Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41709 Publications

Identification of the main contributions to the conductivity of epitaxial InN

Komissarova, T. A.; Jmerik, V. N.; Ivanov, S. V.; Drachenko, O.; Wang, X.; Yoshikawa, A.

Abstract

Complex effect of different contributions (spontaneously formed In nanoparticles, near-interface, surface, and bulk layers) on electrophysical properties of InN epitaxial films is studied. Transport parameters of the surface layer are determined from the Shubnikov-de Haas oscillations measured in undoped and Mg-doped InN films at magnetic fields up to 63 T. It is shown that the In nanoparticles, near-interface, and bulk layers play the dominant role in the electrical conductivity of InN, while influence of the surface layer is pronounced only in the compensated low-mobility InN:Mg films.

Keywords: InN; Shubnikov-de Haas; magneto-transport

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Permalink: https://www.hzdr.de/publications/Publ-15919


Tunable narrowband THz pulse generation in scalable large area photoconductive antennas

Krause, J.; Wagner, M.; Winnerl, S.; Helm, M.; Stehr, D.

Abstract

The generation and characterization of narrowband THz pulses by means of chirped pulse difference frequency generation in Auston-switch type photoconductive antennas is reported. Using optical pulses with energies in the range from 1 nJ to 1µJ, we generate THz pulses with up to 50 pJ in energy and electric field strengths on the order of 1 kV/cm. Two emitter concepts are investigated and circumvention of the fast saturation for small area excitation by scaling of the THz emitter is demonstrated.

Keywords: Terahertz; ultrafast

  • Open Access Logo Optics Express 19(2011)20, 19114

Permalink: https://www.hzdr.de/publications/Publ-15918


Effect of leukotriene inhibitors on evolution of experimental brain contusions

Voigt, C. L. M.; Donat, C. K.; Härtig, W.; Förschler, A.; Arendt, T.; Meixensberger, J.; Schuhmann, M. U.

Abstract

Aims: Leukotriene levels increase in cerebrospinal fluid following controlled cortical impact (CCI) injury in rats. We investigated the impact of leukotrienes on contusion size by the effect of two different leukotriene inhibitors in the CCI model.

Methods: 92 male Sprague-Dawley rats were investigated at 24h and 72h after CCI with MRI (n= 40) and immunohistochemistry (n=52). Animals received vehicle or either MK886, an inhibitor of 5-lipoxygenase activating protein, or Boscari, a mixture of boswellic acids, acting as competitive non-redox 5-lipoxygenase inhibitors prior to trauma and then every 8 hours until sacrifice.

Results: Global ICP was within normal limits and unaffected by treatment. T2 weighted MRI showed a reduction of lesion volume in treatment groups at 72h by -21% (p<0.01), which was reflected in a smaller lesion area determined from a NeuN labelled section (-17% to -20%, p<0.05). Qualitative characterization by triple immunofluorescence and Fluorojade B staining showed progressive rarefaction of neurons, glia and vasculature in the contusion core, whereas in the pericontusional zone astro- and microglia were up-regulated in the presence of dying neurons. Treatment resulted in an improved survival of NeuN labelled neurons in the pericontusional cortex (+15% to +20%, p<0.05).

Conclusions: Two differently acting leukotriene inhibitors lead to an attenuation of lesion growth and improved pericontusional neuronal survival following CCI. Therefore, leukotrienes seem to be involved in brain contusion growth and pericontusional secondary injury. Leukotriene inhibition should be further investigated as therapeutic option to counteract secondary growth of traumatic brain contusions and to possibly improve pericontusional neuronal survival.

Permalink: https://www.hzdr.de/publications/Publ-15917


“yl”-Oxygen Exchange in Uranyl(VI) Ion: A Mechanism Involving (UO2)2(μ-OH)22+ via U-Oyl-U Bridge Formation

Tsushima, S.

Abstract

Szabó and Grenthe (Inorg. Chem. 2007, 46, 9372-9378) suggested from NMR spectroscopy that the “yl”-oxygen exchange in dioxo uranium(VI) ion in acidic solution occurs via an OH-bridged binuclear complex (UO2)2(μ-OH)2 2+. Here, an “yl”-oxygen exchange pathway involving the (UO2)2(μ-OH)2 2+ is studied by B3LYP density functional theory calculations. The oxygen exchange takes place via an intramolecular proton shuttle between the oxygen atoms in (UO2)2(μ-OH)2(H2O)6 2+. The direct proton transfer from the hydroxo bridge or from the coordinating water to the “yl”-oxygen in (UO2)2(μ-OH)2(H2O)6 2+ appears to be negligible because of an exceedingly high activation barrier (~ 170 kJ mol-1). The exchange mechanism in (UO2)2(μ-OH)2(H2O)6 2+ can be described by a multi-step pathway that leads to the formation of an oxo bridge between two uranyl(VI) centers (U-Oyl-U bridge). The activation enthalpy Δ H of the reaction obtained at the B3LYP level is 94.7 kJ mol-1 and is somewhat larger than the experimental value of 80 ± 14 kJ mol-1. However, the discrepancy between theory and experiment is at the acceptable level. The formation of an oxo bridge between the two uranyl(VI) centers was found to be the key step in proton shuttling, indicating that uranyl(VI) complexes with a stable oxo bridge (such as trinuclear (UO2)33-O)(OH)3 +) may have even faster “yl”-oxygen exchange rates than (UO2)2(μ-OH)2 2+.

Permalink: https://www.hzdr.de/publications/Publ-15916


Determination of the 60Fe Half-Life – a successful Collaboration in ERAWAST

Rugel, G.

Abstract

The radionuclide 60Fe is an important nuclide in nuclear astrophysics. Its half-life has been determined with a sample from a copper beam dump at PSI. After characterization of the beam dump and an intense chemical preparation the final sample material was measured to determine the half-life. This was done with an activity measurement in Munich and a number of 60Fe atoms measurement at PSI. This results in a half-life of (2.62 +/- 0.04) Myr [1].
Some of the important aspects of the work will be reported.
References
[1] G. Rugel, T. Faestermann, K. Knie, G. Korschinek, M. Poutivtsev, D. Schumann, N. Kivel, I. Günther-Leopold, R. Weinreich, M. Wohlmuther, Phys. Rev.Lett. 103, 072502.

Keywords: accelerator mass spectrometry; half-life; astrophysics

  • Lecture (Conference)
    2nd Workshop on Exotic Radionuclides from Accelerator Waste for Science and Technology (ERAWAST II), 29.08.-02.09.2011, Villigen, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-15915


Determination of uranium(VI) sorbed species in calcium silicate hydrate phases: A laser-induced luminescence spectroscopy and batch sorption study

Tits, J.; Geipel, G.; Mace, N.; Eilzer, M.; Wieland, E.

Abstract

Batch sorption experiments and time-resolved luminescence spectroscopy investigations were carried out to study the U(VI) speciation in calcium silicate hydrates for varying chemical conditions representing both fresh and altered cementitious environments. U(VI) uptake was found to be fast and sorption distribution ratios (R-d values) were very high indicating strong uptake by the C-S-H phases. In addition a strong dependence of pH and solid composition (Ca:Si mol ratio) was observed. U(VI) luminescence spectroscopy investigations showed that the U(VI) solid speciation continuously changed over a period up to 6 months in contrast to the fast sorption kinetics observed in the batch sorption studies. Decay profile analysis combined with factor analysis of series of spectra of U(VI) - C-S-H suspensions, recorded with increasing delay times, revealed the presence of four luminescent U(VI) species in C S H suspensions, in agreement with the batch sorption data. Along with the aqueous UO2(OH)(4)(2-) species and a Cauranate precipitate, two different sorbed species were identified which are either bound to silanol groups on the surface or incorporated in the interlayer of the C-S-H structure.

Keywords: uranium; sorption; luminescence

Permalink: https://www.hzdr.de/publications/Publ-15914


Long-range superexchange in Cu2A2O7 (A = P, As, V) as a key element of the microscopic magnetic model

Janson, O.; Tsirlin, A.; Sichelschmidt, J.; Skourski, Y.; Weickert, F.; Rosner, H.

Abstract

A microscopic magnetic model for alpha-Cu2P2O7 is evaluated in a combined theoretical and experimental study. Despite a dominant intradimer coupling J1, sizable interdimer couplings enforce long-range magnetic ordering at TN = 27 K. The spin model for a-Cu2P2O7 is compared to the models of the isostructural beta-Cu2V2O7 and alpha-Cu2As2O7 systems. As a surprise, coupled dimers in a-Cu2P2O7 and alternating chains in alpha-Cu2As2O7 contrast with a honeycomb lattice in beta-Cu2V2O7. We find that the qualitative difference in the coupling regime of these isostructural compounds is governed by the nature of AO4 side groups: d elements (A = V) hybridize with nearby O atoms forming a Cu-O-A-O-Cu superexchange path, while for p elements (A = P, As) the superexchange is realized via O-O edges of the tetrahedron. Implications for a broad range of systems are discussed.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Physical Review B 83(2011), 10.1103/PhysRevB.83.094435

Permalink: https://www.hzdr.de/publications/Publ-15913


EPR study of the two-dimensional quantum magnet Cu(en)(H2O)2SO4

Tarasenko, R.; Orendácová, A.; Cizmár, E.; Orendác, M.; Zvyagin, S.; Wosnitza, J.

Abstract

Electron paramagnetic resonance (EPR) spectra of Cu(en)(H2O)2SO4 (en = ethylendiamine) single crystals were measured in the X-band range at temperatures 4 K and 300 K in magnetic fields up to 0.5 T. The angular dependence of the g-factor and EPR linewidths were studied. The analysis of the g-factor confirmed, that coordinating ligands around the Cu(II) ion form a distorted octahedron elongated along the local z axis and the distortion is maintained down to low temperatures. The increase of the linewidth observed at low temperatures can be ascribed to the onset of short-range magnetic correlations previously observed in specic heat studies. The reduction of the period in the angular dependence of the linewidth observed at 4 K cannot be explained by the existence of two crystallographic non-equivalent Cu(II) positions. The analysis of the angular dependence of the linewidth suggests the potential occurence of Dzyaloshinski-Moriya interaction and anisotropic exchange coupling in CUEN.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Poster
    The European Conference Physics of Magnetism 2011 (PM´11), 27.06.-01.07.2011, Poznan, Poland

Permalink: https://www.hzdr.de/publications/Publ-15912


Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field

Zvyagin, S. A.; Ozerov, M.; Wosnitza, J.; Čižmár, E.; Feyerherm, R.; Manmana, S. R.; Mila, F.

Abstract

Due to recent progress in theory and the growing number of physical realizations, low-dimensional quantum magnets continue to receive a considerable amount of attention. They serve as model systems for investigating numerous fascinating phenomena in materials with cooperative ground states, in particular, induced by high magnetic fields. The way a magnetic field changes the ground-state properties and, correspondingly, the low-energy excitation spectrum of low-dimensional magnets is one of the fundamental aspects in quantum magnetism. Here, magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions that exhibits a field-induced spin gap, are probed by means of pulsed-field electron spin resonance spectroscopy in fields up to 63 T. In particular, we report on a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG investigation of the spin-1/2 Heisenberg chain with a staggered transverse field

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences)
    German Estonian Workshop, 13.-15.06.2011, Cottbus, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15911


Thermal expansion and magnetostriction of GdAg2, and relations to the magnetoelastic paradox

Mehboob, N.; Rotter, M.; Doerr, M.; Royanian, E.; Müller, H.; Grytsiv, A.; Skourski, Y.

Abstract

The antiferromagnet GdAg2 has been shown to be a good model system for the magnetoelastic paradox (MEP), because it exhibits large symmetry conserving magnetoelastic strains and the antiferromagnetic propagation vector breaks the tetragonal lattice symmetry (therefore a large symmetry breaking magnetoelastic strain can be expected in a single q magnetic structure). As in many similar Gd based compounds no symmetry breaking strain has been found in the experiment. In order to investigate this MEP further, we have measured magnetostriction and magnetization on a textured polycrystal. The behaviour closely resembles that of GdNi2B2C, the prototype system for the magnetoelastic paradox (MEP). Our forced magnetostriction data indicate that the crystal distorts in applied magnetic field and gives further evidence that the MEP is a low field effect. The observed phase transitions are in agreement with available specific heat and neutron diffraction data. Moreover, the saturation magnetic field was measured in high pulsed magnetic fields and agrees well with the value calculated from the Standard Model of Rare Earth Magnetism (SMREM).

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Permalink: https://www.hzdr.de/publications/Publ-15910


Safety Monitoring of Components and Materials of Nuclear Power Plants

Gokhman, A. R.; Bergner, F.

Abstract

Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-9at%Cr and Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 1.5 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. For both alloys a saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC for the doses above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. CD modeling of Cr precipitates has been done with taking into account of deviation of this system from the ideal cluster gas. A specific surface tension of about 0.17 J/m2 between the alpha matrix and the Cr-rich alpha' precipitate and the rate at which Cr monomers are absorbed about 7.94 m-1 were found as best fit values for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS. Taking into account the formation and migration of Fe-Cr interstitial as additional link between the CD master equations for the self-defects and the CD master equations for the Cr precipitates, may lead to improve CD results for irradiated Fe-9at%Cr alloy. The assumption on the constant composition of Fe-Cr precipitates under neutron irradiation has been checked by means of new master equation of CD respect of the distribution function of clusters not only on size but also on composition. The slight dependence of the composition on the size of Fe-Cr precipitates is found.

  • Invited lecture (Conferences)
    NATO Advanced Research Workshop “Nanodevices and Nanomaterials for Ecological Security”, 20.-23.06.2011, Riga-Jurmala, Latvia

Permalink: https://www.hzdr.de/publications/Publ-15909


Transport studies at the Mott transition of the two-dimensional organic metal κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1−x

Yasin, S.; Dumm, M.; Salameh, B.; Batail, P.; Mézière, C.; Dressel, M.

Abstract

The two-dimensional organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1−x undergoes a transition from an insulator to a superconductor upon substituting Cl by Br. We have performed in and out-of-plane electric-transport measurements on the alloyed series with x = 20%, 40%, 70%, 80%, 85%, and 90% as a function of temperature in order to explore the bandwidth-controlled phase transition between the Mott insulator and the Fermi-liquid. All crystals exhibit a similar semiconducting behavior of ρ(T) from room temperature down to 100 K. Below approximately 50 K, a metal-to-insulator transition is found for compounds with x < 70%. Out of this Mott insulating state, magnetic order develops below TN ≈ 25 K. The Br-rich samples cross a bad-metal regime before they become coherent metals and eventually superconducting at Tc ≈ 12 K. For these systems the resistivity at Tc ≤ T ≤ T0 reveals a ρ(T) ∝ T2 dependence associated with a strongly correlated Fermi-liquid, limited by some characteristic temperature T0. The conclusions are corroborated by data from microwave, magnetic and optical experiments.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • European Physical Journal B 79(2011), 383-390

Permalink: https://www.hzdr.de/publications/Publ-15908


Interplay of spin and lattice degrees of freedom in the frustrated antiferromagnet CdCr2O4: High-field and temperature-induced anomalies of the elastic constants

Bhattacharjee, S.; Zherlitsyn, S.; Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Moessner, R.; Zhitomirsky, M. E.; Lemmens, P.; Tsurkan, V.; Loidl, A.

Abstract

Temperature and magnetic field studies of the elastic constants of the chromium spinel CdCr2O4 show pronounced anomalies related to strong spin-phonon coupling in this frustrated antiferromagnet. A detailed comparison of the longitudinal acoustic mode propagating along the [111] direction with a theory based on an exchange-striction mechanism leads to an estimate of the strength of the magnetoelastic interaction. The derived spin-phonon coupling constant is in good agreement with previous determinations based on infrared absorption. Further insight is gained from intermediate and high magnetic field experiments in the field regime of the magnetization plateau. The role of the antisymmetric Dzyaloshinskii-Moriya interaction is discussed.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Physical Review B 83(2011), 184421

Permalink: https://www.hzdr.de/publications/Publ-15907


Magnetic and magnetoelastic anomalies of an Er2Co17 single crystal in high magnetic fields

Andreev, A. V.; Skourski, Y.; Kuzmin, M. D.; Yasin, S.; Zherlitsyn, S.; Daou, R.; Wosnitza, J.; Iwasa, A.; Kondo, A.; Matsuo, A.; Kindo, K.

Abstract

A high-field study of magnetization (up to 68 T) and magnetoelastic properties (up to 60 T) of Er2Co17 is reported. The most significant effect, a first-order transition from the collinear ferrimagnetic to a canted state, is observed at about 40 T with H || [001]. The transition is accompanied by a prominent magnetization jump as well as by step-wise anomalies of the magnetoelastic properties. Thus, the volume of the crystal reduces by about 4 per mil, while the speed of transverse sound in the [001] direction increases by as much as 5 per mil. At higher temperatures the anomalies gradually become smaller and less sharp before they finally disappear at ∼50 K. The anisotropy constants of the Er sublattice and the molecular field thereon have been determined from the magnetization curves.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Physical Review B 83(2011), 184422

Permalink: https://www.hzdr.de/publications/Publ-15906


NMR signal averaging in 62 T pulsed fields

Meier, B.; Greiser, S.; Haase, J.; Herrmannsdörfer, T.; Wolff-Fabris, F.; Wosnitza, J.

Abstract

Nuclear Magnetic Resonance (NMR) experiments in pulsed high magnetic fields up to 62 Tat the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden) are reported. The time dependence of the magnetic field is investigated by observing various free induction decays (FIDs) in the vicinity of the maximum of the field pulse. By analyzing each FID's phase and its evolution with time the magnetic field's time dependence can be determined with high precision. Assuming a quadratic or cubic dependence on time near the field maximum its confidence is found to be better than +/- 0.03 ppm at low fields and +/- 0.8 ppm near 62 T. In turn, the thus obtained time dependence of the field can be used to demodulate and phase-correct all FIDs so that they appear phase-locked to each other. As a consequence signal averaging is possible. The increase in signal-to-noise ratio is found to be close to that expected theoretically. This shows that the intrinsic time dependence of the pulsed fields can be removed so that the NMR signals appear to be taken at rather stable static field. This opens up the possibility of performing precise shift measurements and signal averaging also of unknown, weak signals if a reference signal is measured during the same field pulse with a double-resonance probe.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Journal of Magnetic Resonance 210(2011), 1-6

Permalink: https://www.hzdr.de/publications/Publ-15905


Recent ultrasound results obtained in pulsed magnetic fields

Nemoto, Y.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences)
    User Meeting und Midterm Review EuroMagNET II, 22.-24.06.2011, Toulouse, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-15904


High-field ESR in low-dimensional spin systems

Zvyagin, S.

Abstract

Due to recent progress in theory and the growing number of physical realizations, low-dimensional quantum magnets continue to receive a considerable amount of attention. They serve as model systems for investigating numerous fascinating phenomena in materials with cooperative ground states, in particular, induced by high magnetic fields. In this presentation I will focus on high-frequency and high-field Electron Spin Resonance (ESR) studies of copper pyrimidine dinitrate (Cu-PM), a spin-1/2 Heisenberg antiferromagnetic chain system with alternating g-tensor and Dzyaloshinskii-Moriya interactions in magnetic fields up to 63 T. Due to the alternations, this material exhibits a field-induced gap, observed by us directly. Signatures of three breather branches and a soliton are identified in magnetic fields up to 25 T. The experimental data are sufficiently detailed to make a very accurate comparison with predictions based on the quantum field sine-Gordon theory. We report also on a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG investigation of the spin-1/2 Heisenberg chain with a staggered transverse field.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences)
    International Conference "Resonances in Condensed Matter", 21.-25.06.2011, Kazan, Russia

Permalink: https://www.hzdr.de/publications/Publ-15903


Coexistence of ferromagnetism and superconductivity in single-phase Bi3Ni nanostructures

Herrmannsdörfer, T.; Skrotzki, R.; Wosnitza, J.; Köhler, D.; Boldt, R.; Ruck, M.

Abstract

Superconductivity and magnetic order, two fundamental ground states of condensed matter, are observed to be competitive in many materials. In the case of predominantly ferromagnetic exchange interactions, superconductivity is suppressed in almost any representative. The quantity of materials, however, in which a coexistence of superconductivity and ferromagnetism might be studied, could be larger than ever thought.
Here we demonstrate the coexistence of superconductivity and ferromagnetism in Bi3Ni nanostructures which have been prepared by making use of novel chemical-reaction paths. We have characterized their magnetic and superconducting properties by means of magnetometry and electrical-transport measurements. Other than in bulk geometry, submicron-sized particles and quasi one-dimensional nanoscaled strains of single-phase Bi3Ni undergo ferromagnetic order [1]. Superconductivity in confined Bi3Ni emerges in the ferromagnetically ordered phase and is stable up to remarkably high magnetic fields. Uniquely, ferromagnetic hysteresis at zero resistance is observed in nanostructured Bi3Ni. As a result, a magnetic hysteresis loop occurs while the material is in the superconducting state.
The coexistence of superconductivity with ferromagnetic order would most likely be possible in the case of triplet pairing. The absence of an inversion center of the lattice of confined Bi3Ni would allow for the formation of an antisymmetric spatial component of the electron-wave function and could lead to a significant admixture of a spin-triplet component of the order parameter. However, as the lattice of bulk Bi3Ni is centrosymmetric, the question remains as to whether the loss of structural long-range order at the surface of confined nanostructures could induce antisymmetry of the charge carrier wave function. Nuclear magnetic resonance experiments in high magnetic fields* may now open a chance to get deeper insight in the symmetry of the superconducting wave function in k space.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences)
    International Conference "Resonances in Condensed Matter", 21.-25.06.2011, Kazan, Russia

Permalink: https://www.hzdr.de/publications/Publ-15902


NMR Signal Averaging in Pulsed Fields

Meier, B.

Abstract

The first Nuclear Magnetic Resonance (NMR) experiments at the Helmholtz-Zentrum Dresden-Rossendorf in pulsed high magnetic fields that peak at maximum flux-density up to 62 Tesla are described. The temporal properties of the magnetic field B(t) in the vicinity of the field maximum are characterized using 1H and 2H NMR single-pulse excitation. The error in B(t) is smaller than 0.1 ppm, which allows making precise predictions concerning the initial and time evolution of the NMR signal’s phase near the field maximum. We demonstrate that the various free induction decays that are excited near a single field pulse maximum, e.g., during 25 milliseconds, can be demodulated from the intrinsic time dependence and corrected for the initial phase making signal-averaging possible in pulsed fields.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Invited lecture (Conferences)
    User Meeting and Midterm Review EuroMagNET II, 22.-24.06.2011, Toulouse, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-15901


Annual Online Report 2009

Bartho, A.

Abstract

Internet-Jahresbericht 2009 des FZD

Keywords: Annual Online Report 2009 of the FZD

  • Communication & Media Relations
    Internet-Jahresbericht 31.05.2010

Permalink: https://www.hzdr.de/publications/Publ-15900


AER Working Group D on VVER Safety Analysis – Report of the 2011 Meeting

Kliem, S.

Abstract

The AER Working Group D on VVER reactor safety analysis held its 20th meeting in Stockholm, Sweden, during the period 12-13 April, 2011. The meeting was hosted by the Royal Institute of Technology (KTH) and was held in conjunction with the third workshop on the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and the fifth workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 18 participants attended the meeting of the working group D, 12 from AER member organizations and 6 guests from non-member organization. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.

The meeting started with a general information exchange about the recent activities in the participating organizations.

The given presentations and the discussions can be attributed to the following topics:

  • Code validation and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and 7th AER Dynamic Benchmark
  • Thermal hydraulic analyses
  • Safety analyses and code developments
  • Future activities

A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files can be obtained from the chairman.

  • Contribution to proceedings
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany
    Proceedings of the 21st AER Symposium, Budapest: MTA KFKI, 9789633726464, 417-423
  • Lecture (Conference)
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-15899


Viscosities of the quasigluon plasma

Bluhm, M.; Kämpfer, B.; Redlich, K.

Abstract

We investigate bulk and shear viscosities of the gluon plasma within relaxation time approximation to an effective Boltzmann-Vlasov type kinetic theory by viewing the plasma as describable in terms of quasigluon excitations with temperature dependent self-energies. The found temperature dependence of the transport coefficients agrees fairly well with available lattice QCD results. The impact of some details in the quasigluon dispersion relation on the specific shear viscosity is discussed.

Permalink: https://www.hzdr.de/publications/Publ-15898


Benzenedithiol: A Broad-Range Single-Channel Molecular Conductor

Kim, Y.; Pietsch, T.; Erbe, A.; Belzig, W.; Scheer, E.

Abstract

More than a decade after the first report of singlemolecule conductance, it remains a challenging goal to prove the exact nature of the transport through single molecules, including the number of transport channels and the origin of these channels from a molecular orbital point of view. We demonstrate for the archetypical organic molecule, benzenedithiol (BDT), incorporated into a mechanically controllable break junction at low temperature, how this information can be deduced from studies of the elastic and inelastic current contributions. We are able to tune the molecular conformation and thus the transport properties by displacing the nanogap electrodes. We observe stable contacts with low conductance in the order of 10E-3 conductance quanta as well as with high conductance values above ∼0.5 quanta. Our observations show unambiguously that the conductance of BDT is carried by a single transport channel provided by the same molecular level, which is coupled to the metallic electrodes, through the whole conductance range. This makes BDT particularly interesting for applications as a broad range coherent molecular conductor with tunable conductance.

Keywords: Single molecule; break junction; inelastic electron tunneling spectroscopy; benzenedithiol; single-level model

Permalink: https://www.hzdr.de/publications/Publ-15897


Proceedings 6th Workshop “Radiochemical Analysis for Use and Decommissioning of Nuclear Facilities, the Declaration of Waste and Radiation Protection” (RCA) and the 23rd Seminar “Activation Analysis & Gamma Spectrometry” (SAAGAS)

Steinhauser, G.; Merchel, S.; Knappik, R.; (Editors)

  • Contribution to proceedings
    Proceedings 6th Workshop “Radiochemical Analysis for Use and Decommissioning of Nuclear Facilities, the Declaration of Waste and Radiation Protection” (RCA) and the 23rd Seminar “Activation Analysis & Gamma Spectrometry” (SAAGAS), 06.-09.09.2011, Dresden, Deutschland
    6th Workshop “Radiochemical Analysis for Use and Decommissioning of Nuclear Facilities, the Declaration of Waste and Radiation Protection” (RCA) and 23rd Seminar “Activation Analysis & Gamma Spectrometry” (SAAGAS)

Permalink: https://www.hzdr.de/publications/Publ-15896


Photoneutron Cross Sections for Au Revisited: Measurements with Laser Compton Scattering gamma-Rays and Data Reduction by a Least-Squares Method

Itoh, O.; Utsunomiya, H.; Akimune, H.; Kondo, T.; Kamata, M.; Yamagata, T.; Toyokawa, H.; Harada, H.; Kitatani, F.; Goko, S.; Nair, C.; Lui, Y.

Abstract

Photoneutron cross section measurements were made for Au in the entire energy range of the (gamma,n) channel based on a direct neutron counting with quasi-monochromatic gamma-rays produced in inverse Compton scattering of laser photons with relativistic electrons. The data were analyzed by a least-squares method to deduce photoneutron cross sections. The analysis significantly reduced experimental uncertainties compared with those resulting from the photon difference method. The result is compared with the previous data by direct neutron counting with gamma-rays produced in positron annihilation in flight and by photoactivation with bremsstrahlung. The present data are in good agreement with the previous data near the neutron threshold, while there remain some discrepancies between the present and the previous data above 10 MeV

  • Journal of Nuclear Science and Technology 48(2011)5, 834-840

Permalink: https://www.hzdr.de/publications/Publ-15895


Editorial Nuclear analytical methods: We've got the hammer for your nail

Steinhauser, G.; Merchel, S.; Knappik, R.

Abstract

From 6 to 9 September 2010, the 6th Workshop “Radiochemical Analysis for Use and Decommissioning of Nuclear Facilities, the Declaration of Waste and Radiation Protection” (RCA) and the 23rd Seminar “Activation Analysis & Gamma Spectrometry” (SAAGAS) were jointly held in Dresden Rossendorf (Germany). In fact, we observe that not only the conferences grow together but also our research fields constantly expand to other areas and seek collaboration in topics that are all but traditionally “nuclear”. The spectrum of the presentations ranged from classical archaeometry to tests on cable fires in power plants. From provenance studies of traffic-related particulate matter to nutritional studies on trace elements in honey. From activation studies for the decommissioning of nuclear facilities to the application of mobile neutron sources for future moon explorations. The remarkable variety of different topics is the best evidence for the universal applicability of nuclear techniques, notably nuclear analytical techniques. With numerous non-nuclear analytical methods being ubiquitously available, we feel that the analytical community sometimes seems to oversee the advantages nuclear techniques (such as activation or ion beam analysis) may offer for their specific problems. We are sure that in many cases, a nuclear technique can be the method of choice for certain analytical challenges.

Thus, we are looking forward to keep on the tradition of these nuclear-based workshops and seminars. The 7th RCA will be held again at Dresden-Rossendorf, whereas the 24th SAAGAS will probably move on to the Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II) at Munich. We are looking forward to these events with keen anticipation and wish the organisers all the best. We hope the upcoming seminars will be as successful as the joint SAAGAS & RCA – event in 2010 with 30 oral presentations – including two invited contributions by Rolf Michel (University of Hanover, Germany) and Sönke Szidat (University of Berne, Switzerland) and one evening lecture for the public by Max Bichler (Atominstitut Vienna, Austria)—and 17 posters!

This special issue in Applied Radiation and Isotopes contains seven selected contributions from RCA-SAAGAS. We thank our sponsors and co-organisers (AMETEK/ORTEC, AREVA, CANBERRA, Dr. Westmaier GmbH, Fachverband für Strahlenschutz, Gesellschaft Deutscher Chemiker, Landeshauptstadt Dresden, Kerntechnische Gesellschaft, Wirtschaftsverband Kernbrennstoff Kreislauf) for their support of RCA-SAAGAS and especially for supporting this issue. The hard work of numerous reviewers is highly appreciated: Thanks to all of you. We finally thank Elsevier for providing a forum for our cumulative contributions. We are sure that this issue will be highly visible in the analytical community. Besides, we hope it will stimulate further collaborations between nuclear and non-nuclear sciences.

In conclusion we are proud to say: We are the Nuclear Analytical Methods: We may have gotten the hammer for your nail! So do not hesitate to contact us.

Keywords: activation analysis; nuclear

Permalink: https://www.hzdr.de/publications/Publ-15894


FZD Journal 05: Meilensteine - Forschen für die Welt von morgen

Bohnet, C.; Bartho, A.; Hampel, U.; Knauer, R.; Bradbury, M. H.; Schuster, N.; Urban-Eicheler, B.; Gebel, S.

Abstract

Das Journal des Forschungszentrums Dresden-Rossendorf

  • Communication & Media Relations
    Journal 31.03.2010
    23 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15893


Internet-Jahresbericht 2009

Bartho, A.

Abstract

Jahresbericht 2009 des FZD

  • Communication & Media Relations
    Jahresbericht 31.03.2010

Permalink: https://www.hzdr.de/publications/Publ-15892


Annual Report Highlights 2010

Bartho, A.; Bohnet, C.; Bilow, U.

Abstract

Annual Report of the HZDR 2010

  • Communication & Media Relations
    Annual Report 31.05.2011

Downloads

Permalink: https://www.hzdr.de/publications/Publ-15891


Jahresbericht Highlights 2010

Bartho, A.; Bohnet, C.; Bilow, U.

Abstract

Jahresbericht des HZDR 2010

  • Communication & Media Relations
    Jahresbericht 30.04.2011
    27 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15890


Insider 1/2011

Bartho, A.

Abstract

Mitarbeiterzeitung des HZDR

  • Communication & Media Relations
    Mitarbeiterzeitung 31.01.2011
    4 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15889


Standortplan

Bohnet, C.

Abstract

Standortplan des HZDR

Keywords: Site Plan of the HZDR

  • Communication & Media Relations
    Standortplan 31.01.2011

Permalink: https://www.hzdr.de/publications/Publ-15888


Forschen für die Welt von morgen

Bohnet, C.

Abstract

Imageflyer des HZDR

  • Communication & Media Relations
    Imageflyer 30.06.2011
    23 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15887


Research for the World of Tomorrow

Bohnet, C.

Abstract

Imageflyer des HZDR

Keywords: Image Flyer of the HZDR

  • Communication & Media Relations
    Imageflyer 31.07.2011
    23 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15886


FZD intern 56

Bartho, A.; Bohnet, C.

Abstract

Mitarbeiterzeitung des FZD

  • Communication & Media Relations
    Mitarbeiterzeitung 30.06.2010
    12 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15885


FZD intern 55

Bartho, A.; Bohnet, C.

Abstract

Mitarbeiterzeitung des FZD

  • Communication & Media Relations
    Mitarbeiterzeitung 31.03.2010
    12 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15884


Diffusion, degradation or on-site stabilisation – identifying causes of kinetic processes involved in metal-humate complexation

Lippold, H.; Eidner, S.; Kumke, M. U.; Lippmann-Pipke, J.

Abstract

The applicability of equilibrium models for humic-bound transport of toxic or radioactive metals is affected by kinetic processes leading to an increasing inertness of metal-humic complexes. The chemical background is not yet understood. It is widely believed that bound metals undergo an in-diffusion process within the humic colloids, changing from weaker to stronger binding sites.
In this work, we focused on the competition effect of aluminium(III) on complexation of terbium(III) or europium(III) as analogues of trivalent actinides. By using ion exchange and spectroscopic methods, their bound fractions were determined for solutions of Al and humic acid that had been pre-equilibrated for different periods of time. While the amount of bound Al remained unchanged, its blocking effect was found to increase over a time frame of 2 days, which corresponds to the kinetics of the increase in complex inertness reported in most pertinent studies. Thus, the derived “diffusion theory” turned out to be inapplicable, since it cannot explain an increase in competition for the “initial” sites. A delayed degradation of polynuclear species (as found for Fe) does not occur. Consequently, the temporal changes must be based on structural rearrangements in the vicinity of bound Al, complicating the exchange or access. Time-dependent studies by laser fluorescence spectroscopy (steady-state and time-resolved) yielded evidence of substantial alterations, which were, however, immediately induced and did not show any significant trend on the time scale of interest, suggesting that the stabilisation process is based on comparatively moderate changes.

Keywords: Aluminium; Competition; Complexation; Humic substances; Kinetics; Lanthanides

Permalink: https://www.hzdr.de/publications/Publ-15883


FZD intern 58

Bartho, A.; Bohnet, C.

Abstract

Mitarbeiterzeitung des FZD

  • Communication & Media Relations
    Mitarbeiterzeitung 31.12.2010
    10 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15882


Insider 2/2011

Bartho, A.

Abstract

Mitarbeiterzeitung des HZDR

  • Communication & Media Relations
    Mitarbeiterzeitung 30.06.2011
    10 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15881


Struktur-Affinitäts-Studien zu VAChT-Liganden: Synthese und In-Vitro-Bindung neuer Vesamicolanaloga

Barthel, C.; Wenzel, B.; Sorger, D.; Schweiger, S.; Deuther-Conrad, W.; Jäckel, P.; Sabri, O.; Schüürmann, G.; Brust, P.; Steinbach, J.

Abstract

Ziel:

Ein wichtiges neuropathologisches Merkmal der Alzheimer Demenz ist die Degeneration cholinerger Nervenzellen. Als Bestandteil des cholinergen Transmittersystems wird der vesikuläre Acetylcholintransporter (VAChT) als mögliches Target zur bildgebenden Darstellung cholinerger Funktionsveränderungen im Hirn angesehen. Vesamicol (2-(4-Phenylpiperidin-1-yl)cyclohexanol) ist ein hoch-affiner, nicht-kompetitiver Inhibitor für den VAChT. Obwohl diese Verbindung auf Grund der vorhandenen Affinität zu Sigma-Rezeptoren (σ1/σ2) eine geringe Selektivität aufweist, dient sie als Leitstruktur bei der Entwicklung von PET-Radioliganden für den VAChT. Es ist bisher keine andere Verbindung bekannt, die mit annähernd hoher Affinität an den VAChT bindet. Ziel dieser Struktur-Affinitäts-Studie ist es, eine Vielzahl systematisch strukturell modifizierter Vesamicolanaloga zu synthetisieren und die Affinität zum VAChT und zu Sigma-Rezeptoren zu bestimmen. Diese Daten bilden die Grundlage für die Entwicklung eines 3D-QSAR-Modells, das erstmals beide Targets einbeziehen wird und somit erlauben sollte, einen hochaffinen und selektiven VAChT-Liganden zu entwickeln.

Methoden:

Die Synthese der Analoga erfolgte ausgehend von geeigneten Epoxidvorläufern durch nukleophile Epoxidringöffnung mit strukturell verschiedenen Aminen. Durch den Einsatz von Lithiumsalzen konnte ein Teil der Synthesen regioselektiv gesteuert werden. Die Produkte der nicht-regioselektiven Synthesen wurden mit Hilfe präparativer HPLC getrennt. Die Identifizierung der Analoga erfolgte durch HPLC, NMR und MS. Die Bindungsaffinitäten (Ki-Werte) zum VAChT wurden mit Hilfe kompetitiver Bindungsassays an mit Ratten-VAChT-cDNA stabil transfizierten PC12-Zellen und (-)-[3H]Vesamicol als Radioligand bestimmt.

Ergebnisse:

Es wurden zunächst die drei Klassen der Vesamicole, F-Benzylethervesamicole und Aminobenzovesamicole synthetisiert und deren Affinität zum VAChT bestimmt. Die neuen Analoga weisen strukturelle Veränderungen mit sowohl sterischen als auch elektronischen Einflüssen in den Ringen A, B und C des Vesamicolgrundgerüstes auf. Modifikationen am Ring A wurden durch die Synthese unterschiedlicher Epoxidvorläufer ermöglicht. Der Einsatz strukturell verschiedener Amine zur nukleophilen Epoxidringöffnung führte zu Änderungen in den Ringen B und C. Die untersuchten drei Klassen von Vesamicolanaloga zeigten sehr unterschiedliche VAChT-Bindungsaffinitäten. Sie lagen im Bereich von Ki = 96,5 ± 19,3 nM bis Ki > 400 µM. Wie erwartet, wurden innerhalb der Klassen (Derivate unterscheiden sich in Ring B oder C) große Affinitätsunterschiede beobachtet. Allerdings wurden auch unerwartete Werte bei vergleichbaren Derivaten der drei Klassen (Unterschied in Ring A) beobachtet. Im Vergleich zum (-)-Vesamicol (Ki = 24,4 ± 4,4 nM) wiesen alle untersuchten Verbindungen eine geringere Affinität zum VAChT auf.

Schlussfolgerungen:

Bereits nach diesen ersten Ergebnissen hat sich deutlich gezeigt, dass Vorhersagen bezüglich der Affinität zum VAChT von Klasse zu Klasse nicht möglich sind und der Einfluss struktureller und elektronischer Änderungen am Vesamicolgrundgerüst tendenziell nicht vorausgesagt werden kann. Dies bestätigt die Notwendigkeit der geplanten quantitativen Struktur-Affinitäts-Studie, bei der die Daten systematisch strukturell modifizierter Verbindungen zu Grunde gelegt werden.

  • Lecture (Conference)
    19. Jahrestagung der Arbeitsgemeinschaft Radiochemie/Radiopharmazie der DGN, 15.-17.09.2011, Ochsenfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15880


Interaction of humic acid with actinides: Influence of heteroatomic functional groups other than carboxylic groups

Sachs, S.; Schmeide, K.; Bernhard, G.

Abstract

The role of heteroatomic functional groups other than carboxylic groups on the interaction behavior of humic acids (HA) with actinides is widely unconsidered. Applying synthetic HA the influence of reduced sulfur functionalities on the U(VI) complexation and the Np(V) reduction by HA was studied. Reduced sulfur functionalities have been identified as complexing and redoxactive sites in HA.

Keywords: Humic acid; Uranium; Neptunium; Complexation; Reduction; Sulfur; Reduced sulfur; Humic acid model substances; Synthetic humic acid

  • Contribution to proceedings
    Workshop peat and humic substances: Current research in chemical, physical and biological characterization of peat, 28.-30.09.2011, Zittau, Germany
    Workshop Peat and Humic Substances Current research in chemical, physical and biological characterization of peat, Zittau: University of Applied Sciences Zittau/Görlitz, 978-3-941521-01-8, 17-20
  • Invited lecture (Conferences)
    Workshop peat and humic substances: Current research in chemical, physical and biological characterization of peat, 28.-30.09.2011, Zittau, Germany

Permalink: https://www.hzdr.de/publications/Publ-15879


Constitutive expression of hydrophobin HFB1 from Trichoderma reesei in Pichia pastoris and its pre-purification by foam separation during cultivation

Kottmeier, K.; Günther, T. J.; Weber, J.; Kurtz, S.; Ostermann, K.; Rödel, G.; Bley, T.

Abstract

Hydrophobins are small surface-active proteins that have considerable potential for use in applications ranging from medical and technical coatings, separation technologies, biosensors, and personal care. Their wider use would be facilitated by the availability of recombinant tailor-made hydrophobins. We successfully expressed the class II hydrophobin HFB1 from Trichoderma reesei in Pichia pastoris under the control of the constitutive GAP (glyceraldehyde 3-phosphate dehydrogenase) promoter. Avoiding the use of the AOX1 (alcohol oxidase 1) promoter prevents the costs and risks associated with the storage and delivery of methanol used as an inducer. Efficient secretion of hydrophobin was achieved using either the alpha-factor prepro-peptide or the native secretion signal of HFB1. The secreted hydrophobins have been isolated with a purity of up to 70% using in situ foam separation during the cultivation process. Coating experiments and surface pressure measurements demonstrated the activity of the hydrophobins. An immunodot assay showed the accessibility of carboxyterminally fused tags of the hydrophobin, which is necessary for potential applications using functionalized hydrophobins. The presented data show that Pichia pastoris is a suitable system for production of constitutively expressed and secreted active hydrophobin, allowing for in situ pre-purification using foam separation.

Keywords: Hydrophobin; HFB1; Pichia pastoris; heterologous expression; foam separation; surface active protein

Permalink: https://www.hzdr.de/publications/Publ-15878


Insider extra Juli 2011

Bohnet, C.

Abstract

Mitarbeiterzeitung des HZDR

  • Communication & Media Relations
    Mitarbeiterzeitung 15.07.2011
    2 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15877


Terahertz nonlinear optics of intra-exciton transitions in quantum wells

Wagner, M.; Schneider, H.; Stehr, D.; Winnerl, S.; Teich, M.; Andrews, A. M.; Schartner, S.; Strasser, G.; Helm, M.

Abstract

In our contribution we investigate nonlinear optics related to the hydrogen-like intraexciton 1s-2p heavy-hole (hh) transition in GaAs/AlGaAs quantum wells. Tuning intense terahertz (THz) light of the Dresden free-electron laser around this resonance we report (i) efficient sideband generation and (ii) clear evidence of the Autler-Townes effect.

Keywords: free-electron laser; sideband generation; Autler-Townes; AC Stark

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    EP2DS19/MSS15, 25.-29.07.2011, Tallahassee, USA

Permalink: https://www.hzdr.de/publications/Publ-15876


Coherent control of a THz-intersubband polarization in a quantum well

Wagner, M.; Helm, M.; Sherwin, M. S.; Stehr, D.

Abstract

Ultrashort terahertz pulses in the far-infrared spectral region centered around 2 terahertz are used to coherently control an intersubband polarization in a GaAs/AlGaAs quantum well structure at low temperature. While the first THz pulse excites a macroscopic polarization between the quantum well first and second subband, a second, temporally delayed, control pulse switches the polarization off or refreshes it depending on the relative time delay between the pulses. The switching is directly demonstrated in the time-domain for the few picosecond long free-induction decay of the induced polarization. Model calculations based on the optical Bloch equations agree well with the experimental data.

Keywords: terahertz; ultrafast; coherent control; intersubband polarization; free-induction decay

  • Poster
    EP2DS19/MSS15, 25.-29.07.2011, Tallahassee, USA

Permalink: https://www.hzdr.de/publications/Publ-15875


Microfocus infrared ellipsometry characterization of air-exposed graphene flakes

Weber, J. W.; Hinrichs, K.; Gensch, M.; van de Sanden, M. C. M.; Oates, T. W. H.

Abstract

Graphene and ultrathin graphite flakes prepared by exfoliation were characterized by microfocus synchrotron infrared mapping ellipsometry. The dielectric function of graphene in a dry-air atmosphere is determined and compared to that of ultrathin graphite, bulk graphite and gold. The imaginary part of graphene was revealed to be about an order of magnitude higher than that of graphite. Comparing the conductivity to an optical model considering intraband transitions we discuss the effects of environmental exposure, relevant for real-world applications.

Permalink: https://www.hzdr.de/publications/Publ-15874


NanoTrack - Untersuchung des Lebenszyklus von Nanopartikeln anhand von [45Ti]TiO2 und [105Ag]Ag0

Franke, K.; Hildebrand, H.; Mehnert, R.; Mai, E.; Freyer, A.; Bilz, E.; Isaacson, C.; Schirmer, K.; Ammann, A.; Sigg, L.

Abstract

Die Herstellung und Nutzung von nanopartikelhaltigen Polymersystemen hat in den letzten Jahren deutlich zugenommen. Während die Vorteile und gewünschten Eigenschaften von Nanokompositmaterialien vielfach gezeigt werden konnten (z. B. selbstreinigende, kratzfeste Oberflächen, antibakterielle Wirkung des Ag+ aus Ag0-NP), sind die erforderlichen Kenntnisse zur Risikobewertung der typischerweise in Lacksystemen und Beschichtungen eingebrachten Nanopartikel (z. B. TiO2, Ag0) bisher unzureichend. Für nanopartikuläres TiO2 und Ag0 bietet sich zur Technologiefolgeabschätzung der Einsatz von radioisotopischen Sonden an. Die Radiomarkierung von Nanopartikeln eröffnet eine hoch sensitive Nachweismöglichkeit und eignet sich für ein qualitatives und quantitatives Prozessmonitoring, z. B. hinsichtlich des Verhaltens von Nanopartikeln während Alterung und Verschleiß der Kompositmaterialien bis hin zu einer Abschätzung der Freisetzungsraten und des Transports der Nanopartikel in der Umwelt sowie Wechselwirkungen mit Organismen. Die modellhafte Erfassung relevanter Prozesse ermöglicht im Ergebnis Schlussfolgerungen für die Weiterentwicklung von Nanokompositmaterialien.
Im Verbundprojekt NanoTrack werden nanopartikelhaltige (TiO2, Ag0) Modelllacksysteme auf Acrylat-Basis hergestellt und einer beschleunigten Bewitterung ausgesetzt. Dabei konnte für ein Lacksystem mit nanoskaligem TiO2 (P 25, Evonik Industries, dp,TiO2 ≈ 21 nm, Maschinenauftrag mit einer Nassschichtdicke von 4 µm) nach ca. 500 h UV-A-Bestrahlung (Intensität ~ 15 mW/cm2) festgestellt werden, dass die organische Lackmatrix nahezu vollständig zerstört wurde und ein Nanopartikelaustrag somit erfolgen könnte. In Abbildung 1 ist der zeitliche Verlauf des Abbaus einer Polyacrylat-TiO2-Nanokomposit-Beschichtung durch UV-A-Bestrahlung dargestellt. Mittels Infrarot¬spektroskopie (FTIR-ATR) und thermogravimetrischen Messungen konnte dieses Ergebnis eindeutig bestätigt werden. Des Weiteren konnte gezeigt werden, dass die freigesetzten Partikel meist nicht als Primärpartikel, sondern mindestens als Verbünde von wenigen Teilchen, überwiegend jedoch als mikroskalige Aggregate vorliegen.
Modellrechnungen ergaben, dass die im Vergleich zur Schwerkraft sehr starke Dipol-Anziehung der polaren, nanoskaligen TiO2-Teilchen praktisch das Auftreten freier Primärpartikel verhindert.

Abbildung 1: Zeitlicher Verlauf des Abbaus einer Polyacrylat-TiO2-Nanokomposit-Beschichtung (TiO2 P 25, Evonik Industries); A) original, B) t = 2 d (50.000 fache Vergrößerung); C) t = 4 d, D) t = 8 d, E) t = 16 d (75.000 fache Vergrößerung); REM-Aufnahmen: IOM

Für den sensitiven Partikelnachweis werden radiomarkierte Nanopartikel des gleichen Typs (P 25, [44Ti]TiO2 bzw. [110mAg]Ag0) eingesetzt. Die authentische Markierung erfolgte mittels diffusiven Eintrags von Radionukliden in Nanopartikel. Dabei konnten radiochemische Ausbeuten von über 98 % erreicht werden. Die Stabilität der Radiomarkierung wurde in wässrigen Systemen in Abhängigkeit vom pH-Wert der Suspension und der Zeit untersucht. Dabei konnte gezeigt werden, dass die radioisotopischen Sonden physikalisch und chemisch stabil mit den Nanomaterialien verbunden sind und dem Chemismus der Partikel folgen (z. B. Lösungsgleichgewicht Ag0-NP ⇄ Ag+).
Die Radiomarkierung erlaubt auch den Nachweis von Nanopartikeln in komplexen Medien. Im Projekt werden die Wechselwirkungen der Partikel mit Geomatrizes und der Transport in durchströmten Systemen untersucht. Ein weiterer wichtiger Aspekt ist die Beurteilung der Ökotoxizität der freigesetzten Nanopartikel. Werden diese in Oberflächengewässer eingetragen, kann es zu Wechselwirkungen mit lebenden Organismen kommen. Biofilme werden als potenzielle Senke für technische Nanomaterialien beschrieben. Diese sind ein wichtiger Bestandteil von Ökosystemen und könnten dazu beitragen, dass Partikel über die Nahrungsaufnahme höherer Organismen (z. B. Daphnien) in Nahrungsketten eingetragen werden. Systematische Studien sollen zu detaillierten Erkenntnissen hinsichtlich der Mobilität und möglicher Risiken der eingesetzten TiO2 und Ag0-NP für die Umwelt führen.
Die ganzheitliche Betrachtung von Nanopartikeln in Lacksystemen und Beschichtungen hinsichtlich Produktion, Alterung und Verschleiß, Partikelfreisetzung und deren Verbleib in der Umwelt soll als Datengrundlage für eine Risikoabschätzung dienen und zur Validierung und ggf. Anpassung von Lackformulierungen beitragen.

  • Poster
    WING.DE 2011, 04.-06.10.2011, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15873


Fast propagation of weakly pinned domain walls and current-assisted magnetization reversal in He+-irradiated Pt/Co/Pt nanotracks

Cormier, M.; Mougin, A.; Ferré, J.; Jamet, J.-P.; Weil, R.; Faßbender, J.; Baltz, V.; Rodmacq, B.

  • Poster
    MORIS 2011, 22.06.2011, Nijmegen, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-15872


Radiolabeling of phosphatidylserine-binding peptides with prosthetic groups N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]maleimide ([18F]FBAM) and N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB)

Kapty, J.; Kniess, T.; Wuest, F.; Mercer, J. R.

Abstract

The widely used (18)F-prosthetic group N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB) and the recently developed N-[6-(4-[(18)F]fluorobenzylidene)aminooxyhexyl]maleimide ([(18)F]FBAM) were investigated for radiolabeling of two representative phosphatidylserine-binding peptides. The prosthetic groups were compared with respect to required reactions conditions for optimum labeling, radiolabeling yield and chemoselectivity. The N-terminus labeled product produced by reaction of [(18)F]SFB with binding peptide LIKKPF was produced in 18% radiochemical yield while no N-terminus labeled product could be isolated following [(18)F]SFB reaction with PDGLSR. When the peptides were modified by addition of a cysteine residue at the N-terminus they provided almost quantitative radiochemical yields with [(18)F]FBAM. Results indicate that for the peptides in this study, [(18)F]FBAM is a more useful prosthetic group compared to [(18)F]SFB due to its excellent chemoselectivity and high radiochemical yield.

Keywords: Apoptosis; Phosphatidylserine; PET; [18F]SFB; [18F]FBAM

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-15871


Vorstellung des Instituts für Radiochemie zum Dies academicus

Steudtner, R.

Abstract

Vorstellung des IRC, Arbeitsgebiete des IRC, Präsentation möglicher Semesterarbeiten

  • Lecture (others)
    Dies academicus 2011, 08.06.2011, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15868


Late Quaternary rock uplift rate at the northern margin of the Central Anatolian Plateau: inferences from pediment surfaces and multiple cosmogenic nuclides

Yildirim, C.; Schildgen, T. F.; Echtler, H. P.; Strecker, M. R.; Melnick, D.; Niedermann, S.; Merchel, S.; Martschini, M.; Steier, P.

Abstract

The northern margin of the Central Anatolian Plateau spans the northward arched part of the Pontide Mountains between the North Anatolian Fault to the south and the Black Sea to the north. Crustal deformation between the North Anatolian Fault and the Black Sea is integrally tied to the evolution of the Central Anatolian Plateau. The asymmetric topographic pattern, coupled with the spatial distribution and geometry of faults, suggest that the northern margin of the plateau has constituted an active accretionary orogenic wedge with northward polarity between the North Anatolian Fault and the abyssal plain of the Black Sea (Figure). To explore the mode and rate of rock uplift that is associated with internal deformation in the accretionary orogenic wedge, we dated incised and deformed pediments by measuring in situ produced 10Be, 21Ne and 36Cl concentrations.
The key target area for our analysis is the Kastamonu intramontane basin. We mapped a suite of six gravel-covered pediment surfaces in the basin that rise 175-180m (P1), 115-130 m (P2), 70-80 m (P3), 45-54 m (P4), 25-35 m (P5) and 12-22 m (P6) above the river. One set of samples was collected along the trunk stream of the Kastamonu basin to estimate trunk stream incision rates, and a second set of samples was collected from local surfaces that have been deformed and incised in response to faulting in the accreationary orogenic wedge.
The surfaces within the basin have exposure ages that range from about. (7.8±0.9) ka to (437 ±64) ka. The temporal distribution of the abandonment ages suggests that specific climatic conditions do not promote abandonment of pediment surfaces in the Kastamonu Basin. The abandonment ages and strath heights of the surfaces yield incision rates that range from 0.20 to 0.49 mm/yr along the trunk stream of the Kastamonu Basin. We used an average fluvial incision rate to calculate rock uplift rate, i.e., incision between the 70-80 m (P2) and 12-22 m (P6) pediments along the trunk stream of the Kastamonu Basin. This gives ~0.27 mm/yr of average vertical rock uplift rate between ca. 437 and 22 ka in the internal part of the Central Pontides.
The highest incision rates (1.04 to 3.16 mm/yr) in the basin are obtained from local surfaces deformed by faults along the basin margins. Topographic profiles across the local pediment surfaces show discernable warping in evidence of out of sequence faulting and partial accommodation of internal deformation in the orogenic wedge. We believe that out-of-sequence faulting and internal deformation indicate a subcritical state of the orogenic wedge at the northern margin of the Central Anatolian Plateau.

Keywords: dating; TCN; in-situ; cosmogenic radionuclides; AMS

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  • Poster
    7th TOPO-EUROPE Workshop - A forum investigating the cause and creation of the topography of Europe, 06.-09.10.2011, Davos, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-15867


Experimente zur Entstehung und Wirkung kosmischer Magnetfelder

Stefani, F.

Abstract

Seit langem ist bekannt, dass die Magnetfelder von Planeten, Sternen und Galaxien durch Selbsterregung in strömenden elektrisch leitfähigen Fluiden, den sogenannten hydromagnetischen Dynamoeffekt, erzeugt werden. Weniger bekannt ist hingegen die bedeutende Rolle, die Magnetfelder bei der kosmischen Strukturbildung spielen. So sind die beobachteten hohen Wachstumsraten von Sternen und Schwarzen Löchern nur erklärbar, wenn die Akkretionsscheiben, aus denen sie gefüttert werden, turbulent sind und damit Drehimpuls effektiv nach außen transportieren können. Die Ursache dieser Turbulenz liegt in der destabilisierenden Wirkung von Magnetfeldern auf rotierende Strömungen, die als Magneto-Rotations-instabilität bezeichnet wird.
Der Vortrag gibt zunächst eine kurze Einführung in die Theorien zur Entstehung und Wirkung kosmischer Magnetfelder. Im Mittelpunkt stehen dann die Flüssigmetall-Experimente des letzten Jahrzehnts, in denen sowohl der Dynamoeffekt als auch die Magneto-Rotationsinstabiliät untersucht worden sind. Im Detail werden insbesondere das Rigaer Dynamo-Experiment und das PROMISE-Experiment am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) besprochen.
Zum Schluss werden die Pläne für ein neues großes Dynamoexperiment am HZDR vorgestellt, in dem Selbsterregung in einer nur durch Präzession getriebenen Strömung von flüssigem Natrium nachgewiesen werden soll.

  • Invited lecture (Conferences)
    Greifswalder Physikalisches Kolloquium, 23.06.2011, Greifswald, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15866


Theory of a liquid metal Tayler experiment

Rüdiger, G.; Gellert, M.; Stefani, F.

Abstract

The nonaxisymmetric Tayler instability of toroidal magnetic fields is studied for conducting incompressible fluids between two coaxial cylinders. The inner cylinder is assumed as thin. The outer radius of the container is 5 cm. The electric current may be homogeneous so that the azimuthal magnetic field is proportional to the radius. Endplates are not considered. The azimuthal mode number of the perturbation is fixed to m = 1.

  • Lecture (Conference)
    17th International Couette-Taylor Workshop, 25.-27.07.2011, Leeds, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-15865


Radiosynthesis of a 18F-labeled 2,3-diarylsubstituted indole via McMurry coupling for functional characterization of cyclooxygenase-2 (COX-2) in vitro and in vivo

Kniess, T.; Laube, M.; Bergmann, R.; Graf, F.; Steinbach, J.; Wuest, F.; Pietzsch, J.

Abstract

The radiosynthesis of 3-(4-[18F]fluorophenyl)-2-(4-methylsulfonylphenyl)-1H-indole [18F]3 as PET radiotracer for functional characterization of cyclooxygenase-2 (COX-2) in vitro and in vivo is described. [18F]3 was prepared by McMurry cyclization of a 18F-labeled intermediate with low valent titanium and zinc via a two-step procedure in a remote controlled synthesizer unit including HPLC purification and solid phase extraction. In this way [18F]3 was synthesized in 80 min synthesis time in 10% total decay corrected yield from [18F]fluoride in radiochemical purity >98% and a specific activity of 74-91 GBq/µmol. [18F]3 was evaluated in vitro using pro-inflammatory stimulated THP-1 and COX-2 expressing tumor cell lines (FaDu, A2058, HT-29), where the radiotracer uptake was shown to be consistent with up regulated COX-2 expression. The stability of [18F]3 was determined by incubation in rat whole blood and plasma in vitro and by metabolite analysis of arterial blood samples in vivo, showing with 75% of original compound after 60 min an acceptable high metabolic stability. In vivo kinetics and tumor uptake were investigated by dynamic small animal PET studies on HT-29 tumor-bearing mice, and revealed in contrast to the in vitro results no substantial tumor accumulation of [18F]3. These data indicate that the radiotracer is not suitable for functional imaging of COX-2 in rodent models in vivo. However it should be noted that McMurry cyclization in PET chemistry gives access to 18F-labeled diaryl-substituted heterocyles that hold promise as new radiolabeled COX-2 inhibitors.

Involved research facilities

  • PET-Center

Permalink: https://www.hzdr.de/publications/Publ-15864


Characterization and local magnetic modification of ion irradiated GaMnAs

Li, L.; Yao, S. D.; Roshchupkina, O.; Prucnal, S.; Akhmadaliev, S.; Campion, R. P.; Rushforth, A. W.; Fassbender, J.; Helm, M.; Gallagher, B. L.; Timm, C.; Schmidt, H.; Zhou, S.

Abstract

We study the influence of ion irradiation on magnetic, magneto-transport and structural properties in Ga0.94Mn¬0.06As films. The carrier concentration is accurately controlled by defects introduced via ion irradiation. Magnetic properties strongly depend on the hole concentration. We present the modification of coercivity, magnetic anisotropy, and magnetotransport properties during such a procedure. By x-ray diffraction and Raman spectra, we exclude the effects from structural changes. Using lithograph made resist mask, one can realize planar local structures with different magnetic properties, indicating the promising future of ion irradiation for spintronics device fabrication.

Keywords: GaMnAs; ferromagnetism; ion irradiation

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Permalink: https://www.hzdr.de/publications/Publ-15863


The correlation between structure and magnetism of Ni-implanted TiO2 annealed at different temperatures

Ding, B.; Cheng, F.; Pan, F.; Fa, T.; Yao, S.; Potzger, K.; Zhou, S.

Abstract

In this paper, the structural and magnetic properties of Ni metal implanted TiO2 single crystals are discussed. Ni nanocrystals (NCs) have been formed in TiO2 after ion implantation. Their crystalline sizes were increased with increasing post-annealing temperature. Metallic Ni nanocrystals inside the TiO2 matrix are stable up to an annealing temperature of 1073 K. The Ni NCs forming inside TiO2 are the major contribution of the measured ferromagnetism.

Keywords: Diluted magnetic oxides; Ion implantation; TiO2

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Permalink: https://www.hzdr.de/publications/Publ-15862


The influence of temperature and small organic ligands on the sorption of Eu(III) on Opalinus Clay

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

Abstract

The influence of temperature up to 50°C and small organic ligands (citrate, tartrate) on the sorption of Eu(III) on the natural clay rock Opalinus Clay (OPA) under aerobic (p(CO2) = 10^(-3.5) atm) synthetic OPA pore water conditions (pH 7.6, I = 0.4 M) was investigated. Batch sorption experiments and time-resolved laser-induced fluorescence spectroscopy (TRLFS) were used to study these influencing factors on the Eu(III) sorption.
Sorption isotherms and distribution coefficients Rd (15°C: log Rd = 4.50 ± 0.05 … 50°C: log Rd = 5.54 ± 0.06) at 2•10^(-9) M Eu(III) as a function of the solid-to-liquid ratio (up to 3 g•L^(-1)) and temperature were determined. A significant temperature dependency of the Eu(III) sorption was observed. With rising temperature the Eu(III) sorption increases. The surface reaction is endothermic (sorption enthalpy ~ 50 kJ•mol^(-1)). Using TRLFS, a surface species with a luminescence lifetime of (201 ± 9) microseconds was identified.
In the presence of tartrate or citrate the Eu(III) sorption decreases with increasing ligand concentration due to a complex formation of Eu(III) in solution, with citrate having a more pronounced influence on the sorption than tartrate. With the batch sorption experiments it can be shown that at a citrate concentration larger than 10^(-5) M and at a tartrate concentration larger than 10^(-4) M an increasing Eu(III) desorption occurs. This result is supported by TRLFS measurements, which show the correlation between the complexation of Eu(III) by citrate or tartrate in solution and the Eu(III) desorption process. Possible Eu(III) citrate or Eu(III) tartrate surface species on OPA could not be detected using TRLFS.

Keywords: Europium(III)/citrate/tartrate/temperature dependence/batch sorption experiments/TRLFS

Permalink: https://www.hzdr.de/publications/Publ-15861


Fracture mechanics characterisation of the beltline welding seam of the decommissioned WWER-440 reactor pressure vessels of nuclear power plant Greifswald Unit 4

Viehrig, H.-W.; Altstadt, E.; Houska, M.; Valo, M.

Abstract

The paper presents data measured for trepans sampled from decommissioned WWER-440 reactor pressure vessel of the NPP Greifswald Unit 4 the main focus being on fracture toughness characterisation according to test standard ASTM E1921. Large variation of the evaluated reference temperature values T0 across the wall of the multilayer beltline welding seam was observed. Generally, the through wall variation of the T0-values does not follow the ductile-to-brittle transition temperature (TT) shift predicted by the Russian code and in fact the non-fluence dependent variation of the T0-values is comparable to the variation predicted by the code. Metallographic investigations show that the T0-values measured with TS oriented Charpy size SE(B) specimens from different thickness locations of the multilayer welding seams strongly depend on the metallographic structure at the specimen crack tip. The RPV integrity is accessed taking into account a pressurised thermal shock scenario.

Keywords: decommissioned reactor pressure vessel; weld metal; fracture toughness; Master Curve; specimen orientation; integrity assessment

Permalink: https://www.hzdr.de/publications/Publ-15860


Lead in diagenetic pyrite: evidence for Pb-tolerant bacteria in a red-bed Cu deposit, Quebec Appalachians, Canada

Cabral, A. R.; Beaudoin, G.; Munnik, F.

Abstract

Diagenetic pyrite from the Silurian continental red bed-hosted Transfiguration cupriferous deposit in the Quebec Appalachians, Gaspé Belt, Canada, contains up to ~2% (m/m) Pb. This large Pb content in pyrite contrasts with experimental determinations that indicate solubility of <0.1% (m/m) PbS in pyrite at high temperature. The distribution of Pb in pyrite is heterogeneous, with plumbiferous domains occurring as patches and concentric growth layers alternating with Mn- and Mo-bearing zones. The plumbiferous pyrite is surrounded by As- and Cu-rich rims. This compositional heterogeneity, however, is elusive under normal backscattered-electron (BSE) imaging, but it can be recognized under high-gain BSE. Proton-induced X-ray emission (PIXE) confirms the presence of Pb. Plumbiferous pyrite with >0.1% (m/m) Pb has rarely been described; it is thus possible that plumbiferous pyrite may have been overlooked in metalliferous deposits worldwide. The plumbiferous pyrite from Transfiguration has a light S-isotope composition that is characteristic of bacterial sulphate reduction. We suggest that Pb in diagenetic pyrite indicates Pb-tolerant bacterial activity and, perhaps, constitutes a biosignature of bacterial tolerance to Pb in ancient sedimentary systems.

Keywords: plumbiferous pyrite; Pb-tolerant bacteria; high-gain BSE; PIXE; Canada

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Permalink: https://www.hzdr.de/publications/Publ-15859


The atomic layer deposition of SrB2O4 films using the thermally stable precursor Bis(tris(pyrazolyl)borate)strontium

Saly, M. J.; Munnik, F.; Winter, C. H.

Abstract

The atomic layer deposition (ALD) of strontium borate films is carried out using bis(tris(pyrazolyl)borate)strontium (SrTp2) and water as precursors. Self-limiting ALD growth is established at 350°C with SrTp2 and water pulse lengths of ≥ 2.0 s and ≥ 0.3 s, respectively. An ALD window is observed from 300 to 375 °C, in which the growth rate is 0.47A per cycle. The thin film compositions are assessed by elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). ERDA suggests compositions of SrB2O4 at growth temperatures of <350 °C, but the boron/strontium and oxygen/strontium ratios are lower than those of SrB2O4 at 350 and 400 °C.Within the ALD window, hydrogen concentrations range from 0.37(42) to 0.87(7) at.-%, and the carbon and nitrogen concentrations are below the detection limits. XPS analyses on representative strontium borate thin films show all expected ionizations. X-ray diffraction (XRD) experiments reveal that the as-deposited films are amorphous. The surface morphology is assessed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The rms surface roughness of typical 2µm x 2 µm areas for films deposited at 325 and 350 °C are 0.3 and 0.2 nm, respectively. SEM images of these films show no cracks or pinholes.

Keywords: Atomic layer deposition; Strontium; Strontium borate; Thin film growth; Tris(pyrazolyl)borate ligands

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Permalink: https://www.hzdr.de/publications/Publ-15858


Proceedings of the 12th International Conference on Plasma Surface Engineering, Garmisch-Partenkirchen, Germany,13-17 September 2010

Cavaleiro, A.; Czerwiec, T.; Helmersson, U.; van der Kolk, G.; Möller, W.; Oehr, C.; Tietema, R.; (Editors)

Abstract

Konferenz-Proceedings ohne Abstract

  • Book (Editorship)
    Amsterdam: Elsevier BV, 2011
    610 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15856


Spatially resolved Langmuir probe measurements of a magnetically enhanced hollow cathode arc plasma

Zimmermann, B.; Fietzke, F.; Möller, W.

Abstract

Hollow cathode arc discharges are efficient plasma sources and are applied in substrate pretreatment or plasma-activated deposition processes. In order to generate large volume homogeneous plasmas to guarantee uniformity of plasma activation and coating properties, in the presented configuration a ring-shaped anode is positioned coaxially around the hollow cathode tube. A magnetic field is applied, which is axial within the cathode tube and spreads out in the deposition chamber. In order to characterize the hollow cathode plasma, spatially resolved Langmuir probe measurements have been carried out. The charge carrier densitymaximum on the cathode tube axis reaches values up to 1013cm−3. With increasing distance from the plasma source, the plasma density decreases and shows a smoother lateral profile. Maxwellian electron energy distribution functions are observed with spatially homogeneous electron temperatures in the range 1–4 eV. Increasing the chamber pressure leads to higher plasma densities and lower electron temperatures. Reduction of the gas flow through the hollow cathode tube results in a strong rise of the plasma density over two orders of magnitude. The magnetic field supports the low gas flow mode and leads to higher plasma densities, too. The results of the Langmuir probe measurements are discussed by means of the active zonemodel and are further related to optical emission measurements performed in the vicinity of the hollow cathode orifice.

  • Surface & Coatings Technology 205(2011), S393-S396

Permalink: https://www.hzdr.de/publications/Publ-15855


Structure investigation of U(IV) and Th(IV) silica colloids at near-neutral pH by combining X-ray scattering and X-ray absorption spectroscopy

Hennig, C.; Weiss, S.; Dreissig, I.; Banerjee, D.; Zänker, H.; Brendler, E.; Scheinost, A. C.; Bernhard, G.

Abstract

The solubility and environmental mobility of tetravalent actinides is a widely discussed issue. Already at low pH tetravalent actinides show a strong tendency towards hydrolysis followed by the formation of oligomers and oxyhydroxide colloids. Such colloids may show a high groundwater mobility at certain physicochemical conditions. However, An(IV) oxohydroxide colloids polymerize and precipitate already far below neutral pH values. One of the reasons is that the isoelectric point of oxyhydroxide colloids is at neutral pH.

Is it known that trivalent actinides undergo a complexation with silicic acid resulting in colloidal species which are stable at neutral pH [4]. We found in recent studies that silica is also able to stabilize uranium(IV) colloids at near-neutral pH through modification of the inner structure and by influencing the surface charge [5]. Further studies indicate that thorium(IV) shows a similar behavior. The colloid structure and the formation process was investigated by a combination of synchrotron-based X-ray scattering and spectroscopy experiments supported by TEM, XPS, UV-Vis and 29Si MAS NMR.

The U(IV) and Th(IV) silica colloids are stabilized in water-borne state by the surface charge which seems to be determined by modifications of the particle structure. The presence of silica at the colloid surface is one major reason for the shift of the isoelectric point to lower pH values which results in a long-term stability of such colloidal suspensions at near-neutral pH for several years [5]. The colloid particle size determined by photon correlation spectroscopy, ultrafiltration and ultracentrifugation shows a typical size distribution of ≤ 20 nm. TEM and XRD investigations reveal that the internal structure of U(IV) and Th(IV) silica colloids is highly amorphous. EXAFS measurements indicate a direct bond of U(IV) and Th(IV) with silica, but do not show metal-oxygen-metal bonds. In contrast, HEXS shows clearly such metal-oxygen-metal bonds. The reason of this difference is attributable to different scattering processes of X-rays and photoelectrons which will be discussed in more detail. The internal structure of the U(IV) and Th(IV) silica colloid particles is comprised of An-O(H)-An bonds which are successively replaced by An-O(H)-Si bonds and oxygen atoms from bound aquo ions, oxo and hydroxo groups. The stability of such colloids suggests that the assessment of actinide behaviour in the aquatic environment should take the possible existence of An(IV)-silica colloids into consideration.

Keywords: EXAFS; HEXS; Uranium; Thorium

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  • Invited lecture (Conferences)
    GDCh Wissenschaftsforum Chemie 2011, 04.-07.09.2011, Bremen, Germany

Permalink: https://www.hzdr.de/publications/Publ-15854


Nickel-related defects in ZnO – A deep-level transient spectroscopy and photo-capacitance study

Schmidt, M.; Brachwitz, K.; Schmidt, F.; Ellguth, M.; von Wenckstern, H.; Pickenhain, R.; Grundmann, M.; Brauer, G.; Skorupa, W.

Abstract

Electronic defects in nickel-doped zinc oxide thin films have been investigated by means of capacitance spectroscopy. The samples were grown by pulsed laser deposition on a-plane sapphire substrates. Nickel was introduced into the films (a) during growth and (b) by implantation of Ni ions and subsequent thermal annealing. From deep-level transient spectroscopy it was concluded that a nickel-related trap, TNi2, with an energy level approximately 540 meV below the conduction band edge was formed. Photo-capacitance (PCAP) measurements performed on the nickel-implanted sample proved the existence of a further nickel-related trap, TNi1, in the midgap. The photo-ionisation cross-section spectra of this state were calculated from the PCAP transients and gave evidence that TNi1 and TNi2 are two levels of the same defect, TNi, which is possibly nickel on a tetrahedral lattice site. A model for TNi is proposed.

Keywords: ion implantation; zinc oxide; nickel; deep-level transient spectroscopy; photo-capacitance; pulsed laser deposition

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Permalink: https://www.hzdr.de/publications/Publ-15853


Stable Platinum Isotope Measurements in Presolar Nanodiamonds by TEAMS

Wallner, A.; Melber, K.; Merchel, S.; Ott, U.; Forstner, O.; Golser, R.; Kutschera, W.; Priller, A.; Steier, P.

Abstract

Nanodiamonds are stardust grains commonly found in primitive meteorites. They survived the formation of the solar system and kept their own individuality. Measurements of traceelement isotopic signatures in these grains will help understanding heavy element nucleosynthesis in massive stars and dust formation from their ejecta. We have continued previous attempts to search for stable Pt isotope anomalies in nanodiamonds via trace element accelerator mass spectrometry (TEAMS). The instalment of a new injector beam line at the VERA facility allowed studying low traces of stable elements in different materials. Moreover, recent experiments showed that VERA provides the required measurement precision together with a low Pt machine background. Here, we observed for the first time an indication for enhancements of 198Pt/195Pt isotope ratios in two diamond residues prepared by different chemical separation techniques from the Allende meteorite. Variations in other isotopic ratios were within analytical uncertainty, and no anomaly was identified in a third diamond fraction.

Keywords: TEAMS; trace elements; Pt; super novae; presolar grains; nanodiamonds

Permalink: https://www.hzdr.de/publications/Publ-15852


In-situ study of growth of carbon nanotube forests on conductive CoSi(2) support

Bayer, B.; Zhang, C.; Blume, R.; Yan, F.; Fouquet, M.; Wirth, C.; Weatherup, R.; Lin, L.; Baehtz, C.; Oliver, R.; Knop-Gericke, A.; Schlogl, R.; Hofmann, S.; Robertson, J.

Abstract

The growth of high density vertically aligned carbon nanotube forests on conductive CoSi(2) substrate layers is characterized by in situ x-ray photoemission spectroscopy and x-ray diffraction. We use in situ silicidation to transform as loaded, low conductivity CoSi supports to highly conductive CoSi(2) during nanotube growth. These cobalt silicide films are found to be stable against oxidation and carbide formation during growth and act as an excellent metallic support for growth of aligned nanotubes, resembling the growth on the insulating Fe/Al(2)O(3) benchmark system. The good catalytic activity is attributed to interfacial reactions of the Fe catalyst particles with the underlying CoSi(2) support. We obtain ohmic conduction from the support layer to the carbon nanotube forest.

Keywords: RAY PHOTOELECTRON-SPECTROSCOPY; CHEMICAL-VAPOR-DEPOSITION; INTEGRATED-CIRCUITS; CATALYST-SUPPORT; OHMIC CONTACTS; SILICIDES; FUTURE; IRON; INTERCONNECTS; NANOPARTICLES

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Permalink: https://www.hzdr.de/publications/Publ-15851


ROCOM experiments on boron dilution conducted within the NRG/EdF Project – Scenario 1

Kliem, S.; Franz, R.

Abstract

In the frame of the project ordered by NRG Petten (Purchase order: NRG-P2144963) experiments on two boron dilution scenarios have to be conducted at the ROCOM test facility.
Both scenarios are based on a hypothetical boron dilution accident following a SBLOCA in a PWR. A slug of unborated coolant has been accumulated in one of the loops. The re-established natural circulation drives the slug towards the reactor pressure vessel (RPV). In the vessel the slug mixes with the coolant of the downcomer and with the emergency core cooling water (ECC) which is injected into two other loops (Scenario 1) or into the loop with the slug (Scenario 2).
The boundary conditions on loop flow rates and temperature (density) differences are based on corresponding experiments at the PKL test facility operated by AREVA (Hertlein, 2003) and are described in the technical annex being a part of the project order (Kliem, 2010).
The well-proven wire-mesh sensor technology developed by HZDR over the last years is used to quantify the mixing of the slug and the ECC water on the way from the loops to the core inlet plane.
This report gives an overview about the ROCOM test facility and describes the experimental results on the first scenario.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2011
    HZDR\FWS\2011\04
    56 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-15850


Use of plasma treatment to grow carbon nanotube forests on TiN substrate

Esconjauregui, S.; Bayer, B.; Fouquet, M.; Wirth, C.; Yan, F.; Xie, R.; Ducati, C.; Baehtz, C.; Castellarin-Cudia, C.; Bhardwaj, S.; Cepek, C.; Hofmann, S.; Robertson, J.

Abstract

Hydrogen plasma pretreatment is used to enforce the growth of vertically-aligned carbon nanotube forests on TiN substrates. The evolution of the substrate, catalyst, and nanotubes are studied by in situ and ex-situ photoemission and X-ray diffraction in order to understand the growth mechanism. We find that TiN retains its crystallographic structure and its conductivity during plasma pretreatment and nanotube growth, which is confirmed by electrical measurements. Plasma pretreatment is found to favor the growth of nanotube forests by root growth, as it binds the catalyst nanoparticles more strongly to the substrate than thermal pretreatment. We find that plasma pretreatment time should be limited, otherwise poor or no growth is found.

Keywords: CHEMICAL-VAPOR-DEPOSITION; RAY PHOTOELECTRON-SPECTROSCOPY; TITANIUM; MULTILAYERS; METAL; FILMS

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Permalink: https://www.hzdr.de/publications/Publ-15849


Carbon nanotube forest growth on NiTi shape memory alloy thin films for thermal actuation

Bayer, B. C.; Sanjabi, S.; Baehtz, C.; Wirth, C. T.; Esconjauregui, S.; Weatherup, R. S.; Barber, Z. H.; Robertson, S. H. J.

Abstract

Actuation frequencies in thermally triggered Shape Memory Alloy (SMA) thin films are limited by the slow heat transport into/out of the films. Carbon Nanotubes (CNTs) are known to exhibit an exceptionally high thermal conductivity. Thus, we propose to thermally contact SMA films with CNTs to increase SMA actuation frequencies by enhanced heat transport through the CNTs. The basic requirement for this envisaged nanotube application is to obtain CNT forest growth on a SMA material while retaining a reversible martensitic transformation, as required for Shape Memory Effect exploitation. We show how such growth can be achieved on thin films of the SMA material NiTi. Future work is needed to measure thermal properties and obtainable cycling frequencies of CNT-SMA structures.

Keywords: Carbon nanotubes; Shape memory alloys; Chemical vapour deposition; NiTi; Thermal management

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Permalink: https://www.hzdr.de/publications/Publ-15848


Support-Catalyst-Gas Interactions During Carbon Nanotube Growth on Metallic Ta Films

Bayer, B.; Hofmann, S.; Castellarin-Cudia, C.; Blume, R.; Baehtz, C.; Esconjauregui, S.; Wirth, C. T.; Oliver, R. A.; Ducati, C.; Knop-Gericke, A.; Schlogl, R.; Goldoni, A.; Cepek, C.; Robertson, J.

Abstract

We present a detailed study of processes and interactions occurring during the Fe-catalyzed chemical vapor deposition of carbon nanotubes on metallic Ta supports. In situ X-ray photoemission spectroscopy and X-ray diffraction show that the Fe catalyst increases the reactivity of Ta toward oxidation and carbide formation, whereas Ta promotes the reduction of Fe. This causes an unusual temperature dependence of carbon nanotube growth, where at low temperatures (similar to 550 degrees C) vertically aligned forests of carbon nanotubes with ohmic contacts grow readily on metallic Ta, whereas at high temperatures (>600 degrees C) nanotube growth is sparse because of the diffusion of Fe away from the surface through grain boundaries of in situ formed polycrystalline Ta(2)O(5). The Fe-Ta model system highlights general material selection criteria for nanotube applications that require a conductive support.

Keywords: CHEMICAL-VAPOR-DEPOSITION; RAY PHOTOELECTRON-SPECTROSCOPY; INTERCONNECT APPLICATIONS; BETA-TANTALUM; INTEGRATION; ELECTRODES; BARRIER; SILICON; LAYERS; XPS

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Permalink: https://www.hzdr.de/publications/Publ-15847


Achieving coherent phase transition in palladium–hydrogen

Wagner, S.; Uchida, H.; Burlaka, V.; Vlach, M.; Vlcek, M.; Lukac, F.; Cizek, J.; Baehtz, C.; Bell, A.; Pundt, A.

Abstract

The thermodynamics of structural phase transformations in thin films depends on the mechanical stress that can be released by plastic deformation. For thin films below a critical film thickness, plastic deformation is energetically unfavourable: thus, the system stays coherent and stress remains. For PdH(c) films less than 22 nm thick, a new situation emerges: while the interfaces between matrix and hydride precipitates remain coherent throughout the complete phase transition, misfit dislocations form between the hydride phase and the substrate.

Keywords: Palladium; Hydrogen; Thin films; Phase transformations; Coherency

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Permalink: https://www.hzdr.de/publications/Publ-15846


Hydrogen desorption properties of melt-spun and hydrogenated Mg-based alloys using in situ synchrotron X-ray diffraction and TGA

Kalinichenka, S.; Röntzsch, L.; Baehtz, C.; Weißgärber, T.; Kieback, B.

Abstract

Three magnesium-based alloys, Mg90Ni10, Mg80Ni10Y10 and Mg85Cu5Ni5Y5, were prepared by melt-spinning and compared regarding their hydrogen desorption properties.Their hydrogen desorption kinetics after activation and hydrogenation was investigated by thermogravimetry at different temperatures in the range from150 °C to 250 °C. It was found that Mg80Ni10Y10 exhibits a much faster desorption kinetics in comparison toMg90Ni10 and Mg85Cu5Ni5Y5 of upto1.3wt.%-H2/min. The corresponding crystal phase transformations were investigated in detail by insitu synchrotron X-ray diffraction. It was found that the kinetics of hydrogenation is controlled by different reaction pathways for Mg90Ni10, Mg80Ni10Y10 and Mg85Cu5Ni5Y5.

Keywords: Hydrogen storage material; Metal hydride; Magnesium alloy; Mg; Ni; Cu; Y; Melt spinning; Nanocrystallinity; Dehydrogenation kinetics; In situ synchrotronX-ray diffraction

Involved research facilities

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Permalink: https://www.hzdr.de/publications/Publ-15845


PT symmetry and spontaneous symmetry breaking in microwave billiards

Bittner, S.; Dietz, B.; Günther, U.; Harney, H. L.; Miski-Oglu, M.; Richter, A.; Schäfer, F.

Abstract

We demonstrate the presence of parity-time (PT) symmetry for the non-Hermitian two-state Hamiltonian of a dissipative microwave billiard in the vicinity of an exceptional point (EP). The shape of the billiard depends on two parameters. The Hamiltonian is determined from the measured resonance spectrum on a fine grid in the parameter plane. On a curve, which passes through the EP, the Hamiltonian has either real or complex conjugate eigenvalues. An appropriate basis choice reveals its PT symmetry. Spontaneous symmetry breaking occurs at the EP.

Keywords: PT symmetry; microwave billiard; microwave cavity; PT phase transition; exceptional point; spontaneous symmetry breaking

Permalink: https://www.hzdr.de/publications/Publ-15844


Passive PT-symmetry breaking in open 2-channel systems

Günther, U.

Abstract

The talk consists of two parts. In the first part we demonstrate theoretically that microwave billiards can be used to experimentally study PT-symmetric two-channel setups, i.e. PT-symmetric (2×2)-matrix models. This is due to the possibility to embed PT-symmetric matrix Hamiltonians with passive PT-symmetry breaking into the general S-matrix formalism for open multi-channel systems --- with fine-tuned parameter values to ensure PT-symmetry of the effective Hamiltonians. In this way we are able to provide evidence for hidden PT-symmetric configurations in microwave experiments performed at TU Darmstadt during the last years. This means that beside the two experiments on active and passive PT-symmetry breaking on optical waveguide systems we report on a third type of experiments: passive PT-symmetry breaking in microwave cavities (microwave billiards).

In the second part of the talk, we present explicit parametrizations of generalized matrix-type P- and T-symmetry operators for 2×2 matrix Hamiltonians. These parametrizations might turn out useful for future experiments.

collaborative work with S. Bittner, B. Dietz, H.-L. Harney, M. Miski-Oglu, A. Richter and F. Schaefer

see also: arXiv:1107.4256

Keywords: PT symmetry; microwave cavity; microwave billiard; exceptional point; spontaneous symmetry breaking; PT phase transition; 2-channel system; S-matrix formalism; generalized PT symmetry; passive PT symmetry

  • Invited lecture (Conferences)
    Quantum Physics with Non-Hermitian Operators, 15.-25.06.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-15843


Application of Ex-vessel Neutron Dosimetry Combined with In-core measurements for Correction of Neutron Source Used for RPV Fluence Calculations

Borodkin, P. G.; Borodkin, G. I.; Khrennikov, N. N.; Konheiser, J.

Abstract

The paper deals with calculational and semi-analytical evaluations of VVER-1000 reactor core neutron source distributions and their influence on measurements and calculations of the integral through-vessel neutron leakage. Neutron activation measurements analyzed in the paper were carried out in ex-vessel air cavity at different NPP units with VVER-1000 during different fuel cycles. Time-integrated neutron source distributions used for DORT calculations were prepared by two different approaches based on a) calculated fuel burn-up (standard routine procedure) and b) in-core measurements by means of SPD & TC (new approach). Taking into account that fuel burn-up distributions in operating VVER may be evaluated now by analytical methods (calculations) only, it is needed to develop new approaches for testing and correction of calculational evaluations of neutron source. Results presented in this paper allow to consider a reverse task of alternative estimation of fuel burnup distributions. The approach proposed is based on adjustment (fitting) of time-integrated neutron source distributions, and hence fuel burn-up patterns in some part of reactor core, on the base of ex-core neutron leakage measurement, neutron-physical calculation and in-core SPD & TC measurement data.

Keywords: VVER-1000; DORT; TRAMO; Neutron activation measurements

  • Lecture (Conference)
    14th International Symposium on Reactor Dosimetry, May 22-27, 2011, Omni Mount Washington Resort, Bretton Woods, New Hampshire, 22.-27.05.2011, Bretton Woods, New Hampshire, USA

Permalink: https://www.hzdr.de/publications/Publ-15842


Application of Different Nuclides in Retrospective Dosimetry

Konheiser, J.; Mittag, S.; Viehrig, H.-W.

Abstract

Activities of nuclides produced by neutron irradiation of reactor-pressure-vessel (RPV) steel are used to validate respective fluence calculations. Niobium, nickel and technetium isotopes from RPV trepans of the decommissioned NPP Greifswald (VVER-440) have been analyzed. The activities were determined by TRAMO (Monte-Carlo) fluence calculations,,newly applying 640 neutron-energy groups and ENDF/B7 data. Compared to former results, up to 20% higher fluences have been computed, leading to somewhat better agreement of measurement and calculation, particularly in case of Tc-99.

Keywords: fluence calculations; Nonte-Carlo program; retrospective dosimetry; Niobium; Nickel; Technetium

  • Lecture (Conference)
    14th International Symposium on Reactor Dosimetry, 22.-27.05.2011, Bretton Woods, New Hampshire, USA

Permalink: https://www.hzdr.de/publications/Publ-15841


Stacked Ge nanocrystals with ultrathin SiO2 separation layers

Zschintzsch, M.; von Borany, J.; Jeutter, N. M.; Mücklich, A.

Abstract

The aim of this work is the tailored growth of Ge nanocrystals (NCs) in (GeOx/SiO2) multilayers (ML) for photovoltaic applications. For this purpose the fabrication of regularly stacked Ge NCs separated by ultrathin SiO2 layers is essential to enable charge carrier transport by direct tunnelling. In this paper we report on the fabrication of 50x(GeOx /SiO2) multilayer stacks via reactive dc magnetron sputtering and Ge NCs formation after subsequent annealing. It is shown that magnetron sputtering allows us to deposit very regular ML stacks with a total thickness of about 300 nm, characterized by ultrathin (down to 1 nm) and very smooth (roughness ∼ 0.6 nm) SiO2 separation layers. A main challenge is to keep these properties for a thermal budget necessary to form Ge NCs. For this reason, the temperature dependence of phase separation. Ge crystallization and ML morphology was investigated by Rutherford backscattering, x-ray scattering, Raman spectroscopy and electron microscopy. The formation of size confined Ge NCs of about 5 nm after annealing of only 550°C is confirmed. This low thermal budget ensures the suppression of GeO emanation and multilayer stability. Spectroscopic ellipsometry was applied to determine the optical Ge NC bandgap to (1.65 ± 0.5) eV.

Keywords: annealing; elemental semiconductors; germanium; germanium nanocrystals; nanofabrication; nanoparticles; growth; quantum confinement; quantum dots; multilayer; phase separation; Raman; phonon confinement, semiconductor growth; semiconductor thin films; silicon nanocrystals; sputter deposition; superlattices; transmission electron microscopy; tunnelling; X-ray scattering; spectroscopic ellipsometry

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15840


Effects of shape and size on countercurrent flow limitation in flow channels simulating a PWR hot leg

Kinoshita, I.; Murase, M.; Yoichi, U.; Lucas, D.; Vallée, C.; Tomiyama, A.

Abstract

A numerical study is presented to examine the effects on countercurrent flow limitation (CCFL) of shape and size of hot leg models with a rectangular cross section. The CCFL was described in terms of Wallis parameters using the channel height H as the characteristic length. Numerical simulations, using the CFD software code FLUENT 6.3.26, were done for the air-water CCFL experiments carried out previously at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in the 1/3 scale hot leg model with a rectangular channel (HxW = 0.25x0.05 m2), and the results were compared with the air-water CCFL data obtained at Kobe University in the 1/5 scale hot leg model with rectangular cross section (HxW = 0.15x0.01 m2) and the results of simulations. It was found that both the height-to-width ratio and the size of the cross section affected the CCFL characteristics in the Wallis diagram. Comparison of CCFL characteristics in rectangular channels with those in circular channels showed that the hydraulic diameter, Dh, was a major cross section geometry term influencing the CCFL characteristics. CCFL constants of the Wallis correlation were about 0.61 on average for the range of 0.05 m < Dh < 0.75 m but became small for Dh < 0.0254 m, and these tendencies were well reproduced by the numerical simulations.

Keywords: PWR hot leg; countercurrent gas-liquid flow; CCFL; rectangular channel; numerical simulation

Involved research facilities

  • TOPFLOW Facility

Permalink: https://www.hzdr.de/publications/Publ-15839


Correlation for Countercurrent Flow Limitation in a PWR Hot Leg

Murase, M.; Tomiyama, A.; Lucas, D.; Kinoshita, I.; Utanohara, Y.; Yanagi, C.

Abstract

Numerical simulations have been done to evaluate CCFL (countercurrent flow limitation) in a PWR hot leg under reflux condensation by using a VOF (volume of fluid) method implemented in the CFD software, FLUENT6.3.26. The calculated CCFL characteristics have been verified and agreed well with known values including the UPTF data at 1.5 MPa. Therefore, in this paper, parameter calculations using the VOF method were done for system pressures up to 8 MPa under PWR full-scale conditions with the diameter of 750 mm. As a result, calculated CCFL characteristics in the Wallis diagram were slightly mitigated from 0.1 MPa to 1.5 MPa with increasing system pressure, but they did not change from 1.5 MPa to 8 MPa. The CCFL database calculated in this study and values measured under air-water and steam-water conditions were used to derive a CCFL correlation and its uncertainty, where the CCFL constant was . Most of the CCFL data and the current correlation predictions were within the uncertainty of +-0.03.

Keywords: reflux condensation; PWR hot leg; countercurrent gas-liquid flow; CCFL; numerical simulation

Involved research facilities

  • TOPFLOW Facility

Permalink: https://www.hzdr.de/publications/Publ-15838


An analytical solution for the consideration of the effect of adjacent fuel elements

Merk, B.; Rohde, U.

Abstract

A new analytical method is described to deal with the Leakage Environmental Effect – the influence of the adjacent fuel element on the cross section preparation. The method is discussed and classified in comparison with other methods given in the literature. The new method is based on the analytical solution of the two group diffusion equation for two adjacent fuel elements. The specifics needed to create a highly efficient analytical solution are discussed. The very promising quality of the results for this highly efficient method is demonstrated on a homogeneous test case and on several heterogeneous combinations of two fuel elements described in the PWR MOX/UO2 CORE TRANSIENT BENCHMARK. One important advantage is the unproblematic extension of the solution to two-dimensional problems, since the analytical solution for each fuel element will be of the identical structure. Only the filled in data for the four fuel element quarters will vary. The coupling of the fuel elements does not affect the exponential solutions, only the constants attached to the single exponentials. Thus, the coupling will be solved in a system of linear equations.

Keywords: Analytical Solution; Homogenization; Cross Section Preparation; Leakage Assembly Environmental Effect; Diffusion Equation

Permalink: https://www.hzdr.de/publications/Publ-15837


Surface protection of titanium and titanium-aluminum alloys against environmental degradation at elevated temperatures

Yankov, R. A.; Kolitsch, A.; von Borany, J.; Mücklich, A.; Munnik, F.; Donchev, A.; Schütze, M.

Abstract

Experiments have been undertaken to explore the possibility of creating an oxygen barrier coating, which is effective in preventing oxidation and oxygen embrittlement of Ti and several low-Al content Ti-base alloys during exposure to oxidizing environments at elevated temperatures. The fabrication process has involved three steps, namely co-deposition of Ti and Al by magnetron sputtering onto a substrate material to be protected, followed by vacuum annealing and plasma immersion ion implantation of fluorine. The first two steps produce an overlay of γ-TiAl while the last step provides the necessary conditions for bringing about the halogen effect upon subsequent high-temperature oxidation. Analysis techniques such as cross-sectional transmission electron microscopy (XTEM) in conjunction with electron energy loss spectroscopy (EELS), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and elastic recoil detection (ERD) have been used to study the microstructure, phase formation and depth distribution of the elements in the coating material. Following oxidation in air at 600°C for 100 h, specimens have been prepared for metallographic analysis, and their cross sections have been characterized by scanning electron microscopy (SEM) in combination with EDX, and electron probe microanalysis (EPMA). The results obtained show that during the oxidation exposure the coating is capable of forming a protective alumina-containing scale which serves as an oxygen barrier, thereby preventing oxygen embrittlement. In addition, since the only constituents of the coating are Ti and Al, it exhibits excellent chemical substrate compatibility.

Keywords: titanium; titanium-base alloys; oxidation; protection

Involved research facilities

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Permalink: https://www.hzdr.de/publications/Publ-15836


Experiments on main steam line break in the test facilities PKL and ROCOM

Umminger, K.; Dennhardt, L.; Kliem, S.

Abstract

Non-isolable main steam line breaks in PWRs cause a rapid depressurization of the affected steam generator. This leads to increased heat transfer from the primary to the secondary side and thereby to a fast cooldown transient on the primary side. Under certain boundary conditions the reactor pressure vessel integrity considering PTS (pressurized thermal shock) and potential recriticality following entrainment of colder water into the core area are important aspects to be assessed. Complementary tests in the PKL (system behavior) and ROCOM (mixing behavior in the RPV downcomer and lower plenum) facilities have been performed on this subject. This paper summarizes the main outcome of these experiments and their use for safety analysis.

  • Contribution to proceedings
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, paper 279
  • Lecture (Conference)
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Canada

Permalink: https://www.hzdr.de/publications/Publ-15835


Population balance modelling of isothermal bubbly-cap flows using two-group averaged bubble number density apporach

Cheung, S. C. P.; Yeoh, G. H.; Tu, J. Y.; Krepper, E.; Lucas, D.

Abstract

Considerable attention has been concentrated on describing the temporal and spatial evolution of two-phase geometrical structure caused by the effects of bubble interactions in gas-liquid flows. In the published literature, the transport phenomena of dispersed bubbles in bubbly flow conditions can be regarded in a similar view of the drag and interaction of spherical bubbles, which have brought about the development of most coalescence and break-up mechanisms based primarily on the assumption of interaction between such bubbles. Nevertheless, cap bubbles which are precursors to the formation of slug units in the slug flow regime with increasing volume fraction become ever more prevalent at high gas velocity conditions. It has been shown through many experiments that interaction behaviors between non-spherical bubbles in a liquid flow are remarkably different when compared to those of spherical bubbles. It is therefore imperative additional mechanisms of bubble interactions need to be considered, particularly for cap bubbles, in addition to typical mechanisms that have been established for spherical bubbles. In this work, a two-group modeling of bubbly-cap flows via the transport equations of the average bubble number density has been considered to predict the bubble size distribution of the different bubbles co-flowing with the liquid. Based on the computational fluid dynamics (CFD) framework, a three-fluid model was solved, one set of conservation equations for the liquid phase while two sets of conservation equations for the gas phase with one being Group 1 spherical bubbles and the other depicting Group 2 cap bubbles. The drag and non-drag characteristics of the different sizes and shapes of bubbles were thus accounted via the different momentum equations representing Groups 1 and 2 bubbles. In this initial assessment, the bubble mechanistic models proposed by Hibiki and Ishii (2000) have been adopted to describe the intra-group and inter-group interactions. The numerical predictions were evaluated against the experiment data of the TOPFLOW facility for vertical, upwards, air-water flows in a large pipe diameter (Lucas et al., 2010).

Keywords: CFD; hydrodynamics; chemical reactors

Involved research facilities

  • TOPFLOW Facility
  • Contribution to proceedings
    8th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries, 21.-23.06.2011, Trondheim, Norway

Permalink: https://www.hzdr.de/publications/Publ-15834


THz physics with a free-electron laser

Helm, M.

Abstract

THz physics with a free-electron laser

Keywords: Terahertz; free-electron laser

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    THz Science and Technology - The Castle Meeting, 03.-06.07.2011, Schloss Rauischholzhausen, Deutschland, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15833


Np(V) reduction by humic acid: Contribution of reduced sulfur functionalities to the redox behavior of humic acid

Schmeide, K.; Sachs, S.; Bernhard, G.

Abstract

The role of sulfur-containing functional groups in humic acids for the Np(V) reduction in aqueous solution has been studied with the objective to specify individual processes contributing to the overall redox activity of humic substances. For this, humic acid model substances type M1-S containing different amounts of sulfur (1.9, 3.9, 6.9 wt.%) were applied. The sulfur functionalities in these humic acids are dominated by reduced-sulfur species, such as thiols, dialkylsulfides and/or disulfides. The Np(V) reduction behavior of these humic acids has been studied in comparison to that of the sulfur-free humic acid type M1 at pH 5.0, 7.0 and 9.0 under anaerobic conditions by means of batch experiments. For Np redox speciation in solution, solvent extraction and ultrafiltration were applied. In addition, redox potentials of the sample solutions were monitored. At pH 5.0, both rate and extent of Np(V) to Np(IV) reduction was found to increase with increasing sulfur content of the humic acids. At pH 7.0 and 9.0, sulfur functional groups had only a slight influence on the reduction behavior of humic acid toward Np(V). Thus, in addition to quinoid moieties and non-quinoid phenolic OH groups, generally acknowledged as main redox-active sites in humic substances, sulfur functional groups have been identified as further redox-active moieties of humic substances being active especially in the slightly acidic pH range as shown for Np(V). Due to the low sulfur content of up to 2 wt.% in natural humic substances, their contribution to the total reducing capacity is smaller than that of the other redox-active functional groups.

Keywords: Neptunium; Tetravalent; Humic acid; Redox-active groups; Sulfur functional groups

Permalink: https://www.hzdr.de/publications/Publ-15832


Sorption and diffusion of U(VI) in the system Opalinus Clay/pore water in the absence and presence of organic ligands

Schmeide, K.; Joseph, C.; Bernhard, G.

Abstract

Argillaceous rock is investigated as potential host rock and backfill material for nuclear waste repositories. For safety assessment, knowledge on the migration behavior of potentially released actinides in this environment is required. Since clay rock contains natural organic matter, we studied the influence of various organic ligands on the sorption of U(VI) (1•10-6 M) onto the clay rock Opalinus Clay (Mont Terri, Switzerland) under aerobic conditions applying synthetic Opalinus Clay pore water (I = 0.36 M, pH 7.6 [2]) as background electrolyte at 25°C. It was found that the low U(VI) sorption onto Opalinus Clay in the absence of ligands (Kd = (0.0222 ± 0.0004) m3/kg [1]) further decreases with increasing concentration of low molecular weight organic acids (1•10-5 to 1•10-2 M) due to complex formation in aqueous solution. The mobilizing effect of the organic ligands on U(VI) increases in the following sequence: formate < lactate ~ acetate ~ propionate < tartrate < citrate. For instance, in the presence of citrate (1•10-2 M), which has been identified as important ligand in radioactive waste problems, the Kd value for U(VI) amounts to only (0.0011 ± 0.0003) m3/kg. The influence of the organic ligands on the U(VI) sorption onto Opalinus Clay correlates with the stability of the respective U(VI) complexes. In contrast, humic acid (50 mg/L) does not change U(VI) sorption.
The diffusion of U(VI) (1•10-6 M) in intact Opalinus Clay bore core samples was studied under anaerobic conditions in the absence and presence of humic acid (10 mg/L) at 25°C. From the U(VI) and humic acid diffusion profiles, obtained after three months of diffusion time, diffusion and distribution coefficients were determined using the modeling software COMSOL Multiphysics 3.3 [3]. The Kd value of the U(VI) sorption onto Opalinus Clay could be confirmed by the results of diffusion experiments. Humic acid does not have a significant influence on U(VI) diffusion in Opalinus Clay.
[1] Joseph, C., Schmeide, K., Sachs, S., Brendler, V., Geipel, G., Bernhard, G.: Sorption of uranium(VI) onto Opalinus Clay in the absence and presence of humic acid in Opalinus Clay pore water. Chem. Geology 284, 240-250 (2011).
[2] Pearson, F.J.: Opalinus Clay experimental water: A1Type, Version 980318, PSI Internal Report TM-44-98-07. Paul Scherrer Institut, Villigen, Switzerland (1998).
[3] Finite-element software package. http://www.comsol.com.

Keywords: Uranium; sorption; diffusion; citric acid; lactic acid; humate; opalinus

  • Poster
    NEA ClayClub Workshop - Clays under Nano- to Microscopic Resolution, 06.-08.09.2011, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-15831


Leitlinie für PET und SPECT–Untersuchungen von Hirntumoren mit radioaktiv markierten Aminosäuren

Langen, K.-J.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Drzezga, A.; Grünwald, F.; Krause, B. J.; Kuwert, T.; Sabri, O.; Tatsch, K.; Weber, W. A.; Schreckenberger, M.

Abstract

Diese Leitlinie fasst die Ansichten der Arbeitsgemeinschaft Neuronuklearmedizin der Deutschen Gesellschaft für Nuklearmedizin zusammen. Das Ziel dieser Leitlinie ist es, den Arzt bei der Indikationsstellung, der Durchführung, der Interpretation und der Dokumentation der Ergebnisse einer PET oder SPECT Untersuchung mit radioaktiv markierten Aminosäuren bei Patienten mit zerebralen Gliomen zu unterstützen. Damit soll ein hoher Qualitätsstandard bei der Durchführung dieser Untersuchung erreicht werden, welcher die diagnostische Relevanz dieser Methode in der praktischen Anwendung erhöht.

Permalink: https://www.hzdr.de/publications/Publ-15830


Evaluation of an autonomous sensor swarm for fermentation reactor applications

Reinecke, S.; Schubert, M.; Kryk, H.; Hampel, U.

Abstract

Advanced monitoring of the spatio-temporal distribution of process parameters in large scale vessels and containers such as storage tanks as well as stirred chemical or bioreactors offers a high potential for enhanced investigation and further optimization of plants and embedded processes. This pertains especially to fermentation biogas reactors, where a number of process parameters, such as the temperature profile, distribution of pH, gas-liquid fraction in the substrates as well as flow characteristics, such as velocity profiles, dead zone locations and short-circuits of liquids, are of interest to engineers and operators. Autonomous sensor concepts enable the metrological acquisition of spatially distributed parameters by means of intelligent instrumented flow followers.
We developed and tested the concept of an autonomous sensor swarm that can be introduced into a process vessel to track the long-term spatial distribution of process parameters [1]. The prototype swarm comprises of robust and neutrally buoyant capsules (diameter 42 mm) each equipped with a measurement electronics that autonomously measures and records the output from miniaturized onboard sensors for temperature (0 to 70°C), pressure (0 to 200 kPa with immersion depth in the range of 0 to 10 m) and 3D-acceleration (±6g).
The performance of the sensor capsules were firstly evaluated in a fermentation reactor environment . A swarm of seven capsules was deployed in a 1000 L vessel of a stirred model fermenter. A highly viscous aqueous solution of straw was used with a dry mass concentration of about 5.5%, density 950 kg*m-3, viscosity 250 mPa*s at a shear rate of 10 s-1 and constant ambient temperature T = 19°C. The central three-blade impeller stirrer with a diameter of 0.324 m was adjusted at a rotation speed of 4.4 s-1. Thus, the capsules faced a maximum rotational speed of 4.5 m*s-1. After one hour of operation, the impeller was shifted from 200 mm above vessel ground to 324 mm along the mixer’s shaft to simulate varying mixing conditions. The sensor swarm was recovered after two hours of residence in the process environment.
All acquired data from the seven capsules were analyzed and they properly represent the conditions in the vessel. Temporal evolution of the vertical flow component can be observed from the capsule’s immersion depth which is calculated from the measured pressure. As mentioned above, the process temperature was kept constant at 19°C which was captured by the swarm correctly. However, also vertical temperature profiles may be extracted using the measured immersion depth, which was not reasonable under these isothermal conditions. Additional information about the fluid dynamics, the mixing behaviour and the distribution of dead zones are obtained from the recorded acceleration data. Changes in the setup such as the modification of the vertical impeller position are also reflected in the data.

  • Lecture (Conference)
    1st European Congress of Applied Biotechnology, 26.-29.09.2011, Berlin, Germany
  • Open Access Logo Contribution to proceedings
    1st European Congress of Applied Biotechnology, 26.-29.09.2011, Berlin, Germany, 25.-29.09.2011, Berlin, Deutschland
    8th European Congress of Chemical Engineering/1st European Congress of Applied Biotechnology

Permalink: https://www.hzdr.de/publications/Publ-15829


Design of a modular signal processing board (MSPB) for gamma-ray imaging applications

Bieberle, A.; Berger, R.; Yadav, R.; Schleicher, E.; Hampel, U.

Abstract

In this paper a new modular signal processing board (MSPB) for high-resolution gamma-ray computed tomography (GCT) is presented. The MSPB is optimised for parallel signal processing of eight detector channels operating in pulse counting mode. Signal processing stages comprise of variable gain amplifiers, pulse height discrimination stages, 13-bit counters with corresponding latches as well as logic circuitry for coordinated data transfer with a multitude of MSPBs. The digital signal processing units are realised in commercially available complex programmable logic devices (CPLD). Each MSPB is addressable by an 8-bit DIP-switch which allows the use of up to 256 modules or 2048 detector pixels within one detector system. The geometry of the MSPB allows a multiple and seamless detector module arrangement which eases the adaptation of a given gamma-ray detector system to specific industrial and laboratory applications. The choice of the electronic devices and the thermal design was optimised for low power consumption in order to minimise internal heat production, which would affect the characteristics of the detector’s intrinsic gain strongly. Thermal measurements have been executed to prove the functionality of the thermal design.

Keywords: modular gamma radiation detector; pulse signal processing

Permalink: https://www.hzdr.de/publications/Publ-15828


Application of the ultrasound Doppler method for flow measurements in LBE alloys

Eckert, S.; Gerbeth, G.

Abstract

Design and optimisation of the thermal hydraulics of liquid metal reactor systems is strongly based on numerical simulations of the related fluid flow and heat & mass transfer processes. Whereas these numerical simulations are essentially based on local flow phenomena (small-scale vortices, turbulence or sub-grid scale modeling), experimental results are often limited to integral flow rates or local related data like temperature or pressure. Local velocity measurements would be highly desirable but are mostly lacking due to the very limited possibilities for velocity measurements in liquid metals.
During the last decades the Ultrasound Doppler Velocimetry (UDV) became a very powerful tool to measure the velocity structure of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it becomes very attractive for liquid metal applications. In addition, it can principally operate through the channel wall though a direct contact to the melt reduces ultrasonic losses. However, in case of hot metallic melts the user is confronted with a number of specific problems: First of all, the application of the ultrasonic transducers is usually restricted to maximum temperatures of 150°C. The transmission of a sufficient amount of ultrasonic energy from the transducer to the fluid has to be guaranteed. Here, the acoustic coupling and the wetting conditions have to be considered as important issues. Moreover, the flow has to be seeded with reflecting particles to obtain Doppler signals from the fluid.

Keywords: flow measurements; ultrasound Doppler velocimetry; LBE alloys; accelerator-driven systems (ADS)

  • Invited lecture (Conferences)
    KTH seminar on "Thermohydraulics in energy production", 13.07.2011, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-15827


Off-shell transport of broad resonances and dilepton production at SIS energies

Wolf, G.; Kämpfer, B.; Zétényi, M.

Abstract

The time evolution of vector meson spectral functions is studied within a Boltzmann-Uehling-Uhlenbeck (BUU) type transport model. Applications focus on ρ and ω mesons being important pieces for the interpretation of the dielectron invariant mass spectrum. Since the evolution of the spectral functions is driven by the local density, the in-medium modifications turn out to compete, in this approach, with the known vacuum contributions.

Permalink: https://www.hzdr.de/publications/Publ-15826


Determination of Ni Release in NiTi SMA with Surface Modification by Nitrogen Plasma Immersion Ion Implantation

de Camargo, E. N.; Lobo, A. O.; Da Silva, M. M.; Ueda, M.; Garcia, E. E.; Pichon, L.; Reuther, H.; Otubo, J.

Abstract

NiTi SMA is a promising material in the biomedical area due to its mechanical properties and biocompatibility. However, the nickel in the alloy may cause allergic and toxic reactions and thus limiting its applications. It was evaluated the influence of surface modification in NiTi SMA by nitrogen plasma immersion ion implantation (varying temperatures, and exposure time as follows: <250°C/2 h, 290 °C/ 2 h, and 560 °C/1 h) in the amount of nickel released using immersion test in simulated body fluid. The depth of the nitrogen implanted layer increased as the implantation temperature increased resulting in the decrease of nickel release. The sample implanted in high implantation temperature presented 35% of nickel release reduction compared to reference sample.

Permalink: https://www.hzdr.de/publications/Publ-15825


Impact of the System Matrix Modeling Complexity on Reconstruction Quality in Compton Camera Imaging

Schöne, S.; Kormoll, T.; Shakirin, G.; Enghardt, W.; Fiedler, F.

Abstract

The impact of the degree of complexity of system matrix modeling in in-vivo dose monitoring of ion radiation was investigated.
The effect of different complexity levels on time performance and the reconstruction quality is shown.

Keywords: image reconstruction; Compton camera; dose monitoring; ion beam therapy; SPECT; image quality

  • Poster
    11th International Meeting on Fully Three-Dimensional Image Reconstruction in Radiology and Nuclear Medicine, 11.-15.07.2011, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15824


Dynamics of Interlayer Coupled Magnetic Vortex Pairs

Wintz, S.; Bunce, C.; Körner, M.; Strache, T.; Raabe, J.; Quitmann, C.; McCord, J.; Erbe, A.; Fassbender, J.

Abstract

A magnetic vortex structure consists of a planar magnetization curl with a perpendicularly magnetized nanoscopic core in its center. As a consequence of the different combinations possible for the curl’s rotation sense (circulation: c ∈ {+1,-1}) and the orientation the core (polarity: p ∈ {+1,-1}), magnetic vortices occur with opposite handednesses. When excited by magnetic fields or spin polarized currents, magnetic vortices exhibit different kinds of eigen modes of which the gyrotropic core mode is most prominent. It corresponds to an orbiting of the core around its equilibrium position, where the sense of motion is determined by p as a topological charge only[1,2]. The static and dynamic properties of single layer vortices have been the subject of numerous fundamental investigations during the past decades[e.g.1,2,3], which also led to the proposal of their application for memory devices[4] and spin-torque oscillators[5].
On the technological context as well as from a basic perspective, the coupling between spatially confined vortices is a key issue. Here we report on the magnetization dynamics of coupled vortex pairs, separated by a nonmagnetic spacer in a stacked geometry. Besides magnetodipolar interaction, interlayer exchange coupling (IEC) can be present in such a system, depending on the spacer material and thickness. We have experimentally identified two nongenerate configurations for both, IEC and purely dipolar coupled vortex pairs regarding their relative circulation orientations by means of scanning transmission x-ray microscopy (STXM)[6]. Time-resolved STXM furthermore allows to probe the layer-specific response of coupled vortex pairs to magnetic excitations. By this, we have observed a principally different core gyration behavior for the different circulation configurations. Also, a collective reorientation of the core polarities has been detected for sufficiently strong excitations.

Keywords: vortex coupling; magnetization dynamics; x-ray microscopy

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  • Poster
    56th Annual Conference on Magnetism & Magnetic Materials, 30.10.-03.11.2011, Scottsdale, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-15823


Radiolabelling of nanoparticles for life-cycle studies

Franke, K.; Gottschalch, U.; Hildebrand, H.

Abstract

An increasing number of products containing engineered nanoparticles (NP) raises the question of potential impacts of the applied NP on the environment. During production, application and final disposal, NP-containing products undergo multiple physical (e.g. abrasion) and chemical (e.g. weathering) processes, that potentially influence and alter the availability and mobility of NP. Crucial factors for the fate of NP in the environment are the degree of particle release from materials as well as the degradability/modification and transport behavior. The investigation of these processes requires experimental tools for extremely sensitive particle tracking.
Radiolabelling of NP enables a highly sensitive detection in on-line and in-situ experiments and allows to distinguish sub-processes within complex interactions. It is essential for the application of radiolabelled NP in experimental studies that the radiolabelling process does not alter particle properties and that the radioactive labelling remains stable within the chemical milieu of the experimental setup. Therefore, the introduction of radionuclides during the NP-synthesis might be the most appropriate radiolabelling method. However, in some cases the investigation of commercially available NP is required to represent the original properties of the materials used in industrial products.
This study presents a method for the radiolabelling of Ag0-NP and TiO2-NP. The radiolabelling was done with 110mAg and 44Ti/45Ti, respectively. Labelling yields, stability tests and comparative NP-characterization are presented.

  • Poster
    3rd - International Nuclear Chemistry Congress, 18.-23.09.2011, Terrasini - Palermo, Italien

Permalink: https://www.hzdr.de/publications/Publ-15822


Erprobung von Messtechnik zur Untersuchung und Optimierung strömungsmechanischer und holztechnologischer Abläufe in Refinern

Bieberle, A.; Cartland-Glover, G.

Abstract

Die Produktion von Holzfasern beinhaltet eine Vielzahl physikalisch-technologischer Prozesse, deren Komplexität vom Holzplatz bis zur Zerfaserung deutlich zunimmt. Da die Wirkungsweise und physikalische Zusammenhänge der Zerfaserung im Refiner zum gegenwärtigen Zeitpunkt nur in geringem Maße beschrieben werden können, kann eine Prozesseinstellung zur definierten und reproduzierbaren Faserqualität nicht durchgeführt werden. Vorhandenes Wissen beruht auf Erfahrungen und empirisch gefundenen Zusammenhängen, nicht aber auf wissenschaftlich fundierten Erkenntnissen. Deshalb soll mit Hilfe verschiedenster Messtechniken versucht werden, Informationen zum Prozess des Faserstofftransportes im Refiner zu erhalten, die anschließend zur Validierung eines CFD Modell des Laborrefiners genutzt werden können. Später sollen – so weit vorhanden – energiebezogene Schwachstellen im CFD Modell des Refiners erkannt und reduziert werden, so dass ein neues energieoptimiertes Refinergehäuse entwickelt werden kann.

Keywords: Gamma-CT; Leifähigkeitsmesstechnik; Holzrefiner

  • Other report
    Dresden: HZDR, 2011
    70 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15821


Gamma-induced positron spectroscopy at a superconducting linear accelerator

Wagner, A.; Anwand, W.; Butterling, M.; Cowan, T.; Jungmann, M.; Krause-Rehberg, R.

Abstract

A new and unique setup for Positron Annihilation Spectroscopy has been established at a superconducting linear electron accelerator at Helmholtz-Zentrum Dresden-Rossendorf (Germany). The accelerator runs in continuous wave mode with variable bunch repetition rates up to 26 MHz delivering pulsed bremsstrahlung with energies up to 16 MeV. After collimation the photon beam impinges onto the sample where positrons are generated by means of pair production throughout the entire volume. Short gamma bunches below 5 ps duration allow for positron lifetime spectroscopy using the accelerator’s radiofrequency as time reference. Positron lifetime and Doppler broadening Spectroscopy are employed by a coincident measurement (Age-Momentum Correlation) of the time-of-arrival and energy of annihilation photons which in turn significantly reduces the background of scattered photons resulting in spectra with high signal to background ratios. Monte-Carlo simulations of the entire setup using the GEANT4 framework have been performed in order to yield optimum positron generation rates for various sample materials and improve background conditions.
The production of positrons inside the sample allows for experiments using bulk samples, gases, fluids, and even samples with high intrinsic radioactivity which would be hampered by accidental coincidences in source-based lifetime spectroscopy systems. Positron lifetime spectroscopy results will be presented for water, lead, activated reactor steel, and biological samples, as well.

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  • Lecture (Conference)
    Workshop Ionen- und Positronenstrahlen, 04.-05.07.2011, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15820


Ion beam assisted deposition of C:Ni composites: Growth of regular nanostructures by surface-layer-limited phase separation

Abrasonis, G.; Krause, M.; Mücklich, A.; Heller, R.; Heinig, K. H.; Gemming, S.; Möller, W.

Abstract

Nanostructures influence materials properties dramatically due to size, shape and interface effects. Thus the control over the structure at the nanoscale is a key issue in nanomaterials science. The interaction of hyperthermal ions with solids is confined to some nanometers. It can be used to control the morphology evolution during multiphase film deposition. Ion induced displacements occur in a thin surface layer of the growing film where they increase the atomic mobility for the phase separation. Here the growth-structure relationship of C:Ni (~15 at.%) nanocomposite films grown by oblique incidence (~45°) ion beam assisted deposition is reported. This nanocomposite is relevant in the context of sensing, fusion, electrochemistry, tribology, information storage and spintronics. The influences of the flux of an assisting Ar+ ion beam (0-140 eV) as well as of an elevated substrate temperature have been studied. The formation of elongated nickel nanoparticles is strongly promoted by the ion beam assistance. Moreover, the metal nanocolumns no longer align with the advancing surface, as in the case without ion assistance, but with the incoming ions. Furthermore, a window of conditions is established where the ion assistance leads to the formation of regular composition modulations with a well defined periodicity and tilt. As the dominating driving force for the pattern formation is of physical origin, this approach might be applicable to other immiscible systems.

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  • Lecture (Conference)
    EMRS Spring Meeting 2011, 09.-13.05.2011, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-15819


Ion-assisted growth of carbon-transition metal nanocomposite thin films: from self-organization to spin-dependent transport

Abrasonis, G.; Krause, M.; Oates, T. W. H.; Kovacs, G. J.; Mücklich, A.; Persson, P. O. A.; Heinig, K. H.; Tucker, M. D.; Bilek, M. M. M.; Möller, W.

Abstract

Morphology control, especially at the nanoscale, is of primary importance in the field of thin film materials. Our results on energetic-ion-assisted growth of carbon-transition metal nanocomposite thin films are reported here. The films were grown by ion beam assisted deposition (IBAD) and ionized physical vapour deposition (iPVD) using a pulsed filtered cathodic vacuum arc (PFCVA). The two methods differ in the way the ion energy is transferred into the near surface layers: for IBAD the bombarding Ar+ ions transfer the energy via collisions to the near-surface layers of nanocomposite films while for PFCVA the energetic species are themselves the film forming material. The influence of the metal type, metal-to-carbon ratio, ion energy and ion incidence angle on the morphology has been studied.

During growth under energetic bombardment at low temperatures, atomic displacements are caused solely by impacting energetic ions, resulting in phase separation in an advancing surface layer. If the metal amount surpasses a critical value, this layer switches to an oscillatory mode, and a nanoscale precipitation pattern emerges. For iPVD, the ion induced atomic mobility is not isotropic, as it would be in the case of thermally excited migration, but conserves to a large extent the initial direction of the incoming ions, resulting in a tilting of the periodic precipitation structures for oblique ion incidences. The metal nanopatterns no longer align with the advancing surface, but with the incoming ions. The experimental observations are consistent with metal (recoil) ion sub-plantation into light carbon as the key atomistic mechanism. As the dominating driving force for the pattern formation is of neither thermal nor chemical origin, we believe that the presented results are applicable to other immiscible or partially miscible systems as well. Applications of these nanopatterns for sensing and spin manipulation are discussed.

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  • Invited lecture (Conferences)
    2011 MRS Spring Meeting, 25.-29.04.2011, San Francisco, California, United States of America

Permalink: https://www.hzdr.de/publications/Publ-15818


A novel 3D Model of the human Cannabinoid receptor 2 in its active state helps to develop new radiotracers for positron emission tomography (PET)

Günther, R.; Deuther-Conrad, W.; Fischer, S.; Rühl, T.; Steinbach, J.; Brust, P.

Abstract

PET is a method, which provides images of functional processes in living humans. Thus, there is a strong need for highly selective positron emitting radiotracers. In order to develop such compounds for imaging of human cannabinoid receptors type 2 (hCB2) we constructed a 3 dimensional model of the human cannabinoid receptor in its active state based on the recently published X-ray structure 3qak (Xu et al., Science 2011;332:322-327) of the human adenosine receptor A2a (hAA2R). The model served as a guide for the rational design of hCB2-selective N-aryl oxadiazoles, which were synthetized, tested for their receptor affinity and evaluated concerning a suitable site for labeling with 18F, the most preferred PET radionuclide.

Methods: The sequence of the hCB2 receptor was aligned to that of hAA2R by multiple sequence alignment. 10 models of hCB2 were constructed based on structure 3qak using the MOE software package (Molecular Operating Environment, CGC Inc., Montreal). The best model was simulated in a solvated lipid bilayer for 15 ns using the Amber03 force field as implemented in the software package Yasara (Yasara Biosciences GmbH, Wien). The N-aryl oxadiazoles were synthesized in a two-step approach. Hydroxylamine hydrochlorides and benzonitriles reacted for 24 h at 80 °C under diffuse light. After drying the intermediate, addition of succinic acid anhydrides at room temperature under diffuse light yielded the final products. Ki values of the compounds were determined in competitive radioligand displacement studies on hCB1- and hCB2-CHO cell homogenates in the presence of [3H]CP55940.

Results: 1) The 3D model of hCB2 is in good agreement with experimental data and
2) remains in its conformation during a 15 ns MD simulation. 3) The synthesized N-aryl oxadiazoles bind selectively on hCB2 receptors with a ratio of Ki(CB1):Ki(CB2) of up to 10,000. 4) Based on molecular docking studies, the compounds most likely bind with their N-aryl-moiety (R) inside the proposed binding pocket indicating, that 5) introduction of 18F on the ring system at position 3 of the oxadiazole is most promising.

Conclusions: Our model of the hCB2-receptor provides insights into binding of ligands and allows improvement and design of hCB2-selective ligands by means of rational design. N-aryl oxadiazoles can serve as scaffolds for the synthesis of selective hCB2 PET radioligands.
Acknowledgment: This work was supported by DFG (Br 1360/12-1).

  • Poster
    Cannabinoid conference 2011, 08.-10.09.2011, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15817


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