Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The complexation of perrhenate (ReO4-) anions by the uranyl (UO22+) cation is investigated by joined molecular dynamics simulations and spectroscopic (UV-Vis, TRLFS and EXAFS) studies in aqueous solution, acetonitrile and three ionic liquids (ILs), namely [Bmi][Tf2N], [Me3BuN][Tf2N] and [Bu3MeN][Tf2N] that are based on the same Tf2N- anion (bis(trifluoromethylsulfonyl)imide) and either Bmi+ (1-butyl,3-methylimidazolium), Me3BuN+ or Bu3MeN+ cations. They show that ReO4- behaves as a weak ligand in aqueous solution and as a strong ligand in acetonitrile and in the ILs. In aqueous solution, the simulated UO2(ReO4)2 complex quickly dissociates to form the UO2(H2O)52+ species, while in acetonitrile the simulated UO2(ReO4)53- complex forms from dissociated ions and remains stable along 100 ns of dynamics. When the UO2(ReO4)n2-n complexes (n = 1 to 5) are simulated in the ILs, the uranyl cation remains coordinated to the ReO4- ligands, and to additional OTf2N oxygens when n < 5. To assess the relative stabilities of these complexes, we computed the free energy profiles for stepwise ReO4- complexation by uranyl (PMF calculations). In the two studied ILs, perrhenate complexation is favoured, leading to the UO2(ReO4)53- species in [Bmi][Tf2N] and to UO2(ReO4)42- in [Bu3MeN][Tf2N]. Furthermore, in both acetonitrile and [Bmi][Tf2N] solutions, MD and PMF simulations support the formation of dimeric uranyl complexes [UO2(ReO4)4]24- with two bridging ReO4- ligands. The simulation results are qualitatively consistent with spectroscopic observations in the different solvents, without firmly concluding, however, on the precise composition and structure of the complexes in the solutions.

Based on strong-field QED in the Furry picture we use the Dirac-Volkov propagator to derive a compact expression for the differential emission probability of the two-photon Compton process in a pulsed intense laser field. The relation of real and virtual intermediate states is discussed, and the natural regularization of the on-shell contributions due to the finite laser pulse is highlighted. The inclusive two-photon spectrum is two orders of magnitude stronger than expected from a perturbative estimate.

Lithium silicate thin films, which are interesting materials for example in lithium ion batteries, were grown by the atomic layer deposition technique from lithium hexamethyldisilazide [LiHMDS, Li(N(SiMe₃)₂)] and ozone precursors. Films were obtained at a wide deposition temperature range between 150 and 400 °C. All the films were amorphous except at 400 °C, where partial decomposition of LiHMDS was also observed. The growth behavior was examined in detail at 250 °C, and saturation of growth rates and refractive indices with precursor doses was confirmed, thereby verifying self-limiting surface reactions. Likewise, the linear thickness dependence of the films with the number of deposition cycles was verified. Strong dependence of growth rate and film composition on deposition temperature was also seen. Overall, the amorphous films grown at 250 °C had a stoichiometry close to lithium metasilicate (Li_2.0SiO_2.9) with 0.7 at. % carbon and 4.6 at. % hydrogen impurities. The corresponding growth rate and refractive index (n₅₈₀) were 0.8 A/cycle and about 1.55.

Auger decay, i.e. the spontaneous emission of an electron upon relaxation of the atomic shell, carries valuable information about the electronic structure and dynamics of atoms and their compounds. While the energetic properties are well investigated, little is known about the detailed temporal profile of Auger electron wave packets. Here we furnish evidence, that under certain conditions Auger electrons are subject to an energetic chirp imprinting a non-linear change of energy over time on the escaping wave packet. The origin of this unexpected finding is shown to be the exchange of energy between the Auger electron and a slightly earlier emitted photoelectron in the presence of a laser field. The interpretation in terms of this long-range electron correlation is substantiated by fs-time-resolved experiments on the xenon NOO and Kr MNN Auger decay together with extensive theoretical modelling using semi-classical as well as quantum-mechanical simulations.

Tetravalent cerium (Ce(IV)) is known to be one of the most commonly-used oxidizing agents in various chemical studies, such as organic synthesis. Furthermore, it recently draws considerable attention to its catalytic applications to water oxidation or biotechnology. As a versatile catalytic oxidant, Ce(IV) is often employed in the form of aqueous solution. Therefore, fundamental knowledge of Ce(IV) species in aqueous solution is essential not only for discussing its functionality in the applied systems, but also for further developing its applications; nevertheless, the nature of Ce(IV) species in aqueous solution is far less well understood. In this context, the present study aims to elucidate the chemical speciation and complex structure of soluble Ce(IV) species formed on hydrolysis, which is the most fundamental reaction of metal cations in the aqueous solution system, by employing X-ray absorption spectroscopy (XAS), high energy solution X-ray scattering (HEXS), and dynamic light scattering (DLS).
The obtained XAS data have clearly showed the systematic growing of Ce–Ce bonding in the soluble Ce(IV) hydrolytic species, as an increase in pH. This indicates that some soluble polymeric or cluster complexes are formed on the hydrolysis of Ce(IV). The diffraction patterns of Ce(IV) hydrolytic species have further revealed that the observed polymeric or cluster complex has a crystalline structure, not the amorphous one. The results of the detailed analysis on XAS and HEXS data will be presented on site, along with the DLS data for discussing the size of Ce(IV) hydrolytic polymers/clusters and its aging effect.

Es ist kein Abstract vorhanden.

Granite is the aspired potential host rock material for future nuclear waste storage in Sweden. The Äspö Hard Rock Laboratory (Äspö HRL) today is an interdisciplinary research facility for geological disposal in granite rock. The research within the Äspö HRL programme involves international cooperation with various countries including Germany.
This presentation drafts the operations done at Äspö and the contribution by the IRC. Here the objectives and results of the study on the interaction of uranium(VI) with Pseudomonas fluorescens, a strain that has been isolated at the Äspö site, are presented. Explicitly results about the accumulation capability of the strain, TRLFS investigations and potentiometric titration results are shown.

The radiation emitted by axially channeled electrons has been investigated by computer simulations. Using the Doyle-Turner approximation for the atomic scattering factor and taking thermal vibrations of the crystal atoms into account, two-dimensional continuous potentials for the <100> and <110> crystallographic axes of a thin Ge single crystal have been calculated. The trajectories, velocities and accelerations of channeled electrons are obtained by solving numerically the classical equations of motion in three dimensions. In the framework of classical electrodynamics, these data allow realistic simulations of spectral-angular distributions and energy spectra of axial channeling radiation as well.

The NeuLAND detector at the R3B experiment at the future FAIR facility in Darmstadt aims to detect fast neutrons (0.2–1.0 GeV) with high time and spatial resolutions . This task can be performed either with a scintillator or based on the multigap resistive plate chamber (MRPC) technology. Here, prototyping and test for an MRPC-based solution are discussed. In order to reach 90% detection efficiency, the final detector must consist of 50 consecutive MRPC stacks. Each stack contains a 4 mm thick anode made of iron converter material, with an additional 4 mm of converter material between two stacks. The secondary charged particles stemming from hadronic interactions of the high energetic neutrons in the converter will be detected in the MRPCs. As part of the ongoing development effort, a number of prototypes for this detector have been developed and built. They have been tested in experiments with a single-electron beam with picosecond resolution at the superconducting linac ELBE (Dresden, Germany). The results of the tests are presented here, and an outlook is given.

The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T {\simeq} 30 {\cdot} 106 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the RGB (red giant branch) phase of the star or to the pollution of the primordial gas by an early population of massive AGB (asymptotic giant branch) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. The activation of this cycle depends on the rate of the 15N(p,{\gamma})16O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances. We present a new measurement of the 15N(p,{\gamma})16O reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 {\cdot} 106 K and 780 {\cdot}106 K. This range includes the 15N(p,{\gamma})16O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars. With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.

The 44Ti(alpha,p)47V reaction is of crucial importance for the destruction of Ti-44 in the alpha-rich freezeout of a supernova. Here I report on a feasibility study. Using radioactive Ti-44 and alpha-emitting sources and sputtering simulations, I study the feasibility and safety of a possible experiment using an alpha-beam from an accelerator and a radioactive Ti-44 target.

Presentation of the complexation of Uranium(VI) with selected Schiff bases in methanol investigated by UV/Vis spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS)

Positron emission tomography (PET) is a dedicated tool for quality assurance in ion beam therapy. By measuring the spatial distribution of positron emitters generated via nuclear interactions between projectiles and atomic nuclei of the tissue during the therapeutic irradiation, conclusions on the accuracy of the dose localization can be drawn. In the following, the physical background as well as the technical realization of PET is depicted. Furthermore, current PET installations for quality assurance of proton and ion beam therapy are presented.

I will review the state of the art of stable-ion beam experiments for nuclear astrophysics. Special mention will be made of the so-called solar abundance problem and the contributions that experimental nuclear astrophysics may make to solve it. Topics where ERAWAST nuclides have played a special role will be mentioned.

I will review the status of the standard solar model, with special mention given to the so-called solar abundance problem that ha recently developed. Then, I will discuss the experimental status of the nuclear reactions of the carbon-nitrogen-oxygen (CNO) cycle of hydrogen burning.

Numerical and experimental modelling of a VGF-type (VGF - Vertical Gradient Freeze) buoyant flow under the influence of both travelling and rotating magnetic fields (TMF and RMF, respectively) is presented. Low-temperature flow experiments were carried out using a GaInSn alloy as model fluid. Radial heating and cooling of the melt leading to a meridional double vortex flow like in typical VGF growth, was introduced using a double-walled melt container. The flow was found to be significantly influenced by the mutual interaction of buoyant and electromagnetically driven forces. With increasing axial temperature difference, the buoyant flow becomes more concentrated in the upper and lower part of the melt leaving an extended melt zone with low flow velocity around the mid-height. Furthermore, VGF-type buoyancy is found to stabilize TMF- and RMF-induced melt flows. Besides, the time evolution of the flow just above the stability threshold is studied. In the case of combined VGF-type/RMF flow complex fluctuation patterns are observed, which depends sensitively on the applied thermal field.

The international LUNA collaboration studies nuclear reactions at very low energy, directly relevant to the Sun. To this end, it uses a 0.4 MV accelerator deep underground in the Gran Sasso laboratory in Italy. I will review the motivations, techniques and achievements of LUNA.

Bacterial isolates from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) possess high affinities to heavy metals and uranium. This binding effect is caused by the components of the bacterial cell wall, mainly effected by surface layer proteins.
Aim of this work is the construction of a stable multi-layer system for the simulation of cell walls of Gram-positive bacteria and the investigation of metal interactions with single compounds and whole complex systems.
The quartz crystal microbalance (QCM-D) and atomic force microscopy (AFM) is used to track and control this multi-layer formation.
First result of these tasks is the proof of recrystallization of S-layer proteins as part of the cell wall of Bacillus spec. JG-B53 via QCM-D and AFM.

no abstract;
Vortrag ohne Abstrakt!

Heterologous expression is a common method of molecular biology, which finds applications for example in up scaling of protein production and structural analyses of naturally unexpressed proteins. An experimental setup is started by the amplification of the template gene. Afterwards this gene is cloned into coiled DNA, called vectors and transformed into the host organism. The desired protein, which is encoded by the cloned gene, is produced inside the host organism. Host strains are for example Escherichia coli, Lactococcus lactis or Pichia pastoris.

Presentation of motivation and objectives of the PhD theses “Spectroscopic characterization of trivalent actinides Am and Cm on bacterial cell walls” and “Evidence and characterization of silica-containing colloids of tetravalent Th, U, Np”.

We report on carrier relaxation dynamics close to the Dirac point in epitaxially grown graphene under pulsed excitation with 10 – 250 meV photons. With decreasing photon energy, we identify different regimes – induced transmission with bi- and single-exponential decay as well as induced absorption - and discuss their physical origin.

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

Gründungsveranstaltung Abbe Center of Photonics

High Intensity Laser- and Plasma Physics in collaboration with Helmholtz Institute Jena

The Target Normal Sheath Acceleration mechanism is perhaps the most robust, and certainly the most studied, process by which protons and ions are accelerated to multi-MeV energies in ultra-intense laser-matter interactions. It is characterized by the generation of superstrong TV/m ambipolar electric fields in the relativistic electron sheath on the rear-surface of laser-irradiated thin foils, and the subsequent quasi-neutral plasma expansion driven by the electron thermal pressure. The maximum achievable ion energies should increase with increasing hot electron temperature and density, depending upon the laser pulse parameters and the geometry of the target and laser-plasma interaction. To date, proton energies of up to 67.5 MeV have been observed. In this talk, techniques to further increase the proton and ion energies from TNSA will be reviewed, with emphasis on experimental results from the FZD Draco Ti:Sa laser and with our collaboration partners working at several higher energy Nd:glass lasers world-wide. Scaling of the proton energy with the laser pulse energy and intensity, pulse length and contrast, and by variation of the target geometry and properties, such as thickness, transverse size, and by target shaping, will be discussed.

Enhanced Positron Creation in Ultra-Intense Laser-Matter Interactions

Milestones and perspectives of the projected test stand to capture and transport laser-accelerated proton beams. Workshop GSI Darmstadt

Proposal for PHELIX Experiment Time, GSI-PPAC

Proposal for PHELIX Experiment Time, GSI-PPAC

We present results of an exclusive measurement of the first excited state of the Σ hyperon, Σ(1385)⁺, produced in p+p->Σ⁺+K⁺+n at 3.5 GeV beam energy. The extracted data allow to study in detail the invariant mass distribution of the Σ(1385)⁺. The mass distribution is well described by a relativistic Breit-Wigner function with a maximum at m₀=1383.2±0.9 MeV/c² and a width of 40.2±2.1 MeV/c². The exclusive production cross-section comes out to be 22.27±0.89±1.56+3.07−2.10 μb. Angular distributions of the Σ(1385)⁺ in different reference frames are found to be compatible with the hypothesis that 33% of Σ(1385)⁺ result from the decay of an intermediate Δ⁺⁺ resonance.

Since superconductivity has been discovered one century ago, scientists search for new materials that show this fascinating ground state of matter. Recent investigations on superconductivity of elemental group-IV semiconductors like diamond [1] and silicon [2] lead to a new debate about the mechanism and technological potential of these unusual superconductors.
In our previous work, we have shown the possibility of creating highly Ga doped Ge layers via Ga-ion implantation and subsequent short-time annealing. As a consequence of the high doping level, these layers are intrinsically superconducting below 1 K [3]. Furthermore we investigated the feasibility of embedding superconducting layers in Si-SiO₂ heterostructures not via doping but by Ga precipitation reaching critical temperatures of 7 K [4] with equivalent processing steps.
From these investigations, the question arises if it is possible to combine highly doped semiconducting regions with intrinsic and extrinsic superconducting structures having different critical temperatures. We used again Ga implantation in Ge covered by a 30 nm SiO₂ layer and flash-lamp annealing to create a complex layer structure showing various transitions in different superconducting states. The first transition occurs at 7 K and can be attributed to Ga-rich precipitates at the Ge-SiO₂ interface. Due to the superconductivity of the underlying highly doped germanium layer, a second transition is observed at around 1 K. Recent results on the structural and electrical properties of the heterostructures will be presented.

[1] E. A. Ekimov et al., Nature (London) 428, 542 (2004).
[2] E. Bustarret et al., Nature 444, 465 (2006).
[3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102, 217003 (2009); V. Heera et al., Journal of Applied Physics 107, 053508 (2010).
[4] J. Fiedler et al., Phys. Rev. B 83, 214504 (2011); R. Skrotzki et al., Appl. Phys. Lett. 97 192505 (2010).

Es hat kein Abstract vorgelegen.

Pattern formation on Si(001) through 2 keV Kr+ ion beam erosion under ultra high vacuum conditions is investigated by in situ scanning tunneling
microscopy, ex situ atomic force microscopy and electron microscopy. Under these conditions, at room temperature for fluences up to ≈ 2×10^22 ions m^-2 no ion beam patterns develop for angles ϑ <= 55° with respect to the global surface normal. Only for shallow incidence with 60° <= ϑ <= 81° pronounced patterns form. These patterns expose facets for which the ion beam angle q with respect to the local surface normal of each facet is in the stable range, i.e. outside 60° <= q <= 81°. Analysis of the fluence dependence of pattern formation was conducted in the unstable range with ϑ = 63° and ϑ = 75°. While the speed of pattern evolution depends strongly on the angle of incidence, the sequence does not. The flat surface evolves via small amplitude, regular ripple patterns to large amplitude, irregular facet patterns. The regular ripple pattern transforms through a coarsening mechanism to a facetted pattern.
Co-deposition of stainless steel during ion beam erosion results in well developed hole, dot and ripple patterns already for small ion fluences. Codeposition induced pattern formation does not depend on the deposition method as it takes place for both, co-sputter deposition and co-evaporation. The key factor selecting the type of pattern realized is the ion-to-impurity arrival ratio. While in a broad range from 150 K to 440 K pattern formation is rather temperature independent, dramatic changes take place above a threshold temperature ≈ 600 K, when structures of crystalline iron silicide are shaped on the surface. For these high temperatures needles and sponge patterns with amplitudes of the order of 100 nm and directed towards the ion beam evolve. Variation of the angle between ion beam and impurity source has a significant effect on pattern formation. The larger this angle, the more efficient is pattern formation. This observation points to the relevance of shadowing.

Under specific conditions low energy ion beam sputtering of surfaces leads to self-organized periodic patterns. These can be ripple patterns with periodicities in the nanometer range for oblique ion incidence or hexagonal dot patterns on compound materials for normal ion incidence. Recently, periodic nanohole patterns were observed on Ge surfaces when sputtered at normal incidence using a 5 keV Ga+ focused ion beam (FIB) [1]. These patterns resemble the dot patterns on GaSb mirrored with respect to the surface plane, suggesting a similar formation mechanism.
In this work we studied the pattern formation using FIB and compared the results with patterns produced by sputtering with a broad beam. In case of the focused beam a variation of the incidence angle as well as a variation in the energy of the incoming Ga+ ion on a Ge substrate was done. Using a broad Ga+ beam leads to the same pattern formation on Ge independent of scanning. Additionally GaSb dot patterns were produced using a broad beam of Ar+ and the size dependence of the energy of the incoming ion was studied. A comparison of both patterns shows no flux dependence in case of Ga+ sputtered on Ge (neither for FIB nor for broad beam), whereas the size and also the shape of the GaSb dots changes with flux.
[1] Q. Wei, X. Zhou, B. Joshi, Y. Chen, K. Li, Q. Wei, K. Sun, and L. Wang, Adv. Mater. 21, 2865 (2009).

Various elements like Pd, Cr, Ta, as well as several rare-earth elements can be used to modify the magnetic properties of thin ferromagnetic films. They are incorporated either by co-sputtering or ion implantation and are well known to reduce the Curie temperature, saturation magnetization, anisotropy and damping [1,2]. In combination with lithographic masking this allows for magnetic property patterning at the nanoscale [3]. In thin ferromagnetic films, the magnetization dynamics are governed by
intrinsic effects like Gilbert damping and spin-pumping but also by extrinsic effects like two-magnon scattering due to inevitable defect structures. By lithographic nanopatterning or by using ion-eroded, nanoscale periodically modulated substrates (ripples) as templates we are able to artificially create and thus control those defect structures necessary to induce two-magnon scattering. The damping contributions are disentangled from linewidth measurements by broadband ferromagnetic resonance technique.

Controlling spin relaxation is essential for spintronic and spin torque applications. Manipulating spin relaxation allows the adjustment of magnetization reversal speed at microwave frequencies. Moreover, the critical current in spin torque devices can be reduced and tuned. In the experiment it is possible to distinguish between the intrinsic and extrinsic relaxation channels. The latter can be tailored with respect to the intensity and anisotropic behaviour. In particular, methods for inducing elementary relaxation channels of uniaxial symmetry and their impact on the magnetization dynamics are discussed in this presentation. Fe-based thin films have been studied by means of the ferromagnetic resonance technique, by which the intrinsic and extrinsic relaxation processes can be disentangled. While the former are rather isotropic and can be adjusted via spin-orbit interaction, the latter can be modified in an advanced way. It is shown, how crystalline defects, inhomogeneities of chemical composition, and interface modifications can induce the 2-magnon scattering. Control and systematic manipulation of these parameters allow tailoring the overall spin relaxation in a desired manner with respect to the direction of magnetization and precessional frequency.

Ziel:

Die Herstellung von ⁶¹Cu hoher spezifischer Aktivität erfordert besonders aufwändige Maßnahmen, um Metallkontaminationen sowohl durch Cu-Isotope als auch durch andere Metalle zu minimieren. Dementsprechend müssen die herkömmlichen Methoden ververfeinert werden, um ⁶¹Cu sowohl in hoher Qualität als auch effektiv herstellen zu können. Vergleichswerte über spezifische Aktivitäten von ⁶¹Cu sind in der Literatur selten zu finden. McCarthy et al. [1] berichten zu spez. Aktivitäten von ⁶¹Cu im Bereich von 47 bis 190 GBq/µmol; erzeugt durch ⁶¹Ni(p,n)⁶¹Cu und ⁶⁰Ni(d,n)⁶¹Cu-Reaktion. Eine Alternative dazu stellt die ⁶⁴Zn(p,α)⁶¹Cu-Reaktion dar [2]. Das hierfür genutzte Targetmaterial ⁶⁴Zn (99,3% Isotopenanreicherung) ist im Vergleich zu angereichertem ⁶¹Ni weitaus weniger kostenintensiv.

Methoden:

Für die Bestrahlung am Zyklotron wird ein massiver Targetträger aus Gold verwendet, auf dem ca. 100 mg angereichertes ⁶⁴Zn (99,3% Isotopenanreicherung) abgeschieden sind. Die radiochemische Trennung erfolgt über Ionenaustauschtechniken nach Literaturangaben [3-8]. Die angewandte Methode nutzt eine Ionenaustauscherkaskade, die aus zwei Kationenaustauscher-Säulen und einer Anionenaustauscher-Säule besteht. Dabei sorgt der doppelte Kationenaustauscherschritt für die effektive Abtrennung von Galliumisotopen (^66/67/68Ga) und die Anionenaustauscher-Säule für die Trennung des ⁶¹Cu vom Zn-Targetmaterial. Der Gesamtprozess zur Gewinnung des gereinigten ⁶¹Cu dauert eine Stunde. Die Methode umfasst die Wiedergewinnung des eingesetzten ⁶⁴Zn, welches danach zur erneuten Verwendung zur Verfügung steht. Das optimierte Verfahren nutzt kleinere Ionenaustauschersäulen als bisher und ausschließlich wässrige Salzsäure; Details vgl. Thieme et al. [2]. Die Ermittlung der spezifischen Aktivität erfolgt über TETA-Titrationen und ICP-MS-Analysen. Es wurden Bestrahlungen an zwei verschiedenen Zyklotronen durchgeführt: am Cyclone 18/9 (IBA, Belgien) des Instituts für Radiopharmazie, Dresden-Rossendorf und am CC 18/9 (Efremov Institut, St. Petersburg, Russland) des Turku PET Centre in Turku, Finnland.

Ergebnisse:

Die Bestrahlungen mit dem Cyclone 18/9 wurden mit 12 µA und 16 MeV durchgeführt. Dies führte innerhalb von 30 Minuten zu Ausbeuten von ca. 300 MBq ⁶¹Cu (EOB). Am CC 18/9 wurde mit 30 µA, 13 MeV, 30 Minuten gearbeitet. Dabei wurden ebenfalls 330-400 MBq ⁶¹Cu (EOB) erzeugt, bei einer Bestrahlungszeit von 3 Stunden bis zu 1150 MBq⁶¹Cu (EOB). Am CC 18/9 wurde eine extrem hohe spezifische Aktivität des ⁶¹Cu von über 1000 GBq/µmol erreicht. Demgegenüber fielen die spezifischen Aktivitäten am Cyclone 18/9 deutlich ab, es konnte nur eine spezifische Aktivität von ca. 2 GBq/µmol erzielt werden. Wahrscheinlich tritt in diesem Fall eine Kontamination mit stabilem Kupfer schon während der Bestrahlung auf. Möglicherweise geht diese von der Targethalterung am Zyklotron aus, da sie nicht wie beim CC 18/9 komplett aus Aluminium, sondern größtenteils aus Messing besteht. Bisherige Versuche zum Schutz des Targetträgers und des Targetmaterials vor derartigen Kontaminationen bzw. der Versuch, Kontaminationen während des Trennprozesses zu verhindern, blieben erfolglos.

Schlussfolgerungen: Die Ergebnisse zeigen, dass es prinzipiell möglich ist, ⁶¹Cu mit hoher spezifischer Aktivität mit Hilfe der ⁶⁴Zn(p,α)61Cu-Reaktion herzustellen. Die genutzte radiochemische Trennmethode bietet sich hervorragend für eine routinemäßige Herstellung von ⁶¹Cu an.

Referenzen:

[1] McCarthy, D. W.; Bass, L. A.; Cutler, P. D.; Shefer, R. E.; Klinkowstein, R. E.; Herrero, P.; Lewis, J. S.; Cutler, C. S.; Anderson, C. J.; Welch, M. J. (1999) Nucl. Med. Biol. 26, 351-358
[2] Thieme, S.; Walther, M.; Pietzsch, H.-J.; Steinbach, J. in: Technetium and other radiometals in chemistry and medicine (Mazzi, U.; Eckelman, W. C.; Volkert, W. A. eds.), pp 475-478, SGE Editoriali, Padova, Italy
[3] Kraus, K. A.; Moore, G. E. (1953) J. Am. Chem. Soc. 75, 1460-1462
[4] O'Brien, H. A. (1969) Int. J. Appl. Radiat. Isot. 20, 121-124
[5] Neirinckx, R. D. (1977) Int. J. Appl. Radiat. Isot. 28, 802-804
[6] Jamriska, D. J.; Taylor, W. A.; Ott, M. A.; Heaton, R. C.; Phillips, D. R.; Fowler, M. M. (1995) J. Radioanal. Nucl. Chem. Art. 195, 263-270
[7] Smith, S. V.; Waters, D. J.; Di Bartolo, N. (1996) Radiochim. Acta 75, 65-68
[8] Rowshanfarzad, P.; Sabet, M.; Jalilian, A. R.; Kamalidehghan, M. (2006) Appl. Radiat. Isot. 64, 1563-1573

Clay minerals which are components of potential host rock formations for nuclear waste repositories can contain small organic molecules like formate, citrate or lactate. Such small organic molecules can like the ubiquitous humic acids influence the migration behavior of radionuclides. Different substituted benzoic acids can mimic the main functionalities and are often used as model compounds for humic substances.
The understanding of the complex behavior of radionuclides with such natural organic matter and the thermodynamic quantification of the interaction especially at elevated temperatures is of great importance to simulate and predict their migration behavior in the environment, particularly in the near field of nuclear waste disposals where higher temperatures are prevailing.
We present the investigation of the complex behavior of Am(III) and Eu(III) with lactate and salicylate at ambient and elevated temperatures with time-resolved laser-induced fluorescence spectroscopy (TRLFS) and the resulting thermodynamic data (reaction enthalpy, reaction entropy). Whereas the complexation with lactate is for both cations nearly temperature independent, is the complexation with salicylate clearly an endothermic reaction.

Important questions regarding the scaling of laser plasma (wakefield) electron acceleration are if, as in conventional architectures, a number of plasma accelerators can be staged and if it can be combined with conventional accelerators with reasonable efficiency and stability.
At the FZD, we are therefore combining the 150 TW laser beam of the Ti:Sapphire system Draco (up to 4 J on target in about 25 fs pulse duration [1] and to be upgraded to at least 500 TW until 2012) with the electron beam of the superconducting linear accelerator ELBE in the energy range between 15 and 35 MeV. ELBE routinely provides bunches of up to 70 pC charge with a pulse duration in the ps range, which is obviously not well matched to the laser pulse parameters, but will serve as a starting point for first experiments. Pulse compression techniques combined with the use of the recently installed photo electron gun should ultimately provide bunches in the 100 fs and nC range. A fully shielded target area has been set up allowing for co- and counter-propagating laser and electron beams. Currently pulse synchronization issues are examined experimentally.

Moreover, Thomson scattering of the laser light from the relativistic electron bunch [2] can be used for the generation of hard X-rays (few ten keV) without the need for electron acceleration to the GeV level. Although in the common head-on geometry and in the linear regime only about 10^6 photons per laser pulse can be expected. This number should be sufficient for applications in pump probe experiments. A significant increase in the rate can be expected when for short electron pulses the matching of the temporal overlap is improved by a tilted pulse front approach [3] which has been extensively simulated.

[1] K. Zeil, et al., New Journal of Physics, 12, special issue to appear in april 2010
[2] for an overview with respect to ELBE parameters, see A. Debus, et al., Proc. SPIE, 9780819476333, 735908 (2009) and refs. therein.
[3] A. Debus, et al., Applied Physics B in press (2010)

Vortrag über die Grundlagen der Ionentherapie

Ultra-intense laser interactions with solid foils are studied as a means to produce relativistic positron plasmas, which has been proposed as a potential laboratory for understanding positron-electron plasma aspects of gamma-ray bursts [1]. Initial experiments with high energy Nd:glass lasers have revealed a strong dependence of the positron yield, and energy distribution, on the thin-foil target thickness [2]. This arises from the contribution of so-called “trident” electro-production positrons, beyond the photo-production which dominates in thick targets [3]. Prospects for thin-target positron production and detection in 100 TW-class ultra-short pulse laser experiments will be presented

References
[1] E.P. Liang, S.C. Wilks and M. Tabak, Phys. Rev. Lett. 81, 4887 (1998).
[2] T. E. Cowan et al., Laser Part. Beams 17, 773 (1999).
[3] H. Chen et al., Phys. Rev. Lett. 102, 105001 (2009).

Bombesins (BN) containing ^99mTc ‘4+1’ complexes may be useful to detect tumors expressing the gastrinreleasing peptide receptor (GRPR). Derivatives of the formula [^99mTc(NS₃R)(L2-BN_st)] were synthesized, in which Tc(III) is coordinated by an isocyanide L2-BN_st bearing the peptide (BN_st=βAla-βAla-Gln-Trp-Ala-Val-Gly-His-Cha-Nle-NH₂) and a tetradentate chelator NS₃R. NS₃R consists of 2,2′,2″-nitrilotriethanethiol (NS₃) bearing a crown ether (NS₃crown), an aliphatic amine (NS₃en) and a tricarboxylic acid (NS₃(COOH₃). Nonradioactive Re compounds were prepared and analysed by electrospray ionization mass spectrometry. The structural similarity to the ^99mTc conjugates was demonstrated by their identical HPLC elution profiles. The lipophilicity of [^99mTc(NS₃R)(L2-BN_st)] decreased depending on the coligands NS₃crown (log D_O/W, pH=7.4, 0.98±0.11), NS₃en (−0.49±0.07) and NS₃(COOH)₃ (−2.01±0.09). Biodistribution in normal rats was characterized by an increasing kidney uptake and a decreasing uptake into the liver corresponding to the reduced lipophilicity of the conjugates. The pancreatic uptake expressed by the organ/blood ratio of standardized uptake values at 60 min p.i. in rats was 8.6±1.2 for [^99mTc(NS₃en)(L2-BN_st)] and higher compared to the other conjugates. The pancreas/liver ratio of the SUV at 60 min p.i. in rats was highest for [^99mTc(NS₃(COOH)₃)(L2-BN_st)] at 8.4±1.3. [^99mTc(NS₃en)(L2-BNst)] was further studied in tumor-bearing mice and its pancreas/blood and pancreas/liver ratios were lower, however the pancreas/kidney ratios were higher in mice compared to rats. The activity uptake of [^99mTc(NS₃en)(L2-BN_st)] into the PC-3 tumor xenografts was low (%ID/g: 0.83±0.18 at 60 min; SUV: 0.21±0.05 at 60 min) but specific.

In this work we studied the interaction of a ½〈1 1 1〉{1 1 0} edge dislocation with Cu-rich precipitates, mimicking those that are known to form in RPV steels. We have applied a combination of Monte Carlo and molecular dynamics techniques to explore the structure and obstacle strength of Cu–Ni-vacancy clusters of nanometric size below the resolution limit of transmission electron microscopy. The results show that the strength of Cu-vacancy, Cu–Ni and Cu–Ni-vacancy clusters is comparable or even smaller than that of pure Cu clusters, but considerably smaller than the strength of pure vacancy clusters or nanovoids. Thus, the enrichment of small Cu precipitates by Ni atoms and/or a small amount of vacancies does not increase their obstacle strength, at least in the case of edge dislocations.

Ultrashort pulse laser proton acceleration is demonstrated to yield energies hitherto only accessible with high energy lasers. Up to 20 MeV protons are observed with the FZD Draco Ti:Sa laser with ~30 fs pulses and only 2 J. This proton energy range allows for first well controlled applications. The radiation dose per shot observed for energies above 10 amounts to few Gy and thus provides excellent starting conditions for the irradiation of in vitro tumour cells with the aim of determining dose dependent biological damage. A first experiment demonstrates the availability of all components indispensable for systematic radiobiological studies: A laser-plasma accelerator providing stable proton spectra with maximum energy exceeding 15MeV over hundreds of pulses and applicable doses of a few Gy within few minutes, a beam transport and filtering system, an in-air irradiation site, a dedicated dosimetry system providing both online dose monitoring and a precise absolute dose information applied to the cell sample, and the full infrastructure for analysing radiation induced damage in cells.

[1] S.D. Kraft, K. Zeil, et al., New J. Phys. 12, 085003 (2010).

Recent successes in laser-ion acceleration have motivated research towards laser-driven compact accelerators for medical therapy. Realizing laser-ion acceleration for medical therapy will require adapting both the laser-ion acceleration to the medical requirements, as well as the treatment methodology to the foreseeable laser constraints. Three key scientific and technological challenges are identified: increasing laser-accelerated proton energies to 250 MeV; developing compact, strong field magnetic beam manipulation systems; and development of real-time in-vivo dosimetry to enable pulse-by-pulse active feedback and control. Progress in each of these key areas are reviewed, with special emphasis on the prospect of increasing the energy of laser accelerated protons by modifications of the Target Normal Sheath Acceleration process.

Proton acceleration from thin foils and reduced mass targets is studied with the 150 TW Ti:Sa DRACO Laser at FZD. DRACO has ~30 fs pulses, with up to 5 J at 10 Hz, and a contrast of 1e-10 in the ps regime, and 1e-9 to 1e-10 in the ns regime. Proton spectra are measured in radiochromic film stacks and magnetic spectrometers. Flat metallic foils exhibit a near-linear scaling of the maximum proton energy with laser power, consistent with [1] in the limiting case of ultrashort laser pulses [2]. Despite the high laser contrast, a slight deformation of the target rear surface results in a reproducible deflection of the emission of energetic protons away from the target normal direction [2]. The mass limited targets of 2 μm thick Si, were fabricated by MEMS techniques and ranged from 20x20 µm2 to 100x100 µm2 lateral size. Significant influence of the target edge and supporting stalks is observed, which depending on size can both both increase or decrease the maximum proton energy in comparison to a flat foil.

[1] J. Schreiber et al., PRL 97, 045005 (2006).
[2] K. Zeil et al., NJP 12, 045015 (2010)

The laser-acceleration of protons to 67.5 MeV has recently been observed at the LANL Trident laser using novel cone targets [1]. The measured enhancement in proton energy is understood from collisional Particle in Cell simulations, which show that the hot electron temperature, responsible for the Target Normal Sheath Acceleration at the cone-top, is significantly increased when the laser grazes the cone wall. This is due to the extraction of electrons from the cone wall by the laser electric field, and their boost in the forward direction by the vxB term of the Lorentz force. This is in contrast to previous predictions of optical collection and wall-guiding of electrons in angled cones [2]. This new mechanism should enable new and more robust target designs for reaching high laser-accelerated proton energies.

[1] S.A. Gaillard, invited talk NI3.00004.
[2] Y. Sentoku et al, Phys. Plasmas 11, 3083 (2004).

In the past, the suitability of Er for Si-based light emission was already investigated in detail. However, much less attention has been paid to Nd and Ho which exhibit several emission lines in the near infrared according to their 4f energy level scheme. In this work we measure the electrical and electroluminescence properties of Nd- and Ho-implanted MOS structures and compare them with the corresponding properties of Er-implanted devices. Based on these results their suitability for integrated photonic devices is discussed.

We report on recent data of e⁺e^- pair emission in proton nucleus collisions at energies above the light vector meson production thresholds. Invariant mass distributions for the p+Nb system at Ekin = 3.5 GeV are compared to data from elementary p+p reactions at the same beam energy. We observe a constant π⁰/ω yield ratio for both systems but an excess in the mass region above the π⁰ mass. Furthermore we present here the normalization procedure that was applied to p+Nb collisions by measuring the production of negative pions in the HADES acceptance.

As well known, the signal-to-noise ratio (SNR) of PET images can be considerably low. This is especially true for whole-body examinations of heavy patients, for respiratorygated studies, and dynamic studies with short frames. In these cases linear smoothing filters (LF) such as a Gaussian filter are applied in order to achieve an acceptable SNR. Image resolution is, however, considerably reduced by these LFs. This affects detectability and quantification of small structures. Interesting
alternatives to LFs are non-linear, locally adaptive filters (NLF), which enable noise reduction while preserving sharp edges.
It was the aim of this study to investigate the performance of a special NLF (bilateral filter, BF) when applied to images with a low SNR. In three phantom studies using a cylinder phantom with sphere inserts different signal-to-background ratios have been investigated. In addition, images with different noise levels were generated. Finally, respiratory-gated whole-body studies were analyzed. All data were filtered, both with BF and LF. The results were analyzed regarding noise level, image resolution and relative signal recovery.
In the phantom studies BF is able to preserve the spatial resolution near the edges of the spheres while improving the noise characteristics. Signal recovery even of small spheres is not significantly reduced. Using LF compromises the spatial
resolution and leads to unacceptable reduction of signal recovery. The positive properties of BF were also apparent when applying it to single gates of respiratory-gated studies, which otherwise were not suitable for visual inspection.
NLF is a powerful alternative to LFs commonly used in PET. For studies with high noise and high signal-to-background ratios using NLFs represents a suitable filter for edge preserving image enhancement. Its performance, however, is critically dependent on a sensible choice of its intensity and spatial dependent part.

Introduction:

The aim of this work is the development of bifunctional chelating agents (BFCAs) for mild and selective labelling of proteins with copper radioisotopes. In this perspective, the triazacyclononane derivative with two pyridyl pendant arms 1
(DMPTACN) seems to be useful. DMPTACN 1 and its bombesin conjugates can readily form very stable radiocopper(II) complexes under physiological conditions.1 The remaining secondary amine group of ligand 1 may be utilized to introduce the isothiocyanate group allowing the conjugation to appropriate biomolecules, e.g. proteins/antibodies by thiourea-bridging.
Results and Discussion:
Compound 1 was synthesized by a eleven-step sequence according to the previously published procedure.1 Treating the secondary amino group of 1 with 2-bromoacetamide reagents gave the appropriate N-Boc protected predecessors 2 (Figure 1). Subsequent cleavage of the Boc protection group with trifluoroacetic acid led smoothly to the 4-aminophenyl and 4-aminobenzyl derivatives of DMPTACN 3. In the last step, the isothiocyanates 4, synthesized by the reaction of
2 with thiophosgen proved to be high yielding. First labelling experiments of DMPTACN isothiocyanates 4 with [⁶⁴Cu]CuCl2 were performed in 0.1M MES/NaOH buffer at a pH = 6.2 and 251C, resulting in a radiochemical purity of higher than 99% within few minutes. The reactivity of the ⁶⁴Cu-labeled isothiocyanates with primary amino groups was tested using glycine as model compound. Applying a ten-fold excess of glycine, the reaction was completed after 4 h at room temperature. To prove the potential to label proteins, the monoclonal antibody C225 was investigated. In a first approach, ligands 4 were radiolabelled with ⁶⁴Cu, and subsequently conjugated to C225. For this pre-labelling strategy, a specific activity of 2.5 GBq/mmol was obtained. The post-labelling approach is more practical. The achievable ligand-toantibody ratios were 5:1, analyzed by Maldi-Tof mass spectrometry. Rapid labelling of the DMPTACN-containing antibody with [⁶⁴Cu]CuCl₂ was achieved to give a specific activity of 304 GBq/mmol.
Conclusion:
DMPTACN isothiocyanates are attractive bifunctional agents for the radiocopper(II)-labelling of proteins featuring very high chemical stabiliy.
Reference
[1] G. Gasser, L. Tjioe, B. Graham, M. J. Belousoff, S. Juran, M. Walther, J.-U. Ku¨ nstler, R. Bergmann, H. Stephan, L. Spiccia, Bioconjugate Chem. 2008, 9, 719–730.

Introduction:

The macrocyclic chelator 1,4,7–triazacyclononane triacetic acid (NOTA) is very suitable to label molecules with ⁶⁴Cu or ⁶⁸Ga due to its fast complex formation resulting in thermodynamically and kinetically stable complexes. Here we describe a convenient synthesis procedure for maleimide-functionalized NOTA derivatives for stable binding thiol groups of carrier molecules such as peptides, oligonucleotides or antibodies. This principle is examplified by coupling of thiol-modified L-oligonucleotides which are of great interest for pre-targeting approaches in radio-immunotherapy 1.
Results and discussion:
NOTA-monomaleimide 3 and NOTA-bismaleimide 4 were synthesized by nucleophilic addition of aminoethyl maleimide 1 or bismaleimide 2 to p–SCN-Bn-NOTA. At the next reaction step the NOTA-maleimides were conjugated
with a 50-mercaptohexyl-modified L-oligonucleotide.
⁶⁴Cu or ⁶⁸Ga labelling of conjugates 5 and 6 occurred very fast and with good radiochemical yields in NH₄OAc buffer. The specific activities resulted in 13.0 GBq/mmol for [⁶⁴Cu]Cu5, 6.7 GBq/mmol for [68Ga]Ga5, 5.8 GBq/mmol for [64Cu]Cu6 and 2.6 GBq/mmol for [⁶⁸Ga]Ga6. Small animal PET imaging in mice with [⁶⁴Cu]Cu5 showed that after 2 hours most of the injected activity was located in the bladder.
Conclusion:
The new ligand systems show advantages which make them interesting for further biological studies, namely the easy synthesis procedure, the fast labelling with ⁶⁴Cu or ⁶⁸Ga and the transferability of the conjugation principle to other carrier molecules such as peptides or antibodies.
Reference
[1] J. Schlesinger et al., Bioconjugate Chem. 2008, 19, 928–939.

Objectives:

The purpose was to develop applicable synthetic strategies for the preparation of new NOTAmaleimides for site-specific introduction into radiopharmaceutically relevant (macro)molecules. This approach should be characterized by low synthetic effort and high grade of flexibility concerning length and chemical nature of spacer units connecting the NOTA to the maleimide entities.
Methods:
To translate the idea and above stated requirements, the commercially available 1 and 2 were used as starting NOTA compounds. For the covalent attachment of maleimide derivatives with different linkers (aliphatic C₂ to C₆ as well as PEG₂₈), two synthetic pathways were investigated (scheme 1). The first is based on nucleophilic addition reaction of an aromatic isothiocyanate with a primary amino group. Due to the limited availability of amino functionalized maleimides, a second protocol was developed. Therefore, the aromatic amino group of 2 was used for coupling reactions with NHS-ester functionalized maleimide derivatives. After establishment of these two
methods, a selection of products was engaged in coupling reactions with thiol modified L-oligonucleotides (L-DNA) for tumor pretargeting studies.

Results:

The high sensitivity of the starting materials as well as the products 3a-b and 4a-e in terms of hydrolyzation side reactions necessitated optimization of reaction parameters (solvent, pH value, stoichiometry, reaction time, etc.). Yields of 30-40 % and 83-86 % for 3a-b and 4a-d were achieved, respectively. A yield of 50 % was attained for the PEG₂₈ derivative 4e. High specific activities resulted upon labeling different L-DNA-NOTA conjugates with ⁶⁴Cu and ⁶⁸Ga for biodistribution studies in Wistar rats.
Conclusions:
As a proof of concept, we demonstrate the practicability of these two methods by engaging various linkers. The broad variety of commercially available NHS-ester modified maleimides in respect to different spacer length, shape, and polarity emphasizes the high flexibility for the design of tailored NOTA-maleimides for diverse applications.

Objectives:

Complementary L-oligonucleotides (L-ONs) are characterized by high metabolic stability and low immunogenicity, in combination with the absence of natural hybridization targets and therefore represent a potential effector and conjugated with the targeting antibody as binding pairs in pretargeting technologies. PEG modification of the L-DNA will allow the pharmacokinetic tailoring of the effector molecules. Therefore we studied the effect of various sizes of PEG conjugates on the hybridisation of the L-DNA molecules with the complementary L-DNA-Cetuximab conjugates.
Methods:
Cetuximab as targeting probe for the endothelial growth factor receptor was a) modified with 1,4,7 triazacyclononane-1,4,7-triacetic acid (NOTA), b) modified with maleimide moieties by conjugation of the bifunctional cosslinker 4 maleimidobutyric acid N-hydroxysuccinimide ester (GMBS), c) conjugated with the complementary thiol-bearing single strand 17mer-c-L-DNA-SH. The degree of bound NOTA, maleimide and c-L DNA were determined by MALDI-TOF or UV/VIS spectroscopy. HS-PEG-L-DNAs with PEG sizes of 2, 5 and 10 kDa were conjugated with NOTA-maleimide and labelled with ⁶⁴Cu⁺⁺. The hybridisation was carried out in vitro with the radiolabeled L-DNA in different stoichiometrical ratios to NOTA-c-L-DNA-Cetuximab and analysed by agarose gel electrophoresis or UV-spectroscopy.
Results:
Four different L-DNA-Cetuximab-conjugates bearing 2.2±0.8, 2.9±1.1, 4.9±1.4 and 9±2 L-DNA chains (mean±SEM, n=3) were synthesized. PEGs with molecular masses of 2, 5 and 10 kDa did not clearly influence the hybridization of the ⁶⁴Cu-NOTA-PEG-L-DNA-conjugates with the complementary DNA-Cetuximab in vitro. Maximal hybridisation was reached in ratios equal and larger than 1:1 calculated from the DNA amount. The number of bound c-L-DNA on Cetuximab in the radioactive titration experiments were 2, 2.5, 5 and 9.5, which well agreed with 2.2, 2.9, 4.9 and 9, respectively, determined by direct UV/VIS spectroscopy of the c-L-DNA-NOTA-Cetuximab-conjugates.
Conclusion:
The effector ⁶⁴Cu-NOTA-PEG-L-DNA and the targeting probe NOTA-c-L-DNA-Cetuximab were synthesised, characterized and tested. The number of c-L-DNA on the Cetuximab was sufficient for in vitro hybridisation. The size of the PEG spacer did not clearly influence the in vitro hybridisation of the c-L-DNA-NOTA-Cetuximab-conjugates. This characteristic of the studied L-ON derivatives seems to be suitable for in vivo application. The potential of this L-ON approach in the pretargeting technology is currently under in vitro and in vivo investigation.

Die kombinierte PET/CT Bildgebung hat nach ihrer klinischen Einführung im Jahr 2001 in kurzer Zeit große Bedeutung in der Onkologie und Strahlentherapie erlangt (siehe z. B. [1-7]). Die Fähigkeit zur quasi-simultanen akkuraten morphologischen CT- und funktionellen PET-Bildgebung bei methodenbedingt gewährleisteter guter räumlicher Korrespondenz der beiden tomographischen Bilddatensätze ist der wesentliche Grund hierfür.

Die Gerätetechnik hat sich in diesen rund zehn Jahren kontinuierlich fortentwickelt. CT-seitig erfolgte hier ein Übergang von den initial verwendeten Einzeilengeräten zu den heute üblichen 64-128-Zeilengeräten, welche die im Vergleich zur PET ohnehin gute Ortsauflösung der CT weiter verbessern, v.a. aber die Untersuchungszeiten deutlich verkürzen. Auch PET-seitig wurden und werden große Fortschritte in der Gerätetechnik erreicht, die im folgenden noch näher diskutiert werden sollen, da insbesondere die kontinuierliche Verbesserung der PET-Bildgebung für den prospektiven Nutzen der PET/CT für die Belange der Strahlentherapie von entscheidender Bedeutung ist.

Maßgebliches Interesse besteht aus strahlentherapeutischer Sicht daran, die durch die PET gelieferte Information hinsichtlich verschiedener relevanter Parameter wie Tumorstoffwechsel und -hypoxie in eine individualisierte Bestrahlungsplanung optimal einzubringen. Aus messtechnischer Sicht sind die hauptsächlichen Anforderungen an die funktionelle PET/CT-Bildgebung in diesem Zusammenhang: Gewährleistung der bestmöglichen Koregistrierung von CT- und PET-Bilddaten, hohe Genauigkeit der quantitativen funktionellen PET-Parameter (z. B. SUV-Werte und Targetvolumen) und möglichst hohe (praktisch nutzbare) räumliche Auflösung der PET.

Ion irradiation during film growth has a strong impact on structural properties. Linear stability analysis is employed to study surface instabilities during ion-assisted growth of binary alloys. An interplay between curvature-dependent ion-driven and deposition-driven instabilities is investigated. We demonstrate that ion irradiation of growing binary alloys leads to the formation of composition-modulated surface patterns. It is shown that the ion-to-atom arrival ratio R is the pattern control parameter. Close to the instability threshold we identify different regimes of instabilities driven by ion- or deposition-induced surface roughness processes, or roughness-composition feedback interactions. In particular, the synergistic effects of the curvature-dependent displacement and deposition coupling to the preferential sputtering or to the preferential diffusivity are found to induce instabilities and pattern formation. Depending on the film growth and ion-irradiation conditions, the instabilities show stationary or oscillating behavior. The latter one is exclusively connected with ion irradiation. The corresponding phase diagrams are presented in terms of experimentally accessible parameters. This shows an alternative way to control surface patterning and to grow three-dimensional laterally or vertically ordered nanostructures.

Das Nuklid 44Ti (Halbwertszeit 59 Jahre) wird in Supernovae erzeugt. Die Gamma-Strahlung aus seinem Zerfall lässt sich in weltraumgestützten Gamma-Teleskopen nachweisen und kann als Werkzeug zum Test von Supernova-Modellen genutzt werden. Hierfür ist eine genaue Kenntnis der Kernreaktionsraten für die Erzeugung und Zerstörung von 44Ti erforderlich. Die 40Ca(alpha,gamma)44Ti-Reaktion dominiert die Erzeugung von 44Ti. Ihre Rate wird von einer Vielzahl von Resonanzen bestimmt. Um präzise Daten zu gewinnen, wurde die Stärke des Resonanztripletts bei 4.5MeV Gamma-Energie am Dresdner 3MV Tandetron sowohl mittels in-beam Gamma-Spektrometrie als auch durch eine Aktivierungsmessung im Felsenkeller-Niederniveaumesslabor gemessen. Eine Untersuchung der bestrahlten Proben mittels Beschleunigermassenspektrometrie ist geplant. – Gefördert von der EU (FP7-SPIRIT 227012) und der DFG (BE 4100/2-1).

Many physical vapor deposition (PVD) methods involve the energetic particle bombardment of growing film surfaces. While the source, energy and flux of such energetic particles strongly depend on the PVD method, the basic processes they induce on the film surface are similar. Such an irradiation has a beneficial effect on different structural properties of coatings or thin films such as densification, grain morphology, adhesion, texture. This has a direct impact on the mechanical, tribological, electrical, optical or chemical performance of such films.

The aim of this talk is to give a brief overview on (i) different PVD techniques involving energetic particles and (ii) basic ion-solid interaction processes and how they influence the thin film growth process. Some recent results of our group on the ion-assisted growth of nanocomposite thin films will be also presented.

Liquid metal batteries, i.e. batteries in which both electrodes as well as the electrolyte are in the liquid state, usable for grid-scale energy storage have received considerable attention recently . A current and comprehensive account focusing on their applicability in future large scale storage systems is provided by Bradwell, earlier investigations of the technology were oriented on smaller units and thermally regenerative electrochemical systems.

A battery with fully liquid active inventary has a number of advantages: when densities are chosen properly, the battery is self-assembling due to stable stratification. Liquid-liquid interfaces allow for very fast kinetics and thereby rapid charging and discharging. Structureless (liquid) electrodes are insusceptible to aging providing nearly unlimited cyclability. Liquid metal batteries may be built from abundant and cheap feedstock. NaS and ZEBRA batteries share several of the advantages mentioned above, but require large initial investments due to their complicated construction, which is mainly dictated by the fragile ceramic electrolyte. In any case, scalability is a key enabler for cheap grid storage and ease of scale-up is one of the main underlying assumptions of liquid metal battery development. However, large electrode areas and high current densities imply large total current per cell and here electromagnetics together with fluid mechanics - i.e. magnetohydrodynamics - comes into play.

Aluminium reduction cells - which are often mentioned to have sparked the idea for large scale energy storage using liquid metals, see, e.g., - suffer from an interfacial instability which puts a constraint on the minimum electrolyte thickness. While this limitation has also to be considered, our focus is on another kind of instabilty, which limits the upper size of liquid metal batteries and is known in astrophysics under the label Tayler instability (TI). In our context, the TI is a kink-type (i.e. non-axisymmetric) instability that occurs if the current through a column of liquid metal exceeds some critical value in the order of kA, depending on the material properties. If this current threshold is exceeded, the TI would lead to a stirring of the battery inventory destroying the stable density stratification and short-circuiting the electrodes. Due to its potentially dramatic consequences, the TI should definitely be avoided during liquid metal battery operation.

One possibility to circumvent the instability is to use cells with a central bore. Depending on the ratio of bore to cell diameter, the instability can be shifted to higher total currents. Feeding a current through the bore opposing the current in the cell is a means to suppress the TI totally and would therefore be preferred in practical settings.

The photoluminescence (PL) emission of semiconductor quantum wells (QWs) at low temperatures for low and intermediate excitation densities shows long rise times, as only zero-momentum states can directly couple to the photons. The relaxation of the electron-hole plasma into the k=0 state and the binding of free electron-hole pairs into excitons has been extensively studied and debated in literature. Amo et al. [1] studied the effects of the sudden warming of the relaxing carrier distribution by applying a second, time-delayed interband excitation pulse.
We present a detailed study on time-resolved photoluminescence from an undoped GaAs/AlGaAs multiple QW sample quenched by a time-delayed mid-infrared (MIR) pulse causing an intersubband transition. Our experimental technique is based on the synchronization of a pulsed table-top Ti:sapphire laser with a free-electron laser (FEL) operating in continuous pulsing mode (13 MHz). The user facility FELBE at Helmholtz-Zentrum Dresden-Rossendorf is tunable and covers a wavelength range from 4 to 280 µm. The picosecond Ti:sapphire laser pulses operating at a photon energy of 1.64 eV create a free-carrier density of approximately 5x1010 cm-2 per well in the MQW structure via interband excitation. The PL is detected by a streak camera attached to a grating spectrometer, which allows for spectral and temporal resolution of the signal (see Fig. 1b). PL quenching is induced by a delayed MIR pulse from the FEL tuned to the intersubband energy of the sample of 172 meV (7.2 µm). Since the MIR pulses (~2 ps) are much shorter than the PL recovery time, a clear sharp dip appears in the PL transient at the arrival time of the MIR pulse. The PL recovers to a slightly higher intensity as compared to the unperturbed case due to particle conservation (see Fig. 1b). As no carriers are newly injected, the carrier dynamics can be directly studied from the PL recovery within the time resolution of our experimental setup (~ 25 ps).
The experimental data can be accurately described by a rate-equation model, where possible states in the conduction band are reduced to two effective levels. The PL recovery time was found to be the same as the PL rise time for all studied MIR fluences and temporal positions of the dip. This implies that the PL recovery accounts for the cooling of the carrier distribution rather than the formation of radiative states. The observed cooling time linearly decreases with MIR fluence due to lattice heating induced by the FEL. Performing polarization sensitive measurements, we were able to discriminate the contributions of free-carrier absorption from that of intersubband absorption, where the latter is 20 times more efficient than the free-carrier absorption (see Fig. 2). This approach also provides a new method to investigate the strictness of the polarization selection rules for intersubband absorption.

[1] A. Amo, D. Ballarini, D. Sanvitto, E. Kozhemyakina, L.Vina, A. Lemaitre, D. Bajoni, and J. Bloch, Appl. Phys. Lett 92, 061912 (2008).

The occurrence of a PTS in a reactor vessel is an important phenomenon for assessing nuclear reactor safety. New experiment was conducted at HZDR, focused on thermal mixing processes in the cold leg and the downcomer of two-phase PTS case. Present work reports CFD analysis of steady-state air-water case. CFD analysis was conducted with two turbulence-modeling approaches, RANS and LES. Multiphase situation was modeled with VOF approach. Simulations were performed using the ANSYS Fluent 12 package. Comparison of computed temperatures results and measurements along the thermo-couple lines revealed results depend on the turbulence model used.

We present three examples of infrared spectroscopic investigations of semiconductors: exciton dressed states in quantum wells, pump-probe measurements on graphene, and near-field spectroscopy of buried quantum dots.

Using low-frequency terahertz pulses we present ultrafast optical switching of a coherent intersubband polarization in a semiconductor quantum well.

The correct analysis of the Pressurized Thermal Shock requires the simulation of the thermal mixing that occurs when cold Emergency Core Cooling (ECC) water is injected into the cold leg, where it flows to the downcomer and mixes with the hot coolant present in the primary circuit. In the framework of the NURISP (NUclear Reactor Integrated Simulation Project) project attempts are being made to improve the CFD modeling for two-phase PTS scenarios. For this purpose, two steady-state reference cases from the TOPFLOW-PTS experimental program were defined: one for air-water and one for steam-water flow. The current paper focuses only on the steam-water reference case. The pre-test simulations were performed with the commercial CFD code ANSYS CFX 12.0. The simulations of the steam-water reference test predicted a thermal stratification in the cold leg at the entrance into the downcomer and in the downcomer itself.

Eingeladener Vortrag ohne Abstract

Knowledge in speciation is a requirement in investigations about migration paths of heavy metal con-taminations in the natural environment. A very helpful tool with an extremely low detection limit for analyzing speciation of certain radioactive heavy metal ions like uranium (VI) is the Time-resolved Laser-induced Fluores-cence Spectroscopy (TRLFS). This technique is particularly useful for detection of speciation from those ions in very low, but environmental relevant concentrations. So TRLFS can be useful in safety assessment concerning migration behaviour of fluorescent and radioactive elements.
In this study, TRLFS was applied to determine the uranium speciation in natural occurring seepage water sam-ples, and in soil water samples, all samples collected from test site “Gessenwiese” close to Ronneburg in Eastern Thuringia (Germany), were analyzed by TRLFS. This test site was installed as part of a research program of the Friedrich Schiller University Jena for investigations within the area of recultivated former uranium mining heaps.
The TRLFS measurements on water samples collected within test site Gessenwiese revealed that the uranium speciation in these seepage waters and soil waters is dominated by the hydrolyzed and monomer uranium (VI) sulfate species UO₂SO₄(aq). The analysis were based on the position of the peak maxima from the fluorescence signal, and their mono-exponential decay curve. Despite of the presence of high amounts of well-known fluores-cence quenchers like iron (up to 18.3 ppm) and manganese (up to extend of 97.4 ppm), the obtained uranium (VI) fluorescence signals from the natural surface and soil water samples showed sufficiently high intensity and thus could be analysed.
The here presented results are a convincing example for the suitability of TRFLS in analyzing the speciation of uranium from natural occurring water samples with pH values between 3.2 and 4.0. They were published in [1] and via Open Access.

Reference:

[1] N. Baumann, T. Arnold and M. Longschinski, J Radioanal Nucl Chem, accepted Aug. 2011

Cannabinoid receptors (CB) are G-protein coupled receptors involved in many physiological processes, like learning, appetite, nociception and others. Two subtypes (termed CB1 and CB2) are involved in slightly different processes [1]. Thus, it is important to gain more insight into the the cannabinoid receptor system and the potential effects of cannabinoid therapeutics.

By combining [2] 3D-QSAR, pharmacophore modeling, comparative modeling and molecular docking we could identify features responsible for receptor subtype specificity. Various pharmacophore models were derived from in-house libraries and data available in the literature. 3D structures of both receptor subtypes were created employing comparative modeling methods. The models were subjected to molecular simulations in solvated lipid bilayers to sample different receptor conformations. The models were used for molecular docking studies with small compound libraries.
Employing the data obtained in the pharmacophore/3D-QSAR studies as additional constraints delivered valuable information on affinity and selectivity of the compounds towards CB1 and CB2. The results from this synergistic modeling approach could improve our understanding of the protein–ligand interactions involved.
[1] Pertwee, RG. Ligands that target cannabinoid receptors in the brain: from THC to anandamide and beyond Addict Biol 2008, 13:147–159.
[2] This synergistic approach has been implemented into the MOE modeling package (MOE: Chemical Computing Group Inc. Montreal. H3A 2R7 Canada. http://www.chemcomp.com)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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