Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

A major limitation for future nanotechnology, particularly for bottom-up manufacturing is the non-availability of 2-dimensional massively parallel probe arrays. Scanning proximity probes are uniquely powerful tools for analysis, manipulation and bottom-up synthesis: they are capable of addressing and engineering surfaces at the atomic level and are the key to unlocking the full potential of Nanotechnology. Generic massively parallel intelligent cantilever-probe platforms is demonstrated through a number of existing and ground-breaking techniques. A packaged VLSI NEMS-chip (Very Large Scale Integrated Nano Electro Mechanical System) incorporating 128 proximal probes, fully addressable with control and readout interconnects and advanced software will be presented.

The AER working group D on VVER reactor safety analysis held its 16th meeting in Paris, France during the period 08-09 May 2007. The meeting was hosted by the CEA France. It followed the final workshop on the OECD/DOE/CEA VVER-1000 Coolant Transient Benchmark held at 07 May. Altogether 11 participants attend the meeting of the working group D, 7 from AER member organizations and 4 guests from non-member organizations. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations. The given presentations and the discussions can be attributed to the following topics:
• Code development and benchmarking for reactor dynamics applications
• Safety analysis methodology and results
• Future activities
New solutions for three different benchmarks were presented and discussed. These are the Second AER Dynamic Benchmark on control rod ejection at hot zero power (S. Kliem, FZD), the VVER-1000 Coolant Transient Benchmark (E. Syrjälahti, VTT) and the stationary AER-FCM101 Benchmark considering a VVER-1000 reactor (C. Parisi, UniPisa).
A. Kereszturi (AEKI) presented a statistical evaluation of the possibility to observe a fuel assembly misloading event. The second presentation of E. Syrjälahti was dedicated to the description how best-estimate coupled code calculations at VTT are supported by uncertainty and sensitivity analyses. K. Velkov (GRS) presented preliminary results of BIPR8KN/ATHLET calculations with a very detailed resolution of the calculation grid on the assessment of coolant mixing inside VVER-1000 assembly heads. Coolant mixing experiments at three different mixing test facilities, modeling different reactor types, were presented and compared by S. Kliem. A calculation study using the coupled code system KORSAR/GP on the consequences of the injection of a slug of unborated water into the reactor core was described by G. Ponomarenko (Gidropress).
A list of the participants and a list of the handouts provided at the meeting are attached to the report. The handouts can be obtained in electronic form from the chairman.

ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using amulti-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H2O2 pre-treatment induced ohmic to rectifying contact conversion on Au/n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure.

EPOS (the ELBE POsitron Source) is a running project to build an intense, bunched positron beam for materials research. It makes use of the bunched electron beam of the ELBE radiation source (Electron Linac with high Brilliance and low Emittance) at the Research Centre Dresden-Rossendorf (40 MeV, 1 mA). ELBE has unique timing properties, the bunch length is <5 ps and the repetition time is 77 ns. In contrast to other Linacsmade for Free Electron Lasers (e.g., TTF at DESY, Hamburg), ELBE can be operated in full cw-mode, i.e., with an uninterrupted sequence of bunches. The article continues an earlier publication. It concentrates on details of the timing system and describes issues of radiation protection.

Positrons, positive muons and deuterons were used – when applicable – to probe the production and thermal stability of defects at room temperature either by electron irradiation or He-ion implantation in zirconia stabilized by yttria in the cubic phase. change in the positron lifetime or in the muon spin relaxation occurs after electron irradiation, indicating a positron saturation trapping the annealed state, owing to the presence of structural defects inherent to phase stabilization. In contrast, after helium implantation, even at low fluence (~10^14 cm^-2), slow positron implantation spectroscopy reveals the presence of a new type of defect (being trapping effective than the native ones), whereas neither positronium nor muonium are detected. The diffusion of helium was followed after 3He-ion implantation and subsequent annealing using the 3He(d,p)4He nuclear reaction. A two-Gaussian distribution fit indicates
a part of the helium atoms is trapped at the projection range location, most likely in gas bubbles, while the other part diffuses gasses after heat treatment already at around 1/5 of the melting temperature. In spite of differences in depths and concentrations by the present techniques, a fairly good correlation is observed between the various results.

The present work reports on microstructure investigations of hydrogen-loaded nanocrystalline Gd films by means of slow positron implantation spectroscopy combined with in situ synchrotron radiation X-ray diffraction. It is found that the virgin films contain a high density of vacancy-like open volume defects at grain boundaries which trap positrons. These defects represent trapping sites also for hydrogen. With increasing hydrogen concentration the transformation from the a- into the b-phase (GdH2) takes place in the film. Accumulation of hydrogen at grain boundaries causes a decrease of positron localization at defects. The transformation into the b-phase is completed at xH ≈ 1.6 H/Gd. Contrary to bulk Gd specimens, the g-phase (GdH3) is not formed in the nanocrystalline Gd films.

Hydrogen loading of thin films introduces very high compressive stresses which grow in magnitude with increasing hydrogen concentration. When the hydrogen-induced stresses exceed a certain critical inplane stress value, the loaded film starts to detach from the substrate. This results in the formation of buckles of various morphologies in the film layer. Defect studies of a hydrogen loaded Pd film which undergoes a buckling process are presented, using slow positron implantation spectroscopy, in situ acoustic emission, and direct observations of the film structure by transmission electron and optical microscopies. It is found that buckling of the filmoccurs at hydrogen concentrations xH ≥ 0.1 and causes a significant increase of the dislocation density in the film.

This thesis deals with infrared studies of impurity states, ultrafast carrier dynamics as well as coherent intersubband polarizations in semiconductor quantum structures such as quantum wells and superlattices, based on the GaAs/AlGaAs material system. In the first part it is shown that the 2pz confined impurity state of a semiconductor quantum well develops into an excited impurity band in the case of a superlattice. This is studied by following theoretically the transition from a single to a multiple quantum well or superlattice by exactly diagonalizing the three-dimensional Hamiltonian for a quantum well system with random impurities. Intersubband absorption experiments, which can be nearly perfectly reproduced by the theory, corroborate this interpretation, showing that at low temperatures in the low doping density regime all optical transitions originate from impurity transitions. These results also require reinterpretation of previous experimental data.
The relaxation dynamics of interminiband transitions in doped GaAs/AlGaAs superlattices in the mid-IR are studied. This involves single-color pump-probe measurements to explore the dynamics at different wavelengths, which is performed with the Rossendorf freeelectron laser (FEL), providing picosecond pulses in a range from 3-200 μm and are used for the first time within this thesis. In these experiments, a fast bleaching of the interminiband transition is observed followed by thermalization and subsequent relaxation, whose time constants are determined to be 1-2 picoseconds. This is followed by an additional component due to carrier cooling in the lower miniband. In the second part, two-color pump-probe measurements are performed, involving the FEL as the pump source and a table-top broad-band tunable THz source for probing the transmission changes. These measurements allow a separate specification of the cooling times after a strong excitation, exhibiting time constants from 230 ps to 3 ps for different excitation densities and miniband widths. In addition, the dynamics of excited electrons within the minibands is explored and their contribution quantitatively extracted from the measurements.
Intersubband absorption experiments of photoexcited carriers in single quantum well structures, measured directly in the time-domain, i.e. probing coherently the polarization between the first and the second subband, are presented. From the data we can directly extract the density and temperature dependence of the intersubband dephasing time between the two lowest subbands, ranging from 50 up to 400 fs. This all optical approach gives us the ability to tune the carrier concentration over an extremely wide range which is not accessible in a doped quantum well sample. By varying the carrier density, many-body effects such as the depolarization and their influence on the spectral position as well as on the lineshape on the intersubband dephasing are studied. Also the difference of excitonic and free-carrier type excitation is discussed, and indication of an excitonic intersubband transition is found.

Recently we reported on single-color pump-probe measurements in doped superlattices (SLs) where we could observe a fast interminiband relaxation (1-2 ps) and much slower components due to subsequent cooling of the electron gas [1]. Pumping and probing at the same wavelength always results in a mixture of these two processes. However, strongly coupled SLs exhibit a broad absorption range so that excitation at a specific k-value in the mini-Brillouin zone influences the electron distribution over the entire zone (see inset of Fig. 1). In order to separate the inter- from the intra-miniband contributions we have performed two-color pump-probe experiments allowing to monitor exclusively the dynamics within the lower miniband. Infrared pulses from the free-electron laser FELBE were used as pump, and broadband THz pulses, generated by phase-matched optical rectification of 10 fs near-infrared pulses, as the probe. The relaxation behavior was studied for three GaAs/Al0.3Ga0.7As SLs having nearly he same doping concentration but different widths of the lower miniband, i.e., 10, 22, and 45 meV. To study the cooling behavior at T=5 K, the FEL pulses were tuned to the high-energy transition at the zone center, while the probe pulse was set to the zone-edge transition. After excitation to the second miniband, the electrons thermalize and relax back to the ground miniband, efficiently heating the electron gas. According to the linear absorption spectrum, this heating leads to induced absorption at the probe energy. For the SL structures with miniband widths below the optical phonon energy we measured cooling times of 40-50 ps for pump intensities higher than 20 MW/cm². For smaller pump intensities the time constants rose up to 200 ps (see Fig. 1). The sample with the miniband width of 45 meV showed a much shorter cooling time of 3.5 ps. This can be explained by the enhanced relaxation via the emission of LO phonons. We will also report room-temperature measurements, where the initially strong absorption is reduced by relaxation towards the zone center which has been depleted by the pump pulse.
References:
[1] D. Stehr et al., Appl. Phys. Lett. 88, 151108 (2006).

Nuclear dipole strength in the tail of the giant dipole resonance

An analytical solution for the startup of an external source in a homogeneous subcritical reactor problem is developed. The problem is described through an approximation of the Boltzmann Transport equation, the Telegrapher's or time dependent P1 equation. The analytical solution to the problem is expressed in terms of a Green's function.

We report on a new measurement of 14N(p,gamma)15O for the ground state capture transition at E_p = 360, 380 and 400 keV, using the 400 kV LUNA accelerator. The true coincidence summing effect the major source of error in the ground state capture determination has been significantly reduced by using a Clover-type gamma detector.

Elastomer materials filled with magnetically and/or electrically susceptible particles promise to have different functionality than conventional elastomers, and therefore, could likely be applied in state-of-the-art control technologies [1]. Of particular interest are elastomers filled with metal coated carbon black (MCCB), which filler fulfils its reinforcing function to the rubber meanwhile changing the elastomer´s electro-magnetic properties. Thus, the rheological and viscoelastic properties of rubber can be changed and controlled by subjecting the compound to a magnetic field.

Recently, the LUNA collaboration has carried out a high precision measurement on the ³He(alpha,gamma)⁷Be reaction cross section with both activation and on-line ? -detection methods at unprecedented low energies. In this paper the results obtained with the activation method are summarized. The results are compared with previous activation experiments and the zero energy extrapolated astrophysical S factor is determined using different theoretical models.

The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted by solar models and in the 7Li abundance obtained in big-bang nucleosynthesis calculations. In the seminar I will report on a new precision experiment on this reaction performed by the LUNA collaboration.

Using a windowless gas target, the high beam intensity of the LUNA2 accelerator, and the Gran Sasso low background gamma-counting facilities, the 3He(alpha,gamma)7Be cross section has been determined by the activation method [1] and by in-beam gamma spectrometry [2] at 90 -- 170 keV center-of-mass energy with a total uncertainty as low as 4%. The new LUNA data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the 3He(alpha,gamma)7Be astrophysical S-factor to solar energies.

The talk will end with an outlook on the 2H(alpha,gamma)6Li experiment planned for the next year at LUNA.

[1] D. Bemmerer et al. (LUNA Collaboration), Phys. Rev. Lett. 97, 122502 (2006)
[2] F. Confortola et al. (LUNA Collaboration), Phys. Rev. C 75, 065803 (2007)

The photodisintegration cross section of the nucleus 92Mo is important for p-process nucleosynthesis. The superconducting electron accelerator ELBE at Forschungszentrum Dresden-Rossendorf provides the possibility to investigate photodisintegration with bremsstrahlung using the photoactivation technique. The reaction 92Mo(gamma,p)91Nb was studied using the decay of 91mNb with a 60.9 d half-life at ELBE [1]. Now the reaction 92Mo(gamma,n)91Mo has been probed using the new pneumatic delivery system to determine the activity of 91mMo (half-life: 65 s). Since the isomer 91mMo decays also into 91mNb it was necessary to measure this process to separate the (gamma,n) from (gamma,p) contributions.
[1] M. Erhard, C. Nair et al., PoS (NIC-IX) 056 (2006)

A generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into the CFD code CFX. The model enables the subdivision of the dispersed phase into a number of size groups regarding the mass balance as well as regarding the momentum balance.

In this work, the special case of polydispersed bubbly flow is considered. By simulating such flows, the mass exchanged between bubble size classes by bubble coalescence and bubble fragmentation, as well as the momentum transfer between the bubbles and the surrounding liquid due to bubble size dependent interfacial forces have to be considered. Particularly the lift force has been proven to play an important role in establishing a certain bubble size distribution dependent flow regime.

In a previous study (Krepper et al. 2005) the application of such effects were considered and justified and a general outline of such a model concept was given. In this paper the model and its validation for several vertical pipe flow situations is presented. The experimental data were obtained from the TOPFLOW test facility at the Forschungszentrum Dresden-Rossendorf (FZD). The wire-mesh technology measuring local gas volume fractions, bubble size distributions and velocities of gas and liquid phases was employed.

The inhomogeneous MUSIG model approach was shown as capable of describing bubbly flows with higher gas content. Particularly the separation phenomenon of small and large bubbles is well described. This separation have been proven as a key phenomenon in the establishment of the corresponding flow regime. Weaknesses in this approach can be attributed to the characterization of bubble coalescence and bubble fragmentation, which must be further investigated.

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The solubility and the speciation of uranium(VI) in water at neutral pH with mM total uranium concentrations (Utot) is dominated by polymeric hydroxo species (e.g., (UO2)2(OH)22+ and (UO2)3(OH)5+). Thermodynamic data of various polymeric species had been reviewed and were published as OECD/NEA database [1]. However, direct structural information of polymeric uranyl hydroxo species are scarce. Here EXAFS in combination with quantum chemical calculations can serve as a powerful tool to explore the structure of polymeric uranyl hydroxo species in order to correlate thermodynamic speciation [1] with structural information from EXAFS. For instance, this method can provide both U-U distances and U-U coordination numbers, and can be a direct proof of the presence of dimeric and trimeric complexes. (UO2)3(OH)5+ and (UO2)3(O)(OH)3+ are stoichiometric equivalent but they significantly differ in the U-U distance and can be distinguished by EXAFS. In this work, the structures of uranyl trimeric hydroxo complexes in aqueous solution have been studied by the B3LYP hybrid density functional theory (DFT) calculations and were compared with EXAFS structural information and thermodynamic speciation.
We studied the structure of trimeric uranyl(VI) hydroxo species including (UO2)3(OH)5+ and (UO2)3(O)(OH)3+ by DFT calculations, and obtained that the U-U distances vary between 3.83 and 4.30 Å. Among them, two species were found to be energetically favorable. One is (UO2)3(O)(OH)3+ having oxo bridging in the center with an average U-U distance of 3.83 Å. The other is (UO2)3(OH)5+ with no bridging oxygen in the center and an average U-U distance of 4.30 Å. A previous EXAFS and 17O-NMR study on the trimeric uranyl hydroxo complex by Moll et al.[2] reports the U-U distance of 3.80 Å and coincides well with the structure of (UO2)3(O)(OH)3+ obtained by DFT calculations. The EXAFS/DFT results are also discussed together with thermodynamic speciation of uranyl(VI) under the given condition (pH, Utot, I, etc.) and with Raman spectroscopic data of various polymeric hydroxo species obtained by Nguyen-Trung et al. [3]. Not only the structural information, but also the kinetics of the proton transfer in (UO2)3(O)(OH)3+ to yield (UO2)3(OH)5+ was studied.
[1] Guillaumont, R.; Fanghänel, T.; Fuger, J.; Grenthe, I.; Neck,V.; Palmer, D.A.; Rand, M.H. Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium; Elsevier Science Publishing Company, Inc.: New York, 2003; Vol. 5.
[2] Moll, H.; Reich, T.; Szabo, Z. Radiochim. Acta 2000, 88, 411.
[3] Nguyen-Trung, C.; Palmer, D.A.; Begun, G.M.; Peiffert, C.; Mesmer, R.E. J.Sol.Chem. 2000, 29, 101.

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The structures of aqueous U(VI), U(IV) and Th(IV) sulfato complexes were investigated by LIII edge EXAFS spectroscopy in solutions with total sulfate concentrations ranging from 0.05 to 3 M. U(VI), U(IV) and Th(IV) sulfate samples comprises both, sulfate in monodentate and bidentate co-ordination. In equimolar [SO4 2-]total/U(VI) solutions, the species distribution is dominated by monodentate sulfate co-ordination with a U-Smon distance of 3.57±0.02 Å. With increasing [SO4 2-]total/U(VI) ratio, bidentate co-ordination becomes dominant with a U-Sbid distance of 3.11±0.02 Å. In general, in all systems the bidentate co-ordination becomes dominant with increasing sulfate co-ordination. An exclusively bidentate co-ordination was observed only for U(VI) with high total sulfate concentration. The aqueous Th(IV) sulfate comprises both, monodentate and bidentate co-ordination with Th-S distances of 3.14±0.02 and 3.81±0.02 Å, respectively. A similar co-ordination is obtained for U(IV) sulfato complexes at pH 1 with U-S distances of 3.08±0.02 Å and 3.67±0.02 Å. These parameters were used to identify the structure of some corresponding thermodynamic species. The EXAFS data suffer from double-electron resonances that will be discussed in a second contribution.

Selenium oxoanions are abiotically reduced on Fe(II/III) hydroxide (green rust) and Fe(0) metal surfaces to Se oxidation states of 0, -I or –II with relatively slow reaction kinetics 1, 2]. The unequivocal phase characterization by EXAFS spectroscopy, which is a key for the determination/prediction of Se solubility, was hindered by incomplete reduction, insufficient spectral data ranges and the similarity in short-range structures of the potential mineral phases. In a recent study [3], however, we were able to clearly identify the reduction product of selenite co-sorbed with Fe2+ to montmorillonite as nano-particulate, trigonal Se(0) by collecting low-noise EXAFS spectra at 15 K (Rossendorf Beamline at ESRF, Grenoble, France) and by employing advanced data analysis methods [4, 5]. Here, we present data on the reduction of selenite by green rust, magnetite, siderite and mackinawite. In the presence of green rust, selenite was completely reduced to trigonal Se(0) within one day, which was further converted to ferroselite (orthorombic FeSe2) within one month. The associated Fe(II) oxidation and magnetite formation quantified by Moessbauer spectroscopy allowed us to establish the following reaction scheme: 32 [FeII 12FeIII 5(OH)34 Cl-5 H2O](s) + 38 SeIVO3 2- ⇔ 19 [FeIISe-I 2](s) + 175 [FeIIFeIII 2O4 formed. The observed differences in reaction end products and reduction kinetics may significantly affect Se bioavailability and Se migration.
References
[1] Myneni, S. C. B., Tokunaga, T. K., and Brown, G. E.
(1997) Science 278, 1106-1109.
[2] Scheidegger, A. M., Grolimund, D., Cui, D., et al. (2003)
J Phys. IV 104, 417-420.
[3] Charlet, L., Scheinost, A. C., Tournassat, C., et al. (2007)
Geochim. Cosmochim. Acta, in review.
[4] Scheinost, A. C., Rossberg, A., Vantelon, D., et al. (2006)
Geochim. Cosmochim. Acta 70, 3299-3312.
[5] Rossberg, A., Reich, T., and Bernhard, G. (2003) Anal.
Bioanal. Chem. 376, 631-638.

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THz physics at the Research Center Dresden-Rossendorf: From scalable photoconductive THz antennas to near-field microscopy of ferroelectrics using a free-electron laser

The structures of uranyl(VI) hydroxo dimer and trimer in aqueous solution were studied by EXAFS, FTIR, and UV-vis spectroscopy and also by density functional theory (DFT) calculations. DFT calculations show that (UO2)2(OH)22+ have two bridging hydrxo groups with the U-U distance of 3.88 Å which had a good agreement with EXAFS measurement. For hydroxo trimer complex, DFT calculations show that (UO2)3(O)(OH)3+ with oxo bridging in the center is energetically favored above its stoichiometric equivalent (UO2)3(OH)5+. This idea was confirmed by the EXAFS measurements where a shorter U-U distance of 3.83 Å was observed and the presence of oxo bridging in the center was confirmed. Several stable intermediates which lie several tens of kJ/mol above the stable energy minimum, (UO2)3(O)(OH)3+, were identified and their structures, energies, and intramolecular proton transfer reaction are discussed.

The liquid metal ion source, is now the basis of focused ion beams systems that use a variety of heavy metal ions (with currents of 1pA – 30nA) which can be focused into diameters smaller than 10nm with current densities of several A/cm2. The predominate use of these systems has been in various aspects of IC fabrication. Implantation is an essential process for the fabrication of electronic devices and integrated circuits. One of the most important parameters in the operation of focused ion beam (FIB) columns is the energy spread of the ion beam, normally expressed as the full width at half the maximum height of the energy distribution (FWHM). When it was demonstrated that failure analysis and integrated circuit modification could be done with focused ion beams utilizing liquid metal ion sources, the resulting technological “push” for high performance caused the rapid development of new ion beam instrumentation. Among other applications, FIBs are now used for research lithography, direct implantation (using alloy metal ion sources with ion species including As, B, Bi, Ga, Ge, Au and Be), lithographic mask repair and a wide variety of micromachining uses.
An interesting element for materials investigation and modification is bismuth, which offers a broad spectrum of applications. Silicon doped with bismuth is an interesting choice because the ionization energy of Bi in Si is much larger than that of other group-V elements. Turning now to the present work we investigated a BiGa LMIS. We present the energy spread (ΔΕ) of the main ions of the beam drawn from the BiGa source as a function of source current (i). In conclusion, even though the deviation from the 2/3 power law of the low – current portion of the ΔΕ versus I curves has been explained in terms of instabilities at the emitter that set in at a particular level of current.

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelength ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures were found on a large variety of materials, such as semiconductors, metals, and insulating surfaces. The formation and early evolution of the ripple patterns can be qualitatively reproduced by a linear continuum equation derived by Bradley and Harper. However, at longer times nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
In this work we report on the simultaneous formation of two perpendicular ripple modes on amorphized Si(100) during high fluence sputtering at sub-keV energies. The evolution of both modes was studied for two different energies and over a wide range of fluence. Coarsening of both ripple modes was found. The wavelengths of the two modes are of the order of a few ten and several hundred nanometers, respectively, and show similar time dependence. To gain better understanding of the evolution of the surface morphology, the results are compared to simulations of the damped Kuramoto-Sivashinsky equation, finding good qualitative agreement.

For an adequate simulation of poly-disperse bubbly flows the consideration of the bubble size distribution is required, since the interaction between the liquid and the gas bubbles sensitively depends on the bubble size. In the frame of multi-fluid models this can be done by dividing the gas phase into a number of bubble classes. To test sub-models suitable for implementation into CFD codes a simplified test solver suitable for vertical pipe flow was developed and successfully applied in the last years. It considers a number of bubble classes, but resolves volume fractions of the single bubbles classes, velocities and turbulence parameter only in radial direction. Progress was achieved especially for the models reflecting the momentum transfer between gas and liquid phases (models on bubble forces). The situation is still unsatisfying regarding the simulation of bubble coalescence and break-up. One of the reasons may come from shortcoming in the calculation of turbulence parameters. Local bubble coalescence and break-up rates strongly depend on local turbulence parameter, namely and i. Bubble induced turbulence is presently considered in most CFD codes as well as in the Test-Solver by an additional term for the turbulent viscosity to obtain more accurate velocity calculations. In order to improve the local values of turbulence parameter it is necessary to include source term into the equations of the turbulence model itself. For the case of the Turbulence model such source term can be found in Literature. A simplified turbulence model was implemented in the test solver. In this work this simple model was replaced by two-phase model along with a source term out of the literature. The model was numerically solved and successfully implemented into the Test-Solver. The new calculated results were validated against old simple model calculations as well as against experimental data from MTLoop (DN50) and TOPFLOW (DN200). New calculations with model and source term bring clear improvements upon old ones and resolves significant discrepancies appeared in old calculations in DN200 data. A comparison with CFX 5.7 calculations for some points in DN50 is presented as well. The comparison shows the need for implementation of the source term in CFD calculations.

Cell- and lattice calculations are the fundament for all deterministic static and transient 3D full core calculations. The spatial discretization used for the cell- and lattice calculations influences the results for these transport solutions significantly. The arising differences in the neutron flux distribution due to different spatial discretization are demonstrated. These differences in the flux distribution cause significant changes in the kinf value. An evaluation of the kinf value for the case of infinitely fine discretization is made. The influence of the discretization on the calculation of homogenized few group cross sections which are forwarded to the 3D full core calculations is investigated. Strategies for improving the discretization are developed and their influence on the calculation time is evaluated.

The interplay of the effects of geometry and collective motion on d–α correlation functions is investigated for central Xe+Au collisions at E/A=50 MeV. The data cannot be explained without collective motion, which could be partly along the beam axis. A semi-quantitative description of the data can be obtained using a Monte Carlo model, where thermal emission is superimposed on collective motion. Both the emission volume and the competition between the thermal and collective motion influence significantly the shape of the correlation function, motivating new strategies for extending intensity interferometry studies to massive particles.

Natural-circulation characteristics at low pressure/low power have been studied by performing experimental investigations and numerical simulations.
The PANDA large scale facility was used to provide valuable, high quality data on natural circulation characteristics as a function of several parameters and for a wide range of operating conditions. The new experimental data allow for testing and improving the capabilities of the thermal-hydraulic computer codes to be used for treating natural-circulation loops in a range with increased attention.
This paper presents a synthesis of a part of the results obtained within the EU-Project NACUSP “Natural circulation and stability performance of Boiling Water Reactors”. It does so by using the experimental results produced in PANDA and by showing some examples of numerical simulations performed with the thermal-hydraulic code ATHLET.

Electromagnetic dipole-strength distributions up to the particle separation energies are studied for the stable even-even nuclides 92,94,96,98,100 Mo in photon scattering experiments at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf. The influence of inelastic transitions to low-lying excited states has been corrected by a simulation of gamma cascades using a statistical model.
After corrections for branching ratios of ground-state transitions, the photon-scattering cross-sections smoothly connect to data obtained from (gamma,n)-reactions. With the newly determined electromagnetic dipole response of nuclei well below the particle separation energies the parametrisation of the isovector giant-dipole resonance is done with improved precision.

The technique of positron emission tomography is the only known method to monitor the dose delivery precision of ion beam radiotherapy three-dimensionally, in-vivo and non-invasively. The different approaches of PET therapy monitoring and their clinical impact are described. In addition, the feasibility of extending the method of in-beam PET for hard photon beams is discussed.

Natural uranium contains the isotope U-238 of 99.3% and the isotope U-235 of 0.7 %. U-235 has to be enriched for using uranium as nuclear fuel. Depleted uranium (DU) is a by-product in that enriching process. It is accumulated in considerable amounts in this process all over the world. Due to its high density (19.1 g/cm3) DU is used as counterweights in ships and airplanes in the civil industry. In addition, DU is utilised for military purposes both in cladding for armoured vehicles and projectiles.
Such projectiles were used by NATO troops in the wars of Iraq, Serbia, and Bosnia. At impact the projectile becomes pulverized and transferred as finely dispersed powder into soil and may cause long-term ecological problems especially in agriculturally used areas. Consequently, the public was alarmed and discussions concerning possible health risks for civil population and soldiers who came into contact with DU arose.

Electromagnetic, i.e. Lorentz forces can be used to control the flow of conducting fluids. This holds true even if the electrical conductivity is only weak, as in the case of electrolytes like sea-water.

The applications of streamwise, wall parallel Lorentz forces to generic flow configurations will be exemplified with experimental data from flat plate boundary layers and separated flows around cylinders and hydrofoils. These results demonstrate the ability of stationary Lorentz forces to change the velocity profile in boundary layers and thereby to improve their stability properties, as well as to completely suppress separation. Time dependent Lorentz forces are used to mitigate the lift loss and drag increase of hydrofoils caused by flow separation. In this case, the versatility of Lorentz force actuators allows for detailed experimental investigations especially of the effects of excitation frequency and wave form.

Finally, the impact of the low conductivity on the energy balance of Lorentz force actuators is discussed.

A composite specimen (cylinder) consisting one half each of dunite and quartzite was superimposed (shock) deformed (16-34 GPa). Intracrystalline residual strain was determined from diffraction pattern, obtained using synchrotron radiation at beamline ROBL (ESRF Grenoble). Considerable differences in residual microstrain were determined as the interface is approached. Moreover, the tendencies in size evolution of scattering crystallites were evaluated by diffraction peak shape analysis. The superimposed deformation produced a new microsize structure in dunite, but was only modifying the macrostructure in quartzite, which already exists before the superimposed deformation. Otherwise, the size of scattering crystallites (related to foliation) of quartzite was reduced about six times more than that of dunite (in relation to the newly formed structure).

The complex [BuMeIm]2[UCl6] was characterized in the solid state and in a solution of [BuMeIm][Tf2N] room temperature ionic liquid using single-crystal XRD, EXAFS, visible absorption spectroscopy and NMR techniques.The structure of solid [BuMeIm]2[UCl6] contains two crystallographically independent formula units (U(1) and U(2)).The U–Cl distances in UCl6 2 anions range from 2.576(6) to 2.638(4) A ˚ , the average values being 2.621(6) and 2.601(8) A ˚ for U(1) and U(2), respectively.The BuMeIm+ cations have four different conformations of C4H9 chains.The shortest distances between the centres of the five-member rings of the BuMeIm+ cations and U atoms of [UCl6]2 anions are in the range 5.53–4.90 A ˚ .Single-crystal XRD data reveal the existence of a hydrogen bond between the most acidic H atom of the imidazolium ring (C2) and the chloride anion of the UCl6 2 octahedron, with the shortest distance Cl H(C2) equal to 2.57 A ˚ .Quantitative EXAFS measurements indicate that the octahedral complex UCl6 2(RU–Cl = 2.632(2) A ˚ ) is the predominant chemical form of U(IV) in [BuMeIm][Tf2N] solution.Visible absorption spectroscopy and 1H NMR spectroscopy confirm the existence of hydrogen bonding between theUCl6 2 anion and the acidic proton of the BuMeIm+ cation in RTIL solution, similar to that in the solid state.

Der Vortrag gibt einen Überblick über die Anwendung der Computertomographie in verfahrenstechnischen und strömungsdiagnostishcen Problemstellungen. Behandelt werden insbesondere die Röntgen- und Gammastrahlentomographie.

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance with the development of the nano-technology. For special purposes like writing ion implantation for doping or ion beam synthesis (IBS) in the µm- as well as in the nm-range without any lithographic steps ion species other than gallium become more and more relevant. Therefore mass separated FIB systems equipped with alloy liquid metal ion sources (LMIS) play an increasing role.
So a Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the IBS at elevated sample temperatures and subsequent annealing for the fabrication CoSi2 nano-structures down to 20 nm on Si(111) and Si(100) substrates. The combination of FIB implantation (top-down approach) and self organization processes (bottom-up approach) during IBS can provide a spatial reduction of the locally implanted structures. A further investigated process is the defect induced formation of CoSi2 nanoparticles and nanowires using other ions than cobalt in the FIB (Au, Nd, Si, Ga), focused down to a spot diameter less than 30 nm at room temperature, and a Co deposited film on the rare side of the wafer. In this case crystalline CoSi2 nanowires of 10 – 30 nm diameter and a length up to some ten micrometer always aligned along the (110) orientations have been observed. These structures were studied using SEM/EDX and AFM analysis as well as by electrical characterization after contacting with W-pads, fabricated by FIB MO-CVD.
Other processes for the fabrication of nanstructures, like templating, 3D ion milling and the combination of FIB implantation and wet chemical anisotropic etching will be presented and discussed.
The high resolution mass separated Rossendorf FIB system, equipped with the CANION 31Mplus column (Orsay Physics) was applied with different (alloy) liquid metal ion sources (CoNd, AuSi, Ga) to demonstrate a emerging possibilities of nanostructure fabrication.

The complex formation of the uranyl ion, UO22+, with chloride ions in acetonitrile has been investigated by principal component analysis of UV-vis absorption and U L3–edge EXAFS spectra. As a function of increasing [Cl]/[UO22+] ratio the species [UO2(H2O)5]2+, [UO2Cl(H2O)2(MeCN)2]+, [UO2Cl2(H2O)(MeCN)2], [UO2Cl3(MeCN)2] and [UO2Cl4]2 have been observed. The determined distances in the first coordination sphere are: U-Oax = 1.77 Å, UOH2O = 2.43 Å, UNMeCN = 2.53 Å and UCl = 2.68 Å. From the intermediate solution with the [Cl]/[UO22+] ratio of 2 a crystalline precipitate has been obtained. The crystal structure of this compound, [(UO2)4(2-Cl)4(3-O)2(H2O)2(CH3CN)4]•(CH3CN), has been determined.

Palladized biomass of typical Gram negative bacteria (Desulfovibrio desulfuricans and Escherichia coli) is well documented as a potentially useful catalyst for reduction of metallic species such as Cr(VI). This bionanocatalyst can be sourced from Pd-waste and scrap leachates via biocrystallization. A major industrial application of precious metal catalysts is in hydrogenation and hydrogenolysis reactions whereby, respectively, H is added across unsaturated bonds and halogen substituents can be removed from aromatic rings. Gram positive bacteria have not been evaluated previously as potential supported Pd-bionanocatalysts. We compare the activity of ‘Bio-Pd(0)’ supported on the fundamentally different Gram negative (Desulfovibrio) and Gram positive (Bacillus) bacterial surfaces, and evaluate the activity of the two types of ‘Bio-Pd(0)‘ in a standard reference reaction, the hydrogenation of itaconic acid, against a commercially available catalyst (5% Pd on carbon). The results show that the bionanocatalysts have a similar activity to the commercial material and biomanufacturing from waste sources may be an economic alternative to conventional processing for catalyst production as precious metal prices continue to rise.

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance with the development of the nano-technology. For special purposes like writing ion implantation for doping or ion beam synthesis (IBS) in the µm- as well as in the nm-range without any lithographic steps ion species other than gallium become more and more relevant. Therefore mass separated FIB systems equipped with alloy liquid metal ion sources (LMIS) play an increasing role.
A Co-FIB obtained from a Co36Nd64 alloy LMIS was applied for the IBS at elevated sample temperatures and subsequent annealing for the fabrication CoSi2 nano-structures down to 20 nm on Si(111) and Si(100) substrates. The combination of FIB implantation (top-down approach) and self organization processes during IBS (bottom-up approach) can provide a spatial reduction of the FIB implanted structures. A second investigated process is the defect induced formation of CoSi2 nanoparticles and nanowires using other ions than cobalt in the FIB, focused down to a spot diameter less than 30 nm at room temperature. The source for Co atoms for the NW growth was a 10 nm thin Co film evaporated onto the rear side of the wafer. The FIB irradiation of Nd, Ga, Si and Au ions and doses of 1015-1017 cm-2 creates a broad spectrum of defects in the substrate. Subsequent annealing leads amongst others to the formation of rod-like extended {311}-defects, which act as a prime source of transient enhanced diffusion of impurities in silicon. Also these defects can dissolve and form other rod-like defects always aligned to the (110) direction with a diameter of 10 – 20 nm and a length of some hundred nm. The heat treatment (1000°C, 30 min, N2) leads to a gettering of cobalt atoms in these defects followed by a CoSi2 formation through Ostwald ripening which stabilizes the origin of the defect rods. The obtained crystalline CoSi2 nanowires showed a diameter of 10 – 30 nm and a length up to some ten micrometer always aligned along the (110) orientations independent of the FIB writing direction with respect to the wafer orientation. These structures were studied by SEM/EDX and AFM analysis as well as by electrical characterization after contacting with W-pads, fabricated by FIB MO-CVD [1].
Furthermore, the high resolution mass separated Rossendorf FIB system, equipped with a CANION 31Mplus column (Orsay Physics) and a Ga liquid metal ion source (LMIS) as well as with different alloy LMIS (CoNd, AuSi, etc.) was used to fabricate other nanostructures.

[1] C. Akhmadaliev, B. Schmidt and L. Bischoff, Appl. Phys. Lett. 89 (2006) 223129

Response of microbial community of a depleted uranium waste to treatments with U(VI) and/or nitrate was studied by using molecular methods. The applied 16S rRNA- and narG-gene retrievals, demonstrated that the samples harbour a large number of hidden species inducible by nitrate, some of which are also capable to tolerate U. The changes in bacterial community depended on the salt solutions used and on the aeration condition. The archaeal populations, in contrast, were shifted to one particular group, independently on the art of the treatments. After longer incubations with U(VI) the initial structure of the bacterial community started to recover, indicating that the added U was no longer bio-available.

The structural phases of C:Ni nanocomposite thin films prepared by ion beam co-sputtering at temperatures 25°C =< T =< 500°C were characterized by NIR Raman spectroscopy. Ni was found to cata-lyse sixfold ring clustering and graphitisation of carbon in C:Ni nanocomposites.

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The magnetorotational instability (MRI) is believed to play a crucial role in the formation of stars and black holes. By destabilizing otherwise stable Keplerian flows, the MRI enables outward transport of angular momentum in accretion discs which is a necessity for the growth of the central objects. Usually, MRI is investigated under the assumption of an externally applied axial magnetic field. However, the effort to investigate the MRI in a liquid metal experiment can be dramatically reduced if the purely axial magnetic field is replaced by a helical magnetic field. We summarize the results of a various Taylor-Couette experiments with the liquid metallic alloy GaInSn under the influence of helical magnetic fields that show typical features of MRI at Reynolds numbers of the order 1000 and Hartmann nubers of the order 10.

Plasma immersion ion implantation (PIII) of nitrogen on AISI 316L austenitic stainless steel has been investigated at four different negative implantation biases (5, 10, 15, 20 kV) and two different pulse-on-times (5 and 10 mu s) for developing a nitrogen/nitride-rich corrosion resistive layer. Post implanted specimens were examined by X-ray diffraction, and subjected to potentiodynamic polarization tests in 1 wt.% NaCl solution. PIII at - 15 kV shows significant and optimum improvement in corrosion resistance.

The electrophilic metal fragment [^99mTc(N)(PNP)]²⁺ (PNP = diphosphane ligand) has been employed for the labeling of fatty acid chains of different lengths. To provide a site-specific group for the attachment of the metallic moiety, the fatty acid derivatives were functionalized by appending a bis-mercapto or, alternatively, a dithiocarbamato π-donor chelating systems to one terminus of the carbon chain to yield both dianionic and monoanionic bifunctional li-gands (L). The resulting complexes, [^99mTc(N)(PNP)(L)]^0/+, exhibited the usual asymmetrical structure in which a Tc≡N group was surrounded by two different bidentate chelating ligands. Dianionic ligands gave rise to neutral complexes, while monoanionic ligands afforded mono-cationic species. Biodistribution studies were carried out in rats. An isolated perfused rat heart model was employed to assess whether the new labeled fatty acids still were recognized as substrates for β-oxidation. Results showed that only monocationic complexes accumulated in myocardium to a significant extent. Conversely, neutral complexes were not efficiently re-tained into the heart region and rapidly washed out. In isolated perfused rat heart experiments, monocationic complexes exhibited a behavior similar to that of the monocationic flow tracers ^99mTc-MIBI and ^99mTc-DBODC with almost identical extraction values, a result that could be attributed to the presence of the monopositive charge. Instead, a slightly lower myocardial ex-traction was found for neutral complexes. Comparison of the observed kinetic behavior of neutral complexes in the isolated perfused rat heart model with that of the myocardial meta-bolic tracer [¹²³I]IPPA revealed that the introduction of the metallic moiety partially hamper recognition of the labeled fatty acids by cardiac enzymes and, consequently, their behavior did not completely reflect myocardial metabolism.

When amorphous silica is bombarded with energetic ions, various types of defects are created as a consequence of ion-solid interaction (oxygen deficient centers (ODC), non-bridging oxygen hole centers (NBOHC), E'-centers, etc.). Luminescent peaks from oxygen deficiency centers at 2.7 eV, non-bridging oxygen hole centers at 1.9 eV and defect centers with emission at 2.07 eV were observed by changing the concentration of implanted Gd3+ ions. Charge trapping in Gd-implanted SiO2 layers was induced using constant current electron injection to study the electroluminescence intensity with dependence on the applied voltage change. The process of electron trap generation during high field carrier injection results in an increase of the electroluminescence from non-bridging oxygen hole centers. Direct correlation between electron trapping and the quenching of the electroluminescence at 2.07 eV and 2.7 eV was observed with variation of the implanted Gd concentration.

The presented alloy liquid metal ion source enables a long term stable emission of Li ions. By using a Ga35Bi60Li5 alloy the difficulties in handling chemically very active lithium as a source material could be overcome. The mass spectrum and the energy spread of the certain ion species are presented and discussed. For lithium a FWHM of the energy distribution of about 2 eV at an emission current of about 1 µA was found as it is predicted by the theory due to the m1/3 dependence of the energy spread on mass of the projectile ion.

We report the changes in 100 keV Kr ion-irradiated nanoscale Co/Pt multilayers at different temperatures and fluences.We observe irradiation-induced changes in their structural and magnetic properties. Ion beam-induced mixing across the interfaces leads to the formation of a CoPt ordered/disordered phase. Alarge increase in the coercivity is also observed when the irradiation is performed at room temperature. Such an enhancement in the coercivity is attributed to defect clustering and CoPt ordered/disordered phase formation. The mechanism of phase formation is explained in light of the heat of formation rule.

Mineral wool insulation debris, which is generated during a loss-of-coolant-accident (LOCA), has the potential to undermine the long-term recirculation capability of the emergency core coolant system (ECCS) in a nuclear power plant. Most importantly, ECCS pumps are faced with an increasing pressure drop while insulation debris accumulates at the pump suction strainers. The presented study aims at modelling the pressure drop of flows across growing cakes of compressible, fibrous materials and at the implementation of the model into a general-purpose 3D computational fluid dynamics (CFD) code. Computed pressure drops are compared with experimentally found values. The ability of the CFD implementation to simulate 3D flows with a non-uniformly distributed particle phase is exemplified using a step-like channel geometry with a horizontally embedded strainer plate.

The effect of neutron flux on the formation of irradiation-induced clusters in reactor pressure vessel (RPV) steels is an unresolved issue. Small-angle neutron scattering was measured for a neutron-irradiated RPV weld material containing 0.22 wt% impurity Cu. The experiment was focused on the influence of neutron flux on the formation of irradiation-induced clusters at fixed fluence. The aim was to separate and tentatively interpret the effect of flux on the characteristics of the cluster size distribution. We have observed a pronounced effect of neutron flux on cluster size, whereas the total volume fraction of irradiation-induced clusters is insensitive to the level of flux. The result is compatible with a rate theory model according to which the range of applied fluxes covers the transition range from a flux-independent regime to a regime of cluster growth slowing down with increasing flux. The results are confronted with measured irradiation-induced changes of mechanical properties.

In an effort to develop ^99mTc-labelled fatty acids (FAs) for myocardial metabolism and flow imaging, several ^99mTc analogues according to the ‘3+1’ and the ‘4+1’-mixed ligand approach were synthesized and myocardial extraction was evaluated in non-working isolated guinea pig hearts. Biodistribution patterns in guinea pigs were determined exemplarily of one FA analogue.

We give an overview of the production of highly charged ions in the room-temperature Dresden EBIT and its successors, the Dresden EBIS and Dresden EBIS-A, and their application in different areas. Due to their compact design they are favored for the study and use of the interaction of ions with surfaces. In particular, interaction processes with highly charged ions are of special interest due to their properties, such as the high yield of secondary particles, which open up new techniques in surface structuring and materials analysis. Single ion hits are found to create hillock-like structures on the nanoscale which is shown for a HOPG surface irradiated by argon ions. Since the ion beams that are extracted from the Dresden EBIT and EBIS devices are characterized by a small beam emittance other applications come into focus, such as in FIB technology where there is a great demand for beams of noble gases. First results of the production of a helium ion beam in the Nano-FIB at ! LPN/CNRS employing a Dresden EBIT are presented. Furthermore molecular fragments can be produced, shown by means of a spectrum of propane fragments, which not only are of interest in life sciences.

Performance assessment studies in underground disposal of radioactive or toxic waste need to consider all reactive interactions between waste and its surroundings. Thermodynamic equilibrium and reaction path calculations represent an important tool for this purpose. The reliability of the results depends first of all on the quality of the thermodynamic database used for the calculations. Several quality criteria of thermodynamic databases are discussed in connection with the characteristics of current database projects [Nuclear Energy Agency Thermochemical Database (NEA-TDB), Yucca Mountain database, Dortmund Databank (DDB), Common Thermodynamic Database (CTD), FreeGS, and Thermodynamic Reference Database (THEREDA)] including the situation for molten salts. The future role of the IUPAC standard for thermophysical and thermochemical data storage is emphasized.
Keywords: thermodynamic databases; radioactive waste disposal; geochemical databases; ThermoML; performance assessment studies.

NiCl2-4SC(NH2)2 (DTN) is a quantum spin-1 chain system with strong easy-pane anisotropy and a new material for studying the magnon condensation in magnetic fields. In this talk, I will present tunablefrequency electron spin resonance (ESR) studies of magnetic excitations in DTN in fields up to 25 T. First, I am going to show how the high-field ESR can be used for describing the temperature-field phase diagram and the low-temperature magnetization data in the field-induced ordered phase of DTN. Second, I will report on the first conclusive observation of the two-magnon bound states, which is a unique feature of the high-field spin-polarized phase of spin-1 large-D Heisenberg chains. Third, based on the analysis of the ESR data, I am going to discuss the relevance of the underlying physics in DTN to the field-induced Bose-Einstein Condensation phenomenon in quantum antiferromagnets. Finally, I will briefly talk about recent developments of the high-field ESR Program at the Dresden High Magnetic Field Laboratory.

We have studied the thermodynamic properties of single-crystalline TbFe₃(BO₃)₄. Magnetization measurements have been carried out as a function of magnetic field (up to 50 T) and temperature up to 350 K with the magnetic field both parallel and perpendicular to the trigonal c axis of the crystal. The specific heat has been measured in the temperature range 2–300 K with a magnetic field up to 9 T applied parallel to the c axis. The data indicate a structural phase transition at 192 K and antiferromagnetic spin ordering at T_N≈40 K. A Schottky anomaly is present in the specific-heat data around 20 K, arising due to two low-lying energy levels of the Tb³⁺ ions being split by f-d coupling. Below T_N, magnetic fields parallel to the c axis drive a spin-flop phase transition, which is associated with a large magnetization jump. The highly anisotropic character of the magnetic susceptibility is ascribed mainly to the Ising-like behavior of the Tb³⁺ ions in the trigonal crystal field. We describe our results in the framework of a unified approach which is based on mean-field approximation and crystal-field calculations.

Dipole-strength distributions up to the neutron-separation energies of the even-mass Mo isotopes from {92}Mo to {100}Mo and of the N=50isotones {88}Sr, {89}Y, {90}Zr have been investigated in photon-scattering experiments using the bremsstrahlung facility at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf. A measurement using polarised bremsstrahlung impinging on {88}Sr revealed that all resolved transitions with energies greater than 6 MeV in this nuclide except for one are E1 transitions. The intensity distributions obtained from the measured spectra after a correction for detector response and a subtraction of atomic background in the target contain a continuum part in addition to the resolved peaks. It turns out that the dipole strength in the resolved peaks amounts to about 30\% of the total dipole strength while the continuum contains about 70\%. In order to estimate the distribution of inelastic transitions and to correct the ground-state transitions for their branching ratios simulations of gamma-ray cascades were performed. The photoabsorption cross sections obtained in this way connect smoothly to (\gamma,n) cross sections and give novel information about the strength on the low-energy tails of the Giant Dipole Resonances below the neutron-separation energies. The experimental cross sections are compared with predictions of a Quasiparticle-Random-Phase Approximation in a deformed basis. The calculations describe the experimentally observed increase of the dipole strengths with increasing neutron number of the Mo isotopes as a consequence of increasing nuclear deformation.

In der vorliegenden Arbeit wird eine Methodik zur Analyse von Borverdünnungsstörfallen im Nachkühlbetrieb von Druckwasserreaktoren vorgestellt und angewandt.
Eine wesentliche Voraussetzung für eine realistische Analyse ist dabei die adäquate Modellierung der Vermischung des in den kalten Strang eingespeisten deborierten Pfropfens mit dem hochborierten Umgebungswasser.
Für das früher entwickelte Vermischungsmodell SAPR wurden an der Versuchsanlage ROCOM Übertragungs¬funktionen für die Vermischung im RDB bei kleinen Geschwindigkeiten ermittelt. Diese Übertragungsfunktionen, die in das bestehende Modell eingebaut und erfolgreich validiert wurden, decken alle möglichen Strömungszustände hinsichtlich der Anzahl der aktiven Nachkühlschleifen ab.
Mit Hilfe des gekoppelten neutronenkinetisch/thermohydraulischen Programms DYN3D/ATHLET wurde in Kombination mit diesem Vermischungsmodell ein unterstellter Borverdünnungsstörfall bei Einspeisung deborierten Kühlmittels im Nachkühlbetrieb unter Verwendung einer generischen Kernbeladung analysiert.
Die aus einer Kombination von stationären und transienten Rechnungen bestehende Methodik wurde auf das Strömungsregime mit einer arbeitenden Nachkühlpumpe angewandt. Zuerst wurde eine Parameterstudie mit stationären DYN3D-Rechnungen durchgeführt. Im deren Ergebnis wurde gezeigt, dass bei realistischer Berücksichtigung der Kühlmittelvermischung im RDB borfreie Kühlmittelmengen unter 8 m3 keine Rekritikalität des abgeschalteten Reaktors verursachen. Diese Aussage gilt für die verwendete Kernbeladung.
Für borfreie Kühlmittelmengen von 8 m3 bis zum Maximalwert von 15 m3 wurden transiente Analysen durchgeführt. Dazu wurde zwei Kernmodelle für das gekoppelte Programm DYN3D/ATHLET, eins bestehend aus 193 Kühlkanälen (1:1 Modellierung) und eins mit einer reduzierten Anzahl der Kühlkanäle (41) erstellt. Die mit dem SAPR-Modell berechneten Zeitkurven der Borkonzentration am Kerneintritt wurden als Randbedingungen an das untere Plenum angeschlossen. Aus Rechenzeitgründen wurde die Hauptzahl der Analysen mit dem reduziertem Modell durchgeführt. Ergänzend wurde für das maximale Pfropfenvolumen eine Rechnung mit dem detaillierten Modell durchgeführt.
Letzter Variationsparameter war die Anzahl der aktiven Schleifen im Nachkühlbetrieb. Hierbei wurden ausgewählte Schritte der Analyse für die veränderten hydraulischen Randbedingungen wiederholt. Es ergab sich, dass der 2- und 3-Schleifenbetrieb die höchsten statischen Reaktivitätseinträge aufweist. Die höchste Leistung nach der Rekritikalität sowie die höchsten Werte der Brennstoff- und Hüllrohrtemperatur werden im 4-Schleifenbetrieb berechnet, während im 1-Schleifenbetrieb der geringste Abstand zur Siedekrise und die höchste Stabbelastung ausgewiesen wurden.
Für diesen Zustand wurde eine Heißkanalanalyse durchgeführt. Obwohl in dieser Analyse über einen gewissen Zeitraum das Auftreten der Siedekrise berechnet wird, kam es in keiner der durchgeführten Rechnungen zu Erhöhungen der Brennstoffzentral- bzw. der Hüllrohrtemperatur über zulässige Grenzwerte.

The Bragg-chain model of the two-dimensional (2D) vortex state at high magnetic field is extended to an array of coupled superconducting (SC) layers. Application to YNi2B2C and MgB2 yields good quantitative agreement with high-field magnetization measurements, indicating that the smeared transitions observed in these materials are, at least in great part, due to SC fluctuations. The analysis indicates, however, that the thermodynamic properties of these materials, as well as of other strongly type-II superconductors, at low magnetic fields near the SC transition, are not connected to those at high magnetic fields (and low T) with a single scaling function, since the SC energy gap near T-c0 significantly underestimates the amplitude of the SC order parameter at high magnetic fields.

Dipole strength in N=50 nuclei studied in photon-scattering experiments at ELBE

The present work is aimed to analyzing the influence of the plasma potential in the efficiency of plasma immersion ion implantation (PIII) process with nitrogen, at high temperatures (550 degrees C and 800
degrees C), applied to the Ti6Al4V alloy to increase its wear resistance. Treatments with plasma potentials (PP) at 420 V and 90 V were carried out. In the first case, in accordance with AES (Auger Electron Spectroscopy) analysis, nitrogen rich layers of 100 nm and 150 nm of thickness had been obtained, for total treatment times of 60 min and 120 min, respectively. For the treatments with lower PP of 90 V, the treated layers thicknesses have been measured by GDOS (Glow Discharge Optical Spectroscopy) and their values are 1 mu m and 1.5 mu m for treatments of 120 min and 240 min, respectively. The hardness values were determined for the samples treated with high PP by nanoindentation technique and a significant increase was observed for this treatment,
reaching 11 GPa (60 m! in) and 19 GPa (120 min), which can be compared to 3.5-4.0 GPa obtained for the untreated samples. Pin-on-disk wear tests show that wear resistance increases after all these treatments. The friction coefficient as well as the wear rates are measured with a tribometer.

For hardness measurements, the indentation depth is about 10% of the effective information depth under static loading. A change of the wear mechanism is observed under lateral loading conditions in oscillating ball-on-disc tests for nitrided austenitic stainless steel with an expanded austenite surface layer from abrasive to a subsurface plastic flow with a redistribution of the inserted nitrogen. This leads to an effective nitriding depth about 3-5 larger than the actual nitrided zone.

Hydrogenated amorphous silicon with high compressive stress and hydrogen concentration as high as the hydrogen solubility limit has been studied. The concentrations of total hydrogen and bonded hydrogen have been determined by nuclear reaction analysis and infrared transmission spectroscopy, respectively. The amount of molecular hydrogen has been estimated as a difference between these two concentrations. Silicon ion implantation has been used to transform the hydrogen molecules into silicon-bonded hydrogen. The sensitivity of the Fourier transform infrared spectrometer to the expected variations in the bonded hydrogen concentration has been proved using hydrogen implantation. It has been concluded that in spite of high hydrogen content in the material the concentration of molecular hydrogen in the studied films is below 1 at.% and is not the reason for the high internal stress.

Fluorescence-Infrared-Cross-Correlation Spectroscopy: A Novel Approach to the Study of Domain Coupling in Proteins

Proton-regulated side chain lipid interactions in conformational switching by transmembrane G-protein-coupled receptors

Molecular switching in GPCRs: FTIR- and fluorescence-Spectroscopic Identification of Functional Modules in Rhodopsin

Am Forschungszentrum Dresden-Rossendorf ist seit einigen Jahren ein Freie-Elektronenlaser (FEL) in Betrieb, der mittlerweile einen Wellenlängenbereich zwischen 3 und 200 Mikrometer (entsprechend Frequenzen zwischen 1.5 und 100 THz) überstreicht. Nach einer Beschreibung der Maschine und ihrer wesentlichen Eigenschaften und Parameter sollen einige der ersten Experimente diskutiert werden:

(1) Untersuchung der zeitaufgelösten Dynamik von Elektronen in Halbleiter-Übergittern mittels Pikosekunden pump-probe Spektroskopie.
(2) Nahfeldmikroskopie von ferroelektrischen Domänen in der Nähe von Phonon-Resonanzen.

The short tutorial on fundamentals and applications of spectroscopic ellipsometry was given. The sensitivity of the technique in different configurations, problems of data acquisition and analysis have been addressed.

B+ and P+ ions were implanted into Ge wafers covered with an amorphous surface layer of 150 nm. After this, FLA in Ar atmosphere was used as post-implantation heat treatment. Flash lamp radiation with Xenon flash lamps having a spectrum in the visible range of light and a pulse length of 3 or 20 ms allowed an ultra-short heating up of the near surface region. In this way, a modification of the structure of the amorphous layer containing the implanted range was possible. Depth profiles of defects, especially of vacancy-type, were investigated by SPIS before and after FLA.
It could be shown that the remaining vacancy-type defect structure depends on the parameters of the process of heat treatment, and that these defects could not be completely removed by FLA.
These results will be compared with such from SRIM 2006 calculations (Stopping and Range of Ions in Matter) and Rutherford Backscattering Spectrometry (RBS).

Majority of the light elements up to iron are formed by successive rounds of thermonuclear fusion burning in the stellar interiors. The nuclei heavier than iron (Z>26) are being synthesized mainly by neutron-capture reactions – the astrophysical r-and s-processes. But the 35 neutron deficient stable isotopes between Se and Hg, the so-called p-nuclei, are shielded from the rapid neutron capture by stable isobars [1]. The possible site for the formation of p-nuclei are astrophysical scenarios like supernova explosions and their production mechanism is understood as chains of photodisintegrations of the type (γ, n), (γ, p) or (γ, α) on heavy seed nuclei. The natural abundances of the p-nuclei are in the order of 0.01 – 1%. For the network calculations that yield the p-nuclei abundances, precise values of the relevant astrophysical reaction rates are necessary. The data used presently for p-process nucleosynthesis modelling are mainly based on theoretical cross sections obtained from Hauser-Feshbach statistical model calculations. In this context, the knowledge of the experimental cross sections of the p-nuclei is of crucial importance. We are focussing on the photo-dissociation studies of various medium-mass nuclei and our aim is to get more accurate experimental cross sections which will surely be able to improve the present astrophysical network calculations. To study the p-nuclei by the method of bremsstrahlung induced activation, the superconducting electron accelerator ELBE delivers beams up to 40 MeV energy with average currents up to 1mA. An overview on the experimental facilities for nuclear physics at the superconducting electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf, Germany will be given . In particular, the photodissociation studies on the p-nuclei 92Mo and 144Sm will be discussed.

In burning stellar environments like supernova explosions, the temperatures are high enough for the production of heavy neutron deficient nuclei, the so-called p-nuclei. These are thought to be produced in such explosive scenarios either through chains of photodisintegration reactions on heavy seed nuclei. The modelling of the nucleosynthesis for the p-nuclei is mainly based on statistical model calculations. In this context, the knowledge of the experimental cross sections for the prediction of the p-nuclei abundances is of crucial importance and to forward in this direction we have started and experimental program at the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf . Photodisintegration measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed via photoactivation technique with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. In particular the (gamma,alpha) reactions of the mentioned nuclei were studied for the first time at different endpoint energies above and close to the threshold. The bremsstrahlung facility and the experimental area are deigned so as to facilitate the studies under optimized background conditions. To probe the fascinating investigations on short-lived nuclei a new pneumatic delivery system has been built recently. First experiments on the short-lived decays following the reaction 144Sm(gamma,n) is discussed. The activation yields from all measurements are compared with calculations using cross sections from recent Hauser-Feshbach models .

Radiochemistry with the short-lived positron emitters ¹¹C (¹¹C, t_1/2 =20.38 min) and ¹⁸F (¹⁸F, t_1/2 = 109.6 min) represents special challenges in terms of synthesis time and applicable labelling techniques. The implementation of modern organic chemistry methods into ¹¹C and ¹⁸F radiochemistry has steadily expanded the number of ¹¹C- and ¹⁸F- labelled PET radiotracers. The review wants to address the progress in the development of palladium-mediated carbon-carbon and carbon-heteroatom bond formations based on the readily available labelling precursors [¹¹C]methyl iodide and 4-[¹⁸F]fluorohalobenzenes (4-[¹⁸F]bromofluorobenzene and 4-[¹⁸F]fluoroiodobenzene).

Die Sitzung Energiesysteme – Energiewirtschaft (Energy Systems - Energy Economics) unter der Leitung von Herrn Dr.-Ing. Hans-Georg Willschütz (Forschungszentrum Dresden-Rossendorf e.V., Dresden, D) umfasste vier Vorträge, die sich mit den Perspektiven für neue Kernkraftwerke in Litauen und den Niederlanden, Strompreisentwicklungen und -angeboten in Deutschland und Aspekten der zukünftigen nuklearen Entsorgung befassten. Die Sitzung stieß auf reges Interesse und wurde zeitweilig von über 70 Teilnehmern besucht.

In explosive stellar environments like supernovae, the temperatures are high enough for the production of heavy neutron-deficient nuclei, the so-called p-nuclei. Up to now, the knowledge of the reaction rates of p-nuclei is based on theoretical parameterizations using statistical model calculations. At the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf, we aim to measure the photodisintegration rates of heavy nuclei experimentally. Photoactivation measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. First experiments on the short-lived decays following the reaction 144Sm(gamma,n) are carried out using a pneumatic delivery system for rapid transport of activated samples. The activation yields are compared with calculations using cross sections from recent Hauser-Feshbach models.

Slug flow is potentially hazardous to the structure of the system due to the strong oscillating pressure levels formed behind the liquid slugs. It is usually characterized by an acceleration of the gaseous phase and by the transition of fast liquid slugs, which carry out a significant amount of liquid with high kinetic energy. For the experimental investigation of air/water flows, a horizontal channel with rectangular cross-section was build at Forschungszentrum Dresden-Rossendorf (FZD). Experimental data were used to check the feasibility to predict the slugging phenomenon with the existing multiphase flow models build in ANSYS CFX. Further it is of interest to prove the understanding of the general fluid dynamic mechanism leading to slug flow and to identify the critical parameters affecting the main slug flow parameters (like e.g. slug length, frequency and propagation velocity; pressure drop).
For free surface simulations, the inhomogeneous multiphase model was used, where the gaseous and liquid phases can be partially mixed in certain areas of the flow domain. In this case the local phase demixing after a gas entrainment is controlled by buoyancy and interphase drag and is not hindered by the phase interface separating the two fluids. A further decision has to be made regarding the applied fluid morphology and interphase drag law for the multiphase flow. The fluid-dependent shear stress transport (SST) turbulence models were selected for each phase. Damping of turbulent diffusion at the interface has been considered. The k-ω based SST model accounts for the transport of the turbulent shear stress and gives highly accurate predictions of the onset and the amount of flow separation under adverse pressure gradients. The tail of the calculated slug and the flow behind it is in good agreement with the experiment. The entrainment of small bubbles in front of the slug could not be observed in the calculation. However, the front wave rolls over and breaks. It is created due to the high air velocity. In contrast to the measurement, the slug period is increasing with the time in the calculation. This could be a result of different amount of water in the channel at the beginning of experiment and CFD simulation. While in the simulation, the liquid phase covers 78% of the channel, it represents about 70% at the beginning of the experiment. Furthermore, in the experiment, this value is also reduced by a first slug which carries a significant amount of water out of the channel. This first slug could not be simulated. The behavior of slug propagation at the experimental setup was qualitatively reproduced, while quantitative deviations require a continuation of the work.
As some uncertainties were noticed at the inlet of this channel, the HAWAC (Horizontal Air/Water Channel) with well defined inlet boundary conditions dedicated to co-current flows was built. A picture sequence recorded during slug flow was compared with the equivalent CFD simulation made with the code ANSYS CFX. The two-fluid model was applied with a special free surface treatment. Due to an interfacial momentum transfer, it was possible to generate slugs based on instabilities. The behaviour of slug generation and propagation at the experimental setup was qualitatively reproduced, while deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of interfacial momentum should be analysed in the future. Furthermore, experiments like pressure and velocity measurements are planned and will allow quantitative comparisons, also at other superficial velocities.

Single-crystals of chromium doped with 1016 119Sn ions per cm2 and energies ranging between 45 and 190 keV were investigated with conversion electron M¨ossbauer spectroscopy (CEMS), Auger electron spectroscopy (AES), grazing angle X-ray diffraction (GAXRD), and scanning electron microscopy (SEM). The M¨ossbauer spectra were found to be significantly different than those of the bulk. Both the maximum and the average hf. field values were higher by a factor of ∼3 than the corresponding quantities for the bulk. The overall shape of the spectra is also different. GAXRD study has revealed that the near-surface zone of the investigated samples has a nanocrystalline structure with the average size of grains ranging between ∼20 and ∼40 nm. The latter seems to be the main reason for the observed enhancement of the spin-density and its distortion.

Nanostructured magnetic materials such as arrays of nanowires and filled nanotubes exhibit unique and tuneable magnetic properties e.g. the anomalous high coercivity, which make them favourable for applications in high density magnetic recording media.
We show effective CVD-routes for the defined growth of ensembles as well as individuals of metall-filled carbon nanotubes (Fe, Co, Ni) on structured silicon substrates and alumina substrates. The filled nanotubes were obtained due to continuous decomposition (thermic or plasma) of metal-containing precursors or hydrocarbons at 750-850°C. The nanotube dimensions can be controlled by the size of the catalyst on the substrate and with the reaction conditions. Further we report about a homogeneous embedding procedure of the CNT ensembles in a solid matrix. After the mechanical treatment the remaining nanotube stubs are analyzed with the magnetometer. In addition detailed investigations with transmission electron microscopy (TEM), atomic force microscopy (AFM) and Moessbauer spectroscopy give new insightes in the growth of filled carbon nanotubes.

Entwickelt wird eine einfache und leicht handhabbare Methode, die sich vorzugsweise bei der Gammatomographie mit hoch- und monoenergetischer Strahlung zur Korrektur von Streustrahlungsartefakten eignet. Der Grundgedanke besteht darin, dass zwischen der im Untersuchungsobjekt bestehenden Schwächungsverteilung der Primärstrahlung und der Verteilung der vom einzelnen Objektpunkt ausgehenden Streustrahlung eine Faltungsoperation vorgenommen wird.

We develop a straightforward and easy to be used method that lends itself preferably to tomography with high and mono energetic Gamma radiation for correction of scattered radiation artifacts. It is the basic idea of the method to convolve the attenuation distribution of the impinging radiation with the scattered radiation that is emitted from the individual points of the object under investigation.

Unwanted secondary phases are one of the major problems in diluted magnetic semiconductor (DMS) creation. Here we show possibilities to avoid such phases in Fe implanted and post-annealed ZnO(0001) single crystals. While -Fe nanoparticles are formed after such doping in as-polished crystals, high temperature (1273 K) annealing in O2 or high vacuum before implantation suppresses these phases. Thus, the residual saturation magnetization in the pre-annealed ZnO single crystals is about 20 times lower than for the as-polished ones and assigned to indirect coupling between isolated Fe ions rather than to clusters.

The talk consists of two parts. In the first part, a brief overview of projective Hilbert space structures related to exceptional points (EPs) is presented. The apparent contradiction between operator (matrix) perturbation schemes related to root-vector expansions and expansions in terms of eigenvectors for diagonal spectral decompositions is projectively resolved. In the second part of the talk, the gained insight is used for a geometric analysis of the brachistochrone problem for non-Hermitian as well as for PT-ssymmetric/pseudo-Hermitian quantum mechanical systems. The passage time contraction for non-Hermitian Hamiltonians compared to Hermitian ones is attributed to a distance contraction in projective Hilbert space due to non-unitary evolution. In the limiting case when a parameter dependent Hamiltonian approaches an EP in its spectral decomposition the distance between the coalescing eigenvectors vanishes and with it the passage time of the brachistochrone.

Quantum mechanics (QM) is reexamined from the view-point of operator equivalence classes. Two assumptions are used as starting points:

1.) Any operator with a diagonal spectral decomposition, purely real spectrum and which is densely defined in a suitable Hilbert space may describe a physical observable.
2.) Two sets of observables with operators which are related by a similarity transformation (i.e. which are elements from operator equivalence classes and lie on corresponding conjugacy orbits) are physically indistinguishable. In other words, the physical properties related to the observables X and AXA^-1 are exactly the same when A is a non-singular bounded operator (Hilbert space "relativity principle").
This implies that a given set of observables which is equivalent to a set with all operators Hermitian in a corresponding Hilbert space will not lead to the appearance of new properties compared to conventional QM. In contrast, if a set of observables consists of Hermitian and non-Hermitian operators in a certain Hilbert space then new effects can be expected which will go beyond those of conventional QM.
In this respect we analyze the evolution of a Hermitian observable governed by a non-Hermitian Hamiltonian.
The general approach is illustrated by a toy model 2×2 matrix Hamiltonian as it was recently used by Bender et al [Phys. Rev. Lett. 98 (2007) 040403] for considerations of a PT-symmetric quantum brachistochrone problem. We calculate the corresponding spin flip probabilities and show that the spin flips in non-Hermitian models may have flip (passage) times which are shorter or longer compared to those of Hermitian systems. The effect depends on the concrete exceptional point which is approached in the parameter space of the model.

Nach einem einleitenden Überblick über die CFD-Aktivitäten
der Abteilung Magnetohydrodynamik im FZD werden aktuelle
numerische Ergebnisse zum genannten Thema vorgestellt, welches
Bestandteil des Sonderforschungsbereiches 609 ist.

Reactivation of the cell cycle, including DNA replication, might play a major role in Alzheimer’s disease (AD). A more than diploid DNA content in differentiated neurons might alternatively result from chromosome mis-segregation during mitosis in neuronal progenitor cells. It was our objective to distinguish between these two mechanisms for aneuploidy and to provide evidence for a functional cell cycle in AD. Using slide-based cytometry, chromogenic in situ hybridization, and PCR amplification of alu-repeats, we quantified the DNA amount of identified cortical neurons in normal human brain and AD and analyzed the link between a tetraploid DNA content and expression of the early mitotic marker cyclin B1. In the normal brain, the number of neurons with a more than diploid content amounts to ~10%. Less than 1% of neurons contains a tetraploid DNA content. These neurons do not express cyclin B1, most likely representing constitutional tetraploidy. This population of cyclin B1-negative tetraploid neurons, at a reduced number, is also present in AD. In addition, a population of cyclin B1-positive tetraploid neurons of ~2%of all neurons was observed in AD. Our results indicate that at least two different mechanisms need to be distinguished giving rise to a tetraploid DNA content in the adult brain. Constitutional aneuploidy in differentiated neurons might be more frequent than previously thought. It is, however, not elevated in AD. In addition, in AD some neurons have re-entered the cell cycle and entirely passed through a functional interphase with a complete DNA replication.

Capabilities of the X-ray attenuation contrast radioscopy were utilized to provide a real-time diagnostic technique of the melt flow during unidirectional solidification of a Ga-30wt%In alloy from the bottom which is significantly affected by solutal convection. The solidification process was visualised using a microfocus X-ray tube. The X-ray facility provided shadow radiographs at spatial resolutions of about 10 µm at frame repetition rates of 25 Hz. We used the optical flow approach to derive information about the velocity field ahead of the solidification front and in the mushy zone from the observed displacement of the brightness patterns appearing during the X-ray image sequence. Buoyancy-driven flow patterns were found at length scales much larger than the length scales of the solidifying microstructure. A strong coupling between convection and dendritic growth became apparent via flow-induced modifications of the concentration profile in the liquid.

Der Vortrag gibt einen Überblick über die am FZD laufenden Arbeiten zur Qualifikation von CFD Codes für Mehphasenströmungen. Neben einer Darstellung der Motivation für die Arbeiten wird die enge Verknüpfung zwischen Experimenten, Modellentwicklung, Implementierung der Modelle in den CFD-Code CFX und die anschließende Validierung eingegangen. Exemplarisch wird das an der Modellentwicklung und Validierung für polydiperse Blasenströmungen dargestellt. Ein Ausblick auf zukünftige Arbeiten wird gegeben.

The investigation of insulation debris generation, transport and sedimentation becomes more important with regard to reactor safety research for Pressurized and Boiling Water Reactors, when considering the long-term behaviour of emergency core coolant systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of a disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb or impinge on the emergency core cooling systems.
Open questions of generic interest are for example the particle load on strainers and corresponding pressure drop, the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow. A joint research project on such questions is being performed in cooperation with the University of Applied Science Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation and the development of Computational Fluid Dynamic (CFD) models for the description of particle transport phenomena in coolant flow. While the experiments are performed at the University Zittau/Görlitz, the theoretical work is concentrated at Forschungszentrum Dresden-Rossendorf.
In the present paper, the basic concepts for CFD modelling are described and experimental results are presented. Further experiments are designed and feasibility studies were performed.

Die Anwendbarkeit des Master Curve-(MC-)Konzepts zur Charakterisierung des Zähigkeitszustandes bestrahlter Reaktordruck¬behälter-(RDB-)Stähle wurde an drei RDB-Stählen überprüft: IAEA-Referenzstahl 3JRQ57, 1JFL11 (vergleichbar mit 22NiMoCr3-7) sowie russischer WWER-440 Grundwerkstoff KAB-B. In Zugversuchen, Charpy-V-Tests, Risswiderstandskurven nach ASTM E1820 und Master Curve Tests zur Bestimmung der Referenztemperatur T₀ nach ASTM E1921 wurden der unbestrahlte Ausgangszustand, je drei Bestrahlungszustände bis hin zu Neutronenfluenzen von 100∙10¹⁸ n/cm² (E>1MeV) sowie bei 475°C/100h thermisch ausgeheilte Zustände untersucht. Mit zusätzlichen auf dem MC-Konzept basierenden Auswerteverfahren nach SINTAP, multimodalem MC-Ansatz (MML) sowie der Unified Curve erfolgte die Bewertung des Einflusses von Materialinhomogenitäten und möglicher MC-Formänderung bei hohen Fluenzen.
Wie erwartet geht Neutronenbestrahlung mit Verfestigung und Duktilitätsabnahme einher, d.h. Härte, Festigkeitskennwerte, Charpy-V-Übergangstemperaturen T_28J und T_41J sowie T₀ steigen mit der Neutronenfluenz, während die Bruchdehnung und Hochlagenzähigkeit abnehmen. Am bestrahlungsempfindlichsten reagiert der Stahl 3JRQ57, gefolgt von KAB-B und 1JFL11. Durch die Ausheilbehandlung von 475°C/100h erholen sich die Werkstoffkennwerte der Zugversuche, Charpy-V-Tests und MC-Versuche auf den jeweiligen unbestrahlten Ausgangszustand. Die technischen Ersatzkennwerte für duktile Rissinitiierung bleiben relativ unbeeinflusst von der Neutronenbestrahlung. Die MC nach ASTM E1921 beschreibt die Bruchzähigkeits-Temperaturverläufe für alle drei RDB-Stähle in allen Bestrahlungs- und Ausheilzuständen gut. Bei den niedrig und mittel bestrahlten Zuständen liegen meist mehr als 5% der K_Jc(1T)-Werte unterhalb der MC-Kurve für 5% Versagenswahrscheinlichkeit. Die MC beschreibt den hoch bestrahlte Zustand (ca. 100∙10¹⁸ n/cm², E>1MeV) aller drei RDB-Stähle sehr gut, auch für Daten außerhalb des Gültigkeitsbereiches T₀±50K, und auch für den bestrahlungsempfindlichen 3JRQ57 mit inhomogenem Gefüge. Die Unified Curve überbewertet den Einfluss der Neutronenbestrahlung auf die MC-Kurvenform. Eine mögliche Formänderung der MC durch Neutronenbestrahlung konnte bei keinem der drei untersuchten RDB-Stähle nachgewiesen werden.

We present a nonresonant photoconductive terahertz detection antenna suitable for detection of both focused and unfocused terahertz radiations. Our system consists of a scalable terahertz emitter based on an interdigitated electrode structure and a detection antenna with similar electrode geometry. While the emitter is fabricated on semi-insulating GaAs we compare different ion-implanted GaAs-based detection antennas. We studied the dependence of the measured terahertz signal on the power and spot size of the gating laser pulse. In addition we compare the performance of our antenna with that of electro-optical sampling.