, Dresden, Germany

Publ.-Id: 17791

Alpha self-irradiation effect on the local structure of the U0.85Am0.15O2+x solid solution

Prieur, D.; Martin, P. M.; Lebreton, F.; Delahaye, T.; Jankowiak, A.; Laval, J.-P.; Scheinost, A. C.; Dehaudt, P.; Blanchart, P.

Uranium–americium mixed oxides are promising fuels for achieving an efficient Am recycling. Previous studies on U0.85Am0.15O27x materials showed that the high a activity of 241Am induces pellet swelling which is a major issue for cladding materials design. In this context, X-ray Diffraction and X-ray Absorption Spectroscopy measurements were used to study self-irradiation effects on U0.85Am0.15O27x local structure and to correlate these results with those obtained at the macroscopic scale. For a cumulative a decay dose equal to 0.28 dpa, it was shown that non-defective fluorite solid solutions were achieved and therefore, that the fluorite structure is stable for the studied doses. In addition, both interatomic distance and lattice parameter expansions were observed, which only partially explains the macroscopic swelling. As expected, an increase of the structural disorder with self-irradiation was also observed.

Keywords: XAFS; self-irradiation; nuclear fuel; nuclear waste; Am

Related publications

Publ.-Id: 17790

Moderating material to compensate the drawback of high minor actinide containing transmutation fuel on the feedback effects in SFR cores

Merk, B.

The use of fine distributed moderating material to enhance the feedback effects and to reduce the sodium void effecting SFRs is described. The drawback on the feedback effects due to the introduction of minor actinides into SFR fuel is analyzed. The possibility of compensation of the effect of the minor actinides on the feedback effects by the use of fine distributed moderating material is demonstrated. The consequences of the introduction of fine distributed moderating material into fuel assemblies with fuel configurations foreseen for minor actinide transmutation is analyzed and the positive effects on the transmutation efficiency are shown. Finally, the possible increase of the Americium content to improve the transmutation efficiency is discussed, the limit value of Americium is determined and the possibilities given by an increase of the Hydrogen content are analyzed.

Keywords: enhanced feedback; transmutation; fast reactror; Americium; Curium

Publ.-Id: 17789

Thermal stability of moderating material used to enhance the feedback coefficients in SFR cores

Merk, B.

Recently, the use of moderating materials in fuel assemblies for Sodium cooled fast reactors has been investigated and published in several papers (e. g. Annals of Nuclear Energy 38, 5, Annals of Nuclear Energy 38, 11 (2011)). Especially the fine distribution of the moderating material in a layer inside the fuel rod or inside the wire spacer has shown very promising results for the enhancement of the feedback coefficients. Additionally, this arrangement is very attractive since it causes only a very limited influence on the safety relevant fuel assembly structure and on the operational parameters. A detailed investigation on the use of moderating material for transmutation fuels has proven that a compensation of the negative influence on the feedback coefficients caused by the Minor Actinides is possible. The critics on the limited thermal stability of the suggested ZrH based moderating material has been a major issue in the discussion of all up to now published publications. In this work the problem will be solved with the help of t change of the hydrogen bearing metal compound. In a first step an overview on possible metal materials will be given and properties as well as manufacturing issues will be discussed. Additionally, an insight will be given into the relationship of the hydrogen content of the compound and the resulting thermal stability. Based on this relation the reasons for the choice of Yttrium are described. In a second step the transferability of the old results gained for ZrH will be proven by a detailed comparison of different important reactor physical parameters for cases using identical amounts of ZrH and YH.
Thermal stability of the moderating material up to more than 1300°C can be ensured by the use of Yttrium-mono-hydride as moderating material. The topic will be closed by a survey on the existing operation experience with YH in fast reactors and a comparison of the raw material costs for Zirconium and Yttrium.

Keywords: fast reactor; enhanced feedback effects; moderating material; Yttrium hydride; thermal stability

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

Publ.-Id: 17788

The Molten Salt Fast Reactor as Transmutation System

Merk, B.; Rohde, U.; Scholl, S.

The basic development and design of a molten salt reactor with fast neutron spectrum (Molten Salt Fast Reactor – MSFR) is the target of the EVOL project in FP7. The MSFR offers certain advantages in the view of transmutation compared to solid fuelled reactor types. In the first part, these advantages will be discussed in a comparison with the sodium cooled fast reactor technology and the research challenges will be analyzed. In the second part, cycle studies for the MSFR, based on the EVOL benchmark design, will be given for different configurations – core with U-238 fertile, a fertile free core and a core with Th-232 as fertile material. For all cases, the transmutation potential will be determined and a significant improvement in the transmutation performance for the case with Th as fertile will be demonstrated. The time evolution of different important isotopes will be analyzed. Additionally, the used tool HELIOS 1.10 and the adaptations needed for the simulation of a MSFR will be described.

Keywords: molten salt fast reactor; molten salt reactor; fast reactor; transmutation

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

Publ.-Id: 17786

Progress in fast reactor operation and new trends to increased inherent safety

Merk, B.; Stanculescu, A.; Chellapandi, P.; Hill, R.

The reasons for the renewed interest in fast reactors and an overview of the progress in sodium cooled fast reactor operation and design in the last ten years is given. The relevance of feedback effects for safe reactor design is described, and a new method for the enhancement of feedback effects in fast reactors is proposed. The excellent operational performance of sodium cooled fast reactors in this period is highlighted as a sound basis for the development of new fast reactors. Experimental reactors demonstrating the inherent safety of advanced sodium cooled fast reactor designs are described and the potential safety improvements resulting from the use of fine distributed moderating material are demonstrated. Finally, the fast reactor specifics are analysed with regard to the Fukushima accident.

Keywords: fast reactor history; fast reactor technology; enhanced feedback; inherent safety

Publ.-Id: 17785

Sorption of Se(VI) and Se(IV) oxyanions onto maghemite: a macroscopic and spectroscopic study

Jordan, N.; Ritter, A.; Foerstendorf, H.; Scheinost, A. C.; Heim, K.; Weiß, S.; Brendler, V.

79Se, a long-lived (t1/2 ~ 3.27 × 105 years) and radiotoxic fission product, was identified by safety performance assessments to be one of the most contributing isotopes to the total radioactivity that could be potentially released to the biosphere. Selenium has a quite complex speciation, with four main oxidation states, depending on both the pH and the redox potential of the surrounding environment. Sorption of selenium oxyanions onto mineral surfaces (iron, alumina, titanium oxides and clays) has been extensively investigated based on batch experiments and spectroscopic studies. However, the sorption processes of selenium oxyanions onto maghemite was not explicitly studied before and thus the potential ability of maghemite to significantly retard selenium migration in the environment is therefore still unknown. Maghemite was identified as a corrosion product of steel waste canisters and iron archaeological analogues, and is also a ubiquitous mineral in the environment.
In this work, we investigated in detail the sorption of selenium(VI) and selenium(IV) onto maghemite (γ-Fe2O3), for the first time. The effect of pH and ionic strength was studied by batch experiments. Sorption of both oxyanions onto maghemite was found to decrease with increasing pH. An increase of the ionic strength (from 0.01 M to 0.1 M) impacted the sorption of selenium(VI), while it had no significant effect for selenium(IV) uptake. Electrophoretic mobility measurements revealed that the isoelectric point (pHIEP) of maghemite was shifted to lower pH values upon selenium(IV) sorption, while it was not significantly modified upon selenium(VI) sorption. By combining EXAFS and in situ ATR FT-IR spectroscopic measurements, the formation of inner-sphere complexes during selenium(IV) sorption onto maghemite was observed. Selenium(VI) sorption proceeded via the formation of predominant outer-sphere complexes (together with a small amount of inner-sphere complexes).

Keywords: selenium; sorption; EXAFS; IR; maghemite

Related publications

  • Lecture (Conference)
    Selen2012 - Selenium in geological, hydrological and biological systems, 08.-09.10.2012, Karlsruhe, Germany

Publ.-Id: 17784

Inertial wave observations in liquid metal by means of ultrasound Doppler velocimetry

Räbiger, D.; Vogt, T.; Franke, S.; Eckert, S.; Gerbeth, G.; Czarske, J.

This experimental study considers the transient flow inside a liquid metal column exposed to a pulsed rotating magnetic field. To measure two-dimensional velocity fields of the secondary flow in the radial-meridional plane a novel ultrasound Doppler system was used. A linear ultrasound transducer array equipped with 25 transducer elements is used to measure the flow field in a square plane of 67 x 67 mm². The application of advanced processing techniques like a simultaneous excitation of multiple transducer elements and a segmented array technique enable high data acquisition rates as well as a high spatial resolution. The measurements revealed transient flow regimes showing distinct inertial oscillations and coherent vortex structures.

Keywords: Ultrasound Doppler method; flow field measurements; electromagnetic stirring; rotating magnetic field; inertial waves; flow control

  • Lecture (Conference)
    ISUD8 - 8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Deutschland
  • Contribution to proceedings
    ISUD8 - 8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Deutschland

Publ.-Id: 17783

Magnetic properties of Co/Pd multilayers films deposited on GaSb nanocones

Ball, D. K.; Günther, S.; Fritzsche, M.; Lenz, K.; Varvaro, G.; Makarov, D.; Mücklich, A.; Facsko, S.; Fassbender, J.; Albrecht, M.

The magnetic properties of ferromagnetic thin films fabricated on nanostructured templates is strongly affected by the surface morphology. Low energy ion irradiation of GaSb yields to a self organized hexagonal pattern that can serve as templates for subsequent deposition of magnetic films.
In this respect, curvature effects and influence of pattern symmetry result in a substantial modification of the magnetization reversal behavior of individual magnetic nanostructures and their assemblies.
Curvature-driven changes can be beneficial to reduce the switching field, which is advantageous for magnetic data storage applications, especially for the recording concept known as bit patterned media (BPM). In the BPM concept, an individual bit will be stored in a single magnetic nanostructure. Candidates for a recording layer are films with strong out-of-plane magnetic anisotropy (Ku) such as hard magnetic FePt alloys and [Co/Pd(Pt)]n multilayers.
Here, we aim at the fabrication of arrays of magnetic [Co/Pd]n multilayers on top of selfassembled nanocone templates created on GaSb(100) single crystal using a Ar+ ion erosion technique. By tailoring the irradiation conditions, the self-organized assemblies of nanocones were modified in size and periodicity. Due to the self-organization, large patterned areas can be fabricated which is challenging using e-beam lithography.
Macroscopic magnetic measurements performed using vector-VSM magnetometry (vVSM) indicate that all samples possess the magnetic easy axis perpendicular to the cone surface. The remanence as well as the coercivity decreases with increasing cone size, as the letter leads to a larger angular spread of easy axis following the morphology of the pattern. Additionally, MFM characterization shows that in the case of small cone structures the underlying cone pattern results in a pinning of magnetic domain walls on cone locations as there is a clear correlation between the morphology and positions of magnetic domain walls. For larger cone sizes, exchange decoupled magnetic caps are achieved with single domain areas confined to the cones apexes.

Related publications

  • Poster
    Joint European Magnetic Symposia (JEMS 2012), 09.-14.09.2012, Parma, Italien

Publ.-Id: 17782

NMR Investigations of the intra- and intermolecular exchange phenomena of the 3,5-dimethylpyrazolylsilane ClSi(pz*) and related compounds

Bitto, F.; Kretzschmar, J.; Brendler, E.; Kroke, E.

Chlorine substituted 3,5-dimethylpyrazolyl (pz*) silanes exhibit interesting inter- and intramolecular exchange phenomena. Intermolecular reactions involving Si-N vs. Si-Cl dismutation cause equilibria between the three species Cl2Si(pz*)2, ClSi(pz*)3 (main component) and Si(pz*)4. Intramolecular exchange is interpreted as a “dangling” of the pz*-moieties in every pyrazolyl silane molecule itself.[1] These phenomena were investigated with one and two dimensional NMR spectroscopic methods at variable temperatures. The “dangling” of the pz*-moieties is slowed down with decreasing temperature and are best visible in the spectra recorded at -40°C. The use of 1H-29Si-HMBC spectroscopy (heteronuclear multiple bond correlation) allows to assign the olefinic protons to the corresponding silicon species. In the EXSY (exchange spectroscopy) spectra the exchange between the pz*-methyl groups and the NOE (nuclear overhauser effect) correlation between the methyl groups and the olefinic protons are observed at the same time in one spectrum. The data obtained with EXSY and HMBC-spectroscopy in combination with variable temperature 1H NMR allows qualitative conclusions concerning the rate of exchange and the dependence on the silicon corresponding species.

[1] F. Bitto, J. Wagler, E. Kroke, Eur. J. Inorg. Chem. 2012, in press, doi:10.1002/ejic.201101409.

Keywords: NMR spectroscopy; H,Si-HMBC; H,H-NOESY, H,H-EXSY; 3,5-dimethylpyrazolyl silanes

  • Poster
    4th EuCheMS Chemistry Congress, 26.-30.08.2012, Prag, Tschechische Republik

Publ.-Id: 17781

Dual-beam irradiation of friction stir spot welding of nanostructured ferritic oxide dispersion strengthened alloy

Chen, C.-L.; Richter, A.; Kögler, R.; Wu, L.-T.

Friction stir spot welding (FSSW) is a very promising technique for the joining of oxide dispersion strengthened (ODS) materials without oxide particle agglomeration and loss in mechanical properties in the weld zone. Heating and severe plastic deformation can significantly alter the originally as-received material. The local microstructure determines the weld mechanical properties, which are analyzed by nanointendation. The FSSW region consists of three different zones: the base material, the thermo-mechanically affected zone and the heat affected zone. Irradiation of the FSSW area was performed with a Fe+/He+ dual ion beam. Hardness changes within the welding zones and variation with irradiation damage are discussed.

Keywords: Nanostructured material; oxide dispersion strengthened (ODS) alloys; friction stir welding; nanoindentation; irradiation damage

Related publications

Publ.-Id: 17780

Neutronic analysis of SFR core with HELIOS-2, SERPENT, and DYN3D codes

Rachamin, R.; Wemple, C.; Fridman, E.

In this study, HELIOS-2 deterministic transport code and Serpent Monte-Carlo (MC) reactor physics code were considered as tools for preparation of few-group constants for sodium cooled fast reactor (SFR) analysis. Initially, applicability of the mainly LWR-oriented HELIOS-2 code to the modeling of SFR lattices was investigated and recommendations for methodological modifications were given. At the next stage the methodology for few-group cross section generation for fuel and non-multiplying regions of SFR core was proposed. Afterward, few-group constants produced by HELIOS-2 and Serpent employing the proposed methodology were used by nodal diffusion code DYN3D for the analysis of a reference SFR core. Finally, the DYN3D results were verified against the full core Serpent MC solution. The full core DYN3D results obtained using few-group constants produced by Serpent agreed very well with that of the reference full core MC simulations. The use of HELIOS-2 based few-group constants led to somewhat reduced agreement between reference MC and DYN3D results. The implementation of the suggested modifications to the HELIOS-2 methodology can potentially improve its modeling accuracy for SFR lattices.

Keywords: HELIOS-2; Serpent; Monte Carlo; DYN3D; few-group cross section generation; sodium cooled fast reactor

Publ.-Id: 17779

AMS Measurements of Supernova-Produced Radionuclides in Deep-Sea Sediment Cores

Feige, J.; Wallner, A.; Winkler, S. R.; Merchel, S.; Fifield, L. K.; Korschinek, G.; Rugel, G.

Accelerator Mass Spectrometry (AMS) provides the highest sensitivity for measurements of long-lived radionuclides with half-lives in the order of million years. We will apply this method to search for live supernova (SN)-produced radionuclides on Earth.
An indication to recent SN activity in our solar neighborhood is the existence of a thin, hot cavity in the local interstellar medium, embedding our solar system. This so called superbubble, the Local Bubble, was produced by multiple SN explosions, starting ~14 Myr ago. Nuclides, which are synthesized in massive stars and during their explosions, are then entrained in the SN shell and may be transported to the solar system, if such an event happens within a short distance.
Two deep-sea sediment cores originating from the Indian Ocean have been selected to search for the SN-produced radionuclides 26Al, 53Mn, 60Fe and 244Pu in the time range of 2-3 Myr. We aim to measure these isotopes at different laboratories with high time resolution with the goal to confirm a previously found SN signal in a ferromanganese crust from the Pacific Ocean.

Keywords: supernovae; radionuclide; AMS; sediments

Related publications

  • Poster
    62. Jahrestagung der Österreichischen Physikalischen Gesellschaft, 18.-21.09.2012, Graz, Österreich

Publ.-Id: 17778

The Search for Supernova-Produced Radionuclides in Deep-Sea Sediments with AMS

Feige, J.; Wallner, A.; Winkler, S. R.; Merchel, S.; Fifield, K. L.; Korschinek, G.

We will search for supernova-produced radionuclides in deep-sea sediment cores originating from the Indian Ocean. We aim to measure the long-lived radionuclides 26Al (t1/2 = 0.7 Myr), 60Fe (t1/2 = 2.6 Myr), 53Mn (t1/2 = 3.7 Myr) and 244Pu (t1/2= 80 Myr) at different laboratories in sediment samples with high time resolution.
A positive signal will also confirm a previous finding of an enhanced 60Fe content in a ferromanganese crust [1]. The above mentioned radionuclides are commonly synthesized in massive stars and ejected by supernova (SN) explosions. If such a SN event happens in the solar vicinity, the expanding SN envelope might hit the solar system and leave certain traces in terrestrial archives. An indication to recent SN activity is the existence of a cavity consisting of thin, hot gas in the local interstellar medium, embedding our solar system. This superbubble, called the Local Bubble, was presumably produced by 14-20 SN explosions starting 14 Myr ago [2].
Because SNe and their ejecta are a site for dust formation, there might be a chance of finding such radionuclides in dust particles deposited in such terrestrial archives, like deep-sea sediments. The measurements will be carried out with accelerator mass spectrometry (AMS) utilizing laboratories with the highest sensitivities for these long-lived radionuclides.
[1] K. Knie, et al., Physical Review Letters 93, 17 (2004).
[2] B. Fuchs et al., Monthly Notices of the Royal Astronomical Society 373, 993-1003 (2006).

Keywords: supernovae; AMS; radionuclide; sediments

Related publications

  • Poster
    496. Wilhelm und Else Heraeus-Seminar - Astrophysics with modern small-scale accelerators, 06.-10.02.2012, Bad Honnef, Deutschland

Publ.-Id: 17777

Supernova-Dust in Deep-Sea Sediment Cores

Feige, J.; Wallner, A.; Winkler, S. R.; Merchel, S.; Fifield, L. K.; Korschinek, G.; Rugel, G.

Because supernovae (SNe) and their ejecta are a site for dust formation, there might be a chance of finding supernova-produced radionuclides in dust particles deposited in terrestrial archives, like deepsea sediments. Measurements will be carried out with Accelerator Mass Spectrometry (AMS), which provides the highest sensitivity for measurements of long-lived radionuclides with half-lifes in the order of million years.
An indication to recent SN activity in our solar neighborhood is the existence of a thin, hot cavity in the local insterstellar medium, embedding our solar system. This so called superbubble, the Local Bubble, was produced by multiple SN explosions, starting ~14 Myr ago (Fuchs et al. 2006). Nuclides, which are synthesized in massive stars and during their explosions, are then entrained in the SN shell, condensed into dust, and may be transported to the solar system and thus into Earth archives, if such an event happens within a short distance.
Two deep-sea sediment cores originating from the Indian Ocean have been selected to search for the SN-produced radionuclides 26Al, 53Mn, 60Fe and 244Pu in the time range of 2-3 Myr. We aim to measure these isotopes at different laboratories with high time resolution with the goal to confirm a previously found SN signal in a ferromanganese crust from the Pacific Ocean (Knie et al. 2004),

Keywords: supernovae; AMS; radionuclide; sediments

Related publications

  • Poster
    International conference of the European Science Foundation EuroGENESIS CoDustMas network action, 05.-08.11.2012, Ascona, Schweiz

Publ.-Id: 17776

AMS within CoDustMas: Nanodiamonds and SN-signatures

Wallner, A.; Vockenhuber, C.; Güttler, D.; Feige, J.; Fifield, L. K.; Korschinek, G.; Melber, K.; Merchel, S.; Ott, U.; Paul, M.; Rugel, G.; Steier, P.; Tims, S.

Via accelerator mass spectrometry (AMS) two relevant aspects to dust formation and evolution are studied in the laboratory: First, the measurement of trace element isotope ratios in presolar nanodiamonds isolated from meteorites, e.g. isotope ratios of stable Pt isotopes to extract r-process nucleosynthesis signatures. Recent experiments demonstrate the applicability of AMS for measuring Pt isotope signatures in material from the Allende meteorite [1,2]. The second aspect relates to the search for live supernova (SN)-produced radionuclides in terrestrial deep-sea archives [3-5]. In particular, we focus on longer-lived isotopes with half-lives of the order of million years. Previous time-resolved measurements of a deep-sea manganese crust identified a clear 60Fe enrichment about 2.5 Ma in the past [6]. This anomaly is interpreted as evidence for a nearby SN. With improved time resolution we continue this search by investigating two deep-sea sediment cores from the Indian Ocean for a possible signal of the SN-candidates 26Al, 53Mn, 60Fe, and potentially 244Pu [7].
An overview of the technique of AMS will be given and its potential for such studies and some selected applications will be discussed. In particular, the experimental proof of r-process scenarios via the direct observation of nuclides generated in the r-process such as the significance of new data for Pt isotope ratios measured in nanodiamonds will be presented and new technical approaches will be detailed [1,2]. We will exemplify the high sensitivity of AMS via the search of r-process 244Pu complementing the recent finding of live 60Fe in a manganese crust.
References: [1] U. Ott et al. PASA 29 (2012) 90; [2] A. Wallner et al. NIMB (2012); [3] J. Ellis et al., AstrophysJ. 470 (1996) 1227; [4] G. Korschinek et al., Radiocarbon 38 (1996) 68; [5] M. Paul et al., J.Radioanal.Nucl.Chem. 272, (2007) 243; [6] K. Knie et al. PRL 93 (2004) 171103; [7] J. Feige et al. PASA 29 (2012) 109.

Keywords: AMS; supernova; radionuclide; presolar grains; nanodiamonds; deep-sea sediments; meteorite

Related publications

  • Poster
    International conference of the European Science Foundation EuroGENESIS CoDustMas network action, 05.-08.11.2012, Ascona, Schweiz

Publ.-Id: 17775

Evidences for a more restricted Icelandic Ice cap re-advance after the Bølling warming period

Meriaux, A.-S.; Delunel, R.; Merchel, S.; Finkel, R. C.

Moraines dated north of Vatnajökull by cosmogenic surface exposure dating show that the Icelandic Ice cap (IIS) was less extended during the Younger Dryas than previously suggested. The data imply that this glacial advance was more complex and restricted in some glacial valleys in NE Iceland. While the IIS margins are relatively well constrained offshore by marine or coastal evidences, little is known about their onshore characteristics and rates of recession during the warmer Holocene periods. This is especially the case in the NE of Iceland where volcanic activity and major outburst floods (jökulhlaups) have removed a large amount of morphological evidences of past ice margins. Our study aimed at filling this chronological gap of the IIS inland during the late Quaternary deglaciation by dating past preserved ice margins using 36Cl and 3He cosmogenic nuclides. We studied moraines and outwash located 44 km, 48 km and 60 km north of Vatnajökull, between the Jökulsà à Fjöllum and Jökulsà à Brú, the main northern glacial river systems draining the icecap. Preliminary 36Cl ages of the northernmost moraine at Skessugardur, 60 km north of present-day IIS and 65 km away from the coastline, indicate that the minimum exposure ages derived from Ca-rich plagioclases range from 11.0 ± 1.2 ka to 13.4 ± 1.4 ka with an average at 12.2 ± 1.0 ka (±1 sigma=6), using the local Icelandic production rates for Ca spallation of Licciardi et al. (2008). These ages are close to the Younger Dryas at a time when the Icelandic Ice Sheet is thought to have re-advanced further north toward the coastline. Overall, our results call for a revision of our understanding of the IIS deglaciation history and provide new tie-points for the calibration of the IIS models.
References: Licciardi et al., EPSL 267 (2008) 365–377.

Keywords: Ice sheets; Quaternary geochronology; Cosmogenic-nuclide exposure dating; AMS; TCN; radionuclide

  • Poster
    American Geophysical Union, Fall Meeting 2012, 03.-07.12.2012, San Francisco, USA

Publ.-Id: 17774

Decadal to Millennial scale erosion rates in the Nepal Himalayas

Andermann, C.; Bonnet, S.; Gloaguen, R.; Crave, A.; Merchel, S.; Braucher, R.; Bourlès, D. L.

On a sub-millennial time scale the spatial distribution of erosion is controlled to first order by tectonics, relief, and possibly precipitation, and secondly by vegetation, lithology, temperature and human activity. The Himalayas form a very distinct orographic barrier with a pronounced rainfall gradient from the South to the North and have a very rugged terrain, causing highly dynamic surface processes and fast erosion rates. Thus, the Himalayas provide an ideal site of investigation to study erosion and constrain its controlling factors. In this contribution we present an integrated comparison of mean catchment erosion rates, calculated from in-situ produced 10Be cosmogenic isotope concentration in river sands (representative for millennial time scales) and suspended sediment measurements (integrating the annual to decadal time spans). We discuss erosion rates and patterns in the context of precipitation-landscape features of the studied catchments. The samples cover all major rivers, and several minor tributaries of the Narayani watershed (30,000 km2) in central Nepal. They represent all lithologies, topographic units and climate regimes across the Himalayan range. The erosion rates, both from cosmogenic nuclide analysis and suspended sediment measurements, range from 0.1 to 4 mm/yr. These agree well between the two methods and also with already published data for the major outlet stations at the Himalayan front. However, in the Middle and High Himalayas the cosmogenic erosion rates are significantly higher than those from suspended sediment measurements. While on the short term (intra-annual) a clear relation between precipitation and erosion can be observed, the cosmogenic erosion rates show no clear dependency with the basin wide precipitation pattern. Furthermore, no relation could be observed with the dominant lithological units and the degree of glaciation.
Our observations confirm the overall established relationship between erosion rates, relief and slope, showing clearly that topography exerts a predominant control on spatial erosion rates on the millennial timescale. However, we observe a different relationship between main stream basins (> 250 km2) and small tributary basins (< 250 km2). Small basins show in general lower erosion rates than larger basins for respectively the same topographic characteristics.

Keywords: Hydrology; Erosion; Geomorphological geochronology; hillslope; AMS; TCN; radionuclide

Related publications

  • Poster
    American Geophysical Union, Fall Meeting 2012., 03.-07.12.2012, San Francisco, USA

Publ.-Id: 17773

Ion-irradiation induced damage in FeCr alloys characterized by nanoindentation

Heintze, C.; Bergner, F.; Hernández-Mayoral, M.

Self-ion irradiation in combination with nanoindentation offers the possibility to characterize irradiation damage in a broad range of irradiation temperature and fluence. Nanoindentation results are reported for binary FeCr alloys of commercial purity with nominal chromium contents of 2.5, 9 and 12 at%. The irradiation conditions considered include irradiations at room temperature, 300°C and 500°C. Special features of this work are roughly rectangular damage profiles produced by multi-step irradiations with different ion energies and exploitation of the load dependence of hardness for indentation loads in the range of 2 to 500 mN. The effects of Cr content, fluence and irradiation temperature are discussed. Irradiation-induced changes of the microstructure were characterized by means of transmission electron microscopy (TEM). Hardening features and their contribution to the observed irradiation-induced hardness changes will be discussed in the framework of a tentative two-feature hardening model. Small-angle neutron scattering (SANS) data reported for neutron-irradiated conditions of the same alloys will be taken into account.

Keywords: Self-ion irradiation; nanoindentation; TEM; irradiation hardening; FeCr alloys

  • Invited lecture (Conferences)
    CAARI 2012 - 22nd International Conference on the Application of Accelerators in Research and Industry, 05.-10.08.2012, Fort Worth, USA

Publ.-Id: 17772

Complexation behaviour of U(VI) and Eu(III) with Schiff Bases investigated by laserinduced spectroscopy

Lindner, K.; Günther, A.; Bernhard, G.

Actinides and lanthanides play an increasing important role in present time. Actinides can be released into the natural environment especially from mining areas by weathering, erosion and anthropogenic activities as well as by nuclear incidents and thus represents a hazard potential for humans. Lantha-nides occur in nature rarely, but they are significant in the glass and ceramics industries, metallurgy and the cracking of petroleum. New supramolecular complexing agents with N, O, S donor function are developed to separate the metals of the d- and f-block and enriched rare earths. Schiff Bases are essential basic components of these new organic ligands. In this study the complexation of uranium(VI) and europium(III) with the Schiff bases N-benzylideneaniline (NBA), 2-(2-hydroxybenzyliden-amino)phenol (HBAP) and alpha-(4-hydroxyphenyl-imino)-p-cresol (HPIC) was investigated in methanolic solution using time-resolved laserinduced fluorescence spectroscopy (TRLFS) at room and cryogenic temperature and in the case of the uranium(VI)-Schiff bases systems by applying of TRLFS with ultrashort laser pulses (fs-TRLFS).
The measurements of the uranyl luminescence in alcoholic solution at room temperature show strong quenching effects by solvent. These quenching effects could be minimized by measurements at cryogenic temperature (153 K). There is a decrease in fluorescence of the uranium(VI) with the addition of the Schiff Base. A wavelength shift can not be observed, which indicate that the complex seems not to fluoresce.
The europium(III) fluorescence at room temperature is not affected by the methanol. But it turns out that the europium(III) in methanol solution forms an asymmetric complex in comparison to the Eu(III)-water complex. The europium(III) fluorescence decrease with addition of Schiff Base. The observed splitting of the peaks indicates that two different europium(III) species exist in the system.
The fs-TRLFS as a sensitive speciation technique was used to determine the luminescence properties of formed complexes in the uranium(VI)-NBA, uranium(VI)-HBAP and uranium(VI)-HPIC systems. The emission signals show hypsochromic, bathochromic or hypsochromic shifts in comparison to the emission maxima of the uncomplexed ligand. The intensity of the ligand fluorescence increase with the increasing uranium(VI) concentration. The fs-TRLFS investigation opens up the possibilities for the determination of very short-lived complex species via the fluores-cence of the organic compounds by delocalized p-electron systems. Corresponding to the first analyses of the time resolved measurements the luminescence lifetimes of the free ligand and the uranium(VI) complex species are in the range from 2-4 ns. Through the change of the emission properties of organic ligands or metals can be observed the complexation with uranium(VI) and europium(III) and calculated corresponding complex formation constants.

Keywords: fs-TRLFS; Cryo TRLFS; uranium(VI); europium(III); Schiff Bases

  • Poster
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.11.-07.12.2012, Dresden, Deutschland

Publ.-Id: 17771

Lower head failure

Altstadt, E.

During a severe accident in a pressurized water reactor with core melt, the reactor pressure vessel integrity may be threatened by the relocation of molten corium into the lower head and the formation of a molten pool.This book section describes the thermal and mechanical phenomena in the reactor pressure vessel.

Keywords: Reactor pressure vessel failure; core melt down; in-vessel melt retention; nuclear reactor

  • Book chapter
    Bal Raj Sehgal: Nuclear Safety in Light Water Reactors: Severe Accident Phenomenology, Amsterdam etc.: Academic Press Elsevier, 2012, 978-0-12-3888446-6, 145-155

Publ.-Id: 17770

Combination of spectroscopic methods for the identification of U(VI) spezies formed by selected bacteria, algae and fungi

Günther, A.; Vogel, M.; Roßberg, A.; Raff, J.; Bernhard, G.

Microorganisms like bacteria, algae and fungi have a significant influence on the immobilization, mo-bilization and transport of radionuclides like uranium and other heavy metals in the biological and geological environment via the soil and water path. To understand the mechanisms of uptake, trans-port, deposition, degradation and the behavior of actinides in different biological and geological sys-tems structural knowledge about the formed actinides species are of great importance and are essential for a reliable assessment of these processes.
Arthrobacter (bacteria), Chlorella vulgaris (green algae) and Schizophyllum commune (fungi) bind significant amounts of uranium(VI) in the pH range from 4 to 7 and contact time of two days. Trans-mission electron microscopy and scanning electron microscopy investigations showed mainly interac-tions of uranium with parts of cell walls of the selected biomass. By investigations of transparent fun-gal cells were identified additionally uranium containing accumulates inside originally living cells.For the determination of the functionalities, which are important for the binding and mobilization or immobilization of uranium, the interaction of uranium(VI) with metabolic active bacterial, algal and fungal cells was investigated by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS) and X-ray absorption fine structure spectroscopy (EXAFS). The measured luminescence spectra of uranyl containing cell species of all investigated organisms show bathochromic shifts of the uranyl emission bands in comparison to the corresponding emission signals of the uranyl species in the initial solution independent of the uranium concentration and the pH value of the solution. The com-parison of the obtained biomass spectra with luminescence properties of uranyl model compounds demonstrated the carboxylic and organic/inorganic phosphate groups are responsible for uranium binding on the biomass with varying contributions dependent on the microbial biomass, cell status and uranium concentration in the initial sorption solution. The dominant interaction of uranium(VI) with organic/inorganic phosphate groups could be verified by corresponding EXAFS investigations.

Keywords: Bacteria; algae; fungi; uranium; TRLFS; EXAFS

Related publications

  • Poster
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Deutschland

Publ.-Id: 17769

Transient magneto-photoluminescence quenching by intra-excitonic THz absorption

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

Optical properties of III-V semiconductor heterostructures are strongly influenced by excitons. With increasing carrier confinement, as in quantum wells and quantum dots, the exciton binding energy increases. This results in distinct features in absorption and emission spectra arising from the excitonic transitions and recombinations. The temporal behavior of the optical properties of these systems is also influenced by the exciton dynamics. Recently, there has been an increasing interest on the study of intraexcitonic transitions. The energy separations of the excitonic states (1s, 2s, 2p, and so on) fall in the terahertz (THz) frequency range. Intense and tunable THz sources like free electron lasers have been used to probe these transitions. However, most experiments like optically detected magnetic resonance measurements, were done in the time integrated mode and the intraexcitonic carrier dynamics could not be probed.
Here we present our work on time resolved measurements of photoluminescence (PL) quenching in presence of a varying external magnetic field. We performed measurements on GaAs/AlGaAs multiple quantum well sample with a narrow PL line width (2 meV) associated with the 1s heavy-hole exciton. THz pulses from a free electron laser were used to induce intraexcitonic transitions resulting in the quenching of the PL. The quench manifested itself as a dip in the PL transient during the incidence of the THz pulse and the depth of the dip was proportional to the THz absorption. The intraexcitonic transition energies were tuned using an external magnetic field. Excitonic 1s-2p and cyclotron resonances appeared as maxima in the plot of the dip depth vs. magnetic field. Time resolved measurement enabled us to investigate the relaxation dynamics of the 2p state which does not undergo radiative recombination and thus cannot be observed directly in the PL spectra. The carriers excited to the 2p state, by the THz pulse, eventually relaxed back to the 1s-state resulting in the gradual recovery of the 1s PL intensity after the quench. Some of the carriers in the 2p state however got scattered to the 2s state resulting in the enhancement of the 2s emission during the incidence of the THz pulse. This is a direct consequence of intraexcitonic carrier transfer between the 2p and 2s states. From magnetic field dependence of the THz induced 2s emission intensity we showed the possibility of externally controlling intraexcitonic transitions.

Keywords: excitons; terahertz; GaAs quantum wells; transient photoluminescence

Related publications

  • Poster
    ICPS2012 - 31st International Conference on the Physics of Semiconductors, 29.07.-03.08.2012, Zürich, Schweiz

Publ.-Id: 17766

Untersuchungen zur magnetfeldkontrollierten Auftriebskonvektion in einem Czochralski-Tiegel

Cramer, A.; Pal, J.; Gerbeth, G.

Die Untersuchungen zur physikalischen Modellierung der Strömung in einer Czochralski-Geometrie umfassen Ultraschall-Doppler Geschwindigkeits- und Temperaturmessungen, Letztere mit dünnen, und damit hinreichend schnell ansprechenden, Thermoelementen. Um ähnliche Wärmetransporteigenschaften, wie sie bspw. bei der Züchtung von Siliziumkristallen vorliegen, zu haben, wurde die niedrig-schmelzende ternäre Legierung GaInSn eingesetzt. Die kleine Prandtlzahl Pr « 1 dieses de facto Standard-Modellfluids für derartige Untersuchungen liegt im Bereich der Halbleiterschmelzen und sorgt für die Dominanz von Wärmeleitung über konvektiven Transport. Das Strömungsfeld zeigt eine komplexe nicht achsen­sym­metrische Topologie. Reine Moden mit einer bestimmten azimuthalen Wellenzahl, über die in der Literatur oftmals berichtet wird, wurden nicht gefunden. Vielmehr manifestiert sich die Konvektionsstruktur in der Überlagerung der achsen­symmetrischen (azimuthale Wellenzahl m = 0) mit einer monozellulären (m = 1) Mode. Die Temperaturmessungen zeigen, dass die in vielen anderen Arbeiten gefundene Dämpfung der unerwünschten auftriebsinduzierten Tempe­ra­tur­fluk­tu­ationen durch Anwendung eines rotierenden Magnetfeldes nicht reproduziert werden können.

Keywords: Crystal growth; Czochralski technique; electromagnetic flow control; damping of turbulence; rotating magnetic field

  • Lecture (Conference)
    Elektroprozesstechnik, 06.-07.09.2012, Ilmenau-Heyda, Deutschland
  • Contribution to proceedings
    Elektroprozesstechnik, 06.-07.09.2012, Ilmenau-Heyda, Deutschland
    Tagungsband Elektroprozesstechnik 2012

Publ.-Id: 17765

A tool for semiautomatic evaluation of PET data for range verification in ion beam therapy

Helmbrecht, S.; Enghardt, W.; Georg, D.; Kuess, P.; Schubert, M.; Fiedler, F.


The positron emission tomography (PET) is a clinically proven method for verification of ion beam therapy. Due to fundamentally different physical processes leading to dose and activity the evaluation is based upon a comparison between the β+-emitter distribution measured during or after irradiation and a Monte-Carlo prediction from the treatment plan. A visual comparison slice by slice requires well trained personnel and is very time consuming. Furthermore, the reproducibility is low.
A software is presented that allows a semi-automatic and guided comparison of prediction an measurement to overcome the mentioned difficulties.

Material and Methods:

The range of the primary particles is the crucial parameter affecting the position of dose deposition and also the activity distribution. A direct extraction of the range from a β+-emitter distribution is not feasible, however, the range difference between two data sets can be determined. Therefore, a one dimensional range comparison algorithm was enhanced and extended to three dimensions. It generates a two dimensional matrix of range deviations, that represents the complete activity distribution.
A comprehensive software has been developed providing an intuitive graphical user interface to perform different evaluation methods. A statistical evaluation provides information about the overall agreement between measurement and prediction. System inherent fluctuations can be easily taken into account by using the statistic criterion. However, small deviations can be overlooked.
Hence the software provides different methods for analysis of local deviations. The matrix of range deviations is projected into the CT images to allow a fast localization of possible critical areas.
The gamma index is used to take stochastic fluctuations into account that are caused by the relatively low cont rates compared to the classic diagnostic usage of PET.
A common issue during fractionated ion beam therapy is the filling of cavities in the beam path due to physiological processes between two fractions. Such a change in the filling status can cause severe changes in the particle range and thereby a failure in dose deposition. Hence the filling of cavities is automatically evaluated, the result is presented graphically to the user.
For the development in-beam PET data captured at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany during patient treatment from 1997 to 2008 was used. All fractions from 6 patients were evaluated visually to check the performance of the range comparison algorithm and the feasibility of the different displaying possibilities of the software.
The feasibility of the statistical criterion has been tested on artificial range modifications. In simulated β+ -emitter distributions of 6 patients the range was shifted in the shape of a truncated quadratic pyramid with a maximum change of ± 4 mm, ± 6 mm and ± 10 mm water equivalent path length. These modified distributions have been compared to the measurement. By applying the statistical criterion a classification of the data sets was performed, i.e. the system had to decide whether a distribution was range modified.


From the classification results of the data sets the true positive and false positive rate was calculated to quantify the quality of the algorithm. For ±10 mm a true positive rate (TPR) of 90 % and a false positive rate (FPR) of 12 % and was reached, for ±6 mm a TPR of 82 % and a FPR of 26 % and for ± 4 mm a TPR of 72 % and an FPR of 26 %, respectively. This shows the abilities of the statistical criterion but also the limitations in the case of small deviations that make a local evaluation necessary. The comparison of the visual evaluation and the local results of the algorithm shows a good correlation. Differences in the result of the range comparison algorithm and the valuation of a human evaluator are rare.


Despite system inherent difficulties like low count rates and physiological washout effects that blur the obtainable images, PET is a powerful tool for range verification in ion beam therapy. For a routine application a systematic and easy usable software tool is required. The developed tool combines a statistical approach to gain information about the overall agreement between measurement and prediction with local criterion. An intuitive graphical user interface allows also less trained personnel to evaluate the PET data.

Keywords: PT-PET; ion-beam therapy

  • Contribution to proceedings
    ICTR-PHE 2012 - International Conference on Translational Research in Radiation Oncology, 01.03.2012, Genf, Schweiz: Elsevier
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 102(2012)Suppl., S42-S43
    DOI: 10.1016/S0167-8140(12)70080-4

Publ.-Id: 17764

Fano effect due to ponderomotive coupling in intersubband response of semiconductor quantum wells

Baudisch, M.; Wagner, M.; Schneider, H.; Stehr, D.; Helm, M.; Atkinson, P.; Huo, Y.; Schmidt, O. G.; Andrews, A. M.; Strasser, G.

Using terahertz-time-domain spectroscopy, it has been demonstrated before that an intersubband transition in photoexcited undoped quantum wells reveals a Fano-like line shape in transmission spectra due to the phase-sensitive coupling of ponderomotive and intersubband currents [ D. Golde et al. Phys. Rev. Lett. 102 127403 (2009)]. In the present experimental study on GaAs/AlGaAs quantum wells we attempt to delineate the observability conditions of this phenomenon. We find that intensity-based Fourier-transform infrared (FTIR) spectroscopy cannot uncover these ponderomotive effects. However, for time-domain spectroscopy they are shown not to be limited to the case of optically excited electrons, but can be seen in doped samples as well.

Keywords: intersubband transition; terahertz; Fano; ponderomotive; quantum well; GaAs/AlGaAs

Publ.-Id: 17763

Terahertz nonlinear optics using intra-excitonic quantum well transitions: Sideband generation and AC Stark splitting

Wagner, M.; Schneider, H.; Stehr, D.; Winnerl, S.; Andrews, A. M.; Schartner, S.; Strasser, G.; Helm, M.

We present experiments investigating nonlinear optics in the terahertz (THz) range related to the 1s–2p intra-excitonic heavy-hole transition in GaAs/AlGaAs multiquantum wells (MQWs). Driven by intense THz fields of the Dresden free-electron laser the system exhibits two different phenomena: (i) we observe efficient near-infrared (NIR) sideband generation as a perturbative effect in the transmission of a narrowband NIR laser, and (ii) we present unambiguous evidence for the intra-excitonic Autler–Townes splitting, a non-perturbative effect.

Keywords: AC Stark effect; Autler–Townes effect; excitons; sidebands; terahertz

Related publications

Publ.-Id: 17762

Pt(II) and Pd(II) Pyrrolidine-Dithiocarbamates Investigated by XPS

Wenisch, R.; Montagner, D.; Helm, M.; Forrer, D.; Tondello, E.; Gross, S.

In the present contribution, a series of four metal dithiocarbamates, namely 1-pyrrolidinecarbodithioate methyl ester (PyDTM) of Pd(II) and Pt(II), PtCl2(PyDTM), PtBr2(PyDTM), PdBr2(PyDTM), PdCl2(PyDTM), were analysed by x-ray Photoelectron Spectroscopy (XPS). Besides the wide scan spectra, detailed spectra for the C 1s, O 1s, N 1s, S 2s, S 2p, Pt 4f (for Pt-based compounds), Pd 3d (for Pd-based compounds), Cl 2p (for Cl containing compounds), Br 3p (for Br containing compounds) regions were acquired and the related data are presented and discussed.

Keywords: organic compounds; palladium compounds; X-ray photoelectron spectra; dithiocarbamates; coordination compounds; metal-sulphur bond; platinum; palladium; sulphur

Publ.-Id: 17761

Reconstruction of 4D in-beam PET data for quality control of moving target irradiation in ion beam therapy

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

no abstract available

Publ.-Id: 17760

GaAs photocathode status in Dresden-Rossendorf

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

We introduce in this talk the developing status of GaAs photocathode for SRF gun. A new preparation chamber and transfer system has been designed. The test result of unactived bulk GaAs in SRF gun is reported here. Some experience for NEA-photocathode activation through GaN experiments is discussed.

Keywords: GaAs; photocathode; SRF gun

Related publications

  • Invited lecture (Conferences)
    EuCARD SRF Annual Review, 29.-30.03.2012, Berlin, Germany

Publ.-Id: 17759

Curium(III) as intrinsic luminescence probe for direct speciation studies in biogeochemical systems

Moll, H.; Lütke, L.; Raff, J.; Brendler, V.; Bernhard, G.

Knowledge concerning the speciation of actinides is essential to understand their fate and behavior in the environment. Moreover, the speciation of actinides influences their behavior in biological systems (e.g., microbes) in terms of chemical toxicity and radiotoxicity. Since many years we are successfully operating a unique pulsed flash lamp pumped Nd:YAG-­OPO laser system (Powerlite Precision II 9020 laser equipped with a Green PANTHER EX OPO from Continuum, Santa Clara, CA, USA) designed especially to detect the luminescence of trivalent actinides and lanthanides (e.g., Cm, Eu). The luminescence spectra were detected using an optical multi-channel analyzer-system, consisting of an Oriel MS 257 monochromator and spectrograph with a 300 or 1200 line mm-1 grating and an Andor iStar ICCD camera (Lot-Oriel Group, Darmstadt, Germany). The potential of this system for direct speciation studies of Curium(III) in biogeochemical systems will be presented on the basis of selected examples. These examples cover geochemical systems: the aqueous Cm(III) phosphate system [1] and biological systems: (a) Cm(III) speciation studies with cells of a groundwater strain of Pseudomonas fluorescens [2] and (b) Cm(III) complexation with bacterial surface-layer proteins [3].

Acknowledgement: This work was partly funded by BMWi under contract number 02E10618. The authors are indebted to the U.S. Department of Energy, Office of Basic Energy Sciences, for the use of 248Cm via the transplutonium element production facilities at Oak Ridge National Laboratory; 248Cm was made available as part of collaboration between HZDR and the Lawrence Berkeley National Laboratory (LBNL).

[1] Moll, H. et al. (2011) Radiochim. Acta 99, 775-782.
[2] Moll, H. et al. (2012) Geomicrobiol. J., in press.
[3] Moll, H. et al. (2011) Poster at the 13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products (MIGRATION 2011), 18.-23.09.2011, Beijing, PR China.

Keywords: curium; TRLFS; speciation; biogeochemical systems

  • Contribution to proceedings
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Deutschland
  • Poster
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Deutschland

Publ.-Id: 17758

Cellular and molecular properties of 90Y-labeled cetuximab in combination with radiotherapy on human tumor cells in vitro

Saki, M.; Toulany, M.; Sihver, W.; Zenker, M.; Heldt, J.-M.; Mosch, B.; Pietzsch, H.-J.; Baumann, M.; Steinbach, J.; Rodemann, H. P.

Purpose. Anti-EGFR antibody cetuximab (C225) is used in combination with radiotherapy of head and neck squamous cell carcinoma (HNSCC) patients. We investigated whether conjugation of cetuximab with trans-cyclohexyl-diethylene-triamine-pentaacetic acid (CHX-A″-DTPA) and radiolabeling with 90Yttrium affect the molecular and cellular function of cetuximab and improve its combined effect with external-beam irradiation (EBI).Methods. The following cell lines were used: HNSCC UT5, SAS, FaDu, as well as A43, Chinese hamster ovary cells (CHO), and human skin fibroblast HSF7. Binding affinity and kinetics, specificity, retention, and the combination of 90Y-cetuximab with EBI were evaluated.Results. Control cetuximab and CHX-A″-DTPA-cetuximab blocked the proliferation activity of UT5 cells. In combination with EBI, CHX-A″-DTPA-cetuximab increased the radiosensitivity of UT5 to a similar degree as control cetuximab did. In contrast, in SAS and HSF7 cells neither proliferation nor radiosensitivity was affected by either of the antibodies. Binding [90Y]Y-CHX-A″-DTPA-cetuximab (90Y-cetuximab) to EGFR in HNSCC cells occurred time dependently with a maximum binding at 24 h. Retention of 90Y-cetuximab was similar in both HNSCC cell lines; 24 h after treatment, approximately 90% of bound activity remained in the cell layer. Competition assays, using cell membranes in the absence of an internalized fraction of cetuximab, showed that the cetuximab affinity is not lost as a result of conjugation with CHX-A″-DTPA. Cetuximab and CHX-A″-DTPA-cetuximab blocked EGF-induced Y1068 phosphorylation of EGFR. The lack of an effect of cetuximab on EGF-induced Akt and ERK1/2 phosphorylation and the inhibition of irradiation (IR)-induced Akt and ERK1/2 phosphorylation by cetuximab were not affected by DTPA conjugation. 90Y-cetuximab in combination with EBI resulted in a pronounced inhibition of colony formation of HNSCC cells.Conclusions. Conjugation of CHX-A″-DTPA to cetuximab does not alter the cellular and biological function of cetuximab. 90Y-labeling of cetuximab in combination with EBI may improve radiotherapy outcome.

Keywords: Head and neck squamous cell carcinoma; EGFR; Cetuximab; 90Yittrium; 90Y-cetuximab

Publ.-Id: 17756

Prozess und Ergebnisse der Visions- und Zielbildung in einem komplexen Forschungsprojekt am Beispiel des ProSIN Projekts DER

Klossek, A.

Die identifizierte Forschungslücke wird im vorliegenden Arbeitspapier aufgegriffen und konkret anhand des Fallbeispiels der Kooperationsplattform „Deutsches EnergieRohstoff-Zentrum Freiberg (DER)“ analysiert. Ziel des vorliegenden Arbeitspapieres ist es dementsprechend, den Entstehungs- und Gestaltungsprozess einer Vision, von Zielen und von Strategien in komplexen Forschungsprojekten strukturiert und fallstudienbasiert anhand des DER Projektes zu beschreiben. Aus der Fallstudienanalyse sollen ferner Gestaltungs- und Optimierungsansätze für zukünftige Kooperationsplattformen ähnlicher Art abgeleitet werden.

  • Open Access Logo Contribution to external collection
    in: DER Working Papier Series Nr. 1/2012, Freiberg: Deutsches EnergieRohstoff-Zentrum, 2013

Publ.-Id: 17755

EtherCAT Feldbusknoten: Entwicklung, Systemunterstützung und -kompatibilität

Kaever, P.

Die Verwendung selbst entwickelter Feldbusknoten und deren Einbindung in kommerzielle Automatisierungssysteme erfordert in der frühen Phase des Produktlebenszyklus einen erhöhten Entwicklungsaufwand. Nach erfolgreicher Integration bieten Hersteller von Automatisierungssystemen eine langfristig stabile und leistungsfähige Umgebung zur Projektierung und Programmierung von Anlagen, welche langfristig den Aufwand zur Pflege minimiert. Zur Überprüfung der Funktionsfähigkeit des Gesamtsystems ist die durch Testwerkzeuge unterstützte Systemkompatibilität eine entscheidende Voraussetzung. Die Vorgehensweise bei der Systemintegration eines Slave Device und der Prüfung der Systemkompatibilität wird im Folgenden vorgestellt.

Keywords: Fieldbus; slave devices; product life cycle; industrial Ethernet; EtherCAT; system integration; device test

  • Open Access Logo Contribution to proceedings
    103. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2012, 12.-14.3.2012, Dresden, Deutschland
    103. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2012, ed.: Peter Göttlicher, 22607 Hamburg, Germany: Verlag Deutsches Elektronen-Synchrotron, 978-3-935702-65-2, 47-53
  • Lecture (Conference)
    103. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2012, 12.-14.3.2012, Dresden, Deutschland

Publ.-Id: 17754

Diffusive racetrack oxidation in a Ti sputter target by reactive high power impulse magnetron sputtering

Audronis, M.; Abrasonis, G.; Munnik, F.; Heller, R.; Chapon, P.; Bellido-Gonzalez, V.

This paper reports experimental results for near-surface Ti sputter target oxidation in a magnetron racetrack during reactive high power impulse magnetron sputtering (HIPIMS) at various optical plasma monitoring set-points in the transition region between ‘metal’ and ‘poisoned’ target states. Oxygen depth profiles were obtained by nuclear reaction analysis and glow discharge optical emission spectroscopy. Ti target surface oxidation depth as induced by reactive HIPIMS was found to depend on the process set-point as well as discharge conditions. Deepest oxidation was observed when operating close to ‘fully poisoned (FP)’ or in ‘FP’ regime with oxygen profiles extending as deep as ∼0.5μm (oxygen concentration >=5 at%). Oxygen profiles obtained indicate the occurrence of oxygen bulk diffusion. Process induced elevated target surface temperature, magnetic field and plasma assistance are suggested to contribute substantially to these profiles. Based on these findings it is proposed that ion-bombardment-assisted thermal diffusion is a third target poisoning mechanism that can be taking place and is therefore important in reactive HIPIMS in addition to the two currently accepted mechanisms—ion implantation and chemisorption. Under the conditions investigated in this work, diffusive oxidation was most significant when operating in the lower part of the hysteresis loop. Reactive HIPIMS processes that will facilitate significant diffusive sputter target surface oxidation will also be expected to exhibit wider hysteresis and longer target cleaning times after substantial target poisoning.

Related publications

Publ.-Id: 17753

Position-resolved Positron Annihilation Lifetime Spectroscopy

Wagner, A.; Butterling, M.; Fiedler, F.; Fritz, F.; Kempe, M.; Cowan, T. E.

A new method which allows for position-resolved positron lifetime spectroscopy studies in extended volume samples is presented. In addition to the existing technique of in-situ production of positrons inside large (cm3) bulk samples using high-energy photons up to 16 MeV from bremsstrahlung production, granular position-sensitive photon detectors have been employed. A beam of intense bremsstrahlung is provided by the superconducting electron linear accelerator ELBE (Electron Linear Accelerator with high Brilliance and low Emittance) which delivers electron bunches of less than 10 ps temporal width and an adjustable bunch separation of multiples of 38 ns, average beam currents of 1 mA, and energies up to 40 MeV. Since the generation of bremsstrahlung and the transport to the sample preserves the sharp timing of the electron beam, positrons generated inside the entire sample volume by pair production feature a sharp start time stamp for positron annihilation lifetime studies with high timing resolutions and high signal to background ratios due to the coincident detection of two annihilation photons. Two commercially available detectors from a high-resolution medial positron-emission tomography system are being employed with 169 individual Lu2SiO5:Ce scintillation crystals, each. In first experiments, a positron-lifetime gated image of a planar Si/SiO2 (pieces of 1 cm × 2 cm size) sample and a 3-D structured metal in Teflon target could be obtained proving the feasibility of a three dimensional lifetime-gated tomographic system.

Keywords: position-resolved positron lifetime spectroscopy; superconducting LINAC

Related publications

Publ.-Id: 17752

Isospin observables from fragment energy spectra

Liu, T. X.; Lynch, W. G.; Tsang, M. B.; Hodges, R. K.; Liu, X. D.; Tan, W. P.; van Goethem, M. J.; Verde, G.; Wagner, A.; Xi, H. F.; Xu, H. S.; Famiano, M.; de Souza, R. T.; Charity, R. J.; Sobotka, L. G.; Showalter, R. H.

The energy spectra of light charged particles and intermediate mass fragments from 112Sn+112Sn and 124Sn+124Sn collisions at an incident energy of E/A=50 MeV have been measured with a large array of Silicon strip detectors. We used charged particle multiplicities detected in a near-4 array to select data from the central collision events. We study isospin observables analogous to ratios of neutron and proton spectra, including double ratios and yield ratios of t/3He and of asymmetries constructed from fragments with Z=3-8. Using the energy spectra, we can construct these observables as functions of kinetic energy and observe a large difference in the fragment observables if fragments contributing to sequential decays are included.

Keywords: intermediate mass fragment; nuclear multifragmentation; silicon strip detector; CsI detector; light charged particle spectra

Publ.-Id: 17751

Visualisierung der Cyclooxygenase-2 mittels optischer Bildgebung in vitro und in vivo bei tumorassoziierten Prozessen

Tondera, C.

kein Abstract verfügbar

  • Diploma thesis
    Friedrich-Schiller-Universität Jena, Biologisch-Pharmazeutische Fakultät, 2012
    100 Seiten

Publ.-Id: 17750

Photobiology: the biological impact of sunlight in carcinogenesis

Pietzsch, J.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    1st Klixx Solar Workshop on Photophysics, Photochemistry and Photobiology, 13.-14.07.2012, Madrid, Spain

Publ.-Id: 17749

Targeting cyclooxygenase-2 and oxidant stress pathways for attenuation of radiation-induced vascular dysfunction

Pietzsch, J.; Laube, M.; Ullm, S.; Sehn, F.; Pietzsch, F.-J.; Knieß, T.

Radiotherapy of various cancers is closely associated with increased cardiovascular morbidity and mortality. Arachidonic acid metabolites are supposed to play a key role in radiation-induced vascular dysfunction.
This investigation was performed in order to evaluate the effects of novel selective cyclooxygenase-2 (Cox-2) inhibitors (coxibs) on radiation-induced formation of eicosanoids via Cox-2 and oxidant stress pathways in both human arterial endothelial cells (EC model) and rat aortic rings (AR model), respectively. In order to assess acute effects (24 h) of X-ray radiation at moderate doses (2, 4, and 10 Gy) without or with presence of coxibs (EC model: cyclopentene/indole/indomethacin derivatives; AR model: indole derivatives; celecoxib as reference) compared to sham-irradiated controls, the following parameters were measured: Cox-2 protein induction, release of prostaglandins, release of isoprostanes, and formation of lipid and protein oxidation products (LO/PO). Irradiation of EC and AR without presence of coxibs resulted in a dose-dependent augmentation of all parameters studied. When EC and AR were exposed to Cox-2 inhibitors (0.1, 1, and 10 µM), during and for 24 h post irradiation, indole derivatives showed highest potency to inhibit release of both prostaglandins and isoprostanes. Furthermore, indole derivatives significantly decreased LO/PO formation, indicating a direct interaction with oxidant stress-pathways. By contrast, both cyclopentene and indomethacin derivatives (and celecoxib) mainly inhibited prostaglandin release, but showed only slight effects on formation of isoprostanes and LO/PO. Model experiments using human low density lipoproteins showed that indole derivatives differently interact with oxidation of polyunsaturated fatty acids and protein amino acid side chains, than the cyclopentene/indomethacin derivatives, suggesting a physico-chemical rationale for observed antioxidative activity. The reduction of radiation-induced vascular dysfunction by antioxidative coxibs may widen the therapeutic window of Cox-2 targeted treatment.

  • Lecture (Conference)
    6th European Congress of Pharmacology (Ephar 2012), 17.-20.07.2012, Granada, Spain
  • Contribution to proceedings
    6th European Congress of Pharmacology (Ephar 2012), 17.-20.07.2012, Granada, Spain
    Proceedings of the 6th European Congress of Pharmacology, Bologna: Medimond, 978-88-7587-670-8, 87-90

Publ.-Id: 17748

18F-Labeled phosphopeptide-cell-penetrating peptide dimers with enhanced cell uptake properties in human cancer cells

Richter, S.; Bouvet, V.; Wuest, M.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Neundorf, I.; Wuest, F.

Phosphopeptides represent interesting compounds to study and elucidate cellular protein phosphorylation/dephosphorylation processes underlying various signal transduction pathways. However, studies of phosphopeptide action in cells are severely constrained by the negatively charged phosphate moiety of the phosphopeptide resulting in poor transport through the cell membrane. The following study describes the synthesis and radiopharmacological evaluation of two 18F-labeled phosphopeptide-cell-penetrating peptide dimers. The polo-like kinase-1-binding hexaphosphopeptide H-Met-Gln-Ser-pThr-Pro-Leu-OH was coupled to cell-penetrating peptides (CPPs), either sC18, a cathelicidin-derived peptide, or the human calcitonin derivative hCT(18-32)-k7.

Radiolabeling was accomplished with the prosthetic group N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) using both, conventional and microfluidic-based bioconjugation of [18F]SFB to N-terminal end of phosphopeptide part of the peptide dimers. Cellular uptake studies in human cancer cell lines HT-29 and FaDu cells at 4 °C and 37 °C and small animal PET in BALB/c mice were utilized for radiopharmacological characterization.

Isolated radiochemical yields ranged from 2% to 4% for conventional bioconjugation with [18F]SFB. Significantly improved isolated radiochemical yields of up to 26% were achieved using microfluidic technology. Cellular uptake studies of radiolabeled phosphopeptide and phosphopeptide-CPP dimers indicate enhanced internalization of 50% ID/mg protein after 2 h for both phosphopeptide dimers compared to the phosphopeptide alone (< 1% ID/mg protein). In vivo biodistribution of 18F-labeled peptide dimers was determined with small animal PET revealing a superior biodistribution pattern of sC18-containing peptide dimer MQSpTPL-sC18 [18F]4.

[18F]SFB labeling of the phosphopeptide-CPP dimers using a microfluidic system leads to an improved chemoselectivity towards the N-terminal NH2 group compared to the conventional labeling approach. Cell-penetrating peptide sC18 can be considered as an ideal molecular shuttle for intracellular delivery of the Plk1-PBD-binding hexaphosphopeptide as demonstrated by its favourable radiopharmacological profile.

Keywords: 18F; Phosphopeptides; Cell-penetrating peptides (CPP); Microfluidic; Positron emission tomography (PET)

Publ.-Id: 17747

Experimente zur Entstehung von Titan-44 in Supernovae

Schmidt, K.

In dieser Diplomarbeit wurde das astrophysikalisch interessante Resonanztriplett der Reaktion 40Ca(α,γ)44Ti bei 4,5MeV untersucht. Am 3-MV-Tandetron des Helmholtz-Zentrums Dresden-Rossendorf wurden dafür die Energien von Protonen- und -Strahlen kalibriert, Anregungsfunktionen im Energiebereich der drei Resonanzen aufgenommen, vier CaOTargets aktiviert und deren Struktur mittels der Reaktion 40Ca(p,γ)41Sc überprüft. Im Felsenkeller-Niederniveaumesslabor wurde anschließend die Aktivität der Proben gemessen. Schließlich konnte die Summe der Resonanzstärken bei 4497 und 4510 keV -Energie im Laborsystem zu (12;8 2;3) eV und die Summe der Resonanzstärken des gesamten Tripletts, d.h. zusätzlich bei 4523 keV, zu (12;0 2;0) eV bestimmt werden. Bei der ersten Resonanzstärke konnte die Unsicherheit im Vergleich zur Literatur von 19% auf 18% verbessert werden. Außerdem bieten die Daten der vorliegenden Arbeit die Grundlage, zukünftig die Unsicherheiten noch erheblich weiter zu reduzieren.

In this thesis the astrophysically interesting resonance triplet of the 40Ca(α,γ)44Ti reaction at 4.5MeV has been studied. For this purpose energies of proton and beams provided by 3MVTandetron at Helmholtz-Zentrum Dresden-Rossendorf have been calibrated. Excitation functions of energy regions near the resonances and in-beam spectra of four different targets have been measured. The 40Ca(p,γ)41Sc reaction has been used to scan the structure of the activated targets. Afterwards their activity has been measured in the underground laboratory Felsenkeller Dresden. Hence the sum of resonance strengths at laboratory energies of 4497 and 4510 keV of (12:8 2:3) eV has been determined as well as the sum of the total triplet strength, including 4523 keV, of (12:0 2:0) eV. In the case of the first resonance, the uncertainty was decreased from 19% to 18 %. Furthermore the results of this work establish a basis for reaching much lower uncertainties in the future.

Keywords: Ti-44; supernova; nuclear astrophysics; activation; 40Ca(alpha; gamma)44Ti; Tandetron; Felsenkeller

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-020 2012
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 17746

The 14N(p,γ)O15 reaction studied at low and high beam energy

Marta, M.

The Bethe-Weizsäcker cycle consists of a set of nuclear reactions that convert hydrogen into helium and release energy in the stars. It determines the luminosity of low-metal stars at their turn-off from the main-sequence in the Hertzsprung-Russel diagram, so its rate enters the calculation of the globular clusters’ age, an independent lower limit on the age of the universe. The cycle contributes less than 1% to our Sun’s luminosity, but it produces neutrinos that can in principle be measured on Earth in underground experiments and bring direct information of the physical conditions in the solar core, provided that the nuclear reaction rate is known with sufficient precision.
The 14N(p,γ)15O reaction is the slowest reaction of the Bethe-Weizs¨acker cycle and establishes its rate. Its cross section is the sum of the contributions by capture to different excited levels and to the ground state in 15O. Recent experiments studied the region of the resonance at Ep = 278 keV. Only one modern data set from an experiment performed in 1987 is available for the high-energy domain. Both energy ranges are needed to constrain the fit of the excitation function in the R-matrix framework and to obtain a reliable extrapolated S-factor at the very low astrophysical energies.
The present research work studied the 14N(p,γ)15O reaction in the LUNA (Laboratory for Underground Nuclear Astrophysics) underground facility at three proton energies 0.36, 0.38, 0.40MeV, and in Dresden in the energy range Ep = 0.6 - 2MeV. In both cases, an intense proton beam was sent on solid titanium nitride sputtered targets, and the prompt photons emitted from the reaction were detected with germanium detectors.
At LUNA, a composite germanium detector was used. This enabled a measurement with dramatically reduced summing corrections with respect to previous studies. The cross sections for capture to the ground state and to the excited states at 5181, 6172, and 6792 keV in 15O have been determined. An R-matrix fit was performed for capture to the ground state, that resolved the literature discrepancy of a factor two on the extrapolated S-factor. New precise branching ratios for the decay of the Ep = 278 keV resonance were measured.
In Dresden, the strength of the Ep = 1058 keV resonance was measured relative to the well-known resonance at Ep = 278 keV, after checking the angular distribution. Its uncertainty is now half of the error quoted in literature. The branching ratios were also measured, showing that their recommended values should be updated. Preliminary data for the two most intense transitions off resonance are provided.
The presence in the targets of the other stable nitrogen isotope 15N with its well- known isotopic abundance, allowed to measure the strength of two resonances at Ep = 430 and 897 keV of the 15N(p,αγ)12 C reaction, improving the precision for hydrogen depth profiling.

Keywords: Nuclear astrophysics; CNO cycle; TiN solid target; Tandetron; LUNA; Clover detector

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-019 2012
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 17745

Utilisation of a Hybrid Approach for Immersive Industrial Process Control Visualisation

Skripcak, T.; Tanuska, P.; Schmeißer, N.

The objective of this paper is to present a proposal of hybrid system architecture for industrial process control visualisation. Leveraging of interoperability standard protocols for industrial automation, it is possible to create process agnostic visualisations. An application of this approach will lead to a hybrid system, which provides HMI (Human Machine Interface) layer for simulation, as well as real-world based industrial processes. An immersive 3-D visualisation is examined for the purpose of complex real-time process variables exploration. Reasonable 3-D visualisation types for industrial process HMI are identified. The idea is to create an immersive virtual environment for displaying industrial process related information, in order to help human operators to understand observed system behaviour and support them in the decision making process.

Keywords: SCADA/HMI; n-D visualisation; OPC; simulation

  • Contribution to proceedings
    International Conference on Internet and Multimedia Technologies (ICIMT'12), 24.-26.10.2012, San Francisco, USA
    Proceedings of International Conference on Internet and Multimedia Technologies 2012., Hong Kong: International Association of Engineers, 978-988-19251-6-9, 415-420

Publ.-Id: 17743

Intra-excitonic coherent nonlinear optics in quantum wells: the Autler-Townes effect and beyond

Helm, M.

Excitons in quantum wells represent a quasi-hydrogenic system, scaled down in energy to the meV (or THz) range due to the effective mass of the electrons and the dielectric constant. We take advantage of a free-electron laser as a narrow-band, intense THz source and drive the intra-excitonic heavy-hole 1s-2p transition in an undoped GaAs/AlGaAs multiquantum well (MQW). Probing the near-bandgap absorption with broad-band light from a 10 fs Ti: sapphire laser, we demonstrate the Autler-Townes splitting of the 1s exciton, giving evidence for dressed states. While the basic features at relatively low intensities follow the predictions of a simple two-level model, strong deviations are observed at higher THz fields in the 10 kV/cm range. At such field strengths, the rotating-wave approximation is not valid anymore, and also the two-level approximation breaks down, as higher excitonic bound states and the continuum cannot be neglected. Striking features are a peak reversal and overall blue shift of the Rabi sidebands with increasing field strength and a saturation of the splitting, going along with a line broadening that may indicate the onset of field ionization. Relevant for possible applications, signatures of this AC Stark effect are visible up to room temperature, with a THz induced threefold (at 200 K) near-infrared transmission modulation on a picosecond time scale. The above results are corroborated by recent measurements on an InGaAs/GaAs MQW with narrower exciton linewidth and corresponding calculations based on the semiconductor Bloch equations.

Keywords: terahertz; excitons; Autler-Townes; free-electron laser; semiconductor quantum well

Related publications

  • Invited lecture (Conferences)
    31th International Conference on the Physics of Semiconductors (ICPS 2012), 29.07.-03.08.2012, Zürich, Schweiz

Publ.-Id: 17742

Perfect alloys for spin Hall current induced magnetization switching

Gradhand, M.; Fedorov, D. V.; Zahn, P.; Mertig, I.; Otani, Y.; Niimi, Y.; Vila, L.; Fert, A.

We propose a device that allows for magnetization switching in nanomagnets by means of a pure spin current induced by the spin Hall effect. For this purpose we combine the ideas of magnetization switching of a ferromagnet by a spin current caused by the spin accumulation at a ferromagnet/nonmagnet interface with the electronic measurement of the direct spin Hall effect, and the theoretical material design to identify systems with a large spin Hall angle and an appropriate spin diffusion length. We will discuss the device design with respect to the size of the charge and spin currents. Based on ab initio calculations, we predict dilute alloys ideally suited for this application. Noble metals with single-sheeted Fermi surfaces doped with either heavy impurities like Bi and Pb in Cu or Bi in Ag and light impurities like C and N in Au seem to be the best candidates for a spin Hall angle larger than 5%.

Publ.-Id: 17741

Magnetoacoustic investigation of the Jahn-Teller effect in chromium doped ZnSe crystal

Gudkov, V. V.; Bersuker, I. B.; Yasin, S.; Zherlitsyn, S.; Zhevstovskikh, I. V.; Mayakin, V. Y.; Sarychev, M. N.; Suvoro, A. A.

Ultrasonic investigation of ZnSe:Cr2+ crystal was carried out at low temperatures in magnetic field applied along the wave vector. The observed anomalies in magnetic field dependences of attenuation and wave number evidence for existence of resonant transitions between the energy levels of the Jahn-Teller tetrahedral complex CrSe4.

Publ.-Id: 17740

Direct imaging of spin wave emission from magnetic vortex cores

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

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

Keywords: magnetic vortex; spin wave emission; x-ray microscopy

  • Lecture (Conference)
    12th Joint MMM/Intermag Conference, 14.-18.01.2013, Chicago, USA

Publ.-Id: 17739

Transient Response of a Separated Flow over a Two-Dimensional Wing to a Short Duration Pulse

Williams, D.; Albrecht, T.; Weier, T.; Gerbeth, G.

A Lorentz force actuator located at the leading edge of a two-dimensional wing at 16 degrees angle of attack was used to introduce short-duration disturbances into a separated flow. The transient response of the separated region at Re = 10,000 was documented using time-resolved PIV measurements. The direction of the Lorentz force was changed between downstream and upstream directed disturbances, and details of the resulting flow field structures and lift measurements were studied. Saturation of the peak lift amplitude occurs as the actuation amplitude is increased from 0.0054 < Cμ < 0.21 percent with the pulse duration fixed at 0.1 convective time. The effect of the pulse duration time on the lift response was examined using a fixed pulse amplitude, which showed that saturation occurred when pulse durations exceed 0.5 convective times. Differences in the coherent structures resulting from the upstream/downstream directed actuation were identified using the FTLE method. The initial development of the disturbed shear layer was strongly dependent on the direction of actuation, but the larger-scale separation did not show much difference. The relaxation of the separated region to the original flow state was essentially independent of the direction of actuation.

Keywords: flow control; Lorentz force; Finite-Time Lyapunov Exponent

  • Lecture (Conference)
    American Physical Society 65th Annual Fall Meeting, Division of Fluid Dynamics, 18.-20.11.2012, San Diego, USA

Publ.-Id: 17738

The Influence of Thermo-Solutal Convection on Freckle Formation and Dendritic Growth

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

In-situ observations of the solidification process under the influence of thermo-solutal convection were obtained by means of X-ray radioscopy within a Hele-Shaw cell filled with Ga-25wt%In alloy. The density-driven melt flow causes the formation of vertical freckles (“chimneys”) and changes the mushy zone characteristics. Experimental conditions have been identified which promote the formation of freckles in the Ga-In alloy. A strong coupling exists between the spatial and temporal properties of the flow field and the stability of segregation channels. Stable vortex flow provides a continuous upwards flow of solute-rich melt above the channel and an influx through the mushy zone towards the chimney. We also focused on the analysis of dendrite growth and microstructure features, for instance, dendrite orientation, primary and secondary arm spacing. The quantitative analysis of the flow field, temperature distribution and microstructure characteristic gives a better understanding of the complex interplay between melt flow and solidification process.

Keywords: X-ray radioscopy; thermo-solutal convection; chimneys; Ga-In alloy; mushy zone; melt flow; solidification; dendrite growth

  • Lecture (Conference)
    2013 TMS Annual Meeting & Exhibition / Frontiers in Solidification Science, 03.-07.03.2013, San Antonio, TX, USA

Publ.-Id: 17737

Microscopic Modelling of Freckle Formation during Directional Solidification and Its Verification via In situ X-ray Observation

Yuan, L.; Shevchenko, N.; Eckert, S.; Karagadde, S.; Lee, P. D.

A 3D microscale solidification model, resolving complex interaction of solute partition and diffusion, interdendritic thermosolutal convection, dendrite formation and remelting, was used to study freckle formation for unidirectional solidified Ga-In alloys. The simulated results are validated against real time, in situ X-ray radiographic experiments, highlighting both similarities and differences between model and experiment. The redistribution of solute concentration and the formation of segregated solutal channels were both captured by the numerical model. Effects of thermo-solutal convection due to temperature and solute concentration variations were investigated and the formation of segregated solutal channels (freckles) was also examined in detail. With the assistance of the numerical solution, an improved understanding of the freckle channel formation at the microstructural level was provided.

Keywords: Freckle Formation; Directional Solidification; in situ X-ray radiographic experiments; 3D microscale solidification model; Thermosolutal convection; Computational model

  • Lecture (Conference)
    2013 TMS Annual Meeting & Exhibition/ Frontiers in Solidification Science, 03.-07.03.2013, San Antonio, TX, USA

Publ.-Id: 17736

Time dependent 2D flow structure measurements arising from melt stirring by means of various AC magnetic fields

Franke, S.; Räbiger, D.; Czarske, J.; Gerbeth, G.; Eckert, S.

We present an experimental study concerning the flow inside an isothermal liquid metal column exposed to various magnetic field configurations. This paper is aimed at highly resolved, quantitative velocity measurements in the eutectic alloy GaInSn by means of the pulsed-wave ultrasound Doppler method. A novel ultrasound system was used to measure two-dimensional velocity fields of the secondary flow in the radial-meridional plane. The imaging system employs two arrays each of 25 transducer elements allowing for a fast electronic traversing with concurrently high spatial and temporal resolution. The study considers time-modulated fields or combinations of traveling magnetic fields (TMF) and rotating magnetic fields (RMF) revealing different flow structures and flow intensities. The results demonstrate different variants of electromagnetic melt stirring, some of them showing the potential to enhance the stirring efficiency and to optimize casting properties during solidification.

Keywords: Ultrasound Doppler method; flow field measurements; electromagnetic stirring; rotating magnetic field; magnetohydrodynamics; flow control

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

Publ.-Id: 17735

Tilting of carbon encapsulated metallic nanocolumns in carbon-nickel nanocomposite films by ion beam assisted deposition

Krause, M.; Mücklich, A.; Oates, T. W. H.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Baehtz, C.; Shalimov, A.; Gemming, S.; Abrasonis, G.

The influence of assisting low-energy (~50-100 eV) ion irradiation effects on the morphology of C:Ni (~15 at.%) nanocomposite films during ion beam assisted deposition (IBAD) is investigated. It is shown that IBAD promotes the columnar growth of carbon encapsulated metallic nanoparticles. The momentum transfer from assisting ions results in tilting of the columns in relation to the growing film surface. Complex secondary structures are obtained, in which a significant part of the columns grows under local epitaxy via the junction of sequentially deposited thin film fractions. The influence of such anisotropic film morphology on the optical properties is highlighted.

Keywords: Nanocomposites; Ion beam assisted deposition; TEM; GISAXS

Related publications

Publ.-Id: 17734

Self-assembled isolated monodisperse NiO1+gamma nanoparticles as catalytic templates for nanomaterials synthesis

Houweling, Z.; Geus, J.; Harks, P.; Heller, R.; Schropp, R.

We present the self-organization of isolated monodisperse nickel oxide (NiO1+gamma) nanoparticles on surfaces of arbitrary area sizes. Ni films deposited on titanium oxynitride support films are annealed in a nitrogen/air environment at atmospheric pressure for various annealing times. After the annealing treatments, randomly distributed spatially isolated NiO1+gamma, nanoparticles that are anchored to the support film are observed with a site-density of 11 +/- 1 mu m(-2) and with dimensions of 16 +/- 2 nm in height and 82 +/- 10 nm in diameter. The anchored nanoparticles, once formed, are immobile during further annealing, even for annealing times of 40 min or annealing temperatures of 800 degrees C, making the nanoparticle formation a well-controlled process that yields templates suitable for further processing at elevated temperatures. We demonstrate the utilization of these NiO1+gamma nanoparticle templates as nucleation sites for carbon nanotubes at temperatures of around 680 degrees C.

Related publications

Publ.-Id: 17733

Nanoparticles in Organic Solvents with Polymers – Stability and Consequences upon Material Synthesis through Spray Drying and Melt Moulding

Rudolph, M.; Turan, C.; Kirchberg, S.; Ziegmann, G.; Peuker, U. A.

It is a well accepted fact that nanoparticles and their industrial and commercial use have the potential to improve properties of modern materials substantially. Especially polymeric materials are attractive for incorporating nanoparticles with special properties only apparent in the nanoscale. One main consideration in processing such composite materials is to prevent the nanoparticles from agglomerating or even worse aggregating. In this paper a modular process method is presented based on a mixture of sterically stabilized nanoparticles in an organic solvent with soluble polymers and subsequent spray drying to quickly yet thermally carefully remove the solvent. The method has the potential for large scale production of highly filled nanoparticle-polymer-composites. However the bottleneck of this method is the unknown interaction of polymers and stabilized nanoparticles. We present the impact of depletion flocculation and subsequent phase separation or stabilization by adsorbing polymers on the dispersion of the nanoparticles. It is shown that the processing method is more adequate when compared to traditional melt moulding. The best magnetite nanoparticle stability in dichloromethane is achieved using ricinoleic acid. Besides flocculates we can identify separate primary particles in the composite. The size of the floccules is in the lower micrometer range for nanoparticles 15 nm in size.

  • Book chapter
    Tiddy, Gordon; Tan, Reginald: NanoFormulation, Cambridge: RSC Publishing, 2012, 978-1-84973-524-7, 177-187

Publ.-Id: 17732

High-temperature stability of c-Si surface passivation by thick PECVD Al2O3 with and without hydrogenated capping layers

Saint-Cast, P.; Kania, D.; Heller, R.; Kuehnhold, S.; Hofmann, M.; Rentsch, J.; Preu, R.

We are studying the thermal stability of thick hydrogenated amorphous aluminum oxide (Al2O3) layers (20-50 nm) prepared by a high-throughput plasma-enhanced chemical-vapor-deposition (PECVD) technique for the electrical passivation of crystalline silicon surfaces. These passivation layers can be applied alone or covered by a capping layer like amorphous hydrogenated silicon nitride (SiNx) or amorphous hydrogenated silicon oxide (SiOx), also prepared by PECVD. After firing at 870 degrees C for approximately 3 s, the layers show blistering for Al2O3 of 30 nm or higher, independently from the capping layer. For thinner Al2O3, no blistering can be observed even using scanning electron microscope (SEM).
Very long carrier lifetimes up to 900 mu s was obtained in passivated p-Si (1 Omega cm) wafer after annealing and firing, without observing a strong influence of the layer thickness and the capping layer. All the layer stacks, including the stacks with SiNx capping layer, show high negative charge densities in the layer (1-4 x 10(12) cm(-2)). Additionally, low interface defect densities (similar to 10(11) cm(-2) eV(-1)), which could be achieved with and without a hydrogenated capping layer, were measured even after firing. To explain these phenomena, hydrogen concentration depth profiles were measured by nuclear reaction analysis. These measurements have shown that, at the Al2O3-Si interface, hydrogen atomic concentration ranging 5-7% after annealing and 4% after firing are obtained independently from the capping hydrogen concentration. We conclude that PECVD Al2O3 layers of 20 nm or thicker can provide enough hydrogen to passivate the interface defects, even after a high te!
mperature step. However, the layer thickness should be limited to 30 nm in order to avoid the blistering.

Related publications

Publ.-Id: 17731

Nanocomposites based on technical polymers and sterically functionalized soft magnetic magnetite nanoparticles: Synthesis, processing, and characterization

Kirchberg, S.; Rudolph, M.; Ziegmann, G.; Peuker, U. A.

This experimental study deals with the synthesis, processing, and characterization of highly filled nanocomposites based on polyvinyl butyral/magnetite (PVB/Fe3O4) and polymethylmethacrylate/magnetite (PMMA/Fe3O4). The nanoparticles are synthesized in an aqueous coprecipitation reaction and show a single particle diameter of approximately 15nm. The particles are sterically functionalized and covered by PVB and PMMA in a spray drying process. The synthesized compound particles are further processed by injection molding to test specimens with filler contents up to 14.5vol.-%. PVB and PMMA specimen are processed as a reference as well. The distribution of the nanoparticles is characterized by microscopy. Besides a minor number of agglomerates and aggregates the nanoparticles are distributed homogeneously in the PVB composites. Furthermore, the injection molded specimens are characterized with regard to their thermal degradation, polymer structure, and their mechanical and magnetic properties. The presence of nanoparticles capped with ricinoleic acid shows significant decrease in degradation temperature and in glass transition temperature of PVB. The degradation temperature of PMMA is increased by adding nanoparticles capped with oleic acid. Dynamic-mechanical properties as well as the magnetic permeability of PVB and PMMA are improved significantly by adding nanoparticles.

Keywords: Aqueous coprecipitation; Degradation temperatures; Dynamic mechanical property; Experimental studies; Filler contents; Functionalized; Injection-molded specimens; Polymer structure; Polyvinyl butyral; Ricinoleic acid; Single particle; Soft magnetics; Spray drying process; Test specimens

Publ.-Id: 17730

A TGA-FTIR perspective of fatty acid adsorbed on magnetite nanoparticles-Decomposition steps and magnetite reduction

Rudolph, M.; Erler, J.; Peuker, U. A.

The fatty acid stabilization of magnetite nanoparticles is important for a broad field of studies and applications. In numerous previous studies TGA analyses are applied to investigate these compounds and draw conclusions such as magnetite concentration and surface grafting densities of the chemisorbed molecules. There are however deviations in interpretation of the analysis results. In the presented work we contribute to the discussion on the inert gas decomposition of the fatty acid ricinoleic acid adsorbed on the surface of magnetite nanoparticles with a priori knowledge of magnetite concentration. We report on impacts of autoxidation of the fatty acid as well as significant reduction of magnetite from carbonaceous residues. The findings are based on subsequent gas analysis with FTIR coupled to the TG device. We show how stoichiometric calculations on the reduction in the temperature range of 600-900°C let conclude that the residues are most probably from the chemisorbed fatty acid molecules. Only the physically adsorbed fatty acid molecules have decomposed or detached before 600°C. In context to the investigations on chemically adsorbed fatty acid on magnetite we compare the decomposition of pristine fatty acid and fatty acid physically adsorbed on a high surface area SiO 2 nanopowder. Three distinct steps of decomposition which have often been reported before are found and accounted.

Keywords: Decomposition; FTIR; Magnetite; Nanoparticles; Reduction; Ricinoleic acid; TGA

Publ.-Id: 17729

Ultrasonic flow measurements and bubble detection in gas-stirred metallic melts

Vogt, T.; Andruszkiewicz, A.; Eckert, K.; Odenbach, S.; Eckert, S.; Gerbeth, G.

In this study we investigate the flow structure in a liquid metal cylinder while a bubble driven recirculation flow is superposed with a rotating magnetic field (RMF). The flow structure and the bubble detection were measured by means of the ultrasound Doppler velocimetry (UDV) and ultrasound transit-time technique (UTTT). The measurements revealed the potential of the RMF to control both the amplitude of the meridional flow and the bubble distribution and to provide an effective mixing in the whole fluid volume. Various periodic flow patterns were observed in a certain parameter range with respect to variations of the magnetic field strength and the gas flow rate.

Keywords: bubble detection; bubble flow; rotating magnetic field; udv

  • Open Access Logo Contribution to proceedings
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Deutschland
    Proceedings of ISUD8
  • Lecture (Conference)
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Deutschland

Publ.-Id: 17728

Magnetization dynamics of Co antidot lattices

Neudert, A.; Bali, R.; Kostylev, M.; Adeyeye, A.; Römer, F. M.; Wagner, K.; Farle, M.; Lenz, K.; Lindner, J.; Fassbender, J.

We have systematically investigated the static and dynamic magnetic properties of Co(t nm)/CoO(5 nm)/Cu(2 nm) antidot square lattices as a function of Co thickness [1]. The Co film thicknesses in the different samples are 25, 50, 75, and 100 nm, respectively. The antidot pattern forms a square lattice with a wavelength of 415 nm (center to center) and the hole diameters were varied in the different samples (145, 185, 225, and 265 nm, respectively).
The static magnetic properties were measured using in-plane magneto-optical Kerr effect (MOKE) magnetometry. Measuring magnetization loops at different in-plane angles we could determine the orientation dependence of coercive (Hc) and saturation (Hs) fields. Both fields show angular dependencies that form a 4-fold anisotropy with hard axes along the [10] directions. Those anisotropies in Hc and Hs can be explained by the geometry of the lattice by taking into account the hole diameter.
Dynamic measurements were done using time-resolved MOKE experiments and different ferromagnetic resonance (FMR) setups (Vector Network Analyzer (VNA)-based and classical detection using a shortened microwave cable). For the 50 nm thick sample with holes of 145 nm diameter a transition of the main mode from a lower frequency branch to a higher one was observed at a field of around 900 Oe and a frequency of around 6 GHz along the [10] direction. A similar transition between main modes is also visible for larger hole diameters as well as for larger film thicknesses. Due to the coexistence of 2 modes at a fixed frequency it is not a real frequency gap but on the other hand the two branches are also not connected, rather the main precessional magnitude transitions from the lower branch to the higher branch.
Angular FMR scans show a strong signal for a 4-fold anisotropy with the hard axes along the [10] directions and a weak signal for additional hard axes along the [11] directions, confirming the findings of the static angular loop measurements done with MOKE magnetometry.

Keywords: magnetization dynamics; antidot lattice; FMR

  • Poster
    2012 IEEE International Conference on Microwave Magnetics (ICMM 2012), 26.-29.08.2012, Kaiserslautern, Deutschland

Publ.-Id: 17727

Imaging of the brain serotonin transporters (SERT) with a new fluorine-18 labelled fluoromethyl-analogue of McN5652 and PET in humans

Hesse, S.; Brust, P.; Mäding, P.; Becker, G.-A.; Patt, M.; Seese, A.; Sorger, D.; Luthardt, J.; Steinbach, J.; Sabri, O.

Abstract wird nachgereicht.

  • Poster
    The 9th International Symposium on Functional Neuroreceptor Mapping of the Living Brain (NRM2012), 09.-11.08.2012, Baltimore, USA
  • Abstract in refereed journal
    Journal of Cerebral Blood Flow and Metabolism 32(2012), 100-127
    DOI: 10.1038/jcbfm.2012.79
    ISSN: 0271-678X

Publ.-Id: 17726

Thermophysical properties of the liquid Pb84.1-Au15.9 eutectic alloy

Plevachuk, Y.; Sklyarchuk, V.; Yakymovych, A.; Eckert, S.; Gerbeth, G.

Lead-gold eutectic alloy is under intense consideration as target material of spallation sources. The thermohydraulic design of such a target or related coolant systems requires a reliable data basis regarding the temperature dependent physical properties of such alloys. We present measurements of the electrical and thermal conductivity, thermoelectric power, viscosity and surface tension for liquid Pb-Au alloys of eutectic composition in a wide temperature range between the melting point and about 1000 K.

Keywords: thermophysical properties; lead-gold eutectics

Publ.-Id: 17725

PET Imaging of Cerebral Nicotinic Acetylcholine Receptors (nAChRs) in Early Alzheimer’s Disease (AD) Assessed with the New Radioligand (–)-[18F]Norchloro-Fluoro-Homoepibatidine ((–)-[18F]Flubatine)

Sabri, O.; Wilke, S.; Graef, S.; Becker, G.; Hesse, S.; Sattler, B.; Schönknecht, P.; Wagenknecht, G.; Smits, R.; Hoepping, A.; Steinbach, J.; Brust, P.

Abstract wird nachgereicht.

  • Poster
    The 9th International Symposium on Functional Neuroreceptor Mapping of the Living Brain (NRM2012), 09.-11.08.2012, Baltimore, USA
  • Abstract in refereed journal
    Journal of Cerebral Blood Flow and Metabolism 32(2012), 55-55
    DOI: 10.1038/jcbfm.2012.78
    ISSN: 0271-678X

Publ.-Id: 17724

In the search for a dream job - discovering your own potential.

Werniewicz, K.

Getting a job in today’s extremely competitive world is not a trivial task. Getting a job which in parallel meets your interest, field of expertise and overall skills as well as satisfying your ambitions and financial expectations, is a real challenge.
Luckily most of us do enjoy the challenging tasks and if we are armed with an excellent education, curiosity for life, and desire for further self-development, the challenges tend to motivate rather than hinder us in advancing our goals. A final measure of your success will be your own satisfaction.
The following workshop attempts to demonstrate the opportunities and tools available to young academics for their career development. These include:

  • Career path selection – making the most of your potential
  • Mobility – building an international career
  • Do I have the skill set and expertise people are looking for? – expanding your professional and interpersonal skills via diverse trainings
  • Job adverts - getting lucky in your job search
  • Shaping the future – preparing a career strategy, and finally
  • How to turn an initial failure into an ultimate success
These aspects will all be discussed and illustrated by examining my own experiences.
The most important message to be delivered by this workshop is that in chasing your dreams for a perfect job you must not fear changes. Only through exploring new areas, listing to your own needs and constructively responding to them, will you be able to find a position that suits you.
Remember, you always have a choice!
  • Invited lecture (Conferences)
    The BioTiNet Summer School "Titanium in Medicine", 04.-08.06.2012, Caldes d’Estrac, Barcelona, Spain

Publ.-Id: 17723

Verification and validation of numerical models of the transport of insulation debris

Cartland Glover, G. M.; Kratzsch, A.; Krepper, E.; Renger, S.; Seeliger, A.; Zacharias, F.; Alt, S.; Kästner, W.; Kryk, H.; Weiss, F.-P.

Damage to insulation materials located near to a primary circuit coolant leak may compromise the operation of the emergency core cooling system (ECCS). Insulation material in the form of mineral wool fiber agglomerates (MWFA) maybe transported to the containment sump strainers, where they may block or penetrate the strainers. Though the impact of MWFA on the pressure drop across the strainers is minimal, corrosion products formed over time may also accumulate in the fiber cakes on the strainers, which can lead to a significant increase in the strainer pressure drop and result in cavitation in the ECCS.
An experimental and theoretical study performed by the Helmholtz-Zentrum Dresden-Rossendorf and the Hochschule Zittau/Görlitz is investigating the phenomena that maybe observed in the containment vessel during a primary circuit coolant leak. The study entails the generation of fiber agglomerates, the determination of their transport properties in single and multi-effect experiments and the long-term effect that corrosion and erosion of the containment internals by the coolant has on the strainer pressure drop.
The focus of this paper is on the verification and validation of numerical models that can predict the transport of MWFA. A number of pseudo-continuous dispersed phases of spherical wetted agglomerates represent the MWFA. The size, density, the relative viscosity of the fluid-fiber agglomerate mixture and the turbulent dispersion all affect how the fiber agglomerates are transported. In the cases described here, the size is kept constant while the density is modified. This definition affects both the terminal velocity and volume fraction of the dispersed phases. Note that the relative viscosity is only significant at high concentrations.
Three single effect experiments were used to provide validation data on the transport of the fiber agglomerates under conditions of sedimentation in quiescent fluid, sedimentation in a horizontal flow and suspension in a horizontal flow. The experiments were performed in a rectangular column for the quiescent fluid and a racetrack type channel that provided a near uniform horizontal flow. The numerical models of sedimentation in the column and the racetrack channel found that the sedimentation characteristics are consistent with the experiments. For channel suspension, the heavier fibers tend to accumulate at the channel base even at high velocities, while lighter phases are more likely to be transported around the channel.

Keywords: Mineral Wool Fiber Agglomerates; Loss of Coolant Accidents; Containment Sump; Computational Fluid Dynamics; Multiphase Flow

Publ.-Id: 17722

Core-Core Interaction in Spin-Torque Double-Vortex Oscillators

Sluka, V.; Kákay, A.; Deac, A. M.; Bürgler, D. E.; Hertel, R.; Schneider, C. M.

Magnetic vortex states are determined by two binary parameters: The vorticity refers to the sense of rotation of the curling in-plane magnetization; the polarity determines the up or down orientation of the out-of-plane magnetized vortex core [1]. Due to their unique nano-scale properties, magnetic vortices may be used in a wide range of applications. However, to exploit their full potential, ways must be sought to measure the core polarity. Due to the smallness of the vortex core, this has so far been a difficult task requiring elaborate imaging techniques [2-4].
Here we present a combined experimental and numerical study on double vortex oscillators. Our samples are all-metallic nanopillars 150 nm in diameter that contain a Fe(30)/Ag(6)/Fe(15) pseudo spin valve. The geometry of the Fe disks is chosen as to stabilize configurations with two stacked vortices. By applying d.c. cpp-currents, we excite magnetization dynamics corresponding to gyrotropic vortex motion. We show that the coupled dynamics of the two vortices split into a fine structure of modes. As confirmed by micromagnetic simulations, the different frequencies correspond to different vorticity-polarity combinations of the double vortex system. In particular, changes in relative core polarity between the two vortices lead to frequency differences of the order of 100 MHz. Our results therefore suggest a way to measure vortex core polarities by electrical means.
[1] E. Feldtkeller, and H. Thomas, Phys. kondens. Mat. 4 (1965) 8.
[2] T. Shinjo et al., Science 289 (2000) 930.
[3] A. Wachowiak et al., Science 298 (2002) 577.
[4] A. Vansteenkiste et al., Nature Phys. 5 (2009) 332.

  • Poster
    21th International Colloquium on Magnetic Films and Surfaces (ICMFS2012), 24.-28.09.2012, Shanghai, China

Publ.-Id: 17721

Spin-Transfer Torque-Induced Dynamics of CoFe/Pd Superlattice-Based Nano-Oscillators in Perpendicular Magnetic Field

Sluka, V.; Fowley, C.; Bernert, K.; Deac, A. M.; Rippard, W. H.; Pufall, M. R.; Russek, S. E.

Spin-transfer torque provides a mechanism that can be employed to control magnetization on the nano-scale [1,2]. This scheme is used in spin-torque nano-oscillators (STNOs) where it is used to excite steady state precession of the magnetization, leading to microwave emission. Typical STNOs are nanopillars comprising two in-plane magnetized layers [3], one of which has a fixed magnetization while the other one is susceptible to spin-transfer torque. In such configurations, spin-torque generally leads to small angle or clam shell precession of the free layer around an in-plane easy axis of magnetization.
In this work, we investigate a different type of oscillator: The device consists of an in-plane magnetized CoFe layer and an out-of-plane magnetized [CoFe/Pd] superlattice. While the in-plane magnetized layer is confined to about 70 nm, the perpendicular layer is extended. In contrast to common STNOs, our structure is designed as to enable spin-torque-induced excitation in each of the layers. In the experiment, the spin-torque-excited magnetization dynamics is investigated with respect to the sample current and the applied out-of-plane magnetic field. For both current polarities, dynamic states are observed. Considering both layers separately, the in-plane magnetized layer contributes to the dynamics in either case of the current sign, however, the spin-torque asymmetry [4] allows excitation of the perpendicular layer only for one polarity. Since the observable signal is due to the relative motion of the layers’ magnetizations, the output frequency is significantly reduced compared to the frequency of each individually precessing layer. The concept of using the frequency difference between two dynamic layers coupled by spin-torque might be particularly useful for customizing STNOs for microwave generation.

1) J. C. Slonczewski, J. Magn. Magn. Mater. 159, (1996) L1.
2) L. Berger, Phys. Rev. B 54, (1996) 9353.
3) S. I. Kiselev et al., Nature 425, (2003) 380.
4) J. C. Slonczewski, J. Magn. Magn. Mater. 247, (2002) 324.

  • Poster
    21th International Colloquium on Magnetic Films and Surfaces (ICMFS2012), 24.-28.09.2012, Shanghai, China

Publ.-Id: 17720

Switching voltages and back-hopping in magnetic tunnel junctions with different geometries

Bernert, K.; Sluka, V.; Fowley, C.; Gan, H.; Fassbender, J.; Deac, A. M.

A spin-polarized current flowing through a ferromagnet can exert a torque on the local magnetization [1,2], which induce switching or steady state precession. Spin-transfer switching can be used as writing scheme in magnetic random access memory (MRAM), while spin-torque-driven precession can be exploited to design RF oscillators for telecommunication devices. Presently, the majority of spin-torque devices are based on a magnetic tunnel junction (MTJ) with an MgO barrier. A key step towards the practical implementation as MRAM elements is the reduction of the critical voltages [3].
Several groups have reported that MTJs exhibit the so-called ‘back-hopping’, whereby reliable switching is achieved with voltages of the order of the switching voltage, while a larger applied bias induces a telegraph-noise behaviour [4,5]. Back-hopping is characteristic for MTJs, since it has not been observed in metallic multilayers, and raises concerns for designing industrially-competitive MRAM devices. Here, we demonstrate that a potential cause for this phenomenon is the field-like (out-of-plane) spin-torque, which has been found to be much larger in MgO-MTJs than in metallic spin-valves, where it can be neglected [6]. In MgO-MTJs, however, the field-like torque can be of the order of 30% of the in-plane torque [7], and needs to be taken into account. We evaluate the switching phase diagram by analytically and numerically solving the modified Landau-Lifshitz-Gilbert equation which includes both (in-plane) (Slonczewski-like) and field-like torque terms for different geometries. The quadratic dependence of the field-like torque on the applied voltage [8] translates into a more complex correlation between the critical bias and the external field, altering the shape of the phase diagram as demonstrated experimentally [9]. It also explains back-hopping at a large bias for specific geometries, in agreement with experimental results.

[1] J. C. Slonczewski, J. Magn. Magn. Mater. 159 (1996) L1.
[2] L. Berger, Phys. Rev. B 54 (1996) 9353.
[3] Z. Diao et al., J. Phys.: Cond. Mat. 19 (2007) 165209.
[4] J. Z. Sun et al., J. Appl. Phys. 105 (2009) 07D109.
[5] T. Min et al., J. Appl. Phys. 105 (2009) 07D126.
[6] M. A. Zimmler et al., Phys. Rev. B 70, 184438 (2004).
[7] J. C. Sankey et al., Nat. Phys. 4, 67 (2008).
[8] C. Heiliger and M. Stiles, Phys. Rev. Lett. 100 (2008) 186805.
[9] S.-C. Oh et al., Nat. Phys. 5, 898 (2009).

Keywords: Spin-Torque Oscillators; Spin-Transfer Switching; Magnetic Random Access Memory

  • Lecture (Conference)
    2012 IEEE International Conference on Microwave Magnetics (ICMM 2012), 26.-29.08.2012, Kaiserslautern, Germany
  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS), 24.-28.09.2012, Shanghai, China

Publ.-Id: 17719

Microwave dynamics in point contact spin valve structures combining in-plane and out-of-plane magnetic layers with in-plane magnetic fields

Fowley, C.; Sluka, V.; Bernert, K.; Gan, H. D.; Deac, A. M.; Rippard, W. H.; Pufall, M. R.; Russek, S. E.

Point contact spin transfer devices combining perpendicularly and in-plane magnetized layers are good candidates to fulfill the requirements of high power, low line-width and close to zero applied field operation [1][2]. We present experimental results on spin transfer torque oscillators combining an extended out-of-plane (CoFe/Pd) magnetized layer and a lithographically patterned in-plane (CoFe) magnetized layer.
High frequency magnetization dynamics as a function of current in such devices are explored for in-plane applied magnetic field. In general, the recorded oscillation frequency is lower than that which would be expected for dynamics associated with a single layer in the device (calculated for the given Ha and Ms of each layer). The individual dynamics of each layer are calculated, individually, from numerical integration of the LLG equation taking into account the Slonczewski spin transfer torque including the spin transfer asymmetry characterized by λ [3]. Microwave oscillations are observed at zero applied magnetic field. However, due to canting of the perpendicular layer in the in-plane applied magnetic field, the current dependent frequency of the system changes slope when the relative magnetization orientations are changed from perpendicular to parallel.
A.M.D. and C.F. acknowledge financial support from the Swiss National Foundation Ambizione grant (PZ00P2_131808).
[1] Houssameddine, D. et al., Nature Mat. 6, 447 (2007).
[2] Rippard, W.H., et al., Phys. Rev. B. 81, 014426 (2010).
[3] Slonczewski, J.C., J. Magn. Magn. Mater. 247, 324 (2002).

Keywords: Spin transfer torque; spin transfer oscillators; numerical integration

Related publications

  • Poster
    21th International Colloquium on Magnetic Films and Surfaces (ICMFS), 24.-28.09.2012, Shanghai, China

Publ.-Id: 17718

Investigation of dipole strength in (gamma, gamma) and (n,gamma) experiments

Massarczyk, R.; Schwengner, R.; Junghans, A.; Schramm, G.; Grosse, E.

The talk is an overview of our dipole strength experiments and analysis in Dresden and Budapest. It was presented to the IRMM nuclear physics group as foundation for our collaboration in the future 77Se (n,gamma) experiment.

Keywords: photon strength function; neutron capture; statistical analysis

Related publications

  • Lecture (others)
    Seminar, 14.03.2012, Geel, Belgium

Publ.-Id: 17717

Quick-look report of the ROCOM Tests 1.3, 2.1 and 2.2 conducted within the OECD PKL2 Project

Kliem, S.; Franz, R.

In the frame of the OECD PKL 2 Project the Test G3.1 was conducted at the PKL test facility. This test was dedicated to the investigation of a fast cool down transient. The transient was initiated by a main steam line break. One of the objectives of this test was to create experimental data for the the qualification of thermal hydraulic codes against Pressurized Thermal Shock (PTS) and re-criticality aspects. To investigate in more detail the thermal hydraulic behavior inside the reactor pressure vessel (RPV) complementary tests on the coolant mixing were conducted at the ROCOM (Rossendorf Coolant Mixing) test facility. Experimental results at the RPV inlet derived from the Test G3.1 were used as boundary conditions for the ROCOM tests. In the ROCOM Test 1.3 a specific aspect of the behavior of an ECC water stripe was investigated. The goal of the Tests 2.1 and 2.2 was the re-criticality issue, more specific, the investigation of the possibility of the formation of a sector with overcooled water at the core inlet.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2012
    0038 Seiten
    ISSN: 2191-8708, eISSN: 2191-8716

Publ.-Id: 17716

Parametric resonance in a periodically perturbed von-Karman flow

Giesecke, A.; Stefani, F.

We have performed numerical simulations of the kinematic induction equation in order to examine the dynamo efficiency of an axisymmetric von-Karman-like flow suct to time-dependent non-axisymmetric velocity perturbations. The numerical model is based on the setup of the French Von-Karman-Sodiuynamo and the flow measurements from a model water experiment conducted at the University of Navarra in Pamplona,ain. We find two distinct regimes of dynamo action that depend on the azimuthal drift of an (m=2) vortex like floerturbation. For comparatively slowly drifting vortices we observe a narrow window with enhanced growth-rates anddrift of the magnetic eigenmode that is synchronized with the flow perturbation drift. For larger vortex drift an abrupt transition to independently drifting magnetic eigenmode occurs and the field amplitude is modulated with twice the vortex driftequency. The sudden change between the resonant regime and the modulated regime is identified as an spectral exceonal point where eigenvalues and eigenfunctions of two previously independent modes collapse.

Keywords: Dynamo; Simulation

  • Lecture (Conference)
    European GDR Dynamo & MHD Days, 01.-04.10.2012, Nice, France

Publ.-Id: 17715

Research on the reactor physics and reactor safety of VVER reactors – Selected contributions to the XXIst Symposium of the Atomic Energy Research organization

Aszodi, A.; Kliem, S.

The Atomic Energy Research (AER) is an organization of 22 institutions (utilities, re-search institutes and universities) from nine countries. The common interest within this organ-ization is the research on topics related to all aspects of the operation of VVER reactors. AER provides the only regular scientific-technical co-operation for the VVER user countries. The organization is also open to institutions from countries not operating VVER reactors. . In 2011, the XXIst Symposium was organized in Dresden, Germany, from September 19 till 23. It was hosted by the Institute of Safety Research of the Helmholtz-Zentrum Dresden-Rossendorf. Altogether 61 papers were presented during this Symposium. The organizing committee selected 15 papers from the Symposium for this special issue of Kerntechnik, representing the whole spectrum of the activities of the AER.

  • Kerntechnik 77(2012)4, 212-212
    ISSN: 0932-3902

Publ.-Id: 17714

Sound velocity measurements in fluids using echo signals from scattering particles

Lenz, M.; Bock, M.; Kühnicke, E.; Pal, J.; Cramer, A.

A novel approach for measuring the speed of sound in fluids with scattering particles is presented. Potential fields of application for sound velocity measurements in fluids are process control, environmental measurement technology and medicine, where sound velocity can be used as an indicator of temperature, concentration or mass density. Similar to the pulsed Doppler application, the method also works non-invasively and uses the echo signals from scattering particles suspended in the fluid. The basic idea is that the ultrasonic time of flight to the focus position z depends on the speed of sound c in a well-defined way. The time of flight to the focus can be extracted from the echo signals, because the stray echo is strongest for the scattering particles being located in the sound focus and can thus be used to determine the speed of sound. Results are shown for different homogeneous fluids with sound velocities between 1116 m/s (ethanol, 50 °C) and 2740 m/s (eutectic GaInSn). Measurements have shown that a statistical measurement uncertainty of about 0,1 % was achieved with the underlying set-up. Further results of recent measurements in water having a temperature gradient show that the method is even capable of measuring the sound velocity with local resolution.

Keywords: speed of sound; material characterisation; scattering particles; annular array

  • Contribution to proceedings
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering ISUD8, 19.-21.09.2012, Dresden, Deutschland
    Sound velocity measurements in fluids using echo signals from scattering particles
  • Lecture (Conference)
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering ISUD8, 19.-21.09.2012, Dresden, Deutschland

Publ.-Id: 17713

Mikro- und (Ultra)spurenelementanalyse - ein wichtiges Werkzeug für die Suche und Erkundung von Erzlagerstätten

Renno, A. D.

Auf den ersten Blick ein Widerspruch – ist die Analyse von Spurenelementen in sehr kleinen Dimensionen bei der Suche nach Erzlagerstätten von entscheidender Bedeutung. Ohne solchen Analysen können wir die Lagerstätten nicht ressourcenschonend und nachhaltig nutzen.

Keywords: Ressourcenanalytik; Ultraspurenelement; Mikroanalyse

Related publications

  • Lecture (others)
    Dresdner Lange Nacht der Wissenschaften, 06.07.2012, Dresden, Deutschland

Publ.-Id: 17712

Flow measurements in a model of the Czochralski crystal growth process

Pal, J.; Cramer, A.; Gerberth, G.

An experimental study of the buoyancy-induced flow in a model of a Czochralski crystal growth system was conducted. Ultrasonic velocimetry was used to measure fluid velocities. To have similar thermal boundary conditions as in an industrial growth facility, a double walled glass crucible flown through by a heating fluid was chosen to hold the fluid. Similarity of the heat transfer conditions was achieved by selecting a liquid metal as the fluid under investigation, which was the ternary alloy GaInSn having a Prandtl number of 0.021. Because of the double-walled crucible, measurements through the container wall are difficult if ever possible. Since the availability of relatively short ultrasonic transducers it is practicable to have the sensor immersed into the fluid. Measurements of the radial velocity component shortly below the melt surface across the entire diameter of the crucible at various azimuthal angles reveal the complex flow structure of natural convection in a Czochralski crucible. As it is not to be expected to grow high quality mono-crystalline crystals from such a non-axisymmetric flow, rotating magnetic fields (RMF) are often proposed to render the flow more axisymmetric. This paper also addresses the question what happens to the buoyancy-driven flow when such an RMF is applied.

Keywords: Czochralski crystal growth; Rayleight-Benard convection; ultrasonic flow measurement; magnetohydrodynamics; electromagnetic stirring

  • Contribution to proceedings
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering ISUD8, 19.-21.09.2012, Dresden, Deutschland
    Flow measurements in a model of the Czochralski crystal growth process
  • Lecture (Conference)
    8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering ISUD8, 19.-21.09.2012, Dresden, Deutschland

Publ.-Id: 17711

Investigation of dual-beam-implanted oxide-dispersed-strengthened FeCrAl alloy by positron annihilation spectroscopy

Kögler, R.; Anwand, W.; Richter, A.; Butterling, M.; Mücklich, A.; Ou, X.; Reuther, H.; Chen, C.-L.; Wagner, A.

Oxide-dispersion-strengthened (ODS) FeCrAl steel is a class with promising materials to be applied for future nuclear applications. However, radiation damage, especially the formation of vacancy clusters or gas-filled bubbles, may result in hardness increase and the loss of ductility. Positron annihilation spectroscopy (PAS) is demonstrated to be a very useful and non-destructive analysis method to detect and to determine open volume defects of sub-nm size in ODS alloy. Synchronized dual beam implantation of Fe and He ions is performed to simulate the radiation damage caused by (n, α) reactions and to avoid induced activation. For room temperature implantation, i.e. without significant point defect recombination, the differences in the defect formation are shown by comparison between irradiation of ODS alloy and pure Fe bulk. The open volume defects created in ODS alloy are vacancy clusters closely connected with dispersed Y oxide nanoparticles. Their profiles are in reasonable qualitative agreement with the hardness profiles, indicating a relationship between sub-nm vacancy clusters or He bubbles and the hardness of the material. In heat-treated ODS alloy, containing larger vacancy clusters, the radiation induced hardness increase is more distinctive than for as-received ODS alloy.
For irradiation at a moderately enhanced temperature of 300°C open volume defects are drastically reduced. The few remaining defects are vacancy clusters of the same type as in as-received ODS alloy. Close to the surface the open volume defects completely disappear. These results are in agreement with the hardness measurements showing little hardness increase in this case.
The suitability of ODS-based materials for nuclear applications was verified.

Keywords: Radiation resistant materials; ODS steel; simultaneous dual beam ion implantation; vacancy clusters; He bubbles; hardness

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Publ.-Id: 17710

The synthesis of cutting-edge laboratory methodology and highly effective analytical service - Resource analytics at the newly founded Helmholtz-Institute Freiberg for Resource Technology (Germany)

Renno, A. D.; Gutzmer, J.; Merchel, S.; Möckel, R.; Krause, J.; Rugel, G.; Haser, S.; Ziegenrücker, R.; Michalak, P. P.

Based on an initiative of the German Federal Government the Helmholtz Institute Freiberg for Resource Technology (HIF) is being established jointly by the Helmholtz-Zentrum Dresden-Rossendorf and the TU Bergakademie Freiberg. The new institute is to make a vital contribution towards implementing the national German strategy on raw materials. These visions and aims form the intellectual basis for the scientific work at the HIF:

  • New technologies for utilization of mineral and metal containing resources from complex domestic and foreign deposits
  • Contribution to global environmental protection by means of material and energy efficient extraction and use of raw materials
  • Economic networks between Germany and resource countries based on sustainable technologies provided to German industry by the Helmholtz Institute (technology in exchange for access to raw materials)
  • Training of new generation of highly qualified academic and technical staff for German industry and academia
The chemical and phase analysis of all natural and synthetic materials involved in the supply chain, named as resource analytics, is one of the backbones of the HIF. During implementation of the Department of analytics we embark on the following strategy:
  • Concentration of all competences and capacities in one department available to all other departments
  • Avoiding isolated applications
  • Strict integration of the analysts during acquisition and design of projects
  • Consistent integration of further development of laboratory methodology into scientific projects of the respective departments.
We describe the rationales and present first results of our landmark projects in resource analytics:
  • High-speed PIXE of natural and synthetic materials
  • Super-SIMS
  • Automated mineralogy
  • Reference materials for microanalytical methods
and demonstrate the interplay with the common projects of the HIF.

Keywords: Resource Analytics; Super-SIMS; High-speed PIXE; Automated Quantitative Mineralogy; Reference Materials

Related publications

  • Lecture (Conference)
    GEOANALYSIS 2012 - The 8th International Conference on the Analysis of Geological and Environmental Materials, 16.-20.09.2012, Búzios, Rio de Janeiro, Brasilien

Publ.-Id: 17709

Universal Presence of Elements – still a valid concept?

Renno, A. D.

In 1936 Ida Noddack published her landmark paper “Über die Allgegenwart der chemischen Elemente” – in English „About Universal presence of Elements“ (Noddack, 1936). In this article she states: “Alle chemischen Elemente kommen in allen Mineralien vor.“ – in English: „All chemical elements are present in all minerals.” This conclusion was based in the painstaking trace element analysis of bulk minerals. She was able to document the presence of such chemical elements as Re in sphalerite down to 10 ppb (Noddack, 1936).
It was, of course impossible for her to anticipate the development of modern microanalytical instrumentation, which is able to operate routinely at the picogram test portion range.
The Helmholtz- Institute Freiberg for Resource Technology is currently working to establish the Super-SIMS method (Döbeli et al, 1994) for analysis of minerals, ores and other materials related to resource technology. The extreme sensitivity of this technique raises the question of the validity of the concept of Universal Presence of Elements. It is expected that the Super-SIMS we will be able to quantify some elements down to the 1 ng/g level (10-12 atoms/atoms) in ideal matrices. Using a commercial available ion probe we will be able to focus the ion beam down to 2 µm in diameter, equivalent to a sampling mass at or below the sub-ng level.
Simulations of the probabilities of finding elements of interest at such low target concentrations show that the Super-SIMS will reach the point that the chance of measuring these elements in such small sampling volumes will be less than 10 %.This leads to a number of new questions which need to be addressed when addressing the topic of a given element yes-or-no. Is the amount of an ultratrace element in a mineral determined by the concentration in the bulk mineral or by the analytical capabilities?
Is it still possible to describe the geochemical behavior of ultratrace elements if the probability of detection of such elements in very tiny volumes approaches zero?
What are the driving forces behind the geochemical behavior of such ultratrace elements?
We hope that the new Super-SIMS facility will help to answer such question in the not too distant future.


Döbeli M., Nebiker P.W., Suter M., Synal H.A., Vetterli D. (1994) „Accelerator SIMS for trace element detection. In: Nucl Instr Meth B85:770–774.
Noddack, I. (1936) “Über die Allgegenwart der chemischen Elemente” in: Angewandte Chemie, Vol. 49(47), pp. 835-854)

Keywords: Geochemistry; Super-SIMS; Universal Presence of Elements; Ultratrace Element; Analytical Geochemistry

Related publications

  • Lecture (Conference)
    GEOANALYSIS 2012 - The 8th International Conference on the Analysis of Geological and Environmental Materials, 16.-20.09.2012, Búzios, Rio de Janeiro, Brasilien

Publ.-Id: 17708

Reference Materials in Automated Quantitative Mineralogy – experiences and approaches at the Freiberg Geometallurgy Laboratory

Haser, S.; Renno, A. D.; Bartzsch, A.; Weißflog, C.; Sandmann, D.; Schulz, B.; Gutzmer, J.

Quantitative mineralogy done by automated image acquisition, signal processing and analysis became the principle driving force behind geometallurgical research projects and industrial applications. The same analytical methodology is used in forensic examinations, as well as for petrological, mineralogical and archaeometrical studies.
Recent developments in instrumental techniques, new algorithms for image and signal processing and growing computing power form the basis for this enormous development. The level of automation, the reproducibility and 'superhuman' never-tiring endurance have made this methodology virtually indispensable.
As a consequence of this development, due to the growing economic impact and foreseeable individual consequences as the result of forensic studies, laboratories using automated quantitative mineralogical methods have to face more and more question relating to:

  • the accuracy and trueness of measurement,
  • measurement precision and measurement reproducibility, and
  • metrological traceability.
The routine usage of reference materials (RM) is one of the cornerstones to meet such requirements.
The principle of measurement is the combined detection of back-scattered electron intensities and X-ray spectra, both depending basically on chemical properties of the material studied. Automated quantitative mineralogy is consequently no true (primary) phase analytical method (PAM) and has to be traced back to primary PAMs.
To identify the RMs needed the quantitative mineralogical measurement needs to be separated into distinct steps and tangible variables that influence the success of these steps. The main steps, excluding sampling, are:
1. sample preparation,
2. image acquisition,
3. X-ray spectra acquisition,
4. X-ray spectra processing,
5. image processing including stereological reconstruction of 3-D features,
6. calculation of derived data like mineral mode, particle size distribution, particle shapes,
degree of liberation or the resolution of intergrowth relationships.
In general, quality management for steps 2 and 3 is well established and described in standardized procedures and well covered with RMs. However, the lack of suitable RMs affects all the other steps significantly.
The largest contribution to the uncertainty budget is sample preparation. The preparation of “in-house” standards will improve the situation, but will not reach the effects of future RMs. RMs to assess the correct and reproducible processing of X-ray spectra and the stereological reconstruction are easier to define and fabricable, but very scarce.
The experience of the Freiberg Geometallurgy Laboratory with missing suitable RMs is illustrated and missing inter-laboratory comparability of results is identified as the most serious challenge. First approaches to a solution, focusing on the creation of “in-house” standards as a first step towards a broader approach involving other laboratories worldwide, are presented and critically evaluated.

Keywords: Automated Quantitative Mineralogy; Reference Materials; Geometallurgy; Sample Preparation; Uncertainty Budget

  • Lecture (Conference)
    Microanalytical Reference Materials - An MAS Topical Conference, 15.-17.05.2012, Golden, USA

Publ.-Id: 17707

Element- and method-specific test for microhomogeneity of major and trace elements in reference materials

Renno, A.

Homogeneity is a relative property of a sample in relation to the measurement (analytical method), the measurand (analyte), and the intended purpose, like the usage as a reference material (RM). The verification of homogeneity is essential to define a RM as fit for purpose. As a result of the lack of suitable RMs for microanalytical methods bulk RMs are used to calibrate the instruments, to validate methods, to estimate uncertainty, and for internal quality control.
To proof the superiority of synthetic mineral phases over natural ones as RMs for microanalytical methods we started to synthesize, different feldspars, pyrite and columbite/tantalite in the framework of a research project founded by the European Union (ESF) and the Free State of Saxony [1]. We hope that our attempt act as a trigger for forthcoming efforts in the production and certification of such RMs. The usage of these synthetic minerals will not restricted to a single analytical method, like electron probe microanalysis or LA-ICP-MS, non-destructive and destructive.
The assessment of homogeneity is an integral part of the synthesis tests and of the following certification. The test comprises several steps considering the relative character of microhomogeneity. This specific feature requires that all such tests have to be adapted to the specific analytical method, the specific element, and the type of microheterogeneity.
Five types of microheterogeneity were defined, based on the work of Malissa [2], Danzer [3], Kempenaers et al. [4], and Inczédy [5].
•random (stochastic) type
•systematic type
•nugget type
•island type
•periodic type.
A particular sampling strategy was defined for each type of microheterogeneity. The single calculations consider the different element- and method dependent 'information values', by using simulation software like CASINO, PENEPMA, SRIM or PyMCA.
The second step is the assessment of a critical mass in the sense of Danzer [6] and Kempenaers et al. [4] for every element.
The last measure requires the specification of the minimal volume of the whole synthesized mineral and the distance between sub-samples to be checked for microhomogeneity, following the procedures described by Chayes [7] for classical modal analysis of rocks [8].
[1]P.P. Michalak, A.D. Renno, S. Merchel, F. Munnik, M. Wiedenbeck, Microsc. Microanal. 17 (Suppl 2), 2011, 852-853.
[2]H. Malissa, K. Swoboda, Radex, 1963, 494.
[3]K. Danzer, Spectroch. Acta, 1984, 949-954.
[4]L. Kempenaers et al., Anal. Chem., 2002, 5017-5026.
[5]J. Inczédy, Talanta, 1982, 643-645.
[6]K. Danzer, Talanta, 1977, 561-565.
[7]F. Chayes, Petrographic Modal Analysis – An elementary statistical appraisal, John Wiley & Sons, New York, 1956.
[8]This project is supported by the European Union (ESF) and the Free State of Saxony. Many thanks to the custodians of the Geoscientific Collections in Freiberg for saving and providing an invaluable source of material. Motivating discussions on several facets of this study with Jens Gutzmer, Michael Wiedenbeck, Uwe Reinholz, and Slavo Michalak were very helpful.

Keywords: Reference Materials; Homogeneity; Heterogeneity; Homogeneity Test

  • Invited lecture (Conferences)
    Microanalytical Reference Materials - An MAS Topical Conference, 15.-17.05.2012, Golden, USA

Publ.-Id: 17706

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