Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
Reduktion von Uran(VI) durch Vitamin C
Meurich, M.;
...Das Ziel der Forschungen ist die Wechselwirkung und Mobilität von Actiniden (wie z.B. Uran, Plutonium, usw.) auf molekulare Ebene in Geo- und Biosystemen aufzuklären und auf makromolekulare Systeme zu übertragen. Anwendungen finden sie unter anderem in der Entwicklung und Einschätzung von Sanierungsmethoden im Uranerzbergbau oder der Aufklärung des Verhaltens störfallbedingter radioaktiver Kontaminationen in der Umwelt. Im Mittelpunkt der Forschung mit Uran stehen dessen Wechselwirkungen mit natürlichen Organika. Zu diesen Organika gehören auch die Bioliganden wie Saccharide, Peptide und Kohlenhydrate. Uran kommt in der Natur mit den Oxidationsstufen +4 und +6 vor. Unter den gegeben normalen oxidierenden Bedingungen ist aber nur die Oxidationsstufe +6 stabil. Daher ist zu untersuchen, ob unter nicht oxidierenden Bedingungen und durch Anwesenheit von Bioliganden die Bildung von vierwertigem Uran möglich ist, da bekannt ist, dass diese einen Einfluss auf den Oxidationszustand von Uran haben. Der wichtigste Unterschied dieser beiden Oxidationsstufen ist die Löslichkeit. Die geringe Löslichkeit von U(IV) führt zu einer Immobilisierung des Urans. Die Salze des sechswertigen Urans haben dagegen eine sehr große Löslichkeit. Durch die Anwesenheit von Bioliganden im Boden könnte es daher zu einer Anreicherung von Uran kommen, da diese die Fähigkeit besitzen, U(VI) zu U(IV) reduzieren. Eines dieser Bioliganden ist Vitamin C, welches reduzierende Eigenschaften aufweist. Ziel dieser Arbeit ist es, die Reduktion von sechswertigem Uran zu vierwertigem Uran durch Vitamin C zu untersuchen und mit UV/VIS-Spektroskopie nachzuweisen.
  • Other report
    Hochschule Zittau / Görlitz: Praxissemesterarbeit, 2009
    62 Seiten

Publ.-Id: 13472 - Permalink

Photoluminescence of uranium(VI): quenching mechanism and role of uranium(V)
Tsushima, S.; Götz, C.; Fahmy, K.;
The photoluminescence of uranium(VI) is observed typically in the wavelength range 400 - 650 nm with the lifetime of several hundreds μs and is known to be quenched in the presence of various halide ions (case A) or alcohols (case B). Here, we show by density functional theory (DFT) calculations that the quenching involves an intermediate triplet excited state which exhibits uranium(V) character. The DFT results are consistent with previous experimental findings suggesting the presence of photo-excited uranium(V)–radical pair during the quenching process. In the ground state of uranyl(VI) halides, the ligand contributions to the highest occupied molecular orbitals increase with the atomic number (Z) of halide ion allowing larger ligand-to-metal charge transfer (LMCT) between uranium and halide ion. Consequently, larger quenching effect is expected as Z increases. The quenching mechanism is essentially the same in case A and B, and is driven by an electron transfer from the quencher to the UO22+ entity. The relative energetic stabilities of the triplet excited state define the "fate" of uranium so that in case A uranium(V) is oxidized back to uranium(VI), while in case B uranium remains as pentavalent.
Keywords: luminescence • triplet state • ab initio• quenching • photochemistry • halide

Publ.-Id: 13471 - Permalink

Terahertz studies on semiconductor quantum heterostructures in the low and high field regime
Wagner, M.;
In this thesis we investigate experimentally certain aspects of the interaction of terahertz (THz) radiation with intersubband transitions and excitonic transitions in semiconductor quantum wells.
The first part deals with a more fundamental view on an intersubband transition in a symmetric, undoped GaAs/AlGaAs multiple quantum well. After optical excitation of carriers, the considered electronic conduction intersubband transition is probed in the low-intensity linear regime using broadband THz pulses. These pulses are detected via field-resolved electro-optic sampling. While the sample’s terahertz absorption shows the expected single peak of the resonant intersubband transition, the differential transmission spectra, i.e. the photoexcitation-induced changes in transmission, display strong Fano signatures. On the basis of a microscopic theory, we show that they originate from a phase sensitive superposition of THz current and ponderomotive current. The latter one results from the wiggling motion of carriers induced by the accelerating THz field. Our findings demonstrate for the first time that the ponderomotive contribution has to be taken into account also at the lowest THz intensities. The following issues consider the interaction with THz pulses of higher intensity from the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf.
In one experiment we investigate efficient second order sideband generation in the GaAs/AlGaAs multiple quantum well mentioned above. To this end a near-infrared laser tuned to excitonic interband transitions is mixed inside the sample with the inplane polarized FEL beam to create the sum- and difference-frequencies between them. We compare the sideband efficiencies for the THz beam tuned to the interexcitonic heavy-hole light-hole transition and to the intraexcitonic heavy-hole 1s-2p transition. In the latter case we achieve a ten times higher n=+2 low-temperature efficiency around 0.1%. This value is comparable to previous studies in the literature, but our approach involves different transitions in a much simpler geometry. At room temperature the efficiency drops only by a factor of 7 for low THz powers.
The last part of this thesis addresses another fundamental quantum-mechanical phenomenon: the splitting of an absorption line in a strong THz field. In the same abovementioned quantum well sample the FEL wavelength is tuned near the intraexcitonic 1s-2p heavy-hole transition. The THz radiation induces a power-dependent splitting of the heavy-hole 1s exciton absorption line which manifests itself in the transmitted spectrum of a broadband near-infrared probe beam. The FEL-wavelength-dependent strength of this so-called Autler-Townes splitting is discussed on the basis of a simple two-level model.
Keywords: infrared spectroscopy, quantum well, ponderomotive current, Fano, sideband, Autler-Townes splitting
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-532 2010
    ISSN: 1437-322X


Publ.-Id: 13470 - Permalink

A novel method to fabricate silicon nanowire p-n junctions by a combination of ion implantation and in-situ doping
Das Kanungo, P.; Kögler, R.; Werner, P.; Gösele, U.; Skorupa, W.;
We demonstrate that axial p-n junction silicon nanowire (Si NW) diodes can be fabricated over a large area (5` Si wafer) by applying two existing doping techniques in succession. We doped the lower segments of the NWs p-type, in situ during growth with boron by molecular beam epitaxy, and the upper segments n-type, ex situ with phosphorus by ion implantation and subsequent rapid thermal annealing. No structural defects were observed in the NWs by transmission electron microscopy after implantation and rapid thermal annealing. Electrical measurements of individual NWs showed excellent diode characteristics with ideality factors higher than 2. Such high ideality factor can be attributed to the surface-states assisted recombination-generation in the depletion region of the p-n junction. The combined doping technique reduces the unwanted lateral doping and the extended overlapping region between n and p-doped segments in the NWs which is common in pure in situ doping. Our fabrication technique can be easily applied to form arrays of Si NW diodes for solar cells and other applications.
Keywords: Si Nano-wires, Doping, Ion implantation, p-n junction

Publ.-Id: 13468 - Permalink

Trans-RP gettering and out-diffusion of oxygen implanted into highly B-doped silicon
Kögler, R.; Dubois, C.; Gerlach, J. W.; Hutter, H.; Mücklich, A.; Skorupa, W.;
Implantation of 18O into highly B-doped and undoped silicon provides the possibility to investigate the effect of B-doping and to distinguish the processes of in-diffusion and out-diffusion of oxygen by profiling of 16O and 18O, respectively. The simultaneous in- and out-diffusion of oxygen was observed at 1000°C under oxidizing conditions. For silicon, heavily B-doped to concentrations of ≥ 1019 B cm-3, oxygen tends to diffuse out toward the surface. Moreover, a fraction of the oxygen from both sources, implanted 18O and in-diffused 16O, also migrates deep into the substrate and is trapped far beyond the mean ion range RP in the depth of x ≈ 3RP at the so-called trans-RP gettering peak.
In undoped silicon oxygen accumulation only takes place at vacancy-type defects introduced by ion implantation at a position shallower than RP.
The mobility of oxygen implanted into B-doped Si is higher than for implantation into undoped Si. Highly mobile defects are suggested to be formed in B-doped silicon beside the common mobile interstitial oxygen, Oi, and the immobile SiOX precipitates. These I OXBY defects may involve self-interstitials, I, and O and B atoms. The trans-RP peak appears due to the decay of these defects and the segregation of their constituents.
Keywords: Ion implantation, implantation-related defects, diffusion, B-doped silicon, oxygen
  • Contribution to proceedings
    Gettering and Defect Engineering in Semiconductor Technology XIII (GADEST 2009), 26.09.-02.10.2009, Döllnsee-Schorfheide, Deutschland
    Gettering and Defect Engineering in Semiconductor Technology XIII (GADEST 2009), Stafa-Zuerich Swizerland: Trans Tech Publications, ISSN 1012-0394, 375-380

Publ.-Id: 13467 - Permalink

Visualizing acidophilic microorganisms in biofilm communities using acid stable fluorescence dyes
Brockmann, S.; Arnold, T.; Schweder, B.; Bernhard, G.;
Bacteria in acidophilic biofilm communities, i.e. acid streamers and snotites, obtained from a subsurface mine in Königstein were visualized by fluorescence microscopy using four new fluorescent dyes (DY-601XL, V07-04118, V07-04146, DY-613). The pH of the bulk solution in which these bacteria thrive was pH 2.6 to 2.9. The new fluorescent dyes were all able to clearly stain and microscopically visualize in-situ the bacteria within the biofilm community without changing pH or background ion concentration. The commonly used fluorescent dyes DAPI and SYTO 59 were also applied for comparison. Both dyes, however, were not able to visualize any bacteria in-situ, since they were not stable under the very acid conditions.
In addition, dye V07-04118 and dye DY-613 also possess the ability to stain larger cells which were presumably eukaryotic origin and may be attributed to yeast cells or amoeba-like cells. PCR analyses have shown that the dominant bacterial species in these acidophilic biofilm communities was a gram negative bacterium of the species Ferrovum myxofaciens. The presented four new dyes are ideal for in-situ investigations of microorganisms occurring in very acid conditions, e.g. in acidophilic biofilm communities when in parallel information on pH sensitive incorporated fluorescent heavy metals should be acquired.
Keywords: acidophilic macroscopic streamer, snotite, acid mine drainage, acid stable fluorescence dyes
  • Journal of Fluorescence 20(2010)4, 943-951

Publ.-Id: 13466 - Permalink

Annual Report 2008 - Institute of Safety Research
Weiß, F. P.; Rindelhardt, U.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-524 2009


Publ.-Id: 13464 - Permalink

Characterization of discharge during depressurization of foaming systems using conductivity wire-mesh sensors
Imhof, H.; Tost, K.; Thiele, S.; Hampel, U.; Steinbach, J.;
To characterize depressurization events the discharge over time needs to be determined as well as its composition. In depressurization research so far the use of gamma densitometers is well established [1]. An alternative technology is wire-mesh tomography. In the experiments carried out their usability to characterize the discharge while venting is investigated for the first time.
Application of wire-mesh tomography allows investigation of multiphase flows with high spatial and temporal resolution. The cross-sectional phase distribution in a vessel or pipe can be characterized based on local measurements of electrical conductivity of the fluid by means of crossing electrodes. This sensing technology was introduced about ten years ago as a conductivity measuring modality [2]. Since then it has been employed to the study of numerous single phase and two-phase flow phenomena, such as gas/water and steam/water two-phase flows in components in nuclear power plants, cavitation and pressure shock phenomena in fluid pipelines, water transport processes in soil and flow structures in bubble columns. The general design of a wire-mesh sensor can be seen in Figure 1. Additional information, such as flow rates, can be gained by combining signals of two wire-mesh sensors. By analysing the cross-sectional phase distributions of two distant sensors in a pipe with cross-correlation techniques one obtains velocity and consequently flow rate information.
First experiments using a setup equipped with wire-mesh sensors show that discharge over time and its composition can be measured. Analysis of experiments depressurizing a reactor filled 66.7% with water at a pressure of 5barg shows that in the horizontal pipe slug flow can be observed. Waves of the slug flow can be identified. A distinction between single-phase and two-phase discharge can be made using the sensors. Most importantly it can be seen, Figure 2, that comparing these experiments with experiments without sensors shows no differences in pressure decrease over time in the reactor and mass discharge.
Experiments depressurizing comparable foaming systems with the same experimental conditions show differing results. Foaming was achieved by adding Falterol, isobutanol and SDS. Results of the wire-mesh sensors are comparable to the results of non-foaming systems. Slug flow can be observed that can be characterized concerning mass discharge rates and composition. As shown in Figure 3 major differences crop up when looking at pressure decrease over time and mass discharge. The sensors either hinder the flow or foam the liquid which results in slower pressure decrease rates in the reactor. Thus longer periods of two-phase discharge can be observed. This increases the overall mass discharge from 23% to 39%.
  • Contribution to proceedings
    19th International Congress of Chemical and Process Engineering, 28.08.-01.09.2010, Prag, Czech Republic
    Characterization of discharge during depressurization of foaming systems using conductivity wire-mesh sensors
  • Lecture (Conference)
    19th International Congress of Chemical and Process Engineering CHISA 2010, 28.08.-01.09.2010, Prague, Czech Republic

Publ.-Id: 13463 - Permalink

High-precision (p,t) reaction measurement to determine 18Ne(alpha,p)21Na reaction rates
Matic, A.; van den Berg, A. M.; Harakeh, M. N.; Wörtche, H. J.; Berg, G. P. A.; Couder, M.; Fisker, J. L.; Görres, J.; Leblanc, P.; O'Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.; Shimbara, Y.; Fujita, H.; Wakasa, T.; Hess, P. O.; Brown, B. A.; Schatz, H.;
x-ray bursts are identified as thermonuclear explosions in the outer atmosphere of accreting neutron stars. The thermonuclear runaway is fueled by the alphap process that describes a sequence of (alpha,p) reactions triggered by the 18Ne(alpha,p)21Na breakout reaction from the hot CNO cycles. We studied the level structure of the compound nucleus 22Mg by measuring the 24Mg(p,t)22Mg reaction at the Grand Raiden spectrometer at Research Center for Nuclear Physics, Osaka. A large number of alpha-unbound states was identified and precise excitation energies were determined. Based on shell model and alpha-cluster model calculations we predict the level parameters for determining the stellar reaction rate of 18Ne(alpha,p)21Na for a wide temperature range. x-ray burst simulations have been performed to study the impact of the reaction on the x-ray burst luminosity.

Publ.-Id: 13462 - Permalink

Controlled reduction of the nucleation field in Co/Pt multilayer wires
Moser, J.; Kobs, A.; Vogel, A.; Gerhardt, T.; Bolte, M.; Im, M.-Y.; Fischer, P.; Wintz, S.; Merkt, U.; Oepen, H. P.; Meier, G.;
Due to their narrow domain walls, nanowires with high uniaxial out-of plane anisotropy are interesting candidates for spin-momentum transfer studies. Since high current densities can change or destroy the wires investigated, weak pinning potentials allowing the controlled and reliable depinning of domain walls at low current densities are desirable. A prerequisite for the preparation of a domain wall at such pinning sites are nucleation fields smaller than the fields required to depin the domain wall from the respective pinning site. We suggest two methods to tune the nucleation field of lithographically designed Co/Pt multilayer wires. The magnetization reversal of the wires is investigated by means of transmission X-ray microscopy. An up to fourfold reduction of the nucleation field could be achieved through altering the lateral shape of the wires or by depositing Fe stripes on top. The authors gratefully acknowledge financial support by the DFG and the DOE.
Keywords: magnetism, domain wall, nanowire, pinning, Co/Pt multilayers, nucleation field
  • Poster
    DPG-Frühjahrstagung der Sektion kondensierte Materie, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 13461 - Permalink

Heterologous expression of a surface layer-like protein in E. coli causes a drastic morphological change of the cell
Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.;
Bacterial envelope proteins, so called surface layers (S-layer) are widely spread pararcrystalline surface structures which coat the cells of lots of bacterial strains and all archaea. They are mostly composed of protein monomers which form via self-assembling high regular two dimensional arrays. The S-layer proteins we investigate are from bacterial strains recovered from uranium mining waste pile Haberland in Saxony, Germany.
Their S-layer proteins selectively bind uranium and protect the cells from its toxicity. These special S-layer characteristics make them interesting for many technological applications such as filter materials, biosensors, as functional surfaces, or for example as drug containers.
In order to produce S-layer proteins in a high efficient way a heterologous expression in Escherichia coli is essential. In our study, the S-layer-like protein SllB of Lysinibacillus sphaericus JG-A12 was expressed in E. coli Bl21. Noteworthy, recombinant protein production resulted in a high stability of the cells against mechanical and chemical treatment. These unusual cells were analyzed by light microscopy, AFM and TEM. All methods demonstrated a total changed cell morphology with long filaments in the beginning of the exponential growth stage and 5-200 µm long tube like transparent structures at the end of the exponential growth stage containing E. coli single cells. Analyses by SDS-PAGE, N-terminal sequencing and IR-spectroscopy showed that the tube-like structures consist of outer membrane associated with recombinant surface layer proteins. These findings point to a disordered cell division. However, the underlying mechanism of these morphological changes are not known and will be analyzed in future. The long filaments, in combination with high expression level, good growth and high stability make these unusual E. coli cells interesting for biotechnological applications. In addition, these results cast a new light on one of the best studied microorganisms.
Keywords: S-layer, Escherichia coli, heterologous expression, tube-like structures
  • Lecture (Conference)
    VAAM-Jahrestagung 2010, 28.-31.03.2010, Hannover, Deutschland

Publ.-Id: 13460 - Permalink

TOPFLOW experiments on counter-current flow limitation in a model of the hot leg of a PWR
Vallee, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.;
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Forschungszentrum Dresden-Rossendorf (FZD). The hot leg model is devoted to optical measurement techniques, therefore, a flat test section design was chosen and equipped with large windows. In order to enable the operation at high pressures, the test section is installed in the pressure chamber of the TOPFLOW test facility of FZD, which is used to perform the experiments under pressure equilibrium with the inside atmosphere. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux-condenser cooling mode appearing in some small break LOCA scenarios. The fluids used were air and water at room temperature and pressures of up to 3.0 bar, as well as steam and water at pressures of up to 50 bar and the corresponding saturation temperature of 264°C. One selected 50 bar experiment is presented in detail and the flow behaviour observed with the high-speed camera is analysed.

Furthermore, the flooding characteristics obtained from the different experimental runs are presented in terms of the Wallis parameter and Kutateladze number, which are commonly used in the literature. However, both parameters fail to properly correlate the data: a discrepancy is observed between the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes into account the effect of the fluid viscosities on the CCFL. Finally, the new parameter was validated successfully against the UPTF data. This shows that the proposed modification of the Wallis parameter allows a significant improvement for experimental series with variation of the viscosities.
Keywords: two-phase flow, flooding, counter-current flow limitation, hot leg, pressurised water reactor, Wallis parameter, viscosity
  • Lecture (Conference)
    NURISP open General Seminar, 30.11.-01.12.2009, Dresden, Germany

Publ.-Id: 13459 - Permalink

Comparison of countercurrent flow limitation experiments performed in two different models of the hot leg of a PWR with rectangular cross-section
Vallée, C.; Seidel, T.; Lucas, D.; Tomiyama, A.; Murase, M.;
In order to investigate the two-phase flow behaviour during counter-current flow limitation in the hot leg of a pressurised water reactor, two test models of were built: one at the Kobe University and the other at the TOPFLOW test facility of Forschungszentrum Dresden-Rossendorf (FZD). Both test facilities are devoted to optical measurement techniques, therefore, a flat hot leg test section design was chosen. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux condenser cooling mode appearing in some accident scenarios. The fluids used were air and water, both at room temperature. The pressure conditions were varied from atmospheric in Kobe to 3.0 bar absolute at TOPFLOW. According to the presented review of the literature, very few data is available on flooding in channels with rectangular cross-section, and no experiments were performed in the past in such rectangular models of a hot leg. Usually, the macroscopic effects of CCFL are represented in a flooding diagram, where the gas flow rate is plotted versus the discharge water flow rate. Commonly, the non-dimensional superficial velocity (also known as Wallis parameter) is used to plot the flooding diagram. However, the classical definition of the Wallis parameter contains the pipe diameter as characteristic length, which was originally defined by Wallis (1961) for counter-current flow limitation in vertical pipes and not in near horizontal channels with rectangular cross-section. In order to be able to perform comparisons with pipe experiments and to extrapolate to the power plant scale, the appropriated characteristic length should be determined.

Because the experimental projects on this subject at the Kobe University and at FZD were launched independently, a detailed comparison of both test facilities is presented. With respect to the CCFL behaviour, it is shown that the essential parts of the two hot leg test sections are very similar. This geometrical analogy allows to perform meaningful comparisons. However, clear differences concerning the dimensions of the cross-section (H x W = 150 x 10 mm² in Kobe, 250 x 50 mm² at FZD) allow to point out the right characteristic length for hot leg models with rectangular cross-sections. The hydraulic diameter, the channel height and the Laplace critical wavelength (leading to the Kutateladze number) were tested. The experimental results obtained on both test facilities show clearly that the channel height is the suited characteristic length. Finally, the experimental results are compared with similar experiments and empirical correlations for pipes available in the literature. In spite of the scatter of the data and of the different correlations, the overall agreement is good.
Keywords: two-phase flow, flooding, counter-current flow limitation, hot leg, pressurised water reactor, Wallis parameter, rectangular channel
  • Contribution to proceedings
    18th International Conference on Nuclear Engineering (ICONE18), 17.-21.05.2010, Xi'an, China, Paper ICONE18-30089
  • Lecture (Conference)
    18th International Conference on Nuclear Engineering (ICONE18), 17.-21.05.2010, Xi'an, China
  • Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 133(2011)5, 052917
    DOI: doi:10.1115/1.4002884

Publ.-Id: 13458 - Permalink

From nature for nature – bioinsipred nanocomposite materials for environmental technology
Raff, J.; Weinert, U.; Günther, T.; Matys, S.; Kutschke, S.; Pollmann, K.;
Microorganisms like bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example, intensively studied at the Institute of Radiochemistry of the Forschungszentrum Dresden-Rossendorf, is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins prevent the uptake and any sustainable damage of the cell by toxic and/or radioactive metals. The S-layers itself form highly ordered and mono-molecular envelopes around bacterial and archaeal cells. Noteworthy is their ability to self-assemble in suspension, on surfaces and at interfaces. Furthermore S-layers of different bacteria are able to fulfil different functions and thus may act as immobilization matrix for exoenzymes, as molecular sieve, as ion and molecule trap or they protect the cell from being affected by the immune defence of host organism, by other bacteria or by lytic enzymes. By combining these unique features of S-layer proteins, smart coatings on many different surface can be realized. Currently at the Institute of Radiochemistry, S-layer based functional coatings are under development for the production of (photo)catalytic active materials, metal selective filters or highly specific biosensors. Therefore possible applications are the elimination of pharmaceuticals and germs, the detoxification of metals, the removal of toxic metals, the recovery of noble metals or the detection of pharmaceuticals and other organic matter in water. Additionally, combinations of functionalities are possible using a layer-by-layer technique, offering a wide field for the development of new nanostructured biocomposites for environmental technology.
  • Poster
    Jahrestagung der Vereinigung für Allgemeine und Angewandte Mikrobiologie (VAAM), 28.-31.03.2009, Hanover, Deutschland
  • Poster
    nano tech 2010 –International Nanotechnology Exhibition and Conference “Green Nanotechnology, 17.-19.02.2009, Tokyo, Japan

Publ.-Id: 13457 - Permalink

Deep levels in Ni doped ZnO Materials Research Society
Schmidt, M.; Ellguth, M.; Brachwitz, K.; Brandt, M.; von Wenckstern, H.; Pickenhain, R.; Grundmann, M.; Brauer, G.; Skorupa, W.;
  • Poster
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Publ.-Id: 13456 - Permalink

Divacancy-hydrogen complexes in zinc oxide
Kuriplach, J.; Brauer, G.; Melikhova, O.; Cizek, J.; Prochazka, I.; Anwand, W.;
  • Lecture (Conference)
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Publ.-Id: 13455 - Permalink

Investigation of interaction of hydrogen with defects in zirconia
Melikhova, O.; Kuriplach, J.; Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.;
  • Lecture (Conference)
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Publ.-Id: 13454 - Permalink

A nodal approach to the solution of the multi-group SP3 equations in trigonal geometry
Duerigen, S.; Grundmann, U.; Mittag, S.;
The core model DYN3D developed for 3-D analyses of steady states and transients in thermal reactors is being extended by a simplified P3 (SP3) version for hexagonal fuel assemblies with a view to new reactor types such as high-temperature reactors.
Keywords: DYN3D SP3 SP3 nodal method hexagonal geometry trigonal geometry triangular geometry
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 04.-06.05.2010, Berlin, Germany
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 04.-06.05.2010, Berlin, Germany

Publ.-Id: 13453 - Permalink

Use of the local Pu-239 concentration as an indicator of burnup spectral history in DYN3D
Bilodid, I.; Mittag, S.;
Reactor dynamics codes such as DYN3D use two-group cross sections (XS) which depend on local burnup, given in terms of the energy produced per fuel mass (MWd/kgHM). However, a certain burnup value can be reached under different spectral conditions depending on moderator density and other local parameters. Neglecting these spectral effects, i.e. applying the summary-burnup value only, can cause considerable errors in the calculated power density.
This paper describes a way to take into account spectral-history effects. It is shown that the respective XS correction linearly depends on the actual Pu-239 concentration. The applicability of the method was proved not only for usual uranium oxide fuel, but also for mixed uranium/plutonium oxide (MOX) and fuel assemblies with burnable absorber. The code DYN3D was extended by new subroutines which calculate the actual distribution of Pu-239 in the core and apply a spectral-history correction for the XS.
Keywords: cross section library, history effects, spectral history, burnup, DYN3D

Publ.-Id: 13452 - Permalink

Complexation of protactinium(V) with poly(amino)carboxylic acids
Mendes, M.; Le Naour, C.; Hamadi, S.; Den Auwer, C.; Moisy, P.; Di Giandomenico, V. M.; Hennig, C.;
Protactinium is experiencing a renewal of interest in the frame of nuclear reactors based on thorium fuel. The isotopes 233Pa (intermediate in the production of the fissile 233U) and 231Pa (radiotoxic) are namely produced through nuclear reactions on 232Th: Aside from a possible use of thorium as nuclear fuel for energy production, studies on protactinium may provide additional information about the coordination chemistry of light actinides. The literature devoted to protactinium in aqueous solution is characterized by scarce and controversial thermodynamic data that originate from the strong tendency of Pa(V) towards hydrolysis and polymerization especially in non-complexing media. Modeling the behavior of this element in the reactor, in the reprocessing steps, in the geosphere and in physiological medium requires thermodynamic and structural data relevant to these various environments. The present work is the continuation of our previous studies devoted to hydrolysis and complexation of Pa(V) with sulfate ions. The aim is now to collect thermodynamic and structural data on Pa(V) in the presence of oxalic (H2C2O4) and diethylene-triamine-pentaacetic (H5DTPA) acids.
The apparent formation constants of Pa(V) complexes with oxalate and DTPA5- were deduced from tracer level experiments using the isotope 233Pa at ~10 12 M. At such low concentration of element, only partition or transport methods based on radiation detection can be used5. In this work, the technique of solvent extraction involving the chelating agent thenoyl-trifluoro-acetone (TTA) was chosen. The aqueous phase was a mixture of NaClO4, HClO4 and H2C2O4 or H5DTPA. The dissociation constants H2C2O4 or H5DTPA were taken from references. Firstly, extraction data, collected at constant ionic strength and temperature allowed to determine the maximum order of Pa(V) complexes, the mean charge of the predominant complex in aqueous phase and the number of TTA molecules per Pa atom in the extracted species. Secondly, a systematic study of the variations of the distribution coefficient D of Pa(V) as function of the free ligand concentrations performed at different temperature values, led to the determination of thermodynamic data relevant to complexation equilibria (formation constants, enthalpy and entropy variations). Figure 1 illustrates the variations of D as function of free DTPA5- concentration when temperature increases from 10 to 60°C. Whatever the temperature, these curves characterize the formation of a (1,1) complex that stability constant can be derived from the variations of (D0/D-1) as function of DTPA5-. At 25°C, the constant relative to the equilibrium PaO(OH)2+ + DTPA5- + H+ ↔ PaODTPA2- + H2O has been estimated to log1 = 29,0 ± 0,4 for an ionic strength equal to 3 M. In the oxalate system, the existence of the complexes (1,1) and (1,2) has been unambiguously demonstrated.
Since no structural information can be deduced from tracer level experiments, X-ray Absorption Spectroscopy measurements were performed on 231Pa samples in oxalic acid. As in concentrated sulfuric acid8, XANES spectra do not display the feature of the linear di-oxo bond that characterizes U, Np, Pu and Am at their higher oxidation states, whereas the analysis of EXAFS data has unambiguously demonstrated the presence of a short mono-oxo bond (1.73 Å).
Keywords: Protactinium, EXAFS
  • Lecture (Conference)
    Actinides 2009, 12.-17.07.2009, San Franzisco, USA

Publ.-Id: 13451 - Permalink

Coordination of the limiting U(IV) carbonate species in aqueous solution – a comparative EXAFS and XRD investigation
Emmerling, F.; Hennig, C.; Kraus, W.; Ikeda-Ohno, A.; Scheinost, A. C.;
The carbonate anion is one of the most important ligand in natural waters. The solubility of heavy metals like uranium is strongly affected by carbonate through the forming anionic complexes [1]. Uranium is well soluble in oxidation state VI. The oxidation state V is rather instable due to the fast disproportionation reaction. In contrast, the solubility of uranium IV is rather low. The situation changes completely in presence of carbonate. Because the disproportionation reaction of U(V) is strongly enforced by cation-cation interactions, strong ligands like carbonate are able to suppress this reaction. In consequence, U(V) can be stabilized over months in carbonate solution. Although U(IV) strongly tent to form polynuclear species and colloids, carbonate enhances its solubility by forming mononuclear U(IV) carbonato complexes. The coordination of U(VI) and U(V) has been described. The coordination of the limiting U(IV) carbonate complex is actual under debate. The aim of this study is to determine the coordination of the solution species and to preserve it, if possible, in a crystal structure. Because EXAFS provides only a radial distribution function of the next interatomic distances but no information on their spatial arrangement, the comparison with the crystal structure provide necessary information on the ligand arrangement. We used EXAFS again to follow the crystallization process and to proof that no rearrangement of carbonate occurs during the crystallization process.
Keywords: U(IV) carbonato complexes, EXAFS, XRD
  • Poster
    17. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 09.-12.03.2009, Hannover, Germany

Publ.-Id: 13450 - Permalink

Formation and structure of uraninite colloids
Hennig, C.;
Because uranium(IV) has a very low solubility over a wide pH range it is considered as immobile under anaerobic conditions. The solid uraninite may occur as nano-sized colloid which is very mobile in the environment. Conditions of the colloid formation and the reaction mechanisms will be discussed.
Keywords: EXAFS, colloids
  • Invited lecture (Conferences)
    Tu Bergakademie Freiberg, Institut für Geologie, 25.2.2009, Freiberg, Germany

Publ.-Id: 13449 - Permalink

Optical properties of silver nanowire arrays with 35 nm periodicity
Ranjan, M.; Oates, T. W. H.; Facsko, S.; Möller, W.;
We present highly ordered Ag nanowire arrays with 35 nm periodicity grown on patterned templates. The optical properties measured using generalized ellipsometry exhibit strong anisotropy. Dielectric functions are calculated by fitting the Jones matrix elements with a biaxial layer model, accounting for both metallic behavior and localized surface plasmon resonances. The amplitude and wavelength maximum of the plasmon resonance perpendicular to the wires increase with increasing wire width and thickness. The dielectric coefficients of 10-mm-wide nanowires showa transition behavior from insulating inUVto metallic above 550 nm. Their potential application as polarizationdependent plasmonic-scattering transparent conductive electrodes is discussed.
Keywords: nanowires, plasmonics, ellipsometry

Publ.-Id: 13448 - Permalink

Positron annihilation spectroscopy using high-energy photons
Butterling, M.; Anwand, W.; Brauer, G.; Cowan, T. E.; Hartmann, A.; Jungmann, M.; Kosev, K.; Krause-Rehberg, R.; Krille, A.; Schwengner, R.; Wagner, A.;
The superconducting electron accelerator ELBE (Electron Linac with high Brilliance and low Emittance) at the Research Centre Dresden-Rossendorf (Germany) serves as a high-intensity bremsstrahlung photon-source delivering a pulsed beam (26 MHz) with very short bunches (<5 ps). The photons are being converted into positrons by means of pair production inside the target material thus forming an intense positron source.
The accelerator machine pulse is used as time reference allowing positron lifetime spectroscopy. We performed positron annihilation spectroscopy by pair production in different sample materials and used coincidence techniques to reduce the background due to scattered photons significantly in order resulting in spectra of extraordinary high quality.
Keywords: superconducting electron accelerator ELBE bremsstrahlung positrons pair production lifetime spectroscopy
  • Physica Status Solidi (A) 207(2010)2, 334-337

Publ.-Id: 13447 - Permalink

Integration of DYN3D into the NURESIM platform and coupling with FLICA
Kliem, S.; Gommlich, A.; Rohde, U.;
The presentation gives an overview about the implementation of DYN3D into the NURESIM platform and the coupling with the thermal-hydraulic code FLICA-4.
  • Lecture (others)
    NURISP - General Seminar, 30.11.-01.12.2009, Dresden, Germany

Publ.-Id: 13446 - Permalink

Absence of ferromagnetic-transport signatures in epitaxial paramagnetic and superparamagnetic Zn0.95Co0.05O films
Ye, S.; Ney, V.; Kammermeier, T.; Ollefs, K.; Zhou, S.; Schmidt, H.; Wilhelm, F.; Rogalev, A.; Ney, A.;
Paramagnetic (PM) and superparamagnetic (SPM) Zn0.95Co0.05O epitaxial films display similar temperature and magnetic field dependent anisotropic magnetoresistance (MR) effects. The high structural quality of the PM films is confirmed by x-ray linear dichroism. A classical two-band model describes these MR effects well, and reveals the same intrinsic origin of the transport signatures in PM and SPM Zn0.95Co0.05O films. The temperature dependent resistivity of the respective films arises from a Mott variable-range hopping process. The absence of the anomalous Hall effect in the SPM film provides another evidence for lacking contributions from the SPM phase to the magnetotransport properties. Moreover, above the blocking temperature of SPM Zn0.95Co0.05O films, the M(H)-curve can be described by a Langevin function, indicating the presence of approximately 2 nm large magnetic nanoparticles. Therefore, only the contribution of PM Co2+ ions in Zn0.95Co0.05O films to the transport behavior can be found, thus demonstrating that 2 nm large magnetic Co nanoparticles does not interact with the carriers.

Publ.-Id: 13445 - Permalink

Winkel- und Energieverteilung bei Magnetron Sputtern
Neidhardt, J.; Möller, W.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Analytische Massenspektrometrie in der Oberflächentechnik – Grundlagen und Anwendung, 25.11.2009, Dresden, Deutschland
  • Contribution to proceedings
    Analytische Massenspektrometrie in der Oberflächentechnik – Grundlagen und Anwendung, 25.11.2009, Dresden, Deutschland

Publ.-Id: 13444 - Permalink

Atomic Billiard – Materials Science using hyperthermal Ions
Neidhardt, J.;
Ions and atoms are in their properties much alike. Except the electrical charge, which enables us to control the velocity and direction of ions in contrast to atoms in a fairly straight forward and precise way. Just the voltage of a ordinary car battery (12 V) can accelerate for instance an Ar+ ion to approximately 7.6 km/s – almost the velocity required to leave the earths orbit (1st cosmic velocity 11.2 km/s). If these fast projectiles impact on surfaces, their defined directionality and momentum provides for a game of billiard on smallest level possible. The extreme conditions of the collisions are widely utilized in materials science for unique analysis and non thermal synthesis methods, as for example just thermal excitation of Ar at room temperature (20°C) results in “only” 0.35 km/s.
The lecture will therefore introduce sources of ions and ways to control their energy and directionality (plasmas, accelerators, ion optics), with a short outlook on the underlying physics. Further, the basic principles of ion-surface interactions will be described and examples for their applications will be given, both for synthesis as well as analysis methods. For the first, thin film deposition and ion implantation methods, for the latter, ion-beam analysis methods, such as elastic recoil detection, Rutherford backscattering and nuclear reaction analysis, will be exemplarily elucidated.
  • Lecture (others)
    Dozentvorlesung, 16.11.2009, Linköping, Schweden

Publ.-Id: 13443 - Permalink

Assessment of early-phase accident management strategies in a station backout scenario for VVER-1000 Reactors
Tusheva, P.; Schäfer, F.; Reinke, N.; Weiss, F.-P.;
In recent years, many NPPs have developed and implemented severe accident management guidelines (SAMG). It is the primary objective of developing SAMG to prevent or mitigate the consequences of severe accidents by keeping the reactor pressure vessel (RPV) integrity and reducing the load to the containment. In a hypothetical Station Blackout accident all active safety systems are unavailable. Without additional measures this would lead to heating-up of the reactor core with severe core degradation. To avoid or to limit the consequences of a possible core heat up, different accident management strategies can be applied.

This paper presents an assessment of early-phase accident management actions for VVER-1000 reactors. In particular Primary Side Depressurization (PSD) is investigated as a basic strategy for managing severe accidents under high pressure conditions.
In addition, Secondary Side Depressurization (SSD) is also being investigated. It aims at fast reduction of the secondary pressure and feeding the steam generators’ secondary side with water from the feed water tank or from a different source. In that way, the heat removal from the primary to the secondary side can be significantly enhanced and the core heat-up at high pressure can be delayed.

A number of simulations with different criteria for actuation of the PSD procedure and additional SSD were performed using the thermal-hydraulic system code ATHLET. This paper provides a detailed modelling of the reactor coolant system and the required safety systems, analysis of the thermal-hydraulic and safety parameters and description of the physical phenomena. Special attention is given to the possibilities of preventing or at least delaying an extended core heat-up depending on the availability of the operational and safety systems. The effectiveness of the applied accident management measures and the effect on the accident progression were studied in order to assess the maximum response time for operators’ intervention.
Keywords: accident management measures, station blackout, depressurization
  • Contribution to proceedings
    ICONE 18, 17.-21.05.2010, Xi'an, China
  • Lecture (Conference)
    ICONE 18, 17.-21.05.2010, Xi'an, China, 17.-21.05.2010, Xi'an, China

Publ.-Id: 13442 - Permalink

High-Energy Protons from closely stacked, ultra-thin foils
Kluge, T.; Bussmann, M.; Zeil, K.; Kraft, S. D.; Schramm, U.; Cowan, T. E.;
Ions accelerated from solid foils using ultra-intense laser pulses may have major impact on applications such as cancer therapy. While such ion beams typically have a low emittance and high charge density their maximum energy still falls short of therapy requirements. Analytic scaling laws for micrometer targets suggest an increase in maximum energy when reducing the pulse duration down to an optimum value. Further energy increase has recently been proposed when using ultra-thin foils or micro-structured targets.
We propose a new target design based on novel stacked foils which may lead to an acceleration of ions to even higher energies by a single high-intensity (~1020 -1021 W/cm2 ) ultra-short laser pulse. In contrast to complex schemes relying on the use of synchronized laser pulses predicting a comparable ion energy gain, here the time interval between the irradiation of the individual foils is determined by their spacing.
We present an analysis of the fundamental acceleration mechanism and will focus on the electron dynamic during the laser interaction with the target. Based on thorough simulations and an analytic description of the laser interaction we will show how the enhanced electron dynamics in the early stages of the interaction leads to the gain in maximum ion energy observed in our simulations. Based on this analysis, for relevant target parameters we deduce optimum values and their scalings.
  • Lecture (Conference)
    ULIS2009, 24.-29.05.2009, Frascati, Italia

Publ.-Id: 13441 - Permalink

Untersuchungen zur Bestimmung der EPS–Zusammensetzung in natürlichen urankontaminierten Biofilmen
Gründig, I.;
In dieser Diplomarbeit wurde die Zusammensetzung der EPS-Komponenten von natürlichen Biofilmen untersucht. Die Untersuchungen ergaben, dass die EPS der verschiedenen Biofilme sehr unterschiedliche Zusammensetzungen bezogen auf die Komponenten Proteine, Kohlenhydrate und Uronsäuren aufwiesen. Dabei war der Lipidgehalt in den Biofilmen am höchsten. Umweltfaktoren wie Standort oder fließendes Wasser wirken sich auf die Zusammensetzung der EPS aus.
Keywords: biofilm, extracellular polymeric substance, thin-layer chromatography, proteins, carbohydrates, lipids, uronic acids
  • Other report
    Dresden: FZD (Diplomarbeit), 2009
    97 Seiten

Publ.-Id: 13440 - Permalink

Low-Divergent, Energetic Electron Beams from Ultra-Thin Foils
Kluge, T.; Bussmann, M.; Gaillard, S. A.; Flippo, K. A.; Gautier, D.; Gall, B.; Lockard, T.; Lowenstern, M. E.; Mucino, J. E.; Sentoku, Y.; Zeil, K.; Kraft, S. D.; Schramm, U.; Cowan, T. E.; Sauerbrey, R.;
In this work we report on a recent experiment where an energetic, well-collimated electron beam has been observed in the laser direction following the short pulse (600 fs) high-intensity laser interaction with ultra-thin solid foils. These results are in contrast to the typical low-energy divergent electrons accompanying ions in the target normal direction usually seen in solid targets.We observe the foils being preheated and expanded by ASE prior to the main pulse which makes them transparent for the laser. The experimental evidence as well as 2D particle-in-cell simulations suggest the excitation of a wakefield that can accelerate electrons to energies of tens of MeV.
Keywords: Laser, Proton, Electron, Acceleration, Wakefield
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) 2010, 10.3.2010, Hannover, Deutschland

Publ.-Id: 13439 - Permalink

Influence of irradiation on metabolism and metastatic potential of B16-F10 melanoma cells
Mosch, B.; Müller, K.; Steinbach, J.; Pietzsch, J.;
To analyse short term and long term X-ray irradiation effects on proliferation, viability, glucose and amino acid uptake of murine melanoma cells in vitro and metastasis in vivo.

Materials and methods:
B16-F10 melanoma cells were irradiated with different doses of X-ray irradiation (200 kV) in the range from 1-20 Gy. One, two and three days respectively 7, 14 and 21 days after treatment cells were analysed concerning cell growth, viability, proliferation, cell cycle distribution, glucose and amino acid transport. Moreover the capability of the cells for in vivo metastasis was examined.

As short term response on irradiation we detected decreased cell growth, viability and arrest in the G2/M phase of the cell cycle. Long term response involves re-start of proliferation, increased cell growth and glucose uptake but still decreased viability and amino acid transport. In vivo metastasis is lost immediately after irradiation and regained to a low extent beyond two weeks time for recurrence of cells before injection.

In vitro data suggest that surviving melanoma cells compensate the initial irradiation-dependent damage of proliferation within three weeks possibly by increase in glucose uptake. For metastasis in vivo the role of additional mechanisms is strongly suggested.

Publ.-Id: 13438 - Permalink

Prediction of clonogenic cell survival curves based on the number of residual DNA double strand breaks measured by γH2AX staining
Menegakis‌, A.; Yaromina‌, A.; Eicheler‌, W.; Dörfler, A.; Beuthien-Baumann, B.; Thames, H. D.; Baumann‌, M.; Krause, M.;
To assess the potential of using the residual phosphorylation of histone H2AX (γH2AX) after irradiation as a marker of radiosensitivity invitro.

Material and methods:
Confluent cell cultures of FaDu and SKX human squamous cell carcinoma lines were irradiated with graded single doses. Twenty-four hours after irradiation cells were seeded for standard colony forming assay (CFA). In parallel, staining for γH2AX was performed to visualise the residual foci.

In the CFA, FaDu showed a higher radioresistance than SKX. After analysis of the residual foci data, we constructed ‘predicted’ survival curves using two different methods. First, the proportion of nuclei with <3 foci was found to correlate closely with the observed surviving fraction (SF) in FaDu, with a slight overestimation of the true SF in SKX. Second, there was a strong linear correlation of the mean number of residual foci and observed −lnSF. Based on regression analysis, we calculated the SF for both cell lines based on the mean number of residual γH2AX foci. This second approach again led to a good correlation of predicted and observed SF values in FaDu and a (slight) overestimation in SKX.

Conclusion:In the two cell lines investigated the mean number of residual foci of γH2AX can be used to predict differences in the radiation dose response relationship invitro.

Publ.-Id: 13437 - Permalink

ODD-PARITY BANDS OF Ru-108, Ru-110, Ru-112
Luo, Y.; Zhu, S.; Hamilton, J.; Ramayya, A.; Goodin, C.; Li, K.; Che, X.; Hwang, J.; Lee, I.; Jiang, Z.; Ter-Akopian, G.; Daniel, A.; Stoyer, M.; Donangelo, R.; Frauendorf, S.; Dimitrov, V.; Zhang, J.; Cole, J.; Stone, N.; Rasmussen, J.;
Two similar sets of odd-parity bands are observed in each of three even-even neighbors, Ru-108,Ru-110,Ru-112, from a study of prompt spontaneous-fission gamma rays at Gammasphere. A careful study of the odd-parity levels of these nuclei shows evidence for the features of chiral doubling. Comparisons are made with reported other candidates for chiral doubling.

Publ.-Id: 13436 - Permalink

Hydrogen-induced defects in Pd films
Cizek, J.; Prochazka, I.; Melikhova, O.; Vlach, M.; Zaludova, N.; Brauer, G.; Anwand, W.; Egger, W.; Sperr, P.; Hugenschmidt, C.; Gemma, R.; Pundt, A.; Kirchhelm, R.;
Hydrogen absorbed in crystalline solids causes a lattice expansion and the formation of hydride phases. Contrary to free standing bulk samples, thin films are fixed at substrates, which prevent their in-plane expansion. This makes hydrogen-induced expansion of thin films highly anisotropic and leads to the formation of high stresses in hydrogen loaded thin films. As a consequence, lattice defects may be created in thin films loaded with hydrogen. This work reports about defects created by hydrogen loading in epitaxial Pd films deposited on Al2O3 substrates by cold cathode beam sputtering. Hydrogen-induced defects are characterized by positron annihilation spectroscopy performed with variable energy slo positron beams. Extended studies of defect depth profile and its development with increasing concentration of hydrogen are performed by measurement of Doppler broadening of annihilation profile using a continuous positron beam. Selected states are investigated also by positron lifetime spectroscopy on an intense pulsed positron beam. Firstly, the microstructure of virgin films is characterized. Subsequently, the hydrogen concentration in the films is increaxed step-by-step by electrochemical charging. The development of the film microstructure and the evolution of defects are investigated.
  • Physica Status Solidi (C) 6(2009)11, 2364-2366

Publ.-Id: 13435 - Permalink

Positron trapping at vacancy-hydrogen complexes in zinc oxide
Kuriplach, J.; Melikhova, O.; Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.;
  • Lecture (Conference)
    Advanced Science Research Symposium “Positron, muon, and other exotic particle beams for materials science and atomic/molecular sciences”, 10.-12.11.2009, Tokai, Japan

Publ.-Id: 13434 - Permalink

Investigation of hydrogen interaction with defects in zirconia
Melikhova, O.; Kuriplach, J.; Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.;
Defect studies of a ZrO2 + 9 mol. % Y2O3 single crystal were performed in this work using a high resolution positron lifetime spectroscopy combined with slow positron implantation spectroscopy. In order to elucidate the nature of positron trapping sites observed experimentally, the structural relaxations of several types of vacancy-like defects in zirconia were performed and positron characteristics for them were calculated. Relaxed atomic configurations of studied defects were obtained by means of ab initio pseudopotential method within the supercell approach. Theoretical calculations indicated that neither oxygen vacancies nor their neutral complexes with substitute yttrium atoms are capable of positron trapping. On the other hand, zirconium vacancies are deep positron traps and are most probably responsible for the saturated positron trapping observed in yttria stabilized zirconia single crystals. However, the calculated positron lifetime for zirconium vacancy is apparently longer than the experimental value corresponding to a single-component spectrum measured for the cubic ZrO2 + 9 mol. % Y2O3 single crystal. It was demonstrated that this effect can be explained by hydrogen trapped in zirconium vacancies. On the basis of structure relaxations, we found that zirconium vacancy – hydrogen complexes represent deep positron traps with the calculated lifetime close to the experimental one. In zirconium vacancy – hydrogen complexes the hydrogen atom forms an O-H bond with one of the nearest neighbour oxygen atoms. The calculated bond length is close to 1 Å.
  • Poster
    Advanced Science Research Symposium “Positron, muon, and other exotic particle beams for materials science and atomic/molecular sciences”, 10.-12.11.2009, Tokai, Japan
  • Open Access LogoJournal of Physics: Conference Series 225(2010), 012035
    DOI: 10.1088/1742-6596/225/1/012035

Publ.-Id: 13433 - Permalink

Application of pulsed laser annealing to ferromagnetic GaMnAs
Bürger, D.; Zhou, S.; Pandey, M.; Genzer, J.; Roshchupkina, O.; Anwand, W.; Reuther, H.; Gottschalch, V.; Helm, M.; Schmidt, H.;
In this experimental and theoretical work we focus on the technique of pulsed laser annealing applied to the metastable ferromagnetic semiconductor GaMnAs. Analytical heatflow calculations are used to illustrate the position and time dependent temperature distribution during the laser annealing process. Such heatflow calculations will also play an indispensable role for the preparation of new diluted ferromagnetic semiconductors by ion implantation and subsequent annealing. The structural, magnetic, and magnetotransport properties of ferromagnetic GaMnAs have been probed in dependence on the annealing parameters, e.g. the number of laser pulses and the pulse length. Annealing with a single KrF laser pulse of 30 ns and 0.26 J/cm2 with the photon energy above the GaAs bandgap energy leads to similar magnetic properties like annealing with a single 3 ns Nd:YAG laser pulse with the photon energy below the GaAs bandgap energy. We observed that possibly due to Mn diffusion and decreasing hole concentration, several laser pulses degrade the structural and magnetic properties of GaMnAs. Our results reveal the largest saturation magnetization for a single KrF laser pulse.
Keywords: implantation, pulsed laser annealing, diffusion, diluted magnetic semiconductor

Publ.-Id: 13432 - Permalink

Characterization of 57Fe implanted SnO2 films by Mossbauer spectroscopy and Nuclear Inelastic Scattering
Nomura, K.; Németh, Z.; Rykov, A.; Reuther, H.;
The as implanted sample at room temperature and post-annealed samples did not show Kerr effect, but the sample implanted with 1x1017 Fe ions/cm2, heated at 300°C, showed a little Kerr effect although the magnetic sextets were not clearly observed in 57Fe CEM spectra. The Kerr effect disappeared after postannealing. This suggests that the number of magnetic defects decreases by absorption of oxygen [1]. We also showed that the bulk magnetization is enhanced by co-doping of Sb and Fe into SnO2 powder [2]. We have analyzed the nanostructure of SnO2 films doped with 57Fe by conversion electron Mossbauer spectroscopy (CEMS) and nuclear inelastic scattering (NIS) at SPring8. We implanted 57Fe with 5x1016 ions/cm2 into SnO2 films containing 0.1% Sb and 3% Sb at the substrate temperature of 500°C in vacuum. Kerr rotation angles for 0.1% Sb doped SnO2 film were larger than that for 3%Sb doped SnO2 films. The samples post-annealed at 400°C for 6 hours also showed the Kerr effect. DCEM spectra were measured by discriminating conversion electrons with a back scattered type of gas counter [3]. As the results, four subspectra were observed: two doublets are assigned to paramagnetic Fe3+ and Fe2+ species and two broad sextets to site A and site B of magnetite. For 0.1%Sb doped SnO2 films the relative area of the magnetite phase was larger than for 3%Sb doped SnO2 films. After post-annealing, two sextets changed into one broad sextet, which is due to fine maghemite. The ferromagnetic behaviors of Fe implanted tin oxide films were attributed mainly due to the formation of magnetite for the as implanted samples and of maghemite for the post-annealed samples, respectively, rather than magnetic defects.
  • Lecture (Conference)
    Asia-Pacific Symposium on Radiochemistry (APSORC-09), 29.11.-04.12.2009, Napa, California, USA

Publ.-Id: 13431 - Permalink

Characterization of 57Fe implanted and annealed SnO2 (3% Sb) films by depth selective conversion electron Mossbauer spectroscopy (DCEMS)
Nomura, K.; Iio, S.; Hirose, Y.; Nemeth, Z.; Yamamoto, K.; Reuther, H.;
SnO2 (3% Sb) films were implanted with 5x1016 57Fe ions/cm2 at the substrate temperature of 500°C, and annealed at high temperatures between 400°C and 800°C . These films were characterized by depth selective conversion electron Mössbauer spectroscopy (DCEMS) using a back scattered type of gas proportional counter, and measured by Kerr effect magnetometer. Kerr effect measurements of the SnO2 films showed ferromagnetism at room temperature. The Mossbauer spectra of the as implanted films consisted of paramagnetic doublets of Fe3+ and Fe2+ species and two broad sextets, which showed site A and site B of fine magnetite. The Kerr rotation angles increase step by step with post-annealing up to 700°C. This phenomenon was attributed mainly to ferromagnetic maghemite produced by post-annealing.
  • Lecture (Conference)
    Asia-Pacific Symposium on Radiochemistry (APSORC-09), 29.11.-04.12.2009, Napa, California, USA
  • Open Access LogoJournal of Nuclear and Radiochemical Sciences 11(2010), 1-5

Publ.-Id: 13430 - Permalink

Novel biosensors based on aptamer functionalized bacterial surface layers (S-layers)
Pollmann, K.; Weinert, U.; Guenther, T.; Raff, J.;
Bacterial surface layers (S-layers) are the outermost protein-layer of many bacterial cells and archaea. The ability of the proteins to self-assemble on interfaces and surfaces to two-dimensional paracrystalline arrays, as well as the possibility to use these arrays as template for the deposition of nanoparticles makes them attractive for many technical applications such as filter materials, catalytic surfaces, electronic devices, or sensory surfaces.

Here we present a new concept of biosensors based on the application of S-layers. These biosensors are composed of three compounds:
1) Bacterial surface layer; these proteins are used for the nano-structuring of surfaces such as SiO2-wafers or glass; they provide a huge amount of orientated functional groups that can be used for coupling of molecules to the surface, thus introducing a high level of functionality in a small device
2) Aptamers, working as receptors; aptamers are oligonucleotides that specifically bind chemical compounds via their three-dimensional structure; the aptamers are coupled to S-layers
3) Fluorophores for detection, coupled to S-layers; two fluorophores are used as donor/acceptor pair; appropriate excitation/emission spectra and closest proximity permit FRET; FRET is interrupted when the analyte is binding to the aptamers

Our project that started in April 2009 aims the development of biosensors specific for pharmaceuticals such as antibiotics in waters. These chemicals are frequently found in surface waters and have been designated as a new class of pollutants. The novel sensor systems may facilitate the easy detection of these low-concentrated compounds.
Keywords: S-layer; biosensor; aptamer; FRET
  • Poster
    Biosensors 2010, 26.-28.05.2010, Glasgow, United Kingdom

Publ.-Id: 13429 - Permalink

Study of metastable states of the precipitates in reactor steels under neutron irradiation
Gokhman, A.; Bergner, F.;
The Lifshitz - Slezov theory is applied to study the metastable statesof the matrix damage clusters, MDs, and the copper enriched clusters, CECs, in neutron irradiated steels. It was found that under irradiation conditions the CECs are at the Ostwald stage for a neutron fluence of about 0.0002 dpa. The time dependence of number density, MDN, is determined by summarizing all differential equations of the master equation for MDs with neglecting of dimmers concentration in comparison with concentration of the single vacancies and subtraction of the number CECs that replace the MDs, namely vacancy clusters, due to the diffusivity of copper and other impurity atoms to them. For binary Fe-0.3wt%Cu under neutron irradiation with dose 0.026, 0.051, 0.10 and 0.19 dpa the volume content of the precipitates from the SANS experiment is found to be about 0.229, 0.280, 0.237 and 0.300 vol% respectively. The volume fraction of CECs in these samples is 0.195 vol% and the calculated volume fraction of MDs is 0.034, 0.085, 0.042 and 0.105 vol% for doses 0.026, 0.051, 0.10 and 0.19 dpa respectively.
Keywords: metastable states, neutron irradiation, clusters, Ostwald stage
  • Contribution to external collection
    S. Rzoska, A. Drozd-Rzoska, V. Mazur: Metastable systems under pressure, Heidelberg, New York: Springer, 2010, 978-90-481--3408-3, 411-418

Publ.-Id: 13428 - Permalink

The role of the soft-iron impellers in the VKS dynamo experiment
Giesecke, A.; Stefani, F.; Gerbeth, G.;
A crucial point for the understanding of the von-Karman-Sodium (VKS) dynamo experiment is the influence of soft-iron impellers.

Numerical simulations of a VKS-like dynamo with a large localized permeability distribution that resembles the shape of the flow driving impellers clearly demonstrate that the common simplified treatment of the impellers, by demanding vanishing tangential field components at the top and the bottom boundaries, is not justified. The high permeability domain within the dynamo active region provides an significant enhancement of the axisymmetric field mode, whereas the first non-axisymmetric mode remains nearly unaffected.

To circumvent the restrictions of Cowling's theorem, still some alpha-effect is required for a growing axisymmetric field. However, the scaling behavior with the value of the disk permeability indicates that the necessary magnitude of alpha can be very small. The applied (homogenous) alpha-effect should be regarded as the simplest example how the soft iron disks facilitate growing axisymmetric solutions at reasonable parameter values. A complementary and more detailed approach will have to consider a non-axisymmetric flow variation in terms of azimuthally drifting equatorial vortices that have been observed in water experiments reported by de La Torre & Burguette (2007).
Keywords: Dynamo VKS Simulations Permeability
  • Lecture (Conference)
    Dynamos d'un point de vue numerique et experimental, 07.-09.12.2009, Marseille, France

Publ.-Id: 13427 - Permalink

TRLFS – a powerful tool to study the interactions of actinides in geo- and biosystems
Raditzky, B.; Götz, C.; Heller, A.; Vogel, M.; Baumann, N.; Geipel, G.;
The poster describes the method of time-resolved laser-induced fluorescence spectroscopy (TRLFS). It is a very sensitive experimental method, which enables studies at submicromolar concentrations relevant to environmental conditions. The poster presents various applications of the method in our scientific studies as well as in cooperations with other institutions.
Keywords: TRLFS, fluorescence, speciation, actinides, interaction
  • Poster
    4th Graduate Students Seminar, 16.-18.09.2009, Krögis, Deutschland

Publ.-Id: 13426 - Permalink

Estimation of diffusion coefficient by photoemission electron microscopy in ion-implanted nanostructures
Batabyal, R.; Patra, S.; Roy, A.; Roy, S.; Bischoff, L.; Dev, B. N.;
We have fabricated parallel stripes of nanostructures in an n-type Si substrate by implanting 30 keV Ga+ ions from a focused ion beam (FIB) source. Two sets of implantation were carried out. In one case, during implantation the substrate was held at room temperature and in the other case at 400 °C. Photoemission electron microscopy (PEEM) was carried out on these samples. The implanted parallel stripes, each with a nominal dimension of 4000 nm x 100 nm, appear as bright regions in the PEEM image. Line scans of the intensities from the PEEM image were recorded along and across these stripes. The intensity profile at the edges of a line scan is broader for the implantation carried out at 400 °C compared to room temperature. From the analysis of this intensity profile, the lateral diffusion coefficient of Ga in silicon was estimated assuming that the PEEM intensity is proportional to Ga concentration. The diffusion coefficient at 400 °C has been estimated to be ~1.3 x 10-15 m2/s. Across the stripes an asymmetric diffusion profile has been observed, which has been related to the sequence of implantation of these stripes and the associated defect distribution due to lateral straggling of the implanted ions.
Keywords: Photoemission electron microscopy; Nanostructures fabricated by focused ion beam; Diffusion in nanostructures
  • Lecture (Conference)
    2nd Int. Conf. on Physics at Surfaces and Interfaces PSI2009, 23.-27.02.2009, Puri, India
  • Applied Surface Science 256(2009), 536-540

Publ.-Id: 13425 - Permalink

Vibrational spectra of silicon implanted polymethyl-methacrylate (PMMA) and poly-propylene (PP)
Baleva, M.; Zlateva, G.; Tsvetkova, T.; Balabanov, S.; Bischoff, L.;
Infra-red (IR) and Raman spectroscopy studies were used to characterize different polymer materials implanted with low energy Si+ ions (E = 30 keV, D = 1.1017 cm-2). Two kinds of polymer were studied - poly-methyl-methacrylate (PMMA), and poly-propylene (PP). Silicon ion implantation resulted in the breaking down of bonds in the substrate structures, and the emergence of newly formed bonds. The IR and Raman studies thus show that the implantation of Si+ into PMMA and PP leads to the formation of amorphous and nano-crystalline graphite, predominantly in the PP samples. The presence of SiC particles and unreacted Si atoms is also observed in the implanted polymer material.
Keywords: Polymers; Ion implantation; Vibrational spectroscopy
  • Journal of Optoelectronics and Advanced Materials 11(2009)10, 1420-1423

Publ.-Id: 13424 - Permalink

Comments on the holonomy of eigenvector bundles in the vicinity of higher-order exceptional points and on the Lie group structure underlying the embedding of the PTQM brachistochrone into a two-qubit system
Günther, U.;
On the poster new findings on two different topics are presented --- related separately to geometric (Berry) phases in non-Hermitian quantum systems in higher-dimensional Hilbert spaces and to the specific realization properties of PT-symmetric quantum brachistochrones in two-qubit systems fulfilling the Aharonov-Anandan lower bound on quantum evolution times.
Specifically, in the first part of the poster we present new results on the holonomy properties of eigenvector bundles of non-Hermitian operators which can be mapped into simplest versally deformed n-th order Jordan blocks. (This generalizes earlier considerations on similar setups with 2-dimensional Jordan blocks [1].)
In the second part of the poster, we start from the embedding of the PT-symmetric brachistochrone into a Hermitian two-qubit system (as recently proposed in [2]) and show that the resulting evolution of the two-qubit system is itself a conventional quantum brachistochrone lying exactly on the non-local Lie-group orbit induced by one of the non-trivial entanglement generators.

[1] U. Günther, I. Rotter and B. Samsonov, "Projective Hilbert space structures at exceptional points", J. Phys. A 40, 8815 (2007), arXiv:0704.1291[math-ph].
[2] U. Günther and B. Samsonov, "Naimark-dilated PT-symmetric brachistochrone", Phys. Rev. Lett. 101, 230404 (2008),
Keywords: non-Hermitian operators, PT quantum mechanics, exceptional points, holonomy, monodromy, versal deformations, geometric phase, Berry phase, quantum brachistochrone, Lie group orbit, two-quibit systems, entanglement, entanglement generator
  • Poster
    Aharonov Bohm Effect and Berry Phase Anniversary 50/25 2009, 14.-15.12.2009, Bristol, United Kingdom

Publ.-Id: 13423 - Permalink

Reactive Magnetron Sputtering of (GeOx-SiO2) Superlattices for Nanocrystal Synthesis
Zschintzsch, M.; Jeutter, N. M.; von Borany, J.; Mücklich, A.;
Recently semiconductor nanocrystals (NC) attracted additional interest because they might have the potential for adapting solar cell devices to a broader irradiance spectra. It is believed that this could be realized by size-controlled bandgap engineering of multiple junction solar cells. The feasibility of bandgap shifts up to 2 eV has been proofed for NC's of Ge or Si in the size from 1 to 5nm [1].
However, the fabrication of dense (>10-12cm²), small and equally sized NC’s in a suitable matrix remains still a remarkable challenge.

The main focus of this work is the manufacturing of Ge-NC superlattice structures in silica matrix for photovoltaic application. DC reactive sputtering was used to deposit sequentially GeOx and SiO2 layers on Si wafers with thermally oxidized silica surface layer (500 nm). The sputter rate from the elemental targets was quite small (< 0.2 Å/s) to achieve good layer quality. The GeOx and SiO2 layer thicknesses could be tuned independently with the deposition time. It was possible to vary the composition from elemental Ge to GeO2 by adjusting the partial pressure of oxygen (p = 0 to 0.02 Pa) in the sputter chamber (sputter gas: Ar, p = 0.5 Pa). With increasing substrate temperature (RT up to 400°C) the oxygen content had to be increased as well in order to get the same x-value. Subsequent annealing led to Ge crystallisation with intrinsic cut-off size due to the silica separation layers.

In-situ characterization revealed the temperature dependent growth of the Ge-NC by grazing incidence x-ray diffraction (GID) and the layer interface roughness by x-ray reflectometry (XRR). Ge-NC’s being 2 to 5 nm small could be detected above 500°C. Interface roughnesses of about 1 nm showed that the fabrication of very thin separation layers allowing direct tunnelling should be possible.

Ex-situ analysis via Rutherford backscattering (RBS) provided the matrix of dependencies between the temperature, the deposition rate, the partial pressure of oxygen and the stoichometry. With the help of transmission electron microscopy (TEM) it was possible to gain local information about shape, size and crystallinety of the Ge-NC’s. Raman spectroscopy allowed a more global view on the size and shape of the nanocrystals and on the ratio of amorphous and crystalline Ge parts.

[1] Martin A. Green, Third generation photovoltaics, Springer, 2006, ISBN 1437-0379
  • Lecture (Conference)
    E-MRS Spring Meeting, 08.-12.06.2009, Strasbourg, Frankreich

Publ.-Id: 13421 - Permalink

Prototype coupling of the CFD code ANSYS CFX with the 3D neutron kinetic core model DYN3D
Kliem, S.; Rohde, U.; Schütze, J.; Frank, T.;
The CFD code ANSYS CFX has been coupled with the neutron-kinetic core model DYN3D. ANSYS CFX calculates the fluid dynamics and related transport phenomena in the reactor’s coolant and provides the corresponding data to DYN3D. In the fluid flow simulation of the coolant, the core itself is modeled within the porous body approach. DYN3D calculates the neutron kinetics and the fuel behavior including the heat transfer to the coolant. The physical data interface between the codes is the volumetric heat release rate into the coolant. In the prototype that is currently available, the coupling is restricted to single-phase flow problems. In the time domain an explicit coupling of the codes has been implemented so far.
Steady-state and transient verification calculations for a small-size test problem confirm the correctness of the implementation of the prototype coupling. This test problem was a mini-core consisting of nine real-size fuel assemblies. Comparison was performed with the DYN3D stand-alone code. In the steady state, the effective multiplication factor obtained by the ANSYS CFX/DYN3D codes shows a deviation of 9.8 pcm from the DYN3D stand-alone solution. This difference can be attributed to the use of different water property packages in the two codes. The transient test case simulated the withdrawal of the control rod from the central fuel assembly at hot zero power. Power increase during the introduction of positive reactivity and power reduction due to fuel temperature increase are calculated in the same manner by the coupled and the stand-alone codes. The maximum values reached during the power rise differ by about 1 MW at a power level of 50 MW. Beside the different water property packages, these differences are caused by the use of different flow solvers.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland
    Tagungsband der Jahrestagung Kerntechnik 2010 paper 104, Berlin: INFORUM GmbH
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland

Publ.-Id: 13420 - Permalink

Coupling of the neutron-kinetic core model DYN3D with the thermal hydraulic code FLICA-4 within the NURESIM platform
Gommlich, A.; Kliem, S.; Rohde, U.; Gomez, A.; Sanchez, V.;
Within the FP7 NURISP project the 3D neutron-kinetic core model DYN3D has been implemented into the NURESIM platform. Further, the coupling of DYN3D with the thermal hydraulic code FLICA-4 has been accomplished for steady-state calculations using the NURESIM tools. Two different test cases were used to verify the coupling. Comparisons with DYN3D stand-alone calculations confirm the correctness of the code coupling.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland
    Tagungsband der Jahrestagung Kerntechnik 2010 paper 111, Berlin: INFORUM GmbH
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland

Publ.-Id: 13419 - Permalink

Thermodynamic Data of Uranyl Carbonate Complexes from Absorption Spectroscopy
Götz, C.; Geipel, G.; Bernhard, G.;
Aqueous uranyl carbonate complexes play an important role in the hydrogeology of uranium mining areas and nuclear waste disposals. The uranyl carbonate complexes are strong and predominant at the range of pH 7-12. The chemical equilibrium is temperature dependent. From the temperature dependency of the equilibrium constant it is possible to determine the reaction enthalpy and entropy.
From absorption spectroscopy the concentration of the formed complex and then the equilibrium constant can be determined.
In our work thermodynamical data for the formation of the uranyl carbonate complex UO2(CO3)34- were determined by absorption spectroscopy. Therefore absorption spectra of solutions with uranyl ions and carbonate ions at pH 9 in the temperature range from 10°C to 70°C were recorded.
Keywords: uranyl carbonate, enthalpy, entropy, absorption spectroscopy, thermodynamics
  • Poster
    3rd Graduate Students Seminar, 27.-29.08.2008, Limbach-Oberfrohna, Deutschland

Publ.-Id: 13418 - Permalink

UV-vis spectroscopy of Am(III)-salicylate complexation at low metal concentrations
Müller, M.; Acker, M.; Taut, S.; Bernhard, G.;
The complexation of the trivalent Americium ion with salicylic acid was investigated using a Liquid Waveguide Capillary Cell (LWCC) for UV/vis spectroscopy, enabling measurements at very low metal concentrations.
Keywords: americium, salicylic acid, UV/vis spectroscopy, complexation
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-511 Januar 2009, 64-64

Publ.-Id: 13417 - Permalink

UV/vis Spectroscopy of Eu(III) and Am(III) Complexes with Small Organic Acids at Variable Temperatures
Müller, M.; Acker, M.; Taut, S.; Bernhard, G.;
Thermodynamic data for reactions of trivalent Actinides in the host rock environment are required for analysis of long-term safety of nuclear waste disposals in clay. We analyzed the complexation behaviour of Eu(III) and Am(III) with benzoic acid derivatives, which structures are similar to the natural organic matter.
Keywords: UV/vis spectroscopy, complexation, americium, europium, temperature dependence, thermodynamic data
  • Poster
    Migration 09, 20.-25.09.2009, Kennewick, Washington, United States of America

Publ.-Id: 13416 - Permalink

Komplexierung von Am(III) mit Zitronensäure bei niedrigen Konzentrationen und variabler Temperatur
Mueller, M.; Acker, M.; Taut, S.; Bernhard, G.;
Mittels UV-vis Spektroskopie wurden die Stabilitätskonstanten von Am-Citratkomplexen bei verschiedenen temperaturen zwischen 20 und 60°C bestimmt. Durch den Einsatz einer Liquid Waveguide Capillary Cell (LWCC) konnte mit sehr kleinen Am-Konzentrationen gemessen werden.
Keywords: UV-vis spectroscopy, Americium, Citric acid, complexation, termperature dependence
  • Poster
    Wissenschaftsforum der GDCh, Fachgruppentagung Nuklearchemie, 30.08.-02.09.2009, Frankfurt am Main, Deutschland

Publ.-Id: 13415 - Permalink

PET-Tracer für die onkologische Diagnostik: Welche radiomarkierten Substanzen sind relevant?
Knieß, T.; Steinbach, J.;
Krebserkrankungen entstehen aus Veränderungen in den Wechselwirkungen zwischen Onkogenen und Tumorsupressorganen, welche unter normalen physiologischen Bedingungen für die Regulierung des Zellwachstums und der Zellteilung verantwortlich sind. Das Verhalten der Krebszelle wird dabei durch eine Vielzahl von Faktoren aus dem genetischen und Mikormilieu des Organismus bestimmt. Als Ergebnis der genetischen Abweichungen treten bestimmte funktionale Veränderungen auf. So sind Tumorzellen durch erhöhten Stoffwechsel (Glukosemetabulismus, Aminosäuretransport, Protein-, DNA- und Lipidsynthese) sowie durch angiogene und hypoxische Prozesse charakterisiert, welche unweigerlich zu der Ausbildung von unkontrollierten Läsionen führen.

Der vorliegende Artikel gibt einen kurzen Überblick über die zur Zeit in der Klinik verwendeten mit den Radionukliden 18F und 11C markierten PET Radiotracer für die onkologische Diagnostik und beschreibt kurz ihre Herstellung und das Prinzip ihrer spezifischen Anreicherung.
  • Onkologische Pharmazie 11(2009)4, 4-5

Publ.-Id: 13413 - Permalink

The relevance of mean dose rate and energy spectrum for the different biological effectiveness of laser accelerated electrons
Naumburger, D.; Beyreuther, E.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Richter, C.; Pawelke, J.;
The new technology of laser acceleration, which promises radiotherapy accelerators of compact size and reasonable costs, results in ultra-short pulsed particle beams (in the region of 100 fs) with very high pulse dose rate (more than 1012 Gy/min). One important step before potential medical application is the radiobiological characterisation of this new radiation quality. Therefore, in vitro cell irradiations with laser accelerated electrons have been performed at the Jena Titanium:Sapphire (JETI) laser system. The obtained dose-effect-curves have been measured for two cell lines (tumor cell line FaDu, normal tissue cell line184A1) and biological endpoints (residual H2AX/53BP1 foci and clonogenic survival assay) revealing a reduced biological effectiveness of laser accelerated MeV electrons in comparison to continuous 200 kV X-ray reference irradiation.
In addition to the ultra-high pulse dose rate of the JETI electron beam this radiation quality differs also in energy spectrum and average dose rate from the 200 kV X-rays.
A negligible influence of the mean dose rate on biological effectiveness was confirmed by measuring the same cell response to 200 kV X-ray irradiation at 0.35 Gy/min (mean dose rate of the JETI electron beam) and at 1.4 Gy/min applied for reference irradiation. The influence of the energy spectrum was investigated by cell irradiation at a medical linear accelerator (LINAC). The two cell lines already studied at JETI have been irradiated with monoenergetic 6 MeV electrons according to the mean energy of the JETI electron beam. Clonogenic survival and residual DNA-DSB were determined for the LINAC electrons and compared to 200 kV X-rays, both radiations being similar in time-structure and mean dose rate. No difference in the number of residual H2AX/53BP1 foci after 24 h has been measured for both (quasi) continuous beams. In contrast increased clonogenic survival was found for the LINAC electrons compared to 200 kV X-rays as expected by the known increase of biological effectiveness with decreasing secondary electron energy. However, the decreased biological effectiveness is less pronounced for the LINAC electrons in comparision to the JETI laser electrons. Therefore, the remaining influence of the ultra-high pulse dose rate of JETI electrons is currently investigated.

This work has been supported by BMBF (no. 03ZIK445).
  • Poster
    12. Jahrestagung der Gesellschaft für Biologische Strahlenforschung GBS, 30.09.-02.10.2009, Essen, Deutschland
  • Contribution to proceedings
    12. Jahrestagung der Gesellschaft für Biologische Strahlenforschung GBS, 30.09.-02.10.2009, Essen, Deutschland

Publ.-Id: 13409 - Permalink

Influence of high pulse dose rate on biological effectiveness of laser accelerated electrons
Laschinsky, L.; Beyreuther, E.; Karsch, L.; Leßmann, E.; Naumburger, D.; Richter, C.; Pawelke, J.;
The novel technology of particle acceleration based on high intensity lasers is characterised by ultra-short pulse particle beams and high pulse dose rate. Before a potential medical application such beams have to be characterized in terms of their radiobiological properties. Hence, systematic in vitro cell experiments were performed with laser accelerated electrons by using the Jena titanium:sapphire (JETI) laser system. As presented last year, residual H2AX/53BP1 foci and clonogenic survival for four human cell lines were therefore analysed. The dose response curves show a reduced radiobiological effectiveness for laser accelerated MeV electrons in comparison to the continuous 200 kVp X-rays. Conceivable reasons for the measured differences in the radiobiological effectiveness between both radiation qualities could be the difference in energy spectrum and mean dose rate as discuss in a separate contribution. The influence of the high pulse dose rate of the laser accelerated electron beam was investigated by using pulsed electron beams generated by the electron accelerator ELBE (Electron Linac for beams with high Brilliance and low Emittance) at Forschungszentrum Dresden-Rossendorf. The variable time structure of the ELBE electron beam allows pulsed irradiation as well as quasi-continuous irradiations, whereas the pulse doses are tunable over more than six orders of magnitude. Hence, ELBE can be used to mimic both ultra-short pulses of laser accelerated electrons as well as quasi-continuous electron beam as delivered by a conventional therapeutic linac. These two pulse regimes were applied in systematic in vitro cell studies by using monoenergetic electrons of 20 MeV. For a comparison the ELBE experiments were performed similar to the JETI experiments. Therefore, the same cell lines (FaDu, 184A1, additional HDF and F153) and the two biological endpoints (residual H2AX/53BP1 foci, clonogenic survival) were investigated. Preliminary results show no difference in the biological effectiveness between pulsed and quasi-continuous ELBE electrons as well as continuous X-rays.

The work was supported by the BMBF, grant no. 03ZIK445
  • Poster
    12. Jahrestagung der Gesellschaft für Biologische Strahlenforschung GBS Essen, 30.09.-02.10.2009, Essen, Deutschland
  • Contribution to proceedings
    12. Jahrestagung der Gesellschaft für Biologische Strahlenforschung GBS Essen, 30.09.-02.10.2009, Essen, Deutschland

Publ.-Id: 13408 - Permalink

U(VI) sorption and reduction by Fe(II) sorbed on montmorillonite
Chakraborty, S.; Boivin, F.; Banerjee, D.; Scheinost, A.; Mullet, M.; Ehrhardt, J.-J.; Brendle, J.; Vidal, L.; Charlet, L.;
The influence of surface bound Fe(II) on uranium oxidation state and speciation was studied as a function of time and pH (6.1-8.5) in U(VI)-Fe(II)-montmorillonite (Ca-montmorillonite) system under CO2-free, anoxic (O2 <1 ppmv) conditions. The results show a rapid removal of U(VI) from the aqueous solution within 1 h under all pH conditions. U LIII-edge X-ray absorption near-edge structure (XANES) spectroscopy shows that 96% of the total sorbed U(VI) is reduced at pH 8.5. However, the extent of reduction significantly decreases at lower pH values, in line with specifically sorbed Fe(II) decreasing. The reduction kinetics followed by X-ray photoelectron spectroscopy (XPS) during 24 h at pH 7.5 demonstrates the presence of partially reduced surface species containing both U(VI) and U(IV). Thermodynamically predicted mixed valence solids like U3O8/β-U3O7/U4O9 do not precipitate as verified by transmission electron microscopy (TEM) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. This is also supported by the bicarbonate extractionresults. The measured redox potentials of Fe(II)/montmorillonite suspensions are controlled by the Fe(II)/ hydrous ferric oxide (HFO(s)) couple at pH 6.1 and by the Fe(II)/ γ-FeOOH(s) couple at pH 7.5. The U(VI) reduction mechanism is suggested by considering individual U(VI), U(IV) surface complexes with Fe(II) specifically sorbed on strong and weak sites of montmorillonite.
Keywords: Uranyl, Montmorillonite, EXAFS spectroscopy
  • Environmental Science & Technology 44(2010)10, 3779-3785

Publ.-Id: 13407 - Permalink

Scale resolved simulations of the OECD/NEA−Vattenfall T-junction benchmark
Höhne, T.;
Mixing of fluids in T-junction geometries is of significant interest for nuclear safety research. The most prominent example is the thermal striping phenomena in piping T-junctions, where hot and cold streams join and turbulently mix, however not completely or not immediately at the T-junction. This results in significant temperature fluctuations near the piping wall, either at the side of the secondary pipe branch or at the opposite side of the main branch pipe. The wall temperature fluctuation can cause cyclical thermal stresses and subsequently fatigue cracking of the wall. The issue of thermal striping has been observed in light water reactors (LWRs) as several incidents of high-cycle fatigue at coolant mixing junctions have been detected - mainly in piping T-junctions - in nuclear plants, like the failure event at Civaux 1. These incidents occurred usually in piping of diameter 5-20 cm and the most susceptible parts to thermal fatigue are mixing T-junctions of the Residual Heat Removal (RHR) system in both boiling (BWR) and pressurized water reactors (PWR). This has raised thermal fatigue to be a serious safety concern and an important aspect on ageing and life management of nuclear plants with LWR. A typical value for the temperature difference between the hot/cold streams is 160°C. Critical parameters for thermal fatigue analyses are frequencies (ω), temperature differences (T), number of cycles (N), and material properties. Most damaging thermal loads appear to be due to large scale turbulent fluctuations of low frequency (3-10 Hz). From a thermal hydraulic standpoint, the accurate prediction of such large coherent eddies is a challenging task, requiring CFD and advanced turbulence modelling. Significant effort has been put in the experimental investigation of the thermal fatigue and thermal striping phenomena due to thermal mixing in pipe T-junctions. In November 2008, a T-junction thermal mixing test was carried out at the Älvkarleby Laboratory of Vattenfall Research and Development (VRD) in Sweden. Data from this test have been reserved specifically for this CFD benchmark exercise. The test section is constructed from Plexiglas, and the junction itself from one solid block into which the main and branch pipes fit. The temperatures of the water in the main and branch pipes were maintained at 15°C and 30°C, respectively, with minimal heat loss. Special care was taken to provide simple and well-defined inlet boundary conditions to remove ambiguities in defining the CFD input data. Temperature fluctuations near pipe walls were measured using thermocouples. These were placed around the inner wall perimeter of the main pipe at seven stations downstream of the junction and at one station upstream. All thermocouples were positioned 1 mm from the wall. Velocity profiles upstream and downstream of the junction were measured using a two-component LDV system. These were positioned at each inlet, and at the outlet. Data are in the form of mean values, RMS values and turbulence statistics. The numerical prediction of thermal mixing and striping in terms of temperature amplitude and frequency using the current CFD technology is a computational intensive and challenging task. By the physics of the phenomenon, the flow is turbulent and highly transient and the thermal striping at pipe walls is affected by the formation and propagation of large-scale turbulent structures in space and time. The aim is therefore a CFD turbulence model validation study and a detailed CFD experiment comparison. Turbulence model approaches to be studied in the present validation study include URANS SST as well as scale resolving turbulence models (LES).
Keywords: T-junction, CFD, mixing, LES, Vattenfall, OECD
  • Contribution to proceedings
    CFD4NRS-3, 14.-16.09.2010, Washington, USA
  • Poster
    CFD4NRS-3, 14.-16.09.2010, Washington, USA

Publ.-Id: 13406 - Permalink

CFD simulation of fibre material transport in a PWR core under loss of coolant conditions
Höhne, T.; Grahn, A.; Kliem, S.; Weiß, F. P.;
The aim of the numerical simulations carried out in this study was to determine how and where mineral wool fibres are deposited across the grid spacers of the fuel elements of a German PWR. The spacer grid is modelled as a strainer which completely retains the insulation material carried by coolant and reaching the plane of the spacers. The accumulation of the insulation material gives rise to the formation of a compressible fibrous cake whose permeability to the coolant flow is calculated in terms of the local amount of deposited material and the local value of the superficial liquid velocity. The calculations showed that the fibers material at the uppermost spacer grid plane is not evenly distributed. Later when the inner circulation has stopped, the insulation material can also be distributed into other regions of the spacer plane. Further investigations are necessary to determine the accumulation of insulation material for a longer period of time. Also steam production in the core or re-suspension of the insulation material during back flow should be considered.
Keywords: CFD, fibre, rock wool transport, PWR, Core
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland
    CD-ROM, paper 055
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2010, 04.-06.05.2010, Berlin, Deutschland

Publ.-Id: 13405 - Permalink

Final disposal of nuclear waste - long-term safety assessment and radionuclide migration in the geosphere
Raditzky, B.;
The presentation gives an overview of the history of nuclear power, radioactive waste - it's classification and composition, as well as final waste disposals in deep geological formations.
  • Lecture (others)
    2nd Graduate Students Seminar, 26.-28.09.2007, Rabenberg, Deutschland

Publ.-Id: 13404 - Permalink

Sorption of Uranium(VI) on Opalinus Clay in the Absence and Presence of Humic Acid
Joseph, C.; Schmeide, K.; Sachs, S.;
Natural clays are dicussed as possible host rocks for nuclear waste repositories. Natural clays contain also organic substances, like humic acids (HA), known for their ability to bind metal ions, e.g. actinides like uranium. Due to this, HA can influence the actinide migration. In this study the effect of HA presence on the U(VI) sorption onto the natural clay, opalinus clay from Mont Terri (Switzerland), is presented.
Beside the mineralogy of the clay and the composition of the synthetic opalinus clay pore water, the speciation of U(VI) in opalinus clay pore water and the sorption results onto opalinus clay in the two background electrolytes, 0.1M NaClO4 and synthetic opalinus clay pore water, are shown. It was concluded, that the released calcium ions determine the speciation and affect as a consequence the sorption behavior of U(VI) and also HA onto opalinus clay.
Keywords: U(VI), humic acid, opalinus clay, opalinus clay pore water, 0.1M NaClO4, speciation, sorption, calcium ions
  • Poster
    4th Graduate Students Seminar, 16.-18.09.2009, Krögis, Germany

Publ.-Id: 13403 - Permalink

Sorption of Uranium(VI) on Opalinus Clay in Absence and Presence of Humic Acid
Joseph, C.; Schmeide, K.; Sachs, S.;
For nuclear waste disposal in geological formations, possible host rocks in Germany are salt rock (Gorleben), granite rock and clay. Currently, intense examinations on natural clay are taking place in a joint project funded by the Federal Ministry of Economics and Technology. An important part of this is the investigation of sorption and migration processes resulting from the actinide interaction with natural clay and the determination of the influence of clay organic matter on these processes. In this regard, the sorption of uranium(VI) on natural clay is examined. Furthermore, the influence of organic matter, such as fulvic acids (FA) and humic acids (HA), known for their ability to bind metal ions, is investigated.
Here some characteristics of the natural clay, opalinus clay from Mont Terri (Switzerland), and the synthetic opalinus clay pore water are shown. The speciation of uranium(VI) in this pore water in the absence and presence of HA is presented. The sorption of uranium(VI) in the absence and presence of HA onto opalinus clay and onto the reference clay mineral kaolinite is compared .
Keywords: uranium(VI), humic acid, opalinus clay, opalinus clay pore water, sorption, speciation, characterization
  • Poster
    3rd Graduate Students Seminar, 27.-29.08.2008, Limbach-Oberfrohna, Germany

Publ.-Id: 13402 - Permalink

Vibrational spectroscopy of actinyl complexes
Müller, K.; Li, B.;
Vibrational spectroscopy potentially provides structural information of molecule complexes. Actinyl ions, e.g. AnO2 n+ (An=U,Np; n=1,2) can be identified by the frequency of their antisymmetric stretching vibrational mode νas which generally correlates with the character of the molecular environment, i.e. number and type of ligand, of the actinyl ion group. [1]
The migration behavior of actinides in the geosphere is strongly influenced by sorption processes at water-mineral oxide interfaces [2]. The sorption of neptunium(V) at low concentration levels (50 μM) on model oxide surfaces (TiO2, SiO2, ZnO) was investigated in situ at different pH (4.0 – 7.6). For the first time, in situ formation of inner-sphere bidentate Np(V) surface complexes onto oxides was observed by FT-IR spectroscopy [3]. Unequivocal assignments of thermodynamic reaction constants are feasible.
To investigate the U(VI) chemotoxicity at a molecular level, the coordination between U(VI) and different protein functional groups under
physiological relevant conditions is investigated.The highly phosphorylated protein phosvitin serves as a model system for the elucidation of the molecular interaction of uranyl with native proteins in aqueous solution. [4,5] Soluble protein-U(VI) complexes in aqueous solution evidence preferential U(VI) complexation to phosphoryl groups of the protein side chains. In combination with X-ray spectroscopy molecular structures such as the postulated “Feldman complex” can be verified [6].

[1] K. Müller, H. Foerstendorf, S. Tsushima, V. Brendler, G. Bernhard (2009), Journal of Physical Chemistry A 113, 6626-6632.
[2] G. R. Choppin (2007), Journal of Radioanalytical and Nuclear Chemistry 273, 695-703
[3] K. Müller, H. Foerstendorf, V. Brendler, G. Bernhard (2009) Environmental Science & Technology, 43, 7665-7670
[4] R. Shainkin, G.E. Perlmann (1971) Journal of Biological Chemistry 246, 2278-2284.
[5] B.M. Byrne, A.D.V. Schip, J.A.M. Vandeklundert, A.C. Arnberg, M. Gruber, G. Ab (1984) Biochemistry 23, 4275-4279.
[6] B. Li, H. Foerstendorf, J. Raff, G. Bernhard (2007) Geochim. Cosmochim. Acta 71, A567.
  • Poster
    FZD PhD-Seminar 2009, 16.-18.09.2009, Krögis, Deutschland

Publ.-Id: 13401 - Permalink

Complexation of europium(III) with organic ligands and in human body fluids studied by TRLFS
Heller, A.; Rönitz, O.; Barkleit, A.; Bernhard, G.;
An(III) exhibit very high radioactivity and therefore pose a great health risk for humans in case of accidental release/incorporation. Their metabolism and speciation in body fluids is not yet fully known and our studies shall help to adress this lack of knowledge. Ln(III) are used in radiological medicine e.g. as contrast agents and exhibit similar physico-chemical properties as An(III) but no radioactivity. Therefore Ln(III) are often used as analogs for An(III). In the present study the complexation of Eu(III) with different organic ligands, which are components of natural biofluids, as well as its speciation in natural human urine samples were investigated. Results show, that Eu(III) speciaition in urine samples with lower pH is dominated by citric acid complexation while in samples with higher pH inorganic complexes are formed.
Keywords: europium(III), complexation, speciation, organic ligands, citric acid, amino acids, urea, urine, trivalent actinides
  • Poster
    FZD-PhD-Seminar, 16.-18.09.2009, Krögis, Deutschland

Publ.-Id: 13400 - Permalink

Spectroscopic investigations of U(VI) interaction with monocellular green algae Chlorella vulgaris
Vogel, M.; Günther, A.; Raff, J.;
The sorption behavior of uranium(VI) to the monocellular green algae Chlorella vulgaris was investigated in tap water and mineral medium. The initial and final solutions as well as the formed uranyl-algae-complexes were characterized by time-resolved laser-induced fluorescence spectroscopy.
Keywords: biosorption, uranium, TRLFS
  • Poster
    3rd Graduate Students Seminar, 27.-29.08.2008, Limbach-Oberfrohna, Deutschland

Publ.-Id: 13399 - Permalink

The various applications of the CLSM-technique
Brockmann, S.; Arnold, T.; Großmann, K.; Krawczyk-Bärsch, E.;
The confocal laser scanning microscopy is often referred to as computer tomography for the cells. Its main advantage in comparison to the common fluorescence microscopy is the possibility to generate optical slices inside of a sample. The CLSM-System of the Institute of Radiochemistry (IRC) comprises some special characterizing highlights which were presented in this poster.
Keywords: CLSM, Laser-system
  • Poster
    3rd Graduate Students Seminar, 27.-29.08.2008, Limbach-Oberfrohna, Deutschland

Publ.-Id: 13398 - Permalink

Final disposal of nuclear waste
Dreissig, I.; Glorius, M.; Joseph, C.;
Characteristics and policy of radioactive waste disposal in Germany.
Keywords: Radioactive waste repository
  • Poster
    2nd Graduate Students Seminar, 26.-28.09.2007, Rabenberg, Deutschland

Publ.-Id: 13397 - Permalink

Influence of the algae Chlorella vulgaris on the environmental behavior of uranium – a spectroscopic study
Vogel, M.;
The binding of uranium(VI) to the green algae Chlorella vulgaris was investigated with different spectroscopic techniques.
  • Lecture (others)
    4th Graduate Students Seminar, 16.-18.09.2009, Krögis, Deutschland

Publ.-Id: 13396 - Permalink

Investigation of Biofilms from naturally uranium contaminated environments
Brockmann, S.; Arnold, T.; Krawczyk-Bärsch, E.; Zirnstein, I.;
Investigation of Biofilms from naturally uranium contaminated environments
Keywords: Biofilms, Uranium, microbial diversity, CLSM
  • Poster
    4th Graduate Students Seminar, 16.-18.09.2009, Krögis, Deutschland

Publ.-Id: 13395 - Permalink

Uranium(IV) colloids in near-neutral solutions
Dreißig, I.; Weiß, S.; Zänker, H.; Bernhard, G.;
Uranium(IV) colloids were investigated by ultrafiltration, ultracentrifugation and light scattering techniques. Results confirm that the particle size of these colloids depends on the initial silicic acid content and pH.
Keywords: U(IV), silicic acid, colloid, particle size, tetravalent actinides
  • Poster
    4th Graduate Students Seminar, 16.-18.09.2009, Krögis, Deutschland

Publ.-Id: 13394 - Permalink

Synchronized force and particle image velocimetry measurements on a NACA 0015 in post stall under control of time periodic electromagnetic forcing
Cierpka, C.; Weier, T.; Gerbeth, G.;
The paper shows the results of an experimental investigation of flow control by periodic actuation by streamwise Lorentz forces at the leading edge of a NACA0015 profile. Synchronized force and time resolved particle image velocimetry (PIV) measurements were performed in a sodium hydroxide channel for Reynolds numbers of Re = 0.5 105 and 105. A wavelet algorithm was used to detect vortical structures and allows to relate these large scale structures to the observed lift and drag forces. Additional information about the mechanism of momentum transfer in the flow was gained by proper orthogonal decomposition of the data. In order to minimize the energetic effort of the flow actuation, the investigation focuses on small momentum coefficients. For small angles of attack a complete reattachment of the flow can be established by the actuation, whereas for large angles of attack the interaction of vortical structures becomes more prominent. The paper discusses the effects of excitation frequency and wave form for two qualitatively different flow regimes .It shows that the proper choice of the excitation frequency is very important for large angles of attack. The optimal excitation frequency was examined as a function of the angle of attack.
Keywords: active flow control, Lorentz force, flow separation

Publ.-Id: 13393 - Permalink

Infrared and THz spectroscopy of semiconductor quantum structures with modelocked tabletop and free-electron lasers
Schneider, H.;
Es gibt hierzu kein Abstract.
  • Lecture (others)
    Seminar, Rensslaer Polytechnic Institute, 14.09.2009, Troy, NY, USA

Publ.-Id: 13392 - Permalink

Two-photon intersubband transition physics and detectors
Schneider, H.; Winnerl, S.; Drachenko, O.; Helm, M.; Liu, H. C.; Song, C.; Maier, T.; Walther, M.; Faist, J.;
Two-photon quantum well infrared photodetectors (QWIPs) take advantage of a resonant intermediate state, thus leading to a resonantly enhanced optical nonlinearity which is six orders of magnitude stronger than in a bulk semiconductor. This approach results in an extremely sensitive quadratic detector for mid-infrared and terahertz radiation, which is useful for quadratic autocorrelation measurements of mid-infrared optical pulses from free-electron lasers (FEL), modelocked quantum cascade lasers, and nonlinear optical converters. The time resolution of this detector is limited by the intersubband dynamics associated with the intermediate state. Therefore, the two-photon QWIP provides interesting opportunities for studies of the associated intersubband population and polarization lifetimes.
We report on electron intersubband relaxation and dephasing in n-type InGaAs/AlGaAs quantum wells by femtosecond two-photon photocurrent spectroscopy. The approach enables us to determine systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes [1]. By varying the excitation energy, it is also possible to tune the two-photon transition from resonant, yielding optimum resonant enhancement with a real intermediate state, to nearly-resonant, with a virtual but resonantly enhanced intermediate state [2]. For autocorrelation purposes, the latter configuration improves time resolution whilst partially retaining a resonant enhancement of the two-photon transition strength.
Exploiting the two-photon QWIP approach for pulse monitoring of mid-infrared sources, we have performed autocorrelation measurements at wavelengths in the mid-infrared and Terahertz regimes using ps optical pulses from the FEL at the Forschungszentrum Dresden Rossendorf. In particular, quadratic detection at wavelengths around 5.5 μm is still possible at room temperature [3], which is crucial for applications in practical systems. A two-photon detector which works below the Reststrahlen band at 42 μm (7.1 THz) will also be reported.
[1] H. Schneider, T. Maier, M. Walther, H. C. Liu, Appl. Phys. Lett. 91, 191116 (2007).
[2] H. Schneider, T. Maier, H. C. Liu, M. Walther, Opt. Express 16, 1523 (2008).
[3] H. Schneider, H. C. Liu, S. Winnerl, O. Drachenko, M. Helm, J. Faist, App. Phys. Lett. 93, 101114 (2008).
Keywords: Quantum well infrared photodetector, two-photon intersubband transition, quadratic autocorrelation, GaAs/AlGaAs
  • Invited lecture (Conferences)
    10-th International Conference on Intersubband Transitions in Quantum Wells (ITQW 2009), Montréal, 06-11.09.2009, 06.-11.09.2009, Montréal, Kanada

Publ.-Id: 13391 - Permalink

Kolloidale Suspensionen von Carbon Nanotubes und ihre Wechselwirkung mit Schwermetallionen (Uranylionen)
Zänker, H.; Schierz, A.;
Es wird allgemein davon ausgegangen, dass in Wissenschaft, Technologie, Medizin und täglichem Leben eine schnelle Zunahme der Anwendung von Engineered Nanoparticles (ENPs) bevorsteht. Gegenwärtig existiert noch relativ wenig Wissem über das Verhalten von ENPs in der aquatischen Umwelt. Unsere Untersuchungen hatten das Ziel, Informationen über das Verhalten von Carbon Nanotubes (CNTs) als potentiellen Trägern von Schadstoffen im Falle einer unbeabsichtigten Freisetzung von CNTs in die Umwelt zu gewinnen. Die Experimente zeigten, dass unbehandelte CNTs in wässriger Suspension wenig kolloidale Stabilität besitzen. Auch die Sorptionskapazität der unbehandelten CNTs für Uran(VI) ist gering. Die Oberflächenmodifizierung der CNTs durch Oberflächenoxidation mittels eines Gemischs aus konzentrierter HNO3 und konzentrierter H2SO4 erhöhte die kolloidale Stabilität in neutralem Wasser jedoch sehr stark. Außerdem stieg die Sorptionskapazität für Uran, welches als ein Beispiel für ein toxisches Schwermetall diente, stark an durch die Oberflächenbehandlung. Die Sorptionsdaten des Urans konnten am besten durch eine Langmuir-Adsorptionsisotherme gefittet werden. Der Anstieg der kolloidalen Stabilität und der Sorptionskapazität war zurückzuführen auf die Bildung von neuen funktionellen Gruppen auf der CNT-Oberfläche durch Oberflächenoxidation. Diese Gruppen (Carboxylgruppen) konnten durch FTIR-Spektroskopie auch detektiert werden. Ein anderer Weg, die kolloidale Stabilität der CNTs zu erhöhen war die Zugabe von kleinen Mengen an Huminsäure zu Suspensionen von unbehandelten CNTs.
Keywords: Carbon nanotubes, functionalisation, colloidal stability, uranium sorption
  • Contribution to proceedings
    Wasser 2009, Jahrestagung der Wasserchemischen Gesellschaft - Fachgruppe in der GDCh, 18.-20.05.2009, Stralsund, Deutschland
    Wasser 2009, ISBN 978-3-936028-56-0, 341-344
  • Poster
    Wasser 2009, Jahrestagung der Wasserchemischen Gesellschaft - Fachgruppe in der GDCh, 18.-20.05.2009, Stralsund, Deutschland

Publ.-Id: 13390 - Permalink

Anomalous wear-out phenomena of Europium-implanted light emitters based on a metal–oxide-semiconductor structure
Rebohle, L.; Lehmann, J.; Prucnal, S.; Nazarov, A.; Tyagulskii, I.; Tyagulskii, S.; Kanjilal, A.; Voelskow, M.; Grambole, D.; Skorupa, W.; Helm, M.;
The anomalous wear-out phenomena of Eu-implanted metal–oxide-semiconductor devices were investigated. It will be shown that in contrast to other rare earth elements the electroluminescence (EL) intensity of Eu-implanted SiO2 layers can rise under constant current injection before the known EL quenching will start. Under certain circumstances this rise may amount up to two orders of magnitude. The EL behaviour will be correlated with the microstructural and electrical properties of the devices. Transmission electron microscopy and Rutherford backscattering spectroscopy were applied to trace the development of Eu / Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer. The hydrogen profile within the SiO2-SiON interface region was determined by nuclear reaction analysis. Current-voltage characteristics, EL decay times and the progression of the voltage and the EL spectrum with increasing charge injection were measured to study charge and trapping phenomena in the oxide layer to reveal details of the EL excitation mechanism. A first qualitative model for the anomalous life time behaviour is proposed.
Keywords: Europium Si based light emission electroluminescence wear-out
  • Journal of Applied Physics 106(2009), 123103

Publ.-Id: 13389 - Permalink

Physical limitations of the hot electron impact excitation mechanism in electrically driven Si-based light emitters
Rebohle, L.;
Electrically driven Si-based light emitters will give a major impact on the development of integrated photonic applications. However, despite the remarkable success which was achieved in the last two decades on this field none of the different Si-based light emitters of today can compete with III-V light emitters or organic LEDs in terms of efficiency and life time. In many cases the applied voltage is also uncomfortably high.
The present work explores the physical limitations of voltage downscaling for those light emitters whose electrical excitation mechanism is based on impact excitation of hot electrons. In detail, the drop down of the electroluminescence power efficiency with decreasing SiO2 thickness of Tb-implanted devices is investigated. It will be experimentally shown that there is a dark zone with an extension of about 20 nm behind the injecting interface in which the hot electrons have not yet gained enough kinetic energy in order to excite the Tb3+ luminescence centers. In addition, the replacement of the host matrix SiO2 by SiON results in a decrease of power efficiency by two orders of magnitude which is consistent with experimental data about the hot energy distribution in these media.
Keywords: electroluminescence rare earth Si-based light emitter
  • Lecture (Conference)
    IBEDM 2009, 2.10.2009, Tossa de Mar, Spanien

Publ.-Id: 13388 - Permalink

Si-based light emitters How bright is the future?
Rebohle, L.;
Electrically driven Si-based light emitters will give a major impact on the development of integrated photonic applications. However, despite the remarkable success which was achieved in the last two decades on this field none of the different Si-based light emitters of today can compete with III-V light emitters or organic LEDs in terms of efficiency and life time. In many cases the applied voltage is also uncomfortably high.

The presentation discusses several aspects of the suitability of Si-based light emitters for applications on the example of rare earth implanted MOS structures. In the first part it will be shown that in case the electrical excitation mechanism is based on impact excitation of hot electrons there is a dark zone behind the injection interface in which luminescence centers will not be excited. With a dark zone extension in the order of 20 nm this limits the possibility to downscale the oxide layer thickness and thus the applied voltage. The second part of the presentation reports about ongoing activities to utilize Si-based light emitters for biosensors. Finally, the topic of Si-based light emitters embedded in photonic architectures is briefly addressed.
Keywords: Si-based light emitters rare earth electroluminescence dark zone
  • Lecture (others)
    Seminarvortrag, 29.9.2009, Barcelona, Spanien

Publ.-Id: 13387 - Permalink

Rare earth implanted MOS light emitting devices
Rebohle, L.;
Rare earth implanted MOS light emitting devices are one of the most promising candidates for Si-based light emission and provide – depending on the implanted element – strong electroluminescence from the UV through the visible up to the IR. The talk will start with an introduction to rare earth’s and the special features of their electronic structure, and will focus than on the electroluminescence properties and the possibilities to enhance efficiency and operation life time of such devices. Finally the suitability for potential applications, especially in biosensing, will be discussed.
Keywords: Rare earth Si-based light emission electroluminescence
  • Lecture (others)
    Seminarvortrag, 8.5.2008, Hongkong, China

Publ.-Id: 13386 - Permalink

Selenium-79, a highly mobile radionuclide in the environment?
Scheinost, A. C.;
Current research results contradict the previously assumed high mobility of the radionuclide Se-79 from nuclear waste repositories
  • Lecture (others)
    Wissenschaft Presse Konferenz, 19.-20.01.2009, Grenoble, France

Publ.-Id: 13385 - Permalink

The Rossendorf Beamline at ESRF: Current status and prospects
Scheinost, A. C.;
overview on technical aspects as well as on research highlights in 2009
  • Lecture (Conference)
    10th Annual FWR/PSI-LES Meeting, 28.-29.10.2009, Villigen, Switzerland

Publ.-Id: 13384 - Permalink

A comparative study of actinide complexation in three ligand systems with increasing complexity
Jeanson, A.; Dahou, S.; Guillaumont, D.; Moisy, P.; Auwer, C. D.; Scheinost, A. C.; Hennig, C.; Vidaud, C.; Subra, G.; Solari, P. L.;
The complexation of thorium, neptunium and plutonium at oxidation state +IV with three ligands of increasing complexity has been investigated. These ligands are relevant for bio inorganic systems. The first ligand is the small nitrilotriacetic acid that often play the role of protecting ligands against hydrolysis. EXAFS results for the Th to Pu series have been correlated to quantum chemical calculations and show an homogeneous behavior of the actinide at oxidation state +IV. For larger ligands, steric effects may become significant and one can ask how the ligand may accommodate the large actinide cation coordination sphere. Model pentapeptides have been synthesized and tested as complexing agents. Comparison with NTA shows that the molecular arrangements are radically different. The third ligand system is transferrin, a diferric metalloptrotein that is well known to coordinate a large variety of cations from transition metals of f-elements. Metalloproteins bear primary, secondary and tertiary structures that all play a crucial role in bonding. At a given oxidation state (+IV), but for various atomic numbers (Th, Np, Pu) EXAFS data at the cation LIII edge exhibit significant coordination discrepancies that are related to a changes in protein geometry. In that sense, the metalloprotein may be viewed as a complex system.
Keywords: EXAFS actinoides complexation neptunium thorium plutonium
  • Lecture (Conference)
    XAFS14, 26.-31.07.2009, Camerino, Italy
  • Open Access LogoAbstract in refereed journal
    Journal of Physics: Conference Series 190(2009), 012185
    DOI: 10.1088/1742-6596/190/1/012185

Publ.-Id: 13383 - Permalink

The microbial ecology of land and water contaminated with radioactive waste; towards the development of bioremediation options for the nuclear industry
Geissler, A.; Selenska-Pobell, S.; Morris, K.; Livens, F. R.; Lloyd, J. R.;
The high financial and environmental costs associated with remediation of land contaminated through 60 years of global nuclear activity has underpinned the development of new passive in situ bioremediation processes for sites contaminated with nuclear waste. Many of these processes rely on successfully harnessing newly discovered natural biogeochemical cycles of key radionuclides and fission products. Of particular note are strategies that involve enzymatic and indirect redox transformations of actinides such as uranium, neptunium and plutonium and fission products such as technetium. This chapter will discuss the recent advances that have been made in understanding the microbial colonization of radioactive environments and the biological basis of microbial transformations of radioactive waste in these settings. In addition, the impact of co-contaminants such as nitrate on both the microbial ecology of sediments and radionuclide speciation will also be discussed.
  • Contribution to external collection
    L. Batty, K. Hallberg: Ecology of Industrial Pollution, Cambridge/United Kingdom: Cambridge University Press, 2010, 226-241

Publ.-Id: 13382 - Permalink

Monitoring of the biogeochemical changes induced by increased U(VI) concentrations in natural environments
Selenska-Pobell, S.;
Natural bacterial community structures in the wetlands of uranium mill-tailings with different geographic origin (Germany and USA) and possessing various levels of uranium contamination were studied. Comparative analyses of bacterial communities via direct molecular approaches based on 16S rRNA gene sequences revealed strong predominance of Gamma-, Beta-, or Deltaproteobacteria in dependence on the geographic origin and on the anthropologic history of the studied wastes. In all studied samples novel, yet to be cultured, Betaproteobacterial populations were identified. It was possible to culture representatives of Gamma-Pseudomonas as well as some Alphaproteobacteria (mainly representatives of Sphingomonas sp.) and also different groups of Firmicutes.
Treatments of the samples from one of the studied uranium wastes with uranyl nitrate resulted in a strong shifting in the natural bacterial community and proliferation of representatives of Gamma-, Betaproteobacteria, and/or Firmicutes, depending on the aeration conditions of the experiments. The increased size of the mentioned bacterial populations was confirmed by using a combination of direct monitoring methods based on 16S rRNA and narG genes.
The fate of the added U(VI) in a form of uranyl nitrate was monitored via Time Resolved Laser-induced Fluorescence Spectroscopic (TRLFS) analysis. The latter demonstrated that almost all added uranium was complexed in uranyl phosphate compounds.
Transmission Electron Microscopic (TEM) and X-ray Absorption Spectroscopic (XAS) analyses of the interactions of particular uranium waste bacterial isolates with U(VI) under conditions, corresponding to the natural ones, revealed that the added uranium is immobilized mainly on their cell walls via sorption by organic phosphate groups and/or via precipitation in inorganic uranyl phosphate mineral phases (biomineralization). The observed biomineralization process was connected to release of orthophosphate by the stressed by the treatments bacterial cells. No reduction of U(VI) to U(IV) was observed at the studied oligotrophic conditions which are relevant to the natural ones in the studied wastes.
  • Invited lecture (Conferences)
    Workshop on “Genetic monitoring in Wetlands -2009”, 12.-16.10.2009, Sofia, Bulgarien

Publ.-Id: 13381 - Permalink

Biomineralization of Uranium and Nanocluster Formation by Microorganisms
Selenska-Pobell, S.; Merroun, M.;
Bacteria and archaea are the most ubiquitous organisms in terrestrial and aquatic environments. They play a major role in deposition and weathering of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the different metal binding potential of their cell wall components.
The talk will focus on cell wall dependent accumulation and biomineralization of uranium by particular Gram-positive and Gram-negative bacteria recovered from uranium mining wastes. By using TEM, EXAFS and TRLF we were able to demonstrate that the Gram-negative and most of the Gram-positive bacteria inhabiting the oligotrophic uranium mining waste pile soils immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. Particular Gram-positive isolates, possessing highly ordered proteinaceous surface layers (S-layers), are immobilizing U(VI) by both phosphate groups from their peptidoglycan and also by the carboxylic groups of the aspartate and glutamate stretches of their S-layers.
In addition, the cell wall supported formation of metallic palladium and gold nano-clusters by some bacteria and archaea will be presented. Despite of the different mechanisms of the biological deposition of Pd by Gram-negative and Gram-positive bacteria, the nanoparticles formed by both had almost identical size and catalytic activity. The Au nanoclusters formed by bacteria and archaea had significantly different physical properties.
  • Lecture (Conference)
    13th IACIS International Conference on Surface and Colloid Science, Session: Biomineralization, 14.-19.06.2009, New York, USA

Publ.-Id: 13380 - Permalink

Bacterial isolates from extreme environments and their interactions wit uranium and other xenobiotics
Selenska-Pobell, S.;
Interactions of the natural isolate Pseudomonas rhodesiae R5 with U(VI) and different compounds were studied by using TEM, EXAFS and wet chemistry experiments. The ability of the strain to accumulate U(VI) via bio-sorption and bio-mineralization was demonstrated. TEM analyses revealed that the U(VI) accumulates were exclusively localized on the cell wall. EXAFS analyses demonstrated that the formed U(VI) accumulates represented meta-autunite-like phases.
The strain P. rhodesiae R5 demonstrated a high capability to utilize phenol compounds as well and was used for construction of biofilms on polyethylene oxide cryogels (PEO-biogels). The latter were effectively applied for decontamination of phenol polluted waters.
  • Lecture (others)
    Invited talk at the University of Sofia, Department of Ecology, 06.11.2009, Sofia, Bulgarien

Publ.-Id: 13379 - Permalink

Motion Compensation in Positron Emission Tomography: Performance of a Clinical Integration at the PET centre Dresden-Rossendorf
Langner, J.;
Positron emission tomography (PET) is a well-established functional imaging method used in nuclear medicine. It allows for retrieving information about biochemical and physiological processes in vivo. The currently achievable spatial resolution of PET is about 5mm for brain acquisitions and about 8mm for whole-body acquisitions. However, recent improvements in image reconstruction methods point to a resolution of 2mm in the near future. Typical acquisition times range from minutes to hours due to the low signal-to-noise ratio of the measuring principle of PET, as well as due to the monitoring of the metabolism of the patient over a certain time. Therefore, patient motion increasingly limits the possible spatial resolution of PET. In addition, patient immobilizations are only of limited benefit in this context. Thus, if kept uncorrected, patient motion leads to a relevant resolution degradation and incorrect quantification of metabolic parameters.
In this talk, the results of a novel motion compensation method for clinical brain PET acquisitions developed at the research centre Dresden-Rossendorf (Forschungszentrum Dresden-Rossendorf ) in cooperation with the nuclear medicine department of the university hospital of the Technical University Dresden are presented. By using an external motion tracking system, information about the head motion of a patient is continuously acquired during routine PET acquisitions. Based on the motion information, an event-based motion compensation algorithm performs spatial transformations of all registered coincidence events, thus utilizing the raw data of a PET system - the so-called list-mode data. For routine acquisition of this raw data, methods have been developed which allow for the first time to acquire list-mode data from an ECAT Exact HR+ PET scanner within an acceptable time frame. Furthermore, methods for acquiring the patient motion in clinical routine and methods for an automatic analysis of the registered motion have been developed. For the clinical integration of the aforementioned motion compensation approach, the development of additional methods (e.g. graphical user interfaces) was also part of this work.
After development, optimisation and integration of the event-based motion compensation in clinical use, analysis with example data sets have been performed. Noticeable changes could be demonstrated by analysis of the qualitative and quantitative effects after the motion compensation. From a qualitative point of view, image artefacts have been eliminated, while quantitatively, the results of a tracer kinetics analysis of a FDOPA acquisition showed relevant changes in the R0k3 rates of an irreversible reference tissue two-compartment model. Thus, it could be shown that an integration of an event-based motion compensation method which is based on the utilization of the raw data of a PET scanner, as well as the use of an external motion tracking system, is not only reasonable and possible for clinical use, but also shows relevant qualitative and quantitative improvements for PET imaging.
  • Invited lecture (Conferences)
    Columbia Kreitchman PET Center, 10.11.2009, New York, USA

Publ.-Id: 13377 - Permalink

Especiación química del uranio (VI) precipitado por la bacteria marina Idiomarina loihiensis MAH1: Caracterización espectroscópica por TRLFS
Morcillo De Amuedo, F.; Reitz, T.; Arias Peñalver, J. M.; Gonzalez Muñoz, M. T.; Merroun, M. L.;
Los océanos cubren aproximadamente un 70% de la superficie terrestre, de ahí que sean uno de los mayores sumideros de radionucleidos de origen antropogénicos (1). En el caso del mar mediterráneo, se ha estimado una deposición de 12 y 0.12 PBq de 137Cs and 239,240Pu, respectivamente, entre 1956 y 1996, debido principalmente a la realización de pruebas nucleares (2). El destino final de estos radionucleidos son los sedimentos marinos, aunque pueden permanecer en la columna de agua a concentraciones bajas, quedando biodisponibles para los organismos presentes. Algunos estudios han demostrado que estos ambientes marinos están habitados por una variedad de especies microbianas que podrían interaccionar con estos radionucleidos mediante diferentes mecanismos tales como bioadsorción, acumulación intracelular y precipitación, entre otros. Estos mecanismos ayudan tanto a la movilización como la inmovilización de estos elementos en el medio acuático, alterando, por tanto, su biodisponibilidad. El objetivo del trabajo actual era determinar la especiación química del uranio precipitado por la bacteria marina Idiomarina loihiensis MAH1 en agua de mar mediante espectroscopia de fluorescencia inducida por laser en tiempo resuelto (TRLFS) bajo condiciones medioambientales (a bajas concentraciones de U in agua de mar)

The oceans cover approximately 70% of the Earth’s surface. Hence, they are one of the biggest sinkhole for anthropogenic released radionuclides. In case of the Mediterranean sea, there has been estimated a deposition of 12 and 0.12 PBq of 137Cs and 239,240Pu, respectively, between 1956 and 1996 primarily due to the performance of nuclear tests. The marine sediments are the final destination of these radionuclides, although they can remain in the water column to low concentrations, remaining bioavailable for the present organisms. Some studies have demonstrated that these marine environments are inhabited by a variety of microbial species that might interact with these radionuclides by means of such different mechanisms like, for example, biosorption, intracellular accumulation and precipitation. These mechanisms support the mobilization or immobilization of these elements in the aquatic environment, altering, therefore, his bioavailability. The objective of the present work was to determine the chemical speciation of the uranium precipitated by the marine bacterium Idiomarina loihiensis MAH1 at environmental conditions (low concentrations of U) in sea water by using time-resolved laser-induced fluorescence spectroscopy (TRLFS).
  • Poster
    XXII Congreso Nacional de la Sociedad Española de Microbiología, 21.-24.09.2009, Almeria, Spanien

Publ.-Id: 13376 - Permalink

Investigation on primary side oriented accident management measures in a station blackout scenario for a VVER-1000 reactor
Tusheva, P.; Schaefer, F.; Reinke, N.; Altstadt, E.; Rohde, U.; Weiss, F.-P.; Hurtado, A.;
A consequence of a total loss of AC power supply (station blackout) leading to unavailability of major active safety systems is that the safety criteria ensuring a secure operation of the nuclear power plant would be violated and a consequent core heat-up with possible core degradation would occur. In such an accident a special accident management measure (primary side depressurization) can be applied to reduce the primary pressure and to activate the injection from the passive emergency core cooling systems (accumulators). The analyses presented in this paper are aiming at a detailed investigation of the accident sequence and the possibilities to prevent or to mitigate a damage of the reactor core. A main objective of the investigation is to evaluate the effectiveness of the applied accident management measure. The analyses are performed using the codes ASTEC and ATHLET developed by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH).
Keywords: severe accidents, accident management measures, station blackout, VVER-1000 reactors

Publ.-Id: 13375 - Permalink

Application of a grid based hybrid finite volume/boundary element method for simulations of the kinematic induction equation with insulating boundary conditions.
Giesecke, A.; Stefani, F.; Gerbeth, G.;
The experimental realization of dynamo excitation as well as theoretical and numerical examinations of the induction equation have shown the relevance of boundary conditions and material properties for a self-sustaining dynamo. Generally, in non-spherical geometry typical insulating boundary conditions are described by elaborated schemes (e.g. solving of the Laplace equation in an extended domain) or by simplifying approximations (pseudo vacuum). A different approach is provided by a modified integral equation procedure, commonly known as the boundary element method (BEM). Integrating the Laplace equation on the boundaries allows to overcome the difficulties of the non-local character of insulating boundary conditions and the direct computation of the magnetic field next to an insulator becomes possible. However, within the interior of a field producing domain geometric constraints or varying material properties (e.g. electrical conductivity of the container walls or localized high-permeability material) might also play a role.
Keywords: nunerical simulations dynamo insulator boundary conditions boundary element method
  • Lecture (others)
    SFB Meeting, 12.11.2009, Dresden, Deutschland

Publ.-Id: 13374 - Permalink

Quantitative Kelvin probe force microscopy
Baumgart, C.; Helm, M.; Schmidt, H.;
In this paper we report on the investigation of electrostatic forces between a conductive probe and semiconducting materials by means of Kelvin probe force microscopy measurements. Due to the formation of an asymmetric electric dipole at the semiconductor surface, the measured Kelvin bias is related with the difference between Fermi energy and respective band edge. Quantitative Kelvin probe force microscopy measurements on semiconductors, namely on a conventional dynamic random-access memory cell and on a cross-sectionally prepared Si epilayer structure, are presented.
  • Contribution to proceedings
    MRS Fall Meeting Boston, 30.11.-04.12.2009, Boston, MA, USA

Publ.-Id: 13373 - Permalink

Frequency dependent Kelvin probe force microscopy on locally doped Si
Baumgart, C.; Helm, M.; Schmidt, H.;
Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to buried doped regions in cross-sectionally prepared Si epilayer structures and to shallow doped regions in a conventional dynamic random access memory (DRAM) cell. Frequency dependent KPFM measurements were performed under ambient conditions by means of an Anfatec Level-AFM with a 2nd amplifier and p- and n-type conductive NSC15 probes from MikroMasch. Using an active mixer, the excitation amplitude of the NSC15 probes is almost independent of the operation frequency. The frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped Si are probed.
  • Poster
    MRS Fall Meeting Boston, 30.11.-04.12.2009, Boston, MA, USA

Publ.-Id: 13372 - Permalink

Solid state spectroscopy using an infrared free-electron laser
Helm, M.;
A free electron laser covering a wavelength range of nearly two spectral decades (3-300 µm or 1-100 THz) has been in operation at our research center for a few years. I will present a few examples of the research done with it, taking advantage if its high peak and average power and picosecond time structure.
I will present measurements of carrier relaxation in semiconductor quantum dots, where the relaxation time varies by three orders of magnitude (2 ps to 1.5 ns), if the energy level spacing is changed by only a factor of two (30 meV to 15 meV). This can be explained in the quantum dot polaron picture.
The high average power allows one to perform near-field microscopy experiments. We can image ferroelectric domains on BaTiO3 surfaces purely due to their optical contrast resulting from a slight anisotropy of the dielectric function. Sweeping the FEL wavelength across a phonon resonance results in a reversal of optical contrast, which demonstrates the resonant nature of the interaction. The spatial resolution is 150 nm, about 1/100 of the wavelength.
Finally I will discuss a nonlinear mixing experiment, where THz sidebands of 800 nm radiation are generated in a semiconductor quantum well system, and briefly describe first cyclotron resonance experiments using the FEL in the pulsed magnetic field.
Keywords: free electron laser, spectroscopy, infrared
  • Lecture (others)
    Kolloquium am Institute for Molecules and Materials, Radboud University, The Netherlands, 10.11.2009, Nijmegen, The Netherlands

Publ.-Id: 13371 - Permalink

Comparison of bismuth emitting liquid metal ion sources
Bischoff, L.; Pilz, W.; Mazarov, P.; Wieck, A. D.;
Four different liquid metal ion sources (LMIS), working with pure Bi as well as with Bi containing alloys (Au13Bi87, Ga38Bi62, Ga35Bi60Li5) were investigated with respect to the emission behaviour as a function of current and temperature, the mass spectra and the energy distribution of the individual ion species. Additionally, for the pure Bi LMIS the sputtering rates for Bi ions and clusters on a Si, SiO2 and Ge substrates were compared with that of Ga projectile ions using a mass separating focused ion beam system.
Keywords: Bismuth alloy LMIS; mass spectra; energy spread; FIB.

Publ.-Id: 13370 - Permalink

Quantitative Electrical Nanometrology - Kelvin Probe Force Microscopy Measurements on Semiconductors
Baumgart, C.; Streit, S.; Helm, M.; Schmidt, H.;
In this paper state of the art electrical nanometrology techniques are reviewed with the focus on semiconducting materials. The basics of scanning capacitance microscopy, scanning spreading resistance microscopy, scanning microwave microscopy, and Kelvin probe force microscopy, and their applicability on various material systems are discussed. Quantitative Kelvin probe force microscopy measurements on semiconductors, namely on a conventional dynamic random-access memory cell and on a cross-sectionally prepared Si epilayer structure, are presented.

Publ.-Id: 13369 - Permalink

Injected wake field acceleration with a 40 MeV electron linac
Kraft, S.; Jochmann, A.; Erler, C.; Debus, A.; Bussmann, M.; Sauerbrey, R.; Schramm, U.; Cowan, T.;
Over the last years multiple research groups achieved multi-MeV to GeV electron beams. Ultrashort bunches and a very low emittance combined with a high bunch charge offer a wide range of applications nevertheless the reproducibility of those beams is one of the main problems. External injection into a plasma wake is a promising concept to separate the influence of different input parameters from each other for more control of experimental results and to improve reproducibility. At the Research Center Dresden-Rossendorf the 150TW laser system DRACO was set up next to an superconducting electron accelerator. This will give the opportunity to study wake field acceleration in more detail. In this talk the present status of the experiment, ongoing upgrades and future plans will be described.
  • Lecture (Conference)
    51st Annual Meeting of the APS Division of Plasma Physics, 02.-06.11.2009, Atlanta, USA

Publ.-Id: 13368 - Permalink

Anwendung von Ultraschallverfahren zur Charakterisierung von Flüssigmetall-Zweiphasenströmungen
Eckert, S.; Zhang, C.; Gerbeth, G.;
Die Injektion von Gasblasen wird oft in metallurgischen Prozessen zur Veredlung oder Entgasung metallischer Schmelzen eingesetzt. Eine Optimierung der Prozessabläufe kann nur auf Grundlage eines umfassenden Verständnisses der Strömungs- und Transportvorgänge erfolgreich sein. Dies erfordert neben numerischen Simulationen eine realitätsnahe experimentelle Modellierung in Flüssigmetallen. Für diese Modellexperimente besteht ein großer Bedarf an geeigneter Messtechnik zur Bestimmung der Strömungsstruktur und der Blaseneigenschaften.
In den letzten Jahren hat die Ultraschallströmungsmesstechnik im Hinblick auf einen Einsatz in Flüssigmetallen eine spürbare Entwicklung erfahren und ihre Eignung für Messungen in Zweiphasenströmung unter Beweis gestellt. Im Vortrag werden das Ultraschall-Doppler und das Ultraschall-Laufzeitverfahren vorgestellt. Mit Hilfe des Ultraschall-Doppler Verfahrens können gleichzeitig Flüssigmetall- und Blasengeschwindigkeit bestimmt werden. Das Laufzeitverfahren liefert komplementäre Daten über die geometrische Struktur der Blasen und des Blasenschwarms. Dies betrifft insbesondere Blasendurchmesser, Blasenform und raumzeitliche Ausdehnung des Blasenschwarms. Spezifische Probleme der Verfahren, insbesondere bei höheren Gasgehalten, werden diskutiert und zukünftige Entwicklungsperspektiven aufgezeigt.
Keywords: Liquid metal two-phase flow, bubbly flow, Flow measurements, Ultrasound-Doppler method
  • Lecture (others)
    Festkolloquium anlässlich des 70. Geburtstags von Prof. Dr. E. Kaiser, 06.11.2009, Dresden, Deutschland

Publ.-Id: 13367 - Permalink

Prototype coupling of the CFD software ANSYS CFX with the 3D neutron kinetic core model DYN3D
Kliem, S.; Rohde, U.; Schütze, J.; Frank, T.;
The CFD code ANSYS CFX has been coupled with the neutron-kinetic core model DYN3D. ANSYS CFX calculates the fluid dynamics and related transport phenomena in the reactor’s coolant and provides the corresponding data to DYN3D. In the fluid flow simulation of the coolant, the core itself is modeled by the porous body approach. DYN3D calculates the neutron kinetics and the fuel behavior including the heat transfer to the coolant. The physical data interface between the codes is the volumetric heat release rate into the coolant. In the prototype that is currently available, the coupling is restricted to single-phase flow problems. In the time domain an explicit coupling of the codes has been implemented so far.
Steady-state and transient verification calculations for a small-size test problem confirm the correctness of the implementation of the prototype coupling. This test problem was a mini-core consisting of nine real-size fuel assemblies. Comparison was performed with the DYN3D stand-alone code. In the steady state, the effective multiplication factor obtained by the ANSYS CFX/DYN3D codes shows a deviation of 9.8 pcm from the DYN3D stand-alone solution. This difference can be attributed to the use of different water property packages in the two codes. The transient test case simulated the withdrawal of the control rod from the central fuel assembly at hot zero power. Power increase during the introduction of positive reactivity and power reduction due to fuel temperature increase are calculated in the same manner by the coupled and the stand-alone codes. The maximum values reached during the power rise differ by about 1 MW at a power level of 50 MW. Beside the different water property packages, these differences are caused by the use of different flow solvers.
Keywords: Computational Fluid Dynamics, 3D neutron kinetics, Code coupling
  • Contribution to proceedings
    PHYSOR 2010, 09.-14.05.2010, Pittsburgh, USA
    Proceedings of the PHYSOR 2010, La Grange Park, Illinois, USA: ANS, 9780894480799
  • Lecture (Conference)
    PHYSOR-2010, 09.-14.05.2010, Pittsburgh, USA

Publ.-Id: 13366 - Permalink

Integration der Positronen-Emissions-Tomographie in die Strahlentherapie mit hochenergetischen Photonen
Kunath, D.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-525 2009


Publ.-Id: 13365 - Permalink

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