Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Development of Radioligands for PET Imaging of Neurodegeneration
Brust, P.;
  • Invited lecture (Conferences)
    Kolloquiumsreihe des Universitätsklinikums Tübingen, 22.07.2013, Tübingen, Deutschland

Publ.-Id: 19526 - Permalink


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

Publ.-Id: 19525 - Permalink


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

Publ.-Id: 19523 - Permalink


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.

Publ.-Id: 19522 - Permalink


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

Publ.-Id: 19521 - Permalink


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

Publ.-Id: 19520 - Permalink


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

Publ.-Id: 19519 - Permalink


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

Publ.-Id: 19518 - Permalink


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

Publ.-Id: 19517 - Permalink


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

Publ.-Id: 19516 - Permalink


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

Publ.-Id: 19515 - Permalink


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

Publ.-Id: 19514 - Permalink


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

Publ.-Id: 19513 - Permalink


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

Publ.-Id: 19512 - Permalink


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

Publ.-Id: 19511 - Permalink


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

Publ.-Id: 19510 - Permalink


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

Publ.-Id: 19509 - Permalink


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

Publ.-Id: 19508 - Permalink


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

Publ.-Id: 19507 - Permalink


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

Publ.-Id: 19506 - Permalink


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

Publ.-Id: 19505 - Permalink


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

Publ.-Id: 19504 - Permalink


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 LogoContribution to proceedings
    The 45th Annual Meeting on Nuclear Technology, 06.-08.05.2014, Frankfurt, Deutschland

Publ.-Id: 19503 - Permalink


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

Publ.-Id: 19502 - Permalink


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

Publ.-Id: 19501 - Permalink


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

Publ.-Id: 19499 - Permalink


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

Publ.-Id: 19497 - Permalink


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

Publ.-Id: 19496 - Permalink


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

Publ.-Id: 19495 - Permalink


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

Publ.-Id: 19494 - Permalink


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

Publ.-Id: 19493 - Permalink


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

Publ.-Id: 19492 - Permalink


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

Publ.-Id: 19491 - Permalink


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

Publ.-Id: 19490 - Permalink


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 LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-043 2013
    ISSN: 2191-8708

Downloads:

Publ.-Id: 19489 - Permalink


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

Publ.-Id: 19488 - Permalink


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 LogoContribution 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

Publ.-Id: 19487 - Permalink


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

Publ.-Id: 19486 - Permalink


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

Publ.-Id: 19485 - Permalink


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 LogoContribution 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

Publ.-Id: 19484 - Permalink


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

Publ.-Id: 19483 - Permalink


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

Publ.-Id: 19482 - Permalink


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.

Publ.-Id: 19481 - Permalink


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

Publ.-Id: 19480 - Permalink


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

Publ.-Id: 19479 - Permalink


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

Publ.-Id: 19478 - Permalink


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

Publ.-Id: 19477 - Permalink


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

Publ.-Id: 19476 - Permalink


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

Publ.-Id: 19474 - Permalink


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

Publ.-Id: 19473 - Permalink


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

Publ.-Id: 19472 - Permalink


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

Publ.-Id: 19471 - Permalink


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

Publ.-Id: 19470 - Permalink


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

Publ.-Id: 19469 - Permalink


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

Publ.-Id: 19468 - Permalink


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

Publ.-Id: 19467 - Permalink


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

Publ.-Id: 19466 - Permalink


Hydroxyalkylation with Cyclic Sulfates: Synthesis of Carbazole Derived CB2 Ligands with Increased Polarity
Lueg, C.; Galla, F.; Frehland, B.; Schepmann, D.; Daniliuc, C. G.; Deuther-Conrad, W.; Brust, P.; Wünsch, B.;
In order to increase the polarity of the potent CB2 ligand 1a, the homologous hydroxyalkyl carbazoles 2a–c were prepared and pharmacologically evaluated. An important step in the synthesis is the hydroxyalkylation of carbazole with cyclic sulfates providing the 2-hydroxyethyl and 3-hydroxypropyl derivatives 5a and 5b in a one-step reaction. The final propionamides 2a–c were prepared using the recently reported coupling reagent COMU1. The X-ray crystal structure of 2c displays an almost coplanar arrangement of the 3-phenyl-1,2,4-oxadiazole biaryl system. The increased polarity of 2a is associated with an almost 100-fold reduced CB2 affinity. The 3-hydroxypropyl derivative 2b represents the best compromise between lipophilicity and CB2 affinity (Ki=33 nM).
Keywords: Carbazole derivatives CB2 receptor ligands Cyclic sulfates Structure affinity relationships X-ray crystal structure analysis

Publ.-Id: 19465 - Permalink


Hybridization-driven orthorhombic lattice instability in URu2Si2
Yanagisawa, T.; Mombetsu, S.; Hidaka, H.; Amitsuka, H.; Akatsu, M.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Huang, K.; Janoschek, M.; Maple, M. B.;
We have measured the elastic constant (C11-C12)/2 in URu2Si2 by means of high-frequency ultrasonic measurements in pulsed magnetic fields H ║ [001] up to 61.8 T in a wide temperature range from 1.5 to 116 K. We found a reduction of (C11-C12)/2 that appears only in the temperature and magnetic field region in which URu2Si2 exhibits a heavy-electron state and hidden order. This change in (C11-C12)/2 appears to be a response of the 5f electrons to an orthorhombic and volume conservative strain field εxxyy with Γ3 symmetry. This lattice instability is likely related to a symmetry-breaking band instability that arises due to the hybridization of the localized f electrons with the conduction electrons and is probably linked to the hidden-order parameter of this compound.

Publ.-Id: 19464 - Permalink


Thermodynamic properties of the anisotropic frustrated spin-chain compound linarite PbCuSO4(OH)2
Schäpers, M.; Wolter, A. U. B.; Drechsler, S.-L.; Nishimoto, S.; Müller, K.-H.; Abdel-Hafiez, M.; Schottenhamel, W.; Büchner, B.; Richter, J.; Ouladdiaf, B.; Uhlarz, M.; Beyer, R.; Skourski, Y.; Wosnitza, J.; Rule, K. C.; Ryll, H.; Klemke, B.; Kiefer, K.; Reehuis, M.; Willenberg, B.; Süllow, S.;
We present a comprehensive macroscopic thermodynamic study of the quasi-one-dimensional (1D) s =½ frustrated spin-chain system linarite. Susceptibility, magnetization, specific heat, magnetocaloric effect, magnetostriction, and thermal-expansion measurements were performed to characterize the magnetic phase diagram. In particular, for magnetic fields along the b axis five different magnetic regions have been detected, some of them exhibiting short-range-order effects. The experimental magnetic entropy and magnetization are compared to a theoretical modeling of these quantities using density matrix renormalization group (DMRG) and transfer matrix renormalization group (TMRG) approaches.Within the framework of a purely 1D isotropic model Hamiltonian, only a qualitative agreement between theory and the experimental data can be achieved. Instead, it is demonstrated that a significant symmetric anisotropic exchange of about 10% is necessary to account for the basic experimental observations, including the three-dimensional (3D) saturation field, and which in turn might stabilize a triatic (three-magnon) multipolar phase.

Publ.-Id: 19463 - Permalink


Entwicklung, Synthese und F-18-Markierung eines fluoralkylierten Triazinderivates zur Bildgebung der Phosphodiesterase 2A mittels PET
Schröder, S.; Wenzel, B.; Kranz, M.; Egerland, U.; Teodoro, R.; Deuther-Conrad, W.; Fischer, S.; Höfgen, N.; Steinbach, J.; Brust, P.;
Ziel/Aim:
Phosphodiesterasen (PDE´s) sind Enzyme, die in allen menschlichen Zellen exprimiert werden und die zyklischen Nucleotide cAMP und/oder cGMP hydrolysieren. PDE-Inhibitoren verzögern den Abbau dieser sekundären Botenstoffe und beeinflussen physiologische Prozesse. Die PDE2A zeigt eine hohe, spezifische Expression im Gehirn sowie in bestimmten Tumoren und ist vermutlich an der Pathophysiologie entsprechender Erkrankungen beteiligt. Ziel unserer Arbeiten ist die Darstellung eines radiomarkierten PDE2A-Inhibitors für die Bildgebung der PDE2A mittels PET.

Methodik/Methods:
Ausgehend von einer Triazin-Leitstruktur (1) wurden ein neues Fluorpropyl-Derivat* als Referenzverbindung für Affinitätsstudien sowie der entsprechende Tosylat-Präkursor für eine einstufige F-18-Markierung entwickelt. Die nukleophile F-18-Fluorierung erfolgte in Acetonitril bei 80°C in 15 Minuten. Der Radioligand wurde mittels semi-präparativer HPLC isoliert, über eine RP18 light SPE-Kartusche gereinigt und in 0,9%iger NaCl-Lösung formuliert. Die Analytik des Endproduktes erfolgte mittels Radio-DC und Radio-HPLC.
* 9-(2-Fluor-5-(3-fluorpropoxy)phenyl)-2-methoxy-7-methylimidazo[5,1-c]pyrido[2,3-e][1,2,4]triazin

Ergebnisse/Results:
Die Leitstruktur (IC50: 4,12 nM**), das neue Fluorpropyl-Derivat (IC50: 11,4 nM**) und der Tosylat-Präkursor wurden mit einer Gesamtsyntheseausbeute von je 70 - 80% erhalten. Der Radioligand wurde mit einer Markierungsausbeute von 75,4 ± 4,9% (n = 5), einer radiochemischen Ausbeute von ~ 57% (n = 2), einer spezifischen Aktivität von ~ 54 GBq/µmol (n = 2) und einer radiochemischen Reinheit von ≥ 99,5% erfolgreich synthetisiert.
** Enzymassay (1)

Schlussfolgerungen/Conclusions:
Die bisherigen Ergebnisse zeigen, dass ein neuartiger F-18-markierter und hochaffiner PDE2A-Radioligand erfolgreich dargestellt werden kann. Die Charakterisierung dieses neuen F-18-Propyl-Derivates wird mittels TierPET/MR und Untersuchungen zur Metabolisierung sowie Autoradiographie erfolgen.

Literatur/References:
(1) Patent WO2010/054253 A1
  • Lecture (Conference)
    Nuklearmedizin2014, 26.-29.03.2014, Hannover, Deutschland
  • Open Access LogoAbstract in refereed journal
    Nuklearmedizin 53(2014), A44

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Publ.-Id: 19462 - Permalink


CMR-B-Scalar Sensor Application for High Magnetic Field Measurement in Nondestructive Pulsed Magnets
Balevičius, S.; Žurauskienė, N.; Stankevič, V.; Herrmannsdörfer, T.; Zherlitsyn, S.; Skourski, Y.; Wolff-Fabris, F.; Wosnitza, J.;
In this paper, we present the investigation of the axial and radial magnetic-field distribution inside and outside of the bore of a nondestructive pulsed-field coil presently installed at the Dresden High Magnetic Field Laboratory (HLD). The array used for these magnetic-field measurements was made up of three CMR-B-scalar sensors based on nanostructured La-Sr-Mn-O films. The investigations were performed at a temperature of 270 K and at a peak field of 46 T. The experimental results fit well with calculations obtained using ANSYS code based on the finite element method (FEM). It is concluded that the CMR-B-scalar sensors can be successfully used for the investigation of the magnetic-field distribution in pulsed high magnetic field coils.

Publ.-Id: 19461 - Permalink


Development and validation of models for bubble coalescence and breakup
Liao, Y.;
A generalized model for bubble coalescence and breakup has been developed, which is based on a comprehensive survey of existing theories and models. One important feature of the model is that all important mechanisms leading to bubble coalescence and breakup in a turbulent gas-liquid flow are considered. The new model is tested extensively in a 1D Test Solver and a 3D CFD code ANSYS CFX for the case of vertical gas-liquid pipe flow under adiabatic conditions, respectively. Two kinds of extensions of the standard multi-fluid model, i.e. the discrete population model and the inhomogeneous MUSIG (multiple-size group) model, are available in the two solvers, respectively. These extensions with suitable closure models such as those for coalescence and breakup are able to predict the evolution of bubble size distribution in dispersed flows and to overcome the mono-dispersed flow limitation of the standard multi-fluid model.
For the validation of the model the high quality database of the TOPFLOW L12 experiments for air-water flow in a vertical pipe was employed. A wide range of test points, which cover the bubbly flow, turbulent-churn flow as well as the transition regime, is involved in the simulations. The comparison between the simulated results such as bubble size distribution, gas velocity and volume fraction and the measured ones indicates a generally good agreement for all selected test points. As the superficial gas velocity increases, bubble size distribution evolves via coalescence dominant regimes first, then breakup-dominant regimes and finally turns into a bimodal distribution. The tendency of the evolution is well reproduced by the model. However, the tendency is almost always overestimated, i.e. too much coalescence in the coalescence dominant case while too much breakup in breakup dominant ones. The reason of this problem is discussed by studying the contribution of each coalescence and breakup mechanism at different test points. The redistribution of the gaseous phase from the injection position at the pipe wall to the whole cross section is overpredicted by the Test Solver especially for the test points with high superficial gas velocity. Besides the models for bubble forces, the simplification of the Test Solver to a 1D model has an influence on the redistribution process. Simulations performed using CFX show that a considerable improvement is achieved with comparison to the results delivered by the standard closure models. For the breakup-dominant cases, the breakup rate is again overestimated and the contribution of wake entrainment of large bubbles is underestimated. Furthermore, inlet conditions for the liquid phase, bubble forces as well as turbulence modeling are shown to have a noticeable influence, especially on the redistribution of the gaseous phase.
Keywords: multi-fluid model, coalescence model, breakup model, coalescence frequency, breakup frequency
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-041 2013
    ISSN: 2191-8708
  • Doctoral thesis
    TU Dresden, 2013
    204 Seiten

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Publ.-Id: 19460 - Permalink


Improving processing by adaptation to conditional geostatistical simulation of block compositions
Tolosana-Delgado, R.; Mueller, U.; van den Boogaart, K. G.; Ward, C.; Gutzmer, J.;
Theoretically, exploitation of an ore deposit could be optimized by adapting the beneficiation processes to the properties of each individual ore block being extracted. Such an adaptation can involve switching on and off certain processes, or setting their controlling parameters. These decisions depend typically on physical and chemical attributes. Physical parameters are relevant both at macroscopic and microscopic scale, whereas chemical attributes include both the concentration of the value element, and the presence and abundance of penalty elements. As a first step towards adaptive processing, this contribution explores mapping those adaptive decisions which are based on the composition in value and penalty elements of the selective mining unit or mining block.

Cokriging and geostatistical simulation are reasonable tools to provide information about the concentration of these elements, both in expected value and uncertainty. However, when the sum of total penalty and value elements approaches 100%, it is mandatory that geostatistical results do not exceed that sum. Moreover, some processing techniques work by applying a filter to the composition of material that is being processed, so that their partial output concentration can be taken as a known portion of their input concentration. In such a context, the use of geostatistics on the raw data will deliver inconsistent results, which can be avoided via log-ratio methods: a one-to-one log-ratio transformation is applied to the raw data, followed by modelling via classical multivariate geostatistical tools, and subsequent back-transform of predictions and simulations. Results satisfy the constant sum constraints by construction, even in simulations. Furthermore, filtering processes behave linearly if expressed in terms of log-ratios.

To illustrate the approach, a toy example is used, where a 4-component system (consisting of a value element, two penalty elements and some liberable material, each representing a material type or a set of minerals) is beneficiated through a chain of technical processes. A sequence of milling, desliming and flotation is applied to separate most of the value element, and the product is classified in three qualities. Knowing all processing costs and selling prices, a compositional geostatistical simulation framework can be run to map the best processing choices and qualities as a function of the available measurements of the percentages of the four components, instead of mapping these percentages themselves. In doing so, the uncertainty about gains can be quantified at the same time.
Keywords: Change of support, compositional data analysis, geometallurgy, stochastic optimisation
  • Open Access LogoThe Journal of the Southern African Institute of Mining and Metallurgy 115(2015), 13-26

Publ.-Id: 19459 - Permalink


Coolant mixing experiments in the upper plenum of the ROCOM test facility
Prasser, H.-M.; Kliem, S.;
We have performed measurements of the turbulent mixing in the upper plenum of the ROCOM test facility sometimes ago (Grunwald et al., 2003). Since the data reflects the phenomenon very clearly, we are convinced that the results of the experiments can be used for the code validation with regard to the described effect.

Publ.-Id: 19458 - Permalink


Fracture mechanics characterisation of reactor pressure vessel multi-layer weld metal
Viehrig, H.-W.; Houska, M.; Kalkhof, D.; Schindler, H.-J.;
Fracture toughness of the multi-layer beltline welding seam of the Biblis C reactor pressure vessel was characterized by the test standard ASTM E1921. The reference temperature, T0, was determined for different thickness positions of the multi-layer welding seam. Additionally, the influence of the specimen orientation on T0 was investigated. In contrast to the T-S orientation (crack extension through the thickness) the crack front of the T-L oriented specimens (crack extension in welding direction) penetrates several welding beads. By means of fractographic and metallographic analyses it was shown that the distribution of the crack initiation sites is not necessarily correlated to the structure of the different welding beads along the crack front. Furthermore, it was found that the scatter of the KJc values determined with T-S specimens is significantly higher than in case of the T-L specimens. T0 values measured at different thickness locations of the multi-layer welding seam vary in a range of about 40 K.
Keywords: reactor pressure vessel, multi-layer welding seam, specimen orientation, fracture toughness, Master Curve approach, reference temperature

Publ.-Id: 19457 - Permalink


Synthesis of a series of VAChT ligands as basis for the development of 18F-labelled radiotracers for imaging in brain
Barthel, C.; Wenzel, B.; Schüürmann, G.; Brust, P.;
The department of Neuroradiopharmaceuticals is part of the Helmholtz-Zentrum Dresden-Rossendorf and deals with the development of radiotracers for brain research using positron emission tomography (PET).
Those tracers are ligands labelled with radioactive isotopes which bind to selected biomolecules in brain. Due to this specific binding it is possible to visualise neurotransmission processes in living organisms. For the development of such ligands it is necessary to synthesise various organic compounds and to determine their in-vitro binding affinity to the desired biological target. Afterwards, a promising candidate is selected for labelling with a short-lived radioactive nuclide such as fluorine-18.
The vesicular acetylcholine transporter (VAChT) is located in cholinergic areas in brain and is an interesting target for the in-vivo imaging of neuronal deficits as observed in Alzheimer’s disease. It is known that vesamicol (2-(4-phenylpiperidin-1-yl)cyclohexanol) acts as a high-potential inhibitor for this transporter and thus represents the chemical lead for the development of VAChT-radioligands. The aim of our studies is to develop a selective ligand by varying the vesamicol-skeleton in a systematic manner at its’ three ring structures and determining the binding profile of the resulting derivatives. These in-vitro data are correlated with the various chemical structures leading to a three dimensional computational model, a so-called quantitative structure affinity relationship (QSAR). Based on those results, we will be able to find a promising candidate for radiolabelling studies and further investigations.
  • Poster
    12. Research Festival Leipzig 2013, 19.12.2013, Leipzig, Deutschland
  • Contribution to proceedings
    Leipzig Research Festival for Life Sciences 2013, 19.12.2013, Leipzig, Deutschland
    Abstract Book, Leipzig: Universität Leipzig, 978-3-9810760-9-7, 162-162

Publ.-Id: 19456 - Permalink


Development of a 18F-labelled PDE2A ligand
Schröder, S.; Wenzel, B.; Kranz, M.; Teodoro, R.; Deuther-Conrad, W.; Fischer, S.; Steinbach, J.; Brust, P.;
Phosphodiesterasen (PDE´s) sind Enzyme, die in allen menschlichen Zellen exprimiert werden und die zyklischen Nucleotide cAMP und/oder cGMP hydrolysieren. PDE-Inhibitoren verzögern den Abbau dieser sekundären Botenstoffe und beeinflussen physiologische Prozesse. Die PDE2A zeigt eine hohe, spezifische Expression im Gehirn sowie in bestimmten Tumoren und ist vermutlich an der Pathophysiologie entsprechender Erkrankungen beteiligt. Ziel unserer Arbeiten ist die Darstellung eines radiomarkierten PDE2A-Inhibitors für die Bildgebung der PDE2A mittels Positronen-Emissions-Tomographie (PET).
Auf Grundlage des Patents WO2010/054253 A1 wurde eine für die PDE2A hochaffine und selektive Triazin-Leitstruktur (TA-05, IC50: 4,12 nM) ausgewählt. Diese Leitstruktur wurde in einer fünfstufigen, optimierten Syntheseroute dargestellt und vollständig charakterisiert. Ausgehend von TA-05 wurden ein neues Fluorpropyl-Derivat (TA-P2) als Referenzverbindung für Affinitätsstudien sowie der entsprechende Tosylat-Präkursor (TA-P4) für eine einstufige 18F-Markierung entwickelt. Die nukleophile 18F-Fluorierung von TA-P4 führte zu einem neuen, hochaffinen PDE2A-Radioliganden (18F-TA-P2), der erfolgreich isoliert, gereinigt und mittels Radio-DC sowie Radio-HPLC analysiert wurde. Die biologische Charakterisierung von 18F-TA-P2 wird derzeit mittels TierPET/MR und Untersuchungen zur Metabolisierung sowie Autoradiographie bearbeitet.
  • Poster
    12th Leipzig Research Festival for Life Sciences 2013, 19.12.2013, Leipzig, Deutschland
  • Contribution to proceedings
    12th Leipzig Research Festival for Life Sciences 2013, 19.12.2013, Leipzig, Deutschland
    12th Leipzig Research Festival for Life Sciences 2013, Leipzig: Universität Leipzig, 978-3-9810760-9-7, 174-174

Publ.-Id: 19455 - Permalink


Topography-controlled alignment of DNA origami nanotubes on nanopatterned surfaces
Teshome, B.; Facsko, S.; Keller, A.;
The controlled positioning of DNA nanostructures on technologically-relevant surfaces represents a major goal along the route toward the full-scale integration of DNA-based materials into nanoelectronic and sensoric devices. Previous attempts to arrange DNA nanostructures into defined arrays mostly relied on top-down lithographic patterning techniques combined with chemical surface functionalization. Here we combine two bottom-up techniques for nanostructure fabrication, i.e., self-organized nanopattern formation and DNA origami self-assembly, in order to demonstrate the electrostatic self-alignment of DNA nanotubes on topographically patterned silicon surfaces. Self-organized nanoscale ripple patterns with periodicities ranging from 20 nm to 50 nm are fabricated by low-energy ion irradiation and serve as substrates for DNA origami adsorption. Electrostatic interactions with the charged surface oxide during adsorption direct the DNA origami nanotubes to the ripple valleys and align them parallel to the ripples. By optimizing the pattern dimensions and the Debye length of the adsorption buffer, we obtain an alignment yield of ~ 70 %. Since this novel and versatile approach does not rely on any chemical functionalization of the surface or the DNA nanotubes, it can be applied to virtually any substrate material and any top-down or bottom-up nanopatterning technique. This technique thus may enable the wafer-scale fabrication of ordered arrays of functional DNA-based nanowires.
Keywords: DNA nanostructures, DNA origami, self-assembly, nanopatterning, atomic force microscopy
  • Nanoscale 6(2014), 1790-1796
    DOI: 10.1039/C3NR04627C
  • Poster
    DNA-Based Nanotechnology: Digital Chemistry, 05.-09.05.2014, Dresden, Germany
  • Poster
    DPG-Frühjahrstagung, 30.03.-04.04.2014, Dresden, Germany
  • Poster
    Trends in Nanotechnology International Conference (TNT2015), 07.-11.09.2015, Toulouse, France

Publ.-Id: 19454 - Permalink


Potenziale der Rückgewinnung von Sekundärrohstoffen in Verbundprojekten der BMBF Fördermaßnahme r³ - Strategische Metalle und Mineralien; Tagungsband 9. Sächsischer Kreislaufwirtschaftstag Freiberg, 21. - 22.11.2013.
Dürkoop, A.;
Um die Versorgung mit metallischen Rohstoffen für Deutschland zukünftig nachhaltig zu sichern, hat das BMBF im Jahr 2012 die r3-Fördermaßnahme mit dem Fokus auf strategische Metalle und Mineralien ins Leben gerufen. Die nichtenergetischen Rohstoffe sind von zunehmender Wichtigkeit für die internationale Wettbewerbsfähigkeit der deutschen Wirtschaft. Die Versorgungssicherheit dieser Rohstoffe nimmt jedoch in den letzten Jahren stark ab, da zum Einen der Bedarf an beispielsweise Hightech-Metallen steigt wodurch Verknappungen am Markt drohen und zum Anderen ist Deutschland im hohen Maße von Importen aus dem Ausland abhängig. Sekundärrohstoffe sind hingegen in Deutschland vorhanden, werden aber derzeit hinsichtlich Hightech-Metalle nicht ausgeschöpft.
Aus diesen Gründen setzt sich die Bundesregierung mit der Hightech-Strategie 2020 (2010a) und der Rohstoffstrategie (2010b) dafür ein, neue Technologien und innovative Verfahren mit dem Ziel des effizienten Umgangs mit diesen Rohstoffen zu entwickeln.
Ein zentraler Leitgedanke der Hightech-Strategie 2020 ist, die Wettbewerbsfähigkeit in Deutschland durch eine erhöhte Innovationskraft zu stärken. Dafür fördert das Bundesministerium für Bildung Forschung innerhalb des Rahmenprogrammes „Forschung für nachhaltige Entwicklung“ die Fördermaßnahme r³ mit 30 Millionen €. Die Fördermaßnahme „r³ – Innovative Technologie für Ressourceneffizienz – Strategische Metalle und Mineralien“ umfasst insgesamt 28 Verbundforschungsprojekte, die mit max. drei Jahren Laufzeit zwischen 2012 und Anfang 2016 auf den Themenfeldern Recycling, Einsparung und Substitution, städtischer Bergbau (Urban Mining) und Bewertungsmethoden forschen. Insgesamt umfasst r³ mehr als 128 Einzelprojekte, davon 69 Industrieprojekte. So wird die Förderung durch BMBF von 30 Millionen € durch den zusätzlichen Eigenanteil der Industrieunternehmen von 12 Millionen € auf insgesamt 42 Millionen € erhöht.
Keywords: Resource Efficiency, Strategic Metals and Minerals, Substitution, Recycling, Urban Mining
  • Invited lecture (Conferences)
    9. Sächsischer Kreislaufwirtschaftstag, 21.-22.11.2013, Freiberg, Deutschland
  • Contribution to proceedings
    9. Sächsischer Kreislaufwirtschaftstag, 21.-22.11.2013, Freiberg, Deutschland
    9. Sächsischer Kreislaufwirtschaftstag

Publ.-Id: 19453 - Permalink


Near-Surface Strain in Icosahedra of Binary Metallic Alloys: Segregational vs. Intrinsic Effects
Pohl, D.; Wiesenhütter, U.; Mohn, E.; Schultz, L.; Rellinghaus, B.;
A systematic structural analysis of of FePt, CuAu and Au icosahedral nanoparticles is presented. The uncovered particles are prepared by inert gas condensation and thermally equilibrated through in-flight optical annealing. Aberration-corrected high resolution Transmission electron microscopy reveals that the crystal lattice is significantly expanded near the particle surface. These experimental findings are corroborated by molecular statics simulations which show that this near-surface strain originates from both intrinsic strain due to the icosahedral structure and a partial segregation of the larger of the two alloy constituents to the particle surface.
Keywords: FePt Nanoparticles HRTEM

Publ.-Id: 19452 - Permalink


Preprocessing of structured spectral data to improve the predictive accuracy of Self-Organising Maps
Domaschke, K.; Rossberg, A.; Villmann, T.;
In this paper, we propose a new approach using structural information of spectral data during a preprocessing procedure to upgrade the ability of subsequent analysis methods. A composite data set of measured spectra is given, which contains dierent mixtures of a few spectral components. Using chemical knowledge and a small subset of the mixture information, we are able to evaluate these spectral components out of the given data set and use this information in addition for the following analysis of the composite data set. In our case, we apply the Self-Organizing Map according to Kohonen to predict the unknown mixture subset of the dierent spectral components within the measured data.
Keywords: Self-Organizing maps, spectral data, unmixing, blind source separation
  • Open Access LogoContribution to proceedings
    European Symposium on Artificial Neural Networks, Computational Intelligence and Machine Learning, 23.-25.04.2014, Bruges, Belgium
    Proceedings of the European Symposium on Artificial Neural Networks, Computational Intelligence and Machine Learning

Publ.-Id: 19450 - Permalink


High magnetic field study of the Tm2Fe17 and Tm2Fe17D3.2 compounds
Isnard, O.; Andreev, A. V.; Kuz’Min, M. D.; Skourski, Y.; Gorbunov, D. I.; Wosnitza, J.; Kudrevatykh, N. V.; Iwasa, A.; Kondo, A.; Matsuo, A.; Kindo, K.;
A magnetization study of a Tm2Fe17 single crystal and aligned powder of the deuteride Tm2Fe17D3.2 has been carried out in steady (14 T) and pulsed (60 T and, in one case, up to 74 T) magnetic fields at temperatures between 1.5 and 300 K. Tm2Fe17 is a ferrimagnet with TC = 295 K and a spontaneous moment of 22 μB/f.u. at T = 4.2 K. Of particular interest are low-temperature magnetization curves along the sixfold crystal axis c, which is an easy direction in Tm2Fe17 and a hard direction in the deuteride. In either case the magnetization increases with magnetic field undulatorily in broad steps whose height is a multiple of the atomic moment of Tm, μTm = 7 μB. In Tm2Fe17, the positions of the steps yield information on the Fe-Tm molecular field, 48 T on the Tm 2d site and 60 T on the Tm 2b site, whereas the crystal field parameter A66 is found from the widths of the steps: A66(b) = −35 Ka0−6 and A66(d) = −26 Ka0−6 (here a0 is the Bohr radius). It also proves possible to estimate the other sixth-order crystal field parameter: A60 ∼ −4 Ka0−6 (on average for both sites). Less information can be extracted from the powder data for the deuteride. Thus, the mean molecular field on Tm in Tm2Fe17D3.2 is found to be 49 T or 9% less than in the parent binary compound.

Publ.-Id: 19448 - Permalink


Similarities between single and multilayer particle deposition and resuspension experiments in turbulent flows
Barth, T.; Hampel, U.;
This report is a comparative review of several particle transport experiments, which were performed within the framework of the two large scale European projects namely THINS (Thermal Hydraulics of Innovative Nuclear Systems) and ARCHER (Advanced Reactor for Cogeneration of Heat & Electricity R&d). Background motivation is the carbonaceous dust issue of the High Temperature Reactor (HTR). Radio-contaminated dust was found deposited all over the inner surfaces in the primary circuit of different HTR research reactors after a certain operational time. In case of an accidental scenario such as the depressurisation of the primary circuit the dust may be remobilised by the turbulent flow and becomes a considerable source term when escaping the system boundaries. The safety assessment requires a fundamental understanding of the interaction between the wall-deposited particle multilayer and the turbulent flow field. Thus, we performed a set of experiments to explore the particle deposition and resuspension characteristics in various geometries by means of high-end measurement instrumentation.
Two air-driven small-scale test facilities were designed to generate a particle laden turbulent flow field under well-defined conditions. The flow was downscaled using Reynolds similarity and the aerosol particles were described by its aerodynamic mobility. The first facility was designed for the THINS project and is called Gas Particle Loop. Here, the particle deposition and resuspension was studied in a horizontal turbulent duct flow. The flow field was captured by means of a stereoscopic Particle Image Velocimetry system. The airborne particles were classified using Aerodynamic Particle Sizer spectrometry and the wall deposited particles were captured by means of optical microscopy and laser distance sensors. It was found that the deposition of micron-sized particles mainly depends on the aerodynamic particle size and the fluid friction velocity. Particle resuspension was found to take place in intermittent events once a critical friction velocity was exceeded. The second facility was constructed for the ARCHER project and is called Pebble Bed Loop. Here, a particle laden turbulent flow in a pebble bed was generated. The aerosol particles were radio-labelled with the isotope fluorine 18 and the spatiotemporal distribution of the particle deposits in the pebble bed was recorded by means of positron emission tomography (PET) during various flow regimes. Assuming a homogeneous distribution of the initial activity over the particles, the activity recorded by the PET scanner directly correlates to the amount of deposited particles. The geometry of the pebble bed was captured by means of a gamma ray computed tomography (CT) scan. The result of this campaign is a time resolved 3D PET-CET overlay. Basic characteristics of the particle deposition and resuspension behaviour in the GPLoop were relocated in the results of the experiments in the PBLoop. The available data set provides a new insight into the particle transport behaviour in turbulent flows and may be used for the development of numerical methods for the prediction of the dust behaviour during accidental scenarios of HTRs.
  • Contribution to proceedings
    International Workshop on Thermal Hydraulics of Innovative Nuclear Systems, 20.-22.01.2014, Modena, Italien
    Proceedings of THINS 2014

Publ.-Id: 19447 - Permalink


Coexistence of Ising and XY Spin Systems on a Single Tb Atom in TbCoGa5
Sanada, N.; Amou, Y.; Watanuki, R.; Suzuki, K.; Yamamoto, I.; Mitamura, H.; Sakakibara, T.; Akatsu, M.; Nemoto, Y.; Goto, T.;
The tetragonal compound TbCoGa5 exhibits two successive magnetic transitions at TN1 = 36.2 and TN2 = 5.4 K. The results of the measurement of the magnetic susceptibility and specific heat indicate that the c- and ab-components of the magnetic moments of Tb3+ show independent antiferromagnetic orderings at TN1 and TN2, respectively. In this work, we have investigated the physical properties of TbCoGa5 in a magnetic field. Single crystals of TbCoGa5 were grown and their specific heat, electrical resistivity, magnetization and elastic constant were measured. The magnetic exchange interactions in TbCoGa5 are discussed referring to the result of the magnetization process. Additionally, the present and previous results are summarized in a magnetic phase diagram. The magnetic phase diagram indicates that the behavior of TN1 in a changing magnetic field is similar to that of an Ising spin system, and the behavior of TN2 is similar to that of an XY spin system. Thus, we conclude that Ising and XY spin systems coexist on a single Tb atom in TbCoGa5.
Keywords: TbCoGa5, successive component-separated magnetic transitions, magnetization process, metamagnetic transition, magnetic phase diagram

Publ.-Id: 19446 - Permalink


Study of particle deposition and resuspension in pebble beds using positron emission tomography
Barth, T.; Kulenkampff, J.; Ludwig, M.; Bras, S.; Gründig, M.; Franke, K.; Lippmann-Pipke, J.; Hampel, U.;
This report describes the application of gamma-ray computed tomography (CT) and positron emission tomography (PET) for the investigation of particle transport in a model of a High Temperature Reactor (HTR) pebble bed. Micron sized liquid and graphite particles were radioactively labelled and the deposition and resuspension of particle multilayers in the pebble bed was studied. The particle laden turbulent flow in a model pebble bed was scaled by Reynolds similarity and was generated by an air driven small-scale test facility at ambient conditions. The pebble bed geometry was recorded by a CT to determine the bed porosity and pebble orientation. Two sets of experiments were performed. Firstly, radio-labelled liquid particles were dispersed into the flow to study pure particle deposition over a wide fluid velocity range. In a second set of experiments, radio-labelled graphite particles were injected into the flow and particle deposition and resuspension was studied in succession. Activity spots appeared on the front sides of the single pebbles indicating the formation of particle multilayers on the pebble surfaces. After the deposition experiment, the aerosol generator was switched off and the fan speed was stepwise increased to induce particle resuspension. A time resolved 3D PET-CT overlay provides a completely new insight into the particle multilayer formation and removal.
Keywords: High Temperature Reactor; pebble bed; particle transport; Positron Emission Tomography"
  • Contribution to proceedings
    7th World Congress on Industrial Process Tomography, WCIPT7, 02.-05.09.2013, Krakau, Polen
    Proceedings of WCIPT7

Publ.-Id: 19445 - Permalink


Complex magnetic phase diagram of a geometrically frustrated Sm lattice: Magnetometry and neutron diffraction study of SmPd2Al3
Pospíšil, J.; Nénert, G.; Miyashita, S.; Kitazawa, H.; Skourski, Y.; Diviš, M.; Prokleška, J.; Sechovský, V.;
Magnetism in SmPd2Al3 was investigated on a single crystal by magnetometry and neutron diffraction. SmPd2Al3 represents a distinctive example of a Sm magnetism exhibiting complex magnetic behavior at low temperatures with four consecutive magnetic phase transitions at 3.4, 3.9, 4.4, and 12.5 K. The rich magnetic phase diagram of this compound reflects the specific features of the Sm3+ ion, namely, the energy nearness of the ground-state multiplet J = 5/2 and the first excited multiplet J = 7/2 in conjunction with strong crystal field influence. Consequently, a significantly reduced Sm magnetic moment in comparison with the theoretical Sm3+ free-ion value is observed. Despite the strong neutron absorption by natural samarium and the small Sm magnetic moment (∼0.2 μB), we have successfully determined the magnetic k vector (1/3, 1/3, 0) of the phase existing in the temperature interval 12.5–4.4 K. This observation classifies the SmPd2Al3 compound as a magnetically frustrated system. The complex magnetic behavior of this material is further illustrated by kinetic effects of the magnetization, inducing a rather complicated magnetic structure with various metastable states.

Publ.-Id: 19444 - Permalink


Single particle resuspension experiments in turbulent channel flows
Barth, T.; Preuß, J.; Hampel, U.;
The resuspension of spherical single particles from a hydraulically smooth wall into a turbulent flow is studied. Special attention is given to the particle diameter, the material composition, the critical friction velocity and the inceptive motion of the resuspending particles. The experiments were performed in an air-driven small-scale test facility. The particles on the channel floor were detected and classified by means of an optical microscope combined with a digital camera. Furthermore, the turbulent flow field was recorded using a conventional Particle Image Velocimetry (PIV) system. A statistical sufficient monolayer of spherical particles was generated on the channel floor by dispersing the particles into the flow during a pure deposition regime. Afterwards, particle resuspension was induced by the stepwise increase of the fluid velocity. The resuspension was quantified by the fraction of resuspended particles against the friction velocity for a diameter range between 3 and 45 µm. It was found that particles begin to resuspend when a critical friction velocity is exceeded. A decreasing tendency between the particle diameter and the critical friction velocity was found for particles in the present size range and the results are in good consistency to other investigations.
Keywords: resuspension, aerosol particle, turbulent channel flow, loss of coolant accident
  • Contribution to proceedings
    8th International Conference on Multiphase Flow, ICMF 2013, 26.-31.05.2013, Jeju, Korea
    Proceedings of ICMF 2013

Publ.-Id: 19443 - Permalink


Multilayer deposition and resuspension experiments of graphite particles between periodic steps in turbulent channel flows
Barth, T.; Reiche, M.; Hampel, U.;
This report describes an experimental study about graphite particle multilayer deposition and resuspension between periodic steps in turbulent channel flows. Background motivation is the carbonaceous dust safety issue in the High Temperature Reactor. In the present study the particle deposition and resuspension scenarios were fluid dynamically downscaled and were reproduced under simplified conditions in an air-driven small-scale test facility. Periodic steps were placed in a square duct test section to induce a complex flow field characterized by flow separations, recirculation and reattachment zones.
The turbulent flow field was recorded by means of a stereo Particle Image Velocimetry system. Polydisperse graphite particles matching the size range of HTR dust were dispersed into the flow field during a pure deposition regime. The multilayer build up between the periodic steps was measured using a laser distance sensor coupled with a linear stage. The particle layer build up showed a linear tendency against time and the deposition velocities are in good agreement with similar investigations. After the deposition scenario the aerosol generator was switched off and the fan speed of the test facility was stepwise increased to initiate particle resuspension. It was found that the resuspension started to begin in the reattachment area between the steps. The entire multilayer was already removed by the flow at friction velocities at which single particle resuspension starts to begin. Furthermore, particle bed porosity determinations were performed by gravimetrical and x-ray methods to characterize the packing properties. The present results indicate similarities between the single and the multilayer particle deposition and resuspension process.
Keywords: deposition, resuspension, graphite particles, turbulent flow, periodic steps, high temperature reactor, loss of coolant accident
  • Contribution to proceedings
    8th International Conference on Multiphase Flow, ICMF 2013, 26.-31.05.2013, Jeju, Korea
    Proceedings of ICMF 2013

Publ.-Id: 19442 - Permalink


Magnetic properties and anisotropy of orthorhombic DyMnO3 single crystal
Pekala, M.; Wolff-Fabris, F.; Fagnard, J.-F.; Vanderbemden, P.; Mucha, J.; Gospodinov, M. M.; Lovchinov, V.; Ausloos, M.;
An orthorhombic DyMnO3 single crystal has been studied in magnetic fields up to 14 T and between 3 K and room temperature. The field dependent ordering temperature of Dy moments is deduced. The paramagnetic Curie Weiss behavior is related mainly to the Dy3+ sublattice whereas the Mn sublattice contribution plays a secondary role. DC magnetization measurements show marked anisotropic features, related to the anisotropic structure of acubic system stretched along a body diagonal, with a magnetic easy axis parallel to the crystallographic b axis. A temperature and field dependent spin flop transition is observed below 9 K, when relatively weak magnetocrystalline anisotropy is overcome by magnetic fields upto 1.6 T.
Keywords: Manganite, Magnetization, Magnetic anisotropy

Publ.-Id: 19441 - Permalink


Study of particle deposition and resuspension in pebble beds using positron emission tomography
Barth, T.; Kulenkampff, J.; Ludwig, M.; Bras, S.; Gründig, M.; Franke, K.; Lippmann-Pipke, J.; Hampel, U.;
This work describes an experimental study about the transport behavior of carbonaceous dust in a High Temperature Reactor (HTR) pebble bed. Carbonaceous dust may be formed during reactor operation and deposits on the inner surfaces of the HTR primary circuit. In case of a loss of coolant accident (LOCA) this dust may be resuspended and released into the environment. Since the dust is a carrier of fission products this dust is a considerable source term and has to be analyzed with respect to such accidental scenarios.
The particle deposition and resuspension behavior was experimentally investigated in a pebble bed by means of Positron Emission Tomography (PET). The turbulent flow field was generated by an air-driven small scale test facility. The pebble bed was fluid mechanically downscaled by the pebble bed related Reynolds number. The pebble bed geometry was analyzed by a 3D gamma ray computed tomography scan for the precise determination of the pebble orientation and the bed porosity.
Two sets of PET experiments were conducted. First, monodisperse liquid aerosol particles were labeled with the radioisotope (18F) and dispersed into the turbulent flow field. PET was used for the temporal and spatial recording of the particle deposition process.
In the second set of PET measurements, the liquid particles were replaced by technical graphite dust matching the particle size distribution usually found in the HTR primary circuit. The graphite dust was also labeled with 18F before being dispersed into the turbulent flow field. Deposition experiments were conducted at rather low fluid velocities to purely study the particle precipitation. Subsequently, the fan power of the facility was stepwise increased and the PET scanner recorded the particle resuspension process online. The existing data sets give a unique 3D and time resolved insight into the particle transport process in such a complex geometry. The data can be further used for CFD code development to predict the particle behavior during a LOCA in an HTR.
  • Contribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-15, 12.-15.05.2013, Pisa, Italien
    Proceedings of NURETH-15

Publ.-Id: 19440 - Permalink


DNA Origami Substrates for Highly Sensitive Surface-Enhanced Raman Scattering
Prinz, J.; Schreiber, B.; Olejko, L.; Oertel, J.; Rackwitz, J.; Keller, A.; Bald, I.;
DNA nanotechnology holds great promise for the fabrication of novel plasmonic nanostructures and the potential to carry out single-molecule measurements using optical spectroscopy. Here, we demonstrate for the first time that DNA origami nanostructures can be exploited as substrates for surface-enhanced Raman scattering (SERS). Gold nanoparticles (AuNPs) have been arranged into dimers to create intense Raman scattering hot spots in the interparticle gaps. 15 nm AuNPs covered with TAMRA-modified DNA have been placed at a nominal distance of 25 nm to demonstrate the formation of Raman hot spots. To control the plasmonic coupling between the nanoparticles and thus the field enhancement in the hotspot, the size of AuNPs has been varied from 5 nm to 28 nm by electroless Au deposition. By the precise positioning of a specific number of TAMRA molecules in these hot spots, surface-enhanced Raman scattering (SERS) with highest sensitivity down to the few-molecule level is obtained.
Keywords: DNA origami, Nanoparticles, Raman spectroscopy, Self-assembly
  • The Journal of Physical Chemistry Letters 4(2013), 4140-4145
    DOI: 10.1021/jz402076b

Publ.-Id: 19439 - Permalink


Magnetic phase diagram of clathrate compound Ce3Pd20Si6 with quadrupolar ordering
Ono, H.; Nakano, T.; Takeda, N.; Ano, G.; Akatsu, M.; Nemoto, Y.; Goto, T.; Dönni, A.; Kitazawa, H.;
We present results of specific heat measurements on a Ce3Pd20Si6 single crystal and construct the magnetic phase diagram for the three cubic principal directions [100], [110] and [111]. The highly anisotropic phase diagram is discussed and can be qualitatively explained by the Zeeman splitting at the 8c-site. For B ‖ [100], the present study found two different quadrupolar ordered phases, which meet the paramagnetic phase at a tri-critical point and establish the new phase boundaries.

Publ.-Id: 19438 - Permalink


Paramagnetic Meissner Effect and Strong Time Dependence at High Fields in Melt-Textured High-TC Superconductors
Gouvea, C. D. P.; Dias, F. T.; Vieira, V. D. N.; Silva, D. L. D.; Schaf, J.; Wolff-Fabris, F.; Rovira, J. J. R.;
In this work we report on systematic field-cooled magnetization experiments in melt-textured YBa2Cu3O7−δ samples containing Y211 precipitates. Magnetic fields up to 14 T were applied either parallel or perpendicular to the ab planes and a strong paramagnetic response related to the superconducting state was observed. This effect is known as paramagnetic Meissner effect (PME). The magnitude of the PME increases when the field is augmented. This effect shows a strong paramagnetic relaxation, such that the paramagnetic moment increases as a function of the time. The pinning by the Y211 particles plays a crucial role in the explanation of this effect and our results suggest that the pinning capacity can produce a strong flux compression into the sample, originating the PME and the strong time dependence.
Keywords: Melt-textured YBaCuO, Paramagnetic Meissner effect, Time dependence

Publ.-Id: 19437 - Permalink


Determination of the intersublattice exchange interactions in GdCo12-xFexB6 (x= 0-3) intermetallic compounds by high field magnetization measurements
Diop, L. V. B.; Isnard, O.; Skourski, Y.; Ballon, G.;
High field magnetization measurements up to 60 T on free powder samples from GdCo12-xFexB6 (x = 0-3) compounds are reported. The data were used to evaluate the microscopic exchange interaction integral, JGd-3d, between Gd and 3d (Co,Fe) spins. The systems are ferrimagnets; they order magnetically between TC = 95 K for x = 3 and TC = 165 K for x = 0. The low temperature magnetization curves as well as the temperature dependence of intrinsic magnetic parameters are determined by magnetic measurements in pulsed magnetic field. The average magnetic moment µCo+Fe per mean transition metal atom (Co + Fe) is small and increases with increasing Fe concentration from 0.44 µ B for x = 0 to 0.51 µB for x = 3 at T = 4 K. From high field magnetization curves, a value of JGd-3d/kB = -4.65 K is derived for x = 0, whereas mean field approximation yields a much larger 3d-3d exchange integral of JCo-Co/kB = 105 K. The obtained results reveal an increase of JGd-3d/kB with Fe concentration. For x = 0.5, the intersublattice coefficient nGd-3d is found to keep an almost constant value of 5.87 ± 0.13 T*f.u.*µB-1 whatever the temperature in the 2 to 60 K range.

Publ.-Id: 19436 - Permalink


Low-Temperature Softening Due to Vacancy Orbital with Γ8 Quartet Ground State in Boron-Doped Floating Zone Silicon
Baba, S.; Akatsu, M.; Mitsumoto, K.; Komatsu, S.; Horie, K.; Nemoto, Y.; Yamada-Kaneta, H.; Goto, T.;
We have carried out low-temperature ultrasonic measurements using shear-mode ultrasound to clarify the quantum state of a vacancy orbital in boron-doped silicon grown by the floating zone (FZ) method. The elastic constants (C11 - C12)/2 and C44 of the transverse mode exhibit considerable softening below 2 and 5 K down to the base temperature of 30 mK, respectively. The elastic constant C44 measured by the three ultrasonic modes (kx, uy), (kz, ux), and (kx, uz) shows the different magnetic field dependences among the configurations under applied magnetic fields along the z-axis. The elastic softening and the magnetic field dependence of the elastic constants are accounted for by the quadrupole susceptibility based on the energy level scheme of the vacancy orbital with a Γ8 quartet ground state and Γ7 doublet excited state located at an energy of 1 K. The difference in C44 between the two ultrasonic modes (kz, ux) and (kx, uz) at fields along the z-axis indicates that the Γ8 quartet ground state is slightly split by local strain in the silicon sample. The quantum state of the vacancy orbital is expected to be sensitive to strain because of the extremely large quadrupole-strain coupling energy of gΓ ≈ 105 K due to the extensively spreading orbital radius of r ≈ 1 nm. The differences in variation of the low-temperature softening and magnetic field dependence among eight samples cut out from different locations of the present boron-doped FZ silicon ingot evidence the inhomogeneous distribution of the vacancy concentration.
Keywords: vacancy, boron-doped FZ silicon, ultrasound, quadrupole

Publ.-Id: 19435 - Permalink


Recycling von Gallium mit Dialyseverfahren
Zeidler, O.;
Der Vortrag geht auf die Probleme des Ga-Recyclings aus Rückständen der GaAs-Wafererzeugung ein. Daraufhin werden ein gesamtheitliches Konzept für die Zusammenlegung der Abwässer sowie ein neu entwickeltes Dialyseverfahren zur weiteren Behandlung dieser vorgestellt. Aktuelle Ergebnisse zur dialytischen Trennung des Galliums von der Hauptverunreinigung Arsen werden ausführlich diskutiert und ein Ausblick auf weitere Untersuchungen gegeben.
  • Invited lecture (Conferences)
    Fachausschusses Sondermetalle der GDMB, 23.-24.10.2013, Reutte, Österreich

Publ.-Id: 19434 - Permalink


Current-driven flow instabilities in large-scale liquid metal batteries, and how to tame them
Weber, N.; Galindo, V.; Stefani, F.; Weier, T.;
The use of liquid metal batteries is considered as one promising option for electric grid stabilisation. While large versions of such batteries are preferred in view of the economies of scale, they are susceptible to various magnetohydrodynamic instabilities which imply a risk of short-circuiting the battery due to the triggered fluid flow. Here we focus on the current driven Tayler instability and give critical electrical currents for its onset as well as numerical estimates for the appearing flow structures and speeds. Scaling laws for different materials, battery sizes and geometries are found. We further discuss and compare various means for preventing the instability.
Keywords: Tayler instability, liquid metal battery, simulation, OpenFOAM

Publ.-Id: 19433 - Permalink


Neogene to Quaternary ash deposits in the Coastal Cordillera in northern Chile: Distal ashes from supereruptions in the Central Andes
Breitkreuz, C.; de Silva, S. L.; Wilke, H. G.; Pfänder, J. A.; Renno, A. D.;
Silicic volcanic ash deposits investigated at 14 localities between 22° and 25°S in the Chilean Coastal Cordillera are found to be the distal ash fall from supereruptions in the Central Andean cordillera several hundreds of kilometers to the east. Depositional textures, modal composition and granulometry of the ashes and tuffs (the latter lithified by halite and gypsum under ultra-arid conditions) allow for a distinction between primary fallout/aeolian deposits (mean 4 - 5 Φ, sorting 1.5 - 2Φ) and secondary deposits that formed by down wash from hill slopes during local rain fall. Primary volcanic components comprise two types of glass shards (with small stretched vesicles and coarse-walled with rounded to elliptic vesicles), and biotite. Previously published studies on ash deposits in the north Chilean Coastal Cordillera reported 14 40Ar/39Ar and K/Ar ages on biotite or sanidine ranging between 6.66 ± 0.13 and 0.6 ± 0.4 Ma. In this project, three 40Ar/39Ar ages on biotite have been determined for samples from the Cuenca del Tiburón, the northern margin of Salar de Navidad and from the Quebrada de la Chimba (3.9 ± 0.1 Ma, 4.1 ± 0.1 Ma, 6.0 ± 0.1 Ma, respectively). The range of the 17 ages coincides with the Late Miocene to Quaternary ages of the major ignimbrite-forming eruptions of the high Andes to the east such as the Altiplano Puna Volcanic Complex (APVC). Electron microprobe data of glass and biotite of the Coastal Cordillera ashes have been compared with data from major ignimbrites of the APVC, of other major Central Andean volcanic fields, and of marine ashes (ODP Leg 201). Additional new biotite microprobe data from three APVC ignimbrites (Pastos Grandes, Pujsa and Guacha) have been included in the present study. Biotite composition of the investigated Coastal Cordillera ashes is similar to those of ignimbrites from the APVC. In particular, based in Fe, Mg, Mn and Ti, distal equivalents of the 3.96 ± 0.08 Ma Atana and/or 4.09 ± 0.02 Ma Puripicar and of the 5.6 ± 0.2 Ma Pujsa and/or the 5.56 ± 0.01 Ma Guacha eruptions can be identified. In addition, based only on age relations, distal ash units of the Pastos Grandes, Tatio and Purico eruptions may be present in the Coastal Cordillera. Composition of glass is comparable to APVC ignimbrite matrix glass and to marine glass, however, significant alkali depletion and SiO2 enrichment is attributed to in situ alteration. The identification of these ashes demonstrates for the first time that the supereruptions in the southern Central Andes gave rise to voluminous ash clouds, most likely co-ignimbrite. The present outcrops represent ash dispersed by easterly winds, consistent with atmospheric models that show favorable westward-directed winds existing in the upper troposphere/stratosphere during the southern summer in the southern Central Andes. This requires that current volume estimates for the major eruptions to be considered minima with a significant augmentation likely.
Keywords: Supereruptions, Central Andes, co-ignimbrite ash clouds, 40Ar/39Ar ages, biotite composition, granulometry

Publ.-Id: 19432 - Permalink


Permanent magnet electron beam ion source/trap systems with bakeable magnets for improved operation conditions
Schmidt, M.; Zschornack, G.; Kentsch, U.; Ritter, E.;
EBIS/T systems provide ions of intermediate up to the highest ion charge states via electron impact ionization by a dense electron beam. In order to produce highly charged ions in an EBIS/T high electron beam densities of several hundred A/cm2 are necessary to realize high ionization factors and compensate for charge destructive processes such as charge exchange etc. The required electron beam compression is realized via an axial magnetic field. Two different EBIS/T magnet design approaches have been established over the past decades: Superconducting magnets with high magnetic fields of several Tesla (significant initial and maintenance costs), Compact permanent magnets with magnetic fields of Sub-Tesla (low initial and maintenance costs). Comparing both solutions shows that the produced ion species and current output of the permanent magnet EBIS/T suits most of the user requirements.
  • Poster
    International Conference on Ion Sources 2013, 09.09.2013, Chiba, Japan
  • Review of Scientific Instruments 85(2014)2, 02B704
    DOI: 10.1063/1.4828723

Publ.-Id: 19430 - Permalink


A Compact, Versatile Low-Energy Electron Beam Ion Source
König, G.; Thorn, M.; Zschornack, J.; Schmidt, A.;
Electron Beam Ion Sources (EBIS) were originally developed to produce highly charged ions (HCI) [1]. For this purpose, high density electron beams at electron beam energies higher than the ionization potential of the desired ion species are required leading to the development of high energy and high current devices working with superconducting magnet coils.
For applications with focus on low and intermediate charge states EBIS/T with high-energy density rare-earth permanent magnets are an economic and compact alternative [2-5]. EBIS/T setups for electron beam energies of 2 keV and below have become more interesting recently. They can be used as sources of electromagnetic radiation in the UV, EUV, and visible light region for calibration purposes, as reference source for emission and absorption spectroscopy with ions of intermediate charge states in astrophysical experiments, as ion sources for research in radiation biology and medicine, and for the diagnostics of plasmas in fusion devices in the low energy range.
  • Poster
    International Conference on Ion Sources 2013, 09.09.2013, Chiba, Japan
  • Review of Scientific Instruments 85(2014)2, 02B703
    DOI: 10.1063/1.4826687

Publ.-Id: 19429 - Permalink


Electron beam ion sources for use in second generation synchrotrons for medical particle therapy
Zschornack, G.; Ritter, E.; Schmidt, M.; Schwan, A.;
Cyclotrons and first generation synchrotrons are the commonly applied accelerators in medical particle therapy nowadays. Next generation accelerators such as Rapid Cycling Medical Synchrotrons (RCMS), direct drive accelerators, or dielectric wall accelerators have the potential to improve the existing accelerator techniques in this field. Innovative accelerator concepts for medical particle therapy can benefit from ion sources which meet their special requirements. In the present paper we report on measurements with a superconducting Electron Beam Ion Source, the Dresden EBIS-SC, under the aspect of application in combination with RCMS as a well proven technology. The measurements indicate that this ion source can offer significant advantages for medical particle therapy. We show that a superconducting EBIS can deliver ion pulses of medically relevant ions such as protons, C4 + and C6 + ions with intensities and frequencies required for RCMS [S. Peggs and T. Satogata, “A survey of Hadron therapy accelerator technology,” in Proceedings of PAC07, BNL-79826- 2008-CP, Albuquerque, New Mexico, USA, 2007; A. Garonna, U. Amaldi et al., “Cyclinac medical accelerators using pulsed C6 +/ H+2 ion sources,” in Proceedings of EBIST 2010, Stockholm, Sweden, July 2010]. Ion extraction spectra as well as individual ion pulses have been measured. For example, we report on the generation of proton pulses with up to 3 × 109 protons per pulse and with frequencies of up to 1000 Hz at electron beam currents of 600 mA.
  • Poster
    International Conference on Ion Sources 2013, 09.09.2013, Chiba, Japan
  • Review of Scientific Instruments 85(2014)2, 02B702
    DOI: 10.1063/1.4827306

Publ.-Id: 19428 - Permalink


Charge Exchange and Energy Loss of Slow Highly Charged Ions in 1 nm Thick Carbon Nanomembranes
Wilhelm, R. A.; Gruber, E.; Ritter, R.; Heller, R.; Facsko, S.; Aumayr, F.;
Experimental charge exchange and energy loss data for the transmission of slow highly charged Xe ions through ultra thin polymeric carbon membranes are presented. Surprisingly, two distinct exit charge state distributions accompanied by charge exchange dependent kinetic energy losses are observed. The energy loss for ions exhibiting large charge loss shows a quadratic dependency on the incident charge state, indicating that equilibrium stopping force values do not apply in this case. Additional angle resolved transmission measurements and reduction of the layer thickness due to a structural phase transition of the membrane lead to the conclusion that a charge state enhanced elastic scattering potential is the main reason for the increase in energy loss rather than charge state enhanced inelastic losses. Thus, the presented results connect scattering experiments of ions on gaseous and on solid targets.
Keywords: slow highly charged ion, HCI, carbon nanomembranes, CNM, stopping power, ion charge state, charge exchange

Publ.-Id: 19427 - Permalink


Bubbly flows with fixed polydispersity: validation of a baseline closure model
Rzehak, R.; Krepper, E.;
For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas-liquid multiphase flow, closures are needed for bubble forces, bubble-induced turbulence, as well as bubble-coalescence and -breakup. The quest for models with a broad range of applicability allowing predictive simulations is an ongoing venture. Reasonable success has been achieved so far for flows that are amenable to a monodisperse approximation for the bubble size which limits the latter to no more than a few mm.
In the present work we extend the validation to flow in which bubbles with a broad distribution of sizes up to ~10mm are present, but the shape of the distribution remains unchanged during the flow development. The existence of such conditions which we term “fixed polydispersity” is deduced from the experimental data. For this kind of situation the complexity of the closure problem is reduced since a balance between bubble-coalescence and -breakup prevails that allows to neglect these processes and simply impose a fixed bubble size distribution. Conclusions towards best practice guidelines for modeling bubbly flows are drawn and needs for further research identified.
Keywords: dispersed gas liquid multiphase flow, Euler Euler two fluid model, fixed polydispersity, closure relations, CFD simulation, model validation

Publ.-Id: 19425 - Permalink


Surface-Mediated Formation of Pu(IV) nanoparticles at the Muscovite-Electrolyte Interface
Schmidt, M.; Lee, S. S.; Wilson, R. E.; Knope, K. E.; Bellucci, F.; Eng, P. J.; Stubbs, J.; Soderholm, L.; Fenter, P.;
The formation of Pu(IV)-oxo-nanoparticles from Pu(III) solutions by a surface- enhanced redox/polymerization reaction at the muscovite (001) basal plane is reported, with a continuous increase in plutonium coverage observed in situ over several hours. The sorbed Pu extends > 70 Å from the surface with a maximum concentration at 10.5 Å and a total coverage of >9 Pu atoms per unit cell area of muscovite (0.77 µg Pu/cm²) (determined independently by in situ resonant anomalous x-ray reflectivity and by ex situ alpha-spectrometry). The presence of discrete nanoparticles is confirmed by high resolution atomic force microscopy. We propose that the formation of these Pu(IV) nanoparticles from an otherwise stable Pu(III) solution can be explained by the combination of a highly concentrated interfacial Pu-ion species, the Pu(III) – Pu(IV) redox equilibrium, and the strong proclivity of tetravalent Pu to hydrolyze and form polymeric species. These results are the first direct observation of such behavior of plutonium on a naturally occurring mineral, providing insights into understanding the environmental transport of plutonium and other contaminants capable of similar redox/polymerization reactions.
Keywords: plutonium – colloids – nanoparticles – X-ray scattering – sorption – crystal truncation rods – resonant anomalous x-ray reflectivity

Publ.-Id: 19424 - Permalink


Die Versorgung mit wirtschaftskritischen Rohstoffen – Eine Ursachensuche und -analyse
Gutzmer, J.; Klossek, A.;
Mineralische sowie insbesondere metallhaltige Rohstoffe sind für die Wertschöpfung aller hochentwickelten Volkswirtschaften von elementarer Bedeutung. Gleichzeitig entstammen diese Rohstoffe letztlich alle der Erdkruste – und damit einem Reservoir von endlicher Größe. Auch wenn die gesamte Größe dieses Reservoirs, auch Geopotenzial genannt, für keinen mineralischen oder metallhaltigen Rohstoff bisher ausgeschöpft wird, so werden die zur Verfügung stehenden Rohstoffkörper (Lagerstätten) zunehmend minderwertiger und teurer in ihrer Erschließung, ihrem Abbau und ihrer Verarbeitung.
Durch den technischen Fortschritt wird sich die Rohstoffabhängigkeit noch weiter verschärfen, wobei insbesondere der Bedarf an bislang technologisch wenig genutzten Metallen dramatisch steigen wird. Wurden in den 1980er-Jahren für die Herstellung eines Computerchips noch zwölf verschiedene Rohstoffe benötigt, sind es heute bis zu sechzig. Prognosen zufolge lassen technischer Wandel und Innovationen den Bedarf an Technologiemetallen wie Gallium (Ga), Neodym (Nd), Indium (In), Germanium (Ge), Scandium (Sc), Platin (Pt) oder Tantal (Ta) bis 2030 auf ein Vielfaches der heutigen Weltproduktionsmenge steigen (Angerer et al. 2009).
Nicht nur technischer Wandel und Innovationen katapultieren den internationalen Rohstoffbedarf nach oben. Auch die steigende Weltbevölkerung gerade in Entwicklungs- und Schwellenländern wie China und Indien oder die Wachstumssprünge in der Wirtschaftsleistung vieler dieser Länder beeinflussen den weltweiten Bedarf nach metallhaltigen Rohstoffen dramatisch. So ist schon jetzt klar, dass die Wirtschaftsmacht China ihren eigenen immens ansteigenden Rohstoffbedarf nicht nur aus eigenen, teilweise bereits heute schon nach außen hin reglementierten Rohstoffvorkommen decken kann, sondern bei weiter steigendem volkswirtschaftlichem Wachstum alle Kategorien mineralischer und metallischer Rohstoffe in zunehmendem Maße auch von außen zukaufen muss.
In letzter Instanz führen diese globalen Entwicklungen zu Lieferrestriktionen, sich verteuernden Rohstoffen und zu Rohstoffknappheit. Rohstoffe, deren Verfügbarkeit für Zukunftstechnologien gesichert werden muss, die eine große Hebelwirkung für die Wirtschaft haben und von denen bereits ein relativ geringer Mengeneinsatz damit zu einer hohen zusätzlichen Wertschöpfung in Hochtechnologiebereichen beiträgt, werden als „wirtschaftsstrategische“ Rohstoffe bezeichnet (BMBF 2012). Rohstoffe, deren Versorgungslage sich für die Wirtschaft mittel- bis langfristig als kritisch erweisen könnte, sind als „kritisch“ zu bezeichnen (ebd.), sodass die vorliegende Studie in Anlehnung an beide Definitionen von „wirtschaftskritischen Rohstoffen“ spricht. Was genau macht jedoch einige der bereits genannten Rohstoffe wirtschaftskritischer als andere, und wie kann auf unterschiedlichen gesellschaftlichen Ebenen mit dieser Rohstoffkritikalität umgegangen werden? Dieser Frage widmet sich die vorliegende Studie.
Keywords: criticality of mineral raw materials
  • Book chapter
    Kausch, P., Bertau, M., Gutzmer, J., Matschullat, J.: Strategische Rohstoffe — Risikovorsorge, Heidelberg: Springer Spektrum, 2014, 978-3-642-39704-2, 59-74

Publ.-Id: 19423 - Permalink


Sensitivity study on Xe depletion in the high burn-up structure of UO2
Holt, L.; Schubert, A.; van Uffelen, P.; Walker, C. T.; Fridman, E.; Sonoda, T.;
Experimental results for the Xe depletion in high burn-up fuel are presented from the High Burnup Rim Project (HBRP). In this project a number of UO2 fuel discs with 235U enrichment of 25.8 wt% were irradiated. The Xe content of the fuel discs was analysed by means of electron probe microanalysis (EPMA) with respect to burn-up and temperature. The influence of the burn-up and temperature on Xe concentration was investigated using a multi-physics approach involving various simulation tools. The temperature influence was modelled by the means of the temperature dependent effective burn-up. Good agreement was found between the modelled temperature threshold of the effective burn-up and the experimental temperature threshold between un- and restructured fuel in the HBRP. However, a systematic difference is observed between the onset burn-up derived from the Xe measurements in highly enriched discs such as those of HBRP and the corresponding values derived from irradiated Light Water Reactor (LWR) fuel rods and reported in the open literature. A sensitivity study identified the neutron flux spectrum and the fission product yields as main reasons for the observed differences.

Publ.-Id: 19422 - Permalink


Calculation of effective point kinetics parameters in the Serpent 2 Monte Carlo code
Leppanen, J.; Aufiero, M.; Fridman, E.; Rachamin, R.; van der Marck, S.;
This paper presents the methodology developed for the Serpent 2 Monte Carlo code for the calculation of adjoint-weighted reactor point kinetics parameters: effective generation time and delayed neutron fractions. The calculation routines were implemented at the Politecnico di Milano, and they are based on the iterated fission probability (IFP) method. The developed methodology is mainly intended for the modeling of small research reactor cores, and the results are validated by comparison to experimental data and MCNP5 calculations in 31 critical configurations.
Keywords: Serpent, Monte Carlo, adjoint-weighted time constants, effective generation time, effective delayed neutron fraction

Publ.-Id: 19421 - Permalink


Surface patterning of GaAs under irradiation with very heavy polyatomic Au ions
Bischoff, L.; Böttger, R.; Heinig, K.-H.; Facsko, S.; Pilz, W.;
Self-organization of surface patterns on GaAs under irradiation with very heavy polyatomic Au ions has been found. The patterns depend on the ion mass, the substrate temperature as well as the incidence angle of the ions. At room temperature, under normal incidence the surface remains flat, whereas above 200 °C nanodroplets of Ga appear after irradiation with monatomic, biatomic as well as triatomic Au ions of kinetic energies in the range of 10 to 30 keV per atom. In the intermediate temperature range of 100 to 200 °C meander- and dot-like patterns form, which are not related to Ga excess. Under oblique ion incidence up to 45° from the surface normal, at room temperature the surface remains flat for mon- and polyatomic Au ions. For bi- and triatomic ions, in the range 60° ≤ a ≤ 70° ripple patterns have been found, which become shingle-like for a ≥ 80°, whereas the surface remains flat for monatomic ions.
Keywords: surface morphology, ripples, nanodots, FIB, polyatomic ions, GaAs, Au

Publ.-Id: 19420 - Permalink


Modelling of Nuclear Fuel under Accident Conditions by means of TRANSURANUS
van Uffelen, P.; van de Laar, J.; Schubert, A.; Di Marcello, V.; Vlahovic, L.; Holt, L.;
The TRANSURANUS fuel performance code, which is developed at the JRC-ITU and in collaboration with many partner institutes since more than three decades, has been adapted in order to be able to simulate design basis accident (DBA) conditions.

In a first step, the developments and associated validation work will be summarised for LOCA conditions. This part includes modifications in the model for large strains, for the crystallographic phase transition in zircaloy, and for burst release and large cladding deformations.

In a second step, the ongoing work for simulations of RIA conditions will be outlined that include the model for the plenum temperature, along with the separate effect studies and detailed model developments made in parallel by means of multi-scale and multi-physics tools for the high burnup structure.

Finally, the perspectives of model developments and needs for further verification and validation in the frame of international benchmark exercises dedicated to DBA simulations and the first phase of a sever accident, i.e. when the cylindrical fuel rod geometry is preserved, will be presented for discussion.
  • Contribution to proceedings
    Technical meeting on modelling of water-cooled fuel including design basis and severe accidents, 28.10.-01.11.2013, Chengdu, China
    Proceedings of the technical meeting on modelling of water-cooled fuel including design basis and severe accidents
  • Lecture (Conference)
    Technical meeting on modelling of water-cooled fuel including design basis and severe accidents, 28.10.-01.11.2013, Chengdu, China

Publ.-Id: 19419 - Permalink


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