Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

kein Abstract

In silicon-nanocluster (Si-NC) memories, Si-NC embedded in the gate oxide of a MOSFET are used to store and release electrons thereby modifying the threshold of a transistor. This article describes the formation of its core functional structure, the Si-NC MOS memory capacitor, by annealing a SiO2/SiOX (x < 2) stack, deposited onto a thin direct tunneling oxide on silicon by a sputtering method. To achieve a high density of isolated Si-NC, both, the initial silicon excess in the SiOX layer and the thermal annealing treatment must be optimized. Optimum conditions are expected just at the end of the nucleation stage of the NC ensemble. Therefore the effect of various rapid thermal anneals (RTA) on SiOX/Si structures with different silicon excess x was investigated focusing on two optical methods: infrared absorption and photoluminescence (PL). The rate of nucleation and phase separation was found to depend strongly on both, silicon excess and annealing temperature. The characteristic size dependence of Si-NC PL was used to differentiate annealing regimes yielding NC ensembles being 'frozen' in the process of nucleation or in their growth/ripening phase respectively. Additionally, Si-NC MOS memory capacitors were prepared and characterized using both, optical and electrical tests. The devices prepared under optimized conditions yield a high flat-band shift and good charge retention characteristics.

High-spin states in the N = Z nucleus ⁷²Kr were populated using
the ⁴⁰Ca(³⁶Ar,2p2n) reaction at a beam energy of 145 MeV.
The yrast band has been observed up to a tentative spin of 20 h.
Nonyrast rotational structures have also been observed for the first time.
The alignment of g _9/2 protons and neutrons in the yrast band is observed to
be significantly delayed relative to the heavier even-even Kr isotopes.
Exact deformed cranked shell model calculations suggest that this could be due to the combined effect
of isovector (T = 1) and isoscalar (T = 0) neutron-proton pairing correlations.

Tritium depth profiles in carbon have been determined at the Rossendorf AMS facilities during the past seven years. The samples have been cut from tiles of the inner walls of the fusion reactors ASDEX-upgrade Garching, JET Culham and TFTR Princeton. The high tritium content required a dedicated AMS facility to prevent any contamination of the versatile 3 MV Tandetron. It is based on an SF6-insulated 100 kV tandem accelerator equipped with a DLC stripper foil of about 1µg/cm². Depth profiles of deuterium and other light elements can also be measured in SIMS mode or AMS mode depending on concentrations.

We measured photoelectron yield, light output, decay times of the light pulses, cerium concentration, energy resolution and time resolution of LSO:Ce manufactured by different laboratories and LGSO:Ce. The LSO samples show excellent scintillation properties: high light output, close to 30,000 ph/MeV and good energy resolution of 7.3% FWHM for ¹³⁷Cs gamma-source full energy peak. Time resolution measured in geometry fulfilling the PET scanners requirements is equal to 450 ps.
We also present results from the measurements with LGSO:Ce by Hitachi Chemical Co., which is of similar chemical composition to LSO. LGSO, at present stage of development, shows about 20% lower light output than LSO and energy resolution of 12.4% FWHM for 662 keV gamma-rays.
LSO crystals used in our studies posses similar in scintillation properties, although we suppose that the details of the productions method are different due to the differences in Ce concentration. LGSO is a new and very promising scintillator due to lower background radiation in comparison to LSO, but it features worse energy resolution and smaller number of photoelectrons.

The double differential dilepton spectrum dN/ (dM² dM _^ ²)
at fixed transverse mass M _^ allows a direct access to the vector meson spectral
functions. Within a fireball model the sensitivity of dN/ (dM²dM _^ ²) against variations of both the in-medium properties of mesons and the dynamics of the fireball is investigated. In contrast to the integrated invariant-mass spectrum dN/dM², in the spectrum dN/dM²dM _^ ² with fixed M _^ the ω signal is clearly seen as bump riding on the ρ background even in case of strong in-medium modifications.

High-spin states in the doubly odd N=75 nuclei Pm-136 and Eu-138 were populated following the Sn-116(Mg-24,p3n) and Cd-106(Cl-35,2pn) reactions, respectively. A new ΔI = 1 band is reported in Eu-138 and new data are presented for the recently reported band in Pm-136. Polarization and angular correlation measurements have been performed to establish the relative spin and parity assignments for these bands. Both bands have been assigned the same πh _11/2νh _11/2 structure as the yrast band and are suggested as candidates for chiral twin bands.

The chiral-twin candidate bands recently observed in ¹³⁶Pm have been extended to high spins [I = (21)] using the Gammasphere γ-ray spectrometer and the Microball charged-particle detector array.
A more-detailed spectroscopy of the bands was possible, where the rotational alignments and B(M1)/B(E2) ratios confirm that both sequences have the πh _11/2νh _11/2 configuration. Particle-rotor calculations of intraband and interband transition
strength ratios of the chiral-twin bands are compared with experimental values for the first time. Good agreement was found between the predicted transition strength ratios and the experimental values, thus supporting the possible chiral nature of the configuration in πh _11/2νh _11/2
¹³⁶Pm.

The discrete symmetries of the rotating mean field lead to a variety of rotation
al bands with different sequences of spin and parity. We focus on the
breaking of chiral symmetry in rotating triaxial nuclei.

The conduction electrons in clusters of simple metal atoms are approximatively i
ndependent and free. Nucleons in nuclei also behave as delocalized
and independent fermions. This generic behavior generates analogies between
metal clusters and nuclei, such as the shell structure, the shapes,
and the dipole vibration mode. However, there are also major differences
that arise from the presence of ions in metal clusters. Fission of nuclei and
clusters, and particle emission from them, reveal these differences.

The concept of spontaneous symmetry breaking is applied to the rotating mean field of nuclei. The description is based on the tilted-axis cranking model, which takes into account that the rotational axis can take any orientation with respect to the deformed density distribution. The appearance of rotational bands in nuclei is analyzed, focusing on weakly deformed nuclei at high angular moment um. The quantization of the angular momentum of the valence nucleons leads to new phenomena. Magnetic rotation represents the quantized rotation of the anisotropic current distribution in a near pherical nucleus. The restricted amount of angular momentum of the valence particles causes band termination. The discrete symmetries of the mean-field Hamiltonian provide a classification scheme of rotational bands. New symmetries result from the combination of the spatial symmetries of the density distribution with the vector of the angular momentum. The author discusses in detail which symmetries appear for a reflection-symmetric density distribution and how they show up in the properties of the rotational bands. In particular, the consequences of rotation about a nonprincipal axis and of breaking the chiral symmetry are analyzed. Also discussed are which symmetries and band structures appear for non-reflection-symmetric mean fields. The consequences of breaking the symmetry with respect to gauge and isospin rotations are sketched. Some analogies outside nuclear physics are mentioned. The application of symmetry-restoring methods to states with large angular momentum is reviewed.

Experimental data on charged kaon phase space distributions and strangeness sidewards
flow measured with the FOPI detector at SIS/GSI are presented.
Comparisons are made with the predictions of transport models investigating the in-medium
kaon-nucleon potential.

Stoichiometric TiAl and two quasi-technical TiAl alloys were investigated in the temperature range of 800¯1000°C with regard to the halogen microalloying effect on oxidation resistance. The halogens Br, Cl, F and I were introduced into the material surface by ion implantation with different doses and energies before the thermogravimetric oxidation experiments were started. The results show that a very low "homeopathic" amount of these halogens at the oxide scale/metal interface activates a mechanism of selective Al-oxidation which changes oxidation behavior
from fast mixed titania/alumina kinetics to slow pure alumina kinetics. A model is described which explains this change in kinetics supported by quantitative data from thermodynamic calculations. The halogen microalloying effect offers a high potential for the improvement of oxidation resistance of TiAl alloys for technical applications.

The parameters of a superconducting RF gun cavity have been measured in a test cryostat of DESY. A field strength of 31.8 MV/m at the cathode has been obtained.

3C-SiC have been implanted with carbon ions at 60 keV to a dose of 3x10^17 and 1x10^18 cm^-2. All of the implantation experiments were carried out at elevated temperature in the range of 900°C-1200°C to study the phases, which are formed, when excess carbon is introduced into the SiC lattice. At 1100^C and at 1200°C small diamond grains are formed; these are embedded in the SiC and form perfectly oriented crystallites of a few nm size. Diamond is formed in SiC at 900°C as well, however, at high dose rate the impinging carbon ions can destroy the nucleated diamond grains.

no abstract delivered from author

no abstract delivered from author

no abstract delivered from author

no abstract delivered from author

no abstract delivered from author

ANKE is a new experimental facility for the spectroscopy of products from proton
-induced reactions on internal targets. It has recently been implemented in the accelerator ring of the cooler synchrotron COSY of the Forschungszentrum Jülich (FZ-Jülich), Germany. The device consists of three dipole magnets, various target installatio ns and dedicated detection systems. It will enable a variety of hadron-physics experiments like meson production in elementary proton-nucleon processes and studies of medium modifications in proton-nucleus interactions.

no abstract delivered from author

Formation and transformation of metastable alloys by ion irradiation are discussed on example of the systems Al-Fe, Ta(N), Ta(O), Fe-Cr. By ion beam mixing of Al-Fe multilayers with an overall composition of 60 to 85 at.% Al using 150 keV Fe ions metastable structures were formed. For 80 to 85 at% Al amorphous alloys have been observed. The formation amorphous interface regions cross-beam pulsed laser deposition (CBPLD) is demonstrated. Amorphus thin diffusion barriers of Ta were formed by ion implantation of nitrogen and oxygen. Fe-Cr thin layers with Cr concentration from 27 to 62 at.% Cr prepared by CBPLD show different metastable structures depending on the Cr content. These layers are paramagnetic at rom temperature. By ion irradiation it is possible to transform these alloys into a bcc structure with a ferromagnetion iron rich component.

no abstract delivered from author

no abstract delivered from author

Contrary to expectations to obtain a continuous series of supersaturated b.c.c. Fe-Cr solid solutions by co-deposition of both metals in cross-beam PLD, there form unusual for this materials system metastable intermetallic phases. The structure of alloys develops from a tetragonally distorted bcc at low Cr-content through a face centered orthorhombic to a partly ordered promitive orthorhombic crystal structure of the A15- like type at nearly equiatomiccomposition. It seems to be the first observation of an ordering of restrictedly soluble components under the bombardment of hyperthermal species in PLD. Intriguing fact is that these metastable phases are initially paramagnetic (PM) at room temperature but become ferromagnetic (FM)after annealing in a temperature range 400-500 C ore under ion bombardment. The induced PM-FM transformation in the alloys is demonstrated to be useful for formation of stable lateral magnetic microstructures.

Titanium foil is employed for electron transparent windows in the electron beam dry scrubber process. The foil suffers corrosion, which limits the window life. Here, the examination of palladium-coated window, prepared by ion beam assisted deposition and plasma source ion assisted deposition (PSIAD), after service in a pilot-scale plant is reported. Most significantly, the adhesion of the coating was reduced by the flue gas. Where the coating remained adherent, corrosion was negligible. Elswhere, generalmintergranular and pitting corrosin occured. A PSIAD coating provided the best performance.

Fe/Cr-Multischichten zeigen GMR (giant magnetoresistance) Effekte, die in der Anwendungstechnik (Magnetoelektrik, Sensorik, Speichertechnologie) von besonderer Bedeutung sind. Magnetische Multischichten werden deshalb gegenwärtig vielerorts untersucht. In diesem Zusammenhang werden die Einflüsse der unterschiedlichen Verfahren der Schichtabscheidung studiert.
Durch die Reflektivitätsuntersuchungen mittels Synchrotronstrahlung können die durch MBE abgeschiedenen Einzelschichten auch im Fe/Cr-Multischichtsystem hinsichtlich Schichtdicke, Dichte, Rauhigkeit und Interface-Morphologie recht genau charakterisiert werden.

Double layers of Fe-Cr and Co-Cu, respectively, were prepared on oxidized Si substrates by pulsed laser deposition (PLD). The interfacial roughness structure was studied by synchrotron X-ray reflectivity measurements at the absorption K-edges using the contrast enhancement due to resonant scattering. The results are determined from simulations of the measured specular and diffuse scans. Whereas in Fe-Cr double layers the rms-interface width for Fe deposition on Cr (sigma_Cr = 0.70 ± 0.1 nm) is not very different from that of Cr deposition on Fe (sigma_Fe = 0.85 ± 0.1 nm), in Co-Cu double layers, in contrast, for Cu deposition on Co, the width (sigma_Co = 0.65 ± 0.1 nm) is much smaller than for Co deposition on Cu (sigma_Cu = 1.5 ± 0.15 nm). On the basis of the fractal model to describe the interface roughness morphology, from the off-specular scans the lateral roughness correlation length, xi, and the roughness exponent, h, were determined. For both types of double layers extremely high xi-values (larger than 2 µm) were found. However, the flatness is accompanied by a high short-scale roughness (jaggedness), expressed by a small h-parameter (h = 0.25 ± 0.05). Both facts were found to be characteristic for the 'as-deposited' state of such metal/metal layers prepared by PLD.

The exclusive production cross sections for ω and Φ mesons have been measured in proton-proton reactions at p_lab=3.67 GeV/c.
The observed Φ/ω cross section ratio is (3.8±0.2^+1.2 _-0.9)×10^-3.
After phase space corrections, this ratio is enhanced by about an order of magnitude relative to naive predictions based upon the Okubo-Zweig-Iizuka (OZI) rule, in comparison to an enhancement by a factor ~ 3 previously observed at higher beam momenta. The modest increase of this enhancement near the production threshold is compared to the much larger increase of the Φ/ω ratio observed in specific channels of pp annihilation experiments.
Furthermore, differential cross section results are also presented which indicate that although the Φ meson is predominantly produced from a ³P₁ proton-proton entrance channel, other partial waves contribute significantly to the production mechanism at this beam momentum.

We have studied the nonproportionality and intrinsic energy resolution of cerium doped YSO, GSO, LSO and LGSO crystals. While LSO and YSO have similar light output, GSO and LGSO have ca. 70% and 20% lower light output than LSO, respectively. YSO, a compound containing fairly light elements, was expected to have proportional light output vs. energy, like YAP:Ce. Surprisingly it has almost the same nonproportional as LSO and GSO. The nonproportionality of YSO is followed by large values of intrinsic energy resolution. The comparison of the nonproportionality of YSO-LSO and YAP-LuAP pairs indicates that high proportionality is connected with the structure of the crystal and not with the presence of light elements. To our knowledge, this is the first study of nonproportionality and intrinsic resolution for LGSO.

kein Abstract

Boron ion implantation of thermochemically polished chemical vapor deposited diamond films with multienergies ranging between 24 and 150 keV and a total dose of about 2E16 cm-2 is used to get p-type conductivity. n-type conductivity is achieved by lithium ion implantation of the diamond films with a single energy of 50 keV and a dose of 2E16 cm-2. The intrinsic areas separating the p- and n-doped regions form the active areas of the diodes into which charge carriers are simultaneously injected upon bias. Onset voltages of < 10 V are due to the low concentration (~1E14 cm-3) of nitrogen related centers in the diamond films. The current–voltage (I–V) characteristics of the p-i-n diodes manifest trap filling, Frenkel–Poole emission, thermionic emission, and space charge limited current regimes. At 300°C, currents as high as 12 mA are measured at a forward bias of 100 V. Rectification ratios of up to about four orders of magnitude are achieved. They increase with increasing width of the i-region within the measured i-region of 3–10 µm, as a result of the considerable decrease of the reverse bias current relative to the forward bias current.

The spectroscopic quadrupole moment of the high-spin, high-K five-quasiparticle isomer (K^π=[(35^-)/2], T_1/2=750(80) ns, E_i = 3349 keV) in ¹⁷⁹W has been determined using the level mixing spectroscopy method.
A value Q_s = 4.00([(+0.83) || (-1.06)])e b was derived, which corresponds to an intrinsic quadrupole moment Q₀ = 4.73([(+0.98) || (-1.25)])e b and to a quadrupole deformation β₂ = 0.185([(+0.038) || (-0.049)]).
These values differ significantly from the deduced ground-state quadrupole moments and are in disagreement with the current theoretical predictions in this mass region.

There are numerous applications for tritium (3H) as a tracer isotope in biomedicine commonly combined with the liquid scintillation counting method. The use of accelerator mass spectrometry (AMS), a rather new detection method, would enlarge and open new possibilities for tritium applications in biomedicine, especially when sample volumes are small. The tritium in the samples has to be transformed to solid form yielding high output of negative hydrogen current. The sample preparation for tritiated water is done in two steps: firstly extracting water from the biological sample and secondly, extracting hydrogen/tritium from the water and forming a chemically suitable compound for the AMS system.
In this paper a chemical procedure for the sample preparation is described. The results of the first measurements of tritiated water with known activity using AMS detection technique will also be presented.

kein Abstract

The hybrid version of tilted axis cranking has been used to study the existence of magnetic rotation in the ΔI = 1 bands of odd-A ^79,81,83,85Rb isotopes.
The bands are found to be built on prolate three quasiparticle π(g_9/2) Ä n[g_9/2(fp)¹] configuration.
The results exhibit a rapid onset and decline of magnetic rotation as we go from N = 42 to 48.
The ⁸³Rb appears to be a better case of magnetic rotation among these four Rb isotopes.

Humic Substances in Performance Assessment of Nuclear Waste Disposal: Actinide and Iodine Migration in the Far-Field

Untersuchungen über die Komplexierung und die Migration von Actiniden und nichtradioaktiven Stoffen mit Huminsäuren unter geogenen Bedingungen - Komplexierung von Huminsäuren mit Actiniden in der Oxidationsstufe IV Th, U, Np

kein Abstract

Using the Hamiltonian that consists of the separable quadrupole + pairing forces and the cranking term, we analyze the correlations associated with shape, orientation, and particle-number fluctuations in rotating nuclei. Quantum fluctuations around mean field solutions are treated in the random phase approximation (RPA), with special emphasis on the restoration of
rotational symmetry and particle number conservation. The mean field calculations have been made within the self-consistent cranking model. The effect of the RPA correlation energy for the moment of inertia is studied with the integral representation method proposed.

Untersuchungen über die Komplexierung und die Migration von Actiniden und nichtradioaktiven Stoffen mit Huminsäuren unter geogenen Bedingungen - Komplexierung von Huminsäuren mit Actiniden in der Oxidationsstufe IV Th, U, Np

Untersuchung über die Komplexierung und die Migration von Aktiniden und nichtradioaktiven Stoffen mit Huminsäuren unter geogenen Bedingungen - Komplexierung von Huminsäuren mit Aktiniden in der Oxidationsstufe IV Th, U, Np.

This work is the completion of a series of reports describing the nitrogen-fixing bacterial symbionts of sulla (Hedyzarum coronarium L., Leguminosae) and providing the grounds for their proposal as a new taxon. The introduction summarizes a large amount of previous evidence gathered on the physiology, genetics and ecology of such organisms, which have in the past been referred to provisionally as "Rhizobium hedysari". Upon adding 16S rRNA sequencing, amplified rDNA restriction analysis of the rrn operon, DNA-DNA hybridization homology and analysis of low-molecular-mass RNA species, it is concluded that the group of strains that specifically nodulate sulla consists of a coherent set of isolates that differ from previously described rhizobia to an extend that warrants the construction of the species boundary. The name Rhizobium sullae sp. nov. is proposed, with isolate IS123T (=USDA4950T = DSM 14623T) as the type strain.

Autor/Institut
Dipartimento di Biotecnologie Agrarie, Universita di Padova, Agripolis, Strada Romea16, 35020 Legnaro, Padova, Italy; Molecular Microbiology Group, Institute of Radiochemistry, Forschungszentrum Rossendorf, D-01314 Dresden, Germany; Departamento de Microbio-logia y Genetica, Universidad de Salamanca, Avda del Campo Charro s/n, 37007 Salamanca, Spain; Department of Microbiology, Michigan State University, East Lansing, MI 48824, USA; Dipartimento di Chimica e Biotecnologie Agrarie, Universita di Pisa, via del Borghetto 80, Pisa, Italy

The pollution of the environment with toxic metals is one of the most severe problems of our industrial age. Uranium mining waste piles are a subject of particular attention, because in the soils, sediments, and drainage waters of these environments significant amounts of many hazardous metals are present, such as uranium, selenium, molybdenum, arsenic, cadmium, chromium, mercury, lead, copper, nickel and zinc (Francis, 1990). In addition, significant amounts of thorium, radium, polonium and other decay products may also be present in the so-called uranium 'mill tailings' where the extraction of uranium from the ores was performed.

Even in the most heavily polluted uranium wastes, large numbers of bacteria are present (Cerda et al., 1993; Goebel & Stackebrandt, 1994; Shippers et al., 1994). Moreover, different groups of bacteria can interact in different ways with metals and radionuclides (see Chapters ????). Some of the most important mechanisms by which bacteria can biotransform and influence the mobilization and/or immobilisation of metals are listed below:

i) direct oxidation and/or reduction of metals, which affect their solubility (DiSpirito & Tuovinen, 1982; Lovley, 1993; Nelson et al., 1999; Sharma et al. 2000; Wildung et al., 2000);
ii) direct or indirect oxidation of metal sulfides and the associated solubilization of certain elements (Bosecker, 1997; Krebs & Brandl, 1997);
iii) indirect alteration of metal speciation caused by microbially-induced pH and Eh changes in the medium (Bosecker, 1997; Bacelar-Nicolau & Johnson, 1999);
iv) bioaccumulation [biosorption by cell surface polymers (DiSpirito et al., 1983; Douglas & Beveridge, 1998; Macaskie et al., 1992; Panak et al., 1999; Selenska-Pobell et al., 1999; Valentive et al., 1996) and/or uptake of metals inside the cells (Klaus et al., 1999; Marques et al., 1991; Purchase et al., 1997)];
v) bio-mineralization, including induction of metal precipitation by specific metabolic functions and the consequent generation of minerals (Brown and Beveridge, 1998; Douglas and Beveridge, 1998; Francis, 1998);
vi) release of biosorbed metals by chelation, alkylation, or decomposition (Bosecker, 1997; Francis, 1990; Francis et al., 1998).
It is clear that the bacterial activities described above strongly influence the fate and migration of toxic metals in and outside the sites where uranium mining has been performed. In addition to the living cells, significant amounts of different bacterial metabolites are present in the wastes and these also interact with the heavy metals and influence their behaviour. For these reasons, knowledge of the diversity and activity of the indigenous bacteria in the uranium waste piles is of fundamental importance for understanding the biogeochemical processes occurring in these environments and especially for modelling the migration of the heavy metals and radionuclides.

Until recently, information about bacterial diversity in uranium waste piles was limited to several studies dealing with culturable bacteria (Berthelot et al., 1997; Cerda et al., 1993; Francis et al., 1991; Goebel & Stackebrandt, 1994; Shippers et al., 1994). This, however, is not sufficient because only a few percent of natural bacterial populations can be cultured and studied in the laboratory (Chapter 2) due to our limited knowledge of the nutrient requirements and other life-necessities for most bacterial species in nature (Pace, 1997; Service, 1997; Ward et al., 1990). The development and application of molecular approaches in bacterial ecology during the last decade has revealed a tremendous prokaryotic diversity which was overlooked by traditional culture enrichment techniques (Byers et al., 1998; Chandler et al., 1997; Dojka et al., 2000; Pace, 1997; Service, 1997).

One of these approaches, 16S rDNA retrieval, has been applied to analysis of bacterial diversity in deep granitic rocks and in an aquifer around a nuclear fuel repository in Sweden (chap...

The synthesis of hydroxyl silylated thiols as monodentate ligands is described. These monodentates were used to build with Re and ^99mTc trimethyl-, triethyl- and triphenyl-silylated ‚3+1' mixed ligand complexes, using 3thiapentane-1,5-dithiol as co-ligand. The Re complexes were characterized by ¹H NMR and elemental analysis, the ^99mTc complexes were detected by radio HPLC. While the trimethyl silylated derivatives hydrolysed in aqueous media, the triethyl- and triphenyl silylated complexes have proved to be stable in neutral solutions.

Bacterial diversity was studied in several uranium mining waste piles and mill-tailings in Germany (Johanngeorgenstadt, Schlema/Alberoda, Gittersee/Coschütz) and in the USA (Shiprock, New Mexico and Gunnison, Colorado) using direct molecular approaches. Significant differences were found between bacterial communities distributed in the uranium mill-tailings and in the uranium mining waste piles. The predominant bacterial groups in the water and soil samples collected from the mill-tailings were gamma-, beta-, and delta-Proteobacteria, representatives of Cytophaga/Flavobacterium/Bacteroides (CFB) group and also Gram-positive bacteria with low G+C content. In contrary, in the uranium mining waste piles representatives of alpha-Proteobacteria and such of Holophaga/Acidobacterium division were predominant. In both environments, however, presence of related groups of gamma-Proteobacteria was demonstrated.
In parallel, the method of enrichment culturing was applied and particular indigenous bacterial strains were cultured from the uranium wastes and their interactions with U and some other metals were studied. In particular, microdiverse bacterial isolates belonging to Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, Desulfovibrio vulgaris (oxamicus), Bacillus sphaericus, B. cereus, B. thuringiensis, B. megaterium, Clostridium sp., and Pseudomonas sp. were recovered and characterized.
Vegetative cells, spores and S-layers of one uranium mining waste pile isolate, namely Bacillus sphaericus JG-A12, able to accumulate reversibly high amounts of toxic metals from drain waters of the U wastes, were used for construction of bacteria-based biological ceramics (biocers) for bioremediation. Biosorption and desorption of U and Cu by the constructed biocers were studied in model experiments and it was demonstrated that they possess very high metal binding capacity and are suitable for reversible usage. The latter demonstrates that uranium mining waste piles are a reservoir of bacteria prospective for in situ bioremediation of these environments.

kein Abstract, nur Folien

The cross section for the production of ω mesons in proton-proton collisions has been measured in a previously unexplored region of incident energies. Cross sections were extracted at 92 MeV and 173 MeV excess energy,
respectively. The angular distribution of the ω at ε=173 MeV is strongly anisotropic, demonstrating the importance of partial waves beyond pure s-wave production at this energy.

To qualify CFD codes for two-phase flows, they have to be equipped with constitutive laws describing the interaction between the gaseous and the liquid phases. In the case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. To obtain detailed experimental data, an electrode wire-mesh sensor was used, which enables the measurement of the phase distribution with a very high resolution in space and in time. Air-water flow at ambient conditions in a vertical pipe (51.2 mm inner diameter) is investigated to have well defined boundary conditions. Local bubble size distributions are calculated from the data. The measurements were done in different distances from the gas injection device. As a result the development of bubble size distributions as well as the development of the radial gas fraction profiles can be studied. It was found, that the bubble size distribution as well as local effects determine the transition from bubble flow to slug flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow to slug flow in case of stationary flow in a vertical pipe.

kein Abstract

kein Abstract

Summary. We used a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray (EDX) analysis to conduct molecular scale studies on U(VI) interaction with three recently described eco-types of A. ferrooxidans. On the basis of the information obtained by using these methods, we conclude that uranyl phosphate complexes were formed by the cells of the three eco-types studied. The uranium accumulated by A. ferrooxidans cells was located mainly within the extracellular polysaccharides and on the cell wall. We suggest that at toxic levels when uranium enters the bacterial cells A. ferrooxidans can detoxify and efflux this metal by a process in which its polyphosphate bodies are involved.

Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Numerous experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work /REM 1993/, /THF 1997/, /CHU 1999/.
For pre- and post-test calculations of Lower Head Failure experiments like OLHF or FOREVER it is necessary to model creep and plasticity processes. Therefore a Fi-nite Element Model is developed at the FZR using a numerical approach which avoids the use of a single creep law employing constants derived from the data for a limited stress and temperature range. Instead of this a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. A main task for this approach is the generation and validation of the CDB. Additionally the implementation of all relevant temperature dependent material properties has been performed. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied.
The validation of the numerical model is performed by the simulation of and com-parison with experiments. This is done in 3 levels: starting with the simulation of sin-gle uniaxial creep tests, which is considered as a 1D-problem. In the next level so called “tube-failure-experiments” are modeled: the RUPTHER-14 and the “MPA-Meppen”-experiment. These experiments are considered as 2D-problems. Finally the numerical model is applied to scaled 3D-experiments, where the lower head of a PWR is represented in its hemispherical shape, like in the FOREVER-experiments. This report deals with the 1D- and 2D-simulations.
An interesting question to be solved in this frame is the comparability of the French 16MND5 and the German 20MnMoNi55 RPV-steels, which are chemically nearly identical. Since these 2 steels show a similar behavior, it should be allowed on a lim-ited scale to transfer experimental and numerical data from one to the other.

Institutsseminar, in der Universität Leipzig ,
Institut für Biochemie; no abstract delivered from author

Bacteria in uranium waste piles are of special interest for bioremediation, because they are adapted to high concentrations of heavy metals in these environments. One bacterial isolate from a uranium mining waste pile "Haberland" near the town of Johanngeorgenstadt in Saxony, Germany, Bacillus sphaericus JG-A 12, possesses a surface layer (S-layer) protein which differs significantly from the other S-layers studied up to date. Interestingly, the N-terminal domain (182 amino acid residues) of this S-layer is almost identical to that of B. sphaericus NCTC 9602 which was also analyzed in our laboratory. Vegetative cells and spores of the two B. sphaericus strains accumulate selectively large amounts of U, Pb, Cd, Cu and Al from the highly polluted drain waters of the uranium waste. The interaction of the S-layers of the two strains with U, Pt and Pd were studied in particular, using IR spectroscopy and EXAFS spectroscopy. The ability of the vegetative cells, spores and S-layers of the two B. sphaericus strains to interact with metal ions makes them prospective for bioremediation. Results on entrapping of vegetative cells of B. sphaericus JG-A 12 and B. sphaericus 9602 in SiO2 ceramics using the sol-gel process, will be presented.

Beim Abriß von Nuklearanlagen fallen große Mengen Bauschutt an, die mit Radionukliden kontaminiert sein können. Da diese Kontaminationen häufig nahe der Freigabewerte liegen, ist für die Entscheidung, ob das Material als radioaktiver Abfall behandelt werden muß oder freigegeben werden kann, eine schnelle und exakte Meßmethode notwendig. Eine direkte Messung der a-aktiven Nuklide im stehenden Gebäude ist auf Grund der geringen Reichweite der a-Strahlung und ihrer Absorption im Beton nicht möglich. Die übliche chemische Analyse der a-aktiven Nuklide ist sehr arbeits- und zeitaufwendig und somit ungeeignet.
Im Rahmen dieses Projektes wurde die Methode der direkten a-Spektrometrie nach nur mechanischer Präparation des Betons bis zur technischen Anwendungsreife weiterentwickelt. In einem aus zwei Schritten bestehenden Zerkleinerungsprozeß wurden Suspensionen mit mittleren Partikeldurchmessern von 0,5 µm hergestellt. Die Meßproben mit einem Durchmesser von 20 cm und Schichtdicken zwischen 1 und 2,5 µm wurden durch Sprühen auf die Probenträger und anschließendes Trocknen hergestellt. Für die Stabilität der Suspensionen wurden Peptisatoren und Tenside getestet, die agglomeratfreie Suspensionen und damit gleichmäßige Schichten garantieren. Die Spektren dieser Proben wurden in einer Gitterionisationskammer (GIK) aufgenommen. Es wurden Untersuchungen zur Verringerung des Nulleffektes der GIK durchgeführt, um die Nachweisgrenze der Methode zu verringern. Die Spektrenauswertung erfolgte durch Peakfitting mit einer der Peakform angepaßten kombinierten Gaußschen und exponentiellen Funktion. Eine zweite Methode zur Spektrenanalyse ist das verbesserte Programm WINKRUM, basierend auf Strahlungstransportberechnungen. Dieses Modell berücksichtigt Partikelgrößenverteilung und Packungsdichte, spezifische Dichte, Schichtdicke, Parameter der GIK und die Energie der Actiniden.
Mit dieser Direktmessung dünner Meßproben können a-aktive Nuklide bis zu einer Nachweisgrenze von 0,005 bis 0,02 Bq/g (abhängig von der a-Energie) in Multielementspektren innerhalb von 28 h bestimmt werden.

Fördernde Institution
Bundesministerium für Bildung und Forschung (BMBF)
53170 Bonn

BMBF 02S 7768 6

Rückbau von Nuklearanlagen:

große Mengen Bauschutt z. B. KKW Greifswald 1.800.000Mg

Abfallminimierung: Trennung von kontaminiertem und unbelastetem Material.
1m³ Abfall kosten (ohne Behälter, Analytik, Transport)
Morsleben 12.500DM
Schacht Konrad 25.000DM

hohe Anforderung an die Freimessung nach den gesetzlichen Freigabekriterien - Bestimmung alpha-strahlender Nuklide bisher zeit- und arbeitsaufwendig

neu: Entwicklung einer schnellen Direktmeßmethode zur Einzelnuklidbestimmung von Alpha-Strahlern
- rein mechanische Probenaufbereitung
- dünne großflächige Meßproben

• Spektrenmessung und Peakentfaltung Bestimmung aller Nuklide in einer Meßprobe
• Vergleich mit unbelastetem Material (natürliche Radioaktivität in vergleichbarer Größenordnung)

Förderung:

Bundesministerium für Bildung und Forschung
02 S 7442 2, 02 S 7655 8, 02 S 7768

The isospectrality problem is studied for the operator of the spherical hydromagnetic alpha^2-dynamo. It is shown that this operator is formally pseudo-Hermitian (J-symmetric) and lives in a Krein space. Based on the J-symmetry, an operator intertwining Ansatz with first-order differential intertwining operators is tested for its compatibility with the structure of the alpha^2-dynamo operator matrix. An intrinsic structural inconsistency is obtained in the set of associated matrix Riccati equations. This inconsistency is interpreted as a no-go theorem which forbids the construction of isospectral alpha^2-dynamo operator classes with the help of first-order differential intertwining operators.

During a hypothetical accident the reactor pressure vessel internals of boiling water reactors can be exposed to considerable loads resulting from temperature gradients and pressure waves. The finite element (FE) analysis is an efficient tool to evaluate the consequences of those loads by computing the maximum mechanical stresses in the components. 3 dimensional FE models were developed for the core shroud, the upper and the lower core supporting structure, the steam separator pipes and the feed water distributor. The models of core shroud, upper core support structure and lower core support structure were coupled by means of the substructure technique. All FE models can be used for thermal and for structural mechanical analyses. As an example the FE analysis for the case of a station black-out scenario (loss of power supply for the main circulating pumps) with subsequent emergency core cooling is demonstrated. The transient temperature distributions within the core shroud and within the steam dryer pipes as well were calculated based on the fluid temperatures and the heat transfer coefficients provided by thermo-hydraulic codes. At the maximum temperature gradients in the core shroud, the mechanical stress distribution was computed in a static analysis with the actual temperature field being the load. It could be shown that the maximum resulting material stresses do not exceed the permissible thresholds fixed in the appropriate regulations. Another scenario which was investigated is the break of a feed water line leading to a non-symmetric subpressure wave within the reactor pressure vessel. The dynamic structural response of the core shroud was assessed in a transient analysis. Even for this load case the maximum resulting stresses remain within the allowed limits at any time.

The Institute of Safety Research (IfS) of the Forschungszentrum Rossendorf (FZR) e.V. is constructing a new large-scale multipurpose test facility TOPFLOW (Transient Two Phase Flow Test Facility). This facility will be probably put into operation in the next two months. For an effective evaluation of the start up experiments and the acceptance trials against the vendors FZR starts with the preparation of automated software tools for the measurement data logging and automation software DIAdem, which is distributed by National Instruments (NI). In a first step an interface for the coupling of a water/steam material property library LiblF97 of the university of applied science Zittau/Görlitz was developed.
This report describes the programming of the General Control Interface (GPI) and its coupling with DIAdem. Additionally the capability of this coupling in connection with autosequences for data evaluation was investigated. Further on effective methods for the TOPFLOW data evaluation were demonstrated and tested against a concrete example. Currently no TOPFLOW data are available. Therefore one selected NOKO experiment was evaluated and first practical experiences were collected. Even this example is easy understandable and clearly seen, it contains every step, which is necessary for the TOPFLOW data evaluation. This contains the opening of files, determination of water/steam material properties with the Dynamic-Link-Library LibIF97.dll, the linkage of different data channels and the generation of layouts for graphics and reports.

The tools presented in this report are an important steps for the evaluation of the experimental data of TOPFLOW. These tools will be adapted now for the assessment of the acceptance trails. Further on now the generation of the automated software sequences for the first scientific tests are developed.

Four triethyl(triphenyl)siloxyalkyl(aryl)thiolato(3-thiapentane-1,5-dithialato)oxorhenium(V) complexes viz. triethylsiloxyethylthiolato-(3-thiapentane-1,5-dithialato)oxorhenium(5), triethylsiloxypropylthiolato-(3-thiapentane-1,5-dithialato)oxorhenium(6), triethylsiloxyphenylthiolato-(3-thiapentane-1,5-dithialato)oxorhenium(8) and triphenylsiloxyethylthiolato-(3-thiapentane-1,5-dithialato)oxorhenium(7) were synthesized by a new route reacting chloro-(3-thiapentane-1,5-dithialato)oxorhenium(V) with bis silylated mercaptoalkanols or mercaptophenol. Stability of the compounds in acetonitrile-water (1:1) solution at different temperature and pH was studied by reverse phase HPLC method. Compound 5 was found to be the most stable in acetonitrile-water system with respect to both temperature and pH changes.

no abstract delivered from author

We report a first attempt
(i) to derive constraints on the energy loss of charm quarks in a deconfined medium from the recent PHENIX data of single-electron transverse momentum spectra and
(ii) to estimate the resulting suppression of dileptons from correlated semi-leptonic decays of open charmed mesons.
The momentum imbalance of photon-tagged light-quark jetsis also considered.

CAREM is an Argentine project to achieve the development, design and construction of an innovative, simple and small Nuclear Power Plant (NPP). This NPP has an indirect cycle reactor with some distinctive and characteristic features (e.g. integrated primary cooling system by natural circulation, self-pressurized primary system and passive safety systems, etc.). In the frame of an IAEA forwarded HUMAN RESOURCES DEVELOPMENT - “Advice on CAREM passive emergency condenser” at the Centro Atómico in San Carlos de Bariloche (Argentina) German experimental as well analytical investigation of passive safety systems - mainly performed at the research centers Jülich and Rossendorf were presented. During this visit it was decided that FZR should determine the emergency condenser capacity by using the ATHLET code with and without the condensation module extension KONWAR (condensation inside horizontal tube). These results should be compared and assessed with existing RELAP calculations.
The ATHLET and ATHLET/KONWAR calculations of the emergency condenser were used for minimizing the user influence performed with exactly the same nodalization scheme and the same initial and boundary conditions than the RELAP calculations. The comparison of all three computational results shows that the required condenser capacities were achieved. The magnitudes were in order of up to 12%. An additionally performed evaluation of local flow parameters show large deviations especially for the heat transfer coefficients at the inner and outer tube wall. Due to the good validation progress of KONWAR by an extensive module validation against NOKO and HORUS experiments, the focus of the further investigation were concentrated on the boiling heat transfer. A comparison of the ATHLET boiling model (according to Forster and Zuber in combination with the equation of Thom for the determination of temperature difference between wall and saturated fluid) with other models from literature (Borishansky, Fritz, Gormenflo, Stefan and Abdelsalam) shows a strong underestimation of heat transfer coefficients in low pressure conditions. Therefore the model of Forster and Zuber is replaced against the model of Stefan and Abdelsalam. The calculations with ATHELT/KONWAR were repeated and show now a better agreement (deviations less equal than 3 %) with the RELAP results.

A dedicated AMS facility for depth profiling of tritium in carbon samples containing higher quantities of tritium has been installed, tested and applied for routine measurements in the Forschungszentrum Rossendorf. It is based on an SF6-insulated 100 kV tandem accelerator equipped with a thin diamond-like carbon (DLC) stripper foil of about 1 µg/cm2. The carbon samples have been cut from tiles of the inner wall of the fusion experiments ASDEX-upgrade Garching/Germany, JET Culham/GB and TFTR Princeton/USA. Depth profiles of deuterium and other light elements can be measured simultaneously using the Faraday cup at the entrance of the accelerator (SIMS mode of the facility) or in the case of very low concentrations after acceleration using a particle detector (AMS mode).

A miniaturized ion selective electrode (ISE) for Cu2+ ions was developed, specially for application in a microfluidic system. The electrode preparation is based on a silicon wafer substrate which is coated with a Cu deposit in the range of 50 - 200 nm. The Cu layer is quantitatively converted into CuS by treatment in a sulphidic ambient. The chip electrode has a size of 5x5 mm2 and was mounted on a spacer chip coupled to the fluidic microcell using a chip clip technology. The coupling is liquid tight and reversible, admitting an easy exchange of the chip electrodes. The effective electrode area in contact with the liquid of the microsystems flow channel amounts to about 4 mm2.
Sensitivity measurements were performed stationary and in the flow through cell. Good Nernstian response of 29 mV/pCu between pCu 5 and 1 has been found and is in agreement with reference measurements carried out with a commercial ISE.
The rapid response observed also in the most diluted solutions used, is related to the thin, non porous structure of the CuS layer, minimizing diffusion effects during changing the test solutions. The adhesion of the sensitive CuS layer is different for the substrates Si, SiO2 and Si3N4 and depends on their history, roughness and evaporation conditions.

Low-resistivity ( < 0.1 Ohm cm at room temperature), p-type SiC layers were produced by the combination of high dose Al implantation in n-type, 6H-SiC at low temperature, subsequent ion-beam-induced crystallization by means of Si irradiation at 500°C and high temperature annealing at 1500°C. The implanted SiC layers have a nanocrystalline structure consisting of randomly oriented grains of 3C-SiC. The electrical properties of the nanocrystalline and single-crystalline reference samples were investigated by sheet resistance and Hall measurements in dependence on temperature. In comparison with the standard doping process the hole concentration is enhanced by more than one order of magnitude. This can be explained by a higher solid solubility of Al in nanocrystalline SiC. Current-voltage measurements across the vertical p-n-junction in the heavily doped nanocrystalline and single-crystalline samples demonstrated the equivalence of the diode quality.

The aim of this work was to find a correlation between the electrical, optical and microstructural properties of thin SiO2 layers containing group IV nanostructures produced by ion beam synthesis. The investigations were focused on two main topics: The electrical properties of Ge- and Si-rich oxide layers were studied in order to check their suitability for non-volatile memory applications. Secondly, photo- and electroluminescence (PL and EL) results of Ge-, Si/C- and Sn-rich SiO2 layers were compared to electrical properties to get a better understanding of the luminescence mechanism.

The Phi-meson production cross section is measured for the first time at a sub-threshold energy of 1.93 AGeV in ⁵⁸Ni+⁵⁸Ni collisions. The Phi data were obtained within the acceptance of the CDC/Barrel subsystem of the FOPI detector. For a sample of 4.7x10⁶ central events, after background subtraction, 23 Phi candidates were observed. Extensive simulation calculations of the detector performance are shown in a detailed comparison to the data, aiming at a good understanding of the apparatus response and at a reliable determination of the efficiencies, production probability and possible systematic errors. A filter procedure is elaborated, which is meant to facilitate the comparison of any theoretical calculation with the data in the detector acceptance. How to extrapolate the result to a Phi-meson cross section in 4\pi is also discussed. This first result on pseudo-vector mesons can now be compared to existing data for the same reaction at the same incident energy for various outgoing channels, K⁺ and K^- included. It suggests that a significant fraction (at least 20%) of the K^--mesons is originating in the decay of the Phi showing that the two channels are strongly correlated. A first comparison to existing model calculations indicates the possible role of the Rho-meson channels in Phi production.

The quality of single crystals grown by the floating-zone method is strongly determined by the geometry of the solid-liquid phase boundary which, in turn, can be significantly influenced by the convection in the molten zone.
We describe a novel inductor design which allows a strong influence on the flow filed. Numerical simulations are presented for the design of such a two-phase inductor.

We present numerical results of a linear 3-D stability analysis of a square lid-driven cavity flow under the influence of an external magnetic field which is directed parallel to the lid. The Lorentz force has a strong influence on the flow structure, thereby changing number, shape and strength of the eddies inside. Although increasing magnetic fields are able to damp 3-D instability, in a parameter region around Re=3000, several branches of the neutral stabiliy curve do exist. This leads to a non-monotonic behaviour of receptivity to 3-D disturbances as the strength of the magnetic field is increased.

We present the main observable features connected with magnetic field saturation in the Riga dynamo experiment, and try to explain them in terms of a simplified numerical model of back-reaction.

In June 2002, a new series of experimental runs was carried out at the Riga dynamo facility. Compared with the experiments in November 1999 and July 2000, the new experiments have delivered much more magnetic field data with higher radial resolution and with sampling rates up to 10 kHz. The range of propeller rotation rates has been extended to higher values, giving new
information on the kinematic and the saturation regime for higher magnetic Reynolds numbers.

The possibility of velocity reconstruction in electrically conducting fluids from external measurements of different induced magnetic fields is studied numerically. It is shown that for a reliable velocity reconstruction the effect of the electric potential at the fluid boundary on the induced magnetic field should be taken into account.

Stability and transition to turbulence in a flow driven by a rotating magnetic field is studied experimentally. Intermittent signals have been obtained clearly below the linear stability threshold.

Strömungen elektrisch leitfähiger Flüssigkeiten, insbesondere von flüssigen
Metallen und Halbleiterschmelzen, lassen sich mit Magnetfeldern in
kontaktloser Weise stark beeinflussen. Es wird eine Übersicht gegeben zu
diesen Arbeiten im Rahmen des SFB 609 "Elektromagnetische
Strömungsbeeinflussung in Metallurgie, Kristallzüchtung und Elektrochemie"
und am FZR. Die inverse Herangehensweise, maßgeschneiderte Magnetfelder für
die im jeweiligen Prozeß wünschenswerten Strömungen bzw. Wärme- und
Stofftransporte zu entwickeln, wird vorgestellt. Es werden Möglichkeiten zur
Magnetfeldbeeinflussung metallischer Strahlen aufgezeigt, die für das
Sprühkompaktieren interessant sein könnten.

The report gives an overview on the activities of the Institute of Safety Research in 2001.

Bei Anlegen eines elektrischen Feldes an einen Kristall würde der Strom ohne Streuung nicht auf unendlich anwachsen, sondern (fast) auf Null absinken. Dieses im ersten Moment paradoxe Phänomen, das mit der periodischen Struktur des Kristallgitters zusammenhängt, kann semiklassisch als sogenannte Bloch-Oszillation und quantenmechanisch durch die Ausbildung einer Wannier-Stark-Leiter verstanden werden. Beide Beschreibungsweisen führen zu einer Lokalisierung der Elektronen.
Nach einer grundlegenden Darstellung dieses Phänomens möchte ich einen Streifzug durch seine lange Geschichte unternehmen, die ihren Ausgangspunkt in einer Arbeit von Zener aus dem Jahre 1934 hat. Die „Gegenwart“ hat erst um 1990 durch den experimentellen Nachweis in Halbleiterübergittern begonnen. Vieles wurde seither verstanden, viele andere Dinge sind noch offen, wie zum Beispiel die Realisierung eines elektrisch getriebenen Bloch-Oszillators als THz-Quelle oder -Verstärker, wie 1970 von Esaki und Tsu vorgeschlagen. Ich werde aktuelle Experimente, Theorien, Probleme und neue Konzepte diskutieren.

We present the centrality dependence of proton and deuteron rapidity distributions in Ru+Ru collisions at 400A MeV. Data are compared with Isospin Quantum Molecular Dynamics calculations (IQMD) under various assumptions on the nucleon-nucleon cross-section in the medium. The rapidity spectra of both particles can be reproduced by IQMD with a free nucleon-nucleon cross-section for the most central collisions. The ratio of baryon rapidity distributions in isospin asymmetric collision systems shows incomplete mixing and partial transparency of both the projectile and target nuclei at this beam energy.

A novel type of mixed-ligand Tc(III) complexes, [Tc(SCH₂CH₂-E-CH₂CH₂S)(PR₂S)] (E = S, N(CH₃); PR₂S = phosphinothiolate with R = aryl, alkyl) is described. These "3+2"-coordinated complexes can be prepared in a two-step reduction/substitution procedure via the appropriate chloro-containing oxotechnetium(V) complex [TcO(SES)Cl] (E = S, N(CH₃). Tc(III) compounds have been fully characterized both in solid and solution states and found to adopt the trigonal-bipyramidal coordination geometry. The equatorial trigonal plane is formed by three thiolate sulfurs atoms, whereas the phosphorus of the bidendate P,S ligand and the neutral donor of the tridendate chelator occupy the apical positions. The ⁹⁹Tc(III) complexes have been proven to be identical with the ^99mTc-agents prepared at the no-carrier-added level by comparison of the corresponding UV-Vis and radiometric HPLC profiles. Challenge experiments with glutathione clearly indicated that this tripeptide has no effect on the stability of the ^99mTc complexes in solutions. Biodistribution studies were carried out in rats at 5 and 120 minutes post injection. The substituents at the bidendate P,S ligand significantly influenced the biodistribution pattern. Remarkable differences were observed especially in brain, blood, lungs and liver. All the complexes were able to penetrate the blood-brain-barrier of rat brain and showed a relatively fast washout from the brain.

Poster of experimental results of time resolved investigations of nitrogen implanted GaAs

Nanocrystals of silicon carbide were synthesized inside natural diamond using high dose silicon implantation. In order to retain the diamond structure, however, implantation was done at 900 °C. The samples were subsequently annealed in an rf-heated furnace at 1500 °C for 10 minutes. X-ray diffraction (XRD), IR absorption spectrometry and high-resolution cross-sectional transmission electron microscopy (HRTEM) are used to investigate formation and structure of SiC nanocrystallites in the implanted diamond. Raman spectroscopy contributed to trace implantation-induced destruction of the diamond. A first characterization of the electrical properties of the implanted and annealed samples is done by four point probe measurements. The results indicate a highly conductive, buried layer inside the diamond. This layer contains cubic SiC nanocrystals, which are perfectly aligned with the diamond lattice. However, when fluence exceeds a critical value of 5.3×1017 Si+cm-2, the diamond is irreversibly damaged and defect conduction type dominates.

Ion beam induced crystallization was used to transform amorphized, heavily Al doped SiC layers to nanocrystalline material. The morphology of the as-implanted and the annealed layers was studied by XTEM. The electrical properties were analyzed by sheet resistance and Hall measurements and compared with crystalline reference samples. A high-temperature annealing step is necessary to activate the implanted Al acceptor atoms. During annealing the mean grain size of the nanocrystals grow from 3 nm to 37 nm. The Al doped, nanocrystalline SiC has a much lower sheet resistance than the crystalline reference samples. It was found that this is due to the enhanced hole concentration which could be explained by a higher solid solubility of Al in the nc SiC.

We have investigated the synthesis of nanostructures as well as the control of their size and location by means of ion beams. The phase separation and interface kinetics under ion irradiation give new possibilities to control the growth of nanostructures. Additionally, the chemical decomposition of the host matrix by collisional mixing may contribute to self-organization of nanostructures, especially at interfaces. It is shown how collisional mixing during ion implantation affects nanocrystal (NC) synthesis and how ion irradiation through NCs modifies their size and size distribution. An analytical expression for solute concentration around an ion-irradiated NC were found which may be written like the well-known Gibbs-Thomson relation. However, parameters have modified meanings which has a tremendous impact on the evolution of NC ensembles. Thus, inverse Ostwald ripening of NCs resulting in an unimodal NC size distribution is predicted, which has been confirmed experimentally for Au NCs in SiO2 and by kinetic lattice Monte-Carlo simulations. At interfaces, the same ion-irradiation induced mechanism may result in self-organization of NCs in a thin d-layer. Collisional decomposition of SiO2 may enhances the NC d-layer formation in SiO2 at the Si/SiO2 interface. The distance of the self-organized NC d-layer from the SiO2/Si interface makes it interesting for non-volatile memory applications.

Continuing our strategy for a targeted therapy of metastatic renal cell carcinoma (RCC), a tumor which resists chemo- or radiotherapy, we now determined the primary structure of the antigen binding region of the monoclonal antibody 138H11. MAb 138H11, produced against human renal gamma-glutamyltransferase (GGT), stained over 99% clear cell and papillary RCC as well as other carcinomas on frozen sections, showing a membranous expression of the target antigen. In contrast, in normal kidneys GGT is restricted to the brush-border in the lumen of proximal tubules and thus not accessible to the circulation. Human tumor-bearing kidneys perfused in an
extra-corporeal system with 99mTc-138H11 revealed a high, specific uptake into the tumor. In vivo, a 138H11-Calicheamicin theta conjugate was very effective in reducing the tumor size and preventing or significantly delaying the regrowth of residual tumor cells in xenografted nude mice (Cancer Res. 2000, 60, 6089-6094). However, these nude mice are not useful for evaluating ADCC of naked 138H11 or immunoactivating conjugates. For creating a syngenic, immunocompetent mouse model bearing a tumor sensitive to mAb 138H11, we stably transfected the murine RCC RENCA cell line with the human GGT-gene. FACS-analysis revealed that transfected cells were positive for mAb 138H11, in contrast to wild type cells. The transfected cells were growing s.c. in
Balb/c mice without signs of rejection by the host. The mice showed a higher uptake of 99m-Tc-labelled 138H11 into the GGT positive RENCA tumors compared to the wild type tumors. This new model will be usful in the future for evaluating therapeutic effects of potential constructs made with the newly cloned recombinant 138H11-derivatives such as stabilized scFv, diabodies and triabodies.

A method is described for identifying tumor tissue by means of FTIR microspectroscopy and positron emission tomography (PET). Thin tissue sections of human squamous carcinoma from hypopharynx (FaDu) and human colon adenocarcinoma (HT-29) grown in nude mice were investigated. FTIR spectroscopic maps of the thin tissue sections were generated and evaluated by Fuzzy C-Means (FCM) clustering and principal component analysis (PCA). The processed data were reassembled into images and compared to stained tissue samples and to PET. Tumor tissue could successfully be identified by this FTIR microspectroscopic method, while it was not possible to accomplish this with PET alone. On the other hand, PET permitted the non-invasive screening for suspicious tissue inside the body, which could not be achieved by FTIR.

no abstract delivered from author