Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The fabrication of more and more miniaturized electronic and photonic devices relies on new, ingenious methods for the fabrication of spatially controlled nanostructures. Examples are electronic devices based on semiconducting nanowires and photonic devices based on chains of metallic nanoclusters that guide light by coupled surface plasmons. In this contribution a template-directed ion beam synthesis of nanowires and regular nanocluster chains will be presented. As templates, V-grooves etched in (001)Si and subsequently oxidized are used. High fluence Ge⁺ implantation is carried out into the SiO₂ layer at 70 keV. Thereby, the implanted Ge enriches themselves in the V-groove bottom to a critical amount, which may result in nanowire formation by nucleation, growth and coalescence during subsequent thermal treatment. TEM investigations indicate the formation of a nanowire buried in the SiO₂ at the V-groove bottom. Kinetic lattice Monte Carlo simulations of the nanowire formation process were performed in order to understand the phase separation mechanism and results are compared to TEM images. Furthermore, it is shown that even ideal nanowires show a instability and form during long-lasting annealing equal-spaced and equal-sized nanoclusters "nanocluster chains" by self-organization.

In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed

In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed.

Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and substrate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced, which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient in understanding nanocluster evolution. Various aspects of precipitate evolution during implantation, formation of ordered arrays of nanophase domains by focused ion implantation and compound nanocluster synthesis are discussed.

In the first part of this paper we present a quantitative trapping model that includes detrapping to describe the diffusion of nitrogen in austenitic stainless steel during successful nitriding. Calculated nitrogen depth profiles, assuming a diffusion pre-exponential factor D0 = 10-3 cm2/s, a diffusion activation energy Ed = 1.1 eV, and a detrapping activation energy Et2d = 1.45 eV, show good agreement with experimental nitrogen depth profiles
obtained from a sample that has been subsequently nitrided with 14N and 15N. The plausibility of a trapping mechanism is also supported by a number of phenomenological and thermodynamical arguments. In the second part of this paper we present a modelling approach for the evolution of the thickness of the surface oxide layer during successful nitriding. The approach bases on the assumption that the surface oxide layer thickness is completely controlled by the interplay of sputtering and oxidation and differentiates between oxide layer growth limited by diffusion and oxide layer growth limited by the rate of oxygen supply. The applicability of this approach is supported by experimental data obtained by real-time elastic recoil detection analysis during ion nitriding at different combinations of ion energy and oxygen partial pressure.

Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and substrate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced,
which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient
in understanding nanocluster evolution. Various aspects of
precipitate evolution during implantation, formation of
ordered arrays of nanophase domains by focused ion implantation
and compound nanocluster synthesis are discussed.

The production of pions and kaons has been measured in Au+Au collisions at beam energies from 0.6 to 1.5 AGeV with the Kaon Spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.

Under ion irradiation collisional mixing competes with phase separation if the irradiated
solid consists of immiscible components. If a component is a chemical compound,
there is another competition between collisional forced chemical dissociation of the
compound and its thermally activated re-formation. Especially at interfaces between
immiscible components, irradiation processes far from thermodynamical equilibrium
may lead to unexpected phenomena. If the formation of nanoclusters (NCs) occurs
during ion implantation, the phase separation caused by ion implantation induced
supersaturation can be superimposed by phenomena caused by collisional mixing.
In this contribution it will be studied how collisional mixing during high-fluence ion
implantation affects NC synthesis and how ion irradiation through a layer of NCs
modifies their size and size distribution. Inverse Ostwald ripening of NCs will be
predicted theoretically and by kinetic lattice Monte-Carlo simulations. The
mathematical treatment of the competition between irradiation-induced detachment
of atoms from clusters and their thermally activated diffusion leads to a Gibbs-
Thomson relation with modified parameters. The predictions have been confirmed by
experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The
unusual behavior results from an effective negative capillary length, which will be
shown to be the reason for inverse Ostwald ripening. Another unexpected
phenomenon to be addressed is self-organization of NCs in a delta-layer parallel to
the Si/SiO2 interface. Such delta-layers were found when the damage level at the
interface was of the order of 1...3 dpa. It will be discussed that the origin of the delta-
layer of NCs can be assigned to two different mechanisms: (i) The negative interface
energy due to collisional mixing gives rise to the formation of tiny clusters of substrate
material in front of the interface, which promotes heteronucleation of the implanted
impurities. (ii) Collisional mixing in the SiO2 produces diffusing oxygen, which may be
consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes
denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si
excess promotes heteronucleation too. Independent of the dominating mechanism of
self-organization of a delta-layer of NCs, its location in SiO2 close to the
SiO2/Si interface makes it interesting for non-volatile memory application.

Under ion irradiation collisional mixing competes with phase separation if the irradiated
solid consists of immiscible components. If a component is a chemical compound,
there is another competition between collisional forced chemical dissociation of the
compound and its thermally activated re-formation. Especially at interfaces between
immiscible components, irradiation processes far from thermodynamical equilibrium
may lead to unexpected phenomena. If the formation of nanoclusters (NCs) occurs
during ion implantation, the phase separation caused by ion implantation induced
supersaturation can be superimposed by phenomena caused by collisional mixing.
In this contribution it will be studied how collisional mixing during high-fluence ion
implantation affects NC synthesis and how ion irradiation through a layer of NCs
modifies their size and size distribution. Inverse Ostwald ripening of NCs will be
predicted theoretically and by kinetic lattice Monte-Carlo simulations. The
mathematical treatment of the competition between irradiation-induced detachment
of atoms from clusters and their thermally activated diffusion leads to a Gibbs-
Thomson relation with modified parameters. The predictions have been confirmed by
experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The
unusual behavior results from an effective negative capillary length, which will be
shown to be the reason for inverse Ostwald ripening. Another unexpected
phenomenon to be addressed is self-organization of NCs in a delta-layer parallel to
the Si/SiO2 interface. Such delta-layers were found when the damage level at the
interface was of the order of 1...3 dpa. It will be discussed that the origin of the delta-
layer of NCs can be assigned to two different mechanisms: (i) The negative interface
energy due to collisional mixing gives rise to the formation of tiny clusters of substrate
material in front of the interface, which promotes heteronucleation of the implanted
impurities. (ii) Collisional mixing in the SiO2 produces diffusing oxygen, which may be
consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes
denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si
excess promotes heteronucleation too. Independent of the dominating mechanism of
self-organization of a delta-layer of NCs, its location in SiO2 close to the
SiO2/Si interface makes it interesting for non-volatile memory application.

We consider a simple model of inverse dynamo theory consisting of a spherically symmetric alpha^2-dynamo with unknown radial dependence of alpha. Using an evolutionary strategy, we try to reconstruct this radial dependence of alpha from a finite number of given data, e.g. from a few real or complex eigenvalues and/or from the assumption that the field is confined to the dynamo region. Although for planetary dynamos the direct applicability of our specific model is very limited, the principle of inversion is quite general and might be useful for cosmic dynamos as well as for the emerging laboratory dynamo community.

The present study describes the synthesis of the [¹⁸F]fluoromethyl analogue of (+)-McN5652 ([¹⁸F]FMe-McN) as a new potential tracer for the serotonin transporter. In vitro binding studies have shown that FMe-McN displays only slightly lower affinity for the serotonin transporter (K_i=2.3 ± 0.1 nM) than (+)-McN5652 (K_i=0.72 ± 0.2 nM). The radiofluorinated tracer [¹⁸F]FMe-McN was prepared by reaction of normethyl (+)-McN5652 with the fluoromethylation agent [¹⁸F]bromofluoromethane in an overall radiochemical yield of 5 ± 1% (decay-corrected, related to [¹⁸F]fluoride) and with high specific radioactivity (200 - 2000 GBq/µmol at the end of synthesis).

Our four years experience in operation and maintenance of the PET cyclotron "CYCLONE 18/9" is given. Improvements at the CYCLONE 18/9 are presented as well as results of the routine radionuclide production.

After synthesis of fluorine-18 labelled analogues by [¹⁸F]fluorobenzoylation at the alpha-amino group, biodistribution and elimination of individual advanced glycation endproducts, namely N^epsilon-carboxymethyllysine and N^epsilon-carboxyethyllysine, was studied in comparison to lysine in rats after intravenous injection using positron emission tomography (PET).
The [¹⁸F]radiofluorinated amino acids were fast distributed via the blood, followed by a rapid excretion through the kidneys. Elimination kinetics were similar for both AGEs and lysine. For CML and CEL, but not for lysine, a temporary liver accumulation could be observed, which was not connected with any metabolisation or enterohepatic circulation. No further accumulation in any tissues was observable, indicating that increased tissue levels of CML or CEL, which have been described for certain disorders, are exclusively derived from endogenous origin and should not depend on a dietary intake. Under uremic conditions, however, an impaired kidney function might result in a significant increase of the AGE-load of blood and tissues. PET based on ¹⁸F-labelled AGEs proved to be a promising tool to elucidate the physiological fate of post-translationally modified amino acids and to clarify the role of AGEs as possible "glycotoxins".

4-([¹⁸F]fluoro)benzoyl-neurotensin(8-13) (¹⁸FB-Arg⁸-Arg⁹-Pro¹⁰-Tyr¹¹- Ile¹²-Leu¹³-OH, 1) and two analogs stabilized in one and two positions (¹⁸FB-Arg⁸Psi(CH₂NH)Arg⁹-Pro¹⁰-Tyr¹¹- Ile¹²-Leu¹³-OH, 2, ¹⁸FB-Arg⁸Psi(CH₂NH)Arg⁹-Pro¹⁰-Tyr¹¹-Tle¹²-Leu¹³-OH, 3) were synthesized in a radiochemical yield of 25 - 36% and a specific activity of 5 - 15 GBq/mmol. The peptides were evaluated in vitro and in vivo for their potential to image tumors, overexpressing neurotensin receptor 1 (NTR1) by positron emission tomography (PET). All analogs exhibited in vitro binding affinity in the low nanomolar range to NTR1-expressing human tumors, measured by quantitative receptor autoradiography, HT-29 and WiDr cells, and to sections of tumors derived from these cell lines in mice. The radiotracers were internalized in the cells in vitro, and the fluorinated peptides were able to mobilize intracellular Ca²⁺ of WiDr cells. In in vivo studies in rats and in mice bearing HT-29 cell tumors, only a moderate uptake of the radioligands into the studied tumors was observed, presumingly due to degradation in vivo and fast elimination by the kidneys. In comparison with the other analogs, the specific tumor uptake expressed as tumor-to-muscle relation was highest for the radioligand 3. The blood clearance of 3 was reduced by co-injection of peptidase inhibitors. The catabolic pathways of the radiofluorinated peptides were elucidated. The results suggest that the high binding affinity to NTR1 and the stabilization against proteolytic degradation are not yet sufficient for tumor imaging by PET.

The evolution of the mean size and the size distribution of Au nanoclusters (NCs) under high-energy ion irradiation has been studied. Au NCs were synthesized in a 480 nm thick SiO2 layer by 330 keV Au+ implantation and subsequent annealing at T = 1000 °C for 1h in dry O2. XTEM images show a 70 nm thick layer of Au NCs, being centered at the projected ion range Rp(330keV) = 100 nm, having a mean NC size of 5 nm at Rp, and resembling the broad LSW size distribution of diffusion controlled Ostwald ripening. Post-irradiation of the Au NCs by 4.5 MeV gold ions were used in order to tailor their size and size distribution. The high-energy Au+ irradiation were performed at 190...210 °C with a fluence of (0.5...1.0)x1016 cm-2. By the post-irradiation no gold was deposited into the SiO2 layer, the Au+ ions come to rest in the (001)Si substrate at Rp(4.5MeV) = 1 mm. XTEM images of the post-irradiated Au NCs show a strong decrease of their mean size as well as the width of their size distribution. The observed NC evolution under ion irradiation agrees with recent theoretical predictions and kinetic Monte-Carlo simulations.

Co/Cu multilayers were prepared by cross-beam pulsed laser deposition and characterised by high-angle X-ray diffraction as well as specular and off-specular reflection. Using synchrotron radiation at the K-edge energy of Co and Cu to enhance the scattering contrast, the study shows that the roughness of these multilayers is well described by the fractal model of self-affine structures. For the pulsed laser deposited layers an extremely large lateral correlation length, xi, of the vertically correlated interfacial roughness is found (xi >1 µm) which exceeds the xi-value of the uncorrelated roughness by about two orders. The interfaces are very jagged (roughness exponent, h, between 0.15 and 0.3). The root mean square roughness, sigma, of the Cu/Co and Co/Cu interfaces are of the same order compared with the values reported for sputtered layers.

Abstract: Co nanoparticles fabricated by ion beam synthesis in SiO2 films were inve-stigated with TEM and SQUID technique. The variation of the thermal treatment enables the formation of Co nanoclusters of different sizes ranging from 2 to 40 nm. Small nanoclusters of about 2-3 nm are amorphous, whereas clusters above 7 nm show the configuration of cubic Co nanocrystals. Measurements of magnetization at tem-peratures between 2 K and 360 K reveal superparamagnetic behaviour for the small nanoclusters up to 3 nm and ferromagnetism for clusters above 7 nm .

In preparation for the characterization of Sg as oxide hydroxide a new high temperature gas chromatography apparatus based on the OLGA design was developed. However, the time-consuming recluster step was replaced by direct deposition of species leaving the chromatographic column on metal foils. In test experiments with short-lived Mo isotopes a retention time of 9 s was determined for an isothermal temperature of 1270 K, sufficient to study Sg isotopes.
A model based on the theory of supersonic jet and on simple geometrical considerations reproduces the data of direct condensation experiments quite well.

The formation of Ge nanowires in V-grooves has been studied experimentally as well as theoretically. As substrate oxide covered Si V-grooves were used formed by anisotropic etching of (001)Si wafers and subsequent oxidation of their surface. Implantation of 1E17 Ge+ cm^-2 at 70 keV was carried out into the oxide layer covering the V-grooves.
Ion irradiation induces shape changes of the V-grooves, which are captured in a novel continuum model of surface evolution. It describes theoretically the effects of sputtering, redeposition of sputtered atoms, and swelling. Thereby, the time evolution of the target surface is determined by a nonlinear integro-differential equation, which was solved numerically for the V-groove geometry. A very good agreement is achieved for the predicted surface shape and the shape observed in XTEM images. Surprisingly, the model predicts material (Si, O, Ge) transport into the V-groove bottom which also suggests an Ge accumulation there proven by STEM-EDX investigations.
In this Ge rich bottom region, subsequent annealing in N2 atmosphere results in the formation of a nanowire by coalescence of Ge precipitates shown by XTEM images. The process of phase separation during the nanowire growth was studied by means of kinetic 3D lattice Monte-Carlo simulations. These simulations also indicate the disintegration of continuous wires into droplets mediated by thermal fluctuations. Energy considerations have identified a fragmentation threshold and a lower boundary for the droplet radii which were confirmed by the Monte Carlo simulation.
The here given results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations as well as chains of equally spaced clusters with nearly uniform diameter.

Im Sommer 1999 wurde im Forschungszentrum eine Zweistrahlführung in Betrieb genommen. Dieses System gestattet, Ionenarten aus unterschiedlichen Beschleunigern gleichzeitig in die Experimentierstationen zu lenken. In der Doppelimplantationsstation wird die Zweistrahlführung zur Synthese neuartiger Materialien genutzt. In der Analysestation wird die Zweistrahlführung in Kombination mit einem magnetischen Browne-Buechner-Spektrometer eingesetzt, um komplexe und hochgenaue Materialanalysen durchzuführen. Das System überträgt Ionen des gesamten Teilchen- und Energiespektrums von 3-MV-Tandetron-Beschleuniger und 500-kV-Ionenimplanter mit minimalen Intensitätsverlusten zu den Experimenten. Steuerung und Kontrolle von Beschleunigern, Strahlführung und Experiment erfolgen in einem hierarchischen Rechnernetz. Die hier beschriebene Zweistrahlanlage ist Teil eines Projekts zur umfassenden Kopplung von Basisgeräten des Forschungszentrums.

Activation measurements results at non-standard surveillance positions of the VVER-1000 Novovoronesh-5 have been used to verify neutron fluence calculations for pe-ripheral reactor regions with large flux gradients. Fluence integrals and activities of irradiated detectors and specimens had been calculated by three laboratories using different transport calculation methods: 2D/1D-SN synthesis, 3D-SN and the Monte Carlo method. The results obtained by different calculations and by activation measurements have been compared. The differences between measured and calculated activities as well as between the different calculation results were reasonable. Possible causes of discrepancies are discussed.

The term “intersubband transitions” has been coined to describe optical transitions between confined electronic states in semiconductor quantum structures. In this lecture I will discuss the basic underlying physics of intersubband transitions in quantum wells and discuss their recent applications for real optoelectronic devices, as there are the quantum cascade laser (QCL) and the quantum well infrared photodetector (QWIP).

Concerning the physics, the basic concept of intersubband transitions appears extremely simple; yet a detailed understanding of all aspects, such as absorption strength and frequency, polarization dependence and linewidth, requires a careful consideration of band structure, many-body physics and electromagnetism.

The first observation of intersubband absorption was reported in 1974 in Si accumulation layers and 1985 in GaAs quantum wells. Since then, intense research has driven the development of high-sensitivity intersubband infrared detectors and focal-plane arrays, which are now commercially available. Intersubband lasers have been realized in 1994 and are now covering a spectral range from 4 to 17 m. I will discuss the physics and performance of these optoelectronic devices, also in comparison to conventional band-gap detectors and lasers.

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Ich moechte einen Ueberblick ueber die optischen Eigenschaften von Halbleiteruebergittern im Infrarot- und THz-Spektralbereich geben, die ja im wesentlichen von Inter- und Intraminibanduebergaengen herruehren. Die theoretischen Ueberlegungen werden durch verschiedene experimentelle Resultate illustriert - z. B. Interminibandabsorption und ihre Anwendung zur Analyse der Elektronen Verteilungsfunktion oder thermisches "quenching" der Intraminibandabsorption. Abschliessend diskutiere ich die Erweiterung obiger
Messungen auf Uebergitter mit einem vertikalen elektrischen Feld, d.h. die Untersuchung von Wannier-Stark-Leitern und Bloch-Oszillatoren.

Atomic-scale calculations were performed for the first time to investigate mechanical
properties of amorphous carbon films grown by a realistic simulation of ion-beam deposition process. The simulated films have a thickness of a few nanometers and reproduce the main structural features of real films, with the bulk content of sp3 bonded atoms varying from 35 to 95%, depending on the ion energy (E = 20-80 eV). Employing empirical interatomic potentials for carbon, the average bulk stresses as well as the atomic-level stress distributions were calculated and analysed. The bulk stresses were found to depend not only on the ion energy, but also on the film quality, in particular, on such structural inhomogeneities as local fluctuations of the sp3 fraction with the depth. The local variation of the bulk stress from the average value considerably increases as the local content of sp2 bonded atoms increases. Elastic constants of amorphous carbon films were also computed using the method of inner elastic constants, which allows for the stress dependence of elastic constants to be analysed. This investigation showed how the Young's modulus varies as a function of the lateral bulk stress in an amorphous film.

This paper continues the presentation of detailed results of the EU-sponsored RESQUE project. Within the RESQUE project it was planned to determine the dependence of Charpy-V test results on tolerance deviations and different end block materials in reconstituted specimens. The conventional Charpy-V parameters - the total impact energy, lateral expansion and shear fracture appearance - are not significantly affected by the effects of oversized dimensional variability. Disturbing load oscillations arise from some of the geometrical deviations. This influences the characteristic yield load, yield deflection and impact energy at load maximum. In comparison to the existing scatter there is no significant effect of the end block material on the main Charpy parameters and the characteristic loads.

Vascular stents activated with radioactive isotopes are planned to be used in clinical practice to prevent restenosis in human coronary arteries after balloon angioplasty. Medical stents are cylindrical meshes and their complex geometry is usually treated for energy dose calculation with approximate dose point kernel(DPK) approach. The important point missed in the DPK approach is the absence of the stent material and, hence, the absence of energy absorption inside the stent. We have performed a comparison between DPK and exact Monte Carlo calculations for some simplified stent models. It appears that DPK approximation significantly overestimates pike dose values especially for the case of gamma-emitting sources. We suggest DPK kernel normalization, which minimizes the difference at relatively far distances, while significant discrepancies near the stent surface still remain.

The surface sorption process of Cm (III) onto smectite and kaolinite was investigated by time-resolved laser fluorescence spectroscopy (TRLFS) in the trace concentration range. We conclude that at low pH Cm(III) is sorbed onto kaolinite and smectite as an outer-sphere complex and retains its complete primary hydration sphere. With increasing pH, inner-sphere adsorption onto kaolinite and smectite occurs via the aluminol edge sites. The same evolution of the Cm(III)-clay surface species as a function of pH was observed for both minerals. Starting at a pH ³ 5, we observe the formation of a ºAl-O-Cm2+(H2O)5 surface complex, which is replaced by a second species at higher pH. The second surface complex may be a monodentate ºAl-O-Cm+(OH)(H2O)4 species or bidentate º(Al-O)2-Cm+(H2O)5 species. The Cm(III)/clay surface complexes are characterised by their emission spectra (peak maxima at 598.8 nm and 603.3 nm) and their fluorescence lifetime (both 110±7 µs). An important result for the mobility and bioavailability of radionuclides is that no incorporation of Cm(III) into the bulk clay structure was observed.

Im Mehrzweck-Thermohydraulik-Versuchsstand NOKO wurde die Wirksamkeit verschiedener passiver Sicherheitssysteme oder deren Komponenten untersucht. Passive Sicherheitssysteme besitzen keine Komponenten, die zur Funktionsfähigkeit Fremdenergie benötigen.
Bei Nachrechnungen der Experimente mit den waagerecht angeordneten Notkondensatorbündeln hatte sich ergeben, dass die verwendeten Rechenprogramme wohl die integral abgeführte Energie gut berechnen können; die lokalen Kondensationsraten auf der Innenseite der Rohre unterschieden sich bei den eingesetzten Programmen beträchtlich voneinander. Daher wurde im Rahmen einer Dissertation die Kondensation von Wasserdampf und eines Wasserdampf-Stickstoff-Gemisches auf der Innenseite eines waagerechten Rohres untersucht. Durch eine entsprechende Instrumentierung war die Dicke des Kondensatfilms sowie dessen Struktur zu ermitteln. In einem besonders instrumentierten Rohr des 2. Notkondensator-Bündels wurden hierzu Nadelsonden eingebaut, deren Eintauchtiefe mit Hilfe von Schrittmotoren verändert werden konnte. Diese beweglichen Nadelsonden wurden im wandnahen Bereich hin und her gefahren, um so die Filmdicke zu registrieren. Zusätzlich waren die Nadelsonden mit Thermoelementen ausgestattet, die gleichzeitig eine Messung der Temperaturverteilung in der Grenzschicht ermöglichten.

The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under Ar atmosphere at ionic strength of 0.1 M NaClO4. pH is varied between 2 and 10 and the metal ion concentration between 2.7.10-7 and 4.5.10-5 mol/L. With increasing pH, two Cm(III)-alumina surface species are identified which are attributed to ºAl-O-Cm2+(H2O)5 and ºAl-O-Cm+(OH)(H2O)4. The two curium-alumina surface complexes are characterised by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110 µs). In the concentration range investigated, the surface complex formation is not dependent upon the metal ion concentration but only on pH. Also the concentration ratio of the two surface species is found to be independent on the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages.

The synthesis of spatially controlled Ge nanowires and nanoclusters by Ge+ ion implantation in oxidized V-grooves on (001) Si surfaces has been studied experimentally as well as theoretically. The V-grooves were prepared by anisotropic wet chemical etching and thermal oxydation. The SiO2-covered V-grooves were implanted with 70 keV Ge+ ions up to a fluence of 1017 cm-2. Ge accumulates within the SiO2 at the bottom of the V-groove which has been proven by analytical TEM (EDX-mapping). Theoretical studies have shown that the Ge accumulation is caused by the V-groove geometry, forward sputtering, and re-deposition. During subsequent annealing the redistributed Ge forms a nanowire by precipitation, ripening and coalesence. Kinetic lattice Monte Carlo simulations of the nanowire formation process show growth instabilities and self-organization phenomena.

The morphology of the as-implanted damage in silicon is investigated using a recently developed combination of time-ordered computer simulations based on the binary collision approximation (BCA) with classical molecular dynamics (MD) calculations. The method is applied to determine the type and the amount of defects formed within the first nanosecond after ion impact. The depth profile and the total number of different defect species (vacancies, interstitials, disordered atoms, etc.) produced on average per incident ion are calculated for B+ (15 keV), P+ (5, 10, 20, 30 keV), and As+ (15 keV) implantations. It is shown that the as-implanted defect structure depends not only on the nuclear energy deposition per ion but also explicitly on the ion mass. Therefore for each ion species the damage morphology exhibits characteristic features. For heavy ions the percentage of extended defects is higher than for light ions. In all cases investigated the number of free or isolated interstitials exceeds the amount of free vacancies. The results obtained allow a microscopic interpretation of the phenomenological model for the as-implanted damage employed in conventional BCA simulations in order to describe the dose dependence of the shape of ion range profiles. They can be also applied to get more realistic initial conditions for the simulation of the defect kinetics during post-implantation annealing.

The influence of a static transverse magnetic field on a turbulent sodium flow in a channel with a
rectangular cross section is investigated. The turbulence has been forced by mechanical means
employing a grid of cylindrical bars. Electric potential probes have been used to determine the
longitudinal component of the liquid velocity. The experiments cover a wide range of the
non-dimensional parameters Hartmann number (Ha < 3000) and the magnetic interaction parameter
(N < 800). Measurements of the turbulence intensity as a function of the magnetic interaction
number N will be presented and discussed. The measured spectra are essentially different from those
predicted according to the theory of two-dimensional turbulence.

On 11 November 1999, magnetic field self-excitation was observed for the first time in a hydromagnetic experiment at the Riga dynamo facility. In a second experiment in July 2000, the dynamo behaviour in the kinematic as well as in the saturation regime was studied. We report on the results of both experiments and try to understand the saturation mechanism.

Lattice parameter measurements in ion-nitrided surface layers of austenitic stainless steel have been performed using x-ray microbeam diffraction on samples with different nitrogen contents as a function of depth and grain orientation, respectively. The lattice expansion observed in the layers as a result of nitriding is anisotropic due to the presence of elastic strains, but the austenite (fcc) structure is largely retained. Parallel to the layer–substrate interface the expanded lattice is highly relaxed which is, along with significant changes in the surface morphology, indicative of plastic deformation in the nitrided zone.

A systematic series of AISI 316 stainless steel samples has been prepared as a function of exposure time to a nitrogen ion beam. Times from 15 s to 4 h were selected with other conditions maintained as follows: sample temperature = 410oC; accelerating potential = 700 V; beam current density = 2.0 mA/cm2. Compositional, structural, magnetic, and diffusion properties were studied with a combination of x-ray diffraction, backscatter Mössbauer spectroscopy, magnetic force microscopy, surface profilometry, and glow-discharge optical emission spectroscopy. The only N-containing phase detected for all processing times was the high-N-solid-solution phase, γN, and its maximum N content was found to grow rapidly to a saturation value exceeding 30 at.%. A carbon contamination layer, in the form of a C-solid-solution phase, γC, was detected below the γN, and was found to be introduced during the Ar-ion sputter-cleaning/heating step used prior to exposure to the N-ion beam. This C-rich layer is “pushed” ahead of the incoming N. The γN layer thickness growth can be modeled with a simple diffusion-plus-sputtering equation that yields the effective diffusivity and maximum (sputter-limited) γN layer depth for the given processing conditions. The surface roughness increases with processing time. Anisotropy in the lattice expansion for different lattice planes parallel to the sample surface and varying magnetic properties in the different surface grains are observed. This is likely due to a mixture of residual stress and N-composition variation effects. Ferromagnetic maze-like domain structures are observed on the 1 micron size scale.

The hyperfine parameters of the metallic disilicide phase a-FeSi2 at room temperature are determined with high accuracy by conversion electron Mössbauer spectroscopy measurements on a single crystal. It is found that there are two well defined iron environments with different electron densities (isomer shifts 0.202 and 0.257 mm/s, resp.) and different electric field gradients. Both quadrupole splittings are negative (-0.382 and -0.730 mm/s, resp.) and the site occupation for both sites is different.

Natural convection is a basic principle for a lot of industrial processes. As an example for the investigation of natural convection phenomena, the paper describes investigations of a passive heat removal system in advanced designs of nuclear power plants. The SWR-1000 concept of Siemens AG includes emergency condensers. In the Research Centre Jülich at the NOKO test facility experiments were performed, to investigate the heat transfer capability under different operation modes. In the last time experiments with detailed instrumentation of thermocouples on the secondary side were performed, to investigate the heating up phenomena in the pool. The paper describes simulations performed in the FZ-Rossendorf using the CFD-code CFX-4 of AEA-Technology and comparisons to the experiments.

The coolant mixing in the downcomer and the lower plenum during pump start-up has been investigated experimentally at the ROCOM test facility. This facility is a 1:5 linearly scaled model of the KONVOI reactor pressure vessel. Transfer functions for a semi-analytical model have been derived from these experiments. The comparison of the model with further experiments and a computational fluid dynamics calculation is presented.

An 7 Chargen von Druckbehälterstählen russischer Herkunft wurden SANS-Unter-
suchungen im unbestrahlten Zustand, nach Bestrahlung im Reaktor WWER-2
Rheinsberg und nach einer 100-h-Ausheilglühung bei 475 °C durchgeführt. Bestrah-
lung erzeugt in jedem Fall eine erhöhte Kleinwinkelstreuintensität. Die Analyse ihrer
Streuvektorabhängigkeit führt auf Strukturdefekte mit einem mittleren Radius von
ca. 1 nm und einem chargenabhängig variierenden Volumenanteil von 0,03 - 0,71 %. Der Volumenanteil korreliert tendenziell mit der Verschiebung der Sprödbruchüber-
gangstemperatur.

In the framework of the external validation of the thermo-hydraulic code ATHLET Mod 1.2 Cycle A, which has been developed by the GRS, post test analyses of two experiments were done, which were performed at the japanese test facility CCTF. The experiments C2-04/62 and C2-19/79 simulate a double end break in the cold leg of the PWR with ECC injection into the cold leg and with combined ECC injection into the hot and cold legs. The evaluation of the calculated results shows, that the main phenomena can be calculated in a good agreement with the experiment. Especially the behaviour of the quench front and the core cooling are calculated very well.

The hydrolysis of uranium(VI) has been the subject of extensive studies since 50 years because uranyl forms strong comlexes with OH- in solution. A comprehensive discussion and review of the thermodynamic data is published in [1]. We investigated the structure of UO22+ as a function of pH with the aid of U LIII-edge EXAFS spectroscopy. The experiments were carried out at beamline BM20. The equipment allows excellent XAS measurements up to high k-values, 17.5 Å-1 in our case.
The speciation of uranium(VI) at a total concentration of 0.05 M in slightly acidic (pH: 3 to 4) solutions is dominated by the two polynuclear complexes (UO2)2(OH)22+ and (UO2)3(OH)5+. Sample A is an example from this pH region, where (UO2)3(OH)5+ is the dominant species. Structure investigations of these polymeric cations in solution at such uranium concentrations are rare. The formation of polynuclear complexes is clearly confirmed by the U-U interaction at 3.81 Å (Figure 1). Approximately 5 oxygen atoms are coordinated in the equatorial plane at 2.41 Å.
In the following pH region from 6 to 11, the U(VI) speciation is dominated by the precipitation of schoepite phases, UO2(OH)2xH2O (sample B). A longer U-U distance of 3.87 Å was measured. Similar U bond lengths of Ë 3.9 Å were found in schoepite phases. Their structure consists of a network of UO2(OH)2 sheets, where the uranyl centers are connected via a double OH bridge.
In the alkaline pH region (sample C and D), monomeric uranium species are formed. As compared to our previous study [2], we were able to extend the k-space region from 15 Å-1 in [2] up to 17.5 Å-1 and thereby to increase the accuracy. The EXAFS measurements confirm the speciation calculations indicating that UO2(OH)42- is the major species at 0.5 M tetramethylammonium hydroxide (TMA-OH). There are two trends in the EXAFS data, the U-Oaxial bond length increases 1.79, 1.81, and 1.83 Å moving from pH 4.1 to 13.7, while the average U-Oequatorial bond length decreases, 2.41, 2.34, 2.26 Å, respectively. This indicates a stronger bonding of equatorial OH groups with increasing pH. Clark et al. have presented spectroscopic evidence for the formation of a penta-hydroxide complex at high TMA-OH concentrations, however with no information about the equilibrium constant [3]. We have tested the hypothesis of Clark et. al. using 17O-NMR spectroscopy with 17O-enriched "yl" oxygens. The spectrum recorded at 258 K (Figure 2) shows only one peak for UO2(OH)42- in 1 M TMA-OH. However, when increasing the hydroxide concentration to 3 M two peaks were obtained, one with the same shift as in the 1 M TMA-OH solution, 1132.2 ppm, the other at 1135.8 ppm presumably due to UO2(OH)53- (Figure 2). To conclude, the complex UO2(OH)42- has a very broad range of existence in strongly alkaline solution. At very high total concentrations of hydroxide [> 1 M TMA-OH], an additional OH- ligand may coordinate in an associative reaction.

Damage has been observed in keV He ₊ ion-implanted Si away from the projected ion range Rp, mainly around Rp/2. Cu gettering has been used for the detection of irradiation defects which are formed during rapid thermal annealing (RTA) of 800°C/10 min. The transmission electron microscopy (TEM) micrographs show no visible defects at Rp/2. The Cu gettering peak at Rp/2 is well known for MeV-ion-implanted and annealed Si (Rp/2 effect). In this study the corresponding effect is observed for low energy implantation of a light ion like He. The mechanism of the cavity formation when He is implanted into silicon and its influence to the implantation induced point defects recombination during subsequent annealing is discussed.

Acid rock drainage (ARD) solution from an abandoned ore mine (pH 2.7, sulfate concentration 411 mMol/L, Fe concentration 93.5 mMol/L) was investigated by photon correlation spectroscopy, centrifugation, filtration, ultrafiltration, scanning electron microscopy, ICP-MS, AAS, ion chromatography, TOC analysis and X-ray absorption fine structure (EXAFS) spectroscopy. A colloid concentration of $ 1 g/L was found. The prevailing particle size was < 5 nm. The most probable mineralogical composition of the colloidal particles is a mixture of hydronium jarosite and schwertmannite. Conclusions as to the type of binding of arsenic onto the particles are drawn.

A description of the fuel rod behaviour and heat transfer model used in the code DYN3D for the simulation of reactivity initiated accidents (RIA) is given. The model comprises a detailed description of the heat transfer in the gas gap between fuel and cladding by conduction, radiation and fuel-cladding contact. The gas gap behaviour is modeled in a mechanistic way taking into account transient changes of the gas gap parameters based on given conditions for the steady state. Thermal, elastic and plastic deformations of fuel and cladding are taken into account. Metal-water reaction of the cladding material in the high temperature region is considered. The cladding-coolant heat transfer regime map covers the region from one-phase liquid convection to dispersed flow with superheated steam.
For the validation of the model, experiments on fuel rod behaviour during RIAs performed in Russian and Japanese pulsed ressearch reactors with shortened probes of fresh fuel rods are calculated. Comparisons between calculated and measured results are shown and discussed. Numerical studies concerning the fuel rod behaviour under RIA conditions in power reactors are reported about. It is demonstrated, that the fuel rod behaviour at high pressure and mass flow rate in power reactors is different from the behaviour at low pressure and stagnant flow conditions in the experiments. It is shown that the mechanisms of fuel rod failure known from the literature can be qualitatively reproduced by the DYN3D fuel rod model.

Lorentz forces can be used to control the near wall flow of low conducting liquids like sea-water. To achieve force densities strong enough to modify the flow, both magnetic and electric fields have to be applied to the fluid. Here, wall parallel Lorentz forces in streamwise direction were used to influence the velocity profile of a flat plate boundary layer as well as the flow around a symmetric hydrofoil. Velocity measurements inside the boundary layer and direct force measurements are given for the flat plate.
At moderate force strength, the mean velocity profile is characterized by a momentum thickness smaller than in the unforced case, whereas at high enough Hartmann numbers a wall jet develops. Additionally, a turbulent, but approximately non-growing boundary layer has been observed. The effect of a suction-side, streamwise Lorentz force on a NACA-0017-like hydrofoil is quantified by means of force balance measurements. Depending on the angle of attack, two different effects are observed. (1) At small angles of incidence, a moderate increase in lift due to additional circulation is observed. Simultaneously, a decrease in drag of the hydrofoil is caused by the momentum added. (2) At higher angles of attack, where the unforced hydrof oil would normally stall, a more pronounced lift increase and a corresponding drag reduction are observed due to separation prevention.

In the framework of the external validation of the thermal-hydraulic code ATHLET Mod 1.1 Cycle D, which has been developed by the GRS, post test analyses of two experiments were done, which were performed at the french integral test facility BETHSY. During the experiment 5.2 C the complete loss of steam generator feedwater was simulated. The depressurization of the primary circuit and high pressure injection is assumed as an emergency measure. During the experiment 9.3 the break of a steam generator U-tube is simulated. The failure of the high pressure injection is assumed. As accident management measures, the depressurization of the steam generator secondary sides and finally of the primary circuit by opening of the pressurizer valve was investigated. The results show, that the code ATHLET is able to describe the complex scenario in good accordance with the experiment. For both tests the safety related statement could be reproduced.

Au nanoclusters have been synthesized in a 500 nm thick SiO2 layer on (001)Si by 330 keV Au+ implantation of 2x1016 cm-2 and subsequent annealing at T = 1000 °C for 1h in dry oxygen. XTEM images show arround the projected ion range Rp = 100 nm a layer of crystalline Au clusters. At Rp the Au clusters have a mean size of 5 nm and a broad size distribution resembling approximately the LSW distribution of diffusion controlled Ostwald ripening. The Au nanoclusters were subsequently irradiated by 4.5 MeV Au+ ions with a fluence of (0.5...1.0)x1016 cm-2 at 190...210 °C . The high energy Au+ ions come to rest at a depth of 1 µm, i.e. in the Si substrate far below the Au nanoclusters and even below the SiO2 layer. The high energy Au+ irradiation causes a strong decrease of the mean size and of the width of the size distribution of Au nanoclusters. The observed Au nanocluster evolution under ion irradiation agrees qualitatively with recent theoretical predictions and kinitic lattice Monte-Carlo simulations.

The synthesis of spatially controlled Ge nanowires and nanoclusters by Ge+ ion implantation in oxidized V-grooves on (001) Si surfaces has been studied experimentally as well as theoretically. The V-grooves were prepared by anisotropic wet chemical etching and thermal oxydation. The SiO2-covered V-grooves were implanted with 70 keV Ge+ ions up to a fluence of 1017 cm-2. Ge accumulates within the SiO2 at the bottom of the V-groove which has been proven by analytical TEM (EDX-mapping). Theoretical studies have shown that Ge accumulation is caused by the V-groove geometry, forward sputtering, and re-deposition. During subsequent annealing the redistributed Ge forms a nanowire by precipitation, ripening and coalesence. Kinetic lattice Monte Carlo simulations of the nanowire formation process show growth instabilities and self-organization phenomena.

One-dimensional codes are frequently used for the simulation of two phase flow in the field of design, optimization and safety analysis of nuclear and chemical plants. Most of the correlations used by these codes e.g. for pressure drop or heat and mass transfer are valid only for a given flow regime. Steady flow maps are not able to predict the flow pattern in case of transient flows. Recently attempts were made to solve this problem by the introduction of additional equations for the bubble density or corresponding parameters like bubble diameter, bubble volume or interfacial area. Bubble coalescence and break-up rates, which form the source terms in these equations, are determined by local events. That means, they depend on local parameters of turbulence as well as on the local bubble size distribution.

Experimental and theoretical investigations for vertical pipes have shown, that the probability of radial residence of a bubble strongly depends on their diameter. Whereas smaller bubbles tend to move towards the wall, large bubbles are preferably found in the centre of the tube. For the water-air system at ambient conditions a change of the maximum in the radial profiles was found to occur at a bubble diameter of about 5 - 6 mm. This change is very important for the development of the flow.

A one-dimensional model is presented, which predicts the radial volume fraction profiles from a given bubble size distribution. It bases on the assumption of an equilibrium of the forces acting on a bubble perpendicularly to the flow path (non drag forces). For the prediction of the flow pattern this model could be used within an procedure together with appropriate models for local bubble coalescence and break-up.

The stability of the flow driven by the electromagnetic force of a HF levitation coil inside a drop is studied numerically using a spectral code. In the uniform or almost uniform external alternating magnetic field the first instability of the flow is three-dimensional with an azimuthal wave number of m = 3. The corresponding critical Reynolds number varies from 108 to 81 for various skin depth.

The practical application of positron annihilation spectroscopies to SiC, i.e. conventional positron lifetime and Doppler broadening measurements as well as slow positron implantation studies, will be demonstrated and discussed. It will be shown how to finally obtain materials characteristics which are of general interest, i.e. well beyond the ordinary positron annihilation parameters. As a second example, some results from the investigation of Pt layers on alumina will be presented.

Druckstöße und Kavitationsschläge in Rohrleitungen entstehen immer dann, wenn die Strömungsgeschwindigkeit schnell geändert wird. Als Folgen kann man an Rohrleitungs-systemen laute Schläge, von den Halterungen springende Leitungen bis hin zu Leitungsrissen beobachten. In dem Beitrag werden nach einer Aufstellung bekannter Maßnahmen und Diskussion deren Einsatzgrenzen zwei neue, von Fraunhofer UMSICHT und dem Forschungszentrum Rossendorf entwickelte Verfahren zur Vermeidung unerwünschter Drücke in Rohrleitungen, insbesondere von Druckstößen und Kavitationsschlägen, vorgestellt. Durch Anordnung einer Hilfsarmatur hinter der eigentlichen Absperrarmatur ist eine Schnellabsperrung der Rohrleitung ohne Kavitationsschläge möglich. Der Einsatz von Rückschlagklappen stellt hierbei eine kostengünstige Variante dar. Die Kavitationsschläge hinter der Absperrarmatur werden vollständig unterdrückt. Darüber hinaus wird ein neues passives Sicherheitssystem (ABS-Armatur) zur Verhinderung von Druckstößen vorgestellt. Hierbei wirkt der Leitungsdruck stromaufwärts der Absperrarmatur auf ein Scheibenbremssystem, das die Schließbewegung der Armatur beim Ansteigen des Leitungsdruck unterbricht. Sinkt der Druck wieder ab, so wird der Schließvorgang fortgesetzt. Durch Kombination beider neuer Verfahren können sowohl der Druckanstieg stromaufwärts der Armatur als auch die Kollabierung von Kavitationsblasen stromabwärts der Armatur sicher vermieden werden. Durch diese innovativen Maßnahmen kann der Systemdruck in der Rohrleitung niemals unerwünschte Beträge annehmen. Einzeln für sich sowohl als auch in Kombination stellen beide Verfahren passive Sicherheitssysteme für Rohrleitungen dar.

The wire-mesh sensor developed by the Forschungszentrum Rossendorf produces sequences of instantaneous gas fraction distributions in a cross section with a time resolution of 1200 frames per second and a spatial resolution of about 2-3 mm. At moderate flow velocities (up to 1-2 m/s), bubble size distributions can be obtained, since each individual bubble is mapped in several successive distributions. The method was used to study the evolution of the bubble size distribution in a vertical two-phase flow. For this purpose, the sensor was placed downstream of an air injector, the distance between air injection and sensor was varied. The bubble identification algorithm allows to select bubbles of a given range of the effective diameter and to calculate partial gas fraction profiles for this diameter range. In this way, the different behaviour of small and large bubbles in respect to the action of the lift force was observed in a mixture of small and large bubbles.

The view on the production of radiopharmaceuticals for human use in Positron Emission Tomography (PET) has been changing considerably during the last few years. PET has developed from an elitist research method only to a tool covering the research purpose as well the clinical application.
Accordingly, the radioactive substances which have been applied as radiotracers underwent a transformation to radiopharmaceuticals. This is accompanied by the transfer of the pharmaceutical legislation to PET radiopharmaceuticals. Consequently, Marketing and Manufacturing Authorisation becomes more and more important for the production of PET radiopharmaceuticals. To get the manufacturing Authorisation the manufacturer has to apply the guidelines of Good Manufacturing Practise (GMP) by consideration of monographs in pharmacopoeia.
In the lecture, the translation of the GMP regulations to the manufacturing conditions of PET radiopharmaceuticals is presented. This is illustrated by the example of the Rossendorf PET-Centre.

The Budker Institute Novosibirsk made the proposal for a high-power 14 MeV neutron source on the base of a gas dynamic trap (GDT). The GDT is an axisymmetric open trap with a high mirror ratio confining a collisional plasma. To be able to calculate the dynamics of the particle fields appearing inside the existing experimental GDT device of the Budker Institute, and later, inside the neutron source an Integrated Transport Code System (ITCS) is under development. It is to consider the full dependencies of the transport phenomena on space, time, energy and angle variables as well as the interactions between the fields. The paper briefly describes the theoretical and numerical models of the code system and illustrates its first application to calculate the particle fields inside the experimental GDT facility.

This encyclopedia article is a comprehensive overview of the actinide elements. Subdivided in the sections
- Discovery, Occurrence, and Synthesis of the Actinides,
- Radioactivity and Nuclear Reactions of Actinides,
- Applications of Actinides,
- Actinide Metals,
- Actinide Ions, and
- Actinide Compounds and Complexes
the current knowledge of the actinide elements that is generally accepted within the field is presented.

The paper presents calculations of a benchmark problem using the CFD code CFX-4 and the comparison with published experiments. The benchmark comprises the calculation of natural convection in a air-filled cavity with differentially heated walls. The experiments were performed for different orientations of the heated and cooled faces. The calculated Nusselt numbers correspond quite well to the experimental results. The steady state problem was approached by transient calculations. Not for each test case a stable final solution was found. In those cases the correspondent time averaged values were close to the experiment.

The paper presents a method for the prediction of local bubble size distributions from a given bubble size distribution for the entire cross section. The method bases on the assumption of the equilibrium of the forces acting on a bubble perpendicularly to the flow direction. Assuming a large number of bubble size classes radial distributions are calculated separately for all bubble classes. The sum of these distributions is the radial profile of the gas fraction. The results of the model are compared with experimental data for a number of gas and liquid volume flow rates. The experiments were performed at a vertical test loop (inner diameter 50 mm) in FZ-Rossendorf using a wire mesh sensor. The sensor enables the determination of void distributions in the cross section of the loop. A special evaluation procedure supplies bubble size distributions as well as local distributions of bubbles within a predefined interval of bubble sizes. There is a good agreement between experimental and calculated data. In particular the change from wall peaking to core peaking is well predicted.

Considering the specific features of high flux research reactors given by both high heat flux and high flow velocity, the ATHLET condensation model especially in subcooled flow conditions has been extended and a new correlation of critical heat flux (CHF) is implemented. To validate the extended program, the Thermal-Hydraulic Test Loop (THTL) of Oak Ridge National Laboratory (ORNL) was modeled with ATHELT and an extensive series of experiments concerning the onset of thermohydraulic flow instability (OFI) in subcooled boiling regime were calculated

Ziel:

Verschiedene Probenecid-sensitive multispezifische organische Anionentransporter sind in Leber, Niere und Dünndarm an der aktiven Ausscheidung von organischen Anionen beteiligt und werden mit der Medikamentenresistenz bei Chemotherapie in Zusammenhang gebracht. Deshalb wurde als potentieller Radiotracer auf der Basis des anionischen Stoffwechselendproduktes, Carboxymethyllysin und zum Vergleich Carboxyethyllysin und Lysin, mit 18-F markiert und in vitro und in vivo charakterisiert.
Methodik: [N-Alpha-4-[18-F]FB-N-Epsilon-Carboymethyllysin (18-FB-CML), N-Alpha-4-[18-F]FB-N-Epsilon-Carboxyethyllysin (18-FB-CEL) und N-Alpha-4-[18-F]FB-Lysin (18-FB-Lys) wurden mit [18-F]N-Succinimidyl-4-fluorbenzoat unter Trägerzusatz synthetisiert, die in vivo Stabilität mit HPLC und die Bioverteilung und -Kinetik durch Organenentnahme und PET (dynamisch, 30 Aufnahmen, 0-120 min, ECAT HR+) an Ratten charakterisiert.
Ergebnisse:
Alle drei Tracer werden renal (>20 %ID, 5 min p.i., >85 %ID 2 h p.i.) ausgeschieden. Die vorübergehende Akkumulation von 18-FB-CML und 18-FB-CEL in der Niere und der Leber wird durch Probenecid (10 min vor Tracerinjektion, 5 mg/kg Körpergewicht) zu mehr als 50 % gegenüber der Kontrollgruppe gehemmt (5 min p.i.). Unter Probenecid werden auch 2 h p.i. weniger als 50 % der Radioaktivität der Kontrolle in Leber und im Darm gefunden. 18-FB-CML und 18-FB-CEL werden nicht metabolisiert. Durch Probenecid wird in der Leber K1 (18-FB-CML) von 0.42 1/min auf 0.05 1/min verringert.
Schlussfolgerungen:
Die Stabilität von 18-FB-CML in vivo, die Möglichkeit der Hemmung der Akkumulation in Leber, Darm und Niere durch Probenecid, die Halbwertszeit von 18-F, die einfache Biokinetik und die fehlende Chiralität, lassen 18-FB-CML als PET-Tracer für Probenecid-sensitive organische Anionentransporter geeignet erscheinen.

The structure of Np(V) humic acid (HA) complexes at pH 7 was studied by EXAFS. For the first time, the influence of phenolic OH groups on the complexation of HA and Np(V) in the neutral pH range was investigated using a modified natural HA with blocked phenolic OH groups and Bio-Rex70, a cation exchange resin having carboxyl groups as proton exchanging sites. Near-infrared (NIR) spectroscopic measurements verified the formation of Np(V) humates under the applied conditions. Coordination numbers and bond distances were determined for the axial and equatorial coordination shells of neptunium. These were compared to structural parameters of Np(V) hydrates and carboxylates.

The talk starts with a short survey of the concepts for non-volatile memories designed for nanoelectronics. Among different approaches memories based on the charge storage in small semiconductor quantum dots are of particular interest, as they offer an opportunity for integration in the present CMOS-technology. Following this route the "Nanocrystal Memory" - which was first introduced by IBM in 1996 - is discussed in detail regarding its working principle and the corresponding technological challenges. One of the critical points is the fabrication of a shallow band of small semiconductors in the gate oxide of a FET very close, but well separated to the Si/SiO2-interface. Different deposition and ion beam techniques have been successfully applied to realize small Si or Ge nanoclusters with a typical size of 2-5 nm and a density between 10E11…10E12 cm-2. One very promising technique is the ion beam synthesis of nanoclusters, which is mainly applied in the Forschungszentrum Rossendorf. Microstructural investigations have shown, that IBS enables the fabrication of delta-like nanocluster bands, which fulfill very well the requirements for a "nanocrystal" memory. Electrical investigations revealed, that cluster containing thin SiO2 films show a remarkable storage effect even at room temperature, which are characterized by the shift of flatband or threshold voltage of MOS- or FET-structures, respectively. Despite these successful results main questions are still open, so that hopes and challenges are close together.

Ziel:

Entwicklung 18-F-markierter Neurotensinderivate zur Darstellung von hochaffinen Neurotensinrezeptoren (NTR1), die in humanen duktalen Pankreaskarzinomen mit hoher Inzidenz überexprimiert werden, dagegen bei chronischer Pankreatitis oder im normalen Pankreas nicht vorkommen (1).
Methodik:
4-[18-F]Fluorbenzoyl-NT(8-13) [1], 4-[18-F]FB-ArgPsi(CH2-NH)Arg-Pro-Tyr-Ile-Leu [2] und 4-[18-F]FB-ArgPsi(CH2-NH)Arg-Pro-Tle-Leu [3] und weitere Modellpeptide wurden synthetisiert, in vitro mittels Rezeptor Autoradiographie an NTR-exprimierenden humanen Adenokarzinomen und in vivo an humanen (Adenokarzinomzellen) HT-29 und WiDr tumortragenden Mäusen charakterisiert.
Ergebnisse:
Die Tracer binden in vitro, ex vivo und in vivo an NTR1 von tumortragenden Mäusen. Alle Substanzen werden in vitro internalisiert und mobilisieren intrazellulär Ca²⁺. Die Tracer unterscheiden sich in vivo in ihrer proteolytischen Stabilität und ihren Residenzzeiten im Blut. Die moderate Tumoraufnahme begründet sich in unterschiedlicher Bindungsaffinität der Peptide zum NTR1 im proteolytischen Abbau und rezeptorunabhängiger Aufnahme der entstanden 18-F-markierten Kataboliten in Tumor und Muskel. Alle radioaktiven Spaltprodukte wurden identifiziert.

Ligand....IC₅₀± SEM (nM).........Tumor/Muskel Verhältnis (MW±SEM)
..............(humane Ca)...............................(HT-29 Tumor Maus)

...............................................Kontrolle...............NT(8-13)..........Spez..........P..
.......................................................................(5mg/kg KG)........Bindung
NT..........0.86±0.10 (6)........... ......-..........................-...................-.................-
1............0.42±0.05 (6)..........7,27±0,45 (5)........6,89±0,19 (4).........0,38........>0.01
2............0.91±0.20 (6)..........4,68±1,28 (4)........2,12±0,97 (4).........2.56........<0.01
3..............4.1±0.60 (6)..........2,63±0,83 (5)........1,25±0,23 (5).........1.38........<0.005

Schlussfolgerungen:

Es wird ein Schema des Abbaus der 18-F-markierten Peptide vorgeschlagen. Die untersuchten Tracer dienen als Leitsubstanzen für die Entwicklung neuer 18-F-markierter Peptidderivate mit höherer proteolytischen Stabilität bei Erhaltung der Bindungsaffinität zum humanen NTR1 für PET von Pankreastumoren.
(1) Reubi et al., Gut 1998;42:, 546-50

Ziel:

Entwicklung einer schnellen Untersuchungsmethode zur Identifizierung und Quantifizierung von radioaktiv markierten Peptiden am Beispiel des Neurotensins (NT). Neurotensinrezeptoren (NTR1) werden in humanen duktalen Pankreaskarzinomen mit hoher Inzidenz überexprimiert. ¹⁸F-markierten NT-Derivate sollen als Tracer zur hochaffinen Darstellung von NTR1 mittels PET eingesetzt werden.

Methodik:

Zur Ermittlung der in vitro Stabilität wurden 4-[¹⁸F]FB-NT(8-13) (1), 4-[¹⁸F]FB-[Arg⁸Psi(CH₂-NH)Arg⁹]-NT(8-13) (2) und 4-[¹⁸F]FB-[Arg⁸Psi(CH₂-NH)Arg⁹]-NT(8-13) (3) in Rattenblut bzw. -plasmsa bei 37°C über 8 Stunden inkubiert. Die in vivo Untersuchungen wurden an Wistar-Ratten durchgeführt, denen nach Injektion der jeweiligen Verbindung (spezifische Aktivität 5-15 GBq/mmol) über einen Zeitraum von 2 Stunden in regelmäßigen Abständen aterielles Blut entnommen wurde. Die erhaltenen Proben wurden aufgearbeitet und die vorhandenen Abbauprodukte mittels RP-HPLC getrennt. Zur Identifizierung der Katabolite wurde das Eluat fraktioniert und die Fraktionen massenspektrometrisch untersucht.

Ergebnisse:

Es wurden signifikante Unterschiede in der Stabilität der verwendeten Verbindungen erhalten. In vitro konnte ein proteolytischer Abbau nur für (1) und (2) nachgewiesen werden. Dagegen war (3) unter den gewählten Bedingungen stabil. In vivo wurden deutliche Unterschiede bei den Residenzzeiten der Verbindungen beobachtet. (1) und (2) waren bereits 5 min p.i. nicht mehr nachweisbar. Dagegen wurden für (3) 24 min p.i. noch 50 % der Ausgangsverbindung beobachtet. Als Abbauprodukte der Verbindung (1) wurden sowohl in vitro als auch in vivo 4-[¹⁸F]FB-Arg-Arg und 4-[¹⁸F]FB-Arg ermittelt. Die Katabolite von (2) sind dagegen 4-¹⁸F]FB-[Arg⁸Psi(CH₂-NH)Arg⁹]-Pro-Tyr und 4-^[18F]FB-[Arg⁸Psi(CH₂-NH)Arg⁹]-Pro. Bei (3) wurde nur 4-[¹⁸F]FB-[Arg⁸Psi(CH₂-NH)Arg⁹]-Pro als Abbauprodukt nachgewiesen.

Schlußfolgerungen:
Mit der verwendeten Untersuchungsmethode konnten die Katabolite der untersuchten Neurotensinderivate getrennt werden. Durch die Identifizierung und Quantifizierung der Abbauprodukte wurden wichtige Informationen über die protolytischer Stabilität der Peptidbindungen in den einzelnen Verbindungen erhalten, die beim Design neuer ¹⁸F-markierter Neurotensinderivate mit höherer protolytischer Stabilität von entscheidender Bedeutung sind.

Ziel:

Intraluminale Betabestrahlung nach Ballonangioplastie führt zu einer Erniedrigung der neointimalen Proliferation. Eine erfolgversprechende Variante stellt der Einsatz radioaktiv markierter Stents dar (1,2). In der Studie wird die technische Durchführbarkeit der ^186/188Re-Markierung vaskulärer Stents und deren biologischer Effekt zur Inhibition der neointimalen Proliferation im Tiermodell getestet.

Methodik:

Palmaz Stents werden in einem "kitlike"-Verfahren mit ^186/188Re markiert und die Markierungsbedingungen, die Stentoberfläche, die Aktivitätsverteilung, die Thrombogenität sowie die in-vitro Stabilität untersucht. Die markierten Stents und Kontroll Stents werden nach Fütterung einer 0.5%igen Cholesterindiät und Ballonangioplastie in die infrarenalen Aorta von Neuseeland-Kaninchen implantiert. Es erfolgten szintigraphi-sche Messungen zu unterschiedlichen Zeiten und nach 6 Wochen wurden die Gefäße immunhistologisch untersucht.

Ergebnisse:

In Abhängigkeit von der Markierungszeit und der vorgelegten Aktivität gelingt es, definierte Aktivitätsmengen stabil und reproduzierbar auf die Stentoberfläche zu fixieren. In-vitro Untersuchungen in isotonischer Kochsalzlösung und Humanblut beweisen, dass nach 72 Std. Inkubation bei 37°C >95 % der abgeschiedenen ^186/188Re Aktivität am Stent gebunden bleiben. Thrombogenitätsuntersuchungen an markierten Stents ergaben keine Veränderungen im Vergleich zu den unbehandelten Vergleichs-stents. Die Implantation der Stents war bei allen Tieren erfolgreich, nach 14 Tagen verblieben mehr als 90 % des aufgebrachten Rheniums auf der Stentoberläche. Die Neointimafläche ließ sich von 2,2±0,2 mm bei den Kontrollstents auf 0 mm bei den markierten Stents reduzieren.

Schlußfolgerungen:

Es ist gelungen, Palmaz Stents reproduzierbar mit ¹⁸⁶Re und ¹⁸⁸Re zu markieren, wobei die aufgebrachte Aktivität in einem weiten Bereich variiert werden kann. Es wird eine hohe in-vitro und auch in-vivo-Stabilität erreicht, die Stents sind nicht trombogen. Innerhalb von 6 Wochen ließ sich die neointimale Proliferation komplett unterbinden.

1) Fishell et al., Circulation 1994; 90: 2956-2963
(2) Waksman et al., Circulation 1998; 98: I-651:3721

Ein zweiphasiges, aus einer gashaltigen Flüssigkeit bestehendes Medium wird in einer Axialpumpe von einem propellerartigen Laufrad senkrecht zur Drehachse die ses Laufrades transportiert. Die Wechselwirkung zwischen der Gasphase und dem Laufrad soll unter Verwendung von Gamma-Strahlung mittels Tomographie unter sucht werden. Dabei ist für die Rekonstruktion des Objektbildes das Prinzip der so genannten gefilterten Rückprojektion vorgesehen. Die methodischen Grundlagen für die Nutzung dieses Prinzips unter den vorgesehenen geometrischen und meßtech nischen Bedingungen sind Gegenstand dieser Arbeit.

Ion beam synthesis has been applied to fabricate semiconductor (Si, Ge) nanoclusters in thin gate SiO2 films for non-volatile memory applications. The cluster size (2-3 nm), the cluster density (>5x10E11 cm-2) and the short distance to the Si/SiO2 fulfill main requirements for a cluster related memory cell. The charge storage have been clearly established at MOS and transistor structures by the shift of the flatband or threshold voltage, respectively. Typical programming windows are in the order of 1-2 V and the endurance is > 10E6 w/e-cycles. Differences of Si- and Ge-cluster containing SiO2 films with respect to the retention behaviour are finally discussed.

Cosmic magnetic fields, including the magnetic field of the Earth, are produced by the homogeneous dynamo effect in moving electrically conducting fluids. We sketch the history of the underlying theory and comment on previous attempts to realize homogeneous dynamos in laboratory. For the main part, we report on two series of experiments carried out at the Riga dynamo facility. In November 1999 a slowly growing magnetic field eigenmode was observed for the first time in a liquid metal experiment. In July 2000, the magnetic field saturation regime was studied and a number of interesting back-reaction effects were observed. A preliminary interpretation of the measured data is also presented.

^99mTc is the most widely used radionuclide for nuclear medicine diagnostics. Efforts are made to design this unphysiological element for targeting specifically organs and cells. In this respect, lipophilic properties are of importance. We studied lipophilicity on a series of "3+1" mixed ligand oxoTc and -Re complexes with an [S-(CH₂)₂-E-(CH₂)₂-S] chelate unit [E = O, S, N-Me, N-Et] and a thiol ligand with various residues [alkyl, aryl; (CH₂)₂-NMe₂, -NEt₂,-NBu₂, -piperidinyl, -morpholinyl].
The lipophilicity/pH profiles were determined by RP-HPLC. A Perkin-Elmer HPLC Model 1022 equipped with a UV/VIS detector (254 nm) and a PRP-1 column (Hamilton, 250 x 4.1 mm, 10mm) was employed [mobile phase: isocratic eluent acetonitrile / buffer (volume ratio 3:1; pH range: 1.5 - 11); flow rate: 1.5 ml/min].
The lipophilicity determination is based on the linear relationship between the chromato-graphic retention (log k') and log D/P and results in D_HPLC/P_HPLC values. Aniline, benzene, and brombenzene were used as internal standards. The pK_a values were estimated from the turning point of sigmoidal curves and were corrected by using a calibration curve of amine standards since the measurements are performed in organic/aqueous solutions.
For amine group containing complexes (R²), that are used as models of neuroreceptor affine tracers, the influence of lipophilicity and/or pK_a on brain uptake was studied. High brain uptake relates with low pK_a, so that the highest uptake was found for morpholino-bearing complexes (0.9-2.0 % injected dose per rat brain, <5 min p.i.; pK_a 7.1-7.6). The log PHPLC values for Tc complexes are higher than for the corresponding Re complexes.

The Budker Institute of Nuclear Physics Novosibirsk proposed a highly intense 14 MeV neutron source on the base of a gas dynamic trap (GDT). The GDT is an axisymmetric mirror plasma device. In case of the complete effectiveness at the necessary parameters this type of neutron source promises several advantages in comparison to other proposals. Its actual disadvantage is the incomplete data basis which does not yet allow a reliable interpolation of its feasibility. To close this gap is the goal of the experimental and computational research presently being under way. Here the Monte Carlo codes TUBE for the hydrogen gas and MCFIT for the fast ions which have been developed by Forschungszentrum Rossendorf in collaboration with the Budker Institute take an important part. The paper shortly describes the MCFIT code, compares some numerical with measured results and draws certain conclusions.

Technetium(I) thioether carbonyl complexes and their reaction products with histidine were prepared and characterized by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy , various chromatographic and electrophoretic methods and electrospray mass spectrometry. Their behaviour in aqueous solutions was studied on the carrier-added (99Tc) and the no-carrier-added (99mTc) levels. HPLC and electrophoretic studies show the identity of reaction products at both concentration levels. Technetium(I) carbonyl complexes containing a bidentate dithioether ligand, [Tc(CO)3Cl(S-S)], as well as a tridentate carboxylato thioether ligand, [Tc(CO)3(S-S-O)], undergo a ligand exchange reaction with histidine and form the complex [Tc(CO)3His]. EXAFS measurements were performed to estimate structural parameters of the dissolved technetium(I) carbonyl complexes and their reaction products after the challenge experiments. The calculated bond lengths and coordination numbers are in accordance with the expected values and confirm the ligand exchange reactions.

The Budker Institute Novosibirsk made a proposal for a highly intense neutron source on the base of a gas dynamic trap. It is mainly intended for fusion material irradiation. The gas dynamic trap is an axisymmetric open system with a high mirror ratio for the confinement of a collision dominated plasma and a high-energetic ion component which is fed by an oblique neutral beam injection. In addition to research at the experimental facility of the Budker Institute an Integrated Transport Code System is under development in collaboration with the Forschungszentrum Rossendorf. It is to calculate the relevant physical effects connected with the target plasma, fast ions, neutral gas and the neutrons appearing inside the central cell of the device. The paper briefly describes the functions of the main modules and reports on the first exercise devoted to the planned upgrade of the facility.

Am Institut für Sicherheitsforschung (FWS) des Forschungszentrums Rossendorf (FZR) e.V. wird die Mehrzweckthermohydraulikversuchsanlage TOPFLOW (Transient Two Phase Flow Test Facility) zur Untersuchung stationärer und transienter Phänomene in Zweiphasenströmungen sowie zur Entwicklung und Validierung der in Computational Fluiddynamic (CFD) Codes enthaltenen Modelle aufgebaut. Die Versuchsanlage soll im Rahmen des Kompetenzerhaltungsprogramms Kerntechnik von dem Kompetenzzentrum Sachsen bestehend aus der Technischen Universität Dresden, der Hochschule für Technik, Wirtschaft und Soziales Zittau/Görlitz (FH) sowie dem Forschungszentrum Rossendorf e.V. betrieben werden.

We investigate the reaction pp to da₀ ⁺ at COSY and SIS energies together with accompanying background reactions and inclusive particle yields. The a₀ ⁺ is considered as a usual quark model state with two decay channels a₀ ⁺ to K⁺K⁰ and a₀ ⁺ to pi⁺ eta. Cross sections for a₀ ⁺ production as well as for the corresponding nonresonant channels pp to dK⁺K⁰ and pp to dpi⁺eta are compared. Especially in case of the final channel dpi⁺eta high statistics measurements are necessary to extract the a₀ ⁺ signal from the nonresonant background.

Structural properties of sputtered multilayers with different Co-, Cu- and NeFe- sequences of about 2nm individual layer thickness were investigated by means of synchrotron radiation techniques. Correlations between the layer combination and structural parameters such as layer thickness and rms interface roughness derived from specular scans were obtained, whereas the lateral characteristics of the interface morphology investigated by diffuse scattering were found to be similar for all multilayers. Wide angle diffraction measurements yielded lattice plane information, e.g. size-strain effects due to profile broadening and predominating <111> fibre textures.

In nuclei in the mass region of $A \approx 70 - 90$ a variety of phenomena
is observed which are based on single-particle and collective motion of the
nucleons. We discuss the properties of Br and Rb isotopes with neutron numbers
of 38 - 48. In light Br isotopes ($N$ = 37, 38) rotational bands have been
observed up to spins of 65/2 and rotational frequencies of 1.8 MeV. Both
features can be described in terms of the cranked Nilsson-Strutinsky formalism.
In Rb nuclei with $N$ = 45, 47 we found regular magnetic dipole bands
evolving at high spin whereas the low-spin structure of those less deformed
nuclei is irregular. These magnetic dipole bands represent magnetic rotation,
a new rotational mode predicted by the tilted-axis cranking model.
In nuclei at $N$ = 48 we found small collectivity in low-spin states and
multiplets based on multi-particle excitations at high spin. These properties
are interpreted in terms of the shell-model.

Assuming the hypothetical scenario of a severe accident with subsequent core meltdown and formation of a melt pool in the reactor pressure vessel (RPV) lower plenum of a Light Water Reactor (LWR) leads to the question about the behaviour of the RPV. One accident management strategy could be to stabilize the in-vessel debris configuration in the RPV as one major barrier against uncontrolled release of heat and radio nuclides.
To get an improved understanding and knowledge of the melt pool convection and the vessel creep and possible failure processes and modes occurring during the late phase of a core melt down accident the FOREVER-experiments (Failure Of REactor VEssel Retention) are currently underway at the Division of Nuclear Power Safety of the Royal Institute of Technology Stockholm (Sehgal, 1999). These experiments are simulating the behaviour of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurization scenario. The geometrical scale of the experiments is 1:10 compared to a common LWR.
During the first series of experiments the creep behaviour (FOREVER-C) of the vessel under the thermal attack of the melt pool and varying internal pressure loads is investigated. It is intended to enforce the creep process until vessel failure.
Due to the multi axial creep deformation of the vessel with a non-uniform temperature field these experiments are on the one hand an excellent source of data to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used to optimize the experimental procedure and can help to make on-site decisions during the experiment.
Therefore an axisymmetric Finite Element (FE) model is developed based on the multi-purpose code ANSYS/Multiphysics®. Using the Computational Fluid Dynamics (CFD) module the temperature field within the melt pool and within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a creep model which takes into account large temperature, stress and strain variations.

We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca2UO2(CO3)3(aq.), in uranium mining related waters /1/. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with Na2EDTA.
Slope analysis of the log (fluorescence intensity) versus log [Ca2+] with both methods have shown that two calcium ions are bound to form the complex Ca2UO2(CO3)3(aq.). The formation constants determined from the two independent methods are: i) log ßo213 = 25.26 ± 0.71 and ii) log ßo213 = 25.57 ± 0.37.
A bathochrome shift of 0.35 nm between the UO2(CO3)34- complex and the Ca2UO2(CO3)3(aq.) complex was observed in the UV-vis absorption spectrum and in the laser-induced photoacoustic spectrum (LIPAS), giving additional proof for the formation of the calcium uranyl carbonate complex.
EXAFS spectra at the LII and LIII - edges of uranium in uranyl carbonate solutions with and without calcium did not differ significantly. A somewhat better fit to the EXAFS of the Ca2UO2(CO3)3(aq.) complex was obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca2UO2(CO3)3(aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid.
This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.

We studied the complexation of neptunium(IV) with various natural and synthetic humic and fulvic acids at pH 1 using X-ray absorption fine structure (XAFS) spectroscopy to observe the local structure around the neptunium ion. The results were compared to the interaction of neptunium(IV) with Bio-Rex70, a cation exchange resin having solely carboxylic groups. For both neptunium humate complexes and neptunium Bio-Rex70 complexes, 11 oxygen atoms were found at a mean distance of 2.36 Å. This verified that the carboxylic groups of humic substances are responsible for binding neptunium(IV) in the acidic pH range. The humic acid carboxylate groups are predominantly monodentately coordinated to neptunium(IV) ions.

Starting from the tripodal ligand 2,2',2"-nitrilotris(ethanethiol) (NS₃) and isocyanides (CNR) as co-ligands neutral mixed-ligand technetium(III) complexes of the general formulation [Tc(NS₃)(CNR)] have been synthesized and characterized. The ⁹⁹Tc complexes can be obtained by a two-step reduction/substitution procedure starting from [TcO₄]^- via the phosphine-containing precursor complex [Tc(NS₃)(PMe₂Ph)]. As shown by X-ray structural analyses the complexes adopt a nearly ideal trigonal-bipyramidal geometry with the trigonal plane formed by the three thiolate sulfurs of the tripodal ligand. The central nitrogen atom of the chelate ligand and the monodendate isocyanides occupy the apical positions.
The no-carrier-added preparation of the corresponding ^99mTc complexes was performed by a one-step procedure starting from ^99m[TcO₄]^- with stannous chloride as reducing agent.
Biodistribution studies in the rat demonstrated for the nonpolar, lipophilic compounds a significant initial brain uptake. In vitro challenge experiments with glutathione clearly indicated that no transchelation reaction occurs. Furthermore, there were no indications for reoxidation of Tc(III) to Tc(V) species or pertechnetate. We propose this type of complexes as a useful tool in designing of lipophilic ^99mTc or ¹⁸⁶Re/¹⁸⁸Re radiopharmaceuticals.

A theoretical investigation is carried out of the temperature and hydrogen concentration as a function of space in an aluminum workpiece during laser beam welding. The driving force for hydrogen transport is thermal diffusion, where a diffusion current is brought about by a temperature gradient. The sign of the respective transport coefficient is negative for H in Al, which implies that hydrogen will accumulate in the heated regions. Analytical solutions are obtained for the temperature and concentration fields which comprise convective and conductive heat transfer, and hydrogen transport by convection, diffusion and thermal diffusion. The spatial characteristics are discussed in detail using various approximations for the upstream and the downstream region as well as the region close to the keyhole.

PURPOSE:

To check the influence of structural characteristics on their permeation through the blood-Brain barrier (BBB), a set of radioactive [^99mTc]chelates bearing amine groups was synthesized and tested in vitro as well as in vivo.

METHODS:

Compounds with different log P and pK_a values were obtained by complex forming reactions of [^99mTc]pertechnetate with varying substituents. Transport was studied in rats and mice, as well as in an ECV304 cell culture model.

RESULTS:

In vitro higher permeation was found for compounds with electron attracting substituents in beta-position to the amine group (pK_a values 7.4 to 8.3) than for those with more basic amine groups (pK_a values > 8.9) even for similar logD_{ph 7.4}. In vivo brain uptake between 0.8 and 4.8% of the injected dose (ID) per organ was found for the former, whereas < 0.4% ID were present for the latter.

CONCLUSIONS:

Three structurally diverse classes of [^99mTc]chelates showed distinct patterns with regard to brain uptake in vivo and BBB permeability in vitro which could not be predicted by their lipophilicity alone. The close correlation between the data from rats and mice and those obtained with cell cultures render the ECV304 cells an attractive model for the screening of new compounds.

The evolution of strongly interacting matter during the cosmological confimement transition is reviewed. Despite of many proposed relics non specific signal from the rearrangement of quarks and gluons into hadrons has been identified by observations. In contrast to this, several observables in heavy-ion collisions at CERN-SPS energies point to the creation of a matter state near or slightly above deconfinement. We focus here on the analysis of dileptons and direct photons. Similarities and differences of the Big Bang and the Little Bang confinement dynamics are elaborated.

Tc(I) thioether tricarbonyl complexes were prepared and characterised by chromatographic and spectrometric methods. The complexes undergo various ligand exchange reactions in aqueous solutions. In Tc(I) dithioether tricarbonyl complexes of the formula [Tc(CO)₃Cl(S-S)] (S-S = bidentate dithioether ligand) chlorine is substituted by water in aqueous solution. Moreover, we found that Tc(I) tricarbonyl complexes containing a bidentate dithioether ligand, [Tc(CO)₃Cl(S-S)], as well as a tridentate carboxylato dithioether ligand, [Tc(CO)₃Cl(S-S-O)], react with histidine and form the complex [Tc(CO)₃His]. EXAFS measurements were performed to estimate structural parameters of the dissolved Tc(I) tricarbonyl complexes and their substitution products with water and histidine.

Gesamtziel des Vorhabens ist es, den Einfluß der Strömungen in der Schmelze auf die Phasengrenze flüssig-fest im Erstarrungsprozeß zu untersuchen und darüber hinaus eine gezielte Beeinflussung der Konvektion durch geeignete, für den jeweiligen Zweck maßgeschneiderte Magnetfelder vorzunehmen. Die Vielfalt der alternierenden (Strömungsantrieb) und statischen (Strömungsunterdrückung) Magnetfelder erlaubt eine Beeinflussung metallischer Schmelzen in sehr weiten Bereichen.
Umfangreiche Erfahrungen liegen z. B. für die Wirkung rotierender Magnetfelder auf die Strömung vor. Der sich daraus ergebende Einfluß auf das resultierende Erstarrungsgefüge bei reinen Metallen oder binären Legierungen ist teilweise aus der Literatur bzw. eigenen Arbeiten bekannt. Langjährige Vorarbeiten für die Schmelzkontrolle bei Halbleiter-Kristallzüchtungsprozessen bis hin zur industriellen Nutzung derart optimierter Magnetsysteme liegen ebenfalls vor.
Im Projekt sollen systematische Untersuchungen zur Beeinflussung der Erstarrung von Nd-Fe-B-Schmelzen über die Kontrolle der Schmelzströmungen durchgeführt werden. Dazu werden die am IFW Dresden vorhandenen Techniken der Floating-Zone-Züchtung und der elektromagnetischen Levitation eingesetzt. Am Beispiel der Floating-Zone-Züchtung wird demonstriert, wie auf der Basis einer theoretisch-numerischen Analyse der prozeßbedingt im System vorhanden Strömungsarten (Marangoni, HF-Heizung, Auftrieb) eine optimierte und flexible Strömungskontrolle über ein zusätzliches Magnetsystem möglich ist.
Für die elektromagnetische Levitation werden Ergebnisse zur Strömung im Tropfen präsentiert, die sowohl für das Verständnis der Erstarrungsvorgänge als auch die Ermittlung thermophysikalischer Parameter aus derart prozessierten Proben wichtig sind.

We discuss the configurations in which singly and doubly quantized vortex lines coexist in a rotating superfluid. General principles of energy minimization lead to the conclusion that in equilibrium the two vortex species segregate within a cylindrical vortex cluster in two coaxial domains where the singly quantized lines are in the outer annular region. This is confirmed with simulation calculations on descrete vortex lines. Experimentally the coexistence can be studied in rotating superfluid 3He-A. With cw NMR techniques we find the radial distrubution of the two vortex species to depend on how the cluster is prepared: (i) By cooling through Tc in rotation, coexistence in the minimum energy configuration is confirmed. (ii) A disordered agglomerate is formed of one starts with an equilibrium cluster of single quantum vortex lines and adds to it sequentially double quantum lines, by increasing the rotation velocity in the superfluid state. This proves that the energy barriers, which seperate different cluster configurations, are too high for metastabilities to anneal.

Results of experimental investigations of thin films and multilayers of binary systems deposited by PLD at room temperature are presented. Poles of sputtering, implantation, rapid quenching, and solid state diffusion in microstructure formation of thin metal an alloy films synthesized prom pulsed erosion jets are considered. Examples of non-conventional microstructure (amorphization, pseudomorphism, superstructures) formation are given.

Reflektometrieuntersuchung von Fe-Cr-Schichten, die durch Laserablation (PLD) auf einem oxidierten Si(100)-Wafer aufgebracht wurden, mittels Synchrotronstrahlung unter Ausnutzung der anomalen Streuung im Bereich der Fe- bzw.Cr-Absorptionskante. Bestimmung der Interfacebreiten (Sigma rms Rauigkeit) und der Rauigkeitsstruktur (laterale Korrelationslänge und Rauigkeitsexponent) der Fe/Cr-bzw.Cr/Fe-Doppelschichten durch Simulationsrechnungen mit dem Programmcode REFS ( Bede Scientific).

An Eisendisilizid-Einkristallen wurden winkelabhängige Mößbaueruntersuchungen durchgeführt.

Eisen und Magnesium sind über den gesamten Konzentrationsbereich nicht miteinander mischbar. Durch Ionenimplantation ist es jedoch möglich, dünne Legierungsschichten mit beiden Metallen herzustellen.
Bei der vorliegenden Untersuchung wurden Eisenionen in Magnesium implantiert (Energie 200 keV, Dosis bis 1018 /cm²). Die Charakterisierung der so hergestellten Schichten erfolgte mittels Augerelektronen-Spektroskopie, Konversionselektronen-Mössbauerspektroskopie sowie Röntgendiffraktion. Es zeigte sich, dass durch die Implantation Eisenkonzentrationen von über 90 Atom-% erreicht werden konnten. Bei solchen hohen Konzentrationen waren die Schichten magnetisch, es entstand eine Schicht aus a-Eisen, in das Magnesium eingelagert war. Bei niedrigen Eisenkonzentrationen wurde das Eisen auf zwei unterschiedlichen Positionen im Magnesium eingelagert. Temperte man die Schichten bei Temperaturen bis 400 °C, schied sich das Eisen erwartungsgemäss aus

Mittels DCEMS wurde eine tiefenselektive Phasenanalyse der Fe-Disilizid-Bildung in Fe-ionenimplantiertem Si durchgeführt.

Silicon was implanted with high doses of nitrogen and carbon Shallow by PIII.

Reciprocal Space Mapping was performed on Silicon Implanted with Nitrogen and Carbon by
PIII

Porous silicon was implanted with N by PIII.

In some PIII devices the sputtering of the surface under treatment is a problem to overcome.

200 keV Fe ions were implanted into Si(111) at 350 °C .