Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Polyatomic bismuth impacts into germanium: Molecular dynamics study

Anders, C.; Heinig, K.-H.; Urbassek, H.

Using molecular dynamics simulations, we study the effects induced by the impact of Bin (n≤5) clusters with energies in the range of a 3–20 keV/atom into a Ge target. The target consists of Ge including a 10% contribution of randomly distributed Bi atoms. The impacting polyatomic clusters create a long-lived melt pool at the surface. After resolidification, the surface shows a characteristic meniscuslike depression; it is caused both by the missing sputtered atoms and by the volume change of Ge upon melting and amorphization. During cooling, Bi is driven towards the center of the melt pool. A large precipitate forms at the surface (for polyatomic impact) or in the center of the molten pocket (for monatomic impact). The remainder of the resolidified amorphous zone is purified from Bi. We argue that the reason for the demixing of Bi and Ge is the thermophoretic or Soret effect which is caused by the different diffusivities of Bi and Ge in the melt. Bi is sputtered preferentially from the sample. The extent of surface modification, the amount of Bi collected on the surface, the concentration of Bi, and structure of Bi precipitates in the former melt pool are analyzed in their dependence on projectile size, impact energy, and direction.

Keywords: atomistic computer simulation; germanium; polyatomic ions; melting

Publ.-Id: 18934

Advanced Numerical and Experimental Studies to Turbulent Buoyancy Driven Flow in the Primary Circuit of Pressurized Water Reactors

Höhne, T.

Validated and accurate advanced simulation tools, in particular advanced Computational Fluid Dynamics (CFD) simulation methods, are required to further improve the economics and safe operation of future nuclear power plants.
These methods will be beneficiary for Generation III+ and Generation IV reactors.
Buoyancy driven flows are of relevance for boron dilution transients or pressurized thermal shock scenarios.
Therefore, a combined numerical and experimental study of buoyant mixing processes is planned in the project using existing experiments of the HZDR test facility ROCOM.
A systematic determination of the advantages, disadvantages, and accuracy of these advanced CFD simulation methods for application to NRS assessments is planned.
This will contribute to the development of Generation III+ and IV nuclear reactors, and thereby to the utilization of more efficient and more economical nuclear power in the future.


  • Invited lecture (Conferences)
    IAEA Workshop, 17.-19.07.2013, Wien, Österreich

Publ.-Id: 18933

Linear excitation of short propagating spin waves via a pair of layered vortex cores

Wintz, S.; Weigand, M.; Tyberkevych, V. S.; Slobodianiuk, D. V.; Stoll, H.; Raabe, J.; Neudert, A.; Erbe, A.; Lindner, J.; Slavin, A. N.; Fassbender, J.

The investigation of spin wave dynamics in nanomagnetic systems is one of the key topics in modern magnetism. To excite short spin waves, it is typically necessary either to use transducers of the size of a wavelength (micro-striplines or point-contacts) or to excite the spin waves parametrically by a double-frequency spatially uniform microwave signal. Here we demonstrate that the efficient linear excitation of short propagating spin waves is possible in a trilayer in which the magnetic layers form a vortex pair with opposite circulations and parallel cores. Such spin waves are directly observed by time-resolved x-ray microscopy upon application of microwave magnetic fields of appx. 1 mT. We find that for excitation frequencies in the GHz regime, the resulting spin wavelength is continuously tunable in a range between 50 nm and 500 nm by this frequency. Here, the radial spin wave propagation direction depends on the total handedness of the two vortex circulations, revealing a clear non-reciprocity of the spin waves observed. Both, analytic theory and micromagnetic simulations show that such a nanomagnetic system supports a gapless spin wave branch with linear dispersion and strong nonreciprocity, and that the propagating spin waves belonging to this branch can be excited by a spatially uniform microwave signal. Other excitation mechanisms, such as spin-transfer torques or thermal gradients, could be utilized to generate spin waves in the system presented.

  • Poster
    Gordon Research Conferences: Spin Dynamics in Magnetic Nanostructures, 18.08.2013, Hong Kong, China

Publ.-Id: 18932

Results of Testing of Calculation Procedure for Neutron Fluence and Spectrum on the VVER-440 RPV during Operation with new Fuel Compositions

Borodkin, P. G.; Borodkin, G. I.; Adeev, V. A.; Konheiser, J.

In accordance to PNAE G-7-008-89 [1] on the NPP since starting-up should be accounted neutron fluence of RPV, which determines the RPV life-time in accordance to strength calculations. Detailization of these PNAE G-7-008-89 [1] requirements has been represented in the RB-007-99 [2]. Recently elaborated procedure for accounting and prediction of RPV fast neutron fluence has been regulated by normative document RD EO [3].
During NPP unit operation some modernizations have been realized, for example, using of new types of fuel assemblies and new kind of fuel. Changes in the reactor core loading, especially on the core periphery, give influence in the fast neutron fluence on the RPV, which should be evaluated by neutron fluence calculations. The reliability of these calculations should be validated by ex-vessel neutron-activation measurements at NPPs with VVER.
Paper deals with the results of calculations and measurement of fast neutron fluence on the RPV for last fuel cycles of Kola NPP power units, with using new type of fuel, and gives some recommendations for improvement of routine fluence calculation procedures.

Keywords: VVER; neutron fluence; RPV

  • Lecture (Conference)
    Safety Assurance of NPP with WWER, 28.-31.05.2013, Podolsk, Russia
  • Contribution to proceedings
    Safety Assurance of NPP with WWER, 28.-31.05.2013, Podolsk, Russia
    Conference proceedings

Publ.-Id: 18931

Synchrotron X-ray tomography of a Taylor bubble

Boden, S.; Hampel, U.

A profound understanding of the transfer processes in capillary multiphase flow is of primary importance from the viewpoint of fundamental science as well as for practical design and operation of new chemical reaction devices. The desired flow regime in such small channel geometries is surface tension dominated Taylor bubble flow. Still today the lack of precise morphological data on such Taylor bubble capillary two-phase flows calls for the development of adequate measurement techniques providing the necessary spatial resolution for the investigation of the flow structures moving at moderate speeds. Experiments to reveal the shape of moving Taylor bubbles were performed at the ANKA synchrotron radiation source in Karlsruhe, Germany, in capillaries with a hydraulic diameter of dh = 2 mm. The careful examination of the bubble positions in the dataset enabled the generation of consecutive projection images necessary for application of a computerized tomographic reconstruction algorithm to reveal the cross-sectional shape of the Taylor bubble.

Keywords: Taylor bubble flow; X-ray tomography; synchrotron

  • Lecture (Conference)
    7th World Congress on Industrial Process Tomography, 02.-05.09.2013, Krakow, Poland

Publ.-Id: 18930

Thermal-Hydraulic Investigations for Safety Related Tasks

Höhne, T.

The session „Thermal-Hydraulic Investigations for Safety Related Tasks“ was chaired by Thomas Höhne (Helmholtz-Zentrum Dresden - Rossendorf ).
The first presentation on „Comparative analysis of a LOCA for a German PWR with ASTEC and ATHLET-CD“, from Nils Reinke (Co-authors: H.-W. Chan, M. Sonnenkalb, all from the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH, Köln) presented calculations with the German-French severe accident integral code ASTEC for the early phase of the accident, thereby focusing on thermal-hydraulics mainly. He explained that the purpose of this work was mainly to assess the ASTEC code behavior in modeling thermal-hydraulics in the coolant circuit in the early phase of a hypothetical severe accident. This is in particular interesting, since the early phase of the accident determines core heat-up and the subsequent core degradation phase. A comparison is done versus the more mechanistic code system ATHLET-CD/COCOSYS, developed at GRS, too.

Keywords: KTG; Jahrestagung Kerntechnik; Thermal-Hydraulic; CFD

  • atw - International Journal for Nuclear Power 58(2013)10, 587-588

Publ.-Id: 18929

Ortsaufgelöste Analyse von Uranspezies mittels einem gekoppelten System aus CLSM und LIFS

Großmann, K.; Arnold, T.; Brockmann, S.

Die fluoreszierenden Eigenschaften des Urans bei Anregung mit UV-Licht werden zunehmend für spektroskopische Analysen von Uranspezies innerhalb wässriger Proben eingesetzt. Dabei spielen neben den Fluoreszenzeigenschaften der sechswertigen Oxidationsstufe auch zunehmend die der vier- und fünfwertigen Oxidationsstufe eine wichtige Rolle. Bei Fluoreszenzmessungen von Uranverbindungen sind die Emissionsbandenlagen sowie die Fluoreszenzlebenszeit (die Abklingzeit der Fluoreszenzlichtemission nach der Anregung) wichtige Parameter. Durch Abgleich der ermittelten Peaklagen und Lebenszeiten mit denen von Referenzverbindungen lassen sich somit Aussagen zur vorhandenen Uranspezies treffen. Die Detektion von Fluoreszenzemissionsspektren an festen bzw. biologischen Proben mittels (zeitaufgelöster) laserinduzierter Fluoreszenzspektroskopie (TRLFS bzw. LIFS) hat jedoch den Nachteil, dass keine Aussagen zur räumlichen Lokalisation des Urans möglich sind. Gerade in komplexen, biologischen Proben, wie Biofilmverbänden oder mikrobiellen Zellen, sind jedoch Aussagen zum Ort der Urananreicherung in der Probe erwünscht um z.B. zwischen intra- und extrazellulären Urananbindungen unterscheiden zu können.
Die Fluoreszenzeigenschaften der Uran(VI)verbindungen und –minerale können auch zu deren Lokalisation innerhalb von komplexen Proben genutzt werden. So stellt die Anwendung fluoreszenzmikroskopischer Messmethoden eine Möglichkeit dar, Uranpräzipitate und Anreicherungen z.B. in biologischen Proben wie Biofilmen oder Zellen zu lokalisieren und zu visualisieren. Die konfokale Laser-scanning Mikroskopie (CLSM) eignet sich hierbei besonders, da diese Methode eine dreidimensionale Darstellung fluoreszierender Bereiche in komplexen Probenstrukturen ermöglicht. Durch Anwendung geeigneter Fluoreszenzfarbstoffe kann auch die sonstige Probenstruktur abseits der fluoreszierenden Schwermetalle abgebildet werden, wodurch eine räumliche Einordnung innerhalb der Probengeometrie ermöglicht wird [1].
Eine Kopplung der konfokalen Laser-scanning Mikroskopie (CLSM) mit der laserinduzierten Fluoreszenzspektroskopie (LIFS) ermöglicht es Fluoreszenzsignale räumlich, dreidimensional zu lokalisieren und zu visualisieren sowie gleichzeitig entsprechende ortsaufgelöste, fluoreszenz-spektroskopische Daten zu detektieren [2]. Verschiedene erfolgreiche Anwendungen an biologischen Proben aber auch an Mineraloberflächen zeigen, dass es sich bei dieser kombinierten Methode aus Mikroskopie und Spektroskopie um eine zukunftsweisende Technik zur zerstörungsfreien Detektion von fluoreszierenden Schwermetallen und besonders der Uran(VI)spezies handelt. Diese Methode ist besonders vielversprechend hinsichtlich der Detektion von Uran(VI)akkumulationen innerhalb von komplexen Probensystemen deren Struktur und Aufbau durch die Analyse der Uranspezies nicht zerstört werden soll. Dabei zeichnet sich diese Technik durch relativ niedrige Nachweisgrenzen von bis zu 1∙10-6 M für Uran(VI)verbindungen innerhalb des konfokalen Volumens aus.

  • Poster
    7. Workshop RCA, 10.-11.06.2013, Rossendorf, Deutschland

Publ.-Id: 18928

Growth of a three-dimensional anisotropic lattice of Ge quantum dots in an amorphous alumina matrix

Buljan, M.; Roshchupkina, O.; Santic, A.; Holy, V.; Baehtz, C.; Mücklich, A.; Horak, L.; Vales, V.; Radic, N.; Bernstorff, S.; Grenzer, J.

Simple processes for the preparation of semiconductor quantum dot lattices embedded in dielectric amorphous matrices play an important role in various nanotechnology applications. Of particular interest are quantum dot lattices with properties that differ significantly in different directions parallel to the material surface. Here, a simple method is demonstrated for the fabrication of an anisotropic lattice of Ge quantum dots in an amorphous Al2O3 matrix by a self-assembly process. A specific deposition geometry with an oblique incidence of the Ge and Al2O3 adparticles was used during magnetron sputtering deposition to achieve the desired anisotropy. The observed Ge quantum dot ordering is explained by a combination of directional diffusion of adparticles from the Ge and Al(2)O(3)targets and a shadowing process which occurs during deposition as a result of the specific surface morphology. The prepared material shows a strong anisotropy of the electrical conductivity in different directions parallel to the sample surface.

Keywords: Ge quantum dots; self-assembly; conductivity; anisotropy; magnetron sputtering; synthesis

Publ.-Id: 18927

The neutron-proton charge-exchange amplitudes measured in the dp -> ppn reaction

Mchedlishvili, D.; Barsov, S.; Carbonell, J.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Engels, R.; Gebel, R.; Glagolev, V.; Grigoryev, K.; Goslawski, P.; Hartmann, M.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Stein, H.; Steffens, E.; Stockhorst, H.; Stroher, H.; Tabidze, M.; Trusov, S.; Uzikov, Y.; Valdau, Y.; Wilkin, C.

The unpolarised differential cross section and the two deuteron tensor analysing powers A(xx) and A(yy) of the (d) over right arrowp -> {pp}(s)n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27 GeV, data were obtained for small momentum transfers to a {pp}(s) system with low excitation energy. The results at the three lower energies are consistent with impulse approximation predictions based upon the current knowledge of the neutron-proton amplitudes. However, at 2.27 GeV, where these amplitudes are far more uncertain, agreement requires a reduction in the overall double-spin-flip contribution, with an especially significant effect in the longitudinal direction. These conclusions are supported by measurements of the deuteron-proton spin-correlation parameters C-x,C-x and C-y,C-y that were carried out in the (d) over right arrow(p) over right arrow -> {pp}(s)n reaction at 1.2 and 2.27 GeV. The values obtained for the proton analysing power A(y)(p) also suggest the need for a radical re-evaluation of the neutron-proton elastic scattering amplitudes at the higher energy. It is therefore clear that such measurements can provide a valuable addition to the neutron-proton database in the charge-exchange region.

Publ.-Id: 18926

The ternary system U(VI) / humic acid / Opalinus Clay

Joseph, C.

The storage of nuclear waste in deep geological formations is discussed worldwide as the main strategy for nuclear waste management. To ensure the confinement of the nuclear waste, a multiple barrier system which consists of engineered, geo-engineered, and geological barriers will be applied. Thereby, in Germany the definition of the isolating rock zone represents an important safety function indicator.
Clay rock is internationally investigated as potential host rock for a repository and represents a part of the geological barrier. In the present work, the natural clay rock Opalinus Clay from the Mont Terri rock laboratory, Switzerland, was studied.
In Germany, the direct disposal of the spent nuclear fuel without the reprocessing of the spent fuel is preferred. In case of water ingress, radionuclides can be released from the nuclear waste repository into its surroundings, namely the host rock of the repository. Humic acids, ubiquitous in nature, can be found associated with the inorganic components in natural clay rock (1.5×10–3 wt.% in Opalinus Clay). They can be released under certain conditions. Due to their variety of functional groups, humic acids are very strong complexing agents for metal ions. They have inherent redox abilities and a colloidal conformation in solution. Because of these characteristics, humic acids can affect the mobility of metal ions such as actinides. Furthermore, in the near-field of a repository elevated temperatures have to be considered due to the heat production resulting from the radioactive decay of the various radionuclides in the nuclear waste.
This work focuses on the interaction of uranium, as main component of spent nuclear fuel, with Opalinus Clay and studies the influence of humic acid and elevated temperature on this interaction. For investigation of the retention behavior of the clay and the mobility of U(VI) in the system, batch sorption and diffusion experiments were performed. To clarify which U(VI) and humic acid species were present under the applied conditions, aqueous speciation modeling was used. Additionally, the U(VI) speciation in solution and on the clay surface was investigated by spectroscopic methods.

Prior to the investigation of the ternary system U(VI) / humic acid / clay, the applied batches of Opalinus Clay were characterized (e.g., specific surface area, carbon content, cation exchange capacity, elemental composition, particle size distribution). Leaching studies with Opalinus Clay in synthetic Opalinus Clay pore water (pH 7.6, It = 0.34 mol/L) and in NaClO4 (pH 3 – 10, I = 0.1 mol/L) were performed to identify the competing ions and their concentrations in the background electrolytes. These data were used to calculate the U(VI) and humic acid speciation in solution. Calcium and carbonate ions are present under pore water conditions as well as in 0.1 mol/L NaClO4 from pH 7 to 8.5, due to dissolution of calcite (mineral fraction in Opalinus Clay). Thus, the U(VI) speciation is dominated by the aquatic Ca2UO2(CO3)3 complex. In the case of pore water, Ca2UO2(CO3)3(aq) is also the dominant U(VI) species in the presence of humic acid, which was corroborated by time-resolved laser-induced fluorescence spectroscopic measurements. A significantly changed speciation was found in 0.1 mol/L NaClO4 in the presence of humic acid. At pH > 7, the negatively charged UO2(CO3)2HA(II)4– complex determines the U(VI) speciation, thus repressing the Ca2UO2(CO3)3(aq) complex. In addition, the speciation of humic acid is influenced from ions leached out from Opalinus Clay. The CaHA(II) complex is the dominating humic acid species in solution.
Batch sorption experiments in 0.1 mol/L NaClO4 showed that Opalinus Clay has the strongest retardation effect on U(VI) in the pH range from pH 4.5 to 7. However, under environmentally relevant conditions (pH > 7), the sorption of U(VI) onto Opalinus Clay is very weak. Under pore water conditions, a distribution coefficient (Kd) of 0.0222 ± 0.0004 m3/kg was determined, which was shown to be independent of solid-to-liquid ratios ≥ 60 g/L. In addition, in pore water, the U(VI) sorption onto Opalinus Clay is not influenced by humic acid, which is supported by the speciation results. Extended X ray absorption fine-structure investigations confirmed this batch sorption result.
The U(VI) diffusion experiments performed in pore water at 25 °C with Opalinus Clay bore core samples confirmed the Kd value obtained by batch sorption experiments. In the diffusion experiments at 60 °C, a change in the U(VI) speciation occurred. Beside Ca2UO2(CO3)3(aq), a colloidal U(VI) species was formed. Almost equivalent apparent diffusion coefficient (Da) values were determined for the diffusion of the aqueous U(VI) species at 25 and 60 °C through Opalinus Clay. Thus, based on the investigations in the present study the breakthrough of U(VI) through Opalinus Clay is expected to be independent of the temperature and should occur nearly at the same time. Modeling calculations showed that it would take about 10 years until a detectable amount of 233U(VI) (1×10–9 mol/L) migrates through an 11 mm thick Opalinus Clay sample.
Two distinct humic acid size fractions – a large- and a small-sized colloid fraction – diffused through the Opalinus Clay samples. Within three months, the high molecular size humic acid colloids migrated only about 500 µm into the clay, whereas the low molecular size fraction diffused through the entire Opalinus Clay samples and were consequently detected in the receiving reservoirs. These findings demonstrate a filtration effect of the compacted clay. The diffusion experiments revealed that the effect of humic acid on U(VI) diffusion is negligible and, under the studied conditions, independent of temperature.
The obtained results contribute to data bases used for modeling of interaction and migration processes in uranium / clay rock systems. Thus, the collected sorption and diffusion data are not only relevant for safety assessment of nuclear waste repositories but also for any clay-containing system present in the environment, where the geochemical interaction with uranium contaminated water plays a role.
Concerning the suitability of Opalinus Clay as host rock for a nuclear waste repository, it can be concluded, that Opalinus Clay has a relatively high retardation potential for U(VI). In case of water ingress U(VI) as part of the nuclear waste is released into the clay formation. Under near-neutral pH conditions, it will be complexed by calcium and carbonate ions leached out from Opalinus Clay, whereby Ca2UO2(CO3)3(aq) is formed. This complex is only weakly retarded by sorption onto the clay, which can contribute to an enhanced mobility of U(VI) in the host rock. However, the U(VI) migration through the clay rock is governed by molecular diffusion. This decelerates the migration of Ca2UO2(CO3)3(aq) through Opalinus Clay and thus it represents the decisive retardation process in the investigated system. Additionally, under environmentally relevant conditions, humic acid has no significant influence on U(VI) / Opalinus Clay interaction even at an elevated temperature of 60 °C. This was shown by speciation, sorption, as well as diffusion experiments.

Keywords: uranium(VI); humic acid; Opalinus Clay; sorption; diffusion; speciation

  • Doctoral thesis
    TU Dresden, 2013
    163 Seiten

Publ.-Id: 18925

Embrittlement of TiAl after high temperature exposure

Paul, J.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Masset, P.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schimansky, F.-P.; Schumacher, P.; Schütze, M.; Wolf, G.; Yankov, R.

It is well known that the room temperature ductility of gamma-based titanium aluminide alloys is significantly reduced after exposure to elevated temperatures. In some cases exposure can even lead to brittle fracture on reloading of an initially ductile alloy. However the original ductility can be restored if around 30 to 50 µm of the exposed surface is removed before testing. In an attempt to reduce this problem, the effect of coatings combined with halogen treatment on the tensile behaviour of cast + HIPed Ti-48Al-2Cr-2Nb has been investigated. This talk will give a general outline of the embrittlement problem and present current ideas that have been postulated to explain the embrittlement mechanism. Additionally the protective coating methods used in the study will be presented; mechanical test results of specimens that had undergone protective coating treatments are compared to those obtained for un-treated specimens after being oxidised at 900°C for 100 hours.

Keywords: titanium aluminides; oxidation protection; coating

  • Lecture (others)
    International Workshop on Gamma Alloy Technology (GAT 2013), 11.-14.06.2013, Toulouse, France

Publ.-Id: 18924

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

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

Accelerator-driven systems (ADS) are one of the options studied for transmutation of nuclear waste in the European Community. The present study has been done in the frame of the FP7 European project Central Design Team (CDT), which in the years 2009-2012 worked to design the FAst Spectrum Transmutation Experimental Facility (FASTEF) with the goal to demonstrate efficient transmutation of high level waste and associated ADS technology. On this design will be based the MYRRHA reactor at SCK•CEN in Mol (Belgium), which should enter the construction phase in 2015. The heart of the system is a lead-bismuth eutectic (LBE) cooled reactor, working both in critical and in sub-critical operation modes. The neutrons needed to sustain fission in the subcritical mode are produced via spallation processes by a 600 MeV, 4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core. The use of high energy/high current proton beams, in combination with a nuclear reactor core operating in subcritical or critical mode, presents many challenges for various aspects of the design, being radiation shielding and minimization of the induced activation key points.

Keywords: Accelerator Driven Systems; Reactor safety; Monte Carlo; Shielding

  • Contribution to proceedings
    2013 ANS Winter Meeting, Session "Best of ICRS/RSPD 2012" (invited), 10.-14.11.2013, Washington, DC, USA
    Transactions of the American Nuclear Society, Volume 109, La Grange Park, Illinois: American Nuclear Society, ISSN:0003-018X, 1249-1251

Publ.-Id: 18923

Surface complexation and oxidation of SnII by nano-magnetite

Dulnee, S.; Banerjee, D.; Merkel, B.; Scheinost, A. C.

The long-lived fission product 126Sn is of substantial interest in the context of nuclear waste disposal in deep underground repositories. However, the prevalent redox state (di- or tetravalent), the aqueous speciation as well as the reactions at the mineral-water interface under the expected anoxic conditions are still a matter of debate. We therefore investigated the reaction of SnII with a relevant redox-reactive mineral, magnetite (FeIIFeIII2O4) at < 2 ppmv O2, and monitored Sn uptake as a function of pH and time. Tin redox state and local structure was monitored by Sn-K X-ray absorption spectroscopy (XAS). We observed a rapid (< 30 min) uptake and oxidation of SnII to SnIV in the presence of magnetite. The local structure determined by XAS showed two Sn-Fe distances of about 3.15 and 3.60 Å in line with edge and corner sharing arrangements between octahedrally coordinated SnIV and the magnetite surface, indicative of formation of tetradentate inner-sphere complexes between pH 3 and 9, in line with the strong sorption (logRd >5 from pH 3 to 9). Based on the EXAFS-derived surface structure, we could successfully model the sorption data with two different complexes, (Magn_sO)4Sn(OH)2-2 ( -14.97±0.35) prevailing from pH 2 to 9, and (Magn_sO)4Sn(OH)2Fe ( -17.72±0.50), which forms at pH > 9 by co-adsorption of FeII, thereby increasing sorption at this high pH.

Keywords: Sn; Redox; Surface complexation; Nuclear waste; magnetite; EXAFS; XANES; XRD; TEM

Publ.-Id: 18922

Mineralogical characterization of REE mineralization in Norra Kärr alkaline complex, Sweden

Atanasova, P.; Krause, J.; Gutzmer, J.

Alkaline complexes comprise one of the most promising future sources for rare earth element supply. They are particularly enriched in heavy rare earth elements. However, the often complex and highly unusual mineralogy of REE-enriched ores from alkaline complexes pose particular challenges for beneficiation. A geometallurgical approach is required to quantify mineralogical and textural diversity and variability. Based on a geometallurgical model, a suitable approach to beneficiation can be developed. Scanning electron microscope (SEM)-based image analysis can be used to characterize ores as well as beneficiation products. A wide range of tangible mineralogical and textural parameters are constrained for every ore type, including mineral abundance, grain size, and liberation. SEM-based image analysis combined with a quantitative analysis of the chemical composition of the ore minerals is illustrated here for the case of the Norra Kärr alkaline complex, Sweden. Current research focuses on quantitative mineralogical and textural constraints for different lithological domains recognized in the HREE-Zrmineralized zones of the complex. Based on the results, a geometallurgical model will be developed that will be based on the processing characteristics of the different portions of the mineralized zones.

Keywords: rare earth elements; alkaline complex; geometallurgy; eudialyte; nepheline-syenite

  • Contribution to proceedings
    Mineral Deposit Research for a High-tech World: 12th SGA Biannial Meeting, 12.-15.08.2013, Uppsala, Sweden
    Mineral Deposit Research for a High-tech World: 12th SGA Biannial Meeting, 978-91-7403-207-9, 298-301
  • Lecture (Conference)
    Mineral Deposit Research for a High-tech World: 12th SGA Biannial Meeting, 12.-15.08.2013, Uppsala, Sweden
  • Lecture (others)
    FEI User Group Meeting, 08.-09.10.2013, Eindhoven, Holland

Publ.-Id: 18921

Block Kriging for geometallurgical optimization

Tolosana-Delgado, R.; Mueller, U.; van den Boogaart, K. G.; Ward, C.

Adpative processing is often related to the mineral composition of the mining block currently processed. The portions of waste, ore and secondary product minerals considered are always positive and typically sum to 100%, i.e. a composition. A typical solution to predict block averages of spatially dependent quantities would be block kriging. However, kriging is based on spatial correlations and it has been repeatedly shown that correlations of compositional data are spurious and blurred by the constant sum constraint.

Aitchison (1982) proposed a general solution for compositional problems, based on transforming the compositional data to a set of logarithms of ratios of components, and analysing the transformed scores. The transform is chosen to be invertible to ensure that no information is lost in the process. This methodology avoids spurious correlation problems and ensures coherence between results obtained with different subcompositions. Pawlowsky-Glahn and Olea (2004) already adapted the approach for point-support geostatistics, allowing the prediction of point compositions from spatially neighbouring data, without the artefacts induced by using standard multivariate cokriging. Unfortunately upscaling the results of this approach with block kriging is not straightforward, because of the nonlinearity of logratio transforms. Furthermore, we have to consider those nonlinearities created by the dependence on the block composition of extraction efficiency and processing costs of the possible processing choices.

This paper proposes a solution for predicting the conditional expectations of the benefit of processing the block with each processing choice using geostatistical simulations of the local values of the composition and the resulting block integrals. The computation for a large number of blocks can be done efficiently using Cholesky decomposition. The approach also allows the calculation of prediction errors for expected compositions and expected benefit at almost no additional computational cost. Such compositional approach is necessary, e.g.: when processing choices depend on proportions of certain minerals after other components have been removed; or if processing alters the composition in a multiplicative way, by partially removing a portion of some components.

Keywords: Compositional data analysis; optimization; negative bias; uniform conditioning

  • Contribution to proceedings
    23rd World Mining Congress, 11.-15.08.2013, Montreal, Canada

Publ.-Id: 18920

Regression between compositional data sets

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

Linear regression where both the explained and the explanatory variables form compositions are naturally tractable within the log-ratio framework. Fitting such models does not imply any diculty: they can be t in a standard way after applying any one-to-one logratio transformation to each compositional set. Problems arise to test and display the model, due to the large dimension of the model parameters space, and the dicult interpretation of classical hypotheses in terms of the original components. This contribution proposes two graphical representations of the model: in the form of a biplot, parallel to redundacy analysis, and as condence ellipses on the parameters projected onto a set of subcompositions. Each of these representations brings also associated a way to test for certain subcompositional independence hypotheses. An exact, general, Scheffé-like test of independence (for the whole composition or any subcomposition) can be derived from a generalized eigenvalue problem of the matrix of regression coecients and its estimation covariance matrix. For certain hypotheses of independence, classical tests based on Hotelling's T2 or X2 distributions can also be adapted. Any of these tests can be used to calculate the radii of condence ellipses on the parameters, in order to visualize the corresponding tests. This provides a toolbox to reduce the complexity of compositional-to-compositional regression, and enables a structured way of exploring and testing which components of the explanatory set influence which components of the explained set.

  • Open Access Logo Contribution to proceedings
    the 5th International Workshop on Compositional Data Analysis, 03.-07.06.2013, Vorau, Österreich
    Proceedings of the 5th International Workshop on Compositional Data Analysis, 978-3-200-03103-6, 164-188

Publ.-Id: 18919

Compositional regression with unobserved components or below detection limit values

van den Boogaart, K. G.; Tolosana-Delgado, R.; Hron, K.; Templ, M.; Filzmoser, P.

The typical way to deal with zeroes and missing values in compositional data sets is to impute them with a reasonable value, and then the desired statistical model is estimated with the imputed data set, e.g. a regression model. This contribution aims at presenting alternative approaches to this problem within the framework of Bayesian regression with a compositional response. In a first step, a compositional data set with missing data is considered to follow a normal distribution on the simplex, which mean value is given as an Aitchison ane linear combination of some fully-observed explanatory variables. Both the coecients of this linear combination and the missing values can be estimated with standard Gibbs sampling techniques. In a second step, a normally-distributed additive error is considered superimposed on the compositional response, and values are taken as \below the detection limit" (BDLs) if they are \too small" in comparison with the additive standard deviation of each variable (usually, a 3 rule is applied here). Within this framework, the regression parameters and all missing values (including BDLs) can be estimated, albeit this time with a less ecient Metropolis-Hastings algorithm. Both methods estimate the regression coecients without need of any preliminary imputation step, and adequately propagate the uncertainty derived from the fact that the missing values and BDLs are not actually observed, something imputation methods cannot achieve.

  • Open Access Logo Contribution to proceedings
    CoDaWork'2013: the fifth international Workshop on Compositional Data Analysis, 03.-07.06.2013, Vorau, Österreich
    Proceedings of CoDaWork'2013: the fifth international Workshop on Compositional Data Analysis, 978-3-200-03103-6, 10-19

Publ.-Id: 18918

The challenges of adaptive processing to geostatistical prediction

van den Boogaart, K. G.; Konsulke, S.; Tolosana Delgado, R.

Adaptive Processing as proposed in geometallurgy has to rely on spatially interpolated information on geometallurgical parameters like phase composition, size distributions of particles of different phases, grain shape parameters, and portions of value elements in different grains. Using the geostatistically predicted values for adaptive processing, e.g. for the selection of milling diameters, thresholds in physical separation, or choices on using an extra pre-separation step, is typically not optimal. Mathematically this effect is introduced by two forms of nonlinearities: 1) The nonlinear scales of compositions, distributions, and shapes have special properties with respect to geostatistics. Classical geostatistics creates some artefacts for these nonlinear scales. On the other hand, modern geostatistical procedures adapted to these scales do not provide unbiased results with respect to linear transformations of the data (e.g. biased block estimates). 2) Neither economic nor ecological effects (e.g. monetary gain) of processing decisions are linear in the interpolated geometallurgical parameters. These nonlinear transforms are not unbiasedly estimated by the likewise transformed unbiased geostatistical predictions of the geometallurgical parameters. Furthermore, we need to optimize the conditional expectation of the gain, rather than obtain an unbiased estimate. Standard geostatistics as such does not provide the "right sort" of estimates for adaptive processing. A nonlinear kriging procedure is needed to approximate the nonlinearities mentioned before.

We propose to solve these problems simultaneously using a nonlinear geostatistical technique for predicting the target function (the monetary gain), rather than to predict the geometallurgical parameters and compute the gain from them. The optimization can then be performed directly on this estimated function.
It can be shown that this optimization performed on the conditional expectations, not on unbiased predictions, would yield the best possible processing choice. We propose a procedure choosing the processing parameters on an approximation of the conditional expectation. The difficulties with the classical approach and the effectiveness of this new approach are illustrated by a simplified simulation example with a single processing parameter and a simple dependence on the microstructure.

Keywords: geometallurgy; nonlinear geostatistics; optimisation; processing

  • Contribution to proceedings
    23rd World Mining Congress, 11.-15.08.2013, Montreal, Canada
    23rd World Mining Congress 2013 Proceedings, 978-1-926872-15-5

Publ.-Id: 18917

Chemical Equilibria in Compositional Data

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

Chemical equilibria are typically formulated in terms of concentrations and depend on temperature and thermodynamical constants. In simple systems (e.g. aqueous diluted solutions), these equilibria are governed by the chemical master equation or equilibrium constant. In natural systems the chemical composition is often observed incompletely and relative, i.e. according to the compositional principles. This contribution shows how the chemical master equation is related to the geometry of the Aitchison simplex. If the reaction in equilibrium preserve the amount of matter, the equilibrium defines a hyperplane in the Aitchison simplex. When the reaction does not preserve the amount of matter, the equilibrium can be used to infer the total matter per unit volume.

Keywords: chemical master equation; thermodynamical equilibria; Aitchison simplex

  • Contribution to proceedings
    15th Annual Conference of the International Association for Mathematical Geosciences, 02.-06.09.2013, Madrid, Espana
    Mathematics of Planet Earth - Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences: Springer, 978-3-642-32408-6, 107-111
    DOI: 10.1007/978-3-642-32408-6_26

Publ.-Id: 18916

Testing for microhomogeneity in reference materials for microanalytical methods

Tolosana-Delgado, R.; Renno, A. D.; Michalak, P. P.; van den Boogaart, K. G.

It is assumed that reference materials for analytical methods must be homogeneous, i.e. have the same concentration of the relevant element(s) overall, to ensure that they can be used reliably to get comparison values during the analysis with non absolute methods. To ensure such homogeneity becomes increasingly difficult with increasing resolution, up to the point that it is not possible for several microanalytical methods. We propose a way to get reliable comparison values with some types of inhomogeneous material. This is based on multiple probing the reference material. The minimal number of probing spots required for a certain precision level can be derived from the variance calculations. However, using adequate models of local heterogeneity can greatly reduce that number: Geostatistics can be used in random, systematic and periodic heterogeneities, while robust methods are useful in cases of nugget heterogeneities.

Keywords: inhomogeneity; microanalytical methods; calibration; simple kriging

  • Contribution to proceedings
    15th Annual Conference of the International Association for Mathematical Geosciences, 02.-06.09.2013, Madrid, Espana
    Mathematics of Planet Earth - Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences: Springer, 978-3-642-32408-6, 27-32
    DOI: 10.1007/978-3-642-32408-6_7

Publ.-Id: 18915

Compositional Block Cokriging

Tolosana-Delgado, R.; Mueller, U.; van den Boogaart, K. G.; Ward, C.

Estimates of a whole block composition may be useful for improving the assessment and mining of resources, especially if the economic viability depends on more than just one metal or component. Banded Iron Formation (BIF) represents such a case, where optimal exploitation requires evaluation of Fe content, as well as waste and penalty elements. Block cokriging of the whole composition may yield these estimates. To avoid the spurious correlation problem, this should be based on log-ratios of the composition. But due to the non-linearity of the log-ratio transformations, this does not yield a direct change-of-support model. This contribution explores the approximation of this block average compositional cokriging by means of geostatistical simulation within the block. This methodology is illustrated with a BIF deposit of Western Australia.

Keywords: ALN; alr; compositional kriging; LU simulation

  • Contribution to proceedings
    15th Annual Conference of the International Association for Mathematical Geosciences, 02.-06.09.2013, Madrid, Espana
    Mathematics of Planet Earth - Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences: Springer, 978-3-642-32408-6, 713-716
    DOI: 10.1007/978-3-642-32408-6_154

Publ.-Id: 18914

Radiation field characterization and shielding studies

Ferrari, A.; Amato, E.; Margarone, D.

The achieved performances in terms of energy and brightness of laser-accelerated particle beams require a proper shielding assessment for the primary and secondary ionizing radiation, especially when high intensity laser systems operate in repetition rate (typically in the range 0.1-10 Hz). In the frame of the ELI Beamlines project a general shielding study for both the 10 PW (0.016 Hz) and 2 PW (10 Hz) laser beamlines, dedicated to the high energy electron and proton acceleration, has been performed. All the work has been done keeping in mind that we deal with a rapidly evolving field, where not all the parameters that characterize the radiation fields can be completely set at this stage: the precise description of the source particle distributions, double-differential in energy and in angle, can evolve with the improved knowledge, and on the other hand the workload (in terms of shots/day), could be optimized in the future with the increased experience and technological improvements. The general philosophy has been therefore to maintain a realistic approach, always conservative, and adopt where possible flexible solutions. In the present work a summary of the analysis done and the solutions proposed for the longitudinal containment of the radiation in the proton acceleration experimental area is illustrated and discussed.

Keywords: Laser-particle acceleration; Monte Carlo; Shielding

  • Lecture (Conference)
    2nd ELIMED Workshop and Panel, 18.-19.10.2012, Catania, Italy
  • AIP Conference Proceedings 1546(2013), 57-62
    DOI: 10.1063/1.4816607

Publ.-Id: 18913

Effects of dopaminergic treatment on striatal dopamine turnover in de novo Parkinson disease

Storch, A.; Wolz, M.; Beuthien-Baumann, B.; Loehle, M.; Herting, B.; Schwanebeck, U.; Oehme, L.; van den Hoff, J.; Perick, M.; Graehlert, X.; Kotzerke, J.; Reichmann, H.

Objective: To evaluate the effects of levodopa and the dopamine D2 agonist cabergoline on striatal dopamine turnover estimated as the inverse of the effective dopamine distribution volume ratio (EDVR) measured by F-18-dopa PET in de novo Parkinson disease (PD).

Methods: Single-center, parallel-group, randomized, observer-blinded study of cabergoline (3 mg/day) and levodopa (300 mg/day) over 12 weeks in patients with de novo PD. Primary efficacy measure was the change of the side-to-side averaged putaminal EDVR comparing baseline and end-of-maintenance period.

Results: Thirty-five out of 39 randomized patients were assigned to the primary efficacy analysis (cabergoline, n = 17; levodopa, n = 18). At the end of treatment period, mean EDVRs were significantly lower compared to baseline solely in the levodopa group (relative change -1.0 +/- 13.0% in cabergoline [p = 0.525 when compared to baseline], -8.3 +/- 11.8% in levodopa group [p = 0.006]) with a nonsignificant trend between groups (mean relative difference: 7.3% (95% confidence interval -1.2% to 15.8%; p = 0.091). There was significant clinical improvement in both groups at 12 weeks compared to baseline, but no significant differences between groups in clinical and PET secondary outcome measures. Both pharmacologic treatments and PET scanning were well-tolerated and safe.

Conclusion: Putaminal dopamine turnover is increased by levodopa treatment in de novo PD. The nonsignificant trend toward a larger influence by levodopa compared to cabergoline is supported by ancillary statistical analyses. This augmentation of early compensatory events by levodopa might contribute not only to its symptomatic effects, but also to its induction of motor complications.

Publ.-Id: 18912

Pairs of Effective Spin Merons in Ferromagnetic Multilayer Elements

Wintz, S.; Bunce, C.; Neudert, A.; Körner, M.; Strache, T.; Buhl, M.; Erbe, A.; Gemming, S.; Raabe, J.; Quitmann, C.; Fassbender, J.

We report on pairs of diverging/converging spin vortices in Co/Rh/Ni81Fe19 disks. The lateral magnetization distribution of these effective spin merons [1] is directly imaged by means of element-selective x-ray microscopy. By this method, both the circulation and divergence states of the individual layers are identified as antisymmetric [2] (see Figure 1). Magnetization reversal measurements of corresponding continuous films reveal that biquadratic interlayer exchange coupling is the origin for the formation of such effective meron pairs. Furthermore, the effective meron pair’s three-dimensional magnetic structure is determined via micromagnetic simulations. We find that the perpendicular magnetization component is distributed nonhomogeneously, namely M is partially circulating on a flux-closing torus. This toroidal topology enforces a symmetry break, which ties the core polarities to the divergence configuration. Upon excitation, such topology-induced core stabilization could lead to enhanced maximum amplitudes of steady gyration compared to single layer vortices, as the meron pair’s core switching onset velocity is expected to be higher than that of a single vortex.

  • Lecture (Conference)
    58th Conference on Magnetism and Magnetic Materials (MMM), 04.-08.11.2013, Denver, USA

Publ.-Id: 18911

Economic surface treatment of Ti-alloys to improve their resistance against environmental high temperature attack

Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.

High temperature Ti-alloys are usually sophisticated and hence expensive. To allow the use of cheaper alloys at elevated temperatures an economic and easy to apply procedure was developed to improve their high temperature capability. The treatment consists of a combination of Alenrichment in a shallow surface region plus additional fluorination. The Al-enrichment at elevated temperatures leads to the formation of intermetallic TiAl-phases. These phases improve the oxidation resistance of Ti-alloys but not to a sufficient extent. An additional fluorine treatment of the Al-enriched surface leads to the formation of a protective alumina scale due to the fluorine effect. In this paper results from high temperature exposure tests performed on different Ti-alloys without any treatment and with a combination of Al-treatment plus fluorination are presented. The results are discussed in the view of the use of the optimized Ti-components for several high temperature applications.

Keywords: titanium; embrittlement; oxidation

Publ.-Id: 18910

Precise study of the supernova reaction 40Ca(α,γ) 44Ti by activation and in-beam γ-spectroscopy

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

The radioactive nuclide 44Ti is believed to be produced in the α-rich freezeout preceding supernova explosions. The γ-rays from its decay have been observed in space-based γ-observatories for the Cassiopeia A and very recently also SN 1987A supernova remnants. The rates of the nuclear reactions governing the production and destruction of 44Ti should therefore be known with high precision. Over the last years there have been various studies of the 40Ca(α,γ)44Ti reaction, which is dominating the 44Ti production in supernovae. Those studies have been performed using in-beam γ-spectroscopy, activation, accelerator mass spectrometry (AMS), and recoil mass spectrometry via inverse kinematics. However, there are still discrepancies in the resulting reaction rates. Using an α-beam of 1-2 A intensity the strengths of the strongest 40Ca(α,γ)44Ti resonances from 3.5 to 4.5 MeV laboratory α-energy have been studied by in-beam γ-counting and activation. The samples have been analyzed in the ultra-low-background underground γ-counting facility "Felsenkeller Dresden". The target stoichiometry has been determined by nuclear reactions and by elastic recoil detection analysis (ERDA). An AMS measurement of the activated samples is in preparation.

Keywords: alpha rich freeze-out; capture reaction; hydrogen depth profiling

  • Lecture (Conference)
    Workshop on "Open problems and future directions in heavy element nucleosynthesis", 10.-12.04.2013, Debrecen, Hungary
  • Lecture (Conference)
    25th International Nuclear Physics Conference (INPC 2013), 02.-07.06.2013, Firenze, Italy

Publ.-Id: 18909

Electron-induced damage of biotin studied in the gas phase and in the condensed phase at a single-molecule level

Keller, A.; Kopyra, J.; Gothelf, K.; Bald, I.

Biotin is an essential vitamin that is on the one hand relevant for the metabolism, gene expression, and in the cellular response to DNA damage, and on the other hand finds numerous applications in biotechnology. The functionality of biotin is due to two particular sub-structures, the ring structure and the side chain with carboxyl group. The heterocyclic ring structure results in the capability of biotin to form strong intermolecular hydrogen and van-der-Waals bonds with proteins such as streptavidin, whereas the carboxyl group can be employed to covalently bind biotin to other complex molecules. Dissociative electron attachment (DEA) to biotin results in a decomposition of the ring structure and the carboxyl group, respectively, within resonant features in the energy range 0-12 eV, thereby preventing the capability of biotin for intermolecular binding and covalent coupling to other molecules. Specifically, the fragment anions (M-H)-, (M-O)-, C3N2O-, CH2O2-, OCN-, CN-, OH- and O- are observed, and exemplarily the DEA cross section of OCN- formation is determined to be 3·10-19 cm2. To study the response of biotin to electrons within a complex condensed environment we use the DNA origami technique and determine a dissociation yield of (1.1 ± 0.2)·10-14 cm2 at 18 eV electron energy, which represents the most relevant energy for biomolecular damage induced by secondary electrons. The present results thus have important implications for the use of biotin as a label in radiation experiments.

Publ.-Id: 18908

Bildung Zn-haltiger Korrosionsprodukte bei einem Kühlmittelverluststörfall

Hoffmann, W.; Kryk, H.

Im Kühlmittel eines DWR können nach einem Störfall mit Kühlmittelverlust während des Sumpfumwälzbetriebs höhere Konzentrationen an gelöstem Zink auftreten, die durch Korrosion verzinkter Einbauten des Containments verursacht werden. Bei höheren Temperaturen werden feste Korrosionsprodukte ausgeschieden. Die Ausscheidung lief im Batchversuch mit einer Verzögerung ab, was auf komplexe Vorgänge bei der Partikelbildung hinweist. Unterschiede in der chemischen Zusammensetzung zu Produkten, die an Heizelementen entstehen, lassen einen Einfluss der Bildungsbedingungen auf den Reaktionsmechanismus erkennen. Durch die im Notkühlkreislauf vorliegenden Temperaturgradienten können die korrosionsbedingte Zn-Auflösung und Partikelbildung gleichzeitig ablaufen. Die Bildung und Ablagerung von Zn-Korrosionsprodukten im Kern soll durch weiterführende Arbeiten im Rahmen des Projektes untersucht werden.

Keywords: LOCA; Zn corrosion; boric acid; deposition of corrosion products

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2013, 14.-16.05.2013, Berlin, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2013, 14.-16.05.2013, Berlin, Deutschland

Publ.-Id: 18907

Simulation of particle deposition and multilayer formation between periodic steps

Lecrivain, G.; Drapeau-Martin, S.; Barth, T.; Hampel, U.

In a pebble-bed high temperature reactor core where thousands of pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust eventually deposits in the primary circuit of the reactor. The numerical prediction of graphite dust deposition is therefore a key safety issue and needs investigation. The deposition of aerosol graphite particles in a turbulent channel flow obstructed by periodic steps is here numerically investigated at Reynolds number Re = 8,000. Particles in the size range d = 1...100μm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. A two dimensional quasi-static simulation is performed. The quasi-static assumption is motivated by the time duration of the experimental test which lasts several hours. The iterative process is decomposed as follows: a Reynolds Averaged Navier Stokes turbulence model is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After sufficient deposition of the particulate matter, the build-up of the dust layer is computed using mechanics of dry granular material. The wall boundaries of the computational domain are then updated prior to the next flow simulation. The procedure is repeated until the dust layer reaches appropriate growth. The result of the multi-layer deposition matches reasonably well that of the experimental test performed on-site

  • Lecture (Conference)
    Cluster Workshop on Thermal Hydraulics of Innovative Nuclear Systems, 06.-07.02.2013, Stockholm, Sweden

Publ.-Id: 18906

Simulation of particle bed formation between obstacles

Lecrivain, G.; Hampel, U.

In a pebble-bed high temperature reactor core where thousands of pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust eventually deposits in the primary circuit of the reactor. The numerical prediction of graphite dust deposition is therefore a key safety issue and needs investigation. The deposition of aerosol graphite particles in a turbulent channel flow obstructed by periodic steps is here numerically investigated at Reynolds number Re = 10,000. Particles in the size range d = 1...20µm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. A two dimensional quasi-static simulation is performed. The quasi-static assumption is motivated by the time duration of the experimental test which lasts several hours. The iterative process is decomposed as follows: a Reynolds Averaged Navier Stokes turbulence model is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After sufficient deposition of the particulate matter, the build-up of the dust layer is computed using mechanics of dry granular material. The wall boundaries of the computational domain are then updated prior to the next flow simulation. The procedure is repeated until the dust layer reaches appropriate growth. The result of the multi-layer deposition matches reasonably well that of the experimental test performed on-site

  • Lecture (others)
    2nd Ph.D. Reactive Transport Modeling Meeting, 26.03.2013, Leipzig, Dresden

Publ.-Id: 18905

Simulation of graphite dust resuspension in a turbulent square dust flow

Lecrivain, G.; Loyseau, X.; Hampel, U.

In a pebble-bed High Temperature Reactor (HTR) core where thousands of graphite pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the coolant gas and deposits in the primary circuit of the reactor. In the event of a Loss of Coolant Accident (LOCA) radioactive carbonaceous dust may be resuspended and escape the system boundaries. There is therefore a need to predict the dust resuspension during a LOCA.
A resuspension model is here presented and coupled with computational fluid dynamics. A Reynolds-averaged Navier–Stokes is employed to simulate the turbulent flow in a wall-bounded channel flow. Micro-sized graphite particles are initially placed on the bottom wall surface of the virtual channel flow. The gas velocity is gradually increased and the resuspended fraction is plotted as a function of the wall shear velocity. The number of reentrained particles increases with gas velocity. The overall resuspended fraction matches experimental data available from the literature. It is found that particles far from the side walls reenter the turbulent flow much faster than those near the corner.
Findings from this study can be used for the prediction of carbonaceous dust resuspension in a HTR during a LOCA.

  • Open Access Logo Contribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-15.05.2013, Pisa, Italy

Publ.-Id: 18904

Infrared ellipsometry for improved laterally resolved analysis of thin films

Hinrichs, K.; Furchner, A.; Sun, G.; Gensch, M.; Rappich, J.; Oates, T.

In the present article we discuss developments towards increasing the spatial resolution of infrared ellipsometry and ellipsometric microscopy for the study of thin films. Relevant aspects in the interpretation of observed peaks in the infrared (ellipsometric) spectra are discussed. In particular anisotropic effects in dependence of molecular orientations in organic films and the excitation of a macroscopic wave, the Berreman mode, in thin silicon oxide films are addressed. For correct interpretation of measured data optical simulations are essential to avoid incorrect conclusions on band frequency and assignments.

Keywords: FTIR-microscopy; Infrared spectroscopic ellipsometry; molecular orientation; thickness; polymer film; silicon oxide

Publ.-Id: 18903

Speciation of iodine isotopes inside and outside of a contaminant plume at the Savannah River Site

Schwehr, K. A.; Otosaka, S.; Merchel, S.; Kaplan, D. I.; Zhang, S.; Xu, C.; Li, H.-P.; Ho, Y.-F.; Yeager, C. M.; Santschi, P. H.; Aster, T.

A primary obstacle to understanding the fate and transport of the toxic radionuclide 129I (a thyroid seeker) is an accurate method to distinguish it from its stable isotope, 127I, and to quantify its various species at environmentally relevant concentrations (~10-8 M). A pH-dependent solvent extraction and combustion method was paired with accelerator mass spectrometry (AMS) to measure ambient levels of 129I/127I isotope ratios and iodine speciation (iodide (I-), iodate (IO3-), and organo-I (OI)) in aquatic systems. The method exhibits an overall uncertainty of 10% or less for iodide and iodate, and less than 20% for organo-I species concentrations and enabled 129I measurements as low as 0.5 Bq/L in groundwater from the Savannah River Site (SRS) in South Carolina, USA along a pH, redox potential (Eh), and organic carbon gradient. The data confirmed that the 129I/127I ratios and species distribution were strongly pH dependent, consistent with our knowledge that the 129I was emanating from a strongly acidic source. Low 129I concentrations detected in samples collected outside the known 129I plume, as delineated by the Maximum Contaminant Level (MCL) of 1 pCi/L129I (0.037 Bq/L), were still orders of magnitude higher than ambient 129I concentration typically found in the USA groundwater. This is likely due to past atmospheric releases of volatile 129I species by SRS nuclear reprocessing facilities near the study site. The results confirmed the existence of 129I as not only iodide, but as organic iodine and iodate species. This study underscores the importance of understanding a contaminant’s biogeochemistry at multiple concentrations, concentrations below and above regulatory MCLs.

Keywords: Radioiodine (I-129); Iodide; Iodate; Organo-iodine; Accelerator mass spectrometry; AMS; Iodine speciation

Publ.-Id: 18902

Crystallization induced by thermal annealing with millisecond pulses in silicon-on-insulator films implanted with high doses of hydrogen ions

Tyschenko, I. E.; Volodin, V. A.; Voelskow, M.

The crystallization of silicon-on-insulator films, implanted with high doses of hydrogen ions, upon annealing with millisecond pulses is studied. Immediately after hydrogen-ion implantation, the formation of a three-phase structure composed of silicon nanocrystals, amorphous silicon, and hydrogen bubbles is detected. It is shown that the nanocrystalline structure of the films is retained upon pulsed annealing at temperatures of up to similar to 1000A degrees C. As the temperature of the millisecond annealing is increased, the nanocrystal dimensions increase from 2 to 5 nm and the fraction of the nanocrystalline phase increases to similar to 70%. From an analysis of the activation energy of crystal phase growth, it is inferred that the process of the crystallization of silicon films with a high (similar to 50 at %) hydrogen content is limited by atomic-hydrogen diffusion.

Keywords: Crystallization; Flash Lamp Annealing; Hydrogen Implantation; SOI

Publ.-Id: 18901

A new approach to chemical imaging with PIXE using an X-ray colour camera

Munnik, F.; Hanf, D.; Ziegenrücker, R.; Renno, A. D.

A new approach using poly-capillaries has been used for laterally resolved PIXE.
Promising for large area surveys.
The experimental setup is ready and works.

Start of a Ph.D. student in the framework of the Marie-Cure project SPRITE.
Some technical extensions have still to be installed.
Development data-reduction protocols and image reconstruction.
Development of integrated control and analysis software.

Keywords: PIXE; CCD camera

  • Lecture (Conference)
    Workshop „Ionenstrahlen – Forschung und Anwendung“, 12.-13.06.2013, Leipzig, Deutschland

Publ.-Id: 18900

Prozessführung und Echtzeit-Monitoring von Grignard-Reaktionen

Kryk, H.

Als Grignard-Reaktionen werden chemische Reaktionen zwischen einem organischen Halogenid und Magnesium zur entsprechenden magnesium-organischen Verbindung (Grignard-Reagenz) bezeichnet, welche große Bedeutung als Zwischenprodukte für organische Synthesen in der Feinchemie und der pharmazeutischen Industrie haben. Grignard-Reaktionen besitzen aufgrund des spezifischen Prozessverhaltens der stark exothermen Bildungsreaktionen und der hohen Reaktivität der Grignard-Reagenzien ein erhöhtes Gefahrenpotenzial. Hauptgefahrenquellen sind das verzögerte Starten der Reaktion bei unzulässig hoher Halogenid-Konzentration und Halogenid-Akkumulationen im Rührkesselreaktor während des Semibatch-Prozesses durch hohe Dosierraten und/ oder sinkende Reaktionsgeschwindigkeiten. Von großer Bedeutung für die Prozesssicherheit sind deshalb industriell anwendbare Methoden für eine objektive Detektion des Reaktionsstarts und für die Echtzeit-Verfolgung von Edukt-Akkumulationen im Reaktionsgemisch.
In Form eines Übersichtsvortrages werden online-spektroskopische Methoden zur Reaktionsverfolgung mittels FTIR sowie am HZDR entwickelte, auf gekoppelten Energie- und Stoffbilanzen basierende echtzeitfähige Verfahren zur Reaktionsstart-Detektion und zur Verfolgung der Edukt- und Produktkonzentrationen im Reaktionsgemisch eines Rührkesselreaktors vorgestellt und im Detail erläutert. Weiterhin erfolgt der Vergleich zwischen industriell etablierten Detektionsmethoden unter Nutzung konventioneller Prozesssignale sowie analytik- und bilanzbasierten Verfahren, wobei die Vor- und Nachteile der einzelnen Methoden dargestellt werden. Aus den Ergebnissen der bilanzbasierten Reaktionsverfolgung können sicherheitstechnische Kenngrößen abgeleitet werden, die eine inhärent sichere Prozessführung bei gleichzeitiger Erhöhung der Prozesseffizienz ermöglichen.

Keywords: Grignard; process control; FTIR; real-time monitoring; heat balance; process safety; inherent safety

  • Invited lecture (Conferences)
    Firmen-Kolloquium der Saltigo GmbH, 13.06.2013, Leverkusen, Deutschland

Publ.-Id: 18899

Impact of Triaxiality on the Emission and Absorption of Neutrons and Gamma Rays in Heavy Nuclei

Grosse, E.; Junghans, A. R.; Massarczyk, R.

For many spin-0 target nuclei neutron capture measurements yield information on level densities at the neutron separation energy. Also the average photon width has been determined from capture data as well as Maxwellian average cross sections for the energy range of unresolved resonances. Thus it is challenging to use this data set for a test of phenomenological prescriptions for the prediction of radiative processes. An important ingredient for respective calculations is the photon strength function for which a parameterization was proposed using a fit to giant dipole resonance shapes on the basis of theoretically determined ground state deformations including triaxiality. Deviations from spherical and axial symmetry also influence level densities and it is suggested to use a combined parameterization for both, level density and photon strength. The formulae presented give a good description of the data for low spin capture into 124 nuclei with 72

Keywords: Nuclear triaxiality; level density; average radiative width; Maxwellian averaged cross sections; nuclear waste transmtation

Publ.-Id: 18898

Geometallurgical Classification of REE Mineralisation in Alkaline Complexes

Atanasova, P.; Gutzmer, J.; Leijd, M.

Alkaline complexes comprise one of the most promising future sources for future rare earth element supply. They are particularly enriched in heavy rare earth elements. However, the often complex and highly unusual mineralogy of REE-enriched ores from alkaline complexes pose particular challenges for beneficiation. A geometallurgical approach is required to quantify mineralogical and textural diversity and variability. Based on a geometallurgical model, a suitable approach to beneficiation can be developed. SEM-based image analysis can be used to characterize ores as well as beneficiation products. A wide range of tangible mineralogical and textural parameters are constrained for every ore type, including mineral abundance, grain size, and liberation. The use of such an approach is illustrated here for the case of the Norra Kärr alkaline complex, Sweden. The complex is highly deformed and metamorphosed and known currently to contain resources of 41.6 Mt @ 0.57 % TREO with 51 % HREO/TREO and 1.7 % ZrO2 (indicated) and 16.5 Mt @ 0.64 % TREO with 49% HREO/TREO and 1.7 % Zr2O (inferred). Mineralization is hosted by aegirine nepheline-syenites that show a considerable textural and compositional diversity. REE-bearing minerals include eudialyte group minerals and very minor mosandrite and cerite. Zr is hosted by Zr-silicates catapleiite and eudialyte. Current research focuses to provide quantitative mineralogical and textural constraints for different lithological domains recognized in the HREE-Zr-mineralized zones of the complex. Based on the results, a geometallurgical model will be developed that will be based on the processing characteristics rather of the different portions of the mineralized zones.

Keywords: rare earth elements; alkaline complex; geometallurgy

  • Lecture (Conference)
    Critical Minerals 2013, 04.-05.06.2013, Perth, Australia
  • Contribution to proceedings
    Critical Minerals 2013, 04.-05.06.2013, Perth, Australia
    Critical Minerals Conference 2013 - Conference Proceedings, Australia: Australasian Institute of Mining and Metallurgy, 978 1 921522 88 8

Publ.-Id: 18897

Transient increase of the energy gap in superconducting NbN thin Films excited by resonant narrow-band terahertz pulses

Beck, M.; Rousseau, I.; Klammer, M.; Leiderer, P.; Mittendorff, M.; Winnerl, S.; Helm, M.; Gol’tsman, G. N.; Demsar, J.

Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Δ=h. Utilizing intense, narrowband picosecond THz pulses, tuned to just below and above 2Δ=h of a BCS superconductor NbN, we demonstrate that superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced non-thermal electron distribution persisting on a 100 ps timescale.

Keywords: radiation-enhanced superconductivity; NbN; Time resolved spectroscopy

Publ.-Id: 18896

Fast relaxation of free carriers in compensated n- and p-type germanium

Deßmann, N.; Pavlov, S.; Mittendorff, M.; Winnerl, S.; Zhukavin, R.; Tsyplenkov, V.; Shengurov, V.; Shastin, V.; Abrosimov, N.; Riemann, H.; Hübers, H.-W.

The relaxation of free holes and electrons in compensated germanium doped by gallium (p-Ge:Ga:Sb) and antimony (n-Ge:Sb:Ga) has been studied by a pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. The relaxation times vary between 20-300 ps and depend on the incident THz intensity and compensation level. The relaxation times are about five times shorter than previously obtained results for uncompensated n-Ge:Sb and p-Ge:Ga. The results support the development of fast photoconductive detectors in the THz frequency range.

Keywords: Time resolved spectroscopy; THz

  • Lecture (Conference)
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665867

Publ.-Id: 18895

The computation of lipophilicities of 64Cu PET systems based on a novel approach for fluctuating charges

Comba, P.; Martin, B.; Sanyal, A.; Stephan, H.

A QSPR scheme for the computation of lipophilicities of 64Cu complexes was developed with a training set of 24 tetraazamacrocylic and bispidine-based CuII compunds and their experimentally available 1-octanol/water distribution coefficients. A minimum number of physically meaningful parameters was used in the scheme, and these are primarily based on data available from molecular mechanics calculations, using an established force field for CuII complexes and a recently developed scheme for the calculation of fluctuating atomic charges. The developed model was also applied to an independent validation set and found to accurately predict distribution coefficients of potential 64Cu PET (positron emission tomography) systems. A possible next step would be the development of a QSAR-based biodistribution model to track the uptake of imaging agents in different organs and tissues of the body. It is expected that such simple, empirical models of lipophilicity and biodistribution will be very useful in the design and virtual screening of positron emission tomography (PET) imaging agents.

Publ.-Id: 18894

Ultra-fast transistor-based detectors for precise timing of near infrared and THz signals

Preu, S.; Mittendorff, M.; Winnerl, S.; Lu, H.; Gossard, A. C.; Weber, H. B.

A whole class of two-color experiments involves intense, short Terahertz radiation pulses. A fast and moderately sensitive detector capable to resolve both near-infrared and Terahertz pulses at the same time is highly desirable. Here we present the first detector of this kind. The detector element is a GaAs-based field effect transistor operated at room temperature. THz detection is successfully demonstrated at frequencies up to 4.9 Hz. The THz detection time constant is shorter than 30 ps, the optical time constant is 150 ps. This detector is ideally suited for precise, simultaneous resolution of optical and THz pulses and for pulse characterization of high-power THz pulses up to tens of kW peak power levels. The dynamic range of the detector is as large as 65 ± 3 dB/√Hz, enabling applications in a large variety of experiments and setups, also including table-top systems.

Keywords: ultrafast detector; THz detection

Publ.-Id: 18893

Resonance triplet at Eα = 4.5 MeV in the 40Ca(α,γ)44Ti reaction

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

The 40Ca(α,γ)44Ti reaction is believed to be the main production channel for the radioactive nuclide 44Ti in core-collapse supernovae. Radiation from decaying 44Ti has been observed so far for two supernova remnants, and a precise knowledge of the 44Ti production rate may help improve supernova models. The 40Ca(α,γ)44Ti astrophysical reaction rate is determined by a number of narrow resonances. Here, the resonance triplet at Eα = 4497, 4510, and 4523 keV is studied both by activation, using an underground laboratory for the counting, and by in-beam spectrometry. The target properties are determined by elastic recoil detection analysis and by nuclear reactions. The strengths of the three resonances are determined to ωγ = (0.92 ± 0.20), (6.2 ± 0.5), and (1.31 ± 0.24) eV, respectively, a factor of two more precise than before. The strengths of this resonance triplet may be used in future works as a point of reference. In addition, the present new data directly affect the astrophysical reaction rate at relatively high temperatures, above 3.5GK.

Keywords: alpha rich freeze-out; capture reaction; hydrogen depth profiling

Publ.-Id: 18892

InGaAs-based Large Area Photoconductive Emitters For 1.55 µm Excitation

Xu, M.; Mittendorff, M.; Dietz, R.; Göbel, T.; Schneider, H.; Helm, M.; Winnerl, S.

We present a scalable large-area terahertz (THz) emitter designed for excitation with 1.55 µm pump radiation. It is based on an InGaAs heterostructure combined with a microstructured electrode pattern. Electric fields of more than 2.5 V/cm in the THz focus are reached, the spectrum of the pulses extends up to 3 THz.

Keywords: photoconductive THz emitter; 1.55 µm excitation; InGaAs-based THz emitter

  • Poster
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665436

Publ.-Id: 18891

Ultrafast graphene-based THz detection at room temperature

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

We present an ultrafast terahertz detector suitable for wavelengths from 30 μm to 220 μm, which is based on a graphene flake. A logarithmic-periodic antenna is used to couple the radiation to the flake. The detector, characterized by a fast rise time combined with room temperature operation, is well suited for determining timing differences of THz laser pulses.

Keywords: graphene; ultrafast detector; THz detection

  • Lecture (Conference)
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665851

Publ.-Id: 18890

Surface patterning by heavy-ion induced melting

Böttger, R.; Bischoff, L.; Heinig, K.-H.; Liedke, B.; Anders, C.; Urbassek, H. M.

The driving forces for surface patterning by ion bombardment have been under discus-sion for many years. At first, a continuum theory based on competition between the sur-face instability due to curvature dependent sputtering and surface smoothing by Mul-lins-Herring diffusion was proposed [1]. Later, a continuum theory with a surface destabilizing term based on ion impact-induced mass-drift was published [2]. Recently, this momentum transfer to target atoms by ion impacts has been proven to be the dominating driving force for pattern formation in many cases [3]. In case that collision-induced defects cannot reach the surface to form a crater, defect diffusion induced pat-terns like pits and sponges can form. It should be noted that the manifold of beautiful patterns on Si and Ge published recently are caused by metal impurities [4]. Thus, it is now commonly accepted that at normal ion incidence on elemental, amorphous targets no surface patterns should evolve. However, we recently found well-ordered dot patterns at normal irradiation of Ge with polyatomic Bi ions of 10-20 keV kinetic energy per atom [5]. Similar patterns were found with monatomic Bi ion irradiation of heated Ge substrates, when the deposited energy per Ge atom exceeds a critical value within a larger volume [6].
To identify the driving force for this unexpected dot pattern formation, focused ion beam and broad beam studies have been combined with modeling based on molecular dynamics and kinetic Monte-Carlo simulations. The studies prove that these patterns appear only, if nanomelt pools form at the surface of irradiated Ge or Si.
It will be shown that melt pools induce a surface smoothing process like in the well-known laser polishing technology, which evolves as . The competing surface roughening term results from the missing material due to intense sputtering by Bi ions. This leads to a depression of the melt pool surface. For off-normal incidence, the meniscus is shifted with respect to the ion impact point in dependence on the surface slope, which leads to a surface destabilizing up-hill mass drift.
[1] R. M. Bradley and J. M. E. Harper, J. Vac. Sci. Technol. A 6 (1988) 2390.
[2] G. Carter and V. Vishnyakov, Phys. Rev. B 54 (1996) 17647.
[3] C. S. Madi, H. B. George, and M. J. Aziz, J. Phys. Condens. Matter 21 (2009) 224010.
[4] B. Ziberi, M. Cornejo, F. Frost, and B. Rauschenbach, J. Phys. Condens. Matter 21 (2009) 224003.
[5] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko, and W. Pilz, Nucl. Instr. Meth. Phys Res. B 272 (2012) 198.
[6] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz, and B. Schmidt, J. Vac. Sci. Technol. B 30 (2012) 06FF12.

Keywords: silicon; germanium; nanodots; polyatomic ions; melting

  • Lecture (Conference)
    The 17th International Conference on Radiation Effects in Insulators 2013 (REI-17), 30.06.-05.07.2013, Helsinki, Finland

Publ.-Id: 18889

Condensation of the dianion of ethyl acetoacetate with perfluoroalkyl iodides. Application to the synthesis of 3-perfluoroalkylsalicylic acids

Mamat, C.; Langer, P.

3-Perfluoroalkylsalicylic esters and acids were prepared based on the condensation of the dianion of ethyl acetoacetate with various perfluoroalkyl iodides.

Keywords: Dianions Condensation; Organofluorine compounds Arenes; Cyclizations Regioselectivity

Publ.-Id: 18888

Surface Patterning by heavy-ion induced melt pools

Böttger, R.; Bischoff, L.; Liedke, B.; Heinig, K.-H.; Anders, C.; Urbassek, H. M.

The driving forces for surface patterning by ion bombardment have been under discussion for many years. Bradley and Harper developed a continuum theory based on the competition between the surface instability due to curvature dependent sputtering and surface smoothing by Mullins-Herring diffusion [1]. Later, a continuum theory with a surface destabilizing term based on ion impact induced mass drift was published [2]. Recently, this momentum transfer to target atoms by ion impacts has been proven to be the dominating driving force for pattern formation in many cases [3], it can be treated by a neat crater function formalism. In case that the collision-induced defects cannot reach the surface to form a crater function, nonlinear diffusion induced pattern like holes and sponges can form. However, it should be noted that the manifold of beautiful patterns on Si and Ge published recently are dominated by metal impurities [4].
Thus, currently the community arrived at the consensus that at normal ion incidence on elemental, amorphous targets no surface pattern should evolve. However, we recently found well-ordered dot patterns at normal irradiation of Ge with polyatomic Bi ions of ~10…20 keV kinetic energy per atom [5]. Similar patterns (Figure 1) were found with monoatomic Bi ions at elevated Ge substrate temperatures [6], where the energy per Ge atom exceeds a critical value within a larger volume (Figure 2).
To identify the driving force for this unexpected dot pattern formation, focused ion beam and broad beam studies have been combined with modeling based on molecular dynamics and kinetic Monte-Carlo simulations. The studies prove that these patterns appear only, if nanomelt pools form at the Ge surface.
It will be shown that melt pools induce a surface smoothing process like in the well-known laser polishing technology, which evolves as . The competing surface destabilizing term results from the missing material due to intense sputtering by Bi ions. This leads to a depression of the melt pool surface, a meniscus, which is visualized in Figure 3 due to amorphous resolidification after Bi3+ ion impact into c-Ge. For off-normal incidence, the meniscus is shifted with respect to the ion impact point in dependence on the surface slope, which leads to a surface destabilizing up-hill mass drift.

Keywords: self-organized surface patterns; ion irradiation; germanium; silicon; bismuth; polyatomic ions; melting

  • Invited lecture (Conferences)
    International Symposium on Nanoscale Pattern Formation at Surfaces, 26.-30.05.2013, Copenhagen, Denmark
  • Lecture (others)
    Symposium TU Vienna, 28.02.2013, Vienna, Austria

Publ.-Id: 18887

Automated preparation of [18F]AFP and [18F]BFP: Two novel bifunctional 18F-labeling building blocks for Huisgen-click

Pretze, M.; Mamat, C.

A bioorthogonal labeling approach based on the Huisgen-click reaction including the one-step radiosynthesis of two novel versatile and bifunctional labeling building blocks ([18F]AFP) [18F]12 and ([18F]BFP) [18F]6 with the PET radionuclide fluorine-18 is described. Optimized reaction conditions for the fully automated synthesis procedure using the TRACERlab FxFN module gave both piperazine derivatives [18F]6 and [18F]12 with radiochemical yields of 31 9% (S.D., n = 8, d.c.) and 29 5% (S.D., n = 19, d.c.), respectively, within 40 min synthesis time and high specific activities after convenient purification using silica gel cartdridges. First biological studies of both building blocks revealed a remarkable in vitro stability in rat blood as well as rat plasma over more than 60 min. Sample ligation reactions of [18F]6 and [18F]12 with azide and alkyne functionalized amino acid derivatives yielded the corresponding labeled triazoles in good to high RCYs. Moreover, the azide functionalized peptide 17, which is highly affine to the EphB2 receptor due to its SNEW sequence, was synthesized and successfully radiolabeled with [18F]BFP [18F]6 under relatively mild conditions yielding the corresponding triazolyl-peptide [18F]18.

Keywords: Click chemistry; Bioorthogonal; Building block; Automated synthesis; Eph receptor

Publ.-Id: 18886

An Efficient Bioorthogonal Strategy Using CuAAC Click Chemistry for Radiofluorinations of SNEW Peptides and the Role of Copper Depletion

Pretze, M.; Kuchar, M.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Mamat, C.

The EphB2 receptor is known to be overexpressed in various types of cancer and is therefore a promising target for tumor cell imaging by positron emission tomography (PET). In this regard, imaging could facilitate the early detection of EphB2-overexpressing tumors, monitoring responses to therapy directed toward EphB2, and thus improvement in patient outcomes. We report the synthesis and evaluation of several fluorine-18-labeled peptides containing the SNEW amino acid motif, with high affinity for the EphB2 receptor, for their potential as radiotracers in the non-invasive imaging of cancer using PET. For the purposes of radiofluorination, EphB2-antagonistic SNEW peptides were varied at the C terminus by the introduction of l-cysteine, and further by alkyne- or azide-modified amino acids. In addition, two novel bifunctional and bioorthogonal labeling building blocks [18F]AFP and [18F]BFP were applied, and their capacity to introduce fluorine-18 was compared with that of the established building block [18F]FBAM. Copper-assisted Huisgen 1,3-dipolar cycloaddition, which belongs to the set of bioorthogonal click chemistry reactions, was used to introduce both novel building blocks into azideor alkyne-modified SNEW peptides under mild conditions. Finally, the depletion of copper immediately after radiolabeling is a highly important step of this novel methodology.

Publ.-Id: 18885

Design and Development of 99mTc-‘4 + 1’-Labeled Dextran-Mannose Derivatives as Potential Radiopharmaceuticals for Sentinel Lymph Node Detection

Giglio, J.; Fernandez, S.; Jentschel, C.; Pietzsch, H.-J.; Papadopoulos, M.; Pelecanou, M.; Pirmettis, I.; Paolino, A.; Rey, A.

The synthesis, labeling, and biological evaluation of a dextran derivative (DCM-30-iso) as potential radiopharmaceutical for sentinel lymph node imaging is presented. DCM-30-iso bears mannose as active moiety and isocyanide as ligand for technetium through the formation of a ‘4 + 1’ Tc(III) mixed-ligand complex. A second derivative without mannose (DC-25-iso) was also prepared and evaluated as control. DCM-30-iso and DC-25-iso were synthesized from dextran in four steps (>50% overall yield) and characterized by spectroscopic methods. Labeling with 99mTc was achieved by reaction with 2,2¢,2¢¢-nitrilotris(ethanethiol) and 99mTc-EDTA. Radiochemical purity was above 90% and was stable for at least 4 hours postlabeling at 37C. The identity of the 99mTc complex was established through comparative HPLC studies using the well-characterized analogous Re-DC-25-iso complex. Biodistribution and imaging experiments of 99mTc-DCM-30-iso showed high uptake in the popliteal lymph node, which could be blocked with preinjection of mannose, and very low uptake in other nodes and organs. The nonmannosylated 99mTc-DC-25-iso derivative showed negligible uptake in all lymph nodes. The novel dextran-mannose derivative DCM-30-iso can be successfully labeled with 99mTc to give a well-characterized ‘4 + 1’ complex with favorable biological properties as sentinel lymph node imaging agent.

Keywords: ‘4 + 1’ Tc(III) mixed-ligand complexes; dextran; mannose; rhenium; sentinel lymph node imaging; Technetium-99m

Publ.-Id: 18883

The PET-derived tumor-to-blood standard uptake ratio (SUR) is superior to tumor SUV as a surrogate parameter of the metabolic rate of FDG

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

The Standard Uptake Value (SUV) approach in oncological PET has known shortcomings all of which affect the reliability of the SUV as a surrogate of the targeted quantity, the metabolic rate of FDG ([18F]fluorodeoxyglucose), Km. Among the shortcomings are time dependence, susceptibility to errors in scanner and dose calibration, insufficient correlation between systemic distribution volume and body weight, and, consequentially, residual inter-study variability of the arterial input function (AIF) despite SUV normalization. Especially the latter turns out to be a crucial factor adversely affecting the correlation between SUV and Km and causing inter-study variations of tumor SUVs that do not reflect actual changes of the metabolic uptake rate. In this work, we propose to replace tumor SUV by the tumor to blood standard uptake ratio (SUR) in order to distinctly improve the linear correlation with Km.
Methods: Assuming irreversible FDG kinetics, SUR can be expected to exhibit a much better linear correlation to Km than SUV. The theoretical derivation for this prediction is given and evaluated in a group of 9 patients with liver metastases of colorectal cancer for which 15 fully dynamic investigations were available and Km could thus be derived from conventional Patlak analysis.
Results: For any fixed time point T at sufficiently late times p.i. the Patlak equation predicts a linear correlation between SUR and Km under the following assumptions: 1.) approximate shapeinvariance (but arbitrary scale) of the AIF across scans/patients and 2.) low variability of the apparent distribution volume Vr (the intercept of the Patlak Plot). This prediction – and validity of the underlying assumptions – has been verified in the investigated patient group. Replacing tumor SUVs by SURs does improve the linear correlation of the respective parameter with Km from r = 0:61 to r = 0:98.
Conclusion: SUR is an easily measurable parameter that is highly correlated to Km. In this respect it is clearly superior to SUV. Therefore, SUR should be seriously considered as a drop-in replacement for SUV-based approaches.

Keywords: SUV; tumor to blood ratio; PET; PET/CT; therapy response control; FDG

Publ.-Id: 18882

Effects of implantation temperature and thermal annealing on the Ga+ ion beam induced optical contrast formation in a-SiC:H

Tsvetkova, T.; Wright, C. D.; Kitova, S.; Bischoff, L.; Zuk, J.

The effects of implantation temperature and post-implantation thermal annealing on the Ga+ ion beam induced optical contrast formation in hydrogenated silicon–carbon alloy films have been studied. As a result of the implantation a well-expressed ‘‘darkening’’ effect (i.e. absorption edge shift to the longerwavelength/lower-photon-energy region) has been registered. It is accompanied by a remarkable increase of the absorption coefficient up to 2 orders of magnitude in the measured photon energy range (1.5–3.1 eV). The optical contrast thus obtained (between implanted and unimplanted regions of the film material) has been made use of in the form of optical pattern formation by computer-operated Ga+-focused ion beam. Possible applications of this effect in the area of submicron lithography and high-density optical data storage have been suggested with regard to the most widely spread focused micro-beam systems based on Ga+ liquid metal ion sources. The fact that Ga has a very low melting point (Tm = 29.8 C) and an unusual feature of volume contraction on melting are factors which favour Ga incorporation upon ion-implantation as dispersed clusters, or small nanoparticles. It has been previously noted that Ga precipitation into nanoparticles can vary dramatically (in terms of particle size) with Ga concentration and small changes in surface implant temperature, thus affecting the optical properties of the target. The precise role of implantation temperature effects, i.e. the target temperature during Ga+ ion irradiation, on the optical contrast obtainable, has been therefore a key part of this study. Appropriate post-implantation annealing treatments were also studied, since these are expected to offer further benefits in reducing the required ion dose and enhancing contrast, thus increasing the cost-effectiveness of the bit-writing method.

Keywords: Focused ion beams; Optical data storage; Near-field techniques

Publ.-Id: 18881

Surface morphologies of Ge and Si under heavy single-atom and poly-atom ion irradiation

Bischoff, L.; Böttger, R.; Heinig, K.-H.

Well-ordered dot patterns can be obtained at normal irradiation on Ge and Si with polyatomic Bi ions of ~10…20 keV kinetic energy per atom. Similar patterns were found with monoatomic Bi ions at elevated Ge substrate temperatures, when the energy per Ge atom exceeds a critical value.
To identify the driving force for this unexpected dot pattern formation, focused ion beam and broad beam studies have been performed in parallel with molecular dynamics and kinetic Monte-Carlo simulations. This investigation proves that these patterns appear only, if nanomelt pools form at the surface of irradiated Ge or Si. It will be shown that melt pools induce a surface smoothing process like in the well-known laser polishing technology. Contrary, surface destabilization results from the shift of the center of the melt pool meniscus with respect to the ion impact point, where the meniscus arises from the missing material due to sputtering.

Keywords: polyatomic Bi ions; germanium; silicon; melt pool

  • Lecture (Conference)
    Workshop „Ionenstrahlen in Forschung und Anwendung“ & Treffen der DFG-Forschergruppe FOR 845, 12.-14.06.2013, Leipzig, Germany

Publ.-Id: 18880

A methodology for highly accurate results of direct numerical simulations: Drag force in dense gas-solid flows at intermediate Reynolds number

Tang, Y.; Kriebitzsch, S. H. L.; Peters, E. A. J. F.; van der Hoef, M. A.; Kuipers, J. A. M.

Simulations with an iterative immersed boundary method (IBM) are performed to predict the drag force for gas–solid flows at intermediate Reynolds number (Re). A methodology is developed to obtain highly accurate IBM results at relatively low computational cost. First of all, “resolution-free” gas–solid forces are estimated for a face-centered-cubic (FCC) array of monodisperse spheres in terms of the resolution convergence. This data is subsequently used to compute the relocation of the marker points, so as to correct for the resolution dependence of the simulated force on coarser grids. We then assume that the relocation derived from FCC arrays is also valid for the simulations of random arrays. As a result, the accurate gas–solid forces on random arrays can be obtained from the simulations at a relatively low resolution. We have applied this methodology to predict the gas–solid force at Re = 100 and 50, with ϕ varying from 0.1 up to the close-pack limit. The results are consistent with the recently published correlations. A new fit has been proposed for the interaction force at these two specific Reynolds numbers. This methodology makes it feasible to model the dense granular flows of large assemblies at high Re by direct numerical simulations at relatively low computational cost.

Keywords: direct numerical simulation; immersed boundary method; methodology; gas-solid drag; resolution-free

Publ.-Id: 18879

Lighting Up the Inner Workings of LWFA – How Radiative Particle-in-Cell Simulations can Shed New Light into the Dynamics of Laser-Accelerated Electrons

Pausch, R.; Debus, A.; Steiniger, K.; Hübl, A.; Burau, H.; Widera, R.; Bussmann, M.; Schramm, U.

We present simulations of angularly resolved radiation spectra from laser-wakefield accelerated electrons (LWFA) based on classical Liénard-Wiechert potentials ranging from infrared to the X-ray wavelengths.
These radiation spectra give insight into the momentum distribution with a spatial resolution small enough to study in detail the electron dynamics during the formation of the wakefield, the injection of electrons into the wakefield and in the coherent motion of electrons during acceleration. As spectral information is accessible in experiments, our results can serve as a valuable input to new diagnostics. A quantitative comparison of measured and simulated spectra poses a unique method to determine the phase space distribution of electrons in the LWFA process. Our code is capable of computing the spectra of all particles in the simulation and fully accounts for coherent effects. We thus can quantitatively predict the spectral intensities observed in experiment and are able to link them to specific phase space regions much smaller than the plasma wavelength. We show that radiation diagnostics can serve as a powerful tool to understand a large variety of plasma phenomena and how large-scale simulations of Petaflop performance can in the future help to optimize LWFA.

Keywords: radiation spectra; Liénard-Wiechert potentials; LWFA; laser wakefield acceleration; large-scale simulations; Petaflop; plasma phenomena; coherent radiation

  • Lecture (Conference)
    1st European Advanced Accelerator Concepts Workshop, 02.-07.06.2013, La Biodola, Isola d'Elba, Italy

Publ.-Id: 18878

Publication fees for Open Access journals - work flows at Helmholtz Centres

Reschke, E.; Köhler, M.; Wagner, A.; Grosse, K.

Open Access is a new way of publishing. The presentation aims to show how the golden way of Open Access Publishing has to be funding. Based on the "Berlin Declaration to Knowledge in the Science and Humanities" and the "Agreement of the Assembly of Members" (assembly of the directors of the Helmholtz Centres) the Helmholtz Research Centres organized the publishing and funding process in different ways. The presentation shows 4 examples for it: DESY, Forschungszentrum Jülich, GSI Darmstadt and HZDR.

Keywords: Open Access; Funding; Author fees; Publication fees

  • Lecture (others)
    Open Access to Publications and Data in the Research Field "Structure of Matter" of the Helmholtz Association, 10.-11.06.2013, Hamburg, Deutschland

Publ.-Id: 18877

Traveling-Wave Thomson-Scattering and optical FELs

Steiniger, K.; Pausch, R.; Widera, R.; Debus, A.; Kluge, T.; Bussmann, M.; Cowan, T.; Schramm, U.; Sauerbrey, R.

We show that optical free electron lasers in the X-ray range can be realized using Traveling-Wave Thomson-scattering (TWTS). TWTS provides long interaction lengths in the centimeter to meter range with undulator periods in the micron range. These can be accomplished with existing petawatt class lasers as optical wigglers in a side scattering geometry by tilting the laser pulse front. TWTS circumvents both the nonlinear Thomson intensity threshold and the Rayleigh-length limit which in head-on Thomson-scattering prevents the SASE process to occur. Furthermore TWTS offers tuneability in the scattered wavelength via the incidence angle and flexibility in the optical undulator length.
In this talk we discuss the FEL dynamics of relativistic electrons in TWTS and quantify the influence of dispersion effects on the laser pulse properties and showing that they can be suppressed effectively. We present a self-consistent 1.5D FEL-theory which accounts for the oblique incident laser pulse and give scaling laws on the interaction geometry and FEL-amplification with respect to incidence angle and electron beam parameters. We finally present numbers on expected experimental performance for laser and electron beam parameters that will be available at HZDR.

Keywords: traveling-wave; thomson scattering; x-ray; free electron laser; laser pulse

  • Lecture (Conference)
    1st European Advanced Accelerator Concepts Workshop, 02.-07.06.2013, La Biodola, Isola d'Elba, Italy

Publ.-Id: 18876

Resistive Switching in thermally oxidized Titanium Films

Blaschke, D.; Zahn, P.; Skorupa, I.; Scheumann, B.; Scholz, A.; Gemming, S.; Potzger, K.

Polycrystalline rutile TiO2 thin films were prepared on Pt/Ti/SiO2/Si substrates by thermal oxidation of a 100nm thick titanium film at temperatures between 500°C and 800°C. We observed stable nonvolatile unipolar switching in the films oxidized at 600-800°C. Retention measurements showed stable ON and OFF states for a time of at least 24h at room temperature, if there was a sufficient relaxation period between the switching event and the start of the read out process. Without any relaxation time, we observed an increase in resistance in the high resistance state (HRS) after the RESET process. In contrast, the LRS did not show a time dependent resistance change after the SET process.

Keywords: TiO2; resistive switching; thermal oxidation; retention

  • Contribution to proceedings
    Semiconductor Conference Dresden-Grenoble (ISCDG), 2013 International, 26.-27.09.2013, Dresden, Germany
    Semiconductor Conference Dresden-Grenoble (ISCDG), 2013 International: IEEE, 978-1-4799-1250-6
    DOI: 10.1109/ISCDG.2013.6656318
  • Lecture (Conference)
    International Semiconductor Conference Dresden-Grenoble, 26.-27.09.2013, Dresden, Germany

Publ.-Id: 18875

Gated phantom irradiation for 4D in-beam and 4D off-beam PET comparison

Laube, K.; Bert, C.; Enghardt, W.; Helmbrecht, S.; Kaderka, R.; Kurz, C.; Parodi, K.; Saito, N.; Tian, Y.; Fiedler, F.

no abstract available

Keywords: ion beam therapy; intra-fractional motion; in vivo dose monitoring; 4D PET

  • Open Access Logo Contribution to external collection
    Katrin Große: GSI Scientific Report 2012, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung, 2013, 486

Publ.-Id: 18873

The Helmholtz SIMS Network: Cooperation at Multiple Scales

Renno, A. D.; Merchel, S.; Akhmadaliev, S.; Rugel, G.; Ziegenrücker, R.; Döbeli, M.; Richnow, H.-H.; Wiedenbeck, M.

Super-SIMS - also called Accelerator-SIMS or Trace Element Accelerator Mass Spectrometry (TEAMS) - is an ultrasensitive analytical method for the determination of stable elements and isotopes. A Super-SIMS-Set-up is now under installation at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) ion beam centre where we are connecting a conventional SIMS-source (Cameca IMS 6f, formerly installed at the GFZ Potsdam, currently upgraded to a 7f-Auto) to a 6 MV tandem accelerator (Akhmadaliev et al., 2013). A similar set-up has been operated by the ETH Zurich for several years (Maden, 2003).
Due to the acceleration of the extracted sample ions to MeV-energies and their charge reversal from negative to positive ions, Super-SIMS can reach about 2 to 3 orders of magnitude lower detection limits (down to 10-12 or ppt, highly depending on analyte and matrix) as conventional SIMS.
The HZDR Super-SIMS will be part of the Helmholtz-SIMS-Network, called SIGMA, which is currently being developed. Other partners are the Helmholtz Centre for Environmental Research in Leipzig (NanoSIMS & TOF-SIMS currently under installation) and the GFZ Potsdam (High-resolution 1280-HR SIMS under installation). Thus, extensive knowledge exchange will assure the optimal environment for optimizing our highly sophisticated accelerator set-up running. Later, easy access for international users from research institutes from e.g. Brazil, India, Russia and South Africa is planned within SIGMA.
Funding from an Integrated Infrastructure Initiative (I3) from the European Commission within Horizon 2020 will be applied for; this would allow Trans-National Access (TNA) to both Super-SIMS facilities in Dresden and Zurich. An independent User Selection Panel will examine user proposals for TNA. After receiving a positive evaluation, European users can obtain free access to the Super-SIMS-facilities including logistical, scientific and technical support, and travel and accommodation grants. ETH Zurich and HZDR will widen their already established joint research activities from the I3-project SPIRIT (Möller, 2011) to reach the ultimate detection limits, which are possible using the Super-SIMS technique.

Keywords: Super-SIMS; AMS; accelerator-based mass spectrometry

  • Invited lecture (Conferences)
    7th Biennial Geo-SIMS Workshop, Lecture Series "SIMS: Current Strengths and Future Potential", 20.-22.08.2013, Potsdam, Deutschland

Publ.-Id: 18872

Ion-guided microstructure evolution of carbon-nickel nanocomposite films during ion beam assisted deposition: 3D sculpting at the nanoscale

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

Ion assistance during film growth provides unique opportunities to influence the microstructure due to energy transfer and imposed directionality. During nanocomposite film growth at low temperatures (RT to 300°C), phase separation occurs at the growing film surface. A systematic study of ion irradiation as a pure energy and momentum transfer agent in the context of surface diffusion assisted phase separations is, however, lacking. Here the influence of low energy (50-140 eV) assisting Ar+ ion irradiation on the morphology of C:Ni (~ 5 at.% Ni to ~ 50 at.% Ni) thin films will be reported. Two types of ordered nanostructures, - tilted columns and self-organized 3D patterns with well-defined surface periodicity - are identified and characterized. For a given composition of the depositing flux, the transition from the column to the self-organized 3D pattern formation regime as a function of the assisting ion energy is demonstrated. Tilt angle and diameter of the nanocolumns are controlled by the deposition parameters. Complex secondary structures like chevrons with partially epitaxial junctions are grown by sequential deposition. The effects of the metal content and the assisting ion current on the self-organized 3D patterns and surface periodicity are studied. Mechanical and tribological properties of both types of nanostructures will be reported.

Acknowledgement: The work is funded by the European Union, LEI Folgeprojekt D1, "C-basierte Funktionsschichten für tribologische Anwendungen (CarboFunctCoat)", No. 7310000211.

Keywords: Nanocomposites; Ion assistance; pattern formation; microstructure

  • Lecture (Conference)
    E-MRS 2013 SPRING MEETING - Symposium W - Ion beam applications: new and innovative approaches, 26.-31.05.2013, Strasbourg, Frankreich

Publ.-Id: 18871

SWCNT growth from C:Ni nanocomposite templates

Krause, M.; Haluska, M.; Kunze, T.; Mücklich, A.; Hübner, R.; Melkhanova, S.; Bayrak, T.; Abrasonis, G.; Gemming, S.

Single walled carbon nanotubes (SWCNT) grown from C:Ni nanocomposite thin film templates are studied by Raman mapping, scanning, and transmission electron microscopy. The templates consist of few nm thick films of Ni nanoparticles embedded in a protective matrix of amorphous carbon. They are prepared by ion beam sputtering, which allows a precise control of the particle size, shape, and arrangement in a sub nanometer length scale. SWCNT growth is performed by low pressure chemical vapour deposition in C2H2/ H2 at temperatures of about 735°C. The electron micrographs show that a large part of the nanoparticles preserves its initial geometry. The effect of the different particle morphologies on the mean SWCNT diameter and diameter distribution is demonstrated and discussed in the framework of current growth models.

Keywords: Nanocomposites; Single-walled carbon nanotube growth; diameter control; Raman mapping; electron microscopy

  • Poster
    27th International Winterschool on Electronic Properties of Novel Materials (IWEPNM), 02.-09.03.2013, Kirchberg, Österreich
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18870

Microbial Diversity in Opalinus Clay and Interaction of Dominant Microbial Strains with Actinides (Final Report BMWi Project No.: 02 E 10618)

Moll, H.; Lütke, L.; Bachvarova, V.; Steudtner, R.; Geißler, A.; Krawczyk-Bärsch, E.; Selenska-Pobell, S.; Bernhard, G.

For the first time microbial tDNA could be isolated from 50 g unperturbed Mont Terri Opalinus Clay. Based on the analysis of the tDNA the bacterial diversity of the unperturbed clay is dominated by representatives of Firmicutes, Betaproteobacteria, and Bacteriodetes. Firmicutes also dominate after treatment of the clay with R2A medium. Bacteria isolated from Mont Terri Opalinus Clay on R2A medium were related to Sporomusa spp., Paenibacillus spp., and Clostridium spp.. All further investigations are concentrated on the unique isolates Sporomusa sp. MT-2 and Paenibacillus sp. MT-2. Cells of the type Sporomusa sp. MT-2 and Paenibacillus sp. MT-2 were comprehensively analyzed in terms of growing, morphology, functional groups of the cell envelope, and cell membrane structure.
Strong actinide(An)/lanthanide(Ln)-interactions with the Opalinus Clay isolates and the Äspö-strain Pseudomonas fluorescens (CCUG 32456) could be determined within a broad pH range (2-8). The metals bind as a function of pH on protonated phosphoryl, carboxyl and deprotonated phosphoryl sites of the respective cell membrane. The thermodynamic surface complexation constants of bacterial An/Ln-species were determined and can be used in modeling programs. Depending on the used An different interaction mechanisms were found (U(VI): biosorption, partly biomineralisation; Cm(III): biosorption, indications for embedded Cm(III); Pu: biosorption, bioreduction and indications for embedded Pu). Different strategies of coping with U(VI) were observed comparing P. fluorescens planktonic cells and biofilms under the chosen experimental conditions. An enhanced capability of the biofilm to form meta-autunite in comparison to the planktonic cells was proven. Conclusively, the P. fluorescens biofilm is more efficient in U(VI) detoxification.
In conclusion, Mont Terri Opalinus Clay contains bacterial communities, that may influence the speciation and hence the migration behavior of selected An/Ln under environmental conditions.

Keywords: Actinides; uranium; curium; plutonium; Opalinus Clay; microbial interactions; bacteria; speciation; repository

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-036 2013
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 18869

Simple transport system for solid targets

Franke, K.; Hauser, J.

Reduction of the radiation dose during transfer of solid targets from the irradiation position of the cyclotron Cyclone 18/9

Keywords: cyclotron; target; transport system; radiation dose

  • Poster
    IBA User's Meeting 2013, 17.-19.06.2013, Hillerød, Denmark

Publ.-Id: 18868

Closure models for turbulent bubbly flows: a CFD study

Rzehak, R.; Krepper, E.

For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas-liquid multiphase flow, bubble-induced turbulence is one such process for which a satisfactory model is still not available. A common approach to its solution is to add source terms to the single phase two-equation turbulence models. Here we report a comparison of different models of this type some of which have been used previously, some of which are new. To qualify the validity of the different models a set of reference data has been selected from the literature. Together with a suitable model for the bubble forces the most promising variants can be identified. Special attention in this respect is given to the wall force. Guidelines for modeling bubbly turbulence are proposed and needs for further research identified.

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

Publ.-Id: 18867

Polarized Photocathode SRF Guns

Teichert, J.

The talk gives an overview of development and test of superconducting RF photo guns with GaAs photocathodes.

Keywords: Superconducting RF; photo electron injector; photocathode; GaAs; polarized electrons

  • Invited lecture (Conferences)
    EuCARD´13, 10.-14.06.2013, Geneva, Schweiz

Publ.-Id: 18866

Thermodynamic study of the complexation of protactinium(V) with diethylenetriaminepentaacetic acid

Mendes, M.; Leguay, S.; Le Naour, C.; Hamadi, S.; Roques, J.; Moisy, P.; Guillaumont, D.; Topin, S.; Aupiais, J.; Den Auwer, C.; Hennig, C.

The complex formation of protactinium(V) with DTPA was studied at different temperatures (25−50 °C) and ionic strengths (0.1−1 M) with the element at tracer scale. Irrespective of the temperature and ionic strength studied, only one neutral complex with (1:1) stoichiometry was identified from solvent extraction and capillary electrophoresis coupled to ICP-MS (CEICP-MS) experiments. Density Functional Theory (DFT) calculations revealed that two complexes can be considered: Pa(DTPA) and PaO(H2DTPA). The associated formation constants were determined from solvent extraction data at different ionic strengths and temperatures and then extrapolated to zero ionic strength by SIT methodology. These constants are valid, regardless of complex form, Pa(DTPA) or PaO(H2DTPA). The standard thermodynamic data determined with these extrapolated constants revealed a very stable complex formed energetically by an endothermic contribution which is counter balanced by a strong entropic contribution. Both, the positive enthalpy and entropy energy terms suggest the formation of an inner sphere complex.

Keywords: Protactinium; Pa(V); diethylenetriaminepentaacetic acid

Publ.-Id: 18865

Raman spectroscopy and power diffraction study of synthetic Coffinite (USiO4) at high pressures

Bauer, J. D.; Labs, S.; Weiss, S.; Bayarjargal, L.; Curtis, H.; Morgenroth, W.; Bosbach, D.; Hennig, C.; Winkler, B.

Coffinite, USiO4, can form under reducing conditions from UO2 in contact with silica-rich waters (Langmuir’s criterion) [1]. Spent nuclear fuel (SNF) consists to > 90% of UO2, so coffinite needs to be taken into account in the safety assessment as a potential secondary phase. While high pressures are not of specific relevance for a possible final repository for SNF, its structural behaviour at high pressures is of general interest to understand the phase stabilities and to benchmark model calculations. The high pressure behaviour of coffinite has been studied before on natural samples [2,3]. A pressure-induced irreversible phase transformation from the zircon- to the scheelite-type structure was found at about 15 GPa using an alcohol-water mixtures as a pressure medium [3].
Here, synthetic coffinite was studied under high pressure conditions in the diamond anvil cell with neon as quasi-hydrostatic pressure medium up to pressures of 35 GPa. The samples are free of impurities of UO2, as characterized by XRD and HRTEM. Powder diffraction experiments with synchrotron radiation indicate a pressure-induced phase transformation at 18-20 GPa. In contrast to the earlier high pressure study [3], this transformation is reversible on pressure release and no UO2 is formed during the process. A detailed data analysis is currently in progress.
Raman spectra were obtained up to a pressure of 18 GPa. The study of the Raman spectra at higher pressures is on-going.

[1] Langmuir (1978), Geochim. Cosmochim. Acta 42, 547-569
[2] Liu (1982), Earth Plan. Sci. Lett. 57, 110-116
[3] Zhang et al. (2009), Am. Min. 94, 916-920

Keywords: Spent nuclear fuel; Coffinite; USiO4; phase transition zircon-scheelite

  • Lecture (Conference)
    Goldschmidt Conference 2013, 25.-30.08.2013, Florence, Italy

Publ.-Id: 18864

Closure models for turbulent bubbly flows: a CFD study

Rzehak, R.; Krepper, E.

For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas-liquid multiphase flow, bubble-induced turbulence is one such process for which a satisfactory model is still not available. A common approach to its solution is to add source terms to the single phase two-equation turbulence models. We here report a comparison of different models of this type some of which have been used previously, some of which are new. To qualify the validity of the different models a set of reference data has been selected from the literature. Together with a suitable model for the bubble forces the most promising variants can be identified. Special attention in this respect is given to the wall force. Conclusions towards best practice guidelines for modeling bubbly turbulence are drawn and needs for further research identified.

Keywords: dispersed gas liquid multiphase flow; bubble induced turbulence; Euler Euler two fluid model; closure relations; CFD simulation; model validation

  • Contribution to proceedings
    8th International Conference on Multiphase Flow, ICMF2013, 26.-31.05.2013, Jeju, Korea
    Closure models for turbulent bubbly flows: a CFD study
  • Lecture (Conference)
    8th International Conference on Multiphase Flow, ICMF2013, 26.-31.05.2013, Jeju, Korea

Publ.-Id: 18863

CFD Simulation of Counter-current Flow Limitations in a Full Scale Pressurized Water Reactor (PWR) Hot Leg

Darlianto, D.; Agung, R.; Höhne, T.; Prayitno, S.; Lucas, D.

The counter-current gas-liquid two-phase flow in the hot leg of a pressurized water reactor (PWR) has received a special attention for safety regulation in the nuclear industry. One hypothetical scenario is a loss-of-coolant-accident (LOCA) in a PWR, which is caused by the damage at any position of the primary circuit. The analytical simulation of this phenomenon is an essential element to understand safety-related issues in nuclear power plants. It is expected that the introduction of computational fluid dynamics (CFD) tools will enhance the accuracy of the simulation predictions compared to the established one-dimensional thermal hydraulic analyses. Here CFD allows substituting geometry-dependent empirical closure relations with more physically justified closure laws that are formulated at the scale of the structures of the gas–liquid interface.
This paper presents a CFD simulation on the counter-current flow limitation (CCFL) phenomena in a full scale PWR hot leg of Upper Plenum Test Facility (UPTF) Test case No 11 by using a commercial CFD code of ANSYS CFX 13.0, based on the finite volume method for an Euler-Euler model. The grid consist 29,100 hexahedral elements and 30,102 nodes. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model. A new formulation of an interfacial drag coefficient was implemented inside the Algebraic Interfacial Area Density (AIAD) model (Höhne, 2010) into the three-dimensional (3-D) computational fluid dynamics (CFD) code.
To demonstrate the feasibility of the developed drag coefficient in AIAD model, the computed main parameters of the selected test case were compared with experimental data. The results indicated that the quantitative agreement between calculation and experimental data was obtained. This means that the AIAD model combined with the new drag force formulation is a promising way to simulate the phenomena in the frame of an Euler-Euler approach.

Keywords: counter-current flow limitations; AIAD; pressurized water reactor; hot leg; CFD; Upper Plenum Test Facility (UPTF)

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

Publ.-Id: 18862

Baseline Model For CFD Of Dispersed Bubbly Flow

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

A set of closure relations for adiabatic bubbly flow has been collected that represents the best available knowledge and may serve as a baseline for further improvements and extensions to more general situations. Submodels for bubble forces, bubble-induced turbulence and bubble coalescence and breakup are considered. A preliminary validation of the model is presented by comparison to selected tests from the TOPFLOW database. Specific attention is paid to effects of polydispersity. Issues to be addressed in future work are discussed.

Keywords: dispersed gas liquid multiphase flow; bubble induced turbulence; bubble coalecence and breakup; Euler Euler two fluid model; closure relations; CFD simulation

  • Contribution to proceedings
    15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-15, 12.-16.05.2013, Pisa, Italy
  • Poster
    15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-15, 12.-16.05.2013, Pisa, Italy

Publ.-Id: 18861

Numerical simulation of multilayer deposition in an obstructed channel flow

Lecrivain, G.; Drapeau-Martin, S.; Barth, T.; Hampel, U.

Simulation of multilayer deposition of dry aerosol particles in turbulent flows has gained a growing interest in various industrial and research applications. The multilayer deposition of carbonaceous aerosol particles in a turbulent channel flow obstructed by a succession of square ribs is here numerically investigated. The multilayer particle bed growth on the various wall surfaces affects the air flow, which in turn affects the overall deposition rate. An iterative numerical procedure is therefore suggested to simulate the evolution of the graphite layer. The iterative process used to reproduce the layer build-up is decomposed as follows: Reynolds-Avergared Navier Stokes is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After statistically sufficient deposition of particulate matter, the layer build-up is computed using mechanics of dry granular material. The layer build-up model shows good agreement with data obtained from experimental tests carried out on-site.

Publ.-Id: 18860

Swift carbon ion irradiated Nd:YAG ceramic optical waveguide amplifier

Tan, Y.; Luan, Q.; Liu, F.; Akhmadaliev, S.; Zhou, S.; Chen, F.

A high-gain optical waveguide amplifier has been realized in a channel waveguide platform of Nd:YAG ceramic produced by swift carbon ion irradiation with metal masking. The waveguide is single mode at wavelength of 810 and 1064 nm, and with the enhanced fluorescence intensity at around 1064 nm due to the Nd3+ ion emissions. In conjunction with the low propagation loss of the waveguide, about 26.3 dB/cm of the small signal gain at 1064 nm is achieved with an 18 ns pulse laser as the seeder under the 810-nm laser excitation. This work suggests the carbon ion irradiated Nd:YAG waveguides could serve as efficient integrated amplifiers for the signal amplification.

Keywords: Optical amplifiers; Rare-earth-doped materials; Waveguides

Publ.-Id: 18859

Transport in ZnCoO thin films with stable bound magnetic polarons

Kaspar, T.; Fiedler, J.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.

Diluted magnetic ZnCoO films with 5 at.% Co have been fabricated by pulsed laser deposition on c-plane sapphire substrates and Schottky and Ohmic contacts have been prepared in top-top configuration. The diode current is significantly reduced after the diode has been subjected to an external magnetic field. In the reverse bias range the corresponding positive magnetoresistance is persistent and amounts to more than 1800% (50 K), 240% (30 K), and 50% (5 K). This huge magnetoresistance can be attributed to the large internal magnetic field in depleted ZnCoO with ferromagnetic exchange between stable bound magnetic polarons.

Keywords: magnetic semiconductors; spintronics; Schottky contact; depletion layer

Publ.-Id: 18858

CFD modeling for subcooled flow boiling: Actual state and parametric variations

Krepper, E.; Rzehak, R.

For CFD modeling of subcooled flow boiling the Euler/Euler two-phase flow description with heat flux partitioning has been proven to be very successful to analyse experimental data. Robust predictive capabilities of the modeling however require that it is validated for a wide range of parameters. Suitable experiments should yield sufficient information for the verification of the microscopic details of the models. In the presented investigations experiments at the CEA facility DEBORA were investigated in which a vertical pipe was heated from the side wall. Measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size were performed. A comprehensive sensitive study of the wall boiling model showed that quantities with a strong influence on the amount of produced steam are the bubble size at detachment and the nucleation site density. In the paper the potential of the application of a population balance model is demonstrated. The measured gas bubble size profiles show an increase of the bubble size with increased distance from the heated wall caused by bubble coalescence. Furthermore the model framework is shown to be able to describe a shift from wall peak to core peak in the radial gas volume fraction profiles with increasing inlet temperature respective decreasing subcooling temperature.

Keywords: CFD; two phase flow; subcooled boiling; population balance model; DEBORA experiments; model validation

  • Contribution to proceedings
    International Conference on Multiphase Flow 2013, 26.-31.05.2013, Jeju, Südkorea
  • Lecture (Conference)
    International Conference on Multiphase Flow 2013, 26.-31.05.2013, Jeju, Südkorea

Publ.-Id: 18857

Countercurrent flow limitation in a PWR hot leg

Murase, M.; Kinoshita, I.; Utanohara, Y.; Lucas, D.; Tomiyama, A.

In order to evaluate countercurrent flow limitation (CCFL) characteristics in a PWR hot leg under reflux condensation, numerical simulations have been done for pressures of 0.1 MPa < P < 8 MPa using a VOF (volume of fluid) method implemented in the computational fluid dynamics software, FLUENT6.3.26. In this paper, first Wallis-type CCFL correlations for air-water and steam-water conditions were derived using the previously measured data and calculated results. The slope m was 0.70 and CCFL constants were C = 0.63 ± 0.02 and C = 0.655 ± 0.025 for air-water and steam-water conditions, respectively. Then, numerical simulations were additionally done by using the VOF method to evaluate the effect of fluid properties at a pressure of 16 MPa, and it was shown that the Wallis-type CCFL correlation for steam-water conditions could be used in the pressure range of 0.1 MPa < P <16 MPa. Finally, effects of fluid properties on CCFL characteristics were discussed.

Keywords: CCFL; reflux

  • Contribution to proceedings
    NURETH-15 - 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-17.05.2013, Pisa, Italy
    Paper NURETH15-008
  • Lecture (Conference)
    NURETH-15 - 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-17.05.2013, Pisa, Italy

Publ.-Id: 18856

Low-energy M1 strength within the shell model

Schwengner, R.

Magnetic dipole strength functions have been deduced from a large number of M1 transition strengths calculated within the shell model for the nuclides 94Mo, 95Mo, and 90Zr. An enhancement of M1 strength toward low energy has been found for all nuclides considered. This enhancement supports results of recent (3He,3He') and (d,p) experiments, but is at variance with analytical M1 strength functions currently given in reaction-data libraries and used in statistical-reaction codes.

Keywords: Nuclear structure; transition strengths; strength functions; shell model

  • Invited lecture (Conferences)
    4th Workshop on Nuclear Level Density and Gamma Strength, 27.-31.05.2013, Oslo, Norwegen

Publ.-Id: 18855

Mean-field modeling of the interaction of soft iron with helical flows

Giesecke, A.; Stefani, F.

We have performed kinematic simulations of dynamo action of a helical flow of a conducting fluid with a flow geometry in the style of the G.O. Roberts flow. As an extension to the original model, we have taken into account internal rods and/or walls that lie in the center of individual eddies and/or provide a separation of the eddies from each other. These flow guiding fixtures can be made of soft iron with a relative permeability much larger than one and the associated inhomogeneity significantly alters the behavior of the leading dynamo eigenmodes. The investigations are motivated from the roughly unknown induction effects of the forced helical flow that is used in fast reactors to remove the heat from the reactor core and from the supporting impact for dynamo action caused by the presence of soft iron impellers in the von-Karman-Sodium (VKS) dynamo.

Applying the testfield method we have computed the elements of the alpha tensor from direct simulations of a restricted number of helical eddies. The results may be extrapolated to model the combined induction effect of an extremely large number of individual helical eddies that cannot be resolved in direct simulations.

We will show which properties of the small scale induction in principle can be reproduced in a simplified mean-field model and where discrepancies/inconsistencies might arise. Furthermore, we investigate the possibility to include spatial "fluctuations" of the permeability into the framework of simple mean-field simulations.

Keywords: Dynamo

  • Lecture (Conference)
    International Symposium on Geophysical and Astrophysical Dynamos, 07.-12.07.2013, Zürich, Schweiz

Publ.-Id: 18854

Ga Implantation Induced Atomic Mixing in Crystalline and Amorphous Ge Isotope Multilayers

Radek, M.; Bracht, H.; Schmidt, B.; Bougeard, D.; Haller, E. E.

Self-atom mixing induced by Gallium (Ga) implantation in crystalline and amorphous germanium (Ge) is investigated using an isotopic multilayer structure of alternating 73 Ge and nat Ge layers grown by molecular beam epitaxy. The distribution of the implanted Ga atoms and ion-beam induced depth-dependent mixing was determined by means of the secondary ion mass spectroscopy (SIMS). The position and form of the implanted Ga peak is very similar in the amorphous and crystalline Ge and can be reproduced accurately by SRIM simulations, whereas the ion-beam induced self-atom mixing strongly depends on the state of the Ge structure. The data from SIMS-measurements reveal a stronger mixing of the crystalline compared to amorphous structure. Molecular dynamics simulations suggest a higher mixing efficiency in the amorphous structure due to the lower thermal transport capacity. The kinetic energy of the implanted ions cause thermal spikes characterized by localized melted regions. Because of the lower thermal transport capacity of the amorphous structure the thermal spike lasts longer and leads to a higher mixing efficiency. The experimentally observed disparity in the ion-beam mixing efficiency of crystalline and amorphous Ge in comparison with the simulation indicates different mixing mechanisms.

Keywords: ion-beam mixing; Ge; SIMS

  • Lecture (Conference)
    E-MRS 2013 Spring Meeting, Symposium W, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 18853

Atomistic modeling of solid phase recrystallization of amorphous Si and Ge

Posselt, M.

Recrystallization of amorphous Si and Ge continues to be an important issue in nanoelectronic technologies. In order to obtain high dopant concentrations in the nanoscale regions ion implantation at relatively high fluence is required which causes the amorphization of the host material. Subsequently, thermal processing must be used to restore the semiconductor crystal. In planar structures this can be fully achieved by solid-phase epitaxial recrystallization whereas more complex processes take place in fins and nanowires due to the significant influence of surfaces and interfaces. It is highly desirable to understand the recrystallization phenomena on the atomic level. This work presents results of molecular dynamics simulations of solid phase recrystallization in Si and Ge. At first the process of epitaxial recrystallization of amorphous layers is considered and the influence of accuracy of the interatomic potential used in the simulations is discussed. Then the method is ap plied to solid phase recrystallization of fins and nanowires. The incomplete restoration of the host crystal is characterized by the occurrence of defects, stacking faults and polycrystallization.

Keywords: solid phase recrystallization; Si; Ge; molecular dynamics simulations

  • Invited lecture (Conferences)
    E-MRS 2013 Spring Meeting, Symposium K, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 18852

In vivo dose response studies for laser driven particle beams

Oppelt, M.; Baumann, M.; Bergmann, R.; Beyreuther, E.; Brüchner, K.; Kaluza, M.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Reuter, M.; Sävert, A.; Schnell, M.; Schürer, M.; Pawelke, J.

Purpose. The novel technology of proton and ion acceleration by ultra high intensity lasers promises the realization of compact and economic particle accelerators for cancer therapy that can be integrated in already existing clinics. Before potential clinical application possible biological consequences of laser accelerated and therewith ultra-short pulsed particle beams with high pulse dose have to be investigated. As first step in the chain of translational research extensive in vitro dose response studies with laser driven electron and proton beams were performed within the joint research project “onCOOPtics”. We now report on first experiments comparing laser and conventional accelerated particle beams in vivo.
Material and methods. A mouse tumor model suitable for the currently available still low energy (up to ~30 MeV) of laser accelerated protons was established and successfully implemented using laser accelerated electrons, likewise providing information about biological consequences of ultra-short pulsed beams. To apply a prescribed dose to each tumor the prior established laser based 2D in vitro irradiation technology was enhanced for the 3D animal model in terms of beam transport, beam monitoring, dose delivery and dosimetry. A system for mouse fixation, precise tumor positioning and verification at the irradiation site was realized (Schürer et al. 2012). In vivo tumor irradiation was performed at the 30 TW Jena Titanium: Sapphire (JeTi) laser system. Electron pulses of energies up to a few 10 MeV were generated focusing laser pulses of 28 fs duration into a hydrogen gas jet. Murine sarcoma KHT and human squamous cell carcinoma FaDu tumors were irradiated with doses up to 14 Gy at mean dose rates of 1–2 Gy/min. Reference electron irradiation was performed with the same setup and dosimetry system at a conventional therapy LINAC. The radiation induced tumor growth delay was investigated for several hundred mice.
Results. The irradiation campaign was conducted over a period of several months proving the reliability and stability of all implemented setup components and methods. Dose response curves of both beam qualities have been obtained for the direct comparison of ultra-short pulsed laser accelerated and conventional continuous electron beams. The current status of the ongoing data evaluation gives no evidence for a different RBE of laser driven electrons.
Conclusion. The successful establishment of all technical requirements for and the world wide first performance of systematic animal studies with laser accelerated electrons mark an important step towards the clinical application of laser accelerated particle beams. The realization of in vivo studies with laser driven proton beams is now feasible.
1. M Schürer et al (2012) Irradiation system for pre-clinical studies with laser accelerated electrons. Biomed Tech 57(Suppl. 1):62–65
Supported by BMBF grant nr. 03ZIK455 and 03Z1N511.

  • Abstract in refereed journal
    Strahlentherapie und Onkologie 189(2013)Suppl 1, 12-12
  • Lecture (Conference)
    19. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 09.-12.05.2013, Berlin, Deutschland

Publ.-Id: 18851

Mobile uranium(IV)-bearing colloids in a mining-impacted wetland

Wang, Y.; Frutschi, M.; Suvorova, E.; Phrommavanh, V.; Descostes, M.; Osman, A. A. A.; Geipel, G.; Bernier-Latmani, R.

Uranium is known to accumulate in wetland soils, where the precipitation of the sparingly soluble U(IV) mineral uraninite (UO2) under reducing conditions is considered a promising strategy for U immobilization. Here, we investigate the mobility of U in a mining impacted wetland in France that exhibited locations harboring U concentrations of up to 4,000 ppm. A distinct release of U into the stream passing through the wetland is observable. We examine soil and porewater composition as a function of depth at two U hotspots to assess the geochemical conditions leading to this release. The analyses show that U is present in soil as a non-crystalline U(IV) species sorbed onto amorphous Fe-Al-P-Si aggregates through phosphate groups, and that high U(IV) concentrations in porewater are due to the association of U with Fe- and organic matter-containing colloids. These results show that tetravalent U in soil is labile and releases U(IV) to form mobile colloids that ultimately result release of U into the stream. This is the first report of mobile U(IV) colloids in the environment and strongly brings into question the common assumption that U is immobile when present in a tetravalent oxidation state.

Keywords: Uranium; wetland; transport

Publ.-Id: 18850

Using XFELs for Probing of Complex Interaction Dynamics of Ultra-Intense Lasers with Solid Matter

Kluge, T.; Gutt, C.; Huang, L.; Metzkes, J.; Schramm, U.; Bussmann, M.; Cowan, T. E.

We demonstrate the potential of X-ray free-electron lasers (XFEL) to advancethe understanding of complex plasma dynamics by allowing for the first time nanometer and femtosecond resolution at the same time in plasma diagnostics. Plasma phenomena on such short timescales are of high relevance for many fields of physics, in particular in the ultra-intense ultra-short laser interaction with matter. Highly relevant yet only partially understood phenomena may become directly accessible in experiment. These include relativistic laser absorption at solid targets, creation of energetic electrons and electron transport in warm dense matter, including the seeding and development of surface and beam instabilities, ambipolar expansion, shock formation, and dynamics at the surfaces or at buried layers.
We demonstrate the potentials of XFEL plasma probing for high power laser matter interactions using exemplary the small angle X-ray scattering technique, focusing on general considerations for XFEL probing.

  • Physics of Plasmas 21(2014), 033110
    DOI: 10.1063/1.4869331
  • Lecture (Conference)
    HIBEF Kickoff Meeting, 02.-05.06.2013, Hamburg, Deutschland
  • Poster
    HIBEF Kickoff Meeting, 02.-05.06.2013, Hamburg, Deutschland
  • Contribution to WWW
  • Poster
    OncoRay Retreat, 27.-28.03.2014, Dresden, Deutschland
  • Lecture (others)
    Group-Semininar, 6.1.2015, Osaka, Japan

Publ.-Id: 18849

Practical guide for validated memristance measurements

Du, N.; Shuai, Y.; Luo, W.; Mayr, C.; Schueffny, R.; Schmidt, O. G.; Schmidt, H.

Chua [IEEE Trans. Circuit Theory 18, 507-519 (1971)] predicted rather simple charge-flux curves for active and passive memristors (short for memory resistors) and presented active memristor circuit realizations already in the 1970 s. The first passive memristor has been presented in 2008 [D. B. Strukov, G. S. Snider, and D. R. Williams, Nature (London) 453, 80-83 (2008)]. Typically, memristors are traced in complicated hysteretic current-voltage curves. Therefore, the true essence of many new memristive devices has not been discovered so far. Here, we give a practical guide on how to use normalized charge-flux curves for the prediction of hysteretic current-voltage characteristics of memristors. In the case of memristive BiFeO3 thin film capacitor structures, the normalized charge-flux curves superimpose for different numbers of measurement points Ns and a different measurement time per measurement point Ts. Such normalized charge-flux curves can be used for the prediction of current-voltage characteristics for input signals with arbitrarily chosen Ns and Ts.

Keywords: memristance

Publ.-Id: 18848

Three-dimensional simulation of multiphase flows in porous solid foam structures

Subramanian, K.; Schubert, M.; Krepper, E.; Lucas, D.; Hampel, U.

1 Introduction
Ceramic foam packings, due to their high porosity, high specific surface area and low pressure drop are promising alternatives for packing internals used in chemical engineering processes. Photograph of the sponges can be seen in Figure 1. The applications of foam packing as burners and heat exchangers have been widely studied, but as catalyst carriers particularly for gas-liquid systems solid foam behaviour is not yet well understood. Due to its highly porous nature, it is very tough to understand the influence of hydrodynamics on the process performance. The long term goal of this work is to perform three dimensional Computational Fluid Dynamics (CFD) simulations of the evolving gas-liquid patterns considering ceramic foams as column internals and to validate them with experimental X-ray tomographic studies. It is noteworthy to mention that no 3D CFD simulations have been performed considering Ceramic foams as column internals in pilot scale. On the other hand, detailed studies are available considering spherical particles as internals in Trickle bed reactors. The closures will be modified according to the ceramic foam specifications.

2 Modeling Details
To simulate the column with ceramic foam as internals, there are two major requirements. One is the more precise information regarding the geometry and other is the appropriate closures.

The major challenge to grasp the ceramic foam packing as representative ‘porous body’ is to characterize the geometrical parameters such as pore diameter, strut diameter, pores per inch, porosity accurately and to understand the relationship with specific surface and pressure drop. Different empirical correlations are already available in the literature [2, 3]. Some of the correlations proposed in the literature will be used initially in this work.

A two phase Eulerian model is used considering the flow domain as porous. The influence of the liquid and gas drag is added as external source term to liquid and gas momentum equations separately. The drag force between the phases have been taken into account using relative permeability approach which was developed by Saez and Carbonell [4] for packed beds using capillary pressure and relative permeabilities of two phase flows.

As a first step, simulations are performed considering 2 mm spherical particles with porosity of 0.41 as column internals. Column has diameter of 0.3 m and height of 1.3 m. Air and Water is used as test substance. Single orifice with 25mm ID is used as inlet distributor. These simulation results are compared with experimental investigation studies of Marcandelli et. al. [5]. As next, this validated model is transferred to solid foams by mimicking high solid foam porosity of 0.93 with different ppi’s and to validate with in-house experiments performed using X-ray tomographic studies.

[1] Calvo. S., Beugre. D., Crine. M., Leonard. A., Marchot. P., Toye. D., Phase distribution measurements in metallic foam packing using X-ray radiography and micro-tomography, Chemical Engineering and Processing, Vol. 48, pp. no. 1030–1039, (2009).
[2] Dietrich, B., Pressure drop correlation for ceramic and metal sponges, Chemical Engineering Science, Vol. 74, pp. no. 192 – 199, (2012).
[3] Inayat, A., Freund,H., Zeiser, T., Schwieger, W., Determining the specific surface area of ceramic foams : The tetrakaidecahedron model revisited, Chemical Engineering Science, Vol. 66, pp. no. 1179 – 1188, (2011).
[4] Saez, A.E., Carbonell, R.G., Hydrodynamic Parameters for Gas-Liquid Cocurrent Flow in Packed Beds, AIChE Journal, Vol. 31, No.1, pp no. 52- 62, 1985.
[5] Marcandelli, C., Lamine, A.S., Bernard, J.R., Wild, G., Liquid Distribution in Trickle-Bed Reactor, Oil & Gas Science and Technology – Rev. IFP, Vol. 55, No.4, pp no. 407 - 415, 2000.

This work was funded by the Helmholtz Association within the frame of the Helmholtz Energy Alliance "Energy Efficient Chemical Multiphase Processes".

Keywords: CFD; Ceramic foams; Relative permeability; Multiphase flow

  • Poster
    Interpore - 5th International Conference on Porous Media & Annual Meeting, 21.-24.05.2013, Prague, Czech Republic

Publ.-Id: 18847

Numerical simulation of horizontal two-phase flow experiments using a morphology detection model

Höhne, T.

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

Keywords: CFD; horizontal flow; AIAD; ANSYS-CFX

  • Lecture (Conference)
    ANSYS Conference & 31. CADFEM Users' Meeting, 19.-21.06.2013, Mannheim, Deutschland
  • Contribution to proceedings
    ANSYS Conference & 31. CADFEM Users' Meeting, 19.-21.06.2013, Mannheim, Deutschland

Publ.-Id: 18846

Supraleitende Schichten in Halbleitern

Fiedler, J.

  • Lecture (Conference)
    Ionenstrahlen in Forschung und Anwendung, 12.-14.06.2013, Leipzig, Deutschland

Publ.-Id: 18845

Application of gamma-ray tomography for the development of flow regime maps of an inclined rotating fixed-bed reactor

Härting, H.-U.; Bieberle, A.; Schubert, M.; Hampel, U.

This contribution presents the inclined rotating fixed-bed reactor as a new chemical reactor concept for heterogeneous multiphase reactions. Combining the inclined and rotating operation of the fixed-bed, this new process intensification equipment allows for flow regime adjustment at fixed flow rates and overcomes liquid maldistribution. A highly integrated, compact gamma-ray computed tomography system for the non-invasive investigation of the flow regimes in the new reactor is presented, as well. Based on systematic flow experiments, flow regime maps for the inclined rotating fixed-bed reactor are generated for the first time and the effects of varying physico-chemical properties of the liquid phase on the flow regimes are discussed.

Keywords: Gamma-ray computed tomography; process intensification; multiphase flow; fixed-bed reactor; flow regime maps

  • Open Access Logo Contribution to proceedings
    7th World Congress on Industrial Process Tomography, WCIPT7, 02.-05.09.2013, Krakow, Poland, 336-344

Publ.-Id: 18844

Reaktionstechnische und hydrodynamische Untersuchungen an einem geneigt rotierenden Festbettreaktor

Härting, H.-U.; Schubert, M.

Kontinuierlich betriebene Festbettreaktoren mit regellos gepackten Formkatalysa-toren in Rieselfahrweise werden für viele katalytische Gas/Flüssig-Reaktionen einge-setzt. Anwendungen sind beispielsweise die Hydrierung von Alkenen, die Hydro-desulfurierung von Mineralöl oder die Abwasseraufbereitung.
Stellt die Stoffübertragung der Gasphase an die aktiven Zentren des Katalysators den geschwindigkeitsbestimmenden Teilschritt der Reaktion dar, kann die periodische Betriebsweise, z. B. in Form von Strömungsmodulation, eine Erhöhung der Raum-Zeit-Ausbeute bewirken. Weitere Vorteile der periodischen Betriebsweise sind die Verringerung von Fehlverteilungen und die Vermeidung von lokal überhitzten Stellen in der Katalysatorschüttung. Als Nachteile sind die Abnahme der positiven Effekte mit der Reaktorlänge sowie höhere Anforderungen an die Umsetzung im industriellen Maßstab, hervorgerufen durch die transienten Strömungsvorgänge im Reaktor und deren Auswirkungen auf den Anlagenverbund, bekannt.
Durch ein neuartiges periodisches Reaktorkonzept kann der Festbettreaktor unter quasi-stationären Bedingungen betrieben werden. Dabei ist der Reaktor geneigt und rotiert zusätzlich um seine Längsachse.
Durch die Neigung wird die Phasenseparation begünstigt, während die Rotation die periodische Be- und Entnetzung der Katalysatorschüttung hervorruft und somit den Zugang der Gasphase an die aktiven Zentren des Katalysators verbessert.
Mittels Gamma-Computertomographie wurden hydrodynamische Studien unter Variation von Reaktordrehzahl und -neigung sowie Variation von Flüssigphase, Durchsätzen und Packungsmaterial zur Aufklärung der Strömungsformen in einem Rohrreaktor (DI = 0,1 m und L = 1,2 m) durchgeführt.
Zur Bewertung des neuartigen Reaktorkonzepts wurde der Einfluss der Strömungs-formen auf die Raum-Zeit-Ausbeute der Hydrierung von α-Methylstyrol zu Cumol an Palladium auf kugelförmigem γ-Al2O3 untersucht.
Im Beitrag werden ausführlich hydrodynamische Studien und die darauf aufbauenden reaktionstechnischen Untersuchungen vorgestellt.

Keywords: Process Intensification; inclined rotating fixed-bed reactor; gamma-ray computed tomography

  • Poster
    Jahrestreffen Reaktionstechnik 2013, 06.-08.05.2013, Würzburg, Deutschland
  • Open Access Logo Contribution to proceedings
    Jahrestreffen Reaktionstechnik 2013, 06.-08.05.2013, Würzburg, Deutschland
    Tagungshandbuch Jahrestreffen Reaktionstechnik 2013

Publ.-Id: 18843

PT-symmetries in physics and some operator-theoretic challenges

Günther, U.

In the first half of the talk, a brief overview is given about basic results obtained in PT-symmetry related physics since 1998: early numerical indications on the reality of the spectrum of certain non-Hermitian effective Hamiltonians in quantum mechanics, the concrete reality condition for the spectrum, PT phase transitions, self-adjointness in Krein spaces, as well as most recent physical applications in optical waveguide systems, threshold lasers and coherent perfect absorbers.
In the second half of the presentation, we discuss some operator-theoretic challenges like the general structure of the so-called C-operator and its specific Lie group structures. Finally, we comment on the unboundedness of the C-operator for model Hamiltonians with ix^3 potential and possible group-theoretic implications.

Keywords: PT symmetry; quantum mechanics; phase transitions; optical wave guides; threshold lasers; coherent perfect absorbers; microwave cavities; Krein space; C operator; Lie group structures; unbounded operators

  • Lecture (Conference)
    5th Anniversary Workshop of the GAMM Activity Group Applied Operator Theory, 30.-31.05.2013, Berlin, Deutschland

Publ.-Id: 18842

Uranium contents in plants and mushrooms grown on a uranium contaminated site near Ronneburg in Eastern Thuringia/Germany

Baumann, N.; Arnold, T.; Haferburg, G.

Uranium concentrations in cultivated (sunflower, sunchoke, potato) and native plants, plant compartment specimens and mushrooms, grown on a test site within a uranium contaminated area in Eastern Thuringia, were analyzed and compared. This test site belongs to the Friedrich-Schiller University Jena, and is situated on the ground of a former, but now removed uranium mine waste leaching heap. For determination of the U concentrations in the biomaterials, the saps of the samples were squeezed out by using an ultra-centrifuge, after that the uranium concentrations in the saps and the remaining residue were measured, using ICP-MS.
The study further showed that uranium concentrations observed in plant compartment and mushroom fruiting bodies sap samples were always higher than their associated solid residue sample. Also it was found that the detected uranium concentration in the root samples were always higher than were observed in their associated above ground biomass, e.g. in shoots, leaves, blossoms etc.
The highest uranium concentration was measured with almost 40 ppb U in a fruiting body of a mushroom and in roots of butterbur. However, the detected uranium concentrations in plants and mushrooms collected in this study were always lower than in the associated surface and soil water of the test site, indicating that under the encountered natural conditions none of the studied plant and mushroom species turned out to be a hyper-accumulator for uranium, which could have extracted uranium in sufficient amounts out of the uranium contaminated soil.
In addition, it was found that the detected uranium concentrations in the sap samples, despite being above the sensitivity limit, proved to be too low – in combination with the presence of fluorescence quenching substances, e.g. iron and manganese ions, and/or organic quenchers – to extract a useful fluorescence signal, which could have helped to identify the uranium speciation in plants.

Keywords: Uranium (VI); Phytoremediation; Heavy metal contaminated soil; TRLFS

Publ.-Id: 18841

Free-Electron Laser Operation with a Superconducting Radio-Frequency Photoinjector at ELBE

Teichert, J.; Arnold, A.; Büttig, H.; Justus, M.; Kamps, T.; Lehnert, U.; Lu, P.; Michel, P.; Murcek, P.; Rudolph, J.; Schurig, R.; Seidel, W.; Vennekate, H.; Will, I.; Xiang, R.

At the radiation source ELBE a superconducting radio-frequency photoinjector (SRF gun) was developed and put into operation. Since 2010 the gun has delivered beam into the ELBE linac. A new driver laser with 13 MHz pulse repetition rate allows now to operate the free-electron lasers (FELs) with the SRF gun. This paper reports on the first lasing experiment with the far-infrared FEL at ELBE, describes the hardware, the electron beam parameters and the measurement of the FEL infrared radiation output.

Keywords: Superconducting RF; SRF gun; Photo injector; Free-electron laser; Linear accelerator

Publ.-Id: 18840

Atomic Layer Deposition of LiF Thin Films from Lithd and TiF4 Precursors

Mäntymäki, M.; Hämäläinen, J.; Puukilainen, E.; Munnik, F.; Ritala, M.; Leskelä, M.

Lithium fluoride (LiF) is an important optical material with a low refractive index and a large band gap. In this study, thin films of LiF are deposited using atomic layer deposition (ALD). Lithd and TiF4 are used as precursors, and they produce crystalline LiF in the temperature range 250–350 °C. The films are studied with UV-Vis spectrometry, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and elastic recoil detection analysis (ERDA). Adhesion of the films is tested by a Scotch tape test. This ALD process results in LiF films with a growth rate of approximately 1 Å per cycle at 325 °C. According to ERDA measurements, the films are pure LiF with only small O, C, and H impurities.

Keywords: Atomic layer deposition; Lithium fluoride; Thin films

Publ.-Id: 18839

Mapping the local elastic properties of nanopatterned Ge

Bischoff, L.; Böttger, R.; Keller, A.; Facsko, S.

Due to their reduced dimensions, the mechanical properties of nanostructures may differ substantially from those of bulk materials. Quantifying and understanding the nanomechanical properties of individual nanostructures is thus of tremendous importance both from a fundamental and a technological point of view. We employed a recently introduced atomic force microscopy (AFM) mode, i.e., peak-force quantitative nanomechanical imaging, to map the local elastic properties of nanostructured germanium surfaces. This imaging mode allows for the quantitative determination of the Young’s modulus with nanometer resolution. Heavy-ion irradiation was used to fabricate different self-organized nanostructures on Ge surfaces. Depending on the sample temperature during irradiation, nanoporous sponge-like structures and hexagonally ordered nanodots are obtained. The sponge-like Ge surface is found to exhibit a surprisingly low Young’s modulus well below 10 GPa which furthermore depends on the ion energy. For the nanodot patterns, local variations in the Young’s modulus are observed: at moderate sample temperatures, the dot crests have a lower modulus than the dot valley whereas this situation is reversed at high temperatures. These observations are explained by vacancy dynamics in the amorphous Ge matrix during irradiation. Our results furthermore offer the possibility to tune the local elastic properties of nanostructured Ge surfaces by adjusting the ion energy and sample temperature.

Keywords: Nanostructures; Germanium; Youngs Modulus

  • Lecture (Conference)
    International Symposium on Nanoscale Pattern Formation at Surfaces, 26.-30.05.2013, Copenhagen, Denmark

Publ.-Id: 18838

Spin anisotropy in Cu(en)(H2O)2SO4: A quasi-two-dimensional S = 1/2 spatially anisotropic triangular-lattice antiferromagnet

Tarasenko, R.; Orendácová, A.; Cizmár, E.; Matas, S.; Orendác, M.; Potocnák, I.; Siemensmeyer, K.; Zvyagin, S.; Wosnitza, J.; Feher, A.

We have studied in detail the effect of the spin anisotropy on the electron paramagnetic resonance spectra and magnetic properties of Cu(en)(H2O)2SO4, an S = 1/2 spatially anisotropic triangular lattice antiferromagnet. The angular and temperature dependence of the resonance fields as well as the magnetization and magnetic susceptibility reflect the exchange and g-factor anisotropy with Jz/Jx,y < 1 and gz/gx,y > 1, respectively. The exchange anisotropy and Dzyaloshinskii-Moriya interaction are responsible for the main broadening mechanism at higher temperatures while spin-diffusion effects prevail at helium temperatures. The ratio of the uniform susceptibilities calculated along the three crystal directions suggests an easy-axis anisotropy with the a axis as the magnetic easy axis. Its impact on the physical properties of the title compound is discussed.

Publ.-Id: 18837

Observation of an intersublattice exchange magnon in CoCr2O4 and analysis of magnetic ordering

Kamenskyi, D.; Engelkamp, H.; Fischer, T.; Uhlarz, M.; Wosnitza, J.; Gorshunov, B. P.; Komandin, G. A.; Prokhorov, A. S.; Dressel, M.; Bush, A. A.; Torgashev, V. I.; Pronin, A. V.

We report on an investigation of optical properties of multiferroic CoCr2O4 at terahertz frequencies in magnetic fields up to 30 T. Below the ferrimagnetic transition (94 K), the terahertz response of CoCr2O4 is dominated by a magnon mode, which shows a steep magnetic-field dependence. We ascribe this mode to an exchange resonance between two magnetic sublattices with different g factors. In the framework of a simple two-sublattice model (the sublattices are formed by Co2+ and Cr3+ ions), we find the inter-sublattice coupling constant, λ = −(18 ± 1) K, and trace the magnetization for each sublattice as a function of field. We show that the Curie temperature of the Cr3+ sublattice, θ2 = (49 ± 2) K, coincides with the temperature range, where anomalies of the dielectric and magnetic properties of CoCr2O4 have been reported in literature.

Publ.-Id: 18836

Evidence of d-wave superconductivity in K1−xNaxFe2As2 (x = 0,0.1) single crystals from low-temperature specific-heat measurements

Abdel-Hafiez, M.; Grinenko, V.; Aswartham, S.; Morozov, I.; Roslova, M.; Vakaliuk, O.; Johnston, S.; Efremov, D. V.; van den Brink, J.; Rosner, H.; Kumar, M.; Hess, C.; Wurmehl, S.; Wolter, A. U. B.; Büchner, B.; Green, E. L.; Wosnitza, J.; Vogt, P.; Reifenberger, A.; Enss, C.; Hempel, M.; Klingeler, R.; Drechsler, S.-L.

From the measurement and analysis of the specific heat of high-quality K1−xNaxFe2As2 single crystals we establish the presence of large T2 contributions with coefficients αsc ≈ 30 mJ/mol K3 at low T for both x = 0 and x = 0.1. Together with the observed √B behavior of the specific heat in the superconducting state both findings give evidence of d-wave superconductivity on almost all Fermi-surface sheets with an average gap amplitude of Δ0 in the range of 0.4–0.8 meV. The derived 0 and observed Tc agree well with the values calculated within Eliashberg theory, adopting a spin-fluctuation mediated pairing in the intermediate coupling regime.

Publ.-Id: 18835

Vortex lock-in transition and evidence for transitions among commensurate kinked vortex configurations in single-layered Fe arsenides

Li, G.; Grissonnanche, G.; Conner, B. S.; Wolff-Fabris, F.; Putzke, C.; Zhigadlo, N. D.; Katrych, S.; Bukowski, Z.; Karpinski, J.; Balicas, L.

We report an angle-dependent study of the magnetic torque τ (θ) within the vortex state of single-crystalline LaO0.9F0.1FeAs and SmO0.9F0.1FeAs as a function of both temperature T and magnetic field H. Sharp peaks are observed at a critical angle θc at either side of θ = 90◦, where θ is the angle between H and the interplanar c axis. θc is interpreted as the critical depinning angle where the vortex lattice, pinned and locked by the intrinsic planar structure, unlocks and acquires a component perpendicular to the planes. We observe a series of smaller replica peaks as a function of θ and as θ is swept away from the planar direction. These suggest commensurability effects between the period of the vortex lattice and the interplanar distance leading to additional kinked vortex configurations.

Publ.-Id: 18834

Slow spin relaxation induced by magnetic field in [NdCo(bpdo)(H2O)4(CN)6].3H2O

Vrábel, P.; Orendác, M.; Orendácová, A.; Cizmár, E.; Tarasenko, R.; Zvyagin, S.; Wosnitza, J.; Prokleska, J.; Sechovský, V.; Pavlík, V.; Gao, S.

We report on a comprehensive investigation of the magnetic properties of [NdCo(bpdo)(Hsub2O)4(CN)6] . 3H2O (bpdo = 4, 4´-bipyridine-N,N´-dioxide) by use of electron paramagnetic resonance, magnetization, specific heat and susceptibility measurements. The studied material was identified as a magnet with an effective spin S D 1=2 and a weak exchange interaction J/kB = 25 mK. The ac susceptibility studies conducted at audio frequencies and at temperatures from 1.8 to 9 K revealed that the application of a static magnetic field induces a slow spin relaxation. It is suggested that the relaxation in the magnetic field appears due to an Orbach-like process between the two lowest doublet energy states of the magnetic Nd3+ ion. The appearance of the slow relaxation in a magnetic field cannot be associated with a resonant phonon trapping. The obtained results suggest that the relaxation is influenced by nuclear spin driven quantum tunnelling which is suppressed by external magnetic field.

Publ.-Id: 18833

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