Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34800 Publications

PET und Bestrahlungsplanung - technische Aspekten / PET and Radiation Treatment Planning - Technical Aspects

Wolf, U.; Hofheinz, F.; Oehme, L.; van den Hoff, J.


Die Integration der PET in die Bestrahlungsplanung wirft verschiedene technische Probleme auf, welche zurzeit überwiegend noch nicht zufriedenstellend gelöst sind, gegenwärtig aber intensiv untersucht werden. Erste Lösungen für Teilaspekte wie etwa die geometrisch korrekte ROI-Abgrenzung und die Übersetzung dieser Information in DICOM-RT-Structure-Sets für den Import in die Bestrahlungsplanungssysteme existieren mittlerweile, sind aber noch nicht allgemein verfügbar. Es ist jedoch zu erwarten, dass sich die dynamische technische Entwicklung in den nächsten Jahren fortsetzen und zu einer Lösung der noch bestehenden Probleme führen wird.


Integration of PET into radiation treatment planning causes several technical problems, which have not yet been solved satisfactory up to now, but which are currently investigated intensively. First solutions of some aspects such as geometrically correct ROI delineation and the translation of this information into DICOM-RT Structure Sets for import into the radiation treatment planning systems have already been developed, but are not yet generally available. It is to be expected, however, that the dynamic technical development will continue in the next years and lead to solution of the currently persisting problems.

Keywords: PET, CT; radiation treatment planning; DICOM-RT - 3D-ROIs; volumetry

Publ.-Id: 11094

PET in der Strahlentherapie: Perspektiven / PET in Radiation Oncology - Perspectives

Baumann, M.; Beuthien-Baumann, B.; Zips, D.

Die Positronen-Emissions-Tomografie (PET) hat einen wichtigen Stellenwert in der modernen Strahlentherapie erlangt. Die Integration der funktionellen PET-Daten in die Bestrahlungsplanung wurde durch die Fusion von CT und PET in einem Gerät wesentlich erleichtert. Entwicklungs- und Optimierungsbedarf besteht jedoch in der Definition der Tumorgrenzen im PET und im Umgang mit Atembewegungen. Neben dem am häufigsten zur Anwendung kommenden Radiopharmakon 18F-Fluordesoxyglukose (FDG) sind die Anwendung von Hypoxiemarkern und Radiotracerentwicklungen für die Visualisierung anderer definierter radiobiologischer Resistenzmechanismen wünschenswert.

Positron emission tomography (PET) has evolved as an important tool in modern radiotherapy. Integration of functional PET data into radiation treatment planning is facilitated due to PET-CT scanner, optimizing data fusion. Optimization of definition of tumour borders and reduction of movement artifacts is warranted. Besides the application of 18F-fluorodeoxyglucose (FDG) utilization of tracers visualizing hypoxia and the development of novel tracers depicting other defined biological mechanisms of radioresistance is a promising avenue for future research.

Keywords: PET, CT; FDG; radiation treatment planning; radiation biology; hypoxia; theragnostics

Publ.-Id: 11093

Hydrolysis and dimerization of Th4+ ion

Tsushima, S.

Hydrolysis of Th4+ in aqueous solution was studied by density functional theory (DFT) calculations. First, stable coordination numbers (CNs) of Th4+ hydrolysis products were studied systematically, and it was found that the CN significantly decreases as a stepwise hydrolysis reaction proceeds. The fourth hydrolysis product Th(OH)4 0 has CN 6 with an octahedron coordination. Th(OH)4 0 can readily form a dimer complex Th2(OH)8 0 via a Th-OH-Th bridging through an exergonic reaction with a Gibbs energy change of -24.0 kJ/mol. Consequently, dimerization inhibits Th(OH)4 0 to stay as stable aqueous species. The calculated result is in agreement with the fact that there is no direct evidence to confirm the presence of Th(OH)4 0 while oligomeric species such as Th4(OH)16 0 are presumably present. Similar calculations on the Th4+ disulfato complex reveal that the CN and the average Th-O distance of Th(SO4)2 0 remain almost the same as those in the Th4+ aquo ion, which is also in agreement with experimental data.

Keywords: Hydrolysis; tetravalent; actinide; thorium; quantum chemistry

Publ.-Id: 11092

Ion-induced nanopatterns on silicon: experiment, theory, and application

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 reproduced 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.
In this talk, recent experimental results on the evolution of ripple morphologies on Si(100) surfaces during high-fluence ion sputtering will be presented and compared to numerical integrations of the damped Kuramoto-Sivashinsky equation. In addition, promising applications of nanorippled substrates as templates in thin film growth will be discussed.

  • Lecture (others)
    Seminar, 15.02.2008, Madrid, Spain
  • Lecture (others)
    Seminar, 27.02.2008, Madrid, Spain

Publ.-Id: 11091

Medical Physics Activities in the Integrated EU Project BioCare

Möckel, D.

Presentation of the Medical Physics Activities in the Integrated EU Project BioCare

  • Invited lecture (Conferences)
    3rd Meeting of the Scientific Advisory Board of OncoRay, 28.02.2008, Dresden, Deutschland

Publ.-Id: 11090

The interplay of PVD growth parameter and nanostructuring of C:Co and C:V nanocomposites

Berndt, M.; Abrasonis, G.; Krause, M.; Mücklich, A.; Kolitsch, A.; Möller, W.

The growth regimes of C:V and C:Co nanocomposite thin films (metal content of ~15 and 30 at.%) grown by ion beam co-sputtering in the temperature range of RT-500°C are investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy at two excitation wavelengths (532 nm and 785 nm) have been used to characterize the microstructure of carbon and metal coexisting constituents of the nanocomposites. In order to reveal the influence of the transition metal on the encapsulating matrix, pure carbon films were deposited at the same temperatures.
C:Co and C:V nanocomposites exhibit a fine-grained structure at deposition temperatures below 300°C. At higher temperatures C:Co films tend to form nanocolumns, whereas the globular structure is preserved for C:V. X-ray patterns show low degree of crystallinity of the nanoparticles in C:Co and C:V composites.
Raman spectroscopy results show that the presence of metal significantly enhances the formation of aromatic clusters. This enhancement occurs independently on metal nanoparticle size, shape and phase.

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.2.2008, Berlin, Germany

Publ.-Id: 11089

Room temperature ferromagnetism in ZnO films due to defects

Xu, Q.; Schmidt, H.; Zhou, S.; Potzger, K.; Helm, M.; Hochmuth, H.; Lorenz, M.; Setzer, A.; Esquinazi, P.; Meinecke, C.; Grundmann, M.

ZnO films were prepared by pulsed laser deposition on a-plane sapphire substrates under N2 atmosphere. Ferromagnetic loops were obtained with the SQUID at room temperature, which indicate a Curie temperature much above room temperature. No clear ferromagnetism was observed in intentionally Cu-doped ZnO films. This excludes that Cu doping into ZnO plays a key role in tuning the ferromagnetism in ZnO. 8.8 % negative magnetoresistance probed at 5 K at 60 kOe on ferromagnetic ZnO proves the lack of s-d exchange interaction. Anomalous Hall effect (AHE) was observed in ferromagnetic ZnO as well as in non-ferromagnetic Cu-doped ZnO films, indicating that AHE does not uniquely prove ferromagnetism. The observed ferromagnetism in ZnO is attributed to intrinsic defects.

Keywords: diluted magnetic semiconductor; ZnO; ferromagnetism; anomalous Hall effect; magnetoresistance

Publ.-Id: 11088

Enzymatic properties of an ecto-nucleoside triphosphate diphosphohydrolase from Legionella pneumophila; substrate specificity and requirement for virulence

Sansom, F. M.; Riedmaier, P.; Newton, H. J.; Dunstone, M. A.; Müller, C. E.; Stephan, H.; Byres, E.; Beddoe, T.; Rossjohn, J.; Cowan, P. J.; D'Apice, A. J. F.; Robson, S. C.; Hartland, E. L.

Legionella pneumophila is the predominant cause of Legionnaires’ disease, a severe and potentially fatal form of pneumonia. Recently, we identified an ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) from L. pneumophila, termed Lpg1905, which enhances intracellular replication of L. pneumophila in eukaryotic cells. Lpg1905 is the first prokaryotic member of the CD39/NTPDase1 family of enzymes that are characterized by the presence of five apyrase-conserved regions (ACR) and the ability to hydrolyse nucleoside tri- and diphosphates. Here we examined the substrate specificity of Lpg1905 and showed that apart from ATP and ADP, the enzyme catalysed the hydrolysis of GTP and GDP but had limited activity against CTP, CDP, UTP and UDP. Based on amino acid residues conserved in the ACR regions of eukaryotic NTPDases, we generated five site directed mutants, Lpg1905E159A, R122A, N168A, Q193A and W384A. While the mutations, E159A, R122A, Q193A and W384A abrogated activity completely, N168A resulted in decreased activity because of less affinity for nucleotides. When introduced into the lpg1905 mutant strain of L. pneumophila, only N168A (and not the isoforms E159A, R122A, Q193A and W384A) partially restored the ability of L. pneumophila to replicate in THP-1 macrophages. Following intratracheal inoculation of A/J mice, none of the Lpg1905E159A, R122A, Q193A, W384A or N168A isoforms were able to restore virulence to an lpg1905 mutant during lung infection, thereby demonstrating the importance of NTPDase activity to L. pneumophila infection. In addition, the kinetic studies undertaken here demonstrated important differences to mammalian NTPDases, which may be exploited in the design of novel inhibitory compounds to microbial NTPDases for use as anti-infective agents.

  • Journal of Biological Chemistry 283(2008)19, 12909-12918

Publ.-Id: 11087

Magnetic properties of amorphous, p-type conducting CuCr0.95Mg0.05O2 and CuCr0.93Mg0.05Mn0.02O2

Xu, Q.; Schmidt, H.; Zhou, S.; Potzger, K.; Helm, M.; Hochmuth, H.; Lorenz, M.; Meinecke, C.; Grundmann, M.

CuCr0.95Mg0.05O2 has been reported to be p-type oxide semiconductor with the highest conductivity determined by the Seebeck effect [1]. We prepared conductive, polycrystalline and amorphous CuCr0.95Mg0.05O2 and CuCr0.93Mg0.05Mn0.02O2 films on a-plane sapphire substrates by pulsed laser deposition under different O2 partial pressure and substrate temperature. Hall measurements were performed to study the majority carrier type in these films. The polycrystalline CuCr0.95Mg0.05O2 and CuCr0.93Mg0.05Mn0.02O2 films are n-type conducting up to 290 K, while in amorphous CuCr0.95Mg0.05O2 and CuCr0.93Mg0.05Mn0.02O2 films the type of majority charge carriers changes from n-type to p-type around 270 K. Interestingly, the structure has little influence on the magnetic properties of the films. The well-known antiferromagnetic to paramagnetic transition was observed in both polycrystalline and amorphous CuCr0.95Mg0.05O2 films at 25 K, while the CuCr0.93Mg0.05Mn0.02O2 films revealed no antiferromagnetic ordering below 25 K.
[1] R. Nagarajan et al. J. Appl. Phys. 89, 8022 (2001)

Keywords: diluted magnetic semiconductor; p-type oxide; Hall effect

  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 24.-29.02.2008, Berlin, Germany

Publ.-Id: 11086

High energy Xe+ ion beam induced ripple structures on silicon

Hanisch, A.; Grenzer, J.; Facsko, S.; Winkler, I.; Biermanns, A.; Grigorian, S.; Pietsch, U.

Ion beam bombardment on semiconductor surfaces leads to welldefined morphological structures in the nanoscale range. Due to the impact of ions a self-organized wave-like surface structure develops. Ion bombardment causes an amorphization of a surface-adjacent layer of several nanometers and creates a periodical structure on the surface as well as at the amorphous-crystalline interface. We investigate the dependence of the periodicity on the crystallography of (100) silicon bombarded with Xe+ ions, the ion beam incidence and the azimutal angle of the sample surface. So far we found that the ripple wavelength scales with the ion energy in a range of 5 to 70 keV. In order to understand the initiation of the ripple formation we also ask the question which role the initial surface structure plays. Therefore we investigate the formation of ripples on pre-structured and rough surfaces such as wafers with an intentional miscut. Therefore, we not only introduce a certain initial roughness but also vary the orientation of the (100) lattice plane in respect to the surface. We try to distinguish between ion beam induced surface defects (sputter erosion) and the influence of the crystalline Si lattice (strain) on the ripple formation.

Keywords: nanostructures ion-beam patterning

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.08, Berlin, Germany

Publ.-Id: 11085

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

Biermanns, A.; Pietsch, U.; Grigorian, S.; Grenzer, J.; Facsko, S.; Hanisch, A.; Carbone, D.; 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 40keV. 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 grazingincidence - 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. This different relaxation may play a driving role in pattern formation at the interface.

Keywords: ion-beam erosion X-ray scattering nanostructures

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.08, Berlin, Germany

Publ.-Id: 11084

Magnetoresistance in n-type conducting Co-doped ZnO

Xu, Q.; Hartmann, L.; Schmidt, H.; Hochmuth, H.; Lorenz, M.; Spemann, D.; Grundmann, M.

Series of Co-doped Al-codoped ZnO films with electron concentration at 5 K ranging from 8.31017 cm-3 to 9.91019 cm-3 were prepared by pulsed laser deposition under different O2 pressure and substrate temperature. The magnetoresistance (MR) effect was studied between 5 K and 290 K with fields up to 6 T, showing large electron concentration and temperature dependence. A large positive MR of 124 % has been observed in the film with the lowest electron concentration of 8.31017 cm-3, while only negative MR of –1.9 % was observed in the film with an electron concentration of 9.91019 cm-3 at 5 K. The positive MR is attributed to the quantum correction on the conductivity due to the s-d exchange interaction induced spin-splitting of the conduction band [1]. The negative MR is attributed to the magnetic field suppressed weak localization [1]. The modelled superimposed positive and negative MR agrees well with the experimentally observed MR and hints towards the physical origin of MR in Co-doped ZnO [2].
[1] P. A. Lee and T. V. Ramakrishnan, Rev. Mod. Phys. 57, 287 (1985)
[2] Q. Xu, L. Hartmann, H. Schmidt, H. Hochmuth, M. Lorenz, D. Spemann, and M. Grundmann, Phys. Rev. B 76, 134417 (2007)

Keywords: diluted magnetic semiconductors; ZnO; magnetoresistance; exchange interaction; weak localization

  • Lecture (Conference)
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 24.-29.02.2008, Berlin, Germany

Publ.-Id: 11083

Polycrystalline Mn-alloyed indium tin oxide films

Scarlat, C.; Schmidt, H.; Xu, Q.; Vinnichenko, M.; Kolitsch, A.; Helm, M.; Iacomi, F.

Magnetic ITO films are interesting for integrating ITO into magnetooptoelectronic devices. We investigated n-conducting indium tin oxide (ITO) films with different Mn doping concentration which have been grown by chemical vapour deposition using targets with the atomic ratio In:Sn:Mn=122:12:0, 114:12:7, and 109:12:13 [1]. The average film roughness ranges between 30 and 50 nm and XRD patterns revealed a polycrystalline structure. Magnetotransport measurements revealed negative magnetoresistance for all the samples, but high field positive MR can be clearly observed at 5 K with increasing Mn doping concentration. Spectroscopic ellipsometry (SE) has been used to prove the existence of midgap states in the Mn-alloyed ITO films revealing a transmittance less than 80%. A reasonable model for the ca. 250 nm thick Mn-alloyed ITO films has been developed to extract optical constants from SE data below 3 eV. Depending on the Mn content, a Lorentz oscillator placed between 1 and 2 eV was used to model optical absorption below the band gap.[1]C. Baban et al. E-MRS 2007, Straßbourg.

  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11081

Empirical pseudopotential calculation of strain induced birefringence in ZnO

Fritsch, D.; Schmidt, H.

One big challenge in the fabrication of ZnO-based heterostructure devices is the lattice mismatch between ZnO films and substrates and the different thermal expansion coefficients inducing biaxial strain. There is currently also much interest in ZnO doped with 3d transition metal ions for spintroncis applications and the detection of ferromagnetic signatures by magneto-optical measurements of ordering induced birefringence being most intense around the critical point structure of the dielectric function. A quantitative understanding of Zeeman splitting far away from the center of Brillouin zone is still an open question and requires a separation of strain and magnetic field induced modifications of electronic band strcucture. We report on the effect of strain on the birefringence in ZnO films grown on Al2O3 or on SiC substrates. The imaginary part of the dielectric function has been calculated b means of the empirical pseudopotential method. Thereby we also accounted for relativistic effects in form of te spin-orbit interaction, for the energy-dependence of the crystal potential through the use of nonlocal model potentials, and for excitonic conrtibutions to the dielectric functiuon fue to discrete excitonic states and Coulomb enhanced band-to-band transitions.

Keywords: ZnO; birefringence

  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11080

Magnetism of the high spin molecules [Mn4L6](BF4)2·2CH3-CN·H2O and [CrIIIMnII3 (PyA)6Cl3]

Prinz, M.; Raekers, M.; Kuepper, K.; Chaudhuri, P.; George, S. J.; Neumann, M.

We have studied the electronic and magnetic structure of high spin molecules by spectroscopic investigations in combination with theoretical calculations. We present results on [MnII4 L6](BF4)2·2CH3CN·H2O (Mn4)and the hetero nuclear, spin frustrated molecule [CrIIIMnII3 (PyA)6Cl3] (CrMn3), which have been studied using X-ray photoelectron spectroscopy (XPS), X-ray absorption and emission spectroscopy (XAS, XES), and X-ray magnetic circular dichroism (XMCD). Magnetic measurements of Mn4 show a magnetization saturation of about 20 μB/f.u. at a magnetic field of B = 7 T and a temperature of T = 2 K. From XMCD measurements of Mn4 at T = 5 K and B = 5 T we obtained a high magnetic moment of 18.5 μB/f.u, whereas a quenching of the Mn orbital moments was observed (morb = 0.4 μB/f.u.). The element selective MnII and CrIII dichroic signals of the CrMn3 complex at B = 5 T and T = 5 K where recorded. For the three MnII ions a magnetic moment of 15 μB was determined. For both complexes we will present a comparison to XAS/XMCD charge transfer multiplet calculations.

Keywords: magnetic high spin molecules; electronic structure; x-ray magnetic circular dichroism

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

Publ.-Id: 11079

Manganese implanted GaAs films

Bürger, D.; Schmidt, H.; Xu, Q.; Kolitsch, A.; Winnerl, S.; Schneider, H.; Zhou, S.; Potzger, K.; Helm, M.; Biehne, G.; Gottschalch, V.

Electron spin preservation has been proven in unmagnetic GaAs over several μm by time-resolved luminescence measurements. The synthesis of Mn-alloyed GaAs has introduced a controllable spin degree of freedom in the GaAs device technology. Approx. 1 μm thick n-type (Si) and p-type (Zn) GaAs films have been grown on highly conducting n- and p-GaAs substrates by metalorganic chemical vapour deposition. For magnetotransport measurements reference samples have been grown on insulating substrates. Mn+ ion beam implantation with 300/150 keV at 200°C yielded a boxlike Mn-implantation profile of the 250 nm thick GaAs surface layer with a nominal implantation dose dependent Mn content of 1 and 5 at%. Rapid thermal annealing has been performed at 650°C for 10 s. Magnetic properties have been investigated by means of SQUID-magnetometry. The relation between concentration of free charge carriers, defect formation and magnetoresistance effects in manganese implanted GaAs will be discussed.

Keywords: GaAs; ion implantation; magnetic semiconductor; magnetoresistance; DLTS

  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11078

Charge accumulation in a type-II Ge/Si heterostructure

Henkel, C.; Biehne, G.; Grundmann, M.; Wagner, G.; Stoffel, M.; Schmidt, O. G.; Schmidt, H.

The main motivation for mixing a small amount of Ge into Si for example by the self-organized growth of a stack of Ge dots into Si [1], is the controlled modification of the electronic band structure in strained Si namely charge carrier mobility and optical transition probabilities [2]. We report on charge accumulation in fivefold stacks of Ge quantum dots embedded in the n-region of a p+n-Si diode. By means of thermal admittance spectroscopy, capacitance voltage and deep level transient spectroscopy measurements [3] electron confinement in the type II Ge/Si-heterostructures, barrier effects of the quantum wells and wetting layers and defect states in the n-region of the sample associated with the surrounding Si-matrix have been probed. By relating these results to the self consistently modeled electronic band-structure and capacitance voltage characteristic charge accumulation in quantum confined electron states in the investigated type II Ge/Si-heterostructures is clearly revealed.
[1] A. Malachias, T. H. Metzger, M. Stoffel, O.G. Schmidt and V. Holy, Thin Solid Films 515, 5587 (2007)
[2] O.G. Schmidt and K. Eberl, Phys. Rev. B 61, 20 (2000)
[3] M. Gonschorek, H. Schmidt, J. Bauer, G. Benndorf, G. Wagner, G.E. Cirlin and M. Grundmann, Phys. Rev. B 74, 115312 (2006)

Keywords: Ge/Si; space charge spectroscopy

  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11077

High Resolution Measurement of the Thermal Expansion Coefficient of Semiconductor Multilayer Lateral Nanostructures

Brueser, B.; Pietsch, U.; Grigorian, S.; Panzner, T.; Grenzer, J.; Zeimer, U.

We measured the thermal expansion coefficient of a vertically stacked multi-quantum-well structure buried under a thick GaAs top layer before and after lateral patterning of the GaAs top layer. After patterning the thermal expansion coefficient of the whole multi-quantum-well structure differs from that of the planar structure by about 20%. Based on calculations in terms of methods of finite elements the effect is explained by the influence of the strain field originating from the bottom edges of the etched nanostructure. Due to the long range nature of this strain field the strain release within the individual quantum wells changes as a function from the distance from the valley.

Keywords: nanostructrues; X-ray scattering

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany
  • Physica Status Solidi (A) 205(2008)2, 316-320

Publ.-Id: 11076

X−ray investigations on CoSi2 nano wires manufactured by focused ion beam synthesis

Grenzer, J.; Bischoff, L.; Biermanns, A.

Nanowires and chains of nanoparticles are of emerging interest in nano-electronics, nano-optics and plasmonics as well as for their monolithic integration into microelectronic devices; CoSi2 is a promising material due to its CMOS-compatibility in micro-electronics technology. It shows metallic behaviour with low resistivity and high thermal stability. It is well known that cobalt disilicide films can be formed in silicon by implanting Co in stoichiometric concentration and a subsequent annealing procedure. Ion beam synthesis allows the fabrication of epitaxial buried or surface CoSi2 layers on silicon. Sub-micron patterns with feature dimensions much smaller than 100nm can be directly produced by writing focused ion beam (FIB) cobalt implantation.
We have studied the strain of the Si host lattice in the surrounding area of a single nanostructures depending on their crystallographic orientation using high resolution x-ray diffraction in combination with a highly focused (≈ 3µm) x-ray beam at the beam line ID1 at the ESRF. The pattern measured directly on the wire shows a small peak indicating tensile strain (approx. −1.4%). This feature can be only found if the beam focused on a nano wire whereas its intensity changes
with the layer width.

Keywords: nao wire; x-ray scattering

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany
  • Poster
    9th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, XTOP 2008, 15.-19.09.2008, Linz, Austria

Publ.-Id: 11075

Interaction between molten corium UO2+X - ZrO2- FeOy and VVER vessel steel

Bechta, S. V.; Granovsky, V. S.; Khabensky, V. B.; Krushinov, E. V.; Vitol, S. A.; Sulatsky, A. A.; Gusarov, V. V.; Almiashev, V. I.; Lopukh, D. B.; Bottomley, D.; Fischer, M.; Piluso, P.; Miassoedov, A.; Tromm, W.; Altstadt, E.; Fichot, F.; Kymalainen, O.

In case of an in-vessel corium retention (IVR) the deterioration of vessel steel properties can be caused both by the steel melting and by its physicochemical interaction with corium. The interaction behavior has been studied in the medium-scale experiments with a prototypic corium within the METCOR project. The resulting experimental data give an insight into the steel corrosion during its interaction with UO2+x-ZrO2-FeOy melt in air and steam. It has been observed that the corrosion rate is almost the same in air and steam atmosphere; if the temperature on the interaction interface increases beyond a certain level, corrosion intensifies, which is explained by the formation of liquid phases in the interaction zone. The available experimental data have been used for developing a correlation of corrosion rate versus heat flux density and temperature.

Keywords: Physiochemical Corium-steel interaction; vessel ablation

  • Contribution to proceedings
    2008 International Congress on Advances in Nuclear Power Plants (ICAPP), 08.-12.06.2008, Anaheim, California, United States
  • Lecture (Conference)
    2008 International Congress on Advances in Nuclear Power Plants (ICAPP '08), 08.06.-12.08.2008, Anaheim, California, United States

Publ.-Id: 11074

European Research on the Corium issues within the SARNET Network of Excellence

Journeau, C.; Bonnet, J. M.; Godin-Jacqmin, L.; Piluso, P.; Tarabelli, D.; Altstadt, E.; et al.

Within SARNET, the corium topic covers all the behaviors of corium from early phase of core degradation to in or ex-vessel corium recovery with the exception of corium interaction with water, direct containment heating and fission product release. The corium topic regroups in three work packages the critical mass of competence required to improve significantly the corium behavior knowledge.
The spirit of the SARNET networking is to share the knowledge, the facilities and the simulation tools for severe accidents, so to reach a better efficiency and to rationalize the R&D effort at European level. Extensive benchmarking has been launched in most of the areas of research. These benchmarks were mainly dedicated to the recalculation of experiments, while, in the next periods, a larger focus will be given to integral experiments or reactor applications. Eventually, all the knowledge will be accumulated in the ASTEC severe accident simulation code through physical model improvements and extension of validation database. This paper summarizes the progress that has been achieved in the frame of the networking activities. A special focus is placed on the melt pool and debris coolability and corium-concrete interaction, in which, the effects due to multidimensional geometries and heterogeneities has been shown, during SARNET, to play a crucial role and for which further research is still needed.

Keywords: Nuclear reactors; severe accident; in-vessel cooling ex-vessel corium cooling

  • Contribution to proceedings
    2008 International Congress on Advances in Nuclear Power Plants (ICAPP'08), 08.-12.06.2008, Anaheim, United States
    Proceedings of ICAPP ‘08
  • Lecture (Conference)
    2008 International Congress on Advances in Nuclear Power Plants (ICAPP'08), 08.-12.06.2008, Anaheim, California, United States

Publ.-Id: 11073

Progress on PWR lower head failure predictive models

Koundy, V.; Fichot, F.; Willschuetz, H.-G.; Altstadt, E.; Nicolas, L.; Lamy, J.-S.; Flandi, L.

A good understanding of the mechanical behaviour of the reactor pressure vessel (RPV) lower head is necessary both for severe accident assessment and for the definition of appropriate accident mitigation strategies. Indeed, a well-characterized failure of the lower head leads to a better evaluation of the quantity and kinetics with which core material can escape into the containment. These are the initial conditions for several ex-vessel events such as direct heating of the containment or molten core-concrete interaction.
In this context, the objectives of the joint on-going work of the WP10-2 group of SARNET are: 1) improvement of predictability of the time, mode and location of RPV failure; 2) development of adequate models with the ultimate aim of being included into integral codes; 3) interpretation / analysis of experiments with models / codes combined with sensitivity studies; and 4) better understanding of the breach opening process in order to better characterize the corium release into the containment.
Different approaches are considered: a simplified but well predicting model recently implemented in the severe accident Astec and Icare-Cathare codes, and viscoplasticity models implemented in the Cast3m, Ansys and Code_Aster finite element codes. Several failure criteria are considered: stress criterion, strain criterion and damage evaluation (coupled way or post-evaluation).
In this paper, the OLHF-1 experiment has been used to assess the models, to perform sensitivity studies and to evaluate failure criteria that could be applied in the case of reactors. All the partners performed 2D axisymmetric analyses, allowing the evaluation of time, mode and location of vessel failure. Nevertheless, CEA conducted further 3D calculations in order to study crack propagation and the corresponding results will be presented separately at the end of the paper. The numerical formulation of the different models used is given and a comparison of experimental and numerical results is presented. The paper also shows the progress made with the objective of defining failure criteria that can be used for reactor vessel applications.

Keywords: lower head failure; severe accident; pressurized water reactor; in-vessel melt retention

  • Nuclear Engineering and Design 238(2008), 2420-2429

Publ.-Id: 11072

U(VI) sorption onto environmental relevant minerals: vibrational spectroscopy and complementary tools

Müller, K.; Foerstendorf, H.; Krepelova, A.; Baumann, N.; Brendler, V.

The sorption onto minerals along groundwater flow paths is an important mechanism determining the migration behaviour of uranium(VI) in the natural environment. The U(VI) surface complexation on several mineral phases was studied applying different spectroscopic methods. Using ATR-FTIR spectroscopy an in-situ investigation of U(VI) sorption onto kaolinite and titanium dioxide was performed at a micromolar concentration range. Thin mineral films are deposited on the surface of the crystal of an ATR flow cell. When U(VI) passes through the cell, characteristic absorption changes are observed representing sorption processes of U(VI) on the mineral surfaces. From the spectra the formed sorption complexes can be deduced.
The characteristic asymmetric stretching vibration of the uranyl ion is red-shifted by 40 cm–1 upon surface complexation of the UO22+ ion on kaolinite probably indicating strong sorption due to inner-sphere surface complexation. In homology, red shifts were also observed in the IR spectra of the titanium dioxide system, but the extent of the frequency shifts differs among different TiO2 samples.
In order to gain more information of the U(VI) complexes formed on the kaolinite surface, time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied [1]. Two U(VI) surface species, differing in the amount of water molecules in their coordination environment, could be identified. For the U(VI)-TiO2 system significant different spectroscopic response was observed for anatase and rutile. TRLFS investigations of anatase suspensions were hampered by strong quenching effects of the mineral phase. In contrast, the measurements of U(VI) in the rutile suspensions yield reasonable results.
A third spectroscopic method used for the characterization of the formed U(VI) complexes on surfaces of kaolinite and ferrihydrite is extended X-ray absorption fine structure (EXAFS) [2].
The obtained spectroscopic results serve as a data base for the development and the parameterization of models describing surface complexation phenomena.

1. Krepelova, A.; Brendler, V.; Sachs, S.; Baumann, N.; Bernhard, G. Environmental Science & Technol-ogy 2007, 41, (17), 6142-6147.
2. Reich, T.; Moll, H.; Arnold, T.; Denecke, M. A.; Hennig, C.; Geipel, G.; Bernhard, G.; Nitsche, H.; Allen, P. G.; Bucher, J. J.; Edelstein, N. M.; Shuh, D. K., Journal of Electron Spectroscopy and Related Phe-nomena 1998, 96, (1-3), 237-243.

  • Lecture (others)
    Seminar at National Commission of Atomic Energy (CNEA) of Argentina, 21.04.2008, San Martin, Argentina

Publ.-Id: 11070

Alpha-radiation damage in diamond

Nasdala, L.; Gigler, A. M.; Wildner, M.; Grambole, D.; Zaitsev, A. M.; Harris, J. W.; Hofmeister, W.; Milledge, H. J.; Satitkune, S.

We studied both the extent and distrubution of structural damage in diamond crystals that was generated through either natural or artificial irradiation with alpha particles (i.e., He2+ ions with energies in the MeV range), and the related formation of colour-centres. A range of non-destructive micro-techniques was applied. The generation of damage in the (crystalline) diamond is accompanied by lattice expansion, which is detected by a down-shift of the diamond LO=TO Raman band (compare [1]). This expansion is why radiation-damaged spots at the surface of natural diamond crystals often have an up-domed shape. At high irradiation doses ≥1016 ions per cm2, diamond may be transformed locally into an amorphous state (maximum damage generated at the far ends of helium trajectories).
Visible radiation-induced green colouration of diamond (mainly caused by a broad absorption band at ∼16000 cm-1 assigned to the GR1 centre) is generated at moderate doses of 1014−1015 He ions per cm2 [2,3]. This irradiation resulted in a lowly damaged state (maximum damage ≤0.005 dpa).
[1] Nasdala et al. (1995) Eur. J. Mineral. 7, 471−478. [2] Vance et al. (1973) Miner. Mag. 39, 349−360. [3] Zaitsev, A.M. (2001) Optical porperties of diamond. Springer, 502 p.

  • Lecture (Conference)
    Goldschmidt 2008, 13.-18.07.2008, Vancouver, Canada
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 72(2008)12, A672

Publ.-Id: 11069

Numerical and experimental modeling of the melt flow in a traveling magnetic field for Vertical Gradient Freeze crystal growth

Galindo, V.; Grants, I.; Lantzsch, R.; Paetzold, O.; Gerbeth, G.

A Traveling Magnetic Field (TMF) is attractive for Vertical Gradient Freeze crystal growth as it offers a direct flow driving mechanism. A combination of the driving TMF with a superimposed DC magnetic field leads to a damping effect on the fluctuations of the flow velocity, which have to be reduced in order to get a crystal with enhanced material properties. We present numerical and experimental results on the TMF driven flow in an isothermal model fluid in a cylindrical geometry. The TMF is generated by a system of six equidistant coils, which are fed by a three phase current power supply to create an up- or downward directed traveling field. Special attention is focused on the skin effect of the electromagnetic fields for varying field frequency, and its influence on the resulting melt velocity. The stability of the flow was analyzed with help of a spectral code. Critical values for the driving force and the period of the oscillating flow near those critical points were found in a good concordance with experiments.

Keywords: Traveling Magnetic Field Vertical Gradient Freeze crystal growth Numerical and experimental modeling

  • Lecture (Conference)
    79th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), 31.03.-04.04.2008, Bremen, Germany

Publ.-Id: 11068

Revised and extended level scheme of the doubly-odd nucleus 188Ir

Jungclaus, A.; Modamio, V.; Egido, J. L.; Schwengner, R.; Algora, A.; Bazzacco, D.; Escrig, D.; Fernandez, M. A.; Fraile, L. M.; Lenzi, S.; Marginean, N.; Martinez, T.; Napoli, D. R.; Ur, C. A.

High-spin states in the doubly odd Z = 77 nucleus 188Ir were studied using the reaction 186W(7Li, 5n) at 59 MeV and the GASP spectrometer for gamma-ray detection. The level structures recently suggested to be built on the known 4.1(3) ms isomeric state of this nucleus have been considerably revised and extended and an isomer with a lifetime of 17.7(2) ns has been identified within the main decay sequence. In addition two rotational bands built on low spin states below the ms isomer have been observed for the first time. The basic features of the excitation scheme of 188Ir are discussed within the Hartree-Fock-Bogoliubov theory within the Lipkin-Nogami approach with the finite-range density-dependent Gogny force.

Keywords: Nuclear structure; gamma-ray spectroscopy; Hartree-Fock-Bogoliubov theory

Publ.-Id: 11066

Computational study of anisotropic epitaxial recrystallization in 4H-SiC

Gao, F.; Zhang, Y.; Posselt, M.; Weber, W. J.

Two nano-sized amorphous layers were created within a crystalline cell to study anisotropic expitaxial recrystallization using molecular dynamics (MD) methods in 4H-SiC. Both amorphous layers were created with the normal of the amorphous-crystalline (a-c) interfaces along the [0001] direction, but one had a microscopic extension along the [(1) over bar2 (1) over bar0] direction, i.e. the dimension along the [(1) over bar2 (1) over bar0] direction is much larger than that along the [(1) over bar 010] direction (I-x model), and the other had a microscopic extension along the [(1) over bar 010] direction (I-y model). The amorphous layer within the I-x model can be completely recrystallized at 2000 K within an achievable simulation time, and the recrystallization is driven by a step-regrowth mechanism. On the other hand, the nucleation and growth of secondary ordered phases are observed at high temperatures in the I-y model. The temperature for recrystallization of the amorphous!
layer into high-quality 4H-SiC is estimated to be below 1500 K. Compared with other models, it is found that the regrowth rates and recrystallization mechanisms depend strongly on the orientation of 4H-SiC, whereas the activation energy spectra for recrystallization processes are independent of any specific polytypic structure, with activation energies ranging from 0.8 to 1.7 eV.

Keywords: computer simulation; SiC; recrystallization; defects

Publ.-Id: 11065

The liquid lead taget at nELBE

Galindo, V.; Erlebach, S.; Gerbeth, G.; Weiss, F.-P.

The radiation source ELBE (Electron Linear accelerator with high Brilliance and low Emittance) at Forschungszentrum Dresden-Rossendorf (FZD) has a superconducting linear accelerator with electron energies up to 40 MeV as a central instrument, and it will be used to produce sub-ns neutron pulses by stopping the electrons in a heavy radiator and producing neutrons by bremsstrahlung photons through (gamma,n) reactions. The neutron radiator consists of a liquid lead circuit. The volume of the radiator for the neutron production is chosen as small as possible in order to avoid multiple n scattering, which would broaden the neutron pulse. Power deposition of the electron beam in the small radiator volume of 1cm3 reaches up to 25 kW and any solid high Z number material would melt. A liquid lead target circulated by an electromagnetic pump is presented as a suitable solution. The heating power introduced by the electrons is removed through an additional heat exchanger. Typical flow velocities of the lead are between 1 m/s and 5 m/s in the radiator section. From the thermal and mechanical point of view, molybdenum turned out to be the most suited target wall material in the region where the electrons impinge on the neutron radiator. Model experiments in a pilot facility and numerical simulations of the flow, temperature and thermal stress distributions in the loop and
simulation of the efficiency of a lead-GaInSn-water heat exchanger are presented.

Keywords: liquid lead neutron target

  • Lecture (Conference)
    Workshop on modern methods using fast neutrons for research related to the transmutation of nuclear waste, 13.-15.02.2008, Dresden, Germany

Publ.-Id: 11064

Experimental nuclear astrophysics deep underground at Gran Sasso

Bemmerer, D.

The Laboratory Underground for Nuclear Astrophysics (LUNA) in the Gran Sasso underground facility, Italy, has been designed to measure low cross sections for astrophysical purposes. The 3He(alpha,gamma)7Be study at LUNA has recently been completed [1,2], and the impact of the data on big-bang nucleosynthesis and solar 7Be and 8B neutrinos will be discussed. During the year 2007, two measurement campaigns have been performed at LUNA: First, a precision study of ground state capture in the 14N(p,gamma)15O reaction. This study will help in the interpretation of the 15O neutrino data expected from the Borexino detector at Gran Sasso. Second, a study of the 25Mg(p,gamma)26Al reaction producing radioactive 26Al, a tracer of live nucleosynthesis in our galaxy. Gamma-rays from 26Al have been observed in the satellite-based Integral gamma-ray observatory.

The scientific program for the next years at the current LUNA 400 kV accelerator includes the study of the 2H(alpha,gamma)6Li reaction for big-bang nucleosynthesis and the study of 15N(p,gamma)16O and several other reactions of the CNO cycles. In closing, selected experiments that would benefit from the background suppression that is evident deep underground will be reviewed.

[1] D. Bemmerer et al. (LUNA collab.), Phys. Rev. Lett. 97, 122502 (2006)
[2] F. Confortola et al. (LUNA collab.), Phys. Rev. C 75, 065803 (2007)

  • Invited lecture (Conferences)
    Seminar Nukleare Astrophysik, 10.01.2008, München, Deutschland

Publ.-Id: 11063

Experimentelle Nukleare Astrophysik im Felsenkeller

Bemmerer, D.

Recent photoactivation experiments involving irradiations at the ELBE bremsstrahlung facility and underground gamma-counting in the Felsenkeller underground laboratory (VKTA Dresden) are presented. In addition, data from a feasibility study on in-beam gamma-spectrometry studies in shallow underground laboratories are shown here.

  • Invited lecture (Conferences)
    Kolloquium 25 Jahre Niederniveaumesslabor Felsenkeller, 31.01.2008, Dresden, Germany

Publ.-Id: 11062

The strong correlation between structural properties of the buffer layer and the exchange bias phenomena

Liedke, M. O.; Cantelli, V.; Grenzer, J.; Markó, D.; Mücklich, A.; Fassbender, J.

The exchange coupling strength as a function of the buffer layer thickness is investigated for several carefully chosen seed materials. The crystal microstructure of the ferromagnetic(FM)-antiferromagnetic(AF) interface is directly related to the roughness and dimensionality of the buffer layer surface, which scales not only with such parameters as a texture and grain sizes but can be discussed as well in the frame of the wetting behavior of subsequent films. Particularly, it is shown that strong wetting between the substrate and the next layer can decrease the surface dimensionality and improve the growth conditions for the subsequent films. Thus, the smoothness of the FM-AF interface improves significantly which leads to a much stronger exchange coupling across the interface. In addition, it is demonstrated that the magnitude of the exchange bias is proportional to the grain sizes distribution, which is in good agreement with theoretical predictions.

Keywords: exchange bias; buffer layer; wetting; grain sizes; thermal fluctuations; roughness; unidirectional anisotropy

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

Publ.-Id: 11061

In-beam PET measurements of biological half-lives of 12C irradiation induced β+-activity

Fiedler, F.; Sellesk, M.; Crespo, P.; Jülich, R.; Parodi, K.; Pawelke, J.; Pönisch, F.; Enghardt, W.

no abstract available

Keywords: in-beam PET; washout; ion therapy

  • Contribution to external collection
    in: GSI Scientific Report 2006 GSI Report 2007-1, Darmstadt: GSI, 2007, 364

Publ.-Id: 11060

Auf dem Weg zu einer Strahlentherapie mit laserbeschleunigten Teilchen - erste Dosis-Effekt-Kurven für laserbeschleunigte Elektronen

Beyreuther, E.; Enghardt, W.; Hümmerich, J.; Karsch, L.; Lessmann, E.; Pawelke, J.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.

Fragestellung: Die klassischen Teilchenbeschleuniger bieten einige 10 Pikosekunden (Elektronen) bzw. Nanosekunden (Protonen und Ionen) lange Pulse der Partikelstrahlung an. Mit der neuartigen Technologie der Laserbeschleunigung ist es möglich kürzere Teilchenpakete (einige 10 Femtosekunden) mit wesentlich geringerer Pulsfrequenz (einige Hertz gegenüber Megahertz) bei höherer Pulsintensität zu erhalten. Für eine Verwendung dieser Technologie in der Strahlentherapie muss eine möglicherweise andere biologische Wirksamkeit, sei es durch eine die andere Zeitstruktur oder durch die höhere Pulsdosisleistung, gegenüber den klassischen Teilchenstrahlen untersucht werden. Im Vortrag werden die weltweit ersten Zellbestrahlungen mit laserbeschleunigten Elektronen vorgestellt und diskutiert.
Methodik: Die Experimente wurden an dem 10-Terrawatt-Lasersystem JETI in Jena durchgeführt. Die Elektronenpakete haben eine Länge von ca. 150 fs und eine Wiederholrate von 2,5 Hz. Wichtige Vorraussetzungen für strahlenbiologische Experimente waren die Anpassung des Lasersystems, der Aufbau einer geeigneten Strahlführung und eines Dosimetriesystems. Bei einer ersten Serie von in-vitro Zellbestrahlungen mit Strahlendosen im Bereich von 0,3 bis 5 Gy wurde die Anzahl der Doppelstrangbrüche zu verschiedenen Zeitpunkten nach Bestrahlung in zwei Zelllinien bestimmt.
Ergebnisse: Das Lasersystem wurde erfolgreich für Zellbestrahlungen angepasst, d.h. die Zellproben werden homogen ausgeleuchtet und die Strahleigenschaften sind gut reproduzierbar. Die applizierte Dosis kann in Echtzeit monitoriert werden. Dadurch wird die Kontrolle und Steuerung der Zellbestrahlungen erleichtert. Eine genaue Dosisbestimmung ist nach der Bestrahlung mit Filmen, die am Zellkulturhalter befestigt waren, für jede Probe einzeln möglich. Das Gesamtsystem kann für systematische Untersuchungen eingesetzt werden, wie in einer ersten Zellbestrahlung demonstriert wurde. In diesem Experiment wurden Dosis-Effekt-Kurven bestimmt. Um eindeutige Aussagen zu erhalten, müssen die in Auswertung befindlichen Daten mit weiteren Experimenten ergänzt werden.
Schlussfolgerungen: In Zukunft werden systematische Messungen für verschiedene Tumor- und Normalgewebszellen sowie verschiedene biologische Endpunkte durchgeführt.

  • Lecture (Conference)
    14. Jahrestagung der Deutschen Gesellschaft für Radioonkologie / 25. Jahrestagung der Österreichischen Gesellschaft für Radioonkologie, Radiobiologie und Medizinische Strahlenphysik, 01.-04.05.2008, Wien, Austria
  • Contribution to proceedings
    14. Jahrestagung der Deutschen Gesellschaft für Radioonkologie / 25. Jahrestagung der Österreichischen Gesellschaft für Radioonkologie, Radiobiologie und Medizinische Strahlenphysik, 01.-04.05.2008, Wien, Austria
    Auf dem Weg zu einer Strahlentherapie mit laserbeschleunigten Teilchen - Erste Dosis-Effekt-Kurven für laserbeschleunigte Elektronen.: Strahlenther. Onkol. 184 (2008) 51

Publ.-Id: 11059

Spectral singularities and self-orthogonality of eigenvectors

Günther, U.; Graefe, E.-M.; Korsch, H.-J.; Niederle, A.; Rotter, I.; Samsonov, B.

A brief overview of some mathematical aspects connected with the occurrence of spectral singularities will be presented. Based on simple matrix models we discuss stratified manifolds in parameter spaces on which the matrix eigenvalues degenerate. We comment on discriminant sets and similarity relations to canonical Jordan structures, demonstrate the mechanism underlying the formation of self-orthogonal (isotropic) eigenvectors, relate it to corresponding projectors. Special emphasis will be laid on the break-down of similarity transformations, the formation of corresponding transformation singularities and their resolution via projective extensions. Structural links to ultrarelativistic spinor models will be sketched. Finally, we comment on versal deformations and an unfolding rule for higher-order spectral singularities connected with the Hessenberg type of the perturbation.

Keywords: spectral; singularity; Jordan structure; exceptional point; self-orthogonality; isotropy; versal deformation; projective extension; ultra-relativistic limit; Hessenberg matrix

  • Invited lecture (Conferences)
    Experimental Realizations of Self-Orthogonality, 23.-28.03.2008, Haifa, Israel

Publ.-Id: 11058

Bacterial interactions with uranium: an environmental perspective

Merroun, M.; Selenska-Pobell, S.

The presence of actinides in radioactive wastes is of major concern because of their potential for migration from the waste repositories and long-term contamination of the environment. Studies have been and are being made on inorganic processes affecting the migration of radionuclides from these repositories to the environment but it is becoming increasingly evident that microbial processes are of importance as well. The relevance of microorganisms to actinide behavior arises from the overlap of the biosphere with the geosphere and the transformations that occur because of their interactions. The present study is intended to give a brief overview of the key processes implicated in the interaction of actinides e.g. uranium with bacterial strains isolated from different extreme environments relevant to radioactive repositories. A complex methodological approach involving a combination of wet chemistry, transmission electron microscopy, and advanced solid state speciation techniques is used. Fundamental understanding of the interaction of these bacteria with U will be useful for developing appropriate radioactive waste treatments, remediation and long-term management strategies as well as for predicting the microbial impacts on the performance of the radioactive waste repositories.

Keywords: Uranium; Bacteria; Interaction mechanisms; Multidisciplinary approach; Radioactive wastes

Publ.-Id: 11057

Anwendung des in-beam PET Therapiemonitorings auf Präzisionsbestrahlungen mit Helium-Ionen

Fiedler, F.

no abstract available

Keywords: in-beam PET; ion therapy; 3He

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-494 2008
    ISSN: 1437-322X


Publ.-Id: 11056

XAS study of Am2Zr2O7 pyrochlore - Evolution under alpha self irradiation.

Martin, P.; Belin, R.; Valenza, P.; Pieragnoli, A.; Scheinost, A.

Management of long-lived nuclear wastes is, after safety, the main issue of nuclear industry, both in terms of scientific challenge as well as public acceptance. Among the different options that have been envisioned and explored for minor actinides over the past thirty years, two alternatives currently remain: long term disposal in a safe repository or nuclear wastes “burning” in a so-called transmutation process. Materials selected for such applications have to meet the following criteria: high incorporation amount of actinides, good structural and chemical stability, low thermal dilatation and resistance to radiation.
Among the various ceramics envisaged, zirconia based pyrochlore oxides of composition An2Zr2O7 (An=actinide) appear to be a very good candidate. Results obtained with lanthanide pyrochlores submitted to ion-beam irradiation show that Zr based pyrochlores, unlike Ti based, remain crystalline with a transition from pyrochlore structure to a defect fluorite structure [1]. However, this strong radiation tolerance still has to be confirmed on alpha emitter materials (e.g. americium). In that prospect, 241Am2Zr2O7 sample was synthesized [2] and its evolution under the effect of alpha self-irradiation as a function of time was followed by XRD. Figure 1 shows the transition from the pyrochlore phase to a defect-fluorite phase after ~200 days as the superstructure peaks (marked ) slowly vanish and completely disappear after about 200 days [3].

Keywords: Americium; zirconium; pyrochlore; XAS

  • Contribution to proceedings
    Plutonium Futures "The Science" 2008, 07.-11.07.2008, Dijon, France

Publ.-Id: 11055

A non-Hermitian PT-symmetric Bose-Hubbard model: eigenvalue rings from unfolding higher-order exceptional points

Graefe, E.-M.; Günther, U.; Korsch, H.-J.; Niederle, A.

We study a non-Hermitian PT-symmetric generalization of an N-particle, two-mode Bose-Hubbard system, modeling for example a Bose-Einstein condensate in a double well potential coupled to a continuum via a sink in one of the wells and a source in the other. The effect of the interplay between the particle interaction and the non-Hermiticity on characteristic features of the spectrum is analyzed drawing special attention to the occurrence and unfolding of exceptional points (EPs). We find that for vanishing particle interaction there are only two EPs of order N+1 which under perturbation unfold either into [(N+1)/2] eigenvalue pairs (and in case of N+1 odd, into an additional zero-eigenvalue) or into eigenvalue triplets (third-order eigenvalue rings) and (N+1)mod 3 single eigenvalues, depending on the direction of the perturbation in parameter space. This behavior is described analytically using perturbational techniques. More general EP unfoldings into eigenvalue rings up to (N+1)th order are indicated.

Keywords: Hubbard model; Bose-Einstein condensate; non-Hermitian operators; PT-symmetry; Krein space; exceptional points; Jordan block; Jordan chain; singularities; LeVerrier-Faddeev technique; Newton diagram technique

Publ.-Id: 11054

Effekt der Bestrahlungsdosis auf die lokale Tumorkontrolle korreliert mit prätherapeutischer [18F]FDGAufnahme von FaDu-Tumoren in Nacktmäusen

Schütze, C.; Beuthien-Baumann, B.; Bergmann, R.; Hessel, F.; Kotzerke, J.; Baumann, M.

In vielen Tumoren unterschiedlicher Patienten wie auch innerhalb eines individuellen Tumors kann eine heterogene [18F]FDGAufnahme nachgewiesen werden. Derzeit ist nicht bekannt ob diese intratumorale Heterogenität mit dem Ansprechen von Tumorsubvolumina korreliert und als biologischer Marker für eine heterogene Dosis-Verschreibung z.B. Dosis-Eskalation partieller Volumina verwendet werden kann. Für diese Fragestellung haben wir in einer präklinischen Modellsituation die Heterogenität der [18F]FDG-Aufnahme und den Dosis-Effekt in einer einzelnen, in Nacktmäusen transplantierten humanen Tumorzelllinie untersucht.

Die hSCC Zelllinie FaDu wurde subkutan auf das Hinterbein von NMRI Nacktmäusen transplantiert. Ab einem Tumordurchmesser von 7 mm erfolgte die Aufnahme in das Experiment. Jedes Tier erhielt eine [18F]FDG-PET-Untersuchung (microPET® P4, CTI) direkt vor Bestrahlung zur Bestimmung des Maximum Standardized Uptake Value (SUVmax). Die Einzeldosisbestrahlungen mit 25 Gy oder 35 Gy erfolgten
unter ambientem Blutfluss mit 200 kV Röntgenstrahlen (0.5 mm Cu, ∼ 1 Gy min-1). 62 Tiere wurden in dieser Studie untersucht, davon befinden sich noch fünf Tiere im Follow-up. Experimenteller Endpunkt war die lokale Tumorkontrolle am Tag 120 nach Bestrahlung.

Die Spanne der SUVmax-Werte reichte von 0.72 bis 3.47, der Median war 1.59. Die lokalen Tumorkontrollraten für alle 62 Tiere betrugen 28% nach Bestrahlung mit 25 Gy und 57% nach 35 Gy (Kaplan-Meier-Analyse, Logrank-Test p = 0.007). Im nächsten Schritt wurde eine univariate
Analyse der Dosis-Effekt-Beziehung für die entsprechend des Median SUVmax stratifizierten Tiere durchgeführt. Für Tumoren < Median SUVmax
betrug die lokale Kontrolle 37% nach 25 Gy vs. 47% nach 35 Gy (p = 0.37). Im Gegensatz dazu fand sich ein signifikanter Unterschied der lokalen
Tumorkontrollraten für Tumoren > Median SUVmax (15% nach 25 Gy vs. 68% nach 35 Gy, p = 0.002). In der multivariaten Cox-Analyse mit
Strahlendosis und SUVmax als kontinuierliche Variablen, konnte eine signifikante Verringerung des Rezidivrisikos mit ansteigender Strahlendosis
(p = 0.007) und ein grenzwertig, signifikanter Effekt des SUVmax-Wertes nachgewiesen werden (p = 0.06).

Diese Daten zeigen einen größeren Effekt der Bestrahlungsdosis auf die lokale Kontrolle in Tumoren mit initial hoher [18F]FDG-Aufnahme im Vergleich zu Tumoren derselben Tumorlinie mit niedriger [18F]FDG-Aufnahme. Diese Ergebnisse unterstützen die Hypothese, dass ein prätherapeutisches [18F]FDG-PET wichtige Informationen für die Verschreibung einer heterogenen Bestrahlungsdosis liefern kann. In dieser Studie wurde nur ein Tumormodell und Einzeldosisbestrahlung untersucht. Weitere Experimente mit anderen Tumormodellen und fraktionierter Bestrahlung sind notwendig.

Gefördert im Rahmen des EU-Projektes „BioCare“ Molecular Imaging for Biologically Optimized Cancer Therapy #505785.

  • Poster
    DEGRO 2007,13. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 07.-10.06.2007, Hannover, Deutschland
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 183(2007)1, 63
    DOI: 10.1007/s00066-007-1001-1

Publ.-Id: 11053

Erste Dosis - Effekt - Kurven für laserbeschleunigte Elektronen

Beyreuther, E.; Enghardt, W.; Hümmerich, J.; Karsch, L.; Lessmann, E.; Nicolai, M.; Pawelke, J.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.

Das Verbundprojekt "onCOOPtics - Hochintensitätslaser für die Radioonkologie" hat sich zum Ziel gesetzt eine neuartige und auf Laser basierende Technologie zur Erzeugung von Teilchenstrahlung für die Krebstherapie zu implementieren. Im Unterschied zu den klassischen, in der Strahlentherapie eingesetzen, Partikelstrahlungen, bestehen diese neuartigen Teilchenstrahlen aus wesentlich kürzeren Teilchenpaketen (einige 10 Femtosekunden gegenüber Piko- bzw. Nanosekunden Länge), die mit geringerer Pulsfrequenz (einige Hz statt MHz) aber höherer Pulsdosisleistung erzeugt werden. Diese Unterschiede in den Strahleigenschaften und ihr Einfluss auf die biologische Wirksamkeit müssen hinsichtlich eines möglichen Therapieeinsatzes untersucht werden; erste in - vitro Zellbestrahlungsexperimente mit laserbeschleunigten Elektronen hierzu werden im Vortrag vorgestellt.
Die ersten Experimente wurden mit dem 10 TW - Lasersystem JETI der Universität Jena durchgeführt. Mit diesem Lasersystem werden Elektronen aus einem Gasjet - Target heraus beschleunigt, wobei Elektronenpakete mit einer Länge von ca. 150 fs und einer Wiederholfrequenz von 2,5 Hz erzeugt werden. Das Lasersystem wurde an strahlenbiologische Erfordernisse, d.h. ausreichend großer Strahlfleck und hohe Dosisleistung, sowie von Bestrahlung zu Bestrahlung gut reproduzierbare Strahleigenschaften, angepasst und Zellbestrahlungen mit zwei verschiedenen Zelllinien im Dosisbereich von 0,3 bis 5 Gy durchgeführt. Zur Kontrolle der Experimente wurden verschiedene Systeme zur Strahl- bzw. Dosismonitorierung und retrospektiven Dosisbestimmung eingesetzt. Während der Bestrahlungen wurde die Elektronenstrahlintensität mit einem Faraday - Cup überwacht und die Dosisleistung im Strahl mittels Ionisationskammern gemessen. Die am Zellort applizierte Dosis wurde nach der Bestrahlung mittels Filmdosimeter, welche direkt vor den Zellproben positioniert waren, bestimmt.
Eine erste strahlenbiologische Charakterisierung der laserbeschleunigten Elektronen erfolgte mit dem Nachweis von DNS Doppelstrangbrüchen über die Antikörper - Doppelmarkierung von g - H2AX und 53BP1, zwei Molekülen, die direkt nach Bestrahlung an den Doppelstrangbrüchen der DNS aktiviert werden. Für beide untersuchten Zelllinien konnten erste Dosis - Effekt - Kurven dieses biologischen Endpunkts für verschiedene Zeitpunkte nach Bestrahlung bestimmt werden. Eindeutige Aussagen, auch im Vergleich zu verschiedenen Referenzstrahlungen, werden aber erst nach Abschluss der Experimentreihe möglich sein.
Ein Ausblick auf zukünftige Arbeiten mit verschiedenen Zelllinien und weiteren biologischen Endpunkten wird ebenfalls im Vortrag gegeben.

  • Poster
    17. Symposium Experimentelle Strahlentherapie und klinische Strahlenbiologie, 28.02.-01.03.2008, Dresden, Germany
  • Contribution to proceedings
    17. Symposium Experimentelle Strahlentherapie und klinische Strahlenbiologie, 28.02.-01.03.2008, Dresden, Germany
    Band 17: Selbstverlag, 1432-864X

Publ.-Id: 11052

BACOPP-D as treatment in patients with advanced Hodgkin lymphoma

Naumann, R.; Wetzko, K.; Haenel, A.; Friedrichsen, K.; Zschuppe, E.; Schmidt, H.; Moelle, M.; Dawel, M.; Beuthien-Baumann, B.; Schwanebeck, U.; Ehninger, G.; Haenel, M.

The development of the escalated BEACOPP regimen let to an improved outcome in patients with advanced Hodgkin Lymphoma (HD9 study of the GHSG). However, the application of high dose etoposide (cumulative 4,8 g/m2 per 8 cycles) seems to be associated with an
increased incidence of secondary MDS and AML, respectively. Therefore, the aim of our ongoing multicenter pilot study is to evaluate the efficacy
and toxicity of the etoposide free as well as dose intensified BACOPP-D protocol.

Since May 2000 a total of 115 patients with Hodgkin Lymphoma (HL) stage IIB, III, and IV were treated with BACOPP-D which included cyclophosphamide 1250 mg/m2 (d1), adriamycin 25 mg/m2(d1+2), dacarbazine 250 mg/m2 (d1-3), procarbazine 100 mg/m2 (d1-7), prednisolone 40 mg/m2 (d1-14), bleomycin 10 mg/m2(d8) and vincristine 1,4 mg/m2 (maximum 2 mg, d8) at three-weekly intervals with granulocyte colony-stimulating factor (G-CSF). A consolidating involved field radiation (30 Gy) was performed only in patients who achieved less than CR following chemotherapy. Initial staging and post-treatment control included PET monitoring.

Until now 97 patients (median age 35 years, range 17-65; 61 male, 36 female) are assessable for toxicity and treatment outcome. We analyzed the acute toxicity for 728 cycles of BACOPP-D. CTC/WHO grade III/IV haematological toxicities per patient were observed as follows:
leukopenia 93%, anemia 39%, and thrombocytopenia 33%. CTC grade III/IV non-haematological side effects included documented infection (4%) and lung toxicity (one patient with reversible bleomycininduced pneumonitis). A total of 85 patients (88%) achieved complete remission, 9 patients (9%) achieved partial remission, three patients (3%) had progressive disease. At a median observation time of 39 months (0,9-77 months), six patients have relapsed, and nine deaths were documented (4 HL-specific and 3 treatment related deaths, 1 death due to ruptured Meckel diverticulum with peritonitis, one 65 year-old woman died in CR following myocardial infarction caused by coronary heart disease). One patient developed a second neoplasia (hypopharyngeal carcinoma in an alcoholic). The overall survival and freedom from treatment failure rates at 39 months were 91% and 85%, respectively.

BACOPP-D regimen appears as a feasible and safe treatment protocol with moderate acute toxicity in patients with advanced HL. No secondary AML or MDS occured until now.

  • Open Access Logo Abstract in refereed journal
    Haematologica -The Hematology Journal 92(2007)5, 69
  • Poster
    7th International Symposium on Hodgkin Lymphoma, 03.-07.11.2007, Köln, Deutschland

Publ.-Id: 11051

Comparison of three quantum chemical ab initio methods for band structure calculations: the hydrogen fluoride chain

Bezugly, V.; Albrecht, M.; Birkenheuer, U.

Three different many-body wave-function-based ab initio methods for the calculation of correlated (or quasi-particle) band structures of periodic systems are presented: the local Hamiltonian approach, the incremental self-energy method, and the crystal orbital variant of the algebraic diagrammatic construction. All three methods explicitly exploit the local nature of electron correlation, and by consequently switching to representations in localized Wannier orbitals O(N) scaling could be achieved in all three cases. These methods were applied to single (HF)2 zigzag chains as found in solid hydrogen fluoride using the same geometries and basis sets. Essentially identical quasi-particle band structures were obtained, corroborating the appropriateness of the different concepts pursued in each of the presented quantum chemical correlation methods for band structures of infinite systems.

Keywords: quantum chemistry; electronic structure; band structure; electron correlation; local correlation methods; excited-states; hydrogen fluoride chains

  • Open Access Logo Journal of Physics: Conference Series 117(2008), 012006

Publ.-Id: 11050

Experimental CFD grade data for stratified two-phase flows

Vallee, C.; Lucas, D.; Beyer, M.; Pietruske, H.; Schütz, P.; Carl, H.

Stratified two-phase flows were investigated at two test facilities with horizontal test-sections. For both, rectangular channel cross-sections were chosen to provide optimal observation possibilities for the application of optical measurement techniques. In order to show the local flow structure, high-speed video observation was applied, which delivers the high resolution in space and time needed for CFD code validation.

The Horizontal Air/Water Channel (HAWAC) is made of acrylic glass and allows the investigation of air/water co-current flows at atmospheric pressure and room temperature. At the channel inlet, a special device was designed for well-defined and adjustable inlet boundary conditions. For the quantitative analysis of the optical measurements performed at the HAWAC, an algorithm was developed to recognise the stratified interface in the camera frames. This allows to make statistical treatments for comparison with CFD calculation results. As an example, the instable wave growth leading to slug flow is shown from the test-section inlet. Moreover, the hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was investigated in this closed channel. The structure of the hydraulic jump over time is revealed by the calculation of the probability density of the water level. A series of experiments show that the hydraulic jump profile and its position from the inlet vary sensibly with the inlet boundary conditions due to the momentum exchange between the phases.

The second channel is built in the pressure vessel of the TOPFLOW facility, which is used to perform air/water and steam/water experiments at pressures of up to 5.0 MPa and temperatures of up to 264°C, but under pressure equilibrium with the vessel inside. In the present experiment, the test-section represents a flat model of the hot leg of the German Konvoi pressurised water reactor scaled at 1:3. The investigations focus on the flow regimes observed in the region of the elbow and of the steam generator inlet chamber, which are equipped with glass side walls. An overview of the experimental methodology and of the acquired data is given. These cover experiments without water circulation, which can be seen as test cases for CFD development, as well as counter-current flow limitation experiments, representing transient validation cases of a typical nuclear reactor safety issue.

Keywords: two-phase flow; stratified flow; horizontal flow; high-speed video observation; image processing; hot leg

  • Contribution to proceedings
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
    Paper HOR-05
  • Poster
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
  • Nuclear Engineering and Design 240(2010), 2347-2356
    DOI: 10.1016/j.nucengdes.2009.11.011

Publ.-Id: 11049

Nuclear physics in astrophysics III

Bemmerer, D.; Grosse, E.; Junghans, A.; Schwengner, R.; Wagner, A.

Introduction to the proceedings volume of the Europhysics Conference "Nuclear Physics in Astrophysics III", March 2007, Dresden

Publ.-Id: 11048

Untersuchung von Spektraleigenschaften kugelsymmetrischer alpha2-dynamos mit Techniken der Funktionalanalysis und Operatortheorie, Singularitätentheorie und Bifurkationstheorie

Gerbeth, G.; Stefani, F.; Günther, U.

Kosmische Magnetfelder werden durch Selbsterregung in strömenden elektrisch leitfähigen Flüssigkeiten erzeugt. Lang andauernde Phasen relativer Feldstabilität können dabei von kurzen Phasen mit hoher Dynamik und damit einhergehenden Feldumpolungsprozessen unterbrochen werden. Jüngste numerische Untersuchungen an einem einfachen Dynamo-Modell im Sättigungsregime, dem kugelsymmetrischen alpha2-Dynamo mit algebraischem alpha-Quenching, deuten darauf hin, dass dynamische Feldumpolungen für eine Vielzahl von Dynamo-Konfigurationen auftreten und sich unter geeigneten Bedingungen eventuell sogar experimentell erzeugen lassen. Als wesentliches Kriterium für das Auftreten einer Feldumpolung konnte bisher das Vorhandensein eines spektralen Entartungspunktes mit Phasenübergang von nichtoszillierendem zu oszillierendem Dynamo-Regime in der Nähe des spektralen Nullpunktes identifiziert werden. Im Rahmen des einjährigen DFG-Projektes wurden anhand einfacher Dynamo-Modelle theoretische Grundlagenuntersuchungen zur Dynamik von Feldumpolungen durchgeführt.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    ISSN: 1437-322X

Publ.-Id: 11047

Nonlinear multidimensional cosmological models with form fields: stabilization of extra dimensions and the cosmological constant problem

Günther, U.; Moniz, P.; Zhuk, A.

We consider multidimensional gravitational models with a nonlinear scalar curvature term and form fields in the action functional. In our scenario it is assumed that the higher dimensional spacetime undergoes a spontaneous compactification to a warped product manifold. Particular attention is paid to models with quadratic scalar curvature terms and a Freund-Rubin-like ansatz for solitonic form fields. It is shown that for certain parameter ranges the extra dimensions are stabilized. In particular, stabilization is possible for any sign of the internal space curvature, the bulk cosmological constant and of the effective four-dimensional cosmological constant. Moreover, the effective cosmological constant can satisfy the observable limit on the dark energy density. Finally, we discuss the restrictions on the parameters of the considered nonlinear models and how they follow from the connection between the D-dimensional and the four-dimensional fundamental mass scales.

Keywords: string theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction; higher order curvature corrections

Publ.-Id: 11046

Multidimensional cosmology and asymptotical AdS

Günther, U.; Moniz, P.; Zhuk, A.

A non-linear gravitational model with a multidimensional geometry and quadratic scalar curvature is considered. For certain parameter ranges, the extra dimensions are stabilized if the internal spaces have negative curvature. As a consequence, the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. The homogeneous and isotropic external space is asymptotically AdS. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets an additional restriction on the parameters of the considered non-linear models.

Keywords: string theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

Publ.-Id: 11045

Asymptotical AdS from nonlinear gravitational models with stabilized extra dimensions

Günther, U.; Moniz, P.; Zhuk, A.

We consider non-linear gravitational models with a multidimensional warped product geometry. Particular attention is payed to models with quadratic scalar curvature terms. It is shown that for certain parameter ranges, the extra dimensions are stabilized if the internal spaces have negative constant curvature. In this case, the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. As a consequence, the homogeneous and isotropic external space is asymptotically AdS. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets a restriction on the parameters of the considered non-linear models.

Keywords: string theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

Publ.-Id: 11044

Gravitational excitons - fluctuating particles from extra dimensions

Günther, U.; Zhuk, A.

We show that for warped product space-times the conformal (geometric moduli) excitations of the internal compactified factor spaces should be observable as massive scalar fields in the external space-time. These scalar fields (gravitational excitons) describe weakly interacting particles and can be considered as dark matter component. On the other hand, they provide possible values for the effective cosmological constant.

Keywords: String theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction; dark matter

  • Contribution to external collection
    W. Janke, A. Pelster, H.-J.Schmidt, M. Bachmann: Fluctuating paths and fields. Dedicated to Hagen Kleinert on the occasion of his 60th birthday., Singapore: World Scientific, 2001, 981-02-4648-X, 721-728

Publ.-Id: 11043

Gravitational excitons as dark matter

Günther, U.; Zhuk, A.

In earlier work it was pointed out that for warped product spacetimes the conformal (geometrical moduli) excitations of the internal compactified factor spaces should be observable as massive scalar fields in the external spacetime. Here we show that these scalar fields (gravitational excitons) describe weakly interacting particles and can be considered as dark matter component. Masses of the gravexcitons are defined by the form of the effective potential of the theory and the stabilization scales of the internal space. This implies that different stabilization scales result in different types of DM. An essential role is played by the effective potential. On the one hand, its minima fix possible stabilization scales of the internal spaces; on the other hand, they provide possible values for the effective cosmological constant.

Keywords: string theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction; dark matter

  • Contribution to proceedings
    Cosmology and Particle Physics (CAPP 2000), 17.-28.07.2000, Verbier, Switzerland
    Proceedings of the Conference on Cosmology and Particle Physics (CAPP 2000), New York: Springer, 1-56396-986-6, 371-374

Publ.-Id: 11042

Remarks on dynamical stabilization of internal spaces in multidimensional cosmology

Günther, U.; Zhuk, A.

The possibility of dynamical stabilization of an internal space is investigated for a multidimensional cosmological model with minimal coupled scalar field as inflaton. It is shown that a successful dynamical compactification crucially depends on the type of interaction between the geometrical modulus field and the inflaton and its decay products. In the considered model a stable compactification can be ensured via trapping of the modulus field by a minimum of the effective potential.

Keywords: moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

Publ.-Id: 11041

Stabilization of internal spaces in multidimensional cosmology

Günther, U.; Zhuk, A.

Effective 4-dimensional theories are investigated which were obtained under dimensional reduction of multidimensional cosmological models with a minimal coupled scalar field as matter source. Conditions for the internal space stabilization are considered and the possibility for inflation in the external space is discussed. The electroweak as well as the Planck fundamental scale approaches are investigated and compared with each other. It is shown that there exists a rescaling for the effective cosmological constant as well as for gravitational exciton masses in the different approaches.

Keywords: moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

Publ.-Id: 11040

Multidimensional perfect fluid cosmology with stable compactified internal dimensions

Günther, U.; Zhuk, A.

Multidimensional cosmological models in the presence of a bare cosmological constant and a perfect fluid are investigated under dimensional reduction to 4-dimensional effective models. Stable compactification of the internal spaces is achieved for a special class of perfect fluids. The external space behaves in accordance with the standard Friedmann model. Necessary restrictions on the parameters of the models are found to ensure dynamical behavior of the external (our) universe in agreement with observations.

Keywords: moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

Publ.-Id: 11039

On stable compactification with Casimir-like potential

Günther, U.; Kriskiv, S.; Zhuk, A.

Multidimensional cosmological models with a higher dimensional space-time manifold are investigated under dimensional reduction. In the Einstein conformal frame, the effective potential for the internal scale factors is obtained. The stable compactification of the internal spaces is achieved due to the Casimir effect. In the case of more than one internal space a Casimir-like ansatz for the energy density of the massless scalar field fluctuations is proposed. Stable configurations with respect to the internal scale factor excitations are found in the cases of one and two internal spaces.

Keywords: string theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

  • Gravitation and Cosmology 4(1998), 1-16

Publ.-Id: 11038

Stable compactification and gravitational excitons from extra dimensions

Günther, U.; Zhuk, A.

We study inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold under dimensional reduction. Stability due to different types of effective potentials is analyzed for specific configurations of internal spaces. Necessary restrictions on the parameters of the models are found and masses of gravitational excitons (small inhomogeneous excitations of the scale factors of the internal spaces near minima of effective potentials) are calculated.

Keywords: string theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

  • Hadronic Journal 21(1998), 279-318

Publ.-Id: 11037

Gravitational excitons from extra dimensions

Günther, U.; Zhuk, A.

We study inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold under dimensional reduction and show that small inhomogeneous excitations of the scale factors of the internal spaces near minima of effective potentials should be observable as massive scalar particles (gravitational excitons) in the external space-time.

Keywords: string theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

  • Contribution to proceedings
    8th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories (MG 8), Jerusalem, Israel, 22-27 June 1997, 22.-27.06.1997, Jerusalem, Israel
    8th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories (MG 8), Singapore: World Scientific, 981-02-3793-6, 517-519

Publ.-Id: 11036

Gravitational excitons from extra dimensions

Günther, U.; Zhuk, A.

nhomogeneous multidimensional cosmological models with a higher-dimensional space-time manifold M=M0×∏i=1 nMi (n>~1) are investigated under dimensional reduction to D0-dimensional effective models. In the Einstein conformal frame, small excitations of the scale factors of the internal spaces near minima of an effective potential can be observed as massive scalar fields in the external space-time. Parameters of models that ensure minima of the effective potentials are obtained for particular cases and masses of gravitational excitons are estimated.

Keywords: string theory; moduli stabilization; scalar-tensor theory; higher dimensional gravity; dimensional reduction

Publ.-Id: 11035

Experimental Study on the Air/water Counter-current Flow Limitation in a Model of the Hot Leg of a Pressurised Water Reactor

Deendarlianto; Vallee, C.; Lucas, D.; Beyer, M.; Pietruske, H.; Carl, H.

An experimental investigation on the air/water counter-current two-phase flow in a horizontal rectangular channel connected to an inclined riser has been conducted. This test-section representing a model of the hot leg of a pressurized water reactor is mounted between two separators in a pressurized experimental vessel. The cross-section and length of the horizontal part of the test-section are (0.25 m × 0.05 m) and 2.59 m, respectively, whereas the inclination angle of the riser is 50°. The flow was captured by a high-speed camera in the bended region of the hot leg, delivering a detailed view of the stratified interface as well as of dispersed structures like bubbles and droplets. Countercurrent flow limitation (CCFL), or the onset of flooding, was found by analyzing the water levels measured in the separators. The counter-current flow limitation is defined as the maximum air mass flow rate at which the discharged water mass flow rate is equal to the inlet water mass flow rate.
From the high-speed observations it was found that the initiation of flooding coincides with the formation of slug flow. Furthermore, a hysteresis was noticed between flooding and deflooding. The CCFL data was compared with similar experiments and empirical correlations available in the literature. Therefore, the Wallis-parameter was calculated for the rectangular cross-sections by using the channel height as length, instead of the diameter. The agreement of the CCFL curve is good, but the zero liquid penetration was found at lower values of the Wallis parameter than in most of the previous work. This deviation can be attributed to the special rectangular geometry of the hot leg model of FZD, since the other investigations were done for pipes.

Keywords: Two-phase flow; counter-current flow; CCFL; flooding; deflooding; PWR; hot leg; rectangular channel; TOPFLOW

Publ.-Id: 11033

Counter-current flow limitation experiments in a model of the hot leg of a pressurised water reactor

Vallee, C.; Deendarlianto; Lucas, D.; Beyer, M.; Pietruske, H.; Carl, H.

The counter-current flow limitation was investigated experimentally in a flat model of the hot leg of a pressurised water reactor. Counter-current flow limitation, or the onset of flooding, was found by analysing the water levels measured in the separators. A confrontation with high-speed observation images indicates that the initiation of flooding coincides with the reversal of the flow in the horizontal part of the hot leg due to high air velocities.

Furthermore, the CCFL data was compared with empirical correlations for analogue geometries available in the literature. This comparison shows that the Wallis-parameter can be applied to rectangular cross-sections by using the channel height as length, instead of the diameter. The obtained flooding curve is similar to those reported by other investigators, but its slope and the gaseous Wallis parameter for zero penetration are lower. This is attributed to the geometry of the hot leg model.

Keywords: hot leg; pressurised water reactor; PWR; two-phase flow; counter-current flow; counter-current flow limitation; CCFL

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Deutschland
    Jahrestagung Kerntechnik 2008 - Fachsitzungen / Topical Sessions, Berlin: INFORUM Verlags- und Verwaltungsgesellschaft
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2008, 27.-29.05.2008, Hamburg, Deutschland
  • atw - International Journal for Nuclear Power 53(2008)8/9, 546-549

Publ.-Id: 11032

Modeling free surface flows relevant to a PTS scenario: comparison between experimental data and three RANS based CFD-codes - Comments on the CFD-experiment integration and best practice guideline

Bartosiewicz, Y.; Seynhaeve, J.-M.; Vallee, C.; Höhne, T.; Laviéville, J.

This paper presents some results concerning a benchmark for stratified two-phase flows conducted in the frame of the European Platform for NUclear REactor SIMulations (NURESIM). This benchmark relies on the FZD slug flow experiment performed in the Horizontal Air/Water Channel (HAWAC). For this test bench, special experimental arrangements have been taken in order to be able to properly model the boundary and initial conditions with CFD. A picture sequence recorded with a high-speed camera was used as reference for comparison with the simulations. For this benchmark, three different codes have been tried out. CFX was used with a turbulent two-fluid model in which a special turbulence damping function was implemented in the specific dissipation rate of the turbulent kinetic energy. This allowed a good qualitative representation of the slug dynamics, even though quantitative comparison were less relevant because of difficulties in modelling the inlet instabilities. The VOF approach in its laminar and turbulent form was also tried out trough the FLUENT code and was found to be inappropriate for those conditions due to the high velocity slip between phases. Moreover, NEPTUNE_CFD was tested with a new implemented model allowing free surface location and the computation of momentum transfer across this interface. This Large Interface Model (LIM) enables to detect "stratified cells" from the other and hence to apply local closure law. With this model, the results agreed well with experimental data qualitatively and quantitatively. This benchmark experience also allowed to draw basis concerning a best practice guideline in numerical simulation related to those flows in nuclear thermal hydraulics.

Keywords: stratified two-phase flow; free surface flow; slug flow; CFD; benchmark

  • Contribution to proceedings
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
    Paper HOR-01
  • Lecture (Conference)
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
  • Nuclear Engineering and Design 240(2010), 2375-2381
    DOI: doi:10.1016/j.nucengdes.2010.04.032

Publ.-Id: 11031

A comparison of the magnetic properties of proton- and iron-implanted graphite

Barzola-Quiquia, J.; Höhne, R.; Rothermel, M.; Setzer, A.; Esquinazi, P.; Heera, V.

In this work we have investigated the changes of the magnetic properties of highly oriented pyrolytic graphite samples after irradiation either with ~3×1014 protons or 3.5×1013 ... 3.5×1014 iron ions with energies in the MeV range. Our results show that iron and proton irradiations can produce similar paramagnetic contributions depending on the implantation temperature. However, only protons induce a ferromagnetic effect.

Keywords: Magnetic semiconductors; Interactions of particles and radiation with matter; Carbon; diamond; graphite

Publ.-Id: 11030

Assessment of CFD codes for nuclear reactor safety problems

Smith, B. L.; Bieder, U.; Graffard, E.; Heitsch, M.; Henriksson, M.; Höhne, T.; Komen, E.; Mahaffy, J.; Moretti, F.; Morii, T.; Mühlbauer, P.; Rohde, U.; Scheuerer, M.; Song, C.-H.; Zigh, G.

This report is a consolidation of document NEA/SEN/SIN/AMA(2005)3, which aimed to evaluate the existing CFD assessment basis, identify gaps that need to be filled in order to adequately validate CFD codes for application to NRS problems, and propose a methodology for establishing assessment matrices relevant to NRS needs. The document is a revision of the original, and has been compiled by members of an expert Writing Group, WG2, under the auspices of the OECD/NEA secretariat. The group met three times during the period January 2005 to August 2007, the dates chosen to coordinate with the activities of the sister groups WG1 (Best Practice Guidelines) and WG3 (Multiphase Extensions).
The group has concentrated on single-phase phenomena, considering that two-phase CFD is not yet of sufficient maturity for a useful assessment basis to be constructed and that identification of the development areas (the task of Writing Group 3) should be undertaken first. The organisation of the report reflects the tasks the Group set itself.
To review critically the NRS problems where the use of CFD is needed for the analysis or where its use is expected to result in major benefits.
To review critically the existing assessment basis for CFD application to NRS issues.
To identify the gaps in the technology base, and the need for further development effort.
To organise a web-based NRS assessment database, regulated by an NEA webmaster.
To continue to look for suitable experiments that could form the basis of benchmarking exercises that are specifically tailored to NRS needs.
To organise an International Workshop, with OECD/NEA sponsorship, to promote the availability and distribution of experimental data suitable for NRS benchmarking, and to monitor the current status of CFD validation exercises relevant to NRS issues.
Beyond 2007, an amalgamation of Writing Groups WG1, WG2 and WG3, together with the NEA web-master and secretariat, is proposed to drive the activities further. This would be a core group of no more than five persons, meeting once per year.
This document is now submitted to the Working Group on the Analysis and Management of Accidents (GAMA) for evaluation.

Keywords: OECD; CFD; NEA; WG2

  • Other report
    Paris: NEA/CSNI/R(2007)13, 2008
    136 Seiten

Publ.-Id: 11028

Spectroscopic characterization of Pt complexation and nanocluster formation on Bacillus sphaericus JG-A12 S-layer

Jankowski, U.; Fahmy, K.; Hennig, C.; Selenska-Pobell, S.; Merroun, M.

In this study, a combination of X-ray absorption spectroscopy (XAS) and Fourier transformed infrared (FT-IR) was used to investigate at molecular scale the coordination of Pt(II) to the S-layer sheets B. sphaericus JG-A12, and to characterize the formation of Pt nanoacluster using this protein layer as template.

  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-489 Februar 2008, 43-43
    ISSN: 1437-322X

Publ.-Id: 11027

Interactions of Paenibacillus sp. JG-TB8 and Sulfolobus acidocaldarius with U(VI): spectroscopic and microscopic studies.

Reitz, T.; Merroun, M. L.; Selenska-Pobell, S.

In this work, a combination of wet chemistry, spectroscopic and microscopic techniques was used to investigate and compare the interactions of uranium(VI) with one representative each of the domains Bacteria and Archaea. The bacterial strain Paenibacillus sp. JG-TB8 was isolated from a microbial consortium cultured from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. This consortium consisted not only of bacteria of the division Firmicutes but also of mesophilic 1.1b-Crenarchaeota. Because isolation approaches of these archaeal strains failed until now, the thermophilic relative Sulfolobus acidocaldius, which has already been found in comparable soil samples, was used for this study.
The U(VI) sorption studies showed that the cells of both microbial strains accumulated significant amounts of uranium.X-ray absorption spectroscopy was used to characterize, at molecular scale, the local coordination of uranium associated with the cells of the studied microorganisms. XANES analysis showed that in both cases the oxidation state of the U(VI) added to the cells was unchanged indicating that U(VI) was not reduced. The EXAFS spectrum of the U(VI) complexes formed by the cells of Paenibacillus sp. JG-TB8 showed a high similarity to that of meta-autunite, indicating that this radionuclide is precipitated by the cells as a meta-autunite-like phase. These uranium precipitates were located at the cell surface and intracellularly as needle-like fibrils as was demonstrated by transmission electron microscope analyses. In the case of Sulfolobus acidocaldarius, EXAFS analysis showed that the structural parameters of the uranium complexes formed by this archaeon are similar to those arising from the complexation of uranium with organic phosphate compounds such as fructose 6-phosphate.

  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 703-710
  • Lecture (Conference)
    5th International Conference Uranium Mining and Hydrology (UMH V), 14.-18.09.2008, Freiberg, Germany

Publ.-Id: 11025

Spectroscopic characterization of Pt-complexation and nanoparticle formation on S-layer protein of bacillus sphaericus JG-A12

Jankowski, U.; Fahmy, K.; Hennig, C.; Selenska-Pobell, S.; Merroun, M.

The strain Bacillus sphaericus JG-A12, isolated from the uranium mining waste pile called Haberland in Saxony, Germany, is capable of selective and reversible accumulation of radionuclides and toxic metals. It was demonstrated that the main role by metal binding is played by the surface of protein layer.
The S-layer possesses a highly ordered lattice structure and can serve as a template for production transportation of noble metals.
The aim of this study was the characterization of the secondary structure and the stability of the protein after complexation Pt and also after the formation of nanoclusters by reduction.
The measurements by Fourier transformed infrared spectroscopy (FT-IR), revealed that the structure of the S-layer protein is stabilized after both sorption or reduction of Pt(II) against acidification.
An aspect for this conclusion is pH induced infrared absorption changes of the Pt(II)-bound S-layer. An effect of different pH-values is the protonation of carboxylic acids caused the reduction of the COO- stretching modes. The denaturation occurs near by pH of 0.8. This is shown by the downshift of amid I absorption.
The aim of the EXAFS measurement was the identification of functional groups of the s-layer protein which are involved in binding Pt(II) or Pt(0). The analysis which has been carried out at synchrotron beam line at ESRF in Grenoble approves the results of IR measurements for identification of functional groups. The first shell contains at a distance of 2.01 ± 0.02 Å oxygen and nitrogen whereas the system can not distinguish between this elements. In the second were found Pt-Pt bindings and the third was dominated by Pt-C bindings.

  • Poster
    School on synchrotron X-ray and IR Methods Focusing on Environmental Sciences, 21.-23.01.2008, Karlsruhe, Deutschland

Publ.-Id: 11024

Interactions of U(VI) with members of a microbial consortium recovered from a uranium mining waste pile: spectroscopic and microscopic studies.

Reitz, T.; Merroun, M. L.; Selenska-Pobell, S.

In this work, a combination of wet chemistry, spectroscopic and microscopic techniques was used to investigate the interactions of U(VI) with the cells of Paenibacillus sp. JG-TB8, a bacterial strain enriched from a microbial consortium isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. This consortium consisted of mesophilic 1.1b-Crenarchaeota and bacteria of the division Firmicutes.
The U(VI) sorption studies showed that cells of the studied Paenibacillus strain accumulated up to 85 mg U/g dry biomass from a solution with an uranium concentration of 120 mg U/l.
X-ray absorption spectroscopy was used to characterize, at molecular scale, the local coordination of uranium associated with the cells of the studied bacterium. XANES analysis showed that the oxidation state of the U(VI) added to the cells was unchanged indicating that U(VI) was not reduced. The EXAFS spectrum of the U(VI) complexes formed by the cells of Paenibacillus sp. JG-TB8 showed a high similarity to that of meta-autunite, indicating that this radionuclide is precipitated by the cells as a meta-autunite-like phase. These uranium precipitates were located at the cell surface and intracellularly as needle-like fibrils as was demonstrated by transmission electron microscope analyses.
The results found in this study indicated that the cells of Paenibacillus sp. JG-TB8 are involved in the biomineralization of uranium at aerobic and acidic conditions.

  • Poster
    School on Synchrotron X-ray and IR Methods Focusing on Environmental Sciences, 21.-23.01.2008, Karlsruhe, Germany

Publ.-Id: 11023

VOF-Simulation des freien Aufstiegs von Öltropfen in Wasser

Schmidtke, M.; Bothe, D.

Die Resultate von VoF-Simulationen zum freien Aufstieg von Öltropfen in Wasser werden mit experimentellen Beobachtungen verglichen. Kleine Öltropfen steigen geradlinig mit einem stationären Nachlauf auf. Große Tropfen steigen in den Simulationen zunächst geradlinig auf mit einem stabilem Nachlauf, dessen Länge mit der Zeit anwächst. Der Tropfen beschleunigt, bis der Nachlauf instabil wird. Mit dem Einsetzen periodischer Wirbelablösung sinkt die Aufstiegsgeschwindigkeit ab auf die Endgeschwindigkeit. Die periodische Wirbelablösung im Nachlauf großer Tropfen geht einher mit einer Formoszillation und einer zickzackförmigen Trajektorie. Es werden Aufstiegsgeschwindigkeit, Tropfenform und Bewegungsverhalten in Abhängigkeit von der Tropfengröße ermittelt und mit experimentellen Resultaten verglichen. Der Dragkoeffizient für zickzackförmig aufsteigende Tropfen ist deutlich höher als für geradlinig aufsteigende Tropfen.

Keywords: Oil drops; drag coefficient; vortex shedding; volume of fluid

  • Lecture (Conference)
    "Mehrphasenströmungen", Jahrestagung des ProcessNet Fachausschusses, 10.-14.03.2008, Weihenstephan / Freising, Deutschland

Publ.-Id: 11022

FTIR study of the photoinduced processes of plant phytochrome phyA using isotope-labeled bilins and DFT calculations

Schwinté, P.; Foerstendorf, H.; Hussain, Z.; Gärtner, W.; Mroginski, M.-A.; Hildebrandt, P.; Siebert, F.

FTIR spectroscopy was employed to analyse the chromophore structure in the parent states Pr and Pfr of plant phytochrome phyA and the respective photoproducts lumi-R and lumi-F. The spectra were obtained from phyA adducts assembled with either uniformly or selectively isotope-labeled phytochromobilin and phycocyanobilin. The interpretation of the experimental spectra is based on the spectra of chromophore models calculated by density functional theory. Global 13C-labelling of the tetrapyrrole allows for the discrimination between chromophore and protein bands in the FTIR difference spectra. All IR difference spectra display a prominent difference band attributable to a stretching mode with large contributions from the methine bridge between the inner pyrrole rings (B-C stretching). Due to mode coupling, frequencies and isotopic shifts of this mode suggest that the Pr chromophore may adopt a distorted ZZZssa geometry with a twisted A-B methine bridge. The transition to lumi-R is associated with only minor changes of the amide I bands indicating limited protein structural changes during the isomerization site of the C-D methine bridge. Major protein structural changes occur upon the transition to Pfr in which the chromophore adopts a ZZEssa-like state. In addition, specific interactions with the protein alter the structure of the B-C methine bridge as concluded from the substantial downshift of the respective stretching mode. These interactions are removed during the photoreaction to lumi-F which affords a ZZZssa-like structure of the chromophore and involves only small protein structural changes.

Keywords: vibrational spectroscopy; chromophore-protein interaction; photoisomerization; isotope- labelling; conformational changes; resonance Raman

Publ.-Id: 11021

Computation of the lift force for single bubbles in a simple shear flow

Schmidtke, M.; Bothe, D.; Warnecke, H.-J.

Bubbles in shear flows experience a lift force, causing them to migrate sideward while they are rising. This lateral migration is also observed in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force – expressed by the lift force coefficient – for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. The pressure and the velocity fields near the interface are investigated and the contribution of dynamic pressure and the circulation of the lift force are discussed.

Keywords: rise of bubbles; lift coefficient; Volume of Fluid method; shear flow

  • Lecture (Conference)
    Fachausschußsitzung VDI-GVC "Mehrphasenströmungen", 07.-08.03.2007, Baden-Baden, Deutschland

Publ.-Id: 11020

Short time thermal processing of materials -beyond electronics and photonics to pipe organ materials

Skorupa, W.

There is a clear and increasing interest in short time thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of processing in the millisecond or nanosecond range. This was recently driven by the need of suppressing the so-called Transient Enhanced Diffusion in advanced boron-implanted shallow pn-junctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields related to silicon technology and beyond. This talk reports shortly about the restart in flash lamp annealing of the Rossendorf group in collaboration with other groups and further on recent experiments regarding shallow junction engineering in germanium, annealing of ITO layers on glass and plastic foil to form an conductive layer as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that short time thermal processing features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century - as a completely different world of materials processing!

Keywords: flash lamp annealing; short time thermal processing; ion implantation; annealing; silicon; transient enhanced diffusion; germanium; silicon dioxide; zinc oxide; indium tin oxide; silicon carbide; silicon based light emission; MOS structures; lead casting; organ pipe materials

  • Invited lecture (Conferences)
    Seminar des Walter-Schottky-Institutes der TU München, 12.02.2008, Garching, Deutschland

Publ.-Id: 11019

Measurements of transient flow fields driven by a discontinuously applied rotating magnetic field

Räbiger, D.; Eckert, S.; Gerbeth, G.

This experimental study considers the transient liquid metal flow which is generated inside a cylindrical container by discontinuously applying a rotating magnetic field (RMF). The focus is on the fluid motion arising from the impulsive spin-up from the resting state, a single pulse or a sequence of RMF pulses. The ultrasonic Doppler velocimetry (UDV) has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both the primary, swirling flow and the secondary flow in the radial-meridional plane. The experimental results show an excellent agreement with recently published numerical results. The investigations reveal that the recirculating flow in the radial- meridional plane undergoes characteristic oscillations. Periodic reversals of the meridional flow direction can be observed for a specific length of the RMF pulses.
Our results demonstrate that the utilisation of a time-modulated rotating magnetic field (RMF) offers a considerable potential to provide optimal flow pattern for an efficient melt mixing. For instance, such tailored methods of electromagnetic stirring can be applied during the solidification of metal alloys, where a well-aimed modification of casting properties is achieved by controlling the melt flow in the bulk and adjacent to the solidification front.

Keywords: liquid metal; rotating magnetic field; spin-up; flow measurements; Ultrasound Doppler method

  • Lecture (Conference)
    GAMM 2008, 31.03.-04.04.2008, Bremen, Germany

Publ.-Id: 11018

Giant stability enhancement of rare-earth implanted SiO2 light-emitting devices by an additional SiON protection layer

Sun, J. M.; Rebohle, L.; Prucnal, S.; Helm, M.; Skorupa, W.

The electrical stability of rare-earth implanted SiO2 light emitting devices was improved by using a SiON dielectric buffer layer in an indium-tin-oxide/SiON/SiO2:Tb /Si device structure. At the expense of a small increase of the electroluminescence threshold voltage, a large increase of the breakdown electric field from 7.5 to 10.5 MV/cm was obtained in the SiO2:Tb layer, and the maximum injection current density was increased by three orders of magnitude from 4 mA/cm2 to 4 A/cm2 . The operation time of the electroluminescence devices was increased by more than three orders of magnitude at an injection current density of ~4 mA/cm2. Our experimental results are consistent with a theoretical model proposed for designing a stable and efficient thin-film light emitting device containing double-stacked dielectric layers.

Keywords: rare earth; electroluminescence; MOS; Terbium; Si-based light emission

  • Applied Physics Letters 92(2008)7, 071103

Publ.-Id: 11017

Synthesis of a Se0/calcite composite using hydrothermal carbonation of Ca(OH)2 coupled with a complex selenocystine fragmentation.

Montes-Hernandez, G.; Charlet, L.; Renard, F.; Scheinost, A. C.; Bueno, M.; Fernández-Martínez, A.

In this study, the hydrothermal carbonation of calcium hydroxide under high CO2-Ar pressure (90 bar) coupled with a complex selenocystine fragmentation under O2-poor and O2-rich conditions was carried out by using a semi-batch
system (sampling with time) in order to synthesize an elemental selenium (Se0)/calcite composite. Under O2-poor conditions (i.e. with purge stage), the composite was mainly characterized by spherical selenium nanoparticles
(<500nm) deposed on the calcite matrix. The carbonate matrix was constituted by nano- and micro rhombohedral crystals (<2µm) and micrometric agglomerates and/or aggregates (<5mµ). For this case, the spherical Se nanoparticles give
a stable red coloration to the composite. In contrast, under O2-rich conditions (i.e. without purge stage), the composite was characterized by hexagonal selenium microparticles (<25µm) dispersed in the calcite matrix. For this case, a gray coloration of composite was observed. In conclusion, the gas purge in the system and the selenocystine dose (mg/kgwater) play a crucial role on the selenocystine fragmentation mechanism during Ca(OH)2 suspension heating (at 90°C) and carbonation stages, this leading the precipitation/growth of elemental selenium with different morphologies and particles sizes. Consequently, it was noticed that the selenocystine fragmentation participates to the precipitation/growth of calcite with unusual morphologies. Finally, the results presented here demonstrate that Se0/calcite composite, with spherical or hexagonal morphologies for elemental selenium can be produced, this composite possibly with a high potential for medical (ex. dietary supplement) or industrial (ex. pigments) applications.

  • Crystal Growth & Design 8(2008)7, 2497-2504

Publ.-Id: 11015

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

Scheinost, A. C.; Kirsch, R.; Banerjee, D.; Fernandez-Martinez, A.; Zaenker, H.; Funke, H.; Charlet, L.

The long-lived radionuclide 79Se is one of the elements of concern for the safe storage of high-level nuclear waste, since clay minerals in engineered barriers and natural aquifer sediments strongly adsorb cationic species, but to lesser extent anions like selenate (SeVIO42−) and selenite (SeIVO32−). Previous investigations have demonstrated, however, that SeIV and SeVI are reduced by surface-associated FeII, thereby forming insoluble Se0 and Fe selenides. Here we show that the mixed FeII/III (hydr)oxides green rust and magnetite, and the FeII sulfide mackinawite reduce selenite rapidly (< 1 day) to FeSe, while the slightly slower reduction by the FeII carbonate siderite produces elemental Se. In the case of mackinawite, both S−II and FeII surface atoms are oxidized at a ratio of one to four by producing a defective mackinawite surface. Comparison of these spectroscopic results with thermodynamic equilibrium modeling provides evidence that the nature of reduction end product in these FeII systems is controlled by the concentration of HSe−; Se0 forms only at lower HSe− concentrations related to slower HSeO3− reduction kinetics. Even under thermodynamically unstable conditions, the initially formed Se solid phases may remain stable for longer periods since their low solubility prevents the dissolution required for a phase transformation into more stable solids. The reduction by Fe2+-montmorillonite is generally much slower and restricted to a pH range, where selenite is adsorbed (pH < 7), stressing the importance of a heterogeneous, surface-enhanced electron transfer reaction. Although the solids precipitated by the redox reaction are nanocrystalline, their solubility remains below 6.3 × 10− 8 M. No evidence for aqueous metal selenide colloids nor for Se sorption to colloidal phases was found. Since FeII phases like the ones investigated here should be ubiquitous in the near field of nuclear waste disposals as well as in the surrounding aquifers, mobility of the fission product 79Se may be much lower than previously assumed.

Keywords: Selenium redox nuclear waste XAFS XANES

  • Journal of Contaminant Hydrology 102(2008), 228-245
  • Lecture (Conference)
    Migration ´09 - 12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 11013

Pressure independence of intensity clamping during filamentation: theory and experiment

Bernhardt, J.; Liu, W.; Chin, S. L.; Sauerbrey, R.

Because of the dynamic equilibrium between Kerr self-focussing and plasma induced defocusing
and the inexistence of collisional ionization the critical intensity during femtosecond laser
filamentation in air is independent of pressure. An analytical analysis is given which is justified
by a direct experimental verification.
PACS: 42.65.Jx, 52.38.Hb, 52.70.Kz

Keywords: Pressure independence of intensity clamping during filamentation; Theory and experiment

  • Applied Physics B 91(2008)1, 45-48

Publ.-Id: 11012


Sauerbrey, R.; Schramm, U.

Keywords: Laser-Particle-Acceleration; Electron laser field; Laser ion acceleration; Applications

  • Invited lecture (Conferences)
    GSI Kolloquium, 22.01.2008, Darmstadt, Deutschland

Publ.-Id: 11011

Laser-driven proton oncology - a unique new cancer therapy?

Ledingham, K. W. D.; Galster, W.; Sauerbrey, R.

In 2000, the University of Strathclyde, collaborating with the Rutherford Appleton Laboratory, organized the first workshop dealing with the potential of highpower laser technology in medicine. Two areas of potential were identified: firstly the production of positron emission tomography (PET) isotopes; and secondly, the potential for laser-accelerated proton and heavy ion beams for therapy. The attendees, mainly clinicians and radiation physicists, emphasised that the laser community should concentrate on developing laser and target technology for therapy rather than isotope production because of the potential advantages over conventional accelerator technology for that purpose. On the 30 March 2007, the universities of Strathclyde and Paisley organized a follow-up meeting to identify the progress made in laser-driven proton and ion beam technology with applications leading to proton and ion beam therapy for deep-seated tumours. The meeting was supported by the Scottish Uni!
versities Physics Alliance (SUPA) - an organization set up in Scotland to bring together all of the physics departments collaborating with life scientists to work on ground-breaking new science which no single university could attempt. This is a summary of the meeting.

Keywords: highpower laser technology in medicine; positron emission tomography (PET); laser-accelerated proton and heavy ion beams for therapy; laser-driven proton and ion beam technology

Publ.-Id: 11009

Yttrium-86-labelled human serum albumin microspheres: relation of surface structure with in vivo stability

Schiller, E.; Bergmann, R.; Pietzsch, J.; Noll, B.; Sterger, A.; Johannsen, B.; Wunderlich, G.; Pietzsch, H.-J.

Radiolabelled particles are an attractive tool in the therapy of malignancies of the liver. We consider particles manufactured from denatured human serum albumin (HSA) as useful carriers of therapeutic radionuclides. Covalent attachment of suitable chelators onto the surface of the spheres promises an easy access to radiolabelled HSA microspheres.

We synthesized 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (DOTA) bearing smooth, medium-rough and rough surfaced HSA microspheres (mean diameter: 25 μm). In vitro stability of 86Y-labelled particles was determined after incubation in human plasma and in a DTPA challenge experiment. In vivo stability of 86Y DOTA-HSA microspheres was determined after single intravenous application in rats. Subsequently, the particles were completely trapped in the lung microvasculature. Thus, the lung serves in our experiments as target organ.

DOTA-HSA microspheres were 86Y labelled in reproducible high yields (N95%). No differences between smooth and rough surfaced spheres were found for both DOTA coupling and 86Y labelling. Labelled microspheres showed high in vitro stability in human plasma and in DTPA solution with only 8±1% and 2±0% loss of radioactivity from the surface, respectively, 48 h postinjection (pi). The three batches (smooth, medium-rough and rough surfaced microspheres) differed considerably in their radioactivity recovery in the lungs of rats 48 h pi. Smooth particles showed the highest in vivo stability of the radiolabel on the surface of the spheres, presumably because of slower proteolytic degradation.

We found that for the preparation of HSA-derived microspheres for radiotherapeutic application, smooth surfaced spheres are superior to rough spheres due to their higher in vivo stability of the radionuclide fixation.

Keywords: Human serum albumin microspheres; Yttrium-86; In vivo stability; Radiolabelled particles; Radiotherapy

Publ.-Id: 11008

Präparative Reinigung polarer, mehrfunktionaler Liganden

Röhrich, A.

kein Abstract verfügbar

  • Lecture (others)
    Workshop - Möglichkeiten und Grenzen der HPLC in den Lebenswissenschaften, 01.02.2008, Dresden, Deutschland

Publ.-Id: 11007

Soft X-ray Absorption and Emission Spectroscopic Investigation of Carbon and Carbon:Transition Metal Composite Films

Abrasonis, G.; Berndt, M.; Krause, M.; Kuepper, K.; Munnik, F.; Kolitsch, A.; Möller, W.

Carbon and C:V, C:Co, C:Cu nanocomposite films grown by ion beam cosputtering in the temperature range from room temperature (RT) to 500 °C are investigated. Soft X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) have been used to determine electronic structure of the occupied and unoccupied electronic states of the coexisting carbon and transition metal (TM) constituents. The results from the spectroscopy are supplemented by the film composition data and TM inclusion phase structural information obtained by elastic recoil detection analysis and X-ray diffraction, respectively. The TM(2p) XAS shows that V (Cu) is in carbidic (metallic) state over the whole temperature range, while Co shows a transition from a carbidic toward a metallic state when the growth temperature increases from RT to 500 °C. The C(1s) XAS demonstrates that the increase in the growth temperature favors the formation of graphite-like structures in carbon films. On the other hand, the TM metal incorporation strongly promotes the sp3 admixture in the surrounding carbon phase which manifests itself through a significant increase in the intensity of a feature in the C(1s) XAS spectra positioned at ~291 eV resulting from 1s → σ* transitions. In addition, the codeposition of TM atoms with carbon enhances the formation of carbon structures with the prominent peak between π* and σ* regions in the C(1s) XAS spectra positioned at ~288.5 eV. The effect is independent of the TM tendency to form carbides or TM state (carbidic metallic) while its magnitude increases concomitantly with the TM content and decreases when the crystallinity degree of the inclusion phase increases. The results are discussed on the basis of the nanoparticle imposed curvature on the surrounding carbon network and interactions at the atomic level at the C−TM interfaces.

Publ.-Id: 11005

Question of dynamic chirality in nuclei: The case of 134Pr

Tonev, D.; de Angelis, G.; Brant, S.; Petkov, P.; Dewald, A.; Dönau, F.; Balabanski, D. L.; Zhong, Q.; Pejovic, P.; Bazzacco, D.; Bednarczyk, P.; Camera, F.; Curien, D.; Della Vedova, F.; Fitzler, A.; Gadea, A.; Lo Bianco, G.; Lenzi, S.; Lunardi, S.; Marginean, N.; Möller, O.; Napoli, D. R.; Orlandi, R.; Sahin, E.; Saltarelli, A.; Valiente Dobon, J.; Zell, K. O.; Zhang, J.-Y.; Zhang, Y. H.; Frauendorf, S.

Lifetimes of exited states in 134Pr were measured by means of the recoil distance Doppler-shift and Doppler-shift attenuation techniques. The branching ratios and the electric or magnetic character of the transitions were also investigated. The experiments were performed at IReS, Strasbourg, using the EUROBALL IV spectrometer, in conjunction with the inner bismuth germanate ball and the Cologne coincidence plunger apparatus. Exited states in 134Pr were populated in the fusion-evaporation reaction 119Sn(19F, 4n)134Pr. The possible chiral interpretation of twin bands was investigated in the two-quasiparticle triaxial rotor and interacting boson-fermion-fermion models. The analysis of the wave functions has shown that the possibility for the angular momenta of the proton, neutron, and core to find themselves in the favorable, almost orthogonal geometry, is present but is far from being dominant. The structure is characterized by large beta and gamma fluctuations. The existence of doublets of bands in 134Pr can be attributed to weak chirality dominated by shape fluctuations.

Publ.-Id: 11004

n+ doping of Ge by P implantation and subsequent RTA or FLA

Posselt, M.; Wündisch, C.; Schmidt, B.; Anwand, W.; Grötzschel, R.; Mücklich, A.; Skorupa, W.; Hortenbach, H.; Gennaro, S.; Bersani, M.; Guibertoni, D.; Möller, A.; Pelzing, P.; Clarysse, T.; Simoen, E.; Satta, A.; Bracht, H.

Abstract not available. For details, please contact the first author.

Keywords: Electrical doping; Germanium; Ion Implantation; Diffusion; Activation

  • Lecture (others)
    Seminar talk at IMEC Leuven (Belgium), 07.02.2008, Leuven, Belgium

Publ.-Id: 11003

Neptunium(V) reduction by humic substances of varying functionality

Schmeide, K.; Bernhard, G.

The time dependence of the reduction of Np(V) to Np(IV) by humic substances of varying functionality has been studied under anaerobic conditions between pH 3.5 and pH 9.0. Synthetic humic acids with pronounced redox functionality were studied in comparison to natural humic substances. For Np redox speciation in solution solvent extraction, NIR absorption spectroscopy and ultrafiltration were applied. Exemplary, the application of a synthetic HA is shown for the study of the Np(IV) sorption onto kaolinite in the presence of HA.

Keywords: neptunium; pentavalent; tetravalent; humic acid; sorption; reduction

  • Contribution to proceedings
    Plutonium Futures “The Science” 2008, 07.-11.07.2008, Dijon, France
  • Poster
    Plutonium Futures “The Science” 2008, 07.-11.07.2008, Dijon, France

Publ.-Id: 11002

Hydrophile, macrocyclische Amine: Reinigung mit Problemen

Ruffani, A.

kein Abstract verfügbar

  • Lecture (others)
    Workshop „Möglichkeiten und Grenzen der HPLC in den Lebenswissenschaften“, 01.02.2008, Dresden-Rossendorf, Deutschland

Publ.-Id: 11001

Bis(2-pyridylmethyl) derivatives of 1,4,7-triazacyclononane: promising ligands for radiolabeling of biomolecules

Ruffani, A.

kein Abstract verfügbar

  • Lecture (Conference)
    5th SUPRAPHONE Meeting, 29.05.-01.06.2008, Prague, Czech Republic

Publ.-Id: 11000

1,4,7-Triazacyclononane (TACN) ligands with pendant pyridyl arms - New versatile bifunctional chelating agents (BFCAs)

Ruffani, A.; Stephan, H.; Steinbach, J.; Gasser, G.; Spiccia, L.; Graham, B.

Radiopharmaceuticals based on metallic radionuclides, such as 64/67Cu, 99mTc, 186/188Re and 86/90Y, are often used for diagnostic and therapeutic purposes (1, 2). These nuclides are usually enveloped in organic ligands, such as heteromacrocyclic systems. To be effective, the ligands have to show fast metal complexation kinetics, form complexes with high in vitro and in vivo stability and contain a group that can be linked to biomolecules. We have developed a new ligand scaffold - based on bis(2-pyridylmethyl)triazacyclononane (DMPTACN) – that satisfies these requirements. This structure allows for the introduction of linker groups, such as carboxylic acids, maleinimide or isothiocyanate, thereby facilitating coupling of targeting molecules.

A new TACN derivative, containing two pyridyl pendant arms as well as a carboxylic group for coupling to biomolecules has been synthesized and its copper(II) binding properties investigated. Conjugation of a stabilized octapeptide (bombesin βAla-βAla-[Cha13, Nle14]) was successfully achieved via amide coupling (3). Both the free ligand and the bombesin bioconjugate can rapidly form very stable radiocopper complexes. In vitro ligand competition experiments and stability studies in rat plasma medium gave no evidence of transchelation or demetalation. Biodistribution studies of the bombesin conjugate revealed an accumulation of the compound in the pancreas, which is the organ with highest levels of gastrin-releasing peptide receptor (GRPR) targeted by bombesin.
Our radiopharmalogical data indicate that bifunctional chelating TACN agents are attractive candidates for developing new copper radiotherapeutics. In this perspective, particular BFCAs will be attached to carrier molecules, such as oligonucleotides, antibodies and synthetic polymers, to deliver radiocopper isotopes to target tissues.

1. Anderson C.J., Welch M.J. (1999) Metal complexes as diagnostic tools. Coord. Chem. Rev. 184, 3-66.
2. Volkert W.A., Hoffman T.J. (1999) Therapeutic radiopharmaceuticals. Chem. Rev. 99, 2269-2292.
3. Gasser G., Tjioe L., Graham B., Belousoff M. J., Juran S., Walther M., Künstler J.U., Bergmann R., Stephan H., Spiccia L. (2008)
Synthesis, Copper(II) Complexation, 64Cu-Labeling, and Bioconjugation of a New Bis(2-pyridylmethyl) Derivative of 1,4,7-
Triazacyclononane. Bioconjugate Chem. In press

  • Lecture (Conference)
    7th International Symposium on Polymer Therapeutics: from Laboratory to Clinical Practice, 26.-28.05.2008, Valencia, Spain

Publ.-Id: 10999

Patterning of magnetic structures on austenitic stainless steel by ion beam nitriding

Menendez, E.; Martinavicius, A.; Liedke, M. O.; Abrasonis, G.; Fassbender, J.; Sort, J.; Surinach, S.; Baro, M. D.; Nogues, J.

Nitriding of austenitic stainless steel (ASS) at moderate temperatures (~400ºC) leads to the formation of the supersaturated nitrogen solid solution often called in the literature “expanded austenite” or γN phase [1,2]. This causes an enhancement of the microhardness and the wear resistance without loss of the corrosion resistance. Moreover, this phase shows ferromagnetic behavior, whose origin is linked to the expansion of the austenite (γ) lattice due to the incorporation of nitrogen atoms into interstitial positions [3,4]. Actually, since there is a nitrogen depth profile and the onset of ferromagnetism is connected with nitrogen concentrations of ~15 at.%, the nitrided layer consists of two magnetically different parts (paramagnetic and ferromagnetic) determined by the obtained nitrogen concentration.

In this study, we report the influence of the nitriding temperature and time on the ASS ferromagnetic properties. AISI 304L ASS polycrystalline samples (discs of 10 mm diameter and 2 mm thickness) have been ion beam nitrided in the temperature range of 300-400ºC. The ion energy and the ion current density were ~1 keV and 0.5 mA/cm2 (the corresponding ion flux of ~5•1015 ions•cm-2•s-1), respectively. The processing times were 5 and/or 30 minutes [2]. Periodic arrays of ferromagnetic structures in the micrometer range have been prepared at the surface of the samples using a 2000 mesh Cu transmission electron microscopy grid as a shadow mask (mesh size of 7.5 x 7.5 µm2, 12.5 µm pitch, 20 µm thickness and 3.05 mm diameter). The structure was characterized by X-ray diffraction (XRD) and nuclear reaction analysis (NRA). The magnetic properties were determined by magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM).
The XRD patterns of the nitrided ASS samples are presented in Figure 1. The XRD pattern consistent with the FCC lattice structure can be identified for the virgin ASS sample (not shown). For the nitrided samples, each austenite peak exhibits a satellite peak, located at lower diffraction angles which is related with the formation of the “expanded austenite”. The amount of this “expanded” phase increases with the processing temperature, as it is evidenced by the increase of intensity of the γN XRD peaks in detriment to the γ ones.
This is consistent with NRA observations. For instance, a nitrided layer of around 1 µm depth is obtained in the sample nitrided at 400ºC for 30 min, whereas ~15 at.% of nitrogen is obtained around 0.5 µm of depth.
MOKE measurement results of the virgin and the nitrided sample at 400°C for 5 min are compared in Figures 2(a) and 2(b) (patterned area).
It can be seen that the virgin sample does not show any hysteretic behavior, i.e. it is non-ferromagnetic. Conversely, the nitrided samples show clear hysteresis loops indicating the existence of ferromagnetic constituents in the nitrided layer. Figure 2(c) shows the AFM image of a patterned area of the nitrided sample which shows that a moderate sputtering process of the surface has taken place during nitriding resulting in the formation of the periodic array of squared pits. Figure 2 (d) is the corresponding MFM image in an applied magnetic field of 70 mT, where a magnetic dipolar contrast can be clearly seen in each entity, confirming the feasibility of the production of periodic arrays of isolated ferromagnetic structures. It is worth noting that the hysteresis behavior of the continuously nitrided areas and the patterned ones are quite similar due to the fact that the induced ferromagnetic structures are relatively large (micrometer range), leading to entities with magnetic multi-domain configurations.

[1] M.P. Fewell et al., Surf. Coat. Technol. 131, 300 (2000)
[2] G. Abrasonis, et al., J. Appl. Phys. 97, 083531 (2005)
[3] O. Öztürk and D.L. Williamson, J. Appl. Phys. 77, 3839 (1995)
[4] J. Baranowska, Vacuum 81, 1216 (2007)

Keywords: magnetism; stainless steel; nitriding; patterning; ion

  • Poster
    International Conference on Magnetics, Intermag 2008, 04.-08.05.2008, Madrid, Spain

Publ.-Id: 10998

Sc3AlN - A New Perovskite

Höglund, C.; Birch, J.; Beckers, M.; Alling, B.; Czigány, Z.; Mücklich, A.; Hultman, L.

Sc3AlN with perovskite structure has been synthesized as the first ternary phase in the Sc-Al-N system. Magnetron sputter epitaxy at 650 °C was used to grow single-crystal, stoichiometric Sc3AlN(111) thin films onto MgO(111) substrates with ScN(111) seed layers as shown by elastic recoil detection analysis, X-ray diffraction, and transmission electron microscopy. The Sc3AlN phase has a lattice parameter of 4.40 Å, which is in good agreement with the theoretically predicted 4.42 Å. Comparisons of total formation energies show that Sc3AlN is thermodynamically stable with respect to all known binary compounds. Sc3AlN(111) films of 1.75 µm thickness exhibit a nanoindentation hardness of 14.2 GPa, an elastic modulus of 249 GPa, and a room-temperature electrical resistivity of 41.2 µΩ cm.

Publ.-Id: 10997

Entwicklung des Neutronentransportcodes TransRay und Untersuchungen zur zwei- und dreidimensionalen Berechnung effektiver Gruppenwirkungsquerschnitte

Beckert, C.

Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing in 3D wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert.
Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (Vakuum oder Dampf) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: Lineare Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.

Keywords: Reactor physics; calculational methods; neutron transport; transport methods; ray tracing; cross sections; cell calculation; absorber rod; void

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-492 2008
    ISSN: 1437-322X


Publ.-Id: 10996

Radiation damage in helium-implanted diamond

Nasdala, L.; Grambole, D.; Harris, J. W.; Wildner, M.; Hofmeister, W.

Diamond platelets were implanted with 8.8 MeV He2+ ions, the equivalent of alpha particles generated in the natural 212Po ---> 208Pb decay (Th decay chain). Implantation densities were varied in the range 1012 - 1017 ions per cm². Visible green colouration was produced at He2+ fluences _>1015 cm-2. The radioinduced colour is mainly due to a broad absorption band at ca. 16000 cm-1, which is assigned to the GR1 centre. Raman line scans showed that a narrow, stongly damaged area is formed ca. 29 µm below the sample surface. This corresponds very well with the distribution of Frenkel-type defects as predicted by Monte Carlo simulations using the SRIM program 1. Raman data obtained from naturally radiocoloured diamonds are discussed in light of our new results.
1 Ziegler JF, Biersack JP, Littmark U. The stopping and range of ions in solids. Pergamon Press, New York, 1985.

  • Lecture (Conference)
    8th International Conference on Raman Spectroscopy Applied to the Earth Sciences (GeoRaman08), 02.-06.06.2008, Ghent, Belgium
  • Contribution to proceedings
    8th International Conference on Raman Spectroscopy Applied to the Earth Sciences (GeoRaman08), 02.-06.06.2008, Ghent, Belgium
    Book of abstracts, 52

Publ.-Id: 10995

The origin of the Energy-Dose window in Separartion-by-Implanted-Oxygen (SIMOX) materials processing

Koegler, R.; Ou, X.; Skorupa, W.; Moeller, W.

Separation-by-Implantated-Oxygen (SIMOX) is an established technique to manufacture a buried oxide layer in silicon (SOI) by ion implantation and annealing. The so called energy-dose window defines implantation parameters suitable for the formation of a continuous buried oxide layer with the lowest ion dose. The study concerns the reason why defined combinations of ion energy and ion dose result in a high quality oxide layer. Excess defects induced by the O implantation are shown to influence the oxide layer formation. The depth distribution of excess defects fits very well with the final depth position of the oxide layer for O implants in the energy-dose window.

Keywords: Ion implantation; silicon-on-insulator; SIMOX; defects; oxygen

Publ.-Id: 10994

Comparative investigation of the interaction of uranium with lipopolysaccharide and peptidoglycan

Barkleit, A.; Moll, H.; Bernhard, G.

Microorganisms are very important for the bioremediation of the environment because they are able to adsorb radionuclides and other heavy metals. They significantly influence mobilization and immobilization of metal ions in soils.
We investigated representative the complexation of the uranyl ion with main parts of bacterial cell walls. Lipopolysaccharide (LPS) is the principal component of the cell wall of gram-negative bacteria, whereas peptidoglycan (PGN) represents the basis of the cell wall of gram-positve bacteria. Both biomolecules contain a high density of metal-binding functionalities like carboxyl, amino, and hydroxyl groups. LPS offers additionally a high amount on phosphoryl groups, which are missing in PGN.
We investigated the interaction of the uranyl cation (UO22+) with the biopolymers LPS and PGN by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH range (2.4 – 9) and at environmentally relevant low uranium concentrations (10-4 – 10-5 M).
Using potentiometric titration, the dissociation constants of the respective functional groups were determined. Furthermore essential uranyl complexes and their stability constants were identified.
With the aid of time-resolved laser-induced fluorescence spectroscopy (TRLFS) the luminescence properties of uranyl complexes with the biopolymers and the associated stability constants were investigated. At low pH values both biomolecules effect an increase of the luminescence intensity and a red-shift of about 8-10 nm, compared to the free UO22+ ion. With LPS the luminescence intensity increases up to pH 8. In contrast to LPS, the PGN polymer causes a decrease of the luminescence intensity over pH 4.5, indicating, that a non-luminescent complex has built.
As a result from both methods, we found that the uranyl ion prefers with LPS phosphoryl coordination, whereas PGN, with a lack of phosphoryl groups, forms stable carboxylate complexes.

  • Lecture (Conference)
    5th International Conference Uranium Mining Hydrogeology (UMH V), 14.-18.09.2008, Freiberg, Germany
  • Contribution to external collection
    Broder J. Merkel, Andrea Hasche-Berger: Uranium, Mining and Hydrogeology, Berlin: Springer Verlag, 2008, 978-3-540-87745-5, 753-754

Publ.-Id: 10993

Theoretical study on the highest oxidation states of Pu

Tsushima, S.

It has been demonstrated recently that quantum chemical calculations can accurately perdict redox potentials of An(VI)/An(V) couples (An = U, Np, Pu, Am) if multireference effect and spin-orbit effects are treated properly [1,2]. The An(VI)/An(V) redox potentials obtained at the multireference CASPT2 level calculations with spin-orbit corrections were found to have fairly good agreement with those obtained by experiments.
Here, I extend such calculations to the higher oxidation states of actinide, namely Pu(VII) and Pu(VIII). Pu(VII) is known to be meta-stable in aqueous solution. Recently, Nikonov et al. have suggested that Pu(VIII) may be obtained by the ozonation of Pu(VI), although they were not able to find a direct evidence for the presence of Pu(VIII) [3]. The present work aims to discuss from a theoretical point of view whether or not Pu(VIII) may exist in water. Geometry optimizations and energy calculations of the complexes were performed at the B3LYP level, and spin-orbit effects were calculated separately at the CASSCF level.
The redox potential of the PuVIIIO4(OH)2 2-/ PuVIIO4(OH)2 3- couple was found to be as high as ~1.7V. At very high pH, Pu(VII) may exist as a penta-oxo complex, PuVIIO5(OH)4-. The redox potential of PuVIIIO5(OH)3-/ PuVIIO5(OH)4- couple was found to be ~1.3V. Spin-orbit effect was found to play a very important role for the total redox potential because the ground state energy lowering of Pu(VII) due to the spin-orbit splitting depends highly on the number of coordinating oxo ligands. The effect of coordinating ligands (OH-, CO3 2- etc.) and coordination number on the total redox potential was also studied. The calculations suggest that Pu(VIII) is unlikely to exist in both acidic and alkaline aqueous solutions, while Pu(VIII) may be present in non-aqueous solvents with a large redox window.

[1] Tsushima,S; Wahlgren, U.; Grenthe, I. J. Phys. Chem. A 2006, 110, 9175.
[2] Shamov, G.A.; Schreckenbach, G. J. Phys. Chem. A 2005, 109, 10961.
[3] Nikonov, M.V.; Gogolev, A.V.; Tananaev, I.G.; Myasoedov, B.F. Radiochemsitry 2004, 46, 340.

Keywords: Plutonium; quantum chemistry; redox potential

  • Lecture (Conference)
    Plutonium Futures "The Science" 2008, 07.-11.7.2008, Dijon, France

Publ.-Id: 10992

Natural and Engineered Nanoparticles in the Environment: A presentation of current activities of the AK Aquatic Nanoscience & Nanotechnology

von der Kammer, F.; Baalousha, M.; Baun, A.; Hassellov, M.; Delay, M.; Thieme, J.; Zänker, H.; Neumann-Hensel, H.; Handy, R.; Hochella, M.

For more than two decades aquatic chemistry is constantly gaining knowledge about nanoscale processes in the environment. While in early years the co-transport of contaminants in the saturated zone of aquifers has been in the focus of aquatic nanosciences and nanogeosciences, nowadays the research activities have broadened and span across several disciplines. In the course of R & D activities on nanomaterials the question of the behavior, fate and useful or adverse effects of nanoparticles in the environment arose and has boosted the activities quite substantially. The working group Aquatic Nanosciences and Nanotechnology has responded to the current development by inviting European scientists from different fields to contribute their expertise into the group’s discussions and activities while still keeping the core expertise on characterization techniques inherited from the former working group “Colloids”. In 2007 the working group organized an international workshop which was held in Vienna during the 10th and 11th December. The aim of the event was to offer a platform for bridging the different disciplines and exchange the current knowledge in the fields. Scientists from aquatic and environmental chemistry, nanogeosciences, nano-engineering, eco-toxicology and risk assessment presented their contributions to the current state of the art. The overall conclusions drawn from 29 presentations are given.

Keywords: Natural nanoparticles; engineered nanoparticles; environment; natural waters

  • Lecture (Conference)
    Wasser 2008. Jahrestagung der Wasserchemischen Gesellschaft, 28.-30.04.2008, Trier, Germany

Publ.-Id: 10991

Dipole-strength functions studied in photon-scattering experiments at ELBE

Schwengner, R.

Dipole-strength functions studied in photon-scattering experiments at ELBE

  • Invited lecture (Conferences)
    Seminar, 15.01.2008, Durham, North Carolina, USA

Publ.-Id: 10990

P implantation into preamorphized germanium and subsequent annealing: Solid phase epitaxial regrowth, P diffusion, and activation

Posselt, M.; Schmidt, B.; Anwand, W.; Grötzschel, R.; Heera, V.; Mücklich, A.; Wündisch, C.; Skorupa, W.; Hortenbach, H.; Gennaro, S.; Bersani, M.; Giubertoni, D.; Möller, A.; Bracht, H.

Phosphorus implantation (30 keV, 3x1015 cm−2) into preamorphized Ge and subsequent rapid thermal or flash lamp annealing is investigated. During annealing a significant P diffusion in amorphous Ge is not observed. However, the fast solid phase epitaxial regrowth causes a rapid redistribution of P. After completion of the regrowth and at temperatures above 500 °C, a concentration-dependent diffusion of P in crystalline Ge takes place and leads to considerable loss of P toward the surface. An appreciable influence of implantation defects on the diffusion coefficient of P is not detected. For 60 s rapid thermal annealing at 600 °C and for 20 ms flash lamp annealing at 900 °C, the junction depth and the sheet resistance vary between 140 and 200 nm and between
50 and 100 Ohm, respectively, and the maximum electrical activation of P is about 3–7 x1019 cm−3

Keywords: Germanium; electrical doping; ion implantation; annealing; diffusion; activation; solid-phase epitaxial regrowth

  • Journal of Vacuum Science & Technology B 26(2008), 430-434

Publ.-Id: 10989

Beschleunigen mit Licht

Schramm, U.

Keywords: Laserplasma Beschleuniger

  • Invited lecture (Conferences)
    Physikalisches Kolloquium, 23.10.2007, Dresden, Germany

Publ.-Id: 10988

Equation of state for strongly interacting matter: collective effects, Landau damping and predictions for LHC

Schulze, R.; Bluhm, M.; Kämpfer, B.

Abstract for the description of the hydrodynamic phase of strongly interacting matter in relativistic HIC the equation of state (EOS) is of utmost importance. Lattice QCD can provide useful information on the EOS, mainly for small net baryon densities. The QCD quasiparticle model (QPM) provides a means to map lattice results into regions relevant for a variety of experiments. Recent work has enabled us to include collectives modes and damping effects into the QPM. Among physical implications are predictions for forthcoming heavy-ion collisions at LHC/ALICE.

Keywords: QCD; equation of state; EOS; quasiparticle; model; plasmon; plasmino; plasmons; plasminos; quark; gluon; plasma; Landau; damping; characteristics

  • Contribution to proceedings
    XLVI International Winter Meeting on Nuclear Physics, 20.-26.1.2008, Bormio, Italy
    Proceedings of the XLVI International Winter Meeting on Nuclear Physics, Milano: Università degli Studi di Milano, 63-69
  • Contribution to WWW
  • Lecture (Conference)
    XLVI International Winter Meeting on Nuclear Physics, 22.01.2008, Bormio, Italien

Publ.-Id: 10987

Prospects for Applications of Laser-Accelerated Particles

Schramm, U.; Sauerbrey, R.

Invited talk on possible medical applications of laser accelerated particle beams

Keywords: laser ion acceleration; FELs

  • Invited lecture (Conferences)
    International Symposium on Ultrafast Intense Laser Science ISUILS 07, 24.-27.9.2007, Pisa, Italy

Publ.-Id: 10986

Focusing and transport of laser-accelerated protons with quadrupoles

Schollmeier, M.; Geißel, M.; Flippo, K.; Becker, S.; Blazevic, A.; Grüner, F.; Harres, K.; Nürnberg, F.; Rambo, P.; Schramm, U.; Schreiber, J.; Schwarz, J.; Atherton, B.; Habs, D.; Hegelich, B. M.; Roth, M.

Focusing and transport of laser-accelerated protons with quadrupoles

Keywords: Laser acceleration of ions; beam transport; quadrupole lenses PMQ

  • Contribution to external collection
    in: GSI Jahresbericht, Darmstadt: GSI, 2008

Publ.-Id: 10985

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