Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Ultra fast electron beam X-ray CT scanner for two-phase flow measurement

Fischer, F.; Hampel, U.

Two-phase flows are of primary importance in the understanding of thermal hydraulic phenomena in nuclear light water reactors. The qualification of CFD codes for the simulation of stationary and even transient two-phase flows in complex three dimensional geometries requires extending our knowledge toward the details of the flow structure under various thermal hydraulic conditions. At Forschungszentrum Dresden-Rossendorf the thermal hydraulic test facility TOPFLOW is currently extensively used to conduct two-phase flow experiments which aim at the disclosure of fine flow structure details in generic and also more complex geometries. Consequently, we have extended our measurement technology for two-phase flow to highspeed X-ray tomography which offers non-intrusive flow measurement at high pressure and high temperatur at a speed comparable to the wire-mesh sensor [2], [3], [4], [5]. For that reason we have developed a scanned electron beam X-ray apparatus where a electron beam is swept around an object on a circular X-ray target. Thus a rapidly moving X-ray spot is generated. The apparatus can perform cross-sectional imaging at high frame rates and will in the future be extended to other measurement features, such as multi-plane tomography, phase velocity measurement, higher scanning diameters and high energy X-rays. This paper introduce the scanner design, discuss major performance parameters along with an application example and show how this scanner will be applied to air-water and steam-water two-phase flow measurement in a vertical test section of the TOPFLOW facility.

Keywords: electron beam X-ray CT; two-phase flow measurement

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11972

Inverse energy transfer process during electroluminescence in Er-doped SiO2 layers containing Ge nanocrystals

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

For a comparative study of the energy transfer mechanism during room temperature electroluminescence (EL), two sets of samples have been prepared by implanting either Ge and Er ions (type-I) or Si and Er ions (type-II) into a 200 nm SiO2 layer combined with rapid-thermal-annealing. Three reference samples have been prepared by implanting only Er, Ge or Si ions in SiO2 followed by post-implantation annealing. The formation of Si and Ge nanocrystals (NCs) was confirmed by transmission electron microscopy. The metal-oxide-semiconductor dot structure was prepared by depositing indium-tin-oxide and Al films on the front and rear sides of the structure. Quantum-confinement mediated recombination of carriers in Si-nanocrystals (Si-NCs) as well as the triplet (T1) → singlet (S0) transition in the O3-Si-Si-O3 oxygen deficient centre (ODC) provides the 750 and 475 nm bands, respectively, in the only Si-implanted sample. Conversely, the 525, 550, 660 and 1532 nm emissions corresponding to the deexcitation of the 2H11/2, 4S3/2, 4F9/2 and 4I13/2 states to the ground state 4I15/2 of the Er3+, respectively, were recorded for the Er-doped SiO2 layer. A blue-violet light at ~400 nm, representing the T1→S0 transition in the O3-Si-Ge-O3 ODC, was observed in the Ge-NCs embedded SiO2 layer. Although the intensity of the Er-related visible/infrared EL signals in type-I sample was found disappearing/decreasing with a concomitant enhancement of the 400 nm band, a sharp rise in intensity of the 1532 nm Er EL at the expense of the Si-NC related 750 nm band was evidenced in type-II sample. While the later result confirms the energy transfer mechanism from Si-NCs to the nearest Er3+, the former finding can be explained in terms of the energy transfer from Er3+ to the Ge-related ODC.

Keywords: nanocrystals; Ge; electroluminescence

  • Lecture (Conference)
    IBMM2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11971

Measurement of dynamic liquid distributions in a fixed bed using electrical capacitance tomography and capacitance wire mesh sensor

Matusiak, B.; Da Silva, M. J.; Romanowski, A.; Hampel, U.

An intricate problem associated with fixed bed operation is liquid maldistribution, which denotes the fact that the liquid does not homogeneously flow through the bed. In a comparative study we evaluated two capacitance imaging methods - capacitance wire mesh sensor and electrical capacitance tomography (ECT) - with respect to their capability of measuring static and dynamic liquid holdup in a fixed bed. We performed experiments in a column of 100 mm diameter, packed with commercial porous Al2O3 catalyst particles. The column was operated at ambient pressure. Inlet flow of isopropanol from various point sources was applied at rates of 40 L/h and 60 L/h. The capacitance wire mesh sensor as an invasive instrument is able to disclose flow structures at higher spatial resolution and was therefore considered as the reference instrument for liquid holdup measurement. We found that both methods predict dynamic liquid holdup in the column in a similar way with only small systematic deviation. The results therefore prove that non-invasive electrical capacitance tomography can reliably measure cross-sectional dynamic liquid holdup in a fixed bed, even with a simple and fast linear back projection reconstruction algorithm.

Keywords: Wire-mesh sensor; ECT; Multiphase flow; Trickle bed; Liquid holdup; Liquid distribution

  • Industrial & Engineering Chemistry Research 49(2010)5, 2070-2077
    DOI: 10.1021/ie900988f

Publ.-Id: 11970

Research needed for improving heavy ion therapy

Kraft, G.; Kraft, S. D.

The large interest in heavy ion therapy is stimulated from its excellent clinical results. The bases of this success are the radiobiological and physical advantages of heavy ion beams and the active beam delivery used for an Intensity Modulated Particle Radiotherapy (IMPT). Although heavy ion therapy has reached a high degree of perfection for the clinical use there is still large progress possible to improve this novel technique: In order to extend IMPT to more tumor entities and to tailor the planning more individually for each patient in an adaptive way, radiobiological work both experimentally and theoretically is required. It is also not clear whether the neighboring ions to carbon could have a clinical application as well. For this extension basic biological works as well as physics experiments have to be performed.

On the technical side many improvements of the used equipment seems to be possible. Two major topics are the extension of IMPT to moving organs and the transition to more compact and therefore cheaper particle accelerators.

In this paper these topics are treated to some extent in order to give an outline of the great future potential of ion beam therapy.

Publ.-Id: 11969

Spectral-history modeling in DYN3D burnup calculations

Bilodid, Y.; Mittag, S.

Burnup spectral-history effects are reflected in deviations in the actual nuclide concentrations within the fuel. The deviations of different nuclides are correlated. It is possible to treat the nuclide concentration change by tracing only one nuclide – Pu-239. Implementation of historical correction for 2-group cross sections method in DYN3D is described in this paper.

Keywords: DYN3D; spectral-history effects; burnup history effect; burnup; cross sections

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 11968

Nitrogen diffusion in single crystalline austenitic stainless steel: ion energy and flux effects

Martinavičius, A.; Abrasonis, G.; Möller, W.; Chumlyakov, Y.

Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding is investigated. Single crystalline AISI 316L austenitic stainless steel (ASS) with orientation (001) has been ion beam nitrided at 400 °C using a Kaufman-type ion source. The acceleration voltage has been varied from 450 to 1200 eV, and the current density from 0.3 to 0.7 mA cm−2. XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The nitrogen depth profiles have been determined using nuclear reaction analysis (NRA). The profiles of nitrided samples can be depicted by an initial quasi-linear decrease followed by a sharp leading edge. The nitrogen penetration depth is significantly higher for higher implantation energies as well as for higher current densities. The result cannot be explained by the difference of the sputtering rate.
The “trapping-detrapping” model, which is able to reproduce the full shape of the nitrogen depth, has been used to fit nitrogen depth profiles and extract the diffusion coefficient values. The nitrogen profile fitting shows that the nitrogen diffusion coefficient strongly depends on irradiation flux and ion energy during ion beam nitriding, confirming the tendencies deduced directly from the nitrogen distribution profiles.

  • Lecture (Conference)
    22nd International Conference on Surface Modification Technologies - SMT22, 24.09.2008, Trollhättan, Sweden

Publ.-Id: 11967

Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding and subsequent thermal annealing

Martinavičius, A.; Abrasonis, G.; Möller, W.; Templier, C.; Rivière, J. P.; Declémy, A.; Chumlyakov, Y.

Nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding and subsequent annealing is investigated. Single crystalline [orientations (001), (110) and (111)] and polycrystalline AISI 316L austenitic stainless steel (ASS) has been ion beam nitrided at 400 °C for 60 min using a Kaufman-type ion source with an acceleration voltage of 1 keV and a current density of 0.5 mA cm−2. XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The samples have been subsequently vacuum annealed at 400°C for 30 min. The nitrogen distribution profiles have been determined using nuclear reaction analysis (NRA). The profiles of as-nitrided samples can be depicted by an initial quasi-linear decrease followed by a sharp leading edge. Despite identical nitriding conditions, the nitrogen penetration depth is significantly higher in the single crystal with the (001) orientation than in the samples with the orientations (011) or (111) which cannot be explained by the orientational dependence of the sputtering rate. The surface concentration for the single crystal with the (001) orientation was about 27 at.% with the depth of the quasi-linear part about 1.5 µm. For the orientations (011) and (111) the surface concentration was 25 at.% and the depth of the quasi-linear part about 1 µm and 0.7 µm respectively. Polycrystalline ASS presents an intermediate case. Subsequent annealing results in the decrease of near-surface nitrogen concentration, flattening of the quasi-linear part of the depth profile and nitrogen inward diffusion without any detectable nitrogen loss due to out-diffusion.
The “trapping-detrapping” model, which is able to reproduce the full shape of the nitrogen depth profile in as-nitrided as well as subsequently annealed single crystalline ASS, has been used to fit nitrogen depth profiles and extract the diffusion coefficient values. The nitrogen profile fitting shows that the nitrogen diffusion coefficient is strongly orientation dependent during ion beam nitriding confirming the tendencies deduced directly from the nitrogen distribution profiles. This anisotropy is not present during thermal annealing, while the diffusion coefficients extracted from the fitting exhibit significantly lower values than those obtained from as-nitrided samples.

  • Poster
    Eleventh International Conference on Plasma Surface Engineering, 16.09.2008, Garmisch-Partenkirchen, Germany

Publ.-Id: 11966

Fe nanoparticles embedded in MgO crystals

Shalimov, A.; Potzger, K.; Geiger, D.; Lichte, H.; Talut, G.; Misiuk, A.; Reuther, H.; Stromberg, F.; Zhou, S.; Baehtz, C.

Iron nanoparticles embedded in MgO crystals were synthesized by Fe+ ion implantation at an energy of 100 keV and varying fluences from 3*10E16 to 3*10E17 cm-2. Investigations of structural and magnetic properties of Fe nanoparticles have been performed using magnetometry, x-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy, as well as by theoretical Preisach modeling of bistable magnetic systems. It has been found that alpha- and gamma-Fe nanoparticles are formed for all fluences. The content of the alpha-Fe phase increases at higher fluences and after annealing. The influence of post implantation annealing at 800 C in vacuum and under enhanced up to 10 kbar hydrostatic pressure in argon atmosphere on the formation of nanoparticles has been analyzed. Investigations have been performed within DFG project PO1275/2-1 ”SEMAN”.

Keywords: magnetic nanoparticles; iron; Preisach modelling

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 11965

’Invisible’ ferromagnetic secondary phases in Co doped ZnO

Potzger, K.; Zhou, S.; Muecklich, A.; Xu, Q.; Schmidt, H.; Helm, M.; Fassbender, J.

The search for ferromagnetic transition-metal doped ZnO, i.e., diluted magnetic semiconductors (DMS), has turned into the search for unwanted secondary phases by high-resolution structural analysis [1]. Such phases even can lead to anomalous Hall effect arising from charge carrier spin polarization. In this talk we show that the general analysis technique for the identification, i.e. x-ray diffraction spectroscopy, fails to identify a recently observed kind of ferromagnetic inclusions with heavy crystalline disorder. We discuss the properties of those clusters using the popular Co:ZnO system.
[1] K. Potzger, S. Q. Zhou, H. Reuther, A. Mucklich, F. Eichhorn, N. Schell, W. Skorupa, M. Helm, J. Fassbender, T. Herrmannsdorfer, T. P. Papageorgiou, Appl. Phys. Lett. 88, 052508 (2006).

Keywords: zno; diluted magnetic semiconductors

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 11964

Accelerator mass spectrometry (AMS) and ion beam analysis (IBA) with the new 6 MV accelerator at FZ Dresden-Rossendorf

Munnik, F.; Grambole, D.; Grötzschel, R.; Merchel, S.; Neelmeijer, C.

Since more than 30 years IBA is performed at the Forschungszentrum Dresden-Rossendorf (FZD) for the determination of element distributions. Due to continuous upgrades of the different experimental set-ups, we are able to routinely perform:
• Rutherford Backscattering Spectrometry (RBS) & Channeling (C-RBS)
• Nuclear Reaction Analysis (NRA)
• Elastic Recoil Detection Analysis (ERDA)
• Particle-Induced X-Ray (PIXE) and Gamma-Emission (PIGE)
Most of our applications lie within material sciences. We are able to measure non-destructively “all natural” elements, i.e. H to U; most elements with lateral, some in 3-D resolution with the following typical parameters (matrix- and analyte-depending):
• depth resolution: 1-30 nm
• depth range: nm-µm
• lateral resolution: few µm
• usual mapping area: 2x2 mm2
• maximum sample size: 3x10 cm2 (vacuum) & “unlimited” (external beam)
• detection limits: ~10 µg/g (H); 500 µg/g – 1% (He-F); 10-100 µg/g (Na-U)
For some elements, e.g. H/D, isotope analysis is also possible.
In summer 2009, our 5 MV van-de-Graaff accelerator will be replaced by the latest 6 MV Tandetron model [1], which is even more sophisticated than the lately installed 5 MV one in Southern France [2]. The new accelerator will need less maintenance generally allowing more beam time. It might be also possible to expand from two to three 8-hour-shifts a day with the new fully automatic system. Scientifically, the main advantages are an increased depth range by a factor of 2 for ERDA and improved detection limits for NRA.
In addition, the machine will have special equipment for AMS [3]. There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses (e.g. isobars) are nearly completely eliminated. Thus, AMS provides much lower detection limits compared to conventional mass spectrometry (isotope ratios: 10-10-10-15).
In contrast to common low-energy AMS facilities, which have mainly specialized in radiocarbon analyses (14C), the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV. Especially in environmental and geosciences, the determination of long-lived (t1/2 > 0.3 Ma) cosmogenic radionuclides like 10Be, 26Al, and 36Cl became more and more important within the last decades [4]. Using these nuclides dating of e.g. volcanic eruptions, rock avalanches, earth quakes, and glacier movements is possible.
References: [1] A. Gottdang et al., Nucl. Instr. and Meth. B 2002, 190, 177. [2] M.G. Klein et al., Nucl. Instr. and Meth. B 2008, 266, 1828. [3] [4] J.C. Gosse and F.M. Phillips, Quat. Sci. Rev. 2001, 20, 1475.

Keywords: accelerator mass spectrometry; ion beam analysis

  • Poster
    ANAKON 2009, 17.-20.03.2008, Berlin, Deutschland

Publ.-Id: 11963

The role of aspartyl-rich pentapeptides in comparative complexation of actinide(IV) and iron(III). Part 1

Jeanson, A.; Berthon, C.; Coantic, S.; Den Auwer, C.; Floquet, N.; Funke, H.; Guillaneux, D.; Hennig, C.; Martinez, J.; Moisy, P.; Petit, S.; Proux, O.; Quemeneur, P.; Solari, P. L.; Subra, G.

Although there is a tremendous volume of data available on the interaction of actinides with living organisms as plants, nearly all the studies are limited to macroscopic or physiological 3 measurements with no specific information at the molecular level. Peptides allow the study of complex coordination chemistry, as that involving actinide(IV) and proteins, without the intricacy of tertiary structure properties. For that purpose, a linear pentapeptide, acetyldiaspartyl-prolyl-diaspartyl-amide (Ac-Asp-Asp-Pro-Asp-Asp-NH2, called PP1 in this report), was synthesized and investigated as a potential chelating ligand of thorium(IV), neptunium(IV), and/or plutonium(IV) cations. Comparison with biological relevant iron(III) cation is also provided. Noteworthy, PP1 was able to prevent Np(IV) from hydrolysis into an insoluble precipitate. Spectrophotometry, 13C NMR and EXAFS at the iron K edge and actinide L3 edges were used to probe the cation coordination sphere and better describe the cation-peptide interaction. The complexes were found to be polynuclear with oxo or hydroxo bridged cations, Fe(III) forming a binuclear complex, Th(IV), Np(IV) or Pu(IV) forming a polynuclear complex with higher nuclearities.

Keywords: Peptides; Actinides; EXAFS

  • New Journal of Chemistry 33(2009), 976-985

Publ.-Id: 11962

Ultrafast infrared and THz spectroscopy of semiconductor quantum structures

Schneider, H.

This talk gives an overview on our activities in nonlinear laser spectroscopy using the free-electron laser at FZD and tabletop lasers. Our research concentrates on III-V semiconductor quantum wells and superlattices. In particular, I will discuss two-photon absorption and photocurrent autocorrelation involving intersubband transitions in quantum wells at mid-infrared wavelengths.

  • Lecture (others)
    Seminar, IIN-IFW Dresden, 12.12.2008, Dresden, Deutschland

Publ.-Id: 11961

Two-photon photocurrent studies of electron intersubband dynamics in multiple quantum wells

Schneider, H.

Quantum wells comprising three equidistant subbands, two of which are bound in the well and the third one in the continuum, result in a resonantly enhanced coefficient for two-photon absorption, which is by six orders of magnitude stronger than in usual semiconductors. Exploiting this nonlinearity in two-photon detectors, quadratic autocorrelation of a free-electron laser has recently been demonstrated at room temperature [1]. Temporal resolution of such a two-photon autocorrelator is only limited by the sub-ps intrinsic time constants of the intersubband transition, namely the intersubband relaxation time and the phase relaxation time. Using sub-ps mid-infrared pulses, the approach allows us to determine systematically the dependence of these time constants on structural parameters, and to discriminate between different scattering processes [2].
[1] H. Schneider, H. C. Liu, S. Winnerl, O. Drachenko, M. Helm, J. Faist, Appl. Phys. Lett. 93, 101114 (2008).
[2] H. Schneider, T. Maier, M. Walther, H. C. Liu, Appl. Phys. Lett. 91, 191116 (2007).

Keywords: intersubband transition; two-photon absorption; quantum well infrared photodetector; phase relaxation; autocorrelation

  • Invited lecture (Conferences)
    International Workshop on Nonequilibrium Nanostructures (NONNA'08), 01.-06.12.2008, Dresden, Germany

Publ.-Id: 11960

Uporaba metode datiranja površinske izpostavljenosti na primeru podora Veliki vrh

Mrak, I.; Merchel, S.; Benedetti, L.; Braucher, R.; Bourlès, D.; Finkel, R. C.; Reitner, J. M.

O podoru v Velikem vrhu (Košuta, Karavanke) ni zanesljivih zgodovinskih zapisov, vendar pa le ti obstajajo o podoru na Dobraču (25.1.1348), ki je od Velikega vrha oddaljen 46 km [1]. Podor je povzročil potres in naša hipoteza je bila, da je tudi podor v Velikem vrhu posledica istega dogodka. Tako smo s pomočjo metode datiranja površinske izpostavljenosti [2] analizirali vzorce matične kamnine v steni Velikega vrha ter vzorce s površine podornih blokov. Ugotavljali smo vsebnost 36Cl, ki se je začel tvoriti po podoru. Na podlagi poznavanja števila atomov 36Cl na gram Ca na leto izpostavljenosti, čas dogodka (podor) izračunamo iz koncentracij 36Cl izmerjenih s pomočjo pospeševalnika (AMS). Prvi rezultati kažejo, da sta se podora na Dobraču in Velikem vrhu zgodila istočasno, natančne analize podatkov pa še potekajo.

Zahvala: Del raziskave sofinancira program CRONUS-EU (Marie-Curie Action 6. okvirni program #511927).

Literatura: [1] C. Hammerl, Historical earthquake research – methods used as a basis for the hazard assessment applied to the earthquake of 1348 in Villach (Austria), Proceedings of the Third International Symposium on Historical Earthquakes in Europe (Prague 1991). [2] J. C. Gosse, F. M. Phillips, Terrestrial in situ cosmogenic nuclides: theory and application, Quaternary Science Reviews, 20 (2001) 1475.

The rockfall Veliki vrh is located in the valley Pod Košuto (Geben stream watershed Karavanke Mountains, Slovenia). The highest point of the researched area is Veliki vrh (2086 m); the lowest is the settlement Plaz (650 m). Among the geomorphologic processes nowadays the linear denudation and erosion prevails (the most common inclination of the surface is between 21-32° in 33-55°).
Between the settlement of Plaz and the Zajemen farm immense amounts of rockfall debris are present in different sizes, from big blocks (up to 10 x 10 m) to granule. The smaller grain sizes (fine sand, coarse silt…) are missing and the grain edges are sharp. The lithology of the material is the same as the one forming the Košuta ridge - Triassic Dachstein limestone and reefy limestone.
There are no reliable historical data about the rockfall event beside the oral heritage in form of a fairy tale describing the catastrophic falling of rocks over the settlement in the valley, killing many people and forcing the survivors to establish a new settlement further downstream. However, there are numerous written records about a historic rockfall taking place about 46 km away at Dobratsch, Carinthia on 25th January 1348 [1]. That rockfall was induced by an earthquake with the epicenter situated at Friuli (~74 km distance to Veliki vrh). There are no other records of natural hazards within historical times for the area, thus, it seems very likely that the same earthquake triggered both rockfalls. To test this hypothesis, we have applied the surface exposure dating method [2] on samples taken from the fresh bedrock and big boulders originating from the Veliki vrh rockfall.
As the long-lived radionuclide 36Cl is the product of nuclear reactions induced by the high-energy cosmic ray particles in a Ca-rich rock, its concentration can be used as a dating tool. The material has been previously shielded and production of 36Cl started as recently as the rockfall took place. Then, freshly produced surfaces – bedrock and boulders – have been exposed to cosmic rays launching the clock. As the so-called production-rate, i.e. how many atoms per gram Ca per year exposure, can be calculated for a certain environment, a precise time for the rockfall can be deduced from the 36Cl concentrations measured by accelerator mass spectrometry (AMS).
Preliminary results suggest a simultaneous timing of both rockfalls: Dobratsch and Veliki vrh. Detailed data analysis is in preparation.

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

  • Poster
    1. Trienalni Posvet, Naravne Nesrece v Sloveniji (NNS '08 - 1st Symposium Natural Disasters in Slovenia), 11.12.2008, Ljubljani, Ljubeljana, Sloveniji , Slowenien

Publ.-Id: 11959

On the axissymmetric dominance of the magnetic field in the VKS dynamo experiment.

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

In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.

A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data of water experiments, leads to dynamo action if a critical value for the magnetic Reynolds number is exceeded.

In case of an axisymmetric velocity field the simulations always result in a non-axisymmetric eigenfield which is dominated by the azimuthal m=1-mode. However, in contradiction to this expected result, the experimental realisation exhibits an axissymmetric field configuration.

Until today, no satisfactory explanations for the dominating m=0-mode are established. A recently presented approach is based on an alpha-effect caused by helical fluid motions between the impeller blades that drive the flow. However, it turned out, that the necessary
amplitude which is required for m=0 dominated solutions is well above realistic values that might be realized in the experiment.

Further potential explanations involve non-axissymmetric contributions either caused by a drifting large scale vortex structure as observed in water experiments or introduced through the azimuthal varying high permeability region from the ferrous impeller blades, which should ideally give rise to a strong axisymmetric azimuthal field component within the impeller region.

Keywords: Dynamo

  • Lecture (Conference)
    11th MHD days, 01.-03.12.2008, Ilmenau, Germany

Publ.-Id: 11958

Equation of state for QCD matter in a quasiparticle model

Schulze, R.; Kämpfer, B.

A phenomenological QCD quasiparticle model provides a means to map lattice QCD results to regions relevant for a variety of heavy-ion collision experiments at larger baryon density. We report on effects of collectives modes and damping on the equation of state.

Keywords: QCD quasipaticle model QPM heavy ion collective modes Landau damping equation of state EOS

Publ.-Id: 11957

Light emitting field effect transistor with two self-aligned Si nanocrystal layers

Beyer, V.; Schmidt, B.; Heinig, K.-H.; Stegemann, K.-H.

Light emitting field-effect transistors based on narrow layers of silicon nanocrystals (NCs) in the gate oxide were fabricated. Direct quantum mechanical electron and hole tunneling into NCs was achieved by self-alignment of NCs-interface-distances to ~2 nm. The direct tunneling reduces oxide degradation, prolongs device lifetime and increases operation speed. Self-alignment occurs during thermal treatment of ion irradiated stacks of 50 nm polycrystalline silicon/15 nm SiO2 / (001)Si substrate. An alternating voltage (ac) was applied to the gate to inject charges into the NCs. Due to injection by direct tunneling, electroluminescence extends to higher ac frequencies than reported so far.

Keywords: Si nanocrystals; Si based light emission; electroluminescence; photoluminescence; ion irradiation; memory; MOSFET; Ostwald ripening

  • Applied Physics Letters 95(2009), 193501

Publ.-Id: 11956

Terawatt diode-pumped Yb:CaF2 laser

Siebold, M.; Hornung, M.; Boedefeld, R.; Podleska, S.; Klingebiel, S.; Wandt, C.; Krausz, F.; Karsch, S.; Uecker, R.; Jochmann, A.; Hein, J.; Kaluza, M. C.

We present what we believe to be the first terawatt diode-pumped laser employing single-crystalline Yb:CaF2 as the amplifying medium. A maximum pulse energy of 420 mJ at a repetition rate of 1 Hz was achieved by seeding with a stretched femtosecond pulse 2 ns in duration, preamplified to 40 mJ. After recompression, a pulse energy of 197 mJ and a duration of 192 fs were obtained, corresponding to a peak power of 1 TW. Furthermore, nanosecond pulses containing an energy of up to 905 mJ were generated without optical damage.

Keywords: Diode pumped laser caf2

  • Optics Letters 33(2008)23, 2770-2772

Publ.-Id: 11955

Additional PET/CT in week 5-6 of radiotherapy for patients with stage III non-small cell lung cancer as a means of dose escalation planning?

Gillham, C.; Zips, D.; Poenisch, F.; Evers, C.; Enghardt, W.; Abolmaali, N.; Zoephel, K.; Appold, S.; Hoelscher, T.; Steinbach, J.; Kotzerke, J.; Herrmann, T.; Baumann, M.

Background and purpose: Loco-regional failure after radiotherapy with total doses of 60-70 Gy for non-small cell lung cancer (NSCLC) remains a major clinical problem. Escalation of radiation dose is often limited because of exceeding normal tissue constraints. The present study was designed to test the hypothesis that a reduction in disease volume during radiotherapy detected by FDG PET/CT would facilitate radiation dose escalation, whilst remaining within normal tissue constraints.
Materials and methods: Ten patients with localised inoperable NSCLC were prospectively enrolled. Each received standard 3D-conformally planned radiotherapy to a dose of 66 Gy in 33 fractions over 6.5 weeks. FDG PET/CT imaging in the treatment position was performed prior to treatment and repeated following 50 or 60 Gy. CT and PET-delineated gross tumour volumes were generated and a composite created. A margin of 15 mm was added in all planes to form the planning target volume (PTV). Treatment planning was performed to compare two dose escalation strategies: 78 Gy delivered to the initial PTV with treatment in two phases (shrinking field), i.e., 66 Gy to the initial PTV with a 12 Gy-boost to the PTV after 50/60 Gy. As an alternative planning approach the maximal dose without exceeding normal tissue constraints was evaluated for each patient (individualized dose prescription).
Results: There was a median PTV reduction after 50/60 Gy of 20%. Delivering 78 Gy to the initial PTV could have been achieved in 4/10 patients. Of the remaining 6, delivering 78 Gy to the initial PTV would have exceeded normal tissue constraints and no benefit was seen when delivered in two phases. The results from the individualized dose prescription indicated a higher median maximal dose when treatment would be given in two phases compared to one phase resulting in a modest increase of calculated tumour control probability.
Conclusions: Our data suggest that despite tumour shrinkage determined by subsequent FDG PET/CT during treatment the tested adaptive targeting strategy would result only in a modest improvement in the context of dose escalation. Further studies on the optimal use of FDG PET/CT and other approaches for dose escalation in loco-regionally advanced NSCLC are warranted.

Keywords: Lung cancer; PET/CT; Dose escalation; Adaptive targeting; Radiotherapy

Publ.-Id: 11954

Experimental investigation of Lorentz-force controlled flat-plate boundary layer with a laser Doppler velocity profile sensor

Shirai, K.; Voigt, A.; Neumann, M.; Büttner, L.; Czarske, J.; Cierpka, C.; Weier, T.; Gerbeth, G.

The application of Lorentz forces for flow control has been investigated in the field of magnetohydro-dynamics (MHD) research since it is capable of generating required mass force to control electrically conductive liquid flows. Separation control of a hydrofoil using Lorentz force has been intensively investigated in the MHD division in the Forschungszentrum Dresden-Rossendorf (FZD) in Germany.
Vortex structures around the hydrofoil have been investigated by Weier et al. (for example [1]). They investigated the vortex structure of the separated flow with particle image velocimetry (PIV) to seek optimum control of separation [2].
However, PIV has limitations particularly in the near-wall region which indeed is of great interest.
In general PIV has an accuracy of velocity measurement about a few percent at best optimized condition [3]. Hence, the application of PIV to the region of low turbulence has a difficulty to evaluate the real turbulence coming from the flow. Besides, the application of PIV to the near-wall region is problematic because of high velocity gradient and strong reflection at the wall. In addition, proper evaluation of velocity field near the wall is hindered when strong Lorentz force is applied. The electric current induced for generating the Lorentz force electrolyzes the liquid and generates bubbles at the wall. Unfortunately, the higher the induced current, the stronger the bubbles are generated.
Therefore, it is demanded to use a measurement technique capable of velocity measurement at low turbulence degree near the wall surface at bubbly conditions. Laser Doppler velocity profile sensor developed in the TU Dresden is attractive since it has high resolution (micrometer range) and accuracy (<0.1%) of velocity profile measurement demanded in the above application. The sensor has been successfully applied to the near-wall region of a turbulent channel flow [4].
The purpose of the present investigation is to study the fundamental mechanism of the flow control with Lorentz force. For that reason, the velocity profile near the wall is measured with the velocity profile sensor. As a first test, the preliminary experiment described in this abstract focused in the feasibility of measurement close to the wall under bubbly conditions and to observe the difference of the flow regime with and without Lorentz force applied.

Keywords: Lorentz force; laser Doppler Velocimetry

  • Lecture (Conference)
    6th International Symposium on Turbulence and Shear Flow Phenomena (TSFP6), 22.-24.05.2009, Seoul, Korea
  • Contribution to proceedings
    6th International Symposium on Turbulence and Shear Flow Phenomena (TSFP6), 22.-24.06.2009, Seoul, Südkorea
    Turbulence and Shear Flow Phenomena, Vol II, 755-760

Publ.-Id: 11951

Uranium coordination in liquids and amorphous solids determined by EXAFS spectroscopy

Hennig, C.

The combination of UV-Vis and EXAFS to determine species distribution and structure will be discussed.

Keywords: EXAFS; UV-Vis; uranium

  • Lecture (others)
    University of Siegen, Inorganic Chemistry, 24.11.2008, Siegen, Germany

Publ.-Id: 11950

Influence of ionic strength, pH and silicate on colloidal UO2 formation

Hennig, C.

The solubility of uranium in aqueous solutions under anaerobic conditions is low and the probability of solid UO2 formation increases with the U(IV) concentration. Only in solutions with low pH and high ionic strength the U(IV) hydrate itself is stable even at higher U(IV) concentrations. With increasing pH several U(IV) hydroxides becomes dominant. Below their solubility limits two solid phases can be observed, i.e. the microcrystalline UO2 and the amorphous UO2•xH2O/U(OH)4 which both can occur as colloids in solution. Also the presence of silicate influence the formation and structure of U(IV) nanoparticles. However, even in solutions with equimolar ratio of UO2 and SiO2 the precipitation do not result in the formation of a USiO4-like phase, which can be observed easily under hydrothermal conditions. Some structural aspects of the resulting solid phases have been investigated with x-ray diffraction, EXAFS and wide angle x-ray scattering techniques and will be briefly discussed.

Keywords: EXAFS; XRD; HEXS; UO2

  • Lecture (others)
    Ecole Polytechnique Federale Lausanne (EPFL) Environmental Microbiology Laboratory (EML), 20.11.2008, Lausanne, Switzerland

Publ.-Id: 11949

Influence of annealing on the Er luminescence in Si-rich SiO2 layers co-implanted with Er ions

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

The impact of rapid thermal annealing (RTA) in producing samples by sequential implantation of Si and Er ions into a 200 nm SiO2 layer combined with different annealing cycles as well as the corresponding room-temperature visible and infrared photoluminescence (PL) have been studied. The Er-related PL intensity at 1533 nm for the samples prepared by implanting Si with subsequent annealing, followed by Er implantation and final annealing (type-I) was found to be stronger than the one produced similarly but without the first annealing step (type-II). In fact, the 1533 nm peak intensity in the optimized RTA processed sample is comparable to the PL yield of the furnace-annealed sample. Moreover, the excitation wavelength (405 nm) was found to be suitable for exciting the Si=O related point defects in the SiO2 layer, and can provide a PL band with a maximum at ~580 nm. While this band was further intensified in presence of Si nanocrystals (Si NCs), it became weaker by introducing additional Er3+ ions with a concomitant rise of the 1533 nm Er PL, confirming the visible range pumping of Er3+. The detailed spectral analyses suggest that the 580 nm band is the result of the excitation/deexcitation mechanism in molecule like states in Si=O or the Si=O state mediated recombination of carriers in Si NCs according to the model proposed by Wolkin et al. [Phys. Rev. Lett. 82, 197 (1999)]. The samples were further characterized by transmission electron microscopy and Fourier-transform infrared-spectroscopy. The time resolved PL measurements and a modelling by rate equations were also performed to determine and justify the energy migration mechanism from Si NC to the neighbouring Er3+.

Keywords: Nanocrystals; RTA; defects; photoluminescence

  • Journal of Applied Physics 104(2008)10, 103522-1-103522-9

Publ.-Id: 11948

Probing channeling radiation influenced by ultrasound

Wagner, W.; Azadegan, B.; Büttig, H.; Grigoryan, L. S.; Sobiella, M.; Pawelke, J.

The effect of ultrasonic vibrations excited in quartz single crystals on channeling radiation (CR) emitted by relativistic electrons was probed experimentally at medium energy at the radiation source ELBE.

Essential preconditions for these investigations have been created by preceding series of measurements of planar CR on alpha-quartz as well as by extensive theoretical work concerning the treatment of the influence of ultrasound (US) on CR emission. First dedicated experiments became possible because the interaction phenomena and expected effects could certainly be predicted and simulated.

Compressional waves of suitable frequency were induced in x-cut quartz crystals by means of appropriately designed RF cavities applying the reverse piezoelectric effect. Although at the available electron energies the necessary resonance condition has been reached only for selected transitions of electrons channeled along specific crystallographic planes of the quartz single crystal, the occurrence of US stimulated CR should be evident.

Keywords: channeling radiation; quartz single crystal; ultrasound

  • Contribution to proceedings
    3rd International Conference on Charged and Neutral Particles Channeling Phenomena (Channeling 2008), 25.10.-01.11.2008, Erice, Sicily, Italy
    Probing channeling radiation influenced by ultrasound, Singapore, London: World Scientific, Science and Culture Series
  • Invited lecture (Conferences)
    3rd International Conference on Charged and Neutral Particles Channeling Phenomena (Channeling 2008), 25.10.-01.11.2008, Erice, Sicily, Italy

Publ.-Id: 11947

THEREDA - Ein Beitrag zur Langzeitsicherheit von Endlagern für nukleare und nichtnukleare Abfälle

Altmaier, M.; Brendler, V.; Hagemann, S.; Herbert, H.-J.; Marquardt, C.; Moog, H.; Neck, V.; Richter, A.; Voigt, W.; Wilhelm, S.

Im Rahmen von Langzeitsicherheitsanalysen für deutsche Endlager radioaktiver bzw. Untertagedeponien chemotoxischer Abfälle sowie weiterer Einsatzfelder (Altlastensanierung) wird eine einheitliche und umfassende thermodynamische Referenzdatenbasis dringend benötigt. Der ehemalige „Arbeitskreis Thermodynamische Standarddatenbasis“ (ATS) hatte sich die Aufgabe gestellt, eine solche Datenbasis zu realisieren. Die Aktivitäten des ATS werden seit Juli 2006 im Projektverbund „THEREDA“ (Thermodynamische Referenzdatenbasis) von BMBF, BMWi und BfS zunächst für 3 Jahre gefördert. THEREDA setzt sich aktuell aus 5 Partnerinstitutionen zusammen, die im Wesentlichen die deutschen Forschungsinstitutionen auf dem Gebiet der Endlagersicherheitsforschung repräsentieren. THEREDA soll die Transparenz und Belastbarkeit der Sicherheitsanalysen in Deutschland entscheidend verbessern und stellt erstmalig konsistente thermodynamische Datensätze für die in Deutschland diskutierten Endlageroptionen bereit. Für jede thermodynamische Größe werden anhand eindeutig definierter Evaluierungskriterien Qualitätsstufen angegeben, mithilfe derer Anwender Daten, entsprechend der jeweiligen spezifischen Problemstellungen, gezielt einbeziehen oder ausschließen können. Für fehlende thermodynamische Daten werden im Rahmen von THEREDA begründete Schätzwerte ermittelt, sodass Modellrechnungen zur Sicherheitsanalyse in Zukunft auf einer deutlich breiteren Datenbasis durchgeführt werden können.
Die Datenbasis wird in einer Datenbank zentral verwaltet und Anwendern über das Internet frei und unentgeltlich verfügbar sein. Importformate, um THEREDA in die gängigsten Modellierungscodes (EQ3/6, PHREEQC, Geochemist’s Workbench, CHEMAPP, usw.) überführen zu können, werden ebenfalls unentgeltlich zur Verfügung gestellt.

Long-term safety analyses of German repositories of radioactive waste as well as underground repositories for chemical toxic waste and other uses (contaminated site remediation) urgently require a standardized, comprehensive thermodynamic reference database. The former "Thermodynamic Standard Database Working Party" was set up to establish such a database. The activities of that group have been supported within the integrated “THEREDA” (Thermodynamic Reference Database) project since July 2006 for an initial period of 3 years by the German Federal Ministries of Education and Research, of Economics, and by the Federal Office of Radiation Protection. THEREDA at present is composed of 5 partner institutions essentially representing the key German research institutions in the field of repository safety research.
THEREDA is to improve the transparency and validity of safety analyses in Germany and, for the first time, provides consistent thermodynamic datasets for the repository options discussed in Germany. Quality levels are indicated for each thermodynamic quantity on the basis of unambiguously defined evaluation criteria, which allow users to either include or exclude data in accordance with the specific problems at hand. Missing thermodynamic data are substituted in THEREDA by well-founded estimates, thus permitting future model calculations for safety analysis to be carried out on a clearly broader basis of data. The data are managed centrally in a database and will be available to users free of charge on the Internet. Import formats allowing THEREDA to be transferred into the most common modeling codes (EQ3/6, PHREEQC, Geochemist’s Workbench, CHEMAPP, etc.) are also made available free of charge.

Keywords: THEREDA; thermodynamic database; modelling; long term safety analyses

  • atw - International Journal for Nuclear Power 54(2008)4, 249-253

Publ.-Id: 11946

Complexation of Actinides with Organic and Inorganic Ligands

Geipel, G.; Bernhard, G.

Two basic requirements are needed for speciation calculations – a database including stability constants of the formed species and a computerized program for the real calculation. For the input analytical data or theoretical concentrations of the basic species can be used.
Hydroxide and carbonate are two of the most important environmental ligands. Fuger /1/ resumes many available data.
Up to now several databases have been developed /2-6/. However, the most up-to-date and best-reviewed databases for the actinide elements uranium, neptunium, plutonium and americium are the NEA databases /4, 7/. For speciation calculations the listed data should be used including the desired estimations for correction of the ionic strength. Two estimates are widely used:

  • Adapted SIT (Specific Ion Interaction Theory) method /4/.
  • Davies equation, including extension for high ionic strength /5/.

On the basis of the database several program codes can be used for calculation of the species distribution as function of concentrations, pH, ionic strength. Which one will be selected depends on experience of the user. The most important input in such calculations is the use of a correct and validated database.

The most useful program code is EQ 3/6 /8/. The estimation of the stability constants at the ionic strength of the solution to be calculated is included in this program. Also reactions at the interphase gas/liquid can be included.
A newer code is SPECIES /9/. The input is comfortable; also a program code for the estimation of formation constants at different ionic strength is available. However, and this is mentioned by the authors, the attached database (SC Database) should be used only after checking of the original literature. The program is not able to include reactions with gas phases (CO2/CO2 (a.)).
Also available on the web is the program MEDUSA /10/. In the program a database is included and there is also the possibility to correct the used stability constants.

Keywords: Speciation; Trace elements; Distribution diagrams

  • Invited lecture (Conferences)
    School cum Workshop on Trace Element Speciation (SElS-08), 21.-29.11.2008, Kolkata, India

Publ.-Id: 11945

Spectroscopic Techniques in Actinide Speciation Studies

Geipel, G.; Bernhard, G.

The determination of the behavior of actinides in the environment needs several spectroscopic techniques, adapted to spectroscopic properties and concentration ranges of these elements in the environment.

New techniques for the speciation of actinides have been developed during the past decades. Three main requirements are of importance:

  • License for handling of radioactive elements, especially for α-emitting actinides.
  • Availability of actinides, especially the higher actinides are available only in small amounts.
  • Speciation methods covering the concentration range of actinides expected or found in nature.

Speciation analysis can be distinguished into two types: non-invasive and invasive methods. Among the first group are spectroscopic methods. They are not restricted to the form of the species (solid, liquid, gas). Non-invasive methods need usually no treatment of the sample and allow the direct speciation of an element in its environment. Invasive methods in general are applicable to solids and solutions. They need normally a pretreatment and a separation of the sample. Sequential extraction can be used for the determination of species in solid systems. Besides for the separation of actinides /1/ extraction techniques are important for the determination of oxidation states of the actinides in solution. For example the oxidation states of plutonium can be determined using α-thenoyltrifluoroacetone (TTA) at pH = 0. Tetravalent plutonium is extracted to the organic phase, whereas all other oxidation states and polymeric plutonium remain in the aqueous phase. The same extraction procedure after addition of chromate allows to separate plutonium(III) and plutonium(IV). Other common extraction agents are tributylphosphate (TPB) and bis(2-ethyl-hexyl)-hydrogen-phosphate (HDEHP).

Keywords: Spectiation; Trace elements; Spectroscopy

  • Invited lecture (Conferences)
    School cum Workshop on Trace Element Speciation (SElS-08), 21.-29.11.2008, Kolkata, India

Publ.-Id: 11944

THEREDA - A Thermodynamic Reference Database

Moog, H.; Brendler, V.; Gester, S.; Richter, A.; Altmaier, M.; Marquardt, C.; Neck, V.; Hagemann, S.; Herbert, H.-J.; Willms, T.; Voigt, W.; Wollmann, G.; Wilhelm, S.

Part of the process to ensure the safety of radioactive waste disposal is the predictive modeling of the solubility of certain toxic components in a complex aqueous solution. To ensure the reliability of thermodynamic equilibrium modeling as well as to facilitate the comparison of such calculations done by different institutions it is necessary to create a mutually accepted thermodynamic reference database.

To meet this demand several institutions in Germany joined efforts and created THEREDA. THEREDA is a relational databank whose structure was designed in a way that facilitates internal consistency of thermodynamic data entered. It serves as backend to a variety of peripheral programs which allow for adding, editing, and extracting subsets of data. Data considered cover the needs for Gibbs Energy Minimizers and Law-of-Mass-Action-programs alike. Interaction parameters for an arbitrary number of mixed phases and p,T-functions of thermodynamic data may also entered. To enhance public use THEREDA is accessible via internet.

The paper gives an account about the present state of THEREDA as well as of future developments.

Keywords: THEREDA; thermodynamic database; waste disposal; internet

  • Lecture (Conference)
    Waste Management Conference WM 2009, 01.-05.03.2009, Phönix (AZ), USA
  • Contribution to proceedings
    Waste Management Symposium 2009: Waste Management for the Nuclear Renaissance, 01.-05.03.2009, Phoenix (Arizona), USA
    Waste Management Symposium 2009: Waste Management for the Nuclear Renaissance (8 Vols): Curran Associates, Inc., 9781615672523

Publ.-Id: 11943

Self-organized nanopatterns by ion erosion

Keller, A.; Facsko, S.; Möller, W.

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures have been found on a large variety of materials, such as semiconductors, metals, and insulating surfaces. The formation and early evolution of the ripple patterns can be qualitatively described by a linear continuum equation derived by Bradley and Harper. At longer times, however, nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
This talk will provide an overview of ion-induced pattern formation and summarize the theoretical basics. Recent experimental results on the evolution of nanoscale ripple patterns on amorphous surfaces during high-fluence ion sputtering will be presented and compared to the predictions of different continuum models. In addition, promising applications of nanorippled substrates as templates in thin film growth will be discussed.

  • Lecture (others)
    Seminar, 18.11.2008, Aarhus, Denmark

Publ.-Id: 11942

How can plants deal with the relatively high toxic uranium?

Viehweger, K.; Geipel, G.

Uranium is a widespread radioactive toxic heavy metal, released into the biosphere mostly by military purposes and nuclear industry. It is taken up by plant root systems and its chemical toxicity is much more dangerous than the radiological. Thus cell suspensions of rape (Brassica napus) revealed specific extracellular defence reactions after uranium exposure. These include characteristic pH-shifts of the culture medium caused by contact with the heavy metal. At the same time a transient release of fluorescent compounds from the cells occurred. These phytoalexins probably belong to the widespread group of flavonoids detected by HPLC and thin layer chromatography (TLC). They are able to interact with uranium, can alter the redox status of the metal and hence should protect the cell against this heavy metal poisoning. To gain an insight in these interactions time-resolved laser-induced fluorescence spectroscopy (TRLFS) and absorption spectroscopy were performed.
Former uranium mining sides in Eastern Germany were screened for uranium accumulating plants. An Arabidopsis halleri subspecies with high soil–plant transfer factors could be identified. Therefore a laboratory model system with this plant was established for investigations of uptake and sequestration of this metal. The initial characterisation of this experimental setup was carried out using “root-elongation-tests” to calculate the tolerance index and the measurement of some photosynthetic traits after uranium contact, respective.
Further research is under way to identify intracellular defence mechanisms, e.g. the involvement of glutathione and in this matter the formation of proteins possessing thiol groups (phytochelatins).

Keywords: Protein; plant cell; uranium

  • Invited lecture (Conferences)
    Kolloqiumsreihe des GTSC, 10.12.2008, Berkeley, USA

Publ.-Id: 11941

Uranium – species trace analytics in the nanomolar concentration range

Geipel, G.; Viehweger, K.; Bernhard, G.

Uranium is a ubiquitous element. Besides this depleted uranium amunition as well as uranium mining and milling and manifold other use of uranium leads to an increase of uranium contamination in the environment.
Application of laser-induced and time-resolved methods allow the direct determination of uranium speciation at extremely low concentrations. This behaviour can be directly observed due to the properties extraorbitant luminescence properties of uranium-(VI).
Especially the uranium ammunition can generate locally high concentrations of uranium in the environment. Weathering processes of the uranium metal lead in a first step to the formation of uranium minerals. Depending on the composition of the soil the formation of several types of minerals can be estimated. Especially the content of phosphate from fertilizers and the aluminium from soil components are involved in the mineral formation.
By use of time-resolved laser-induced fluorescence spectroscopy (TRLFS) the mineral type can be determined without any destruction. A large database of luminescence spectra, obtained from uranium minerals of the collection of the Technical University Mining Academy Freiberg, enables us to identify the formed uranium mineral. In a second step the formed minerals than undergo further weathering processes, forming dissolved uranium species.
In the former uranium mining areas of eastern Germany we could discover a new dissolved uranium carbonate species. However, the uranium concentration of about 2 mg/L in these mining related waters is relatively high. Nevertheless the carbonate and calcium concentration are high enough to form a very stable dicalcium-uranyl-tricarbonate species. This species is of great importance, as its existence explains the uranium migration at the Hanford site.
The pure carbonate species do not show any luminescence properties at room temperature. Therefore the samples have to be frozen to temperatures below 220 K, in order to minimize the dynamic quench effect of the carbonate anion. This increases also the luminescence intensity and the luminescence lifetime of all carbonate containing species.
Following the possible transport of uranium under environmental conditions we may start with the weathering of uranium compounds in the soil or in a mining waste rock pile. The seepage water contains about 2 mg/L uranium and the speciation is mainly influenced be the formation of the dicalcium-uranyl-tricarbonate species. The input of these seepage water leads to a dilution of the uranium by about three orders of magnitude. Using the cryogenic technique in TRLFS we could also determine the uranium speciation in the river water nearby the former uranium mining area. The uranium concentration was about 2 µg/L uranium and in the river water mainly uranyl-tricarbonate species are formed.
In this case uranium may come back to the food chain by the production of mineral waters. We have studied the uranium speciation in several German mineral waters with uranium concentrations between 50 ng/L and 5 µg/L.
Contact of dissolved uranium with living cells at ambient conditions changes dramatically the uranium speciation. Some examples fluorescence properties of uranium species relevant to the environment are shown. The change of this speciation can be observed then due to a change in luminescence properties. Besides of several organic phosphate binding forms although other uranium species were found as uranium bond to phenolic and thiol groups. Some of them do not emit any luminescence at room temperature. Nevertheless low temperature measurements allow the assignment of species not fluorescing at room temperature, due to strong dynamic quench effects of H2O molecules and COO- groups.

Keywords: Uranium; Trace concentration; species determination

  • Invited lecture (Conferences)
    Kolloqiumsreihe des GTSC, 10.12.2008, Berkeley, USA

Publ.-Id: 11940

THz beam line for pump probe experiments at FLASH: recent results and developments from the comissioning

Gensch, M.; Fruehling, U.; Stojanovic, N.; Seidel, W.; Tavella, F.; Wieland, M.; Schade, U.; Lee, J. S.; Hübers, H.-W.; Semenov, A.; Duesterer, S.; Grimm, O.; Hahn, U.; Ploenjes, E.; Saldin, E. L.; Kocharyan, V.; Schneidmiller, E.; Rossbach, J.; Feldhaus, J.; Drescher, M.; Yurkov, M. V.

At the vacuum ultraviolet (VUV) free electron laser in Hamburg (FLASH) an infrared (IR) beamline is currently being comissioned that will allow novel pump-and-probe experiments combining coherent IR pulses with the FEL radiation in the VUV spectral range. It provides useful IR, respectively THz, radiation generated by a purpose built undulator over the wavelength range from 200 micron to presently 14 micron. The undulator is implemented “in series” to the VUV undulators of FLASH and the length of the IR beamline can be matched to that of an existing VUV beamline so that overlap with VUV pulses generated by the same electron bunch can be achieved. Hence natural synchronization of the two pulses is expected. First results of the comissioning are shown and an outlook on future experiments and upgrades of the beamline as well as its photondiagnostics will be given.

  • Poster
    FLASH users-meeting and kick-off workshop: THZ beamline, 08.-10.09.2008, Hamburg, Deutschland

Publ.-Id: 11939

THz free-electron laser FELBE at the radiation source ELBE

Seidel, W.

This paper reviews the basic properties of the infrared free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf. A few highlight experiments using the cw-operation are discussed. Driven by a superconducting linear accelerator, FELBE continuously generates infrared pulses with a repetition rate of 13 MHz. In addition, operation in a macropulse modus (pulse duration >100µs, repetition rate ≤ 25 Hz) is possible. At present FELBE delivers µJ pulses with typical duration of about 0.9-30 ps in the wavelength range 4-230 µm. Furthermore we give an outlook on the experiments will use the beam of FELBE in the High Magnetic Field Laboratory Dresden (HLD). The HLD will provide pulsed magnetic fields up to 60 T. It operates as a user facility since 2007.

  • Invited lecture (Conferences)
    FLASH users-meeting and kick-off workshop: THZ beamline, 08.-10.09.2008, Hamburg, Deutschland

Publ.-Id: 11938

Three years of cw-operation at FELBE - Experiences and applications

Seidel, W.; Cizmar, E.; Drachenko, O.; Helm, M.; Justus, M.; Lehnert, U.; Michel, P.; Ozerov, M.; Schneider, H.; Schurig, R.; Stehr, D.; Wagner, M.; Winnerl, S.; Wohlfarth, D.; Zvyagin, S.; Kehr, S. C.; Eng, L. M.

This paper reviews the basic properties of the infrared free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf. A few highlight experiments using the cw-operation are discussed. Driven by a superconducting linear accelerator, FELBE continuously generates infrared pulses with a repetition rate of 13 MHz. In addition, operation in a macropulse modus (pulse duration >100µs, repetition rate ≤ 25 Hz) is possible. At present FELBE delivers µJ pulses with typical duration of about 0.9-30 ps in the wavelength range 4-230 µm. Furthermore we give an outlook on the experiments will use the beam of FELBE in the High Magnetic Field Laboratory Dresden (HLD). The HLD will provide pulsed magnetic fields up to 60 T. It operates as a user facility since 2007.

  • Poster
    30th International Free Electron Laser Conference FEL 2008, 24.-29.08.2008, Gyeongju, Korea
  • Contribution to proceedings
    30th International Free Electron Laser Conference FEL 2008, 24.-29.08.2008, Gyeongju, Korea

Publ.-Id: 11937

Absorption spectroscopy of Eu and Am with a Liquid Waveguide Capillary Cell

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

The combination of UV-vis spectroscopy with a LWCC results in a higher sensitivity and allows measurements at low heavy metal concentrations. We demonstrate the utility of the LWCC for the investigation of complex formation between heavy elements and organic substances by showing the first results achieved with Eu and Am.

Keywords: UV-vis; europium; americium; LWCC; detection limit; complexation

  • Poster
    Seventh International Conference on Nuclear and Radiochemistry (NRC7), 24.-29.08.2008, Budapest, Hungary

Publ.-Id: 11936

Determination of the polarization characteristics of the ELBE free electron laser

Lee, J. S.; Gensch, M.; Hinrichs, K.; Seidel, W.; Schade, U.

In this work, we investigated polarization characteristics of the ELBE infrared free electron laser at the experimental position by adapting imaging ellipsometry technique. We found that the laser beam has a Gaussian-like power distribution with a diameter of 3–4 mm and exhibits a linearly polarized character throughout the whole area investigated. We also evaluated the degree of polarization amounting to 98% which demonstrates a tiny depolarization effect during the beam transfer via several optical elements from the source to the experimental position.

Keywords: Free electron laser; Infrared; Polarization; Stokes parameter

  • Infrared Physics and Technology 51(2008)6, 537-540

Publ.-Id: 11935

Assessment of surface area normalisation for interpreting distribution coefficients (K(d)) for uranium sorption

Payne, T. E.; Brendler, V.; Comarmond, M. J.; Nebelung, C.

Adsorption of radionuclides on soils and sediments is commonly quantified by distribution coefficients (K(d) values). This paper examines the relationship between K(d) values for uranium(VI) adsorption and the specific surface area (SSA) of geologic materials. We then investigate the potential applicability of normalising uranium (U) K(d) measurements using the SSA, to produce 'K(a) values' as a generic expression of the affinity of U for the surface. The data for U provide a reasonably coherent set of K(a) values on various solid phases, both with and without ligands. The K(a) representation provides a way of harmonising datasets obtained for materials having different specific surface areas, and accounting for the effects of ligands in different systems. In addition, this representation may assist in developing U sorption models for complex materials. However, a significant limitation of the K(a) concept is that sorption of radionuclides at trace levels can be dominated by interactions with specific surface sites, whose abundances are not reflected by the SSA. Therefore, calculated K(a) values should be interpreted cautiously.

Keywords: Sorption; Specific Surface Area; Radionuclides; Retardation; Nuclear Waste; Contamination; Database; Modelling

  • Lecture (Conference)
    SPERA'08 - 10th South Pacific Environmental Radioactivity Conference, 24.-27.11.2008, Christchurch, New Sealand
  • Journal of Environmental Radioactivity 102(2011), 888-895
    DOI: 10.1016/j.jenvrad.2010.04.005

Publ.-Id: 11932

Bakterielle Hüllproteine (S-Layer) und ihre technische Anwendung

Raff, J.

Bakterielle S-Layer bilden als hoch geordnete Oberflächenstruktur bei vielen Bakterien und Archaeen die Grenzfläche zwischen Zelle und Umgebung. Als solche besitzen diese Proteinhüllen zahlreiche interessante Eigenschaften, die für die Entwicklung neuer Materialien genutzt werden können. Der Vortrag gibt einen Überblick über die laufenden und geplanten Arbeiten mit bakteriellen S-Layern .

  • Lecture (others)
    Vortrag im Rahmen des Besuchs des Sächsischen Textilforschungsinstituts, 18.11.2008, Chemnitz, Deutschland

Publ.-Id: 11931

Solving the stellar 62Ni problem with AMS

Dillmann, I.; Rugel, G.; Faestermann, T.; Korschinek, G.; Lachner, J.; Maiti, M.; Poutivtsev, M.; Walter, S.; Käppeler, F.; Erhard, M.; Junghans, A. R.; Nair, C.; Schwengner, R.; Wagner, A.

The nucleosynthesis of elements heavier than iron can be almost completely ascribed to the ’slow’ and the ’rapid’ neutron capture processes. Among the nuclei involved, long-lived radioactive isotopes like 63Ni (t1/2= 100.1 yr) assume key positions, because their beta-decay rate becomes comparable to the neutron capture rate. The resulting competition leads to branchings in the s-process nucleosynthesis path. An accurate knowledge of the stellar neutron capture cross sections of 62,63Ni is required since these two cross sections affect the entire weak s-process flow towards heavier nuclei (A about 90). Until recently the experimental values for the (n,gamma) cross section of 62Ni at stellar temperatures (kT=30 keV) ranged between 12 and 37 mb. Stellar models using the lower value revealed a strong overproduction of 62Ni in postexplosive production factors of supernova type II explosions which intensified the question if this is due to uncertainties in the stellar models or in the nuclear input. This discrepancy could now be solved by two activations with following AMS using the GAMS setup at the Munich tandem accelerator which are also in perfect agreement with a recent time-of-flight measurement. The resulting (preliminary) Maxwellian cross section at kT=30 keV was determined to be <>30keV = 23.4 ± 4.6 mb. Additionally, we have measured for the first time the 64Ni(gamma,n)63Ni cross sections close to threshold which can transformed into the inverse 63Ni(n,gamma) channel by detailed balance. Photoactivations at 13.5 MeV, 11.4 MeV and 10.3 MeV were carried out with the ELBE accelerator at Forschungszentrum Dresden-Rossendorf. A first short AMS measurement of the sample activated at 13.5 MeV revealed a cross section smaller by more than a factor of 2 compared to previous predictions.

Keywords: nucleosynthesis neutron capture branching supernova photoactivation accelerator masse spectrometry

  • Contribution to proceedings
    AMS-11 - THE 11th International Conference on Accelerator Mass Spectrometry, 14.-19.09.2008, Roma, Italy
    Nuclear Instruments and Methods in Physics Resarch B: Elsevier
  • Nuclear Instruments and Methods in Physics Research B 268(2010), 1283
    DOI: 10.1016/j.nimb.2009.10.153

Publ.-Id: 11930

Influence of biofilms on the migration behavior of radionuclides

Krawczyk-Bärsch, E.; Arnold, T.; Großmann, K.

Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in the EPS of a living multispecies biofilm grown on biotite plates. These particles ranged between 1 and 7 µm in width and up to 20 µm in length and were located at the bottom and at the edges of biofilms colonies. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilm.
Electrochemical microsensor studies of the O2 concentrations within the biofilm identified depleted zones closer to the biofilm/air interface which may trigger uranium redox processes. The microsensor profile measurements in the stable multispecies biofilms exposed to uranium in ecologically relevant concentrations (1x10-5 and 1x10-6 M) showed that the O2 concentration decreased faster with increasing biofilm depth compared to the uranium free biofilms. In the uranium containing biofilms, the O2 consumption, calculated from the steady-state microprofiles, showed high consumption rates of up to 61.7 nmol cm-3 s-1 in the top layer (0–70 µm) and much lower consumption rates in the lower zone of the biofilms. Staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI) confirmed the high respiratory activities of the bacteria in the upper layer by confocal laser fluorescence microscopy (CLSM). The fast decrease in the oxygen concentrations in the biofilm profiles showed that the bacteria in the top region of the biofilms, i.e., the metabolically most active biofilm zone, battle the toxic effects of aqueous uranium with an increased respiratory activity. This increased respiratory activity results in O2 depleted zones closer to the biofilm/air interface which may trigger uranium redox processes, since suitable redox partners, e.g., extracellular polymeric substance (EPS) and other organics (e.g., metabolites), are sufficiently available in the biofilm porewaters. Such redox reactions may lead to precipitation of uranium (IV) solids and consequently to a removal of uranium from the aqueous phase.

Keywords: biofilm; uranium microscopy; microsensor

  • Poster
    IP FUNMIG Final Workshop, 24.-27.11.2008, Karlsruhe, Germany

Publ.-Id: 11929

Strahlenschutz im PET-Zentrum Dresden-Rossendorf

Preusche, S.; Füchtner, F.; Zessin, J.; Beuthien-Baumann, B.; Bergmann, R.; Walther, M.

kein Abstrakt verfügbar

  • Invited lecture (Conferences)
    Strahlenschutz in Medizin, Forschung und Industrie, 13.-14.11.2008, Hamburg, Deutschland

Publ.-Id: 11928

Conduction at domain walls in oxide multiferroics

Seidel, J.; Martin, L. W.; He, Q.; Zhan, Q.; Chu, Y.-H.; Rother, A.; Hawkridge, M. E.; Maksymovych, P.; Yu, P.; Gajek, M.; Balke, N.; Kalinin, S. V.; Gemming, S.; Wang, F.; Catalán, G.; Scott, J. F.; Spaldin, N. A.; Orenstein, J.; Ramesh, R.

We report the observation of room temperature electronic conductivity at ferroelectric domain walls in BiFeO3. The origin and nature of the observed conductivity is probed using a combination of conductive atomic force microscopy, high resolution transmission electron microscopy and first-principles density functional computations. We show that a structurally driven change in both the electrostatic potential and local electronic structure (i.e., a decrease in band gap) at the domain wall leads to the observed electrical conductivity. Additionally we demonstrate the potential for device applications of such conducting nanoscale features.

Keywords: multiferroics; domain walls; boundary conductivity; bismuth ferrate

Publ.-Id: 11927

Structure, electronics and transport properties in nanostructured materials

Gemming, S.

Transition metal chalcohalides MX2 can form a wealth of diverse nanostructures, largely as a function of the synthesis conditions. The obtained structures range from large octahedral and fullerene-like hollow clusters and cylindrical nanotubes close to the nominal composition M:X = 1:2 to smaller, two-dimensional platelet-shaped clusters under sulfur excess and to one-dimensionally elongated nanowires under sulfur-deficient conditions. All of those structures exhibit specific electronic properties that differ from the ones of the pure bulk and open up a large spectrum of nanostructure applications, that still includes the lubricant aspect, but reaches further to catalysis and electronic transport. One-dimensionally delocalized electronic states provide the basis for the higher activity, reactivity and conductivity in nanostructured MX2. Larger triangular and hexagonal platelets exhibit a so-called 'brim'-state along the circumference of the cluster, which assists the activation of sulfur atoms contained in raw oil; hence platelet-based catalysts are employed for desulfurization. One-dimensional wires with compositions MX an M2X3 are composed of a central metallic wire coated by an insulating sulfur and/or halide shell. They exhibit a very high structural regularity, hence, ballistic conductivity may be obtained in such structures. The stability, structure and metallicity of such wires have been calculated in excellent accordance with recent scanning-probe experiments. In addition, the calculations showed, that wires can act as electromechanical switches, because they undergo a symmetry-dependent metal-insulator transition upon twisting. Thus, metal chalcohalide nanostructures are versatile building blocks for nanoscale catalytic and electronic devices.

Keywords: molybdenum sulfide; metal chalogenide; chalcohalide; nanowire; platelet; density-functional calculations

  • Lecture (others)
    SFB 767 - Controlled Nanosystems: Interaction and Interfacing to the Macroscale, 20.-21.11.2008, Konstanz, Deutschland

Publ.-Id: 11926

Flux dependence of cluster formation in neutron irradiated weld material – Small-angle neutron scattering experiments and rate theory simulation

Bergner, F.; Birkenheuer, U.; Ulbricht, A.; Weiss, F.-P.

Small-angle neutron scattering was applied to investigate the size distribution of irradiation-induced defect-solute clusters in a reactor pressure vessel weld material containing 0.22 wt% copper. In order to identify flux effects the material was exposed to neutron irradiations at two different levels of neutron flux in such a manner that the same value of neutron fluence was accumulated. We observed a pronounced effect of neutron flux on the cluster size, whereas the total volume fraction of the irradiation-induced clusters was found to be insensitive to the level of flux. The result is compatible with a rate theory model according to which the range of applied fluxes covers the transition from a flux-independent regime at lower fluxes to a regime of decelerating cluster growth. The issue of the effect of flux on the mechanical properties is also addressed.

  • Poster
    IEEE Dresden 2008, 20.-24.10.2008, Dresden, Deutschland
  • Contribution to proceedings
    IEEE Dresden 2008, 20.-24.10.2008, Dresden, Deutschland
    IEEE 2008 Nuclear Science Symposium Conference Record

Publ.-Id: 11925

Accelerator mass spectrometry (AMS) and ion beam analysis (IBA) with the new 6 MV accelerator at FZ Dresden-Rossendorf

Merchel, S.; Grambole, D.; Grötzschel, R.; Munnik, F.; Neelmeijer, C.

Ion beam analysis @ FZD
Since more than 30 years ion beam analysis is performed at the Forschungszentrum Dresden-Rossendorf (FZD) for the determination of element distributions. Due to continuous upgrades of the different experimental set-ups, we are able to routinely perform:
• Rutherford Backscattering Spectrometry (RBS) & Channeling (C-RBS)
• Nuclear Reaction Analysis (NRA)
• Elastic Recoil Detection Analysis (ERDA)
• Particle-Induced X-Ray Emission (PIXE)
• Particle-Induced Gamma-Ray Emission (PIGE)

State-of–the art with “old” 5 MV accelerator
Most of our applications lie within material sciences. We are able to measure non-destructively “all natural” elements, i.e. hydrogen to uranium, most elements with lateral, some even in 3-D resolution with the following typical parameters (highly depending on matrix and elements):
• depth resolution: 1-30 nm
• depth range: nm-µm
• lateral resolution: few µm
• usual mapping area: 2x2 mm2
• maximum sample size: 3x10 cm2 (vacuum) & “unlimited” (external beam)
• detection limits: ~10 µg/g (H); 500 µg/g – 1% (He-F); 10-100 µg/g (Na-U)
For some elements, e.g. H/D, isotope analysis is possible.

Outlook for “new“ 6 MV accelerator
In summer 2009, the 30-year-old Russian-made van-de-Graaff 5 MV accelerator will be replaced by the latest 6 MV Tandetron model from HVE, which is even more sophisticated than the lately installed 5 MV version from Southern France. Our new accelerator will need of course less maintenance allowing more beam time for real measurements with respect to our old one. It might be also possible to expand from two to three 8-hour-shifts a day with the new fully automatic system.
Scientifically, the main advantages for ion beam analysis are an increased depth range by a factor of 2 for ERDA and improved detection limits for NRA. In addition, the machine will be installed with special equipment for accelerator mass spectrometry (AMS).

There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses (e.g. isobars) are nearly completely eliminated. Thus, AMS generally provides much lower detection limits in comparison to conventional mass spectrometry (typical isotope ratios 10-10-10-15). Our AMS system will offer excellent measurement capabilities also for external users.
In contrast to common low-energy AMS facilities in Europe, which have mainly specialized in radiocarbon analyses (14C), the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV.
Especially in environmental and geosciences, the determination of long-lived (t1/2 > 0.3 Ma) cosmogenic radionuclides like 10Be, 26Al, and 36Cl became more and more important within the last decades. Using these nuclides dating of mass movements, e.g. volcanic eruptions, rock avalanches, earth quakes, and glacier movements is possible.

Keywords: ion beam analysis; accelerator mass spectrometry; comogenic nuclides

  • Poster
    Seminar Activation Analysis and Gamma-Spectroscopy (SAAGAS 22), 25.-27.02.2009, Wien, Austria

Publ.-Id: 11924

On the reliability of target element data for cosmogenic nuclide exposure dating

Merchel, S.; Bichler, M.; Sterba, J. H.

Radioactive or stable cosmogenic nuclides are products of nuclear reactions induced by cosmic rays. The development of the interdisciplinary field of the quantification of cosmogenic nuclides has been increased dramatically in the last decades. Especially, the progress in the field of accelerator mass spectrometry (AMS) improved detection limits and accuracy and allows nowadays the determination of radionuclide concentrations as low as of 104-105 atoms/(g rock).
In particular, in-situ produced cosmogenic nuclides – so-called terrestrial cosmogenic nuclides (TCN) - have proved to be valuable tools for quantifying Earth's surface processes. Here, the work-horses are 10Be and 26Al in quartz, and 36Cl in Ca- or K-rich minerals.
In siliceous environments both radionuclides, 10Be and 26Al, are pure high-energy spallation products, thus, the influence on the secondary neutron field by changing trace element concentrations in the original bulk matrix is negligible. Another advantage: Usually, quartz can be easily cleaned from other mineral phases making the normalization to (g SiO2)-1, i.e. only two target elements, very straightforward. There is usually no need for a full chemical analysis.

In contrast, 36Cl can be produced by several different nuclear reactions: Spallation on different target elements, mainly Ca and K (to a lesser extent Ti and Fe), induced by high-energy neutrons and muons. Thus, every sample that will be analysed for TCNs has to be chemically analyzed for the main target elements, too. Additionally, as 36Cl can be produced by thermal neutron-capture on 35Cl, trace elements influencing the thermal neutron field have to be unavoidably also measured. This includes U and Th as “background”-neutron emitter, all elements with high neutron absorption cross sections like B, Gd, and Sm, and all light elements, which take part in (gamma,n)-reactions. Thus, a complete bulk rock analysis (for the neutron field) and measurements of the main target elements in the dissolved fraction are absolutely necessary. As 36Cl concentrations will be normalized to (g Ca)-1, (g K)-1 etc., the overall result cannot be more precise then the corresponding target element data.

We have selected typical samples with different fractions of silicate- and calcite-rich phases to have them analyzed by the method of choice of most TCN-user: inductively coupled plasma optical emission spectrometry (ICP-OES). Unfortunately, the two French CNRS laboratories involved, CEREGE and CRPG-SARM, did not produce concordant results for all elements of interest. Thus, we have tested the capability of two non-destructive activation analysis methods: We performed Instrumental Neutron Activation Analysis (INAA) ourselves at Vienna and we sent aliquots for Prompt Gamma Activation Analysis (PGAA) to Budapest.

The four laboratories performed differently depending on the analyte. For example, all methods produce CaO-data with unacceptable high uncertainties. PGAA seems to underestimate the true CaO-value of some samples. K2O-data (@ 0.1-0.7%) by ICP-OES has exceptional high uncertainties and is constantly lower as corresponding INAA- and PGAA-data. As a conclusion, it seems advisable to use more than a single analytical method, if precise TCN applications are intended.

Keywords: terrestrial cosmogenic nuclides (TCN); cosmogenic nuclide exposure dating; INAA; PGAA; ICP-OES

  • Poster
    Seminar Activation Analysis and Gamma-Spectroscopy (SAAGAS 22), 25.-27.02.2009, Wien, Austria

Publ.-Id: 11923

36Cl exposure dating with a 3-MV tandem

Steier, P.; Golser, R.; Kutschera, W.; Martschini, M.; Merchel, S.; Orlowski, T.; Priller, A.; Vockenhuber, C.; Wallner, A.

36Cl AMS measurements at natural isotopic concentrations have yet been performed only at tandem accelerators with 5 MV terminal voltage or beyond. We have developed a method to detect 36Cl at natural terrestrial isotopic concentrations with a 3-MV system, operated above specifications at 3.5 MV.
An effective separation was obtained with an optimized split-anode ionization chamber design (adopted from the ETH/PSI Zurich AMS group), providing a suppression factor of up to 30.000 for the interfering isobar 36S. Despite the good separation, a relatively high sulfur output from the ion source (36S-/35Cl- = 5×10-11) resulted in a background corresponding to 36Cl/Cl = 3×10-14. The method was applied to samples containing between 105 and 106 atoms 36Cl/g rock from sites in Italy and Iran, which were already investigated by other laboratories for surface exposure dating. The 36Cl/Cl ratios in the range from 2×10-13 to 5×10-12 show a generally good agreement with the previous results.
These first measurements demonstrate that also 3-MV tandems, constituting the majority of dedicated AMS facilities, are capable of 36Cl exposure dating, which is presently the domain of larger facilities.

Keywords: 36Cl; AMS; isobar separation

Publ.-Id: 11922

A multi-radionuclide approach for in-situ produced terrestrial cosmogenic nuclides: 10Be, 26Al, 36Cl and 41Ca from carbonate rocks

Merchel, S.; Benedetti, L.; Bourlès, D. L.; Braucher, R.; Dewald, A.; Faestermann, T.; Finkel, R. C.; Korschinek, G.; Masarik, J.; Poutivtsev, M.; Rochette, P.; Rugel, G.; Zell, K.-O.

In contrast to siliceous environments, there is a severe lack of cosmogenic nuclides, which can be used for in-situ dating of calcareous environments. Thus, we have investigated other nuclides than 36Cl as possible dating tools by cross-calibration. Cosmogenic 10Be is highly contaminated with atmospheric 10Be and cannot be removed quantitatively, even by a very sophisticated chemical cleaning procedure. Only working on clay-free calcite provides correct 10Be data, giving a 2.7 times higher production rate of 10Be from CaCO3 than from SiO2. Though, the production rate of 26Al is only ~4.6% (CaCO3 relative to SiO2), 26Al can be easily determined in calcite, as the low intrinsic 27Al concentration yields to nearly as high 26Al/27Al as within corresponding quartz. The measurement of 41Ca, mainly produced via thermal-neutron-capture, is hindered by very low 41Ca/Ca: < 2.5x10-15.

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

Publ.-Id: 11921

Experimental insight into the radiation resistance of zirconia-based americium ceramics

Belin, R. C.; Martin, P. M.; Valenza, P. J.; Scheinost, A. C.

Ceramics intended for use as nuclear fuels, transmutation targets or actinide immobilization matrices have to endure severe conditions including internal radiation. While zirconia-based materials with defect-fluorite structure have shown high tolerance against external ion-beam irradiation, few experimental studies have demonstrated that these structures also resist under more realistic conditions, i.e. with homogeneous internal radiation from α-emitting actinides within the structure. Here, we provide for the first time experimental insight into the radiation-resistance mechanisms of americium pyrochlore 241Am2Zr2O7. We combined X-ray diffraction and X-ray absorption spectroscopy to probe changes of both the long-range and the short-range structure. The phase transition from the pyrochlore to the defect-fluorite structure was accompanied with an unusual negative lattice expansion. Once the fluorite structure was reached, neither volume changes nor amorphization were observed over a time course of 4 years corresponding to 0.8 dpa. The disorder relaxation proceeds through the simultaneous formation of cation antisites and oxygen Frenkel pairs, in line with former molecular dynamics studies. Moreover, EXAFS analysis revealed a disruption in the long-range order and a markedly different development in the local environments of zirconium and americium: while Am-O polyhedra show an increasing disorder, the Zr-O polyhedral units remain unchanged. However, they rotate along edges and corners, thereby reducing the structural strain imposed by the growing disorder around americium. We believe it is this particular property of the compound that provides the remarkable resistance to radiation, making it attractive for a wide range of nuclear applications.

Keywords: americium; EXAFS; XRD; Rietveld; ceramics; pyrochlore; transmutation; radiation resistance; Frenkel pairs

  • Inorganic Chemistry 48(2009), 5376-5381
    DOI: 10.1021/ic900369b
  • Lecture (Conference)
    Actinides 2009, 12.-17.07.2009, San Francisco, USA

Publ.-Id: 11920

Highest Pulsed Magnetic Fields in Science and Technology, Assisted by Advanced Finite-Element Simulations

Herrmannsdörfer, T.; Zherlitsyn, S.; Wosnitza, J.

The generation of high magnetic fields for scientific and industrial applications, in particular those techniques which meet critical limits of field strength, coil heating, and mechanical stress as well, require a careful design and modelling based on finite-element simulation. In order to describe the mutual dependences of the electrical, thermodynamical, and mechanical processes in such systems in a reasonable way, the use of multi-physics modules of the finite-element software packages becomes more and more relevant. Here, the designs based on finite- element simulations of pulsed magnetic field coils for extreme magnetic flux densities up to 100 Tesla as well as pulsed power supplies for the generation of electrical current pulses up to the Mega-Ampere range are presented. A survey on recent technical progresses in science and industry is given.

  • Invited lecture (Conferences)
    COMSOL Conference 2008, 04.-06.11.2008, Hannover, Germany

Publ.-Id: 11919

In-situ investigations at BM20-ROBL

Grenzer, J.; Baehtz, C.; Beckers, M.; Jeutter, N. M.; von Borany, J.

The beamline BM20 operated by the Forschungszentrum Dresden-Rossendorf is located at ESRF storage ring and divided into two experimental stations for spectroscopy and diffraction. A double crystal monochromator provides an energy range from 6 to 30 keV. A six-circle goniometer allows different scattering and diffraction methods like XRR, XRD, GID and GISAXS, additionally even in combination with X-ray spectroscopy. Different detector systems (point, one, two dimensional or energy dispersive) as well as an additional detector bank for large area detectors are available. A major part of ROBL-MRH experiments are performed as in-situ X-ray studies using a dual magnetron sputtering deposition chamber equipped optionally with an ion gun for ion beam bombardment and erosion. Using a hemispherical Beryllium dome scattering experiments can be carried out up to 1200°C under vacuum conditions.
The focus of the beamline research is on thin film investigations and on new nanostructured materials. X-ray investigations are a very important tool to find the correlation between the functional and the corresponding structural properties that are generating this function and to explain the influence of different deposition conditions, substrate parameters etc. by the underlying physical processes making it possible to design thin films with specific properties.
By the use of the deposition chamber for reactive magnetron sputtering thin films of Ti2AlN were for the first time synthesized. Different ways of synthesis, the thermal and phase behavior were investigated [1, 2].
A key element for the development of a new generation of solar cells are nanocrystalline materials. In-situ studies of the growth of SiO2/GeOx multilayers were carried out to create Ge nanocrystalls by subsequent thermal decomposition or directly by sputtering at elevated temperatures.

[1] C. Höglund et al.; Appl. Phys. Lett., 90, 174106, (2007).
[2] M. Beckers et al.; Appl. Phys. Lett., 89, 074101, (2006).

Keywords: synchrotron radiation; nanostructures

  • Lecture (Conference)
    Materials Science and Engineering 2008 - MSE08, 01.-04.09.2008, Nuernberg, Germany

Publ.-Id: 11918

X-ray scattering and diffraction from ion beam induced ripples in crystalline silicon

Biermanns, A.; Pietsch, U.; Grenzer, J.; Hanisch, A.; Facsko, S.; Carbone, G.; Metzger, T. H.

We report on periodic ripple formation on Si(001) surfaces after bombardment with Xe+ ions with energies between 5 and 35 keV under incidence angles of 65 degrees and 70 degrees. The sputter process leads to the formation of a rippled amorphous surface layer, followed by a rippled interface toward crystalline material. Using grazing-incidence small-angle scattering and diffraction, we show that the surface morphology is exactly reproduced at the interface. In addition, we observe that the crystal lattice close to the interface is anisotropically expanded. The lattice expansion parallel to the ripples is larger than those perpendicular to them.

Keywords: X-ray scattering; Ion beam irradiation

  • Journal of Applied Physics 104(2008)4, 044312
  • Lecture (Conference)
    XTOP 2008 - 9th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, 15.-19.09.2008, Linz, Austria

Publ.-Id: 11917

Neue Kupferchelatoren auf der Basis von pyridinhaltigen 1,4,7-triazacyclononan-Liganden

Ruffani, A.; Stephan, H.; Fähnemann, S.; Bergmann, R.; Steinbach, J.

Ziel/Aim: Ziel der Arbeit ist die Entwicklung von bifunktionellen Markierungsbausteinen für eine milde und selektive Radiomarkierung von biologisch aktiven Molekülen mit dem Positronenstrahler Kupfer-64. In diesem Zusammenhang sind Pyridin-haltige Derivate des 1,4,7-Triazacyclononans (TACN) besonders geeignet, weil sie sehr stabile Kupfer(II)-Komplexe bilden sowie eine schnelle Komplexbildungskinetik aufweisen. Weiterhin ist es leicht möglich, diese Verbindungen mit Maleinimid- und Isothiocyanat-Derivaten oder Aktivestern zu modifizieren und damit an Biomoleküle zu kuppeln. Erste Untersuchungen zeigen, dass Komplexe von Kupfer-64 mit einem TACN-Carbonsäurederivat sowie ein entsprechendes Peptidkonjugat auf der Basis eines stabilisierten Bombesinfragments BBN(7-14) eine hohe in vitro- und in vivo-Stabilität besitzen.[1] Bombesin und dessen Derivate weisen eine hohe Affinität zum Gastrin Releasing Peptide Rezeptor (GRPR) - der auf einer Vielzahl von Tumoren, wie Brust-, Prostata- und Pankreaskarzinomen, überexprimiert ist - auf. Aus diesem Grund sind radioaktiv markierte BBN-Derivate für die Diagnostik und Therapie von Tumoren sehr interessant.

Methodik/Methods: Die Umsetzung von Aminoethylmaleinimid mit einem TACN-Carbonsäurederivat durch Peptidkupplung mittels HBTU in Anwesenheit der Hünigbase DIPEA führt zu einer Maleinimid-haltigen TACN-Verbindung. In analoger Weise wurden über eine Peptidkupplung, stabilisierte BBN(7-14)-Derivate an TACN-Liganden gebunden. Ein weiterer vielseitig einsetzbarer Synthesebaustein wurde durch Umsetzung von zweifach pyridylmethylsubstituiertem TACN mit einem Boc-geschützten Phenylendiamin-Derivat erhalten. Durch Abspaltung der Schutzgruppe erhält man das freie Amin, das durch Behandlung mit Thiophosgen in das Isothiocyanat überführt wird.

Ergebnisse/Results: Markierungsstudien des Maleinimid-funktionalisierten TACN-Derivates mit Kupfer-64 weisen auf eine sehr schnelle Komplexbildungskinetik unter physiologischen Bedingungen hin. Untersuchungen mit dem Modellpeptid Glutathion zeigen, dass dieser Markierungsbaustein sehr effektiv an Thiolgruppen bindet. Bioverteilungsstudien mit Cu-64-Komplexen von TACN-Bombesin-Konjugaten in Wistar Ratten ergaben eine Anreicherung des Radiotracers im Pankreas. Untersuchungen mittels Kleintier-PET an PC-3 Tumor-Mäusen zeigten eine Akkumulation dieser Tracer im Tumorgewebe, so dass eine klare Visualisierung der Tumore möglich ist.

Schlussfolgerungen/Conclusions: Bifunktionelle Liganden auf der Basis von pyridinhaltigen TACN-Derivaten können unter physiologischen Bedingungen effektiv mit Kupfer-64 markiert werden. Die mit Maleinimid-, Isothiocyanat-Gruppen und Aktivester funktionalisierten TACN-Derivate können effizient an Biomoleküle gekuppelt werden. TACN-Bombesin-Konjugate besitzen ein hohes Anwendungspotential zur Darstellung von GRPR-reichem Gewebe.

[1] G. Gasser et al., Bioconjugate Chem. 2008, 19, 719-730.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A55
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11916

Time resolved and nonlinear spectroscopy of semiconductor quantum structures using an infrared free-electron laser

Helm, M.

there is no abstract available

Keywords: free electron laser; semicondcutor quantum structures; infrared spectroscopy

  • Lecture (others)
    Seminarvortrag Universität Marburg, 07.11.2008, Marburg, Deutschland

Publ.-Id: 11915

New Density Functional Theory Investigations of Vanadium Silicides

Thieme, M. B.; Gemming, S.

Vanadium and silicon form several binary compounds; the most well characterized structures have
the compositions V:Si= 3:1, 5:3, 6:5, 1:2. Spin-Density-functional band-structure calculations with the
Projector Augmented Wave-method have been carried out to investigate the structural properties and the
phase stability for the experimentally known binary crystals.

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11914

The system Vanadium:Silicon - an ion-beam generated diluted magnetic semiconductor? – a case study

Thieme, M. B.; Gemming, S.; Potzger, K.; Anwand, W.; Grötzschel, R.; Grenzer, J.

Since approximately 20 years we have controversial discussions about the possibility of ion beam generated diluted magnetic semiconductors (DMS) primarily transition metals in silicon. Now a detailed study has been done for the system Vanadium:Silicon. Vanadium and silicon form several binary compounds; the most well characterized structures have the compositions V:Si= 3:1, 5:3, 6:5, 1:2; as well as different constellations of substitutional and interstitial vanadium atoms in a silicon crystal matrix. Suitable magnetic properties of a semiconductor are important for DMS.

  • Poster
    IBMM 08 - 16th International Conference on Ion Beam Modification of Materials, 03.09.2008, Dresden, Deutschland

Publ.-Id: 11913

Master Curve testing of highly irradiated IAEA RPV steels JRQ and JFL

Viehrig, H.-W.; Zurbuchen, C.

While the Master Curve (MC) method is gradually entering brittle fracture safety assessment procedures world-wide, knowledge is still lacking about its limits of applicability to highly neutron irradiated material. In this paper two reactor pressure vessel (RPV) steels A533B Cl. 1 (IAEA reference material code JRQ) and A508 Cl.3 (code JFL) were scrutinized for possible deviations of the postulated invariant MC shape and the MC validity for macroscopically inhomogeneous microstructure. Besides tensile and Charpy-V tests, MC tests were performed on Charpy size three-point bend specimens in the unirradiated, neutron irradiated with fluences up to nearly 1020 n/cm² (E>1MeV) and recovery heat treated condition. Evaluation procedures include Master Curve reference temperature T0 determination according to ASTM E1921-05 as well as additional analysis methods such as SINTAP, multimodal MC method (MML) and the Unified Curve (UC). Integrity assessment according to ASME Code Cases N-629 and N-631has been applied. It is shown that the standard MC concept provides a precise description of the fracture toughness for all conditions, even exceptionally well for the highly irradiated state. No MC shape change could be observed, whereas the UC concept indicates a significant influence of irradiation on the fracture toughness curves for the highly irradiated JRQ.

Keywords: Fracture Toughness; RPV steels, neutron irradiation, Master Curve; Unified Curve

  • Lecture (Conference)
    Workshop on Trend Curve Development for Surveillance Data with Insight on Flux Effects at High Fluence: Damage Mechanisms and Modelling, 19.-21.11.2008, Mol, Belgium

Publ.-Id: 11912

THEREDA - Online

Richter, A.; Brendler, V.

Der Zugang zur THEREDA-Datenbank erfolgt über die URL Der Internetzugang vereint dabei die Schnittstelle für externe Nutzer zum Abfragen von Datensätzen sowie eine Schnittstelle zur Administration des gesamten Internetauftritts im Rahmen des Content Management Systems (CMS) Joomla! Joomla! ist Open Source Software, durch die große Community, die das Projekt ständig weiterentwickelt, ist gewährleistet, dass ein problemloser Zugriff auf den Inhalt und die Datenbank über einen sehr langen Zeitraum erfolgen kann. Mit Joomla! verfügt THEREDA über ein sehr gutes Tool, die Datenbank mit geringem Pflegeaufwand und über einen langen Zeitraum zur Verfügung zu stellen. Über erhalten Besucher der Webseite Informationen zum Projekt und den THEREDA-Partnern, können Dokumente downloaden sowie Links zu anderen relevanten Projekten finden. Zusätzlich nutzen die Mitglieder des Verbundprojektes die Internetseite als Intranet (nach Anmeldung). Im Vortrag werden der gegenwärtige Stand des THEREDA-Online-Auftrittes und die interaktiven Möglichkeiten für die Nutzer vorgestellt.

Keywords: THEREDA; Thermodynamic Database; online; downloads; interactive; CMS; Joomla

  • Lecture (Conference)
    Fachgespräch "Entwicklung einer thermodynamischen Referenzdatenbasis - THEREDA", 12.11.2008, Karlsruhe, Deutschland

Publ.-Id: 11911

Respiratory Gating Facilitating 4D Imaging in MRI, CT, and FDG-PET for GTV Definition in Patients with NSCLC

Abolmaali, N.; Abramyuk, A.; Koch, A.; Richter, C.; Hoinkis, C.; Zips, D.; Zöphel, K.; Enghardt, W.; Baumann, M.

Respiratory motion blurs PET-images and may cause localization errors in studies acquired using breath holding such as CT and MRI. To reduce motion related influences on radiation therapy planning of lung cancer, image acquisition may be gated. The aim of our study was to compare motion of primary lung tumors as detected by respiration gated data acquired with PET, CT, MRI.

So far, this ongoing study included four patients (median age 72.5 years) with NSCLC scheduled for radiation therapy. All patients were investigated under free breathing conditions and respiratory gated FDG-PET, CT and MRI. Image data was separated into eight comparable gates uniformly distributed over the breathing cycle. After blinded GTV-definition, volumes and centers of volumes (COV) were generated from all gates and all modalities. Comparative statistics were done using t-tests, confidence intervals and Lin's concordance analysis.

Median tumor volumes in PET, CT and MRI were 28 ml, 69 ml, and 46 ml, respectively. t-tests revealed significant differences for the comparison CT/MRI (p=0.04) and PET/CT (p=0.05), but not for MRI/PET (p=0.09). The medians of the maximum distances the COV traveled during the entire breathing cycle in PET, CT and MRI were 0.42 cm, 0.95 cm, 0.93 cm, respectively. t-tests revealed nearly significant differences between PET and CT (p=0.06) and MRI and PET (p=0.06), while the result for CT and MRI was in good agreement (p=0.74). Lin’s concordance analysis (OCCC=0.172) revealed best congruency between CT and MRI (rho=0.55), only fair congruency between MRI and PET (rho=0.2) and poor congruency between PET and CT (rho=0.02).

In our early experience, the differences in GTV-definition of NSCLC in 4D imaging by PET, CT and MRI are mainly related to the observer’s experience. As shown in other tumors before, PET revealed the smallest tumor volume. Due to the low movement of the tumors evaluated in the patients included so far, results are preliminary. Nevertheless, results suggest that MRI may be applicable in radiation therapy planning for GTV-definition. The inclusion of a higher number of patients with pronounced tumor movement during breathing is required.

Gated 4D imaging in NSCLC may increase planning accuracy in radiation oncology. In selected patients, gated radiation therapy might be advantageous and may reduce toxicity in normal tissues.

  • Lecture (Conference)
    RSNA 2008, 30.11.-05.12.2008, Chicago, USA

Publ.-Id: 11910

Small animal PET with hCT-derived cell-penetreting peptides

Bergmann, R.; Közle, I.; Neundorf, I.

Cell-penetrating peptides (CPP) derived from the native peptide hormone human calcitonin (hCT) represent a high potential drug delivery system for in vivo intracellular targeting of diagnostic and therapeutic compounds. Cell penetration of hCT-derived substances was verified in vitro, however, the knowledge about CPP in vivo distribution and metabolism is very limited. Therefore we studied the in vivo radiopharmacology of Ga-68 radiolabeled DOTA modified, hCT-derived CPP in rats using small animal PET (1).

Three hCT-derived peptides (hCT(9-32), LGTYTQDFNKFHTFPQTAIGVGAPNH2; [f12,16]-hCT(9-32), LGTfTQDfNKFHTFPQTAIGVGAP-NH2; random (rd)-hCT(9-32), FLTAGQNTIQTPVKTGGHFPFADY-NH2) were at the N-terminus modified with DOTA. The internalization of the stabilized peptide, biodistribution and kinetics of the radiolabeled Ga-68-DOTA-hCT(9-32) or Ga-68-DOTA-[f12,16]-hCT(9-32) or Ga-68-DOTA-rd-hCT(9-32) were studied with small animal PET. The arterial blood at different time points, and urine were analyzed for radio-metabolites.

Ga-68-DOTA-[f12,16]-hCT(9-32) was in vitro internalized. In vivo the radio-peptides were eliminated mainly by the renal system, more than 50% of the injected dose was found at 60 min after injection in the urine, only small amounts of the activity were detected in the intestine. The general activity retention in the body was low, except the kidneys. The blood clearance of the original peptides reached terminal half-lifes of Ga-68-DOTA-hCT(9-32) 15.9 min, Ga-68-DOTA-[f12,16]-hCT(9-32) 20.9 min, Ga-68-DOTA-rd-hCT(9-32) 15.8 min; the relative AUC in comparison to Ga-68-DOTA-hCT(9-32) were 100%, 170%, and 51%, respectively. The patterns of metabolic cleavage in the arterial blood were different. The Ga-68-DOTA-[f12,16]-hCT(9-32) was metabolized to three radio-metabolites after 30 min, the other radiopeptides were degraded to more than five radioactive metabolites.

It was shown that D-amino acid modifications of the sequence hCT(9-32) resulted in an increased in vivo stability and lower retention in the kidney cortex. The blood clearance and the elimination of the Ga-68-DOTA-peptides were relatively high and should be decreased by structural changes to enhance the tissue uptake of this drug carrier system.

(1) Neundorf I, Rennert R, et Bergmann R, Bioconjug Chem. 2008 Aug;19(8):1596-603.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A78
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11909

Phasenkorrelierte Schwächungskorrektur von 4D-PET mit Hilfe von 4D-CT

Richter, C.; Just, U.; Pönisch, F.; Enghardt, W.

wird nachgereicht

  • Lecture (Conference)
    „Der Wiener Kongress“ - DEGRO ÖGRO 2008, 01.-04.05.2008, Wien, Austria
  • Contribution to proceedings
    „Der Wiener Kongress“ - DEGRO ÖGRO 2008, 01.-04.05.2008, Wien, Österreich
    Strahlentherapie und Onkologie - Abstactband zum DEGRO-ÖGRO-Kongress, München: Urban&Vogel, 61-61

Publ.-Id: 11908

Repeat 4D-CTs during fractionated radiotherapy of lung cancer: a clinical protocol providing a basis of target definition for gated radiotherapy

Hoinkis, C.; Appold, S.; Enghardt, W.; Reiffenstuhl, C.; Richter, C.; Wieczorkowski, L.; Zips, D.; Zöphel, K.; Kotzerke, J.; Baumann, M.

Purpose: Planning target volume definition is one of the crucial points for gated radiotherapy. To gain reliable information on variability of tumour position and tumour motion during the course of fractionated radiotherapy a longitudinal study was implemented.

Patients and Methods: Patients with locally advanced, inoperable non small cell lung cancer are enrolled in a clinical protocol for curative treatment with 66 Gy @ 2 Gy. For treatment planning a 4D-FDG-PET/4D-CT with phase correlated attenuation correction of the PET in treatment position was performed (Biograph 16, Siemens). Target volumes are derived from the Internal Target Volume (ITV) + 7 mm (Clinical Target Volume) + 8 mm (Planning Target Volume) for the first week. The latter margin is reduced to 5 mm after 6 fractions if deviations in tumour location are small. For treatments patients are positioned by X-ray verification (ExacTrac-Xray, BrainLab). Repeat 4D-CT scans are acquired with an in-room CT (Primatom, Siemens) directly before treatment for the first 5 fractions and subsequently twice per week (i.e. 16 4D-CTs per patient). Immediate evaluation of the 4D-CTs includes verification of patient positioning and adequateness of treatment fields (Pinnacle, Philips). Further evaluation of data includes intra- and interfractional variability of tumour volume and centre of gravity. Margins will be evaluated simulating gated radiotherapy.

Results: The protocol started in January 2008. Up to now 5 patients are enrolled, 2 of them have completed their treatment. For the first 5 patients a PTV reduction to 79,5 % (SD 2,1 %) after the first treatment week could be reached, which led to a decrease of Mean Lung Dose of 0.7 Gy (SD 0.3 Gy). Preliminary evaluation of the 4D data shows minor intrafractional variability of the tumour volume compared to greater interfractional variations. The preliminary data rather suggest variability in contouring than true variability in tumour volume. The trajectory of centre of gravity associates with the tumour motion.

Conclusion: The preliminary data suggest only small setup variability during treatment. Extension of the data base and further analysis will address if dose escalation by introducing gated radiotherapy is possible.

Supported by BMBF (03ZIK/OncoRay) and Siemens Medical Solutions.

  • Poster
    ESTRO 2008, 14.-17.09.2008, Göteburg, Konungariket Sverige
  • Abstract in refereed journal
    Radiotherapy and Oncology 88(2008)Suppl. 2, S376-S377

Publ.-Id: 11907

Small animal PET investigation of regional pulmonary perfusion in prone and supine position of rats

Bergmann, R.; Richter, T.; Közle, I.; Schiller, E.; Ragaller, M.; Steinbach, J.

Aim: Ga-68 radiolabeled human albumin microspheres (Ga-68-DOTA-HSAM) with a diameter of 20 µm are expected to lodge in the pulmonary capillaries. The purpose of the study was to quantify the pulmonary perfusion (Qr) in prone and supine position in terms of their imaging manifestations in healthy rats.

Methods: The animal research committee of the Landesdirektion Dresden approved the animal facilities and the experiments according to institutional guidelines and the German animal welfare regulations. Seven anesthetized, spontaneous breathing Wistar rats (297 +/- 53 g), were positioned either in prone (n=3) or supine (n=4) position and Ga-68-DOTA-HSAM were infused. Qr was achieved by imaging the radioactivity distribution in the lungs. The animal PET 3D volume data were reconstructed with 3D OSEM MAP algorithm. After first measurement animals were arranged in opposite position and the PET measurement was repeated. The 3D data were at first manually coregistered and residual differences in the relative positioning of the lungs were corrected user independent (Rover, ABX GmbH, Germany). Masks for defining regions of interest (ROI) were set in the coregistered volume data for all animals. Mean normalized Qr values (Qmean) of the dorsal and ventral parts of the lungs were calculated of the basis of an automatic ROI-setting including threshold analysis.

Results: Vertical gradient of regional perfusion was significantly steeper in the supine, -0.131 ± 0.01 %/cm, than in the prone animals -0.055 ± 0.01 %/cm (P = 0,002), indicating that the vertical distribution of regional perfusion was in dependent regions more accentuated in the supine than in the prone infused animals. Changes in the vertical gradient after rotation in the opposite position resulted in a vertical gradient of -0.093 ± 0.031 %/cm in prone position. Vertical gradient in the supine position of prone infused animals was -0.093 ± 0.015 %/cm. Position changes did not produce significant changes in vertical gradient in supine (P = 0.125) and in prone infused animals (P = 0.25).
Conclusions: Ga-68-DOTA-HSAM (20µm) can be used for pulmonary perfusion studies in rats with small-animal PET. Qmean was not affected by posture, whereas vertical gradient indicating significant decrease from dependent to the nondependent regions of Qr in supine infused animals in supine position. Lung structure distribution changes are less pronounced than perfusion distribution changes in prone and supine position.
Distribution pattern of regional perfusion in prone and supine position in normal rat lungs will be used as reference data set for studies on injured rat lungs.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A92
  • Poster
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11905

Event-basierte Bewegungskorrektur in der klinischen Routine

Langner, J.; Mölle, H.; Dittrich, S.; Hofheinz, F.; Oehme, L.; Beuthien-Baumann, B.; van den Hoff, J.

Eine event-basierte Bewegungskorrektur verbunden mit einer räumlichen Transformation jeder Line-of-Response (LOR) erlaubt eine exakte Korrektur von Patientenbewegungen in der PET. In den letzten Jahren haben wir bereits verschiedene Verbesserungen dieses Verfahrens vorgestellt. Neben Optimierungen zur klinischen Akquisition von List-Mode Daten, sowie der Entwicklung von Methoden zur Analyse der Patientenbewegungen wurde gezeigt, dass mit der Reduzierung der durch das limitierte Gesichtfeld begründeten Artefakte (Out-of-FOV) ein letztes wichtiges Hindernis für die klinische Nutzung bei Hirnmessungen beseitigt werden konnte. Ziel der nunmehr vorliegenden Arbeit war es, nach der klinischen Integration den Einfluss dieser Bewegungskorrektur innerhalb eines Patientenkollektivs mit starken Patientenbewegungen genauer zu quantifizieren.

Für die klinische Nutzung wurden zwei graphische Nutzeroberflächen entwickelt, die eine einfache Aufnahme von Bewegungs- und List-Mode Daten ermöglichen. Nach erfolgter Akquisition werden die Daten vollautomatisch verarbeitet und bewegungskorrigiert. Für die Evaluation des Einflusses der Bewegungskorrektur auf die Bildqualität bzw. Quantifizierung dynamischer PET Aufnahmen wurden aus einem Patientenkollektiv von [18F]DOPA Hirnstudien N=15 Patientendaten anhand der Größe der Bewegung ausgewählt. Für den jeweils unkorrigierten und korrigierten Datensatz wurden 8 ROIs innerhalb des Striatum sowie eine Referenz-ROI positioniert. Neben dem Vergleich der Zeit-Aktivitäts-Kurven (TAC) wurde mittels eines irreversiblen Zweikompartment-Modells mit Referenzgewebe die jeweiligen Einstromraten (R0k3) durch eine Patlak Auswertung berechnet und durch Kalkulation parametrischer Bilder entsprechend mit den Werten der unkorrigierten Daten verglichen.

Die entwickelten Benutzeroberflächen erlauben eine einfache Nutzung der List-Mode- sowie Bewegungsaufnahme in der klinischen Routine. Beim Vergleich der Datensätze konnten qualitative Verbesserungen sowie ein besseres Signal-to-Noise-Ratio (SNR) durch die Korrektur festgestellt werden. Des Weiteren zeigt die quantitative Auswertung der dynamischen Aufnahmen Unterschiede von bis zu 30% im Verlauf der TACs. Auch die Auswertung der 0k3 Parameter zeigt eine relevante Änderung und der Vergleich der parametrischen Bilder eine Reduzierung von Artefakten.

Durch die einfache Bedienung der Benutzeroberflächen konnten diese nunmehr für die generelle Aufnahme von Hirnaufnahmen an unserer Einrichtung etabliert werden. Bei der Auswertung der Patientendaten zeigte sich, dass die event-basierte Bewegungskorrektur nicht nur die Bildqualität sondern auch die Quantifizierung der Tracerkonzentrationen bei PET-Hirnstudien positiv beeinflusst. In Folge dessen werden nun alle Hirnaufnahmen mit deutlicher Patientenbewegung in unserer Einrichtung standardmäßig mit der event-basierten Bewegungskorrektur durchgeführt.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A22
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11904

A Comparison of CT-Based Attenuation Correction Strategies for PET Data of Moving Structures

Richter, C.; Hoinkis, C.; Just, U.; Pönisch, F.; Woithe, J.; Enghardt, W.

Respiratory motion introduces image artefacts not only in standard 3D-CT but also in 3D-PET images due to two reasons: (a) Smearing of the activity concentration and (b) an incorrect attenuation correction. In 4D-PET the effect of smearing becomes negligible but the influence of incorrect attenuation correction remains important.
To investigate the quantitative influence of attenuation correction on both PET acquisition methods (3D- and 4D-PET), a comprehensive phantom study was performed using a respiratory motion mimicking phantom on a dedicated Siemens Biograph 16 PET/CT, which had the extended capability of acquiring 4D-PET and 4D-CT data. The used respiratory motion phantom is able to simulate typical lung tumor motion in two dimensions with two possible patterns of respiration. The 3D- and 4D PET data sets were corrected with different CT attenuation data, namely a standard 3D-CT (pitch 1.5), a slow 3D-CT (pitch 0.5), an ultraslow 3D-CT (pitch 0.15), and also an average CT and a maximum intensity projection, both calculated from a 4D-CT (pitch 0.1). Additionally, the 4D-PET was corrected phase-wise with the 4D-CT (phase-correlated attenuation correction). For that purpose the synchronization between 4D-PET and 4D-CT has been verified. The reconstructed PET images were analyzed concerning the reconstructed volume, the activity concentration and the full width half maximum (FWHM) of the activity distribution in the direction of the highest phantom movement. Additionally, the motion amplitude of the phantom was obtained from the 4D-PET data sets.
Our results suggest that attenuation correction of 3D-PET data should be performed with a slow CT. However, the 4D PET data should be reconstructed using phase-correlated attenuation correction with a 4D-CT.

  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
    IEEE Conference Report
  • Poster
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany

Publ.-Id: 11903

Small animal PET with new Cu-64-chelating ligands coupled to stabilized bombesin

Bergmann, R.; Walther, M.; Juran, S.; Gasser, G.; Pietzsch, J.; Stephan, H.; Steinbach, J.

Aim: Gastrin releasing peptide receptors (GRPR) are overexpressed in different human tumors like prostate, breast and squamous cell carcinomas. The goal of this study was to compare the biodistribution and metabolism of a stabilized bombesin analogue radiolabeled with two new Cu-64-complexes for PET imaging of GRPR expression in xenografted mice.

Methods: Cu-64 was complexed with a bis(2-pyridylmethyl) derivative of 1,4,7-triazacyclononane (TAC) and a bispidine 1,5-dicarboxylic acid derivative (Cu-64-N2Py4-OH(COOH)2) conjugated to a stabilized bombesin (BBN) derivative βhomoGlu-βAla-βAla-[Cha13, Nle14]BN(7-14) (Garcia Garoya et al. 2007). Biodistribution, elimination, and metabolism were studied in rats. Tumor accumulation was exemplarily evaluated with small animal PET in xenografted mice bearing prostate (PC3), squamous cell carcinoma (FaDu), and colorectal (HT-29) human tumors. Cu-64 chloride was studied for comparison.

Results: PET imaging of Cu-64-N2Py4-OH(COOH)2-BBN in mice 1 h after injection revealed tumor-to-background ratios of 2.1 (PC3), 2.4 (FaDu control), 1.0 (FaDu blocked), and 1.5 (HT-29). The uptake found in PC3 tumors with tissue sampling was significantly higher (5.3 control; 2.6 blocked). In comparison to the Cu-64-TAC-BBN, the uptake of Cu-64-N2Py4-OH(COOH)2-BBN in rat pancreas and intestine was lower but the accumulation in kidney, liver, and stomach was higher. The metabolic stabilities of the Cu-64-labeled BBN‘s studied were comparable. More than 85% of the original substances were remained after 1 hour in vitro incubation with rat blood or blood plasma. In vivo all compounds were fast metabolized in rats, and lower than 5% of the original compounds were recovered in arterial blood plasma 1 hour after injection. However, the metabolism in xenografted nude mice was slower, after 1 hour 12% of blood plasma activity correspond to the original compound.

Conclusion: Both investigated new Cu-64 chelating agents conjugated to a stabilized BBN analogue showed typical BBN biodistribution and GRPR specific accumulation in vivo. The differences in biodistribution and metabolism between Cu-64-TAC- and Cu-64-N2Py4-OH(COOH)2) labeled BBN demonstrate the influence of the Cu-64 chelating units on these processes, especially on the nonspecific activity biodistribution. Comparison of biodistribution data of the BBN analogues and Cu-64 chloride indicate only marginal, if any, in vivo copper demetalation, revealing high in vivo stability of the copper complex units. With further optimization of the radiolabeling in particular of specific activity the low specific uptake should increase. The studied chelating agents appear to be promising candidates for copper labeling of peptides under mild conditions.
Partly supported by the 6th framework EU-project “BioCare”, proposal # 505785.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A56
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11901

Kalibrierungsmessungen mit Kugelphantomen führen zu einer fehlerhaften Volumenbestimmung bei schwellwertbasierten Verfahren in der PET

Dittrich, S.; Hofheinz, F.; Langner, J.; Pötzsch, C.; van den Hoff, J.

Für eine genaue Volumenabgrenzung von Zielstrukturen in PET-Aufnahmen mittels schwellwert-basierten Algorithmen wird der Einfluss verschiedener Faktoren (Objektgröße, Bildkontrast, etc.) auf den volumenreproduzierenden Schwellwert üblicherweise durch Kalibrierungsmessungen unter Nutzung von Zylinderphantomen mit eingesetzten Glashohkugeln bestimmt. In einer quantitativen Bewertung einer derartigen Phantommessung wurde auch nach Untergrundsubtraktion eine Abhängigkeit des relativen Schwellwertes vom Bildkontrast nachgewiesen. In der vorliegenden Arbeit soll nun systematisch der Einfluss der inaktiven Glaswand in den Kugelphantomen auf die beobachtete Kontrastabhängigkeit des untergrundbereinigten Schwellwertes untersucht werden.

Es wurden Kalibrierungsmessungen unter Verwendung eines Zylinderphantoms (Durchmesser: 20 cm, Höhe: 18 cm) durchgeführt. Die im Zylinder befindlichen 6 Kugeleinsätze besitzen Volumina von 2,5 ml bis 27 ml und eine Glaswanddicke von 1,2 mm. In 9 Phantommessungen mit einem ECAT EXACT HR+ (Siemens/CTI, Knoxville, Tennessee) wurden der Zylinder und die Kugeln mit unterschiedlichen Aktivitätsmengen (Fluor-18) befüllt um das Signal-Untergrund-Verhältnis und damit den Bildkontrast zu variieren. Der analytische Ausdruck für die Faltung der Objektfunktion (Aktivitätsverteilung) mit der Point Spread Function (PSF) wurde an die aus den experimentellen Bilddaten gewonnenen radialen Aktivitätsprofile angefittet.

Die aus den Least Squares Fits ermittelten Radien sind stets kleiner als die wahren Kugelradien, wenn die inaktive Glaswand in der Objektfunktion vernachlässigt wird. Erst unter expliziter Berücksichtigung der Wanddicke von 1,2 mm der Hohlkugeln in der Objektfunktion verschwindet diese scheinbare Radiusreduktion. Mit den berechneten theoretischen Aktivitätsprofilen der Phantomkugeln konnte zudem eine Absenkung des untergrundbereinigten Schwellwertes bei steigendem Untergrundanteil in den Bilddaten verifiziert werden. Die gemessene Kontrastabhängigkeit des relativen Schwellwertes nach Untergrundsubtraktion konnte daher vollständig mit dem Vorhandensein der inaktiven Glaswände in den Phantomstudien erklärt werden.

Inaktive Wände zur Separation verschiedener Aktivitätsbereiche in PET Phantommessungen verursachen auch nach erfolgter Untergrundsubtraktion eine Kontrastabhängigkeit des volumen-reproduzierenden Schwellwertes. In realen Patientendaten kann daher aufgrund der Abwesenheit inaktiver Wände der untergrundbereinigte optimale Schwellwert als unabhängig vom Bildkontrast angenommen werden. Kalibrierungsmessungen zur Bestimmung des korrekten Wertes für den volumenreproduzierenden Schwellwert können daher auf eine einfache Phantommessung ohne Untergrundaktivität reduziert werden.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A93
  • Poster
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11900

Stability of Yttrium-90-citrate-, Erbium-169-citrate- and Rhenium-186-sulfur-colloid in vitro

Bergmann, R.; Pinkert, J.

Aim: Yttrium-90-citrate- (YMM-1), Erbium-169-citrate- (ERMM-1), and Rhenium-186-sulfur-colloid (Re-186-MM1) were applied in radiosynovectomy (RSO), a local intraarticular injection of radionuclides in colloidal form for radiotherapy. The local metabolism of the colloidal particles is not fully understood; however, knowledge about the leakage is important for risk assessment. Therefore we investigated stability of the radiocolloids by by equilibrium dialysis, which provided information about interaction of the colloids with buffer components, synovia in controlled equilibrium conditions.

Materials & Methods: Carrier added YMM-1, ERMM-1, Re-186-MM1 colloids were dispersed and dialyzed against synovia, different electrolytes and buffers separated by dialysis membranes with a molecular weight cut off (MWCO) of 10,000 Dalton. The activity concentration in the dialysis compartment was studied up to 24 hours. Tl-201-chloride, F-18-FDG, F-18-fluoride, and Er-169-chloride were used as reference tracers.

Results: The equilibria were reached at the latest 10 hours after start of dialysis. The ionic Er-169-chloride (as negative control) and Re-186-perrhenate showed very similar diffusion kinetics compared with reference radiotracers. The colloidal radionuclides, incubated and dialyzed against electrolytes comparable with plasma (MEM Dulbeco medium), human synovia, or phosphate containing buffers were not detected in the dialysis solution (lower 0.5% of applied dose (%ID)), except Re-186-MM1. Significant amounts of compounds were found in the dialysis compartment. Incubation of the colloids with isotonic sodium chloride or 0.1 M hydrochloric acid was followed by an activity release into the dialysis solution YMM-1 (67%ID) and ERMM-1 (62%ID).

Conclusion: The increased stabilities of the carrier added radiocolloids studied in different electrolyte solutions was mainly a result of the presence of phosphate ions. The low solubility of the phosphates of rare earth elements, the binding to synovia proteins, and hydroxylation were the main mechanisms of colloidal particle stabilization or reformation of free or secondary formed Erbium or Yttrium ions. This generally results in formation of particles of low diffusibility, increasing the retention of the radiocolloids inside the joint before the radionuclide-loaded colloidal particles are phagocytozed by macrophages in the inflamed synovial membrane.

  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A72
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland

Publ.-Id: 11899

Optimum Voxel Size for Reconstruction of In Beam PET Data

Shakirin, G.; Crespo, P.; Fiedler, F.; Wagner, A.; Enghardt, W.

At the heavy ion therapy facility at the Gesellschaft für Schwerionenforschung Darmstadt, Germany, an in-beam PET scanner is operated for quality assurance monitoring simultaneously to the therapeutic irradiation. The PET scanner, which is completely integrated into the treatment facility, registers the annihilation γ - rays following the decay of minor amounts of β+ radioactive nuclei produced via nuclear reactions between the ions of the therapeutic beam and the atomic nuclei of the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose distributions can be detected. The solution currently implemented for the reconstruction of in-beam PET data is the ML-EM algorithm adapted to the low statistics case and to the dual head geometry. The size of image elements (voxels) influences significantly the quality of the image. A small voxel size increases the resolution but produces high oscillations of a signal. Large voxels produce homogeneous images, however, with low spatial resolution. The size of the voxel is always a compromise between suppressing signal oscillations which requires larger voxel size, and covering small imaging details which requires smaller voxel size. The standard voxel side-length used for the BASTEI scanner, 1.6875 mm, is exactly 1/4 of the crystal width. For in-beam PET the size of the voxel can be enlarged for typical irradiation fields from the standard (1.6875 mm)3 to 2 × 2 × 3 mm3 without loss of quality. The images reconstructed with bigger voxel are less noisy and still contain enough information about activity in small cavities and deviations of the range. Reconstruction performs almost two times faster for the 2 × 2 × 3 mm3 voxel.

Keywords: in-beam PET; reconstruction; voxel size; radiotherapy; ML-EM; OS-EM; RFS-EM

  • Poster
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
  • Contribution to external collection
    in: GSI Scientific Report 2008, GSI: GSI, 2009
  • Poster
    OncoRay Retreat meeting, 14.-15.01.2009, Bautzen, Germany

Publ.-Id: 11898

On the Optimum Strategy for Subsets Based Reconstruction of In-Beam PET Data

Shakirin, G.; Crespo, P.; Enghardt, W.

At the heavy ion therapy facility at the Gesellschaft für Schwerionenforschung Darmstadt, Germany, an in-beam PET scanner is operated for quality assurance monitoring simultaneously to the therapeutic irradiation. The PET scanner, which is completely integrated into the treatment facility, registers the annihilation γ - rays following the decay of minor amounts of β+ radioactive nuclei produced via nuclear reactions between the ions of the therapeutic beam and the atomic nuclei of the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose distributions can be detected. The solution currently implemented for the reconstruction of in-beam PET data consists of ML-EM and recently developed randomly filled subsets expectation maximization (RFS-EM) algorithms adapted to the low statistics case and to the dual head geometry. We proposed the reconstruction scheme for the subsets based RFS-EM algorithm. The scheme includes 4 iterations only, the number of subsets decreases from iteration to iteration and equals to 8, 6, 4, and 2 subsets, respectively. The scheme has been tested for two typical irradiation cases: head and neck (image space dimensions: 190 × 122 × 122 mm3) and pelvic (398 × 152 × 136 mm3) fields. The image quality was evaluated by means of visual inspection, root mean square error, and sensitivity of the method to the range deviations. The images reconstructed with the proposed RFS-EM scheme are of similar quality as those reconstructed with the reference 50 iterations of ML-EM. High quality of the system matrix is required for RFS-EM reconstructions of large fields.

Keywords: in-beam PET; radiation therapy; reconstruction; ML-EM; RFS-EM; OS-EM

  • Lecture (Conference)
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany
  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Germany

Publ.-Id: 11897

Broad-beam PIXE and µ-PIXE analysis of normal and in vitro demineralized dental enamel

Preoteasa, E. A.; Preoteasa, E.; Kuczumow, A.; Gurban, D.; Harangus, L.; Grambole, D.; Herrmann, F.

Dental enamel has been widely studied by particle-induced x-ray emission (PIXE), but less attention was paid to its demineralization, which leads to caries formation. Using broad-beam PIXE and mu-PIXE, we investigated normal enamel and the in vitro formation of pre-carious lesion in lactic acid solution, aiming also to evaluate intercusp differences within the same tooth. Broad-beam PIXE was performed using 3.0 MeV protons, and µm-PIXE maps of Ca, Fe and Zn were collected with 3.1 MeV protons at similar to 4 mu m resolution. In normal enamel a differentiated Ca-rich surface layer was observed, where Fe and Zn reached their highest levels. In deeper layers, Fe and Zn evidenced quasiperiodic patterns of maxima, possibly due to coupled diffusion-reaction catalytic processes involved in the enamel growth. Both Fe and Zn appeared to be located in a few distinct types of pools. Near the surface, demineralization induced an increase of Fe, Cu, Zn, Sr and Pb with respect to Ca, attr!
ibuted to partial hydroxyapatite dissolution and/or to chelate extraction and concentration of trace metals. Ca maps revealed limited changes in the surface layer and a massive loss in the inner enamel; here, Fe was almost depleted and Zn partially removed. The maps of Ca, Fe and Zn demonstrated major intercusp variations in both normal and altered enamel. Thus, broad-beam PIXE and mu-PIXE, which do not require (semi)thin sectioning of the tooth as the conventional methods, provide compositional and structural insight of normal dental enamel, of its intercusp variability and of the alterations produced by ill vitro demineralization, largely not accessible to the current techniques, and highly relevant for understanding the incipient caries formation.

  • X-Ray Spectrometry 37(2008)5, 517-535

Publ.-Id: 11896

Dipole transition strengths in 26Mg

Schwengner, R.; Rusev, G.; Fujita, Y.; Erhard, M.; de Frenne, D.; Grosse, E.; Junghans, A.; Kosev, K.; Schilling, K. D.; Wagner, A.

Dipole transitions from J = 1+ and 1- states in 26Mg were studied by means of photon scattering. The 1+ and 1- states were excited with bremsstrahlung produced by an electron beam of 13.0 MeV kinetic energy provided by the superconducting electron linear accelerator ELBE. We determined the transition strengths from 1+ and 1- states to the ground state as well as to low-lying states. In addition, we observed a J = 1 state at 11.154 MeV, above the neutron-separation energy of 11.093 MeV, and determined its partial gamma decay width for the first time.

Keywords: Nuclear structure; nuclear astrophysics; photon scattering; dipole transition strengths

Publ.-Id: 11895

Validation of 99mTc-labeled "4+1" fatty acids for myocardial metabolism and flow imaging Part 2: Subcellular distribution

Mirtschink, P.; Stehr, S. N.; Walther, M.; Pietzsch, J.; Bergmann, R.; Pietzsch, H.-J.; Weichsel, J.; Pexa, A.; Dieterich, P.; Wunderlich, G.; Binas, B.; Kropp, J.; Deussen, A.

Our group has synthesized technetium labeled fatty acids which are extracted into the myocardium and sequestered due to H-FABP binding. In this paper we further address the detailed subcellular distribution and potential myocardial metabolism of "4+1" 99mTc-fatty acids (FA).

Experiments were conducted using isolated hearts of wistar rats as well as wildtype and H-FABP-/--mice. Myocardium samples underwent subcellular fractionation (subsarcolemmal and intermyofibrillar mitochondria, cytosol with microsomes as well as nuclei and crude membranes) and analysis by TLC and HPLC.

The largest fraction of tissue radioactivity was associated with the cytosol (79.69 ± 8.88% of the infused dose =ID). 9.07 ± 0.95% and 3.43 ± 1.38% of the ID were associated with the subsarcolemmal and the intermyofibrillar mitochondrial fractions, respectively. In the rat heart, etomoxir, an inhibitor of the carnitin-palmitoyl transferase I, did not significantly decrease radioactivity associated with the mitochondrial fractions, whereas the myocardial extraction of 123I-IPPA (13.26% vs. 49.49% in control) and the radioactivity associated with the subsarcolemmal and the intermyofibrillar mitochondrial fractions was blunted. The percentage of the ID in the mitochondrial and crude fractions increased with the number of NH-amide groups of the FA derivative. Absence of H-FABP significantly decreased the radioactivity count in the cytosolic fraction (P < 0.001). No metabolic products of a 99mTc "4+1" FA could be detected in any isolated hearts. Myocardial 99mTc "4+1" FA extraction reflects binding to H-FABP and membrane structures (including the mitochondrial membrane). However, the compounds do not undergo mitochondrial metabolism, because they do not reach the mitochondrial matrix.

Keywords: Technetium fatty acid; Isolated heart; Subcellular distribution: H-FABP; Etomoxir

Publ.-Id: 11894

Validation of 99mTc-labeled "4+1" fatty acids for myocardial metabolism and flow imaging Part 1: Myocardial extraction and biodistribution

Mirtschink, P.; Stehr, S. N.; Walther, M.; Pietzsch, J.; Bergmann, R.; Pietzsch, H.-J.; Weichsel, J.; Pexa, A.; Dieterich, P.; Wunderlich, G.; Binas, B.; Kropp, J.; Deussen, A.

13C, 18F and 123I fatty acids (FA) are used for myocardial imaging. Recently, our group showed that 99mTc-labeled "4+1" FA are extracted into the rat and guinea pig myocardium. The present study evaluates determinants of myocardial uptake and whole body biodistribution of these FA derivatives. Studies were performed with isolated perfused hearts of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) with a FAT/CD36 deficiency, as well as with heart type FA binding protein knockout mice (H-FABP-/-) and H-FABP+/+. Eight "4+1"-99mTc- FA were applied for 3 min followed by 1 min washout. A mathematical model was used to analyze FA dynamics and binding to proteins. Whole body distribution was studied in rats with and without Tween 80. In vitro fractionation studies with 99mTc- FA assessed red blood cell uptake as well as association with plasma lipoproteins (VLDL, LDL and HDL). Myocardial extraction was 19.0-33.0 % of the infused dose in isolated WKY and 15.2-26.4 % in SHR hearts. However, H-FABP-/- showed a marked reduction of tracer extraction (2.8 ± 0.6%ID vs. 17 ± 2%ID P < 0.001). Uptake in red blood cells (< 1.2%ID) and incorporation into lipoproteins were negligible. Incubation of 99mTc-FA with albumin reduced ventricular extraction (P < 0.001) into the range of established iodinated FA tracers. Tween 80 improved the heart-to-liver ratio in the biodistribution studies. Myocardial uptake of "4+1"-99mTc- FA derivatives is dependent on H-FABP. These substances may therefore provide a new tool to specifically assess regional myocardial changes of H-FABP.

Keywords: Technetium fatty acid; isolated heart; H-FABP; CD36; myocardial imaging

Publ.-Id: 11893

Structure sensitive properties of Al-Si liquid alloys

Sklyarchuk, V.; Plevachuk, Y.; Yakymovich, A.; Eckert, S.; Gerbeth, G.; Eigenfeld, K.

Development and application of new expedient aluminium-based light alloys are a key issue in current materials science. In this study we present measurements of the thermophysical properties of liquid Al-7wt%Si, AlSi7Mg, and AlSi8Cu3 (wt.%) alloys, which are the most utilized casting alloys in the aluminium industry. Experimental data with respect to the density, viscosity, electrical and thermal conductivity have been determined in a wide temperature range and corresponding fit relations have been derived. A comparison with already published data and scaling relations available in the literature is given.

Keywords: Al-Si alloys; density; viscosity; electrical conductivity; thermal conductivity

Publ.-Id: 11892

The impact of a vertically travelling magnetic field on the flow in a cylindrical liquid metal bubble plume

Zhang, C.; Eckert, S.; Gerbeth, G.

This paper describes laboratory experiments for investigations of flow structures and related transport processes in liquid metal bubbly flows under the influence of a travelling magnetic field (TMF). The melt flow is driven by central gas injection into a cylindrical container filled with the low melting point alloy GaInSn. Velocity fields of both the liquid and the gaseous phase were measured non-intrusively using the ultrasound Doppler method. Depending on the travelling direction of the magnetic field, the TMF mainly imposes either a co-current or counter flow with respect to the original bubble-driven circulation. In general, the application of a downward TMF significantly increases the liquid velocity all over the fluid volume. An upward TMF gives rise to more complex structures of the velocity field resulting in alternately arranged up- and downstream regions. Both the upward and downward TMF promote the occurrence of non-steady motions with distinct velocity fluctuations leading to an intensification of related transport processes in the melt and providing the perspective of enhanced mixing efficiencies.

Keywords: fluid flow; liquid metal; bubble plume; magnetic field; mixing

  • Metallurgical and Materials Transactions B 40(2009)5, 700-711

Publ.-Id: 11891

Tunable-frequency ESR as a tool to study magnetic excitations in highly-correlated electron systems

Zvyagin, S.

In this presentation I will talk about recent development of the high-field Electron Spin Resonance program at the Dresden High Magnetic Field Laboratory (HLD) in Rossendorf. A unique feature of the facility is a combination of an extraordinary broad frequency range, 9 GHz - 100 THz (quasi-continuously covered by a number of tunable-frequency radiation sources, including THz-range free-electron laser FELBE) and high magnetic fields (up to 60 T). The talk will be illustrated by tunable-frequency ESR results obtained in sine-Gordon chain material Cu-PM and BEC candidate NiCl2-4SC(NH22 (known as DTN).

  • Lecture (others)
    Einladung durch BESSY, Helmholtz-Zentrum Berlin, 03.11.2008, Berlin-Adlershof, Deutschland

Publ.-Id: 11890

The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution

Hennig, C.; Ikeda, A.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Scheinost, A. C.; Skanthakumar, S.; Wilson, R.; Soderholm, L.; Servaes, K.; Görrler-Walrand, C.; van Deun, R.

investigated by uranium LIII-edge EXAFS and HEXS measurements with the aim to distinguish monodentate and bidentate coordinated sulfate in aqueous solution. UV-vis absorption spectroscopy has been used to differentiate the species and to determine the species distribution as a function of the [SO42−]/[UO22+] ratio. A monodentate coordination prevails in solutions with [SO42−]/[UO22+] ratio of 1, where UO2SO4 is the dominant species. Besides the dominating monodentate sulfate a small amount of bidentate sulfate could be observed, indicating that two isomers may exist for UO2SO4. With increasing [SO42−]/[UO22+] ratio the UO2(SO4)2 2− species becomes the main species. The uranium atom of this species is coordinated by two bidentate sulfate groups.

Keywords: EXAFS; UV-Vis; HEXS; uranyl sulfate; aqueous solution

Publ.-Id: 11889

Vacancy-hydrogen Complexes in ZnO

Kuriplach, J.; Brauer, G.; Melikhova, O.; ČižEk, J.; Procházka, I.; Anwand, W.; Skorupa, W.

Hydrogen is an important impurity in zinc oxide and can be incorporated into the lattice in several ways. Hydrogen can be also bound by vacancies that can be studied using positron annihilation techniques. Here we examine theoretically oxygen and zinc vacancies in ZnO, the latter also with hydrogen atoms inside. Several computational approaches are employed to determine the defect geometries and related positron characteristics. Positron-induced forces are also taken into account. Calculated positron lifetimes are compared with those observed in experiment, which gives an indication of the presence of zinc vacancy-hydrogen complexes in ZnO materials.

Keywords: zinc oxide; vacancy-hydrogen complexes; positron annihilation; positron-induced forces

  • Materials Science Forum 607(2009), 117-121

Publ.-Id: 11888

Structure and Positron Characteristics of Basic Open Volume Defects in Zirconia

Melikhova, O.; Kuriplach, J.; Cizek, J.; Prochazka, I.; Brauer, G.

In this contribution we report on the theoretical study of basic vacancy-like defects in cubic zirconia and yttria stabilized zirconia. In particular, we concentrate on oxygen vacancy, zirconium vacancy and oxygen vacancy – yttrium complex. Relaxed atomic configurations of studied defects are obtained by means of an ab initio pseudopotential method within the supercell approach. Positron characteristics, like positron lifetime and binding energy to defects, are calculated using self-consistent electron densities and potentials taken from ab initio calculations.

Keywords: positron annihilation; open volume defects; zirconia

  • Materials Science Forum 607(2009), 125-127

Publ.-Id: 11887

Planung, Errichtung und Betrieb einer kleintechnischen Anlage zur Aufbereitung von und zur Sulfatabtrennung aus schwefelsaurem Grubenwasser durch Elektrolyse am Standort der GWRA Rainitza der LMBV

Friedrich, H.-J.; Zaruba, A.; Meyer, S.; Kryk, H.

Vertraulicher Abschlussbericht

Auftraggeber: LMBV mbH
Auftragnehmer: Verein für Kernverfahrenstechnik und Analytik Rossendorf e.V.

Leistungszeitraum: 01.04.2006 - 31.08.2008

  • Other report
    Dresden: VKTA, 2008
    75 Seiten

Publ.-Id: 11886

Atomic Layer Deposition of Platinum Oxide and Metallic Platinum Thin Films from Pt(acac)2 and Ozone

Hämäläinen, J.; Munnik, F.; Ritala, M.; Leskelä, M.

Platinum oxide and platinum thin films have been grown by atomic layer deposition (ALD) using Pt(acac)2 (acac ) acetylacetonato) and ozone as precursors. Amorphous platinum oxide thin films were deposited at 120 and 130 °C while metallic platinum films were obtained at 140 °C and above. The sublimation temperature of Pt(acac)2 set the low temperature limit for oxide film deposition. The platinum oxide films were successfully deposited on Al2O3 and TiO2 adhesion layers, soda lime glass, and silicon substrate with native oxide on top. Platinum films were grown on Al2O3 adhesion layer. The platinum oxide had good adhesion to all tested surfaces, whereas metallic platinum films did not pass the common tape test. Resistivities of 50-60 nm thick platinum oxide films were between 1.5 and 5 Ω cm at 130 °C and could be varied with both precursor pulse lengths. The resistivity of about 110 nm thick metallic film deposited at 140 °C was about 11 μΩ cm. The platinum films deposited at higher temperatures suffered from deterioration of thickness uniformity. The platinum oxide films can be reduced in 5% H2 gas under reduced pressure at room temperature to porous platinum structures.

Publ.-Id: 11885

Construction and timing system of the EPOS beam system

Jungmann, M.; Krause-Rehberg, R.; Muller, A.; Krille, A.; Brauer, G.

The Forschungszentrum Dresden-Rossendorf provides an intense pulsed 40 MeV electron beam with high brilliance and low emittance (ELBE). The pulse has a length of 1-10 ps and a repetition time of 77 ns, or in slow mode 616 ns. The EPOS system (ELBE Positron Source) generates by pair production on a tungsten converter and a tungsten moderator an intense pulsed beam of mono-energetic positrons. To transport the positrons to the laboratory (12 m) we constructed a magnetic beam guidance system with a longitudinal magnetic field of 75 G. In the laboratory outside the cave, the positron beam is chopped and bunched according to the time structure, because the very sharp bunch structure of the electron pulses is broadened for the positron beam due to transport and moderation.

Publ.-Id: 11884

EXAFS study of neptunium complex structures in aqueous solution

Hennig, C.; Ikeda-Ohno, A.; Tsushima, S.

Electrochemical and complexation properties of neptunium are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption, and Np LIII-edge X-ray absorption spectroscopy. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III)/(IV) and Np(V)/(VI) is irreversible because they undergo structural rearrangement from spherical coordinating ions (Np3+ and Np4+) to trans-dioxoneptunyl ions (NpO2n+). The redox reaction of the Np(V)/Np(VI) couple involves no structural rearrangement on their equatorial planes in acidic perchlorate solutions. A detailed analysis of EXAFS spectra suggests that Np(IV) forms a decaaquo complex of [Np(H2O)10]4+ in 1.0 M HClO4, while NpV and NpVI exist dominantly as pentaaquoneptunyl complexes, [NpO2(H2O)5]n+ (n = 1 for Np(V) and 2 for NpVI) [1].
Structural information on the sulfate coordination of neptunium in aqueous solution is actually rather scarce. We investigated actinide complexes in aqueous sulfate solution by using samples of 10-50 mM of actinide and total sulfate concentrations, 0.05 ≤ [SO42-] ≤ 10 M. In contrast to the coordination of actinides with carbonate where bidentate coordination always prevails, the coordination with sulfate comprises monodentate and bidentate linkage with a wide variety of combinations. In general, with increasing [SO42-]/[Ann+] ratio the bidentate coordination becomes dominant in solution [2]. As example, at low [SO42-]/[UO22+] ratio, where the UO2SO4(aq) species prevails, the sulfate coordinates in a monodentate and only to a less extend in bidentate fashion. At high [SO42-]/[UO22+] ratio, where UO2(SO4)22- species prevails, bidentate sulfate coordination with the species [UO2(SO4)2bid]2- becomes dominant. In oxidation state IV, up to five coordinating sulfate groups have been observed, mostly with predominant bidentate coordination as for example in the high-charged complex [U(SO4bid)3(SO4mon)2]6- [3]. Np(IV) and Np(VI) follows the tendency of U(IV) and U(VI), whereas Np(V) is weakly coordinated by sulfate, in accordance with its low formation constant. The attempt to preserve solution species in crystal structures led in most of the cases to a rearrangement of bidentate sulfate groups in solution to monodentate–bridging coordination in solid state. The coordination of the solution complexes was optimized by DFT calculation and the results are compared with the experimental observations.

Keywords: EXAFS; Neptunium; aqueous solution

  • Lecture (others)
    JAEA Actinide Network Workshop, 29.10.2008, Tokai, Japan

Publ.-Id: 11883

J-selfadjoint operators with C-symmetries: extension theory approach

Albeverio, S.; Günther, U.; Kuzhel, S.

A well known tool in conventional (von Neumann) quantum mechanics is the selfadjoint extension technique for symmetric operators. It is used, e.g., for the construction of Dirac-Hermitian Hamiltonians with point-interaction potentials. Here we reshape this technique to allow for the construction of pseudo-Hermitian (J-selfadjoint) Hamiltonians with complex point-interactions. We demonstrate that the resulting Hamiltonians are bijectively related with so called hypermaximal neutral subspaces of the defect Krein space of the symmetric operator. This symmetric operator is allowed to have arbitrary but equal deficiency indices . General properties of the C-operators for these Hamiltonians are derived. A detailed study of C-operator parametrizations and Krein type resolvent formulas is provided for J-selfadjoint extensions of symmetric operators with deficiency indices <2,2>. The technique is exemplified on 1D pseudo-Hermitian Schrödinger and Dirac Hamiltonians with complex point-interaction potentials.

Keywords: PT-symmetric quantum mechanics; pseudo-Hermitian operators; Krein space; extension theory; point interactions; hypermaximal neutral subspace; C-operator; super-symmetry; contraction mapping; resolvent; defect index; defect subspace; extension center

Publ.-Id: 11882

The influence of annealing on manganese implanted GaAs films

Bürger, D.; Zhou, S.; Grenzer, J.; Reuther, H.; Anwand, W.; Gottschalch, V.; Helm, M.; Schmidt, H.

Besides low-temperature molecular beam epitaxy, ion implantation provides an alternative route to incorporate Mn into GaAs above the equilibrium solubility limit. However, post-implantation annealing can lead to the formation of secondary phases. In the published papers concerning Mn implanted GaAs, diluted magnetic GaAs is only obtained by pulsed laser annealing. In order to compare the post-annealing effect, we investigate GaMnAs by implanting up to 6 at% Mn followed by rapid thermal and flashlamp annealing. The structural properties were probed by high resolution X-ray diffraction. The magnetic properties were determined by SQUID measurements. Auger electron spectroscopy has been used to profile the depth distribution of Mn in GaAs after implantation and annealing. We elucidate after implantation a loss of As and that during rapid thermal annealing most of the Mn diffuses towards the surface. Flash lamp annealing prevents out-diffusion, but the recrystalisation effciency is low. Only the flash lamp annealed samples reveal weak ferromagnetism.

Keywords: diluted magnetic semiconductor; flashlamp annealing; HRXRD; ion implantation; RBS; RTA

  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1626-1629
  • Poster
    IBMM 2008 - 16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11881

Oxygen gettering in the initial stage of SIMOX process

Ou, X.; Kögler, R.; Mücklich, A.; Skorupa, W.; Möller, W.; Wang, X.

The presentation reported latest results about defect engineering of the SIMOX process

Keywords: Silicon; Oxygen; SIMOX; SOI

  • Lecture (Conference)
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 11880

Gettering layer for oxygen accumulation in the initial stage of SIMOX processing

Ou, X.; Kögler, R.; Skorupa, W.; Möller, W.; Wang, X.; Gerlach, J. W.

A cavity layer or nano-bubble layer introduced by He implantation before the oxygen implantation collects the implanted oxygen and increases the oxygen concentration. The average size and density of the oxygen precipitates formed in the initial stage of the Separation-by-implanted-oxygen (SIMOX) process is conform with the size and density of the cavities pre-formed by He implantation and annealing. The gettering ability of the cavity layer for oxygen is directly related to the area of the internal surface of the cavities. A nano-bubble layer accumulates oxygen in a very narrow range occurring between the damage maximum, DP, and the mean projected ion range, RP. Such a nano-bubble layer is most efficient in oxygen gettering due to their larger area of the internal surface and the small size of the oxide precipitates initially formed at the bubbles.

Keywords: Ion implantation; SIMOX; Defect engineering; Empty volume; Internal surface

  • Contribution to proceedings
    16th International Conference on Ion Beam Modification of Materials (IBMM 2008), 31.08.-05.09.2008, Dresden, Germany: Elsevier
  • Nuclear Instruments and Methods in Physics Research B 267(2009), 1273-1276
    DOI: 10.1016/j.nimb.2009.01.029

Publ.-Id: 11879

Integration of Thin-Film-Fracture-Based Nanowires into Microchip Fabrication

Jebril, S.; Elbahri, M.; Titazu, G.; Subannajui, K.; Essa, S.; Niebelschütz, F.; Röhlig, C.-C.; Cimalla, V.; Ambacher, O.; Schmidt, B.; Kabiraj, D.; Avasti, D.; Adelung, R.

One-step device fabrication through the integration of nanowires (NWs) into silicon microchips is still under intensive scientific study as it has proved difficult to obtain a reliable and controllable fabrication technique.
So far, the techniques are either costly or suffer from small throughput. Recently, a cost-effective method based on thin-film fracture that can be used as a template for NW fabrication was suggested. Here, a way to integrate NWs between microcontacts is demonstrated. Different geometries of microstructured photoresist formed by using standard photolithography are analyzed. Surprisingly, a very simple ‘‘stripe’’ geometry is found to yield highly reproducible fracture patterns, which are convenient templates for fault-tolerantNWfabrication. Microchips containing integrated Au, Pd, Ni, and Ti NWs and their suitability for studies of conductivity and oxidation behavior are reported, and their suitability as a hydrogen sensor is investigated. Details of the fabrication process are also discussed.

Keywords: gas detection; microchip fabrication; nanowires; thin-film fractures

Publ.-Id: 11878

Spinel ferrite nanocrystals embedded inside ZnO: magnetic, electronic and magneto-transport perperties

Zhou, S.; Potzger, K.; Xu, Q.; Kuepper, K.; Talut, G.; Shalimov, A.; Mäucklich, A.; Helm, M.; Fassbender, J.; Arenholz, E.; Schmidt, H.

In this paper we show that spinel ferrite nanocrystals (NiFe2O4, and CoFe2O4) can be texturally embedded inside a ZnO matrix by ion implantation and post-annealing. The ferrite nanocrystals show comparable magnetization with corresponding bulk ferrites. Anomalous Hall effect and positive magnetoresistance have been observed. Our study suggests a ferrimagnet/semiconductor hybrid system for potential applications in magneto-electronics. This hybrid system can be tuned by selecting different transition metal ions (from Mn to Zn) to obtain various magnetic and electronic properties.

Keywords: Ferrite; Ion implantation; X-ray absorption; Magneto-transport

Publ.-Id: 11877

Origin of the ferromagnetism in defective TiO2 single crystals

Zhou, S.; Cizmar, E.; Potzger, K.; Krause, M.; Talut, G.; Helm, M.; Fassbender, J.; Zvyagin, S. A.; Wosnitza, J.; Schmidt, H.

In this paper we show that ferromagnetism can be induced in pure TiO2 single crystals by oxygen ion irradiation. By combining x-ray diffraction, Raman-scattering, and electron spin resonance spectroscopy, a defect complex, Ti^{3+} ions on the substitutional sites accompanied by oxygen vacancies, has been identified in irradiated TiO2. This kind of defect complex results in a lattice strain and a local (TiO_{6-x}) stretching Raman mode. We elucidate that Ti^{3+} ions with one unpaired 3d electron provide the local magnetic moments.

Keywords: TiO2; Induced ferromagnetism; Defects; ESR

  • Physical Review B 79(2009), 113201
    DOI: 10.1103/PhysRevB.79.113201
  • Poster
    International Conference on Magnetism, 26.-31.07.2009, Karlsruhe, Germany


Publ.-Id: 11876

Room temperature ferromagnetism in carbon-implanted ZnO

Zhou, S.; Xu, Q.; Potzger, K.; Talut, G.; Fassbender, J.; Vinnichenko, M.; Grenzer, J.; Helm, M.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.

Unexpected ferromagnetism has been observed in carbon doped ZnO films grown by pulsed laser deposition [Phys. Rev. Lett. 99, 127201 (2007)]. In this letter, we introduce carbon into ZnO films by ion implantation. Room temperature ferromagnetism has been observed. Our analysis demonstrates that (1) C-doped ferromagnetic ZnO can be achieved by an alternative method, i.e. ion implantation, and (2) the chemical involvement of carbon in the ferromagnetism is indirectly proven.

Keywords: ZnO; Diluted magnetic semiconductor; Carbon; ion implantation

  • Applied Physics Letters 93(2008), 232507
    DOI: 10.1063/1.3048076
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 11875

Inverse spinel ZnFe2O4 nanoparticles synthesized by ion implantation and post-annealing: an investigation using X-ray spectroscopy and magneto-transport

Zhou, S.; Potzger, K.; Buerger, D.; Kuepper, K.; Helm, M.; Fassbender, J.; Schmidt, H.

Noncrystalline ZnFe2O4 has been investigated intensively due to the drastic difference in cation distribution compared with bulk materials. We previously synthesized ZnFe2O4 nanoparticles by ion implantation and post-annealing [J. Phys. D-Appl. Phys. 40, (2007) 964]. These ZnFe2O4 nanocrystals are crystallographically oriented inside the ZnO matrix and show a hysteretic behavior upon magnetization reversal at 5 K. Their magnetic properties are explained by assuming that Fe^{3+} ions partially occupy tetrahedral sites. In this paper an X-ray spectroscopic and magneto-transport investigation on ZnFe2O4 nanocrystals in a ZnO matrix will be presented. The occupation of Fe^{3+} at tetrahedral sites has been directly proved. A positive magnetoresistance (MR) effect is observed and is attributed to ordinary MR.

Keywords: ZnFe2O4; X-ray absorption; Magnetoresistance

Publ.-Id: 11874

Sorption of uranium(VI) onto opalinus clay in absence and presence of humic acid

Joseph, C.

An anaerobic opalinus clay sample was characterized (BET, TC, TOC, CEC, XRD, IR). No significant differences between the aerobic and the anaerobic clay could be determined.
For the uranium(VI) sorption onto kaolinite the effect of the background electrolyte was investigated. An explanation for the different results is given by EQ3/6-speciation diagrams. The uranium(VI) sorption onto aerobic opalinus clay (S/L = 60 g/l) in opalinus clay pore water in absence and presence of humic acid was investigated and compared with the according uranium(VI)-humic acid-kaolinite sorption results.

Keywords: opalinus clay; characterization; anaerobic; sorption; uranium(VI); speciation; humic acid; kaolinite

  • Lecture (others)
    Meeting FZD - PSI, 03.-04.11.2008, Rossendorf, Germany

Publ.-Id: 11873

Spectroscopic investigations of U(VI) speciation In cementitious materials

Macé, N.; Wieland, E.; Tits, J.; Dähn, R.; Kunz, D.; Geipel, G.; Scheinost, A. C.

In the Swiss radioactive waste management program, cement is used as a matrix for long-lived intermediate-level waste (ILW), in which Uranium is an important radionuclide. Calcium Silicate Hydrates (C-S-H) are one of the major components of Hardened Cement Paste (HCP). A molecular-level understanding of Uranium uptake processes occurring in cementitious materials is essential to improve long-term predictions in safety analysis. U(VI) uptake by C-S-H (CaO/SiO2 = 1.07) in Artificial Cement pore-Water (ACW) and HCP has been investigated using Time Resolved Laser Fluorescence Spectroscopy (TRLFS) and X-Ray Absorption Spectroscopy (XAS) in order to determine the chemical environment of retained and precipitated U(VI) species in cementitious matrices. Phase X (CaUO4(H2O)x) soddyite and a uranophane ([Ca(H3O)2](UO2)2(SiO4)2(H2O)3) have been chosen as relevant reference compounds.
The main results are:
1) Preliminary TRLFS and XAS results are in a good agreement concerning U(VI) speciation in cementitious systems
2) TRLFS spectra of U(VI) in supernatant ≠ TRLFS spectra of U(VI) in cementitious pastes, i.e. free U(VI) species in ACW ≠ sorbed U(VI) species in cementitious pastes
3) TRLFS and XAS spectra of U(VI) sorbed species in HCP and C-S-H pastes are similar, i.e. C-S-H phases are responsible of U(VI) immobilization in HCP
4) For U(VI) high loading in HCP and U(VI) precipitated in ACW, i.e. U(VI) environment closed to a Ca-uranate phase with long U-Oaxial distances (1.86 ± 0.02) Ǻ
5) For U(VI) low loadings in HCP and C-S-H in ACW, i.e. uranophane-like structure with short UOaxial distances (1.83 ± 0.02) Ǻ

Keywords: cement; nuclear waste; uranium; TRLFS; EXAFS

  • Poster
    Cement08 - 2nd International workshop on Mechanism and Modelling of waste/cement interaction, 12.-16.10.2008, Le Croisic, France

Publ.-Id: 11872

eta and eta-prime production in nucleon-nucleon collisions near thresholds

Kaptari, L. P.; Kämpfer, B.

The production of eta and eta-prime mesons in nucleon-nucleon collisions near thresholds is considered within a one-boson exchange model. We show the feasibility of an experimental access to transition formfactors.

Publ.-Id: 11871

Fracture mechanics characterization of Russian WWER type reactor pressure vessel welding seams

Viehrig, H.-W.; Schuhknecht, J.

The paper is focussed on Master Curve testing according to ASTM E1921-05 [5] of the Russian WWER-440 type reactor pressure vessel steel. Charpy size SE(B) specimens from the beltline welding seam SN0.1.4 of the Greifswald NPP Unit 1 (1st generation WWER-440/V-230) and Unit 2 (2nd generation WWER-440/V213) were investigated in this study. The specimens are TL and TS oriented in the RPV welding seam, this means specimen axis axial to the RPV wall and crack propagation circumferential and through the thickness, respectively. The WWER-440 welding seam consists of a welding root welded with an unalloyed wire Sv-08A and the filling material welded with the alloyed wire Sv-10KhMFT. Fracture toughness values at brittle failure, KJc, measured on Charpy size SE(B) specimens were evaluated following Master Curve analyses as specified in ASTM E1921-05. The results show a wavelike course of the evaluated reference temperature, T0, through the thickness of the welding seams of Unit 1 and Unit 8. The scatter is more pronounced for the irradiated annealed and reirradiated 1st generation RPV of Unit 1.
Another issue was the influence of the specimen orientation and mainly the crack extension direction. While the crack front of a TS specimen is located in a more or less uniform structure, the structure along the crack front of a TL specimen varies, because it usually spans several welding beads. Roughly speaking, TS and TL specimens have a differentiating and integrating behaviour, respectively. A difference in T0 was found also for TS and TL oriented specimens of Unit 8. The lowest T0 was measured on TS specimens from the welding root with 114°C, whereas TL specimens of the same thickness locations gave 62°C.
For the 2nd generation RPV of Unit 8, the KJc values measured on specimens of both orientations generally follow the course of the Master Curve and are enveloped by the fracture toughness curves for 2% and 98% fracture probability. This statement can generally be made also for the first generation RPV of Unit 1, but the scatter of the KJc values is larger compared to the Unit 8 RPV. More values than expected lie below the 2% fractile.
The reason for the scatter in the KJc values and T0 is found in the structure at and along the crack tip, which depends on the welding technology and the specimen orientation. The welding technology applied on the beltline welding seams of the 1st and 2nd WWER-440 RPV generation is different, which is clearly visible in macroscopic section in Figs. 3 and 4. KJc values measured on SE(B) specimens from the thickness locations beyond the welding root of Unit 8 RPV result in a valid T0. KJc values from specimens of the same thickness within the welding seam of Unit 1 show a larger scatter. The majority of KJc values from one thickness location falls below the fracture toughness curve for 2% fracture probability. The reason is seen in the brittle zone in the fusion region between two welding beads. The application of the SINTAP MC extension procedure leads to a conservative T0.
In comparison to the correlative and indirect approach of the fracture toughness estimation in the present codes, the results presented here show that the orientation of the surveillance specimens is crucial for the direct measurement of the fracture toughness. For fracture toughness determinations the specimen orientation should be chosen which either yields the most conservative fracture toughness values or which agrees with the loading and crack extension direction considered in the integrity assessment.

Keywords: reactor pressure vessel; multilayer welding seam; SE(B) specimen; specimen orientation; fracture toughness; Master Curve approach

  • Contribution to proceedings
    12th International Conference on Fracture, 12.-17.07.2009, Ottawa, Kanada
    Proceedings of the 12th International Conference on Fracture
  • Lecture (Conference)
    12th International Conference on Fracture, 12.-17.07.2009, Ottawa, Kanada

Publ.-Id: 11870

Photon data shed new light upon the GDR spreading width in heavy nuclei

Junghans, A. R.; Rusev, G.; Schwengner, R.; Wagner, A.; Grosse, E.

A global study of the electric dipole strength in and below the isovector giant dipole resonance (GDR) is presented for mass numbers A>80. It relies on the recently established remarkably good match between data for the nuclear photo effect to novel photon scattering data covering the region below the neutron emission threshold as well as by average resonance neutron capture (ARC). From the wide energy coverage of these data the correlation of the GDR spreading width with energy can be studied with remarkable accuracy. A clear sensitivity to details of the nuclear shape, i.e. the beta- and gamma-deformations, is demonstrated. Based hereon a new parameterization of the energy dependence of the nuclear electric-dipole strength is proposed which - with only two new parameters - allows to describe the dipole strength in all heavy nuclei with A>80. Although it differs significantly from previous parameterizations it holds for spherical, transitional, triaxial and well deformed nuclei. The GDR spreading width depends in a regular way on the respective resonance energy, but it is independent of the photon energy.

Keywords: Isovector giant dipole resonance; E1 strength function; Lorentzian; Spreading width

Publ.-Id: 11869

The properties of the nanometer thick Si/Ge films-on-insulator produced by Ge+ ion implantation and subsequent hydrogen transfer

Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.

The behaviour of germanium implanted into the SiO2 layers in the vicinity of the bonding interface of silicon-on-insulator (SOI) structures has been studied. The enhanced segregation of the implanted Ge atoms at the Si/SiO2 bonding interface has been observed. Segregated Ge atoms form the layer, which is coherent with the silicon lattice. It is suggested that the formation of intermediate Ge layer is mediated by the occurrence of liquid Ge phase. The effect of Ge on the Hall mobility of holes in the 25 nm thick SOI layer was studied. An increase in the hole mobility by a factor of three was obtained in the SiGe-on insulator structures in comparison with that measured in the respective Ge-free SOI films.

Keywords: SiGe on insulators

  • Physica Status Solidi (C) 5(2008)12, 3724-3727

Publ.-Id: 11868

Influence of the transition metal affinity on the encapsulating carbon medium during the growth of carbon:transition metal nanocomposite films

Berndt, M.; Krause, M.; Abrasonis, G.; Mücklich, A.; Munnik, F.; Kolitsch, A.; Möller, W.

The understanding of the interactions of carbon (C) atoms with transition metals (TM) is of particular importance as these interactions are involved in many processes in nanoscience. However, the underlying fundamental mechanisms are still not well understood. In this work, the influence of the TM chemical affinity to C on the encapsulating carbon nanostructuring is studied during the growth of C:TM nanocomposite films. C:Co and C:V nanocomposites with metal content of ~ 15 and ~ 30 at.% have been grown by ion beam co-sputtering in the temperature range of RT-500°C. The so-grown films have been investigated by the means of elastic recoil detection analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy at two excitation wavelengths (532 nm and 785 nm). In order to highlight the influence of the transition metal on the encapsulating matrix, the results are compared with the pure carbon films deposited at the same temperatures.

Nanocomposite structure is observed for all the C:TM films which consists of metal (or metal carbide) nanograins embedded in carbon medium. The C:V films consist of spherical grains of the diameter of ~2 nm whose size or shape is independent of the growth temperature. Vanadium is in the carbidic state over the whole temperature range of this study. The Co nanoparticles in C:Co films grown at RT also exhibit a spherical shape with a diameter of ~ 2 nm. However, with increasing deposition temperature the Co nanoparticles become elongated the long axis coinciding with the direction of the film growth. A carbide phase is identified for growth temperatures of RT-300°C, while a metallic phase is formed above 300°C.

The embedding carbon phase resembles that of the amorphous carbon at lower growth temperatures, while at elevated growth temperatures (>= 300°C) curved graphenic sheets encapsulating the metal nanoparticles can be identified. Raman spectroscopy shows that both metals enhance 6-fold ring clustering of the carbon phase since the D peak intensity related to the 6-fold ring breathing vibrations is increased in comparison to the pure carbon films. This enhancement occurs independently on the nanoparticle type, size, shape and phase. Besides the D and G peak, a third peak at ~ 1100 cm-1 is identified, which shows a resonance enhancement for visible laser excitation. This peak is absent in pure carbon films. Its intensity in relation to D-G band decreases when the growth temperature increases, while it increases concomitantly with the metal content. Moreover, the position of this peak is independent on the metal type indicating that it is an inherent feature of carbon.

Keywords: composites; ion beam sputtering; metallic and carbon nanostructures

  • Poster
    XXIInd International Winterschool on Electronic Properties of Novel Materials, 01.-08.03.2008, Kirchberg, Austria

Publ.-Id: 11867

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