Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Theoretical calculations of rotating N approximate to Z nuclei with A = 58 - 80 within the cranked Nilsson+Strutinsky approach, cranked relativistic mean field and cranked relativistic Hartree+Bogoliubov theories show good agreement with experiment. They point on the presence of the isovector t = 1 np-pairing, but do not show any indications of the isoscalar t = 0 np-pairing.

Knowledge of the influence of nuclear shell structure on the survival probability of heavy compound nuclei against fission is important for a quantitative understanding of the production rates of spherical super-heavy elements (SHE). Fission probabilities of N = 126 isotones beyond astatine can be used as test cases for the production of spherical super-heavy elements, as those isotones possess a strong shell correction energy and are highly fissile. Here, we report on two new experimental approaches which probe the effect of the closed neutron shell at N = 126 on the competition between fission and particle evaporation using projectile fragmentation and electromagnetic-induced fission of radioactive beams. We conclude that these nuclei lose at least a great part of their stability against fission at low excitation energies and angular momenta-mostly due to the influence of collective contributions in the level density. Implications on the production of spherical SHE will be!
discussed.

We present new measurements of the Be-7(p,gamma)B-8 cross section from (E) over bar (cm) = 116 to 2460 keV. Our new measurements lead to S-17(0) = 22.1 +/- 0.6(expt) +/- 0.6(theor) eV b based on data from (E) over bar (cm) = 116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. We compare our results to other S-17(0) values extracted from both direct (Be-7(p, gamma)B-8) and indirect (Coulomb dissociation and heavy-ion reaction) measurements, and show that the results of these 3 types of experiments are not mutually compatible. We recommend a "best" value, S-17(0) = 21.4 +/- 0.5(expt) +/- 0.6(theor) eV b, based on the mean of all modern direct measurements below the 1(+) resonance.

Thin beta-FeSi2 layers have been prepared by ion beam synthesis (IBS) on (111)Si substrates. The obtained samples have been characterized by means of infrared and Raman spectroscopies. The infrared (IR) transmittance spectra show the absorption at 310 cm(-1) as an indication of the initial nucleation of beta-FeSi2 precipitates during the implantation of iron into silicon substrate. The main feature of the photoluminescence (PL) measurements at 12 K in the beta-FeSi2/(111)Si samples annealed at 850 degreesC for 90 min is an intense peak localized at 0.811 eV. This peak is assigned to optical radiative transitions intrinsic to beta-FeSi2. (C) 2004 Elsevier Ltd. All rights reserved.

Electrons confined in a flat semiconductor quantum dot with a parabolic in-plane potential act like a collective many-particle oscillator under coherent intraband excitation. We investigate theoretically the properties of these oscillators under a simultaneous scale transformation of the lateral dimensions and the electron occupation number. As the lateral size increases from a few nm (typical for self-assembled dots) to the mesoscopic regime, the physics of the system is changing qualitatively: Quantization effects gradually lose importance against Coulomb interactions and eventually the electron lake in a mesoscopic dot resembles a classical Wigner liquid. This parabolically confined "Wigner lake" behaves to the outside like a form-elastic "superparticle" of high charge. It can be coherently controlled by THz dipole radiation just like a single electron, but with reduced Brownian diffusion in the phonon heat bath. We propose a flexible method to fabricate single mesoscopic!
dots of a controlled shape, Coulomb-coupled groups of dots, and almost arbitrary potential landscapes, using current semiconductor technology. As a first example, the collective modes of two Coulomb-coupled superparticles in neighboring dots are calculated. Also, we consider the possibility of steering a superparticle with shaped laser pulses to follow any complex two-dimensional orbit.

We investigate numerically the transition to turbulence in a flat-plate boundary layer controlled by electromagnetic forces. The fluid considered is incompressible, Newtonian and low conductive. Similar to boundary layer suction, when applying a steady, wall-parallel, and streamwise orientated Lorentz force, (as suggested by Gailitis and Lielausis [1] in the early 1960s) the Blasius velocity profile is transformed to an exponential one gaining a critical Reynolds number which is increased by two orders of magnitude.

Two and three dimensional direct numerical simulation (DNS) of both linear and nonlinear stages of the transition process were performed, as well as alinear stability analysis (LSA) of the calculated intermediate velocity profiles. DNS and preliminary LSA results confirm the expected increased stability of the controlled flow. Depending on Lorentz force strength transition to turbulence is delayed or even stopped. Suprisingly, both DNS and LSA results suggest interesting stability characteristics of the intermediate velocity profiles.

In DNS, to initiate transition, small amplitude disturbances are introduced by means of an oscillating body force within a small region near the inflow boundary, forming Tollmien-Schlichting waves (TSW) which grow and decay in uncontrolled case corresponging to linear stability theory. When applying Lorentz force, TSW of all investigated frequencies 0.4 <= F+ <= 3.75 are damped within the computational domain extending over 900 times the inflow displacement thickness d1i. Reynolds number, based on d1i, is 360. The decay rate based on the maximum rms value in wall-normal direction of the streamwise velocity component, is maximum in a region near the onset of control and decreases as the velocity profile approaches the exponential state. This observation could suggest that in the intermediate region there are profiles more stable than the exponential one, although we are aware that from these decay rates one cannot conclude directly the stability of a velocity profile, notably its critical reynolds number. However, our assumption is confirmed by preliminary LSA results where critical Reynolds numbers of intermediate profiles are found to be larger than for the exponential profile.

By three dimensional DNS we show that transition to turbulence can be stopped even in it's late stage. While the evolution of Lambda vorticies from former two dimensional TSW remains almost unchanged, the emerge of Omega vorticies is supressed with increasing Lorentz force strength, thus relaminarizing the flow.

[1] A. Gailitis, O. Lielausis: On a possibility to reduce the hydrodynamic resistance of a plate in an electrolyte. Applied Magnetohydrodynamics, Reports of the Physics Institute Riga, Vol. 12, pp. 143-146, 1961

During reactive sputter deposition, target "poisoning", i.e. the formation of a compound layer at the target surface, may reduce the sputter erosion rate substantially and thereby represent a major limitation to achieve high deposition rates. In order to investigate the formation of the poisoned layer, the TRIDYN program has been employed to simulate the processes that take place at the target surface during sputtering at ion energies which are typical for a magnetron discharge, in a typical gas mixture of Ar with a small (<10%) addition of a reactive gas (e.g. oxygen). The bulk of the sputtering results from Ar ion bombardment, while the reactive gas ions contribute to compound formation due to implantation into the subsurface layer. In addition, reactive gas molecules are adsorbed on the surface and react with target metal atoms to add to the formation of the compound layer. Thus, both chemisorption and ion implantation of energetic reactive ions are the two main mechanism! s for the formation of the poisoned layer.TRIDYN simulations have been performed at varying reactive ion to total ion flux ratio, and at varying ion to reactive neutral flux ratio, for fluences which are sufficiently large to achieve a stationary deposition/erosion balance. The results illustrate that the two mechanisms will generate almost identical shapes of the poisoned layer. They also demonstrate the significance of recoil implantation from the chemisorbed layer for the formation of the compound layer. In agreement with experimental findings, the calculated sputter erosion rate of the target is predicted to decrease monotonically as the partial pressure of the reactive gas increases. The shape of the sputter erosion curve hardly changes between conditions dominated by ion implantation or chemisorption. We therefore conclude that ion implantation basically acts as an additional source of reactive atoms to the target surface.

Background
Bacteria play an important role in biogeochemical transformations and migration of uranium (U) in nature. In order to understand how U(VI) interacts with natural bacterial communities of U mining waste piles a series of microcosm experiments was performed.
Methods
Several portions of a solid sample collected from the U mining waste pile near the city of Johanngeorgenstadt in Germany were supplemented with different amounts of U(VI), starting from the original 40 mg U/kg up to 300 mg/kg.
The solubility of the U originally present and of the added U was assessed by selective sequential extraction (SSE). The composition of bacterial communities present in the original and in the supplemented with U samples was analyzed applying 16S rDNA retrieval by using 43F and 1404R degenerated primers.
Results
SSE analysis demonstrated that in the original sample the main part of uranium was strongly bound in mineral phases. The bacterial community of this sample was predominated by Alphaproteobacteria and by representatives of Holophaga /Acidobacterium phylum.
The bacterial community structure of the sample was noticeable changed by increasing its U content to 100 mg/kg . No Holophaga/Acidobacterium and only a few representatives of Alphaproteobacteria were retrieved in this sample. Instead, a large number of sequences of mainly Gamma-Pseudomonas, and of Arthrobacter sp. were found. The propagation of several populations of Deltaproteobacteria and especially of Geobacter sp. was induced in the sample as well. After 4 weeks of incubation, most of the U added to this sample was still only weakly complexed.
The bacterial community structure of the most contaminated sample, containing 300 mg U/kg, differed significantly from the two samples described above and depended on the aeration conditions during the incubation. In this sample the number of 16S rDNA sequences representing Cytophaga/Flavobacterium /Bacteroides group was extremely high. Arthrobacter sp. populations were also identified but not as strongly predominant.
Conclusions
The addition of U(VI) to a low contaminated U mining waste sample induces significant shifting in the indigenous bacterial populations. The effect of the added U(VI)seems to depend on its amount and on the redox conditions.

Background
Microorganisms strongly influence the migration of radionuclides in the environment. For this reason analysis of natural bacterial and archaeal communities near radioactive wastes deposition sites is of great importance for risk assessments. In this study diversity was studied of the microorganisms indigenous for a monitoring well near the radioactive waste injection site Tomst-7 in Siberia. In addition, interactions of several bacterial isolates from this site with uranium and other metals was investigated.
Methods
Microbial diversity was studied applying the 16S rDNA7F-1513F for bacteria and 16S rDNA21f-958R for archaea. The diversity of the autotrophic bacteria was estimated by direct analysis of different RubisCO gene forms. Oligotrophic bacteria were cultured in low nutrient R2A medium. Interactions of the cultured bacterial isolates with U, Ni, Pb, As, and other metals were studied by using ICP-MS, flow cytometry and X-ray spectroscopic analyses.
Results
Our analyses demonstrated presence of a large number of diverse bacterial and archaeal groups at a depth of about 300m at the Siberian depository site Tomsk-7 where the radioactive wastes were injected. The most predominant bacterial populations were those of Betaproteobacteria mainly from the Rhodocyclus group, of Citophaga/Flavo-bacterium/Bacteroides, and of several novel “Cyanobacteria-like” groups. The RubisCO approach confirmed the Betaproteobacterial predominance in the samples studied.
Bacterial isolates were cultured from the samples belonging to Sphingomonas sp., Brevundimonas sp., Methylobacter sp., and a large microdiverse group of Actinobacteria closely related to Microbacterium oxydans. They tolerated U and other heavy metals in a species- and even strain-specific way. EXAFS analyses demonstrated that the isolates of Microbacterium sp. and of Sphingomonas sp. are complexing U(VI) at pH 4.5 via phosphorus (P) in a form of meta-autunite. The latter was connected to the liberation of inorganic phosphate by these strains due to their exo-phosphatase activity. At lower pH values the U is bound to organic phosphate residues.
Conclusions
The environment around the radioactive waste injection site Tomsk-7 possesses a large variety of microorganisms with a potential to bind and possibly transport radionuclides.

Deep level defects E1/E2 were observed in He-implanted, 0.3 and 1.7 MeV electron-irradiated n-type 6H-SiC. Similar to others' results, the behaviors of E-1 and E-2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E-1/E-2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E-1/E-2. The activation energy and the capture cross section of this defect are E-C-0.31 eV and sigma similar to 8 x 10(-11) cm(2), respectively.

Lorentz forces on the suction side flow of NACA 0015 and PTL IV hydrofoils is investigated experimentally. Emphasis is placed on separation control. Steady as well as time periodic Lorentz forces will be discussed. Their effect is compared mainly in respect of the attainable increase of the maximum lift and in terms of power consumption.

I will discuss two recent advances related to semiconductor light sources in the infrared and THz regions. One example is a quantum cascade laser operating at a wavelength shorter than 4 microns above room temperature with high peak power. It is based on strained InGaAs/InAlAs on InP, with the addition of high barriers of pure AlAs for better confinement and strain compensation. In a novel few-cycle THz emitter we try to combine the advantages of the high electric bias field in photoconductive antennas with a large active area. This is achieved with an interdigitated electrode structure, partially covered in order to mask one field polarity. As a result no destructive interference of the emitted THz wave occurs, which allows upscaling of the device area.

Recent developments at the Dresden High Magnetic Field Laboratory

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

The radiosynthesis and the radiopharmacological evaluation of pyrazolo steroid 2´-(4-fluorophenyl)-21-[¹⁸F]fluoro-20-oxo-11β,17α-dihydroxy-pregn-4-eno[3,2-c]pyrazole [¹⁸F]-2 is described. The radiolabeling was accomplished in 3 - 4 % decay-corrected radiochemical yield within 80 min at an specific radioactivity of 0.8-1.2 Ci/μmol. Biodistribution studies in male Wistar rats showed an initial brain uptake of 0.25 ± 0.03 % ID/g after 5 min, which remained constant over 60 min. The radiopharmacological evaluation of compound [¹⁸F]-2 was completed with autoradiography using rat brain sections and micro-PET imaging.

Further developments for the Dresden High Field Laboratory

In order to design and optimize pulsed field coils, their current leads, and in particular their reinforcement, we currently test commercial Finite Element software of various suppliers. We concentrate on these programs which have implemented so called "multiphysics modules" which are able to solve combined problems as they typically occur in high field techniques: e.g. calculation of the magnetic field from a current distribution along with the resulting Lorentz forces, stresses, dislocations etc.. In detail, we focus on the programs ANSYS, ANSOFT, as well as FEMLAB. We like to give a brief survey of their usefulness, perspectives, and last but not least, of their cost.

In the frame of the high field project Dresden, a new building to be constructed at the research center Rossendorf is in its design phase. The HLD building will be located near the IR-free electron lasers of the superconducting linear accelerator ELBE in order to provide the possibility of IR spectroscopy in high pulsed magnetic fields. Following the present plans, five magnet cells for pulsed magnets, preparation rooms, a lab for superconducting magnets and four labs for accompanying experiments are located around a central room which houses the capacitor bank. In addition, a workshop, stores, and a technical section on one side, as well as the offices for stuff and guests and a control room on the other side are located in separate sections. We present the plans emphasising the ability and the safety items in order to get your feedback.

The novel 2-mercaptoimidazolde derivatives, 1-[4-((2-methoxyphenyl)-1-piperazinyl)-butyl]-2-mercaptoimidazolde (3) and methyl[4-((2-methoxyphenyl)-1-piperazinyl))butyl] (2-mercapto-1-methylimidazol-5-yl)methanamide (8), were efficiently labelled with ¹¹C through methylation of the thioketone function with [¹¹C]methyl iodide. The resulting radioligands 1-[4-((2-methoxyphenyl)-1-piperazinyl))butyl]-2-thio[¹¹C]-methylimidazole ([¹¹C]9) and methyl [4-((2-methoxyphenyl)-1-piperazinyl))butyl] (2-thio[¹¹C]methyl-1-methylimidazol-5-yl)-methanamide ([¹¹C]10) were synthesized in radiochemical yields of 20 - 30 % (decay-corrected, related to [¹¹C]CO₂) at a specific radioactivity of 0.2-0.4 Ci/μmol within 40-45 min including HPLC-purification. The radiochemical purity exceeded 99 %. The reference compounds 9 and 10 were tested in a competitive receptor binding assay to determine their affinity toward the 5-HT_1A recptor. Both compounds exhibit excellent sub-nanomolar affinities (IC₅₀ = 0.576 ± 0.008 nM (9); IC₅₀ = 0.86 ± 0.02 nM (10)) for the 5-HT_1A receptor while displaying a high selectivity towards the 5-HT_2A subtype of receptors (IC₅₀ > 480 nM). By contrast, compound 9 also shows substantial binding for the alpha-adrenergic receptor (IC₅₀ = 3.00 ± 0.02 nM) when compared with compound 10 (IC₅₀ = 54.5 ± 0.6 nM). Preliminary biodistribution studies in rats showed an initial brain uptake of 1.14 ± 0.11 and 0.37 ± 0.04 % ID/g after 5 min, which decreased to 0.18 ± 0.04 and 0.16 ± 0.01 % ID/g after 60 min for compounds [¹¹C]9 and [¹¹C]10, respectively. For both compounds, the cerebellum and rest of the brain uptake are very similar at the different time points. Unlike [¹¹C]9, the radioligand [¹¹C]10 has significant uptake and retention in the adrenal glands. Due to their washout from the brain compounds [¹¹C]9 and [¹¹C]10 seem not to be good condidates as radioligands for imaging 5-HT_1A receptors by PET.

A new facility for experiments in pulsed high magnetic fields is under construction at the Forschungszentrum Rossendorf in Dresden, Germany. Its heart will be a modular 50 MJ / 24 kV capacitor bank in a new laboratory. In order to offer a wide spectrum of experimental possibilities, pulsed field coils are planned in the parameter range 60 T, 50 mm, 1s to 100 T, 20 mm, 0.01 s for maximum field, bore, and pulse duration. Experience in the construction of the pulsed capacitive power supply as well as in the experimental equipment has been gained from a pilot laboratory at the IFW since 1999. The pulsed magnets will be complemented by commercial superconducting magnets for dc fields up to 20 T. Besides many other experimental possibilities, as a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible in pulsed fields by connecting the pulsed field lab to the new free-electron-lasers of the neighbouring superconducting electron linear accelerator ELBE of the FZR.
The laboratory building will be completed in 2004. The 50 MJ power supply can be partly used in 2005 and will be fully operational by 2006. First pulsed test coils have already been built and will be tested in 2004 by the 1.44 MJ / 24 kV pilot power supply manufactured at FZR. The user coils as well as the experimental equipment will be installed in 2006, so that the facility can open its doors as a user laboratory in 2007.

* The HLD project has been jointly submitted for funding by the FZR, the Leibniz-Institut für Festkörper- und Werkstoffforschung IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the Technische Universität Dresden. It is jointly funded for installation by the Bundesministerium für Bildung und Forschung of Germany and the Sächsische Ministerium für Wissenschaft und Kunst in the years 2003 to 2006.

We present measurements of the dc magnetization M(B) of van Vleck paramagnets, e.g. PrNi₅, at high magnetic fields up to B = 60 T. At low fields up to 10 T, we observe magnetizations which increase linearly with the applied field. Beyond 10 T, the magnetizations start to become nonlinear as the result of the shifts of the energy levels of the crystalline electrical field (CEF) states of the 4f-Pr³⁺ electrons through the external field. A significant change of slope of the magnetization M(B) as well as of the corresponding susceptibility dM/dB occurs in PrNi5 at B = 20 T which can be explained by a level crossing of the two lowest singlet CEF states. We compare our data to calculations from a point charge model.

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

Since the first experimental finding of a competition between nuclear magnetism and superconductivity in the nuclear ferromagnet AuIn2, investigations have been extended to Al, Sn, Rh, In, AuAl₂, and very recently to Pr_1-xLa_xTe. The experiments have demonstrated that the contribution of nuclear magnetism to Cooper pair breaking is a common phenomenon. Even in a system with tiny nuclear magnetic moments (e.g. Sn), a reduction of the critical field B_c(T) has been detected at ultralow temperatures. In more detail, the observed influences of nuclear magnetism on superconductivity vary strongly with the size of hyperfine coupling, ranging between a tiny reduction of B_c(T) in the case of weak hyperfine coupling (AuAl₂) and the complete destruction of superconductivity in the opposite case of strongly coupled and hyperfine enhanced nuclear spin systems (e.g. Pr_0.50La_0.50Te). The hyperfine interaction appeares to be the dominant mechanism for the nuclear magnetic contribution to Cooper pair breaking.

In the course of our investigation of the heavy fermion compound CeCu₆,
we have recently performed measurements of the heat capacity as well as elastic neutron diffraction down to ultralow temperatures. In the last decade, various groups have investigated this compound by means of susceptibility, magnetization, nuclear quadrupole resonance, and thermal expansion as well. There is a strong evidence for a magnetic ordering transition at about 2.5 mK. Here we like to present our latest heat capacity data taken at 0.1 mK ≤ T ≤ 100 K as well as neutron diffraction data taken down to 15 mK. These results give further
hints for magnetic correlation effects in CeCu₆.

We have investigated the strongly correlated electronic and nuclear magnetic properties of the cubic Van Vleck paramagnets PrS, PrTe, and PrBi by means of SQUID magnetometry at 2 K≤T≤300 K as well as ac susceptometry at ultralow temperatures, 0.06 mK≤T ≤100 mK. We observe magnetic ordering transitions of the hyperfine enhanced magnetic moments of the ¹⁴¹Pr nuclei in all three compounds. Our ac susceptibility data taken at ultralow temperatures point to antiferromagnetic ground states. The observed Neel temperatures, T_N(PrS, PrTe, PrBi) = 0.09, 0.60, 1.20 mK, scale with the size of the Van Vleck susceptiblity and related hyperfine enhancement factor respectively. The nuclear fcc spin-5\2 antiferromagnets PrS, PrTe, and PrBi are promising candidates for interesting spin structures. Currently we use the metallurgical possibility to substitute Pr by La and Pb in these compounds in order to study the multiple interplay between electronic magnetism, nuclear magnetism, superconductivity (e.g. in Pr_1-xLa_xTe), and semiconductivity (e.g. in Pr_1-xPb_xTe).

Compared to magnetically doped superconductors described by the theory of Abrikosov and Gorkov, electronic singlet ground state systems can have a much larger critical concentration of magnetic impurities, following the model of Keller and Fulde. The recent study of the superconducting Van Vleck paramagnet La_{1-x}Pr_xTe revealed a critical Pr^{3+} concentration x close above 0.50. Surprisingly, in La_{0.50}Pr_{0.50}Te the superconducting state with T_c = 0.20 K appeares not to be stable down to zero temperature. Instead, a reentrant transition to the normal state likely caused by the hyperfine enhanced magnetic moments of the ^{141}Pr nuclei occurs at about 0.02 K. Although these moments are not in a magnetically ordered ground state at T = 0.02 K, their contribution to Cooper pair breaking seems to be even stronger than of ferromagnetically ordered but non enhanced nuclear moments in type-I superconducting AuIn₂.

We have measured the ac susceptibility and resistivity of highly pure samples of the intermetallic compound LaCu₆ down to ultralow temperatures. We have prepared the samples by arc melting of stoichiometric amounts of 99.99\% La and 99.9999\% Cu in a water-cooled copper crucible under Ar protective atmosphere and analysed them by x-ray diffraction and SQUID magnetometry. At T≤T_c = 0.16 K we observe a superconducting transition. Due to the manifold physical properties of isostructural ReCu₆ compounds (e.g. RE = Ce: heavy fermion system, RE = Pr: hyperfine enhanced nuclear spin system, RE = Nd: electronic antiferromagnet), numerous studies of interplay phenomena may become possible in the quasibinary compounds RE_1-xLa_xCu₆, respectively.

Die Internationale Länderkommission Kerntechnik (ILK) hat 2004 eine Stellungnahme zur Bewertung der Nachhaltigkeit der Kernenergie und anderer Technologien zur Stromerzeugung vorgelegt.
Die Bewertung beruht u. a. auf der Quantifizierung von Indikatoren, wie etwa die Produktionskosten oder die CO-2-Emission, die verschiedene Nachhaltigkeitsaspekte charakterisieren und der Aggregation dieser Indikatoren zu einem einzigen Nachhaltigkeitskennwert für jede der betrachteten Energieoptionen.
Die Aggregation kann beispielsweise über den Totalkostenansatz oder mit Hilfe der Multikriteriellen Entscheidungsanalyse (MCDA) erfolgen. Die beiden Verfahren führen in der Regel zu unterschiedlicher Nachhaltigkeitsbewertung. Dies liegt zum einen daran, dass einige der Indikatoren finanziell nicht fassbar sind und deshalb im Totalkostenansatz nicht berücksichtigt werden. Zum anderen sind bei der Aggregation mit Hilfe der MCDA Wichtungsfaktoren für Einzelindikatoren und die "Nachhaltigkeitssäulen" Wirtschaft, Umwelt, Gesellschaft festzulegen. Bislang stehen keine Leitlinien für die Fixierung dieser Gewichtungen zur Vefügung. Der Vortrag stellt die genannten Aggregationsverfahren vor und diskuiterit dann Vor- und Nachteile.

The present paper discuss the posibility to obtain information about the field flatness of a 1.5 cell normal conducting RF gun cavity during the running of the gun. By measurements of the microwave network parameters at room temperature and by measurement of the passband frequencies in the running regime of the gun it is possible to estimate the perturbation of field flatness, caused by an inhomogeneous temperature distribution.

N,N-Dimethyl-2-(2-amino-4-methylthiophenylthio)benzylamine (SMe-ADAM, 1) was found to be a highly potent and selective inhibitor of the serotonin transporter (SERT). This compound was labelled with carbon-11 by methylation of the S-desmethyl precursor 10 with [¹¹C]methyl iodide to obtain the potential positron emission tomography radiotracer [¹¹C]SMe-ADAM. Radiochemical yield was 27  5 % and the specific radioactivity was 26 – 40 GBq/µmol at the end of synthesis . Ex vivo and in vivo biodistribution experiments in rats demonstrated a rapid accumulation of the radiotracer in brain regions known to be rich in SERT, such as the thalamus/hypothalamus region (3.59 ± 0.41 %ID/g at 5 min after injection). This is the highest brain uptake ever reported for this type of radiotracer in rats. The specific uptake reached a thalamus to cerebellum ratio of 6.74 ± 0.95 at 60 min post injection. The [¹¹C]SMe-ADAM uptake in the thalamus was significantly decreased by pre-treatment with fluoxetine to 45 ± 9 % of the control values. Furthermore, no metabolites of [¹¹C]SMe-ADAM could be detected in the SERT rich regions of the rat brain. It is concluded that [¹¹C]SMe-ADAM may be a suitable PET ligand for SERT imaging in the living brain.

The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC magnetic field was examined. The magnetic field lines were aligned either in longitudinal or in transverse direction. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4e-13. The liquid metal was in a cylindrical container at rest. The Ultrasound Doppler Velocimetry (UDV) was applied to determine bubble and liquid velocities simultaneously. The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Within the present interaction number range (N < 2), the applied magnetic field can either increase or decrease the bubble drag coefficient depending on the bubble size and the magnetic interaction parameter. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddy structures in the wake. In case of the longitudinal magnetic field the Strouhal number St decreases with increasing magnetic interaction parameter.

In order to improve the microstructure of casting ingots a rotating magnetic field (RMF) is widely used to stir the liquid phase during solidification. Usually, the interaction between the solidification process and the RMF driven flow has been discussed only in terms of the flow pattern well-known from the laminar, isothermal case being a superposition of a primary swirling flow in azimuthal direction and a secondary flow occurring as a double vortex in the r-z plane. Effects arising from the propagation of the solidification front, the extension of the mush zone or the spin-up of the flow at higher cooling rates are almost not taken into account. We present experimental and numerical investigations concerning the influence of a RMF driven flow on the momentum, heat and mass transfer within a binary Sn-Pb alloys solidified directionally.
Solidification experiments were carried out using a Sn-15wt%Pb alloy in a cylindrical mold positioned on a water-cooled copper chill. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification. The temperature field was monitored using thermocouples. The set-up was enclosed by an inductor providing the RMF. The Taylor numbers Ta were varied between 10e5 and 10e8.
The continuum formulation based model has been adopted for numerical simulations using the following assumptions: all transport properties, such as thermal and electrical conductivity or viscosity, are assumed to be constant; the density of solid phase equals the density of liquid phase; the phases are in local thermodynamic equilibrium; the velocity of solid phase in the upper part of the mushy zone is equal to the velocity of the liquid phase. The mushy region is modeled using a mixture viscosity formulation. The Lorentz force in the Navier-Stokes equation has been calculated by means of an analytical solution for the time-averaged Lorentz force for a finite cylinder. The resulting set of eqiuations is discretized by an implicit finite-volume, finite-difference based method, and solved by using the SIMPLE algorithm.
Our results show that the velocity field undergoes distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case.

Dendritic oxybathophenanthroline ligands (generation 0 to 3) have been synthesized by treatment of 4,7-bis(4´-hydroxyphenyl)-1,10-phenanthroline with the corresponding Fréchet-type dendrons carrying a benzylic bromide function at the focal point. The complexation of copper(II) has been studied by liquid-liquid extraction using the radioisotope ⁶⁴Cu and time-resolved laser-induced fluorescence (TRLFS) measurements in organic media proving the formation of 1:3 complexes (Cu : dendritic ligand). The stability of the copper complexes is mainly determined by the 1,10-phenanthroline core element. The stability constants of the 1:3 complexes were found to be in the order of log K ~ 16 in CHCl₃. On the other hand, increasing generation of the dendritic Fréchet-type branches leads to enhanced shielding of the copper ion from the environment. Additional information about this behaviour was obtained by the fluorescence lifetimes which are much less influenced upon addition of copper(II) salt to solutions of the higher generation ligands.

Mixing in stirred vessels of different density liquids is common operation in the process industry. The hydrodynamic behaviour of such a system could be crucial for the overall process performance. The aim of this work is to numerically predict the dynamics of the mixing process of initially stratified system of two different density liquids. Stratified conditions could occur in the stirred vessel, especially in the case of impeller malfunctioning, i.e. impeller breakdown. This effect might prove to be of significant importance, particularly in the case of reacting liquids for large-scale reactors operating in the industry.
The CFD analyses were performed for a non-baffled stirred vessel reactor, mechanically agitated by the Pfaudler impeller. The two main cases of passive and reactive tracer mixing behaviour were numerically predicted by the means of the CFD software CFX 5.7. In both cases the system of two miscible liquids with different densities was dynamically predicted in 3D from an initially stratified to a complete mixing condition. The full 3D simulation was applied in order to capture the flow instabilities associated with the impeller blade passage, especially pronounced in the first few seconds after the impeller start. In order to study the effect of the free surface deformation on the mixing process, the gas phase was also involved into the system via the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. In the case of the reactive tracer mixing, the alkali was diluted in the lighter liquid. The simulations were performed on different grids in order to obtain grid independent results.
The accuracy of the numerical simulations was evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one which were initially stratified were brought into motion by the rotating impeller. In the case of the passive tracer mixing, the alcoholic phase was coloured by blue dye whereas in the case of the reactive mixing a phenolphthalein indicator was applied. The mixing process was captured by a digital camcorder and subsequently the images were digitally processed. The mixing of different initial lighter phase concentrations was visually investigated to obtain the colour calibration curve. The numerical predictions were evaluated against several locations, close to vessel central line and wall, for which the optical distortion was minimal.

Die Grignard-Chemie erlebt eine Renaissance bei der industriellen Herstellung neuer pharmazeutischer Wirkstoffe, Lebensmitteladditive und Feinchemikalien. Sicherheitsprobleme können aufgrund der sehr großen Exothermie und der hohen Reaktivität der Grignard-Reagenz beim Scale-up in den großtechnischen Maßstab auftreten. Die Hauptgefahrenquelle ist das spontane Starten der Grignard-Reaktion, wenn bereits eine kritische Menge an organischem Halogenid akkumuliert ist, und dann die durchgehende Startreaktion durch den starken Druckanstieg zur Stofffreisetzung führt. Die genaue Bestimmung der reaktionstechnischen Prozessparameter zur Auslegung des Kühlsystems für das Produktions-Betriebsregime wird an einem ge-schlossenen Reaktionskalorimeter mit integriertem in-situ FTIR-Spektrometer für eine industrielle Grignard-Reaktion beschrieben. Weiterhin werden Möglichkeiten zur Detektion des Reaktionsstarts und zur Verfolgung der Halogenid-Akkumulation vorgestellt. Durch den Einsatz der in-situ FTIR-Spektroskopie läßt sich einerseits der Re-aktionsstart eindeutig detektieren, andererseits können sowohl der Verbrauch des organischen Halogenids als auch der Aufbau der Grignard-Reagenz in Echtzeit überwacht werden. Neben den Online-Konzentrationsmessungen können an einem geschlossenen Rührkesselreaktor auch die steilen Anstiege der Reaktortemperatur und des Druckes sowie die Wärmebilanz zum Nachweis des Reaktionsstarts genutzt werden. Durch Online-Konzentrationsmessungen und/oder Wärmebilanzmessungen ist es außerdem möglich, das Einschlafen der Hauptreaktion durch Verunreinigungen zu erkennen und das spätere Wiederstarten zu verhindern. Darüber hinaus konnte nachgewiesen werden, daß im geschlossenen Reaktionskalorimeter die reaktionstechnischen Parameter, wie Induktionszeit, Dauer des Startprozesses und Reaktionsenthalpie, wesentlich genauer als im offenen Reaktor gemessenen werden können. Ferner werden Untersuchungen dieser Grignard-Reaktion im adiabatischen Reaktionskalorimeter (PhiTecII) diskutiert, das auch zur Dimensionierung von Notentlastungssystemen dienen kann.

A non-baffled stirred vessel reactor was investigated computationally with CFX-5 numerical package. The mixing of two miscible liquids with different densities was dynamically predicted from an initially stratified to a complete mixing condition. Although for a non-baffled vessel an axi-symmetric behaviour can be expected, the process was regarded as three dimensional in order to demonstrate the local instabilities associated with the blade passage. Additionally, the gas phase was involved into the simulations to investigate the effect of the free surface deformation on the mixing process. The two-phase gas-liquid interactions were modelled using the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. The grid elements size was kept relatively low because of the dynamic behaviour of the liquid surface central vortex. Furthermore, the available turbulence models were considered to obtain the closest possible match with the experimental observations. In such a way, the stirred vessel hydrodynamics was dynamically calculated in 3-D in order to study the effect of the density difference.
The numerical simulations were evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one, which were initially stratified, were brought into motion by the means of the rotating impeller and the mixing process was captured by digital camcorder and subsequently the images were digitally processed. Several points, close to vessel central line and wall, for which the optical distortion was minimal were considered for evaluation of the numerical predictions.
The hydrodynamics of the above described system is of particular concern for many chemical and biochemical reactions engineered to take place in stirred vessel reactor. Although the initial conditions were to some extend idealised in order to avoid some complications raised by the presence on an injection, the studies showed strong influence on the density difference on the homogenisation. Such so called idealised conditions, however, also might occur in the stirred vessel, especially in the case of impeller malfunctioning. In case of impeller stoppage, i.e. breakdown, different density liquids present in the vessel might get stratified. This effect might prove to be of significant importance, especially in the case of reacting liquids for large-scale reactors operating in the industry.

Seit 10 Jahren wird in Deutschland das Programm "Sonne in der Schule" durchgeführt. An mehr als 1000 Schulen wurden dabei netzgekoppelte Photovoltaik-Anlagen errichtet. Im Beitrag werden die erreichten Betriebsergebnisse dieser Anlagen dargestellt. Darüber hinaus wird auf die Nutzung der Anlagen im Unterricht eingegangen.

The formation of a thin strained Si layer on top of a strain-relaxed SiGe buffer is a recent approach to improve the drive current of complementary metal-oxide-semiconductor devices by inducing strain within the transistor channel. At the same time, advanced process technologies require junction formation processes with minimal diffusion and very high dopant activation. Solid-phase epitaxial regrowth is a low temperature process based on preamorphization and subsequent regrowth leading to highly activated and shallow junctions. In this letter, we investigate the stability of the thin strained Si layer, during solid-phase epitaxial regrowth process by monitoring the Ge redistribution/strain after the preamorphization step (without any anneal) and after the thermal regrowth process.

The Institute of Safety Research of the Forschungszentrum Rossendorf, Germany, has developed electrode-mesh sensors, which allow the measurement of the electrical conductivity distribution in a flow duct. This can be used either for the detection of the gaseous phase in a gas-liquid flow or for mixing studies in single phase flow, when the components have different electric conductivities. Due to the high measuring rate each bubble is mapped in several successive instantaneous frames. This allows to obtain bubble size distributions as well as bubble-size resolved gas fraction profiles beside the visualisation and the calculation of profiles of the time-averaged void fraction. The sensor is widely used to study the evolution of the flow pattern in an upwards air-water flow. The experiments aim at closure equations describing forces acting on bubbles as well as coalescence and fragmentation frequencies for the implementation in CFD-codes. Some other prominent examples of the application of wire-mesh sensors were given, like (1) boiling water reactor stability studies, (2) the visualization of cavitation at fast-acting cut-off valves, (3) the visualization of the flow structure behind a closing globe valve, and finally (4) mixing studies in single-phase flow at the ROCOM test facility in Rossendorf, which are aimed at the mixing of deborated slugs during boron dilution transients.

Second subject of the paper is radiation tomography. A gamma-tomography setup for imaging a periodically changing density field is described. It is based on a time-resolved acquisition of the detector signals. It was used to visualize the gas fraction distribution within the impeller of an axial turbo-pump operating at about 1500 rpm, that delivered a gas-liquid mixture, as well as to a hydraulic clutch (coupling). In the field of X-ray tomography, the status of the development of an ultra-fast system based on a scanning electron beam is presented. An electron beam is linearly deflected over a tungsten target with a frequency of 1 kHz. X-rays generated by the traveling focus penetrate the object and arrive at a detector line placed behind the object. The detectors are read-out with a sufficiently high speed in order to obtain projections of the density distribution in different projecting directions, which change thanks to the scanning. First results showing tomographic image sequences of a phantom consisting of small spheres kept in arbitrary motion in a cylindrical test box will be presented. Moving spheres of 3 mm diameter with cylindrical holes of 1 mm diameter were resolved at a framing rate of 1 kHz.

Der Vortrag plädiert für einen Mix aus Atomenergie und erneuerbaren Energien, um die Versorgung für die Zukunft sicher zu stellen. Kernkraftwerke sind ebenso wirtschaftlich, wie heute die Energiegewinnung aus fossilen Brennstoffen, jedoch mit wesentlich geringeren Stoffströmen verbunden: Der Ertrag aus der Spaltung von einem Kilogramm Uran 235 oder Plutonium 239 entspricht dem aus der Verbrennung von rund 2800 Tonnen Steinkohle. Dies ist die Stärke der Kernenergie, denn dadurch ist sie die einzige Primärenergiequelle, bei der die Abfälle vollständig erfasst und geordnet entsorgt werden können. Unrealistisch ist die Vorstellung, Deutschland könne seinen Energiebedarf bis 2050 zur Hälfte aus regenerativen Quellen decken. Speichermöglichkeiten sind begrenzt, weshalb bei idealen Witterungsbedingungen Überkapazitäten auftreten würden, die nicht verwertet werden könnten. Bei einer Flaute oder bedecktem Himmel wiederum müsste Strom importiert oder beispielsweise aus fossilen Kraftwerken eingespeist werden. Beides würde den ohnehin schon hohen Strompreis aus diesen Quellen in unvertretbare Höhen treiben. Weiterhin betrachtet werden die Verfügbarkeit von Spaltmaterial, der erreichte Stand bei der Sicherheit der Kernkraftwerke sowie die Endlagerproblematik.

Gefährlich, riskant, umweltschädigend, gesundheitsschädlich, unverantwortbar, unwirtschaftlich, unsozial, nicht nachhaltig - das sind Adjektive, mit der die Nutzung der Kernenergie zur Stromversorgung häufig belegt wird. Tatsächlich tragen die Kernkraftwerke jedoch stabil zur kostengünstigen Stromversorgung bei. In Deutschland haben sie einen Anteil von 30 %, in einigen Ländern mehr. Unter dem Eindruck spürbar anwachsender Brennstoffpreise bei den fossilen Energieträgern und immer deutlicher werdender Folgen der Klimaveränderungen mehren sich die Stimmen, die eine Renaissance der Kernenergie für notwendig halten. In einer solchen Situation ist es wichtig, die Potenzen der Energiegewinnung durch Kernspaltung zu kennen und die wichtigsten Behauptungen der Kernenergiegegner kritisch zu hinterfragen. Speziell für Deutschland wird ein Blick auf die gängigen Konzeptionen zur Energiestrategie der nächsten 50 Jahre geworfen. Letztendlich wird der Schluss gezogen, dass langfristig ein Umsteuern auf einen Mix aus nuklearen und regenerativen Energiequellen erfolgen muss, um zu einer nachhaltigen und ökonomisch, sozial und ökologisch vertretbaren Energieversorgung zu gelangen.

The turbulence of the liquid phase has a signi cant dispersion e ect on the migration of bubbles in a vertical ow. Based on a double averaging approach and by adopting the Favre averaged velocity, a generalized model, called the Favre Averaged Drag (FAD) Model, was developed for the turbulent dispersion force for Eulerian simulations of multiphase ows [Burns et al., 2004]. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the inter phase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation makes the sense of the double averaging approach straightforward. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will signi cantly increase the computational e ciency. We also provide validation and evaluation for this model by numerical and experimental investigations of bubbly ows in a vertical pipe. The experimental data were obtained by using the wire-mesh sensor technique. The computations were carried out by applying poly-dispersed models. The emphasis is to examine the model applicability under various ow conditions including bubbly ows with a wall peak and a core peak of the gas volume fraction, ows in the transition region between them, and in the nely dispersed ow regime. The e ect of the drag force model on the turbulent dispersion force was also examined.

This paper reports about the DYN1D-MSR code development and dynamics studies of the molten salt reactors (MSR) – one of the ‘Generation IV International Forum’ concepts. In this forum the graphite-moderated channel type MSR based on the previous Oak Ridge National Laboratory research is considered.
The liquid molten salt serves as a fuel and coolant, simultaneously and causes two physical peculiarities: the fission energy is released predominantly directly into the coolant and the delayed neutrons precursors are drifted by the fuel flow. The drift causes the spread of delayed neutrons distribution to the non-core parts of primary circuit and it can lead to a reactivity loss or gain in the case of fuel flow acceleration or deceleration, respectively. Therefore, specific 3D tool based on in house code DYN3D was developed in FZR. The code DYN3D-MSR is based on the solution of two-group neutron diffusion equation by the help of a nodal expansion method and it includes models of delayed neutrons drift and specific MSR heat release distribution.
In this paper the development and verification of 1D version DYN1D-MSR of the code is described. The code has been validated with the experimental data gained from the molten salt reactor experiment performed in the Oak Ridge and after the validation it was applied to several typical transients (overcooling of fuel at the core inlet, reactivity insertion, and the fuel pump trip).

Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. At the Institute of Safety Research of the FZR a finite element model has been developed simulating the thermal processes and the viscoplastic behaviour of the vessel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal hydraulic and the mechanical calculations are sequentially and recursively coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool. The model was applied to pre-and post test calculations for the FOREVER test series of the KTH Stockholm. First calculations for a PWR geometry were performed to work out differences and commonalities between prototypic scenarios and scaled experiments.

General information on the ISTC program are given. The working procedures of the CEG-SAM are explained and the currently running ISTC projects related to SAM are presented in brief.

Due to their abilities for complex and colloid formation as well as their redox properties, humic acids influence the migration of actinides in the environment. Therefore, risk assessments, related to the behavior of actinides in the environment, require basic knowledge on the interaction of humic acids with metal ions. Thus, the interaction of humic acids with actinides is studied, e.g., the Np(V)-humic acid-complexation and the redox stability of uranium(VI) humate complexes, applying synthetic and natural humic acids.

We report on the first analysis of directed and elliptic flow with the new method of Lee-Yang zeroes. Experimental data are presented for Ru+Ru reactions at 1.69A GeV measured with the FOPI detector at SIS/GSI. The results obtained with several methods, based on the event-plane reconstruction, on Lee-Yang zeroes, and on multi-particle cumulants (up th 5th order) applied for the first time at SIS energies, are compared. They show conclusive evidence that azimuthal correlations between nucleons and composite particles at this energy are largely dominated by anisotropic flow.

Turbulence dispersion has a significant dispersion effect on the migration of bubbles in a vertical flow. Based on a double averaging approach and by adopting the Favre averged velocity, we developed the Favre Averaged Drag (FAD) turbulent dispersion force model for Eulerian simulations of multiphase flows. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the interphase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation explains the physical mechanism and makes the sense of the double averaging approach straightford. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will significantly increase the computational efficiency.

We also provide a systematic model evaluation based on numerical simulations of bubbly flows in a vertical pipe using both mono- and poly-dispersed flow models. The numerical results for the radial distribution of the gas concentration were compared with the experimental data measured by using the wire-mesh sensor technique. The results confirm that the bubble size and the liquid flow Reynolds number have a strong effect on the turbulent dispersion as is shown in the model derivation.

The aim of this work is to characterize the complexation ability of F-, BF4 -, PF6 -, and Tf2N- toward uranyl ions in aqueous solution. These anions were chosen as they represent the anionic part of the most studied roomtemperature ionic liquids. Time-resolved emission spectroscopy and X-ray absorption spectroscopy were used to retrieve structural data on the complexes formed. The results obtained were compared with computational data.
Tf2N- does not complex uranyl, even at high concentration. Other fluorinated acids form inner-sphere complexes with U(VI), in a monodentate fashion in the case of BF4 and PF6.

In this contribution, results of predictive atomistic computer simulations are presented which describe the ion beam synthesis of single-crystalline CoSi2 nanowires (NWs) embedded in Si. In order to simulate the Co implantation, the binary collision codes TRIDYN and TRIM were adapted to the particular experimental situation of a finely focused Co ion beam of a few tens of nanometers in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described.
Due to the systems tendency towards a reduction of interfacial free energy (Rayleigh instability), it will be demonstrated that the orientation of the Co implantation profile to the Si matrix influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)/Si(111) interface, faceting forces occur if the Co implantation profile is not aligned with the Si-[011] direction. Thus, intentional misalignment is a possible way to a controlled decay of the NW into a chain of monodisperse and equidistant nanoclusters which is applicable as plasmon waveguide.

The presentation discusses the application of X-ray micro-tomography to the measurement of size, shape and porosity of polymer particles.

In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.

We introduce a new method to noninvasively and continuously measure the swelling process of the nasal mucosa. Thereby we use light of different wavelengths in the near infrared range which is transilluminated through the nasal tissue and whose extinction is recorded as a function of time. From the temporal and spectral extinction data we are able to extract characteristic parameters that describe the swelling process quantitatively by means of a regression type parameter estimation algorithm. Furthermore, we show the capability of the method to quantify hemoglobin saturation in the surplus blood volume and introduce a bilateral measurement approach that allows us to examine the swelling process in both nasal cavities simultaneously. The method has been applied to the nasal allergen provocation test and verified on a limited number of volunteers.

The presentation discusses the application of conventional X-ray CT, X-ray cone beam CT and ultrafast limited angle X-ray CT to the measurement of phase distributions in multiphase flow problems.

Hexapotassium dihydrogen monotitanoundecatungstocobaltate(II) tridecahydrate, K₆H₂[TiW₁₁CoO₄₀]×13H₂O, crystallizes from aqueous solution in the cubic space group P43m. The structure was refined as an inversion twin. The [TiW₁₁CoO₄₀]^8- anion has a Keggin structure with one W-atom site occupied by titanium and a central tetrahedral CoO₄ group.

I will discuss two recent advances related to semiconductor light sources in the infrared and THz regions. One example is a quantum cascade laser operating at a wavelength shorter than 4 microns above room temperature with high peak power. It is based on strained InGaAs/InAlAs on InP, with the addition of high barriers of pure AlAs for better confinement and strain compensation. In a novel few-cycle THz emitter we try to combine the advantages of the high electric bias field in photoconductive antennas with a large active area. This is achieved with an interdigitated electrode structure, partially covered in order to mask one field polarity. As a result no destructive interference of the emitted THz wave occurs, which allows upscaling of the device area.

Humic acids (HA) comprise an important part of natural organic materials. Due to their interactions with organic and inorganic pollutants produced by human activity, they play a significant role in biochemical cycles of ecosystems. By the formation of soluble anionic complexes with the range of more or less toxic metals, including radionuclides, HA can affect the transport of these contaminants. Therefore, the understanding of their impact on the actinide migration in geologic environments is essential for a reliable safety assessment of nuclear waste disposal sites. In the present study the influence of HA on the U(VI) sorption onto kaolinite was studied. Kaolinite represents a well-defined model substance for clay-rich host formations.
Batch experiments were combined with EXAFS spectroscopy to obtain molecular-level information on the interaction of U(VI) with HA (14C-labeled HA) and kaolinite (KGa-1b).
Three kinds of batch experiments were performed under different experimental conditions: HA sorption in the absence of U(VI), U(VI) sorption in the absence and U(VI) sorption in the presence of HA. The sorption curves have shown that the U(VI) sorption on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 and HA presence. U(VI) sorption increases with pH up to pH 8.5, then it decreases. In the absence of CO2, no decrease is observed. In the presence of CO2 HA effects U(VI) adsorption onto kaolinite over the entire pH range. At pH < 5 the presence of HA enhances the U(VI) uptake relative to the HA-free system because the adsorbed HA forms additional binding sites for U(VI). In the pH range between pH 5 and pH 8.5 the U(VI) sorption decreases in the presence of HA due to desorption of HA from the kaolinite surface resulting in the formation of dissolved U(VI)-HA complexes. At pH > 8.5 uranium sorption increases again relative to the HA-free system (Fig.1).
We performed EXAFS measurements with U(VI)-HA-kaolinite sorbates in order to characterize the surface complexes of U(VI) in the presence of HA. Results of the spectroscopic measurements are interpreted and compared with the EXAFS results in the binary system without HA [1] to obtain information on the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.

The TRIDYN collisional computer simulation has been modified to account for emission of ionic species and molecules during sputter depth profiling, by introducing a power law dependence of the ion yield as a function of the oxygen surface concentration, and by modelling the sputtering of monoxide molecules. The results are compared to experimental data obtained with dual beam TOF-SIMS depth profiling of ZrO2/SiO2/Si high-k dielectric stacks with thicknesses of the SiO2 interlayer of 0.5, 1, and 1.5 nm. Reasonable agreement between experiment and computer simulation is obtained for most of the experimental features, demonstrating the effects of ion-induced atomic relocation, i.e. atomic mixing and recoil implantation, and preferential sputtering. The depth scale of the obtained profiles is significantly distorted by recoil implantation and the depth-dependent ionization factor. A pronounced double peak structure in the experimental profiles related to Zr is not explained by the computer simulation, and is attributed to ion-induced bond breaking and diffusion, followed by a decoration of the interfaces by either mobile Zr or O.

The GRS methodology to assess the uncertainty of the calculation results of computer simulation codes was applied to the coupled code system DYN3D/ATHLET, consisting of a 3D neutron kinetic core model and a thermal hydraulic system code. It was used to make a statistical analysis of the result parameters from the output data of the DYN3D/ATHLET-calculation. A number of variation calculations with randomly distributed input parameters within given boundaries was carried out. On that basis, time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations.

The polarization dependence of U L1 edge EXAFS spectra is relatively simple because the photoelectron is excited from ground state (l = 0) to one excited state (l = 1). By contrast, the polarization dependence is more complicated at the L2 and L3 edges were the photoelectron is excited from p ground state into final states s (l = 0) and d (l = 2). The EXAFS expression of L2 and L3 edges comprises here pure s, pure d and coupled s-d states. The polarization effect at the U L1 and L3 edges was investigated using a single crystal of Ca[UO2PO4]2•6H2O. The high symmetry in the equatorial shell allows to compare successful the measurements with the theory. In a second part two types of applications will be discussed. It will be shown, that powder samples have a texture which can lead to an erroneous determination of coordination numbers. A use of the magic angle allows to avoid this problem. A second example will be discussed where the polarization dependency can be used to determine the orientation of actinyl ions sorbed at mineral surfaces.

Lecture on the present status of ion irradiation in exchange bias systems.

Risk assessments of actinide-contaminated soils and sediments require detailed knowledge of actinide speciation and its long-term kinetics. Former Saxonian mine tailings, which have been covered but else left undisturbed, are ideally suited to study changes in uranium speciation over timescales of decades. We investigated the major uranium species in two samples from buried mine tailings using a combination of Synchrotron-based microfocus-techniques (μ-XRF, μ-XRD with micrometer resolution), bulk EXAFS spectroscopy, and chemical extractions.
In sample F1 (5 m depth, oxic, pH 8, U=440 mg/kg, high Ca, S, Pb, Cu, Zn concentrations), uranium is diffusely distributed among aggregates of layer silicates (muscovite, illite and kaolinite). The chemical extractions and EXAFS results confirm that uranium is sorbed to these minerals, but is not incorporated into their crystal structure. Sorption is also in line with the high pH and low carbonate concentrations in pore water. In sample F3 (12 m depth, oxic, pH 4, U=430 mg/kg), the combination of μ-XRF and μ-XRD enabled us to identify several U(IV) and U(VI) containing minerals like coffinite, uraninite, uranyl hydroxide, and vanuralite. Only a minor part of U is sorbed to layer silicates as confirmed by chemical extractions and EXAFS spectroscopy.
At smaller depth (F1, 5 m), sulfuric acid from the ore extraction procedure was completely neutralized by the construction waste used as cover material, resulting in precipitation of jarosite and gypsum. Even 30 years after the ore extraction, uranium remains highly soluble. At greater depth (F3, 12 m), the low pH from ore extraction was conserved. The presence of U(IV) minerals suggest either precipitation of secondary (IV) minerals due to microbial redox activity, or incomplete dissolution of primary (IV) minerals due to ore processing inefficiency of these older sediments. The U(IV) minerals were recalcitrant during chemical extractions, suggesting low uranium solubility even at oxic redox conditions. The results demonstrate a very high variability of uranium speciation and hence potential mobility, which seems to depend on geochemical parameters and site history, but shows little influence of time.

The light meson dilepton identification in the HADES detection system is based on an invariant mass reconstruction of their decay into e⁺e^- pairs. Methods of the dilepton signal reconstruction in the HADES spectrometer and preliminary dilepton spectra for C+C reactions at 2 AGeV are presented in this paper. In the signal reconstruction particularly important is the reduction of the huge combinatorial background arising from wrong combinations of electrons and positrons into un-like sign pairs. A purity of the dilepton signal is determined by using GEANT simulation with the full HADES geometry and a realistic detector response.

FELBE is an acronym for the free-electron laser (FEL) at the Electron Linear accelerator with high Brilliance and Low Emittance (ELBE) located at the Forschungszentrum Rossendorf in Dresden, Germany. This FEL is a source of pulsed, coherent light which is continuously tunable over the infrared wavelength range from 5 to 25 µm. This will be enlarged to about 150 µm in late 2006.
At the FELBE facility a laboratory suitable for radiochemistry research was installed. This lab is classified as a controlled zone for investigations of certain radionuclides obeying to all aspects of radiation protection. The maximum activity of the investigated radioactive samples can add up to 105 times of the admissible limit. A glove box provides the possibility to perform experiments on sensitive samples which have to be kept in an inert gas atmosphere.
The time structure of the pulsed FEL beam is related to the frequency of the electron pulses of the accelerator which offers a 13 MHz repetition rate in macropulses of a few 100 μs at up to 25 Hz. A continuous 13 MHz regime is also available as well as single pulse selection down to a frequency of 1 Hz. The energy of the infrared pulses is up to 1 µJ/pulse depending on the wavelength.
The FELBE facility is a member in the Integrated Infrastructure Initiative (I3) on synchrotron and free-electron laser science (IA SFS) within the 6th framework programme of the EU. With this grant, external users of FELBE can be financially supported ("transnational access").
In our first experiment we use the FEL beam for investigation of mineral surfaces by Phototermal Beam Deflection (PTBD) spectroscopy. The PTBD technique is based on the theory of photothermal spectroscopy which describes the conversion of absorbed energy of a light beam incident on a sample into heat by nonradiative de-excitation processes. In typical PTBD experiments the magnitude signal is proportional to the slope of the induced displacement of the sample surface. There is a direct proportionality between the observed signal and the absorption coefficient of the material under investigation which provides a direct access to infrared absorption spectra with a very low detection limit is provided.
Furthermore, the PTBD technique is capable to gain spatial information (microspectrometry) of the sample’s surface since generation and detection of the thermal wave occurs generally in the submillimeter length scale. This may result in a microspectrometric technique for determining the distribution e.g. of sorbed metal species on mineral surfaces.

The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive wastes. The mobility of this radionuclide is controlled by its interactions with ions, minerals and microorganisms present in nature. As a consequence of their small size and diverse metabolic activities, bacteria are able to interact intimately with uranium and other metal ions present in their environment. Assessment of the potential hazard posed by the presence of uranyl-bacterial complexes, as well as the development and application of accurate contaminant transport models, requires an understanding of the speciation of uranium associated with bacteria. This paper summarizes the effect of pH on the speciation of uranium bound by about fifteen bacterial strains isolated from uranium mining wastes. Microbiological methods in combination with Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Infrared (IR) spectroscopy, Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) were applied. EXAFS analysis showed that the cells of the most bacterial strains studied precipitate U(VI) as m-autunite-like phase at pH 4.5, probably due to the release of the inorganic phosphate from the cells as result of the acidic phosphatase activity. However, at pH 2 uranium formed complexes with organically bound phosphates of the cell surface. At pH 3, both organic and inorganic phosphate uranyl species occur together. No structural differences of the uranium complexes formed by three types of Acidithiobacillus ferrooxidans at above mentioned pH values were found, indicating the implication of organic phosphate moieties in the complexation. However, in the case of B. sphaericus JG-A12 the uranium bonding was consistent with the formation of complexes with organic bound phosphate and carboxylate groups of the cell surface. We applied Iterative Target Test Factor Analysis to determine the speciation at different pH values quantitatively from the EXAFS spectra. Transmission electron microscopy and energy dispersive X-ray analysis revealed species and even strain-specific extracellular and/or intracellular uranium accumulations to varying degrees. Different hypothesis explaining the different coordination chemistry of uranium to bacteria in function of the pH of the uranium solution in terms of solubility of m-autunite and/or microbial activity will be discussed.

The High Acceptance DiElectron Spectrometer HADES has been recently commissioned at GSI, Darmstadt. It has been designed for systematic studies of hadron properties inside nuclear matter. We report first preliminary results on invariant masses of e⁺e^--pairs which were measured in ¹²C + ¹²C collisions at E_kin=2 GeV*A. The analysis methods are briefly outlined and a comparison with detailed Monte-Carlo simulations is shown.

The identification of light mesons in the HADES spectrometer is based on an invariant mass reconstruction of their decay into e⁺e^- pairs. In the delepton (e⁺e ) signal reconstruction particularly important is the reduction of a combinatorial background arising from wrong combinations of e⁺ and e^- to unlike sign pairs. The purity of the dilepton signal is determined by using GEANT simulations. The analysis methods of the dilepton signal and combinatorial background reconstruction will be presented.

The High Acceptance DiElectron Spectrometer (HADES) has been recently commissioned at GSI Darmstadt. It has been designed to study hadron properties inside nuclear matter via measurements of dielectron decays in proton, pion and heavy ion induced reactions in 1−2 AGeV energy range. We report first preliminary results on invariant masses of e⁺e⁻ pairs measured in ¹²C + ¹²C collisions at E=2 AGeV and compare them to simulations based on UrQMD transport model. In summary we present and discuss planned experiments.

Due to their strong ability for complex and colloid formation, humic acids influence the speciation and consequently the migration behavior of actinide ions in the environment. In order to perform a trustworthy risk assessment for the conception of future nuclear waste repositories as well as for the remediation of former uranium mining and milling areas, reliable thermodynamic data on the interaction of uranium with humic acids under geogenic conditions are necessary.
The U(VI) complexation by humic acids was already the subject of a number of previous investigations. However, these studies were predominately performed in the acidic pH range, were the hydrolysis of the uranyl ion can be neglected. Only few studies exist on the interaction of U(VI) with humic acids under neutral pH conditions where ternary U(VI) humate complexes are formed.
In the present study we investigate the complexation of U(VI) by purified Aldrich humic acid at pH 7 under exclusion of CO2 ([HA]: 2 mg/L; [U]: 1·10-6-1·10-5 M, I: 0.1 M NaClO4). Under the studied experimental conditions and in absence of humic acid, U(VI) occurs in form of the following species: UO2OH+, UO2(OH)2(aq), (UO2)3(OH)5+, (UO2)4(OH)7+. The speciation is dominated by 62-73 % of (UO2)3(OH)5+. Based on this speciation, the formation of ternary uranyl hydroxy humate complexes is assumed. For determination of the U(VI) and humic acid speciation in solution we apply the conventional time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses, respectively. For identification and quantification of the U(VI) species in solution, fluorescence spectra were measured for the relevant U(VI) hydrolysis species. The experimental data are evaluated applying the metal ion charge neutralization model [1], which describes the metal ion complexation by humic acids.

[1] Kim, J.I., Czerwinski, K.R.: Complexation of Metal Ions with Humic Acids: Metal Ion Charge Neutralization Model. Radiochim. Acta 73, 5 (1996).

Humic acids (HA) comprise an important part of natural organic materials. By the formation of soluble complexes with radionuclides, HA can affect the transport of these contaminants. Therefore, the understanding of the impact of HA on the actinide migration in geologic environments is essential for a reliable safety assessment of nuclear waste disposal sites. In the present study we investigated the influence of HA on the U(VI) sorption onto kaolinite. Kaolinite represents a well-defined model substance for clay-rich host formations.
Batch experiments were combined with EXAFS spectroscopy to obtain molecular-level information on the interaction of U(VI) with HA (14C-labeled) and kaolinite (KGa-1b) in natural systems.
From our batch experiments it is known that the sorption of U(VI) on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 and HA presence. U(VI) sorption increases with pH up to pH 7.5, then it decreases. In the absence of CO2, no decrease is observed. In the presence of CO2 HA effects U(VI) adsorption onto kaolinite over the entire pH range. At pH < 5 the presence of HA enhances the U(VI) uptake relative to the HA-free system because the adsorbed HA forms additional binding sites for U(VI). In the pH range between pH 5 and pH 8.5 the U(VI) sorption decreases in the presence of HA due to desorption of HA from the kaolinite surface resulting in the formation of dissolved U(VI)-HA complexes. At pH > 8.5 uranium sorption increases again relative to the HA-free system.
Previously, EXAFS spectroscopy was applied to study the structure of the U(VI) adsorbed on kaolinite [1], but no EXAFS was measured in the system U(VI)-HA-kaolinite. Therefore, we performed EXAFS measurements with U(VI)-HA-kaolinite sorbats in order to characterize the surface complexes of U(VI) in the presence of HA. Results of the spectroscopic measurements are interpreted and compared with the EXAFS results in the binary system without HA to obtain the information on the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.

An electrochemical cell was developed for in situ investigations of radioactive materials using X-ray absorption spectroscopy. Due to the specific safety requirements for handling of radioactive materials the electrochemical cell had to be gas tight. The spectro-electrochemical cell comprises two safety compartments and a special electrode arrangement in order to avoid any gas release.

Microbes are widely distributed in nature and they can strongly influence the migration of actinides in the environment. Microorganisms in concentrations of 1x103 to 5x106 cells ml-1 were estimated by Pedersen et al. in the aquifer system of the Äspö Hard Rock Laboratory (Äspö HRL) in Sweden. The number of sulfate-reducing bacteria (SRB) was between 101 to 2x104 cells ml-1. We investigated the interaction of the SRB Desulfovibrio äspöensis, DSM 10631T, with plutonium. The 242Pu was provided as a mixture of ca. 46% Pu(VI) and ca. 34% Pu(IV)-polymer. Interactions between bacteria and plutonium in mixed oxidation states were not yet intensively investigated.
In this study, accumulation experiments were performed in order to obtain information about the amount of the Pu bound by bacteria in dependence on the contact time and the [Pu]initial at pH 5. We used liquid-liquid-extractions and absorption spectroscopy to determine the Pu speciation. In agreement with the results obtained with U(VI) [2] and Np(V), we found a strong dependence of the amount of accumulated Pu with [Pu]initial. Based on our results and taking into consideration the findings of Panak et al. [3], we developed a model describing the interaction of Pu(VI) and Pu(IV)-polymers with D. äspöensis. In a first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. The Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 24 h of contact time. Most of the formed Pu(V) dissolves due to the weak complexing properties. The dissolved Pu(V) disproportionates to Pu(IV) and Pu(VI) which are then interacting with functional groups of the cell surface structure. Indications were found also for a penetration of Pu species inside the bacterial cells.

[1] Pedersen, K.: Microbial processes in radioactive waste disposal. SKB Technical Report TR-00-04 (2000).
[2] Moll, H.; Merroun, M.; Stumpf, Th.; Geipel, G.; Selenska-Pobell, S.; Hennig, C.; Roßberg, A.; Bernhard, G.: Interaction of Desulfovibrio äspöensis with Actinides, presented at the MIGRATION’03, Gyeongju, Korea (2003).
[3] Panak, P. J.; Nitsche, H.: Radiochim. Acta 89, 499 (2001).

This work was funded by the BMWi under contract number: 02E9491.

Naturally occurring aquatic humic substances (humic and fulvic acids) are known to effect the speciation and thus, the migration behavior of actinide contaminants in environmental systems due to their complexing and redox properties and their ability to form colloids. Therefore, to understand and predict the mobility of actinides in natural aquifer systems, amongst others, information on their redox stability in the presence of humic substances is necessary.
In the present work, the time dependence of the reduction of Np(V) to Np(IV) by humic substances of varying functionality has been studied under anaerobic conditions between pH 3.5 and pH 9. Synthetic humic acids with pronounced redox functionality (type Cat-Gly and Hyd-Glu) [1] were studied in comparison to natural humic substances (Aldrich humic acid, Kranichsee fulvic acid). For Np speciation in solution liquid-liquid extraction, laser-induced photoacoustic spectroscopy (LIPAS), NIR absorption spectroscopy, and ultrafiltration were applied. In comparison to the natural humic substances, the synthetic humic acids lead to a much stronger reduction of Np(V) to Np(IV) [2]. The Np(IV) formed in the course of the experiments is stabilized as Np(IV) humate. The tetravalent oxidation state remained constant for several months.
The redox capacities of the synthetic humic acids, which are significantly higher than those of the natural humic substances, can be attributed to their higher phenolic/acidic OH group contents compared to natural humic substances. The dominating role of phenolic/acidic OH groups for the reduction of Np(V) by humic substances could be verified applying a synthetic humic acid with blocked phenolic/acidic OH groups (type Hyd-Glu-PB). Furthermore, the influence of NO3- on the Np(V) reduction by humic substances was studied.
The results have shown that by application of the synthetic humic acids with distinct redox functionalities actinides can be stabilized in lower oxidation states, e.g. in complexation and sorption studies.

[1] Sachs, S., Schmeide, K., Brendler, V., Krepelová, A., Mibus, J., Geipel, G., Heise, K.H., Bernhard, G.: Investigation of the Complexation and the Migration of Actinides and Non-radioactive Substances with Humic Acids under Geogenic Conditions. Complexation of Humic Acids with Actinides in the Oxidation State IV Th, U, Np. FZR-399, Wissenschaftlich-Technische Berichte, Forschungszentrum Rossendorf, Dresden 2004.
[2] Schmeide, K., Geipel, G., Bernhard, G.: Study of the Neptunium(V) Reduction by Various Natural and Synthetic Humic Substances. In: FZKA 7070, Wissenschaftliche Berichte (G. Buckau, ed.). Forschungszentrum Karlsruhe, Karlsruhe 2005, 19-31.

The diffusion of humic acid (HA) in Georgia kaolinite KGa-1B was studied. The compacted clay plug was conditioned with a 0.01 M NaClO4 + 1 mM NaN3 solution at pH 5.2. The effective porosity ε and the effective diffusion coefficient De of water were determined using tritiated water (HTO). A synthetic 14C-labeled HA type M42 with a concentration of 11.0 mg/L and a specific activity of (17.0 ± 0.5) MBq/g was used as tracer. We applied a steady-state through-diffusion technique with constant gradient. The particle size distribution of HA was determined by ultrafiltration.

The migration of HA in compacted clay is governed by diffusion. However, compared to an ionic tracer some characteristics are observed. The De values found for HA (2·10^13 to 2·10^12 m^2/s) are about two to three orders of magnitude lower than that of HTO. Likewise the rock capacity factor α(HA) amounts to only 10 % to 50 % of ε. The spatial extension of the humic colloids constricts their mobility in the narrow pore space thus increasing the tortuosity of the diffusion path and decreasing the pore volume accessible for HA. This phenomenon is referred to as size exclusion effect. In [1] a significant adsorption of HA on KGa-1B was found (Kd = 680 ml/g at pH 5.2) which would result in a value for α above unity. Obviously, the size exclusion dominates the HA migration.
The particle size distributions of the high and the low concentration reservoir differ significantly. The mean particle size shifts from about 50 kD in the high to less than 1 kD in the low concentration reservoir. Only small particles are able to pass the pore system. This is in agreement with the HA distribution in the clay plug where most of the tracer was found at the high concentration boundary.

Brain imaging techniques have provided substantial insight into the pathophysiology of hepatic encephalopathy (HE). Magnetic resonance imaging gave hint to the fact that there is an increased deposition of manganese especially in the basal ganglia. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) showed that the preference of the basal ganglia might be due to differences in regional cerebral blood flow and an additional redistribution of blood flow from the cortex to subcortical regions in cirrhotics. PET studies using ammonia as tracer showed that the cerebral metabolism of ammonia and the permeability of the blood brain barrier for ammonia is increased in cirrhotic patients compared to healthy controls. The regional ammonia supply is in accordance with the regional blood flow. In accordance with these findings fluorodesoxyglucose-PET-studies of the brain in cirrhotics showed characteristic alterations of glucose utilisation in the patients with a relative decrease of the glucose utilisation of the cingulate gyrus, the frontomedial, frontolateral, and parieto-occipital cortex, while the glucose utilisation of the basal ganglia, the hippocampus, and the cerebellum was relatively increased. These findings fit well with the clinical characteristics of early stages of HE such as deficits in attention, visuo-spatial orientation, visuo-constructive abilities, motor speed, and accuracy.

BACKGROUND AND PURPOSE: Hypoxia of clonogenic tumor cells is a major reason for radioresistance and hence local failure in radiotherapy. The objective of the present study was to test the efficacy of the hypoxic cell sensitizer isometronidazole (ISO) during fractionated irradiation in two different human squamous cell carcinomas. MATERIAL AND METHODS: Local control was evaluated for FaDu (radiobiological hypoxic fraction [rHF] 7%) and GL tumors (rHF 0.1%) after single-dose (SD) irradiation under ambient conditions and after 30 fractions within 6 weeks (30 f/6 w). ISO was applied 60 min before SD irradiation at a concentration of 100 mg/kg body weight (b.w.) or 750 mg/kg b.w. in both tumors. During fractionated irradiation, ISO was applied daily 60 min before each fraction (100 mg/kg b.w., in FaDu also 750 mg/kg b.w.). RESULTS: 100 mg/kg b. w. ISO did not improve local control after SD irradiation or 30 f/6 w in both tumor models. Application of 750 mg/kg b. w. ISO significantly decreased the SD-TCD(50) in FaDu tumors (dose-modifying factor [DMF] = 1.2; p = 0.01) but not in the better oxygenated GL tumor. ISO at 750 mg/kg b.w. also significantly improved local control of FaDu tumors after 30 fractions in 6 weeks (DMF = 1.2; p = 0.01), indicating that hypoxic clonogenic cells in FaDu tumors are not only present before start of irradiation but also limit the efficacy of treatment during a fractionated course of radiotherapy. CONCLUSION: ISO at a concentration of 750 mg/kg b.w. shows an efficacy as a hypoxic cell sensitizer in severely hypoxic FaDu tumors but not in less hypoxic GL tumors. This supports the principle of hypoxic cell sensitization and improvement of local control of hypoxic tumors by nitroimidazole derivatives. However, doses of 750 mg/kg b. w. before each fraction may be difficult to achieve in the clinical situation. This, in light of the fact that other well-tolerable hypoxic cell sensitizers such as nimorazole with clinically proven efficacy at daily oral doses of < 3 g are available, limits the potential usefulness of ISO for radiation oncology.

The Stille reaction with 4-[(18)F]fluoroiodobenzene as a novel approach for the synthesis of radiotracers for monitoring COX-2 expression by means of PET has been developed. Optimized reaction conditions were elaborated by screening of various catalyst systems and solvents. By using optimized reaction conditions (18)F-labelled COX-2 inhibitors [(18)F]- and [(18)F]- could be obtained in radiochemical yields of up to 94% and 68%, respectively, based upon 4-[(18)F]fluoroiodobenzene.

Oxidative modification of low-density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Assessing the metabolic fate of oxidized LDL (oxLDL) in vivo with radiotracer techniques is hindered by the lack of suitable sensitive and specific radiolabeling methods. We evaluated an improved methodology based on the radiolabeling of native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 ((18)F) by conjugation with N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB). We investigated whether radiolabeling of LDL induces adverse structural modifications. Results suggest that radiolabeling of both nLDL and oxLDL using [(18)F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively. Thus, radiolabeling of LDL using [(18)F]SFB could prove to be a promising approach for studying the kinetics of oxLDL in vivo.

Surface chemistry during wet chemical etching in alkaline KOH solution and dry etching in SF6/O2 plasma of high dose Ga+ implanted Si has been investigated by means of secondary ion mass spectroscopy (SIMS) and x-ray induced photoelectron spectroscopy (XPS). During wet chemical etching in a KOH/H2O solution a thin layer of GaOx of < 1 nm thickness is formed, which has been investigated more in detail by angle-resolved XPS.. In the case of dry reactive ion etching the surface chemistry is quite different. In this case a more enhanced oxidation of Ga takes place due to the high reactivity of atomic oxygen from the SF6/O2 plasma. SIMS results show that during RIE a Ga rich surface layer forms and therefore an enhanced Ga oxidation takes place leading to a thicker GaOx layer compared to wet chemical treatment. XPS depth profiling points at a stoichiometry of nearly completely oxidized Ga (Ga2O3) layer free from Si with a thickness of about 5 ... 10 nm. The etch rate lowering in Ga+ as- implanted silicon is ascribed to the formation of gallium oxide at the Si surface during the etch processes.

B-C-N thin films of a wide composition range were deposited by reactive d.c. magnetron sputtering of targets with different B/C ratio in an Ar/N2 atmosphere. The bonding characteristics of these amorphous films were investigated by Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy. The results of both characterisation methods indicate that real ternary compounds in which all three elements are bound to each other are only formed when at least one element has a low concentration in the film (and therefore could be considered as an impurity). Otherwise the deposited material tends to a phase separation into binary compounds and single phases.

Low resistance spin-dependent tunnel junctions are investigated for read-head applications due to their large tunneling magnetoresistance effect and low junction resistance-area product. Typical full junction structures can be Ta 70Å/NiFe 70Å/MnIr 80Å/CoFe 35Å/Hf(x)Al(y)O(z) t/CoFe 35Å/NiFe 40Å/Ta 30Å, with t around 10 Å, annealed to temperatures up to 250ºC. We analysed simpler structures with RBS experiments at a grazing angle of incidence in order to study the junction only. Heavy ion- and He-ERDA experiments were also done. The composition of the HfAlO barrier is determined, showing that a slightly substoichiometric oxide is formed. On annealing at 240ºC, the interfaces of the barrier become sharper. TEM results confirm that the barrier is continuous after annealing. This is related to an increase in the tunnel magnetoresistance signal from 4% to 13.5% after annealing.

A study of the mixing of a deborated slug during start-up of the first coolant pump in VVER-1000 type reactors was performed with the commercial CFD package CFX-5.7 using experimental results of the 1:5 scaled test facility. The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor CFX-5 and contains 2.5 Mio. tetrahedral elements. The CAD geometry and the grid model include the inlet nozzles, the downcomer incl. spacer elements and the lower plenum with the elliptical sieve plate and internals. Parts of the complicated lower plenum structures were modeled with the porous media approach in CFX-5, which uses directed resistance coefficients.

The output of the Best Practice Guidelines for optimizing the numerical studies of boron dilution transients in different reactor types was used in the numerical simulation. The discretisation scheme in time was set to second order Euler and in space to High Resolution. The SST turbulence model was taken.

The modeled deborated slug first arrives at the core inlet of the reactor pressure vessel in the neighboring areas at the outer case of the starting loop. Later the slug is almost homogenously distributed over the core inlet plane. The minimum averaged deboration value in the experiment and the CFD calculation is in good agreement when using a constant wall temperature (72%). The existing time offset in the numerical calculation could not been clarified.

In this work, junctions with reduced Hf coupling were fabricated by ion beam deposition and oxidation, using CoFeB electrodes. The CoFeB layer has a strong (110) texture that can be the origin of lower Hf and coercivity when compared with CoFe. Junctions processed down to 2x4 um2 with 40Å thick CoFeB bottom electrodes have 42% of tunneling magnetoresistance (TMR), (R x A ~400 Ohm um2), Hc of ~10 Oe and Hf of ~2 Oe. CoFe-based junctions (R x A ~500W Ohm um2) have lower TMR (~35%) and larger Hf (~5-6 Oe) and Hc (~12-14 Oe). Local chemical composition analysis of the cross section indicated Fe-O segregation without Co grown on top of the barrier for CoFe-based junctions and not for CoFeB ones.

A PtMn/NiFe exchange bias system with an exchange bias field of 180 Oe was magnetically patterned by means of a low fluence focused ion beam. A 1 µm wide stripe pattern with the long axis (1000 µm) oriented parallel to the exchange bias field direction has been irradiated by 2x10¹⁴ Ga⁺/cm². In the irradiated area the coercivity is reduced and the exchange bias field vanishes, while in the nominally non-irradi-ated region between the irradiated stripes the exchange bias field is reduced to approximately 35 Oe. This reduction is attributed to the magnetic coupling of the irradiated stripes to their intervening non-irradiated regions. Magnetic domain imaging by means of Kerr microscopy and magnetic force microscopy support this interpretation.

To improve the performance of critical part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments mixing PIII and ion nitriding processes. A combination of high pressure (4 x 10(1)Pa), moderate temperature (up to 450degreesC) glow discharge nitriding with low pressure (8 x 10(-2)Pa) and low DC bias voltage ion nitriding (or DC PIII) was implemented. Depending on the particular conditions of the treatment and the depth probed, mixed phases of gamma(N) and epsilon were measured in the treated SS304 steel sample. This near surface modification resulted in an improved hardness (up to a factor of 2.7 x) of the sample which could also enhance its wear properties. Surface modification of T16Al4V alloy and SS304 steel by a combination of PIII and subsequent ion nitriding was investigated as well. Nitrogen ions were implanted into the specimens at 15 keV and then ion nitrided at ! low pressure (7 x 10(-2)Pa) with a bias of -800 V. Compared to the untreated samples, the hardness of Ti6Al4V alloy and the steels could be improved significantly. AES results indicated high retained doses in both samples, confirming the high efficiency of this hybrid process.

An apparatus for laser-induced breakdown detection (LIBD) was established, which is aimed at in-situ detection of aquatic colloids of a particle size down to < 50 nm and a particle concentration down to the ppt range. LIBD is based on the generation of dielectric breakdown events on individual colloid particles by pulses of a focused laser (cf. [1]). A diode pumped Nd:YAG laser is used as light source and is operated at maximum power for stability reasons. The pulse energy is controlled by a combination of two Fresnel rhombs and a calcite polarizer. The beam is focused into a quartz cell containing the particle suspension to be analyzed. The breakdown events are simultaneously observed by a CCD camera and by piezoelectric detectors.

Polystyrene latex standards of different particle size were diluted with de-ionized water (Membrapure) to mass concentrations of the ppt and ppb range. These solutions were used for the calibration of the LIBD system.

Two particle systems of environmental relevance were studied by LIBD.
First, a nearly particle-free spring water of a small stream was investigated. Photon correlation spectroscopy, an alternative technique of particle detection, was too insensitive to find particles in this water. Both the raw sample of this stream water and centrifugates/filtrates of the water could be successfully investigated and consistent results were provided by LIBD. Second, uranium(IV) colloids were generated in a glove box (N2 atmosphere) by cathodic reduction of uranium(VI) followed by the successive increase of the pH by coulometric titration. The formation of these colloids was traced by LIBD.

[1] Walther, C., Bitea, C., Hauser, W., Kim, J.I. and Scherbaum, F.J.
Laser Induced Breakdown Detection for the Assessment of Colloid Mediated Radionuclide Migration. Nucl. Instr. and Meth. B 195 (2002) 374-388

Feasibility study of wrist watched based radiation survey meter

Mechanische und optische Anforderungen an die Cavity des FEL

A start-up procedure for natural-circulation Boiling Water Reactors is illustrated. The procedure, developed in order to avoid flashing-induced instabilities at low pressures and low powers, does not require any additional system. The reactor vessel is pressurized while steam is produced outside the core and riser sections. In this way, the firsts stage of the pressurization takes place with the reactor operating in single-phase natural-circulation conditions, thus without occurrence of flashing-induced flow oscillations. At the same time, a smooth steam production and pressurization of the system is achieved. A simple analytical model is applied to the ESBWR of General Electric to have a first impression on the order of magnitude of the parameters involved and to verify whether the start-up of the reactor can be achieved in reasonable times. The feasibility of the procedure is then studied in details by means of the ATHLET code (Lerchi and Austregesilo, 2003), developed by GRS (Germany). This code has been successfully qualified against low-pressure flashing-induced instabilities within the framework of the EU project NACUSP

Colloids can either stimulate or retard the transport of actinides. Environmental colloids are formed by a variety of mechanisms. The most important one is the precipitation of secondary phases. There have already been several publications on colloid generation within water bod-ies due to chemical reactions after the mixing of waters of different chemical composition or after access of air. Much less information exists about a different mechanism of colloid for-mation in the nature – the direct production of secondary mineral colloids at the water-rock interface by the weathering of rock material.

The formation of colloids during the weathering of ground phyllite from an abandoned ura-nium mine and the sorption of uranium(VI) onto these colloids were studied. Centrifugation and ultrafiltration were applied. A method to differentiate between the primary mineral col-loids of the phyllite and the precipitated secondary mineral colloids was developed.

Significant amounts of colloids of the 101 to 102 nm size class were found in the suspension of ground phyllite after weathering times of 87 h to 792 h. Considerable fractions (up to 10 mg/L) of these 101 to 102 nm colloids consisted of secondary minerals. The following compo-sition of the freshly precipitated colloids is to be expected: Ferihydrite, aluminosilicates, amorphous Al(OH)3, gibbsite, possibly iron silicates, possibly iron-alumino silicates. It should be emphasized that a significant fraction of the secondary mineral colloids was composed of iron(III) compounds which is of relevance for the sorption behaviour of these colloids. A more detailed mineralogical characterization of the colloids is underway. The 101 to 102 nm secondary mineral colloids were relatively stable and remained in colloidal suspension over longer periods of time.

The direct formation of secondary mineral colloids at the mineral-water interface by the weathering of rock material is an alternative to the well-known mechanism of colloid forma-tion by the mixture of different water bodies or by aeration of a water body. This direct mechanism of colloid production occurs during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine dumps. Colloids produced by this mechanism can influence the transport of actinides since they have a large specific surface area and a high sorption affinity for heavy metals. This was demonstrated for uranium(VI).

Information on molecular speciation provides a basis for the reliable assessment of actinide migration in the environment. We use several methods for the separation of colloids from liquids (e.g. ultracentrifugation, ultrafiltration) in combination with spectroscopic techniques (EXAFS, ATR-FTIR, Mössbauer) and modeling of surface complexation reactions. This enables us to investigate the speciation of colloid-borne uranium in waters occurring in or escaping from abandoned uranium mines during the remediation process. Mine flooding was simulated on a 100 L scale by mixing acid mine water of elevated U concentration with oxic, near-neutral groundwater until pH~5.5 was reached. The freshly formed colloids adsorbed 95% of the total uranium and consisted mainly of 2-line ferrihydrite (Fh) besides traces of aluminum, sulfur, silica, and carbon compounds. EXAFS analysis at the U-LIII absorption edge suggested a bidentate surface complex of UO22+ on FeO6 octahedra, but two minor backscattering contributions in close vicinity to the absorber remained unexplained. Since only Al could be excluded as backscattering atom, we studied U sorption on Fh at pH 5.5 in presence and in absence of sulfate, silicate, and atmospheric CO2 to clarify the bond structure.

EXAFS showed the unknown backscattering contributions in all the sorption samples regardless of the presence or absence of the tested components. Contrary to structural models proposed in the literature, bidentately complexed carbonate ligands do not explain our experimental EXAFS data. But ATR-IR spectra showed that U-carbonato complexes must be involved in the sorption of uranyl on Fh. These results are not contradictory if the carbonate ligands were bound monodentately. Nevertheless, carbon cannot act as backscattering atom in carbonate-free samples prepared in N2 atmosphere. We propose a new structural model including exclusively Fe, H, and O atoms in which the bidentately bound UO22+ is oriented in a way that yields a distance of ~2.9 Å to the O atom of an adjacent, edge-shared FeO6 octahedron. This model predicts a second Fe shell at ~4.35 Å which tightly fits the experimental data.

In summary, uranium may form different sorption complexes with colloidal ferric hydroxides: a binary bidentate uranyl complex with modified orientation, and ternary U-carbonato complexes with monodentate linkage of the carbonate ligand. The affinity of carbonate and uranyl to form such complexed surface species will increase when sorption sites with high affinity, as provided by colloidal Fh, are present.

The renewed interest on MSR systems has stimulated the development of computational tools assigned for analysis and simulation of MSR systems. The code system is a tool developed at Forschungszentrum Rossendorf for the analysis of burn-up behavior and transient simulation of Molten Salt Reactors. The computing method is based on the coupling between the well-known Monte Carlo transport code MCNP-4C2 and the burn-up code ORIGEN 2.1. In the second part the contribution shows applications of the system DYN3D-MSR dynamics code for Molten Salt Reactors, which is based on FZR two groups diffusion code DYN3D designed for dynamics calculation of light water reactors.

This contribution shows some applications of code HELIOS at Research Center Rossendorf. These are: A cell assembly models of the European Pressurized Water Reactor (EPR), including burnup calculations, with HELIOS Version 1.6, and applications of a typical pressurized water reactors of the type KONVOI with HELIOS Version 1.6 & 1.7 and comparisons with the lattice transport and burnup code CASMO 4. The second part gives remarks what can be done better in future codes.