Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Approved and published publications
Only approved publications

42469 Publications

Depth-filtration model for compressible fibrous cakes

Grahn, A.; Kryk, H.; Kästner, W.; Alt, S.; Kratzsch, A.

Abstract

Flow through fibrous materials is encountered in a number of industrial applications, such as paper making, air and liquid filtration or manufacture of composite materials. Particle retention and pressure drop in beds of fibrous materials are difficult to predict because such beds easily compact under the action of fluid drag forces and thus exhibit significant variations of hydraulic and filtration properties along the flow direction and with time. This study proposes a semi-empirical model to calculate the time dependent clogging of compressible fibrous cakes due to the capturing of suspended particles as they pass through the cake. An experimental and a data evaluation procedure are suggested for determining the empirical parameters of the model equations.

Keywords: depth filtration; pressure drop; compressible fibre cake

Permalink: https://www.hzdr.de/publications/Publ-16041


Study on severe accidents and countermeasures for VVER-1000 reactors using the integral code ASTEC

Tusheva, P.; Schäfer, F.; Reinke, N.; Altstadt, E.; Kliem, S.

Abstract

The research field focussing on the investigations and the analyses of severe accidents is an important part of the nuclear safety. To maintain the safety barriers as long as possible and to retain the radioactivity within the airtight premises or the containment, to avoid or mitigate the consequences of such events and to assess the risk, thorough studies are needed. On the one side, it is the aim of the severe accident research to understand the complex phenomena during the in- and ex-vessel phase, involving reactor-physics, thermal-hydraulics, physico-chemical and mechanical processes. On the other side the investigations strive for effective severe accident management measures.

This paper is focused on the possibilities for accident management measures in case of severe accidents. The reactor pressure vessel is the last barrier to keep the molten materials inside the reactor, and thus to prevent higher loads to the containment. To assess the behaviour of a nuclear power plant during transient or accident conditions, computer codes are widely used, which have to be validated against experiments or benchmarked against other codes. The analyses performed with the integral code ASTEC cover two accident sequences which could lead to a severe accident: a small break loss of coolant accident and a station blackout. The results have shown that in case of unavailability of major active safety systems the reactor pressure vessel would ultimately fail. The discussed issues concern the main phenomena during the early and late in-vessel phase of the accident, the time to core heat-up, the hydrogen production, the mass of corium in the reactor pressure vessel lower plenum and the failure of the reactor pressure vessel. Additionally, possible operator’s actions and countermeasures in the preventive or mitigative domain are addressed. The presented investigations contribute to the validation of the European integral severe accidents code ASTEC for VVER-1000 type of reactors.

Keywords: Severe accidents; severe accident management; SBLOCA; SBO; primary side depressurization; vessel failure; ASTEC

  • Kerntechnik 77(2012)4, 271-277

Permalink: https://www.hzdr.de/publications/Publ-16040


Microbial Life in Uranium-contaminated Milieus

Zirnstein, I.; Gagell, C.; Arnold, T.; Krawczyk-Bärsch, E.; Röske, I.

Abstract

Microorganisms often form communities, so-called biofilms, in its natural habitats. In every territory of the world they play an important role. Biofilms contain different types of microorganisms e.g. bacteria, fungi, amoebae, algae etc. Together with the self-produced matrix, called EPS (extracellular polymeric substances), they constitute a kind of microenvironment. The supply of nutrients is mediated by open water channels. Just the same way toxic heavy metals could possibly infiltrate the biofilm. In order to understand the migration and transport processes of uranium in nature it is necessary to study the interaction of uranium with biofilms.
Biofilms are located in the former uranium mine Königstein (Saxony) in a depth of 250 m. There are two types of biofilms: stalactite-like biofilms and drainage biofilms. The water is characterized by high concentrations of uranium, protons and sulfate ions. The microscopic and genetic analysis of the Königstein biofilms revealed a rich diversity of microorganisms within the biofilm. Astonishing, we also found fungi and eukaryotes such as amoebae, insects, ciliates among bacteria to live under the extreme conditions of the mine.
Königstein mine was flooded last year (2010). Other mining sites of Saxony were flooded a long time ago. Recent studies compare the microbial diversity after (selected mining sites) and before (Königstein mine) flooding. The aim of the work is to visualize the whole biofilm and to analyze its interaction with uranium.

  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-16039


Intelligente Strömungsfolger zur räumlichen Parametererfassung in großskaligen Behältern

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

Abstract

Die räumliche Erfassung relevanter Prozessparameter wird bei einer Vielzahl industrieller Anwendungen durch den begrenzten Zugang zum Prozess erschwert. Beispiele sind Reaktoren mit Rührwerken, Bioreaktoren, Fermenter und Schüttgutbehälter. In solchen Behältern ist die Installation von fest angebrachten Sensoren und Kabelverbindungen oft nicht realisierbar oder unerwünscht. Herkömmliche Messsonden werden üblicherweise nur lokal installiert, womit die Erfassung räumlich verteilter Parameter nur eingeschränkt möglich ist. Zudem sind räumlich auflösende Apparate, wie Kameras oder Tomographiemesssysteme, meist nicht anwendbar. Daher bietet die Überwachung der räumlichen Verteilung relevanter Prozessparameter ein hohes Potential für die verbesserte Untersuchung und die Optimierung der Anlagen und Prozesse.
Speziell für Fermenter sind der lokale Vergärungsgrad von Biomasse, Temperaturprofile, pH-Wertverteilungen, Gas- und Flüssigkeitsbestandteile im Substrat sowie lokale Strömungscharakteristiken (Geschwindigkeitsprofile, Totzonen, Kurzschlussströmungen) für die Einschätzung der Prozesseffizienz von Interesse. Dabei kann es oft ausgehend von wenigen physikalischen Basisparametern, wie Temperatur und Druck, Rückschlüsse auf die Effektivität der Heiz- und Rührregime geben. Autonome Sensortechnologien ermöglichen die messtechnische Erfassung verteilter Parameter durch den Einsatz intelligenter Strömungsfolger und gewinnen deshalb zunehmend an Bedeutung für Anwendungen in der Prozessindustrie.
Zur Erfassung räumlich verteilter Parameter in Prozessbehältern wurde ein Schwarm autonomer Sensorkapseln mit einer zugehörigen Basiseinheit entwickelt und getestet. Die Validierung des Messsystemes erfolgte unter realen Strömungsbedingungen in einem Pilotfermenter. Die aufgenommenen Messdaten und die daraus extrahierten Parameterprofile liefern neuwertige und verlässliche Informationen über den Zustand im Prozess und die vorherrschenden Strömungsbedingungen.

  • Lecture (Conference)
    Mess- und Regelungskonzepte in der Lebensmittel- und Umweltbiotechnologie, 18.10.2011, Gerlingen, Deutschland
  • Contribution to proceedings
    Mess- und Regelungskonzepte in der Lebensmittel- und Umweltbiotechnologie, 18.10.2011, Gerlingen, Deutschland, 18.10.2011, Gerlingen, Deutschland
    Fachgruppentagung Mess- und Regelungskonzepte in der Lebensmittel- und Umweltbiotechnologie

Permalink: https://www.hzdr.de/publications/Publ-16038


Biofilms growing in an underground Uranium mine

Zirnstein, I.; Gagell, C.; Arnold, T.; Krawczyk-Bärsch, E.; Röske, I.

Abstract

The eukaryotic diversity of biofilm microorganisms in the underground uranium mine Königstein in Saxony/Germany was studied by molecular methods and microscopy. The Königstein mine is currently in the process of remediation. Due to technical leaching with sulphuric acid, the mine water is characterized by low pH, high concentrations of toxic heavy metals and uranium (up to 3×10-4 M) (Arnold et al. 2010). Biofilms in the Königstein mine grew underground in the mine galleries in a depth of 250 m (50 above sea level) either as stalactite-like slime communities or as acid streamers in the drainage channels. Previously conducted studies on the bacterial diversity in both biofilm communities in the uranium mine Königstein showed that beta-proteobacterium affiliated with Ferrovum myxofaciens, also designated “Ferribacter polymyxa” were identified as dominating bacterial species (Brockmann et al. 2010).
Biofilms are not only composed of bacteria, but may also include archaea and eukaryotic organisms. The eukaryotic diversity of the Königstein biofilms was analysed by molecular methods, i.e. 18S rDNA PCR, cloning and sequencing, which were used to determine the DNA-fragments of the microorganism, and by microscopic investigations. It was found that the eukaryotic biofilm communities of the Königstein environment showed a limited number of different heterotrophic species and consist of a variety of lineages belonging to nine major taxa: Ciliates, Flagellates, Amoebae, Heterolobosea, Fungi, Apicomplexa, Stramenopiles, Rotifers and Arthropoda and in addition a large number of uncultured eukaryotes, denoted as acidophilic eukaryotic cluster (AEC). As dominant eukaryotic species in the underground Königstein environment were identified Vahlkampfia species, Bodo species, and Oxytricha species. Flagellates, e.g. Bodo saltans, Stramenopiles, e.g. Diplophrys archeri and Rotifers were discovered for the first time in acid mine drainage (AMD) milieus characterized by high concentrations of uranium.
These eukaryotes in the studied biofilms are part of a biofilm community and represent a cycle of a food chain. This study shows that not only bacteria and archaea were identified in extreme AMD environments, but also eukaryotic species were found. These observed eukaryotes may influence significantly carbon cycling and metal immobilization within biofilms.

Keywords: Eukaryote; uranium; acid mine drainage; biofilm; microbial diversity; snottite; acid streamer; 18S rDNA PCR; Light microscopy

  • Lecture (Conference)
    10th symposium on remediation, 04.-05.10.2011, Jena, Germany

Permalink: https://www.hzdr.de/publications/Publ-16037


Carrier relaxation in epitaxial graphene photoexcited near the Dirac point

Winnerl, S.; Orlita, M.; Plochocka, P.; Kossacki, P.; Potemski, M.; Winzer, T.; Malic, E.; Knorr, A.; Sprinkle, M.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.

Abstract

We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 - 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical phonon frequency, however, owing to the presence of hot carriers, optical phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes.

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-16036


Room-temperature operation of a unipolar nanodiode at terahertz frequencies

Balocco, C.; Kasjoo, S. R.; Lu, X. F.; Zhang, L. Q.; Alimi, Y.; Winnerl, S.; Song, A. M.

Abstract

We report on the room-temperature electrical rectification at 1.5 THz of a unipolar nanodiode based on symmetry breaking in a nanochannel. The exploitation of its nonlinear diodelike characteristic and intrinsically low parasitic capacitance enables rectification at ultrahigh speed. The zero-voltage threshold and unique planar layout make the nanodiode suitable for building large arrays. This is the highest speed reported in nanorectifiers to date.

Involved research facilities

Related publications

  • Applied Physics Letters 98(2011), 223501

Permalink: https://www.hzdr.de/publications/Publ-16035


Near-field spectroscopy on semiconductor micro- and nanostructures at FELBE

Winnerl, S.

Abstract

The combination of near-field microscopy with spectral resolution in the mid-infrared and terahertz range can address a large number of specific elementary and collective excitations locally. This is of interest for a variety of materials such as semiconductors, strongly correlated materials and biomolecules.
The free-electron laser FELBE provides a quasi-cw beam of radiation tunable in the range from 4 – 230 µm (photon energy 310 – 5 meV) for a scattering near-field microscope (sSNOM) based on a home-built atomic-force microscope. We demonstrate its potential to obtain quantitative information on buried semiconductor structures by determining the carrier concentration of boron-implanted stripes in a silicon matrix [1]. To this end, FELBE is tuned in the region of the plasma resonance of the holes in the implanted regions and the contrast of the sSNIM images is analyzed. Next we present a study of spectroscopy on exciting nanostructures, namely self-assembled InAs quantum dots. Due to their three-dimensional confinement, the dots exhibit atom-like states. However, many of the key features such as extremely sharp optical transition lines (at low temperature) are masked by the variation of energy levels from dot-to-dot due to differences in size and composition. Therefore in recent years many techniques have been developed to study single quantum dots. We address doped InAs quantum dots overgrown with 70 nm of GaAs by tuning the wavelength to intersublevel transitions of conduction band states. In Fig. 1 sSNIM images are shown for the photon energies of 86 meV and 91 meV. While for the first one, which corresponds to the p-d electronic resonance in the dots, individual quantum dots are clearly resolved, the contrast vanishes for the slightly higher photon energy. A similar behavior is observed for photon energies around 122 meV, corresponding to the s-d transition in the dots. The resonances of individual quantum dots measured with the sSNIM exhibit a linewidth of about 5 meV. This is about 4 times smaller than the inhomogeneously broadened linewidth obtained at room temperature from an ensemble of quantum dots.

This work was performed in collaboration with R. Jacob, J. Bhattacharyya, D. Stehr, H. Schneider, M. Helm (HZDR), M. T. Wenzel, H.-G. von Ribbeck, L. M. Eng (TU Dresden), S. C. Kehr (Univ. St. Andrews, St. Andrews, UK) P. Atkinson, A. Rastelli, O. G. Schmidt (IFW Dresden).

References
[1] R. Jacob, S. Winnerl, H. Schneider, M. Helm, M. T. Wenzel, H.-G. von Ribbeck, L. M. Eng, and S. C. Kehr, Opt. Express 18, 26206 (2010).

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    6th Workshop on Infrared Specrtoscopy and Microscopy with Accelerator-Based Sources, 04.-08.09.2011, Trieste, Italy

Permalink: https://www.hzdr.de/publications/Publ-16034


Relaxation dynamics in graphene excited in the mid and far infrared

Winnerl, S.; Orlita, M.; Plochocka, P.; Schneider, H.; Helm, M.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.

Abstract

The relaxation dynamics is of key importance for understanding basic properties of graphene as well as for electronic and optoelectronic device applications. Various degenerate and two-color pump-probe studies have been carried out for excitation energies E = 1.6 eV [1-5].
We performed degenerate pump-probe spectroscopy at much lower energies (E = 15 – 250 meV) by applying a free-electron laser as a source of tunable picosecond radiation pulses. We investigated multilayer graphene samples grown by thermal decomposition on the carbon terminated surface of 6H-SiC. For the largest photon energy E = 245 meV the observed pump-probe signals can be characterized by two relaxation times of 0.5 ps and 5 ps at a lattice temperature of 10 K. For the lower photon energies the relaxation times are much longer, namely 15 ps for E = 72 meV and 25 ps for both E = 30 meV and E = 20 meV. The faster relaxation at 245 meV is attributed to the contribution of optical phonons, while at the lower energies only acoustic phonons are involved. This interpretation is corroborated by studying the temperature dependence of the pump-probe signals. While for the highest photon energy both the relaxation times and maximum transmission change depend only weakly on temperature, for lower photon energies the transmission change decreases rapidly and the relaxation times get much faster when the temperature is increased. Furthermore we find that the pump-induced transmission change saturates for moderate intensities (1 – 10 µJ/cm^2, depending on photon energy) and a maximum transmission change of about 10 % can be achieved. This is valuable information for the application of graphene as a saturable absorber in the mid and far infrared range.
While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV. The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy). We discuss the experimental results and a simple model based on rate equations.

References
[1] J.M. Dawlaty et al., Appl. Phys. Lett. 92, 042116 (2008).
[2] D. Song et al., Phys. Rev. Lett. 101, 157402 (2008).
[3] P.A. George et al., Nano Lett. 8 ,4248 (2008).
[4] H. Wang et al., Appl. Phys. Lett., 96, 081917 (2010).
[5] D. Sun et al., Phys. Rev. Lett. 104, 136802 (2010).

Involved research facilities

Related publications

  • Poster
    Graphene Week 2011, 24.04.-29.09.2011, Obergurgl, Austria

Permalink: https://www.hzdr.de/publications/Publ-16033


Enroute to investigating protein dynamics under selective vibrational excitation at the THz FEL FELBE

Bauer, C.; Gensch, M.; Heberle, J.

Abstract

We aim at investigating proteins under the irradiation with intense THz radiation tuned in resonance to specific vibrational modes. This approach is much in analogy to recent experiments that showed selective vibrational control in complex materials [01, 02, 03]. To achieve the necessary sensitivity for protein dynamics we combine a novel time-resolved IR difference spectroscopic setup with uniquely intense, tunable narrow bandwidth THz radiation (1.2 – 66 THz) of the THz free electron laser FELBE.

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-16032


The coherent THz facility at ELBE: Enroute to naturally synchronized THz pump THz probe experiments beyond the 100 J pulse energy limit and single shot electron bunch diagnostics

Gensch, M.

Abstract

At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at FLASH [1,2] the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses. The pulse energies are expected to exceed the 100 J limit at scalable repetition rates between 1 and 200 KHz (cw), thereby the coherent THz facility will represent a worldwide unique facility. Besides user experiments the laboratory is also foreseen as a test bed for THz-based electron bunch diagnostics (arrival time, bunch form, …) on cw linear accelerators. The current status of the project and planned experiments are presented.
[1] M. Gensch et. al., The new THz undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[2] U. Fruehling, M. Wieland, M. Gensch et. al., Single-shot Terahertz-field driven Streak camera, Nature Photonics 3 (2009), 523.
[3] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch et. al., Few Femtosecond Timing at 4th Generation X-ray light sources, Nature Photonics 5 (2011), 162.

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    Brookhaven National Lab - Ultrafast Meeting, 07.10.2011, New York, USA

Permalink: https://www.hzdr.de/publications/Publ-16031


The coherent THz facility at ELBE: Enroute to naturally synchronized THz pump THz probe experiments beyond the 100 J pulse energy limit and single shot electron bunch diagnostics

Gensch, M.

Abstract

At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at FLASH [1,2] the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses. The pulse energies are expected to exceed the 100 J limit at scalable repetition rates between 1 and 200 KHz (cw), thereby the coherent THz facility will represent a worldwide unique facility. Besides user experiments the laboratory is also foreseen as a test bed for THz-based electron bunch diagnostics (arrival time, bunch form, …) on cw linear accelerators. The current status of the project and planned experiments are presented.
[1] M. Gensch et. al., The new THz undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[2] U. Fruehling, M. Wieland, M. Gensch et. al., Single-shot Terahertz-field driven Streak camera, Nature Photonics 3 (2009), 523.
[3] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch et. al., Few Femtosecond Timing at 4th Generation X-ray light sources, Nature Photonics 5 (2011), 162.

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    Kolloquium PTB, 16.08.2011, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16030


Multijoule scaling of laser-induced condensation in air

Petrarca, M.; Henin, S.; Stelmaszczyk, K.; Bock, S.; Kraft, S.; Schramm, U.; Vaneph, C.; Vogel, A.; Kasparian, J.; Sauerbrey, R.; Weber, K.; Wöste, L.; Wolf, J.-P.

Abstract

Using 100 TW laser pulses, we demonstrate that laser-induced nanometric particle generation in air increases much faster than the beam-averaged incident intensity. This increase is due to a contribution from the photon bath, which adds up with the previously identified one from the filaments and becomes dominant above 550 GW/cm2. It appears related to ozone formation via multiphoton dissociation of the oxygen molecules and demonstrates the critical need for further increasing the laser energy in view of macroscopic effects in laser-induced condensation.

Keywords: 42.65.Jx Beam trapping; 52.38.-r Laser-plasma interactions; 92.60.Mt Particles and aerosols; 92.60.Nv Cloud physics and chemistry; self-focusing and thermal blooming

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-16026


Dose controlled radiobiological experiments with ultra-short pulse laser accelerated proton beams

Schramm, U.

Abstract

Dose controlled radiobiological experiments with ultra-short pulse laser accelerated proton beams

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    Laser and Plasma Accelerators Workshop 2011, 20.-24.06.2011, Wuzhen and Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-16025


Radiobiological applications of laser accelerated ion beams and visions for future research infrastructure

Schramm, U.

Abstract

Radiobiological applications of laser accelerated ion beams and visions for future research infrastructure

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    Fourth EMMI workshop on Plasma Physics with Intense Heavy Ion and Laser Beams, 02.-04.05.2011, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16024


Combining real-space data analysis of HEXS and XAS to determine the structure of amorphous colloids

Hennig, C.

Abstract

Structure analyses of amorphous colloids suffer from absence of periodic structural order and restrict the analytical techniques to near-order sensitive ones like real-space analysis of high-energy X-ray scattering (HEXS) and X-ray absorption spectroscopy (XAS). High-energy X-ray scattering provides precise distances and quantitative electron densities, but comprise scattering contributions from all scattering pairs in the structure whose separation becomes difficult with increasing number of elements involved. EXAFS, in contrast, is an element selective technique and provides exclusively structural information from the direct neighborhood of the absorbing atom, but suffer often from destructive interference effects as soon as the symmetry of the structure becomes low. A combination of these techniques is widely able to overcome their individual restrictions. Basic principles and examples will be discussed in detail.

Keywords: EXAFS; HEXS

Involved research facilities

Related publications

  • Lecture (Conference)
    Workshop on Analysis of Diffraction Data in Real Space, ADD2011, 12.-14.10.2011, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-16023


Numerical and experimental modeling of VGF-type buoyant flow under traveling magnetic field

Galindo, V.; Niemietz, K.; Pätzold, O.; Gerbeth, G.; Stelter, M.

Abstract

Experimental and numerical modeling of a Vertical Gradient Freeze-type buoyant flow under a traveling magnetic field is presented. Low-temperature flow experiments were carried out using a GaInSn alloy. Radial heating and cooling of the melt leading to a double vortex buoyant flow like in typical VGF growth was introduced and systematically varied by means of a model furnace. The combined VGF-TMF flow was investigated with focus on the transition from a stationary to a time-dependent flow regime. The stability threshold was found to be significantly influenced by the mutual interaction of electromagnetically driven and buoyant flows.

Keywords: crystal growth; traveling magnetic field; vertical gradient freeze

  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Corsica, France
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 193-197
  • Lecture (Conference)
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Corsica, France

Permalink: https://www.hzdr.de/publications/Publ-16022


Investigations of nano structures on ta-C films made by gallium FIB lithography

Philipp, P.; Bischoff, L.

Abstract

Hydrogen free Diamond like carbon films (DLC) with high sp3 content, fabricated by mass filtered vacuum arc deposition and modified by Ga+ FIB irradiation were investigated.

For electrical characterization at room temperature van-der-Pauw structures were written by direct Ga+ FIB lithography. The sheet resistance RS decreases with increasing ion fluence due to the increase of the sp2 content in the irradiated regions, where a minimum of RS = 290 at 1.6 x 1017 cm2 was achieved. Hall measurements were used to study the charge carrier mobility. Therefore 4- and 6-terminal device structures were fabricated by combining FIB and optical lithography on DLC layers. The layers with a thickness in the range between 20 and 110 nm had a sp3 content above 65% and are deposited on a Si substrate. The FIB made structures were partly covered by 400x400 µm² Au contact pads, produced by lift off technique. Hall measurement results are interpreted as a function of the Ga+ fluence, the structure size and the DLC layer thickness. For a second set of samples a SiO2 interface layer between DLC and Si substrate was used to avoid leakage current through the bulk Si. The results for the two sample types are compared and the influence to the leakage current will be discussed. Additionally, conducting graphitic nanowires were investigated (length 10 µm, width 200 nm to 5 µm) delivering a resistance of 130 k for 5 µm width and 300 M for 300 nm width, respectively.

Ga+ irradiation under higher temperatures shows dot formation due to Ga segregation that was observed above 400°C at fluences higher than 1 x 1016 cm2. The Ga-dots were studied by SEM/EDX and AFM. Increasing Ga+ fluence leads to an increase of the dot areal density. Diameter and height of the dots are growing with temperature.

Ion beam induced graphitization of DLC films by FIB in the nanoscale offers prospective applications of conductive nanostructures in an insulating matrix.

Keywords: tetrahedral amorphous carbon; focused ion beam; graphitization; nano-structures; van-der-Pauw

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-16019


Quantitative analysis of the order of Bi ion induced dot patterns on Ge

Böttger, R.; Bischoff, L.; Facsko, S.; Schmidt, B.

Abstract

We demonstrate that the temperature dependent focused ion beam irradiation of (100) Ge surfaces with 20 keV Bi+ ions leads to variably ordered hexagonal dot pattern. We show that the average information gain about the spatial order can be signicantly increased by image preprocessing transforming the power spectral density into the pair correlation function. Order parameters are derived from the pair correlation function for the comparison of highly ordered patterns.

Keywords: nanodots; nanoholes; pair correlation function; hexagonal order; image analysis

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-16018


Experiments with neutrons and photons at ELBE

Schwengner, R.

Keywords: Neutron scattering; fast neutrons; neutron capture; cold neutrons; photon scattering; bremsstrahlung; cross sections; statistical model; strength function; level density; transmutation

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    The Fourteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, 28.08.-02.09.2011, Guelph, Canada
  • Contribution to proceedings
    The Fourteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, 28.08.-02.09.2011, Guelph, Canada
    Proceedings of the Fourteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics

Permalink: https://www.hzdr.de/publications/Publ-16010


A method for correct averaging in transmission radiometry

Hampel, U.; Wagner, M.

Abstract

Transmission radiometry with photon or particle radiation is a common technique for the measurement of thickness, density and composition of materials, e.g. in production lines and in multiphase flow metering. Moreover, radiation transmission measurement is the basis for many imaging techniques, such as x-ray and gamma ray tomography. A common problem associated with transmission measurement is correct temporal averaging for time-varying material properties. Averaging the intensity signal at the detector over time and taking this mean to calculate average ray attenuation leads to incorrect results when attenuation changes within the integration period. This paper discusses the implications of this systematic error and introduces a methodology for correct averaging which is applicable even to very low intensity measurements.

Keywords: transmission radiometry; dynamic error

Permalink: https://www.hzdr.de/publications/Publ-16009


Novel Ge nanopattern by heavy Bi monomer irradiation

Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.; Pilz, W.; Heinig, K.-H.; Facsko, S.

Abstract

Surface pattern on Ge induced by Bi cluster ions doffer drastically from morphology after monomer irradiation. Large aspect ratios of dots and ripples and crystalline surfaces after cluster irradiation have been observed. A novel patterning mechanism explains the dot formation qualitatively by means of local tiny melt pools induced by ion impact . Moreover this model predicts the formation of dot pattern even for monomer irradiation at elevated temperature. The aim of this work is to investigate the pattern formation by heavy Bi monomer bombardment. Surface pattern obtained at room temperature and under normal incidence are investigated in an ion energy range from 4 to 60 keV. A energy driven pattern transition from hole over dot to sponge like structures is observed. Moreover, the pattern formation by Bi monomer ions is investigated at elevated temperatures showing a energy dependent transition from sponge to dot like pattern.

Keywords: Bi ion monomer cluster pattern formation

Involved research facilities

Related publications

  • Lecture (Conference)
    Nanoscale pattern formation at surfaces, 18.-22.09.2011, El Escorial, Spain

Permalink: https://www.hzdr.de/publications/Publ-16008


Engineered Nanoparticles and Their Identification Among Natural Nanoparticles

Zänker, H.; Schierz, A.

Abstract

Due to the huge excess of natural nanoparticles, the identification and quantification of engineered nanoparticles is a big challenge to the analyst. Moreover, identification in a qualitative sense and quantification by mass concentration alone is not sufficient since the potential environmental hazard arising from engineered nanoparticles is controlled by a number of further properties of the particles. The most important methods of nanoparticle fractionation and nanoparticle detection are discussed. It is shown that coupled techniques are increasingly applied. Dedicated techniques that are tailored to the search for a certain targeted engineered nanoparticle are more promising than universal approaches that aim at the search for any engineered nanoparticles. Analyses should not rely on only one method but several complementary methods should be used.

Keywords: Engineered nanoparticles; environmental hazard; fractionation; detection; coupled methods

Permalink: https://www.hzdr.de/publications/Publ-16007


Microfluidic system for endocrine disrupting chemicals detection in waterish solution

Cherkouk, C.; Rebohle, L.; Howitz, S.; Skorupa, W.

Abstract

We present a microfluidic cell plate for endocrine disrupting chemicals (EDCs) detection, like estrogenic activity, in waterish solution. This platform technology consists of four independent micro flow units made of polydimethylsiloxane (PDMS) and glass, which enables a selective detection of up to four species of the EDCs per one-way chip containing the corresponding immobilized receptor. The concept of the detection is based on direct fluorescence analysis. In order to found out the electrical parameters of the microfluidic system electroluminescence (EL) measurements as a function of the concentration of the QD800 dye were investigated. Finally, the microfluidic device was attached to the flow control system. Different edge filters were tested in order to attenuate the MOSLED light signal and to maximize the QD800 dye signal at 800 nm which works best for a 780 nm edge filter. Measurements using an integrated photo diode as detector were performed to point out the relationship between the dark and photo current.

Keywords: Si-based light emission; biosensor; microfluidic; fluorescence; estrogen; EDC

  • Poster
    Eurosensor XXV, 05.-8.9.2011, Athen, Griechenland
  • Contribution to proceedings
    Microfluidics and LoC, 05.-8.9.2011, Athen, Griechenland, Holand: Elsevier

Permalink: https://www.hzdr.de/publications/Publ-16006


Secondary Electron Emission from Surfaces during Focused Ion Beam Irradiation

Bischoff, L.; Böttger, R.

Abstract

Scanning ion microscopy (SIM) based on secondary electron (SE) imaging initiated by focused ion beam (FIB) irradiation of surfaces can yield important information about the topography, the material changes or crystallographic orientations of a specimen. Compared to a scanning electron microscope (SEM) based on a similar principle the information comes from a very near surface region due to the small penetration depth of the ions. A disadvantage of the SIM is the lower spatial resolution and the fact that energetic ions damage the surface during imaging by implantation and sputtering processes.
The aim of this work is to investigate the behavior of a mass-separated FIB working with a bismuth liquid metal ion source which emits a broad spectrum of single and double charged monomers as well as cluster ions in the frame of the examination of the self-organization of nano-pattern on surfaces under heavy ion erosion [3]. The study of all interactions of the primary beam within the surface and the knowledge of the fundamental parameters leads to a more correct interpretation of the secondary electron images.

Keywords: FIB; secondary electron emission; work function

Involved research facilities

Related publications

  • Lecture (Conference)
    Nanoscale pattern formation at surfaces, 18.-22.09.2011, El Escorial, Spain

Permalink: https://www.hzdr.de/publications/Publ-16005


Study of Formation and Thermodynamic Properties of Aqueous U(VI) – Uric Acid System by Time – Resolved Laser – Induced Fluorescence Spectroscopy (TRLFS)

Osman, A. A. A.; Geipel, G.

Abstract

Background
Due to the progression of uranium content in the bio-sphere at present, uranium is expected to be increasingly accumulated in the food chain and eventually in the living organisms. To get valuable information and to understand its toxicity, behaviour and distribution in such cellular level; knowledge about uranium (VI) speciation in biosystems will be useful for evaluating toxicity after uranium exposure. Little is known about interaction and behaviour of uranium with some biomolecules (e.g. urea and uric acid) that commonly present in biological fluids or in bio-system. In attempt to provide information in this context, we investigate some important thermodynamic data upon complexation of uranium with some single bioligands, viz., uric acid using TRLFS.

  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-16000


Complexation of An(III)/Ln(III) with Borates

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

Abstract

Investigations to the mobilisation of radionuclides are essential in the risk assessment of radionuclides in the environment and the safety assessment of nuclear waste repositories. The mobilisation of radionuclides takes place for instance by the formation of water soluble complexes or sorption processes on mineral surfaces. Concerning the required risk and safety assessments a wide knowledge about the chemical and physical behavior of radionuclides, particularly actinides, is needed. Thus, interaction studies of radionuclides are carried out, e.g. complexation studies with components of the environmental compartments (humic acids, bioligands, inorganic ligands, bacteria, …).
Borates (e.g. boric acid B(OH)3 and its salts or esters) are ubiquitous compounds in the environment (rocks, soils, natural waters) and are used in many applications, e.g. glass production, detergents, agriculture and nuclear technology. Thus, there are many sources for the release of borates in the environment. But although there is a relevance of borates in the environment and, perhaps, in nuclear waste repositories, the Ln(III)/An(III)-borate system is investigated insufficiently.
The work concentrates on the complex formation in the An(III)/Ln(III)-borate system. The influence of temperature and ionic strength on the complexation will be investigated.

Keywords: Europium; Americium; borates; complexation studies; temperature; ionic strength

  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-15999


Simulations of RUTA-70 reactor with CERMET fuel using DYN3D/ATHLET and DYN3D/RELAP5 coupled codes

Kozmenkov, Y.; Rohde, U.; Baranaev, Y.; Glebov, A.

Abstract

RUTA-70 is a pool type reactor with the rated power of 70 MW designed as a district heat supplying facility. The basic design principles of this reactor are simplicity of the design and a high safety level due to a low pressure and a large coolant inventory in the primary system. The core design with the CERMET fuel rods also contributes to the reactor safety due to a high thermal conductivity of the fuel matrix and its role as the additional barrier to the fission products release.

RUTA-70 model for simulations with the internally coupled code systems DYN3D/ATHLET and DYN3D/RELAP5 was developed. A 3-D power distribution in the core is calculated by DYN3D with thermal-hydraulic feedback from the system codes. The reactor facility model includes reactor pool, two reactor loops, circulation pumps, primary and the secondary heat exchangers and core channels. The core model consists of 16 fuel assemblies in the 60-degree symmetry sector with different burnable absorber (Gd) concentrations.

The steady-state with the rated reactor parameters and a BDB accident scenario were simulated with the DYN3D/ATHLET and DYN3D/RELAP5 coupled code systems to verify these codes. The simulated accident is initiated by the trip of two operating primary circulation pumps. Additionally to the initial event the SCRAM failure is postulated.

The compared codes give close predictions for the initial and final states of the accident but not for the transition between them. The observed deviations are explained by differences in the subcooled boiling models of the system codes ATHLET and RELAP5. Both simulations confirm a high level of the reactor inherent safety. The allowed safety margins were not reached.

Keywords: pool type reactor; low pressure; CERMET fuel; coupled code; accident simulation; subcooled boiling; reactor stability

  • Contribution to proceedings
    21st Symposium of AER on VVER Reactor Physics and Safety, 19.-23.09.2011, Dresden, Deutschland
    Proceedings of the 21st Symposium of AER on VVER Reactor Physics and Safety, 595-613
  • Lecture (Conference)
    21st Symposium of AER on VVER Reactor Physics and Safety, 19.09.-23.11.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15998


Effect of superimposed magnetic field on hydrogen evolution reaction

Koza, J.; Mühlenhoff, S.; Zabinski, P.; Nikrityuk, P.; Eckert, K.; Uhlemann, M.; Gebert, A.; Weier, T.; Schultz, L.; Odenbach, S.

Abstract

The effect of uniform magnetic fields on hydrogen evolution reaction during metal deposition and water electrolysis was investigated by means of electrochemical techniques coupled with in-situ microscopic observation, velocity measurements and numeric simulation. The desorption of hydrogen bubbles is enhanced in applied magnetic fields independent on their orientation relative to electrode surface. The origin of this effect is attributed to Lorentz force driven convection generated by the applied magnetic field.

Keywords: two-phase flow; electrolysis; Lorentz force

  • Lecture (Conference)
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 789-793

Permalink: https://www.hzdr.de/publications/Publ-15997


On the action of magnetic gradient forces in microstructured copper deposition

Mutschke, G.; Tschulik, K.; Weier, T.; Uhlemann, M.; Bund, A.; Alemany, A.; Fröhlich, J.

Abstract

The relative influence of the Lorentz force and the magnetic gradient force on micro-structured copper deposition is studied with simple magnetic elements consisting of cylindrical permanent magnets are placed closely behind the surface of the cathode. Analytical findings and numerical simulations reveal that for magnets of small diameter the magnetic gradient force dominates. Experimental investigations find that the thickness of the deposited copper layer increases in the vicinity of the magnets. The combined analysis of simulations and experiments shows that this enhancement of mass transfer results from a local convection towards the electrode which is forced by the magnetic gradient force.

Keywords: electrodeposition; Lorentz force; magnetic gradient force

  • Lecture (Conference)
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 725-728

Permalink: https://www.hzdr.de/publications/Publ-15996


The simplified P3 approach on a trigonal geometry in the nodal reactor code DYN3D

Duerigen, S.; Fridman, E.

Abstract

DYN3D is a three-dimensional nodal diffusion code for steady-state and transient analyses of Light-Water Reactors (LWRs) with square and hexagonal fuel assembly geometries. Currently, several versions of the DYN3D code are available including a multi-group diffusion and a simplified P3 (SP3) neutron transport option. In this work, the multi-group SP3 method based on trigonal-z geometry was developed. The method is applicable to the analysis of reactor cores with hexagonal fuel assemblies and allows flexible mesh refinement, which is of particular importance for VVER-type Pressurized Water Reactors (PWRs) as well as for innovative reactor concepts including block type High-Temperature Reactors (HTRs) and Sodium Fast Reactors (SFRs). In this paper, the theoretical background for the trigonal SP3 methodology is outlined and the results of a preliminary verification analysis are presented by means of a simplified VVER-440 core test example. The accordant cross sections and reference solutions were produced by the Monte Carlo code SERPENT. The DYN3D results are in good agreement with the reference solutions. The average deviation in the nodal power distribution is about 1%.

Keywords: DYN3D; simplified P3; SP3; trigonal; hexagonal; nodal

  • Contribution to proceedings
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany
  • Lecture (Conference)
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-15995


Simulation of AER-7 benchmark problem with the coupled code DYN3D/ATHLET

Kozmenkov, Y.; Kliem, S.

Abstract

The 7th dynamic benchmark is the most recent problem specified within the AER activities on verification of the coupled neutronic/thermal-hydraulic codes. This is the VVER-440 transient initiated by re-connection of the isolated reactor circulation loop filled with a low-temperature coolant. During the transient a core power excursion with a non-symmetric radial distribution is expected due to incomplete coolant mixing at the core inlet.

The externally coupled code system DYN3D/ATHLET developed in HZDR was used in the benchmark simulation. In the case of external coupling all neutronic and thermal-hydraulic parameters of the core are calculated by the 3D code of neutron kinetics DYN3D.

The computer model of the VVER-440 reactor used in the AER-7 calculations represents a modified version of the earlier developed input deck for the AER-6 benchmark simulation. The model includes 6 reactor loops with the main circulation pumps and steam generators. The secondary system is modelled up to the turbine valves. The 3D core model includes all 349 fuel assemblies (assembly-by-assembly approach).

The main results of the benchmark calculation are presented and discussed.

Keywords: dynamic benchmark; VVER-440; coupled code verification; 3D core model

  • Contribution to proceedings
    21st Symposium of AER on VVER Reactor Physics and Safety, 19.-23.09.2011, Dresden, Deutschland
    Simulation of AER-7 benchmark problem with the coupled code DYN3D/ATHLET, 449-462
  • Lecture (Conference)
    21st Symposium of AER on VVER Reactor Physics and Safety, 19.-23.09.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15994


Millisecond flash-lamp annealing of LaLuO3

Lehmann, J.; Shevchenko, N.; Mücklich, A.; von Borany, J.; Skorupa, W.; Schubert, J.; Lopes, J. M. J.; Mantl, S.

Abstract

Metal-oxide-semiconductor capacitors containing the alternative high-k dielectric LaLuO3 were treated by flash lamp annealing (FLA). Capacitance–voltage (C–V) and current–voltage (J–V) characteristics reveal an increase in the capacitance for the flashed samples while the very low leakage current of the LaLuO3 is retained. Microstructural investigations confirm the thermal stability of the film even after FLA at 1200 °C, 20 ms.

Keywords: High-k dielectrics; Alternative high-k dielectrics; Higher-k dielectrics; Ternary rare earth oxides; Ternary high-k oxides; Rare-earth based gate oxides; Electrical properties

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15993


DNS and experiments of electromagnetic flow control on an inclined flat plate

Albrecht, T.; Weier, T.; Gerbeth, G.; Metzkes, H.; Stiller, J.

Abstract

We investigate the separated flow around an inclined flat plate at a Reynolds number of 104 by Direct Numerical Simulation (DNS) and time-resolved Particle Image Velocity (PIV). Flow separation is suppressed using sinusoidally and rectangularly oscillating Lorentz forces in streamwise direction. An rms momentum coefficient of 2.25% increases the time-averaged lift, deduced from PIV by a global momentum approach, by 20–45%. Whereas sinusoidal forcing increases both lift and drag, rectangular waves create no significant additional drag. Analysis of the DNS flow structures reveals different immediate vortex dynamics induced by the actuation.

Keywords: flow control; Lorentz force; flow separation

  • Poster
    8th International Pamir Conference on Fundamental and Applied MHD, 05.09.2011, Borgo, Frankreich
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Frankreich
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 375-379

Permalink: https://www.hzdr.de/publications/Publ-15992


Image based in-vivo dosimetry: from PET to in-beam SPECT

Fiedler, F.; Dersch, U.; Golnik, C.; Kormoll, T.; Enghard, W.

Abstract

Radiation therapy is an important treatment modality in cancer therapy. New radiation species, like protons and light ions have the potential of increasing tumor conformality of irradiation. Because of the way these particles deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the damage of the surrounding healthy tissue. Such high precision radiotherapy treatment requires efficient quality assurance techniques. Small changes in the irradiated volume will lead to a mismatch of the deposited dose maximum and the tumor. This causes missing dose in the tumor volume and potential damage to healthy tissue. Therefore, a dose monitoring system is highly desirable. Between 1997 and 2008, the in-beam Positron Emission Tomography (PET) method was used at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany, for monitoring the dose delivered by 12C beams. Since the positive clinical impact of the method has been shown at the Dresden Proton Therapy facility an in-room PET/CT will be installed for the same purpose.
Due to inherent limitations of this method, a direct quantification of the delivered dose is not feasible. Therefore, another approach based on dose monitoring by detection of prompt gamma rays is currently under investigation. For this purpose a Compton camera design was evaluated with respect to the special requirements and conditions that arise from this application. Different concepts were compared by means of simulation. Now the construction of a first prototype is under way.

Keywords: in vivo dosimetry; in-beam PET; in-beam SPECT

  • Invited lecture (Conferences)
    SCINT 2011 - 11th International Conference on Inorganic Scintillators and their Applications, 12.-16.09.2011, Gießen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15991


Potential Use of Thorium in PWRs

Fridman, E.

Abstract

There has been a recent revival of interest in Th-based fuel cycles, particularly for commercial Pressurized Water Reactors (PWR), motivated primarily by their potential to address concerns related to the proliferation potential, saving of natural uranium resources, and waste disposal of the conventional uranium fuel cycle. The objective of this talk is to provide an overview of some of the recent studies examining implementation scenarios, potential benefits and drawbacks associated with the use of Th-based fuels in current generation of PWRs.

  • Invited lecture (Conferences)
    494. Wilhelm und Else Heraeus-Seminar on Innovative Nuclear Power in a Closed Fuel Cycle Scenario, 05.-08.12.2011, Physikzentrum Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-15990


Paradox of Velikhov-Chandrasekhar and the ultimate limit for the onset of helical magnetorotational instability

Oleg N. Kirillov, F. S.

Abstract

The magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable accretion discs. By using theWKB approximation and methods of singular function theory, we resolve two different paradoxes of MRI that appear in the limits of infinite and vanishing magnetic Prandtl number. For the latter case we derive a new strict limit of the critical Rossby number. This new limit of Roc = −0.802, which appears for a finite Lundquist number of Lu= 0.618, extends the formerly known inductionless Liu limit of Roc = −0.828 valid at Lu = 0.

Keywords: MHD; Rossby number; Lundquist number; helical magnetorotational instability

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

Permalink: https://www.hzdr.de/publications/Publ-15988


Standard and helical magnetorotational instability: How singularities create paradoxal phenomena in MHD

Kirillov, O. N.; Stefani, F.

Abstract

The magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable rotating shear flows, e.g., in Couette-Taylor cells and in accretion disks. What laws of differential rotation are susceptible to the destabilization by the axial or helical magnetic field? The answer to this vital for astrophysical and experimental applications question inevitably leads to the study of spectral and geometrical singularities on the instability threshold. The singularities provide a connection between seemingly discontinuous stability criteria and thus explain paradoxes in the theory of MRI that were kept poorly understood since 1950s. By using the WKB approximation and methods of singular function theory, we resolve two different paradoxes of magnetorotational instability that appear in the limits of infinite and vanishing magnetic Prandtl number. For the latter case we derive a new strict limit of the critical Rossby number. This new limit of Roc = −0.802, which appears for a finite Lundquist number of Lu = 0.618, extends the formerly known inductionless Liu limit of Roc = −0.828 valid at Lu = 0.

Keywords: Magnetorotaional instability; singularity theory; helical magnetorotational instability; Rayleigh line; Velikhov-Chandrasekhar paradox; inductionless HMRI

  • Invited lecture (Conferences)
    Kolloquium des Instituts für Analysis, Dynamik und Modellierung, 13.-15.07.2011, Universität Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15987


Singularities in Structural Optimization of the Ziegler Pendulum

Kirillov, O. N.

Abstract

Structural optimization of non-conservative systems with respect to stability criteria is a research area with important applications in fluid-structure interactions, friction-induced instabilities, and civil engineering. In contrast to optimization of conservative systems where rigorously proven optimal solutions in buckling problems have been found, for nonconservative optimization problems only numerically optimized designs have been reported. The proof of optimality in non-conservative optimization problems is a mathematical challenge related to multiple eigenvalues, singularities in the stability domain, and non-convexity of the merit functional. We present here a study of optimal mass distribution in a classical Ziegler pendulum where local and global extrema can be found explicitly. In particular, for the undamped case, the two maxima of the critical flutter load correspond to a vanishing mass either in a joint or at the free end of the pendulum; in the minimum, the ratio of the masses is equal to the ratio of the stiffness coefficients. The role of the singularities on the stability boundary in the optimization is highlighted, and an extension to the damped case as well as to the case of higher degrees of freedom is discussed.

Keywords: Parametric optimization; singularities on the stability boundary; non-conservative system; non-self-adjoint operator; Jordan block

  • Open Access Logo Acta Polytechnica 51(2011)4, 32-43

Permalink: https://www.hzdr.de/publications/Publ-15986


Paradoxes of magnetorotational instability and their geometrical resolution

Kirillov, O. N.; Stefani, F.

Abstract

Magnetorotational instability (MRI) triggers turbulence and enables outward transport of angular momentum in hydrodynamically stable accretion discs. By using the WKB approximation and methods of singular function theory, we resolve two different paradoxes of MRI that appear in the limits of infinite and vanishing magnetic Prandtl number. For the latter case, we derive a strict limit of the critical Rossby number. This limit of Roc=−0.802, which appears for a finite Lundquist number of S=0.618, extends the formerly known inductionless Liu limit of Roc=−0.828 valid at S=0.

Keywords: Standard magnetorotational instability; helical magnetorotational instability; paradox of Velikhov and Chandrasekhar; paradox of inductionless HMRI; Liu limit; magnetic Prandtl number; WKB; Plucker conoid

Permalink: https://www.hzdr.de/publications/Publ-15984


Materials research at the Helmholtz-Beamline at European XFEL: Ideas for proposals

Posselt, M.

Abstract

not available, please contact the author

Keywords: laser-solid interaction; ion-solid interaction; kinetic processes; X-ray analysis; XFEL

  • Lecture (Conference)
    Workshop on Petawatt-Lasers at Hard X-Ray Light Sources Dresden-Rossendorf, September 5 to 9, 2011, 05.-09.09.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-15983


TEM investigation contributing to the comprehension of superconductivity in Ga-doped Si

Mücklich, A.; Fiedler, J.; Heera, V.

Abstract

TEM investigation contributing to the comprehension of superconductivity in Ga-doped Si

Keywords: Ga ion implantation; rapid thermal annealing; superconductivity

Involved research facilities

Related publications

  • Poster
    MC2011, Microscopy Conference 2011, 28.08.-02.09.2011, Kiel, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15982


Electrical properties of ZnO nanorods studied by conductive atomic force microscopy

Beinik, I.; Kratzer, M.; Wachauer, A.; Wang, L.; Lechner, R. T.; Teichert, C.; Motz, C.; Anwand, W.; Brauer, G.; Chen, X. Y.; Hsu, X. Y.; Djurisic, A. B.

Abstract

ZnO nanostructures are promising candidates for the development of novel electronic devices due to their unique electrical and optical properties. Here, we present a complementary electrical characterization of individual upright standing and lying ZnO nanorods using conductive atomic force microscopy (C-AFM). Initially, the electrical properties of the arrays of upright standing ZnO NRs were characterized using two-dimensional current maps. The current maps were recorded simultaneously with the topography acquired by contact mode AFM. Further, C-AFM was utilized to determine the local current-voltage (I-V) characteristics of the top and side facets of individual upright standing NRs. Current-voltage characterization revealed a characteristic similar to that of a Schottky diode. Detailed discussion of the electrical properties is based on local I-V curves, as well as on the 2D current maps recorded from specific areas.

Keywords: ZnO nanorods; conductive atomic force microscopy; electrical properties

Involved research facilities

  • P-ELBE

Permalink: https://www.hzdr.de/publications/Publ-15981


Deep level transient spectroscopic study of oxygen implanted melt grown ZnO single crystal

Ye, Z. R.; Lu, X. H.; Ding, G. W.; Fung, S.; Ling, C. C.; Brauer, G.; Anwand, W.

Abstract

Deep level traps in melt grown ZnO single crystal created by oxygen implantation and subsequent annealing in air were studied by deep level transient spectroscopy measurement between 80 and 300 K. The EC–0.29 eV trap (E3) was the dominant peak in the as-grown sample and no new defects were created in the as-O-implanted sample. The single peak feature of the deep level transient spectroscopy (DLTS) spectra did not change with the annealing temperature up to 750 °C, but the activation energy decreased to 0.22 eV. This was explained in terms of a thermally induced defect having a peak close to but inseparable from the original 0.29 eV peak. A systematic study on a wide range of the rate window for the DLTS measurement successfully separated the Arrhenius plot data originated from different traps. It was inferred that the E3 concentration in the samples did not change after the O-implantation. The traps at EC–0.11, EC–0.16 and EC–0.58 eV were created after annealing. The EC–0.16 eV trap was assigned to an intrinsic defect. No DLTS signal was found after the sample was annealed to 1200 °C.

Keywords: deep level transient spectroscopy; ZnO single crystal; oxygen implantation; deep level traps

Involved research facilities

  • P-ELBE

Permalink: https://www.hzdr.de/publications/Publ-15980


Risiko und Risikoakzeptanz kerntechnischer Anlagen

Werner, M.

Abstract

Ausgehend von geeigneten Definitionen der zentralen Begriffe Zuverlässigkeit, Risiko und Sicherheit im technischen Sinn ergibt sich die grundsätzliche Möglichkeit der Bestimmung des Risikos für technische Systeme. Im Rahmen der Zuverlässigkeits- und Risikoanalyse können diese mathematisch belastbaren Definitionen auch die Stochastik von technischen Ausfällen und dadurch ausgelösten Unfällen berücksichtigen.
In Zusammenhang mit dem Sicherheitskonzept für deutsche Kernkraftwerke werden determinierte und probabilistische Methoden zur Bestimmung des Risikos bei der Nutzung der Kernenergie angewendet. Hierbei werden insbesondere auf das gestaffeltes Sicherheitskonzept, das Schutzzielkonzept sowie bestimmte Auslegungsprinzipien zur Verminderung des kerntechnischen Risikos eingegangen.
In einem weiteren Teil des Vortrages wird auf die Fragestellung im Umgang mit dem Restrisiko der kerntechnischen Nutzung eingegangen. Der Vergleich von wahrgenommenen mit tatsächlichen Risiken im technischen Bereich wie auch im Alltagsleben fällt häufig sehr unterschiedlich aus. Auch hängt die Akzeptanz eines Risikos sehr stark von einem zu erwartenden Nutzen ab.
Die methodische Darstellung von Risikoakzeptanz und Risikowahrnehmung auf der individuellen sowie auf der gesellschaftlichen Ebene ist nur im Rahmen komplexer Zusammenhänge möglich.

Keywords: risk analysis; risk acceptance; nuclear energy

  • Contribution to proceedings
    Zittauer Kraftwerkschemisches Kolloquium, 22.-23.09.2011, Zittau, Deutschland
    Wissenschaftliche Berichte der Hochschule Zittau/Görlitz

Permalink: https://www.hzdr.de/publications/Publ-15979


Time Efficient Fabrication of Ultra Large Scale Nano Dot Arrays Using Electron Beam Lithography

Grebing, J.; Faßbender, J.; Erbe, A.

Abstract

Many applications in plasmonics or sensorics require large scale arrays of nano-sized dot structures with rather high surface coverages. Typical dimensions, e.g., 50nm diameter, 200nm center-center distance, 1000µm × 1000µm arrays, quickly lead to extremely high numbers of objects in the design to be handled by both the software and the lithography system. In case of the aforementioned dimensions this would amount to be about 2.5 × 107 objects.

Using regular techniques the dots would be represented by a matrix of circles or dots in the design – or references to those, for that matter. Any changes in the layout of the structures would require a rather large effort since every object or reference would have to be edited. Additionally, with commonly used lithography systems the writing times quickly exceed reasonable values due to the beam settling times normally required for each object in the design. Even with values as low as 1ms the overall sum of the settling times would be roughly 7hrs. This is excluding the actual writing times!

The alternative method for the creation of ultra large scale nano dot arrays presented here is astonishingly simple and does not require any particular efforts: In electron beam lithography, exposure is based on single pixels – or dots – with defined distances (step size). The overlap of the single pixels yields the desired continuous structures. Thus, separating these pixels by the distance required for the lattice of nano dots, i.e., setting the step size to the lattice constant, would result in the desired lattice. This may be achieved by underexposing a regular rectangle by a factor of about 1/10 of the clearing dose, i.e., the result is a lattice of separated dots. The diameter of the dots may be adjusted within certain limits by the dose used for exposure.

As a result not only the writing times are strongly decreased – depending on the parameters many hours of processing time may be saved – but also handling of an array of dots is simplified to the action on rectangles or other shapes in the GDSII editor. No hassle with millions of dots is required.

As a proof of principle, different large lattices have been produced using a Raith 150TWO system in a lift-off process with PMMA or ZEP as resists on silicon. Additionally, a 4000µm × 4000µm lattice with a lattice constant of 500nm has been produced in an etching process with HSQ as the resist and reactive ion beam etching (RIBE) structuring gold on glas as a possible application for plasmonic sensors. Compared to the regular technique the processing times could be greatly reduced. The resulting samples show almost perfect lattices, the shape of the dots is also of good quality. Multiple exposures with shifted write fields also enables fabrication of hexagonal lattices or dipole structures.

Keywords: electron beam lithography; plasmonics; photonic crystal

Permalink: https://www.hzdr.de/publications/Publ-15978


Axisymmetric magnetic field modes in heterogeneous domains

Giesecke, A.; Stefani, F.; Gerbeth, G.

Abstract

Inspired by the setup of the von-K\'arm\'an-Sodium (VKS) dynamo experiment numerical simulations of the kinematic induction equation have been carried out in a cylindrical domain. A localized internal distribution of large relative permeability is considered that represents soft iron material within a conducting fluid flow.

So called paramagnetic pumping at the interface between fluid and soft iron causes a selective enhancement of the axisymmetric azimuthal field component, ultimately leading to a decoupling between poloidal and toroidal magnetic field. For moderate magnetic Reynolds numbers, the poloidal component decays faster than the toroidal part or the simplest non-axisymmetric mode ($m1$). This effect only concerns the necessarily decaying axisymmetric field and does not occur in case of a larger/smaller electrical conductivity.

The phenomenon requires a particular setup e.g. a thin disk-like permeability distribution and remains restricted to the axisymmetric field modes. However, these properties indeed apply to the VKS dynamo.

The separation of poloidal and toroidal modes might be important with regard to mean field dynamo models of the VKS dynamo since the decoupling effectively disrupts the possibility for a closure of the dynamo cycle. However, the separation of the axisymmetric field modes can be prevented by an non-axisymmetric permeability distribution, which might give a hint why dynamo action is absent in experiments where the fluid flow is driven by an impeller system composed of soft iron disks and stainless steel blades.

Keywords: Dynamo

  • Lecture (Conference)
    iGDR Meeting, Cargesse 2011, 12.-16.09.2011, Cargese, France

Permalink: https://www.hzdr.de/publications/Publ-15976


Vibrational spectroscopy of actinyl complexes

Gückel, K.

Abstract

Vibrational spectroscopy potentially provides structural information of molecule complexes. Actinyl ions can be identified by the frequency of their antisymmetric stretching vibrational mode which generally correlates with the character of the molecular environment of the actinyl ion group.
In this study the sorption behavior and the formed complexes of Uranium(VI) on gibbsite in inert gas and ambient atmosphere were analyzed by means of ATR FT-IR spectroscopy.

  • Poster
    6th PhD Seminar HZDR, 05.-07.10.2011, Rabenberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15975


Temperature Impact on the Sorption of Selenate onto Anatase

Franzen, C.; Jordan, N.; Müller, K.; Meusel, T.; Brendler, V.

Abstract

The radioactive isotope Selenium-79 is a long-lived fission product found in nuclear waste. Due to its long half live of 3.27 ∙ 105 years [1] it is expected to be one of the most contributing isotopes concerning safety assessments of nuclear waste underground repositories. The control of the mobility and bioavailability of selenium is therefore of great importance for a safe disposal of radioactive waste.
One major process controlling selenium mobility and bioavailability is the adsorption onto mineral surfaces of both the geological and engineered barrier.
The present study focuses on the impact of temperature on the sorption of selenate (SeO42-) onto anatase (TiO2). The sorption of selenate onto anatase at different temperatures (25°C – 60°C) was investigated both with batch experiments and ATR-FT-IR spectroscopy. In order to explain possible differences in sorption at higher temperatures, the surface of the anatase was investigated.

Keywords: Selenate; Se(VI); Anatase; Sorption; HighTemperatures

  • Poster
    HiTAC Workshop, 09.11.2011, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15974


Tectonic implications of fluvial incision and pediment deformation at the northern margin of the Central Anatolian Plateau based on multiple cosmogenic nuclides

Yildirim, C.; Schildgen, T.; Echtler, H.; Melnick, D.; Bookhagen, B.; Çiner, A.; Niedermann, S.; Merchel, S.; Martschini, M.; Steier, P.; Strecker, M.

Abstract

We document Quaternary fluvial incision driven by fault-controlled surface deformation in the inverted intermontane Gökırmak Basin in the Central Pontide mountains along the northern margin of the Central Anatolian Plateau. In situ-produced 10Be, 21Ne and 36Cl concentrations from gravel-covered fluvial terraces and pediment surfaces along the trunk stream of the basin (the Gökırmak River) yield model exposure ages ranging from 7.0 ± 0.6 ka to 337 ± 43 ka and average fluvial incision rates over the past ~340 ka of 0.28 ± 0.01 mm a-1. Similarities between river incision rates and coastal uplift rates support the inference that regional uplift is responsible for the river incision. Model exposure ages of surfaces on deformed pediments along tributaries of the trunk stream range from 48 ± 4 ka to 96 ± 9 ka, demonstrating that the thrust faults responsible for the pediment deformation were active at least until those times, and possibly remained active afterwards. Together, our data demonstrate cumulative incision that is linked to active internal shortening and uplift of ~0.3 mm a-1 in the Central Pontide orogenic wedge at the northern margin of the Central Anatolian Plateau.

Keywords: Central Anatolian Plateau; Northern Margin; Central Pontides; Orogenic Wedge; Fluvial Incision; Uplift; accelerator mass spectrometry; TCN; terrestrial cosmogenic nuclide; exposure age

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15973


Langlebige Radionuklide in Geo-/Biosystemen

Steudtner, R.; Großmann, K.; Joseph, C.; Vogel, M.; Brendler, V.

Abstract

Nach der Katastrophe in Fukushima im März 2011 beschloss die Bundesregierung den schrittweisen Ausstieg aus der Atomenergie bis zum Jahre 2022. Innerhalb dieser elf Jahre sollen die neun verbliebenen Atomkraftwerke vom Netz genommen werden. Aber in diesen Zeitraum wird es keine endgültige Lösung zum Thema der Endlagerung in Deutschland geben. Zurzeit werden die in Deutschland anfallenden radioaktiven Abfälle in Zwischenlager gebracht. Für schwach- und mittelradioaktive Stoffe sind es die Landessammelstellen der Bundesländer. Die Kernkraftwerke und Forschungseinrichtungen besitzen standortbezogene Zwischenlager. Die hochradioaktiven Abfälle aus der Wiederaufarbeitung abgebrannter Brennelemente werden nach der erteilten Genehmigung zur Aufbewahrung in den zwei zentralen Zwischenlagern in Ahaus und Gorleben gelagert.
Für die Genehmigung zum Bau eines Endlagers muss der Sicherheitsnachweis zur Endlagersicherheit geführt werden. Der umfassende Sicherheitsnachweis enthält die Aspekte der Errichtungs- und Betriebsphase (Sicherheitsnachweise für die Betriebsphase) und die Aspekte der Nachbetriebsphase im Langzeitsicherheitsnachweis. Im Langzeitsicherheitsnachweis werden alle qualitativen und quantitativen Analysen und Argumente zur Begründung der Sicherheit für die Nachbetriebsphase eines Endlagersystems zusammengeführt [1]. Der Langzeitsicherheitsnachweis unterteilt sich in:
­ - die Langzeitsicherheitsanalyse mit Konsequenzenanalyse,
­ - Aussagen zur Robustheit und Zuverlässigkeit der Sicherheitsbewertung,
­ - Ergänzende Argumente: Indikatoren, Analoga, etc.
Die Langzeitsicherheitsanalyse kann als die standortspezifische Analyse der Funktion des Endlagersystems im Hinblick auf die radiologischen Konsequenzen verstanden werden und beinhaltet die Untersuchung des zukünftigen Verhaltens eines verschlossenen Endlagers mit radioaktiven Abfällen innerhalb eines vorgegebenen Nachweiszeitraums (1 Million Jahre) [1].
Ziel der Langzeitsicherheitsanalyse ist es mögliche Ursachen und Abläufe einer Freisetzung von Radionukliden aus einem verschlossenen Endlager sowie deren zukünftige Auswirkungen auf die Umwelt und die Bevölkerung vorherzusagen.
Die derzeitig sicherste Entsorgung für radioaktive Stoffe ist die Endlagerung in tiefen geologischen Formationen [2]. Diese Lagerung weist ein Multibarrierensystem auf, welches die radioaktiven Abfälle von der Biosphäre isolieren soll. Ein aus mehreren unabhängigen Barrieren bestehendes System soll den Schadstoffaustrag aus dem Endlager wirkungsvoll verhindern [3]. Es setzt sich zusammen aus:
­ - Technische Barriere
o Brennstoffmatrix
o Container
­ - Geotechnische Barriere
o Verfüllung der Bohrlöcher
o Untertägiges Dammsystem
o Verfüllung des Schachtsystems
­ - Geologische Barriere
o Wirtsformation (Salz, Granit, Ton)
o Deckgebirge mit Aquifersystem
In der Langzeitsicherheitsanalyse wird angenommen, dass es im Endlager zum Wassereintritt kommt. Dies hat zur Folge, dass die Behälter korrosiv zersetzt werden und es zur Auflösung der Abfallmatrix kommt. Infolgedessen können die Radionuklide mobilisiert werden und durch die verschiedenen Barrieren in die Biosphäre gelangen. Während des Transportes von der Geo- zur Biosphäre können die freigesetzten Radionuklide eine Vielzahl von Wechselwirkungen eingehen. Dabei spielen neben ihrem Komplexbildung-, Sorption- und Diffusionsverhalten, die Kolloidbildung und die Wechselwirkungen mit Mikroorganismen, Biofilmen, Pflanzen und letztendlich mit dem menschlichen Organismus die wichtigsten Rollen. Wir, das Institut für Radiochemie, wollen mit Hilfe unserer umfangreichen analytischen Möglichkeiten zur Identifizierung und Beschreibung der ablaufenden Prozesse beitragen. An fünf Beispielen sollen die verschiedenen Arbeiten im Institut für Radiochemie (IRC) näher vorgestellt werden.

1. Fein, E., I. Müller-Lyda, and A. Rübel, Endlagerung wärmeentwickelnder radioaktiver Abfälle in Deutschland, in Wissenschaftlich-Technische Berichte GRS-247. 2008, Gesellschaft für Anlagen- und Reaktorsicherheit mbH: Braunschweig / Darmstadt.
2. Auswahlverfahren für Endlagerstandorte, Empfehlungen des AkEnd – Arbeitskreis Auswahlverfahren Endlagerstandorte. 2002: (www.akend.de).
3. Geckeis, H., V. Metz, and B. Kienzler, Geochemisches Verhalten der Radionuklide im Multibarrierensystem nuklearer Endlager. Nachrichten - Forschungszentrum Karlsruhe, 2004. 36(2): p. 110-115.

Keywords: Uran; Endlager; Speziation

  • Invited lecture (Conferences)
    Zittauer Kraftwerkschemisches Kolloquium, 22.09.-23.11.2011, Lückendorf, Deutschland
  • Contribution to proceedings
    Zittauer Kraftwerkschemischen Kolloquium, 22.09.-23.11.2011, Lückendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15972


Preliminary multi-method spectroscopic approach for the uranium(VI) hydrolysis at temperatures up to 60°C

Steudtner, R.; Müller, K.; Meusel, T.; Brendler, V.

Abstract

For the safety assessment of high-level nuclear waste repositories in deep geologic formations, the understanding of actinide migration behaviour is one of the most important issues. In recent decades, the solution chemistry, e.g. hydrolysis [1], complexation with inorganic ligands [1], but also the interactions of the actinides at interfaces with the geo- and biosphere have been intensely investigated [2]. However, because of the experimental difficulties, only few studies have been performed at temperatures outside the range 20 – 30°C which hampers the prediction of actinide reactive transport in the environment of heat generating high-level nuclear waste repositories.
The speciation of (radioactive) metal ions in solution will be affected by the thermal conditions, since the properties of water, e.g. density, dielectric constant, viscosity, ion product, are altered with temperature and pressure [3,4].
The formation and distribution of U(VI) hydrolysis species is predicted to depend strongly on the temperature. In particular the stability of U(VI) polynuclear hydroxo complexes, which are dominant species at 25°C may change. According to experimental studies of other metal ions, namely Al(III) and La(III), the nuclearity of polynuclear complexes decreases upon increasing temperature [5,6]. At 25°C several spectroscopic techniques, namely UV-vis, TRLFS, EXAFS and vibrational spectroscopy have been applied for identification and structural characterization of U(VI) hydroxo species [7-10]. At elevated temperatures, TRLFS was used for the determination of luminescent characteristics of single hydroxo species as a function of the temperature [11,12]. But, approaches to examine alterations in the thermodynamic data itself are rare.
In this study, we investigate the U(VI) hydrolysis reactions up to 60°C using a multi-methodical approach by application of TRLFS and ATR FT-IR spectroscopy. The spectral data is compared to computed speciation patterns based on state-of-the-art thermodynamic models.

1.Guillaumont, R. et al., Update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technetium. Chemical Thermodynamics Vol. 5, OECD Nuclear Energy Agency, Elsevier (2003).
2.Brendler, V. et al., RES3T-Rossendorf expert system for surface and sorption thermodynamics, Journal of Contaminant Hydrology 281-291 (2003).
3.Marshall, W.L. et al., Io product of water substance, 0 - 1000°C, 1-10,000 bars - New international formulation and its background, Journal of Physical and Chemical Reference Data 2, 295-304 (1981).
4.Fernandez, D.P. et al., A formulation for the static permittivity of water and steam at temperatures from 238 K to 873 K at pressures up to 1200 MPa, including derivatives and Debye-Huckel coefficients, Journal of Physical and Chemical Reference Data 4, 1125-1166 (1997).
5.Mesmer, R.E. et al., Acidity measurements at elevated temperatures. 5. Aluminum ion hydrolysis, Inorg. Chem. 10, 2290-2296 (1971).
6.Ciavatta, L. et al., The hydrolysis of the La(II) ion in aqueous perchlorate solution at 60°C, Polyhedron 6, 1283-1290 (1987).
7.Meinrath, G., Uranium(VI) speciation by spectroscopy, J. Radioanal. Nucl. Chem. 1-2, 119-126 (1997).
8.Moulin, C. et al., Time-resolved laser-induced fluorescence as a unique tool for low-level uranium speciation, Appl. Spectrosc. 4, 528-535 (1998).
9.Müller, K. et al., Aqueous uranium(VI) hydrolysis species characterized by attenuated total reflection Fourier-transform infrared spectroscopy, Inorg. Chem. 21, 10127-10134 (2008).
10.Tsushima, S. et al., Stoichiometry and structure of uranyl(VI) hydroxo dimer and trimer complexes in aqueous solution, Inorg. Chem. 25, 10819-10826 (2007).
11.Eliet, V. et al., Time-resolved laser-induced fluorescence of uranium(VI) hydroxo-complexes at different temperatures, Appl. Spectrosc. 1, 99-105 (2000).

Keywords: U(VI); TRLFS; ATR FT-IR; high temperature

  • Poster
    HiTAC - High Temperature Aqueous Chemistry, 09.11.2011, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15971


Nano-structure analysis of Fe implanted SnO2 films by 57Fe and 119Sn CEMS

Nomura, K.; Reuther, H.

Abstract

SnO2 films were implanted with 57Fe at substrate temperatures of room temperature and 300°C. The chemical states of Fe and Sn were characterized by 57Fe CEMS and 119Sn CEMS, respectively. The implanted Fe species exist as Fe(II) and Fe(III) in SnO2 films, which also are reduced into Sn(II)on the implanted surface. The as prepared and post annealed at 500°C samples did not show Kerr effect, but the sample implanted with 1 × 1017 Fe ions/cm2 at 300°C showed Kerr effect although magnetic sextets were not clearly observed in the 57Fe CEM spectra. The Kerr effect disappeared after annealing. It suggests that the number of magnetic defects decreases by absorption of oxygen. Magnetic relaxation appeared in the case of low implantation of 5 × 1016 Fe ions/cm2, which is considered to be due to antiferromagnetism or paramagnetic relaxation.

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15970


Planar optical waveguides in Bi4Ge3O12 crystal fabricated by swift heavy-ion irradiation

Yang, J.; Zhang, C.; Chen, F.; Akhmadaliev, S.; Zhou, S.

Abstract

We report on the fabrication of the planar waveguides in the Bi4Ge3O12 crystal by using 17 MeV C5+ or O5+ ions at a fluence of 2×1014 ions/cm2. The reconstructed refractive index profiles of the waveguides produced by either C5+ or O5+ irradiation are the “well” + “barrier” pattern distribution. The two-dimensional modal profiles of the planar waveguides, measured by using the end-coupling arrangement, are in good agreement with the simulated modal distributions. After thermal annealing treatment at 260°C for 30 min, the propagation loss for C5+ and O5+ irradiated waveguides could be reduced down to ~1.1 dB/cm and ~4.8 dB/cm, respectively, which exhibit acceptable guiding qualities for potential applications in integrated optics.

Keywords: Integrated optics devices; Waveguides

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15969


Direct observation of preferential transport pathways in salt rocks by means of GeoPET

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

Abstract

Migration of radionuclides out of a salt-based repository requires transport pathways, where substances propagate by molecular diffusion or even pressure-driven advection. Diffusion coefficients and permeability, being very low in most intact saline rocks, are likely to increase considerably under geomechanical stress, inevitably occurring for instance in the excavation damage zone. Observation and evaluation of transport processes in such heterogeneously structured materials are most demanding, because they likely occur in either extremely localized, macroscopic but rare fractures or in dispersed, mostly indiscernible but still connected microscopic voids.
Applying salt solutions labelled with radionuclides we are able to observe such processes directly and - presumably for the first time with due resolution and sensitivity – with our GeoPET method. The same processes are studied with Lattice-Boltzmann flow simulations on µCT-based images of the same samples. This strategy contrasts the common use of computer simulations based on a priori material parameters, and allows for the matching of flow simulation results in “real structures” with real time flow monitoring in the same samples. Here we report on results obtained from a number of drill cores from the ancient Stassfurt salt mine and its overburden, including aged backfill material, which has been analysed in the framework of our joint research project, funded by the Federal Ministry of Education and Research (BMBF) (Wolf et al., 2010).

Keywords: PET; reactive transport; Lattice Boltzmann; transport experiments

  • Lecture (Conference)
    ABC-Salt Workshop, 07.-08.11.2011, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15968


16 kW Upgrade of the 1.3 GHz ELBE RF-System with Solid State Amplifiers

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.

Abstract

The superconducting CW- LINAC (1.3 GHz) of the radiation source ELBE is in permanent operation since May 2001/1/. In 2011 an upgrade program of ELBE is in progress to support additional applications. One part of the program is to double the RF-power per cavity to at least 16 kW. Since we started ELBE in May 2001 substantial progress was made in all fields contributing accelerator science. As far as RF-amplifier technology is concerned IOT-based and Solid State Amplifiers compete with klystrons. To prepare for the power upgrade of ELBE we developed a couple of activities, like:

Test of the ELBE RF-couplers and waveguide windows
Test of an available 30 kW IOT amplifier with beam
Test of a 10 kW solid state amplifier (SSPA) with beam
Test of two 10 kW SSPA’ s with beam
Redesign of the Low level RF controller
Redesign of the technical water cooling.

Keywords: LINAC RF; ELBE RF; 1300 MHz Solid State Power Amplifiers; 1,3 GHz SSPA; SC LINAC Power RF; LINAC RF IOT; Paralleling Solid State Power Rf Amplifiers

Involved research facilities

Related publications

  • Open Access Logo Contribution to proceedings
    IPAC 2011 (Second International Particle Accelerator Conference), 04.-09.09.2011, San Sebastian, Spain
    16 kW Upgrade of the 1.3 GHz ELBE RF-System with Solid State Amplifiers: JACoW, 379-381
  • Poster
    IPAC 2011, 04.-09.09.2011, San Sebastian, Spain

Permalink: https://www.hzdr.de/publications/Publ-15967


Microspectroscopy on perovskite-based superlenses

Kehr, S. C.; Yu, P.; Liu, Y. M.; Parzefall, M.; Khan, A. I.; Jacob, R.; Wenzel, M. T.; Ribbeck, H.-G.; Helm, M.; Zhang, X.; Eng, L. M.; Ramesh, R.

Abstract

Superlenses create sub-diffraction-limit images by reconstructing the evanescent fields arising from an object. We study the lateral, vertical, and spectral field distribution of three different perovskite-based superlenses by means of scattering-type near-field microscopy. Subdiffraction- limit resolution is observed for all samples with an image contrast depending on losses such as scattering and absorption. For the three lenses superlensing is observed at slightly different frequencies resulting in an overall broad frequency range of 3.6 THz around 20 THz.

Keywords: superlens; terahertz; perovskite; oxide; near-field microscopy; free-electron laser

Involved research facilities

Related publications

  • Open Access Logo Optical Materials Express 1(2011), 1051-1060
    ISSN: 2159-3930

Permalink: https://www.hzdr.de/publications/Publ-15966


XPS analysis and valence band structure of a low-dimensional SiO2/Si system after Si+ ion implantation

Zatsepin, D. A.; Mack, P.; Wright, A. E.; Schmidt, B.; Fitting, H.-J.

Abstract

A X-ray photoelectron spectroscopy (XPS) of valence band (VB) and core levels are performed for a SiO2/p-Si heterostructure containing a thin oxide layer of d = 20 nm thickness and implanted by Siþ ions. With an implantation energy of 12 keV the maximum density of the implanted Si+ profile is located close to the SiO2–Si interface at a depth of 18 nm, but a piling-up of Si is also found immediately beneath the surface up to 2 nm, i.e., within the escape depth of XPS electrons. Thus we may expect a partial phase separation associated with Si aggregation and nanocluster formation imbedded in a nonstoichiometric SiOx matrix. By means of XPS and in comparison to X-ray emission spectroscopy (XES) the related changes of the VB structure are investigated.

Keywords: electronic structure; ion implantation; SiO2; X-ray emission spectra; X-ray photoelectron spectra

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15965


Large-eddy simulation of single-phase pressurized thermal shock

Loginov, M. S.; Shams, A.; Komen, E.; Höhne, T.

Abstract

Pressurized Thermal Shock (PTS) is identified as one of the safety issues where Computational Fluid Dynamics (CFD) can bring real benefits. Turbulence modeling may impact the overall accuracy of the calculated thermal loads on the Reactor Pressure Vessel (RPV) walls. Therefore advanced methods for turbulent flows are required. In the current paper, we summarize our efforts on large-eddy simulations (LES) of a complex turbulent mixing in the RPV. First, the mesh resolution is investigated, and a comparison procedure is established. The analysis have shown necessity of comparison in both time and frequency domains. Next, a validation against experiment is performed using three cases with different flow rates in the primary loop. The validation results have successfully reproduced the flow patterns and have shown good quantitative agreement for the near-wall temperature drop.

Keywords: CFD; LES; PTS

  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Kanada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), CD-ROM
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Kanada

Permalink: https://www.hzdr.de/publications/Publ-15964


Multi.Modal Imaging Using Bispidine-Derivatives

Fähnemann, S.

  • Lecture (Conference)
    8th Supraphone Meeting, 07.-10.09.2011, Funchal, Portugal

Permalink: https://www.hzdr.de/publications/Publ-15963


Mehrfunktionelle Bispidinderivate für die duale Bildgebung

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

Abstract

Die Multimodale Bildgebung („Molecular Imaging“) ermöglicht durch die Kombination unterschiedlicher Verfahren eine verbesserte Diagnostik und ist damit Grundlage für eine zielgerichtete personalisierte Therapie von komplexen Krankheiten, wie z. B. Krebs. In diesem Zusammenhang werden insbesondere Computertomographie (CT), Magnetresonanztomographie (MRT), Positronen-Emissions-Tomographie (PET), Single- Photon-Emission-Computed-Tomography (SPECT) und optische Bildgebung eingesetzt [1, 2].
Derivate von 3,7-Diaazabicyclo[3.3.1]nonanen (Bispidine) bieten die Möglichkeit für ein duales Labeling. Sie bilden sehr stabile Komplexe mit radioaktiven Kupferisotopen und gestatten nach entsprechender Funktionalisierung mit Vektormolekülen eine Visualisierung von Tumoren mittels PET [3]. Bispidinliganden verfügen darüber hinaus über weitere funktionelle Gruppen, die die Einführung von Farbstoffen und zielsuchenden Molekülen gestatten.

Die Funktionalisierung der Hydroxygruppe (C9-OH) des Bispidins mit einem Fluoreszenzfarbstoff kann mittels Aktivesterbildung durch Umsetzung mit Chlorameisensäurenitrophenylester und anschießender Urethanbildung mit einem aminofunktionalisierten Farbstoffmolekül realisiert werden.
Es wird über die Synthese derartiger Liganden sowie die Charakterisierung der Fluoreszenzeigenschaften und die Markierung mit dem PET-Radionuklid 64 Cu berichtet.

Literatur:

[1] J.V. Frangioni, J. Clin. Oncol. 2008, 26, 4012-4021.
[2] A. Louie, Chem. Rev. 2010, 110, 3146-3195.
[3] S. Juran, M. Walther, H. Stephan, R. Bergmann, J. Steinbach, W. Kraus, F. Emmerling, P. Comba, Bioconjugate Chem. 2009, 20, 347-359.

  • Poster
    GDCH-Wissenschaftsforum 2011, 04.-07.09.2011, Bremen, D

Permalink: https://www.hzdr.de/publications/Publ-15962


Multiple Spectroscopic and Microscopic Study on Hydrolysis of Tetravalent Cerium: In-situ Characterization of Ce(IV) Hydrolytic Species in an Aqueous Solution

Ikeda, A.

Abstract

Because of its chemical similarity and stable tetravalent oxidation state in solution, cerium (Ce) is often employed as an analogue of tetravalent actinides (An(IV)) in various research fields related with actinides. Besides, its dioxide compound, CeIVO2, has recently attracted considerable attention owing to its wide variety of industrial applications, such as catalysis, oxygen storage, fuel cells, or luminescent materials.
Hydrolysis is one of the most fundamental reactions of metal ions in an aqueous solution. In fact, the hydrolysis behaviour of tetravalent cerium (Ce(IV)) has been studied and often compared with those of An(IV) in order to evaluate its suitability as an analogue of An(IV). Furthermore, the hydrolysis–precipitation process of cerium ions is also of great importance in its industrial applications, since it is one of the most straightforward and simple methods to produce CeO2. However, despite these importance of hydrolysis reaction in the basic- and applied research fields for Ce, most of the precedent studies have focused on its thermodynamical aspects, and still little has been known about the complex structure of Ce(IV) hydrolytic species formed in solution. In this study, multi-spectroscopic (i.e., X-ray absorption spectroscopy (XAS), high energy X-ray scattering (HEXS), dynamic light scattering (DLS)) and microscopic (TEM) techniques have been employed to structurally characterize the hydrolytic Ce(IV) species in an aqueous solution. The results indicate that nanocrystalline CeO2 forms and grows up in an aqueous solution as the hydrolysis proceeds with increasing pH. On the presentation, the results will be also discussed with the corresponding An(IV) hydrolytic species.

Keywords: lanthanides; cerium; Ce(IV); hydrolysis; XAS; HEXS; DLS; TEM

Involved research facilities

Related publications

  • Invited lecture (Conferences)
    Lecture (invited), 27.09.2011, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-15961


Immobilization of uranium in biofilm microorganisms exposed to groundwater seeps over granitic rock tunnel walls in Olkiluoto, Finland

Krawczyk-Bärsch, E.; Lünsdorf, H.; Arnold, T.; Bok, F.; Steudtner, R.; Pedersen, K.; Lehtinen, A.; Brendler, V.

Abstract

In the underground rock characterization facility tunnel "ONKALO" in Finland massive biofilms were observed attached to the fractured bedrock at a depth of 70 m. Experiments were performed in the laboratory to study the effect on the behavior of uranium in biofilms by adding uranium to the fracture water with a final uranium concentration (4 x10-5 M) relevant for what can be expected from an injured and leaking waste canister in the far-field during a nuclear event in a HLW repository. The results obtained by analysis, microsensor measurements, TRLFS investigation, EF-TEM/EELS studies and thermodynamic calculations clearly indicate that biofilms have to be considered as microenvironments, which differ significantly from the surrounding medium. Inside the biofilm a pH of 5.37 was recorded, which is about 3.5 units lower than the pH of the surrounding fracture water. Similarly, the redox potential of +73 mV is approximately 420 mV lower than the redox potential measured in the fracture water. The addition of uranium results in an increase of the pH in the biofilm to 7.27 and a decrease of the redox potential to -164 mV mV. The changes of redox potential and pH are influencing the bioavailability of uranium since microbial metabolic processes are sensitive to metals and their speciation. EF-TEM investigations showed that in the biofilm uranium was immobilized intracellular in bacteria by a biologically mediated uranyl phosphate formation similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O). In contrast, TRLFS studies of the contaminated fracture water showed aqueous uranium carbonate species, most likely Ca2UO2(CO3)3, which was formed using the available high amount of carbonate from the water. The results are in agreement with the thermodynamic calculation of the theoretical predominance field of uranium species, formed in the uranium contaminated fracture water at the measured geochemical parameters.
Our studies clearly demonstrate that biological systems have to be considered as a part of natural systems in respect to radionuclide immobilization. They are contributing to an improved understanding on the response mechanisms of biofilms towards radionuclides in respect to safety assessments of the radioactive waste repositories.

Keywords: uranium; biofilms; microsensors; TEM; TRLFS; thermodynamic calculation

Permalink: https://www.hzdr.de/publications/Publ-15960


Electrochemical behaviour of tetrachloro and tetrabromo uranyl complexes in room temperature ionic liquids

Sornein, M.-O.; Cannes, C.; Le Naour, C.; Mendes, M.; Hennig, C.

Abstract

The redox properties of tetrahalo uranyl(VI) complexes ([UVIO2X4]2 with X = Cl or Br) have been investigated in the ionic liquids [BuMeIm][Tf2N] and [MeBu3N][Tf2N], where [BuMeIm]+ and [MeBu3N]+ are respectively the 1-butyl-3-methylimidazolium and the tributylmethylammonium cations, both associated with the bis(trifluoromethylsulfonyl)imide anion [Tf2N]. The results suggest that the reduction of [UVIO2X4]2 occurs via an Electron transfer – Chemical reaction – Electron transfer mechanism (ECE mechanism). We have shown by voltammetry that the first electron transfer is quasi-reversible and involves one electron, leading to the tetrahalo uranium(V) complex. This compound undergoes a chemical reaction and its stability depends both on the halide ligand and on the ionic liquid. The most stable complex is [UVO2Cl4]3 in [BuMeIm][Tf2N]. We have assumed that the [BuMeIm]+ cation interacts more strongly by H-bonding than the [MeBu3N]+ cation with the uranium complex, as it is the case for other anionic uranium species. Moreover, in presence of excess chloride ions, the consecutive chemical reaction is not observed anymore by cyclic voltammetry.

Keywords: Uranium; Ionic liquid; Redox properties; Tetrachloro complex; Tetrabromo complex

Permalink: https://www.hzdr.de/publications/Publ-15959


Uptake and binding of U(VI) by the green alga Chlorella vulgaris

Vogel, M.; Günther, A.; Raff, J.; Bernhard, G.

Abstract

For the risk assessment of radionuclides in the environment a comprehensive elucidation of the migration behavior of U(VI) in biosphere is necessary. Aim of this study was the quantitative and structural characterization of the interaction between U(VI) and the green alga Chlorella vulgaris at U(VI) concentrations from 5 μM to 1 mM, and in the pH range of 4.4 to 7.0 with special focus on metabolic activity. The obtained findings of the sorption experiments demonstrate clearly, the interactions with U(VI) are heavily influenced by the U(VI) concentration and the status of the Chlorella cells. Living cells bind in a 0.1 mM U(VI) solution at pH 4.4 within 5 min 14.3±5.5 mg U/g dry biomass and dead cells 28.3±0.6 mg U/g dry biomass. Furthermore, Chlorella cells die at concentration higher than 0.1 mM within 48 h. Interestingly, at lower U(VI) concentration of 5 μM, living cells firstly bind almost all U(VI) within the first 5 min of incubation. But then algal cells mobilize up to 80% of the bound U(VI) during ongoing incubation. The release of metabolism related substances is suggested to cause this mobilization of U(VI). As potential leachates for algal-bound U(VI) oxalate, citrate and ATP were tested and found to be able to mobilize more than 50% of the algal-bound U(VI).
The formed U(VI)-algae-complexes were structurally characterized by TRLF, EXAFS and ATR-FTIR spectroscopy. Obtained results demonstrate carboxylic and organic/inorganic phosphate groups were involved in the U(VI) complexation with varying contributions dependent on cell status, U(VI) concentration and pH.
With the help of TEM U(VI) was detected in form of 30-70 nm needle-like deposits in the cell wall of living algae.

Keywords: uranium; algae; Chlorella; biosorption; TRLFS; EXAFS; ATR-FTIR; TEM

Involved research facilities

Related publications

  • Lecture (Conference)
    10th symposium on remediation/ 10. Sanierungskolloquium, 03.-05.10.2011, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15958


Long term irradiation phenomena in RPV steels - the LONGLIFE project

Altstadt, E.; Bergner, F.; Hein, H.

Abstract

The increasing age of European Nuclear Power Plants and envisaged extensions of reactor pressure vessel (RPV) lifetimes up to 80 years require the accurate prediction and management of RPV neutron irradiation embrittlement. LONGLIFE (“Treatment of long term irradiation embrittlement effects in RPV safety assessment”) is a collaborative project of the 7th Framework Programme of EURATOM. This project has been initiated as the next step forward towards obtaining an improved understanding of irradiation effects in RPV steels under conditions representative of long term operation (LTO) of RPVs. Phenomena which might become important at high neutron fluences (such as late-blooming effects and flux effects) must be considered in detail as part of the process of upgrading safety assessments and embrittlement surveillance procedures to underwrite the safety of LTO of RPVs. The work starts with the collection and evaluation of plant-specific information and data such as target neutron fluences for LTO and the chemical compositions of the materials. This includes a survey of available results of RPV materials data from decommissioned plants of validating surveillance data and studying specific irradiation effects relevant for LTO. Microstructural data are obtained from different techniques with the aim of assessing the adequacy of current dose-damage models with respect to their relevance to the mechanisms of irradiation damage associated with LTO of RPVs. Complementary mechanical tests are performed in order to address gaps in existing experimental data. Microstructural data pertaining to the evolution of irradiation damage are correlated with changes in mechanical properties, and the most important influencing factors will be identified. Surveillance guidelines for LTO of RPV base materials and welds will be developed as one of the principal outputs of the project. The scope of work and the project structure are outlined in the paper. Two LTO relevant phenomena – late blooming effect and flux effect – are discussed more detailed.

Keywords: Reactor Pressure Vessel Steel; Irradiation Embrittlement; Long Term Operation

  • Book chapter
    T. Yamamoto: Effects of Radiation on Nuclear Materials: 25th Volume, STP 1547, USA: ASTM International, 2013, 978-0-8031-7533-4, 096205STP
    DOI: 10.1520/STP104113
    Cited 2 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-15957


Single-ion induced surface nanostructures - A comparison between slow highly-charged and swift heavy ions

Aumayr, F.; Facsko, S.; El-Said, A. S.; Trautmann, C.; Schleberger, M.

Abstract

The present topical review focuses on recent advances in the understanding of the formation of surface nanostructures, an intriguing phenomenon in ion - surface interaction due to the impact of individual ions. In many solid targets, swift heavy ions produce narrow cylindrical tracks accompanied by the formation of a surface nanostructure. More recently, a similar nanometric surface effect has been revealed for the impact of individual, very slow but highlycharged ions. While swift ions transfer their large kinetic energy to the target via ionization and electronic excitation processes (electronic stopping), slow highly-charged ions produce surface structures due to potential energy deposited at the top surface layers. Despite the differences in primary excitation, the similarity between the nanostructures is striking and strongly points to a common mechanism related to the energy transfer from the electronic to the lattice system of the target. A comparison of surface structures induced by swift heavy ions and slow highly-charged ions provides valuable insight to better understand the formation mechanisms.

Keywords: highly-charged ions; swift heavy ions; ion-surface interaction; nanostructures; AFM; STM; hillocks; craters; pits; tracks; kinetic energy; potential energy; sputtering; electron emission; KBr; LiF; CaF2; BaF2; SrTiO3; TiO2; mica; polymers; PMMA; HOPG; Si; Au

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15956


Design of Radioligands for PET Imaging of Neuropsychiatric and Neurodegenerative Diseases

Brust, P.

  • Lecture (others)
    Kolloquium, 03.11.2011, Magdeburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15955


Numerical study of a bubble plume generated by bubble entrainment from an impinging jet

Zidouni Kendil, F.; Krepper, E.; Bousbia Salah, A.; Lucas, D.; Mataoui, A.

Abstract

The current paper presents the prediction results of a bubbly flow under plunging jet conditions using multiphase mono- and poly-dispersed approaches. The models consider interfacial momentum transfer terms arising from drag, lift, and turbulent dispersion force for the different bubble sizes. The turbulence is modeled by an extended k–ε model which accounts for bubble induced turbulence. Furthermore in case of a poly-dispersed air–water flow the bubble size distribution, bubble break-up and coalescence processes as well as different gas velocities in dependency on the bubble diameter are taken into account using the Inhomogeneous MUSIG model. This model is a generalized inhomogeneous multiple size group model based on the Eulerian modeling framework which was developed in the framework of a cooperative work between ANSYS-CFX and Forschungszentrum Dresden-Rossendorf (FZD). The latter is now implemented into the CFD code CFX.
According to the correlation on the lateral lift force obtained by Tomiyama (1998); this force changes its sign in dependence on the bubble size. Consequently the entrained small bubbles are trapped below the jet. They can escape from the bubble plume only by turbulent fluctuations or by coalescence. If the size of the bubbles generated by coalescence exceeds the size at which the lift force changes its sign these large bubbles go out from the plume and rise to the surface.
A turbulent model based on an additional source term for turbulence kinetic energy and turbulence eddy dissipation equation is compared to the common concept for modeling the turbulence quantities proposed by Sato et al. (1981). It has been found that the large bubble distribution is slightly affected by the turbulence modeling which affects particularly the bubble coalescence and break-up process.

Keywords: impinging jet; CFD; experiments; simulations; lift bubble force; population balance model

Permalink: https://www.hzdr.de/publications/Publ-15954


Structural, Electronic, and Magnetic Properties of Quasi-1D Quantum Magnets [Ni(HF2)(pyz)2]X (pyz = pyrazine; X = PF6-, SbF6-) Exhibiting Ni-FHF-Ni and Ni-pyz-Ni Spin Interactions

Manson, J. L.; Lapidus, S. H.; Stephens, P. W.; Peterson, P. K.; Carreiro, K. E.; Southerland, H. I.; Lancaster, T.; Blundell, S. J.; Steele, A. J.; Goddard, P. A.; Pratt, F. L.; Singleton, J.; Kohama, Y.; Mcdonald, R. D.; Del Sesto, R. E.; Smith, N. A.; Bendix, J.; Zvyagin, S. A.; Kang, J. H.; Lee, C.; Whangbo, M. H.; Zapf, V. S.; Plonczak, A.

Abstract

[Ni(HF2)(pyz)2]X {pyz = pyrazine; X = PF6 - (1), SbF6 - (2)} were structurally characterized by synchrotron X-ray powder diffraction and found to possess axially compressed NiN4F2 octahedra. At 298 K, 1 is monoclinic (C2/c) with unit cell parameters, a = 9.9481(3), b = 9.9421(3), c = 12.5953(4) angstrom, and beta = 81.610(3) degrees while 2 is tetragonal (P4/nmm) with a = b = 9.9359(3) and c = 6.4471(2) angstrom and is isomorphic with the Cu-analogue. Infinite one-dimensional (1D) Ni-FHF-Ni chains propagate along the c-axis which are linked via mu-pyz bridges in the ab-plane to afford three-dimensional polymeric frameworks with PF6 - and SbF6 - counterions occupying the interior sites. A major difference between 1 and 2 is that the Ni-F-H bonds are bent (similar to 157 degrees) in 1 but are linear in 2. Ligand field calculations (LFT) based on an angular overlap model (AOM), with comparison to the electronic absorption spectra, indicate greater pi-donation of the HF2 - ligand in 1 owing to the bent Ni-F-H bonds. Magnetic susceptibility data for 1 and 2 exhibit broad maxima at 7.4 and 15 K, respectively, and lambda-like peaks in d chi T/dT at 6.2 and 12.2 K that are ascribed to transitions to long-range antiferromagnetic order (TN). Muon-spin relaxation and specific heat studies confirm these TN's. A comparative analysis of chi vs T to various 1D Heisenberg/Ising models suggests moderate antiferromagnetic interactions, with the primary interaction strength determined to be 3.05/3.42 K (1) and 5.65/6.37 K (2). However, high critical fields of 19 and 37.4 T obtained from low temperature pulsed-field magnetization data indicate that a single exchange constant (J(1D)) alone is insufficient to explain the data and that residual terms in the spin Hamiltonian, which could include interchain magnetic couplings (J(perpendicular)), as mediated by Ni-pyz-Ni, and single-ion anisotropy (D), must be considered. While it is difficult to draw absolute conclusions regarding the magnitude (and sign) of J(perpendicular) and D based solely on powder data, further support offered by related Ni(II)-pyz compounds and our LFT and density-functional theory (DFT) results lead us to a consistent quasi-1D magnetic description for 1 and 2.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Inorganic Chemistry 50(2011), 5990-6009

Permalink: https://www.hzdr.de/publications/Publ-15953


Frustrated couplings between alternating spin-1/2 chains in AgVOAsO4

Tsirlin, A.; Nath, R.; Sichelschmidt, J.; Skourski, Y.; Geibel, C.; Rosner, H.

Abstract

We report on the crystal structure and magnetic behavior of the spin-1/2 compound AgVOAsO4. Magnetic susceptibility, high-field magnetization, and electron spin resonance measurements identify AgVOAsO4 as a gapped quantum magnet with a spin gap Delta similar or equal to 13 K and a saturation field mu0Hs similar or equal to 48.5 T. Extensive band structure calculations establish the microscopic magnetic model of spin chains with alternating exchange couplings J similar or equal to 40 K and J' similar or equal to 26 K. However, the precise evaluation of the spin gap emphasizes the role of interchain couplings which are frustrated due to the peculiar crystal structure of the compound. The unusual spin model and the low energy scale of the exchange couplings make AgVOAsO4 a promising candidate for an experimental investigation of Bose-Einstein condensation in high magnetic fields.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Physical Review B 83(2011)14, 144412

Permalink: https://www.hzdr.de/publications/Publ-15952


Control of Rectifying and Resistive Switching Behavior in BiFeO3 Thin Films

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

Abstract

BiFeO3 thin films have been grown on Pt/Ti/SiO2/Si substrates with pulsed laser deposition using Au as the top electrode. The resistive switching property of the Au/BiFeO3/Pt stack has been significantly improved by carefully tuning the oxygen pressure during the growth, and a large switching ratio of ∼4500 has been achieved. The deposition pressure modifies the concentration of oxygen vacancies and the rectifying behavior of the Au/BiFeO3 junction, and consequently influences the resistive switching behavior of the whole stack. The switching takes place homogeneously over the entire electrode, and shows a long-term retention.

Keywords: resistive switching; BiFeO3; nonvolatile

Permalink: https://www.hzdr.de/publications/Publ-15951


Coherent control of a THz intersubband polarization in a voltage controlled single quantum well

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

Abstract

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

Keywords: coherent control; terahertz; intersubband polarization; ultrafast

  • Applied Physics Letters 99(2011), 131109

Permalink: https://www.hzdr.de/publications/Publ-15950


Metal Nanoparticles/Nanowires Selfassembly on Ripple Patterned Substrate - Mechanism, Properties and Applications

Ranjan, M.

Abstract

Plasmonic properties of self-assembled silver nanoparticles/nanowires array on periodically patterned Si (100) substrate are reported with special attention on the mechanism of nanoparticles self-assembly. The advantage of this bottom up approach over other self-assembling and lithographic methods is the flexibility to tune array periodicity down to 20 nm with interparticle gaps as low as 5 nm along the ripple.
Ripple pattern have shallow modulation (~2 nm) still particles self-assembly was observed in non-shadow deposition. Therefore adatoms diffusion and kinetics is important on ripple surface for the self-assembly. PVD e-beam evaporation method used for deposition has proven to be superior to sputter deposition due to lower incident flux and lower atom energy. It was found that particles self-assembly largely dependent on angle of incidence, substrate temperature, and deposition direction due to ripple asymmetric tilt. Ostwald ripening observed during annealing on ripples substrate has striking dependency on ripple periodicity and was found to be different compared to Ostwald ripening on flat Si surface.
In-situ RBS measurements of deposited silver on flat and rippled substrate confirmed different sticking of atoms on the two surfaces. The difference between maximum and minimum of the calculated local flux show a peak at an incidence angle of 70o with respect to surface normal. This explains the best alignment of particles at this angle of incidence compare to others.
Self-assembled nanoparticles are optically anisotropic, i.e. they exhibit a direction dependent shift in LSPR. The reason of the observed anisotropy is a direction dependent plasmonic coupling. Different in plane and out of the plane dielectric coefficients calculated by modelling Jones matrix elements, confirms that nanoparticle/nanowire array are biaxial anisotropic (ex ¹ ey ¹ ez). The nanoparticles are predominantly insulating while nanowires are both metallic and insulating depending on the dimension.
Silver nanoparticles/nanowires self-aligned on pre-patterned rippled substrate are presented for the first time as an active SERS substrate. Anisotropic SERS response in such arrays is attributed to different field enhancement along and across the ripples. Strong plasmonic coupling in elongated nanoparticles chain results in significantly higher SERS intensity then spherical nanoparticles/nanowires and non-ordered nanoparticles. Higher SERS intensity across the nanowires array in comparison to along the array (bulk silver) confirms electromagnetic field enhancement (hot-junction) is responsible for SERS phenomenon.
Self-assembly of cobalt nanoparticle on ripple pattern substrate is also reported. Due to less adatom mobility and higher sticking cobalt self-assembly is possible only at much higher temperature. A strong uniaxial magnetic anisotropy was observed not observed for non ordered cobalt particles.

Involved research facilities

Related publications

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-007 2011
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads

Permalink: https://www.hzdr.de/publications/Publ-15949


Zur Wechselwirkung von Uran mit den Bioliganden Citronensäure und Glucose

Steudtner, R.

Abstract

Um das Verhalten von Actiniden im Menschen (Stoffwechsel), in geologischen und in biologischen Systemen vorherzusagen, ist es erforderlich deren Speziation genau zu kennen. Zur Bestimmung dieser wird das chemische Verhalten des Urans hinsichtlich Komplexbildungsreaktionen und Redoxreaktionen in Modellsystemen untersucht. Anhand der gewonnenen thermodynamischen Konstanten und dem Redoxverhalten können Risikoabschätzungen für das jeweilige untersuchte System getroffen werden.
Das umweltrelevante Uran(IV)-Uran(VI)-Redoxsystem besitzt mit der metastabilen fünfwertigen Oxidationsstufe einen zumeist kurzlebigen Zwischenzustand. Innerhalb dieser Arbeit gelang es erstmalig die Uran(V)-Fluoreszenz mittels laserspektroskopischer Methoden nach zu weisen. Beispielsweise konnte das Bandenmaximum von aquatischem Uranyl(V) im perchlorhaltigem Medium (λex = 255 nm) mit 440 nm, bei einer Fluoreszenzlebensdauer von 1,10 ± 0,02 μs bestimmt werden. Die fluoreszenzspektroskopische Untersuchung eines aquatischen [U(V)O2(CO3)3]5--Komplexes (λex= 255 nm und 408 nm) zeigte bei Raumtemperatur keine Fluoreszenz.
Durch Anwendung der Tieftemperaturtechnik wurden bekannte Quencheffekte des Carbonats unterdrückt, so dass bei beiden Anregungswellenlängen ein für Uran(V) typisches Fluoreszenzspektrum im Bereich von 375 nm bis 450 nm, mit Bandenmaxima bei 401,5 nm (λex = 255 nm) und 413,0 nm (λex = 408 nm) detektiert werden konnte. Darüber hinaus konnte bei 153 K (λex = 255 nm) eine Fluoreszenzlebensdauer von 120 ± 0,1 μs bestimmt werden. Untersetzt wurden diese fluoreszenzspektroskopischen Nachweise durch mikroskopische Studien verschiedener Uran(IV)-Festphasen (Uraninit…UO2, Uran(IV)-Tetrachlorid…UCl4) und einer sulfathaltigen Uran(IV)-Lösung (UIVSO4). Diese wurden durch kontinuierliche Sauerstoffzufuhr zu Uran(VI) oxidiert. Die ablaufende Oxidation wurde mit dem konfokalen Laser Scanning Mikroskop (CLSM) verfolgt, wobei die Proben mit einer Wellenlänge von 408 nm zur Fluoreszenz angeregt wurden. Die auftretenden Bandenmaxima bei 445,5 nm (UO2), bei 445,5 nm (UCl4) und bei 440,0 nm (UIVSO4) konnten eindeutig der Uran(V)-Fluoreszenz zugeordnet werden.
Zur Bestimmung thermodynamischer Konstanten mit Hilfe der Tieftemperaturfluoreszenz wurde zunächst der Einfluss der Temperatur auf das Fluoreszenzverhalten des freien Uranyl(VI)-Ions näher betrachtet. Es zeigte sich, dass mit Erwärmung der Probe (T>298 K) die Fluoreszenzlebensdauer von 1,88 μs (298 K) deutlich absinkt. Die Fluoreszenzintensität verringerte sich dabei um 2,3 % pro 1 K zwischen 273 K und 313 K. Im Gegensatz dazu, steigt die Fluoreszenzlebensdauer um das 150-fache auf 257,9 μs bei einer Verminderung der Temperatur (T <298 K) auf 153 K. Das weitere Absenken der Temperatur (T <153 K) zeigte keinen Einfluss auf die Fluoreszenzlebensdauer. Die Lage der Hauptemissionsbanden des freien Uranyl(VI)-Ions (488,0 nm, 509,4 nm, 532,4 nm, 558,0 nm, 586,0 nm) zeigte bei diesen Untersuchungen keine temperaturabhängige Verschiebung.
Die Validierung der Tieftemperaturtechnik zur Bestimmung thermodynamischer Konstanten mittels zeitaufgelöster laserinduzierten Fluoreszenzspektroskopie erfolgte anhand des Uran(VI)-Citrat-Systems. Im Gegensatz zu bisherigen fluoreszenzspektroskopischen Betrachtungen bei Raumtemperatur wurde das Fluoreszenzsignal bei tiefen Temperaturen mit einsetzender Komplexierung nicht gequencht, woraus die Ausprägung einer gut interpretierbaren Fluoreszenz resultierte. Die Analyse der spektralen Daten mit SPECFIT ergaben mit log β 101 = 7,24 ± 0,16 für den [UO2(Cit)]--Komplex und log β 202 = 18,90 ± 0,26 für den [(UO2)2(Cit)2]2--Komplex exakt die in der Literatur angegebenen Stabilitätskonstanten. Zudem konnten Einzelkomponentenspektren mit Bandenmaxima bei 475,3 nm, 591,8 nm, 513,5 nm, 537,0 nm und 561,9 nm für den 1:0:1-Komplex und 483,6 nm, 502,7 nm, 524,5 nm, 548,1 nm und 574,0 nm für den 2:0:2-Komplex und Fluoreszenzlebensdauern von 79 ± 15 μs (1:0:1) und 10 ± 3 μs (2:0:2) bestimmt werden.
Zur Modellkomplexierung des Uran-Citrat-Systems wurde in dieser Arbeit auch das Komplexbildungsverhalten von U(IV) in Gegenwart von Citronensäure untersucht. Hierbei wurden über den gesamten pH-Wertbereich gelöste Uran-Citrat-Spezies spektroskopisch nachgewiesen und die Stabilitätskonstanten sowie die Einzelkomponentenspektren für die neu gebildeten Uran(IV) und (VI)-Spezies bestimmt. Für die neu gebildeten Citrat-Komplexe des sechswertigen Urans wurden Komplexbildungskonstanten von log β 203 = 22,67 ± 0,34 ([(UO2)2(Cit)3]5-) und log β 103 = 12,35 ± 0,22 ([UO2(Cit)3]7-) und für die Komplexe des vierwertigen Urans von log β 1-21 = -9,74 ± 0,23 ([U(OH)2Cit]-) und log β 1-31 = -20,36 ± 0,22 ([U(OH)3Cit]2-) bestimmt.
Untersuchungen zum Redoxverhalten von Uran in Gegenwart von Citronensäure zeigten unter aeroben und anaeroben Versuchsbedingungen eine photochemische Reduktion vom U(VI) zu U(IV), welche spektroskopisch nachgewiesen werden konnte. Dabei zeigt speziell die Reaktion unter oxidierenden Bedingungen, welchen großen Einfluss vor allem organischen Liganden auf das chemische Verhalten des Urans haben können. Sowohl die Reduktion unter O2- als auch die unter N2-Atmosphäre, weisen ein Maximum bei einem pH-Wert von 3,5 bis 4 auf. Unter anaeroben Bedingungen reduziert die Citronensäure mit ca. 66 %, 14 % mehr Uran(VI) zu Uran(IV) als unter anaeroben Bedingungen mit ca. 52 %.
Ab einem pH-Wert von 7 konnte eine Reduktion nur unter sauerstofffreien Bedingungen festgestellt werden.
Die Wechselwirkung von U(VI) in Gegenwart von Glucose wurde hinsichtlich Reduktion und Komplexierung des Uran(VI) betrachtet. Mit Hilfe der zeitaufgelösten laserinduzierten Fluoreszenzspektroskopie bei tiefen Temperaturen wurde dabei ein Uranyl(VI)-Glucose-Komplex nachgewiesen. Die Komplexierung wurde lediglich bei pH 5 beobachtet und weist eine Komplexbildungskonstante von log β I=0,1 M = 15,25 ± 0,96 für den [UO2(C6H12O6)]2+-Komplex auf. Mit einer Fluoreszenzlebensdauer von 20,9 ± 2,9 μs und den Hauptemissionsbanden bei 499,0nm, 512,1 nm, 525,2 nm, 541,7 nm und 559,3 nm konnte der Uranyl(VI)-Glucose-Komplex fluoreszenzspektroskopisch charakterisiert werden. Unter reduzierenden Bedingungen wurde, ab pH-Wert 4 eine auftretende Umwandlung vom sechswertigen zum vierwertigen Uran durch Glucose in Gegenwart von Licht beobachtet. Der Anteil an gebildetem Uran(IV) steigt asymptotischen bis zu einem pH-Wert von 9, wo das Maximum mit 16 % bestimmt wurde. Als Reaktionsprodukt der Redoxreaktion wurde eine Uran(VI)-Uran(IV)-Mischphase mit der Summenformel [UIV(UVIO2)5(OH)2]12+ identifiziert.
Mit Hilfe der cryo-TRLFS wurde, durch Verminderung von Quencheffekten die Uranspeziation in natürlichen Medien (Urin, Mineralwasser) direkt bestimmt. Proben mit Uran-Konzentrationen von < 0,1 μg/L konnten dadurch analysiert werden. In handelsüblichen Mineralwässern wurde die zu erwartende Komplexierung durch Carbonat nachgewiesen. Im Urin zeigte sich in Abhängigkeit vom pH-Wert eine unterschiedliche Uranspeziation. Die fluoreszenzspektroskopische Untersuchung wies bei niedrigerem pH-Wert (pH<6) eine Mischung aus Citrat- und Phosphat-Komplexierung des U(VI) und bei höheren pH-Wert (pH>6) eine deutliche Beteilung von Carbonat an der Komplexierung auf. Diese Ergebnisse stehen in sehr guter Übereinstimmung mit theoretischen Modellrechnungen zur Uranspeziation im Urin.
Die in dieser Arbeit gewonnenen Ergebnisse zeigen, dass für eine zuverlässigere Prognose des Urantransportes in Geo- und Biosphäre in Zukunft nicht nur Betrachtungen zur Komplexchemie, sondern auch zum Redoxverhalten des Urans nötig sind, um die Mobilität in der Natur richtig abschätzen zu können.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-008 2011
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads

Permalink: https://www.hzdr.de/publications/Publ-15948


Annual Report 2010 - Institute of Ion Beam Physics and Materials Research

von Borany, J.; Heera, V.; Fassbender, J.; Helm, M.

Abstract

The Institute of Ion Beam Physics and Materials Research (IIM) is one of the six institutes of what was called Forschungszentrum Dresden-Rossendorf (FZD) until the end of 2010, but since this year 2011 is called “Helmholtz-Zentrum Dresden-Rossendorf (HZDR)”. This change reflects a significant transition for us: it means that the research center is now member of the Helmholtz Association of German Research Centers (HGF), i.e., a real government research laboratory, with the mission to perform research to solve fundamental societal problems. Often to date those are called the “Grand Challenges” and comprise issues such as energy supply and resources, health in relation to aging population, future mobility, or the information society.
This Annual Report already bears the new corporate design, adequate for the time of its issueing, but reports results from the year 2010, when we were still member of the Leibniz Association (WGL). Our research is still mainly in the fields of semiconductor physics and materials science using ion beams. The institute operates a national and international Ion Beam Center, which, in addition to its own scientific activities, makes available fast ion technologies to universities, other research institutes, and industry. Parts of its activities are also dedicated to exploit the infrared/THz freeelectron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. For both facilities the institute holds EU grants for funding access of external users.

Involved research facilities

Related publications

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-002 2011
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads

Permalink: https://www.hzdr.de/publications/Publ-15947


Annual Report 2010 - Institute of Radiochemistry

Bernhard, G.; Foerstendorf, H.; Richter, A.; Viehweger, K.

Abstract

At the beginning of 2011, the former Forschungszentrum Dresden-Rossendorf (FZD) was fully integrated into the Helmholtz Association, as Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Therefore, the present Annual Report 2010 of the Institute of Radiochemistry (IRC) is published as the first HZDR-Report.

The Institute of Radiochemistry is one of the six Research Institutes of this centre. IRC contributes to the research program “Nuclear Safety Research” in the “Research Field of Energy” and performs basic and applied research in radiochemistry and radioecology. Motivation and background of our research are environmental processes relevant for the installation of nuclear waste repositories, for remediation of uranium mining and milling sites, and for radioactive contaminations caused by nuclear accidents and fallout. Because of their high radiotoxicity and long half-life the actinides are of special interest.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-001 2011
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads

Permalink: https://www.hzdr.de/publications/Publ-15946


Quality assurance in accelerator mass spectrometry: Results from an international round-robin exercise for 10Be

Merchel, S.; Bremser, W.; Akhmadaliev, S.; Arnold, M.; Aumaître, G.; Bourlès, D. L.; Braucher, R.; Caffee, M.; Christl, M.; Fifield, L. K.; Finkel, R. C.; Freeman, S. P. H. T.; Ruiz-Gómez, A.; Kubik, P. W.; Martschini, M.; Rood, D. H.; Tims, S. G.; Wallner, A.; Wilcken, K. M.; Xu, S.

Abstract

The first international round-robin exercise for the measurement of the long-lived radionuclide 10Be has been conducted. Ten participating accelerator mass spectrometry (AMS) facilities have each measured three samples at the 10-12-10-14 10Be/9Be level. All results have been made traceable to the NIST SRM 4325 standard to avoid additional discrepancies that arise when different facilities use different calibration materials. Hence, the data concentrates on pure measurement distinctions. Multivariate statistical investigations have been performed to reveal a bias between facilities, i.e. two distinguished groups could be identified. Maximum discrepancies between two single facilities are in the range of 6-31% depending on the absolute 10Be/9Be value. These findings should be considered when comparing 10Be data produced at one AMS facility with that produced at another facility, which is e.g. often the case for in-situ 10Be dating studies. Round-robin exercises are a very helpful tool as part of an overall quality assurance scheme to improve the accuracy, and not only the precision, of AMS data.

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

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15945


Spin-polarized transport in pulsed-laser annealed Ge:Mn

Bürger, D.; Zhou, S.; Kovacs, G. J.; Helm, M.; Schmidt, H.

Abstract

The incorporation of transition metal dopants in semiconductors above their solubility limit is the main challenge for the fabrication of diluted ferromagnetic semiconductors. Low temperature molecular beam epitaxy (LT-MBE) is the standard technique for the fabrication of GaAs:Mn. For Ge:Mn the LT-MBE approach seems to be successful to grow Mn rich clusters or nanowires [1]. Nevertheless, hysteretic magnetotransport properties were not observed in such Ge:Mn nanostructures. On the other hand, pulsed laser annealing is a successful annealing method far from thermodynamic equilibrium and a promising technique for the fabrication of ferromagnetic Ge:Mn [2] and for III-V semiconductors [3]. In this work, Mn has been implanted into nearly intrinsic n-Ge substrates up to a depth of around 100 nm at low temperatures and annealed by pulsed laser annealing. We observed the same hysteretic properties up to 30 K via SQUID magnetization as well as via magnetotransport measurements. Furthermore, Ge:Mn films show a spontaneous magnetization in field-cooled SQUID measurements below 250 K. Segregated secondary phases with a regular distance slightly above 50 nm have been detected by HRTEM measurements near the sample surface. At elevated temperatures the confirmation of similar magnetization and magnetotransport properties of the p-Ge:Mn surface layer is hampered by the significant contribution of the underlying n-Ge substrate to the conductivity. Further experiments with insulating substrates and proper etching methods are necessary to clarify the ferromagnetic contribution of each individual layer.

[1] M. Jamet et al., Nature. Mat. 5, 653 (2006)
[2] Shengqiang Zhou et al., Phys. Rev. B 81, 165204 (2010)
[3] M. A. Scarpulla et al., Appl. Phys. Lett. 82, 1251 (2003)

Involved research facilities

Related publications

  • Poster
    Spintech VI, 01.-05.08.2011, Matsue, Japan

Permalink: https://www.hzdr.de/publications/Publ-15944


Spin-polarized hole transport in pulsed laser annealed Ge:Mn up to 30 K

Bürger, D.; Zhou, S.; Kovacs, G. J.; Schmidt, H.

Abstract

The incorporation of transition metals dopants in semiconductors over their solubility limit is the main challenge for the fabrication of diluted ferromagnetic semiconductors. Low temperature molecular beam epitaxy (LT-MBE) is the standard technique for the fabrication of GaAs:Mn. Nevertheless, for Ge:Mn [1] the LT-MBE approach seems to be not successful to reach hole concentrations necessary for hole mediated ferromagnetism. On the other hand, pulsed laser annealing is a successful nonequilibrium annealing method and a promising technique for the fabrication of diluted Ge:Mn [2] and for III-V semiconductors, e.g. GaAs:Mn [3]. Recently we fabricated a ca. 100 nm thick Ge:Mn film by low temperature Mn-implantation followed by pulsed laser annealing and observed hole-mediated ferromagnetism up to 30 K via SQUID magnetization as well as magnetotransport measurements. The anisotropy of ferromagnetic Ge:Mn films will be discussed. Moreover, the Ge:Mn films show a remanent magnetization up to 220 K which is lower than the Curie temperature of typical Mn_xGe_y clusters [1]. The confirmation of spin-polarized hole transport up to 220 K becomes difficult because at elevated temperatures the conductivity is mainly determined by the Ge substrate.
[1] M. Jamet et al., Nature. Mat. 5, 653 (2006)
[2] Shengqiang Zhou et al., PRB 81, 165204 (2010)
[3] Danilo Bürger et al., PRB 81, 115202 (2010

Keywords: Ge:Mn; implantation; pulsed laser annealing; ferromagnetic semiconductor

Involved research facilities

Related publications

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15943


Hysteretic anomalous Hall effect in a ferromagnetic, Mn-rich Ge:Mn nanonet

Bürger, D.; Zhou, S.; Höwler, M.; Ou, X.; Kovacs, G.; Reuther, H.; Mücklich, A.; Skorupa, W.; Helm, M.; Schmidt, H.

Abstract

Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by pulsed laser annealing with a pulse duration of 300 ns. Due to a segregation instability during laser annealing, Mn segregates at the liquid-solid interface and an approximately 40 nm thick Ge:Mn surface layer is strongly enriched with Mn. Plan-view images reveal a percolating Mn-rich nanonet. Hysteretic anomalous Hall effect has been observed up to 30 K, but it vanishes after etching away the 40 nm thick Mn-rich Ge:Mn surface layer. The nanonet seems to support the correlation between magnetization and hysteretic Hall resistance. Intrinsic scattering in the threads or vertices of this nanonet may lead to the observed anomalous Hall effect.

Keywords: GeMn; implantation; pulsed laser annealing; ferromagnetic semiconductor; percolation; segregation; instability; nanonet

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15942


Magneto-optical properties of ferromagnetic thin films under saturated magnetization conditions

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

Abstract

Vector-magneto-optical generalized ellipsometry (VMOGE) allows to perform generalized Mueller matrix ellipsometry in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. We measured the magneto-optical properties of Fe, Co, and Ni thin films on ZnO substrates and extracted the wavelength dependent magneto-optical dielectric tensor together with the coupling constant Q under saturation magnetization conditions via model analysis. We converted our magneto-optical dielectric tensor of Fe, Co, and Ni into the optical conductivity tensor and the results agreed well with the literature experimental values.

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

  • Poster
    6th International School and Conference on Spintronics and Quantum Information Technology (SPINTECH6), 01.-05.08.2011, Matsue, Japan

Permalink: https://www.hzdr.de/publications/Publ-15941


Advanced tomographic techniques for flow imaging in columns with flow distribution packings

Schubert, M.; Bieberle, A.; Barthel, F.; Boden, S.; Hampel, U.

Abstract

Design and optimization of separation units, e. g., distillation and absorption columns with flow distribution packings, require detailed knowledge about the internal flow conditions and their impact on the process behavior. This in turn calls for suitable measuring techniques, which can give a detailed insight into such devices, especially for studies on a laboratory and pilot scale. Traditional instrumentation, such as compartment-type liquid collectors installed below packings, or distributed temperature, pressure and conductivity probes, often falls too short if detailed knowledge on flow conditions is required. This concerns especially local liquid holdup, liquid maldistribution, liquid films thickness, wetting of the packing surface, or bubble size and droplet distribution at trays. Advanced imaging techniques, such as tomography, have found only marginal attention in investigations of separation columns with structured and modern dumped flow distribution packings, mostly due to limited spatial and temporal resolution but also due to prevailing technological problems encountered in such applications. In this study, the potentials and limits of some of the most recently emerged tomographic imaging modalities for multiphase flows have been investigated and reviewed, i.e., ultra-fast X-ray tomography, high-resolution gamma-ray tomography, wire-mesh sensor techniques, and X-ray microtomography with respect to a possible application in separation columns with flow distribution packings.

Permalink: https://www.hzdr.de/publications/Publ-15940


Unusual non-head-to-tail chains in the crystal structure of glycyl-L-glutamyl-L-phosphoseryl-L-leucine

Heine, K. B.; Fairweather, K. A.; Heine, A.; Clegg, J. K.; Jolliffe, K. A.

Abstract

The structure of glycyl-L-glutamyl-L-phosphoseryl-L-leucine, (C16H29N4O11P)2.3H2O, has monoclinic (P21) symmetry. The dimeric structure is characterized by an unusual non-head-to-tail arrangement based on an extended intermolecular hydrogen bonding network. Two of the three H2O molecules included in the network are disordered. The protonation constants of the tetrapeptide were determined as log K1 = 1.50, log K2 =3.63, log K3 =4.32, log K4 =6.08 and log K5 =8.65 by potentiometric pH titration.

Permalink: https://www.hzdr.de/publications/Publ-15938


Magnetic layer formation on plasma nitrided CoCrMo alloy

Öztürk, O.; Okur, S.; Pichon, L.; Liedke, M. O.; Riviere, J. P.

Abstract

In this study structural and magnetic character of the expanded austenite phase (γN) layer formed on a medical grade CoCrMo alloy by a low-pressure Radio-Frequency plasma nitriding process was investigated. The formation of the expanded austenite phase is facilitated at a substrate temperature near 400 °C for 1, 2, 4, 6 and 20 h under a gas mixture of 60% N2–40% H2. The magnetic state of the γN layers was determined by a surface sensitive technique, magneto-optic Kerr effect (MOKE), and with a scanning probe microscope in magnetic force mode (MFM). Strong evidence for the ferromagnetic nature of the γN-(Co,Cr,Mo) phase is provided by the observation of stripe domain structures and the hysteresis loops. The ferromagnetic state for the γN phase observed here ismainly linked to large lattice expansions (~10%) due to high N contents (~30 at.%). As an interstitial impurity, nitrogen dilates the host lattice i.e. the Co–Co (or Fe–Fe) distance is increased, which strongly influences the magnetic interactions. An analogy between the magnetic properties of the expanded phases, γN-(Fe,Cr,Ni) and γN-(Co,Cr,Mo), formed in austenitic stainless steel alloys and the CoCrMo alloy of this study is made, and it is suggested that the ferromagnetic states for the γN-(Co,Cr,Mo) and γN-(Fe,Cr,Ni) phases may be correlated with the volume dependence of the magnetic properties of fcc-Co/Co4N and fcc-Fe/Fe4N, respectively.

Keywords: CoCrMo alloy; expanded austenite structure; plasma nitriding; ferromagnetism; MOKE; MFM

  • Surface & Coatings Technology 205(2011), S280-S285
    ISSN: 0257-8972
  • Contribution to proceedings
    12th International Conference on Plasma Surface Engineering, 13.-17.09.2010, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-15937


Magnetic anisotropy modifi cations of single crystalline rippled Fe

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

Abstract

Ion erosion as a tool for nanostructuring has proven its versatility with respect to surface morphology modifications. Ion irradiation parameters, e.g. ion energy, fluence, incident angle, and sample temperature, can be varied in order to assemble self-organized periodically ordered arrays of nano-dots and ripples. Particularly, nanopatterning of magnetic materials is meaningful because not only the surface morphology is affected, but the overall magnetic properties are accordingly modified. Here we present a novel bottom-up method of magnetic film patterning, where ordered periodic MgO ripple surfaces with a wavelength on the nanometer scale, ion sculptured along a few arbitrary in-plane orientations and outstandingly fully crystalline upon ion irradiation, are coated by a magnetic Fe layer. Due to a cubic symmetry of Fe an in-plane fourfold magnetic anisotropy is induced and in addition, an uniaxial magnetic anisotropy arises due to the surface morphology. The uniaxial magnetic anisotropy orientation and strength is controlled by an arbitrarily chosen irradiation direction with respect to the sample plane and the ripple wavelength is set by the ion energy, respectively. Thus an ensemble of twofold and fourfold anisotropy is created and analyzed by ferromagnetic resonance, magnetooptic Kerr effect, and X-ray diffraction techniques. Theoretical analysis reveals both the anisotropy fields and their directions that are in agreement with the experiment. This work is supported by DFG FA314/6-1.

Keywords: ion erosion; magnetization; magnetic anisotropy; ripples; Fe; MgO; MOKE; FMR; XRD; GID

Involved research facilities

Related publications

  • Lecture (Conference)
    The European Conference PHYSICS OF MAGNETISM 2011, 27.06.-01.07.2011, Poznan, Poland

Permalink: https://www.hzdr.de/publications/Publ-15936


Magnetic anisotropy investigations in single crystalline Fe films on ripple MgO templates

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

Abstract

Ion erosion of MgO substrates produces highly ordered surface patterns. The so-called ripples are not only induced along any arbitrary in-plane orientation but outstandingly, they stay crystalline upon ion irradiation. Due to the low lattice mismatch single crystalline Fe films can be grown onto these periodically modulated MgO(100) templates. Despite the intrinsic magnetic property of bcc Fe, i.e. cubic anisotropy, an additional ripple morphology driven uniaxial magnetic anisotropy is introduced. Thus an ensemble of twofold and fourfold symmetry is created, which is confirmed by ferromagnetic resonance and magneto-optic Kerr effect measurements. The orientation and strength of the uniaxial anisotropy, which mainly originates from shape and step-edge contributions, depends on the angle of the ripple ridges elongation with regard to the [100] direction of MgO and on the Fe film thickness, respectively. Theoretical analysis reveals anisotropy fields and orientations of both anisotropy contributions that are in agreement with the experiment.

Keywords: ion erosion; magnetization; magnetic anisotropy; ripples; Fe; MgO; MOKE; FMR

Involved research facilities

Related publications

  • Lecture (Conference)
    75th Annual Meeting of the DPG and DPG Spring Meeting, 13.-18.03.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15935


Formation and structural characterization of thioantimony species and their natural occurrence in geothermal waters

Planer-Friedrich, B.; Scheinost, A. C.

Abstract

Previously postulated from laboratory studies, the occurrence of antimony-sulfur species in geothermal waters could now be proven using anion-exchange chromatography-inductively coupled plasma-mass spectrometry. The two thioantimony species detected by AEC-ICP-MS in oxic synthetic antimonite-sulfide solutions were assigned to tri- and tetrathioantimonate based on their S/Sb ratios and structural characterization by X-ray absorption spectroscopy (XAS). XAS confirmed that the initial species formed under anoxic conditions from antimonite at a 10-fold sulfide excess is trithioantimonite. Trithioantimonite rapidly transforms to tetrathioantimonate in the presence of oxygen or to antimonite at excess OH(-) versus SH(-) concentrations, and escapes chromatographic detection. In natural geothermal waters, up to 30% trithioantimonate and 9% tetrathioantimonate were detected. Their occurrence increased at increasingly alkaline pH and with increasing sulfide and decreasing oxygen conce!
ntrations. Considering the large sulfide excess (100 to 10 000-fold) the proportion of thioantimonates formed under natural conditions is lower than expected from synthetic solutions. Together with the observed high thioarsenate concentrations (>80% of total arsenic), this indicates that in direct competition with arsenic for a limited source of sulfide, thioantimonates form less spontaneously than thioarsenates. Interactions of arsenic and antimony with sulfur can therefore be decisive for similarities or differences in their environmental behavior.

Keywords: antimony; thiocomplexes; thermal waters; EXAFS; XANES

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15934


Annealing of heterogeneous phase TiO2 films: An X-ray absorption and morphological study

Gago, R.; Redondo-Cubero, A.; Vinnichenko, M.; Vázquez, L.

Abstract

Heterogeneous TiO(2) films with nanocrystalline (nc-) rutile and amorphous (a-) phases were annealed in vacuum up to 450 degrees C. The structural and morphological changes were studied by in situ X-ray absorption and ex-situ X-ray diffraction and atomic force microscopy. The annealing process leads to phase and morphological changes depending on the initial phase mixture. Films with dominant nc-rutile phase are quite stable whereas in a-TiO(2)-containing films the a-TiO(2) regions crystallize into nc-anatase at 300 degrees C. The latter is attributed to the initial anatase-like character of a-TiO(2). Interestingly, at 450 degrees C nc-anatase or nc-rutile is preferentially promoted for high or low initial a-TiO(2) contents, respectively.

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15933


Al-doped ZnO films grown by reactive magnetron sputtering: properties evolution and secondary phase formation

Vinnichenko, M.; Cornelius, S.; Krause, M.; Gago, R.; Munnik, F.; Kolitsch, A.; Moeller, W.

Abstract

Reactive pulsed magnetron sputtering (RPMS) using high metal to oxygen flux ratio is know to provide high-quality transparent and electrically conductive Al-doped ZnO (AZO) films at low temperatures (Ts<200 °C) [1]. However, in this case electrical properties of AZO films strongly depend on deposition temperature and the films even turn insulating at Ts>350 °C [2]. It has been shown that energy deposition during growth due to the elevated TS and from the flux of energetic particles incident on the substrate causes preferential Zn desorption. This leads to a higher Al concentration in the films, which exceeds the solubility limit and triggers the formation of an insulating metastable homologous (ZnO)3Al2O3 phase. This phase impedes crystal growth (decreasing the grain size) and causes a significant increase of free electron scattering which leads to observed increase of the film electrical resistivity [2]. Little is known about effect of this phase formation on the AZO film optical properties, although it is of special importance for understanding of the influence of the secondary phase formation on the fundamental and above-band gap band-to-band electron transitions in this material.

In order to clarify the problem the films with defined Al concentrations (0-20 at.%) grown by RPMS at temperatures ranging from RT to 550 °C were investigated. They were characterized by Hall-effect measurements, spectroscopic ellipsometry and Raman spectroscopy. These results were complemented by the Rutherford back scattering, elastic recoil detection analysis, X-ray diffraction and X-ray absorption near edge structure (XANES) measurements.

The comparison of undoped ZnO and AZO films with the highest crystallinity shows that an incorporation of ~1 at.% of Al leads to the best electrical properties, although (ZnO)3Al2O3 phase signature appears in its Al K-edge XANES spectra even at this low dopant concentration. This is accompanied by the broadening of the allowed ZnO Raman lines and appearance of the broad band around 565 cm-1 which is interpreted as a defect-enhanced A1 LO mode. Increase of Al concentration up to 8-10 at.% leads to deterioration of the film electrical properties accompanied by an increase of the (ZnO)3Al2O3 phase-related peaks in Al K-edge spectra. At this level of doping the allowed ZnO Raman lines are no longer detectable, but the defect-induced Raman features change their intensity distribution. Finally, increasing cFAl>10 at.% leads to formation of electrically insulating nanocrystalline films, which show even more intense (ZnO)3Al2O3 phase-related XANES peaks. The band gap of these films is significantly broader compared to that of undoped ZnO or conductive AZO layers. The latter may be understood in analogy to optical properties of the metastable wurtzite MgxZn(1-x)O alloys.

[1] B. Szyszka, Thin Solid Films 351, 164 (1999)
[2] M. Vinnichenko et al, Appl. Phys. Lett. 96, 141907 (2010).

Involved research facilities

Related publications

  • Lecture (Conference)
    MRS Spring Meeting 2011 (Symposium S: Plasma-assisted Materials Processing and Synthesis), 25.-29.04.2011, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-15932


Magnetostructural Transitions in a Frustrated Magnet at High Fields

Tsurkan, V.; Zherlitsyn, S.; Felea, V.; Yasin, S.; Skourski, Y.; Deisenhofer, J.; Krug Von Nidda, H.-A.; Lemmens, P.; Wosnitza, J.; Loidl, A.

Abstract

Ultrasound and magnetization studies of bond-frustrated ZnCr2S4 spinel are performed in static magnetic fields up to 18 T and in pulsed fields up to 62 T. At temperatures below the antiferromagnetic transition at TN1 ≈ 4 K, the sound velocity as a function of the magnetic field reveals a sequence of steps followed by plateaus indicating a succession of crystallographic structures with constant stiffness. At the same time, the magnetization evolves continuously with a field up to full magnetic polarization without any plateaus in contrast to geometrically frustrated chromium oxide spinels. The observed high-field magnetostructural states are discussed within a H-T phase diagram taking into account the field and temperature evolution of three coexisting spin structures and subsequent lattice transformation induced by the magnetic field.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Physical Review Letters 106(2011), 247202

Permalink: https://www.hzdr.de/publications/Publ-15931


Low-Temperature Elastic Properties of Non-Kramers Doublet Compound PrMg3

Araki, K.; Mitsumoto, K.; Akatsu, M.; Nemoto, Y.; Goto, T.; Suzuki, H. S.; Tanida, H.; Takagi, S.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.

Abstract

We have investigated low-temperature elastic properties of PrMg3 with a non-Kramers Γ3 doublet ground state by using ultrasonic measurements under high field up to 18 T down to 20 mK. A softening of the elastic constant (C11−C12)/2 has been observed below 8 K due to the non-magnetic Γ3 doublet possessing electric quadrupole Ou and Ov with Γ3 symmetry and magnetic octupole Txyz with Γ2. This result appreciably is deviated from a theoretical fitting of the quadrupole susceptibility based on the crystal-electric-field levels below 800 mK. Furthermore, the (C11−C12)/2 shows strange magnetic dependence up to 18 T below 1.7 K, which are inconsistent with the theoretical results

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Open Access Logo Journal of Physics: Conference Series 273(2011), 012133

Permalink: https://www.hzdr.de/publications/Publ-15930


Upper Critical Magnetic Field in Ba0.68K0.32Fe2As2 and Ba(Fe0.93Co0.07)2As2

Gasparov, V. A.; Drigo, L.; Audouard, A.; Sun, D. L.; Lin, C. T.; Bud’Ko, S. L.; Canfield, P. C.; Wolff-Fabris, F.; Wosnitza, J.

Abstract

We report measurements of the temperature dependence of the radio frequency magnetic penetration depth in Ba0.68K0.32Fe2As2 and Ba(Fe0.93Co0.07)2As2 single crystals in pulsed magnetic fields up to 60 T. From our data, we construct an H–T-phase diagram for the interplane (H || c) and in-plane (H || ab) directions for both compounds. For both field orientations in Ba0.68K0.32Fe2As2 we find a concave curvature of the Hc2(T) lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism we can describe Hc2(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair breaking is not essential for Ba(Fe0.93Co0.07)2As2. For this electron-doped compound, the data support a Hc2(T) dependence that can be described by the Werthamer–Helfand–Hohenberg model for H || ab and a two-gap behavior for H || c.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • JETP Letters 93(2011)11, 667-672

Permalink: https://www.hzdr.de/publications/Publ-15929


Effect of composition and pressure on phase transitions in FexO at low temperature

Glazyrin, K.; Dubrovinsky, L.; Klotz, S.; Uhlarz, M.; Wosnitza, J.; Hansen, T.; Dubrovinskaia, N.

Abstract

We report the results of high-resolution neutron powder diffraction studies of FexO (x = 0.925, 0.94) in the vicinity of the low-temperature antiferromagnetic transition and at pressures up to 8 GPa. Our analysis shows that the P-T phase diagram of FexO is strongly affected by the composition and defect structure of the material. We observe the divergence of critical temperatures of magnetic and structural transitions. In contrast to the stoichiometric antiferromagnet MnO, we find no correlation between the magnitude of the magnetic moment of iron and the degree of the rhombohedral distortion in FexO. We suggest that the defect structure of antiferromagnetic FexO significantly influences the temperature of the structural transition.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Journal of Applied Physics 110(2011), 026109

Permalink: https://www.hzdr.de/publications/Publ-15928


High-field magnetization of Ho2Fe17

Skourski, Y.; Kuzmin, M. D.; Skokov, K. P.; Andreev, A. V.; Wosnitza, J.

Abstract

The magnetization of a Ho2Fe17 single crystal has been measured along the principal crystallographic directions in pulsed magnetic fields up to 60 T. Stepwise discontinuities in the magnetization occur at 45 and 55 T along the [120] and [100] directions, respectively. The data allowed us to deduce the molecular field at the Ho site. As a cross check, the molecular field was determined as well from a magnetization measurement when the Ho2Fe17 single crystal was let rotate freely. Both values are in good agreement with each other.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)
  • Physical Review B 83(2011), 214420

Permalink: https://www.hzdr.de/publications/Publ-15927


Status of proton therapy based on high intensity lasers - the first dose-response curves of laser accelerated protons

Karsch, L.; Baumann, M.; Beyreuther, E.; Burris-Mog, T.; Kraft, S.; Laschinsky, L.; Metzkes, J.; Naumburger, D.; Oppelt, M.; Richter, C.; Schramm, U.; Schürer, M.; Zeil, K.; Pawelke, J.

Abstract

Fragestellung: Die klassischen Protonenbeschleuniger liefern einige Nanosekunden lange Pulse mit hoher Wiederholfrequenz im Megahertzbereich. Mit der neuartigen Technologie der Laser Beschleunigung werden hingegen kürzere, nur einige Pikosekunden lange Teilchenpakete mit wesentlich geringerer Pulsfrequenz von einigen Hertz bei gleichzeitig viel höherer Pulsintensität erzeugt. Vor einem Einsatz der Laserbeschleunigung in der Strahlentherapie muss die möglicherweise abweichende biologische Wirksamkeit, sei es durch die andere Zeitstruktur oder durch die höhere Pulsdosisleistung, gegenüber den klassischen Teilchenstrahlen untersucht werden. Im Beitrag wird der Stand der neuen Technologie im Hinblick auf eine Protonentherapie diskutiert und die weltweit ersten systematischen Zellbestrahlungen mit Bestimmung von Dosis-Effekt-Kurven für Laser beschleunigte Protonen vorgestellt.
Methodik: Wichtige Voraussetzungen für die Nutzung Laser beschleunigter Teilchen in der klinischen Therapie oder auch für strahlenbiologische Experimente sind die Anpassung des Lasersystems, sowie der Aufbau einer geeigneten Strahlführung und eines Dosimetriesystems. Die Zellbestrahlungen wurden am 150-Terrawatt-Lasersystem DRACO im Helmoltz-Zentrum Dresden-Rossendorf durchgeführt. Die Protonenpulse haben eine Länge von ca. 1 ps und eine Wiederholrate von 0,2 Hz. In einer ersten Serie von in-vitro Zellbestrahlungen mit Strahlendosen im Bereich von 0,3 bis 4 Gy wurde der Anteil der überlebenden Zellen und die 24 h nach Bestrahlung verbliebenen DNA-Doppelstrangbrüche für die Tumor-Zelllinie SKX bestimmt. Zusätzlich wurden Referenzbestrahlungen an einem Tandembeschleuniger mit kontinuierlichen Protonenstrahlen und einer 200 kV-Röntgenröhre durchgeführt.
Ergebnisse: Die neue Technologie bietet ein hohes Potenzial zur Verbesserung der Strahlentherapie mit Protonen. Insbesondere sind kleine, preiswerte Anlagen denkbar, die in bestehende Kliniken integriert werden können. Die präzise dosimetrische Erfassung Laser beschleunigter Strahlen ist möglich. Die biologische Wirksamkeit zwischen konventionell und Laser beschleunigten Protonen zeigt in Zellbestrahlungen keinen signifikanten Unterschied.
Schlussfolgerung: Die ersten Schritte zur Entwicklung einer neuen, auf Hochintensitätslasern basierenden Protonentherapieanlage sind erfolgreich durchgeführt worden. Weitere Untersuchungen zur biologischen Wirksamkeit am Tiermodell müssen erfolgen. Ausserdem sind weitere Entwicklungen und Verbesserungen der Laser Beschleuniger notwendig, damit ein klinischer Einsatz möglich wird.
Die Arbeit wird gefördert durch das BMBF 03ZIK445.

Involved research facilities

Related publications

  • Contribution to proceedings
    DEGRO 2011 17. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 02.-05.06.2011, Wiesbaden, Deutschland
    Strahlentherapie und Onkologie 187: Suppl., München: Urban&Vogel, 7

Permalink: https://www.hzdr.de/publications/Publ-15926


Visualization of spin dynamics in single nanosized magnetic elements

Banholzer, A.; Narkowicz, R.; Hassel, C.; Meckenstock, R.; Stienen, S.; Posth, O.; Suter, D.; Farle, M.; Lindner, J.

Abstract

The design of future spintronic devices requires a quantitative understanding of the microscopic linear and nonlinear spin relaxation processes governing the magnetization reversal in nanometer-scale ferromagnetic systems. Ferromagnetic resonance is the method of choice for a quantitative analysis of relaxation rates, magnetic anisotropy and susceptibility in a single experiment. The approach offers the possibility of coherent control and manipulation of nanoscaled structures by microwave irradiation. Here, we analyze the different excitation modes in a single nanometer-sized ferromagnetic stripe. Measurements are performed using a microresonator set-up which offers a sensitivity to quantitatively analyze the dynamic and static magnetic properties of single nanomagnets with volumes of (100 nm)(3). Uniform as well as non-uniform volume modes of the spin wave excitation spectrum are identified and found to be in excellent agreement with the results of micromagnetic simulations which allow the visualization of the spatial distribution of these modes in the nanostructures.

Permalink: https://www.hzdr.de/publications/Publ-15925


HZDR Developments for Fast Reactor Design

Merk, B.; Duerigen, S.; Rohde, U.; Kliem, S.

Abstract

Current work at HZDR will be presented with special emphasis on the development strategy for the DYN3D code as a main component of a diverse 3D coupled core simulation tool for fast reactors and on the work on designable feedback coefficients for sodium cooled fast reactors.
DYN3D is a code for steady-state and transient analysis, currently updated for the use for fast reactors. The code has been extended to multi-group use as well as to the solution of the SP3 equations on rectangular and recently to triangular grid. First verification results for the new triangular multi-group solver will be presented and compared to a HELIOS reference solution. The thermal hydraulics of the code has already been updated with the sodium properties for the steady state and transient core simulation. In an industry funded project the fuel rod modeling will be improved by coupling with a fuel rod analysis code and by extension of the model to consider fuel rod expansion. First full core tests for SFR will be performed within ESFR. LFR validation will be performed on the Guinevere experiments at Mol/Belgium in the project FREYA. Validation of the code for SFR is foreseen in a cooperation project with the IPPE in Obninsk/Russia, already under negotiation. After these validation projects, DYN3D will be a diverse, well validated 3D nodal code for fast reactor steady state and transient analysis.
The new idea of improving the safety coefficients by the insertion of moderating material will be presented. The effect of moderating material on the sodium void effect, the neutron spectrum, and the kinf is investigated. The use of a zirconium hydride ZrH moderator improves the fuel temperature effect, the coolant effect of the system and the sodium void effect significantly. All changes lead to a significant increase in stability of the fast reactor against transients. The effect of different spatial arrangements of the moderating material is investigated. It is demonstrated, that the insertion of the moderating material does not have a significant influence on the fuel element power and burnup distribution. The use of fine distributed moderating material creates a new degree of freedom in the design of sodium cooled fast reactors without implying constraints on the core and the fuel element design. It opens the way to create designable feedback effects in a fast reactor core to optimize the response of the reactor core to transients and incidents. The moderating material has only a small influence on the breeding effect and the MA production.

Keywords: DYN3D; fast reactor; designable feedback coefficients

  • Contribution to proceedings
    IAEA Technical Meeting on “Fast Reactor Physics and Technology", 14.-18.11.2011, Kalpakkam, India
  • Lecture (Conference)
    IAEA Technical Meeting on “Fast Reactor Physics and Technology", 14.-18.11.2011, Kalpakkam, India

Permalink: https://www.hzdr.de/publications/Publ-15924


Influence of dipolar energy on the magnetization reversal in magnetization-modulated thin film systems: Model and experiment

Martin, N.; Mönch, I.; Schäfer, R.; Fassbender, J.; Schultz, L.; McCord, J.

Abstract

Laterally patterned magnetic hybrid structures display novel magnetic reversal properties, which are related to the fundamental exchange coupling between material interfaces. We present an analytical model that depicts the influence of dipolar fields inmesoscopic structureswith modulated saturationmagnetization on the magnetization reversal and the local magnetic states, as well as the occurrence of a lateral exchange-spring effect. This is done by confining a lateral array of stripes with alternating saturation magnetizationMS in a micrometer-sized square, introducing external boundary conditions to the system. The calculations were performed for distinct stripe and array sizes, as well as different MS values. From the calculations a stability region of array and stripe sizes is derived, in which the lateral exchange-spring effect occurs. The obtained modeling results were found to be in agreement with the experimental data. The model adds a building block to the fundamental understanding of magnetic hybrid structures.

Keywords: magnetism; hybrid structures; ion irradiation; patterning; Kerr microscopy

Involved research facilities

Related publications

Permalink: https://www.hzdr.de/publications/Publ-15923


Shear and bulk viscosities of the gluon plasma in a quasiparticle description

Bluhm, M.; Kämpfer, B.; Redlich, K.

Abstract

Shear and bulk viscosities of deconfined gluonic matter are investigated within an effective kinetic theory by describing the strongly interacting medium phenomenologically in terms of quasiparticle excitations with medium-dependent self-energies. We show that the resulting transport coefficients reproduce the parametric dependencies on temperature and coupling obtained in perturbative QCD at large temperatures and small running coupling. The extrapolation into the nonperturbative regime results in a decreasing specific shear viscosity with decreasing temperature, exhibiting a minimum in the vicinity of the deconfinement transition, while the specific bulk viscosity is sizable in this region, falling off rapidly with increasing temperature. The temperature dependence of specific shear and bulk viscosities found within this quasiparticle description of the pure gluon plasma is in agreement with available lattice QCD results.

Permalink: https://www.hzdr.de/publications/Publ-15922


Years: 2024 2023 2022 2021 2020 2019 2018 2017 2016


Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.] [330.] [331.] [332.] [333.] [334.] [335.] [336.] [337.] [338.] [339.] [340.] [341.] [342.] [343.] [344.] [345.] [346.] [347.] [348.] [349.] [350.] [351.] [352.] [353.] [354.] [355.] [356.] [357.] [358.] [359.]