Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35879 Publications

Quantitative dopant profiling in semiconductors: A new approach to Kelvin probe force microscopy

Baumgart, C.

Failure analysis and optimization of semiconducting devices request knowledge of their electrical properties. To meet the demands of today’s semiconductor industry, an electrical nanometrology technique is required which provides quantitative information about the doping profile and which enables scans with a lateral resolution in the sub-10 nm range. In the presented work it is shown that Kelvin probe force microscopy (KPFM) is a very promising electrical nanometrology technique to face this challenge. The technical and physical aspects of KPFM measurements on semiconductors required for the correct interpretation of the detected KPFM bias are discussed. A new KPFM model is developed which enables the quantitative correlation between the probed KPFM bias and the dopant concentration in the investigated semiconducting sample. Quantitative dopant profiling by means of the new KPFM model is demonstrated by the example of differently structured, n- and p-type doped silicon. Additionally, the transport of charge carriers during KPFM measurements, in particular in the presence of intrinsic electric fields due to vertical and horizontal pn junctions as well as due to surface space charge regions, is discussed. Detailed investigations show that transport of charge carriers in the semiconducting sample is a crucial aspect and has to be taken into account when aiming for a quantitative evaluation of the probed KPFM bias.

Keywords: semiconducting devices; doping profile; Kelvin probe force microscopy; KPFM

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-026 2012
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 17893

Fine distributed moderating material to enhance feedback coefficients in lead cooled fast reactor experiment

Merk, B.

Recently, the use of moderating materials in fuel assemblies for Sodium cooled fast reactors (SFRs) has been investigated and published in several papers (Annals of Nuclear Energy 38, 5, Annals of Nuclear Energy 38, 11 (2011)). Especially the fine distribution of the moderating material has shown very promising results for the enhancement of the feedback coefficients in Sodium cooled fast reactors. The validity of the HELIOS results has been demonstrated in a comparison with MCNP and the transferability of the effect to full core calculations has been shown.
In a new attempt, it will be demonstrated, that the concept of enhanced feedback coefficients is transferable to lead cooled fast reactors (LFRs). The demonstration is based on a test for the configuration of the zero power experimental setup GUINEVERE in the VENUS facility at SCK•CEN in Mol/Belgium, since this experiment could serve for a first real experimental test to confirm the simulations. The calculations are based on the preliminary design of the fuel assemblies of the currently running subcritical experiments at GUINEVERE. The effect of the moderating material on the neutron spectrum, on the kinf, and on the fuel temperature feedback of the zero power facility is shown, discussed and compared to SFRs. The thermal stability of the hydrogen bearing compound is of paramount importance for the use of moderating material in a LFR. An insight will be given into the relationship of the hydrogen content of the compound and the resulting thermal stability. Thermal stability of the moderating material up to more than 1300°C can be ensured by the use of Yttrium-mono-hydride as moderating material.
Over all it is demonstrated, that the use of fine distributed moderating material has the potential to open the stage for designable feedback coefficients not only in sodium cooled fast reactors, but also in lead cooled fast reactors. An important point is that the enhanced feedback effects can be achieved without creating a major influence on the operational parameters and core coolability.

Keywords: Lead Cooled Fast Reactor; Fast Reactor; Enhanced Feedback Effects; Moderating Material; Yttriumhydride; GUINEVERE

  • Contribution to proceedings
    2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea
    Proceedings of ICAPP'13
  • Lecture (Conference)
    2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea

Publ.-Id: 17892

The molten salt fast reactor as transmutation system in the view of the nuclear phase-out

Merk, B.; Rohde, U.; Scholl, S.

The basic development and design of a molten salt reactor with fast neutron spectrum (Molten Salt Fast Reactor – MSFR) is the target of the EVOL project in FP7. The MSFR offers certain advantages in the view of transmutation compared to solid fuelled reactor types. In the first part, these advantages will be discussed in a comparison with the sodium cooled fast reactor technology and the research challenges will be analyzed.
In the second part, a strategy for the optimization of the transmutation efficiency is developed, based on the findings of a former study, for different configurations – core with U-238 fertile, a fertile free core and a core with Th-232 as fertile material. The study has identified advantageous use of Thorium as fertile material. The final aim of this study is dictated by the phase out decision of the German government. Transmutation in the German view thus is focused on the determination of the maximal transmutation efficiency and on an as much as possible reduced left over of transuranium elements (TRUs) in the end of reactor life core. This is a prerequisite, since there is no future reactor foreseen and the reminders have to be put into a final repository. This minimal left over is achieved by a two step operation, first a TRU burning phase with continuous feed in a salt configuration with Thorium as fertile material, second a deep burning phase utilizing the U-233 bred in the blanket of the core as feed. In the calculation results, the time evolution of different important isotopes will be analyzed for both phases. It will be demonstrated, that transmutation rates up to more than 90% can be reached, while the production of undesired high elements like Californium is very limited. Based on these results a rough approximation will be given on the required number of reactors for the transmutation of the German TRU stockpile and the left over will estimated. Additionally, the used tool HELIOS 1.10 and the adaptations needed for the simulation of a MSFR will be described.

Keywords: Transmutation; Molten Salt Reactor; Molten Salt Reactor; Thoruim; Nuclear Phase Out

  • Contribution to proceedings
    2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea
    Proceedings of ICAPP'13
  • Lecture (Conference)
    2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea

Publ.-Id: 17891

Acceleratorbased super-radiant coherent THz sources: Challenges and Opportunities

Gensch, M.

The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow-bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4th generation X-ray light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges ranging.
[1] G.L. Carr et. al., High power terahertz radiation from relativistic electrons, Nature 420 (2002), 153.
[2] M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[3] U. Fruehling et. al., Single-Shot THz-field-driven X-ray streak camera, Nat. Photon. 3 (2009), 523.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Light
sources, Nat. Photon. 5 (2011), 162.
[5] D. Daranciang et. al., Single-cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent
transition radiation, Appl. Phys. Lett. 99 (2011), 141117.

  • Invited lecture (Conferences)
    Seminar des Fritz Haber Instituts, 22.10.2012, Berlin, Deutschland

Publ.-Id: 17890

Temperature stable 1.3 um emission from GaAs

Prucnal, S.; Gao, K.; Anwand, W.; Helm, M.; Skorupa, W.; Zhou, S.

Gallium arsenide has outstanding performance in optical communication devices for light source purposes. Different approaches have been done to realize the luminescence from GaAs matching the transmission window of optical fibers. Here we present the realization of quasi- temperature independent photoluminescence at around 1.3 um from millisecond-range thermally treated GaAs. It is shown that the VAs donor and X acceptor pairs are responsible for the 1.3 um emission. The influence of the flash-lamp-annealing on the donor-acceptor pair (DAP) formation in the nitrogen and manganese doped and un-doped semi-insulating GaAs wafers were investigated. The concentration of DAP and the 1.3 um emission can be easily tuned by controlling doping and annealing conditions.

Keywords: Optical communications; Optical properties; Photoluminescence; Ion Implantation; GaAs; Flash Lamp Annealing

  • Open Access Logo Optics Express 20(2012), 26075-26081

Publ.-Id: 17889

A 3D-QSAR Model for Cannabinoid Receptor (CB2) Ligands Derived from Aligned Pharmacophors

Günther, R.; Deuther-Conrad, W.; Moldovan, R.; Fischer, S.; Brust, P.

Cannabinoid (CB) receptors have gained much attention as markers for various brain tumours and potential therapeutic targets of neuropathic pain and mood disorders. Two CB receptors have been cloned and described: CB1, predominantly expressed in the brain and CB2, primarily found in the peripheral system but also in brain. The CB2 receptor is suggested to be involved in various neurodegenerative diseases, such as Alzheimer's or Parkinson's disease [1]. Early and non-invasive diagnosis and therapy monitoring of such diseases is desired. Positron-Emission-Tomography (PET) allows imaging of functional processes in living humans. For this, compounds with positron emitting labels like 18F are used. Due to the high sensitivity of PET, such radiotracers must bind to the target protein with high selectivity.
Here, we utilise AutoGPA [2] implemented in the modelling suite MOE (Chemical Computing Group Inc., Montreal) to compute grid potentials build upon a 3D-QSAR model derived from a library of CB2 selective N-Aryl-oxadiazolylpropionamides.
Since a proper alignment of the molecules prior the analysis is crucial to the successful application of these models in further studies, the molecules were aligned based on their pharmacophore features. The obtained model delivers also knowledge of the 3D-structure of the binding site, which, in turn, can be used to refine 3D-models of the CB2 receptor. The steric and electrostatic contour maps are applied for identification of regions suitable for labelling with 18F, the most preferred PET radionuclide.
[1] Scotter EL, Abood ME, Glass M: The Endocannabinoid System as a Target for the Treatment of Neurodegenerative Disease. Br J Pharmacol 2010, 160:480-498
[2] Asakawa N, Kobayashi S, Goto J, Hirayama N: AutoGPA: A novel 3D-QSAR method based on grid potential analysis and pharmacophore alignment. Poster presentation at 10th InCoB - 1st ISCB Asia Joint Conference (InCoB2011/ISCB-Asia 2011); Kuala Lumpur, Malaysia

  • Poster
    8th German Conference on Chemoinformatics (GCC2012), 11.-13.11.2012, Goslar, Deutschland
  • Poster
    BIOTEC Forum "Bioinformatics and Computational Biology", 06.-07.12.2012, Dresden, Deutschland

Publ.-Id: 17888

The generalized two phase flow CFD model (GENTOP)

Lucas, D.; Hänsch, S.; Krepper, E.; Höhne, T.

In recent years many attempts were done to qualify CFD codes for multiphase flows. There is a clear progress e.g. for simulating dispersed bubbly or droplet flows on the one hand and stratified flows with large interfaces on the other hand. However many multiphase flows occurring in nature and technical applications are characterized by transitions between dispersed and continuous morphologies. Examples are bubble entrainment caused by plunging jets or by rolling waves. With presently available CFD-codes such transitions can be simulated only for some idealized cases. Simulations applying the multi-fluid model which is frequently applied for simulations on large technical systems provide some results for such transitions but they are rather caused by numerical effects than on physical basis. For this reason a new concept basing on the multi-fluid model and combining the previously developed MUSIG (Multi size bubble group model) and AIAD (Algebraic Interfacial Area Density) approaches was developed. It can be considered as a two-phase, three-field approach which includes a continuous liquid phase, one or more dispersed gas phases and a continuous gas phase. Transitions between dispersed and continuous gas phases are reflected by coalescence and breakup models. The paper presents the GENTOP concepts and simulations demonstrating the capabilities of the concept.

  • Lecture (Conference)
    6th Japanese - European Two-Phase Flow Group Meeting, 23.-27.09.2012, Kumamoto, Japan

Publ.-Id: 17887

Validation of models for bubbly flows and cap flows using one-group and two-group average bubble number density

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

Gas-liquid flows with wide range of bubble sizes are commonly encountered in many nuclear gas-liquid flow systems. In tracking the changes of gas volume fraction and bubble size distribution under complex flow conditions, numerical studies have been performed to validate predictions of the onegroup and two-group approaches against experimental measurements for upward gas-liquid flows in vertical pipes. These experiments have been strategically chosen because of particular flow conditions yielding specific trends of bubble size evolution, which provided the necessary means of carrying out thorough assessments of bubble coalescence and break-up kernels. Predictions of one-group approach for bubbly flows were in good agreement with experimental data. Predictions of two-group approach for bubbly and cap flows were in reasonable agreement with experimental data; additional insights into the appropriate bubble interaction mechanisms are still required for cap flows. Nevertheless, the encouraging results demonstrated the capability of both approaches in capturing the dynamical changes of bubbles size due to bubble interactions and the transition from “wall peak” to “core peak” gas volume fraction profiles caused by the presence of small and large bubbles.

  • Contribution to proceedings
    CFD4NRS-4 - The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology - OECD/NEA and IAEA Workshop, 10.-12.09.2012, Daejeon, Korea
  • Lecture (Conference)
    CFD4NRS-4 - The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology - OECD/NEA and IAEA Workshop, 10.-12.09.2012, Daejeon, Korea

Publ.-Id: 17886

Numerical simulation and modeling of a laboratory MWD mud siren pressure pulse propagation in fluid filled pipe

Namuq, M. A.; Reich, M.; Al-Zoubi, A.

This article presents modeling and numerical simulations of a laboratory mud siren pressure pulse propagation in a water filled pipeline. The unsteady flow behavior is simulated and modeled with ANSYS CFX11 (Computational Fluid Dynamics (CFD) commercial code). Time domain simulations were performed for three different carrier frequencies of the mud siren, and the results were also analyzed in frequency using a Fast Fourier Transformation code in MATLAB. The estimated results from the model are compared with real experimental data in both time and frequency domain in order to validate the model. A pretty good agreement is obtained between the predicated and measured pressure pulses at different locations along the pipeline for all experimental runs.

  • Oil Gas European Magazine 38(2012)3, 125-131

Publ.-Id: 17885

Microscopic observation of aerosol particle deposition in turbulent channel flows

Barth, T.; Lécrivain, G.; Lehmann, A.; Preuss, J.

The transport behaviour of carbonaceous dust in the primary circuit of a High Temperature Reactor (HTR) plays an important role in the safety assessment during a Design Basis Accident (DBA). Carbonaceous dust is formed mainly due to friction between graphite fuel elements (Kissane, 2009). In a pebble bed reactor the dust forms due to abrasion of graphite material between the pebbles. During reactor operation it is a safety issue to precisely predict the dust deposition and the corresponding resuspension rate of particles released into the containment during a DBA.
Deposition of aerosol particles has been investigated e.g. by Sippola & Nazaroff (2004). These experiments have been performed in steel ducts at Reynolds numbers and with particle relaxation times observed in a HTR. Their results follow the “v-shaped” curve of the non-dimensional deposition velocity against particle relaxation time and show a dependency on flow speed, particle size and orientation of the duct.
More recently, an Euler-Lagrange CFD simulation of particle deposition in a turbulent square duct flow has been performed by Lecrivain (2012). It was found that the friction velocity significantly influences the particle deposition velocities.
Deposition experiments of liquid and solid particles in a fully developed horizontal turbulent square duct flow are performed to further study the deposition behaviour of aerosol particles. The oil liquid particles (DEHS) are generated by a condensational aerosol generator (TOPAS, SLG 270). The aerodynamic particle size distribution and the particle number concentration of the suspended particles are determined by isokinetic sampling using an Aerodynamic Particle Sizer Spectrometer (TSI. APS 3321). The particle size distributions are fairly monodisperse for particles with daero = [1.5, 2.5, 3.5, 4.5] µm. The solid aerosol particles are microspheres (AkzoNobel, Expancel DU, d50 = 6.5 µm) and are injected into the flow field by means of a solid aerosol generator (TOPAS, SAG 410). The particle mass flow rate and the particle concentration are precisely adjusted by the feed rate of the SAG. The particle size distribution of the airborne particles is measured by means of Scanning Electron Microscopy (SEM). The size distributions gained by the APS and the SEM analysis are used to calibrate the size distributions obtained by an optical microscope.
A commercial light microscope equipped with a CMOS camera is mounted underneath the test section of the channel. It is focused on the inside surface of the channel floor which consists of a glass plate coated with indium tin oxide to remove electrostatic charges. This allows a time-resolved in situ observation of the particle deposition processes. A standard LED light source illuminates the microscope’s 6 x 4 mm² field of view and the CMOS camera records the scatter light of the wall deposited particles. The measurement uncertainty for particles larger than 2 µm is assumed to be 24%.
Figure 1 illustrates the time averaged deposition velocities for varying friction velocities. The CFD results of Lecrivain (2012) and Sipolla & Nazaroff (2004) are also plotted for comparison purposes. In the particle relaxation time range τ+ = 0.001..10 the deposition velocity increases with decreasing friction velocity. which is also observed elsewhere. It is assumed that the effect of gravitational settling leads to an increase of deposition velocity for decreasing flow speed. The results of this study also capture this tendency. Nevertheless, the scatter in the data has to be further investigated.

Keywords: Turbulent flow; particle deposition; microscopic observation; isokinetic sampling; spectrometry

  • Poster
    European Aerosol Conference 2012, 02.-07.09.2012, Granada, Spanien

Publ.-Id: 17884

Effect of the Lagrangian integral time scale estimation on particle deposition

Lecrivain, G.; Barth, T.; Hampel, U.

In a high temperature pebble-bed reactor, carbonaceous dust is conveyed by the cooling carrier phase and eventually deposits in the primary circuit of the reactor. In hypothetical severe accident, a dose of radioactive graphite dust may escape the system boundaries. The accurate prediction of transport and deposition of graphite particles is therefore a key primary safety issue.The numerical prediction of carbonaceous dust transport and deposition in turbulent flows is a key safety issue. Most particle tracking procedures make use of the Lagrangian integral time scale to reproduce the turbulent dispersion of the discrete phase. In the present Lagrangian particle tracking procedure, the effect of the Lagrangian integral time scale near the wall is thoroughly investigated.

Keywords: nuclear aerosols; deposition velocity; numerical simulation; CFD

  • Poster
    European Aerosol Conference 2012, 02.-07.09.2012, Granada, Spain

Publ.-Id: 17883

Simulation of particle deposition and layer formation between periodic steps

Lecrivain, G.; Drapeau-Martin, S.; Reiche, M.; Barth, T.; Hampel, U.

In a pebble-bed high temperature reactor core where thousands of pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust eventually deposits in the primary circuit of the reactor. The numerical prediction of graphite dust deposition is therefore a key safety issue and needs investigation. The deposition of aerosol graphite particles in a turbulent channel flow obstructed by periodic steps is here numerically investigated at Reynolds number Re = 8,000. Particles in the size range d = 1...100µm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. A two dimensional quasi-static simulation is performed. The quasi-static assumption is motivated by the time duration of the experimental test which lasts several hours. The iterative process is decomposed as follows: a Reynolds Averaged Navier Stokes turbulence model is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After sufficient deposition of the particulate matter, the build-up of the dust layer is computed using mechanics of dry granular material. The wall boundaries of the computational domain are then updated prior to the next flow simulation. The procedure is repeated until the dust layer reaches appropriate growth. The result of the multi-layer deposition matches reasonably well that of the experimental test performed on-site

Keywords: Particle deposition; particle dispersion; graphite particles; dust layer build-up; turbulent flow; obstructed channel flow

  • Lecture (Conference)
    13th Workshop on two-phase flows, 17.-20.09.2012, Halle, Deutschland

Publ.-Id: 17882

Selective Extraction of 85Sr2+ with modified Calix[4]arenes in a liquid-liquid system

Poetsch, M.; Mansel, A.; Schnorr, R.; Haupt, S.; Kersting, B.

90Sr is a long-lived radionuclide (T1/2 = 28.6 a), which is produced as a by-product in nuclear power plants in the decay chain of uranium. In case of release in the biosphere, it can be concentrated in aquatic systems or in soil. It follows the food chain from environment to fauna and human. Due to its chemically similarity to calcium, it can be incorporated in bones. Stable isotopes of strontium might not be harmful, but radioactive analogues can lead to bone disorders and diseases, including leukaemia [1].
Calix[4]arenes represent an important class of supramolecules having various applications, e.g. in the recovery of nuclear fission products of uranium, like cesium or strontium.[2] We synthesised and structurally analysed calix[4]arene-based extractants as shown in Fig. 1 in order to investigate their binding ability towards strontium in liquid-liquid extraction systems.
An aqueous phase was traced using the short-lived radionuclide 85Sr (T1/2 = 64.9 d), which was produced and purified at the in-house 18 MeV-cyclotron [3]. To quantify the extraction behaviour of the calix[4]arenes, the remaining amounts of 85Sr in the aqueous phases after the extraction, were recorded using gamma spectrometry. We systematically investigated the influence of various experimental parameters. Figure 1 shows extraction behaviour of various calix[4]arene derivatives depending on the pH of the aqueous strontium phase. Under alkaline conditions of the aqueous strontium phase, extraction yields of >(90±4)% were obtained for calix[4]arenes derivatives having carbonyl binding sites. Furthermore, the competition of inorganic and organic impurities to the extraction performance was studied. The impurities are in naturally occurring concentrations of ions like sodium, calcium, acetate or tartaric acid as groundwater ingredients. By simulating a synthetic groundwater, extraction of strontium was per-formed in yields up to (86±6)%.
In further experiments, the calix[4]arene-strontium complex is going to be analysed spectroscopically with the aim to investigate the complex formation behaviour.

The authors gratefully thank the German Federal Ministry of Education and Research (BMBF) for financial support of this study (project no. 02NUK014).

[1] Wallova, G., N. Kandler, and G. Wallner, Monitoring of radionuclides in soil and bone samples from Austria. Journal of Environmental Radioactivity, 2012. 107: p. 44-50.
[2] Otho, K., Review of the extraction behavior of metal cations with calixarene derivatives. Solvent Extraction Research and Development, 2010. 17: p. 1-18.
[3] Mansel, A., et al., Production of 85Sr at a 18 MeV-cyclotron and purification for geochemical investigations, 2012. (submitted)

Keywords: calixarene radio strontium liquid-liquid extraction complex

  • Poster
    Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Deutschland

Publ.-Id: 17881

CMOS integrated antenna-coupled field-effect-transistors for the detection of radiation from 0.2 to 4.3 THz

Boppel, S.; Lisauskas, A.; Mundt, M.; Seliuta, D.; Minkevičius, L.; Kašalynas, I.; Valušis, G.; Krozer, V.; Mittendorff, M.; Winnerl, S.; Roskos, H. G.

Using 150-nm CMOS process technology, various patch antenna coupled detectors have been implemented with different antenna resonance frequencies spanning from 0.2 to 4.3 THz.. These devices employ self-mixing in n-channel field-effect transistors and operate well above the transistors’ cutoff frequency. Detector designs are based on a novel concept which couples the signal to the drain, which facilitates detection also at electronic frequencies applicable to e. g. device calibration. The theoretical description of device operation by Dyakonov and Shur is extended to include the new boundary conditions and any gate bias. Additionally device impedance, responsivity and noise equivalent power are considered. The different transport regimes (i.e. quasi-stationary (QS), distributed resistive and plasmonic mixing) and their transitions are theoretically discussed and experimentally accessed. Responsivity values of 1344 V/W at 585 GHz, 90 V/W at 3.1 THz and 11 V/W at 4.3 THz are reported. At 0.585 THz we report the optical noise-equivalent-power (NEP) of 13 pW/√Hz at optimum gate bias and at 3.1 THz of 163 pW/√Hz. Under ideal 0.585 THz coupling conditions and room temperature operation, a NEP as low as 2 pW/√Hz is predicted. All values are normalized to the physical antenna area.

Keywords: Submillimeter wave detectors; Terahertz detectors; patch antennas; CMOS; terahertz direct detection; distributed resistive self-mixing; plasmonic detection

Publ.-Id: 17880

Universal phase relation between longitudinal and transverse fields observed in focused terahertz beams

Winnerl, S.; Hubrich, R.; Mittendorff, M.; Schneider, H.; Helm, M.

We directly observe longitudinal electromagnetic fields in focused freely propagating terahertz beams of radial and linear polarization. Employing electro-optic detection, which is phase sensitive, allows one to selectively detect longitudinal and transverse field components. A phase shift of pi/2 between transverse and longitudinal field components is revealed. This phase shift is of universal nature, as it does not depend on the mode, frequency and focusing conditions. We show that the universal phase relation is a direct consequence of the divergence-free nature of electromagnetic waves in vacuum. In the experiments we observe the phase shift of pi/2 for all frequency components of single-cycle THz radiation pulses of both radial and linear polarization. Additionally we show that the longitudinal field of a radially polarized THz beam has a smaller spot size as compared to the transverse field of a linearly polarized beam that is focused under the same conditions. For field-sensitive measurements this property can be exploited even for moderate focusing conditions. Furthermore the phase-sensitive detection of longitudinal electromagnetic fields opens up new possibilities to study their interaction with electronic excitations in semiconductor nanostructures.

Keywords: longitudinal electromagnetic fields; terahertz vector beams; Bessel Gauss beams; radially polarized beams

Publ.-Id: 17879

Time-resolved spectroscopy on epitaxial graphene in the infrared spectral range: relaxation dynamics and saturation behavior

Winnerl, S.; Göttfert, F.; Mittendorff, M.; Schneider, H.; Helm, M.; Winzer, T.; Malic, E.; Knorr, A.; Orlita, M.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.

We present the results of pump-probe experiments on multilayer graphene samples performed in a wide spectral range, namely from the near-infrared (photon energy 1.5 eV) to the terahertz (photon energy 8 meV) spectral range. In the near infrared, exciting carriers and probing at higher photon energies provides direct evidence for a hot carrier distribution. Furthermore spectroscopic signatures of the highly doped graphene layers at the interface to SiC are observed in the near-infrared range. In the mid-infrared range, the various relaxation mechanisms, in particular scattering via optical phonons and Auger-type processes, are identified by comparing the experimental results to microscopic modelling. Changes from induced transmission to induced absorption are attributed to probing above or below the Fermi edge of the graphene layers. This effect occurs for certain photon energies in the near infrared range, where it is related to highly doped graphene layers at the interface to SiC, and in the far infrared range for the quasi-intrinsic graphene layers. In addition to the relaxation dynamics, the saturation of pump-induced bleaching of graphene is studied. Here a quadratic dependence of the saturation fluence on the pump photon energy in the infrared spectral range is revealed.

Keywords: relaxation dynamics in graphene; ultrafast spectroscopy on graphene; graphene saturable absorber

Publ.-Id: 17878

Large area photoconductive THz emitter for 1.55 µm excitation based on an InGaAs heterostructure

Mittendorff, M.; Xu, M.; Dietz, R. J. B.; Künzel, H.; Sartorius, B.; Schneider, H.; Helm, M.; Winnerl, S.

We present scalable large area terahertz (THz) emitters based on a nanoscale multilayer InGaAs/InAlAs heterostructure and a microstructured electrode pattern. The emitters are designed for pump lasers working at the telecommunication wavelength of 1.55µm. Electric THz fields of more than 2.5 V/cm are reached with moderate pump powers of 80 mW, the corresponding spectrum extends up to 3 THz. The saturation characteristics have been investigated for different pump laser spot sizes. For small pump powers of less than 50 mW the emitted THz field is nearly independent of the spot size, for higher pump powers and small spot sizes a clear saturation of the generated THz pulse can be observed. Hence the usage of scalable emitters is especially promising for high power fibre laser systems. The spectral content of the generated radiation is nearly independent of the parameters spot size, pump power, and bias voltage, which allows for stable operation in spectroscopic applications.

Keywords: photoconductive THz emitter; 1.55 µm excitation; InGaAs-based THz emitter

Publ.-Id: 17877

Influence of intergranular exchange coupling on the magnetization dynamics of CoCrPt:SiO2 granular media

Brandt, R.; Tibus, S.; Springer, F.; Fassbender, J.; Rohrmann, H.; Albrecht, M.; Schmidt, H.

We investigate the effect of Co+ irradiation on the magnetization dynamics of CoCrPt:SiO2 granular media. Increasing irradiation levels reduce the saturation magnetization and effective anisotropy, which decrease the intrinsic magnetization precession frequency. Furthermore, increasing intergranular exchange coupling results in a qualitative change in the behavior of the magnetic material from a collection of individual grains to a homogeneous thin film, as evidenced in both the switching behavior and dynamics. The frequency change cannot be explained by single crystal macrospin modeling, and can only be reproduced by the inclusion of the dipolar effects and anisotropy distribution inherent in a granular medium.

Keywords: ion irradiation; ion implantation; magnetism; magnetic storage

Publ.-Id: 17876

GPGPU for Kinetic Lattice Monte Carlo Simulations

Kelling, J.

Kinetic lattice Monte Carlo (KLMC) methods have for long been applied successfully for the atomistic large scale simulations of processes like annealing or ion beam treatment as well as for the study of scaling phenomena. Increasing the size of simulated systems is indispensable to get closer to the experiment as well as obtaining more accurate numerical estimates. In a time of stagnating sequential performance in computers parallelization is the only way to reach this goal. We have successfully taken on the implementation of two different methods for GPUs. In this talk I will outline the potential of general purpose processing on GPUs (GPGPU) for KLMC methods alongside presenting some of our key results.

  • Lecture (others)
    CCoE Seminar, 11.10.2012, TU-Dresden WIL/A317, Deutschland

Publ.-Id: 17875

GGR Biennial Critical Review: Analytical Developments Since 2010

Wiedenbeck, M.; Bugoi, R.; Duke, M. J. M.; Dunai, T.; Enzweiler, J.; Horan, M.; Jochum, K. P.; Linge, K.; Košler, J.; Merchel, S.; Morales, L.; Nasdala, L.; Stalder, R.; Sylvester, P.; Weis, U.; Zoubir, A.

Advances in the chemical and isotopic characterisation of geological and environmental materials can often be ascribed to technological improvements in analytical hardware. Equally, the creation of novel methods of data acquisition and interpretation, including access to better reference materials, can also be crucial components enabling important breakthroughs. This biennial review highlights key advances in either instrumentation or data acquisition and treatment which have appeared since January 2010. This review is based on the assessments by scientists prominent in each of the given analytical fields; it is not intended as an exhaustive summary, but rather provides insight from experts of the most significant advances and trends in their given field of expertise. In contrast to earlier reviews, this presentation has been formulated into a unified work, providing a single source covering a broad spectrum of geoanalytical techniques. Additionally, some themes that were not previously emphasised, in particular TIMS, accelerator-based methods and vibrational spectroscopy, are also presented in detail.

Keywords: TIMS; isotopic analysis; geochronology; ICP-MS; laser ablation; mass spectrometry; ICP-AES; calibration; environmental sampling; FIB; 3D imaging; SIMS; particle search; AMS; Ion Beam Analysis; radionuclides; Raman; FTIR; neutron activation; INAA; reference materials; microanalysis

Publ.-Id: 17874

Investigation of bacterial survival strategies in metalliferous environments: Molecular biological studies on S-layer proteins

Lederer, F.; Raff, J.; Pollmann, K.

Generally, heavy metal contamination of the environment is a result of either natural events like volcanic emissions or human activities such as mining processes. High concentrations of heavy metals are toxic to the majority of organisms. However, several bacteria exhibit surprising strategies to survive in metalliferous environments. These strategies are attractive for novel bio-based resource technologies. Their understanding is the purpose of our research.

Lysinibacillus sphaericus JG-B53, an isolate from the uranium mining waste pile Haberland, was studied using genome sequencing analyses in order to identify strain intrinsic survival strategies like surface (S) layer proteins with metal specific binding affinities and metal specific transporter proteins. Using the Next generation sequencing technology and bioinformatic analyses of the whole genome sequence of L. sphaericus JG-B53 with the Genomics Workbench (CLC bio) we identified 15 putative S-layer protein genes and 3 metal ion exporter protein genes for metals that occur in the natural habitat of Lysinibacillus sphaericus JG-B53. Their characteristics were analysed with multiple gene and protein analyzing programs. The protein expression was analyzed using cDNA analyses (Lederer, 2012; Lederer et al, 2013) .
Future studies will analyse recombinant S-layer proteins regarding their lattice symmetry and metal binding affinities.

Lederer FL 2012. Genetic characterization, heterologous expression and application of S-layer proteins from the bacterial isolates Lysinibacillus sphaericus JG-B53 and Lysinibacillus sphaericus JG-A12. PhD Thesis, University of Rostock.
Lederer FL, Weinert U, Günther T, Raff J, Pollmann K. 2013. Identification of survival strategies of Lysinibacillus sphaericus JG-B53 in heavy metal and radionuclide contaminated soil. In preparation.

  • Poster
    GETGEOWEB - Genomic and Transcriptomic in Geobiotechnology and White Biotechnology, 29.-30.10.2012, Freiberg, Germany

Publ.-Id: 17873

Isolationsmaterialbelastete Kühlmittelströmung im Kern – CFD-Modellentwicklung und Untersuchung von Korrosionsprozessen

Kryk, H.; Cartland-Glover, G.; Grahn, A.; Hoffmann, W.; Lecrivain, G.

Im Rahmen der deutschen Reaktorsicherheitsforschung wurden im Vorhaben 1501363 durch das Helmholtz-Zentrum Dresden-Rossendorf theoretische, experi-mentelle und methodische Untersuchungen zum hydrodynamischen und physiko-chemischen Verhalten von freigesetzten Isolationsmaterialfragmenten bzw. Korrosi-onsprodukten in Kühlmittelströmungen kerntechnischer Anlagen nach Kühlmittelverluststörfällen durchgeführt. Das Vorhaben baut auf den Ergebnissen der Forschungsvorhaben 1501270 und 1501307 auf und wurde in enger Kooperation mit der Hochschule Zittau/Görlitz (Vorhaben 1501360) realisiert.
Schwerpunkte der Arbeiten bildeten Erweiterungen und Verbesserungen der im Rahmen der o.g. Forschungsvorhaben entwickelten Methoden und Modelle zur dreidimensionalen CFD-Simulation der isolationsmaterialbelasteten Kühlmittelströmung im Containment-Sumpf unter Einbeziehung der Modellierung von Anlagerungs- und Ablösevorgängen von Isoliermaterial-Fasern und Debris an Rückhaltevorrichtungen im Notkühlkreislauf (z.B. Sumpfansaugsiebe). Die Modellentwicklung und –validierung erfolgte auf Basis von an der HS Zittau/Görlitz durchgeführten Experimenten. Weiterhin wurde der Einfluss chemischer Effekte, insbesondere der Korrosion feuerverzinkter Containment-Einbauten, auf die Wasserchemie und das Verblockungsverhalten von mit Isoliermaterial-Fasern belegten Rückhaltevorrichtungen untersucht. Auf Basis der Versuchsergebnisse erfolgte die Identifikation des mechanistischen Korrosionsmodells sowie der Haupt-Einflussfaktoren auf den Korrosions- und den Verblockungsmechanismus. Diese bildeten die Basis für die Ableitung möglicher Maßnahmen zur Minderung des Korrosions- und Verblockungspotenzials.

Keywords: Kühlmittelverluststörfall; CFD; Tiefenfiltration; Isolationsmaterial; Korrosion; chemische Langzeiteffekte; Feuerverzinkung; Sumpfsiebverstopfung; Modellierung; Experiment

  • Other report
    Dresden: HZDR\FWD\2012\01, 2012
    306 Seiten

Publ.-Id: 17872

Design, synthesis and biological evaluation of ultrasmall iron oxide nanoparticles for cancer imaging

Pombo Garcia, K.; Zarschler, K.; Stephan, H.; Steinbach, J.

There is currently a great interest in the application of nanoparticles for molecular imaging [1]. This results in the development of both, organic and inorganic nanoparticles functionalized in a way that radionuclides, targeting ligands, and different biopolymers can be attached in order to provide an imaging signal and alter the pharmacokinetic properties [2]. Ultrasmall supraparamagnetic iron oxide (Fe3O4) nanoparticles (USPIOs) are one of the most widely studied nanomaterials. USPIOs possess unique magnetic properties that make them attractive candidates as advanced biomedical materials [3]. Furthermore, the biocompatibility and favourable pharmacokinetic profile of USPIOs makes them suitable to be used as multifunctional agents. They can serve as contrast agents for clinical use in magnetic resonance imaging (MRI), positron emission tomography (PET) and optical imaging (OI) [4]. One strategy to improve retention of nanoparticles in tumours and accumulation in cancer cells is active targeting to specific cell membrane receptors. The epidermal growth factor receptor (EGFR) is overexpressed in more than 30% of all epithelial cancers [5]. With a wide clinical application of EGFR-targeted therapy, our effort is focused on obtaining magnetic nanoparticles to target EGFR for early diagnosis. This work aims at the development of new nanotracers based on USPIOs coated with a biodegradable polymer that are also decorated with agents for radiochemical and/or fluorescence imaging and EGFR-specific ligands as targeting units.
Fig 1: (A) Schematic representation of the crystal structure magnetite and (B) TEM image of iron oxide nanoparticles. The production of hydrophobic USPIOs has been achieved using thermal decomposition of metal-oleate precursors. These reaction of metal chlorides and sodium oleate. The subsequent precipitation procedure gives monodisperse nanocrystals within a size of 4-5 nm as it shown figure 1B [8]. The main limitation of using USPIOs for in vivo applications is their instability under physiological conditions. Different biocompatible polymers such as polyvinylalcohol, polyacrylic acid have been tested for the hydrophilic coating of the iron oxide core to make them stable in aqueous solution [9]. After an intensive physicochemical characterization including studies of their stability in water and several buffers, the carboxy methyl polyvinyl alcohol (CMPVA) was chosen as the most suitable coating agent for the surface modification of USPIOs [10]. The stability of the USPIOs coated with CMPVA was studied in water and different buffer solutions, where it was found that they were stable up to two months. Figure 2 shows the size distribution using DLS (dynamic light scattering, Zetasizer Malvern) of a representative sample and its zeta potential in water.
Fig 2: (A) DLS size by number (8±2nm) and (B) Zeta potential (-35mV) of coated CMPVA-USPIOs. Our first goal was to engeneer and functionalize the surface of the hydrophilic USPIOs. This included the attachment of the fluorescent label BODIPY to the CMPVA shell. This enabled the USPIOs to be suitable for in vitro binding and uptake studies in cancer cells by fluorescence imaging. Furthermore, preliminary radiolabeling studies (64Cu) have been undertaken using USPIOs decorated with functional copper chelating agents, such as NOTA. Radio-HPLC and Radio-TLC have been applied to get information about the labelling efficiency and stability of the 64Cu-labeled USPIOs. From our point of view, the generated nanoparticles possess promising features as novel imaging agents for in vivo cancer diagnostics. Experiments concerning the bioconjugation of EGFR-specific peptides on the surface of USPIOs are currently underway.

1. Barreto, J.A., et al., Nanomaterials: Applications in Cancer Imaging and Therapy. Advanced Materials, 23(12): p. H18-H40, 2011.
2. Cheon, J. and J.-H. Lee, Synergistically Integrated Nanoparticles as Multimodal Probes for Nanobiotechnology. Accounts of Chemical Research, 41(12): p. 1630-1640, 2008.
3. Huang, H.-C., et al., Inorganic nanoparticles for cancer imaging and therapy. Journal of Controlled Release, 155(3): p. 344-357, 2011.
4. Laurent, S., et al., Magnetic Iron Oxide Nanoparticles: Synthesis, Stabilization, Vectorization, Physicochemical Characterizations, and Biological Applications. Chemical Reviews, 108(6): p. 2064-211, 2008.
5. Mayo, C., et al., Pharmacogenetics of EGFR in lung cancer: perspectives and clinical applications. Pharmacogenomics, 13(7): p. 789-802, 2012.
6. Creixell, M., et al., Preparation of epidermal growth factor (EGF) conjugated iron oxide nanoparticles and their internalization into colon cancer cells. Journal of Magnetism and Magnetic Materials, 322(15): p. 2244-2250, 2010.
7. Li, Z., et al., Identification and characterization of a novel peptide ligand of epidermal growth factor receptor for targeted delivery of therapeutics. The FASEB Journal, 19(14): p. 1978-1985, 2005..
8. Park, J., et al., Ultra-large-scale syntheses of monodisperse nanocrystals. Nat Mater, 3(12): p. 891-895, 2004..
9. Zhang, F., et al., Polymer-Coated Nanoparticles: A Universal Tool for Biolabelling Experiments. Small, 7(22): p. 3113-3127, 2011.
10. Liong, M., et al., Carboxymethylated Polyvinyl Alcohol Stabilizes Doped Ferrofluids for Biological Applications. Advanced Materials, 22(45): p. 5168-5172, 2010.

Keywords: development; synthesis; functionalization biological evaluation of USPIOs; Design; ultrasmall iron oxide nanoparticles cancer imaging

  • Poster
    Nanotechitaly, 21.-23.11.2012, Venice, Italy

Publ.-Id: 17871

Fe-doped InN layers grown by molecular beam epitaxy

Wang, X.; Liu, S.; Ma, D.; Zheng, X.; Chen, G.; Xu, F.; Tang, N.; Shen, B.; Zhang, P.; Cao, X.; Wang, B.; Huang, S.; Chen, K.; Zhou, S.; Yoshikawa, A.

Fe-doped InN have been grown by molecular-beam-epitaxy. It is found that Fe-doping leads to drastic increase of residual electron concentration, which is different from semi-insulating property of Fe-doped GaN. However, this heavy n-type doping can't be fully explained by Fe-concentration. Further analysis shows that more unintentionally-doped impurities such as hydrogen and oxygen are incorporated with increasing [Fe] and surface is degraded with high density pits, which probably are the main reasons for electron generation and mobility reduction. Photoluminescence of InN is gradually quenched by Fe-doping. It shows that Fe-doping is one of good choices to control electron density in InN.

Keywords: Fe-doping; InN; MBE

Publ.-Id: 17870

Copper binding to S100A12: suggested role in oxidative modification of lipids and proteins.

Pietzsch, J.

kein Abstract verfügbar

  • Poster
    22nd IUBMB & 37th FEBS, 04.-09.09.2012, Sevilla, Spain
  • Abstract in refereed journal
    FEBS journal 279(2012), 200

Publ.-Id: 17869

Protein and non-protein biomarkers in melanoma: a critical update.

Tandler, N.; Mosch, B.; Pietzsch, J.

Melanoma is the most malignant type of all skin neoplasms. Its worldwide incidence has steadily increased during the past decades, suggesting a probable melanoma ‘epidemic’. Although current clinical, morphologic, and histopathologic methods provide insights into disease behavior and outcome, melanoma is still an unpredictable disease. Once in an advanced stage, it remains a disastrous affliction with scarce therapeutic options. Therefore, significant efforts need to be made in finding informative biomarkers or surrogate markers that could aid or improve early diagnosis of melanoma, its correct staging, the discrimination of other pathological conditions as well as indicate patients’ prognosis or the most appropriate therapeutic regimes. Ideally these markers are secreted into body fluids and easily amenable to the design of non-invasive clinical tests. A critical view on the current debate on serologic protein markers, e.g., lactate dehydrogenase, tyrosinase, and melanoma inhibiting activity, and some selected non-protein markers, e.g., 5-Scysteinyl-dopa and circulating nucleic acids, will be offered and novel innovative approaches currently being explored will be discussed. Special emphasis is put on the S100 family of calcium binding proteins that is more and more emerging as a potentially important group of both molecular key players and biomarkers in the etiology, progression, manifestation, and therapy of neoplastic disorders, including malignant melanoma. Notably, S100B and, possibly, other S100 proteins like S100A4 are assumed to fulfill requirements which make them strong biomarker candidates in melanoma. Moreover, S100 proteins receive attention as possible targets of therapeutic intervention moving closer to clinical impact.

Keywords: Diagnostic markers; Melanomata; Molecular targets; Pigment cells; Prognostic markers; Serological markers; Skin cancer; Stem cell-like markers; S100 proteins; Therapy monitoring

Publ.-Id: 17868

Evaluation of metabolically stabilized 18F-labeled bombesin analogs for imaging GRP receptors in prostate cancer

Richter, S.; Wuest, M.; Krieger, S. S.; Parry, J. J.; Rogers, B.; Bergmann, R. K.; Wuest, F.

Objectives: According to GLOBOSCAN 2008 the worldwide prostate cancer incidence rates will increase to about 1.7 million new cases per year in 2030. In recent years, bombesin and bombesin analogs have attracted much attention as high affinity and selectivity ligands for the gastrin-releasing peptide (GRP) receptor. The GRP receptor was found to be overexpressed and implicated in a variety of human tumors including prostate cancer. Radiolabeled bombesin and bombesin analogues belong to an interesting class of new diagnostic probes for molecular imaging of GRP receptor-expressing prostate cancer. This study describes the synthesis and radiopharmacological evaluation of a high affinity and metabolically stabilized 18F-labeled bombesin analog for PET imaging of GRP receptors in prostate cancer. Methods: Three modified bombesin analogs bearing an aminovaleric (BBN-1, BBN-2), or an aminooctanoic acid linker (BBN-3) were tested in a competitive binding assay against 125I-[Tyr4]-BBN for their binding to the GRP receptor. A calcium release assay in human prostate cancer cells (PC3) was performed to determine agonistic or antagonistic behaviour. The derivative with the highest affinity to GRP (BBN-2) was selected to be conjugated with the prosthetic labeling agent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) in borate buffer (pH=8.2) for 30 min at 40°C to synthesize the desired 18F-labeled bombesin analog. Tumor-targeting of [18F]BBN-2 was evaluated in PC3 tumor-bearing male nude mice with biodistribution experiments (mean ± SD) and dynamic small animal PET studies. Results: The competitive binding assay revealed IC50-values between 8.7 and 16.7 nM for BBN-1, BBN-2 and BBN-3 against 125I-[Tyr4]-BBN versus 3.0 nM for I-[Tyr4]-BBN. All three stabilized bombesin analogs are GRP receptor antagonists. 18F-labeled [18F]BBN-2 was prepared in 30% radiochemical yield (based upon [18F]SFB) within 80 min including HPLC purification, evaporation of HPLC eluent and formulation in 0.9% saline. The radiochemical purity exceeded 95%, and the specific activity was determined to be 20 GBq/µmol. [18F]BBN-2 showed reasonable metabolic stability in mouse blood resulting in 65% of intact radiolabeled peptide after 60 min p.i.. Uptake of [18F]BBN-2 into PC3 tumors was 2.75±1.82 %ID/g after 5 min and 2.45±1.25 %ID/g after 60 min p.i.. The receptor specificity of [18F]BBN-2 was confirmed by effective blocking of the radiotracers uptake in the presence of non-radioactive BBN-2 resulting in 0.76±0.51 %ID/g at 60 min p.i. (n=4; p<0.05). Dynamic PET imaging resulted in SUV60min values of 0.58 for [18F]BBN-2 versus 0.24 (n=2) for [18F]BBN-2 with BBN-2 pre-dosing in PC3 tumors. Conclusions: The present study showed that 18F-labeled bombesin analog [18F]BBN-2 is a suitable PET radiotracer with favourable metabolic stability for molecular imaging of GRP receptor-positive prostate cancer.

  • Lecture (Conference)
    World Molecular Imaging Congress (WMIC) 2012, 05.-08.09.2012, Dublin, Ireland

Publ.-Id: 17867

Biodistribution of 68Ga-Labeled DOTA-Bisphosphonates

Bergmann, R.; Meckel, M.; Kubicek, V.; Roesch, F.

Aim: Main indications of oncologic skeletal imaging are metastatic diseases in skeleton, bone pain in patients with known cancer, and primary bone tumors. Benign bone diseases like pediatric/adult back pain, bone viability and Paget's disease are also important indications of skeletal imaging. There are numerous studies with [18F]fluoride PET demonstrating the clinical utility. Similar characteristics show Tc-99m-labeled bisphosphonates. Combining the bone seeking properties, the advantages of PET, and the potential labeling with therapeutic radionuclides we studied DOTA-phosphonates radiolabeled with [68Ga]Ga3+. Methods: The following macrocyclic tetraaza based phosphonate chelators were used BPAMD ((4-{[(bis-phosphonomethyl) carbomoyl]methyl}-7,10-bis-(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl)-acetic acid, BPAPD ((4-{[(bis-phosphonopropyl)carbomoyl]methyl}-7,10-bis-(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl)-acetic acid and BPPED Tetraethyl 10-{[(2,2-bis-phosphonoethyl)hydroxyphosphoryl]methyl}-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid. The DOTA based phosphonate ligands were labeled with [68Ga]GaCl3. The radiochemical purity of the labeled products was >95% determined with radio thin-layer chromatography. The biodistribution and biokinetics were compared with [18F]fluoride and [99mTc]Tc-MDP in Wistar rats using dissection, small animal PET and SPECT. All activity concentration data were calculated as SUV. Results: The compounds were labeled with high yields in ammonium acetate buffer with 68Ga, followed by a purification step using a cation exchange resin. High uptake values were detected for all 68Ga-phosphonates in the femura. The accumulation of [68Ga]BPPED in the bone was the highest and comparable with the uptake of [18F]Fluoride and [99mTc]Tc-MDP. The blood clearance of the [68Ga]BPPED was the fastest with a biexponential kinetics and half-life of 0.4 min and 6.9 min. The [68Ga]BPPED bone to blood ratio was also superior, however, not so large like of [18F]Fluoride and [99mTc]Tc-MDP. Conclusion: The [68Ga]BPPED showed in a preclinical setting excellent characteristics for skeletal imaging. It seems to be also a potential candidate for radionuclide therapy in oncology.

  • Poster
    World Molecular Imaging Congress (WMIC) 2012, 05.-08.09.2012, Dublin, Ireland

Publ.-Id: 17866

Investigations of unstable flows in magnetic fields relevant for industrial applications

Eckert, S.; Gerbeth, G.; Pal, J.; Räbiger, D.; Shevchenko, N.; Timmel, K.; Vogt, T.

Various types of magnetic fields are applied for electromagnetic flow control in many industrial applications such as metallurgy, casting, crystal growth or electrochemistry. The first part of this paper considers the electromagnetic damping of instabilities by DC magnetic fields (so-called “Electromagnetic Brakes”), which are exploited for casting of steel or aluminum. The magnetic field tends to damp 3D flow perturbations leading to the development of 2D flow structures aligned with the magnetic field direction. However, this effect is not equivalent to a complete damping of turbulent fluctuations as it might be expected at a first glance. The magnetic field application may even enhance local velocity fluctuations in the continuous casting process. This feature that a DC magnetic field may give rise to non-steady, non-isotropic flow structures has to be taking into account for designing of tailored magnetic fields in the continuous casting process.
AC magnetic fields are used in metallurgy and crystal growth for melt stirring or the suppression of instabilities, respectively. The second part of this contribution provides a brief insight into flow phenomena in a liquid metal column resulting from the application of diverse AC magnetic fields, for instance time-modulated or superposed fields.

Keywords: Liquid metal; flow instability; electromagnetic fields; electromagnetic flow control

  • Invited lecture (Conferences)
    European GDR Dynamo & MHD Days 2012, 01.-04.10.2012, Nice, France

Publ.-Id: 17865

Magnetic Mn5Ge3 nanocrystals embedded in crystalline Ge: a magnet/semiconductor hybrid synthesized by ion implantation

Zhou, S.; Zhang, W.; Shalimov, A.; Wang, Y.; Huang, Z.; Buerger, D.; Mücklich, A.; Zhang, W.; Schmidt, H.; Helm, M.

The integration of ferromagnetic Mn5Ge3 with the Ge matrix is promising for spin injection in a silicon-compatible geometry. In this paper, we report the preparation of magnetic Mn5Ge3 nanocrystals embedded inside the Ge matrix by Mn ions implantation at elevated temperature. By X-ray diffraction and transmission electron microscopy, we observe crystalline Mn5Ge3 with variable size depending on the Mn ion fluence. The electronic structure of Mn in Mn5Ge3 nanocrystals is 3d6 configuration, the same as in bulk Mn5Ge3. A large positive magnetoresistance has been observed at low temperatures. It can be explained by the conductivity inhomogeneity in the magnetic/semiconductor hybrid system.

Keywords: Magnetic nanocrystals; Ion implantation; Magnetoresistance

Publ.-Id: 17864

Ferromagnetic InMnAs on InAs Prepared by Ion Implantation and Pulsed Laser Annealing

Zhou, S.; Wang, Y.; Jiang, Z.; Weschke, E.; Helm, M.

Ferromagnetic InMnAs has been prepared by Mn ion implantation and pulsed laser annealing. The InMnAs layer reveals a saturated magnetization of 2.6 µB/Mn at 5 K and a perpendicular magnetic anisotropy. The Curie temperature is determined to be 46 K, which is higher than those in previous reports with similar Mn concentrations. Ferromagnetism is further evidenced by the large magnetic circular dichroism.

Keywords: Ferromagnetic semiconductors; Ion implantation; Pulsed Laser annealing

Publ.-Id: 17862

Depth profile of the tetragonal distortion in thick GaMnAs layers grown on GaAs by Rutherford backscattering/channeling

Zhou, S.; Chen, L.; Shalimov, A.; Zhao, J.; Helm, M.

We provide a direct measurement of the tetragonal distortion in thick GaMnAs as a function of depth by Rutherford backscattering combining with channeling. The thick GaMnAs film is tetragonally strained and the tetragonal distortion is found to be depth independent. Our finding excludes strain relaxation as the origin of the uniaxial in-plane magnetic anisotropy observed in GaMnAs.

Keywords: Rutherford backscattering/channeling spectrometry

Publ.-Id: 17861

The chemical way to ion irradiation

Faßbender, J.

Local proton irradiation causes a chemical reaction that leads to nanopatterned magnetic media. The technique has strong potential for improving high-density data storage and other types of applications involving nanostructuring of materials.

Keywords: Ion irradiation; ion implantation; magnetism

Publ.-Id: 17860

Topology and origin of effective spin meron pairs in ferromagnetic multilayer elements

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

We report on pairs of converging-diverging spin vortices in Co/Rh/NiFe trilayer disks. The lateral magnetization distribution of these effective spin merons is directly imaged by means of element-selective x-ray microscopy. By this method, both the divergence and circulation states of the individual layers are identified to be antisymmetric. Reversal measurements on corresponding continuous films reveal that biquadratic interlayer exchange coupling is the cause for the formation of the effective meron pairs observed. Furthermore their three-dimensional magnetization structure is determined by micromagnetic simulations. It is shown that in order to reduce magnetic surface and volume charges the magnetic induction aligns along a flux-closing torus. This toroidal topology enforces a symmetry break, which links the core polarities to the divergence configuration.

Keywords: spin vortex; spin meron; vortex coupling; interlayer coupling; topology; x-ray microscopy

Publ.-Id: 17859

Library services of the Helmholtz-Zentrum Dresden-Rossendorf

Reschke, E.

In this slide show some topics of the library services will be presented, for example search for books, for journal articles, to use the SFX Linking service, how to use the licensed datatbasaes from home, publishing services of the library.

Keywords: Online catalogue; interlibrary loan; Linking services; document request; copyright; open access

  • Invited lecture (Conferences)
    7. Doktorandenseminar im IFA Schöneck, 08.-10.10.2012, Schöneck/Vogtl., Germany

Publ.-Id: 17858

Functional arterial spin labeling: Optimal sequence duration for motor activation mapping in clinical practice

Raoult, H.; Ferré, J.-C.; Petr, J.; Bannier, E.; Stamm, A.; Barillot, C.; Gauvrit, J.-Y.

Purpose: To determine the minimal optimal fASL sequence duration allowing steady and reproducible motor activation mapping.
Materials and methods: Three MRI sessions including fASL and BOLD fMRI sequences were performed on 12 healthy subjects at 3T with a 32-channel coil. The raw 7 min fASL sequence was truncated to obtain six fASL sequences with durations ranging from 1 to 6 min. All the resulting fASL activations were compared between themselves and with both the 7 min fASL and BOLD activations. Quantitative parameters assessed activation location (activated volume, barycenter and distance between barycenters), activation quantification (activation-related cerebral blood flow), and intra-individual reproducibility across fMRI sessions.
The statistical analysis was based on ANOVA and Tukey’s multiple comparisons.
Results: Four min fASL achieved steady location and quantification of activation with the activated volume corresponding to 81% of the 7 min fASL volume and a barycenter located 1.2 mm from the 7 min fASL barycenter and 3.0 mm from the BOLD fMRI barycenter. Four min fASL reproducibility was high and statistically equivalent to 7 min values.
Conclusion: A 4 min fASL sequence is thus a reliable tool for motor activation mapping and suitable for use in clinical practice.

Publ.-Id: 17857

Spectroscopic evidence of NOx formation and band-gap narrowing in N-doped TiO2 films grown by pulsed magnetron sputtering

Gago, R.; Redondo-Cubero, A.; Vinnichenko, M.; Lehmann, J.; Munnik, F.; Palomares, F. J.

N-containing TiO2 (TiO2:N) films have been grown by reactive pulsed magnetron sputtering (RPMS) with different N2/O2 mixtures and substrate temperatures (Ts) up to 450 °C. In this way, highly-doped films (N between 5 and 8 at.%) have been produced, as derived by elastic recoil detection analysis. The structural properties have been studied by grazing-incidence X-ray diffraction (GIXRD), X-ray absorption near-edge structure (XANES) and X-ray photoemission spectroscopy (XPS). On unheated substrates, the films are X-ray amorphous and N incorporation induces a transformation from rutile-like to highly disordered anatase-like structures. The crystal growth is enhanced by increasing Ts, being the effect larger for doped films. In this way, nearly single-phase (nanocrystalline) anatase TiO2:N films are achieved. The latter can be related to the imprinted anatase-like character by N incorporation observed on unheated substrates. XANES reveals that N sites are preferentially in the form of N2 or NOx (nitrite-like) complexes for growth on unheated and heated substrates, respectively. The dominant formation of NOx structures is corroborated by XPS, together with a small contribution of N at substitutional sites. Spectroscopic ellipsometry shows an effective reduction of the optical band-gap for doped films. A maximum decrease of ~0.3 eV at Ts =450 °C is observed, which correlates with a rigid red-shift of the valence band XPS spectra. The spectroscopic results indicate that band-gap narrowing is due to N interstitials as NOx complexes.

Publ.-Id: 17856

Nanopatterning dynamics on Si(100) during oblique 40-keV Ar+ erosion with metal codeposition: Morphological and compositional correlation

Redondo-Cubero, A.; Gago, R.; Palomares, F. J.; Mücklich, A.; Vinnichenko, M.; Vazquez, L.

The formation and dynamics of nanopatterns produced on Si(100) surfaces by 40-keV Ar+ oblique (α = 60◦) bombardment with concurrent Fe codeposition have been studied. Morphological and chemical analysis has been performed by ex situ atomic force microscopy, Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and scanning and transmission electron microscopies. During irradiation, Fe atoms incorporated into the target surface react with Si to form silicides, a process enhanced at this medium-ion energy range. The silicides segregate at the nanoscale from the early irradiation stages. As the irradiation proceeds, a ripple pattern is formed without any correlation with silicide segregation. From the comparison with the pattern dynamics reported previously for metal-free conditions, it is demonstrated that the metal incorporation alters both the pattern dynamics and the morphology. Although the pattern formation and dynamics are delayed for decreasing metal content, once ripples emerge, the same qualitative pattern of morphological evolution is observed for different metal content, resulting in an asymptotic saw-tooth-like facetted surface pattern. Despite the medium ion energy employed, the nanopatterning process with concurrent Fe deposition can be explained by those mechanisms proposed for low-ion energy irradiations such as shadowing, height fluctuations, silicide formation and segregation, ensuing composition dependent sputter rate, and ion sculpting effects. In particular, the interplay between the ion irradiation and metal flux geometries, differences in sputtering rates, and the surface pattern morphology produces a dynamic compositional patterning correlated with the evolving morphological one.

Publ.-Id: 17855

Uncertainties in Activity Calculations of different Nuclides in Rector Steels by Neutron Radiation

Konheiser, J.; Ferrari, A.

Activation processes in a nuclear power plant are mainly due to neutron reactions. The determination of the neutron fluences in the reactor pressure vessel (RPV) is therefore the main task of the reactor dosimetry and the good experience for the activity evaluation has to be used. From 2005 to 2009 trepans were gained from the RPV of decommissioned nuclear power plant in Greifswald for the embrittlement investigation. For the first time, samples could be taken from the inner part of the RPV and activity measurements were performed. Experimental results were obtained for 93Nb, 63Ni and 99Tc. The calculations of the neutron fluences were carried out with the TRAMO Monte Carlo code. Based on these fluence values, the time-dependent activities of different nuclides were estimated. The calculated/experimental (C/E) activity ratios for the selected samples fluctuate between 0.37 and 0.91 for Niobium, while for 63Ni and 99Tc they are approximately between 0.6 and 0.91. The influence of different parameters on the results, for example the boron acid concentration, the thermal data and the local position, are here investigated and discussed.

Keywords: Monte Carlo calculation; decommissioning; neutron fluence calculation; activity calculations

  • Lecture (Conference)
    12th International Conference on Radiation Shielding (ICRS-12) 17th Topical Meeting of the Radiation Protection and Shielding Division of the American Nuclear Society (RPSD-2012), 02.-07.09.2012, Nara, Japan

Publ.-Id: 17854

Using statistical measures for automated comparison of in-beam PET data

Kuess, P.; Birkfellner, W.; Enghardt, W.; Helmbrecht, S.; Fiedler, F.; Georg, D.

Purpose: Positron emission tomography (PET) is considered to be the state of the art technique to monitor particle therapy in vivo. To evaluate the beam delivery the measured PET image is compared to a predicted β +-distribution. Nowadays the range assessment is performed by a group of experts via visual inspection. This procedure is rather time consuming and requires well trained personnel. In this study an approach is presented to support human decisions in an automated and objective way.
Methods: The automated comparison presented uses statistical measures, namely, Pearson’s correlation coefficient (PCC), to detect ion beam range deviations. The study is based on 12 in-beam PET patient data sets recorded at GSI and 70 artificial beam range modifications per data set. The range modifications were 0, 4, 6, and 10 mm water equivalent path length (WEPL) in positive and negative beam directions. The reference image to calculate the PCC was both an unmodified simulation of the activity distribution (Test 1) and a measured in-beam PET image (Test 2). Based on the PCCs sensitivity and specificity were calculated. Additionally the difference between modified and unmodified data sets was investigated using the Wilcoxon rank sum test.
Results: In Test 1 a sensitivity and specificity over 90% was reached for detecting modifications of ±10 and ±6 mm WEPL. Regarding Test 2 a sensitivity and specificity above 80% was obtained for modifications of ±10 and −6 mm WEPL. The limitation of the method was around 4 mm WEPL.
Conclusions: The results demonstrate that the automated comparison using PCC provides similar results in terms of sensitivity and specificity compared to visual inspections of in-beam PET data. Hence the method presented in this study is a promising and effective approach to improve the efficiency in the clinical workflow in terms of particle therapy monitoring by means of PET.

Keywords: in-beam PET; particle therapy monitoring; Pearson’s correlation coefficient

Publ.-Id: 17853

Abiotic reductive immobilization of U6+ by biogenic mackinawite

Veeramani, H.; Scheinost, A. C.; Monsegue, N.; Qafoku, N. P.; Kukkadapu, R.; Newville, M.; Lanzirotti, A.; Pruden, A.; Murayama, M.; Hochella, M.F.

During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in-situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze abiotic U6+ reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe1+xS, x = 0 to 0.11) to reduce U6+ abiotically was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U6+ indicate the formation of nanoparticulate UO2. This study suggests the relevance of Fe(II) and sulfide bearing biogenic minerals in mediating abiotic U6+ reduction, an alternative pathway in addition to direct enzymatic U6+ reduction.

Keywords: abiotic reduction; uranium; mackinawite

Publ.-Id: 17852

2-Carbaborane-3-phenyl-1H-indoles—Synthesis via McMurry Reaction and Cyclooxygenase (COX) Inhibition Activity

Laube, M.; Neumann, W.; Scholz, M.; Lönnecke, P.; Crews, B.; Marnett, L. J.; Pietzsch, J.; Kniess, T.; Hey-Hawkins, E.

Cyclooxygenase-2 (COX-2) inhibitors have been in the focus of medicinal chemistry for years and many compounds exhibiting high selectivity and affinity were developed. As carbaboranes represent interesting pharmacophores as phenyl mimetics in drug development, this paper presents the synthesis of carbaboranyl derivatives of COX-2-selective 2,3-disubstituted indoles. Despite the lability of carbaboranes under reducing conditions, 2-carbaborane-3-phenyl-1H-indoles could be synthesized by McMurry cyclization of the corresponding amides. While the meta-carbaboranyl-substituted derivatives (3a-c) lacked COX inhibition activity, the orthocarbaboranyl analog (3d) was active but showed a selectivity shift towards COX-1.

Publ.-Id: 17851

Microbial life in flooded underground uranium mines in Saxony

Gagell, C.; Arnold, T.; Röske, I.

First results with regard to microbial life in flooded underground uranium mines in Saxony are presented.

  • Poster
    HZDR Doktorandenseminar, 10.10.2012, Schöneck, Deutschland

Publ.-Id: 17850

Laser-induced spectroscopy - A method for the determination of complexation behaviour of metals by organic ligands

Lindner, K.; Günther, A.; Bernhard, G.

Presentation of the complexation of Uranium(VI) with selected Schiff bases in methanol investigated by cryo-TRLFS and fs-TRLFS.

Keywords: cryo-TRLFS; fs-TRLFS; Uranium(VI); Schiff Bases

  • Poster
    PhD seminar 2012, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 17849

Investigation of the mobility of uranium (VI) in argillaceous rock at higher salinity

Fritsch, K.; Schmeide, K.

Three types of rock are considered for nuclear waste repositories: salt domes, crystalline rock and argillaceous rock. In this work, clay minerals and natural argillaceous rock are the subject of interest. North German clay deposits have high ionic strength pore water, up to 4 mol L-1. Therefore in the event of container failure, the nuclear waste will be in an environment of high salinity. To study the retention of radionuclides in clays in salinar systems, the experiments in the current project are carried out at high ionic strengths. Previous research(1) at HZDR investigated U(VI) sorption and diffusion at Opalinus clay and kaolinite in natural pore water and sodium perchlorate at low ionic strengths.

Keywords: nuclear waste repositories; uranium sorption; argillaceous rock; clay; uranium

  • Poster
    PhD seminar 2012, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 17848

Krein spaces and PT Quantum Mechanics

Günther, U.

A few basic facts about PT Quantum Mechanics (PTQM) are presented. Specifically, the underlying mathematical structures are briefly sketched, including Krein spaces (Hilbert spaces endowed with indefinite metric structures), J-selfadjointness, spectral singularities and PT phase transitions, the C-operator and the mapping between local PTQM and, in general, nonlocal conventional QM. The features are illustrated by following expamples: PT-symmetric Bose-Hubbard models (which may describe e.g. Bose-Einstein condensates with well balanced particle injection and extraction) and PT-symmetric brachistochrones and tachistochrones. Finally, recent realizations and applications in optical systems and microwave billiards are discussed --- including corresponding experiments.

Keywords: PT quantum mechanics; Krein spaces; spectral singularities; phase transitions; nonlocal quantum mechanics; Bose-Hubbard model; Bose-Einstein condensate; quantum brachistochrone; tachistochrone; optical systems; microwave billiards

  • Invited lecture (Conferences)
    Physics Meeting in Amazonia, 24.-28.09.2012, Belem, Brazil

Publ.-Id: 17847

Stabilization of prolate deformation at high spin in 75Kr

Steinhardt, T.; Eberth, J.; Skoda, S.; Thelen, O.; Schwengner, R.; Dönau, F.; Plettner, C.; Schnare, H.; de Angelis, G.; Napoli, D. R.; Farnea, E.; Gadea, A.; Jungclaus, A.; Lieb, K. P.; Wadsworth, R.

The neutron-deficient nucleus 75Kr has been studied in two EUROBALL experiments. The analysis yielded a considerably extended level scheme including two newly observed excited high spin bands. The results are interpreted in the framework of the cranked Nilsson-Strutinsky approach. The calculations compare well to the experimentally established level scheme and predict the nucleus to be mainly prolate or triaxially deformed at high spin. Evidence for an oblate-prolate shape coexistence could not be found at high spin.

Keywords: Nuclear structure; silicon detectors; cranked Nilsson-Strutinsky model; neutron detectors; EUROBALL; HPGe detectors; gamma-ray spectroscopy

Publ.-Id: 17846

Synthesis and characterization of a percolating, ferromagnetic, Mn-rich Ge:Mn nanonet with hysteretic transport properties

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

The coupling of the magnetization state with the electrical transport properties of a magnetic semiconductor is one big step to new spintronics devices. The coupling can be proved by SQUID magnetization and Hall resistance measurements. In a previous work we fabricated ferromagnetic Ge:Mn by Mn ion implantation and pulsed laser annealing (PLA) and observed a clear hysteretic Hall resistance correlated with the magnetization below 10 K [1]. Recently, by applying optimized PLA conditions, we fabricated a percolating, Mn-rich Ge:Mn nanonet with hysteretic Hall resistance up to 30 K [2]. This nanonet is embedded in crystalline Ge:Mn between 5 nm and 40 nm under the sample surface. The reason for the formation of the nanonet is a constitutional undercooling of the liquid Ge-Mn-alloy during the recrystallization process using a relatively long pulse length of 300 ns which helped to imprint an optimal temperature profile during PLA [3]. We applied etching to confirm the contribution of the nanonet to the electrical transport properties. In the future such nanonets may be used to spin-polarize free charge carriers in magnetic semiconductors at room temperature. Because the nanonet can be selectively etched, substrates with ordered “nano-channels” can be fabricated which may be also useful in the field of nanoimprint-lithography. [1] S. Zhou et al., Phys. Rev. B 81, 165204 (2010) [2] D. Bürger et al., Appl. Phys. Lett. 100, 012406 (2012) [3] J. Narayan, J. Appl. Phys. 52, 1289 (1981)

Keywords: pulsed laser annealing; pulsed laser melting; ion implantation; Hall resistance; ferromagnetism; constitutional supercooling; nanonet

  • Lecture (Conference)
    E-MRS 2012 Fall Meeting, 17.-21.09.2012, Warschau, Polen

Publ.-Id: 17845

Hydrogen interaction with defects in ZnO

Lukac, F.; Cizek, J.; Vlcek, M.; Prochazka, I.; Vlach, M.; Anwand, W.; Brauer, G.; Traeger, F.; Rogalla, D.; Becker, H.-W.; Wagner, S.; Uchida, H.; Bähtz, C.

In the present work hydrothermally grown ZnO single crystals were electrochemically charged with hydrogen. The influence of hydrogen on ZnO microstructure was investigated by positron annihilation spectroscopy (PAS) combined with X-ray diffraction (XRD) using synchrotron radiation. Hydrogen concentration in the samples was determined by nuclear reaction analysis (NRA). It was found that a high concentration of hydrogen can be introduced into ZnO by electrochemical loading. At low concentrations absorbed hydrogen causes elastic volume expansion of ZnO crystal. At higher concentration, hydrogen-induced stresses exceed the yield stress in ZnO and plastic deformation of the crystal takes place leading to formation a defected subsurface layer in the crystals.

Keywords: zinc oxide; hydrogen defects; positron annihilation spectroscopy

Publ.-Id: 17844

Synthesis, in silico, in vitro, and in vivo investigation of 5-[11C]methoxy-substituted sunitinib, a tyrosine kinase inhibitor of VEGFR-2

Caballero, J.; Muñoz, C.; Alzate-Morales, J. H.; Cunha, S.; Gano, L.; Bergmann, R.; Steinbach, J.; Kniess, T.

Sunitinib® (SU11248) is a highly potent tyrosine kinase inhibitor targeting vascular endothelial growth factor receptor (VEGFR). Radiolabeled inhibitors of receptor tyrosine kinases (RTKs) might be useful tools for monitoring RTKs levels in tumor tissue giving valuable information for anti-angiogenic therapy. Herein we report the synthesis of 5-methoxy-sunitinib 5 and its 11C-radiolabeled analogue [11C]-5. The non-radioactive reference compound 5 was prepared by Knoevenagel condensation of 5-methoxy-2-oxindole with the corresponding substituted 5-formyl-1H-pyrrole. A binding constant (Kd) of 20 nM for 5 was determined by competition binding assay against VEGFR-2. In addition, the binding mode of sunitinib® and its 5-methoxy substituted derivative was studied by flexible docking simulations. These studies revealed that the substitution of the fluorine at position 5 of the oxindole scaffold by a methoxy group did not affect the inhibitor orientation, but affected the electrostatic and van der Waals interactions of the ligand with residues near the DFG motif of VEGFR-2. 5-[11C]methoxy-sunitinib ([11C]-5) was synthesized by reaction of the desmethyl precursor with [11C]CH3I in the presence of DMF and NaOH in 17±3% decay-corrected radiochemical yield at a specific activity of 162-205 GBq/µmol (EOS). In vivo stability studies of [11C]-5 in rat blood showed that more than 70% of the injected compound was in blood stream, 60 min after administration.

Keywords: sunitinib®; VEGFR; docking; molecular dynamics; MM-GBSA; carbon-11; radiolabeling

Publ.-Id: 17843

High-field magnetism and magnetoacoustics in uranium intermetallic antiferromagnets

Andreev, A. V.; Skourski, Y.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.

We report on studies on the magnetic and magnetoacoustic properties of uranium intermetallic antiferromagnets UCo2Si2, UCu0.95Ge, UIrGe and U2Ni2Sn in pulsed magnetic fields up to 60 T, where they undergo metamagnetic transitions. The measurements were performed in the temperature range from 1.4 to 100 K. The magnetic ordering and the metamagnetic transitions are accompanied by pronounced anomalies in the ultrasound velocity and the ultrasound attenuation. All studies were performed on single crystals grown by the Czochralski method in a tri-arc furnace.

Publ.-Id: 17842

Interplay between crystal field splitting and Kondo effect in CeNi9Ge4-xSix

Gold, C.; Gross, P.; Peyker, L.; Eickerling, G.; Simeoni, G. G.; Stockert, O.; Kampert, E.; Wolff-Fabris, F.; Michor, H.; Scheidt, E.-W.

The pseudo-ternary solid solution CeNi9Ge4-xSix (0 ≤ x ≤ 4) has been investigated by means of x-ray diffraction, magnetic susceptibility, specific heat, electrical resistivity, thermopower and inelastic neutron scattering studies. The isoelectronic substitution of germanium by silicon atoms causes a dramatic change of the relative strength of competing Kondo, RKKY an crystal field (CF) energy scales. The strongest effect is the continuous elevation of the Kondo temperature TK from approximately 3.5 K for CeNi9Ge4 to about 70 K for CeNi9Si4. This increase of the Kondo temperature is attended by a change of the CF level scheme of the Ce ions. The interplay of the different energy scales results in an incipient reduction of the ground state degeneracy from an effectively fourfold degenerate non-magnetic Kondo ground state with unusual non-Fermi-liquid features of CeNi9Ge4 to a lower one, followed by an increase towards a sixfold, fully degenerate ground state multiplet in CeNi9Si4 (TK ~ ΔCF).

Publ.-Id: 17841

Advanced biotechnology for extraction and recovery of metals

Raff, J.; Lehmann, F.; Moll, H.; Kutschke, S.; Pollmann, K.

In an era of dwindling resources and rising prices new procedures for the exploitation, beneficiation and recycling of especially industrial relevant metals are in demand. Such elements are essential for modern high tech industry and development of future techno¬logies. Interestingly, nature itself offers promising approaches in these fields. Some organisms are thusly able to mobilize metals not only from ores but also from electrical and electronical equipment waste by bioleaching [Bosecker K. 1997, Brantley et al. 2001, Brandl H. et al. 2001]. Bioleaching is already used for the large scale production of copper especially in ores with low metal content. Furthermore, other species or biomolecules are able to selectively bind and accumulate metals [Pollmann et al. 2006], allowing the con-struction of metal selective filter materials. In addition, some organisms trigger the formation of minerals or are able to form different kinds of biominerals by themselves, representing also a way to separate metals [Wang X. and W.E.G. Müller 2009]. In combination with established physical and chemical processes, such biotechnological approaches have a high potential to improved metal beneficiation and recycling.
Within the biotechnology group at the Helmholtz Institute Freiberg for Resource Technology such new procedures for extracting, treating and recycling metals such as copper or rare earths using microbes are under development. Whereas the bioleaching related research is just at the beginning and the investigation of biomineralization pro¬cesses for metal separation is planned for the future, the group has long-term experience in the investigation of the interaction of metals with biomass and especially in the selective metal binding by proteins and other bioligands. Within radioecological research, bacterial isolates were investigated that possess so called surface-layer (S-layer) proteins, forming a closed protein lattice on many bacteria and archaea protecting the cells from being affected by environ¬mental influences. In case of such bacteria living in highly heavy metals contaminated environments, their S-layers have high metal binding capacity and high stability. Furthermore, they possess different metal binding sites. There are many less specific binding sites, binding large amounts of precious metals such as Pt, Pd and Au as well as radioactive metals such as U. Metals such as Fe, Co, Ni, Cu and Zn are not bound or only in small quantities. In addition, there are several highly specific binding sites, binding Ca, Cm and Eu. First results indicates, that the binding affinity of these metals differs significantly. As the metal binding additionally depends on the pH and differs from metal to metal, S-layer proteins possess a high application potential for the specific separation of industry relevant metals.

Keywords: Biotechnology; biosorption; bioleaching; metals

  • Lecture (Conference)
    GeoHannover 2012, 01.-03.10.2012, Hannover, Deutschland

Publ.-Id: 17840

QCM-D a versatile tool for biosorption processes

Suhr, M.; Drechsel, N.; Günther, T.; Matys, S.; Raff, J.; Pollmann, K.

Bacterial isolates from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) possess high affinities to heavy metals e.g. uranium. This binding effect is caused by the components of the bacterial cell wall, mainly affected by surface layer proteins.
Aim of this work is to investigate metal interaction processes like biosorption with Gram-positive bacteria and their main cell wall components.
In addition to the standard analytical methods, the quartz crystal microbalance with dissipation monitoring is used to track and control the biological layer formation and metal deposition. This method allows the real time detection of sorption processes on a molecular level and gives further information to viscoelastic properties. Subsequent atomic force microscopy (AFM) studies enable the imaging of bio nanostructures and reveal complex information of structural properties.
Some selected results of these experiments will be shown on this poster.

Keywords: QCM-D; bacteria; Biosorption; metals; S-layer; lipids; interaction; AFM

  • Poster
    7th Annual Ph.D. seminar, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 17839

Do microorganisms influence the transport of radionuclides in Uranium-contaminated underground mines?

Zirnstein, I.; Arnold, T.; Röske, I.

Microorganisms are ubiquitous, also in extreme environments e.g. in environments with high salinity, in very hot and acid waters or underneath thick slides of ice. In the former uranium mine Königstein exist also an extreme environment, due to the very low pH (2.7), the high concentrations of heavy metals and uranium. Nevertheless microorganisms in form of biofilms exist in a depth of 250 meters in this mine. Since 2010 the underground mine was flooded and is no longer accessible for sampling. For investigations in mine biofilms the microorganisms in the mine water have to be cultivated above ground in flow cells or in a biofilm reactor. The microorganisms in the mine water should grow on special biofilm carriers in the reactor. Our studies may contribute to new remediation measures for heavy metal contaminated mine waters.

  • Lecture (Conference)
    7th PhD Seminar, 08.-10.10.2012, Schöneck, Germany

Publ.-Id: 17838

Biofilms in a Uranium contaminated acid mine drainage environment

Zirnstein, I.; Arnold, T.; Krawczyk-Bärsch, E.; Wobus, A.; Röske, I.

The Königstein mine is currently in the process of remediation and represents an underground acid mine drainage (AMD) environment. 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). 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 (snottites) or as acid streamers in the drainage channels. Previously conducted studies on the bacterial diversity in both biofilm communities showed that beta-proteobacterium affiliated with Ferrovum myxofaciens, also designated “Ferribacter polymyxa” were identified as dominating bacterial species. The eukaryotic diversity of the Königstein biofilms was analysed by molecular methods, i.e. 18S rDNA PCR, cloning and sequencing 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).
Since 2010 the underground mine was flooded and is no longer accessible for sampling. For investigations in mine biofilms the microorganisms in the mine water have to be cultivated above ground in flow cells or in a biofilm reactor. The microorganisms in the mine water should grow on special biofilm carriers in the reactor. Our studies may contribute to new remediation measures for heavy metal contaminated mine waters.

  • Poster
    1st Transnational Workshop "GETGEOWEB": Genomics and Transcriptomics in Geobiotechnolgy and White Biotechnology, 29.-30.10.2012, Freiberg, Germany

Publ.-Id: 17837

Optical Excitation of Josephson Plasma Solitons in a Cuprate Superconductor

Dienst, A.; Casandruc, E.; Zhang, L.; Eckstein, M.; Fausti, D.; Hoffmann, M.; Khanna, V.; Dean, N.; Gensch, M.; Winnerl, S.; Seidel, W.; Pyon, S.; Takayama, T.; Takagi, H.; Cavalleri, A.

Josephson Plasma Waves are linear electromagnetic modes that propagate along the planes of cuprate superconductors, sustained by oscillatory tunnelling supercurrents. These waves exhibit a plasmonic resonance in the GHz , to THz frequency range, depending on the interlayer coupling strength. For strong electromagnetic fields, the supercurrents approach their critical value and the electrodynamics become highly nonlinear , . Josephson Plasma Solitons (JPS) are breather excitations , that emerge in this regime, bound vortex/antivortex pairs that self-localize , , and propagate without dispersion. We experimentally excite such solitons using intense narrowband radiation from an infrared Free Electron Laser, tuned to the 2-THz Josephson Plasma Resonance of La1.84Sr0.16CuO4. The JPS is revealed by the appearance of long-lived transparency window in the spectral region immediately below the plasma resonance, which is opaque to small-amplitude waves. This reshaping of the optical properties originates from Fano-type coupling between probe waves and the JPS. Optical control of solitonic excitations in superconductors opens up possibilities in THz opto-plasmonics or in the manipulation of high-Tc superconductivity.

Publ.-Id: 17836

Das Metallbindungsverhalten von Membranen Gram-positiver Bakterien

Drechsel, N.

Für das Verständnis von Mobilität und Stabilität von Metallen, wie z.B. Schwermetallen, in der Umwelt, stellt die Untersuchung der Metallsorption einen wichtigen Faktor dar. Für die weiterführende Erforschung von Wechselwirkungsprozessen der Mikroorganis-men und deren Metallbindungseigenschaften ist es notwendig, die Sorption verschie-dener Metalle durch Mikroorganismen und zellulären Bestandteilen zu untersuchen.
In der vorliegenden Bachelorarbeit werden die Wechselwirkungen von umweltrele-vanten Metallen mit biologischen Komponenten untersucht. Dazu dienen die bak-teriellen Haldenisolate Lysinibacillus sphaericus JG-A12 und Lysinibacillus sp. JG-B53. Diese zeigten bereits in vorangegangenen Untersuchungen sehr hohe Metallbindungs-kapazitäten. Für die Sorptionsversuche werden die Schwer- und Edelmetalle Platin, Palladium, Blei, Cadmium, Europium und Gold und das Halbmetall Arsen verwendet. Durch die Einbeziehung von isolierten Zellwandbestandteilen der Gram-positiven Mikroorganismen, wie z.B. S-Layer-Proteine und Membranlipide sollen genauere Kenntnisse der Sorptionseigenschaften der biologischen Komponenten erlangt werden. Als analytische Verfahren werden die ICP-MS und die QCM-D eingesetzt. Durch einen Vergleich der zwei Bakterien werden unterschiedliche Metallselektivitäten aufgedeckt, die in weiteren Forschungsvorhaben und Anwendungsgebieten Einsatz finden können.

Keywords: Biosorption; QCM-D; Bakterien; S-Layer; Lipide; Metalle; Metallinteraktionen

  • Bachelor thesis
    HZDR und Hochschule Mittweida, 2012
    98 Seiten

Publ.-Id: 17835

Electromagnetic dipole strength up to the neutron separation energy from 196Pt(γ,γ′) and 195Pt(n,γ) reactions

Massarczyk, R.; Schramm, G.; Junghans, A. R.; Schwengner, R.; Anders, M.; Belgya, T.; Beyer, R.; Birgersson, E.; Ferrari, A.; Grosse, E.; Hannaske, R.; Kis, Z.; Kögler, T.; Kosev, K.; Marta, M.; Szentmiklosi, L.; Wagner, A.; Weil, J. L.

The dipole strength in the nucleus 196-Pt was investigated using two different experimental methods. The photon spectrum from the deexcitation of a state after cold neutron capture in 195-Pt is influenced by the dipole strength and nuclear level density in 196-Pt as is also the gamma-ray spectrum from photon scattering on 196-Pt. In a combined analysis of data from the research reactor in Budapest and the bremsstrahlung facility at the ELBE accelerator in Dresden, the GEANT4 code was used to calculate detector response and efficiency. Also the influence of non-nuclear scattered photons was determined and allows us to take into account the continuum of unresolved states. The statistical code gammaDEX was used to estimate branching ratios and compare simulated and experimental spectra. Using information from both experiments it was possible to obtain a temperature parameter of 600\,keV for the constant temperature level density model. For the dipole strength a small extra strength over tail of the Giant Dipole Resonance in the region below the neutron energy separation was found.

Keywords: neutron capture; strength functions; nuclear structure; statistical calculations

Publ.-Id: 17833

From terahertz science and technology to semiconductor quantum structures and back

Helm, M.

I will give an overview about modern terahertz science and technology and discuss some applications of THz radiation. Then I will present the physics of semiconductor quantum wells and show how such structures can be developed into a so-called quantum cascade laser working in the THz range

Keywords: terahertz; laser; semiconductor

  • Invited lecture (Conferences)
    Lecture at Southeastern University, 18.09.2012, Nanjing, China

Publ.-Id: 17832

Process Monitoring of tracer transport through artificial soil with GeoPET

Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.; Enzmann, F.; Khan, F.; Kersten, M.; Stoll, M.; Ritschel, T.; Totsche, K. U.

Positron-Emission-Tomography (PET) enables direct and quantitative monitoring of the spatiotemporal distributions of dissolved inert and/or reactive PET-nuclides and PET-nuclide-labelled compounds during their passage through decimeter-scaled material samples. We apply our biomedical PET-scanner (ClearPET, Raytest) exclusively to geomaterial samples and reach the physical limit of spatial resolution of nearly 1 mm with pico-molar sensitivity.
Artificial soil columns (68.5% fine-medium sand, 25.5% coarse silt, 5% Illit, 1% Goethit) have been prepared in Jena. µCT-images have been produced at the Bundesanstalt für Materialforschung und –prüfung (BAM) and analysed in Mainz. They show layering and inhomogeneous water saturation, yet a roughly homogeneous grain distribution. PET-imaging was conducted during flow-through experiments into the upright column, which is perpendicular to the scanner axis.
First flow experiments have been conducted with – presumably – conservative tracers ([18F]KF (decay time 109.77 min) and Eosin). Conventional break-through curves (BTCs) have been recorded both by fluorescence detection of Eosin and with a Gamma Radioactivity Flow-Through Monitor (Gabi Star, Raytest). From the transport process observation by sequential PET-imaging we could derive longitudinal BTCs during the tracer propagation through the column. Further, it could be shown that 18F- was slightly retarded and - more significantly - the effective pore volume was inhomogeneous (preferential transport through the sample).
These experiments will be repeated on newly constructed columns with plastic endplates (instead of the original stainless steel ones) and an optimized dead volume.
To preliminarily conclude, we demonstrated that the combined tomographic information on pore structure and spatio-temporal transport process observation in a soil model column yields an essential gain in information for describing and parameterizing transport processes, compared to input-output experiments. Such measurements represent the experimental control of ab-initio model simulations of conservative and reactive transport, e.g. [64Cu]MCPA), and of the interpretation of conventional input-output transport experiments, conducted by the partners.

Keywords: Reactive Transport; PET; Process Observation

  • Poster
    Annual Meeting DFG Priority Programme SPP1315 "Biogeochemical Interfaces in Soil", 10.-12.10.2012, Dornburg, Deutschland

Publ.-Id: 17830

Verification of the trigonal-geometry diffusion and SP3 models of the code DYN3D

Duerigen, S.; Nikitin, E.; Mittag, S.

DYN3D is a three-dimensional nodal diffusion code for steady-state and transient analyses of Light-Water Reactors with square and hexagonal fuel assembly geometries, applicable also to innovative reactor concepts. Currently, several versions of the DYN3D code are available including a multi-group diffusion and simplified P3 (SP3) neutron transport option.
In this work, both the diffusion and SP3 method in trigonal geometry are verified by means of fine-mesh homogenized reference solutions. Good agreement is observed for eigenvalues, neutron flux and power distributions. Mesh refinement studies show that the trigonal nodal DYN3D methods converge well to the fine-mesh references. Furthermore, an anisotropic-scattering benchmark problem was chosen to show the advantage of the SP3 method over the diffusion approach.

Keywords: simplified P3; SP3; nodal method; trigonal; triangular; hexagonal; DYN3D; mesh refinement

  • Open Access Logo Contribution to proceedings
    22nd SYMPOSIUM of ATOMIC ENERGY RESEARCH (AER) on VVER Reactor Physics and Reactor Safety, 01.-05.10.2012, Pruhonice, Czech Republic
  • Lecture (Conference)
    22nd SYMPOSIUM of ATOMIC ENERGY RESEARCH (AER) on VVER Reactor Physics and Reactor Safety, 01.-05.10.2012, Pruhonice, Czech Republic

Publ.-Id: 17829

Femtosecond Level Synchronization of a Linac Based super-radiant THz Facility

Kuntzsch, M.; Röser, F.; Lehnert, U.; Gensch, M.; Bousonville, M.; Schlarb, H.; Stojanovic, N.; Vilcins-Czvitkovits, S.

The superconducting radiofrequency (SRF) electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is currently upgraded with an SRF Gun and a femtosecond (fs) electron beamline to enable continuous wave operation with bunch charges of up to 1 nC and bunch durations down to 100 fs (RMS). The new femtosecond electron beamline will be used to drive two coherent THz sources and one X-ray source based on Thomson scattering. The two different THz sources, one narrow bandwidth undulator source and one broad bandwidth coherent transition/diffraction source, are guided into a dedicated THz Laboratory where they can be combined with various fs-laser systems. For the planned THz pump laser probe experiments, synchronization of the external pump-probe lasers on the fs- level is essential. Our approach is based on an optical synchronization system, adapted from a similar system installed at FLASH [*]. That system will be installed in collaboration between DESY and HZDR. In this contribution we will discuss the layout of the synchronization scheme and first ideas for measurements of the arrival time jitter of the THz pulses to evaluate the achieved degree of timing stability.

Keywords: ELBE Synchronization THz

  • Poster
    Free-Electron Laser Conference, 26.-31.08.2012, Nara, Japan

Publ.-Id: 17828

Optical Synchronization at HZDR

Kuntzsch, M.

The superconducting electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf is currently upgraded to enable continuous wave operation with bunch charges of up to 1 nC and durations down to 200 fs (RMS). The new beamline will drive a THz source and an X-ray source based on Thomson scattering. In collaboration with DESY, Hamburg, an optical synchronization system based on a mode locked master laser is currently being set up to ensure timing stability on the few 10 fs level. This talk is giving an overview on different synchronization concepts, the implementation at ELBE and the first comissioning results.

Keywords: ELBE Synchronization

  • Invited lecture (Conferences)
    1st ARD Workshop ST3 “ps-fs Electron and Photon Beams”, 21.-23.08.2012, Hamburg, Germany

Publ.-Id: 17827

Temperature grid sensor for the measurement of spatial temperature distributions

Schäfer, T.; Schubert, M.; Hampel, U.

This paper presents results of the development and application of a new temperature grid sensor based on the wire-mesh sensor principle. The grid sensor consists of a matrix of 256 Pt1000 platinum chip resistors and an associated electronics that measures the grid resistances with a multiplexing scheme at high speed. The individual sensor elements can be spatially distributed on an object surface and measure transient temperature distributions in real time. The advantage, compared to other temperature field measurement approaches, such as infrared cameras, is that the object under investigation can be thermally insulated and radiation properties of the surface do not play a role for measurement accuracy. The sensor principle is therefore suited for various industrial monitoring applications. Its applicability for surface temperature monitoring has been demonstrated by conduction and analysis of heating and mixing experiments in a vessel.

Keywords: temperature grid sensor; temperature measurement; wire-mesh sensor; thermal surface monitoring

Publ.-Id: 17826

REECOB: 20 Years of Rare Earth Element Calcium Oxoborates Crystal Growth Research

Möckel, R.; Reuther, C.; Götze, J.

Rare earth element calcium oxoborates (REECOB, REECa4O[BO3]3) represent a group of materials for non-linear optics and with useful piezoelectric properties under high-pressure and high-temperature conditions making it applicable as sensor materials in extreme environments. High-quality crystals with appropriate size are generally grown from a melt by the Czochralski method. This article presents a compilation and comparison of crystal growth parameters and properties of members of the REECOB group from the literature with those of own growth experiments. Recent studies provided new data concerning the melting temperature of REECOB members, such as ca. 1475°C for SmCa4O(BO3)3 (SmCOB). In addition, first data on the change of thermal expansion coefficients of SmCOB are presented and discussed.

Keywords: REECOB; oxoborate; Czochralski

Publ.-Id: 17825

Investigation of the Eu(III)-B(OH)3-Organic System

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

Borates and organic matter (humic and fulvic acids, small organic molecules) are ubiquitous compounds in the environment (rocks, soils, natural waters).
Concerning the safety and risk assessment for a nuclear waste repository the interaction between trivalent lanthanides and actinides and borates is interesting to study. Borates occur in salt deposits (possible host rock for nuclear waste repositories) and can be release due to corrosion of vitrified waste block (borosilicate glass) and storage containers.
The investigations concentrate on the reaction between Eu(III) and borates in aqueous solution.
For boric acid (B(OH)3) no and for polyborates weak complexation properties concerning Eu(III) are observed.
The complexation between Eu(III) and salicylate is influenced by boric acid due to the formation of a borate ester.
Furthermore at pH 6 the formation of a solid Eu borate species in presence of polyborates is observed. The formation of the solid Eu borate species depends on the polyborate concentration and ionic strength.

Keywords: lanthanides; actinides; europium; boric acid; borates; polyborates

  • Poster
    Annual Ph.D. seminar, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 17824

Broadband, diode pumped Yb:SiO2 multicomponent glass laser

Loeser, M.; Röser, F.; Reichelt, A.; Siebold, M.; Grimm, S.; Litzkendorf, D.; Schwuchow, A.; Kirchhof, J.; Schramm, U.

Fabrication, spectroscopic properties, and laser performance of a Yb:SiO2 multicomponent glass have been investigated in this paper. The glass system composed of SiO2, Al2O3, and La2O3 excels in terms of a high thermal stress resistance compared to other laser glasses. The laser experiments were conducted with a 3.4 mm thick and 0.9 mol. % Y2O3 doped sample. A maximum slope efficiency of 51%, a maximum optical to optical efficiency of 42%, and a tuning range from 1010–1090 nm was realized. Due to the promising laser properties and a straightforward fabrication technique it may well qualify as an alternative gain medium in high-energy, ultrashort pulse laser systems.

Keywords: Lasers, diode-pumped; Lasers, solid-state; Lasers, tunable; Rare earth and transition metal solid-state lasers; Laser materials; Lasers, ytterbium

  • Optics Letters 37(2012)19, 4029-4031

Publ.-Id: 17823

Hades experiments: investigation of hadron in-medium properties

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

Hadron modications in nuclear matter are discussed in connection to chiral symmetry restoration and/or hadronic many body eects. Experiments with photon, proton and heavy ion beams are used to probe properties of hadrons embedded in nuclear matter at different temperatures and densities. Most of the information has been gathered for the light vector mesons ρ, ω and φ. HADES is a second generation experiment operating at GSI with the main aim to study in-medium mass modication by means of dielectron production at SIS18/Bevelac energy range. Large acceptance and excellent particle identication capabilities allows also for measurement of strangeness production. These abilities combined with the variety of beams provided by the SIS18 allows for characterization of properties of the dense baryonic matter properties created in heavy ion collisions at these energies. A review of recent experimental results obtained by HADES is presented, with main emphasis on hadron properties in nuclear matter.

Publ.-Id: 17822

High rate deposition of amorphous hydrogenated carbon films by hollow cathode arc PECVD

Zimmermann, B.; Fietzke, F.; Klostermann, H.; Lehmann, J.; Munnik, F.; Möller, W.

Amorphous hydrogenated carbon films (a-C:H) are of increasing importance in science and applications. However, most deposition techniques applied suffer from a low deposition rate. In this paper, a high rate process based on hollow cathode arc PECVD is presented. A magnetically enhanced hollow cathode arc plasma has been used to activate the precursor acetylene. The argon-acetylene plasma has been characterized by energy-resolved mass spectrometry revealing a large variety of dissociation and polymerization products as well as their kinetic energy distributions, which are related to the spatial distribution of ion generation. A-C:H layers have been deposited on flat substrates with rates of up to 1 µm/min. Depending on the deposition conditions, polymeric, graphitic, and diamond-like carbon films with a nanoindentation hardness of 18.2 GPa have been produced and analyzed by Raman spectroscopy and scanning electron microscopy. In order to obtain the film composition, elastic recoil detection analysis and Rutherford backscattering spectrometry have been applied.

Keywords: hollow cathode arc; plasma diagnostics; amorphous hydrogenated carbon; diamond-like carbon; plasma-enhanced chemical vapor deposition; elastic recoil detection analysis

Publ.-Id: 17821

Investigation of upward cocurrent gas-liquid pipe flow using ultrafast X-ray tomography and wire-mesh sensor

Zhang, Z.; Bieberle, M.; Barthel, F.; Szalinski, L.; Hampel, U.

Ultrafast X-ray tomography and wire-mesh sensor as two high-speed imaging modalities were applied to study upward gas-liquid flow in a vertical pipe of 50 mm inner diameter. High speed scanning of the flow cross-section was performed with 2500 frames per second with both modalities. Sequences of two-dimensional distributions of local gas fraction were acquired and further analyzed. Radial profiles of time averaged gas fraction distributions show a good agreement for both imaging techniques. Furthermore radial gas velocity profiles were obtained from a temporal cross-correlation of the image data of both measurement techniques and also bubble size distributions from binarized image data were compared.

Keywords: gas-liquid flow; ultrafast X-ray tomography; wire-mesh sensor

Publ.-Id: 17820

Insider 6 / 2012

Weigl, A.

Mitarbeiterzeitung des HZDR

Keywords: HZDR in-house paper

  • Communication & Media Relations
    Mitarbeiterzeitung 31.07.2012
    8 Seiten

Publ.-Id: 17819

Kelvin probe force microscopy for characterizing functionalized semiconductor surfaces for nano and biotechnologies

Baumgart, C.; Habicht, S.; Feste, S.; Helm, M.; Müller, A.-D.; Schmidt, H.

Kelvin probe force microscopy (KPFM) is one of the most promising non-contact electrical nanometrology technique to characterize functionalized semiconductor. We present its applicability to determine surface-near electrostatic forces in locally doped silicon structures. Those electrostatic forces may be used to position and control nano and biomaterials on doped semiconductor carriers. Furthermore, quantitative dopant profiling by means of KPFM measurements [1] is successfully demonstrated on a conventional static random access memory (SRAM) cell, on cross-sectionally prepared Si epilayers, and on arrays of horizontal Si nanowires [2] by applying a recently introduced new explanation of the measured KPFM signal. Additionally, the influence of local, carrier-depleted space charge regions and of the electric fields across them is discussed. It is explained how drift and diffusion of injected charge carriers in intrinsic electric fields influence the surface-near electrostatic forces [3]. Surface-near electrostatic forces may be enhanced above pn junctions and KPFM is successfully employed to locate pn junctions in doped silicon structures, e.g. along the B-doped and As-doped Si nanowires. [1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B, 80, 085305 (2009). [2] S. F. Feste, J. Knoch, S. Habicht, D. Buca, Q.-T. Zhao, S. Mantl, Solid-State Electronics, 53, 1257 (2009). [3] C. Baumgart, A.-D. Müller, F. Müller, and H. Schmidt, Phys. Stat. Sol. A, 208, 777 (2011) (editor’s choice).

  • Lecture (Conference)
    E-MRS Fall Meeting 2012, 17.-21.09.2012, Warsaw, Poland

Publ.-Id: 17818

Optical probing of TNSA acceleration conditions

Metzkes, J.; Zeil, K.; Kluge, T.; Kraft, S. D.; Bussmann, M.; Cowan, T. E.; Schramm, U.

Laser-plasma based accelerators, where a high intensity laser interacts with a solid target, represent a promising concept for compact and cost-efficient ion sources.
As the acceleration takes place on ultra-fast timescales and very small spatial scales of only a few µm, information about the acceleration processes in the plasma are generally derived indirectly, e.g. through particle or radiation diagnostics. Optical probing techniques however can give direct access to the plasma dynamics on the fs to ps timescale.
In this poster we will present pump-probe experiments performed at the high-intensity laser DRACO at the HZDR, Germany. Seeking information about the conditions of the critical density surface in the plasma, we simply image the probe reflected from the target surface without doing tomography. The curvature of the reflecting critical surface translates into characteristic angular patterns in the reflected probe beam which can be traced back to the original surface shape using a ray-tracing model of the experiment.
In our experiments, the pump beam was the 150 TW DRACO beam with a pulse length of 30 fs and a central wavelength of 800 nm. The probe beam was derived from the mean beam, frequency doubled, and had a pulse duration of ~100fs. Both beams were synchronized and the probe could be delayed with respect to the main beam with a resolution of ~200 fs. The imaging of the probe was performed with a large-aperture objective yielding a high spatial resolution of ~2µm.
As a result, we compared the critical surface deformation and dynamics for different target materials (metal and silicon) and target shapes, observing a strong influence of the lateral target size.

  • Poster
    32nd European Conference on Laser Interaction with Matter (ECLIM 2012), 10.-14.09.2012, Warschau, Polen

Publ.-Id: 17817

Time resolved FT-IR difference spectroscopy of vibrational control experiments on bacteriorhodopsin

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

Our goal is to investigate how photoreactions of proteins can be controlled by intense THz radiation tuned in resonance to specific vibrational modes, in analogy to coherent control experiments conducted by femtosecond (fs) NIR laser pulses [1]. For this we combine a time-resolved IR difference spectroscopic setup with uniquely intense, tunable narrow bandwidth THz radiation at the picosecond (ps) beamline of the THz free electron laser FELBE [2].

  • Poster
    Jahrestagung der Deutschen Gesellschaft für Biophysik (DGfB), 24.-29.09.2012, Göttingen, Deutschland

Publ.-Id: 17816

Direct observation of prompt pre-thermal laser ion sheath acceleration

Metzkes, J.; Zeil, K.; Kluge, T.; Bussmann, M.; Cowan, T.; Kraft, S.; Sauerbrey, R.; Schramm, U.

High-intensity laser-plasma ion generation is promising as a compact, low-cost proton source for applications like ion beam therapy. Using a femtosecond table-top laser system, we study the intra-pulse phase of the laser driven proton acceleration and show that protons efficiently gain energy in these early times [1].

In recent laser-ion acceleration experiments performed at the 150 TW Draco laser in Dresden, Germany, we have demonstrated the importance of a precise understanding of the electron dynamics in solids on an ultra-short time scale. For example, with ultra-short laser pulses a description based purely on the evolution of a thermal electron ensemble, as in standard TNSA models, is not sufficient anymore. Rather, non-thermal effects during the ultra-short intra-pulse phase of laser-electron interaction in solids become important for the acceleration of ions when the laser pulse duration is in the order of only a few 10s of femtoseconds. While the established maximum ion energy scaling in the TNSA regime goes with the square root of the laser intensity, for such ultra short pulse durations the maximum ion energy is found to scale linear with laser intensity [2], motivating the interest in such laser systems.
Investigating the influence of laser pulse contrast, laser polarization and laser incidence angle on the proton maximum energy and angular distribution, we present recent advances in the description of the laser interaction with solids, focusing on the implications of intra-pulse non-thermal phenomena on the ion acceleration.


1. K. Zeil, J. Metzkes, T. Kluge, M. Bussmann, T.E. Cowan, S. D. Kraft, R. Sauerbrey and U. Schramm, Direct observation of prompt pre-thermal laser ion sheath acceleration, Nature Communications 3 (874), 2012

2. K. Zeil, S. D. Kraft, S. Bock, M. Bussmann, T.E. Cowan, T. Kluge, J. Metzkes, T. Richter, R. Sauerbrey and U. Schramm, Scaling of proton energies in ultrashort pulse laser plasma acceleration, New Journal of Physics 12 (045015), 2010

  • Lecture (Conference)
    32nd European Conference on Laser Interaction with Matter (ECLIM 2012), 10.-14.09.2012, Warschau, Polen
  • Lecture (Conference)
    SPIE Optics + Optoelectronics 2013, 15.-18.04.2013, Prague, Czech Republic

Publ.-Id: 17815

Segmentierung von Gasblasen aus Röntgentomographiedaten von zweiphasigen Rohrströmungen

Banowski, M.; Bieberle, M.; Wagner, M.; Lucas, D.; Hoppe, D.; Harnisch, J.; Hampel, U.

In der Präsentation wird das bildgebende Messverfahren „ultraschnelle Röntgentomographie“ vorgestellt sowie die Versuchsanlage TOPFLOW kurz erläutert. Die verschiedenen, zur Segmentierung von Gasblasen entwickelten und getesteten Algorithmen werden ebenfalls vorgestellt und deren Ergebnisse anhand von Phantommessungen qualitativ und quantitativ verglichen. Die jeweiligen Vor- und Nachteile der Algorithmen werden beispielhaft gezeigt und mögliche weitere Lösungsansätze diskutiert.

Keywords: two-phase; measuring technique; X-ray; tomography; pipe flow; bubble detection

  • Lecture (Conference)
    DBV-Workshop - Workshop für Digitale Bildverarbeitung, 04.09.2012, Zittau, Deutschland

Publ.-Id: 17814

Ion mass and energy distributions in the DC magnetron sputtering of AZO from metallic and ceramic targets

Wilde, C.; Cornelius, S.; Vinnichenko, M.

technique to fabricate transparent conductive oxides. Especially in large-scale solar cell production a combination of good electrical and optical properties along with low production costs is of crucial importance. AZO can be sputter-deposited reactively (i.e. with addition of O2) using a metallic target or non-reactively using a ceramic target. On the one hand, non reactive processes are easy to control and they provide high-quality films with high reproducibility, but on the other hand, ceramic Al-doped ZnO targets are much more expensive compared to the metallic ones. Therefore, the understanding of differences between these two techniques is of vital importance for the improvement of process control, stability and, finally, properties of reactively sputtered AZO, especially in large-scale fabrication. In this contribution we report results of systematic comparison of ion mass and energy distributions in magnetron plasma using reactive and non reactive DC process of AZO film growth. The measurements were performed with the orifice of mass-spectrometer facing the magnetron target race track. We present the results of comparison in a broad range of particles’ energy for different deposition conditions with a main focus on high energetic ions and fragments. It is shown that in case of sputtering of ceramic target the ratio of high to low energetic ions is substantially higher than that of metallic target. The contribution from high energetic particle fragments is also more pronounced in that case. Therefore, from point of ion energy distributions, a well established reactive process has a potential to provide better properties for AZO layer.

Keywords: AZO; TCO; mass spectrometry; ion energy distribution; DC magnetron sputtering

  • Poster
    13th International Conference on Plasma Surface Engineering (PSE 2012), 09.-14.09.2012, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 17813

Resonance production in p+p, p+A and A+A collisions measured with HADES

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

The knowledge of baryonic resonance properties and production cross sections plays an important role for the extraction and understanding of medium modications of mesons in hot and/or dense nuclear matter. We present and discuss systematics on dielectron and strangeness production obtained with HADES on p+p, p+A and A+A collisions in the few GeV energy regime with respect to these resonances.

Publ.-Id: 17812

Dipole strength on the tail of the giant dipole resonance

Schwengner, R.

Keywords: Photon scattering; bremsstrahlung; monoenergetic polarized gamma rays; photoabsorption; dipole strength; reaction rates; statistical models; RPA; QPM

  • Invited lecture (Conferences)
    VIII. Tours Symposium on Nuclear Physics and Astrophysics, 02.-07.09.2012, Black Forest, Deutschland

Publ.-Id: 17811

Morphology induced two-magnon scattering in thin NiFe films

Körner, M.; Lenz, K.; Fritzsche, M.; Facsko, S.; Fassbender, J.

When studying magnetization dynamics of thin magnetic films, intrinsic as well as extrinsic spin relaxation processes have to be taken into account. While intrinsic processes, summarized as Gilbert damping, are well known and studied for the last decades, the focus now has shifted to extrinsic contributions. In this context the two-magnon scattering (TMS) is of particular interest. This type of scattering is induced within thin magnetic films by defects and inhomogeneities. It was shown that periodic magnetic patterns can serve as defect structure, e.g. by periodically varying the magnetization saturation using ion beam irradiation combined with periodic sample patterning by electron beam lithography. Due to irradiation of the material a local variation of the magnetic properties can be achieved [1], where the TMS strength is set by the periodicity of the modification. However, directly patterning the material is time consuming and not suitable for large scale manufacturing. Hence a self-organized nanoscale patterning is more favorable. Broad ion beam erosion is a well-established technique for structuring large surface areas. By varying the irradiation parameters, e.g. ion energy, fluence, and incident angle sinusoidally modulated surfaces (ripples) can be created with a periodicity tuneable over a wide range [2]. Growing magnetic materials on these ripples imprints the corrugation to the material and induces by dipolar effects a wavelength dependent uniaxial magnetic anisotropy (UMA). Furthermore the imprinted corrugation can serve as a spin wave scattering center, modifying the two-magnon damping contribution. Here we present the influence of the substrate surface corrugation on the magnetic damping properties of 30 nm thin Ni80Fe20 (Py) films grown by molecular beam epitaxy at room temperature on rippled Si substrates. Due to ion beam erosion of flat Si as well as natural oxidation of the substrate prior to film deposition, Py films grown on top exhibit a polycrystalline structure that suppresses the intrinsic magneto-crystalline anisotropy almost completely. The in-plane magnetostatic and dynamic properties of these samples were investigated by means of angular and frequency dependent vector network analyzer ferromagnetic resonance (VNA-FMR).
Starting with a planar reference sample the angular together with the frequency dependent linewidth measurements reveal a Gilbert dominated relaxation process, whereby no TMS can be observed. Due to the polycrystalline film structure, only a very weak magnetic anisotropy is observed. This uniaxial magnetic anisotropy (UMA) has a two-fold symmetry and is randomly aligned with respect to the sample edges. Changing to rippled substrates the grown Py film maintains its polycrystalline structure. Depending on the ripple wavelength λ, ranging from 25 nm to 230 nm, an UMA is induced with its easy axis always aligned parallel to the ripple ridges. The strength of the UMA decays with increasing wavelength and is strongest for λ=25 nm. In this case no influence of the corrugation on the damping is observed. This changes drastically for samples with a higher wavelength of λ=230 nm. While the UMA is reduced to the value of the planar reference sample the linewidth measurements now show clear indications for defect induced TMS. This is shown in Fig. 1a, where the peak-to-peak linewidth is plotted as a function of the in-plane magnetic field angle (open circles). Modeling the linewidth results in a Gilbert contribution that is constant for all in-plane field orientations. Additionally an angle dependent TMS contribution is found, which consists of a small four-fold and a dominating two-fold (uniaxial) part. Thereby the direction of minimal linewidth aligns parallel with the ripple ridges, which in turn defines the uniaxial symmetry of the damping. Fig. 1b depicts the frequency dependent measurements parallel (red squares) and perpendicular (green circles) to the ripple ridges. In parallel configuration the damping is purely Gilbert-like, as already observed in the reference measurement. The monotonous increase of the linewidth with applied microwave frequency is instead lost in case of the perpendicular geometry. Here, a preeminent peak is observed with its center at f=10 GHz. Following the description of Barsukov et al. [1] this excessive linewidth increase is a result of defect induced TMS, where the width and frequency position of the peak is determined by the scattering potential, created by the corrugation of the film. The origin and wavelength dependence of these morphology induced linewidth manipulation will be discussed in detail.
We thank I. Barsukov, J. Lindner, and P. Landeros for fruitful discussions. This work is supported
by DFG grant no. FA 314/6-1.
1) I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)
2) J. Fassbender et al., New J. Phys. 11, 125002 (2009)

  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012, 24.-28.09.2012, Shanghai, China

Publ.-Id: 17810

Frequency dependence of spin relaxation in periodic systems

Körner, M.; Barsukov, I.; Römer, F. M.; Lenz, K.; Meckenstock, R.; Hemken To Krax, S.; Banholzer, A.; Grebing, J.; Lindner, J.; Farle, M.; Fassbender, J.

In the presence of a periodic scattering potential the spin relaxation in ultrathin ferromagnets is not a monotonous function of the frequency. The spin relaxation rate is found to substantially increase at characteristic frequencies related to the periodicity of the magnon scattering potential (see Fig. 1). This is experimentally confirmed in Ni80Fe20 thin films by artificially introducing different scattering periodicities [1]. The lateral struvturing of the thin film is achieved by Cr+ ion implantation with at an energy of 5 keV and a fluence of 5 × 10E15 ions/cm2 through a 100 nm thick polymethyl methacrylate (PMMA) resist covering the whole sample area. Electron beam lithography was used to fabricate 1 mm long-stripes of width s0 and spacing s1 (i.e., with periodicity l = s0 + s1) within the PMMA resist so that the surface becomes Cr-implanted in a stripewise manner. Frequency dependent Ferromagnetic resonance spectroscopy reveals that the magnetic damping may be increased at specific frequencies by a factor of up to 100%.
This work is supported by the DFG, SFB 491, Grants No. FA 314/6-1 and No. FA 314/3-2.
[1] I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)

  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012, 24.-28.09.2012, Shanghai, China

Publ.-Id: 17809

Magnonic Crystals By Means Of Patterned Ion Implantation

Fassbender, J.; Körner, M.; Lenz, K.; Strache, T.; Banholzer, A.; Grebin, J.; Lindner, J.; Barsukov, I.; Römer, F.; Meckenstock, R.; Hemken To Krax, S.; Farle, M.; McCord, J.; Mönch, I.; Mattheis, R.

Ion implantation is a standard process in semiconductor tech¬nology. However, since a doping of metals typically does not have such a tremendous effect as compared to semiconductors ion implantation in metals to achieve a desired electrical, optical or magnetic property is much less explored. A combination of litho-graphy and ion implantation to achieve a lateral ion implantation pattern is a novel route to design and construct artificial materials like photonic or magnonic crystal which rely on the local band gap or spin wave dispersion engineering [1].
The contribution will provide an overview over the different physical mechanisms which allow modifying and tailoring the dynamical magnetic properties, i. e., magnetic damping even in an anisotropic fashion, aiming at the creation of new functional materials. In one example [2] it is demonstrated that the mag¬netic damping parameter in a ferromagnetic/antiferromag¬ne¬tic/ferro¬magnetic trilayer stack can be continuously and spatially varied between two extremal values (see Fig. 1). In a second example [3] the creation of a lateral magnetization pattern by ion implantation gives rise to additional and anisotropic relaxation channels. Potential areas of application are magnonic crystals and band-stop filters in the GHz range.

Acknowledgement: This work was supported by Deutsche Forschungsgemeinschaft SFB491, FA 314/3, FA314/6-1 and MC 9/7.

[1] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
[2] J. McCord, T. Strache, I. Mönch, R. Mattheis, J. Fassbender, Phys. Rev. B 83, 224407 (2011).
[3] I. Barsukov, F. M. Römer, R. Meckenstock, K. Lenz, J. Lindner, S. Hemken to Krax, A. Banholzer, M. Körner, J. Grebing, J. Fassbender, M. Farle, Phys. Rev. B 84, 140410(R) (2011).

Keywords: ion irradiation; ion implantation; magnetic films; modification; magnonics; dynamics

  • Lecture (Conference)
    18th International Conference on Ion Beam Modification of Materials (IBMM2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 17808

Tailoring perpendicular anisotropy in Co/Pd multilayers by ion irradiation

Osten, J.; Greene, P.; Ende, T.; Iwata, N.; Lenz, K.; Liu, K.; Fassbender, J.

A major obstacle towards the increase in areal magnetic recording density and the decrease in bit size is the retention of thermal stability while maintaining reasonable write fields. Materials with graded magnetic anisotropy are promising candidates to solve this problem. Here we demonstrate the approach of using post-deposition ion irradiation to tailor the perpendicular anisotropy in Co/Pd multilayer thin films. The films, with uniform as well as graded perpendicular anisotropy, were synthesized by magnetron sputtering. Based on TRIDYN simulations, different primary ion energies are chosen to achieve varying penetration depths of the ions creating a depth dependent anisotropy grading. Before and after ion irradiation, MOKE as well as magnetometry measurements were employed to detect the changes of the magnetic properties. In the irradiated layer of the film domain nucleation is promoted (Fig. 1). Upon ion irradiation, the Co/Pd films exhibit reduced coercivity and remanence with increasing energies. Higher ion energies have a more pronounced effect on reducing the perpendicular anisotropy. The archived anisotropy grading also depends on the original film stack.

Keywords: ion irradiation; magnetism; magnetic recording; thermal stability; graded media

  • Poster
    18th International Conference on Ion Beam Modification of Materials (IBMM 2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 17807

Self-consistent isotopic comparative method used to determine dependence of secondary-yields on oxygen concentration in Si-O system up to 33%

Dupuy, J. C.; Prudon, G.; Dubois, C.; Kögler, R.; Akhmadaliev, S.; Perrat-Mabilon, A.

Yields of B+,O+,Si+, B-, O-, and Si- versus oxygen concentration were determined in Si under Ar+ bombardment using the isotopic comparative method (ICM). Samples containing a near-uniform low concentration of 18O and a Gaussian-like profile of 16O with high concentration were fabricated by multi-energy ion implantation. ICM allows to determine the oxygen concentration profile by secondary-ion mass spectrometry. The ion yield can be measured as a function of the oxygen concentration up to 33 at%. Whatever the charge of the secondary ions, all relative ion yields are enhanced with increasing oxygen concentration. Very strong matrix effects due to oxygen are found for B+ (>100), whereas moderate or slight matrix effects are found for Si+ and O- (>10) and for Si-, B-, and O+ (<4). Relative ion yields of B+ and Si+ differ versus oxygen, whereas they are identical for B- and Si-. The relative ionization probability versus oxygen for Si+ agrees very well with the results of William´s group.

Keywords: SIMS; matrix effect; ion yield; silicon-oxygen system; ICM

  • Surface and Interface Analysis 45(2013)1, 369-372
    Online First (2012) DOI: 10.1002/sia.5108

Publ.-Id: 17806

Zeitaufgelöste (4D) Rekonstruktion von in-beam PET Daten für das Dosismonitoring bei der Bestrahlung bewegter Zielvolumina in der Ionentherapie

Laube, K.; Bert, C.; Fiedler, F.; Helmbrecht, S.; Priegnitz, M.; Saito, N.; Enghardt, W.

no abstract available

Keywords: in-beam PET; moving targets; ion beam therapy

  • Lecture (Conference)
    43. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik e. V. (DGMP), 26.-29.09.2012, Jena, Deutschland

Publ.-Id: 17805

Time resolved (4D) reconstruction of in-beam PET data for the dose monitoring of intra-fractionally moving target volumes in ion beam therapy

Laube, K.; Bert, C.; Fiedler, F.; Helmbrecht, S.; Parodi, K.; Priegnitz, M.; Saito, N.; Enghardt, W.

In-beam positron emission tomography (PET) with a double-head PET scanner has been successfully applied for the in situ dose monitoring of about 440 patients with static tumour entities within a pilot project at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. For future treatment of intra-fractionally moving tumours, mainly located in the lung or liver, a dose monitoring is highly desired since complex beam delivery strategies and continuous respiration-related density changes in the irradiated tissue increase the risk for dose errors. Conventional three-dimensional (3D) in-beam PET measurements taken from moving structures would result in a reproduction of a blurred activity distribution and would, therefore, impede correct dose verification. An implemented motion compensated (4D) reconstruction routine based on the existing 3D Maximum Likelihood Expectation Maximization (MLEM) algorithm has been tested by phantom experiments performed at the GSI facility. Homogeneous polymethyl methacrylate (PMMA) phantoms of dedicated geometries have been irradiated with 12C pencil beams and in-beam PET data acquisition was performed throughout irradiation and additional time beyond to gain better statistics. Motion mitigation techniques of rescanning, gating or tracking have been used for a homogeneous dose deposition in the PMMA targets which performed a one-dimensional cos2- or cos4-shaped motion perpendicular to the beam direction. 4D reconstruction results have been compared to static reference measurements and to reconstruction results without consideration of the
target motion. Evaluation outcome with respect to the conservation of lateral and distal gradients in the reconstructed activity distributions will be shown at the workshop. Furthermore, the acquisition of required input parameters from the accelerator, the motion acquisition and the motion compensation systems and the data handling before reconstruction, like the temporal synchronization of all signals, as well as the necessary improvements for clinical usage of the 4D in-beam PET dose monitoring will be discussed.

Keywords: in-beam PET; moving targets; ion beam therapy; reconstruction

  • Lecture (Conference)
    Tomography, data processing and image reconstruction for medicine and engineering, 10.-12.09.2012, Dresden, Deutschland

Publ.-Id: 17804

Generalizations of Matérn's hard-core point processes

Teichmann, J.; Ballani, F.; van den Boogaart, K. G.

Matérn’s hard-core processes are valuable point process models in spatial statistics. In order to extend their field of application, Matérn’s original models are generalized here, both as point processes and particle processes. The thinning rule uses a distancedependent probability function, which controls deletion of points close together. For this general setting, explicit formulas for first- and second-order characteristics can be given. Two examples from materials science illustrate the application of the models.

Keywords: Point process; marked Poisson process; Matérn hard-core process; dependent thinning; independent thinning; pair correlation function

Publ.-Id: 17803

Entwicklung und Synthese von [18F]Flubatine für die Visualisierung von α4β2 nikotinischen Acetylcholinrezeptoren (nAChRs)

Smits, R.; Hoepping, A.; Fischer, S.; Hiller, A.; Funke, U.; Deuther-Conrad, W.; Steinbach, J.; Sabri, O.; Brust, P.

Ziel: Bei Patienten mit Alzheimer-Demenz (AD) ist die Verfügbarkeit nikotinischer Acetylcholinrezeptoren (nAChR), insbesondere des α4β2 Subtyps im Gehirn reduziert [1]. Die Visualisierung dieser Rezeptoren könnte zu einer frühzeitigen Diagnose der AD beitragen. Die zur Zeit zur Verfügung stehenden Radioliganden haben entweder eine unzureichende Affinität zum Rezeptor oder weisen eine sehr langsame Bindungskinetik auf. Der neue Ligand [18F]Flubatine bietet wesentliche Vorteile. Beide Enantiomere besitzen eine hohe in vitro Affinität [2] und zeigen eine schnelle cerebrale Bindungskinetik in der Maus [3] und im Schwein [4]. Erste humane PET-Studien bestätigen eine hohe Aufnahme im Thalamus, eine geringe unspezifische Bindung und das Erreichen des Bindungsgleichgewichtes in weniger als zwei Stunden. Für die Durchführung von klinischen Studien und für eine potentielle routinemäßige Anwendung war es notwendig, die bestehende Präkursorsynthese zu optimieren. Ein neuer enantiomerenreiner Präkursor soll eine einfache, robuste und effiziente Radiosynthese erlauben, mit dem Ziel der Automatisierung der Tracerproduktion. Zu diesem Zweck wurden eine kleine Bibliothek von Präkursoren mit verschiedenen Schutzgruppen und Abgangsgruppen synthetisiert und getestet.

Methodik: Als Startmaterial für die Synthese der neuen Präkursoren diente das Cbz-geschützte 8-Aza-bicyclo[3.2.1]oct-6-en-3-on, das nach literaturbekannten Verfahren dargestellt wurde. Nach einer reduktiven Heck-Reaktion zur Einführung des Pyridylrestes konnte die C3-Ketofunktion in einer dreistufigen Sequenz deoxygeniert werden. Die Abspaltung der Cbz-Schutzgruppe lieferte den [18F]Flubatine-Standard, dessen Racematspaltung mittels chiraler HPLC gelang. Im Anschluss wurden verschiedene Schutzgruppen und Fluchtgruppen eingeführt, deren [18F]-Markierung untersucht und optimiert wurde. Die Radiomarkierung der verschiedenen Präkursoren erfolgte über ein zweistufiges Verfahren bestehend aus trägerfreier, nucleophiler Radiofluorierung und Abspaltung der Schutzgruppe.

Ergebnisse: Die besten Resultate wurden mit dem Boc-geschützten Trimethylammonium-Präkursor erzielt. Die Ausbeute der unter Phasentransfer-Bedingungen durchgeführten Radiomarkierung betrug 90±5%. Nach Abspaltung der Schutzgruppe mit 1N HCl und Aufreinigung mittels semipräparativer HPLC konnte enantiomerenreines [18F]Flubatine in einer radiochemischen Ausbeute von 70±5% und einer spezifischen Aktivität >750 GBq/µmol erhalten werden.

Schlussfolgerungen: Die Radiosynthese von [18F]Flubatine konnte durch den Einsatz des neuen, enantiomerenreinen Präkursors entscheidend verbessert werden und ermöglicht eine automatisierte Produktion zur klinischen Evaluierung des Radioliganden.

  • Lecture (Conference)
    20. Jahrestagung der AG Radiochemie/Radiopharmazie der DGN, 04.-06.10.2012, Bad Honnef, Deutschland

Publ.-Id: 17802

Severe accident research in the core degradation area: An example of effective international cooperation between the European Union (EU) and the Commonwealth of Independent States (CIS) by the International Science and Technology Center

Bottomleya, D.; Stuckert, J.; Hofmann, P.; Tocheny, L.; Hugon, M.; Journeau, C.; Clément, B.; Weber, S.; Guentay, S.; Hozer, Z.; Herranz, L.; Schumm, A.; Oriolo, F.; Altstadt, E.; Krause, M.; Fischer, M.; Khabensky, V. B.; Bechta, S. V.; Veshchunov, M. S.; Palagin, A. V.; Kiselev, A. E.; Nalivaev, V. I.; Goryachev, A. V.; Zhdanov, V.; Baklanov, V.

The International Science and Technology Center (ISTC) was set up in Moscow to support nonproliferation of sensitive knowledge and technologies in biological, chemical and nuclear domains by engaging scientists in peaceful research programmes with a broad international cooperation. The paper has two following objectives:
1) to describe the organization of complex, international, experimental and analytical research of material processes under extreme conditions similar to those of severe accidents in nuclear reactors and,
2) to inform briefly about some results of these studies.
The main forms of ISTC activity are Research Projects and Supporting Programs. In the Research Projects informal contact expert groups (CEGs) were set up by ISTC to improve coordination between adjacent projects and to encourage international collaboration. The European Commission was the first to use this. The CEG members – experts from the national institutes and industry – evaluated and managed the projects’ scientific results from initial stage of proposal formulation until the final reporting. They were often involved directly in the project’s details by joining the Steering Committees of the project. The Contact Expert Group for Severe Accidents and Management (CEG-SAM) is one of these groups, five project groups from this area from the total of 30 funded projects during 10 years of activity are detailed to demonstrate this: (1) QUENCH-VVER from RIAR, Dimitrovgrad and IBRAE, Moscow, and PARAMETER projects (SF1–SF4) from LUCH, Podolsk and IBRAE, Moscow; these concerned a detailed study of bundle quenching from high temperature; (2) Reactor Core Degradation; a modelling project simulating the fuel
rod degradation and loss of geometry from IBRAE, Moscow; (3) METCOR projects from NITI, St. Petersburg on the interaction of core melt with reactor vessel steel; (4) INVECOR project, NNE Kurchatov City, Kazakhstan; this is a large-scale facility to examine the vessel steel retention of 60 kg corium during the decay heat; and finally, (5) CORPHAD and PRECOS projects, NITI, St. Petersburg undertook a systematic examination of refractory ceramics relevant to in-vessel and ex-vessel coria, particularly examining poorly characterised, limited data or experimentally difficult systems.

Keywords: Severe accident management; core melt down; nuclear reactors; in-vessel melt retention

Publ.-Id: 17801

Impact of 5-lipoxygenase inhibitors on the spatiotemporal distribution of inflammatory cells and neuronal COX-2 expression following experimental traumatic brain injury in rats

Härtig, W.; Michalski, D.; Seeger, G.; Voigt, C.; Donat, C. K.; Dulin, J.; Kacza, J.; Meixensberger, J.; Arendt, T.; Schuhmann, M. U.

Inflammation induced by traumatic brain injury (TBI) is considered as contributor to neuronal death with poor outcome. Although anti-inflammatory strategies were beneficial in experimental TBI, clinical translations mostly failed, probably caused by the complexity of involved cells and mediators. We recently showed in a rat model of controlled cortical impact (CCI) that leukotriene inhibitors (LIs) attenuate contusion growth and improve neuronal survival. This study focuses on spatiotemporal characteristics of macrophages and granulocytes, typically involved in inflammatory processes, and neuronal COX-2 expression. Further, effects of LIs (Boscari/MK-886) were evaluated by quantifying CD68+, CD43+ and COX-2+ cells 24 and 72 h post-CCI in the parietal cortex (PC), CA3 region (CA3r), dentate gyrus (DG) and visual/auditory cortex (v/aC). Correlations were applied to identify inter-cellular relationships. At 24 h, untreated animals showed granulocytes in all regions investigated, decreasing towards 72 h. In contrast, macrophages increased from 24 to 72 h post-CCI in the PC and v/aC. COX-2+ neurones showed no temporal dynamics, except of an increase in the CA3r towards 72 h. Treatment reduced granulocytes at 24 h in the pericontusional penumbra and hippocampus, and reduced macrophages at 72 h in the PC and v/aC. COX-2 expression remained unaffected by LIs, except of time-specific reactions in the DG (increase/decrease at 24/72 h). Interrelations confirmed concomitant cellular reactions beyond initial trauma site. In conclusion, LIs attenuated the cellular inflammatory response following CCI and therefore become attractive as potential treatment strategy. Future studies should clarify region-specific effects and feasible time windows for applying LIs after CCI.

Keywords: Traumatic brain injury; Neuronal death; Macrophage; Granulocyte; COX-2

Publ.-Id: 17800

Reconstruction of Gebel Kamil’s irradiation history

Merchel, S.; Akhmadaliev, S.; Fimiani, L.; Haubold, R.; Herrmann, S.; Korschinek, G.; Ott, U.; Pavetich, S.; Rugel, G.

Data of the lighter cosmogenic radionuclides 10Be, 26Al, 36Cl, and 41Ca are now easily attainable at the accelerator mass spectrometry facility DREAMS [1]. Accompanied by the heavier radionuclides 53Mn and 60Fe, which are measured at the 14 MV tandem at Munich, and stable noble gas nuclides from MPI Mainz, complete and unique exposure histories of extraterrestrial material can be reconstructed.
One of the first meteorites investigated by this team is Gebel Kamil, an ungrouped Ni-rich ataxite that produced an impact crater (Ø: 45 m) in southern Egypt. Two neighboured shrapnel (S) samples and two from the only individual (I) fragment (~83 kg) have been analysed. Comparison with Monte-Carlo calculations of production rates indicate that Gebel Kamil was exposed as a meteoroid body of >120 cm radius. Samples I originate from a moderate shielding of 18-25 cm, whereas samples S are from a deeper position of 53-65 cm. Most reliable 36Cl-36Ar ages of I and S are ~450 Ma calculated after [3].
Ackn.: L. Folco (meteorite) & accelerator crews (support AMS). Ref.: [1] Akhmadaliev et al. (2012) NIMB, in print. [2] Folco et al., Science 329 (2010) 804. [3] Ammon et al., MAPS 44 (2009) 485.

Keywords: cosmogenic; AMS; meteorite

  • Lecture (Conference)
    Joint meeting “Paneth Kolloquium”, “The first 10 million years of the solar system” (DFG SPP 1385) & “MEMIN” (DFG FOR 887), 09.-12.10.2012, Nördlingen, Duetschland

Publ.-Id: 17799

Growth mode and texture development in Ni-Ti shape memory alloy (SMA) films during co-sputtering deposition – An in situ synchrotron radiation study

Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.

In-situ X-ray scattering measurements were carried out during Ni-Ti shape memory alloy film processing at the Rossendorf Beamline (BM20-ESRF). The experiments performed with a two-magnetron sputter deposition chamber mounted into the six-circle diffractometer of the beamline enabled us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters (Ti target power) during film growth. The results show that the type of substrate plays an important role for the preferential orientation of sputtered Ni-Ti films. Amorphous SiO2 and TiN buffer layers were used to successfully control their crystallographic orientations. The deposition conditions leading to films mainly containing grains with (100) or (110) planes of the B2 phase parallel to the film surface are presented. The control of texture is an important achievement since it has a strong influence on the extent of the strain recovery of the Ni-Ti films. The deposition of graded Ni-Ti films by deliberately changing the Ti:Ni ratio, thereby altering microstructure and transformation temperatures across the film thickness, provided significant data for the optimisation of the deposition parameters in order to fabricate films with a “two-way” actuation (films with a combination of superelasticity and shape memory characteristics). This is a plus for the miniaturization of Ni–Ti films based devices in the field of micro-electro-mechanical systems since no consideration has to be paid to a resetting spring.

  • Poster
    MPA 2012 – 6th International Meeting on Developments in Materials, Processes and Applications of Emerging Technologies, 02.-04.07.2012, Alvor, Portugal

Publ.-Id: 17798

Terahertz nonlinear optics of excitons in quantum wells using a free-electron laser

Helm, M.

Keywords: terahertz; quantum well; free electron laser; exciton

  • Invited lecture (Conferences)
    Viennese Symposium on Heterostructures, 07.09.2012, Wien, Österreich

Publ.-Id: 17797

Modification of Ni-Ti surface composition and morphology by plasma immersion ion implantation for biomedical applications

Martins, R. M. S.; Barradas, N.; Alves, E.; Henke, D.; Reuther, H.; Schell, N.; Carmezim, M. J.; Silva, T. M.; Fernandes, J. C. S.

The shape memory effect and superelasticity of Ni-Ti (Nitinol) make it very attractive for biomedical applications. The Ni-Ti alloy (~ 50.4 at.% Ni) selected for this work is austenitic (superelastic) at body temperature. In the frame of the AIM-74 and SPIRIT-77 projects, plasma immersion ion implantation (PIII) has been employed to modify and improve the superficial region of the alloy. The formation of titanium oxynitride (TiNxOy) was achieved by ion implantation of nitrogen. A Ti-rich oxide layer was obtained during the experiments carried out with oxygen. Thus, the parameters to obtain a Ni-depleted surface, which serves as a barrier to out-diffusion of Ni ions from the bulk material, have been successfully established. Furthermore, nanostructured Ni-Ti surfaces have been produced. Synchrotron radiation-based X-ray diffraction data acquired in transmission mode show that the PIII technique only changes the structure of the Ni-Ti alloy top layer preserving superelastic behaviour at body temperature (PIII experiments carried out without intentional heating of the substrate holder). Techniques like thermal oxidation and nitriding also lead to an improved corrosion resistance and Ni-depleted Ni-Ti surface but require high processing temperatures leading to modification of the phase transformation characteristics and loss of specific mechanical properties.

  • Lecture (Conference)
    MPA 2012 - 6th International Meeting on Developments in Materials, Processes and Applications of Emering Technologies, 02.-04.07.2012, Alvor, Portugal

Publ.-Id: 17796

Supernova Dust in Terrestrial Deep-Sea Archives

Feige, J.; Wallner, A.; Fifield, L. K.; Korschinek, G.; Merchel, S.; Rugel, G.; Winkler, S. R.

The long-lived radionuclides 26Al, 53Mn and 60Fe are produced in the late burning phases and during a supernova explosion of a massive star. These nuclides are then ejected into space, condensed into dust and, if the supernova occurs in a close distance to the solar system, might be able to reach the Earth. An indication for a close-by supernova in the past, deduced from a signal about 2 Myr ago, has already been identified in a ferromanganese crust [1]. Deep-sea sediments, with higher accumulation rates, provide a higher time resolution and allows therefore a more precise dating of the signal.
Here, samples of two sediment cores originating from the Indian Ocean are analyzed to search for supernova signals. Currently, the only method sensitive enough to detect these signals is accelerator mass spectrometry. Additionally to the supernova-produced nuclides, 10Be, which is constantly produced by cosmic rays in the Earth's atmosphere, is measured to date the sediment cores. First 10Be and 26Al data are presented and discussed.
[1] Knie, K., et al. (2004), Phys. Rev. Lett. 93, 17.

Keywords: supernovae; AMS; radionuclide

  • Poster
    Joint meeting “Paneth Kolloquium”, “The first 10 million years of the solar system” (DFG SPP 1385) & “MEMIN” (DFG FOR 887), 09.-12.10.2012, Nördlingen, Deutschland

Publ.-Id: 17795

Radiosynthesis of racemic and enantiomerically pure (–)-[18F]flubatine – A promising PET radiotracer for neuroimaging of α4β2 nicotinic acetylcholine receptors

Fischer, S.; Hiller, A.; Smits, R.; Hoepping, A.; Funke, U.; Wenzel, B.; Cumming, P.; Sabri, O.; Steinbach, J.; Brust, P.

(–)-[18F]flubatine is a promising agent for visualization by PET of cerebral α4β2 nicotinic acetylcholine receptors (nAChRs), which are implicated in psychiatric and neurodegenerative disorders. Here, we describe a substantially improved two-step radiosynthesis strategy for (–)-[18F]flubatine, based on the nucleophilic radiofluorination of an enantiomerically pure precursor followed by deprotection of the intermediate. An extensive leaving group/protecting group library of precursors was tested. Application of a trimethylammonium-iodide precursor with a Boc protecting group provided the best results: Labeling efficiencies of 80-95%, RCY of 60±5%, radiochemical purity of >98%, and a specific activity of >350 GBq/µmol. The radiosynthesis is easily transferable to an automated synthesis module.

Keywords: Fluorine-18; Positron emission tomography; Neuroimaging; α4β2 nicotinic acetylcholine receptors; α4β2 ligands; Radiosynthesis; Leaving groups; Protecting groups

Publ.-Id: 17794

PET/MR for therapy response evaluation in malignant lymphoma: initial experience

Platzek, I.; Beuthien-Baumann, B.; Langner, J.; Popp, M.; Schramm, G.; Ordemann, R.; Laniado, M.; Kotzerke, J.; van den Hoff, J.

Object: To evaluate the feasibility of positron emission tomography/magnetic resonance imaging (PET/MR) with 18fluoro-2-deoxyglucose (FDG) for therapy response evaluation of malignant lymphoma.
Materials and methods: Nine patients with malignant lymphoma who underwent FDG-PET/MR before and after chemotherapy were included in this retrospective study. Average time between the two scans was 70 days. The scans were evaluated independently by two nuclear medicine physicians. The Ann Arbor classification was used to describe lymphoma stage. Furthermore, the readers also rated PET image quality using a five point scale. Weighted kappa was used to calculate interrater agreement.
Results: The initial scan showed foci of increased FDG uptake in all patients, with Ann Arbor stage varying between I and IV. In the follow-up examination, all but one patient showed complete response to chemotherapy. PET image quality was rated as very good or excellent for all scans. Interrater agreement was excellent regarding Ann Arbor stage (kappa = 0.97) and good regarding image quality (kappa = 0.41). Conclusion PET/MR shows promising initial results for therapy response evaluation in lymphoma patients.

Keywords: PET; MRI; Lymphoma

  • Open Access Logo Magnetic Resonance Materials in Physics, Biology and Medicine 26(2013)1, 49-55
    Online First (2012) DOI: 10.1007/s10334-012-0342-7

Publ.-Id: 17793

PET/MR in head and neck cancer: initial experience

Platzek, I.; Beuthien-Baumann, B.; Schneider, M.; Gudziol, V.; Langner, J.; Schramm, G.; Laniado, M.; Kotzerke, J.; van den Hoff, J.

Purpose: To evaluate the feasibility of PET/MRI (positron emission tomography/magnetic resonance imaging) with FDG (18F-fluorodeoxyglucose) for initial staging of head and neck cancer.
Methods: The study group comprised 20 patients (16 men, 4 women) aged between 52 and 81 years (median 64 years) with histologically proven squamous cell carcinoma of the head and neck region. The patients underwent a PET scan on a conventional scanner and a subsequent PET/MRI examination on a whole-body hybrid system. FDG was administered intravenously prior to the conventional PET scan (267–395 MBq FDG, 348 MBq on average). The maximum standardized uptake values (SUVmax) of the tumour and of both cerebellar hemispheres were determined for both PET datasets. The numbers of lymph nodes with increased FDG uptake were compared between the two PET datasets.
Results: No MRI-induced artefacts where observed in the PET images. The tumour was detected by PET/MRI in 17 of the 20 patients, by PET in 16 and by MRI in 14. The PET/MRI examination yielded significantly higher SUVmax than the conventional PET scanner for both the tumour (p<0.0001) and the cerebellum (p00.0009). The number of lymph nodes with increased FDG uptake detected using the PET dataset from the PET/MRI system was significantly higher the number detected by the stand-alone PET system (64 vs. 39, p00.001).
Conclusion: The current study demonstrated that PET/MRI of the whole head and neck region is feasible with a wholebody PET/MRI system without impairment of PET or MR image quality.

Keywords: PET/MRI; Head and neck cancer

  • Open Access Logo European Journal of Nuclear Medicine and Molecular Imaging 40(2013), 6-11
    Online First (2012) DOI: 10.1007/s00259-012-2248-z

Publ.-Id: 17792

Intraband carrier dynamics in quantum dots and quantum wells

Bhattacharyya, J.; Zybell, S.; Winnerl, S.; Hopkinson, M.; Wilson, L. R.; Andrews, A. M.; Strasser, G.; Helm, M.; Schneider, H.

Optical properties of self assembled quantum dots (QDs) have dominant inhomogeneous broadening due to the distribution of size and composition of the QDs in the ensemble. The carrier dynamics in such systems is affected by the neighboring dots due to interdot diffusion of carriers. In this work we investigate the intraband relaxation mechanisms in the QDs. We performed time-resolved photoluminescence (PL) quenching measurements on InAs/GaAs self assembled QDs. The samples were excited by near infrared laser pulses and the time and wavelength resolved PL was measured by a streak camera. During the decay of the PL, a THz pulse from a free electron laser, tuned to the intersublevel transition energy of the QDs, was made incident on the sample. This THz pulse induced quenching of the PL, shown by the dip in Fig.1, by re-exciting carriers to higher levels within the QDs. These carriers eventually relaxed back to the ground state (s-state) resulting in the recovery of the s-state PL intensity. Thus, the recovery of the PL was directly related to carrier relaxation dynamics in the QDs. The mechanisms involved were (i) ISL relaxation, where the excited carriers in the QDs directly fell back into the s-state of the same dot and (ii) transfer to adjacent dots via the wetting layer by multiphoton absorption or tunneling. To distinguish these two effects we performed measurements on two samples grown simultaneously but post-growth annealed at different temperatures resulting in different ISL relaxation times of 60 ps and 1.5 ns. From rate equation model fit of the measured data we found that the recovery time of the quenched PL was independent of the ISL relaxation times. This implied that the carrier relaxation within the dots was dominated by mechanisms other than ISL transition. Comparison of the amount of recovered PL signals for different emission energies showed that there was loss of carriers at higher PL energies, as showed in Fig.1(a), and gain of carriers after recovery for lower emission energies [Fig.1(b)]. This indicates carrier transfer among adjacent QDs. Therefore, even for quite low QD densities (4 x 10^10 cm-2 for our samples), interdot carrier transfer plays an important role in intraband carrier relaxation in self assembled QDs.

Keywords: Photoluminescence quenching; FEL; Intraband transition; quantum dots; quantum well

  • Lecture (Conference)
    International conference on superlattices, nanostructures and nanodevices, 22.-27.07.2012, Dresden, Germany

Publ.-Id: 17791

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