Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
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.;
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

Publ.-Id: 15860 - Permalink


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.;
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

Publ.-Id: 15859 - Permalink


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.;
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

Publ.-Id: 15858 - Permalink


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)
Konferenz-Proceedings ohne Abstract
  • Book (Editorship)
    Amsterdam: Elsevier BV, 2011
    610 Seiten

Publ.-Id: 15856 - Permalink


Spatially resolved Langmuir probe measurements of a magnetically enhanced hollow cathode arc plasma
Zimmermann, B.; Fietzke, F.; Möller, W.;
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

Publ.-Id: 15855 - Permalink


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

Publ.-Id: 15854 - Permalink


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.;
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

Publ.-Id: 15853 - Permalink


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.;
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

Publ.-Id: 15852 - Permalink


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.;
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

Publ.-Id: 15851 - Permalink


ROCOM experiments on boron dilution conducted within the NRG/EdF Project – Scenario 1
Kliem, S.; Franz, R.;
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

Publ.-Id: 15850 - Permalink


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.;
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

Publ.-Id: 15849 - Permalink


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.;
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

Publ.-Id: 15848 - Permalink


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.;
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

Publ.-Id: 15847 - Permalink


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.;
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

Publ.-Id: 15846 - Permalink


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.;
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

Publ.-Id: 15845 - Permalink


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.;
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

Publ.-Id: 15844 - Permalink


Passive PT-symmetry breaking in open 2-channel systems
Günther, U.;
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

Publ.-Id: 15843 - Permalink


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.;
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

Publ.-Id: 15842 - Permalink


Application of Different Nuclides in Retrospective Dosimetry
Konheiser, J.; Mittag, S.; Viehrig, H.-W.;
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

Publ.-Id: 15841 - Permalink


Stacked Ge nanocrystals with ultrathin SiO2 separation layers
Zschintzsch, M.; von Borany, J.; Jeutter, N. M.; Mücklich, A.;
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

Publ.-Id: 15840 - Permalink


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.;
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

Publ.-Id: 15839 - Permalink


Correlation for Countercurrent Flow Limitation in a PWR Hot Leg
Murase, M.; Tomiyama, A.; Lucas, D.; Kinoshita, I.; Utanohara, Y.; Yanagi, C.;
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

Publ.-Id: 15838 - Permalink


An analytical solution for the consideration of the effect of adjacent fuel elements
Merk, B.; Rohde, U.;
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

Publ.-Id: 15837 - Permalink


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.;
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

Publ.-Id: 15836 - Permalink


Experiments on main steam line break in the test facilities PKL and ROCOM
Umminger, K.; Dennhardt, L.; Kliem, S.;
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

Publ.-Id: 15835 - Permalink


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

Publ.-Id: 15834 - Permalink


THz physics with a free-electron laser
Helm, M.;
THz physics with a free-electron laser
Keywords: Terahertz, free-electron laser
  • Invited lecture (Conferences)
    THz Science and Technology - The Castle Meeting, 03.-06.07.2011, Schloss Rauischholzhausen, Deutschland, Deutschland

Publ.-Id: 15833 - Permalink


Np(V) reduction by humic acid: Contribution of reduced sulfur functionalities to the redox behavior of humic acid
Schmeide, K.; Sachs, S.; Bernhard, G.;
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

Publ.-Id: 15832 - Permalink


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.;
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

Publ.-Id: 15831 - Permalink


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.;
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.

Publ.-Id: 15830 - Permalink


Evaluation of an autonomous sensor swarm for fermentation reactor applications
Reinecke, S.; Schubert, M.; Kryk, H.; Hampel, U.;
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 LogoContribution 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

Publ.-Id: 15829 - Permalink


Design of a modular signal processing board (MSPB) for gamma-ray imaging applications
Bieberle, A.; Berger, R.; Yadav, R.; Schleicher, E.; Hampel, U.;
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

Publ.-Id: 15828 - Permalink


Application of the ultrasound Doppler method for flow measurements in LBE alloys
Eckert, S.; Gerbeth, G.;
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

Publ.-Id: 15827 - Permalink


Off-shell transport of broad resonances and dilepton production at SIS energies
Wolf, G.; Kämpfer, B.; Zétényi, M.;
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.

Publ.-Id: 15826 - Permalink


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.;
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.

Publ.-Id: 15825 - Permalink


Impact of the System Matrix Modeling Complexity on Reconstruction Quality in Compton Camera Imaging
Schöne, S.; Kormoll, T.; Shakirin, G.; Enghardt, W.; Fiedler, F.;
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

Publ.-Id: 15824 - Permalink


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

Publ.-Id: 15823 - Permalink


Radiolabelling of nanoparticles for life-cycle studies
Franke, K.; Gottschalch, U.; Hildebrand, H.;
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

Publ.-Id: 15822 - Permalink


Erprobung von Messtechnik zur Untersuchung und Optimierung strömungsmechanischer und holztechnologischer Abläufe in Refinern
Bieberle, A.; Cartland-Glover, G.;
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

Publ.-Id: 15821 - Permalink


Gamma-induced positron spectroscopy at a superconducting linear accelerator
Wagner, A.; Anwand, W.; Butterling, M.; Cowan, T. E.; Jungmann, M.; Krause-Rehberg, R.;
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.
Keywords: Positron Annihilation Spectroscopy superconducting linear electron accelerator pulsed bremsstrahlung pair production Age-Momentum Correlation
  • Lecture (Conference)
    Workshop Ionen- und Positronenstrahlen, 04.-05.07.2011, München, Deutschland

Publ.-Id: 15820 - Permalink


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

Publ.-Id: 15819 - Permalink


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

Publ.-Id: 15818 - Permalink


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.;
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

Publ.-Id: 15817 - Permalink


Biodistribution and radiation dosimetry of (-)-F18-NCFHEB, a new tracer for imaging of cerebral alpha4beta2 nicotinic acetylcholine receptors (nAChRs) with PET
Sattler, B.; Wilke, S.; Starke, A.; Habermann, B.; Schildan, A.; Patt, M.; Smits, R.; Hoepping, A.; Graef, S.; Schoenknecht, P.; Hegerl, U.; Fischer, S.; Brust, P.; Steinbach, J.; Sabri, O.;
Objectives: (-)-[F-18]Norchloro-fluoro-homoepibatidine ((-)-NCFHEB) is a new tracer for neuroimaging of alpha4beta2 nAChRs with PET. To assess the putative radiation risk after application of the radioligand, the biodistribution, organ doses (OD) and the effective dose (ED) were determined in a phase 0/1 trial.
Methods: Whole body dosimetry of (-)-NCFHEB was performed in 3 healthy volunteers (59.6±3.9a; weight 74.3±3.1kg; 2m, 1f). The subjects were sequentially PET/CT-imaged up to 7h post i.v. injection of 353.7±10.2 MBq of(-)-NCFHEB on a SIEMENS Biograph16 PET/CT-system with 9 bed positions (BP) per frame, 1.5-6min/BP, CT-attenuation correction (AC) and iterative reconstruction (OSEM, 4 iterations, 8 subsets). All micturated urine was collected up to 7 hours post injection. Urine samples were weighed and measured for radioactivity concentration [Bq/ccm] in a well counter. All relevant organs were defined by volumes of interest using the structural information from the AC-CT. Exponential curves were fitted to the time-activity-data. The ODs were calculated using the adult male model with OLINDA. The ED was calculated using tissue weighing factors as published in the ICRP 103/2007.
Results: The fraction of radioactivity that was eliminated via urine was 22.2±1.2%. The highest OD was received by the urinary bladder (80.2±37.8), followed by the liver (44.7±5.4) and the kidneys (38.6±5.1). The highest contribution to the ED was by the lungs (3.7±0.6), the urinary bladder (3.2±1.5) and the stomach (2.9±0.7). The ED by i.v. application of (-)-NCFHEB is 22.6±0.7 (all in [μSv/MBq]).
Conclusion: The ED after i.v. application of 370 MBq (-)-NCFHEB is 8.3 mSv. This is well in accordance to values obtained with other [F-18]-labeled compounds. These favorable dosimetry data prove the tolerability of the radiation risk caused by the tracer and encourage the further development of (-)-NCFHEB as a clinical tool for imaging of alpha4beta2 nAChRs with PET.
References: The trial is granted by the German Federal Ministry of Education and Research (Nr. 01EZ0820)
  • Lecture (Conference)
    EANM'11 Annual Congress of the European Association of Nuclear Medicine, 15.-19.10.2011, Birmingham, United Kingdom
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 38(2011), S148

Publ.-Id: 15816 - Permalink


First in man study with the new radioligand (-)-[18F]-norchloro-fluoro-homoepibatidine (NCFHEB) to image alpha4beta2 cerebral nicotinic acetylcholine receptors (nAChRs) in early Alzheimer’s disease (AD) with PET
Sabri, O.; Wilke, S.; Gräf, S.; Lengler, U.; Gertz, H.-J.; Schönknecht, P.; Habermann, B.; Becker, G.; Luthardt, J.; Patt, M.; Kendziorra, K.; Meyer, P.; Hesse, S.; Barthel, H.; Wagenknecht, G.; Höpping, A.; Hegerl, U.; Brust, P.;
Using 2-[18F]F-A85380 (2FA) PET we recently demonstrated significant cerebral nAChR declines in early AD which correlated significantly with the loss of cognitive function [1]. However, 2FA is not well suited in routine use because of slow kinetics, acquisition times up to 7 hours, and limited nAChR selectivity. Thus, we developed the new tracer NCFHEB [2] and report here on the worldwide first human NCFHEB-PET results.

6 mild AD patients (NINCDS-ADRDA, age 76.7±5.9, MMSE 23.8±3.0) and 5 age-matched healthy controls (HCs, MMSE 28.4±1.1), all nonsmokers and naïve for central acting medication, underwent NCFHEB-PET (370 MBq, 3D-acquisition, ECAT Exact HR+). Dynamic 0-270min p.i. scans were acquired and corrected for motion (SPM2). Kinetic modeling was applied to 29 brain VOI-based tissue-activity curves (VOIs defined on individual MRI) using a one-tissue compartment model with measured arterial input function. Total distribution volume (DV) and binding potential (BP, reference region: corpus callosum) were used to characterize specific binding.

Image quality of NCFHEB scans was clearly superior to 2FA, and a 20 minutes scan already adequate for visual analysis. All 29 regions were well described with one-tissue compartment. PET data acquired over only 90 minutes were sufficient to estimate all kinetic parameters precisely indicating a fast receptor binding kinetic (much faster than for 2FA). DVs in HCs increase as expected with receptor density: Corpus callosum (DV: 4.81±0.32), posterior cingulate (8.92±0.66), temporal (9.03±0.44), pons (11.00±1.19), thalamus (24.32±2.96). The AD patients showed extensive BP reductions in frontal, parietal, temporal, anterior and posterior cingulate cortices, caudate, and hippocampus (all p<0.05) compared to HCs.

Due to the significant shorter acquisition time and superior image quality NCFHEB appears to be a much more valuable tracer than 2FA to image nAChRs in humans. Early AD patients show significant declines of nAChRs in brain regions typically affected by AD pathology. These results indicate that NCFHEB-PET has a great potential as a biomarker for early AD diagnosis.

References:
1. Kendziorra et al., Eur J Nucl Med Mol Imaging 2010
2. Brust et al., Synapse 2008

This trial is granted by the German Federal Ministry of Education and Research (Nr. 01EZ0820)
  • Lecture (Conference)
    EANM'11 Annual Congress of the European Association of Nuclear Medicine, 15.-19.10.2011, Birmingham, United Kingdom
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 38(2011), S122-S123

Publ.-Id: 15815 - Permalink


Turbulence measurements in a rotating magnetic field driven flow
Cramer, A.; Pal, J.; Gerbeth, G.;
Four-wire electric potential difference probes are used to record timeseries of two local velocity components in a flow driven by a rotating magnetic field. It is demonstrated that statistical properties of turbulence in an electromagnetically driven flow can be extracted from the signals, although they are predominated by noise, disturbances mainly owing to the operation of switching power supplies in modern installations, and filter characteristics of the data acquisition system. For three physical systems, which are two experimental cells with significantly different sizes filled with different melts and two magnetic systems, it is shown that the micro Eulerian scale exhibits a power law dependence on the mean flow velocity over a range of the dimensionless driving force, the Taylor number, of more than three orders of magnitude. In terms of Reynolds numbers, this range starts in the transitional regime slightly above the threshold of instability and spreads two orders of magnitude. It is examined whether the flow with the highest velocities might be called a developed turbulent regime. Energy spectra are calculated from the timeseries and are discussed in the framework of existing theory.
Keywords: turbulence measurement, electric potential difference probe, rotating magnetic field, magnetohydrodynamics

Publ.-Id: 15814 - Permalink


Zur Aufnahme und Bindung von U(VI) durch die Grünalge Chlorella vulgaris
Vogel, M.;
Uran kann sowohl durch geogene als auch anthropogene Vorgänge in die Umwelt gelangen. Dazu zählen natürliche Uranerzvorkommen und deren Leaching sowie die Auswaschung von Uran aus den Hinterlassenschaften des ehemaligen Uranerzbergbaus. Die Aufklärung des Verhaltens von Uran in der Geo- und Biosphäre ist für eine Risikoabschätzung des Migrationsverhaltens von Radionukliden in der Umwelt notwendig. Algen sind in der Natur weit verbreitet und die wichtigste Organismengruppe in den aquatischen Lebensräumen. Durch ihre ubiquitäre Verbreitung in der Natur ist ihr Einfluss auf das Migrationsverhalten von Uran in der Umwelt von grundlegendem Interesse z.B. um effektive und wirtschaftliche Remediationsstrategien für Wässer zu entwickeln. Außerdem stehen Algen am Beginn der Nahrungskette und spielen eine wirtschaftlich relevante Rolle als Nahrung beziehungsweise Nahrungsergänzungsmittel. Die Möglichkeit des Transfers von algengebundenem Uran entlang der Nahrungskette könnte eine ernsthafte Gesundheitsgefahr für den Menschen darstellen.
Das Ziel dieser Arbeit war die quantitative und strukturelle Charakterisierung der Wechselwirkung zwischen Uran(VI) und der Grünalge Chlorella vulgaris im umweltrelevanten Konzentrations- und pH-Wertbereich unter besonderer Berücksichtigung der Stoffwechselaktivität.
Die in dieser Arbeit erzielten Ergebnisse der Sorptionsexperimente zeigen deutlich den maßgeblichen Einfluss des Stoffwechselstatus von Chlorella auf die Wechselwirkung mit Uran. So kann in Gegenwart von umweltrelevanten Urankonzentrationen eine Remobilisierung von zuvor passiv gebundenem Uran durch die stoffwechselaktiven Algen erfolgen. Die in Abhängigkeit von der Stoffwechselaktivität, der Urankonzentration und dem pH-Wert mit den Algenzellen gebildeten Uran(VI)-Komplexe wurden strukturell mit Hilfe der spektroskopischen Methoden TRLF-, EXAFS- und ATR-FTIR-Spektroskopie charakterisiert. Mittels TEM konnte Uran in Form von 30-70 nm großen nadelförmigen Ablagerungen in der Zellwand der lebende Algenzellen nachgewiesen werden.
Die in dieser Arbeit erhaltenen Ergebnisse leisten einen wichtigen Beitrag zur Vorhersage des Migrationsverhaltens von Uran unter umweltrelevanten Bedingungen und der radiologischen Risikobewertung von geogen und anthropogen auftretendem Uran.
Keywords: uranium, algae, biosorption,TRLFS, EXAFS, ATR-FTIR, TEM
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-005 2011
    ISSN: 1437-322X

Downloads:

Publ.-Id: 15813 - Permalink


The new 6 MV AMS-facility DREAMS at Dresden
Akhmadaliev, S.; Heller, R.; Hanf, D.; Rugel, G.; Merchel, S.;
A new 6 MV electrostatic tandem accelerator has been put into operation at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). It will be used for ion beam analysis as well as for material modification via high-energy ion implantation. The system is also equipped for accelerator mass spectrometry and opens a new research field at HZDR and the Helmholtz Association. The research activity at the DREsden Accelerator Mass Spectrometry facility (DREAMS) based on a 6 MV Tandetron is primarily dedicated to the long-lived radioisotopes of 10Be, 26Al, 36Cl, 41Ca, and 129I.
DREAMS background levels have been found of 4.5x10-16 for 10Be/9Be, 8x10-16 for 26Al/27Al, 3x10-15 for 36Cl/35Cl and 8x10-15 for 41Ca/40Ca, respectively. The observed background of 2x10-13 for 129I/127I originates from intrinsic 129I from AgI produced from commercial KI. The introduction of quality assurance approaches for AMS, such as the use of traceable calibration materials and taking part in interlaboratory comparisons, guarantees high accuracy data for future DREAMS users.
During first experiments an energy calibration of the accelerator has been carried out using the nuclear reaction 1H(15N,γα)12C yielding an energy correction factor of 1.019.
Keywords: accelerator mass spectrometry, electrostatic accelerator

Publ.-Id: 15812 - Permalink


L.E.J. Brouwer's heavy particle in a rotating vessel and ion traps: a curious dissipative system with pure imaginary eigenvalues
Kirillov, O.;
In 1918 Brouwer considered stability of a heavy particle in a rotating vessel. This was the first demonstration of a rotating saddle trap which is a mechanical analogue for quadrupole particle traps of Penning and Paul. We revisit this pioneering work in order to uncover its intriguing connections with classical rotor dynamics and fluid dynamics, stability theory of Hamiltonian and non-conservative systems as well as with the modern works on crystal optics and atomic physics. In particular, we find that the boundary of the stability domain of the undamped Brouwer's problem possesses the Swallowtail-like singularity corresponding to the quadruple zero eigenvalue. In the presence of dissipative non-conservative forces there is a couple of exceptional points in the spectrum that correspond to the Whitney umbrella singularities on the boundary of the asymptotic stability domain. The handles of the umbrellas form a set where all eigenvalues of the system are pure imaginary despite the presence of the dissipative non-conservative forces. This classical dissipative system demonstrates a non-trivial connection between the regions with pure imaginary and complex spectrum in the space of parameters that may give a useful insight to how regions with real and complex spectrum could be connected in the case of near PT-symmetric Hamiltonians.
Keywords: Rotating saddle trap, dissipation, Lyapunov stability, gyroscopic stabilization, multiple eigenvalues, exceptional point, stability boundary
  • Invited lecture (Conferences)
    Quantum Physics with Non-Hermitian Operators, International Seminar and Workshop, 15.-25.06.2011, Dresden, Deutschland

Publ.-Id: 15811 - Permalink


The Velikhov-Chandrasekhar paradox in magnetorotational instability and related phenomena
Kirillov, O.; Stefani, F.;
The magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable rotating shear flows, e.g., in accretion disks. What laws of differential rotation are susceptible to the destabilization by the axial or helical magnetic field? The answer to this question, which is vital for astrophysical and experimental applications, inevitably leads to the study of spectral and geometrical singularities on the instability threshold. The singularities provide a connection between seemingly discontinuous stability criteria and thus explain several paradoxes in the theory of MRI that were kept poorly understood since 1950s.
Keywords: Magnetorotational instability, helical magnetorotational instability, inductionless HMRI, Rossby number, Pluecker conoid, instability threshold
  • Invited lecture (Conferences)
    SPT 2011, Symmetry and Perturbation Theory, 05.-12.06.2011, Otranto near Lecce, Italy

Publ.-Id: 15810 - Permalink


Standard and helical magnetorotational instability: How singularities create paradoxal phenomena in magnetohydrodynamics
Kirillov, O.; Stefani, F.;
The magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable rotating shear flows, e.g., in accretion discs. What laws of differential rotation are susceptible to the destabilization by the axial or helical magnetic field? The answer to this vital for astrophysical and experimental applications question inevitably leads to the study of spectral and geometrical singularities on the instability threshold of the operator of this problem. The singularities provide a connection between seemingly discontinuous stability criteria and thus explain several paradoxes in the theory of MRI that were kept poorly understood since 1950s.
Keywords: Magnetorotational instability, Velikhov-Chandrasekhar paradox, Liu limit, Rayleigh criterion
  • Poster
    Quantum Physics with Non-Hermitian Operators, International Seminar and Workshop, 15.-25.06.2011, Dresden, Deutschland

Publ.-Id: 15809 - Permalink


Atom probe tomography and small-angle neutron scattering applied to reactor pressure vessel weld material from decommissioned nuclear power plant
Bergner, F.; Ulbricht, A.; Viehrig, H.-W.; Nishida, K.; Soneda, N.; Valo, M.;
Trepans of weld metal were taken from the decommissioned reactor pressure vessel of Greifswald Unit 4. As-irradiated material from two through-thickness positions (Layers 4 and 6) of the weld was characterized by SANS and APT. For SANS, irradiated and annealed (475°C/152 h) material was taken as reference. We have found that (1) Cu and Si levels are higher in both matrix and clusters of Layer 6. This causes more and larger clusters to form in Layer 6 resulting in higher hardness and BDT temperature, although neutron exposure was lower for Layer 6. (2) The mean cluster composition and concentration deduced from APT are in considerable disagreement with SANS data. A possible overestimation of Fe in clusters and the presence of vacancies may solve the discrepancy.
  • Lecture (Conference)
    E-MRS Spring Meeting, 09.-13.05.2011, Nizza, Frankreich

Publ.-Id: 15808 - Permalink


fabrication, tuning, treatment and testing of two 3.5 cell photo-injektor cavities for the elbe linac
Arnold, A.; Murcek, P.; Teichert, J.; Xiang, R.; Grigory, V. E.; Kneisel, P.; Stirbet, M.; Turlington, L.;
As part of a CRADA (Cooperative Research and Development Agreement) between Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and Thomas Jefferson Lab National Accelerator Facility (TJNAF) we have fabricated and tested two 1.3 GHz 3.5 cell photo-injector cavities from polycrystalline RRR niobium and large grain RRR niobium, respectively. The cavity with the better performance will replace the presently used injector cavity in the ELBE linac*. The cavities have been fabricated and pre-tuned at TJNAF, while the more sophisticated final field tuning, the adjustment of the external couplings and the field profile measurement of transverse electric modes for RF focusing** was done at FZD. The following standard surface treatment and the vertical test was carried out at TJNAF’s production facilities. A major challenge turned out to be the rinsing of the cathode cell, which has small opening (Ø10mm) to receive the cathode stalk. Another unexpected problem encountered after etching, since large visible defects appeared in the least accessible cathode cell. This contribution reports about our experiences, initial results and the on-going diagnostic work to understand and fix the problems.
  • Poster
    15th International Confernce on RF Superconductivity, 25.-29.07.2011, Chicago, USA

Publ.-Id: 15807 - Permalink


Nanoanalysis of lanthanum scandate MOS capacitors addressing reliability after local current flow
Hippler, M.; Streit, S.; Lehmann, J.; Skorupa, W.; Schmidt, H.; Helm, M.; Lopes, J. M. J.; Schubert, J.; Huber, H.-P.; Kienberger, F.; Mantl, S.;
The capacitance of series LaScO3-SiO2 capacitors on Si substrates has been investigated in the same DC bias range and at the same operation frequencies by admittance and scanning microwave microscopy (SMM) measurements on the 10(-3) cm2 scale and 100 nm2 scale, respectively. By SMM measurements it is shown that changes in the series capacitance due to local current flows persist and that such nanoscale changes can be induced by slow speed SMM scans at a constant DC bias.
Keywords: C-V measurement, scanning microwave microscopy, LaScO₃-SiO₂ capacitor
  • Contribution to proceedings
    IEEE Semiconductor Conference Dresden, 27.-28.09.2011, Dresden, Deutschland
  • Lecture (Conference)
    IEEE Semiconductor Conference Dresden, 27.-28.09.2011, Dresden, Deutschland

Publ.-Id: 15805 - Permalink


Cluster Dynamics Study of Defect Evolution in Neutron-Irradiated Dilute and Concentrated Fe-Cr Alloys
Gokhman, A. R.; Bergner, F.; Birkenheuer, U.; Ulbricht, A.;
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 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.
Keywords: Cluster dynamics, neutron irradiation, chromium iron alloys, defects
  • Lecture (Conference)
    25th Research Workshop Nucleation Theory and Applications, 16.-23.04.2011, Dubna, Russia

Publ.-Id: 15804 - Permalink


CFD-Modelling of subcooled boiling and applications in the nuclear technology
Krepper, E.;
The verification of design improvements of a fuel assembly of a nuclear reactor core and their influence on the critical heat flux require expensive experiments. Therefore the supplementation or even the replacements of experiments by numerical analyses are of relevant interest in fuel assembly design. The CFD modeling has the potential of simulation independent on the certain geometry.
The presentation describes the actual state of CFX modeling of subcooled boiling and their possible contribution for rod bundle design. The comparative investigation of different designs is possible at least qualitatively. For more quantitatively reliable results the models have to be improved. In the presentation the demands on the accuracy of measured values are established. Most promising results are expected by tomographic methods like by fast X-ray tomography.
Keywords: CFD, wall boiling
  • Invited lecture (Conferences)
    Jahrestagung Kerntechnik 2011, 17.-19.05.2011, Berlin, Germany

Publ.-Id: 15803 - Permalink


Coupling of a population balance approach with the RPI wall boiling model: Parameter investigation & inhomogeneous MUSIG-RPI validation
Krepper, E.; Rzehak, R.;
The capabilities of CFD for wall boiling are investigated. In the DEBORA tests Dichlorodifluoromethane (R12) was used as the working fluid. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size. Coupling the wall boiling model with a population balance model several phenomena can be described. Measurements show an increase of bubble size by coalescence after leaving the heated wall. Increasing the inlet temperature and the amount of generated vapour a shift of the measured radial gas fraction profile from wall to core peak was observed. The explanation is the changing lift coefficient for large bubbles, which can be considered by the inhomogeneous MUSIG population balance model.
Keywords: CFD, two phase flow, wall boiling, momentum exchange, population balance
  • Lecture (Conference)
    9th FZD & ANSYS Short Course and Workshop "Multiphase Flow - Simulation, Experiment and Applications", 08.-10.06.2011, Rossendorf, Germany

Publ.-Id: 15802 - Permalink


Uptake of selenium(VI) and selenium(IV) onto anatase and rutile
Jordan, N.; Foerstendorf, H.; Scheinost, A. C.; Lützenkirchen, J.; Schild, D.; Weiß, S.; Heim, K.; Brendler, V.;
In the context of nuclear waste management, long-term safety assessments have shown that selenium-79 could be one of the major isotopes contributing to the global radioactivity potentially reaching the biosphere. The present study focuses on the sorption of selenium oxyanions, i.e. selenium(VI) and selenium(IV), onto pure anatase and rutile phases, in order to complete the thermodynamic databases used for safety assessments of water contamination. A combination of both macroscopic (batch sorption and zeta potential measurements) and microscopic measurements (ATR FT-IR, EXAFS) have been used. To avoid an activation of anatase photocatalytic properties, all tubes were covered by aluminum foil. Results showed that both phases have higher affinity towards selenium(IV) compared to selenium(VI). Sorption of both oxyanions was at a maximum in the acidic pH range and decreased when the pH became more alkaline Batch experiments evidenced ionic strength dependence of the selenium(VI) sorption, while no impact was noticed for selenium(IV). No reduction of Se oxyanions at both homogenous and heterogeneous levels was noticed during HG-AAS and XPS measurements. During electrophoretic mobility measurements, no shift of the isoelectric point of anatase (pHIEP) upon selenium(VI) sorption was observed, while selenium(IV) retention decreased the pHIEP to lower pH values. Based on ATR FT-IR and EXAFS spectroscopic observations, we concluded that selenium(VI) is sorbed onto TiO2 as outer-sphere surface complexes, while selenium(IV) forms primarily inner-sphere complexes. Finally, selenium sorption onto TiO2 was described by a multisite surface complexation model (CD-MUSIC).
  • Contribution to proceedings
    Geological Disposal of Radioactive Waste: Underpinning Science and Technology, 18.-20.10.2011, Loughborough, United Kingdom
    Uptake of selenium(VI) and selenium(IV) onto anatase and rutile

Publ.-Id: 15801 - Permalink


Radiation from a charged particle-in-flight from a laminated medium to vacuum
Grigoryan, L. S.; Mkrtchyan, A. R.; Khachatryan, H. F.; Arzumanyan, S. R.; Wagner, W.;
The radiation from a charged particle-in-flight from a semi-infinite laminated medium to vacuum and back, from vacuum to the laminated medium, has been investigated.Expressions for the spectral-angular distribution of radiation energy in vacuum were obtained for both the cases with no limitations on the amplitude and variation profile of the laminated medium permitivity.
Keywords: periodic structures, relativistic particles, radiation
  • Contribution to proceedings
    VIII Internat. Symp. on Radiation from Relativistic Electrons in Periodic Structures (RREPS-2009), 07.-11.09.2009, Zvenigorod, Russia
    Journal of Physics: Conference Series, Vol. 236 (2010), Bristol, UK: IOP Publishing Ltd, ISSN: 1742-6588

Publ.-Id: 15800 - Permalink


Inbetriebnahme des HZDR-Zyklotrons in Leipzig: Herstellung und Reinigung von n.c.a. Radionukliden 56Co und 85Sr
Mansel, A.; Franke, K.; Fischer, S.; Steinbach, J.;
Seit 1. März 2011 ist an der Forschungsstelle Leipzig des HZDR das Zyklotron „Cyclone 18/9“ der Herstellerfirma IBA (Belgien) nach einer Bauphase von nur zwei Jahren und einer Errichtungsphase durch IBA von einem Monat in Betrieb. Es können Protonen bzw. Deuteronen von Energien bis zu 18 MeV bzw. 9 MeV erzeugt werden. Neben der Herstellung von Standardradionukliden für die radiopharmazeutische Forschung (11C, 15O, 18F) erlaubt dieser Energiebereich auch Kernreaktionen mit mittelschweren und schweren Elementen (z. B. Sc-, Fe-, Rb-, Te- und Tl-Targets) zur Herstellung von längerlebigen Radionukliden (Halbwertszeiten von Tagen bis Wochen). für georadiochemische Untersuchungen. Derzeit werden Verfahren zur Herstellung und Reinigung diverser Radionuklide getestet und weiterentwickelt. Im besonderen sollen die no-carrier-added (n.c.a.) Radionuklide 56Co (T1/2 = 77,3 d) und 85Sr (T1/2 = 64,9 d) durch die Kernreaktionen 56Fe(p,n)56Co bzw. 85Rb(p,n)85Sr für aktuelle Projekte mit hohen spezifischen Aktivitäten aus eigens hergestellten Targets (Aluminium-Backing) produziert und die isotopenangereicherten Targetmaterialien zurückgewonnen werden. Die ersten Bestrahlungen wurden bei einem Strahlstrom von bis zu 40 µA für wenige Minuten an der Feststoff-Beamline durchgeführt. Die Abtrennung von 85Sr vom bestrahltem RbCl erfolgte durch Auflösen des Targets in Wasser, Eindampfen und Auflösen in 8 M HNO3. Anschliessend erfolgte Säulenchromatographie mit dem strontiumspezifischem Kronenether Sr-Spec.[1] Hierbei eluiert das Rb (Target) quantitativ mit 8 M HNO3. Das 85Sr wurde durch Waschen mit Wasser quantitativ erhalten (100 %). Die Abtrennung von 56Co vom bestrahltem Eisen erfolgte durch Auflösen des metallischen Eisens mit einer 1:1 Mischung aus 8 M HCl / 30 % H2O2.[2] Nach dem Eindampfen wurde der Rückstand mit 5,2 M HCl aufgenommen und das Fe3+ viermal mit HCl-gesättigem tert-Butylmethylether extrahiert. Nach schonendem Eindampfen der wässrigen Phase und Anionenaustauschchromatographie mit DOWEX 1x8 in 8 M HCl wird 56Co durch Waschen mit 4 M HCl eluiert. Spuren von Fe3+ und Al3+ aus dem Target-Backing verbleiben auf der Säule. Die radiochemische Ausbeute für 56Co beträgt ~ 83 %.
Literatur:
[1] E. P. Horwitz et al., Solvent Extr. Ion Exch. 1990, 8, 557. [2] M. C. Lagunas-Solar et al., Int. J. Appl. Radiat. Isot. 1979, 30, 25.
  • Poster
    GDCh Wissenschaftsforum Chemie 2011, 04.-07.09.2011, Bremen, Deutschland

Publ.-Id: 15799 - Permalink


Lattice damage and secondary phase formation in yttria stabilised zirconia implanted with Fe at different temperatures
Zhou, S.; Shalimov, A.; Wang, Y.; Potzger, K.;
In this paper we report on the lattice damage and nanocrystalline secondary phase formation in Fe implanted Yttria stabilised zirconia (YSZ) up to a peak concentration of 10%. The implantation temperature has been varied between room temperature and 1000°C. Samples were characterized using Rutherford backscattering/channeling and x-ray diffraction. We observed that (1) YSZ remains partially crystalline even after Fe implantation at room temperature and the lattice damage can be partially recovered if implantation is performed at elevated temperatures; (2) crystalline bcc-Fe nanoparticles have formed and grown with increasing implantation temperature. The nanoscale Fe precipitates and the YSZ matrix have a crystallographic orientation relationship.
Keywords: Yttria stabilised zirconia, Ion irradiation, Damage accumulation, Secondary phase formation

Publ.-Id: 15796 - Permalink


Production of cosmogenic radionuclides at great depth: a multi element approach
Braucher, R.; Merchel, S.; Borgomano, J.; L. Bourlès, D.;
For the last two decades, in situ produced cosmogenic nuclides are increasingly applied in Earth sciences to quantify surface processes. In parallel, significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry (AMS) allows more precise measurements. However, among all the published works on cosmogenic nuclides, only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production. Thus, an approach to investigate in situ produced cosmogenic nuclides 10Be, 26Al and 36Cl along a single 11-meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched. These measurements have been used to quantify muon-induced productions based on natural samples for each studied nuclide. Contrary to the currently most often used calculation of muon-induced production parameters which are based on irradiation experiments at discrete energies, productions based on natural samples are considering the entire energy range of particles reaching the ground surface. The evolution of 36Cl concentrations with depth needs to agree with those parameters deduced from 10Be and 26Al data. This is optimized when considering a fast muon-induced 36Cl production contribution and a spallation production rate at Sea Level High Latitude (SLHL) of (42.0 ± 2.0) atoms 36Cl gCa-1 a-1 (1sigma uncertainty).
Keywords: Cosmogenic nuclides, depth profile, production rate, muon, Be-10, Al-26, Cl-36

Publ.-Id: 15795 - Permalink


Influence of Proton Elastic Scattering on Soft Error Generation of SRAMs
Kosmata, M.; Auerhammer, J.; Zier, M.; Schlaphof, F.; Schreiter, F.; von Borany, J.;
It is known that protons usually do not deposit sufficient energy in a Static Random Access Memory (SRAM) cell to produce single-event-upsets (SEU) by direct ionization. In this work a model for the influence of elastic scattered protons is presented which explains the experimentally obtained SEU rate for protons at energies well below the Coulomb barrier threshold. A quantitative fit-parameter free calculation of upsets is provided. Experimental results of low energetic proton irradiation of a 32 nm silicon-on-insulator (SOI) SRAM are presented to validate the model.
Keywords: elasic scattering, proton irradiation, SEU, SRAM
  • Lecture (Conference)
    Conference on Radiation Effects on Components and Systems, 19.-23.09.2011, Sevilla, Spain
  • Contribution to proceedings
    Conference on Radiation Effects on Components and Systems, 19.-23.09.2011, Sevilla, Spain
    Radiation and Its Effects on Components and Systems (RADECS): IEEE, 978-1-4577-0585-4, 186-190
    DOI: 10.1109/RADECS.2011.6131301

Publ.-Id: 15794 - Permalink


High-resolution RBS investigation of LaLuO3 as candidate for a second-generation high-k material
Kosmata, M.; Zier, M.; Munnik, F.;
The ever-shrinking MOSFET (metal–oxide–semiconductor field-effect transistor) requires new materials that exhibit a higher dielectric constant compared to SiO2, for the gate dielectric [1]. Currently underway is the search for second-generation high-k materials [2] with higher permittivity, superior thermodynamic stability in contact with Si [3], matching band alignment with Si [4] and processing compatibility with poly-Si and metal gate electrodes. A suitable candidate material is lanthanum lutetium oxide (LaLuO3, LLO). During the so-called “gate first” manufacturing process, the gate oxide stack is subjected to thermal treatment. It is, therefore, important, to investigate the thermal stability of the deposited layer stack.

The samples under investigation are stacks of Si/LaLuO3/Si made by FZ Jülich, before and after annealing at 900°C. The samples have been studied with standard RBS (Rutherford Backscattering Spectrometry), high-resolution RBS and high-resolution TEM (Transmission Electron Microscopy). Standard RBS measurements have been performed under a scattering angle of 170° and two different angles of incidence to the surface normal (0° and 70°), where the first provides good separation of La and Lu in the spectrum and the latter higher depth resolution. These two measurements give the total amount of La, Lu and O and to a minor degree the depth profile of these elements. However, the results indicate some mixing of Si into the LLO, but the depth resolution was insufficient to obtain unambiguous results. High-resolution TEM could not provide a definitive answer either. Therefore, high-resolution RBS has been employed to investigate this question.

The high-resolution RBS set-up [5] consists of a Browne-Buechner type magnetic spectrometer and a position sensitive detector coupled to a 3 MV Tandetron accelerator. A 2.024 MeV C2+ ion beam has been used. The spectrometer is located at a forward scattering angle of 35° to maximise the depth resolution and scattering cross-section, achieving an energy resolution of < 0.1%. Due to the limited length of the position sensitive detector, only a narrow energy window of < 0.1 E0 can be analysed. Therefore, not all elements and also often not the whole width of one layer in the sample can be measured in one run and several measurements with a shifted energy window have to be performed. These individual spectra can be analysed simultaneously using WiNDF [6] or in a more intuitive approach, all partial spectra are combined in one complete spectrum. For this purpose, the counts were re-binned into new energy bins of 1 keV width, considering a different channel to energy calibration for each spectrum. For an internal self-consistency check the partial spectra overlap a certain amount and the final spectrum is obtained by averaging the overlapping data.

The resulting spectra for a sample before and after thermal treatment clearly show a redistribution of Si during annealing. This work will be continued with an investigation of the annealing temperature dependence and different annealing processes on the intermixing of Si.

References
[1] http://www.itrs.net/links/2009itrs/home2009.htm.
[2] M. Li et al. Adv. in Sci. and Techn. 45 (2006) 1342.
[3] E.P. Gusev et al. Microelectronic Engineering 59 (2001) 341.
[4] J. Robertson. Appl. Surf. Sci. 190 (2002) 2.
[5] R. Grötzschel et al. Nucl. Instr. Meth. B219 (2004) 344.
[6] N.P. Barradas, C. Jeynes, R.P. Webb, Appl. Phys. Lett. 71 (1997) 291.
Keywords: High resolution RBS, Rutherford Backscattering Spectrometry, high-k Material, Browne-Buchner
  • Lecture (Conference)
    6th International Workshop on Igh-Resolution Depth Profiling, 27.-30.06.2011, Paris, France

Publ.-Id: 15793 - Permalink


Forming an oxidation protective coating on titanium and titanium-base alloys
Endler, R.; Yankov, R. A.; Kolitsch, A.; Mücklich, A.; von Borany, J.; Munnik, F.; Voelskow, M.; Donchev, A.; Schütze, M.;
We report on the fabrication of a coating for protecting α-Ti and Ti-base alloy surfaces from environmental oxidation and embrittlement at elevated temperatures. The fabrication process involves the deposition of Ti and Al by dual magnetron sputtering followed by vacuum annealing (700°C, 8 h) to form a layer of γ-TiAl, which is finally treated by plasma-based ion implantation of fluorine to provide the necessary conditions for activating the so-called halogen effect. The resulting coating forms a protective alumina-containing scale upon subsequent high-temperature oxidation in air, thereby rendering the coated substrate material resistant to oxygen diffusion and embrittlement. Two types of F-containing precursor gases, namely a mixture of difluoromethane and argon (CH2F2+25% Ar), and a mixture of silicon tetrafluoride and argon (SiF4+25% Ar) have been employed for implanting fluorine. It has been shown that the SiF4/Ar plasma-based process is much more efficient in terms of implantation time (twice as short compared with that of the CH2F2/Ar-based treatment). Moreover, the co-implantation of Si is helpful as it results in an additional enhancement of the halogen effect. A variety of analytical techniques such as XRD, ERD, RBS and XTEM in conjunction with EELS and EDXS have been used for characterization. We present analysis data detailing the microstructure and the phase formation in the coating material. The structure and quality of the coating appear to be independent of the substrate material. Moreover, the ability to form, in a reproducible manner, thin films of γ-TiAl on various substrates has also relevance to high-temperature microelectronics applications (diffusion barriers, conduction lines etc). Thus, the results of this study may serve to broaden the range of TiAl uses.
  • Poster
    11th International Workshop on Plasma-Based Ion Implantation and Deposition (PBII&D 2011), 08.-12.09.2011, Harbin, China

Publ.-Id: 15792 - Permalink


Oxidation protection of TiAl alloys by plasma-based ion implantation of fluorine
Yankov, R. A.; Kolitsch, A.; von Borany, J.; Munnik, F.; Mücklich, A.; Donchev, A.; Schütze, M.;
Plasma-based ion implantation (PBII) of fluorine is a promising technique for enhancing the high-temperature oxidation resistance of γ-TiAl alloys. This talk is in two parts. The first part summarizes our recent progress in utilizing the PBII process. Experimental results are presented that give an insight into the behavior of the ion-implanted fluorine and its role in the formation of a protective alumina scale under conditions of both isothermal and thermal cyclic oxidation at temperatures in the range of 720° to 1050°C. Although PBII of F is not yet a commercially feasible proposition, shown are examples that give a flavor of potential applications (turbine blades and turbochargers). The second part of the talk deals with enhancing the environmental durability of Ti and some low-Al content (typically < 10 at.%) Ti-base alloys at elevated temperatures by forming a protective coating on the alloy surface. The coating is accomplished through a three-step process, namely co-deposition of Ti and Al by magnetron sputtering onto a substrate material followed by vacuum annealing to form a layer of γ-TiAl, which is finally treated by PIII of F to provide the necessary conditions for triggering the halogen effect. Shown are analysis data detailing the microstructure and the phase formation in the coating material.
  • Lecture (Conference)
    4th International Workshop on Titanium Aluminides, 13.-16.09.2011, Nürnberg, Germany

Publ.-Id: 15791 - Permalink


Investigation of the life cycle of nanoparticles by means of radiolabelling - NanoTRACK
Hildebrand, H.; Franke, K.;
The application of engineered nanoparticles (NP) in industrial production is still increasing since NPs are known to provide unique properties to the products. Within the NanoTRACK project, surface coatings containing Ag0 and TiO2 NPs are under study. In case of weathering, aging or abrasion of the coatings, NPs could be released, potentially in small amounts. Nevertheless, concentrations could be high enough to cause significant environmental impacts. To be able to follow the life cycle of these NPs, a new radiolabelling technique for commercially available nanomaterials is under development. Radiolabelling provides the unique chance to study the fate and behaviour of (even single) NPs in complex environmental media such as surface water, soil or aquifer sediments.
  • Poster
    1. Clustertreffen der BMBF-Fördermaßnahmen NanoCare und NanoNature, 10.-11.05.2011, Frankfurt am Main, Deutschland

Publ.-Id: 15790 - Permalink


Surface protection of titanium against degradation in high-temperature oxidizing environments
Yankov, R. A.; von Borany, J.; Mücklich, A.; Munnik, F.; Kolitsch, A.; Donchev, A.; Schütze, M.;
Titanium exhibits an extraordinary combination of desirable properties that make it an important engineering material. However, a fundamental limitation of Ti is its high affinity for oxygen at temperatures of 500°-600°C, which results in oxygen embrittlement and reduces the maximum use temperature to below 500°C.
It is now well-established that a γ-TiAl alloy containing Al between 45-55 at.% may be rendered oxidation resistant at temperatures above 700°C by introducing fluorine into its near-surface region (the so-called fluorine effect). Upon subsequent high-temperature oxidation, a γ-TiAl alloy modified in such a way acquires a stable, adherent and highly protective alumina scale.
We have developed a protective γ-TiAl-based coating for α-Ti that serves as an efficient barrier to the oxygen in-diffusion, thereby preventing embrittlement of the material and raising its maximal service temperature. The coating is accomplished by using a three-step process, namely (i). magnetron sputter co-deposition of Ti and Al onto the Ti substrate; (ii) vacuum annealing resulting in the formation of a γ-phase TiAl layer; and (iii) introduction of fluorine by plasma immersion ion implantation.
Analytical techniques such as XTEM/EELS, XRD, ERDA and EDX have been used for materials characterization. Oxidation testing in air at temperatures of 600° to 700°C indicates that the coating provides adequate oxidation protection of α-Ti due to the alumina scale formation on the coating surface.
  • Poster
    E-MRS Spring Meeting, Symposium K (Protective Coatings and Thin Films), 09.-13.05.2011, Nice, France

Publ.-Id: 15789 - Permalink


Untersuchung des Lebenszyklus von TiO2- und Ag0-Nanopartikeln - NanoTRACK
Hildebrand, H.;
Vorstellung des Projektes NanoTRACK, der Projektpartner und erster Ergebnisse
  • Lecture (Conference)
    1. Clustertreffen der BMBF-Fördermaßnahmen NanoCare und NanoNature, 10.-11.05.2011, Frankfurt am Main, Deutschland

Publ.-Id: 15788 - Permalink


Spektroskopische Untersuchung der Komplexbildung von Curium(III) und Europium(III) mit dem Bioliganden Citrat
Heller, A.; Barkleit, A.; Bernhard, G.;
Dreiwertige Actinide (An(III)) wie Curium sind künstlich erzeugte, radioaktive Elemente, die bei der nuklearen Energiegewinnung in Kernkraftwerken entstehen. Durch nicht fachgerechte Lagerung radioaktiven Abfalls können sie in die Umwelt und damit auch in die Nahrungskette des Menschen gelangen. Dreiwertige Lanthanide (Ln(III)) wie Europium hingegen sind radioinaktive Elemente, die natürlich vorkommen und in Technik und Medizin vielfältig verwendet werden. Folglich kann der Mensch sowohl mit An(III) als auch Ln(III) in Kontakt kommen bzw. sie inkorporieren. Da sich diese Elemente im Körper anreichern und ihn durch ihre Radio- bzw. Schwermetalltoxizität schädigen können, stellen sie eine ernste Gesundheitsgefahr für den Menschen dar. Es ist daher von enormer Wichtigkeit, das Verhalten dieser Metallionen im menschlichen Körper auf molekularer Ebene aufzuklären.
Citrat ist ein niedermolekularer Bioligand, der in allen menschlichen Körperflüssigkeiten und anderen Biofluiden vorkommt. Die Komplexbildung von 3 ∙ 10-7 M Cm(III) und 3 ∙ 10-5 M Eu(III) mit diesem Liganden wurde mit der zeitaufgelösten laserinduzierten Fluores-zenzspektroskopie (TRLFS) sowie der Fouriertransformierten Infrarotspektroskopie mit abgeschwächter Totalreflexion (ATR-FT-IR) untersucht. Dabei wird Citronensäure als vierprotonige Säure aufgefasst und das Citrat folglich als CitH3- bezeichnet. Bei Ligandkonzentrationen von 10-5 – 10-3 M wurde im Bereich pH 2 – 12 mittels TRLFS die Bildung verschiedener Cm(III)- bzw. Eu(III)-Komplexe vom Typ MCitH, MCitH2CitH2-, M(CitH)23- und M(Cit)25- nachgewiesen und die entsprechenden Komplexstabilitätskonstanten berechnet. Die Citrat-Komplexierung erwies sich dabei einerseits stärker als die Hydrolyse beider Metallionen, die im untersuchten pH-Bereich kaum auftrat. Andererseits zeigte ein Vergleich mit den publizierten Stabilitäts-konstanten anorganischer Cm(III)- und Eu(III)-Komplexe, dass Citrat auch mit Sulfat, Carbonat und Phosphat um die Bindung der Metallionen konkurrieren kann und daher ein starker Ligand für An(III) und Ln(III) ist. Die Struktur der gebildeten Komplexe wurde mittels ATR-FT-IR näher untersucht. Bei dem MCitH-Komplex (pH 2 – 4) zeigte sich, dass die Carboxyl-Gruppen des Citrats im Komplex zwar deprotoniert, allerdings nicht alle drei an der Metallbindung beteiligt sind. Im Falle des MCit--Komplexes (pH 8 – 12) wurde demgegenüber gezeigt, dass alle Carboxyl-Gruppen an der Metallbindung beteiligt sind. Darüber hinaus konnte für diesen Komplex auch die Deprotonierung der Hydroxyl-Gruppe durch die Komplexbildung nachgewiesen werden.
Im menschlichen Urin bilden organische Säuren wie Citrat eine Hauptkomponente. Lumineszenzspektroskopische Untersuchungen natürlicher Urinproben, denen in vitro Cm(III) oder Eu(III) zugegeben wurde, zeigten, dass beide Metallionen in Proben mit leicht saurem Wert pH ≤ 5,7 als Citrat-Komplexe gebunden werden. Erst bei höheren Werten pH ≥ 5,8 spielen anorganische Urinbestandteile eine Rolle für die Bindung von Cm(III) und Eu(III). Dies zeigt, dass Citrat bei Betrachtung einer Metallspeziation in Biofluiden ein potentiell bedeutender Ligand ist und nicht vernachlässigt werden darf.
Keywords: actinides(III), lanthanides(III), biofluids, TRLFS, heavy metal complexation, citrate
  • Poster
    GDCh-Wissenschaftsforum Chemie 2011, 04.-07.09.2011, Bremen, Deutschland
  • Contribution to proceedings
    GDCh-Wissenschaftsforum Chemie 2011, 04.-07.09.2011, Bremen, Deutschland

Publ.-Id: 15787 - Permalink


X-ray tomography of Taylor bubbles in capillary two-phase flow
Boden, S.; Bieberle, A.; Hampel, U.;
To develop a profound understanding of the transport phenomena at the fluidic interfaces of Taylor bubble two-phase flows, knowledge of the flow topology and precise data on the morpholoy of characteristic flow structures such as liquid film thickness and bubble shape has to be gained. The given presentation describes the experimental approach to accomplish these goals.
Keywords: High-resolution high-speed X-ray tomography, Taylor bubble, Capillary two-phase flow
  • Lecture (others)
    Jahrestagung des Schwerpunktprogramms SPP 1506 "Transport Processes At Fluidic Interfaces", 10.-12.04.2011, Regensburg, Deutschland

Publ.-Id: 15786 - Permalink


4th Generation THz-Lightsources in Dresden: Potential for Characterisation of Organic Materials
Gensch, M.;
An overview over the existing and planned 4th Generation THz Lightsources at the HZDR are given and potential applications to polymerscience are discussed.
  • Invited lecture (Conferences)
    IPF Colloquium, 17.03.2011, IPF Dresden, Deutschland

Publ.-Id: 15785 - Permalink


Schnelle tomographische Bildgebungsverfahren für Mehrphasenströmungen
Hampel, U.; Schubert, M.; Barthel, F.;
Tomographische Bildgebungsverfahren sind heute vor allem aus der Medizin und der zerstörungsfreien Prüfung bekannt. Sie werden aber auch als äußerst vielversprechend für die Analyse komplexer Strömungsvorgänge, etwa in chemischen Apparaten, erachtet. Besonderes Interesse besteht hierbei in der Aufklärung hydrodynamischer Phänomene in Mehrphasenapparaten, wie beispielsweise Blasensäulen, Kolonnen, Festbettreaktoren und Wirbelschichten, in denen die Hydrodynamik die Stoff- und Wärmetransportvorgänge sowie das makroskopische Reaktionsgeschehen entscheidend beeinflussen. Allerdings müssen tomographische Messverfahren für solche Anwendungen besonders schnell sein, da sich Strömungsstrukturen in einer räumlichen Skale von Millimetern im Allgemeinen im Millisekundenmaßstab ändern. In der jüngeren Vergangenheit wurden mit der Gittersensormesstechnik und der ultraschnellen Röntgentomographie zwei Messverfahren entwickelt, die diese Anforderungen erfüllen. Ihre Funktionsprinzipien und Anwendungen werden in diesem Artikel beschrieben.
Keywords: Mehrphasenströmung, Tomographie, Gittersensor

Publ.-Id: 15784 - Permalink


Nuclear Safety Research at the Helmholtz-Zentrum Dresden-Rossendorf
Hampel, U.;
The presentation gives an overview on the research activities at HZDR in the programme Nuclear Safety Research. It highlights research topics in transmutation, nuclear reactor safety and radiochemistry.
Keywords: nuclear safety research
  • Invited lecture (Conferences)
    IMEKO MI2011 Joint IMEKO TC11 TC19 TC20 International Symposia METROLOGICAL INFRASTRUCTURE ENVIRONMENTAL AND ENERGY MEASUREMENTS International Symposium of Energy Agencies of Mediterranean Countries MEDITERRANEAN INDUSTRY OF THE SUN, 15.-17.06.2011, Dubrovnik, Croatia

Publ.-Id: 15783 - Permalink


Hydrodynamik und Stofftransport – Experimente mit hochauflösender Messtechnik
Hampel, U.;
Der Vortrag illustriert Wege zur Messung hydrodynamischer Parameter in Blasensäulen mittels hochauflösender bildgebender Messverfahren, wie Röntgen- und Gammastrahlentomographie. Möglichkeiten und Grenzen des Einsatzes werden ebenso diskutiert, wie ein Bezug zur hydrodynamischen Modellierung.
Keywords: bubble columns, computed tomography, multiphase measurement
  • Invited lecture (Conferences)
    DFG Rundgespräch „Transportprozesse in reaktiven Blasenströmungen„, 09.-10.06.2011, Fulda, Germany

Publ.-Id: 15782 - Permalink


Nuclear Safety and Thermal Fluid Dynamics Research at Helmholtz-Zentrum Dresden-Rossendorf
Hampel, U.;
Der Vortrag gibt einen Überblick über die Forschungsaktivitäten des HZDR im Bereich Nukleare Sicherheitsforschung und Mehrphasen-Thermofluiddynamik. Dabei werden einzelne Forschungsthemen und insbesondere neue Ergebnisse der CFD-Modellierung und Messtechnikentwicklung für Mehrphasenströmungen vorgstellt.
Keywords: nuclear safety research, thermal fluid dynamics
  • Lecture (others)
    Workshop Strömungssimulation und Messtechnik in der Energie- und Verfahrenstechnik, 01.06.2011, Karlsruhe, Germany

Publ.-Id: 15781 - Permalink


Reactor safety and radioecology research at the Helmholtz-Zentrum Dresden-Rossendorf
Hampel, U.;
The presentation gives an overview on the research activities at HZDR in the programme Nuclear Safety Research. It highlights research topics in transmutation, nuclear reactor safety and radiochemistry and eludes possibilities of future cooperations with Russia and the Kurchatov Insitute in particular.
Keywords: nuclear safety research
  • Invited lecture (Conferences)
    Helmholtz-Kurchatov Workshop, 24.05.2011, Moscow, Russia

Publ.-Id: 15780 - Permalink


Thermal fluid dynamics research at Helmholtz-Zentrum Dresden-Rossendorf
Hampel, U.;
Der Vortrag gibt einen Einblick in die Arbeiten zur Mehrphasen-Thermofluiddynamik am HZDR. Insbesondere werden hochauflösende Zweiphasenmesstechnik mit dem Schwerpunkt Gas-Flüssig-Systeme vorgestellt.
Keywords: thermal fluid dynamics, multiphase flow measurement
  • Lecture (others)
    Workshop Gasgetriebene Fluiddynamik in Kolonnenböden, 17.05.2011, Ludwigshafen, Germany

Publ.-Id: 15779 - Permalink


Tomographic imaging methods for multiphase flows
Hampel, U.;
The presentation introduces into wire mesh sensors, gamma ray and x-ray tomography as sophisticated tomographic imaging techniques applicable in multiphase flow studies and process imaging. These techniques have recently been developed at HZDR and have been used in different scientific applications, such as steam-water two phase flow studies in nuclear safety research and multiphase flow studies in process technology. The presentation both gives an overview over physical measuring principles along with different and unique applications in science and industry.
Keywords: wire-mesh sensor, gamma ray tomography, x-ray tomography, process tromography, multiphase flow
  • Invited lecture (Conferences)
    34th Advisory Board Meeting of Tulsa University Separation Technology Projects, 10.-11.05.2011, Tulsa, USA
  • Invited lecture (Conferences)
    76th Advisory Board Meeting of Tulsa University Fluid Flow Projects, 12.05.2011, Tulsa, USA
  • Invited lecture (Conferences)
    Multiphase Metering Roundtable, 12.-13.05.2011, Tulsa, USA

Publ.-Id: 15778 - Permalink


Nukleare Sicherheitsforschung am HZDR
Hampel, U.;
Der Vortrag gibt einen Überblick über laufende und zukünftige Aktivitäten des HZDR auf dem Gebiet der Nuklearen Sicherheitsforschung
Keywords: nuclear safety research
  • Lecture (Conference)
    WKET Strategieworkshop, 18.04.2011, Dresden, Germany

Publ.-Id: 15777 - Permalink


Experimente zu isolierten Phänomenen - Verweilzeitverteilung von Gasblasen
Hampel, U.; Schubert, M.;
Der Vortrag gibt einen Überblick über Methoden zur Bestimmung von Gasverweilzeiten in Blasensäulen und allgemeinen Zweiphasenströmungesszenarien. Es werden diverse lokale und integrale Messmethoden vorgestell und deren Leistungsfähigkeit und Anwendungsgrenzen bewertet.
Keywords: residence time, gas dispersion, two-phase flow, bubble columns
  • Invited lecture (Conferences)
    Campus Blasensäulen, 02.03.2011, Fulda, Germany

Publ.-Id: 15776 - Permalink


Acceptor deactivation in silicon nanowires analyzed by scanning spreading resistance microscopy
Koegler, R.; Ou, X.; Geyer, N.; Das Kanungo, P.; Schwen, D.; Werner, P.; Skorupa, W.;
Vertical p-type Si nanowires (NWs) "in-situ" doped during growth or "ex-situ" by B ion implantation are investigated regarding their acceptor activation. Due to the much higher surface to volume ratio of the NW in comparison to bulk material the surface effect plays an important role in determining the doping behaviour. Dopant segregation and fixed positive charges at the Si/SiO2 interface result in an acceptor deactivation. The B concentration introduced into the NW has to balance the deactivation effects in order to reach the intended electrical parameters.
Scanning spreading resistance microscopy is used for the electrical characterization of the NWs. This analysis method provides images of the local resistivity of NW cross sections. Resistivity data are converted into acceptor concentration values by calibration. The study demonstrates that scanning spreading resistance microscopy is a suitable analysis method capable to spatially and electrically resolve Si NWs in the nanometer-scale.
The NW resistivity is found to be size dependent and shows a significant increase as the NW is below 25 nm in diameter. The obtained data can be explained by a core-shell model with a highly conductive NW core and low conductive shell.
Keywords: Si nanowires, doping, ion implantation, scanning spreading resistance microscopy
  • Contribution to proceedings
    Gettering and Defect Engineering in Semiconductor Technology XIV (GADEST 2011), 25.-30.09.2011, Loipersdorf, Österreich
    Gettering and Defect Engineering in Semiconductor Technology XIV, Stafa-Zuerich Swizerland: Trans Tech Publications, 50-55
  • Lecture (Conference)
    Gettering and Defect Engineering in Semiconductor Technology XIV (GADEST 2011), 25.-30.09.2011, Loipersdorf, Österreich

Publ.-Id: 15775 - Permalink


Spektroskopische Untersuchungen zur Komplexbildung von Cm(III) und Eu(III) mit organischen Modellliganden sowie ihrer chemischen Bindungsform in menschlichem Urin (in vitro)
Heller, A.;
Dreiwertige Actinide (An(III)) und Lanthanide (Ln(III)) stellen im Falle ihrer Inkorporation eine ernste Gefahr für die Gesundheit des Menschen dar. An(III) sind künstlich erzeugte, stark radioaktive Elemente, die insbesondere bei der nuklearen Energiegewinnung in Kernkraftwerken entstehen. Durch Störfälle oder nicht fachgerechte Lagerung radioaktiven Abfalls können sie in die Umwelt und die Nahrungskette des Menschen gelangen. Ln(III) sind hingegen nicht radioaktive Elemente, die natürlicherweise vorkommen und für vielfältige Anwendungen in Technik und Medizin abgebaut werden. Folglich kann der Mensch sowohl mit An(III) als auch Ln(III) in Kontakt kommen bzw. sie inkorporieren. Es ist daher von enormer Wichtigkeit, das Verhalten dieser Elemente im menschlichen Körper aufzuklären. Während makroskopische Vorgänge wie Verteilung, Anreicherung und Ausscheidung bereits sehr gut untersucht sind, ist das Wissen hinsichtlich der chemischen Bindungsform (Speziation) von An(III) und Ln(III) in Körperflüssigkeiten noch sehr lückenhaft.
In der vorliegenden Arbeit wurde daher erstmals die chemische Bindungsform von Cm(III) und Eu(III) in natürlichem menschlichem Urin (in vitro) spektroskopisch aufgeklärt und die gebildeten Komplexe identifiziert. Hierzu wurden auch grundlegende Untersuchungen zur Komplexierung von Cm(III) und Eu(III) in synthetischem Modellurin sowie mit den urinrelevanten organischen Modellliganden Harnstoff, Alanin, Phenylalanin, Threonin und Citrat durchgeführt und die noch unbekannten Komplexbildungskonstanten bestimmt. Abschließend wurden alle experimentellen Ergebnisse mit Literaturdaten und Vorherberechnungen mittels thermodynamischer Modellierung verglichen. Auf Grund der hervorragenden Lumineszenzeigenschaften von Cm(III) und Eu(III) konnte insbesondere auch die Eignung der zeitaufgelösten laserinduzierten Fluoreszenzspektroskopie (TRLFS) als Methode zur Untersuchung dieser Metallionen in unbehandelten, komplexen biologischen Flüssigkeiten demonstriert werden.
Die Ergebnisse dieser Arbeit liefern damit neue Erkenntnisse zu den biochemischen Reaktionen von An(III) und Ln(III) in Körperflüssigkeiten auf molekularer Ebene und tragen zu einem besseren Verständnis der bekannten, makroskopischen Effekte dieser Elemente bei. Darüber hinaus sind sie die Grundlage weiterführender in-vivo-Untersuchungen.
Keywords: Actinide, Lanthanide, TRLFS, Biofluide, Schwermetallkomplexierung
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-006 2011
    ISSN: 1437-322X

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Publ.-Id: 15774 - Permalink


Maleimido-Functionalized NOTA Derivatives as Bifunctional Chelators for Site-Specific Radiolabeling
Förster, C.; Schubert, M.; Pietzsch, H.-J.; Steinbach, J.;
Two basic and simple synthetic routes for mono- and bis-maleimide bearing 1,4,7-triazacyclononane-N,N’,N’’-triacetic acid (NOTA) chelators as new bifunctional chelators are described. The syntheses are characterized by their simplicity and short reaction times, as well as practical purification methods and acceptable to very good chemical yields. The usefulness of these two synthetic pathways is demonstrated by the preparation of a set of mono- and bis-maleimide functionalized NOTA derivatives. In conclusion, these two methods can easily be expanded to the syntheses of further tailored maleimide-NOTA chelators for diverse applications.
Keywords: 1,4,7-triazacyclonone-1,4,7-triacetic acid; NOTA; site-specific; maleimide; ethylene glycol spacer

Publ.-Id: 15773 - Permalink


Fabrication of horizontal silicon nanowire arrays on insulator by ion irradiation
Ou, X.; Kögler, R.; Wei, X.; Mücklich, A.; Wang, X.; Skorupa, W.; Facsko, S.;
We report a simple and potentially mass productive technique to fabricate horizontal single crystalline Si nanowire arrays on insulating substrate based on a self-organized pattern formation mechanism during Xe+ ion beam irradiation of Si-on-insulator material. A periodic ripple surface pattern is created by ion irradiation at 67o incidence angle to the surface normal. The transfer of this pattern to the oxide interface results in an array of electrically disconnected parallel ordered Si nanowires on the insulating oxide. Doping of the nanowires was demonstrated by boron ion implantation and annealing. The morphology and resistivity of the narrow nanowires with large aspect ratio were analysed by cross sectional transmission electron microscopy and scanning spreading resistance microscopy, respectively. Physical reasons of the observed low carrier activation are discussed.
Keywords: Si nanowires, doping, silicon on insulator

Publ.-Id: 15772 - Permalink


Gamma-Induced Positron Spectroscopy (GiPS) at a superconducting electron linear accelerator
Butterling, M.; Anwand, W.; Cowan, T. E.; Hartmann, A.; Jungmann, M.; Krause-Rehberg, R.; Krille, A.; Wagner, A.;
A new and unique setup for Positron Annihilation Spectroscopy has been established and optimized at the superconducting linear electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (Germany). The intense, pulsed (26 MHz) photon source (bremsstrahlung with energies up to 16 MeV) is used to generate positrons by means of pair production throughout the entire sample volume. Due to the very short gamma bunches (<5 ps temporal length), the facility for Gamma-induced Positron Spectroscopy (GiPS) is suitable 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 the annihilation photons which in turn significantly reduces the background of scattered photons resulting in spectra with high signal to background ratios.

Simulations of the setup using the GEANT4 framework have been performed to yield optimum positron generation rates for various sample materials and improved background conditions.
Keywords: Positron Annihilation Spectroscopy, Age-Momentum Correlation, Bremsstrahlung

Publ.-Id: 15771 - Permalink


PIV measurements on the formation of the flow field and aerosol particle distribution in a turbulent square duct flow
Barth, T.; Banowski, M.; Hampel, U.;
The formation of the flow field and spatial aerosol particle distribution play an important role in various industrial applications. Regarding experiments on aerosol particle transport phenomena in turbulent flows it is of essential interest to generate a homogeneously mixed air stream. Particle Image Velocimetry (PIV) measurements have been conducted in order to characterize the turbulent mixing process in a small-scale gas/aerosol test facility which is designed for the investigation of deposition and resuspension of nuclear aerosol particles. The turbulent flow field in a square duct (Red = 8.9k..43k) is seeded with DEHS droplets in the size range of approximately dPaero = 2 µm. Firstly, the downstream formation of particle mixing is quantified in terms of spatial distribution of scatter light intensity of the PIV images. It is found that sufficient mixing of the aerosol particles is accomplished at 8 to 10 hydraulic diameters downstream of the injection point. Furthermore, the formation of the flow field is evaluated in terms of time mean averaged velocity as well as velocity fluctuations. These values are presented at successive downstream positions and display the development of the turbulent boundary layer. It is shown that the near wall turbulent region of the test section nicely follows the universal slope of a well developed turbulent boundary layer. Nevertheless, the flow field formation still takes place after 20 hydraulic diameters.
Keywords: aerosol particles, Particle Image Velocimetry, turbulent flow, quadrant count method
  • Contribution to proceedings
    MULTIPHASE FLOW 2011 - 6th International Conference on Computational and Experimental Methods in Multiphase and Complex Flow, 15.-17.06.2011, Kos, Griechenland
    PIV measurements on the formation of the flow field and aerosol particle distribution in a turbulent square duct flow

Publ.-Id: 15770 - Permalink


Design and commissioning of a small-scale gas/aerosol test facility for the investigation of deposition and resuspension of nuclear aerosol particles
Barth, T.; Banowski, M.; Hampel, U.;
Very High Temperate Reactors (VHTRs) are helium cooled, graphite moderated reactors for cogeneration of electricity and process heat up to 1000°C. Two basic fuel element designs exist: pebble bed and prismatic type.
During HTR standard service several amounts of irradiated graphite dust arises due to mechanical abrasion between graphite pebbles and oxidation processes resulting from helium impurities. This graphite dust deposits in the primary system. Only a limited amount of knowledge is available on the quantity of dust formed during standard service and on its spatial distribution in the primary circuit. However, the dust behaviour during a Design Basis Accident (DBA) such as a pipe break with respect to particle deposition and resuspension characteristics is rather unknown. It is of essential interest to predict how much irradiated graphite dust might exit into the containment in case of such a DBA.
A small-scale gas/aerosol test facility is designed to investigate the dynamic behaviour of the carrier phase and the complex nuclear aerosol particle motions. A brief literature review on nuclear aerosol transport and the basic design of the test facility are presented here. The turbulent flow fields captured with a Particle Image Velocimetry (PIV) system are illustrated in terms of time mean averaged velocity profiles. It is found that the wall-near region is well developed after 17 hydraulic diameters downstream of the inlet and that the core flow formation is still in progress. The formation of the aerosol particle distribution is also presented in terms of light intensity distribution of the raw PIV images. Results from this study show that the aerosol particles are evenly distributed within the fluid after 8-10 hydraulic diameters downstream of the injection point which agrees with other estimated values from various authors.
In addition, different test aerosols have been injected into the flow by means of a aerosol generator and the airborne particle number concentration, as well as the aerodynamic particle size distribution were measured by means of a Laser Aerosol Particle Size Spectrometer. Basic results on aerosol formation are presented in this work.
Keywords: Aerosol particle, deposition, High Temperature Reactor, Particle Image Velocimetry, resuspension
  • Contribution to proceedings
    European Nuclear Young Generation Forum 2011, 17.-22.05.2011, Prag, Tschechien
    Design and commissioning of a small-scale gas/aerosol test facility for the investigation of deposition and resuspension of nuclear aerosol particles

Publ.-Id: 15769 - Permalink


Enhanced dipole strength and its consequences for reaction rates
Schwengner, R.;
http://www.hzdr.de/FWK/MITARB/rs/TalkOslo2011.pdf
Keywords: Photon scattering, bremsstrahlung, statistical reaction models, photonuclear reactions, radiative capture, cross sections
  • Invited lecture (Conferences)
    3rd Workshop on Level Density and Gamma Strength, 23.-27.05.2011, Oslo, Norwegen

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Publ.-Id: 15768 - Permalink


Effect of He+ Irradiation on SRO in Fe-Cr Alloys
Dubiel, S. M.; Reuther, H.; Cieślak, J.;
Effect of He+ Irradiation on SRO in Fe-Cr Alloys
  • Poster
    7th Seeheim Workshop on Mössbauer Spectroscopy, 13.-17.06.2011, Frankfurt/Main, Deutschland

Publ.-Id: 15767 - Permalink


Magnetism in Ge Produced by Implantation with Fe and Mn ions
Reuther, H.; Talut, G.; Mücklich, A.; Stromberg, F.;
Since several years there have been strong efforts to produce a new class of semiconductors: diluted magnetic semiconductors (DMS). They should expand the functionality of the common semiconductors by using not only the electrical charge but also the spin of the electrons for the information transfer. Ferromagnetism in semiconductors can be provided by doping with transition metal atoms. One possible doping method is ion implantation.

Besides silicon, germanium is one of the most important elements for semiconductor industry. Recent studies have shown that Ge is generally suitable as base material for DMS. But, doping with only one dopant (Mn or Fe) often results in the formation of clusters which are assumed to be inappropriate for the electronic and magnetic properties. Doping with two dopants, however, may prevent phase separation and the dopant atoms are placed either interstitial or substitutional in the Ge lattice.

We present a method of Fe and Mn double implantation and subsequent flash lamp annealing for Ge(Mn,Fe) preparation. For characterization of their properties different analysing methods were applied: conversion electron Mössbauer spectroscopy (CEMS), Auger electron spectroscopy, super conducting quantum interference device magnetometry and transmission electron microscopy (TEM).

The implantation conditions were chosen in a way that the maximum Fe or Mn concentrations reached about 6 atomic percent and that the peak of the concentration profile lay at about 50 nm. Implantations were performed both at room temperature (RT) and at 260°C.

Room temperature CEM spectra of all as implanted samples consisted of a broad doublet which can be decomposed in two single doublets. This indicates that iron atoms are fixed at two different lattice positions. Magnetic splittings did not occur. Magnetization measurements of the RT-implanted samples showed no indication of ferromagnetism even at 4 K while the magnetization curves of the samples implanted at elevated temperature reveal a clear ferromagnetic hysteresis. The shape of the curves has a typical signature for a growth of magnetic clusters which are undesirable, i.e. implantation at elevated temperature seems to be an improper preparation method for DMS.

Further treatment of the samples implanted at RT is more promising. CEM spectra of the annealed samples were doublets too. However, the CEM spectrum of one sample contained also a singlet. A CEM spectrum of this sample recorded at 80 K revealed a magnetic hyperfine field distribution and a discrete sextet.

Magnetisation measurements showed clear hysteresis loops indicating magnetism but no clustering which was confirmed by TEM. Hence it can be concluded that double ion implantation at RT and subsequent flash lamp annealing could be a way for producing DMS.
  • Lecture (Conference)
    7th Seeheim Workshop on Mössbauer Spectroscopy, 13.-17.06.2011, Frankfurt/Main, Deutschland

Publ.-Id: 15766 - Permalink


Buoyancy driven mixing studies of natural circulation flows using ROCOM experiments and CFD
Höhne, T.; Kliem, S.; Rohde, U.;
Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the four loop 1:5 scaled ROCOM mixing test facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV).

In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied. From the test matrix experiments with 0 resp. 2% density differences between the de-borated slugs and the ambient coolant were used to validate the CFD software ANSYS CFX. To model the effects of turbulence on the mean flow a higher order Reynolds stress turbulence model was employed and a mesh consisting of 6.4 million hybrid elements was utilized. Only the experiments and CFD calculations with modeled density differences show stratification in the downcomer. Depending on the degree of density differences the less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core. The validation proves that ANSYS CFX is able to simulate appropriately the flow field and mixing effects of coolant with different densities.
Keywords: ROCOM, CFD, density difference, RPV

Publ.-Id: 15765 - Permalink


Strip Readout RPC Based on Low Resistivity Glass Electrodes
Petris, M.; Petrovici, M.; Simion, V.; Bartos, D.; Caragheorgheopol, G.; Dohrmann, F.; Hildenbrand, K. D.; Kämpfer, B.; Kotte, R.; Naumann, L.; Stach, D.; Williams, M. C. S.; Wüstenfeld, J.;
We present the prototype of a Resistive Plate Counter equipped with electrodes made from Pestov Glass (~ 1010 Ω cm). It is aimed as solution for TOF subdetector of CBM experiment at the future FAIR facility in Darmstadt. Details of the design and the construction are introduced. Results of tests with radioactive sources and of in-beam investigations on time resolution and counting rate capability are discussed.
  • Open Access LogoRomanian Journal of Physics 56(2011), 349-358

Publ.-Id: 15764 - Permalink


Laboratory Measurements on Fresh Terrestrial Gas-hydrate-bearing Sediment Cores
Kulenkampff, J.; Spangenberg, E.;
Physical properties (saturation, grain size distribution, porosity, permeability, resistivity, ultrasonic velocity and attenuation) of terrestrial gas-hydrate-bearing core samples from the Mallik 5L-38 gas-hydrate research well have been investigated in the field laboratory under simulated in situ conditions with a specially designed core analysis system (FLECAS). Twenty samples were prepared immediately after core retrieval and mounted into the pressure vessel at deep frozen conditions. Electrical resistivity, ultrasonic P-wave and S-wave velocities and amplitudes were recorded during the whole procedure, while the samples were brought to in situ pressure and temperature. A strong decrease of all parameters, especially of the P-wave and Swave amplitudes, could be observed at the melting point of ice. Smaller changes occurred later, apart from the loss of mechanical strength and a distinct recovery of the ultrasonic amplitudes, when the gas hydrate decomposition was initialized by the release of the pore pressure or by heating above the stability threshold. The gas-hydrate decomposition started instantaneously when the pore pressure was released, took about 20 min, and was accompanied by a temperature drop of about 3°C at the sample surface. Only small variations were found in the bulk parameters of the unconsolidated sand samples remaining after gas-hydrate decomposition. This explains the uniform behavior of all samples from the gas-hydrate zone of the Mallik well. This data set provides an experimental basis for formation evaluation and a reference for realistic studies with gas hydrates that are synthetically grown in sediments in the laboratory.
  • Contribution to external collection
    Michael Riedel, Eleanor C. Willoughby, Satinder Chopra: Laboratory Measurements on Fresh Terrestrial Gas-hydrate-bearing Sediment Cores, Tulsa: Society of Exploration Geophysicists, 2011, 978-1-56080-218-1, 321-328

Publ.-Id: 15763 - Permalink


Velocity and Resistivity Measurements of Artificial Gas-hydrate-bearing sediment.
Spangenberg, E.; Kulenkampff, J.;
An experimental device designed and developed to grow methane hydrate in the pore space of a sediment was successfully used with a glass bead sample. The underlying idea for the experiment is that methane dissolved in water is transported with upward moving fluids from its place of origin at greater depths to formations in the hydrate stability field where the methane is removed from the pore water to form hydrate. This process is simulated in a closed loop flow system in which methane charged water from a gas/water reservoir outside the hydrate stability field is pumped into the sediment sample cell in the stability field for methane hydrate. The fluid depleted of methane, then flows back into the gas/water reservoir to be recharged with methane.
The electrical resistivity and sonic wave velocity was measured during the process of hydrate formation from methane dissolved in the pore water without a free gas phase. In addition to the sample properties, we measured the resistivity of the circulating water in order to determine the amount of water consumed by hydrate formation from the increase of salinity and to determine the formation resistivity
factor and resistivity index. The electrical resistivity and sonic velocity of the sample increased from 5.1 Ωm and 2036 m/s at 100% water
saturation to 265 Ωm and 3770 m/s at about 95% hydrate saturation, whereas the water resistivity decreased from 1.39 to 1.08 Ωm.
Keywords: methane hydrate, physical properties
  • Contribution to external collection
    Michael Riedel, Eleanor C. Willoughby, Satinder Chopra: Geophysical Characterization of Gas Hydrates, Tulsa, USA: Society of Exploration Geophysicists, 2010, 978-1-56080-218-1, 313-320

Publ.-Id: 15762 - Permalink


The impact of climate transitions on the radionuclide transport through a sedimentary aquifer
Flügge, J.; Noseck, U.; Schneider, A.; Stockmann, M.;
High-level radioactive waste is to be disposed of in deep geological formations. In long-term safety assessments for nuclear waste repositories, geological time scales have to be considered. Drastic climatic changes are expected to occur during that time. This will not only change the boundary conditions and the flow regime, but as well the geochemical environment in the aquifers. Modeling the groundwater flow and contaminant transport over long time scales requires a powerful tool, which is not only able to deal with large heterogeneous areas and long periods in time, but as well to simulate the contaminant transport, taking the hydrogeochemical interactions and the radioactive decay into account. The two codes d³f (distributed density-driven flow) and r³t (radionuclides, reaction, retardation, and transport) are being developed to handle those requirements. So far, the sorption coefficient Kd, which is dependent on the geochemical environment, especially pH, pCO2, ionic strength and concentration of complexing and competing ions, is regarded to be constant for each hydrogeological unit. In our project, we focus on the development and the implementation of a methodology to use temporally and spatially variant sorption coefficients – so called “smart Kd-values” – in the transport code r³t by introducing the transport of relevant components in solution and a pre-computed Kd-matrix with values being dependent on these components. In Germany, the Gorleben salt dome is being investigated as a potential site for a nuclear waste repository. Comprehensive data are available on its hydrogeological configuration. The groundwater flow is dominated by the leaching of salt at the contact of the lower aquifer to the salt dome, resulting in a density-driven groundwater flow. Transitions between different climate states, which are known from the geological past, are modeled with the flow code d³f coupled with the transport code r³t. A sea water inundation will lead to a decrease in the flow velocities and a horizontal salinity-dependent stratification of the groundwater, while a formation of permafrost in the upper aquifer and an inflow of large glacial melt water volumes into the lower aquifer will lead to low salinities and high flow velocities in the unfrozen zones. In our presentation, we focus on the impact of climate transitions on the temporally and spatially variable hydrogeological environment and thus on the migration of radionuclides.
  • Lecture (Conference)
    International Conference on Groundwater: Our Source of Security in an uncertain Future, 19.-21.09.2011, Pretoria, South Africa

Publ.-Id: 15761 - Permalink


Influence of crystal orientation and ion bombardment on the nitrogen diffusivity in single-crystalline austenitic stainless steel
Martinavičius, A.; Abrasonis, G.; Möller, W.;
The nitrogen diffusivity in single crystalline AISI 316L austenitic stainless steel (ASS) during ion nitriding has been investigated at different crystal orientation ((001), (110), (111)) under variation of ion flux (0.3 − 0.7 mA cm−2), ion energy (0.5 − 1.2 keV) and temperature (370 − 430C). The nitrogen depth profiles obtained from nuclear reaction analysis are in excellent agreement with fits using the model of diffusion under the influence of traps, from which diffusion coefficients were extracted. At fixed ion energy and flux, the diffusivity varies by factor up to 2.5 at different crystal orientation. At (100) orientation, it increases linearly with increasing ion flux or energy. The findings are discussed on the basis of atomistic mechanisms of interstitial diffusion, and potential lattice distortions, local decomposition and ion induced lattice vibrational excitations.
Keywords: Stainless steel, 316L, Nitriding, Diffusion

Publ.-Id: 15760 - Permalink


High-field cyclotron resonance spectroscopy of novel semiconductor structures
Drachenko, O.;
An overview of recent cyclotron resonance activities at Dresden high magnetic field laboratory
Keywords: cyclotron resonance
  • Lecture (others)
    Lectures at the University of Kiev, 07.06.2011, Kiev, Ukraine

Publ.-Id: 15759 - Permalink


Terahertz induced intra-excitonic Autler-Townes effect in semiconductor quantum wells up to room temperature
Teich, M.; Wagner, M.; Schneider, H.; Helm, M.; Stehr, D.;
When light is resonant with a material excitation the optical Stark or Autler-Townes (AT) effect couples the involved energy states and alters their energy, i.e. the states get "dressed" by the light-matter interaction. This fundamental quantum-mechanical feature of light-matter interaction was originally observed in atomic spectroscopy. However, despite some theoretical work, it took a long time to the first observation of the AT effect for terahertz (THz) light coupled to hole and electron intersubband transitions in semiconductor quantum wells. Recently we have reported clear evidence of the intra-excitonic AT effect at low temperature. In that work the 1s to 2p transition of an exciton, i.e. an hydrogen-like electron-hole pair in a quantum well, was driven resonantly with strong THz light from the HZDR free-electron laser (FEL). A distinct power- and wavelength dependent splitting of the 1s absorption line has been observed in the near-infrared (NIR) transmission. Here we extend our study up to room temperature. NIR transmission spectra of the GaAs/AlGaAs multiple quantum well are recorded for a series of different temperatures, THz frequencies and THz intensities. When tuning the THz photon energy around the 1s-2p intra-excitonic transition energy that lies at 9 meV, we observe a line splitting when pumping near resonance, and low- and high-energy shoulders, respectively, when pumping above and below resonance. This behavior, the AT effect, is still observable up to a temperature of 200 K where the thermal energy is 17 meV and exceeds the exciton ionization energy of 10 meV. Hence, the excitonic system is quite robust. By delaying the NIR pulse in time with respect to the THz pulse, we find that the induced absorption change occurs adiabatically during the THz pulse. This ultrashort absorption modulation that is present even at elevated temperatures can in principle be exploited for NIR modulators or switches.
Keywords: GaAs/AlGaAs MQW, terahertz (THz) light, Autler-Townes (AT) effect, free-electron laser (FEL)
  • Lecture (Conference)
    5. THz-Frischlinge Treffen 2011, 06.-08.06.2011, Regensburg, Deutschland

Publ.-Id: 15758 - Permalink


New PET radioligands for imaging of cannabinoid receptors type 2
Rühl, T.; Günther, R.; Deuther-Conrad, W.; Fischer, S.; Krautscheid, H.; Steinbach, J.; Wünsch, B.; Brust, P.;
Objectives: Cannabinoid receptors play an important role in neuroprotection after acute neuronal injury such as traumatic brain injury, stroke, and epilepsy, as well as in chronic neurodegenerative disorders such as multiple sclerosis, Parkinson’s, and Alzheimer’s disease. By means of neuroimaging with positron emission tomography (PET), a better understanding of the involvement of the cannabinoid system in these diseases in living humans will be achieved. Furthermore, neuroimaging with 18F-labelled CB receptor ligands will be useful for monitoring treatment effects. However, there is a need for radioligands selective for cannabinoid receptors type 2 (CBR2) which are suitable for PET imaging in humans. Therefore, N-arylamide oxadiazoles, recently described potent, highly selective and orally bio-available CBR2 agonists [1], were proposed as lead for the development of CBR2 PET radioligands [2].

Methods: The novel radiotracers [18F]2, [18F]4, and [18F]6 (Figure 1) were synthesized via nucleophilic aromatic substitution of the respective nitro precursor 1 and 3 and the bromine precursor 5 in DMF under microwave conditions (pulse mode, ≤ 150 W, ≤ 132°C, diffuse light). Ki values of precursor compounds 1, 3, and 5 and reference compounds 2, 4, and 6 were determined in competitive radioligand displacement studies on [3H]CP55940-labelled hCB1- and hCB2-CHO cell homogenates.

Results: We present the first examples for labelling of 3-aryl-1,2,4-oxadiazoles by nucleophilic aromatic substitution [3]. The tracers [18F]2, [18F]4 and [18F]6 were prepared with 3%, 3% and 28% radiochemical yield (RCY). The reference compounds 2 and 4 possess the highest CBR2 affinity (KiCBR2 ~ 5 nM) and selectivity vs. CBR1 (KiCBR1 > 1000 nM) within the structural series investigated (Figure 1). The structure of 1 has been determined by single crystal X-ray diffraction (space group P 1¯ ; R1 = 0.043).


Figure 1. Molecular structure of 1 (50 % ellipsoids) and Ki values of N-arylamide oxadiazole-based CB2 receptor ligands

Conclusions: Due to a high CBR2 affinity and selectivity, the reference compounds 2 and 4 can be expected to be suitable for imaging studies. The CBR2 affinity of reference compound 6 is relatively weak probably because of the unsubstituted R1 (R1 = H). The RCY of [18F]2 and [18F]4 have to be improved to perform PET studies. Nevertheless, the current RCY of [18F]2 and [18F]4 should allow first animal experiments on radiotracer kinetics and metabolism.

Research Support: Work was supported by DFG (Br 1360/12-1).
References: [1] Cheng, Y. et al. (2008), J. Med. Chem. 51, 5019-5034, [2] Evens, N. et al. (2010), Current Topics in Medicinal Chemistry 10, 1527-1543, [3] Rühl, T. et al. (2010), DE 10 2010 063 974.5
  • Poster
    ISRS2011, 28.08.-02.09.2011, Amsterdam, The Netherlands
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011)1, 254-254

Publ.-Id: 15756 - Permalink


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