Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We present large-area emitters [1] based on InGaAsN which show efficient THz emission for excitation wavelengths up to 1.35 μm [2].
The substrate material consists of a 1000 nm GayIn1-yAs1-xNx (y=0.11 and x=0.04) layer grown by molecular-beam epitaxy on semi-insulating GaAs. On top there is an additional GaAs/Al0.3Ga0.7As heterostructure with thicknesses of 5 nm for the GaAs and 60 nm for the AlGaAs layer, respectively. Transmission measurements with a Fourier spectrometer reveal a bandgap corresponding to a wavelength of 1.5 μm. The resistance of a complete device with an active area of 1 mm2 is 0.3 MΩ. This allows operation with high bias fields (30 kV/cm) without being limited by heating. For excitation an optical parametric oscillator (OPO), tunable between 1.1 μm and 1.5 μm, is used. The pulse duration is 280 fs (FWHM). The THz signal is detected using electro-optical sampling with a 1 mm thick ZnTe crystal. The gating beam (λ = 820 nm) for detection is split off from a Ti:sapphire oscillator which drives the OPO.

[1] A. Dreyhaupt, et al., Appl. Phys. Lett. 86, 121114 (2005).
[2] F. Peter et al., Appl. Phys. Lett. 93, 101102 (2008).

Hexagonal manganites are oxides, in which structural, electronic, and magnetic degrees of freedom are coupled in a complex manner. Therefore, such materials have the potential for novel, nanoscale sensing and switching applications. Manganites are composed of dense-packed hexagonal manganese oxide layers with strong in-plane and weak interlayer coupling, thus the possible spin configurations may be studied with the help of a two-dimensional model Hamiltonian. Special focus is directed to the efficient sampling of the configuration space at low temperatures and concepts for improved importance sampling will be discussed.

The electronic transport of electrons and holes through stacks of functionalized quaterthiophene molecules as part of a novel organic ferroic field-effect transistor is investigated. The novel application of a ferroelectric instead of a dielectric substrate provides a bit-wise switching of the ferroelectric domains and enables the opportunity of employing the polarization field of these domains as a gate field in an organic semiconducting device. An already established phenomenological model called multilayer organic light-emitting diodes (MOLED) [1] is extended to transverse fields and numerical results are discussed. Model-specific parameters are determined with the help of experimental and theoretical methods.

[1] Houili et al., Comp. Phys. Comm. 156, 103-122 (2003)

Organic semiconductors, which might be suitable for logical as well as optical applications, have attracted a lot of scientific effort in recent years. This includes the understanding of the underlying transport mechanisms, the improvement of the transport characteristics and possible fields of application. The electronic transport through stacks of functionalized quaterthiophene molecules as part of a novel organic device is presented and investigated by means of a phenomenological approach called multilayer organic light-emitting diode (MOLED) [1]. Numerical results including the tuning of carrier injection and optical activity will be discussed.

[1] Houili et al., Comp. Phys. Comm. 156, 103-122 (2003)

Previously, UPt₂Si₂ has been described as a moderately mass enhanced antiferromagnet with a transition temperature of T_N = 32K [1]. In contrast, and more recently, it has been demonstrated that UPt₂Si₂ closely resembles the tetragonal heavy fermion superconductor/hidden order material URu₂Si₂ in various physical properties [2,3]. We present a detailed study of high field magnetization and resistivity on single crystalline UPt₂Si₂. While up to now the high field behavior of UPt₂Si₂ was discussed in terms of a crystalline electric field scheme applied to an f electron local moment system [4], we show that the high field behavior is much more complex than previously thought. In particular, the magnetic phase diagrams derived from our measurements contain various field induced phases, again analougous to URu₂Si₂. We compare the phase diagrams of both systems and discuss possible scenarios accounting for such behavior in UPt₂Si₂.

We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced a series of Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 6%, i.e., a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with T_c up to 0.5 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field reflecting the two-dimensional character of the superconducting state in the thin Ge:Ga layer having an effective depth of only 60 nm. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si [1] and diamond [2], our work reports another unexpected obervation of superconductivity in doped elemental semiconductors.

(2-amino-5-methylpyridinium)₂CuBr₄, abbreviated as (5-MAP)₂CuBr₄, has been characterized as a square S=1/2 Heisenberg antiferromagnetic lattice [1,2]. The compound consists of two-dimensional sheets of highly distorted CuBr₄ tetrahedra separated by the organic cations. The magnetic coupling constants are 6.5 K for the intra-sheet coupling, 1.5 K for a residual inter-sheet coupling, with both interactions in effect resulting in an antiferromagnetic transition occurring at T_N = 3.8 K. Here we report a single crystal high magnetic field study on (5-MAP)₂CuBr₄, with magnetic fields up to 40 T at temperatures down to 1.5 K. From the data additional information on local anisotropies such as of the g-factor can be obtained and will be discussed.

The metal-organic compound [Cu(pyz)₂(HF₂)]X with X = PF₆ exhibits a quasi-cubic lattice of copper ions (S = 1/2), but the magnetic properties show a predominantly two-dimensional (2D) nature due to a large anisotropy in the exchange couplings. The magnetic entropy and the antiferromagnetic ordering, eventually occurring at about 4 K, were investigated by specific-heat measurements. For this we established a continuous relaxation-time technique, using a single relaxation process to get specific heat data over a wide temperature range. The calorimetric investigations, performed between 2 and 100 K and in magnetic fields up to 14 T, have revealed a non-monotonic field dependence of the ordering temperature. The results are as expected from the model for a S = 1/2 2D square-lattice quantum Heisenberg antiferromagnet with an additional weak interlayer exchange (via Cu-F-H-F-Cu bonds). In comparison to the X = BF₄ compound, the antiferromagnetically ordered phase extends to much higher temperatures. In a more detailed analysis, we can extract all exchange interactions with an interlayer coupling ten times larger than in X = BF₄. Thus, the 2D character is significantly reduced in X = PF₆.

The discovery of superconductivity in iron pnictides has opened up a new class of high-T_c superconductors. It is quite remarkable that superconductivity is induced in layers of FeAs. These layers are separated by either rare-earth oxides or barium, which when doped act as charge-carrier reservoir. Single crystals of the (122) phase are currently available. We have determined the temperature dependence of the critical field H_c2, for various single crystals of K-doped BaFe₂As₂ using ac-transport measurements. The experiments were done at the pulsed-field facility in Dresden in fields up to 60 T applied parallel and perpendicular to the superconducting planes. The obtained phase diagram serves as an excellent benchmark for theoretical models of the order parameter.

Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic order. Combining conventional far-infrared Fourier-transform and THz-range free electron laser electron spin resonance (ESR) techniques, magnetic excitations in the hexagonal multiferroic materials YMnO₃ and LuMnO₃ have been studied. In the antiferromagnetically (AFM) ordered phase the gap in the excitation spectrum (~ 42 and ~ 48 cm⁻¹ for YMnO₃ and LuMnO₃, respectively) was observed directly. Similar slope of the frequency-field dependences of the AFM resonance modes, ~ 0.5 cm⁻¹/T, was found for both compounds. A fine structure of the AFM resonance absorption has been revealed by means of high-resolution ESR techniques, which can be explained taking into account a finite interaction between the neighboring Mn³⁺ layers.

We present new specific-heat data for two different YNi₂B₂C single crystals grown by a zone-melting method. The two samples (T_c,A = 15.26(4) K, T_c,B = 15.6(1) K) were studied in magnetic fields up to B = 9 T in the temperature range from T = 0.35 . . . 20 K, using both a relaxation and a heat-pulse method. In the superconducting state (B = 0) we find an uncommon dependence of the electronic contribution to the specific heat, C_el(T), strenghtening the assumption of a multiband nature of the superconducting state of YNi₂B₂C. A quantitative analysis of C_el(T) evidences multiple electronic contributions from electrons with very different electron-phonon coupling strengths, thus exhibiting several different superconducting energy gaps Δ(T,B = 0). This feature is in agreement with recent de Haas – van Alphen results [1] and point-contact spectroscopy data [2].

Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Combining conventional far-infrared Fourier-transform and THz-range free electron laser electron spin resonance (ESR) spectroscopy techniques, magnetic excitations in hexagonal multiferroic YMnO3 and LuMnO3 in the antiferromagnetically (AFM) ordered phase have been studied. The gap in the excitation spectrum (˜42 and ˜48 cm-1 for YMnO3 and LuMnO3, respectively) was observed directly. Similar slope of the frequency-field dependences of AFM resonance modes, ˜ 0.5 cm-1/T, was revealed for both compounds. A fine structure of AFM resonance absorption has been revealed by means of high-resolution ESR techniques, which can be explained taking into account a finite interaction between the neighboring Mn^3+ layers. The work was done in collaboration with M. Ozerov, D. Kamensky, E. Cizm'ar, J. Wosnitza, A.K. Kolezhuk, D. Smirnov, H.D. Zhou, and C.R. Wiebe.

We report on high field magnetic properties of the silver vanadium phosphate Ag₂VOP₂O₇. This compound has a layered crystal structure, but the specific topology of the V-P-O framework gives rise to a one-dimensional spin system, a frustrated alternating chain. Low-field magnetization measurements and band structure calculations show that Ag₂VOP₂O₇ is close to the dimer limit with the largest nearest-neighbor interaction of about 30 K. High-field magnetization data reveal the critical fields µ₀H_c1 = 23 T (closing of the spin gap) and µ₀H_c2 = 30 T (saturation by full alignment of the magnetic moments). From H_c1 to H_c2 the magnetization increases sharply similar to the system of isolated dimers. Thus, the magnetic frustration in Ag₂VOP₂O₇ bears little influence on the high-field properties of this compound.

Efficient white electroluminescence is obtained from metal-oxynitride-oxide-silicon (MONOS) structures with a silicon rich SiO2/SiON interface as an active layer. Samples containing only silicon show white electroluminescence (EL) under constant current excitation of 500 A. The EL spectra consist of three main bands associated with the neutral oxygen vacancy at 430 nm (NOV), E’ centers at about 550 nm and nonbridging oxygen hole centers (NBOHC) peaking at 650 nm. After Gd codoping into the SiO2:Si-nc layer the light emitted from the MONOS structure observed by naked eye is clearly white but the constant current needed for the EL excitation is reduced five times. Additionally, a fourfold increase of the electroluminescence power efficiency after Gd codoping was observed.

The investigation of reactor pressure vessel (RPV) materials from decommissioned NPPs offers the unique opportunity to scrutinize the irradiation behaviour under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterisation. The paper describes the investigation of trepans taken from the decommissioned WWER-440 first generation RPVs of the Greifswald NPP. Those RPVs represent different material conditions such as irradiated (I), irradiated and recovery annealed (IA) and irradiated, recovery annealed and re-irradiated (IAI). The working program is focussed on the characterisation of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921-05 to determine the fracture toughness of the RPV steel in different thickness locations.
In a first step the trepans taken from the RPV Greifswald Unit 1 containing the X-butt multilayer submerged welding seam and from base metal ring 0.3.1 both located in the beltline region were investigated. Unit 1 represents the IAI condition. It is shown that the Master Curve approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behaviour. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on sub size Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens.
The evaluated T0 from the trepan of base metal ring 0.3.1 varies through the thickness of the RPV wall. T0 increases from -120°C at the inner surface to -104°C at a distance of 33 mm from it and again to -115°C at the outer RPV wall. The KJc values generally follow the course of the MC, although the scatter is large. The re-embrittlement during 2 campaigns operation can be assumed to be low for the weld and base metal.

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Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carrier-mediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases.

In-situ produced cosmogenic nuclides have proved to be valuable tools for quantifying Earth's surface processes. Here, the work-horses are ¹⁰Be and ²⁶Al in quartz-rich minerals, and ³⁶Cl in Ca- or K-rich minerals. Several attempts to find new matrix-product-pairs have been yet performed, especially with respect to broaden the time-scale to both more ancient [1] and more recent (historic) times. Thus, we have investigated other nuclides than ³⁶Cl as possible dating tools by cross-calibration in accompanied calcite- and quartz-rich samples from Antarctica (DV3 & Joh) and Southern France (Ciot).
AMS measurements of ¹⁰Be and ²⁶Al have been performed at the French 5 MV-AMS facility ASTER, ³⁶Cl at CAMS, LLNL, USA, and ⁴¹Ca at the Maier-Leibnitz-Laboratory. As we could only perform a single run for ⁴¹Ca measurements, all results can be regarded as preliminary.
Ratios between different nuclides from the same matrix (CaCO₃) and ratios of ¹⁰Be or ²⁶Al from CaCO₃ and SiO₂ can be compared with pure physical model calculations [2] giving us experimental terrestrial production rates for ¹⁰Be, ²⁶Al and ⁴¹Ca from Ca and CaCO₃.
As shown earlier [3], cosmogenic ¹⁰Be is highly contaminated with atmospheric ¹⁰Be and cannot be removed quantitatively from calcite samples, even by an improved chemical cleaning procedure [4]. Only working on clay-free calcite provides correct ¹⁰Be data, giving a 2.7 times higher production rate of ¹⁰Be from CaCO₃ than from SiO₂. Though, the production rate of ²⁶Al is only ~4.6% (CaCO₃ relative to SiO₂), ²⁶Al can be easily determined in calcite, as the low intrinsic ²⁶Al concentration yields to nearly as high ²⁶Al/²⁷Al as within corresponding quartz.
The measurement of ⁴¹Ca, mainly produced via thermal-neutron-capture, is hindered by very low ⁴¹Ca/Ca: <2.9x10^-15. Of course, ⁴¹Ca counting statistics are poor: Measured ⁴¹Ca/Ca values are based on total counts of 1-5. Nevertheless, the reproducibility (Joh & Joh-WC) is excellent. All our data are lower than the already published one from rock samples, i.e. lower than the six surface samples (3-63 x 10^-15) of Henning et al. [5] and Kutschera et al. [6] and lower than the surface and strongly shielded sample at 11 m depth (3.4-7.6 x 10^-15) of Middleton et al. [7].
The low ⁴¹Ca/Ca ratios make it very unlikely that ⁴¹Ca could be generally used for in-situ dating of calcareous environments, especially as there is little hope that background level for CaF₂-targets will improve, thus asking for very sophisticated and time-consuming CaH₂-target preparation and handling [9].

Acknowledgments
We appreciate the help of D. Lal (UCSD), M. Arnold and G. Aumaître (CEREGE), J. Lachner and I. Dillmann (TU Munich), S. Nardon (ENI S.p.A., Milan) and J. Borgomano (U Marseille). This work was partially funded within the framework of CRONUS-EU (Marie-Curie Action 6^th FP; #511927).
References
[1] J.M. Schaefer et al., EPSL 251 (2006) 334.
[2] J. Masarik et al., NIMB 259 (2007) 642.
[3] S. Merchel et al., Quat. Geochronol. 3 (2008) 299.
[4] S. Merchel et al., NIMB, in review.
[5] W. Henning et al., Science 236 (1987) 725.
[6] W. Kutschera et al., Radiocarbon 31 (1989) 311.
[7] R. Middleton et al., Radiocarbon 30 (1989) 305.
[8] G. Korschinek and W. Kutschera, NIM144 (1977) 343.

The Forschungszentrum Dresden-Rossendorf expands its measurement capability by another highly-sensitive analytical method: accelerator mass spectrometry (AMS). The method will be mainly used for the determination of long-lived cosmogenic radionuclides. In contrast to ordinary decay counting, AMS scientists do not wait for the disintegration of a radioactive nucleus. In fact, they determine directly the not-yet-decayed radionuclides by mass spectrometry, which is much more efficient.
There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses e.g. isobars, are nearly completely eliminated. Thus, AMS generally provides much lower detection limits in comparison to conventional mass spectrometry. Our AMS system offers excellent measurement capabilities also for external users. In contrary to common low-energy AMS facilities in Europe, which have mainly specialized in radiocarbon analyses (¹⁴C), the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV.
The benefits from using AMS for radiation protection, nuclear safety, nuclear waste, radioecology, phytology, nutrition, toxicology, and pharmacology research are obvious and manifold: Smaller sample sizes, easier and faster sample preparation, higher sample throughput and the redundancy for radiochemistry laboratories will largely reduce costs. Lower detection limits will widen applications to shorter and longer time-scales and to sample types that could never been investigated before.
In environmental and geosciences, the determination of long-lived cosmogenic radionuclides like ¹⁰Be, ²⁶Al, and ³⁶Cl became more and more important within the last twenty years. Using these nuclides dating of suddenly occurring mass movements, e.g. volcanic eruptions, rock avalanches, tsunamis, meteor impacts, earth quakes and glacier movements, is possible. The so-called in-situ produced cosmogenic nuclides have proved to be valuable tools for quantifying Earth's surface processes also on longer time-scales and wider areas, e.g for the determination of basin-wide erosion rates. Additionally, glacier movements and data from ice cores containing atmospherically produced nuclides give hints for the reconstruction of historic climate changes and providing information for the validation of climate model predicting future changes.
Within the project CRONUS-EU the European-wide interdisciplinary network has focussed on basic data problems, that could strongly influence the quality of applications in geosciences. We have e.g. performed round-robin exercises and lowest-level measurements at different AMS facilities and cross-calibrations, searched for explanations for discrepancies in published production rates, explored new nuclide-matrix possibilities, and investigated in detail other sources of errors like scaling and nuclear reaction models.

Biofilms were formed on poly(ethylene oxide) (PEO) cryogels by using bacteria cultured from xenobiotics polluted environments in order to investigate their phenol biodegradation capability. PEO cryogels were synthesized via UV irradiation cross linking of moderately frozen aqueous system. Two xenobiotics tolerant bacterial isolates KCM R5 and KCM RG5 were used to construct the biofilms on the surfaces of the cryogels. Obtained PEO-biofilms were assessed for their ability to remove phenol at concentrations – 300, 400, 600 and 1 000 mg L-1 for 28 days. The biofilm PEO-KCM RG5 removed phenol up to 600 mg L-1/24h, whereas the biofilm PEO-KCM R5 was able to degrade up to 1 000 mg L-1/24h. The high content of free-water in the cryogels allowed reproduction of the used bacteria. Short initial adaptation of the PEO-biofilms with 100 mg L-1/24h phenol was crucial for protecting the bacterial cells forming the biofilm from dead. The obtained results showed that the liquid debit through the biofilms at the 28-th day was lower if compared to the initial one. Cryogels demonstrated non-toxicity, high biocompatibility with bacteria and excellent mechanical characteristics. After the aggressive phenol treatment the PEO-biofilms remained compact, porous and elastic. The investigated new biological materials demonstrate potential for application in the industrial wastewater treatment technologies.

The incorporation of Ge into cubic and hexagonal silicon carbide is compared for three different doping methods: ion-implantation; molecular beam epitaxy and liquid phase epitaxy.

Due to its large absorption coefficient, zinc telluride proved to be useful for the production of high-efficiency multi-junction solar cells. Nowadays ZnTe with a mixture of zincblende and wurtzite phases is fabricated by thin film growth techniques. The optical properties of both phases have been extensively studied by ab initio density functional methods [1]. Here we focus on the question whether the effective electron and hole mass in ZnTe are small enough to meet the high-efficiency expectation of the ZnTe absorber material in solar cells and present direction dependent effective mass and Luttinger and Luttinger-like parameters of cubic and wurtzite ZnTe, respectively. Making use of the transferability of ionic model potential parameters [2] and the experimentally known transition energies of different II-VI compounds ZnX (X=O, S, Se, Te), we obtained one single set of cationic model parameters for the Zn atom. The calculations have been performed by means of the empirical pseudopotential method using a simple empty core model potential.
[1] S. Zh. Krazhanov, P. Ravindran, A. Kjekshus, H. Fjellvag, and B.G. Svensson, Phys. Rev. B 75, 155104 (2007).
[2] D. Fritsch, H. Schmidt, M. Grundmann, Appl. Phys. Lett. 88, 124104 (2006), Phys. Rev. B 69, 165204 (2004).

Aiming for new magnetic properties, the lateral combination of different magnetic properties into hybrid magnetic thin film structures are of increasing interest. We investigated exchange bias patterned thin NiFe/IrMn films to correlate the static and dynamic magnetization processes of the artificial hybrid material to the intrinsic material properties. Arrays of stripes with modulated exchange bias, i.e. exchange bias strength and direction, and a periodicity of a few micrometers were created. Inductive magnetometry revealed a distinct influence of geometry and orientation on the magnetization loop yielding either single-step shifted hysteresis loops or two-step loops with exchange spring effect. By means of high resolution Kerr microscopy, this could be attributed to either coherently or separately reversed stripe magnetization. As for the dynamics, the films exhibited either multiple resonance frequencies (as superposition of the input properties) or a single hybrid resonance frequency. The acquired frequencies at zero bias field as well as according damping parameters could be varied by a factor of about two. The different phenomena are discussed in terms of direct exchange coupling via the extended NiFe film as well as quasi-magnetostatic interactions at the stripe interfaces.

The magnetic anisotropy direction and strength of amorphous FeCoSiB thin films was modified locally by masked ion implantation without alteration of the magnetic material’s structure and the intrinsic magnetic properties of the ferromagnetic film. The changes were introduced by local ion implantation in a SiO2 covering and protection layer, inducing additional stress-induced magnetic anisotropy to the magnetostrictive ferromagnetic layer. Hybrid hysteresis curves combining switching and rotational processes were measured and the underlying local variation of magnetic anisotropy was confirmed by magnetic domain observations. A good agreement between the calculated stress distribution and the experimentally obtained magnetic data was found. The described indirect method, relying purely on magneto-elastics, introduces a new path to the creation or alteration of magnetic properties subsequent to magnetic film preparation in structured magnetic samples without introducing any structural changes to the ferromagnetic layers.

Using a homotopic family of boundary eigenvalue problems for the meanfield α2-dynamo with helical turbulence parameter α(r)= α₀ + γΔα(r) and homotopy parameter β∈[0,1], we show that the underlying network of diabolical points for Dirichlet (idealized, β=0) boundary conditions substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for Robin (physically realistic, β = 1) boundary conditions. In the (α₀,β,γ)-space the Arnold tongues of oscillatory solutions at β =1 end up at the diabolical points for β = 0. In the vicinity of the diabolical points the space orientation of the 3D tongues, which are cones in first-order approximation, is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding α-profiles leading to spectral exceptional points, which are important ingredients in recent theories of polarity reversals of the geomagnetic field.

Absorption and transmission spectra of broadband terahertz pulses are measured to probe the intersubband response of an optically excited quantum-well heterostructure. While the terahertz absorption shows the single peak of the resonant intersubband transition, the transmission spectra display strong Fano signatures due to the phase sensitive superposition of ponderomotive and terahertz currents as predicted by our microscopic theory.

The migration of hazardous neptunium is strongly affected by sorption processes at the solid-water interface. Up to now, almost no spectroscopic data are available to characterize Np(V) species on a molecular level. For the first time, the speciation in aqueous solution and the sorption of Np(V) at a micromolar concentration level onto metal oxides were studied using NIR and in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy providing reference data for future investigations of neptunyl(V) sorption processes on natural mineral phases under environmental conditions.
The obtained spectra of aqueous Np(V) solutions confirmed the predominance of the fully hydrated species NpO2+ up to pH 7.7, predicted by the updated NEA TDB. From the Np(V) sorption studies on TiO2, stable surface species of NpO2+ are derived. The type of the sorbed species can be elucidated by a spectral shift (~ 30 cm−1) to lower wavenumbers of the antisymmetric stretching vibration ν3(NpO2+) compared to the aqueous species suggesting an inner-sphere complexation. Outer-sphere complexation is found to play a minor role due to the independence of the sorption species throughout the pH range 4 – 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2 and ZnO indicate structurally similar bidentate surface complexes.

THz sideband generation is a nonlinear mixing process where a near-infrared (NIR) laser beam is mixed with a THz beam to generate new frequencies (sidebands) ω around the NIR frequency: ω = ω_NIR ± n × ω_THz (with integer n). This effect has been investigated in various semiconductor systems (e. g., in bulk GaAs [1] and in multi quantum wells [2]).
We report on third-order nonlinear mixing between a NIR laser and a free-electron laser (FEL) in an undoped AlGaAs/GaAs multi quantum well. Differently from the literature where electronic and heavy-hole intersubband transitions were used, we are covering different transitions by tuning the FEL wavelength. We directly compare the n=+2 sideband generation efficiency when the FEL pumps the heavy-hole light-hole transition with the efficiency when the intraexcitonic 1s-2p transition of the heavy-hole is pumped. In the latter case the efficiency increases up to 0.2%, which is comparable to the best values achieved for an even stronger n=+1 sideband process [2].

[1] M. A. Zudov et al., Phys. Rev. B 64, 121204, 2001
[2] S. G. Carter et al., Appl. Phys. Lett. 84, 840, 2004

This experimental study is concerned with the secondary meridional flow during the time if the fluid spins up from rest. A cylindrical cavity with an aspect ratio of unity is filled with liquid metal and suddenly exposed to an azimuthal body force generated by a rotating magnetic field (RMF). Vertical profiles of the axial velocity have been measured by means of the ultrasound Doppler velocimetry. The flow measurements confirm a theoretical study by Nikrityuk et al. (2005) who suggested the existence of two stages during the RMF-driven spin-up, in particular the so-called initial adjustment phase followed by an inertial phase which is dominated by inertial oscillations of the secondary flow. Evolving instabilities of the double-vortex structure of the secondary flow have been detected at a Taylor number of 1.24´105 confirming the predictions of Grants and Gerbeth (2002). Perturbations in form of Taylor-Görtler vortices have been observed just above the instability threshold.

Tin-bismuth alloys are under intense consideration as favourable lead-free solders for consumer electronics and telecommunications. The electrical and thermal conductivity, viscosity, surface tension and density were studied in a wide temperature range above the liquidus. The scaling relations have been proposed. A comparison with data available in the literature is given.

The pursuit of better product quality and higher productivity of the continuous casting of steel makes the flow control in tundish and mould and the initial solidification control in the mould to important issues. Numerous sophisticated numerical simulations concerned with the metal flow during the casting process need a fundamental experimental validation. The use of water models gives the advantage to save expense and to be able to apply a number of well-proofed measuring methods. However, a generalisation of these results to liquid metal flows has to be considered as questionable because the true values of flow parameters (Re, Pr, Gr, Ha, etc.) are difficult to meet. In many cases, for instance liquid metal flows with strong temperature gradients, two-phase flows or applications of electromagnetic fields, the flow phenomena cannot be modelled correctly by means of water experiments.
In this paper we present a new experimental facility CONCAST for modeling the continuous casting process by using the low melting point alloy BiSn. The facility operates at temperatures of 200°C-300°C. Main parameters of the facility and dimensions of the test sections will be shown. The resultant possibilities with respect to flow investigations in tundish, submerged entry nozzle and mould will be discussed. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic or electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range until 300°C.
First experimental results will be presented which have been obtained using a small-scale preliminary set-up with the room temperature alloy GaInSn. Measurements of the liquid flow in the mold will be compared with accompanying numerical calculations. The application of electromagnetic fields for flow and solidification control in steelmaking will be a crucial point of the future working program.

The application of an RMF during the solidification of a metal alloy may cause macrosegregations, which are the result of the secondary flow in the form of a double vortex structure appearing in a rotating flow due to the Ekman pumping effect. The aim of this work is to improve the understanding of the influence of turbulent RMF-driven flows on the final macrosegregation during unidirectional columnar and equiaxed solidification of a binary metal alloy. The weakly turbulent flow was modeled by means of direct numerical simulations in an axisymmetric approach, where the transient heat and mass transfer was simulated by means of a standard mixture model. Both types of solidification, columnar and equiaxed, were considered by the application of both a permeability and a hybrid model to treat the fluid flow in the mushy zone. Our analysis shows that the oscillations of the radial flow are damped by the rather high viscosity of the slurry region formed by the mixture of equiaxed dendrites and interdendritic liquid. The transport of the equiaxed dendrites towards the axis of the cylinder results in a faster cooling of the melt and a convex shape of the mushy zone. The final macrosegregation is significantly smaller in comparison with the columnar solidification. An increase of the Taylor number leads to a further decrease of the macrosegregation in the middle of the sample for two reasons. First, the enhancement of turbulent mixing of the rejected solute and floating dendrites with the bulk liquid mediated by the T-G vortices, and second, the transport of floating dendrites by the flow reduces the ‘washing’ effect, given by the convective transport of the rejected solute from the solid interface, in comparison with non-movable dendrites.

A spectrometer has been developed to measure relativistic electrons produced in di®erent types of plasmas, like: tokamak plasmas, laser produced plasmas. The spectrometer consists of 9 YSO (Y2SiO5 : Ce) crystals, which are shielded by stainless steel ¯lters. The absolute calibration of the spectrometer was performed at the superconducting electron linear accelerator ELBE. The spectrometer can provide information about energy distribution of electrons and their numbers for the energy range between 4 and 30 MeV. The spectrum is analyzed by means of the Monte Carlo 3D Geant4 code.

In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.
A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data from water experiments, leads to dynamo action, and a strong influence of boundary conditions and additional (stagnant) fluid layers around the active domain is observed.
An additional source term for dynamo action exists in case of a spatially varying conductivity distribution. A very simple set-up -- serving as a proof of concept -- is given by a steady axial flow in an infinite cylinder with inhomogenous container walls. Such a configuration is sufficient for dynamo action, however, the critical Reynolds number might be too large for the realisation in a simple laboratory-sized experiment.
Similiar effects appear in case of permeability inhomogenities, where increased gradients might also lead to a significant reduction of the critical Reynolds number.

In-beam PET has become a quality assurance tool providing valuable clinical feedback for static tumor entities and shall be extended to monitor the treatment of intra-fractional moving tumors like in the lung or
liver which are subjected to respiratory motion. The potential of 4D in-beam PET for the detection of possible malfunction of the motion compensated beam delivery has been investigated by means of systematic phantom experiments at the clinical in-beam PET installation at GSI Darmstadt. The new system for tracking moving targets with the scanned ion beam at GSI Darmstadt was used to adapt the Bragg peak positions laterally and in depth. The pencil beam has been rescanned on a horizontal line in a phantom placed at the central plane of the double head PET scanner with an energy corresponding to 60mm penetration depth while the target was performing a one dimensional periodic motion perpendicular to the beam direction. 4D PET data were compared with an appropriate 3D PET measurement which followed immediately after the dynamic acquisition. It is shown for different irradiation scenarios that in-beam PET is capable for detecting treatment errors for moving target irradiation.

Seven new Multiwire Drift Chambers of plane 1 for the High - Acceptance Di - Elektron Spectrometer (HADES) are assembled in the Detector workshop of the Forschungszentrum Dresden - Rossendorf.
We present the results of test performed on the first chamber in comparison with the main design parameters .
End of 2008 one detector was completely equipped with the new generation of the readout system designed for the high multiplicity environment as provided in collisions of heavy systems at HADES @ FAIR.
The chamber was investigated with cosmic rays and β ⁹⁰Sr source. The obtained results show that the new design fulfills the equirements with respect to efficiency, accuracy and rate capability.
These chambers will be installed in 2009 to be armed for the upcoming heavy ion program.

The complexation of uranium(VI) with glucose was studied in the pH range from pH 2 to 6 by time resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature (RT) and for the first time under cryogenic conditions of 153 K (cryo-TRLFS). A uranyl(VI) glucose complex was spectroscopically identified by cryo-TRLFS measurements at pH 5. At lower pH values only the free uranyl(VI) ion was identified. The study revealed that quenching effects severely influenced the TRLFS measurements conducted at RT and significantly reduced the uranium(VI) fluorescence signal. This decrease in U(VI) fluorescence intensity is usually used to calculate complex formation constants of non-fluorescent uranyl(VI) organic complexes. However, our cryo-TRLFS results clearly showed that the observed decrease in U(VI) fluorescence intensity at RT for the samples at pH 2 to 4 is not attributed to the formation of such a non-fluorescent U(VI) glucose complex, i.e. to static quenching, but related to dynamic quenching of glucose on the uranyl(VI) fluorescence. At higher pH values the formation of uranyl(VI) glucose complexes were suppressed by the formation of uranyl(VI) carbonate species. The detected uranyl(VI) glucose complex was characterized by five emission bands at 499.0, 512.1, 525.2, 541.7, and 559.3 nm. The respective fluorescence lifetime determined at 153 K was 20.9 ± 2.9 µs. The uranyl(VI) glucose complex formation constant was calculated for the first time to be logßI = 0.1 M = 15.35 ± 0.91. Comparing this constant with formation constants of other important environmentally relevant inorganic ligands, in particular carbonate, it became evident that glucose only may influence the transport behaviour of uranium in a very small pH region of about 5. Our cryo-TRLFS investigation opens up new possibilities for the determination of complex formation constants since interfering quenching effects often encounter at RT are suppressed by measurements at cryogenic conditions.

Neptunium is one of the most problematic actinides for long-term storage of the radioactive waste. Acetate (AcO-) is one of the important organic ligands occurring in natural environment. To study complexation reactions of Np(V) and Np(VI) with AcO-, we performed titration experiments based on UV-Vis-NIR spectroscopy. Furthermore, we used cyclic voltammetry to obtain information on the stability field of the individual solution species. However, it is difficult to extract structural information solely from these techniques. Therefore, we additionally adopted X-ray absorption fine structure (XAFS) spectroscopy to detect complexation reaction and molecular structure of Np(VI)- and Np(V)-AcO- complexes in aqueous solution.
The UV-Vis-NIR absorption spectra of the Np(VI)-AcO- system as a function of pH do not show any isosbestic points, indicating the presence of more than two equilibria. As a result of stability constant refinement, the spectral change is indicated as a 3-step complexation reaction of NpVIO2(AcO)n2-n (n = 1, 2, 3). The evaluated stability constants are log K1 = 2.98 ± 0.01, log b2 = 4.60 ± 0.01, and log b3 = 6.34 ± 0.01, which are comparable with the values reported previously. For comparison reasons the complex formation of Np(VI)-AcO- was investigated by XAFS spectroscopy (XANES and EXAFS). The refinement analysis of the XAFS spectra revealed similar stability constants (log K1 = 2.87 ± 0.03, log b2 = 4.20 ± 0.06, and log b3 = 6.00 ± 0.01). The k3-weighted EXAFS spectra of NpVIO2(AcO)n2-n (n = 0, 1, 3) provided structural data consistent with the complex stoichiometry, being well-explained by bidentate coordination of AcO- (Np-Oax: 1.76-1.77 Å, Np-Oeq: 2.43-2.47 Å, Np-Ccarbo: 2.87 Å, Np-Cterm: 4.38 Å) which are consistent with the crystal structure of NaNpVIO2(AcO)3.
Also in the UV-Vis-NIR spectrum of a pH series of the Np(V)-AcO- system, no isosbestic points were detected. The refinement analysis resulted also in 3-step complexation equilibrium of NpVO2(AcO)n1-n (n = 1, 2, 3) with the stability constants log K1 = 1.93 ± 0.01, log b2 = 3.11 ± 0.01, and log b3 = 3.56 ± 0.01. This result is corroborated by the structural data obtained from EXAFS (Np-Oax: 1.83-1.85 Å, Np-Oeq: 2.51 Å, Np-Ccarbo: 2.90-2.93 Å) which are comparable with the crystal structure of BaNpVO2(AcO)3.
The observed stability constants were used to calculate a Paurbaix diagram. The validity of the assumed complexation reactions was confirmed by comparing the boundary of the stability field between Np(V) and Np(VI) species with experimental Np(V/VI) redox potentials.

MoS₂ nanomaterials synthesized by sulphurization of Mo₆S₂I₈ nanowires were studied by wavelength dependent Raman spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy (HRTEM). The transformation process leads to a variety of selective morphologies of the MoS₂ product, like coaxial nanotubes, i.e. nanotubes with split walls, “mama”- tubes with encapsulated MoS₂ fullerene-like particles, or other hybrid nanostructures. The temperature inside our horizontal fluidized-bed reactor directly determines the final morphology of the product. A temperature above 850°C leads to a formation of MoS₂ “mama”– tubes, while below 850°C the growth of coaxial MoS₂ nanotubes in which a number of multiwall nanotubes grow coaxially separated by gaps is favored. HRTEM was used to study how MoS₂ layers form from outside of precursor nanowires toward inside and to observe the nucleation of fullerene-like particles. Results of a possible oxidation during the Raman experiments are correlated with partially or fully oxidized Mo₆S₂I₈ nanowires of the composition MoO_3-x, which can be afterwards also sulphurized resulting in MoS₂ polycrystalline nanowires.
By the means of Raman and X-ray diffraction spectroscopies we have studied effect of temperature and duration of the sulphurization process. We followed the stages of the transformation to explore the chemical reaction kinetics.

Fullerene-like WS₂ nanoparticles and WS₂ nanotubes are studied by wavelength dependent Raman spectroscopy. The response from the nanomaterials is compared to that of 2H-WS₂ crystals and microcrystalline 2H-WS₂ powder. The Raman signatures point to a hexagonal 2H stacking of the WS₂ layers in all nanostructures. While the wave numbers of 1^st and 2^nd order Raman scattering show only little dependence, the line widths and the intensity ratios exhibit a systematic evolution with respect to the specific WS₂ nanostructure. The sulfur-sulfur stretching mode range is particularly sensitive to the different stages of disorder and is suitable for the diagnostic classification of the WS₂ nanostructures. Raman mapping across the nanoparticles is used to distinguish between disorder and surface effects on the vibrational spectra. All the experiments were performed at low laser power, since the transformation into WO₃ is induced already at moderate illumination due to the limited photo- and thermal stability of the materials.

This work is supported by the European Union sixth Framework Program (FOREMOST project under contract NMP3-CT-2005-515840).

Abstract: The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species
of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl) imide ([Hbet][Tf2N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu2(bet)8(H2O)4][Tf2N]6,
[Eu2(bet)8(H2O)2][Tf2N]6·2H2O, and [Y2(bet)6(H2O)4][Tf2N]6 were found to
consist of dimers. These rare-earth complexes are well soluble in the ionic
liquids [Hbet][Tf2N] and [C4mim]- [Tf2N] (C4mim=1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, 1H, 13C, and 89Y NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry.

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S100A12 has been implicated in inflammation. However, the role of extracellular S100A12 in vivo is still unclear. We report a novel methodology using radiolabeling of human recombinant S100A12 with the positron-emitter fluorine-18 and the use of ¹⁸F-S100A12 in cell assays in vitro and in small animal positron emission tomography (PET) studies in rats in vivo. For S100A12 radiolabeling N-succinimidyl-4-(¹⁸F)fluorobenzoate was used. S100A12 was shown to stimulate secretion of cytokines by macrophages and endothelial cells. In vitro assays revealed specific binding of ¹⁸F-S100A12 to the soluble receptor for advanced glycation endproducts (sRAGE) and, furthermore, to membrane RAGE on both cell types. Cell interaction of ¹⁸F-S100A12 was inhibited by RAGE inhibitors like glycated LDL and, interestingly, also by scavenger receptor ligands, e.g., maleylated albumin, and by lectines. PET data showed sustained temporary association of ¹⁸F-S100A12 with tissues expressing RAGE, e.g., lung and endothelium in vivo. Moreover, specific accumulation of ¹⁸F-S100A12 in tissues enriched in cells expressing scavenger receptors, e.g., liver and spleen, was observed. Concluding, ¹⁸F-radiolabeling of S100A12 and the use of PET allow discrimination of the kinetics and the metabolic fate of S100A12 in vivo. The approach provides a novel probe for functional characterization of inflammation in rodent models of disease.

Natural organic matter (NOM) released by microorganisms and plants is ubiquitous in waters, soils and sediments. NOM can form relatively stable aqueous complexes with U(VI) and may interact like U(VI) with mineral surfaces. In systems containing U(VI), NOM and mineral surfaces binary and ternary sorption complexes have to be considered. These intricate interactions may profoundly influence the mobility of U(VI). However, the study of such a ternary system requires first its decomposition into simpler binary subsystems. Here we show the interaction of U(VI) with relatively simple carboxylic acids. Acetic, succinic and DL-tartaric acid were used as model compounds to simulate the different -COOH and -OH functionalities of the structurally more complicated, polyelectrolytic NOM.

Aqueous complexes of U(VI) with the model compounds were investigated by applying UV-VIS and EXAFS measurements. UV-VIS pH titration experiments were performed to identify the binary complexes formed in large excess of organic ligands and to derive their speciation. Uranium LIII-edge EXAFS spectra of pH series were then measured. Based on the speciation derived from UV-VIS spectroscopy, we were able to derive the EXAFS spectra of the pure U(VI) complexes from the EXAFS spectral mixtures by means of iterative target transform factor analysis [1]. Shell fit and an inversion method was then applied to validate their structures.
The uranium acetate and succinate complexes are characterized by a bidentate coordination of the carboxylic group. Furthermore, the formation of seven-membered rings can be rejected in the uranium succinate system. In contrast, the tartaric acid system is much more complicated because tartaric acid is able to form tridentate chelates with uranium using two carboxylic and one alcoholic groups. These chelates were identified to be dimeric at lower pH (3-5) and trimeric at higher pH (6-7). In addition, the structure of the trimer is also validated by the U-O radial pair distribution function (PDF) which is directly calculated from the EXAFS spectrum by an inversion method. The PDF of the oxygen atoms in the equatorial plane of U(VI) is asymmetric and gives evidence for one central oxygen atom linking the three uranyl ions of the trimer in a much shorter U-O distance than the remaining equatorial U-O distances.
In conclusion, we can provide structural models for the aqueous complexes of U(VI) with acetate, succinate and tartrate – the substances used as model compounds for NOM in this study.

[1] A. Rossberg, T. Reich, G. Bernhard, Anal. and Bioanal. Chem. 376, 631 (2003).

Bacteria are the most ubiquitous organisms in all terrestrial and aquatic environments. The talk will focus on cell wall dependent accumulation and biomineralization of uranium by particular Gram-positive and Gram-negative bacteria recovered from different extreme habitats. By using TEM, EXAFS and TRLF we were able to demonstrate that the Gram-negative and most of the Gram-positive bacteria inhabiting oligotrophic environments such as deep subsurface layers or heavy metal and pesticides polluted industrial sites immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. Some of the isolates demonstrated high capability to utilize phenol compounds as well. These properties of the studied extremophile bacterial isolates are promising for development of bioremediation approaches for heavy metal and phenol polluted environments

Poster über die Integration von PET in die Strahlentherapie mit hochenergetischen Photonen

The Landweber iteration method (1) is used to construct the radial pair distribution function (PDF) from an EXAFS spectrum. The PDF as solution of the fundamental EXAFS integral equation is determined in a stable way without additional supplementary conditions due to the semi-convergent behaviour of the Landweber iteration.
For the correct determination of the PDF it is important to know the energy shift dE0. If dE0 is unknown then usually it is determined by a shell fit of the spectrum before an inversion method is applied. If the shell fit model is incorrect then the determined dE0 is erroneous and an inverse method would give a wrong PDF. This leads in turn to the conclusion that the recent inversion procedures are only applicable if the structural model for the investigated system is already known; hence they are not “stand-alone” methods.

We developed an algorithm based on the Landweber iteration for deriving the appropriate dE0. The performance was tested by several theoretical and experimental EXAFS spectra of metal hydrates (U(IV), Np(IV), Th(IV), Cm(III)). For the estimation of the optimum number of iterations we adopted the L-curve concept which was recently used for the determination of the optimal regularization parameter in Tichonov’s method [2]. The examples show that the Landweber iteration in combination with the simultaneous determination of dE0 and the L-curve concept for the estimation of the optimum number of iterations is a robust way to calculate the PDF. The approach enables the calculation of the PDF even for strong overlapping shells like for Cm(III) hydrate.

(1) Landweber, L. Am. J. Math. 73, 615-624 (1951).
(2) Kunicke, M., et al. Physica Scripta T115, 237–239 (2005).

Abstract about the potential of in-beam PET within IGRT

In-beam positron emission tomography (in-beam PET) is a valuable in situ method for quality assurance in radiation therapy. It is well investigated for therapy with carbon ions and has been successfully implemented clinically at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. The extension of this efficient technique to other radiation treatment modalities may be worthwhile. For protons, 3-He, 7-Li, and 16-O the feasibility has already been experimentally shown. Furthermore, it seems to be feasible for the case of radiotherapy with high-energy photons, since positron emitters are generated by photons with energies above 20 MeV due to (gamma, n) photo-nuclear reactions (predominantly 11-C and 15-O in tissue). In this regard, promising conclusions have been obtained by Geant4 simulations as well as by off-beam PET experiments using a conventional PET scanner. The next step was the installation of a small double head positron camera consisting of two bismuth germanate (BGO) block detectors at the irradiation site to measure the generated beta+ activity distribution simultaneously to the irradiation. The relation between deposited dose and beta+ activity density was quantified. The obtained results are presented and compared to that of off-beam PET experiments. Higher activities as well as an improved contrast between materials of different stoichiometry are achieved by measuring in-beam, showing the advantage of in-beam PET over off-beam PET. Thus, the application of in-beam PET to radiation therapy with high-energy photons can be useful for quality assurance, comprising monitoring of dose delivery, patient positioning and tumor response.

This work presents the development of analytical approximation solutions for a space-time dependent neutron transport problem in two energy groups for a one dimensional system consisting of a homogenized medium with a central external source. The approximation solutions are developed using Green's functions, the influence of the delayed neutrons is not considered. Qualitative results for a given system are analyzed. A detailed comparison of the developed analytical approximation solutions with solutions with one energy group and with results gained by the time dependent diffusion equation without separation of space and time is given.

Für Speziations- und Sorptionsuntersuchungen mit Plutonium steht am Institut für Radiochemie des FZ Dresden-Rossendorf ²⁴²Pu (T_1/2 3,755*10⁵ Jahre) zur Verfügung, das eine Reinheit von 99,93 Atom% hat. Da die übrigen enthaltenen Plutoniumisotope zum Teil wesentlich kürzere Halbwertszeiten haben (²⁴⁰Pu: T_1/2 6563 Jahre, ²³⁸Pu: T_1/2 87,7 Jahre, ²⁴¹Pu: T_1/2 14,35 Jahre), ist der Aktivitätsanteil dieser Isotope erheblich. Das Material wurde vor 29 Jahren hergestellt, so dass zusätzlich zu den Plutoniumisotopen die Tochter von ²⁴¹Pu, das ²⁴¹Am, zu beachten ist. Es besteht die Aufgabe, schnell für eine Vielzahl von Proben den Gehalt des ²⁴²Pu zu bestimmen. Das wird durch Flüssigszintillation erreicht, bei der zunächst eine alpha/beta Separation durchgeführt wird und anschließend durch Spektrenentfaltung [1] der Peak des ²⁴²Pu vom gemeinsamen ²³⁸Pu/²⁴¹Am-Peak getrennt wird.

[1] Nebelung, C., Baraniak, L., 2007. Simultaneous Determination of ²²⁶Ra, ²³³U and ²³⁷Np by Liquid Scintillation Spectrometry. Applied Radiation and Isotopes, 65, 209-217.

Flavonoids belong to a class of secondary plant metabolites. They are one of the largest classes of plant phenolics. All flavonoids consist of a 15 carbon skeleton. Flavonoids are most commonly known at least for four main properties: colored (to attract animals), absorbing ultraviolet light (to protect against damage), antimicrobial activity (to protect against bacterial or fungal infection) and antioxidant activity (which may be responsible for anticancer benefits) [1].
The structure of flavonoids is dominated by phenolic hydroxyl groups.

We studied the complex formation of the flavonoid kaempferol with uranium. Kaempferol is a 3,5,7-Trihydroxy-2- (4-hydroxyphenyl)-4H-1- benzopyran-4-on. As stated already flavonoids show strong absorption spectra in the UV-range. The change in their spectroscopic data was used to determine the stability constants. Spectra were evaluated with the factor analysis program Specfit [2]. All spectra of flavonoids show isosbestic points indicating a clear interaction between kaempferol and uranium(VI).
A strong interaction was found for kaempferol. The derived stability constant was assigned to be log β121 = 31.7 ± 0.4 at an ionic strength of 0.1 M for the reaction

UO22+ + C15H5O64- + 2 H+ → UO2C15H7O6 (1)

Data derived from studies with quercetin and hesperetin show an analogue stability constant for the non-charged complex.
We assume that the complex formation occur by a ring formation, whereas the flavonoids form rings between the phenolic group in position 3 or 5 respectively and the ketone oxygen in the benzopyran-4-one ring [3].

[1] Tiaz L, Zeiger E Plant Physiology 2006 4. Edition, Sinauer Associates Inc.
[2] Binstead R A, Jung B, Zuberbühler A D Specfit Global analysis system Spectrum Software Associates 2000-2003
[3] Malesev D, Kuntic V 2007 J. Serb. Chem. Soc. 72 921

The photoexcitation of a inner-shell photoelectron is is usually accompanied by the excitation of outher-shell electrons. Early systematic studies were performed with noble gases because their absorption signal is not affected by photoelectron backscattering from neighbored atoms. Up to now, most of the elements until Bi were investigated for multieletron excitations even in the presence of photoelectron backscattering effects from extended X-ray absortion fine structure. All elemets with Z > Bi comprise only radioactive isotopes and their mutielectron features are more difficult accesible. Recently we found evidence for multielectron excitations even in the L-absorption edges of actinide hydrates [1,2]. The actinides investigated up to now are Th, Pa, U, Np, Pu and Am. The strongest resonances result from [2p4f] double electron excitations, but there is also evidence for [2p5d] excitations. The [2p4f] resonance energies follow systematically the trend observed by Di Cicco and Filipponi for Hg, Pb and Bi [3]. The actinide elements show numerous oxidation states in particular for Np and Pu, where they range from III to VII. The electronic configuration involves besides 6d states partly filled 5f shells. The 5f states are less strictly located than the 4f states of the lanthanides, and can therefore participate in the chemical bond. This electronic configuration influences the physical and chemical properties and posses a large variation in the coordination geometry including transdioxo cations, AnO2n+ (n = 1 and 2). There is a clear correlation of the oxidation state, coordination geometry and the spectral feature of the multielectron resonance, resulting from final state density. The change in the resonance intensity of the single electron 2p6d transition as function of the electron configuration correspond well with the double-electron [2p4f] resonance intensity.

Neptunium shows a complex redox chemistry comprising reversible redox couples like Np(VI)/Np(V) and Np(IV)/Np(III), as well as irreversible couples like Np(V)/Np(IV). The reversibility of Np(VI)/Np(V) is rather unique among the actinides, because other actinide redox couples like U(VI)/U(V) and Pu(VI)/Pu(V) are prone to disproportionation effects in weakly complexing media [1,2]. The basics of reversible redox behavior is well explained by electron transfer without changes of the ligand arrangement, whereas the irreversibility of the transition Np(V)/Np(IV) is due to the formation or release of the NpO2+ oxygen atoms of the trans-dioxo moiety. However, also the reversible transitions may become quasi-reversible and irreversible for several reasons, e.g. as function of ligand exchange and electron transfer kinetics. Structural information on the neptunium redox species in aqueous solution is currently rather scarce. Therefore we performed a systematic study based on cyclic voltammetry, electrolysis, UV-Vis-NIR and EXAFS spectroscopy of the Np redox species in presence of the oxoanions ClO4, SO42, NO3 and CO32. The redox couple Np(V)/Np(IV) remains reversible in non-complexing ClO4 by retaining associated H2O molecules, but becomes irreversible already in weakly coordinating NO3 media [2]. The Np(V)/Np(IV) couple becomes more irreversible in presence of stronger ligands like SO42 and CO32. The slow kinetics of the Np(V)/Np(IV) couple in cyclic voltammetry results in a superposition with the reversible Np(IV)/Np(III) couple. The related species were partly separated by electrolysis and their coordination was analyzed independently. The redox couple Np(VI)/Np(VII) could be observed only in CO32 media at high pH. It is also irreversible as result of a rearrangement of the inner-sphere coordination. The neptunium sulfate system comprises a larger variety of isomers due to similar Gibbs free energies for monodentate and bidentate coordination. A comparison along the series Th(IV) - U(IV) - Np(IV) reveals that the monodentate sulfate coordination decreases whereas the bidentate coordination increases. This trend was studied by DFT calculations and will be discussed in terms of solvation energy and covalency of the molecular bonds.

Purpose: In recent years, laser-based acceleration of charged particles has rapidly progressed and medical applications, e.g., in radiotherapy, might become feasible in the coming decade. Requirements are monoenergetic particle beams with long-term stable and reproducible properties as well as sufficient particle intensities and a controlled delivery of prescribed doses at the treatment site. Although conventional and laser-based particle accelerators will administer the same dose to the patient, their different time structures could result in different radiobiological properties. Therefore, the biological response to the ultrashort pulse durations and the resulting high peak dose rates ofthese particle beams have to be investigated. The technical prerequisites, i.e., a suitable cell irradiation setup and the precise dosimetric characterization of a laser-based particle accelerator, have to be realized in order to prepare systematic cell irradiation experiments.

Methods: The Jena titanium:sapphire laser system (JETI) was customized in preparation for cell irradiation experiments with laser-accelerated electrons. The delivered electron beam was optimized with regard to its spectrum, diameter, dose rate, and dose homogeneity. A custom-designed beam and dose monitoring system, consisting of a Roos ionization chamber, a Faraday cup, and EBT-1 dosimetry films, enables real-time monitoring of irradiation experiments and precise determination of the dose delivered to the cells. Finally, as proof-of-principle experiment cell samples were irradiated using this setup.

Results: Laser-accelerated electron beams, appropriate for in vitro radiobiological experiments, were generated with a laser shot frequency of 2.5 Hz and a pulse length of 80 fs. After laser acceleration in the helium gas jet, the electrons were filtered by a magnet, released from the vacuum target chamber, and propagated in air for a distance of 220 mm. Within this distance a lead collimator (aperture of 35 mm) was introduced, leading, along with the optimized setup, to a beam diameter of 35 mm, sufficient for the irradiation of common cell culture vessels. The corresponding maximum dose inhomogeneity over the beam spot was less than 10% for all irradiated samples. At cell position, the electrons posses a mean kinetic energy of 13.6 MeV, a bunch length of about 5 ps (FWHM), and a mean pulse dose of 1.6 mGy/bunch. Cross correlations show clear linear dependencies for the online recorded accumulated bunch charges, pulse doses, and pulse numbers on absolute doses determined with EBT-1 films. Hence, the established monitoring system is suitable for beam control and a dedicated dose delivery. Additionally, reasonable day-to-day stable and reproducible properties of the electron beam were achieved. Conclusions: Basic technical prerequisites for future cell irradiation experiments with ultrashort pulsed laser-accelerated electrons were established at the JETI laser system. The implemented online control system is suitable to compensate beam intensity fluctuations and the achieved accuracy of dose delivery to the cells is sufficient for radiobiological cell experiments. Hence, systematic in vitro cell irradiation experiments can be performed, being the first step toward clinical application of laser-accelerated particles. Further steps, including the transfer of the established methods to experiments on higher biological systems or to other laser-based particle accelerators, will be prepared.

Recent ab initio calculations predict that As(III)- and As(V)-thioanions can occur simultaneously in sulfidic environments under commonly encountered pH conditions. However, unambiguous structural characterizations for the two homologue series of thioarsenites or thioarsenates are still missing. In the present study, the molecular structures of synthesized mono-, di-, and tetrathioarsenate were characterized by XRD and XAS in their solid state and dissolved at alkaline or near-neutral pH-conditions. The determined As(V)-S and As(V)-O bond distances of 2.13-2.18 Å and 1.70 Å, respectively, are consistent with the theoretical expectations for thioarsenates and can be clearly differentiated from the respective As(III)-bondings, with 2.24-2.34 Å and 1.78 Å. The XANES edge positions of the individual thioarsenates (mono- 11871 eV, di- 11870, and tetrathioarsenate 11869.5) lie between those of As2O5 (11872.3 eV) and As2O3 (11868.2 eV) and reveal the influence of increasing sulfur substitution by decreasing bond energies and hence absorption edge energy. These thioarsenates can be clearly distinguished from the species formed upon acidification of tetrathioarsenate below pH 6.3. These species were identified as thioarsenites. Their XANES edge energy of ca. 1 eV below that of As2O3 indicates the redox-state change from As(V) to As(III), which is further confirmed by the increased As-S distance of 2.23-2.28 Å corresponding to As(III)-S species. At pH 3, the detection of As-As-bonds indicates the beginning formation of colloids, most likely amorphous As2S3. Our results indicate that in synthetic solutions, thioarsenites can form as transitory species between dissolved thioarsenates at near-neutral pH and AsS-precipitates formed under acidic conditions.

Main objectives of new fuel developed for Generation III/IV systems are economy of resources, minimized volume and lower long-term potential radiotoxicity of ultimate wastes and proliferation risk reduction. To achieve these goals, one major fuel cycle option under evaluation is co-management of the actinides (An) in an integrated closed fuel cycle.1 Co-management of two (or more) actinides implies separating these actinides from the fission products, most often by hydrometallurgical processes, and then converting them to solid forms to re-fabricate fresh fuel or dedicated fuels or targets. Considering the significant amount of minor actinides and the different designs of future nuclear fuels, including mixed actinide pellets, composite materials or spherical particles, various uranium-actinide(s) wet co-conversion routes are currently investigated at the CEA-ATALANTE facility. Once the precipitation is achieved, the resulting mixed-actinide compound is calcined into a mixed oxide. As this compound will be the solid precursor of fuel or a dedicated transmutation target, controlling its composition at the molecular scale is of major importance. Usually, solid solution structures are studied using diffraction methods. But, as demonstrated in a previous study2, in order to fully investigate the ideality of a solid solution, X-ray absorption spectroscopy (XAS) using synchrotron radiation is an extremely suitable technique.
The subject of this paper is the study of (U1-x,Pux)O2 (with x=0.15, 0.28, 0.45 and 0.50) solid solutions synthesized by two co-conversion routes: the first one based on the oxalic co-precipitation of U(IV) and Pu(III) complex3 and the second on the internal gelation of a U(VI)-Pu(IV) or U(IV)-Pu(III) solution4. Before XAS experiments, samples were characterized by X-Ray diffraction and exhibit the expected cubic face centered structure with lattice parameters in agreement with Vegard Law.
XAS experiments were performed at the Rossendorf Beamline (BM20) located at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). For each sample, plutonium LII and U LIII-edge were collected at 15K using a helium cryostat.

The aluminate complexes of uranyl ion cannot be obtained in aqueous solutions due to the hydrolysis of U(VI). However, U(VI) is known to be readily adsorbed with alumina from aqueous near-neutral solutions owing to the formation of inner-sphere, bidentate complexes at the surface [1]. Herein, for the first time we present the data indicating possibility of uranyl aluminate (UrAl) formation as nanoparticles dispersed in alumina matrix.
The precursor for UrAl was prepared by U(VI) precipitation with ammonia (pH=11) in the presence of mesoporous alumina MSU-X under the effect of power ultrasound (f = 20 kHz, Pac = 0.6 Wcm-2, Ar, T = 37°C). Finally, solids were centrifuged, washed until neutral pH with pure water, dried at 70°C and annealed at 800°C prior to low resolution TEM, U LIII XAFS and 27Al MAS NMR analysis.
The sample with 5 weight % of uranium yields an orange air-stable product after annealing. TEM images show uranium nanoparticles with an average size of about 5 nm dispersed in alumina matrix. XAFS spectrum of this sample reveals the presence of uranyl group with a U=O trans-dioxo distance equal to 1.80 (0.01) Å. Both XANES and EXAFS spectra are quite similar to the spectra obtained with uranyl ions adsorbed onto alumina at pH 6.
27Al MAS NMR spectra of initial MSU-X alumina exhibits three peaks assigned to octahedral, tetrahedral, and pentagonal local environment of aluminum. According to literature, pentagonal coordination of aluminum is typical for protonated boehmite-like forms of alumina, AlO(OH) [2]. Heating of MSU-X without uranium causes sharp decrease in pentagonal aluminum occupancy. By contrast, with 5% of uranium NMR spectra after annealing at 800°C clearly indicate the presence of aluminum ions coordinated by five oxygen atoms, which could be assigned to uranyl coordination with AlO2- anions.
The increase of uranium concentration to 30 weight % causes formation of green-black solids after annealing at 800°C. TEM measurements demonstrate formation of 50 nm uranium crystallites embedded into alumina matrix. EXAFS spectrum of this sample exhibits the absence of UO22+ groups and a strong U-U interaction with a characteristic distance of 4.39 (0.01) Å comparable with U3O8 reference sample.
Presumably UrAl is formed during the calcination of precursor only at low content of uranium hydrolyzed species finely dispersed or adsorbed at alumina surface. Otherwise, annealing leads to predominated formation of uranium oxides, probably, due to the favorable kinetics of solid state reaction. Thus, interaction of uranyl ions with alumina matrix represents a relatively rare example of real nanochemistry, when the chemical composition of species is a strong function of the particle size. In conclusion, it should be emphasized that a further structural study is necessary to refine the UrAl structure.
Acknowledgements This work was supported by European ACTINET and French PARIS Research Programs.
References
1. Sylwester E.R., Hudson E.A., Allen P.G. Geochim. Cosmochim. Acta, 64 (2000) 2431-2438.
2. Wang J.A., Bokhimi X., Morales A., Novaro O., Lopez T., Gomez R. J. Phys. Chem. B, 103 (1999) 299-303.

There is a continuous need for processes aimed at the selective uptake of toxic metal ions from dilute wastewaters and industrial process streams. Insofar, solid-liquid extraction processes using chelating agents grafted onto hydrophilic supports are appealing. The Institut de Chimie Moléculaire de l'Université de Bourgogne has designed a series of hybrid organic-inorganic materials for the selective uptake of toxic metal ions, including actinides [1]. These extracting agents are obtained by grafting functionalized tetraazamacrocyclic ligands (cyclen and cyclam derivatives) on the surface of silica-gel beads. In collaboration with the Commissariat à l'Energie Atomique (CEA Center of Valduc), one of these modified gel has been prepared on a semi-industrial scale and used in the final decontamination step of real effluents for removing the residual -emitters (U, Pu, Am) contained at the sub-g/L level. This process allowed the successful decontamination of more than 50 m³ wastewaters, with a residual radioactivity level of less than 5 Bq/m³.
We have used XAFS to investigate the coordination scheme of UO22+ and Pu4+ cations at the surface of the organic-inorganic hybrid materials. The results show that surface complexes are formed through a combined action between the reactive solid support, namely amorphous silica, and the chelating groups appended on the immobilized ligands [2].

[1] F. Barbette, F. Rascalou, H. Chollet, J. L. Babouhot, F. Denat, R. Guilard, Anal. Chim. Acta, 502, 179-187, 2004.
[2] L. Giachini, S. Faure, M. Meyer, L.V. Nguyen, B. Batifol, H. Chollet, R. Guilard, A.C. Scheinost, C. Hennig, Proceedings of the 5th Workshop on Speciation, Techniques, and Facilities for Radioactive Materials at Synchrotron Light Sources (Actinide XAS 2008), in press.

The long-term safety of radioactive waste disposal in deep geological repositories with respective reliable predictions is an important fact in the disposal site selection process. To ensure the safety geochemical modeling calculations using comprehensive and consistent thermodynamic data are required.
The relational databank THEREDA will provide such thermodynamic datasets. It takes into account specific German requirements (high ionic strengths in salt host rocks) and temperatures up to 100°C. Available databases do not suffice these needs because of very restrictive data selection procedures or heterogeneous and inconsistent data. THEREDA mainly builds on data derived from solution experiments with a focus on ternary and higher systems.
The application of referential integrity, thermodynamic dependencies, alternative datasets and uncertainty estimates allows THEREDA to deliver tailor-made parameter files for use in geochemical modeling software like EQ3/6, GWB and ChemApp.
To enhance public use THEREDA is accessible via internet.

THEREDA provides consistent thermodynamic datasets to assist the long-term safety assessment of nuclear waste repositories. It meets specific German requirements (high salinities and temperatures). THEREDA is build on a relational SQL-database. The application of referential integrity, thermodynamic dependencies, alternative datasets and uncertainty estimates allows to deliver tailor-made parameter files for use in geochemical modelling software like EQ3/6, GWB and ChemApp covering law-of-mass-action and Gibbs-energy-minimization codes.

Tetravalent uranium is generally regarded as sparingly soluble and hence immobile in the aquatic environment. The solubility product of UO2·xH2O was determined by laser-induced breakdown detection (LIBD). For the given reaction, UO2·xH2O + 4 H+ = U4+ + (2+x) H2O, a value of log Ksp0 = -54.30 ± 1.0 was found (cf. [1]). It results in U(IV) solubilities of about 10-8 M in the near-neutral pH region. On the other hand, hexavalent uranium is much more soluble, in particular if carbonate is present in a water. Calculations with the EQ3/6 geochemical speciation software (thermodynamic data from the NEA data base) were performed for a typical oxic groundwater in equilibrium with air CO2 and varying pH. They yielded uranium solubilities of as much as 10-5 M in the near-neutral pH region. Normally, uranium is regarded as mobile under typical groundwater conditions in geochemistry.
However, this apparently clear picture can be counteracted if colloids come into the play. By our laboratory experiments (cf. [2]) the formation of intrinsic U(IV) colloids in the presence of silicate was demonstrated. The possibility that U(IV) forms colloids can not be ruled out also in the aquatic environment. In the colloidal form U(IV) is “undissolved” in the thermodynamic sense of the word but nevertheless mobile. Second, the high mobility of U(VI) in groundwaters or mine waters can be significantly reduced by scavenging and co-precipitation of U(VI) due to the formation of pseudocolloids with unstable (coagulating) ferrihydrite colloids. Laboratory mine flooding simulation experiments were carried out and it was found that more than 98 % of the U(VI) present was scavenged by such colloids ([3, 4]). It follows that both transport-facilitating effects of colloids on “immobile” contaminants such as U(IV) and transport-impeding effects on “mobile” contaminants such as U(VI) may play a part. It is the geochemical ambiance that decides which effect prevails. A comparison of geochemical cases (uranium mine / nuclear waste depository, oxidizing/reducing, acidic/near-neutral) is given.

[1] Opel K., Weiß S., Hübener S., Zänker H., Bernhard G., Radiochim. Acta 95 (2007) 143-149.
[2] Zänker, H., Opel, K., Weiß, S., Hübener, S., Bernhard, G., 2nd Annual Workshop of the IP FUNMIG, 21.-23.11.2006, Stockholm.
[3] Zänker, H., Richter, W., Hüttig, G., Coll. Surf. A: Physicochem. Eng. Aspects 217 (2003) 21-31.
[4] Ulrich, K.-U., Rossberg, A., Foerstendorf, H., Zänker, H., Scheinost, A., Geochim. Cosmochim. Acta 70 (2006) 5469-5487.

In Germany, the investigated host rocks for nuclear waste disposal in deep geological formations are salt, crystalline rock and argillaceous rock. Natural clay contains organic matter, such as humic acid (HA), which has an influence on the sorption of metal ions. In this work, we studied the uranium(VI) sorption onto the reference clay mineral kaolinite and the natural opalinus clay in absence and presence of HA. The results are compared with our previous studies focused on kaolinite [1].
The influence of the background electrolyte on uranium(VI) sorption onto kaolinite was investigated. The NaClO4 electrolyte previously used [1] was compared with synthetic opalinus clay pore water (I = 0.42 M, pH 7.6) [2]. The experiments show that a lower amount of uranium(VI) is adsorbed onto the clay when the opalinus clay pore water is used. This behavior can be explained with the uranium(VI) speciation. At pH 7.6, the speciation in opalinus clay pore water is dominated by the neutral aquatic Ca2UO2(CO3)3 complex, which has a lower sorption affinity towards kaolinite than the charged UO2(CO3)34-, (UO2)2CO3(OH)3- and UO2(CO3)22- species formed in the NaClO4 system (I = 0.42 M) at pH 7.6.
In the presence of HA (10 mg/L, 50 mg/L), in opalinus clay pore water a lower percental amount of uranium(VI) is adsorbed onto kaolinite. But the concentration of HA has no influence on the amount of sorbed uranium(VI). The reason is that HA has no influence on the uranium(VI) speciation in opalinus clay pore water at pH 7.6, thus, no uranium(VI) humate complexes are formed. The decrease of sorbed uranium(VI) in presence of HA is only due to the competition for surface binding sites between uranium(VI) and HA. These results are in contrast to the results obtained in the NaClO4 system (I = 0.1 M) [1]. There, the speciation of uranium(VI) in NaClO4 changes because aqueous uranium(VI) humate complexes are formed. Due to this and due to a competition for surface binding sites, the percental amount of sorbed uranium(VI) decreases. This effect is increased with increasing HA concentration.
Furhermore, the uranium(VI) sorption onto kaolinite and opalinus clay in opalinus clay pore water was compared. Results show a stronger sorption of uranium(VI) onto kaolinite (2.8 ± 0.2 µg/m²) than onto opalinus clay (0.049 ± 0.002 µg/m²). Since opalinus clay has a higher specific surface area than kaolinite (opalinus clay: Asp = 42 m²/g; kaolinite: Asp = 11.7 m²/g [1]), and contains a higher amount of iron-containing minerals (opalinus clay: 5 wt.% Fe; kaolinite: 0.27 wt.% Fe [1]), which are able to sorb uranium(VI) very well [3], this result is unexpected. To clarify this observation, leaching experiments with opalinus clay applying the two background electrolytes are performed in order to determine the release of ions into the solution in dependence on time and pH and to investigate their influence on the uranium(VI) sorption. We studied the pH dependence of the uranium(VI) sorption onto opalinus clay in absence and presence of HA, and compared this with previous results obtained for kaolinite [1].

[1] A. Křepelová et al., Radiochim. Acta 2007, 94, 825.
[2] F.J. Pearson, PSI Internal Report TM-44-98-07 1998, Paul Scherrer Institute, Villigen, Switzerland.
[3] K. Schmeide et al., Radiochim. Acta 2000, 88, 723.

The surface damage (sputtered atoms, adatoms, surface vacancies) produced by ion impact is determined by random displacement of the atom at impact point. Using the statistics of this damage for multiple ion impacts in 3D kinetic lattice Monte Carlo simulations, the self-organization of nano-scale surface pattern by the competition between damage creation and damage diffusion/annealing is studied. Especially, anisotropic displacement of surface atoms creates ripple formation even sputtering is suppressed. The ripple wavelength follows a power low of fluence and temperature of substrate. Local temperature enhancement of impact points refers also Frenkel-pair and ripples on f.c.c.(110) surface. The direction of ripples depends on the temperature of migration atoms which is corresponding to the experimental result of Ag(110) ion bombardment.

A detailed knowledge of the sorption processes of uranium(VI) onto titanium(IV) dioxide (TiO2) can serve as a model for the elucidation of molecular processes on more complex mineral surfaces. Because of the high stability, low solubility over a wide pH range and the well-known structure of TiO2, sorption studies with U(VI) can be carried out throughout a large range of experimental parameters [1-3].

In this work, we used attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy in an in situ investigation of the sorption processes of U(VI) onto TiO2. A set of highly purified and well characterized TiO2 phases from different origins differing in the ratio of the most stable polymorphs, i.e. anatase and rutile, in specific surface area and in particle size distribution was investigated. Irrespective of the composition of the mineral phase, it was shown that U(VI) mainly forms a similar inner sphere complex, showing an absorption maximum shifted of about 20 cm−1 to lower wavenumbers compared to the aqueous species.

The influence of the aqueous speciation on the sorption process was studied using different concentrations of the actinide ions and at different pH values. The high sensitivity of the in situ ATR FT-IR technique allows the study of U(VI) concentrations down to the lower micromolar range. From these results, it is concluded that only one significant surface U(VI) complex forms in the pH range between 4 and 7, and across a range of aqueous uranyl concentrations. The surface speciation of uranyl therefore involves fewer species than the aqueous speciation in these experimental systems, as is consistent with the findings of a previous study [4].

Furthermore, the capability of a fast scanning of IR spectra makes it feasible to carry out time-resolved experiments of the sorption processes with a time resolution in the sub-minute time range. It is shown that in the early steps of the U(VI) sorption a transient species is formed on the mineral phase showing a clearly red-shifted absorption maximum. After prolonged sorption the IR spectra indicate the formation of a stable surface species which is commonly found on TiO2 phases. These findings give new insights into the surface complex formation of U(VI) on titanium dioxide at a molecular level.

[1] Den Auwer, C., Drot, R., Simoni, E., Conradson, S. D., Gailhanou, M. and de Leon, J. M. (2003) "Grazing incidence XAFS spectroscopy of uranyl sorbed onto TiO2 rutile surfaces." New J. Chem. 27, 648-655.
[2] Wazne, M., Meng, X. G., Korfiatis, G. P. and Christodoulatos, C. (2006) "Carbonate effects on hexavalent uranium removal from water by nanocrystalline titanium dioxide." J. Hazard. Mater. 136, 47-52.
[3] Vandenborre, J., Drot, R. and Simoni, E. (2007) "Interaction mechanisms between uranium(VI) and rutile titanium dioxide: From single crystal to powder." Inorg. Chem. 46, 1291-1296.
[4] Lefèvre, G., Kneppers, J. and Fédoroff, M. (2008) "Sorption of uranyl ions on titanium oxide studied by ATR-IR spectroscopy." J. Colloid Interface Sci. 327, 15-20.

The impact of radioactivity can generate optically active defect centers in minerals. These defects may first affect light absorption, i.e., they may cause radio-coloration or -de-coloration. Second, radio-induced defects may enhance or suppress luminescence emissions of their host minerals. The action of such centers is, for instance, seen in spotted diamond specimens showing green or brown radio-coloration (the latter is typically associated with yellowish-green photoluminescence). Another example is the yellow broad-band luminescence emission of zircon, which is commonly observed in cathodo- and photoluminescence spectra of this mineral. So study whether, and how, natural alpha radiation generates and affects such centers, flat polished diamond and zircon samples were irradiated in a tandem accelerator facility with 8.8 MeV He²⁺ ions, which are the analog of alpha particles generated in the ²¹²Po α-decay (Th decay chain).
Helium ions were found to penetrate 29 μm into diamond and 32 μm into zircon, respectively, which corresponds very well to ranges predicted by Monte Carlo simulations using the SRIM code. Notable pale green coloration of diamond was observed to start at 10¹⁴ to 10¹⁵ He/cm². Spots irradiated with 10¹⁷ He/cm² appeared dark green and were found to show initial amorphization. Green colors transformed to orange-brown through heat-treatment at about 550 °C, which is mainly due to the disappearance of the ∼16,000 cm^-1 GR1 band. The latter process was found to be associated with the appearance of intense green UV-induced photoluminescence. Associated observations include strong volume expansion due to the accumulated radiation-damage, which may result in notable up-doming of radiohaloes. First studies of He-implanted zircon indicated a similar luminescence behavior, with an irradiation-induced broad-band yellow emission at 575 nm. This emission band decreases in intensity in samples that were affected by natural radiation damage prior to the He irradiation experiment.
The observed depth profiles of the luminescence emission intensity in the two minerals correspond to the calculated defect distribution profiles but not to the ionization distribution profiles. This suggests that ionization alone is insufficient to create optically active centers. Additional carbon- (diamond) and oxygen-irradiation experiments (zircon) were done to generate similar structural damage with an elemental species which is already present in the respective host mineral. Observations on these samples are largely similar to those on He-irradiated samples. Consequently, optically active centers are related to structural point defects that are created by atomic knock-ons whereas our observations did not yield independent evidence which suggests that He ions themselves might be optically active species.

DYN3D is a three-dimensional core model for dynamic and depletion calculations in light water reactor cores with quadratic or hexagonal fuel assembly geometry. The neutron kinetic model is based on the solution of the three dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal hydraulic model of the reactor core and the fuel rod model are implemented in the module FLOCAL, which is a part of DYN3D.
The paper gaves an overview on the application possibilities of DYN3D.

We present phase space distributions and multiplicities of K+, K- and phi mesons produced in Ar+KCl reactions at a kinetic beam energy of 1.756 AGeV and measured with the HADES spectrometer. The inverse slope parameters and yields of kaons supplement the systematics of previous measurements. The percentage of K- mesons coming fromphi decay is found to be 18+- 7%.

HADES is a versatile magnetic spectrometer aimed at studying dielectron production in pion, proton and heavy-ion induced collisions. Its main features include a ring imaging gas Cherenkov detector for electron-hadron discrimination, a tracking system consisting of a set of 6 superconducting coils producing a toroidal field and drift chambers and a multiplicity and electron trigger array for additional electron-hadron discrimination and event characterization. A two-stage trigger system enhances events containing electrons. The physics program is focused on the investigation of hadron properties in nuclei and in the hot and dense hadronic matter. The detector system is characterized by an 85% azimuthal coverage over a polar angle interval from 18 to 85 degree, a single electron efficiency of 50% and a vector meson mass resolution of 2.5%. Identification of pions, kaons and protons is achieved combining time-of-flight and energy loss measurements over a large momentum range. This paper describes the main features and the performance of the detector system.

We present the results of a study of charged pion production in 12C + 12C collisions at incident beam energies of 1A GeV and 2A GeV using the HADES spectrometer at GSI. The main emphasis of the HADES program is on the dielectron signal from the early phase of the collision. Here, however, we discuss the data with respect to the emission of charged hadrons, specifically the production of pi+- mesons, which are related to neutral pions representing a dominant contribution to the dielectron yield. We have performed the first large-angular range measurement of the distribution of pi+- mesons for the 12C + 12C collision system covering a fairly large rapidity interval. The pion yields, transverse-mass and angular distributions are compared with calculations done within a transport model, as well as with existing data from other experiments. The anisotropy of pion production is systematically analyzed.

Humic substances influence the speciation and migration behavior of toxic and radiotoxic metal ions, such as actinides, in the environment. Depending on their origin, humic substances contain different amounts of sulfur ranging from 0.1 to 3.6% and 0.5 to 1.43% in soil and aquatic humic substances, respectively [1]. Reduced, intermediately oxidized and highly oxidized sulfur functionalities occur in humic substances [1]. Although sulfur functionalities occur in small concentrations, they can play an important role in the complexation of selected metal ions. Knowledge about the impact of sulfur functionalities on the metal ion complexation by humic substances and their significance compared to oxygen- and nitrogen-containing functional groups helps to improve complexation models for humic substances. Consequently, this contributes to a more reliable geochemical modeling of the interaction processes between humic matter and metal ions in the environment.
In the present work sulfur-containing humic acid (HA) model substances have been synthesized to study the influence of sulfur functionalities on the metal ion complexation by HA. HA type M1-S with different sulfur contents was synthesized from xylose, phenylalanine, glycine, and cysteine and the resulting products were characterized. The identity of the sulfur species was determined by X-ray photoelectron spectroscopy (XPS). XPS results of HA M1-S with 1.94 wt-% sulfur indicate the occurrence of at least two different sulfur species. About 82% of sulfur occurs in form of reduced sulfur species (e.g., thiols, dialkylsulfide and/or disulfides) and about 18% of sulfur is attributed to sulfoxides.
The uranium(VI) complexation of HA with different sulfur contents (0, 1.94 and 3.94 wt-%) has been studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses. Applying the metal ion charge neutralization model [2] comparable complexation constants with a mean value of logβ0.1M = 6.3 ± 0.1 were determined by TRLFS. However, with increasing sulfur content of the HA an increase in the uranium(VI) loading capacities from 26 ± 4 to 37 ± 2% (pH 3.8) was observed. This indicates that with increasing amounts of sulfur functionalities more sites become available for the complexation of uranium(VI) by HA.

Risk assessments predicting the transport of actinides under environmentally relevant conditions require basic knowledge of their solubility, their interaction with complexing ligands, their sorption and redox behavior as well as their ability to form colloids. Under reducing conditions as prevalent in deep underground nuclear waste repositories and in the depth of flooded uranium mines, actinide species occur in lower oxidation states. Both the speciation and the mobility of actinides in aquatic systems strongly depend on their oxidation state. For instance, in contrast to the soluble and mobile uranium(VI), uranium(IV) is much less mobile due to the low solubility of uranium(IV) hydrous oxide (UO2•xH2O(am)). However, in the presence of inorganic and organic ligands also uranium(IV) may become mobile due to formation of soluble complexes. Also the mobility of plutonium depends strongly on the existing oxidation states and the chemical species formed. Thus, the speciation of low-valent actinides in aqueous solution has to be studied to predict their migration behavior in natural environments.
Data for the complexation of uranium(IV) and plutonium(III) with inorganic and organic ligands are scarce or vary strongly. In the present study, the complexation behavior of the model ligands citric acid, succinic acid, mandelic acid and glycolic acid is studied and compared to that of humic acid. These model ligands stand for a variety of organic ligands in aqueous systems. The actinide complexation by model ligands and humic acid is studied applying UV-vis absorption spectroscopy and ultrafiltration, respectively.
The stability constants for 1:1 and 1:2 uranium(IV) citrate complexes of the type MpHqLr were determined with log ß101 = 13.5 ± 0.2 and log ß102 = 25.1 ± 0.2 [1]. This shows a strong interaction between uranium(IV) and the ligand. The uranium(IV) complexation with mandelic and glycolic acid is weaker. Stability constants for 1:1 and 1:2 uranium(IV) ligand complexes of the type MpHqLr were determined with log ß101 = 4.53 ± 0.09 and log ß102 = 8.02 ± 0.13 for mandelate and with log ß101 = 4.71 ± 0.08 and log ß102 = 8.25 ± 0.15 for glycolate (I = 1.0 M). Speciation calculations show that due to complexation with organic ligands the solubility and thus, the mobility of uranium(IV) in aquatic systems is increased.
Also plutonium(III) is strongly complexed by organic ligands and humic acid under environmentally relevant conditions which shows the need for speciation studies of plutonium in aqueous solutions containing various complexing agents.

[1] Schmeide, K., Bernhard, G.: Spectroscopic Study of the Uranium(IV) Complexation by Organic Model Ligands in Aqueous Solution. In: Uranium, Mining and Hydrogeology (Merkel, B.J.; Hasche-Berger, A. eds.), Springer Verlag, Berlin, 591-598 (2008).

A two-photon detector based on intersubband transitions in GaAs/AlGaAs quantum wells operating in the Terahertz regime below the Reststrahlenband is reported. Resonantly enhanced optical nonlinearities enables sensitive quadratic detection at pJ pulse energies. We demonstrate its use in a quadratic autocorrelator for far-infrared picosecond pulses at around 7 THz.

The long-term safety analysis of nuclear waste disposals in clay formations requires detailed knowledge of the interaction of actinides at relevant temperatures (up to 100 °C). It is well known that the migration behaviour of the actinides is strongly influenced by natural organic matter (NOM) from the clay. However, the current thermodynamic database is lacking fundamental data about the temperature-dependent complexation of americium (and its analogue europium) with small organic acids, which are structural similar components of natural organic matter in the clay.

We present our results for the complexation of both Am(III) and Eu(III) with 2-hydroxybenzoic acid (salicylic acid), 1,2,4,5-benzentetracarboxylic acid (pyromellitic acid) and 2,3-dihydroxbutanedioic acid (L-tartaric acid) in the temperature range from 20 to 50°C, at ionic strength of 0.1 mol/l NaClO4 and pH below 6.

For the first time, temperature-dependent UV-Vis spectroscopic measurements with a Liquid Waveguide Capillary Cell were used for complexation investigations. Due to the long optical path length of the capillary cell (up to 2 m) very low americium and europium concentrations can be measured. Thus, the presented absorption measurements were carried out at Am(III) concentrations below 5e-7 mol/l and Eu(III) concentration below 5e-4 mol/l. For all investigated model ligands we observed a slight shift of the absorption maxima of Eu(III) (394 nm) and Am(III) (504 nm) spectra of 0.5 to 2 nm to higher wavelengths due to the complexation.
We first validated the method with europium: at 25°C the determined constants for the 1:1 complexes of europium salicylate, europium pyromellitate and europium L tartrate with logß111=15.4+/-0.06, logß112 = 14.3 +/-0.2, logß111=7.9+/-0.3 respectively, are in good agreement with the literature values [1], [2].
For the americium salicylate system, both a 1:1 complex and a 1:2 complex were observed at pH 4. The stability constants of these complexes are logß111= 15.42+/-0.06 and logß122=30.98+/-0.05 and comparable to the reported ones for the analogous complexes with europium [1]. With increasing temperature, the stability constants for both complex systems increase, indicating an endothermic complexation reaction. The same behaviour is expected for the americium pyromellitate system, where just a 1:1 complex with log ß112=15.03+/-0.1 can be reported until now.

The temperature dependence and the interaction of americium with L-tartrate is presently under investigation. The stability constants and thermodynamic parameters (enthalpy, entropy, Gibbs energy) of all above investigated systems are reported.

[1] Aoyagi, N. et al. Radiochemica Acta, Vol. 92, 2004, 589-593
[2] R. Kulshrestha, S. Sengar, M. Singh, Indian J. of Chemistry 26A, 1987, 940-943

no abstract available

Kinetic 3D lattice Monte-Carlo simulation of ion beam induced surface modification was performed for f.c.c. (100) surface and preliminary Crystal-TCAS calculations of 5keV As+ on Si(001) have been simulated. By KMC, the observed surface patterning was depending on the incidence angle even the direction of ion-induced surface atom displacement is arbitrary next lattice position. Angular dependency of the sputtering yield by the Crystal-TCAS calculation has been studied.

In this paper we introduce an algorithm for the creation of polyhedral approximations for objects represented as strongly connected sets of voxels in three-dimensional binary images. The algorithm generates the convex hull of a given object and modifies the hull afterwards by recursive repetitions of generating convex hulls of subsets of the given voxel set or subsets of the background voxels. The result of this method is a polyhedron which separates object voxels from background voxels. The objects processed by this algorithm and also the background voxel components inside the convex hull of the objects are restricted to have genus 0. The second aim of this paper is to present some improvements to our convex hull algorithm to reduce computation time.

Uranium(VI), is known to be the most stable oxidation state of uranium in oxygenated waters, with the uranyl ion UO22+ forming soluble hydroxo and carbonate complexes [1, 2]. Thermodynamic unstable U(IV) complexes might be formed in oxygenated waters by photoreduction of U(VI) supplied by solar radiation. Although U(VI) photoinduced reduction is reported to occur in acidic solutions, it is prevented at neutral conditions because of structural arrangements resulting from hydrolysis reactions. However, sorbed U(VI) species at the water-mineral interface on particles with semiconducting properties, e.g. TiO2 have shown different redox behavior than solution species [3-5].

TiO2 is the material mostly applied for the investigation of photocatalysis, due to its exceptional optical and electronic properties, chemical stability and low cost. Anatase was found photocatalytically more active than rutile [6]. The mixed sample of 80% antase and 20% rutile Degussa P-25 was investigated for U(VI) photoreduction using laser fluorescence spectroscopy [3, 4]. ATR FT-IR spectroscopy, which was applied to photoreactions of oxalic acid, has not been applied for U(VI), yet.

We investigated the effects of UV-visible light on the sorption processes of U(VI) onto TiO2 by application of in situ ATR FT-IR spectroscopy. Thus, changes of the excitation wavelength and the TiO2 phase, namely anatase, rutile, and a mixture of both (P-25), were considered. Furthermore, the results were compared to photoeffects observed for U(VI) sorption onto ZnO.

From the obtained spectra different photoinduced effects on U(VI) sorption onto different TiO2 phases are derived. Photocatalysis is clearly suggested for the P-25 sample. In contrast, pure anatase and rutile did not show spectral differences for the sorption mechanisms under dark and light conditions. Furthermore, the photoreaction was found to be limited to incident light with wavelengths below 580 nm. The comparison between TiO2 and ZnO evidence a higher photoactivity for TiO2.

1.Guillaumont, R.; Fanghänel, T.; Fuger, J.; Grenthe, I.; Neck, V.; Palmer, D. A.; Rand, M. H., Update on the Chemical Thermodynamics of U, Np, Pu, Am and Tc. Elsevier: Amsterdam, 2003.
2.Müller, K.; Brendler, V.; Foerstendorf, H., Inorganic Chemistry 2008, 47, (21), 10127-10134.
3.Eliet, V.; Bidoglio, G., Environmental Science & Technology 1998, 32, (20), 3155-3161.
4.Selli, E.; Eliet, V.; Spini, M. R.; Bidoglio, G., Environmental Science & Technology 2000, 34, (17), 3742-3748.
5.Amadelli, R.; Maldotti, A.; Sostero, S.; Carassiti, V., Journal of the Chemical Society-Faraday Transactions 1991, 87, (19), 3267-3273.
6.Litter, M. I., Applied Catalysis B-Environmental 1999, 23, (2-3), 89-114.

Neptunium (Np) is one of the most important components of nuclear waste to consider for the long-term safety assessment of nuclear waste repositories and hence, great attention is paid to its geochemistry and migration behavior [1]. Among the various geochemical processes, the migration of actinides in the environment is strongly affected by molecular reactions at the solid-water interface, e.g. sorption onto mineral phases, surface precipitation, and colloid formation [2]. In aqueous solution the pentavalent form dominates the neptunium speciation under a wide range of environmental conditions [1]. Thus, reliable results of Np(V) sorption data and its molecular speciation at the water-mineral interface are crucial to allow an improved modeling of Np migration in the environment. Vibrational spectroscopy is a useful tool for the in situ identification of molecular species in aqueous solution and sorbed onto mineral surfaces [3, 4]. Using attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy, the type of the sorbed species, e.g. inner- and outer-sphere complex, can be elucidated by shifts of the antisymmetric stretching vibration ν3 of the Np=O bond compared to the aqueous species.

In this study, we investigated the Np(V) speciation in aqueous solution and upon sorption onto oxides of titanium, silicon, and zinc at a micromolar concentration level by application of NIR and ATR FT-IR spectroscopy.

The obtained spectra of aqueous 50 µM Np(V) solution confirmed the predominance of the fully hydrated neptunyl(V) species NpO2+ up to pH 7.7 at inert gas atmosphere, excluding atmospheric CO2, as was predicted by the updated NEA thermodynamic database [5]. Upon sorption of 50 µM Np(V) on TiO2 at pH 7.6 at inert gas atmosphere, NpO2+ forms stable surface species. The formation of an inner-sphere complex can be derived from the significant shift of the band representing the antisymmetric stretching vibration ν3 of the NpO2+ ion. Furthermore, since the spectra of the sorption processes show no significant deviations within the pH range from 4 to 7.6, and no indications of aqueous NpO2+ species are obtained, the formation of outer-sphere complexes can be neglected. Additionally, from the on-line monitored measurements it is obvious that only one Np(V) surface species is formed during the sorption experiments.

A comparative in situ ATR FT-IR investigation of Np(V) sorption onto TiO2, SiO2 and ZnO indicates the formation of structurally similar inner-sphere surface complexation. From minor spectral deviations of the ν3 band representing the Np(V) surface species bidentate complexes can be suggested.

For future spectroscopic investigations of neptunyl sorption at the water-mineral interface the present work may provide vibrational reference data for the interpretation of more complex systems relevant for environment.

1.Kaszuba, J. P.; Runde, W. H., Environmental Science & Technology 1999, 33, (24), 4427-4433.
2.O'Day, P. A., Reviews of Geophysics 1999, 37, (2), 249-274.
3.Lefevre, G., Advances in Colloid and Interface Science 2004, 107, (2-3), 109-123.
4.Müller, K.; Brendler, V.; Foerstendorf, H., Inorganic Chemistry 2008, 47, (21), 10127-10134.
5.Guillaumont, R.; Fanghänel, T.; Fuger, J.; Grenthe, I.; Neck, V.; Palmer, D. A.; Rand, M. H., Update on the Chemical Thermodynamics of U, Np, Pu, Am and Tc. Elsevier: Amsterdam, 2003.

Humic acids have a great influence on the migration of actinides and heavy metals. To get a quantitative understanding of the humic acid / actinide interaction on a molecular level, we investigate the complexation behavior of trivalent lanthanides and actinides with different functionalized benzoic acids as model compounds for humic acids. Our primary objective is to determine the temperature dependence of the complexation behavior, because in radioactive waste repositories one can observe elevated temperatures and concerning this matter only few investigations are known.

In this study, we present the reaction of Eu(III) with 2-hydroxybenzoate (salicylate), 2,5-dihydroxybenzoate and 1,2,4,5-benzenetetracarboxylate (pyromellitate), investigated with time-resolved laser-induced fluorescence spectroscopy (TRLFS) at different temperatures (10-50°C).

The Eu pyromellitate complex system shows strong luminescence behavior. The intensity of the 5D0 7F2 transition band increases with increasing ligand concentration. With increasing temperature, the total emission intensity decreases slightly. At lower pH (around 3) a MHL complex species with a stability constant of logK = 3.92 (25°C) could be determined. The lifetime of about 125 µs indicates, according to the equation of Kimura et al. (n(H2O) = 1.07 x (1/t -0.62) [1]), the exclusion of 1 water molecule from the first shell, implying an inner sphere complex with monodentate coordination. At pH around 5, a ML complex species (logK = 4.74, 25°C) was identified. The lifetime of about 135 µs stands for the substitution of 2 water molecules, according to an inner sphere complex with bidentate coordination. The lifetimes remain constant over the determined temperature range, as well as the lifetime of the free Eu3+(aq) ion. With increasing temperature, the stability constants increase, indicating an endothermic complexation reaction. The thermodynamic parameters of the Eu pyromellitate complexes were calculated to be ΔH = 9.4 kJ mol-1, ΔG = 22.3 kJ mol-1, ΔS = 106 J mol-1 K-1 (MHL; 25 °C) and ΔH = 15.2 kJ mol-1, ΔG = 28.1 kJ mol-1, ΔS = 145 J mol-1 K-1 (ML; 25 °C); these values are in good agreement with the literature [2]. The Eu complexes with salicylate and 2,5-dihydroxybenzoate show no luminescence behavior; only static and dynamic quenching is observable. For both ligands, the complex stability constants for a 1 : 1 complex species each could be determined. With increasing temperature, the stability constant also increases in both cases, indicating again an endothermic complexation reaction. The stability constants and thermodynamic parameters of these complexes are reported and compared with those determined by UV-vis spectroscopy with a liquid waveguide capillary cell (LWCC).

[1] T. Kimura, G.R. Choppin, Y. Kato, Z. Yoshida, Radiochim. Acta 72 (1996) 61-64.
[2] G.R. Choppin, E.N. Rizkalla, T.A. El-Ansi, A. Dadgar, J. Coord. Chem. 31 (1994) 297-304.

The calcium-binding protein α-amylase (α-1,4 glucan-4-glucanhydrolase) catalyzes the degradation of starch and glycogen. It is widely distributed in plants, animals, and microorganisms. In saliva and pancreas it is a main enzyme which is built in high amounts. Incorporated heavy metals like actinides firstly come into contact with saliva. In order to explore the origin of the well known toxic effect of these metals we investigate the interaction between UO22+ and Eu3+ (as an inactive analogue for threefold actinides) with the main constituents of saliva like α-amylase.

The influence of UO22+ and Eu3+ on the enzyme activity was tested with the α-amylase assay method by Bernfeld [1]. Both metal ions have a strong inhibition effect even at very low metal to α-amylase ratios. Sorption experiments showed a high binding capacity of α-amylase and that in the sorption maximum (pH 6-7) the protein can bind up to a tenfold molar excess of the metal ions. Both metal ions displace the Ca2+ ion, which is the central metal ion in the protein, even at equimolar amounts. UO22+ and Eu3+ seem to occupy first the Ca2+ binding place and then other potential metal binding sites in the protein. The binding process occurs in a short time, so that after 5 minutes the main metal amount is accumulated by α-amylase.

The UO22+ and Eu3+ α-amylase complexes were investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS) and extended x-ray absorption fine structure (EXAFS) spectroscopy. In case of UO22+ and TRLFS, we observed in the pH range 3-7 a red shift of the peak maxima and two different luminescence lifetimes, indicating the formation of two different UO22+ protein complex types. With EXAFS spectroscopy two different binding types were identified. At equimolar metal to ligand ratio we identified a fourfold coordination of UO22+ with only monodentate binding carbonyl groups. With excess of UO22+ the binding properties changes and higher coordination numbers are observed with indication of monodentate and bidentate binding carbonyl and carboxylate groups. For the Eu3+ α-amylase complex, the luminescence lifetimes show that 2 or 3 water molecules remain in the first coordination sphere. EXAFS measurements points at the presence of monodentate and bidentate coordinated carbonyl or carboxylate groups.

[1] P. Bernfeld, Methods in Enzymology 1(1955) S. 149-158

The 241Am2Zr2O7 phase undergoes a structural transition from pyrochlore to defect fluorite driven by alpha self-irradiation. In an effort to better understand the underlying phenomena of this order-disorder transition, powder X-ray diffraction (PXRD) and X-ray absorption fine-structure (XAFS) spectroscopy experiments were conducted on two samples aged for 40 days (0.02 dpa) and 370 days (0.21 dpa), respectively. While the XAFS data support the phase transition observed by XRD, they reveal different local coordinations of americium and zirconium. The transition occurs through oxygen Frenkel and cation antisite formation. The XAFS, clearly showed that the ZrO polyhedron is stable against irradiation, probably a main factor explaining the excellent resistance to amorphization observed for americium zirconia defect fluorite structures.

The present study aims at modelling the pressure drop of flows across growing cakes of compressible, fibrous materials which may form on the upstream side of containment sump strainers after a loss-of-coolant accident (LOCA). The model developed is based on the coupled solution of a differential equation for the change of the pressure drop in terms of superficial liquid velocity and local porosity of the fibre cake and a material equation that accounts for the compaction pressure dependent cake porosity. Details of its implementation into a general-purpose three-dimensional computational fluid dynamics code (CFD) are given. An extension to this basic model is presented, which simulates the time dependent clogging of the fibre cake due to capturing of suspended particles as they pass trough the cake. The extended model relies on empirical relations which model the change of pressure drop and removal efficiency in terms of particle deposit in the fibre cake.

Aufgabe der vorliegenden Erfindung ist es, eine Anordnung zur Röntgen-Computertomographie anzugeben, die ohne einen axialen Versatz zwischen Brennfleckbahn und Röntgendetektorbogen auskommt und dennoch einen im Sinne der tomographischen Bildrekonstruktion vollständigen Projektionsdatensatz liefert. Gelöst wurde die Aufgabe durch die Kombination zweier Target-Detektor-Einheiten, die mit einem geringen axialen Versatz in zwei Ebenen angeordnet sind.
Der hauptsächliche Vorteil der beschriebenen Anordnung zur Röntgen-Computertomographie mit zwei Tomographieebenen besteht darin, dass Target- und Röntgendetektorbogen jeder Einheit vollständig innerhalb einer axialen Ebene angeordnet werden können und durch die Kombination beider Datensätze eine vollständige tomographische Datenaufnahme von einer axialen Ebene des Untersuchungsobjektes möglich ist. Damit wird eine höchstmögliche Bildqualität und axiale Ortsauflösung erreicht. Die Anordnung kann insbesondere für Elektronenstrahltomographen oder andere Computertomographie-Scanner mit feststehendem Quell-Detektorverbund angewendet werden. Besonders vorteilhaft ist sie für sich axial bewegende Objekte, zum Beispiel Rohrströmungen, da dort die Bewegung zwischen den Ebenen dem Untersuchungsobjekt inhärent ist und somit ohne zusätzlichen Aufwand sehr schnelle Prozesse mit hoher lateraler und axialer Ortsauflösung sowie hoher zeitlicher Auflösung abgebildet werden können.

Presentation about in-beam PET in the context of IGRT

Microbial diversity in xenobiotics polluted soils was investigated by the 16S rRNA gene approach. The samples studied were collected from the vicinity of a Pb-Zn (KCM) smelter and pesticides manufacturing plant situated in South Bulgaria. ICP-MS analyses showed that some metals such as Zn, Pb, Cu, Cd, As, Ni and Hg exceeded in high extent the maximum permission standard. Two 16S rRNA gene clone banks were constructed – KCM-B and KCM-C. The main part of the studied microbial communities consisted of members of Proteobacteria (and ) - 42 % for KCM-B and 72 % for the KCM-C sample. In both soils Proteobacteria were registered in equal content of 28 %. Acidobacteria, Holophaga, Cytophaga/Flavo-bacterium/Bacteroides, AD1 and other novel divisions were represented as well.
Most of the identified bacterial groups were closely related to bacteria inhabiting other extreme environments such as uranium mill-tailings, sulphide mines, mine drainages and dumps, metal-rich sediments, soils contaminated with polychlorinated hydrocarbons, deserts, and Antarctic permafrost. Some of the closest relatives of several identified groups were xenobiotics-degrading bacteria inhabiting a hexane-degrading biofilm, 1,2-dichloropropan transforming bacteria and phosphorous eliminating bacteria.

Magnetron-plasma enhanced chemical vapour deposition (PECVD) is a process tool which allows the deposition of plasma polymer coatings at process pressures below 1 Pa. The striking features of this technology are the relatively easy realisation of large area deposition as well as the possibility of the combination with sputtering processes for multilayer coating designs. SiOxCy coatings were deposited on polymer film in a roll-to-roll deposition machine. Dynamic deposition rates as high as 120 nm*m/min were achieved. The process was set up with both the monomer hexamethyldisiloxane and the monomer tetraethylorthosilicate (TEOS) and with mixtures thereof. The coatings were analysed by Fourier transform infrared spectroscopy. This method identifies the existence of different types of Si–O bonding in the layer. The results show how the layer properties are linked to the plasma parameters of the deposition process. The properties were compared to sputtered SiO2 and to layers obtained by other PECVD processes. Elastic recoil detection analysis (ERDA) was used in order to determine the composition of the samples. Both IR spectroscopy and ERDA revealed that the usage of TEOS provided more SiO2-like layers. The process was applied to the deposition of optical multilayer coating in a roll-to-roll coating system.

Photo-nuclear reactions were investigated using a high power table-top laser. The laser system at the University of Jena (I ~ 3-5×1019 W cm-2) produced hard bremsstrahlung photons (kT~2.9 MeV) via a laser-gas interaction which served to induce (γ, p) and (γ, n) reactions in Mg, Ti, Zn and Mo isotopes. Several (γ, p) decay channels were identified using nuclear activation analysis to determine their integral reaction yields. As the laser-generated bremsstrahlung spectra stretches over the energy regime dominated by the giant dipole resonance (GDR), these yield measurements were used in conjunction with theoretical estimates of the resonance energies Eres and their widths Γres to derive the integral reaction cross-section σint(γ,p) for 25Mn, 48, 49Ti, 68Zn and 97, 98Mo isotopes for the first time. This study enabled the determination of the previously unknown cross-section ratios for these isotopes. The experiments were supported by extensive model calculations (Empire) and the results were compared to the Thomas-Reiche-Kuhn (TRK) dipole sum rule as well as to the experimental data in neighboring isotopes and good agreement was observed. The Coulomb barrier and the neutron excess strongly influence the ratios for increasing target proton and neutron numbers.

We investigated the possibility to trigger real-scale lightning using ionized filaments generated by ultrashort laser pulses in the atmosphere. Under conditions of high electric field during two thunderstorms, we observed a statistically significant number of electric events synchronized with the laser pulses, at the location of the filaments. This observation suggests that corona discharges may have been triggered by filaments.

We present a high-resolution gamma-ray computed tomography (CT) system for the measurement of cross-sectional time-averaged void distributions in thermo hydraulic facilities. The system has been carefully designed for harsh operating conditions, such as varying temperature fields and strong magnetic fields, typically produced by thermal hydraulic test loops with direct electric bundle heating. Measurements are non invasive, thus the two-phase flow in the test section is not influenced. The gamma-ray CT system consists of a collimated 137Cs isotopic source, a gamma radiation detector arc including 320 single elements, a pulse processing unit and a thermal stabilisation unit. The spatial resolution of the CT system is about 2 mm in plane. Recently, the thermal design of the detector arc is improved to secure maintenance of constant temperature of thermally sensitive components under changing environmental conditions. This turned out to be a key issue for achieving accurate quantitative measurements. First results of laboratory measurements on a bundle mock-up with this improved system are presented.

The basics of quantum mechanical brachistochrones are briefly sketched for Hermitian systems as well as for PT-symmetric systems --- as the latter have been recently proposed by Bender, Brody, Jones and Meister (BBJM) in [C. M. Bender et al, Phys. Rev. Lett. 98, 040403 (2007)]. Using a mainly geometric approach, the hidden new features of this PT-symmetric brachsistochrone with its close relation to non-diagonalizable operator realizations with non-trivial Jordan block structures and spectral singularities (spectral exceptional points) are discussed. Furthermore the Naimark dilation technique as basic tool for an extension toward possible experimental implementations is explained. The remarkable links to wormhole-type setups and entangled states (Einstein's 'spooky action') are highlighted and sketched geometrically. The talk is mainly based on [Phys. Rev. Lett. 101, 230404 (2008)].

Driven by the progress in accelerator mass spectrometry (AMS) and its spreading application within geosciences, the number of samples with low isotopic ratios will increase. Therefore, we have examined the linearity of ¹⁰Be/⁹Be as a function of isotope ratio by distributing three secondary standards (dilutions of NIST4325: 10^-12-10^-14) to nine AMS labs. The problem of low ratio samples is even more crucial for ³⁶Cl. Thus, we have prepared large quantities of three ³⁶Cl/Cl solutions from a certified ³⁶Cl activity (NIST4943) by dilution with NaCl. AgCl precipitated from these solutions (10^-11-10^-13) has been distributed to nine AMS labs. We are still awaiting some final results, but first results from eight labs for each nuclide show that these interlaboratory exercises are very valuable, as they show maximum differences between individual AMS labs up to 35% for 10Be, and 25% for ³⁶Cl, respectively.
Our data indicate that actual ³⁶Cl measurements at LLNL, PRIME Lab and ANU can differ by more than 10%. The implications of this for ³⁶Cl in-situ production rates, determined earlier at these facilities, cannot be ignored. Some, although not all, of the current disagreement concerning ³⁶Cl production rates may result from these discrepancies. However, we are assuming that our new data at the 10^-12-10^-13 level are still representative for earlier measurements of in-situ samples at that level.
This work was partially funded by CRONUS-EU (Marie-Curie Action, 6^th FP #511927).

The analysis of pristine and functionalized carbon nanotubes by X-ray spectromicroscopy was demonstrated. It was shown that both the generation of COOH groups due to functionalization and the reaction of these groups with hexavalent uranium (surface complexation) influenses the NEXAFS spectra. The method may become a promising tool for "mapping" chemical properties such as the presence or absence of chemical elements or the type of binding between these elements on the surface of carbon nanotubes.

For up-to-date safety analyses and lifetime assessments of nuclear power plants (NPPs) fracture mechanical based methods are indispensable. When two Swiss NPPs were planned in the 1970s, no standards existed concerning the geometry or testing of pre-cracked Charpy-V-size surveillance specimens. Therefore, the guideline HSK-AN-425 was drafted for fracture toughness evaluation by dynamic testing. Before becoming a Swiss standard it is to be thoroughly checked for potential pitfalls. Furthermore, it has to be verified that surveillance specimens of those NPPs with shorter cracks than recommended in present standards are eligible for fracture mechanics assessment.

Experiments were performed on unirradiated commercial NPP steel 22NiMoCr3-7.
Quasi-static Master Curve (MC) reference temperature T0 were evaluated according to ASTM E1921 on Charpy-size (width B=0.4T, 1T=1 inch=25.4mm) single edge bend (SE(B)) specimens with crack lengths of 3 mm and 5 mm as well as 1T-C(T) specimens. Furthermore, transferability of surveillance specimen results to heavy-walled structures was checked with SE(B) specimens of B=0.4T, 0.8T, 1.6T and 3.2T. Dynamic MC results were retrieved from instrumented impact tests performed at 1.2 to 2.4 m/s in which T0 was calculated according to HSK-AN-425 and also by a modified ASTM 1921 method. Quasi-static J resistance curves were obtained according to standards ASTM E1820, ISO12135 and ESIS-P2.

In quasi-static MC tests it could be demonstrated that SE(B) specimens with 3 mm and 5 mm fatigue cracks yield the same T0 of ca. -80°C. Thus, surveillance 0.4T-SE(B) specimens with 3 mm crack length may be used for safety assessment without further modifications. The transferability of small-scale results to structural behaviour was proven. T0 obtained from 1T-C(T) specimens is 15K above T0 from 0.4T-SE(B) specimens.

The dynamic MC T0 (v=2.4m/s) is nearly equal for 0.4T-SE(B) specimens of both crack lengths but is ca. 80K above the quasi-static T0.

Small surveillance specimens do not yield valid quasi-static J resistance curve crack initiation values as requirements based on size unnecessarily invalidate all of the results. The idea of using a size criterion to limit J values should be re-evaluated. Ductile crack initiation values are highly dependent on the evaluation standard used. Ordered from highest to lowest, JIc(E1820) > J0.2BL(ISO 12135) > J0.2(ESIS-P2) > Ji(stretch zone width, ISO 12135). Ji is said to be a physically sound crack initiation value but numerous problems arise in stretch zone width determination. It is often not traceable throughout the whole crack front, affected by subjectivity and intricate for irradiated material.

I will introduce the free electron laser at the Forschungszentrum Dresden-Rossendorf, which covers a wavelength range between 3 and 200 micrometers with picosecond pulses. Then I will discuss a few experiments which focus on temporal and spatial resolution, respectively. The former refers to pump-probe experiments on semiconductor quantum structures and the latter to near-field spectro-microscopy on ferroelectrics.

It is generally believed that the 1.5 um Er luminescence is enhanced by transferring energy from Si nanocrystals to the nearest Er3+ ions in Er-doped Si-rich SiO2 layers during optical pumping. Here, the influence of Ge nanocrystals instead of excess Si in the same environment is studied using electroluminescence technique on metal-oxide-semiconductor structures. An increase of the 400 nm electroluminescence intensity with a concomitant reduction of the Er-related emission is observed. This is explained in the light of an inverse energy transfer process from Er3+ to the Ge-related oxygen-deficiency centers.

One of the main challenging tasks in the prospective technology is the buckling suppression of the 3C-SiC film due to the melting and solidification process and the stress relief as a consequence of the short time Si melting during the Flash Lamp Annealing. To overcome this effect and to stabilize a flat surface morphology an alternative i-FlASiC process was developed. This work refers to the influence of the layer stack modifications by doping and meltstop formation by ion implantation on the wafer buckling. The samples were studied by transmission electron microscopy, high resolution x-ray diffraction and infrared ellipsometry. The aim was to optimize the doping and flash lamp annealing conditions in relation to the i-FLASiC layer stack modification.

The reducing properties of humic substances (humic acid (HA) and fulvic acid (FA)) of varying functionality towards Np(V) have been studied under anaerobic conditions between pH 3.5 and pH 9.0 in batch experiments. For Np redox speciation in solution solvent extraction, NIR absorption spectroscopy and ultrafiltration were applied. The reduction rate varied with type of humic substances, solution pH, HA to Np concentration ratio, and equilibration time. In comparison to natural humic substances, synthetic HA with designed redox properties lead to a stronger reduction of Np(V) to Np(IV). The reducing capacities of humic substances towards Np(V) could be correlated to their phenolic/acidic OH group content, which includes both hydroquinone-like moieties and non-quinonoid phenols. By applying a synthetic HA with blocked phenolic/acidic OH groups, the dominance of phenolic/acidic OH groups as the redox-active moieties of humic substances was verified.
The Np(IV) formed in the course of the experiments is predominantly humic colloid-bound. Np(IV) oxo/hydroxide colloids, that might be formed in addition, are stabilized by adsorbed humic substances. The remaining Np(V) occurs as NpO₂ ⁺ ion or Np(V) humate depending on pH. The ability of synthetic HA to effectively maintain Np in the tetravalent state during complexation experiments could be shown.

Available experimental results indicate that the addition of Cr to Fe and steels significantly influences the response of Fe-Cr alloys and ferritic/martensitic high-Cr steels to neutron irradiation. A level of 9 at% Cr is of particular interest because this composition is close to the boundary of the Fe-Cr miscibility gap. Furthermore, it corresponds to the composition of several candidate steels for application in nuclear technology. However, experimental evidence has been incomplete so far. The reported study by means of small-angle neutron scattering is devoted to the effect of neutron irradiation at 300°C up to fluences of 0.6 and 1.5 dpa on the microstructure of an Fe-9at%Cr alloy. We have observed a pronounced irradiation-induced increase of scattering cross-sections for both magnetic and nuclear scattering. Bimodal size distributions of irradiation-induced defect-solute clusters have been reconstructed. The restrictions on the composition of these clusters have been discussed in terms of the scattering contrast. We have found that vacancy clusters and alpha’-particles alone cannot explain the full set of experimental findings. The remaining inconsistency can be solved by taking into account a contribution of impurity carbon.