Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34877 Publications

Intensity of optical absorption close to the band edge in strained ZnO films

Fritsch, D.; Schmidt, H.; Schmidt-Grund, R.; Grundmann, M.

Besides other one of the remarkable properties making wurtzite ZnO such an interesting material is its large exciton binding energy of about 60 meV, leading to stable excitons at room-temperature. Also, the Curie temperature of this wide-gap material has been predicted to lie above room temperature, making ZnO alloyed with magnetic ions a possible material for spintronics applications. One big challenge in the fabrication of the ZnO-based heterostructure devices is the lattice mismatch between the ZnO films and the substrates and the different thermal expansion coefficient inducing biaxial strain. This work reports on the electronic band structure of biaxially strained ZnO for strains along the a- or c-axis ranging from -1% to 1 %, as calculated by means of the empirical pseudopotential method. Thereby, we also account for relativistic effects in the form of the spin-orbit interaction, as well as for the energy dependence of the crystal potential through the use of nonlocal model potentials. Moreover, the application of a variable plane wave basis set allows us to directly obtain the strain-induced variations of the electronic and the optical properties of wurtzite ZnO.

Keywords: ZnO; emipirical pseudopotential method; dielectric function

  • Journal of the Korean Physical Society 53(2008)1, 123-126

Publ.-Id: 12018

Homoepitaxial ZnO thin films by PLD: Structural properties

Lorenz, M.; Wagner, G.; Rahm, A.; Schmidt, H.; Hochmuth, H.; Schmid, H.; Mader, W.; Brandt, M.; von Wenckstern, H.; Grundmann, M.

Homoepitaxial ZnO films deposited on annealed hydrothermal O-face ZnO single crystals show superior structural quality. This is demonstrated by narrow ZnO(00.2) rocking curves with FWHM of typically 23 to 35 arcsec, and nearly dislocation-free TEM cross sections. Nominally undoped ZnO films indicate a minor in-plane strain of about 250 ppm and no out-of-plane strain. Target doping by 0.01% P2O5 or 0.5% Li3N results in pseudomorphic film growth without in-plane strain. Increasing doping concentration of 0.1 and 1% P2O5 results in both in-plane and out-of-plane strain up to 0.9 % indicating relaxed films. The O-face polarity of the homoepitaxial ZnO films is confirmed by convergent beam electron diffraction.

Keywords: ZnO; pulsed laser deposition

Publ.-Id: 12017

THz sideband generation in multi quantum wells

Wagner, M.; Schneider, H.; Helm, M.; Schartner, S.; Andrews, A. M.; Roch, T.; Strasser, G.

Ac THz electric fields which couple strongly with intraband excitations in semiconductors can lead to spectral sidebands when an interband excitation is present. In this nonlinear mixing process a near-infrared (NIR) laser beam is mixed with a THz beam to generate sidebands around the NIR frequency with a frequency spacing equal to the THz frequency or multiples of it. In the last years this effect has been investigated in various semiconductor systems (i.e. in bulk GaAs or in multi quantum wells).
We investigated the third-order nonlinear mixing process between a near-infrared laser and a free-electron laser in an undoped symmetric AlGaAs/GaAs multi quantum well. Differently from the literature where electronic intersubband transitions were used, we are using the transition between the heavy-hole and light-hole states. This transition around 73 µm is pumped close to normal incidence by FELBE, the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf. The picosecond NIR laser is transmitted through the sample where the GaAs substrate has been etched away. It is focused on the entrance slit of the spectrometer of a Streak-camera system. With the Streak-camera temporal and spectral measurements are possible.
The n=+2 sideband conversion efficiency is of the order of 0,005% with respect to the incoming NIR intensity. Among other things we present the power dependency on NIR and FEL intensity and the resonance behavior with respect to the NIR and FEL wavelengths.

Keywords: THz sidebands; free-electron laser; FEL

  • Poster
    GDRE-THz workshop 2008 Paris, 25.-26.09.08, Paris, Frankreich
  • Poster
    EOS Annual Meeting 2008, 29.09.-02.10.2008, Paris, Frankreich
  • Poster
    Nonna 2008 - Workshop on Nonequilibrium Nanostructures, 01.-06.12.2008, Dresden, Deutschland

Publ.-Id: 12016

High electron mobility of phosphorous-doped homoepitaxial ZnO thin films grown by pulsed-laser deposition

Brandt, M.; von Wenckstern, H.; Schmidt, H.; Rahm, A.; Biehne, G.; Benndorf, G.; Hochmuth, H.; Lorenz, M.; Meinecke, C.; Butz, T.; Grundmann, M.

The transport properties of phosphorous-doped ZnO thin films, grown by pulsed-laser deposition on thermally pretreated hydrothermally grown ZnO single-crystal substrates, are reported. The ZnO:P thin films show very good morphological and structural properties as confirmed by atomic force microscopy (AFM), high resolution x-ray diffraction, and Rutherford backscattering (RBS) channeling. Steps of height c/2 are visible in AFM investigations for all samples. For an oxygen partial pressure of 0.1 mbar, two-dimensional growth was found. RBS channeling of a ZnO:P film shows a minimum yield of 0.034 which is comparable to that of an annealed substrate (0.033). Hall effect measurements revealed that all films are n-type for the present growth conditions. Peak mobilities of 800 cm^2/Vs have been observed around 70 K, in line with the high structural quality of the samples. Room-temperature mobility in ZnO:P is up to 170 cm^2/Vs.

Keywords: ZnO; phosphorous-doping

Publ.-Id: 12015

X-ray scattering and diffraction from Xe-induced ripples in crystalline (001) silicon

Biermanns, A.; Pietsch, U.; Grenzer, J.; Hanisch, A.; Facsko, S.; Carbone, G.; Metzger, H.

The formation of surface-nanostructures with a characteristic size ranging from several nanometer up to microns has attracted significant interest in the last decades in the context of fabrication of novel opto-electronic and storage devices. One kind of those nanostructures are wave-like patterns (ripples) produced by an interplay between a roughening process caused by ion beam erosion (sputtering) of the surface and smoothening processes caused by surface diffusion. In this contribution we report on investigations of patterned Si (001) surfaces after irradiation with Xe-ions using ion-energies up to 70keV. During the sputtering, an amorphous surface-layer is formed followed by a rather sharp interface towards crystalline material, showing the same morphology as the surface. The structures of the amorphous layer and the amorphous-crystalline interface were studied by means of grazing incidence- small angle scattering (GISAXS) and diffraction (GID) using synchrotron-radiation. We found that the crystal structure at the interface is expanded along the ripples, caused by the creation of defects inside the surface region, whereas this expansion is strongly reduced across the ripples, which can be explained by an anisotropic defect distribution close to the amorphous-to-crystalline interface.

Keywords: nanostructures ion-beam patterning GISAXS GID

  • Poster
    16th International Conference on Ion Beam Modification of Materials - IBMM 08, 31.07.-05.09.2008, Dresden, Germany

Publ.-Id: 12014

Paramagnetism in Co-doped ZnO films

Xu, Q.; Zhou, S.; Markó, D.; Potzger, K.; Fassbender, J.; Vinnichenko, M.; Helm, M.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.

Co-doped ZnO films with various electron concentrations up to 4.61×1019 cm-3 at room temperature were prepared by pulsed laser deposition on a-plane sapphire substrates. Only paramagnetism was observed down to 2 K for all the samples, which was also confirmed by x-ray magnetic circular dichroism (XMCD) measurements at 30 K. The average magnetic moment per Co2+ ion is significantly smaller than the expected moment for Co2+ ions (L=1.07, S=3/2), mainly due to the antiferromagnetic exchange interaction between the neighbouring Co2+ ions in the ZnO matrix. Also clustering instead of a uniform distribution of Co2+ ions may play a role. The formation of Co clusters is hindered at higher substrate temperature during the thin film growth. Clear anomalous Hall effect was observed in the highly conducting Co-doped ZnO films at low temperatures up to 100 K.

Keywords: diluted magnetic semiconductor; paramagnetism; anomalous Hall effect

Publ.-Id: 12013

X-ray absorption and photoelectron spectroscopy investigation of selenite reduction by FeII-bearing minerals

Funke, H.; Scheinost, A.

Wavelet transform (WT) has been proven as a valuable tool for EXAFS data analysis for structures, where two types of backscattering atoms are at the same distance from the central atom [1-3]. WT provides not only radial distance resolution of the spectra like the Fourier transform, but resolves also the wave vector space permitting to probe the discrimination of atoms by their elemental nature.
A short introduction to the continuous WT will be given. The variation of the parameters of the Morlet mother wavelet will be used to build an adapted wavelet for the analysis of specific EXAFS spectra. Thereby the analysis of the (Heisenberg) uncertainty boxes of the Morlet wavelet is a central point to understand the resolution limitations of the WT as well as the form of the wavelet ridges.
Two examples for the use of WT for EXAFS data analysis will be given.
First, the method is applied to a structural problem of Zn-Al layered double hydroxides, demonstrating the homogeneity of the metal cation distribution in the hydroxide layers. Depending on the specific problem, either the well-known Morlet wavelet was used, or a newly developed FEFF-Morlet wavelet, based on theoretical EXAFS back scattering functions.
Second, the reduction from soluble selenium species to elemental Se and iron selenides by Fe containing minerals is examined in detail [4]. Here, the wavelet analysis is used to answer the question: Is Se coordinated to Se atoms/elemental Se or to the Fe (and Se) atoms? This analysis is performed by comparison to well–known reference spectra.
In the outlook two open questions will be discussed: the k weighting and the destructive interference by phase shifts.

[1] H. Funke, A. C. Scheinost, and M. Chukalina, Phys. Rev B, 71, 094110, 2005.
[2] H. Funke, M. Chukalina, and A. C. Scheinost, J. Synchrotron Rad. 14, 426-432, 2007.
[3] M. Muñoz, P. Argoul, and F. Farges, Am. Mineral. 88, 694, 2003.
[4] A. C. Scheinost, L. Charlet , Environ. Sci. Technol. 42, 1984, 2008.

  • Lecture (Conference)
    Workshop on X-ray absorption spectroscopy and advanced XAS techniques, 06.-10.10.2008, Villigen, Switzerland

Publ.-Id: 12012

S-Layer für neue Nanomaterialien

Pollmann, K.; Raff, J.

Im Rahmen des Vortrags werden die Arbeiten zur Herstellung von Nanopartikeln und Nanomaterialien mit Hilfe von bakteriellen Hüllproteinen vorgestellt und Möglichkeiten einer zukünftigen Zusammerarbeit diskutiert.

  • Lecture (others)
    Koordinierungstreffen mit dem Leibniz-Institut für Katalyse e.V. der Universität Rostock, Außenstelle Berlin, 17.04.2008, Berlin, Deutschland

Publ.-Id: 12009

Tailoring the FePt orientation on amorphous substrates by magnetron sputtering, structural and magnetic investigations

Cantelli, V.; Grenzer, J.; von Borany, J.; Fassbender, J.

Towards an increase of the magnetic recording density, materials with a high magnetic anisotropy are strongly recommended to overcome the physical limits due to superparamagnetism. For this reason, FePt alloys are widely studied because of the excellent magnetocrystalline anisotropy (KU ~ 5-8 x 10-7 erg/cm3) and large magnetic moments at 300K. [1] But, for perpendicular recording media, a (001) preferential orientation, perpendicular to the layer surface, is required.
10 and 15 nm Fe55Pt45 layers were deposited by dual magnetron sputtering on amorphous SiO2 / Si (001) substrate, varying the deposition methods, form co-deposition to monolayers sequence deposition, and working gas, from Ar to Xe, at 0.3 Pa.
The Ar plasma is more energetic than the Xe one: it is characterized by sputtered atoms with a mean energy of about 12 eV and Ar reflected neutrals, reaching a mean energy of about 100 eV when backscattered from the Pt target. This energy budget that enhance the surface adatom mobility during deposition (few eV are required), and create vacancies (E > 40 eV), that decrease the phase transition temperature to 450°C for thin layers. [2]
But, the impact of energetic atoms supports a vertical layers intermixing resulting in a randomly oriented FePt A1 structure at RT. Subsequent Rapid Thermal Annealing at 750°C is completely transforming the layer into the L10 phase, with a coercivity field HC = 1 T, but introducing a weak perpendicular magnetic anisotropy, not evidencing any difference between the deposition techniques.
The reduction of the plasma energy, by using Xe as working gas, is not decreasing the layer magnetic properties (HC = 1 T) after annealing, but strongly enhance the (001) preferential orientation, with a dispersion of the (001) direction around the surface normal of 6°, already in the co-deposition experiment.
The layer by layer technique, associated with Xe plasma, supports the (001) layer orientation after RTA at 750°C, underlining the importance to reduce the elements diffusion path to an atomistic scale. [3]

[1] H. Kanazawa, G. Lanhoff, T. Suzuki, J. Appl. Phys. 87 (2000) 6143
[2] V. Cantelli, J. von Borany, A. Mücklich, Shengqiang Zhou, J. Grenzer,
Nucl. Instr. and Meth. B, 257, 1-2 (2007) 406-410.
[3] M. L. Yan, N. Powers, D. J. Sellmyer, J. Appl. Phys. 93, 8292 (2003)

Keywords: FePt; sputtering gas; (001) orientation

  • Lecture (Conference)
    53th Conference on Magnetism and Magnetic Materials, 10.-14.11.2008, Austin Texas, USA
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12007

Experiments on nuclear astrophysics in Dresden

Bemmerer, D.

Recent experimental work on nuclear astrophysics questions at Research Center Dresden-Rossendorf (FZD) is discussed. Several large scale experimental facilities hosted in the city of Dresden/Germany have been used. The ELBE accelerator provides a 40 MeV intensive electron beam driving secondary radiation sources, for example bremsstrahlung and neutron time-of-flight. At the FZD ion beam center, a study on hydrogen burning is underway. The Felsenkeller shallow-underground counting facility in Dresden is used for a study of the astrophysical p-process.

  • Invited lecture (Conferences)
    Seminar, INFN sezione di Padova, 27.11.2008, Padua, Italy
  • Invited lecture (Conferences)
    Nuclear Physics Seminar, 14.05.2009, Legnaro (PD), Italien

Publ.-Id: 12006

MRPC prototype developments for NeuLAND/R3B at FZ Dresden Rossendorf

Bemmerer, D.; Yakorev, D.; Stach, D.; Wagner, A.

Multigap resistive plate chamber detector (MRPC) prototypes for the future NeuLAND detector at R3B/FAIR have been developed and built at Forschungszentrum Dresden-Rossendorf. The prototypes have been submitted to a variety of tests, including highly precise timing measurements at the ELBE electron beam in Dresden. Results and future perspectives of MRPC prototyping for NeuLAND by the Dresden group are discussed.

  • Lecture (Conference)
    Joint R3B/EXL/ELISE Collaboration Meeting, 11.-14.10.2008, Göteborg, Sweden

Publ.-Id: 12005

Präzise Kernphysik für die Sonne

Bemmerer, D.

Neue astronomische Beobachtungen ermöglichen es, ein bisher unerreicht genaues Bild unserer Sonne zu zeichnen. Solch ein Bild ist erforderlich, um den langfristigen Einfluss der Sonne auf das Erdklima zu verstehen, und um aus der Sonne einen kalibrierten Referenzstern zu machen.

Allerdings gibt es beim Verständnis der für die Energieproduktion im Sonneninnern verantwortlichen Kernfusionsreaktionen noch Diskrepanzen. Um sie aufzuklären, sind präzise kernphysikalische Messungen vonnöten. In dem Vortrag werden in Dresden und am Gran Sasso (Italien) untersuchte und für die Sonne relevante Kernreaktionen diskutiert und gezeigt, wie die neu gewonnenen Daten bisher bestehende Genauigkeitslücken schließen.

Abschließend wird auch auf die Auswirkungen der neuen Daten auf das Verständnis der Urknall-Nukleosynthese und der Entstehung der chemischen Elemente in Sternen, die schwerer als die Sonne sind, eingegangen.

  • Invited lecture (Conferences)
    Physikalisches Kolloquium, 02.12.2008, Dresden, Deutschland

Publ.-Id: 12004

The 3He(alpha,gamma)7Be S-factor at solar energies: The prompt gamma experiment at LUNA

Costantini, H.; Bemmerer, D.; Confortola, F.; Formicola, A.; Gyürky, G.; Bezzon, P.; Bonetti, R.; Broggini, C.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Imbriani, G.; Junker, M.; Laubenstein, M.; Lemut, A.; Limata, B.; Lozza, V.; Marta, M.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.

The 3He(alpha,gamma)7Be process is a key reaction in both Big-Bang nucleosynthesis and p–p chain of Hydrogen Burning in Stars. A new measurement of the 3He(alpha,gamma)7Be cross section has been performed at the INFN Gran Sasso underground laboratory by both the activation and the prompt gamma detection methods. The present work reports full details of the prompt gamma detection experiment, focusing on the determination of the systematic uncertainty. The final data, including activation measurements at LUNA, are compared with the results of the last generation experiments, and two different theoretical models are used to obtain the S -factor at solar energies.

Publ.-Id: 12003

The effect of the sputtering gas (Ar, Xe) on FePt clusters formation. Structural and magnetic properties

Cantelli, V.; Grenzer, J.; von Borany, J.; Fassbender, J.

In this study it will be reported about the effect of the sputtering gases, Ar and Xe, on FePt clusters formation using magnetron sputtering deposition at high working pressures. Two different deposition techniques were investigated, a sequential layer by layer deposition and a co-deposition of Fe and Pt. All layers with bulk equivalent thicknesses between 3 to 5 nm were realized at RT and subsequently rapid thermal annealed in order to induce the A1-L10 ordering transformation at 550°C.
The highest L10 fraction in the annealed samples was found using Xe as sputtering gas: Xe decreases the transformation activation energy and therefore, reduces the critical thickness necessary to obtain the strong ferromagnetic phase.
The Ar assisted depositions give FePt clusters with the L10 phase only if the layer-by-layer growth is used, whereas for Xe no differences in the deposition techniques were observed.

Keywords: FePt; Magnetron sputtering; sputtering gases; clusters

  • Lecture (Conference)
    53th Conference on Magnetism and Magnetic Materials, 10.-14.11.2008, Austin Texas, USA
  • Contribution to proceedings
    53th Conference on Magnetism and Magnetic Materials, 10.11.-14.12.2008, Austin Texas, USA
    Journal of Applied Physics 105(2009), 07B529-07B529-3
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany


Publ.-Id: 12002

Cavity layer introduction in SIMOX technology

Ou, X.; Kögler, R.; Mücklich, A.; Skorupa, W.; Möller, W.; Wang, X.

The oral conference contribution reports about latest results of the improvement of the SIMOX process for fabrication of silicon-on-insulator (SOI) materials by defect engineering.

Keywords: SOI; SIMOX; ion implantation; defect engineering

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 12001

Kelvin probe force microscopy imaging of cross-sections of Si multilayer structures

Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Möller, A.; Schmidt, H.

Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of surface potentials. We present its applicability to cross-sectionally prepared p-p+ Si multilayer structures. The contact potential difference (CPD) image between tip and sample has been recorded by means of an Anfatec Level-AFM with a 2nd amplifier and NSC15 probes from MikroMash. Using an active mixer, the excitation amplitude of the NSC15 probes is almost independent on the working frequency. The probed CPD signal difference between the layers ranges between 60 meV and 850 meV and can be correlated to the variation of the diffusion potential in the Si multilayer structure. The p-type of majority charge carriers and the corresponding acceptor dopant profile have been pinpointed by scanning capacitance measurements. Starting from the known donor dopant concentration in the NSC15 probe, we simulated the CPD and determined the acceptor concentration in the whole p-p+ Si multilayer structure. From the frequency dependence of the CPD we can clearly distinguish between surface and bulk effects.

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12000

Influence of the fluid properties on co-current two-phase flows in a horizontal channel connected to a riser

Vallee, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.; Pietruske, H.; Schütz, P.; Carl, H.

0In the event of a loss-of-coolant-accident (LOCA) in a pressurised water reactor (PWR), emergency strategies have to be mapped out in order to guarantee the reliable removal of the decay heat from the reactor core. During a hypothetical small break LOCA with failure of the high pressure emergency core cooling system, the decay heat has to be released to the secondary circuit over the steam generators. Therefore, the primary circuit is designed to forward a natural circulation if the main coolant pumps are not available. Furthermore, if steam is generated in the primary circuit due to its depressurisation, stratified two-phase flow regimes can occur in the main cooling lines, which could be relevant for the reactor safety. It is intended that a computational fluid dynamics (CFD) approach could increase the simulation accuracy of such transient accident scenarios compared to the state of the art system codes.

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 is the line connecting the reactor pressure vessel (RPV) to the steam generator (SG) and is composed of a horizontal pipe, a 50° upward bend and an inclined riser (Figure 1). The hot leg model is operated in the pressure chamber of the TOPFLOW facility of FZD (Figure 1), which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. Therefore, the test section does not have to support overpressures and can be designed with thin materials. Consequently, parts of the test section could be equipped with big size windows for the application of optical observation techniques, also at reactor typical boundary conditions. In order to provide optimal observation possibilities, a flat test-section design was chosen with a width of 50 mm.

Co-current flow experiments were performed in the hot leg model, simulating a two-phase natural circulation in the primary circuit of a PWR. The experiments were done with air and water at 3.0 bar and room temperature as well as with steam and water at pressures up to 50 bar and the corresponding saturation temperature (i.e. up to 264°C). Over this range of boundary conditions, the main fluid properties vary significantly. The frequency distribution of the water level measured in the RPV simulator was used to characterise the flow in the hot leg (Figure 2). It was found that the form of the distribution informs about the stationarity of the water flow to the steam generator: the flatter the distribution, the more discontinuous the transport of water over time. This tendency was confirmed by the high-speed video observations (Figure 3), which were also used to identify the flow regime. Furthermore, Figure 2 shows a comparison between the frequency distributions obtained from the air/water and the steam/water experiments. Generally, the distributions are flatter for the cold experiments than for the hot ones. This shows that, due to the lower surface tension and viscosity, the transport of water induced by the gas is more constant in time for the steam/water flow.

Keywords: two-phase flow; co-current flow; fluid properties; hot leg; pressurised water reactor; PWR

  • Contribution to proceedings
    ExHFT-7 - 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland, Krakow: AGH University of Science and Technology Press, 978-83-7464-235-4, 443-452
  • Lecture (Conference)
    ExHFT-7 - 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland

Publ.-Id: 11999

Comparison of air/water and steam/water flooding experiments in a model of the hot leg of a pressurised water reactor

Vallee, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.; Pietruske, H.; Schütz, P.; Carl, H.

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 (PWR) was built at Forschungszentrum Dresden-Rossendorf (FZD). Counter-current flow limitation (CCFL) experiments were performed with air and water at room temperature and pressures up to 3.0 bar as well as with steam and water at pressures up to 50 bar and the corresponding saturation temperature of 264°C.

One selected 50 bar experiment is presented, analysed and high-speed camera images are shown. Furthermore, the flooding curves 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 correlate properly 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.

Keywords: two-phase flow; air water flow; steam water flow; flooding; counter-current flow limitation; CCFL; hot leg; pressurised water reactor; PWR; Wallis parameter; viscosity

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany, Berlin: INFORUM Verlags- und Verwaltungsgesellschaft mbH, Compact221
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11998

Library Information Services - not only books in shelves

Reschke, E.

The presentation shows the Library information services, focused on the elctronic services within the intranet and the internet. The main point was the link resolver for linking services.

Keywords: online catalogue; document deliver; Interlibrary loan; elctronic databases; virtual library; publishing; copyright; document managment systems; open access

  • Lecture (others)
    FZD Lecture, 01.12.2008, Dresden, Deutschland

Publ.-Id: 11997

On the influence of spatial discretization on cross-sction preparation during burnup calculations with HELIOS 1.9

Merk, B.

Cell- and burnup calculations are the fundament for all deterministic static and transient 3D full core calculations for different operational states of the reactor. The spatial discretization used for the c burnup calculations influences the results for the used integral transport solutions significantly. The arising differences in the infinite multiplication factor and in the localized burnup ditribution in the fuel rod for identical averaged burnup are shown and analyzed. Special emphasis is given to the influence of different discretization strategies on the calculation of homogenized two group cross sections which are forwarded to the 3D full core calculations .

Keywords: Cell- and Lattice calculation; cross section preparation; HELIOS; Discretization; Burnup calculation; Depletion

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 11995

Sicherheitsorientierte Regelungsstrategien für Batch- und Semibatch-Prozesse in der Feinchemie

Kryk, H.; Hessel, G.

Insbesondere in der Feinchemie und der pharmazeutischen Industrie erfolgt die Produktion von Spezialchemikalien meist im Batch- oder Semibatch-Betrieb in sog. Mehrzweckanlagen. Als Reaktionsgefäße kommen Rührkesselreaktoren zum Einsatz. Das instationäre und nichtlineare Prozessverhalten ist dabei durch eine Reihe von Einflussfaktoren gekennzeichnet, welche sich sowohl auf die Prozesssicherheit als auch auf die Effizienz des Gesamtverfahrens auswirken können. Demgegenüber werden jedoch gerade in Mehrzweckanlagen meist konventionelle Prozessgrößen für die Steuerung komplexer chemischer Prozesse verwendet. Da PAT bei Mehrzweckanlagen nur in begrenztem Umfang einsetzbar ist, stehen Echtzeit-Informationen über Konzentrationsverläufe, die für den Prozesszustand und das Gefahrenpotenzial des Prozesses kennzeichnend sind, oftmals nicht zur Verfügung. Somit besteht für den Operator das Problem, tolerierbare von unerwünschten Prozessabweichungen zu unterscheiden und die Ursachen bestimmter Prozess-Trends zu identifizieren. Von besonderer Bedeutung ist die Entwicklung und Etablierung industriell anwendbarer Methoden für eine objektive Detektion des aktuellen Prozesszustandes in Echtzeit sowie für die frühzeitige Identifikation unerwünschter Betriebszustände. Aus diesen Gründen entwickelt das Institut für Sicherheitsforschung des FZD bereits seit Jahren Methoden zum Online-Monitoring sicherheitsrelevanter Batch- und Semibatch-Prozesse. Zur Vermeidung des Einsatzes von teuren und empfindlichen Online-Analysesystemen, wurden Methoden entwickelt, welche auf Echtzeit-Stoff- und Energiebilanzen basieren. Diese können den Anlagenfahrern als Hilfe zur Objektivierung der Prozessführung und, im Falle unerwünschter Prozesszustände, als Werkzeug zur Handlungsempfehlung für geeignete Gegenmaßnahmen dienen.
Die Idee ist nun, aufbauend auf die bisherigen Entwicklungen, derartige Verfahren als Komponente einer sicherheitsbasierten Regelungsstrategie zu nutzen. Die Echtzeit-Resultate des Monitoring-Systems könnten dann als Führungsgrößen für eine entsprechende Prozessregelung, bis hin zur inhärent sicheren, vollautomatischen Betriebsweise von Batch-Prozessen in Mehrzweckanlagen, genutzt werden.

  • Invited lecture (Conferences)
    ProcessNet-Arbeitsausschuss "Sicherheitsgerechtes Auslegen von Chemieanlagen", 19.-20.11.2008, Frankfurt a.M., Deutschland

Publ.-Id: 11994

The influence of different thermal hydraulic models on the results of a DYN3D boron dilution transient calculation

Kliem, S.; Mittag, S.; Rohde, U.; Weiß, F.-P.; Kozmenkov, Y.

The availability of three different thermal hydraulic models for the neutron kinetic core model DYN3D gave the possibility to investigate their influence on the results of a boron dilution transient. Quantitative differences were found in the single solutions. So the different degree of numerical diffusion in the boron transport models affects the height and time of the first power peak. Differences were also found in the heat transfer and the drift flux models. Concerning assessed safety criteria like maximum fuel and cladding temperature as well the DNB ratio the same conclusions can be drawn from all calculations: Safety-relevant margins are not reached. A spreading of the calculated data is present but there are no qualitative differences in the consid-ered transient.

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
    Tagungsband der Jahrestagung Kerntechnik 2009, paper 114, Berlin: INFORUM GmbH
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 11993

Complexation of uranium(IV) with fluoride and phosphate using TRLFS

Lehmann, S.

A novel TRLFS system was set up for investigation of short-lived fluorescence emitting metal ions like uranium(IV) or americium(III). This laser system was applied to study the complexation of uranium(IV) with fluoride and phosphate and to determine their respective complex formation constants.

Keywords: uranium(IV) fluoride; uranium(IV) phosphate; time-resolved laser fluorescence spectroscopy

  • Lecture (others)
    Workshop of the Institute of Radiochemistry (IRC) and the Paul Scherrer Institute (PSI), Villigen , Switzerland, 03.-04.11.2008, Dresden, Germany

Publ.-Id: 11992

Computational Fluid Dynamics (CFD) for gas-liquid flows

Lucas, D.; Tiselj, I.; Hassan, Y.; Moretti, F.

Computational Fluid Dynamics (CFD) codes are widely used in industrial applications for single phase flows, e.g., in the automotive or aircraft industries. On the other hand the application of CFD for multiphase systems is not yet mature. Safety analyses related to nuclear light water reactors require reliable simulations for different scenarios including two-phase flow situations. Prominent examples for Pressurized Water Reactor (PWR) analyses are the prevention from Departure from Nucleate Boiling (DNB) which is related to Critical Heat Flux (CHF) or the Pressurized Thermal Shock (PTS) problem which has to be considered in connection with some hypothetical Loss of Coolant Accident (LOCA) scenarios and may also lead to two-phase flow situations in the cold leg and in the downcomer. In case of Boiling Water Reactors (BWR) analyses e.g. the prevention from Dryout is an important issue. The special issue of the on Science and Technology of Nuclear Installations Journal on "Computational Fluid Dynamics (CFD) for Gas-Liquid Flows" discusses the state of the art and the progress regarding CFD simulations on such two-phase flows.

Keywords: CFD; two-phase

Publ.-Id: 11991

A novel time-resolved laser fluorescence spectroscopy system for research on complexation of uranium(IV)

Lehmann, S.; Geipel, G.; Grambole, G.; Bernhard, G.

Research on the chemical speciation of complexes by determining the fluorescence properties of metal ions whose emitted fluorescence lifetime is in the range of only few nanoseconds, has been very limited to date due to a lack of the technical possibilities necessary to conduct respective measurements. We were able to overcome the technical problems and set up a new time-resolved laser fluorescence spectroscopy system that meets the requirements to carry out research on the fluorescence properties of metal ions with very short fluorescence lifetimes such as uranium(IV) and its compounds. We investigated the fluorescence of uranium(IV) in perchloric acid and determined the detection limit of uranium(IV) to be 1 ± 10-6M. Additionally, we found the fluorescence decay time of uranium(IV) to be 2.73 ns ± 0.40 ns. Further application of the novel laser system addressed the complexation of uranium(IV) with fluoride by studying the fluorescence properties during reaction. Evaluation of the data recorded resulted in the finding of a 1 : 1 complex (uranium(IV) : fluoride). We determined the corresponding complex formation constant of uranium(IV) fluoride (UF)3+ with logβº = 9.43 ± 1.94. The application of our novel time-resolved laser fluorescence spectroscopy system demonstrated that speciation measurements of metal ions and their compounds with very short-lived fluorescence lifetimes can be conducted successfully. Using this laser system, analytical investigation of such elements and compounds is possible in environmentally relevant concentration ranges.

Keywords: time-resolved laser fluorescence spectroscopy; uranium(IV) fluoride; detection limit; fluorescence lifetime; complex formation constant

  • Spectrochimica Acta Part A 73(2009)5, 902-908

Publ.-Id: 11990

Main results of the European project NURESIM on the CFD-modelling of two-phase Pressurized Thermal Shock (PTS)

Lucas, D.; Bestion, D.; Coste, P.; Pouvreau, J.; Morel, C.; Martin, A.; Boucker, M.; Bodele, E.; Schmidtke, M.; Scheuerer, M.; Smith, B.; Dhotre, M. T.; Niceno, B.; Lakehal, D.; Galassi, M. C.; Mazzini, D.; D’Auria, F.; Bartosiewicz, Y.; Seynhaeve, J.-M.; Tiselj, I.; ŠTrubelj, L.; Ilvonen, M.; Kyrki-Rajamäki, R.; Tanskanen, V.; Laine, M.; Puustinen, J.

Pressurized Thermal Shock (PTS) and Direct Contact Condensation (DCC) were identified by the European project EUROFASTNET as two of the most important industrial needs related to nuclear reactor safety where CFD may bring a real benefit. One typical PTS scenario limiting the Reactor Pressure Vessel (RPV) lifetime is cold water Emergency Core Cooling (ECC) injection into the cold leg during a hypothetical SB-LOCA. The injected water mixes with the hot fluid present in the cold leg and the mixture flows towards the downcomer where further mixing with the ambient fluid takes place. Such a scenario may lead to high thermal gradients in the structural components and consequently to thermal stresses. Therefore, the loads upon the RPV must be reliably assessed. The NURESIM sub-project 2 (Thermohydraulics) Work Package 2.1 focuses on a two-phase flow configuration resulting from a partially or fully uncovered cold leg. In the case of a partially uncovered cold leg, a stratification of cold water on the bottom of the cold leg with counter-current flow of hot water and steam on top of this cold-water layer may occur. There is mixing between hot and cold water. Condensation takes place at the free surfaces between steam and water, e.g. at the cooling water jet. Mixing and condensation are strongly dependent on the turbulence in the fluids. Reliable numerical simulations are required. Two-phase PTS constitutes one of the most challenging exercises for a Computational Fluid Dynamics (CFD) simulation. Presently available CFD tools are not yet able to reproduce all the separate phenomena taking place in the cold leg and the downcomer during the ECC injection, let alone an accurate simulation of the whole process. Improvements of the two-phase modelling capabilities have to be undertaken to qualify the codes for the simulation of such flows. A really accurate simulation of all the phenomena that occur in the scenario will only be possible in the far future and a step-by-step improvement of the quality of the forecasts is necessary. However, a reasonable prediction of the most important phenomena may be reached in a short or medium term and the use of CFD in industrial studies related to PTS is already possible in the frame of some limitations.

Keywords: Pressurized Thermal Shock; CFD; two-phase flow

  • Kerntechnik 74(2009), 238-242

Publ.-Id: 11989

Experimental and numerical analysis of coolant mixing in VVER-1000 in the framework of TACIS project R2.02/02

Höhne, T.; Rohde, U.; Melideo, D.; Moretti, F.; D'Auria, F.; Shishov, A.; Lisenkov, E.

A pump start-up experiment with the presence of a tracer slug, conducted on a Gidropress mixing facility in the framework of TACIS Project R2.02/02, was simulated with the CFD code ANSYS CFX. The numerical results were compared against the experimental data, which consist in tracer concentration measurements at several locations at the core inlet. The results showed an good agreement with the experiment from the qualitative point of view: in particular, the morphology of the tracer concentration distribution at the core inlet was correctly described. This qualitative agreement is quite an important achievement, since the addressed scenario is featured by a complex, highly three-dimensional, flow distribution in the downcomer. From a quantitative point of view, the results in terms of maximum perturbation (and related timing), core-averaged perturbation are also satisfactory. The perturbation peak is over-predicted by 5%, which is comparable with the experimental uncertainty. The predicted time history of the core-averaged perturbation shows a less smooth trend than the experiment, which seems to indicate a less effective mixing.

Keywords: CFD; pump start up; VVER-1000

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 11986

Superconducting Ge:Ga layers produced by ion implantation and flash lamp annealing

Heera, V.; Herrmannsdörfer, T.; Ignatchik, O.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Wosnitza, J.; Helm, M.

Recently, superconductivity has been discovered in heavily boron-doped group IV semiconductors like diamond [1] and silicon [2]. Because theoretical studies predict only a weak tendency to superconductivity in heavy p-type doped Ge [3] investigations of the low-temperature transport behaviour in Ge are still lacking.
In order to obtain superconductivity in group IV semiconductors, heavy p-type doping above the metal-insulator-transition and low lattice damage is required. The combination of both conditions make it difficult to apply ion implantation as doping technique. The challenge is to reconstruct the damaged or even amorphized crystal lattice and to activate the acceptor atoms after implantation by annealing, avoiding at the same time long range diffusion and precipitation of the acceptors in the supersaturated semiconductor. So far only in-situ doping during growth (high-temperature-high-pressure synthesis [1] and chemical vapour deposition) for boron-doped diamond and ultra-short-time laser melting of the Si surface in BCl3 atmosphere (gas immersion laser doping [2]) have met these conditions.
Here an alternative process compatible with semiconductor technology is presented. Ga implantation and flash lamp annealing in the ms range enables the production of Ga supersaturated (up to 15 at%) crystalline Ge layers which become superconducting below 0.5 K.
The layer structure investigated by AES, XTEM, RBS/C and the electrical transport properties at low temperatures are reported.

[1] E. A. Ekimov, V. A. Sidorov, E. D. Bauer, et al. , Nature 428 (2004) 542
[2] E. Bustarret, C. Marcenat, P. Achatz, et al., Nature 444 (2006) 465
[3] L. Boeri, J. Kortus, O. K. Anderson, J. Phys. Chem. Solids 67 (2006) 552

Keywords: Germanium; Ga-Implantation; Flash lamp annealing; superconductivity

  • Poster
    IBMM 2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 11985

Structural identification of thioarsenates by EXAFS

Suess, E.; Scheinost, A. C.; Bostick, B. C.; Merkel, B. J.; Wallschlaeger, D.; Planer-Friedrich, B.

short-range structure of thioarsenite and mono-, di-, tri-, and tetra-arsenate determined by XAS

Keywords: arsenic; EXAFS; XANES; XAS; thioarsenate; thioarsenite

  • Poster
    Synchrotron Environmental Science IV, 11.-13.12.2008, San Francisco, USA
  • Poster
    AGU Fall Meeting 2008, 15.-19.12.2008, San Francisco, USA

Publ.-Id: 11984

NanoFoto - Neue Wege zur verwertungsorientierten Netzwerkbildung in der Nanobiotechnologie

Pollmann, K.; Raff, J.

Ziel des Vortrags ist es, einen Überblick über die laufenden und geplanten Aktivitäten im Rahmen des NanoFoto-Projekts zu geben. Wissenschaftlich steht die Nutzung bakterieller Hüllproteine zur Entwicklung fotokatalytisch aktiver Schichten zur Eliminierung von Arzneimittelrückständen aus Wasser im Mittelpunkt. Ergänzt werden die wissenschaftlichen Arbeiten durch zahlreiche Maßnahmen zur Verwertung erhaltener Ergebnisse und zur verwertungsorientierten Netzwerkbildung.

  • Lecture (others)
    Kick-off Meeting / 1. Workshop „Entwicklung und Erprobung neuer Instrumente zur Bildung von Verwertungs- und Transfernetzen in der Leibniz-Gemeinschaft“, 11.03.2008, Berlin, Deutschland
  • Lecture (others)
    2. Projekt-Workshop zum Thema „Verwertungsorientierte Netzwerke“, 16.12.2008, Berlin, Deutschland

Publ.-Id: 11982

Granular magnetic ZnO: structure, magnetism and transport properties

Zhou, S.; Potzger, K.; Xu, Q.; Shalimov, A.; Schmidt, H.; Helm, M.; Fassbender, J.

Transition metal (TM) doped ZnO has been extensively investigated due to its potential application as a diluted magnetic semiconductor with Curie temperature above room temperature (RT). After one decade effort, however the research community realized that (i) ZnO diluted with TM ions only shows paramagnetism [1], and (ii) the observed ferromagnetic signal mostly originates from secondary phases [2,3]. The aim of our research is now to investigate the application potential of granular structures which are created by TM ion implantation into ZnO single crystals. By varying implantation and post-annealing temperatures, we can control the chemical state of TM ions. ZnO with dispersed TM ions can be obtained by ion implantation at temperatures below RT or by using defective ZnO substrates. In this case, TM ions are in ionic states, and only show paramagnetism. Concerning the nature of phase separation, three regimes have been established. (I) ZnO embedded with TM nanocrystals can be obtained by ion implantation at elevated temperatures (e.g. 350oC) and by post-annealing at mild temperatures (below 350oC). In this regime, TM ions are mostly in metallic states (i.e. Fe, Co, Ni). Co and Ni nanocrystals have crystallographic orientation relationship with the ZnO matrix [2]. (II) ZnO embedded with nanocrystalline spinel ferrites AFe2O4 (A=Zn, Co, Ni) can be obtained by co-implantation pulsing post-annealing at 800 oC [4,5]. (III) ZnO embedded with disordered nanosized regions can be obtained by ion implantation with very large ion-fluences. The heavily disordered nanosized regions consists of large Co concentration [6]. Although ferromagnetism has been observed in all the three regimes, magneto-transport properties are drastically different. Only ordinary magneto-resistance (MR) has been observed in regimes I and II, while the samples in regime III reveal negative MR and anomalous Hall effect simultaneously. The anomalous Hall resistivity is saturated at low field giving hope for applicability in spintronics.

[1] A. Ney, , et al., Phys. Rev. Lett. 100, 157201 (2008)
[2] S. Zhou, et al., Phys. Rev. B 77, 035209 (2008).
[3] K. Potzger, and S. Zhou, phys. stat. sol. (a), submitted (2008).
[4] S. Zhou, et al., J. Phy. D-Appl. Phys., 40, 964 (2007).
[5] S. Zhou, et al., Phys. Rev. B, submitted (2008).
[6] K. Potzger, et al., Appl. Phys. Lett., submitted (2008).

  • Poster
    Magnetism meets Semiconductors: Spin Phenomena in Heterostructures and Novel Materials, 05.-07.01.2009, Bad Honnef, Germany
  • Poster
    5th International School and Conference on Spintronics and Quantum Information Technology, 04.-11.07.2009, Krakow, Poland

Publ.-Id: 11981

Magneto-transport properties of nanocomposite cobalt/carbon systems

Zhou, S.; Berndt, M.; Bürger, D.; Abrasonis, G.; Heera, V.; Fassbender, J.; Helm, M.; Schmidt, H.

In producing diluted magnetic semiconductors (DMS), it remains challenging to obtain a uniform distribution of magnetic ions. Composite ferromagnet/semiconductor systems are easily formed when the concentration of magnetic ions is larger than its solubility at given preparation conditions. This is usually considered as a failure for spintronics applications. However, as long as the embedded (nano)ferromagnets can polarize charge-carriers in the semiconducting matrix, the composite systems can also fullfill spintronics requirements. For example, nanocomposite systems with ferromagnetic MnAs nanocrystals being epitaxially embedded inside GaAs matrix reveal a giant magnetoresistance [1]. Recently, the phase separation in Mn doped Ge [2] and Si [3] has been indentified by high resolution characterization techniques. Therefore, the research interest in composite ferromagnet/semiconductor systems arises in parallel with that in DMS materials. Here we present the magnetic and magneto-transport properties of cobalt nanocrystals embedded inside carbon. Co(40%)/C nanocomposite films were prepared by ion beam co-sputtering method using silicon substrates with a 500 nm thick oxide layer. The phase separation was controlled by varing substrate temperatures from room temperature to 500 °C. We have measured their magnetic and magneto-transport properties. Two significant observations will be discussed: (i) a giant anomalous Hall effect (AHE) amounting to 2 μohm cm compared with pure Co metal [4], and (ii) a negative magnetoresistance. This encourages future applications in Hall sensors and spintronic-devices.

  • Poster
    Magnetism meets Semiconductors: Spin Phenomena in Heterostructures and Novel Materials, 05.-07.01.2009, Bad Honnef, Germany
  • Lecture (Conference)
    SPIE Europe Microtechnologies for the New Millennium, 04.-06.05.2009, Dresden, Germany
  • Poster
    International Conference on Magnetism, 26.-31.07.2009, Karlsruhe, Germany

Publ.-Id: 11980

ZnO-based magnetic tunnel junctions

Zhou, S.; Xu, Q.; Hartmann, L.; Mücklich, A.; Helm, M.; Biehne, G.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.

Spin-polarized tunnel magnetoresistance (TMR) effects occur when two ferromagnets are separated by a thin insulator. The resistance of the tunneling current changes with the relative magnetization orientation of the magnetic bottom and top electrode. The research in this field is fuelled by the demanding of magnetoresistive random access memory (MRAM) devices. Novel MRAM cells are based on magnetic tunnel junctions with current-induced switching. It has been shown that semiconductors need a current pulse for switching which is two orders of magnitude smaller in comparison to metals. Using wide-gap magnetic semiconductors, e.g. ZnO, the magnetic tunnel structure may be transparent and may possess a Curie temperature above room temperature. In this talk, we report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as the bottom electrode and Co as the top electrode prepared by pulsed laser deposition and thermal evaporation [1], respectively. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 separation layer and tunnelled through the amorphous part of the Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices.
[1] Q. Xu et al., Phys. Rev. Lett. 101, 076601 (2008)

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 11979

Semiconductor-based tunnel structures: preparation and application

Zhou, S.; Schmidt, H.

Spin-polarized tunnel magnetoresistance (TMR) effects occur when two ferromagnets are separated by a thin insulator. The resistance of the tunneling current changes with the relative magnetization orientation of the magnetic bottom and top electrode [1,2]. The research in this field is fuelled by the demanding of magnetoresistive random access memory (MRAM) devices. In 2004, Parkin et al. were able to make Fe/MgO/Fe junctions with 200% TMR at room temperature [3]. However, the development of high-density metal-based MRAM scale devices is hampered by large switching fields and multidomain structures. Theoretically, diluted magnetic semiconductors (DMS) reveal a larger degree of spin polarization and therefore also bigger spin transport effects. Mn-doped GaAs is a successful DMS and magnetic tunnel junctions based on epitaxially grown GaMnAs/AlAs/GaMnAs have shown promising TMR values up to 75% at 8 K [5]. Novel MRAM cells are based on magnetic tunnel junctions with current-induced switching. It has been shown that semiconductors [6] need a current pulse for switching which is two orders of magnitude smaller in comparison to metals [7]. Using wide-gap magnetic semiconductors, e.g. ZnO, the magnetic tunnel structure may be transparent and may possess a Curie temperature above room temperature [9,10].

In this talk, we report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as the bottom electrode and Co as the top electrode prepared by pulsed laser deposition and thermal evaporation [11], respectively. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 separation layer and tunnelled through the amorphous part of the Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices. Additionally, we will show preliminary results of Si:Mn based tunnelling structures. In this system, SiO2 is the barrier layer while ferromagnetic granular Si:Mn obtained by Mn ion implantation into Si and Co are the bottom and top electrode, respectively.

[1] J. S. Moodera et al., Phys. Rev. Lett. 74, 3273 (1995).
[2] T. Miyazaki et al., J. Magn. Magn. Mater. 139, L231 (1995).
[3] S. S. P. Parkin et al., Nat. Mat. 3, 862 (2004).
[4] S. D. Sarma et al., Solid State Commun. 119, 207 (2001).
[5] M.Tanaka et al., Phys.Rev. Lett. 87, 026602 (2001).
[6] M. Yamanouchi et al., Nature 428, 539 (2004).
[7] J.A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000).
[8] T. Jungwirth et al., Phys. Rev. B 72, 165204 (2005).
[9] T. Dietl et al., Science 287, 1019 (2000).
[10] K. Sato et al., Jpn. J. Appl. Phys. 39, L555 (2000).
[11] Q. Xu et al., Phys. Rev. Lett. 101, 076601 (2008)

  • Invited lecture (Conferences)
    International Workshop on Advances in Spintronic Materials: Theory and Experiment, 26.-28.11.2008, Duisburg, Germany

Publ.-Id: 11978

n-type diamond produced by MeV lithium implantation in channeling direction

Chernyshev, V.; Meijer, J.; Grambole, D.; Herrmann, F.; Dagkaldiran, U.; Wieck, A.

Natural diamond implanted with lithium ions at high energy (E = 2MeV) in axial channeling direction is investigated. Hall measurements show n-type conductivity caused by the lithium implantation. These measurements show two regions in the Arrhenius plot for both resistance and charge carrier concentration. The resistance measurement in the low and high temperature range revealed the activation energies of E-Rlow = 406meV and E-Rhigh = 105meV. The slope for the charge carrier concentration shows a more complex behaviour. After annealing, the n-type conductivity caused by implanted lithium disappears.

  • Diamond and Related Materials 17(2008)11, 1933-1935

Publ.-Id: 11977

Breakup and coalescence models for turbulent air-water mixtures in a vertical pipe

Liao, Y.; Lucas, D.

The evolution of bubble size distribution and radial air volume fraction was studied by an efficient 1D test solver. New constitutive models for bubble coalescence and breakup due to different mechanisms, including coalescence due to turbulent fluctuation, velocity shear and wake entrainment, and breakup due to turbulent fluctuation, velocity shear and interfacial slip velocity, was proposed. Simulation results showed that at relatively low superficial gas velocities, the bubble size was small and had a narrow distribution, and coalescence was predominant; with an increase in the superficial gas velocity, large bubbles began to form due to the dominance of coalescence, resulting in a much wider bubble size distribution, and breakup became dominant. The simulation results were compared with the recent experimental data achieved on the TOPFLOW facility and good agreements were achieved.

Keywords: new models; bubble coalescence and breakup; bubble size distribution; radial gas volume fraction

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11976

A Silver Containing Liquid Alloy Ion Source

Mazarov, P.; Bischoff, L.; Pilz, W.; Wieck, A.

A Silver-Germanium Liquid Alloy Ion Source (LAIS) was developed and is available. Good beam performance was obtained for application in any commercial focused ion beam (FIB) system. Emission current dependent measurements were carried out of the mass spectra and energy spreads of all ion components. The ratios of doubly- and singlecharged clusters to single-charged monomer ions were determined. The AgGe-LMAIS can be very helpful for controlled formation of silver quantum wires.
[1] Thibaut Capron Phys. Rev. B77, 033102 (2008).

Keywords: Silver-Germanium Liquid Alloy Ion Source; Focused Ion Beam; Quantum Wires

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 11975

Alloy Liquid Metal Ion Sources for new FIB applications

Bischoff, L.; Pilz, W.; Mazarov, P.; Wieck, A.

Recently, mass separated focused ion beams (FIB) become an increasing interest for local doping in nano-devices for optical, electrical or magnetic applications [1]. So on the basis of very stable metallic glass alloys, like AuSi or AuGe with a low melting point at 365°C different ion sources were developed and tested due to their performance in FIB systems. In detail, Au68Ge22B5Ni5, Au80Si12Sb8, Au68Ge28Mn10 alloys were analysed concerning the on-set and emission behaviour and the mass spectra. Among clusters, molecular ions, single and doubly charged species such important ions like boron for p-doping in silicon, antimony for n-doping in silicon or manganese for quantum dot fabrication in II-VI semiconductors (CdSe, CdS, ZnS) could be extracted.
[1] L. Bischoff, NIM B266 (2008) 1846.

Keywords: alloy liquid metal ion source; dopands; cluster

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 11974

Focused ion beam activities at FZD

Bischoff, L.

During the last decades, focused ion beams (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance within the nanotechnology. For special purposes like ion milling, ion beam writing for doping or patterning from the µm- to the nm-range without any lithographic steps using Gallium and also other ion species which are of increasing interest. An introduction in design and operation of mass separated FIB systems, equipped with alloy liquid metal ion sources and the development and characterization of suited ion sources is given.
Examples, like ion beam synthesis of CoSi2 nano-structures, sputtering investigations and applications, the formation of ripples under FIB irradiation or the fabrication of NEMS structures on SOI substrates should demonstrate the manifold utilization of the microbeam technology.
Finally an outlook to prospective work with FIB in FZD is presented.

Keywords: Focused Ion Beam; alloy Liquid Metal Ion Source; Nanotechnology

  • Lecture (others)
    Institutsseminar, 14.11.2008, Bochum, Deutschland

Publ.-Id: 11973

Ultra fast electron beam X-ray CT scanner for two-phase flow measurement

Fischer, F.; Hampel, U.

Two-phase flows are of primary importance in the understanding of thermal hydraulic phenomena in nuclear light water reactors. The qualification of CFD codes for the simulation of stationary and even transient two-phase flows in complex three dimensional geometries requires extending our knowledge toward the details of the flow structure under various thermal hydraulic conditions. At Forschungszentrum Dresden-Rossendorf the thermal hydraulic test facility TOPFLOW is currently extensively used to conduct two-phase flow experiments which aim at the disclosure of fine flow structure details in generic and also more complex geometries. Consequently, we have extended our measurement technology for two-phase flow to highspeed X-ray tomography which offers non-intrusive flow measurement at high pressure and high temperatur at a speed comparable to the wire-mesh sensor [2], [3], [4], [5]. For that reason we have developed a scanned electron beam X-ray apparatus where a electron beam is swept around an object on a circular X-ray target. Thus a rapidly moving X-ray spot is generated. The apparatus can perform cross-sectional imaging at high frame rates and will in the future be extended to other measurement features, such as multi-plane tomography, phase velocity measurement, higher scanning diameters and high energy X-rays. This paper introduce the scanner design, discuss major performance parameters along with an application example and show how this scanner will be applied to air-water and steam-water two-phase flow measurement in a vertical test section of the TOPFLOW facility.

Keywords: electron beam X-ray CT; two-phase flow measurement

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11972

Inverse energy transfer process during electroluminescence in Er-doped SiO2 layers containing Ge nanocrystals

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

For a comparative study of the energy transfer mechanism during room temperature electroluminescence (EL), two sets of samples have been prepared by implanting either Ge and Er ions (type-I) or Si and Er ions (type-II) into a 200 nm SiO2 layer combined with rapid-thermal-annealing. Three reference samples have been prepared by implanting only Er, Ge or Si ions in SiO2 followed by post-implantation annealing. The formation of Si and Ge nanocrystals (NCs) was confirmed by transmission electron microscopy. The metal-oxide-semiconductor dot structure was prepared by depositing indium-tin-oxide and Al films on the front and rear sides of the structure. Quantum-confinement mediated recombination of carriers in Si-nanocrystals (Si-NCs) as well as the triplet (T1) → singlet (S0) transition in the O3-Si-Si-O3 oxygen deficient centre (ODC) provides the 750 and 475 nm bands, respectively, in the only Si-implanted sample. Conversely, the 525, 550, 660 and 1532 nm emissions corresponding to the deexcitation of the 2H11/2, 4S3/2, 4F9/2 and 4I13/2 states to the ground state 4I15/2 of the Er3+, respectively, were recorded for the Er-doped SiO2 layer. A blue-violet light at ~400 nm, representing the T1→S0 transition in the O3-Si-Ge-O3 ODC, was observed in the Ge-NCs embedded SiO2 layer. Although the intensity of the Er-related visible/infrared EL signals in type-I sample was found disappearing/decreasing with a concomitant enhancement of the 400 nm band, a sharp rise in intensity of the 1532 nm Er EL at the expense of the Si-NC related 750 nm band was evidenced in type-II sample. While the later result confirms the energy transfer mechanism from Si-NCs to the nearest Er3+, the former finding can be explained in terms of the energy transfer from Er3+ to the Ge-related ODC.

Keywords: nanocrystals; Ge; electroluminescence

  • Lecture (Conference)
    IBMM2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11971

Measurement of dynamic liquid distributions in a fixed bed using electrical capacitance tomography and capacitance wire mesh sensor

Matusiak, B.; Da Silva, M. J.; Romanowski, A.; Hampel, U.

An intricate problem associated with fixed bed operation is liquid maldistribution, which denotes the fact that the liquid does not homogeneously flow through the bed. In a comparative study we evaluated two capacitance imaging methods - capacitance wire mesh sensor and electrical capacitance tomography (ECT) - with respect to their capability of measuring static and dynamic liquid holdup in a fixed bed. We performed experiments in a column of 100 mm diameter, packed with commercial porous Al2O3 catalyst particles. The column was operated at ambient pressure. Inlet flow of isopropanol from various point sources was applied at rates of 40 L/h and 60 L/h. The capacitance wire mesh sensor as an invasive instrument is able to disclose flow structures at higher spatial resolution and was therefore considered as the reference instrument for liquid holdup measurement. We found that both methods predict dynamic liquid holdup in the column in a similar way with only small systematic deviation. The results therefore prove that non-invasive electrical capacitance tomography can reliably measure cross-sectional dynamic liquid holdup in a fixed bed, even with a simple and fast linear back projection reconstruction algorithm.

Keywords: Wire-mesh sensor; ECT; Multiphase flow; Trickle bed; Liquid holdup; Liquid distribution

  • Industrial & Engineering Chemistry Research 49(2010)5, 2070-2077
    DOI: 10.1021/ie900988f

Publ.-Id: 11970

Research needed for improving heavy ion therapy

Kraft, G.; Kraft, S. D.

The large interest in heavy ion therapy is stimulated from its excellent clinical results. The bases of this success are the radiobiological and physical advantages of heavy ion beams and the active beam delivery used for an Intensity Modulated Particle Radiotherapy (IMPT). Although heavy ion therapy has reached a high degree of perfection for the clinical use there is still large progress possible to improve this novel technique: In order to extend IMPT to more tumor entities and to tailor the planning more individually for each patient in an adaptive way, radiobiological work both experimentally and theoretically is required. It is also not clear whether the neighboring ions to carbon could have a clinical application as well. For this extension basic biological works as well as physics experiments have to be performed.

On the technical side many improvements of the used equipment seems to be possible. Two major topics are the extension of IMPT to moving organs and the transition to more compact and therefore cheaper particle accelerators.

In this paper these topics are treated to some extent in order to give an outline of the great future potential of ion beam therapy.

Publ.-Id: 11969

Spectral-history modeling in DYN3D burnup calculations

Bilodid, Y.; Mittag, S.

Burnup spectral-history effects are reflected in deviations in the actual nuclide concentrations within the fuel. The deviations of different nuclides are correlated. It is possible to treat the nuclide concentration change by tracing only one nuclide – Pu-239. Implementation of historical correction for 2-group cross sections method in DYN3D is described in this paper.

Keywords: DYN3D; spectral-history effects; burnup history effect; burnup; cross sections

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11968

Nitrogen diffusion in single crystalline austenitic stainless steel: ion energy and flux effects

Martinavičius, A.; Abrasonis, G.; Möller, W.; Chumlyakov, Y.

Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding is investigated. Single crystalline AISI 316L austenitic stainless steel (ASS) with orientation (001) has been ion beam nitrided at 400 °C using a Kaufman-type ion source. The acceleration voltage has been varied from 450 to 1200 eV, and the current density from 0.3 to 0.7 mA cm−2. XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The nitrogen depth profiles have been determined using nuclear reaction analysis (NRA). The profiles of nitrided samples can be depicted by an initial quasi-linear decrease followed by a sharp leading edge. The nitrogen penetration depth is significantly higher for higher implantation energies as well as for higher current densities. The result cannot be explained by the difference of the sputtering rate.
The “trapping-detrapping” model, which is able to reproduce the full shape of the nitrogen depth, has been used to fit nitrogen depth profiles and extract the diffusion coefficient values. The nitrogen profile fitting shows that the nitrogen diffusion coefficient strongly depends on irradiation flux and ion energy during ion beam nitriding, confirming the tendencies deduced directly from the nitrogen distribution profiles.

  • Lecture (Conference)
    22nd International Conference on Surface Modification Technologies - SMT22, 24.09.2008, Trollhättan, Sweden

Publ.-Id: 11967

Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding and subsequent thermal annealing

Martinavičius, A.; Abrasonis, G.; Möller, W.; Templier, C.; Rivière, J. P.; Declémy, A.; Chumlyakov, Y.

Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding and subsequent annealing is investigated. Single crystalline [orientations (001), (110) and (111)] and polycrystalline AISI 316L austenitic stainless steel (ASS) has been ion beam nitrided at 400 °C for 60 min using a Kaufman-type ion source with an acceleration voltage of 1 keV and a current density of 0.5 mA cm−2. XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The samples have been subsequently vacuum annealed at 400°C for 30 min. The nitrogen distribution profiles have been determined using nuclear reaction analysis (NRA). The profiles of as-nitrided samples can be depicted by an initial quasi-linear decrease followed by a sharp leading edge. Despite identical nitriding conditions, the nitrogen penetration depth is significantly higher in the single crystal with the (001) orientation than in the samples with the orientations (011) or (111) which cannot be explained by the orientational dependence of the sputtering rate. The surface concentration for the single crystal with the (001) orientation was about 27 at.% with the depth of the quasi-linear part about 1.5 µm. For the orientations (011) and (111) the surface concentration was 25 at.% and the depth of the quasi-linear part about 1 µm and 0.7 µm respectively. Polycrystalline ASS presents an intermediate case. Subsequent annealing results in the decrease of near-surface nitrogen concentration, flattening of the quasi-linear part of the depth profile and nitrogen inward diffusion without any detectable nitrogen loss due to out-diffusion.
The “trapping-detrapping” model, which is able to reproduce the full shape of the nitrogen depth profile in as-nitrided as well as subsequently annealed single crystalline ASS, has been used to fit nitrogen depth profiles and extract the diffusion coefficient values. The nitrogen profile fitting shows that the nitrogen diffusion coefficient is strongly orientation dependent during ion beam nitriding confirming the tendencies deduced directly from the nitrogen distribution profiles. This anisotropy is not present during thermal annealing, while the diffusion coefficients extracted from the fitting exhibit significantly lower values than those obtained from as-nitrided samples.

  • Poster
    Eleventh International Conference on Plasma Surface Engineering, 16.09.2008, Garmisch-Partenkirchen, Germany

Publ.-Id: 11966

Fe nanoparticles embedded in MgO crystals

Shalimov, A.; Potzger, K.; Geiger, D.; Lichte, H.; Talut, G.; Misiuk, A.; Reuther, H.; Stromberg, F.; Zhou, S.; Baehtz, C.

Iron nanoparticles embedded in MgO crystals were synthesized by Fe+ ion implantation at an energy of 100 keV and varying fluences from 3*10E16 to 3*10E17 cm-2. Investigations of structural and magnetic properties of Fe nanoparticles have been performed using magnetometry, x-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy, as well as by theoretical Preisach modeling of bistable magnetic systems. It has been found that alpha- and gamma-Fe nanoparticles are formed for all fluences. The content of the alpha-Fe phase increases at higher fluences and after annealing. The influence of post implantation annealing at 800 C in vacuum and under enhanced up to 10 kbar hydrostatic pressure in argon atmosphere on the formation of nanoparticles has been analyzed. Investigations have been performed within DFG project PO1275/2-1 ”SEMAN”.

Keywords: magnetic nanoparticles; iron; Preisach modelling

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 11965

’Invisible’ ferromagnetic secondary phases in Co doped ZnO

Potzger, K.; Zhou, S.; Muecklich, A.; Xu, Q.; Schmidt, H.; Helm, M.; Fassbender, J.

The search for ferromagnetic transition-metal doped ZnO, i.e., diluted magnetic semiconductors (DMS), has turned into the search for unwanted secondary phases by high-resolution structural analysis [1]. Such phases even can lead to anomalous Hall effect arising from charge carrier spin polarization. In this talk we show that the general analysis technique for the identification, i.e. x-ray diffraction spectroscopy, fails to identify a recently observed kind of ferromagnetic inclusions with heavy crystalline disorder. We discuss the properties of those clusters using the popular Co:ZnO system.
[1] K. Potzger, S. Q. Zhou, H. Reuther, A. Mucklich, F. Eichhorn, N. Schell, W. Skorupa, M. Helm, J. Fassbender, T. Herrmannsdorfer, T. P. Papageorgiou, Appl. Phys. Lett. 88, 052508 (2006).

Keywords: zno; diluted magnetic semiconductors

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 11964

Accelerator mass spectrometry (AMS) and ion beam analysis (IBA) with the new 6 MV accelerator at FZ Dresden-Rossendorf

Munnik, F.; Grambole, D.; Grötzschel, R.; Merchel, S.; Neelmeijer, C.

Since more than 30 years IBA is performed at the Forschungszentrum Dresden-Rossendorf (FZD) for the determination of element distributions. Due to continuous upgrades of the different experimental set-ups, we are able to routinely perform:
• Rutherford Backscattering Spectrometry (RBS) & Channeling (C-RBS)
• Nuclear Reaction Analysis (NRA)
• Elastic Recoil Detection Analysis (ERDA)
• Particle-Induced X-Ray (PIXE) and Gamma-Emission (PIGE)
Most of our applications lie within material sciences. We are able to measure non-destructively “all natural” elements, i.e. H to U; most elements with lateral, some in 3-D resolution with the following typical parameters (matrix- and analyte-depending):
• depth resolution: 1-30 nm
• depth range: nm-µm
• lateral resolution: few µm
• usual mapping area: 2x2 mm2
• maximum sample size: 3x10 cm2 (vacuum) & “unlimited” (external beam)
• detection limits: ~10 µg/g (H); 500 µg/g – 1% (He-F); 10-100 µg/g (Na-U)
For some elements, e.g. H/D, isotope analysis is also possible.
In summer 2009, our 5 MV van-de-Graaff accelerator will be replaced by the latest 6 MV Tandetron model [1], which is even more sophisticated than the lately installed 5 MV one in Southern France [2]. The new accelerator will need less maintenance generally allowing more beam time. It might be also possible to expand from two to three 8-hour-shifts a day with the new fully automatic system. Scientifically, the main advantages are an increased depth range by a factor of 2 for ERDA and improved detection limits for NRA.
In addition, the machine will have special equipment for AMS [3]. There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses (e.g. isobars) are nearly completely eliminated. Thus, AMS provides much lower detection limits compared to conventional mass spectrometry (isotope ratios: 10-10-10-15).
In contrast to common low-energy AMS facilities, which have mainly specialized in radiocarbon analyses (14C), the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV. Especially in environmental and geosciences, the determination of long-lived (t1/2 > 0.3 Ma) cosmogenic radionuclides like 10Be, 26Al, and 36Cl became more and more important within the last decades [4]. Using these nuclides dating of e.g. volcanic eruptions, rock avalanches, earth quakes, and glacier movements is possible.
References: [1] A. Gottdang et al., Nucl. Instr. and Meth. B 2002, 190, 177. [2] M.G. Klein et al., Nucl. Instr. and Meth. B 2008, 266, 1828. [3] [4] J.C. Gosse and F.M. Phillips, Quat. Sci. Rev. 2001, 20, 1475.

Keywords: accelerator mass spectrometry; ion beam analysis

  • Poster
    ANAKON 2009, 17.-20.03.2008, Berlin, Deutschland

Publ.-Id: 11963

The role of aspartyl-rich pentapeptides in comparative complexation of actinide(IV) and iron(III). Part 1

Jeanson, A.; Berthon, C.; Coantic, S.; Den Auwer, C.; Floquet, N.; Funke, H.; Guillaneux, D.; Hennig, C.; Martinez, J.; Moisy, P.; Petit, S.; Proux, O.; Quemeneur, P.; Solari, P. L.; Subra, G.

Although there is a tremendous volume of data available on the interaction of actinides with living organisms as plants, nearly all the studies are limited to macroscopic or physiological 3 measurements with no specific information at the molecular level. Peptides allow the study of complex coordination chemistry, as that involving actinide(IV) and proteins, without the intricacy of tertiary structure properties. For that purpose, a linear pentapeptide, acetyldiaspartyl-prolyl-diaspartyl-amide (Ac-Asp-Asp-Pro-Asp-Asp-NH2, called PP1 in this report), was synthesized and investigated as a potential chelating ligand of thorium(IV), neptunium(IV), and/or plutonium(IV) cations. Comparison with biological relevant iron(III) cation is also provided. Noteworthy, PP1 was able to prevent Np(IV) from hydrolysis into an insoluble precipitate. Spectrophotometry, 13C NMR and EXAFS at the iron K edge and actinide L3 edges were used to probe the cation coordination sphere and better describe the cation-peptide interaction. The complexes were found to be polynuclear with oxo or hydroxo bridged cations, Fe(III) forming a binuclear complex, Th(IV), Np(IV) or Pu(IV) forming a polynuclear complex with higher nuclearities.

Keywords: Peptides; Actinides; EXAFS

  • New Journal of Chemistry 33(2009), 976-985

Publ.-Id: 11962

Ultrafast infrared and THz spectroscopy of semiconductor quantum structures

Schneider, H.

This talk gives an overview on our activities in nonlinear laser spectroscopy using the free-electron laser at FZD and tabletop lasers. Our research concentrates on III-V semiconductor quantum wells and superlattices. In particular, I will discuss two-photon absorption and photocurrent autocorrelation involving intersubband transitions in quantum wells at mid-infrared wavelengths.

  • Lecture (others)
    Seminar, IIN-IFW Dresden, 12.12.2008, Dresden, Deutschland

Publ.-Id: 11961

Two-photon photocurrent studies of electron intersubband dynamics in multiple quantum wells

Schneider, H.

Quantum wells comprising three equidistant subbands, two of which are bound in the well and the third one in the continuum, result in a resonantly enhanced coefficient for two-photon absorption, which is by six orders of magnitude stronger than in usual semiconductors. Exploiting this nonlinearity in two-photon detectors, quadratic autocorrelation of a free-electron laser has recently been demonstrated at room temperature [1]. Temporal resolution of such a two-photon autocorrelator is only limited by the sub-ps intrinsic time constants of the intersubband transition, namely the intersubband relaxation time and the phase relaxation time. Using sub-ps mid-infrared pulses, the approach allows us to determine systematically the dependence of these time constants on structural parameters, and to discriminate between different scattering processes [2].
[1] H. Schneider, H. C. Liu, S. Winnerl, O. Drachenko, M. Helm, J. Faist, Appl. Phys. Lett. 93, 101114 (2008).
[2] H. Schneider, T. Maier, M. Walther, H. C. Liu, Appl. Phys. Lett. 91, 191116 (2007).

Keywords: intersubband transition; two-photon absorption; quantum well infrared photodetector; phase relaxation; autocorrelation

  • Invited lecture (Conferences)
    International Workshop on Nonequilibrium Nanostructures (NONNA'08), 01.-06.12.2008, Dresden, Germany

Publ.-Id: 11960

Uporaba metode datiranja površinske izpostavljenosti na primeru podora Veliki vrh

Mrak, I.; Merchel, S.; Benedetti, L.; Braucher, R.; Bourlès, D.; Finkel, R. C.; Reitner, J. M.

O podoru v Velikem vrhu (Košuta, Karavanke) ni zanesljivih zgodovinskih zapisov, vendar pa le ti obstajajo o podoru na Dobraču (25.1.1348), ki je od Velikega vrha oddaljen 46 km [1]. Podor je povzročil potres in naša hipoteza je bila, da je tudi podor v Velikem vrhu posledica istega dogodka. Tako smo s pomočjo metode datiranja površinske izpostavljenosti [2] analizirali vzorce matične kamnine v steni Velikega vrha ter vzorce s površine podornih blokov. Ugotavljali smo vsebnost 36Cl, ki se je začel tvoriti po podoru. Na podlagi poznavanja števila atomov 36Cl na gram Ca na leto izpostavljenosti, čas dogodka (podor) izračunamo iz koncentracij 36Cl izmerjenih s pomočjo pospeševalnika (AMS). Prvi rezultati kažejo, da sta se podora na Dobraču in Velikem vrhu zgodila istočasno, natančne analize podatkov pa še potekajo.

Zahvala: Del raziskave sofinancira program CRONUS-EU (Marie-Curie Action 6. okvirni program #511927).

Literatura: [1] C. Hammerl, Historical earthquake research – methods used as a basis for the hazard assessment applied to the earthquake of 1348 in Villach (Austria), Proceedings of the Third International Symposium on Historical Earthquakes in Europe (Prague 1991). [2] J. C. Gosse, F. M. Phillips, Terrestrial in situ cosmogenic nuclides: theory and application, Quaternary Science Reviews, 20 (2001) 1475.

The rockfall Veliki vrh is located in the valley Pod Košuto (Geben stream watershed Karavanke Mountains, Slovenia). The highest point of the researched area is Veliki vrh (2086 m); the lowest is the settlement Plaz (650 m). Among the geomorphologic processes nowadays the linear denudation and erosion prevails (the most common inclination of the surface is between 21-32° in 33-55°).
Between the settlement of Plaz and the Zajemen farm immense amounts of rockfall debris are present in different sizes, from big blocks (up to 10 x 10 m) to granule. The smaller grain sizes (fine sand, coarse silt…) are missing and the grain edges are sharp. The lithology of the material is the same as the one forming the Košuta ridge - Triassic Dachstein limestone and reefy limestone.
There are no reliable historical data about the rockfall event beside the oral heritage in form of a fairy tale describing the catastrophic falling of rocks over the settlement in the valley, killing many people and forcing the survivors to establish a new settlement further downstream. However, there are numerous written records about a historic rockfall taking place about 46 km away at Dobratsch, Carinthia on 25th January 1348 [1]. That rockfall was induced by an earthquake with the epicenter situated at Friuli (~74 km distance to Veliki vrh). There are no other records of natural hazards within historical times for the area, thus, it seems very likely that the same earthquake triggered both rockfalls. To test this hypothesis, we have applied the surface exposure dating method [2] on samples taken from the fresh bedrock and big boulders originating from the Veliki vrh rockfall.
As the long-lived radionuclide 36Cl is the product of nuclear reactions induced by the high-energy cosmic ray particles in a Ca-rich rock, its concentration can be used as a dating tool. The material has been previously shielded and production of 36Cl started as recently as the rockfall took place. Then, freshly produced surfaces – bedrock and boulders – have been exposed to cosmic rays launching the clock. As the so-called production-rate, i.e. how many atoms per gram Ca per year exposure, can be calculated for a certain environment, a precise time for the rockfall can be deduced from the 36Cl concentrations measured by accelerator mass spectrometry (AMS).
Preliminary results suggest a simultaneous timing of both rockfalls: Dobratsch and Veliki vrh. Detailed data analysis is in preparation.

Keywords: accelerator mass spectrometry; terrestrial cosmogenic nuclides (TCN); cosmogenic nuclide exposure dating

  • Poster
    1. Trienalni Posvet, Naravne Nesrece v Sloveniji (NNS '08 - 1st Symposium Natural Disasters in Slovenia), 11.12.2008, Ljubljani, Ljubeljana, Sloveniji , Slowenien

Publ.-Id: 11959

On the axissymmetric dominance of the magnetic field in the VKS dynamo experiment.

Giesecke, A.; Stefani, F.; Gerbeth, G.

In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.

A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data of water experiments, leads to dynamo action if a critical value for the magnetic Reynolds number is exceeded.

In case of an axisymmetric velocity field the simulations always result in a non-axisymmetric eigenfield which is dominated by the azimuthal m=1-mode. However, in contradiction to this expected result, the experimental realisation exhibits an axissymmetric field configuration.

Until today, no satisfactory explanations for the dominating m=0-mode are established. A recently presented approach is based on an alpha-effect caused by helical fluid motions between the impeller blades that drive the flow. However, it turned out, that the necessary
amplitude which is required for m=0 dominated solutions is well above realistic values that might be realized in the experiment.

Further potential explanations involve non-axissymmetric contributions either caused by a drifting large scale vortex structure as observed in water experiments or introduced through the azimuthal varying high permeability region from the ferrous impeller blades, which should ideally give rise to a strong axisymmetric azimuthal field component within the impeller region.

Keywords: Dynamo

  • Lecture (Conference)
    11th MHD days, 01.-03.12.2008, Ilmenau, Germany

Publ.-Id: 11958

Equation of state for QCD matter in a quasiparticle model

Schulze, R.; Kämpfer, B.

A phenomenological QCD quasiparticle model provides a means to map lattice QCD results to regions relevant for a variety of heavy-ion collision experiments at larger baryon density. We report on effects of collectives modes and damping on the equation of state.

Keywords: QCD quasipaticle model QPM heavy ion collective modes Landau damping equation of state EOS

Publ.-Id: 11957

Light emitting field effect transistor with two self-aligned Si nanocrystal layers

Beyer, V.; Schmidt, B.; Heinig, K.-H.; Stegemann, K.-H.

Light emitting field-effect transistors based on narrow layers of silicon nanocrystals (NCs) in the gate oxide were fabricated. Direct quantum mechanical electron and hole tunneling into NCs was achieved by self-alignment of NCs-interface-distances to ~2 nm. The direct tunneling reduces oxide degradation, prolongs device lifetime and increases operation speed. Self-alignment occurs during thermal treatment of ion irradiated stacks of 50 nm polycrystalline silicon/15 nm SiO2 / (001)Si substrate. An alternating voltage (ac) was applied to the gate to inject charges into the NCs. Due to injection by direct tunneling, electroluminescence extends to higher ac frequencies than reported so far.

Keywords: Si nanocrystals; Si based light emission; electroluminescence; photoluminescence; ion irradiation; memory; MOSFET; Ostwald ripening

  • Applied Physics Letters 95(2009), 193501

Publ.-Id: 11956

Terawatt diode-pumped Yb:CaF2 laser

Siebold, M.; Hornung, M.; Boedefeld, R.; Podleska, S.; Klingebiel, S.; Wandt, C.; Krausz, F.; Karsch, S.; Uecker, R.; Jochmann, A.; Hein, J.; Kaluza, M. C.

We present what we believe to be the first terawatt diode-pumped laser employing single-crystalline Yb:CaF2 as the amplifying medium. A maximum pulse energy of 420 mJ at a repetition rate of 1 Hz was achieved by seeding with a stretched femtosecond pulse 2 ns in duration, preamplified to 40 mJ. After recompression, a pulse energy of 197 mJ and a duration of 192 fs were obtained, corresponding to a peak power of 1 TW. Furthermore, nanosecond pulses containing an energy of up to 905 mJ were generated without optical damage.

Keywords: Diode pumped laser caf2

  • Optics Letters 33(2008)23, 2770-2772

Publ.-Id: 11955

Additional PET/CT in week 5-6 of radiotherapy for patients with stage III non-small cell lung cancer as a means of dose escalation planning?

Gillham, C.; Zips, D.; Poenisch, F.; Evers, C.; Enghardt, W.; Abolmaali, N.; Zoephel, K.; Appold, S.; Hoelscher, T.; Steinbach, J.; Kotzerke, J.; Herrmann, T.; Baumann, M.

Background and purpose: Loco-regional failure after radiotherapy with total doses of 60-70 Gy for non-small cell lung cancer (NSCLC) remains a major clinical problem. Escalation of radiation dose is often limited because of exceeding normal tissue constraints. The present study was designed to test the hypothesis that a reduction in disease volume during radiotherapy detected by FDG PET/CT would facilitate radiation dose escalation, whilst remaining within normal tissue constraints.
Materials and methods: Ten patients with localised inoperable NSCLC were prospectively enrolled. Each received standard 3D-conformally planned radiotherapy to a dose of 66 Gy in 33 fractions over 6.5 weeks. FDG PET/CT imaging in the treatment position was performed prior to treatment and repeated following 50 or 60 Gy. CT and PET-delineated gross tumour volumes were generated and a composite created. A margin of 15 mm was added in all planes to form the planning target volume (PTV). Treatment planning was performed to compare two dose escalation strategies: 78 Gy delivered to the initial PTV with treatment in two phases (shrinking field), i.e., 66 Gy to the initial PTV with a 12 Gy-boost to the PTV after 50/60 Gy. As an alternative planning approach the maximal dose without exceeding normal tissue constraints was evaluated for each patient (individualized dose prescription).
Results: There was a median PTV reduction after 50/60 Gy of 20%. Delivering 78 Gy to the initial PTV could have been achieved in 4/10 patients. Of the remaining 6, delivering 78 Gy to the initial PTV would have exceeded normal tissue constraints and no benefit was seen when delivered in two phases. The results from the individualized dose prescription indicated a higher median maximal dose when treatment would be given in two phases compared to one phase resulting in a modest increase of calculated tumour control probability.
Conclusions: Our data suggest that despite tumour shrinkage determined by subsequent FDG PET/CT during treatment the tested adaptive targeting strategy would result only in a modest improvement in the context of dose escalation. Further studies on the optimal use of FDG PET/CT and other approaches for dose escalation in loco-regionally advanced NSCLC are warranted.

Keywords: Lung cancer; PET/CT; Dose escalation; Adaptive targeting; Radiotherapy

Publ.-Id: 11954

Experimental investigation of Lorentz-force controlled flat-plate boundary layer with a laser Doppler velocity profile sensor

Shirai, K.; Voigt, A.; Neumann, M.; Büttner, L.; Czarske, J.; Cierpka, C.; Weier, T.; Gerbeth, G.

The application of Lorentz forces for flow control has been investigated in the field of magnetohydro-dynamics (MHD) research since it is capable of generating required mass force to control electrically conductive liquid flows. Separation control of a hydrofoil using Lorentz force has been intensively investigated in the MHD division in the Forschungszentrum Dresden-Rossendorf (FZD) in Germany.
Vortex structures around the hydrofoil have been investigated by Weier et al. (for example [1]). They investigated the vortex structure of the separated flow with particle image velocimetry (PIV) to seek optimum control of separation [2].
However, PIV has limitations particularly in the near-wall region which indeed is of great interest.
In general PIV has an accuracy of velocity measurement about a few percent at best optimized condition [3]. Hence, the application of PIV to the region of low turbulence has a difficulty to evaluate the real turbulence coming from the flow. Besides, the application of PIV to the near-wall region is problematic because of high velocity gradient and strong reflection at the wall. In addition, proper evaluation of velocity field near the wall is hindered when strong Lorentz force is applied. The electric current induced for generating the Lorentz force electrolyzes the liquid and generates bubbles at the wall. Unfortunately, the higher the induced current, the stronger the bubbles are generated.
Therefore, it is demanded to use a measurement technique capable of velocity measurement at low turbulence degree near the wall surface at bubbly conditions. Laser Doppler velocity profile sensor developed in the TU Dresden is attractive since it has high resolution (micrometer range) and accuracy (<0.1%) of velocity profile measurement demanded in the above application. The sensor has been successfully applied to the near-wall region of a turbulent channel flow [4].
The purpose of the present investigation is to study the fundamental mechanism of the flow control with Lorentz force. For that reason, the velocity profile near the wall is measured with the velocity profile sensor. As a first test, the preliminary experiment described in this abstract focused in the feasibility of measurement close to the wall under bubbly conditions and to observe the difference of the flow regime with and without Lorentz force applied.

Keywords: Lorentz force; laser Doppler Velocimetry

  • Lecture (Conference)
    6th International Symposium on Turbulence and Shear Flow Phenomena (TSFP6), 22.-24.05.2009, Seoul, Korea
  • Contribution to proceedings
    6th International Symposium on Turbulence and Shear Flow Phenomena (TSFP6), 22.-24.06.2009, Seoul, Südkorea
    Turbulence and Shear Flow Phenomena, Vol II, 755-760

Publ.-Id: 11951

Uranium coordination in liquids and amorphous solids determined by EXAFS spectroscopy

Hennig, C.

The combination of UV-Vis and EXAFS to determine species distribution and structure will be discussed.

Keywords: EXAFS; UV-Vis; uranium

  • Lecture (others)
    University of Siegen, Inorganic Chemistry, 24.11.2008, Siegen, Germany

Publ.-Id: 11950

Influence of ionic strength, pH and silicate on colloidal UO2 formation

Hennig, C.

The solubility of uranium in aqueous solutions under anaerobic conditions is low and the probability of solid UO2 formation increases with the U(IV) concentration. Only in solutions with low pH and high ionic strength the U(IV) hydrate itself is stable even at higher U(IV) concentrations. With increasing pH several U(IV) hydroxides becomes dominant. Below their solubility limits two solid phases can be observed, i.e. the microcrystalline UO2 and the amorphous UO2•xH2O/U(OH)4 which both can occur as colloids in solution. Also the presence of silicate influence the formation and structure of U(IV) nanoparticles. However, even in solutions with equimolar ratio of UO2 and SiO2 the precipitation do not result in the formation of a USiO4-like phase, which can be observed easily under hydrothermal conditions. Some structural aspects of the resulting solid phases have been investigated with x-ray diffraction, EXAFS and wide angle x-ray scattering techniques and will be briefly discussed.

Keywords: EXAFS; XRD; HEXS; UO2

  • Lecture (others)
    Ecole Polytechnique Federale Lausanne (EPFL) Environmental Microbiology Laboratory (EML), 20.11.2008, Lausanne, Switzerland

Publ.-Id: 11949

Influence of annealing on the Er luminescence in Si-rich SiO2 layers co-implanted with Er ions

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

The impact of rapid thermal annealing (RTA) in producing samples by sequential implantation of Si and Er ions into a 200 nm SiO2 layer combined with different annealing cycles as well as the corresponding room-temperature visible and infrared photoluminescence (PL) have been studied. The Er-related PL intensity at 1533 nm for the samples prepared by implanting Si with subsequent annealing, followed by Er implantation and final annealing (type-I) was found to be stronger than the one produced similarly but without the first annealing step (type-II). In fact, the 1533 nm peak intensity in the optimized RTA processed sample is comparable to the PL yield of the furnace-annealed sample. Moreover, the excitation wavelength (405 nm) was found to be suitable for exciting the Si=O related point defects in the SiO2 layer, and can provide a PL band with a maximum at ~580 nm. While this band was further intensified in presence of Si nanocrystals (Si NCs), it became weaker by introducing additional Er3+ ions with a concomitant rise of the 1533 nm Er PL, confirming the visible range pumping of Er3+. The detailed spectral analyses suggest that the 580 nm band is the result of the excitation/deexcitation mechanism in molecule like states in Si=O or the Si=O state mediated recombination of carriers in Si NCs according to the model proposed by Wolkin et al. [Phys. Rev. Lett. 82, 197 (1999)]. The samples were further characterized by transmission electron microscopy and Fourier-transform infrared-spectroscopy. The time resolved PL measurements and a modelling by rate equations were also performed to determine and justify the energy migration mechanism from Si NC to the neighbouring Er3+.

Keywords: Nanocrystals; RTA; defects; photoluminescence

  • Journal of Applied Physics 104(2008)10, 103522-1-103522-9

Publ.-Id: 11948

Probing channeling radiation influenced by ultrasound

Wagner, W.; Azadegan, B.; Büttig, H.; Grigoryan, L. S.; Sobiella, M.; Pawelke, J.

The effect of ultrasonic vibrations excited in quartz single crystals on channeling radiation (CR) emitted by relativistic electrons was probed experimentally at medium energy at the radiation source ELBE.

Essential preconditions for these investigations have been created by preceding series of measurements of planar CR on alpha-quartz as well as by extensive theoretical work concerning the treatment of the influence of ultrasound (US) on CR emission. First dedicated experiments became possible because the interaction phenomena and expected effects could certainly be predicted and simulated.

Compressional waves of suitable frequency were induced in x-cut quartz crystals by means of appropriately designed RF cavities applying the reverse piezoelectric effect. Although at the available electron energies the necessary resonance condition has been reached only for selected transitions of electrons channeled along specific crystallographic planes of the quartz single crystal, the occurrence of US stimulated CR should be evident.

Keywords: channeling radiation; quartz single crystal; ultrasound

  • Contribution to proceedings
    3rd International Conference on Charged and Neutral Particles Channeling Phenomena (Channeling 2008), 25.10.-01.11.2008, Erice, Sicily, Italy
    Probing channeling radiation influenced by ultrasound, Singapore, London: World Scientific, Science and Culture Series
  • Invited lecture (Conferences)
    3rd International Conference on Charged and Neutral Particles Channeling Phenomena (Channeling 2008), 25.10.-01.11.2008, Erice, Sicily, Italy

Publ.-Id: 11947

THEREDA - Ein Beitrag zur Langzeitsicherheit von Endlagern für nukleare und nichtnukleare Abfälle

Altmaier, M.; Brendler, V.; Hagemann, S.; Herbert, H.-J.; Marquardt, C.; Moog, H.; Neck, V.; Richter, A.; Voigt, W.; Wilhelm, S.

Im Rahmen von Langzeitsicherheitsanalysen für deutsche Endlager radioaktiver bzw. Untertagedeponien chemotoxischer Abfälle sowie weiterer Einsatzfelder (Altlastensanierung) wird eine einheitliche und umfassende thermodynamische Referenzdatenbasis dringend benötigt. Der ehemalige „Arbeitskreis Thermodynamische Standarddatenbasis“ (ATS) hatte sich die Aufgabe gestellt, eine solche Datenbasis zu realisieren. Die Aktivitäten des ATS werden seit Juli 2006 im Projektverbund „THEREDA“ (Thermodynamische Referenzdatenbasis) von BMBF, BMWi und BfS zunächst für 3 Jahre gefördert. THEREDA setzt sich aktuell aus 5 Partnerinstitutionen zusammen, die im Wesentlichen die deutschen Forschungsinstitutionen auf dem Gebiet der Endlagersicherheitsforschung repräsentieren. THEREDA soll die Transparenz und Belastbarkeit der Sicherheitsanalysen in Deutschland entscheidend verbessern und stellt erstmalig konsistente thermodynamische Datensätze für die in Deutschland diskutierten Endlageroptionen bereit. Für jede thermodynamische Größe werden anhand eindeutig definierter Evaluierungskriterien Qualitätsstufen angegeben, mithilfe derer Anwender Daten, entsprechend der jeweiligen spezifischen Problemstellungen, gezielt einbeziehen oder ausschließen können. Für fehlende thermodynamische Daten werden im Rahmen von THEREDA begründete Schätzwerte ermittelt, sodass Modellrechnungen zur Sicherheitsanalyse in Zukunft auf einer deutlich breiteren Datenbasis durchgeführt werden können.
Die Datenbasis wird in einer Datenbank zentral verwaltet und Anwendern über das Internet frei und unentgeltlich verfügbar sein. Importformate, um THEREDA in die gängigsten Modellierungscodes (EQ3/6, PHREEQC, Geochemist’s Workbench, CHEMAPP, usw.) überführen zu können, werden ebenfalls unentgeltlich zur Verfügung gestellt.

Long-term safety analyses of German repositories of radioactive waste as well as underground repositories for chemical toxic waste and other uses (contaminated site remediation) urgently require a standardized, comprehensive thermodynamic reference database. The former "Thermodynamic Standard Database Working Party" was set up to establish such a database. The activities of that group have been supported within the integrated “THEREDA” (Thermodynamic Reference Database) project since July 2006 for an initial period of 3 years by the German Federal Ministries of Education and Research, of Economics, and by the Federal Office of Radiation Protection. THEREDA at present is composed of 5 partner institutions essentially representing the key German research institutions in the field of repository safety research.
THEREDA is to improve the transparency and validity of safety analyses in Germany and, for the first time, provides consistent thermodynamic datasets for the repository options discussed in Germany. Quality levels are indicated for each thermodynamic quantity on the basis of unambiguously defined evaluation criteria, which allow users to either include or exclude data in accordance with the specific problems at hand. Missing thermodynamic data are substituted in THEREDA by well-founded estimates, thus permitting future model calculations for safety analysis to be carried out on a clearly broader basis of data. The data are managed centrally in a database and will be available to users free of charge on the Internet. Import formats allowing THEREDA to be transferred into the most common modeling codes (EQ3/6, PHREEQC, Geochemist’s Workbench, CHEMAPP, etc.) are also made available free of charge.

Keywords: THEREDA; thermodynamic database; modelling; long term safety analyses

  • atw - International Journal for Nuclear Power 54(2008)4, 249-253

Publ.-Id: 11946

Complexation of Actinides with Organic and Inorganic Ligands

Geipel, G.; Bernhard, G.

Two basic requirements are needed for speciation calculations – a database including stability constants of the formed species and a computerized program for the real calculation. For the input analytical data or theoretical concentrations of the basic species can be used.
Hydroxide and carbonate are two of the most important environmental ligands. Fuger /1/ resumes many available data.
Up to now several databases have been developed /2-6/. However, the most up-to-date and best-reviewed databases for the actinide elements uranium, neptunium, plutonium and americium are the NEA databases /4, 7/. For speciation calculations the listed data should be used including the desired estimations for correction of the ionic strength. Two estimates are widely used:

  • Adapted SIT (Specific Ion Interaction Theory) method /4/.
  • Davies equation, including extension for high ionic strength /5/.

On the basis of the database several program codes can be used for calculation of the species distribution as function of concentrations, pH, ionic strength. Which one will be selected depends on experience of the user. The most important input in such calculations is the use of a correct and validated database.

The most useful program code is EQ 3/6 /8/. The estimation of the stability constants at the ionic strength of the solution to be calculated is included in this program. Also reactions at the interphase gas/liquid can be included.
A newer code is SPECIES /9/. The input is comfortable; also a program code for the estimation of formation constants at different ionic strength is available. However, and this is mentioned by the authors, the attached database (SC Database) should be used only after checking of the original literature. The program is not able to include reactions with gas phases (CO2/CO2 (a.)).
Also available on the web is the program MEDUSA /10/. In the program a database is included and there is also the possibility to correct the used stability constants.

Keywords: Speciation; Trace elements; Distribution diagrams

  • Invited lecture (Conferences)
    School cum Workshop on Trace Element Speciation (SElS-08), 21.-29.11.2008, Kolkata, India

Publ.-Id: 11945

Spectroscopic Techniques in Actinide Speciation Studies

Geipel, G.; Bernhard, G.

The determination of the behavior of actinides in the environment needs several spectroscopic techniques, adapted to spectroscopic properties and concentration ranges of these elements in the environment.

New techniques for the speciation of actinides have been developed during the past decades. Three main requirements are of importance:

  • License for handling of radioactive elements, especially for α-emitting actinides.
  • Availability of actinides, especially the higher actinides are available only in small amounts.
  • Speciation methods covering the concentration range of actinides expected or found in nature.

Speciation analysis can be distinguished into two types: non-invasive and invasive methods. Among the first group are spectroscopic methods. They are not restricted to the form of the species (solid, liquid, gas). Non-invasive methods need usually no treatment of the sample and allow the direct speciation of an element in its environment. Invasive methods in general are applicable to solids and solutions. They need normally a pretreatment and a separation of the sample. Sequential extraction can be used for the determination of species in solid systems. Besides for the separation of actinides /1/ extraction techniques are important for the determination of oxidation states of the actinides in solution. For example the oxidation states of plutonium can be determined using α-thenoyltrifluoroacetone (TTA) at pH = 0. Tetravalent plutonium is extracted to the organic phase, whereas all other oxidation states and polymeric plutonium remain in the aqueous phase. The same extraction procedure after addition of chromate allows to separate plutonium(III) and plutonium(IV). Other common extraction agents are tributylphosphate (TPB) and bis(2-ethyl-hexyl)-hydrogen-phosphate (HDEHP).

Keywords: Spectiation; Trace elements; Spectroscopy

  • Invited lecture (Conferences)
    School cum Workshop on Trace Element Speciation (SElS-08), 21.-29.11.2008, Kolkata, India

Publ.-Id: 11944

THEREDA - A Thermodynamic Reference Database

Moog, H.; Brendler, V.; Gester, S.; Richter, A.; Altmaier, M.; Marquardt, C.; Neck, V.; Hagemann, S.; Herbert, H.-J.; Willms, T.; Voigt, W.; Wollmann, G.; Wilhelm, S.

Part of the process to ensure the safety of radioactive waste disposal is the predictive modeling of the solubility of certain toxic components in a complex aqueous solution. To ensure the reliability of thermodynamic equilibrium modeling as well as to facilitate the comparison of such calculations done by different institutions it is necessary to create a mutually accepted thermodynamic reference database.

To meet this demand several institutions in Germany joined efforts and created THEREDA. THEREDA is a relational databank whose structure was designed in a way that facilitates internal consistency of thermodynamic data entered. It serves as backend to a variety of peripheral programs which allow for adding, editing, and extracting subsets of data. Data considered cover the needs for Gibbs Energy Minimizers and Law-of-Mass-Action-programs alike. Interaction parameters for an arbitrary number of mixed phases and p,T-functions of thermodynamic data may also entered. To enhance public use THEREDA is accessible via internet.

The paper gives an account about the present state of THEREDA as well as of future developments.

Keywords: THEREDA; thermodynamic database; waste disposal; internet

  • Lecture (Conference)
    Waste Management Conference WM 2009, 01.-05.03.2009, Phönix (AZ), USA
  • Contribution to proceedings
    Waste Management Symposium 2009: Waste Management for the Nuclear Renaissance, 01.-05.03.2009, Phoenix (Arizona), USA
    Waste Management Symposium 2009: Waste Management for the Nuclear Renaissance (8 Vols): Curran Associates, Inc., 9781615672523

Publ.-Id: 11943

Self-organized nanopatterns by ion erosion

Keller, A.; Facsko, S.; Möller, W.

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures have been found on a large variety of materials, such as semiconductors, metals, and insulating surfaces. The formation and early evolution of the ripple patterns can be qualitatively described by a linear continuum equation derived by Bradley and Harper. At longer times, however, nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
This talk will provide an overview of ion-induced pattern formation and summarize the theoretical basics. Recent experimental results on the evolution of nanoscale ripple patterns on amorphous surfaces during high-fluence ion sputtering will be presented and compared to the predictions of different continuum models. In addition, promising applications of nanorippled substrates as templates in thin film growth will be discussed.

  • Lecture (others)
    Seminar, 18.11.2008, Aarhus, Denmark

Publ.-Id: 11942

How can plants deal with the relatively high toxic uranium?

Viehweger, K.; Geipel, G.

Uranium is a widespread radioactive toxic heavy metal, released into the biosphere mostly by military purposes and nuclear industry. It is taken up by plant root systems and its chemical toxicity is much more dangerous than the radiological. Thus cell suspensions of rape (Brassica napus) revealed specific extracellular defence reactions after uranium exposure. These include characteristic pH-shifts of the culture medium caused by contact with the heavy metal. At the same time a transient release of fluorescent compounds from the cells occurred. These phytoalexins probably belong to the widespread group of flavonoids detected by HPLC and thin layer chromatography (TLC). They are able to interact with uranium, can alter the redox status of the metal and hence should protect the cell against this heavy metal poisoning. To gain an insight in these interactions time-resolved laser-induced fluorescence spectroscopy (TRLFS) and absorption spectroscopy were performed.
Former uranium mining sides in Eastern Germany were screened for uranium accumulating plants. An Arabidopsis halleri subspecies with high soil–plant transfer factors could be identified. Therefore a laboratory model system with this plant was established for investigations of uptake and sequestration of this metal. The initial characterisation of this experimental setup was carried out using “root-elongation-tests” to calculate the tolerance index and the measurement of some photosynthetic traits after uranium contact, respective.
Further research is under way to identify intracellular defence mechanisms, e.g. the involvement of glutathione and in this matter the formation of proteins possessing thiol groups (phytochelatins).

Keywords: Protein; plant cell; uranium

  • Invited lecture (Conferences)
    Kolloqiumsreihe des GTSC, 10.12.2008, Berkeley, USA

Publ.-Id: 11941

Uranium – species trace analytics in the nanomolar concentration range

Geipel, G.; Viehweger, K.; Bernhard, G.

Uranium is a ubiquitous element. Besides this depleted uranium amunition as well as uranium mining and milling and manifold other use of uranium leads to an increase of uranium contamination in the environment.
Application of laser-induced and time-resolved methods allow the direct determination of uranium speciation at extremely low concentrations. This behaviour can be directly observed due to the properties extraorbitant luminescence properties of uranium-(VI).
Especially the uranium ammunition can generate locally high concentrations of uranium in the environment. Weathering processes of the uranium metal lead in a first step to the formation of uranium minerals. Depending on the composition of the soil the formation of several types of minerals can be estimated. Especially the content of phosphate from fertilizers and the aluminium from soil components are involved in the mineral formation.
By use of time-resolved laser-induced fluorescence spectroscopy (TRLFS) the mineral type can be determined without any destruction. A large database of luminescence spectra, obtained from uranium minerals of the collection of the Technical University Mining Academy Freiberg, enables us to identify the formed uranium mineral. In a second step the formed minerals than undergo further weathering processes, forming dissolved uranium species.
In the former uranium mining areas of eastern Germany we could discover a new dissolved uranium carbonate species. However, the uranium concentration of about 2 mg/L in these mining related waters is relatively high. Nevertheless the carbonate and calcium concentration are high enough to form a very stable dicalcium-uranyl-tricarbonate species. This species is of great importance, as its existence explains the uranium migration at the Hanford site.
The pure carbonate species do not show any luminescence properties at room temperature. Therefore the samples have to be frozen to temperatures below 220 K, in order to minimize the dynamic quench effect of the carbonate anion. This increases also the luminescence intensity and the luminescence lifetime of all carbonate containing species.
Following the possible transport of uranium under environmental conditions we may start with the weathering of uranium compounds in the soil or in a mining waste rock pile. The seepage water contains about 2 mg/L uranium and the speciation is mainly influenced be the formation of the dicalcium-uranyl-tricarbonate species. The input of these seepage water leads to a dilution of the uranium by about three orders of magnitude. Using the cryogenic technique in TRLFS we could also determine the uranium speciation in the river water nearby the former uranium mining area. The uranium concentration was about 2 µg/L uranium and in the river water mainly uranyl-tricarbonate species are formed.
In this case uranium may come back to the food chain by the production of mineral waters. We have studied the uranium speciation in several German mineral waters with uranium concentrations between 50 ng/L and 5 µg/L.
Contact of dissolved uranium with living cells at ambient conditions changes dramatically the uranium speciation. Some examples fluorescence properties of uranium species relevant to the environment are shown. The change of this speciation can be observed then due to a change in luminescence properties. Besides of several organic phosphate binding forms although other uranium species were found as uranium bond to phenolic and thiol groups. Some of them do not emit any luminescence at room temperature. Nevertheless low temperature measurements allow the assignment of species not fluorescing at room temperature, due to strong dynamic quench effects of H2O molecules and COO- groups.

Keywords: Uranium; Trace concentration; species determination

  • Invited lecture (Conferences)
    Kolloqiumsreihe des GTSC, 10.12.2008, Berkeley, USA

Publ.-Id: 11940

THz beam line for pump probe experiments at FLASH: recent results and developments from the comissioning

Gensch, M.; Fruehling, U.; Stojanovic, N.; Seidel, W.; Tavella, F.; Wieland, M.; Schade, U.; Lee, J. S.; Hübers, H.-W.; Semenov, A.; Duesterer, S.; Grimm, O.; Hahn, U.; Ploenjes, E.; Saldin, E. L.; Kocharyan, V.; Schneidmiller, E.; Rossbach, J.; Feldhaus, J.; Drescher, M.; Yurkov, M. V.

At the vacuum ultraviolet (VUV) free electron laser in Hamburg (FLASH) an infrared (IR) beamline is currently being comissioned that will allow novel pump-and-probe experiments combining coherent IR pulses with the FEL radiation in the VUV spectral range. It provides useful IR, respectively THz, radiation generated by a purpose built undulator over the wavelength range from 200 micron to presently 14 micron. The undulator is implemented “in series” to the VUV undulators of FLASH and the length of the IR beamline can be matched to that of an existing VUV beamline so that overlap with VUV pulses generated by the same electron bunch can be achieved. Hence natural synchronization of the two pulses is expected. First results of the comissioning are shown and an outlook on future experiments and upgrades of the beamline as well as its photondiagnostics will be given.

  • Poster
    FLASH users-meeting and kick-off workshop: THZ beamline, 08.-10.09.2008, Hamburg, Deutschland

Publ.-Id: 11939

THz free-electron laser FELBE at the radiation source ELBE

Seidel, W.

This paper reviews the basic properties of the infrared free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf. A few highlight experiments using the cw-operation are discussed. Driven by a superconducting linear accelerator, FELBE continuously generates infrared pulses with a repetition rate of 13 MHz. In addition, operation in a macropulse modus (pulse duration >100µs, repetition rate ≤ 25 Hz) is possible. At present FELBE delivers µJ pulses with typical duration of about 0.9-30 ps in the wavelength range 4-230 µm. Furthermore we give an outlook on the experiments will use the beam of FELBE in the High Magnetic Field Laboratory Dresden (HLD). The HLD will provide pulsed magnetic fields up to 60 T. It operates as a user facility since 2007.

  • Invited lecture (Conferences)
    FLASH users-meeting and kick-off workshop: THZ beamline, 08.-10.09.2008, Hamburg, Deutschland

Publ.-Id: 11938

Three years of cw-operation at FELBE - Experiences and applications

Seidel, W.; Cizmar, E.; Drachenko, O.; Helm, M.; Justus, M.; Lehnert, U.; Michel, P.; Ozerov, M.; Schneider, H.; Schurig, R.; Stehr, D.; Wagner, M.; Winnerl, S.; Wohlfarth, D.; Zvyagin, S.; Kehr, S. C.; Eng, L. M.

This paper reviews the basic properties of the infrared free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf. A few highlight experiments using the cw-operation are discussed. Driven by a superconducting linear accelerator, FELBE continuously generates infrared pulses with a repetition rate of 13 MHz. In addition, operation in a macropulse modus (pulse duration >100µs, repetition rate ≤ 25 Hz) is possible. At present FELBE delivers µJ pulses with typical duration of about 0.9-30 ps in the wavelength range 4-230 µm. Furthermore we give an outlook on the experiments will use the beam of FELBE in the High Magnetic Field Laboratory Dresden (HLD). The HLD will provide pulsed magnetic fields up to 60 T. It operates as a user facility since 2007.

  • Poster
    30th International Free Electron Laser Conference FEL 2008, 24.-29.08.2008, Gyeongju, Korea
  • Contribution to proceedings
    30th International Free Electron Laser Conference FEL 2008, 24.-29.08.2008, Gyeongju, Korea

Publ.-Id: 11937

Absorption spectroscopy of Eu and Am with a Liquid Waveguide Capillary Cell

Müller, M.; Schott, J.; Acker, M.; Taut, S.; Barkleit, A.; Bernhard, G.

The combination of UV-vis spectroscopy with a LWCC results in a higher sensitivity and allows measurements at low heavy metal concentrations. We demonstrate the utility of the LWCC for the investigation of complex formation between heavy elements and organic substances by showing the first results achieved with Eu and Am.

Keywords: UV-vis; europium; americium; LWCC; detection limit; complexation

  • Poster
    Seventh International Conference on Nuclear and Radiochemistry (NRC7), 24.-29.08.2008, Budapest, Hungary

Publ.-Id: 11936

Determination of the polarization characteristics of the ELBE free electron laser

Lee, J. S.; Gensch, M.; Hinrichs, K.; Seidel, W.; Schade, U.

In this work, we investigated polarization characteristics of the ELBE infrared free electron laser at the experimental position by adapting imaging ellipsometry technique. We found that the laser beam has a Gaussian-like power distribution with a diameter of 3–4 mm and exhibits a linearly polarized character throughout the whole area investigated. We also evaluated the degree of polarization amounting to 98% which demonstrates a tiny depolarization effect during the beam transfer via several optical elements from the source to the experimental position.

Keywords: Free electron laser; Infrared; Polarization; Stokes parameter

  • Infrared Physics and Technology 51(2008)6, 537-540

Publ.-Id: 11935

Assessment of surface area normalisation for interpreting distribution coefficients (K(d)) for uranium sorption

Payne, T. E.; Brendler, V.; Comarmond, M. J.; Nebelung, C.

Adsorption of radionuclides on soils and sediments is commonly quantified by distribution coefficients (K(d) values). This paper examines the relationship between K(d) values for uranium(VI) adsorption and the specific surface area (SSA) of geologic materials. We then investigate the potential applicability of normalising uranium (U) K(d) measurements using the SSA, to produce 'K(a) values' as a generic expression of the affinity of U for the surface. The data for U provide a reasonably coherent set of K(a) values on various solid phases, both with and without ligands. The K(a) representation provides a way of harmonising datasets obtained for materials having different specific surface areas, and accounting for the effects of ligands in different systems. In addition, this representation may assist in developing U sorption models for complex materials. However, a significant limitation of the K(a) concept is that sorption of radionuclides at trace levels can be dominated by interactions with specific surface sites, whose abundances are not reflected by the SSA. Therefore, calculated K(a) values should be interpreted cautiously.

Keywords: Sorption; Specific Surface Area; Radionuclides; Retardation; Nuclear Waste; Contamination; Database; Modelling

  • Lecture (Conference)
    SPERA'08 - 10th South Pacific Environmental Radioactivity Conference, 24.-27.11.2008, Christchurch, New Sealand
  • Journal of Environmental Radioactivity 102(2011), 888-895
    DOI: 10.1016/j.jenvrad.2010.04.005

Publ.-Id: 11932

Bakterielle Hüllproteine (S-Layer) und ihre technische Anwendung

Raff, J.

Bakterielle S-Layer bilden als hoch geordnete Oberflächenstruktur bei vielen Bakterien und Archaeen die Grenzfläche zwischen Zelle und Umgebung. Als solche besitzen diese Proteinhüllen zahlreiche interessante Eigenschaften, die für die Entwicklung neuer Materialien genutzt werden können. Der Vortrag gibt einen Überblick über die laufenden und geplanten Arbeiten mit bakteriellen S-Layern .

  • Lecture (others)
    Vortrag im Rahmen des Besuchs des Sächsischen Textilforschungsinstituts, 18.11.2008, Chemnitz, Deutschland

Publ.-Id: 11931

Solving the stellar 62Ni problem with AMS

Dillmann, I.; Rugel, G.; Faestermann, T.; Korschinek, G.; Lachner, J.; Maiti, M.; Poutivtsev, M.; Walter, S.; Käppeler, F.; Erhard, M.; Junghans, A. R.; Nair, C.; Schwengner, R.; Wagner, A.

The nucleosynthesis of elements heavier than iron can be almost completely ascribed to the ’slow’ and the ’rapid’ neutron capture processes. Among the nuclei involved, long-lived radioactive isotopes like 63Ni (t1/2= 100.1 yr) assume key positions, because their beta-decay rate becomes comparable to the neutron capture rate. The resulting competition leads to branchings in the s-process nucleosynthesis path. An accurate knowledge of the stellar neutron capture cross sections of 62,63Ni is required since these two cross sections affect the entire weak s-process flow towards heavier nuclei (A about 90). Until recently the experimental values for the (n,gamma) cross section of 62Ni at stellar temperatures (kT=30 keV) ranged between 12 and 37 mb. Stellar models using the lower value revealed a strong overproduction of 62Ni in postexplosive production factors of supernova type II explosions which intensified the question if this is due to uncertainties in the stellar models or in the nuclear input. This discrepancy could now be solved by two activations with following AMS using the GAMS setup at the Munich tandem accelerator which are also in perfect agreement with a recent time-of-flight measurement. The resulting (preliminary) Maxwellian cross section at kT=30 keV was determined to be <>30keV = 23.4 ± 4.6 mb. Additionally, we have measured for the first time the 64Ni(gamma,n)63Ni cross sections close to threshold which can transformed into the inverse 63Ni(n,gamma) channel by detailed balance. Photoactivations at 13.5 MeV, 11.4 MeV and 10.3 MeV were carried out with the ELBE accelerator at Forschungszentrum Dresden-Rossendorf. A first short AMS measurement of the sample activated at 13.5 MeV revealed a cross section smaller by more than a factor of 2 compared to previous predictions.

Keywords: nucleosynthesis neutron capture branching supernova photoactivation accelerator masse spectrometry

  • Contribution to proceedings
    AMS-11 - THE 11th International Conference on Accelerator Mass Spectrometry, 14.-19.09.2008, Roma, Italy
    Nuclear Instruments and Methods in Physics Resarch B: Elsevier
  • Nuclear Instruments and Methods in Physics Research B 268(2010), 1283
    DOI: 10.1016/j.nimb.2009.10.153

Publ.-Id: 11930

Influence of biofilms on the migration behavior of radionuclides

Krawczyk-Bärsch, E.; Arnold, T.; Großmann, K.

Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in the EPS of a living multispecies biofilm grown on biotite plates. These particles ranged between 1 and 7 µm in width and up to 20 µm in length and were located at the bottom and at the edges of biofilms colonies. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilm.
Electrochemical microsensor studies of the O2 concentrations within the biofilm identified depleted zones closer to the biofilm/air interface which may trigger uranium redox processes. The microsensor profile measurements in the stable multispecies biofilms exposed to uranium in ecologically relevant concentrations (1x10-5 and 1x10-6 M) showed that the O2 concentration decreased faster with increasing biofilm depth compared to the uranium free biofilms. In the uranium containing biofilms, the O2 consumption, calculated from the steady-state microprofiles, showed high consumption rates of up to 61.7 nmol cm-3 s-1 in the top layer (0–70 µm) and much lower consumption rates in the lower zone of the biofilms. Staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI) confirmed the high respiratory activities of the bacteria in the upper layer by confocal laser fluorescence microscopy (CLSM). The fast decrease in the oxygen concentrations in the biofilm profiles showed that the bacteria in the top region of the biofilms, i.e., the metabolically most active biofilm zone, battle the toxic effects of aqueous uranium with an increased respiratory activity. This increased respiratory activity results in O2 depleted zones closer to the biofilm/air interface which may trigger uranium redox processes, since suitable redox partners, e.g., extracellular polymeric substance (EPS) and other organics (e.g., metabolites), are sufficiently available in the biofilm porewaters. Such redox reactions may lead to precipitation of uranium (IV) solids and consequently to a removal of uranium from the aqueous phase.

Keywords: biofilm; uranium microscopy; microsensor

  • Poster
    IP FUNMIG Final Workshop, 24.-27.11.2008, Karlsruhe, Germany

Publ.-Id: 11929

Strahlenschutz im PET-Zentrum Dresden-Rossendorf

Preusche, S.; Füchtner, F.; Zessin, J.; Beuthien-Baumann, B.; Bergmann, R.; Walther, M.

kein Abstrakt verfügbar

  • Invited lecture (Conferences)
    Strahlenschutz in Medizin, Forschung und Industrie, 13.-14.11.2008, Hamburg, Deutschland

Publ.-Id: 11928

Conduction at domain walls in oxide multiferroics

Seidel, J.; Martin, L. W.; He, Q.; Zhan, Q.; Chu, Y.-H.; Rother, A.; Hawkridge, M. E.; Maksymovych, P.; Yu, P.; Gajek, M.; Balke, N.; Kalinin, S. V.; Gemming, S.; Wang, F.; Catalán, G.; Scott, J. F.; Spaldin, N. A.; Orenstein, J.; Ramesh, R.

We report the observation of room temperature electronic conductivity at ferroelectric domain walls in BiFeO3. The origin and nature of the observed conductivity is probed using a combination of conductive atomic force microscopy, high resolution transmission electron microscopy and first-principles density functional computations. We show that a structurally driven change in both the electrostatic potential and local electronic structure (i.e., a decrease in band gap) at the domain wall leads to the observed electrical conductivity. Additionally we demonstrate the potential for device applications of such conducting nanoscale features.

Keywords: multiferroics; domain walls; boundary conductivity; bismuth ferrate

Publ.-Id: 11927

Structure, electronics and transport properties in nanostructured materials

Gemming, S.

Transition metal chalcohalides MX2 can form a wealth of diverse nanostructures, largely as a function of the synthesis conditions. The obtained structures range from large octahedral and fullerene-like hollow clusters and cylindrical nanotubes close to the nominal composition M:X = 1:2 to smaller, two-dimensional platelet-shaped clusters under sulfur excess and to one-dimensionally elongated nanowires under sulfur-deficient conditions. All of those structures exhibit specific electronic properties that differ from the ones of the pure bulk and open up a large spectrum of nanostructure applications, that still includes the lubricant aspect, but reaches further to catalysis and electronic transport. One-dimensionally delocalized electronic states provide the basis for the higher activity, reactivity and conductivity in nanostructured MX2. Larger triangular and hexagonal platelets exhibit a so-called 'brim'-state along the circumference of the cluster, which assists the activation of sulfur atoms contained in raw oil; hence platelet-based catalysts are employed for desulfurization. One-dimensional wires with compositions MX an M2X3 are composed of a central metallic wire coated by an insulating sulfur and/or halide shell. They exhibit a very high structural regularity, hence, ballistic conductivity may be obtained in such structures. The stability, structure and metallicity of such wires have been calculated in excellent accordance with recent scanning-probe experiments. In addition, the calculations showed, that wires can act as electromechanical switches, because they undergo a symmetry-dependent metal-insulator transition upon twisting. Thus, metal chalcohalide nanostructures are versatile building blocks for nanoscale catalytic and electronic devices.

Keywords: molybdenum sulfide; metal chalogenide; chalcohalide; nanowire; platelet; density-functional calculations

  • Lecture (others)
    SFB 767 - Controlled Nanosystems: Interaction and Interfacing to the Macroscale, 20.-21.11.2008, Konstanz, Deutschland

Publ.-Id: 11926

Flux dependence of cluster formation in neutron irradiated weld material – Small-angle neutron scattering experiments and rate theory simulation

Bergner, F.; Birkenheuer, U.; Ulbricht, A.; Weiss, F.-P.

Small-angle neutron scattering was applied to investigate the size distribution of irradiation-induced defect-solute clusters in a reactor pressure vessel weld material containing 0.22 wt% copper. In order to identify flux effects the material was exposed to neutron irradiations at two different levels of neutron flux in such a manner that the same value of neutron fluence was accumulated. We observed a pronounced effect of neutron flux on the cluster size, whereas the total volume fraction of the irradiation-induced clusters was found to be insensitive to the level of flux. The result is compatible with a rate theory model according to which the range of applied fluxes covers the transition from a flux-independent regime at lower fluxes to a regime of decelerating cluster growth. The issue of the effect of flux on the mechanical properties is also addressed.

  • Poster
    IEEE Dresden 2008, 20.-24.10.2008, Dresden, Deutschland
  • Contribution to proceedings
    IEEE Dresden 2008, 20.-24.10.2008, Dresden, Deutschland
    IEEE 2008 Nuclear Science Symposium Conference Record

Publ.-Id: 11925

Accelerator mass spectrometry (AMS) and ion beam analysis (IBA) with the new 6 MV accelerator at FZ Dresden-Rossendorf

Merchel, S.; Grambole, D.; Grötzschel, R.; Munnik, F.; Neelmeijer, C.

Ion beam analysis @ FZD
Since more than 30 years ion beam analysis is performed at the Forschungszentrum Dresden-Rossendorf (FZD) for the determination of element distributions. Due to continuous upgrades of the different experimental set-ups, we are able to routinely perform:
• Rutherford Backscattering Spectrometry (RBS) & Channeling (C-RBS)
• Nuclear Reaction Analysis (NRA)
• Elastic Recoil Detection Analysis (ERDA)
• Particle-Induced X-Ray Emission (PIXE)
• Particle-Induced Gamma-Ray Emission (PIGE)

State-of–the art with “old” 5 MV accelerator
Most of our applications lie within material sciences. We are able to measure non-destructively “all natural” elements, i.e. hydrogen to uranium, most elements with lateral, some even in 3-D resolution with the following typical parameters (highly depending on matrix and elements):
• depth resolution: 1-30 nm
• depth range: nm-µm
• lateral resolution: few µm
• usual mapping area: 2x2 mm2
• maximum sample size: 3x10 cm2 (vacuum) & “unlimited” (external beam)
• detection limits: ~10 µg/g (H); 500 µg/g – 1% (He-F); 10-100 µg/g (Na-U)
For some elements, e.g. H/D, isotope analysis is possible.

Outlook for “new“ 6 MV accelerator
In summer 2009, the 30-year-old Russian-made van-de-Graaff 5 MV accelerator will be replaced by the latest 6 MV Tandetron model from HVE, which is even more sophisticated than the lately installed 5 MV version from Southern France. Our new accelerator will need of course less maintenance allowing more beam time for real measurements with respect to our old one. It might be also possible to expand from two to three 8-hour-shifts a day with the new fully automatic system.
Scientifically, the main advantages for ion beam analysis are an increased depth range by a factor of 2 for ERDA and improved detection limits for NRA. In addition, the machine will be installed with special equipment for accelerator mass spectrometry (AMS).

There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses (e.g. isobars) are nearly completely eliminated. Thus, AMS generally provides much lower detection limits in comparison to conventional mass spectrometry (typical isotope ratios 10-10-10-15). Our AMS system will offer excellent measurement capabilities also for external users.
In contrast to common low-energy AMS facilities in Europe, which have mainly specialized in radiocarbon analyses (14C), the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV.
Especially in environmental and geosciences, the determination of long-lived (t1/2 > 0.3 Ma) cosmogenic radionuclides like 10Be, 26Al, and 36Cl became more and more important within the last decades. Using these nuclides dating of mass movements, e.g. volcanic eruptions, rock avalanches, earth quakes, and glacier movements is possible.

Keywords: ion beam analysis; accelerator mass spectrometry; comogenic nuclides

  • Poster
    Seminar Activation Analysis and Gamma-Spectroscopy (SAAGAS 22), 25.-27.02.2009, Wien, Austria

Publ.-Id: 11924

On the reliability of target element data for cosmogenic nuclide exposure dating

Merchel, S.; Bichler, M.; Sterba, J. H.

Radioactive or stable cosmogenic nuclides are products of nuclear reactions induced by cosmic rays. The development of the interdisciplinary field of the quantification of cosmogenic nuclides has been increased dramatically in the last decades. Especially, the progress in the field of accelerator mass spectrometry (AMS) improved detection limits and accuracy and allows nowadays the determination of radionuclide concentrations as low as of 104-105 atoms/(g rock).
In particular, in-situ produced cosmogenic nuclides – so-called terrestrial cosmogenic nuclides (TCN) - have proved to be valuable tools for quantifying Earth's surface processes. Here, the work-horses are 10Be and 26Al in quartz, and 36Cl in Ca- or K-rich minerals.
In siliceous environments both radionuclides, 10Be and 26Al, are pure high-energy spallation products, thus, the influence on the secondary neutron field by changing trace element concentrations in the original bulk matrix is negligible. Another advantage: Usually, quartz can be easily cleaned from other mineral phases making the normalization to (g SiO2)-1, i.e. only two target elements, very straightforward. There is usually no need for a full chemical analysis.

In contrast, 36Cl can be produced by several different nuclear reactions: Spallation on different target elements, mainly Ca and K (to a lesser extent Ti and Fe), induced by high-energy neutrons and muons. Thus, every sample that will be analysed for TCNs has to be chemically analyzed for the main target elements, too. Additionally, as 36Cl can be produced by thermal neutron-capture on 35Cl, trace elements influencing the thermal neutron field have to be unavoidably also measured. This includes U and Th as “background”-neutron emitter, all elements with high neutron absorption cross sections like B, Gd, and Sm, and all light elements, which take part in (gamma,n)-reactions. Thus, a complete bulk rock analysis (for the neutron field) and measurements of the main target elements in the dissolved fraction are absolutely necessary. As 36Cl concentrations will be normalized to (g Ca)-1, (g K)-1 etc., the overall result cannot be more precise then the corresponding target element data.

We have selected typical samples with different fractions of silicate- and calcite-rich phases to have them analyzed by the method of choice of most TCN-user: inductively coupled plasma optical emission spectrometry (ICP-OES). Unfortunately, the two French CNRS laboratories involved, CEREGE and CRPG-SARM, did not produce concordant results for all elements of interest. Thus, we have tested the capability of two non-destructive activation analysis methods: We performed Instrumental Neutron Activation Analysis (INAA) ourselves at Vienna and we sent aliquots for Prompt Gamma Activation Analysis (PGAA) to Budapest.

The four laboratories performed differently depending on the analyte. For example, all methods produce CaO-data with unacceptable high uncertainties. PGAA seems to underestimate the true CaO-value of some samples. K2O-data (@ 0.1-0.7%) by ICP-OES has exceptional high uncertainties and is constantly lower as corresponding INAA- and PGAA-data. As a conclusion, it seems advisable to use more than a single analytical method, if precise TCN applications are intended.

Keywords: terrestrial cosmogenic nuclides (TCN); cosmogenic nuclide exposure dating; INAA; PGAA; ICP-OES

  • Poster
    Seminar Activation Analysis and Gamma-Spectroscopy (SAAGAS 22), 25.-27.02.2009, Wien, Austria

Publ.-Id: 11923

36Cl exposure dating with a 3-MV tandem

Steier, P.; Golser, R.; Kutschera, W.; Martschini, M.; Merchel, S.; Orlowski, T.; Priller, A.; Vockenhuber, C.; Wallner, A.

36Cl AMS measurements at natural isotopic concentrations have yet been performed only at tandem accelerators with 5 MV terminal voltage or beyond. We have developed a method to detect 36Cl at natural terrestrial isotopic concentrations with a 3-MV system, operated above specifications at 3.5 MV.
An effective separation was obtained with an optimized split-anode ionization chamber design (adopted from the ETH/PSI Zurich AMS group), providing a suppression factor of up to 30.000 for the interfering isobar 36S. Despite the good separation, a relatively high sulfur output from the ion source (36S-/35Cl- = 5×10-11) resulted in a background corresponding to 36Cl/Cl = 3×10-14. The method was applied to samples containing between 105 and 106 atoms 36Cl/g rock from sites in Italy and Iran, which were already investigated by other laboratories for surface exposure dating. The 36Cl/Cl ratios in the range from 2×10-13 to 5×10-12 show a generally good agreement with the previous results.
These first measurements demonstrate that also 3-MV tandems, constituting the majority of dedicated AMS facilities, are capable of 36Cl exposure dating, which is presently the domain of larger facilities.

Keywords: 36Cl; AMS; isobar separation

Publ.-Id: 11922

A multi-radionuclide approach for in-situ produced terrestrial cosmogenic nuclides: 10Be, 26Al, 36Cl and 41Ca from carbonate rocks

Merchel, S.; Benedetti, L.; Bourlès, D. L.; Braucher, R.; Dewald, A.; Faestermann, T.; Finkel, R. C.; Korschinek, G.; Masarik, J.; Poutivtsev, M.; Rochette, P.; Rugel, G.; Zell, K.-O.

In contrast to siliceous environments, there is a severe lack of cosmogenic nuclides, which can be used for in-situ dating of calcareous environments. Thus, we have investigated other nuclides than 36Cl as possible dating tools by cross-calibration. Cosmogenic 10Be is highly contaminated with atmospheric 10Be and cannot be removed quantitatively, even by a very sophisticated chemical cleaning procedure. Only working on clay-free calcite provides correct 10Be data, giving a 2.7 times higher production rate of 10Be from CaCO3 than from SiO2. Though, the production rate of 26Al is only ~4.6% (CaCO3 relative to SiO2), 26Al can be easily determined in calcite, as the low intrinsic 27Al concentration yields to nearly as high 26Al/27Al as within corresponding quartz. The measurement of 41Ca, mainly produced via thermal-neutron-capture, is hindered by very low 41Ca/Ca: < 2.5x10-15.

Keywords: accelerator mass spectrometry; terrestrial cosmogenic nuclides (TCN); cosmogenic nuclide exposure dating

Publ.-Id: 11921

Experimental insight into the radiation resistance of zirconia-based americium ceramics

Belin, R. C.; Martin, P. M.; Valenza, P. J.; Scheinost, A. C.

Ceramics intended for use as nuclear fuels, transmutation targets or actinide immobilization matrices have to endure severe conditions including internal radiation. While zirconia-based materials with defect-fluorite structure have shown high tolerance against external ion-beam irradiation, few experimental studies have demonstrated that these structures also resist under more realistic conditions, i.e. with homogeneous internal radiation from α-emitting actinides within the structure. Here, we provide for the first time experimental insight into the radiation-resistance mechanisms of americium pyrochlore 241Am2Zr2O7. We combined X-ray diffraction and X-ray absorption spectroscopy to probe changes of both the long-range and the short-range structure. The phase transition from the pyrochlore to the defect-fluorite structure was accompanied with an unusual negative lattice expansion. Once the fluorite structure was reached, neither volume changes nor amorphization were observed over a time course of 4 years corresponding to 0.8 dpa. The disorder relaxation proceeds through the simultaneous formation of cation antisites and oxygen Frenkel pairs, in line with former molecular dynamics studies. Moreover, EXAFS analysis revealed a disruption in the long-range order and a markedly different development in the local environments of zirconium and americium: while Am-O polyhedra show an increasing disorder, the Zr-O polyhedral units remain unchanged. However, they rotate along edges and corners, thereby reducing the structural strain imposed by the growing disorder around americium. We believe it is this particular property of the compound that provides the remarkable resistance to radiation, making it attractive for a wide range of nuclear applications.

Keywords: americium; EXAFS; XRD; Rietveld; ceramics; pyrochlore; transmutation; radiation resistance; Frenkel pairs

  • Inorganic Chemistry 48(2009), 5376-5381
    DOI: 10.1021/ic900369b
  • Lecture (Conference)
    Actinides 2009, 12.-17.07.2009, San Francisco, USA

Publ.-Id: 11920

Highest Pulsed Magnetic Fields in Science and Technology, Assisted by Advanced Finite-Element Simulations

Herrmannsdörfer, T.; Zherlitsyn, S.; Wosnitza, J.

The generation of high magnetic fields for scientific and industrial applications, in particular those techniques which meet critical limits of field strength, coil heating, and mechanical stress as well, require a careful design and modelling based on finite-element simulation. In order to describe the mutual dependences of the electrical, thermodynamical, and mechanical processes in such systems in a reasonable way, the use of multi-physics modules of the finite-element software packages becomes more and more relevant. Here, the designs based on finite- element simulations of pulsed magnetic field coils for extreme magnetic flux densities up to 100 Tesla as well as pulsed power supplies for the generation of electrical current pulses up to the Mega-Ampere range are presented. A survey on recent technical progresses in science and industry is given.

  • Invited lecture (Conferences)
    COMSOL Conference 2008, 04.-06.11.2008, Hannover, Germany

Publ.-Id: 11919

In-situ investigations at BM20-ROBL

Grenzer, J.; Baehtz, C.; Beckers, M.; Jeutter, N. M.; von Borany, J.

The beamline BM20 operated by the Forschungszentrum Dresden-Rossendorf is located at ESRF storage ring and divided into two experimental stations for spectroscopy and diffraction. A double crystal monochromator provides an energy range from 6 to 30 keV. A six-circle goniometer allows different scattering and diffraction methods like XRR, XRD, GID and GISAXS, additionally even in combination with X-ray spectroscopy. Different detector systems (point, one, two dimensional or energy dispersive) as well as an additional detector bank for large area detectors are available. A major part of ROBL-MRH experiments are performed as in-situ X-ray studies using a dual magnetron sputtering deposition chamber equipped optionally with an ion gun for ion beam bombardment and erosion. Using a hemispherical Beryllium dome scattering experiments can be carried out up to 1200°C under vacuum conditions.
The focus of the beamline research is on thin film investigations and on new nanostructured materials. X-ray investigations are a very important tool to find the correlation between the functional and the corresponding structural properties that are generating this function and to explain the influence of different deposition conditions, substrate parameters etc. by the underlying physical processes making it possible to design thin films with specific properties.
By the use of the deposition chamber for reactive magnetron sputtering thin films of Ti2AlN were for the first time synthesized. Different ways of synthesis, the thermal and phase behavior were investigated [1, 2].
A key element for the development of a new generation of solar cells are nanocrystalline materials. In-situ studies of the growth of SiO2/GeOx multilayers were carried out to create Ge nanocrystalls by subsequent thermal decomposition or directly by sputtering at elevated temperatures.

[1] C. Höglund et al.; Appl. Phys. Lett., 90, 174106, (2007).
[2] M. Beckers et al.; Appl. Phys. Lett., 89, 074101, (2006).

Keywords: synchrotron radiation; nanostructures

  • Lecture (Conference)
    Materials Science and Engineering 2008 - MSE08, 01.-04.09.2008, Nuernberg, Germany

Publ.-Id: 11918

X-ray scattering and diffraction from ion beam induced ripples in crystalline silicon

Biermanns, A.; Pietsch, U.; Grenzer, J.; Hanisch, A.; Facsko, S.; Carbone, G.; Metzger, T. H.

We report on periodic ripple formation on Si(001) surfaces after bombardment with Xe+ ions with energies between 5 and 35 keV under incidence angles of 65 degrees and 70 degrees. The sputter process leads to the formation of a rippled amorphous surface layer, followed by a rippled interface toward crystalline material. Using grazing-incidence small-angle scattering and diffraction, we show that the surface morphology is exactly reproduced at the interface. In addition, we observe that the crystal lattice close to the interface is anisotropically expanded. The lattice expansion parallel to the ripples is larger than those perpendicular to them.

Keywords: X-ray scattering; Ion beam irradiation

  • Journal of Applied Physics 104(2008)4, 044312
  • Lecture (Conference)
    XTOP 2008 - 9th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, 15.-19.09.2008, Linz, Austria

Publ.-Id: 11917

Neue Kupferchelatoren auf der Basis von pyridinhaltigen 1,4,7-triazacyclononan-Liganden

Ruffani, A.; Stephan, H.; Fähnemann, S.; Bergmann, R.; Steinbach, J.

Ziel/Aim: Ziel der Arbeit ist die Entwicklung von bifunktionellen Markierungsbausteinen für eine milde und selektive Radiomarkierung von biologisch aktiven Molekülen mit dem Positronenstrahler Kupfer-64. In diesem Zusammenhang sind Pyridin-haltige Derivate des 1,4,7-Triazacyclononans (TACN) besonders geeignet, weil sie sehr stabile Kupfer(II)-Komplexe bilden sowie eine schnelle Komplexbildungskinetik aufweisen. Weiterhin ist es leicht möglich, diese Verbindungen mit Maleinimid- und Isothiocyanat-Derivaten oder Aktivestern zu modifizieren und damit an Biomoleküle zu kuppeln. Erste Untersuchungen zeigen, dass Komplexe von Kupfer-64 mit einem TACN-Carbonsäurederivat sowie ein entsprechendes Peptidkonjugat auf der Basis eines stabilisierten Bombesinfragments BBN(7-14) eine hohe in vitro- und in vivo-Stabilität besitzen.[1] Bombesin und dessen Derivate weisen eine hohe Affinität zum Gastrin Releasing Peptide Rezeptor (GRPR) - der auf einer Vielzahl von Tumoren, wie Brust-, Prostata- und Pankreaskarzinomen, überexprimiert ist - auf. Aus diesem Grund sind radioaktiv markierte BBN-Derivate für die Diagnostik und Therapie von Tumoren sehr interessant.

Methodik/Methods: Die Umsetzung von Aminoethylmaleinimid mit einem TACN-Carbonsäurederivat durch Peptidkupplung mittels HBTU in Anwesenheit der Hünigbase DIPEA führt zu einer Maleinimid-haltigen TACN-Verbindung. In analoger Weise wurden über eine Peptidkupplung, stabilisierte BBN(7-14)-Derivate an TACN-Liganden gebunden. Ein weiterer vielseitig einsetzbarer Synthesebaustein wurde durch Umsetzung von zweifach pyridylmethylsubstituiertem TACN mit einem Boc-geschützten Phenylendiamin-Derivat erhalten. Durch Abspaltung der Schutzgruppe erhält man das freie Amin, das durch Behandlung mit Thiophosgen in das Isothiocyanat überführt wird.

Ergebnisse/Results: Markierungsstudien des Maleinimid-funktionalisierten TACN-Derivates mit Kupfer-64 weisen auf eine sehr schnelle Komplexbildungskinetik unter physiologischen Bedingungen hin. Untersuchungen mit dem Modellpeptid Glutathion zeigen, dass dieser Markierungsbaustein sehr effektiv an Thiolgruppen bindet. Bioverteilungsstudien mit Cu-64-Komplexen von TACN-Bombesin-Konjugaten in Wistar Ratten ergaben eine Anreicherung des Radiotracers im Pankreas. Untersuchungen mittels Kleintier-PET an PC-3 Tumor-Mäusen zeigten eine Akkumulation dieser Tracer im Tumorgewebe, so dass eine klare Visualisierung der Tumore möglich ist.

Schlussfolgerungen/Conclusions: Bifunktionelle Liganden auf der Basis von pyridinhaltigen TACN-Derivaten können unter physiologischen Bedingungen effektiv mit Kupfer-64 markiert werden. Die mit Maleinimid-, Isothiocyanat-Gruppen und Aktivester funktionalisierten TACN-Derivate können effizient an Biomoleküle gekuppelt werden. TACN-Bombesin-Konjugate besitzen ein hohes Anwendungspotential zur Darstellung von GRPR-reichem Gewebe.

[1] G. Gasser et al., Bioconjugate Chem. 2008, 19, 719-730.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A55
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11916

Time resolved and nonlinear spectroscopy of semiconductor quantum structures using an infrared free-electron laser

Helm, M.

there is no abstract available

Keywords: free electron laser; semicondcutor quantum structures; infrared spectroscopy

  • Lecture (others)
    Seminarvortrag Universität Marburg, 07.11.2008, Marburg, Deutschland

Publ.-Id: 11915

New Density Functional Theory Investigations of Vanadium Silicides

Thieme, M. B.; Gemming, S.

Vanadium and silicon form several binary compounds; the most well characterized structures have
the compositions V:Si= 3:1, 5:3, 6:5, 1:2. Spin-Density-functional band-structure calculations with the
Projector Augmented Wave-method have been carried out to investigate the structural properties and the
phase stability for the experimentally known binary crystals.

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11914

The system Vanadium:Silicon - an ion-beam generated diluted magnetic semiconductor? – a case study

Thieme, M. B.; Gemming, S.; Potzger, K.; Anwand, W.; Grötzschel, R.; Grenzer, J.

Since approximately 20 years we have controversial discussions about the possibility of ion beam generated diluted magnetic semiconductors (DMS) primarily transition metals in silicon. Now a detailed study has been done for the system Vanadium:Silicon. Vanadium and silicon form several binary compounds; the most well characterized structures have the compositions V:Si= 3:1, 5:3, 6:5, 1:2; as well as different constellations of substitutional and interstitial vanadium atoms in a silicon crystal matrix. Suitable magnetic properties of a semiconductor are important for DMS.

  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 03.09.2008, Dresden, Deutschland

Publ.-Id: 11913

Master Curve testing of highly irradiated IAEA RPV steels JRQ and JFL

Viehrig, H.-W.; Zurbuchen, C.

While the Master Curve (MC) method is gradually entering brittle fracture safety assessment procedures world-wide, knowledge is still lacking about its limits of applicability to highly neutron irradiated material. In this paper two reactor pressure vessel (RPV) steels A533B Cl. 1 (IAEA reference material code JRQ) and A508 Cl.3 (code JFL) were scrutinized for possible deviations of the postulated invariant MC shape and the MC validity for macroscopically inhomogeneous microstructure. Besides tensile and Charpy-V tests, MC tests were performed on Charpy size three-point bend specimens in the unirradiated, neutron irradiated with fluences up to nearly 1020 n/cm² (E>1MeV) and recovery heat treated condition. Evaluation procedures include Master Curve reference temperature T0 determination according to ASTM E1921-05 as well as additional analysis methods such as SINTAP, multimodal MC method (MML) and the Unified Curve (UC). Integrity assessment according to ASME Code Cases N-629 and N-631has been applied. It is shown that the standard MC concept provides a precise description of the fracture toughness for all conditions, even exceptionally well for the highly irradiated state. No MC shape change could be observed, whereas the UC concept indicates a significant influence of irradiation on the fracture toughness curves for the highly irradiated JRQ.

Keywords: Fracture Toughness; RPV steels, neutron irradiation, Master Curve; Unified Curve

  • Lecture (Conference)
    Workshop on Trend Curve Development for Surveillance Data with Insight on Flux Effects at High Fluence: Damage Mechanisms and Modelling, 19.-21.11.2008, Mol, Belgium

Publ.-Id: 11912

THEREDA - Online

Richter, A.; Brendler, V.

Der Zugang zur THEREDA-Datenbank erfolgt über die URL Der Internetzugang vereint dabei die Schnittstelle für externe Nutzer zum Abfragen von Datensätzen sowie eine Schnittstelle zur Administration des gesamten Internetauftritts im Rahmen des Content Management Systems (CMS) Joomla! Joomla! ist Open Source Software, durch die große Community, die das Projekt ständig weiterentwickelt, ist gewährleistet, dass ein problemloser Zugriff auf den Inhalt und die Datenbank über einen sehr langen Zeitraum erfolgen kann. Mit Joomla! verfügt THEREDA über ein sehr gutes Tool, die Datenbank mit geringem Pflegeaufwand und über einen langen Zeitraum zur Verfügung zu stellen. Über erhalten Besucher der Webseite Informationen zum Projekt und den THEREDA-Partnern, können Dokumente downloaden sowie Links zu anderen relevanten Projekten finden. Zusätzlich nutzen die Mitglieder des Verbundprojektes die Internetseite als Intranet (nach Anmeldung). Im Vortrag werden der gegenwärtige Stand des THEREDA-Online-Auftrittes und die interaktiven Möglichkeiten für die Nutzer vorgestellt.

Keywords: THEREDA; Thermodynamic Database; online; downloads; interactive; CMS; Joomla

  • Lecture (Conference)
    Fachgespräch "Entwicklung einer thermodynamischen Referenzdatenbasis - THEREDA", 12.11.2008, Karlsruhe, Deutschland

Publ.-Id: 11911

Respiratory Gating Facilitating 4D Imaging in MRI, CT, and FDG-PET for GTV Definition in Patients with NSCLC

Abolmaali, N.; Abramyuk, A.; Koch, A.; Richter, C.; Hoinkis, C.; Zips, D.; Zöphel, K.; Enghardt, W.; Baumann, M.

Respiratory motion blurs PET-images and may cause localization errors in studies acquired using breath holding such as CT and MRI. To reduce motion related influences on radiation therapy planning of lung cancer, image acquisition may be gated. The aim of our study was to compare motion of primary lung tumors as detected by respiration gated data acquired with PET, CT, MRI.

So far, this ongoing study included four patients (median age 72.5 years) with NSCLC scheduled for radiation therapy. All patients were investigated under free breathing conditions and respiratory gated FDG-PET, CT and MRI. Image data was separated into eight comparable gates uniformly distributed over the breathing cycle. After blinded GTV-definition, volumes and centers of volumes (COV) were generated from all gates and all modalities. Comparative statistics were done using t-tests, confidence intervals and Lin's concordance analysis.

Median tumor volumes in PET, CT and MRI were 28 ml, 69 ml, and 46 ml, respectively. t-tests revealed significant differences for the comparison CT/MRI (p=0.04) and PET/CT (p=0.05), but not for MRI/PET (p=0.09). The medians of the maximum distances the COV traveled during the entire breathing cycle in PET, CT and MRI were 0.42 cm, 0.95 cm, 0.93 cm, respectively. t-tests revealed nearly significant differences between PET and CT (p=0.06) and MRI and PET (p=0.06), while the result for CT and MRI was in good agreement (p=0.74). Lin’s concordance analysis (OCCC=0.172) revealed best congruency between CT and MRI (rho=0.55), only fair congruency between MRI and PET (rho=0.2) and poor congruency between PET and CT (rho=0.02).

In our early experience, the differences in GTV-definition of NSCLC in 4D imaging by PET, CT and MRI are mainly related to the observer’s experience. As shown in other tumors before, PET revealed the smallest tumor volume. Due to the low movement of the tumors evaluated in the patients included so far, results are preliminary. Nevertheless, results suggest that MRI may be applicable in radiation therapy planning for GTV-definition. The inclusion of a higher number of patients with pronounced tumor movement during breathing is required.

Gated 4D imaging in NSCLC may increase planning accuracy in radiation oncology. In selected patients, gated radiation therapy might be advantageous and may reduce toxicity in normal tissues.

  • Lecture (Conference)
    RSNA 2008, 30.11.-05.12.2008, Chicago, USA

Publ.-Id: 11910

Small animal PET with hCT-derived cell-penetreting peptides

Bergmann, R.; Közle, I.; Neundorf, I.

Cell-penetrating peptides (CPP) derived from the native peptide hormone human calcitonin (hCT) represent a high potential drug delivery system for in vivo intracellular targeting of diagnostic and therapeutic compounds. Cell penetration of hCT-derived substances was verified in vitro, however, the knowledge about CPP in vivo distribution and metabolism is very limited. Therefore we studied the in vivo radiopharmacology of Ga-68 radiolabeled DOTA modified, hCT-derived CPP in rats using small animal PET (1).

Three hCT-derived peptides (hCT(9-32), LGTYTQDFNKFHTFPQTAIGVGAPNH2; [f12,16]-hCT(9-32), LGTfTQDfNKFHTFPQTAIGVGAP-NH2; random (rd)-hCT(9-32), FLTAGQNTIQTPVKTGGHFPFADY-NH2) were at the N-terminus modified with DOTA. The internalization of the stabilized peptide, biodistribution and kinetics of the radiolabeled Ga-68-DOTA-hCT(9-32) or Ga-68-DOTA-[f12,16]-hCT(9-32) or Ga-68-DOTA-rd-hCT(9-32) were studied with small animal PET. The arterial blood at different time points, and urine were analyzed for radio-metabolites.

Ga-68-DOTA-[f12,16]-hCT(9-32) was in vitro internalized. In vivo the radio-peptides were eliminated mainly by the renal system, more than 50% of the injected dose was found at 60 min after injection in the urine, only small amounts of the activity were detected in the intestine. The general activity retention in the body was low, except the kidneys. The blood clearance of the original peptides reached terminal half-lifes of Ga-68-DOTA-hCT(9-32) 15.9 min, Ga-68-DOTA-[f12,16]-hCT(9-32) 20.9 min, Ga-68-DOTA-rd-hCT(9-32) 15.8 min; the relative AUC in comparison to Ga-68-DOTA-hCT(9-32) were 100%, 170%, and 51%, respectively. The patterns of metabolic cleavage in the arterial blood were different. The Ga-68-DOTA-[f12,16]-hCT(9-32) was metabolized to three radio-metabolites after 30 min, the other radiopeptides were degraded to more than five radioactive metabolites.

It was shown that D-amino acid modifications of the sequence hCT(9-32) resulted in an increased in vivo stability and lower retention in the kidney cortex. The blood clearance and the elimination of the Ga-68-DOTA-peptides were relatively high and should be decreased by structural changes to enhance the tissue uptake of this drug carrier system.

(1) Neundorf I, Rennert R, et Bergmann R, Bioconjug Chem. 2008 Aug;19(8):1596-603.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A78
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11909

Phasenkorrelierte Schwächungskorrektur von 4D-PET mit Hilfe von 4D-CT

Richter, C.; Just, U.; Pönisch, F.; Enghardt, W.

wird nachgereicht

  • Lecture (Conference)
    „Der Wiener Kongress“ - DEGRO ÖGRO 2008, 01.-04.05.2008, Wien, Austria
  • Contribution to proceedings
    „Der Wiener Kongress“ - DEGRO ÖGRO 2008, 01.-04.05.2008, Wien, Österreich
    Strahlentherapie und Onkologie - Abstactband zum DEGRO-ÖGRO-Kongress, München: Urban&Vogel, 61-61

Publ.-Id: 11908

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