Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We present a large photoconductive THz emitter[1] consisting of two interdigitated metallization layers on a semi-insulating GaAs substrate.
The photoexcited carriers are unidirectional accelerated by a bias voltage providing an electric field. This leads to a subsequent emission of THz radiation. The second metallization inhibits the optical excitation in every second period of the electrode structure in order to prevent destructive interference. We analyse the spatial profile of such an emitter excited with unfocused fs optical pulses from an Ti:sapphire amplifier with an average power of 60mW at a 1kHz repetition rate. The resulting THz beam has a bandwidth from 0.1 THz to 4 THz and a field amplitude of up to 6kV/cm (Ubias = 30V ). The focussed THz spot was mapped out and analyzed with respect to the frequency. A strong increase of the beam diameter with decreasing frequency was found. Saturation behavior was observed by changing the excitation density.
[1] A. Dreyhaupt, S.Winnerl, T.Dekorsy, and M.Helm, Appl. Phys 86,
121114 (2005)

In the frame of the TOPFLOW project, vertical pipe flow is experimentally studied in order to develop and validate models for bubble forces as well as for bubble coalescence and fragmentation in a gas-liquid two-phase flow. The advantage of TOPFLOW [1] consists in the combination of (1) a large scale of the test channel with (2) a wide operational range both in terms of the superficial velocities and the system pressure and finally (3) the availability of an instrumentation that is capable in resolving structures of the gas-liquid interface, namely the wire-mesh sensors.
After a large number of experiments in plain vertical pipes, which are the basis of the development for a multi-bubble size model for ANSYS CFX 10.0, the large test section with a nominal diameter of DN200 was used to study the flow field around an asymmetric obstacle. This is an ideal test case for the CFD code validation, since the obstacle creates a pro-nounced three-dimensional two-phase flow field. Curved stream lines, which form significant angles with the gravity vector, a recirculation zone in the wake and a flow separation at the edge of the obstacle are phenomena widespread in real industrial components and installations. Recently, test series were performed with an air-water flow at ambient conditions as well as with a steam-water mixture at a saturation pressure of 6.5 MPa. Before the experiments were commissioned, an ANSYS CFX 10.0 pre-test calculation was carried out for one of the experimental tests, which resulted in a good agreement with the experiment in terms of all significant qualitative details of the void fraction and velocity distributions.

In the frame of the TOPFLOW project, vertical pipe flow is experimentally studied in order to develop and validate models for bubble forces as well as for bubble coalescence and fragmentation in a gas-liquid two-phase flow. The advantage of TOPFLOW consists in the combination of (1) a large scale of the test channel with (2) a wide operational range both in terms of the superficial velocities and the system pressure and finally (3) the availability of an instrumentation that is ca-pable in resolving structures of the gas-liquid interface, namely the wire-mesh sensors. Results are presented for tests with steam-water mixture at a saturation pressure of up to 6.5 MPa. The measured radial gas fraction profiles and bubble size distributions show in detail the influence of the fluid properties to the flow structure and its evolution along the flow path when compared to earlier results obtained at identical superficial velocities in an air-water flow. The results from the high-pressure tests are of particular interest for the validation of CFD codes for an application in the field of nuclear reactor safety. A significant influence of the physical properties to the flow structure was found: the steam-water flow at high pressure compared to the air water flow under ambient conditions shows less tendency to develop large bubbles and a bimodal bubble size distribution but is characterised by larger bubble sizes in the region of the small bubble peak.

Das Interesse an der Entwicklung von Radiopharmaka auf der Basis von Radiometallen wird durch eine Reihe von Faktoren wie zunehmende Verfügbarkeit der Nuklide (Generatoren, Zyklotron), einfache Markierung von Liganden und wachsende Anwendungsmöglichkeiten in klinischen Zentren gestärkt. In Abhängigkeit von den kernphysikalischen Eigenschaften der Radiometallnuklide ergeben sich Einsatzmöglichkeiten in der nuklearmedizinischen Diagnostik und Therapie.
Für Kupfer stehen eine Reihe von Radionukliden zur Verfügung, die einen diagnostischen und therapeutischen Einsatz erlauben. Es werden verschiedene Anwendungsmöglichkeiten diskutiert und eigene Arbeiten zur Entwicklung neuer Chelatsysteme vorgestellt. Das betrifft sechszähnige Chelate auf der Basis des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) sowie dendritische Liganden.

Air-water two-phase flow tests in a large vertical pipe of 194.1 mm inner diameter are reported. Close to the outlet of a 9 m tall test section two wire-mesh sensors are installed that deliver instantaneous void fraction distributions over the entire cross section with a resolution of 3 mm and 2500 Hz used for fast flow visualization. Void-fraction profiles, gas velocity profiles and bubble size distributions were obtained. A comparison to a small pipe of 52.3 mm inner diameter (DN50) revealed significant scaling effects. Here, the increase of the air flow rate leads to a transition from bubbly via slug to churn turbulent flow. This is accompanied by an appearance of a second peak in the bubble size distribution. A similar behavior was found in the large pipe, though the large bubbles have a significantly larger diameter at identical superficial velocities, the peak is less high but wider. These bubbles move more freely in the large pipe and show more deformations. Shapes of such large bubbles were characterized in three dimensions. They can rather be complicated and far from ideal Taylor bubbles. Also the small bubble fraction tends to bigger sizes in the large pipe.

Changes in the structure of the microbial community of a soil sample from the uranium mining waste pile Haberland near the town Johanngeorgenstadt in Germany were investigated after addition and incubation with uranyl or sodium nitrate. For this purpose a sample with a natural uranium content of 26 mg/kg was treated with uranyl and sodium nitrate solutions (pH 4.0) and incubated under aerobic and anaerobic conditions for different periods of time. Afterwards total DNA was extracted from both treated and untreated samples, 16S rRNA gene fragments were amplified by PCR using primers specific for the domains of Bacteria or Archaea and then cloned. The predominant microbial populations were identified by restriction fragment length polymorphism and their 16S rRNA genes were sequenced and phylogenetically affiliated. The 16S rRNA gene retrieval revealed that representatives of Acidobacteria and of Alphaproteobacteria were dominating the bacterial community of the untreated sample. The increasing of the uranium content up to 100 mg/kg with a subsequent incubation for four weeks under aerobic conditions stimulated a propagation of Pseudomonas spp., Arthrobacter spp., and Geobacter spp. In a parallel sample supplemented with sodium nitrate under the same conditions mainly denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes were induced. In another sample, which was longer incubated (14 weeks) even with a higher uranium content, U-sensitive Bacteroidetes and alphaproteobacterial populations were predominant. The latter indicates that at that later stages of incubation the added U(VI) was not anymore bioavailable. In a parallel sample incubated under anaerobic conditions mainly Betaproteobacteria were stimulated. Additionally, some sequences closely related to Clostridium spp. were found in the anaerobic sample.
Archaeal diversity in the uranyl and sodium nitrate treated samples decreased in comparison to the untreated sample. All retrieved archaeal sequences were closely related to representatives of Crenarchaeota.
Our results represent the first cultivation-independent analysis of changes in the structure of a natural microbial community of a particular environment induced by the addition of uranyl or sodium nitrate.

Positron emission tomography (PET) is currently the only technically feasible method for invivo, non-invasive monitoring of the precision of the dose delivery in highly conformal ion therapy. Online (in-situ) implementation offers the attractive advantages to detect the significant contribution from short-lived emitters e.g. 15O, reduce image degradation due to perfusion and acquire data in treatment position. To date, clinical applications of online PET have been limited to the concluded trial of range verification with radioactive isotopes prior to stable ion irradiation at Lawrence Berkeley Laboratory (LBL), USA, and the ongoing routine monitoring of stable carbon ion irradiation at the Gesellschaft für Schwerionenforschung Darmstadt (GSI), Germany. The rapidly growing number of proton therapy facilities is stimulating the research on the applicability of PET monitoring to protons. However, due to instrumentation restrictions and costs, most of the former and ongoing studies were carried out offline at remote, conventional PET scanners. Extensive in-beam phantom experiments with proton beams were recently finished at GSI using the available dedicated, unique online tomographic positron camera. The main results, providing novel insight and supporting the applicability and usefulness of online PET for proton therapy monitoring, will be reported.

The search for superconductivity in platinum as well as studies of the interplay of superconductivity and nuclear magnetism will be reviewed. The pair breaking mechanism between nuclear magnetic moments and Cooper pairs will be described.

Intersubband (ISB) transitions in semiconductor quantum wells (QWs) can be employed for various mid-infrared optoelectronic devices. Presently there is strong interest to extend the available wavelength range into the near infrared, by using materials with a large conduction band offset. To achieve such short wavelengths thin QWs are required, where the first excited state inside the QW may lie higher than some state related to indirect valleys. Examples for such material systems are strained InGaAs/AlAs or lattice matched InGaAs/AlAsSb, both grown on InP. We have studied the ISB relaxation dynamics in multi QWs of both material systems by femtosecond pump-probe measurements. The transient transmission as a function of the pump-probe delay does not show a single-exponential decay, indicating a more complicated relaxation dynamics. This can be caused by transfer of electrons to X- or L- states in the QWs or the barriers. We will show results on samples with different QW thicknesses and compare them to simulations based on rate equations.

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Im Kapitel Elektroenergiebereitstellung werden die verschiedenen Techniken zur Stromerzeugung dargestellt. Diese umfassen neben den konventionellen Wärmekraftwerken auch Kernkraftwerke, Wasserkraftwerke und Kraftwerke zur Wandlung erneuerbarer Energien.

Isopeptide bonds between the varepsilon-amino group of lysine and the gamma-carboxamide group of glutamine are formed during strong heating of pure proteins or, more important, by enzymatic reaction mediated by transglutaminases. Despite the wide use of a microbial transglutaminase in food biotechnology, up to now little is known about the metabolic fate of the isopeptide N(varepsilon)-(gamma-glutamyl)-L-lysine. In the present study, N-succinimidyl-4-[¹⁸F]fluorobenzoate was used to modify N(varepsilon)-(gamma-glutamyl)-L-lysine at each of its two alpha-amino groups, resulting in the 4-[¹⁸F]fluorobenzoylated derivatives, for which biodistribution, catabolism, and elimination were investigated in male Wistar rats. A significant different biochemical behavior of the two labelled isopeptides was observed in terms of in vitro stability, in vivo metabolism as well as biodistribution. The results suggest that the metabolic fate of isopeptides is likely to be dependent on how they are reabsorbed - free or peptide bound.

The human organism is exposed to numerous processes that generate reactive oxygen species (ROS). ROS may directly or indirectly cause oxidative modification and damage of proteins. Protein oxidation is regarded as a crucial event in the pathogenesis of various diseases ranging from rheumatoid arthritis to Alzheimer's disease and atherosclerosis. As a representative example, oxidation of low density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Data concerning the role of circulating oxidized LDL (oxLDL) in the development and outcome of diseases are scarce. One reason for this is the shortage of methods for direct assessment of the metabolic fate of circulating oxLDL in vivo. We present an improved methodology based on the radiolabelling of apoB-100 of native LDL (nLDL) and oxLDL, respectively, with the positron emitter fluorine-18 (¹⁸F) by conjugation with N-succinimidyl-4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB). Radiolabelling of both nLDL and oxLDL using [¹⁸F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively, in vitro. The method was further evaluated with respect to the radiopharmacological properties of both [¹⁸F]fluorobenzoylated nLDL and oxLDL by biodistribution studies in male Wistar rats. The metabolic fate of [¹⁸F]fluorobenzoylated nLDL and oxLDL in rats in vivo was further delineated by dynamic positron emission tomography (PET) using a dedicated small animal tomograph (spatial resolution of 2 mm). From this study we conclude that the use of [¹⁸F]FB-labelled LDL particles is an attractive alternative to, e.g., LDL iodination methods, and is of value to characterize and to discriminate the kinetics and the metabolic fate of nLDL and oxLDL in small animals in vivo.

Photoconductive emitters are an attractive way for impulsive generation of THz radiation. There are two main categories, namely large-aperture emitters and interdigitated electrodes coupled to antennas. Large-aperture emitters have the advantage of a high active volume, while interdigitated structures provide high electric fields for efficient acceleration of photogenerated carriers. We present a large-aperture emitter consisting of a interdigitated metal-semiconductor-metal (MSM) structure, which combines both advantages. A second metallization layer, which is electrically insulated from the first one, blocks the optical excitation in every second period of the MSM structure, resulting in an unidirectional acceleration of carriers in the device. Focussing fs optical pulses with an average power of 100 mW from a Ti:sapphire oscillator on the emitter lead to THz field amplitudes of up to 85 V/cm (Ubias = 65 V). Excitation with unfocussed radiation from a 1 kHz repetition rate Ti:sapphire amplifier system (average power 10 mW) provided THz field amplitudes of 6 kV/cm (Ubias = 23 V). In case of the excitation with the Ti:sapphire amplifier system a pronounced nonlinear behavior of the THz field amplitude with respect to both the excitation density and the bias electric field was observed.

Growing evidence indicates that oxidative modification of low-density lipoprotein (LDL) is increased in diabetes mellitus; however, the mechanism(s) of this phenomenon is still unclear. Gamma-Glutamyl semialdehyde (gammaGSA) is a product of hemin (Fe³⁺-protoporphyrin IX)-catalyzed oxidation of apolipoprotein B-100 (apoB- 100) proline and arginine residues. On reduction, gammaGSA forms 5-hydroxy-2-aminovaleric acid (HAVA). This report describes the application of sensitive HAVA assay, to characterize gammaGSA formation in LDL under normo- and hyperglycemic conditions, both in vitro and in vivo. In vitro studies revealed that apoB-100 proline and arginine residues are not oxidized to HAVA by HOCl or the myeloperoxidase/hydrogen peroxide (H₂O₂) oxidation system. Cu²⁺, Cu²⁺/H₂O₂, and Fe²⁺ induced only minor HAVA formation. In contrast, the hemin oxidation system appeared reactive toward LDL apoB-100 proline and arginine residues. The resulting significant HAVA formation was specifically inhibited by a redox-inert ferric iron chelator. Glucose further enhanced hemin-induced increase in relative electrophoretic mobility of LDL and apoB-100 HAVAformation. In vivo we observed elevated concentrations of HAVA in LDL apoB-100 in patients with impaired glucose tolerance and with manifest diabetes mellitus. In conclusion, glucose promotes iron-mediated oxidation of apoB- 100 proline and arginine residues via a superoxide-dependent mechanism, thus rendering the LDL particles more atherogenic. The findings (a) identify a potential mechanism of enhanced atherogenesis in subjects with diabetes mellitus and (b) support the value of HAVA as a specific marker of LDL apoB-100 oxidation.

Scattering scanning near- field optical microscopy (s-SNOM) is based on the interaction between an optically scattering nano-particle (AFM tip) and a dielectric sample. The size of the scatterer defines the optical resolution of the microscope, which is on the order of a few nanometers. On that scale, the optically anisotropic properties of most samples have to be taken into account [1]. To examine the influence of optical anisotropy on the scattering signal, we excite a ferroelectric sample close to its phonon resonance in the mid infrared regime. As the precisely tunable light source at infrared wavelengths we used a free electron laser (FEL). We have measured the near-field signal at several wavelengths while scanning the sample, as well as the tip-sample distance dependence of the scattered light signal for the 1st, 2nd, and 3rd harmonic signal. The anisotropy is revealed for different sample orientations. Not only are we presenting the first tunable IR near-field measurements on ferroelectric lithium niobate and barium titanate single crystals, but furthermore are our measurements in excellent accordance with recent calculations of optical anisotropy in such systems [1].
[1] S. Schneider, et al., Phys. Rev. B 71, 115418 (2005)

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Intersubband absorption in quantum wells (QW) and superlattices usually requires the presence of doping atoms, inevitably giving rise to disorder by randomly distributed hydrogenic impurity states (Coulomb potentials). It has been shown that in particular the 1s-2pz transition plays the role of an impurity-shifted intersubband transition, clearly observed in superlattices at low temperature, but recently also in isolated quantum wells.
In an attempt to understand the inter-miniband absorption spectra in doped superlattices on a more profound level than the usual variational approach for the impurity states, we have performed numerical calculations of the absorption spectra, by exactly diagonalizing the fully three-dimensional Schrödinger equation for a certain number of N coupled QWs (N=1..20), in an areal sheet of 100 x 100 nm2. The impurities are placed in the middle of each QW, but randomly distributed in the xy plane. The resulting energy levels and wave functions are used to calculate the absorption spectra.
For the case of a single QW the well known results for a quasi 2D impurity are reproduced, in particular the 2pz state (or 2p0, i.e. m=0) lies just below the second subband. More interesting is the double QW. Here it turns out that each subband level gets “its own” m=0 type impurity level, all of which can be optically reached from the 1s ground state.
It is now most interesting to observe how this evolves into a superlattice (SL). We find that, at low temperature, there remain two absorption peaks even at low doping, when only the 1s ground state is occupied: the transition to the 2pz-type excited state, just below the second miniband, but also a transition to an impurity state pinned to the top of the second miniband (and a weaker continuum in between). This result requires re-interpretation of data reported in the past: at low temperature and low doping, the high-energy peak in the SL absorption spectrum is not the miniband transition at kz=0, but an impurity transition to the state near the top of the excited miniband. This also explains a hitherto not understood behavior: the high-energy peak does not disappear, when the SL is driven through the metal-insulator transition by a magnetic field into the insulating regime, when only the impurity states are occupied, but the miniband states are empty. This is the first calculation which treats quantum well and random impurity potential on the same footing. At higher doping, screening and impurity band formation sets in, and the resulting Mott transition can be treated by the same method.

Many references from the cast metal literature consider the application of sonic vibrations, mechanical or electromagnetic stirring as a tool to promote the formation of fine, equiaxed grains during solidification. The application of time varying magnetic fields can be considered as an effective tool to organize a well-defined flow structure in the liquid phase affecting the nucleation and solidification parameters. Once a flow occurs in the liquid melt during solidification, nucleation and grain growth are mainly governed by the convective transport of heat and solute. The consequences on the structure of solidified ingots are widely discussed in the literature. So it is known, that the application of mechanical or electromagnetic stirring promotes the formation of fine, equiaxed grains [1-4].
In this paper experimental and numerical investigations will be presented concerning the influence of a flow driven by a rotating magnetic field (RMF) on the momentum, heat and mass transfer within binary Sn-Pb alloys solidified directionally. Solidification experiments were carried out considering the directional solidification of Pb Sn and Al-Si alloys from a water cooled copper chill. A rotating magnetic field (RMF) was applied for melt agitation. Thermocouples were used to measure the temperature field during solidification. Profiles of the velocity in the liquid phase were determined by means of Ultrasound Doppler velocimetry (UDV) [5].
Our results show that the forced convection influences significantly the concentration as well as the temperature profile ahead of the solidification front. The convective transport of solute reduces the thickness of the solutal boundary layer and increases the constitutional supercooling. The RMF-application provokes a distinct grain refinement for all considered alloy compositions and equiaxed growth has shown to be encouraged. A flow effect can be supposed both on the presence of nuclei in the melt and suitable conditions allowing them to grow in competition with the columnar front.

The solidification process and the resulting microstructure of Nd-Fe-B alloys in consideration of melt convection has been investigated experimentally with a specially designed forced crucible rotation technique. Samples were subjected to well-defined forced rotation and vibration, respectively, during induction heating and solidification. A concerted microstructure evolution is possible by enhancement or suppression of the melt convection. As a result, the microstructure pattern, mainly the volume fraction of the soft magnetic -Fe phase, vary strongly with the strength of the internal flow motion. A distinct reduction of the -Fe volume fraction in samples with strong melt rotation was observed by measuring the magnetic moment. Moreover, the melt flow was studied numerically taking into account the coupled heat and fluid flow fields. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields.

Bubble driven flows have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenize the physical and chemical properties of the melt or to refine the melt. For such gas-liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way.
Compared to the numerous experimental studies on the movement of bubbles in transparent liquids , especially in water, the number of publications dealing with gas bubbles rising in liquid metals is comparatively small. The shortage of suitable measuring techniques can be considered as one reason for the slow progress in the investigations of gas-liquid metal flows. Powerful optical methods are obviously not available for measurements in liquid metals. The majority of measurements in liquid metal two-phase flows published until now was obtained using local conductivity probes, hot wire anemometer or optical fiber probes to determine quantities such as void fraction, bubble and liquid velocity or the bubble size. However, measurements with any local probe disturb the flow in a significant way, especially if the structures to be investigated reach dimensions comparable to the probes. In the case of opaque liquids the application of acoustic or ultrasonic sensors offers a possibility to get information about the flow structure and bubble quantities. We applied the Ultrasound Doppler Velocimetry (UDV) for measurements of the velocity structure in liquid metal bubbly flows. Because of the ability to work non-invasively in opaque fluids and to deliver complete velocity profiles in real time it is very attractive for liquid metal applications.
In our experiments we investigated the consequence of an application of a DC magnetic field on both the bubble and the liquid velocity. The motion of single argon bubbles rising in GaInSn were analyzed in terms of the terminal velocity, the drag coefficient, the oscillation frequency of the bubble velocity and the Strouhal number. Because the gas bubble is electrically non-conducting, it does not experience the effect of the electromagnetic force directly. However, the bubble behaviour is influenced by the magnetically induced modifications in the liquid flow structure around the bubble. The measurements reveal a distinct effect of the magnetic field on the bubble velocity as well as the bubble wake. The magnetic field application leads to a mitigation of the horizontal components of the bubble velocity resulting in a more rectilinear bubble path. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. As a result of the interaction between magnetic field and liquid flow electric currents were induced inside the liquid causing a damping of the flow by Joule dissipation. However, a characteristic feature of the electromagnetic dissipation is the anisotropy. Thus, the application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction.

The contactless handling of electrically conducting liquids by the application of magnetic fields makes this technology attractive for many industrial applications. The possibility to superimpose different kind of fields allows to generate a variety of flow structures being beneficial, for instance, to control the heat and mass transfer.
The further optimization of liquid metal flows in industrial technologies requires experimental data of the flow field to understand the process and the consequences of an intervention using electromagnetic fields. Numerical simulations alone are often of limited value. Realizing this situation, the motivation arises to perform laboratory studies using cold liquid metals as a model of realistic processes. The main feature of such cold (temperatures up to about 300°C) liquid metal models is the availability of measuring techniques allowing to analyse the local transport phenomena with a sufficient resolution. Some applications using the ultrasound Doppler velocimetry (UDV) will be presented showing the capability of this technique to measure velocity profiles in liquid metal flows. Note that water models of liquid metal processes are only meaningful if the melt flow Reynolds number represents the only determining parameter of the transport processes under consideration, which is seldom the case for real casting processes. As soon as temperature gradients, free-surface phenomena, two-phase flows or electromagnetic phenomena play a role, the water model is always of very limited value.
Some examples for model experiments will be presented showing the flow modelling of an investment casting process of aluminium alloys, the electromagnetic stirring of liquid metals and the solidification of metallic alloys affected by time-dependant magnetic fields, respectively.

Objectives: The routine ¹⁸F labeling of biomacromolecules like peptides and proteins should involve simple and efficient radiolabeling methods based on readily available prosthetic groups. 2-[¹⁸F]Fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) as the most important PET radiotracer is available in almost every PET center. However, there are only very few examples using [¹⁸F]FDG as a building block for the radiosynthesis of ¹⁸F-labeled compounds.
The present study describes the use of [¹⁸F]FDG as a 18F building block for the convenient single-step synthesis of thiol-reactive prosthetic group [¹⁸F]FDG-maleimidehexyloxime ([¹⁸F]FDG-MHO). The potential of this novel [¹⁸F]FDG-based prosthetic group was evaluated by the reaction with thiol group-containing biomacro-molecules.

Methods: The reaction was performed using a 0.9% NaCl solution of [¹⁸F]FDG and N-(6-aminoxyhexyl)maleimide in 80% ethanol. The mixture was heated at 100°C in a sealed vial for 15 min. Then, ethanol was evaporated and [¹⁸F]FDG-MHO was purified by HPLC. Conjugation of [¹⁸F]FDG-MHO to thiol groups was investigated by the reaction with the tripeptide glutathione and the protein Annexin-V.

Results: [¹⁸F]FDG-MHO was obtained in 45-69 % radiochemical yield after HPLC purification in a total synthesis time of 50 min. The use of [¹⁸F]FDG-MHO as a selective thiol-reactive reagent was first exemplified using various concentrations of glutathione. The reaction was monitored by radio-TLC. At glutathione concentrations ranging from 30 µmol to <100 pmol we found complete consumption of the labeling agent. The application of [¹⁸F]FDG-MHO was further investigated by the conjugation to Annexin-V that contains one accessible cysteine side chain. Radiolabeling yields of up to 80% (based upon [¹⁸F]FDG-MHO) could be achieved.

Conclusion: The thiol-reactive prosthetic group [¹⁸F]FDG-MHO derived from readily available [¹⁸F]FDG has been developed. The labeling experiments using glutathione as a model peptide and Annexin-V as protein indicate that [¹⁸F]FDG-MHO can be used for the mild and selective ¹⁸F labeling of thiol group-containing biomacro-molecules like peptides and proteins.

Das Interesse an der Entwicklung von Radiopharmaka auf der Basis von Radiometallen wird durch eine Reihe von Faktoren wie zunehmende Verfügbarkeit der Nuklide (Generatoren, Zyklotron), einfache Markierung von Liganden und wachsende Anwendungsmöglichkeiten in klinischen Zentren gestärkt. In Abhängigkeit von den kernphysikalischen Eigenschaften der Radiometallnuklide ergeben sich Einsatzmöglichkeiten in der nuklearmedizinischen Diagnostik und Therapie.
Unsere Untersuchungen konzentrieren sich auf die Radionuklide ^64/67Cu und ¹⁸⁸Re. Es werden neue Chelatsysteme, die über einen zielsuchenden und einen komplexbildenden Teil für metallische Radionuklide verfügen, vorgestellt. Das betrifft insbesondere sechszähnige Chelate auf der Basis des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) und dendritische Liganden. Als zielsuchende Biomoleküle können prinzipiell Antikörper, spezifische Peptide oder Aptamere eingebaut werden. Möglichkeiten der radioaktiven Markierung von Nukleinsäurebausteinen werden diskutiert.

Nachrechnung von Durchsatzparametern eines Leser Sicherheitsventils mit CFX-10
Gitter: 1 Million Hexaeder Zellen
CFX-Rechnungen mit Standard-Eingabedatensatz:
-Druckrandbedingung Eintritt und Austritt, Subdomain für Wasser und Luft
Sehr gute Übereinstimmung bei allen Durchsatzkennlinien, aber:
-systematische Abweichung bei Luft im Falle hoher Ansprechdrücke durch Realgasverhalten u. hohe Ma-Zahlen
CFX-Rechnung mit Zweiphasengemisch bei 2 bar Überdruck, 1 mm Blasendurchmesser, 4% Gasanteil, monodispers
-Erhöhnung des Volumenanteils der Gasphase in Abhängigkeit von Druckabsenkung konnte abgebildet werden
-Vergleich mit Experimenten

Research at extreme material conditions can lead to new scientific knowledge. As an example, experiments at low temperatures and high magnetic fields have improved the understanding of matter dramatically in the last century. Nowadays, we dispose of the technology to reach ultralow temperatures, highest magnetic fields and even to produce material structures on length scales on which the geometrical size dominates physical properties. In this talk, research examples on superconducting nanogranular metals, quantum functional intermetallic compounds, nuclear magnetic superconductors, as well as magnetic high temperature superconductors will be presented. In addition, magnetic cooling technology and the non-destructive generation of highest pulsed magnetic fields will be briefly introduced along with facilities, e.g. the new Dresden High Magnetic Field Laboratory (HLD)*.

*HLD is a new large scale facility for the generation of pulsed magnetic fields up to 100 T which is under construction during 2003 to 2006 and which will open its doors for users in early 2007.

Compared to their bulk counterparts, micro- and nanogranular materials can reveal a diverse physical appearance. In particular, their magnetic and superconducting behaviour can be drastically influenced. As a prominent example, the superconductivity of compacted granular Pt will be presented.
Pt has been cooled down to an equilibrium temperature of phonons, electrons and nuclear magnetic moments of 1.5 µK, lower than all other materials so far [1]. However, superconductivity has not been observed in bulk Pt. Surprisingly, superconductivity occurs in compacted microgranular Pt [2]. The weakened impurity magnetism in powdered Pt (spin glass behaviour at mK temperatures) may play the crucial role in adjusting the balance between electron-phonon interaction and competing magnetic interactions. As a proof, we have also investigated Pt powders with a higher impurity content observing lower Tc values. In addition, low frequency phonons from the Pt surface could influence the electron-phonon interaction. In further investigated nanoscale Pt powders, the superconducting transition temperature is about 20 times larger than detected in the micrometer sized grains [3].

[1] W. Wendler, T. Herrmannsdörfer, S. Rehmann, F. Pobell, Europhys. Lett. 38, 619 (1997)
[2] R. König, A. Schindler, T. Herrmannsdörfer, Phys. Rev. Lett. 82, 4528 (1999)
[3] A. Schindler et al., Europhys. Lett. 58, 885 (2002)

The intermetallic compound Pr(1-x-y)La(x)Pb(y)Te shows a wide spectrum of physical phenomena. Depending on the metallurgical composition as function of x and y, the compound changes its behavior from nuclear magnetic order to super- or semiconductivity. In addition, there are interesting interplay effects between these ground states. In consequence, Pr(1-x-y)La(x)Pb(y)Te may serve as an interesting material for quantum-computing applications. In this contribution, we focus on our recent investigation of the magnetic properties of Pr(1-y)Pb(y)Te. We present data of the magnetisation taken at 1.8 K < T < 350 K for various compositions y = 0, 90, 99, 99.9 %, i.e. turning the system from a van Vleck paramagnet, y = 0, into a doped semiconductor, y = 99.9 %.

The intermetallic compound Pr(1-x-y)La(x)Pb(y)Te shows a wide spectrum of physical phenomena. Depending on the metallurgical composition, the compound changes its behaviour from hyperfine enhanced nuclear magnetic order to super- or semiconductivity. In addition, there are interesting interplay effects between these ground state phenomena. In consequence, Pr(1-x-y)La(x)Pb(y)Te may
serve as an interesting quantum functional compound for quantum computing experiments. In this paper, the hyperfine enhanced nuclear magnetic and superconducting properties are pointed out.

Die phänomenologischen Grundlagen und prinzipiellen Gesetzmäßigkeiten zur Berechnung von Feldern und Kräften in Magnetfeldspulen wurden bereits vor 185 Jahren von Hans Christian Oersted, André Marie Ampère, Jean-Baptiste Biot, Felix Savart und anderen geschaffen. Seit etwa 130 Jahren können elektromagnetische Fragestellungen nach Einführung der Maxwellschen Gleichungen umfassend bearbeitet werden. Man könnte daher annehmen, dass Magnetfeldspulen, die uns zudem in sämtlichen Bereichen des täglichen Lebens wie bei der Energieerzeugung, dem Transport, der Unterhaltungselektronik, der Datenverarbeitung oder der Medizintechnik als vertraute technische Komponenten begegnen, kaum mehr als ingenieurtechnische oder physikalische Herausforderung betrachtet werden können. Insbesondere scheinen die Möglichkeiten grenzenlos zu sein, seit die Supraleitertechnik selbst spektakuläre Dauerstromspulen für z. B. Kernspin-Tomographen oder Fusionsexperimente ermöglicht. Dennoch kann die Berechnung von Magnetfeldspulen eine wissenschaftliche Herausforderung darstellen. Dies gilt z. B. für Spulen sehr hoher Feldhomogenität und Feldstabilität, insbesondere aber für Spulen besonders hoher Feldstärke.

Experimental results on separation control by time periodic Lorentz forces are reported for hydrofoils in the Reynolds number range 10^4 - 10^5. Force measurements reveal that in a small frequency around the most effective excitation frequency control authority is a function of the peak momentum input. The vorticity distribution derived from phase averaged laser doppler anemometry shows different vortical structures for excitation with varying wave forms. The effect of the excitation wave form on the attainable lift gain is interpreted as resulting from these different vortex structures.

The decay heat model implemented in the three-dimensional core model DYN3D is described. The equations solved in DYN3D for transport of the coolant and the heat conduction in the fuel rods are presented. The solution scheme is outlined.

Transient analyses for VVER reactors performed with the computer code DYN3D are described. The decay heat after the shutdown of a VVER-440 is considered. A Xenon oscillation transient in a VVER-1000 is presented. The results for control rod ejections and control rod withdrawal in VVER-440 and VVER-1000 reactors are shown. A boron dilution transient in a VVER-440 by using the coolant mixing model of DYN3D is presented.

Computational Fluid Dynamics (CFD) models for two-phase flows always require closure relations representing the nature of the forces acting at the interface between the participating phases. This is vital for the modelling of momentum transfer term. In case of a gas-liquid flow, it is expressed in terms of forces acting on bubbles. The present study uses instantaneous high-speed video observations of the bubble motion to validate models for the interfacial forces.
The turbulent diffusion coefficient of the gaseous phase is obtained by a statistical evaluation of the movement of bubbles in a swarm, which is affected by the turbulence of the liquid phase. After the bubble trajectories were identified, the lateral displacement of bubbles was statistically analysed by constructing probability density functions. The dispersion coefficients of the standard distributions were found to grow proportionally to the square-root of the time. This supports the assumption of a diffusion model for the lateral displacement. Deviations from the linear dependency were identified to be the result of deterministic oscillatory motions of the rising bubbles.
Another objective is objective is to demonstrate the capabilities of the high-speed stereo-imaging technique to study the single (isolated) bubble dynamics in a vertical bubble column. The reconstruction algorithm of the 3D bubble trajectories from the stereo images of the bubble projection is presented. The bubble size, shape, orientation as well as bubble aspect ratio are investigated.
The first results of experiments on bubble motion in a vary narrow flat bubble column (width-100 mm, depth-8 mm, height – 600 mm) obtained for the validation of numerical predictions achieved using DNS-based analyses (Wörner et al. FZK) are presented. Results of high-speed video measurements of bubble parameters (bubble shape, size, rising velocity etc.) as well as PIV measurements of velocity of the liquid phase are discussed.

The configuration of the reactor core used in the steady-state AER-FCM-101 benchmark is described. The results of different options of the DYN3D code are compared with the reference solution.

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We report on impulsive generation of terahertz (THz) radiation with more than 1.5 kV/cm field amplitude at MHz repetition rates, using an interdigitated photoconducting device. The approach provides an average THz power of 190 µW corresponding to an optical-to-THz conversion efficiency of 2.5 × 10^-4. Optimum conditions are achieved when the excitation spot size is on the order of the THz wavelength.

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Cells and S-layer sheets of B. sphaericus JG-A12 were used as templates for the deposition of metallic gold nanoclusters using dimethyl amino borane (DMAB) as reducing agent . Gold LIII-edge XAS measurements confirmed the formation of Au(0) nanoclusters in both cases. In this Talk, the preliminary results on the size and the structure of the Au nanoclusters deposited on cells and S-layer protein of B. sphaericus JG-A12 will be presented.

Microbial diversity was studied in ground waters collected from a monitoring well at the radioactive waste depository Tomsk-7, Siberia, Russia, applying the 16S rDNA retrieval. The results demonstrated dominance of Betaproteobacteria, Bacteroidetes, and a novel “Cyanobacteria-like” group. The archaeal populations are represented by methanogens and three distinct clusters of Crenarchaeota. The autotrophic bacterial diversity was estimated via the RubisCO approach and the results confirm the dominance of Betaproteobacteria. Oligotrophic bacteria, from the groups of Alphaproteobacteria and Actinobacteria were isolated from the studied site. The strains tolerate relatively high concentration of different heavy metals and interact effectively with uranium. EXAFS analysis demonstrated that they immobilize U(VI) at pH 4.5 extracellularly in a form of meta-autunite. At pH 2 the U was bound by the organic phosphate residues of the cells. The environment around the radioactive waste repository site Tomsk-7 possesses microorganisms with a potential to bind and transport radionuclides.

The contribution splits into three parts. (1) Theory and experiment of polarization dependent EXAFS at the U L1 and U L3 edge will be compared. (2) The effect of the temperature on the EXAFS Debye-Waller factor will be analyzed. (3) In-situ EXAFS experiments with changing electrochemical potential will be presented.

In the past, the chemistry of uranium was focused on its mining and milling for production of high pure uranium compounds as initial matter of reactor fuel elements for energy production and breeding of plutonium for weapons production. In this sense, the recovery of uranium and plutonium from the used reactor fuel elements was also technical realized. The increasing input into bio-sphere by uranium mining and milling and industrial processes like production of cement, fossil fuels, and fertilizers has led to the realization of the importance of environmental chemistry of uranium. Starting from uranium content in geo-and bio-systems, about the chemical behavior - the speciation of uranium - is reported in selected environmental compartments like seepage water, bacteria, and plants. The results obtained
by various spectroscopic methods show that the speciation of uranium is dominated in surface waters by uranyl carbonate complex in opposite to the speciation in bacteria and p! lants. In these compartments the speciation is dominated by binding of uranium on carboxylic and phosphorous containing functional groups.

Microorganisms are involved in biogeochemical transformations and migration of uranium in the environment. In order to study the influence of U(VI) on natural bacterial and archaeal communities, a soil sample collected from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt was treated with different amounts of uranyl or sodium nitrate as a control. The samples were incubated for different periods of time and at different aeration conditions and their microbial communities were analyzed by the 16S rDNA retrieval using bacteria- and archaea-specific primers. Bacterial community of the untreated sample was predominated by Alphaproteobacteria and Acidobacteria. The increasing of the uranium content up to 100 mg U/kg with a subsequent incubation for four weeks under aerobic conditions stimulated a propagation of Pseudomonas spp., Arthrobacter spp. and Geobacter spp. Treatment of a parallel sample with sodium nitrate under the same conditions induced a strong propagation of denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes. After a longer incubation of fourteen weeks even in most contaminated samples containing 300 mg U/kg U-sensitive Bacteroidetes and alphaproteobacterial populations were stimulated. In parallel samples incubated under anaerobic conditions mainly Betaproteobacteria were identified. Archaeal diversity of the uranyl and sodium nitrate treated samples was significantly lower than in untreated samples and only sequences related to Crenarchaeotea were found. Our results demonstrate for the first time changes in the structure of a natural microbial community induced by incubation with uranyl nitrate for different periods of time and at different aeration conditions.

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Colloid release and deposition in soils and sorption of inorganic and organic pollutants to soil colloids are strongly influenced by the composition and chemical heterogeneity of colloidal soil particles. To investigate the chemical heterogeneity of organic soil colloids at the particle scale, we used synchrotron scanning transmission X-ray microscopy (STXM) and C-1s near-edge X-ray absorption fine structure (NEXAFS) spectroscopy on 49 individual particles isolated from the surface horizons of three forest soils. Stacks of 130 images of each particle were collected at different X-ray energies between 280 and 310 eV. From these image arrays, NEXAFS spectra were obtained for each pixel and analyzed by principle component analysis and cluster analysis (PCA-CA) to characterize the intraparticle heterogeneity of the organic components. The results demonstrate that the organic matter associated with water-dispersible soil colloids is chemically heterogeneous at the single-particle scale. PCA-CA identified at least two distinct regions within single particles. However, the spectral variations between these regions were much smaller than the variations of averaged NEXAFS spectra representing different particles from the same soil horizon, implying that interparticle heterogeneity is much larger than intraparticle heterogeneity. Especially the contents of aromatic and carboxyl carbon exhibited a large variability. Overall, the NEXAFS spectra of water-dispersible soil colloids were similar to the NEXAFS spectrum of the humic acid fraction, but differed clearly from the fulvic acid and dissolved organic matter fractions extracted from the same soil horizon using conventional techniques.

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The strain Bacillus sphaericus JG-A12, isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, is capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from uranium waste waters. The cells of this strain are enveloped by a surface layer protein (S-layer). The highly regular structure of this S-layer with many pores of identical size offers good binding sites for different kinds of molecules and provides nucleation sites for the formation of metal nanoclusters or minerals. In this study we demonstrate that B. sphaericus JG-A12 cells and their purified S-layer protein sheets were capable to reduce Au to metallic nanoclusters in the presence of reducing agents such as molecular H2. The gold nanoparticles were regularly distributed and sized according to the pores of the S-layer lattice. The metallic nature of the clusters was confirmed by different techniques such as extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge (XANES) spectroscopy, UV-vis spectroscopy, X-ray powder diffraction (XRD), and transmission electron microscopic (TEM) analysis. The size of the gold nanoparticles was estimated to be almost 1 nm. Our results demonstrate that B. sphaericus JG-A12 can be used to prepare gold nanoparticles for industrial applications.

In order to better understand the mechanisms of actinide uptake by specific biomolecules, it is essential to explore the intramolecular interactions between the cation and the protein binding site. Although this has long been done for widely investigated transition metals, very few studies have been devoted to complexation mechanisms of actinides by active chelation sites of metalloproteins. In this field, X-ray absorption spectroscopy has been extensively used as a structural and electronic metal cation probe. The two examples that are presented here are related to two metalloproteins in charge of iron transport and storage in eukaryote cells: transferrin and ferritin. U(VI)O-2(2+),
Np(IV) and Pu(IV) have been selected because of their possible role as contaminant from the geosphere.

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Intensive studies of the surface-layer (S-layer) protein of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 demonstrated its capability to bind uranium with high affinity and selectivity. But there are still many open questions. Therefore several other S-layer carrying Bacillus isolates were investigated. The latter were recovered from the same uranium mining waste pile as JG-A12, but from a site 5 times more contaminated with uranium. First experiments included analyses of the uranium binding by intact cells and by purified S-layers, determination of posttranslational modifications of the S-layer proteins and comparisons with the S-layer protein of B. sphaericus JG-A12 by using immunoassay methods.
Altogether 21 isolates were investigated. 9 S-layer positive Bacillus sp. isolates were identified. Using modified standard protocols, the S-layers of all isolates were successfully extracted. None of the proteins were glycosylated but all were phosphorylated in different degree. Interestingly, the cells of the half of the investigated isolates possess lower uranium binding capacities than the cells of B. sphaericus JG-A12. In contrast to that all S-layer proteins of the investigated isolates have significantly higher uranium binding capacities. Further investigations of the mechanisms responsible for the extremely high uranium binding capacity of some S-layers are in progress.

Extended X-ray absorption fine structure (EXAFS) analysis was performed on uranyl orthosilicate, (UO2)(2)SiO4 . 2H(2)O, and uranium(VI) sorbed onto silicic acid and silica gel. Uranyl orthosilicate was investigated as a reference for EXAFS studies of similar but non-crystalline uranium, oxygen, and silicon containing samples. Fitting the EXAFS spectrum yields the following distances for the first four coordination shells of uranium: U-O-ax = 1.79 Angstrom, U-O-eq = 2.38 Angstrom, U-Si = 3.16 Angstrom, and U-U = 3.88 Angstrom. These values agree well with results from single-crystal X-ray diffraction (XRD) measurements. Structural parameters of light elements such as oxygen and silicon at distances greater than 3.5 Angstrom could not he detected without a priori knowledge of their presence. The EXAFS spectra of uranyl species sorbed at pH 4 onto silicic acid and silica gel are identical indicating similar uranyl coordination. The main characteristic of the surface species are two well-separated oxygen coordination shells in the equatorial uranyl plane at 2.27 and 2.50 Angstrom. The results of the EXAFS analysis favor the interpretation of the uranyl surface species as an inner-sphere, mononuclear, bidentate complex.

Sample analysis of seepage waters from old uranium mill tailings in Saxony and Thuringia shows both phosphate and uranium contents up to 10(-5) molar. Therefore the impact of phosphate on the speciation and transport behavior of uranium has to be investigated. At present, available complexation data are based only on few experiments and are not fully consistent. Therefore, the complex stability constants of the various uranyl(if) phosphate complexes were determined Over a pH range from 2 to 5 for uranyl and phosphate concentrations to 10(-6) molar, using potentiometric titrations and time-resolved laser-induced fluorescence spectroscopy (TRLFS). Fluorescence lifetimes were obtained for the free uranyl cation and uranyl phosphate complexes. Stability constants were determined for the complexes UO2(H2PO4)(2)(aq), UO2(H2PO4)(+) and UO2HPO4(aq), using the software C-LETAGROP [1] and SQUAD [2]. The results are compared with the values recommended by NEA [3] and with some recent publications.

Chemical speciation of U(VI) in natural seepage water and corresponding model solutions was investigated by time-resolved laser-induced fluorescence spectroscopy. Calculations of uranium speciation in this medium show that UO2(CO3)(3)(4-) and UO2(CO3)(2)(2-) should be the major individual components. Due to the very low fluorescence intensity, the pure uranyl carbonate complexes could not be measured directly by TRLFS. However, a uranium fluorescence spectrum was recorded from seepage water samples. The TRLFS investigations show that the main component of uranium in this seepage water is a calcium uranium carbonate complex. The main fluorescence wavelengths of this complex are at 463.9, 483.6, 502.8, 524.3 and 555.4 nm. The fluorescence lifetime of the species is 64+/-17 ns. This study shows that the calcium content of the water has a great influence on the uranium speciation. For the first time, the existence of a calcium uranium carbonate complex - {Ca-2[UO2(CO3)3]}((ag.)) - is reported. The stability constant was determined to be log beta = 26.8+/-0.7. Existing thermodynamic data bases do not contain this species and modeling calculation must lead to erroneous results in the medium under investigation.

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The influence of highly functionalized saccharic and phenolic polymers that are formed in the process of hydrothermal wood degradation on the uranium(VI) adsorption onto metamorphic rocks and sediments from the Saxon uranium mining sites Schlema-Alberoda and Konigstein was investigated in a laboratory study. Uranium(VI) adsorption from a simulated mine water takes place on the majority of rocks and sediments such as granite, gneiss, basalt, sandstone and clay marl. Exceptions are phyllite and clay stone that do not bind any uranium from the mine water. Polymeric wood degradation products such as fragments of celluloses and lignin increase the uranium(VI) adsorption whereas the presence of saccharic and phenolic monomers (vanillic acid and gluconic acid) leads to a lower adsorption.

The uranyl(VI) malonate complex formation was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH 4 and an ionic strength of 0.1 M NaClO₄. The uranium concentration was 5 × 10^-6 M at ligand concentrations from 1 × 10^-5 to 1 × ^-2 M.

The measured fluorescence lifetimes of the 1:1 and 1:2 uranyl(VI) malonate complexes are 1.24 ± 0.02 µs and 6.48 ± 0.02 µs, respectively. The fluorescence lifetime of the uranyl(VI) ion is 1.57 ± 0.06 µs in 0.1 M perchloric media. The main fluorescence bands of the malonate complexes show a bathochromic shift compared to the uranyl(VI) ion and are centered at 494 nm, 515 nm and 540 nm for the 1:1 complexes and at 496 nm, 517 nm and 542 nm for the 1:2 complex. The spectra of the individual uranyl(VI) malonate complexes were calculated using a multi exponential fluorescence decay function for each intensity value at each wavelength, covering the entire wavelength range. Stability constants were determined for the complexes UO₂C₃H₂O₄°_(aq) and UO₂(C₃H₂O₄)₂ ^2- from results of spectra deconvolution using a least square fit algorithm (logβ₁° = 4.48 ± 0.06, logβ₂° = 7.42 ± 0.06 or logK₂° = 2.94 ± 0.04). The results are compared with literature values obtained by potentiometric measurements.

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The dissolution of chlorite with intermediate Fe-content was studied macroscopically via mixed flow experiments as well as microscopically via atomic force microscopy (AFM). BET surface area normalized steady state dissolution rates at 25 °C for pH 2 to 5 vary between 1012 and 1013 mol/m2.s. The order of the dissolution reaction with respect to protons was calculated to be about 0.29. For pH 2 to 4, chlorite was found to dissolve non-stoichiometrically, with a preferred release of the octahedrally coordinated cations. The additional release of octahedrally coordinated cations may be due to the transformation of chlorite to interstratified chlorite/vermiculite from the grain edges inward. In-situ atomic force microscopy performed on the basal surfaces of a chlorite sample, which has been preconditioned at pH 2 for several months, indicated a defect controlled dissolution mechanism. Molecular steps with height differences which correspond to the different subunits of chlorite, e.g. TOT sheet and brucite like layer, originated at surface defects such or compositional inhomogenities or cracks, which may be due to the deformation history of the chlorite sample. In contrast to other sheet silicates, at pH 2 nanoscale etch pits occur on the chlorite basal surfaces within flat terraces terminated by a TOT-sheet as well as within the brucite like layer. The chlorite basal surface dissolves layer by layer, because most of the surface defects are only expressed through single TOT or brucite-like layers. The defect controlled dissolution mechanism favours dissolution of molecular steps on the basal surfaces compared to dissolution of the grain edges. At pH 2 the dissolution of the chlorite basal surface is dominated by the retreat of 14 Å steps, representing one chlorite unit cell. The macroscopic and microscopic chlorite dissolution rates can be linked via the reactive surface area as identified by AFM. The reactive surface area with respect to dissolution consists of only 0.2% of the BET-surface area. A dissolution rate of 2.5 109 mol/m2s was calculated from macroscopic and microscopic dissolution experiments at pH 2, when normalized to the reactive surface area.

The picosecond dynamics of electrons in a doped GaAs/AlGaAs superlattice have been investigated by pump-probe experiments using an infrared free-electron laser. We observe a fast bleaching of the interminiband absorption followed by thermalization and a slower cooling component. The latter can lead to a positive or negative transmission change, resulting from the temperature dependence of the linear absorption spectrum at the respective wavelength. We show that the superlattice in contrast to quantum wells provides a unique picosecond thermometer for the electron temperature based on the dependence of the absorption on the electron distribution function.

Nowadays the investigation of paintings is mainly done by means of X-ray radiography or ultra violet and infrared reflectometry. The latter is a non-invasive technique since the very low photon energies of the infrared radiation precludes damage to the paint by breaking molecular bonds as it is known to occur with UV-radiation.
Another advantage of infrared reflectometry appears when it is extended to picosecond pulses in the THz frequency band: X-ray radiography provides only an additive signal from absorption by all paint layers, which may be sufficient for revealing older painting hidden below the surface but does not provide information on the sequence of paint layers. However, THz time domain spectroscopy has the potential for providing depth information from the paint layers. In addition to this, the substances which the paint consist of can be identified by their absorption lines in the frequency spectrum of the reflected ps-THz-pulses.
Particularly evident is the potential of the THz technique for the investigation of wall paintings where X-ray radiography cannot be applied. Conventional infrared reflectometry is unsuitable for detecting hidden paintings when the cover layer is thick as it often is the case with wall paintings. THz-radiation is able to penetrate thicker layers and become partly reflected from them, thereby retrieving useful information from the depth.
The present contribution provides first results of transmission measurements on paintings in the frequency band up to 5 THz. It becomes evident that the different paints show a significantly different THz transmission. First THz transmission images of paintings give rise to the hope that hidden wall pictures can be made visible using a reflection geometry.

A high-resolution THz-spectrometer with 9kHz scan-rate is demonstrated for acquisition of THz-field-transients with 1ns duration without mechanical delay line. Spectra up to 3THz with a 40dB signal-to-noise ratio are acquired within 250 s.

Die faszinierende Erfolgsgeschichte von Leuchtdioden (engl.: light emitting diode, LED) und Laserdioden wird vorgestellt. Es wird erklärt, wie Licht unterschiedlicher Farbe mit LEDs erzeugt wird und welche besondere Rolle blaue LEDs spielen. Neben weißen Leuchtdioden, die ein hohes Potential für zukünftige Alltagsbeleuchtung besitzen, werden auch aktuelle Forschungsergebnisse zu siliziumbasierenden LEDs diskutiert.

Die faszinierende Erfolgsgeschichte von Leuchtdioden (engl.: light emitting diode, LED) und Laserdioden wird vorgestellt. Es wird erklärt, wie Licht unterschiedlicher Farbe mit LEDs erzeugt wird und welche besondere Rolle blaue LEDs spielen. Neben weißen Leuchtdioden, die ein hohes Potential für zukünftige Alltagsbeleuchtung besitzen, werden auch aktuelle Forschungsergebnisse zu siliziumbasierenden LEDs diskutiert.

We demonstrate a rapid scanning high-resolution THz spectrometer capable of acquiring THz field transients with 1 ns duration without mechanical delay line. The THz spectrometer is based on two 1-GHz Ti:sapphire femtosecond lasers which are linked with a fixed repetition rate difference in order to perform high-speed asynchronous optical sampling. One laser drives a high-efficiency large-area GaAs based THz emitter, the other laser is used for electro-optic detection of the emitted THz-field. At a scan rate of 9 kHz a time resolution of 230 fs is accomplished. High-resolution spectra from 50 GHz up to 3 THz are obtained and water absorption lines with a width of 11 GHz are observed. The use of femtosecond lasers with 1 GHz repetition rate is essential to obtain rapid scanning and high time-resolution at the same time.

Complex formation between the uranyl ion and nitrate ions in acetonitrile and the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]) has been studied by absorption, magnetic circular dichroism (MCD) and uranium LIII EXAFS spectroscopy. The experimental results point to the existence of a trinitrate species [UO2(NO3)3]– with D3h symmetry in both solvents. The atomic distances in the uranium(VI) coordination sphere for the trinitrato complex in acetonitrile are U–Oax = 1.770.01 Å and U–Oeq = 2.480.01 Å. EXAFS data show that the uranyl ion in the ionic liquid is surrounded by six oxygen atoms in the equatorial plane at a distance of 2.490.01 Å. The U–N distance of 2.920.01 Å indicates a bidentate coordination of the nitrate group in both solvents. A structural comparison is made between the uranyl trinitrato complex anion [UO2(NO3)3]– and the uranyl tricarbonato complex anion [UO2(CO3)3]4–. No evidence is found for the presence of uranyl nitrato complexes in aqueous solution. The optical absorption, MCD and EXAFS spectra resemble those of the hydrated free uranyl ion. There are two axial oxygen atoms at 1.770.01 Å and five equatorial oxygen atoms at 2.410.01 Å. These values agree well with structural parameters obtained for the uranyl aqua ion.

The Master Curve (MC) approach used to measure the transition temperature, T0, has been standardized in the ASTM Standard Test Method E 1921 in 1997. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centered (ferritic) structure only. In reality, due to the manufacturing process, the steels in question are seldom fully macroscopically homogeneous.
The fracture toughness values measured on Charpy size SE(B) specimens of base metal from the Greifswald Unit 8 RPV show a large scatter. The basic MC evaluation following ASTM E1921 supplies a MC with many fracture toughness values which lie below the 1% fracture probability line. It is therefore suspected that this material is macroscopically inhomogeneous. In this paper, two recent extensions of the MC for inhomogeneous material are applied on these fracture toughness data.

Steady states and transients in thermal reactors with standard core loadings are simulated with the nodal codes based on the three-dimensional diffusion equation for two energy groups of neutrons. The assembly wise cross sections are generated with cell codes solving the transport equation for many energy groups in two-dimensions assuming reflecting boundary conditions. Loading cores with higher content of MOX fuel and the increase of the fuel cycle length is challenging for the standard methods. Different neutron spectra of UO2 and MOX fuel, inhomogeneities inside the fuel as-semblies arising during the exposure in the reactor lead to discrepancies which needs an improvement of the applied methods. The core model DYN3D which is ap-plied for three-dimensional analyses of thermal reactor cores with quadratic or hex-agonal fuel assemblies is based on standard methods. The first step of the code enhancement consists in the extension to multi energy groups. The OECD/NEA and U.S. NRC PWR MOX/UO2 Core Transient Benchmark which is a well defined problem with a complete set of data is used as a means for verification of the modifi-cations of DYN3D. The core chosen for the simulation is based on four-loop West-inghouse PWR power plant similar to the reactor used for Plutonium disposition in the U.S. Steady-state calculations with the non-consideration and consideration of the assembly discontinuity factors (ADF), with a different number of energy groups, and with different number of nodes per assembly are compared with a reference so-lution generated by the DeCart. A Two-group solutions is also compared with a published PARCS diffusion solution.

The modeling of complex transients in Nuclear Power Plants (NPP) remains a challenging topic for Best Estimate (BE) three-dimensional coupled code computational tools. Nowadays, this technique is extensively used since it allows decreasing conservatism in the calculation models by performing more realistic simulations based on a more precise consideration of multidimensional effects under complex transients in NPPs. This paper represents a contribution to the assessment and validation of coupled code technique through the Kolzoduy VVER-1000 pump trip test. The coupled REALP5/3.3-PARCS/2.6 and DYN3D/3-RELAP5/3.3 code systems are used in simulations. The obtained results are assessed against experimental data and also through the code-to-code comparison.

The DYN3D/RELAP5 computational model of VVER-1000 has been developed and adjusted for simulations with the parallel running scheme (PVM) of RELAP5/PARCS. Also, the macroscopic cross-section library used in the DYN3D/RELAP5 calculations has been adapted to meet the input requirements of PARCS. Prior to the test simulations, the RELAP5/PARCS model of the plant has been assessed in the standalone PARCS and RELAP5 test calculations.

A reasonably good agreement between the experimental data and the calculated results is obtained. For the initial state, the observed discrepancies are mainly due to the absence of ADF correction and the evaluation of the Doppler feedback effect. During the transient, the deviations are mainly due to the combined effect of the measurement uncertainty in the control rod axial position and the estimation of the Doppler effect.

A two-dimensional benchmark problem for a VVER-1000 hot zero-power state with fresh fuel loading is presented. The reference solution has been obtained by many-group heterogeneous transport-theory calculations with the code Mariko, applying the method of characteristics. An equivalent two-group diffusion problem has been defined by homogenized two-group diffusion parameters and discontinuity factors for the fuel assemblies and the radial reflector nodes. The two-group nodal neutron diffusion model DYN3D has been verified against this benchmark. The DYN3D errors in the relative assembly-wise power distribution vary between -1.6 % and +1.1 %, the deviation in k-eff is –50 pcm.

A non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine, was experimentally and numerically studied. The system under investigation comprises air as gas phase and isopropanol as liquid phase at room temperature. The initially stationary isopropanol and air were brought into motion by the rotating impeller. The X-Ray cone beam tomography measurements were taken at five different stirrer speeds with thresholds of 50 rpm starting from 1000 rpm at which the gas inducement occurs for the given operating conditions. The final stirrer speed was 1200 rpm at which the central vortex virtually reaches the impeller. Additionally, video observations, performed with a digital camcorder, were taken to study the unsteady behaviour of the central vortex.
CFX 10.0 numerical software was used to carry out the computational fluid dynamics analyses of the stirred tank reactor. A full three dimensional approach was adopted in order to capture the unsteady behaviour of the central vortex. Transient and steady state numerical calculations were performed. Four steady state simulations, at stirrer speed from 200 to 800 rpm, were conducted to obtain an initial guess of the flow field and the phase distribution for the steady state and the transient simulations at 1000 rpm. The numerical predictions above 1000 rpm used the previous simulation results as an initial guess. Starting from 1000rpm, five steady state simulations were performed at stirrer speed thresholds of 50 rpm to be compared with the experimental observations. The transient numerical predictions were compared with visual observations, since the X-Ray cone beam tomography provides an average phase distributions more suitable for comparison with the steady state predictions. The tetrahedral mesh with above 1500000 elements was globally refined since a detailed view in the whole geometry is required. The inhomogeneous two-phase flow model with the particle transport model was applied to the system with momentum transfer described by the drag force and turbulence transfer modelled by Sato enhanced eddy viscosity model. The gas phase was modelled as dispersed fluid with a mean diameter of 1 mm and the liquid phase as continuous fluid. Different turbulence models were considered for the liquid phase but the k-ε turbulence model was found to be the most computationally stable and was used in the simulations. The gas phase turbulence was modelled using the dispersed phase zero equation. The flow was regarded as buoyant and implemented using the density difference model.
The CFD predictions closely mimic the experimental observations for the central vortex depth as well as for its spread out. The results demonstrate the X-Ray cone beam tomography and the CFD capabilities to capture the two-phase flow in detail, which can provide valuable information for the industry. In particular the special gas phase distribution, which can also have time-dependent behaviour, can have a crucial impact on the reactor performance. This can be in detail predicted by the computational fluid dynamic software, which can prove to be an essential tool for the reactor optimisation and scale-up.

Microbes are widely distributed in nature and they can strongly influence the migration of actinides in the environment. This investigation describes the interaction of plutonium in mixed oxidation states (Pu(VI) and Pu(IV)-polymers) with cells of the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis DSM 10631T, which frequently occurs in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden. In this study, accumulation experiments were performed in order to obtain information about the amount of Pu bound by the bacteria in dependence on the contact time and the initial plutonium concentration. We used solvent extractions, UV-vis absorption spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy to determine the speciation of Pu oxidation states. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to study the coordination of the Pu bound by the bacteria. In the first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. Solvent extractions showed that 97 % of the initially present 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 from the cell envelope back to the aqueous solution due to the weak complexing properties of this plutonium oxidation state. Indications were found for a penetration of Pu species inside the bacterial cells.

A new sensor was developed for an improved visualisation and quantification of the coolant mixing in the downcomer of the ROCOM test facility. This sensor spans a measuring grid of 64 azimuthal and 32 positions over the height of the downcomer On behalf of an experiment with the start-up of the main coolant pump the possibilities of the new sensor are demonstrated.

We report the variable temperature vibrational properties of single crystals of the S=1/2 Heisenberg antiferromagnet VOHP O₄ *1/2 H₂O. A pair of peaks in the far infrared spectral response may be due to magnetic excitations. We invoke a dynamic Dzyaloshinskii-Moriya mechanism to explain the activation and polarization dependence of the singlet-to-triplet gap in the far infrared, and we identify the low-energy phonons that likely facilitate this coupling. The spin-gap values are compared to those obtained via magnetic susceptibility, electron spin resonance, and neutron scattering. Vibrational mode splitting in VOHP O4 * 1 / 2 H2 O indicates a weak local symmetry breaking near 180 K , and the low-temperature redshift of V-O and H-O related modes demonstrates enhanced low-temperature hydrogen bonding. The low lattice symmetry is important for the proposed magnetoelastic interactions.

The present paper reports on our efforts in modelling the pressure drop buildup at sump strainers obstructed by mineral fibrous insulation material after a Loss of Coolant Accident (LOCA). Special attention is drawn to the compressibility of the fibrous filter cake. Comparison of numerical results with pressure drop measurements has been provided.

FZR has 10 years of experience using ANSYS CFX software for CFD applications focused on nuclear reactor applications and more recently also chemical process simulations. These CFD activities are very closely connected to experimental investigations at facilities in the institute. Using advanced two-phase flow measurement techniques, a comprehensive data base for CFD code verification is being created. So in addition to single-phase flow nuclear reactor engineering applications, development and verification of physical models for two-phase flows can be performed. FZR is participating in the German initiative on CFD applications in nuclear reactor safety research in close co-operation with the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS, the German nuclear safety authority) and ANSYS. The group of young and highly motivated CFD scientists that has been established at the institute also has a significant portion of the 100 processor Linux cluster of the FZR at its disposal. The FZR coordinated the experimental and analytical investigations of turbulent mixing inside pressurized water reactors (PWRs) performed within the EC project FLOMIX-R (Fluid mixing and flow distribution in the reactor circuit). The purpose of this project was to describe coolant mixing phenomena, particularly for severe accident scenarios. Such scenarios include steam line breaks and boron dilution, where mixing of coolant from different loops moderates the inflow of water with insufficient boron content or temperature into the reactor core. These changes can lead to reactor power excursions (rapid increase in reactor power) due to positive reactivity effects. An example of a typical boron dilution scenario is during start-up of the first main coolant pump after a slug of low borated water has formed in one of the cooling loops, where mixing is largely forced by the momentum introduced by the pump starting. Another safety issue arises during emergency core cooling (ECC) situations, when cold water is injected into a hot cooling loop. In this case, buoyancy-driven mixing is influenced by density differences in the fluid and is typical for so-called pressurized thermal shock (PTS) scenarios. When a streak of cold ECC water touches the reactor pressure vessel (RPV) wall, unacceptable thermal stresses can occur. Measurement data from several sets of mixing experiments, using advanced measurement techniques with enhanced temporal and spatial resolution, improved the basic understanding of turbulent mixing and provided data for CFD code verification.
Selected experiments were then simulated using ANSYS CFX and applying best practice guidelines (BPGs), a set of systematic procedures for quantifying and reducing numerical errors. BPGs were applied when considering computational grid resolution and time step, turbulence models, internal geometry modelling, boundary conditions, numerical schemes, and convergence criteria. These investigations highlighted the importance of grid quality, and also the need to minimize numerical diffusion by using second order discretization. In fact, first order schemes were found
to sometimes even provide physically incorrect results. ANSYS CFX was well able to predict the experimental flow patterns and mixing phenomena for both buoyancy-driven and momentum-driven flows. Two-equation turbulence models like k-ω or SST were found to be suitable for momentum-driven slug mixing, while Reynolds stress models provided better results for buoyancy driven mixing.
Comprehensive multiphase flow models, advanced turbulence models, second order discretization, and scalable parallel performance all combine to make ANSYS CFX a valuable tool at FZR. ANSYS CFX software has been instrumental in the development and verification of best practices guidelines for the use of CFD in nuclear safety analyses.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was combined with batch experiments to study the sorption of uranium(VI) onto gibbsite (γ-Al(OH)₃).
Two uranyl surface species with fluorescence lifetimes of 330 ± 115 ns and 5600 ± 1640 ns, respectively, were identified.
The first species was dominating the more acid pH region whereas the second one became gradually more prominent towards higher pH values. The fluorescence spectra of both adsorbed uranyl(VI) surface species were described with six characteristic fluorescence emission bands situated at 479.5 ± 1.1, 497.4 ± 0.8, 518.7 ± 1.0, 541.6 ± 0.7, 563.9 ± 1.2, and 585.8 ± 2.1 nm. The surface species with the short-lived fluorescence lifetime of 330 ns is attributed to a bidentate mononuclear inner-sphere surface complex in which the uranyl(VI) is bound to two reactive OH- groups at the broken edge linked to one Al. The second surface species with the significant longer fluorescence lifetime of 5600 ns was attributed to small sorbed clusters of polynuclear uranyl(VI) surface species. The longer fluorescence lifetime of the long-lived uranyl surface species at pH 8.5 is explained with the growing average size of the adsorbed polynuclear uranyl surface species.
Spectroscopic evidence of sorbed U(VI) surface species on quartz and kaolinite, also obtained by TRLFS were presented and compared with the U(VI) gibbsite system.

An overview on applied MHD projects of the Rossendorf MHD department will be given.

Es wird eine Übersicht zur kontaktlosen Kontrolle von Metallschmelzen und zur Messung von Strömungsgeschwindigkeiten gegeben.

This report gives a review on existing experimental data for the development, verification and valida-tion of models for the simulation of a two-phase PTS situation. This includes single effect data, which are useful for the development and validation of closure models for CFD codes as well as integral test data for the validation of the applicability of the code for PTS situations. For the development and validation of closure models for CFD codes, data are required with a high resolution in space and time. There is a need of additional data. Information on the planned TOPFLOW PTS experimental programme is also included in the report.

This report identifies PTS-scenarios for the French 900 MW CPY PWR, the German 1300 MW Kon-voi reactor, the Loviisa 400 MW VVER, the Russian VVER-1000 and the Czech VVER-100. Accord-ing to the resulting basic flow conditions relevant physical phenomena for the simulation of the scenes during Emergency Core Cooling (ECC) injection into the cold leg are identified. The main focus is on two-phase flow phenomena. The state of the art of modelling these phenomena and needs for models improvement are discussed. Thus the report is a suitable basis for the specification of the main topics to be provided in Task T2.1.4 of the NURESIM project.

wird nachgereicht

At present in-beam PET is the only possibility for an in-situ monitoring of the particle delivery in hadron tumor therapy and there is a unique clinical implementation at the Gesellschaft fuer Schwerionenforschung (GSI) Darmstadt.
Several heavy ion treatment facilities are under construction, which will provide a large variety of ions from protons to oxygen. This requires a precise knowledge of the spatial distribution of beam induced positron emitters in the irradiated volume. For the 3He-case experiments at GSI with three mono-energetic 3He-beams of 130.03 AMeV to 207.92 AMeV have been carried out. The beams were stopped in homogeneous thick targets consisting of PMMA, graphite and water. Results on the production rate and the spatial distribution of 3He ion induced beta+-activity will be presented and compared with data from 12C-irradiation. From these, the accuracy and resolution for determining the range of the 3He primary beams is deduced. Furthermore, energy dependent thick target cross sections for different reaction channels leading to positron emitters will be estimated from the experimental data.

It is shown that the 2pz confined impurity state of a semiconductor quantum well develops into an excited impurity band in the case of a superlattice. This is studied by following theoretically the transition from a single to a multiple quantum well or superlattice by exactly diagonalizing the three dimensional Hamiltonian for a quantum well system with random impurities. Intersubband
absorption experiments, which can be nearly perfectly reproduced by the theory, corroborate this interpretation, which also requires re-interpretation of previous data.

Although Electron Paramagnetic Resonance (EPR) has been a very successful method to investigate transition metal ions in coordination complexes and biomolecules, not all such ions can be subject to conventional EPR investigations even if they are paramagnetic. In particular, high-spin (S > 1/2) species pose serious challenges to spectroscopists, and of these, the non-Kramers (integer-spin) ions have been long considered ‘EPR-silent’ at conventional frequencies and fields.
We propose a novel EPR-related technique that takes an advantage of tunable sources operating in the sub-THz range of frequencies in conjunction with very high magnetic fields (up to 25 Tesla) to determine accurate intrinsic spin Hamiltonian parameters not only for a variety of non-Kramers transition metal ions (such as Ni²⁺, Mn³⁺, and Fe²⁺) that have traditionally been termed ‘EPR-silent’, but also for those Kramers (half-integer) species that are poorly characterized in their high-spin states, such as Co2+.
The obtained parameters can serve to better characterize the electronic structure of the ions in question, in combination with other experimental methods.

The conditions for the manifestation of transient effects in fission are carefully examined by analysing experimental data where fission is induced by peripheral heavy-ion collisions at relativistic energies. Experimental total nuclear fission cross sections of U-238 at 1 A GeV on gold and uranium targets are compared with the predictions of a nuclear-reaction code, where transient effects in fission are modeled using different approximations to the numerical time-dependent fission-decay width: a new analytical description based on the solution of the Fokker-Planck equation and two widely used but less realistic descriptions, a step function and an exponential-like function. The experimental data are only reproduced when dissipation is considered. The influence of transient effects on the fission process, as well as the deduced value of the dissipation strength P, depends strongly on the approximation applied for the time-dependent fission-decay width. In particular, a metic! ulous analysis sheds severe doubts on the use of the exponential-like in-growth function. Finally, we investigate which should be the characteristics of experimental observables to be most sensitive to transient effects in fission. The pertinence of observables related to the excitation energy at saddle is discussed.

Die Löslichkeitsprodukte kristallinen und amorphen Urandioxids werden durch die Kombination von coulometrischer Titration einer U(IV)-Lösung und der Detektion der bei Überschreitung der Löslichkeit entstehenden Kolloide mittels laserinduzierter Breakdown-Detektion (LIBD) bestimmt. Die Quantifizierung von U(VI)-Spuren erfolgt mittels laserinduzierter Fluoreszenzspektroskopie.
Die Partikelgröße der entstehenden Kolloide und die Ionenstärke wird in den thermodynamischen Berechnungen berücksichtigt. Für die kristalline Modifikation resultiert log K_sp = -59,6, für die amorphe Modifikation log K_sp = -54,4.
Ergänzende Untersuchungen mittels EXAFS-Spektroskopie bestätigen das Vorliegen der kristallinen Modifikation.

The favourable long-half life, the ease of production and the low enery of the emitted positron make ¹⁸F an ideal radionuclide for PET imaging. Radiochemistry of ¹⁸F basically relies of two distinctive types of reactions: nucleophilic and electrophilic reactions. All syntheses of ¹⁸F-labelled radiotracers are based on either [¹⁸F]fluoride ion or [¹⁸F]fluorine gas as simple the primary labelling precursors which are obtained directly from the cyclotron. They can be applied either directly to the radiosynthesis or they can be transformed into more complex labelling precursors enabling the multi-step built up of organic tracer molecules. The topic of this review is a survey on the application of several ¹⁸F-labelled aryl fluorides as building blocks derived from no-carrier-added (n.c.a.) [¹⁸F]fluoride to built up small mono-molecular PET radiotracers at high specific radioactivity by multi-step synthesis procedures.

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Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the four loop 1:5 scaled ROCOM mixing test facility. Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied.

From the test matrix an experiment with 2% density difference between the de-borated slugs and the ambient coolant was used to validate the CFD software ANSYS CFX. To model the effects of turbulence on the mean flow a Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used.

The experiment and CFD calculation show a stratification in the downcomer. The less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core.The validation proves that ANSYS CFX is able to simulate appropriately the flow field and mixing effects of coolant with different densities.

Our research group has focused on mercaptoimidazole derivatives as the lead structure to design radioactive probes for in vivo imaging of 5-HT_1A receptors. This type of compounds can be labelled directly with ¹¹C or can be used to prepare tripodal ligands suitable to stabilize the fac-[M(CO)₃]⁺ (M = Re, ^99mTc) moieties.^1,2 Interestingly, this versatility allows an easy assessment of the influence of the bulkier metallic fragment on the biological properties of PET (¹¹C) or SPECT (^99mTc) radioligands bearing a common pharmacophore.
Scheme 1
In this communication, we report on the radiosynthesis, characterization and biological evaluation of mercaptoimidazole piperazinyl derivatives labelled with ¹¹C (1) and with ^99mTc (2 and 3) (Scheme 1). It will be discussed their interest as radioactive probes for imaging 5-HT_1A receptors by means of PET or SPECT, as well as the effect of the presence of the organometallic moiety on the affinity and biodistribution profile of the compounds.
Acknowledgments: R. Garcia and L. Maria thank FCT for PhD and Post-Doc grants, respectively. This work has been partially supported by the FCT (POCTI/2001/QUI/42939).
[1] Garcia, R; Xavier, C.; Paulo, A.; Santos, I.; Kniess, T.; Bergmann, R.; Wüst, F. J. Labelled Cpd. Radiopharm. 2005, 48, 301.
[2] Garcia, R.; Paulo, A.; Domingos, A.; Santos, I.; Ortner, K.; Alberto, R. J.Am Chem. Soc. 2000, 122, 11240.