Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

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

Permalink: https://www.hzdr.de/publications/Publ-15778
Publ.-Id: 15778


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

Permalink: https://www.hzdr.de/publications/Publ-15777
Publ.-Id: 15777


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

Permalink: https://www.hzdr.de/publications/Publ-15776
Publ.-Id: 15776


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

Permalink: https://www.hzdr.de/publications/Publ-15775
Publ.-Id: 15775


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 Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-006 2011
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-15774
Publ.-Id: 15774


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

Permalink: https://www.hzdr.de/publications/Publ-15773
Publ.-Id: 15773


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

Permalink: https://www.hzdr.de/publications/Publ-15772
Publ.-Id: 15772


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

Permalink: https://www.hzdr.de/publications/Publ-15771
Publ.-Id: 15771


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

Permalink: https://www.hzdr.de/publications/Publ-15770
Publ.-Id: 15770


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

Permalink: https://www.hzdr.de/publications/Publ-15769
Publ.-Id: 15769


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

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-15768
Publ.-Id: 15768


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

Permalink: https://www.hzdr.de/publications/Publ-15767
Publ.-Id: 15767


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

Permalink: https://www.hzdr.de/publications/Publ-15766
Publ.-Id: 15766


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

Permalink: https://www.hzdr.de/publications/Publ-15765
Publ.-Id: 15765


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 Logo Romanian Journal of Physics 56(2011), 349-358

Permalink: https://www.hzdr.de/publications/Publ-15764
Publ.-Id: 15764


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

Permalink: https://www.hzdr.de/publications/Publ-15763
Publ.-Id: 15763


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

Permalink: https://www.hzdr.de/publications/Publ-15762
Publ.-Id: 15762


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

Permalink: https://www.hzdr.de/publications/Publ-15761
Publ.-Id: 15761


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

Permalink: https://www.hzdr.de/publications/Publ-15760
Publ.-Id: 15760


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

Permalink: https://www.hzdr.de/publications/Publ-15759
Publ.-Id: 15759


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

Permalink: https://www.hzdr.de/publications/Publ-15758
Publ.-Id: 15758


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

Permalink: https://www.hzdr.de/publications/Publ-15756
Publ.-Id: 15756


Novel PDE10A ligand as a PET probe for imaging: Pharmacological and toxicological evaluation

Nieber, K.; Erdmann, S.; Siegert, F.; Schwan, G.; Brust, P.; Sträter, N.; Altenburger, R.; Briel, D.

Phosphodiesterases (PDE) are enzymes that inactivate the intracellular second messengers cAMP and cGMP. Of all known PDE enzymes, the PDE10A has the most restricted distribution, with high expression in the brain. PDE10 mRNA and protein are highly abundant in the medium spiny neurons of the striatum, the principal input site of the basal ganglia. Inhibitors of PDE10A may be a novel therapeutic approach to the treatment of diseases characterized by a reduced activity of these neurons, such as schizophrenia. Noninvasive imaging of PDE10A using positron emission tomography (PET) would allow the distribution of this enzyme to be studied in vivo in this disease. Therefore, a novel quinoxalin derivative has been designed as a potent and selective inhibitor of the PDE10A. The aim of the present study was to evaluate in vitro the pharmacological and toxicological profile of this compound. The quinoxalin derivative inhibits the PDE10A with a Ki of 32 nM. It did not alter the the basal and ATP-stimulated intracellular Ca2+ concentration as well as the membrane potential in neuronal cells up to 100 µM. Cell-based cytotoxicity assays using human neuroblastoma (SH-SY5Y), kidney (HEK 293) and hepatocyte (HEPG2) cell cultures were established to screen cytotoxic effects. The quinoxalin derivative had no effect on cell viability and cell damage after long-term incubation (36 h and 48 h). Additionally, zebra fish embryos were used as indicators for toxic stress. The quinoxalin derivative did not show toxic effects (mortality or deformation) up to 1 µM.
The results indicate that the novel quinaxoline derivative is a suitable candidate to develop a PET probe for in vivo imaging.

  • Poster
    8th IBRO World Congress on Neuroscience, 14.-18.07.2011, Florence, Italy

Permalink: https://www.hzdr.de/publications/Publ-15755
Publ.-Id: 15755


Estimation of the radiation dose by the PET tracer (-)-[F-18]-NCFHEB for imaging of cerebral alpha4beta2 nicotinic acetylcholine receptors (nAChRs) using a preclinical animal model

Sattler, B.; Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Patt, M.; Wilke, S.; Smits, R.; Hoepping, A.; Brust, P.; Sabri, O.

Objectives: (-)-[F 18]-Norchloro-fluoro-homoepibatidine ((-)-NCFHEB) is a new tracer for neuroimaging of alpha4beta2 nAChRs with PET. To preclinically assess the absorbed radiation dose after application of the tracer, biodistribution, organ doses (OD) and effective dose (ED) were determined after injection of CD1 mice with the radioligand.
Methods: 27 female CD1 mice (weight: 28.2±2.1g) were injected i.v. with 0.75±0.33MBq of (-)-NCFHEB into the V. caudata lateralis. At 5, 15, 30, 45, 60, 90, 120, 180 and 240 min. p.i. the mice were sacrificed (n=3 per time). Brain, heart, lung, stomach, small intestine, large intestine, liver, kidneys, urinary bladder, spleen, thymus, pancreas, adrenals, ovaries, blood, skin, muscle and the skeleton were isolated, weighed and counted in a -counter to determine mass and radioactivity. Time and mass scales were adapted to the human scales. Exponential curves were fitted to the time-activity-data (%ID/g, and %ID/organ). ODs and the ED were calculated using OLINDA.
Results: The highest OD was received by the urinary bladder (104.0 µSv/MBq) and the kidneys (24.2 µSv/MBq). The highest contribution to the ED was by the urinary bladder (5.2 µSv/MBq) and the ovaries (2.1 µSv/MBq). The ED following an i.v. injection of (-)-NCFHEB is 14.2 µSv/MBq.
Conclusions: The ED after i.v. application of 370 MBq (-)-NCFHEB to humans was estimated to be 5.3 mSv. This risk assessment encourages the transfer (-)-NCFHEB from preclinical to clinical studies and to further develop the tracer as a clinical tool for PET imaging of nAChRs.
Research Support: The study was supported by the German Federal Ministry of Education and Research (Nr. 01EZ0820)

  • Poster
    SNM 58th Annual Meeting, 04.-08.06.2011, San Antonio, Texas, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 52(2011), 1454

Permalink: https://www.hzdr.de/publications/Publ-15754
Publ.-Id: 15754


Cerebral alpha4beta2 nicotinic acetylcholine receptors (nAChRs) in early Alzheimer disease (AD) assessed with the new PET tracer (-)-[18F]-norchloro-fluoro-homoepibatidine (NCFHEB)

Sabri, O.; Wilke, S.; Graef, S.; Schoenknecht, P.; Becker, G.; Patt, M.; Wagenknecht, G.; Hoepping, A.; Hegerl, U.; Brust, P.

Objectives: Using 2-[18F]F-A85380 (2FA) PET we showed significant nAChRs declines in early AD (EJNMMI 2010). However, this tracer is not well suited in routine use for early AD-diagnosis because of slow kinetics, acquisition times up to 7 hours, and limited nAChR selectivity. Thus, we developed the new tracer NCFHEB (Synapse 2008). This is the worldwide first ongoing human NCFHEB-PET study.
Methods: 6 mild AD-patients (age 76.7±5.9, MMSE 23.8±3.0) and 5 age-matched healthy controls (HC, age 71.1±5.3, MMSE 28.4±1.1) underwent NCFHEB-PET (370 MBq, 3D, ECAT Exact HR+) from 0-270 min p.i. Kinetic modeling was applied to tissue-activity curves in 29 individual MRI-defined ROIs (1 tissue compartment model: 1TCM, arterial input-function). Total distribution volume (DV) and binding potential (BP, reference: corpus callosum) were calculated.
Results: NCFHEB image quality was clearly superior to 2FA, and a 20 min scan already adequate for visual analysis. PET data acquired over only 90 min were sufficient to estimate all kinetic parameters precisely (1TCM) indicating a fast receptor binding kinetic (much faster than for 2FA). DVs in HCs increased as expected with receptor density: Corpus callosum (DV: 4.8±0.3), post cingulate (8.9±0.6), temporal (9.0±0.4), thalamus (24.3±2.9). AD-patients showed extensive BP reductions in frontal, parietal, temporal, cingulate cortices, and hippocampus compared to HCs (all p<0.05).
Conclusions: Significant shorter acquisition times and superior image quality indicate that NCFHEB is a more valuable tracer than 2FA to image human nAChRs. Early AD-patients show significant nAChRs declines in AD-affected brain ROIs. NCFHEB-PET has a great potential to be tested as a biomarker for early AD-diagnosis

  • Poster
    SNM 58th Annual Meeting, 04.-08.06.2011, San Antonio, Texas, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 52(2011), 1267

Permalink: https://www.hzdr.de/publications/Publ-15753
Publ.-Id: 15753


Development of a 7-(2-[18F]fluoroethoxy)-6-methoxy-quinazoline derivative as a PET radiotracer for PDE10A: synthesis,m potency and radiolabeling

Schwan, G.; Funke, U.; Deuther-Conrad, W.; Egerland, U.; Nieber, K.; Sträter, N.; Brust, P.; Briel, D.

Es ist kein Abstract vorhanden.

  • Poster
    Sächsischer Biotechnologietag Dresden, 02.05.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15752
Publ.-Id: 15752


Alpha7 nicotinic acetylcholine receptors as potential target for imaging traumatic brain injury with positron emission tomography

Brust, P.

Es ist kein Abstract vorhanden.

  • Invited lecture (Conferences)
    23rd Biennial Meeting of ISN-ESN, 28.08.-01.09.2011, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-15751
Publ.-Id: 15751


Development of Radioligands for PET Imaging of Neurological and Psychiatric Diseases

Brust, P.

Es ist kein Abstract vorhanden.

  • Invited lecture (Conferences)
    METPETS Consortium - Meeting, 20.06.2011, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-15750
Publ.-Id: 15750


Ion beam analysis studies of ancient glass bracelets discovered in Bucharest

Bugoi, R.; Poll, I.; Manucu-Adamesteanu, G.; Calligaro, T.; Pichon, L.; Neelmeijer, C.; Eder, F.

Eight fragments of glass bracelets from the XVIII-XIXth centuries discovered in Bucharest were analyzed using external IBA methods (PIXE-PIGE) at AGLAE tandem, C2RMF, Paris and at HZDR tandem, Dresden. The investigated objects had different glass recipes, indicating their manufacturing in several workshops. Cupric oxide was the blue cromophore for all analyzed glass fragments.

Keywords: historical glass; glass bracelets; compositional analysis; IBA; PIXE; PIGE; Bucharest

  • Open Access Logo Romanian Reports in Physics 63(2011)4, 912-922

Permalink: https://www.hzdr.de/publications/Publ-15749
Publ.-Id: 15749


Second harmonic generation of swift carbon ion irradiated Nd:GdCOB waveguides

Ren, Y.; Jia, Y.; Chen, F.; Lu, Q.; Akhmadaliev, S.; Zhou, S.

We report on the second harmonic generation at ~532 nm of optical waveguides in Nd:GdCOB produced by swift carbon ion irradiation. The fabricated waveguide shows good guiding property. Under pump of ~1064-nm fundamental light, the optical conversion efficiency of the frequency doubling is 0.48% W−1 and 6.8% W−1 for continuous wave and pulsed laser beams, respectively.

Keywords: Waveguides, planar; Nonlinear optics, integrated optics; Nonlinear optical materials; Lasers, frequency doubled

Permalink: https://www.hzdr.de/publications/Publ-15747
Publ.-Id: 15747


Optical Nonlinearities in Quantum Wells

Schneider, H.

There is no abstract.

  • Invited lecture (Conferences)
    ROSENCHER’s OPTO-ELECTRONIC DAY, 24.05.2011, Palaiseau, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-15746
Publ.-Id: 15746


High-field terahertz spectroscopy of semiconductor quantum structures

Schneider, H.

This seminar gives an overview on recent experimental studies involving terahertz (THz) and mid-infrared radiation from the free-electron laser facility FELBE in Dresden, Germany. In particular, cyclotron resonance spectroscopy and aperture-less near-field microscopy will be addressed as examples for linear measurements. Moreover, nonlinear THz photocurrents originating from two-photon excitation between subbands in semiconductor quantum wells allow for measurements of intersubband relaxation and dephasing times and for quadratic autocorrelation of THz pulses. The final part of this talk will concentrate on nonlinear two-color THz spectroscopy, in particular THz sideband generation and coherent dynamics involving excitons dressed by strong THz beams.

Keywords: terahertz free-electron laser spectroscopy; intersubband relaxation; quadratic detection; semiconductor quantum well excitons

  • Lecture (others)
    Seminar, Université Paris VII, 12.05.2011, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-15745
Publ.-Id: 15745


Surface nanostructuring of SrTiO3 single crystals by slow highly charged ions and swift heavy ions

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Facsko, S.; Trautmann, C.; Aumayr, F.

Single crystals of strontium titanate have been irradiated with both slow highly charged Xe ions extracted from an Electron Beam Ion Trap and swift heavy Xe ions. After irradiation, the crystals were investigated by scanning force microscopy in air. In both cases nanohillocks due to impact of individual projectiles were observed. This similarity originates from the fact that both swift heavy ions and slow highly charged ions initially transfer their energy to the electronic system of the target, leading to a localized region of high electronic excitation. This electronic excitation is subsequently transferred to the lattice atoms by electron–phonon coupling, leading to pronounced lattice heating. The formation of surface hillocks can then be ascribed to a melting process. We also present first evidence for the existence of a potential energy threshold for nanohillock formation on strontium titanate surfaces by slow highly charged ions.

Keywords: Highly charged ions; Nanostructures; Ion-surface-interaction; Scanning force microscopy; Strontium titanate; SrTiO3

Permalink: https://www.hzdr.de/publications/Publ-15744
Publ.-Id: 15744


n-InAs nanopyramids fully integrated into silicon

Prucnal, S.; Facsko, S.; Baumgart, C.; Schmidt, H.; Liedke, M. O.; Rebohle, L.; Shalimov, A.; Reuther, H.; Kanjilal, A.; Mücklich, A.; Helm, M.; Zuk, J.; Skorupa, W.

InAs with an extremely high electron mobility (up to 40000 cm2/Vs) seems to be the most suitable candidate for better electronic devices performance. Here we present synthesis of inverted crystalline InAs nanopyramids (NPs) in silicon using a combined hot ion implantation and millisecond flash lamp annealing techniques. Conventional selective etching was used to form the InAs/Si heterojunction. The current-voltage measurement confirms the heterojunction diode formation with the ideality factor of n=4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.

Keywords: heterojunction; flash lamp annealing; InAs; heteronanowires; silicon

Permalink: https://www.hzdr.de/publications/Publ-15743
Publ.-Id: 15743


An approach for few femtosecond timing of fourth generation X-ray lightsources and single shot electron bunch diagnostics

Gensch, M.

Fourth-generation X-ray light sources are being developed to deliver laser-like X-ray pulses at intensities and/or repetition rates that are beyond the reach of table-top devices. An important class of experiments at these new facilities comprises pump–probe experiments, which are designed to investigate chemical reactions and processes occurring on the molecular or even atomic level, and on the timescale of a few femtoseconds. Good progress has been made towards the generation of ultrashort X-ray pulses (for example, at FLASH or LCLS), but experiments suffer from the intrinsic timing jitter between the X-ray pulses and external laser sources. Here I present a new approach that provides few-femtosecond temporal resolution for pump probe experiments at FLASH. The method uses residual coherent terahertz radiation generated at the end of the X-ray undulator by the same electron bunch that emits the X-ray pulse. It can therefore be applied at any advanced light source working with ultrashort electron bunches and undulators. The employed instrumentation also has a high potential to allow analysis of the electron bunch form on a single shot basis. An outlook on how the method will be employed at the currently upgraded cw electron linac ELBE at the HZDR to aid laser-electron interaction experiments with dedicated TW and PW lasers is also given

  • Invited lecture (Conferences)
    X-FEL Seminar, 25.03.2011, Hamburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-15741
Publ.-Id: 15741


Photondiagnostics at X-Ray FEL´s

Gensch, M.

SASE FEL´s have now truly evolved into the long anticipated so called 4th generation of accelerator based X-ray light sources. A number of piloting experiments are proof that these novel X-ray sources provide radiation with the theoretically predicted unprecedented properties such as femtosecond pulse duration or Gigawatt peak power in a photon energy range extending from the soft X-ray into the hard X-ray regime. However, the success of these facilities depends strongly on the availability of suitable photon diagnostics. To be precise, due to the stochastic nature of the SASE process, properties such as pulse energy, wavelength, pulse duration and arrival time are varying from pulse to pulse and more complex experiments will crucially depend on the determination of these properties for every individual X-ray pulse. In this talk, the state of the art of currently available photon diagnostic is discussed and novel single shot techniques for the measurement of X-ray pulse duration [1] and arrival time [2] are presented.
[1] U. Fruehling, M. Wieland, M. Gensch et. al., Single-Shot THz-field-driven X-Ray streak camera, Nature Photon. 3 (2009), 528.
[2] F. Tavella, N. Stojanovic, G.A. Geloni and M. Gensch, Few-femtosecond timing at fourth-generation X-ray light sources, accepted.

  • Invited lecture (Conferences)
    DIPAC 2011, 15.-19.05.2011, Hamburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-15740
Publ.-Id: 15740


CFD Simulation of Counter-current Two-phase Flow in a Model of PWR Hot Leg

Deendarlianto; Höhne, T.; Lucas, D.; Vallée, C.

This paper provides a numerical study of the phenomena around the counter-current flow limitation (CCFL) of air-water and steam-water in a model of the hot leg pressurized water reactor (PWR). The calculations were conducted using the commercial CFD software, CFX 13.0 (ANSYS CFX), based on the finite volume method for an Euler-Euler model or free surface model. The simulations were carried out in fully transient manner using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model. In the present numerical study, the drag coefficient was approach by using the Algebraic Interfacial Area Density (AIAD). Next, an image processing technique was also developed in order to obtain the liquid film thickness data in a model PWR hot leg from the high-speed video observations. The results indicated that quantitative agreement between calculation and experimental data was obtained for the occurrence of flooding point and water level inside the hot leg channel.

Keywords: Numerical simulation; Computational fluid dynamics; Counter-current flow limitation; PWR; Drag force

  • Lecture (Conference)
    Multiphase Flows Workshop, Simulation, Experiment and Application, 09.-10.06.2011, Dresden, Germany
  • Contribution to proceedings
    Multiphase Flows Workshop, Simulation, Experiment and Application, 09.-10.06.2011, Dresden, Germany
    Proceeding of the 9th Multiphase Flows Workshop, Simulation, Experiment and Application

Permalink: https://www.hzdr.de/publications/Publ-15739
Publ.-Id: 15739


A novel pilot program for homogeneity testing of natural analogs of synthetic mineral reference materials

Michalak, P. P.; Renno, A. D.; Wiedenbeck, M.; Merchel, S.; Munnik, F.

The growing demand for elements (PGE, REE and refractory metals) desired by the high-tech industry stresses the need for searching for them in non-conventional raw materials. Natural variability of distribution of such elements within the matrices of mineral carriers, frequently, at the micro- and submicrometer level requires employing high-resolution spatial microanalytical techniques as an essential step in quantitative measurements as well as quality assurance procedures (Renno et al. 2010). The necessity for providing reliable, traceable and comparable results for such measurements at the picogram sampling scale makes the use of certified reference materials to be of critical importance. The database of certified reference materials in the form of solutions, powders, pellets, glass beads etc. has been developed by several research groups as well as governmental agencies with certifying capabilities (Jochum 2010). Unfortunately, among such materials natural and synthetic minerals are scarce (Jochum 2010, Wiedenbeck 2010).
Such a lack of mineral reference materials was an incentive for creating a consortium of several German scientific and federal institutions with a common goal of providing a sufficient quantity of synthetic mineral reference materials with concentrations of economically important elements certified at the submicrometer level useful for in-situ analyses with a number of microanalytical methods.
Due to various geological processes natural minerals may develop heterogeneous elemental distribution as well as many structural features that seriously limit their suitability as reference materials. A logical assumption on superiority of synthetic minerals over natural minerals can be made as far as one is able to control chemical and structural homogeneity of the grown crystal. This can be assured by inventing robust homogeneity testing procedure employing both absolute and matrix-corrected methods.
In this study we introduce a systematic approach to homogeneity testing of reference materials using their natural analogs. Microanalytical techniques were selected and introduced on a step-by-step basis in a sequence, depending on their sensitivity and spatial resolution: light and electron microscopy, EPMA, SIMS, PIXE-PIGE, LA-ICPMS, μ-SXRF. The pilot program was launched using three minerals, each representing a different group of minerals of a specific interest to the industry: pyrite, columbite-tantalite and sanidine. All specimens were tested with reflected-light microscopy and scanning electron microscopy (BSE images) and showed no inhomogeneities apart from cracks and some minor inclusions. The results of the chemical homogeneity test will be presented in detail.
The research was supported by the Free State of Saxony, European Union and Helmholtz Association.
References:
[1] A.D. Renno et al., 2010: A development strategy for creating a suite of reference materials for the in-situ microanalysis of non-conventional raw materials. Abstract V51C-2210 presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec.
[2] K.P. Jochum, 2010: Reference materials for in situ microanalysis: Successes and needs, Goldschmidt Conference Abstracts 2010, A470.
[3] M. Wiedenbeck, 2010: Challenges facing the production of RMs for geochemical microanalyses, Goldschmidt Conference Abstracts 2010, A1130.

Keywords: reference materials; spatially resolved analysis

  • Poster
    89. Jahrestagung der Deutschen Mineralogischen Gesellschaft (DMG) in Kooperation mit der Deutschen Kristallographischen Gesellschaft (DGK) und der Österreichischen Mineralogischen Gesellschaft (ÖMG), 20.-24.09.2011, Salzburg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-15738
Publ.-Id: 15738


Fachsitzung: „CFD-Methoden für sicherheitsrelevante Fragestellungen“

Höhne, T.; Schaffrath, A.

Die Leitung der Sitzung hatte Herr Dr. Th. Höhne vom Helmholtz-Zentrum Dresden- Rossendorf, und Herr Dr. A. Schaffrath (TÜV NORD SysTec GmbH & Co. KG) inne.

Keywords: Jahrestagung Kerntechnik; CFD; Fachsitzung; nukleare Sicherheitsforschung

  • atw - International Journal for Nuclear Power 56(2011)7, 419-423

Permalink: https://www.hzdr.de/publications/Publ-15737
Publ.-Id: 15737


XANES and EXAFS analysis of oxidation state and local structure of plutonium reacted with iron oxides under anoxic conditions

Kirsch, R.; Fellhauer, D.; Altmaier, M.; Rossberg, A.; Fanghänel, T.; Charlet, L.; Scheinost, A. C.

Iron minerals form as corrosion products of zero-valent iron and steel in the “near field”, are present in many "far field" barriers (clay or granite) and occur widely in natural sediments. Depending on redox conditions, ground water composition and microbial activity, iron(hydr)oxides such as goethite (-FeOOH), lepidocrocite (-FeOOH), magnetite (FeIIFeIII2O4), and maghemite (-Fe2O3) have been observed as corrosion products of steel [1,2]. The solubility and complexation behavior of plutonium in aqueous systems are highly oxidation state dependent. As Iron(hydr)oxides have been shown to undergo redox reactions with plutonium [3-5] and to form plutonium surface complexes [6], they are expected to control to a large extent the migration behavior of plutonium. For example, sorption of Pu(V) to hematite, goethite and magnetite was found to be accompanied by surface mediated reduction to Pu(IV) [3-5,7]. While many previous laboratory studies have been conducted under air, the intention of our work was to investigate redox reactions of Pu with common iron oxides under well controlled and anoxic conditions to better simulate deep underground conditions. We combined in-situ oxidation state analysis on the mineral surfaces using advanced XAS techniques with wet chemical characterization of redox conditions and thermodynamic modeling. The part of the joint work focusing on aqueous Pu chemistry and thermodynamic description of Pu redox state distribution is presented at Migration’11 by Fellhauer et al..
Synthetic hematite, goethite, maghemite and magnetite were allowed to react under anoxic conditions (O2 ≤ 10 ppmv) in carbonate free 0.1 M NaCl with aqueous 242Pu(III) and 242Pu(V). Pu-LIII-edge XANES and EXAFS spectra were collected after 40 days and six months at the Rossendorf Beamline at ESRF, France, to assess in-situ oxidation states and local structures of plutonium reaction products. All measurements were carried out at 15 K using a closed-cycle He cryostat to reduce thermal disorder in the samples and avoid beam-induced changes in oxidation state.
After reaction with hematite, Pu(V) was largely reduced to Pu(IV) while Pu(III) was oxidized to Pu(IV). For example, after 6 months of reaction with hematite at pH 7.5, 30 % Pu(V) and 70 % Pu(IV) were observed for the sample with Pu(V)initial. Under similar reaction conditions, Pu(III)initial yielded 20 % Pu(V) and 80 Pu(IV). Despite these similar oxidation state distributions of Pu associated with the solid phase, [Pu] concentrations in solution differ for most of the 6 months reaction period by about two orders of magnitude. Final [Pu] concentrations are 2×10 10 M for the Pu(III)initial and 6×10 9 M for the Pu(V)initial samples. The EXAFS spectra gave no evidence for the formation of a solid PuO2 phase.
In magnetite suspensions at pH 6 and pH 8, reduction of Pu(V) to Pu(III) and formation of a Pu(III)-magnetite surface sorption complex was observed. In this surface complex, situated on (111) surfaces with octahedral termination, one Pu atom is linked via three oxygen atoms to three edge-sharing FeO6-octahedra. Due to the tridentate nature of the complex, it is likely to be very stable and play an important role in controlling Pu-magnetite reactions and Pu mobility under reducing conditions. However, at a higher plutonium loading (1 Pu atom / 29 nm2 instead of 1 Pu atom / 58 nm2) and with Pu(V)initial, only 60 % of Pu is surface complexed Pu(III)ads while about 40 % is present as solid PuO2. After 6 months, solution concentrations for Pu(III)initial or Pu(V)initial were at or below the detection limit of ~5×10 11 M (242Pu measured with liquid scintillation counting or ICP-MS).
Reaction with maghemite at pH 6 yielded very similar oxidation state distributions and solution concentrations for Pu(III)initial and Pu(V)initial samples. Changes in Pu(III) / Pu(IV) ratios in the reaction products can be attributed to differing residual Fe(II) contents (maghemite was prepared by oxidation of magnetite). After six months of reaction, Pu was present as 80% Pu(IV). As with magnetite, iron backscatterering indicates formation of an inner sphere surface complex. Formation of a solid PuO2 phase does not occur.
These data highlight the importance of plutonium surface complexation on different iron oxides in controlling environmental [Pu] concentrations. In particular, conservation of non negligible amounts of Pu(V) with hematite (20 to 30 % after 6 months) and goethite (45 % Pu(V) after 40 days) contrasts with published data [5]. In addition, our results highlight the necessity to consider trivalent Pu(III) species in addition to tetravalent Pu(IV) species and PuO2(am,hyd) for risk assessment under reducing conditions.

Keywords: plutonium redox hematite goethite maghemite magnetite XANES EXAFS

  • Contribution to proceedings
    Migration 2011 - 13th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2011, Beijing, China
    Migration 2011 - 13th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, Peking, China: Peking University

Permalink: https://www.hzdr.de/publications/Publ-15736
Publ.-Id: 15736


Plutonium redox reactions with iron oxides under anoxic conditions

Kirsch, R.; Fellhauer, D.; Altmaier, M.; Rossberg, A.; Fanghänel, T.; Charlet, L.; Scheinost, A. C.

The environmental fate of plutonium, the major transuranium actinide in nuclear waste, is largely impacted by its sorption onto [1] and redox reactions [2] with iron oxide minerals that form as corrosion products of steel in the "near field" and occur widely in sediments. To obtain information on oxid-ation state and local structure, we reacted 242Pu as electro-lytically prepared Pu(V) or Pu(III) (1×10-5 M) under anoxic conditions in carbonate free 0.1 M NaCl with hematite, goethite, maghemite and magnetite. Pu-LIII-edge XAFS spectra were collected after 40 d and 6 months of reaction.
Results and Discussion
After reaction of either Pu(III) or Pu(V) with hematite (α-Fe2O3), Pu associated with the solid phase ( > 99.9 % of added Pu) is mainly present as Pu(IV) and up to 30 % Pu(V). Also after reaction with goethite (γ-FeOOH) both Pu(IV) (55 %) and Pu(V) (45 %) are present. For both minerals, EXAFS spectra show no strong Fe-backscattering from the substrate and also give no evidence for the formation of a solid PuO2 phase. In contrast, EXAFS spectra of Pu reacted with maghemite (γ-Fe2O3) and magnetite (Fe3O4) are charac-terized by strong iron backscattering, indicating the formation of inner-sphere surface sorption complexes. With maghemite, oxidation state mixtures of Pu(III) and Pu(IV) or Pu(IV) and Pu(V) were found while with magnetite, Pu(III) was the predominant oxidation state [3]. However, in one case and probably due to an increased Pu / magnetite surface area ratio, formation of PuO2 after reaction of Pu(V) with magnetite was observed. These results highlight the importance of plutonium surface complexation on different iron oxides in controlling environmental [Pu] concentrations. Further, for risk assessment under reducing conditions where Fe(II)-bearing oxides such as magnetite exist, it is necessary to consider trivalent in addition to tetravalent plutonium species and PuO2(am,hyd).
[1] Novikov et al. (2006) Science 314, 638-641. [2] Powell et al. (2005) Environ. Sci. Technol. 39, 2107-2114. [3] Kirsch et al. (2011) submitted to Environ. Sci. Technol.

Keywords: plutonium redox iron oxides magnetite maghemite hematite goethite

  • Contribution to proceedings
    Goldschmidt 2011, 12.-19.08.2011, Prague, Czech Republic
    Proceedings of the Goldschmidt Conference 2011, Cambridge, UK: Cambridge Publications, 1194

Permalink: https://www.hzdr.de/publications/Publ-15735
Publ.-Id: 15735


Validation of a new surface drag formulation within the Morphology Detection Algorithm AIAD for improving horizontal two-phase flow simulations

Höhne, T.; Vallée, C.; Apanasevich, P.

This paper presents different CFD-simulations on flows which are relevant for nuclear reactor safety using a new modelling approach for the interfacial drag at free surfaces. The developed drag coefficient model was implemented together with the Algebraic Interfacial Area Density (AIAD) model (Höhne, 2009) into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The applications considered include the prediction of counter-current flow limitations (CCFL) in a PWR hot leg, the development of hydraulic jump during the air-water co-current flow in a horizontal channel, and pressurized thermal shock (PTS) phenomena in a PWR cold leg and downcomer. For the modelling of these tasks, an Euler–Euler approach was used. This approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model.

To demonstrate the feasibility of the present approach, the computed main parameters of each case were compared with experimental data. It is shown that the CFD calculations agree well with the experimental data. This indicates that the AIAD model combined with new drag force modeling is a promising way to simulate the phenomena in frame of the Euler-Euler approach. Moreover the further validation of the model by including mass transfer effects should be carried out.

Keywords: Computational fluid dynamics (CFD); Algebraic interfacial area density (AIAD) model; Drag coefficient; Pressurized water reactor (PWR); Hot leg; Cold leg; Counter-current flow limitation (CCFL); Hydraulic jump; Slug flow; Stratified flow; Pressurized thermal shocks (PTS); Downcomer

  • Contribution to proceedings
    Multiphase Flows: Simulation, Experiment and Application, 08.-10.06.2011, Dresden, Deutschland
    CD-ROM
  • Lecture (Conference)
    Multiphase Flows: Simulation, Experiment and Application, 08.-10.06.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15734
Publ.-Id: 15734


41 Jahre Betrieb des Rossendorfer Zyklotrons U-120 - Eine Bildersammlung

Guratzsch, H.; (Editor)

Das Rossendorfer Zyklotron ist ein "klassisches" Zyklotron mit 120 cm Polschuhdurchmesser. Als klassisches Zyklotron verfügt es über ein rotationssymmetrisches Magnetfeld. Mit der in radialer Richtung abfallenden Magnetfeldstärke wir die "weiche" Fokussierung erreicht.
Zunächst wurde das Zyklotron für die kernphysikalische Grundlagenforschung genutzt. Später überwogen die Herstellung von Radionukliden, die Neutronenerzeugung für medizinische und radiochemische Anwendungen sowie spezielle Dünnschichtaktivierungen für die Verschleißforschung.
Die Betriebszeit des Zyklotrons erstreckte sich über einen Zeitraum von 41 Jahren, von August 1958 bis Dezember 1999.

Keywords: Zyklotron

  • Other report
    Dresden: FZ Rossendorf, 2000
    20 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15733
Publ.-Id: 15733


Determination of muon attenuation lengths in depth profiles from in situ produced cosmogenic nuclides

Braucher, R.; Bourlès, D.; Merchel, S.; Vidal Romani, J.; Fernadez-Mosquera, D.; Marti, K.; Leanni, L.; Chauvet, F.; Arnold, M.; Aumaître, G.; Keddadouche, K.

Cosmogenic nuclides are important tools to understand and quantify the processes that control the development and evolution of landscapes during the Quaternary. Among all published studies, few are related to the accurate and precise determination of the physical parameters governing their production in the Earth's crust surface (in-situ produced cosmogenic nuclides) and its evolution as a function of depth below the Earth's surface. Currently, it is nearly impossible to advocate global parameters that could be used worldwide. Indeed, at each sampling site, not only the geometry and the mineralogy will differ but also their evolution as a function of depth. In this paper, a new approach based on the measurement of the evolution of cosmogenic nuclide concentrations along depth profiles to determine the muon attenuation lengths is proposed. In this study, the determined attenuation length will integrate the potential effect of the chemical composition of the overlying matrix and will take into account the entire energy range of the incident particles. More, when denudational steady state is reached, muon contributions can be determined. When scaled to sea level, these contributions are similar for a given nuclide whatever the site where they have been determined. The average weighted muon contribution are (0.028 ± 0.004) at/g/a for 10Be, (0.233±0.045) at/g/a for 26Al and (1.063 ± 0.329) at/g/a for 36Cl and are valid within the depth range 0 - 6500 g/cm2.

Keywords: Cosmogenic nuclides; muon; attenuation length; depth profile

Permalink: https://www.hzdr.de/publications/Publ-15732
Publ.-Id: 15732


Sorption and interfacial redox of Sn(II) under anoxic conditions: Magnetite vs. anatase

Dulnee, S.; Banerjee, D.; Rossberg, A.; Scheinost, A. C.

The long-lived fission product 126Sn is of substantial interest in the context of nuclear waste deposition in deep underground repositories. However, the redox state (di- or tetravalent) under the expected anoxic conditions is still a matter of debate. We therefore investigated the stability of Sn(II) in the presence of a highly redox-reactive mineral, magnetite (FeIIFeIII2O4), in comparison to a non-redox-reactive, anatase (TiO2).
Sorption experiments were performed at < 2 ppm O2, and redox state and local structure was monitored over time by X-ray absorption spectroscopy (XAS).
We found a rapid (< 30 min) oxidation of Sn(II) to Sn(IV) in the presence of magnetite. Although solubility calculation predicted the precipitation of SnO2, the local structure determined by XAS showed two Sn-Fe distances of about 3.15 and 3.60 Å in line with edge and corner sharing arrangements between octahedrally coordinated Sn(IV) and the magnetite surface, indicative of inner-sphere complexation. The structure of the complex remained largely unchanged up to an equilibration time of 1 month.
After 30 min reaction with anatase, Sn(II) was conserved. However, even with the redox-inert anatase, Sn(II) oxidized to Sn(IV) over time, forming an Sn(IV) inner-sphere complex with Sn-Ti distances at 3.24 and 3.53 Å. Therefore, our results clearly indicate that Sn(IV) is the most relevant oxidation state to be considered even under reducing conditions, and that inner-sphere complexation is a relevant retention mechanism.

Keywords: Sn; Sorption; Magnetite; Anatase; Redox; XAFS; Molecular structure

  • Poster
    Goldschmidt2011, 14.-19.08.2011, Prague, Czech Republic
  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-15731
Publ.-Id: 15731


Countercurrent flow limitations in a pressurized water reactor

Deendarlianto; Höhne, T.; Murase, M.

In the event of hypothetical accident scenarios in a pressurized water reactor (PWR), emergency strategies have to be mapped out, in order to guarantee the reliable removal of decay heat from the reactor core. One essential passive heat removal mechanism is the reflux cooling mode. It can appear during a small break loss-of-coolant-accident (LOCA) or because of loss of residual heat removal (RHR) system during mid loop operation at plant outage. In the scenario of a loss-of-coolant-accident (LOCA) in a PWR, it is considered that the reactor will be depressurized and vaporization will take place. Should this lead to “reflux condensation”, which may be a favorable event progression, the generated steam will flow to the steam generator. This steam will condense in the steam generator and the condensate will flow back through the hot leg to the reactor, resulting in countercurrent steam/water flow.

For a given condensate flow rate, if the steam mass flow rate increases to a certain value, a portion of the condensate will exhibit a partial flow reversal by the steam in the opposite flow direction towards the steam generator. This phenomenon is known as counter-current flow limitation (CCFL). The keys to CCFL control is an improved understanding of these conditions, development of a suitable experimental data base, novel tools to characterize the practical conditions in order to produce a better physical CCFL model.

We invite investigators to contribute original research articles as well as review articles that will simulate the continuing efforts to understanding this important phenomenon. We are interested also in articles that explore the CCFL in a simple pipe configuration in order to support the physic behind the CCFL phenomena.

Potential topics include, but are not limited to:
• New experimental investigations on the counter-current gas-liquid two-phase flow in a PWR hot leg as well as in downcomer and tie plate during blow down
• Development of experimental database on CCFL in a simple pipe/channel construction.
• Development of phenomenological and analytical model for the prediction of CCFL in a certain part of a PWR as well as in a simple channel construction.
• Computational fluid dynamics (CFD) effort on CCFL and relating phenomena, such as, water hammer, steam-condensation and reflooding behavior.
• Latest experimental techniques require to investigate CCFL and provide data for CFD validation
• Future discussion on R&D need about CCFL issues, with a focus on fuel coolability and relating severe accidents in a nuclear reactor

Keywords: CCFL; CFD; AIAD

Permalink: https://www.hzdr.de/publications/Publ-15730
Publ.-Id: 15730


Magneto-optical coupling of ferromagnetic thin films investigated by vector-magneto-optical generalized ellipsometry

Mok, K. M.; Kovacs, G. J.; McCord, J.; Li, L.; Helm, M.; Schmidt, H.

We performed generalized Mueller matrix ellipsometry measurements in a magnetic field of arbitrary orientation and magnitude up to 400 mT at room temperature and probed the magneto-optical response of capped, ferromagnetic Fe, Ni20Fe80, Co, Ni80Fe20, and Ni thin films on ZnO substrates in the spectral range from 300 to 1100 nm. We determined the off-diagonal elements in the magneto-optical dielectric tensor under saturated magnetization conditions in the sample surface plane via a model analysis. The off-diagonal elements depend on the net spin polarization and the electronic band structure of the ferromagnetic thin films. For the pure ferromagnetic metals Fe, Co, and Ni, the converted off-diagonal elements agree well with the reported experimental optical conductivity data. As a result we use the extracted wavelength-dependent magneto-optical coupling constant to predict the wavelength-dependent magneto-optical response of different Ni/Fe multilayer structures.

Keywords: magneto-optics; Mueller matrix; generalized ellipsometry; ferromagnetic

Permalink: https://www.hzdr.de/publications/Publ-15729
Publ.-Id: 15729


Combined electromagnetic tomography for determining two-phase flow characteristics in the submerged entry nozzle and in the mould of a continuous-casting model

Wondrak, T.; Eckert, S.; Gerbeth, G.; Klotsche, K.; Stefani, F.; Timmel, K.; Peyton, A.; Terzija, N.; Yin, W.

The paper describes experiments on the combined determination of the distribution of liquid metal and argon in the submerged entry nozzle (SEN) and of the flow in the mould of a small-scale physical model of a continuous slab caster. For visualizing the metal distribution in the SEN, Mutual Inductance Tomography (MIT) is applied, while the flow in the mould is determined by Contactless Inductive Flow Tomography (CIFT). The results of the latter are validated in part by Ultrasonic Doppler Velocimetry (UDV). Accompanying measurements provide information about the levels in the tundish and in the mould, as well as on the pressure in the SEN. Depending on the gas flow rate, various flow regimes are identified, among them mould level oscillations, transitions between double and single vortex flows, and transient single port ejections.

Permalink: https://www.hzdr.de/publications/Publ-15728
Publ.-Id: 15728


Magnetic properties of granular CoCrPt:SiO2 recording media deposited on GaSb nanocones

Ball, D. K.; Günther, S.; Krone, P.; Fritzsche, M.; Varvaro, G.; Makarov, D.; Lenz, K.; Mücklich, A.; Facsko, S.; Fassbender, J.; Albrecht, M.

Investigation of the magnetization reversal in arrays of magnetic nanostructures is relevant for both fundamental understanding as well as application for magnetic data storage. We present a study of the magnetization reversal in granular CoCrPt:SiO2 recording media with weakly interacting magnetic grains grown onto prestructured templates fabricated by ion irradiation of GaSb. By tuning the irradiation conditions assemblies of nanocones of different size and periodicity were prepared. Columnar CoCrPt grains with their c-axis normal to the surface of the cones were formed as evidenced by HR-TEM. The spread of the c-axis of these grains results in a tilted easy magnetization axis with respect to the substrate normal. Investigation of the integral magnetic properties by vector-VSM reveals a decrease of the remanence with increasing cone size. The magnetic domain patterns observed by MFM suggest that the CoCrPt behaves as a single-domain cap structure on the cones.

  • Poster
    INTERMAG 2011 Taipei, IEEE International Magnetics Conference, 25.-29.04.2011, Taipei, Taiwan

Permalink: https://www.hzdr.de/publications/Publ-15727
Publ.-Id: 15727


Morphology Induced Magnetic Anisotropy of Thin Films Deposited on Nanoscale Ripple Substrates

Körner, M.; Liedke, M. O.; Lenz, K.; Ranjan, M.; Fritzsche, M.; Facsko, S.; Fassbender, J.; von Hörsten, U.; Krumme, B.; Wende, H.

The control of static and especially dynamic magnetic response of ferromagnetic thin films is one of the utmost challenges in applied magnetism. Therefore the adjustment of magnetic anisotropy and the connected resonance frequency, as well as the magnetic damping parameter are of fundamental importance to insure functionality in existing and envisioned spintronic applications.
Here we indirectly tailor the effective magnetic properties of magnetic thin films by changing the morphology of substrates with periodically modulated patterns on the nanometer scale [1]. These well ordered surface modulations (ripple) can be produced by low energy ion beam erosion and are tuneable over a wide range [2]. Thin magnetic films deposited on these ripple surfaces repeat the surface profiles of the patterns and thus an additional uniaxial magnetic anisotropy is induced. Results are shown for thin films of Fe, Co as well as the quasi-Heusler compound Fe3Si. The effective magnetic anisotropy is determined by means of angular- as well as frequency-dependent ferromagnetic resonance measurements using a vector network analyzer based setup. We find a strong uniaxial magnetic anisotropy induced by the ripple surface, which is superimposed on the cubic anisotropy in the case of single crystalline films. Influences of the rippled surface on the magnetic damping parameter will be discussed.
This work is supported by DFG grant FA 314/6-1.

[1] M. Körner et al., Phys. Rev. B 80, 214401 (2009).
[2] J. Fassbender et al., New Journal of Physics 11, 125002 (2009).

  • Poster
    IEEE Magnetics Society Summer School, 22.-28.05.2011, New Orleans, USA

Permalink: https://www.hzdr.de/publications/Publ-15725
Publ.-Id: 15725


Improved 36Cl Performance at the ASTER HVE 5 MV Accelerator Mass Spectrometer National Facility

Finkel, R. C.; Arnold, M.; Aumaître, G.; Benedetti, L.; Bourlès, D. L.; Keddadouche, K.; Merchel, S.

The HVE 5 MV ASTER AMS national facility at CEREGE was accepted in 2007. Since then we have continued to optimize performance for 36Cl. Cl-36 analyses use AgCl, a Cs negative ion sputter source, Ar stripping to +5 in the terminal of the Tandetron™ accelerator at 5 MV and a Si3N4 postacceleration stripper foil to enhance suppression of 36S relative to 36Cl. The major challenges to obtaining the desired performance for Earth science applications are ion source memory, mass fractionation effects, 36S isobar suppression and sensitivity. Redesign of the SO110 ion source by HVE to change the size of the aperture and the shape of cathode significantly reduced ion source memory to less than ~0.1%, a level that can be compensated for by matching standards to samples. We observe small systematic drifts in 35Cl/37Cl ratios over time, the source of which is not yet determined.
Measurement of standards indicates that this effect limits the precision of 35Cl/37Cl ratio determination to about 2%. 36S is suppressed in several ways. First, the sample chemistry has been designed to reduce S to very low levels. Second, cathodes are constructed of low-S nickel, enabling direct target loading without the use of AgBr pre-packing. Third, a post-acceleration Si3N4 stripper foil differentially absorbs energy from 36Cl and 36S. A ubsequent electrostatic deflector is then able to suppress 36S by a factor of ~5x10-3. Differential energy loss in the detector further suppresses 36S by about 10-4, for an overall suppression of 5x10-7. 36S count rates are typically equivalent to a background 36Cl/Cl of <10-15. At typical 35Cl currents of 20 μA samples with 36Cl/35Cl of 5x10-14 can be measured to ± 6% statistical uncertainty with one hour of analysis time. Typical machine blanks have 36Cl/Cl ~2x10-15.

Keywords: accelerator mass spectrometry; 36Cl capability; ASTER; ion source memory

Permalink: https://www.hzdr.de/publications/Publ-15724
Publ.-Id: 15724


Magnetic anisotropy engineering: single crystalline Fe films on ripple surfaces

Liedke, M. O.; Körner, M.; Lenz, K.; Strache, T.; Shalimov, A.; Ranjan, M.; Facsko, S.; Fassbender, J.; McCord, J.

Nanostructuring by means of ion erosion has proven its versatility with respect to the surface morphology control. By varying different ion irradiation parameters, e.g. ion energy, fluence, incident angle, and sample temperature, the assembly of self-organized periodically ordered arrays of nano-dots [1] and ripples [2] is possible. This has been proven for semiconductors as well as for metals [3,4]. Especially, nanopatterning of magnetic materials is intriguing due to the fact that not only the surface morphology is affected, but the overall magnetic properties are accordingly modified. For example, ion bombardment of single crystal Fe films enables the manipulation of the in-plane uniaxial magnetic anisotropy (UMA) that is associated with the ripple morphology [5].

Here we present a novel bottom-up method of magnetic film patterning, where a highly ordered periodic MgO ripple surface with a wavelength on the nanometer scale is coated by a magnetic Fe layer. The modulations can be induced along any arbitrary in-plane orientation and outstandingly, the surface stays crystalline upon ion irradiation. Thus, due to the low lattice mismatch single crystalline Fe can be grown onto such templates. Despite the intrinsic magnetic cubic anisotropy (CA) of bcc Fe additional UMA is introduced.

As a reference a model cubic system, i.e. Fe on flat MgO(100), has been grown. 15 nm of Fe (tFe) was deposited onto the MgO(100) substrate at room temperature by means of molecular beam epitaxy (MBE). In-plane magneto-optic Kerr effect (MOKE) and ferromagnetic resonance (FMR) angular measurements were performed revealing clear evidence of a four-fold symmetry (CA; K4||/M=186.3 Oe) superimposed with a very small two-fold symmetry contribution (UMA; K2||/M=2 Oe). The magnetic reversal curves (MRCs) shown in Fig. 1a (top panel) correspond to three distinguished sample orientations with respect to the angle φH of the external magnetic field. The curves represent the hard (HA), intermediate, and easy (EA) magnetization orientations of the cubic system. The MRC at φH=18° exhibits a two-jump magnetization process that is a consequence of nucleation and propagation of 90° domain walls (DWs), which is confirmed by magnetic domain observations performed by magneto-optical Kerr microscopy.

In a second step, ripple MgO substrates of a wavelength λrip≈20 nm were prepared (for the AFM micrograph refer to Fig. 1a, top panel) and coated with Fe. Several Fe thicknesses were evaporated in the range of 5-30 nm onto templates with a few distinct in-plane ripple orientations with respect to the MgO [100] direction (0°≤φrip≤60°). Thus, due to the combination of the periodic morphology and the intrinsic magnetic properties of Fe, an ensemble of two-fold and four-fold magnetic symmetry is created. This is confirmed by FMR and MOKE measurements. In general, the UMA originates from dipolar and step-edge effects. The orientation and strength of the UMA depends on the angle of ripple ridges elongation φrip with respect to the MgO [100] direction and Fe film thickness, respectively. First evidence of strong UMA emerges already from MRCs analysis as shown for a sample with φrip≈25° (Fig. 1a, bottom panel), where for in-plane orientations between HA and EA directions a three-jump magnetization process is found. From Kerr microscopy investigations, the magnetization reversal process can be described as a subsequent nucleation and propagation of 90°, 180°, and then again 90° DWs. FMR analysis, i.e. fit of the in-plane angular resonance frequency fres dependence, reveals anisotropy fields and orientations of both anisotropy contributions (Fig. 1b). E.g., for the ripple sample with tFe=15 nm the CA and UMA fields are K4||/M=306 Oe and K2||/M=20 Oe, respectively. Both values are strongly increased relative to flat Fe films. Moreover, the orientation of the UMA coincides with the elongation direction of the ripple ridges for all the samples. In addition, we find that the UMA decreases as a function of Fe thickness, whereas the CA behaves the opposite way. The origin and interaction of the magnetic anisotropy contributions will be discussed in detail. References: [1] S. Facsko et al., Science 285, 1551 (1999)
[2] E. Chason et al., Phys. Rev. Lett. 72, 3040 (1994)
[3] R. Moroni et al., Phys. Rev. Lett. 91, 167207 (2003)
[4] F. Bisio et al., Phys. Rev. Lett. 96, 057204 (2006)
[5] Q. F. Zhan et al., Phys. Rev. B 80, 094416 (2009)

  • Lecture (Conference)
    IEEE International Magnetics Conference, Intermag 2011, 25.-29.04.2011, Tapei, Taiwan

Permalink: https://www.hzdr.de/publications/Publ-15723
Publ.-Id: 15723


Experiments for real time in-vivo dosimetry

Fiedler, F.

no abstract available

Keywords: in-vivo dosimetry; ion therapy; prompt gamma imaging; in-beam PET; TOF PET

  • Invited lecture (Conferences)
    KVI PAC Meeting, 22.06.2011, Groningen, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-15722
Publ.-Id: 15722


Operating a high QE photocathode inside a SRF gun, introducing the HZDR/ELBE SRF gun, and plans for operation of GaAs cathodes at HZDR

Teichert, J.

  • Lecture (Conference)
    Workshop on photocathodes for high brightness, high average current beams, 30.-31.05.2011, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-15720
Publ.-Id: 15720


Slice-Emittance Measurements at ELBE/SRF-Injector

Teichert, J.; Rudolph, J.; Kamps, T.; Abo-Bakr, M.

The linear accelerator ELBE delivers high-brightness electron bunches to multiple user stations, including an IR-FEL. The current thermionic injector is being replaced by a superconducting rf photoinjector (SRFinjector) which promises higher beam quality. Using a transfer chicane, beam from the SRF-injector can be injected into the ELBE linac. Detailed characterization of the electron beam is achieved by measuring the vertical slice emittance of the beam. To perform this measurement a combination of rf zero-phasing, spectrometer dipole and quadrupole scan is used. The electron beam is accelerated by the first cavity of the ELBE accelerator module and send through a second cavity which is operated at zero-crossing of the rf. In doing so a linear energy-time correlation is induced to the beam. The chirped beam is send through a spectrometer dipole and the longitudinal distribution can be made visible on a scintillator screen. Performing a quadrupole scan allows the determination of the emittance for di_erent slices. This paper explains the working principle of the method and the experimental setup and shows results of performed simulations as well as first measurement results.

  • Poster
    DIPAC 2011, 16.-18.05.2011, Hamburg, Deutschland
  • Open Access Logo Contribution to proceedings
    DIPAC 2011, 16.-18.05.2011, Hamburg, Deutschland
    Proceedings of DIPAC 2011, 416-418

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Permalink: https://www.hzdr.de/publications/Publ-15719
Publ.-Id: 15719


Pulsed Mode Operation and Longitudinal Parameter Measurement of the Rossendorf SRF Gun

Teichert, J.; Arnold, A.; Buettig, H.; Justus, M.; Lehnert, U.; Michel, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Xiang, R.; Klemz, G.; Kamps, T.; Rudolph, J.; Schenk, M.; Will, I.

The Rossendorf SRF gun with a 3 1/2 cell cavity has been operated since 2007. It has produced CW beam with the electron energy of 3 MeV and the average current up to 16 μA. The electron beam of the gun has successfully injected the ELBE superconducting linac since 2010. The Nb cavity has shown constant quality during the operation and for the Cs2Te photocathode life time of months could be obtained. Recently the gun started to run in the pulsed mode with higher gradient. The longitudinal parameters have been measured in this mode. The dark current arose from the high gradient is studied. The main field emission source has been found to be the half cell. Meanwhile, two modified 3+1/2 cell niobium cavities have been fabricated and tested in Jlab. In this paper the new status of the SRF gun will be presented, and the latest results of the beam experiments will be discussed.

  • Poster
    IPAC 2011, 04.-09.09.2011, San Sebastian, Spain
  • Open Access Logo Contribution to proceedings
    IPAC 2011, 04.-09.09.2011, San Sebastian, Spain
    Proceedings of IPAC2011, 262-264

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Permalink: https://www.hzdr.de/publications/Publ-15718
Publ.-Id: 15718


Operational Experience of NC Cathodes Inside SRF Gun Cavity

Teichert, J.

  • Lecture (Conference)
    Workshop on Photocathodes for RF guns, 01.-02.03.2011, Lecce, Italy

Permalink: https://www.hzdr.de/publications/Publ-15717
Publ.-Id: 15717


Cryostats and Mechanics

Murcek, P.

German-Turkish Workshop on Superconducting Accelerators for FEL and Bremsstrahlung Applications

  • Lecture (Conference)
    German-Turkish Workshop on Superconducting Accelerators for FEL and Bremsstrahlung, 31.01.-03.02.2011, Antalya, Turkey

Permalink: https://www.hzdr.de/publications/Publ-15715
Publ.-Id: 15715


Superconducting Resonators

Arnold, A.

  • Lecture (Conference)
    German-Turkish Workshop on Superconducting Accelerators for FEL and Bremsstrahlung Applications, 31.01.-03.02.2011, Antalya, Turkey

Permalink: https://www.hzdr.de/publications/Publ-15714
Publ.-Id: 15714


PET imaging of central σ 1 receptors: Automated synthesis and purification of [18F]fluspidine

Maisonial, A.; Funke, U.; Fischer, S.; Hiller, A.; Wünsch, B.; Steinbach, J.; Brust, P.

Objectives: Sigma1 (σ1) receptors represent attractive targets for the development of new therapeutic drugs and diagnostic imaging agents for various cerebral diseases. Currently, there is a growing interest in the development of selective and high affinity radioligands for in vivo imaging studies of these receptors using positron emission tomography (PET). With this view, we recently developed a promising fluorinated radioligand, [18F]fluspidine, which offers great potential for neuroimaging of central σ1 receptors with PET [1,2]. Herein we report on a first reliable and high yield automatic synthesis of [18F]fluspidine.
Methods: The synthesis of [18F]fluspidine was performed in a lead-shielded hot cell using a modified TRACERlab FXFN synthesizer. The synthesis module is schematized in Figure 1. First, target water solution was passed through a preconditioned anion exchange cartridge (1). Trapped [18F]fluoride was then eluted to the reactor (2) with a potassium carbonate solution (3). A solution of K2.2.2 in acetonitrile (4) was added and the mixture was dried azeotropically according to standard procedures. The K[18F]F-K2.2.2-carbonate complex reacted with the corresponding tosylate precursor in acetonitrile (5) at 85°C for 15 minutes. After cooling, the crude reaction mixture was diluted with water (6) and directly applied to an isocratic semi-preparative RP-HPLC for purification (7), featured by three optional systems of mobile (organic solvent/H2O with no, neutral or acidic buffer) and stationary phase (nonpolar and polar encapped RP). The appropriate fraction was collected in a flask prefilled with water (8) and the whole solution was passed through a solid phase extraction cartridge (9). The trapped radiotracer was then washed with water (10) and finally eluted to the product vial (11) with absolute ethanol (12).

Results: Nucleophilic radiofluorination of the tosylate precursor was optimized regarding reaction time, temperature and concentration to reach labelling efficiencies > 87%. After purification by semi-preparative HPLC and solid phase extraction methods, [18F]fluspidine was produced within 60-75 minutes for the entire process with an overall radiochemical yield of 37.9 ± 3.9% (based on cyclotron-produced [18F]fluoride ion). The radiochemical purity exceeded 99 % in all cases and the specific activity determined at the end of the process was > 120 GBq/µmol.
Conclusions: A rapid one-pot automated procedure for the regular and consistent production of [18F]fluspidine was successfully accomplished with highly reproducible yields as well as high radiochemical purity and specific activity. The implementation of this radiosynthesis into a commercial platform will make [18F]fluspidine easier accessible for further preclinical and clinical studies.
Research Support: This work was supported by the Deutsche Forschungsgemeinschaft.
References: [1] Große Maestrup, E. et al. (2011), Bioorg. Med. Chem., 19, 393-405, [2] Fischer, S. et al. (2011), Eur. J. Nucl. Med. Mol. Imaging., 38, 540-551.

  • Poster
    ISRS2011, 28.08.-02.09.2011, Amsterdam, The Netherlands
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011)1, 420-420

Permalink: https://www.hzdr.de/publications/Publ-15713
Publ.-Id: 15713


Radiosynthesis, in vitro and in vivo evaluation of a 7-(2-[18F]fluoroethoxy)-6-methoxyquinazoline derivative for imaging PDE10A with PET

Funke, U.; Schwan, G.; Scheunemann, M.; Maisonial, A.; Hiller, A.; Fischer, S.; Deuther-Conrad, W.; Egerland, U.; Briel, D.; Nieber, K.; Sträter, N.; Brust, P.

Objectives: To improve some of the cognitive symptoms of schizophrenia, a 6,7-dimethoxy-4-pyrrolidinylquinazoline has been designed as a potent and selective brain penetrable inhibitor of phosphodiesterase 10A (PDE10A, Ki,PDE10A = 4 nM [1]). Based on this structure we developed a 7-[18F]fluoroethoxy-derivative [18F]I as potential PET radiotracer for imaging PDE10A in brain.
Methods: Non-radioactive reference compounds and precursors were prepared by multi-step syntheses and screened for their PDE10A inhibition as well as selectivity in enzyme activity studies. Radiolabelling of the derivative of highest PDE10A inhibition was initially performed via conversion of 1,3-bistosyloxyethane into [18F]fluoroethyltosylate using n.c.a. K[18F]F-K2.2.2-carbonate complex, and subsequently direct etherification of a deprotonated 7-hydroxy-derivative II to [18F]I (Fig. 1, left-hand). Afterwards, one-step radiosynthesis was developed by direct substitution of a 7-tosyloxy-analogue III with n.c.a. [18F]fluoride (Fig. 1, right-hand). [18F]I was purified by SPE and semi-preparative radio-HPLC. Samples were monitored by radio-TLC and -HPLC. Lipophilicity (logD7.0-7.4) was determined by shake-flask as well as HPLC methods. Further pharmacological characterisation of [18F]I included in vitro determination of PDE10A affinity (KD,PDE10A, PDE10A transfected SF21 cells), in vivo biodistribution and brain uptake studies, metabolism and ex vivo brain autoradiography in female CD-1 mice, with validation of target specificity by homologous competition (I, 5 mg/kg at 15 min before radiotracer) and pre-treatment with high PDE10A specific MP-10 (5 mg/kg at 15 min before radiotracer).

Results: Two-step radiosyntheses of [18F]I resulted in radiochemical yields (RCY) of 18-29% (3.5-4.5 h, based on [18F]F- aqueous solution) and radiochemical purities (RP) of 92-99%. Improvement was obtained by direct radiofluorination: RCY of 17-40% (3-4 h), RP ≥ 99% and specific activities of 110-1110 GBq/mol. By homologous competition assays a KD,PDE10A of 14 nM was estimated. The logD7.0-7.4 was determined with ~ 2.6. According to this a sufficiently high initial brain uptake has been observed (2.3%ID/g at 5 min p.i. in striatum). However, radioligand binding in vivo (1.14%ID/g 60 min p.i.) was not inhibited by competition with I (1.3%ID/g) as well as MP-10 (1.4%ID/g). In plasma and brain, respectively, 70% and 96% of the radioactivity detected at 30 and 60 min p.i. corresponded to native radioligand. No evidence for defluorination of the radioligand was obtained.
Conclusions: Convenient radiochemical results, a moderate lipophilicity and a high PDE10A affinity indicate [18F]I to be a suitable radiotracer. However, further structural optimization is needed to improve the in vivo properties and to make this radioligand appropriate for neuroimaging of PDE10A with PET.
Research Support: Europäischer Fond für regionale Entwicklung (EFRE).
References: [1] Chappie, T.A. et al. (2007), J. Med. Chem., 50, 182-185.

  • Poster
    ISRS2011, 28.08.-02.09.2011, Amsterdam, The Netherlands
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011)1, 268-268

Permalink: https://www.hzdr.de/publications/Publ-15712
Publ.-Id: 15712


Synthesis and evaluation of THIQ based indoles as potential PET radioligands for imaging the serotonin transporter

Funke, U.; Ben-Daniel, R.; Scheunemann, M.; Fischer, S.; Hiller, A.; Rühl, T.; Deuther-Conrad, W.; Patt, M.; Mishani, E.; Steinbach, J.; Sabri, O.; Brust, P.

Objectives: The serotonin transporter (SERT) is crucial for the regulation of the synaptic concentration of serotonin and is a primary target in the development of antidepressants. To provide access to new efficient ligands for the SERT binding site for PET imaging, N-substituted tetrahydroisoquinoline (THIQ) derivatives both of electron-deficient 3-cyclohexyl and 3-propylindole were selected as lead. Thus, cis-5-cyanoindole-3-yl cyclohexylamine (CFPI, Ki,hSERT = 6.2 nM) labelled with fluorine-18 [1] and the 5-fluoroindole-3-yl propylamine (FMI, Ki,hSERT = 4.1 nM) labelled with carbon-11 [2] were developed as new PET-agents. Here we report on the labelling of CFPI and FMI, and the evaluation of both radiotracers in vivo.
Methods: [18F]CFPI was synthesized via nucleophilic etherification of the corresponding tetrahydroisoquinolin-6-ol with 1-[18F]fluoro-2-tosyloxyethane ([18F]FETos) as secondary labelling agent. It was obtained by a two-step process followed by semipreparative HPLC purification with an overall RCY of 13±7% (decay corrected EOB, total synthesis time 180 min). [11C]FMI was synthesized similarly by an etherification process of the corresponding tetrahydroisoquinolin-6-ol with [11C]CH3I to yield the product with RCY 10±4% (decay corrected EOB, total synthesis time 27 min). The brain uptake kinetics and the target specicficity of [18F]CFPI was investigated in female CD-1 mice by organ distribution at 5, 30, 60, and 120 min p.i., and blocking studies at 60 min p.i. (n=4 per time point). The distribution of [11C]FMI in the brain of juvenile pig was assessed by dynamic PET imaging under baseline and consecutively blocking conditions (n=2). Pre-treatment with citalopram (5 mg/kg) as selective SERT ligand was used to asses the specificity of the binding of [11C]FMI. For comparison, [11C]DASB was investigated in an additional animal.


Results: Radiotracers were obtained in radiochemical purity of ≥99%, with specific activity of 1500 GBq/µmol for [11C]FMI and 150 GBq/µmol for [18F]CFPI. PET scans were performed after i.v. injection of 0.5 – 1 GBq [11C]FMI. In comparison to [11C]DASB with a midbrain-to-cerebellum ratio of 2 at 120 min p.i., [11C]FMI displayed no specific accumulation in SERT-relevant regions (midbrain-to-cerebellum ratio ~1 at 120 min p.i.). Furthermore, pre-tretament with citalopram did not affect the uptake of [11C]FMI in different brain regions as observed by the time activity curves. Comparable results were obtained in biodistribution studies on [18F]CFPI. After i.v. injection of ~ 300 kBq [18F]CFPI, brain-to-plasma ratios of <1 were determined at each time up to 120 min p.i. Low clearance from the brain and other organs implies a high non-specific binding. Pre-treatment with citalopram was without effect on the activity distribution or elimination route of [18F]CFPI.
Conclusions: The in vivo data obtained for [11C]FMI in pig brain and [18F]CFPI in mice indicate a high non-specific binding of the two radiolabelled N-substituted THIQ derivatives. Therefore, both [11C]FMI and [18F]CFPI are not suitable as SERT-selective PET radioligands.
Research Support: Work was supported by DFG, BMBF and Joint German-Israeli Research Program (MOST #1888).
References: [1] Funke, U. et al. (2008), Biorg. Med. Chem. Lett. 18, 4727-3047, [2] Ben-Daniel, R. et al. (2008) Biorg. Med. Chem. 16, 6364-6370.

  • Poster
    ISRS2011, 28.08.-02.09.2011, Amsterdam, The Netherlands
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 54(2011)1, 284-284

Permalink: https://www.hzdr.de/publications/Publ-15711
Publ.-Id: 15711


Electron Sources

Teichert, J.

  • Lecture (Conference)
    German-Turkish Workshop on Superconducting Accelerators for FEL and Bremsstrahlung Applications, 31.01.-02.03.2011, Antalya, Turkey

Permalink: https://www.hzdr.de/publications/Publ-15710
Publ.-Id: 15710


Ge-Si-O phase separation and Ge nanocrystals growth in Ge:SiO2/SiO2 multilayers – A new dc magnetron approach

Zschintzsch, M.; Sahle, C. J.; von Borany, J.; Sternemann, C.; Mücklich, A.; Nyrow, A.; Schwamberger, A.; Tolan, M.

Ge:SiOx /SiO2 multilayers are fabricated using a new reactive dc magnetron sputtering approach. The influence of the multilayer stoichiometry on the ternary Ge–Si–O phase separation and the subsequent size-controlled Ge nanocrystal formation is explored by means of x-ray absorption spectroscopy, x-ray diffraction, electron microscopy and Raman spectroscopy. The ternary system Ge–Si–O reveals complete Ge–O phase separation at 400°C which does not differ significantly to the binary Ge–O system. Ge nanocrystals of < 5 nm size are generated after subsequent annealing below 700°C. It is shown that Ge oxides contained in the as-deposited multilayers are reduced by a surrounding unsaturated silica matrix. A stoichiometric regime was found where almost no GeO2 is present after annealing. Thus, the Ge nanocrystals become completely embedded in a stoichiometric silica matrix favouring the use for photovoltaic applications.

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

Permalink: https://www.hzdr.de/publications/Publ-15708
Publ.-Id: 15708


The French accelerator mass spectrometry facility ASTER after 4 years: Status and recent developments on 36Cl and 129I

Arnold, M.; Aumaître, G.; Bourlès, D. L.; Keddadouche, K.; Braucher, R.; Finkel, R. C.; Nottoli, E.; Benedetti, L.; Merchel, S.

Since the acceptance tests of the French 5 MV accelerator mass spectrometry facility ASTER in 2007, routine measurement conditions for the long-lived radionuclides 10Be and 26Al have been established. Yearly sample throughput as high as over 3300 unknowns has been reached for 10Be in 2010. Unacceptable cross-contamination for volatile elements has been largely solved by an ion source upgrade allowing 36Cl measurements at ASTER. However, recent long-term tests using 35Cl/37Cl samples with strongly varying ratios have shown that identical targets lead to different 35Cl/37Cl results at the 2-4% level when being measured after a time gap of 24 hours while the source is running other samples. Besides time dependent mass fractionation, another very likely reason for this effect might be source memory, thus, asking for sophisticated measurement strategies and improved data evaluation and eventually further ion source improvement. Finally, after establishing quality assurance by cross-calibration of secondary in-house 26Al and 41Ca standards and taking part in round-robin exercises of 10Be and 36Cl, a two-step cross-calibration of secondary in-house 129I standards has been performed. The NIST 3231 containing 129I/127I at 0.981 x 10-6 has been used for step-wise dilution with NaI to produce gram-quantities of lower-level standards for every-day use. The resulting material SM-I-9 (129I/127I: ~1 x 10-9) has been measured vs. AgI produced from the two NIST ampoules with (0.982+0.012) x 10-8 solution using minimum chemistry. In a second stage, SM-I-10 and SM-I-11 with ratios of ~1 x 10-10 and ~1 x 10-11, respectively, have been cross-calibrated against SM-I-9. Individual uncertainties of the traceable secondary standards are 1.3-1.4 % (2σ), mainly originating from the given uncertainty of the primary NIST 3231 at 10-8. The cross-contamination for iodine is in the range of 0.4-0.6% within the first 20 hours of running the source.

Keywords: accelerator mass spectrometry; terrestrial cosmogenic nuclides (TCN); calibration

Permalink: https://www.hzdr.de/publications/Publ-15707
Publ.-Id: 15707


Fracture mechanics characterisation of forged base metal ring of the decommissioned reactor pressure vessel of NPP Greifswald WWER-440 unit 4

Viehrig, H.-W.; Houska, M.; Altstadt, E.; Kuechler, R.

The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald NPP representing the first generation of Russian type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs represent different material conditions viz. irradiated, irradiated & annealed and irradiated, annealed and re-irradiated. The paper presents test results measured on the trepan taken from the forged base metal ring 0.3.1. located in the reactor core region of the Unit 4 RPV. This unit was shut down after 11 years of operation and represents the irradiated condition. The key part of the testing is focused on the determination of the reference temperature T0 following the ASTM test standard E1921-10. The T0 of 11 thickness locations from the inner to the outer RPV wall varies between 112°C and 130°C with a mean value of 121°C. These are very low values for WWER RPV steel irradiated with fluences between 5.4 to 1.2•1019n/cm2 (E>0.5 MeV) from the inner to the outer RPV wall.
The fracture toughness values at cleavage failure, KJc, measured on LS oriented pre-cracked and side-grooved Charpy size SE(B) specimens from defined thickness locations of the forged ring strongly scatter. More than allowed 2% of the specimen size adjusted KJc-1T values lie below the fracture toughness curve for 2% fracture probability. The application of modified MC based evaluation methods indicates the material as non-homogeneous. Because of very low KJc values the SINTAP step 3 evaluation gave a maximum T0SINTAP of -40°C. The multimodal MC evaluation of KJc values from all thickness locations gives a T0MM of -118°C and a standard deviation of 25 K. The course of the fracture toughness curves evaluated by multi modal approach also do not represent the measured KJc values since more than 2% lie below the fracture toughness curve for 2% fracture probability. The reason for the occurrence of very low KJc values is seen in intergranular planes detected on the fractured surfaces of the specimens.

Keywords: reactor pressure vessel steel; neutron irradiation; fracture toughness; Master Curve approach; non-homogeneous steel; SINTAP; multimodal approach

  • Book chapter
    T. Yamamoto: Effects of Radiation on Nuclear Materials: 25th Volume, STP 1547, USA: ASTM International, 2013, 978-0-8031-7533-4
    DOI: 10.1520/STP104056

Permalink: https://www.hzdr.de/publications/Publ-15706
Publ.-Id: 15706


Trehalose renders dauer larva of Caenorhabditis elegans resistant to extreme desiccation

Erkut, C.; Penkov, S.; Khesbak, H.; Vorkel, D.; Verbavatz, J. M.; Fahmy, K.; Kurzchalia, T. V.

Water is essential for life on Earth. In the absence of it, however, some organisms are able to interrupt their life cycle and enter an ametabolic state, known as anhydrobiosis [1, 2]. Upon reappearance of water, anhydrobiotes can resume life activities. How can an organism cope with depletion of water? What are the molecular principles of anhydrobiosis? It is assumed that sugars (in particular trehalose) are instrumental for survival under anhydrobiotic conditions and for the preservation of cellular structure [3, 4]. However, the role of trehalose remained obscure since the corresponding evidence was purely correlative and based mostly on in vitro studies. So far, genetic manipulations on trehalose metabolism of anhydrobiotic animals with the aim to study desiccation tolerance have not been reported. In order to study molecular mechanisms of anhydrobiosis, we decided to make use of one of the best genetic models, Caenorhabditis elegans. In this study we show that C. elegans dauer larva is a true anhydrobiote: Under defined conditions it can survive extreme desiccation and lose up to 98% of its body water. This ability is correlated with a several fold increase in the amount of trehalose. To study the role of trehalose, we produced a strain that cannot synthesize it and show that mutant larvae do not survive even mild dehydration. This strain allowed us dissecting the function of trehalose on the cellular and molecular levels. Light and electron microscopy show that one of the major functions of trehalose on the cellular level is the preservation of membrane organization. Fourier-transform infrared spectroscopy of whole worms suggests that this is achieved by preserving homogeneous and compact packing of lipid acyl chains. The damage in the absence of trehalose occurs already during desiccation and spectroscopy allows distinguishing a “dry, yet alive” larva from a “dry and dead” one.

Keywords: in vivo infrared spectroscopy; lipid order; anhydrobiosis

  • Current Biology 21(2011)15, 1331-1336

Permalink: https://www.hzdr.de/publications/Publ-15705
Publ.-Id: 15705


Motion compensation in emission tomography

van den Hoff, J.; Langner, J.

With the ever-improving spatial resolution available in single photon emission computed tomography (SPECT) and, especially, in positron emission tomography (PET), the unavoidable organ and subject motion is becoming one of the dominant factors limiting the practically achievable spatial resolution in the tomographic images. Moreover, uncorrected subject motion can lead to potentially severe image artifacts and compromise the quantitative integrity of the data.The latter is of special importance in PETwhere quantitative assessment of tracer concentrations is commonplace both in static investigations via so-called standardized uptake values (SUVs) and in dynamic studies aiming at tracer kinetic modeling and quantification of the corresponding transport constants. Correction of the heart cycle – related motion in cardiac applications has a long tradition and is covered extensively in the literature. Correction of breathing-related organmotion in emission tomography, however, has drawn considerable interest only in recent years in the context of oncological PET.This ismainly due to the demands of therapy responsemonitoring and radiation treatment planning. The third important area is high-precision motion correction of random head motion in brain investigations. In this chapter, we give an overview of the methods employed to minimize – and possibly eliminate – the motion influence in emission tomography.

  • Book chapter
    C. Grupen and I. Buvat: Handbook of particle detection and imaging, Berlin, Heidelberg: Springer, 2011, 978-3-642-13270-4, 1007-1043

Permalink: https://www.hzdr.de/publications/Publ-15704
Publ.-Id: 15704


Photoinduced Melting of Antiferromagnetic Order in La0:5Sr1:5MnO4 Measured Using Ultrafast Resonant Soft X-Ray Diffraction

Ehrke, H.; Tobey, R. I.; Wall, S.; Cavill, S. A.; Fo¨Rst, M.; Khanna, V.; Garl, T.; Stojanovic, N.; Prabhakaran, D.; Boothroyd, A. T.; Gensch, M.; Mirone, A.; Reutler, P.; Revcolevschi, A.; Dhesi, S. S.; Cavalleri, A.

We used ultrafast resonant soft x-ray diffraction to probe the picosecond dynamics of spin and orbital order in La0:5Sr1:5MnO4 after photoexcitation with a femtosecond pulse of 1.5 eV radiation. Complete melting of antiferromagnetic spin order is evidenced by the disappearance of a (0.25; 0.25; 0.5) diffraction peak. On the other hand, the (0.25; 0.25; 0) diffraction peak, reflecting orbital order, is only partially reduced. We interpret the results as evidence of destabilization in the short-range exchange pattern with no significant relaxation of the long-range Jahn-Teller distortions. Cluster calculations are used to analyze different possible magnetically ordered states in the long-lived metastable phase. Nonthermal coupling between light and magnetism emerges as a primary aspect of photoinduced phase transitions in manganites.

Permalink: https://www.hzdr.de/publications/Publ-15703
Publ.-Id: 15703


THz control in correlated electron solids: sources and applications

Foerst, M.; Hoffmann, M.; Dienst, A.; Kaiser, S.; Rini, M.; Tobey, R. I.; Gensch, M.; Manzoni, C.; Cavalleri, A.

Materials with strongly correlated electrons often show rich phase diagramswith dramatic differences in physical properties as doping, applied pressure, or magnetic fields are changed. Even subtle perturbations can cause colossal rearrangements in the electronic spectrum, and irradiation with light can be used to drive spectacular rearrangements in the structural, electronic, and magnetic properties.
Here, we discuss the use of THz radiation to selectively excite one single degree of freedom at a time to drive a phase change. This is in contrast to what is done in most studies, which achieve photo-induced phase transitions by non-specific excitation in the visible spectral range. This chapter will combine a summary of developments in instrumentation for strong THz fields with some selected scientific applications of THz control of correlated electron systems.

  • Book chapter
    K.-E. Peiponen et al.: Terahertz Spectroscopy and Imaging, Springer Series in Optical Sciences 171, Berlin Heidelberg: Springer-Verlag, 2012
    DOI: 10.1007/978-3-642-29564-5_23

Permalink: https://www.hzdr.de/publications/Publ-15702
Publ.-Id: 15702


Probing properties of nuclear matter with HADES

Pietraszko, J.; Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Huck, P.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Pechenov, V.; Pechenova, O.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wendisch, C.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

This paper presents a review of selected physics results obtained at GSI Helmholtzzentrum für Schwerionenforschung GmbH by HADES (High-Acceptance Di-Electron Spectrometer). The e+e− pair emission measured for proton and heavy-ion induced collisions is reported together with results on strangeness production. The future HADES activities at the planned FAIR facility are also discussed.

  • Open Access Logo Proceedings of Science (2011), PoS(BORMIO2011)054

Permalink: https://www.hzdr.de/publications/Publ-15701
Publ.-Id: 15701


Structural and functional investigation of astaxanthin binding to the catalytic domain of matrix metalloprotease MMP-13

Sayed, A.; Elsayed, M. M.; Tucker, P.; Fahmy, K.

Matrix metalloproteases (MMPs) are zinc-containing proteases involved in the remodeling and breakdown of extracellular matrix proteins. Overexpression of the MMPs has been associated with a variety of diseases ranging from periodontal disease and arthritis to tumor invasion and metastasis. The majority of the more powerful synthetic inhibitors of MMPs incorporate a hydroxamate group, but exhibit low selectivity and are toxic. In a recent modeling study, Astaxanthin (AST), a carotenoid with potent antioxidant property, has been shown to be a potential inhibitor of MMP-13 function by occupying a binding site near the active center of the enzyme (Bika´di et. al. 2006). In our ongoing project, we investigate the binding of AST to the catalytic domain of MMPs using biochemical and ultimately crystallization to validate the proposed action of AST. Along these lines, the catalytic domain of MMP-13 (cdMMP-13) was expressed in E.coli BL21(DE3) CodonPlus and refolded using a novel effective refolding method. Our results reveal that AST has a potent inhibitory effect on cdMMP-13 activity, however, determination of IC50% or Ki is difficult due to fast oxidation and structural instability of AST. Ongoing work aims at optimizing the inhibition conditions and improving the refolding yield to allow analyzing structure and function of the AST-bound MMP-13 in more detail.
Bikádi et al. (2006) Bioorg Med Chem 14:5451-8.

  • Contribution to proceedings
    8th European Biophysics Congress, 23.-27.08.2011, Budapest, Hungary
    European Biophysics Journal with Biophysics Letters 40 (2011), 58-59

Permalink: https://www.hzdr.de/publications/Publ-15700
Publ.-Id: 15700


Spectroscopic investigation of the structure and function of the copper ATPase CopB of Enterococcus hirae

Groß, M.; Solioz, M.; Fahmy, K.

The Cu+-ATPase CopB of Enterococcus hirae is a bacterial P-type ATPase involved in resistance to high levels of environmental copper by expelling excess copper. The membrane protein CopB was purified from an over-expressing strain and solubilized in dodecyl-maltoside. By UV circular dichroism the secondary structure is predicted to contain 40-50 % alpha-helices and 10-15% beta-sheets in agreement with estimates based on homology with the Ca ATPase SERCA1. We present CD-spectroscopic data on thermal unfolding of the protein to address the influence of the binding of the ATP analogs ATPgS and the fluorescent analog mant-ATP on the protein stability. Such analogs are used to mimic functional states of the ATPase but undergo different interactions with the binding site that are not well characterized. We propose a competition-based assay for nucleotide binding using CD-spectroscopy to deduce the occupancy of the nucleotide-binding site by non-fluorescent nucleotides. Alternatively, the change of intrinsic fluorescence of mant-ATP upon binding to the ATPase is exploited in these assays. Finally, we show how the simultaneous measurement of protein CD and nucleotide fluorescence in thermal denaturation experiments may help to determine the stability of several functional conformational states of CopB.

Keywords: circular dichroism; nucleotide binding

  • Contribution to proceedings
    8th European Biophysics Congress, 23.-27.08.2011, Budapest, Hungary
    European Biophysics Journal with Biophysics Letters 40 (2011), 168

Permalink: https://www.hzdr.de/publications/Publ-15699
Publ.-Id: 15699


FTIR and calorimetric investigation of the effects of trehalose and multivalent cations on lipid structure

Abu Sharkh, S.; Oertel, J.; Fahmy, K.

The structure of membrane lipids is of fundamental importance for the integrity of cell and organelle membranes in living organisms. Membrane lipids are typically hydrated and their headgroup charges counter-balanced by solvated ions. Consequently, water loss can induce severe structural changes in lipid packing (lyotropic transitions) and can lead to the damage of lipid membranes even after rehydration. This can be one out of several factors that affect the viability of organisms undergoing desiccation. Many organisms, however, are resistant to even extreme water loss. Some of them synthesize trehalose which has been shown to be associated with survival of desiccation in phylogenetically diverse organisms (yeast, nematodes, brine shrimp, insect larvae, resurrection plants, and others). Here we have studied hydration sensitive transitions in model lipids to determine the effect of trehalose and electrostatics on lipid order. Hydration pulse-induced time-resolved Fourier-transform infrared (FTIR) difference spectroscopy was used to address hydration-dependent lipid structure as a function of trehalose. In combination with differential scanning calorimetry and studies of Langmuir-Blodget films we arrive at a structural and energetically consistent picture of how trehalose can affects lipidic phase behaviour and support a native lipid structure under water loss. Experiments were performed on model lipids with different headgroups and native lipids from desiccation-tolerant organisms.

Keywords: infrared spectroscopy; anhydrobiosis

  • Contribution to proceedings
    8th European Biophysics Congress, 23.-27.08.2011, Budapest, Hungary
    European Biophysics Journal with Biophysics Letters 40 (2011), 72

Permalink: https://www.hzdr.de/publications/Publ-15698
Publ.-Id: 15698


Coupling of the hydration shell of B-DNA to conformational substates and peptide recognition studied by time-resolved FTIR spectroscopy

Khesbak, H.; Savchuk, O.; Tsushima, S.; Fahmy, K.

Biomolecular recognition typically proceeds in an aqueous environment, where hydration shells are a constitutive part of the interacting species. The coupling of hydration shell structure to conformation is particularly pronounced for DNA with its large surface to volume ratio. Conformational substates of the phosphodiester backbone in B-DNA contribute to DNA flexibility and are strongly dependent on hydration. We have studied by rapid scan FTIR spectroscopy the isothermal BI-BII transition on its intrinsic time scale of seconds. Correlation analysis of IR absorption changes induced by an incremental growth of the DNA hydration shell identifies water populations w1 (PO2--bound) and w2 (non-PO2--bound) exhibiting weaker and stronger H-bonds, respectively, than those in bulk water. The BII substate is stabilized by w2. The water H-bond imbalance of 3-4 kJ mol-1 is equalized at little enthalpic cost upon formation of a contiguous water network (at 12-14 H2O molecules per DNA phosphate) of reduced (OH) band width. In this state, hydration water cooperatively stabilizes the BI conformer via the entropically favored replacement of w2-DNA interactions by additional w2-water contacts, rather than binding to BI-specific hydration sites. Such water rearrangements contribute to the recognition of DNA by indolicidin, an antimicrobial 13-mer peptide from bovine neutrophils which, despite little intrinsic structure, preferentially binds to the BI conformer in a water-mediated induced fit. In combination with CD-spectral titrations, the data indicate that in the absence of a bulk aqueous phase, as in molecular crowded environments, water relocation within the DNA hydration shell allows for entropic contributions similar to those assigned to water upon DNA ligand recognition in solution.

Keywords: infrared spectroscopy; molecular recognition; DNA structure

  • Contribution to proceedings
    8th European Biophysics Congress, 23.-27.08.2011, Budapest, Hungary
    European Biophysics Journal with Biophysics Letters 40 (2011), 45

Permalink: https://www.hzdr.de/publications/Publ-15697
Publ.-Id: 15697


Flash II: Perspectives and challenges

Faatz, B.; Baboi, N.; Ayvazyan, V.; Balandin, V.; Decking, W.; Duesterer, S.; Eckoldt, H.; Feldhaus, J.; Golubeva, N.; Honkavaara, K.; Koerfer, M.; Laarmann, T.; Leuschner, A.; Lilje, L.; Limberg, T.; Noelle, D.; Obier, F.; Petrov, A.; Ploenjes, E.; Rehlich, K.; Schlarb, H.; Schmidt, B.; Schmitz, M.; Schreiber, S.; Schulte-Schrepping, H.; Spengler, J.; Staack, M.; Tavella, F.; Tiedtke, K.; Tischer, M.; Treusch, R.; Vogt, M.; Willner, A.; Bahrdt, J.; Follath, R.; Gensch, M.; Holldack, K.; Meseck, A.; Mitzner, R.; Drescher, M.; Miltchev, V.; Ronsch-Schulenburg, J. J.; Rossbach, J.

FLASH has been a user facility since 2005, delivering radiation in the wavelength range between 7 and 47 nm using the SASE principle. After the present upgrade, the wavelength range is extended to 4.45 nm. With the third harmonic accelerating module in place to linearize the longitudinal phase space, the stability and reproducibility of the machine is substantially improved. The user requests for beam time by far exceeds the time available. In order to increase user beam time and to improve the radiation properties delivered to users, a major extension of the user facility called FLASH II has been proposed by DESY in collaboration with the HZB. FLASH II is a seeded FEL in the parameter range of FLASH. As logical continuation, the seeding with HHG which started with sFLASH will result in direct seeding. Because in the foreseeable future there will probably not be HHG seed lasers available at high repetition rates down to wavelengths of 4 nm, a cascaded HGHG scheme is proposed to produce short wavelengths.
After a first design report, the project now enters its technical design phase. During this time, the FLASH beam parameters after the present upgrade 2009/2010 will be characterized and the present design will be re-evaluated and adjusted. In addition, start-to-end simulations will complete the simulations which have been performed so far, including a design of the extraction area.

Keywords: Free-electron laser; XUV FEL

Permalink: https://www.hzdr.de/publications/Publ-15696
Publ.-Id: 15696


Few-femtosecond timing at fourth-generation X-ray light sources

Tavella, F.; Stojanovic, N.; Geloni, G.; Gensch, M.

Fourth-generation X-ray light sources are being developed to deliver laser-like X-ray pulses at intensities and/or repetition rates that are beyond the reach of table-top devices. An important class of experiments at these new facilities comprises pump–probe experiments, which are designed to investigate chemical reactions and processes occurring on the molecular or even atomic level, and on the timescale of a few femtoseconds. Good progress has been made towards the generation of ultrashort X-ray pulses (for example, at FLASH1 or LCLS2),but experiments suffer from the intrinsic timing jitter between the X-ray pulses and external laser sources3. In this Letter, we present a new approach that provides few-femtosecond temporal resolution. Our method uses coherent terahertz radiation generated at the end of the X-ray undulator by the same electron bunch that emits the X-ray pulse. It can therefore be applied at any advanced light source working with ultrashort electron bunches and undulators.

Permalink: https://www.hzdr.de/publications/Publ-15695
Publ.-Id: 15695


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 4.5·10-16 for 10Be/9Be, 8·10-16 for 26Al/27Al, 3·10-15 for 36Cl/35Cl and 8·10-15 for 41Ca/40Ca, respectively. The observed background of 2·10-13 for 129I/127I originates from intrinsic 129I from AgI produced from commercial KI (MERCK).
During first experiments at the accelerator an energy calibration of the machine has been carried out. For this purpose the 1H(15N,γ α)12C nuclear reaction has been used. The charge states of the 15N ion of 1+, 2+ and 3+ corresponding to different terminal voltages of the accelerator have been chosen to obtain an absolute energy calibration.

Keywords: Accelerator Mass Spectrometry; AMS; electrostatic accelerator

  • Contribution to proceedings
    AMS-12, Twelfth International Conference on Accelerator Mass Spectrometry, 21.-25.03.2011, Wellington, New Zealand
    Accelerator Mass Spectrometry, Nucl. Instr. and Meth. B (2012), North-Holland: Elsevier

Permalink: https://www.hzdr.de/publications/Publ-15694
Publ.-Id: 15694


Bio-Au nanoparticles on archaeal and bacterial S-layers

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

Gold nanoparticles with substantially different properties were produced by using two alternative S-layer templates. The first one was a bacterial template, representing sheets of the S-layer of Bacillus sphaericus; the second one was in a form of empty cells (ghosts) consisting of the so-called SlaA-layer of the thermoacidophilic archaeon Sulfolobus acido-caldarius. The archaeal SlaA-layer is resistant not only to high temperatures and acidity but also to detergents, that allowed to purify the SlaA-layer-ghosts keeping the shape of the cells. The production of the Au nanoparticles was performed according to [1,2] in a two-step procedure by using DMAB as a reducing agent.
We demonstrate that the SlaA-ghosts of S. acido-caldarius serve as a very efficient template for complete reduction of Au(III) to Au(0). In the case of using S-layer sheets of B. sphaericus only 40 % of the added Au(III) was reduced to Au(0) [2]. The size of the archaeal bio-Au nanoparticles was about 2.5 nm, while those of the bacterial ones was about 4 nm. The most stricking property of the archaeal bio-Au nanoparticles is, however, that that they are paramagnetic, in contrast to the bacterial ones and also to bulk gold, which are diamagnetic. As demonstrated by SQUID magnetometry, the archaeal bio-Au possesses an unusually large magnetic moment of about 0.1 µB/Au atom. HR-TEM combined with EDX analysis revealed that the archaeal Au nanoparticles are bound to sulfur atoms. The latter originate from the thiol groups of the cystein amino acid residues which are characteristic for the SlaA-layer of S. acidocaldarius but absent in the S-layer of B. sphaericus. Surprisingly, the magnetic moment of the archaeal bio-Au nanoparticles is substantially larger than the ones observed for thiol capped, chemically produced Au nanoclusters [3]. We suggest that the unusual shape and the biochemical characteristics of the SlaA-ghosts are responsible for the observed extraordinary properties of the archaeal bio-Au.

[1] Merroun et al. (2007) Mat. Sc. Tech. 27, 188-192.
[2] Jankovski et al. (2010) Spectroscopy 24, 177-181, 2010.
[3] Crespo et al. (2004) Phys. Rev. Lett. 93, 087204.

  • Lecture (Conference)
    Goldschmidt2011, 14.-19.08.2011, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-15693
Publ.-Id: 15693


Combined correction of recovery effect and motion blur for SUV quantification of solitary pulmonary nodules in FDG PET/CT

Apostolova, I.; Wiemker, R.; Paulus, T.; Kabus, S.; Dreilich, T.; van den Hoff, J.; Plotkin, M.; Mester, J.; Brenner, W.; Burchert, R.; Klutmann, S.

Objective: We evaluate a fully data-driven method for the combined recovery and motion blur correction of small solitary pulmonary nodules (SPNs) in F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT).
Methods: The SPN was segmented in the low-dose CT using a variable Hounsfield threshold and morphological constraints. The combined effect of limited spatial resolution and motion blur in the SPN’s PET image was then modelled by an effective Gaussian point-spread function (psf). Both isotropic and non-isotropic psfs were used. To validate the method, PET/CT measurements of the NEMA/IEC spheres phantom were performed. The method was applied to 50 unselected SPNs ≤30 mm from routine patient care.
Results: Recovery of standardised uptake value (SUV) in the phantom image was significantly improved by combined recovery and motion blur correction compared with recoveryonly correction, particularly with the non-isotropic model (residual average error 10%). In the patient images, automated segmentation and fit of the effective psf worked properly in all cases. Volume-equivalent diameter ranged from 4.9 to 27.8 mm. Uncorrected maximum SUV ranged from 0.9 to 13.3. Compared with recoveryonly correction, combined correction with the non-isotropic model resulted in a ‘relevant’ (≥30%) SUV increase in 47 SPNs (94%).
Conclusions: Correction of both recovery and motion blur is mandatory for accurate SUV quantification of SPNs.

Keywords: Solitary pulmonary nodule; FDG; SUV; Recovery correction; Motion correction

Permalink: https://www.hzdr.de/publications/Publ-15692
Publ.-Id: 15692


Radiotracer studies on the mobility of radionuclides in clay matrices containing organic matter: Elementary processes and influence of heterogeneous structures

Lippold, H.; Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.

In einem Übersichtsvortrag wurden die wesentlichen Forschungsergebnisse vorgestellt, die in der zurückliegenden Bewilligungsphase des Verbundprojektes erzielt wurden. Themenschwerpunkte des Vortrages waren (i) die Rekonstruktion ternärer Systeme (Metall / Huminstoff / Tonmineral) aus Verteilungskoeffizienten in den binären Randsystemen, (ii) Zeitabhängigkeiten im Konkurrenzeffekt von Fe(III) und Al(III) bzgl. der Huminstoff-Komplexbildung von Radionukliden, (iii) Dynamik von Huminstoff-Adsorptionsgleichgewichten, (iv) PET-Untersuchungen von Transportprozessen in intaktem Opalinuston, (v) Monte-Carlo-Simulation von Streuprozessen zur PET-Bildkorrektur.

  • Lecture (others)
    Abschlussworkshop zum Verbundvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 17.-18.05.2011, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15691
Publ.-Id: 15691


An Experiment-Based Approach for Predicting Positron Emitter Distributions Produced during Therapeutic Ion Irradiation

Priegnitz, M.; Fiedler, F.; Kunath, D.; Laube, K.; Enghardt, W.

In-beam positron emission tomography (PET) is a valuable method for a beam-delivery independent dose monitoring in radiation therapy with ion beams. Up to now, its clinical feasibility has been demonstrated for patient irradiation with carbon ions. From radiobiological point of view it is highly desirable to perform tumor irradiation also with other light ions. To extend the application of in-beam PET also to these ions, extensive knowledge about positron emitter production via nuclear fragmentation reactions during ion irradiation is necessary. To model the positron emitter production correctly, cross sections for all possible nuclear reactions occurring in the tissue during irradiation and leading to positron emitters are required. Since these cross sections are available only for a few reaction channels in the required energy range, a novel approach for estimating the positron emitter production from experimental data is introduced. The prediction of positron emitter distributions is based on depth dependent thick target yields, which are derived by linear superposition of measured yields in water, graphite and polyethylene as reference materials. Results on the prediction of positron emitter distributions in polymethyl methacrylate (PMMA) as well as inhomogeneous targets induced by lithium and carbon irradiation are presented. By comparison with data deduced from experiments, it is shown that a rather accurate prediction of positron emitter distribution is feasible using this method.

Keywords: In-beam positron emission tomography; ion beam tumor therapy; positron emitter distribution; prediction method

Permalink: https://www.hzdr.de/publications/Publ-15690
Publ.-Id: 15690


Hydrogen mediated ferromagnetism in ZnO single crystals

Khalid, M.; Esquinazi, P.; Spemann, D.; Anwand, W.; Brauer, G.

We investigated the magnetic properties of hydrogen plasma treated ZnO single crystals by SQUID magnetometry. In agreement with the expected hydrogen penetration depth we found ferromagnetic behavior located at the first 20 nm of the H-treated surface of ZnO with magnetization at saturation up to 6 emu/g at 300 K and Curie temperature Tc > 400 K. In the ferromagnetic samples a hydrogen concentration of a few atomic percent in the first 20 nm surface layer was determined by nuclear reaction analysis. The saturation magnetization of H-treated ZnO increases with the concentration of hydrogen.

Keywords: ZnO; hydrogen plasma treatment; ferromagnetic behavior

  • Open Access Logo New Journal of Physics 13(2011), 063017

Permalink: https://www.hzdr.de/publications/Publ-15689
Publ.-Id: 15689


Two-region diffusion model for the improved analysis of ADS experiments

Glivici-Cotruţă, V.; Merk, B.

A fast lead core and an external neutron source create rapidly varying transients in which the spatial and time effects are important, and, in combination with a thick lead reflector, impose a constraint on an application of the traditional point reactor kinetics approximation. Thereby, for the foreseen GUINEVERE experiments a two-region space and time dependent diffusion approximation was chosen to be solved and analysed. It is necessary to represent the solution for two-region core owing to a presence of an external neutron source, sub-criticality of the system, and an increasing impact of the reflector in a small experimental reactor, as well as due to the inaccuracy of the diffusion approximation around the core reflector, core blanket interfaces, and throughout fast reactor blankets. This two-region solution without separation of space and time gives a significantly improved methodology for the analysis of the future experiments like GUINEVERE. The efficiency of the derived solution over the accurate numerical solutions (like Monte Carlo calculation, for example) lies in a comparatively short calculation time, which is of major importance for the on-line monitoring the reactivity of a subcritical reactor system.

Keywords: Yalina; experimental analysis; Green’s function; Two-region diffusion equation; GUINEVERE experiment

  • Open Access Logo Contribution to proceedings
    The 22nd International Conference on Transport Theory, 11.-15.09.2011, Portland, USA
  • Lecture (Conference)
    The 22nd International Conference on Transport Theory, 11.-15.09.2011, Portland, USA

Permalink: https://www.hzdr.de/publications/Publ-15688
Publ.-Id: 15688


Evaluation of the ASTM and ISO J initiation procedures by applying the unloading compliance technique to reactor pressure vessel steels

Arora, K. S.; Viehrig, H.-W.

Other than the brittle failure, the ductile behavior of the aged reactor pressure vessels (RPV) steels is also of interest for the integrity assessment and the evaluation of the irradiation response. The fracture toughness of high toughness materials like RPV steels can be characterized by a J-R curve. Since, the RPV steel material available for testing purposes, like surveillance specimens is limited the single specimen method is used for J-R curve determination. In this study, J-R curves were measured on Charpy size SE(B) and 1T-C(T) specimens of different RPV steels in the un¬irradiated and irradiated condition. It was observed that despite the available sophisticated instrumentation and strict implementation of the recommended test procedures, J-initiation value for all the different material specimens tested, could not be ascertained according to the tests standards ASTM E1820-09 und ISO 12135. For charpy size SE(B) specimens, it was found that though in irradiated condition valid JIc/J0.2BL values could be obtained but in un-irradiated condition especially for high toughness RPV steels it was not possible. The evaluation showed that the aoq fit of the ASTM standard compensates uncertainties in the initial J-Δa value resulting in reliable and more number of qualified test results. But these uncertainties strongly influence the A parameters of the ISO fit and the J0.2BL(B) value. Additionally, in ISO evaluation, the lower offset of the first exclusion line and a higher slope results in lower J0.2BL values compared to ASTM analysis. Furthermore, for the two specimen geometries the course of J-R curves up to the JQ value was similar even for high toughness material, but the lower specimen size was disqualified due to the lower prescribed Jlimit.. Similarly, the J-R curves for un-irradiated and irradiated condition had a similar course up to the J0.2BL value, even for extremely high irradiation induced embrittlement.

Keywords: fracture toughness; ductile tearing; J-R curve; single specimen approach; unloading compliance; ASTM E1820; ISO 12135; reactor pressure vessel steels

  • Journal of Testing and Evaluation 39(2011)6, 10.1520/JTE103405
    DOI: 10.1520/JTE103405

Permalink: https://www.hzdr.de/publications/Publ-15687
Publ.-Id: 15687


Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling

Kehr, S. C.; Liu, Y. M.; Martin, L. W.; Yu, P.; Gajek, M.; Yang, S.-Y.; Yang, C.-H.; Wenzel, M. T.; Jacob, R.; von Ribbeck, H.-G.; Helm, M.; Zhang, X.; Eng, L. M.; Ramesh, R.

A planar slab of negative-index material works as a superlens with sub-diffraction-limited resolution, as propagating waves are focused and, moreover, evanescent waves are reconstructed in the image plane. Here we demonstrate a superlens for electric evanescent fields with low losses using perovskites in the mid-infrared regime. The combination of near-field microscopy with a tunable free-electron laser allows us to address precisely the polariton modes, which are critical for super-resolution imaging. We spectrally study the lateral and vertical distributions of evanescent waves around the image plane of such a lens, and achieve imaging resolution of λ/14 at the superlensing wavelength. Interestingly, at certain distances between the probe and sample surface, we observe a maximum of these evanescent fields. Comparisons with numerical simulations indicate that this maximum originates from an enhanced coupling between probe and object, which might be applicable for multifunctional circuits, infrared spectroscopy and thermal sensors.

Keywords: Physical Sciences; Materials science; Optical physics; near-field microscopy; infrared

Permalink: https://www.hzdr.de/publications/Publ-15686
Publ.-Id: 15686


Temperature dependence of complexation, sorption and diffusion in the system uranium(VI)/clay organics/clay rock

Schmeide, K.; Joseph, C.; Steudtner, R.

The temperature dependence of U(VI) lactate and citrate complexation as well as the temperature dependence of the U(VI) migration in Opalinus Clay in the absence and presence of clay organics is shown.

Keywords: U(VI); complexation; sorption; diffusion; Opalinus Clay; citric acid

  • Lecture (others)
    Abschlussworkshop zum Verbundvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 17.-18.05.2011, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15684
Publ.-Id: 15684


Structural modifications induced by FIB implantation in magnetic thin films

Roshchupkina, O. D.; Grenzer, J.; Strache, T.; McCord, J.; Fritzsche, M.; Muecklich, A.; Baehtz, C.; Fassbender, J.

Recently, there is a rise of interest in fabrication and investigation of nanometre sized magnetic objects. Magnetic properties can easily be manipulated by ion beam implantation. Focused-ion beam (FIB) techniques are one way to combine both nanopatterning and implantation. The main difference between standard ion implantation and FIB implantation is the beam current density, which could lead to differences in the structural and magnetic properties. The aim of this work is to compare both implantation techniques in terms of structural changes and to relate them to magnetic property changes.
For our investigation we have used 50 nm thick non-ordered nano-crystalline permalloy (Ni81Fe19) films modified by a 30 keV Ga+ ion beam. The magnetic properties were characterised via magneto-optic Kerr effect measurements at room temperature. Both types of implantation demonstrate a degradation of saturation magnetisation with increasing ion fluence. For structural investigations we have applied several techniques. We have used the advantage of non-destructive X-ray techniques to study the structural changes. Besides X-ray diffraction, providing the long-range order information, EXAFS measurements to probe the local structure were performed. Both methods are statistical ones, whereas TEM imaging provides information on a local scale.
Implantation leads to a crystallite growth from ~12 nm up to ~25 nm and further texturing of the material towards (111) direction at almost constant lattice parameter. In the case of FIB implanted samples the TEM images show crystallites growing through the entire film at high implantation fluences. The EXAFS analysis shows an almost perfect near-order coordination, corresponding to an fcc cell; only in the vicinity of the Ga atoms a small local deviation could be observed. In general FIB and standard implantation demonstrate similar behaviour with a shift in the fluence value. These results let us conclude that the simple presence of the Ga atoms is the dominating effect leading the degradation of saturation magnetisation.

Keywords: Focused-ion beam; EXAFS

  • Lecture (Conference)
    8th Autumn School on X-ray Scattering from Surfaces and Thin Layers, 04.-07.10.2011, Smolenice, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-15683
Publ.-Id: 15683


FIB induced structural modifications in thin magnetic films

Roshchupkina, O.; Grenzer, J.; Strache, T.; Fritzsche, M.; Mücklich, A.; Fassbender, J.

Focused ion beam irradiation is a versatile tool that can be used for magnetic nanostructuring. In this work we compare both FIB irradiation and a standard implantation taking into account their distinctive irradiation features. A 50nm thick permalloy layer (Ni80Fe20) irradiated with different Ga+ ion fluences was used for the investigations. The structure was studied via XRD and EXAFS measurements carried out on the ESRF ROBL and ID01 facilities. Additionally TEM and magneto-optic Kerr effect magnetometry were performed. Both types of irradiation demonstrate a similar behaviour: increasing the ion fluence causes a further material crystallization and a decrease of the magnetic moment. However FIB irradiation leads to a stronger crystallite growth due to the high current densities used.

Keywords: Focused ion beam; EXAFS

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-15682
Publ.-Id: 15682


Nonvolatile bipolar resistive switching in Au/BiFeO3/Pt

Shuai, Y.; Zhou, S.; Bürger, D.; Helm, M.; Schmidt, H.

Nonvolatile bipolar resistive switching has been observed in an Au/BiFeO3/Pt structure, where a Schottky contact and an Ohmic contact were formed at the Au/BiFeO3 and BiFeO3/Pt interface, respectively. By changing the polarity of the external voltage, the Au/BiFeO3/Pt is switched between two stable resistance states without an electroforming process. The resistance ratio is larger than two orders of magnitude. The resistive switching is understood by the electric field – induced carriers trapping and detrapping, which changes the depletion thickness.

Keywords: BiFeO3; nonvolatile; resistive switching; Schottky

  • Journal of Applied Physics 109(2011), 124117

Permalink: https://www.hzdr.de/publications/Publ-15681
Publ.-Id: 15681


Experimental investigation of the collection efficiency of a PTW Roos ionization chamber irradiated with pulsed beams at high pulse dose with different pulse lengths

Karsch, L.; Richter, C.; Pawelke, J.

In gas-filled ionization chambers as radiation detectors, the collection of the charge carriers is affected by the recombination effect. In dosimetry this effect must be accounted for by the saturation correction factor k(S). The physical description of the correction factor by Boag, Hochhauser and Balk for pulsed radiation is well established. However, this description is only accurate when the pulse length is short compared to the collection time of the ionization chamber. In this work experimental investigations of the saturation correction factor have been made for pulses of 4 mu s up to pulse doses of about 230 mGy, and the theory of Boag, Hochhauser and Balk was again confirmed. For longer pulses, however; the correction factor decreases and at a pulse duration of about 200 mu s reaches 75% of the value valid for short pulses. This reduced influence of the ion recombination is interpreted by the reaction kinetics of ion recombination as a second-order reaction. This effect is negligible for PTW Roos chambers at clinical linear accelerators with 4 mu s pulse duration for pulse doses up to 120 mGy.

Permalink: https://www.hzdr.de/publications/Publ-15680
Publ.-Id: 15680


THEREDA - Thermodynamic Reference Database. Summary of Final Report

Altmaier, M.; Brendler, V.; Bube, C.; Marquardt, C.; Moog, H. C.; Richter, A.; Scharge, T.; Voigt, W.; Wilhelm, S.

A long term safety assessment of a repository for radioactive waste requires evidence, that all relevant processes, which might have a significant positive or negative impact on its safety, are known and understood. In the case of brine intrusion into the disposal area, it has to be demonstrated, that the initiated chemical reactions don’t lead to an undue release of radionuclides into the biosphere. The starting point for this is to assess the solubility of contaminants in the solutions interacting with the waste. Solubility estimations can either be based on experimental data determined at conditions closely resembling those in the repository or on thermodynamic calculations.
A so called “thermodynamic database” created from experimental data is the basis for thermodynamic model calculations. Several research institutions in Germany are working on an improvement of the thermodynamic database. This work comprises investigations into fundamental thermodynamic data (such as vapour pressures or solubili-ties) as well as the application of sophisticated analytical or spectroscopic tools, which allow insight into aqueous speciation or structural details of surface complexes as basis for correct chemical and thermodynamic models.
Experience teaches that thermodynamic equilibrium calculations performed by different experts readily become difficult to compare and evaluate. This is only in part due to ill-defined (and -documented!) boundary conditions imposed on the calculations, but is frequently related to the use of different thermodynamic data or different conceptual models underlying them. Further difficulties arise by the fact that thermodynamic data used for a calculation actually are strongly interrelated; modification of an individual value without adapting the dependent values leads to “inconsistent” data. If applied in a calculation, this may lead to erroneous results, often unnoticed by the user.
As a result, in different institutions various databases exist that are appropriate for spe-cific tasks. However, they might lead to different results when they are applied to the same problem. This situation is unacceptable, both from a scientific point of view and considering the special public awareness for the final disposal of radioactive waste.
In 2002, a working group of five institutions was established for the creation of a com-mon thermodynamic database for nuclear waste disposal in deep geological formations (HZDR, GRS, TU BAF, KIT, AF-Consult). The common database was named THEREDA: Thermodynamic Reference Database.
It was agreed that the newly created database should be operated jointly by all members of the working group. In the mean term it is intended, that its usage becomes mandatory for geochemical model calculations for nuclear waste disposal in Germany. Furthermore, it was agreed that the new database should be developed along the guidelines long-term usability, easy access, applicability, internal consistency, comprehensiveness, documentation.
Activities within the time for which this report is valid cover a wide range of aspects. At first, a data model had to be designed from scratch which allows for the storage of thermodynamic data, at the same time facilitating export into code-specific parameter files. Creating the data model emphasis was laid upon its long term usage. Thus, a degree of abstraction was chosen which exceeds todays necessities and allows for future extensions. Technically the databank is implemented on a web server. Programs were created, which permit reading and writing access to the data. From the created webpages programs can be called that produce code specific parameter files ready for download upon specific request by the user.
THEREDA can thus be thought of as a databank in conjunction with a suite of peripheral programs, which aims at administrating, processing and extracting data. The data export is intended for the use in programs that calculate thermodynamic equilibria in aqueous solutions at temperatures which are of potential interest for hydrogeochemical systems in general and solutions containing hazardous contaminants like radionuclides or heavy metals in particular. As such, THEREDA is not designed to hold primary experimental data, neither data concerning any liquid other than aqueous solu-tion, e. g. melts or other substances which are stable under conditions beyond those where aqueous solutions may exist. Emphasis is laid on the correct calculation of ex-perimentally determined solubilities and aqueous speciation. Accompanying the above mentioned activities the working group agreed upon guide-lines which are to be followed upon selection and assessment of data. A system of quality assuring measure was set up; this comprises technical aspects relating to the databank as well as criteria determining how data are to be internally reviewed prior to release (auditing). As an external measure of quality assurance an internet forum was established to feedback questions and requirements from realistic problems into the project. A handbook was written to guide users in the handling of THEREDA (for the time being in german only).
Finally, thermodynamic data were entered. They comprise the system of oceanic salts as well as species and solid phase of a variety of radio-toxic and chemo-toxic ele-ments. This piece of work is on-going. At present, benchmark calculations are prepared. The first release of data will cover the system of oceanic salts (apart from C).

Keywords: THEREDA; thermodynamic reference database; repository; radioactive waste; equlibrium calculations; hydrogeochemical modelling

  • Other report
    Braunschweig: Gesellschaft für Anlagen- und Reaktorsicherheit, 2011
    63 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15679
Publ.-Id: 15679


Nonvolatile resistive switching in BiFeO3 thin films

Shuai, Y.; Zhou, S.; Bürger, D.; Helm, M.; Schmidt, H.; Slesazeck, S.; Mikolajick, T.

Nonvolatile resistive switching has been observed in an Au/BiFeO3/Pt structure, where a Schottky contact and an Ohmic contact were formed at the Au/BiFeO3 and BiFeO3/Pt interface, respectively. By changing the polarity of the external voltage, the Au/BiFeO3/Pt is switched between two stable resistance states with a resistance ratio larger than two orders of magnitude. Based on a systematic investigation of its electrical properties with an emphasize on its transport characteristics, a model associated with the redistribution of oxygen vacancies and the formation of an electron hopping path is proposed, which agrees well with our experimental observations. In the present work we found that the electron hopping can be controlled and utilized to realize bipolar resistive switching, which is promising for future high density memory devices.

Keywords: BiFeO3; resistive switching; Schottky; electron hopping

  • Lecture (Conference)
    E-MRS 2011 SPRING MEETING, 08.05.2011, Nice, France
  • Lecture (Conference)
    ISPSA 2011, 05.-08.07.2011, Jeju, Republic of Korea

Permalink: https://www.hzdr.de/publications/Publ-15678
Publ.-Id: 15678


Reduced leakage current in BiFeO3 thin films with rectifying contacts

Shuai, Y.; Zhou, S.; Streit, S.; Reuther, H.; Bürger, D.; Slesazeck, S.; Mikolajick, T.; Helm, M.; Schmidt, H.

BiFeO3 thin films were grown on Pt/c-sapphire substrates by pulsed laser deposition with different growth rates. With increasing growth rate the leakage current is decreased and the conduction mechanism changes from bulk-limited Poole-Frenkel emission to interface-limited Schottky emission. In the present work, we show that only the growth rate of the BiFeO3 films close to the metal contacts has to be increased in order to reduce the leakage current and to observe saturated polarization-electric field hysteresis loops.

Keywords: BiFeO3; leakage current; rectifying contact

Permalink: https://www.hzdr.de/publications/Publ-15677
Publ.-Id: 15677


"Forschen für den Mittelstand"

Joehnk, P.; Wolf, B.

"Dresdner Industrietage" - eine Initiative des Arbeitskreises Industrierat im Bundesverband mittelständischer Wirtschaft e.V. in Kooperation mit der TU Dresden, der HTW Dresden, der Hochschule Zittau/Görlitz sowie weiteren wissenschaftlichen Einrichtungen Sachsens ... unter aktiver Mitwirkung zahlreicher sächsischer Mittelstands- und Branchenvereinigungen

  • Lecture (others)
    10. Dresdner Industrietage - Der Mittelstand lädt ein", 11.05.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15676
Publ.-Id: 15676


Nanoparticle Formation in Solids

Schmidt, B.; Heinig, K.-H.

Nanoparticles in solids can be formed through phase separation in mixtures of immiscible components. The relaxation of far-from-equilibrium mixtures towards equilibrium can proceed via self-organization of nanostructures. Depending on the degree of supersaturation, phase separation proceeds via nucleation and growth of nanoparticles or spinodal decomposition.
One of the main goals of materials research using chemical and physical vapour deposition (CVD and PVD) as well as ion beams is to synthesize nanostructures. A great effort is currently devoted to NC fabrication for micro- and optoelectronics by these techniques, because they are compatible with CMOS technology.
At first, the present contribution addresses the Si NC formation in the gate oxide by conventional ion beam synthesis (IBS) and by ion beam mixing of SiO2/Si interfaces, with special emphasis on well-controlled size and position tailoring. The two approaches will be compared and technological challenges will be discussed. Compared to conventional Si NC synthesis by Si+ ion implantation into the gate oxide, ion-beam-induced interface mixing takes advantage of self-alignment, i.e., the Si NCs are formed in SiO2 at a well-controlled distance of ~2 nm from the Si/SiO2 interfaces. Applications in non-volatile nanocrystal memories and in light emitting field-effect transistors (LEFET) are demonstrated.
Then, the phase separation by spinodal decomposition of Si-rich SiO2 layers grown by PVD (or CVD) into isolated Si NCs and percolated Si sponge-like nanostructures will be considered. Promising application in future thin film solar cells will be discussed.
The work is partially supported by BMBF (TUR 09/240).

Keywords: Nanoparticles; Ion beam synthesis; PVD synthesis; Si nanoparticle memory; Si nanoparticle electroluminesence; Si nanostructure PV cell

  • Invited lecture (Conferences)
    E-MRS Spring Meeting, 09.-13.05.2011, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-15675
Publ.-Id: 15675


Herstellung und Untersuchung von (selbstorganisierten) Nanostrukturen – Das NVision 40 am HZDR

Fritzsche, M.

Es handelt sich um einen Überblicksvortrag über die am NVision untersuchten und/oder hergestellten Nanostrukturen und ihre Verwendung am HZDR.

  • Invited lecture (Conferences)
    CrossBeam® Workshop, 03.-04.05.2011, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15673
Publ.-Id: 15673


Swift Heavy Ion Shaping of Sub-Micron Structures

Ferhati, R.; Fritzsche, M.; Amirthapandian, S.; Guilliard, N.; Weishaar, T.; Bolse, W.

We applied swift heavy ions (SHI) for shaping of already existing submicron- and nano-scale structures by irradiation at small angles and simultaneous azimuthal rotation. The investigated samples consisted of 100nm thick films of NiO or ZnO deposited on an oxidized Si-wafer by reactive magnetron sputtering. Prestructuring into 3-dimensional sub-μm and nm-sized objects with quadratic or rectangular cross-sections was done by means of focused ion beam technique. The process produced a grid of perpendicular lines cut into the film, reaching from the surface down to the interface and having line distances varying between 5 μm and 250 nm. These samples were then irradiated with SHI in the chamber of our new in-situ scanning electron microscope (SEM) installed at the M1-beamline of the UNILAC.

  • Contribution to external collection
    K.Große: GSI Scientific Report 2010, GSI Report 2011-01, GSI Darmstadt: GSI Helmholtzzentrum f¨ur Schwerionenforschung, 2011, 391

Permalink: https://www.hzdr.de/publications/Publ-15672
Publ.-Id: 15672


Phase formation and separation in NiO/SiO2 and NiO/Si layer systems during swift heavy ion irradiation

Ferhati, R.; Guilliard, N.; Fritzsche, M.; Bolse, W.

We have recently investigated restructuring effects in thin oxide films (NiO, Fe2O3 and ZnO on pure Si- or oxidized Si-substrates) during swift heavy ion (SHI) irradiation. On the one hand we have observed that the films rupture upon SHI bomdardment under normal ion incidence and exhibit dewetting patterns similar to those observed for liquid polymer films on Si. On the other hand, grazing incidence irradiation of NiO-films leads to an instability against cracking perpendicular to the beam direction projected onto the surface and subsequent growth of an almost periodic lamellae pattern with lamellae thicknesses of the order of 100 nm and heights of the order of 2 µm. Subsequent irradiation under perpendicular directions at sufficiently low ion fluences results in a more or less rectangular crack pattern, i.e. the generation of spacially separated rectangular NiO-plates on top of the substrate. By further irradiation under grazing incidence and continuous azimuthal rotation of the sample, the oxide plates shrink in their lateral dimensions and grow in height. At the same time the egdes become round and finally a ”forest” of cylindrical NiO-pillars with radii of the order of 100 nm forms. However, because of the irregular cracking, the pillar are not arranged in a regular manner and exhibit a wide distribution of heigth and radius. These limitations can be overcome by replacing the initial cracking due to the ”Grinfeld instability” by artificial production of regularely ordered rectangular ”oxide plates” utilizing the focused ion beam (FIB) technique. SHI irradiation under grazing angle incidence and continuous azimuthal rotation than indeed results in the formation of regularely ordered objects of various (not only pillar-like) shapes, depending on the size of the initial plate. These phenomena can be understood in terms of the ”ion hammering effect” and ion-induced visco-elastic flow due to yield stresses and surface tensions as well as interface energies (capillary forces). However, until now it is not clear whether or not the above described phenomena are influenced also by phase formation and separation in the film and at its interfaces. Related studies require the utilization of phase- or at least element-sensitive analysis techniques with good lateral spacial or/and depth resolution. In the present report we’ll present our first EDX- (Energy Dispersive X-Ray Spectroscopy) and XPS- (Foto-Electron Spectroscopy) results on SHI irradiated coherent as well as pre-structured NiO-layers on Si and SiO2, respectively.

  • Contribution to external collection
    Prof. Dr. Peter Michler, Prof. Dr. Wolfgang Bolse: Annual Report 2010, Institut für Halbleiteroptik und funktionale Grenzflächen, Universität Stuttgart, Stuttgart: Universität Stuttgart, 2011, 50-51

Permalink: https://www.hzdr.de/publications/Publ-15671
Publ.-Id: 15671


In-situ investigation of swift-heavy-ion shaping of micron- and submicron structures

Ferhati, R.; Fritzsche, M.; Bolse, W.

Materials modification by swift heavy ion (SHI) irradiation has become a field of investigation in the early 80’s, when Klaumünzer and Schumacher observed that irradiation of metallic glasses with swift heavy ions of some MeV/amu results in anistropic plastic deformation (shrinking along and expansion perpendicular to the beam direction). Since such a behaviour is reminiscent of treating a metal sheet with a hammer, it is often called hammering effect”. Trinkaus has theoretically explained this phenomenon by the local rapid solid-liquid-solid phase transition, which is caused by the passage of a SHI through the material with sufficient ionisation cross-section (electronic stopping power). This transient melting and rapid resolidification (within some tens of ps) of a cylinder (ion track) of typically 10 nm in diameter along the ion trajectory creates tensile stresses along and compressive stresses perpendicular to the ion track axis. As we have shown before, these induced stresses may result in surface instabilities of thin oxide films, causing self-organised restructuring into lamellae- and pillar-like patterns on a nm-scale.
Here we will report about the continuation of our recently started exploration of the potential use of the hammering effect for shaping and modifying micron and sub-micron structures by swift heavy ion irradiation. In addition to the results on pre-structured NiO-films presented in the preceeding annual report we will now discuss the results of our recent experiment on pre-structured ZnO-films on oxidized Si-wafers and compare them with the previous study.

  • Contribution to external collection
    Prof. Dr. Peter Michler, Prof. Dr. Wolfgang Bolse: Annual Report 2010, Institut für Halbleiteroptik und funktionale Grenzflächen, Universität Stuttgart, Stuttgart: Universität Stuttgart, 2011, 48-49

Permalink: https://www.hzdr.de/publications/Publ-15670
Publ.-Id: 15670


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