Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Changes in hardness and elasticity of a Ti6Al4V alloy under helium irradiation

Chen, S. H.; Schumacher, G.; Xu, Z. Y.; Richter, E.

Ti6Al4V specimens have been irradiated at different temperatures with 200 keV He ions. Microhardness and elastic modulus of the unirradiated and irradiated specimens were measured by means of the nano-indentation technique and analyzed using the Oliver-Pharr method. The indentation depth of all samples is 700 nm, which is comparable in magnitude to the ion range. The subsurface structure of the Ti6Al4V specimens was investigated by the X-ray diffraction technique. The measurements indicate that the microhardness increased with the irradiation temperature from room temperature to 600 degrees C while the elastic modulus almost monotonically decreased. The Irradiation at 700 degrees C, however, caused softening and slight increase of the elastic modulus within the surface layer of the specimens. The hardening and reduction of the elastic modulus of the Ti6Al4V alloy under irradiation conditions used in this study is tentatively explained by a model based on the presence of point defects and dispersed obstacles of P-precipitates. The softening and slight increase of elastic modulus of helium-irradiated Ti6Al4V at 700 degrees C might be related to the coarsening of beta-precipitates and formation of the hybrid gamma-TiH phase in alpha-phase.

  • Journal of Nuclear Materials 358(2006)1, 26-34

Publ.-Id: 9064

DYN3D-MSR spatial dynamics code for Molten Salt Reactors

Krepel, J.; Rohde, U.; Grundmann, U.; Weiß, F.-P.

The development of spatial dynamics code for Molten Salt Reactors (MSR) is reported in this paper. The graphite-moderated channel type MSR - one of the 'Generation IV' concepts - was selected for the numerical simulation. It has several peculiarities (e.g. the drift of delayed neutrons precursors), which disable the use of standard dynamics codes. Therefore, the own DYN3D-MSR code was developed. It is based on the light water reactor code DYN3D and it allows transients simulation by 3D neutronics and parallel channel thermal-hydraulics. The neutronics and thermal-hydraulics were modified for the MSR peculiarities, where the experience from DYN1D-MSR development was exploited. The code was validated on experimental results from the MSRE experiment done in Oak Ridge National Laboratory and by the comparison with other codes especially with the 1D version. However, by the 3D code transients can be simulated, where space-dependant efforts are relevant, like local blockage of fuel channels or local temperature perturbations.

Keywords: Molten; Salt; Dynamics; MSR; MSRE; MSBR

  • Annals of Nuclear Energy 34(2007), 449-462

Publ.-Id: 9063

Corrigendum to "Nickel assisted metal induced crystallization of silicon: Effect of native silicon oxide layer"

Pereira, L.; Martins, R. M. S.; Schell, N.; Fortunato, E.; Martins, R.

This work focuses on the role of the native oxide layer (SiO2) on the nickel (Ni)-assisted crystallization of amorphous silicon (a-Si). In some samples, the native oxide was removed using a HF-diluted solution before Ni layers with 0.5 nm be deposited on a-Si. The results show that the presence of a thin SiO2 layer of about 3 nm between the a-Si and the Ni delays the crystallization process. Ellipsometry data show that, after annealing for 5 h at 500 °C, the HF-cleaned sample presents a crystalline fraction of 88%, while the one with the native oxide has only 35%. This difference disappears after 20 h where both samples present similar crystalline fraction. These facts are also reflected on the film's electrical properties, where the activation energy for samples annealed for 5 h rises from 0.42 eV to 0.55 eV, when the oxide layer is removed. After 20 h and 30 h, the activation energy is around 0.55 eV for both kinds of samples, meaning that films with similar electrical properties are now obtained. However, the XRD data suggest the presence of some structural differences attributed to slight differences on the crystallization process.

Keywords: Polycrystalline silicon; Nickel-assisted crystallization; Spectroscopic ellipsometry

  • Thin Solid Films 511-512(2006), 275-279
  • Poster
    E-MRS 2005, 31.05.-03.06.2005, Strasbourg, France

Publ.-Id: 9062

Novel wire-mesh sensor for the investigation of non-conducting fluids

Da Silva, M. J.; Schleicher, E.; Hampel, U.

Conductivity wire-mesh sensors have been successfully employed in the investigation of two-phase flows in the past. Since the measuring principle requires at least one continuous conductive phase, wire-mesh sensors have almost exclusively been used for the investigation of air-water or steam-water systems. Nevertheless, non-conducting fluids such as oil or organic liquids often occur in industrial applications, for instance, in chemical and petrochemical industry. The experimental investigation of multiphase flows involving non-conducting fluids is therefore of large interest. For this reason we developed a novel wire-mesh sensor based on measurements of the electrical permittivity (capacitance) which is suitable for the investigation of non-conducting fluids. The prototype sensor consists of two layers of 16 steel wires each. The system can at the moment produce cross-sectional phase distribution images with 625 frames per second. Sensor and associate electronic were evaluated showing good accuracy and reproducibility in the permittivity measurement. Initial results of an air-oil bubbly flow as well as a slug flow measurement are presented.

Keywords: capcitance measurement; relative permittivity; wire-mesh sensor; two-phase flow; non-conducting fluid

  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Proceedings of 6th International Conference on Multiphase Flow, paper S7_Thu_B_51, 978-3-86010-913-7
  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9061

Analysis of wafer stresses during millisecond thermal processing

Smith, M.; Seffen, K.; Mc Mahon, R.; Voelskow, M.; Skorupa, W.

A flash lamp has been used to uniformly anneal large wafers with diameters approaching 100 mm. The equipment applies a pulse, with duration of 3-20 ms, resulting in large transient thermal gradients in the wafer. In this paper, we present separate models of the thermal reaction of this process and its effect upon the mechanical behavior, in order to predict stresses and shape changes, and to capture practical phenomenon. We further use the model to follow changes in the expected response consequent on altering process conditions, such as preheating and pulse duration, as well as exploring important issues associated with scaling to large wafer sizes. This work presents an initial description of the thermomechanical response of wafers to flash lamp annealing in the millisecond time regime and is therefore fundamental to the use of this technique in the fabrication of semiconductor devices.

Keywords: flash lamp annealing stress silicon model

  • Journal of Applied Physics 100(2006)6, 63515

Publ.-Id: 9059

Actinide, lanthanide, and fission product speciation and electrochemistry in ionic melts

Bhatt, A. I.; Kinoshita, H.; Koster, A. L.; May, I.; Sharrad, C.; Steele, H. M.; Volkovich, V. A.; Fox, O. D.; Jones, C. J.; Lewin, B. G.; Charnock, J. M.; Hennig, C.

We report the results of recent research that we have undertaken to increase our understanding of key actinide and fission product speciation in a range of ionic melts. These results will be used to develop novel electrochemical methods of separation of uranium and plutonium from irradiated nuclear fuel. Our studies in high temperature alkali metal melts (including LiCl and the eutectics LiCl-KCl and CsCI-NaCl) have focussed on in-situ speciation of U, Tc and Ru using both Electronic Absorption Spectroscopy (EAS) and X-ray Absorption Spectroscopy (XAS). The XAS studies have included Extended X-Ray Absorption Fine Structure (EXAFS) and X-Ray Absorption Near Edge Structure (XANES) measurements. We report what could be unusual uranium speciation in high temperature melts and evaluate the likelihood of Ru or Tc volatilisation during plant operation. Our studies in lower temperature melts, commonly known as ionic liquids, have focussed on salts containing tertiary alkyl group 15 cations and the bis(trifluoromethylsulphonyl)imide anion, melts which we know to have exceptionally wide electrochemical windows. We report Ln, Th, U and Np speciation (XAS, EAS and vibrational spectroscopy) and electrochemistry in these melts.


  • ACS Symposium Series 933(2006), 219-231

Publ.-Id: 9058

Electrical conductivity surface sensor for two-phase flow imaging in a hydrodynamic coupling

Da Silva, M. J.; Sühnel, T.; Thiele, S.; Schleicher, E.; Hampel, U.; Kernchen, R.

For the measurement of fluid distributions inside a hydrodynamic coupling we have developed a high-speed surface sensor based on the measurement of the electrical conductivity. Two sensors are placed on the pressure-side and the suction-side walls of a blade channel inside the coupling. The sensors are composed by approximately 1000 interdigitated sensing structures. The system is supplied by a battery and has a wireless link to communicate with a PC. Sensor and electronics have been so designed that the whole system can rotate together with the coupling pump wheel. The electronics measures the conductivity of the liquid of each sensing structure in a multiplexed manner which effectively gives images of the instantaneous liquid distribution over the sensor surface. Frame frequencies of up to 10,000 images per second can be reached. We have applied the surface sensor to measure the fluid distribution in a test coupling for different slip conditions. Initial results are presented and discussed.

Keywords: electrical conductivity; surface sensor; fluid distribution; imaging; two-phase flow; hydrodynamic coupling

  • Contribution to proceedings
    International Conference on Multiphase Flow, 09.-13.07.2007, Leipzig, Germany
    Proceedings of 6th International Conference on Multiphase Flow, paper PS7_12, 978-3-86010-913-7
  • Poster
    International Conference on Multiphase Flow, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9057

Time-dependent radioactivity distribution in MAFF

Nebel, F.; Zech, E.; Faestermann, T.; Krücken, R.; Maier-Komor, P.; Assmann, W.; Szerypo, J.; Groß, M.; Kester, O.; Thirolf, P. G.; Grötzschel, R.

The Munich Accelerator for Fission Fragments is planned to be installed at the FRM II in Garching. It will operate a uranium-carbide-loaded graphite matrix as a target for neutron-induced fission. The radioactive reaction fragments leave the ion source as both, atoms and ions. For radiation safety it is imperative to have a basic understanding of the fragment distribution within the beam line.

Atoms leaving the graphite matrix will spread like a gas and stick to surfaces depending on their species. A probabilistic Monte-Carlo approach is used to predict the surface coating of internal surfaces of the beam line for all fission nuclides. To decrease calculation time, the problem is reduced to two dimensions with the surface areas being a measure for the probability, that they are hit by a particle. The program is completely time dependent to implement radioactive decay.

Ions leaving the fission ion source are transported by electrostatic means towards the mass pre-separator, a low-resolution dipole magnet with a complex slit system in the focal plane. All unwanted ions are stopped at the slits, resulting in a high level of radioactive contamination. While it is advantageous for shielding purposes to have the majority of the contamination in one point, precautions must be taken to ensure that it stays that way. Material corrosion caused by sputtering will release previously implanted radionuclides. To reduce this effect, different methods are under investigation, one of which is changing the slit geometry. The considered designs will be described and experimental results will be shown.

Keywords: Radiation damage; Radiation safety; Radioactive beam; Reactor experiment; Ion implantation

  • Nuclear Instruments and Methods in Physics Research A 561(2006)1, 83-89

Publ.-Id: 9056

Radioactivity distribution at MAFF

Nebel, F.; Szerypo, J.; Zech, E.; Faestermann, T.; Groetzschel, R.; Gross, M.; Habs, D.; Krucken, R.; Maier-Komor, P.; Thirolf, P.; Yakushev, A.

A detailed account on the distribution of radioactive nuclei in the vacuum system of the planned Munich Accelerator for Fission Fragments (MAFF) located at the FRM-II research reactor is presented. Tools used for the simulation of spacial and temporal distribution of radionuclides are explained. The latter allows for a detailed activity budget as well as estimates for the mass-separated ion yields at MAFF. Additionally, a concept to reduce the activity release from the MAFF slit system due to surface sputtering is presented. It is shown, that the use of low-density carbon foam, as a surface coating, reduces sputtering by orders of magnitude.

Keywords: Theory, design, and computerized simulation; Materials; Safety; Beam handling; beam transport

  • European Physical Journal A 29(2006)3, 369-381

Publ.-Id: 9055

Focused-ion-beam-assisted fabrication of polymer rolled-up microtubes

Luchnikov, V.; Stamm, M.; Akhmadaliev, C.; Bischoff, L.; Schmidt, B.

A focused ion beam (FIB) has been applied to the fabrication of polymer microtubes via the rolling-up technique from poly(4-vinyl pyridine)/polystyrene bilayer films deposited on the top of a sacrificial aluminum layer covering a silicon wafer. The bending forces in the film arise due to different swelling of the bilayer components in acidic water and lead to rolling of the film. The dimensions and position of the rolled-up tubes can be controlled by FIB milling (sputtering) of geometrically well-adjusted openings in the polymer films. This technique can be applied to the structuring of scrolled films formed from different materials without the use of lithographically patterned photoresists. The geometrical patterning of the tube interior can also be done by FIB irradiation.

Keywords: Focused ion beam; polymers; roll-up; nanotubes

  • Journal of Micromechanics and Microengineering 16(2006)8, 1602-1605

Publ.-Id: 9054

Molecular characterization of actinide oxocations from protactinium to plutonium

Den Auwer, C.; Guilbaud, P.; Guillaumont, D.; Moisy, P.; Le Naour, C.; Trubert, D.; Simoni, E.; Digiandomenico, V.; Hennig, C.; Scheinost, A.

For industrial, environmental and public health purposes, actinide chemistry has been the subject of considerable efforts since the 50’s. Aqueous redox chemistry, ionic selective recognition, uptake by specific biomolecules or compartments of the geosphere are some of the major fields of investigation. The physical-chemical properties of the actinide elements strongly depend on the 5f/6d electronic configuration. Some of them (U, Np, Pu and Am) can form AnO2n+ (n= 1, 2) oxocations, so-called actinyls, with two strong An-O covalent bonds. In any case, the cation polyhedron is characterized by large, flexible coordination spheres with various stable and metastable metal oxidation states. Protactinium, as the first actinide with 5f-electrons involved in bonding, occupies a key position in the actinide series. At formal oxidation state V (its most stable oxidation state in solution as well as in the solid state) Pa(V) corresponds to the formal 5f0 electronic configuration. U(VI) also corresponds to the formal oxidation state 5f0 and is most often encountered as the stable oxocationic form UO22+. The first stable form of U, Np or Pu at formal oxidation state (V) under atmospheric conditions is NpO2+ with formal 5f2 electronic configuration. U(V) is highly unstable under atmospheric conditions and Pu(V) dismutates into Pu(IV) and Pu(VI). On the other hand, the existence of the PaO2+ form in solution and in solid state is highly improbable and has never been reported. In solution, XAFS at the actinide LIII edge is an ideal structural probe of the cation coordination sphere. Furthermore, coupling the XAFS data with molecular dynamics calculations leads to a better description of the cation-solvent interactions. In addition, disorder can explicitly be taken into account using time spaced snapshots of the molecule. This is particularly important when large polyhedra are composed of ligands of similar types as water molecules. This presentation addresses the structural characterization of actinide cations at oxidation states (V) and (VI) as one walks across the periodic table from Z = 91 (protactinium) to Z = 94 (plutonium). For the fist time to our knowledge, the occurrence of the oxocation form of Pa(V) in H2SO4 solution has been inferred from EXAFS and XANES data at the Pa LIII edge. A structural comparison between Pa, U, Np and Pu oxocations in aqueous solution at formal oxidation states (V) and (VI) is carried out. These results are corroborated by quantum chemical and molecular dynamics calculations.

Keywords: Actinides; EXAFS; XANES

  • Lecture (Conference)
    Actinide-XAS, 18.-20.9.2006, Karlsruhe, Germany

Publ.-Id: 9053

EXAFS and UV-VIS investigation of the first coordination sphere of the uranyl ion in UO2(NO3)2(TBP)2

Servaes, K.; Hennig, C.; van Deun, R.; Görller-Walrand, C.

The coordination behaviour of the uranyl ion UO22+ has regained interest due to the problem of nuclear waste management and environmental issues. At the end of the nuclear fuel cycle, reprocessing of the spent nuclear fuel mainly occurs by means of liquid-liquid extraction. During the PUREX process, the spent fuel is dissolved in a nitric acid solution. Uranium is extracted from the aqueous nitric acid fuel solution with an organic phase containing tri-n-butylphosphate (TBP; extracting agent). However, little is known about the structure of the chemical species involved in the liquid-liquid extraction process. The first coordination sphere of the uranyl ion UO22+ in UO2(NO3)2(TBP)2 was studied using UV-Vis absorption spectroscopy, EXAFS spectroscopy and 31P-NMR. The characteristic vibrational fine structure in the UV-Vis absorption spectrum points at a high symmetrical complex. The uranium polyhedron is composed of two axial oxygens located at 1.77 ± 0.01 Å, four nitrate (bidentate) oxygens at 2.52 ± 0.01 Å and two phosphate oxygens (TBP) located at 2.38 ± 0.01 Å.

Keywords: UV-vis; EXAFS; uranium

  • Poster
    Actinide-XAS, 18.-20.9.2006, Karlsruhe, Germany

Publ.-Id: 9052

Combined techniques for studying actinide complexes in room temperature ionic liquids

Gaillard, C.; Billard, I.; Mekki, S.; Ouadi, A.; Hennig, C.; Denecke, M.

The first coordination sphere of the uranyl cation in room temperature ionic liquids "IL's" results from the competition between its initially bound counterions, the IL anions, and other anions (e.g. present as impurities, or added to the solution). We present a joined spectroscopic (UV-visible and EXAFS) – simulation study of the coordination of uranyl initially introduced either as its UO2X2 salts (X- = nitrate NO3-, triflate Tf-, perchlorate ClO4-) or as UO2(SO4) in a series of imidazolium – based ILs (A- = PF6-, Tf2N-, BF4-), as well as in the Me3NBuTf2N IL. The solubility and dissociation of the uranyl salts are found to depend on the nature of X- and A-. For instance, in the BumimTf2N liquid, UO2(SO4) is insoluble, the UO2(NO3)2 salt dissolves without dissociation, while the UO2(Tf)2 and UO2(ClO4)2 salts are soluble, likely in their complexed and dissociated form, respectively.

Keywords: room temperature ionic liquids; lanthanides; actinides; EXAFS

  • Lecture (Conference)
    Actinide-XAS, 18.-20.9.2006, Karlsruhe, Germany

Publ.-Id: 9051

Uranium chloro complexes in hydrophobic room temperature ionic liquid: structural investigation and redox properties

Cannes, C.; Nikitenko, S.; Le Naour, C.; Trubert, D.; Hennig, C.; Moisy, P.

U(IV) hexachloro complexes were studied in hydrophobic room temperature ionic liquids [BuMeIm][Tf2N] and [MeBu3N][Tf2N] to determine their structure, speciation and redox properties (BuMeIm+ and MeBu3N+ are 1-butyl-3-methyl-imidazolium and tri-n-butylmethylammonium respectively, and Tf2N- is bis(trifluoromethyl-sulfonyl)imide).
As the Tf2N- anion is known to be a weak ligand exhibiting oxygen coordination as 1-O or 2-O,O to actinides or lanthanides, the U(IV) chloro complex could be under the general chemical form UClx(Tf2N)y(4-x-y).
The diffuse UV-vis solid state reflectance of both U(IV) complexes agree closely with the absorption spectra obtained in ionic liquids. It is well known that U(IV) hexachloro complex has a centrosymmetric octahedral arrangement in the solid state as well as in acetonitrile solution. It can be concluded that octahedral anion UCl62- is the predominant form of U(IV) in Tf2N- based ionic liquids. EXAFS measurements were also performed to investigate the coordination sphere of U(IV) chloro complex in [BuMeIm][Tf2N]. The results confirmed that the octahedral complex UCl62- is the predominant chemical form of U(IV) in Tf2N- based hydrophobic ionic liquids and a competing reaction with Tf2N- can be excluded. The U-Cl distance measured in [BuMeIm][Tf2N] is 2.632(2) Å and is slightly longer than that in solid state. Probably, it can be related to some stronger H-bonding of UCl62- with BuMeIm+ cation in ionic liquid than that of solid.

Keywords: UV-vis; EXAFS; ionic liquid; uranium

  • Lecture (Conference)
    EuChem conference on molten salts and ionic liquids 2006, 16.-22.09.2006, Hammamet, Tunisia

Publ.-Id: 9050

Elemental redistribution and Ge loss during ion-beam synthesis of Ge nanocrystals in SiO2 films

Beyer, V.; von Borany, J.

The elemental redistribution and Ge loss in low-energy Ge+ implanted SiO2 films during wet-chemical cleaning and annealing procedures are investigated. Two effects of major importance for Ge nanocrystal formation have been found. Moisture components (H2O vapor, H+, OH-) penetrate into the damaged oxide during storage, wet chemical cleaning or annealing procedures and lead to a hydrogen and oxygen enrichment in the near-surface oxide. Furthermore, atomic collisions during Ge implantation result in an oxygen excess (with respect to SiO2 stoichiometry) underneath the Ge profile. The local net ratio of Ge and excess oxygen determines, whether the implanted Ge is incorporated into the SiO2 network as spatially fixed GeO2, oxidizes to mobile GeO or remains as elemental Ge forming nanocrystals. Apart from very shallow profiles, where a drastic Ge loss is observed simply by cleaning in chemical solutions containing H2O2, the main Ge loss occurs during annealing. The highly mobile GeO is identified to be responsible for both, Ge redistribution or even loss, if diffusing GeO meets the SiO2 surface and emanates into the annealing ambient. Annealing in Ar/H2 mixtures at < 900°C reduces the Ge loss due to the reduction of Ge oxides. The enhanced Ge mobility (as GeO) is described as an oxygen vacancy assisted mechanism which also explains the influence of the Si/SiO2 interface on the Ge diffusivity. Finally, the consequences of Ge redistribution and loss for Ge nanocrystal memory device fabrication are discussed.

Keywords: ion beam synthesis; germanium; nanocrystal; SiO2; oxygen vacancy; GeODC

Publ.-Id: 9049

Probing six-fold ring clusters in alloyed sp2 dominated carbon thin films by the means of Raman spectroscopy

Abrasonis, G.; Krause, M.; Gago, R.; Kolitsch, A.; Möller, W.

The six-fold ring clustering in sp2-dominated pure carbon (C), nitrogenated carbon (CNx) and nickel alloyed carbon (C:Ni) thin films is investigated by Raman spectroscopy as a function of substrate temperature. Films have been grown by direct and dual ion beam sputtering, ion beam assisted evaporation and magnetron sputtering, resulting in amorphous, graphite-like, fullerene-like, paracyanogenlike, and in the case of C:Ni films – nanocomposite - structures.
Raman spectra in the wave-number region of 900–2000 cm−1 exhibit usually two main peaks positioned at ~1360 and ~1560–1590 cm−1 which are denoted conventionally by D and G, respectively, the G peak corresponding to in-plane bond stretching vibrations (it can be present in aromatic clusters as well as in chain structures) and the D peak corresponding to breathing vibrations of aromatic rings (it can be present only in ring structures). The total intensity of these peaks is proportional to the amount of the sp2 phase, while their relative ratio provides the information on the six-fold ring cluster size.
The results show that each type of atomic arrangement results in a characteristic set of the Raman spectra parameters, which describe the degree of aromatic clustering, bond length and angle distortion and order in sixfold structures1.
In the case of pure C films, the atomic structure evolves with substrate temperature from a disordered network to nanocrystalline planar graphitic configurations, with a progressive promotion in size and ordering of sixfold ring clusters1.
Nitrogen incorporation favors the promotion of sixfold rings in highly disordered networks produced at low temperatures, but precludes the formation of extended graphite-like clusters at elevated substrate temperatures (>400°C). In the latter case, N introduces a high degree of disorder in sixfold ring clusters and enhances the formation of a fullerene-like microstructure1.
The presence of Ni slightly favours the six-fold ring clustering at low temperatures (<300°C), while Raman spectra at higher temperatures have similar features for both C and C:Ni films. For deposition temperatures lower than 300°C, the the absolute intensity of the D-G band decreases by more than one order of magnitude despite the similar total amount of deposited material and one additional Raman line at around 1100 cm-1 appear indicating the presence of new carbon structures in the film. This correlates with the Ni segregation into nickel carbide or nickel nanoparticles occurring at T~300°C, thus segregated Ni and C phases may undergo separate ordering paths at higher temperatures. In contrast, a mixed C-Ni phase is formed at lower temperatures and the precipitation C sp2 phase is hindered.
1. G. Abrasonis, R. Gago, M. Vinnichenko, U. Kreissig, A. Kolitsch, and W. Möller, Phys. Rev. B 73, 125427 (2006).

  • Lecture (Conference)
    4th International Workshop on Nanoscale Spectroscopy and Nanotechnology, 17.-21.09.2006, Rathen, Germany

Publ.-Id: 9046

Low energy ion accelerated diffusion of interstitial nitrogen in austenitic stainless steel

Abrasonis, G.; Möller, W.; Ma, X. X.; Keller, A.; Facsko, S.

N diffusion in austenitic stainless steel (ASS) under low energy Ar ion bombardment is investigated. ASS samples were ion beam nitrided at 400°C with the N ion energy of 1 keV and flux of 3.11015 s-1 cm-2. The nitriding time was adjusted to obtain a thickness of the nitrided layer of ~1m. The samples were subsequently annealed at 400°C under simultaneous 700 eV Ar+ bombardment with different fluxes (1.3-3.8×1015 s-1 cm-2). N depth profiles were obtained using nuclear reaction analysis, and the phase structure was measured using X-ray diffraction (XRD). XRD reveals the modified layer to be composed of only γN phase in both as-nitrided and Ar+ irradiated samples, with no evidence of nitride formation. It is observed that Ar+ bombardment increases the N mobility in the depths far beyond the ion penetration depth, resulting in an increased broadening of the N depth profile as a function of Ar+ flux. This effect cannot be explained by any established mechanism of radiation enhanced diffusion. Another set of samples was annealed at 400°C under low flux (4×1011 s-1 cm-2) 700 eV Ar ion bombardment of variable charge state (from 1+ to 8+). These charge states correspond to the potential energies of 16-578 eV. The latter is dissipated by electronic excitations in metals. It was found that low flux Ar ion bombardment enhances the N mobility; however, the ion potential energy does not play any role on deep N diffusion. The latter indicates that N diffusion enhancement over large distances (~1 m) is due to nuclear collisional processes during ion stopping in the matter. Tentatively, the observed phenomenon is discussed in terms of collisionally induced quasi-particles which propagate large distances from the layers directly affected by ion bombardment enhancing interstitial N diffusion.

Keywords: radiation enhanced diffusion; quasi-particles; ion nitriding; austenitic stainless steel

  • Lecture (Conference)
    Tenth International Conference on Plasma Surface Engineering, 10.-15.09.2006, Garmisch-Partenkirchen, Germany

Publ.-Id: 9045

Construction of an S-layer protein exhibiting modified self-assembling properties and enhanced metal binding capacities

Pollmann, K.; Matys, S.

The functional S-layer protein gene slfB of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 was cloned as a PCR-product into the expression vector pET Lic/Ek 30 and heterologous expressed in E.
coli Bl21(DE3). The addition of His-tags to the N- and C-termini enabled the purification of the recombinant protein by Ni chelating chromatography. The Ni-binding capacity of the His-tagged recombinant S-layer protein was compared with that of the wild-type S-layer. The ICP-MS analyses demonstrate a significantly enhanced Ni-binding capability of the recombinant protein. In addition, the self-assembling properties of the purified modified S-layer proteins were studied by light microscopy and SEM. Whereas the wild-type S-layer proteins re-assembled into regular cylindric structures, the His-tagged S-layer proteins reassembled into regular sheets that formed globular agglomerating structures. The nanoporous structure of the protein meshwork together with its enhanced Ni-binding capacity makes the recombinant S-layer attractive as a novel self-assembling biological template for the fabrication of metal nanoclusters and construction of nanomaterials that are of technical interest.

Publ.-Id: 9044

XPS depth profiling of oxide scales of stainless steels formed in high-temperature aqueous conditions

Ignatova, V. A.; van Dyck, S.; Groetzschel, R.; Moeller, W.

In this work, we studied the oxide scales of AISI 304 and AISI 316 stainless steels formed under hightemperature aqueous conditions using X-ray photoelectron spectroscopy (XPS) together with sputter depth profiling. Two samples of SS 304 and 316 were prepared by exposing them to water at 300 °C containing 100 ppm boric acid and 7 ppm lithium hydroxide in an autoclave. In the case of sputtering with 3 keV argon ions, the elemental distribution as a function of the sputtering time was obtained. The formation of two oxide layers was observed – one mainly iron-based on top, and a second at a greater depth, consisting mainly of chromium-iron oxides. The depth scale of the profiles was calibrated by measuring the oxygen profile using Rutherford backscattering spectroscopy (RBS). On the basis of the distribution of the three oxidised alloying constituents (Fe, Cr, Ni) with respect to depth and elemental state, a relative increase of Fe2+ at the surface was found, while the chromium was depleted at the surface and Cr3+ tended to increase at the oxide/substrate interface. In order to estimate possible ion-beam-induced effects due to the ion sputtering, the profiles were compared to the computer-simulated ones obtained by a dynamic TRIM computer code. The simulations included only collisional effects during the sputtering process.

Publ.-Id: 9043

Modelling of the Corium-RPV-Wall Interaction in the Frame of an In-Vessel-Retention Scenario

Altstadt, E.; Willschütz, H.-G.

The improbable scenario of a severe accident with core meltdown and formation of a melt pool in the lower plenum of a Light Water Reactor (LWR) Pressure Vessel (RPV) can result in the failure of the RPV and the discharging of the melt to the con-tainment. One accident management strategy could be to stabilize the in-vessel de-bris or melt pool configuration in the RPV as one major barrier against uncontrolled release of heat and radionuclides into the containment of the plant.
Based on the successful simulation and analysis work of the FOREVER-experiments the models have been developed further to simulate the prototypical scenario of an In-Vessel-Retention in large PWRs. Based on recently observed results of the METCOR-Experiments it is known that the vessel wall ablation in case of melt-wall-contact can take place well below the steel melting point of T = 1493 °C. The FE-model developed at FZD is now improved to consider the time dependent thermo chemical wall ablation process.

Keywords: severe accident; nuclear power station; core melt down; melt steel wall interaction; corrosion/ablation; residual wall thickness

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2007, 22.-24.05.2007, Karlsruhe, Deutschland
    Beiträge zur Jahrestagung Kerntechnik 2007, Proceedings on CD-ROM, Paper 328, Berlin: INFORUM Verlags- und Verwaltungsgesellschaft mbH, 293-299

Publ.-Id: 9042

Experimental modelling using low melting point metallic melts: Relevance for metallurgical engineering

Eckert, S.; Gerbeth, G.; Räbiger, D.; Willers, B.; Zhang, C.

This paper describes model experiments with low melting point liquid metals as an important tool to investigate the flow structure and related transport processes in melt flows being relevant for metallurgical applications. Three examples have been selected to demonstrate the benefit of such experiments, namely the electromagnetic stirring of a metallic melt in a pool, the directional solidification of Al-Si alloys under the influence of an electromagnetically driven flow and the behaviour of a liquid metal bubble plume if a vertically traveling field is applied. Results of flow measurements will be presented and the relevance for metallurgical processes will be discussed.

Keywords: liquid metal; magnetic field; electromagnetic stirring; solidification; bubble plume

  • Steel Research International 78(2007)5, 419-425

Publ.-Id: 9041

Einfluss von HS auf die U(VI) Sorption an Kaolinit: TRLFS-Untersuchungen

Krepelova, A.; Sachs, S.; Brendler, V.; Baumann, N.

Understanding the migration behavior of actinides is important for the reliable long-term risk assessment of potential nuclear waste repositories. Humic acids (HA) comprise an important part of natural organic materials. HA are soluble in the pH range of natural waters and have the ability for complex and colloid formation. Due to these properties HA can affect the speciation of actinide ions, and therefore, their migration in the environment. In the present study we investigated the influence of HA on the U(VI) sorption onto kaolinite.
We used time-resolved laser-induced fluorescence spectroscopy (TRLFS) in order to characterize the species of U(VI) adsorbed onto kaolinite in the absence and presence of HA. Two adsorbed U(VI) surface species on kaolinite were identified in the pH range of pH 5.0 to pH 8.5. Obtained results help to improve the understanding of the geochemical interactions of hexavalent actinides in environment.

Keywords: U(VI); Humic Acid; TRLFS; Adsorption

  • Lecture (others)
    PSI/LES - FZD/IR Meeting, 05.-06.10.2006, Dresden, Germany

Publ.-Id: 9040

Cylindrical anisotropic alpha2 dynamos

Avalos-Zuniga, R.; Xu, M.; Stefani, F.; Gerbeth, G.; Plunian, F.

We explore the influence of geometrical variations on the structure and the time-dependence of the magnetic field that is induced by kinematic alpha2 dynamos in a finite cylinder. The dynamo action is due to an anisotropic alpha tensor which can be derived from an underlying columnar flow. The investigated geometry variations concern, in particular, the aspect ratio of height to radius of the cylinder, and the thickness of the annular space to which the columnar flow is restricted. Motivated by the quest for laboratory dynamos which exhibit Earth-like features, we start with modifications of the Karlsruhe dynamo experiment. Its dynamo action is reasonably described by an alpha2 mechanism with anisotropic alpha tensor. We find a critical aspect ratio below which the dominant magnetic field changes from an equatorial dipole to an axial dipole. Similar results are found for alpha2 dynamos working in an annular space when a radial dependence of alpha is assumed. Finally, we study the effect of varying aspect ratios of dynamos with an alpha tensor depending both on r and z. In this case only dominant equatorial fields are found and most of the solutions are oscillatory, contrary to all previous cases where the resulting
fields are steady.

Publ.-Id: 9039

Defect engineering in the initial stage of SIMOX processing

Kögler, R.; Mücklich, A.; Vines, L.; Krecar, D.; Kuznetsov, A.; Skorupa, W.

Defect engineering for SiO2 precipitation was investigated during ion beam synthesis in the first stage of SIMOX fabrication. Vacancy-type defects were created in Si: (i) a buried nanocavity layer was pre-fabricated by He implantation and subsequent annealing, and (ii) excess vacancies were generated during oxide synthesis by an additional simultaneous high-energy Si irradiation.
A narrow nanocavity layer was found to be an excellent nucleation site that favors effectively the SiO2 formation. Such a cavity layer must be adjusted to the excess vacancy profile of the O implant. The excess vacancy generation by simultaneous dual implantation minimizes the defect production in Si. However, it is inappropriate to form a narrow oxide layer due to the too broad distribution of excess vacancies.

Keywords: SOI; SIMOX; ion implantation; defect engineering; Si

  • Lecture (Conference)
    15th International Conference Ion Beam Modification of Materials (IBMM 2006), 18.-22.09.2006, Taormina, Italy
  • Contribution to proceedings
    15th International Conference Ion Beam Modification of Materials (IBMM 2006), 18.-22.09.2006, Taormina, Italy
    Nuclear Instruments and Methods in Physics Research B 257(2007): Elsevier, 161-164

Publ.-Id: 9038

Determination of velocity and angular displacement of bubbly flows by means of wire-mesh sensors and correlation analysis

Hoppe, D.; Grahn, A.; Schütz, P.

For the analysis of air-water bubbly flows in vertical pipes a method is presented which determines the radial profiles of velocity and angular displacement of the gaseous phase. Measurements rely on two so-called wire-mesh sensors, put into the flow behind each other and capturing the electrical conductivity distribution in the pipe cross-section at two different axial positions. The time-resolved signal is directly translated into transient two-dimensional distributions of the gaseous phase at both sensor positions. Sensor data analysis is based on two-dimensional cross-correlation within concentric cylindrical planes. The axial and angular displacement of the gaseous phase manifest themselves as the maximum position of the cross-correlation function.

Keywords: two-phase flow; phase distribution; flow velocity; angular displacement; wire-mesh sensor; cross-correlation

Publ.-Id: 9037

Accurate determination of optical and electronic properties of ultra-thin silver films for biosensor applications

Oates, T. W. H.; Ryves, L.; Bilek, M. M. M.; Mckenzie, D. R.

Ultra-thin metal films are widely utilised for surface-enhanced Raman scattering and surface adsorption spectroscopy. We present in situ spectroscopic ellipsometry investigations of the growth of ultra-thin silver films, from island growth through percolation and continuous film growth. Silver films are deposited using a pulsed filtered cathodic vacuum arc, which provides precise control and reproducibility of the film growth conditions. Plasmon polariton resonances are determined for the growing islands below the percolation threshold. As the surface coverage increases a second oscillator, attributed to bulk plasma resonances, is required to accurately model the ellipsometric data. Postdeposition optical and electronic changes are observed for island films and the origins of these changes are investigated using the ellipsometric data

Keywords: Nanoparticles; Plasmon resonance; Spectroscopic ellipsometry

  • Sensors and Actuators B 109(2005), 146-152

Publ.-Id: 9036

The characteristics of gas/liquid flow in large risers at high pressures

Azzopardi, B. J.; Omebere-Iyari, N. K.; Lucas, D.; Beyer, M.; Prasser, H.-M.

Although, most of the work reported on two-phase flows are limited to small pipe diameters, two-phase flow in large risers are increasingly being encountered in the petroleum and nuclear industries. In the present work, a wire mesh sensor was employed to obtain void fraction and bubble size distribution data and visualizations of steam/water flow in a large vertical pipe (194mm in diameter) at 46bar. For comparison purposes, measurements were made at similar phase velocities and physical properties to the data of Omebere-Iyari et al. (2006), which is for the flow of a nitrogen/naphtha mixture in a similar-sized riser. There exist significant differences between both sets of data. Churn-turbulent flow is observed in the present work instead of slug flow which differs from the intermittent and semi-annular flow patterns reported by Omebere-Iyari et al. (2006). The mean void fraction of the nitrogen/naphtha data is higher that of the present steam/water data. On examination of radial void fraction profiles, core peak distributions are observed for the present work in contrast to the wall peak profiles predicted for the data of Omebere-Iyari et al. (2006) using a power law relationship.

Keywords: two phase flow; nitrogen/naphtha flow; large vertical pipe; steam/water flow; high pressure

  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Gas/liquid flow in large risers; paper: S6_Thu_A_47

Publ.-Id: 9034

Uranyl Coordination in Ionic Liquids: The Competition between Ionic Liquid Anions, Uranyl Counterions, and Cl- Anions Investigated by Extended X-ray Absorption Fine Structure and UV-Visible Spectroscopies and Molecular Dynamics Simulations

Gaillard, C.; Chaumont, A.; Billard, I.; Hennig, C.; Ouadi, A.; Wipff, G.

The first coordination sphere of the uranyl cation in room-temperature ionic liquids (ILs) results from the competition between its initially bound counterions, the IL anions, and other anions (e.g., present as impurities or added to the solution). We present a joined spectroscopic (UV-visible and extended X-ray absorption fine structure)-simulation study of the coordination of uranyl initially introduced either as UO2X2 salts (X- ) nitrate NO3 -, triflate TfO-, perchlorate ClO4 -) or as UO2 (SO4) in a series of imidazolium-based ILs (C4mimA, A- ) PF6 -, Tf2 N-, BF4 - and C4mim ) 1-methyl-3-butyl-imidazolium) as well as in the Me3NBuTf2N IL. The solubility and dissociation of the uranyl salts are found to depend on the nature of X- and A-. The addition of Cl- anions promotes the solubilization of the nitrate and triflate salts in the C4mimPF6 and the C4mimBF4 ILs via the formation of chloro complexes, also formed with other salts. The first coordination sphere of uranyl is further investigated by molecular dynamics (MD) simulations on associated versus dissociated forms of UO2X2 salts in C4mimA ILs as a function of A- and Xanions.
Furthermore, the comparison of UO2Cl4 2-, 2 X- complexes with dissociated X- anions, to the UO2X2, 4
Cl- complexes with dissociated chlorides, shows that the former is more stable. The case of fluoro complexes is also considered, as a possible result of fluorinated IL anion’s degradation, showing that UO2F4 2- should be most stable in solution. In all cases, uranyl is found to be solvated as formally anionic UO2XnAmCl p 2-n-m-p complexes, embedded in a cage of stabilizing IL imidazolium or ammonium cations.

Keywords: Ionic liquids; uran; complexation; EXAFS

  • Inorganic Chemistry 46(2007), 4815-4826

Publ.-Id: 9033

Structural investigation of Neptunium(V) in toxicological processes

Den Auwer, C.; Moisy, P.; Guillaumont, D.; Vidaud, C.; Funke, H.; Hennig, C.

General understanding needs to be deepened of intramolecular interactions engaged in molecular actinide species, i.e. physical chemical mechanisms that drive the affinity of chelating ligands for actinide cations still needs to be deepened. In this field, X-ray absorption spectroscopy has been extensively used as a structural and electronic metal cation probe. Combination with more traditional spectroscopic techniques such as spectrophotometry is an ideal tool for the understanding of the chelation mechanism. Metallobiomolecules are considered elaborate inorganic complexes with well-designed metal active sites. Although the various interaction processes between essential cations important to biology and proteins are widely studied, focus on the actinides is more seldom. Actinide impact on biological cycles has been motivated by risk assessments related to the wide use of nuclear fuel sources and industrial or military applications. In particular, the interaction between these cations with the biological active complexation sites are only partially understood.

Keywords: EXAFS; Neptunium(IV)

  • Materials Research Society Symposium Proceedings 893(2006), 315-323

Publ.-Id: 9032

Speciation of technetium and rhenium complexes by in situ XAS-electrochemistry

Poineau, F.; Fattahi, M.; Den Auwer, C.; Hennig, C.; Grambow, B.

A spectro-electrochemical cell was developed in order to study the speciation of radio-elements in thermodynamic unstable redox states using in situ XAS spectroscopy. This cell was used for the speciation of Re and Tc complexes in chloride media. Experiments on Re were carried out with the aim to validate the functionality of the experimental set-up. During electro-reduction of Re(VII) in HCl media, EXAFS and XANES studies were performed in order to reveal the formation of chloro-oxygenated compounds of Re(IV). The speciation of technetium in aqueous solutions of deep geological deposits for radioactive waste is important to predict its mobility under reducing conditions. XANES spectra showed that electro-reduction of Tc(VII) in chloride media leads to a position of K-edge absorption which agrees with a Tc(IV)/Tc(III) mixture.

Keywords: Technetium; Rhenium; EXAFS; Speciation; Spectro-electrocemistry

Publ.-Id: 9031

Eine Frage der Kühlbarkeit / A question of cooling ability (coolability)

Willschütz, H.-G.

Wie kann die Bevölkerung vor den Folgen eines hypothetischen schweren Kernschmelzunfalls in einem Reaktor geschützt werden? Welche Schutzvorkehrungen sind vorgesehen? Neue Antworten auf diese Fragen werden in der Reaktorsicherheitsforschung erarbeitet. Dass Forschungsaktivitäten im Bereich hypothetischer Ereignisse mit äußerst geringer Eintrittswahrscheinlichkeit eine Sicherheitskultur auf hohem Niveau unterstützen und weitere Verbesserungsvorschläge auch für bestehende Anlagen ermöglichen, belegen Ergebnisse einer Forschungsarbeit zur Rückhaltbarkeit von Kernschmelze im Reaktordruckbehälter.

Keywords: Nuclear Power Plant; Severe Accident; Core Melt Down; Physical Barriers; In-Vessel-Retention

  • Brennstoff, Wärme, Kraft: BWK 58(2006)12, 27-30

Publ.-Id: 9030

A toy model of PT-symmetric Quantum Mechanics, the Squire equation and UV-IR-duality

Günther, U.; Stefani, F.; Znojil, M.

Some facts about the spectrum of a PT-symmetric quantum mechanical (PTSQM) toy model with potential V(x)=Gx2(ix)ν in a box x∈[-L,L] are presented for the parameter region ν∈[-2,0]. The corresponding Hamiltonian is selfadjoint in an appropriately chosen Krein space and for ν=-1 the spectral problem maps into that of the hydrodynamic Squire equation. It is shown that in the limit L→∞ a spectral singularity occurs and that the PTSQM ⇄ Squire mapping can be interpreted as a special type of strong-coupling ⇄ weak-coupling (UV-IR) duality. Finally, the system behavior in the vicinity of a spectral triple point is sketched.
partially based on:
J. Math. Phys. 46, (2005), 063504, math-ph/0501069.
Czech. J. Phys. 55, (2005), 1099-1106, math-ph/0506021.

Keywords: PT-symmetric Quantum Mechanics; Krein space; spectral analysis; spectral triple point; UV-IR duality

  • Invited lecture (Conferences)
    6th Workshop "Operator Theory in Krein Spaces and Operator Polynomials", 14.-17.12.2006, Berlin, Germany

Publ.-Id: 9029

What can we learn from diffuse scattering about actinide coordination in solutions?

Hennig, C.

The presentation comprises an introduction in the theory of diffuse scattering, experimental conditions, classical technique and difference technique, LAXS and HEXS. Several typical examples and potential applications will be discussed.

Keywords: Actinides; Uranium; diffuse scattering; LAXS; HEXS

  • Lecture (others)
    ROBL Seminar, 21.11.1006, Grenoble, France

Publ.-Id: 9026

Application of EXAFS spectroscopy for structural analysis of actinide compounds in solution

Hennig, C.

An overview on EXAFS on applications on actinide structure investigation in solution will be given.

Keywords: EXAFS; Actinides

  • Invited lecture (Conferences)
    Chemistry Department of the Argonne National Laboratory, 31.10.2006, Chicago, United States

Publ.-Id: 9025

Bacterial S-layers as template for the formation of Pd nanoclusters

Hennig, C.; Fahmy, K.; Merroun, M.; Pollmann, K.; Raff, J.; Savchuk, O.; Selenska-Pobell, S.

Nano-catalysts made from palladium and other noble metals promise to accelerate chemical reactions even at low temperatures. Critical for the efficiency of such nano-catalysts is a perfect control of their cluster-size. By using the surface protein layer (so-called S-layer) of a bacterium, particles with a uniform size distribution of 50 to 80 Pd atoms can be generated. For the first time, the bonding sites between the metal and the S-layer protein have been characterized. Hereby, the prerequisite is given to manipulate this protein by genetic engineering enabling the design of materials with new optic, magnetic and catalytic properties.
The uranium uptake mechanism were investigated by EXAFS performed at the Rossendorf Beamline. The measurements revealed that the purified S-layer proteins of this bacterium coordinate uranium through phosphate groups of phosphorylated serine and threonine in a monodentate mode as well as through carboxyl groups of aspartic and glutamic acids in a bidentate mode.
The heavy metal binding capacity of the S-layer led to the idea to use it as template for the formation of Pd nanoclusters. Within the pores of the S-layer, isolated from vegetative bacteria, Pd(II) solutions are reduced to metallic palladium by the use of hydrogen.
In order to investigate the metal-protein interactions and their impact on the secondary structure, a solution of Pd(II) ions has been sorbed on the S-layer matrix. The combination of Fourier transform infrared spectroscopy and EXAFS spectroscopy revealed that the surface Pd(II) is predominantly coordinated by aspartic and glutamic residues through 4 nitrogen and oxygen atoms at a distance of 2.01 Å. In contrast to U(VI), that binds to carboxyl and phosphate groups, Pd(II) binds exclusively to the carboxyl groups of the S-layer. The topology of nitrogen- and carboxyl-bearing side chains appears to mediate the binding of heavy metals to aspartic and glutamic acids. These side chains are thus targets for the design of engineered S-layer based nanoclusters.

Keywords: EXAFS; Rossendorf Beamline; Palladium; S-layer

  • Contribution to external collection
    in: ESRF Highlights 2007, Grenoble: ESRF, 2007, 83-84

Publ.-Id: 9024

The effect of flash lamp annealing on Fe implanted ZnO single crystals

Potzger, K.; Anwand, W.; Reuther, H.; Zhou, S.; Talut, G.; Fassbender, J.; Brauer, G.; Skorupa, W.

The effect of flash lamp annealing applied to ZnO single crystals implanted with 3.6 at. % Fe has been studied. For intermediate light power, the implantation induced surface defects could be annealed without creation of secondary phases within the implanted region. At the same annealing temperatures, however, ion beam induced open volume defects start to increase in size. Recrystallization is initiated for the highest light power applied, i.e. the ion beam induced lattice disorder reflected by the minimum channelling yield of Rutherford backscattering spectroscopy decreases from 76 % to 46 % and the open volume defects are annealed. At the same time, the Fe3+ fraction increases at the cost of the Fe2+ states. Weak ferromagnetic properties are induced, that are mainly associated with nanoparticles

Keywords: ZnO; Diluted magnetic semiconductors; ion implantation; flash lamp annealing

  • Journal of Applied Physics 101(2007)3, 033906
  • Lecture (Conference)
    71. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 26.-30.3.2007, Regensburg, Germany

Publ.-Id: 9023

Resonance effects in α2-dynamos

Kirillov, O.; Günther, U.

First results on a perturbation theory for α2-dynamos with non-constant spherically symmetric α-profiles are presented. The basics of the mathematical technique is demonstrated on a simplified model with idealized boundary conditions (BCs). Such BCs allow for a full semi-analytical treatment of the problem due to the selfadjointness of the dynamo operator in a so called Krein space --- a Hilbert space with an additional indefinite metric structure.
Starting point of the consideration is the model with constant α-profile α₀ which is exactly solvable. The eigenvalues λ of such a model form a mesh-like branch structure in the (α₀,Re λ)-plane. The nodes of this mesh (the intersection points of the branches) are double semi-simple eigenvalues (diabolical points) of algebraic and geometric multiplicity 2.
A Krein space related perturbation theory as well as a Galerkin technique for the numerical treatment of inhomogeneous perturbations of the α-profile have been developed. With the help of these tools, a very pronounced α-resonance pattern has been found in the deformations of the spectral mesh as well as in the unfolding of the diabolical points. The selection rules of this resonance pattern are defined by the Fourier coefficients of the perturbations leading to a strong correspondence between the characteristic length scale of the α-perturbations and the decay rates of the coherently induced field excitations. Such correlations will exist also in models with realistic BCs and may provide a qualitative explanation for some specifics of field reversal processes --- supporting corresponding numerical simulations on more realistic dynamo setups.
Furthermore, an estimation technique has been developed for obtaining optimal α-profiles for which α2-dynamos can become overcritical in oscillatory regimes. This basic technique is demonstrated explicitly for a simplified monopole (l=0) model, where it leads to a bound on the Fourier components of the α-profile. The capability of the used Galerkin approach is demonstrated in extending the strength of the α-perturbations from weakly perturbed regimes to strongly perturbed ones.
Extensions of the presented techniques to spherically symmetric α2-dynamos with realistic boundary conditions are in preparation.

Keywords: MHD dynamo; Krein space; perturbation theory; spectral analysis; spectral singularities; diabolical points; exceptional points

  • Lecture (Conference)
    9th MHD Days 2006, 04.-05.12.2006, Heidelberg, Germany

Publ.-Id: 9022

Boron dilution analyses at reactor shutdown conditions using the coupled code DYN3D/ATHLET

Kliem, S.; Rohde, U.

A parameter study of a hypothetical boron dilution event during the work of the RHRS was performed. Based on a validated coolant mixing model for the lower plenum of the RPV, realistic boron concentration curves at the inlet into each fuel assembly were obtained and used for a number of stationary and transient core calculations. For the generic core loading pattern used in the calculations, in the stationary calcu-lations recriticality is reached for slug volumes of about 8 m3 if the realistic core inlet boron concentration distribution is used. Transient core calculations from 8 to the maximum initial slug volume of 15 m3 showed, that the maximum calculated fuel and cladding temperature values are below critical values. Although in all calculations local coolant boiling occurs over several tenths of seconds, the integrity of the fuel is always ensured according to the calculation results.

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2007, 22.-24.05.2007, Karlsruhe, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2007, 22.-24.05.2007, Karlsruhe, Germany
    Proceedings of the Annual Meeting on Nuclear Technology 2007: INFORUM GmbH, 51-57

Publ.-Id: 9018

Silicon-on-insulator microcavity light emitting diodes with two Si/SiO2 Bragg reflectors

Potfajova, J.; Sun, J. M.; Schmidt, B.; Dekorsy, T.; Skorupa, W.; Helm, M.

Light emitting pn-diodes were fabricated on a 5.8 µm thick n-type Si device layer of a silicon-on-insulator (SOI) wafer using standard silicon technology and boron implantation. The thickness of the Si device layer was reduced to 1.3 µm, corresponding to a 4λ-cavity for λ = 1150nm light. Electroluminescence spectra of these low Q-factor microcavities are presented. Addition of Si/SiO2 Bragg reflectors on the top and bottom of the device (3.5 and 5.5 pairs, respectively) is predicted to lead to spectral emission enhancement by ∼270.

Keywords: Silicon; Electroluminescence; Resonant cavity

  • Journal of Luminescence 121(2006)2, 290-292
    DOI: 10.1016/j.jlumin.2006.08.006
  • Poster
    E-MRS 2006 Spring Meeting, 29.05.-02.06.2006, Nizza, Frenkreich

Publ.-Id: 9017

Asymptotic methods for spherically symmetric MHD α2-dynamos

Kirillov, O.; Günther, U.

We consider two models of spherically-symmetric MHD α2-dynamos --- one with idealized boundary conditions (BCs) and one with physically realistic BCs. As it has been shown in our previous work, the eigenvalues λ of a model with idealized BCs and constant α-profile α₀ are linear functions of α₀ and form a mesh in the (α₀,Re λ)-plane. The nodes of the spectral mesh correspond to double-degenerate eigenvalues of algebraic and geometric multiplicity 2 (diabolical points). It was found that perturbations of the constant α-profile lead to a resonant unfolding of the diabolical points with selection rules of the resonant unfolding defined by the Fourier coefficients of the perturbations. In the present contribution we present new exact results on the spectrum of the model with physically realistic BCs and constant α₀. For non-degenerate (simple) eigenvalues perturbation gradients are found at any particular α₀. We present a detailed study of the spectral behavior of the α2-dynamo operator over a family of homotopic deformations of the BCs between idealized ones and physically realistic ones. Furthermore, we demonstrate that although the spectral singularities are lifted, a memory about their locations remains deeply imprinted in the homotopic family of the spectral deformations due to a hidden underlying invariance.

Keywords: MHD dynamo; homotopic deformation; homotopic invariance; non-Hermitian operator; spectral analysis

  • Lecture (Conference)
    6th International Congress on Industrial and Applied Mathematics (iciam 07), 16.-20.07.2007, Zürich, Switzerland

Publ.-Id: 9016

Single-pion production in pp collisions at 0.95 GeV/c (I)

Abd El-Samad, S.; Bilger, R.; Brinkmann, K.-T.; Clement, H.; Dietrich, M.; Doroshkevich, E.; Dshemuchadse, S.; Erhardt, A.; Eyrich, W.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Geyer, R.; Gillitzer, A.; Hauffe, J.; Hesselbarth, D.; Jaekel, R.; Jakob, B.; Karsch, L.; Kilian, K.; Koch, H.; Kress, J.; Kuhlmann, E.; Marcello, S.; Marwinski, S.; Meier, R.; Möller, K.; Morsch, H. P.; Naumann, L.; Roderburg, E.; Schönmeier, P.; Schulte-Wissermann, M.; Schroeder, W.; Steinke, M.; Stinzing, F.; Sun, G. Y.; Wächter, J.; Wagner, G. J.; Wagner, M.; Weidlich, U.; Wilms, A.; Wirth, S.; Zhang, G.; Zupranski, P.

The single-pion production reactions pp → dπ+, pp → npπ+ and pp → ppπ0 were measured at a beam momentum of 0.95GeV/c ( T p ≈ 400MeV) using the short version of the COSY-TOF spectrometer. The implementation of a central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements. Thus, all pion production channels were recorded with 1-4 overconstraints. The total and differential cross-sections obtained are compared to previous data and theoretical calculations. Main emphasis is put on the discussion of the ppπ0 channel, where we obtain angular distributions different from previous experimental results, however, partly in good agreement with recent phenomenological and theoretical predictions. In particular, we observe very large anisotropies for the π0 angular distributions in the kinematical region of small relative proton momenta revealing there a dominance of proton spinflip transitions associated with π0 s and d partial waves and emphasizing the important role of π0 d-waves.

Keywords: PACS. 13.75.Cs Nucleon-nucleon interactions; 25.10.+s Nuclear reactions involving few-nucleon systems; 25.40.Ep Inelastic proton scattering; 29.20.Dh Storage rings

Publ.-Id: 9015

Study of spectator tagging in the reaction np → ppπ- with a deuteron beam

Abdel-Bary, M.; Brinkmann, K.-T.; Clement, H.; Doroshkevich, E.; Dshemuchadse, S.; Erhardt, A.; Eyrich, W.; Freiesleben, H.; Gillitzer, A.; Jäkel, R.; Karsch, L.; Kilian, K.; Kuhlmann, E.; Möller, K.; Morsch, H. P.; Naumann, L.; Paul, N.; Pizzolotto, C.; Ritman, J.; Roderburg, E.; Schönmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sun, G. Y.; Teufel, A.; Ucar, A.; Wagner, G. J.; Wagner, M.; Wintz, P.; Wüstner, P.; Zupranski, P.

The reaction dppppπ- has been studied in a kinematically complete experiment at a single beam momentum pd =1.85 GeV/c (T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free nppppπ- reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron.

Keywords: .Cs Nucleon-nucleon interactions; Nuclear reactions involving few-nucleon systems; Dh Storage rings

Publ.-Id: 9014

Scanning probe microscopy with cantilever arrays

Rangelow, I.; Ivanov, T.; Volland, B.; Dontsov, D.; Sarov, Y.; Ivanova, K.; Persaud, A.; Filenko, D.; Nikolov, N.; Schmidt, B.; Zier, M.; Gotszalk, T.; Sulzbach, T.

This paper reports on to the realization of piezoresistive cantilever-Arrays used in scanning probe microscopy (SPM). Sensors for the SPM are peculiar microsystems since the combination of physical and microtechnological principles allows to gain an insight into the material science at nanoscale. Moreover SPM technology is opening new horizons in fundamental research and gives a chance to employ new interaction principles for the realization of new sensors and sensor arrays. Physical, biological, and chemical values and interactions can effectively be detected and analyzed using cantilevers, where the nanomechanical interactions can be transformed into an electric signal. The basic issues for the realization of a complete system of self-actuated, piezoresistive cantilever arrays are described.

Keywords: Piezoresistive cantilever arrays; scanning force microscopy; microsystems; nanosystems

Publ.-Id: 9013

Bubble recognition algorithms for the processing of wire-mesh sensor data

Prasser, H.-M.; Beyer, M.

Wire-mesh sensors deliver sequences of instantaneous, two-dimensional gas fraction distributions from a measuring cross-section. The spatial and temporal resolutions are high enough to reflect individual bubbles in much more than one measuring frame during their passage through the sensor plane. The bubbles can therefore be detected by a pattern recognition method based on the identifications of connected areas of gas-filled elements in the array of local instantaneous gas fractions, available as a function of the lateral co-ordinates x,y and as function of time. Algorithms were presented in earlier publications, which are based on a recursive fill procedure that assigns individual bubble numbers to the elements of the gas fraction array. This procedure has to rely on a threshold for the cancellation of the recursive fill, because the gas fraction data are affected by noise. The choice of the correct threshold is difficult, since a too high gas fraction threshold leads to unrealistic bubble fragmentation, while a too low threshold provokes unrealistic unification of bubbles. In previous papers an optimum approach was found by introducing a differential threshold determined for each bubble individually from the maximum gas fraction inside the given bubble to identify the cores of the bubbles. This is combined with an agglomeration step, where elements with a gas fraction below the threshold are assigned to already existing bubble cores, if these elements were not yet assigned to a bubble in the recursive fill step.
In the present paper, the algorithm will be analysed by applying it to synthetic measuring data, which is generated by placing bubbles of known geometrical parameters into the discretization measuring grid defined by the wire-mesh geometry. The discretization is performed with due care to reflect the fact that the gas-liquid interface at the periphery of the bubbles crosses control volumes of the measuring grid, producing local instantaneous void fractions of intermediate values. The synthetic signals are furthermore superposed by synthetic white noise. It is shown that the original bubble recognition algorithm needs to be improved in certain cases: (a) Unrealistic fragmentation in axial (time) direction may occur, when bubbles cross the sensor plane with a low velocity. (b) non-realistic coalescence becomes dominating at very high gas fractions, where bubbles of complex shape occur. Different improvements were tested. Unrealistic coalescence is avoided by introducing a criterion to terminate the recursive fill algorithm, which are based on the local gradient of the gas fraction. A second approach relies on a repair algorithm, which unites unrealistic fragments in an additional processing step after the preliminary bubble recognition. This repair algorithm takes benefit from a-priory knowledge to distinguish realistic close neighbour bubbles from unrealistic bubble fragments divided by an early truncation of the bubble recognition. After the check against synthetic bubbles, the algorithms are applied to real measuring data from gas-liquid flows in vertical pipes and the results obtained by the different algorithms are compared.

Keywords: wire-mesh sensor; measurement technique; bubble identifikation; bubble recognition algorithm

  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Lecture (Conference)
    International Conference on Multiphase flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 9012

A globally diagonalizable α2-dynamo operator, SUSY QM and the Dirac equation

Günther, U.; Samsonov, B.; Stefani, F.

A new class of semi-analytically solvable MHD α2-dynamos is found based on a global diagonalization of the matrix part of the dynamo differential operator. Close parallels to SUSY QM are used to relate these models to the Dirac equation and to extract non-numerical information about the dynamo spectrum.

Keywords: MHD dynamo; Krein space; operator theroy; supersymmetric Quantum Mechanics; Dirac equation; quasi-exactly solvable model; perturbation theory; Jordan structure

Publ.-Id: 9011

A bubble size distribution model for the numerical simulation of bubbly flows

Ruyer, P.; Seiler, N.; Beyer, M.; Weiss, F.-P.

This study carried out at the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) concerns the bubbly flow numerical simulation. One of the determining features of the two-phase flow is the topology of the flow. Local interfacial area concentration, say ai, allows to determine the exchange surface for momentum, heat and mass transfers between liquid and vapor. In the case of bubbly flow the size of the inclusion, say D, (through the non-dimensional Eötvös number) determines essential liquidvapor momentum transfers such as the lift force (e.g. (Tomiyama et al. 1995)). The corresponding fields ai and D are functions of history, flow conditions, as well as local events such as coalescence, break-up and phase change. This justifies to model their evolution thanks to additional transport equations (in addition to momentum, mass and energy balance equations). Several approaches can then be distinguished, namely the population balance (Coulaloglou and Tavlarides 1977), the two-group interfacial area transport (Fu and Ishii 2002) or the moment densities (Kamp et al. 2001). The purpose of the present study is to examine the ability of the NEPTUNE_CFD code to predict bubble size distribution in complex flow configurations.
A series of experiments performed at FZD in the frame of the TOPFLOW project allows to determine the local structure of the two-phase flow including the bubble size local distribution. We focus more particularly on bubbly air-water flows around an asymmetric obstacle in the section of a vertical pipe (see (Prasser et al. 2006)). The presence of the obstacle induces a pronounced three-dimensional effect as well as coalescence events. We perform numerical simulations with the NEPTUNE_CFD code of these experiments. The NEPTUNE_CFD code (see (Guelfi et al. 2005)) is based on the two-fluid model formulation. It is developed in the frame of a research program supported by EDF, CEA, IRSN and AREVA_NP. In the present study, two different levels of description of the bubble size distribution in space and time are considered. At the first level of description, the bubble size distribution is determined thanks to an interfacial area equation allowing to define locally a single bubble size (monodisperse flow). At the second level we consider locally a spectrum of bubble sizes (polydisperse flow) with the help of a moment densities approach. We incorporate the model within NEPTUNE_CFD and present the resulting gain in accuracy of the simulation. Perspectives concerning improvement of the numerical modelling of bubble size distribution are discussed.

Keywords: two-phase flow; NEPTUNE_CFD; bubble size distribution

  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Contribution to proceedings
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    paper: S6_Thu_A_48

Publ.-Id: 9009

Crystallographically oriented magnetic ZnFe2O4 nanoparticles synthesized by Fe implantation into ZnO

Zhou, S.; Potzger, K.; Reuther, H.; Talut, G.; Eichhorn, F.; von Borany, J.; Skorupa, W.; Helm, M.; Fassbender, J.

In this paper, a correlation between structural and magnetic properties of Fe-implanted ZnO is presented. High fluence Fe+ implantation into ZnO leads to the formation of superparamagnetic α-Fe nanoparticles. High vacuum annealing at 823 K results in the growth of α-Fe particles, but the annealing at 1073 K oxidizes the majority of the Fe nanoparticles. After a long term annealing at 1073 K, crystallographically oriented ZnFe2O4 nanoparticles are formed inside ZnO with the orientation relationship of ZnFe2O4(1 1 1)[1 1 0]//ZnO(0 0 0 1)[11 2 0]. These ZnFe2O4 nanoparticles show a hysteretic behaviour upon magnetization reversal at 5 K.

Keywords: ZnO; Magnetism of nanostructures; Ferrite

  • Journal of Physics D: Applied Physics 40(2007), 964-969

Publ.-Id: 9008

Annual Report 2005 - Institute of Safety Research

Weiss, F.-P.; Rindelhardt, U.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-457 2006
    ISSN: 1437-322X


Publ.-Id: 9007

Synthesis of 18F-labeled neurotensin(8-13) via copper-mediated 1,3-dipolar [3+2]cycloaddition reaction

Ramenda, T.; Bergmann, R.; Wüst, F.

The copper(I)-mediated 1,3 dipolar [3+2]cycloaddition between terminal alkynes and azides, also referred to as click-chemistry, was used to synthesize a 18F-labeled neurotensin(8-13) (NT(8-13)). 4-[18F]Fluoro-N-(prop-2-ynyl)benzamide [18F]1 as novel terminal alkyne building block could successfully be coupled with azide-functionalized NT(8-13) 4 to give the corresponding 18F-labeled NT(8-13) derivative [18F]5 product in 66% yield as determined by radio-HPLC. The in vitro binding affinity of 18F-labeled NT(8-13) derivative [18F]5 was determined to be 66 nM.

  • Letters in Drug Design & Discovery 4(2007)4, 279-285

Publ.-Id: 9005

Investigations into the Formation of Intrinsic Colloids and Pseudocolloids of Uranium(IV)

Zänker, H.; Opel, K.; Weiß, S.; Hübener, S.; Bernhard, G.

Investigations into the formation of intrinsic colloids and pseudocolloids of uranium(IV) were performed. Coulometric titrations of strongly acidic U(IV) solutions in HClO4/NaClO4 medium were carried out in order to find the pH of first colloid formation. Laser-induced breakdown detection (LIBD) was applied for the detection of traces of uranium colloids as the pH was increased. The pH values at the onset of colloid formation were used for thermodynamic calculations aimed at determining the solubility products of crystalline and amorphous uranium dioxide. Furthermore, the UO2·xH2O(am) colloids were investigated for their colloidal stability. Zeta potentials of ≥ 30 mV were found for pH values of less than 4. The point of zero charge was found at pH ~ 6.9. Colloidal suspensions of 1 mMol/L UO2·xH2O(am) at a pH value of 2.5 proved to be stable over > 1.5 years. The interaction of the forming UO2·xH2O(am) colloids with other colloid-forming species was tested. Therefore, coulometric titrations of U(IV) solutions in the presence of (a) dissolved Al(III) and (b) dissolved silicate were carried out. The presence of Al(III) does not significantly influence the formation of the UO2·xH2O(am) colloids, and the presence of U(IV) does not significantly influence the behaviour of Al(III). Also silicate does not significantly influence the pH of UO2·xH2O(am) colloid formation. However, the presence of U(IV) significantly influences the behaviour of the silicate (formation of pseudocolloids). The nature of the interaction between the silicate and the U(IV) is not yet known (adsorption? formation of a coffinite precursor?). EXAFS experiments to elucidate the local structure around the U(IV) atoms in the pseudocolloids are under preparation.

Keywords: Uranium(IV); uranium dioxide; intrinsic colloids; pseudocolloids; aluminum; silicate

  • Lecture (Conference)
    2nd Annual Workshop of the IP FUNMIG, 21.-23.11.2006, Stockholm, Sweden

Publ.-Id: 9004

Mixed-ligand 68Ga complexes with tetradentate/monodentate NS3/N ('4+1') coordination: Relation of structure with in vitro stability

Noll, B.; Smuda, C.; Hecht, M.; Kraus, W.; Pietzsch, H.-J.

Gallium forms complexes of the general formula [Ga(NS3)NHR2], where NS3 is the tripodal ligand tris(2-mercaptoethyl) amine and secondary amines (NHR2) are co-ligands. Structure determinations reveal trigonal-bipyramidal structure of the mononuclear species and the tendency of solvent-coordinated species [Ga(NS3)solv] (solv: water, methanol) to condensate to trinuclear species. Challenge experiments with the plasma protein transferrin, performed with the respective Ga-68 complexes, show enhanced stability of the aminederived species [Ga(NS3)NHR2] with piperidine and imidazole derivatives as the most stable complexes.

Keywords: Ga complexes; tris(2-mercaptoethyl) amine; in vitro stability; challenge experiments

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGE Editoriali, 2006, 88-89884-04-5, 227-228

Publ.-Id: 9003

Relativistic approaches to investigations of few-nucleon systems

Dorkin, S. M.; Kaptari, L. P.; Kämpfer, B.; Semikh, S. S.

Theoretical approaches used in investigations of relativistic effects in high energy lepton and hadron collisions with few nucleon systems are analyzed. The Bethe-Salpeter formalism for describing interacting systems of two spinor particles both in the continuum and bound state is described in detail. Special attention is paid to partial expansions taking into account the analytic properties of Bethe-Salpeter amplitudes and unitary transformations correlating different representations of partial amplitudes. Mathematical methods of numerical solution of equations are considered. Results of calculation of relativistic corrections and effects of interactions in the final state in particular reactions with the deuteron, namely, inelastic pD backward scattering and in reactions of deuteron break-up with production of correlated pairs, are presented.

  • Physics of Particles and Nuclei 37(2006), 867-898

Publ.-Id: 9002

Theta+ formation in inclusive gamma D to pK-X

Titov, A. I.; Kämpfer, B.; Date, S.; Ohashi, Y.

We analyze the possibility to produce an intermediate Tp via a KN to Tp formation process in gamma D to pK-X (X=nK+,pK0) reactions at some specific kinematical conditions, in which a pK- pair is knocked out in the forward direction and its invariant mass is close to the mass of Ls (Ls equiv Lambda(1520)). The Theta+ signal may appear in the [gamma D,pK-] missing mass distribution. The ratio of the signal (cross section at the Theta+ peak position) to the smooth background processes varies from 0.7 to 2.5 depending on the spin and parity of Tp, and it decreases correspondingly if the pK- invariant mass is outside of the Ls-resonance region. We analyze the recent CLAS search for the Tp in the gamma D to pK-nK+ reaction and show that the conditions of this experiment greatly reduce the Tp formation process making it difficult to extract a Tp peak from the data.

  • Physical Review C 74(2006), 055206

Publ.-Id: 9001

omega - pi gamma* transition form factor in proton-proton collisions

Kaptari, L. P.; Kämpfer, B.

Dalitz decays of omega and rho mesons, omega to pi0gamma* topi0 e+e- and rho0 to pi0gamma* to pi0 e+e-, produced in pp collisions are calculated within a covariant effective meson-nucleon theory.
We argue that the omega transition form factor F_{omega to pi0gamma*} is experimentally accessible in a fairly model independent way in the reaction pp to pp pi0 e+ e- for invariant masses of the pi0 e+ e- subsystem near the omega pole.
Numerical results are presented for the intermediate energy kinematics of envisaged HADES experiments.

  • European Physical Journal A 31(2007)2, 233-243

Publ.-Id: 9000

Rhenium complexes of dimercaptosuccinic acid derivatives for targeted radiotherapy

Pietzsch, H.-J.; Heinrich, T.; Kraus, W.; Jentschel, C.; Seifert, S.; Spies, H.

This work is part of efforts to develop chelating agents for stable binding and easy conjugation of Re-188 to biologically interesting structures. Starting from the high in vivo stability of [188ReO(DMSA)2]- we want to exploit this coordination system for the design of 188ReO(V) chelates which are stable towards re-oxidation to perrhenate under conditions of radiopharmaceutical procedures. Therefore a new type of tetradentate ligand has been synthesized by bridging two molecules on N-N'-diisobutyl-2,3-dimercaptosuccinamide with N-(3-aminopropyl)propane-1,3diamine. The resulting stereoisomeric tetrathiolato S4ligand forms anionic five-coordinated oxorhenium(V) complexes by ligand exchange reaction of NBu4[ReOCl4]in methanol. Without addition of base the compounds will be isolated as "betain", [ReO(S4)], with the protonated nitrogen of the bridge as a internal "counter ion".
Two representatives have been characterized in solid state and found to adopt the expected square-pyramidal coordination geometry. The equatorial plane is formed by four thiolate sulfur atoms, whereas the oxygen occupies the apical position. The orientation of the metal oxo group is exo in relation to the carbamido groups in both isomers. The complexes are stereoisomeric regarding the junction of the triamine chain. The Re-188 labelling procedure runs fast, in good yields and under mild conditions, making the new complexes interesting as access to stable Re-188 radiotherapeutics.

T. Heinrich, W. Kraus, H.-J. Pietzsch et al. Inorg. Chem., 44, 9930-9937 (2005).

  • Lecture (Conference)
    37. International Conference on Coordination Chemistry, 13.-18.09.2006, Cape Town, South Africa
  • Contribution to proceedings
    37. International Conference on Coordination Chemistry, 13.-18.09.2006, Cape Town, South Africa
    37th International Conference on Coordination Chemistry (ICCC) eds: D.J. Robinson, I.M. Robinson, 1-920-01705-4, 52

Publ.-Id: 8999

Uranium - an unique luminescent element - New observations in different oxidation states -

Geipel, G.

Vortrag über Lumineszenzeigenschaften des Urans in verschiedenen Oxidationsstufen

  • Invited lecture (Conferences)
    Kolloqium an der Nukleartechnischen Fakultät der Czech Technical University, 09.11.2006, Prague, Czech Republic

Publ.-Id: 8998

Hypochlorite-induced oxidation of low-density lipoproteins and high-density lipoprotein modifies their potential role in atherogenesis

Kopprasch, S.; Grässler, J.; Pietzsch, J.

Substantial evidence has accumulated that the myeloperoxidase (MPO)/hydrogen peroxide/hypochlorite system of phagocytes plays a critical role not only in antimicrobial defence but also in chronic inflammatory conditions like atherosclerosis. Oxidation of low-density lipoproteins (LDL) by hypochlorite (OCl-LDL) results in physico-chemical modifications of both the protein and lipid moiety of the lipoprotein molecule. Following oxidation OCl-LDL display a number of proatherogenic and proinflammatory properties including stimulation of phagocyte oxidant generation, induction of leukocyte degranulation, and increase of phagocyte adhesion to endothelial cells. Importantly, the class B scavenger receptors CD36 and SR-BI are receptors for OCl-LDL. This fact may explain the high uptake of OCl-LDL in macrophages, leading to the formation of foam cells. Our investigations revealed that OCl-LDL upregulates the gene expression of CD36 and PPAR in macrophages dose- and time-dependently while modulating SR-BI expression differently in dependence on incubation conditions. The antiatherogenic properties of high-density lipoproteins (HDL) are suggested to be mainly associated with its SR-BI-mediated reverse cholesterol transport. In addition we could demonstrate that HDL possesses anti-inflammatory actions by inhibiting OCl-LDL-induced increase in phagocyte respiratory burst and adhesion to endothelial cells. The protective role of HDL was substantially attenuated when HDL apolipoproteins were oxidized by hypochlorite. Our in vitro data show that hypochlorite-oxidized lipoproteins could mimic fundamental atherogenic and inflammatory processes therefore underlying the potential role of hypochlorite oxidation as pathogenetic factor in vivo.

  • Contribution to external collection
    Pietzsch, J.: Protein Oxidation and Disease, Recent Research Developments in Pathological Biochemistry 1, Trivandrum, Kerala, India: Research Signpost, 2006, 81-308-0028-4, 179-196

Publ.-Id: 8997

Protein oxidation in diabetes mellitus

Julius, U.; Obrosova, I. G.; Pietzsch, J.

Growing evidence indicates that diabetes mellitus is accompanied by oxidative stress. In addition to lipids and nucleic acids, proteins also undergo oxidation. Diabetic patients have several groups of oxidatively modified proteins, i.e., advanced glycation end-products, carbonylated proteins, and advanced oxidation protein products, in the circulation. Oxidized proteins have also been detected in tissues of animals with experimental diabetes. Oxidative modifications of mitochondrial proteins are blunted in diabetic conditions. Of special interest is the oxidation of apolipoprotein B-100, the structural protein of low density lipoproteins. Oxidatively modified apolipoprotein B-100 molecules had been detected in atherosclerotic lesions as well as in the circulation. Oxidatively altered proteins lead to vascular damage. Increased oxidative stress was also observed in gestational diabetes. Protein oxidation plays a major role in the development of diabetes complications and has been implicated in the pathogenesis of diabetic nephropathy, neuropathy and retinopathy. In diabetic nephropathy which develops as a result of complex interplay of hemodynamic and metabolic factors, oxidative protein modifications contribute to albuminuria, mesangial expansion, glomerulosclerosis and tubulo-interstitial fibrosis. There is also strong experimental evidence that morphological abnormalities of diabetic retinopathy, such as pericyte dropout, formation of acellular capillaries, are associated with non-enzymatic glycosylation (glycation) and accumulation of advanced glycation end-products. Protein oxidation also takes place in the lens and plays a central role in the development of cataract. Growing evidence implicates advanced protein glycoxidation and lipoxidation in the pathogenesis of both somatic and autonomic diabetic neuropathy, and, in particular, motor and sensory nerve conduction deficits, neurovascular dysfunction, diabetic neuropathic pain and loss of sensory function, and morphological abnormalities characteristic for peripheral and autonomic neuropathy.

  • Contribution to external collection
    Pietzsch, J.: Protein Oxidation and Disease, Recent Research Developments in Pathological Biochemistry 1, Trivandrum, Kerala, India: Research Signpost, 2006, 81-308-0028-4, 293-325

Publ.-Id: 8996

In vivo catabolism of hypochlorite-modified low density lipoproteins (LDL): insights from small animal positron emission tomography studies

Hoppmann, S.; Steiniger, B.; Strobel, K.; Haase, C.; Pietzsch, J.

Oxidative modification of LDL apolipoprotein (apo) B-100 by myeloperoxidase-generated hypochlorous acid (HOCl) is regarded as a crucial event in atherogenesis. Exemplarily, HOCl-modified LDL (OCl-LDL) apoB-100 has been shown to be present in the human aortic vessel wall from various stages of atherosclerotic lesion evolution. On the other hand, data concerning the role of circulating OCl-LDL in the development of atherosclerosis are scarce. One reason for this is the shortage of methods for direct assessment of metabolism of oxidatively modified LDL in vivo. We report an improved methodology for radiolabeling of both native LDL (nLDL) and HOCl-LDL with the positron-emitter fluorine-18 (18F) by N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) and the use of [18F]fluorobenzoylated LDL particles in dynamic positron emission tomography (PET) studies in rats. As model reactions, nLDL were modified in vitro by 3 mM NaOCl. For radiolabeling, pools of chemically and biochemically well characterized human nLDL and OCl-LDL were used. Preparation of [18F]SFB was achieved by module-assisted synthesis within 68 min with radiochemical yields of 36±2% (corrected for decay) and purity of >95%. LDL labeling with [18F]SFB resulted in radiochemical yield of 30±10% (nLDL; corrected for decay) and 10±5% (OCl-LDL), respectively, with specific radioactivity of 50-400 GBq/µmol. Radiolabeling of native and modified LDL using [18F]SFB caused neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality in vitro, respectively. The method was further evaluated with respect to the uptake of [18F]fluorobenzoylated native and modified LDL particles, respectively, in various human cells. Biodistribution studies in rats revealed high in vivo stability for the [18F]fluorobenzoylated LDL particles. The metabolic fate of [18F]fluorobenzoylated nLDL and OCl-LDL particles in vivo was delineated by dynamic PET studies using a dedicated small animal positron emission tomograph. Dynamic PET data demonstrated a significantly enhanced catabolism of OCl-LDL when compared with nLDL. The in vivo distribution and kinetics of both native and modified LDL particles in the rat correlated well with the anatomical localization of LDL receptors and scavenger receptors. In conclusion, [18F]SFB-labeling of LDL and the use of small animal PET provide a valuable tool to discriminate the kinetics and the metabolic fate of both native and oxidatively modified LDL in animal models in vivo.

  • Contribution to external collection
    Pietzsch, J.: Protein Oxidation and Disease, Recent Research Developments in Pathological Biochemistry 1, Trivandrum, Kerala, India: Research Signpost, 2006, 81-308-0028-4, 197-219

Publ.-Id: 8995

Technetium coupled to biologically active moieties

Pietzsch, H.-J.; Künstler, J.-U.; Spies, H.

Many 99mTc pharmaceuticals were designed for the measurement of organ function, based on regional blood flows, ion transport, and cellular rentention. Organ specificity is governed by molecular characteristics (e.g., size, shape, charge) and physiological factors.
Primarily, these radiotracers are coordination complexes of technetium leaving either a positive or a negative charge; neutral, lipophilic complexes pass the blood-brain barrier. Organ function is related to regional perfusion (e.g., brain, heart). Hepatocyte function is measured by the excretion of iminodiacetic acid (IDA) derivatives into bile, simulating the active transport of bilirubin. Increased osteogenic activity correlates with increased regional uptake of 99mTc-diphosphonate complexes in bone structures, delineating tumor and metastatic growth. The functional state of the kidneys as measured by active tubular secretion requires a negatively charged complex with a carboxylate anion.
99mTc pharmaceuticals based on coordination complexes with functionalized ligands are also known as "Tc essentials"; those concerning labeled particles and macromolecules are called "Tc-tagged" radiopharmaceuticals. A variety of chelating agents have been developed for complex formation with certain oxidation states of technetium, providing the structural requirements for uptake and rentention (Schwochau 1000). Examples of Tc essentials are shown in Fig. 2.3.1.
The outstanding interest in the development of novel 99mTc pharmaceuticals is documented in recent reviews (Hom and Katzenellenbogen 1997; Johannsen and Pietzsch 2002a; Jurisson and Lydon 1999)

  • Contribution to external collection
    Zolle, I.: Tc-99m Pharmaceuticals - Preparation and Quality Control in Nuclear Medicine, Berlin Heidelberg New York: Springer-Verlag, 2007, 10: 3-540-33989-2, 40-58

Publ.-Id: 8994

Stannous chloride in the preparation of 99mTc radiopharmaceuticals

Spies, H.; Pietzsch, H.-J.

kein Abstract verfügbar

  • Contribution to external collection
    Zolle, I.: Tc-99m Pharmaceuticals - Preparation and Quality Control in Nuclear Medicine, Berlin Heidelberg New York: Springer-Verlag, 2007, 10: 3-540-33989-2, 59-66

Publ.-Id: 8993

C78 cage isomerism defined by trimetallic nitride cluster size: a computational and vibrational spectroscopic study

Popov, A. A.; Krause, M.; Yang, S.; Wong, J.; Dunsch, L.

Molecular structure of Dy3N@C78 and Tm3N@C78 clusterfullerenes are addressed by the IR and Raman vibrational spectroscopic studies and DFT computations. Firstly, extensive semiempirical calculations of 2927 isomers of C78 hexaanions followed by DFT optimization were applied to establish their relative stability. Then, DFT calculations of a series of M3N@C78 (M=Sc, Y, Lu, La) isomers were performed which have shown that the stability order of the isomers depends on the cluster size. While the Sc3N cluster is planar in the earlier reported Sc3N@C78 (D3h: 24109) clusterfullerene, relatively large Y3N and Lu3N clusters would be forced to be pyramidal inside this cage, which would result in their destabilization. Instead, these clusters remain planar in the non-IPR C2: 22010 isomer making Y3N@C78 and Lu3N@C78 clusterfullerenes with this cage structure the most stable ones. Finally, on the basis of a detailed analysis of their IR and Raman spectra supplemented with DFT vibrational calculations, the recently isolated Tm3N@C78 and the major isomer of Dy3N@C78 are assigned to the non-IPR C2: 22010 cage structure. A detailed assignment of their experimental and computed IR and Raman spectra is provided to support this conclusion and to exclude other cage isomers.

Keywords: Endohedral Fullerenes; Structure Determination; Vibrational Spectroscopy

Publ.-Id: 8992

Deviation from the Planarity - a Large Dy3N Cluster Encapsulated in an Ih-C80 Cage: An X-ray Crystallographic and Vibrational Spectroscopic Study

Yang, S.; Troyanov, S. I.; Popov, A. A.; Krause, M.; Dunsch, L.

The high-yield synthesis of Dy3N@C80 (I) opens the possibility of characterizing its molecular and vibrational structures. We report on the structure determination of Dy3N@C80 (I) by X-ray crystallographic study of single crystal of Dy3N@C80 (I)•Ni(OEP)•2C6H6, revealing a nearly planar Dy3N cluster encapsulated in an Ih-C80 cage. The vibrational structure of Dy3N@C80 (I) is studied by FTIR and Raman spectroscopy in combination with force-field calculations. A correlation was found between the antisymmetric metal-nitrogen stretching vibration and the structure of the M3N cluster of M3N@C80 (I) (M = Y, Gd, Tb, Dy, Ho, Tm). Moreover, a stronger interaction between the encaged nitride cluster and the C80 carbon cage was found in the class II M3N@C80(I) (M=Y, Gd, Tb, Dy, Ho, Tm) than in Sc3N@C80 (I). This study demonstrates that the cluster size (determined by the ionic radius of the metals involved) plays the dominating role in the structure of the M3N cluster in M3N@C80 (I).

Keywords: endohedral fullerenes; nitride clusters; vibrational spectroscopy; structure elucidation; X-ray crystallography

  • Journal of the American Chemical Society 128(2006)51, 16733-16739
    DOI: 10.1021/ja066814i

Publ.-Id: 8990

Nanocluster Memories by Ion Beam Synthesis of Si in SiO2

Schmidt, B.

Self-assembling of Si-nanocrystals (NCs) in gate oxides, with special emphasis on size and position tailoring and their application as discrete charge storage centers in nanocrystal memories area great challange to materials research with ion beams. The Si NCs for these multi-dot floating-gate memories have been produced by ion irradiation through SiO2/Si-interfaces. Si excess within SiO2 is formed by ion beam mixing of Si from the Si substrate and from the poly-Si capping layer into the gate oxide. Ion irradiation with 3x1015 -10x1015 Si+ cm-2 at 50-100 keV through 50 nm poly-Si and 15 nm SiO2 on (001)Si results in a considerable Si excess. At the upper and lower interfaces of the gate oxide, this ion irradiation forms a metastable SiOx composition. Si NCs are formed by phase separation into Si and SiO2 during post-irradiation thermal treatment. Adjacent to the recovering interfaces, narrow SiO2 zones becomes denuded of excess Si. More distant excess Si precipitates as Si NCs in the gate oxide. This approach was applied to nMOSFET-NC-memory fabrication in the standard CMOS line at ZMD. MOSFET characteristics in terms of write/erase voltage, duration of the programming time, endurance and retention have been evaluated.

Keywords: Ion beam irradiation; Si nanocrystals; MOSFET-nanocrystal memory

  • Lecture (Conference)
    2nd Workshop "Hybrid Nanostructured Materials - Synthesis, Properties, Applications", 08.-09.11.2006, Dresden, Germany
  • Open Access Logo Materials Science - Poland 25(2007)4, 1213-1222

Publ.-Id: 8989

Image reconstruction for fast X-ray computed tomography of multiphase flows

Bieberle, M.; Hampel, U.

Electron beam X-ray computed tomography is a measurement method, which allows imaging of cross sectional density distributions of an object of interest with a frame rate of more than 1000 images per second. This is very attractive for multiphase flow measurements because flow velocities of 1 m/s and more can be resolved without influencing the flow.
Contrary to conventional tomography, electron beam X-ray CT comprises no mechanical rotated components but a fast moving X-ray source generated by a deflected electron beam. Unfortunately, the static arrangement of the system impedes the acquisition of a complete tomography data set of one imaging plane. Either, there is an offset between source and detector plane or the data acquisition is limited to an angular range smaller than 180°. In the first case, the image resolution in flow direction is reduced depending on the offset, whereas the image reconstruction of the second case tends to limited-angle artifacts in form of skewed object structures.
To minimize the artifacts in image reconstruction the algorithms were adapted to this special limited-angle case. They are mostly based on the iterative reconstruction algorithms ART and MART (additive and multiplicative algebraic reconstruction technique), because they are more flexible and modifiable than common filtered backprojection methods. Especially the reconstruction of two-phase flows permits the incorporation of a priori knowledge into the reconstruction process because only the phase distribution of one known attenuation coefficient has to be recovered.
We will explain the measurement setup and our reconstruction methods in detail. Furthermore, we will present the results of the reconstruction of simulated 2D and 3D two-phase flow data as well as measured data from static and dynamic phantoms imitating real flow scenarios.

Keywords: multiphase flow imaging; x-ray computed tomography

  • Contribution to proceedings
    6th International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    Proceedings of ICMF 2007, Paper S7_Thu_C_55
  • Lecture (Conference)
    International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 8988

Synthesis, in vitro stability studies, and bioconjugation of Rhenium-188 complexes with tetradentate/monodentate NS3/P ('4+1')coordination

Schiller, E.; Pietzsch, H.-J.; Tisato, F.; Refosco, F.; Seifert, S.; Spies, H.

Rhenium(III) mixed-ligand complexes with tetradentate/monodentate (‘4 + 1’) coordination of the general formula [Re(NS3)(PRR’R’’)] (NS3 = tris-(2-mercaptoethyl)amine and derivatives thereof, PRR’R’’ = tertiary phosphine) are promising candidates for the development of rhenium-188 complexes for radiotherapeutic applications. In order to understand relationships between the structure of 188Re ‘4+1’ complexes and their in vitro stability we synthesized a series of rhenium model complexes using various combinations of NS3 derivatives and monodentate phosphorus(III) ligands and determined their stability at MBq activity level in human plasma. As an outcome of these investigations we are able to roughly estimate which ligands are suitable for a rational complex design with regard to high in vitro and in vivo stability. Subsequently, the most stable representative was investigated at GBq activity level showing no detectable degradation of the rhenium-188 complex in pharmaceutical preparation up to 2 hours after preparation. This stable 188Re ‘4+1’ complex was furthermore successfully conjugated to the model peptide arginine-tyrosine using the water-soluble N-hydroxy-sulfosuccinimidyl activated ester of the monodentate phosphine ligand. In summary, our results show the great potential of 188Re ‘4+1’ complexes for labelling biomolecules for therapeutic purposes.

Keywords: rhenium-188 complexes; in vitro Stability; peptide labelling

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGE Editoriali, 2006, 88-89884-04-5, 479-482

Publ.-Id: 8987

Simulation study on multilayer limited angle scanned electron beam X-ray CT arrangements for two-phase flow measurements

Bieberle, M.; Hampel, U.; Prasser, H.-M.; Schleicher, E.

Recently, we presented a limited angle computed tomography approach that utilises a scanned electron beam X-ray source to produce multiple projections of an object. From these projections cross sectional images of the object are reconstructed by using iterative reconstruction algorithms. Tests with static as well as dynamic objects proved that the scan rate of the electron beam allows tomographic imaging with 1000 frames per second at an in-plane resolution of 1 mm. In a simulation study on three-dimensional flow data sets obtained with a fast and high-resolution conductivity wire-mesh sensor under real two-phase flow conditions we have shown, that this approach is capable to recover the in-plane phase structure of the flow. However, two problems arise when this measuring method is utilized for quantitative analysis of two-phase flows. Firstly, by acquiring a time sequence of cross sectional images of one plane in the flow no information about the volumetric structure of the flow can be obtained without knowing the different phase velocities. Secondly, the static arrangement of the X-ray focal spot path and the detector arc in one plane allows only a limited angular range from which projections are available. The missing data leads to artefacts in the reconstructed images which increase with the size and complexity of the imaged structures. For these reasons, simulation studies on different extended measurement arrangements with a two-dimensional beam deflection unit including multilayer imaging have been performed. The presentation will be focused on these different arrangements and their influence on the phase structure recovery of two-phase flows.

Keywords: limited angle X-ray CT; two-phase flow measurements

  • Contribution to proceedings
    5th World Congress on Industrial Process Tomography (WCIPT5), 03.-06.09.2007, Bergen, Norway
    Proceedings of the 5th World Congress on Industrial Process Tomography, 259-264
  • Lecture (Conference)
    5th World Congress on Industrial Process Tomography (WCIPT5), 03.09.2007, Bergen, Norway

Publ.-Id: 8986

Interactions of microbes found at Äspö underground lab with actinides such as curium, plutonium and uranium

Moll, H.

Sulfate-reducing bacteria (SRB) frequently occur in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden. The new SRB strain Desulfovibrio äspöensis could be isolated. Results describing the basic interaction mechanisms of uranium, curium, and plutonium with cells of D. äspöensis DSM 10631T will be presented. The interaction experiments with the actinides showed that the cells are able to remove all three actinides from the surrounding solution. The amount of removed actinide and the interaction mechanism varied among the different actinides.
The main U(VI) removal occurred after the first 24 h. The contact time, pH and [U(VI)]initial influence the U removal efficiency. The presence of uranium caused a damaging of the cell membranes. TEM revealed an accumulation of U inside the bacterial cell. D. äspöensis are able to form U(IV). A complex interaction mechanism takes place consisting of biosorption, bioreduction and bioaccumulation.
In the case of 242Pu, solvent extractions, UV-vis- and XANES spectroscopy were used to determine the speciation of the Pu oxidation states. In the first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. Solvent extractions showed that 97 % of the initially present Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 24 h of contact time. Most of the formed Pu(V) dissolves from the cell envelope back to the aqueous solution due to the weak complexing properties of this plutonium oxidation state. Indications were found for a penetration of Pu species inside the bacterial cells.
In the case of curium at a much lower metal concentration of 3x10-7 M, a pure biosorption of Cm(III) on the cell envelope forming an inner-sphere surface complex most likely with organic phosphate groups was detected.
To summarize, the strength of the interaction of D. äspöensis with the selected actinides at pH 5 and actinide concentrations ≥ 10 mg/L ([Cm] 0.07 mg/L) follows the pattern: Cm > U > Pu.

Keywords: microbial interactions; Desulfovibrio äspöensis; actinides

  • Lecture (Conference)
    2nd Annual Workshop of the IP FUNMIG, 21.-23.11.2006, Stockholm, Sweden
  • Contribution to proceedings
    2nd Annual Workshop of the IP FUNMIG, 21.-23.11.2006, Stockholm, Schweden
    Interactions of microbes found at Äspö underground lab with actinides such as Curium, Plutonium and Uranium, Bromma: CM Digitaltryck AB,, 1404-0344, 131-137

Publ.-Id: 8985

A novel approach for 99mTc labelling of peptides organometallic Tc(III) complexes for conjugation of bombesin derivatives

Künstler, J.-U.; Veerendra, B.; Sieckman, G. L.; Smith, C. J.; Pietzsch, H.-J.

Among peptides for tumour targeting bombesin (BBS), binding to gastrin releasing peptide receptors (GRPR) and overexpressed by e.g. prostate and breast carcinomas has a great potential. Thus, various labelled bombesins were described in the literature showing a varying pharmacokinetic behaviour depending on the labelling approach, the spacer between the radiometal moiety and the N-terminus as well as modifications in the peptide sequence.
In this study, the bioactive minimal sequence BBS(7-14) was labelled by the Tc-“4+1” mixed-ligand system, where Tc(III) is coordinated by a monodentate isocyanide bearing the peptide and the tetradentate tripodal chelator tris(2-mercaptoethyl)-amine (NS3).
BBS(7-14) was N-terminally modified with Gly-Gly-Gly, β-Ala and Ser-Ser-Ser as spacer groups and functionalized with 4-isocyanomethyl benzoic acid or 4-isocyanobutyric acid. 99mTc labelling was performed in a two-step ligand exchange procedure starting from 99mTc-EDTA/mannitol. The Re analogues were used as references for chemical characterization and in receptor-binding studies. Complex bearing β-Ala-BBN(7-14) exhibited a GRPR-affinity in the subnanomolar range and high uptake in human prostate (PC-3) cancer cells, whereas pancreatic uptake in biodistribution studies using normal mice was low.

Keywords: Technetium; '4+1' Mixed-ligand Complexes; Organometallic; Bombesin; Peptide Labelling

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGE Editoriali, 2006, 88-89884-04-5, 317-318

Publ.-Id: 8984

99mTc-labelled RGD-Peptide using the "4+1" mixed-ligand approach

Giglio, J.; León, E.; Rey, A.; Künstler, J.-U.; Gniazdowska, E.; Pietzsch, H.-J.

This paper presents the 99mTc-labelling and evaluation of two isocyanide (4-isocyanomethylbenzoic acid = L1, 4-isocyanobutanoic acid= L2) derivatives of the peptide c(RGDyK) using the "4+1" mixed-ligand chelate system. Starting from the precursor 99mTc-EDTA labelling was achieved by reaction of the isocyanide-bearing peptide and the tetradentate ligand containing three non-coordinating carboxyl groups (NS3(COOH)3) resulting in 99mTc(NS3(COOH)3)(L1-c(RGDyK)), 1 and 99mTc(NS3(COOH)3)(L2-c(RGDyK)), 2. A radiochemical purity (RP) of 60% was obtained for both peptides and HPLC purification resulted in RP>95% and stability was >90% after 24h. Plasma protein binding was 27% for 1 and 15% for 2. Both complexes showed preferential renal excretion. Uptake in induced B16F1 murine melanoma was moderate for both compounds but higher tumour/muscle ratios were achieved for 1 at all time points.

Keywords: Tc "4+1" mixed-ligand complexes; 99mTc labelled peptides; RGD peptides

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGE Editoriali, 2006, 88-89884-04-5, 331-332

Publ.-Id: 8983

86Y-labelled L RNA oligonucleotides as Molecular Probes for Positron Emission Tomography (PET)

Schlesinger, J.; Bergmann, R.; Klußmann, S.; Wüst, F.; Pietzsch, H.-J.

A short 5’-aminohexyl-functionalised L RNA oligonucleotide 1 (sequence: UGA CUG ACU GAC 3’, MW 3975) was used to study the influence of two different 86Y DOTA chelates on the biodistribution in Wistar rats. The L-oligonucleotide 1 was conjugated with 1,4,7,10 tetraazacyclododecane-N,N’,N’’,N’’’-tetraacetic acid (DOTA) using N-succinimide ester (DOTA-NHS) 2 and isothiocyanate derivative (p SCN bz DOTA) 4 to afford the corresponding amide 3 and thiourea 5, respectively. Both DOTA-functionalised L RNA oligonucleotides 3 and 5 were labelled with the medium half-life positron-emitting radiometal 86Y (t1/2 = 14.7 h) in 76 % and 85 % radiochemical yield. 86Y-Complexes 3a and 5a represent the first examples of L-oligonucleotides labelled with the positron emitter 86Y.
The in vivo biodistribution of 86Y-complex 3a showed a faster elimination from the body via the kidneys compared to thiourea-containing 86Y-complex 5a. Transient accumulation of radioactivity in the kidneys and the adrenals was found for both 86Y-complexes 3a and 5a. After incubation of 86Y-complex 5a in whole rat blood at 37°C no noticeable decomposition could be observed over 12 h as confirmed by HPLC-analysis

  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U.Mazzi: Rhenium and Other Metals in Chemistry and Nuclear Medicine, Padova: SGEditoriali, 2006, 88-89884-04-5, 211-214

Publ.-Id: 8982

Positron Emission Tomography

van den Hoff, J.

kein Abstract verfügbar

  • Contribution to external collection
    D. Ganten and K. Ruckpaul: Encyclopedic Reference of Genomics and Proteomics in Molecular Medicine, ed., Heidelberg, New York: Springer Verlag, 2006, 3-540-44244-8, 1446-1449

Publ.-Id: 8981

Reversals made simple: some new results

Stefani, F.; Gerbeth, G.; Günther, U.; Xu, M.; Sorriso-Valvo, L.

We present new results of a very simple model of Earth's magnetic field reversals which is based on an alpha^2 dynamo under the influence of noise. This reversal model relies on the existence of exceptional points of the spectrum of the non-selfadjoint dynamo operator. As new aspects of this model, we delineate its connection with the van der Pol oscillator, we demonstrate a remarkable agreement with the characteristic time scales and the well-known asymmetry of real reversals, and we discuss the deviation from Poissonian statistics in real reversal sequences and in our model. Finally, we present some speculations on the influence of the size of the inner core on the spectral properties of the dynamo operator and on the reversal rate.

  • Lecture (Conference)
    9th MHD Days 2006, 04.-05.12.2006, Heidelberg, Germany

Publ.-Id: 8980

Observation of magnetorotational instability in a liquid metal Taylor-Couette experiment

Gundrum, T.; Gerbeth, G.; Stefani, F.; Rüdiger, G.; Hollerbach, R.

Magnetic fields can play an active role in the formation of stars and black holes by virtue of the Magnetorotational Instability (MRI) which enables outward transport of angular momentum in accretion discs. Using a combination of axial and azimuthal magnetic fields, we provide experimental evidence of the MRI in a liquid metal Taylor-Couette experiment with Reynolds numbers of the order 1000 and Hartmann nubers of the order 10. The MRI mode in the liquid metal alloy GaInSn is measured by Ultrasonic Doppler Velocimetry.

  • Lecture (Conference)
    9th MHD Days 2006, 04.-05.12.2006, Heidelberg, Germany

Publ.-Id: 8979

Proton single voxel spectroscopy of different adipose tissue deposits in mice

Strobel, K.; van den Hoff, J.; Pietzsch, J.

Accumulation of excess abdominal visceral fat has been shown to play crucial roles in the development of cardiovascular disease as well as the development of obesity-related disorders like Diabetes mellitus, hyperlipidemia, and hypertension.
In the last years, rodent models have gained an important role in the investigation of adipose tissue (AT) biology and disorder. In this line, non-invasive differentiation and characterization of various AT deposits in the living animal is a current challenge. Magnetic resonance spectroscopy (MRS) at high magnetic field strength can help us to learn more about lipids in vivo. MRS is applied for brown adipose tissue (BAT), as well as intra-abdominal white adipose tissue (WAT) deposits in mice.
All experiments were carried out in NMRI mice and nude mice. Morphological differentiation between various BAT and WAT deposits was obtained by 1H-MRI at 7 Tesla using a Biospec 70/30 (Bruker, Germany). 1H-MRS has been performed to quantify in vivo the different lipid patterns in BAT and WAT deposits using a volume selective PRESS sequence on 1 to 8 mm3 voxels.
In both nude mice and NMRI mice the various BAT and WAT deposits were clearly distinguished from the non-AT tissue with excellent contrast by T1-weighted MSME MRI sequences. The high resolution spectra obtained at 7 T allow identification of at least 9 different proton resonances specific for lipids, and, thus, for calculation of mono- to polyunsaturated fatty acid ratio in vivo. In this study, nude mice showed a 3-fold higher degree of polyunsaturation of triglyceride fatty acid acyl chains in BAT when compared to NMRI mice. No significant differences were observed in WAT deposits.
High-resolution MRS is a potentially useful tool for studying the biology of different BAT and WAT deposits non-invasively in small experimental animals in vivo.

  • Lecture (others)
    User Meeting 2006 der Fa. Bruker Biospin MRI GmbH, 09.-12.10.2006, Ettlingen, Germany

Publ.-Id: 8978

Impact of tumour hypoxia on the FDG uptake in two human tumour models on nude mice investigated with PET, autoradiography and functional histology

Beuthien-Baumann, B.; Gabrys, D.; Wüllrich, K.; Hofheinz, F.; Krause, M.; Bergmann, R.; Hessel, F.; Yaromina, A.; Eicheler, W.; Baumann, M.

kein Abstract verfügbar

  • Abstract in refereed journal
    Radiotherapy and Oncology Suppl. 1(2006), S142
  • Lecture (Conference)
    ESTRO-Conference, 09.-12.10.2006, Leipzig, Germany

Publ.-Id: 8977

PET-based investigation of cerebral activation following intransal trigeminal stimulation

Hummel, T.; Beuthien-Baumann, B.; Heinke, M.; Oehme, L.; van den Hoff, J.; Gerber, J. C.

kein Abstract verfügbar

  • Abstract in refereed journal
    Chemical Senses 31(2006), A60-A61
  • Lecture (Conference)
    AChems 28th Annual Meeting, 26.-30.04.2006, Sarasota/Florida, USA

Publ.-Id: 8976

Labeling of low-density lipoproteins using the 18F-labeled thiol-reactive reagent N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]maleimide [18F]FBAM

Berndt, M.; Pietzsch, J.; Wüst, F.

The novel thiol group-selective bifunctional 18F-labeling agent N-[6-(4-[18F]fluoro-benzylidene)aminooxyhexyl]maleimide ([18F]FBAM) has been developed. The bifunctional labeling precursor 4 containing a thiol-reactive maleimide group and a carbonyl group-reactive aminooxy group was prepared in only three steps in a total chemical yield of 59%.
Subsequent radiolabeling with 4-[18F]fluorobenzaldehyde gave the bifunctional 18F-labeling agent [18F]FBAM in 29% radiochemical yield. In a typical experiment 3.88 GBq of [18F]fluoride could be converted into 723 MBq of [18F]FBAM within 69 min. Conjugation of [18F]FBAM with thiol groups was exemplified with the cystein-containing tripeptide glutathione and with various apolipoproteins of human low density lipoproteins (LDL) subfractions. The latter one was evaluated with respect to uptake of [18F]FBAM-LDL subfractions in human hepatoma cells (HepG2) in vitro. In vivo biodistribution studies in rats revealed high stability for the [18F]FBAM-LDL subfractions. Moreover, the metabolic fate of the [18F]FBAM-LDL subfractions in vivo was delineated by dynamic PET studies using a dedicated small animal tomograph. Data were compared to former studies using the NH2-reactive 18F-labeling agent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). Compound [18F]FBAM can be considered to be an excellent prosthetic group for the selective and mild 18F-labeling of thiol group-containing biomolecules suitable for subsequent investigations in vitro and in vivo.

Publ.-Id: 8975

Advances in the Production, Processing and MicroPET Image Quality of Technetium-94m

Bigott, H. M.; Laforest, R.; Liu, X.; Ruangma, A.; Wüst, F.; Welch, M.

This work involves the production, processing and imaging of the short-lived, rarely used positron emission tomography (PET) radionuclide technetium-94m (94mTc). Our procedures are an extension of methods reported in the literature and are detailed within. A key modification was the development of a single step that combines purification and concentration of an aqueous 94mTc-pertechnetate solution, which both reduces processing time and increases the final concentration of the solution. Additionally, a convenient method for the direct recovery of 94mTc into an organic solvent was developed, eliminating the solvent transfer step needed for organic syntheses using 94mTc.
Each of these advances potentially extends the scope of syntheses possible with this short-lived radionuclide. To explore the imaging potential of 94mTc, we carried out phantom imaging studies on small-scale high-resolution PET scanners to estimate the limitations of detection associated with 94mTc and PET. Preliminary studies demonstrate that useful images can be obtained with modern image reconstruction algorithms when using a correction for the cascade gamma ray contamination.

  • Nuclear Medicine and Biology 33(2006)7, 923-933

Publ.-Id: 8974

Excitation dynamics in La0.875Sr0.125MnO3 measured by resonant Auger electron and resonant x-ray emission spectroscopies

Mentes, T. O.; Bondino, F.; Magnano, E.; Zangrando, M.; Kuepper, K.; Galakhov, V. R.; Mukovskii, Y. M.; Neumann, M.; Parmigiani, F.

The charge transfer dynamics of an underdoped manganite is probed by resonant x-ray emission and Auger electron spectroscopies at the Mn L3 edge. The dispersion of peak positions, as the incident photon energy is tuned through the absorption threshold, gives direct information on the relaxation rate in terms of the core-hole lifetime and the localization behavior of the states involved. The charge transfer time is found to be around 0.45 fs, with a dependency on the final state d-band occupancy.

Keywords: PACS: 79.60.-i; 72.15.Lh; 71.70.Ch; 78.70.En

Publ.-Id: 8973

CFD-Analysen der Kühlmittelvermischung in Druckwasserreaktoren

Höhne, T.

Buoyancy driven mixing was investigated under simulated natural circulation conditions at the test facility ROCOM.
Experiments with density differences between the ECC water (higher density) resp. the de-borated slugs (lower density) and the ambient coolant was used to validate the CFD software CFX.
A Reynolds stress turbulence model was employed to model the effects of turbulence on the mean flow.
Hybrid meshes consisting at least of 2 million nodes and 4 million elements were used.
The experiment and CFD calculations show in both cases significant mixing effects due to the density differences.
The CFX-5 calculations show a good qualitative agreement with the data. At some local positions differences in the predicted and measured concentration fields occur. The obtained experimental and numerical results can be used for further studies of the core behavior using coupled thermo-hydraulic and neutron-kinetic code systems.
Next Steps: Improvement of turbulence models, calculation with different Reynolds Stress models or DES

Keywords: CFD; Coolant Mixing

  • Lecture (others)
    DECHEMA/GVC-Arbeitsausschuß “Sicherheitsgerechtes Auslegen von Chemieapparaten“, 22.11.2006, Lampertheim, Deutschland

Publ.-Id: 8972

Strahlentherapieplanung bei Hirntumoren mit 18F-3-O-methyl-fluordopa (18F-OMFD) und Positronen-Emissions-Tomographie (PET)

Ahlheit, H.; Oehme, L.; Winkler, C.; Blank, H.; Grabowski, J.; Füchtner, F.; Hoepping, A.; Kotzerke, J.; Beuthien-Baumann, B.

kein Abstract verfügbar

  • Abstract in refereed journal
    Strahlentherapie und Onkologie 182(2006)1, V11-3
  • Lecture (Conference)
    12. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 25.-28.05.2006, Dresden, Germany

Publ.-Id: 8971

Structure and Stability of Molybdenum Sulfide Fullerenes

Bar-Sadan, M.; Enyashin, A. N.; Gemming, S.; Popovits-Biro, R.; Hong, S. Y.; Prior, Y.; Tenne, R.; Seifert, G.

MoS2 nanooctahedra are the smallest stable close-cage structures of MoS2, i.e. the genuine inorganic fullerenes. Here, a combination of experiments and density-functional tight-binding calculations with molecular dynamics annealing are used to elucidate the structures and electronic properties of octahedral MoS2 fullerenes. The calculations show that the octahedra are stable beyond n(Mo)>100, but with the loss of 12 S atoms at the six corners. In contrast to the semi-conducting bulk and nanotubular structures, the Fermi level of the octahedra is situated within a band, hence the nano-octahedra are metalloid. A model derived from these calculations for the treatment of larger structures shows that, in agreement with experiment, multiwall nanooctahedra are stable over a limited size range of about 10^4 to 10^5 atoms; beyond that size, the clusters are converted into spherical nanoparticles. These theoretical findings concerning the critical size for the structural transition, the under-stoichiometry in S, and the electronic nature of the nanooctahedra are confirmed by TEM experiments on particles synthesized by laser ablation.

Keywords: inorganic fullerenes; molybdenum sulfide; density-functional

Publ.-Id: 8969

Quasi-Particle Perspective on Equation of State

Bluhm, M.; Schulze, R.; Seipt, D.; Kämpfer, B.

We propose a procedure for determining the equation of state of strongly interacting matter needed in a
hydrodynamical description of relativistic heavy-ion collisions.

Keywords: QCD equation of state; elliptic flow; quasi-particle model

  • Contribution to proceedings
    Quark Confinement and Hadron Spectrum VII, 02.-07.09.2006, Ponta Delgada Acores, Portugal, 387-390
  • AIP Conference Proceedings 892(2007), 387-390

Publ.-Id: 8968

Quasi-particle perspective on critical end-point

Bluhm, M.; Kämpfer, B.

Within a quasi-particle model for the equation of state of strongly interacting matter for two quark flavors we include phenomenologically features of the QCD critical point and discuss its impact on the equation of state. In particular, we investigate the influence on the quark number susceptibility and the pattern of isentropic trajectories which describe the evolutionary paths of matter during the hydrodynamical expansion of a heavy-ion collision.

  • Contribution to proceedings
    Critical Point and Onset of Deconfinement, 03.-06.07.2006, Florence, Italy
    Proceedings of Science CPOD 2006, 004

Publ.-Id: 8967

Orbitofrontal Dysfunction Related to Both Apathy and Disinhibition in Frontotemporal Dementia

Peters, F.; Perani, D.; Herholz, K.; Holthoff, V.; Beuthien-Baumann, B.; Sorbi, S.; Pupi, A.; Degueldre, C.; Lemaire, C.; Collette, F.; Salmon, E.

Orbitofrontal metabolic impairment is characteristic of the frontal variant of frontotemporal dementia (fv-FTD), as are early changes in emotional and social conduct. Two main types of behavioral disturbances have been distinguished in fv-FTD patients: apathetic and disinhibited manifestations. In this study, we searched for relationships between brain metabolism and presence of apathetic or disinhibited behavior. Metabolic activity and behavioral data were collected in 41 fv-FTD patients from European PET centers. A conjunction analysis of the PET data showed an expected impairment of metabolic activity in the anterior cingulate, ventromedial and orbital prefrontal cortex, the dorsolateral prefrontal cortex and the left anterior insula in fv-FTD subjects compared to matched controls. A correlation was observed between disinhibition scores on the Neuropsychiatric Inventory scale and a cluster of voxels located in the posterior orbitofrontal cortex (6, 28, -24). Comparison of brain activity between apathetic and nonapathetic fv-FTD patients from two centers also revealed a specific involvement of the posterior orbitofrontal cortex in apathetic subjects (4, 22, -22). The results confirm that the main cerebral metabolic impairment in fv-FTD patients affects areas specializing in emotional evaluation and demonstrate that decreased orbitofrontal activity is related to both disinhibited and apathetic syndromes in fv-FTD.

Keywords: Frontotemporal dementia; Positron emission tomography; Apathy; Disinhibition; Social conduct

  • Dementia and Geriatric Cognitive Disorders 21(2006), 373-379
    DOI: 10.1159/000091898

Publ.-Id: 8966

11C-Acetat positron-emission-tomography for occult prostate cancer

Froehner, M.; Beuthien-Baumann, B.; Wirth, M. P.

We report, to our knowledge previously not described, a case of occult prostate cancer, in which 11C-acetate positron emission tomography disclosed tumor manifestation after failure of conventional diagnostic procedures.

Keywords: Prostate cancer; Occult; Positron emission tomography; Bone scan; Metastases

  • Urologic Oncology 24(2006), 410-411

Publ.-Id: 8965

Decomposition of metabolic brain clusters in the frontal variant of frontotemporal dementia

Salmon, E.; Kerrouche, N.; Herholz, K.; Perani, D.; Holthoff, V.; Beuthien-Baumann, B.; Degueldre, C.; Lemaire, C.; Luxen, A.; Baron, J.-C.; Collette, F.; Garraux, G.

Previous studies that measured brain activity in frontotemporal dementia (FTD) used univariate analyses, examining each region of interest separately. We explored in a multicenter European research program the principal brain clusters characterized by a common variability in cerebral metabolism in FTD. Seventy patients with frontal variant (fv) FTD were selected according to international clinical recommendations; principal component analysis (PCA) was performed on FDG-PET metabolic images, looking for covariance clusters in this large population. A first metabolic cluster included most of the lateral and medial prefrontal cortex, bilaterally; PC1 scores correlated with performances on memory and executive neuropsychological tasks. Moreover, FDG-PET images in fv-FTD were further characterized by a metabolic covariance in two clusters comprising the subcallosal medial frontal region, the temporal pole, medial temporal structures and the striatum, separately in the left and in the right hemisphere. The study provides original data-driven arguments for metabolic involvement of separate brain clusters in the rostral limbic system, corresponding to pathological poles differentially affected in each FTD patient.

Publ.-Id: 8964

Experimental and numerical results on the fluid flow driven by a traveling magnetic field

Lantzsch, R.; Galindo, V.; Grants, I.; Zhang, C.; Pätzold, O.; Gerbeth, G.; Stelter, M.

A traveling magnetic field (TMF) driven convection and its transition from a laminar to a time-dependent flow is studied by means of ultrasonic Doppler velocimetry and numerical simulations. The experimental setup comprises a cylindrical cavity containing the electrically conducting model fluid GaInSn and a system of six equidistant coils, which are fed by an out-of-phase current to create an up- or downward directed TMF. Hence, a Lorentz force is induced in the melt which leads to meridional flow patterns. For numerical simulations commercial codes (Opera/Fidap) and a spectral code are used. The characteristic parameters of the magnetohydrodynamic model system are chosen close to the conditions used for Vertical Gradient Freeze (VGF) crystal growth. The axisymmetric basic flow and its dependence on the dimensionless shielding parameter S are examined. It is shown that, for S>10, the flow velocity decreases significantly, whereas almost no influence is found for a smaller shielding parameter. The critical Reynolds number for the onset of instability is found in the range of 300-450. Good agreement between experimental results and the numerical simulations is achieved.

Keywords: Fluid Flows; Magnetic Fields; Stirring; Growth from melt

Publ.-Id: 8963

Effect of pseudophosphorylation and cross-linking by lipid peroxidation and advanced glycation end product precursors on tau aggregation and filament formation

Kuhla, B.; Haase, C.; Flach, K.; Lüth, H.-J.; Arendt, T.; Münch, G.

Accumulation of hyperphosphorylated tau protein as paired helical filaments (PHFs) in pyramidal neurons is a major hallmark of Alzheimer’s disease. Besides hyperphosphorylation, other modifications of the tau protein such as crosslinking are likely to contribute to the characteristic features of PHFs, including their insolubility and resistance against proteolytic degradation. In this study, we have investigated if the four reactive carbonyl compounds acrolein, malondialdehyde, glyoxal and methylglyoxal accelerate the formation of tau oligomers, thioflavin T positive aggregates and fibrils using wild-type and seven pseudophosphorylated mutant tau proteins. Acrolein and methylglyoxal were the most reactive compounds, followed by glyoxal and malondialdehyde in terms of formation of tau dimers and higher molecular weight oligomers. Furthermore, acrolein and methylglyoxal induced the formation of thioflavin T fluorescent aggregates in a triple pseudophosphorylation mimicking mutant to a slightly higher degree than wild type tau. Analysis of the tau aggregates by electron microscopy study showed that formation of fibrils using wild type tau and several tau mutants could be observed with acrolein and methylglyoxal but not with glyoxal and malondialdehyde. Our results suggest that reactive carbonyl compounds, particularly methylglyoxal and acrolein, could accelerate tangle formation in vivo, and that this process could be slightly accelerated, at least in the case of methylglyoxal and acrolein, by hyperphosphorylation. Interference with the formation or the reaction of these reactive carbonyl compounds could be a promising way of inhibiting tangle formation and neuronal dysfunction in Alzheimer’s disease and other tauopathies.

Publ.-Id: 8962

Ion implantation-induced damage depth profile determination in SiC by means of RBS/C and bevelling technique

Romanek, J.; Grambole, D.; Herrmann, F.; Voelskow, M.; Posselt, M.; Skorupa, W.; Zuk, J.

Ion implantation-induced damage depth profiles of 450 keV Al+ ion-implanted 6H-SiC were studied using RBS/C technique for implantations along channeling direction and non-channeling direction with fluence of 3.4 1015 cm2. Bevelling method of sample preparation was used to get access to the deeper situated layers over the whole damaged region and below. To determine damage degree at the specific depth of the bevelled sample, RBS/C technique combined with a 3 MeV Li2+ ion beam of size of about 30 micrometer x 30 micrometer was utilized (micro-RBS/C). The micro-RBS/C method combined with the bevelling technique gave us a possibility to probe deeper reaching damage regions than in the case of conventional RBS/C investigations. It also utilizes a near-surface part of backscattered spectra, which is slightly influenced by damage created by probing ions and a random fraction of probing beam. Additionally, there is no need to perform energy calibration of detector for backscattered particles. Due to much smaller sample area hit by probing ions of micro-beam, the required fluence, comparable to that at conventional RBS/C measurements is obtained at much lower charge. Negligibly small effect of bevelling-induced mechanical damage has been observed in this study. The obtained results by micro-RBS/C method validate the results of computer simulations (Crystal-TRIM software).

Keywords: Ion implantation damage; SiC; micro-RBS

  • Nuclear Instruments and Methods in Physics Research B 251(2006), 148-156

Publ.-Id: 8960

Uranmunition im Boden: - Spektroskopische Untersuchungen zur Sekundärphasenbildung auf abgereichertem Uran

Baumann, N.

Zusammenfassung und Interpretation der Ergebnisse von TRLFS-Messungen an einer Probe von abgereichertem Uran (DU), welches zuvor 182 Tage bei Raumtemperatur einer Calziumphosphatlösung ausgesetzt war. Durch diese Messung konnte die Bildung der Sekundärphase Meta-Autunit und damit eine Reaktion von DU mit der Lösung spektroskopisch nachgewiesen werden.

  • Invited lecture (Conferences)
    Vortragsreihe des Schwerpunktes Bio-Geo der Friedrich-Schiller-Universität Jena, 07.11.2006, Jena, Germany

Publ.-Id: 8959

Quantification of beta+ activity generated by hard photons by means of PET

Möckel, D.; Müller, H.; Pawelke, J.; Sommer, M.; Will, E.; Enghardt, W.

Positron emission tomography (PET) as a method for quality assurance in radiotherapy is well-investigated in the case of therapy with carbon ion beams and successfully applied at the Heavy Ion Medical Accelerator at Chiba (HIMAC), Japan, and the Gesellschaft für Schwerionenforschung (GSI), Germany. By measuring the beta{}^+ activity distribution during the irradiation (in-beam PET) valuable information on the precision of the dose deposition can be obtained. To extend this efficient technique to other radiation treatment modalities may be worthwhile. For example, since positron emitters are generated by high energy photons with energies above 20~MeV due to (gamma{},~n) reactions (predominantly {11}C and {15}O in tissue) in-beam PET seems to be feasible for the radiation therapy with high-energy photons as also shown in Geant4 simulations. Quantitative results on the activation of tissue-equivalent materials at hard photon beams were obtained by performing off-beam PET experiments. Homogeneous PMMA phantoms as well as inhomogeneous phantoms were irradiated with high energy bremsstrahlung. After the irradiation the distributions of the generated positron emitters in the phantoms were measured using a conventional PET scanner. Furthermore, the depth-dose-distributions were determined by means of optically stimulated luminescence detectors. In the experiments an activity per dose comparable to that produced in a typical patient irradiation with carbon ions could be achieved for 34~MV bremsstrahlung. In addition, a high contrast in the PET images for materials with different density and stoichiometry could be detected. Thus, further research concerning the development of in-beam PET seems to be worthwhile.

Publ.-Id: 8958

RBE of 10 kV X-rays determined for the Human Mammary Epithelial Cell Line MCF-12A

Lehnert, A.; Lessmann, E.; Pawelke, J.; Dörr, W.

Presently, an extended discussion about the dependence of the relative biological effectiveness (RBE) on photon energy takes place. The increasing amount of in vitro data in the low-energy region indicates this is a complex dependence which is influenced by the endpoint and cell line studied. In the present investigation, the RBE of 10 kV rays (W anode) was determined relative to 200 kV X-rays (W anode, 0.5 mm Cu filter) for cell survival in the dose range 1 - 10 Gy and induction of micronuclei in the range 0.5 - 3.6 Gy for the human mammary epithelial cells MCF-12A. The RBE for cell survival was found to increase with decreasing dose, being 1.21 ± 0.03 at the 10 % survival rate. Considerably higher values were obtained for the micronucleus induction, where RBEM obtained from the ratio of the linear coefficients of the dose-effect curves was equal to 2.6 ± 0.4 for the fraction of binucleated cells (BNC) with micronuclei (MN) and 4.1 ± 1.0 for the number of MN per BNC. These values, together with our previous data, support a monotonic increase in RBE with decreasing photon energy down to the mean energy of 7.3 keV used in the present study.

Keywords: soft X-rays; RBE; X-ray tube; clonogenic survival; micronucleus test; human mammary epithelial cells; MCF-12A

Publ.-Id: 8957

Radiolabelling of multimeric neurotensin(8-13) analogues with the short-lived positron emitter fluorine-18

Hultsch, C.; Berndt, M.; Bergmann, R.; Wüst, F.

Neurotensin receptors are expressed with high incidence in several human tumour entities. Thus, radiolabelled neurotensin derivatives might be used for tumour targeting. However, its application is limited by insufficient metabolic stability. Metabolic stability might be improved by the synthesis of multivalent peptides.
Three methods for 18F-labelling of dimeric and tetrameric
neurotensin(8-13) derivatives were evaluated with respect to the labelling yield and the required peptide amounts. Labelling using N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) gave low radiochemical yield for the dimeric peptides. Coupling of the tetramer with [18F]SFB was not successful. Furthermore, labelling of aminooxy-functionalized neurotensin(8-13) derivatives using 4-[18F]fluorobenzaldehyde ([18F]FBA) was investigated. High yields were obtained for the dimer whilst coupling of the tetramer only gave low yields.
In contrast to these findings, labelling of sulfhydryl-functionalized
neurotensin(8-13) derivatives using the maleinimide 4-[18F]fluorobenzaldehyde O-[6-(2,5-dioxo-2,5-dihydro-pyrrol-1-yl)-hexyl]-oxime ([18F]FBAM) resulted in high radiochemical yields for both, the dimer and the tetramer. Therefore, [18F]FBAM seems to be the most suitable 18F-labelling agent for multivalent neurotensin(8-13) derivatives.

Publ.-Id: 8956

Synthesis of 18F-labelled stilbenes from 4-[18F]fluorobenzaldehyde using the Horner-Wadsworth-Emmons reaction

Gester, S.; Pietzsch, J.; Wüst, F.

The first application of the Horner-Wadsworth-Emmons reaction in 18F-chemistry is described. This carbonyl-olefination reaction was performed via a “multi-step/one-pot” reaction by the coupling of benzylic phosphonic acid esters (3,5-bis-methoxymethoxybenzyl)-phosphonic acid diethyl ester 2e, (4-methoxymethoxybenzyl)-phosphonic acid diethyl ester 3e and (4-dimethyl-aminobenzyl)phosphonic acid diethyl ester 4d) with 4-[18F]fluorobenzaldehyde to give the corresponding 18F-labelled stilbenes [18F]2g, [18F]3g and [18F]4e exclusively as the expected E-isomers. The radiochemical yields ranged from 9 to 22% (based upon [18F]fluoride, including HPLC purification). The specific activity reached up to 90 GBq/µmol.

Keywords: 18F-labelled stilbenes; [18F]fluorobenzaldehyde; Horner-Wadsworth-Emmons reaction

  • Journal of Labelled Compounds and Radiopharmaceuticals 50(2007)2, 105-113
    DOI: 10.1002/jlcr.1172

Publ.-Id: 8955

Neurotensin Receptors in Adeno- and Squamous Cell Carcinoma

Haase, C.; Bergmann, R.; Oswald, J.; Zips, D.; Pietzsch, J.

Background: Peptide receptors seem to be good markers for receptor targeting because of their overexpression in human cancer. Understanding the role of receptors and their cognate ligands is currently used for both diagnosis and therapy. Candidates playing a key role in tumor biology are the neurotensin receptors (NTR). The expression of NTR in HT-29 cells (human colon adenocarcinoma cell line) and FaDu cells (human squamous cell carcinoma cell line) and in corresponding tumor xenografts on nude mice, was investigated. Materials and Methods: Quantitative RT-PCR of the three receptor subtypes was carried out to study mRNA expression. Receptor protein expression was analyzed by immunohistochemistry with specific antibodies for the three known neurotensin receptors NTR1, NTR2 and NTR3. Results: Analysis of receptor mRNA revealed a strong expression of NTR3 and a weak expression of NTR1 and NTR2 in cultured cells and xenografts. Examining the protein levels, a strong signal for NTR1 was detected in tumor cells and xenografts and only a weak signal was detected for NTR3. Conclusion: Since the receptor protein is targeted in vivo, the enhanced protein expression of NTR1 in xenografts could be a useful tool for molecular targeting with radioligands and for further characterization of carcinogenic processes.

Keywords: Neurotensin; neurotensin receptor; Tumor xenograft model; HT-29; FaDu

  • Open Access Logo Anticancer Research 26(2006), 3527-3534

Publ.-Id: 8954

Synthesis and radiopharmacological characterization of [11C]AL-438 as a nonsteroidal ligand for imaging brain glucocorticoid receptors

Wüst, F.; Knieß, T.; Bergmann, R.; Henry, B.; Pietzsch, J.

The radiosynthesis and the radiopharmacological characterization of [11C]AL-438 as a nonsteroidal ligand for the glucocorticoid receptor (GR) is described. Radiolabelling of the corresponding desmethyl precursor 10 with [11C]MeI gave [11C]AL-438 in decay-corrected radiochemical yields of 30±4% (based upon [11C]CO2) within 35 min at a specific radioactivity of 10-15 GBq/µmol at the end-of-synthesis. The radiopharmacological evaluation of [11C]AL-438 involved biodistribution and small animal PET imaging in rats, and autoradiography studies using rat brain sections.
Biodistribution studies were performed in male Wistar rats and demonstrated high radio-activity uptake in pituitary and brain. However, the inability of high dose corticosterone to block binding would suggest that the radioactivity accumulation in the brain was not receptor-mediated.

  • Bioorganic & Medicinal Chemistry Letters 17(2007), 4035-4039

Publ.-Id: 8953

Bispidine - Ein neues Chelatsystem zur stabilen Bindung von Radiokupfernukliden

Juran, S.; Walther, M.; Stephan, H.; Steinbach, J.

Die Arbeiten zielen auf die Entwicklung von radioaktiven Kupfer(II)-Komplexen mit hoher thermodynamischer Stabilität und schneller Komplexbildungskinetik auf der Basis des 3,7-Diazabicyclo[3.3.1]nonans (Bispidin). Voruntersuchungen haben gezeigt, dass sechszähnige Derivate, die Pyridinfunktionen enthalten, am aussichtsreichsten sind (1). Durch Einführen von Kopplungsstellen am Bispidin soll die Anknüpfung an Biomoleküle ermöglicht werden.
Es wird über die Darstellung von hexadentaten Bispidinderivaten berichtet sowie deren Möglichkeiten zur Kopplung an Biomoleküle diskutiert. Des Weiteren werden Ergebnisse radiopharmakologischer Untersuchungen mit Cu-64 und Cu-67 präsentiert. Schwerpunkt dabei werden in vitro Stabilitätsuntersuchungen und Bioverteilungsstudien sein.

Die Synthese der Bispidinliganden erfolgt durch zwei aufeinanderfolgende Mannich-Kondensationen, wobei Pyridin- und Imidazol-Edukte eingesetzt wurden. An ausgewählten Vertretern wurden Möglichkeiten zur Kopplung an Biomoleküle erprobt. Die entsprechenden Biokonjugate wurden mittels semipräparativer HPLC gereinigt und radioaktiv markiert. Stabilitätstests im Rattenplasma und in Anwesenheit von Konkurrenzliganden (Glutathion, Cyclam) erfolgten.

Es wurden eine Reihe neuer Bispidinliganden dargestellt und die in vitro Stabilität entsprechender Kupfer(II)-Komplexe getestet. Das Bispidingrundgerüst wurde so modifiziert, dass Biomoleküle über eine Carboxylfunktion angekoppelt werden können. Für eine Peptidkopplung erwies sich der Einsatz von HBTU als Reagenz in Anwesenheit von DIPEA am geeignesten. Die dargestellten Konjugate weisen eine günstige Kinetik der Komplexierung sowie eine hohe Stabilität sowohl im Rattenplasma als auch in Anwesenheit von Konkurrenzliganden auf. Es konnte keine Transchelatisierung des Kupfers nachgewiesen werden.

Die dargestellten Kupfer(II)-Komplexe mit sechszähnigen Bispidinliganden weisen eine sehr hohe Stabilität auf und verfügen damit über ein hohes inhärentes Anwendungspotential für radiopharmazeutische Anwendungen in Diagnostik (Cu-64, PET) und Therapie (Cu-67, Endoradionuklidtherapie). Zum Erzielen eines selektiven Anreicherns der radioaktiven Kupferkomplexe im Zielgewebe, sollen sich weitere Untersuchungen insbesondere mit der Kopplung von Antikörpern an das Grundgerüst hexadentater Bispidin-Derivate befassen. Kleintier-PET-Untersuchungen ausgewählter Konjugate sollen sich anschließen.

(1) H. Stephan, S. Juran, M. Walther, J. Steinbach, K. Born, P. Comba
Synthesis, characterization and evaluation of novel chelating agents for copper radionuclides in „Technetium, Rhenium and other Metals in Chemistry and Nuclear Medicine“, U. Mazzi (Ed.), SGE Editoriali, Padova, Italy, 2006, 7, 219-222.

  • Lecture (Conference)
    45. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2007, Hannover, D
  • Abstract in refereed journal
    Nuklearmedizin 46(2007), A42

Publ.-Id: 8952

Validation of CFD models for mono- and polydisperse air-water two-phase flows in pipes

Frank, T.; Zwart, P.; Krepper, E.; Prasser, H.-M.; Lucas, D.

Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, where one of the phases is continuous and the other phase consists of gas or vapor of the liquid phase. The validation of the CFD multiphase flow models against detailed experimental data for simplified flow configurations is a basic requirement for the accurate prediction of more complex flows, like e.g. multiphase flow in fuel rod assemblies with spacer grids under the conditions from ONB to DNB including bulk and wall boiling in a pressurized polydisperse liquid-vapor flow. This paper is therefore aimed on validation of the underlying multiphase flow modeling concepts for gas-liquid monodisperse and polydisperse bubbly flows. CFD predictions using ANSYS CFX and taking into account interphase momentum transfer (drag and non-drag forces) as well as bubble break-up and coalescence are compared to experiments of MT-Loop and TOPFLOW test facilities (FZ Rossendorf, Germany). Best Practice Guidelines have been applied in order to allow for a systematic error quantification and thoroughly assessment of model formulations.

Keywords: CFD; Multiphase flow; experiments; bubble forces; monodispersed flow; polydispersed flow; multiple bubble size classes; model validation; best practice guidelines

  • Lecture (Conference)
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS, 05.-09.09.2006, Garching, Germany
  • Contribution to proceedings
    OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS, 05.-09.09.2006, Garching, Germany
    Proceedings paper B6-32
  • Nuclear Engineering and Design 238(2008), 647-659
    DOI: doi:10.1016/j.nucengdes.2007.02.056

Publ.-Id: 8951

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