Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33397 Publications

Forming-free resistive switching in multiferroic BiFeO3 thin films with enhanced nanoscale shunts

Ou, X.; Shuai, Y.; Luo, W.; Siles, P. F.; Kögler, R.; Fiedler, J.; Reuther, H.; Zhou, S.; Hübner, R.; Facsko, S.; Helm, M.; Mikolajick, T.; Schmidt, O. G.; Schmidt, H.
A controlled shunting of polycrystalline oxide thin films on the nanometer length scale opens the door to significantly modify their transport properties. In this paper, the low energy Ar(+) irradiation induced shunting effect of forming-free, non-volatile resistive switching in polycrystalline BiFeO3 thin film capacitor-like structures with macroscopic bottom and top contacts was investigated. Oxygen atoms at the BiFeO3 surface are preferentially sputtered by Ar(+) ion irradiation and oxygen vacancies and a metallic Bi phase are formed at the surface of the BiFeO3 thin film before deposition of the top contacts. A phenomenological model is that of nanoscale shunt resistors formed in parallel to the actual BiFeO3 thin film capacitor-like structure. This model fits the noticeable increase of the retention stability and current density after irradiation. The formation of stable and conductive shunts is further evidenced by conductive atomic force microscopy measurements.
Keywords: resistive switching, Ar irradiation, shunting, oxygen vacancy, current retention, BiFeO3

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Permalink: https://www.hzdr.de/publications/Publ-19571
Publ.-Id: 19571


Hollandite-type TiO2: a new negative electrode material for sodium-ion batteries

Perez-Flores, J. C.; Baehtz, C.; Kuhna, A.; Garcia-Alvaradoa, F.
The electrochemical properties of TiO2 with the hollandite structure (TiO2(H)) as a negative electrodematerial for sodium-ion batteries are reported. TiO2(H) was obtained from hollandite K0.21TiO2 by an oxidation–ion extraction process. Na/TiO2(H) cells exhibit a large first discharge capacity of 280 mA h g1 down to 0.2 V. After the first discharge the Na/TiO2(H) cells develop a reversible charge–discharge capacity of 85 mA h g1 at C/8 rate in the 2.5–0.2 V voltage range; this corresponds to the reversible insertion of 0.25 Na per TiO2(H) formula unit. Chronoamperometry and potentiostatic intermittent titration techniques were used to further characterize the electrochemical reaction mechanism. Structural changes in the TiO2(H) electrode upon sodium insertion and extraction have been studied by ex situ XRD and high resolution in situ synchrotron diffraction techniques, for which appropriately modified coin-type cells were used. It is seen that sodium insertion into TiO2(H) is commenced with a single-phase solid solution followed by a structural transition from tetragonal I4/m to monoclinic I2/m symmetry, in which the skeleton framework is retained. The reversible transition includes few structural changes with a small volume change of only 1.1%. Fourier difference maps deduced from SXRD patterns revealed the location of Na ions in 4i sites in the tunnel space. The coordination arrangement around Na ions is distorted capped trigonal prisms formed by seven oxygen atoms. Although still far from the theoretical capacity (335 mA h g1), the cycling properties at a low insertion potential together with the host framework stability indicate the feasibility of TiO2 with the hollandite structure as a negative electrode material for Na-ion batteries.
Keywords: sodium-ion batterie, in-situ XRD, hollandite

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Permalink: https://www.hzdr.de/publications/Publ-19570
Publ.-Id: 19570


Unusual crystallization behavior in Ga-Sb phase change alloys

Putero, M.; Coulet, M.-V.; Ouled-Khachroum, T.; Muller, C.; Baehtz, C.; Raoux, S.
Combined in situ X-ray scattering techniques using synchrotron radiation were applied to investigate the crystallization behavior of Sb-rich Ga-Sb alloys. Measurements of the sheet resistance during heating indicated a reduced crystallization temperature with increased Sb content, which was confirmed by in situ X-ray diffraction. The electrical contrast increased with increasing Sb content and the resistivities in both the amorphous and crystalline phases decreased. It was found that by tuning the composition between Ga:Sb = 9:91 (in at.%) and Ga:Sb = 45:55, the change in mass density upon crystallization changes from an increase in mass density which is typical for most phase change materials to a decrease in mass density. At the composition of Ga:Sb = 30:70, no mass density change is observed which should be very beneficial for phase change random access memory (PCRAM) applications where a change in mass density during cycling is assumed to cause void formation and PCRAM device failure.
Keywords: PCRAM, XRD, XRR, phase change material

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Permalink: https://www.hzdr.de/publications/Publ-19569
Publ.-Id: 19569


Phase transition in stoichiometric GaSb thin films: Anomalous density change and phase segregation

Putero, M.; Coulet, M.-V.; Ouled-Khachroum, T.; Muller, C.; Baehtz, C.; Raoux, S.
The crystallization of stoichiometric GaSb thin films was studied by combined in situ synchrotron techniques and static laser testing. It is demonstrated that upon crystallization, GaSb thin films exhibit an unusual behaviour with increasing thickness and concomitant decreasing mass density while its electrical resistance drops as commonly observed in phase change materials. Furthermore, beyond GaSb amorphous-to-crystalline phase transition, an elemental segregation and a separate crystallization of a pure Sb phase is evidenced.
Keywords: PCRAM, XRD, XRR, synchrotron

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Permalink: https://www.hzdr.de/publications/Publ-19568
Publ.-Id: 19568


Observing Graphene Grow: Catalyst−Graphene Interactions during Scalable Graphene Growth on Polycrystalline Copper

Kidambi, P. R.; Bayer, B. C.; Blume, R.; Wang, Z.-J.; Baehtz, C.; Weatherup, R. S.; Willinger, M.-G.; Schloegl, R.; Hofmann, S.
Complementary in situ X-ray photoelectron spectroscopy (XPS), X-ray diffractometry, and environmental scanning electron microscopy are used to fingerprint the entire graphene chemical vapor deposition process on technologically important polycrystalline Cu catalysts to address the current lack of understanding of the underlying fundamental growth mechanisms and catalyst interactions. Graphene forms directly on metallic Cu during the high-temperature hydrocarbon exposure, whereby an upshift in the binding energies of the corresponding C1s XPS core level signatures is indicative of coupling between the Cu catalyst and the growing graphene. Minor carbon uptake into Cu can under certain conditions manifest itself as carbon precipitation upon cooling. Postgrowth, ambient air exposure even at room temperature decouples the graphene from Cu by (reversible) oxygen intercalation. The importance of these dynamic interactions is discussed for graphene growth, processing, and device integration.
Keywords: Graphene, chemical vapor deposition (CVD), polycrystalline copper (Cu), in situ X-ray photoelectron spectroscopy, in situ X-ray diffractometry, environmental scanning electron microscopy, intercalation

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Permalink: https://www.hzdr.de/publications/Publ-19567
Publ.-Id: 19567


Introducing Carbon Diffusion Barriers for Uniform, High-Quality Graphene Growth from Solid Sources

Weatherup, R. S.; Baehtz, C.; Dlubak, B.; Bayer, B. C.; Kidambi, P. R.; Blume, R.; Schloegl, R.; Hofmann, S.
Carbon diffusion barriers are introduced as a general and simple method to prevent premature carbon dissolution and thereby to significantly improve graphene formation from the catalytic transformation of solid carbon sources. A thin Al2O3 barrier inserted into an amorphous-C/Ni bilayer stack is demonstrated to enable growth of uniform monolayer graphene at 600 °C with domain sizes exceeding 50 μm, and an average Raman D/G ratio of <0.07. A detailed growth rationale is established via in situ measurements, relevant to solid-state growth of a wide range of layered materials, as well as layer-by-layer control in these systems.
Keywords: Graphene, solid carbon, low temperature, diffusion barrier, in situ, XPS, XRD

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Permalink: https://www.hzdr.de/publications/Publ-19566
Publ.-Id: 19566


Interlaboratory study of the ion source memory effect in 36Cl accelerator mass spectrometry

Pavetich, S.; Akhmadaliev, S.; Arnold, M.; Aumaître, G.; Bourlès, D.; Buchriegler, J.; Golser, R.; Keddadouche, K.; Martschini, M.; Merchel, S.; Rugel, G.; Steier, P.
Understanding and minimization of contaminations in the ion source due to cross-contamination and long-term memory effect is one of the key issues for accurate accelerator mass spectrometry (AMS) measurements of volatile elements. The focus of this work is on the investigation of the long-term memory effect for the volatile element chlorine, and the minimization of this effect in the ion source of the Dresden accelerator mass spectrometry facility (DREAMS). For this purpose, one of the two original HVE ion sources at the DREAMS facility was modified, allowing the use of larger sample holders having individual target apertures. Additionally, a more open geometry was used to improve the vacuum level. To evaluate this improvement in comparison to other up-to-date ion sources, an interlaboratory comparison had been initiated. The long-term memory effect of the four Cs sputter ion sources at DREAMS (two sources: original and modified), ASTER (Accélérateur pour les Sciences de la Terre, Environnement, Risques) and VERA (Vienna Environmental Research Accelerator) had been investigated by measuring samples of natural 35Cl/37Cl-ratio and samples highly-enriched in 35Cl (35Cl/37Cl ~1000). Besides investigating and comparing the individual levels of long-term memory, recovery time constants could be calculated. The tests show that all four sources suffer from long-term memory, but the modified DREAMS ion source showed the lowest level of contamination. The recovery times of the four ion sources were widely spread between 60 – 1390 s, where the modified DREAMS ion source with values between 155 – 260 s showed the fastest recovery in 80% of the measurements.
Keywords: Accelerator Mass Spectrometry (AMS); volatile elements; chlorine; negative ion sputter sources; long-term memory effect; interlaboratory comparison

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Permalink: https://www.hzdr.de/publications/Publ-19565
Publ.-Id: 19565


Performance of the modied DREAMS ion source for 36Cl applications

Pavetich, S.; Akhmadaliev, S.; Merchel, S.; Rugel, G.; Ziegenrücker, R.
First analyses of real 36Cl-AMS samples were performed with the newly developed low memory-eect ion source at the DREsden Accelerator Mass Spectrometry (DREAMS) facility [1, 2]. Considerable improvements have been reached with respect to the overall ion source performance. Especially, parameters like current output, ion source fractionation eects, normalization factors, blank values and sulphur suppression factors have been investigated to enhance accuracy of 36Cl data.
Applications cover a wide spectrum, which implies also highly variable 36Cl/35+37Cl-ratios ranging from nearly background level of ~10-15 up to 10-10. Samples from aquifers in arid regions for groundwater dating and modelling were analysed. Meteorite samples were measured to investigate the constancy of the galactic cosmic radiation, production rates from sulphur, and reconstruction of exposure histories of individual meteorites.
Acknowledgements: C. Wilske, B. Merkel (TUBAF), T. Müller (UFZ), U. Ott (MPI Mainz), T. Smith (U Bern), G. Domenech i Surinyach (U Barcelona), DREAMS-Operators.
[1] S. Pavetich et al., NIMB, submitted.
[2] Sh. Akhmadaliev et al., NIMB 294 (2013) 5.
Keywords: accelerator mass spectrometry, chlorine, sputter negative ion sources, meteorites, groundwater dating
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 17.-21.03.2014, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19563
Publ.-Id: 19563


Anisotropy of Hydrogen Diffusivity in ZnO

Čížek, J.; Lukáč, F.; Vlček, M.; Vlach, M.; Procházka, I.; Traeger, F.; Rogalla, D.; Becker, H.-W.; Anwand, W.; Brauer, G.; Wagner, S.; Uchida, H.; Pundt, A.; Bähtz, C.
Hydrogen absorption and diffusivity in high quality ZnO crystals were investigated in this work by X-ray diffraction combined with slow positron implantation spectroscopy and electrical resistometry. ZnO crystals were covered by a thin Pd over-layer and electrochemically charged with hydrogen. It was found that absorbed hydrogen causes plastic deformation in a subsurface region. The depth profile of hydrogen concentration introduced into the crystal was determined by nuclear reaction analysis. Enhanced hydrogen concentration was found in the subsurface region due to excess hydrogen atoms trapped at defects introduced by plastic deformation. Hydrogen diffusion in ZnO crystals with various orientations was studied by in-situ electrical resistometry. It was found that hydrogen diffusion in the c-direction is faster than hydrogen diffusion in the a-direction most probably due to open channels existing in the wurtzite structure along the c-axis.
Keywords: zinc oxide, hydrogen, nuclear reaction analysis, electrical resistivity, X-ray diffraction

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Permalink: https://www.hzdr.de/publications/Publ-19562
Publ.-Id: 19562


Development of a general coupling interface for the fuel performance code TRANSURANUS tested with the reactor dynamics code DYN3D

Holt, L.; Rohde, U.; Seidl, M.; Schubert, A.; van Uffelen, P.
A general interface is presented for coupling the TRANSURANUS fuel performance code with thermal hydraulics system codes, sub-channel codes or reactor dynamics codes. Beside its generality, other main characteristics of this interface are the calculation at either fuel assembly or fuel rod level, one-way or two-way coupling, automatic switch from steady to transient conditions in TRANSURANUS (including update of the material properties etc.), writing of all TRANSURANUS output files and manual pre- and post-calculations with TRANSURANUS in standalone mode. The TRANSURANUS code can be used in combination with this coupling interface in various scenarios: different fuel compositions in the reactor types BWR, PWR, VVER, HWR and FBR, time scales from milliseconds (i.e. RIA) over seconds/ minutes (i.e. LOCA) to years (i.e. normal operation) and thence different reactor states.

As first application of the interface the reactor dynamics code DYN3D was coupled in order to analyze the impact of a more detailed description of the fuel rod behavior during system transients. More precisely, the influence of the high burn-up structure formation, geometry changes and fission gas release are included. In the coupling, DYN3D provides only the time-dependent rod power and thermal hydraulics conditions to TRANSURANUS, which in turn transfers parameters like fuel temperature and cladding temperature back to DYN3D. Results of the coupled code system are presented for a control rod ejection transient in a German PWR, along with a sensitivity study for the full core. The results reveal that the detailed fuel rod behavior modeling influences the neutron kinetics in the core due to the Doppler reactivity effect of the fuel temperature. In particular it appears that for high burn-up fuel DYN3D-TRANSURANUS systematically calculates higher value for the node centerline fuel temperature compared to DYN3D standalone. The main reasons of the differences seem to be the UO2 material properties (e.g. thermal conductivity), and the radial power density profile over the fuel pellet radius.

Furthermore results of the DYN3D-TRANSURANUS code system are shown for the planed RIA experiment CIP3-1 in the CABRI water loop facility in France. The experimental data including time-dependent rod power was taken from the recent RIA fuel codes benchmark organized by the OECD/NEA. DNB is predicted by calculations under the typically PWR coolant conditions in CIP3-1.

No convergence problems occurred for DYN3D-TRANSURANUS. The coupled code system can improve the assessment of safety criteria, at a reasonable computational cost since it rises on average only by a factor 4 on the same workstation for RIA (determined from reaching the initial state of the transient), when compared to the DYN3D code standalone.

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Permalink: https://www.hzdr.de/publications/Publ-19560
Publ.-Id: 19560


Two-way Coupling between the Reactor Dynamics Code DYN3D and the Fuel Performance Code TRANSURANUS at Assembly Level

Holt, L.; Rohde, U.; Seidl, M.; Schubert, A.; van Uffelen, P.; Macián-Juan, R.
In the last two decades the reactor dynamics code DYN3D was coupled to thermal hydraulics codes, sub-channel code and CFD codes. These earlier developed code systems allow modelling of the phenomena in higher degree of detail. Nevertheless all of them contain a simplified fuel behaviour model, i.e. without taking into account the fission gas release during normal operation, off-normal conditions and transient. Furthermore, no two-way coupling to a fuel performance code has so far been reported in the open literature for calculating a full core with detailed and well validated fuel behaviour correlations.

A new two-way coupling approach between DYN3D and the fuel performance code TRANSURANUS is presented. In the coupling, DYN3D provides only the time-dependent rod power and thermal hydraulics conditions to TRANSURANUS, which in turn transfers parameters like fuel temperature and cladding temperature back to DYN3D. The main part of the development is a so-called general TRANSURANUS coupling interface that is applicable for other reactor dynamics codes, thermal hydraulics codes and sub-channel codes. Beside its generality, other characteristics of this interface are the calculation at either fuel assembly or fuel rod level, one-way or two-way coupling, automatic switch from steady to transient conditions in TRANSURANUS (including update of the material properties etc.), writing of all TRANSURANUS output files and manual pre- and post-calculations with TRANSURANUS in standalone mode. The TRANSURANUS code can be used in combination with this coupling interface in various scenarios: different fuel compositions in the reactor types BWR, PWR, VVER, HWR and FBR, time scales from milliseconds (i.e. RIA) over seconds/ minutes (i.e. LOCA) to years (i.e. normal operation) and thence different reactor states.

Results of DYN3D-TRANSURANUS are shown for a control rod ejection transient in a UO2 core of a German PWR. In particular it appears that for all burn-up levels DYN3D-TRANSURANUS systematically calculates higher values for the node fuel enthalpy (max. difference of 46 J/g) and node centerline fuel temperature (max. difference of 180 K) compared to DYN3D standalone in best estimate calculations. These differences can be completely explained by the more detailed TRANSURANUS modelling of fuel thermal conductivity, radial heat release profile and heat transfer in the gap. As known from fuel performance codes, the modelling of the heat transfer in the gap is sensitive and causes also larger differences in case of low burn-up.

No convergence problems occurred for DYN3D-TRANSURANUS. The coupled code system can improve the assessment of safety criteria, at a reasonable computational cost with a running time of less than six hours without parallelization.
  • Contribution to proceedings
    22nd International Conference on Nuclear Engineering (ICONE 2014), 07.-11.07.2014, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-19559
Publ.-Id: 19559


Completeness of DYN3D Coupling Approaches by the European Fuel Performance Code TRANSURANUS – Full Core Analysis for a Reactivity Initiated Accident (vorläufiger Titel)

Holt, L.
Es handelt sich um ein Compact.
  • Lecture (Conference)
    45th Annual Meeting on Nuclear Technology (Workshop Preserving Competence), 06.-08.05.2014, Frankfurt, Germany

Permalink: https://www.hzdr.de/publications/Publ-19558
Publ.-Id: 19558


Volatilisation of Lead by Using Chlorination Agent Magnesium Chloride

Scharf, C.; Lenzen, P.; Ditze, A.
Zinc- and lead-containing waste materials such as steel mill electric arc furnace dust are mainly processed by the Waelz process (volatilisation under reducing conditions). Especially, the addition of carbon as reducing agent to the initial mixture contributes to the desired reaction kinetics and progress. However, the removal of the element lead is not completely. It remains partly as water-soluble compounds in the Waelz slag in the order of magnitude of 3 mass % which prevents the use in road construction. Starting from the idea lead can be volatilised by using an additional chlorinating agent like magnesium chloride first principle investigations are made. Therefore the pure model substances PbO, MgCl2 and C are used. The formation and volatilisation of PbCl2 is assumed, because of its high vapor pressure. Favorable thermodynamic conditions exist in particular for MgCl2 as chlorinating agent. It should therefore be clarified how far PbO reacts with MgCl2 - also in the presence of C - to PbCl2 in a temperature range of 800 to 1000 °C. First experiments show promising results, not only for the pure substances but also for electric arc furnace dust.
Keywords: Lead; Lead chloride; Magnesium chloride; Recycling; Vapor pressure; Volatilisation
  • Open Access Logo Contribution to proceedings
    European Metallurgical Conference 2011, 26.-29.06.2011, Düsseldorf, Germany
    Proceeding of EMC 2011, 978-3-940276-37-7, 505-518

Permalink: https://www.hzdr.de/publications/Publ-19557
Publ.-Id: 19557


Recycling von Magnesium

Scharf, C.; Ditze, A.
Obwohl Magnesium das achthäufigste Element der Erde ist und die Rohstoffe für seine Gewinnung als reines Metall fast unbegrenzt verfügbar sind, ist seine Herstellung sehr energieintensiv. Dieses vor allem wegen der großen Bindungsaffinität zu Sauerstoff und Chlor. Folglich besitzt das Recycling [1] eine hohe Bedeutsamkeit, da der Metallschrott bereits den Energieinhalt der Reduktion zum Metall innehat.
  • Open Access Logo Book chapter
    K.J.Thomè-Kozmiensky, D.Goldmann: Recycling und Rohstoffe - Band 4, Berlin: TK Verlag Karl Thomè-Kozmiensky, 2011, 978-3-935317-67-2, 215-234

Permalink: https://www.hzdr.de/publications/Publ-19556
Publ.-Id: 19556


Fundamentals of Chlorination of Lead Oxide Using Magnesium Chloride

Scharf, C.; Ditze, A.
Zinc-and lead-containing waste materials such as steel mill electric arc furnace dust are mainly processed by the Waelz process (volatilisation of zinc under reducing conditions). However, the removal of the element lead is not completely. It remains partly as water-soluble compounds in the Waelz slag in the order of magnitude of 3 mass-% which prevents the use in road construction. - Starting from the idea lead can be volatilised by using an additional chlorinating agent like magnesium chloride first principle investigations with pure model substances PbO and MgCl 2 were made. Thereby, the formation and volatilisation of PbCl 2 is assumed, because of its high vapor pressure. Besides the favorable thermodynamic conditions using MgCl 2 as chlorinating agent the reaction kinetics are of special interest. Volatilisation experiments in the temperature range of 800 °C to 1000 °C showed promising results.
Keywords: Kinetics; Lead; Lead chloride; Magnesium chloride; Recycling; Vapor pressure; Volatilisation; Waelz process
  • Open Access Logo Worl of Metallurgy - ERZMETALL 64(2011)4, 205-209

Permalink: https://www.hzdr.de/publications/Publ-19555
Publ.-Id: 19555


Removal of nickel from magnesium melts by precipitation with zirconium

Ditze, A.; Scharf, C.
Magnesium scrap is often contaminated with nickel, copper and iron. Especially nickel is detrimental in regard to the corrosion properties of magnesium. Ways have to be found for the removal of nickel from magnesium to initiate actually the recycling of post consumer scrap. Experiments at 660, 720 and 770°C comprise the determination of the solubilities of nickel and zirconium in magnesium and the identification of the precipitates. Based on this, equlibrium constants and interaction parameters were calculated. These values enable the estimation of the necessary zirconium addition for the removal of nickel by precipitation to low contents in liquid magnesium.
  • Open Access Logo Contribution to proceedings
    9th International Conference on magnesium alloys and their applications, 08.-12.07.2012, Vancouver, Canada
    Proceedings of the 9th International Conference on magnesium alloys and their applications, 889-894

Permalink: https://www.hzdr.de/publications/Publ-19554
Publ.-Id: 19554


Presentation of patented secondary magnesium alloy – Subsequent basic research: Investigation of influence of dendritic microstructure on corrosion properties.

Scharf, C.; Lakoma, P.; Ditze, A.
As first step in the past a patented secondary magnesium alloy AZC1231 (Aluminium = 12mass.-%, Zinc = 3mass.-% and Cu = up to 1 mass.-%) was developed to close the loop of magnesium material flow. The impurity tolerant AZC1231 was tested in a real die casting process to prove feasibility resulting in navigation device housing. Corrosion properties show interesting effects because the noble copper was disposed by copper solving and copper encircling phases. The influence of the microstructure plays therefor a very important role. A new basic research project was started to investigate dendritic microstructure regarding grain size, dendrite formation, eutectic refinement and distribution of Mg17Al12(β)-phase of magnesium alloys with aluminium contents from 0 to 12 mass.-%. The aim is evaluation of secondary dendrite arm spacings at defined cooling conditions which are responsible for a columnar or equiaxed macrostructure containing dendritic microstructure. Subsequent corresponding corrosion behaviour has to be examined by immersion testing method.
Keywords: secondary magnesium alloy, AZC1231, corrosion properties, microstructure, secondary dendrite arm spacing
  • Contribution to proceedings
    International Conference "Recycling of Non-Ferrous Metals", 06.-08.02.2013, Krakow, Poland
    International Conference "Recycling of Non-Ferrous Metals"

Permalink: https://www.hzdr.de/publications/Publ-19553
Publ.-Id: 19553


Interaction between Nickel and Zirconium in liquid Magnesium

Ditze, A.; Scharf, C.
Magnesium scrap is often contaminated with nickel, copper and iron. Especially nickel is detrimental in regard to the corrosion properties of magnesium. Ways have to be found for the removal of nickel from magnesium to initiate actually the recycling of post consumer scrap. Experiments at 660,720 and 770 °C comprise the determination of the solubilities of nickel and zirconium in magnesium and the identification of the precipitates. Based on this, equilibrium constants and interaction parameters were calculated. These values enable the estimation of the necessary zirconium addition for the removal of nickel by precipitation to low contents in liquid magnesium.
Keywords: Activity; Activity coefficient; Equilibrium constant; Gibbs free energy; Interaction parameter; Intermetallic phases; Magnesium; Nickel; Refining; Zirconium
  • Open Access Logo Worl of Metallurgy - ERZMETALL 66(2013)3, 168-174

Permalink: https://www.hzdr.de/publications/Publ-19552
Publ.-Id: 19552


SHI induced enhancement in green emission from nanocrystalline CdS thin films for photonic applications

Kumar, P.; Saxena, N.; Chandra, R.; Gao, K.; Zhou, S.; Agarwal, A.; Singh, F.; Gupta, V.; Kanjilal, D.
Intense green emission is reported from nanocrystalline CdS thin films grown by pulsed laser deposition. The effect of ion beam induced dense electronic excitation on luminescence property of CdS films is explored under irradiation using 70 MeV 58Ni6+ ions. It is found that swift heavy ion beam irradiation enhances the emission intensity by an order of 1 and broadens the emission range. This feature is extremely useful to enhance the performance of different photonic devices like light emitting diodes and lasers, as well as luminescence based sensors. To examine the role of energy relaxation process of swift heavy ions in creation/annihilation of different defect levels, multi-peaks are fitted in photoluminescence spectra using a Gaussian function. The variation of contribution of different emissions in green emission with ion fluence is studied. Origin of enhancement in green emission is supported by various characterization techniques like UV-visible absorption spectroscopy, glancing angle X-ray diffraction, micro-Raman spectroscopy and transmission electron microscopy. A possible mechanism of enhanced GE due to ion beam irradiation is proposed on the basis of existing models.
Keywords: Ion beam irradiation; Nanocrystalline CdS thin films; Photoluminescence; Pulsed laser deposition

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Permalink: https://www.hzdr.de/publications/Publ-19551
Publ.-Id: 19551


Preclinical dose assessment and biodistribution of [F-18]DBT-10, a new α7 nicotinic acetylcholine receptor (α7-nAChR) imaging ligand.

Kranz, M.; Sattler, B.; Deuther-Conrad, W.; Teodoro, R.; Donat, C. K.; Wenzel, B.; Scheunemann, M.; Patt, M.; Sabri, O.; Brust, P.
Objectives :
In vivo imaging of α7-nAChR provide important information for CNS disorders such as schizophrenia, Alzheimer disease, brain tumors etc. Due to the lack of suitable radiotracers a new structure, DBT-10 (Ki=0.3nM), was developed for brain imaging. To assess the radiation risk to humans after i.v. injection the biodistribution, organ doses (OD) and the effective dose (ED) were determined in mice (M) and piglets (P).

Methods :
Image based (M: Mediso nanoScan PET/MRI, P: SIEMENS Biograph16 PET/CT) whole body dosimetry was performed in 3 female M (age: 11 w, weight: 27.8 g) and 3 female P (age: 7 w, weight: 15.8 kg). The anesthetized animals were PET-imaged up to 5h post i.v. injection of 13.1 MBq, 165.5 MBq [18]DBT-10, followed by iterative reconstruction including MR- or CT-based attenuation correction respectively. The organs were defined by volumes of interest. Exponential curves were fitted to the time-activity-data (%ID/g). Time and mass were adapted to the human scale. The ODs were calculated using OLINDA and the ED using tissue weighting factors (ICRP103).

Results:
Following the i.v. injection of [18]DBT-10 no adverse effects on the basis of vital function monitoring were observed. The highest OD [µSv/MBq] was received in M by pancreas (35.5) and urinary bladder (30.0), in P by pancreas (60.8) and spleen (58.8). The highest contribution to ED [µSv/MBq] was in M by red marrow (2.4) and lungs (1.5), in P by liver (2.0) and lungs (1.9). The estimated ED [µSv/MBq] to humans is 12.7 (M), 13.7 (P).

Conclusions :
Considering an underestimation of 40% in preclinical dosimetry, the radiation risk, to humans (M: 6.4 mSv/300MBq, P: 6.8 mSv/300MBq) is well within the range of other F-18 labeled radiotracers. These results encourage to transfer [18]DBT-10 to the clinical study phase and further develop it as a clinical tool for imaging of α7-nAChR.

References:
[1] M.Schrimpf, K. Sippy, C. Briggs et al., SAR of α7 nicotinic receptor agonists derived from tilorone: Exploration of a novel nicotinic pharmacophore, Bioorganic & Medicinal Chemistry Letters, Volume 22, Issue 4, 15 February 2012, Pages 1633-1638, ISSN 0960-894X.

[2] B. Sattler, M. Kranz, M. Patt et al. Incorporation dosimetry of F-18-Flubatine - Comparison of animal model data with first-in-man results. Journal of Nuclear Medicine 2012; 53(suppl): 1503.
  • Poster
    SNMMI 2014 Annual Meeting, 07.-11.06.2014, St. Louis, Missouri, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 55(2014)1, 1143

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Permalink: https://www.hzdr.de/publications/Publ-19550
Publ.-Id: 19550


Synthesis and F-18 labeling of a 2-fluoro dibenzothiophene sulfone derivative, as a potential alpha-7 nicotinic acetylcholine receptor (α7 nAChR) imaging agent

Scheunemann, M.; Teodoro, R.; Wenzel, B.; Kranz, M.; Deuther-Conrad, W.; Brust, P.
Aim:
The homopentameric α7 nAChR is proposed to be implicated in the pathophysiology of various diseases, e.g. schizophrenia, Alzheimer disease and tumors. Due to a relatively low concentration of α7 subtype binding sites in brain an appropriate PET radiotracer for quantitative molecular imaging requires a sufficiently high receptor affinity. Based upon a novel pharmacophoric lead structure (1) consisting of a diazabicyclononane as amine scaffold, connected to a tricyclic aromatic moiety we developed DBT-10, as potential PET radiotracer for imaging α7 nAChR in brain.

Methods:
DBT-10 was prepared in four steps from 2-nitro-dibenzothiophene in 31% overall yield. Binding affinity for α7 nAChRs was evaluated in vitro by competitive inhibition experiments using H-3 methyllycaconitine. The radiotracer was synthesized by nucleophilic F-18 fluoro-for-nitro aromatic substitution. Animal PET/MR was performed to investigate the radiotracer kinetics in brain.

Results:
A preliminary α7 nAChR affinity of Ki=0.67±0.36 nM (n=4) was determined for DBT-10. For F-18 labeling, 0.5-1.4 mg of NO2-precursor was converted in the presence of F-18 fluoride, K222/K2CO3 in DMF for 10 min at 140°C with 67-87% labeling yield. F-18 DBT-10 was obtained after purification (30% ACN, H2O, 0.05% TFA, isocratic on Reprosil-Pur AQ 250x10 mm) in 99% RCP and identified by HPLC coinjection of DBT-10. Animal PET/MR revealed fast kinetics of F-18 DBT-10 in mice brain with SUVmax ~1.5 at 3´ p.i.

Conclusions:
The 2-fluoro-dibenzothiophene based DBT-10 was readily prepared and radiolabeled (2). Product F-18 DBT-10 displayed a marked brain uptake in mice and about four-fold higher affinity than our previous α7 nAChR-selective radiotracers suggesting improved suitability for PET imaging.
References:
(1) Schrimpf M. et al. Bioorg. Med. Chem. Lett. 2012, 22, 1633-38; (2) Concurrent to our work a recent paper describes two PET tracers based on the same pharmaceutical lead: Gao et al. J. Med. Chem. 2013, 56, 7574-89.
  • Lecture (Conference)
    NuklearMedizin2014, 26.-29.03.2014, Hannover, Deutschland
  • Open Access Logo Abstract in refereed journal
    Nuklearmedizin 53(2014), A26

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Publ.-Id: 19549


Präklinisches PET/MRT – Eine potentielle Methode zur Abschätzung der Strahlenexposition des Menschen durch neue Radioliganden

Kranz, M.; Sattler, B.; Patt, M.; Donat, C. K.; Deuther-Conrad, W.; Hiller, A.; Smits, R.; Hoepping, A.; Sattler, T.; Sabri, O.; Steinbach, J.; Brust, P.
Ziel
Bildbasierte Dosimetrie mittels präklinischer hybrider PET Systeme ermöglicht die Abschätzung der Strahlenexposition durch neue Radiopharmazeutika für die Anwendung am Menschen. Bisherige Untersuchungen beschränken sich auf Kombinationen mit CT. Zur Evaluierung eines neuen präklinischen PET/MRT-Systems stellen wir an Mäusen erhobene Daten mit an Ferkeln (PET/CT) erhobenen Daten und einer post mortem Aktivitätsverteilung in Organen (AV) an Mäusen, nach Injektion von [18F]Flubatine, gegenüber.

Methodik
Die Messung der kumulierten Organaktivität (OA) erfolgte an einem präklinischen PET/MRT (nanoScan®, Mediso) bzw. PET/CT (Biograph 16, Siemens). Es wurden 3 narkotisierte CD1 Mäuse (12 Wochen, 30g) bzw. 3 Ferkel (43 Tage, 14kg) bis zu 4 h nach i.v. Injektion von [18F]Flubatine dynamisch untersucht. Die Definition von Volumes of Interest erlaubte die Bestimmung der OA. Die AV von [18F]Flubatine in 27 CD1 Mäusen wurde mittels Sektion und Messung im γ-Counter bestimmt. Die Zeit-Aktivitäts Daten wurden auf die Verhältnisse im Menschen skaliert und durch exponentielle Anpassung dargestellt. Die Berechnung der Organdosis (OD) erfolgte mit OLINDA, die der effektiven Dosis (ED) nach ICRP 103.

Ergebnisse
Mit PET/MRT wurde die höchste OD (μSv/MBq) in den Nieren (47,5±2.0) und der Blase (33,4±0.06) berechnet, während der größte Beitrag zur ED (μSv/MBq) im Magen (1,8±0.1) sowie der Lunge (1,7±0.7) vorliegt. Die ED nach Injektion von [18F]Flubatine ist 12,1±0.7 und nahezu identisch mit dem Ergebnis der in vitro gewonnenen AV (12,5). Die ED beim Ferkelversuch mit PET/CT lag bei 14,3±0.7.

Schlussfolgerungen
Am Beispiel von [18F]Flubatine wurde gezeigt, dass es mit dem präklinischen PET/MRT-System möglich ist, eine Abschätzung der ED für den Menschen vorzunehmen. Die Untersuchung weiterer Radiotracer ist erforderlich, um diese Aussage zu erhärten. Die Studie bestätigt frühere Ergebnisse, nach denen die präklinische Inkorporationsdosimetrie die ED für den Menschen unterschätzt.
  • Lecture (Conference)
    NuklearMedizin2014, 26.-29.03.2014, Hannover, Deutschland
  • Open Access Logo Abstract in refereed journal
    Nuklearmedizin 53(2014), A69

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Publ.-Id: 19548


Thyrogener Einfluss auf die Aktivierung braunen Fettgewebes (BAT) bei Mäusen

Zeisig, V.; Kranz, M.; Krause, K.; Steinhoff, K.; Tönjes, A.; Deuther-Conrad, W.; Fasshauer, M.; Brust, P.; Sabri, O.; Hesse, S.
Hintergrund/Ziel:
Braunes Fettgewebe (BAT) hat eine essentielle Funktion in der Wärmeregulation und im Energiehaushalt. Seine Aktivierung erfolgt über β3-adrenerge Rezeptoren, die auf zellulärer Ebene eine vermehrte Konversion von T4 in T3 bewirkt und hierüber die mitochondriale Wärmeerzeugung stimuliert. Eine direkte thyrogene BAT-Aktivierung wurde jedoch bislang nicht gezeigt. Ziel unserer Untersuchung war es daher, den direkten Einfluss peripherer Schilddrüsenhormone auf eine BAT-Aktivierung nachzuweisen.

Methodik:
Es wurden jeweils 3 hyper-, hypo- und euthyreote Black 6-Mäuse mit F-18-FDG im Kleintier PET/MRT (nanoScan®, Mediso) untersucht (i.p-Injektion; ID:15 MBq; Raumtemperatur). Die Tracerapplikation erfolgte intraperitoneal. Mittels MR-basierter VOI-Analyse (PMOD vers. 3.3) typischer Regionen von braunem Fettgewebe (nuchal) wurde die Glukoseaufnahme (SUVmean) bestimmt, um Rückschlüsse auf eine mögliche BAT-Aktivierung ziehen zu können.

Ergebnisse:
Im SUVmean-Vergleich zeigten die hyperthyreoten Tiere eine bereits visuell erfassbare, FDG-Mehranreicherung gegenüber der euthyreoten Kontrollgruppe (8,61±2,05 vs 6,04±0,52; p=0,16; MV±SD) in den untersuchten Körperregionen. In den hypothyreoten Mäusen konnte ein verminderter FDG-Uptake beobachtet werden (SUVmean=3,2±0,04; p<0,002; MV±SD).

Schlussfolgerungen:
Unsere Ergebnisse bestätigen einen thyrogenen Einfluss auf die murine BAT-Aktivität. Es konnte gezeigt werden, dass eine Hypothyreose eine verminderte BAT-Aktivierung bewirkt, eine Hyperthyreose eine BAT-Stimulierung zur Folge hat. Inwieweit sich diese Ergebnisse auch im Menschen nachweisen lassen, soll gegenwärtig eine prospektive Studie zeigen.
  • Lecture (Conference)
    NuklearMedizin2014, 52. Jahrestagung der DGN, 26.-29.03.2014, Hannover, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 53(2014)A61

Permalink: https://www.hzdr.de/publications/Publ-19547
Publ.-Id: 19547


Formation and structure of polynuclear actinide(IV) carboxylates in aqueous solution

Hennig, C.
Polyanuclear An(IV) carboxylate complex were identified in aqueous solution. The related complex species were preserved in crystals and their structures were determined. The structural identity of the species in solution and in solid state was tested by EXAFS spectroscopy.
Keywords: actinides, carboxylates, EXAFS, XRD
  • Invited lecture (Conferences)
    Laboratoire des Interactions Ligand-Actinide / CEA Marcoule, 19.12.2013, Marcoule, France

Permalink: https://www.hzdr.de/publications/Publ-19546
Publ.-Id: 19546


Processing of agglomerated red filter dust in the converter operation from metallurgical point of view

Scharf, C.; Ditze, A.
Red filter dust (RFD) from steel works contains up to 50 mass% iron, which therefore can serve as raw material for steel production. It should be possible to recycle a fraction of the RFD in the converter process of a steel works wherein also scrap for recycling is used. The aim was the investigation of the reduction behavior of the iron oxide in the RFD. This was accomplished by contact of the dust with pig iron containing up to 3.9 mass% carbon and also by addition of bio‐char to the dust, creating self‐reducing briquettes. The experimental results were compared to the theoretical achievable iron oxide reduction. The reaction time of selected briquettes was calculated by a kinetic approach. Additional the behavior of lead and zinc in the dust was investigated. The mass balance of the converter process indicated the influence of the dust recycling especially regarding the zinc mass flow.

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Publ.-Id: 19545


Gas-Liquid distribution in tubular reactors with solid foam packings

Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.
The axial evolution of gas-liquid distribution patterns in co-current downward gas-liquid two-phase flow through solid foam packings of different pore density expressed by pores per inch was experimentally studied. The experimental results are based on time-averaged capacitance measurements of the liquid phase with embedded wire-mesh sensors, positioned at different axial heights of the solid foam packing. The measurements revealed the spatial distribution of the liquid phase saturation, which was applied to quantify the degree of liquid maldistribution. Both the spray nozzle and the multipoint distributor provide rather uniform initial liquid distributions across the foam packings with low maldistribution factors at superficial liquid velocities above 0.009 mis. However, the uniform initial irrigation deteriorates along the foam packing length, in particular for foams with low pore density. The gas flow rate does not significantly influence the liquid distribution. Furthermore, the foam's ability to radially spread the liquid phase in the cross-section downstream from a single drip point distributor was studied and found to be low, independent from the pore density.

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Publ.-Id: 19544


Archaeometallurgical studies of bronze age objects from the romanian cultural heritage

Bugoi, R.; Constantinescu, B.; Popescu, A. D.; Munnik, F.
This paper reports the chemical composition of some ancient metallic objects dated to the Bronze Age period and found on Romanian territory.Preliminary ED-XRF measurements were performed on cleaned areas of artefacts, while the nuclear microprobe experiments were conducted on tiny fragments detached from the same zones. The identified trace-elements led to some speculations about the employed metallurgical procedures and raw materials. Thus, the chemical composition of the Early Bronze Age dagger found at Ocniţa suggests its manufacturing by smelting a mixture of copper and arsenic ores, while the Late Bronze Age artefacts have compositional patterns supporting the idea of connections and exchanges between the ancient populations living along the Danube river.
Keywords: PIXE, archaeometallurgy, chemical composition, bronze, arsenical copper, Bronze Age.
  • Open Access Logo Romanian Reports in Physics 65(2013)4, 1234-1245

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Publ.-Id: 19543


Evaluation of Large 3600MWth Sodium-Cooled Fast Reactor Neutronic OECD Benchmarks

Buiron, L.; Rimpault, G.; Fontaine, B.; Fridman, E.; Keresztúri, A.; Pataki, I.; Kugo, K.; Sugino, K.; Uematsu, M. M.; Yamaji, A.; Gulliford, J.; Kim, T. K.; Stauff, N. E.; Taiwo, T. A.; Lin Tan, R.; Kozlowski, T.; Parisi, C.; Ponomarev, A.
In the frame of the Working Party on Reactor and System (WPRS), an international mandate has been proposed to work towards a shared neutronic analysis of several Generation-IV Sodium-cooled Fast Reactor (SFR) concepts. This paper summarizes the results obtained for large cores benchmark by participants from numerous institutes of different countries (ANL, CEA, ENEA, HZDR, JAEA, KFKI, KIT, UIUC). This paper gathers results using different calculation methods and systems to estimate the core reactivity and isotopic composition evolution, neutronic feedbacks and power distribution. For the different core concepts analyzed, a satisfactory agreement between participants was obtained despite the different schemes of calculation used. A good agreement is generally obtained when comparing compositions after burnup, the delayed neutron fraction, the Doppler coefficient, and the sodium void worth. However, some noticeable discrepancies between the k-effective values were observed and are explained in this paper. These are mostly due to the different neutronic libraries employed (JEFF3.1, ENDF/B-VII.0 or JENDL-4.0) and in a less extend calculations methods.
Keywords: 3600MWth SFR, oxide, carbide, OECD Benchmark
  • Contribution to proceedings
    PHYSOR2014, 28.09.-03.10.2014, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-19542
Publ.-Id: 19542


Generation of One-Group Self-Shielded Cross Sections with Multi-Group Approach for Monte Carlo Burnup Codes

Kotlyar, D.; Shwageraus, E.; Fridman, E.
Allowing Monte Carlo (MC) codes to perform fuel cycle calculations requires coupling to a point depletion solver. In order to perform depletion calculations, one-group (1-g) cross sections must be provided in advance. This paper focuses on generating accurate 1-g cross section values that are necessary for evaluation of nuclide densities as a function of burnup. The proposed method is an alternative to the conventional direct reaction rate tally approach, which requires extensive computational efforts. The method presented here is based on the multi-group (MG) approach, in which pre-generated MG sets are collapsed with MC calculated flux. In our previous studies, we showed that generating accurate 1-g cross sections requires their tabulation against the background cross-section (σ0) to account for the self-shielding effect. However, in previous studies, the model that was used to calculate σ0 was simplified by fixing Bell and Dancoff factors. This work demonstrates that 1-g values calculated under the previous simplified model may not agree with the tallied values. Therefore, the original background cross section model was extended by implicitly accounting for the Dancoff and Bell factors. The method developed here reconstructs the correct value of σ0 by utilizing statistical data generated within the MC transport calculation by default. The proposed method was implemented into BGCore code system. The 1-g cross section values generated by BGCore were compared with those tallied directly from the MCNP code. Very good agreement (<0.05%) in the 1-g cross values was observed. The method does not carry any additional computational burden and it is universally applicable to the analysis of thermal as well as fast reactor systems.
Keywords: Monte Carlo; BGCore; Multi group; one-group cross sections
  • Contribution to proceedings
    PHYSOR2014, 28.09.-03.10.2014, Kyoto, Japan
    Proceedings of PHYSOR2014

Permalink: https://www.hzdr.de/publications/Publ-19541
Publ.-Id: 19541


Regioselective Synthesis of Trichloromethyl-Substituted Salicylates and Cyclohexenones by One-Pot Cyclizations of 1,3-Bis(trimethylsilyloxy)buta-1,3-dienes

Reimann, S.; Bunescu, A.; Petrosyana, A.; Sharif, M.; Erfle, S.; Mamat, C.; Ghochikyan, T. V.; Saghyan, A. S.; Spannenberg, A.; Villinger, A.; Langer, P.
A variety of 6-(trichloromethyl)salicylates (=2-hydroxy-6-(trichloromethyl)benzoates) were prepared by TiCl4-mediated cyclization of 1,3-bis(trimethylsilyloxy)buta-1,3-dienes with 1,1,1-trichloro-4,4-dimethoxybut-3-en-2-one. The employment of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) as Lewis acid resulted in the formation of trichloromethyl-substituted cyclohexenones. The cyclizations proceeded with good-to-very-good regioselectivities.

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Publ.-Id: 19540


Towards a high field THz source operating at few 100 kHz repetition rates

Gensch, M.; Kovalev, S.; Green, B.; Bauer, C.; Kuntzsch, M.; Golz, T.; Al-Shemmary, A.; Hauser, J.; Voigtlaender, J.; Wustmann, B.; Koesterke, I.; Asgekar, V.; Freitag, M.; Lehnert, U.; Teicher, J.; Justus, M.; Seidel, W.; Ilgner, C.; Winnerl, S.; Schneider, H.; Geloni, G.; Radu, I.; Kampfrath, T.; Wall, S.; Cavalleri, A.; Heberle, J.; Michel, P.; Fisher, A.; Mueller, A.-S.; Stojanovic, N.; Helm, M.; Schramm, U.; Cowan, T.
At the ELBE accelerator a unique super-radiant THz source is currently under developement. It aims at delivering fourier-limited THz pulses with pulse energies of up to 100 microJ at reprates of up to 500 kHz (cw). This corresponds to transient electric elds in the GV/m regime or transient magnetic elds in the few T regime. First results from the commissioning are discussed.
  • Poster
    DPG Spring Meeting 2014, 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19539
Publ.-Id: 19539


Analytical properties of the quark propagator from truncated Dyson-Schwinger equation in complex Euclidean space

Dorkin, S. M.; Kaptari, L. P.; Hilger, T.; Kämpfer, B.
In view of the mass spectrum of heavy mesons in vacuum the analytical properties of the solutions of the truncated Dyson-Schwinger equatio for the quark propagator within the rainbow approximation are analysed in some detail. In Euclidean space, the quark propagator is not an analytical function possessing, in general, an infinite number of singularities (poles) which hamper to solve the Bethe-Salpeter equation. However, for light mesons (with masses M_{q\bar q} <= 1 GeV) all singularities are located outside the region within which the Bethe-Salpeter equation is defined. With an increase of the considered meson masses this region enlarges and already at masses >= 1 GeV, the poles of propagators of u,d and s quarks fall within the integration domain of the Bethe-Salpeter equation. Nevertheless, it is established that for meson masses up to M_{q\bar q}~=3 GeV only the first, mutually complex conjugated, poles contribute to the solution. We argue that, by knowing the position of the poles and their residues, a reliable parametrisation of the quark propagators can be found and used in numerical procedures of solving the Bethe-Salpeter equation. Our analysis is directly related to the future physics programme at FAIR with respect to open charm degrees of freedom.

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Publ.-Id: 19538


Baryon resonance production and dielectron decays in proton-proton collisions at 3.5 GeV

Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Göbel, K.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kornakov, G.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.
We report on the investigation of baryon resonance extraction and their subsequent electromagnetic decays in proton-proton collisions at the kinetic energy of 3:5 GeV based on data measuer with HADES. The exclusive channels npπ+ and ppπ0 as well as ppe+e- are studied simultaneously for the first time. The invariant masses and angular distributions of the pion-nucleon system were studied and compared to simulations based on a resonance model ansatz assuming saturation of the pion production by an incoherent sum of baryonic resonances (R) with masses < 2 GeV/c2. A very good description of the one-pion production is achieved allowing for an estimate of individual Δ and N* production cross sections which are used to calculate the dielectron yields from R -> pe+e- decays. Two models of the resonance dielectron decays are examined assuming a point-like RNγ* coupling and the dominance of the ρ meson. The results of model calculations are compared to the data from the exclusive ppe+e- channel by means of the dielectron and pe+e- invariant mass distributions.

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Publ.-Id: 19537


Residual gamma H2AX foci predict local tumour control after radiotherapy

Koch, U.; Hohne, K.; von Neubeck, C.; Thames, H. D.; Yaromina, A.; Dahm-Daphi, J.; Baumann, M.; Krause, M.
Purpose: Evaluation of micromilieu-dependent quantified gamma H2AX foci as a potential predictive biomarker in well-oxygenated tumour areas in 9 HNSCC xenograft models in vivo.

Materials & methods: GammaH2AX foci were quantified in perfused tumour areas 30 min (initial gamma H2AX foci) and 24 h (residual gamma H2AX foci) after exposure to a single dose of 4 Gy. The initial and residual normalised gamma H2AX foci were correlated with TCD50 after single dose irradiation under clamped blood flow (SDclamp) or a fractionated irradiation setting under ambient blood flow (fx).

Results: A significant negative correlation between initial and residual normalised gamma H2AX foci and TCD50 SDclamp and TCD50 fx for 9 HNSCC tumour xenograft models in vivo was found. Residual normalised gamma H2AX foci showed higher intertumoural variability and their correlation with TCD50 was more robust.

Conclusions: For the first time a significant negative correlation between gamma H2AX foci and local tumour control after irradiation has been demonstrated. Our results underline the potential of residual gamma H2AX foci as a predictive biomarker for local tumour control after radiotherapy
Keywords: gamma H2AX; Radiotherapy; DNA repair; Local tumour control; Tumour micromilieu; Biomarker

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Publ.-Id: 19536


Clinical perspectives of cancer stem cell research in radiation oncology

Butof, R.; Dubrovska, A.; Baumann, M.
Radiotherapy has a proven potential to eradicate cancer stem cells which is reflected by its curative potential in many cancer types. Considerable progress has been made in identification and biological characterisation of cancer stem cells during the past years. Recent biological findings indicate significant inter- and intratumoural and functional heterogeneity of cancer stem cells and lead to more complex models which have potential implications for radiobiology and radiotherapy. Clinical evidence is emerging that biomarkers of cancer stem cells may be prognostic for the outcome of radiotherapy in some tumour entities. Perspectives of cancer stem cell based research for radiotherapy reviewed here include their radioresistance compared to the mass of non-cancer stem cells which form the bulk of all tumour cells, implications for image- and non-image based predictive bio-assays of the outcome of radiotherapy and a combination of novel systemic treatments with radiotherapy.
Keywords: Cancer stem cells; Radiation oncology; Radiobiology

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Simultaneous PLK1 inhibition improves local tumour control after fractionated irradiation

Krause, M.; Kummer, B.; Deparade, A.; Eicheler, W.; Pfitzmann, D.; Yaromina, A.; Kunz-Schughart, L. A.; Baumann, M.
Purpose: Polo-like kinase 1 (PLK1) plays an important role in mitotic progression, is frequently overexpressed and associated with a poor prognosis of cancer patients, thus providing a promising target in anticancer treatment. Aim of the current project was to evaluate the effect of the novel PLK1 inhibitor BI 6727 in combination with irradiation.
Material and methods: In vitro proliferation and radiation cell survival assays as well as in vivo local tumour control assays after single treatment and combined radiation and drug application were carried out using the squamous cell carcinoma models A431 and FaDu. In addition, cell cycle phases were monitored in vitro and in vivo.
Results: BI 6727 showed a dose-dependent antiproliferative effect and an increase in the mitotic fraction. BI 6727 alone reduced clonogenic cell survival, while radiosensitivity in vitro (SF2) and in vivo (single-dose TCD50 under clamped hypoxia) was not affected. In contrast, local tumour control was significantly improved after application of BI 6727 simultaneously to fractionated irradiation (A431: TCD50 = 60.5 Gy [95% C.I. 57; 63] after IR alone and <30 Gy after combined treatment; FaDu: 49.5 Gy [43; 56 Gy] versus 32.9 Gy 126; 40]).
Conclusions: Despite the lack of direct cellular radiosensitisation, PLK1 inhibition with BI 6727 during fractionated irradiation significantly improves local tumour control when compared to irradiation alone. This result is likely explained by a considerable effect on cell cycle and an independent cytotoxic potential of BI 6727.
Keywords: Radiotherapy; PLK1 inhibition; Cell cycle; Local tumour control; Combined treatment

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Publ.-Id: 19534


Implementation of Cascade Gamma and Positron Range Corrections for I-124 Small Animal PET

Harzmann, S.; Braun, F.; Zakhnini, A.; Weber, W. A.; Pietrzyk, U.; Mix, M.
Small animal Positron Emission Tomography (PET) should provide accurate quantification of regional radiotracer concentrations and high spatial resolution. This is challenging for non-pure positron emitters with high positron endpoint energies, such as I-124: On the one hand the cascade gammas emitted from this isotope can produce coincidence events with the 511 keV annihilation photons leading to quantification errors. On the other hand the long range of the high energy positron degrades spatial resolution. This paper presents the implementation of a comprehensive correction technique for both of these effects.
The established corrections include a modied sinogram-based tail-fitting approach to correct for scatter, random and cascade gamma coincidences and a compensation for resolution degradation effects during the image reconstruction. Resolution losses were compensated for by an iterative algorithm which incorporates a convolution kernel derived from line source measurements for the microPET Focus 120 system. The entire processing chain for these corrections was implemented, whereas previous work has only addressed parts of this process. Monte Carlo simulations with GATE [1] and measurements of mice with the microPET Focus 120 show that the proposed method reduces absolute quantication errors on average to to 2.6% compared to 15.6% for the ordinary Maximum Likelihood Expectation Maximization algorithm. Furthermore resolution was improved in the order of 11-29% depending on the number of convolution iterations.
In summary, a comprehensive, fast and robust algorithm for the correction of small animal PET studies with I-124 was developed which improves quantitative accuracy and spatial resolution.
Keywords: Monte Carlo simulations, cascade gamma coincidences, non-pure positron emitter, positron range, positron emission tomography (PET), image resolution

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Publ.-Id: 19533


Discovery of the cancer stem cell related determinants of radioresistance

Peitzsch, C.; Kurth, I.; Kunz-Schughart, L.; Baumann, M.; Dubrovska, A.
Tumors are known to be heterogeneous containing a dynamic mixture of phenotypically and functionally different tumor cells. The two concepts attempting to explain the origin of intratumor heterogeneity are the cancer stem cell hypothesis and the clonal evolution model. The stochastic model argues that tumors are biologically homogenous and all cancer cells within the tumor have equal ability to propagate the tumor growth depending on continuing mutations and selective pressure. By contrast, the stem cells model suggests that cancer heterogeneity is due to the hierarchy that originates from a small population of cancer stem cells (CSCs) which are biologically distinct from the bulk tumor and possesses self-renewal, tumorigenic and multilineage potential. Although these two hypotheses have been discussed for a long time as mutually exclusive explanations of tumor heterogeneity, they are easily reconciled serving as a driving force of cancer evolution and diversity. Recent discovery of the cancer cell plasticity and heterogeneity makes the CSC population a moving target that could be hard to track and eradicate. Understanding the signaling mechanisms regulating CSCs during the course of cancer treatment. can be indispensable for the optimization of current treatment strategies.
Keywords: Cancer stem cells; Radioresistance; Biomarkers; Microenvironment

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Publ.-Id: 19532


Comment on: "Transconvolution and the virtual positron emission tomograph: A new method for cross calibration in quantitative PET/CT imaging"

Hofheinz, F.; van den Hoff, J.
kein Abstract verfügbar - "Letter to the Editor"

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Publ.-Id: 19531


Performance Evaluation of Stationary and Semi-Stationary Acquisition with a Non-Stationary Small Animal Multi-Pinhole SPECT System

Lange, C.; Apostolova, I.; Lukas, M.; Huang, K. P.; Hofheinz, F.; Gregor-Mamoudou, B.; Brenner, W.; Buchert, R.
Purpose
Step-and-shoot mode with many angular steps results in long frame duration limiting the capability of single-photon emission computed tomography (SPECT) for fast dynamic scans. The present study evaluates acquisition with reduced angular sampling for fast imaging in preclinical research with the nanoSPECT/CTplus four-head multi-pinhole system.
Procedures
Measurements with line sources, homogeneity phantoms and a Jaszczak phantom filled with 99mTc or 123I were performed to evaluate the ‘stationary’ and ‘semi-stationary’ acquisition mode (one or two detector positions, respectively) with respect to spatial resolution, quantification, noise properties and image artefacts. An in vivo mouse study was performed with 99mTc-MAG3.
Results
The fast acquisition modes resulted in only minor degradation of spatial resolution and quantification accuracy. Statistical noise in reconstructed images was significantly reduced compared to conventional SPECT, particularly at low count statistics. Stationary acquisition resulted in streak artefacts and spatial distortion.
Conclusions
The semi-stationary acquisition mode of the nanoSPECT/CTplus allows fast dynamic SPECT with tolerable loss of image quality.
Keywords: SPECT, Dynamic imaging, Stationary, Performance evaluation

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Publ.-Id: 19530


Nickel Induced Crystallization of Carbon During Deposition

Wenisch, R.; Hübner, R.; Krause, M.; Gemming, S.; Abrasonis, G.
Crystallization kinetics of ion beam sputtered carbon on polycrystalline nickel thin films is investigated. The process temperature is significantly reduced in comparison to annealing of an amorphous carbon film without the aid of a transition metal. The degree of graphitization and the average grain size of the resulting films are examined by means of Raman-spectroscopy and high resolution transmission electron microscopy. The chemical state of the carbon atoms is analyzed by X-ray photoelectron spectroscopy. Additionally, nuclear reaction analysis confirms the temperature independence of the carbon absorption on the nickel surface. We believe that the process holds a potential for the synthesis of crystalline thin films or single layers of different 2D nanomaterials.
Keywords: nickel, carbon, graphite, amorphous carbon, physical vapor deposition, Rutherford back-scattering, nuclear reaction analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron spectroscopy
  • Poster
    2013 MRS Fall Meeting & Exhibit, 01.-06.12.2013, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-19529
Publ.-Id: 19529


Nickel Induced Crystallization of Carbon During Deposition

Wenisch, R.; Gemming, S.; Abrasonis, G.
A single-step process for the preparation of very thin polycrystalline carbon films on uniform nickel thin films is presented. The process temperature is significantly reduced in comparison to annealing of an amorphous carbon film without the aid of a transition metal. The degree of graphitization and the average grain size of the resulting films are examined by means of Raman-spectroscopy and transmission electron microscopy. The chemical state of the carbon atoms is analyzed by X-ray photoelectron spectroscopy. Additionally, nuclear reaction analysis is employed to confirm the temperature independence of the carbon absorption on the nickel surface. We believe that the process holds a potential for the synthesis of crystalline thin films or single layers of different 2D nanomaterials.
Keywords: nickel, carbon, physical vapor deposition, graphite, amorphous carbon, Rutherford back-scattering, nuclear reaction analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie 2013, 10.-15.03.2013, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19528
Publ.-Id: 19528


Fluence calculation and reaction rates determination at the reactor pressure vessel Kola 3

Konheiser, J.; Borodkin, P.; Borodkin, G.
In this work, different geometric positions which have influence on the radiation conditions of the samples are investigated. Thus, the uncertainties can be determined in the fluence values of surveillance specimens. The fluence calculations were carried out by the codes TRAMO and DORT. This study was accompanied by ex-vessel neutron dosimetry experiments at at Kola NPP, Unit 3 (VVER-440/213), which provide the basis for validation of calculated neutron fluences. The main neutron-activation monitoring reactions were 54Fe(n,p)54Mn and 58Ni(np)58Co. The activity measurements were carried out by SEC NRS.
Good agreement as between the deterministic and stochastic calculation results and between the calculations and the ex-vessel measurements was found. The average difference between measured and calculated values is 5%. The influence of the channels for surveillance specimens and the shielding effect of a baffle rib on the monitors and on the Monte-Carlo calculated results was studied.
The differences of fast neutron fluences in the depth of surveillance specimens could be up to 30% depending on the direction to the core. Based on these calculations the lead factor of specimens is very large and has high uncertainty. The maximum fluence of RPV may be achieved after two cycles. These uncertainties should be taken into account during validation of calculated results by SS neutron dosimetry.
Keywords: Neutron fluence monitor, Monte-Carlo, surveillance specimens, TRAMO, VVER440
  • Lecture (others)
    13. AAA Usergroup Meeting, 02.12.2013, Garching bei München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19527
Publ.-Id: 19527


Development of Radioligands for PET Imaging of Neurodegeneration

Brust, P.
  • Invited lecture (Conferences)
    Kolloquiumsreihe des Universitätsklinikums Tübingen, 22.07.2013, Tübingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19526
Publ.-Id: 19526


SP3 solution versus diffusion solution in pin-by-pin calculations and conclusions concerning advanced methods

Litskevich, D.; Merk, B.
Opportunities for and limitations of the use of the SP3 solution instead of the diffusion solution are given and discussed. Due to existing limitations, the use of a hybrid method consisting of nodal full core calculations coupled with an advanced transport solution based on the current coupling collision probability method with an orthonormal flux expansion is proposed. The method seems to be promising compared to adaptive mesh using refined geometry but without refined detail information, which is deleted by the homogenization process and compared to brute force full core pin-by-pin using advanced transport solvers.
Keywords: SP3 approximation, diffusion approximation, current coupling collision probability, transport equation

Permalink: https://www.hzdr.de/publications/Publ-19525
Publ.-Id: 19525


Ultrafast spectroscopy of super high frequency mechanical modes of doubly clamped beams

Ristow, O.; Merklein, M.; Grossmann, M.; Hettich, M.; Schubert, M.; Bruchhausen, A.; Grebing, J.; Erbe, A.; Mounier, D.; Gusev, V.; Scheer, E.; Dekorsy, T.; Barretto, E. C. S.
We use ultrafast pump-probe spectroscopy to study the mechanical vibrations in the time Domain of doubly clamped silicon nitride beams. Beams with two different clamping conditions are investigated. Finite element method calculations are performed to analyse the mode spectra of both structures. By calculating the strain integral on the surface of the resonators, we are able to reproduce the effect of the detection mechanism and identify all the measured modes. We Show that our spectroscopy technique combined with our modelling tools allow the investigation of several different modes in the super high frequency range (3-30 GHz) and above, bringing more information about the vibration modes of nanomechanical resonators.
Keywords: nanomechanical resonators, ASOPS, Optical spectroscopy

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Publ.-Id: 19523


On the role of fluoro-substituted nucleosides in DNA radiosensitization for tumor radiation therapy

Kopyra, J.; Keller, A.; Bald, I.
Gemcitabine (2’,2’-difluorocytidine) is a well-known radiosensitizer routinely applied in concomitant chemoradiotherapy. During irradiation of biological media with high-energy radiation secondary low-energy (< 10 eV) electrons are produced that can directly induce chemical bond breakages in DNA by dissociative electron attachment (DEA). Here, we investigate and compare DEA to the three molecules 2’-deoxycytidine, 2’-deoxy-5-fluorocytidine, and gemcitabine. Fluorination at specific molecular sites, i.e., nucleobase or sugar moiety, is found to control electron attachment and subsequent dissociation pathways. The presence of two fluorine atoms at the sugar ring results in more efficient electron attachment to the sugar moiety and subsequent bond cleavages. For the formation of the dehydrogenated nucleobase anion, we obtain an enhancement factor of 2.8 upon fluorination of the sugar, whereas the enhancement factor is 5.5 when the nucleobase is fluorinated. The observed fragmentation reactions suggest enhanced DNA strand breakage induced by secondary electrons when gemcitabine is incorporated into DNA.

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Publ.-Id: 19522


Bacterial Diversity at Abandoned Uranium Mining and Milling Sites in Bulgaria as Revealed by 16S rRNA Genetic Diversity Study

Radeva, G.; Kenarova, A.; Bachvarova, V.; Flemming, K.; Popov, I.; Vassilev, D.; Selenska-Pobell, S.
Radionuclide and heavy metal contamination influences the composition and diversity of bacterial communities, thus adversely affecting their ecological role in impacted environments. Bacterial communities from uranium and heavy metal-contaminated soil environments andmine waste piles were analyzed using 16S rRNA gene retrieval. A total of 498 clones were selected, and their 16S rDNA amplicons were analyzed by restriction fragment length polymorphism, which suggested a total of 220 different phylotypes. The phylogenetic analysis revealed Proteobacteria, Acidobacteria, and Bacteroidetes as the most common bacterial taxa for the three sites of interest. Around 20–30 % of the 16S rDNA sequences derived from soil environments were identified as Proteobacteria, which increased up to 76 % (mostly Gammaproteobacteria) in bacterial communities inhabiting the mine waste pile. Acidobacteria, known to be common soil inhabitants, dominated in less contaminated environments, while Bacteroidetes were more abundant in highly contaminated environments regardless of the type of substratum (soil or excavated gravel material). Some of the sequences affiliated with Verrucomicrobia, Actinobacteria, Chloroflexi, Planctomycetes, and Candidate division OP10 were site specific. The relationship between the level of contamination and the rate of bacterial diversity was not linear; however, the bacterial diversity was generally higher in soil environments than in the mine waste pile. It was concluded that the diversity of the bacterial communities sampled was influenced by both the degree of uranium and heavy metal contamination and the site-specific conditions.
Keywords: Bacterial diversity, 16S rRNA gene, Uranium and heavy metal contamination

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Publ.-Id: 19521


Radiosynthesis of 5-(2-[18F]fluoroethyl)-sunitinib as inhibitor of VEGFR-2-first results

Knieß, T.; Kuchar, M.; Bergmann, R.; Steinbach, J.; Pietzsch, J.
Aim:
Radiolabeled inhibitors of receptor tyrosine kinases (RTK) might be suitable probes for monitoring pathophysiological situations related to enhanced expression of the vascular endothelial growth factor receptor (VEGFR). Imaging of angiogenesis with PET could facilitate for the individual patient the evaluation of e.g. the success of corresponding anti-angiogenic chemotherapy or monitoring the stimulation of the endogenous adaptive vessel growth after implantation of
bioMaterials. For this purpose we developed an 18F-radiolabeled probe, 5-(2-[18F]fluoroethyl)-sunitinib basing on the lead structure of sunitinib®, a multi-kinase inhibitor selective to VEGFR-2.
Materials and Methods:
The non-radioactive reference compound 5-(2-fluoroethyl)-sunitinib was synthesized by Knoevenagel condensation of 5-(2-fluoroethyl)-indoline-2-one with N-[2-(diethylamino)ethyl]-2,4-dimethyl-5-formyl-1H-pyrrole-3-carboxamide. Two suitable precursors for radiolabeling, A and B were obtained by reacting a 5-(2-bromoethyl)-substituted sunitinib derivative with silver 4-toluenesulfonate and silver methanesulfonate, respectively. [18F]Fluoride was produced by the 18O(p,n)18F reaction from [18O]H2O in a 18/9 cyclotron (IBA), separated by an anion exchange cartridge (QMA, Waters) and activated by azeotropic drying with acetonitrile in a stream of nitrogen before use. In a set of radiolabeling experiments 4 mg of precursor A or B were reacted with [18F]fluoride in 500μL of solvent at a scheduled temperature regime for 20 min. The yield of 5-(2-[18F]fluoroethyl)-sunitinib was determined by radio-TLC (silicagel, THF/TEA=9/1).
Results:
The non-radioactive 5-(2-fluoroethyl)-sunitinib was investigated in a competition binding assay against VEGFR-2; a Kd value of 9 nM is justifying its classification as specific inhibitor. The radiolabeling reaction of the precursors A and B was performed at temperatures varying from 60, 90, and 120°C in one of the following solvents: acetonitrile, DMF, and DMSO. As result it turned out that for both precursors in DMF and DMSO only poor labeling yields about 2% could be achieved, whereas by using acetonitrile at 90°C the yield of 5-(2-[18F]fluoroethyl)-sunitinib increased to 7-9%. Reaction temperatures higher than 90°C lead to fast and complete decomposition of the precursors as monitored by several non-radioactive by-products on TLC. Notably no difference in yield was observed by using the methanesulfonyl- or the 4-toluenesulfonyl-precursor.
Conclusions:
The new VEGFR-2 targeted radiolabeled probe 5-(2-[18F]fluoroethyl)-sunitinib was successfully synthesized by radiofluorination of the corresponding methanesulfonyl- or 4-toluenesulfonyl-substituted precursor with [18F]fluoride. First attempts to transfer the labeling method to a remote-controlled system were successful. By now a procedure for the purification of the radiotracer by semipreparative HPLC and SPE is under development to enable the radiopharmacological evaluation.
  • Poster
    Annual Congress of the European Association of Nuclear Medicine, 19.-23.10.2013, Lyon, France
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 40(2013), S316

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Publ.-Id: 19520


Electronic transport through short dsDNA measured with mechanically controlled break junctions: New thiol–gold binding protocol improves conductance

Liu, S. P.; Artois, J.; Schmid, D.; Wieser, M.; Bornemann, B.; Weisbrod, S.; Marx, A.; Scheer, E.; Erbe, A.
It is shown that double-stranded DNA which is directly coupled to gold via a modified thymidine base exhibits a higher conductance than reported for DNA coupled to metal electrodes using different binding schemes. The measurements of electrical conductance are performed in a mechanically controlled break junction setup in aqueous solution and in high vacuum at room temperature. The current–voltage characteristics obtained in vacuum can be understood if a single molecular energy level determines the transport.
Keywords: molecular electronics, DNA, charge transport, nanoelectronics

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Publ.-Id: 19519


Biomolekül-unterstützte Photokatalysatoren zur Wasserreinigung

Raff, J.; Vogel, M.; Matys, S.; Bobeth, C.
Bakterielle S-Layer-Proteine stellen eine vielversprechende Immobilisierungsmatrix für Photokatalysatoren (ZnO, TiO2) in Biokompositmaterialien dar. Dabei können die strukturellen Eigenschaften der photokatalytisch aktiven Materialien bei der de-novo Synthese durch die S-Layer ebenso positiv beeinflusst werden wie die Haftung von kommerziell erhältlichen Nanopartikeln auf Trägermaterialien. Die auf diese Weise hergestellten Biokompositmaterialien haben eine höhere katalytische Aktivität als vergleichbare Referenzmaterialien.
Gegenüber der Radikaleinwirkung während der Photokatalyse sind die S-Layer-Proteine relativ stabil und werden vor einer möglichen Fragmentierung durch OH-Radikale zunächst quervernetzt. Die OH-Radikal-Scavenging-Kapazität von gelösten S-Layer-Proteinen konnte mit 2.39 x 105 (mg protein)-1 s-1 bestimmt werden. Damit ist die Scavenging-Kapazität im selben Größenordnungsbereich wie die von typischem Abwasser und somit vergleichsweise niedrig. Auf Basis der S-Layer-Proteine konnte so erfolgreich ein immobiles photokatalytisch aktives Biokompositmaterial entwickelt werden.
Keywords: S-layer, coatings, photocatalyst
  • Invited lecture (Conferences)
    Photokatalyse-Kolloquium, 09.10.2013, Frankfurt am Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19518
Publ.-Id: 19518


Intelligente Biomoleküle zur Funktionalisierung von Kunststoffoberflächen beim Endanwender

Raff, J.
Die Natur hat über Jahrmillionen für viele Probleme optimale Lösungen entwickelt. Ein Paradebeispiel dafür sind Zellmechanismen und -strukturen, die Organismen ein Überleben in extremen Habitaten erlauben. Von herausragender Bedeutung dafür ist die Grenzschicht zwischen Zelle und Umwelt. Im Reich der Bakterien hat die Natur eine besonders vielseitige und multifunktionale Klasse von Proteinen entwickelt, so genannte Hüllproteine oder auch S-Layer-Proteine. Diese Proteine bilden autokatalytisch ein nanostrukturiertes und hochgeordnetes Gitterpolymer auf der Zelloberfläche aus.
Auf Basis dieser Proteine wurde eine Technologieplattform entwickelt, die eine Funktionalisierung zahlreicher technischer Oberflächen durch einen einfachen nasschemischen Prozess im Tauchverfahren erlaubt. Das Verfahren ist umweltfreundlich und kann in gängigen Industrieanlagen und ohne Spezialkenntnisse eingesetzt werden. Auf diese Weise können nicht nur ultradünne leitfähige Schichten aufgebracht werden sondern auch (photo)katalytisch aktive Nanopartikel hochgeordnet und hochdicht unter Erhalt einer maximalen Reaktivität immobilisiert werden. Derartig hergestellte Beschichtungen sind sehr stabil im Sinne einer hohen Haftfestigkeit und chemischen Beständigkeit.
Keywords: S-layer, functional coatings
  • Invited lecture (Conferences)
    Mitteldeutscher Kunststofftag 2013, 26.-27.06.2013, Erfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19517
Publ.-Id: 19517


Structure and energetics of Y-Ti-O nanoclusters in bcc Fe: A combined DFT and Monte Carlo Study

Devaraj, M.; Posselt, M.
Oxide Dispersion Strengthened (ODS) steels consist of a ferritic matrix with dispersed oxide particles having a size of few nanometers. Due to this nanostructure ODS materials exhibit remarkable properties such as high-temperature stability and radiation tolerance. The detailed structure and composition of the nanoclusters containing Y, Ti, O, along with other alloying and impurity elements, is still under discussion. In this work simulated annealing based on the Metropolis Monte Carlo method on a rigid lattice is used in order to determine the structure of the oxide nanoclusters with the lowest formation energy. The ferritic matrix of ODS steels is modeled by bcc-iron. Extensive DFT calculations of point defects and small clusters containing Y, Ti, O and vacancies were performed to obtain the parameters describing the atomic interactions on the rigid lattice. In this work, apart from simple pairwise atomic interactions, many body interactions such as triple interactions are determined from extensive DFT calculations of the oxide clusters. Triple interactions are found to be important additions in order to correctly reproduce the experimentally observed structure of nanoclusters.
Keywords: ODS materials, oxide nanoclusters, computer simulations
  • Lecture (Conference)
    International Workshop on ODS Materials, 08.07.2013, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19516
Publ.-Id: 19516


Properties of yttria-based oxide nanoclusters in iron: An atomistic study

Devaraj, M.; Posselt, M.
In order to get informations please contact the authors.
Keywords: ODS materials, oxide nanoclusters, computer simulations
  • Lecture (Conference)
    5th Workshop on Nuclear Fe Alloys: Modeling and Experiment, 28.-29.11.2013, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-19515
Publ.-Id: 19515


Wear, Plasticity, and Rehybridization in Tetrahedral Amorphous Carbon

Kunze, T.; Posselt, M.; Gemming, S.; Konicek, A. R.; Carpick, R. W.; Pastewka, L.; Moseler, M.
Abstract Wear in self-mated tetrahedral amorphous carbon (ta-C) films is studied by molecular dynamics and nearedge X-ray absorption fine structure spectroscopy. Both theory and experiment demonstrate the formation of a soft amorphous carbon (a-C) layer with increased sp2 content, which grows faster than an a-C tribolayer found on selfmated diamond sliding under similar conditions. The faster sp3 --> sp2 transition in ta-C is explained by easy breaking of prestressed bonds in a finite, nanoscale ta-C region, whereas diamond amorphization occurs at an atomically sharp interface. A detailed analysis of the underlying rehybridization mechanism reveals that the sp3 --> sp2 transition is triggered by plasticity in the adjacent a-C. Rehybridization therefore occurs in a region that has not yet experienced plastic yield. The resulting soft a-C tribolayer is interpreted as a precursor to the experimentally observed wear.
Keywords: wear, tribology, amorphous carbon, computer simulations, X-ray absorption fine structure sprectroscopy
  • Tribology Letters 53(2014), 119-126
    DOI: 10.1007/s11249-013-0250-7
  • Poster
    7th International Conference on Multiscale Materials Modeling (MMM 2014), 06.-10.10.2014, Berkeley, USA

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Publ.-Id: 19514


Life cycle studies of TiO2 nanoparticles

Schymura, S.; Hildebrand, H.; Franke, K.
Investigations of the life cycle of TiO2 nanoparticles are presented, from release out of surface coatings, over transport in the environment, to the uptake into benthic organisms. TiO2 nanoparticles get released from surface coatings with the degradation of the coating. The mobility of the released particles in the environment is mainly governed by the presence of stabilizers and ionic strength of the medium. While natural organic matter such as fulvic acids can stabilize TiO2 suspensions, the presence of, for instance, Ca2+ leads to aggregation and adsorption to geomaterials. Released and deposited nanoparticles can to a certain degree be taken up by nematodes in the benthic system depending on the surface functionalization.
Keywords: TiO2, nanoparticles, life cycle, environment, transport, release
  • Lecture (Conference)
    Cycleur Meeting 2013, 11.-12.12.2013, Ispra, Italy

Permalink: https://www.hzdr.de/publications/Publ-19513
Publ.-Id: 19513


Atomistic study on structure and energetics of yttria-based oxide nanoclusters in bcc-iron

Devaraj, M.; Posselt, M.
Oxide Dispersion Strengthened (ODS) steels consist of a ferritic matrix with dispersed nanometer-size oxide particles. Compared to conventional steels these materials exhibit two remarkable properties that are not fully understood yet: (i) Stability: Up to rather high temperatures the number and size of the oxygen-rich nanoparticles do not change significantly. (ii) Tolerance: The nanoclusters act as sinks for transmutation helium, vacancies and self-interstitials. The first property is the reason for the improved creep strength at high temperature, whereas the second property is related to the radiation resistance of these materials. Therefore, ODS steels are promising candidates for applications as structural materials in extreme environments, i.e. at high temperature and intense particle irradiation, such as in advanced nuclear fission and fusion reactors.
The detailed structure and composition of the nanoclusters containing Y, Ti, O, along with other minor alloying and impurity elements, is still under discussion. In this work simulated annealing (SA) based on the Metropolis Monte Carlo method on a rigid lattice is used in order to determine the structure of the oxide nanoclusters with the lowest formation energy. The ferritic matrix of ODS steels is modeled by bcc-iron. Since cluster sizes up to a few nm are of interest, first-principle methods cannot be used throughout since they are computationally too expensive. However, extensive first-principle calculations on the structure and energetics of point defects and small clusters must be performed in order to obtain the parameters describing the atomic interactions in the rigid lattice used for SA. In this work not only parameters for pair interactions but also for triple interactions are determined. SA is performed for various clusters and the results are compared with available experimental and theoretical data from literature. The binding energies of the oxide nanoclusters obtained in this work can be used as input parameters of coarse-grained method such as object kinetic Monte Carlo simulations and rate theory that are often used to consider the evolution of a system of nanoclusters.
Keywords: ODS materials, oxide nanoclusters, computer simulations
  • Lecture (Conference)
    2013 MRS Fall Meeting & Exhibit, Symposium ZZ, 01.-06.12.2013, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-19512
Publ.-Id: 19512


Confinement effects in solid phase recrystallization of silicon nanowires

Posselt, M.
There are several routes to produce advanced nanowire transistors based on silicon. In order to obtain the desired electrical properties doping of the nanowires is required. Ion implantation is one of the favored methods to introduce dopant atoms in a controlled manner. If relatively high ion fluences are needed the originally single-crystalline nanowire is amorphized. Subsequently, thermal processing must be used to restore the silicon crystal and to activate the dopants electrically. In planar structures a complete restoration can be achieved by solid-phase epitaxial recrystallization, whereas more complex processes take place in the nanowires, due to the significant influence of surfaces and interfaces. It is highly desirable to understand the recrystallization in such confined systems on the atomic level. This work presents results of molecular dynamics simulations of solid phase recrystallization of silicon nanowires. It is shown that for embedded and free nanowires the recrystallization rate is significantly modified compared to the planar solid phase epitaxy. In general the original crystal cannot be restored completely. In dependence on whether embedded or free nanowires are investigated several phenomena are observed, such as stacking fault and twin formation, random nucleation of separate crystalline grains, as well as edge rounding and necking. The simulation results are in qualitative agreement with experimental findings.
Keywords: nanowires, silicon, solid phase recrystallization, computer simulations
  • Poster
    2013 MRS Fall Meeting & Exhibit, Symposium SS, 01.-06.12.2013, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-19511
Publ.-Id: 19511


Untersuchung der Haftung zwischen Pulverpartikeln und strukturierten Oberflächen mithilfe der Vibrationsmethode / Investigation of Powder Particle Adhesion on Structured Surfaces Using the Vibration Method

Hartmüller, J.; Rudolph, M.; Weiler, R.; Ripperger, S.
Die Vibrationsmethode ermöglicht die schnelle und effiziente Ermittlung von Partikelhaftkraftverteilungen zwischen strukturierten Oberflächen und pulverförmigem Schüttgut unter dem Einfluss verschiedener atmosphärischer Bedingungen. In diesem Beitrag werden die Haftkräfte von Fließmittel-beschichtetem Stärkepulver auf Druckpapier bei verschiedenen relativen Luftfeuchten untersucht und mit Modellen der Partikelhaftung infolge von van-der-Waals-Kräften und von Flüssigkeitsbrücken verglichen.

The vibration method allows the rapid and efficient measurement of particle adhesion force distributions between structured surfaces and powdery bulk material under different atmospheric conditions. The adhesion forces between printing paper and glidant covered starch particles under different humidities will be determined and compared with models of particle adhesion due to van der Waals forces and liquid bridges.
Keywords: Adhesion force distribution Adhesion force measurement Humidity Particle adhesion van der Waals forces Vibration method

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Permalink: https://www.hzdr.de/publications/Publ-19510
Publ.-Id: 19510


Surface Nanopatterning by Irradiation with Heavy Polyatomic Ions

Heinig, K.-H.; Liedke, B.; Urbassek, H.; Anders, C.; Böttger, R.; Bischoff, L.
The driving forces for surface patterning by ion bombardment have been under discussion for many years. Bradley and Harper proposed a competition between the surface instability due to curvature dependent sputtering and the surface smoothing by Mullins-Herring diffusion. Later, Carter and Vishnyakov proposed another surface destabilizing term based on ion impact induced mass drift. The groups of Aziz (Harvard) and Nordlund (Helsinki) have recently proven that this momentum transfer to target atoms by ion impacts is the dominating driving force for pattern formation in many cases. However, in cases where collision-induced bulk defects cannot reach the surface forming a “crater”, defect diffusion induced patterns like pits and sponges can form. Another complicating fact is that the manifold of beautiful patterns on Si and Ge published recently are dominated by metal impurities. Thus, it is now commonly accepted that at normal ion incidence on elemental, amorphous targets no surface pattern should evolve.
However, we found recently [1,4] well-ordered dot patterns at normal irradiation on Ge and Si with polyatomic Bi ions of ~10…20 keV kinetic energy per atom (see 3D SEM and XTEM image). Similar patterns were found with monoatomic Bi ions at elevated Ge substrate temperatures, when the energy per Ge atom exceeds a critical value [2].
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 [3] and kinetic Monte-Carlo simulations [4]. 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. The surface destabilizing term 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.
1. L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko, W. Pilz; NIM B272 198 (2012).
2. R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz, B. Schmidt; JVST B30, 06FF12 (2012).
3. C. Anders, K.-H. Heinig, H. Urbassek; to be submitted to Phys. Rev. B (2013).
4. R. Böttger, K.-H. Heinig, L. Bischoff, B. Liedke, R.Hübner, W. Pilz; submitted to Adv. Materials (2013).
Keywords: ion irradiation, polyatomic ions, self-organisation, surface pattern, theory
  • Invited lecture (Conferences)
    2013 EMN Spring Meeting "Energy Materials Nanotechnology", 08.-11.04.2013, Orlando, USA

Permalink: https://www.hzdr.de/publications/Publ-19509
Publ.-Id: 19509


Si Nanocrystal Networks for Photovoltaic Applications

Ozen, E.; Gundogdu, S.; Keles, U.; Bulutay, C.; Aydinli, A.; Heinig, K.-H.; Rigato, V.
Self-assembling during spinodal decomposition of Si nanocrystals in a dielectric matrix is a very promising synthesis process of novel nanocrystaline Si structures for 3rd generation thin-film solar cells. Thanks to quantum confinement in nanocrystals, this approach can be utilized to improve the single band gap silicon solar cells efficiency by spectrum management through the incorporation of larger band gap nanocrystaline silicon into the solar cell structure allowing a better use of the solar spectrum.
Conventional techniques use high-temperature processing to activate the spinodal decomposition process. However, these methods are incompatible with glass substrates or thin-film stacked structures usually employed in mass production techniques (e.g in pilot lines for deployment of solar cells). An alternative approach reducing the thermal budget and allowing localised processing is the laser irradiation of substochiometric silicon oxides.
We present cw laser annealing of Si-rich oxide thin films with varying Si content to obtain Si nanocrystals embedded in silica. SiOx thin films with x<2 were obtained by plasma enhanced chemical vapor deposition (PECVD). Hydrogen or nitrogen diluted silane (SiH4) gas was used as the Si source and two different precursor gasses, N2O and CO2, were used for oxygen incorporation. We have achieved the control of the Si ratio in the films by adjusting the relative gas flow ratios. Fine tuning the Si excess in SiOx and optimizing the annealing conditions is pursued to control the inter-nanocrystal distance to generate a network of Si nanocrystals with controlled Si/SiO2 phase separation. Our computational studies of silicon nanowire networks based on realistic pseudopotential techniques have unraveled the systematics of the band gap variation under topological and structural variations. With the aid of these atomistic modeling tools, nanocrystal networks are optimized for solar cell applications.
We have investigated the nanocrystal network formation for different composition samples. In the case of PECVD grown Si-rich oxides, different elements such as nitrogen, carbon and especially hydrogen can be present in the films. A detailed elemental study has been performed to determine the precise composition of the films using ion beam techniques such as elastic recoil detection analysis (ERDA) and Rutherford back scattering (RBS), as well as X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The Si/SiO2 phase separation has been studied by energy filtered Transmission Electron Microscopy (EFTEM) and the nanowires' diameters have been identified to be in the order of a few nanometers suggesting the possibility of quantum confinement.
This research is supported by TÜBITAK-BMDF grant no 109R037
Keywords: Nanocomposite, Si, SiO2, Sponge, photovoltaic, EFTEM, theory
  • Poster
    2013 MRS Spring Meeting, Symposium R: Nanostructured Semiconductors and Nanotechnology, 01.-05.04.2013, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-19508
Publ.-Id: 19508


Network of Percolated Si Filaments in SiO2: A Nanocomposite-absorber for Thin-film PV Cells

Heinig, K.-H.; Aydinli, A.; Schmidt, B.; Liedke, B.; Friedrich, D.; Keles, U.; Bulutay, C.
Si-based thin film PV cells suffer from a rather low efficiency. This leads to a relatively small market share, although their module prices are comparably low. Here, we present a novel nanostructured Si-based thin film PV cell absorber, which has the potential to increase the efficiency substantially without increasing the module costs.
Spinodal decomposition of metastable SiO into Si and SiO2 is a promising synthesis process of nanostructured Si absorbers for 3rd generation thin-film solar cells. Under appropriate conditions of SiO deposition and subsequent heat treatment, self-organization of a network of percolated Si filaments embedded in SiO2 has been achieved. The SiO layers have been produced by different techniques, sputtering, CVD and e-beam evaporation. Spinodal decomposition has been activated by Rapid Thermal Processing (RTP, several seconds), very Rapid Thermal Processing (vRTP, dwell time tens of msec), and laser annealing. If, after phase separation, the volume fraction of elemental Si exceeds ~30%, then Si forms a percolated network of Si filaments, which will be proven by the aid of Energy-Filtered Transmission Electron Microscopy (EFTEM) images. The diameters of the filaments are in the range of 2…5 nm and can be tuned by the thermal treatment. Due to the small diameters, the band gap is dominated by the quantum size effect. As the wire diameters coarsens with time of heat treatment like t^1/3, and because the Si bandgap opens for nm-structures by quantum confinement, a band gap engineering for PV cell optimization becomes feasible.
This is in excellent agreement with large-scale simulations on the network formation using our 3D kinetic lattice Monte-Carlo program. Electronic band structure calculations of such nanostructured silicon will be presented too. It will be shown that up-scaling of the nanocomposite fabrication as described above to the industrial scale is feasible with available technologies.
The work performed within the project “RainbowEnergy” is supported by the German ministry BMBF and the Turkish funding agency TÜBITAK
Keywords: Nanocomposite, Si, SiO2, Nanosponge, photovoltaic, phase separation, band gap, theory
  • Lecture (Conference)
    2013 MRS Spring Meeting, Symposium A: Film Silicon Science and Technology, 01.-05.04.2013, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-19507
Publ.-Id: 19507


Low-energy Ion-beam-activated Growth of Ordered Nanocomposites - Modeling and Computer Simulations vs Experiments

Heinig, K.-H.; Abrasonis, G.; Liedke, B.
Co-sputtering of immiscible components like Al/Si, Metals/C, Metals/Si, Si/SiO2 etc. leads usually to artificially mixed solids which are metastable but nevertheless useful for applications up to a certain operation temperature. The components or their compounds are either mixed (on the atomic scale) into a state far from thermodynamic equilibrium, or they become phase separated (on the nanoscale) into a composite like a ceramic and a metal in a cermet. Phase separation can occur ion-beam-activated during growth, or thermally activated in a subsequent annealing step.
It will be shown how, during co-sputtering, a high atomic mobility in the growing top layer allows for an almost complete phase separation and, eventually, the fabrication of regular order of the precipitated components. Thus, growth of hexagonally ordered silicide nanowires embedded in silicon has been demonstrated by biased co-sputtering of metals and silicon at elevated substrate temperature [Yasui et al., Adv.Mater. 2007,19, 2797]. Here, well-ordered metal/carbon and Si/SiO2 nanocomposites will be shown, and their evolution will be demonstrated by 3D kinetic lattice Monte Carlo simulations. Predictive atomistic simulations on spatiotemporal scales of experiments will be presented which give a guideline for fabrication of nanocomposites having self-organized structures with a high degree of order.
Keywords: atomistic simulations, sputter deposition, ion irradiation, self-organisation, pattern formation
  • Invited lecture (Conferences)
    2013 MRS Spring Meeting, Symposium UU: Plasma and Low-Energy Ion-Beam-assisted Processing and Synthesis of Energy-related Materials, 01.-05.04.2013, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-19506
Publ.-Id: 19506


Nanomelt-Induced Surface Patterning by Polyatomic Ions

Heinig, K.-H.; Liedke, B.; Urbassek, H.; Anders, C.; Böttger, R.; Bischoff, L.
It is the current understanding that no surface patterns form on elemental amorphous semiconductors by keV-ions if the beam hits the surface perpendicularly and if contamination with certain metals is avoided. This has been experimentally proven by many groups and is theoretically predicted by the two dominating theories of Bradley/Harper and Carter/Vishnyakov. In contrast to this we find under normal impact of heavy, polyatomic ions very pronounced, hexagonally ordered dot patterns [1]. Using monatomic ions of the same element, fluence and energy per atom, the surface remains flat. Consequently, the patterning must result from the collective action of several energetic atoms bombarding the surface in the same point at the same time. Recently we showed [1] that this collective action causes surface patterns only if in the collision cascade the mean energy posited per substrate atom exceeds the melting threshold. In Ge substrates heated to a sufficiently high temperature, the melting threshold can be also overcome by monatomic Bi+ ions [2]. The figure shows a MD simulation for a Bi_3^ ++ ion impact on Ge with an energy per Bi atom of 20keV. A melt pool forms at the surface, which is quenched after a few hundreds of ps into an amorphous phase[3]. In Si substrates, patterns form (i.e. the melting threshold is reached) even at elevated T only with polyatomic ions [4]. Here it will be shown that this pattern formation is driven by capillary forces: On the one hand, melting minimizes the surface locally which, by many ion impacts, leads to a global smoothing of the surface in accordance to (similar to laser polishing). On the other hand, the missing matter (due to sputtering) results in a melt pool meniscus (see figure), whose center is shifted with respect to the ion impact point for tilted surfaces. Thus, downhill from the impact more matter is missing, which is effectively an uphill current leading to a surface
destabilizing term . As usual, the competition of these two processes results in pattern selforganization
Keywords: ion irradiation, self-organisation, surface pattern, MD simulation, theory
  • Invited lecture (Conferences)
    18th International Conference on Surface Modification of Materials by Ion Beams, 15.-20.09.2013, Kusadasi, Izmir, Turkey

Permalink: https://www.hzdr.de/publications/Publ-19505
Publ.-Id: 19505


Mechanisms of surface pattern formation under irradiation with heavy ions

Heinig, K.-H.; Liedke, B.; Urbassek, H.; Anders, C.; Bischoff, L.; Böttger, R.
The driving force for surface pattern formation under ion irradiation has been under discussion for many years. Bradley and Harper suggested that curvature dependent sputtering is the source for the surface instability. Later on, Carter and Vishnyakov concluded that the transfer of the ion momentum to atoms causes a mass drift which smoothes the surface but destabilizes it at large off-normal impact angles. Thus, no pattern formation is expected for normal incidence on elemental semiconductors. However, very recently we found that normal incidence irradiation of Ge with ultraheavy ions (Bi_3^++ , Bi_2^+, 10...20 keV/atom) leads to very pronounced, hexagonally ordered dot pattern [1]. This pattern form if the energy density deposited close to the surface in a single ion impact exceeds a threshold, which can be achieved by ultraheavy ions or by substrate heating [2]. A model of pattern formation based on transient melt pool formation with local surface minimization will be presented. [1] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko, W. Pilz, NIMB 272 (2012) 198; [2] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz, B. Schmidt, JVST B30 (2012) 06FF12.
Keywords: ion irradiation, self-organisation, surface pattern, theory
  • Invited lecture (Conferences)
    DPG Frühjahrstagung der Sektion Kondensierte Materie "Physik und Materialwissenschaften mit Ionenstrahlen", 10.-15.03.2013, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19504
Publ.-Id: 19504


Development and verification of a transport solver for DYN3D

Litskevich, D.; Merk, B.
The computer code DYN3D is widely used for safety estimation of nuclear power plants. It has been developed in Helmholtz-Zentrum Dresden-Rossendorf, Germany. The last version of the DYN3D code can be used for investigations of transients in light water reactors cores with hexagonal or quadratic fuel assemblies. Moreover, the multigroup SP3-approximation can be used for reactors with quadratic and hexagonal fuel assemblies.
The DYN3D code is based on the nodal expansion method. It applies for the calculations fuel assembly wise homogenized cross-sections and determines fluxes homogenized for each node in the core. But in many cases for safety calculations good knowledge of power and temperature distributions on nodal level is not enough. In most cases the ability to predict accurately the local pin powers in nuclear reactors is necessary.
In the work a new methodology for pin-power calculations in chosen nodes has been proposed. The main idea is to determine the pin wise power distribution inside fuel assemblies applying a transport solver using unstructured mesh with boundary conditions extracted from the 3D full core nodal diffusion solution. In this technique the global calculation is used to define partial incoming currents as boundary conditions for a local problem.
In the work, advanced method for solution of transport equation based on the current coupling collision probability method with orthonormal flux expansion was proposed and tested for the single cell . In the present work the proposed transport methodology is extended from the level of single cell to full assembly level. The developed transport solver has been used for the solution of a one group fixed source problem as well as for a multigroup eigenvalue problem. The results of the calculations demonstrate good agreement with the results of Monte-Carlo calculations as well as with the results of HELIOS calculations.
Keywords: DYN3D, transport equation, current coupling collision probability
  • Lecture (Conference)
    The 45th Annual Meeting on Nuclear Technology, 06.-08.05.2014, Frankfurt, Deutschland
  • Open Access Logo Contribution to proceedings
    The 45th Annual Meeting on Nuclear Technology, 06.-08.05.2014, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19503
Publ.-Id: 19503


Use of Mineral Liberation Analysis (MLA) in the Characterization of Lithium-Bearing Micas

Gutzmer, J.; Sandmann, D.
The capabilities and opportunities of the application of automated mineralogy for the characterization of lithium-bear- ing zinnwaldite-micas are critically assessed. Samples of a crushed greisen-type ore comprising mostly of quartz, topaz and zinnwaldite (Li-rich mica) were exposed to further comminution by cone crusher and high voltage pulse power fragmentation. Product properties were analyzed by using a Mineral Liberation Analyser (MLA) and the obtained min- eralogical and mineral processing relevant parameters were carefully evaluated with special focus on the characteristics of zinnwaldite. The results illustrate that both samples contain a significant quantity of very fine particles that are prod- ucts of comminution. The modal mineralogy in the different sieve fractions is characterized by the accumulation of minerals of low hardness in the finest fraction and the enrichment of topaz, having a high hardness, in the somewhat larger fractions. Based on the results of mineral association data for zinnwaldite, a displacement of the muscovite-quartz ratio, in comparison to the results of modal mineralogy, was observed by indicating good quartz-zinnwaldite boundary breakage and weak muscovite-zinnwaldite breakage. Liberation as well as mineral grade recovery curves indicate that fraction -1000 to +500 μm is most suitable for beneficiation. The results of this study demonstrate that SEM-based im- age analysis, such as MLA, can effectively be used to investigate and evaluate phyllosilicate minerals in a fast and pre- cise way. It is shown that the results of MLA investigations, such as modal mineralogy, are in good agreement with other analytical methods such as quantitative X-ray powder diffraction.
Keywords: Mineral Liberation Analysis; Zinnwaldite; Conventional Comminution; High Voltage Pulse Power Fragmentation

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Permalink: https://www.hzdr.de/publications/Publ-19502
Publ.-Id: 19502


Production of 135La by proton irradiation of enriched 135Ba and purification by ion exchange chromatography

Mansel, A.; Franke, K.
The global demand for the rare earth elements has been dramatically enlarged. Therefore, it needs a detailed understanding in ore chemistry and separation methods. To simulate these processes, we will use the radiotracer technique. 135La (T1/2 = 19.4 h) was choosen as a typical representative element (radionuclide) for the rare earth elements. The isotope can be produced by the nuclear reaction 135Ba(p,n)135La at a cyclotron. We used our recently installed cyclotron Cyclone® 18/9 (IBA) by irradiation of the isotope enriched 135Ba (94.9%). The [135Ba]BaCO3 was pressed in an aluminium holder with a diameter of 3 mm and a depth of 300 µm . The target was covered by a 100 µm thick aluminium foil to avoid loss of the material during irradiation. The irradiation was done at a beam of 18 MeV protons and a current of 20 µA for 7 hours. After cooling for 2 hours the [135Ba]BaCO3 was dissolved with 2 ml 0.095 M nitric acid. The separation of the radionuclide 135La and the target material 135Ba was performed by ion exchange chromatography with Ln-Resin-C (TRISKEM). The target solution was eluated on the resin and the resin was washed four times with 2 ml 0.095 M nitric acid to remove the 135Ba. Afterwards, the 135La was stripped by triple washing of the resin with 6 M nitric acid. The combined 135La solutions were evaporated to dryness and the residue was dissolved in 0.1 M nitric acid. The detection of 135La was done by liquid scintillation counting. The target material was recovered by evaporating the 135Ba fractions to dryness, dissolving the residue with water and precipitation of the carbonate by bubbling with carbon dioxide.
Keywords: Barium target, Proton irradiation, Lanthanum, Radionuclide, Separation, Cyclotron
  • Poster
    17th Radiochemical Conference, 11.-16.05.2014, Marianske Lazne, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-19501
Publ.-Id: 19501


Investigation into the formation of Np(IV) silica colloids

Husar, R.; Weiss, S.; Hennig, C.; Hübner, R.; Zänker, H.; Bernhard, G.
In the near and far field of nuclear waste repositories lower oxidations states of the actinides (An) are expected to become predominant because of the prevalent reducing conditions. Due to the low solubility at neutral pH, tetravalent actinides (An(IV)) are assumed to reveal immobile migration behaviour. Nevertheless, a high environmental mobility has been found, e.g. for Pu(IV), which is obviously related to the formation of An(IV) eigencolloids or to the sorption of the heavy metal ions onto other colloids. In the laboratory, An(IV)O2×H2O colloids for Th(IV) and Np(IV) have been synthesized. Regarding to erosion processes in repository sites, e.g. on glasmolds and ubiquitous occurring matter, the interaction of An(IV) with carbonate and silicate compounds and the potential formation of colloids has to be considered carefully. In particular, former studies evidenced the formation of U(IV) and Th(IV) silica-containing colloids.
We developed a method to generate aqueous Np(IV) solutions, explicitly excluding the presence of other oxidation states, for the synthesis of silica-containing colloids. Under anaerobic conditions, Np(IV) carbonate solutions in presence and absence of silicate were investigated by TEM, EXAFS, UV-vis spectroscopy, ultrafiltration, LSC and DLS (dynamic light scattering). When silicate was admixed to such a solution Np(IV) is prevented from precipitation and the spectrum obtained differs from that of dissolved Np(IV) in 1.0 M carbonate. The absorption band at 741 nm is significantly increased and in dependence of the concentration of silica shifted to 747 nm. Thus, the formation of colloidal Np(IV) silicate is strongly suggested. Furthermore, the colloid-disperse Np(IV) silicate solution exhibits an increased scattering light intensity and diameters of the particles were determined in the range from 1 to 20 nm. Ultrafiltration removes these particles and the respective UV-vis spectrum shows considerably reduced absorption bands. In addition to the disappearance of the previously observed absorption bands around 745 nm, the concentration of Np was reduced from 1.0 × 10−3 to 0.1 × 10−3 M and 1.8 × 10−3 to 0.3 × 10−3 M. All these findings can be explained by a colloidal behaviour. Moreover it is ascertained that these colloidal systems are stabil over a period of more than 120 days. In presence of silicate we observed a stabilized dispersion of Np(IV) silica colloids. Hence, Np(IV) may become waterborne even if the limit of solubility is exceeded. The existence of such colloids has never been reported so far.
Keywords: actinides neptunium nanoparticles nanocrystallinity neptiniumdioxide
  • Lecture (Conference)
    Migration 2013, 08.-13.09.2013, Brighton, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-19499
Publ.-Id: 19499


Investigations into the formation of Np(IV) silica colloids

Husar, R.; Weiss, S.; Hennig, C.; Zänker, H.; Bernhard, G.
Knowledge of the migration and mobility of actinides is an important issue to predict potential release of radiotoxic elements from nuclear waste repositories. Under the reducing conditions expected for the disposal zone, the tetravalent form of the actinides An (An = Th, U, Np, Pu) is predominant. Due to the low solubility at neutral pH, An(IV) are considered as immobile under these conditions. Nevertheless, high environmental mobility has been found. This fact is related with the formation of An(IV) eigencolloids or the sorption on other colloids.

Here Neptunium(IV) forms silicate-containing colloids when the limit of solubility is exceeded in presence of soluble silicate.
The formation and stability of Np(IV)-silica colloids was investigated by EXAFS, liquid LSC, ICP-MS, UV-Vis spectroscopy and light scattering
Keywords: actinides, neptunium, silica, colloids, nanoparticles
  • Lecture (others)
    13. Koordinierungsgespräch Paul-Scherer-Institut/LES – HZDR/IRE, 17.-19.07.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19497
Publ.-Id: 19497


16.6 J chirped femtosecond laser pulses from a diode pumped Yb:CaF2 amplifier

Kessler, A.; Hornung, M.; Keppler, S.; Schorcht, F.; Hellwing, M.; Liebetrau, H.; Körner, J.; Sävert, A.; Siebold, M.; Schnepp, M.; Hein, J.; Kaluza, M.
We report the amplification of laser pulses at a center wavelength of 1034 nm to an energy of 16.6 J from a fully diode pumped amplifier using Yb:CaF2 as the active medium. Pumped by a total optical power of 300 kW from high-power laser diodes, a gain factor of g = 6.1 was achieved in a nine-pass amplifier configuration agreeing with numerical simulations. A measured spectral bandwidth of 10 nm full width at half maximum, FWHM promises a bandwidth-limited compression of the pulses down to a duration of 150 fs. These are to our knowledge the most energetic laser pulses achieved from a diode pumped chirped pulse amplifier so far.
Keywords: Lasers and laser optics, Lasers, diode-pumped, Ultrafast optics

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Permalink: https://www.hzdr.de/publications/Publ-19496
Publ.-Id: 19496


Formation of dendritic crystal structures in thin silicon films on silicon dioxide by carbon ion implantation and high intensity large area flash lamp irradiation

Voelskow, M.; Endler, R.; Schumann, T.; Mücklich, A.; Ou, X.; Liepack, E. H.; Gebel, T.; Peeva, A.; Skorupa, W.
In this paper, we use large area light pulse induced melting of deposited thin silicon films on oxidized silicon wafers to prepare coarse grained dendritic crystal structures. The results show that the addition of carbon prevents the agglomeration of the molten silicon films and largely influences the crystallisation process. The low solubility of carbon in liquid silicon and its effect on the silicon melting temperature induce a distinctive lateral dendritic grain growth. XTEM, SEM, AFM and ToF-SIMS investigations have been performed to study the crystallisation process and to characterise the resulting film structure
Keywords: Dendrites; Segregation; Solidification; Growth from melt; Liquid phase epitaxy; Semiconductor silicon

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Permalink: https://www.hzdr.de/publications/Publ-19495
Publ.-Id: 19495


Femtosecond laser micromachined ridge waveguide lasers in Nd:YAG ceramics

Jia, Y.; de Aldana, J.; Akhmadaliev, S.; Zhou, S.; Chen, F.
We report on the fabrication of ridge waveguides in Nd:YAG ceramic by using femtosecond laser micromachining of the surface of a He ion implanted planar waveguide. Under optical pump of 808 nm light, continuous wave waveguide lasers have been realized at 1.06 μm at room temperature in the Nd:YAG ceramic ridge waveguide system, reaching a maximum output power of 46 mW. The lasing threshold of ∼64.9 mW and the slope efficiency of 42.5% are obtained for the ridge waveguide system, which shows superior lasing performance to the Nd:YAG ceramic planar waveguide.
Keywords: Optical waveguides; Nd:YAG ceramic; Femtosecond laser micromachining

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Permalink: https://www.hzdr.de/publications/Publ-19494
Publ.-Id: 19494


Long-term activity of biohybrid coatings of atrazine-degrading bacteria Pseudomonas sp. ADP

Pannier, A.; Lehrer, T.; Vogel, M.; Soltmann, U.; Böttcher, H.; Tarre, S.; Green, M.; Raff, J.; Pollmann, K.
The atrazine-degrading bacterial strain Pseudomonas sp. ADP was immobilized by the sol–gel process within thin silica layers coated onto water-retaining carrier materials (expanded clay pellets and scoria). The performance of the obtained biohybrid material has been investigated concerning long-term activity under non-growth conditions. Experiments were run in phosphate buffer containing atrazine (20 mg/l) as the sole source of carbon and nitrogen. Even after one year of consecutive batch tests, P. ADP immobilized onto expanded clay pellets showed a high atrazine degradation activity. In the course of long-term batch experiments, the average amount of removed atrazine was about 94% during each assay cycle. Staining with CTC revealed that in spite of cultivation under non-growth conditions over a period of one year, immobilized cells were still vital and showed respiratory activity.
Keywords: sol-gel, silica coatings, biohybrid material, encapsulation, Pseudomonas sp. ADP, atrazine

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Permalink: https://www.hzdr.de/publications/Publ-19493
Publ.-Id: 19493


Holocene paleo-environmental signals from Akademii Nauk ice cap (Severnaya Zemlya, Russian Arctic)

Fritzsche, D.; Opel, T.; Wagenbach, D.; Mcconnell, J. R.; Merchel, S.; Rugel, G.
The project is focused on the analysis of a 724 m long ice core drilled on Akademii Nauk ice cap to bedrock within a joint German-Russian project in 1999 to 2001. Beside stable water isotope rates major ion and black carbon content were measured to get information about the regional climate and environmental history. 10Be concentration is used to improve the age depth relationship of the core which is up to now based on interpretation of volcanic signals and in between counting of seasonal isotopic cycles only.
Keywords: climate, environment, ice, AMS, cosmogenic radionuclide
  • Bulletin “ICE” edited by the International Glaciological Society 164(2014), 5

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Permalink: https://www.hzdr.de/publications/Publ-19492
Publ.-Id: 19492


Innovative eco-efficient biohydrometallurgy process for the recovery of strategic and rare metals

Kutschke, S.
Presentation of the project "EcoMetals" which focuses on innovative eco-efficient biohydrometallurgy process for the recovery of strategic and rare metals
Keywords: biohydrometallurgy copper shale
  • Lecture (others)
    Conference European Copper Resource Potential, 29.10.2013, Lubin, Poland

Permalink: https://www.hzdr.de/publications/Publ-19491
Publ.-Id: 19491


Uranium(VI) retention in clay rocks with saline pore waters

Fritsch, K.; Schmeide, K.
Argillaceous rock is considered as one of the possible host rock types for radioactive waste repositories in Germany. Therefore, it is necessary to examine the retention behaviour of argillaceous rock towards long-lived radionuclides, such as uranium. In this study, the bentonite montmorillonite is used as a model clay. The sorption of uranium(VI) onto montmorillonite is studied in NaCl and CaCl2, in dependence on pH and ionic strength.
Keywords: uranium sorption, argillaceous rock,clay, uranium, montmorillonite, high ionic strength
  • Poster
    Kompetenzzentrum Ost für Kerntechnik, 12.12.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19490
Publ.-Id: 19490


Wechselwirkung von Uran(VI) mit Biofilmen

Brockmann, S.; Arnold, T.; Bernhard, G.
Natürliche Biofilme von zwei urankontaminierten Standorten, dem ehemaligen Uranbergwerk in Königstein (Sachsen) und dem Gebiet der ehemaligen Aufstandsfläche der Gessenhalde (Thüringen), wurden in dieser Arbeit näher untersucht. An beiden Standorten konnte in den Minenwässern die hochmobile, gelöste Uranspezies Uranylsulfat (UO2SO4) als dominierend nachgewiesen werden.
Aufgrund der Instabilität vieler kommerzieller Fluoreszenzfarbstoffe bei niedrigen pH-Werten war eine gezielte Anfärbung der Mikroorganismen in den sauren Biofilmen nicht möglich, ohne den pH-Wert der Biofilmproben anzuheben, was die Probenchemie maßgeblich verändert. In Kooperation mit der Firma DYOMICS (Jena, Deutschland) wurden neue, kommerziell nicht erhältliche, säurestabile Farbstoffe erstmals hinsichtlich ihrer Eignung zur Anfärbung von Mikroorganismen in sauren Biofilmen ohne Veränderung des pH-Wertes sowie der sonstigen Probenchemie getestet. Die neuen Farbstoffe DY-601XL, V07-04118, V07-04146 und DY-613 zeigten eine Eignung für solche Färbungen, da sie eine intensive Anfärbung der Mikroorganismen bei niedrigen pH-Werten unter pH 3 – 4 herbeiführen und außerhalb des Emissionsbereiches von Uran fluoreszieren.
In dieser Arbeit wurde die Fähigkeit von Euglena Mutabilis-Zellen zur Bioakkumulation des Urans im pH-Wertbereich 3 – 6 in den Hintergrundmedien Natriumperchlorat (9 g/l) oder Natriumsulfat (3,48 g/l) an lebenden Zellen untersucht. Unabhängig vom Medium konnte bei sauren pH-Werten um pH 3 – 4 über 90 % des vorgelegten Urans aus den Probelösungen abgetrennt werden.
Die Speziation des an den Euglena-Zellen akkumulierten Urans, wurde mittels laserinduzierter Fluoreszenzspektroskopie (LIFS) untersucht. Es zeigte sich, dass unabhängig vom Hintergrundmedium, Lebenszustand und pH-Wert eine vergleichbare neue Uranspezies an den Zellen gebildet wird. Durch den Vergleich der Daten aus den LIFS-Messungen mit Referenzwerten, konnte die gebildete Uranspezies auf eine Anbindung durch (organo)phosphatische und/oder carboxylische funktionelle Gruppen eingegrenzt werden. Mit Hilfe der zeitaufgelösten FT-IR-Spektroskopie konnte die carboxylische Anbindung des Urans an toten Zellen nachgewiesen werden. Ein Ausschluss der (organo)phosphatischen Komplexierung konnte jedoch mit dieser Methode nicht geführt werden.
Untersuchungen zur Lokalisation des Urans an bzw. in den Zellen, mittels der gekoppelten CLSM/LIFS-Technik zeigten erstmals ein Indiz für die intrazelluläre Akkumulation von Uran in den lebenden Zellen. Ergänzende TEM/EDX-Messungen bestätigten die intrazelluläre Aufnahme und belegen eine Akkumulation in runden bis ovalen Zellorganellen, bei denen es sich vermutlich um Vakuolen oder Vakuolen-ähnliche Vesikel handelt. An den toten Zellen konnte mit diesen Methoden kein Uran detektiert werden. Dies lässt auf eine passive, homogen verteilte Biosorption des Urans an die verfügbaren Bindungsplätze an der Zelloberfläche der toten Biomasse schließen.
Keywords: Uranium – Biofilm – Bioaccumulation - Speciation
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-043 2013
    ISSN: 2191-8708

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Permalink: https://www.hzdr.de/publications/Publ-19489
Publ.-Id: 19489


Simulation of thermal fluid dynamics in parabolic trough receiver tubes with direct steam generation using the computer code ATHLET

Hoffmann, A.; Merk, B.; Hirsch, T.; Pitz-Paal, R.
In the present feasibility study the system code ATHLET, which originates from nuclear engineering, is applied to a parabolic trough test facility. A model of the DISS (DIrect Solar Steam) test facility at Plataforma Solar de Almería in Spain is assembled and the results of the simulations are compared to measured data and the simulation results of the Modelica library "DissDyn". A profound comparison between ATHLET Mod 3.0 Cycle A and the "DissDyn" library reveals the capabilities of these codes. The calculated mass and energy balance in the ATHLET simulations are in good agreement with the results of the measurements and confirm the applicability for thermodynamic simulations of DSG processes in principle. Supplementary, the capabilities of the 6-equation model with transient momentum balances in ATHLET are used to study the slip between liquid and gas phases and to investigate pressure wave oscillations after a sudden valve closure.
Keywords: parabolic trough, direct steam generation, numerical simulation, DISS test facility, Modelica library ’DissDyn’, ATHLET
  • Kerntechnik 79(2014)3, 175-186

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Permalink: https://www.hzdr.de/publications/Publ-19488
Publ.-Id: 19488


Validierung instrumentierter Strömungsfolger in einem Rührbehälter

Reinecke, S.; Hampel, U.
Zur Untersuchung der Prozesse in Mischbehältern wurde am HZDR das Konzept instrumentierter, Strömungsfolger entwickelt. Diese können als auftriebsneutrale Sensorpartikel in großen Behältern, wie z. B. Biogasfermentern, Bioreaktoren und Belebtschlammbecken, eingesetzt werden und erfassen dabei kontinuierlich Prozessparameter. Nach der Rückgewinnung der Sensorpartikel aus dem Prozess werden die Daten einem computergestützten Analysesystem zur Verfügung gestellt. Die entwickelten prototypischen Sensorpartikel bestehen aus auftriebsneutralen Kapseln, welche mit einer integrierten Messelektronik ausgestattet sind. Das Systemkonzept berücksichtigt derzeit miniaturisierte Sensoren für die Umgebungstemperatur, die vertikale Position als Funktion des hydrostatischen Drucks sowie für die Beschleunigung. Die Funktionstüchtigkeit der Sensorpartikel wurde bereits unter realen Strömungsbedingungen von Biogasfermentern nachgewiesen. Im Beitrag werden die Ergebnisse weiterführender Validierungsexperimente mit den Sensorpartikeln in einem Rührbehälter mit Wasser und einer viskosen Glycerin-Lösung bei verschiedenen Rührerdrehzahlen vorgestellt. Die Messdaten der Sensorpartikel lassen Aussagen über die Homogenität der Vermischung, das axiale Strömungsprofil und die Struktur grobballiger Wirbel zu. Weiterhin wurden mit den Sensorpartikeln Zirkulationszeiten ermittelt und mit Referenzdaten aus Salztracermessungen verglichen. Basierend auf den Zirkulationszeiten wurden relevante Parameter von Rührwerksmodellen, wie z. B. Zirkulationsbeiwerte, und Parameter von Dispersionsmodellen, wie die PECLÉT-Zahl, bestimmt. Zudem wurde in dem Rührbehälter das Strömungsfolgeverhalten der Sensorpartikel untersucht und Rückschlüsse auf die Anwendung in z. B. Biogasfermentern gezogen.
Keywords: Strömungsfolger, Sensorpartikel, Autonomer Sensor, Makrovermischung, Modellparameter
  • Open Access Logo Contribution to proceedings
    11. Dresdner Sensor-Symposium, 09.-11.12.2013, Dresden, Deutschland
    11. Dresdner Sensor-Symposium, 978-3-9813484-5-3, 456-461
    DOI: 10.5162/11dss2013/L15
  • Poster
    11. Dresdner Sensor-Symposium, 09.-11.12.2013, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-19487
Publ.-Id: 19487


Instrumentierte Strömungsfolger zur räumlichen Parametererfassung in großskaligen Behältern

Reinecke, S.; Hampel, U.
Zur langzeiterfassung räumlich verteilter Parameter in großskaligen Behältern, wie Chemiereaktoren, Biogasfermentern oder Belebtschlammbecken, wurde ein Konzept instrumentierter, strömungsfolgender Sensoren entwickelt. Diese sind bezogen auf die Makroskale von Mischprozessen in Großbehältern aufgrund ihrer geringen Baugröße als strömende Partikel bzw. Sensorpartikel zu betrachten. In Experimenten an Technikumsanlagen, wie einem Fermenter, einer Blasensäule und einem Schleifenreaktor, wurde die Funktionstüchtigkeit der Sensorpartikel gezeigt. Die Analyse der aufgenommenen Messdaten und die daraus extrahierten räumlichen Parameterprofile zeigen, dass die vorherrschenden Strömungsbedingungen innerhalb des Behälters über einen längeren Zeitraum erfasst werden können und der Zustand des Prozesses abgebildet wird. Es können Aussagen über die Homogenität der Vermischung, die axiale Feststoffverteilung bzw. die Suspensionsgüte, das axiale Strömungsprofil und die Struktur grobballiger Wirbel getroffen werden. Weiterhin können anhand gemessener Zirkulationszeitverteilungen relevante Parameter von Rührwerksmodellen, wie z. B. Zirkulationsbeiwerte und äquivalente Förderhöhen, und Parameter von Dispersionsmodellen, wie die PECLÉT-Zahl, bestimmt werden. Der Beitrag gibt einen Überblick über die Sensortechnik sowie deren Anwendungsprinzip an Kläranlagen und Biogasfermentern und zeigt die derzeitigen Grenzen des Messsystems auf. Weiterhin werden die Ergebnisse der Technikumsversuche vorgestellt. Durch den Vergleich zu Referenzmessungen wird die Qualität der mit den Sensorpartikeln gemessenen Daten verdeutlicht.
  • Contribution to proceedings
    Mess- und Regelungstechnik in abwassertechnischen Anlagen, 15.-16.10.2013, Fulda, Deutschland
    Mess- und Regelungstechnik in abwassertechnischen Anlagen, Konzepte-Erfahrungen-Trends, Hennef: DWA, 978-3-944328-44-7, 33-33
  • Lecture (Conference)
    Mess- und Regelungstechnik in abwassertechnischen Anlagen, 15.-16.10.2013, Fulda, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19486
Publ.-Id: 19486


Analyse leichter Elemente mittels Kernreaktionsanalyse an der Ionenstrahlmikrosonde

Freiherr, C.; Eder, F.; Merchel, S.; Munnik, F.; Neelmeijer, C.; Renno, A.
Ein etabliertes Verfahren der chemischen Analyse mittels Ionenstrahlen ist die simultane Anwendung verschiedener Methoden wie Rutherford Backscattering Spectrometry (RBS), Particle-Induced X-Ray Emission (PIXE), Nuclear Reaction Analysis (NRA) und Particle-Induced Gamma Emission (PIGE). Am Ionenstrahlzentrum des HZDR haben wir die Möglichkeit, derartige Messungen mit einem fokussierten Ionenmikrostrahl durchzuführen, welcher eine laterale Auflösung von bis zu 3x3µm² liefert. Zur Zeit liegt der Schwerpunkt unserer Arbeiten auf der quantitativen Analyse von Lithium, Bor und Fluor. Die Messung derart leichter Elemente wird durch die isotopensensitiven Methoden PIGE und NRA ermöglicht. Hierbei werden durch die beschleunigten Projektilionen Kernreaktionen mit den Atomen der Probe induziert und deren Reaktionsprodukte (Photonen bzw. massive Teilchen) detektiert. Die Eignung verschiedener Kernreaktionen wird diskutiert und erste Resultate anhand untersuchter Referenzmaterialien und geologischer Proben vorgestellt. Zudem werden - dank der Zerstörungsfreiheit der Methoden - hochsensible Kunst- und Kulturgutproben untersucht.
Keywords: Nuclear Reaction Analysis, NRA, Particle-Induced Gamma Emission, PIGE, lithium, boron, fluorine, nuclear microprobe
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 02.04.2014, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-19485
Publ.-Id: 19485


Validation of flow following sensor particles with ERT in a stirred vessel

Reinecke, S.; Deutschmann, A.; Jobst, K.; Hampel, U.
Validation of flow following sensor particles was conducted using ERT in a stirred vessel (volume  80 L) of non-NEWTONIAN liquid. The particles give a significant contrast in the ERT images (5% of signal variation) and thus can be easily detected. Average fluid circulation times were estimated from (i) the measured vertical position of the sensor particle, (ii) the fluctuating ERT signals of single ERT-planes and (iii) the measured mixing times of ERT-NaCl-tracer experiments. The estimated average circulation times of all the three methods are comparable for the two investigated impeller positions. The excellent detectability of the particles and the consistent results confirm the feasibility of the ERT method for further validation of flow following sensor particles in stirred vessels.
Keywords: Flow Follower; Sensor Particle; ERT; Stirred Vessel; Hydrodynamics
  • Open Access Logo Contribution to proceedings
    7th World Congress on Industrial Process Tomography (WCIPT 7), 02.-05.09.2013, Krakow, Poland
    Proceedings of WCIPT7
  • Lecture (Conference)
    7th World Congress on Industrial Process Tomography (WCIPT 7), 02.-05.09.2013, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-19484
Publ.-Id: 19484


Study on a simulation-based scatter correction for high-resolution gamma-ray tomography

Hampel, U.; Wagner, M.; Bieberle, A.
A simulation-based scatter correction algorithm is applied on CT data sets of mockup measurements acquired from the high-resolution gamma-ray tomography system of the Institute of Fluid Dynamics at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Based on the initially reconstructed image and on previous knowledge about the material distributions of the scanned object, a first-order scatter sinogram is simulated which allows a correction of the original data set. For two different mockups, the amount of the scatter and the shape of the imaging artifacts are analyzed.
Keywords: gamma-ray; computed tomography; scatter correction
  • Contribution to proceedings
    7th World Congress on Industrial Process Tomography, WCIPT7, 02.09.-05.12.2013, Kraków, Poland
    Proceedings of WCIPT7

Permalink: https://www.hzdr.de/publications/Publ-19483
Publ.-Id: 19483


Topology and Origin of Effective Spin Meron Pairs in Ferromagnetic Multilayer Elements

Wintz, S.
Topological spin textures, such as vortices or skyrmions, are attracting significant attention because of their intriguing fundamental proper- ties as well as their promising applicability in memory devices or spin torque oscillators. A particular topological texture that was theoreti- cally predicted is the two-dimensional hedgehog state, also known as a ’Spin Meron’. It had been unclear, however, whether this kind of highly divergent magnetization structure can exist in real continuum systems. Only recently, evidence for the occurrence of meron-like states was reported for trilayer elements consisting of two ferromagnetic lay- ers and a non-ferromagnetic interlayer [1]. On this background we now present a direct proof for the existence of meron-like states in trilayer elements via direct magnetic imaging. We also show that in the pres- ence of biquadratic interlayer exchange coupling, such meron-like pair states may even represent the magnetic ground state of the system. Interestingly, the highly divergent magnetization distribution induces an additional, three-dimensional torus vortex that in-turn causes a symmetry break for the allowed topological pair configurations. [1] C. Phatak et al., Phys. Rev. Lett. 108, 067205 (2012). [2] S. Wintz et al., Phys. Rev. Lett. 110, 177201 (2013).
Keywords: spin textures, topology
  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19482
Publ.-Id: 19482


Bayesian trend analysis of extreme wind using observed and hindcast series o Catalan coast, NE Mediterranean Sea

Egozcue, J. J.; Ortego, M. I.; Tolosana-Delgado, R.
It has been suggested that climate change might modify the occurrence rate and magnitude of large ocean-wave and wind storms. The hypothesised reason is the increase of available energy in the atmosphere-ocean system. Forecasting models are commonly used to assess these effects, given that good quality data series are often too short. However, forecasting systems are often tuned to reproduce the average behavior, and there are concerns on their representativity for extremal regimes. We present a methodology of simultaneous analysis of observed and hindcasted data with the aim of extracting potential time drifts as well as systematic regime discrepancies between the two data sources. The method is based on the Peak-Over- Threshold (POT) approach and the Generalized Pareto Distribution (GPD) within a Bayesian estimation framework. In this context, storm events are considered points in time, and modelled as a Poisson process. Storm magnitude over a reference threshold is modelled with a GPD, a flexible model that captures the tail behaviour of the magnitude distribution. All model parameters, i.e. shape and location of the magnitude GPD and the Poisson occurrence rate, are affected by a trend in time. Moreover, a systematic difference between parameters of hindcasted and observed series is considered. Finally, the posterior joint distribution of all these trend parameters is studied using a conventional Gibbs sampler. This method is applied to compare hindcast and observed series of 10-minute average windspeed at a deep buoy location off the Catalan coast (NE Spain, Western Mediterranean; buoy data from 2001; REMO wind hindcasting from 1958 on). Appropriate scale and domain of attraction are discussed, and the reliability of trends in time are addressed.

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Permalink: https://www.hzdr.de/publications/Publ-19481
Publ.-Id: 19481


The radiation reaction effect in ultra intense laser foil interactions

Klimo, O.; Jirka, M.; Masek, M.; Limpouch, J.; Bussmann, M.; Korn, G.
Since the radiation reaction effect on electron propagation is very small in most cases, it can be usually neglected and the Lorentz force equation can be applied. However, ultra-intense lasers with normalized vector potential of the order of 100 can accelerate electrons to relativistic velocities with very high gamma factor. When the electron is accelerated to such high velocities the amount of emitted radiation may become large and radiation damping and emission of energetic photons should be considered. This work studies the influence of the radiation reaction force on laser interaction with solid foil targets. It compares different approaches adopted in PIC simulations to take into account the radiation reaction. The simulations of a counter-propagating relativistic electron and an ultra-intense laser beam demonstrate a strong energy loss of electrons due to non-linear Compton scattering. The interaction of ultra-intense laser pulse with solid foil is studied using PIC simulations. It is shown that the effect of radiation reaction strongly depends on the recirculation of high-energy electrons. When the recirculation is efficient, the radiation coming from the target is much more intense and it shows different spectral and angular characteristics.
Keywords: radiation reaction, laser, acceleration, ion, solid density, target, electron, particle-in-cell, pic, simulation
  • Contribution to proceedings
    SPIE Optics and Optoelectronics 2013, 15.-18.04.2013, Praha, Česká republika
    Proceedings of the SPIE 8780, High-Power, High-Energy, and High-Intensity Laser Technology; and Research Using Extreme Light: Entering New Frontiers with Petawatt-Class Lasers: SPIE, 87801O
    DOI: 10.1117/12.2017213

Permalink: https://www.hzdr.de/publications/Publ-19480
Publ.-Id: 19480


Kluge et al. Reply

Kluge, T.; Cowan, T. E.; Debus, A.; Schramm, U.; Zeil, K.; Bussmann, M.
A Reply to the Comment by C. Thaury et al.
Keywords: electron temperature, relativistic, scaling, laser, pulse, ultra-short, high-power

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Permalink: https://www.hzdr.de/publications/Publ-19479
Publ.-Id: 19479


Stratified & Segregated Flow Modelling - Interfacial Area Density Models – AIAD

Höhne, T.
Today: Limits in simulating stratified & segregated two phase flow
Algebraic Interfacial Area Density Model (AIAD)
Free Surface Drag
Turbulence Damping
Sub-grid wave turbulence (SWT)
Verification and Validation is going on – more experimental data are required for the validation
Keywords: AIAD, Free Surface Drag, Sub-grid wave turbulence (SWT)
  • Lecture (Conference)
    11th Short Course “Multiphase Flow: Simulation,Experiment and Application”, 26.-27.11.2013, Dresden, Deutschland
  • Contribution to proceedings
    11th Short Course “Multiphase Flow: Simulation, Experiment and Application”, 26.-27.11.2013, Dresden, Deutschland
    CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-19478
Publ.-Id: 19478


Characterization of gas-liquid flow mixing by means of helical static mixer

Rabha, S.; Krepper, E.; Zidouni, F.; Grugel, F.; Schubert, M.; Rzehak, R.; Lucas, D.; Hampel, U.
Static mixer is an attractive alternative to conventional gas-liquid contactor, widely used for mixing and heat transfer between two fluids in various process applications. Knowledge on the limits of number and dimension of the static mixer element are important for packing optimization for desired mixing. The present work are designed to investigate the flow mixing pattern in a upward gas-liquid (air - water) flows in a column packed with helical static mixer. Experiments are carried out in a column of diameter (DT = 0.08 m) packed with helical static mixer (length 80 mm/ diameter 80 mm) using ultrafast electron beam X- ray tomography. The effect of number of static mixer element (3 – 9), liquid velocity (UL = 0.02 & 0.6 m/s), gas velocity (0.15 ≤ UG ≤ 0.6 m/s) on hydrodynamic parameters like gas holdup, bubble size distribution, etc. and pressure drop across the static mixer are studied. Corresponding CFD simulations using the Euler-Euler model implemented in CFX 14 for some selective cases are also done. The predicted axial and radial gas phase distribution considering different mono-dispersed bubbles classes (3, 5.8 and 8 mm) and poly-dispersed bubble classes are studied and validated with experimental results.
Keywords: Static mixer, gas-liquid flows, ultrafast electron beam X-ray tomography, Euler-Euler
  • Lecture (Conference)
    11th Multiphase flow conference and short course, 26.-28.11.2013, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19477
Publ.-Id: 19477


A Baseline Model for Monodispersed Bubbly Flow

Rzehak, R.; Ziegenhein, T.; Krepper, E.; Lucas, D.
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. A large body of work using different closure relations of varying degree of sophistication exists, but no complete, reliable, and robust formulation has been achieved so far.

As a step towards this goal, an attempt is made here to collect the best available description for all aspects known to be relevant for adiabatic bubbly flows where only momentum is exchanged between liquid and gas phases. The resulting baseline model is validated against a number of data sets taken from the literature. Quantitative deviations between simulated and measured values indicate the need for further model development. The main advantage however is, that no model adjustment has been made at all for the different data sets.
Keywords: dispersed gas liquid multiphase flow, Euler Euler two fluid model, fixed polydispersity, closure relations, CFD simulation, model validation
  • Lecture (Conference)
    Joint HZDR & ANSYS Conference - 11th Multphase Flow Conference & Short Course - Simulation, Experiment and Application, 26.-28.11.2013, Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19476
Publ.-Id: 19476


Multi-Scale Modelling Techniques - GENTOP

Lucas, D.; Hänsch, S.
In multiphase flows interfaces may span over a wide range of sizes. In a multi fluid approach interfaces smaller as well as larther than the typical size of the numerical grid may occur. While the small interfaces (bubbles and drops) should be represent by smeared phase volume fractions the large structures should be resolved in a CFD simulation. Also transitions between contineous and dispersed morphologies of teh phases may occur.
The lecture discusses the issues for modelling such flows and the basic ideas of the GENTOP concept. Domonstration simulations using the GENTOP concept show the cpabablities of this approach.
Keywords: multiphase, morphology, multi-scale, bubble, drop, seggregated flow, coalescence, breakup
  • Lecture (Conference)
    11th Multiphase Flow Conference and Short Course, 26.-28.11.2013, Dresden, Deutschland
  • Lecture (Conference)
    12th Multiphase Flow Conference and Short Course, 25.-27.11.2014, Dresden, Deutschland
  • Lecture (Conference)
    13th Multiphase Flow Conference and Short Course, 24.-26.11.2015, Dresden, Deutschland
  • Lecture (Conference)
    14th Multiphase Flow Conference and Short Course, 08.-10.11.2016, Dresden, Deutschland
  • Lecture (Conference)
    17th Multiphase Flow Conference and Short Course, 11.-15.11.2019, Dresen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19474
Publ.-Id: 19474


Visualisation of boiling processes in a 3x3 rod bundle using ultrafast X-ray tomography

Barthel, F.; Franz, R.; Hampel, U.
Boiling processes are an effective way of heat transfer in thermo hydraulic facilities, such as heat exchangers and reactor cores of nuclear power plants. To run these processes safe and efficient comprehensive studies of flow physics within boiling fluids are needed. Within the frame of the coordinated project “Modeling, simulation and experiments for boiling phenomena in pressurized water reactors” (BMBF FZK 02NUK010) HZDR developed and built up an experimental facility for the study of boiling flows in 3 × 3 rod bundle geometry. While representing a fuel element segment of a pressurized water reactor, the bundle depicts every main geometrical dimension. The facility is operated with RC318 refrigerant fluid. The bundle is electrically heated by a dc power supply, which allows heat flux values of up to 0.2MW/m². Ultrafast electron beam X-ray tomography has been used at this experiment. Therefore the bundle was designed for a coaxial electrical current to flow through, to minimize the residual magnetic field, which would interfere with the electron beam deflection. Thus, the center rod - outer rod heat flux ratio is 64:1. The boiling processes will be expected around the centre rod. Beside standard instrumentation for fluid temperature, pressure and flow rate an extensive thermo-instrumentation of centre rod allows axial rod wall temperature measurements and safely shut down when exceeding a certain surface temperature. The goal of these experiments is to gain Access to very transient boiling phenomena, such as quenching or pulsating of vaporized fluid in bündle geometries with previously unseen temporal resolution. First experimental results have been achieved and will be introduced and discussed in this article.
Keywords: electron beam computed tomography, boiling processes, rod bundle
  • Lecture (Conference)
    7th World Congress on Industrial Process Tomography - WCIPT7, 02.-05.09.2013, Kraukow, Poland

Permalink: https://www.hzdr.de/publications/Publ-19473
Publ.-Id: 19473


Work in Progess Seminar: PIConGPU - The World's Fastest Particle-in-Cell Plasma Simulation

Huebl, A.; Pausch, R.; Bussmann, M.; Burau, H.; Bernholdt, D. E.; Cowan, T. E.; Debus, A.; Garten, M.; Helm, A.; Juckeland, G.; Kluge, T.; Liebschner, S.; Nagel, W. E.; Pugmire, D.; Schmitt, F.; Schneider, B.; Schramm, U.; Schuchart, J.; Steiniger, K.; Widera, R.
WIP Seminar from November 29th, 2013. Particle-in-Cell algorithm, GPUs, PIConGPU, recent topics.
Keywords: PIConGPU, Accelerator, CUDA, Laser Particle, Acceleration, Simulation, Gordon Bell
  • Lecture (others)
    Work-in-Process (WIP) Seminar, 29.11.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19472
Publ.-Id: 19472


Ultrafast 3D X-ray tomography of a wire-mesh sensor in operation in a two-phase flow

Bieberle, M.; Stürzel, T.; Hampel, U.; Laurien, E.
An ultrafast 3D X-ray tomography modality (3D-CT) has been developed in order to study highly dynamic interface structures in multiphase flows. The wire-mesh sensor (WMS) is an intrusive measurement device that quantifies the phase fraction distribution of a two-phase flow within the cross-section of a pipe or column. The WMS is a valuable low-cost imaging technique, but is known to affect the flow at low liquid superficial velocities, which leads to overestimation of the measured gas fraction. In this study, the influencing effect of a WMS on a water-air two-phase flow has been investigated in detail by simultaneous 3D-CT imaging.
Keywords: ultrafast; 3D imaging; X-ray; computed tomography; wire-mesh sensor
  • Lecture (Conference)
    7th World Congress on Industrial Process Tomography, WCIPT7, 02.-05.09.2013, Krakow, Poland
  • Contribution to proceedings
    7th World Congress on Industrial Process Tomography, WCIPT7, 02.-05.09.2013, Krakow, Poland
    Proceedings of WCIPT7, 595-604

Permalink: https://www.hzdr.de/publications/Publ-19471
Publ.-Id: 19471


Interaction of U(VI) with Äspö diorite: A batch and in situ ATR FT-IR sorption study

Schmeide, K.; Gürtler, S.; Müller, K.; Steudtner, R.; Joseph, C.; Bok, F.; Brendler, V.
Pristine diorite drill cores, obtained from the Äspö Hard Rock Laboratory (HRL, Sweden), were used to study the retention behavior of fresh, anoxic crystalline rock material towards the redox-sensitive uranium. Batch sorption experiments and spectroscopic methods were applied for this study. The impact of various parameters, such as solid-to-liquid ratio (2 to 200 g/L), grain size (0.063 – 0.2 mm, 0.5 – 1 mm, 1 – 2 mm), temperature (room temperature and 10 °C), contact time (5 to 108 days), initial U(VI) concentration (3x10-9 to 6x10-5 M), and background electrolyte (synthetic Äspö groundwater and 0.1 M NaClO4) on the U(VI) sorption onto anoxic diorite was studied under anoxic conditions (N2). Comparatively, U(VI) sorption onto oxidized diorite material was studied under ambient atmosphere (pCO2 = 10-3.5 atm). Conventional distribution coefficients, Kd, and surface area normalized distribution coefficients, Ka, were determined. The Kd value for the U(VI) sorption onto anoxic diorite in Äspö groundwater under anoxic conditions by investigating the sorption isotherm amounts to 3.8 ± 0.6 L/kg which corresponds to Ka = 0.0030 ± 0.0005 cm (grain size 1 – 2 mm). This indicates a weak U sorption onto diorite which can be attributed to the occurrence of the neutral complex Ca2UO2(CO3)3(aq) in solution. This complex was verified as predominating U species in synthetic Äspö groundwater by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Compared to U sorption at room temperature under anoxic conditions, U sorption is further reduced at decreased temperature (10 °C) and under ambient atmosphere. The U species in aqueous solution as well as sorbed on diorite were studied by in situ time-resolved attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. A predominant sorbing species containing a UO2(CO3)34- moiety was identified. The extent of U sorption onto diorite was found to depend more on the low sorption affinity of the Ca2UO2(CO3)3(aq) complex than on reduction processes of uranium.
Keywords: uranium, granite, adsorption, infrared spectroscopy, laser fluorescence spectroscopy, speciation, Ca2UO2(CO3)3(aq), calcium uranyl carbonate

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Permalink: https://www.hzdr.de/publications/Publ-19470
Publ.-Id: 19470


Determination of bubble velocities in vertical gas-liquid pipe flows using ultrafast X-ray tomography

Banowski, M.; Patmonoaji, A.; Lucas, D.; Hampel, U.
The development of new two-phase flow CFD models is an important goal for industry and research. Such new CFD models have to be validated with suitable experimental quantitative data with high spatial and temporal resolution. Such data are generated by wide experimental series at the vertical titanium pipe test section of the TOPFLOW test facility. Using ultrafast X-ray tomography, air-water and steam-water experiments at co-current upward and downward flows were performed as soon as counter current flows. These generated data were segmentated and analyzed with in-house codes into quantitative data like gas hold ups, velocity profiles, bubble size distributions or interfacial area densities.
In this publication, different methods for determining bubble velocities are presented. The results are discussed as soon as compared.
Keywords: Two-phase flow, bubbles, velocity, X-ray tomography, TOPFLOW
  • Lecture (Conference)
    11th Multiphase Flow Conference and Short Course, 26.-28.11.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19469
Publ.-Id: 19469


RPV long term operation: open issues

Ballesteros, A.; Altstadt, E.
This paper describes key open issues which are being debated nowadays by experts in the field, and for which clarification is essential for a safe operation of the nuclear power plants during life extension. Notably: late blooming effects in low Cu steels; effects of Cu, Ni, Mn, and P on the irradiated microstructure and on hardening and embrittlement; use of material test reactor data for assessment in power reactors (including flux and spectrum effects); Master Curve versus Unified Curve and fracture toughness behavior of highly irradiated material; embrittlement in RPV zones out of the traditional beltline (“the expanding beltline”); embrittlement trend curves at high neutron fluence, where data are scarce; re-embrittlement after annealing.
Keywords: Reactor pressure vessel, Neutron embrittlement, Long term operation, Flux effect, Late Blooming

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Permalink: https://www.hzdr.de/publications/Publ-19468
Publ.-Id: 19468


Monitoring radiation embrittlement during life extension periods

Ballesteros, A.; Altstadt, E.; Gillemot, F.; Hein, H.; Wagemans, J.; Rouden, J.; Barthelmes, J.; Wilford, K.; Serrano, M.; Brumovsky, M.; Chaouadi, R.; Ortner, S.
This paper presents guidelines to monitor radiation embrittlement of reactor pressure vessels (RPV) during life extension periods (to 60 or 80 years) or for the long term operation of nuclear power plants (NPP). The guidelines were developed in 2012-2013 by a Task Group of the international project LONGLIFE. The work performed responds to the need of guidance to treat long term irradiation effects within the ageing management of NPPs, since the standard RPV surveillance programmes were designed only to cover a time period of 40 years. The guidelines intend to support specialists in the field and managers in the plant to choose among the most adequate techniques and methods available today to extend the use of their current RPV surveillance programme beyond design life, or implement a new programme when needed. The study performed identifies weaknesses of the standard surveillance programmes in providing data needed for long term operation, and proposes solutions and tools to solve and/or mitigate the lack or scarcity of surveillance material for their use in life extension. Guidance is also given on methods and strategies to generate reliable surveillance data in the high fluence range.
Keywords: Reactor pressure vessel, Long term operation, Neutron embrittlement, Surveillance

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Permalink: https://www.hzdr.de/publications/Publ-19467
Publ.-Id: 19467


Self-organized surface nanopatterns on Cd(Zn)Te crystals induced by medium-energy ion beam sputtering

Gago, R.; Vazquez, L.; Agullo-Rueda, F.; Vinnichenko, M.; Carcelen, V.; Olvera, J.; Plaza, J. L.; Dieguez, E.
Cadmium telluride (CT) and Zn-doped (similar to 4 at%) CT (CZT) crystals grown by the Bridgman method were mechanically polished to achieve mirror-like surfaces and subsequently irradiated with medium-energy (30-200 keV) Ar+ ions under oblique incidence (60 degrees with respect to the target normal). Atomic force microscopy shows that ion sputtering induces the formation of self-organized ripple nanopatterns with wavevector parallel to the ion beam projection on the surface on both CT and CZT targets. The ripple wavelength and amplitude (surface roughness) increase with ion energy. Even with such low doping level, the pattern formation dynamics differs between both materials and, in general, CZT surfaces roughen more easily than CT. In addition, an orthogonal ripple mode develops for extended irradiation, which is more prominent in CZT crystals. Spectroscopic ellipsometry reveals that the C(Z) T crystals have a high radiation hardness since ion bombardment does not induce an amorphized surface layer. This fact also implies that the nanostructured surfaces have significant photoluminescence response, one to two orders of magnitude larger than from as-prepared crystals. These results show that large-area (similar to cm(2)) surface nanostructuring by ion beams can be implemented in the fabrication of future C(Z) T-based devices.
Keywords: THIN-FILMS; CDTE; EVOLUTION; CDZNTE; BOMBARDMENT; ROUGHNESS; EPITAXY

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Permalink: https://www.hzdr.de/publications/Publ-19466
Publ.-Id: 19466


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