Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

DC resistivity and electron spin resonance (ESR) measurements have been performed on the two-dimensionalorganicconductor k-(BEDT-TTF)₂Hg(SCN)₂Cl. Due to electronic correlations, the compound undergoes a transition from a metallic to an insulating state at T_MI= 34 K.The ESR parameters exhibit a drastic change below T_afm=27K that evidences a magnetic phase transition. Int his low-temperature state, we observe the characteristics of antiferromagnetic resonances in the angular dependence of the g-value.

Using time resolved photoluminescence (PL) quenching measurements, we investigated inplane carrier transfer in InAs/GaAs self-assembled quantum dots (QDs). THz pulses from a free-electron laser tuned to the intersublevel transition energy were used to excite carriers to higher levels causing quenching in the PL. These carriers could either fall back to the lower energy states and recombine or get transferred to adjacent QDs. The relaxation of the carriers was directly reflected in the recovery of the PL signal. Comparing measurements from two samples, we found that the redistribution of carriers into the neighbouring QDs is the dominant mechanism of carrier relaxation. The data were fitted using a rate equation model to estimate the PL recovery time which we attribute to the interdot carrier transfer time.

The presentation gives an overview on the safety evaluation methodology applied in Germany after the Fukushima event. The general idea of the used evaluation methodology is described. The different evaluation topics based on natural and civilization caused threats will be discussed. Additionally, the new postulated incidents for the safety evaluation are presented. Conclusions are drawn on the applicability of the methodology, originally derived for light water reactors, to fast reactors.

Different current and planned experiments (MUSE, YALINA, Guinevere) are designed to study the zero power neutron physical behavior of accelerator driven systems (ADS). The detailed analysis of the kinetic space-time behavior of the neutron flux is important for the evaluation of these ADS experiments. Current analysis for all these experiments is based on the standard methods - Sjöstrand method and Slope method – both based on the point kinetics equations. The point kinetics equations are developed from different approximations to the transport equation. Nevertheless, all these partial differential equations of the transport equation are solved by the separation of space and time to derive the point kinetics equations. The separation of space and time does not provide useful results for cases with strongly space-time dependent external source like it appears during the shutdown of the external neutron source. In recent years, two big projects have been launched to solve the problem of sub-criticality determination in ADS experiments and for the future during ADS operation. In the 6th European Framework program in the integrated project EUROTRANS, the domain 2, ECATS has been dedicated to ADS experiments and the analysis methods for the experiments. In the same time frame, the IAEA has launched the coordinated research project: ”Analytical and Experimental Benchmark Analyses of Accelerator Driven Systems (ADS)”. Different correction methods based on Monte Carlo Results for the YALINA-Booster system have been derived for the Sjöstrand method as well as for the Slope method in EUROTRANS/ ECATS. Good results have been achieved with this correction method for the analysis of the detectors in the thermal zone. Nevertheless, there is still a problem existing in the fast zone which is the really important zone, since the follow up experiment GUINEVERE and the foreseen facility MHYRRA will be a pure fast system. The results for the analysis of the fast zone of YALINA-Booser are still not convincing, even with the use of correction factors. Good results, but once more only for the thermal and the reflector positions, have been shown in the IAEA CRP by the US American group, especially. These results rely on the use of correction factors form deterministic calculations. The conclusion of the IAEA meeting suggests for further activities, maybe a further CRP among others, the following two topics: “Online Reactivity Monitoring and Control of Sub-critical System”; and “Determination of Sub-criticality Level and Uncertainties Analyses”.

Especially in Europe, the status of the core and system simulation is an essential point for the licensing of future nuclear reactor plants. In the light water reactor (LWR) technology, the development of modern coupled thermal hydraulics/neutronics simulation tools has undergone a rapid development in the late 90ies and during the first years of the new century. The simulation standard in LWR is described with a detailed view into the available codes and methods including the calculation chain for the coupled thermal hydraulics/neutronics steady state core analysis. Further on, the simulation capabilities for the load following and for the transient analysis in LWR cores are discussed. The overview will be closed with a description of the coupled simulations for the core integrated into the whole reactor system using the core simulators together with the system simulation codes for the description of transients which are induced or influenced by the primary or even the secondary system.
The current capabilities for the simulation of the core and system behavior of fast reactors in steady state as well as during transients are discussed in comparison with the described state-of-the-art in LWR to demonstrate the currently available possibilities and to define the development demand.
Advantage in the development of simulation codes for fast reactors can be taken from the state-of-the-art available in LWR technology. Conclusions are drawn about the required extensions needed to make the LWR code systems usable for fast reactor simulation. Two code systems under development and validation are presented to give an insight into the newest advances in the topic. The major point in the future for these works is the validation of the extended codes. For his topic, an outlook is given to the IAEA CRP on the EBR-II benchmark proposed by the Argonne National Lab., which is a good opportunity for the code validation.

Standard Big Bang nucleosynthesis predicts a very low abundance of the minor lithium isotope 6Li, which is instead believed to be produced by cosmic rays over time. However, recently 6Li has been detected in very old metal-poor stars, leading to the question whether its Big Bang production might be stronger than believed. The key reaction for 6Li production in the Big Bang is d(alpha,gamma)6Li. Using the deep underground LUNA 400 kV accelerator at the Gran Sasso Laboratory in Italy, a direct measurement of the cross section is underway. The contribution will report on this experiment, collected data, methods to analyze them, and preliminary results.

Initial tests of KETEK 3*3mm^2 SiPM's are presented, for the readout of BC408 scintillator material.

The plans for working package 4 (photosensors) within the NUPNET NEDENSAA project are reviewed, with a focus on planned efforts at TU Dresden, Uppsala, and INFN.

The goals and design of the future NeuLAND detector at FAIR are presented.

The 2H(alpha,gamma)6Li reaction dominates the production of lithium-6 in standard big bang nucleosynthesis. Due to its exceedingly low cross section, this reaction has never been studied experimentally at the relevant energies, and consequently the adopted reaction rate depends on uncertain extrapolations. A direct study of the 2H(alpha,gamma)6Li cross section is currently underway at the LUNA 400 kV accelerator, located deep underground in the Gran Sasso laboratory, Italy. The expected data lie directly at big-bang energies. It is hoped that they help constrain non-standard lithium-6 production scenarios, by putting the standard Big Bang production on a solid experimental footing.

In addition to the well-known 7Li problem of Big Bang nucleosynthesis, observations of 6Li in very metal poor stars hint at a possible Big Bang Li problem. Network calculations show that the 2H(𝛼,𝛾)6Li reaction dominates 6Li production in the Big Bang, but there are no direct experimental data on this reaction at relevant energies. An experiment on this reaction is underway at the 400kV underground accelerator LUNA in Gran Sasso/Italy, and preliminary data will be shown. In addition, recent LUNA work on the 15 N(p,𝛾)16O, 17O(p,𝛾)18 F, and 25Mg(p,𝛾)26Al reactions and a planned 22Ne(p,𝛾)23Na study will be briefly discussed, and an outlook will be given.

The status and perspectives for a possible accelerator in the shallow underground facility Felsenkeller in Dresden is reviewed.

The status and future of underground laboratories for nuclear astrophysics are reviewed

Mitarbeiterzeitung des HZDR

Tetravalent actinides show a strong tendency toward hydrolysis already at low pH. Below the onset of hydrolysis they commonly form monomeric complexes with carboxylate ligands. As the pH reaches the hydrolysis limit, olation and oxolation occur as competing reactions. We observed under these circumstances the formation of several well-defined hexanuclear carboxylate complexes. Recent thermodynamic studies suffer from the lack of structural information on such solution species. EXAFS spectroscopy is well suited to gain this information and has been applied to study U(IV), Th(IV), Np(IV) and Pu(IV) carboxylates and amino-carboxylates in aqueous solution and solid state. A comparison with the corresponding single crystal data supports the structure analysis of the solution species. We found that the carboxylic group acts as terminating ligand and stabilizes nanosized hexanuclear clusters in solution as well as in solid state. It is important to note that this reaction prevents the formation of hydrolysis products as well as the formation of An(IV) hydrous oxide colloids.

Magnetic Vortices are of great interest for storage media for quite a while. Different control methods are used to manipulate them. We now use scanning transmission x-ray microscopy (STXM) to image the magnetic configurations within the different layer of a trilayer system of Cobalt/Copper/Permalloy. The dominant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling. The corresponding behaviors of the magnetization configurations in a static magnetic field, as well as in an oscillating magnetic field, are investigated. The emerging movement of the core can be tuned with the amplitude and frequency of the field. The interactions of the two cores and their individually resonance frequencies are studied. This implies the corresponding resistance changes within different configurations at different magnetic fields and currents as well as the shifting of the core.

Introduction
Fluorochromatic labeling of organic nanoparticles is often used to investigate their biodistribution in animal models. However, this technique is descriptive in nature and does not allow for signal quantification. Furthermore, fluorochromatic labeling changes chemical and physical properties and is therefore thought to change the distribution characteristics of nanoscaled particles. We therefore hypothesized that radioactive labeling facilitates a quantifiable determination of the biodistribution of nanoparticles.

Material and Methods
47 NMRI-mice received 35S- labeled, 7 ± 1,5 nm sized dendritic Polyglycerol Sulfate (dPGS) or unlabelled dPGS intravenously or subcutaneously. Radioactivity from tissues at different times up to 21 days was analyzed by surface-counts, autoradiography, liquid-scintillation, imager-survey and histological photoemulsion.

Results
Radioactivity measurements allowed for a tissue- and time-dependent quantification of the labelled dPGS. Radioactively-labelled dPGS were still quantifiable in liver and spleen after 21 days following intravenous injection. Subcutaneous application resulted in a similar but delayed distribution kinetic.

Discussion
The biodistribution of dPGS was quantitatively determined by all methods used for radioactivity testing. This approach should provide an innovative, sensitive and adaptable method to detect nanoparticles without changing their biorelevant properties.

The spin relaxation process of thin Ni80Fe20 (Py) films is influenced by introducing a periodic scattering potential using ion beam techniques. These potentials can be created in two ways: (i) by Cr+ implantation into the surface of the Py film, using a lithographically defined mask. (ii) by using nanometer scale periodically modulated substrates (ripple) that change the morphology of the Py film grown on top [2].
The magnetic damping contributions are determined by frequencydependent ferromagnetic resonance measurements using a vector network analyzer. For both sample systems we find several strongly enhanced linewidth peaks over a wide frequency range. By varying the scattering potential, the frequency positions of the damping peaks are preselectable.
This work is supported by DFG grant FA 314/6-1 and SFB 491.
[1] I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011).
[2] J. Fassbender et al., New Journal of Physics 11, 125002 (2009).

In this study we examined the impact of two microbial representatives from actually discussed potential geological formations for nuclear waste storage on the U(VI) speciation. Pseudomonas fluorescens CCUG 32456A isolated from the granitic aquifers at the Äspö Hard Rock Laboratory, Sweden, and a novel strain of the genus Paenibacillus from clay samples of the Mont Terri Rock Laboratory, Switzerland, which we have recently isolated and been able to cultivate, were investigated. To assess the U(VI) interaction with surface functional groups of theses strains, potentiometric titration in combination with time-resolved laser-induced fluorescence spectroscopy (TRLFS) were applied. Based on the stability constants of U(VI) complexes with the bacterial surface functional groups U(VI) species distributions in presence of both strains in dependence on the pH were calculated. The differences in the U(VI) speciation with both strains and the influencing factors will be discussed in detail.

Mitarbeiterzeitung des HZDR

Mitarbeiterzeitung des HZDR

Transition between turbulent flow regimes is studied experimentally in a cylinder of liquid mercury heated from below under the influence of a rotating magnetic field. The latter creates a rotating flow which almost completely suppresses the temperature fluctuation near horizontal boundaries at a much lower angular velocity than a simple mechanical rotation. Our experiment confirms that this effect persists in the deep turbulent range to Grashof numbers as high as about 10^9. An intermediate range is observed for Gr > 2 × 10^8 with the temperature fluctuation suppressed in the core but near the sidewall. This is explained by turbulent friction replacing the Coriolis force as the leading retarding force. The linear instability of a simplified model is studied numerically. The model considers a base flow consisting of a uniform rotation and a formally independent uniform meridional flow in a cylinder with an adverse vertical temperature gradient. The model shows that the bulk meridional flow being itself much slower than the rotation is able to delay the Rayleigh-Bénard instability.

Chemokines are small secreted proteins with important roles in immune responses. They consist of a conserved three-dimensional (3D) structure, so-called IL8-like chemokine fold, which is supported by disulfide bridges characteristic of this protein family. Sequence- and profile-based computational methods have been proficient in discovering novel chemokines by making use of their sequence-conserved cysteine patterns. However, it has been recently shown that some chemokines escaped annotation by these methods due to low sequence similarity to known chemokines and to different arrangement of cysteines in sequence and in 3D. Innovative methods overcoming the limitations of current techniques may allow the discovery of new remote homologs in the still functionally uncharacterized fraction of the human genome.
We report a novel computational approach for proteome-wide identification of remote homologs of the chemokine family that uses fold recognition techniques in combination with a scaffold-based automatic mapping of disulfide bonds to define a 3D profile of the chemokine protein family. By applying our methodology to all currently uncharacterized human protein sequences, we have discovered two novel proteins that, without having significant sequence similarity to known chemokines or characteristic cysteine patterns, show strong structural resemblance to known anti-HIV chemokines. Detailed computational analysis and experimental structural investigations based on mass spectrometry and circular dichroism support our structural predictions and highlight several other chemokine-like features. The results obtained support their functional annotation as putative novel chemokines and encourage further experimental characterization.
The identification of remote homologs of human chemokines may provide new insights into the molecular mechanisms causing pathologies such as cancer or AIDS, and may contribute to the development of novel treatments. Besides, the genome-wide applicability of our methodology based on 3D protein family profiles may open up new possibilities for improving and accelerating protein function annotation processes.

Supported nanostructured photocatalysts were improved by using novel biohybrid materials based on bacterial S-layer proteins. Within the development of advanced photocatalytic materials supported with bacterial S-layer proteins, the OH radical scavenging capacity of suspended S-layer proteins in a photocatalytic system was determined with 2.39 × 105 (mg protein)−1 s−1 using tertiary butanol OH radical assay. Furthermore, applying the photocatalyst in suspension, S-layer proteins inhibit the photocatalytic process by covering the ZnO nanoparticles. This effect is related to the protein concentration and can be described by a saturation function. S-layer proteins were not conspicuously damaged, such as fragmentation, by photocatalytic treatment. Only a slight cross-linking was visible by gel electrophoresis. For future use, immobilized S-layer proteins will be utilized in significantly lower amounts. Therefore the inhibition by covering particles and the relatively low scavenging capacity will not strongly affect the OH radical yield of the final composite. These findings were also confirmed by degradation experiments with diclofenac. Based on these findings it can be concluded that the implementation of nanoscaled biocomposite materials using S-layer proteins for the preparation of multi-functional coatings for photocatalytic applications is promising.

Titanium nitrides have good mechanical, biomedical and optical properties, therefore they are used to harden and protect cutting and sliding surfaces and as a non-toxic exterior for bio-medical applications. Nitrogen plasma immersion implantation (Pill), in which the diffusion of nitrogen from low pressure r.f. plasma is combined with the implantation of nitrogen ions at energies up to 30 kV, is an effective tool for nitriding titanium and titanium alloys. In this work, samples of pure titanium were nitrided by Pill at different negative high voltage pulses. The properties and the characteristics of the processed samples were evaluated using X-ray diffraction (XRD), Auger electron spectroscopy (AES), ball-on-disk type tribometer, surface profilemeter, and ellipsometry measurements. The results show that, the wear resistance of the untreated sample in comparison to the PIII treated samples is extremely poor and the friction coefficient for the PIII treated samples is decrease!
d to the half value in comparison to the untreated titanium, this attributed to the formation of the solid solution titanium alpha-Ti(N) and the cubic TiN phases. Ellipsometric measurements were carried out on the PIII treated samples at different negative high voltage pulses. A three layers model was used to fit the calculated data to the experimental ellipsometric spectra. The thickness, surface roughness and refractive index increase with increasing the negative high voltage pulses. The refractive index at 550 nm increases from 1.83 to 2.09 as the negative high voltage pulses increases from 10 to 30 kV.

Implant infection still represents a major clinical problem in orthopedic surgery. We therefore tested the in vitro biocompatibility and antibacterial effects of copper (Cu)- and silver (Ag)-ion implantation. Discs of a commonly used titanium alloy (Ti6AlV4) with an aluminium oxide-blasted surface were treated by Cu- or Ag-ion implantation with different dosage regimen (ranging from 1e15-17 ions cm(-2) at energies of 2-20 keV). The samples were seeded with primary human osteoblasts and cell attachment and proliferation was analyzed by an MTT-assay. In comparison to the reference titanium alloy there was no difference in the number of attached viable cells after two days. After seven days the number of viable cells was increased for Cu with 1e17 ions cm(-2) at 2 and 5 keV, and for Ag with 1e16 ions cm(-2) at 5 keV while it was reduced for the highest amount of Ag deposition (1e17 ions cm(-2) at 20 key). Antibacterial effects on S.aureus and E.coli were marginal for the studied dosages of Cu but clearly present for Ag with 1e16 ions cm(-2) at 2 and 5 keV and 1e17 ions cm(-2) at 20 keV. These results indicate that Ag-ion implantation may be a promising methodological approach for antibacterial functionalization of titanium implants.

Taking into account the recent worldwide strive for raw materials, the emergence of start-ups in the mining sector for rare metals, and tendencies of financial and strategic investors to invest in such companies, the paper critically evaluates the suitability of common methods widely used to valuate mining projects and start-ups. Building on the deficiencies of single methods to capture the specificities of rare earth junior mining companies, which are assumed to be single-project companies, the paper suggests using a combined approach including discounted cash flow, real options, and multipliers methods. Compared to the value obtained by using singular methods, the resulting specific value is argued to better reflect the value of a specific company and project, respectively, within the rare earth junior mining industry.

X-ray absorption spectroscopy (XAS) is well suited to investigate trace amounts of target elements in a variety of matrices, which makes it the method of choice for the investigation of radionuclides in the framework of nuclear waste management. With the Rossendorf Beamline at ESRF (ROBL), a dedicated XAS station for radionuclide research is available, licensed to investigate actinides from throrium to californium with activities up to 185 MBq. In this talk, I will give an overview on nuclear waste related research performed at ROBL, encompassing waste disposal as well as waste reduction.

We report results of magnetization and magneto-acoustic studies on a UCo₂Si₂ single crystal in high magnetic fields. This compound orders antiferromagnetically at the Néel temperature T_N = 83 K and shows at low temperatures a first-order metamagnetic transition (MT) at 45 T with very small hysteresis (µ0ΔH_cr = 0.16 T) to a ferrimagnetic state seen as a sharp jump in the magnetization when the magnetic field is applied along the c direction. The magnetization curve measured along the a axis shows no transition and is linear up to 60 T. The acoustic properties exhibit drastic anomalies in the vicinity of both magnetic phase transitions; the spontaneous and the field-induced one. At T_N, a pronounced change in the sound velocity Δv/v accompanied with a peak in the attenuation Δα has been observed. Whereas Δα only shows a very sharp peak at the MT, Δv/v displays a more complicated behavior; it has a non-monotonous temperature evolution with maximum effects at 30 K, which can be due to the transition changing from first to second order. Our results enabled us to map the phase diagram of UCo₂Si₂ in fields applied along the c axis. We discuss our observations in relation to the magnetism on the U site and the magnetoelastic interaction in this material. *Part of this work was supported by EuroMagNET under the EU contract No. 228043.

At frequencies between 100 GHz and 2.5 THz, we have accurately measured the complex transmission coefficient of LuNi₂B₂C films on MgO substrates using two different setups: a time-domain terahertz spectrometer and a setup based on backward-wave oscillators. For the first time, the development of the superconducting energy gap is directly observed in the optical spectra. From the measured data, we have calculated the optical conductivity and the penetration depth. We have compared the results with the BCS theory, and found an additional absorption at low frequencies. The origin of this absorption may be related to the complex gap structure of the compound with possible nodes. Theoretical calculations are currently under way. Part of this work has been supported by EuroMagNET, EU contract 228043.

Currently, large bone or cartilage defects are stabilized by massivelyinvasive surgery. The permanent implants used for this purpose are either metallic prostheses, or body tissue taken elsewhere from the patient. In a novel tissue-engineering approach, autologous tissue regeneration is guided by implanted magnetic scaffolds under external magnetic field. These scaffolds attract superparamagnetic Fe₃O₄ (magnetite) nanoparticles tagged with Vascular Endothelial Growth Factor (VEGF) molecules. Release of the growth-factor molecules at the scaffold (optionally triggered by ac-field induced hyperthermia) attracts autologous chondrocytes and osteoblasts, which build up fresh bone and cartilage tissue. We report on the magnetic characterization of several biocompatible and biodegradable materials that might serve as scaffold materials.
This project is supported by the European Union’s FP7-Cooperation Programme through the MAGISTER project (Magnetic Scaffolds for in-vivo Tissue Engineering), Large Collaborative Project FP7 - 21468.

The evolution of the band-structure parameters of Ce_1−xYb_xCoIn₅ was studied as a function of Yb doping by systematic de Haas–van Alphen (dHvA) measurements. We found only a small change of the dHvA frequencies and effective masses of CeCoIn5 for a low Yb concentrations (x =0.1). A drastic change of the Fermi surface appears for high dilution, i.e., for x ≥0.55. The experimentally observed Fermisurface topology of YbCoIn₅ is in perfect agreement with the calculated band structure. For small x, the effective masses remain strongly renormalized, whereas for ≥0.55 the masses are reduced dramatically.

The qualification of CFD codes for two-phase flows requires reliable experimental data with high resolution in space and time. Especially data on the transient structure of the interface is required. Bubble sizes play an important role for the evolution of the flow along the flow path. Vertical pipe flow is suitable for model development and validation because of the well-defined boundary conditions and the possibility to observe the evolution of the flow along the pipe. In nuclear reactor safety research often flows with high void fraction have to be considered. Since optical measuring methods fail for such dense flows intrusive techniques as needle tip probes or wire-mesh sensors are frequently used. Due to the intrusive effect these techniques can be applied only for a limited range of flow conditions. This paper presents first quantitative results of measurements done in upwards vertical pipe flows with air-water and steam-water systems using the new non-intrusive ultrafast electron beam tomography.

Hydrogenation of UTGe compounds results in formation of stable alpha- and beta-hydrides, and modification of the crystal structure and magnetic properties. T_C = 3 K of UCoGe increases up to 50 K in beta-hydrides and T_C = 9.5 K of URhGe up to 17 K in alpha-hydrides. The type of magnetic order is changed in UNiGe-H and UIrGe-H. The observed effects are attributed to the increased U-U spacing in the hydrides.

We report on the observation of large, steplike anomalies in the magnetization (ΔM = 0.74 _μB/Ce), in the magnetostriction (Δl/l₀ = 2.0 × 10⁻³), and in the magnetoresistance in polycrystals of the paramagnetic heavyfermion system CeTiGe at a critical magnetic field μ₀H_c ≈ 12 T at low temperatures. The size of these anomalies is much larger than those reported for the prototypical heavy-fermion metamagnet CeRu₂Si₂. Furthermore, hysteresis between increasing and decreasing field data indicate a real thermodynamic, first-order type of phase transition, in contrast to the crossover reported for CeRu₂Si₂. Analysis of the resistivity data shows a pronounced decrease of the electronic quasiparticle mass across H_c. These results establish CeTiGe as a rare metamagnetic Kondo-lattice system, with an exceptionally large, metamagnetic transition of first-order type at a moderate field.

The tetragonal compound UPt₂Si₂ has been characterized as a moderately mass-enhanced system with an antiferromagnetic (AFM) ground state below T_N = 32 K. Here, we present an extensive study of the behavior in high magnetic fields.We have performed pulsed field magnetization and static field resistivity measurements on single crystalline samples UPt₂Si₂. Along the crystallographic a axis, at low temperatures, we find a metamagnetic-like transition in fields of the order 40 T, possibly indicating a first-order transition. Along the crystallographic c axis, in magnetic fields of B ≥ 24 T, we find distinct anomalies in both properties. From our analysis of the data we can distinguish new high-field phases above the AFM ground state. We discuss the emergence of these new phases in the context of Fermi surface effects and the possible occurrence of a Lifshitz or electronic topological transition, this in contrast to previous modelings of UPt₂Si₂ based on crystal electric field effects.

We report the microscopic magnetic model for the spin-1/2 Heisenberg system CdCu₂(BO₃)₂, one of the few quantum magnets showing the 1/2-magnetization plateau. Recent neutron diffraction experiments on this compound [M. Hase et al., Phys. Rev. B 80, 104405 (2009)] evidenced long-range magnetic order, inconsistent with the previously suggested phenomenological magnetic model of isolated dimers and spin chains. Based on extensive density functional theory band structure calculations, exact diagonalizations, quantum Monte Carlo simulations, third-order perturbation theory as well as high-field magnetization measurements, we find that the magnetic properties of CdCu₂(BO₃)₂ are accounted for by a frustrated quasi-2D magnetic model featuring four inequivalent exchange couplings: the leading antiferromagnetic coupling J_d within the structural Cu₂O₆ dimers, two interdimer couplings J_t1 and J_t2, forming magnetic tetramers, and a ferromagnetic coupling J_it between the tetramers. Based on comparison to the experimental data, we evaluate the ratios of the leading couplings J_d : J_t1 : J_t2 : J_it = 1 : 0.20 : 0.45 : −0.30, with J_d of about 178 K. The inequivalence of J_t1 and J_t2 largely lifts the frustration and triggers long-range antiferromagnetic ordering. The proposed model accounts correctly for the different magnetic moments localized on structurally inequivalent Cu atoms in the ground-state magnetic configuration. We extensively analyze the magnetic properties of this model, including a detailed description of the magnetically ordered ground state and its evolution in magnetic field with particular emphasis on the 1/2-magnetization plateau. Our results establish remarkable analogies to the Shastry-Sutherland model of SrCu₂(BO₃)₂, and characterize the closely related CdCu₂(BO₃)₂ as a material realization for the spin-1/2 decorated anisotropic Shastry-Sutherland lattice.

The low-temperature ultrasonic dispersion in the transverse (C11 - C12)/2 mode of PrMg₃ with the non-Kramers-doublet ground state has been investigated in temperatures down to 20 mK. The dispersion is caused by a thermally activated motions characterized by an Arrhenius-type relaxation time of τ = τ₀ exp(E/k_BT) with low activation energy, E = 500 mK, and slow attempt time, τ₀ = 8.5 x 10^-10) s. The coupling of the electric quadrupoles of the non-Kramers-doublet ground state to transverse lattice vibrations leads to a vibronic ground state with dissipation. The vibronic state in PrMg₃ releases the entropy of k_B ln 2 with lowering temperature across the activation energy. A Kondo-like singlet state due to the binding of the non-Kramers doublet to the lattice vibrations appears at low temperatures far below the activation energy.

The magnetization of a GdMn₆Sn₆ single crystal has been measured in static magnetic fields up to 14 T as well as in pulsed fields up to 60 T. The easy magnetization direction has been confirmed to lie in the basal plane of the hexagonal crystal, the anisotropy within the plane being negligible. However, our data do not corroborate the earlier assertion that GdMn₆Sn₆ is a collinear ferrimagnet. This disagrees with the observed field dependence of magnetization along the easy direction as well as with the temperature dependence of spontaneous magnetization. A way out of the contradiction is to admit that GdMn6Sn6 has a more complex, non-collinear magnetic structure

Chitin is known to adsorb various metals. Therefore, chitin containing materials are taken into consideration as filter materials for contaminated waters. Marine sponges of the order Verongida form three-dimensional networks of fibrous chitin, which can easily be extracted. In the hydrated state, these networks are flexible, mechanically stable and can be cut or pressed into any desired form. Here, we show for the first time that chitin-based networks of sponge origin are useful for effective uranium adsorption. They adsorb U(VI) from solution with a higher sorption capacity than many other chitinous sorbents from fungal biomass. Solid-state NMR, infrared and Raman spectroscopy indicated that the U(VI) is bound to the chitin by weak interactions such as hydrogen bonds. 90 % of the U(VI) could be desorbed using diluted hydrochloric acid. Uranium adsorption and desorption did not result in any destruction of the chitin material.

We present de Haas-van Alphen (dHvA) measurements in the normal and in the superconducting state of LuNi₂B₂C. Inside the superconducting state, we observe quantum oscillations of a spherical Fermi-surface sheet in all crystallographic directions. Apart from the field region close to the phase transition where a strong peak effect hampers the analysis of the dHvA signal, the additional damping of the quantum oscillations inside the superconducting state is much smaller than expected from theory. For the magnetic field aligned along the [100] direction, three different dHvA frequencies are visible in the superconducting state. In particular, the orbit related to a cushion-like Fermi surface does not show any additional damping at and below the upper critical field contrary to theoretical expectations of simple effective one-band theories. Consequently, the superconducting gap on this Fermi-surface sheet can only evolve at lower fields than the observed bulk critical field, B_c2 ≈ 8 T, which clearly points to a Fermi-surface-sheet-dependent gap opening in LuNi₂B₂C.

Heavily Ga implanted Si nanolayers covered with a thin SiO₂ layer exhibit a superconductor-insulator transition in dependence on annealing conditions. The transition characteristics resemble those of ultrathin quench-condensed metal films although the implanted layer differs clearly in composition, width, and nanostructure. This implies a general physical mechanism for the superconductor-insulator transition in thin, disordered layers which is supposed to be a quantum phase transition between dual states - the superconducting and the superinsulating one. The existence of a critical resistance for the phase transition is confirmed.

We report on the first demonstration of a diode pumped, gas cooled, cryogenic multi-slab Yb:YAG amplifier. The performance was characterised over a temperature range from 88 K to 175 K. A maximum small-signal single-pass longitudinal gain of 11.0 was measured at 88 K. When amplifying ns-pulses, recorded output energies were 10.1 J at 1 Hz in a 4-pass extraction geometry and 6.4 J at 10 Hz in a 3-pass setup, corresponding to optical-to-optical conversion efficiencies of 21 % and 16 %, respectively. To our knowledge, this represents the highest pulse energy so far obtained from a cryo-cooled Yb-laser and the highest efficiency from a multi-J DPSSL system.

A comprehensive CFD-grade database on two-phase vertical pipe flow was established during the last years. The experiments were done at the test section "Variable Gas Injection" which is part of the TOPFLOW facility. Data are available on adiabatic air-water flows, condensing steam-water flows and boiling flows. In case of condensing flow steam was injected into sub-cooled water, while boiling was obtained by pressure relief. The measurements and the available databases are presented.

Problem: Different models necessary for dispersed particles and separated continuous phases (interfacial drag etc.)
Aim: To simulate the CCFL phenomenon in a hot leg of PWR on the basis of the flow morphologies and physics.
Counter current flow was successfully simulated in the Hot Leg Channel
A new surface drag model inside the morphology detection algorithm AIAD was introduced, it further improves the physics
The qualitative structure of the flow morphology is similar to the one observed in the experiment (slug flow regime).
The calculated quantitative CCFL characteristics & water levels inside the hot leg channel were in an agreement with the experiments.
CFD calculations of 1:1 scaled UPTF CCFL experiments show very promizing results
The effect of turbulence parameters near the free surface has to be studied in future
Validation of the AIAD model is going on – Official release of the AIAD framework in CFX is on the way

The presentation shows CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns.

Microorganisms have a great potential to bind and thus transport actinides in the environment. Thus microbes indigenous to designated nuclear waste disposal sites have to be investigated regarding their interaction mechanisms with soluble actinyl ions when assessing the safety of a planned repository. This paper presents results on the pH-dependent sorption of U(VI) onto Pseudomonas fluorescens isolated from the granitic rock aquifers at Äspö Hard Rock Laboratory, Sweden. To characterize the U(VI) interaction on a molecular level, potentiometric titration in combination with time-resolved laser-induced fluorescence spectroscopy (TRLFS) were applied. This paper as a result is one of the very few sources which provide stability constants of U(VI) complexed by cell surface functional groups. In addition the bacteria-mediated liberation of inorganic phosphate in dependence on [U(VI)] at different pHs was studied to judge the influence of phosphate release on U(VI) mobilization. The results demonstrate that in the acidic pH range U(VI) is bound by the cells mainly via protonated phosphoryl and carboxylic sites. The complexation by carboxylic groups can be observed over a wide pH range up to around pH 7. At neutral pH fully deprotonated phosphoryl groups are mainly responsible for U(VI) binding. U(VI) can be bound by P. fluorescens with relatively high thermodynamic stability.

The total cross-section of the pp → nK⁺Σ⁺ reaction was measured at COSY using a proton beam with a momentum of p beam = 2.95 GeV/c, corresponding to an excess energy of ε = 129 MeV. The neutron detector COSYnus was added to the time-of-flight spectrometer COSY-TOF which tracks charged primary and secondary particles. Thus a complete reconstruction of the exit channel was feasible by exploiting for both neutron and kaon their time and direction of flight as well as the decay of the Σ⁺-hyperon into a neutral and a charged particle. The cross-section was determined to be between σ = 2.0 and 5.9 μb with 68% confidence. The experimental data published so far by various groups for this reaction are assessed as a whole. We conclude that either the theoretical models lack some important aspect of the reaction mechanism if one takes the experimental data at face value, or the experimental data are inconsistent and therefore theoretical descriptions must fail.

The EU NURISP project (Nuclear Reactor Integrated Simulation Project) continued to improve the CFD modelling for two-phase PTS situations. For this purpose, two reference cases from the TOPFLOW-PTS experimental programme were defined: one for steady air-water and one for steady steam-water flow. The numerical simulations of the reference experiments were done using three different CFD codes: NEPTUNE_CFD, ANSYS FLUENT and ANSYS CFX. Due to technical and time constraints, three different meshes have been used with the three codes. In the air-water test, there is a temperature gradient only in the region upstream from the ECC injection point. ANSYS CFX predicted the temperature in the ECC upstream region well, while NEPTUNE_CFD and ANSYS FLUENT considerably underestimated the temperature there. In the NEPTUNE_CFD computation, a stratified flow was found in the ECC line, contrary to the experimental observation and causing higher velocity of jet, thus influencing the mixing in this area. In the ECC downstream and in the dowmcomer the fluids are well mixed. All the codes managed to predict this prefectly mixed temperature well. From the steam-water pre-test simulations, we could see that only NEPTUNE_CFD and ANSYS CFX predicted a thermal stratification at the entrance into the downcomer. The results of the steam-water test could not be validated due to lack of the experimental data. In the downcomer, NEPTUNE_CFD and ANSYS FLUENT predicted a homogeneous temperature which is very close to the saturated temperature. ANSYS CFX calculated an inhomogeneous temperature there which is considerably lower than in NEPTUNE_CFD and ANSYS FLUENT cases. Moreover, in the ANSYS CFX simulation we could see a downward flowing cold-water plume in the downcomer.

The first part of this presentaion gives an brief overview of the activities done in the Work Package W2.1 of the NURISP SP2 subproject (Thermal Hydraulic). In the second part dicusses conclusions and recommendations for future modelling work.

The presentation gives an overview on the course of the accident and discusses the resaons and consequences.

The presentation gives an introduction to the reactor safety research at HZDR with a special emphasis to the in-house reactor dynamics code DYN3D.

The paper presents CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns.

In the frame of the project ordered by NRG Petten (Purchase order: NRG-P2144963) experiments on two boron dilution scenarios have to be conducted at the ROCOM test facility.
Both scenarios are based on a hypothetical boron dilution accident following a SBLOCA in a PWR. A slug of unborated coolant has been accumulated in one of the loops. The re-established natural circulation drives the slug towards the reactor pressure vessel (RPV). In the vessel the slug mixes with the coolant of the downcomer and with the emergency core cooling water (ECC) which is injected into two other loops (Scenario 1) or into the loop with the slug (Scenario 2).
The boundary conditions on loop flow rates and temperature (density) differences are based on corresponding experiments at the PKL test facility operated by AREVA (Hertlein, 2003) and are described in the technical annex being a part of the project order (Kliem, 2010).
The well-proven wire-mesh sensor technology developed by HZDR over the last years is used to quantify the mixing of the slug and the ECC water on the way from the loops to the core inlet plane.
This report gives an overview about the ROCOM test facility and describes the experimental results on the second scenario. The results on the first scenario have been summarized in an earlier report (Kliem, 2011).

Magnetization orientation in Ga+-irradiated Pt/Co(d(Co))/Pt ultrathin films can be changed in a controlled way by adjusting the ion fluence, F. Two-dimensional (d(Co), F) diagrams of magnetic and magneto-optical properties have been derived. Distinct out-of-plane magnetic anisotropy states with enhanced magneto-optical effects were evidenced for specific (d(Co), F) values. This rich behavior originates from two competing mechanisms: intermixing of Co and Pt atoms at the interfaces and the formation of ordered CoPt alloy phases with high magnetic anisotropy. The irradiation-induced effects open novel routes for both tailoring thin-film magnetic and magneto-optical properties and patterning of magnetic nanostructures.

Despite the emission of only low-energy Auger electrons (ca. 3.6 keV) and the difficulty of obtaining a certified standard, LSC determinations are still reasonable options for a radioanalytical laboratory involved in nuclear installation decommission. Besides accelerator mass spectrometry (AMS), being the most sensitive analytical technique not only for ⁴¹Ca, is gaining increasingly broader accessibility and applicability.
Herein, we present a radiochemical separation procedure developed for ⁴¹Ca determination with LSC and AMS in varying materials (i.e. water, concrete, sediment, soil, and biota). The radioanalytical isolation consists of anion exchange and extraction chromatography as well as carbonate precipitation and recrystallization from organic solvents. Thereby, interfering radionuclides as ⁵⁵Fe, ⁶⁰Co, ¹⁵²Eu, U or actinides are removed with decontamination factors of 10²-10⁴. Quench curves for determining the measurement efficiency are generated with a ⁴¹Ca solution gained from the ⁴¹Ca/⁴⁰Ca certified reference material ERM-AE701. In routine application the procedure is characterized by chemical yields of 25-80%, measurement efficiencies of 1-10% and detection limits of 0.05 Bq g^-1 ash and 0.3 Bq l^-1. Aliquot solutions of LSC can be easily converted into CaF₂-AMS-targets by successive oxalate and fluoride precipitation. Pros and cons for both measurement techniques are addressed based on ⁴¹Ca results from LSC and AMS for the same material.

Extended X-ray absorption fine structure (EXAFS) spec-troscopy has been used to investigate the coordination envi-ronment of U(VI) in cementitious materials. The EXAFS measurements were carried out on U(VI)-doped samples prepared under varying conditions, such as samples from sorption, hydration and diffusion experiments, and using different cementitious materials, such as crushed hydrated hardened cement paste (HCP) and calcium silicate hydrates (C-S-H). The samples had U(VI) loadings ranging between 1 700 µg/g to 45 000 µg/g. Applying principal component analysis (PCA) on 13 EXAFS spectra (each spectra corre-sponding to a minimum of 5 different scans) of the low loading samples, we obtained one single species indicating a similar U(VI) coordination environment for both HCP and C-S-H samples. This result confirms that C-S-H phases control the uptake of U(VI) in the complex cement matrix. The radial structure of this species is similar to a U(VI) surface complex or to U(VI) in uranyl silicate minerals (two axial O atoms at 1.82 ± 0.02 Å; four equatorial O atoms at 2.25 ± 0.01 Å; one Si atom at 3.10 ± 0.03 Å). At high U(VI) loading, PCA revealed a second U(VI) species, with a radial structure similar to that of U(VI) in calcium uranate (two axial O atoms at 1.94 ± 0.04 Å; five equatorial O at-oms at 2.26 ± 0.01 Å; four Ca atoms at 3.69 ± 0.05 Å and five U atoms at 3.85 ± 0.04 Å).
This study suggest that, at low U(VI) loading, U(VI) is bound to C-S-H phases in HCP while at high U(VI) load-ing, the immobilization of U(VI) in cementitious materials is mainly controlled by the precipitation of a calcium uran-ate-type phase.

Objectives: Nicotinic alpha4beta2 acetylcholine receptors (nAChR) are an important target for diagnostic neuroimaging because of their involvement in Alzheimer's disease (AD) and Parkinson's disease. Using 2-[18F]F-A85380 PET a significant decline in alpha4beta2-nAChRs in early AD-patients which correlated to loss of cognitive function was shown (1, 2). However, this tracer was not suited to be used as a biomarker for early AD-diagnosis in a routine clinical set-up because of its unfavourable slow kinetic. Here we used the new radiotracer 18F-Flubatine (18F-NCFHEB) with significantly improved brain uptake, receptor affinity and selectivity (3). nAChR-parameters were determined by full kinetic modeling and the validity of the practically useful tissue ratio and tissue to plasma ratio as receptor parameters was evaluated.

Methods: After intravenous administration of ~370 MBq 18F-Flubatine, the PET brain imaging was performed in 20 healthy controls (HC, age 70.6±4.6) using an ECAT EXACT HR+ system in 3D-acquisition mode. 23 frames were acquired from 0-90 min post injection and motion corrected with SPM2. Kinetic modeling using a 1-tissue compartment model (1TCM) with arterial input-function was applied to the volume of interest (VOI) based tissue-activity curves (TACs) generated for 29 brain regions (anatomically defined via MRI co-registration). Model-based receptor parameters used were the total distribution volume (VT) and the distribution volume ratio (DVR) (reference: posterior corpus callosum). In addition the standardized uptake value ratio (SUVR) (50-70 min) as approximation of the DVR and the tissue- to plasma-concentration ratio (TTPR) (70-90 min) as approximation of VT were used as non model-based receptor parameters.

Results: TACs of all 29 regions could be described adequately with the 1TCM and all kinetic parameters could be reliably estimated from 90 min PET data. VT increased as expected with receptor density. Corpus callosum (VT: 5.68±1.01), frontal (9.18±0.59), parietal (9.10±0.61), pons (11.10±0.86), thalamus (25.03±3.33). Mean TTPR values in frontal and parietal cortices were 2% higher than the corresponding VT values but 7% lower in the thalamus. There was a strong linear correlation between the two sets of TTPR and VT values (r2 = 0.98, p < 10-4) (Fig. 1A). As VT, DVR increased with receptor density. Frontal (DVR: 1.66±0.27), parietal (1.64±0.27), pons (2.01±0.35), thalamus (4.52±0.87). Mean SUVR values in frontal and parietal cortices were very similar to mean DVR values (difference <0.1%) but 15 % lower in the thalamus. However there was a strong linear correlation between the SUVR and DVR values (r2 = 0.97, p < 10-4) (Fig. 1B).

Conclusions: For18F-Flubatine the receptor parameters TTPR and SUVR in cortical regions are in good agreement with corresponding parameters computed by full kinetic modeling. For unbiased estimates of TTPR and SUVR in the thalamus the use of a bolus/infusion scheme for tracer application should be considered.

References: 1. O. Sabri, ..P. Brust: Acetylcholine receptors in dementia and mild cognitive impairment. Eur J Nucl Med Mol Imaging 2008; 35 (Suppl. 1): 30-45.
2. K. Kendziorra, ..O. Sabri: Decreased cerebral 4ß2 nicotinic acetylcholine receptors in living patients with mild cognitive impairment and Alzheimer's disease assessed with positron emission tomography. Eur J Nucl Med Mol Imaging 2010; 38: 515-525.
3. P. Brust, ..O. Sabri: In-vivo measurement of nicotinic acetylcholine receptors with [18F]norchloro-fluoro-homoepibatidine (NCFHEB). Synapse 2008; 62: 205-218.

Ziel/Aim:

Using F-18-A85380 (2FA) PET we recently demonstrated significant cerebral nAChR declines in early AD which correlated significantly with the loss of cognitive function (1-2). However, 2FA is not well suited in clinical routine use because of slow kinetics, acquisition times up to 7 hours, and limited nAChR selectivity. Thus, we developed the new tracer F-18-Flubatine, an epibatidine derivative without toxicity in humans formerly named as F-18-NCFHEB (3) and report here on the worldwide first human Flubatine-PET results.

Methodik/Methods:

16 mild AD patients (NINCDS-ADRDA, age 74.4±6.6, MMSE 23.7±2.8) and 11 age-matched healthy controls (HCs, MMSE 28.5±0.9), all nonsmokers and nave for central acting medication, underwent Flubatine-PET (370 MBq, 3D-acquisition, ECAT Exact HR+). Dynamic 0-270min p.i. scans were acquired and corrected for motion (SPM2). Kinetic modeling was applied to 29 brain VOI-based tissue-activity curves (VOIs defined on individual MRI) using a one-tissue compartment model with measured arterial input function. Total distribution volume (DV) and binding potential (BP, reference region: corpus callosum) were used to characterize specific binding.

Ergebnisse/Results:

Image quality of Flubatine scans was clearly superior to 2FA, and a 20 minutes scan already adequate for visual analysis. All 29 regions were well described with one-tissue compartment. PET data acquired over only 90 minutes were sufficient to estimate all kinetic parameters precisely indicating a fast receptor binding kinetic (much faster than for 2FA).
DVs in HCs increase as expected with receptor density: Corpus callosum (DV: 4.81±0.32), posterior cingulate (8.92±0.66), temporal (9.03±0.44), pons (11.00±1.19), thalamus (24.32±2.96). The AD patients showed extensive BP reductions in frontal, parietal, temporal, anterior and posterior cingulate cortices, caudate, and midbrain (all p<0.05) compared to HCs. There was significant correlation between nAChR reductions and cognitive declines in posterior cingulate, parietal, and temporal cortices, as well as in pons and cerebellum (p<0.05, all r> 0.41).

Schlussfolgerungen/Conclusions:

Due to the significant shorter acquisition time and superior image quality Flubatine appears to be a much more valuable tracer than 2FA to image nAChRs in humans. Early AD patients show significant declines of nAChRs in brain regions typically affected by AD pathology which correlate well with the corresponding cognitive declines. These results indicate that Flubatine-PET has a great potential as a biomarker for early AD diagnosis.

Literatur/References:

(1) Sabri et al. Eur J Nucl Med Mol Imaging 2008; 35 (Suppl. 1): 30-45
(2) Kendziorra et al., Eur J Nucl Med Mol
Imaging 2011; 38: 515-525
(3) Brust et al. Synapse 2008; 62: 205-218
This trial is granted by the German
Federal Ministry of Education and Research (BMBF-Nr. 01EZ0820)

Borates are ubiquitous compounds in the environment (rocks, soils, natural waters) and are used in many applications. Thus, there are many sources for the release of borates in the environment. Another aspect is the occurrence of borates in salt formations, which is important concerning the search of a proper nuclear waste repository.
But although there is a relevance of borates the Ln(III)/An(III)-borate system is investigated insufficiently.
The investigations concentrated on the complexation between Eu(III) and borates in aqueous solution. First results show a small influence of borates on the Eu(III) speciation.

Presently, argillaceous rock formations are under investigation as potential host rocks for nuclear waste repositories. In addition to the diffusion the sorption of radionuclides on mineral phases is an important physicochemical process in a nuclear waste repository in the case of a water inleakage. Concerning the required long-term safety and risk assessment of the storage of high-level radioactive waste the understanding of these processes is essential. The investigations concentrated on the sorption of Eu(III) on OPA under realistic OPA pore water conditions (medium: pH 7.6; ionic strength 0.4 mol•L-1; presence of chloride, sulfate, carbonate) up to 50°C. In addition to the temperature dependent investigations the influence of tartrate and citrate (representatives of NOM) on the Eu(III) sorption was studied.
The sorption is characterized by a very strong binding of Eu(III) to the clay surface and a significant temperature dependency. With rising temperature the Rd value rises, showing that the Eu(III) sorption increases. In the presence of tartrate or citrate the Eu(III) sorption decreases with rising ligand concentration.

The sensitivity of catalytic reactions to concurrent filtration and fines deposition in trickle-bed reactors (TBRs) was assessed by means of the catalytic hydrogenation of alpha-methylstyrene from kaolin-kerosene suspension flows. A negative correlation between catalytic conversion and the specific deposit of the bed resulted from the extra mass-transfer step that built up on the collectors in the course of filtration. The severity of the evolving extra mass-transfer step was sensitive to deposit compaction resulting from higher gas superficial velocities. Furthermore, irreversible catalyst activity losses were observed after catalyst cleanup and were ascribed to irretrievable active sites by catalyst intraparticle fines trapping. Fines accumulation in the catalyst bed was notably reduced by means of high-porosity solid-foam modules used as guard filters and placed upstream of, and adjacent to, the trickle bed. Hydrodynamic studies were carried out with alumina and silicon c!
arbide solid foams to assess their role on the distribution of suspension and the reduction of specific deposit and pressure drop in trickle beds. It was found that the foam capture efficiency critically depended on the open connectivity of foam cells and the physicochemical nature of foam materials. The numbering up of foam modules led to reduced overall specific deposits of the beds and pressure drops, foreseeing a prospect for prolonging the hydrotreatment TBR lifetime, using solid foam as guard beds.

Magnetic nanostructures with graded anisotropy offer a solution to both thermal stability and writability challenges in advanced magnetic recording media. The interlayer exchange coupling lowers the overall coercivity, facilitating the writing process, while the magnetically hard layer provides pinning for the media and ensures its thermal stability. Magnetization reversal in such materials can be influenced by both the magnetic anisotropy gradient along the film depth and the lateral feature size. We have explored magnetization reversal in Co/Pd films and patterned structures. Perpendicular magnetic anisotropy is varied by changing the Co thicknesses or sputtering pressure during growth. Effects of deposition order and ion irradiation have been studied by x-ray diffraction, transmission electron microscopy, magnetometry, and first-order reversal curves. Structural integrity and amount of disorders are found to sensitively influence the magnetic properties. Reversal in highly ordered films is dominated by nucleation, propagation, and annihilation of domain walls while in disordered films magnetization reversal is largely by domain wall pinning and magnetization rotation. Depth-dependent magnetization profiles and magnetic anisotropy have been confirmed by polarized neutron reflectivity. Effects of lateral patterning have been investigated in patterned nanodots (down to 60nm diameter). An increase in coercivity and a modified switching field distribution are observed in patterned structures. This is due to the reduced lateral dimensions which limit the domain nucleation and propagation commonly found in unpatterned films. These results demonstrate attractive features of nanostructures with graded anisotropy towards future magnetic recording applications.

Work supported by the US NSF (DMR-1008791 & ECCS-0925626).

Rotating foam reactors have already shown to give high mass transfer rates compared to stirred tank reactors. For a deeper insight into the hydrodynamics of these reactors, the hydrodynamics of rotating foam reactors were studied using γ-ray tomography. The two-phase flow through the foam block stirrer is mainly influenced by the solid foam pore size and the liquid viscosity. For low viscosity, the optimal foam block pore size was identified in the range between 10 and 20 pores per inch (ppi). With smaller pore size, the gas holdup inside the foam block strongly increases due to bubble entrapment. For higher viscosity, pore sizes larger than 10 ppi have to be used to achieve a sufficient liquid flow rate through the foam block to avoid a strong gradient over the reactor height. The effect of the hydrodynamics on the gas–liquid and liquid–solid mass transfer and the reactor performance are discussed.

Ziel/Aim:

Because specific subtypes of nicotinic acetylcholine receptors (nAChR) are involved in various neurodegenerative diseases, there is a continuing need for their visualization by PET. Compared to epibatidine and the 2-[F-18]F-A-85380, the novel homoepibatidine derivative [F-18]flubatine (formerly named as [F-18]NCFHEB) showed better pharmacological properties, promoting first studies in humans. The former radiosynthesis starting from a bromo precursor was hampered by very low radiochemical yields (RCY ~3%). Therefore, a highly improved approach, transferable to an automated module, was necessary. Herein, we report on comprehensive experiments to improve all steps of radiosynthesis.

Methodik/Methods:

The preparation of [F-18]flubatine is based on a two-step radiosynthesis: The nucleophilic aromatic radiofluorination followed by the cleavage of a protecting group. A variety of new precursors with various LGs and PGs was synthesized and tested under different labelling and purification conditions (such as precursor amount, solvent, temperature, thermal/microwave heating, SPE techniques). As LGs, -Cl, -NO2 and the -N(Me3)3 + group with iodide, triflate and other counter anions were tested. The protective function of ethoxycarbonyl, Fmoc, trityl und Boc at the NH-group was studied as well as their quantitative removal. Both SPE and ion exchange cartridges were tested for purification. Analytical and semi-preparative HPLC separation protocols were developed using RP18-AQ phases (isocratic/gradient method; aqueous MeCN as eluent). Furthermore, the stability of [F-18]flubatine was investigated under chemical and physiological conditions. For optimization, all radiochemical steps were controlled by radio-HPLC and radio-TLC.

Ergebnisse/Results:

Application of the -N(Me3)3 iodide precursor with a Boc-PG (0.5-1.0 mg, MeCN, 83°C) provided by far the best radiochemical results. For the final product labelling efficiencies of 90±5%, RCY 70±5% (n=25), spec. activity of >350 GBq/μmol were achieved within a total time of 2.0 h. Complete deprotection of the Boc-PG succeeded with 1M HCl (90°C, 5 min). Compared to results with other PGs, this enabled high labelling efficiencies without by-products, and thus, an easy, fast and quantitative separation. Prior to the deprotection step, the purification of the crude reaction mixture with a C18 cartridge and elution with 1% HOAc/MeCN increased the RCYs, too. The final product was isolated in very high purity by semi-preparative HPLC (tR ~30 min). [F-18]flubatine was stable in diluted HCl, NaOH and K2CO3 solutions as well as under physiological conditions.Furthermore, a chiral HPLC method was developed to prepare enantiomerically pure flubatine.

Schlussfolgerungen/Conclusions:

Various procedures were tested to get a validated [F-18]flubatine radiosynthesis as a prerequisite for an automated radiotracer production, applicable for human studies.

Literatur/References:

Ziel/Aim:

F-18-Flubatine (früher F-18-NCFHEB) ist ein neuer und vielversprechender Radioligand für die Darstellung von alpha4beta2 nikotinischen Acetylcholinrezeptoren mit PET. Um das Strahlenrisikio durch diesen Tracer abzuschätzen, wurden die Organdosen (OD) und die effektive Dosis (ED) an Schweinen erhoben und mit den Ergebnissen aus Untersuchungen an CD1-Mäusen und Menschen verglichen. Der Ergebnis- und Methodenvergleich dient der Identifizierung des für die Verhältnisse am Menschen am ehesten repräsentativen Tiermodells und als Unterstützung bei der Interpretation der Ergebnisse präklinischer Inkorporationsdosimetrie von Radiotracern für die Hirn-PET.

Methodik/Methods:

Die inkorporationsdosimetrische Untersuchung von F-18-Flubatine wurde an 6 Ferkeln (weibliche Masthybriden, Alter 56±7d; Gewicht: 14±2kg) vorgenommen. Die narkotisierten Tiere (Einleitung mit 20 mg/kg Ketamin und 2 mg/kg Azaperon; 1.5% Isofluran in 70% N2O/30% O2) wurden nach i.v.- Injektion von 188,4±2,8 MBq F-18-Flubatine einer sequentiellen PET-CT-Untersuchung bis zu 4h nach Injektion an einem SIEMENS Biograph16 (6-7 Bettpositionen pro Frame, 1,5-6min/Bettposition, CT-Schwächungskorrektur, iterative Rekonstruktion) unterzogen. Bis zu 4h p.i. wurde Urin gesammelt und dessen Aktivitätskonzentration bestimmt. Die Gewichte der Organe wurden im Rahmen einer Sektion überprüft. Alle den Tracer aufnehmenden Organe wurden CT-geführt mit dreidimensionalen Regionen (VOIs) markiert
und ihr Aktivitätsinhalt nach Recoverykorrektur als Zeit-Aktivitäts-Verlauf (TAC) dargestellt. Die Zeit- und Massenskalen wurden an die menschlichen Skalen angepasst [1]. Mit OLINDA [2] wurden TACs an diese Daten angepasst. ODs wurden unter Verwendung des 73,7kg-"adult male model" bestimmt. Die ED wurde unter Verwendung der Gewebewichtungsfaktoren in der ICRP 103 von 2007 berechnet.

Ergebnisse/Results:

Die präklinischen Untersuchungen ergaben eine ED für den Menschen von 14,0±0,9 μSv/MBq (extrapoliert v. Ferkel) bzw. 14,2μ μSv/MBq (extrapiliert v. CD1-Maus) Die frühklinischen Untersuchungen an gesunden Freiwilligen ergaben eine ED durch F-18-Flubatine von 22,6±0,7μSv/MBq.

Schlussfolgerungen/Conclusions:

Der Vergleich der Ergebnisse der präklinischen mit den klinischen Untersuchungen ergibt, dass erstere die Verhältnisse der Strahlenexposition des Menschen durch F-18-Flubatine um systematisch etwa 30-40% unterschätzen. Dieser Umstand ist bei der Abschätzung der Strahlenexposition des Menschen im Vorfeld frühklinischer Studien anhand präklinischer Daten zu berücksichtigen.

Literatur/References:

[1] Stabin MJ: Fundamentals of Nuclear Medicine Dosimetry, Springer 2008, ISBN 978-0-387-74578-7, 237P
[2] Stabin et. al.: OLINDA/EXM: The Second-Generation Personal Computer Software for Internal Dose Assessment in Nuclear Medicine; JNM 46/6, 2005Die Studie wird vom Bundesministerium für Bildung und Forschung (Nr. 01EZ0820) und vom Strahlenschutzseminar in Thüringen e.V. gefördert.

Weinvestigated the electronic properties of the T2 deep-level in zinc oxide thin films. It was found that T2 preferentially forms under zinc-rich conditions and can be generated by either annealing the samples at reduced oxygen partial pressures (pO2 < 1 bar) or implanting zinc or copper ions, respectively. A strong dependence of its activation energy and high temperature limit of its cross-section for electron capture on the T2 concentration in the sample is reported. Double DLTS measurements showed that the T2 activation energy decreases with increasing electric field due to phonon assisted tunnelling. Furthermore T2 can be photo-ionised with a threshold photon energy of about 700 meV. Depth-resolved concentration profiles of the T2 level in the samples were measured by optical capacitance–voltage spectroscopy.

At a depth of 70 m of the ONKALO tunnel in Finland, 771 m from the tunnel entrance, massive biofilms were observed attached to the tunnel walls where groundwater was seeping from bedrock fractures. During a sample campaign 2010 samples of the biofilms and of the groundwater seeps were taken for laboratory experiments. Microelectrode measurements in the biofilms and in the groundwater seeps indicated that the studied biofilms constituted their own microenvironments, which differed significantly from that of the groundwater seeps. A pH of 5.37 was recorded inside the biofilm, approximately 3.5 units lower than the pH observed in the groundwater seeps. Similarly, the Eh of +73 mV inside the biofilm was approximately 420 mV lower than the Eh measured in the groundwater seeps. In flow cells with detached biofilms uranium was added to the circulating groundwater with a final uranium concentration of 4.25 × 10–5 M. After 42 h the pH increased in the biofilm to 7.27 and the Eh was reduced to –164 mV. The changes of Eh and pH influenced the bioavailability of uranium. EF-TEM investigations indicated that uranium in the biofilm was immobilized intracellularly in microorganisms by the formation of metabolically mediated uranyl phosphate, similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6 H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O).

In contrast, TRLFS studies of the uranium-contaminated groundwater identified aqueous uranium carbonate species, likely (Ca2UO2[CO3]3), formed due to the high concentration of carbonate in the uranium contaminated circulating groundwater. The results agreed with thermodynamic calculations of the theoretically predominant field of uranium species, formed in the uranium-contaminated groundwater at the measured geochemical parameters.

Ion irradiation assistance of the film growth has a strong impact on structural properties. Here, we demonstrate that ion irradiation of growing binary alloys leads to the formation of composition-modulated surface patterns. Be means of linear stability analysis we show that the ion-to-atom arrival ratio is the pattern control parameter. Close to the instability threshold we identify different regimes of instabilities driven by ion-induced surface roughness processes or roughness-composition feedback interactions. In particular, the synergistic effects of the curvature-dependent displacement coupling to the preferential sputtering or to the 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. This presents opportunities to grow 3D laterally or vertically ordered nanostructures.

High Power Impulse Magnetron Sputtering (HIPIMS) is a technologically important Physical Vapour Deposition (PVD) process that is able to provide a highly ionised flux of sputtered species. It is thought to be particularly important for applications where there is a need to coat 3D features. HIPIMS may have other added benefits, as compared to DC or medium frequency (MF) magnetron sputtering, that are related to improved coating structure-property relationship control through self-species ion/plasma assistance. Enhanced structure and properties of PVD thin film materials produced by reactive sputtering are also highly desirable. Significant progress related to providing control means for reactive HIPIMS processes and ensuring stability has been made recently. This paper reports some of the recent process (reactive HIPIMS of Ti in Ar/O2 atmosphere) and products analysis results. The recently developed Plasma Monitoring based method was used to investigate, monitor and control the deposition process. RBS, ERDA, GDOES and Spectroscopic Ellipsometry were used to characterise the samples produced.

When a two-level system is resonantly driven by intense light non-perturbative phenomena such as Rabi oscillations and their frequency equivalent, the AC Stark or Autler-Townes effect, can be observed. The latter one manifests itself in an absorption line splitting where the magnitude is linear in the light field strength and where the symmetry of the splitting is determined by the detuning from resonance. Known from molecular spectroscopy [1], the effect has also been observed in solid state structures with its much broader line widths, e.g. for intersubband transitions [2]. Here, we present the first unambigous evidence of this effect in undoped GaAs/AlGaAs quantum wells using the hydrogen atom like intraexcitonic 1s and 2p states of the heavy-hole exciton. These states with a transition energy of 9 meV are resonantly coupled by strong terahertz light from a free-electron laser. For low fields our findings are qualitatively explained by a simple two-level model whereas deviations occur in the 10 kV/cm field range where the rotating-wave approximation of the simplified model breaks down and exciton ionization occurs. Due to the small Rydberg energy we can easily reach a highly non-trivial regime where the Rabi energy and the transition energy become comparable to the photon energy.
[1] S. H. Autler and C. H. Townes, Phys. Rev. 100, 703 (1955).
[2] S. G. Carter et al., Science 310, 651 (2005).
[3] M. Wagner et al., Phys. Rev. Lett. 105, 167401 (2010).

Ziel / Aim
Es existieren Hinweise auf Veränderungen von α7 nAChR bei neurodegenerativen Erkrankungen, die durch Radioliganden, die eine molekulare Bildgebung dieser Rezeptoren mit PET ermöglichen, erfasst und quantifiziert werden könnten. Wie früher bereits am Beispiel von [F-18]NS10743 (Ki,NS10743 = 11,6 nM) gezeigt, sind 1,4-Diaza-bicyclo[3.2.2]nonan-1,3,4-oxadiazole als Leitstrukturen dafür grundsätzlich geeignet [1].
In dieser Arbeit wird die Radiosynthese der strukturell modifizierten und höher affinen Verbindung [F-18]NS14490 ([F-18]-2-(1,4-Diaza-bicyclo[3.2.2]nonan-4-yl)-5-(1-(2-fluorethyl)-1H-indol-6-yl)-1,3,4-oxadiazol) vorgestellt.

Methodik / Methods
Eine zweistufige Synthese von [F-18]NS14490 erfolgte durch die Umsetzung von [F-18]Fluorethyltosylat, das aus [F-18]F- und Ethylenglykoldistosylat synthetisiert wurde, mit der Verbindung NS14540. Parallel wurde in einer Einstufensynthese [F-18]F- mit dem o-Tosylpräkursor I umgesetzt, der zuvor durch die Tosylierung des entsprechenden Alkohols erhalten wurde. Die Isolierung und Reinigung von [F-18]NS14490 wurde umfassend optimiert und erfolgte durch semipräparative RP-HPLC und anschließende Festphasenextraktion.
Zur physikochemischen Charakterisierung von [F-18]NS14490 wurden Stabilitätsuntersuchungen in verschiedenen wässrigen Pufferlösungen bei pH 7,4 und 40°C durchgeführt sowie der Verteilungskoeffizient logD7,1 in mehreren n-Octanol/Puffer-Extraktionssystemen bestimmt.

Ergebnisse / Results
Während in der Zweistufensynthese Markierungseffizienzen <10% (n = 3) erreicht wurden, war die Einstufensynthese mit einer Markierungseffizienz von bis zu 89% (n = 15) deutlich erfolgreicher.
Nach umfangreicher Optimierung aller Isolierungs- und Reinigungsschritte konnte das Zielprodukt [F-18]NS14490 mit einer radiochemischen Reinheit >98% und einer spezifischen Aktivität > 150 GBq µmol-1 innerhalb einer Gesamtsynthesedauer von zwei bis drei Stunden dargestellt werden (n = 3).
Bei der physikochemischen Charakterisierung zeigte [F-18]NS14490 in den physiologisch ähnlichen Pufferlösungen über einen Zeitraum von 120 Minuten eine Stabilität von >98% (n = 3). Der logD7,1-Wert betrug 1,20 ± 0,02 (n = 8).
Schlussfolgerungen / Conclusions
Die Ergebnisse stellen eine gute Voraussetzung für weiterführende In-vitro- und In-vivo-Studien dar, insbesondere zur Hirn-Aufnahme und zur Selektivität der Bindung von [F-18]NS14490 an α7 nAChR im Gehirn.
Darüber hinaus ist die erarbeitete Synthesevorschrift als Basis für die Entwicklung einer Herstellung von [F-18]NS14490 mit einem Synthesemodul geeignet.
Literatur / References
1. W. Deuther-Conrad et al. Eur J Nucl Med Mol Imaging (2009) 36:791–800

Ziel:

Im Verlauf der Alzheimer Demenz kommt es zur Degeneration cholinerger Nervenzellen. Der präsynaptisch lokalisierte vesikuläre Acetylcholintransporter (VAChT) dient als Target, um diese Veränderungen im Gehirn mit Hilfe molekularer Bildgebung darzustellen. Vesamicol (2-(4-Phenylpiperidin-1-yl)cyclohexanol) ist ein hoch-affiner, nicht-kompetitiver Inhibitor des VAChT und dient als Leitstruktur für die Entwicklung eines PET-Liganden. Aufgrund seiner vorhandenen Affinität zu Sigma-Rezeptoren weist er eine unzureichende Selektivität für die In-vivo-Darstellung cholinerger Hirnareale auf. Systematisch strukturell modifizierte Vesamicolanaloga werden als Bestandteil einer Struktur-Affinitäts-Studie auf ihre Affinität zum VAChT und Sigma-Rezeptoren hin untersucht. Die Ergebnisse sollen zur Entwicklung eines selektiven PET-Liganden für den VAChT führen.
Methoden:
Ausgehend von geeigneten Epoxidvorläufern wurden die Vesamicolanaloga durch nukleophile Epoxidringöffnung mit strukturell verschiedenen Aminen synthetisiert. Ein Teil der Synthesen konnte durch den Einsatz von Lithiumsalzen regioselektiv durchgeführt werden. Die Regioisomere der nicht-regioselektiven Synthesen wurden mit Hilfe präparativer HPLC getrennt. Die isolierten Produkte wurden durch HPLC, NMR und MS charakterisiert. Mit Hilfe kompetitiver Bindungsassays wurden die Bindungsaffinitäten zum VAChT und zu den Sigma-Rezeptoren an mit Ratten-VAChT-cDNA stabil transfizierten PC12-Zellen, Rattencortex (σ1) und Rattenleber (σ2) mit den Radioliganden (-)-H-3-Vesamicol (VAChT), (+)-H-3-Pentazocin (σ1) und H-3-DTG (σ2) bestimmt.
Ergebnisse:
Die drei neuen Gruppen der Vesamicole, F-Benzylether- und Aminobenzovesamicole wurden synthetisiert und im Hinblick auf ihre Affinitäten zum VAChT und den Sigma-Rezeptoren in vitro charakterisiert. Durch Einsatz verschiedener Epoxide konnte die Struktur des Cyclohexylrings (A) des Vesamicolgrundgerüsts variiert werden. Modifikationen am Piperidinylring (B) und Phenylring (C) wurden durch den Einsatz strukturell verschiedener Amine erhalten. Die VAChT-Bindungsaffinitäten reichen vom unteren nanomolaren bis in den mikromolaren Bereich. Dabei wurden erwartungsgemäß innerhalb der Klassen (Unterschied in B bzw. C) große Unterschiede beobachtet. Jedoch lieferten auch vergleichbare Derivate der verschiedenen Klassen (Unterschied in A) sehr unterschiedliche Werte. Die darauf basierenden Selektivitätsfaktoren (Ki(σ1)/Ki(VAChT) bzw. Ki(σ2)/Ki(VAChT)) variierten ebenfalls stark.
Schlussfolgerungen:
Die Ergebnisse zeigen, dass derzeit keine Vorhersage über das Affinitätsprofil einer Verbindung getroffen werden kann, da der Einfluss struktureller Veränderungen nicht sicher einschätzbar ist. Damit wird die Notwendigkeit zur Durchführung einer quantitativen Struktur-Affinitäts-Studie unterstrichen, die auf Grundlage der systematisch strukturell veränderten Vesamicolanaloga beruht.

To investigate the carrier relaxation dynamics in Landau quantized graphene, we performed pump-probe measurements on quasi-neutral sheets of multilayer epitaxial graphene in magnetic fields. Due to the linear dispersion for low energies in graphene, the Landau level (LL) spacing is not equidistant. Hence it is possible to investigate a single LL transition selectively. To this end we performed pump-probe measurements at a wavelength of 16.5 µm and applied a magnetic field of up to 7T. We varied the magnetic field for resonant measurements at three different LL transitions. For the transitions LL-1(-2) -> LL2(1) and LL-2(-3) -> LL3(2) we could observe a slight increase of the pump-probe signal while the relaxation time stayed constant. For the transition LL-1(0) -> LL0(1) the amplitude of the pump-probe signal increased by a factor of 2.5, the relaxation time decreased from 20 ps to 5 ps. To understand the processes, influencing the carrier relaxation, we performed measurements with linearly and circularly polarized radiation. This enables us to distinguish between the transition LL-1->LL0 and LL0->LL1. This revealed complex dynamics involving positive and negative signals. We suggest this to result from different relaxation channels including Auger processes.

Thorium(IV) is able to form meta-stable colloids with silica in aqueous solution at pH ≥ 7 which results concentrations of colloid-borne Th(IV) of 10^-3 M. The colloid structure can be regarded as amorphous because it shows no long-range order, indicated by the absence of distinct structural periodicity > 4 Å. The internal structure of the colloid particles consists of [Th(O(H))n] polyhedra, n = 8-9, coordinated partly by [SiO4] polyhedra with Th-Si distances of 3.25±0.02Å, and partly by [Th(O(H))n] polyhedra with Th-Th distances of 3.98±0.02Å. The near-order coordination shows similarity with that of the orthosilicates thorite, α-ThSiO^4, and huttonite, β-ThSiO^4. XPS analysis of the oxygen bonds revealed the presence of O^2-, OH^- and H2O. The colloids can be classified as oxyhydroxo colloids [(Th,Si)On(OH)4-nxH2O]4-2n-(4-n). Silica occurs in the colloid structure either in mononuclear or oligomeric units, depending on the Si/Th ratio and the silica precursor formed in the initial solution. Silica is enriched at the colloid surface if the concentration of the initial solutions is increased. The solution behavior of the particles was analyzed by in-situ methods. With rising silica content, the particles gradually change from metal oxide type colloids to silica type colloids which can dramatically increase their colloidal stability.

no abstract for this material

Für eine zukünftige Transmutation langlebiger hochradioaktiver Abfälle werden genaue Kernreaktionsdaten insbesonders von Kernreaktionen, wie der neutroneninduzierten Spaltung und der inelastischen Neutronenstreuung benötigt. Am neuen Zentrum fürr Hochleistungsstrahlungsquellen des HZDR wird für diese Messungen eine Photoneutronenquelle im Energiebereich von ca. 0.1 bis 10 MeV mit einer untergrundarmen Neutronenflugstrecke gebaut. Zum Nachweis der neutroneninduzierten Spaltung von Uran- und Plutonium-Isotopen befindet sich ein Experimentaufbau mit Spaltionisationskammern in Vorbereitung. Durch Verwendung dünner Probenschichten und separater digitaler Datenauslese soll eine Pulshöhenseparation der Spaltfragmente von den pile-up Ereignissen aus dem Alpha-Zerfall der Aktiniden erreicht werden. Aktinidenschichten aus U(238) und U(nat) sind bereits am Institut für Kernchemie der Universität Mainz hergestellt worden. Ausgewählte Aktivitäten des TRAKULA Verbundprojekts, wie Entwicklung einer Compton-Kamera zur hochaufgelösten MeV Gamma-Spektroskopie, Beschleunigermassenspektrometrie langlebiger Spaltprodukte, Entwicklung eines Untergrundlabors zur Messung sehr niedriger Alpha-Aktivitäten werden präsentiert. Das TRAKULA Projekt (www.hzdr.de/trakula) wird unterstützt durch das Bundesministerium für Bildung und Forschung (PTKA-WTE 02NUK13A).

Spin vortices have attracted much attention due to their chiral nature and the variety of dynamic phenomena that they exhibit. In this contribution we present experimental findings on vortex coupling in trilayer elements, where two ferromagnetic layers are separated by a nonmagnetic interlayer. For such systems the relative configurations of the in-plane flux rotation senses (circulations) as well as the core orientations (polarities) of vortex pairs are identified by means of scanning transmission x-ray microscopy (STXM). The relevant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling (IEC). Remarkably, a modification of the IEC, which can be induced by ion irradiation, allows to set the circulation configuration of a layered vortex pair to be either antiferromagnetic or ferromagnetic. In addition, time-resolved measurements of the response of interlayer coupled vortex pairs to an excitation by external magnetic fields will be shown.

Linear alkyl benzene (LAB, C6H5CnH2n+1, n = 10 - 13) is the proposed solvent for the SNO+, the Daya Bay Neutrino and LENA experiment. In solution with the commonly used scintillator PPO it is a colourless, odourless and cheap liquid scintillator with a high flash point and low health hazard compared to toluene based ones. The properties of LAB make this scintillator interesting also for nELBE, the neutron time-of-flight facility at Helmholtz-Zentrum Dresden-Rossendorf. A new approach to measure the light yield in the low-energy range using a combination of quasi-monoenergetic photon sources and a Compton-spectrometer is described. The latter allows the measurement of the light yield down to 5 keVee (electron equivalent). The Birks-Parameter was determined for a homemade solution (LAB + 3 g=l PPO) and for NE-213. The light yield (relative to this standard scintillator) was confirmed by measurements using a fluorescence spectrometer. The ability of pulse-shape-discrimination in a mixed n-gamma-field of a 252Cf source was tested using different digital and semi-analogue techniques.

The relative light yields of NE-213 and LAB-based liquid scintillators to electrons were determined in the electron energy range 5-1600 keV using a combination of monoenergetic photon sources and a Compton spectrometer. The light yield was found to be proportional to energy for both types of scintillator and expected deviations below 100 keV were described successfully applying Birks’ law. Digital pulse-shape discrimination in a mixed n-g field of a 252Cf source was investigated for LAB+PPO and LAB+PPO+bis-MSB and compared to NE-213. In combination with these two solutes, LAB shows poorer abilities to separate neutron-induced pulses from photon-induced ones.

A cryogenic time resolved laser induced fluorescence spectroscopy (cryo-TRLFS) was successfully used to identify uranium binding forms in some German mineral waters of exceptionally low concentrations (<3.0 µg/ L). The measurements were performed at 153 K. The spectroscopic data showed a prevalence of aquatic species Ca2UO2(CO3)3 in most of the waters, while UO2(CO3)34- dominates only in a very few samples. The influence of the pH and main water constituents on uranium speciation was discussed. Spectroscopy indicated a good agreement with the modelling results.

Stratified two-phase flows were investigated at different test facilities with horizontal test sections in order to provide an experimental database for the development and validation of computational fluid dynamics (CFD) codes. These channels were designed with rectangular cross-sections to enable optimal observation conditions for the application of optical measurement techniques. Consequently, the local flow structure was visualised with a high-speed video camera, delivering data with high-resolution in space and time as needed for CFD code validation.

Generic investigations were performed at atmospheric pressure and room temperature in two air/water channels made of acrylic glass. Divers preliminary experiments were conducted with various measuring systems in a test section mounted between two separators. The second test facility, the Horizontal Air/Water Channel (HAWAC), is dedicated to co-current flow investigations. The hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was studied in this closed channel. Moreover, the instable wave growth leading to slug flow was investigated from the test section inlet. For quantitative analysis of the optical measurements, an algorithm was developed to recognise the stratified interface in the camera frames, allowing statistical treatments for comparison with CFD calculation results.

The third test apparatus was installed in the pressure chamber of the TOPFLOW test facility in order to be operated at reactor typical conditions under pressure equilibrium with the vessel atmosphere. The test section representing a flat model of the hot leg of the German Konvoi pressurised water reactor (PWR) scaled at 1:3 is equipped with large glass side walls in the region of the elbow and of the steam generator inlet chamber to allow visual observations. The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and water at boundary conditions of up to 50 bar and 264°C. Four types of experiments were performed, including generic test cases as well as transient validation cases of typical nuclear reactor safety issues. As an example, the co-current flow experiments simulate the two-phase natural circulation in the primary circuit of a PWR. The probability distribution of the water level measured in the reactor pressure vessel simulator was used to characterise the flow in the hot leg. Moreover, the flooding behaviour in this conduit was investigated with dedicated counter-current flow limitation experiments. A comparison of the flooding characteristics with similar experimental data and correlations available in the literature shows that the channel height is the characteristic length to be used in the Wallis parameter for channels with rectangular cross-sections. Furthermore, for the analysis of steam/water experiments, condensation effects had to be taken into account. Finally, the experimental results confirm that the Wallis similarity is appropriate to scale flooding in the hot leg of a PWR over a large range of pressure and temperature conditions.

Not least, different examples of comparison between experiment and simulation demonstrate the possibilities offered by the data to support the development and validation of CFD codes. Besides the comparison of qualitative aspects, it is shown exemplarily how to treat the CFD results in order to enable quantitative comparisons with the experiments.

In recent years, the accelerator-driven subcritical reactors (ADSR or ADS) were proposed for the transmutation of the transuranic elements from spent nuclear fuel. ADS can be also used for the energy production from the abundant element thorium. An operation of ADS requires reliable online reactivity determination methods. The classical methods for reactivity calculation have demonstrated strong system dependence in the experimental campaigns (YALINA , MUSE). These methods are based on point kinetics equations. To overcome the problem in the analysis of the space-time behavior of the neutron flux in ADS, the solutions for the space and time dependent diffusion and P1 transport equations were developed analytically. The Green’s function method was applied. The results were compared with the experimental results for the YALINA-Booster facility. The analytical solutions are in a good agreement with the experimental ones. In this work the authors give an overview of the developed solutions and their application for the analysis of the ADS experiments.

Fabrication of dense arrays of nanowires by growth on nanostructured substrates appears to be a promising approach for producing functional nanoscale devices. Ion beam irradiation under carefully controlled conditions produces selforganized ripple patterns on silicon substrates, on which Ag nanowire arrays with nanoscale periodicity have been grown successfully. Here, the linear and nonlinear optical response from native-oxide-covered Si(001) templates, with ripple periodicity between 20 and 50 nm, is reported. Reflection anisotropy spectroscopy (RAS) shows a small, broad peak at 2.5 eV of1x10^-3 amplitude. The RAS response decreases as the periodicity of the ripple structure increases. The nonlinear second-harmonic (SH) response from the samples was also measured, using unamplified femtosecond excitation at 800 nm, by rotating the linear polarized input and detecting either the sor p-polarized SH output.Adecrease in response with increased ripple structure periodicity was observed for the p-in/p-out configuration, when the plane of incidence was orthogonal to the average ripple orientation. Possible origins of the response and future experiments are discussed.

The complex formation of europium(III) with salicylic acid was investigated with time-resolved laser-induced fluorescence spectroscopy (TRLFS) in aqueous solution at elevated temperatures. Three complexes with metal-to-ligand stoichiometries of 1:1, 1:2 and 1:3 could be identified. Stability constants have been calculated for these complexes at various temperatures between 25 and 60 °C. Using the van´t Hoff equation, thermodynamic data (reaction enthalpy ΔrH, reaction entropy ΔrS and reaction energy ΔrG) could be determined. The formation of the 1:1 complex with ΔrH = -2.1 ± 4.9 kJ • mol-1 is nearly temperature independent, whereas the formation of the 1:2 and 1:3 complexes with reaction enthalpies of 12.7 ± 4.8 kJ • mol-1 and 23.3 ± 3.7 kJ • mol-1, respectively, is clearly endothermic.

The Institute of Radiochemistry (IRC) is one of the seven institutes of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The research activities are fully integrated into the “Nuclear Safety Research Program” of the Helmholtz Association and focused on the topic “Safety of Nuclear Waste Disposal”.
The research objectives are to generate better process understanding and data for the long-term safety analysis of a nuclear waste disposal in the deep geological underground. A better knowledge about the dominating processes essential for radionuclide (actinide) mobilization and immobilization on the molecular level is needed for the assessment of the macroscopic processes which determine the transport and distribution of radioactivity in the environment.
Special emphasis is put on the biological mediated transport of long-lived radionuclides in the geosphere and their interaction with different biosystems like biota and human organism for a better calculation of environmental and health risks.
Advanced knowledge is needed for description of the processes dominating at the interfaces between geo- and bio-systems related to the distribution of long-lived radionuclides in various bio-systems along the food chain.

Vorstellung der aktuellen Forschungsergebnisse und geplanten Arbeiten zum Thema Herstellung und Charakterisierung von photikatalytischen S-Layer Nanokompositen.

Vorstellung der wissenschaftlichen Arbeiten und erzielten Ergebnisse in dem NanoNature Verbundprojekt NanoPharm

The recently observed Seebeck spin tunneling, the thermoelectric analog of spin-polarized tunneling, is described. The fundamental origin is the spin dependence of the Seebeck coefficient of a tunnel junction with at least one ferromagnetic electrode. Seebeck spin tunneling creates a thermal flow of spin-angular momentum across a tunnel barrier without a charge tunnel current. In ferromagnet/insulator/semiconductor tunnel junctions, this can be used to induce a spin accumulation Δμ in the semiconductor in response to a temperature difference ΔT between the electrodes. A phenomenological framework is presented to describe the thermal spin transport in terms of parameters that can be obtained from experiment or theory. Key ingredients are a spin-polarized thermoelectric tunnel conductance and a tunnel spin polarization with nonzero energy derivative, resulting in different Seebeck tunnel coefficients Sst ↑ and Sst ↓ for majority and minority spin electrons. We evaluate the thermal spin current, the induced spin accumulation and Δμ/ΔT, discuss limiting regimes, and compare thermal and electrical flow of spin across a tunnel barrier. A salient feature is that the thermally induced spin accumulation is maximal for smaller tunnel resistance, in contrast to the electrically induced spin accumulation that suffers from the impedance mismatch between a ferromagnetic metal and a semiconductor. The thermally induced spin accumulation produces an additional thermovoltage proportional to Δμ, which can significantly enhance the conventional charge thermopower. Owing to the Hanle effect, the thermopower can also be manipulated with a magnetic field, producing a Hanle magnetothermopower.

The migration behavior of heavy metal contaminants like actinyl ions (U, Np) is mainly controlled by sorption processes at water-mineral interfaces. Hence, the investigation of the interactions of actinides with metal oxides such as Al(OH)3, Fe(OOH)x, TiO2, or SiO2, serving as model phases for more complex, naturally occurring minerals in aqueous solution, becomes essential for the safety assessment in the near and far field of nuclear repositories. In this study, gibbsite is used as a mineral model system because it the most common crystalline aluminum hydroxide and an ubiquitous weathering product of aluminosilicate minerals.
Spectroscopic data of surface complexes of uranium(VI) on gibbsite were obtained by in-situ Attenuated total reflection Fourier-transform (ATR FT-IR) and X-ray absorption spectroscopy.
The formation of a monomeric binary inner-sphere surface complex is derived from vibrational spectroscopic and EXAFS data irrespective of the prevailing atmospheric condition and surface loading. In addition, from infrared spectra it was found that U(VI) surface precipitation occurs at a micromolar concentration level after a relatively short contact time in an inert gas atmosphere. However, this is circumvented by lowering the initial U(VI) concentration or in the presence of atmospheric CO2 due to the formation of ternary uranyl carbonato surface complexes. The ternary complex was identified as a dimeric inner-sphere uranyl surface species containing a bidentately coordinated carbonate ligand.
Furthermore, DFT calculations were done to determine the structure and IR spectra of the aqueous dimeric uranyl-carbonate-hydroxo complex.

At the roots of continental flood basalts in the Paraná-Etendeka province are mafic dyke swarms that cover areas of several hundred kilometers. Studies of these dykes have focused mainly on the age, paleomagnetic properties and geochemistry, but less on pressure (P) and temperature (T) conditions of emplacement. However, the P and T conditions under which dyke magmas are stored are crucial for models of magma plumbing systems in flood basalt provinces. The erupted lavas are typically far from primitive compositions and generally show evidence for strong crustal assimilation in addition to magma fractionation. Unknown is where this magma modification took place in the crust. This is the kind of information that dyke studies can provide.
The Henties Bay Outjo dyke swarm (HOD) in NW Namibia is the subject of this study. This is inarguably the best exposed of major dyke swarms associated with South Atlantic rifting and breakup and its geochemical diversity is well documented but aspects relating to the magma dynamics in the dyke swarm have not been studied before. Our approach is to use geochemical data from selected dykes to assess the differentiation and assimilation history of the magmas, and combine that with petrologic constraints on the temperature-pressure conditions of crystallization derived from mineral-melt equilibria.
We have determined P-T estimates from olivine-melt and clinopyroxene-melt equilibria using analysis of phenocrysts by electron microprobe and applying the thermodynamic relations from Putirka (2008), who considered the standard error to be 1.7 kbar and 30 °C. The calculations reflect only mineral-melt (proxied by whole-rock) compositions that are consistent with equilibrium. Crystallization temperatures range from 1040 °C to 1350 °C with a mean (n=58) of 1170 °C. These T-variations are not random, the high-temperature results come from a specific region of dyke emplacement but the reason for this is not yet clear. Olivine-melt temperatures are higher than those from clinopyroxene-melt. The inferred crystallization sequence is in harmony with petrographic and geochemical observations. Pressures of clinopyroxene crystallization range from 0.7 to 7.1 kbar. The average pressure (n=12) is 4.9 kbar, few dykes yielded lower than 3 kbar, and the majority of dykes appear to have crystallized at 4-6 kbar. These estimates can be linked with bulk geochemistry to derive viscosity and melt densities to explore the mechanics of dyke emplacement.

Zircon and monazite from the peraluminous Stolpen granite and related rhyolitic dyke show magmatic as well as post-magmatic textures. The magmatic textures represented mostly by subtle oscillatory zoning are overprinted by post-magmatic fluid interaction which is indicated by elevated contents of Y, P, Th, and U and dissolution textures in altered zircon domains. Late- to postmagmatic fluid-induced crystallization can be divided into two main stages separated by a strong dissolution event: 1st - the formation of Y-, P-, Th- and U-rich rims and 2nd - purification of these domains by trace element release which led to the formation of secondary xenotime and huttonite/thorite. This can be observed both in the granite and its aplitic parts and rhyolite. Patchy zoning in primary monazite from the granite also suggests fluid-induced alterations. Its formation could resulted from the coupled dissolution-reprecipitation processes. Dark patches are depleted in Th, U and Pb which is interpreted as a result of selective removal of these elements from the monazite structure. Beside modification of monazite composition, partial dissolution of monazite grains occurred as well indicating the aggressive character of the fluids. Monazite grains from the rhyolite show slightly different textures and composition. High Ca, Pb, and Si contents and depletion in Th, as well as porous, spongy textures are results of fluid-induced alterations that caused also crystallization of cheralite. Grains with pure monazite composition cannot be found.
Zircon and monazite from the granite are accompanied by fluorite, Y-rich and Nb-rich minerals. High abundance of fluorite suggests elevated fluorine concentration in the fluids which facilitated both the dissolution of zircon and monazite grains and removal of certain elements from their structure. The absence of fluorite in the rhyolite indicates a different nature of the fluids involved in the alteration processes however the porous textures of zircon and monazite suggest their high reactivity as well.
The alteration of primary, magmatic accessory minerals and formation of secondary minerals is interpreted as related to magmatic fluids, which origin cannot be defined precisely on the base of the present data. However their composition (high F-, Y- and Ca- activity) and the mineralogy of the accessory phases suggest that they weren’t derived only from the parental magma itself.

Time-resolved metallographic optical microscopy techniques are used together with magnetic domain imaging to clarify the interaction between magnetic domains and twin boundary motion in magnetic shape memory NiMnGa single crystals. The magnetic field and stress induced magnetic domain formation is imaged by a magneto-optical indicator film technique. Reversible twin boundary motion is visualized up to high actuation speeds. From domain observation at adjacent crystal surfaces the fundamental volume magnetic processes during strain and field induced twin boundary motions are derived. For magnetic field induced structural reorientations a concurrent absence of magnetic domain wall motion is found. In contrast, for strain induced reorientations processes, a complete rearrangement of the magnetic domain structure by the moving twin boundary is observed. Dynamic actuation experiments on twin boundary motion reveal non-linear time effects on twin boundary mobility. In addition to training effects, the maximum field induced strain increases with actuation speed. Both effects can be interpreted as the interaction of moving twin boundaries with local non-fixed defects. The summarized results provide key information for the understanding of the connection of magnetic and crystallographic domains in magnetic shape memory alloys and for the optimization of devices for future technical applications.

We report on the response of multilayer spin textures to static magnetic fields. Coupled magnetic vortex pairs in trilayer elements (ferromagnetic/nonmagnetic/ferromagnetic) are imaged directly by means of layer selective magnetic x-ray microscopy. We observe two different circulation configurations with parallel and opposing senses of magnetization rotation at remanence. Upon application of a field, all of the vortex pairs investigated react with a displacement of their cores. For purely dipolar coupled pairs, the individual core displacements are similar to those of an isolated single layer vortex but also a noticeable effect of the mutual stray fields is detected. Vortex pairs that are linked by an additional interlayer exchange coupling (IEC) mainly exhibit a layer-congruent response. We find that –apart from a possible decoupling at higher fields– these strict IEC vortex pairs can be described by a single layer model with effective material parameters. This result implies the possibility to design multilayer spin structures with arbitrary effective magnetization.

Spin structures have been an interesting topic of magnetism research for many years. Within this field, magnetic vortices have attracted much attention, due to their non-trivial topology and the various dynamic modes they exhibit [1]. A magnetic vortex consists of a planar, flux-closing magnetization curl that turns out of the plane in the central nanoscopic core region. In a single layer structure, the curl’s radial components typically cancel each other out. Recent investigations show that this also holds true for multilayer vortex systems with bilinear interlayer exchange coupling [2]. Here we report on pairs of diverging-converging spin vortices occurring in biquadratically coupled systems. Using magnetic scanning transmission x-ray microscopy (STXM) we directly observe that the individual vortices of such pairs possess a residual radial magnetization component, i.e. ∇Mxy≠0. This implies an additional perpendicular magnetization divergence ∇Mz, for which we compare a continuous model with discrete micromagnetic simulations.
[1] S.-B. Choe et al., Science 304, 420 (2004). [2] S. Wintz et al., Appl. Phys. Lett. 98, 232511 (2011).

Micromagnetic structures have been a subject of magnetism research since many years. Among those structures, magnetic vortices are of special interest as they exhibit a non-trivial topology and various dynamic eigenmodes [1]. Such a vortex consists of a planar flux-closure magnetization curl that turns perpendicular to the plane only in the very small central core region. Both, the curl’s sense (circulation: c) and the core orientation (polarity: p) can be in either of two different states, giving rise to a binary handednes h=cp of the system. Extensive studies on the static and dynamic properties of single layer vortices led to the proposal of their application for memory cells and spin-transfer oscillators. From the viewpoint of these two concepts but also from a fundamental perspective, the coupling between spatially confined vortices is a key issue to address [2].

The U(VI) sorption onto Opalinus Clay, a natural clay rock from Mont Terri, Switzerland, was investigated as a function of pH in the absence and presence of humic acid (HA) under aerobic conditions using 0.1 M NaClO4 as background electrolyte ([U(VI)] = 1×10-6 M, [HA] = 50 mg/L, S/L = 4 g/L, pH 3-10). Due to leaching of Opalinus Clay, several competing ions are present in solution, where especially calcium and carbonate ions affect the speciation of U(VI) and HA in solution and consequently, their sorption properties. At pH > 7.5, the Ca2UO2(CO3)3(aq) complex is formed, which dominates the U(VI) speciation and sorbs only weakly onto Opalinus Clay. In the case of HA, the CaHA(II) complex dominates the HA speciation over a wide pH range. However, in the pH range 4.5-7.5, the presence of HA leads to the formation of the aquatic complex UO2(OH)HA(I), which causes a decreased U(VI) sorption. In the pH range from pH 7.5-8, HA seems to have no influence on the U(VI) sorption. The sorption characteristics of U(VI) on Opalinus Clay were predicted using PHREEQC. Thereby, the investigation was focused on the influence of the binding sites of the iron mineral goethite on U(VI) sorption onto Opalinus Clay.

Based on QCD sum rules we explore the consequences of a scenario for the ρ meson, where the chiral symmetry breaking condensates are set to zero whereas the chirally symmetric condensates remain at their vacuum values. This clean-cut scenario causes a lowering of the ρ spectral moment by about 120 MeV. The complementarity of mass shift and broadening is discussed. A simple parametrization of the ρ spectral function leads to a width of about 280 MeV if no shift of the peak position is assumed.

We present results for the photon spectrum emitted in non-linear Compton scattering of pulsed ultra-strong laser fields off relativistic electrons for intensities up to a0 > 100 and pulse lengths of a few laser cycles. At ultrahigh laser intensity, it is appropriate to average over the sub- structures of the differential photon spectrum. Supplementing this procedure with a stationary phase approximation one can evaluate the total emission probability. We find the photon yield in pulsed fields to be up to a factor of ten larger than results obtained from a monochromatic wave calculation.

The ratios of the cross sections for φ-meson production induced by 2.83-GeV protons on Cu, Ag, and Au nuclei to the respective cross section for C nuclei were measured at the ANKE-COSY facility in the momentum range of 0.6–1.6 GeV/c and the angular range of 0◦–8◦. The product φ mesons were identified by their decay φ → K+K−. The procedure used to separate kaon pairs was described in detail, and all sources of the background and their contribution to the resulting error in the values found for the above cross-section ratios were analyzed. The A dependence of the cross section for φ-meson production was shown to obey the A0.56±0.03 law. The total width of the φ meson at a normal nuclear density was extracted from a comparison of the measured cross-section ratios with the results of calculations based on two theoretical models. The resulting width value exceeds substantially both the vacuum width and the width expected in the absence of the nuclear-matter effect on the properties of the φ meson.