Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The production of beams with low emittance as well as high average current is one of the key techniques for future electron accelerators and next generation light sources. The superconducting radio-frequency photo electron source (SRF gun) has the potential to fulfill the requirements for these new accelerators. The presentation will give an introduction and overview of this type of modern electron injector. The main issues such as niobium cavity design and fabrication, cryomodule, radio-frequency system, photocathodes, drive laser will be discussed. The status of the various R&D project for SRF guns will be presented, and a comparison to alternative high-current injector concepts like DC photo guns and low-frequency, normal-conducting RF guns will be given.

Moraines dated north of Vatnajökull by cosmogenic surface exposure dating show that the Icelandic Ice cap (IIS) was less extended during the Younger Dryas than previously suggested. The data imply that this glacial advance was more complex and restricted in some glacial valleys in NE Iceland. While the IIS margins are relatively well constrained offshore by marine or coastal evidences, little is known about their onshore characteristics and rates of recession during the warmer Holocene periods. This is especially the case in the NE of Iceland where volcanic activity and major outburst floods (jökulhlaups) have removed a large amount of morphological evidences of past ice margins. Our study aimed at filling this chronological gap of the IIS inland during the late Quaternary deglaciation by dating past preserved ice margins using ³⁶Cl and ³He cosmogenic nuclides.
We studied moraines and outwash located 44 km, 48 km and 60 km north of Vatnajökull, between the Jökulsà à Fjöllum and Jökulsà à Brú, the main northern glacial river systems draining the icecap. Preliminary ³⁶Cl ages of the northernmost moraine at Skessugarður, 60 km north of present-day IIS and 65 km away from the coastline, indicate that the minimum exposure ages derived from Ca-rich plagioclases range from 11.0 + 1.2 ka to 13.4 + 1.4 ka with an average at 12.2 + 1.0 ka (+1 sigma, n=6), using the local Icelandic production rates for Ca spallation of Licciardi et al. (2008). These ages are close to the Younger Dryas at a time when the Icelandic Ice Sheet is thought to have re-advanced further north toward the coastline. Overall, our results call for a Revision of our understanding of the IIS deglaciation history and provide new tie-points for the calibration of the IIS models.
References: Licciardi et al., EPSL 267 (2008) 365–377.

The mechanism of selenium(IV) uptake by maghemite was investigated on both the macroscopic and the molecular level. Maghemite nanoparticles exhibited fast adsorption kinetics toward selenium(IV). Batch experiments showed a decreased sorption with increasing pH (3.5-11).
Ionic strength variations (0.01 to 0.1 M NaCl) had no significant influence on selenium(IV) uptake. Electrophoretic mobility measurements revealed a significant shift toward lower values of the isoelectric point of maghemite upon selenium(IV) uptake, suggesting the formation of inner-sphere surface complexes. At the molecular level, using X-ray Absorption Fine-Structure Spectroscopy (EXAFS), the formation of both bidentate binuclear corner-sharing (C-2) and bidentate mononuclear edge-sharing (E-1) inner-sphere surface complexes was observed, with a trend toward solely E-1 complexes at high pH. The absence of a tridentate surface complex as observed for arsenic(III) and antimonite(III) might be due to the relatively small size of the (SeO3)-O-IV unit. These new spectroscopic results can be implemented in reactive transport models to improve the prediction of selenium migration behavior in the environment as well as its monitoring through its interaction with maghemite or maghemite layers at the surface of magnetite. Due to its chemical stability even at low pH and its magnetization properties allowing magnetic separation, maghemite is a promising sorbing phase for the treatment of Se polluted waters.

Erläuterung des Prinzips der Laserprotonenbeschleunigung und Präsentation der Experimente des TNSA Beschleunigungsmechanismus unter Verwendung ultrakurzer Laserpusle. Weiterhin wird die Anwendung der erzeugten Protonenpulse für strahlenbioloigsche Untersuchnungen vorgestellt.

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

he generalized Breit-Wheeler process, i.e. the emission of $e^+e^-$ pairs off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g.\ laser) wave field, is analyzed. We show that the production probability is determined by the interplay of two dynamical effects. The first one is related to the shape and duration of the pulse and the second one is the non-linear dynamics of the interaction of $e^\pm$ with the strong electromagnetic field. The first effect manifests itself most clearly in the weak-field regime, where the small field intensity is compensated by the rapid variation of the electromagnetic field in a limited space-time region, which intensifies the few-photon events and can enhance the production probability by orders of magnitude compared to an infinitely long pulse. Therefore, short pulses may be considered as a powerful amplifier. The non-linear dynamics in the multi-photon Breit-Wheeler regime plays a decisive role at large field intensities, where effects of the pulse shape and duration are less important. In the transition regime, both effects must be taken into account simultaneously. We provide suitable expressions for the $e^+e^-$ production probability for kinematic regions which can be used in transport codes.

Solutions of a kinetic equation are investigated which describe, on a nonperturbative basis, the vacuum creation of quasiparticle electron-positron pairs due to a strong laser field. The dependence of the quasiparticle electron (positron) distribution function and the particle number density is explored in a wide range of the laser radiation parameters, i.e., the wavelength \lambda and amplitude of electric field strength E_0. Three domains are found: the domain of vacuum polarization effects where the density of the e-e+ pairs is small (the "calm valley"), and two accumulation domains in which the production rate of the e-e+ pairs is strongly increased and the e-e+ pair density can reach a significant value (the short wave length domain and the strong field one). In particular, the obtained results point to a complicated short-distance electromagnetic structure of the physical vacuum in the domain of short wavelengths \lambda \lessim \lambda_{acc} = \pi/m. For moderately strong fields E_0 \lesssim E_c=m^2/e, the accumulation regime can be realized where a plasma with a high density of e-e+ quasiparticles can be achieved. In this domain of the field strengths and in the whole investigated range of wavelengths, an observation of the dynamical Schwinger effect can be facilitated.

We have investigated elastic properties of the spin-ice materials Dy₂Ti₂O₇ (DTO) and Ho₂Ti₂O₇ (HTO) for a wide range of temperature and magnetic field. Our studies of the sound characteristics for several acoustic modes evidence a renormalization of the sound velocity and the sound attenuation due to phase transformations at applied magnetic field as well as an interaction with low-energy magnetic excitations (topological defects). The most prominent anomalies are quasi-periodic peaks in the sound velocity and in the sound attenuation observed in DTO due to non-equilibrium processes arising in the external magnetic field. These results were analyzed theoretically using exchange-striction coupling, which shows a good agreement between theory and experiment. The obtained results at high magnetic fields exhibit some pronounced anomalies around 50 T for both compounds. Our calculations including crystal-electric field effects show satisfactory agreement with experiment.

CrVO₄ and CrPO₄ both adopt the same structure type. They can be well described as S=3/2 Heisenberg spin chains with predominant nearest-neighbour only spin exchange interaction. We show here an in-depth investigation into the magnetic structures of both compounds which is complimented by magnetic property measurements. Wherein, we’ve shown that both compounds exhibit a high field phase transition into an unknown state.

The temperature dependence of the spin susceptibilities of S=1, 3/2, 2, 5/2 and 7/2 Heisenberg nearest-neighbor antiferromagnetic 1D spin chains was simulated via Quantum Monte Carlo calculations, within the temperature range of 0.005 ≤ T⋆ ≤ 100 and fitted to Padé approximations with deviations between the simulated and fitted data of the same order of magnitude or smaller than the Quantum Monte Carlo error. To demonstrate the practicality of our theoretical findings, we successfully compared them with the well known 1D chain compound TMMC (d⁵, S=5/2) and the new S=1 Heisenberg spin chain NiTa2O6.

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Accelerator Mass Spectrometry (AMS) provides the highest sensitivity for measurements of long-lived radionuclides with half-lives in the order of million years. We apply this method to search for live supernova (SN)-produced radionuclides on Earth.

The first indication of a SN close-by to the solar system was published by Knie et al. in 2004. AMS measurements of a ferromanganese crust from the Pacific Ocean showed an excess of ⁶⁰Fe corresponding to a time some 2 Myr ago. We have obtained two deep-sea sediment cores from the Indian Ocean, which provide a better time resolution due to higher accumulation rates. We use AMS for measuring concentrations of the long-lived radionuclides ²⁶Al, ⁵³Mn and ⁶⁰Fe in these sediment cores with high time resolution. All three radionuclides, with half-lives between 0.7 and 3.7 Myr, are produced in the late burning phases and during a supernova explosion of a massive star and are ejected into the interstellar medium in the explosion. In contrast to ⁶⁰Fe, which is not produced in-situ on Earth, cosmogenic production of ²⁶Al and ⁵³Mn in the atmosphere and in-situ adds to a potential extraterrestrial signal. Therefore, accurate data are required for these radionuclides. The cosmogenic isotope ¹⁰Be, produced from cosmic rays in the Earth’s atmosphere, is analysed for dating purposes.

We will present our first AMS measurement results for ¹⁰Be (DREAMS facility, Germany) and ²⁶Al (VERA, Austria) and will show that, in addition to ¹⁰Be, ²⁶Al might be a valuable isotope for dating of deep-sea sediment cores for the past few million years.

The valence-fluctuating Eu systems EuX2Si2, with X being the transition metal Co, Ir, or Rh, show different types of ground states, strongly depending on X. The instability of the Eu 4f shell underlies this phenomenon and leads among other effects to different valence states ranging from Eu2+ over mixed valence and intermediate valence behavior to Eu3+ [1]. Investigations on the structure and the magnetic behavior of EuCo2Si2, EuIr2Si2, and EuRh2Si2 have revealed their Eu valence. Further experiments on specific heat and resistivity gave insights to magnetic ordering, electronic correlations, and possible valence fluctuations. We report about a systematic de Haas-van Alphen study on the Fermi-surface development of the EuX2Si2 compounds in magnetic fields up to 35 T. High-quality single crystals were available for the first time. We will focus on the Fermi-surface topology obtained by angle dependent measurements and discuss a comparison to band-structure calculations .

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Three complexes of Mn(III) with "scorpionate" type ligands have been investigated by a variety of physical techniques. The complexes are Tp₂Mn]SbF₆ (1), [Tp₂*Mn]-SbF₆ (2), and [{PhB(MeIm)₃}₂Mn₃ ^- = phenyltris(3-methylimidazol-2-yl)borate anion. The crystal structure of 3a is reported; the structures of 1 and 2 have been previously reported, but were reconfirmed in this work. The synthesis and characterization of [{PhB(MeIm)₃}₂Mn]Cl (3b) are also described. These complexes are of interest in that, in contrast to many hexacoordinate (pseudo-octahedral) complexes of Mn(III), they exhibit a low-spin (triplet) ground state, rather than the high-spin (quintet) ground state. Solid-state electronic absorption spectroscopy, SQUID magnetometry, and high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy were applied. HFEPR, in particular, was useful in characterizing the S = 1 spin Hamiltonian parameters for complex 1, D = +19.97(1), E = 0.42(2) cm^-1, and for 2, D = +15.89(2), E = 0.04(1) cm^-1. In addition, frequency domain Fourier-transform THz-EPR spectroscopy, using coherent synchrotron radiation, was applied to 1 only and gave results in good agreement with HFEPR. Variable-temperature dc magnetic susceptibility measurements of 1 and 2 were also in good agreement with the HFEPR results. This magnitude of zero-field splitting (zfs) is over 4 times larger than that in comparable hexacoordinate Mn(III) systems with S = 2 ground states. Complexes 3a and 3b (i.e., regardless of counteranion) have a yet much larger magnitude zfs, which may be the result of unquenched orbital angular momentum so that the spin Hamiltonian model is not appropriate. The triplet ground state is rationalized in each complex by ligand-field theory (LFT) and by quantum chemistry theory, both density functional theory and unrestricted Hartree-Fock methods. This analysis also shows that spin-crossover behavior is not thermally accessible for these complexes as solids. The donor properties of the three different scorpionate ligands were further characterized using the LFT model that suggests that the tris(carbene)borate is a strong sigma-donor with little or no pi-bonding.

In biomedicine, magnetic nanoparticles provide some attractive possibilities because they possess peculiar physical properties that permit their use in a wide range of applications. The concept of magnetic guidance basically spans from drug delivery and hyperthermia treatment of tumours, to tissue engineering, such as magneto-mechanical stimulation/activation of cell constructs and mechanosensitive ion channels, magnetic cell-seeding procedures, and controlled cell proliferation and differentiation. Accordingly, the aim of this study was to develop fully biodegradable and magnetic nanocomposite substrates for bone tissue engineering by embedding iron-doped hydroxyapatite (FeHA) nanoparticles in a poly(epsilon-caprolactone) (PCL) matrix. X-ray diffraction analyses enabled the demonstration that the phase composition and crystallinity of the magnetic FeHA were not affected by the process used to develop the nanocomposite substrates. The mechanical characterization performed through small punch tests has evidenced that inclusion of 10 per cent by weight of FeHA would represent an effective reinforcement. The inclusion of nanoparticles also improves the hydrophilicity of the substrates as evidenced by the lower values of water contact angle in comparison with those of neat PCL. The results from magnetic measurements confirmed the superparamagnetic character of the nanocomposite substrates, indicated by a very low coercive field, a saturation magnetization strictly proportional to the FeHA content and a strong history dependence in temperature sweeps. Regarding the biological performances, confocal laser scanning microscopy and AlamarBlue assay have provided qualitative and quantitative information on human mesenchymal stem cell adhesion and viability/proliferation, respectively, whereas the obtained ALP/DNA values have shown the ability of the nanocomposite substrates to support osteogenic differentiation.

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A ⁹Be-solution has been chemically prepared from phenakite (Be₂SiO₄) mineral grains as commercial ⁹Be-solutions are too high in long-lived ¹⁰Be. The solution is intended to be used as a carrier for radiochemical separation of ¹⁰Be to be measured by accelerator mass spectrometry (AMS). Thus, accurate data of the ⁹Be-concentration of this solution is essential to guarantee for high-accuracy ¹⁰Be data in the future. After devastating preliminary results (~8% standard deviation), eight laboratories finally produced twelve individual results by four different analytical methods. A certain lab and method bias might be identified by sophisticated statistical evaluation. Some laboratories also (grossly) underestimate their uncertainties. Thus, the simple weighted mean of this round-robin exercise needed to be corrected by introducing additional allowances (Paule-Mandel-approach). The final result has been calculated to (2246 ± 11) µg ⁹Be/(g solution) with a reasonably low weighted standard deviation of 0.49%. The maximum deviation of a single lab value from the weighted mean is 2.4% when removing one Grubbs outlier (11% off from the mean) from the data set. As ¹⁰Be-data, which is usually calculated from measured ¹⁰Be/⁹Be by AMS and stable ⁹Be, cannot be more accurate than the determined ⁹Be-concentration, it seems highly advisable to establish or improve quality assurance by having self-made carrier-solutions analysed at more than a single lab and regularly taking part in round-robin exercises.

The structure, the optical and the mechanical properties of carbon: vanadium nanocomposite thin films (∼1 at.% to 48 at.% V) grown by direct current magnetron sputtering at 110 °C are investigated using X-ray diffraction, Raman spectroscopy, transmission electron microscopy, spectroscopic ellipsometry, and nano-indentation. At all compositions a phase separation into cubic vanadium carbide, VCx, (x ≤ 1) and carbon is observed, the structure of both phases changing continuously with the vanadium content. The film microstructure consists of statistically distributed spherical VCx particles in a carbon matrix at V concentrations of up to about 35 at.%, and at higher V concentrations of elongated, dendrite-like VCx nanocrystallites, which are separated by a carbon tissue phase. The microstructure hints to a transition from purely repeated nucleation dominated growth to a regime with competing repeated nucleation and surface diffusion. The optical properties are controlled by the phase composition of the films. The hardness is nearly independent of the composition, thus enabling the independent tuning of the absorption behavior at constant hardness.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was used to study the speciation of uranium(VI) at very alkaline pH (11–13), at room temperature and in the absence of CO₂. In this case, at pH = 11, two different fluorescence lifetimes appeared, which were attributed to the species UO₂(OH)₃ ⁻ and (UO₂)₃(OH)₇ ⁻. At pH = 13, no fluorescence was detected, indicating that the predominant species, UO₂(OH)₄ ²⁻, is not fluorescent. At pH = 12, the lifetime obtained is attributed to the predominant species UO₂(OH)₃ ⁻.

Because of the absence of fluorescence of the UO₂(OH)₄ ²⁻ species at room temperature, measurements at 10 K were made, obtaining two different lifetimes in the pH range between 12 and 13.5, indicating the presence of two different species: UO₂(OH)₃ ⁻ and UO₂(OH)₄ ²⁻. The difference between the lifetimes allowed the calculation of the contribution of each species to the total fluorescence signal intensity.

From the experiments carried out in the presence of hydrogen peroxide, it was observed that hydrogen peroxide produces a quenching effect to the fluorescence of the uranium species. At pH 12 the quenching is static, which points to the formation of a non-fluorescent complex between U(VI) and hydrogen peroxide. Using the Stern–Volmer equation for static quenching, the equilibrium formation constant of the first species, UO₂O₂(OH)₂ ²⁻, was calculated to be logK⁰ = 28.7 ± 0.4, which is similar to the one determined using UV–Visible spectrometry, 28.1 ± 0.2 Meca et al. (2011).

Spin polarized currents can exert a so-called spin-transfer torque to the magnetic moment of a ferromagnetic layer. One application of this phenomenon is the spin torque nano-oscillator (typically an MgO-based magnetic tunnel junction (MTJ)) which can act as a tunable microwave emission source. However, a more detailed understanding of the spin-torque physics is needed. For example, the spin torque bias dependence of the two spin torque components (in-plane and fieldlike) is still widely discussed in the community [1]. We present results for MgO-MTJs obtained by thermally excited ferromagnetic resonance (TE-FMR). With the help of TE-FMR, the bias dependence of the two spin-transfer torques can be determined from the peak position and linewidth [2]. Microwave measurements were carried out in the frequency range of 1-9 GHz at positive and negative magnetic fields and for different dc current values. Analyzing this data, we could separate the in-plane and field-like spin torque components and determine their bias dependence.

[1] M. H. Jung et al., PRB 81, 134419 (2010).
[2] A. Deac et al., Nature Phys. 4, 803 (2008).

A Mineral Liberation Analyzer (MLA) is a scanning electron microscope, delivering quantitative data on mineralogy and microfabric as well as high resolution spatially resolved mineralogical composition images of rock specimen and particle perpetrates (usually grain mounts). MLA images can be processed to extract 2D information, both compositional (modal mineral composition) and microstructural (mineral associations within a particle, average particle diameter distribution, average grain diameter distribution, etc.). Unfortunately, the available software does not fully take into account the limitations of the actual information available: data are collected over a surface while information would actually be required over a volume; and most of them are actually relative, i.e. compositional. Moreover, there is virtually no statistical method or software devised to process data sets of this kind. This contribution presents this kind of data, their particularities and problems, and provides avenues of discussion towards a solution to these issues.

The usage of compact fluorescent lamps (CFLs) increased in the last years. The gas discharge lamps occupy 22% of the German lighting market in 2006 and 41% in 2010. According to the directive 2002/96/EG end-of-life lighting products shall be recycled.
CLFs consist of glass tube, electronic components, rare earth phosphor, and low quantities of mercury. Used discharge lamps should be collected and recycled via specific companies for waste management. Currently, separation of phosphor components is carried out using flotation or acidic leaching. In the present study, alternative leaching of rare earth phosphor using microorganisms was tested. Interaction of algae, pseudomonads, and bacilli with phosphor has been investigated. Results of full factorial plan show, that certain metals are released at specific conditions. Variables of full factorial plan were pH, amount of phosphor and biomass, and time. Chlorella vulgaris, Pseudomonas fluorescens, and Lysinibacillus sphaericus were incubated with the phosphors in shake flasks. The content of released rare earths was analysed in liquid and biomass via ICP-MS. It was observed that main interactions occur with Y and Eu, the rare earth components of red band phosphor.

Binary and ternary surface complexes of U(VI) and Np(V) on gibbsite were spectroscopically identified. Se(VI) forms two different types of outer-sphere complexes depending on the solid metal oxide.

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The latest results in the Eu-B(OH)3-Organic System are presented:

1) New approach to determine the formation constant of a Eu borates
2) Formation of the solid Eu borate in NaCl medium
3) Quantitative synthesis of Eu borate and structure characterization

Um astrophysikalisch relevante Wirkungsquerschnitte genau und ohne theoretische Unsicherheiten zu messen, sind Beschleunigerexperimente in geschützten Untertagelabors mit ihrer niedrigen Nullrate oftmals der einzige Weg. Bei Edelgasionen kann zur Erzeugung eines intensiven, hochenergetischen Ionenstrahls aufgrund der geringen Elektronenaffinität kein Tandem-Beschleuniger verwendet werden. Stattdessen werden positive Ionen direkt auf dem Hochspannungsterminal und beim Übergang auf Erdpotential beschleunigt. Der für die Installation im Untertagelabor Felsenkeller vorgesehene 5MV Pelletron-Tandem wird mit einer zusätzlichen Radiofrequenz-Ionenquelle auf dem Terminal ausgerüstet, um intensive Bestrahlungen mit Edelgasionen zu ermöglichen. Der aktuelle Stand zur Konstruktion und zum Einbau der Ionenquelle wird vorgestellt. – Unterstützt von NAVI.

The Tayler instability, a current driven instability, originally known from plasma physics may appear in liquid metal batteries. We present a numerical model, implemented in OpenFOAM, able to simulate the Tayler instability in incompressible fluids. The finite volume method code, based on the PISO algorithm and enhanced by a Poisson equation for the electric potential and Biot-Savart integration to obtain the induced magnetic field is used to simulate a recent Tayler experiment. Results of field structure and growth rates of the Tayler instability fit well to the experimental findings.

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

Usually, reactor safety analyses are based on the traditional conservative deterministic approach. An alternative approach to reactor safety analyses uses best estimate computer codes in combination with quantification of uncertainties in model and plant parameters. The German Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) has applied the methodology of uncertainty analysis based on the Wilks’ approach. According to this approach, the number of calculations required to perform a probabilistic estimation of an output parameter with a given coverage/confidence level (e.g., 95%/95%) does not depend on the number of input uncertainty parameters. In this paper, the results of an uncertainty analysis for a Large Break LOCA scenario for a generic German PWR of the Konvoi design are reported. All calculations were performed using the system code ATHLET Mod 2.2 Cycle A. The EXCEL-integrated software SUSA developed by GRS was used for generation of the uncertainty parameter vectors, their incorporation into ATHLET input files and for statistical evaluation of the results.

In case of the release of long-lived radionuclides, e.g., actinides, into the environment, knowledge about their behavior in biosystems is necessary to assess and prevent health risks for humans. This includes knowledge about bioavailability and toxicity of actinides for/onto cells, which are governed to a large extent by their speciation [1]. In order to enable a better understanding of these processes, we study interaction processes of trivalent actinides/lanthanides with mammalian cells on a cellular level combining biochemical and spectroscopic methods. In the present work we studied the cellular tolerance of FaDu cells (human squamous cell carcinoma cell line) toward Eu(III), as an analog for trivalent actinides, and its uptake into the cells as a function of the metal concentration and the nutrient composition. In parallel, the Eu(III) speciation in the culture media was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) to correlate Eu(III) toxicity and uptake with its chemical speciation.

[1] Ansoborlo, E. et al., Biochimie 88 (2006), 1605.

We report a large exchange-bias effect after zero-field cooling the new tetragonal Heusler compound Mn₂PtGa from the paramagnetic state. The first-principles calculation and the magnetic measurements reveal that Mn₂PtGa orders ferrimagnetically with some ferromagnetic inclusions. We show that ferrimagnetic ordering is essential to isothermally induce the exchange anisotropy needed for the zerofield cooled exchange bias during the virgin magnetization process. The complex magnetic behavior at low temperatures is characterized by the coexistence of a field-induced irreversible magnetic behavior and a spin-glass-like phase. The field-induced irreversibility originates from an unusual first-order ferrimagnetic to antiferromagnetic transition, whereas the spin-glass-like state forms due to the existence of antisite disorder intrinsic to the material.

Results of systematic high-frequency electron spin resonance (ESR) studies of Ba₃Cr₂O₈, a weakly coupled S = 1/2 dimer system, in magnetic fields up to 25 T are reported. Two pairs of ESR gapped modes corresponding to transitions from a spin-singlet ground state to the first excited triplet states with gaps, Δ_AB = 563 GHz and Δ_CD = 399 GHz, are revealed below H_c1 = 12.5 T. The detection of the ground-state excitations by means of ESR clearly indicates the presence of a non-secular term allowing these transitions. A complex structure of the microwave absorption spectrum in magnetic fields above H_c1 is observed, those peculiarities are discussed.

In this short review, we report on the recently found growing experimental evidence for the existence of Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) states in quasi-two-dimensional organic superconductors. At high magnetic fields aligned parallel to the conducting organic layers, we observe an upturn of the upper critical field beyond the Pauli limit, as evidenced by specific-heat and torque-magnetization measurements. Inside the superconducting state a second thermodynamic transition emerges. These features appear only in a very narrow angular region close to parallel-field orientation.

The magnetic-field and temperature dependencies of the ultrasound propagation and magnetization of single-crystalline CoCr₂O₄ have been studied in static and pulsed magnetic fields up to 14 and 62 T, respectively. Distinct anomalies with significant changes in the sound velocity and attenuation are found in this spinel compound at the onset of long-range incommensurate-spiral-spin order at T_s = 27 K and at the transition from the incommensurate to the commensurate states at T_l = 14 K, evidencing strong spinlattice coupling. While the magnetization evolves gradually with the field, steplike increments in the ultrasound clearly signal a transition into a new magnetostructural state between 6.2 and 16.5 K and at high magnetic fields.We argue that this is a high-symmetry phase with only the longitudinal component of the magnetization being ordered, while the transverse helical component remains disordered. This phase is metastable in an extended H - T phase space.

The magnetization of ErFe₁₁Ti and HoFe₁₁Ti single crystals was measured in pulsed magnetic fields up to 60 T. A number of field-induced phase transitions were observed. The inter-sublattice molecular fields were found to be 60 T in ErFe₁₁Ti and 73 T in HoFe₁₁Ti.

The Dresden High Magnetic Field Laboratory (HLD) is a user facility which provides scientists with the possibility to perform a broad range of experiments in pulsed magnetic fields. Recent progress in the magnet-technology development at the HLD has led to significant advances in achieving non-destructive pulsed magnetic fields close to the megagauss mark. Using 9.5 MJ dual-coil magnets with 16 mm bore, in 2011 a world-record field of 91.4 T has been achieved. Later 94.2 T have been reached.We report on the magnet design and performance of these magnets as well as on the design for the next generation of dual-coil magnets characterized by interchangeable inner sub-coils and improved control of the axial preload.

Results of electron spin resonance studies of copper pyrimidine dinitrate (Cu-PM, [PM-Cu(NO₃)₂(H₂O)₂]_n, PM= pyrimidine), a spin-1/2 antiferromagnetic chain material with alternating g-tensor and Dzyaloshinskii-Moriya interactions, in pulsed magnetic fields up to 63 T are reported. The field-induced gap shows a nonmonotonic behavior with a minimum in the vicinity of the saturation field H_sat = 48.5 T. This is associated with a transition from the sine-Gordon region to a spinpolarized state with magnon excitations. By comparing the entire set of experimental data with results of density matrix renormalization group calculations for Cu-PM, the validity of the used theoretical approach is proven.

The adsorption of U(VI) in the environment is known to be influenced by the presence of both inorganic and organic ligands in the aqueous phase [1]. In the present study, the ternary system containing U(VI), phosphate and SiO2 is investigated using a batch sorption technique, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). Whilst SiO2 is a predominant component of soils and host rock and the speciation of uranium with phosphate is complex [2], limited studies of the U(VI)/PO4/SiO2 ternary system [3] exist. Nevertheless, such studies have significant relevance in understanding radionuclide migration in geological systems.

[1] Payne, T.E., Lumpkin, G.R. and Waite, T.D. (1998). ‘UraniumVI adsorption on model minerals” in Adsorption of Metals by Geomedia, Chapter 2, p. 75-97, Jenne, E.A., Ed.; Academic Press, San Diego, U.S.A.
[2] Sandino, A. and Bruno, J. (1992). “The solubility of (UO2)3(PO4)2.4H2O(s) and the formation of U(VI) phosphate complexes: Their influence in uranium speciation of natural waters.” Geochimica et Cosmochimica Acta, 56, 4135-4145.
[3] Zhang, H. and Tao, Z. (2002). “Sorption of uranyl ions on silica: Effects of contact time, pH, ionic strength, concentration and phosphate.” Journal of Radioanalytical and Nuclear Chemistry 254(1), 103-107.

It is estimated that China accounts for 94% of the world supply of rare earths (Roskill, 2011). This fact, together with the impact of China’s export policy, poses a substantial risk to the security of the rare earth supply as well as a rare earth price risk. This situation has motivated an increase in the number of rare earth projects under development, i.e., there are currently more than 440 worldwide (Technology Metals Research, 2012). However, economically and environmentally acceptable processing technology to produce tradable products from rare earths (e.g., separated rare earth oxides) is not freely available on the market at the moment. In this respect, a lot of research and development has been initiated on this topic, in academia as well as in industry. Using a proprietary model and scenario-based analysis, we studied the impact that the development of rare earth processing technologies would have on the rare earth market and the economic feasibility of rare earth projects mentioned before. The analysis showed that this impact varies depending on the technology type (e.g., technology can affect project production volume, cost structure or both) and the legal context of the invention (e.g., free or limited by patenting availability of a new technology). The effect of a technology which influences project production volume is not the same as of a technology which changes project cost structure. The impact of a patented processing technology differs from the impact of a processing technology which is freely available on the market. In the case of a new technology which is limited by patenting, its impact depends on the market position (“producing”, “next-coming”, or “not producing” project) of the patent holder. The paper contributes to existing research by studying the dependence of the expected micro- and macroeconomic impact of rare earth processing technology developments on the properties of a new technology (e.g., costs, legal framework etc.). By this means, the paper adds to existing knowledge and attempts to make the rare earths market more transparent and predictable from a perspective outside China.

Mine development cannot progress without observing positive results of economic evaluation, which is the potential profitability of a future mine. According to the discounted cash flow (DCF) method, i.e., the most widely used method in mining, net present value is generally calculated as an indicator of project profitability. However, in the case of critical metals, e.g., rare earth elements (REE), the required for the economic calculations data is problematic to be generated. This is due to the specific features of these metals which also complicate economic evaluation of corresponding projects. Using the recent example of REE the paper explains how exactly their specific features complicate economic evaluation. We suggest possible solutions which include the extension of the DCF method, e.g., by the additional application of game theory, as well as the use of alternative methods, e.g., real options. Finally, we discuss the need for an integrated approach to economic evaluation of REE projects.

Cyclooxygenase-2 (COX-2) is a key player in inflammation. Its overexpression is directly associated with various inflammatory diseases and, additionally, with several processes of carcinogenesis. The development of new selective COX-2 inhibitors (COXIBs) for use in cancer treatment is in the focus of the medicinal chemistry research field. For this purpose, a set of methods is available to determine COX-2 expression and activity in vitro and ex vivo but it is still a problem to functionally characterize COX-2 in vivo. This review focusses on imaging agents targeting COX-2 which have been developed for positron emission tomography (PET) and single photon emission computed tomography (SPECT) since 2005. The literature reveals that different radiochemical methods are available to synthesize COXIBs radiolabeled with fluorine-18, carbon-11, and isotopes of radioiodine. Unfortunately, most of the compounds tested did not show sufficient stability in vivo due to de[¹⁸F]fluorination or de[¹¹C]methylation or they failed to bind specifically in the target region. So, suitable stability in vivo, matching lipophilicity for the target compartment and both high affinity and selectivity for COX-2 were identified as prominent criteria for radiotracer development. Up to now, it is not clear what approach and which model is the most suited to evaluate COX-2 targeting imaging agents in vivo. However, for proof of principle it has been shown that some radiolabeled compounds can bind specifically in COX-2 overexpressing tissues which gives hope for future work in this field.

The processes of dissolution and destabilization during and right after the flooding of a salt mine are in principle well understood but in detail still enigmatic. In our attempt to visualize these mechanisms, a combination of structural imaging as well as computer simulations were performed at the pore scale. High resolution positron emission tomography in situ imaging of fluid flow processes in heterogeneously structured drilling cores were matched with high resolution x-ray computer tomography imaging of effective hydraulic microstructures [1]. The microstructures were used as input for lattice Boltzmann based particle tracking simulations [2]. The space and time resolved combined imaging of hydraulic effective structures and fluid flow processes (Figure 1) allows an estimation of the effective volume within the network of pores and fissures and an estimation of the reactive surface area of rock material. Flow path topology concerning, e.g., fingering phenomena, dispersion and molecular diffusion effects can be quantified, and velocity distribution can be observed in 3D [3].

With PET, we observed the propagation of brine labelled with a PET-tracer (¹²⁴I or ¹⁸F) through a mechanically damaged rock salt drill core, which was structurally characterized with CT. The experiments show, that two heterogeneous effects have to be considered with respect to dissolution and destabilization of the material. The first one is a strong localization of fluid paths dominated by fingering phenomena especially along fissures but also in parts in homogeneous porous areas. As a consequence, fluid in motion uses only a small part of the available pathway even under saturated conditions. The fraction of the internal surface of a rock sample which is exposed to the propagating fluid – the effective reactive surface area – decreases with increasing localization of actual transport paths. Therefore, this effect considerably narrows the part of the pore space, where dissolution or other interactions are likely to occur. This effective pore volume and surface area can be quantified experimentally with PET process observation and with CT-based flow field simulations. The second mechanism is a high variability in the streaming velocity patterns along distinct parts of the fractures. Locally enhanced flow velocities increase local dissolution and cause widening of fracture cross sections. This may lead to a self-enhancing effect of increasing flow velocities and flow rates in saline rock. These results may contribute to the understanding of destabilization and dissolution processes and ultimately pylon collapse upon flooding of a salt mine.

ZnO nanostructures are promising candidates for the development of novel electronic devices due to their unique electrical and optical properties. Here, photoconductive atomic force microscopy (PC-AFM) has been applied to investigate transient photoconductivity and photocurrent spectra of upright-standing ZnO nanorods (NRs). With a view to evaluate the electronic properties of the NRs and to get information on recombination kinetics, we have also performed time-resolved photoluminescence measurements macroscopically.

Dynamic cross-sectional liquid distribution and hold-up in a DN80 separation column filled with structured packings was studied using an ultrafast electron-beam X-ray tomograph with high temporal resolution of 2000 images per second. The modality allows visualisation and characterisation of the counter-current flow before and at the flooding point representing the upper operation limit. Two packings of the same type (Montz B1-MN) with different specific surface area were used to investigate the influence of the packing geometry on the spatial liquid distribution. The system studied was water/air at different gas and liquid loads. The results of the tomographic imaging and corresponding post-processing routines were validated by comparison with conventional draining measurements.

Coalescence and break-up are complex (local) effects which depend on turbulence, shear rate, bubble sizes/polydispersity, local void fraction, bubble shape and material properties
- Complete modeling of all effects that influence these parameters is necessary
- Goal: Defining a general baseline model which covers the effects of bubbly flow

This paper describes the modelling of bubbly flow in a bubble column considering non-drag forces, polydispersity and bubble induced turbulence using the Eulerian two-fluid approach. The set of used closure models describing the momentum exchange between the phases was chosen on basis of broad experiences in modelling bubbly flows at the Helmholtz-Zentrum Dresden-Rossendorf. Polydispersity is modeled using the inhomogeneous multiple size group (iMUSIG) model, which was developed by ANSYS/CFX and Helmholtz-Zentrum Dresden-Rossendorf. Through the importance of a comprehensive turbulence modeling for coalescence and break-up models, bubble induced turbulence models are investigated. A baseline has been used which was chosen on the basis of our previous work without any adjustments. Several variants taken from the literature are shown for comparison. Transient CFD simulations are compared with the experimental measurements and Large Eddy Simulations of Akbar et al. (2012).

The present paper shows the influence of considering polydispersity of bubbly flow, simulating bubble columns with a three-dimensional Eulerian two-fluid model. A complete set of interfacial closure models regarding drag force, lift force, wall force, turbulent dispersion force and bubble induced turbulence is considered. A round bubble column of 0.288 m diameter and 2.5 m height is simulated up to a superficial gas velocity of 1 cm/s and compared with experimental data. It is shown that considering the polydispersity including the non-drag forces, important flow properties of bubble columns are reproduced. Possible influences of swarm effects on the non-drag forces are discussed and needs for further investigations are given.

Data on inclusive pion and eta production measured with the dielectron spectrometer HADES in the reaction p+⁹³Nb at a kinetic beam energy of 3.5 GeV are presented. Our results, obtained with the photon conversion method, supplement the rather sparse information on neutral meson production in proton-nucleus reactions existing for this bombarding energy regime. The reconstructed e+e−e+e− transverse-momentum and rapidity distributions are confronted with transport model calculations which account well for pi0 but deviate for eta.

Element-specific phase-resolved x-ray ferromagnetic resonance (FMR) was used to study spin pumping within Co50Fe50(3)/ Cu(6)/ Ni80Fe20(5) (thicknesses in nm) spin valve structures with large areas, so that edge effects typical of nanopillars used in standard magnetotransport experiments could be neglected. The phase of precession of the Co50Fe50 fixed layer was recorded as FMR was induced in the Ni80Fe20 free layer. The field dependence of the fixed layer phase contains a clear signature of spin transfer torque (STT) coupling due to spin pumping. Fitting the phase delay yields the spin mixing conductance, the quantity that controls all spin transfer phenomena. The STT coupling is destroyed by insertion of Ta into the middle of the Cu layer.

The 79Se isotope, which is a long-lived (t1/2 ~ 3.27 × 105 years[1]) and radiotoxic fission product found in spent nuclear fuels, is of high importance in the context of geological disposal facilities. Safety calculations assessments have shown it to be one of the most contributing isotopes to the total radioactivity that could be potentially released to the biosphere. Selenium has a quite complex speciation, with four main oxidation states, depending on both the pH and the redox potential of the surrounding environment. The concentration, the bioavailability, the mobility, the distribution and the oxidation state of selenium in the environment are greatly influenced by the pH, nature of mineral sorbent as well as potential redox reactions at mineral surfaces. Among the mechanisms which enable selenium retardation and reduces its migration, adsorption processes onto solid surfaces (iron, alumina, titanium oxides) has been extensively investigated at room temperature [2-4].
Our study focuses on selenium(VI) and selenium(IV) sorption onto hematite (α-Fe2O3), which was so far not thoroughly characterized yet. By means of EXAFS and ATR FT-IR spectroscopic studies, it was observed that selenium(VI) forms purely monodentate inner-sphere complexes onto hematite, but the study was only performed at pD 3.5 [5]. To our knowledge, the only spectroscopic characterization of the binary selenium(IV)/hematite system concluded the formation of bidentate bridging inner-sphere complexes onto single hematite crystal using x-ray standing wave (XSW), but the measurements were only performed at pH 4.0 [6]. Hematite was chosen because it is a ubiquitous iron oxide mineral present in the environment. In addition, it is an iron phase often found in rocks and soils in the vicinity of underground repositories [7]).
At the macroscopic level, the effect of pH and ionic strength was studied by means of batch experiments. Sorption of both oxyanions was found to decrease with increasing pH. An increase of the ionic strength (from 0.01 M to 0.1 M) impacted the sorption of selenium(VI), while the selenium(IV) uptake was found to be not significantly affected. Electrophoretic mobility measurements revealed that selenium(IV) sorption shifted the isoelectric point (pHIEP) of hematite to lower pH values, while the pHIEP was not significantly modified upon selenium(VI) sorption. At the molecular level, in situ ATR FT-IR measurements revealed the formation of inner-sphere complexes during selenium(IV) sorption onto hematite, while the sorption of selenium(VI) proceeded via the formation of outer-sphere complexes. Complementary information about the Se reactivity at the hematite surface is provided by EXAFS spectroscopy.
High level and long-lived radioactive wastes are well-known to increase the temperature at the vicinity of the waste disposal site. Such a thermal effect raises the question how the retention of selenium is influenced at elevated temperatures. By means of batch sorption experiments, electrophoretic mobility measurements and in situ ATR FT-IR spectroscopic studies, information and insights about mechanisms involved at higher temperatures (from 25 °C to 60 °C) are provided.

[1] G. Jörg, R. Buhnemann, S. Hollas, N. Kivel, K. Kossert, S. Van Winckel, C.L.V. Gostomski, Appl. Radiat. Isotopes 68 (2010) 2339.
[2] E.J. Elzinga, Y.Z. Tang, J. McDonald, S. DeSisto, R.J. Reeder, J. Colloid Interface Sci. 340 (2009) 153.
[3] N. Jordan, A. Ritter, H. Foerstendorf, A.C. Scheinost, S. Weiss, K. Heim, J. Grenzer, A. Mucklich, H. Reuther, Geochim. Cosmochim. Acta 103 (2013) 63.
[4] A.C. Scheinost, L. Charlet, Environmental Science & Technology 42 (2008) 1984.
[5] D. Peak, D.L. Sparks, Environ. Sci. Technol. 36 (2002) 1460.
[6] J.G. Catalano, Z. Zhang, P. Fenter, M.J. Bedzyk, J. Colloid Interface Sci. 297 (2006) 665.
[7] F. Claret, B.A. Sakharov, V.A. Drits, B. Velde, A. Meunier, L. Griffault, B. Lanson, Clay Clay Min. 52 (2004) 515.

Interactions between cations and natural or synthetic calcite may include incorporation processes, resulting in the irreversibility of some sorption reactions. Calcite is present in soil and sediment materials, and in particular in the Callovo-Oxfordian clay samples from of the French underground laboratory of Bure (France), studied in the context of an underground repository for radioactive waste. Europium has been chosen to be investigated by TRLFS due to its fluorescent properties and because it can serve as an analogue for trivalent actinides. Nickel is toxic as a heavy metal as well as in its radioactive form. Few experimental studies have been made to define its interaction with soil and sediment minerals in general and only a handful of articles report investigations of Ni interaction with calcite. To investigate these irreversible processes, we have chosen to work on the Eu-CO2-NaCl-CaCO3 and Ni-CO2-NaCl-CaCO3 systems at pH 8.4, buffered by calcite under atmospheric conditions.
Our study combines macroscopic batch experiments with spectroscopic investigations (Time Resolved Laser Fluorescence Spectroscopy - TRLFS and Rutherford Backscattering Spectrometry - RBS) to comprehensively characterize these systems.

First, appropriate material for sorption experiments were selected based on characterization studies. Eventually, a calcite powder from SOLVAY (SOCAL U1-R) with a particle size of 0.2 μm for TRLFS investigations was chosen, mainly due to its large BET specific surface area (i.e. 18.4 m2/g). In addition, a calcite powder from OMYA (BL 200), with a bigger particle size (56 μm) and a lower specific surface area (0.7 m2/g) was used for Rutherford Backscattering Spectrometry (RBS) measurements, due to the specific requirements of this technique.
For both powders, Diffuse Reflectance Infra-Red Fourier Transform Spectroscopy (DRIFT), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and elementary analysis confirmed the absence of polymorphic CaCO3 compounds (i.e. vaterite and aragonite).
In order to get a better understanding of incorporation of cations in the structure of calcite, we compared our results obtained on powders with studies on millimetric calcite single crystals from Alfa Aesar, performed under the same experimental conditions as for powders.
The sample preparation consists in open reactor experiments under atmospheric conditions (pCO2 = 10-3.5 atm) in 0.1 M NaCl media. The studied concentrations range from 10-6 to 10-3 M. The experiments were carried out for contact times ranging from 4 hours to 6 months for europium and from 4 hours up to 3 months for nickel. For europium, ICP-AES/ICP-MS analysis of the supernatants showed a strong retention by calcite whatever the initial concentration, contrary to nickel where the retention is depending on the initial concentration.

The second step of the work involved efforts to better understand the time-dependence of Eu and Ni sorption and respective mechanisms.
For each concentration of europium investigated by TRLFS, two species are identified and their fluorescence lifetime increases as the initial concentration decreases and time goes on, corresponding to a gradual loss of water molecules surrounding the europium. For higher concentrations, the species identified appear to correspond to a (co-) surface precipitate and possibly an inner-sphere surface complex with two water molecules retained in the hydration sphere. For lower concentrations, the longer lifetimes observed for one of the two species suggest the incorporation of europium in calcite [1,2].
Rutherford Backscattering Spectrometry (RBS) experiments have been carried out using an alpha particle millibeam at the 4MV Van de Graaff accelerator of IPNL and also on nuclear microprobe of CEA-Saclay. This technique is well adapted to discriminate sorption processes such as: (i) adsorption or co precipitation at the mineral surfaces or (ii) incorporation into the mineral structure (through diffusion for instance). The interpretation of the results shows different sorption behaviors for Ni and Eu. Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation, which confirms the hypothesis of the surface precipitate, and (ii) incorporation up to depths greater than 160 nm after 1 month of sorption. Complementary Scanning Electron Microscopy (SEM) observations of the mineral surfaces at low voltage have also been carried out, which confirmed the heterogeneities detected by RBS measurements.

[1] Fernandes, M. M.; Schmidt, M.; Stumpf, T.; Walther, C.; Bosbach, D.; Klenze, R.; Fanghänel, Th., Journal of Colloid and Interface Science (2008), 321(2), 323-331.
[2] Piriou, B; Fedoroff, M.; Jeanjean, J.; Bercis, L., Journal of Colloid and Interface Science (1997), 194, 440-447.

Based on a detailed statistical analysis of chemical data published in the scientific literature, estimates were made of the minimum amounts of recoverable Ge contained within sulphidic zinc ores and coals, given current processing technologies. It is expected that at least 119 kt (∼7 kt in zinc ores and ∼112 kt in coal) of recoverable germanium exist within proven reserves (at present stage of knowledge) at grades in excess of 100 ppm in sphalerite and 200 ppm in coal, while at least 440 kt (∼50 kt in zinc ores and ∼390 kt in coal) should become recoverable in the future, being associated to coal reserves at 8–200 ppm Ge and zinc resources containing in excess of 100 ppm Ge in sphalerite. Mississippi Valley Type (MVT) deposits are expected to be the most important hosts of germanium-rich sphalerite, while both brown and hard coals are expected to be equally important as hosts of germanium. The approach taken in this publication shows that reliable minimum estimates for the availability of by-product metals lacking suitable reserve/resource data may be attained by using robust statistical methods and geochemical data published in the scientific literature.

1. Motivation
Die Ausbreitung der Actinide in der Umwelt ist in den letzten Jahrzehnten verstärkt in den Fokus der Wissenschaft gerückt, da diese aufgrund ihrer Gewinnung und Wiederaufarbeitung im Zusammenhang mit der zivilen Nutzung der Kernkraft aber auch durch in der Vergangenheit durchgeführten Atomwaffentest sowie durch nukleare Unfälle zu weit verbreiteten Schadstoffen geworden sind.
Das Migrationsverhalten dieser Schwermetalle in Grundwassersystemen wird hauptsächlich von der aquatischen Speziation und von Sorptionsprozessen an der Mineral-Wasser-Grenzfläche bestimmt. Daher ist die Untersuchung der aquatischen Spezies sowie der Wechselwirkungen von Actiniden mit Metalloxiden, die als Modellsyteme für komplexe, natürliche Minerale in wässrigen Lösungen dienen, für die Sicherheitsbewertung von nuklearen Endlagern essentiell. Neben verschiedenen festen Phasen, wie Fe(OOH)x, TiO2, oder SiO2, sind Aluminiumoxide und –hydroxide von besonderem Interesse, da sie Hauptbestandteile von Ton und Tonmineralen sind, die als Wirtsgestein für nukleare Endlager in Frage kommen.

2. Aufgabe
Abgeschwächte Totalreflexion (ATR) FT-IR-Spektroskopie ist eine leistungsfähige Technik zur in-situ und zeitaufgelösten Untersuchung der Speziation und von Sorptionprozessen an der Mineral-Wasser-Grenzflächen bei geringen (µM) Actinylionenkonzentrationen. Die ATR FT IR ermöglicht die Untersu-chung von stark IR-absorbierenden oder optisch dichten Medien und gestattet somit die Analyse von wässrigen Proben.
In dieser Arbeit wird die Wechselwirkung von Uran und Neptunium mit mineralen Modellsystemen, die relevant für das Nah- und Fernfeld von Endlagern sind, in wässrigen Lösungen vorgestellt. Vorrangig konzentriert sich die Arbeit auf den Einfluss von ausgesuchten Anionen auf die Sorptionsprozesse von U und Np. Außerdem wurde die aquatische Speziation von Uran bei erhöhten Temperaturen bestimmt. Die ternären Systeme und der Einfluss der Temperatur auf die Speziation und Sorption wurden untersucht, um strukturelle Informa-tionen über die während der Sorption gebildeten Oberflächenkomplexe zu erhalten.

Of the three main choices for radioactive waste repository host rock—salt dome, argillaceous rock and crystalline rock—Germany has deposits of two eligible rock types. Salt dome, present in Northern Germany, has long been investigated as host rock and in recent years argillaceous rock has come to attention. There are two areas in Germany with sizable clay deposits: In the more populated south of Germany there is a deposit of the already well-researched Opalinus clay (OPA) and in the north of Germany there are clay deposits whose pore waters have a salt concentration of up to 4 mol L-1, ten times that of OPA. The aim of this work is to determine the sorption and diffusion properties of uranium(VI) on/in model clays and OPA at increased salinities in NaCl, KCl, CaCl2 and MgCl2. The basis for this work is formed by sorption experiments with Wyoming montmorillonite (SWy-2) in several strong electrolyte solutions. This also includes leaching experiments.

Argillaceous rock is considered as one of the possible host rock types for radioactive waste repositories. Therefore, it is necessary to examine the retention behaviour of argillaceous rock towards long-lived radionuclides, such as uranium. In this study, the 2:1 clay montmorillonite, consisting of an octahedral alumina sheet sandwiched by two tetrahedral silicate sheets, is used. The sorption of uranium(VI) onto montmorillonite is studied in NaCl, KCl, CaCl₂, and MgCl₂.

The chemical composition of 20 glass bracelet fragments found in Nufaru, a Byzantine site from 10th - 13th centuries A.D., nowadays located on Romania's territory, has been determined using Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE) in external beam mode. Most of the Byzantine bracelet fragments were identified as "mixed natron-plant ash" soda-lime-silica glasses. The obtained chemical compositions indicated that the manufacturing of these finery items was performed using similar raw materials and techniques, in most of the cases involving colored glass recycling. PIXE-PIGE results highlighted the glass chromophores (cobalt, manganese, copper and iron ions) and provided hints about the mineral pigments used to paint the external surface of some bracelets.

Die 14N(p,γ)15O-Reaktion bestimmt als langsamste Kernreaktion die Rate des Bethe-Weizsäcker-Zyklus. Für eine präzise Extrapolation des Wirkungsquerschnitts zu niedrigen Energien ist die genaue Kenntnis der Anregungsfunktion über einen weiten Energiebereich notwendig. Am 3 MV Tandetron des Helmholtz-Zentrums Dresden-Rossendorf wurde der nichtresonante Wirkungsquerschnitt der 14N(p,γ)15O-Reaktion im Bereich von 1-2 MeV Strahlenergie neu untersucht. In dem Vortrag werden vorbereitende Simulationen, erste experimentelle Daten sowie ein Ausblick präsentiert.

Modelle einer Kernkollaps-Supernova sagen vorher, dass Titan-44 (Halbwertszeit = 58,9 a) produziert wird. Dementsprechend werden mehrere Titan-44-Gammastrahlungsquellen in unserer Galaxie erwartet. Jedoch konnte Titan-44 bisher nur in den Supernovaüberresten Cassiopeia A und SN 1987A nachgewiesen werden. 40Ca(𝛼,𝛾)44Ti ist die wichtigste Reaktion, die Titan-44 erzeugt. Ihre Reaktionsrate wird durch mehrere Resonanzen dominiert. Am 3.3 MV Tandetron des Helmholtz-Zentrums Dresden-Rossendorf werden die Verzweigungsverhältnisse mittels in-beam 𝛾-Spektrometrie untersucht und anschließend die Resonanzstärken durch eine Aktivierungsmessung im Niederniveaumesslabor Felsenkeller bestimmt.

Observations of the ⁶Li abundance in very metal-poor stars, if confirmed, show a level of ⁶Li that is several orders of magnitude larger than the production of this nuclide in standard Big Bang nucleosynthesis. The ²H(α,γ)⁶Li nuclear reaction is believed to dominate ⁶Li production in the Big Bang, but there are no directly measured data at relevant energies yet. The reaction has been studied at the LUNA 0.4 MV accelerator, deep underground in the Gran Sasso laboratory in Italy, using an intensive He+ beam and a windowless deuterium gas target. The conclusions from the final data analysis of the experiment will be presented. – Supported in part by DFG (BE 4100/2-1).

A combined theoretical and spectroscopic approach was used to refine structural data of the aqueous dimeric U(VI) species, (UO2)2CO3(OH)3−. Several isomer structures of this complex were already derived from previous X-ray absorption and NMR experiments (Szabó, Z. et al. J. Chem. Soc.-Dalton Trans., 2000, 3158-3161) but due to unequivocal results a distinct structure could not be determined and uncertainties remain. In this work, the Gibbs energies and U–U distances obtained from density functional theory (DFT) calculations predict two isomers, one with a carbonate ligand and one with two hydroxo groups as bridiging groups, as most likely structures. The experimental IR spectrum indicates a bidentate coordination of the carbonate ion and the presence of two spectroscopically specifiable uranyl moieties as it also is predicted by the spectra computed on the base of DFT. Taken together theoretical and experimental results the isomer with a carbonate ligand bridging the two uranyl units appears most likely to represent the predominat structure. Contributions to a small extent of an isomer with a non-bridging carbonate anion can not be completely ruled out.

Kein Abstract zur Veranstaltung. Inhaltliche Zusammenfassung:

Die Wechselwirkung mehrwertiger Metalle mit natürlichem organischem Material kann kinetischen Stabilisierungseffekten unterliegen, was zu Unsicherheiten im Hinblick auf die Anwendbarkeit thermodynamischer Konstanten in Transportmodellierungen führt. Die Reversibilität des Prozesses wurde deshalb in Isotopenaustausch-Studien erstmals direkt und über einen längeren Zeitraum untersucht. Hierzu wurden Bindungsisothermen für [160Tb]Tb(III) an Huminstoff-Flockulaten aufgenommen, wobei 160Tb als Radiotracer simultan oder nachträglich (nach verschiedenen Alterungszeiten des Komplexes von 1 bis 90 Tagen) eingeführt wurde. In allen Fällen wurde im Sättigungszustand ein ungehindertes dynamisches Austausch-Gleichgewicht festgestellt. Langzeitprozesse zulasten der Reversibilität treten also offenbar nicht generell auf.

Colloid-borne transport of radiotoxic metals in the subsurface hydrosphere is a topic of major interest in view of long-term risk assessments for nuclear waste repositories. In particular, interaction with natural organic complexants such as humic substances can be decisive for the mobility of higher-valent metals. Depending on geochemical parameters, migration can be both enhanced and reduced. The respective conditions need to be identified, and models must be able to describe such complex systems by few parameters.

According to the Linear Additive Model, total metal adsorption in the presence of humic matter can be calculated by linking parameters for adsorption of both components and for their interaction with each other. The basics of this approach are also implicit in reactive transport models where humic carriers are considered. The applicability is, however, not unanimously accepted, and modelling results are in part not satisfactory.

Clay rock is being discussed as a potential host formation for a final repository, mainly because of its high adsorption capacity. This barrier function may, however, be subverted by charge screening or competition effects due to the high salt contents of pore waters. Complexation of radionuclides with humic-like clay organics could cause an additional mobilisation. So far, the effect of high ionic strengths on interactions of such organic carriers is unknown.

Within the framework of the planned PhD thesis, these processes will be investigated in detail, using radioactive tracers for interaction studies at high salt contents and for 3D imaging of transport processes by means of Positron Emission Tomography. The Linear Additive Model will be tested for static and dynamic systems, aiming at a specification of criteria for its applicability. To describe the effects of high salinities on a molecular level, mechanistic models for metal-humic interaction and surface complexation will be employed as well. An outline of this topic shall be presented at the meeting.

New results on the differential cross section in deuteron-proton elastic scattering are obtained at the deuteron kinetic energy of 2.5 GeV with the HADES spectrometer. The angular range of 69° – 125° in the center of mass system is covered. The obtained results are compared with the relativistic multiple scattering model calculation using the CD-Bonn deuteron wave function. The data at fixed scattering angles in the c.m. are in qualitative agreement with the constituent counting rules prediction.

Equiatomic FeRh thin films with varying thickness have been prepared on MgO (100) substrates via molecular beam epitaxy (MBE). The optimization of the stoichiometry was monitored using XRD, RBS and AES while the magnetic properties were probed using SQUID magnetometry. XRD results evidence a well ordered CsCl-type crystal structure. By increasing the annealing temperature of the films, the structural quality of the films also increases. Moreover, the known first order phase transition at ~350 K from an antiferromagnetic (AF) to a ferromagnetic (FM) state slightly shifts towards higher temperatures. M-H loops of films annealed at 800 ∘C or 850 ∘C recorded at 300 K show an opening, which is likely related to the magnetic field-induced AFM-FM phase transition. Residual low-temperature ferromagnetic moments are of unknown origin, but likely related to strain or diffusion effects at the surface or interface.

The magnetic and structrual properties of the potential diluted magnetic oxide (DMO), i.e. Co implanted TiO2 thin films have been investigated. These films have been grown by magnetron sputtering on SrTiO3 single crystals. Avoidence of possible magnetic contamination has been verified by magnetometry measurements after substrate preparation and deposition. For magnetic doping, implantations of Co+ ions have been performed at atomic concentrations of 0.5%, 2.5% and 3% respectively. The dependencies between the fluence implanted, defect creation and ferromagnetic properties have been investigated using magnetometry, positron annihilation spectroscopy and structural characterisation.
This work is supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz-Russia Joint Research Group HRJRG−314, and the Russian Foundation for Basic Research, RFBR #12 − 02 − 91321 − 𝑆𝐼𝐺 − 𝑎

Spin polarized currents can exert a torque on a ferromagnetic layer‘s magnetic moment leading to switching or steady-state precession. Spintorque driven ferromagnetic resonance (ST-FMR) is a unique method to measure the magnetic anisotropy, saturation magnetization and damping in a nanoscale structure. ST-FMR can also be used to determine the bias dependence of spin-transfer torques in magnetic tunnel junctions [1- 3]. For different values of applied RF power and DC bias, we swept the RF frequency from 1 to 15 GHz and measured the resulting mixing voltage across our MgO-based tunnel junctions. Not only the low-frequency fundamental mode was observed, but also a higher order mode. We find that the mixing voltage peak shifts with applied DC-field and increases with RF power. Finally, we separate the fieldlike torque contribution from that of the in-plane spin-transfer torque and determine their bias dependence.

Spin pumping driven by ferromagnetic resonance (FMR) injects a spin current through a simple ferromagnetic (FM)/paramagnetic (PM) interface into a PM layer [1]. Due to the inverse spin Hall effect (ISHE), arising from the spin-orbit coupling in the PM layer, the spin current is converted into a charge current. As a result transverse electromotive force perpendicular to the applied magnetic field and to the microwave field is produced [2]. Here we present direct measurements of the ISHE induced by spin pumping in Py/Pt bilayer. We observe a 4mT FMR linewidth broadening for the samples with Pt capping layers due to spin pumping. We also find that the electromotive force varies systematically with changing microwave power and frequency, magnetic-field angle, or temperature. This is consistent with the predictions based on the Landau-Lifshitz-Gilbert equation combined with the models of the ISHE and spin pumping.

Precessional dynamics of a Co50Fe50(0.7)/Ni90Fe10(5)/Dy(1)/Ru(3) (thicknesses in nm) thin film have been explored by low temperature time-resolved magneto-optical Kerr effect and phase-resolved x-ray ferromagnetic resonance measurements. As the temperature was decreased from 300 to 140 K, the magnetic damping was found to increase rapidly while the resonance field was strongly reduced. Static x-ray magnetic circular dichroism measurements revealed increasing ferromagnetic order of the Dy moment antiparallel to that of Co50Fe50/Ni90Fe10. Increased coupling of the Dy orbital moment to the precessing spin magnetization leads to significantly increased damping and gyromagnetic ratio of the film while leaving its magnetic anisotropy effectively unchanged.

We report on the influence of correlated substrate roughness on the two-magnon scattering in 30 nm Ni81Fe19 thin films. Using ion beam erosion periodically modulated substrates (ripple) were produced with wavelengths between 20 nm and 432 nm. This surface corrugation is adopted by magnetic layers grown on top yielding dipolar stray fields if magnetization and ripple ridges are aligned perpendicular. In case of λ ≥ 222 nm the evolving periodic field pattern trigger two-magnon scattering, which depends strongly on the direction of magnetization with respect to the ripple pattern. In-plane broadband ferromagnetic resonance reveals prominent peaks in the frequency dependent linewidth measured perpendicular to the ripple ridges. These peaks can be switched off if the magnetization is aligned along the ripple ridges.

Si and Ge surfaces were irradiated with polyatomic Bi ions at normal incidence with energies between 10 and 20 keV per atom. For comparison, irradiation with monatomic ions was performed. The resulting surface morphologies were studied by SEM, XTEM and AFM. A variety of surface patterns were revealed, which are based on different formation mechanisms. Irradiation of Ge with Bi3 , Bi3 and Bi2 at RT results in a surface morphology of hexagonally ordered dots. They have an aspect ratio close to one, which has not been reported for elemental semiconductors so far [1]. For comparison, Ge irradiated with monatomic Bi ions at RT leads to well-known sponge-like surface layers, whereas with increasing substrate temperature similar dot patterns appear [2]. On Si irradiated at RT with monatomic or polyatomic Bi ions, no dot patterns have been found, which holds for Bi even for T>RT. On Si dot patterns appear only after polyatomic Bi irradiation well above RT.
The surface patterns will be explained by models based on vacancy kinetics and the liquid-solid phase transition. The sponge formation, as suggested in literature, results from vacancy kinetics, and will be demonstrated by kinetic Monte-Carlo simulations. The dot patterns are consistently modeled by ion-induced transient local melt pools, using TRIM simulations and heat conduction calculations.

Eigenvalues of a potential dynamical system with damping forces that are described by an indefinite real symmetric matrix can behave as those of a Hamiltonian system when gain and loss are in a perfect balance. This happens when the indefinitely damped system obeys parity–time (PT ) symmetry. How do pure imaginary eigenvalues of a stable PT -symmetric indefinitely damped system behave when variation in the damping and potential forces destroys the symmetry? We establish that it is essentially the tangent cone to the stability domain at the exceptional point corresponding to the Whitney umbrella singularity on the stability boundary that manages transfer of instability between modes.

The mechanism of exchange between oxygen in UO₂ ²⁺ and that in solvent water has been disputed over last 50 years. It is well–known that the rate of “yl”–oxygen exchange depends heavily on pH, and that there is virtually no exchange at low pH. With increase of pH (pH > 2) the exchange becomes appreciable, and under highly alkaline solution there is a rapid oxygen exchange. These observations led to an idea that there are at least two different exchange mechanisms; one dominating under weakly acidic to neutral pH and another mechanism at very high pH. Szabó and Grenthe [1, 2] used NMR spectroscopy to identify the species involved in “yl”–oxygen exchange and they suggested two binuclear complexes as key species; (UO₂)₂(OH)₂ ²⁺ at low pH and [(UO₂(OH)₄ ^2-)(UO₂(OH)₅ ^3-)] at high pH. How the oxygen exchange takes place in these complexes in atomic scale, however, remains unidentified because the lifetimes of the intermediate species and the transition states of the oxygen exchange are too short to be detected spectroscopically. That is to say, we know they (dimer complexes) did it but we do not know how they managed to do it. Our attempt here is to identify the “yl”–oxygen exchange pathways in these complexes using quantum chemical method thereby proving that oxygen exchange through these complexes are indeed possible – thereby bringing end to the long–disputed arguments over the “yl”–oxygen exchange mechanisms.
First, we studied the “yl”–oxygen exchange pathway via (UO₂)₂(OH)₂ ²⁺ [3]. We used hybrid density functional theory (DFT) with Becke’s three–parameter hybrid functional and Lee–Yang–Parr’s gradient–corrected correlation functional (B3LYP) employing conductor–like polarizable continuum model (CPCM) using Gaussian 09 program (Gaussian Inc.). The small core effective core potential and corresponding basis set was used on uranium and oxygen. Direct proton transfer from the hydroxo bridge or from the coordinating water to the “yl”–oxygen in (UO₂)₂(OH)₂ ²⁺ can be ruled out because we found exceedingly high activation barrier (~170 kJ mol^–1) through these mechanisms. The exchange mechanism in (UO₂)₂(OH)₂ ²⁺ can be described by a multi–step proton transfer pathway that involves the formation of an oxo bridge between the two uranyl(VI) centres (U–Oyl–U bridge). The activation enthalpy of the reaction obtained at the B3LYP level is 94.7 kJ mol^–1 and is somewhat larger than the experimental value of 80 ± 14 kJ mol^–1. However, the discrepancy is at the acceptable level.
Second, we tried to identify the oxygen exchange pathway through [(UO₂(OH)₄ ^2-)(UO₂(OH)₅ ^3-)]. For this attempt, we first studied the speciation of uranyl(VI) in highly alkaline solution by quantum chemical calculations as well as X–ray absorption spectroscopy (XAS). Although various previous studies assumed that hydrolysis of UO₂(OH)₄ ^2– produces UO₂(OH)₅ ^3–, our B3LYP calculations together with previous theory work by others [4,5] suggest that hydrolysis of UO₂(OH)₄ ^2– yields UO₃(OH)₃ ^3–. We studied this point further using XAS at the Rossendorf Beamline (ROBL) in ESRF, Grenoble, France, and we found evidence of the existence of new species UO₃(OH)₃ ^3– in XANES spectra. The sample which contained further hydrolyzed species showed clear shift of the uranium L_III absorption edge compared to the sample containing only UO₂(OH)₄ ^2–.Similar energy shift was observed in Pa(V) when speciation changed from spherical Pa⁵⁺ to mono–oxo PaO³⁺ [6]. Therefore the species beyond UO₂(OH)₄ ^2– is better assigned to UO₃(OH)₃ ^3– rather than UO₂(OH)₅ ^3–. Likewise, the complex described as [(UO₂(OH)₄ ^2-)(UO₂(OH)₅ ^3-)] by Szabó and Grenthe should better be written as [(UO₂(OH)₄ ^2-)(UO₃(OH)₃ ^3-)]. We then studied the “yl”–oxygen pathway within [(UO₂(OH)₄ ^2-)(UO₃(OH)₃ ^3-)] by DFT, and found a realistic pathway which has the activation Gibbs energy of 56.3 kJ mol^–1 at the B3LYP level, which is again in good agreement with the experimental value of 60.8 ± 2.4 kJ mol^–1 obtained by Szabó and Grenthe [2].
Our calculations confirm the “yl”–oxygen exchange mechanisms through (UO₂)₂(OH)₂ ²⁺ and [(UO₂(OH)₄ ^2-)(UO₃(OH)₃ ^3-)], and underscores the role of binuclear species. The formation of U–O_yl–U bridge seems to play a key role in facilitating intramolecular proton shuttling among the oxygen atoms thereby contributing to faster “yl”–oxygen exchange.

[1] Szabó, Z. and Grenthe, I., Inorg. Chem. 2007, 46, 9372–9378.
[2] Szabó, Z. and Grenthe, I., Inorg. Chem. 2010, 49, 4928–4933.
[3] Tsushima, S., Inorg. Chem. 2012, 51, 1434–1439.
[4] Shamov, G. A. and Schreckenbach, G., J. Am. Chem. Soc. 2008, 130, 13735–13744.
[5] Bühl, M. and Schreckenbach, G., Inorg. Chem. 2010, 49, 3821–3827.
[6] Le Naour, C. et al., Inorg. Chem. 2005, 44, 9542–9546.

We consider a cylindrical Couette-Taylor (CT) flow of an electrically conducting viscous and resistive fluid in an external helical magnetic field. Local stability of the flow is studied with respect to three-dimensional perturbations within a short-wavelength approximation. Maximization of the critical Rossby number at the instability threshold is performed with respect to the non-dimensional parameters of the problem characterizing hydrodynamic and magnetic effects. Quite surprisingly, it is found that the critical Rossby number at the threshold of magnetorotational instability in the case of infinitesimally small magnetic Prandtl number is universally bounded from above by a quantity 2 − 2√2 known as the Liu limit, which is below that of Keplerian rotation (−3/4).

Temperature dependent absorption and emission cross-sections of 5at% Yb3+ doped yttrium lanthanum oxide (Yb:YLO) ceramic between 80K and 300K are presented. In addition, we report on the first demonstration of ns pulse amplification in Yb:YLO ceramic. A pulse energy of 102mJ was extracted from a multi-pass amplifier setup. The amplification bandwidth at room temperature confirms the potential of Yb:YLO ceramic for broad bandwidth amplification at cryogenic temperatures.

Bubble characteristics in a cylindrical gas-solid fluidized bed have been studied with a two-fluid model (TFM) based on Kinetic theory of granular flow and validated with experiments performed with X-ray computed tomography (XRT). It is shown that the equivalent bubble diameter increases with height from the gas distributor plate. Experimental and TFM results are in good agreement for glass particles. Darton et al. (1) and Werther (2) correlation slightly over-predict bubble size. XRT and simulations results show similar trend for LLDP and glass particles. KTGF theory performs better for glass particles, and is in good agreement with XRT results.

In the frame of the FP7 European project Central Design Team (CDT), an extensive simulation study has been done to assess the main shielding problems in view of the construction of the MYRRHA accelerator-driven system at SCK•CEN in Mol (Belgium). A method based on the combined use of the two Monte Carlo codes MCNPX and FLUKA has been developed, with the goal to characterize realistic neutron fields around the core barrel and build complex source terms, to be used in detailed analyses of the radiation fields due to the system in operation, and of the coupled residual radiation. The results evidenced a powerful way to analyze the shielding and activation problems, with direct and clear implications on the design solutions.

To support the construction of the MYRRHA accelerator driven system at SCKCEN in Mol (Belgium), in the years 2009-2012 the FP7 European project Central Design Team (CDT) worked at the design of the Fast Spectrum Transmutation Experimental Facility (FASTEF), to demonstrate efficient transmutation of high level waste and associated technology. The heart of the system is a lead-bismuth eutectic (LBE) cooled reactor, working both in critical and subcritical mode. The neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV,  4 mA proton beam, which hits a LBE spallation target located inside the reactor core. Between the many challenges of the design, radiation shielding and minimization of induced activation are key points. To assess the shielding of the reactor core, both critical and sub-critical operation modes have been studied. Since in FASTEF the reactor is foreseen to operate at 100 MW core power in the critical mode and at 94 MW in the subcritical one, the critical mode exhibits the highest lateral neutron fluence at the fuel level, and can be reasonably considered the conservative case for the lateral radiation containment. At the contrary, because of the backscattered radiation from the spallation target and due to the presence of the beam pipe channel, the subcritical operation drives the vertical design. Starting from the MCNPX Monte Carlo models of the core defined in CDT in both the operation modes, neutron spectra have been fully characterized on suitable surfaces and used as input of a second row of FLUKA simulations, where complex source terms have been used. FLUKA has the unique possibility to compute, in the same simulation, the transport of the radiation due to the system in operation and the coupled residual fields, due to the activated materials. The FLUKA/MCNPX comparison of the neutron fluence rates inside the external vessel at different radial and vertical distances from the core barrel shows a very good agreement - at the percent level - and has been used to validate the FLUKA analysis. Dose distributions have been then evaluated from the core barrel to the external containment and the shielding walls in the horizontal direction, up to the last magnet of the proton beam-line and the final roof in the vertical one. Moreover, the activation of key materials has been characterized for typical irradiation patterns. This simulation addressed the optimization of key elements of the design, from the cover plate to the local shielding structure above the last magnet.

Gas-Flüssigkeits-Zweiphasenströmungen in Rohrleitungen sind für die Entwicklung und Validierung zweiphasiger CFD-Codes ein geeigneter generischer Untersuchungsgegenstand. Der Grad an strömungsmorphologischer Komplexität ist relativ hoch, was sich insbesondere in der Ausprägung charakteristischer Strömungsregime mit ihren jeweils spezifischen Impulstransferbeziehungen an der Phasengrenze in Abhängigkeit von Leerrohrgeschwindigkeiten und Stoffwerten äußert. An der TOPFLOW-Versuchsanlage des HZDR werden gegenwärtig umfangreiche experimentelle Studien zu Zweiphasenströmungen in senkrechten Testsektionen für Wasser/Luft- und Wasser/Dampf-Strömungen bis 65 bar Druck durchgeführt. Diese Experimente dienen vordergründig der Erhebung von Messdaten für die CFD-Codeentwicklung. Bei aktuellen Studien an einer DN50 Testsektion kommt die ultraschnelle Röntgentomographie als Messverfahren zum Einsatz. Diese ermöglicht es, den Strömungsquerschnitt mit Bildraten von 2500 Bildern/Sekunde und einer räumlichen Auflösung von etwa 1 mm in zwei jeweils 10 mm entfernten Abbildungsebenen zu visualisieren. Verschiedene Strömungsregime werden durch Wahl der Leerohrgeschwindigkeiten für die Gas- und die Flüssigphase am Versuchsstand eingestellt. Neben der Aufklärung des Strömungsregimes und der Erfassung interessanter Detailstrukturen der Strömung, wie Flüssigkeitslamellen zwischen Gasblasen, Wandfilmstrukturen und Kleinblasenverteilungen im Großblasennachlauf, können radiale Gasgehaltsprofile ebenso wie Gasphasengeschwindigkeiten durch automatisierte Auswerteroutinen extrahiert werden. Fernerhin wird derzeit an Auswertealgorithmen zur Vermessung von Einzelblasen, zur Bestimmung der Phasengrenzflächendichte sowie zur Ermittlung lokaler Flüssigphasengeschwindigkeiten gearbeitet. Im Beitrag werden Ergebnisse ausgewählter Studien zu aufwärtsgerichteten Gleichströmungen sowie Gegenströmungen der Gas- und Flüssigphase vorgestellt.

This thesis presents results on the theoretical description of ion acceleration using ultra-short ultra-intense laser pulses. It consists of two parts. One deals with the very general and underlying description and theoretic modeling of the laser interaction with the plasma, the other part presents three approaches of optimizing the ion acceleration by target geometry improvements using the results of the first part. In the first part, a novel approach of modeling the electron average energy of an over-critical plasma that is irradiated by a few tens of femtoseconds laser pulse with relativistic intensity is introduced.
The first step is the derivation of a general expression of the distribution of accelerated electrons in the laboratory time frame. As is shown, the distribution is homogeneous in the proper time of the accelerated electrons, provided they are at rest and distributed uniformly initially. The average hot electron energy can then be derived in a second step from a weighted average of the single electron energy evolution. This result is applied exemplary for the two important cases of infinite laser contrast and square laser temporal profile, and the case of an experimentally more realistic case of a laser pulse with a temporal profile sufficient to produce a preplasma profile with a scale length of a few hundred nanometers prior to the laser pulse peak. The thus derived electron temperatures are in excellent agreement with recent measurements and simulations, and in particular provide an analytic explanation for the reduced temperatures seen both in experiments and simulations compared to the widely used ponderomotive energy scaling.
The implications of this new electron temperature scaling on the ion acceleration, i.e. the maximum proton energy, are then briefly studied in the frame of an isothermal 1D expansion model. Based on this model, two distinct regions of laser pulse duration are identified with respect to the maximum energy scaling. For short laser pulses, compared to a reference time, the maximum ion energy is found to scale linearly with the laser intensity for a simple flat foil, and the most important other parameter is the laser absorption efficiency. In particular the electron temperature is of minor importance. For long laser pulse durations the maximum ion energy scales only proportional to the square root of the laser peak intensity and the electron temperature has a large impact. Consequently, improvements of the ion acceleration beyond the simple flat foil target maximum energies should focus on the increase of the laser absorption in the first case and the increase of the hot electron temperature in the latter case.
In the second part, exemplary geometric designs are studied by means of simulations and analytic discussions with respect to their capability for an improvement of the laser absorption efficiency and temperature increase. First, a stack of several foils spaced by a few hundred nanometers is proposed and it is shown that the laser energy absorption for short pulses and therefore the maximum proton energy can be significantly increased. Secondly, mass limited targets, i.e. thin foils with a finite lateral extension, are studied with respect to the increase of the hot electron temperature. An analytical model is provided predicting this temperature based on the lateral foil width. Finally, the important case of bent foils with attached flat top is analyzed. This target geometry resembles hollow cone targets with flat top attached to the tip, as were used in a recent experiment producing world record proton energies. The presented analysis explains the observed increase in proton energy with a new electron acceleration mechanism, the direct acceleration of surface confined electrons by the laser light. This mechanism occurs when the laser is aligned tangentially to the curved cone wall and the laser phase co-moves with the energetic electrons. The resulting electron average energy can exceed the energies from normal or oblique laser incidence by several times. Proton energies are therefore also greatly increased and show a theoretical scaling proportional to the laser intensity, even for long laser pulses.

Hochschul- und Wissenschaftsmanagement

Nachhaltigkeit und deren Umsetzung in Wissenschaftscampi unter dem Begriff Green Campus ist ein allgegenwärtiges Thema. Beides - Nachhaltigkeit und Green Campus - sind keine Erfindungen der letzten Jahre, bis heute aber konnten die Begriffe nicht eindeutig definiert werden. Während das Thema "Green Campus" wohl eher unter Marketinggesichtspunkten beim Wettstreit um die besten Köpfe in den USA erfunden und nach Europa übergeschwappt ist, dürfte als erster verbriefter Beschreiber der Nachhaltigkeit ein Sachse sein. Der Begriff Nachhaltigkeit wurde durch den sächsischen Oberberghauptmann Carl von Carlowitz in seinem Werk "Sylvicultura oeconomica" (1713) erstmalig erwähnt.

Workshop on computer science and information technologies

Wissenschaft im Dialog – Kooperative Forschungsstelle Technikstress (KFT) – Arbeit und Technik im Wandel

This paper presents free surface flow simulations using different VOF-like interface capturing methods. Both the interFoam solver available in OpenFOAM and the Free Surface Model implemented in ANSYS CFX are applied for the collapse of a water column hitting an obstacle. The computational results of these established methods are compared to a new multi-field concept which is developed for flow situations with multi-scale interfacial structures. The new concept extends the inhomogeneous MUltiple SIze Group (MUSIG)-Model for polydispersed flows by adding a large-scale continuous gas phase. It represents the largest gas structures whose filtered gas-liquid interfaces are captured within the computational domain. Adequate interfacial transfer formulations are introduced for area density and drag and allow the use of different closure models depending on the local morphology. By including appropriate models for the mass transfer, transitions between dispersed and continuous gas morphologies can be described. Thus not only gas-liquid interfaces for large gas structures are detected, but also small scale bubbles that are entrained under the free surface can be described properly taking into account coalescence- and breakup processes. The concept further improves free surface simulations by including sub-grid information about small waves and instabilities at the free surface. Therefore a new treatment of turbulent kinetic energy is applied via source terms at the free surface.
The application of this concept to the dambreak-case with an obstacle demonstrates the breakup of a continuous gas phase and the appearance of polydispersed gas. The collapse of the water column is accompanied by trapping of gas which breaks up to smaller structures. The quality of interface detection during the simulation is compared to the above mentioned VOF-methods. Furthermore the formation of a bubble size distribution underneath the surface serves as a demonstration of the possible benefit using such an averaged multi-field approach.

This paper presents new results for a generalized approach developed for the simulation of two-phase flow problems with multi-scale interfacial structures. The inhomogeneous Multiple Size Group (MUSIG)-model (Krepper et al., 2008) is extended by a large-scale continuous gas phase whose filtered gas-liquid interface is captured within the Eulerian approach. In the framework of the coalescence- and breakup processes desribed by the MUSIG-model, mass transfers between the continuous gas phase and the bubble size groups have to be modelled additionally. The new concept enables transitions between dispersed and continuous gas morphologies, including the evanescence and appearance of a particular phase. Adequate interfacial transfer formulations, which are consistent with such an approach, are introduced for area density and drag. Following the free surface drag-formulation proposed by Höhne and Vallée (2010) shear stresses are considered within the free surface area.
The application of the concept to the dambreak-case demonstrates the breakup of continuous gas into a polydispersed phase consisting of different bubble sizes due to the collapse of a water column. Both resolved free surface structures as well as the entrainment of bubbles and their coalescence and breakup underneath the surface can be described. The computational results will be compared with experiments of Koshizuka et al. (1995). Simulations have been performed with the CFD-code CFX 14.0.
The paper will further investigate the possible improvement of such free surface simulations by including sub-grid information about small waves and instabilities at the free surface. Therefore a new treatment of turbulent kinetic energy at the free surface via source terms will be applied according to the proposal of Brocchini and Peregrine (2001). A comparison of the results will be used for a discussion of possible new mass transfer models between filtered free surface areas and dispersed bubble size groups as part of the future work.

A new concept for generalized two-phase flows (GENTOP) is presented which combines the idea of the inhomogeneous MUSIG-model and the AIAD-approach. It is used for the simulation of transitions between multi-scale interfacial structures. It is demonstrated using three different exemplary cases: the impinging jet with air entrainment, a bubble column and the dambreak case with an obstacle. Main principles are introduced and recent developments on this concept are presented, including a new source term for sub-grid wave turbulence.

Boric acid (B(OH)3) and (poly)borates are of great interest regarding the mobilization of trivalent actinides in nuclear waste repositories, particularly in salt deposits.
This work describes approaches to determine the stability constant in the Eu(III)-borate system. The stability constant between Eu(III) and borates is in the order of magnitude of 1...2, and with it the borate complexation is very weak.
Furthermore, in presence of polyborates at pH 6 the formation of a solid Eu borate species is observed. The formation rate of the solid Eu borate species depends on the polyborate concentration and salt concentration/type (NaClO4/NaCl). Some structural information of the solid Eu borate were provided from IR spectroscopy, solid-state NMR (11B) and solid-state TRLFS.

The investigation of spin wave excitations in nano-magnetic systems is one of the key topics in modern magnetism. Typically, to excite short spin waves it is necessary either to use transducers of the size of a wavelength (micro-striplines or point-contacts) or to excite waves parametrically by a double-frequency spatially uniform microwave signal. Here we demonstrate that the efficient linear excitation of short propagating spin waves is possible in a tri-layer in which the magnetic layers form a vortex pair with opposite circulations.

The mobility of actinides or other contaminants in the subsurface hydrosphere is considerably influenced by their interaction with natural colloids. Besides inorganic particles, aquatic humic substances are ubiquitous in natural waters, and their complexing ability can dominate the speciation of toxic or radioactive metals [1, 2]. Since humic carriers are subject to a solid-liquid distribution depending on geochemical parameters, an adequate assessment of migration processes needs thorough consideration of all interactions within the ternary system metal – humic substance – solid surface, including adsorption / retardation of humic colloids. Reactive transport models have been developed, taking all these processes into account [3-5]. As a prerequisite, reversibility is commonly assumed.

There is, however, a lack of clarity as to whether full reversibility is actually given for the whole ternary system, especially concerning interactions of humic matter with mineral surfaces and metals. For adsorption of humic substances, strong hysteresis has been observed (hardly any desorption upon dilution) [6-8], and recoveries in column experiments have been found to be far from complete [9, 10]. Regarding metal-humic interaction, it has been reported that complexation of higher-valent metals is accompanied by slow processes leading to an increase in complex inertness, i.e., a growing resistance towards dissociation in the presence of competing ligands or metals [11-13].

In view of these uncertainties, the aim of the present study was to elucidate the reversible / irreversible character of processes controlling humic-bound transport. For this purpose, the principle of tracer exchange was employed to gain insight into the dynamics of equilibria within the ternary system. In case of reversibility, a dynamic equilibrium exists, i.e., a permanent run of adsorption and desorption (or complex formation and dissociation) at equal rates. Such an exchange can be detected by introducing a radiotracer into pre-equilibrated systems where all binding sites are occupied.

The chosen model system for these experiments consisted of terbium(III) (as an analogue of trivalent actinides), humic acid (Aldrich) or fulvic acid (isolated from bog water), and kaolinite (KGa-1b standard material). 160Tb as a radioisotope was produced by neutron activation of 159Tb at the TRIGA Mark II reactor of the University of Mainz. Humic and fulvic acids were radiolabelled by an azo coupling reaction with [14C]aniline [14].

To investigate the dynamics of adsorption equilibria, kaolinite suspensions were first contacted with non-radioactive Tb(III) or humic / fulvic acid at a range of concentrations, covering an adsorption isotherm including the plateau region. Subsequent to a pre-equilibration phase, a small amount of the radiotracer (160Tb(III) or 14C-labelled humic / fulvic acid, respectively) was added. After admitting different time periods for equilibration, tracer exchange was evaluated from the concentration decrease in the supernatant. In additional batch experiments, desorption of humic and fulvic acid upon dilution was examined within a comparable time frame.

Reversibility of Tb(III)-humate complexation was investigated in a similar way. Since humic acid precipitates completely on loading with Tb(III), adsorption systems were generated. Here, times for tracer exchange were kept constant, and pre-equilibration times were varied instead.

As expected, adsorption of Tb(III) onto kaolinite was found to be a fast dynamic equilibrium process. Identical adsorption isotherms were obtained regardless of whether the radiotracer was introduced instantaneously together with the non-radioactive metal or subsequently after 2 days of pre-equilibration. For humic and fulvic acid, such dynamic exchange was proven to exist as well, but at considerably lower rates. In case of subsequent tracer addition, the plateau sections of the isotherms were significantly lowered (notably, not to zero). When equilibration times were increased (from 6 hours to 4 weeks), the plateaus approached the respective isotherm for instantaneous tracer addition. Finally, both isotherms coincided, i.e., the dynamic equilibrium was quantitatively represented by the tracer.

In desorption experiments with humic or fulvic acid, initiated by diluting the supernatant after an adsorption phase, no release was observed in the course of 4 weeks, which seems to be contradictory to the above results. One may conclude that the absence of desorption upon dilution is not necessarily indicative of a static equilibrium without any exchange. Thus, models for humic-bound transport are certainly applicable under appropriate conditions. Nonetheless, when comparing the kinetics of exchange to the kinetics of adsorption for humic / fulvic acid, rate constants differ by one order of magnitude [15]. This discrepancy must be taken into account when conditions of a steady local equilibrium are assigned to a maximum flow velocity.

For complexation of Tb(III) with humic acid, we did not find any indications of stabilisation processes affecting the reversibility. Increasing complex inertness has been observed for a variety of metals such as Al(III), Eu(III), Am(III), Th(IV) or U(VI), on time scales ranging from 2 days up to several months (see [13] for a review). In our tracer exchange experiments, Tb(III)-humate complexes were pre-equilibrated for 1 to 90 days before 160Tb(III) was added and a subsequent equilibration period of 1 day was admitted. In all cases, the binding isotherms were indistinguishable from the binding isotherm obtained for instantaneous tracer addition, i.e., an unresisted dynamic exchange was indicated by the tracer, even after long contact times prior to its introduction. Obviously, increasing complex inertness is not a general phenomenon occurring across all higher-valent metals.

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The properties of electron bunch based on the Laser-Wakefield accelerators (LWFA) vary from shot to shot due to changes in the environment, such as gas jet profile or laser pointing. In order to understand the properties of these ultrashort electron bunches like bunch duration and bunch substructure in the range of 0.7 to 40 fs we are building a broadband-spectrometer for measuring coherent and incoherent transition radiation (TR).
Our TR-spectrometer is able to measure the TR-spectrum from a thin Al-foil in a single shot experiment from UV (200 nm) to mid-IR (12µm) by means of a CCD detector for the UV to VIS range and two array detectors for the NIR and MIR range. In this poster we present our design and calibration results of the detectors.

TRAKULA is a BMBF joint research project in the framework “Energie 2020+” that aims for precise measurements of nuclear data relevant for nuclear transmutation technologies. The collaboration consists of the University of Cologne, the Technical University Dresden, the Johannes-Gutenberg University Mainz, the Technical University Munich, the Physikalisch-Technische Bundesanstalt Braunschweig, and the Helmholtz-Zentrum Dresden-Rossendorf. The topics covered are the production and experimental use of fast neutrons to study nuclear reactions, the spectroscopy with photon beams in the MeV range, the development of a high resolution Compton camera, the measurement of low radioactivities including accelerator mass spectroscopy, and the production of homogeneous thin actinide targets for neutron-induced fission measurements. Graduate seminars have been organized to maintain competencies in the field of nuclear safety and radiation research. All topics are connected to each other by their application to nuclear transmutation and nuclear waste management. The progress of the various topics will be explained and results will be presented. Experiments at the neutron-time-of-flight facility nELBE and measurements of fast neutron induced reactions will be discussed in detail. TRAKULA is supported by the German Federal Ministry of Education and Research (Contract 02NUK13A).

Die für die primordiale Nukleosynthese wichtige Reaktion 𝑑(𝛾, 𝑛)𝑝 wurde am supraleitenden Elektronen-Linearbeschleuniger ELBE mit Bremsstrahlung bei einer Endpunktenergie von 5,0 MeV untersucht [1]. Neutronen mit einer kinetischen Energie von 20 − 1400 keV wurden mit Hilfe der Flugzeit-Detektoren RoLAND (Rossendorf Low-Amplitude- Neutron Detector) nachgewiesen. Wechselwirkungen der emittierten Neutronen mit dem Targetmaterial (23 Schichten aus Aluminium und deuteriertem Polyethylen) und anderen Teilen des Expermientaufbaus (HPGe- und BGO-Detektoren, Bleiabschirmungen, Strahlfänger, Betonwände) haben einen nicht zu vernachlässigenden Einfluss und wurden daher mit FLUKA [2] simuliert. Zusammen mit der experimentell bestimmten Detektoreffektivität erhält man einen Flugzeit-abhängigen Korrekturfaktor für das gemessene Neutronenspektrum. Der Aufbau und die Ergebnisse der Simulation sowie die Bestimmung des Korrekturfaktors und dessen Einfluss auf den ermittelten 𝑑(𝛾, 𝑛)𝑝 Wirkungsquerschnitt werden präsentiert.
[1] R. Hannaske et al., PoS(NIC XI)090 (2010). [2] www.fluka.org
Gefördert durch die DFG (JU 2705/1-1).

The status of the NeuLAND time of flight detector for 0.2-1.0 GeV neutrons for FAIR is reviewed.

Die Modellierung astrophysikalischer Szenarien benötigt Eingabepara- meter, deren Präzision besser als die Genauigkeit der entsprechenden astronomischen Beobachtungen ist. Da für einige solche Szenarien wie die Urknall-Nukleosynthese, die Sonne, rote Riesensterne und Superno- vae in unserer Milchstraße inzwischen eine Vielzahl von Beobachtun- gen vorliegen, wird es notwendig, die Raten der dort stattfindenden Kernreaktionen im Labor neu und präzise zu vermessen. Ein probates Mittel für leichte Kerne sind beschleunigergestützte Experimente bei den astrophysikalisch relevanten Energien, die wegen der beobachteten sehr geringen Zählraten allerdings nur dann Aussicht auf Erfolg haben, wenn die Experimente in von der Höhenstrahlung geschützte unterir- dische Labors verlegt werden. Zur Zeit gibt es nur einen Untertage- Ionenbeschleuniger weltweit, die LUNA 0.4MV Maschine am Gran Sasso (Italien).
Im Sommer 2012 wurde ein gebrauchtes 5 MV Hochstrom-Pelletron gekauft und nach Dresden transportiert. Es soll 2013 im Dresdner Untertagelabor Felsenkeller installiert werden und wird durch seinen Energiebereich einzigartig sein. Der Felsenkeller ist durch eine 47m dicke Felsdecke von der Atmosphäre getrennt. In dem Vortrag werden das wissenschaftliche Programm und der Status des Projekts zusam- mengefasst. – Unterstützt von NAVI.